关于气相渗透法仪器常数问题——一个新模式

气相渗透法广泛用于测定齐聚物和低分子量聚合物的数均分子量(M_n)。分析文献数据和本文的实验证明,仪器常数K值随溶质的分子量而变化。本文提出了一种新的说明 VPO法 K值依赖于溶质分子量的模式,根据此模式,可清楚地说明这种依赖关系。     

A novel synthetic route to 2-alkylpropane-1,3-sultones and its application to the synthesis of 2-alkyl derivatives of tramiprosate

A practical synthetic route to various 2-alkylpropane-1,3-sultones, the key intermediates for the preparation of 2-substituted homotaurines as analogs of tramiprosate, was developed.     

1,3,2—氧氮磷杂环戊烷衍生物晶体结构研究

用X射线衍射方法测定了两个1,3,2-氧氮磷杂环戊烷衍生物的晶体结构:2-二乙氨基-3-(4′-甲基苯甲酰基)-2-硫代-1,3,2-氧氮磷杂环戊烷,C_(14)H_(21)N_2O_2PS(1),空间群为P_(bco),α=0.9057(5)nm,b=1.3974(6)nm,c=2.5130(7)nm,Z=8,R=0.051;2-二乙氨基-3-(2′,4′-二氯苯甲酰基)-2-硫代-1,3,2-氧氮磷杂环戊烷,C_(13)H_(17)N_2O_2PSCl_2(2),空间群P2_1/c,α=0.7375(1)nm,b=1.4370(3)nm,c=1.6015(7)nm,β=93.70(2)°,Z=4,R=0.054。结构均由直接法解出。两个化合物中氧氮磷杂五元环均为半椅式构象。其中P—N键长环内分别为0.1712(2)nm和0.1723(0)nn;环外为0.1620(3)nm和0.1620(0)nm,由于成环作用所致环内P—N键长大于环外的。     

Mechanical properties of SBR-networks: I. Determination of crosslink densities by stress-strain-measurements

The tube model is applied for the treatment of stress-strain measurements on SBR networks. It is shown that this theory allows the separation of crosslink and constraint contributions to the stress-strain behavior and, also, a reliable determination of crosslink densities. The consideration of dynamical contributions is discussed and a special numerical method is developed.     

聚苯乙烯邻氨基苯甲酸负载钯催化剂的加氢性能研究

含有双配位基的聚苯乙烯邻氨基苯甲酸与钯络合物反应制得螫合的配位高分子钯催化剂。用甲醇-水(pH=12)还原可得晶粒分布均匀的胶态钯催化剂,它们对烯烃的加氢具有良好的催化作用。研究表明,钯络合物上原有配体的给予性常数(E_n)与负载后络合催化剂的加氢活性具有良好的线性关系,金属粒径为40—50A的催化剂对己烯-1的加氢活性最高。本文还研究了溶剂极性,载体孔结构及底物对催化剂活性的影响。     

水介质中N-芳基-N'-(2-苯并呋喃甲酰基)硫脲及1-芳甲酰基-4-(2'-苯并呋喃甲酰基)氨基硫脲的合成

苄基三乙基氯化铵(TEBA)存在的水介质中, 2-苯并呋喃甲酰氯、硫氰酸铵与芳胺或芳甲酰肼在室温条件下经一步反应合成N-芳基-N'-(2-苯并呋喃甲酰基)硫脲或1-芳甲酰基-4-(2'-苯并呋喃甲酰基)氨基硫脲, 其中前者尚未见文献报道. 与其它合成方法相比, 该法操作简单、反应条件温和、环境友好.     

桥联双β-环糊精对N-[4-(1-芘基)]丁酰-D/L-苯丙氨酸的手性识别及机理研究

利用紫外-可见吸收和荧光发射光谱, 结合非线性最小二乘法拟合曲线以及分子力学(MM2)模拟系统地研究了手性分子N-[4-(1-芘基)]丁酰-D/L-苯丙氨酸(PDP和PLP, 总称PPs)与β-环糊精(β-CD)、 2-位硒桥联双β-CD(2-SeCD)和2-位碲桥联双β-CD(2-TeCD)的包结能力大小及这3个环糊精对PPs手性识别能力的差异和识别机理. 研究结果表明, PPs不能与单疏水空腔的β-CD形成很好的包结复合物, 与具有较长桥联链的2-TeCD结合能力最强. 2-TeCD与PDP和PLP的结合常数分别为2.33×104和6.07×103 L/mol, 对PPs的手性识别比达到KD/KL=3.84, 高于2-SeCD(KD/KL=2.61). 用MM2模拟得出了PPs与这两个双环糊精形成复合物的三维结构: PPs的绝大部分位于双环糊精两个空腔之间, 但是在这两个复合物中, 苯环与芘环所成的二面角不同. 此外, PPs与这两个双环糊精作用时均存在明显的氢键相互作用, 且2-TeCD强于2-SeCD.     

Consequences of sample size, variable selection, and model validation and optimisation, for predicting classification ability from analytical data

This article discusses problems of validating classification models especially in datasets where sample sizes are small and the number of variables is large. It describes the use of percentage correctly classified (%CC) as an indicator for success of a classification model. For small datasets, %CC should not be used uncritically and its interpretation depends on sample size. It illustrates the use of a common classification method, discriminant partial least squares (D-PLS) on a randomly generated dataset of 200 samples and 200 variables.

An aim of the classifier is to determine whether the null hypothesis (there is no distinction between two classes) can be rejected. Autoprediction gives an 84.5% CC. It is shown that, if there is variable selection, it must be performed independently on the training set to obtain a CC close to 50% on the test set; otherwise, over-optimistic and false conclusions can be reached about the ability to classify samples into groups.

Finally, two aims of determining the quality of a model are frequently confused, namely optimisation (often used to determine the most appropriate number of components in a model) and independent validation; to overcome this, the data should be split into three groups.

There are often difficulties with model building if validation and optimisation have been done on different groups of samples, especially using iterative methods, each group being modelled using properties, such as a different number of components or different variables.     

Intermediates in the transformation of 1,2-dialkylpyrimidinium iodides in the Kost-Sagitullin rearrangement

Intermediate recyclization products were obtained in a study of the Kost-Sagitullin rearrangement of a series of 1,2-dialkylpyrimidinium iodides. The initial attack of the nucleophile leads to the formation of products of the addition of the hydroxyl group, namely, the corresponding pseudo bases. Heating one of these intermediates in ethanol or in the presence of primary amines leads to rearrangement to give a pyridone derivative. Upon heating in chloroform, the pseudo bases readily lose a water molecule and are converted to anhydro bases, namely, derivatives of 1-alkyl-1,2-dihydro-2-methylidenepyrimidine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 894–900, May, 2006.     

Adsorption of the fluoride ion on the surface of various faces of a single crystal of silver: a quantum-chemical study

The fluoride ion adsorption from a gas phase on various faces of a single crystal of silver is studied by a density functional method within a cluster model for metal. The adsorption bond energy is found to increase in the series Ag(100) < Ag(111) < Ag(311) < Ag(110). A substantial structural and energetic heterogeneity of various adsorption sites is revealed. The results are utilized to simulate the electrochemical interface between individual faces of a single crystal of silver and aqueous solutions containing the fluoride ion. It is assumed that the adsorption potential may be represented as the sum of two contributions, one of which describes the metal–ion interaction and the other, the ion solvation energy. The plotted adsorption terms take into account partial degradation of the fluoride ion when adsorbed from an aqueous solution. Estimates of discreteness of the electrical double layer are presented. A conclusion on the maximum manifestation of specific adsorption of the fluoride ion for the Ag(100) face is made.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 232–238.Original Russian Text Copyright © 2005 by Nazmutdinov, Zinkicheva.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.