Assessment of SDS/CTAB-nafcillin sodium interactions in ethanol and ethylene glycol at different temperatures: thermodynamic and micellization perspectives

Abstract

Comprehending the interactions between drugs and surfactants is critically significant for enhancing drug delivery processes and formulating effective drug compositions. This research aims to elucidate the temperature-induced aggregation of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium dodecyl sulphate (SDS) in combination with antibiotic nafcillin sodium (NafNa); in addition to emphasizing the influence of ethanol (EtOH) and ethylene glycol (EG) on micellization. Thermodynamic parameters (change in entropy, ΔS⁰_m; enthalpy, ΔH⁰_m; and Gibbs free energy, ΔG⁰_m) and physicochemical variables (critical micelle concentration, CMC; counter ion dissociation, α) have been used to characterise the interaction between SDS/CTAB and NafNa. The incorporation of NafNa into aqueous CTAB led to an increase in the CMC and α value, whereas a decrease in both was noticed in the case of SDS surfactant. The augmentation of CMC at heightened EtOH/EG concentrations is influenced by the synergistic effect of reduced dielectric constant (DC) and enhanced solvent hydrophobicity. In CTAB + NafNa, the CMC value increases with temperature, while in SDS + NafNa, it initially decreases before subsequently increasing. The SDS/CTAB + NafNa mixture spontaneously micellizes in both pure water and aqueous EtOH/EG environments, as evidenced by the negative ΔG⁰_m values. The − ΔH⁰_m and + ΔS⁰_m values for the drug-surfactant mixture suggest electrostatic and hydrophobic interactions contribute to aggregation, with micellization showing more entropic favorability (ΔS⁰_m > ΔH⁰_m). The results offer critical understanding for scholars aiming to refine parameters, including temperature, concentration, and the incorporation of EtOH/EG additives, to improve the effectiveness and durability of drug delivery systems.