Pleyer Hannes Lukas, Strasdeit Henry, Fox Stefan
Department of Bioinorganic Chemistry and Chemical Evolution, Institute of Chemistry, University of Hohenheim, Garbenstr. 30, 70599, Stuttgart, Germany.
Orig Life Evol Biosph. 2018 Dec;48(4):347-371. doi: 10.1007/s11084-018-9567-4. Epub 2018 Dec 13.
In previous experiments that simulated conditions on primordial volcanic islands, we demonstrated the abiotic formation of hydrophobic porphyrins. The present study focused on the question whether such porphyrins can be metalated by prebiotically plausible metal ion sources. We used water-insoluble octaethylporphyrin (Hoep) as a model compound. Experiments were conducted in a nitrogen atmosphere under cyclic wet-dry conditions in order to simulate the fluctuating environment in prebiotic rock pools. Wetting-drying proved to be a crucial factor. Significant yields of the metalloporphyrins (20-78% with respect to Hoep) were obtained from the soluble salts MCl (M = Mg, Fe, Co, Ni and Cu) in freshwater. Even almost insoluble minerals and rocks metalated the porphyrin. Basalt (an iron source, 11% yield), synthetic jaipurite (CoS, 33%) and synthetic covellite (CuS, 57%) were most efficient. Basalt, magnetite and FeCl gave considerably higher yields in artificial seawater than in freshwater. From iron sources, the highest yields, however, were obtained in an acidic medium (hydrochloric acid with an initial pH of 2.1). Under these conditions, iron meteorites also metalated the porphyrin. Acidic conditions were considered because they are known to occur during eruptions on volcanic islands. Octaethylporphyrinatomagnesium(II) did not form in acidic medium and was unstable towards dissolved Fe. It is therefore questionable whether magnesium porphyrins, i.e. possible ancestors of chlorophyll, could have accumulated in primordial rock pools. However, abiotically formed ancestors of the modern cofactors heme (Fe), B (Co), and F (Ni) may have been available to hypothetical protometabolisms and early organisms.
在之前模拟原始火山岛环境条件的实验中，我们证明了疏水性卟啉的非生物形成。本研究聚焦于这样的卟啉是否能被具有益生元合理性的金属离子源金属化这一问题。我们使用水不溶性八乙基卟啉（Hoep）作为模型化合物。实验在氮气氛围下于循环干湿条件下进行，以模拟益生元岩石池中波动的环境。干湿循环被证明是一个关键因素。从淡水中的可溶性盐MCl（M = Mg、Fe、Co、Ni和Cu）获得了显著产量的金属卟啉（相对于Hoep为20 - 78%）。甚至几乎不溶性的矿物和岩石也能使卟啉金属化。玄武岩（一种铁源，产率11%）、合成硫钴矿（CoS，33%）和合成铜蓝（CuS，57%）最为有效。玄武岩、磁铁矿和FeCl在人工海水中的产率比在淡水中高得多。然而，从铁源中获得的最高产率是在酸性介质（初始pH为2.1的盐酸）中。在这些条件下，铁陨石也能使卟啉金属化。考虑酸性条件是因为已知它们会在火山岛喷发期间出现。八乙基卟啉合镁（II）在酸性介质中不形成，并且对溶解的Fe不稳定。因此，镁卟啉，即叶绿素可能的祖先，是否能在原始岩石池中积累是值得怀疑的。然而，现代辅因子血红素（Fe）、钴胺素（Co）和黄素单核苷酸（Ni）的非生物形成的祖先可能已经可供假设的原代谢和早期生物体利用。
