@misc{oai:repo.qst.go.jp:00071467,
 author = {和氣, 司 and 中西, 郁夫 and 大久保, 敬 and 松本, 謙一郎 and 福住, 俊一 and 小澤, 俊彦 and 鎌田, 正 and 和氣 司 and 中西 郁夫 and 大久保 敬 and 松本 謙一郎 and 小澤 俊彦 and 鎌田 正},
 month = {Jun},
 note = {Ubiquinol, the reduced form of coenzyme Q10, has a hydroquinone structure as an active center and shows an efficient scavenging activity against reactive oxygen species (ROS).  On the other hand, we have recently reported that redox-inactive metal ions, such as Mg(2+) and Al(3+), significantly affect the radical-scavenging activity of phenolic antioxidants, such as flavonoids.  Thus, in this study, we investigated the effect of redox-inactive metal ions on the radical-scavenging activity of hydroquinone and its methylated derivatives as well as on their one-electron oxidation potentials.
Hydroquinones scavenged 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical as a ROS model.  The rates of the DPPH radical-scavenging reactions of hydroquinones in the presence or absence of 0.1 M Mg(ClO(4))(2) or 0.1 M Al(ClO(4))(3) were determined by monitoring the absorbance change at 517 nm due to DPPH radical using a stopped flow technique in deaerated ethanol-H(2)O (9:1 v/v) at 298 K.  The decay of the absorbance at 517 nm obeyed pseudo-first-order kinetics, when the concentration of hydroquinones ([hydroquinones]) was maintained at more than 10-fold excess of the DPPH radical concentration.  The pseudo-first-order rate constants (k(obs)) increase with increasing [hydroquinones], exhibiting first-order dependence on [hydroquinones].  From the slope of the linear plots of k(obs) vs. [hydroquinones], the second-order rate constants (k) were determined for the DPPH radical-scavenging reaction.  The k values of hydroquinones were almost unchanged in the presence of Mg(2+), while they were increased in the presence of Al(3+).  The one-electron oxidation potentials of hydroquinones were determined by second-harmonic alternating current voltammetry in ethanol-H(2)O (9:1 v/v) containing 0.1 M Bu(4)NClO(4) as a supporting electrolyte.  In the presence of the redox-inactive metal ions, the one-electron oxidation potentials remained unchanged as compared to those in their absence.  On the other hand, the one-electron reduction potential of DPPH radical determined from a well-defined reversible wave by cyclic voltammetry in ethanol-H(2)O (9:1 v/v) was slightly shifted in the presence of 0.1 M Mg(2+) and largely shifted in the presence of Al(3+) to the positive direction.
These results indicate that in the presence of Al(3+), the DPPH radical-scavenging reaction of hydroquinones occurred via an electron transfer as a rate-determining step, rather than one-step hydrogen-atom transfer.  Al(3+) may be stabilized DPPH anion produced by one-electron reduction of DPPH radical, leading to the acceleration of the DPPH radical-scavenging reaction., 第24回金属の関与する生体関連反応シンポジウム(SRM2014)},
 title = {ヒドロキノン類のラジカル消去活性に対するレドックス不活性金属イオンの影響},
 year = {2014}
}