International Journal of Quantum Chemistry最新文献

The problem of whether and how the captodative aromatic systems with the donor and acceptor substituents at the same carbon atom of the C=C bond can be more stable than the π-conjugated push-pull counterparts with the two substituents in the vicinal position is analyzed for cyclopentadienyl derivatives possessing an aromatic cyclopentadienyl ring. The analysis of electronic, magnetic, and structural criteria of aromaticity showed that among typical organic donors, such as amines NR₃, ethers R₂O, guanidine (NH₂)₂C=NH, siloxane O(SiH₃)₂, silatrane, the captodative isomers [cyclopentadienylium]⁻C(X⁺) = CH₂ can be more stable than their push-pull isomeric counterparts [cyclopentadienylium]⁻—CH=CH—X⁺. The largest energy difference in favor of the former was found to be ca. 13 kcal/mol for X = NH=C(NH₂)₂.

Cross-linked polyethylene (XLPE) insulation has been used in most advanced power cable technology. Strategies for decreasing the amount of antioxidants have been proposed to reduce conductivity further. In this study, the structural design of a new dual-functional antioxidant has been established. Theoretical investigation of the antioxidative behavior and grafting reaction of the new antioxidant by ultraviolet (UV) radiation was performed using the density functional theory (DFT) method. The reaction potential energy information of the six reaction channels at the B3LYP/6-311+G (d,p) level was obtained. Frontier molecular orbitals (MOs) and natural bond orbital (NBO) charge populations of the designed antioxidant molecule were analyzed. The calculation results indicate that the reaction Gibbs energy barrier of the designed antioxidant and O₂ required to achieve the antioxidative effect is about 0.8 eV lower than that of the polyethylene chain. Moreover, due to the lower reaction Gibbs energy barrier, the reaction active site of the designed antioxidant accepting H is located on the O of the CO groups. The proposed mechanism would be beneficial to understanding the molecular functions of antioxidants and further broadening the design ideas of thermoplastic insulation materials for future advanced power cables.

In double-stranded DNA, a rapid deprotonation of guanine radical cation (G^•+) hinders the long-distance transfer of positive charge (hole). It is significant to explore the proton transfer of G^•+ for designing other DNA structures with high electrical conductivity. The deprotonation of G^•+ is explored in the 1H₂O, 2H₂O, 3H₂O, and 9H₂O models by quantum mechanics (QM) method. The results indicate that the second hydration shell facilitates proton transfer. The QM/molecular mechanics (MM) (ABEEM) method accurately simulates polarization and charge transfer effects through the implementation of the reactive valence-state electronegativity piecewise functions and setting local charge conservation conditions. The QM/MM(ABEEM) method has been developed to investigate the 9H₂O model. The obtained activation energy (16.3 ± 0.8 kJ/mol) through molecular dynamics simulations is consistent with experimental data (15.1 ± 1.5 kJ/mol), demonstrating the accuracy of the QM/MM(ABEEM) method in simulating proton transfer in the DNA system. The deprotonation rate of G^•+ in the free base (1.5 × 10⁷ s⁻¹) is faster than that of G^•+ within double-stranded DNA (10⁶–10⁷ s⁻¹), which indicates that the free G base is an avoidable participant when designing hole transfer carrier due to its rapid deprotonation rate. Concurrently, the relationship between the proton transfer distance and potential barrier is monotone increasing, meaning that the long-range proton transfer corresponds to high energy barrier. The molecule involved in long-range proton transfer of G^•+ is more suitable as DNA electronic devices. This research provides valuable microscopic insight into deprotonation to advance the advancement of DNA structures with high electrical conductivity.

Imidazole structures are significant molecular frameworks in pharmaceutical and energetic material research. The synthesis efficiency and yield of their derivatives often vary greatly, making it challenging to establish reaction regularity. In this study, we investigated two types of imidazole derivatives with notably different synthesis efficiencies and yields. Our findings reveal that the catalysis of H₂O molecules is crucial for ensuring synthesis efficiency, while side reactions are influenced by the acidity of the solution during the process, thereby affecting the synthesis yield. We observed that the energy barrier for the H₂O-catalyzed ipsilateral H transfer process was reduced to 12.0 from 40.1 kcal/mol, significantly enhancing the reaction efficiency. The synthesis of 34-dihydroxyimidazolidine-2-ketone was found to have a low yield of 19.2% due to competitive side reactions in the reaction system, which have higher energy barriers compared to the desired synthesis pathway. These findings provide a theoretical foundation for future research to optimize the synthesis of imidazole derivatives. Enhancing synthesis conditions could significantly benefit pharmaceutical applications and the development of advanced energetic materials.

This work is devoted to the study of the influence of protonation on the photophysical properties of dimethylamino-substituted styryl dyes. The formation of a bond on the unshared nitrogen electron pair involved in conjugation with the dye chromophore changes the mobility of the terminal group of the donor fragment and thereby “switches” the molecule from n-π* to π-π* mode. The correlations found between changes in the electron density of the dye in native form and during protonation and changes in its properties contribute to the study of the ground and excited states of these compounds and the energy transitions between them. Comparison with analog compounds and consideration of vibronic effects allow us to evaluate the potential advantages and limitations of the TD-DFT method in the calculation of electronic transitions in styryl dyes. The work contributes to the understanding of the influence of protonation on the behavior of dyes with a nitrogen atom in the donor part of the chromophore of the molecule. The patterns found can be applied to similar chromophore systems.

Synthesis of novel benzothiazoles via intramolecular CS bond formation reactions is increasingly being explored since they have been found in a wide range of natural products and pharmaceutical agents. Sharma et al. reported the ruthenium-catalyzed preparation of novel benzothiazole derivatives from N-arylthiourea precursors, with a range of reaction yields and selectivity being observed. We have employed a density functional theory-based computational model to investigate the reaction mechanism leading to the benzothiazole product and help uncover the origin of the differing experimental yields and substrate specificities. We proposed a modified mechanistic scheme where the rate-determining step to be the synchronized breaking of the peroxide bond of the oxidizing agent with the concomitant proton-coupled electron transfer from the haloarene urea and a Ru-bound water molecule, not electrophilic RuC bond activation. Evidence for this being the rate-determining step is (a) the barrier is consistent with a lack of kinetic isotope effects associated with the ortho-H atom and (b) the computed rate-determining barriers for 10 N-arylthiourea substrates show good correlation with the observed yield.

Utilizing DFT along with Boltzmann transport theory, the structural, elastic, electrical, optical, and thermoelectric properties of half-Heusler compound RhTiP have been calculated in principle to examine the pressure effect in the range of 0–40 GPa. As pressure increases, the volume and normalized lattice parameter decreased. In addition to satisfying the Born stability criterion, which ensured the compound RhTiP “natural stability,” the zero pressure elastic constants and the pressure-dependent elastic constants are positive up to 40 GPa. The band structure computations guarantee the semiconductor nature of RhTiP, as demonstrated by the presence of electronic band gap of 1.035 eV at zero pressure. Using the Voigt-Reuss-Hill (VRH) averaging scheme under pressure, we have determined the values of this compound's bulk modulus $��B�$, shear modulus $��G�$, Young's modulus $��E�$, Pugh ratio $��B�/�G�$, Poisson's ratio $��v�$, and anisotropy factor $��A�$. Because the bulk modulus responds linearly to pressure, the material's hardness increases as pressure rises. Additionally, under pressures up to 40 GPa, the optical characteristics of RhTiP, including their reflectivity, absorptivity, conductivity, dielectric constant, refractive index, and loss function, were assessed and discussed. Furthermore, the thermoelectric properties are also studied for the materials and supports the tunning of pressure. This study provides a gateway to how the optoelectronic and transport properties of cubic RhTiP could be tuned by employing external pressure.

The use of solar water-splitting technology is anticipated to reduce the disparity between demand and consumption of energy. Herein, CASTEP software is used to investigate the perovskite CsSiX₃ (X = Cl and F) materials by applying GGA-PBE exchange–correlation functional. According to structure properties, compounds possess a cubic structure of “pm3m” by using space group 221. The direct band gaps in the CsSiX₃ (X = Cl and F) compounds are 1.04 and 1.07 eV, respectively. Measures of the density of states and the partial density of states (PDOS) are being utilized to determine the degree of electron localization in several bands. The compounds' optical characteristics are examined by altering their relation between the dielectric function (DF) scales and the pertinent peak. According to our results, the mechanical properties show that CsSiCl₃ is brittle (0.13, 045) and CsSiF₃ is ductile (0.32, 2.52) and stable with covalent bonds. Compounds CsSiCl₃ and CsSiF₃ modulus and elastic constants are {B (8.259, 52.375), E (8.110, 55.082), and G (18.331, 20.790)} and {C₁₁ (13.766, 73.566), C₁₂ (5.506, 41.780), and C₄₄ (10.763, 24.052)} are found, according to mechanical properties. Therefore, such materials can be used for photovoltaic light absorption in the visible spectrum. These materials offer a wide range of possible uses in sensing and solar conversion because compounds combine effectively.