Aggregation properties of levofloxacin in water and ethanol and its interaction with sodium dodecyl sulphate: A thermodynamic study

Abstract

This manuscript reports the determination of critical micelle concentration (CMC) of levofloxacin (LF) in two solvents, water and ethanol, by using surface tension, refractive index and absorbance measurements. The data thus obtained were used to calculate different thermodynamic parameters for micellization process like free energy of micellization, free energy of adsorption, entropy and enthalpy of micellization. The interaction of this drug with anionic surfactant (SDS) was also studied using UV/Visible spectroscopy and conductometry. With rise in temperature, CMC of the drug was found to decrease in ethanol and increase in aqueous solution indicating dominance of lipophobic desolvation over lipophilic desolvation in ethanol and reverse, in case of aqueous solution. A strong drug/surfactant interaction was found to exist. The data obtained from drug/surfactant interaction were also used to find different interaction parameters like partition constant, free energy of partition, binding constant and free energy of binding which are very useful to understand the phenomenon of solubilization. Critical micelle concentration of levofloxacin increases with temperature in aqueous solution and decreases in ethanol. Processes of micellization and adsorption of drug molecules at solution-air interface are spontaneous and results in increase in entropy. The drug shows strong interaction with anionic surfactant (SDS) due to solubilization of drug molecules between ionic head groups of micelles of SDS.