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Issue 9, 2002
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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

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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.

Graphical abstract: 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

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Publication details

The article was received on 05 Jun 2002, accepted on 20 Jun 2002 and first published on 15 Jul 2002


Article type: Paper
DOI: 10.1039/B205380B
Citation: J. Chem. Soc., Perkin Trans. 2, 2002,0, 1520-1524
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    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

    I. Nakanishi, K. Fukuhara, T. Shimada, K. Ohkubo, Y. Iizuka, K. Inami, M. Mochizuki, S. Urano, S. Itoh, N. Miyata and S. Fukuzumi, J. Chem. Soc., Perkin Trans. 2, 2002, 0, 1520
    DOI: 10.1039/B205380B

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