Brister Matthew M, Crespo-Hernández Carlos E
Department of Chemistry , Case Western Reserve University , 10900 Euclid Avenue , Cleveland , Ohio 44106 , United States.
J Phys Chem Lett. 2019 May 2;10(9):2156-2161. doi: 10.1021/acs.jpclett.9b00492. Epub 2019 Apr 18.
Damage to RNA from ultraviolet radiation induces chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential; however, investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5'-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally excited ground state, a long-lived nπ* state, and a receiver triplet state within 200 fs. The receiver state internally converts to the long-lived ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.
紫外线辐射对RNA造成的损伤会诱导核碱基发生化学修饰。弄清楚这些反应中涉及的激发态至关重要；然而，旨在了解核糖核苷酸尿苷5'-单磷酸（UMP）电子能量弛豫途径的研究尚未得到足够关注。在本信函中，对UMP在水溶液中的激发态动力学进行了研究。在267 nm处激发会导致一个三叉事件，该事件会在200飞秒内同时产生振动激发基态、长寿命的nπ态和一个受体三重态。受体态在超快时间尺度内内部转换为长寿命的ππ态。这些结果阐明了电子弛豫途径，并澄清了之前在溶液中对尿嘧啶衍生物进行的瞬态吸收实验。这一机理信息很重要，因为单重态和三重态的长寿命nπ和ππ激发态都被认为会导致有害光产物的形成。
