title: Regeneration of β-Carotene from the Radical Cation by Tyrosine and Tryptophan.
abstract: The phenolic amino acid tyrosine (Tyr) was found more efficient in regenerating β-carotene (β-Car) from the radical cation (β-Car(•+)) than tryptophan (Trp) in the presence of base for conditions where the reduction potentials for Trp and Tyr are comparable. Electron transfer from Tyr in 4:1 chloroform/methanol to β-Car(•+) in the presence of excess base, (CH3)4N(+)OH(-), had a rate close to diffusion control and a second-order rate constant in agreement with the Marcus theory for electron transfer when compared to plant phenols. A maximum of 40% β-Car was regenerated for ten times excess of Tyr as studied by 532 nm laser flash photolysis followed by transient absorption spectroscopy in the visible and near-infrared regions. The nonregenerated fraction of β-Car is assigned to secondary degradation processes. For Trp, the rate constant for regeneration of β-Car(•+) was 1 order of magnitude smaller compared to Tyr and slower than expected from Marcus theory by comparison with plant phenols.
authors.affiliation: †Department of Chemistry, Renmin University of China, Beijing, 100872, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Cheng
authors.affiliation: †Department of Chemistry, Renmin University of China, Beijing, 100872, China.
authors.forename: Rui-Min
authors.initials: RM
authors.lastname: Han
authors.affiliation: †Department of Chemistry, Renmin University of China, Beijing, 100872, China.
authors.forename: Ming-Kuan
authors.initials: MK
authors.lastname: Lyu
authors.affiliation: †Department of Chemistry, Renmin University of China, Beijing, 100872, China.
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang
authors.affiliation: ‡Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D005609:Free Radicals / Q000737:chemistry; D007211:Indoles / Q000737:chemistry; D007700:Kinetics; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry*; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D007211:Indoles; D019207:beta Carotene; D014443:Tyrosine; C030374:indole; D014364:Tryptophan