Department of Bioinorganic Chemistry, Institute of Chemistry, University of Hohenheim , Stuttgart, Germany .
Astrobiology. 2013 Jun;13(6):578-95. doi: 10.1089/ast.2012.0934. Epub 2013 Jun 6.
Tetrapyrroles are essential to basic biochemical processes such as electron transfer and photosynthesis. However, it is not known whether these evolutionary old molecules have a prebiotic origin. We have serendipitously obtained pyrroles, which are the corresponding monomers, in laboratory experiments that simulated the interaction of amino acid-containing seawater with molten lava. The thermal pyrrole formation from amino acids, which so far has only been reported for special cases, can be explained by the observation that the amino acids become metal bonded, for example in (CaCl2)3(Hala)2·6H2O (Hala=DL-alanine), when the seawater evaporates. At a few hundred degrees Celsius, sea salt crusts also release hydrochloric acid (HCl). On primordial volcanic islands, the volatile pyrroles and HCl must have condensed at cooler locations, for example, in rock pools. There, pyrrole oligomerization may have occurred. To study this possibility, we added formaldehyde and nitrite, two species for which plausible prebiotic sources are known, to 2,4-diethylpyrrole and HCl. We found that even at high dilution conjugated (oxidized) oligomers, including octaethylporphyrin and other cyclic and open-chain tetrapyrroles, were formed. All experiments were conducted under rigorously oxygen-free conditions. Our results suggest that primitive versions of present-day biological cofactors such as chlorophylls, bilins, and heme were spontaneously abiotically synthesized on primordial volcanic islands and thus may have been available to the first protocells.
四吡咯类化合物对于电子转移和光合作用等基本生化过程至关重要。然而，目前尚不清楚这些古老的分子是否具有前生物起源。我们在模拟含氨基酸海水与熔融岩浆相互作用的实验室实验中偶然获得了吡咯，吡咯是相应的单体。迄今为止，只有在特殊情况下才报道过氨基酸的热吡咯形成，这可以通过观察到氨基酸与金属键合来解释，例如在（CaCl2）3（Hala）2·6H2O（Hala=DL-丙氨酸）中，当海水蒸发时。在几百摄氏度下，海盐壳也会释放盐酸（HCl）。在原始火山岛上，挥发性吡咯和 HCl 必须在较冷的地方凝结，例如在岩石池中。在那里，吡咯可能会发生低聚反应。为了研究这种可能性，我们向 2,4-二乙基吡咯和 HCl 中添加了甲醛和亚硝酸盐，这两种物质都有合理的前生物来源。我们发现，即使在高稀释条件下，也形成了共轭（氧化）低聚物，包括八乙基卟啉和其他环状和开链四吡咯类化合物。所有实验均在严格无氧条件下进行。我们的结果表明，原始版本的当今生物辅因子，如叶绿素、胆红素和血红素，可能是在原始火山岛上通过非生物方式自发合成的，因此可能存在于第一批原细胞中。
