Preparation and characterization of inclusion complexes between cyclodextrins and agricultural toxic substances

Abstract

The primary goal of this work was to investigate the solubilizing ability of various ßCDs. ßCD, methyl- ßCD and G₂-ßCD, when complexed with several pesticides (Carbendazim, Carbendazim 50 WP, Methidathion, Carbaryl and Carbaryl 85 WP). The effect of ßCD and its derivatives on the aqueous solubility of pesticides was evaluated by the phase solubility technique. Methyl-ßCD showed more solubilizing ability for four pesticides than ßCD and G₂- ßCD except in the case of carbendazim 50 WP of which no solubility increase was observed with all of ßCDs. Solubility increase was the highest for methyl-ßCD increase the carbaryl 85 WP. The presence of 100mM methyl- ßCD increased the carbaryl 85 WP solubility approximately 18.4 folds. The formation constant was determined to be 223.187 M⁻¹. The next step was to prepare carbaryl 85 WP/methyl-ßCD complex at the molar ratios of 1:1, 1:2 and 2:1 in solid state. The methods were by physical-mixing, co-precipitation, kneading and freeze-dying. Differential Scanning Calorimeter (DSC) and Fourier Transform Infrared (FTIR) analysis were used to confirm the inclusion in solid state. The DSC curves for kneading and freeze-drying mixtures did not show the endothermic peak characteristics of free carbaryl, but the small new endothermic peak was observed. FTIR analysis showed a shift of the major peak of carbonyl group in carbaryl molecule from 1717 to 1744 and 1734 cm⁻¹ in kneading and freeze-dried mixtures, respectively. The result from two analyses suggested the formation of an inclusion complex. Methyl-ßCD-carbaryl complex demonstrated higher and faster dissolution rate, higher thermal and UV stability but lower toxicity than its parent carbaryl compound.