Production of activated species of oxygen during the chromate(VI)-ascorbate reaction: implication in carcinogenesis.

The reaction of chromate and ascorbate in a 1:1 molar ratio at pH 7.4 and 37 degrees C produces a Cr(V) signal observable by EPR at g = 1.980. When this reaction is carried out in aerated media and in the presence of formate, carboxylate radicals (COO.-) can be trapped as DMPO-COO.- spin adducts (DMPO, 5,5-dimethyl-1-pyrroline N-oxide). The use of a known complexant of Cr(V), 2-ethyl-2-hydroxybutyric acid, produces a different Cr(V) signal at g = 1.978 and a decrease of the DMPO-COO.- signal. Hydroxyl radicals are not detected in the media. The oxidizing behavior is suggested to be produced by activation of molecular oxygen present in the reaction mixture.