Abstract
Hydroxyhydroquinone (HHQ) (1,2,4-benzenetriol), one of the metabolites of benzene and a component in roasted coffee beans, generated a 0.5-0.6 equimolar amount of hydrogen peroxide in a neutral solution by consuming dissolved oxygen. The consumption of dissolved oxygen and production of hydrogen peroxide by HHQ were greater than those by pyrogallol (1,2,3-benzenetriol), and much greater than those by hydroquinone and chlorogenic acid. Consumption of dissolved oxygen and generation of hydrogen peroxide by HHQ, and decomposition of HHQ were completely inhibited by Cu, Zn-, Mn- and Fe-superoxide dismutase (SOD). HHQ generated the semiquinone radical(s) as assessed by electron spin resonance studies, and also the colored quinoid forms of HHQ as assessed by colorimetry. SOD also inhibited the formation of the semiquinone radical(s) and the quinoid forms of HHQ. The results indicate that superoxide plays an important role as a catalyst in the generation of hydrogen peroxide from HHQ in a neutral solution.
