高电荷球形大分子对一价离子与二价离子的竞争吸附
Competitive sorption of mono- versus di-valent ions by highly charged globular macromolecules
摘要：
当一个高度带电的球状大分子，如树枝状的纳米凝胶或带电的纳米凝胶，被浸入生理电解质溶液中时，溶液中的一价和二价反离子以一定的比例与大分子结合，从而几乎完全电中和它。对于生物介质中的带电大分子，结合的一价和二价离子的数量比对所需的功能是决定性的。这样的吸附比的理论预测是具有挑战性的，因为竞争的静电（价），离子特异性，结合饱和效应。在这里，我们设计和讨论了几个近似模型来预测这样的平衡吸附比，通过扩展和结合建立静电结合理论，如唐南，朗缪尔，曼宁以及泊松-玻尔兹曼方法，系统地研究竞争性吸收的一价和二价抗衡离子的大分子。我们比较和适合我们的模型粗粒度（隐式溶剂）的球状树枝状聚甘油硫酸酯（dPGS）在盐溶液中的混合价的计算机模拟数据。dPGS在生物系统中的大分子载体应用中具有很高的潜力，同时构成了高电荷大分子的良好模型系统。最后，我们使用模拟知情的模型来外推和预测静电功能，如有效电荷作为二价离子浓度的函数，用于广泛的dPGS代（大小）。
英文摘要：
When a highly charged globular macromolecule, such as a dendritic polyelectrolyte or charged nanogel, is immersed into a physiological electrolyte solution, monovalent and divalent counterions from the solution bind to the macromolecule in a certain ratio and thereby almost completely electroneutralize it. For charged macromolecules in biological media, the number ratio of bound mono- versus di-valent ions is decisive for the desired function. A theoretical prediction of such a sorption ratio is challenging because of the competition of electrostatic (valency), ion-specific, and binding saturation effects. Here, we devise and discuss a few approximate models to predict such an equilibrium sorption ratio by extending and combining established electrostatic binding theories such as Donnan, Langmuir, Manning as well as Poisson-Boltzmann approaches, to systematically study the competitive uptake of mono- and di-valent counterions by the macromolecule. We compare and fit our models to coarse-grained (implicit-solvent) computer simulation data of the globular polyelectrolyte dendritic polyglycerol sulfate (dPGS) in salt solutions of mixed valencies. The dPGS has high potential to serve in macromolecular carrier applications in biological systems and at the same time constitutes a good model system for a highly charged macromolecule. We finally use the simulation-informed models to extrapolate and predict electrostatic features such as the effective charge as a function of the divalent ion concentration for a wide range of dPGS generations (sizes).
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