Thermodynamic Study of Cyclodextrins Complexation with Benzimidazolic Antihelmintics in Different Reaction Media

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Abstract
The main purpose of this work was to accomplish a comparative study about cyclodextrins complexation equilibria with three benzimidazolic antihelmintics: albendazole (Alb), mebendazole (Meb) and thiabendazole (Thiab).The complexation process with four different cyclodextrins (α-, β-, γ-, and HP-β-CDs) was investigated under various temperatures and different reaction media (aqueous solution buffered at pH 7.5, dimethylsulfoxide (DMSO) and DMSO/water at 25/75, 50/50, 75/50 (w/w) mixtures). It was studied by electronic absorption and 1H NMR (NOESY) spectroscopy. Binding constants were determined by electronic absorption spectroscopic method, the ΔH and ΔS complexation values were evaluated and discussed according to the diverse factors that affect the chemical interactions in these systems. Solubility has also been determined by the Higuchi and Connors method. In general, albendazole and mebendazole exhibit similar complexation behavior, while thiabendazole acts differently. Classic and non-classic solvophobic effects are mainly the driving and stabilizing forces for complex formation, with the exception in some Thiab-CDs interactions. In all cases, DMSO, an aprotic solvent, should be considered as an active component of the reaction systems.