Interaction of biopolymers with cationic dyes: Spectral and thermodynamic studies

Abstract

The interaction between a cationic dye pinacyanol chloride and an acidic capsular polysaccharide isolated from <em>Klebsiella</em> serotype K14 has been studied by spectral measurements. Thermodynamic parameters like entropy change, enthalpy change and free energy change have also been evaluated for the interaction. The acidic capsular polysaccharide, having two potential anionic sites, glucuronic acid and pyruvic acid, interacts strongly with dye cations by inducing metachromasy and blue shift of about 110 nm is observed in the visible absorption spectrum of the dye. At [polymer]/[dye] &asymp;30, a distinct &micro; band at 490 nm appears as a single banded spectrum with complete removal of &alpha;- and &beta;- bands. Studies on reversal of metachromasy by addition of different co-solvents indicate progressive destruction of metachromatic compounds. It is also observed that the added substances are used as hydrophobic bond breakers and thus a reversal of metachromasy occurs. Thermodynamic parameters evaluated from spectral data have been used to elucidate the nature of interaction of the polymers with dye cations.