Photodynamics of alternative DNA base isoguanine
Photodynamics of alternative DNA base isoguanine
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DOI：
10.1039/c9cp01622h
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发表时间：
2019-07-07
影响因子：
3.3
通讯作者：
de Vries, Mattanjah S.
中科院分区：
文献类型：
--
作者：
Gate, Gregory;Szabla, Rafal;de Vries, Mattanjah S.
异鸟嘌呤是一种替代性核碱基，已被提议作为扩展遗传密码的组分。它也被认为是一种与原始信息聚合物具有潜在相关性的分子。在这里，我们仔细研究异鸟嘌呤的光动力学，因为光稳定性已被提出作为早期地球上生物分子构建模块的益生元选择的关键标准。我们讨论了共振增强多光子电离，红外-紫外双共振光谱和泵探测测量进行此分子的激发态行为的跟踪其不同的互变异构形式在气相中。这些实验，当面对高度精确的量子化学计算和非绝热动力学模拟提供了一个完整的机制图片的互变异构体特定的光动力学的异鸟嘌呤。我们的研究结果表明，紫外光激发的烯醇互变异构体的异鸟嘌呤是相对较短的寿命，因此光稳定。相比之下，生物学上更相关的酮形式被困在黑暗的n π * 状态，这些状态的寿命足够长，可以参与破坏性的光化学。与典型的核碱基相比，所产生的较低的光稳定性可能是异鸟嘌呤未被掺入DNA和RNA的原因之一。
Isoguanine is an alternative nucleobase that has been proposed as a component of expanded genetic codes. It has also been considered as a molecule with potential relevance to primordial informational polymers. Here, we scrutinize the photodynamics of isoguanine, because photostability has been proposed as a critical criterion for the prebiotic selection of biomolecular building blocks on an early Earth. We discuss resonance-enhanced multiphoton ionization, IR-UV double resonance spectroscopy and pump-probe measurements performed for this molecule to track the excited-state behaviour of its different tautomeric forms in the gas phase. These experiments, when confronted with highly accurate quantum chemical calculations and nonadiabatic dynamics simulations provide a complete mechanistic picture of the tautomer-specific photodynamics of isoguanine. Our results indicate that UV-excited enol tautomers of isoguanine are relatively short lived and therefore photostable. In contrast, the biologically more relevant keto forms are trapped in dark n pi* states which are sufficiently long lived to participate in destructive photochemistry. The resulting lower photostability compared to canonical nucleobases may have been one of the reasons why isoguanine was not incorporated into DNA and RNA.