华根霉脂肪酶有机相酯合成活性的重塑

研究了具有较高酯合成活性的华根霉膜相关脂肪酶及其沉淀酶蛋白的重折叠处理过程, 发现膜成分及表面活性剂可能是影响其活性的关键因素. 进一步考察了影响异源表达的可溶性华根霉脂肪酶r27RCL酯合成活性重塑的关键因子及作用阶段. 研究结果表明, 表面活性剂对脂肪酶的酯合成活性具有关键影响, 直接添加表面活性剂可使酯合成活性显著提高. 在7种不同表面活性剂中, 两性离子表面活性剂LPC14将r27RCL的酯合成活性提高了5.75倍. 分子动力学模拟结果表明, 在有机相反应中, 表面活性剂的添加使脂肪酶催化三联体之间的氢键作用力得到加强, 从而提高了脂肪酶的有机相酯合成能力.     

Structure and Bonding in Cyclic Sulfur-Nitrogen Compounds—Molecular Orbital Considerations

The molecular structures of monocyclic sulfur-nitrogen ring systems, such as S₂N₂, S₃N, S₄N and S₅N, can be considered as examples of electron rich (4n + 2)π systems. The structures of S₄N₄, S₄N, P₄S₄, As₄S₄ and the bicyclic structures S₄N, S₄N as well as S₅N₆ can be rationalized on the basis of a planar tetrasulfur tetranitride with 12π electrons.     

Monitoring the Hydrolysis of Olive Oil Catalyzed by Lipase via Acid Value Detection

IntroductionThe lipase-catalyzed hydrolysis of oils is widelyused for the preparation of glycerides and fatty acidsbecause of the substrate specificity of lipase[1—3]. Thereaction is carried out under mild conditions.Candidalipolyticalipase is a nonspeci…     

Cross‐Linked Micelles with Enzyme‐Like Active Sites for Biomimetic Hydrolysis of Activated Esters

Enzymes have substrate‐tailored active sites with optimized molecular recognition and catalytic features. Although many different platforms have been used by chemists to construct enzyme mimics, it is challenging to tune the structure of their active sites systematically. By molecularly imprinting template molecules within doubly cross‐linked micelles, we created protein‐sized nanoparticles with catalytically functionalized binding sites. These enzyme mimics accelerated the hydrolysis of activated esters thousands of times over the background reaction, whereas the analogous catalytic group (a nucleophilic pyridyl derivative) was completely inactive in bulk solution under the same conditions. The template molecules directly controlled the size and shape of the active site and modulated the resulting catalyst's performance at different pHs. The synthetic catalysts displayed Michaelis–Menten enzymatic behavior and, interestingly, reversed the intrinsic reactivity of the activated esters during the hydrolysis.     

EHMO方法的分子轨道定域化

用Foster-Boys的定域化准则讨论了EHMO方法的分子轨道定域化问题,提出用双中心重叠积分近似计算双中心轨道偶极矩积分方法,得到的EHMO定域分子轨道与严格定域化结果接近,与从头计算方法的定域化结果定性一致。     

Studies of the Rate Constant of Levodopa Methyl Ester Hydrolysis by LC

This paper investigates the hydrolysis kinetics of levodopa methyl ester in 0.05–1.5 M HCl between 37 and 75°C. An isocratic HPLC assay was developed for simultaneous determination of levodopa methyl ester and levodopa in the hydrolysate of levodopa methyl ester. A series of hydrolysis rate constants were obtained and the effects of hydrogen ion concentration and temperature on the reaction were evaluated. It was found that pH was a key factor at low temperature, but that when the temperature was raised, temperature became in turn the most influent factor on the hydrolysis. From the measured pseudo-first order reaction rate constants, the activation energy for levodopa methyl ester hydrolysis in 0.5, 1.0 and 1.5 M HCl were calculated to be 71.24, 74.32 and 76.57 kJ mol⁻¹, respectively. Revised: 24 May and 15 August 2005     

简单Hückel分子轨道理论判断H4分子及离子的几何构型

简单Hückel分子轨道理论是结构化学课程内容的主要知识点之一,主要用于计算π电子成平面分布的离域体系的电子结构和轨道能量。本文把该理论推广到H_4非离域体系,定性地计算H_4非离域体系的轨道能量,帮助学生理解Walsh规则应用举例中难以理解的H_4构型为直线型,但H_4~+为四面体构型的原因。     

Theoretical Definition of a Functional Group and the Molecular Orbital Paradigm

It is the purpose of this review to demonstrate that the empirical classification of the observations of chemistry in terms of the properties assigned to functional groups is a consequence of and is predicted by physics. This is accomplished by showing that the atoms and functional groups of chemistry can be identified with bounded space-filling objects whose properties are defined by quantum mechanics. The quantum mechanical definition of a group is combined with a new pictorial representation of its form to obtain a unified picture which should make it eminently recognizable to chemists. This picture, when combined with the demonstrated ability of these groups to recover the measured properties of atoms in molecules, is offered as one which meets the expectations a chemist associates with the concept of a functional group. The manner in which this physical definition of a group differs fundamentally from models of functional groups based upon molecular orbital theory is discussed.     

计算化学在分子轨道教学中的应用

分子轨道理论是理解分子电子结构与微观性质的重要理论之一,也是本科生与研究生结构化学教学中的重点与难点。学生对原子轨道组合形成分子轨道、分子轨道能级交叉混合等知识的理解缺乏形象直观、定量的认识。本文通过基于量子化学或密度泛函理论的Gaussian 03计算软件,计算、绘制并分析了F_2、O_2、N_2、HF、CO等的分子轨道能级图,将学生较难理解的内容定量、直观地呈现出来,形象地解释了分子轨道成键原则与电子填充原则等分子轨道理论中的重难点,加深了学生对分子轨道理论的理解,特别是sp轨道混杂导致的σ_(2p_z)与π_(2p)轨道能级交叉这一难点,激发了学生学习的主动性和积极性,提高了教学质量。在此基础上,利用分子轨道理论分析了CO_2的电子结构,使学生学会应用分子轨道理论解决实际问题,巩固了相关课堂理论知识。     

磷酸镁铝分子筛的交换与催化性能研究

用红外与程序升温脱附氨法考察了磷酸镁铝分子筛的酸性,测定了94℃时Ni~(2+)与其进行离子交换的等温线,并在不同温度考察交换上Ni~(2+)后分子筛的催化加氢、裂解活性。     

Comment on “Symbolic Calculation of Two‐Center Overlap Integrals Over Slater‐type Orbitals”

Published by Gümü?. and Özdo?an formulas for the evaluation of two‐center overlap integrals (Gümü?, S.; Özdo?an, T. J. Chin. Chem. Soc. 2004, 51, 243) are critically analyzed. It is demonstrated that the formulas presented in this work are not original and they can easily be derived from the relationships contained in our papers (Guseinov, I. I. J. Phys. B 1970 , 3, 1399; Phys. Rev. A 1985 , 32, 1864; J. Mol Struct. (Theochem) 1995 , 336, 17) by changing the summation indices and application of a simple algebra. It should be noted that the symbolic results of overlap integrals between different combinations of quantum numbers given in Table 1 and 2 can also be obtained from the use of established in above mentioned our papers general formulas or presented in the literature relations for overlap integrals in terms of the products of molecular auxiliary functions A_n(p) and B_n(pt) (see, e.g., Lofthus, A. Mol. Phys. 1962 , 5, 105).     

超临界水中醋酸锌水解反应的分子动力学模拟

氧化锌(ZnO)是一种重要的化工原料, 超临界水热合成法制备纳米ZnO的第一步是锌盐与碱或水发生水解反应生成Zn(OH)₂, 后者接着脱水生成ZnO. 以Zn(CH₃COO)₂为原料, 直接和超临界水(SCW)反应能够制备纳米级的ZnO颗粒, 但对反应机理的探讨较少. 本研究利用分子动力学模拟超临界条件下Zn(CH₃COO)₂水解反应过程中的结构和能量变化, 发现Zn(CH₃COO)₂在SCW中容易聚集成无定形的团簇, 1个Zn²⁺平均和5个CH₃COO^-和1个H₂O配位, 形成6配位的八面体结构. 处于Zn(CH₃COO)₂团簇和SCW界面的Zn²⁺能够和更多的H₂O配位. 水解反应后系统的势能降低, 同时伴随Zn(CH₃COO)₂团簇结构的改变. 反应产物OH^-分布在Zn(CH₃COO)₂团簇内部, 富集Zn²⁺, 而CH₃COOH则分布在SCW中. 本文的工作为超临界水热合成的反应过程提供了基本的理论依据.     

A Highly Efficient UV‐C Absorber Based on Theoretical and Experimental Studies

Based on two published UV absorbing molecules 2‐(5′‐tert‐butyl‐2′‐hydroxyl)benzotriazole (Tinuvin‐PS ) and hydroxybenzophenone (HBP ), both having characteristic absorption capability, a refined UV absorber, 2‐(3′‐benzoyl‐2′‐hydroxy‐5′‐tert‐butylphenyl)benzotriazole, has been synthesized. This new UV absorber exhibits a wider absorption range and better thermal stability compared to either Tinuvin‐PS and HBP and a higher absorption efficiency in the UV ‐C range. Theoretical studies reveal that the UV ‐C absorption arises from the electron density transfer from the Tinuvin‐PS moiety to the HBP moiety and the enhanced absorption efficiency is ascribed to the presence of the carbonyl's π system.     

An Enzymatic N‐Acylation Step Enables the Biocatalytic Synthesis of Unnatural Sialosides

Chitin is one of the most abundant and cheaply available biopolymers in Nature. Chitin has become a valuable starting material for many biotechnological products through manipulation of its N‐acetyl functionality, which can be cleaved under mild conditions using the enzyme family of de‐N‐acetylases. However, the chemoselective enzymatic re‐acylation of glucosamine derivatives, which can introduce new stable functionalities into chitin derivatives, is much less explored. Herein we describe an acylase (CmCDA from Cyclobacterium marinum) that catalyzes the N‐acylation of glycosamine with a range of carboxylic acids under physiological reaction conditions. This biocatalyst closes an important gap in allowing the conversion of chitin into complex glycosides, such as C5‐modified sialosides, through the use of highly selective enzyme cascades.     

Kinetics and Protein‐Inhibitor Docking Studies of Enantiomers of exo‐2‐Norbornyl‐N‐n‐butylcarbamates as Pseudomonas Lipase Inhibitors to Probe the Enantioselectivity of the Enzyme

The Pseudomonas species lipase inhibition shows enantioselectivity for R‐enantiomer over S‐enantiomer of exo‐2‐norbornyl‐N‐n‐butylcarbamates. R‐, S‐, and racemic‐exo‐2‐norbornyl‐N‐n‐butylcarbamates are all characterized as pseudo substrate inhibitors of the enzyme. Thus, the mechanism for Pseudomonas species lipase‐catalyzed hydrolysis of the inhibitor is formation of the first enzyme‐inhibitor Michaelis complex via nucleophilic attack of the active site serine to the inhibitor (K_i step) then formation of the butylcarbamyl enzyme intermediate from this complex (k₂ step). Comparison of bimolecular rate constants (k_i = k₂ / K_i) of the inhibitors indicates that R‐enantiomer is 1.8 times more potent than S‐enantiomer. Thus, Pseudomonas species lipase shows enantioselectivity of 1.8 for R‐exo‐2‐norbornyl‐N‐n‐butyl‐carbamate over S‐exo‐2‐norbornyl‐N‐n‐butylcarbamate. Protein‐ligand interaction studies on both enantiomers of exo‐2‐norbornyl‐N‐n‐butylcarbamate as inhibitors of Pseudomonas species lipase using AutoDock suggest that R‐enantiomer binds more tightly into the active site of the enzyme than S‐enantiomer. The norbornyl ring of S‐exo‐2‐norbornyl‐N‐n‐butylcarbamate is repulsive to Ser 82 and His 251 of the catalytic triad as well as to Met 16 of the oxyanion hole. These repulsions may create few unfavorable interactions between S‐exo‐2‐norbornyl‐N‐n‐butylcarbamate and the enzyme and make this inhibitor a less potent one.     

Influence of Microwave Irradiation on the Lipase‐Catalyzed Ring‐Opening Polymerization of ε‐Caprolactone

Summary: The microwave (MW)‐assisted lipase‐catalyzed ring‐opening polymerization of ε‐caprolactone in boiling solvents was investigated for the first time. In case of boiling toluene or benzene the MW‐assisted reaction proceeded significantly slower compared to oil bath heating. On the other hand, using boiling diethyl ether as solvent, an increase of the polymerization rate due to MW irradiation was found. Yield, molecular weight measurements, and MALDI‐TOF analysis supported the results.

Reactivity of the MW‐assisted ring‐opening polymerization of ε‐caprolactone compared with conventional thermal heating in different solvents.     

S‐endo‐2‐Norbornyl‐N‐n‐butylcarbamate as a Potential Pseudomonas Lipase Inhibitor to Probe the Enantioselectivity of the Enzyme by Kinetic and Molecular Docking Evaluation

Obesity is a complex health issue and it can cause many health and social problems. Previous studies reported that lipase is a main target for obesity treatment. We synthesized R‐exo‐2‐norbornyl‐N‐n‐butylcarbamate and S‐exo‐2‐norbornyl‐N‐n‐butylcarbamate as potential pseudomonas lipase inhibitors to probe the enantioselectivity of the enzyme and demonstrated that R‐exo‐2‐norbornyl‐N‐n‐butylcarbamate had better enzyme enantioselectivity, ki and the docking model with Pseudomonas species lipase in our previous studies. In this article, we reported the property of the Pseudomonas species lipase inhibitors, R‐and S‐endo‐2‐norbornyl‐N‐n‐butylcarbamate and compared the docking models of these two compounds with R‐ and S‐exo‐2‐norbornyl‐N‐n‐butylcarbamates by AutoDock. We found that S‐endo‐2‐norbornyl‐N‐n‐butylcarbamate has the best enantioselectivity, ki and docking model and this study could provide useful information about enzyme enantioselectivity for the development of Pseudomonas species lipase inhibitors for obesity treatment.