Recent advances in the prebiotic chemistry of RNA have come by focusing on paradoxes that make RNA a prebiotic chemists nightmare". These include the ease with which ribose and its precursors decompose to tars, difficulties making phosphate esters in water, challenges making bonds that join ribose to bases, and the low yield of bases made in redox neutral atmospheres. Such foci prevent our going down “rabbit holes” that become decreasingly relevant to the origins problem as we descend. Key to solving paradoxes is “bespoke” chemistry that was likely unavoidable on a prebiotic Earth. For example, HCHO and glycolaldehyde must have formed in Hadean atmospheres, and must have reacted with volcano-produced sulfur dioxide to form stable sulfonates that precipitated onto semi-arid subaerial surfaces [1][2]. Once there, they must have undergone aldol reactions guided by borate minerals to give higher carbohydrate sulfonates, also stabilized as borates. Also unavoidable were phosphate anhydrides in those surfaces. While the Hadean atmosphere was overall redox neutral, a last sterilizing impactor (LSI, before ~4.3 Ga [3]) must have delivered metallic Fe and Ni to that atmosphere, making it a productive source of HCN, HCCCN, HNCNH, and other reduced base precursors. Precipitating on the same surface, any ribose there would have reacted to give cyclic ribose phosphate. Ni-catalysis would have given ribonucleosides, and borophosphate minerals would have converted these to ribonucleoside 5'-phosphates. Various silicates create oligomeric RNA from these and stabilize it. Experiments supporting this view have not generated a mechanism to obtain homochirality. Further, the amount of subaerial semi-arid surface on Hadean Earth is a large source of uncertainty. For the second, Mars offers an intriguing alternative.

Origin of life under an RNA-first model: Chemistry that could not not have happened

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.