Solvent properties governing protein partitioning in polymer/polymer aqueous two-phase systems

Distribution coefficients of various proteins were measured in aqueous Dextran–Ficoll, Dextran–PES, and Ficoll–PES two-phase systems, containing 0.15 M NaCl in 0.01 M phosphate buffer, pH 7.4. The acquired data were combined with data for the same proteins in different systems reported previously [29,30] and known solvatochromic solvent properties of the systems [17] to characterize the protein–solvent interactions. The relative susceptibilities of proteins to solvent dipolarity/polarizability, solvent hydrogen bond acidity, solvent hydrogen bond basicity, and solvent ability to participate in ion–ion and ion–dipole interactions were characterized. These parameters, which are representative of solute–solvent interactions, adequately described the partitioning of the proteins in each system. It was found that the relative susceptibilities of proteins to solvent dipolarity/polarizability are interrelated with their relative susceptibilities to solvent hydrogen bond acidity and solvent hydrogen bond basicity similarly to those established previously for small nonionic organic compounds.