Predicting Solvation Free Energies and Thermodynamics in Polar Solvents and Mixtures Using a Solvation-Layer Interface Condition

TL;DR

This paper introduces a modified dielectric continuum model called SLIC that accurately predicts ion solvation thermodynamics and free energies in various polar solvents and mixtures without extensive fitting, enhancing predictive capabilities.

Contribution

The authors develop the SLIC model with two key modifications, improving prediction accuracy for solvation thermodynamics across diverse solvents and mixtures without fitting solute radii.

Findings

SLIC predicts transfer free energies within 2.5 kJ/mol for nine water-co-solvent mixtures.

The model accurately reproduces entropies and heat capacities.

SLIC works well for biologically relevant solvents like urea and DMF.

Abstract

We demonstrate that with two small modifications, the popular dielectric continuum model is capable of predicting, with high accuracy, ion solvation thermodynamics in numerous polar solvents, and ion solvation free energies in water--co-solvent mixtures. The first modification involves perturbing the macroscopic dielectric-flux interface condition at the solute--solvent interface with a nonlinear function of the local electric field, giving what we have called a solvation-layer interface condition (SLIC). The second modification is a simple treatment of the microscopic interface potential (static potential). We show that the resulting model exhibits high accuracy without the need for fitting solute atom radii in a state-dependent fashion. Compared to experimental results in nine water--co-solvent mixtures, SLIC predicts transfer free energies to within 2.5 kJ/mol. The co-solvents include both protic and aprotic species, as well as biologically relevant denaturants such as urea and dimethylformamide. Furthermore, our results indicate that the interface potential is essential to reproduce entropies and heat capacities. The present work, together with previous studies of SLIC illustrating its accuracy for biomolecules in water, indicates it as a promising dielectric continuum model for accurate predictions of molecular solvation in a wide range of conditions.