Eosin Y–macromolecule complexes. Part 2.—Interactions between eosin Y and polycations, a cationic surfactant and proteins

The binding of eosin Y to poly-L-lysine has been found to be purely electrostatic in nature, in contrast to its binding to poly(p-xylyl viologen) which had both an electrostatic and a hydrophobic component. The strength of binding was assessed by a determination of the association constants, assuming dimer formation, and critical electrolyte concentrations where possible. Dye binding is weaker at pH 3.1, where the eosin Y molecule has a single negative charge, than at pH 7.3, where it has two negative charges. Similarities are shown between the interactions which occur to form the eosin Y–poly-L-lysine and the eosin Y–cetyl pyridinium (at pre-micellar concentration) complexes as well as between the eosin Y–poly(p-xylyl viologen) complex and those formed by eosin Y and some proteins.