ESR spin trapping detection of hydroxyl radicals in the reactions of Cr(V) complexes with hydrogen peroxide.

Electron spin resonance (ESR) measurements provide direct evidence for the involvement of Cr(V) in the reduction of Cr(VI) by NAD(P)H. Addition of hydrogen peroxide (H2O2) to NAD(P)H-Cr(VI) reaction mixtures suppresses the Cr(V) signal and generates hydroxyl (.OH) radicals (as detected via spin trapping), suggesting that Cr(V) reacts with H2O2 to generate the .OH radicals. Reaction between H2O2 and a Cr(V)-glutathione complex, and between H2O2 and several Cr(V)-carboxylato complexes also produces .OH radicals. These results suggest that Cr(V) complexes catalyze the generation of .OH radicals from H2O2, and that .OH radicals might play a significant role in the mechanism of Cr(VI) cytotoxicity.