An experimental chemical reactor for peptide formation, elongation and accumulation on the Primitive Earth
Résumé
In this contribution, starting from a set of molecules that could have been available on the early earth, we will present a chemical reactor capable of promoting amino acid activation and condensation, for their elongation into oligopeptides allowing the accumulation of peptide chains in environments considered as prebiotic. Organic matter available on the early Earth may have two origins. The first reservoir of material derived from exogenous inputs that correspond to organic compounds brought to the Earth via comets or (micro-) meteorites. A second pool of organic matter was available from the atmosphere of the primitive Earth, in which photochemistry or processes induced by lightning can have led to low-molecular weight chemical intermediates of interest for the development of further prebiotic chemistry under favorable conditions. This kind of chemistry may have been present at certain stages of the evolution of the surface (atmosphere/ocean) of the Earth, some 3.5 to 4 billion years ago. One of our aims is to identify new chemical pathways allowing the formation of oligopeptides under prebiotic conditions starting from these two reservoirs of organic matter. Our initial studies have identified several possible pathways leading to peptide formations either under oxidizing conditions (with assistance of oxides of nitrogen) or under reductive ones, with cyanic acid and cyanate (or its precursor urea) and amino acids as only required starting materials. Through these reactions, amino acids are activated and condensed into oligopeptides which once formed, elongate from their N-terminal residue. We have subsequently shown that under certain conditions the amino terminus can react with cyanic acid which limits peptide elongation to short peptide chains. To overcome these limitations to peptide elongations, reagents could be available within the above mentioned reservoirs to enable elongation no longer at the N-terminal residues, but at C-terminal residues through a C-terminal activation.