Xueli Cheng

Catalytic mechanisms of Au11 and Au11-nPtn (n=1–2) clusters: a DFT investigation on the oxidation of CO by O2

The oxidation of CO catalyzed by clusters of Au11, Au10Pt and Au9Pt2 was investigated using the M06 functional suite of the density functional theory. Au and Pt atoms were described with the double-ζ valence basis set Los Alamos National Laboratory 2-double-z (LanL2DZ), whereas the standard 6-311++G(d,p) basis set was employed for the C and O atoms. Our theoretical model showed that (1) after coordination to Au and Au-Pt cluster, O2 and CO are apparently activated, and Mulliken charges show that the gold atoms in the active sites of Au11 are negatively charged; (2) Au-Pt clusters with 11 atoms can effectively catalyze the oxidation of CO by O2; (3) Au11 exhibits good catalytic performance for the oxidation of CO; (4) oxidation of CO occurs preferably on the Au–Pt active sites in Pt-doped clusters, and the single-center mechanisms are more favorable energetically than the two-center mechanisms; (5) after adsorption, an O2 molecule oxidates two CO molecules via stepwise mechanisms; and (6) the catalytic processes are highly exothermic.

Receptor-based QSAR study for a series of 3,3-disubstituted-5-aryl oxindoles and 6-aryl benzimidazol-2-ones derivatives as progesterone receptor inhibitors

Receptor-based comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were performed on a series of 54 progesterone receptor (PR) inhibitors. The established CoMFA model from the training set gives statistically significant results with the cross-validated q 2 of 0.534 and non-cross-validated of 0.947. The best CoMSIA model was derived by the combination of steric field and hydrophobic field with a q 2 of 0.615 and of 0.954. A test set of 18 compounds was used to validate the predictive ability of the two models. The predicted correlation coefficients are 0.681 and 0.677 for CoMFA and CoMSIA models, respectively. Based on the CoMFA maps, the key structural characters of progesterone receptor inhibitors are identified. Moreover, the binding modes of oxindoles and benzimidazol-2-ones are also given by the quantum mechanical/molecular mechanical (QM/MM) calculations. This may provide useful information for drug design.

Role of F− in the hydrolysis–condensation mechanisms of silicon alkoxide Si(OCH3)4: a DFT investigation

The hydrolysis and condensation mechanisms of tetramethoxysilane aided by F− were investigated with Gaussian03 program package. The coordination of F− to tetramethoxysilane and the first-order hydrolysis of the fluorotetramethoxysilane anion were studied extensively with both CPCM full optimization and CPCM single-point energy (SPE) calculations, and the single-point energies agree well with those obtained from the full optimization with CPCM solvation model. The coordination of F− decreases the Mulliken charge on the Si atom and the energy gap between the HOMO and LUMO, and alters the shape of the frontier orbitals. Our calculations show that entropic effects elevate potential energy surface (PES) profiles distinctly, but have a minor influence on the free energy barriers. With the aid of F−, the hydrolysis barriers of fluorotetramethoxysilane anion and the dimerization free energy barriers before entropic corrections decrease from 104, 106, 109, 109 and 136, 104, 99, 94 to kJ mol−1 to 84.2, 88.5, 77.2, 81.9 and 82.2, 80.0, 87.7, 88.7 kJ mol−1, respectively, compared with the neutral hydrolysis and condensation barriers. These barriers are much lower than the corresponding neutral SN2 ones, but only slightly higher than the SN1 ones. The role of nucleophile F− is similar to HO−.

Theoretical investigations on the synthesis mechanism of cyanuric acid from NH3 and CO2

AbstractIn the synthesis of cyanuric acid from NH3 and CO2, urea and isocyanic acid OCNH are two pivotal intermediates. Based on density functional theory (DFT) calculations, the synthesis mechanism of cyanuric acid from NH3 + CO2 was investigated systematically. Urea can be synthesized from NH3 and CO2, and cyanuric acid can be obtained from urea or NH3 + CO2. In the stepwise mechanism of cyanuric acid from urea or NH3 + CO2, the energy barriers are relatively high, and the condition of high pressure and temperature does not decrease the energy barriers. Our theoretical model shows that cyanuric acid is actually acquired from OCNH via a one-step cycloaddition reaction. FigureThe synthesis mechanism of cyanuric acid from NH3 and CO2 was revealed systematically with density functional theory methods relative to 3NH3 + 3CO2

3D-QSAR Studies on C24-Monoalkylated Vitamin D3 26,23-Lactones and their C2α-Modified Derivatives with Inhibitory Activity to Vitamin D Receptor

The ligand‐based three‐dimensional quantitative structure‐activity relationship (3D‐QSAR) for 82 inhibitors of 25‐dehydro‐1α‐hydroxyvitamin D3‐26,23‐lactone analogs has been studied by using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models. The established CoMFA model in training set gives a cross‐validated q2 value of 0.516 and a non‐cross‐validated rncv2 value of 0.667, while the CoMSIA model results in q2=0.517 and rncv2=0.632. In general, the predictive ability of the CoMFA model is superior to that of the CoMSIA model, with rpred2=0.639 for the CoMFA and rpred2=0.619 for the CoMSIA model. Based on the CoMFA contour maps, some key structural characters of vitamin D3 analogs responsible for inhibitory activity are identified, and some new C2α‐modified 24‐alkylvitamin D3 lactone analogs with high predicted pIC50 values are designed. The ligand functional group mutations by FEP simulation and docking studies reveal the rationality of the molecular design.