Electrostatic potentials and protein partitioning in aqueous two‐phase systems

Abstract

AbstractA thermodynamic analysis unambiguously relates interfacial‐electrostatic‐potential differences measured with Ag/AgCl capillary electrodes to the equilibrium properties of an aqueous two‐phase system. Interfacial electrostatic potentials were measured as a function of total α‐cyclodextrin concentration in an aqueous two‐phase system containing 9.1 wt. % poly (ethylene glycol), 6.1 wt. % Dextran T‐70, and 1‐mM potassium iodide. An order‐of‐magnitude increase in the interfacial electrostatic potential was observed as the total concentration of α‐cyclodextrin increased from 0 to 1 mM. Measured partition coefficients for α‐chymotrypsin, lysozyme, and bovine serum albumin depend strongly on α‐cyclodextrin concentration. For example, as the concentration of α‐cyclodextrin rises from 0 to 1 mM, the partition coefficient of lysozyme decreases from 1.7 to 0.55. These measurements are in good agreement with theoretical expectations.