Permethylated β-cyclodextrin/pesticide complexes: X-ray structures and thermogravimetric assessment of kinetic parameters for complex dissociation

Abstract

The X-ray crystal structures of the inclusion complexes formed between three pesticides (two organophosphorus insecticides and one chloroacetanilide herbicide) and permethylated β-cyclodextrin (TRIMEB) are reported. The complexes TRIMEB–fenitrothion (1), TRIMEB–fenthion (2) and TRIMEB–acetochlor (3) are members of a commonly occurring isostructural series. The mode of inclusion of the two organophosphate insecticides is very similar, while the acetochlor molecule, which is structurally quite distinct from the two insecticide molecules, adopts a somewhat different position within the TRIMEB cavity. In addition to the structural elucidation of these complexes, their thermal behaviour was investigated using isothermal and non-isothermal thermogravimetry. The isothermal results showed that the dissociation of the guest molecules from the TRIMEB cavities can best be described by two mechanisms, namely a first-order reaction model and a three-dimensional diffusion model. Both the isothermal and non-isothermal methods allowed the determination of the activation energies of the guest loss process for each complex.