Spectral studies on the interaction of cationic dye/surfactants with Klebsiella K28 capsular polysaccharide

Spectral studies on the interaction of acidic capsular polysaccharide (SPS), isolated from Klebsiella K28, with cationic dye and surfactants have been reported. The polymer induced strong metachromasy (∼100 nm blue shift) in the cyanine dye pinacyanol bromide (PCYB). The SPS consists of d-glucose, d-galactose, d-mannose and d-glucuronic acid (2:1:2:1 molar ratio) in hexasaccharide repeating units. Glucouronic acid acted as potential anionic binding sites. 1:1 stoichiometry of the SPS–dye complex indicated the association of every potential anionic binding site of the polymer and its stacking conformation. Addition of different cosolvents resulted reversal of metachromasy. Oppositely charged surfactant–SPS binding was evaluated by dye incorporation technique. Cationic surfactants replaced bound dye molecules, thus the original band intensity of dye got increased. From the spectral data, binding constants of polymer–surfactant aggregates were calculated.