Pulsed Electron Nuclear Double Resonance Studies of Carotenoid Oxidation in Cu(II)-Substituted MCM-41 Molecular Sieves
- 8 April 2008
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry B
- Vol. 112 (17), 5449-5457
- https://doi.org/10.1021/jp711310u
Abstract
Carotenoid (Car) radical intermediates formed upon catalytic or photooxidation of lutein (I), 7'-apo-7',7'-dicyano- beta-carotene (II), and lycopene (III) inside Cu(II)-MCM-41 molecular sieves were studied by pulsed electron nuclear double resonance (ENDOR) spectroscopies. The Davies and Mims ENDOR spectra (15-20 K) were simulated using the hyperfine coupling constants predicted by density functional theory (DFT) calculations. The DFT calculations revealed that upon chemical oxidation, carotenoid radical cations (Car(center dot+)) are formed, whereas carotenoid neutral radicals (#Car(center dot)) are produced by proton loss (indicated by #) from the radical cation. This loss is to first order independent of polarity or hydrogen bonding for carotenoids I, II, or III inside Cu(II)-MCM-41 molecular sieves.Keywords
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