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Deuterium isotope effects on interaction energies and geometrical parameters in several H3O+(D3O+)...ene and H3O+(D3O+)...yne complexes, which involve O‐H(D)...π interactions, have been analyzed using the MP2 level of the multi‐component molecular orbital method (MC_MP2), which can incorporate the nuclear quantum effects of light nuclei, such as protons and deuterons. The MC_MP2 calculations revealed that D3O+ replacement reduced the interaction energies of the complexes and induced changes in geometrical parameters. In addition, natural energy decomposition analysis (NEDA) revealed a strong correlation between the H/D isotope effects on the H/D...π distances and on each energy component. [ABSTRACT FROM AUTHOR]

By introducing main–group elements such as boron and bismuth to π‐conjugated systems, it is possible to modify the optical properties of π‐conjugated materials through orbital interactions between the orbital on the elements and π/π*‐orbitals, and the heavy atom effect. Moreover, bismuth, which is the heaviest stable element, induces a significant heavy atom effect, making organobismuth compounds promising for applications as phosphorescent materials. In this study, we synthesized new room–temperature phosphorescent materials by incorporating bismuth into thiophene units. The phosphorescence properties of these materials, such as emission lifetime and wavelength, could be further controlled by combining tricoordinate boron with the thienylbismuth structures. The synthesized bismuth‐ and boron–containing thiophene compounds exhibited phosphorescence at room temperature in both solution and solid states. Furthermore, the introduction of boron raised the energy of the triplet state in the π‐conjugated system, resulting in a blue shift of the phosphorescence wavelength. The analysis of photoluminescence properties and TD‐DFT calculations revealed that the introduction of bismuth enhances phosphorescence properties, whereas the introduction of boron further promotes intersystem crossing. [ABSTRACT FROM AUTHOR]

P450nor is a heme-containing enzyme that catalyzes the conversion of nitric oxide (NO) to nitrous oxide (N2O). Its catalytic mechanism has attracted attention in chemistry, biology, and environmental engineering. The catalytic cycle of P450nor is proposed to consist of three major steps. The reaction mechanism for the last step, N2O generation, remains unknown. In this study, the reaction pathway of the N2O generation from the intermediate I was explored with the B3LYP calculations using an active center model after the examination of the validity of the model. In the validation, we compared the heme distortions between P450nor and other oxidoreductases, suggesting a small effect of protein environment on the N2O generation reaction in P450nor. We then evaluated the electrostatic environment effect of P450nor on the hydride affinity to the active site with quantum mechanics/molecular mechanics (QM/MM) calculations, confirming that the affinity was unchanged with or without the protein environment. The active center model for P450nor showed that the N2O generation process in the enzymatic reaction undergoes a reasonable barrier height without protein environment. Consequently, our findings strongly suggest that the N2O generation reaction from the intermediate I depends sorely on the intrinsic reactivity of the heme cofactor bound on cysteine residue. [ABSTRACT FROM AUTHOR]

To understand the mechanism of the H–D exchange reaction for synthesizing various deuterium-labeled molecules on heterogeneous metal catalysts as a first step, we analyzed the effects of H/D isotopes on the adsorption of H2O/D2O and their dissociated OH/OD and H/D species on the Pt(111) surface. We applied the combined plane-wave and localized basis set method developed by us to directly treat the electronic structures of the surface and the localized adsorbed region and the nuclear quantum effect of H and D. The results showed that the adsorption energies for the D-compounds on the Pt surface were larger than those for the H-compounds. This is in keeping with the experimental observations. The difference in the distance between the adsorbates and the Pt surface induced by the H/D isotope effect depends on the bonding characteristics. While the distance between D2O and the Pt surface was longer than that in the H2O case, the distance between the D atom and the Pt surface was shorter than that for the H atom. This is the first report on the geometrical differences between H and D based on a systematic analysis of water and its dissociated species. [ABSTRACT FROM AUTHOR]

κ-H3(Cat-EDT-TTF)2 (H-TTF) is a hydrogen-bonded π-electron system which was found to reveal C2/c symmetry at 50–293 K, while its isotopologue, κ-D3(Cat-EDT-TTF)2 (D-TTF), showed the phase transition at 185 K from C2/c to P1̅. To elucidate the origin of such a difference, we calculated the potential energy curves (PECs) for the hydrogen transfer along the H-bonds in these conductors. We found that both the π-stacking and the hydrogen nuclear quantum effect drastically affected the hydrogen transfer energy. By taking account of both effects, we obtained a symmetric single-well effective PEC for H-TTF, which indicated that the hydrogen was always located at the center of the H-bond. By contrast, the effective PEC of D-TTF was a low-barrier double-well, indicating that the position of the H-bonded deuterium would change according to the temperature. We concluded that the π-stacking and the nuclear quantum effect were the key factors for the appearance of phase transition only in D-TTF. [ABSTRACT FROM AUTHOR]

Multicomponent quantum mechanical(MC_QM) calculations with polarizablecontinuum model (PCM) have been tested against liquid 1H NMR chemical shifts for a test set of 80 molecules. Improvementfrom conventional quantum mechanical calculations was achieved forMC_QM calculations. The advantage of the multicomponent scheme couldbe attributed to the geometrical change from the equilibrium geometryby the incorporation of the hydrogen nuclear quantum effect, whilethat of PCM can be attributed to the change of the electronic structureaccording to the polarization by solvent effects. [ABSTRACT FROM AUTHOR]