Interpretation of preferential interaction coefficients of nonelectrolytes and of electrolyte ions in terms of a two-domain model

Abstract

For a three-component system consisting of solvent (1), polymer or polyelectrolyte (2J), and a nonelectrolyte or electrolyte solute (3), a two-domain description is developed to describe thermodynamic effects of interactions between solute components (2J) and (3). Equilibrium dialysis, which for an electrolyte solute produces the Donnan distribution of ions across a semipermeable membrane, provides a fundamental basis for this two-domain description whose applicability is not restricted, however, to systems where dialysis equilibrium is established. Explicit expressions are obtained for the solute-polymer preferential interaction coefficient gamma 3,2J (nonelectrolyte case) and for gamma +,2J and gamma -,2J, which are corresponding coefficients defined for single (univalent) cations and anions, respectively: gamma +,2J = magnitude of ZJ + gamma -,2J = 0.5(magnitude of ZJ + B-,2J + B+,2J) - B1,2Jm3/m1 Here B+,2J, B-,2J, and B1,2J are defined per mole of species J, respectively, as the number of moles of cation, anion, and water included within the local domains that surround isolated molecules of J; ZJ is the charge on J; m3 is the molal concentration of uniunivalent electrolyte, and m1 = 55.5 mol/kg for water.(ABSTRACT TRUNCATED AT 250 WORDS) © 1995, The Biophysical Society. All rights reserved.