CCBG, DETEMA, Facultad de Química, Isidoro de María 1616, Montevideo 11800, Uruguay.
Department of Chemistry, Physical and Biophysical Chemistry, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld, Germany.
Biomolecules. 2020 Apr 9;10(4):573. doi: 10.3390/biom10040573.
Flavin cofactors, like flavin adenine dinucleotide (FAD), are important electron shuttles in living systems. They catalyze a wide range of one- or two-electron redox reactions. Experimental investigations include UV-vis as well as infrared spectroscopy. FAD in aqueous solution exhibits a significantly shorter excited state lifetime than its analog, the flavin mononucleotide. This finding is explained by the presence of a "stacked" FAD conformation, in which isoalloxazine and adenine moieties form a π-complex. Stacking of the isoalloxazine and adenine rings should have an influence on the frequency of the vibrational modes. Density functional theory (DFT) studies of the closed form of FAD in microsolvation (explicit water) were used to reproduce the experimental infrared spectra, substantiating the prevalence of the stacked geometry of FAD in aqueous surroundings. It could be shown that the existence of the closed structure in FAD can be narrowed down to the presence of only a single water molecule between the third hydroxyl group (of the ribityl chain) and the N7 in the adenine ring of FAD.
黄素辅因子，如黄素腺嘌呤二核苷酸（FAD），是生命系统中重要的电子穿梭体。它们催化广泛的一电子或两电子氧化还原反应。实验研究包括紫外-可见以及红外光谱。在水溶液中，FAD 的激发态寿命明显短于其类似物黄素单核苷酸。这一发现可以通过存在“堆叠”的 FAD 构象来解释，其中异咯嗪和腺嘌呤部分形成π-复合物。异咯嗪和腺嘌呤环的堆叠应该会对振动模式的频率产生影响。在微溶剂（显式水）中使用 FAD 的闭合形式的密度泛函理论（DFT）研究来重现实验红外光谱，证实了 FAD 在水环境中堆叠构象的普遍性。可以表明，FAD 中闭合结构的存在可以归结为在 FAD 的核糖基链的第三个羟基（OH）和腺嘌呤环的 N7 之间仅存在单个水分子。
