Abstract: It was shown by EPR and W-VIS studies that one-electron transfer reactions between 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 than or equal to [DDQ] exhibit a structureless singlet line with g = 2.0066 +/- 0.0002 which is attributed to a CTC. Increasing the temperature gives rise to 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.

Cite: Polyakov N. , Konovalov V. , Leshina T. , Luzina O. , Salakhutdinov N. , Konovalova T. , Kispert L.
One-electron transfer product of quinone addition to carotenoids EPR and optical absorption studies
Journal of Photochemistry and Photobiology A: Chemistry. 2001. V.141. N2-3. P.117-126. DOI: 10.1016/S1010-6030(01)00429-4 WOS Scopus РИНЦ OpenAlex

Dates:

Published print:

Jul 1, 2001

Identifiers:

Web of science:	WOS:000169668100004
Scopus:	2-s2.0-0035797207
Elibrary:	13365846
OpenAlex:	W2189917602

Citing:

DB	Citing
Web of science	17
Scopus	21
Elibrary	20
OpenAlex	17

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