Excited state dynamics of 7-deazaguanosine and guanosine 5′-monophosphate
Excited state dynamics of 7-deazaguanosine and guanosine 5′-monophosphate
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DOI：
10.1063/5.0038123
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发表时间：
2021-02-21
影响因子：
4.4
通讯作者：
Crespo-Hernandez, Carlos E.
中科院分区：
文献类型：
--
作者：
Krul, Sarah E.;Hoehn, Sean J.;Crespo-Hernandez, Carlos E.
DNA和RNA核碱基的微小结构修饰对它们的激发态动力学和电子弛豫途径有显著影响。在本研究中，利用飞秒宽带瞬态吸收光谱研究了7-去氮鸟苷和5 ' -单磷酸鸟苷在水溶液和甲醇和水的混合物中的激发态动力学。瞬态光谱的收集使用光子密度，以确保没有寄生多光子诱导信号从溶剂化电子。用二组分或三组分动力学模型可以很好地拟合数据。通过分析稳态、时间分辨、计算计算和甲醇-水混合物的结果，提出了两种分子的一般弛豫机制：L-b -> L-a -> (1)pi sigma (*)(ICT) -> S-0，其中(1)pi sigma (*)（ICT）表示具有显著pi sigma（*）特征的分子内电荷转移激发单重态。一般来说，与5 ' -单磷酸鸟苷相比，7-去氮鸟苷的内转化寿命更长。(1) π σ (*)（ICT）态到基态的内部转换在两个分子中发生在几皮秒的相似时间尺度上。总的来说，结果表明，单个氮原子取代鸟嘌呤部分7位的甲基（C-H）基团稳定了(1)pi pi (*) L-b和L-a状态，并改变了它们的势能面拓扑结构，从而使7-去氮鸟嘌呤的弛豫动力学比鸟嘌呤5 ' -单磷酸鸟嘌呤的弛豫动力学减慢，但对(1)pi sigma (*)（ICT）状态向基态的内部转换没有影响。
Minor structural modifications to the DNA and RNA nucleobases have a significant effect on their excited state dynamics and electronic relaxation pathways. In this study, the excited state dynamics of 7-deazaguanosine and guanosine 5 ' -monophosphate are investigated in aqueous solution and in a mixture of methanol and water using femtosecond broadband transient absorption spectroscopy following excitation at 267 nm. The transient spectra are collected using photon densities that ensure no parasitic multiphoton-induced signal from solvated electrons. The data can be fit satisfactorily using a two- or three-component kinetic model. By analyzing the results from steady-state, time-resolved, computational calculations, and the methanol-water mixture, the following general relaxation mechanism is proposed for both molecules, L-b -> L-a -> (1)pi sigma (*)(ICT) -> S-0, where the (1)pi sigma (*)(ICT) stands for an intramolecular charge transfer excited singlet state with significant pi sigma (*) character. In general, longer lifetimes for internal conversion are obtained for 7-deazaguanosine compared to guanosine 5 ' -monophosphate. Internal conversion of the (1)pi sigma (*)(ICT) state to the ground state occurs on a similar time scale of a few picoseconds in both molecules. Collectively, the results demonstrate that substitution of a single nitrogen atom for a methine (C-H) group at position seven of the guanine moiety stabilizes the (1)pi pi (*) L-b and L-a states and alters the topology of their potential energy surfaces in such a way that the relaxation dynamics in 7-deazaguanosine are slowed down compared to those in guanosine 5 ' -monophosphate but not for the internal conversion of (1)pi sigma (*)(ICT) state to the ground state.