Formation and evolution of C-C, C-O, C[double bond, length as m-dash]O and C-N bonds in chemical reactions of prebiotic interest.

Abstract

A series of prebiotic chemical reactions yielding the precursor building blocks of amino acids, proteins and carbohydrates, starting solely from HCN and water is studied here. We closely follow the formation and evolution of the pivotal C-C, C-O, C[double bond, length as m-dash]O, and C-N bonds, which dictate the chemistry of the molecules of life. In many cases, formation of these bonds is set in motion by proton transfers in which individual water molecules act as catalysts so that water atoms end up in the products. Our results indicate that the prebiotic formation of carbon dioxide, formaldehyde, formic acid, formaldimine, glycolaldehyde, glycine, glycolonitrile, and oxazole derivatives, among others, are best described as highly nonsynchronous concerted single step processes. Nonetheless, for all reactions involving double proton transfer, the formation and breaking of O-H bonds around a particular O atom occur in a synchronous fashion, apparently independently from other primitive processes. For the most part, the first process to initiate seems to be the double proton transfer in the reactions where they are present, then bond breaking/formation around the reactive carbon in the carbonyl group and finally rupture of the C-N bonds in the appropriate cases, which are the most reluctant to break. Remarkably, within the limitations of our non-dynamical computational model, the wide ranges of temperature and pressure in which these reactions occur, downplay the problematic determination of the exact constraints on the early Earth.