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Photooxidation of Other B-Vitamins as Sensitized by Riboflavin

de O. R. Arrivetti, Leandro, Scurachio, Regina S., Santos, Willy G., Papa, Thiago B. R., Skibsted, Leif H., Cardoso, Daniel R.
Journal of agricultural and food chemistry 2013 v.61 no.31 pp. 7615-7620
biotin, fluorescence, niacin, photooxidation, pyridoxal phosphate, riboflavin
Pyridoxal phosphate (PLP) was found to deactivate triplet-excited riboflavin (Rib) in aqueous solution with a deactivation constant of 3.0 ± 0.1 × 10⁸ L mol–¹ s–¹ at 25 °C. Likewise, PLP was found to quench the fluorescence emission of ¹Rib* with ¹kq = 1.0 ± 0.1 × 10¹¹ 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 ¹Rib* deactivation constant of 3.4 ± 0.4 × 10¹⁰ L mol–¹ s–¹. Triplet quenching is assigned as one-electron transfer rather than hydrogen-atom transfer from PLP to ³Rib*, 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.