Differential staining of polyanions according to critical electrolyte concentration principles in mixed solvents

Three types of cationic reagent—cellulosic anion exchangers, cationic phthalocyanin dyes and detergents—formed insoluble complexes with the polyanions heparin, chondroitin-4-sulphate, hyaluronate, alginate and DNA. Dissociation of their complexes by MgCl₂ was a critical phenomenon, occurring at a sharply defined concentration, the critical electrolyte concentration (CEC), in water and in water-organic-solvent mixtures. CECs of polysulphates were always higher than those of polycarboxylates or polyphosphates, especially in the presence of dimethyl sulphoxide or ethanol. The latter effect should improve biochemical fractionations and differential histochemical staining of polyanions. A general theoretical framework is proposed. Complex formation is promoted by electrostatic attractions, and results in a loss of polymer mixing energy. Electrolytes suppress the electrostatic interaction, thus preventing complex formation. More efficient suppression of the electrostatic interaction is required in a ‘worsening’ solvent, i.e. where a rise in CEC occurs. Plots of CEC against solvent composition are interpreted on these bases. Available data on electrolyte solutions account for specific ionic effects. The dissociation of phthalocyanin dye micelles in aqueous dimethyl sulphoxide, etc, was studied spectroscopically. The results support and extend the conclusions derived from the insoluble anion-exchange celluloses. The general concepts serve as a bridge between biochemical and histochemical fractionations (i.e. specific staining of substrates).     

固定化纤维素酶及其在食品中的应用研究

固定化纤维素酶因其良好的稳定性和可重复使用性在许多领域得到广泛的应用,因此也成为广大科学工作者的研究热点之一。文章介绍了固定化纤维素酶的定义、研究现状、常用载体及其在食品工业中的应用,并指出了固定化纤维素酶发展方向,旨在为今后的深入研究提供理论指导。     

A Comparative Study of Commercial Modified Celluloses as Bread Making Additives

The effect of commercial modified celluloses: microcrystalline cellulose, carboxymethyl cellulose, and hydroxypropylmethyl cellulose on bread quality attributes and their potential protective effect with respect to bread staling were analyzed. Two levels of gums were assayed (0.5 and 1.5 g/100 g flour). The best performance was obtained with carboxymethyl cellulose and hydroxypropylmethyl cellulose F 4 M at both levels; these gums led to higher specific volumes and a better crumb texture as measured by texture profile analysis. In general, crumbs were softer, more cohesive, and resilient and exhibited lower chewiness values. Other gums like microcrystalline cellulose and hydroxypropylmethyl cellulose F50 did not improve bread quality on the same extent. Mechanical spectra obtained by dynamic mechanical analysis assays indicated a marked change in molecular mobility when carboxymethyl cellulose was present. Bread staling was evaluated by texture profile analysis, moisture loss, and calorimetric assays. Gums did not avoid retrogradation and even exhibited an accelerating effect, probably due to changes in water retention and migration during storage. However, in most cases, final crumb hardness in samples with hydrocolloids was lower than that in the control sample.     

精制脱脂棉高吸水材料制备工艺的研究

研究了由精制脱脂棉经过醚化、交联等反应制备纤维状高吸水材料的工艺过程。讨论了影响产品吸水倍率的几个因素 ,并进行了差热测试。产品吸水倍率达 1 0 0 m L/g,在 85℃的失水率小于 1 2 %。     

X‐ray diffraction methods in the study of the effect of microwave heating on the transformation of cellulose I into cellulose II during mercerization

X‐ray diffraction (XRD) techniques were used in the study of the effect of microwave (MW) heating on the structural properties of cotton celluloses I and II and on the mercerization mechanism of cotton fibers. Samples of celluloses I and II were MW heated at 900 W for different times ranging from 10 to 40 min. The obtained data revealed that MW heating of cellulose II in opened glass tubes produces no significant effects on the resolution of its XRD patterns, whereas the most evident effects occur when cotton fibers (cellulose I) are heated in opened tubes at 900 W for 10 and 20 min. Also, mixtures of cotton fibers and aqueous solution of NaOH with different concentrations were exposed to MW radiation for different times and different powers. It was found that MW heating has no considerable effects on the mechanism of transformation of cellulose I into cellulose II during mercerization. On the other hand, MW heating of cotton fibers during mercerization reduces the values of concentration of NaOH in the aqueous solution and the time of treatment that are needed for the complete transformation of cellulose lattice type I into cellulose lattice type II without any heating. Also it was found that the magnitude of reductions depends on the applied power. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

H型和Na型羧基纤维素表面改性接枝己内酯的比较研究

利用TEMPO/NaBr/NaClO反应体系将纤维素表面的C6-伯羟基氧化成羧基,获得羧基纤维素;以羧基纤维素为原料、己内酯为接枝共聚改性剂,通过开环聚合,合成了表面接枝聚己内酯的纤维素产物。讨论了H型和Na型羧基纤维素接枝己内酯的情况;红外光谱、核磁共振、X射线衍射、表面光电子能谱、表面接触角、热重等分析表明,H型羧基纤维素接枝己内酯的接枝率高于Na型羧基纤维素,且其接枝产物的疏水性更好、热稳定性更高。     

茜素红S掺杂聚苯胺/纤维素纸基电极材料的制备及性能研究

本研究利用茜素红S掺杂调控聚苯胺层,以获得高性能纤维素纸基电极材料,并对其结构组成及性能进行研究。结果表明,茜素红S掺杂提高了聚苯胺颗粒的多孔性和负载量,从而提高了聚苯胺/纤维素纸基电极材料的热稳定性、导电性能和电化学性能。电化学测试表明,在电流密度为1 mA/cm²时,纸基电极材料的面积比电容为1960 mF/cm²,高于以往的研究。本研究为利用传统造纸工艺开发高性能、廉价、绿色的纸基功能材料提供了新的参考。     

碳酸氢钠的微胶囊化

采用喷雾干燥法,研制了以乙基纤维素和单甘酯为壁材,以碳酸氢钠为芯材的微胶囊化产品.结果表明以乙基纤维素作为壁材制得的微胶囊化碳酸氢钠产品具有较高的产率和效率,其微胶囊化的工艺参数为喷雾干燥进风温度190℃,出风温度100℃,固形物含量25%,芯材与壁材的比例为83∶17.     

Graphene Oxide-Assisted Multiple Cross-Linking of MXene for Large-Area,High-Strength,Oxidation-Resistant,and Multifunctional Films

Transition metal carbides/nitrides (MXenes) with metallic electrical conductivity and excellent processability attract increasing attention for assembling multifunctional macrostructures. However, the challenges, involving poor mechanical strength, inferior oxidation stability, and limited scalable manufacturing, impede their wide applications. Herein, the large-area, high-strength, ultra-flexible hybrid films are developed through the multiple physical and chemical cross-linking of MXene/cellulose films facilitated by graphene oxide. The MXene-based films manifest significantly improved hydrophobicity, water/solvent resistance, and oxidation stability, and meanwhile, maintain excellent conductivity and electromagnetic interference shielding performance. The X-band surface-specific shielding effectiveness (SE) of 18,837.5 dB cm² g⁻¹ and an SE over 60 dB in an ultra-broadband frequency range are achieved, comparable to the best shields ever reported. Furthermore, the wearable films demonstrate excellent photothermal antibacterial and electrothermal deicing applications. Thus, such high-performance MXene-based films developed through a facile and scalable manufacturing method have substantial application prospects in flexible electronics, thermotherapy, electromagnetic compatibility, and aerospace.