Formation of Homo- and Hetero- Peptides by Condensation of Non-Activated Amino Acids on Oxides: from Prebiotic to Fine Chemistry

The formation of peptides from non-activated amino acids on mineral surfaces was likely among the prebiotic chemical events relevant for the origin of life [1]. Noteworthy, abiotic-like conditions can be a proof of principle of the occurrence of reactions in a “atom economy” regime. Indeed, the issues of reagent waste and cost associated with amide bond formation are among hot topics in fine chemistry. Catalysed reactions are quite attractive for this purpose, and an ambitious step ahead would be catalytic solvent-free syntheses of polypeptides from non-activated amino acids. In this respect, the effectiveness of TiO₂ and SiO₂ nanoparticles in promoting the formation of long poly-Gly was recently demonstrated [2]. Key aspects of the model experimental conditions were the initial removal of water adsorbed from the catalyst, the admission of amino acid molecules on the catalyst from the vapour phase (by sublimation) and the removal of water produced during the reaction.
This was the first observation of the sequential occurrence of (i) the catalytic formation of polypeptides up to 16 units long and (ii) the self-assembling of the formed polypeptides into closely packed aggregates containing both helical and β-sheet-like patches [2]. The investigation was then extended to Ala and to the possibility to produce (-Gly)_n-(Ala)_m hetero-polypeptides. Insights on the amide bond formation mechanism were obtained experimentally for TiO₂ as catalyst, and by molecular modelling for the reaction occurring on SiO₂.

References
[1] Ferris, J. P.; Hill, A. R.; Liu, R. H.; Orgel, L. E. Nature, 1996, 381, 59-61.
[2] Martra, G.; Deiana, C.; Sakhno, Y.; Barberis, I.; Fabbiani, M.; Pazzi, M.; Vincenti, M. Angewandte Chemie International Edition, 2014, 53, 4671-4674.