Effect of Magnesium Ion on the Radical-Scavenging Rate of Pterostilbene in an Aprotic Medium: Mechanistic Insight into the Antioxidative Reaction of Pterostilbene
Ikuo Nakanishi,
Yoshimi Shoji,
Kei Ohkubo,
Megumi Ueno,
Kei Shimoda,
Ken-ichiro Matsumoto,
Kiyoshi Fukuhara,
Hiroki Hamada
Affiliations
Ikuo Nakanishi
Quantum RedOx Chemistry Group, Institute for Quantum Life Science (iQLS), Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology (QST), Inage-ku, Chiba 263-8555, Japan
Yoshimi Shoji
Quantum RedOx Chemistry Group, Institute for Quantum Life Science (iQLS), Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology (QST), Inage-ku, Chiba 263-8555, Japan
Kei Ohkubo
Quantum RedOx Chemistry Group, Institute for Quantum Life Science (iQLS), Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology (QST), Inage-ku, Chiba 263-8555, Japan
Megumi Ueno
Quantitative RedOx Sensing Group, Department of Radiation Regulatory Science Research, National Institute of Radiological Sciences (NIRS), Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology (QST), Inage-ku, Chiba 263-8555, Japan
Kei Shimoda
Department of Biomedical Chemistry, Faculty of Medicine, Oita University, Yufu City, Oita 879-5593, Japan
Ken-ichiro Matsumoto
Quantitative RedOx Sensing Group, Department of Radiation Regulatory Science Research, National Institute of Radiological Sciences (NIRS), Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology (QST), Inage-ku, Chiba 263-8555, Japan
Kiyoshi Fukuhara
School of Pharmacy, Showa University, Shinagawa-ku, Tokyo 142-8555, Japan
Hiroki Hamada
Department of Life Science, Okayama University of Science, Kita-ku, Okayama 700-0005, Japan
Pterostilbene (PTS), a methylated analog of resveratrol (RSV), has recently attracted much attention due to its enhanced bioavailability compared to RSV. However, little is known about the radical-scavenging mechanism of PTS. In this study, we investigated the effect of Mg(ClO4)2 on the scavenging reaction of galvinoxyl radical (GO•) by PTS in acetonitrile (MeCN). GO• was used as a model for reactive oxygen radicals. The second-order rate constant (kH) for the GO•-scavenging reaction by PTS was more than threefold larger than that by RSV, although thermodynamic parameters, such as the relative O–H bond dissociation energies of the phenolic OH groups, ionization potentials, and HOMO energies calculated by the density functional theory are about the same between PTS and RSV. The oxidation peak potential of PTS determined by the cyclic voltammetry in MeCN (0.10 M Bu4NClO4) was also virtually the same as that of RSV. On the other hand, no effect of Mg (ClO4)2 on the kH values was observed for PTS, in contrast to the case for RSV. A kinetic isotope effect of 3.4 was observed when PTS was replaced by a deuterated PTS. These results suggest that a one-step hydrogen-atom transfer from PTS to GO• may be the rate-determining step in MeCN.
