A quantitative model for partition in aqueous multiphase systems.

A model for the partition of charged molecules in aqueous multiphase systems has been developed. The partition coefficient of one component, or the overall partition coefficient of a number of components, between two arbitrary phases is expressed in terms of the difference in electrical potential between the phases (due to electrolytes present in the system), the net charges of the partitioned components and their partition coefficients in a (sometimes hypothetical) uncharged state. The fraction of material in one phase has also been described as a function of the net charges of the partitioned components. The model fits well to experimental data for partition of chromate, pyridine, ribonuclease A, two types of CO-hemoglobin and an enzyme mixture (yeast lysate) in three-phase systems consisting of poly(ethylene glycol), dextran, Ficoll and water. Minor deviations from the model are construed to be a pH-dependent uptake of ions. The data have also been used to detect differences in solvation of similar proteins, as well as the presence of several forms of some glycolytic enzymes present in yeast lysate.