Compound-Specific Carbon Isotope Compositions of Aldehydes and Ketones in the Murchison Meteorite

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.