Adsorption kinetics and solubilisation of ciprofloxacin in quaternary ammonium-based surface-active compounds: experimental and computational study†

Abstract

The adsorption and aggregation of amphiphiles at different solvent interfaces are of great scientific and technological importance. In this study, interfacial tension measurements of surface-active compounds—ionic liquid 2-dodecyl-2,2dimethylethanolammonium bromide (12Cho.Br) and cationic surfactant cetyltrimethylammonium bromide (CTAB)—were conducted both in the absence and presence of ciprofloxacin (CIP). Equilibrium interfacial tension (EIFT) measurements and conductivity data demonstrate the effect of CIP on the critical micellar concentration and surface excess concentration of 12Cho.Br and CTAB. Additionally, dynamic interfacial tension (DIFT) measurements were performed to compare the interfacial tension of pure 12Cho.Br and CTAB solutions, as well as those in the presence of the drug (with and without 0.3% acetic acid), as a function of time. The DIFT analysis revealed that the adsorption of 12Cho.Br and CTAB at the air–water interface followed a mixed diffusion-adsorption controlled mechanism. The adsorption processes of 12Cho.Br and CTAB molecules were studied over short time intervals (t → 0) and longer time intervals (t → ∞). The adsorption behaviour was correlated with concentration and the presence of energy barriers. In the presence of CIP, the diffusion coefficient was compared to that of the pure 12Cho.Br and CTAB systems to assess its effect on adsorption and to validate the participation of CIP in DIFT relaxations. Additionally, DIFT measurements were employed to investigate CIP solubility in different SAC systems. Data from the relaxation profiles across a range of concentrations were used to determine the solubility limit of the drug molecules. The solubility data obtained from DIFT correlates strongly with the UV spectroscopy results. Furthermore, DFT calculations provide insights into the frontier orbital structures and physicochemical parameters of complex formations.