2-F-环氧丁烷与几种生物小分子间的赝氢键结构

采用密度泛函B3LYP(Becke,three-parameter,Lee-Yang-PaH)/6-311++G**和HF(Hartree Fock)/6-311++G**方法,从理论上探讨了2-F-环氧丁烷分别与几种常见而重要的生物小分子咪唑(Iminazole)、噻唑(Thiazole)和恶唑(Oxazo1e)等分子间的弱相互作用,发现分子间同时存在N…H常规氢键和C-F…H-C赝氢键结构.弱相互作用能计算表明3个复合物的相对稳定性相当.计算结果表明,在C-F…H-C赝氢键结构中,与电子的直接供体F密切相关的共价键C-F键长增大,伸缩振动的频率红移,而作为电子受体的H-C基团,其C-H键伸缩振动光谱蓝移;另外,电子密度拓扑性质表明C-F…H-C赝氢键的共价性及离子性均与常规氢键相当.     

RuH2和RuN2电子组态与光谱性质的从头计算

用量子化学从头算方法在B3LYP/6 311G 的水平上 ,研究了RuH2 和RuN2 可能的电子组态和光谱性质 .结果表明 ,RuH2 的3 B2 和5Σ-态对应于静电作用的物理吸附态 .RuN2 的一重态和三重态的计算结果跟钌单晶面上的实验值相接近 .而RuN2 在C∞v对称性时 ,五重态5Σ-的计算频率比实验值稍低 .在C2v对称性时 ,五重态的计算频率值则更低 ,3 B2 和5A1态不能稳定存在     

Self-interstitial solute interaction in aluminium base alloys: Problems of data interpretation

The interpretation of electrical resistivity measurement results of Al base alloys is critically discussed. Correct numerical data evaluation with respect to the atomistic properties r_c/r_p, r_t and Pf^t/Pf is yet impossible for Al and its alloys because of the overlapping of Ic and Id recovery for those electron irradiations for which damage rate measurements exist and because of the unexplained scatter of initial damage rate data.     

ZnSe小团簇结构稳定性和电子性质研究

文章研究了小尺寸的(ZnSe)n团簇(n=2-16)的结构和电子性质.通过手工搭建得到团簇结构,用DMol软件包进行结构优化和能量计算,最后分析计算结果 .研究结果表明,对于n=2-4,平面环状结构的能量最低;对于n=5,非平面环状结构的能量最低;对于n=6-12,空心笼状结构的能量最低;对于n=13,核-壳笼状结构的能量最低;对于n=14-16,依旧是空心笼状结构的能量最低.通过分析(ZnSe)_n团簇(n=2-16)的电子性质,我们可以得到,(ZnSe)_9团簇、(ZnSe)_(12)团簇具有很好的稳定性.     

Molecular Dynamics Simulation of Temperature-dependent Flexibility of Thermophilic Xylose Isomerase

构建了嗜热栖热菌木糖异构酶与底物木糖的复合物模型,并运用NAMD2.5软件对其在300 和360 K下进行了10 ns的分子动力学模拟. 对该酶的回旋半径、亚基间相互作用及残基柔性进行了计算与统计分析,确定了该酶在360 K时柔性残基及区域. 研究发现与300 K相比,360 K时木糖异构酶中B-因子增幅较大的残基主要可分为两组：一组位于催化结构域,是由残基55～80组成的helex-loop-helix区域,另一组位于其亚基界面上. 研究表明高温下该酶催化结构域回旋半径增加,可能加速了活性中心的运动从而有利于D-木糖的异构化反应.在360 K时亚基界面上减少了8个氢键和5个离子对,这可能也是高温下其整体结构刚性下降并且活性升高的主要原因,该结果也对文献报道的该酶E372G突变体冷适应的实验现象进行了解释. 研究结果揭示了嗜热栖热菌木糖异构酶温度和结构柔性之间的关系.     

Bis-chelate Fe(III) complex of an azomethine at the focal point of a branched ester functionalized with cyclohexylbenzoic acid

A Fe(III) complex with Cl counter ion based on a branched Schiff base has been synthesized and studied. The compound was produced by the reaction of the Schiff base with FeCl₃ at room temperature in benzene–ethanol. The complex is symmetric, i.e., bis-chelate, with an octahedral coordination of Fe. The compound revealed phase transitions of the “solid–solid” type. The complex displayed a temperature-induced spin transition (S?=?1/2???5/2) which was detected by EPR.     

Direct Synthesis of a Dimeric Mixed-Anions Bismuth(III) Complex: Synthesis and Structural Characterization of [Bi2(Phen)4(No3)4.4I0.6]I3 (A New Dimeric Compound)

A direct synthetic method of mixing Bi(NO₃)₃ and NaI with 1,10-phenanthroline yielded red crystals of [Bi₂(phen)₄(NO₃)_4.4I_0.6]I₃. In this complex the cationic part is in fact binuclear and contains two [Bi(phen)(NO₃)_1.7I_0.3] groups linked via a bridging NO^? ₃ anion. The I^? ₃ anion was not coordinated to bismuth(III) and the lone pair of valence electrons of the bismuth(III) ions appears to be stereochemically inactive. There are two independent NO^? ₃ anions, one coordinated to bismuth but another shares a position with I^? anion. The final results of crystallography show that 40% of these positions are occupied by NO^? ₃ anions and 60% by I^? anions that are coordinated to bismuth atom in bidentate fashion (NO^? ₃) and in unidentate fashion (I^?). An interesting point is that the I^? ₃ anion was produced by direct synthetic method (Branched tube method). There is a π-π stacking interaction between the parallel aromatic rings around the Bi(III) ion.     

过氧硝酸分解势能面的理论研究

使用密度泛函理论B3LYP/6-311+ G(2d,2p)研究了过氧硝酸的最低能量结构．采用耦合簇方法CCSD(T)/aug-cc-pVDZ首次分别扫描了过氧硝酸沿氧-氮和氧-氧键的分解势能面．计算结果表明在氧-氮势能面上,当O3—N4键长是2.82 ?时,对应的疏松过渡态的能垒是25.6 kcal/mol;在氧$-$氧键的势能面上,当O2—O3键长是2.35 ?时,对应的疏松过渡态的能垒是37.4 kcal/mol．这表明过氧硝酸更容易分解为HO₂和NO₂．     

APICOPHILICITY AND RING-STRAIN IN FIVE-COORDINATE PHOSPHORANES

Abstract

In order to dicuss mechanism in organophosphorus chemistry a number of assumptions have to be made. Among them are: (a) that substitutions at tetrahedral phosphorus proceed via five-coordinate intermediates; (b) these intermediates are trigonal bipyramidal; (c) they are formed by apical attack and decompose by apical loss; and (d) if sufficiently long-lived, they may undergo permutational isomerization, that is the ligands may alter their relative dispositions round the phosphorus, before going on to products or back to reactants.

Assuming that the course of a given substitution is dictated primarily by thermodynamic considerations, in order to understand the course of that substitution one needs to know how to assess the relative stabilities of the four isomeric tbps (trigonal bipyramids) that can be formed initially and of the others that could be formed by subsequent isomerization, the barriers to those isomerizations, and the relative rates of the various product-forming steps. We have concentrated on the first of these factors and this lecture describes our attempts to provide the necessary data.

The energy difference between two isomeric tbps can be analyzed in terms of changes in the relative apicophilicities¹ of the groups occupying apical positions, changes in ring-strain as small rings move between apical-equatorial and diequatorial positions, and changes in steric strain. I shall consider each of these in turn. Ligand subset symmetry may also have to be taken into account.^1,2