Kinetics and mechanism of the reaction of a nitroxide radical (Tempol) with a phenolic antioxidant

In the absence of redox-active transition metal ions, the removal of Tempol by Trolox occurs by a simple bimolecular reaction that, most probably, involves a hydrogen transfer from phenol to nitroxide. The specific rate constant of the process is small (0.1 M-1 s(-1)). Metals can catalyze the process, as evidenced by the decrease in rate observed in the presence of diethylenetriaminepentaacetic acid (DTPA). Furthermore, addition of Fe(II) (20 muM ferrous sulfate and 40 muM EDTA) produces a noticeable increase in the rate of Tempol consumption.