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 [K 3 PO 4 , K 2 CO 3 , (NH 4 ) 2 -SO 4 , Li 2 SO 4 , MnSO 4 , ZnSO 4 , and NaOH] were measured by the free energy of transfer of a methylene group ∆G CH 2 . 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 expressed by the difference in polymer concentration between the phases [delta poly(ethylene glycol) (∆PEG), delta ethylene oxide monomer (∆EO)] or the tie line length (TLL). The distributions of a wide range of solutes differing in structure and functionality were also measured in PEG/salt ABSs, and the results were compared to the corresponding 1-octanol/water partition coefficients. These data were used to develop a linear free energy relationship (LFER) based on Abraham's generalized solvation equation, enabling a direct comparison to be made between the solvent properties of PEG/salt ABSs and those of traditional solvent/water systems used, for example, in the determination of log P. Similar comparisons are also enabled with the properties of certain aqueous micellar systems.

PEGylated Inorganic Nanoparticles

“…It is often used in aqueous biphasic system (ABS) because of its ability to display phase separation under controlled conditions which can be exploited in bioseparation. [49,50] A colloidal suspension of NPs is generally charged and provides electrostatic stability to the suspension. [51] However a change in the dispersing medium of NPs to serum or cellular environment leads to loss of surface charge over time and results in aggregation of the NPs.…”

Cooperativity between various types of polar solute–solvent interactions in aqueous media

“…The solute preferential distribution between the aqueous phases is mainly driven by different solute-solvent interactions [13][14][15][16][17] and it can be described as [4][5][6][15][16][17]:…”

Some Novel Liquid Partitioning Systems: Water−Ionic Liquids and Aqueous Biphasic Systems

“…39,40 Aqueous biphasic systems (ABSs) represent critical phenomena 41 that occur in aqueous solution when two or more polymers, or a polymer and a salt, are added to water above critical concentrations or temperatures. 36,37 Two immiscible liquid phases are formed as a result without the involvement of any organic solvent but still with the potential for use in the differential partition and extraction of a wide variety of solutes. Solutes as varied in molecular size as inorganic ions, small organic molecules, biological macromolecules, colloidal inorganic particles, viruses, and even cells [28][29][30][31][32][33][34][35][36][37] can all be successfully partitioned between the phases with the correct choice of ABS.…”

“…36,37 Two immiscible liquid phases are formed as a result without the involvement of any organic solvent but still with the potential for use in the differential partition and extraction of a wide variety of solutes. Solutes as varied in molecular size as inorganic ions, small organic molecules, biological macromolecules, colloidal inorganic particles, viruses, and even cells [28][29][30][31][32][33][34][35][36][37] can all be successfully partitioned between the phases with the correct choice of ABS.The solubilizing properties of solutions of polymer molecules in aqueous solution have been used to effect the extraction and fractionation of a wide variety of target solutes. The apparent similarities between many of these aqueous polymeric systems, including cloudpoint extraction (CPE), micellar extraction (ME), aqueous biphasic systems (ABSs), and extractions using thermoseparating polymers, have recently been reviewed.…”