title: Regeneration of β-Carotene from Radical Cation by Eugenol, Isoeugenol, and Clove Oil in the Marcus Theory Inverted Region for Electron Transfer.
abstract: The rate of regeneration of β-carotene by eugenol from the β-carotene radical cation, an initial bleaching product of β-carotene, was found by laser flash photolysis and transient absorption spectroscopy to be close to the diffusion limit in chloroform/methanol (9:1, v/v), with a second-order rate constant (k2) of 4.3 × 109L mol-1s-1at 23 °C. Isoeugenol, more reducing with a standard reduction potential of 100 mV lower than eugenol, was slower, with k2= 7.2 × 108L mol-1s-1. Regeneration of β-carotene following photobleaching was found 50% more efficient by eugenol, indicating that, for the more reducing isoeugenol, the driving force exceeds the reorganization energy for electron transfer significantly in the Marcus theory inverted region. For eugenol/isoeugenol mixtures and clove oil, kinetic control by the faster eugenol determines the regeneration, with a thermodynamic backup of reduction equivalent through eugenol regeneration by the more reducing isoeugenol for the mixture. Clove oil, accordingly, is a potential protector of provitamin A for use in red palm oils.
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Hui-Ting
authors.initials: HT
authors.lastname: Chang
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Cheng
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Rui-Min
authors.initials: RM
authors.lastname: Han
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang
authors.affiliation: Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Leif H
authors.identifier: http://orcid.org/0000-0003-1734-5016
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D045783:Clove Oil / Q000737:chemistry*; D004579:Electron Transport; D005054:Eugenol / Q000031:analogs & derivatives* / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry*; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D045783:Clove Oil; D005609:Free Radicals; D019207:beta Carotene; D005054:Eugenol; C036643:isoeugenol
keywords: carotenoid regeneration; electron transfer; eugenol; inverted region; photobleaching