Interaction of monovalent and divalent counterions with some carboxylic polysaccharides

Abstract

AbstractEleven samples of carboxylic polysaccharides were studied. The activity coefficients γ have been measured for monovalent (Na+) and divalent (Ca2+) counterions. There is no specific influence of the structure of the chain on γ values. Agreement with theoretical values confirms the rigidity of the chain; for low charge density, the theoretical treatment seems to be incorrect. Selectivity is discussed in term of selectivity coefficient K and free energy of exchange ΔG; ΔG is linearly related to the charge density but K which characterizes the competition of the two counterions is sensitive to the nature of the chain. The carboxymethylamyloses present a larger selectivity whose origin is not discussed here. The last point treated is the intrinsic constant of dissociation of polyacids. The pK0 values are practically independent of the nature of the polyelectrolyte and of the charge density; the values are close to the pK0 of monomeric unit and are not affected by the position of COOH in the anhydroglucose ring.