title: Pulsed electron nuclear double resonance studies of carotenoid oxidation in Cu(II)-substituted MCM-41 molecular sieves.
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*+) 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.
authors.affiliation: Department of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, Alabama 35487, USA.
authors.forename: Jesse
authors.initials: J
authors.lastname: Lawrence
authors.forename: A Ligia
authors.initials: AL
authors.lastname: Focsan
authors.forename: Tatyana A
authors.initials: TA
authors.lastname: Konovalova
authors.forename: Peter
authors.initials: P
authors.lastname: Molnar
authors.forename: Jozsef
authors.initials: J
authors.lastname: Deli
authors.forename: Michael K
authors.initials: MK
authors.lastname: Bowman
authors.forename: Lowell D
authors.initials: LD
authors.lastname: Kispert
mesh_terms: 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*
chemical_list: D005609:Free Radicals; C509968:MCM-41; D002338:Carotenoids; D012822:Silicon Dioxide; D003300:Copper; D000077276:Lycopene; D014975:Lutein