Search

Research has been conducted on silylenes. The results of density functional and ab initio studies demonstrate that these compounds can produce complexes with BH (sub)3, and that these complexes possess 3c-2e bridges.

Density functional theory modelling has been used to design Mo and W-based catalysts MoIII(tBu)(CO) and WIII(tBu)(CO) for CO2 hydrogenation and HCOOH dehydrogenation, which are bio-mimics of the active site of formate dehydrogenase. Based on DFT calculations, the molybdenum and tungsten based complexes are good catalysts in the +3 oxidation state for CO2 hydrogenation with free energies of 24.03 and 21.31 kcal mol−1, respectively. Such a low barrier indicates that our newly designed Mo and W-based complexes are very efficient for CO2 hydrogenation or HCOOH dehydrogenation catalysis. Overall, our computational results provide in depth insights that can serve as a great tool for the design and development of new and efficient molybdenum and tungsten based catalysts for CO2 hydrogenation or HCOOH dehydrogenation. [ABSTRACT FROM AUTHOR]

An ab initio study of the complexes formed by hypohalous acids and monohaloamines (designated as HAX where A = O or NH and X = Cl, Br, or I) with RCHO (R = H, CH, OCH, and NH) carbonyl compounds has been carried out at the MP2/aug-cc-pVTZ computational level for comparative study on hydrogen bonds with halogen bonds. Two types of complexes are formed by their combination -RCHO···HAX and RCHO···XAH (A = O or NH) named as hydrogen-bonded and halogen-bonded, respectively, although other weak interactions also coexist in both types of complexes. Analysis of the BSSE-corrected interaction energies reveals that hydrogen bond strength decreases with an increase in size of X atom (i.e., HACl > HABr > HAI) while reverse trend is indicated for halogen-bonded complexes (HACl < HABr < HAI). For the carbonyl compounds, the interaction energies for both hydrogen- and halogen-bonded complexes follow the same order of HCHO < CHCHO < (CHO)CHO < (HN)CHO. Vibrational frequency analysis suggests that both the H-O and H-N bonds are red-shifted while C-H bonds are blue-shifted in hydrogen-bonded complexes. Similarly, the X-O/X-N and C-H bonds are red- and blue-shifted respectively in halogen-bonded; however, the magnitude of red shift for X-O and X-N bonds in halogen-bonded complexes is much smaller than that of H-O and H-N bonds in hydrogen-bonded complexes. The MEP, NBO, and AIMALL methods have been utilized to understand structure, properties, and nature of the interaction stabilizing these two types of the complexes. Relationship of the interaction energies with MEP, charge transfer (CT), and change in % s character obtained from NBO analysis is also drawn for both complexes. [ABSTRACT FROM AUTHOR]

In the present study, five-membered heterocyclic ring systems containing oxygen with one, two, three, and four nitrogen atoms in the ring along with their isomeric forms and their corresponding 1:1 water complexes have been fully optimized at the ab initio molecular orbital theory and Density Functional Theory (DFT) using aug-cc-pVDZ basis set. The optimized geometric parameters and stabilization energies of the complexes are reported. The study suggests that nitrogen of heterocyclic ring is a stronger hydrogen bond acceptor in comparison to oxygen and ability of nitrogen to act as hydrogen bond acceptor increases in the order oxazole (OZ) > oxadiazole (ODZ) > oxatriazole (OTZ) > oxatetrazole (OTTZ). The results are corroborated by Natural Bond Orbital (NBO) analysis, Quantum Theory of Atoms in Molecules (QTAIM), Symmetry Adapted Perturbation Theory (SAPT), and Molecular Electrostatic Potential (MEP) studies. The blue- and red-shifts in the hydrogen bond donors X-H (X = O, C) stretching frequencies have also been analyzed. Hydrogen bond ability has also been governed in the presence of reactivity descriptors including chemical potential ( μ), global hardness ( η), and electrophilicity index ( ω). [ABSTRACT FROM AUTHOR]

N&bond;H bond dissociation enthalpies for the substituted ammonia, amine, amides, and their thio- and seleno-analogs have been studied employing ab initio and density functional methods. The orbital interactions involving lone pair of electrons on nitrogen and substituent, electrostatic interactions, spin delocalization, and hydrogen bonding are the important factors affecting the stability of the molecule and the radical. The molecule stabilization effect and radical stabilization effect have been calculated using isodesmic reactions in order to analyze the effect of substituent on the stabilization of the molecule and the radical. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

Density functional methods have been employed to characterize the gas phase conformations of selenocysteine. The 33 stable conformers of selenocysteine have been located on the potential energy surface using density functional B3LYP/6-31+G* method. The conformers are analyzed in terms of intramolecular hydrogen bonding interactions. The proton affinity, gas phase acidities, and bond dissociation energies have also been evaluated for different reactive sites of selenocysteine for the five lowest energy conformers at B3LYP/6-311++G*//B3LYP/6-31+G* level. Evaluation of these intrinsic properties reflects the antioxidant activity of selenium in selenocysteine. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

Density functional theory modelling has been used to design Mo and W-based catalysts MoIII(tBu)(CO) and WIII(tBu)(CO) for CO2 hydrogenation and HCOOH dehydrogenation, which are bio-mimics of the active site of formate dehydrogenase. Based on DFT calculations, the molybdenum and tungsten based complexes are good catalysts in the +3 oxidation state for CO2 hydrogenation with free energies of 24.03 and 21.31 kcal mol-1, respectively. Such a low barrier indicates that our newly designed Mo and W-based complexes are very efficient for CO2 hydrogenation or HCOOH dehydrogenation catalysis. Overall, our computational results provide in depth insights that can serve as a great tool for the design and development of new and efficient molybdenum and tungsten based catalysts for CO2 hydrogenation or HCOOH dehydrogenation.