Solvent Properties of Aqueous Biphasic Systems Composed of Polyethylene Glycol and Salt Characterized by the Free Energy of Transfer of a Methylene Group between the Phases and by a Linear Solvation Energy Relationship

Abstract

Aqueous biphasic systems (ABSs) composed of poly(ethylene glycol) (PEG) and salt have been examined as potential environmentally benign solvents for liquid/liquid extraction. These systems might also represent an alternative to traditional solvent/water systems used in quantitative structure−activity relationships (QSARs). For the application and design of these systems, it is important to have a thorough understanding of the nature of the solvent and its interactions with the solute, and thus, PEG/salt ABSs have been characterized to this end by a variety of methods. The relative hydrophobicities of several PEG/salt ABSs composed of different molecular weights of PEG (1000, 2000, and 3400) and a variety of inorganic salts [K3PO4, K2CO3, (NH4)2SO4, Li2SO4, MnSO4, ZnSO4, and NaOH] were measured by the free energy of transfer of a methylene group ΔGCH2. These results indicate that the relative hydrophobicity of a PEG/salt ABS is a function of only the degree of phase divergence of the biphasic system as exp...