Computational study of conformational preferences of thioamide-containing azaglycine peptides

The effect of thioamide substitution on the conformational stability of an azaglycine-containing peptide, For-AzaGly-NH2 (1), was investigated for the sake of finding possible applications by using ab initio and DFT methods. As model compounds, For-[psiCSNH]-AzaGly-NH2 (2), For-AzaGly-[psiCSNH]-NH2 (3), and For-[psiCSNH]-AzaGly-[psiCSNH]-NH2 (4) were used. Two-dimensional phi-psi potential energy surfaces (PESs) for 2-4 were calculated at the B3LYP/6-31G*//HF/6-31G* level in gas (epsilon = 1.0) and in water (epsilon = 78.4) by applying the isodensity polarizable continuum model (IPCM) method. On the basis of these PESs, the minimum energy conformations for 2-4 were characterized at the B3LYP level with 6-31G*, 6-311G**, and 6-31+G** basis sets. The remarkable structural effect of thioamide substitution for 2-4 is that beta-strand structure is observed as a global or local minimum. The minima of 2-4 are also compared with those for glycine and thioamide-containing glycine peptides. Our theoretical results demonstrate that compounds 2-4 would be used to design controllable secondary structures.     

Molecular Replacement Studies of Cucurmosin from Cucurbita Moschata:Structure Homology with Trichosanthin

1 INTRODUCTION Many plants contain proteins that are capable of inactivating ribosomes and therefore are called ribosome-inactivating proteins or RIPs[1]. RIPs are RNA N-glycosidases that inactivate ribosomes through a site-specific deadenylation of the large ribosomal RNA[2, 3]. RIPs are also capable of inactivating many nonribosomal nucleic acid substrates and can be considered as polynucleotide: adenosine glycosidases[4～6]. There are two types of RIPs: type I, single chain pr…     

铝与溴代二甲氨基苯基荧光酮的多元配合物的光度研究

本文研究了在表面活性剂存在性，铝与溴代二甲氨基苯基荧光酮的显色反应。在弱酸性介质中，Ａｌ＾３＋ＢＤＭＡＦ－ＣＴＭＡＢ三元配合物在水浴加热至７０℃－８０℃时形成，其最大吸收波长为５７７ｎｍ，Ａｌ＾３＋：ＢＤＭＡＦ＝１：２，表观摩尔吸光系数为１．３４×１０＾５Ｌ．ｍｏｌ＾－１．ｃｍ＾－１，表观稳定常数为７．４×１０＾５。在ＰＨ９．５－１０．５的氨性缓冲介质中，Ａｌ＾３＋－Ｆ＾－－ＢＤＭＡＦ－非离子表面     

研磨法合成1,2,3,6-四氢嘧啶-2-酮衍生物

以NH₂SO₃H为催化剂, 室温无溶剂条件下, 研磨芳醛、β-酮酸酯和尿素合成了一系列1,2,3,6-四氢嘧啶-2-酮衍生物. 该方法具有反应条件温和、操作简便、环境友好、产率高等优点.     

信息型常见毒物质谱用户库的建立及其在毒物快速筛选上的应用研究

质谱定性是目前世界上最通用的定性分析方法之一,在法庭科学领域毒物分析实践中,质谱一直是对未知样品进行药毒物筛选检测的利器.     

催化动力学极谱法测定痕量钼

在稀Ｈ２ＳＯ４介质中，钼（Ⅵ）对硫酸联氨还原乙基橙的反应有强烈的催化作用。建立了催化动力学极谱法测定痕量钼的新体系，方法线性范围为２０－３００ｎｇ／ｍＬ，检出限为３．５４ｎｇ／ｍＬ。方法应用于尿中中钼的测定，结果满意。     

LnSrNiO4-λ系列复合氧化物的物化性质与对NO分解的催化性能

用柠檬酸络合法合成了Ｋ２ＮｉＦ４结构的ＬｎＳｒＮｉＯ４－λ（Ｌｎ＝Ｌａ，Ｐｒ，Ｎｄ，Ｓｍ，Ｇｄ）系列稀土取代类钙钛石型复合氧化物催化剂，对该系列催化剂的固态物理、化学性质及其对ＮＯ分解的催化性能进行研究。结果表明，该系列复合氧化物催化剂对ＮＯ分解活性都很高，在此基础上对该系列复合氧化物中稀土元素对ＮＯ分解反应的取代效应进行了探讨。     

异核配合物K_2[Co(Dipc)_2]·7H_2O的合成、性质、结构和热分解动力学研究(英文)

0IntroductionItiswellknownthatcobalt?candisplayvariouscoordinationpolyhedron,theusualcoordinationnum-bervaryingfromfourtosix,whilemanyreportsonthecrystalandmolecularstructureareofsimplecobalt?complex,relativelyfewcasesconcernheteronuclearcomplexes.Recently,somestructuresofheteronuclearcompoundscontainingpyridine-2,6-dicarboxylicacidhavebeendetermined犤1～4犦,becauseoftheirimportantroleincoordinationchemistry,catalyticreactions,magneticmaterialandbiologicalsystem.Wereporthereanovelstructureofco…     

On some variational approximations in two-dimensional classical lattice systems

A new derivation is presented of some variational approximations for classical lattice systems that belong to the class of cluster-variation methods, among them the well-known Bethe-Peierls and Kramers-Wannier approximations. The limiting behavior of a hierarchical sequence of cluster-variation approximations, the so-calledC hierarchy, is discussed. It is shown that this hierarchy provides a monotonically decreasing sequence of upper boundsf _n on the free energy per lattice sitef and thatf _n f asn . Our results are based on extension theorems for states given on subsets of the lattice, which might be of some independent interest, and on an application of transfer matrix concepts to the variational characterization of translation-invariant equilibrium states.