Kroonblawd Matthew P, Lindsey Rebecca K, Goldman Nir
Physical and Life Sciences Directorate , Lawrence Livermore National Laboratory , Livermore , CA 94550 , USA . Email:
Department of Chemical Engineering , University of California , Davis , California 95616 , USA.
Chem Sci. 2019 May 21;10(24):6091-6098. doi: 10.1039/c9sc00155g. eCollection 2019 Jun 28.
Proteinogenic amino acids can be produced on or delivered to a planet impacting abiotic sources and consequently were likely present before the emergence of life on Earth. However, the role that these materials played in prebiotic scenarios remains an open question, in part because little is known about the survivability and reactivity of astrophysical organic compounds upon impact with a planetary surface. To this end, we use a force-matched semi-empirical quantum simulation method to study impacts of aqueous proteinogenic amino acids at conditions reaching 48 GPa and 3000 K. Here, we probe a relatively unstudied mechanism for prebiotic synthesis where sudden heating and pressurization causes condensation of complex carbon-rich structures from mixtures of glycine, the simplest protein-forming amino acid. These carbon-containing clusters are stable on short timescales and undergo a fundamental structural transition upon expansion and cooling from predominantly sp-bonded tetrahedral-like moieties to those that are more sp-bonded and planar. The recovered sp-bonded structures include large nitrogen containing polycyclic aromatic hydrocarbons (NPAHs) with a number of different functional groups and embedded bonded regions akin to oligo-peptides. A number of small organic molecules with prebiotic relevance are also predicted to form. This work presents an alternate route to gas-phase synthesis for the formation of NPAHs of high complexity and highlights the significance of both the thermodynamic path and local chemical self-assembly in forming prebiotic species during shock synthesis. Our results help determine the role of comets and other celestial bodies in both the delivery and synthesis of potentially significant life building compounds on early Earth.
构成蛋白质的氨基酸可以在撞击非生物源的行星上产生或被输送到该行星上，因此很可能在地球生命出现之前就已存在。然而，这些物质在生命起源前的场景中所起的作用仍是一个悬而未决的问题，部分原因是对于天体有机化合物撞击行星表面后的生存能力和反应性知之甚少。为此，我们使用一种力匹配的半经验量子模拟方法，来研究在高达48吉帕和3000开尔文的条件下，含蛋白质的氨基酸水溶液的撞击情况。在这里，我们探索了一种相对未被研究的生命起源前合成机制，即突然加热和加压会导致由最简单的形成蛋白质的氨基酸甘氨酸混合物中形成富含碳的复杂结构的缩合。这些含碳簇在短时间尺度上是稳定的，并且在从主要是sp键合的四面体状部分膨胀和冷却到更多是sp键合且平面的部分时会经历基本的结构转变。回收的sp键合结构包括具有许多不同官能团的含氮大的多环芳烃（NPAHs）以及类似于寡肽的嵌入键合区域。还预测会形成许多与生命起源相关的小有机分子。这项工作为形成高复杂性的NPAHs提供了一种气相合成的替代途径，并突出了在冲击合成过程中形成生命起源前物种时热力学路径和局部化学自组装的重要性。我们的结果有助于确定彗星和其他天体在早期地球上潜在重要的生命构建化合物的输送和合成中所起的作用。
