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Photochemical stability and reactivity of sodium pyruvate: Implications for organic analysis on Ceres

Presentation #114.02 in the session Laboratory Investigations (Oral Presentation)

Published onOct 23, 2023
Photochemical stability and reactivity of sodium pyruvate: Implications for organic analysis on Ceres

Ceres is a high priority target for future planetary missions, with the detection of organics by the Dawn mission, and evidence for deep liquid. Additionally, Ceres is believed to have FeS-containing iron minerals and iron oxide minerals (magnetite) which may shield organics from degradation in the case of photochemistry, and are known to exhibit photocatalytic activity with organics. However, it is still not well understood what organic processes may be occurring on Ceres. Understanding how organics are altered under irradiated conditions in a lab setup can be extrapolated to how organics may evolve on Ceres, which is important for contextualizing results from a future surface mission to Ceres. Therefore, we explored irradiation of sodium pyruvate (NaPyr; C3H3NaO3), an important precursor in prebiotic chemistry. It is a key metabolic molecule that has been detected in carbonaceous meteorites (15 nmol/g; ALH 83102), and pyruvate is a precursor to the amino acid alanine (C3H7NO2). Further, NaPyr has aliphatic bonds, underscoring its relevance to VNIR observations of Ceres.

NaPyr controls were tested in vacuum irradiation experiments. Residual gas analyzer (RGA) high-vacuum experiments included the synthesis of FeOOH mineral in an anaerobic chamber, active vacuum, and constant UV irradiation to simulate solar irradiation on Ceres. The sample was also measured via Raman spectroscopy, liquid chromatography-mass spectrometry (LCMS), and nuclear magnetic resonance spectroscopy (NMR).

NaPyr was observed to be reactive under the conditions in the static vacuum tests, supported by visible darkening of the sample. Additionally, new peaks were observed in the NMR spectra. For LCMS data, new products were observed in the irradiated samples compared to the controls. Under active vacuum, decarboxylation was observed, among other products via RGA analysis. An increase in mass was observed in the CO2 m/z peaks and product formation was consistent with the irradiation cycles, which suggests UV irradiation is the cause of the product formation. Additionally, alanine and NaPyr were combined with 50:50 Fe(II):Fe(III) FeOOH mineral for RGA analysis, in which a significant increase in CO2 was observed, consistent with irradiation cycles.

In summary, we determined that NaPyr is reactive both independently and with synthetic FeOOH minerals. These results imply that a variety of astrobiologically relevant organics may be reactive under Ceres-like conditions. Understanding this spectrum of possibilities is important for preparing for a future Ceres Sample Return mission, as outlined by the Planetary Decadal Survey.

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