Temperature effects on the one-electron reduction potentials of nitroaryl compounds.
Pulse radiolysis was used to establish one-electron transfer equilibria between radical cations of methyl or benzyl viologens (V2+) and nitroaryl compounds (ArNO2): a nitroimidazole (misonidazole or metronidazole), 4-nitrobenzoate or nitrofurazone. The equilibrium constants in water at pH 8 were estimated over the temperature range approximately 5 to 75 degrees C. The difference delta E in mid-point one-electron reduction potentials between the nitro compounds and the viologens varied with temperature T; increasing temperature made the nitro compounds apparently less electron-affinic compared to the effects of temperature on the viologen potential. Values of delta(delta E)/delta T were in the range -0.7 to -1.1 mV K-1 at 25 degrees C. If delta[E(V2+/V.+)]/delta T = -0.9 mV K-1 for methyl viologen then delta[E(ArNO2/ArNO2.-)]/delta T is about -2 mV K-1 for these compounds.
Wardman
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Cancer Research Campaign, Mount Vernon Hospital, Northwood, Middlesex, U.K.
Clarke
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D001594:Benzyl Viologen / Q000737:chemistry; D005609:Free Radicals; D008795:Metronidazole / Q000737:chemistry*; D008920:Misonidazole / Q000737:chemistry*; D015394:Molecular Structure; D009579:Nitrobenzoates / Q000737:chemistry*; D009583:Nitrofurazone / Q000737:chemistry*; D010084:Oxidation-Reduction; D010269:Paraquat / Q000737:chemistry; D011675:Pulse Radiolysis; D013696:Temperature
D005609:Free Radicals; D009579:Nitrobenzoates; D001594:Benzyl Viologen; D008795:Metronidazole; D008920:Misonidazole; C008629:4-nitrobenzoic acid; D010269:Paraquat; D009583:Nitrofurazone