Ultraviolet radiation induced damage to DNA/RNA can lead to chemical modifications to the nucleosides, and understanding the excited states involved is the key to reveal the mechanism of those reactions. 5-Halogen cytidines are metabolized DNA/RNA nucleoside byproducts that exhibit very important biological functions in the process of nucleic acid methylation as well as DNA/RNA damage repairing. However, despite the accumulation of knowledge about their biological functions, the effects of halogen substitution on the excited states of canonical nucleoside have not received much attention. In this work, the excited-state dynamics of 5-fluorocytidine, 5-chlorocytidine, and 5-bromocytidine is investigated. Excitation at 295 nm results in a bifurcation event that leads to sub-picosecond decay to ground state and population of intramolecular charge transfer states which have several to tens of picosecond lifetimes. The results elucidate the general excited-state relaxation pathways in 5-halogen cytidines, and the intrinsic charge transfer state may affect the halogen bonding that stabilizes DNA and protein structures when 5-halogen cytidines are excited.

中文翻译：

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飞秒时间分辨光谱显示5-卤代胞苷中的分子内电荷转移

紫外线引起的DNA / RNA损伤可导致核苷发生化学修饰，了解所涉及的激发态是揭示这些反应机理的关键。5-卤素胞苷是代谢的DNA / RNA核苷副产物，在核酸甲基化以及DNA / RNA损伤修复过程中表现出非常重要的生物学功能。然而，尽管积累了关于它们的生物学功能的知识，但是卤素取代对规范核苷的激发态的影响并未引起太多关注。在这项工作中，研究了5-氟胞苷，5-氯胞苷和5-溴胞苷的激发态动力学。295 nm处的激发导致分叉事件，导致亚皮秒衰减至基态，并且分子内电荷转移状态的填充具有数十皮秒的寿命。结果阐明了5-卤素胞苷中一般的激发态弛豫途径，当5-卤素胞苷被激发时，固有的电荷转移状态可能影响稳定DNA和蛋白质结构的卤素键。