量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
Thank you very much for using our website. On the 11th of March 2019, this site was moved from our own network server to the JAIRO Cloud network server. If you previously bookmarked this site, that bookmark will no longer work. We would be grateful if you could bookmark the website again. Thank you very much for your understanding and cooperation.
Resveratrol (1), 3,5,4'-trihydroxy-trans-stilbene, found in grapes is one of the representative antioxidants that shows a plethora of remarkable biological properties. On the other hand, pterostilbene (2), a methylated analog of 1, has attracted much attention due to its enhanced bioavailability as compared to that of 1. However, little is known about the radical-scavenging mechanism of 2. There are two mechanisms in the radical-scavenging reaction of phenolic antioxidants: a one-step hydrogen-atom transfer from the phenolic OH group; and an electron transfer followed by proton transfer. Redox inactive metal ions, such as magnesium ion (Mg2+), are a powerful tool to distinguish between these two mechanisms, because electron-transfer reactions are known to be accelerated by their presence. In fact, a significant acceleration in the radical-scavenging reaction of 1 was observed in the presence of Mg2+ in acetonitrile (MeCN), suggesting that the reaction may proceed via the electron-transfer mechanism (Chem. Lett. 2007, 36, 1276). We report herein the effect of Mg2+ on the scavenging reaction of galvinoxyl radical (GO) by 2 in MeCN. GO has been frequently used as a reactivity model of reactive oxygen radicals to estimate the activity of antioxidants.
Upon mixing of 2 with GO on a UNISOKU RSP-1000-02NM stopped-flow spectrophotometer in MeCN at 298 K, a gradual decrease in the absorption band at 428 nm due to GO was observed, indicating that 2 efficiently scavenged GO. From the time course change in the absorbance at 428 nm, the second-order rate constant (k) for the reaction between 2and GO was determined to be 1.3 × 10 M−1 s−1, which is about 3-fold larger than that of 1 (4.1 M−1 s−1). When Mg(ClO4)2 (0.1−0.3 M) was added to the 2−GO system, no effect of Mg2+ on the k values was observed. Thus, the GO-scavenging reaction by 2 may proceed via the one-step hydrogen-atom transfer rather than the electron transfer followed by proton transfer.
Effect of Magnesium Ion on the Radical-Scavenging Reaction of Pterostilbene and the Mechanism
