Prebiotic Phosphorylation of Uridine using Diamidophosphate in Aerosols

Abstract

One of the most challenging fundamental problems in establishing prebiotically plausible routes for phosphorylation reactions using phosphate is that they are thermodynamically unfavorable in aqueous conditions. Diamidophosphate (DAP), a potentially prebiotically relevant compound, was shown to phosphorylate nucleosides in aqueous medium, albeit at a very slow rate (days/weeks). Here, we demonstrate that performing these reactions within an aerosol environment, a suitable model for the early Earth ocean-air interface, yields higher reaction rates when compared to bulk solution, thus overcoming these rate limitations. As a proof-of-concept, we demonstrate the effective conversion (~6.5-10%) of uridine to uridine-2',3'-cyclophosphate in less than 1 h. These results suggest that aerosol environments are a possible scenario in which prebiotic phosphorylation could have occurred despite unfavorable rates in bulk solution.

Figure 1

A solution of uridine and DAP is atomized into a Teflon chamber, where the aerosol particles are suspended until collection. Following collection on a filter, products are reconstituted in H₂O and injected into an ESI LC-MS for analysis.

Figure 2

Particle volume distribution inside the Teflon chamber (sampled after 20 min of aerosol generation) from atomized solutions without (black) and with (red) 1 eq imidazole.

Figure 3

LC-MS data of collected and reconstituted aerosols. (a) Liquid chromatogram showing the presence of uridine (peak 1) and product 2′,3′-cUMP (peak 2) in aerosols formed without imidazole. The identity of the compounds is verified via negative-mode ESI-MS in (b) and (c) for peak 1 and peak 2, respectively. (d) Liquid chromatogram showing the presence of uridine (peak 3) and product 2′,3′-cUMP (peak 4) in aerosols formed with the inclusion of 1 eq imidazole. The identity of the compounds is verified via negative-mode ESI-MS in (e) and (f) for peak 3 and peak 4, respectively.

Figure 4

LC chromatograms from control experiments to determine contribution from solution dry-down on Teflon filters. Collected aerosols have been reconstituted in 100 µL H₂O. (a) 5 min atomization of a solution of 1 eq uridine + 5 eq DAP + 3 eq MgCl₂, pH adjusted to 5.5 deposited directly onto the filter surface. The 2′,3′-cUMP product percent from these runs was 1.7 ± 0.3%. (b) 5 min atomization of a solution of 1 eq uridine + 5 eq DAP + 3 eq MgCl₂ + 1 eq imidazole, pH adjusted to 5.5 deposited directly onto the filter surface. The 2′,3′-cUMP product percent from these runs was 1.9 ± 0.1%. (c) 5 min atomization of a solution of 1 eq uridine + 3 eq MgCl₂, pH 5.5 deposited directly onto the filter surface, followed by collection of an aerosol of 5 eq DAP and 1 eq imidazole from the bulk chamber. No product was detected. (d) 5 min atomization of a solution of 5 eq DAP and 1 eq imidazole deposited directly onto the filter surface, followed by collection of an aerosol of 1 eq uridine + 3 eq MgCl₂, pH 5.5 from the bulk chamber. No product was detected.

Figure 5

Chemical reaction scheme showing DAP synthesis.