Complexation between low-molecular-weight cationic ligands and negatively charged polymers as studied by capillary electrophoresis frontal analysis

Abstract

The potential of using capillary electrophoresis frontal analysis for the study of low-molecular-weight ligand-polyelectrolyte interactions was assessed. The interaction of the ligands 1-propylpyridinium bromide, 2-propylisochinolinium bromide, and paraquat with the polymer dextran sulfate was investigated as a function of polymer concentration and ionic strength of the buffer solution. Linear binding isotherms were obtained and association constants were determined. The complex formation was independent of the dextran sulfate concentration at low ionic strength. Ligand-polyelectrolyte interactions were strongly dependent on the ionic strength. The interaction of the divalent cation paraquat with the dextran sulfate was much stronger than the interactions of the monovalent cationic ligands with the polyelectrolyte. The binding data obtained were in accord with results obtained by equilibrium dialysis. Capillary electrophoresis frontal analysis has the potential to become a valuable tool for characterization of ligand-polyelectrolyte interactions in drug design as well as in other areas.