The prebiotic synthesis of nucleobases is of particular interest, given the experimental evidence that indicated formation of the nucleobases under abiotic conditions on the Early Earth under high-temperature conditions. Biomolecules have been formed under meteoritic impact scenarios that lead to high temperature and the generation of high energy. Free radical pathways for the formation of biomolecules are appropriate under these conditions. Density functional theory computations were used to study the free radical routes for the formation of nucleobases at the UB3LYP/6-311G(d,p) level. We have found that both 5-aminoimidazole-4-carboxamide (AICA) and 5-(formylamino)imidazole-4-carboxamide (fAICA) are formed first from formamide then the nucleobases are formed. Calculated results show the radical reaction routes of AICA as a precursor for guanine. Both hypoxanthine and xanthine are formed from radical pathways of fAICA. In addition, generation of imino-AICA and imino-fAICA has been shown for the first time to be needed for the production of adenine, purine, and isoguanine. Formation of hypoxanthine and adenine/purine from fAICA and imino-fAICA, respectively, is consistent with experiments performed nearly seven decades ago.

中文翻译：

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高温条件下核糖核酸益生元形成中实验观察到的中间体的反应途径

鉴于实验证据表明在早期地球上高温条件下在非生物条件下会形成核碱基，因此对核碱基的益生元合成特别感兴趣。生物分子是在导致高温和产生高能的气象影响情景下形成的。在这些条件下，用于形成生物分子的自由基途径是合适的。密度泛函理论计算用于研究UB3LYP / 6-311G（d，p）水平上形成核碱基的自由基途径。我们发现5-氨基咪唑-4-羧酰胺（AICA）和5-（甲酰氨基）咪唑-4-羧酰胺（fAICA）首先由甲酰胺形成，然后形成核碱基。计算结果表明，AICA作为鸟嘌呤的前体的自由基反应路线。黄嘌呤和黄嘌呤均由fAICA的自由基途径形成。另外，首次显示了产生亚氨基-AICA和亚氨基-fAICA的生产腺嘌呤，嘌呤和异鸟嘌呤。由fAICA和亚氨基fAICA分别形成次黄嘌呤和腺嘌呤/嘌呤与近七十年前进行的实验一致。