Interactions of bacterial polysaccharides with cationic dyes: Physicochemical studies.

Capsular polysaccharides (SPS) are an integral component of gram-negative bacteria, and also have potential use as vaccine. In this paper, interactions of SPS isolated from Klebsiella strains K20 and K51 with cationic dyes pinacyanol chloride (PCYN) and acridine orange (AO) were studied by absorbance and fluorescence measurements. Both the polysaccharides having glucuronic acid as the potential anionic site induced strong metachromasy (blue shift ~100 nm) in the PCYN. The spectral changes were studied at different polymer/dye molar ratios (P/D = 0-40). A complete reversal of metachromasy was observed upon addition of co-solvents, suggesting the breakaway of dye molecules from the biopolymer matrix. Binding constant, changes in free energy, enthalpy and entropy of the dye polymer complex were also computed from the spectral data at different temperatures to reveal the nature of the interaction. Quenching of fluorescence of AO by the polymers and the incorporated mechanisms were also explored.

Spectrophotometric and spectrofluorometric studies on interaction of cationic dyes with bacterial capsular polysaccharide.

Interaction of Klebsiella K14 capsular polysaccharide with cationic dyes pinacyanol chloride, acridine orange and phenosafranin has been studied by spectrophotometric and spectrofluorometric techniques. The polymer containing both glucuronic acid and pyruvic acid in its repeating unit behaved as a unique polyelectrolyte. It induced blue shift of the absorption band of pinacyanol chloride indicating strong metachromasy. Stoichiometry of the polyanion and the dye cations in the polymer-dye compound (1:2) indicated that both glucuronic acid and pyruvic acid acted as potential anionic sites for interaction with the cationic dye molecules. The stoichiometry of anionic site (of polyanion): cationic site (of dye) in the polymer dye compound was calculated as 1:1. Interaction of the polymer with acridine orange and phenosafranin dyes studied by fluorescence measurements demonstrated Stern-Volmer type of quenching. Equivalent weight of the polymer was determined by spectrophotometric and spectrofluorometric titrations. From the present studies chromotropic property of the polymer was established.