Thermodynamics studies on tyrosine-hydantoin drug-cetyltrimethylammonium bromide mixed micellar system.

In the present paper, we report the micellization, aggregation behavior and thermodynamics of a cationic surfactant viz. cetyltrimethylammonium bromide (CTAB) in absence and presence of tyrosine-hydantoin (TH) drug. The solution behavior of the mixture of CTAB and TH drug has been determined using conductivity, surface tension, UV-visible and fluorescence spectroscopic methods. A strong interaction between the two amphiphiles is indicated from the above measurements. The critical micelle concentration (cmc) of CTAB is found to decrease with increase in the amount of TH in the mixture. The cmc values obtained by these methods are in good agreement with each other. The critical micelle concentration, aggregation number and standard free energy changes of aggregation of the surfactant (CTAB) in aqueous solution in absence and presence of TH are evaluated at different temperatures (294, 303 and 318K). The aggregation number is obtained by the steady-state fluorescence spectroscopic method. Thermodynamic parameters (the standard Gibbs energy change of micellization, ΔG°(m), the standard enthalpy change of micellization, ΔH°(m), the standard entropy change of micellization, ΔS°(m), the standard Gibbs (transfer) energy, (ΔG°(m))(tr)' , and the excess free energy change of micellization, ΔG(ex)) have been evaluated. The negative values of standard Gibbs energy change indicate spontaneous micellization and synergism. The interaction parameter, β(m), activity coefficients (f(1), f(2)) have been evaluated, and using these data we evaluated excess Gibbs energies, which indicate the spontaneity and the stability of the mixed micelles.