Phototransformation of azoxystrobin fungicide in organic solvents. Photoisomerization vs.photodegradation

• Published in: Photochemical & photobiological sciences 2013-11, Vol.12 (12), p.2076-2083
• Main Authors: Chastain, Jeoffrey, ter Halle, Alexandra, de Sainte Claire, Pascal, Voyard, Guillaume, Traikia, Mounir, Richard, Claire
• Format: Article
• Language: English
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1039/c3pp50241d

Azoxystrobin is a systemic fungicide that has a tendency to accumulate at the surface of crop leaves or inside their cuticle where it undergoes photodegradation. Its photochemistry was investigated in n-heptane and isopropanol to mimic the polarity of wax leaves. Using analytical and kinetic data, we demonstrate that azoxystrobin (isomer E) undergoes efficient photoisomerization into the isomer Zwith a quantum yield of 0.75 plus or minus 0.08. This value is 30-fold higher than that reported in aqueous solution. The photoisomerization of isomer Zinto azoxystrobin is more efficient with a chemical yield of 0.95 plus or minus 0.1. In addition, a pseudo photostationary equilibrium is reached when the ratio [azoxystrobin]/[isomer Z] is 2.0 plus or minus 0.1. Photodegradation also takes place from azoxystrobin (quantum yield = 0.073 plus or minus 0.008). Photoproducts mainly arise from bond cleavage between rings and from demethylation of the ether with or without saturation of the acrylate double bond. Theoretical calculations were undertaken to investigate the photoisomerization mechanism and the solvent effect. These data show that the photochemical reactivity of azoxystrobin is enhanced when the solvent polarity decreases and thus should be significant in leaf waxes.