Organic & Biomolecular Chemistry 2005-02-21

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

Index: Org. Biomol. Chem. 3(4) , 626-9, (2005)

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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.