Peroxidizing herbicides

This herbicidal mode of action of pyraflufen-ethyl is similar to those of other peroxidizing herbicides containing a diphenyl ether moiety. Herbicidal effects of pyraflufen-ethyl are revealed as yellowing and browning in the foliar portion, and then death of the whole plant with leaf burn. 

S. Murata, A. Yuda, A. Nakano, Y. Kimura, K. Motoba, T. Mabuchi, Y. Miura, H. Nishizawa, and S. Funayama, Mechanisms of selective action of the peroxidizing herbicide ET-751 on wheat and Galium aparine, in Proceedings of the 1995 Brighton Crop Protection Conference-Weeds, vol. 1, pp. 243-248 (1995). 

Lipid peroxidation, herbicides that induce, 13 297-298 Lipids... 

S -transferase (GST), glutathione (GSH) being the cofactor. These heterocyclic systems are strong peroxidizing herbicides. 

It has been demonstrated that peroxidizing herbicides interfere with the chlorophyll biosynthetic pathway (22) by accumulation of tetrapyrroles (17,18,23,24). It has also been shown that soluble plastidic cytochrome decreases when oxadiazon is present in a concentration when no peroxidation is yet apparent (25). For the identification of the tetrapyrrole the tolerant Bumilleriopsis was helpful. This species excretes large amounts of a tetrapyrrole into the liquid culture medium when treated with peroxidizing herbicides like oxadiazon, chlorophthalim, oxyfluorfen, or LS 82-556. The product found in the medium could be identified by mass and NMR spectrometry as protoporphyrin IX (17). 

Diphenylethers. Different agents can induce peroxidations in photosynthetic membranes. The strongest peroxidative herbicides known are the p-nitrodiphenyl ethers. Although compounds from this group of herbicides can act multifunctionally as electron-transport inhibitors U, 2 ) and energy-transfer inhibitors (1 0), some of them, like oxyfluorfen, exert their dominant phytotoxic action by damaging membrane components. 

I. Iwataki, in Peroxidizing Herbicides, ed. P. Boger, K. Wakabayashi, Springer-Verlag, Berlin, 1999, 73-89. 

A method of detecting herbicides is proposed the photosynthetic herbicides act by binding to Photosystem II (PS II), a multiunit chlorophyll-protein complex which plays a vital role in photosynthesis. The inhibition of PS II causes a reduced photoinduced production of hydrogen peroxide, which can be measured by a chemiluminescence reaction with luminol and the enzyme horseradish peroxidase (HRP). The sensing device proposed combines the production and detection of hydrogen peroxide in a single flow assay by combining all the individual steps in a compact, portable device that utilises micro-fluidic components. 

Pierotti, C., Deal, C., and Derr, E. Activity coefficient and molecular structure, Ind. Chem. Eng. Fundam., 51 95-101, 1959. Pignatello, J.J. Dark and photoassisted Fe -catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide. Environ. 

In natural water, singlet oxygen originating from humic substances has been shown, for example, to oxidize thioether pesticide contaminants such as disulfoton (Zepp et al. 1981). Irradiation of dilute hydrogen peroxide in the presence of various non-sunlight-absorbing herbicides results in enhanced oxidation of these substances (Draper and Crosby 1981). 

ISOTEC is a technology that uses the periodic injection of hydrogen peroxide and proprietary catalysts to oxidize organic contaminants in situ. According to the vendor, this technology can treat soil and groundwater contaminated with chlorinated compounds, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), trichloroethene (TCE), tetrachloroethene (PCE), pesticides, herbicides, as well as benzene, toluene, ethylbenzene, and xylene (BTEX). The ISOTEC technology is commercially available. 

Cyclic photophosphorylation is also a highly energetic reaction. The bipyridyliums, paraquat and diquat (Figure 2.2), divert the electron flow of cyclic photophosphorylation (photosystem I). The capture of an electron from the chlorophyll reduces the herbicide and the reduced herbicide reacts with oxygen to form superoxide. Superoxide produces hydrogen peroxide within the chloroplast and these two compounds interact to form hydroxyl radicals in the presence of an iron catalyst. Hydroxyl radicals are very damaging and lead to the destruction of the cellular components leading to rapid plant death. 

The herbicidal activity of the bipyridyliums depends on their redox properties. Their abilities as one-electron acceptors of the right redox potential (-350 mV for diquat and -450 mV for paraquat) allow them to siphon electrons out of the photosynthetic electron-transport system, competing with the natural acceptors. The radical anion produced is then reoxidized by oxygen, generating the real toxicant, hydrogen peroxide, which damages plant cells. Structure-activity relationships in this series have been reviewed (60MI10701). 

---