Systematic search in conformational analysis

The coupling of conformation to activity and reactivity is a widely accepted concept, and as such has driven the development of tools which execute conformational searches in rapid and robust fashion [T.F. Havel, Prog. Biophys. Molec. Biol., 56 (1991) 43–78; A.R. Leach, In Rev. Comput. Chem.; K.B. Lipkowitz and D.B. Boyd, Ed.; VCH Publishers, Inc.: New York, N.Y., 1991, Vol. II, pp. 1–55]. Among the aims of these methods are the determination of a complete set of local minima from which the global energy minimum can be identified, or the generation of conformations consistent with constraints derived from SAR or structural studies. Most methods fall into two broad categories: those which are random or stochastic, and those which are systematic. Yet another group consists of those which are based on heuristics and artificial intelligence [A.R. Leach, K. Prout, D.P. Dolata, J. Comput. Chem. 11 (1990) 680–693]. The first category is typified by molecular dynamics [W.F. van Gunsteren and H.J.C. Berendsen, Angew. Chem. Int. Ed. Eng., 29 (1990) 992–1023], Monte Carlo [M.P. Alien and D.J. Tildesley, Computer Simulation of Liquids, Oxford Science Publications, 1989], distance geometry [J.M. Blaney and J.S. Dixon, in K.B. Lipkowitz and D.B. Boyd (Eds.), Reviews in Computational Chemistry, VCH, New York, Vol. 5, pp. 299–335, 1994], and other approaches [M. Saunders, J. Comput. Chem., 10 (1989) 203–208] in which the path by which conformational space is examined is ideally completely random, but bounded by the geometries of covalent bond lengths and angles. In traditional systematic searches, the variable to be examined, e.g. torsion angles, is divided into a regular grid. Each and every grid point is evaluated in a systematic fashion to determine its validity. The path through the grid points is regular and defined. In principle, systematic search can, within the resolution of the grid, identify all sterically allowed conformations of a molecule. Consequently, systematic search is an ideal tool for conformational analysis because it is not path dependent and cannot become entrapped in local minima. In this article we review some of the basics of systematic search, algorithmic improvements that have enhanced its speed, and new developments that have increased its accuracy by moving away from the limitations of a fixed torsional grid.     

FRACTAL STRUCTURE OF COLLOIDAL SILVER AND ITS EFFECTS ON SERS INTENSITIES OF CRYSTAL VIOLET

The surface-enhanced Raman spectra (SERS) of crystal violet on colloidal silver particles of different sizes and shapes were measured and the structural effect of the silver aggregates on the SEPS intensities was discussed in terms of fractal geometry. It is found that the SERS band intensities of crystal violet change significantly with the fractal dimension (D) of colloidal silver at 1.251.8.     

Clusters and Aggregates of 1,1′-Bis(diphenylphosphino)ferrocene (dppf)

The emerging interest of ferrocenyl diphosphines in metal complexes has led to some significant developments recently in the clusters, polymetallic aggregates and oligomers of 1,1-bis(diphenylphosphino)ferrocene (dppf). In this review, we shall focus on the synthetic strategies and the chemical, structural and bonding characteristics of these materials.     

Effect of Fluorination on Aggregate Structure of Perylene Diimide

The effect of fluorination on the aggregate structure of a novel fluorinated perylene diimide, N, N‘-diperfluorophenyl-3, 4, 9, 10-perylenetetracarboxylic diimide 1, was investigated by UV-Vis absorptions and the conformation simulations from AM1 semi-empirical quantum mechanics modeling. The results showed that in the solid film 1 molecules stacked with the perfluorinated phenyl groups straightly over or below the perylene cores of the adjacent 1 molecules.     

Self-assembled nanostructures of a biomimetic glycopolymer–polypeptide triblock copolymer

The self-assembling behavior of a biomimetic glycopolymer–polypeptide triblock copolymer in aqueous solution was described and characterized by employing the hydrophobic dye solubilization method and transmission electron microscopy. The large spherical micelles can be easily generated from the dissolution of triblock copolymer in water. The morphology changes from sphere to lamellae, then to worm-like micelle, can be conveniently transformed by initial copolymer concentration. The multivalent interaction of lectins with lactose-installed polymeric aggregates was preliminarily investigated by UV-Vis spectra. Notably, this kind of aggregates may be useful as artificial polyvalent ligands in the investigation of carbohydrate–protein recognition and for the design of site-specific drug delivery systems.     

4-[2-(9,10-二氰蒽)乙烯基]-N-甲基-N-十六烷基苯胺的合成及其吸收光谱行为的研究

通过还原、溴代、氰化、Wittig反应等七步反应设计合成了一新二元电子给体－受体（D－A）化合物：4－［2－（9，10－二氰蒽）乙烯基］－N－甲基－N－十六烷基苯胺（DCACMA，反式）并初步研究了其吸收光谱行为。研究表明，基态下DCACMA分子中电子给体与电子受体（CMA与DCA）间存在显著的电荷转移相互作用，在LB膜及簇集态（DMSO－H2O二元体系中）下，DCACMA分子呈H－型簇集排列。     

New aspects of the single phase aggregate model for oriented polymers

A reinvestigation of the single phase aggregate model (SPAM) of Ward applied to the elastic properties of uniaxially oriented polymers is presented. It is shown that the Voigt and the Reuss orientation average of elastic constants can be represented as a linear transformation in a 5-dimensional vector space. The corresponding transformation matrix can be diagonalized, showing that the eigenvalues of this transformation are the orientation parametersP ₀ =1,P ₂ andP ₄ . Taking advantage of this representation an easy test of applicability of the SPAM is proposed. Possibilities to evaluate the SPAM parameters are reviewed.     

水溶性β-环糊精聚合物和疏水改性聚丙烯酰胺的主客体相互作用

主体环糊精聚合物(β-CDE)与客体疏水改性丙烯酰胺共聚物P(AM/POEA)构成超分子结构的高分子识别体系. 这种客体聚合物是含有少量疏水体(x_POEA＜0.01)的水溶性聚合物, NMR测定结果表明β-CDE和P(AM/POEA)的主客体相互作用是通过环糊精空腔和疏水体POEA形成包结络合物进行的. 在P(AM/POEA)聚合物水溶液中加入β-CDE, 由于主客体聚合物相互作用出现粘度的大幅上升, 增粘的幅度可通过改变聚合物浓度和疏水体含量来调节, 同时对盐浓度和温度的影响也进行了研究. 通过透射电镜直观观察的结果表明, 此类缔合聚合物体系的主客体相互作用生成实心球状多分子聚集体.     

基于虚拟仿真实验教学平台的化工类专业应用创新型人才培养模式

分析了化工类专业实验教学面临的主要问题，指出专业综合实验缺乏是制约化工类专业应用创新型人才培养的关键问题。利用虚拟仿真实验教学的优势，按照"以设计研究型实验为引导、以工程项目为依托、以综合创新竞赛为载体"的教学理念，在构建化工专业虚拟仿真实验课程体系，培养学生大工程观思维，探索开放自主式的实验教学模式等方面，开展了基于虚拟仿真实验教学平台的化工类专业应用创新型人才培养的创新与实践，取得较好成效。