The Oxidative Dimerization of alpha-, beta-, gamma-, and delta-Tocopherols.

Jl, Nilsson; Gd, Daves; Folkers, Kelly McBride

doi:10.3891/acta.chem.scand.22-0207

Cited by 43 publications

(18 citation statements)

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“…Igarashi and Kwi-Hyun [20] [21], during autoxidation of methyl linoleate, obtained a spirodimer and a trimer from a-T (Diels-Alder reaction), which had no antioxidant properties. [3,11,13,18,19]. For a-T a small quantity of a dimer with ethyl bond was identified, and for c-and d-T two dimers with ether-and 5-59 phenyl-bonds.…”

Section: Resultsmentioning

confidence: 99%

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Studies on dimerisation of tocopherols under the influence of methyl linoleate peroxides

Gogolewski¹,

Nogala‐Kałucka²,

Galuba³

2003

Nahrung

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The stability of plant oils is related to the level of polyunsaturated fatty acids and the presence of native antioxidants--especially tocopherols. During storage, lipids or the fat products undergo oxidation and tocopherol dimers and trimers are formed. These compounds possess reducing and antioxidant properties and participate in oxidation clearly inhibiting this process. In the present study, the correlation between levels of peroxides formed during autoxidation of methyl linoleate and simultaneous decomposition of tocopherols was examined. The peroxide value was investigated. Quantities of decomposed tocopherols and formation of their dimers were determined by high-performance liquid chromatography (HPLC). Mass spectrum analysis confirmed thatthe analysed compounds were dimes. Dimerisation of gamma-T begins at the smaller quantity of the methyl linoleate peroxides than dimerisation of delta-T. At the beginning of methyl linoleate autoxidation dimerisation of gamma-T in relation to its loss was smaller. The quantity of gamma-T dimers with ether bonds in total dimers pointed to faster binding of phenoxy radicals than transformation into the phenyl ones. delta-T dimers with phenyl bonds constitute about 65% of the total. The quantity of peroxides in methyl linoleate, necessary for quantitative and qualitative changes of homologous tocopherols, decreased from delta-T to alpha-T.

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Section: Resultsmentioning

confidence: 99%

“…According to Nilsson [18,19] tocopherol phenoxy radicals are originally generated, which are precursors of dimers with ether bonds. After transformation into benzyl radicals they join, through a 5-59 bond, forming c-and d-T homologues, whereas conversion into ethylene radicals results in a-and b-T homologues.…”

Section: Resultsmentioning

confidence: 99%

Studies on dimerisation of tocopherols under the influence of methyl linoleate peroxides

Gogolewski¹,

Nogala‐Kałucka²,

Galuba³

2003

Nahrung

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“…Their biological activity has not been explained yet. The mechanism of dimerization reported by Nilsson et al [20,21] was based on the possible formation of phenoxy radical. The phenoxy radicals having free orto or para position generally dimerize through these centers, forming two types of dimers: diphenol dimers and phenol-phenyl ether dimers [16,17].…”

Section: Introductionmentioning

confidence: 99%

Influence of added menadione (vitamin K3) on dissolution and dimerization of tocopherols and autoxidation of triacylglycerols during storage of plant oils

Kupczyk¹,

Gogolewski²

2001

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The effect of added menadione (vit. K3) to stored rapeseed and soybean oil on the dissolution and dimerization of natural tocopherols and autoxidation of triacylglycerols was studied. Commercial rapeseed and soybean oils with added menadione and pure oil were stored at +20 degrees C in brown and transparent glass bottles. During storage their peroxide value, changes of the content of fatty acids and dissolution of tocopherols were measured. Destruction of individual tocopherols in tested oils with added menadione stored in both dark and transparent glass bottles were greater than in the oil samples without menadione. However, the degradation of individual tocopherols was different in each oil. Addition of menadione to the rapeseed and soybean oils resulted in the accelerated process of autoxidation of these oils. The oxidative state of the oils was lower in the oils stored in transparent bottles than in the oils stored in brown bottles. The prooxidant activity of menadione was additionally activated by light. Menadione added to the vegetable oils influenced the dissolution of natural tocopherols as well as their dimerization. It is conduced that addition of menadione to vegetable oils decreases their nutritive value.

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“…Figure 6 shows the possible oxidation pathways for y-tocopherol (14) in lipids or lipophilic solvents (Nilsson et al, 1968;Yamauchi et al, 1990b). y-Tocopherol transfers a hydrogen atom to a peroxyl radical.…”

Section: Reaction Of A-tocopherol With Phospholipid-peroxyl Radicals mentioning

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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The Oxidative Dimerization of alpha-, beta-, gamma-, and delta-Tocopherols.

Cited by 43 publications

References 0 publications

Studies on dimerisation of tocopherols under the influence of methyl linoleate peroxides

Studies on dimerisation of tocopherols under the influence of methyl linoleate peroxides

Influence of added menadione (vitamin K3) on dissolution and dimerization of tocopherols and autoxidation of triacylglycerols during storage of plant oils

Vitamin E: Mechanism of Its Antioxidant Activity.

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