Influence of pH on the decay of β-carotene radical cation in aqueous Triton X-100: A laser flash photolysis study

El‐Agamey, Ali; El-Hagrasy, Maha A.; Suenobu, Tomoyoshi; Fukuzumi, Shunichi

doi:10.1016/j.jphotobiol.2015.02.026

Cited by 6 publications

(4 citation statements)

References 58 publications

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“…There is much evidence that the strongly oxidizing hydroxyl radical forms adducts with most substrates so that ˙LycOH neutral radical is likely to be a significant product in our cellular studies. 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.…”

Section: Resultsmentioning

confidence: 99%

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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\overset{}{true}

OOLycOH.…”

Section: Resultsmentioning

confidence: 99%

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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“…A recent review [ 67 ] has highlighted a significant apparent disagreement concerning the fate of β-carotene radical cation. El-Agamey and co-workers [ 68 ] studied the effect of pH on the decay of the β-carotene radical cation (HCAR •+ ) while the extensive work of Kispert and co-workers used advanced electron paramagnetic resonance techniques and optical measurements beside electrochemical and theoretical studies [ 67 , 69 , 70 , 71 ]. The Kispert group showed that proton loss from β-carotene radical cation leads to the neutral carotenoid radical (CAR • ) HCAR •+ → CAR • + H + with an absorption maximum around 750 nm.…”

Section: Carotenoidsmentioning

confidence: 99%

“…The Kispert group speculate that in PS II itself photoprotection can arise both by the loss of the excess vibrational energy of the radical cation and by quenching of excited chlorophyll by the carotenoid proton loss neutral radical. However, El-Agamey [ 68 ] used laser flash photolysis to generate the β-carotene radical cation and study its transient absorption in aqueous Triton-X micelles. They observed the decay of the radical cation as a function of pH and conclude that such neutral radicals of β-carotene show no absorption at wavelengths above 550 nm.…”

Section: Carotenoidsmentioning

confidence: 99%

Singlet Oxygen and Free Radical Reactions of Retinoids and Carotenoids—A Review

2018

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We report on studies of reactions of singlet oxygen with carotenoids and retinoids and a range of free radical studies on carotenoids and retinoids with emphasis on recent work, dietary carotenoids and the role of oxygen in biological processes. Many previous reviews are cited and updated together with new data not previously reviewed. The review does not deal with computational studies but the emphasis is on laboratory-based results. We contrast the ease of study of both singlet oxygen and polyene radical cations compared to neutral radicals. Of particular interest is the switch from anti- to pro-oxidant behavior of a carotenoid with change of oxygen concentration: results for lycopene in a cellular model system show total protection of the human cells studied at zero oxygen concentration, but zero protection at 100% oxygen concentration.

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“…Recently, the influence of pH on the decay of β-carotene radical cation in aqueous Triton X-100 to form a β-carotene neutral radical was reported. 34 In that article information on the reactivity toward O 2 was considered and the authors did not agree that the β-carotene neutral radical adsorbs at 750 nm but rather near 535 nm. It must be pointed out that these are two different types of carotenoid neutral radical being discussed.…”

Section: Optical Studies Of Neutral Radicals (Proton Loss Versus Addimentioning

confidence: 99%

Radicals formed from proton loss of carotenoid radical cations: A special form of carotenoid neutral radical occurring in photoprotection

Focsan

Kispert

2017

Journal of Photochemistry and Photobiology B: Biology

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In an organized assembly in Arabidopsis thaliana plant, proton loss from the radical cation of zeaxanthin (Zea) was found to occur under intense illumination, a possible component in photoprotection. A stable neutral radical is formed because of the favorable proton loss at C4(4') position(s) of the terminal ends of Zea that extends the unpaired spin density distribution (notation Zea(4) or Zea(4') by symmetry). Proton loss from the radical cation of β-carotene (β-car) to available proton acceptors was also detected in a PSII sample upon irradiation. A controversial optical absorption peak at 750nm predicted by DFT was attributed to β-carotene neutral radical formed by proton loss at C4(4') position(s) situated on the terminal end(s) (notation β-car(4) or β-car(4') by symmetry), also detected in solid copper-containing MCM-41 molecular sieves (Cu-MCM-41) and by hydrogen atom transfer from β-carotene to hydroxyl radical. Unlike the PSII organized assembly where proton loss occurs from the terminal ends of the radical cation, in the Cu-MCM-41 unorganized assembly proton loss occurs from all positions including the methyl groups on the polyene chain forming neutral radicals with different EPR couplings, different unpaired spin density distribution and different optical absorption peaks. We emphasize here the properties of these neutral radicals for various carotenoids formed under high-light conditions and in different media (solution, solid siliceous materials, and photosynthetic samples).

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Influence of pH on the decay of β-carotene radical cation in aqueous Triton X-100: A laser flash photolysis study

Cited by 6 publications

References 58 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

Singlet Oxygen and Free Radical Reactions of Retinoids and Carotenoids—A Review

Radicals formed from proton loss of carotenoid radical cations: A special form of carotenoid neutral radical occurring in photoprotection

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