Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The interaction of three cephalosporin drugs namely cefadroxyl monohydrate (CFM), cephalexin monohydrate (CLM) and cephradine monohydrate (CDM) with dodecyltrimethylammonium Bromide (DTAB) has been carried out by conductance measurements in aqueous medium and in aqueous solution of K2SO4 salt over temperature range of (303.15 to 318.15) K. For pure DTAB and drug-DTAB systems, three critical micelle concentrations were obtained. The third critical micelle concentration (c. 3) indicates that the spherical micelle turns into rod shape that is sphere to rod transition. The c. values of DTAB are changed due to the addition of cephalosporin drugs. In addition, the change of the values of c. 1, c. 2 and c. 3 with increase of the concentration of drugs indicate the presence of interaction between drug and DTAB. The c. values indicate that micellization for the cephalosporins-surfactant systems in water follow the order: CFM-surfactant less than CDM-surfactant less than CLM-surfactant. The c. values for the cephalosporins - DTAB systems in aqueous K2SO4 are lower in magnitude than those in pure water and the values decrease with increase of the concentrations of K2SO4 at a particular temperature. A significant decrease of c. values in the presence of K2SO4 for cephalosporins-DTAB systems indicates that drug supported ionic micelle formation is much favoured in aqueous K2SO4 solution compared to that in pure water. For cephalosporin- DTAB systems, DG0 m values are negative which indicate that the drugs mediated ionic micelle formation processes are thermodynamically spontaneous. For cephalosporin-DTAB systems in water, the micellization is almost entropy controlled whereas at some temperatures it becomes both entropy and enthalpy controlled. Enthalpy.entropy compensation is observed from a linear relation between enthalpy and entropy changes in all the cases.