Effect of dipeptides on the micellization and thermodynamic parameters of sodium dodecyl sulfonate: Conductometric and fluorimetric studies

Micellization and related thermodynamic parameters of a conventional anionic surfactant sodium dodecyl sulfonate (C12SO3Na) in various compositions of water-dipeptide mixed media have been studied by means of conductivity and fluorescence spectroscopy at five temperatures ranging between 298.15 K and 318.15 K. The electrical conductivity data have been utilized to calculate the values of critical micelle concentration (ccmc) and the counterion binding constant (β) of C12SO3Na. From ccmc values, it is observed that the micellization tendency of the surfactant increases in the presence of dipeptides. Thermodynamic parameters (ΔGmo, ΔHmo and ΔSmo) of micellization of C12SO3Na in aqueous dipeptide solutions have been obtained by applying the mass action model and an enthalpy-entropy compensation effect was observed. The effect of dipeptides on the micellar properties of C12SO3Na depends upon their nature and concentration, as well as the temperature. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of C12SO3Na with dipeptides, and the aggregation behavior of C12SO3Na. The results have been interpreted in terms of solute-solvent interactions and structural changes in the mixed solutions. The interaction difference of C12H25SO3Na/C12H25SO4Na with dipeptides was also studied and it was found that C12H25SO3Na were seen to interact more weakly than their sulfate analogues.

► The addition of dipeptide in water decreases the ccmc and the aggregation number of C12SO3Na. ► Thermodynamic parameters of micellization of C12SO3Na have been obtained. ► Enthalpy-entropy compensation takes place during micellization. ► Dipeptides make microenvironment of C12SO3Na more hydrophobic. ► C12SO3Na interacts with dipeptides more weakly than C12SO4Na.