Understanding Titan’s Prebiotic Chemistry: Synthesizing Amino Acids Through Aminonitrile Alkaline Hydrolysis

Abstract

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 (k) 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.