Abiotic Formation of Nitrile Precursors to Amino Acids and Nucleobases in Interstellar Ice Analogues

Abstract

Amino acids and the five canonical nucleobases have been identified in carbonaceous meteorites such as Murchison and Murray; however, their formation mechanisms under interstellar conditions have remained largely elusive. Here, we report the synthesis of biorelevant nitriles, key precursors to amino acids and nucleobases, in low-temperature interstellar model ices composed of hydrogen cyanide (HCN) irradiated with galactic cosmic ray proxies in the form of energetic electrons. Ammonia (NH₃), trans-diazene (HNNH), methylamine (CH₃NH₂), ammonium cyanide (NH₄CN), ethanimine (CH₃CHNH), and nitriles including isocyanogen (CNCN), cyanamide (NH₂CN), iminoacetonitrile (HNCHCN), N-cyanomethanimine (H₂CNCN), and methyl cyanamide (CH₃NHCN) were identified utilizing vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry combined with Fourier-transform infrared spectroscopy and quadrupole mass spectrometry. These results suggest that previously astronomically undetected trans-diazene, ammonium cyanide, and methyl cyanamide represent suitable targets for future astronomical searches. Furthermore, our findings provide fundamental insights into the non-equilibrium formation pathways leading to nitrogen-bearing molecules including complex nitriles in HCN-rich interstellar ices, thereby advancing our understanding of the abiotic origins of amino acids and nucleobases in extraterrestrial environments.