Journal of Computational Science & Engineering

Abstract: Density functional calculations have been performed to study the stereoselectivities in the direct anti-Mannich reactions catalyzed by chiral 3-trifluoromethanesulfonamido-pyrrolidine. Transition states of the stereochemistry-determining C-C bond-forming step with the enamine intermediate addition to the imine for the subject Mannich reactions are reported. BH and HLYP/6-31G** calculations provide a good explanation for the anti-diastereoselectivities in the chiral pyrrolidine-based amino sulfonmide-catalyzed Mannich reactions. Calculated and observed diastereomeric ratio and enantiomeric excess values are in reasonable agreement.

Abstract: The PW91-GGA density functional theory method was used to investigate the role of the co-adsorption of H2O molecule in the TS-1/H2O2 system. The results show that the formation of the physisorbed 23T-H2O2/H2O is more favored than that of 23T-H2O2 by 5.8 kcal/mol, and the formation of chemisorbed 23T-Ti-OOH(h2)/H2O is more favored than that of 23T-Ti-OOH (h2) by 6.8 kcal/mol. These agree well with the cooperative role of H2O in stabilizing the Ti-OO intermediate. The calculated Ti-O (H2O2) and O-O distances in the chemisorbed 23T-Ti-OOH- (h2)/H2O complex agree well with the available experimental data. The electronic structures of the species are also discussed.

Abstract: Using the quasiclassical trajectory (QCT) method, we theoretically study the reaction F+HCl→HF+Cl on the DHTSN potential energy surface (PES). The distributions of product rovibroational state and the distributions of and are calcula- ted. The results show that the most populated product states are v’=3, j’=0-2 at the collision energy of 6kcal/mol; the product is aligned and oriented at this collision energy.

Abstract: A novel nonlinear method of gene expression programming (GEP) was used to develop nonlinear models for predicting the chromatographic hydrophobicity index. The six descriptors were selected by heuristic method (HM) and were used as the inputs of the linear and nonlinear models respectively. Number of genes, the functions selecting, and the difference of training and test sets are the most important factors for setting up quantitative structure-property relationship (QSPR) model in the GEP method. Results indicate that the GEP is a reliable nonlinear method for building QSPR model.

Keywords: chromatographic hydropho-bicity index, Gene expression programming, quantitative structure-property relationship, HM.

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Abstract: Band gap engineering by doping is a good method to get a visible-light-driven photoca-talyst. Density functional theory (DFT) calculations are used to characterize the doping effect of S substituting for Ti in anatase TiO2. Electronic structure analysis indicated that, just as in the anionic doping case (TiO2-xSx: S substitute for O), the presence of an impurity state in the band gap near valence band O2p induced the visible light activity. Excitations from the impurity state to conduction band may be responsible for the red shift of absorption edge observed in the cationic S-doped TiO2. Doping concentration dependent behavior of band gap energy and red shift of absorption edge for Ti1-xSxO2 is also evidenced just as that for TiO2-xSx. Differences exist in the composition and relative position of the impurity state. Partial density of states analysis shows that it is a mixing of S3p, S3s and Ti3d. Comparing with anionic S, N-doped TiO2, the stronger absorption for Ti1-xSxO2 is evidenced in our calculation. This may be a sign of its observed good performance in photocatalysis.

Abstract: The structures and magnetic properties of Fe6-xSix(x=0-5) clusters have been systematically studied at the BPW91 level in density-functional theory (DFT). Calculated results show that the Fe atoms of the lowest-energy structures of Fe6-xSix clusters tend to go together, and Si atoms tend to occupy surface site bonding with iron atoms as many as possible. The total magnetic moments of Fe6-xSix clusters decrease monotonously with increasing Si atom. The natural population and natural electron configuration reveal that the decrease of the total magnetic moment is directly relevant to the hybridization between Si-3p and Fe-4s.

Abstract:A set of sixty-one 2, 3-Benzodiazepin-4 (thi) one- and 1, 2-phthalazine- related negative allosteric modulators of AMPA receptor was modeled using the descriptors, which were calculated from the molecular structure alone with a quantitative structure-activity relationship technique. The heuristic method and support vector machine were utilized to construct the linear and nonlinear prediction models, lead to correlation coefficients were 0.7930 and 0.7054, respectively. The specific information described by the heuristic linear model could provide some insights into the factors be used drug design process, the prediction results of the linear heuristic method model seemed well than those of support vector machine. Quantitative structure-activity relationship can be used to predict the ED50 of the compounds.

Abstract: The conformational stability, intramolecular H-bond strength, energy barriers, vibrational frequencies and gas-phase basicities of fourteen most stable conformers of ethanolamine in gas phase and in aqueous and carbon tetrachloride solutions have been investigated at B3LYP and MP2 level with 6-311+G(d,p) basis set. In gas phase, the results of two methods suggest that G+1 and G+2 conformers, which possess intramolecular H-bonds, are the two most stable conformers. The population ratios of T-, G-- and G+-type conformers are about 2.2%:48.9%:48.9% (B3LYP), 1.2%:49.4%:49.4% (MP2). The energy barrier of interconversions G+5. T1 is obviously larger than that of T2 T3. In aqueous solution (SCRF-PCM method), the calculations indicate that the stabilizations of ethanolamine conformations are determined by the combination of intramolecular hydrogen bonds and intermolecular solvation of hydroxyl groups. The normal mode analysis for vibrational frequencies shows that the C-O-H bending and the C-O stretching frequencies of the conformers from high energy to low energy are blue-shifted, the O-H stretching frequency is red-shifted conversely. The computed vibrational frequencies in carbon tetrachloride solution are in good agreement with the experimental data. The calculated results of gas-phase basicities of different ethanolamine conformers suggest that the GBs of G+-type conformers are higher than that of T-type conformers.