pH-Dependent Antibiotic Gatifloxacin Interacting with Cationic Surfactant: Insights from Spectroscopic and Chromatographic Measurements

Microheterogeneous surfactant assemblies solubilize and encapsulate active drug molecules and consequently protect them from the adverse environmental conditions. As pseudo-models of biological membranes the associated structures of surfactant molecule are also very handy for investigators to discern their roles in cellular interactions. The present study reveals the molecular interaction of a potential antibiotic, Gatifloxacin (GTF), with cetyltrimethylammonium bromide (CTAB, a quaternary ammonium surfactant) at physiological pH. Chromatographic and spectral–luminescent measurements were performed to probe the GTF–CTAB association and drug–surfactant interaction modes which were quantified by estimating the binding capacities (K_b) and related Gibbs energies at various pH values. The binding values of GTF–CTAB obtained from micellar liquid chromatography measurements are found to be in good agreement with those measured by electronic spectroscopy. Moreover, the data obtained from molecular electrostatic potentials revealed that the slightly basic medium (pH = 7.4) induces hydrophilic character in GTF molecules that may dynamically assist the incorporation of drug molecules into the outer core in the palisade layer of CTAB micelles, which favors penetration binding. In addition to electrostatic intermolecular forces, the hydrophobic aggregates of surfactant molecules are also found to aid solubilization of GTF in the aggregate's corona, which may result in controlled release of the drug.