Application of integral‐equation theory to aqueous two‐phase partitioning systems

Abstract

AbstractA molecular‐thermodynamic model is developed for representing thermodynamic properties of aqueous two‐phase systems containing polymers, electrolytes, and proteins. The model is based on McMillan‐Mayer solution theory and the generalized mean‐spherical approximation to account for electrostatic forces between unlike ions. The Boublik‐Mansoori equation of state for hard‐sphere mixtures is coupled with the osmotic virial expansion truncated after the second‐virial terms to account for short‐range forces between molecules.Osmotic second virial coefficients are reported from low‐angle laser‐light scattering (LALLS) data for binary and ternary aqueous solutions containing polymers and proteins. Ion‐polymer specific‐interaction coefficients are determined from osmoticpressure data for aqueous solutions containing a water‐soluble polymer and an alkali chloride, phosphate or sulfate salt.When coupled with LALLS and osmotic‐pressure data reported here, the model is used to predict liquid‐liquid equilibria, protein partition coefficients, and electrostatic potentials between phases for both polymer‐polymer and polymer‐salt aqueous two‐phase systems. For bovine serum albumin, lysozyme, and α‐chymotrypsin, predicted partition coefficients are in excellent agreement with experiment.