Polyanions and their complexes. Part 10. Mechanism of dye binding to chemically different sites

Abstract

Thermodynamic parameters have been determined for the ion-exchange of Methylene Blue cations with sodium ions or potassium ions on cellulosic polyanions. These polyanions resemble biological oolyelectrolytes with respect to their ion binding characteristics. The chemical nature of the site determines the free energy change for the binding of Methylene Blue in the order SO₃^– > CO₂^– > PO₂^– > CH₂CO₂^–. The mechanism of dye binding is discussed and an explanation is advanced for the influence of the site on the order of binding. It is shown that the affinity of cationic dyes for a polyanion may be predicted from a knowledge of their tendency to aggregate in aqueous solution.