A furan-based hexaazamacrocycle encapsulates a sulfate anion in its cavity showing strong affinity and selectivity for sulfate in water.
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A rigid dinuclear copper(II) complex L based on furan spacers has been synthesized and studied for its binding interactions with halides by colorimetric studies, UV-Vis titrations, and density functional theory (DFT) calculations. Our... more
A rigid dinuclear copper(II) complex L based on furan spacers has been synthesized and studied for its binding interactions with halides by colorimetric studies, UV-Vis titrations, and density functional theory (DFT) calculations. Our results from the titration studies demonstrate that L binds each of the halides in the order of fluoride > chloride > bromide > iodide, correlating directly with the charge density of the respective halide. Fully unconstrained DFT geometry optimizations have been carried out on both the isolated L as well as the anion-bound motifs. Binding energies (DE) were calculated for each of the optimized geometries, yielding an attractive DE of -92.39, -27.14, -23.16, and -13.37 kcal/mol for fluoride, chloride, bromide, and iodide, respectively, which is in accord with our experimental results. The compound has been further investigated for its biocompatibility on HeLa cells, demonstrating an excellent cell viability up to 500 µM concentration.
A thiourea-based tripodal receptor substituted with 3-nitrophenyl groups has been synthesized, and the binding affinity for a variety of anions has been studied by H NMR titrations and nuclear Overhauser enhancement spectroscopy... more
A thiourea-based tripodal receptor substituted with 3-nitrophenyl groups has been synthesized, and the binding affinity for a variety of anions has been studied by H NMR titrations and nuclear Overhauser enhancement spectroscopy experiments in dimethyl sulfoxide-. As investigated by H NMR titrations, the receptor binds an anion in a 1:1 binding mode, showing the highest binding and strong selectivity for sulfate anion. A competitive colorimetric assay in the presence of fluoride suggests that the sulfate is capable of displacing the bound fluoride, showing a sharp visible color change. The strong affinity of for sulfate was further supported by UV-vis titrations and density functional theory (DFT) calculations. Time-dependent DFT calculations indicate that the fluoride complex possesses a different optical absorption spectrum (due to charge transfer between the fluoride and the surrounding ligand) than the sulfate complex, reflecting the observed colorimetric change in these two com...
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Bacterial NO reductase (bacNOR) enzymes utilize a heme/non-heme active site to couple two NO molecules to NO. We show that BF coordination to the nitrosyl O-atom in (OEP)Fe(NO) activates it toward N-N bond formation with NO to generate... more
Bacterial NO reductase (bacNOR) enzymes utilize a heme/non-heme active site to couple two NO molecules to NO. We show that BF coordination to the nitrosyl O-atom in (OEP)Fe(NO) activates it toward N-N bond formation with NO to generate NO. N-isotopic labeling reveals a reversible nitrosyl exchange reaction and follow-up N-O bond cleavage in the NO formation step. Other Lewis acids (B(CF) and K) also promote the NO coupling reaction with (OEP)Fe(NO). These results, complemented by DFT calculations, provide experimental support for the cis: b pathway in bacNOR.
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Understanding the intermolecular interactions between nucleotides and artificial receptors is crucial to understanding the role of nucleic acids in living systems. However, direct structural evidence showing precise interactions and... more
Understanding the intermolecular interactions between nucleotides and artificial receptors is crucial to understanding the role of nucleic acids in living systems. However, direct structural evidence showing precise interactions and bonding features of a nucleoside monophosphate (NMP) with a macrocycle-based synthetic molecule has not been provided so far. Herein, we present two novel crystal structures of uridine monophosphate (UMP) and thymidine monophosphate (TMP) complexes with a macrocycle-based dinuclear receptor. Structural characterization of these complexes reveals that the receptor recognizes UMP through coordinate-covalent interactions with phosphates and π-π stackings with nucleobases and TMP through coordinate-covalent interactions with phosphate groups. Furthermore, the receptor has been shown to effectively bind nucleoside monophosphates in the order of GMP > AMP > UMP > TMP > CMP in water at physiological pH, as investigated by an indicator displacement a...
The selective detection of citrate anions is essential for various biological functions in living systems. A quantitative assessment of citrate is required for the diagnosis of various diseases in the human body; however, it is extremely... more
The selective detection of citrate anions is essential for various biological functions in living systems. A quantitative assessment of citrate is required for the diagnosis of various diseases in the human body; however, it is extremely challenging to develop efficient fluorescence and color-detecting molecular probes for sensing citrate in water. Herein, we report a macrocycle-based dinuclear foldamer (1) assembled with eosin Y (EY) that has been studied for anion binding by fluorescence and colorimetric techniques in water at neutral pH. Results from the fluorescence titrations reveal that the 1·EY ensemble strongly binds citrate anions, showing remarkable selectivity over a wide range of inorganic and carboxylate anions. The addition of citrate anions to the 1·EY adduct led to a large fluorescence enhancement, displaying a detectable color change under both visible and UV light in water up to 2 μmol. The biocompatibility of 1·EY as an intracellular carrier in a biological system...
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Fully chlorinated carborate and dodecaborate cages such as [CHB11Cl11](-) and [Me3NB12Cl11](-) are prominent examples of valuable and chemically rather inert weakly coordinating anions. While both anions can be obtained by chlorination of... more
Fully chlorinated carborate and dodecaborate cages such as [CHB11Cl11](-) and [Me3NB12Cl11](-) are prominent examples of valuable and chemically rather inert weakly coordinating anions. While both anions can be obtained by chlorination of the precursors [CH12B11](-) and [H3NB12H11](-) with SO2Cl2 followed by methylation for the synthesis of [Me3NB12Cl11](-), best results were found using photochemical chlorination with SO2Cl2 for [CH12B11](-) and thermal chlorination with SO2Cl2 for [H3NB12H11](-). The hexachlorinated anion [n-Pr3NB12H5Cl6](-) was formed readily within 30 min by chlorination of [n-Pr3NB12H11](-), but attempts to synthesize isopropyl-substituted ammonio-dodecaborates with a higher chlorination number resulted in the formation of mixtures and partial decomposition. The silver and trityl salts of the anions [CHB11Cl11](-), [Me3NB12Cl11](-), and [n-Pr3NB12H5Cl6](-) as well as the contact ion-pair [Et2Al][Me3NB12Cl11] were also prepared, and the compounds [Ag(NCMe)][Me3N...
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A series of N-alkyl-3-thia-7-azabicyclo[3.3.1]nonan-9-ones and derivatives have been prepared from the reaction of an appropriate 4-thianone, an aldehyde and an amine in a Mannich type condensation. Reduction of the ketones via... more
A series of N-alkyl-3-thia-7-azabicyclo[3.3.1]nonan-9-ones and derivatives have been prepared from the reaction of an appropriate 4-thianone, an aldehyde and an amine in a Mannich type condensation. Reduction of the ketones via Wolff-Kishner conditions produced bicyclic systems with the methylene bridging group. Addition of Grignard reagents to the ketones did yield the expected alcohols. Conformational analysis of the systems was performed via diagnosis of the H and C NMR spectra. A single crystal X-ray diffraction analysis of 2,2,4,4-tetramethyl-6,8-diphenyl-3-thia-7-azabicyclo[3.3.1]nonan-9-one was accomplished and revealed a boat conformer for the nitrogen-containing ring and a chair conformer for the sulfur-containing ring. The ketone crystallized in the triclinic space group P1 (Z=2) with a=6.216 (3), b=10.507 (5), c=15.335 (6) Å, α=86.64 (4), β=86.66 (4), and γ=98.51 (5)° [Vol=986.55 Å].
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The structures of the [mu][sub 3]-ethylidyne tricobalt clusters Cp*[sub 3]Co[sub 3]([mu][sub 3]-CCH[sub 3])[sub 2] (2) and Cp*[sub 3]Co[sub 3]([mu][sub 3]-CCH[sub 3])-([mu][sub 3]-H) (3) were determined by X-ray crystallography. The... more
The structures of the [mu][sub 3]-ethylidyne tricobalt clusters Cp*[sub 3]Co[sub 3]([mu][sub 3]-CCH[sub 3])[sub 2] (2) and Cp*[sub 3]Co[sub 3]([mu][sub 3]-CCH[sub 3])-([mu][sub 3]-H) (3) were determined by X-ray crystallography. The 48-electron cluster 2 consists of an equilateral triangle of cobalt atoms (Co-Co = 2.437(1) [angstrom]) symmetrically capped on each face by a [mu][sub 3]-CCH[sub 3] ligand. Cluster 3 was necessarily disordered
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Heme-hyponitrites are intermediates that form at the bimetallic active sites of bacterial nitric oxide reductases. To probe a possible effect of the Fe-Fe distance on hyponitrite stability, we prepared a bridged bis-porphyrin... more
Heme-hyponitrites are intermediates that form at the bimetallic active sites of bacterial nitric oxide reductases. To probe a possible effect of the Fe-Fe distance on hyponitrite stability, we prepared a bridged bis-porphyrin Fe-hyponitrite compound, namely [(OEP-CH2)Fe]2(μ2,η(1),η(1)-ONNO). Its υNO of 992 cm(-1) (υ15NO of 976 cm(-1)) is close to the υNO of 983 cm(-1) reported previously by us for the crystallographically characterized [(OEP)Fe]2(μ2,η(1),η(1)-ONNO) compound. The bridged bis-porphyrin Fe-hyponitrite complex is unstable with respect to N2O production, supporting the role of the bis-Fe porphyrin system in hyponitrite conversion to N2O. The preparation and crystallographic determination of the bridging sulfato derivative is also reported.
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In the title complex, [Ni(C21H17F2N3)2]2Br4·9H2O, there are two independent metal complexes per asymmetric unit and two ligands per metal complex. The structural features (bond lengths and angles) of the two complexes are almost... more
In the title complex, [Ni(C21H17F2N3)2]2Br4·9H2O, there are two independent metal complexes per asymmetric unit and two ligands per metal complex. The structural features (bond lengths and angles) of the two complexes are almost identical. In each complex, the nickel(II) ion is coordinated in an octahedral environment by six N atoms from two chelating (9E)-N-({6-[(E)-(4-fluorobenzylimino)methyl]pyridin-2-yl}methylene)(4-fluorophenyl)methanammine ligands. The Ni—N bond lengths range from 1.973 (2) to 2.169 (2) Å, while the chelate N—Ni—N angles range from 77.01 (10) to 105.89 (9)°. Additionally, there are four bromide anions and nine solvent water molecules within the asymmetric unit. The water molecules form a hydrogen-bonded network, displaying C—H...O, C—H...Br, O—H...Br, O—H...O and O—H...F interactions into layers parallel to (111). In each unit, the fluorophenyl rings of one ligand are stacked with the central ring of the other ligandviaπ–π interactions, with the closest centro...
Heme-HNO species are crucial intermediates in several biological processes. To date, no well-defined Fe heme-HNO model compounds have been reported. Hydride attack on the cationic ferric [(OEP)Fe(NO)(5-MeIm)]OTf (OEP =... more
Heme-HNO species are crucial intermediates in several biological processes. To date, no well-defined Fe heme-HNO model compounds have been reported. Hydride attack on the cationic ferric [(OEP)Fe(NO)(5-MeIm)]OTf (OEP = octaethylporphyrinato dianion) generates an Fe-HNO product that has been characterized by IR and (1)H NMR spectroscopy. Results of DFT calculations reveal a direct attack of the hydride on the N atom of the coordinated ferric nitrosyl.
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Synthetic protocols and circular dichroism (CD) spectra are reported for a series of oligomers of (R,R)-trans-2-aminocyclopentanecarboxylic acid (trans-ACPC). The two longest oligomers, a hexamer and an octamer, have also been examined... more
Synthetic protocols and circular dichroism (CD) spectra are reported for a series of oligomers of (R,R)-trans-2-aminocyclopentanecarboxylic acid (trans-ACPC). The two longest oligomers, a hexamer and an octamer, have also been examined crystallographically. Both crystal structures show that the ‚-peptide backbone adopts a regular helix that is defined by a series of interwoven 12-membered ring hydrogen bonds ("12-helix"). Each hydrogen bond
The arene-solvated indium(I) species [In(C7H8)3][CHB11Cl11] (1) and [In(C6H5Br)1.5][CHB11Cl11] (2) were obtained by a redox reaction involving the silver salt Ag[CHB11Cl11] and indium powder at 80 °C in a toluene or bromobenzene solution.... more
The arene-solvated indium(I) species [In(C7H8)3][CHB11Cl11] (1) and [In(C6H5Br)1.5][CHB11Cl11] (2) were obtained by a redox reaction involving the silver salt Ag[CHB11Cl11] and indium powder at 80 °C in a toluene or bromobenzene solution. These thermally stable compounds react with triphenylphosphine and the N-heterocyclic carbene 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene under reduction of indium(I) to indium metal and oxidation of the ligands to phosphonium and imidazolium cations contrary to the more commonly observed disproportionation reactions. The presence of 2 equiv of carbene led to deprotonation of the anion to give the dianion [CB11Cl11](2-). Interactions of In(+) with soft donor ligands such as phosphines, olefins, alkynes, and aromatics are weak, and a crystalline solid was only obtained with the nonvolatile phosphinoacetylene Mes2PC≡CPh (Mes = 2,4,6-Me3C6H2). The structure of this compound displays In···C interactions involving the triple bond and the π system of one mesityl group but no In···P contact. Solutions of 2 in fluorobenzene also showed moderate activity as the catalyst for intramolecular hydroamination of primary and secondary aminopentenes. The new compounds were characterized by multinuclear NMR spectroscopy and X-ray diffraction for compounds 1, 2, and 4-6.
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The title compound, C20H10F12N4O4S2, is an organic diaryl di-sulfide compound with tri-fluoro-acetamide substituents at the ortho-positions of each benzene ring. There are two mol-ecules (labeled A and B) in the asymmetric unit. The F... more
The title compound, C20H10F12N4O4S2, is an organic diaryl di-sulfide compound with tri-fluoro-acetamide substituents at the ortho-positions of each benzene ring. There are two mol-ecules (labeled A and B) in the asymmetric unit. The F atoms of three of the -CF3 groups exhibit rotational disorder over two positions each. The S-S bond distances are 2.0914 (7) and 2.0827 (6) Å for mol-ecules A and B, respectively. The dihedral angle between the S-S-C and S-C-C planes is 103.05 (15)° for mol-ecule A and 104.09 (15)° for mol-ecule B. The three-dimensional supra-molecular architecture of the crystal is sustained by numerous N-H⋯O, N-H⋯S and C-H⋯O inter-actions.
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The title compound, [Fe(C64H64N8O4)Cl], is a five-coordinate square-pyramidal porphyrin complex with a chloride ion in the axial position, being coordinated from the protected side of the porphyrin; the Fe(III) atom is displaced by... more
The title compound, [Fe(C64H64N8O4)Cl], is a five-coordinate square-pyramidal porphyrin complex with a chloride ion in the axial position, being coordinated from the protected side of the porphyrin; the Fe(III) atom is displaced by 0.474 (5) Å from the 24-atom mean plane of the porphyrin core towards the chloride. The porphyrin moiety is a 'picket-fence' 5,10,15,20-tetra-kis-[2-(2,2-di-methyl-propanamido)-phen-yl]porph-yrinate (por) group. The Fe-Cl bond length is 2.221 (2) Å and the Fe-N(por) bond lengths are in the range 2.043 (5)-2.063 (5) Å. The supra-molecular architecture of the crystal is sustained by C-H⋯O inter-actions between the pyrrolic and phenyl H atoms of one mol-ecule and the carbonyl O atoms of the 2,2-di-methyl-propanamido groups of adjacent mol-ecules. The methyl groups of three of the four tert-butyl substituents exhibited rotational disorder over two positions. The investigated crystal was twinned by a twofold rotation about the (001) axis with a refined...
The title compound, [Fe(C44H28N4)(C4H6N2)2]·2C4H6N2, is a six-coordinate Fe(II)-porphyrinate complex with the metal located on a center of inversion and coordinated by two axial 1-methyl-imidazole ligands; the complex crystallizes as a... more
The title compound, [Fe(C44H28N4)(C4H6N2)2]·2C4H6N2, is a six-coordinate Fe(II)-porphyrinate complex with the metal located on a center of inversion and coordinated by two axial 1-methyl-imidazole ligands; the complex crystallizes as a 1-methyl-imidazole disolvate. The 1-methyl-imidazole group bonded to the Fe(II) atom [occupancy ratio 0.789 (4):0.211 (4)] and the unbound 1-methyl-imidazole mol-ecule [0.519 (4):0.481 (4)] were disordered. The average Fe-N(porphyrinate) bond length is 1.998 (3) Å and the axial Fe-N(imidazole) bond length is 1.9970 (12) Å. In the crystal, mol-ecules are linked into a three-mol-ecule aggregate by two weak C-H⋯N inter-actions.
A large number of iron-chelating compounds (siderophores) were isolated from supernatants of iron-deficient cultures of a mold isolate, subsequently identified as Aspergillus ochraceous . Siderophores in their iron chelate form were... more
A large number of iron-chelating compounds (siderophores) were isolated from supernatants of iron-deficient cultures of a mold isolate, subsequently identified as Aspergillus ochraceous . Siderophores in their iron chelate form were purified to homogeneity by using Bio-Gel P2, silica gel, and C-18 bonded silica gel (reverse-phase) columns. Most of these compounds, as identified by 1H and 13C nuclear magnetic resonance spectroscopy and X-ray crystallography, belong to the ferrichrome family. The organism produces ferrirubin and ferrichrysin as the predominant and the second major compound (62 and 15% of the total siderophores), respectively. Ferrichrysin appears as the first siderophore in the medium on day 2 of growth. Several of the other siderophores are novel and ranged in quantities from 0.2 to 5% of the total. The trivial names asperchrome A, B1, B2, C, D1, D2, and D3 are proposed for these novel compounds, which are all members of the ferrichrome family, and all but the first ...
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ABSTRACT Two homoleptic Ni(silylene)3 complexes, 1a and 2a, have been synthesized and characterized by X-ray crystallography. Due to steric constraints only three silylenes coordinate to the nickel, generating novel complexes that are... more
ABSTRACT Two homoleptic Ni(silylene)3 complexes, 1a and 2a, have been synthesized and characterized by X-ray crystallography. Due to steric constraints only three silylenes coordinate to the nickel, generating novel complexes that are trigonal planar at the nickel center.
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4(S)-Hydroxyproline (Hyp) residues constitute about 10% of most forms of collagen, the most abundant protein in vertebrates. X-Ray diffraction analysis was used to ascertain how the structure of proline residues is affected by the... more
4(S)-Hydroxyproline (Hyp) residues constitute about 10% of most forms of collagen, the most abundant protein in vertebrates. X-Ray diffraction analysis was used to ascertain how the structure of proline residues is affected by the inductive effect elicited by the hydroxyl group of Hyp residues. N-Acetylproline methylester (1), N-acetyl-4(S)-hydroxyproline methylester (2) and N-acetyl-4(S)- fluoroproline methylester (3) were synthesized, and their crystalline structures were determined at high resolution. The amide bond of crystalline 1 was in the cis conformation, which is the minor isomer in solution, and the pyrrolidine ring of 1 had C gamma-endo pucker. In crystalline 2 and 3 the amide bonds were in the trans conformation, and the pyrrolidine rings had C-exo pucker. The lengths of the bonds between sp3-hybridized carbon atoms in the pyrrolidine ring were significantly shorter in 2 and 3 than in 1, as was predicted by ab initio molecular orbital calculations at the RHF/3-21G level of theory. No significant change in bond length was observed in the other bonds of 1,2 or 3. The pyramidylization of the nitrogen atom increased dramatically in the order: 1 < 2 < 3. Together, these results indicate that electron-withdrawing substituents in the 4-position of proline residues can have a significant influence on the structure of these residues. In particular, the change in pyramidylization suggests that such substituents increase the sp3-character of the prolyl nitrogen atom and could thereby alter the rate of prolyl peptide bond isomerization.
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ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select... more
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ABSTRACT
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The title compound, [Zn2(C21H25N2)2(OH)2], is a binuclear zinc complex formed by two bidentate β-diketiminate (nacnac) ligands and two μ-hydroxide O atoms, bridging two mononuclear units into a centrosymmetric dimeric unit. Each Zn(2+)... more
The title compound, [Zn2(C21H25N2)2(OH)2], is a binuclear zinc complex formed by two bidentate β-diketiminate (nacnac) ligands and two μ-hydroxide O atoms, bridging two mononuclear units into a centrosymmetric dimeric unit. Each Zn(2+) cation is coordinated by two N-donor atoms from the nacnac ligand and two O-donor atoms of hydroxide anions to give a distorted tetra-hedral coordination environment. The Zn-O bond lengths are 1.9643 (13) and 2.0022 (14) Å, and the two Zn-N bond lengths are 1.9696 (14) and 1.9823 (14) Å. The distance between the two Zn(2+) cations in the dimer is 2.9420 (4) Å. Although hydroxide groups are present in the complex, no classical hydrogen-bonding inter-ations are observed because of the bulky β-diketiminate ligands.
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The NH(2)(+) stretching modes of secondary amine salts have been previously studied, but the band assignments are inconsistent between the various studies. This paper assigns characteristic NH(2)(+) group frequencies between approximately... more
The NH(2)(+) stretching modes of secondary amine salts have been previously studied, but the band assignments are inconsistent between the various studies. This paper assigns characteristic NH(2)(+) group frequencies between approximately 2500 and 2400 cm(-1). Crystal structures of four diamine salts are reported here. Vibrational frequencies were calculated with the B3LYP hybrid Hartree-Fock/density functional method and the 6-31G(d) split-valence plus polarization basis set, and the results are in agreement with the experimental frequencies. Deuterium dilution experiments result in a group of sharply featured bands between the NH(2)(+) and the ND(2)(+) stretching bands. These bands, located between 2200 and 2100 cm(-1), are attributed to modes that contain contributions from coupled N-H and N-D stretching motions.
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ABSTRACT
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Page 1. 546 Art ic 1 es Organometallics 1991, 10, 546-551 Disilaselenirane and Disilatellurirane: Synthesis and Crystal Structures Robin Peng-Koon Tan, Gregory R; Gillette, Douglas R. Powell, and Robert West' Depafiment ...
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Synthetic nitrosyl porphyrins with meso-aryl substituents are potential models for the biologically-important NO-bound P460 heme cofactor. A five-coordinate iron nitrosyl tetraaryl-porphyrin (HTPPX-CO2H)Fe(NO) containing a xanthene-based... more
Synthetic nitrosyl porphyrins with meso-aryl substituents are potential models for the biologically-important NO-bound P460 heme cofactor. A five-coordinate iron nitrosyl tetraaryl-porphyrin (HTPPX-CO2H)Fe(NO) containing a xanthene-based meso substituent has been prepared. The crystal structure of this formally {FeNO}7 complex reveals an ordered axial and bent NO ligand (∠FeNO=142.5(6)Å) displaying an off-axis tilt of the nitrosyl N atom from the heme normal by 9.2°. Surprisingly, the porphyrin core does not display the expected asymmetry in FeN(por) distances frequently observed in iron nitrosyl porphyrins. The redox behavior as determined by cyclic voltammetry reveals, in contrast to most (por)Fe(NO) compounds, a fast NO dissociation after electrooxidation in CH2Cl2 to result in a net chemically-irreversible oxidation at Epa=+0.77V vs Ag/AgCl. IR spectroelectrochemistry reveals a recombination, on the spectroelectrochemistry time-scale, of the dissociated NO on oxidation with electrogenerated [(HTPPX-CO2H)Fe]+.