Redox-controlled reactions of nitroarene radiosensitizers in chemical systems

4 Redox-controlled reactions of nitroarene radiosensitizers in chemical systems 

Nitroarenes can react with reducing radicals in two general pathways, radical-addition or outer-sphere electron-transfer, although electron transfer can proceed via adducts in an inner-sphere addition/elimination reaction [98]. Prototypical behaviour was established from electron paramagnetic resonance (epr) experiments [99], which showed that hydroxymethyl radicals reduced nitrobenzene via an intermediate adduct, relatively stable in acid but which underwent base-catalyzed heterolysis  

Reactions of nitroarenes with both sugar and base radicals have been studied in some depth by several groups, summarized in earlier reviews [77-79,93,100]. Thus a radical that clearly forms adducts, such as that derived from an ether, reacted with nitroimidazoles with a redox relationship three times shallower than observed for radiosensitization of mammalian cells [100]  

The rate constant for adduct formation by CH2OH with different nitrobenzenes was also weakly-redox-controlled, equation (20) [101], but the heterolysis of the adducts formed with CHsC HOH was influenced by reduction potential to a greater extent, equation (21) [102]  

More recent studies have provided interesting new information. A comparison was made of the reactions of 4-nitrobenzonitrile or oxygen with a-alkoxyalkyl radicals, models for DNA sugar radicals, produced via reaction of OH with e.g. 

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