Vitamin E: application of the principles of physical organic chemistry to the exploration of its structure and function

Burton, Graham W.; Ingold, K. U.

doi:10.1021/ar00127a001

Cited by 1,104 publications

(748 citation statements)

References 59 publications

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“…Our previous studies addressed the kinetics of propagation of such tocopherol-mediated peroxidation (TMP) of LDL lipids [15] and its inhibition by co-antioxidants [17,27] without examining the important first step of TMP -the transfer of radical centers from the aqueous into the lipid phase of the LDL dispersion (reaction 2 in Scheme 1). We therefore compared the peroxidation of LDL enriched with either c~-or the less reactive y-or ~-TOH [1,2,23]. Fig.…”

Section: Resultsmentioning

confidence: 99%

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Inverse deuterium kinetic isotope effect for peroxidation in human low‐density lipoprotein (LDL): a simple test for tocopherol‐mediated peroxidation of LDL lipids

1995

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a-Tocopherol (a-TOH) can act as a pro-or antioxidant for isolated ubiquinol-10-free human low density lipoprotein (LDL). We demonstrate that a-TOH is a more potent prooxidant than other forms of vitamin E for LDL peroxidation initiated by mild fluxes of aqueous peroxyl radicals and low concentrations of Cu 2+. A simple deuterium exchange test shows that a-TOH switches from pro-to anti-oxidant at Cu2+:LDL ratios > 2.5. The results suggest that this test may be useful to distinguish 'inhibited' peroxidation of emulsion lipids propagated via the lipid peroxyl radical from that mediated via the antioxidant radical.

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Section: Resultsmentioning

confidence: 99%

“…This has led to a veritable explosion of research over the last decade into oxidation of LDL and its prevention by antioxidants, particularly ~-tocopherol (c~-TOH) [1], i.e. the most active and abundant phenolic antioxidant in the lipids of human plasma [2] and extracts of LDL [3].…”

Section: Introductionmentioning

confidence: 99%

Inverse deuterium kinetic isotope effect for peroxidation in human low‐density lipoprotein (LDL): a simple test for tocopherol‐mediated peroxidation of LDL lipids

1995

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“…The phytyl tail is not important for the antioxidant activity of tocopherols. However, the length of the tail is crucial for positioning the molecule at the site where protection is needed in biological systems (Burton & Ingold 1986). Table 3 The reactions responsible for the anti-and pro-oxidant properties oftocopherol (see structures in Fig.…”

Section: Figure 12mentioning

confidence: 99%

Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

Pajunen

Johansson

Hase

et al. 2008

Lipids

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The autoxidation of conjugated linoleic acid (CLA) is poorly understood in spite of increasing interest in the beneficial biological properties of CLA and growing consumption of CLA-rich foods. In this thesis, the autoxidation reactions of the two major CLA isomers, 9-cis,11-transoctadecadienoic acid and 10-trans,12-cis-octadecadienoic acid, are investigated. The results contribute to an understanding of the early stages of the autoxidation of CLA methyl ester, and provide for the first time a means of producing and separating intact CLA methyl ester hydroperoxides as well as basic knowledge on lipid hydroperoxides and their hydroxy derivatives.Conjugated diene allylic monohydroperoxides were discovered as primary autoxidation products formed during autoxidation of CLA methyl esters in the presence and absence oftocopherol. This established that one of the autoxidation pathways of CLA methyl ester is the hydroperoxide pathway.Hydroperoxides were produced from the two major CLA methyl esters by taking advantage of the effect of -tocopherol to promote hydroperoxide formation. The hydroperoxides were analysed and separated first as methyl hydroxyoctadecadienoates and then as intact hydroperoxides by HPLC. The isolated products were characterized by UV, GC-MS, and NMR techniques. In the presence of a high amount of -tocopherol, the autoxidation of CLA methyl ester yields six kinetically-controlled conjugated diene monohydroperoxides and is diastereoselective in favour of one particular geometric isomer as a pair of enantiomers. The primary autoxidation products produced from the two major CLA isomers include new positional isomers of conjugated diene monohydroperoxides, the 8-, 10-, 12-, and 14-hydroperoxyoctadecadienoates. Furthermore, two of these new positional isomers have an unusual structure for a cis,trans lipid hydroperoxide where the allylic methine carbon is adjacent to the cis instead of the usual trans double bond.The 1 H and 13 C NMR spectra of nine isomeric methyl hydroxyoctadecadienoates and of ten isomeric methyl hydroperoxyoctadecadienoates including the unusual cis,trans hydroperoxides, i.e. Me 8-OOH-9c,11t and Me 14-OOH-10t,12c, were fully assigned with the aid of 2D NMR spectroscopy. The assigned NMR data enabled determination of the effects of the hydroxyl and hydroperoxyl groups on the carbon chemical shifts of CLA isomers, identification of diagnostic signals, and determination of chemical shift differences of the olefinic resonances that may help with the assignment of structure to as yet unknown lipid hydroperoxides either as hydroxy derivatives or as intact hydroperoxides.A mechanism for the hydroperoxide pathway of CLA autoxidation in the presence of a high amount of -tocopherol was proposed based on the characterized primary products, their relative distribution, and theoretical calculations. This is an important step forward in CLA research, where exact mechanisms for the autoxidation of CLA have not been presented before. Knowledge of these hydroperoxide formation steps is of cr...

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“…Figure I shows the reaction scheme of a-tocopherol during the autoxidation of unsaturated lipids. a-Tocopherol (1) is a chain-breaking antioxidant to inhibit the propagation step (Burton & Ingold, 1986). o!-Tocopherol donates its phenolic hydrogen atom to a peroxyl radical and converts it to a hydroperoxide.…”

Section: A-tocopherol As the Free Radical Scavengermentioning

confidence: 99%

Vitamin E: Mechanism of Its Antioxidant Activity.

Yamauchi

1997

FSTI

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The antioxidant activity of vitamin E (a-tocopherol) during the peroxidation of unsaturated lipids has been reviewed based on its reaction products. Free-radical scavenging reactions of a-tocopherol take place via the a-tocopheroxyl radical as an intermediate. If a suitable free radical is present, a non-radical product can be formed from the coupling of the free radical with the a-tocopheroxyl radical. The reaction products of a-tocopherol with lipid-peroxyl radicals are 8a-(lipid-dioxy)-a-tocopherones which are hydrolyzed to a-tocopherylquinone. If the supply of oxygen is insufficient, a-tocopherol can trap the carbon-centered radicals of lipids to form 6-0-(lipidalkyl)-a-tocopherols. On the other hand, the dimer and trimer of a-tocopherol is formed by the bimolecular self-reaction of the a-tocopheroxyl radical in a reaction mixture containing a large amount of a-tocopherol. The other product-forming pathway yields isomeric epoxy-a-tocopherylquinones and their precursors, epoxyhydroperoxy-a-tocopherones, but the mechanism of this pathway remains unknown. The reaction products of other vitamin E compounds (7-and 6-tocopherols) during lipid peroxidation are almost the same as those formed from the a-tocopherol. The tocopheroxyl radicals of 7-and 6-tocopherols prefer to react with each other to form dimeric products that are still effective as antioxidants.

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Vitamin E: application of the principles of physical organic chemistry to the exploration of its structure and function

Cited by 1,104 publications

References 59 publications

Inverse deuterium kinetic isotope effect for peroxidation in human low‐density lipoprotein (LDL): a simple test for tocopherol‐mediated peroxidation of LDL lipids

Inverse deuterium kinetic isotope effect for peroxidation in human low‐density lipoprotein (LDL): a simple test for tocopherol‐mediated peroxidation of LDL lipids

Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

Vitamin E: Mechanism of Its Antioxidant Activity.

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