Stable isotope analysis of amino acid enantiomers in the Murchison meteorite at natural abundance levels

摘要

The ability to determine the stable carbon and nitrogen isotope compositions of individual amino acid enantiomers in carbonaceous meteorites can provide insights with respect to their origin(s) and mechanisms of formation. The development of gas chromatography/combustion/isotope ratio mass spectrometry permits such measurements to be made at nanomole to subnanomole levels. Following elution from the gas chromatographic column, the individual compounds are combusted to CO_2 and N_2 which are introduced directly into the source of the isotope ratio mass spectrometer. Our research to date has focused on determining the stable carbon and nitrogen isotope compositions of amino acid enantiomers in unhydrolyzed and hydrolyzed water extracts of the Murchison meteorite (type CM). Our results indicate moderate ((δ~(13)C) to substantial (δ~(15)N) enrichments of the individual components relative to terrestrial materials of biological origin. In general, the amino acids are not racemic (L- enantiomer excess). Amino acid distributions and the similarity of δ~(13)C and δ~(15)N values for the D- and L-enantiomers of individual amino acids supports an extraterrestrial origin for this observed optical activity.