HNCO与NH3,H2O和HF反应机理的理论化学研究

使用Gaussian 03软件，DFT密度泛函方法B3LYP和631 G(d，p)基组，研究和比较了异氰酸(HNCO)与NH3，H2O和HF分子的IRC反应路径，通过振动分析确认了过渡态的结构．计算结果表明3个反应都是放热反应，反应中1个σ键和1个π键断裂，2个新的σ键生成；过渡态最显著的特征是H原子的转移；过渡态是四元环结构，由于NH3，H2O和HF分子中N，O和F原子电负性的不同，四元环形状有比较明显的差异．     

HNCO与XCH2OH(X=CH3、NH2、OH、F)反应机理的理论研究

采用密度泛函(DFT)理论的B3LYP方法,在6-31 G(d,p)水平上按BERNY能量梯度解析全参数优化了HNCO和XCH2OH(X=CH3、NH2、OH、F)反应势能面上各驻点的几何构型,分别找到了这4个反应的过渡态,并通过振动频率分析确认了过渡态结构,通过内禀反应坐标(IRC)计算确认了最低能量反应途径(MEP).讨论了过渡态时的虚频振动模式,对各驻点进行了零点能(ZPE)校正,并计算了4个反应的活化能.研究结果表明,异氰酸的醇解反应是1个亲核加成反应,甲醇取代物和异氰酸分别是电子给体和电子受体,并且甲醇取代物的羟基氢在反应中发挥了重要作用;4个反应均为放热反应,反应中1个σ键和1个π键断裂,2个新的σ键生成;过渡态是四元环结构,由于CH3CH2OH、NH2CH2OH、OHCH2OH、FCH2OH分子中C、N、O、F原子电负性不同,四元环构型存在较明显的差异.     

布洛芬分子手性转变裸反应机理及水分子的催化作用——基于羰基和苯环作H迁移桥梁

采用基于密度泛函理论的B3LYP方法和微扰理论的MP2方法,研究了布洛芬分子手性转变裸反应和水助质子从手性碳向羰基迁移的机理。分子结构分析表明:水助质子从手性碳向羰基迁移过程的8元环过渡态b TS2·2H_2O和10元环过渡态b TS2·3H_2O对应的氢键键角都远大于6元环过渡态b TS2·1H_2O;过渡态b TS2·2H2O的8元环结构基本共面,过渡态a_TS1·3H_2O和b TS2·3H_2O的10元环结构明显偏离平面。反应路径研究发现:标题反应有6条路径,分别是质子只以羰基氧、以甲基碳和羰基O及以羧基和苯环联合作桥,从手性C的一侧迁移到另一侧。势能面计算表明:质子以羧基和苯环联合作桥迁移的路径为优势反应路径,裸反应的决速步吉布斯自由能垒为287.1 k J·mol~(-1),2个水分子构成的链使决速步的吉布斯自由能垒降为144.9 k J·mol~(-1)。结果表明:布洛芬分子的手性转变存在多条可能的路径,水分子对布洛芬分子的H迁移异构反应有明显的催化作用,生命体内水分子的存在、温度的涨落、分子的频繁碰撞和某种酶的作用等综合因素,是导致左旋布洛芬旋光异构的原因。     

次黄嘌呤氢迁移反应机理的理论研究

采用密度泛函理论方法,在B3 LYP/6-31 G**水平下研究了无水催化、水催化次黄嘌呤氢迁移反应的微观机理和势能曲线图.计算结果表明:(1)无水催化时次黄嘌呤经过四元环的过渡态,发生分子内氢迁移反应,实现烯醇式向酮式的转变;(2)1分子水催化次黄嘌呤氢迁移反应过渡态的结构为六元环;(3)2分子水催化次黄嘌呤氢迁移反...     

CH3SH与ClO反应机理的量子化学及电子密度拓扑研究

采用B3LYP方法和6-311G(d,p)基组找到了CH3SH与ClO反应的6个可能的反应通道,得到了各反应通道的反应物、中间体、过渡态和产物的优化构型.对反应过程中若干关键点进行了电子密度拓扑分析,讨论了反应过程中键的断裂、生成和化学键的变化规律.找到了该反应的"结构过渡态"和"结构过渡区",非平面四元环状结构过渡态的发现拓展了原来对环状结构过渡态的定义.     

2-氯吡啶光氯化取代反应机理的量子化学研究

用PM3方法研究了2-氯吡啶光氯化取代反应的过渡态.研究结果表明,生成2,6-二氯吡啶、2,5-二氯吡啶、2,4-二氯吡啶、2,3-二氯吡啶不同产物的每一个反应通道都存在两个过渡态;反应体系沿反应坐标的变化为反应物→反应物络合物→第1过渡态→中间体→第2过渡态→产物络合物→产物;第2过渡态为主过渡态,生成2,6-二氯吡啶反应路径主过渡态的能量及活化能最低,分别为-139612.06和135.39kJ/mol,反应优先生成2,6-二氯吡啶.生成二氯吡啶反应过程中吡啶环反应部位CCl键的形成主要与共轭双键断裂同步,而CH键的断裂主要与共轭双键的重新形成同步.     

甲氧基硫代膦酰二氯自身异构化应机理的理论研究

用量子化学从头计算方法在HF／6－31G水平上研究了甲基硫代磷酰二氯自身异构化反应的微观机理,优化得到了反应物,过渡态和产物的几何构型,经振动分析确证了过渡态的真实性,研究结果表明该异构化反应形成一个四元环过渡态而转变为产物,反应活化能为14.3kJ/mol,反应放热120.6kJ/mol,是一个易于进行的异构化反应。     

CH_3X键断裂电子转移反应的密度泛函理论研究

用密度泛函理论 (DFT)研究CH3 X的键断裂电子转移反应。从几种计算方法的结果比较中选出B3 LYP的DFT方法。随后用B3 LYP方法优化CH3 X的结构 ;计算CH3 X的键断裂电子转移反应的能量变化 ;找到了过渡态并进行了验证。     

甲酰胺热分解反应机理的理论探讨

对甲酰胺的热分解反应进行了精确理论研究,在CAS（6,6）／6－21G优化构型的基础上,用CASPT2法做了单点能量校准,推测反应有2种途径：反应I经三元环过渡态形成NH3和CO产物,反应II经四元环过渡态形成H2和HNCO产物,这2个反应为一对竞争反应,并且有B3LYP,MP2和HF方法进行了对比分析。     

丙酮光解离机制的理论研究——激发三重态位能面上的解离途径及乙酰基的热解离反应

用从头算自洽场分子轨道UHF方法,在3-21G基组上,研究了丙酮分子光解离为乙酰基(CH_3CO)和甲基(CH_3)的解离反应.计算是在(n,π＊)激发三重态势能面上.(n,π)激发三重态的丙酮分子途经一个C_1对称性的过渡态(T S1)生成一个(n,π＊)激发态的乙酰基和一个基态的甲基.该过程是断键和基团构象转化协同进行的单步反应.计算的垂直激发能和激发三重态位能面上的反应活化位垒分别为279.43和141.04kJ·mol~(-1).这些能量值与丙酮光解的实验条件相吻合.用相同的计算方法,进一步探讨了基态乙酰基分解为CH_3和CO分子的热解离反应.解离过程的过渡态(TS2)以σ键伸长为特征.该过程是一个断键在先,基团构象转化在后分开进行的单步反应.计算的活化位垒为56kJ·mol~(-1)与实验值(75kJ·mol~(-1))相接近.     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

<正>~~     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

英文诗歌中的喻类修辞

为了有助于提高英文爱好者的个人情操、文化素养和学习兴趣,以及专业人员对英语学习和研究进行多途径的探索,本文通过一些精选诗歌的引证和分析,着重论述了喻类修辞法在英文诗歌中的运用其及效果。     

Man Is Unable to Change the Miserable Life——Analysis of the Arrangement of Four Characters in The Glass Menagerie

Tennessee Williams is considered as one of the most important American playwrights since World War II.The Glass Menagerie is his first successful drama,which describes a tragic situation of family and means to say that Man is unable to change the miserable life,no matter whatever means he try,This essay focuses on the analysis of the arrangement of the four main characters:Laura.Amanda,Jim and Tom to reveal the theme.Laura is fragile.Amanda is brave.Jim is vital.Tom is sensible.And all of them develop and try the different means to struggle against life,but fail tragically.With the evidence,the paper comes to conclusion naturally that Man is unable to change the miserable life,and he dooms to fail.     

Characterization of root-nodulating bacteria on Retama raetam in arid Tunisian soils

The aim of this study is to investigate the diversity of Retama raetam root-nodule bacteria isolated from arid regions of Tunisia. Twelve isolates, chosen as representative for different 16S rRNA gene patterns, were characterized by 16S rRNA gene sequencing and phenotypic analysis. Isolates were assigned to Sinorhizobium, Rhizobium and Agrobacterium. Symbiotic properties of Sinorhizobium and Rhizobium isolates showed a large diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Strain RK 22 identified as Rhizobium was the most effective isolate.     

An Affordable Accurate Evaluation of the Binding Conformations Predicted by Molecular Docking Studies in Bio-System

正Recently,docking has been widely used to predict the binding-modes of protein-inhibitors,when the crystal complexes structure was absent.Most docking algorithms are able to generate a large number of probable conformations,it,however,is difficult to effectively evaluate these docking poses and identify the most reasonable bindingmode.In the present study,on the basis of the crystallographic data of human 3-hydroxy-3-methylglutaryl coenzyme     

WIMAX与WI-FI技术分析及联合组网

介绍了WiMAX与Wi-Fi两种无线宽带接入技术,并对两者之间的关系及相互之间的影响做了对比及分析,并对WiMAX的关键技术进行了详细说明,最后对两者的联合组网方式做了简单的探讨。