A study of the interaction between proteins and fully-fluorinated and fully-hydrogenated surfactants by ζ-potential measurements

An experimental investigation on the adsorption of two different surfactants, hydrogenated (sodium octanoate (SO)) and fluorinated (sodium perfluorooctanoate (SPFO)) on three proteins (lysozyme, hemoglobin and catalase) by measurements of the zeta-potential (ζ-potential) has been performed in water at the temperature of 298.15 K. The electrophoretic mobility of the complexes has shown hydrophobic adsorption of the surfactants on the protein surface, leading to surface saturation. The number of adsorption sites on the proteins was determined from the observed increases of the ζ-potential as a function of surfactant concentration in the regions of the negative ζ-potential, where the adsorption was a consequence of the hydrophobic effect. The ζ-potentials become more negative as the cmc of surfactant is approached, except in the interaction catalase-sodium octanoate where the ζ-potential become less negative. In the interactions of proteins with the fluorinated surfactant the ζ-potentials are more negative than in the interaction with the hydrogenated surfactant. In the case of catalase the shape of the curve ζ-potential-surfactant concentration suggests induced conformational change on catalase.