ζ-Potential Study on the Interactions between Lysozyme and Sodium n-Alkylsulfates

An experimental investigation on the adsorption of n -alkylsulfates with 8, 10, 12, 14, and 16 carbon atoms in the alkyl chain length on lysozyme at pH 3.2, 7.0, and 10.0 by measurements of the zeta potential (ζ-potential) is described. At pH 7.0 and 10.0, the protein surface has a negative electrokinetic charge while at pH 3.2 the alkylsulfate ions affect the ζ-potential causing a change in the neighborhood of the point of zero charge (pzc) from positive to negative values. Values of the Gibbs energies of adsorption, calculated from the pzc of alkylsulfates of carbon chain lengths 8, 10, and 12 agree with Gibbs energies of binding of n -alkylsulfates to lysozyme and when compared with the adsorption of n -alkyltrimethylammonium ions show that the headgroup interaction is of similar form.