The interaction of two cationic dyes, namely, Azure B (AB) and Pinacyanol chloride (Pcyn) with an anionic polyelectrolyte, namely, sodium carrageenate (NaCar) has been investigated by Spectrophotometric method. The polymer induced metachromasy in the dyes resulting in the shift of the absorption maxima of the dyes towards shorter wavelengths. The stability of the complexes formed between Azure B and sodium carrageenate was found to be lesser than that formed between Pinacyanol chloride and sodium carrageenate. This fact was further confirmed by reversal studies using alcohols, urea surfactants and electrolytes. The interaction parameters revealed that binding between Azure B and sodium carrageenate was mainly due to electrostatic interaction while that between Pinacyanol chloride and carrageenate 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.
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