Abstract
Interactions of the fluoroquinolone antibiotic drug levofloxacin hemihydrate (LFH) with tetradecyltrimethylammonium bromide (TTAB) were studied in water and in the presence of additives sodium chloride (NaCl) and ethanol (C2H5OH) at 303.15 to 323.15K with an interval of 5K. Only one critical micelle concentration (c(*)) was obtained for TTAB in water. However, three different critical micelle concentrations c1</mml:msubsup> (first break), c2</mml:msubsup> (second break, and c3</mml:msubsup> (third break) were observed for LFH+TTAB mixtures in all the cases. The c(*) values for (TTAB+LFH) mixtures in the presence of sodium chloride (NaCl) were lower than those in water. On the contrary, the micellization of TTAB was disfavored by the presence of ethanol and the values of c(*) for (TTAB+LFH) mixed systems were higher than those in water. The micellization was almost enthalpy controlled for (TTAB+LFH) systems in water, and in the aqueous C2H5OH and NaCl solutions but at some temperatures it became both entropy and enthalpy controlled. The standard state Gibbs energy of transfer (trGm degrees), enthalpy of transfer (trHm degrees) and entropy of transfer (trSm degrees) were also determined and are discussed in detail. TTAB and LFH+TTAB systems exhibit excellent enthalpy-entropy compensation in all the cases.