Compound‐specific carbon isotope compositions of aldehydes and ketones in the Murchison meteorite

1,2,3Danielle N. Simkus, 2,4José C. Aponte, 5Robert W. Hilts, 2Jamie E. Elsila, 1Christopher D. K. Herd 
Meteoritics & Planetary Science (in Press) Link to Article [https://onlinelibrary.wiley.com/doi/10.1111/maps.13202]
1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2R3, Canada
2Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
3NASA Postdoctoral Program at NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
4Department of Chemistry, Catholic University of America, Washington, DC, USA
5Department of Physical Sciences, MacEwan University, Edmonton, Alberta T6G 2R3, Canada
Published by arrangement with John Wiley & Sons

Compound‐specific carbon isotope analysis (δ13C) of meteoritic organic compounds can be used to elucidate the abiotic chemical reactions involved in their synthesis. The soluble organic content of the Murchison carbonaceous chondrite has been extensively investigated over the years, with a focus on the origins of amino acids and the potential role of Strecker‐cyanohydrin synthesis in the early solar system. Previous δ13C investigations have targeted α‐amino acid and α‐hydroxy acid Strecker products and reactant HCN; however, δ13C values for meteoritic aldehydes and ketones (Strecker precursors) have not yet been reported. As such, the distribution of aldehydes and ketones in the cosmos and their role in prebiotic reactions have not been fully investigated. Here, we have applied an optimized O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine (PFBHA) derivatization procedure to the extraction, identification, and δ13C analysis of carbonyl compounds in the Murchison meteorite. A suite of aldehydes and ketones, dominated by acetaldehyde, propionaldehyde, and acetone, were detected in the sample. δ13C values, ranging from −10.0‰ to +66.4‰, were more 13C‐depleted than would be expected for aldehydes and ketones derived from the interstellar medium, based on interstellar 12C/13C ratios. These relatively 13C‐depleted values suggest that chemical processes taking place in asteroid parent bodies (e.g., oxidation of the IOM) may provide a secondary source of aldehydes and ketones in the solar system. Comparisons between δ13C compositions of meteoritic aldehydes and ketones and other organic compound classes were used to evaluate potential structural relationships and associated reactions, including Strecker synthesis and alteration‐driven chemical pathways.

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