title: Ultrafast vibrational spectroscopic studies on the photoionization of the α-tocopherol analogue trolox C.
abstract: The initial events after photoexcitation and photoionization of α-tocopherol (vitamin E) and the analogue Trolox C have been studied by femtosecond stimulated Raman spectroscopy, transient absorption spectroscopy and time-resolved infrared spectroscopy. Using these techniques it was possible to follow the formation and decay of the excited state, neutral and radical cation radicals and the hydrated electron that are produced under the various conditions examined. α-Tocopherol and Trolox C in methanol solution appear to undergo efficient homolytic dissociation of the phenolic -OH bond to directly produce the tocopheroxyl radical. In contrast, Trolox C photochemistry in neutral aqueous solutions involves intermediate formation of a radical cation and the hydrated electron which undergo geminate recombination within 100 ps in competition with deprotonation of the radical cation. The results are discussed in relation to recently proposed mechanisms for the reaction of α-tocopherol with peroxyl radicals, which represents the best understood biological activity of this vitamin.
authors.affiliation: Central Laser Facility, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, Harwell Oxford , Didcot, Oxfordshire, OX11 0QX, U.K.
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Parker
authors.forename: Roger H
authors.initials: RH
authors.lastname: Bisby
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Greetham
authors.forename: Philipp
authors.initials: P
authors.lastname: Kukura
authors.forename: Kathrin M
authors.initials: KM
authors.lastname: Scherer
authors.forename: Michael
authors.initials: M
authors.lastname: Towrie
mesh_terms: D065966:Absorption, Physicochemical; D000975:Antioxidants / Q000737:chemistry; D002839:Chromans / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D007259:Infrared Rays; D008958:Models, Molecular; D008968:Molecular Conformation; D055668:Photochemical Processes; D011789:Quantum Theory; D013057:Spectrum Analysis; D013997:Time Factors; D014732:Vibration; D024502:alpha-Tocopherol / Q000031:analogs & derivatives*
chemical_list: D000975:Antioxidants; D002839:Chromans; D005609:Free Radicals; D024502:alpha-Tocopherol; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid