Generalizing The Mean Spherical Approximation as a Multiscale, Nonlinear Boundary Condition at the Solute--Solvent Interface

TL;DR

This paper introduces a multiscale boundary condition based on the mean spherical approximation to improve continuum electrostatic models, accurately predicting solvation free energies and entropies for various solvents and complex molecules.

Contribution

It extends the continuum electrostatic model with a novel HSBC based on MSA, enabling accurate predictions of solvation properties and applicability to complex biomolecules.

Findings

HSBC/MSA reproduces MSA predictions for ions in various solvents

The model accurately predicts solvation free energies and entropies

Applicable to complex molecules like proteins

Abstract

In this paper we extend the familiar continuum electrostatic model with a perturbation to the usual macroscopic boundary condition. The perturbation is based on the mean spherical approximation (MSA), to derive a multiscale hydration-shell boundary condition (HSBC). We show that the HSBC/MSA model reproduces MSA predictions for Born ions in a variety of polar solvents, including both protic and aprotic solvents. Importantly, the HSBC/MSA model predicts not only solvation free energies accurately but also solvation entropies, which standard continuum electrostatic models fail to predict. The HSBC/MSA model depends only on the normal electric field at the dielectric boundary, similar to our recent development of an HSBC model for charge-sign hydration asymmetry, and the reformulation of the MSA as a boundary condition enables its straightforward application to complex molecules such as proteins.