Browsing by Author "Aponte, José C."

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    Compound-specific carbon isotope compositions of aldehydes and ketones in the Tagish Lake meteorite
    (2016) Simkus, Danielle N.; Aponte, José C.; Hilts, Robert; Elsila, Jamie E.; Herd, Christopher D. K.
    Investigating the aldehyde and ketone content of astromaterials provides insight into the abiotic formation of prebiotic compounds on asteroid parent bodies, as aldehydes and ketones are the chemical precursors to α-amino acids in Strecker synthesis reactions. Elucidating amino acid synthesis reactions is important for understanding the origin of prebiotic compounds on Earth and the potential for life beyond our planet. Aldehydes and ketones have been previously detected via gas chromatography mass spectrometry (GC-MS) in a few carbonaceous chondrite meteorites, including Murchison, Bells and Ivuna. However, carbon isotope compositions of aldehydes and ketones in meteorites have not yet been measured. As such, their relationship to amino acids and other compound classes in meteorites have not been fully investigated. Here, we present the first report of compound specific carbon isotope measurements of aldehydes and ketones in meteorite samples.
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    Compound‐specific carbon isotope compositions of aldehydes and ketones in the Murchison meteorite
    (2019) Simkus, Danielle N.; Aponte, José C.; Hilts, Robert; Elsila, Jamie E.; Herd, Christopher D. K.
    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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    New insights into the heterogeneity of the Tagish Lake meteorite: soluble organic compositions of variously altered specimens
    (2019) Simkus, Danielle N.; Aponte, José C.; Elsila, Jamie E.; Hilts, Robert; McLain, Hannah L.; Herd, Christopher D. K.
    The Tagish Lake carbonaceous chondrite exhibits a unique compositional heterogeneity that may be attributed to varying degrees of aqueous alteration within the parent body asteroid. Previous analyses of soluble organic compounds from four Tagish Lake meteorite specimens (TL5b, TL11h, TL11i, TL11v) identified distinct distributions and isotopic compositions that appeared to be linked to their degree of parent body processing (Herd et al. 2011; Glavin et al. 2012; Hilts et al. 2014). In the present study, we build upon these initial observations and evaluate the molecular distribution of amino acids, aldehydes and ketones, monocarboxylic acids, and aliphatic and aromatic hydrocarbons, including compound‐specific δ13C compositions, for three additional Tagish Lake specimens: TL1, TL4, and TL10a. TL1 contains relatively high abundances of soluble organics and appears to be a moderately altered specimen, similar to the previously analyzed TL5b and TL11h lithologies. In contrast, specimens TL4 and TL10a both contain relatively low abundances of all of the soluble organic compound classes measured, similar to TL11i and TL11v. The organic‐depleted composition of TL4 appears to have resulted from a relatively low degree of parent body aqueous alteration. In the case of TL10a, some unusual properties (e.g., the lack of detection of intrinsic monocarboxylic acids and aliphatic and aromatic hydrocarbons) suggest that it has experienced extensive alteration and/or a distinct organic‐depleted alteration history. Collectively, these varying compositions provide valuable new insights into the relationships between asteroidal aqueous alteration and the synthesis and preservation of soluble organic compounds.