Direct short-wave photolysis of chlorpyrifos-methyl and chlorpyrifos-methyl oxon in the presence of cyclodextrins

Abstract

Direct short-wave photolysis of chlorpyrifos-methyl (1) and chlorpyrifos-methyl oxon (2) was studied in the presence of native cyclodextrins (α–, β– and γ–CD) and randomly methylated β–CD (RAMEB). We used for irradiation low pressure Hg lamps emitting at 254 nm and used as solvent 10% acetonitrile (ACN)/H2O solutions. The formation of an inclusion complex between 1 and β–CD was evaluated by UV–vis and NMR techniques. We did observe on UV–vis an interaction with β–CD, a feeble one not enough to enable the determination of the association constants. The experiments allowed us to assess that the presence of cyclodextrins produce a more rapid consumption of 1 and 2 compared to the naked molecules. A much faster photodegradation for the two compounds was observed in the presence of γ–CD. The average, at two wavelengths, of calculated ratios for the enhanced photodegradation of 1 were 1.3, 2.9, 25.8 and 2.9 for α–, β–, γ–CD and RAMEB, while in the case of 2, they reached 1.4, 3.5, 8.5 and 4.1 respectively. Our results indicate that short-wave photolysis of 1 in the presence of cyclodextrins could become a better plausible detoxification mechanism compared with their absence.