Electronic Structure of the Lowest Triplet State of Flavin Mononucleotide
Electronic Structure of the Lowest Triplet State of Flavin Mononucleotide
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DOI：
10.1021/jp305778v
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发表时间：
2012-10-18
影响因子：
2.9
通讯作者：
van Gastel, Maurice
中科院分区：
文献类型：
--
作者：
Kammler, Lydia;van Gastel, Maurice
黄素单核苷酸 (FMN) 是一种有机辅因子，在许多重要的酶促反应中发挥作用，其电子结构已通过电子顺磁共振 (EPR) 光谱、光谱和量子化学进行了研究。特别是，FMN 的三重态是顺磁性的（总自旋 S = 1），可以研究零场分裂参数 D 和 E，这些参数与两个单独占据的分子轨道直接相关。不同pH值下的三重态EPR谱和光吸收谱结合时间相关密度泛函理论（TDDFT）表明FMN的最高占据轨道（HOMO）和最低未占轨道（LUMO）很大程度上不受FMN质子化态变化的影响。相反，较低的双占据轨道的轨道结构发生了巨大的变化。在 AgNO3 存在的情况下进行了额外的 EPR 实验，该实验允许形成具有不同零场分裂参数以及种群和减少速率的 Ag-FMN 三重态。 AgNO3 的添加仅引起光谱的微小变化，表明Ag+离子仅通过二阶自旋-rbit耦合对零场分裂做出贡献，并且轨道结构不受影响。通过结合使用的三种方法，在不同 pH 值下 FMN 的紫外/可见光谱中观察到的谱带被分配给电子跃迁。
The electronic structure of flavin mononucleotide (FMN), an organic cofactor that plays a role in many important enzymatic reactions, has been investigated by electron paramagnetic resonance (EPR) spectroscopy, optical spectroscopy, and quantum chemistry. In particular, the triplet state of FMN, which is paramagnetic (total spin S = 1), allows an investigation of the zero field splitting parameters D and E, which are directly related to the two singly occupied molecular orbitals. Triplet EPR spectra and optical absorption spectra at different pH values in combination with time dependent density functional theory (TDDFT) reveal that the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of FMN are largely unaffected by changes in the protonation state of FMN. Rather, the orbital structure of the lower lying doubly occupied orbitals changes dramatically. Additional EPR experiments have been carried out in the presence of AgNO3, which allows the formation of an Ag-FMN triplet state with different zero field splitting parameters and population and depopulation rates. Addition of AgNO3 only induces small changes in the optical spectrum, indicating that the Ag+ ion only contributes to the zero field splitting by second order spin-rbit coupling and leaves the orbital structure unaffected. By a combination of the three employed methods, the observed bands in the UV/vis spectra of FMN at different pH values are assigned to electronic transitions.