Cyclodextrin inclusion effects on photodegradation rates of organophosphorus pesticides

The inclusion effects of α-, β-, γ-, hexa-2,6-dimethyl α-, and hepta-2,6-dimethyl β-cyclodextrins (CyDs) on the photodegradation of parathion and paraoxon were investigated in methanolic aqueous solution. The above effects of CyDs were in a characteristic relationship with the inclusion depth parameters of the pesticides determined by the rotational-strength analysis of the induced circular dichroism of the inclusion complexes. The inclusion effect of β-CyD was found to inhibit the photodegradation of parathion but to promote that of paraoxon. Basic properties of the CyD inclusion effects were explained in terms of the difference in the degree of proximity between the catalytic sites of the CyD host cavities and the reaction centers of the includes pesticide guests.