The reactivity of carotenoid radicals with oxygen

El‐Agamey, Ali; McGarvey, David J.

doi:10.1080/10715760601087558

Cited by 25 publications

(29 citation statements)

References 31 publications

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“…The nitrogen dioxide reaction with lycopene leads to only lycopene radical cation while the γ‐radiation produces reducing species (solvated electron, superoxide and hydrogen atoms) as well as hydroxyl radicals. The hydroxyl radical can add to many substrates and, with lycopene , this would produce the lycopene‐hydroxyl radical adduct (

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Lyc‐OH) and hence, lycopene will protect the cells by removing the reactive hydroxyl radical. Our new results show this is a less efficient cell protection process in air than removal of oxidizing radicals via formation of the carotenoid radical cation.…”

Section: Resultsmentioning

confidence: 99%

“…Another possible product is the neutral lycopene radical formed via hydrogen atom abstraction . In the presence of oxygen, either radical may add molecular oxygen to form reactive peroxyl radicals leading to species such as

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OOLycOH. We propose that, in our cellular system, such peroxyl radicals are formed in increasing concentration as the oxygen concentration increases.…”

Section: Resultsmentioning

confidence: 99%

“…Another possible product is the neutral lycopene radical formed via hydrogen atom abstraction [30,31]. In the presence of oxygen, either radical may add molecular oxygen to form reactive peroxyl radicals [13] leading to species such as…”

Section: Mechanismsmentioning

confidence: 99%

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A dramatic effect of oxygen on protection of human cells against γ‐radiation by lycopene

Boehm¹,

Edge

Truscott

et al. 2016

FEBS Letters

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Edited by Barry HalliwellReducing radiation damage is important and dietary antioxidants that can protect cells from such damage are of value. Dietary lycopene, a carotenoid found in tomatoes, protects human lymphoid cell membranes from damage by c-radiation. We report that such protective effects are remarkably reduced as the oxygen concentration increases -near zero at 100% oxygen from fivefold protection at 20% oxygen and, dramatically, from 50-fold protection at 0% oxygen. Such huge differences imply that under higher oxygen concentrations lycopene could lead to improved cancer therapy using c-radiation. The cells are not efficiently protected from the superoxide radical by lycopene. Noncellular studies suggest molecular mechanisms for the oxygen effect.

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Section: Resultsmentioning

confidence: 99%

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OOLycOH. We propose that, in our cellular system, such peroxyl radicals are formed in increasing concentration as the oxygen concentration increases.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

A dramatic effect of oxygen on protection of human cells against γ‐radiation by lycopene

Boehm¹,

Edge

Truscott

et al. 2016

FEBS Letters

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“…5) leading to formation of the radical cation, adducts, ion-pairs and carotenoid neutral radicals 41. Previous work has shown that carotenoids can react with thyil radicals and acylperoxyl radicals by addition across the polyene chain to form neutral radicals (PhS-Car • and Acyl-Car-OO • ) that absorb in the visible region (450–550 nm) 42,43. It has also been reported that canthaxanthin and astaxanthin neutral radicals can be generated by first forming the radical anion (eq.…”

Section: Resultsmentioning

confidence: 99%

Formation of Carotenoid Neutral Radicals in Photosystem II

et al. 2009

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β-carotene radicals produced in the hexagonal pores of the molecular sieve Cu(II)-MCM-41 were studied by ENDOR and visible/near IR spectroscopies. ENDOR studies showed that neutral radicals of β-carotene were produced in humid air under ambient fluorescent light. The maximum absorption wavelengths of the neutral radicals were measured and were additionally predicted by using time-dependent density functional theory (TD-DFT) calculations. An absorption peak at 750 nm, assigned to the neutral radical with a proton loss from the 4(4') position of the β-carotene radical cation in Cu(II)-MCM-41, was also observed in photosystem II (PS II) samples using near-IR spectroscopy after illumination at 20 K. This peak was previously unassigned in PS II samples. The intensity of the absorption peak at 750 nm relative to the absorption of chlorophyll radical cations and β-carotene radical cations increased with increasing pH of the PS II sample, providing further evidence that the absorption peak is due to the deprotonation of the β-carotene radical cation. Based on a consideration of possible proton acceptors that are adjacent to β-carotene molecules in photosystem II, as modeled in the X-ray crystal structure of Guskov et al. Nat. Struct. Mol. Biol. 2009, 16, 334-342, an electron-transfer pathway from a β-carotene molecule with an adjacent proton acceptor to P680•+ is proposed.

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“…48 The rate constant for the addition of O 2 to a RAF radical is inversely proportional to the length of its conjugated system. 49 In less polar environments, CARs react with NO 2 • via HAT or RAF. Either way, the resulting radical intermediate should be relatively nonreactive toward O 2 addition (eq 2).…”

Section: → • Initiation: Rh Rmentioning

confidence: 99%

Antioxidative Reaction of Carotenes against Peroxidation of Fatty Acids Initiated by Nitrogen Dioxide: A Theoretical Study

Chen

Huang

2015

J. Phys. Chem. B

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In this study, we investigated the antioxidative functions of carotenes (CARs) against the peroxidation of lipids initiated by nitrogen dioxide using density functional theory. The hydrogen-atom transfer (HAT), radical adduct formation (RAF), and electron transfer (ET) mechanisms were investigated. We chose β-carotene (β-CAR) and lycopene (LYC) and compared their NO2(•) initiations and peroxidations with those of linoleic acid (LAH), the model of the lipid. We found that for CARs ET is more likely to occur in the most polar (water) environment than are HAT and RAF. In less polar environments, CARs react more readily with NO2(•) via HAT and RAF than does the lipid model, LAH. Comparatively, reaction barriers for the RAF between CARs and NO2(•) are smaller than those for the HAT. The additions of O2 to the radical intermediates O2N-CAR(•) and CAR(-H)(•) involve sizable barriers and are endergonic. Other than HAT of LAH, we revealed that lipid peroxidation is likely to be initiated by -NO2 addition and the subsequent barrierless addition of O2. Finally, LYC is a more effective antioxidative agent against NO2(•)-initiated lipid peroxidation than is β-CAR.

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The reactivity of carotenoid radicals with oxygen

Cited by 25 publications

References 31 publications

A dramatic effect of oxygen on protection of human cells against γ‐radiation by lycopene

A dramatic effect of oxygen on protection of human cells against γ‐radiation by lycopene

Formation of Carotenoid Neutral Radicals in Photosystem II

Antioxidative Reaction of Carotenes against Peroxidation of Fatty Acids Initiated by Nitrogen Dioxide: A Theoretical Study

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