Micellar and Thermodynamic Study of CPC and SDBS in the Presence of an Anionic Antibiotic Drug Cloxacillin Sodium: A Temperature and Drug Concentration Effect

Abstract

A study on the micellar and thermodynamic properties of drug-surfactant mixtures is of significant importance in order to achieve optimum therapeutic action of a drug. Therefore, herein, the micellar characteristics of cationic surfactant cetylpyridinium chloride (CPC) as well as anionic surfactant sodium dodecylbenzene sulfonate (SDBS) have been evaluated with the help of conductance measurements in the presence of cloxacillin sodium (CS), an anionic antibiotic drug, at various temperatures ranging from 288.15 to 313.15 K with a step size of 5.0 K. The results indicate that with the increase in the drug concentration, the critical micelle concentration (CMC) of CPC increases continuously, although a decrease in CMC at higher drug concentration (from 2.5 to 10.0 mmol·dm⁻³) has been observed in case of SDBS. The dissimilar behavior of the two surfactants has been explained on the basis of charges on the head groups and the molecular structure of the drug CS. The variation in CMC for both the surfactants shows a non-linear trend with the increase in temperature and exhibits a U-shaped behavior in case of aqueous and aqueous drug solutions. The values of enthalpy of micellization (∆H^o_m) and entropy of micellization (∆S^o_m) indicate that drug-surfactant interactions show endothermic behavior (∆H^o_m > 0) at low temperatures and become exothermic (∆H^o_m < 0) at higher temperatures. The process of micellization has mostly been entropically favored as evidenced from T∆S^o_m > ∆H^o_m.