Solvation of Nanoions in Aqueous Solutions

Abstract

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.

Unveiling Novel Chaotropic Chromatography Method for Determination of Pralidoxime in Nerve Agent Antidote Autoinjectors

“…Their mechanism of action is based on charge delocalization, which is responsible for their ability to disrupt the water solvation shell of the analytes and introduce chaos into the organized ionic solution. The disruption of the solvation shells of the analytes not only exposes their more hydrophobic parts to interactions with the side chains of the stationary phase, thereby increasing retention, but also counteracts the role of the shells in suppressing interactions with the stationary phase, which otherwise leads to rapid elution [35]. In particular, employing chaotropic ions is advantageous for analyzing analytes that incorporate a nitrogen atom (primary, secondary, or tertiary) within their molecular structure, particularly in cases where the analytes exhibit the characteristics of weakly basic compounds.…”

Detailed Study on the Interfacial Interaction between Different Polyoxometalates and Tetronic Block Copolymers Exploring the Langmuir–Blodgett Technique

“…Low charge-density nanoions are thus also called superchaotropes because the observed effects are orders of magnitude larger than those caused by classical chaotropic Hofmeister ions, like I – or SCN – . Overall, charge density of the ions is a key factor dictating the superchaotropic behavior of POMs and nanoions; the lower the charge density, the more prominent the super chaotropic behavior, and in turn, the stronger the binding . These characteristics lead to a wide range of applications, including foam stabilization, cross-linking gel formulations, and biological uses as membrane carriers. ,, Besides, Hohenschutz et al showed that not only POMs, but also ionic boron clusters and organic hydrophobic ions, such as tetraphenyl borate, with low charge density showed a superchaotropic effect .…”

Size and Polarizability of Boron Cluster Carriers Modulate Chaotropic Membrane Transport

“…The peculiar properties of superchaotropic clusters are related to strong dehydration effects and dispersion interactions of these large, charge‐delocalized anions [6,13,21–25] . Due to their high boron content, bulky size, special 3D aromaticity, [26] and biocompatibility, [27] closo ‐borates have been developed as enabling chemical tools for biology and biomedicine [28–32] .…”