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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.