铂配位的腺嘌呤质子化的理论研究

用量子化学从头算研究一系列平面四方金属配体作用于腺嘌呤N₇位点对其质子化的影响。计算结果表明气相中，配合物质子化能力主要受长程静电效应影响，不同金属离子的影响差别甚微。综合考虑极性溶剂影响后长程静电效应影响显著降低。NBO电荷布居分析表明质子化位点电子云密度的变化直接影响该位点质子化能力。     

Carbon-Fluorine Bondings of Fluorinated Fullerene and Graphite

Carbon-fluorine bondings of fluorinated fullerenes and fluorine-graphite intercalation compound C_xF were investigated in detail on the basis of XPS data and the potential model using the charge distribution calculated by semiempirical method. It has been confirmed by the present study that two peaks in the C_1s spectra observed for fluorinated fullerenes are assigned to carbon atoms bonded to fluorine atoms and those unbound to fluorine atoms, and the small difference in charges and Madelung potentials of fluorine atoms in different circumstances well explains the single peak in F_1s spectra of fluorinated fullerenes. In the calculated structures of 1,3-C₆₀F₂ and 1,2-C₆₀F_x (x = 2?6) used as the models of C_xF, three kinds of carbon-fluorine bondings were observed corresponding to nearly ionic, semicovalent and covalent C? F bondings. The calculated result supports that the bi-intercalation structure of stage 1 C_xF consists of nearly ionic and semi-covalent fluorines.     

Cr掺杂对K2La2Ti3O10光催化活性的影响

通过溶胶-凝胶法制备了层状钙钛矿结构的K₂La₂Ti₃O₁₀及Cr掺杂的K₂La₂Ti₃O₁₀，采用X-射线衍射(XRD)、紫外可见漫反射光谱(DRS)、X射线光电子能谱(XPS)等对K₂La₂Ti₃O₁₀及Cr掺杂K₂La₂Ti₃O₁₀进行了表征。以I^-为电子给体、分别在紫外和可见光辐射下研究了K₂La₂Ti₃O₁₀及Cr掺杂K₂La₂Ti₃O₁₀光催化分解水的产氢活性。采用第一性原理，计算了Cr掺杂对K₂La₂Ti₃O₁₀半导体能带结构和态密度的影响，从电子结构的变化揭示了掺杂引起光催化活性差异的原因。结果表明，Cr的掺入能够改善和提高K₂La₂Ti₃O₁₀的光解水的产氢活性；Cr改善和提高K₂La₂Ti₃O₁₀的光解水的产氢活性存在一个最佳的掺杂浓度；当Cr与Ti的物质量的比为0.02∶1时，紫外光催化分解水产氢速率为1 500 μmol·L^-1·h^-1，可见光催化分解水产氢速率为83.6 μmol·L^-1·h^-1，分别为K₂La₂Ti₃O₁₀掺杂改性前产氢速率的26和5倍。     

Semiempirical Molecular Orbital Studies of the Acylation Step in the Lipase‐Catalyzed Ester Hydrolysis

In this study, we present the results from the semiempirical molecular orbital calculations for the acylation step in the lipase‐catalyzed ester hydrolysis. The results reveal that the lowest energy path for the formation of the tetrahedral intermediate is for the serine residue of the catalytic triad to attack the substrate, followed by coupling heavy atom movement and proton transfer. The calculations of four active site models show that the cooperation of the aspartate group and the oxyanion hole is capable of lowering the activation energy by about 16 kcalmol^?1. Our results further suggest that the lipase‐catalyzed ester hydrolysis adopts the single proton transfer mechanism.     

[Co(3,3-tri)(amp)Cl][ZnCl4]一对邻位差向异构体的晶体结构

The crystal structures of a pair isomers of [Co(3,3-tri)(amp)Cl][ZnCl₄] (here 3,3-tri = N-(3-Aminoprop- yl)-1,3-propanediamine; amp=2-(Aminomethyl)pyridine) have been determined by single crystal X-ray diffrac-tion. They are the epimers with the only difference of the orientation of the Sec-NH proton in 3,3-tri ligand. The crystals with the anti-epimer (m1[ZnCl₄]·CH₃OH·H₂O) are monoclinic, space group C2/c with eight molecules in a unit cell of dimensions a=30.401(5)?,b=8.0469(13)?,c=18.817(3)?,β=93.346(3)°,V=4595.3(12)?³,D_c=1.708g·cm^-3,Z=8,F₀₀₀=2416,R=0.0462,R_w=0.1304. The crystals of the syn-epimer (m2[ZnCl₄]·H₂O) are triclinic, space group P1 with two molecules in a unit cell of dimensions a=8.9752(12)?,b=9.8855(12)?,c=12.6886(16)?,α=89.228(3)°,β=76.447(2)°,γ=80.428(3)°,V=1078.8(2)nm³,D_c=1.721g·cm^-3,Z=2,F₀₀₀=568,R=0.0313,R_w=0.0929. The crystal parameters, such as bond lengths and angles, are well consistent with the data of an ab initio computational result (RHF/LANL2DZ opti-mised structure). The average error for bond length is about 1.6%, only two of them in the isomer m3 (Co-N2 and Co-N4) are over 3%, (3.09% and 4.28% respectively). The errormax for bond angle is 2.52%, the bond angles with an over 2% error are only 3.6% out of all bond angles.     

环状芴基张力半导体拉曼光谱理论与实验研究

环状芴基张力半导体由于其特殊的分子结构，发射状排布的p轨道和纳米级空腔等诸多特点，引起了科学家广泛的关注.相对于直链型芴基半导体，环状芴基张力半导体展现出独特的光电性质.然而，迄今为止其振动性质没有被报道.对四元环芴的晶体与直链四聚芴粉末样品进行拉曼光谱表征和归一化处理，并结合理论计算.结果表明，与直链寡聚芴相比，环芴类似于碳纳米管的G峰发生了偏移，并且低频区域拉曼频移峰的峰强增加.其原因是由于张力的引入，改变了芴基主链的骨架和电子结构，加强芴骨架上π电子离域，同时使环芴中每个芴单元都参与到振动中.该研究结果为芴基张力半导体材料拉曼光谱的研究提供了一定的工作基础.     

Quantum chemistry study on B32 and B32H2–32

The structures of B32 and B₃₂H^2–₃₂ with I_h symmetry have been investigated by means of ab initio calculations at STO-3G level. The relationship between molecular orbitals of them has been analyzed and their bonding properties have been discussed. Then the possibility of their existence, as well as the similarity and difference between B₃₂ (B₃₂H^2–₃₂) and C₆₀ (C₆₀H₆₀) have been inferred.     

取代基对氮和氧自由基稳定性影响的理论研究

用MNDO方法，全构型优化，研究了15个氮自由基4-RC6H4NH，和15个氧自由基4-RC6H4O（R＝－H；－OCH3，－Cl，－F，－CN，－COCH3，－NO2，－CH3，－CF3，－SCH3，－C6H5，－Nh2，－BH2，－PH2，－SiH3）的稳定化能．结果表明：－NH2，－CH3，－OCH3，－F基团对自由基起稳定化作用，－CF3，－NO2；－CN，－COCH3，－BH2基团对自由基起去稳定化作用．苯基对氧自由基有较大的稳定化作用，而对氮自由基的稳定性影响较小．－SCH3，－PH2，－SiH3，－Cl基团表现弱的去稳定化作用．计算和实验结果基本相符．     

A Quantum Chemical Study of N14 Cluster

Ab initio molecular orbital theory and density functional theory have been employed to study N₁₄ cluster with low spin at the HF/6-31G*, B3LYP/6-31G*, B3PW91/6-31G*, BP86/6-31G*, and BHLYP/6-31G* levels of theory. Twelve isomers were studied, including one previously investigated cage molecule. The most stable isomer of N₁₄ is a C _2h -symmetric molecule that contains two separated five-membered nitrogen rings connected by a —N=N—N=N— bridge. The second, third, and fifth most stable isomers each have one five-membered nitrogen ring. The theoretical results suggest that the five-membered nitrogen ring gives rise to a particularly stable structural unit, and the more side chains that the five-membered nitrogen ring links with, the less stable the structure will become.     

Theoretical study of initiated reaction mechanism of polymerization of maleic anhydride catalyzed by OH−1 anion

A theoretical study of the polymerization reaction mechanism of maleic anhydride (MA) initiated by hydrate is presented. The reaction pathway has been studied with the density functional theory (DFT) method at the B3LYP/6‐311G** level. The geometrical parameters of transition states (TS) are optimized; intrinsic reaction coordinate (IRC) calculations have also been performed to obtain further credible features. Frequency analyses of all the stationary points are calculated at the same basis sets. The total energies of all geometries are corrected at second‐order Møller–Plesset (MP2)/6‐311G**. Calculation results reveal that the reaction mechanism is attributable to anion polymerization. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006