Interaction of heparin and dextran sulphate with alkali ions

Influence of the ionic strength on condensation of alkali ions and isotopic exchange of 22Na+ in solutions of heparin and dextran sulphate has been studied at 310 K. Though structural charge densities of heparin and dextran sulphate are very similar, the Manning's theory predicts correctly the fraction of the condensed of counter-ions only for heparin, but it underestimated this fraction for dextran sulphate. In solutions of both polyelectrolytes the isotopic exchange is not complete and different. In heparin solutions the fraction of the exchangeable ions is independent of the solution composition and does not exceed 80%. In solutions of dextran sulphate the fraction of the exchangeable ions increases with the excess of the supported electrolyte and for the high excess of the supported electrolyte reaches only about 45%. Different interactions of heparin and dextran sulphate with alkali ions result probably from different conformations of both macromolecules.