Significant effect of polar head group of surfactants on the solubilization of Zein in mixed micellar (SDS–DDAB) media

In recent years, the ability of ionic surfactants such as sodium dodecyl sulfate (SDS) to solubilize the water-insoluble protein Zein in aqueous solution, referred to as the Zein solubilization test, has been investigated to rank the skin irritation potential and protein denaturation potential of surfactants. However, the potential of cationic surfactants towards solubilization of Zein has not been explored much. In present report, the effect of the concentration of cationic surfactant, dodecylethyldimethylammonium bromide (DDAB) on Zein solubilization in the presence of anionic surfactant, SDS has been investigated. It has been observed that the solubilization of the Zein protein induced by SDS is affected by the presence of DDAB. The electrostatic and hydrophobic interactions between two surfactants are the deciding factors for the solubilization of Zein. The estimated values of critical aggregation concentration (cac) and critical micellization concentration (cmc) indicate that the association of Zein with SDS–DDAB takes place at somewhat higher concentration than with SDS. Fluorescence study reveals the more hydrophobic environment for the pyrene in SDS–DDAB in Zein than SDS–DDAB in water. The aggregation behavior of mixed surfactants in the presence of protein has also been analyzed. Thermodynamic study of the colloidal behavior of mixed surfactants depicts that at higher temperature enthalpy factor as well as entropic factor increases however, increase in entropy dominates over enthalpy factor.