Peroxyl Radical Clocks

Roschek, B.; Tallman, Keri A.; Rector, Christopher L.; Gillmore, Jason G.; Pratt, Derek A.; Punta, Carlo; Porter, Ned A.

doi:10.1021/jo0601462

Cited by 76 publications

(125 citation statements)

References 21 publications

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“…In methyl linoleate autoxidation, the rate constant k inh for -tocopherol is 3.8 x 10 6 M -1 s -1 (Tallman et al 2001), which is ca. 60,000 times faster than the self-propagation reaction of methyl linoleate (k=62 M -1 s -1 , Roschek et al 2006). Kinetic studies suggest that the stoichiometric value for -tocopherol is two (Burton & Ingold 1981) i.e.…”

Section: Figure 12mentioning

confidence: 94%

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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Section: Figure 12mentioning

confidence: 94%

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 primary products of PL oxidation are mainly isomeric hydroperoxides [9,12,[57][58][59]. Lecithins are easily dissolved in organic solvents to yield compact reverse micelles [60,61].…”

Section: Phospholipid Oxidationmentioning

confidence: 99%

“…Lecithins are easily dissolved in organic solvents to yield compact reverse micelles [60,61]. In aqueous solutions, lecithin forms multilamellar liposomes or vesicles under the action of ultrasound dispersion [12,56,62]. Using the DLS method, it was found that, at egg lecithin concentrations 10-90 mg/mL, the size of microaggregates observed are equal to 5-6 nm in organic solvents and in water, liposomes are formed with a wide size distribution of 60-1000 nm.…”

Section: Phospholipid Oxidationmentioning

confidence: 99%

“…Another example of the influence of physical factors on the oxidation is the antioxidant polar paradox [6][7][8][9], which is based on the fact that nonpolar antioxidants are efficient in O/W emulsions, because they are located in emulsion droplets together with oxidizable lipids. Polar antioxidants are more efficient in W/O emulsions because they are concentrated at the interfaces [10][11][12]. In the frame of this chapter, the main features of lipid oxidation in homogeneous and micro -heterogeneous oil media, formed by surfactants (W/O microemulsions) will be discussed.…”

Section: Introductionmentioning

confidence: 99%

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Lipid Oxidation in Homogeneous and Micro-Heterogeneous Media in Presence of Prooxidants, Antioxidants and Surfactants

Kancheva¹,

Касаикина²

2012

Lipid Peroxidation

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“…To determine the effect of the isotope reinforcement on the propagation rate constants of Lin autoxidation as compared to that of 11,11-D 2 -Lin, we performed parallel clocking experiments utilizing a linoleate peroxyl radical clock [6,23,24], as well as competition experiments by co-oxidizing 11,11-D 2 -Lin and Lin in solution.…”

Section: Kinetic Measurements Reveal a Large Kie For The Chain Reactimentioning

confidence: 99%

Small amounts of isotope-reinforced polyunsaturated fatty acids suppress lipid autoxidation

Shchepinov

Hill

Lamberson

et al. 2012

Free Radical Biology and Medicine

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Polyunsaturated fatty acids (PUFAs) undergo autoxidation and generate reactive carbonyl compounds that are toxic to cells and associated with apoptotic cell death, age-related neurodegenerative diseases, and atherosclerosis. PUFA autoxidation is initiated by the abstraction of bis-allylic hydrogen atoms. Replacement of the bis-allylic hydrogen atoms with deuterium atoms (termed site-specific isotope-reinforcement) arrests PUFA autoxidation due to the isotope effect. Kinetic competition experiments show that the kinetic isotope effect for the propagation rate constant of Lin autoxidation compared to that of 11,11-D 2 -Lin is 12.8 ± 0.6. We investigate the effects of different isotope-reinforced PUFAs and natural PUFAs on the viability of coenzyme Q-deficient Saccharomyces cerevisiae coq mutants and wild-type yeast subjected to copper stress.Cells treated with a C11-BODIPY fluorescent probe to monitor lipid oxidation products show that lipid peroxidation precedes the loss of viability due to H-PUFA toxicity. We show that replacement of just one bis-allylic hydrogen atom with deuterium is sufficient to arrest lipid autoxidation. In contrast, PUFAs reinforced with two deuterium atoms at mono-allylic sites remain susceptible to autoxidation. Surprisingly, yeast treated with a mixture of approximately 20%:80% isotope-reinforced D-PUFA: natural H-PUFA are protected from lipid autoxidationmediated cell killing. The findings reported here show that inclusion of only a small fraction of PUFAs deuterated at the bis-allylic sites is sufficient to profoundly inhibit the chain reaction of non-deuterated PUFAs in yeast.

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Peroxyl Radical Clocks

Cited by 76 publications

References 21 publications

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

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

Lipid Oxidation in Homogeneous and Micro-Heterogeneous Media in Presence of Prooxidants, Antioxidants and Surfactants

Small amounts of isotope-reinforced polyunsaturated fatty acids suppress lipid autoxidation

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