Evaluation of the Electrostatic Effect on Ionic Reactions in Charged Polyion Systems

可归因于抗衡离子集中在聚合物骨架周围的静电效应使得聚离子-抗衡离子的结合平衡变得复杂。本研究项目的目的是研究吉布斯-唐南概念的适用性，以评估线性和交联线性聚离子（聚离子凝胶）的结合平衡中的静电效应。硫酸葡聚糖（DxS）和羧甲基葡聚糖（CmDx）已被用作线性聚离子的实例，并且磺丙基葡聚糖凝胶和羧甲基葡聚糖凝胶已被用作交联的线性聚离子凝胶的实例。引入一个体积项的反离子浓缩区域允许定义的平均浓度的离子物种在附近的聚离子骨架。DxS和CmDx的反离子结合平衡分析的结果表明，反离子集中区的Donnan势项和体积项都可以简单地表示为聚离子的线性电荷分离和所加盐浓度的函数。聚离子域中的离子气氛被认为对应于由固定离子、抗衡离子和共离子组成的均匀浓缩电解质溶液。通过将每个相的标准状态定义为相同的，促进了关于聚离子域中各种物质的测量性质的有效洞察。用这种方法确定的CmDx和其凝胶类似物的单齿络合物的固有结合常数的值的协议，与它们的单体类似物的相应的金属络合物的值证明了这种方法的价值。本文的系统工作证明，Gibbs-Donnan概念可以应用于任何聚离子的反离子结合平衡的热力学表达式，而不论其形状、外观和固定离子的性质。

An electrostatic effect attributable to counterions being concentrated around the polymer skeleton makes the binding equilibria of polyion-counterions complicated. The objective of the present research project is to examine the applicability of a Gibbs-Donnan concept to evaluate the electrostatic effect in the binding equilibria of linear and cross-linked linear polyions (polyion gels). Dextran sulfate (DxS) and carboxymethyldextran (CmDx) have been used as examples of linear polyions, and sulfopropyl dextran gel and carboxymethyldextran gel have been usesd as examples of cross-linked linear polyion gels. Introduction of a volume term for the counterion concentrating region permits definition of the averaged concentrations of the ionic species in the vicinity of the polyion skeleton. Results of the counterion binding equilibrium analysis of DxS and CmDx revealed that both the Donnan potential term and the volume term for the counterion concentrating region can be expressed simply as a function of the linear charge separation of the polyion and the added salt concentration. The ionic atmosphere in the polyion domain is considered to correspond to a homogeneous concentrated electrolyte solution composed of fixed ions, counterions, and co-ions. By defining the standard state of each phase to be the same, valid insights with respect to the measured properties of the various species in the polyion domain are facilitated. Agreement of the values of the intrinsic binding constants of the monodentate complexes of CmDx and its gel analogs determined with this approach, with those of the corresponding metal complexes of their monomer analogs demonstrate the value of this approach. It has been proved by the present systematic work that the Gibbs-Donnan concept can be applied to the thermodynamic expression of the counterion binding equilibria of any polyions, irrespective of their shapes, appearances, and the nature of the fixed ions.