The reduction potential of benzyl viologen: an important reference compound for oxidant/radical redox couples.
Bipyridinium compounds such as the viologens (V2+) have been used extensively as redox indicators, but radical dimerization leads to reduction potentials of the oxidant/radical one-electron couple, E(V2+/V2+) varying with radical concentration: a particular problem with benzyl viologen. Pulse radiolysis has been used to characterize the one-electron transfer equilibria between methyl (MV2+) or benzyl (BV2+) viologen and a 2-nitroimidazole (misonidazole), and between methyl and benzyl viologens directly. Total radical concentrations were typically approximately 0.4 mumol dm-3 to minimize dimerization. Based on E(MV2+/MV2+) = -450 mV, a value of E(BV2+/BV2+) = -374 mV is now recommended. The implications for other 'reference' redox couples are discussed.
Wardman
P
P
Cancer Research Campaign, Mount Vernon Hospital, Northwood, Middlesex, U.K.
D001594:Benzyl Viologen / Q000737:chemistry*; D005609:Free Radicals; D007700:Kinetics; D008920:Misonidazole / Q000737:chemistry; D010084:Oxidation-Reduction; D010269:Paraquat / Q000737:chemistry; D011675:Pulse Radiolysis; D012996:Solutions
D005609:Free Radicals; D012996:Solutions; D001594:Benzyl Viologen; D008920:Misonidazole; D010269:Paraquat