Preparation of l‐phenylalanine‐imprinted solid‐phase extraction sorbent by Pickering emulsion polymerization and the selective enrichment of l‐phenylalanine from human urine

A novel l‐ phenylalanine molecularly imprinted solid‐phase extraction sorbent was synthesized by the combination of Pickering emulsion polymerization and ion‐pair dummy template imprinting. Compared to other polymerization methods, the molecularly imprinted polymers thus prepared exhibit a high specific surface, large pore diameter, and appropriate particle size. The key parameters for solid‐phase extraction were optimized, and the result indicated that the molecularly imprinted polymer thus prepared exhibits a good recovery of 98.9% for l‐ phenylalanine. Under the optimized conditions of the procedure, an analytical method for l‐ phenylalanine was well established. By comparing the performance of the molecularly imprinted polymer and a commercial reverse‐phase silica gel, the obtained molecularly imprinted polymer as an solid‐phase extraction sorbent is more suitable, exhibiting high precision (relative standard deviation 3.2%, n = 4) and a low limit of detection (60.0 ± 1.9 nmol·L^?1) for the isolation of l‐ phenylalanine. Based on these results, the combination of the Pickering emulsion polymerization and ion‐pair dummy template imprinting is effective for preparing selective solid‐phase extraction sorbents for the separation of amino acids and organic acids from complex biological samples.     

分子链大尺度高取向而小尺度接近无规取向态的非晶态聚对苯二甲酸乙二酯膜片

对非晶态聚对苯二甲酸乙二酯膜片经在Ｔｇ以上单轴拉伸然后淬冷至室温的试样，其物理性质的各向同性或各向异性进行了研究．实验结果说明这种分子链大尺度高度取向而小尺度接近无规取向的非晶态（ＧＯＬＲ态）其折光指数和小形变的拉伸模量是接近各向同性的，而热导率和微波介电常数很可能是各向异性的．     

Effect of solution concentration on the gelation of aqueous polyvinyl alcohol solution

The concentration dependence of cryogenic gelation for aqueous solution of poly(vinyl alcohol) was studied by measuring the apparent gel fraction G and the swelling ratio Q of the gel formed by freezing and thawing. It was found that for the gelation process there were three distinct regions of solution concentration bounded by two concentrations C_gel and C. The gel started to form at C = C_gel, while no visible gel could be detected even upon repeated freezing and thawing of the extremely dilute solutions of C < C_gel. The entire solution was gelatinized as a whole in the high concentration region of C > C. In the intermediate concentration region, C_gel < C < C, which covers three orders of magnitude in concentration, gel and sol phases coexist. Both concentration dependencies of G and Q show two branches jointed at a concentration very close to the overlap concentration C^*. The curve of G?Q versus C shows a sharp cusp. In case the sharp cusp concentration is really the value of C^*, gelation offers a precise method to determine the overlap concentration. ©1995 John Wiley & Sons, Inc.     

Preparation of “dummy” l‐phenylalanine molecularly imprinted microspheres by using ionic liquid as a template and functional monomer

In this study, dummy imprinting technology was employed for the preparation of l‐ phenylalanine‐imprinted microspheres. Ionic liquids were utilized as both a “dummy” template and functional monomer, and 4‐vinylpyridine and ethylene glycol dimethacrylate were used as the assistant monomer and cross‐linker, respectively, for preparing a surface‐imprinted polymer on poly(divinylbenzene) microspheres. By the results obtained by theoretical investigation, the interaction between the template and monomer complex was improved as compared with that between the template and the traditional l‐ phenylalanine‐imprinted polymer. The batch experiments indicated that the imprinting factor reached 2.5. Scatchard analysis demonstrated that the obtained “dummy” molecularly imprinted microspheres exhibited an affinity of 77.4 M·10^?4, significantly higher that of a traditional polymer directly prepared by l‐ phenylalanine, which is in agreement with theoretical results. Competitive adsorption experiments also showed that the molecularly imprinted polymer with the dummy template effectively isolated l‐ phenylalanine from l‐ histidine and l‐ tryptophan with separation factors of 5.68 and 2.68, respectively. All these results demonstrated that the polymerizable ionic liquid as the dummy template could enhance the affinity and selectivity of molecularly imprinted polymer, thereby promoting the development of imprinting technology for biomolecules.     

Recent advances in the observation of disclinations of main-chain nematic polymers

Experimental observation of disclinations of main-chain nematic polymers is reviewed. The geometry of disclination structure is discussed both from observations of schlieren texture and the theory of curvature elasticity for a two-dimensional case with equal splay and bend moduli. The effects of non-equal elastic moduli, the nature of the disclination core and the observation of inversion wails are briefly mentioned. Examples of experimental observation of disclinations of high topological strengths up to S=4 are given. The main experimental methods to map the director field around disclinations are 1) lamellar decoration, 2) band-texture decoration and 3) surface microcrack decoration. The methods are discussed and compared, and examples illustrated by electron micrographs or photomicrographs are presented.     

Viscometric investigation of intramolecular hydrogen bonding cohesional entanglement in extremely dilute aqueous solution of poly vinyl alcohol

An investigation of influence of cryogenic treatment on extremely dilute aqueous solution of poly(vinyl alcohol) (PVA) was performed by viscometry. The solution was frozen in liquid nitrogen or in a freezer at −25°C, then thawed at ambient temperature and concentrated by evacuation. The viscosity of the solution was measured using the dilute method. The experimental results indicated that the viscosity of the solution is related to N, the times of the freezing and thawing cycle, and the temperature for freezing. Undergoing a treatment of freezing and thawing, the viscosity of the solution is decreased, while it can be recovered the value of before the treatment as the solution had been heated at a high temperature. Thus, a conclusion may be obtained; that is, for an extremely dilute aqueous solution of PVA, which concentration is below C_gel, threshold concentration for gelation, an intramolecular hydrogen bonding cohesional entanglement can be formed by freezing as N < 5. However, in the case of N > 5, it not only formed an intramolecular hydrogen bonding but also produced an intermolecular hydrogen bonding. At the same time, the abnormal behavior of reduced viscosity of the solution in extremely dilute concentration region has been explained. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2421–2427, 1997     

柔性链高聚物的单分子链玻璃体和单晶*

本文综述了高分子单链颗粒的制备方法, 包括极稀溶液喷雾法、表面扩张膜法、冷冻干燥法、微乳液聚合法等。介绍和讨论了单链和寡链聚苯乙烯玻璃体微球的性质以及聚环氧乙烷、全同立构聚苯乙烯、顺-1, 4-聚丁二稀、反-1, 4-聚异戊二烯单链单晶电子显微镜和选区电子衍射观察的最新结果。     

不同催化体系制得的聚乙炔的空气稳定性

众所周知,聚乙炔(PA)用电子给体或受体掺杂可成为P-或n-型半导体,甚至变为金属,因而引起人们的巨大兴趣。然而由于PA含有大量共扼双键,所以不管是掺杂前还是掺杂后,都不甚稳定,从而使其在实际应用中带来一定的困难。