Transfer free energies of alkali metal chlorides and of some individual ions in glycerol and water mixtures

Abstract

Staqndard free energies of transfer, ΔG_t⁰, of alkali metal chlorides from water to aqueous mixtures of 10, 30, 50, and 70 wt.% glycerol have been determined from emf measurements of the double cell comprising Ag– AgCl and K(Hg) electrodes at 25°C. These values were divided into individual ion contributions by use of tetraphenyl arsonium tetraphenyl boride (Ph₄AsBPh₄) assumption, the required ΔG_t⁰ values of the reference electrolyte (Ph₄AsPh₄B), obtained by measuring solubilities of KBPh₄, Ph₄AsPi, and KPi (Pi = picrate) in the solvents. The solvation behaviour of the involved ions, as dictated by their respective ΔG_t⁰(i) values, in this as well as in systems of other similar co-solvents like ethanol, ethylene glycol, and urea, suggests that it is determined by one or several effects of acid-base, Born-type, and dispersion interactions. Moreover, comparable stability of PH₄B^–, particularly in aqueous glycerol and urea, suggests that "specific interactions" are possibly responsible for the well_known folding-unfolding phenomenon of native conformation of proteins in presence of co-solvents.