title: Photooxidation of other B-vitamins as sensitized by riboflavin.
abstract: Pyridoxal phosphate (PLP) was found to deactivate triplet-excited riboflavin (Rib) in aqueous solution with a deactivation constant of 3.0 ± 0.1 × 10(8) L mol(-1) s(-1) at 25 °C. Likewise, PLP was found to quench the fluorescence emission of (1)Rib* with (1)kq = 1.0 ± 0.1 × 10(11) L mol(-1) s(-1) as determined by steady state fluorescence. The rather high quenching constant suggests the formation of a ground state complex, which was further confirmed by time-resolved fluorescence measurements to yield a (1)Rib* deactivation constant of 3.4 ± 0.4 × 10(10) L mol(-1) s(-1). Triplet quenching is assigned as one-electron transfer rather than hydrogen-atom transfer from PLP to (3)Rib*, as the reaction quantum yield, Φ = 0.82, is hardly influenced by solvent change from water to D2O, Φ = 0.78. Neither biotin nor niacin deactivates the singlet- or triplet-excited riboflavin as it is expected from their higher oxidation potentials E > 2 V vs NHE.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense 400, CP 780, CEP 13560-970, São Carlos-SP, Brazil.
authors.forename: Leandro
authors.initials: L
authors.lastname: de O R Arrivetti
authors.forename: Regina S
authors.initials: RS
authors.lastname: Scurachio
authors.forename: Willy G
authors.initials: WG
authors.lastname: Santos
authors.forename: Thiago B R
authors.initials: TB
authors.lastname: Papa
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Cardoso
mesh_terms: D005453:Fluorescence; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D012256:Riboflavin / Q000737:chemistry*; D014803:Vitamin B Complex / Q000737:chemistry*
chemical_list: D014803:Vitamin B Complex; D012256:Riboflavin