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Titolo:
Photooxidation of carotenoids in mesoporous MCM-41, Ni-MCM-41 and Al-MCM-41 molecular sieves
Autore:
Konovalova, TA; Gao, YL; Schad, R; Kispert, LD; Saylor, CA; Brunel, LC;
Indirizzi:
Univ Alabama, Dept Chem, Tuscaloosa, AL 35487 USA Univ Alabama TuscaloosaAL USA 35487 Dept Chem, Tuscaloosa, AL 35487 USA Univ Alabama, Ctr Mat Informat Technol, Tuscaloosa, AL 35487 USA Univ Alabama Tuscaloosa AL USA 35487 at Technol, Tuscaloosa, AL 35487 USA Florida State Univ, Natl High Magnet Field Lab, Ctr Interdisciplinary Magnet Resonance, Tallahassee, FL 32310 USA Florida State Univ Tallahassee FL USA 32310 ce, Tallahassee, FL 32310 USA
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 31, volume: 105, anno: 2001,
pagine: 7459 - 7464
SICI:
1520-6106(20010809)105:31<7459:POCIMM>2.0.ZU;2-F
Fonte:
ISI
Lingua:
ENG
Soggetto:
ELECTRON-SPIN-RESONANCE; LARGE-PORE; ENDOR; EPR; ZEOLITES; ALMCM-41; RADICALS; 2,4,6-TRIPHENYLPYRYLIUM; PHOTOIONIZATION; SPECTROSCOPIES;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
42
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:
T.A. Konovalova et al., "Photooxidation of carotenoids in mesoporous MCM-41, Ni-MCM-41 and Al-MCM-41 molecular sieves", J PHYS CH B, 105(31), 2001, pp. 7459-7464

Abstract

Photooxidation of beta -carotene and canthaxanthin in mesoporous MCM-41, Ni-NICM-41, and Al-MCM-41 molecular sieves was studied by 9-220 GHz electronparamagnetic resonance (EPR) and 9 GHz electron nuclear double resonance (ENDOR). X-ray powder diffraction (XRD) measurements established that the MCM-41 pore size (33 Angstrom) was large enough to accommodate carotenoids. Mesoporous MCM-41 molecular sieves are found to be promising hosts for long-lived photoinduced charge-separation between carotenoid radical cations (Car(.+)) and the MCM-41 framework. Incorporating metal ions into siliceous MCM-41 enhances efficiency of carotenoid oxidation. The photoyield and stability of generated carotenoid radical cations increased in the order MCM < Ni-MCM < Al-MCM. Formation of carotenoid radical cations within the Me-MCM-41is due to electron transfer between incorporated carotenoid molecules and metal ions, which act as electron acceptor sites. Detected EPR signals of Ni(I) species provide direct evidence for the reduction of Ni(II) ions by carotenoids. The presence of Ni(II) ions in Ni-MCM-41 was verified by 220 GHzEPR spectroscopy. ENDOR measurements revealed that the central C13-CH3 andC13 ' -CH3 groups of both carotenoids in Al-MCM-41 are rapidly rotating, while mobility of the C9-CH3 and C9 ' -CH3 groups is restricted. We propose that carotenoids are bound to the MCM-41 pore walls via the ends of the polyene chain in close proximity to the C9,9 ' -CH3 groups.

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Documento generato il 11/07/20 alle ore 14:32:35