Assembly nature and physicochemical variables of a mixture of cetyltrimethylammonium bromide + tetradecyltrimethylammonium bromide in aq. levofloxacin hemihydrate drug medium: A conductivity and theoretical approach

Abstract

This study describes the development of mixed micelles between two cationic surfactants of different chain lengths, hexadecyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB), in an aqueous solution of levofloxacin hemihydrate (LFH). The LFH is, an antibiotic drug, used to treat many bacterial infections. The conductivity method was used in this investigation at varying temperatures and concentrations of CTAB. From the conductivity versus [surfactant] plots, the critical micelle concentration (CMC) and degree of ionization (g) were determined. The differences between the experimental CMC and its ideal value (CMCid) revealed the presence of interactions amid two employed amphiphiles in creating the mixed micelles. The CMC of the TTAB + CTAB mixed system decreased as the mole fraction (α1) of CTAB was increased at a specific temperature. The values of X1Rub and X1id were larger than the corresponding stoichiometric mole fraction of CTAB (α1), which indicated that CTAB substituted the TTAB molecules from the mixed micelles, and the contribution of CTAB increased in the mixed micelles with increase of α1. The activity coefficients (f1Rub and f2Rub) also showed the contribution of CTAB in the mixed micellization. Thermodynamic variables including excess free energy (ΔGexRub) were computed. The enthalpy (ΔHm0) and entropy (ΔSm0) of the association process indicated the presence of electrostatic (ion–dipole, ion–ion) interactions as well as hydrophobic interactions between the constituents of the study system.