四氢键二聚体和分子组装

介绍了最近几年新的四氢键有机二聚体研究的进展及其在分子自组装和分子聚 集体化学研究中的应用。     

Kinetic study of nucleophilic reactivity of heterocyclic amines with 4,6-dinitrobenzofuroxan in acetonitrile

The reaction kinetics of 4,6-dinitrobenzofuroxan with five heterocyclic amines was investigated spectrophotometrically (UV–Vis) in acetonitrile at 20 °C. It was observed that the rate constants of these reactions increased as follows: 2-aminopyrimidine > 2-aminothiazole > 2-aminobenzothiazole > 5-amino-3,4-dimethylisoxazole > 2-amino-5-trifluoromethyl-1,3,4-thiadiazole. Further, second-order rate constants (k₁) pertaining to the C–N and C–C bond forming step of these complexation processes fit to the three parameter equation log k (20 °C) = s_N (N + E), allowing the determination of the nucleophilicity parameters (N) of the five heterocyclic amines. The heterocyclic amines were subsequently ranked on the comprehensive nucleophilicity scale defined by Mayr et al. (2003), providing a direct comparison of n-, π-, and σ-nucleophiles.     

Separation and Retention Behavior of Aromatic Carboxylic Acid Isomers by High‐Performance‐Liquid‐Chromatography Using β‐Cyclodextrin Bonded Phase with Diamine‐s‐Triazine Moiety

A β‐cyclodextrin (β‐CD) bonded phase with diamine‐s‐triazine moiety was prepared. The separation and retention behavior of the isomers of five aromatic carboxylic acids, including toluic acid, aminobenzoic acid, nitrobenzoic acid, hydroxybenzoic acid, and naphthoic acid were investigated by a high‐performance liquid chromatography (HPLC) using the β‐CD bonded phase prepared. The influence of mobile phase pH in the range of 2.7‐3.6 on the retention of these analytes was examined. The isomers of the aromatic carboxylic acids, with the exception of nitrobenzoic acid, were optimally and effectively separated at pH 2.7, while the three isomers of nitrobenzoic acid could be well separated at pH 3.3. Compared with the chromatographic results obtained previously on the amine‐s‐triazine‐β‐CD bonded phase, the retention factors of the isomers of aromatic carboxylic acid on the diamine‐s‐triazine‐β‐CD bonded phase increase to a relatively much greater extent. Thus, the functionality of the spacer arm of the bonded phase playing an important role in the retention of aromatic carboxylic acid isomers is demonstrated. The results also imply that the hydrogen‐bonding interaction and the mechanism of anion exchange sorption as well may contribute significantly to the retention mechanisms.     

Application of pharmacia automated FPLC System and PepRPC HR 5/5 bonded phase column for determination of dansylated polyamines

Summary The Pharmacia Automatized FPLC System equipped with a PepRPC HR 5/5 bonded-phase column was tested with dansyl polyamines, toluene, dimethyl- and dibutylphthalate, using either isocratic conditions or linear gradient-elution program of methanol in water as the mobile phase. A simple and reproducible method is described for the quantiation of dansylated natural polyamines, such as putrescine, spermidine and spermine originating from P388/S leukemia cells. Comparing the data from analyses performed in parallel by the Automated FPLC/PepRPC HR 5/5, and a Hewlett-Packard Model 1084B/LiChrosorb RP-8 systems a linear correlation has been found, with a regression coefficient of r=0.974.     

High-performance anion-exchange chromatography of carbohydrates using a new resin and pulsed amperometric detection

Summary This paper reports the results of a study on the use of a new polymer-based, strong anion-exchange, stationary phase for rapid and selective separation of carbohydrates and related compounds by high-pH, anion-exchange chromatography with pulsed amperometric detection. The new adsorbent has been obtained by direct nitration of 2.8 μm, spherical non-porous highly cross-linked, styrene-divinylbenzene copolymer beads, followed by reduction of superficially introduced nitro groups with nascent hydrogen and quaternization of the resultant amino groups with iodomethane. It is reported that by optimizing the ionic strength of the mobile phase, columns packed with the new anion-exchanger can be successfully employed to separate, either in isocratic or gradient elution mode, oligosaccharides, positional isomers of gluco-disaccharides, as well as uronic acids and sugar monophosphates.     

Characterization of immobilized catalases and their application in pasteurization of milk with H2O2

The catalase (fromAspergillus niger) has been immobilized by a chemical method on the pous SiO₂ modified with γ-aminopropyltrietoxysilane, followed with glutaraldehyde and by a physical method in alginate and γ-carrageenan gel. Optimum support:enzyme ratios and pH values were determined for modified SiO₂ in a series of immobilization reactions of catalase in the presence of the crosslinking agent glutaraldehyde, and for alginate and γ-carrageenan in the presence of hemoglobin and bovine serum albimine. pH and temperaturedependent activity variations and the stability properties of immobilized catalase preparations were investigated. Rate constants for H₂O₂ decomposition and catalase deactivation were determined. The decomposition rate of H₂O₂ used in the cold pasteurizatioan of milk were investigated in a discontinuous batch type reactor system. Activity half-lives of immobilized catalase were determined.     

Plastic deformation and performance of engineering polymer materials

The plastic deformation mechanism operating in polymer glasses is analyzed. The whole process consists of two main stages: nucleation of special shear defects, called PSTs (plastic shear transformations), and their disappearance. The important feature of plastic deformation of glasses is the storage of a large amount of internal energy ΔU_def upon straining. Such energy storage is the critical issue for mechanical performance of polymeric material: if the amount of stored energy is high, the appearance of macroscopic failure is very probable while glassy materials collecting a small amount of stored deformation energy are quite ductile. It is proposed that the rate of disappearance of PSTs is a key factor in dissipation of stored deformation energy. A parameter describing the dissipation ability of material upon deformation is introduced.     

2-氨基嘧啶在盐酸介质中对钢的缓蚀性能

用失重法、动电位极化曲线和电化学阻抗谱（EIS）研究了2-氨基嘧啶(2-AP)在1.0~5.0 mol/L HCl溶液中（20~50 ℃）对冷轧钢的缓蚀作用。 结果表明,2-AP对冷轧钢在1.0 mol/L HCl中具有良好的缓蚀作用,且在钢表面的吸附符合校正的Langmuir吸附模型;缓蚀率随缓蚀剂浓度的增加而增大,但随温度的升高和HCl浓度的增加而降低。 2-AP为混合抑制型缓蚀剂;EIS谱呈半圆容抗弧,电荷转移电阻随缓蚀剂浓度的增加而增大。     

芳香化合物在氰基键合填充柱上的电色谱保留行为

在３μｍ氰基键合固定相上实施毛细管电色谱,采用乙腈／Ｔｒｉｓ反相洗脱,在７５μｍｉ．ｄ．×２５ｃｍ的毛细管柱上分离了几种芳香化合物,并对其保留行为进行了研究。利用溶剂特征显色比较法对溶质的保留进行了预测。同时还研究了乙腈的比例对电渗流的影响。对于不保留的溶质,获得了小于２．０的折合塔板数。