Biopolymer-surfactant Interactions: Binding Studies of Cetyltrimethyl Ammonium Bromide, Cetyl Pyridinium Bromide and Dodecyl Trimethyl Ammonium Bromide with Β-lactoglobulin

Binding studies of cationic detergents such as cetyltrimethyl ammonium bromide, Cetyl pyridinium bromide and dodecyl trimethyl ammonium bromide with β Lactoglobulin were carried out by equilibrium dialysis, ultraviolet difference and circular dichroism techniques at 25 C. Binding isotherms at pH 5·0, 7·0 and 9·0 show cooperative binding at all concentrations of detergents and the number of available binding sites in β Lactoglobulin increases with pH. Gibbs free energy of binding calculated on the basis of Wymans’ binding poten tial concept increases with pH indicating increased bind in strength at higher pH. The ultraviolet difference spectra of the detergent complexes with β Lactoglobulin at pH 7·0 and 9·0 in the region of 250-300 nm indicate the involvement of aromatic amino acid residues as probable binding sites and also the carboxylate groups since the binding is cooperative. The circular dichroism spectra also indicate the involvement of aromatic amino acid residues in the binding of these detergents. This is substantiated by the decrease in the intensity of the aromatic positive bands in the near ultraviolet region. The increase in the magnitude of [θ] 222 nm values in the far ultraviolet region with the increase in the concentration of the detergent in the complex indicates conformational changes resulting in an increase of α-helical content producing a more ordered structure of β Lactoglobulin . These binding studies show that at pH 7·0 and 9·0, hydrophobic interactions play a major role, while at pH 5·0 only electrostatic interactions play prominent G Geetha* et al. /International Journal Of Pharmacy&Technology IJPT | July-2012 | Vol. 4 | Issue No.2 | 4231-4245 Page 4232 role in the binding of these detergents.