INCLUSION COMPLEXES AND STABILITY STUDIES OF AN ORGANOPHOSPHOROUS INSECTICIDE WITH CYCLODEXTRINS - SPECTROPHOTOMETRIC AND KINETIC DETERMINATION OF STABILITY CONSTANT

DCPE [alpha-(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) alpha CD, beta CD and hydroxypropyl-beta CD (HP-beta CD) were examined. Stability constants were determined spectrophotometrically, in the case of DCPE-beta CD, according to the spectral changes of DCPE due to the complexation and kinetically,in the case of DCPE-HP-beta CD, according to the changes in the rate constant of DCPE degradation. HP-beta CD has a stabilizing effect on DCPE by decelerating its degradation in aqueous solutions, but alpha CD and beta CD have no effect. Finally, the thermodynamic parameters for the inclusion complex formation between DCPE and HP-beta CD in aqueous solutions were calculated by correlating the changes in the stability constant with temperature.