Micellar parameters and thermodynamics of interaction of fluoroquinolone drugs with cetyldimethylethylammonium bromide

Interaction of fluoroquinolone antibiotic drugs, viz., ciprofloxacin hydrochloride, levofloxacin hemihydrate and lomefloxacin hydrochloride, with the cationic surfactant cetyldimethylethylammonium bromide (CDMEAB) has been studied by conductance measurements in water and in the presence of salts such as NaCl, Na 2 SO 4 and Na 3 PO 4 ·12H 2 O over the temperature range of 298.15–318.15 K. Two critical micelle concentrations ( c *) are obtained for drug-CDMEAB systems in all the cases. The change of c * values of CDMEAB due to the addition of the drugs is indicative of the interaction between drugs and CDMEAB. Favourable micellization of drug-CDMEAB systems is observed in the presence of salts. The ∆ G 0 m values were negative in all the cases. The values of ∆H 0 m and ∆S 0 m reveal that the binding interactions between drug and CDMEAB in water are both electrostatic and hydrophobic in nature. The existence of linear correlation between ∆H 0 m and ∆S 0 m values is observed in all cases.