Departamento de Química/Instituto de Tecnología Química UPV-CSIC, Universitat Politècnica de València, Camino de Vera s/n, E-46022 Valencia, Spain.
Photochem Photobiol Sci. 2014 Feb;13(2):224-30. doi: 10.1039/c3pp50252j.
The photooxygenation of model compounds containing the two enantiomers of naproxen (NPX) covalently linked to histidine (His), tryptophan (Trp) and tyrosine (Tyr) has been investigated by steady state irradiation, fluorescence spectroscopy and laser flash photolysis. The NPX-His systems presented the highest oxygen-mediated photoreactivity. Their fluorescence spectra matched that of isolated NPX and showed a clear quenching by oxygen, leading to a diminished production of the NPX triplet excited state ((3)NPX*-His). Analysis of the NPX-His and NPX-Trp photolysates by UPLC-MS-MS revealed in both cases the formation of two photoproducts, arising from the reaction of singlet oxygen ((1)O2) with the amino acid moiety. The most remarkable feature of NPX-Trp systems was a fast and stereoselective intramolecular fluorescence quenching, which prevented the efficient formation of (3)NPX*-Trp, thus explaining their lower reactivity towards photooxygenation. Finally, the NPX-Tyr systems were nearly unreactive and exhibited photophysical properties essentially coincident with those of the parent NPX. Overall, these results point to a type II photooxygenation mechanism, triggered by generation of (1)O2 from the (3)NPX* chromophore.
通过稳态辐照、荧光光谱和激光闪光光解研究了共价连接组氨酸 (His)、色氨酸 (Trp) 和酪氨酸 (Tyr) 的两种对映体的萘普生 (NPX) 模型化合物的光氧化作用。NPX-His 体系表现出最高的氧介导光反应性。它们的荧光光谱与分离的 NPX 匹配，并通过氧明显猝灭，导致 NPX 三重态激发态 ((3)NPX*-His) 的产生减少。通过 UPLC-MS-MS 对 NPX-His 和 NPX-Trp 光解产物进行分析，在两种情况下都发现了两种光产物的形成，这是由单线态氧 ((1)O2) 与氨基酸部分的反应引起的。NPX-Trp 体系的最显著特征是快速和立体选择性的分子内荧光猝灭，这阻止了 (3)NPX*-Trp 的有效形成，从而解释了它们对光氧化作用的较低反应性。最后，NPX-Tyr 体系几乎没有反应性，并且表现出的光物理性质基本上与母体 NPX 一致。总的来说，这些结果表明存在一种由 (3)NPX* 生色团产生 (1)O2 引发的 II 型光氧化机制。
