Basis set and density functional dependence of vibrational Raman optical activity calculations

We present an extensive investigation of the dependence of the scattering intensity difference of right and left circularly polarized light observed in vibrational Raman optical activity (VROA) on the choice of basis set and exchange-correlation functional. These dependencies are investigated for five molecules for which accurate experimental data are available: (S)-methyloxirane, (R)-epichlorhydrin, (S)-glycidol, (M)-spiro[2,2]pentane-1,4-diene, and (M)-sigma-[4]-helicene. Calculations are presented using the SVWN exchange-correlation functional (LDA), the BLYP exchange-correlation functional, and the B3LYP hybrid functional, using six different basis sets: the cc-pVDZ, cc-pVTZ, aug-cc-pVDZ, aug-cc-pVTZ, Sadlej's polarized basis set, and a minimal VROA basis set recently proposed by Zuber and Hug. It is demonstrated that results from pure gradient-corrected and hybrid functionals are comparable and that the aug-cc-pVDZ and aug-cc-pVTZ basis sets yield similar results. Furthermore, the combination of the small basis set by Zuber and Hug with an accurate force field represents the best compromise between computational accuracy and computational efficiency.     

Theoretical studies of dissociative phosphoryl transfer in interconversion of phosphoenolpyruvate to phosphonopyruvate: solvent effects, thio effects, and implications for enzymatic reactions

The conversion of phosphoenolpyruvate (PEP) to phosphonopyruvate (P-pyr) is catalyzed by PEP mutase via a dissociative mechanism. In this work, we investigate the uncatalyzed reaction using ab initio methods, density functional theory, and the semiempirical MNDO/d method. Comparisons of geometries and relative energies of stationary points (minima and transition states) with density functional results indicate that the semiempirical method is reasonably accurate. Solvent effects are examined using implicit solvent models, including the recently extended smooth conductor-like screening model. Due to the large negative charge carried by the system, solvation is found to drastically alter the location and energy of stationary points along the dissociative reaction pathways. The influence of substituting a nonbridging phosphoryl oxygen by sulfur (thio effects) was also investigated. Implications of these results for the enzymatic reaction are discussed.     

Liquid chromatographic enantiomer resolution of N-fluorenylmethoxycarbonyl alpha-amino acids and their ester derivatives on polysaccharide-derived chiral stationary phases

The liquid chromatographic enantiomer separation of N-fluorenylmethoxycarbonyl (FMOC) protected alpha-amino acids and their ethyl ester derivatives was performed on polysaccharide-derived chiral stationary phases, Chiralcel OD, Chiralpak AD, and Chiralpak AS. In general, Chiralcel OD and Chiralpak AD showed good performance for resolution of N-FMOC alpha-amino acids and their ethyl esters, respectively. All investigated N-FMOC alpha-amino acid enantiomers were baseline separated on Chiralcel OD or Chiralpak AD, whereas N-FMOC alpha-amino acid ethyl ester enantiomers were baseline resolved (alpha = 1.15-3.03) on Chiralpak AD, except for two analytes. The L-enantiomers of all examined FMOC alpha-amino acid ethyl ester derivatives are preferentially retained on Chiralpak AD, while the elution orders of the other enantiomer separations are not consistent.     

Dynamics of excited m-dichlorobenzene

Dichlorobenzene is a precursor molecule of di-oxins, which are some of the most toxic chemicals and are suspected of being mutagenic with the structure of benzene rings containing different numbers of chlorine atoms. They are seriously harmful to the health of human. Therefore, it is necessary to study these aryl chemicals especially dichlorobenzene molecules in great detail. In recent years, a number of groups have investi-gated the molecules of aryl halide. The near ultraviolet absorption sp…     

纳米晶复合Nd2Fe14B/α-Fe合金制备与磁性能的研究

采用熔体快淬及晶化处理工艺制备Nd11Fe71Co8V1.5Cr1B7.5纳米晶合金。经21m·s-1快淬及640℃ 4min晶化处理后,制成的粘结磁体的磁性能最佳,为:Br=0.64T,JHc=903.5kA·m-1,(BH)max=71kJ·m-3。添加Cr元素可提高内禀矫顽力,从而提高最大磁能积。     

α''-取代磺酰基-α,β-不饱和酮的不对称催化环加成反应的研究

在手性金属钛配合物催化剂存在下，研究了α′－取代磺酰基－α，β－不饱和酮的不对称催化环加成反应；讨论了α，β－不饱和酮各种取代磺酰基对反应活性和对映选择性的影响；高收率地合成了高光学纯度的环加成产物，并对环加成产物的构型进行了鉴定。     

带电胶体离子扩散与交换动力学的比较

Taking soil colloid and hydrated silica (quartz sand) as the experimental material, the comparative study has been made on the kinetics of ion diffusion and ion exchange in charged colloid and charged coarse disperse systems. The results showed that ion exchange kinetics in the two systems conform to the kinetic law of ion diffusion. Besides, through this comparative study on the kinetics of ion exchange and ion diffusion, a method has been advanced theoretically to estimate the quantity of adsorbed ion that is located in the inner of the Helmholtz layer. As far as hydrated silica is concerned , there were about 33 per cent of the total adsorbed quantity of Mg2+that were located in the inner of the Helmholtz layer under the given experimental conditions, bu tfor soil colloid the percentage was only 7.5.     

硒与消化系统癌关系的探讨

据不同地貌、地质条件在30个县市按剖面、同步、随机取土壤样品372份．测定硒等微量元素含量．作等级相关分析显示。土壤硒含量与消化系统癌呈负相关关系．作相对危险度、剂量-效应及多因素分析,认为此负相关关系并非偶然现象．