On Some Solution Properties of Synthetic and Biological Polyelectrolytes

The present status of physico-chemical investigations of dilute aqueous solutions of synthetic and biologically important polyelectrolytes was briefly reviewed. It was pointed out that the mean activity coefficient of the solute obeys the cube-root rule in contrast with the square-root dependence found for simple electrolyte cases. This difference was attributed to intermacroion attractive forces originated from strong attractive forces between macroion and gegenions. Furthermore, it was pointed out that a widely accepted assumption pertaining to the liquid junction potential, which is an unavoidable premise of the experimental determination of the single-ion activity, is not valid for polyelectrolyte solutions. From this, it is clear that various conclusions obtainable, for example, from the potentiometric titration should be viewed with great caution. The second virial coefficient for ternary systems, water-polyelectrolyte-simple electrolyte, was obtained from the mean activity coefficient and found to be in good agreement with the value determined by an independent method. The hydration number of various macroions was determined from the partial molar volume, which is a pressure derivative of the mean activity coefficient, and discussed in terms of the electrostrictional hydration and the ice-berg structure promotion around hydrophobic parts of macroions. It was inferred that the solubility of hydrocarbon in water should be influenced by the ice-berg forming tendency of the macroion: in fact the solubilization phenomenon of naphthalene by polymer addition was observed. From the transference measurements, the gegenions were concluded to be fixed outside of the hydration shell of macroions. Finally, polyelectrolytes displayed distinct acceleration effects on reactions between likely charged ionic species. This was found to be due to the enthalpy change caused by polyelectrolyte addition, but not due to enhancement of the collision frequency of reactant ions, contrary to the usually accepted view. The implication of this conclusion was noted in connection with catalytic actions of DNA and RNA.