Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense 400, CP 780, CEP 13560-970, São Carlos-SP, Brazil.
J Agric Food Chem. 2013 Aug 7;61(31):7615-20. doi: 10.1021/jf402123d. Epub 2013 Jul 26.
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.
磷酸吡哆醛 (PLP) 在水溶液中被发现能使三重态激发态核黄素 (Rib) 失活，25°C 时的失活常数为 3.0±0.1×10(8)L mol(-1)s(-1)。同样，PLP 被发现能猝灭（1）Rib的荧光发射，（1）kq 为 1.0±0.1×10(11)L mol(-1)s(-1)，这是通过稳态荧光确定的。相当高的猝灭常数表明形成了基态复合物，这通过时间分辨荧光测量进一步得到证实，得到（1）Rib失活常数为 3.4±0.4×10(10)L mol(-1)s(-1)。三重态猝灭被指定为单电子转移，而不是从 PLP 到 (3)Rib*的氢原子转移，因为反应量子产率 Φ=0.82 几乎不受溶剂从水到 D2O 的变化的影响，Φ=0.78。正如预期的那样，由于生物素和烟酰胺的氧化电位 E > 2 V 相对于 NHE，它们都不能使单重态或三重态激发态核黄素失活。
