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Departamento de Física Atómica, Molecular y de Agregados
Instituto de Física Fundamental (IFF)
Knowing new zeolite-drugs interactions by computational studies
Instituto de Ciencia y Tecnología de Materiales, Universidad de La Habana
Medical and pharmaceutical applications of natural zeolites have enjoyed considerable attention over the last decade. It is known that purified natural clinoptilolite from Tasajeras deposit in Cuba, NZ, does not cause damage to humans. It has been used as raw material in the pharmaceutical industry for the therapy of some pathologies, both in animals and in humans, using different pharmaceutical forms. The possible interaction between organic molecules of pharmaceutical interest and clinoptilolite has been studied using experimental and theoretical tools. Aspirin, metronidazole and sulfamethoxazole has been the evaluated drugs based on their wide use and because they produce side effects associated with gastrointestinal disturbances, which could be attenuated by the clinoptilolite. Regarding experimental studies, the results suggest a poor adsorption of these drugs on the natural clinoptilolite and their ion exchanged modified forms in good agreement with the calculations. In order to develop drug support systems for slow release, a new potential application of purified natural clinoptilolite has been explored, which involves the modification of the zeolite surface with surfactants. The obtained composites can co-adsorb organic molecules, as sulfamethoxazole and metronidazole, due to the variation of the hydrophilic character of the zeolite. In the present work, different combined systems formed by surfactants, drugs, water and a clinoptilolite channel model have been studied using semiempirical calculations. We modelled 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 hydrophobic molecules like sulfamethoxazole is favoured. 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. However, the interaction of the zeolite with cationic surfactant and drugs is very complex and involves many different particles. As first step in some complex system, we have modelled the aggregation process of the cationic surfactant benzalkoniumchloride (BC-R12) in water using molecular dynamics in order to know the size and shape of the micelles. The energy of micelles with different aggregation number (Nagg) in water have been calculated and compared with the analogue system where molecules are randomly distributed. Our result suggest that micelles are more stable than the random systems and the smallest micelle, Nagg = 6, is the most stable. At 5 ps, micelles of intermediate size are reorganized and appear smaller aggregates formed by 7 or 10 molecules. We find that the alkyl chain of the BC-R12 molecule folding back on itself; this effect was observed both in the random and micelle distributions.
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