Electron-transfer mechanism in radical-scavenging reactions by a vitamin E model in a protic medium

• Published in: Organic & biomolecular chemistry Vol. 3; no. 4; p. 626
• Main Authors: Nakanishi, Ikuo, Kawashima, Tomonori, Ohkubo, Kei, Kanazawa, Hideko, Inami, Keiko, Mochizuki, Masataka, Fukuhara, Kiyoshi, Okuda, Haruhiro, Ozawa, Toshihiko, Itoh, Shinobu, Fukuzumi, Shunichi, Ikota, Nobuo
• Format: Journal Article
• Language: English
• Published: England 21.02.2005
• Subjects: Benzhydryl Compounds - chemistry; Biphenyl Compounds - chemistry; Chlorates - chemistry; Chromans - chemistry; Electrochemistry; Electron Spin Resonance Spectroscopy; Electron Transport; Free Radical Scavengers - chemistry; Free Radicals - chemistry; Hydrazines - chemistry; Kinetics; Magnesium - chemistry; Magnesium Compounds - chemistry; Methanol - chemistry; Molecular Structure; Oxidation-Reduction; Picrates; Pyridines - chemistry; Solvents - chemistry; Vitamin E - chemistry
• ISSN: 1477-0520
• DOI: 10.1039/b416572a

The scavenging reaction of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH.) or galvinoxyl radical (GO.) by a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), was significantly accelerated by the presence of Mg(ClO4)2 in de-aerated methanol (MeOH). Such an acceleration indicates that the radical-scavenging reaction of 1H in MeOH proceeds via an electron transfer from 1H to the radical, followed by a proton transfer, rather than the one-step hydrogen atom transfer which has been observed in acetonitrile (MeCN). A significant negative shift of the one-electron oxidation potential of 1H in MeOH (0.63 V vs. SCE), due to strong solvation as compared to that in MeCN (0.97 V vs. SCE), may result in change of the radical-scavenging mechanisms between protic and aprotic media.