PH-dependent probing of levofloxacin assimilated in surfactant mediated assemblies: Insights from photoluminescent and chromatographic measurements

Core-shell architecture of surfactant micelles offers exciting perspectives in biophysical research to mimic biomembranes at molecular level. In the present study, photoluminescent measurements were carried out to probe the potential antibiotic, Levofloxacin (LVF), in the microheterogeneous assemblies offered by Cetrimonium bromide (CTAB, a quaternary ammonium surfactant) under physiological pH conditions. By fitting the experimental data with mathematical models, the modes of interaction of LVF-CTAB combinational system were quantified by estimating the partition coefficient (Kx), the binding capacities (Kb), Stern-Volmer quenching constant (Ksv) and related Gibbs free energies. Binding constant of LVF-CTAB at pH 7.4 was also calculated using micellar liquid chromatography (MLC), which was found in good agreement with the photoluminescent results. The detailed investigation revealed that the binding and partition modes are spontaneous and the quenching mechanism can be ascribed to the static quenching mode initiated by ground-state complex formation. Moreover, the results of molecular electrostatic potential (MEP) revealed that an increase in the pH of the media improves the hydrophilic character as well as the electrophilic attack on the subjected molecule. By benefiting from the electrostatic intermolecular forces, the hydrophobic interactions are also found to play a promising role in the solubilization of LVF in the assemblies' corona. We believe that the true knowledge of host-guest interaction mechanisms concerning model membrane with entrapped fluorophore can help in better understanding of molecular recognition in related phospholipid membrane models.