Premium
Salt Effects on Hydrophobic Solvation: Is the Observed Salt Specificity the Result of Excluded Volume Effects or Water Mediated Ion‐Hydrophobe Association?
Author(s) -
Francisco Olga A.,
Glor Hayden M.,
Khajehpour Mazdak
Publication year - 2020
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201901000
Subject(s) - chemistry , solvation , hofmeister series , salting out , hydrophobic effect , salt (chemistry) , hydrophobe , chaotropic agent , solubility , ion , solvent , excluded volume , solvation shell , hydration energy , aqueous solution , chemical physics , inorganic chemistry , organic chemistry , biochemistry , polymer
The solubility of hydrophobic molecules in water is sensitive to salt addition in an ion‐specific manner. Such “salting‐out” and “salting‐in” properties have been shown to be a major contributor to the measured ion‐specific Hofmeister effects that are observed in many biophysical phenomena. Various theoretical models have suggested a number of disparate mechanisms for salting‐out (salting‐in) of hydrophobic moieties, the most popular of which include preferential interaction, water‐mediated association, and electrostriction models. However, a complete molecular level description of this ion‐specificity is not yet available. This work investigates the ion‐specific nature of hydrophobic solvation by studying how sodium and chloride salts affect the thermodynamics of 1,2‐hexanediol micellization. The results of this study are analyzed in terms of scaled‐particle theory and we show that salt addition can affect hydrophobic solvation in two modalities: salt addition changes the cavitation free energy; salt addition also influences the solvent‐solute interaction energy by changing the hydration of the hydrophobic solute. These two effects are salt specific in nature and we suggest that for small hydrophobic solutes these effects are the main cause of salt‐specific Hofmeister effects on their solubility.