title: Primary photoreactions of phylloquinone (vitamin K1) and plastoquinone-1 in solution.
abstract: The photoreactions of electron transport quinones vitamin K1 (1) and plastoquinone-1 (2) were studied by picosecond pump-probe spectroscopy, nanosecond flash photolysis, step-scan FTIR spectroscopy, and by irradiation in glassy solvents at 77 K with optical and EPR detection. In polar solvents, charge transfer from the beta,gamma-double bond to the quinone moiety initiates intramolecular proton transfer from the side chain, k = 2.7 x 10(11) s-1, yielding 1,3-quinone methide diradicals, which establish a metastable equilibrium between the singlet and the triplet state. Subsequent proton transfer through the solvent forms 1,2-quinone methides. In apolar solvents the predominant primary photoreaction is formation of cyclic 'preoxetane' diradicals (kform > 3 x 10(11) s-1, kdecay approximately 1 x 10(9) s-1), which revert to a photostationary E/Z mixture of the starting materials, unless they are trapped by oxygen. The beta,gamma-double bond in the isoprenoid side chain thus provides two efficient deactivation processes, which prevent the intermolecular photoreactions commonly observed with the parent quinones. A combined mechanistic scheme rationalizes the known photoreactions of 1, 2 and related compounds in solution.
authors.affiliation: Departement Chemie, Universität Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
authors.forename: Martin-A
authors.initials: MA
authors.lastname: Hangarter
authors.forename: Aldo
authors.initials: A
authors.lastname: Hörmann
authors.forename: Yavor
authors.initials: Y
authors.lastname: Kamdzhilov
authors.forename: Jakob
authors.initials: J
authors.lastname: Wirz
mesh_terms: D007700:Kinetics; D010777:Photochemistry; D010971:Plastoquinone / Q000737:chemistry*; D010837:Vitamin K 1 / Q000737:chemistry*
chemical_list: D010837:Vitamin K 1; D010971:Plastoquinone