Photostabilization of the botanical insecticide azadirachtin in the presence of lecithin as UV protectant
Titel:
Photostabilization of the botanical insecticide azadirachtin in the presence of lecithin as UV protectant
Auteur:
Sundaram, K. M. S. Curry, J.
Verschenen in:
Journal of environmental science and health. Part B, Pesticides, food contaminants, and agricultural wastes
Paginering:
Jaargang 31 (1996) nr. 5 pagina's 1041-1060
Jaar:
1996-09
Inhoud:
The phytochemical insecticide, azadirachtin (AZ), undergoes UV-induced photodegradation. Using the isomer AZ-A as a standard, its photochemical stability was studied with and without adding lecithin surfactant as a UV protectant. Standard solutions of pure AZ-A and Margosan-O® were prepared in methanol-hexane with (AZ-A:lecithin, 1:2 by weight) and without lecithin, applied separately onto glass plates and maple (Acer L.) foliage and exposed to radiant energy under controlled conditions. Noticeable photostabilization of AZ-A was achieved in the samples containing lecithin compared to AZ-A samples without the lecithin additive. First-order kinetic evaluation of the data showed that the DTy50 (half-life) and C (rate constant) values for AZ-A with and without lecithin on glass plates were 5.68 d and 0.122, and 5.42 d and 0.128, respectively. The corresponding values for the Margosan-0 formulation were 7.37 d and 0.094, and 6.24 d and 0.111. The DT50 and C values for the pure AZ-A on maple foliage with and without lecithin were 8.77 d and 0.079, and 6.54 d and 0.106, respectively. The corresponding values for the Margosan-0 formulation on foliage were 8.35 d and 0.083, and 7.45 d and 0.093. The kinetic data gave quantitative information regarding the photostabilization of AZ-A in the presence of lecithin. Good UV protection can only be achieved if the additive has the matching Xmax of AZ-A. The mechanism of photostabilization of AZ-A in the presence of lecithin was due to either energy transfer from the excited AZ-A to lecithin and/or competitive absorption of UV photons by the latter.
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