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Nitro free radical formation of diphenyl ether herbicides is not necessary for their toxic action

Authors
Journal
Pesticide Biochemistry and Physiology
0048-3575
Publisher
Elsevier
Publication Date
Volume
23
Issue
2
Identifiers
DOI: 10.1016/0048-3575(85)90003-3

Abstract

Abstract The diphenyl ether herbicides MC 15608 {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-chloromethylbenzoate} and MC 10878 {5-[2-chloro-4-(trifluoromethyl)phenoxy]methyl benzoate} are structurally similar to acifluorfen-methyl (methyl ester of 5-[2-chloro-4-(trifluoromethyl)phenoxy]-nitrobenzoic acid), except that the NO 2 is replaced by a Cl and H, respectively. These diphenyl ether herbicides required light for herbicide toxicity to the green unicellular alga Chlamydomonas eugametos and three major weeds ( Xanthium pennsylvanicum, Abutilon theophrasti, and Ipomoea sp.). Acifluorfen-methyl and MC 15608 toxicity in Chlamydomonas decreased in an atmosphere of nitrogen, and in the presence of the free radical scavengers α-tocopherol and ethanol. Therefore, the mechanism of toxic action of these three different diphenyl ether herbicides is similar and appears to involve some type of free radical reaction. As confirmed by cyclic voltammetry studies, MC 15608 and MC 10878, unlike AFM, cannot readily accept electrons to become free radicals. Therefore, initiation of free radical reactions in polyunsaturated fatty acids of membranes does not necessarily involve direct reduction and reoxidation of the diphenyl ether molecule.

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