Pulsed electron nuclear double resonance studies of carotenoid oxidation in Cu(II)-substituted MCM-41 molecular sieves.
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*+) are formed, whereas carotenoid neutral radicals (#Car*) 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.
Lawrence
Jesse
J
Department of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, Alabama 35487, USA.
Focsan
A Ligia
AL
Konovalova
Tatyana A
TA
Molnar
Peter
P
Deli
Jozsef
J
Bowman
Michael K
MK
Kispert
Lowell D
LD
D002338:Carotenoids / Q000737:chemistry*; D003198:Computer Simulation; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006860:Hydrogen Bonding; D014975:Lutein / Q000737:chemistry; D000077276:Lycopene; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*
D005609:Free Radicals; C509968:MCM-41; D002338:Carotenoids; D012822:Silicon Dioxide; D003300:Copper; D000077276:Lycopene; D014975:Lutein