Salt Effects on Hydrophobic Solvation: Is the Observed Salt Specificity the Result of Excluded Volume Effects or Water Mediated Ion‐Hydrophobe Association?

Abstract

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.

Diffusivity and hydrophobic hydration of hydrocarbons in supercritical CO2 and aqueous brine

“…Brine concentration has an impact on intermolecular interactions between water and hydrophobic molecules by changing the hydration structure. 53 As discussed previously (Fig. 3), the results show that adding salt can affect interactions between salt ions and water molecules.…”

Unexpected inverse correlations and cooperativity in ion-pair phase transfer

“…18 Presumably, strong ion-dipole interactions between charge dense Li + ions and TBP are a prominent factor in LiNO 3 extraction, especially at high electrolyte and extractant concentrations. [26][27][28] However it is important to recognize that the presence of electrolytes can affect extractant driven interfacial chemistry through additional ion-ion, ion-dipole, and dipole-dipole interactions between ions, extractants, solvent, and the diluent molecules. 29,30 This work employs molecular dynamics simulations to probe the equilibrium complexation of LiNO 3 by TBP under PUREX like conditions.…”

PVDF Fibers Modification by Nitrate Salts Doping

“…When considering the deviations, the average values of measured angles are very close to one another. As salts are usually used to alter hydrophobicity of a material [ 32 ], this lack of significant difference is somewhat puzzling. Out of all the three salts, the zinc salt behaves in the most distinctive manner, but that can be seen in the permittivity or optical spectroscopy measurement as well.…”