EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh, UK.
Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.
Phys Chem Chem Phys. 2022 Sep 14;24(35):21406-21416. doi: 10.1039/d2cp03167a.
Potentially prebiotic chemical reactions leading to RNA nucleotides involve periods of UV irradiation, which are necessary to promote selectivity and destroy biologially irrelevant side products. Nevertheless, UV light has only been applied to promote specific stages of prebiotic reactions and its effect on complete prebiotic reaction sequences has not been extensively studied. Here, we report on an experimental and computational investigation of the photostability of 2-thiooxazole (2-TO), a potential precursor of pyrimidine and 8-oxopurine nucleotides on early Earth. Our UV-irradiation experiments resulted in rapid decomposition of 2-TO into unidentified small molecule photoproducts. We further clarify the underlying photochemistry by means of accurate calculations and surface hopping molecular dynamics simulations. Overall, the computational results show efficient rupture of the aromatic ring upon the photoexcitation of 2-TO breaking of the C-O bond. Consequently, the initial stage of the divergent prebiotic synthesis of pyrimidine and 8-oxopurine nucleotides would require periodic shielding from UV light either with sun screening chromophores or through a planetary scenario that would protect 2-TO until it is transformed into a more stable intermediate compound, oxazolidinone thione.
可能导致 RNA 核苷酸的前生物化学反应涉及 UV 辐射期，这对于促进选择性和破坏与生物无关的副产物是必要的。然而，紫外线仅被应用于促进前生物反应的特定阶段，其对完整的前生物反应序列的影响尚未得到广泛研究。在这里，我们报告了对 2-噻唑啉（2-TO）的光稳定性的实验和计算研究，2-TO 是嘧啶和 8-氧嘌呤核苷酸在早期地球上的潜在前体。我们的 UV 辐照实验导致 2-TO 迅速分解为未识别的小分子光产物。我们通过准确的计算和表面跳跃分子动力学模拟进一步阐明了潜在的光化学。总的来说，计算结果表明 2-TO 在光激发下迅速断裂芳香环，C-O 键被打破。因此，嘧啶和 8-氧嘌呤核苷酸发散前生物合成的初始阶段需要周期性地屏蔽来自 UV 光，要么使用太阳屏蔽色素，要么通过行星场景来保护 2-TO，直到它转化为更稳定的中间化合物，唑烷酮硫酮。
