Metal-Independent Reduction of Hydrogen Peroxide by Semiquinones

Abstract

The quinones 1,4-naphthoquinone (NQ), tetramethyl-1,4-benzoquinone (DQ), 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UBQ-0), 2,6-dimethylbenzoquinone (DMBQ), 2,6-dimethoxybenzoquinone (DMOBQ), and 9,10-phenanthraquinone (PHQ) enhance the rate of H2O2 reduction by ascorbate, under anaerobic conditions, as detected from the amount of methane produced after hydroxyl radical reaction with dimethyl sulfoxide. The amount of methane produced increases with an increase in the quinone one-electron reduction potential. The most active quinone in this series, PHQ, is only 14% less active than the classic Fenton reagent cation, Fe2+, at the same concentration. Since PHQ is a common toxin present in diesel combustion smoke, the possibility that PHQ-mediated catalysis of hydroxyl radical formation is similar to that of Fe2+ adds another important pathway to the modes in which PHQ can execute its toxicity. Because quinones are known to enhance the antitumor activity of ascorbate and because ascorbate enhances the formation of H2O2 in tissues, the quinone-mediated reduction of H2O2 should be relevant to this type of antitumor activity, especially under hypoxic conditions.

Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

“…OH radicals can also be generated by the decomposition of organic hydroperoxides (ROOH) contained in SOA, yielding RO radicals . Several studies have reported a metal-independent decomposition of hydroperoxides and organic hydroperoxides driven by substituted quinones producing RO radicals (Sanchez-Cruz et al, 2014;Huang et al, 2015). The presence of Fe(II) or quinones is suggested to enhance ROOH decomposition and the formation of RO and OH radicals (Zhu et al, 2007a(Zhu et al, , b, 2009Sanchez-Cruz et al, 2014).…”

Experimental and Theoretical Reduction Potentials of Some Biologically Active ortho-Carbonyl para-Quinones

“…Consequently, the determination of redox potentials of quinones is currently an issue of great interest. The rational design of quinones with specific redox properties offers a wide variety of applications in pharmaceutical and materials sciences [ 27 , 31 , 32 , 33 ].…”

Oxidation of the plastoquinone pool in chloroplast thylakoid membranes by superoxide anion radicals

“…Hydroxyl radicals could oxidize the PQ‐pool and interfere with the measurements of PQH 2 oxidation by superoxide. The oxidation of the reduced PQ solution in methanol by H 2 O 2 was shown , but it was found that oxidation of quinols by H 2 O 2 proceeded with very low rate . The addition of catalase also prevented in the sample the development of anaerobic conditions, which could result from X‐XO system operation.…”