Short solvent model for ion correlations and hydrophobic association

Abstract

Coulomb interactions play a major role in determining the thermodynamics, structure, and dynamics of condensed-phase systems, but often present significant challenges. Computer simulations usually use periodic boundary conditions to minimize corrections from finite cell boundaries but the long range of the Coulomb interactions generates significant contributions from distant periodic images of the simulation cell, usually calculated by Ewald sum techniques. This can add significant overhead to computer simulations and hampers the development of intuitive local pictures and simple analytic theory. In this paper, we present a general framework based on local molecular field theory to accurately determine the contributions from long-ranged Coulomb interactions to the potential of mean force between ionic or apolar hydrophobic solutes in dilute aqueous solutions described by standard classical point charge water models. The simplest approximation leads to a short solvent (SS) model, with truncated solvent–solvent and solute–solvent Coulomb interactions and long-ranged but screened Coulomb interactions only between charged solutes. The SS model accurately describes the interplay between strong short-ranged solute core interactions, local hydrogen-bond configurations, and long-ranged dielectric screening of distant charges, competing effects that are difficult to capture in standard implicit solvent models.

Dielectric response with short-ranged electrostatics

“…37 and 38 for differing suggestions), and it is hoped that the results that follow will help the development of such theoretical approaches. The results presented here also provide further support to LMFT as a theoretical approach for understanding the solvation of charged species (38,39).…”

“…LMFT provides an elegant statistical mechanical framework that is readily compatible with standard molecular simulation approaches and can be applied in cases when it is not always clear, at least a priori, that conventional mean-field treatments will work. Improving our theoretical descriptions of solvation is one area where LMFT has enjoyed much recent success (38,39,65). This includes both hydrophobic and ionic solvation across a range of length scales.…”

“…Of particular relevance to this work is the recent study of Gao et al (39), in which LMFT was used to probe ion correlations in water. It was found that treating all electrostatic interactions with the SR v0 led to potential of mean forces (PMFs) that disagreed with a full electrostatic treatment.…”

A molecular twist on hydrophobicity

“…It has long been recognized that hydrophobicity is an extremely hard theoretical problem, 12 which has originated a number of sound statistical models with little attention to explicit quantum interactions, that have evolved over time into the current view, 10,[13][14][15][16][17][18][19][20][21][22][23] cemented in the Lum-Chandler-Weeks theory. 24 In this view, hydrophobicity is a complex multicausal phenomenon, which is best explained based on the effects that a particular hydrophobe has on the surrounding hydrogen bonding network among water molecules, as envisioned by Stillinger half a century ago.…”

Size and charge correlations in spherical electric double layers: a case study with fully asymmetric mixed electrolytes within the solvent primitive model

“…The fact that interactions play a major role not only in the design but also in the fabrication of devices, 11 can be directly visualized from a number of experiments that involve ions, radicals, dipoles, and even multipoles. Alongside the direct interactions between the molecular components, the medium 12 or the associated solvent, 13 also plays a major role 14 in the modication of these interactions. 15 For example, crowding effects, 16,17 mostly observed in complex polymeric and biological macromolecular solutions, arise due to the presence of the solvent molecules.…”