Redox Dependence of the Reaction of α-Alkoxyalkyl Radicals with a Series of Oxidants

Oxygen and oxidants enhance the sensitivity of cells to radiation. To understand this effect at the mechanistic level, the redox dependences for the reactivity of weakly reducing α-monoalkoxyalkyl radicals of 1,4-dioxane and tetrahydrofuran with a series of oxidants, for example, quinones, viologens, and nitro-arenes, with one-electron reduction potentials E 7 1 values ranging from −80 to −640 mV, have been determined using the technique of pulse radiolysis. The second-order rate constants for these reactions with the α-monoalkoxyalkyl radicals of 1,4-dioxane and tetrahydrofuran are in the range (0.03−1.5) × 109 and (1.0−6.6) × 109 dm3 mol−1 s−1, respectively. The reactions of the α-alkoxyalkyl radicals of 1,4-dioxane with quinones and viologens involve an outer-sphere electron transfer, in contrast to a reaction with the nitro-arenes to give adducts. The resulting long-lived nitroaromatic adduct radicals were found to react with the reductant, TMPD, probably leading to the formation of hydroxylamine-type products. In cells, adducts formed on reaction of deoxyribose sugar radical with oxidants and subsequent reactions with reductants may contribute to the mechanisms involved in radiosensitization by oxygen and those oxidants that interact through adduct formation.