Insights into the Interactions of Sulfamethoxazole with Organized Assemblies of Ionic and Nonionic Surfactants

This work reports the physicochemical behavior of antibiotic drug sulfamethoxazole (SMX) in the presence of different surfactants, viz., cetyl trimethyl ammonium bromide (CTAB), dodecyl trimethyl ammonium bromide, didodecyl dimethyl ammonium bromide, sodium dodecyl sulfate, sodium deoxycholate, Tween 80, and Tween 20. The drug-surfactant systems were studied by UV-visible and fluorescence spectroscopies to assess the binding constants ( K_b), partition coefficient ( K_x), free energy of partition (Δ G_p), aggregation number ( N_agg), and quenching constant ( K_SV). Solubilization studies were carried out to understand the encapsulation efficiency of the system, which was found to increase as a function of CTAB concentration. Surface tension measurements enabled us to determine the change in critical micelle concentration as well as to calculate the variation in surface parameters of surfactant in the presence of drug, viz., surface pressure (π), surface excess concentration (γ_max), and minimum area ( A_min). In addition, UV-visible, fluorescence, and circular dichroism studies were carried out to check the effects of surfactant-based SMX formulation on serum proteins.