Abstract EANA2026-98

Understanding the emergence of the first informational polymers remains one of the major challenges in origins-of-life research. Although the RNA world hypothesis provides a robust framework for early molecular evolution [1], the prebiotic synthesis and stability of canonical nucleotides under primitive Earth conditions remain problematic, suggesting that alternative protoinformational systems may have preceded RNA [2]. In this context, non-canonical nitrogen heterocycles have been proposed as plausible candidates for a pre-RNA world [3], and some of these potential pre-RNA nucleobases have already been synthesised under plausible hydrothermal conditions using hydrogen cyanide (HCN) as the main reagent [4].

Here, we investigate the synthesis of pyrimidines, triazines and, particularly, carboxylated pyrimidine derivatives generated through alkaline cyanide polymerisation under simulated prebiotic conditions involving continuous aqueous aerosol formation. These experiments were designed to emulate alkaline lakes and aerosol-generating environments that may have existed on the primitive Earth, where bubble–aerosol–droplet cycles could have promoted interfacial chemistries not accessible in bulk aqueous systems [5].

Polymerisation reactions were carried out under anoxic conditions using equimolar NaCN/NH₄Cl solutions (1–0.05 M) at 38 °C for four days under continuous ultrasonic aerosol generation. Additional assays incorporated minerals relevant to prebiotic environments, including silicates, oxides, sulphides and planetary analogue materials, to evaluate their influence on molecular selectivity. Products were analysed before and after hydrolytic treatments under mildly alkaline and strongly basic conditions by gas chromatography–mass spectrometry (GC–MS). A specific analytical method was developed for the unequivocal identification of the target analytes.

The experiments yielded a diverse set of triazines and pyrimidines, including melamine, ammeline, ammelide, cyanuric acid and orotic acid, together with several unidentified compounds displaying fragmentation patterns compatible with carboxylated pyrimidines related to orotic acid. Product diversity and abundance strongly depended on cyanide concentration, hydrolysis conditions and mineral composition. Orotic acid and related carboxylated derivatives were consistently detected across a broad range of experimental conditions, particularly after basic hydrolysis. Several minerals, including pyrite, silica, magnetite, volcanic analogue materials and especially tenorite, enhanced the relative abundance of specific heterocycles, suggesting a catalytic or selective role of mineral interfaces during cyanide polymerisation. Moreover, aqueous aerosols appear to significantly enhance the generation of these potential non-canonical nucleobases compared with conventional hydrothermal simulation experiments.

These results support the hypothesis that alkaline aerosol environments could have acted as efficient microreactors for prebiotic cyanide chemistry, while selected minerals increased molecular selectivity. The formation of carboxylated pyrimidines is particularly relevant because such compounds may undergo decarboxylation reactions leading to canonical nucleobases such as uracil and cytosine. Altogether, this work expands the accessible chemical space of plausible pre-RNA systems and highlights the importance of atmospheric microenvironments and mineral-mediated processes in early Earth prebiotic chemistry.

References

[1] Gilbert, W. Nature 319, 618 (1986).

[2] Ruzov, A.S.; Ermakov, A.S. BioSystems 248, 105411 (2025).

[3] Schuster, G.B.; Cafferty, B.J.; Karunakaran, S.C.; Hud, N.V. J. Am. Chem. Soc. 143, 9279–9296 (2021).

[4] Pérez-Fernández, C.; Vega, J.; Rayo-Pizarroso, P.; Mateo-Martí, E.; Ruiz-Bermejo, M. Sci. Rep. 12, 15140 (2022).

[5] Heindel, J.P.; La Cour, R.A.; Head-Gordon, T. Nat. Commun. 15, 3670 (2024).