Assessment of SDS-sulfathiazole interactions in glucose and urea medium at different temperatures: a conductometric study

Abstract The present investigation employs a conductometric approach to investigate the influence of differing concentrations of the antibiotic drug sulfathiazole (STZ) and the additives glucose/urea on the micellization behavior of the anionic surfactant sodium dodecyl sulfate (SDS) in a slightly acidic environment (рН 5.0) across a range of temperatures. In contrast to SDS in pure water, the CMC (critical micellar concentration) values of SDS decreased in the presence of STZ, facilitating micellization. Urea increases the CMC of the SDS + STZ system, whereas glucose decreases it. Unlike urea, which destabilizes water structure and diminishes hydrophobic contacts, glucose modifies the water structure, decreases the dielectric constant, and alters the electrostatic repulsions among the charged SDS head groups, making it harder for SDS molecules’ hydrophobic tails to form micelles. Thermodynamic parameters (change in entropy of micellization, ΔS 0 m ; enthalpy of micellization, ΔH 0 m ; and Gibbs free energy of micellization, ΔG 0 m ) and physicochemical variables (CMC and counter ion dissociation, α ) have been used to characterise the interaction between SDS and STZ. The negative ΔG 0 m values reveal that the SDS + STZ mixture undergoes spontaneous micellization in both pure water and aqueous glucose/urea environments. The values of −ΔH 0 m and +ΔS 0 m for the SDS + STZ mixture indicate that both electrostatic and hydrophobic interactions play a crucial role in aggregation.