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

Ikuo Nakanishi; Tomonori Kawashima; Kei Ohkubo; Hideko Kanazawa; Keiko Inami; Masataka Mochizuki; Kiyoshi Fukuhara; Haruhiro Okuda; Toshihiko Ozawa; Shinobu Itoh; Shunichi Fukuzumi; Nobuo Ikota

doi:10.1039/b416572a

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

Ikuo Nakanishi, Tomonori Kawashima, Kei Ohkubo, Hideko Kanazawa, Keiko Inami, Masataka Mochizuki, Kiyoshi Fukuhara, Haruhiro Okuda, Toshihiko Ozawa, Shinobu Itoh, Shunichi Fukuzumi, Nobuo Ikota

Department of Chemistry & Nanoscience

Research output: Contribution to journal › Article › peer-review

107 Scopus citations

Abstract

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.

Original language	English
Pages (from-to)	626-629
Number of pages	4
Journal	Organic and Biomolecular Chemistry
Volume	3
Issue number	4
DOIs	https://doi.org/10.1039/b416572a
State	Published - 21 Feb 2005

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@article{45288093aede455e8945b4f79eb5831d,

title = "Electron-transfer mechanism in radical-scavenging reactions by a vitamin E model in a protic medium",

abstract = "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.",

author = "Ikuo Nakanishi and Tomonori Kawashima and Kei Ohkubo and Hideko Kanazawa and Keiko Inami and Masataka Mochizuki and Kiyoshi Fukuhara and Haruhiro Okuda and Toshihiko Ozawa and Shinobu Itoh and Shunichi Fukuzumi and Nobuo Ikota",

year = "2005",

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doi = "10.1039/b416572a",

language = "English",

volume = "3",

pages = "626--629",

journal = "Organic and Biomolecular Chemistry",

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TY - JOUR

T1 - Electron-transfer mechanism in radical-scavenging reactions by a vitamin E model in a protic medium

AU - Nakanishi, Ikuo

AU - Kawashima, Tomonori

AU - Ohkubo, Kei

AU - Kanazawa, Hideko

AU - Inami, Keiko

AU - Mochizuki, Masataka

AU - Fukuhara, Kiyoshi

AU - Okuda, Haruhiro

AU - Ozawa, Toshihiko

AU - Itoh, Shinobu

AU - Fukuzumi, Shunichi

AU - Ikota, Nobuo

PY - 2005/2/21

Y1 - 2005/2/21

N2 - 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.

AB - 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.

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U2 - 10.1039/b416572a

DO - 10.1039/b416572a

M3 - Article

C2 - 15703798

AN - SCOPUS:20044365411

SN - 1477-0520

VL - 3

SP - 626

EP - 629

JO - Organic and Biomolecular Chemistry

JF - Organic and Biomolecular Chemistry

IS - 4

ER -

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

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