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Poly(vinyl alcohol) Molecular Bottlebrushes Nucleate Ice

  • Panagiotis G. Georgiou
    Panagiotis G. Georgiou
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
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    Orcidhttps://orcid.org/0000-0001-8968-1057
  • , 
  • Nina L. H. Kinney
    Nina L. H. Kinney
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
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    Orcidhttps://orcid.org/0000-0003-3123-7361
  • , 
  • Ioanna Kontopoulou
    Ioanna Kontopoulou
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
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  • , 
  • Alexander N. Baker
    Alexander N. Baker
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
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  • , 
  • Steven A. Hindmarsh
    Steven A. Hindmarsh
    Department of Physics, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
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  • , 
  • Akalabya Bissoyi
    Akalabya Bissoyi
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
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  • , 
  • Thomas R. Congdon
    Thomas R. Congdon
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
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  • , 
  • Thomas F. Whale*
    Thomas F. Whale
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
    *Email: [email protected]
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  • , and 
  • Matthew I. Gibson*
    Matthew I. Gibson
    Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
    Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
    *Email: [email protected]
    More by Matthew I. Gibson
    Orcidhttps://orcid.org/0000-0002-8297-1278
Cite this: Biomacromolecules 2022, 23, 12, 5285–5296
Publication Date (Web):November 28, 2022
https://doi.org/10.1021/acs.biomac.2c01097

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Ice binding proteins (IBP) have evolved to limit the growth of ice but also to promote ice formation by ice-nucleating proteins (INPs). IBPs, which modulate these seemingly distinct processes, often have high sequence similarities, and molecular size/assembly is hypothesized to be a crucial determinant. There are only a few synthetic materials that reproduce INP function, and rational design of ice nucleators has not been achieved due to outstanding questions about the mechanisms of ice binding. Poly(vinyl alcohol) (PVA) is a water-soluble synthetic polymer well known to effectively block ice recrystallization, by binding to ice. Here, we report the synthesis of a polymeric ice nucleator, which mimics the dense assembly of IBPs, using confined ice-binding polymers in a high-molar-mass molecular bottlebrush. Poly(vinyl alcohol)-based molecular bottlebrushes with different side-chain densities were synthesized via a combination of ring-opening metathesis polymerization (ROMP) and reversible addition–fragmentation chain-transfer (RAFT) polymerization, using “grafting-to” and “grafting-through” approaches. The facile preparation of the PVA bottlebrushes was performed via selective hydrolysis of the acetate of the poly(vinyl acetate) (PVAc) side chains of the PVAc bottlebrush precursors. Ice-binding polymer side-chain density was shown to be crucial for nucleation activity, with less dense brushes resulting in colder nucleation than denser brushes. This bio-inspired approach provides a synthetic framework for probing heterogeneous ice nucleation and a route toward defined synthetic nucleators for biotechnological applications.

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Introduction

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Ice-binding proteins recognize and bind ice faces, leading to control over their formation (ice-nucleating proteins, INPs) or growth (antifreeze proteins, AFPs). AFPs are well studied and have defined ice-binding sites to engage ice either directly or via an anchored mechanism. (1,2) INPs, in contrast, are less well understood (3) despite being commercialized as extracts from the bacterium Pseudomonas syringae. IBPs have many potential applications across a range of biotechnological and engineering areas where it would be advantageous to control ice formation. (4) The study of INPs is challenging due to the low solubility of the INP and the need for the transmembrane/lipid anchored domains for activity. Davies and co-workers reported recombinant mutated INPs, but it was essential to study activity while attached to the host organism (E.coli) to obtain ice nucleation functional data. (5)
In addition to IBPs, it has emerged that synthetic materials can also bind ice, reproducing the macroscopic properties of IBPs─presenting opportunities not only for biomedical applications but also to understand IBP function. (6−8) Synthetic polymers can be produced with excellent control over architecture and composition, allowing molecular shape and composition to be tuned to probe the material/ice interface. The most active and widely studied ice-binding polymer is poly(vinyl alcohol) (PVA). (9,10) PVA’s ice recrystallization inhibition (IRI) activity can be tuned by varying molecular weight, (11) shape, (12,13) and assembly into particles. (14) PVA binds to ice via hydrogen bonding of the hydroxyl groups, (15,16) but is unique in that most other hydroxylated polymers do not show this function. (17) Antifreeze (glyco)proteins, in contrast, have hydrophobic segments that bind to ice (rather than the glycan hydroxyls), (18−20) underpinning the concept that a molecular mechanisms can lead to similar measurable macroscopic effects.
Considering the success of mimicking the macroscopic property of ice recrystallization inhibition, there remain remarkably few nonprotein ice nucleators, none of which have been designed from the bottom-up. Silver iodide, which has a very similar structure to hexagonal ice, is probably the best known. (21,22) Feldspar (an aluminosilicate) is a potent ice nucleator, (23) and its function appears to be caused by defects rather than the bulk structure. (24) Graphene nanomaterials can also nucleate ice, (25) and the size of the flakes proves crucial. (26) The critical ice nucleus size is predicted to be ∼20 nm for nucleation at −5 °C, (27) supporting the need for aggregates or molecularly large species. Arrays of cholesterol crystals (28) and fractions of lignin (a heterogeneous material) have also been reported to have some activity, (29) alongside marine biogenic particles. (30) Ice-nucleating macromolecules of protein and polysaccharide origin have also been reported, (27,31) but their chemical structures remain unknown.
In general, effective ice nucleators are thought to have a good lattice match to ice, meaning that water molecules bind to the nucleator in spatial locations similar to those they would occupy in ice. According to classical nucleation theory (CNT), the barrier to ice nucleation is due to the energetic cost of forming an interface between supercooled water and ice. By templating ice, a nucleator allows the formation of a smaller ice critical cluster reducing the energy barrier to nucleation and causing ice to form at warmer temperatures. For ice nucleation to occur at warmer temperatures, more significant nucleation sites possessing a lattice match to ice, or at least an ability to bind water in an icelike structure, are required. (3,27)
There are currently no design rules for ice nucleators, but some key observations have been made. There is evidence that when the size of an AFP increases, it can become an INP supported by experimental (32) and modeling evidence. (3) Small IBPs (∼2 nm) nucleate ice at cold temperatures, near to where homogeneous ice nucleation occurs (32) but ice-nucleating proteins (INPs) maintain a coherent lattice match to ice across nucleation sites spanning as many as 30 individual INPs, nucleating ice at −2 °C: (3) This corresponds to 50 nm x 50 nm nucleation sites. Ogawa et al. reported that linear poly(vinyl alcohol), which is known to bind ice, is capable of nucleating ice at temperatures a few degrees above the homogeneous nucleation temperature but did not show a molecular-weight effect in the range tested. (33) Taken together, the above shows an exciting possibility that a chemically defined synthetic ice binder could be engineered to become an ice nucleator if sufficient size, density, and placement of the ice binders can be accessed. A synthetic ice nucleator would enable the first true structure–property relationships to be determined, without using heterogeneous mixtures.
Here, we introduce an ice nucleator platform based on well-defined poly(vinyl alcohol) molecular brushes obtained via a combination of ring-opening metathesis polymerization (ROMP) and reversible addition–fragmentation chain-transfer (RAFT) polymerization, using “grafting-to” and “grafting-through” approaches. We demonstrate that densely grafted PVA bottlebrush polymers exhibit ice nucleation activity and are the first example of a synthetic polymer ice nucleator. Lower-density brush copolymers had reduced activity, demonstrating that confinement of the PVA is essential. These results show that synthetic ice nucleators can be accessed by macromolecular engineering.

Experimental Section

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Materials

All chemicals were used as supplied unless otherwise stated. ROMP catalyst G3 ((H2IMes)(pyr)2(Cl)2Ru = CHPh), cis-5-norbornene-exo-2,3-dicarboxylic anhydride (95%), exo-5-norbornene carboxylic acid (97%), N-boc-ethylenediamine (≥98%), 1-hydroxypyrrolidine-2,5-dione (98%), ethyl vinyl ether (EVE) (≥99%), trifluoroacetic acid (TFA, 99%), mPEG10K-succinimidyl carboxymethyl ester (NHS-mPEG227, Mn ∼ 10,000 Da), poly(ethylene glycol) methyl ether methacrylate (PEGMA20, Mn ∼ 1000 Da), 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (97%), 4,4′-azobis(4-cyanovaleric acid) (ACVA, ≥98%), poly(vinyl alcohol) (Mn ∼ 146,000–186,000 Da, ≥99% hydrolyzed), hydrazine hydrate (reagent grade, 50–60%), lithium aluminum hydride solution (LiAlH4, 1.0 M in THF), 1-hydroxybenzotriazole hydrate (HOBt, ≥97%), triethylamine (TEA, ≥99%), PBS (tablets), and sucrose (≥99.5%) were purchased from Sigma-Aldrich. The monomer vinyl acetate (VAc, ≥99%) was also purchased from Sigma-Aldrich and passed through a column of basic alumina to remove inhibitors prior to use. Potassium ethyl xanthate (98%) was obtained from Alfa Aesar. N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC.HCI, >98%) was purchased from Carbosynth. 2-Bromo-2-methyl-propionic acid (≥98%) and lanolin (anhydrous, USP) was purchased from Acros Organics. Paraffin oil (technical grade) was purchased from VWR International. Solvents of toluene (anhydrous, ≥99.8%), dichloromethane (DCM, anhydrous, ≥99.8%), N,N-dimethylformamide (DMF, anhydrous, ≥99.8%), and tetrahydrofuran (THF, anhydrous, ≥99.9%) were also purchased from Sigma-Aldrich. Dialysis membranes (MWCO = 3.5/300 kDa) were purchased from Spectra/Por. Formvar-carbon-coated (300 mesh) copper grids were purchased from EM Resolutions. Photo-polymerization reactions of vinyl acetate were conducted using an EvoluChem PhotoRedOx Temperature Controlled Box fitted with an EvoluChem LED spotlight (P201-18-2 450–455 nm) with total irradiance of 30 mW cm–2 and light beam angle of 25° operating at a wavelength of λ = 450–455 nm. Ultrapure water used for buffers was of Milli-Q grade (18.2 mΩ resistance).

Photo-Polymerization of Vinyl Acetate Using 2-(Ethoxycarbonothioylthio)-2-methylpropanoic Acid NHS-Ester

2-(Ethoxycarbonothioylthio)-2-methylpropanoic acid NHS-ester (0.10 g, 0.33 mmol, 1 eq) and vinyl acetate (VAc) (8.46 g (9.06 mL), 98.2 mmol, 300 eq) were dissolved in 2.1 mL of dioxane in a 20 mL vial (80% w/w solids content). The resulting solution was degassed by sparging with N2(g) for 30 min, and the sealed vial was incubated at 37 °C with magnetic stirring under 460 nm light irradiation for 8 h. After that time, polymerization was quenched by removing the sealing and exposing it to air. An aliquot of crude polymerization mixture was withdrawn for 1H NMR in CDCl3 for conversion and Mn,NMR analysis. The reaction was rapidly cooled in liquid nitrogen and precipitated into diethyl ether. The polymer was reprecipitated into hexane from THF twice to yield a pale-yellow sticky polymer product that was further dried under vacuum. Mn,NMR was calculated by end-group analysis by comparing the integrations of the −(CH2)2 signals (s, 2.83 ppm) of NHS group with those of the corresponding signals of the −CH signal (d, 3.69–4.02 ppm) of the polymer backbone. 1H NMR (400 MHz, CDCl3): δ (ppm) = 5.05–4.76 5.05–4.76 (br s, 210H, CH2CHO of polymer backbone), 2.83 (s, 4H, CH2CH2 of NHS), 2.17–1.94 (br m, 630H, OC(O)CH3 of polymer side chain), 1.94–1.58 (br m, 420H, CH2CHO of polymer backbone), 1.34 (t, 3H, CH3CH2O). Conversion = 69%, Mn,NMR = 18400 g mol–1 (DPPVAc,NMR = 210). SEC (5 mM NH4BF4 in DMF) Mn,SEC RI= 22800 g mol–1, ĐM,SEC RI = 1.6.

Synthesis of Poly(amino exo-norbornene imide), P(NB-NH2) Homopolymer Precursors via Ring-Opening Metathesis Polymerization (ROMP)

A typical procedure for the synthesis of P(NB-NBoc)50 homopolymer via solution ROMP is described. A stock solution of 100 mg/mL of G3 in CHCl3 and a solution of 173 mg of NB-NBoc (50 eq, 0.57 mmol) in 3.3 mL of CHCl3 were first prepared. Then, 100 μL of G3 stock solution (10 mg, 1 eq, 0.011 mmol) was added to the vial of NB-NBoc monomer solution with rapid stirring, and polymerization was allowed to proceed at room temperature for 1 h (final [NB-NBoc] = 50 mg/mL, final [G3] = 2.9 mg/mL). The polymerization was then quenched by the addition of a few drops of ethyl vinyl ether, and P(NB-NBoc)50 homopolymer was precipitated from diethyl ether, isolated by vacuum filtration, and dried under vacuum prior to 1H NMR and SEC analyses. The procedure was repeated for [NB-NBoc]/[G3] ratios of 100, 200, and 400. 1H NMR (400 MHz, CDCl3) Mn,theo. = 15,300 g mol–1. SEC (DMF + 5 mM NH4BF4) Mn,SEC = 17,600 g mol–1, ĐM,SEC = 1.10.
Next, P(NB-NBoc)50 homopolymer (100 mg, 0.003 mmol) was dissolved in a 1:1 TFA/DCM solution (5 mL) and stirred at room temperature for 4 h. The polymer reaction mixture was concentrated to dryness under reduced pressure to afford a brown residue that was precipitated by the addition of diethyl ether. Removal of the solvent resulted in the isolation of the amino-deprotected polymer product as a brown solid (P(NB-NH2)50). The resulting polymer was then dissolved in DI water and dialyzed against DI water (dialysis membrane MWCO = 3.5 kDa) for approximately 14 h and lyophilized to afford the polymer products as brown solid. The procedure was repeated for P(NB-NBoc)100, 200, and 400 homopolymers. SEC characterization of the resulting deprotected poly(amino exo-norbornene imide) polymers was not possible due to high sample–column interactions. 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 8.04–7.92 (br s, CH2NH2 of polymer side chain), 5.73–5.56 (br m, CHCHCH2 of polymer backbone), 5.56–5.33 (br m, CHCHCH2 of polymer backbone), 3.74–3.48 (br s, CH2CH2NH2 of polymer side chain), 3.48–3.24 (br m, CH2CH2NH2 of polymer side chain), 3.24–2.83 (br s, C(O)CHCH C(O)of polymer backbone), 2.83–2.56 (br s, CHCH2CH of polymer backbone), 2.13–1.80 (br s, CHCH2CH of polymer backbone), 1.62–1.32 (br s, CHCH2CH of polymer backbone).

Synthesis of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n Graft Copolymers via “Grafting-To” Approach

A representative synthesis of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))50 by “grafting-to” is as follows: NHS-PVAc210 (2.0 mg, 0.0002 mmol, 1 eq), P(NB-NH2)50 (0.34 mg, 0.018 mmol, 100 eq), and EDC.HCl (3.5 mg, 0.018 mmol, 100 eq) were dissolved in 6.5 mL of anhydrous DMF, followed by the addition of Et3N (2 μL, 0.018 mmol, 100 eq), and the reaction mixture was stirred at 70 °C for 16 h. An aliquot of the crude reaction mixture was then taken for SEC analysis in DMF (+0.1% LiBr). The resulting polymer mixture was precipitated twice in diethyl ether. The resulting P(NB-NH2)50-g-PVAc210 branched copolymer was then dissolved in methanol (2 mL) following by the addition of hydrazine hydrate solution (5 mL, 50–60% in water) in a stoppered vial. The reaction mixture was stirred at room temperature overnight. The resulting graft copolymer was then dissolved in DI water and dialyzed against DI water (dialysis membrane MWCO = 300 kDa) for approximately 2 weeks to ensure full removal of unfunctionalized PVA210 and lyophilized to afford the polymer product as spongy pale-yellow solid. Procedure was repeated for the synthesis of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))100, 200, 400 and control sample P((P(NB-NH)-g-PEG227)-stat-P(NB-NH2))200. Complete hydrolysis was confirmed by 1H NMR analysis in DMSO-d6. 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 4.74–4.63 (br s, CH2CHOH of polymer side chain), 4.58–4.41 (br s, CH2CHOH of polymer side chain), 4.32–4.18 (br m, CH2CHOH of polymer side chain), 3.99–3.73 (br m, CH2CHOH of polymer backbone), 1.71–1.14 (br m, CH2CHOH of polymer backbone).

Photo-Polymerization of Vinyl Acetate Using NB-CTA

2-(Ethoxycarbonothioylthio)-2-methylpropanoic acid exo-5-norbornene-2-methylamide (0.10 g, 0.32 mmol, 1 eq) and vinyl acetate (VAc) (8.24 g (8.82 mL), 95.7 mmol, 300 eq) were dissolved in 2.1 mL of dioxane in a 20 mL vial (80% w/w solids content). The resulting solution was degassed by sparging with N2(g) for 30 min, and the sealed vial was incubated at 37 °C with magnetic stirring under 460 nm light irradiation for 8 h. After that time, polymerization was quenched by removing the sealing and exposing it to air. An aliquot of crude polymerization mixture was withdrawn for 1H NMR in CDCl3 for conversion and Mn,NMR analysis. The reaction was rapidly cooled in liquid nitrogen and precipitated into diethyl ether. The polymer was re-precipitated into hexane from THF twice to yield a pale-yellow sticky polymer product that was further dried under vacuum. Mn,NMR was calculated by end-group analysis by comparing the integrations of the −(CHCH) signals (s, 6.28 ppm) of norbornene group with those of the corresponding signals of the −CH signal (d, 3.69–4.02 ppm) of the polymer backbone. 1H NMR (400 MHz, CDCl3): δ (ppm) = 6.28 (s, 2H, CHCH of norbornene end group), 5.05–4.76 (br s, 208H, CH2CHO of polymer backbone), 2.83 (s, 4H, CH2CH2 of NHS), 2.17–1.94 (br m, 630H, OC(O)CH3 of polymer side chain), 1.94–1.58 (br m, 420H, CH2CHO of polymer backbone), 1.34 (t, 3H, CH3CH2O). Conversion = 67%, Mn,NMR = 18,400 g mol–1 (DPPVAc, NMR = 208). SEC (5 mM NH4BF4 in DMF) Mn,SEC RI = 17,900 g mol–1, ĐM,SEC RI = 1.40.

Synthesis of PNBn-g-PVA208 Bottlebrush Polymers via ROMP “Grafting-Through” Approach

A representative synthesis of a PNB20-g-PVAc208 bottlebrush polymer by ROMP “grafting-through” is as follows: NB-PVAc208 (100 mg, 0.006 mmol, 20 equiv) was dissolved in 1.9 mL of anhydrous THF in a 3 mL vial equipped with a magnetic stirring bar. To the vial was added 100 μL of a 2.0 mg mL–1 stock solution of G3 in THF (final [NB-PVAc208]/[G3] = 20, [NB-PVAc208] = 50 mg mL–1). The reaction mixture was stirred at room temperature for 2 h. The polymerization was then quenched via addition of a few drops of ethyl vinyl ether. An aliquot of the crude reaction mixture was then taken for SEC analysis in DMF (+0.1% LiBr). The resulting polymer, PNB20-g-PVAc208, was isolated by precipitation from diethyl ether and was dried under vacuum.
The resulting PNB20-g-PVAc210 (50 mg) bottlebrush polymer was then dissolved in methanol (0.5 mL) followed by the addition of and hydrazine hydrate solution (3 mL, 50–60% in water) in a stoppered vial. The reaction mixture was stirred at room temperature overnight. The resulting polymer was then dissolved in DI water and dialyzed against DI water (dialysis membrane MWCO = 300 kDa) for approximately 1 week to ensure full removal of unfunctionalized PVA208 and lyophilized to afford the polymer products as a white solid. The procedure was repeated for the synthesis of PNBn-g-PVAc210 (n = 30, 40). Complete hydrolysis was confirmed by 1H NMR analysis in DMSO-d6. 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 4.74–4.63 (br s, CH2CHOH of polymer side chain), 4.58–4.41 (br s, CH2CHOH of polymer side chain), 4.32–4.18 (br m, CH2CHOH of polymer side chain), 3.99–3.73 (br m, CH2CHOH of polymer backbone), 1.71–1.14 (br m, CH2CHOH of polymer backbone).

Polymerization of Poly(ethylene glycol) Methyl Ether Methacrylate Using 4-Cyano-4-(phenylcarbonothioylthio)pentanoic Acid

A vial was charged with 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (5.0 mg, 0.018 mmol, 1 eq), PEGMA20 (3.58 g, 3.6 mmol, 200 eq), ACVA (1.0 mg, 0.004 mmol, 0.2 eq), and 17 mL of DMF. The vial was then sealed and deoxygenated using three successive cycles of freeze–pump–thaw to remove O2(g). The vial was placed into an aluminum heating block, which had been preheated to 70 °C to initiate polymerization. After 24 h, the polymerization was quenched by exposing the vial to air and submerging it into liquid N2. An aliquot was withdrawn for the determination of monomer conversion by 1H NMR spectroscopy. The polymer was precipitated into diethyl ether from dioxane twice to yield a white polymer product that was further dried under vacuum. 1H NMR (400 MHz, methanol-d4): δ (ppm) = 3.88–3.51 (br s, 16,000H, OCH2CH2 of polymer side chain), 2.48–1.58 (br m, 400H, C(CH3)CH2 of polymer backbone), 1.41–0.76 (br m, 600H, C(CH3)CH2 of polymer backbone), Mn,theo = 200,000 g mol–1. SEC (5 mM NH4BF4 in DMF) Mn,SEC RI = 134,300 g mol–1, ĐM,SEC RI = 2.0.

Results and Discussion

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Our initial hypothesis was that densely packed PVA side chains, to mimic the regular arrays of IBPs which lead to nucleation, were essential. A “grafting-to” approach was first employed, which results in low grafting densities due to steric repulsions between bulky side chains (Figure 1A). (34,35) Poly(norbornene)s bearing primary amines were first synthesized via an N-Boc-protected intermediate monomer (NB-NBoc, Figures S1 and S2), initiated by Grubbs third-generation bispyridyl complex (G3), [M]/[G3] of 50, 100, 200, 400. Full characterization by 1H NMR and size exclusion chromatography (SEC) analysis is shown in Table 1 and Figures S17 and S18. Deprotection of P(NB-NBoc)n with trifluoroacetic acid (TFA) gave the desired poly(amino norbornene imide) P(NB-NH2)n homopolymers (Figure S19).

Figure 1

Figure 1. (A) Design and synthesis of graft PVA-based brush copolymers generated via “grafting-to” procedure. Schematic representation of the synthetic route followed for the preparation of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) graft copolymers. (B) Normalized SEC-RI chromatograms for P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))n copolymer precursors in DMF + 0.1% LiBr and solution characterization of resulting P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) in water via (C) DLS analysis (insets: representative photograph of 1 mg mL–1 aq solutions of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))400). (D) Dry-state TEM image obtained from a 1 mg mL–1 solution of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))400 in water. (E) Representative AFM image obtained from a 5 mg mL–1 solution of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))50 graft copolymer in water.

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Table 1. Molecular Characteristics of P(NB-NBoc)n Prepared via Solution ROMP Using Different Initial [NB-NBoc]/[G3] Ratios, as Determined by 1H NMR Spectroscopy and SEC Analysis
[NB-NBoc]/[G3] % conv.a Mn,theo. (kDa)b Mn,SEC (kDa)c ĐM,SECc
50 >99 15.3 17.6 1.11
100 >99 30.6 34.5 1.11
200 >99 61.3 61.4 1.15
400 >99 122.4 103.8 1.23
a

Monomer conversion calculated from 1H NMR spectroscopy in CDCl3.

b

Calculated from conversion.

c

Mn and ĐM values calculated from PMMA standards using DMF + 5 mM NH4BF4 as the eluent.

ω-N-Hydroxysuccinimide-poly(vinyl acetate) (NHS-PVAc) was then prepared by photo-RAFT/MADIX to maximize end-group fidelity and was subsequently grafted to P(NB-NH2) homopolymers. See the Synthetic Procedures section in the Supporting Information (NHS-PVAc210, Conv. = 69%, Mn,SEC RI = 22.8 kDa, ĐM = 1.56) (Figures S3–S7, Table 2). (36,37) Following isolation, P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) graft copolymers were characterized by SEC analysis revealing bimodal peaks at high-molecular-weight direction. Figure 1B shows corresponding SEC curves of the NHS-PVAc210 side chain (dashed black curve) and the resultant graft copolymers, in which the peak positions of the graft copolymers completely shifted to higher molecular weights. A significant amount of unfunctionalized NHS-PVAc210 was also apparent for all graft copolymer formulations. Grafted side chains (%) of the resulting graft copolymers from SEC analysis were estimated to be ca. 20–40% (Table 2), due to steric repulsions between bulky side chains, limiting grafting density. (34,35) The acetate protecting groups were quantitively removed by an excess of hydrazine hydrate to yield P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n graft copolymers that were purified by dialysis (MWCO = 300 kDa) to remove unfunctionalized PVA210 and characterized by 1H NMR and FTIR spectroscopic analysis (Figures S20 and S21, Supporting Information).
Table 2. Molecular Characteristics of P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) Graft Copolymers as Determined by SEC Analysisc
sample Mn,SEC (kDa)a ĐM,SECa grafted side chains (%)b
NHS-PVAc210 22.8 1.56 ------
P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))50 378.6 1.10 33.0
P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))100 557.4 1.23 24.0
P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))200 1013.4 1.21 22.0
P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))400 1539.4 1.44 17.0
a

Mn and ĐM values calculated from PMMA standards using DMF + 0.1% LiBr as the eluent.

b

Calculated from SEC curves of reaction mixture before and after modification.

c

Grafted side chains (%) = (Mn,SEC RI, graft copolymer – (Mn,P(NB-NH2), theo)/Mn,SEC RI, NHS-PVAc210).

The solution behavior of the resulting PVA graft copolymers was investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). DLS analysis showed that graft copolymer samples exhibited an increase in length upon increasing the backbone of P(NB-NH2)n (Figure 1C). The fact that these traces are multimodal can be rationalized by considering additional relaxations occurring, which contributed to the scattering profile due to the anisotropy of the bottlebrush polymers in solution. (38) Dry-state TEM images of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n confirmed the presence of small cylindrical nanostructures (Figures 1D and S22). Importantly, no large aggregates were observed in the TEM images, indicating that neither graft copolymers were spontaneously self-assembled into higher-order structures when dissolved in aqueous media at room temperature. AFM analysis also showed the formation of some spherical particles (Figures 1E and S23). While the PVA graft copolymers appear to be spherical in the AFM images, they likely exist as cylindrical nanostructures in aqueous environments (as confirmed by TEM analysis) due to their anisotropic dimensions, as has been reported for brush polymers in solution measured using X-ray or neutron scattering analyses. (39,40) Moreover, brush polymers have been shown to de-wet various substrates due to unfavorable surface interactions, causing them to present as globules in AFM images. (13,41)
Next, a series of high-density PVA bottlebrush polymers were prepared using ROMP “grafting-through” approach using a norbornene-end poly(vinyl acetate) macromonomer (NB-PVAc), Figure 2A. Exo-5-norbornene-2-methylamine was synthesized in this case (Figures S8–S15; see the Synthetic Procedures section in the Supporting Information), as it was demonstrated by Matson and co-workers that the choice of anchor group dramatically affects overall ROMP propagation rates with norbornene anhydride-based macromonomers leading to poorer chain extensions and conversions when targeting high Mw bottlebrushes. (42,43)

Figure 2

Figure 2. (A) Design and synthesis of dense PVA-based brush copolymers generated via “grafting-through” procedure. Schematic representation of the synthetic route followed for the preparation of PNBn-g-PVA208 (n = 20, 30, 40) bottlebrush polymers. (B) Normalized SEC-RI chromatograms for PVAc bottlebrush precursors in DMF + 0.1% LiBr and solution characterization of resulting PVA bottlebrushes in water via (C) DLS analysis (inset: representative photograph of 1 mg mL–1 aq solutions of PNB40-g-PVA208). (D) Dry-state TEM images obtained from a 1 mg mL–1 solution of PNB40-g-PVA208 in water; (E) representative AFM images obtained from a 5 mg mL–1 solution of PNB20-g-PVA208 bottlebrush polymer in water.

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A norbornyl xanthate chain-transfer agent (NB-CTA) of 2-(ethoxycarbonothioylthio)-2-methylpropanoic acid exo-5-norbornene-2-methylamide was synthesized and used to prepare an NB-PVAc208 macromonomer via photo-initiated RAFT/MADIX polymerization (NB-PVAc208, Conv. = 67%, Mn,SEC RI = 17.9 kDa, ĐM = 1.4). Bottlebrush polymers were synthesized through ROMP of the norbornene amide end group on the PVAc macromonomer by varying the molar ratio of G3 catalyst ([NB-PVAc208]/[G3]) to achieve PNBn-g-PVAc208 bottlebrush polymers (n = 20, 30 and 40).
SEC analysis revealed low-molecular-weight shoulders, which may correspond to unreacted NB-PVAc208 macromonomer. However, the long low-molecular-weight fraction could also be explained by the premature termination of ROMP polymers. Large ĐM values can be primarily attributed to the employment of a high Mw of PVAc macromonomer with a relatively large dispersity (Figure 2B and Table 3) as well as the above-mentioned premature termination events. In addition, number-average molecular weight values (Mn) determined by SEC analysis were evidently lower than theoretically expected values determined from polymerization conversions. This discrepancy in theoretical and observed Mn likely originates from the branched nature of the bottlebrush polymers, leading to reduced hydrodynamic volumes relative to linear polymers of the same molecular weight and thus increased retention on the SEC columns. Acetate protecting groups were removed by hydrazine hydrate, as confirmed by 1H NMR and FTIR analyses (Figures S24 and S25) to yield PNBn-g-PVA208 (n = 20, 30, 40) bottlebrush polymers that were dialyzed (MWCO = 300 kDa) to ensure removal of unreacted NB-PVA208 macromonomer.
Table 3. Molecular Characteristics of PNBn-g-PVAc208 (n = 20, 30, 40) Bottlebrush Polymers Prepared via ROMP Using Different Initial [NB-PVAc208]/[G3] Ratios, as Determined by 1H NMR Spectroscopy and SEC Analysis
[NB-PVAc208]/[G3] % conv.a Mn,theo. (kDa)b Mn,SEC (kDa)c ĐM,SECc
20 >99 358.0 162.6 2.11
30 >99 537.0 241.1 2.41
40 >99 716.0 340.3 2.39
a

Monomer conversion calculated from 1H NMR spectroscopy in CDCl3.

b

Calculated from conversion.

c

Mn and ĐM values calculated from PMMA standards using DMF + 0.1% LiBr as the eluent.

DLS analysis also confirmed the formation of anisotropic particles and exhibited an increase in size upon increasing the backbone, as expected (Figure 2C). Dry-state TEM images of PNBn-g-PVA208 (n = 20, 30, 40) also confirmed the presence of small cylindrical nanostructures (Figures 2D and S26). AFM analysis again showed the formation of spherical particles, which is likely due to unfavorable surface interactions of PVA side chains with silicon surface, causing them to present as globules (Figures 5 and S27). Since PVA’s side-chain length is by far larger than bottlebrush backbones, it may appear spherical/ellipsoid, but further investigation is beyond the scope of this study as the extended local bottlebrush structure is shown (below) to be sufficient for the intended application.
During the handling of these materials, LCST (lower critical solution temperature) behavior was also observed for dense bottlebrush polymers prepared by ROMP “grafting-through”. This has not previously been reported, due to the absence of high-density PVA copolymers, and was hence explored. It is, however, anticipated that the backbone hydrophobicity for bottlebrushes prepared by “grafting-through” will lead to some self-assembly which may contribute to this behavior. Variable-temperature ultraviolet–visible (UV–vis) spectroscopy showed a cloud point of approximately 51 °C for PNB20-g-PVA208 and 54 °C for PNB40-g-PVA208 (Figure 3A). No apparent LCST behavior was observed for PVA graft copolymers prepared by “grafting-to” except for P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))400 that exhibited a decrease in transmittance at 75 °C, confirming that the side chain density is having a significant impact on the solution behavior of these polymers. DLS temperature ramp experiment for dense bottlebrush polymers showed a stepwise increase in the size of the dissolved nanostructures that occurred as the solution was heated above 40 °C (Figure 3B). Linear PVA homopolymers are known to possess LCST behavior in aqueous media close to water’s boiling point (∼100 °C), which is reduced by alkylation and increases with molecular weight, which agrees with these observations here. (44) The close packing of polymer chains in this bottlebrush state facilitates the exclusion of water upon heating, lowering the temperature at which this transition occurs, and confirms that the solution properties compared to linear polymers are distinct. (45)

Figure 3

Figure 3. Evaluation of the thermoresponsive behavior for P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 400) and PNBn-g-PVA208 (n = 20, 40) bottlebrush polymers by (A) UV–vis spectroscopy and (B) variable-temperature DLS analysis. Samples were run from 20 to 85 °C at 1 mg mL–1 in water, with the UV–vis transmittance spectra recorded at λ = 700 nm (inset: UV–vis cuvettes containing 1 mg mL–1 solution of PNB40-g-PVA208 at 25 °C (left) before and after heating at 85 °C (right)).

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With this panel of bottlebrush polymers prepared, and their solution properties evaluated, the ice-binding interactions were then investigated, by assessment of their IRI (ice recrystallization inhibition) activity (Figure 4A). This was achieved by the “splat assay”, whereby small ice crystals are formed at −78 °C, then allowed to grow at −8 °C, and their growth was measured. (11,46) Smaller MGS (mean grain size) means more ice recrystallization inhibition activity. Figure 4A(I) shows dose-dependent IRI of the polymer library vs controls of linear PVA. In all cases, there was a small but significant increase in IRI activity, with the bottlebrushes (high and low density) inhibiting below 0.1 mg mL–1. It has been previously reported that increasing the molecular weight of PVA increases IRI activity (11) explaining these observations, although architecture-related enhancements cannot be fully ruled out. Voets and co-workers have previously prepared an acrylate-based PVA bottlebrush polymer using ATRP, which also showed no significant change in IRI compared to linear. (13) In this previous work, there was no investigation of ice nucleation activity (see below). Note it was not possible to compare against linear PVA of the same MW, as linear PVA becomes increasingly insoluble in aqueous solutions at high MW, justifying our nonlinear synthetic approach to access PVA, which could not be obtained by conventional methods. The ROMP-derived backbones P(NB-NH2)n (n = 50, 100, 200, 400) were tested as a control (Figure 4A(II)) showing weak IRI. It should be noted that we have previously shown that the facial amphiphilicity of ROMP-derived polymers can lead to observable IRI activity. The magnitude of IRI of the control amino-functional polymers P(BN-NH2) was significantly less than this previous report but is not negligible. (47)

Figure 4

Figure 4. Assessment of ice recrystallization inhibition activity and ice-binding. (A) IRI activity summary of (I) P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) graft copolymers, PNBn-g-PVA208 (n = 20, 30, 40) bottlebrush polymers and (II) P(NB-NH2)n (n = 50, 100, 200, 400) and PEG-based control samples. Error bars are ±SD from a minimum of three repeats. The percent mean grain size (MGS) was reported relative to PBS control. (B) Modified “sucrose sandwich” ice shaping assay images for no additive (I) and 1 mg mL–1 of PVA210 (II), P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))400 (III) and PNB40-g-PVA208 (IV) in 45 wt % sucrose solution.

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A PEG-based graft copolymer (as a non-PVA, nonlinear control) was also synthesized using an N-hydroxysuccinimide-poly(ethylene glycol) (NHS-PEG227) and grafted into the presynthesized poly(amino norbornene imide) P(NB-NH2)200 homopolymer to yield P((P(NB-NH)-g-PEG227)-stat-P(NB-NH2))200 (see the Synthetic Procedures section in the Supporting Information, Figures S28 and S29). A PEG methacrylate monomer (PEGMA20) was also employed to prepare P(PEGMA20)200 homopolymer (Figures S30 and S31). In both cases, nonlinear PEG controls were shown to have no appreciable IRI activity. Ice shaping (in sucrose solutions) showed that the PVA graft copolymers and bottlebrushes lead to more faceting of ice crystals, compared to linear PVA homopolymer (Figures 4B and S32–S35), as the large polymers can span multiple crystals as seen previously for PVA-grafted nanoparticles (14) and AFP dendrimers. (48) Single crystal assays (using a nanoliter osmometer) in contrast did not show shaping, suggesting that steric confinement does impact the ice/polymer interface (Figure S36, Supporting Information).
With the confirmation of ice binding (shown above), ice nucleation measurements could be undertaken. Pure liquid water can supercool to temperatures as low as −40 °C. It is thought that heterogeneous ice nucleators must template an ice critical cluster of a size predicted by classical nucleation theory (CNT). (32) To achieve ice nucleation at −5 °C, a nucleator is predicted to support a cap-shaped cluster possessing a diameter of around 10 nm. (32) As shown in Figures 1C and 2C, the bottlebrushes are above this size threshold.
Two ice nucleation measurement techniques were employed here. To investigate the ice nucleation ability at temperatures close to the homogeneous freezing temperature, water-in-oil emulsion droplets of roughly 2 pL (Figures S37 and S38, Supporting Information) were frozen in a differential scanning calorimeter (DSC) by cooling at 1 °C/min, using a technique similar to that of Marcolli et al. (49)Figure 5B shows the DSC curves obtained, with the onset point of the exothermic peak caused by water crystallization defined as the ice nucleation temperature, Tf. Marcolli et al. found a Tf of −36.5 °C for droplets for emulsions containing pure water droplets of roughly the same size, while Ogawa et al. found aTf of −37.5 °C for a pure water emulsion of smaller droplets. We determined Tf for pure Milli-Q water to be −36.9 °C. This temperature is taken to represent the onset of homogeneous ice nucleation in our system. Similar emulsions containing 2 mg mL–1 linear and bottlebrush PVA samples were prepared so that each emulsion droplet will contain more than a million of even the largest bottlebrush. As shown in Figure 5 linear PVA4000 increased Tf by 3.5 °C compared to pure water (i.e ΔTf = 3.5 °C). For linear PVA210, a ΔTf of 3.2 °C was determined. This is qualitatively consistent with the findings of Ogawa et al., who found that the mass proportion of PVA present in an experiment determined the shift in nucleation temperature, rather than molar concentration (Figure S39). (33) The ΔTf observed for linear PVA is larger than that measured by Ogawa et al. who found a maximum value of approximately 2 °C for 2 mg mL–1 PVA solutions. The reason for this disparity is not clear. We observed that low-density bottlebrushes nucleated at lower temperatures than linear PVA, while high-molecular-weight high-density bottlebrushes nucleated at warmer temperatures, with a maximum ΔTf of 4.5 °C for PNB40-g-PVA208, equivalent to a nucleation onset of −32.4 °C. For both high- and low-density bottlebrushes, a trend to higher nucleation temperatures was observed as the total molecular weight of the polymers increased, noting the large error in SEC of bottlebrushes.

Figure 5

Figure 5. Assessment of ice nucleation activity of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 100, 200, 400) graft copolymers and PNBn-g-PVA208 (n = 20, 30, 40) bottlebrush polymers in (A) droplet fraction frozen for 1 μL water droplets containing various polymers. Confidence intervals were calculated using a Monte Carlo simulation described in the SI. (B) DSC analysis of picoliter water-in-oil emulsion droplets containing the polymers.

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To investigate the nucleation ability of larger quantities of the PVAs, microliter droplet freezing assays (50) were conducted. In this assay, pure water droplets usually freeze at around −33 °C, above the homogeneous nucleation temperature. This is due to the inevitable presence of ice-nucleating impurities in the water and supporting substrates employed. (51) As with the DSC measurements, 2 mg mL–1 solutions were prepared, and each droplet contains >1012 individual PVA molecules. The results are shown in Figure 5A.
Due to the variability of background measurements in this type of experiment, great care needs to be applied in interpreting results. The two linear PVAs (PVA4000 and PVA210) and P(PEGMA20)200 nucleated at temperatures slightly warmer temperatures than the instrument background. As neither of these polymers can bind ice, they provide a negative control for the PVA bottlebrushes. In contrast, the various PVA bottlebrushes were observed to all nucleate ice at temperatures higher than the freezing background and higher than the linear PVAs, showing that this macromolecular engineering approach to high-density PVA does lead to polymeric ice nucleating agents.
The less densely grafted P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) showed intermediate activity, while the densely grafted PNBn-g-PVA208 (n = 20, 30, 40) were more active, suggesting that dense presentation of PVA side chains is essential for nucleation activity─these trends are shown in Figure S39. With the much smaller droplets frozen in the DSC measurements, where each droplet contains molecules of the order of 106, the low-density bottlebrushes nucleated ice less well than linear PVA, while the high-density bottlebrushes nucleated ice better than linear PVA.
High-density PNB40-g-PVA208 was observed to nucleate ice at average temperatures as warm as −19.2 °C, which is unprecedented for a fully synthetic soluble material. We have previously reported that large (>200 nm) polymer nanoparticles with a poly(vinyl pyrrolidone), PVP, corona also nucleated ice at similar temperatures. (52) The large size and dense display in those particles may be related, but the particles did not have variable density coronas so the structure–property relationship was not clear. These particles did show weak ice binding (and IRI) and hence agree with the results here. Soluble extracts from pollen, which are thought to be polysaccharides, have been reported to nucleate ice, but they have not been characterized. (31) It is worth noting that the largest bottlebrushes did show some aggregation in solution, so the contribution of a small number of larger aggregates is impossible to exclude, in this initial report.
There is evidence that ice nucleating protein activity is related to other ice-binding proteins based on their size and packing. (3,32,53) The mechanism(s) of heterogeneous ice nucleation is not fully understood, even for the long-studied ice nucleation protein from Pseudomonas syringae. This is in part due to the challenge of studying membrane-anchored proteins, and that isolation of these as pure protein domains does not recapitulate the 3D assembly. Protein expression techniques only allow for linear extension (in a single protein), whereas this polymeric strategy provides defined macromolecules with multiple ice binding domains in a constrained manner, therefore providing experimental evidence that crowding and size are essential for nucleation, in agreement with modeling of IBPs. (3) CNT suggests that a nucleation site must have a diameter of between 2 and 5 nm, to nucleate ice at −19 °C, with the size depending on the strength of the interaction with the ice critical cluster. The bottlebrushes are each at least 100 nm across and therefore larger than the ice cluster. It seems likely that the occasional patch of bottlebrush surface assumes a conformation that is sufficiently icelike to act as a nucleation site. In our ice nucleation experiments, we kept the mass of polymer per droplet the same while varying the size of the polymers.
This means that our experiments using larger bottlebrushes, which induce ice nucleation at higher temperatures, had less polymer surface area in contact with water. Simulations suggest that curved surfaces nucleate ice less well than flat surfaces. (54) We tentatively suggest that the lesser curvature of the larger bottlebrushes increases the likelihood that they harbor an active site, and that for more rigid conformation, high-density bottlebrushes similarly favor the emergence of larger flat areas of icelike structure in the polymer surfaces. While the magnitude of ice nucleation activity observed here is much less than that for ice nucleating proteins, the ability to sequentially modify a bottom-up synthesized chemical nucleator will enable new avenues of discovery in the study of ice nucleators, not possible with biological materials, or the poorly defined inorganic nucleator.

Conclusions

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Here, we report a synthetic polymer capable of nucleating ice, inspired by how ice-binding proteins assemble into ice-nucleating structures. Our design was based on molecular bottlebrushes with (ice binding) PVA side chains, with the side-chain density tuned using ROMP to enable “grafting-through” (high density) or “grafting-to” (low density). The bottlebrush polymers were fully characterized, confirming the confinement of the PVA chains in the higher-density brushes, which also gave rise to LCST-type behavior, not seen for linear equivalents. The bottlebrush polymers were found to bind ice and retain their potent ice-recrystallization inhibition activity, with a slight increase relative to linear PVA. However, due to the limited solubility of high-MW linear PVA, this effect could be due to the size increase, rather than a pure architectural effect. Using ice nucleation assays, we observed that high-density PVA bottlebrushes significantly increased the ice nucleation temperature compared to other materials. Lower-density PVA brushes also favored nucleation in microliter droplet freezing assays, although they nucleated ice at colder temperatures than linear PVA in an emulsion freezing experiment using picoliter scale droplets. We hypothesize that larger bottlebrushes are more likely to possess an ice nucleation site due to their low degree of curvature and that the conformational rigidity of high-density bottlebrushes is again expected to favor the formation of flat, icelike water–polymer interfaces that can act as ice nucleation sites. The role of aggregates of these brushes could not be excluded. Our strategy of controlling side-chain density would be challenging with protein engineering tools alone. These materials may guide the development of new ice nucleators for cryobiology as synthetic probes to elucidate fundamental mechanisms of action and show that programmable ice nucleation from bottom-up synthesis may be achievable.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.biomac.2c01097.

  • Materials and additional synthetic methods; experimental procedures; synthetic procedures; supplementary NMR, SEC, FTIR, DLS, TEM, and AFM data; and additional ice shaping/nucleation data (PDF)

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Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Authors
    • Thomas F. Whale - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.;  Email: [email protected]
    • Matthew I. Gibson - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.;  Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.;  Orcidhttps://orcid.org/0000-0002-8297-1278;  Email: [email protected]
  • Authors
    • Panagiotis G. Georgiou - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.;  Orcidhttps://orcid.org/0000-0001-8968-1057
    • Nina L. H. Kinney - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.;  Orcidhttps://orcid.org/0000-0003-3123-7361
    • Ioanna Kontopoulou - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
    • Alexander N. Baker - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
    • Steven A. Hindmarsh - Department of Physics, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
    • Akalabya Bissoyi - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
    • Thomas R. Congdon - Department of Chemistry, University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, U.K.
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This project (MIG) received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement nos. 866056 and 899872) and the Royal Society for an Industry Fellowship (191037) joint with Cytiva. This project also received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 814236. T.F.W. thanks the Leverhulme Trust and the University of Warwick for supporting an Early Career Fellowship (ECF- 2018-127). N.K. thanks the Natural Environment Research Council (NE/S007350/1) for a PhD studentship. The Warwick Polymer Research Technology Platform is acknowledged for SEC analysis, and the Warwick Electron Microscopy Research Technology Platform is acknowledged for TEM and AFM. The authors also acknowledge the University of Warwick Advanced Bioimaging Research Technology Platform supported by BBSRC ALERT14 Award BB/M01228X/1 and Dr. S. Bakker for TEM. Dr. D.J Fox is thanked for assistance with the (safe handling) of the LiAlH4 reduction step. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) license to any author-accepted manuscript version arising from this submission.

References

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  5. 5
    Forbes, J.; Bissoyi, A.; Eickhoff, L.; Reicher, N.; Hansen, T.; Bon, C. G.; Walker, V. K.; Koop, T.; Rudich, Y.; Braslavsky, I.; Davies, P. L. Water-Organizing Motif Continuity Is Critical for Potent Ice Nucleation Protein Activity. Nat. Commun. 2022, 13, 5019  DOI: 10.1038/s41467-022-32469-9
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    5
    Water-organizing motif continuity is critical for potent ice nucleation protein activity
    Forbes, Jordan; Bissoyi, Akalabya; Eickhoff, Lukas; Reicher, Naama; Hansen, Thomas; Bon, Christopher G.; Walker, Virginia K.; Koop, Thomas; Rudich, Yinon; Braslavsky, Ido; Davies, Peter L.
    Nature Communications (2022), 13 (1), 5019CODEN: NCAOBW; ISSN:2041-1723. (Nature Portfolio)
    Bacterial ice nucleation proteins (INPs) can cause frost damage to plants by nucleating ice formation at high sub-zero temps. Modeling of Pseudomonas borealis INP by AlphaFold suggests that the central domain of 65 tandem sixteen-residue repeats forms a beta-solenoid with arrays of outward-pointing threonines and tyrosines, which may organize water mols. into an ice-like pattern. Here we report that mutating some of these residues in a central segment of P. borealis INP, expressed in Escherichia coli, decreases ice nucleation activity more than the section's deletion. Insertion of a bulky domain has the same effect, indicating that the continuity of the water-organizing repeats is crit. for optimal activity. The ∼10 C-terminal coils differ from the other 55 coils in being more basic and lacking water-organizing motifs; deletion of this region eliminates INP activity. We show through sequence modifications how arrays of conserved motifs form the large ice-nucleating surface required for potency.
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  6. 6
    Voets, I. K. From Ice-Binding Proteins to Bio-Inspired Antifreeze Materials. Soft Matter 2017, 13, 4808– 4823,  DOI: 10.1039/C6SM02867E
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    6
    From ice-binding proteins to bio-inspired antifreeze materials
    Voets, I. K.
    Soft Matter (2017), 13 (28), 4808-4823CODEN: SMOABF; ISSN:1744-6848. (Royal Society of Chemistry)
    Ice-binding proteins (IBP) facilitate survival under extreme conditions in diverse life forms. IBPs in polar fishes block further growth of internalized environmental ice and inhibit ice recrystn. of accumulated internal crystals. Algae use IBPs to structure ice, while ice adhesion is crit. for the Antarctic bacterium Marinomonas primoryensis. Successful translation of this natural cryoprotective ability into man-made materials holds great promise but is still in its infancy. This review covers recent advances in the field of ice-binding proteins and their synthetic analogs, highlighting fundamental insights into IBP functioning as a foundation for the knowledge-based development of cheap, bio-inspired mimics through scalable prodn. routes. Recent advances in the utilization of IBPs and their analogs to e.g. improve cryopreservation, ice-templating strategies, gas hydrate inhibition and other technologies are presented.
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  7. 7
    Biggs, C. I.; Bailey, T. L.; Graham, B.; Stubbs, C.; Fayter, A.; Gibson, M. I. Polymer Mimics of Biomacromolecular Antifreezes. Nat. Commun. 2017, 8, 1546  DOI: 10.1038/s41467-017-01421-7
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    7
    Polymer mimics of biomacromolecular antifreezes
    Biggs Caroline I; Bailey Trisha L; Ben Graham; Stubbs Christopher; Fayter Alice; Gibson Matthew I; Gibson Matthew I
    Nature communications (2017), 8 (1), 1546 ISSN:.
    Antifreeze proteins from polar fish species are remarkable biomacromolecules which prevent the growth of ice crystals. Ice crystal growth is a major problem in cell/tissue cryopreservation for transplantation, transfusion and basic biomedical research, as well as technological applications such as icing of aircraft wings. This review will introduce the rapidly emerging field of synthetic macromolecular (polymer) mimics of antifreeze proteins. Particular focus is placed on designing polymers which have no structural similarities to antifreeze proteins but reproduce the same macroscopic properties, potentially by different molecular-level mechanisms. The application of these polymers to the cryopreservation of donor cells is also introduced.
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  8. 8
    He, Z.; Liu, K.; Wang, J. Bioinspired Materials for Controlling Ice Nucleation, Growth, and Recrystallization. Acc. Chem. Res. 2018, 51, 1082– 1091,  DOI: 10.1021/acs.accounts.7b00528
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    8
    Bioinspired Materials for Controlling Ice Nucleation, Growth, and Recrystallization
    He, Zhiyuan; Liu, Kai; Wang, Jianjun
    Accounts of Chemical Research (2018), 51 (5), 1082-1091CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. Ice formation, mainly consisting of ice nucleation, ice growth, and ice recrystn., is ubiquitous and crucial in wide-ranging fields from cryobiol. to atm. physics. Despite active research for more than a century, the mechanism of ice formation is still far from satisfactory. Meanwhile, nature has unique ways of controlling ice formation and can provide resourceful avenues to unravel the mechanism of ice formation. For instance, antifreeze proteins (AFPs) protect living organisms from freezing damage via controlling ice formation, for example, tuning ice nucleation, shaping ice crystals, and inhibiting ice growth and recrystn. In addn., AFP mimics can have applications in cryopreservation of cells, tissues, and organs, food storage, and anti-icing materials. Therefore, continuous efforts have been made to understand the mechanism of AFPs and design AFP inspired materials.In this Account, the authors first review the authors' recent research progress in understanding the mechanism of AFPs in controlling ice formation. A Janus effect of AFPs on ice nucleation was discovered, which was achieved via selectively tethering the ice-binding face (IBF) or the non-ice-binding face (NIBF) of AFPs to solid surfaces and studying specifically the effect of the other face on ice nucleation. Through mol. dynamics (MD) simulation anal., the authors obsd. ordered hexagonal ice-like water structure atop the IBF and disordered water structure atop the NIBF. Therefore, the interfacial water plays a crit. role in controlling ice formation.Next, the design and fabrication of AFP mimics with capabilities in tuning ice nucleation and controlling ice shape and growth, as well as inhibiting ice recrystn are discussed. For example, the authors tuned ice nucleation via modifying solid surfaces with supercharged unfolded polypeptides (SUPs) and polyelectrolyte brushes (PBs) with different counterions. The authors found graphene oxide (GO) and oxidized quasi-carbon nitride quantum dots (OQCNs) had profound effects in controlling ice shape and inhibiting ice growth. The authors also studied the ion-specific effect on ice recrystn. inhibition (IRI) with a large variety of anions and cations. All functionalities are achieved by tuning the properties of interfacial water on these materials, which reinforces the importance of the interfacial water in controlling ice formation. Finally, the authors review the development of novel application-oriented materials emerging from the authors' enhanced understanding of ice formation, for example, ultralow ice adhesion coatings with aq. lubricating layer, cryopreservation of cells by inhibiting ice recrystn., and two-dimensional (2D) and three-dimensional (3D) porous materials with tunable pore sizes through recrystd. ice crystal templates. This Account sheds new light on the mol. mechanism of ice formation and will inspire the design of unprecedented functional materials based on controlled ice formation.
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  9. 9
    Inada, T.; Lu, S. S. Inhibition of Recrystallization of Ice Grains by Adsorption of Poly(Vinyl Alcohol) onto Ice Surfaces. Cryst. Growth Des. 2003, 3, 747– 752,  DOI: 10.1021/cg0340300
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    9
    Inhibition of Recrystallization of Ice Grains by Adsorption of Poly(Vinyl Alcohol) onto Ice Surfaces
    Inada, Takaaki; Lu, Shu-Shen
    Crystal Growth & Design (2003), 3 (5), 747-752CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    The effect of poly(vinyl alc.) (PVA) on recrystn. of ice was studied by comparison with the effect of antifreeze protein (AFP) type I. Polycryst. ice wafers consisting of numerous ice grains, whose initial size was <130 μm (i.e., less than the thickness of the ice wafer) were made from solns. contg. PVA or AFP type I at various concns. The ice wafers were annealed between -2.3 and -2.0° for 5 h, and then the size of the ice grains was measured using digital microscopy. Even at a PVA concn. as low as ∼5 × 10-7 mol/L, the size of the annealed ice grains made from the PVA soln. did not change significantly from the initial size, indicating that PVA is as effective as AFP type I in inhibiting ice recrystn. The effectiveness of PVA increased (i.e., the grain size decreased) with increasing molar concn., mol. wt., or degree of hydrolysis of PVA. The function of PVA mols. in the inhibition of recrystn. was analyzed by using the Langmuir adsorption equation.
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  10. 10
    Budke, C.; Koop, T. Ice Recrystallization Inhibition and Molecular Recognition of Ice Faces by Poly(Vinyl Alcohol). ChemPhysChem 2006, 7, 2601– 2606,  DOI: 10.1002/cphc.200600533
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    10
    Ice recrystallization inhibition and molecular recognition of ice faces by poly(vinyl alcohol)
    Budke, Carsten; Koop, Thomas
    ChemPhysChem (2006), 7 (12), 2601-2606CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The effects of poly(vinyl alc.) (PVA) on the Ostwald ripening of polycryst. ice samples are studied. At -6°, ice recrystn. in sucrose solns. is inhibited at PVA concns. down to 0.005 mg mL-1, with a recrystn. inhibition const. of 48.9 mL mg-1. Ice growth-habit expts. reveal mol. recognition of the arrangement of H2O mols. in the ice by PVA mols., and indicate that PVA mols. adsorb to the primary and secondary prism faces of hexagonal ice, 1h. Based on these observations, together with an anal. of the O-atom pattern in ice and the conformation of OH groups in PVA, an adsorption model is proposed. Probably PVA segments adsorb to the primary and secondary prism faces of ice parallel to the c axis with a linear misfit parameter of only 2.7%, most likely via multiple H bonds. The proposed adsorption mechanism is discussed in the light of recent thermal hysteresis and scanning tunneling microscopy expts.
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  11. 11
    Congdon, T.; Notman, R.; Gibson, M. I. Antifreeze (Glyco)Protein Mimetic Behavior of Poly(Vinyl Alcohol): Detailed Structure Ice Recrystallization Inhibition Activity Study. Biomacromolecules 2013, 14, 1578– 1586,  DOI: 10.1021/bm400217j
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    11
    Antifreeze (Glyco)protein Mimetic Behavior of Poly(vinyl alcohol): Detailed Structure Ice Recrystallization Inhibition Activity Study
    Congdon, Thomas; Notman, Rebecca; Gibson, Matthew I.
    Biomacromolecules (2013), 14 (5), 1578-1586CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)
    This manuscript reports a detailed study on the ability of poly(vinyl alc.) to act as a biomimetic surrogate for AF(G)Ps ("antifreeze(glyco)proteins"), with a focus on the specific property of ice-recrystn. inhibition (IRI). Despite over 40 years of study, the underlying mechanisms that govern the action of biol. antifreezes are still poorly understood, which is in part due to their limited availability and challenging synthesis. Poly(vinyl alc.) (PVA) has been shown to display remarkable ice recrystn. inhibition activity despite its major structural differences to native antifreeze proteins. Here, controlled radical polymn. is used to synthesize well-defined PVA, which has enabled us to obtain the first quant. structure-activity relationships, to probe the role of mol. wt. and comonomers on IRI activity. Crucially, it was found that IRI activity is "switched on" when the polymer chain length increases from 10 and 20 repeat units. Substitution of the polymer side chains with hydrophilic or hydrophobic units was found to diminish activity. Hydrophobic modifications to the backbone were slightly more tolerated than side chain modifications, which implies an unbroken sequence of hydroxyl units is necessary for activity. These results highlight the idea that although hydrophobic domains are key components of IRI activity, the random inclusion of addnl. hydrophobic units does not guarantee an increase in activity and that the actual polymer conformation is important.
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  12. 12
    Congdon, T. R.; Notman, R.; Gibson, M. I. Synthesis of Star-Branched Poly(Vinyl Alcohol) and Ice Recrystallization Inhibition Activity. Eur. Polym. J. 2017, 88, 320– 327,  DOI: 10.1016/j.eurpolymj.2017.01.039
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    12
    Synthesis of star-branched poly(vinyl alcohol) and ice recrystallization inhibition activity
    Congdon, Thomas R.; Notman, Rebecca; Gibson, Matthew I.
    European Polymer Journal (2017), 88 (), 320-327CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
    Antifreeze proteins are potent inhibitors of ice crystal growth (recrystn.), which is a highly desirable property for cryopreservation and other low temp. applications. It has emerged that relatively simple polymers based on poly(vinyl alc.) can mimic this activity, but the link between architecture and activity is not known. Here, a trifunctional xanthate was designed and synthesized to prep. star-branched poly(vinyl alcs.) by RAFT/Xanthate mediated polymn., and their ice growth inhibition activity probed for the first time. The trifunctional agent design affords the formation of well-defined star polymers, with no evidence of star-star linking, even at high conversions, and narrow mol. wt. dispersity. It is obsd. that three-arm stars have identical activity to two-armed (i.e. linear) equiv., suggesting that the total hydrodynamic size of the polymer (diam. three-arm ∼ two-arm) rather than total valence of the functional groups is the key descriptor of activity.
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  13. 13
    Olijve, L. L. C.; Hendrix, M. M. R. M.; Voets, I. K. Influence of Polymer Chain Architecture of Poly(Vinyl Alcohol) on the Inhibition of Ice Recrystallization. Macromol. Chem. Phys. 2016, 217, 951– 958,  DOI: 10.1002/macp.201500497
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    13
    Influence of Polymer Chain Architecture of Poly(vinyl alcohol) on the Inhibition of Ice Recrystallization
    Olijve, Luuk L. C.; Hendrix, Marco M. R. M.; Voets, Ilja K.
    Macromolecular Chemistry and Physics (2016), 217 (8), 951-958CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Poly(vinyl alc.) (PVA) is a water-sol. synthetic polymer well-known to effectively block the recrystn. of ice. The effect of polymer chain architecture on the ice recrystn. inhibition (IRI) by PVA remains unexplored. In this work, the synthesis of PVA mol. bottlebrushes is described via a combination of atom-transfer radical polymn. and reversible addn.-fragmentation chain-transfer polymn. The facile prepn. of the PVA bottlebrushes is performed via the selective hydrolysis of the chloroacetate esters of the poly(vinyl chloroacetate) (PVClAc) side chains of a PVClAc precursor bottlebrush. The IRI efficacy of the PVA bottlebrush is quant. compared to linear PVA. The results show that even if the PVA chains are densely grafted onto a rigid polymer backbone, the IRI activity of PVA is maintained, demonstrating the flexibility in PVA polymer chain architecture for the design of synthetic PVA-based ice growth inhibitors.
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  14. 14
    Georgiou, P. G.; Kontopoulou, I.; Congdon, T. R.; Gibson, M. I. Ice Recrystallisation Inhibiting Polymer Nano-Objects: Via Saline-Tolerant Polymerisation-Induced Self-Assembly. Mater. Horiz. 2020, 7, 1883– 1887,  DOI: 10.1039/D0MH00354A
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    14
    Ice recrystallisation inhibiting polymer nano-objects via saline-tolerant polymerisation-induced self-assembly
    Georgiou, Panagiotis G.; Kontopoulou, Ioanna; Congdon, Thomas R.; Gibson, Matthew I.
    Materials Horizons (2020), 7 (7), 1883-1887CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    Chem. tools to modulate ice formation/growth have great (bio)technol. value, with ice binding/antifreeze proteins being exciting targets for biomimetic materials. Here we introduce polymer nanomaterials that are potent inhibitors of ice recrystn. using polymn.-induced self-assembly (PISA), employing a poly(vinyl alc.) graft macromol. chain transfer agent (macro-CTA). Crucially, engineering the core-forming block with diacetone acrylamide enabled PISA to be conducted in saline, whereas poly(2-hydroxypropyl methacrylate) cores led to coagulation. The most active particles inhibited ice growth as low as 0.5 mg mL-1, and were more active than the PVA stabilizer block alone, showing that the dense packing of this nanoparticle format enhanced activity. This provides a unique route towards colloids capable of modulating ice growth.
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  15. 15
    Bachtiger, F.; Congdon, T. R.; Stubbs, C.; Gibson, M. I.; Sosso, G. C. The Atomistic Details of the Ice Recrystallisation Inhibition Activity of PVA. Nat. Commun. 2021, 12, 1323  DOI: 10.1038/s41467-021-21717-z
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    15
    The atomistic details of the ice recrystallisation inhibition activity of PVA
    Bachtiger, Fabienne; Congdon, Thomas R.; Stubbs, Christopher; Gibson, Matthew I.; Sosso, Gabriele C.
    Nature Communications (2021), 12 (1), 1323CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    Understanding the ice recrystn. inhibition (IRI) activity of antifreeze biomimetics is crucial to the development of the next generation of cryoprotectants. In this work, we bring together mol. dynamics simulations and quant. exptl. measurements to unravel the microscopic origins of the IRI activity of poly(vinyl)alc. (PVA)-the most potent of biomimetic IRI agents. Contrary to the emerging consensus, we find that PVA does not require a "lattice matching" to ice in order to display IRI activity: instead, it is the effective vol. of PVA and its contact area with the ice surface which dictates its IRI strength. We also find that entropic contributions may play a role in the ice-PVA interaction and we demonstrate that small block co-polymers (up to now thought to be IRI-inactive) might display significant IRI potential. This work clarifies the atomistic details of the IRI activity of PVA and provides novel guidelines for the rational design of cryoprotectants.
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    Naullage, P. M.; Lupi, L.; Molinero, V. Molecular Recognition of Ice by Fully Flexible Molecules. J. Phys. Chem. C 2017, 121, 26949– 26957,  DOI: 10.1021/acs.jpcc.7b10265
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    16
    Molecular Recognition of Ice by Fully Flexible Molecules
    Naullage, Pavithra M.; Lupi, Laura; Molinero, Valeria
    Journal of Physical Chemistry C (2017), 121 (48), 26949-26957CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Cold-acclimatized organisms produce antifreeze proteins that enable them to prevent ice growth and recrystn. at subfreezing conditions. Flatness and rigidity of the ice-binding sites of antifreeze proteins are considered key for their recognition of ice. However, the most potent synthetic ice recrystn. inhibitor (IRI) found to date is polyvinyl alc. (PVA), a fully flexible mol. The ability to tune the architecture and functionalization of PVA makes it a promising candidate to replace antifreeze proteins in industrial applications ranging from cryopreservation of organs to de-icing of turbine blades. However, an understanding of how PVA recognizes ice remains elusive, hampering the design of more effective IRIs. Here, we used large-scale mol. dynamics simulations to elucidate the mechanism by which PVA recognizes ice. We found that the polymer selectively bound to the prismatic faces of ice through a cooperative zipper mechanism. The binding was driven by H-bonding, facilitated by distance matching between the OH groups in PVA and water at the ice surface. Strong, cooperative binding to ice results from the different scaling of the free energy gains on binding per monomer, and the loss of translational and configurational entropy of the chain. We explained why branching of PVA does not improve its IRI activity, and used the new mol. understanding to propose principles for the design of macromols. that bind efficiently to the basal and prismatic planes of ice, producing hyperactive synthetic antifreeze mols. that could compete with the most effective antifreeze proteins.
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  17. 17
    Biggs, C. I.; Stubbs, C.; Graham, B.; Fayter, A. E. R.; Hasan, M.; Gibson, M. I. Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When Is a New Polymer “Active”?. Macromol. Biosci. 2019, 19, 1900082  DOI: 10.1002/mabi.201900082
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    Garnham, C. P.; Campbell, R. L.; Davies, P. L. Anchored Clathrate Waters Bind Antifreeze Proteins to Ice. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 7363– 7367,  DOI: 10.1073/pnas.1100429108
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    18
    Anchored clathrate waters bind antifreeze proteins to ice
    Garnham, Christopher P.; Campbell, Robert L.; Davies, Peter L.
    Proceedings of the National Academy of Sciences of the United States of America (2011), 108 (18), 7363-7367, S7363/1-S7363/3CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    The mechanism by which antifreeze proteins (AFPs) irreversibly bind to ice has not yet been resolved. The ice-binding site of an AFP is relatively hydrophobic, but also contains many potential hydrogen bond donors/acceptors. The extent to which hydrogen bonding and the hydrophobic effect contribute to ice binding has been debated for over 30 years. Here we have elucidated the ice-binding mechanism through solving the first crystal structure of an Antarctic bacterial AFR. This 34-kDa domain, the largest AFP structure detd. to date, folds as a Ca2+-bound parallel beta-helix with an extensive array of ice-like surface waters that are anchored via hydrogen bonds directly to the polypeptide backbone and adjacent side chains. These bound waters make an excellent three-dimensional match to both the primary prism and basal planes of ice and in effect provide an extensive X-ray crystallog. picture of the AFP:ice interaction. This unobstructed view, free from crystal-packing artifacts, shows the contributions of both the hydrophobic effect and hydrogen bonding during AFP adsorption to ice. We term this mode of binding the "anchored clathrate" mechanism of AFP action.
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    Daley, M. E.; Spyracopoulos, L.; Jia, Z.; Davies, P. L.; Sykes, B. D. Structure and Dynamics of an Alpha-Helical Antifreeze Protein. Biochemistry 2002, 41, 5515– 5525,  DOI: 10.1021/bi0121252
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    19
    Structure and Dynamics of a β-Helical Antifreeze Protein
    Daley, Margaret E.; Spyracopoulos, Leo; Jia, Zongchao; Davies, Peter L.; Sykes, Brian D.
    Biochemistry (2002), 41 (17), 5515-5525CODEN: BICHAW; ISSN:0006-2960. (American Chemical Society)
    Antifreeze proteins (AFPs) protect many types of organisms from damage caused by freezing. They do this by binding to the ice surface, which causes inhibition of ice crystal growth. However, the mol. mechanism of ice binding leading to growth inhibition is not well understood. In this paper, we present the soln. structure and backbone NMR relaxation data of the antifreeze protein from the yellow mealworm beetle Tenebrio molitor (TmAFP) to study the dynamics in the context of structure. The full 15N relaxation anal. was completed at two magnetic field strengths, 500 and 600 MHz, as well as at two temps., 30 and 5 °C, to measure the dynamic changes that occur in the protein backbone at different temps. TmAFP is a small, highly disulfide-bonded, right-handed parallel β-helix consisting of seven tandemly repeated 12-amino acid loops. The backbone relaxation data displays a periodic pattern, which reflects both the 12-amino acid structural repeat and the highly anisotropic nature of the protein. Anal. of the 15N relaxation parameters shows that TmAFP is a well-defined, rigid structure, and the extd. parameters show that there is similar restricted internal mobility throughout the protein backbone at both temps. studied. We conclude that the hydrophobic, rigid binding site may reduce the entropic penalty for the binding of the protein to ice. The β-helical fold of the protein provides this rigidity, as it does not appear to be a consequence of cooling toward a physiol. relevant temp.
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  20. 20
    Mochizuki, K.; Molinero, V. Antifreeze Glycoproteins Bind Reversibly to Ice via Hydrophobic Groups. J. Am. Chem. Soc. 2018, 140, 4803– 4811,  DOI: 10.1021/jacs.7b13630
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    20
    Antifreeze Glycoproteins Bind Reversibly to Ice via Hydrophobic Groups
    Mochizuki, Kenji; Molinero, Valeria
    Journal of the American Chemical Society (2018), 140 (14), 4803-4811CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Antifreeze mols. allow organisms to survive in subzero environments. Antifreeze glycoproteins (AFGPs), produced by polar fish, are the most potent inhibitors of ice recrystn. To date, the mol. mechanism by which AFGPs bind to ice has not yet been elucidated. Mutation expts. cannot resolve whether the binding occurs through the peptide, the saccharides, or both. Here, we used mol. dynamics simulations to det. the mechanism and driving forces for binding of AFGP8 to ice, its selectivity for the primary prismatic plane, and the mol. origin of its exceptional ice recrystn. activity. Consistent with expts., AFGP8 in simulations preferentially adopted the polyproline II (PPII) helix secondary structure in soln. We showed that the segregation of hydrophilic and hydrophobic groups in the PPII helix is vital for ice binding. The binding occurred through adsorption of Me groups of the peptide and disaccharides to ice, driven by the entropy of dehydration of the hydrophobic groups as they nested in the cavities at the ice surface. The selectivity to the primary prismatic plane originated in the deeper cavities it had compared to the basal plane. We estd. the free energy of binding of AFGP8 and the longer AFGP4-6, and found them to be consistent with the reversible binding demonstrated in expts. The simulations revealed that AFGP8 binds to ice through a myriad of conformations that it uses to diffuse through the ice surface and find ice steps, to which it strongly adsorbs. We interpret that the existence of multiple, weak binding sites is the key for the exceptional ice recrystn. inhibition activity of AFGPs.
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  21. 21
    Vonnegut, B. The Nucleation of Ice Formation by Silver Iodide. J. Appl. Phys. 1947, 18, 593– 595,  DOI: 10.1063/1.1697813
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    21
    Nucleation of ice formation by silver iodide
    Vonnegut, B.
    Journal of Applied Physics (1947), 18 (), 593-5CODEN: JAPIAU; ISSN:0021-8979.
    AgI particles have been found to serve as nuclei for the formation of ice crystals in supercooled water and in water vapor supersatd. with respect to ice, probably because it very closely resembles ice in crystal structure. The dimensions of the unit cell of ice and of AgI are the same to within approx. 1%. The max. temp. at which AgI particles serve as nuclei is approx. -4° for particles 1μ in diam., and -8° for particles 100 A. in diam. Mixts. of I and Ag vapors are also effective in producing ice nuclei. The most effective method so far found for producing AgI smokes is the following. A cotton string coated with AgI is fed at a fixed rate into an oxyhydrogen flame. A few in. away from the point at which the AgI is introduced the flame is quenched with a blast of compressed air. This produces an invisible smoke of AgI particles approx. 100 A. in diam. One mg. of AgI per sec. produces in this way approx. 1013 ice nuclei per sec.
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  22. 22
    Marcolli, C.; Nagare, B.; Welti, A.; Lohmann, U. Ice Nucleation Efficiency of AgI: Review and New Insights. Atmos. Chem. Phys. 2016, 16, 8915– 8937,  DOI: 10.5194/acp-16-8915-2016
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    22
    Ice nucleation efficiency of AgI: review and new insights
    Marcolli, Claudia; Nagare, Baban; Welti, Andre; Lohmann, Ulrike
    Atmospheric Chemistry and Physics (2016), 16 (14), 8915-8937CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    AgI is one of the best-investigated ice-nucleating substances. It has relevance for the atm. since it is used for glaciogenic cloud seeding. Theor. and exptl. studies over the last 60 years provide a complex picture of silver iodide as an ice-nucleating agent with conflicting and inconsistent results. This review compares exptl. ice nucleation studies in order to analyze the factors that influence the ice nucleation ability of AgI. The following picture emerges from this anal.: the ice nucleation ability of AgI seems to be enhanced when the AgI particle is on the surface of a droplet, which is indeed the position that a particle takes when it can freely move in a droplet. The ice nucleation by particles with surfaces exposed to air depends on water adsorption. AgI surfaces seem to be most efficient at nucleating ice when they are exposed to relative humidity at or even above water satn. For AgI particles that are completely immersed in water, the freezing temp. increases with increasing AgI surface area. Higher threshold freezing temps. seem to correlate with improved lattice matches as can be seen for AgI-AgCl solid solns. and 3AgI·NH4I·6H2O, which have slightly better lattice matches with ice than AgI and also higher threshold freezing temps. However, the effect of a good lattice match is annihilated when the surfaces have charges. Also, the ice nucleation ability seems to decrease during dissoln. of AgI particles. This introduces an addnl. history and time dependence for ice nucleation in cloud chambers with short residence times.
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  23. 23
    Atkinson, J. D.; Murray, B. J.; Woodhouse, M. T.; Whale, T. F.; Baustian, K. J.; Carslaw, K. S.; Dobbie, S.; Sullivan, D. O.; Malkin, T. L. The Importance of Feldspar for Ice Nucleation by Mineral Dust in Mixed-Phase Clouds. Nature 2013, 498, 355– 358,  DOI: 10.1038/nature12278
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    23
    The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds
    Atkinson, James D.; Murray, Benjamin J.; Woodhouse, Matthew T.; Whale, Thomas F.; Baustian, Kelly J.; Carslaw, Kenneth S.; Dobbie, Steven; O'Sullivan, Daniel; Malkin, Tamsin L.
    Nature (London, United Kingdom) (2013), 498 (7454), 355-358CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    The amt. of ice present in mixed-phase clouds, which contain both supercooled liq. water droplets and ice particles, affects cloud extent, lifetime, particle size and radiative properties. The freezing of cloud droplets can be catalyzed by the presence of aerosol particles known as ice nuclei. One of the most important ice nuclei is thought to be mineral dust aerosol from arid regions. It is generally assumed that clay minerals, which contribute approx. two-thirds of the dust mass, dominate ice nucleation by mineral dust, and many exptl. studies have therefore focused on these materials. Here we use an established droplet-freezing technique to show that feldspar minerals dominate ice nucleation by mineral dusts under mixed-phase cloud conditions, despite feldspar being a minor component of dust emitted from arid regions. We also find that clay minerals are relatively unimportant ice nuclei. Our results from a global aerosol model study suggest that feldspar ice nuclei are globally distributed and that feldspar particles may account for a large proportion of the ice nuclei in Earth's atm. that contribute to freezing at temps. below about -15 °C.
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  24. 24
    Holden, M. A.; Whale, T. F.; Tarn, M. D.; O’Sullivan, D.; Walshaw, R. D.; Murray, B. J.; Meldrum, F. C.; Christenson, H. K. High-Speed Imaging of Ice Nucleation in Water Proves the Existence of Active Sites. Sci. Adv. 2019, 5, eaav4316  DOI: 10.1126/sciadv.aav4316
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    Whale, T. F.; Rosillo-Lopez, M.; Murray, B. J.; Salzmann, C. G. Ice Nucleation Properties of Oxidized Carbon Nanomaterials. J. Phys. Chem. Lett. 2015, 6, 3012– 3016,  DOI: 10.1021/acs.jpclett.5b01096
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    25
    Ice Nucleation Properties of Oxidized Carbon Nanomaterials
    Whale, Thomas F.; Rosillo-Lopez, Martin; Murray, Benjamin J.; Salzmann, Christoph G.
    Journal of Physical Chemistry Letters (2015), 6 (15), 3012-3016CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Heterogeneous ice nucleation is an important process in many fields, particularly atm. science, but is still poorly understood. All known inorg. ice nucleating particles are relatively large in size and tend to be hydrophilic. Hence it is not obvious that carbon nanomaterials should nucleate ice. However, in this paper we show that four different readily water-dispersible carbon nanomaterials are capable of nucleating ice. The tested materials were carboxylated graphene nanoflakes, graphene oxide, oxidized single walled carbon nanotubes and oxidized multiwalled carbon nanotubes. The carboxylated graphene nanoflakes have a diam. of ∼30 nm and are among the smallest entities obsd. so far to nucleate ice. Overall, carbon nanotubes were found to nucleate ice more efficiently than flat graphene species, and less oxidized materials nucleated ice more efficiently than more oxidized species. These well-defined carbon nanomaterials may pave the way to bridging the gap between exptl. and computational studies of ice nucleation.
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  26. 26
    Bai, G.; Gao, D.; Liu, Z.; Zhou, X.; Wang, J. Probing the Critical Nucleus Size for Ice Formation with Graphene Oxide Nanosheets. Nature 2019, 576, 437– 441,  DOI: 10.1038/s41586-019-1827-6
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    26
    Probing the critical nucleus size for ice formation with graphene oxide nanosheets
    Bai, Guoying; Gao, Dong; Liu, Zhang; Zhou, Xin; Wang, Jianjun
    Nature (London, United Kingdom) (2019), 576 (7787), 437-441CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
    Water freezing is ubiquitous and affects areas as diverse as climate, the chem. industry, cryobiol. and materials science. Ice nucleation is the controlling step in water freezing1-5 and has, for nearly a century, been assumed to require the formation of a crit. ice nucleus6-10. But there has been no direct exptl. evidence for the existence of such a nucleus, owing to its transient and nanoscale nature6,7. Here we report ice nucleation in water droplets contg. graphene oxide nanosheets of controlled sizes and show that they have a notable impact on ice nucleation only above a certain size that varies with the degree of supercooling of the droplets. We infer from our exptl. data and theor. calcns. that the crit. size of the graphene oxide reflects the size of the crit. ice nucleus, which in the case of sufficiently large graphene oxides sits on their surface and gives rise to ice formation behavior consistent with classical nucleation theory. By contrast, when the graphene oxide size is smaller than that of the crit. ice nucleus, pinning at the periphery of the graphene oxide deforms the ice nucleus as it grows. This gives rise to a much higher free-energy barrier for nucleation and suppresses the promoting effect of the graphene oxide11. The results provide exptl. information on the existence and temp.-dependent size of the crit. ice nucleus, which has previously only been explored theor. and through simulations12-16. As pinning of a pre-crit. nucleus at a nanoparticle edge is not specific to the ice nucleus on graphene oxides, we expect that our approach could be extended to probe the crit. nuclei in other nucleation processes.
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  27. 27
    Pummer, B. G.; Budke, C.; Augustin-Bauditz, S.; Niedermeier, D.; Felgitsch, L.; Kampf, C. J.; Huber, R. G.; Liedl, K. R.; Loerting, T.; Moschen, T. Ice Nucleation by Water-Soluble Macromolecules. Atmos. Chem. Phys. 2015, 15, 4077– 4091,  DOI: 10.5194/acp-15-4077-2015
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    27
    Ice nucleation by water-soluble macromolecules
    Pummer, B. G.; Budke, C.; Augustin-Bauditz, S.; Niedermeier, D.; Felgitsch, L.; Kampf, C. J.; Huber, R. G.; Liedl, K. R.; Loerting, T.; Moschen, T.; Schauperl, M.; Tollinger, M.; Morris, C. E.; Wex, H.; Grothe, H.; Poeschl, U.; Koop, T.; Froehlich-Nowoisky, J.
    Atmospheric Chemistry and Physics (2015), 15 (8), 4077-4091CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Cloud glaciation is critically important for the global radiation budget (albedo) and for initiation of pptn. But the freezing of pure water droplets requires cooling to temps. as low as 235 K. Freezing at higher temps. requires the presence of an ice nucleator, which serves as a template for arranging water mols. in an ice-like manner. It is often assumed that these ice nucleators have to be insol. particles. We point out that also free macromols. which are dissolved in water can efficiently induce ice nucleation: the size of such ice nucleating macromols. (INMs) is in the range of nanometers, corresponding to the size of the crit. ice embryo. As the latter is temp.-dependent, we see a correlation between the size of INMs and the ice nucleation temp. as predicted by classical nucleation theory. Different types of INMs have been found in a wide range of biol. species and comprise a variety of chem. structures including proteins, saccharides, and lipids. Our investigation of the fungal species Acremonium implicatum, Isaria farinosa, and Mortierella alpina shows that their ice nucleation activity is caused by proteinaceous water-sol. INMs. We combine these new results and literature data on INMs from fungi, bacteria, and pollen with theor. calcns. to develop a chem. interpretation of ice nucleation and water-sol. INMs. This has atm. implications since many of these INMs can be released by fragmentation of the carrier cell and subsequently may be distributed independently. Up to now, this process has not been accounted for in atm. models.
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  28. 28
    Sosso, G. C.; Whale, T. F.; Holden, M. A.; Pedevilla, P.; Murray, B. J.; Michaelides, A. Unravelling the Origins of Ice Nucleation on Organic Crystals. Chem. Sci. 2018, 9, 8077– 8088,  DOI: 10.1039/C8SC02753F
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    28
    Unravelling the origins of ice nucleation on organic crystals
    Sosso, Gabriele C.; Whale, Thomas F.; Holden, Mark A.; Pedevilla, Philipp; Murray, Benjamin J.; Michaelides, Angelos
    Chemical Science (2018), 9 (42), 8077-8088CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Org. mols. such as steroids or amino acids form crystals that can facilitate the formation of ice - arguably the most important phase transition on earth. However, the origin of the ice nucleating ability of org. crystals is still largely unknown. Here, we combine expts. and simulations to unravel the microscopic details of ice formation on cholesterol, a prototypical org. crystal widely used in cryopreservation. We find that cholesterol - which is also a substantial component of cell membranes - is an ice nucleating agent more potent than many inorg. substrates, including the mineral feldspar (one of the most active ice nucleating materials in the atm.). SEM measurements reveal a variety of morphol. features on the surfaces of cholesterol crystals: this suggests that the topog. of the surface is key to the broad range of ice nucleating activity obsd. (from -4 to -20°C). In addn., we show via mol. simulations that cholesterol crystals aid the formation of ice nuclei in a unconventional fashion. Rather than providing a template for a flat ice-like contact layer (as found in the case of many inorg. substrates), the flexibility of the cholesterol surface and its low d. of hydrophilic functional groups leads to the formation of mol. cages involving both water mols. and terminal hydroxyl groups of the cholesterol surface. These cages are made of 6- and, surprisingly, 5-membered hydrogen bonded rings of water and hydroxyl groups that favor the nucleation of hexagonal as well as cubic ice (a rare occurrence). We argue that the phenomenal ice nucleating activity of steroids such as cholesterol (and potentially of many other org. crystals) is due to (i) the ability of flexible hydrophilic surfaces to form unconventional ice-templating structures and (ii) the different nucleation sites offered by the diverse topog. of the cryst. surfaces. These findings clarify how exactly org. crystals promote the formation of ice, thus paving the way toward deeper understanding of ice formation in soft and biol. matter - with obvious reverberations on atm. science and cryobiol.
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  29. 29
    Brennan, K. P.; David, R. O.; Borduas-Dedekind, N. Spatial and Temporal Variability in the Ice-Nucleating Ability of Alpine Snowmelt and Extension to Frozen Cloud Fraction. Atmos. Chem. Phys. 2020, 20, 163– 180,  DOI: 10.5194/acp-20-163-2020
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    29
    Spatial and temporal variability in the ice-nucleating ability of alpine snowmelt and extension to frozen cloud fraction
    Brennan, Killian P.; David, Robert O.; Borduas-Dedekind, Nadine
    Atmospheric Chemistry and Physics (2020), 20 (1), 163-180CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
    Ice-nucleating particles (INPs) produce ice from supercooled water droplets through heterogeneous freezing in the atm. INPs have often been collected at the Jungfraujoch research station (at 3500 m a.s.l.) in central Switzerland; yet spatially diverse data on INP occurrence in the Swiss Alps are scarce and remain uncharacterized. We address this scarcity through our Swiss alpine snow sample study which took place during the winter of 2018. We collected a total of 88 fallen snow samples across the Alps at 17 different locations and investigated the impact of altitude, terrain, time since last snowfall and depth upon freezing temps. The INP concns. were measured using the home-built DRoplet Ice Nuclei Counter Zurich (DRINCZ) and were then compared to spatial, temporal and physicochem. parameters. Boxplots of the freezing temps. showed large variability in INP occurrence, even for samples collected 10 m apart on a plain and 1 m apart in depth. Furthermore, undiluted samples had cumulative INP concns. ranging between 1 and 200 INP mL-1 of snowmelt over a temp. range of -5 to -19 °C. From this field-collected dataset, we parameterized the cumulative INP concns. per cubic meter of air as a function of temp. with the following equation c*air(T) = e-0.7T-7.05, comparing well with previously reported pptn. data presented in Petters and Wright (2015). When assuming (1) a snow pptn. origin of the INPs, (2) a cloud water content of 0.4 g m-3 and (3) a crit. INP concn. for glaciation of 10 m-3, the majority of the snow pptd. from clouds with glaciation temps. between -5 and -20 °C. Based on the obsd. variability in INP concns., we conclude that studies conducted at the high-altitude research station Jungfraujoch are representative for INP measurements in the Swiss Alps. Furthermore, the INP concn. ests. in pptn. allow us to extrapolate the concns. to a frozen cloud fraction. Indeed, this approach for estg. the liq. water-to-ice ratio in mixed-phase clouds compares well with aircraft measurements, ground-based lidar and satellite retrievals of frozen cloud fractions. In all, the generated parameterization for INP concns. in snowmelt could help est. cloud glaciation temps.
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  30. 30
    Wilson, T. W.; Ladino, L. A.; Alpert, P. A.; Breckels, M. N.; Brooks, I. M.; Browse, J.; Burrows, S. M.; Carslaw, K. S.; Huffman, J. A.; Judd, C. A Marine Biogenic Source of Atmospheric Ice-Nucleating Particles. Nature 2015, 525, 234– 238,  DOI: 10.1038/nature14986
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    30
    A marine biogenic source of atmospheric ice-nucleating particles
    Wilson, Theodore W.; Ladino, Luis A.; Alpert, Peter A.; Breckels, Mark N.; Brooks, Ian M.; Browse, Jo; Burrows, Susannah M.; Carslaw, Kenneth S.; Huffman, J. Alex; Judd, Christopher; Kilthau, Wendy P.; Mason, Ryan H.; McFiggans, Gordon; Miller, Lisa A.; Najera, Juan J.; Polishchuk, Elena; Rae, Stuart; Schiller, Corinne L.; Si, Meng; Temprado, Jesus Vergara; Whale, Thomas F.; Wong, Jenny P. S.; Wurl, Oliver; Yakobi-Hancock, Jacqueline D.; Abbatt, Jonathan P. D.; Aller, Josephine Y.; Bertram, Allan K.; Knopf, Daniel A.; Murray, Benjamin J.
    Nature (London, United Kingdom) (2015), 525 (7568), 234-238CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    The amt. of ice present in clouds can affect cloud lifetime, pptn. and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. Sea spray is one of the major global sources of atm. particles, but it is unclear to what extent these particles are capable of nucleating ice. Sea-spray aerosol contains large amts. of org. material that is ejected into the atm. during bubble bursting at the organically enriched sea-air interface or sea surface microlayer. Here we show that org. material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approx. 0.2 μm in size. We find that exudates sepd. from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that org. material assocd. with phytoplankton cell exudates is a likely candidate for the obsd. ice-nucleating ability of the microlayer samples. Global model simulations of marine org. aerosol, in combination with our measurements, suggest that marine org. material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.
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  31. 31
    Dreischmeier, K.; Budke, C.; Wiehemeier, L.; Kottke, T.; Koop, T. Boreal Pollen Contain Ice-Nucleating as Well as Ice-Binding ‘Antifreeze’ Polysaccharides. Sci. Rep. 2017, 7, 41890  DOI: 10.1038/srep41890
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    31
    Boreal pollen contain ice-nucleating as well as ice-binding 'antifreeze' polysaccharides
    Dreischmeier, Katharina; Budke, Carsten; Wiehemeier, Lars; Kottke, Tilman; Koop, Thomas
    Scientific Reports (2017), 7 (), 41890CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromols. when suspended in water. Here we show that birch pollen washing water exhibits also ice-binding properties such as ice shaping and ice recrystn. inhibition, similar to antifreeze proteins. We present spectroscopic evidence that both the ice-nucleating as well as the ice-binding mols. are polysaccharides bearing carboxylate groups. The spectra suggest that both polysaccharides consist of very similar chem. moieties, but centrifugal filtration indicates differences in mol. size: ice nucleation occurs only in the supernatant of a 100 kDa filter, while ice shaping is strongly enhanced in the filtrate. This finding may suggest that the larger ice-nucleating polysaccharides consist of clusters of the smaller ice-binding polysaccharides, or that the latter are fragments of the ice-nucleating polysaccharides. Finally, similar polysaccharides released from pine and alder pollen also display both ice-nucleating as well as ice-binding ability, suggesting a common mechanism of interaction with ice among several boreal pollen with implications for atm. processes and antifreeze protection.
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    Eickhoff, L.; Dreischmeier, K.; Zipori, A.; Sirotinskaya, V.; Adar, C.; Reicher, N.; Braslavsky, I.; Rudich, Y.; Koop, T. Contrasting Behavior of Antifreeze Proteins: Ice Growth Inhibitors and Ice Nucleation Promoters. J. Phys. Chem. Lett. 2019, 10, 966– 972,  DOI: 10.1021/acs.jpclett.8b03719
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    32
    Contrasting Behavior of Antifreeze Proteins: Ice Growth Inhibitors and Ice Nucleation Promoters
    Eickhoff, Lukas; Dreischmeier, Katharina; Zipori, Assaf; Sirotinskaya, Vera; Adar, Chen; Reicher, Naama; Braslavsky, Ido; Rudich, Yinon; Koop, Thomas
    Journal of Physical Chemistry Letters (2019), 10 (5), 966-972CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Several types of natural mols. interact specifically with ice crystals. Small antifreeze proteins (AFPs) adsorb to particular facets of ice crystals, thus inhibiting their growth, whereas larger ice-nucleating proteins (INPs) can trigger the formation of new ice crystals at temps. much higher than the homogeneous ice nucleation temp. of pure water. It has been proposed that both types of proteins interact similarly with ice and that, in principle, they may be able to exhibit both functions. Here we investigated two naturally occurring antifreeze proteins, one from fish, type-III AFP, and one from beetles, TmAFP. We show that in addn. to ice growth inhibition, both can also trigger ice nucleation above the homogeneous freezing temp., providing unambiguous exptl. proof for their contrasting behavior. Our anal. suggests that the predominant difference between AFPs and INPs is their mol. size, which is a very good predictor of their ice nucleation temp.
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    Ogawa, S.; Koga, M.; Osanai, S. Anomalous Ice Nucleation Behavior in Aqueous Polyvinyl Alcohol Solutions. Chem. Phys. Lett. 2009, 480, 86– 89,  DOI: 10.1016/j.cplett.2009.08.046
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    Anomalous ice nucleation behavior in aqueous polyvinyl alcohol solutions
    Ogawa, S.; Koga, M.; Osanai, S.
    Chemical Physics Letters (2009), 480 (1-3), 86-89CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    The effect of polymers on the ice nucleation temp. (T f) was studied in a W/O emulsion using ∼5 μm diam. droplets by differential scanning calorimetry (DSC). Four types of polymers were used. Among them, only poly(vinyl alc.) (PVA) showed the addnl. effect of increasing the T f of the aq. solns. This increase was logarithmic with the concn. of PVA and the difference in mol. wt. did not have any significant effect on T f for the same wt. concn. It was shown that the no. of the structural unit (CH2CHOH) was the key parameter for the increasing degree of T f.
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    Sheiko, S. S.; Sumerlin, B. S.; Matyjaszewski, K. Cylindrical Molecular Brushes: Synthesis, Characterization, and Properties. Prog. Polym. Sci. 2008, 33, 759– 785,  DOI: 10.1016/j.progpolymsci.2008.05.001
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    Cylindrical molecular brushes: Synthesis, characterization, and properties
    Sheiko, Sergei S.; Sumerlin, Brent S.; Matyjaszewski, Krzysztof
    Progress in Polymer Science (2008), 33 (7), 759-785CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Brush-like macromols. are unique polymer mols. whose conformation and phys. properties are controlled by steric repulsion of densely grafted side chains. Mols. can be either flexible or stiff, depending on the grafting d. and the length of the side chains. Mols. can switch their conformation in response to alterations in the surrounding environment, e.g. changes of temp., solvent quality, pH, and ionic strength. Furthermore, one can control mol. conformation and related properties using external stimuli such as light and electromagnetic fields. Mol. brushes are also very informative model systems for exptl. studies of polymer properties. Mols. are readily visualized by at. force microscopy, opening unique opportunities to observe single polymer mols. as they move, order, and react on surfaces. Brush-like mol. architectures are well-known in biol. where they are responsible for various functions including mucociliary clearance of lung airways and mech. performance of articular cartilage. Polymer chem. is currently making the first steps in controlling mol. architecture and understanding the distinctive properties of mol. brushers. This article reviews the characteristic phys. properties of well-defined mol. brushes and the different strategies employed for their prepn., with particular focus on synthesis via controlled radical polymn. techniques.
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    Foster, J. C.; Varlas, S.; Couturaud, B.; Coe, Z.; O’Reilly, R. K. Getting into Shape: Reflections on a New Generation of Cylindrical Nanostructures’ Self-Assembly Using Polymer Building Blocks. J. Am. Chem. Soc. 2019, 141, 2742– 2753,  DOI: 10.1021/jacs.8b08648
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    Getting into Shape: Reflections on a New Generation of Cylindrical Nanostructures' Self-Assembly Using Polymer Building Blocks
    Foster, Jeffrey C.; Varlas, Spyridon; Couturaud, Benoit; Coe, Zachary; O'Reilly, Rachel K.
    Journal of the American Chemical Society (2019), 141 (7), 2742-2753CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A review. Cylinders are fascinating structures with uniquely high surface area, internal vol., and rigidity. On the nanoscale, a broad range of applications have demonstrated advantageous behavior of cylindrical micelles or bottlebrush polymers over traditional spherical nano-objects. In the past, obtaining pure samples of cylindrical nanostructures using polymer building blocks via conventional self-assembly strategies was challenging. However, in recent years, the development of advanced methods including polymn.-induced self-assembly, crystn.-driven self-assembly, and bottlebrush polymer synthesis has facilitated the easy synthesis of cylindrical nano-objects at industrially relevant scales. In this Perspective, we discuss these techniques in detail, highlighting the advantages and disadvantages of each strategy and considering how the cylindrical nanostructures that are obtained differ in their chem. structure, phys. properties, colloidal stability, and reactivity. In addn., we propose future challenges to address in this rapidly expanding field.
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  36. 36
    Yamago, S.; Nakamura, Y. Recent Progress in the Use of Photoirradiation in Living Radical Polymerization. Polymer 2013, 54, 981– 994,  DOI: 10.1016/j.polymer.2012.11.046
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    Recent progress in the use of photoirradiation in living radical polymerization
    Yamago, Shigeru; Nakamura, Yasuyuki
    Polymer (2013), 54 (3), 981-994CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    A review. The effects of photoirradn. in controlled and living radical polymn. (LRP), namely nitroxide-mediated polymn. (NMP), atom-transfer radical polymn. (ATRP), cobalt-mediated radical polymn. (CMRP), reversible addn.-fragmentation chain transfer polymn. (RAFT), organoiodine-mediated radical polymn. (IRP), and organotellurium-mediated radical polymn. (TERP), are summarized. As in the conventional radical polymn., photoirradn. has been used for generating radicals under mild conditions in LRP methods. In addn. to this use, photoirradn. is also used to overcome the difficulties characteristic to each method, such as activation of catalysis, generation of controlling agents, and increasing the polymer-end structure. The most-recent developments in the use of photochem. in LRP are summarized in this review.
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    McKenzie, T. G.; Fu, Q.; Uchiyama, M.; Satoh, K.; Xu, J.; Boyer, C.; Kamigaito, M.; Qiao, G. G. Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization. Adv. Sci. 2016, 3, 1500394  DOI: 10.1002/advs.201500394
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    Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization
    McKenzie Thomas G; Fu Qiang; Qiao Greg G; Uchiyama Mineto; Kamigaito Masami; Satoh Kotaro; Xu Jiangtao; Boyer Cyrille
    Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2016), 3 (9), 1500394 ISSN:2198-3844.
    Recent developments in polymerization reactions utilizing thiocarbonylthio compounds have highlighted the surprising versatility of these unique molecules. The increasing popularity of reversible addition-fragmentation chain transfer (RAFT) radical polymerization as a means of producing well-defined, 'controlled' synthetic polymers is largely due to its simplicity of implementation and the availability of a wide range of compatible reagents. However, novel modes of thiocarbonylthio activation can expand the technique beyond the traditional system (i.e., employing a free radical initiator) pushing the applicability and use of thiocarbonylthio compounds even further than previously assumed. The primary advances seen in recent years are a revival in the direct photoactivation of thiocarbonylthio compounds, their activation via photoredox catalysis, and their use in cationic polymerizations. These synthetic approaches and their implications for the synthesis of controlled polymers represent a significant advance in polymer science, with potentially unforeseen benefits and possibilities for further developments still ahead. This Research News aims to highlight key works in this area while also clarifying the differences and similarities of each system.
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  38. 38
    Aragón, S. R.; Pecora, R. Theory of Dynamic Light Scattering from Large Anisotropic Particles. J. Chem. Phys. 1977, 66, 2506– 2516,  DOI: 10.1063/1.434246
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    Theory of dynamic light scattering from large anisotropic particles
    Aragon, S. R.; Pecora, R.
    Journal of Chemical Physics (1977), 66 (6), 2506-16CODEN: JCPSA6; ISSN:0021-9606.
    The scattered elec. field amplitude autocorrelation function of a dil. soln. of large rigid anisotropic particles is computed in the Rayleigh-Debye approxn. The autocorrelation function for cylindrically sym. particles is an infinite series of decaying exponentials with time consts. τl-1 = q2D + l(l + 1)Θ.perp. contg. both translational and rotational diffusion coeffs. The dynamical terms are weighted by particle form factors and also by exptl. geometry factors which are given in coordinate independent form. Explicit formulas for the form factors of spheres, rods, and thin disks are given. The general formulas reduce to the correct expressions for similar optically isotropic scattering systems.
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    Zhang, Z.; Carrillo, J.-M. Y.; Ahn, S.; Wu, B.; Hong, K.; Smith, G. S.; Do, C. Atomistic Structure of Bottlebrush Polymers: Simulations and Neutron Scattering Studies. Macromolecules 2014, 47, 5808– 5814,  DOI: 10.1021/ma500613c
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    Atomistic Structure of Bottlebrush Polymers: Simulations and Neutron Scattering Studies
    Zhang, Zhe; Carrillo, Jan-Michael Y.; Ahn, Suk-kyun; Wu, Bin; Hong, Kunlun; Smith, Gregory S.; Do, Changwoo
    Macromolecules (Washington, DC, United States) (2014), 47 (16), 5808-5814CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    We have used small angle neutron scattering (SANS) measurement and atomistic mol. dynamics (MD) simulations to investigate the conformation of bottlebrush polymers with poly(norbornene) (PNB) backbone and different sizes of poly(lactide) (PLA) side chains (PNB25-g-PLA5, PNB25-g-PLA10, and PNB25-g-PLA19). At early stage of simulations, stretched side chains with visible spatial-correlations of about 30 Å were obsd. The exptl. measured SANS data, on the other hand, does not exhibit any correlation peaks in the corresponding length scale indicating a compact form rather than a stretched-hairy polymer conformation. As the simulation continued, the spatial correlations between side chains disappeared after about 40 ns of chain relaxation, and the scattering intensity calcd. for the simulated structure becomes reasonably close to the measured one. Statistical approach is used to overcome the time scale limitation and search for optimal conformation space, which also provides a good agreement with the exptl. data. Further coarse-grained simulation results suggest that the side chain conformation strongly depends on the soly. competition among side chain, backbone, and solvent. Significant changes of backbone dynamics due to the side chain encapsulation have been revealed and discussed.
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    Pesek, S. L.; Xiang, Q.; Hammouda, B.; Verduzco, R. Small-Angle Neutron Scattering Analysis of Bottlebrush Backbone and Side Chain Flexibility. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 104– 111,  DOI: 10.1002/polb.24251
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    Small-angle neutron scattering analysis of bottlebrush backbone and side chain flexibility
    Pesek, Stacy L.; Xiang, Qiqi; Hammouda, Boualem; Verduzco, Rafael
    Journal of Polymer Science, Part B: Polymer Physics (2017), 55 (1), 104-111CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
    Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are detd. through small-angle neutron scattering anal. of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a "grafting-through" ring-opening polymn. Scattering profiles are modeled with the empirical Guinier-Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end-to-end distance proportional to N0.55, while the overall bottlebrush increases in size proportional to N0.77. These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in soln. © 2016 Wiley Periodicals, Inc.J. Polym. Sci., Part B: Polym.Phys. 2016.
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    Gallyamov, M. O.; Tartsch, B.; Mela, P.; Potemkin, I. I.; Sheiko, S. S.; Börner, H.; Matyjaszewski, K.; Khokhlov, A. R.; Möller, M. Vapor-Induced Spreading Dynamics of Adsorbed Linear and Brush-like Macromolecules as Observed by Environmental SFM: Polymer Chain Statistics and Scaling Exponents. J. Polym. Sci., Part B: Polym. Phys. 2007, 45, 2368– 2379,  DOI: 10.1002/polb.21253
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    Vapor-induced spreading dynamics of adsorbed linear and brush-like macromolecules as observed by environmental SFM: polymer chain statistics and scaling exponents
    Gallyamov, Marat O.; Tartsch, Bernd; Mela, Petra; Potemkin, Igor I.; Sheiko, Sergei S.; Borner, Hans; Matyjaszewski, Krzysztof; Khokhlov, Alexei R.; Moller, Martin
    Journal of Polymer Science, Part B: Polymer Physics (2007), 45 (17), 2368-2379CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
    Scaling exponents ν, that describe the correlation between mean square end-to-end distances and contour lengths of macromols., were detd. by statistical anal. of scanning force micrographs of single linear poly(2-vinylpyridine) and brush-like poly(butanoate-Et methacrylate)-graft-poly(Bu acrylate) macromols. adsorbed on mica. Using an atm.-controlled scanning force microscope, single adsorbed mols. were collapsed and re-expanded upon being exposed to alc. and water vapor, resp. This manipulated collapse-unfolding was used to equilibrate the mol. structure/conformation. The in situ and real-time scanning force microscopy anal. allows the scientist to quant. characterize end-to-end distances and contour lengths of the mols. directly on the image and to observe differences in the spreading dynamics for the two types of macromols. A distinct difference has been obsd. between the expanded two-dimensional (2D) conformations of linear and brush-like polymer chains. Whereas a scaling exponent ν of 0.73 was found for the expanded 2D conformation of the linear mols., a ν-value of 0.53 was detd. for the expanded 2D conformation of the seemingly stiffer brush-like mols. A theor. explanation of the differences between the 2D conformations of brush-like and linear macromols. is proposed here.
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    Radzinski, S. C.; Foster, J. C.; Chapleski, R. C.; Troya, D.; Matson, J. B. Bottlebrush Polymer Synthesis by Ring-Opening Metathesis Polymerization: The Significance of the Anchor Group. J. Am. Chem. Soc. 2016, 138, 6998– 7004,  DOI: 10.1021/jacs.5b13317
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    Bottlebrush Polymer Synthesis by Ring-Opening Metathesis Polymerization: The Significance of the Anchor Group
    Radzinski, Scott C.; Foster, Jeffrey C.; Chapleski, Robert C.; Troya, Diego; Matson, John B.
    Journal of the American Chemical Society (2016), 138 (22), 6998-7004CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Control over bottlebrush polymer synthesis by ring-opening metathesis polymn. (ROMP) of macromonomers (MMs) is highly dependent on the competition between the kinetics of the polymn. and the lifetime of the catalyst. We evaluated the effect of anchor group chem.-the configuration of atoms linking the polymer to a polymerizable norbornene-on the kinetics of ROMP of polystyrene and poly(lactic acid) MMs initiated by (H2IMes)(pyr)2(Cl)2Ru=CHPh (Grubbs third generation catalyst). We obsd. a variance in the rate of propagation of >4-fold between similar MMs with different anchor groups. This phenomenon was conserved across all MMs tested, regardless of solvent, mol. wt. (MW), or repeat unit identity. The obsd. >4-fold difference in propagation rate had a dramatic effect on the max. obtainable backbone d.p., with slower propagating MMs reducing the max. bottlebrush MW by an order of magnitude (from ∼106 to ∼105 Da). A chelation mechanism was initially proposed to explain the obsd. anchor group effect, but exptl. and computational studies indicated that the rate differences likely resulted from a combination of varying steric demands and electronic structure among the different anchor groups. The addn. of trifluoroacetic acid to the ROMP reaction substantially increased the propagation rate for all anchor groups tested, likely due to scavenging of the pyridine ligands. Based on these data, rational selection of the anchor group is crit. to achieve high MM conversion and to prep. pure, high MW bottlebrush polymers by ROMP grafting-through.
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    Blosch, S. E.; Scannelli, S. J.; Alaboalirat, M.; Matson, J. B. Complex Polymer Architectures Using Ring-Opening Metathesis Polymerization: Synthesis, Applications, and Practical Considerations. Macromolecules 2022, 55, 4200– 4227,  DOI: 10.1021/acs.macromol.2c00338
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    Complex Polymer Architectures Using Ring-Opening Metathesis Polymerization: Synthesis, Applications, and Practical Considerations
    Blosch, Sarah E.; Scannelli, Samantha J.; Alaboalirat, Mohammed; Matson, John B.
    Macromolecules (Washington, DC, United States) (2022), 55 (11), 4200-4227CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A review. Nature shows us that complex mol. architectures lead to unique material properties, and these observations have driven polymer scientists to synthesize complex architectures in an effort to discover how topol. influences properties in synthetic polymers. In this Perspective we discuss a variety of complex architectures synthesized using ring-opening metathesis polymn. (ROMP), including multiblock linear polymers, bottlebrush homopolymers and (multi)block copolymers, dendronized polymers, star polymers, and polymer-biomol. conjugates. Traditional and recently developed synthetic methods including polymn.-induced self-assembly, copolymn. to create gradient structures, and engineering approaches to making complex topologies using ROMP are also reviewed. In this context we highlight emerging applications stemming from these materials, including drug delivery vehicles, nanoscale constructs, and components in light refraction or energy storage, among others. Finally, we conclude with an in-depth discussion on practical considerations in ROMP that enable the highest level of control when synthesizing complex polymer topologies from sterically demanding or otherwise challenging (macro)monomers. Our hope is that this Perspective will guide scientists synthesizing complex polymer architectures toward new and innovative materials with the potential for unique properties and applications.
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    Congdon, T.; Shaw, P.; Gibson, M. I. Thermoresponsive, Well-Defined, Poly(Vinyl Alcohol) Co-Polymers. Polym. Chem. 2015, 6, 4749– 4757,  DOI: 10.1039/C5PY00775E
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    Thermoresponsive, well-defined, poly(vinyl alcohol) co-polymers
    Congdon, Thomas; Shaw, Peter; Gibson, Matthew I.
    Polymer Chemistry (2015), 6 (26), 4749-4757CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Thermoresponsive polymers have attracted huge interest as adaptable biomaterials based on their reversible soly. behavior which can be exploited for controlled drug delivery or cellular uptake. The most famous and successful of these is poly(ethylene glycol) (PEG), but the thermal transition temps. that are practically accessible are not physiol. useful. There are some notable examples of synthetic, responsive, polymers that are highly tunable over a physiol. relevant range, but there is still a need for these to be clin. validated in terms of toxicol. and immunogenity for in vivo usage, in addn. to their widely used in vitro applications. Poly(vinyl alc.), PVA, is an appealing biocompatible polymer which is already used for a huge range of biomedical applications. Here, PVA is shown to be a highly tunable, thermoresponsive polymer scaffold. RAFT/MADIX polymn. is used to obtain a library of well-defined polymers between 8 and 50 kDa. Selective alkanoylation of the obtained PVA enabled the effect of side-chains, end-groups and mol. wt. on the observable transition temps. to be studied by turbidimetry. It was found that increasingly hydrophobic side chains (acetyl, propanoyl, butanoyl), or increasing their d. led to corresponding decreases in cloud point. PVA with just 10 mol% butanoylation was shown to have a thermal transition temp. close to physiol. temps. (37 °C), compared to 70 mol% for acetylation, with temps. in between accessible by controlling both the relative degree of functionalization, or by altering the chain length. Finally, a secondary response to esterase enzymes was demonstrated as a route to 'turn off' the responsive behavior on demand. This study suggests that PVA-derived polymers may be a useful platform for responsive biomaterials.
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    Varlas, S.; Hua, Z.; Jones, J. R.; Thomas, M.; Foster, J. C.; O’Reilly, R. K. Complementary Nucleobase Interactions Drive the Hierarchical Self-Assembly of Core–Shell Bottlebrush Block Copolymers toward Cylindrical Supramolecules. Macromolecules 2020, 53, 9747– 9757,  DOI: 10.1021/acs.macromol.0c01857
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    Complementary Nucleobase Interactions Drive the Hierarchical Self-Assembly of Core-Shell Bottlebrush Block Copolymers toward Cylindrical Supramolecules
    Varlas, Spyridon; Hua, Zan; Jones, Joseph R.; Thomas, Marjolaine; Foster, Jeffrey C.; O'Reilly, Rachel K.
    Macromolecules (Washington, DC, United States) (2020), 53 (22), 9747-9757CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The self-assembly of amphiphilic block copolymers has facilitated the prepn. of a wide variety of nano-objects of diverse morphol. Ready access to these nanostructures has opened up new possibilities in catalysis, sensing, and nanomedicine. In comparison, the self-assembly of large building blocks (i.e., amphiphilic bottlebrush polymers) has received less attention, owing in part to the relatively more challenging synthesis of these macromols. Bottlebrush amphiphiles can self-assemble into uniquely stable spherical nanostructures and can also produce dynamic cylinders with lengths modulated by environmental conditions, motivating further research in this area. Herein, we report the synthesis of core-shell bottlebrush polymers (BBPs) contg. complementary nucleobase functionalities via a combination of ring-opening metathesis polymn. (ROMP) and reversible addn.-fragmentation chain transfer (RAFT) polymn., using a "grafting-from" approach, and their hierarchical self-assembly in aq. media. Mixts. of BBPs contg. thymine or adenine units in their core blocks were found to self-assemble into higher-order cylindrical supramols. upon heating above a crit. temp. This temp. was demonstrated to correspond to the lower crit. soln. temp. (LCST) of the corona-forming poly(4-acryloylmorpholine) block, providing evidence for a unique one-dimensional BBP assembly mechanism. Moreover, the formation of extended supramol. assemblies was preferentially obsd. when both thymine- and adenine-functionalized BBPs were present in equimolar concns., pointing toward an alternating, isodesmic mechanism of organization occurring via nucleobase interactions located at their chain termini. We anticipate that these discoveries will provide the basis for future studies regarding BBP self-assembly, esp. with regard to the formation of stimuli-responsive anisotropic nanostructures.
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    Knight, C. A.; Hallett, J.; DeVries, A. L. Solute Effects on Ice Recrystallization: An Assessment Technique. Cryobiology 1988, 25, 55– 60,  DOI: 10.1016/0011-2240(88)90020-X
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    Solute effects on ice recrystallization: an assessment technique
    Knight C A; Hallett J; DeVries A L
    Cryobiology (1988), 25 (1), 55-60 ISSN:0011-2240.
    Reliable assessment of the effect of a solute upon ice recrystallization is accomplished with "splat cooling," the impaction of a small solution droplet onto a very cold metal plate. The ice disc has extremely small crystals, and recrystallization can be followed without confusing effects caused by grain nucleation. This method confirms the exceptionally strong recrystallization inhibition effect of antifreeze protein from Antarctic fish and shows that grain growth rate is a sensitive function of both grain size and solute concentration.
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    Graham, B.; Fayter, A. E. R.; Houston, J. E.; Evans, R. C.; Gibson, M. I. Facially Amphipathic Glycopolymers Inhibit Ice Recrystallization. J. Am. Chem. Soc. 2018, 140, 5682– 5685,  DOI: 10.1021/jacs.8b02066
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    Facially amphipathic glycopolymers inhibit ice recrystallization
    Graham, Ben; Fayter, Alice E. R.; Houston, Judith E.; Evans, Rachel C.; Gibson, Matthew I.
    Journal of the American Chemical Society (2018), 140 (17), 5682-5685CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Antifreeze glycoproteins (AFGPs) from polar fish are the most potent ice recrystn. (growth) inhibitors known, and synthetic mimics are required for low-temp. applications such as cell cryopreservation. Here we introduce facially amphipathic glycopolymers that mimic the three-dimensional structure of AFGPs. Glycopolymers featuring segregated hydrophilic and hydrophobic faces were prepd. by ring-opening metathesis polymn., and their rigid conformation was confirmed by small-angle neutron scattering. Ice recrystn. inhibition (IRI) activity was reduced when a hydrophilic oxo-ether was installed on the glycan-opposing face, but significant activity was restored by incorporating a hydrophobic dimethylfulvene residue. This biomimetic strategy demonstrates that segregated domains of distinct hydrophilicity/hydrophobicity are a crucial motif to introduce IRI activity, which increases our understanding of the complex ice crystal inhibition processes.
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    Stevens, C. A.; Drori, R.; Zalis, S.; Braslavsky, I.; Davies, P. L. Dendrimer-Linked Antifreeze Proteins Have Superior Activity and Thermal Recovery. Bioconjugate Chem. 2015, 26, 1908– 1915,  DOI: 10.1021/acs.bioconjchem.5b00290
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    Dendrimer-Linked Antifreeze Proteins Have Superior Activity and Thermal Recovery
    Stevens, Corey A.; Drori, Ran; Zalis, Shiran; Braslavsky, Ido; Davies, Peter L.
    Bioconjugate Chemistry (2015), 26 (9), 1908-1915CODEN: BCCHES; ISSN:1043-1802. (American Chemical Society)
    By binding to ice, antifreeze proteins (AFPs) depress the f.p. of a soln. and inhibit ice recrystn. if freezing does occur. Previous work showed that the activity of an AFP was incrementally increased by fusing it to another protein. Even larger increases in activity were achieved by doubling the no. of ice-binding sites by dimerization. Here, the authors have combined the two strategies by linking multiple outward-facing AFPs to a dendrimer to significantly increase both the size of the mol. and the no. of ice-binding sites. Using a heterobifunctional crosslinker, the authors attached between 6 and 11 type III AFPs to a second-generation polyamidoamine (G2-PAMAM) dendrimer with 16 reactive termini. This heterogeneous sample of dendrimer-linked type III constructs showed a >4-fold increase in f.p. depression over that of monomeric type III AFP. This multimerized AFP was particularly effective at ice recrystn. inhibition activity, likely because it can simultaneously bind multiple ice surfaces. Addnl., attachment to the dendrimer has afforded the AFP superior recovery from heat denaturation. Linking AFPs together via polymers can generate novel reagents for controlling ice growth and recrystn.
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    Marcolli, C.; Gedamke, S.; Peter, T.; Zobrist, B. Efficiency of Immersion Mode Ice Nucleation on Surrogates of Mineral Dust. Atmos. Chem. Phys. 2007, 7, 5081– 5091,  DOI: 10.5194/acp-7-5081-2007
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    Efficiency of immersion mode ice nucleation on surrogates of mineral dust
    Marcolli, C.; Gedamke, S.; Peter, T.; Zobrist, B.
    Atmospheric Chemistry and Physics (2007), 7 (19), 5081-5091CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
    A differential scanning calorimeter (DSC) was used to explore heterogeneous ice nucleation of emulsified aq. suspensions of two Arizona test dust (ATD) samples with particle diams. of nominally 0-3 and 0-7 μm, resp. Aq. suspensions with ATD concns. of 0.01-20 wt% have been investigated. The DSC thermograms exhibit a homogeneous and a heterogeneous freezing peak whose intensity ratios vary with the ATD concn. in the aq. suspensions. Homogeneous freezing temps. are in good agreement with recent measurements by other techniques. Depending on ATD concn., heterogeneous ice nucleation occurred at temps. as high as 256 K or down to the onset of homogeneous ice nucleation (237 K). For ATD-induced ice formation Classical Nucleation Theory (CNT) offers a suitable framework to parameterize nucleation rates as a function of temp., exptl. detd. ATD size, and emulsion droplet vol. distributions. The latter two quantities serve to est. the total heterogeneous surface area present in a droplet, whereas the suitability of an individual heterogeneous site to trigger nucleation is described by the compatibility function (or contact angle) in CNT. The intensity ratio of homogeneous to heterogeneous freezing peaks is in good agreement with the assumption that the ATD particles are randomly distributed amongst the emulsion droplets. The obsd. dependence of the heterogeneous freezing temps. on ATD concns. cannot be described by assuming a const. contact angle for all ATD particles, but requires the ice nucleation efficiency of ATD particles to be (log)normally distributed amongst the particles. Best quant. agreement is reached when explicitly assuming that high-compatibility sites are rare and that therefore larger particles have on av. more and better active sites than smaller ones. This anal. suggests that a particle has to have a diam. of at least 0.1 μm to exhibit on av. one active site.
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    Whale, T. F.; Murray, B. J.; O’Sullivan, D.; Wilson, T. W.; Umo, N. S.; Baustian, K. J.; Atkinson, J. D.; Workneh, D. A.; Morris, G. J. A Technique for Quantifying Heterogeneous Ice Nucleation in Microlitre Supercooled Water Droplets. Atmos. Meas. Tech. 2015, 8, 2437– 2447,  DOI: 10.5194/amt-8-2437-2015
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    A technique for quantifying heterogeneous ice nucleation in microlitre supercooled water droplets
    Whale, T. F.; Murray, B. J.; O'Sullivan, D.; Wilson, T. W.; Umo, N. S.; Baustian, K. J.; Atkinson, J. D.; Workneh, D. A.; Morris, G. J.
    Atmospheric Measurement Techniques (2015), 8 (6), 2437-2447CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
    In many clouds, the formation of ice requires the presence of particles capable of nucleating ice. Ice-nucleating particles (INPs) are rare in comparison to cloud condensation nuclei. However, the fact that only a small fraction of aerosol particles can nucleate ice means that detection and quantification of INPs is challenging. This is particularly true at temps. above about -20 °C since the population of particles capable of serving as INPs decreases dramatically with increasing temp. In this paper, we describe an exptl. technique in which droplets of microlitre vol. contg. ice-nucleating material are cooled down at a controlled rate and their freezing temps. recorded. The advantage of using large droplet vols. is that the surface area per droplet is vastly larger than in expts. focused on single aerosol particles or cloud-sized droplets. This increases the probability of observing the effect of less common, but important, high-temp. INPs and therefore allows the quantification of their ice nucleation efficiency. The potential artifacts which could influence data from this expt., and other similar expts., are mitigated and discussed. Exptl. detd. heterogeneous ice nucleation efficiencies for K-feldspar (microcline), kaolinite, chlorite, NX-illite, Snomax and silver iodide are presented.
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    Polen, M.; Brubaker, T.; Somers, J.; Sullivan, R. C. Cleaning up Our Water: Reducing Interferences from Nonhomogeneous Freezing of “pure” Water in Droplet Freezing Assays of Ice-Nucleating Particles. Atmos. Meas. Tech. 2018, 11, 5315– 5334,  DOI: 10.5194/amt-11-5315-2018
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    51
    Cleaning up our water: reducing interferences from nonhomogeneous freezing of "pure" water in droplet freezing assays of ice-nucleating particles
    Polen, Michael; Brubaker, Thomas; Somers, Joshua; Sullivan, Ryan C.
    Atmospheric Measurement Techniques (2018), 11 (9), 5315-5334CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
    Droplet freezing techniques (DFTs) have been used for half a century to measure the concn. of icenucleating particles (INPs) in the atm. and det. their freezing properties to understand the effects of INPs on mixed-phase clouds. The ice nucleation community has recently adopted droplet freezing assays as a commonplace exptl. approach. These droplet freezing expts. are often limited by contamination that causes nonhomogeneous freezing of the "pure" water used to generate the droplets in the heterogeneous freezing temp. regime that is being measured. Interference from the early freezing of water is often overlooked and not fully reported, or measurements are restricted to analyzing the more ice-active INPs that freeze well above the temp. of the background water. However, this avoidance is not viable for analyzing the freezing behavior of less active INPs in the atm. that still have potentially important effects on cold-cloud microphysics. In this work we review a no. of recent droplet freezing techniques that show great promise in reducing these interferences, and we report our own extensive series of measurements using similar methodologies. By characterizing the performance of different substrates on which the droplets are placed and of different pure water generation techniques, we recommend best practices to reduce these interferences. We tested different substrates, water sources, droplet matrixes, and droplet sizes to provide deeper insight into what methodologies are best suited for DFTs. Approaches for analyzing droplet freezing temp. spectra and accounting and correcting for the background "pure" water control spectrum are also presented. Finally, we propose exptl. and data anal. procedures for future homogeneous and heterogeneous ice nucleation studies to promote a more uniform and reliable methodol. that facilitates the ready intercomparison of ice-nucleating particles measured by DFTs.
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  52. 52
    Georgiou, P. G.; Marton, H. L.; Baker, A. N.; Congdon, T. R.; Whale, T. F.; Gibson, M. I. Polymer Self-Assembly Induced Enhancement of Ice Recrystallization Inhibition. J. Am. Chem. Soc. 2021, 143, 7449– 7461,  DOI: 10.1021/jacs.1c01963
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    Polymer Self-Assembly Induced Enhancement of Ice Recrystallization Inhibition
    Georgiou, Panagiotis G.; Marton, Huba L.; Baker, Alexander N.; Congdon, Thomas R.; Whale, Thomas F.; Gibson, Matthew I.
    Journal of the American Chemical Society (2021), 143 (19), 7449-7461CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Ice binding proteins modulate ice nucleation/growth and have huge (bio)technol. potential. There are few synthetic materials that reproduce their function, and rational design is challenging due to the outstanding questions about the mechanisms of ice binding, including whether ice binding is essential to reproduce all their macroscopic properties. Here we report that nanoparticles obtained by polymn.-induced self-assembly (PISA) inhibit ice recrystn. (IRI) despite their constituent polymers having no apparent activity. Poly(ethylene glycol), poly(dimethylacrylamide), and poly(vinylpyrrolidone) coronas were all IRI-active when assembled into nanoparticles. Different core-forming blocks were also screened, revealing the core chem. had no effect. These observations show ice binding domains are not essential for macroscopic IRI activity and suggest that the size, and crowding, of polymers may increase the IRI activity of "non-active" polymers. Poly(vinylpyrrolidone) particles had ice crystal shaping activity, indicating this polymer can engage ice crystal surfaces, even though on its own it does not show any appreciable ice recrystn. inhibition. Larger (vesicle) nanoparticles are shown to have higher ice recrystn. inhibition activity compared to smaller (sphere) particles, whereas ice nucleation activity was not found for any material. This shows that assembly into larger structures can increase IRI activity and that increasing the "size" of an IRI does not always lead to ice nucleation. This nanoparticle approach offers a platform toward ice-controlling soft materials and insight into how IRI activity scales with mol. size of additives.
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  53. 53
    Bissoyi, A.; Reicher, N.; Chasnitsky, M.; Arad, S.; Koop, T.; Rudich, Y.; Braslavsky, I. Ice Nucleation Properties of Ice-Binding Proteins from Snow Fleas. Biomolecules 2019, 9, 532  DOI: 10.3390/biom9100532
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    53
    Ice nucleation properties of ice-binding proteins from snow fleas
    Bissoyi, Akalabya; Reicher, Naama; Chasnitsky, Michael; Arad, Sivan; Koop, Thomas; Rudich, Yinon; Braslavsky, Ido
    Biomolecules (2019), 9 (10), 532CODEN: BIOMHC; ISSN:2218-273X. (MDPI AG)
    Ice-binding proteins (IBPs) are found in many organisms, such as fish and hexapods, plants, and bacteria that need to cope with low temps. Ice nucleation and thermal hysteresis are two attributes of IBPs. While ice nucleation is promoted by large proteins, known as ice nucleating proteins, the smaller IBPs, referred to as antifreeze proteins (AFPs), inhibit the growth of ice crystals by up to several degrees below the m.p., resulting in a thermal hysteresis (TH) gap between melting and ice growth. Recently, we showed that the nucleation capacity of two types of IBPs corresponds to their size, in agreement with classical nucleation theory. Here, we expand this finding to addnl. IBPs that we isolated from snow fleas (the arthropod Collembola), collected in northern Israel. Chem. analyses using CD and Fourier-transform IR spectroscopy data suggest that these IBPs have a similar structure to a previously reported snow flea antifreeze protein. Further expts. reveal that the ice-shell purified proteins have hyperactive antifreeze properties, as detd. by nanoliter osmometry, and also exhibit low ice-nucleation activity in accordance with their size.
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  54. 54
    Lupi, L.; Hudait, A.; Molinero, V. Heterogeneous Nucleation of Ice on Carbon Surfaces. J. Am. Chem. Soc. 2014, 136, 3156– 3164,  DOI: 10.1021/ja411507a
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    Heterogeneous Nucleation of Ice on Carbon Surfaces
    Lupi, Laura; Hudait, Arpa; Molinero, Valeria
    Journal of the American Chemical Society (2014), 136 (8), 3156-3164CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Atm. aerosols can promote the heterogeneous nucleation of ice, impacting the radiative properties of clouds and Earth's climate. The exptl. study of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temps. It is not known which structural and chem. characteristics of soot account for the variability in ice nucleation efficiency. Here the authors use mol. dynamics simulations to study the nucleation of ice from liq. water in contact with graphitic surfaces. Atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. Graphitic surfaces and other surfaces that promote ice nucleation induce layering in the interfacial water, suggesting that the order imposed by the surface on liq. water may play an important role in the heterogeneous nucleation mechanism. The authors study a large set of graphitic surfaces of various dimensions and radii of curvature and find that variations in nanostructures alone could account for the spread in the freezing temps. of ice on soot in expts. A characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency.
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This article is cited by 2 publications.

  1. Akalabya Bissoyi, Yanan Gao, Ruben M. F. Tomás, Nina L. H. Kinney, Thomas F. Whale, Qiongyu Guo, Matthew I. Gibson. Cryopreservation and Rapid Recovery of Differentiated Intestinal Epithelial Barrier Cells at Complex Transwell Interfaces Is Enabled by Chemically Induced Ice Nucleation. ACS Applied Materials & Interfaces 2024, Article ASAP.
  2. Jingcheng Xu, Yulun Wu, Yu Xia, Rida Fatima, Yuesheng Li, Dong-Po Song. Photonic Pigments of Polystyrene-block-Polyvinylpyrrolidone Bottlebrush Block Copolymers via Sustainable Organized Spontaneous Emulsification. ACS Macro Letters 2024, Article ASAP.
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    Figure 1

    Figure 1. (A) Design and synthesis of graft PVA-based brush copolymers generated via “grafting-to” procedure. Schematic representation of the synthetic route followed for the preparation of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) graft copolymers. (B) Normalized SEC-RI chromatograms for P((P(NB-NH)-g-PVAc210)-stat-P(NB-NH2))n copolymer precursors in DMF + 0.1% LiBr and solution characterization of resulting P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) in water via (C) DLS analysis (insets: representative photograph of 1 mg mL–1 aq solutions of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))400). (D) Dry-state TEM image obtained from a 1 mg mL–1 solution of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))400 in water. (E) Representative AFM image obtained from a 5 mg mL–1 solution of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))50 graft copolymer in water.

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    Figure 2. (A) Design and synthesis of dense PVA-based brush copolymers generated via “grafting-through” procedure. Schematic representation of the synthetic route followed for the preparation of PNBn-g-PVA208 (n = 20, 30, 40) bottlebrush polymers. (B) Normalized SEC-RI chromatograms for PVAc bottlebrush precursors in DMF + 0.1% LiBr and solution characterization of resulting PVA bottlebrushes in water via (C) DLS analysis (inset: representative photograph of 1 mg mL–1 aq solutions of PNB40-g-PVA208). (D) Dry-state TEM images obtained from a 1 mg mL–1 solution of PNB40-g-PVA208 in water; (E) representative AFM images obtained from a 5 mg mL–1 solution of PNB20-g-PVA208 bottlebrush polymer in water.

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    Figure 3. Evaluation of the thermoresponsive behavior for P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 400) and PNBn-g-PVA208 (n = 20, 40) bottlebrush polymers by (A) UV–vis spectroscopy and (B) variable-temperature DLS analysis. Samples were run from 20 to 85 °C at 1 mg mL–1 in water, with the UV–vis transmittance spectra recorded at λ = 700 nm (inset: UV–vis cuvettes containing 1 mg mL–1 solution of PNB40-g-PVA208 at 25 °C (left) before and after heating at 85 °C (right)).

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    Figure 4. Assessment of ice recrystallization inhibition activity and ice-binding. (A) IRI activity summary of (I) P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 50, 100, 200, 400) graft copolymers, PNBn-g-PVA208 (n = 20, 30, 40) bottlebrush polymers and (II) P(NB-NH2)n (n = 50, 100, 200, 400) and PEG-based control samples. Error bars are ±SD from a minimum of three repeats. The percent mean grain size (MGS) was reported relative to PBS control. (B) Modified “sucrose sandwich” ice shaping assay images for no additive (I) and 1 mg mL–1 of PVA210 (II), P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))400 (III) and PNB40-g-PVA208 (IV) in 45 wt % sucrose solution.

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    Figure 5. Assessment of ice nucleation activity of P((P(NB-NH)-g-PVA210)-stat-P(NB-NH2))n (n = 100, 200, 400) graft copolymers and PNBn-g-PVA208 (n = 20, 30, 40) bottlebrush polymers in (A) droplet fraction frozen for 1 μL water droplets containing various polymers. Confidence intervals were calculated using a Monte Carlo simulation described in the SI. (B) DSC analysis of picoliter water-in-oil emulsion droplets containing the polymers.

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  • References

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    This article references 54 other publications.

    1. 1
      Bar Dolev, M.; Braslavsky, I.; Davies, P. L. Ice-Binding Proteins and Their Function. Annu. Rev. Biochem. 2016, 85, 515– 542,  DOI: 10.1146/annurev-biochem-060815-014546
      1
      Ice-Binding Proteins and Their Function
      Bar Dolev, Maya; Braslavsky, Ido; Davies, Peter L.
      Annual Review of Biochemistry (2016), 85 (), 515-542CODEN: ARBOAW; ISSN:0066-4154. (Annual Reviews)
      A review. Ice-binding proteins (IBPs) are a diverse class of proteins that assist organism survival in the presence of ice in cold climates. They have different origins in many organisms, including bacteria, fungi, algae, diatoms, plants, insects, and fish. This review covers the gamut of IBP structures and functions and the common features they use to bind ice. We discuss mechanisms by which IBPs adsorb to ice and interfere with its growth, evidence for their irreversible assocn. with ice, and methods for enhancing the activity of IBPs. The applications of IBPs in the food industry, in cryopreservation, and in other technologies are vast, and we chart out some possibilities.
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    2. 2
      Meister, K.; Strazdaite, S.; DeVries, A. L.; Lotze, S.; Olijve, L. L. C.; Voets, I. K.; Bakker, H. J. Observation of Ice-like Water Layers at an Aqueous Protein Surface. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 17732– 17736,  DOI: 10.1073/pnas.1414188111
      2
      Observation of ice-like water layers at an aqueous protein surface
      Meister, Konrad; Strazdaite, Simona; De Vries, Arthur L.; Lotze, Stephan; Olijve, Luuk L. C.; Voets, Ilja K.; Bakker, Huib J.
      Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (50), 17732-17736CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      We study the properties of water at the surface of an antifreeze protein with femtosecond surface sum frequency generation spectroscopy. We find clear evidence for the presence of ice-like water layers at the ice-binding site of the protein in aq. soln. at temps. above the f.p. Decreasing the temp. to the biol. working temp. of the protein (0 °C to -2 °C) increases the amt. of ice-like water, while a single point mutation in the ice-binding site is obsd. to completely disrupt the ice-like character and to eliminate antifreeze activity. Our observations indicate that not the protein itself but ordered ice-like water layers are responsible for the recognition and binding to ice.
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    3. 3
      Qiu, Y.; Hudait, A.; Molinero, V. How Size and Aggregation of Ice-Binding Proteins Control Their Ice Nucleation Efficiency. J. Am. Chem. Soc. 2019, 141, 7439– 7452,  DOI: 10.1021/jacs.9b01854
      3
      How Size and Aggregation of Ice-Binding Proteins Control Their Ice Nucleation Efficiency
      Qiu, Yuqing; Hudait, Arpa; Molinero, Valeria
      Journal of the American Chemical Society (2019), 141 (18), 7439-7452CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Organisms that thrive at cold temps. produce ice-binding proteins to manage the nucleation and growth of ice. Bacterial ice-nucleating proteins (INP) are typically large and form aggregates in the cell membrane, while insect hyperactive antifreeze proteins (AFP) are sol. and generally small. Expts. indicate that larger ice-binding proteins and their aggregates nucleate ice at warmer temps. Nevertheless, a quant. understanding of how size and aggregation of ice-binding proteins det. the temp. Thet at which proteins nucleate ice is still lacking. Here, we address this question using mol. simulations and nucleation theory. The simulations indicate that the 2.5 nm long antifreeze protein TmAFP nucleates ice at 2 ± 1 °C above the homogeneous nucleation temp., in good agreement with recent expts. We predict that the addn. of ice-binding loops to TmAFP increases Thet, but not enough to compete in efficiency with the bacterial INP. We implement an accurate procedure to det. Thet of surfaces of finite size using classical nucleation theory, and, after validating the theory against Thet of the proteins in mol. simulations, we use it to predict Thet of the INP of Ps. syringae as a function of the length and no. of proteins in the aggregates. We conclude that assemblies with at most 34 INP already reach the Thet = -2 °C characteristic of this bacterium. Interestingly, we find that Thet is a strongly varying nonmonotonic function of the distance between proteins in the aggregates. This indicates that, to achieve max. freezing efficiency, bacteria must exert exquisite, subangstrom control of the distance between INP in their membrane.
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    4. 4
      Venketesh, S.; Dayananda, C. Properties, Potentials, and Prospects of Antifreeze Proteins. Crit. Rev. Biotechnol. 2008, 28, 57– 82,  DOI: 10.1080/07388550801891152
      4
      Properties, Potentials, and Prospects of Antifreeze Proteins
      Venketesh, S.; Dayananda, C.
      Critical Reviews in Biotechnology (2008), 28 (1), 57-82CODEN: CRBTE5; ISSN:0738-8551. (Informa Healthcare)
      A review. Antifreeze proteins (AFPs) are a group of proteins that protect organisms from deep freezing temps. and are expressed in vertebrates, invertebrates, plants, bacteria, and fungi. The NMR, x-ray structure, and many spectroscopic studies of AFPs have been instrumental in detg. their structure-function relationships. Mutational studies have indicated the importance of hydrophobic residues in ice binding. Various studies have pointed out that the mechanism of AFP action is through its adsorption on the ice surface, which leads to a curved surface, preventing further growth of ice by the "Kelvin effect.". The AFPs have potential industrial, medical, and agricultural application in different fields, such as food technol., preservation of cell lines, organs, cryosurgery, and cold hardy transgenic plants and animals. However, the applications of AFPs are marred by high cost due to low yield. This review deals with the source and properties of AFPs from an angle of their application and their potential. The possibility of prodn. using different mol. biol. techniques, which will help increase the yield, is also dealt with.
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    5. 5
      Forbes, J.; Bissoyi, A.; Eickhoff, L.; Reicher, N.; Hansen, T.; Bon, C. G.; Walker, V. K.; Koop, T.; Rudich, Y.; Braslavsky, I.; Davies, P. L. Water-Organizing Motif Continuity Is Critical for Potent Ice Nucleation Protein Activity. Nat. Commun. 2022, 13, 5019  DOI: 10.1038/s41467-022-32469-9
      5
      Water-organizing motif continuity is critical for potent ice nucleation protein activity
      Forbes, Jordan; Bissoyi, Akalabya; Eickhoff, Lukas; Reicher, Naama; Hansen, Thomas; Bon, Christopher G.; Walker, Virginia K.; Koop, Thomas; Rudich, Yinon; Braslavsky, Ido; Davies, Peter L.
      Nature Communications (2022), 13 (1), 5019CODEN: NCAOBW; ISSN:2041-1723. (Nature Portfolio)
      Bacterial ice nucleation proteins (INPs) can cause frost damage to plants by nucleating ice formation at high sub-zero temps. Modeling of Pseudomonas borealis INP by AlphaFold suggests that the central domain of 65 tandem sixteen-residue repeats forms a beta-solenoid with arrays of outward-pointing threonines and tyrosines, which may organize water mols. into an ice-like pattern. Here we report that mutating some of these residues in a central segment of P. borealis INP, expressed in Escherichia coli, decreases ice nucleation activity more than the section's deletion. Insertion of a bulky domain has the same effect, indicating that the continuity of the water-organizing repeats is crit. for optimal activity. The ∼10 C-terminal coils differ from the other 55 coils in being more basic and lacking water-organizing motifs; deletion of this region eliminates INP activity. We show through sequence modifications how arrays of conserved motifs form the large ice-nucleating surface required for potency.
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    6. 6
      Voets, I. K. From Ice-Binding Proteins to Bio-Inspired Antifreeze Materials. Soft Matter 2017, 13, 4808– 4823,  DOI: 10.1039/C6SM02867E
      6
      From ice-binding proteins to bio-inspired antifreeze materials
      Voets, I. K.
      Soft Matter (2017), 13 (28), 4808-4823CODEN: SMOABF; ISSN:1744-6848. (Royal Society of Chemistry)
      Ice-binding proteins (IBP) facilitate survival under extreme conditions in diverse life forms. IBPs in polar fishes block further growth of internalized environmental ice and inhibit ice recrystn. of accumulated internal crystals. Algae use IBPs to structure ice, while ice adhesion is crit. for the Antarctic bacterium Marinomonas primoryensis. Successful translation of this natural cryoprotective ability into man-made materials holds great promise but is still in its infancy. This review covers recent advances in the field of ice-binding proteins and their synthetic analogs, highlighting fundamental insights into IBP functioning as a foundation for the knowledge-based development of cheap, bio-inspired mimics through scalable prodn. routes. Recent advances in the utilization of IBPs and their analogs to e.g. improve cryopreservation, ice-templating strategies, gas hydrate inhibition and other technologies are presented.
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    7. 7
      Biggs, C. I.; Bailey, T. L.; Graham, B.; Stubbs, C.; Fayter, A.; Gibson, M. I. Polymer Mimics of Biomacromolecular Antifreezes. Nat. Commun. 2017, 8, 1546  DOI: 10.1038/s41467-017-01421-7
      7
      Polymer mimics of biomacromolecular antifreezes
      Biggs Caroline I; Bailey Trisha L; Ben Graham; Stubbs Christopher; Fayter Alice; Gibson Matthew I; Gibson Matthew I
      Nature communications (2017), 8 (1), 1546 ISSN:.
      Antifreeze proteins from polar fish species are remarkable biomacromolecules which prevent the growth of ice crystals. Ice crystal growth is a major problem in cell/tissue cryopreservation for transplantation, transfusion and basic biomedical research, as well as technological applications such as icing of aircraft wings. This review will introduce the rapidly emerging field of synthetic macromolecular (polymer) mimics of antifreeze proteins. Particular focus is placed on designing polymers which have no structural similarities to antifreeze proteins but reproduce the same macroscopic properties, potentially by different molecular-level mechanisms. The application of these polymers to the cryopreservation of donor cells is also introduced.
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    8. 8
      He, Z.; Liu, K.; Wang, J. Bioinspired Materials for Controlling Ice Nucleation, Growth, and Recrystallization. Acc. Chem. Res. 2018, 51, 1082– 1091,  DOI: 10.1021/acs.accounts.7b00528
      8
      Bioinspired Materials for Controlling Ice Nucleation, Growth, and Recrystallization
      He, Zhiyuan; Liu, Kai; Wang, Jianjun
      Accounts of Chemical Research (2018), 51 (5), 1082-1091CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. Ice formation, mainly consisting of ice nucleation, ice growth, and ice recrystn., is ubiquitous and crucial in wide-ranging fields from cryobiol. to atm. physics. Despite active research for more than a century, the mechanism of ice formation is still far from satisfactory. Meanwhile, nature has unique ways of controlling ice formation and can provide resourceful avenues to unravel the mechanism of ice formation. For instance, antifreeze proteins (AFPs) protect living organisms from freezing damage via controlling ice formation, for example, tuning ice nucleation, shaping ice crystals, and inhibiting ice growth and recrystn. In addn., AFP mimics can have applications in cryopreservation of cells, tissues, and organs, food storage, and anti-icing materials. Therefore, continuous efforts have been made to understand the mechanism of AFPs and design AFP inspired materials.In this Account, the authors first review the authors' recent research progress in understanding the mechanism of AFPs in controlling ice formation. A Janus effect of AFPs on ice nucleation was discovered, which was achieved via selectively tethering the ice-binding face (IBF) or the non-ice-binding face (NIBF) of AFPs to solid surfaces and studying specifically the effect of the other face on ice nucleation. Through mol. dynamics (MD) simulation anal., the authors obsd. ordered hexagonal ice-like water structure atop the IBF and disordered water structure atop the NIBF. Therefore, the interfacial water plays a crit. role in controlling ice formation.Next, the design and fabrication of AFP mimics with capabilities in tuning ice nucleation and controlling ice shape and growth, as well as inhibiting ice recrystn are discussed. For example, the authors tuned ice nucleation via modifying solid surfaces with supercharged unfolded polypeptides (SUPs) and polyelectrolyte brushes (PBs) with different counterions. The authors found graphene oxide (GO) and oxidized quasi-carbon nitride quantum dots (OQCNs) had profound effects in controlling ice shape and inhibiting ice growth. The authors also studied the ion-specific effect on ice recrystn. inhibition (IRI) with a large variety of anions and cations. All functionalities are achieved by tuning the properties of interfacial water on these materials, which reinforces the importance of the interfacial water in controlling ice formation. Finally, the authors review the development of novel application-oriented materials emerging from the authors' enhanced understanding of ice formation, for example, ultralow ice adhesion coatings with aq. lubricating layer, cryopreservation of cells by inhibiting ice recrystn., and two-dimensional (2D) and three-dimensional (3D) porous materials with tunable pore sizes through recrystd. ice crystal templates. This Account sheds new light on the mol. mechanism of ice formation and will inspire the design of unprecedented functional materials based on controlled ice formation.
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    9. 9
      Inada, T.; Lu, S. S. Inhibition of Recrystallization of Ice Grains by Adsorption of Poly(Vinyl Alcohol) onto Ice Surfaces. Cryst. Growth Des. 2003, 3, 747– 752,  DOI: 10.1021/cg0340300
      9
      Inhibition of Recrystallization of Ice Grains by Adsorption of Poly(Vinyl Alcohol) onto Ice Surfaces
      Inada, Takaaki; Lu, Shu-Shen
      Crystal Growth & Design (2003), 3 (5), 747-752CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      The effect of poly(vinyl alc.) (PVA) on recrystn. of ice was studied by comparison with the effect of antifreeze protein (AFP) type I. Polycryst. ice wafers consisting of numerous ice grains, whose initial size was <130 μm (i.e., less than the thickness of the ice wafer) were made from solns. contg. PVA or AFP type I at various concns. The ice wafers were annealed between -2.3 and -2.0° for 5 h, and then the size of the ice grains was measured using digital microscopy. Even at a PVA concn. as low as ∼5 × 10-7 mol/L, the size of the annealed ice grains made from the PVA soln. did not change significantly from the initial size, indicating that PVA is as effective as AFP type I in inhibiting ice recrystn. The effectiveness of PVA increased (i.e., the grain size decreased) with increasing molar concn., mol. wt., or degree of hydrolysis of PVA. The function of PVA mols. in the inhibition of recrystn. was analyzed by using the Langmuir adsorption equation.
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    10. 10
      Budke, C.; Koop, T. Ice Recrystallization Inhibition and Molecular Recognition of Ice Faces by Poly(Vinyl Alcohol). ChemPhysChem 2006, 7, 2601– 2606,  DOI: 10.1002/cphc.200600533
      10
      Ice recrystallization inhibition and molecular recognition of ice faces by poly(vinyl alcohol)
      Budke, Carsten; Koop, Thomas
      ChemPhysChem (2006), 7 (12), 2601-2606CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The effects of poly(vinyl alc.) (PVA) on the Ostwald ripening of polycryst. ice samples are studied. At -6°, ice recrystn. in sucrose solns. is inhibited at PVA concns. down to 0.005 mg mL-1, with a recrystn. inhibition const. of 48.9 mL mg-1. Ice growth-habit expts. reveal mol. recognition of the arrangement of H2O mols. in the ice by PVA mols., and indicate that PVA mols. adsorb to the primary and secondary prism faces of hexagonal ice, 1h. Based on these observations, together with an anal. of the O-atom pattern in ice and the conformation of OH groups in PVA, an adsorption model is proposed. Probably PVA segments adsorb to the primary and secondary prism faces of ice parallel to the c axis with a linear misfit parameter of only 2.7%, most likely via multiple H bonds. The proposed adsorption mechanism is discussed in the light of recent thermal hysteresis and scanning tunneling microscopy expts.
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    11. 11
      Congdon, T.; Notman, R.; Gibson, M. I. Antifreeze (Glyco)Protein Mimetic Behavior of Poly(Vinyl Alcohol): Detailed Structure Ice Recrystallization Inhibition Activity Study. Biomacromolecules 2013, 14, 1578– 1586,  DOI: 10.1021/bm400217j
      11
      Antifreeze (Glyco)protein Mimetic Behavior of Poly(vinyl alcohol): Detailed Structure Ice Recrystallization Inhibition Activity Study
      Congdon, Thomas; Notman, Rebecca; Gibson, Matthew I.
      Biomacromolecules (2013), 14 (5), 1578-1586CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)
      This manuscript reports a detailed study on the ability of poly(vinyl alc.) to act as a biomimetic surrogate for AF(G)Ps ("antifreeze(glyco)proteins"), with a focus on the specific property of ice-recrystn. inhibition (IRI). Despite over 40 years of study, the underlying mechanisms that govern the action of biol. antifreezes are still poorly understood, which is in part due to their limited availability and challenging synthesis. Poly(vinyl alc.) (PVA) has been shown to display remarkable ice recrystn. inhibition activity despite its major structural differences to native antifreeze proteins. Here, controlled radical polymn. is used to synthesize well-defined PVA, which has enabled us to obtain the first quant. structure-activity relationships, to probe the role of mol. wt. and comonomers on IRI activity. Crucially, it was found that IRI activity is "switched on" when the polymer chain length increases from 10 and 20 repeat units. Substitution of the polymer side chains with hydrophilic or hydrophobic units was found to diminish activity. Hydrophobic modifications to the backbone were slightly more tolerated than side chain modifications, which implies an unbroken sequence of hydroxyl units is necessary for activity. These results highlight the idea that although hydrophobic domains are key components of IRI activity, the random inclusion of addnl. hydrophobic units does not guarantee an increase in activity and that the actual polymer conformation is important.
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    12. 12
      Congdon, T. R.; Notman, R.; Gibson, M. I. Synthesis of Star-Branched Poly(Vinyl Alcohol) and Ice Recrystallization Inhibition Activity. Eur. Polym. J. 2017, 88, 320– 327,  DOI: 10.1016/j.eurpolymj.2017.01.039
      12
      Synthesis of star-branched poly(vinyl alcohol) and ice recrystallization inhibition activity
      Congdon, Thomas R.; Notman, Rebecca; Gibson, Matthew I.
      European Polymer Journal (2017), 88 (), 320-327CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
      Antifreeze proteins are potent inhibitors of ice crystal growth (recrystn.), which is a highly desirable property for cryopreservation and other low temp. applications. It has emerged that relatively simple polymers based on poly(vinyl alc.) can mimic this activity, but the link between architecture and activity is not known. Here, a trifunctional xanthate was designed and synthesized to prep. star-branched poly(vinyl alcs.) by RAFT/Xanthate mediated polymn., and their ice growth inhibition activity probed for the first time. The trifunctional agent design affords the formation of well-defined star polymers, with no evidence of star-star linking, even at high conversions, and narrow mol. wt. dispersity. It is obsd. that three-arm stars have identical activity to two-armed (i.e. linear) equiv., suggesting that the total hydrodynamic size of the polymer (diam. three-arm ∼ two-arm) rather than total valence of the functional groups is the key descriptor of activity.
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    13. 13
      Olijve, L. L. C.; Hendrix, M. M. R. M.; Voets, I. K. Influence of Polymer Chain Architecture of Poly(Vinyl Alcohol) on the Inhibition of Ice Recrystallization. Macromol. Chem. Phys. 2016, 217, 951– 958,  DOI: 10.1002/macp.201500497
      13
      Influence of Polymer Chain Architecture of Poly(vinyl alcohol) on the Inhibition of Ice Recrystallization
      Olijve, Luuk L. C.; Hendrix, Marco M. R. M.; Voets, Ilja K.
      Macromolecular Chemistry and Physics (2016), 217 (8), 951-958CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Poly(vinyl alc.) (PVA) is a water-sol. synthetic polymer well-known to effectively block the recrystn. of ice. The effect of polymer chain architecture on the ice recrystn. inhibition (IRI) by PVA remains unexplored. In this work, the synthesis of PVA mol. bottlebrushes is described via a combination of atom-transfer radical polymn. and reversible addn.-fragmentation chain-transfer polymn. The facile prepn. of the PVA bottlebrushes is performed via the selective hydrolysis of the chloroacetate esters of the poly(vinyl chloroacetate) (PVClAc) side chains of a PVClAc precursor bottlebrush. The IRI efficacy of the PVA bottlebrush is quant. compared to linear PVA. The results show that even if the PVA chains are densely grafted onto a rigid polymer backbone, the IRI activity of PVA is maintained, demonstrating the flexibility in PVA polymer chain architecture for the design of synthetic PVA-based ice growth inhibitors.
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    14. 14
      Georgiou, P. G.; Kontopoulou, I.; Congdon, T. R.; Gibson, M. I. Ice Recrystallisation Inhibiting Polymer Nano-Objects: Via Saline-Tolerant Polymerisation-Induced Self-Assembly. Mater. Horiz. 2020, 7, 1883– 1887,  DOI: 10.1039/D0MH00354A
      14
      Ice recrystallisation inhibiting polymer nano-objects via saline-tolerant polymerisation-induced self-assembly
      Georgiou, Panagiotis G.; Kontopoulou, Ioanna; Congdon, Thomas R.; Gibson, Matthew I.
      Materials Horizons (2020), 7 (7), 1883-1887CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
      Chem. tools to modulate ice formation/growth have great (bio)technol. value, with ice binding/antifreeze proteins being exciting targets for biomimetic materials. Here we introduce polymer nanomaterials that are potent inhibitors of ice recrystn. using polymn.-induced self-assembly (PISA), employing a poly(vinyl alc.) graft macromol. chain transfer agent (macro-CTA). Crucially, engineering the core-forming block with diacetone acrylamide enabled PISA to be conducted in saline, whereas poly(2-hydroxypropyl methacrylate) cores led to coagulation. The most active particles inhibited ice growth as low as 0.5 mg mL-1, and were more active than the PVA stabilizer block alone, showing that the dense packing of this nanoparticle format enhanced activity. This provides a unique route towards colloids capable of modulating ice growth.
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    15. 15
      Bachtiger, F.; Congdon, T. R.; Stubbs, C.; Gibson, M. I.; Sosso, G. C. The Atomistic Details of the Ice Recrystallisation Inhibition Activity of PVA. Nat. Commun. 2021, 12, 1323  DOI: 10.1038/s41467-021-21717-z
      15
      The atomistic details of the ice recrystallisation inhibition activity of PVA
      Bachtiger, Fabienne; Congdon, Thomas R.; Stubbs, Christopher; Gibson, Matthew I.; Sosso, Gabriele C.
      Nature Communications (2021), 12 (1), 1323CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      Understanding the ice recrystn. inhibition (IRI) activity of antifreeze biomimetics is crucial to the development of the next generation of cryoprotectants. In this work, we bring together mol. dynamics simulations and quant. exptl. measurements to unravel the microscopic origins of the IRI activity of poly(vinyl)alc. (PVA)-the most potent of biomimetic IRI agents. Contrary to the emerging consensus, we find that PVA does not require a "lattice matching" to ice in order to display IRI activity: instead, it is the effective vol. of PVA and its contact area with the ice surface which dictates its IRI strength. We also find that entropic contributions may play a role in the ice-PVA interaction and we demonstrate that small block co-polymers (up to now thought to be IRI-inactive) might display significant IRI potential. This work clarifies the atomistic details of the IRI activity of PVA and provides novel guidelines for the rational design of cryoprotectants.
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    16. 16
      Naullage, P. M.; Lupi, L.; Molinero, V. Molecular Recognition of Ice by Fully Flexible Molecules. J. Phys. Chem. C 2017, 121, 26949– 26957,  DOI: 10.1021/acs.jpcc.7b10265
      16
      Molecular Recognition of Ice by Fully Flexible Molecules
      Naullage, Pavithra M.; Lupi, Laura; Molinero, Valeria
      Journal of Physical Chemistry C (2017), 121 (48), 26949-26957CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Cold-acclimatized organisms produce antifreeze proteins that enable them to prevent ice growth and recrystn. at subfreezing conditions. Flatness and rigidity of the ice-binding sites of antifreeze proteins are considered key for their recognition of ice. However, the most potent synthetic ice recrystn. inhibitor (IRI) found to date is polyvinyl alc. (PVA), a fully flexible mol. The ability to tune the architecture and functionalization of PVA makes it a promising candidate to replace antifreeze proteins in industrial applications ranging from cryopreservation of organs to de-icing of turbine blades. However, an understanding of how PVA recognizes ice remains elusive, hampering the design of more effective IRIs. Here, we used large-scale mol. dynamics simulations to elucidate the mechanism by which PVA recognizes ice. We found that the polymer selectively bound to the prismatic faces of ice through a cooperative zipper mechanism. The binding was driven by H-bonding, facilitated by distance matching between the OH groups in PVA and water at the ice surface. Strong, cooperative binding to ice results from the different scaling of the free energy gains on binding per monomer, and the loss of translational and configurational entropy of the chain. We explained why branching of PVA does not improve its IRI activity, and used the new mol. understanding to propose principles for the design of macromols. that bind efficiently to the basal and prismatic planes of ice, producing hyperactive synthetic antifreeze mols. that could compete with the most effective antifreeze proteins.
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    17. 17
      Biggs, C. I.; Stubbs, C.; Graham, B.; Fayter, A. E. R.; Hasan, M.; Gibson, M. I. Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When Is a New Polymer “Active”?. Macromol. Biosci. 2019, 19, 1900082  DOI: 10.1002/mabi.201900082
      There is no corresponding record for this reference.
    18. 18
      Garnham, C. P.; Campbell, R. L.; Davies, P. L. Anchored Clathrate Waters Bind Antifreeze Proteins to Ice. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 7363– 7367,  DOI: 10.1073/pnas.1100429108
      18
      Anchored clathrate waters bind antifreeze proteins to ice
      Garnham, Christopher P.; Campbell, Robert L.; Davies, Peter L.
      Proceedings of the National Academy of Sciences of the United States of America (2011), 108 (18), 7363-7367, S7363/1-S7363/3CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      The mechanism by which antifreeze proteins (AFPs) irreversibly bind to ice has not yet been resolved. The ice-binding site of an AFP is relatively hydrophobic, but also contains many potential hydrogen bond donors/acceptors. The extent to which hydrogen bonding and the hydrophobic effect contribute to ice binding has been debated for over 30 years. Here we have elucidated the ice-binding mechanism through solving the first crystal structure of an Antarctic bacterial AFR. This 34-kDa domain, the largest AFP structure detd. to date, folds as a Ca2+-bound parallel beta-helix with an extensive array of ice-like surface waters that are anchored via hydrogen bonds directly to the polypeptide backbone and adjacent side chains. These bound waters make an excellent three-dimensional match to both the primary prism and basal planes of ice and in effect provide an extensive X-ray crystallog. picture of the AFP:ice interaction. This unobstructed view, free from crystal-packing artifacts, shows the contributions of both the hydrophobic effect and hydrogen bonding during AFP adsorption to ice. We term this mode of binding the "anchored clathrate" mechanism of AFP action.
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    19. 19
      Daley, M. E.; Spyracopoulos, L.; Jia, Z.; Davies, P. L.; Sykes, B. D. Structure and Dynamics of an Alpha-Helical Antifreeze Protein. Biochemistry 2002, 41, 5515– 5525,  DOI: 10.1021/bi0121252
      19
      Structure and Dynamics of a β-Helical Antifreeze Protein
      Daley, Margaret E.; Spyracopoulos, Leo; Jia, Zongchao; Davies, Peter L.; Sykes, Brian D.
      Biochemistry (2002), 41 (17), 5515-5525CODEN: BICHAW; ISSN:0006-2960. (American Chemical Society)
      Antifreeze proteins (AFPs) protect many types of organisms from damage caused by freezing. They do this by binding to the ice surface, which causes inhibition of ice crystal growth. However, the mol. mechanism of ice binding leading to growth inhibition is not well understood. In this paper, we present the soln. structure and backbone NMR relaxation data of the antifreeze protein from the yellow mealworm beetle Tenebrio molitor (TmAFP) to study the dynamics in the context of structure. The full 15N relaxation anal. was completed at two magnetic field strengths, 500 and 600 MHz, as well as at two temps., 30 and 5 °C, to measure the dynamic changes that occur in the protein backbone at different temps. TmAFP is a small, highly disulfide-bonded, right-handed parallel β-helix consisting of seven tandemly repeated 12-amino acid loops. The backbone relaxation data displays a periodic pattern, which reflects both the 12-amino acid structural repeat and the highly anisotropic nature of the protein. Anal. of the 15N relaxation parameters shows that TmAFP is a well-defined, rigid structure, and the extd. parameters show that there is similar restricted internal mobility throughout the protein backbone at both temps. studied. We conclude that the hydrophobic, rigid binding site may reduce the entropic penalty for the binding of the protein to ice. The β-helical fold of the protein provides this rigidity, as it does not appear to be a consequence of cooling toward a physiol. relevant temp.
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    20. 20
      Mochizuki, K.; Molinero, V. Antifreeze Glycoproteins Bind Reversibly to Ice via Hydrophobic Groups. J. Am. Chem. Soc. 2018, 140, 4803– 4811,  DOI: 10.1021/jacs.7b13630
      20
      Antifreeze Glycoproteins Bind Reversibly to Ice via Hydrophobic Groups
      Mochizuki, Kenji; Molinero, Valeria
      Journal of the American Chemical Society (2018), 140 (14), 4803-4811CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Antifreeze mols. allow organisms to survive in subzero environments. Antifreeze glycoproteins (AFGPs), produced by polar fish, are the most potent inhibitors of ice recrystn. To date, the mol. mechanism by which AFGPs bind to ice has not yet been elucidated. Mutation expts. cannot resolve whether the binding occurs through the peptide, the saccharides, or both. Here, we used mol. dynamics simulations to det. the mechanism and driving forces for binding of AFGP8 to ice, its selectivity for the primary prismatic plane, and the mol. origin of its exceptional ice recrystn. activity. Consistent with expts., AFGP8 in simulations preferentially adopted the polyproline II (PPII) helix secondary structure in soln. We showed that the segregation of hydrophilic and hydrophobic groups in the PPII helix is vital for ice binding. The binding occurred through adsorption of Me groups of the peptide and disaccharides to ice, driven by the entropy of dehydration of the hydrophobic groups as they nested in the cavities at the ice surface. The selectivity to the primary prismatic plane originated in the deeper cavities it had compared to the basal plane. We estd. the free energy of binding of AFGP8 and the longer AFGP4-6, and found them to be consistent with the reversible binding demonstrated in expts. The simulations revealed that AFGP8 binds to ice through a myriad of conformations that it uses to diffuse through the ice surface and find ice steps, to which it strongly adsorbs. We interpret that the existence of multiple, weak binding sites is the key for the exceptional ice recrystn. inhibition activity of AFGPs.
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    21. 21
      Vonnegut, B. The Nucleation of Ice Formation by Silver Iodide. J. Appl. Phys. 1947, 18, 593– 595,  DOI: 10.1063/1.1697813
      21
      Nucleation of ice formation by silver iodide
      Vonnegut, B.
      Journal of Applied Physics (1947), 18 (), 593-5CODEN: JAPIAU; ISSN:0021-8979.
      AgI particles have been found to serve as nuclei for the formation of ice crystals in supercooled water and in water vapor supersatd. with respect to ice, probably because it very closely resembles ice in crystal structure. The dimensions of the unit cell of ice and of AgI are the same to within approx. 1%. The max. temp. at which AgI particles serve as nuclei is approx. -4° for particles 1μ in diam., and -8° for particles 100 A. in diam. Mixts. of I and Ag vapors are also effective in producing ice nuclei. The most effective method so far found for producing AgI smokes is the following. A cotton string coated with AgI is fed at a fixed rate into an oxyhydrogen flame. A few in. away from the point at which the AgI is introduced the flame is quenched with a blast of compressed air. This produces an invisible smoke of AgI particles approx. 100 A. in diam. One mg. of AgI per sec. produces in this way approx. 1013 ice nuclei per sec.
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    22. 22
      Marcolli, C.; Nagare, B.; Welti, A.; Lohmann, U. Ice Nucleation Efficiency of AgI: Review and New Insights. Atmos. Chem. Phys. 2016, 16, 8915– 8937,  DOI: 10.5194/acp-16-8915-2016
      22
      Ice nucleation efficiency of AgI: review and new insights
      Marcolli, Claudia; Nagare, Baban; Welti, Andre; Lohmann, Ulrike
      Atmospheric Chemistry and Physics (2016), 16 (14), 8915-8937CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      AgI is one of the best-investigated ice-nucleating substances. It has relevance for the atm. since it is used for glaciogenic cloud seeding. Theor. and exptl. studies over the last 60 years provide a complex picture of silver iodide as an ice-nucleating agent with conflicting and inconsistent results. This review compares exptl. ice nucleation studies in order to analyze the factors that influence the ice nucleation ability of AgI. The following picture emerges from this anal.: the ice nucleation ability of AgI seems to be enhanced when the AgI particle is on the surface of a droplet, which is indeed the position that a particle takes when it can freely move in a droplet. The ice nucleation by particles with surfaces exposed to air depends on water adsorption. AgI surfaces seem to be most efficient at nucleating ice when they are exposed to relative humidity at or even above water satn. For AgI particles that are completely immersed in water, the freezing temp. increases with increasing AgI surface area. Higher threshold freezing temps. seem to correlate with improved lattice matches as can be seen for AgI-AgCl solid solns. and 3AgI·NH4I·6H2O, which have slightly better lattice matches with ice than AgI and also higher threshold freezing temps. However, the effect of a good lattice match is annihilated when the surfaces have charges. Also, the ice nucleation ability seems to decrease during dissoln. of AgI particles. This introduces an addnl. history and time dependence for ice nucleation in cloud chambers with short residence times.
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    23. 23
      Atkinson, J. D.; Murray, B. J.; Woodhouse, M. T.; Whale, T. F.; Baustian, K. J.; Carslaw, K. S.; Dobbie, S.; Sullivan, D. O.; Malkin, T. L. The Importance of Feldspar for Ice Nucleation by Mineral Dust in Mixed-Phase Clouds. Nature 2013, 498, 355– 358,  DOI: 10.1038/nature12278
      23
      The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds
      Atkinson, James D.; Murray, Benjamin J.; Woodhouse, Matthew T.; Whale, Thomas F.; Baustian, Kelly J.; Carslaw, Kenneth S.; Dobbie, Steven; O'Sullivan, Daniel; Malkin, Tamsin L.
      Nature (London, United Kingdom) (2013), 498 (7454), 355-358CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      The amt. of ice present in mixed-phase clouds, which contain both supercooled liq. water droplets and ice particles, affects cloud extent, lifetime, particle size and radiative properties. The freezing of cloud droplets can be catalyzed by the presence of aerosol particles known as ice nuclei. One of the most important ice nuclei is thought to be mineral dust aerosol from arid regions. It is generally assumed that clay minerals, which contribute approx. two-thirds of the dust mass, dominate ice nucleation by mineral dust, and many exptl. studies have therefore focused on these materials. Here we use an established droplet-freezing technique to show that feldspar minerals dominate ice nucleation by mineral dusts under mixed-phase cloud conditions, despite feldspar being a minor component of dust emitted from arid regions. We also find that clay minerals are relatively unimportant ice nuclei. Our results from a global aerosol model study suggest that feldspar ice nuclei are globally distributed and that feldspar particles may account for a large proportion of the ice nuclei in Earth's atm. that contribute to freezing at temps. below about -15 °C.
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    24. 24
      Holden, M. A.; Whale, T. F.; Tarn, M. D.; O’Sullivan, D.; Walshaw, R. D.; Murray, B. J.; Meldrum, F. C.; Christenson, H. K. High-Speed Imaging of Ice Nucleation in Water Proves the Existence of Active Sites. Sci. Adv. 2019, 5, eaav4316  DOI: 10.1126/sciadv.aav4316
      There is no corresponding record for this reference.
    25. 25
      Whale, T. F.; Rosillo-Lopez, M.; Murray, B. J.; Salzmann, C. G. Ice Nucleation Properties of Oxidized Carbon Nanomaterials. J. Phys. Chem. Lett. 2015, 6, 3012– 3016,  DOI: 10.1021/acs.jpclett.5b01096
      25
      Ice Nucleation Properties of Oxidized Carbon Nanomaterials
      Whale, Thomas F.; Rosillo-Lopez, Martin; Murray, Benjamin J.; Salzmann, Christoph G.
      Journal of Physical Chemistry Letters (2015), 6 (15), 3012-3016CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Heterogeneous ice nucleation is an important process in many fields, particularly atm. science, but is still poorly understood. All known inorg. ice nucleating particles are relatively large in size and tend to be hydrophilic. Hence it is not obvious that carbon nanomaterials should nucleate ice. However, in this paper we show that four different readily water-dispersible carbon nanomaterials are capable of nucleating ice. The tested materials were carboxylated graphene nanoflakes, graphene oxide, oxidized single walled carbon nanotubes and oxidized multiwalled carbon nanotubes. The carboxylated graphene nanoflakes have a diam. of ∼30 nm and are among the smallest entities obsd. so far to nucleate ice. Overall, carbon nanotubes were found to nucleate ice more efficiently than flat graphene species, and less oxidized materials nucleated ice more efficiently than more oxidized species. These well-defined carbon nanomaterials may pave the way to bridging the gap between exptl. and computational studies of ice nucleation.
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    26. 26
      Bai, G.; Gao, D.; Liu, Z.; Zhou, X.; Wang, J. Probing the Critical Nucleus Size for Ice Formation with Graphene Oxide Nanosheets. Nature 2019, 576, 437– 441,  DOI: 10.1038/s41586-019-1827-6
      26
      Probing the critical nucleus size for ice formation with graphene oxide nanosheets
      Bai, Guoying; Gao, Dong; Liu, Zhang; Zhou, Xin; Wang, Jianjun
      Nature (London, United Kingdom) (2019), 576 (7787), 437-441CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
      Water freezing is ubiquitous and affects areas as diverse as climate, the chem. industry, cryobiol. and materials science. Ice nucleation is the controlling step in water freezing1-5 and has, for nearly a century, been assumed to require the formation of a crit. ice nucleus6-10. But there has been no direct exptl. evidence for the existence of such a nucleus, owing to its transient and nanoscale nature6,7. Here we report ice nucleation in water droplets contg. graphene oxide nanosheets of controlled sizes and show that they have a notable impact on ice nucleation only above a certain size that varies with the degree of supercooling of the droplets. We infer from our exptl. data and theor. calcns. that the crit. size of the graphene oxide reflects the size of the crit. ice nucleus, which in the case of sufficiently large graphene oxides sits on their surface and gives rise to ice formation behavior consistent with classical nucleation theory. By contrast, when the graphene oxide size is smaller than that of the crit. ice nucleus, pinning at the periphery of the graphene oxide deforms the ice nucleus as it grows. This gives rise to a much higher free-energy barrier for nucleation and suppresses the promoting effect of the graphene oxide11. The results provide exptl. information on the existence and temp.-dependent size of the crit. ice nucleus, which has previously only been explored theor. and through simulations12-16. As pinning of a pre-crit. nucleus at a nanoparticle edge is not specific to the ice nucleus on graphene oxides, we expect that our approach could be extended to probe the crit. nuclei in other nucleation processes.
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    27. 27
      Pummer, B. G.; Budke, C.; Augustin-Bauditz, S.; Niedermeier, D.; Felgitsch, L.; Kampf, C. J.; Huber, R. G.; Liedl, K. R.; Loerting, T.; Moschen, T. Ice Nucleation by Water-Soluble Macromolecules. Atmos. Chem. Phys. 2015, 15, 4077– 4091,  DOI: 10.5194/acp-15-4077-2015
      27
      Ice nucleation by water-soluble macromolecules
      Pummer, B. G.; Budke, C.; Augustin-Bauditz, S.; Niedermeier, D.; Felgitsch, L.; Kampf, C. J.; Huber, R. G.; Liedl, K. R.; Loerting, T.; Moschen, T.; Schauperl, M.; Tollinger, M.; Morris, C. E.; Wex, H.; Grothe, H.; Poeschl, U.; Koop, T.; Froehlich-Nowoisky, J.
      Atmospheric Chemistry and Physics (2015), 15 (8), 4077-4091CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Cloud glaciation is critically important for the global radiation budget (albedo) and for initiation of pptn. But the freezing of pure water droplets requires cooling to temps. as low as 235 K. Freezing at higher temps. requires the presence of an ice nucleator, which serves as a template for arranging water mols. in an ice-like manner. It is often assumed that these ice nucleators have to be insol. particles. We point out that also free macromols. which are dissolved in water can efficiently induce ice nucleation: the size of such ice nucleating macromols. (INMs) is in the range of nanometers, corresponding to the size of the crit. ice embryo. As the latter is temp.-dependent, we see a correlation between the size of INMs and the ice nucleation temp. as predicted by classical nucleation theory. Different types of INMs have been found in a wide range of biol. species and comprise a variety of chem. structures including proteins, saccharides, and lipids. Our investigation of the fungal species Acremonium implicatum, Isaria farinosa, and Mortierella alpina shows that their ice nucleation activity is caused by proteinaceous water-sol. INMs. We combine these new results and literature data on INMs from fungi, bacteria, and pollen with theor. calcns. to develop a chem. interpretation of ice nucleation and water-sol. INMs. This has atm. implications since many of these INMs can be released by fragmentation of the carrier cell and subsequently may be distributed independently. Up to now, this process has not been accounted for in atm. models.
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    28. 28
      Sosso, G. C.; Whale, T. F.; Holden, M. A.; Pedevilla, P.; Murray, B. J.; Michaelides, A. Unravelling the Origins of Ice Nucleation on Organic Crystals. Chem. Sci. 2018, 9, 8077– 8088,  DOI: 10.1039/C8SC02753F
      28
      Unravelling the origins of ice nucleation on organic crystals
      Sosso, Gabriele C.; Whale, Thomas F.; Holden, Mark A.; Pedevilla, Philipp; Murray, Benjamin J.; Michaelides, Angelos
      Chemical Science (2018), 9 (42), 8077-8088CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Org. mols. such as steroids or amino acids form crystals that can facilitate the formation of ice - arguably the most important phase transition on earth. However, the origin of the ice nucleating ability of org. crystals is still largely unknown. Here, we combine expts. and simulations to unravel the microscopic details of ice formation on cholesterol, a prototypical org. crystal widely used in cryopreservation. We find that cholesterol - which is also a substantial component of cell membranes - is an ice nucleating agent more potent than many inorg. substrates, including the mineral feldspar (one of the most active ice nucleating materials in the atm.). SEM measurements reveal a variety of morphol. features on the surfaces of cholesterol crystals: this suggests that the topog. of the surface is key to the broad range of ice nucleating activity obsd. (from -4 to -20°C). In addn., we show via mol. simulations that cholesterol crystals aid the formation of ice nuclei in a unconventional fashion. Rather than providing a template for a flat ice-like contact layer (as found in the case of many inorg. substrates), the flexibility of the cholesterol surface and its low d. of hydrophilic functional groups leads to the formation of mol. cages involving both water mols. and terminal hydroxyl groups of the cholesterol surface. These cages are made of 6- and, surprisingly, 5-membered hydrogen bonded rings of water and hydroxyl groups that favor the nucleation of hexagonal as well as cubic ice (a rare occurrence). We argue that the phenomenal ice nucleating activity of steroids such as cholesterol (and potentially of many other org. crystals) is due to (i) the ability of flexible hydrophilic surfaces to form unconventional ice-templating structures and (ii) the different nucleation sites offered by the diverse topog. of the cryst. surfaces. These findings clarify how exactly org. crystals promote the formation of ice, thus paving the way toward deeper understanding of ice formation in soft and biol. matter - with obvious reverberations on atm. science and cryobiol.
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    29. 29
      Brennan, K. P.; David, R. O.; Borduas-Dedekind, N. Spatial and Temporal Variability in the Ice-Nucleating Ability of Alpine Snowmelt and Extension to Frozen Cloud Fraction. Atmos. Chem. Phys. 2020, 20, 163– 180,  DOI: 10.5194/acp-20-163-2020
      29
      Spatial and temporal variability in the ice-nucleating ability of alpine snowmelt and extension to frozen cloud fraction
      Brennan, Killian P.; David, Robert O.; Borduas-Dedekind, Nadine
      Atmospheric Chemistry and Physics (2020), 20 (1), 163-180CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
      Ice-nucleating particles (INPs) produce ice from supercooled water droplets through heterogeneous freezing in the atm. INPs have often been collected at the Jungfraujoch research station (at 3500 m a.s.l.) in central Switzerland; yet spatially diverse data on INP occurrence in the Swiss Alps are scarce and remain uncharacterized. We address this scarcity through our Swiss alpine snow sample study which took place during the winter of 2018. We collected a total of 88 fallen snow samples across the Alps at 17 different locations and investigated the impact of altitude, terrain, time since last snowfall and depth upon freezing temps. The INP concns. were measured using the home-built DRoplet Ice Nuclei Counter Zurich (DRINCZ) and were then compared to spatial, temporal and physicochem. parameters. Boxplots of the freezing temps. showed large variability in INP occurrence, even for samples collected 10 m apart on a plain and 1 m apart in depth. Furthermore, undiluted samples had cumulative INP concns. ranging between 1 and 200 INP mL-1 of snowmelt over a temp. range of -5 to -19 °C. From this field-collected dataset, we parameterized the cumulative INP concns. per cubic meter of air as a function of temp. with the following equation c*air(T) = e-0.7T-7.05, comparing well with previously reported pptn. data presented in Petters and Wright (2015). When assuming (1) a snow pptn. origin of the INPs, (2) a cloud water content of 0.4 g m-3 and (3) a crit. INP concn. for glaciation of 10 m-3, the majority of the snow pptd. from clouds with glaciation temps. between -5 and -20 °C. Based on the obsd. variability in INP concns., we conclude that studies conducted at the high-altitude research station Jungfraujoch are representative for INP measurements in the Swiss Alps. Furthermore, the INP concn. ests. in pptn. allow us to extrapolate the concns. to a frozen cloud fraction. Indeed, this approach for estg. the liq. water-to-ice ratio in mixed-phase clouds compares well with aircraft measurements, ground-based lidar and satellite retrievals of frozen cloud fractions. In all, the generated parameterization for INP concns. in snowmelt could help est. cloud glaciation temps.
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    30. 30
      Wilson, T. W.; Ladino, L. A.; Alpert, P. A.; Breckels, M. N.; Brooks, I. M.; Browse, J.; Burrows, S. M.; Carslaw, K. S.; Huffman, J. A.; Judd, C. A Marine Biogenic Source of Atmospheric Ice-Nucleating Particles. Nature 2015, 525, 234– 238,  DOI: 10.1038/nature14986
      30
      A marine biogenic source of atmospheric ice-nucleating particles
      Wilson, Theodore W.; Ladino, Luis A.; Alpert, Peter A.; Breckels, Mark N.; Brooks, Ian M.; Browse, Jo; Burrows, Susannah M.; Carslaw, Kenneth S.; Huffman, J. Alex; Judd, Christopher; Kilthau, Wendy P.; Mason, Ryan H.; McFiggans, Gordon; Miller, Lisa A.; Najera, Juan J.; Polishchuk, Elena; Rae, Stuart; Schiller, Corinne L.; Si, Meng; Temprado, Jesus Vergara; Whale, Thomas F.; Wong, Jenny P. S.; Wurl, Oliver; Yakobi-Hancock, Jacqueline D.; Abbatt, Jonathan P. D.; Aller, Josephine Y.; Bertram, Allan K.; Knopf, Daniel A.; Murray, Benjamin J.
      Nature (London, United Kingdom) (2015), 525 (7568), 234-238CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      The amt. of ice present in clouds can affect cloud lifetime, pptn. and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. Sea spray is one of the major global sources of atm. particles, but it is unclear to what extent these particles are capable of nucleating ice. Sea-spray aerosol contains large amts. of org. material that is ejected into the atm. during bubble bursting at the organically enriched sea-air interface or sea surface microlayer. Here we show that org. material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approx. 0.2 μm in size. We find that exudates sepd. from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that org. material assocd. with phytoplankton cell exudates is a likely candidate for the obsd. ice-nucleating ability of the microlayer samples. Global model simulations of marine org. aerosol, in combination with our measurements, suggest that marine org. material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.
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    31. 31
      Dreischmeier, K.; Budke, C.; Wiehemeier, L.; Kottke, T.; Koop, T. Boreal Pollen Contain Ice-Nucleating as Well as Ice-Binding ‘Antifreeze’ Polysaccharides. Sci. Rep. 2017, 7, 41890  DOI: 10.1038/srep41890
      31
      Boreal pollen contain ice-nucleating as well as ice-binding 'antifreeze' polysaccharides
      Dreischmeier, Katharina; Budke, Carsten; Wiehemeier, Lars; Kottke, Tilman; Koop, Thomas
      Scientific Reports (2017), 7 (), 41890CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromols. when suspended in water. Here we show that birch pollen washing water exhibits also ice-binding properties such as ice shaping and ice recrystn. inhibition, similar to antifreeze proteins. We present spectroscopic evidence that both the ice-nucleating as well as the ice-binding mols. are polysaccharides bearing carboxylate groups. The spectra suggest that both polysaccharides consist of very similar chem. moieties, but centrifugal filtration indicates differences in mol. size: ice nucleation occurs only in the supernatant of a 100 kDa filter, while ice shaping is strongly enhanced in the filtrate. This finding may suggest that the larger ice-nucleating polysaccharides consist of clusters of the smaller ice-binding polysaccharides, or that the latter are fragments of the ice-nucleating polysaccharides. Finally, similar polysaccharides released from pine and alder pollen also display both ice-nucleating as well as ice-binding ability, suggesting a common mechanism of interaction with ice among several boreal pollen with implications for atm. processes and antifreeze protection.
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    32. 32
      Eickhoff, L.; Dreischmeier, K.; Zipori, A.; Sirotinskaya, V.; Adar, C.; Reicher, N.; Braslavsky, I.; Rudich, Y.; Koop, T. Contrasting Behavior of Antifreeze Proteins: Ice Growth Inhibitors and Ice Nucleation Promoters. J. Phys. Chem. Lett. 2019, 10, 966– 972,  DOI: 10.1021/acs.jpclett.8b03719
      32
      Contrasting Behavior of Antifreeze Proteins: Ice Growth Inhibitors and Ice Nucleation Promoters
      Eickhoff, Lukas; Dreischmeier, Katharina; Zipori, Assaf; Sirotinskaya, Vera; Adar, Chen; Reicher, Naama; Braslavsky, Ido; Rudich, Yinon; Koop, Thomas
      Journal of Physical Chemistry Letters (2019), 10 (5), 966-972CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Several types of natural mols. interact specifically with ice crystals. Small antifreeze proteins (AFPs) adsorb to particular facets of ice crystals, thus inhibiting their growth, whereas larger ice-nucleating proteins (INPs) can trigger the formation of new ice crystals at temps. much higher than the homogeneous ice nucleation temp. of pure water. It has been proposed that both types of proteins interact similarly with ice and that, in principle, they may be able to exhibit both functions. Here we investigated two naturally occurring antifreeze proteins, one from fish, type-III AFP, and one from beetles, TmAFP. We show that in addn. to ice growth inhibition, both can also trigger ice nucleation above the homogeneous freezing temp., providing unambiguous exptl. proof for their contrasting behavior. Our anal. suggests that the predominant difference between AFPs and INPs is their mol. size, which is a very good predictor of their ice nucleation temp.
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    33. 33
      Ogawa, S.; Koga, M.; Osanai, S. Anomalous Ice Nucleation Behavior in Aqueous Polyvinyl Alcohol Solutions. Chem. Phys. Lett. 2009, 480, 86– 89,  DOI: 10.1016/j.cplett.2009.08.046
      33
      Anomalous ice nucleation behavior in aqueous polyvinyl alcohol solutions
      Ogawa, S.; Koga, M.; Osanai, S.
      Chemical Physics Letters (2009), 480 (1-3), 86-89CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      The effect of polymers on the ice nucleation temp. (T f) was studied in a W/O emulsion using ∼5 μm diam. droplets by differential scanning calorimetry (DSC). Four types of polymers were used. Among them, only poly(vinyl alc.) (PVA) showed the addnl. effect of increasing the T f of the aq. solns. This increase was logarithmic with the concn. of PVA and the difference in mol. wt. did not have any significant effect on T f for the same wt. concn. It was shown that the no. of the structural unit (CH2CHOH) was the key parameter for the increasing degree of T f.
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    34. 34
      Sheiko, S. S.; Sumerlin, B. S.; Matyjaszewski, K. Cylindrical Molecular Brushes: Synthesis, Characterization, and Properties. Prog. Polym. Sci. 2008, 33, 759– 785,  DOI: 10.1016/j.progpolymsci.2008.05.001
      34
      Cylindrical molecular brushes: Synthesis, characterization, and properties
      Sheiko, Sergei S.; Sumerlin, Brent S.; Matyjaszewski, Krzysztof
      Progress in Polymer Science (2008), 33 (7), 759-785CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. Brush-like macromols. are unique polymer mols. whose conformation and phys. properties are controlled by steric repulsion of densely grafted side chains. Mols. can be either flexible or stiff, depending on the grafting d. and the length of the side chains. Mols. can switch their conformation in response to alterations in the surrounding environment, e.g. changes of temp., solvent quality, pH, and ionic strength. Furthermore, one can control mol. conformation and related properties using external stimuli such as light and electromagnetic fields. Mol. brushes are also very informative model systems for exptl. studies of polymer properties. Mols. are readily visualized by at. force microscopy, opening unique opportunities to observe single polymer mols. as they move, order, and react on surfaces. Brush-like mol. architectures are well-known in biol. where they are responsible for various functions including mucociliary clearance of lung airways and mech. performance of articular cartilage. Polymer chem. is currently making the first steps in controlling mol. architecture and understanding the distinctive properties of mol. brushers. This article reviews the characteristic phys. properties of well-defined mol. brushes and the different strategies employed for their prepn., with particular focus on synthesis via controlled radical polymn. techniques.
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    35. 35
      Foster, J. C.; Varlas, S.; Couturaud, B.; Coe, Z.; O’Reilly, R. K. Getting into Shape: Reflections on a New Generation of Cylindrical Nanostructures’ Self-Assembly Using Polymer Building Blocks. J. Am. Chem. Soc. 2019, 141, 2742– 2753,  DOI: 10.1021/jacs.8b08648
      35
      Getting into Shape: Reflections on a New Generation of Cylindrical Nanostructures' Self-Assembly Using Polymer Building Blocks
      Foster, Jeffrey C.; Varlas, Spyridon; Couturaud, Benoit; Coe, Zachary; O'Reilly, Rachel K.
      Journal of the American Chemical Society (2019), 141 (7), 2742-2753CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A review. Cylinders are fascinating structures with uniquely high surface area, internal vol., and rigidity. On the nanoscale, a broad range of applications have demonstrated advantageous behavior of cylindrical micelles or bottlebrush polymers over traditional spherical nano-objects. In the past, obtaining pure samples of cylindrical nanostructures using polymer building blocks via conventional self-assembly strategies was challenging. However, in recent years, the development of advanced methods including polymn.-induced self-assembly, crystn.-driven self-assembly, and bottlebrush polymer synthesis has facilitated the easy synthesis of cylindrical nano-objects at industrially relevant scales. In this Perspective, we discuss these techniques in detail, highlighting the advantages and disadvantages of each strategy and considering how the cylindrical nanostructures that are obtained differ in their chem. structure, phys. properties, colloidal stability, and reactivity. In addn., we propose future challenges to address in this rapidly expanding field.
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    36. 36
      Yamago, S.; Nakamura, Y. Recent Progress in the Use of Photoirradiation in Living Radical Polymerization. Polymer 2013, 54, 981– 994,  DOI: 10.1016/j.polymer.2012.11.046
      36
      Recent progress in the use of photoirradiation in living radical polymerization
      Yamago, Shigeru; Nakamura, Yasuyuki
      Polymer (2013), 54 (3), 981-994CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      A review. The effects of photoirradn. in controlled and living radical polymn. (LRP), namely nitroxide-mediated polymn. (NMP), atom-transfer radical polymn. (ATRP), cobalt-mediated radical polymn. (CMRP), reversible addn.-fragmentation chain transfer polymn. (RAFT), organoiodine-mediated radical polymn. (IRP), and organotellurium-mediated radical polymn. (TERP), are summarized. As in the conventional radical polymn., photoirradn. has been used for generating radicals under mild conditions in LRP methods. In addn. to this use, photoirradn. is also used to overcome the difficulties characteristic to each method, such as activation of catalysis, generation of controlling agents, and increasing the polymer-end structure. The most-recent developments in the use of photochem. in LRP are summarized in this review.
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    37. 37
      McKenzie, T. G.; Fu, Q.; Uchiyama, M.; Satoh, K.; Xu, J.; Boyer, C.; Kamigaito, M.; Qiao, G. G. Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization. Adv. Sci. 2016, 3, 1500394  DOI: 10.1002/advs.201500394
      37
      Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization
      McKenzie Thomas G; Fu Qiang; Qiao Greg G; Uchiyama Mineto; Kamigaito Masami; Satoh Kotaro; Xu Jiangtao; Boyer Cyrille
      Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2016), 3 (9), 1500394 ISSN:2198-3844.
      Recent developments in polymerization reactions utilizing thiocarbonylthio compounds have highlighted the surprising versatility of these unique molecules. The increasing popularity of reversible addition-fragmentation chain transfer (RAFT) radical polymerization as a means of producing well-defined, 'controlled' synthetic polymers is largely due to its simplicity of implementation and the availability of a wide range of compatible reagents. However, novel modes of thiocarbonylthio activation can expand the technique beyond the traditional system (i.e., employing a free radical initiator) pushing the applicability and use of thiocarbonylthio compounds even further than previously assumed. The primary advances seen in recent years are a revival in the direct photoactivation of thiocarbonylthio compounds, their activation via photoredox catalysis, and their use in cationic polymerizations. These synthetic approaches and their implications for the synthesis of controlled polymers represent a significant advance in polymer science, with potentially unforeseen benefits and possibilities for further developments still ahead. This Research News aims to highlight key works in this area while also clarifying the differences and similarities of each system.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2svnvVWrtQ%253D%253D&md5=6892212b1e88ee17e938fd3b0fd667ec
    38. 38
      Aragón, S. R.; Pecora, R. Theory of Dynamic Light Scattering from Large Anisotropic Particles. J. Chem. Phys. 1977, 66, 2506– 2516,  DOI: 10.1063/1.434246
      38
      Theory of dynamic light scattering from large anisotropic particles
      Aragon, S. R.; Pecora, R.
      Journal of Chemical Physics (1977), 66 (6), 2506-16CODEN: JCPSA6; ISSN:0021-9606.
      The scattered elec. field amplitude autocorrelation function of a dil. soln. of large rigid anisotropic particles is computed in the Rayleigh-Debye approxn. The autocorrelation function for cylindrically sym. particles is an infinite series of decaying exponentials with time consts. τl-1 = q2D + l(l + 1)Θ.perp. contg. both translational and rotational diffusion coeffs. The dynamical terms are weighted by particle form factors and also by exptl. geometry factors which are given in coordinate independent form. Explicit formulas for the form factors of spheres, rods, and thin disks are given. The general formulas reduce to the correct expressions for similar optically isotropic scattering systems.
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    39. 39
      Zhang, Z.; Carrillo, J.-M. Y.; Ahn, S.; Wu, B.; Hong, K.; Smith, G. S.; Do, C. Atomistic Structure of Bottlebrush Polymers: Simulations and Neutron Scattering Studies. Macromolecules 2014, 47, 5808– 5814,  DOI: 10.1021/ma500613c
      39
      Atomistic Structure of Bottlebrush Polymers: Simulations and Neutron Scattering Studies
      Zhang, Zhe; Carrillo, Jan-Michael Y.; Ahn, Suk-kyun; Wu, Bin; Hong, Kunlun; Smith, Gregory S.; Do, Changwoo
      Macromolecules (Washington, DC, United States) (2014), 47 (16), 5808-5814CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      We have used small angle neutron scattering (SANS) measurement and atomistic mol. dynamics (MD) simulations to investigate the conformation of bottlebrush polymers with poly(norbornene) (PNB) backbone and different sizes of poly(lactide) (PLA) side chains (PNB25-g-PLA5, PNB25-g-PLA10, and PNB25-g-PLA19). At early stage of simulations, stretched side chains with visible spatial-correlations of about 30 Å were obsd. The exptl. measured SANS data, on the other hand, does not exhibit any correlation peaks in the corresponding length scale indicating a compact form rather than a stretched-hairy polymer conformation. As the simulation continued, the spatial correlations between side chains disappeared after about 40 ns of chain relaxation, and the scattering intensity calcd. for the simulated structure becomes reasonably close to the measured one. Statistical approach is used to overcome the time scale limitation and search for optimal conformation space, which also provides a good agreement with the exptl. data. Further coarse-grained simulation results suggest that the side chain conformation strongly depends on the soly. competition among side chain, backbone, and solvent. Significant changes of backbone dynamics due to the side chain encapsulation have been revealed and discussed.
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    40. 40
      Pesek, S. L.; Xiang, Q.; Hammouda, B.; Verduzco, R. Small-Angle Neutron Scattering Analysis of Bottlebrush Backbone and Side Chain Flexibility. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 104– 111,  DOI: 10.1002/polb.24251
      40
      Small-angle neutron scattering analysis of bottlebrush backbone and side chain flexibility
      Pesek, Stacy L.; Xiang, Qiqi; Hammouda, Boualem; Verduzco, Rafael
      Journal of Polymer Science, Part B: Polymer Physics (2017), 55 (1), 104-111CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
      Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are detd. through small-angle neutron scattering anal. of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a "grafting-through" ring-opening polymn. Scattering profiles are modeled with the empirical Guinier-Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end-to-end distance proportional to N0.55, while the overall bottlebrush increases in size proportional to N0.77. These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in soln. © 2016 Wiley Periodicals, Inc.J. Polym. Sci., Part B: Polym.Phys. 2016.
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    41. 41
      Gallyamov, M. O.; Tartsch, B.; Mela, P.; Potemkin, I. I.; Sheiko, S. S.; Börner, H.; Matyjaszewski, K.; Khokhlov, A. R.; Möller, M. Vapor-Induced Spreading Dynamics of Adsorbed Linear and Brush-like Macromolecules as Observed by Environmental SFM: Polymer Chain Statistics and Scaling Exponents. J. Polym. Sci., Part B: Polym. Phys. 2007, 45, 2368– 2379,  DOI: 10.1002/polb.21253
      41
      Vapor-induced spreading dynamics of adsorbed linear and brush-like macromolecules as observed by environmental SFM: polymer chain statistics and scaling exponents
      Gallyamov, Marat O.; Tartsch, Bernd; Mela, Petra; Potemkin, Igor I.; Sheiko, Sergei S.; Borner, Hans; Matyjaszewski, Krzysztof; Khokhlov, Alexei R.; Moller, Martin
      Journal of Polymer Science, Part B: Polymer Physics (2007), 45 (17), 2368-2379CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
      Scaling exponents ν, that describe the correlation between mean square end-to-end distances and contour lengths of macromols., were detd. by statistical anal. of scanning force micrographs of single linear poly(2-vinylpyridine) and brush-like poly(butanoate-Et methacrylate)-graft-poly(Bu acrylate) macromols. adsorbed on mica. Using an atm.-controlled scanning force microscope, single adsorbed mols. were collapsed and re-expanded upon being exposed to alc. and water vapor, resp. This manipulated collapse-unfolding was used to equilibrate the mol. structure/conformation. The in situ and real-time scanning force microscopy anal. allows the scientist to quant. characterize end-to-end distances and contour lengths of the mols. directly on the image and to observe differences in the spreading dynamics for the two types of macromols. A distinct difference has been obsd. between the expanded two-dimensional (2D) conformations of linear and brush-like polymer chains. Whereas a scaling exponent ν of 0.73 was found for the expanded 2D conformation of the linear mols., a ν-value of 0.53 was detd. for the expanded 2D conformation of the seemingly stiffer brush-like mols. A theor. explanation of the differences between the 2D conformations of brush-like and linear macromols. is proposed here.
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    42. 42
      Radzinski, S. C.; Foster, J. C.; Chapleski, R. C.; Troya, D.; Matson, J. B. Bottlebrush Polymer Synthesis by Ring-Opening Metathesis Polymerization: The Significance of the Anchor Group. J. Am. Chem. Soc. 2016, 138, 6998– 7004,  DOI: 10.1021/jacs.5b13317
      42
      Bottlebrush Polymer Synthesis by Ring-Opening Metathesis Polymerization: The Significance of the Anchor Group
      Radzinski, Scott C.; Foster, Jeffrey C.; Chapleski, Robert C.; Troya, Diego; Matson, John B.
      Journal of the American Chemical Society (2016), 138 (22), 6998-7004CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Control over bottlebrush polymer synthesis by ring-opening metathesis polymn. (ROMP) of macromonomers (MMs) is highly dependent on the competition between the kinetics of the polymn. and the lifetime of the catalyst. We evaluated the effect of anchor group chem.-the configuration of atoms linking the polymer to a polymerizable norbornene-on the kinetics of ROMP of polystyrene and poly(lactic acid) MMs initiated by (H2IMes)(pyr)2(Cl)2Ru=CHPh (Grubbs third generation catalyst). We obsd. a variance in the rate of propagation of >4-fold between similar MMs with different anchor groups. This phenomenon was conserved across all MMs tested, regardless of solvent, mol. wt. (MW), or repeat unit identity. The obsd. >4-fold difference in propagation rate had a dramatic effect on the max. obtainable backbone d.p., with slower propagating MMs reducing the max. bottlebrush MW by an order of magnitude (from ∼106 to ∼105 Da). A chelation mechanism was initially proposed to explain the obsd. anchor group effect, but exptl. and computational studies indicated that the rate differences likely resulted from a combination of varying steric demands and electronic structure among the different anchor groups. The addn. of trifluoroacetic acid to the ROMP reaction substantially increased the propagation rate for all anchor groups tested, likely due to scavenging of the pyridine ligands. Based on these data, rational selection of the anchor group is crit. to achieve high MM conversion and to prep. pure, high MW bottlebrush polymers by ROMP grafting-through.
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    43. 43
      Blosch, S. E.; Scannelli, S. J.; Alaboalirat, M.; Matson, J. B. Complex Polymer Architectures Using Ring-Opening Metathesis Polymerization: Synthesis, Applications, and Practical Considerations. Macromolecules 2022, 55, 4200– 4227,  DOI: 10.1021/acs.macromol.2c00338
      43
      Complex Polymer Architectures Using Ring-Opening Metathesis Polymerization: Synthesis, Applications, and Practical Considerations
      Blosch, Sarah E.; Scannelli, Samantha J.; Alaboalirat, Mohammed; Matson, John B.
      Macromolecules (Washington, DC, United States) (2022), 55 (11), 4200-4227CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A review. Nature shows us that complex mol. architectures lead to unique material properties, and these observations have driven polymer scientists to synthesize complex architectures in an effort to discover how topol. influences properties in synthetic polymers. In this Perspective we discuss a variety of complex architectures synthesized using ring-opening metathesis polymn. (ROMP), including multiblock linear polymers, bottlebrush homopolymers and (multi)block copolymers, dendronized polymers, star polymers, and polymer-biomol. conjugates. Traditional and recently developed synthetic methods including polymn.-induced self-assembly, copolymn. to create gradient structures, and engineering approaches to making complex topologies using ROMP are also reviewed. In this context we highlight emerging applications stemming from these materials, including drug delivery vehicles, nanoscale constructs, and components in light refraction or energy storage, among others. Finally, we conclude with an in-depth discussion on practical considerations in ROMP that enable the highest level of control when synthesizing complex polymer topologies from sterically demanding or otherwise challenging (macro)monomers. Our hope is that this Perspective will guide scientists synthesizing complex polymer architectures toward new and innovative materials with the potential for unique properties and applications.
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    44. 44
      Congdon, T.; Shaw, P.; Gibson, M. I. Thermoresponsive, Well-Defined, Poly(Vinyl Alcohol) Co-Polymers. Polym. Chem. 2015, 6, 4749– 4757,  DOI: 10.1039/C5PY00775E
      44
      Thermoresponsive, well-defined, poly(vinyl alcohol) co-polymers
      Congdon, Thomas; Shaw, Peter; Gibson, Matthew I.
      Polymer Chemistry (2015), 6 (26), 4749-4757CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Thermoresponsive polymers have attracted huge interest as adaptable biomaterials based on their reversible soly. behavior which can be exploited for controlled drug delivery or cellular uptake. The most famous and successful of these is poly(ethylene glycol) (PEG), but the thermal transition temps. that are practically accessible are not physiol. useful. There are some notable examples of synthetic, responsive, polymers that are highly tunable over a physiol. relevant range, but there is still a need for these to be clin. validated in terms of toxicol. and immunogenity for in vivo usage, in addn. to their widely used in vitro applications. Poly(vinyl alc.), PVA, is an appealing biocompatible polymer which is already used for a huge range of biomedical applications. Here, PVA is shown to be a highly tunable, thermoresponsive polymer scaffold. RAFT/MADIX polymn. is used to obtain a library of well-defined polymers between 8 and 50 kDa. Selective alkanoylation of the obtained PVA enabled the effect of side-chains, end-groups and mol. wt. on the observable transition temps. to be studied by turbidimetry. It was found that increasingly hydrophobic side chains (acetyl, propanoyl, butanoyl), or increasing their d. led to corresponding decreases in cloud point. PVA with just 10 mol% butanoylation was shown to have a thermal transition temp. close to physiol. temps. (37 °C), compared to 70 mol% for acetylation, with temps. in between accessible by controlling both the relative degree of functionalization, or by altering the chain length. Finally, a secondary response to esterase enzymes was demonstrated as a route to 'turn off' the responsive behavior on demand. This study suggests that PVA-derived polymers may be a useful platform for responsive biomaterials.
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    45. 45
      Varlas, S.; Hua, Z.; Jones, J. R.; Thomas, M.; Foster, J. C.; O’Reilly, R. K. Complementary Nucleobase Interactions Drive the Hierarchical Self-Assembly of Core–Shell Bottlebrush Block Copolymers toward Cylindrical Supramolecules. Macromolecules 2020, 53, 9747– 9757,  DOI: 10.1021/acs.macromol.0c01857
      45
      Complementary Nucleobase Interactions Drive the Hierarchical Self-Assembly of Core-Shell Bottlebrush Block Copolymers toward Cylindrical Supramolecules
      Varlas, Spyridon; Hua, Zan; Jones, Joseph R.; Thomas, Marjolaine; Foster, Jeffrey C.; O'Reilly, Rachel K.
      Macromolecules (Washington, DC, United States) (2020), 53 (22), 9747-9757CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The self-assembly of amphiphilic block copolymers has facilitated the prepn. of a wide variety of nano-objects of diverse morphol. Ready access to these nanostructures has opened up new possibilities in catalysis, sensing, and nanomedicine. In comparison, the self-assembly of large building blocks (i.e., amphiphilic bottlebrush polymers) has received less attention, owing in part to the relatively more challenging synthesis of these macromols. Bottlebrush amphiphiles can self-assemble into uniquely stable spherical nanostructures and can also produce dynamic cylinders with lengths modulated by environmental conditions, motivating further research in this area. Herein, we report the synthesis of core-shell bottlebrush polymers (BBPs) contg. complementary nucleobase functionalities via a combination of ring-opening metathesis polymn. (ROMP) and reversible addn.-fragmentation chain transfer (RAFT) polymn., using a "grafting-from" approach, and their hierarchical self-assembly in aq. media. Mixts. of BBPs contg. thymine or adenine units in their core blocks were found to self-assemble into higher-order cylindrical supramols. upon heating above a crit. temp. This temp. was demonstrated to correspond to the lower crit. soln. temp. (LCST) of the corona-forming poly(4-acryloylmorpholine) block, providing evidence for a unique one-dimensional BBP assembly mechanism. Moreover, the formation of extended supramol. assemblies was preferentially obsd. when both thymine- and adenine-functionalized BBPs were present in equimolar concns., pointing toward an alternating, isodesmic mechanism of organization occurring via nucleobase interactions located at their chain termini. We anticipate that these discoveries will provide the basis for future studies regarding BBP self-assembly, esp. with regard to the formation of stimuli-responsive anisotropic nanostructures.
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    46. 46
      Knight, C. A.; Hallett, J.; DeVries, A. L. Solute Effects on Ice Recrystallization: An Assessment Technique. Cryobiology 1988, 25, 55– 60,  DOI: 10.1016/0011-2240(88)90020-X
      46
      Solute effects on ice recrystallization: an assessment technique
      Knight C A; Hallett J; DeVries A L
      Cryobiology (1988), 25 (1), 55-60 ISSN:0011-2240.
      Reliable assessment of the effect of a solute upon ice recrystallization is accomplished with "splat cooling," the impaction of a small solution droplet onto a very cold metal plate. The ice disc has extremely small crystals, and recrystallization can be followed without confusing effects caused by grain nucleation. This method confirms the exceptionally strong recrystallization inhibition effect of antifreeze protein from Antarctic fish and shows that grain growth rate is a sensitive function of both grain size and solute concentration.
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    47. 47
      Graham, B.; Fayter, A. E. R.; Houston, J. E.; Evans, R. C.; Gibson, M. I. Facially Amphipathic Glycopolymers Inhibit Ice Recrystallization. J. Am. Chem. Soc. 2018, 140, 5682– 5685,  DOI: 10.1021/jacs.8b02066
      47
      Facially amphipathic glycopolymers inhibit ice recrystallization
      Graham, Ben; Fayter, Alice E. R.; Houston, Judith E.; Evans, Rachel C.; Gibson, Matthew I.
      Journal of the American Chemical Society (2018), 140 (17), 5682-5685CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Antifreeze glycoproteins (AFGPs) from polar fish are the most potent ice recrystn. (growth) inhibitors known, and synthetic mimics are required for low-temp. applications such as cell cryopreservation. Here we introduce facially amphipathic glycopolymers that mimic the three-dimensional structure of AFGPs. Glycopolymers featuring segregated hydrophilic and hydrophobic faces were prepd. by ring-opening metathesis polymn., and their rigid conformation was confirmed by small-angle neutron scattering. Ice recrystn. inhibition (IRI) activity was reduced when a hydrophilic oxo-ether was installed on the glycan-opposing face, but significant activity was restored by incorporating a hydrophobic dimethylfulvene residue. This biomimetic strategy demonstrates that segregated domains of distinct hydrophilicity/hydrophobicity are a crucial motif to introduce IRI activity, which increases our understanding of the complex ice crystal inhibition processes.
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    48. 48
      Stevens, C. A.; Drori, R.; Zalis, S.; Braslavsky, I.; Davies, P. L. Dendrimer-Linked Antifreeze Proteins Have Superior Activity and Thermal Recovery. Bioconjugate Chem. 2015, 26, 1908– 1915,  DOI: 10.1021/acs.bioconjchem.5b00290
      48
      Dendrimer-Linked Antifreeze Proteins Have Superior Activity and Thermal Recovery
      Stevens, Corey A.; Drori, Ran; Zalis, Shiran; Braslavsky, Ido; Davies, Peter L.
      Bioconjugate Chemistry (2015), 26 (9), 1908-1915CODEN: BCCHES; ISSN:1043-1802. (American Chemical Society)
      By binding to ice, antifreeze proteins (AFPs) depress the f.p. of a soln. and inhibit ice recrystn. if freezing does occur. Previous work showed that the activity of an AFP was incrementally increased by fusing it to another protein. Even larger increases in activity were achieved by doubling the no. of ice-binding sites by dimerization. Here, the authors have combined the two strategies by linking multiple outward-facing AFPs to a dendrimer to significantly increase both the size of the mol. and the no. of ice-binding sites. Using a heterobifunctional crosslinker, the authors attached between 6 and 11 type III AFPs to a second-generation polyamidoamine (G2-PAMAM) dendrimer with 16 reactive termini. This heterogeneous sample of dendrimer-linked type III constructs showed a >4-fold increase in f.p. depression over that of monomeric type III AFP. This multimerized AFP was particularly effective at ice recrystn. inhibition activity, likely because it can simultaneously bind multiple ice surfaces. Addnl., attachment to the dendrimer has afforded the AFP superior recovery from heat denaturation. Linking AFPs together via polymers can generate novel reagents for controlling ice growth and recrystn.
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    49. 49
      Marcolli, C.; Gedamke, S.; Peter, T.; Zobrist, B. Efficiency of Immersion Mode Ice Nucleation on Surrogates of Mineral Dust. Atmos. Chem. Phys. 2007, 7, 5081– 5091,  DOI: 10.5194/acp-7-5081-2007
      49
      Efficiency of immersion mode ice nucleation on surrogates of mineral dust
      Marcolli, C.; Gedamke, S.; Peter, T.; Zobrist, B.
      Atmospheric Chemistry and Physics (2007), 7 (19), 5081-5091CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
      A differential scanning calorimeter (DSC) was used to explore heterogeneous ice nucleation of emulsified aq. suspensions of two Arizona test dust (ATD) samples with particle diams. of nominally 0-3 and 0-7 μm, resp. Aq. suspensions with ATD concns. of 0.01-20 wt% have been investigated. The DSC thermograms exhibit a homogeneous and a heterogeneous freezing peak whose intensity ratios vary with the ATD concn. in the aq. suspensions. Homogeneous freezing temps. are in good agreement with recent measurements by other techniques. Depending on ATD concn., heterogeneous ice nucleation occurred at temps. as high as 256 K or down to the onset of homogeneous ice nucleation (237 K). For ATD-induced ice formation Classical Nucleation Theory (CNT) offers a suitable framework to parameterize nucleation rates as a function of temp., exptl. detd. ATD size, and emulsion droplet vol. distributions. The latter two quantities serve to est. the total heterogeneous surface area present in a droplet, whereas the suitability of an individual heterogeneous site to trigger nucleation is described by the compatibility function (or contact angle) in CNT. The intensity ratio of homogeneous to heterogeneous freezing peaks is in good agreement with the assumption that the ATD particles are randomly distributed amongst the emulsion droplets. The obsd. dependence of the heterogeneous freezing temps. on ATD concns. cannot be described by assuming a const. contact angle for all ATD particles, but requires the ice nucleation efficiency of ATD particles to be (log)normally distributed amongst the particles. Best quant. agreement is reached when explicitly assuming that high-compatibility sites are rare and that therefore larger particles have on av. more and better active sites than smaller ones. This anal. suggests that a particle has to have a diam. of at least 0.1 μm to exhibit on av. one active site.
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    50. 50
      Whale, T. F.; Murray, B. J.; O’Sullivan, D.; Wilson, T. W.; Umo, N. S.; Baustian, K. J.; Atkinson, J. D.; Workneh, D. A.; Morris, G. J. A Technique for Quantifying Heterogeneous Ice Nucleation in Microlitre Supercooled Water Droplets. Atmos. Meas. Tech. 2015, 8, 2437– 2447,  DOI: 10.5194/amt-8-2437-2015
      50
      A technique for quantifying heterogeneous ice nucleation in microlitre supercooled water droplets
      Whale, T. F.; Murray, B. J.; O'Sullivan, D.; Wilson, T. W.; Umo, N. S.; Baustian, K. J.; Atkinson, J. D.; Workneh, D. A.; Morris, G. J.
      Atmospheric Measurement Techniques (2015), 8 (6), 2437-2447CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
      In many clouds, the formation of ice requires the presence of particles capable of nucleating ice. Ice-nucleating particles (INPs) are rare in comparison to cloud condensation nuclei. However, the fact that only a small fraction of aerosol particles can nucleate ice means that detection and quantification of INPs is challenging. This is particularly true at temps. above about -20 °C since the population of particles capable of serving as INPs decreases dramatically with increasing temp. In this paper, we describe an exptl. technique in which droplets of microlitre vol. contg. ice-nucleating material are cooled down at a controlled rate and their freezing temps. recorded. The advantage of using large droplet vols. is that the surface area per droplet is vastly larger than in expts. focused on single aerosol particles or cloud-sized droplets. This increases the probability of observing the effect of less common, but important, high-temp. INPs and therefore allows the quantification of their ice nucleation efficiency. The potential artifacts which could influence data from this expt., and other similar expts., are mitigated and discussed. Exptl. detd. heterogeneous ice nucleation efficiencies for K-feldspar (microcline), kaolinite, chlorite, NX-illite, Snomax and silver iodide are presented.
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    51. 51
      Polen, M.; Brubaker, T.; Somers, J.; Sullivan, R. C. Cleaning up Our Water: Reducing Interferences from Nonhomogeneous Freezing of “pure” Water in Droplet Freezing Assays of Ice-Nucleating Particles. Atmos. Meas. Tech. 2018, 11, 5315– 5334,  DOI: 10.5194/amt-11-5315-2018
      51
      Cleaning up our water: reducing interferences from nonhomogeneous freezing of "pure" water in droplet freezing assays of ice-nucleating particles
      Polen, Michael; Brubaker, Thomas; Somers, Joshua; Sullivan, Ryan C.
      Atmospheric Measurement Techniques (2018), 11 (9), 5315-5334CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
      Droplet freezing techniques (DFTs) have been used for half a century to measure the concn. of icenucleating particles (INPs) in the atm. and det. their freezing properties to understand the effects of INPs on mixed-phase clouds. The ice nucleation community has recently adopted droplet freezing assays as a commonplace exptl. approach. These droplet freezing expts. are often limited by contamination that causes nonhomogeneous freezing of the "pure" water used to generate the droplets in the heterogeneous freezing temp. regime that is being measured. Interference from the early freezing of water is often overlooked and not fully reported, or measurements are restricted to analyzing the more ice-active INPs that freeze well above the temp. of the background water. However, this avoidance is not viable for analyzing the freezing behavior of less active INPs in the atm. that still have potentially important effects on cold-cloud microphysics. In this work we review a no. of recent droplet freezing techniques that show great promise in reducing these interferences, and we report our own extensive series of measurements using similar methodologies. By characterizing the performance of different substrates on which the droplets are placed and of different pure water generation techniques, we recommend best practices to reduce these interferences. We tested different substrates, water sources, droplet matrixes, and droplet sizes to provide deeper insight into what methodologies are best suited for DFTs. Approaches for analyzing droplet freezing temp. spectra and accounting and correcting for the background "pure" water control spectrum are also presented. Finally, we propose exptl. and data anal. procedures for future homogeneous and heterogeneous ice nucleation studies to promote a more uniform and reliable methodol. that facilitates the ready intercomparison of ice-nucleating particles measured by DFTs.
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    52. 52
      Georgiou, P. G.; Marton, H. L.; Baker, A. N.; Congdon, T. R.; Whale, T. F.; Gibson, M. I. Polymer Self-Assembly Induced Enhancement of Ice Recrystallization Inhibition. J. Am. Chem. Soc. 2021, 143, 7449– 7461,  DOI: 10.1021/jacs.1c01963
      52
      Polymer Self-Assembly Induced Enhancement of Ice Recrystallization Inhibition
      Georgiou, Panagiotis G.; Marton, Huba L.; Baker, Alexander N.; Congdon, Thomas R.; Whale, Thomas F.; Gibson, Matthew I.
      Journal of the American Chemical Society (2021), 143 (19), 7449-7461CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Ice binding proteins modulate ice nucleation/growth and have huge (bio)technol. potential. There are few synthetic materials that reproduce their function, and rational design is challenging due to the outstanding questions about the mechanisms of ice binding, including whether ice binding is essential to reproduce all their macroscopic properties. Here we report that nanoparticles obtained by polymn.-induced self-assembly (PISA) inhibit ice recrystn. (IRI) despite their constituent polymers having no apparent activity. Poly(ethylene glycol), poly(dimethylacrylamide), and poly(vinylpyrrolidone) coronas were all IRI-active when assembled into nanoparticles. Different core-forming blocks were also screened, revealing the core chem. had no effect. These observations show ice binding domains are not essential for macroscopic IRI activity and suggest that the size, and crowding, of polymers may increase the IRI activity of "non-active" polymers. Poly(vinylpyrrolidone) particles had ice crystal shaping activity, indicating this polymer can engage ice crystal surfaces, even though on its own it does not show any appreciable ice recrystn. inhibition. Larger (vesicle) nanoparticles are shown to have higher ice recrystn. inhibition activity compared to smaller (sphere) particles, whereas ice nucleation activity was not found for any material. This shows that assembly into larger structures can increase IRI activity and that increasing the "size" of an IRI does not always lead to ice nucleation. This nanoparticle approach offers a platform toward ice-controlling soft materials and insight into how IRI activity scales with mol. size of additives.
      >> More from SciFinder ®
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    53. 53
      Bissoyi, A.; Reicher, N.; Chasnitsky, M.; Arad, S.; Koop, T.; Rudich, Y.; Braslavsky, I. Ice Nucleation Properties of Ice-Binding Proteins from Snow Fleas. Biomolecules 2019, 9, 532  DOI: 10.3390/biom9100532
      53
      Ice nucleation properties of ice-binding proteins from snow fleas
      Bissoyi, Akalabya; Reicher, Naama; Chasnitsky, Michael; Arad, Sivan; Koop, Thomas; Rudich, Yinon; Braslavsky, Ido
      Biomolecules (2019), 9 (10), 532CODEN: BIOMHC; ISSN:2218-273X. (MDPI AG)
      Ice-binding proteins (IBPs) are found in many organisms, such as fish and hexapods, plants, and bacteria that need to cope with low temps. Ice nucleation and thermal hysteresis are two attributes of IBPs. While ice nucleation is promoted by large proteins, known as ice nucleating proteins, the smaller IBPs, referred to as antifreeze proteins (AFPs), inhibit the growth of ice crystals by up to several degrees below the m.p., resulting in a thermal hysteresis (TH) gap between melting and ice growth. Recently, we showed that the nucleation capacity of two types of IBPs corresponds to their size, in agreement with classical nucleation theory. Here, we expand this finding to addnl. IBPs that we isolated from snow fleas (the arthropod Collembola), collected in northern Israel. Chem. analyses using CD and Fourier-transform IR spectroscopy data suggest that these IBPs have a similar structure to a previously reported snow flea antifreeze protein. Further expts. reveal that the ice-shell purified proteins have hyperactive antifreeze properties, as detd. by nanoliter osmometry, and also exhibit low ice-nucleation activity in accordance with their size.
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    54. 54
      Lupi, L.; Hudait, A.; Molinero, V. Heterogeneous Nucleation of Ice on Carbon Surfaces. J. Am. Chem. Soc. 2014, 136, 3156– 3164,  DOI: 10.1021/ja411507a
      54
      Heterogeneous Nucleation of Ice on Carbon Surfaces
      Lupi, Laura; Hudait, Arpa; Molinero, Valeria
      Journal of the American Chemical Society (2014), 136 (8), 3156-3164CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Atm. aerosols can promote the heterogeneous nucleation of ice, impacting the radiative properties of clouds and Earth's climate. The exptl. study of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temps. It is not known which structural and chem. characteristics of soot account for the variability in ice nucleation efficiency. Here the authors use mol. dynamics simulations to study the nucleation of ice from liq. water in contact with graphitic surfaces. Atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. Graphitic surfaces and other surfaces that promote ice nucleation induce layering in the interfacial water, suggesting that the order imposed by the surface on liq. water may play an important role in the heterogeneous nucleation mechanism. The authors study a large set of graphitic surfaces of various dimensions and radii of curvature and find that variations in nanostructures alone could account for the spread in the freezing temps. of ice on soot in expts. A characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslygsL8%253D&md5=a6efa985c5e7275212f2b8a982ffa9c7

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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.biomac.2c01097.

    • Materials and additional synthetic methods; experimental procedures; synthetic procedures; supplementary NMR, SEC, FTIR, DLS, TEM, and AFM data; and additional ice shaping/nucleation data (PDF)


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