Symmetry calculation for molecules and transition states

The symmetry of molecules and transition states of elementary reactions is an essential property with important implications for computational chemistry. The automated identification of symmetry by computers is a very useful tool for many applications, but often relies on the availability of three‐dimensional coordinates of the atoms in the molecule and hence becomes less useful when these coordinates are a priori unavailable. This article presents a new algorithm that identifies symmetry of molecules and transition states based on an augmented graph representation of the corresponding structures, in which both topology and the presence of stereocenters are accounted for. The automorphism group order of the graph associated with the molecule or transition state is used as a starting point. A novel concept of label‐stereoisomers, that is, stereoisomers that arise after labeling homomorph substituents in the original molecule so that they become distinguishable, is introduced and used to obtain the symmetry number. The algorithm is characterized by its generic nature and avoids the use of heuristic rules that would limit the applicability. The calculated symmetry numbers are in agreement with expected values for a large and diverse set of structures, ranging from asymmetric, small molecules such as fluorochlorobromomethane to highly symmetric structures found in drug discovery assays. The new algorithm opens up new possibilities for the fast screening of the degree of symmetry of large sets of molecules. © 2014 Wiley Periodicals, Inc.     

Development of models for prediction of the antioxidant activity of derivatives of natural compounds

Antioxidants are important for maintaining the appropriate balance between oxidizing and reducing species in the body and thus preventing oxidative stress. Many natural compounds are being screened for their possible antioxidant activity. It was found that a mushroom pigment Norbadione A, which is a pulvinic acid derivative, shows an antioxidant activity; the same was found for other pulvinic acid derivatives and structurally related coumarines. Based on the results of in vitro studies performed on these compounds as a part of this study quantitative structure–activity relationship (QSAR) predictive models were constructed using multiple linear regression, counter-propagation artificial neural networks and support vector regression (SVR). The models have been developed in accordance with current QSAR guidelines, including the assessment of the models applicability domains. A new approach for the graphical evaluation of the applicability domain for SVR models is suggested. The developed models show sufficient predictive abilities for the screening of virtual libraries for new potential antioxidants.     

La(Ⅲ)-乙醇溶液微团簇理论和光谱研究

利用分子光谱和基于密度泛函理论的第一性原理,采用改进的TPSSTPSS泛函方法对C、H、O原子用6-31G基组并添加极化和弥散函数,对La原子选用Def2-SV(P)赝势基组,研究La3+/乙醇溶液微团簇构型。优化计算La3+在水溶液中的溶剂化结构,得出气相中的优化结果可以近似代替液相结果的结论;理论优化计算La3+/乙醇溶液可能存在的结构构型的结果表明,溶剂化数n=6时结构最稳定。采用荧光光谱和核磁共振实验对结果进行了验证,表明La3+的加入使荧光强度显著增强,在高浓度时生成的团簇构型比较稳定,且随着溶剂化数目的增加,O—H键长增大,La3+使其附近的质子产生强大的屏蔽效应,化学位移向高场移动,溶剂化数n=6时绝对误差最小,最稳定,与理论计算结论相吻合。     

二种求算晶体平面间距d_(hkl)的数学方法

用数学方法推导出结构化学晶体学中晶面间距的一般通式,并在此基础上推导出其他晶系的晶面间距(d(hkl))的计算表达式。     

地方工科院校《功能高分子材料》课程教学内容的精选与实践

随着材料学的蓬勃发展,功能高分子材料的种类及用途日益繁多,因而《功能高分子材料》课程教学内容涵盖也不断延伸。针对地方工科院校高分子材料与工程专业人才培养的机制和目标,作者探索实践了如何以学生为本、以社会和行业的人才需求为导向,紧密联系地方经济与行业格局,因时因势对课程教学内容进行优化和完善。在此基础上,通过科学合理的教学实践,使学生既能牢固掌握功能高分子材料的基础知识,又能了解本领域最前沿的科学发展动态,拓宽学习思路,提高学习积极性,增强对专业的认可与对行业的期待。     

最近十年中国头发微量元素研究进展

2006—2015年,是中国头发微量元素研究继续取得重要成果的10年,也是该项研究量质转变的10年。概述了10年内中国头发微量元素研究的进展、现状和发展方向,高通量微量元素组学研究和微量微区分析技术的发展将引领头发微量元素研究领域走向新的高度。     

ZnO衍射花样180°不唯一性的消除

晶体电子衍射花样涉及到界面、位错等缺陷的晶体学性质测定时,需要设法消除180°不唯一性这一问题.应用Tecnai G~2 F20场发射透射电镜精密的倾斜样品台使晶体做有系统的倾转,观察衍射花样的变化并加以分析,从而消除了ZnO粉末单晶花样的180°不唯一性.     

六阶图Q与星图S_n的积图交叉数

目前关于积图的交叉数的研究已经推广到六阶图与星图的积图.研究得到了一个特殊六阶图Q与n个孤立点nK_1的联图交叉数,然后通过收缩的方法,得到了Q与星图S_n的积图交叉数.     

两个广义伽玛分布之间新的Kullback-Leibler距离

在Kullback-Leibler距离的基础上,对Kullback-Leibler距离进行改进,给出了新的Kullback-Leibler距离,并讨论了它的性质.计算了两个不同广义伽玛分布之间新的Kullback-Leibler距离.推导出伽玛分布、Weibull分布、Rayleigh分布、正态分布、指数分布新的Kullback-Leibler距离.另外在新的KullbackLeibler距离下,还得到digamma函数Ψ(x)=(Γ'(x)/(Γ(x))为单调递增函数.