The increasing diversity of complex molecules observed today in space questions the conditions of formation of these witnesses of the evolution of the universe. A set of experimental and theoretical results show the possibility of formation of peptide chains in the absence of any substrate.
The formation of oligopeptides from amino acids is a key step in the emergence of life towards the formation of proteins with multiple functions in living cells, where this reaction is the permanent and complex work of ribosomes. Under abiotic conditions, without a ribosome, how oligopeptides develop remains an open question, even though a wide variety exists among organic compounds found in various astrophysical environments, such as comets or meteorites for example.
By studying the simplest amino acid, glycine, and experimentally simulating its behaviour in a cold gaseous environment, the multidisciplinary Franco-Austrian team has shown that in the molecular clusters thus formed, a few glycine molecules are transformed into a dipeptide and a glycine molecule, rather than associating into glycine pairs, which are certainly protonated but without the peptide bond. Moreover, the reaction does not require contact, no reaction catalysed by the surface of ice grains or dust as conventionally proposed.
By going a step further and simulating a cosmic ray impact on these clusters, by means of an argon atom, the team showed that a single collision in the gas phase induces an additional polymerization by dehydration, thus forming oligopeptides with 3 or even 4 glycine subunits. Thus, peptide chain elongation occurs very well via a unimolecular gas phase reaction in an excited cluster ion.
The implication of these results is important for astrophysical observations that are looking for the signature of small amino acids including glycine. These new results could incite to search for dipeptides in the cold regions of space, which are finally relatively more abundant.
Publication in the JPC 26/01/2023
Press release from Lyon 1 University
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