Dullinger Philipp, Horinek Dominik
Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
J Am Chem Soc. 2023 Nov 1. doi: 10.1021/jacs.3c09494.
In recent years it has been increasingly recognized that different classes of large ions with multiple valency have effects conceptually similar to weakly solvated ions in the Hofmeister series, also labeled by the term chaotropic. The term "superchaotropic effect" has been coined because these effects are much more strongly pronounced for nanometer-sized ions, whose adsorption properties often resemble typical surfactants. Despite this growing interest in these nanometer-sized ions, a simple conceptual extension of the Hofmeister series toward nanoions has not been achieved because an extrapolation of the one-dimensional surface charge density scale does not lead to the superchaotropic regime. In this work, we discuss a generic model that is broadly applicable to ions of nearly spherical shape and thus includes polyoxometalates and boron clusters. We present a qualitative classification scheme in which the ion size appears as a second dimension. Ions of different sizes but the same charge density differ in their bulk solvation free energy. As the ions grow bigger at constant surface charge density, they become more stable in solution, but the adsorption behavior is still governed by the surface charge density. A detailed molecular dynamics simulation study of large ions that is based on a shifted Lennard-Jones potential is presented that supports the presented classification scheme.
近年来，人们越来越认识到，不同类别的多价大离子具有与霍夫迈斯特序列中弱溶剂化离子概念上相似的效应，也被称为离液序列高聚物效应。“超离液序列高聚物效应”这一术语被创造出来，是因为这些效应在纳米尺寸的离子中表现得更为强烈，其吸附特性通常类似于典型的表面活性剂。尽管对这些纳米尺寸的离子的兴趣日益浓厚，但霍夫迈斯特序列向纳米离子的简单概念扩展尚未实现，因为一维表面电荷密度尺度的外推不会导致超离液序列高聚物状态。在这项工作中，我们讨论了一个通用模型，该模型广泛适用于近球形的离子，因此包括多金属氧酸盐和硼簇。我们提出了一种定性分类方案，其中离子大小作为第二个维度出现。不同大小但电荷密度相同的离子在其本体溶剂化自由能方面存在差异。当离子在恒定表面电荷密度下变大时，它们在溶液中变得更稳定，但吸附行为仍由表面电荷密度决定。本文基于移位的 Lennard-Jones 势对大离子进行了详细的分子动力学模拟研究，支持了所提出的分类方案。
