Abstract
A mixture of D- and L-leucine N-Carboxyanhydride (NCA) having an enantiomeric composition of 65.6% L- and 34.4% D-isomer (i.e. 31.2% enantiomeric excess (e.e.)) was polymerized to the extent of 52% with sodium methoxide initiator to yield a polyleucine product the enantiomeric composition of which was 72.7% L- and 27.3% D-leucine (45.4% e.e.). This polymer was in turn partially hydrolyzed by acid, whereupon the unhydrolyzed polyleucine residue was found to have an enantiomeric composition of 77.5% L- and 22.5% D-leucine (55.0% e.e.). Thus the e.e. increase in the partial polymerization step (14.2%) and the partial hydrolysis step (9.6%) combined to total 23.8% for the overall polymerization-hydrolysis sequence. On the basis of these model experiments it is proposed that repetitive partial polymerization hydrolysis reactions, driven by environmental dry-wet cycles, might have been operative on the primitive Earth to engender the abiotic evolution of optically enriched polypeptides.
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Blair, N.E., Bonner, W.A. A model for the enantiomeric enrichment of polypeptides on the primitive Earth. Origins Life Evol Biosphere 11, 331–335 (1981). https://doi.org/10.1007/BF00931487
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DOI: https://doi.org/10.1007/BF00931487