Issue 2, 2024

Free-energy decomposition of salt effects on the solubilities of small molecules and the role of excluded-volume effects

Abstract

The roles of cations and anions are different in the perturbation on solvation, and thus, the analyses of the separated contributions from cations and anions are useful to establish molecular pictures of ion-specific effects. In this work, we investigate the effects of cations, anions, and water separately in the solvation of n-alcohols and n-alkanes by free-energy decomposition. By utilising energy-representation theory of solvation, we address the contributions arising from the direct solute–solvent interactions and the excluded-volume effects. It is found that the change in solvation of n-alcohols and n-alkanes upon addition of salt depends primarily on the anion species. The direct interaction between the anion and solute is in agreement with the Setschenow coefficient in terms of the ranking of salting-in and salting-out for n-alkanes, which corresponds to the extent of accumulation of the anion on the solute surface. For each of the n-alcohols and n-alkanes examined, the excluded-volume component in the Setschenow coefficient is well correlated to the (total) Setschenow coefficient when the salt effects are concerned. The ranking of the excluded-volume component in the variation of the salt species is parallel to the water contribution, which is correlated further to the change in the water density upon the addition of the salt.

Graphical abstract: Free-energy decomposition of salt effects on the solubilities of small molecules and the role of excluded-volume effects

Supplementary files

Article information

Article type
Edge Article
Submitted
01 Sep 2023
Accepted
20 Nov 2023
First published
21 Nov 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2024,15, 477-489

Free-energy decomposition of salt effects on the solubilities of small molecules and the role of excluded-volume effects

S. Hervø-Hansen, D. Lin, K. Kasahara and N. Matubayasi, Chem. Sci., 2024, 15, 477 DOI: 10.1039/D3SC04617F

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