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首页> 外文会议>Instruments, methods, and missions for astrobiology XVI >Impact of pre-biotic synthesis and diagenesis on the distribution, stereochemistry and stable isotope composition of amino acids in carbonaceous meteorites
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Impact of pre-biotic synthesis and diagenesis on the distribution, stereochemistry and stable isotope composition of amino acids in carbonaceous meteorites

机译：益生元合成和成岩作用对碳质陨石中氨基酸的分布，立体化学和稳定同位素组成的影响

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Simulation experiments for prebiotic synthesis result in racemic mixtures (D/L = 1.0) for protein and non-protein amino acids, irrespective of the composition of the precursor gas mixtures or the energy sources employed. It is therefore not surprising that it was commonly assumed that if amino acids in carbonaceous meteorites were formed by similar reactions they would also be racemic. Engel and Nagy and more recently Glavin et al. have shown that protein amino acids in carbonaceous meteorites often exhibit a moderate to strong L-amino acid excess (D/L ＜ 1.0). Engel hypothesized that this extraterrestrial L-excess might be the precursor material from which life as we know it originated. Stable isotope analyses eg confirmed that the L-amino acid excess in meteorites was indigenous rather than the result of contamination subsequent to impact on Earth. A key question that arises is that since there are no known mechanisms for the direct prebiotic synthesis of amino acids with an L-enantiomer excess, how did these compounds come to exist in carbonaceous meteorites? It has been proposed that a series of diagenetic reactions subsequent to synthesis are responsible for the L-enantiomer excess. In this paper, this hypothesis is further explored with respect to explaining the range of D/L values for amino acids in the various types of carbonaceous meteorites as well as in different stones of the same meteorite. Possible effects of diagenesis on the stable isotope compositions of these compounds are also addressed.
机译：益生元合成的模拟实验产生了蛋白质和非蛋白质氨基酸的外消旋混合物（D / L = 1.0），而与前体气体混合物的组成或所使用的能源无关。因此，通常假设如果碳质陨石中的氨基酸是通过相似的反应形成的，它们也将是外消旋的，这不足为奇。恩格尔和纳吉，以及最近的格拉文等。研究表明，碳质陨石中的蛋白质氨基酸经常表现出中等至强烈的L-氨基酸过量（D / L ＜1.0）。恩格尔假设，这种外星L过量可能是我们所知道的生命起源的前体物质。稳定的同位素分析例如证实了陨石中L-氨基酸的过量是本征的，而不是由于撞击地球后受到污染的结果。出现的一个关键问题是，由于尚无直接的益生元直接合成具有L-对映异构体过量氨基酸的已知机制，这些化合物如何在碳质陨石中存在？已经提出，合成后的一系列成岩反应是造成L-对映体过量的原因。在本文中，将进一步探讨该假设，以解释各种类型的碳质陨石以及同一陨石的不同宝石中氨基酸的D / L值范围。还讨论了成岩作用对这些化合物的稳定同位素组成的可能影响。

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