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Zaidi A, Li H, Sliwka HR, Partali V, Ernst H, Melø TB. Energy and electron transfer reactions of polyenic acids with variable chain lengths. Tetrahedron 2013. [DOI: 10.1016/j.tet.2012.10.041] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Zhang Y, Yousef YA, Li H, Melø TB, Naqvi KR. Comparison of the photochemical behaviors of α-tocopherol and its acetate in organic and aqueous micellar solutions. J Phys Chem A 2011; 115:8242-7. [PMID: 21675787 DOI: 10.1021/jp202805k] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photoionization is known to take place when α-tocopherol (TOH) is excited to the S(1) state in a polar medium. It has been previously suggested that TO(•) is formed only as a result of proton release by TOH(•+), a process that is expected to occur, in a protic solvent, on the subnanosecond time scale. Recent redeterminations of the molar absorption coefficients of e(aq)(–) (Hare J. Phys. Chem. A 2010, 114, 1766) and of TOH(•+) and TO(•) (Naqvi J. Phys. Chem. A 2010, 114, 10795) have paved the way for testing the above suggestion, even if subnanosecond time resolution is not available, since it implies the equality of [e(aq)(–)](0) and [TO(•)](0), where [···](0) denotes the concentration of the enclosed species immediately after a nanosecond laser pulse. Nanosecond pump-probe spectroscopy of TOH in aqueous micellar solution (AMS) and two organic solvents with similar polarities (acetonitrile and methanol) has revealed that prompt formation of TO(•) through dissociation (TOH + hν → TO(•) + H(•)) is not negligible even in AMS. In acetonitrile, TOH(•+) and TO(•) are formed with comparable yields, and the former converts quantitatively into TO(•) within 15 μs. In methanol, TO(•) was observed, but no evidence was found for electron ejection from TOH. Only one photoproduct, namely TO(•), could be detected when α-tocopherol acetate (TOAc) was excited to the S(1) state in several polar and nonpolar solvents; TOAc has been found to be a more efficient energy degrader than TOH.
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Affiliation(s)
- Ye Zhang
- Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
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Chen CH, Han RM, Liang R, Fu LM, Wang P, Ai XC, Zhang JP, Skibsted LH. Direct observation of the β-carotene reaction with hydroxyl radical. J Phys Chem B 2011; 115:2082-9. [PMID: 21323327 DOI: 10.1021/jp1100889] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Hydroxyl radical reacts readily with β-carotene following submicrosecond laser photolysis of N-hydroxypyridine-2(1H)-thione (N-HPT) as a "photo-Fenton" reagent generating hydroxyl and thiyl radicals in acetonitrile:tetrahydrofuran (4:1, v/v) solution. On the basis of spectral evidence, and supported by kinetic considerations and thermodynamic calculations, a short-lived transient species, detected by time-resolved absorption spectroscopy with an absorption maximum at ∼750 nm and a lifetime of ∼150 ns at 25 °C under anaerobic conditions, is suggested to be the long-sought neutral β-carotene radical formed by hydrogen-atom abstraction. The transient spectrum is different from the spectra of the β-carotene radical cation (∼1000 nm absorption maximum with a millisecond lifetime), the β-carotene radical adducts (∼520 nm, several microsecond lifetime), the β-carotene radical cation ion pair (∼750 nm, several hundred microsecond lifetime), and the β-carotene radical anion (∼880 nm, a few tens of microsecond lifetime). In parallel, β-carotene reacts with the thiyl radical to yield a sulfur radical adduct with absorption maximum at ∼520 nm with a lifetime of 3.0 μs. For astaxanthin and canthaxanthin, the reaction with the thiyl radical dominates and the neutral radical is hardly formed in agreement with the less reducing properties of these 4,4'-diketo carotenoids without the reactive 4,4'-hydrogens.
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Affiliation(s)
- Chang-Hui Chen
- Department of Chemistry, Renmin University of China, Beijing, 100872
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Arellano JB, Melø TB, Fyfe PK, Cogdell RJ, Naqvi KR. Multichannel Flash Spectroscopy of the Reaction Centers of Wild-type and Mutant Rhodobacter sphaeroides: BacteriochlorophyllB-mediated Interaction Between the Carotenoid Triplet and the Special Pair¶†. Photochem Photobiol 2011. [DOI: 10.1111/j.1751-1097.2004.tb09859.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Naqvi KR, Li H, Melø TB, Webster RD. Spectroscopic Characterization of Neutral and Cation Radicals of α-Tocopherol and Related Molecules: A Satisfactory Denouement. J Phys Chem A 2010; 114:10795-802. [DOI: 10.1021/jp106736x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- K. Razi Naqvi
- Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway, and Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Heng Li
- Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway, and Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - T. B. Melø
- Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway, and Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Richard D. Webster
- Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway, and Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
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Al-Duais M, Hohbein J, Werner S, Böhm V, Jetschke G. Contents of vitamin C, carotenoids, tocopherols, and tocotrienols in the subtropical plant species Cyphostemma digitatum as affected by processing. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2009; 57:5420-5427. [PMID: 19480451 DOI: 10.1021/jf9003626] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The subtropical plant species Cyphostemma digitatum, Vitaceae, is used in central Yemen in traditional medicine, as a culinary herb, and as a source of food flavoring. The contents of vitamin C, vitamin E, and carotenoids and changes caused by common processing were investigated. Carotenoids were determined by reversed phase C30-high-performance liquid chromatography (HPLC) with diode array detection at 470 nm, while tocopherols and tocotrienols were analyzed by using normal phase HPLC with fluorescence detection (excitation, 292 nm; emission, 330 nm). Ascorbic acid was determined spectrophotometrically after reaction with DNP by measuring the absorbance at 520 nm. For the raw material and for the processed commercial food product, both in dried form, reasonable quantities of carotenoids were found in the raw material as follows: lutein, 18.89 +/- 0.73 mg/100 g; zeaxanthin, 9.46 +/- 0.30 mg/100 g; canthaxanthin, 0.21 +/- 0.01 mg/100 g; beta-cryptoxanthin, 0.67 +/- 0.03 mg/100 g; and beta-carotene, 14.60 +/- 0.46 mg/100 g. Household processing reduced the carotenoid contents dramatically; only beta-carotene sustained the processing. Likewise, vitamin C, 49.50 +/- 0.01 mg/100 g in the raw material and 20.30 +/- 0.02 mg/100 g in the processed material, was affected negatively by processing; only 41% was retained after processing. In contrast, the outstanding high content of vitamin E, 82.74 +/- 0.63 mg/100 g in the raw material, was increased by processing to 101.20 +/- 1.38 mg/100 g; it was found in different forms, some of which were rare in other sources.
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Affiliation(s)
- Mohammed Al-Duais
- Institute of Ecology, Friedrich Schiller University Jena, Jena, Germany.
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Naqvi KR, Melø TB, Jávorfi T, González-Pérez S, Arellano JB. Facile method for spectroscopic examination of radical ions of hydrophilic carotenoids. Phys Chem Chem Phys 2009; 11:6401-5. [DOI: 10.1039/b905454e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Sliwka HR, Melø TB, Foss BJ, Abdel-Hafez SH, Partali V, Nadolski G, Jackson H, Lockwood SF. Electron- and energy-transfer properties of hydrophilic carotenoids. Chemistry 2007; 13:4458-66. [PMID: 17340673 DOI: 10.1002/chem.200601527] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The antioxidant activities-expressed as the electron-donating properties-of five hydrophilic carotenoids (carotenoid surfactants) and three related hydrophobic carotenoids were investigated by flash photolysis. The electron-transfer rates of the carotenoids to the triplet state of the sensitizer 2-nitronaphthalene and the energy transfer rates of triplet 2-nitronaphthalene to the carotenoids were determined. The results demonstrate that the electron-donating effects of the hydrophilic and hydrophobic carotenoids were comparable when evaluated in acetonitrile. In the presence of water, however, electron transfer (i.e., antioxidant efficiency) was enhanced by a factor of four for the hydrophilic carotenoids. The increased hydrophilicity of carotenoids, therefore, could expand their antioxidant properties, thus facilitating their use as aqueous-phase radical scavengers. At the same time, it was shown that supramolecular assembly ("aggregation") of the amphiphilic carotenoids prevented electron transfer, thus deactivating the antioxidant function. Modulation of the biophysical properties of carotenoids through synthetic modification is capable of increasing the biological and medical utility of this natural class of predominantly hydrophobic antioxidant compound.
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Affiliation(s)
- Hans-Richard Sliwka
- Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
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Reduction of tetranitromethane by electronically excited aromatics in acetonitrile: Spectra and molar absorption coefficients of radical cations of anthracene, phenanthrene and pyrene. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.07.033] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Bína D, Litvín R, Vácha F, Siffel P. New multichannel kinetic spectrophotometer-fluorimeter with pulsed measuring beam for photosynthesis research. PHOTOSYNTHESIS RESEARCH 2006; 88:351-6. [PMID: 16763876 DOI: 10.1007/s11120-006-9071-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Accepted: 05/01/2006] [Indexed: 05/10/2023]
Abstract
A multichannel kinetic spectrophotometer-fluorimeter with pulsed measuring beam and differential optics has been constructed for measurements of light-induced absorbance and fluorescence yield changes in isolated chlorophyll-proteins, thylakoids and intact cells including algae and photosynthetic bacteria. The measuring beam, provided by a short (2 micros) pulse from a xenon flash lamp, is divided into a sample and reference channel by a broad band beam splitter. The spectrum in each channel is analyzed separately by a photodiode array. The use of flash measuring beam and differential detection yields high signal-to-noise ratio (noise level of 2 x 10(-4) in absorbance units per single flash) with negligible actinic effect. The instrument covers a spectral range between 300 and 1050 nm with a spectral resolution of 2.1, 6.4 or 12.8 nm dependent on the type of grating used. The optical design of the instrument enables measuring of the difference spectra during an actinic irradiation of samples with continuous light and/or saturation flashes. The time resolution of the spectrophotometer is limited by the length of Xe flash lamp pulses to 2 micros.
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Affiliation(s)
- David Bína
- Biological Centre, Academy of Sciences of the Czech Republic, Institute of Plant Molecular Biology, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic
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Abstract
Vitamin E offers protection against oxidative stress and is an efficient quencher of singlet oxygen. A recent report suggests that photo-excitation of vitamin E results in the formation of a triplet state (Naqvi et al. Photochem Photobiol Sci 2, 381 (2003)). This leads to the possibility of the triplet state of vitamin E being able to sensitize singlet oxygen and if this is the case it would be counter productive in terms of the biological protective function of vitamin E. We report the production of singlet oxygen, detected by 1270 nm luminescence, from pulsed laser excitation (308 nm) of vitamin E and an analogue, 2,2,5,7,8-pentamethyl-6-hydroxy-chroman (PMHC), with quantum yields between ~0.1 and 0.2. The luminescence was identified as singlet oxygen from self-quenching by vitamin E with solvent-dependent rate constants similar to published values. Whilst the beneficial antioxidant aspects of vitamin E are well established, these results indicate that vitamin E when directly excited can sensitize singlet oxygen formation and may, therefore, be capable of inducing biochemical and biological damage. The results are discussed in relation to recent reports on the deleterious effects of vitamin E dietary supplementation and pro-oxidant effects of vitamin E.
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Affiliation(s)
- Shakeela Dad
- Biosciences Research Institute, University of Salford, Salford M5 4WT, UK
| | - Roger H Bisby
- Biosciences Research Institute, University of Salford, Salford M5 4WT, UK
| | - Ian P Clark
- Lasers for Science Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
| | - Anthony W Parker
- Lasers for Science Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
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Mohamad SBB, Yousef YA, Melø TB, Jávorfi T, Partali V, Sliwka HR, Razi Naqvi K. Singlet oxygen quenching by thione analogues of canthaxanthin, echinenone and rhodoxanthin. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2006; 84:135-40. [PMID: 16563794 DOI: 10.1016/j.jphotobiol.2006.02.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Revised: 01/22/2006] [Accepted: 02/02/2006] [Indexed: 11/28/2022]
Abstract
Thione analogues of three naturally occurring carotenones (canthaxanthin, echinenone, and rhodoxanthin) were synthesized just over ten years ago, and it was reported that substitution of the oxygen atom by sulphur brings about a large red shift and some broadening in the optical absorption spectrum of the compound. Since the three carotenothiones are scarce, determination of their molar absorption coefficients presents a challenge. A method for relating the molar absorption coefficient of a carotenothione (Car-S) to that of its ketone analogue (Car-O) has been developed, which has revealed that the peak molar absorption coefficient of a Car-S is only about 60% of the corresponding value for Car-O. Using methylene blue as the sensitizer and acetonitrile as the solvent, we have also investigated the quenching (under photostationary conditions) of the 1270nm phosphorescence emission of singlet oxygen by each of the six carotenoids. The data conform to the Stern-Volmer relation, and show that substitution of a carbonyl oxygen atom by sulphur does not lead to an appreciable change in the value of the quenching constant, which is close to 1.5 x 10(10)M(-1)s(-1) for all six quenchers.
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Affiliation(s)
- Samsun B B Mohamad
- Department of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway
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Dad S, Bisby R, Clark I, Parker A. Identification and reactivity of the triplet excited state of 5-hydroxytryptophan. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2005; 78:245-51. [PMID: 15708522 PMCID: PMC1890304 DOI: 10.1016/j.jphotobiol.2004.11.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2004] [Revised: 11/22/2004] [Accepted: 11/22/2004] [Indexed: 11/28/2022]
Abstract
Both the neurotransmitter serotonin and the unnatural amino acid 5-hydroxytryptophan (5HT), contain the 5-hydroxyindole chromophore. The photochemistry of 5HT is being investigated in relation to the multiphoton excitation of this chromophore to produce a characteristic photoproduct with green fluorescence ('hyperluminescence'). Laser flash photolysis (308 nm) of 5HT in aqueous solution at neutral pH produces both the neutral 5-indoloxyl radical (lambda(max) 400-420 nm) and another transient absorption with lambda(max) 480 nm and lifetime of 2 micros in deaerated solutions. Based on quenching by oxygen and beta-carotene, the species at 480 nm is identified as the triplet excited state of 5HT. In acidic solution a new oxygen-insensitive intermediate with lambda(max) 460 is assigned to the radical cation of 5HT. Time-resolved measurements of luminescence at 1270 nm have shown that the triplet state of 5HT is able to react with oxygen to form singlet excited oxygen (1O2*) with a quantum yield of approximately 0.1. However, 5HT has also been found to be an effective quencher of singlet oxygen with a second order rate constant of 1.3 x 10(8) dm3 mol(-1) s(-1). The results are discussed in the light of recent observations on the multiphoton-excited photochemistry of serotonin.
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Affiliation(s)
- S. Dad
- Biosciences Research Institute, University of Salford, Salford M5 4WT, UK
| | - R.H. Bisby
- Biosciences Research Institute, University of Salford, Salford M5 4WT, UK
| | - I.P. Clark
- Lasers for Science Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
| | - A.W. Parker
- Lasers for Science Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
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Arellano JB, Melø TB, Fyfe PK, Cogdell RJ, Naqvi KR. Multichannel Flash Spectroscopy of the Reaction Centers of Wild-type and Mutant Rhodobacter sphaeroides: BacteriochlorophyllB-mediated Interaction Between the Carotenoid Triplet and the Special Pair†¶. Photochem Photobiol 2004. [DOI: 10.1562/0031-8655(2004)79<68:mfsotr>2.0.co;2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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