Ultraviolet (UV) light has long been invoked as a source of energy for prebiotic chemical synthesis, but experimental support does not involve sources of UV light that look like the young Sun. Here we experimentally investigate whether the UV flux available on the surface of early Earth, given a favorable atmosphere, can facilitate a variety of prebiotic chemical syntheses. We construct a solar simulator for the UV light of the faint young Sun on the surface of early Earth, called StarLab. We then attempt a series of reactions testing different aspects of a prebiotic chemical scenario involving hydrogen cyanide (HCN), sulfites, and sulfides under the UV light of StarLab, including hypophosphite oxidation by UV light and hydrogen sulfide, photoreduction of HCN with bisulfite, the photoanomerization of α-thiocytidine, the production of a chemical precursor of a potentially prebiotic activating agent (nitroprusside), the photoreduction of thioanhydrouridine and thioanhydroadenosine, and the oxidation of ethanol (EtOH) by photochemically generated hydroxyl radicals. We compare the output of StarLab to the light of the faint young Sun to constrain the timescales over which these reactions would occur on the surface of early Earth. We predict that hypophosphite oxidation, HCN reduction, and photoproduction of nitroprusside would all operate on the surface of early Earth in a matter of days to weeks. The photoanomerization of α-thiocytidine would take months to complete, and the production of oxidation products from hydroxyl radicals would take years. The photoreduction of thioanhydrouridine with hydrogen sulfide did not succeed even after a long period of irradiation, providing a lower limit on the timescale of several years. The photoreduction of thioanhydroadenosine with bisulfite produced 2′-deoxyriboadenosine (dA) on the timescale of days. This suggests the plausibility of the photoproduction of purine deoxyribonucleotides, such as the photoproduction of simple sugars, proceeds more efficiently in the presence of bisulfite.

中文翻译：

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真实表面紫外线条件下益生元光化学的时间尺度

紫外 (UV) 光长期以来一直被用作益生元化学合成的能源，但实验支持不涉及看起来像年轻太阳的紫外光源。在这里，我们通过实验研究在有利的大气条件下，早期地球表面的紫外线通量是否可以促进各种益生元化学合成。我们为早期地球表面微弱的年轻太阳的紫外线构建了一个太阳模拟器，称为 StarLab。然后，我们尝试了一系列反应，在 StarLab 的紫外光下测试涉及氰化氢 (HCN)、亚硫酸盐和硫化物的益生元化学情景的不同方面，包括紫外光和硫化氢对次磷酸盐的氧化、用亚硫酸氢盐光还原 HCN、 α-硫胞苷的光异构化，潜在益生元活化剂（硝普钠）的化学前体的生产，硫代脱水尿苷和硫代脱水腺苷的光还原，以及通过光化学产生的羟基自由基氧化乙醇（EtOH）。我们将 StarLab 的输出与微弱的年轻太阳的光进行比较，以限制这些反应在早期地球表面发生的时间尺度。我们预测次磷酸盐氧化、HCN 还原和硝普钠的光生产都将在几天到几周内在早期地球表面发生作用。α-硫胞苷的光异构化需要数月才能完成，而从羟基自由基产生氧化产物则需要数年时间。即使经过长时间的照射，硫代脱水尿苷与硫化氢的光还原也没有成功，提供了几年时间尺度的下限。用亚硫酸氢盐光还原硫代脱水腺苷在天的时间尺度上产生 2'-脱氧核糖腺苷 (dA)。这表明嘌呤脱氧核糖核苷酸的光生产（例如单糖的光生产）在亚硫酸氢盐存在下更有效地进行的合理性。