Correlation and prediction of osmotic pressures for three aqueous protein-electrolyte solutions based on the Ross perturbation theory and soft-core three-Yukawa potential

A simple analytic equation of state (EOS) for the three-Yukawa potential is derived based on the Ross variational perturbation theory. The model is used to describe the non-idealities of the aqueous protein-salt solutions. The three-Yukawa potential can describe the double-layer repulsive charge-charge interactions, the attractive dispersion (or the van der Waals) interaction and the hard-sphere repulsion. A soft-core Yukawa repulsion is introduced to replace the hard-core repulsion used in previous hard-core two-Yukawa potential. It is assumed to be able to describe the deformation of protein molecules with heavy weight under pressure. The EOS has been applied to the charged bovine serum albumin (BSA), lysozyme and α-chymotrypsin saline solutions with the various pH values and concentrations, the model parameters are determined by correlation of experimental data. The correlation and prediction results of osmotic pressure are compared with experimental data and other theories in literature. The comparisons show that the three-Yukawa model proposed in this work is reasonable, and the soft-core modification is important for the protein solutions with heavier molecular weight, and is not evident for the protein solutions with lighter molecular weight.