Bipyridyliums

Paraquat, 1, r>dimethyM,4 >bipyridylium dimethylsulphate or dichloride Both salts are... 

A Microcalorimetric Investigation of the Interactions Between Clay Minerals and Bipyridylium Salts, M. H. B. Hayes, M. E. Pick, M. Stacey, and B. A. Toms, Proc. 1972 Int. Clay Conf., (1973) 675-682. 

Methyl viologen (l,T-dimethyl-4,4 -bipyridylium dichloride, MV " ) promotes photoanodic dissolution in aerated CdS solution Figure 8 shows how the rate of dissolution depends on the concentration. The colloid has a weak fluorescence at 620 nm which is quenched by. The curves for fluorescence and dissolution in Fig. 8 are symmetric, which indicates that the two processes have a common intermediate that reacts with M. These effects are explained by the following mechanism ... 

With respect to using methyl viologen as electron relay, it might be of interest to note tlmt MV " can be oxidized by positive holes produced in illuminated colloidal semiconductors such as Ti02 Two oxidation products of MV are 1, 2 -di-hydro-l,r-dimethyl-2 -oxo-4,4 -bipyridylium chloride and 3,4-dihydro-l,r-dime-thyl-3-oxo-4,4 -bipyridylium chloride, which can readily be detected by their strong fluorescences at 516 nm and 528 nm, respectively. These products are also produced in the direct photolysis of MV " solutions and in the reaction of MV "" with OH radicals in homogeneous solution... 

The production of free radicals has been implicated in the mechanism of liver injury due to a number of drugs and toxins. These include adtiamycin (Pritsos et al., 1992), halothane (Neuberger and Williams, 1984), phenobar-bital and thiopental (Kanazawa and Ashida, 1991), carbon tetrachloride (Williams and Burk, 1990), 1,1,2,2-tetrachloroethane (Paolini aal., 1992), and paraquat and related bipyridylium compounds (Togashi a al., 1990 De Gray etal., 1991 Kanazawa and Ashida, 1991 Petty etal., 1992). 

De Gray, J.A., Rao, D.N. and Mason, R.P. (1991). Reduction of paraquat and related bipyridylium compounds to free radical metabolites by rat hepatocytes. Arch. Biochem. Biophys. 289, 145-152. 

Suleiman, S.A. and J.B. Stevens. 1987. Bipyridylium herbicide toxicity effects of paraquat and diquat on isolated rat hepatocytes. Jour. Environ. Pathol. Toxicol. Oncol. 7 73-84. 

While the cytochrome P-450 monooxygenase reaction described in Eq. (1) often involves hydroxylation of carbon, many other reactions are catalyzed by these enzyme systems. These reactions include oxidation of nitrogen and sulfur, epoxidation, dehalogenation, oxidative deamination and desulfuration, oxidative N-, O-, and S-dealkylation, and peroxidative reactions (56). Under anaerobic conditions, the enzyme system will also catalyze reduction of azo, nitro, N-oxide, and epoxide functional groups, and these reductive reactions have been recently reviewed (56, 57). Furthermore, the NADPH-cytochrome P-450 reductase is capable of catalyzing reduction of quinones, quinonimines, nitro-aromatics, azoaromatics, bipyridyliums, and tetrazoliums (58). 

Cationic Diquat dibromide Nitrogen-containing H 85-00-7 l,r-Ethylene-2,2 -bipyridylium dibromide,monohydrate... 

The classical route for producing 2,2 -dipyridyl consists in the dehydrodimerization of pyridine on Raney-Ni using a process developed by the Imperial Chemical Industries [63AHC(2)179 68CI(L)49, 80MI4]. 2,2 -Bipyridyl reacts with ethylene bromide to give l,l -ethylene-2,2 -bipyridylium bromide (diquat). The production of one ton of the diquat (which is widely used as a herbicide) requires 1.2 tons of pyridine [Eq.(17)]. 

Bipyridyliums class of herbicides that includes paraquat... 

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). 

Sugarcane Sower initiation is dependent on day length, temperature, age, moisture, and variety, and can be prevented by chemical applications at, or very close to, the date of floral initiation. The effective chemicals have been of two types (a) photosynthetic inhibitors, such as 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), or (b) leaf-burning, contact chemicals. The very effective bipyridylium herbicides 6,7-dihydrodipyrido[l,2-a 2, r-c]pyrazidinium dibromide (diquat) and 1, l -dimethyl-4,4 -bipyridinium bis (methyl sulfate) (paraquat) combine the two properties, although the... 

The bipyridylium compounds have also been Used experimentally to desiccate sugarcane leaves, and are more effective for this purpose than substituted phenols, oils, and chlorates. The yield of treated cane remained more or less constant for several weeks, and then increased again as new leaves formed. The yield of sucrose decreased as a result of treatment, partly because of the temporary reduction of photosynthesis, and partly as a result of increased stalk-moisture.800... 

A member of the bipyridylium family of herbicides is the compound paraquat (1,1-dimethyl-4,4-bipyridinium ion as the chloride salt) (Figure 5.1). It is a very water-soluble contact herbicide that is active against a broad range of plants and is used as a defoliant on many crops. The compound binds tightly to soil particles following... 

Since their early studies Eley et al. (1959) (see Eley, 1967) have largely confined their attentions to the study of the electronic and structural properties of bipyridinium2+ (TCNQ)2" and related complexes (Ashwell et al., 1975a, b, c Ashwell et al., 1977a, b, c Eley et al., 1977). Most complexes, such as 4,4-bipyridyl (TCNQ)2, five (N,N-dialkyl-4,4 -bipyridylium)2+ (TCNQ)J+ salts (alkyl = methyl, ethyl, propyl, isopropyl and benzyl ), and l,2-di(N-ethyl-4-pyridinium) ethylene2+ (TCNQ), are low gap semiconductors except one form of the last compound which exhibited metallic behaviour. The asterisked complexes comprise planar sheets of TCNQ molecules grouped in tetrads. 

Senesi, N., Dorazio, V. D., and Miano,T. M. (1995). Adsorption mechanisms of s-triazine and bipyridylium herbicides on humic acids from hop field soils. Geoderma 66(3 4), 273-283. 

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