Prebiotic reactions in a Mars analog iron mineral system: effects of nitrate, nitrite, and ammonia on amino acid formation

1Laura M.Barge,1Erika Flores,1Jessica M.Weber,1Abigail A.Fraeman,1,2Yuk L.Yung,3David VanderVelde,4Eduardo Martinez,1Amalia Castonguay,1Keith Billings,4Marc M.Baum
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.038]
1NASA Jet Propulsion Laboratory, California Institute of Technology
2Division of Geological and Planetary Sciences, California Institute of Technology
3Department of Chemistry, California Institute of Technology
4Department of Chemistry, Oak Crest Institute of Science
Copyright Elsevier

Iron minerals are highly reactive drivers of abiotic / prebiotic organic chemistry, and in the presence of ammonia (NH3/NH4+) or other reduced nitrogen (N) compounds, have been shown to promote amino acid synthesis from organic precursors. On early Mars, oxidized nitrogen species (NOx-) such as NO3- and/or NO2- may have been present, which could be reduced by Fe(II) to form various species including N2O and/or NH3/NH4+. The production of NH3/NH4+ from Fe(II)-driven NO3- or NO2- reduction may be able to feed into prebiotic organic reactions including amino acid formation. In this study, we tested whether iron mineral-driven reduction of NO3- or NO2- could provide a source of NH3/NH4+ to form amino acids from two prebiotically relevant precursors (pyruvate and glyoxylate); or, whether an exogeneous source of NH3/NH4+ would be required. We observed that pyruvate and glyoxylate reacted with Fe-oxyhydroxide minerals in NOx–containing experiments to form reduced hydroxy acid products; and in experiments containing only NH3/NH4+, amino acids were also formed. However, significant amino acid formation was not observed in any experiments containing NO3- or NO2- unless sufficient NH4+ was also added; furthermore, colorimetric analysis did not show any generation of NH4+ from NO3- / NO2- reduction at these conditions. NO2- was observed to be highly reactive with Fe2+ and Fe(II)-bearing minerals, resulting in Fe oxidation during mineral precipitation and the formation of oxidized mineral phases (hematite). The Fe(II)/Fe(III) ratio in oxyhydroxide minerals is an important parameter for determining organic product distributions from pyruvate and glyoxylate; therefore, Fe-mediated NOx- reduction does impact organic chemistry. However, amino acid formation, at least under these conditions, would also require an exogenous source of NH3/NH4+ or other reduced N species. These results have implications for organic-N chemistry on early Mars, as well as for some early Earth origin of life scenarios regarding organic synthesis in mineral-containing systems.

Discuss

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s