Polyethylene glycol phase partitioning

The basis for the separation is that when two polymers, or a polymer and certain salts, are mixed together in water, they are incompatible, leading to the formation of two immiscible but predominantly aqueous phases, each rich in only one of the two components [Albertsson, op. cit. Kula, in Cooney and Humphrey (eds.), op. cit., pp. 451 71]. A phase diagram for a polyethylene glycol (PEG)-Dextran, two-phase system is shown in Fig. 22-85. Proteins are known to distribute unevenly between these phases. This uneven distribution can be used for the selective concentration and partial purification of the products. Partitioning between the two phases is controlled by the polymer molecular weight and concentration, protein net charge and... 

Shanbhag, V.P. and Axelsson, C.-G. 1975. Hydro-phobic interaction determined by partition in aqueous two-phase systems. Partition of proteins in systems containing fatty acid esters of polyethylene glycol). Eur. J. Biochem. 60 17-22. 

Johansson, G. (1992) Affinity partitioning in PEG-containing two-phase systems, in Polyethylene Glycol) Chemistry Biotechnical and Biomedical Applications (J. M. Harris, ed.), pp. 73—84. Plenum, New York. 

Upon addition of certain polymers such as polyethylene glycol (PEG) and dextran or salt to water, a phase boundary forms even though the system consists of only one solvent, water. When a mixture of biomolecules such as a fermentation broth or a solution of lysed cells is added to such a system, each type of biomolecule partitions uniquely between the two phases, achieving separation (Kula, 1979,1990 ... 

While it might seem reasonable to use a generic marker such as polyethylene glycol, which is completely eliminated without absorption (used to verify integrity of the epithelial barrier), it is important for the marker to have physical properties similar to the nutrient in question because of the complexity of the postprandial intestinal milieu - a thick slurry of mixed micelles, oil and water phases, and suspended particles. The marker should partition among the phases similarly to the analyte of interest and should have similar intestinal transit times. Thus, sugars must be used to trace sugars, sterols to trace sterols, etc. 

For the extraction of proteins, aqueous two-phase systems (ATPS) are preferred over organic solvents, which usually denature the proteins and render them biologically inactive. They consist of polyethylene glycol (PEG), and a salt (e.g., potassium phosphate) or dextran in water. At concentrations above a critical value, the mixture separates into two phases—one rich in PEG and the other in dextran or salt. In industrial systems, salts are more commonly used because they are relatively inexpensive as compared to dextran. The MW, charge and surface properties of the protein decide how the protein partitions in the system. The nature of the phase components, the MW of the polymer, and the concentration and type of salt used also affect the distribution. ... 

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