Although cation−π interactions play a critical role in biological systems, experimental studies in aqueous environments are limited due to a lack of suitable systems and methods. The recent success in synthesizing water-soluble poly(cation−π) bearing adjacent cationic/aromatic residues provides excellent systems for studying cation−π interactions in aqueous environments. In this study, we investigated competitive cation−π interactions between small cations and macrocations with phenyl groups in hydrogels consisting of various poly(cation−π)s. By measuring the Donnan potential of the hydrogels equilibrated in NaCl solutions of different ionic strengths using the microelectrode technique, the binding ratios of small cations (Na⁺) to the phenyl residues of polymer networks were determined. It was found that when NaCl concentration was lower than the macrocation concentration, the activity coefficient of the counterions (Cl^–) in the hydrogels was very high (~2), indicating that a large amount of excess Cl^– was trapped in the hydrogels due to Na⁺ adsorption on the phenyl groups of the polymer chains via cation−π interactions. Further calculations showed that each phenyl group can adsorb a maximum of 1.5 Na⁺ despite the presence of adjacent macrocations. Additionally, we discuss the mechanism by which small cations compete with adjacent macrocations in poly(cation−π) hydrogels.

尽管阳离子-π相互作用在生物系统中起关键作用，但由于缺乏合适的系统和方法，在水环境中的实验研究受到限制。合成带有相邻阳离子/芳族残基的水溶性聚（阳离子-π）的最新成功为研究水性环境中阳离子-π相互作用提供了出色的系统。在这项研究中，我们研究了由各种聚（阳离子-π）组成的水凝胶中小阳离子和大阳离子与苯基之间的竞争性阳离子-π相互作用。通过使用微电极技术测量在不同离子强度的NaCl溶液中平衡的水凝胶的Donnan势，可得出小阳离子（Na ⁺测定聚合物网络的苯基残基。结果发现，当NaCl浓度比macrocation浓度越低，反离子（Cl组成的活度系数^- ）的水凝胶是非常高（〜2），这表明大量的过量的Cl ^-被困在适当的水凝胶Na ⁺通过阳离子-π相互作用吸附在聚合物链的苯基上。进一步的计算表明，尽管存在相邻的大阳离子，每个苯基最多可吸收1.5 Na ⁺。此外，我们讨论了小阳离子与聚（阳离子-π）水凝胶中的相邻大阳离子竞争的机理。