Theoretical study of the interaction of surfactants and drugs with natural zeolite

The presence of surfactant in a solid surface can modify its properties and improve the adsorption of certain organic molecules. In the present work, different combined systems formed by surfactants, drugs, water and a clinoptilolite channel model have been studied using semiempirical calculations. We modeled the interaction of each organic molecule with the external surface of clinoptilolite model. The results indicate that the cationic surfactant is well adsorbed on the clinoptilolite model unlike the anionic surfactant. The most polar drug, metronidazole, is the best adsorbed on the zeolite model, followed by aspirin and sulfamethoxazole. Taking into account this fact, we also model another system formed by surfactant–drug–water (S–D–W) in order to reproduce the interaction of the different drugs with a cationic surfactant in solution and to evaluate the role of the surfactant in the drug adsorption process. In this system the order of the drug adsorption is opposite to that obtained for the zeolite alone: the adsorption of an hydrophobic molecule like sulfamethoxazole is favored. Moreover, for aspirin and sulfamethoxazole the adsorption enthalpies are higher in the S–D–W system. This fact suggests that the presence of surfactant on the external surface of clinoptilolite could improve the adsorption of some drugs on this zeolite.