ABSTRACT
The interaction of two cationic dyes, namely, toluidine blue (TB) and methylene blue (MB) with an anionic polyelectrolyte, namely, sodium heparinate (NaHep), has been investigated by spectrophotometric method. The polymer induced metachromasy in the dyes resulting in the shift of the absorption maxima of the dyes toward shorter wavelengths. The stability of the complexes formed between TB and NaHep was found to be lesser than that formed between TB and NaHep. This fact was further confirmed by reversal studies using alcohols, urea surfactants, and electrolytes. The interaction parameters revealed that binding between TB and NaHep was mainly due to electrostatic interaction, while that between MB and heparinate is found to involve both electrostatic and hydrophobic forces. The effect of the structure of the dye and its relation to metachromasy has been discussed.
