Interaction of cephradine monohydrate with Cetyldimethylethylammonium Bromide

• We carry out the interaction of CDM drugs with CDMEAB conductometrically.
• We examine the effect of drugs on the critical micelle concentration of CDMEAB.
• Two critical micelle concentrations are obtained for drug-CDMEAB system.
• Electrostatic and hydrophobic interactions between drug and surfactant are proposed.
• Effect of KCl and K2SO4 is observed on interaction between drug and surfactant.

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 c1∗ and c1∗ 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 ΔGm0 values were negative and the spontaneity of micellization process is found to be increased with increase of temperature. The values of ΔH1,m0 and ΔS1,m0 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 ΔH2,m0 and ΔS2,m0 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 ΔHm0 and ΔSm0 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 (ΔmCp0) for micelle formation shows that ΔHm0 comes to be more negative as the temperature rises. The small ΔmCp0 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 ΔHm0 and ΔSm0 values was perceived in all cases.