Electron Spin Resonance Study of the Self-disproportionation of some Semiquinone Radicals in Solution

Abstract

The photolysis of 1,4-benzoquinone, duroquinone, and 1,4-naphthoquinone in isopropanol and in dioxane leads to the observation of e.s.r. spectra of the corresponding semiquinone radicals. The rates of the selfdisproportionation of these radicals were measured by the rotating-sector technique. In the case of 1,4-naphthoquinone, unexpected e.s.r. emission was initially observed by photochemically induced dynamic electron polarization of the semiquinone radicals. Photolysis of anthraquinone in isopropanol gives e.s.r. spectra of the anthrasemiquinone radical anions. Their rate of decay was measured and a mechanism for the decay was suggested. The neutral anthrasemiquinone radical, however, was observed when photolyzed in dioxane.La photolyse de la benzoquinone-l,4,duroquinone et naphtoquinone-1,4 dans I'isopropanol et dans le dioxane, permet d'observer les spectres r.p.e. des radicaux semiquinone correspondants. Les vitesses d'autodismutation de ces radicaux ont kt6 mesurees par la technique du secteur tournant. Dans le cas de la naphtoquinone-1,4, on a observe initialement un spectre d'emission r.p.e. inattendu explique par une polarisation electronique dynamique, induite par voie photochimique, des radicaux semiquinone. La photolyse de l'anthraquinone dans l'isopropanol donne des spectres r.p.e. des radicaux anions anthrasemiquinone. Leur duree de vie a ete mesuree et un mecanisme de leur extinction suggere. Cependant, le radical neutre anthrasemiquinone a ete observe par photolyse dans le dioxane.[Traduit par le journa(] Canadian Journal of Chemistry, 50,3052 (1972)

Chemically induced dynamic nuclear and electron polarization. Part IX. The photolysis of tetrafluoro-p-benzoquinone in dioxane

“…These radicals decay by self-disproportionation with a second-order rate constant at room temperature of 3.2 x 10' M-' s-I. Similar decay kinetics have been reported (2) for other semiquinone radicals in dioxane or isopropanol solution.…”

Curcumin protects against gallic acid-induced oxidative stress, suppression of glutathione antioxidant defenses, hepatic and renal damage in rats

“…One possibility on the mechanism how Gal induces oxidative stress is that the three aromatic phenoxyl groups of Gal (Figure 1) are prone to oxidation with the formation of H 2 O 2 , superoxide anions, quinones and semiquinones. [32][33][34] These metabolites (e.g. superoxides)…”

Chemically Induced Dynamic Electron Polarization. IV. The Photolysis of 1,4-Naphthoquinone

“…Normally lo3 to lo4 (CH,),~OH was found (5). photolysis system has been observed (9). The The time response of the present detection system was SemiquinOne radicals give a totally emissive limited mainly by the Varian 100 kHz modulation unit Spectrum for all components during and was probably not better than about 150 ps.…”