Interactions of glutamine dipeptides with sodium dodecyl sulfate in aqueous solution measured by volume, conductivity, and fluorescence spectra

Densities, conductivities, and fluorescence spectra of {sodium dodecyl sulfate (SDS) + glutamine dipeptide + water} mixtures were measured as a function of temperature. The density data have been utilized to calculate apparent molar volumes, standard partial molar volumes (V2,φo), standard partial molar volumes of transfer from water to aqueous SDS solutions (ΔtVo), the hydration number, partial molar expansibility (Eφo), and Hepler’s constant of glutamine dipeptides. The critical micellar concentration (ccmc) and the degree of counterion dissociation of SDS micelles obtained from electrical conductivity data have been estimated at various concentrations of glutamine dipeptide. Thermodynamic parameters of micellization of SDS in aqueous dipeptide solutions have been determined from ccmc values and an enthalpy–entropy compensation effect was observed for the ternary systems. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with glutamine dipeptide, and the aggregation behavior of SDS. The results have been interpreted in terms of solute–solvent interactions and structural changes in the mixed solutions.

► Ion–ion and ion–polar group interactions are dominant interactions. ► The SDS addition and temperature increase cause a dehydration effect on dipeptides. ► The addition of dipeptide in water decreases the ccmc of SDS. ► Enthalpy–entropy compensation takes place during micellization. ► Micelle aggregation number was decreased by addition of glutamine dipeptides.