UV light can induce chemical reactions in nucleic acids and thereby damage the genetic code. Like all of the five primary nucleobases, the isolated RNA base uracil exhibits ultrafast, nonradiative relaxation after photoexcitation, which helps to avoid photodamage most of the time. Nevertheless, within RNA and DNA strands, commonly occurring photolesions have been reported and are often ascribed to long-lived and delocalized excited states. Our quantum dynamical study now shows that excited-state longevity can also occur on a single nucleobase, without the need for delocalization. We include the effects of an atomistic RNA surrounding in wave packet simulations and explore the photorelaxation of uracil in its native biological environment. This reveals that steric hindrance through embedding in an RNA strand can inhibit the ultrafast relaxation mechanism of uracil, promoting excited-state longevity and potential photodamage. This process is nearly independent from the specific combination of neighboring bases.

中文翻译：

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RNA 环境是导致尿嘧啶光稳定性降低的原因

紫外线可以诱导核酸发生化学反应，从而破坏遗传密码。与所有五种主要核碱基一样，分离的 RNA 碱基尿嘧啶在光激发后表现出超快的非辐射弛豫，这有助于在大多数情况下避免光损伤。然而，在 RNA 和 DNA 链中，已经报道了常见的光损伤，并且通常归因于长寿命和离域激发态。我们的量子动力学研究现在表明，激发态寿命也可以发生在单个核碱基上，而无需离域。我们在波包模拟中包括了原子 RNA 的影响，并探索了尿嘧啶在其天然生物环境中的光松弛作用。这表明通过嵌入 RNA 链的空间位阻可以抑制尿嘧啶的超快弛豫机制，促进激发态寿命和潜在的光损伤。这个过程几乎独立于相邻碱基的特定组合。