Ze-Sheng Li

Theoretical study on the adsorption mechanism of iodine molecule on platinum surface in dye-sensitized solar cells

Abstract By means of density functional theory calculations, the adsorption process of I2 at Pt (111) surface in dye-sensitized solar cells (DSSCs) has been investigated. The obtained adsorption energies and stable structures depending on the adsorption sites of the Pt surface are in good agreement with experimental values. Our results show that the dissociative chemisorption and the non-dissociative chemisorption are competitive for the adsorption of I2 on the Pt surface, and the dissociative pathway is more favored in energy. This study is expected to enrich the understanding on the origin of the excellent heterogeneous catalytic performance of Pt for triiodide reduction and the complex iodine chemistry in DSSCs. Understanding of this adsorption mechanism is helpful for rational screening for redox couple and the Pt-free alternative counter electrode materials.

Theoretical study on the reaction CX3 + SiH(CH3)3 (X = H, F)

Theoretical investigations are carried out on the multiple‐channel reactions, CH3 + SiH(CH3)3 → products and CF3 + SiH(CH3)3 → products. The minimum energy paths (MEP) are calculated at the MP2/6‐311 + G(d,p) level, and energetic information is further refined by the MC‐QCISD (single point) method. The rate constants for major reaction channels are calculated by the canonical variational transition state theory (CVT) with small‐curvature tunneling (SCT) correction over the temperature range 200–1500 K. The theoretical rate constants are in good agreement with the available experimental data and are found to be k1a(T) = 1.93 × 10−24T3.15exp(−1214.59/T) and k2a(T) = 1.33 × 10−25T4.13exp(−397.94/T) (in unit of cm3molecule−1s−1). Our calculations indicate that hydrogen abstraction channel from SiH group is the major channel due to the smaller barrier height among five channels considered.

Theoretical study and rate constants calculation for the reactions X + CF3CH2OCF3 (X = F, Cl, Br)

The multiple‐channel reactions X + CF3CH2OCF3 (X = F, Cl, Br) are theoretically investigated. The minimum energy paths (MEP) are calculated at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for major reaction channels are calculated by canonical variational transition state theory (CVT) with small‐curvature tunneling (SCT) correction over the temperature range 200–2000 K. The theoretical three‐parameter expressions for the three channels k1a(T) = 1.24 × 10−15T1.24exp(−304.81/T), k2a(T) = 7.27 × 10−15T0.37exp(−630.69/T), and k3a(T) = 2.84 × 10−19T2.51 exp(−2725.17/T) cm3 molecule−1 s−1 are given. Our calculations indicate that hydrogen abstraction channel is only feasible channel due to the smaller barrier height among five channels considered.

Theoretical studies on the reactions CH3SCH3 with OH, CF3, and CH3 radicals

The multiple‐channel reactions OH + CH3SCH3 → products, CF3 + CH3SCH3 → products, and CH3 + CH3SCH3 → products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for eight reaction channels are calculated by the improved canonical variational transition state theory with small‐curvature tunneling contribution over the temperature range 200–3000 K. The total rate constants are in good agreement with the available experimental data and the three‐parameter expressions k1 = 4.73 × 10−16T1.89 exp(−662.45/T), k2 = 1.02 × 10−32T6.04 exp(933.36/T), k3 = 3.98 × 10−35T6.60 exp(660.58/T) (in unit of cm3 molecule−1 s−1) over the temperature range of 200–3000 K are given. Our calculations indicate that hydrogen abstraction channels are the major channels and the others are minor channels over the whole temperature range.

Adsorption of water on NaNO3(001) surface from first-principles calculations.

Density functional theory (DFT) calculations were applied to investigate the adsorption of water monomer, water clusters on NaNO(3)(001) surface. Single water molecule is more likely to locate on the bridge site with its H atom attracted by the O atom of nitrate ion and its O atom adjacent to Na(+). Mulliken population analysis shows that fewer electrons transfer from the Na atom of substrate to water molecule. A systematic study of water clusters adsorption at high coverages ranging from 0.5 monolayer (ML), 0.75 ML, 1 ML, 1.25 ML, and 1.5 ML on NaNO(3)(001) surface was also investigated, and the results indicate that for 1 ML water adsorption on NaNO(3)(001) surface, a water chain is formed among four water molecules through hydrogen bonds. Interestingly, the water molecules are linked through hydrogen bonds to form a 14-membered macrocyclic water ring for 1.5 ML adsorption on NaNO(3)(001) surface. Our estimated O-H symmetric stretching frequency (ν(O-H)) will have blueshift with decrease of water coverage, which is consistent with the tendency given by experiments.

Stereoselectivity of chalcone isomerase with chalcone derivatives: a computational study

AbstractChalcone isomerase (CHI) catalyzes the intramolecular cyclization of chalcones into flavonoids. The activity of CHI is essential for the biosynthesis of flavonoids precursors of floral pigments and phenylpropanoid plant defense compounds. In the present study, we explored the detailed binding structures and binding free energies for two different active site conformations of CHI with s-cis/s-trans conformers of three chalcone compounds by performing molecular dynamics (MD) simulations and binding free energy calculations. The computational results indicate that s-cis/s-trans conformers of chalcone compounds are orientated in the similar binding position in the active site of CHI and stabilized by the different first hydrogen bond network and the same second hydrogen bond network. The first hydrogen bond network results in much lower binding affinity of s-trans conformer of chalcone compound with CHI than that of s-cis conformer. The conformational change of the active site residue T48 from indirectly interacting with the substrate via the second hydrogen bond network to directly forming the hydrogen bond with the substrates cannot affect the binding mode of both conformers of chalcone compounds, but remarkably improves the binding affinity. These results show that CHI has a strong stereoselectivity. The calculated binding free energies for three chalcone compounds with CHI are consistent with the experimental activity data. In addition, several valuable insights are suggested for future rational design and discovery of high-efficiency mutants of CHI. FigureStereoselectivity of chalcone isomerase with chalcone derivatives