Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Interaction of cephradine monohydrate (CDM) with Cetyldimethylethylammonium Bromide (CDMEAB) has been studied by conductance measurements in pure form and in the presence of salts like potassium chloride (KCl) and potassium sulphate (K2SO4) over the temperature range of (298.15 to 318.15) K. From conductivity vs. surfactant concentration plots, two critical micelle concentrations like c 1 and c 1 were obtained for (CDM + CDMEAB) systems. The variation of c. values of CDMEAB in the presence of CDM is the indication of the interaction between CDM and CDMEAB. For the (CDM + CDMEAB) system, the values of c. values are higher in magnitude in contrast to that of pure CDMEAB in water over the range in temperature studied. In aqueous solutions of KCl and K2SO4, the c. values are changed with the increase of the concentration of salts and hence the micellization is dependent on salt concentration. The DG0 m values were negative and the spontaneity of micellization process is found to be increased with increase of temperature. The values of DH0 1m and DS0 1m indicated that the drug mediated CDMEAB aggregation in water was controlled at lower temperatures while at higher temperatures the aggregation was both enthalpy and entropy controlled. The DH0 2m and DS0 2m values revealed that the micellization in water was both enthalpy and entropy controlled at lower and higher temperatures though the effect of entropy at middle temperature was dominant. The results indicated that binding interactions between CDM and CDMEAB are both electrostatic and hydrophobic in nature while the contribution of hydrophobic interaction is dominant at lower temperatures. In aqueous solution of KCl, The DH0 m and DS0 m values indicated that the micellization was both enthalpy and entropy controlled at lower temperature while the process was entirely entropy driven at higher temperatures. In case of aqueous K2SO4 solution, the micellization was mostly entropy driven over the range of temperatures studied. The negative molar heat capacity change (DmC0p ) for micelle formation shows that DH0 m comes to be more negative as the temperature rises. The small DmC0p and the overall positive binding entropy indicate slight structural rearrangement of CDMEAB micelle in the course of binding with CDM. The presence of linear correlation between DH0 m and DS0 m values was perceived in all cases.