How cyclodextrins affect the reactivity of organophosphorus insecticides

ELBA I. BUJÁN; NATALIA M. ROUGIER; RAQUEL V. VICO; RITA H. DE ROSSI

Foz de Iguazú

Conferencia; 12th Latin-American Conference on Physical Organic Chemistry; 2013

Universidade Federal de Santa Catarina

Agrochemicals are an important tool for pests’ management; they have been designed to control vectors of some infectious diseases and to reduce the economical loss due to low yield crops. Agrochemicals frequently display low aqueous solubility and are highly toxic. Consequently, their administration results in undesirable collateral effects such as polluting the atmosphere and leaching into groundwater, causing harm to humans and animals. An interesting manner to address these problems is by inclusion of the agrochemicals in cyclodextrins. Cyclodextrins (CDs) are cyclic oligosaccharides composed of glucose molecules. A CD molecule has a hydrophobic cavity that can accept hydrophobic organic compounds such as a pesticide molecule to form an inclusion complex. Thus, successful CD inclusion of agrochemicals can contribute very significantly to the safety and optimum use of these compounds by reducing their volatility, preventing their leaching into groundwater, ensuring that their administration is localized at the target organism and stabilizing them against chemical and photolytic degradation. We have studied the interaction of two phosphorothioate insecticides used in our country: Fenitrothion and Chlorpyrifos-Me, with native and methylated CDs and the effect of the CDs on the reactivity of the insecticides. Fenitrothion forms inclusion complexes with α-, β- and γ-CD, and the methylated TRIMEA, DIMEB and TRIMEB in solution that inhibits the hydrolysis reaction. The highest inhibition was observed with the dimethylated β-CD, DIMEB, and it decreases with the decrease of the association constant (Kass) for the formation of the complex.1 The hydrolysis reaction of Chlorpyrifos-Me is inhibited by α-, β- and γ-CD showing saturation kinetics; the greater inhibition is produced by γ-CD. The reaction with HOO– is weakly inhibited by α- and β-CD whereas γ-CD produces a greater inhibition and saturation kinetics.2 In all cases the inhibition is attributed to the inclusion of the substrate with the reaction center protected from external attack of the nucleophile.