Peptide formation as on the early Earth: from amino acid mixtures to peptides in sulphur dioxide

Abstract The formation of peptide bonds is one of the most important biochemical reaction steps. Without the development of structurally and catalytically active polymers, there would be no life on our planet. Intensive research is being conducted on possible reaction pathways for the formation of complex peptides on the early Earth. Salt-induced peptide formation (SIPF) by metal catalysis is one possible pathway for abiotic peptide synthesis. The high salt concentration supports dehydration in this process. However, the formation of large, complex oligomer systems is prevented by the high thermodynamic barrier of peptide condensation in aqueous solution. Liquid sulphur dioxide proves to be a superior alternative for copper-catalysed peptide condensation. Compared to water, the amino acids are activated in sulphur dioxide, which leads to the incorporation of all 20 proteinogenic amino acids into the resulting proteins and thus to a large variety of products. Strikingly, even extremely low initial reactant concentrations of only 50 mM are sufficient for extensive peptide formation, leading to an overall yield of 2.9% for dialanine in 7 days. The reactions carried out at room temperature and the successful use of the Hadean mineral covellite as a catalyst, suggest a volcanic environment for the formation of the peptide world on early Earth as a likely scenario.