Studies on interaction of cationic dye with bacterial acidic polysaccharide

Abstract

Interaction of acidic capsular polysaccharide isolated from <em>Klebsiella </em>K17 with cationic dye pinacyanol chloride has been investigated by spectral measurements, and thermodynamic parameters of the interaction evaluated. The polymer induces metachromasy in the cationic dye and a blue-shift from 600 nm to 500 nm in the visible absorption spectrum of the dye is observed. The spectral changes have been studied during interaction of the dye cations with the polyanions at different polymer/dye molar ratios. The polyanion-dye compound is formed with polymer/dye stoichiometry of 1:1, indicating formation of stacking conformation. The values of thermodynamic constants, enthalpy of complex formation <em>(Δ.H= - </em>7.02 kcalmol^-1), entropy change <em>(ΔS= - </em>6.80 calmol^-1 deg^-1) and free energy change <em>(ΔG </em>at 307 K = - 4.98 kcalmo)^-1) indicate chromotropic character of the polymer in inducing metachromasy in the cationic dye pinacyanol chloride. Interaction of the polymer with acridine orange dye has also been studied by fluorescence measurements.