Farnsworth Kendra K, McLain Hannah L, Chung Angela, Trainer Melissa G
Center for Space Sciences and Technology, University of Maryland Baltimore County, Baltimore, Maryland 21250, United States.
Planetary Environments Laboratory NASA/GSFC, Greenbelt, Maryland 20771, United States.
ACS Earth Space Chem. 2024 Nov 20;8(12):2380-2392. doi: 10.1021/acsearthspacechem.4c00114. eCollection 2024 Dec 19.
Titan is an ocean world with a plethora of organic material in its atmosphere and on its surface, making it an intriguing location in the search for habitable environments beyond Earth. Settled aerosols will mix with transient surface melts following cryovolcanic eruptions and impact events, driving hydrolysis reactions and prebiotic chemistry. Previous studies have shown that the hydrolysis of laboratory-synthesized Titan organics leads to the production of amino acids and other prebiotic molecules. The exact molecular structure of Titan aerosols remains unclear, yet aminonitriles have been hypothesized to be among the organic components. This laboratory study tested three reaction pathways that could potentially lead to the formation of amino acids: aminoacetonitrile → glycine, 2-aminopropanenitrile → alanine, and 4-aminobutanenitrile → γ-aminobutyric acid. Liquid chromatography mass spectrometry (LCMS) is used to quantify the abundance of amino acids over a 6-month period. We conclude that ammonia plays a key role in the synthesis of amino acids from aminonitriles, while the inclusion of salts (1 wt %) and minerals (25 mg/mL) did not have a significant effect on amino acid formation compared to ammonia. Rate constants () for alkaline hydrolysis of the aminonitriles were calculated. Our results suggest that if Titan's surface melts have a composition, including at least 5% ammonia in water, and if aminonitriles are present in Titan's organic aerosols, then amino acids will likely form. These results are highly relevant to the Dragonfly mission to Titan, which will sample impact melt material at Selk crater to search for prebiotic molecules.
土卫六是一个海洋世界，其大气和表面有大量有机物质，这使其成为寻找地球以外宜居环境的一个有趣地点。沉降的气溶胶会在低温火山喷发和撞击事件后与短暂的表面熔体混合，引发水解反应和前生物化学过程。此前的研究表明，实验室合成的土卫六有机物水解会产生氨基酸和其他前生物分子。土卫六气溶胶的确切分子结构仍不清楚，但氨基腈被推测是有机成分之一。这项实验室研究测试了三种可能导致氨基酸形成的反应途径：氨基乙腈→甘氨酸、2-氨基丙腈→丙氨酸、4-氨基丁腈→γ-氨基丁酸。液相色谱质谱联用仪（LCMS）用于在6个月的时间内定量氨基酸的丰度。我们得出结论，氨在由氨基腈合成氨基酸的过程中起关键作用，而与氨相比，加入盐（1 wt%）和矿物质（25 mg/mL）对氨基酸形成没有显著影响。计算了氨基腈碱性水解的速率常数（）。我们的结果表明，如果土卫六的表面熔体具有一种成分，包括水中至少5%的氨，并且如果氨基腈存在于土卫六的有机气溶胶中，那么氨基酸很可能会形成。这些结果与前往土卫六的“蜻蜓”任务高度相关，该任务将在塞尔克陨石坑采集撞击熔体物质以寻找前生物分子。
