Autoxidation of biological molecules. 1. The antioxidant activity of vitamin E and related chain-breaking phenolic antioxidants in vitro

Download
  1. Get@NRC: Autoxidation of biological molecules. 1. The antioxidant activity of vitamin E and related chain-breaking phenolic antioxidants in vitro (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1021/ja00411a035
AuthorSearch for: ; Search for:
TypeArticle
Journal titleJournal of the American Chemical Society
ISSN0002-7863
Volume103
Issue21
Pages64726477; # of pages: 6
Subject1 naphthol; 6 hydroxy 2,2,5,7,8 pentamethylchroman; alpha tocopherol; beta tocopherol; butylcresol; delta tocopherol; deuterium oxide; gamma tocopherol; mequinol; n,n' diphenyl 1,4 phenylenediamine; styrene; water; chemical reaction kinetics; drug analysis; drug comparison; drug screening; drug structure; in vitro study; isotope effect; structure activity relation; theoretical study; X ray analysis
AbstractThe rate constants, k5, for abstraction by peroxyl radicals of the phenolic hydrogens from a number of phenols have been measured at 30°C. Values of k5 for α-, β-, γ-, and δ-tocopherols are 23.5, 16.6, 15.9, and 6.5 × 105 M-1 s-1, respectively. Like most other phenols these tocopherols react with two peroxyls per molecule and the reaction with peroxyls exhibits a substantial deuterium kinetic isotope effect. α-Tocopherol is the most reactive chain-breaking, phenolic antioxidant known. The simple model compound 4-methoxy-2,3,5,6-tetramethylphenol (TMMP) is much less reactive, with a k5 value of only 2.1 × 105 M-1 s-1. A better model compound is 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC) which has a k5 value of 21.4 × 105 M-1 s-1. The low reactivity of TMMP compared with α-tocopherol and PMHC is attributed to stereoelectronic factors. In TMMP the methoxy group is twisted out of the plane of the aromatic ring by steric forces and, in consequence, the p-type lone pair on the methoxyl oxygen cannot help stabilize the phenoxyl formed upon abstraction of the phenolic hydrogen. However, in the tocopherols and in PMHC the chroman ring system holds the ethereal oxygen's p-type lone pair nearly perpendicular to the aromatic ring, thereby providing additional stabilization for the resultant phenoxyls. This hypothesis has been confirmed by X-ray analysis of TMMP and PMHC and of 4-methoxyphenol and 2,6-di-tert-butyl-4-methoxyphenol. © 1981 American Chemical Society.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21276689
Export citationExport as RIS
Report a correctionReport a correction
Record identifier22ead623-522b-45fa-9b50-2b331c5ccfba
Record created2015-10-13
Record modified2016-05-09
Bookmark and share
  • Share this page with Facebook (Opens in a new window)
  • Share this page with Twitter (Opens in a new window)
  • Share this page with Google+ (Opens in a new window)
  • Share this page with Delicious (Opens in a new window)