COLLOIDAL STABILITY OF PROTEIN-POLYMER SYSTEMS - A POSSIBLE EXPLANATION BY HYDRATION FORCES

In this paper the stability domains of immunoglobulin (IgG fragment) F (ab')(2)-polymer systems have been examined using a low-angle scatteri ng technique, The rates of aggregate formation are expressed in terms of a stability ratio as a function of electrolyte concentration. After the usual rapid aggregation achieved at a certain ionic strength (cri tical coagulation concentration), an abnormal stabilization is observe d with increasing ionic strength. This exceptional stability at high e lectrolyte concentration cannot be explained by the Derjaguin, Landau, Verwey, and Overbeek [B. V. Derjaguin and L. Landau, Acta Physicochim . USSR 14, 633 (1941); E. J. W. Verwey and J. Th. G. Overbeek, Theory of the Stability of Lyophobic Colloids (Elsevier, Amsterdam, 1952), Vo ls. 1 and 2] theory, which attributes the colloidal stability to the L ondon-van der Weals attraction and the electrostatic repulsion. Effect s of electrolyte concentration, counterion valence, pH, protein covera ge, and time on the experimental stability are investigated. A possibl e explanation based on the so-called ''hydration forces'' is proposed.