Serine Octamer Clusters Direct the Chirality of Peptides Formed in Water Microdroplets

The chemistry underlying biological homochirality remains challenging. We propose that noncovalent clusters may have served as the means by which an enantiomeric excess of one amino acid could direct other racemic amino acids toward homochiral biochemistry. Serine has long been known to exhibit a chiral preference when clustering to form the octamer; here, we extend this finding by reporting the effects of a nonzero e.e. serine on the formation of noncovalent clusters with other amino acids as well as on the formation of peptides, their covalent condensation products. We show that (i) enantiopure serine directs racemic leucine and proline to enantioselective dipeptide formation in water microdroplets and (ii) likely intermediates are seen as the proline and leucine substituted serine octamer clusters. This work indicates the relevance of microdroplet sprays, e.g., natural aerosols, to molecular clustering and to homochirality.