Spectral Studies on the Binding Behavior of Cationic Dyes and Surfactants with Bacterial Polysaccharide of Klebsiella K43

The binding behavior of acidic capsular polysaccharide (SPS), isolated from Klebsiella serotype K43, with oppositely charged dyes and surfactants have been studied by way of absorbance and emission spectroscopic measurements. Each repeating unit of the SPS consists of three D-mannose, one D-galactose, and one D-glucuronic acid residue. The anionic polysaccharide exhibited chromotropic character and induced strong metachromasy in the cationic dye, pinacyanol chloride (PCYN) through the formation of a 1:1 stoichiometric complex. Evaluation of thermodynamic parameters, viz., changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS), for the formation of dye-polymer complex and studies on the effect of different cosolvents were also evaluated to shed light on the binding nature as well as the extent of stability of the dye-polymer complex. Fluorescence of the cationic dye acridine orange (AO) was quenched with the progressive addition of SPS, which was found to be of Stern-Volmer type. Cationic surfactants in their pure form as well as in the mixed state with nonionic surfactant (Tween-20), replaced the dye bound to the polymer matrices; thus the original band intensities of the dyes could be reverted. Such studies revealed the involvement of both electrostatic as well as hydrophobic interactions between the dye-polymer as well as surfactant-polymer aggregates.     

Metachromatic behavior of methylorange in the presence of ionenes

The addition of different ionenes, polycations with defined structure and charge distances, to methylorange1 in very dilute solutions of water resulted in an observable shift of the absorption maxima from 464 nm to shorter wavelengths. The extent of this so-called metachromasy effect was found to be dependent on the nature of the hydrophobic unit of the polymer backbone. The comparison of UV/VIS spectra's of these solutions with the absorption of a film of a model substance — a dication with methylorange as counteranion — lead to the conclusion that ionenes undergo an exchange of the counteranions when added to a dilute solution of methylorange. Precipitation is slowed down, but the absorption is equivalent with solid product. The new absorption spectra of methylorange can be explained by the interaction of the quaternary nitrogen with the dye anion.     

Interaction of bacterial acidic polysaccharide with cationic dyes

The interaction of acidic capsular polysaccharide isolated fromKlebsiella K26 with cationic dyes pinacyanol chloride, acridine orange and phenosafranin has been studied by spectral measurements. The polymer induces metachromasy in pinacyanol chloride dye, indicating a blue shift in the visibly absorption spectrum of the dye from 600 to 500 nm. The stoichiometry of polymer/dye in the metachromatic compound, thermodynamic parameters of interaction, and effects of different cosolvents on the stability of the complex have been studied. Spectrophotometric and spectrofluorometric properties of the interaction between the polymer and all three dyes are presented. The chromotropic property of the polymer has been established.