Electron-transfer mechanism in radical-scavenging reactions by a vitamin E model in a protic medium.
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.
Nakanishi
Ikuo
I
Redox Regulation Research Group, Research Center for Radiation Safety, National Institute of Radiological Sciences, Inage-ku, Chiba 263-8555, Japan. nakanis@nirs.go.jp
Kawashima
Tomonori
T
Ohkubo
Kei
K
Kanazawa
Hideko
H
Inami
Keiko
K
Mochizuki
Masataka
M
Fukuhara
Kiyoshi
K
Okuda
Haruhiro
H
Ozawa
Toshihiko
T
Itoh
Shinobu
S
Fukuzumi
Shunichi
S
Ikota
Nobuo
N
D001559:Benzhydryl Compounds / Q000737:chemistry; D001713:Biphenyl Compounds / Q000737:chemistry; D002704:Chlorates / Q000737:chemistry; D002839:Chromans / Q000737:chemistry; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D016166:Free Radical Scavengers / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry*; D006834:Hydrazines / Q000737:chemistry; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D017616:Magnesium Compounds / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010851:Picrates; D011725:Pyridines / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D014810:Vitamin E / Q000737:chemistry*
C048427:2,2,5,7,8-pentamethylchroman; D001559:Benzhydryl Compounds; D001713:Biphenyl Compounds; D002704:Chlorates; D002839:Chromans; D016166:Free Radical Scavengers; D005609:Free Radicals; D006834:Hydrazines; D017616:Magnesium Compounds; D010851:Picrates; D011725:Pyridines; D012997:Solvents; D014810:Vitamin E; C013093:2,6-lutidine; C004931:1,1-diphenyl-2-picrylhydrazyl; D008274:Magnesium; C033775:magnesium chlorate; C020338:galvinoxyl; D000432:Methanol