Formation of amino acids via dark chemistry in the interstellar medium (ISM) cracked

Sristi Raj Rai, Amity University Kolkata

Though we have few existing theories on how life on earth originated, we still have a long way to go answering numerous questions to concretely know about our existence. Without taking a sneak peek into the space occupied by dark dense clouds and the formation of complex organic molecules (COMs), it won’t be possible to progress. One leap in solving this mystery has been achieved when explorers identified the simplest amino acid, glycine (NH₂CH₂COOH) in the coma of the comet extracted by the Stardust mission and 67P/Churyumov-Gerasimenko (67P) by the Rosetta mission. Thus a comet – traveler of open space and leftover of the dawn of the solar system that carries frozen interstellar dust, rock, and gases, is a crucial piece of information to cosmic origins of amino acids on Earth.  

Until now it was believed that the generation of prebiotic species like amino acids (glycine, alanine, serine, and others) can only be formed energetically by utilizing X-ray, UV photon, cosmic rays, etc. similar to later stages of star formation. But, S. Ioppolo and his group explored the non-energetically formation routes such as atom and radical-radical addition surface reactions under conditions that of an early stage of star formation through dark chemistry. A couple of days back they reported in Nature Astronomy with supporting astrochemical models about their successful recreated space-like conditions using a unique ultra-high vacuum system (13-14 K) that resulted in the synthesis of a solid form of glycine and its amine precursor molecule, methylamine (NH₂CH₃) as a side product. 

Their endeavour concluded the fact that these species exist way before stars and planets were created and can even survive the harsh origination process. They also reported that glycine preferred deposition in polar environments like water-rich ices in the interstellar medium (ISM). Thus, this building block of life is present in low but valuable amounts ubiquitously in space and preserves itself by embedding into icy comets and planetesimals. The addition of various functional groups makes glycine the backbone and precursor of all other amino acids and CMOs like glycolaldehyde, ethylene glycol, and glycerol. They are further working to characterize the degree of complexity that lies in the chemical nature achieved in interstellar ice analogs via non-energetic surface reactions at the early stage of star formation. 

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SOURCE – “A non-energetic mechanism for glycine formation in the interstellar medium” by S. Ioppolo, G. Fedoseev, K.-J. Chuang, H.M. Cuppen, A.R. Clements, M. Jin, R.T. Garrod, D. Qasim, V. Kofman, E.F. van Dishoeck and H. Linnartz, 16 November 2020, Nature Astronomy.
DOI:10.1038/s41550-020-01249-0

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