Inclusion complexes and stability studies of an organophosphorous insecticide with cyclodextrins: spectrophotometric and kinetic determination of stability constant

Abstract

DCPE[α-(diethoxyphosphinoximino)dicyclopropylmethane] is a potent organophosphorous insecticide. It is an oily liquid and therefore the most suitable formulation is an ‘emulsifiable concentrate’. In an attempt to develop better formulations, complexes of this insecticide with the cyclodextrins (CDs)αCD, βCD and hydroxypropyl-βCD (HP-βCD) were examined. Stability constants were determined spectrophotometrically, in the case of DCPE–βCD, according to the spectral changes of DCPE due to the complexation and kinetically, in the case of DCPE–HP-βCD, according to the changes in the rate constant of DCPE degradation. HP-βCD has a stabilizing effect on DCPE by decelerating its degradation in aqueous solutions, but αCD and βCD have no effect. Finally, the thermodynamic parameters for the inclusion complex formation between DCPE and HP-βCD in aqueous solutions were calculated by correlating the changes in the stability constant with temperature.