Effects of magnesium ion on kinetic stability and spin distribution of phenoxyl radical derived from a vitamin E analogue: Mechanistic insight into antioxidative hydrogen-transfer reaction of vitamin E

Ikuo Nakanishi, Kiyoshi Fukuhara, Tomokazu Shimada, Kei Ohkubo, Yuko Iizuka, Keiko Inami, Masataka Mochizuki, Shiro Urano, Shinobu Itoh, Naoki Miyata, Shunichi Fukuzumi

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Abstract

The phenoxyl radical 1. of a vitamin E analogue, generated by the reaction of 2,2,5,7,8-pentamethylchroman-6-ol (1H) with 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH.) or galvinoxyl (G.), was significantly stabilized by the presence of Mg2+. Addition of Mg2+ into a solution of 1. resulted in a red shift of the absorption band of 1. as well as a decrease in the g value of the EPR spectrum of 1., indicating a complex formation between 1. and Mg2+. The complexation between the phenoxyl radical and Mg2+ significantly retards the disproportionation reaction of 1. by electronic repulsion between the metal cation and a generated organic cation (1+), leading to stabilization of the organic radical species. No effect of Mg2+ on the rate of hydrogen atom transfer from 1H to DPPH. or to G. was observed, suggesting that the hydrogen-transfer reaction between 1H and DPPH. or G. proceeds via a one-step hydrogen atom transfer mechanism rather than electron-transfer followed by proton transfer.

Original languageEnglish
Pages (from-to)1520-1524
Number of pages5
JournalJournal of the Chemical Society. Perkin Transactions 2
Issue number9
StatePublished - 2002

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