Micellization behavior of cationic surfactant dodecyldimethylethylammonium bromide (DDAB) in the presence of papain

The effect of water-soluble, globular protein papain, on the cmc of a cationic surfactant dodecyldimethylethylammonium bromide (DDAB) in aqueous solution has been studied by using conductivity, viscosity and absorbance spectroscopy. The results obtained show that the interactions between surfactant and protein depend upon the concentration of protein and the temperature. The cmc values of DDAB have been estimated at various concentrations of papain as well as at different temperatures ranging from 283.15 to 303.15 K. The thermodynamic parameters of micellization have been determined from cmc values and an enthalpy–entropy compensation effect also observed for the systems. Thermodynamic parameters (ΔGm°, ΔHm° and ΔSm°) for the micelle systems in the presence of papain have been obtained by applying the mass action model. Viscosity measurements have been performed to evaluate the rheological and conformational changes of protein–surfactant solution. To confirm the interactions between surfactant and protein, absorbance spectroscopy has been performed.