José C. Aponte^a,b, Jason P. Dworkin^b, Jamie E. Elsila^b

^aNASA Postdoctoral Program at NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
^bNASA Goddard Space Flight Center and Goddard Center for Astrobiology, Greenbelt, Maryland 20771, USA

The study of meteoritic organic compounds provides a unique window into the chemical inventory of the early Solar System and prebiotic chemistry that may have been important for the origin of life on Earth. Multiple families of organic compounds have been extracted from the Murchison meteorite, which is one of the most thoroughly studied carbonaceous chondrites. The amino acids extracted from Murchison have been extensively analyzed, including measurements of non-terrestrial stable isotopic ratios and discoveries of L-enantiomeric excesses for α-dialkyl amino acids, notably isovaline. However, although the isotopic signatures of bulk amine-containing fractions have been measured, the isotopic ratios and enantiomeric composition of individual aliphatic amines, compounds that are chemically related to amino acids, remain unknown. Here, we report a novel method for the extraction, separation, identification and quantitation of aliphatic monoamines extracted from the Murchison meteorite. Our results show a complete suite of structural isomers, with a larger concentration of methylamine and ethylamine and decreasing amine concentrations with increasing carbon number. The carbon isotopic compositions of fourteen meteoritic aliphatic monoamines were measured, with δ¹³C values ranging from +21 to +129‰, showing a decrease in ¹³C with increasing carbon number, a relationship that may be consistent with the chain elongation mechanism under kinetic control previously proposed for meteoritic amino acids. We also found the enantiomeric composition ofsec-butylamine, a structural analog to isovaline, was racemic within error, while the isovaline extracted from the same Murchison piece showed an L-enantiomeric excess of 9.7%; this result suggested that processes leading to enantiomeric excess in the amino acid did not affect the amine. We used these collective data to assess the primordial synthetic origins of these meteoritic aliphatic amines and their potential linkage to meteoritic amino acids.

Reference
Aponte JC, Dworkin JP and Elsila JE (in press) Assessing the origins of aliphatic amines in the murchison meteorite from their compound-specific carbon isotopic ratios and enantiomeric composition. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.06.035]
Copyright Elsevier

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