Models of Pesticides inside Cavities of Molecular Dimensions. A Role of the Guest Inclusion in the Dechlorination Process

Abstract

The reduction mechanism of the pesticide vinclozoline (3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-1,3-oxazolidine-2,4-dione) was studied in nonaqueous solvents in the confined environment of a cyclodextrin (CD) cavity. The effect of the cavity dimensions on the mechanism of the redox process was evaluated using glucose as a reference and using three cyclodextrin molecules of different cavity sizes, namely, alphaCD, betaCD, and gammaCD. In the absence of CD the main reduction product of vinclozoline in the first reduction step is dichloroaniline. An addition of glucose leads to a quantitative change of mechanism with 10 products in total. Addition of CD, however, leads exclusively to dechlorination of the phenyl ring. The degree of dechlorination depends strongly on the choice of cyclodextrin molecule. The importance of the complex formation equilibria in the change of the mechanism is supported by a series of semiempirical AM1 quantum-mechanical calculations. Very good correlation (correlation coefficient 0.995) was obtained between the complex stabilization energy of the inclusion complex and the degree of pesticide dechlorination. Additionally, we were able to show that the complexes are stabilized by the formation of intermolecular hydrogen bonds between the host and guest species. CD molecules do not simply act as proton donors in a nonaqueous environment, but also protect parts of the molecule included within the cavity and steer the degradation process toward fewer products.

Electrochemical Cleavage of Carbon‐Chlorine Bonds in Multiply Bridge‐Chlorinated Bicyclo[1.1.1]pentane‐1,3‐dicarboxylic Acids

“…Electrocatalytic dehalogenation of open‐chain dibromides leads to cyclization, whereas cyclic dibromides provide a root to olefins [18] . The reductive cleavage of halogens was confirmed also in the decomposition of pesticides [19−21] …”

Comparative analysis of complexation of pesticides (fenitrothion, methylparathion, parathion) and their carboxylic ester analogues by β-cyclodextrin. Theoretical semiempirical calculations

“…CD complexation protects the guest molecule against atmospheric oxidation of easily oxidizable substances, enhances solubility of poorly soluble ones, and reduces the loss of those that are highly volatile. Also, synthetic pesticides that can be complexed with CDs frequently show modifications of properties [5][6][7][8] such as: enhanced bioavailability, selective toxicity as regards insects, reduced phytotoxicity and long lasting effects in soil due to controlled release properties. The dose of environmental polluting synthetic agrochemicals could thus be significantly reduced and their effectiveness could be improved, if CDs were used in pesticide solution formulations [9].…”