Righetti P G, Caglio S
Department of Biomedical Sciences and Technologies, University of Milano, Italy.
Electrophoresis. 1993 Jul;14(7):573-82. doi: 10.1002/elps.1150140191.
The kinetics of monomer incorporation into a polyacrylamide gel have been studied in a photopolymerization system comprising 100 microM methylene blue in presence of a red-ox system, 1 mM sodium toluenesulfinate (reducer) and 50 microM diphenyliodonium chloride (oxidizer). A precise assessment of gel point (pc) was obtained in a droplet chamber, in which argon was gently bubbled with a fused silica capillary into the reaction mixture. At pc, 50% (+/- 3) acrylamide was incorporated into the matrix, vs. 80% (+/- 4) N,N'-methylenebisacrylamide. This incorporation level remained the same when polymerized in the 2-36 degrees C temperature range. Incorporation continued almost linearly for acrylamide up to 80% conversion. The reaction was continued up to 55 min (at 2 degrees C), at which point bisacrylamide had been essentially consumed (> 99.5% incorporation) and acrylamide had reacted (95%). At 2 degrees C, after gelation, the gel became progressively turbid (the Tyndall effect plateauing at 50 min), but it remained fully transparent if, at the gel point, reaction was continued at 50 degrees C. The consumption of the pendant double bonds of Bis followed the progression of turbidity. It is concluded that, by gelation at 2 degrees C, the nascent chains form clusters held together by hydrogen bonds (melting point at 28 degrees C); such clusters are subsequently "frozen" in the three-dimensional space as the pendant double bonds in the chains react progressively. Such turbid matrices are more porous and less elastic than when the gel is polymerized at 50 degrees C. This process is similar to the "lateral aggregation" occurring when gels are formed in presence of a polymer in solution (e.g. 10 KDa polyethylene glycol; Righetti et al., Electrophoresis 1992, 13, 587-594).
在一个光聚合体系中研究了单体掺入聚丙烯酰胺凝胶的动力学，该体系包含100微摩尔的亚甲基蓝，存在一个氧化还原体系、1毫摩尔的甲苯亚磺酸钠（还原剂）和50微摩尔的二苯基氯化碘鎓（氧化剂）。在一个液滴室中获得了凝胶点（pc）的精确评估，在该液滴室中，氩气通过一根熔融石英毛细管缓慢鼓泡进入反应混合物中。在凝胶点时，50%（±3）的丙烯酰胺掺入到基质中，相比之下，N,N'-亚甲基双丙烯酰胺的掺入率为80%（±4）。当在2至36摄氏度的温度范围内聚合时，这种掺入水平保持不变。对于丙烯酰胺，掺入几乎呈线性持续，直至转化率达到80%。反应持续进行至55分钟（在2摄氏度下），此时双丙烯酰胺已基本消耗殆尽（掺入率>99.5%），丙烯酰胺也已发生反应（95%）。在2摄氏度下，凝胶化后，凝胶逐渐变得浑浊（廷德尔效应在50分钟时达到平稳），但如果在凝胶点时反应在50摄氏度下继续进行，凝胶则保持完全透明。双丙烯酰胺侧链双键的消耗与浑浊度的变化过程一致。可以得出结论，在2摄氏度下凝胶化时，新生链形成由氢键维系在一起的簇（熔点为28摄氏度）；随着链中的侧链双键逐渐反应，这些簇随后在三维空间中“冻结”。与在50摄氏度下聚合凝胶相比，这种浑浊的基质孔隙更多且弹性更小。这个过程类似于在溶液中存在聚合物（例如10千道尔顿的聚乙二醇；里盖蒂等人，《电泳》1992年，第13卷，587 - 594页）时形成凝胶时发生的“横向聚集”。
