Practical analysis of complex coacervate systems

Abstract

Several theoretical treatments of complex coacervation exist: the Voorn-Overbeek theory (1–3), the Veis-Aranyi “dilute phase aggregate model” (4), the Nakajima-Sato model (5), and the Tainaka model (6, 7). These theories are contradictory on many points including the roles of electrostatic and entropy forces, the significance of Huggins interactions, and the type of charge interaction. In this paper an attempt is made to resolve these contradictions and to further characterize the coacervation process. Gelatin/acacia coacervation, the practical example on which the Voorn-Overbeek theory was based, and albumin/gelatin coacervation, which should fit the Veis-Aranyi model, are systematically evaluated. The effects of pH, ionic strength, and polyion concentration are reported. Microelectrophoretic measurements were used to determine optimum pH and ionic strength requirements for complex coacervation. Complex coacervation was suppressed at both high and low ionic strength. All of the above theories predict suppression of coacervation at high ionic strength, but not at low ionic strength. The effect of ionic strength on complex coacervation differed as the total concentration of the polyions was altered. The Voorn-Overbeek theory proved inadequate to describe gelatin/acacia coacervation under the variety of conditions studied. The Veís-Aranyi model as adapted by Tainaka explained most of this data. The albumin/gelatin system followed the Veis-Aranyi model and conformed equally well with Tainaka's adaptation of this theory.