THEORETICAL AND COMPUTATIONAL CHEMISTRY

In this paper the two-photon absorption by a molecule is studied when photons are prepared in a high-dimension entangled state. The light field is prepared in a spatial two-photon qudit state and its interaction with a molecule shows new interference effects observed in the calculated absorption cross-section. Oscillations in the absorption cross-section demonstrate its dependence on the path phases of the two-qudit state. The two-photon absorption cross-section is dependent on the dimension of the two-qudit photonic state.

Calculations were done by applying the B3LYP/6-31++G(d) method on the zwitterionic L-diglycine and L-dialanine to study the solvent effects on their structures and vibrational features. Three models of solvation (implicit, explicit, and explicit in implicit) were used and the subsequent resulting values compared. Even though both dipeptides surrounded by 12 water molecules seem sufficient to stabilize their zwitterionic characters, notably to avoid the proton transfer between the backbone (N t H[Formula: see text], COO (-)) groups, the hybrid model of solvation (explicit in implicit noted 12W/Continuum) appears to be in better agreement with available IR and Raman experiments than explicit and implicit models. The harmonic vibrational modes derived from geometry optimization of L-diglycine and L-dialanine in 12W/Continuum, agree with the available IR and Raman experimental values within 1 % for L-diglycine and 2 % for L-dialanine, and they appear more accurate than those found using the explicit model (12W). Graphical Abstract DFT/6-31++G∗ Optimized structures of L-diglycine (top) and L-dialanine (bottom) surrounded by 12 water molecules all embedded in a continuum.

Salicylate synthase from Mycobacterium tuberculosis, MbtI, initiates the biosynthesis of siderophores by converting chorismate to salicylate. Nevertheless, three more distinct activities for wild-type MbtI have been detected in vitro: isochorismate synthase, isochorismate pyruvate lyase, and chorismate mutase. In this work, hybrid Quantum Mechanics/Molecular Mechanics methods have been used to get the first simulation of the chorismate mutase activity of MbtI.

Transition metal compounds are traditionally considered to be challenging for standard quantum chemistry approximations like coupled cluster (CC) theory, which are usually employed to validate lower level methods like density functional theory (DFT). To explore this issue, we present a database of bond dissociation energies (BDEs) for 74 spin states of 69 diatomic species containing a 3d transition metal atom and a main group element, in the moderately sized def2-SVP basis. The presented BDEs appear to have an (estimated) 3σ error less than 1 kJ/mol relative to the exact solutions to the non-relativistic Born-Oppenheimer Hamiltonian. These benchmark values were used to assess the performance of a wide range of standard CC models, as the results should be beneficial for understanding the limitations of CC models for transition metal systems. We find that interactions between metals and monovalent ligands like hydride and fluoride are well described by CCSDT. Similarly, CCSDTQ appears...

Classical bonding is predominantly understood using the insipid spn hybridization for σ-bonds as well as π bonds and their delocalized variants. Because hybridization ignores intricate differences in the energy and size of valence atomic orbitals, its naïve application to classically bonded boron atoms leads to numerous surprises in bond strengths, frontier MOs/bands, and even geometry. Here we show that the sp dissonance caused by size mismatch between the valence s and p orbitals of boron plays a crucial role in its bonding, subtly distinct from that of carbon and silicon. Unlike the heavier p block elements, boron prefers to actively engage its compact 2s orbitals in bonding. This leads to the overreach of p–p σ-type overlap that reduces its magnitude in the entire B─B bonding range. Consequently, the π-type overlap remains substantial, making its electronic structure visibly distinct in saturated and unsaturated regimes. The deltahedral frameworks offer a compromise by breaking this symmetry-enforced dichotomy of classical σ- and π-type bonding and following alternate electron counts that suit the electron deficiency of the boron. The pathological anatomy of classical B─B σ-bonding also explains the origins of puzzling metallic character and disorder in their classical boride networks even with ideal electron count, unlike deltahedral borides. The implications of sp dissonance are illustrated in classical boron networks of various hybridizations, explaining the unusual preference for unique sp3 lattice with strained four-membered rings in CrB4, origins of observed σ holes in MgB2 that lead to its superconducting nature, and the absence of Peierls distortion in LiB.

Two-photon photoluminescence (TPPL) emission spectra of DNA-gold nanoparticle (AuNP) monoconjugates and the corresponding DNA-linked AuNP dimers are obtained by photon time-of-flight spectroscopy. This technique is combined with two-photon photoluminescence fluctuation correlation spectroscopy (TPPL-FCS) to simultaneously monitor the optical and hydrodynamic behaviour of these nano-assemblies in solution, with single-particle sensitivity and microsecond temporal resolution. In this study, the AuNPs have an average core diameter of 12 nm, which renders their dark-field plasmonic light scattering too weak for single-particle imaging. Moreover, as a result of the lack of plasmonic coupling in the dimers, the optical extinction, scattering and photoluminescence spectra of the DNA-AuNP complexes are not sufficiently different to distinguish between monomers and dimers. The use of TPPL-FCS successfully addresses these bottlenecks and enables the distinction between AuNP monomers and AuNP ...