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Titolo:
One-electron transfer product of quinone addition to carotenoids EPR and optical absorption studies
Autore:
Polyakov, NE; Konovalov, VV; Leshina, TV; Luzina, OA; Salakhutdinov, NF; Konovalova, TA; Kispert, LD;
Indirizzi:
Univ Alabama, Dept Chem, Tuscaloosa, AL 35487 USA Univ Alabama TuscaloosaAL USA 35487 Dept Chem, Tuscaloosa, AL 35487 USA Russian Acad Sci, Inst Chem Kinet & Combust, SB, Novosibirsk 630090, Russia Russian Acad Sci Novosibirsk Russia 630090 B, Novosibirsk 630090, Russia Russian Acad Sci, Inst Organ Chem, SB, Novosibirsk 630090, Russia Russian Acad Sci Novosibirsk Russia 630090 B, Novosibirsk 630090, Russia
Titolo Testata:
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY
fascicolo: 2-3, volume: 141, anno: 2001,
pagine: 117 - 126
SICI:
1010-6030(20010702)141:2-3<117:OTPOQA>2.0.ZU;2-4
Fonte:
ISI
Lingua:
ENG
Soggetto:
PHOTOSYSTEM-II; CHARGE SEPARATION; REACTION CENTERS; CATION RADICALS; POLAR-SOLVENTS; ARYL OLEFINS; SPECTROSCOPY; OXIDATION; ACCEPTOR; SYSTEMS;
Keywords:
carotenoids; quinones; charge-transfer complex; radicals; EPR; H-1-NMR; UV-VIS spectroscopy;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
41
Recensione:
Indirizzi per estratti:
Indirizzo: Kispert, LD Univ Alabama, Dept Chem, Box 870336, Tuscaloosa, AL 35487 USA Univ Alabama Box 870336 Tuscaloosa AL USA 35487 , AL 35487 USA
Citazione:
N.E. Polyakov et al., "One-electron transfer product of quinone addition to carotenoids EPR and optical absorption studies", J PHOTOCH A, 141(2-3), 2001, pp. 117-126

Abstract

It was shown by EPR and W-VIS studies that one-electron transfer reactionsbetween carotenoids (beta -carotene, 8 ' -apo-beta -caroten-8 ' -al, canthaxanthin) and quinones [2,3-dichloro-5,6-dicyano- 1,4-benzoquinone (DDQ), tetrachlorobenzoquinone (CA)] include the formation of a charge-transfer complex (CTC), which exists in equilibrium with an ion-radical pair (Car(.)+ Q(.-)). UV spectra display a new absorption band in the near m region (at 1030 nm) for the beta -carotene-DDQ mixture which is assigned to a CTC. The absorption maximum of this band gradually shifts from 1030 nm to shorter wavelengths and finally corresponds to that of the beta -carotene radical cation (1000 nm). A new absorption band at 340 nm, detected for all systems under study, is attributed to the product of quinone addition to carotenoid. The EPR spectra of the Car-DDQ mixture measured at 77 K when [Car] less thanor equal to [DDQ] exhibit a structureless singlet line with g = 2.0066 +/-0.0002 which is attributed to a CTC. Increasing the temperature gives riseto a new five-line signal with g = 2.0052 +/- 0.0002 and hyperfine coupling constant of 0.6 G due to the DDQ radical anion. At room temperature stable radicals (more than 24 h) with g = 2.0049 +/- 0.0002 and DeltaH(p-p) = 4.3 C were detected. Electron nuclear double resonance (ENDOR) results indicate that these species contain both nitrogen and chlorine atoms. We attribute these signals to a carotenoid-quinone radical adduct. For chloranil paramagnetic species are generated only after irradiation. Both the carotenoid radical cation and the quinone radical anion were observed in this case. Analysis of the isolated reaction product made using the Beilstein test, H-1-NMR and IR spectroscopies suggests that the major product is a carotenoid-hydroquinone ether. A mechanism of the Car-Q adduct formation is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.

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Documento generato il 18/09/20 alle ore 09:45:43