The role of the peptides at the origin of life.

The peptides in biosystems are polymers of L-amino acids, but they racemize slowly by an active isomerization kinetics. The chemical reactions in biosystems are, however, reversible and here we show by a thermodynamics analysis and by comprehensive Molecular Dynamics simulations of models of peptides, that the isomerization kinetics racemizes the peptides at high water activity, in agreement with experimental observations of aging of peptides, but enhances homochirality at a smaller water activity. The main conclusion of the simulations is that it is only possible to obtain and maintain homochirality in the presence of a hydrophobic compact core in a peptide of hundreds of chiral units and at a low water activity, and thus the establishment of homochirality at the origin of life and aging of proteins in biosystems might be strongly connected.