Polyanions and their complexes. Part IX. Binding affinities of inorganic ions to heparin

Abstract

The effect of inorganic ions on the interaction between heparin and Methylene Blue has been studied using pulse radiolysis and visible absorption spectroscopy. The concentration of ions required fully to remove Methylene Blue from the complex, i.e. the limiting salt concentration, decreases in the order Li⁺ > Na⁺ > Cs⁺ > NH₄⁺ > Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺. For inorganic ions of the same valence the strength of binding parallels the size of the hydrated ion, with the smallest ion binding most strongly. The presence of an additional charge increases the strength of binding and outweighs the size effect. Within the group of ions of identical valence the same variation in size exerts a comparable influence on binding strength.