title: A planar catechin analogue having a more negative oxidation potential than (+)-catechin as an electron transfer antioxidant against a peroxyl radical.
abstract: The hydrogen transfer reaction of antioxidative polyphenol with reactive oxygen species has proved to be the main mechanism for radical scavenging. The planar catechin (P1H(2)), in which the catechol and chroman structure in (+)-catechin (1H(2)) are constrained to be planar, undergoes efficient hydrogen atom transfer toward galvinoxyol radical, showing an enhanced protective effect against the oxidative DNA damage induced by the Fenton reaction. The present studies were undertaken to further characterize the radical scavenging ability of P1H(2) in the reaction with cumylperoxyl radical, which is a model radical of lipid peroxyl radical for lipid peroxidation. The kinetics of hydrogen transfer from catechins to cumylperoxyl radical has been examined in propionitrile at low temperature with use of ESR, showing that the rate of hydrogen transfer from P1H(2) is significantly faster than that from 1H(2). The rate was also accelerated by the presence of Sc(OSO(2)CF(3))(3). Such an acceleration effect of metal ion indicates that the hydrogen transfer reaction proceeds via metal ion-promoted electron transfer from P1H(2) to oxyl radical followed by proton transfer rather than via a one-step hydrogen atom transfer. The electrochemical ease of P1H(2) for the one-electron oxidation investigated by second-harmonic alternating current voltammetry strongly supports the two step mechanism for hydrogen transfer, resulting in the enhanced radical scavenging ability.
authors.affiliation: Redox Regulation Research Group, Research Center for Radiation Safety, National Institute of Radiological Sciences, Inage-ku, Chiba 263-8555, Japan.
authors.forename: Ikuo
authors.initials: I
authors.lastname: Nakanishi
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Kentaro
authors.initials: K
authors.lastname: Miyazaki
authors.forename: Wataru
authors.initials: W
authors.lastname: Hakamata
authors.forename: Shiro
authors.initials: S
authors.lastname: Urano
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ozawa
authors.forename: Haruhiro
authors.initials: H
authors.lastname: Okuda
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Nobuo
authors.initials: N
authors.lastname: Ikota
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Fukuhara
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry; D002392:Catechin / Q000031:analogs & derivatives / Q000737:chemistry*; D004563:Electrochemistry; D016166:Free Radical Scavengers / Q000737:chemistry*; D015227:Lipid Peroxidation; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D001555:Benzene Derivatives; D016166:Free Radical Scavengers; D010545:Peroxides; C049375:perhydroxyl radical; C015763:cumene; D002392:Catechin