Stable Isotope Geochemistry of Amino Acid Enantiomer Constituents of Fossil System

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Previous investigations have focused on the distribution and stereochemistry of amino acid constituents of fossils to assess indigeneity. However, the occurrence of amino acids as components of all past and present organisms makes it impossible at this time to precisely determine the extent to which an individual amino acid in a fossil represents original material produced by an organism versus input from the surrounding environment. The primary objective of this investigation is to continue the development of a new set of criteria for evaluating the origin(s) of amino acids in terrestrial and extraterrestrial geologic materials that is based on an assessment of the stable carbon and nitrogen isotope compositions of the individual D- and L-enantiomers of amino acid constituents of these materials. To accomplish this task, a series of experiments are planned to further our understanding of the effects of diagenetic reactions on the stable isotope compositions of individual amino acid enantiomers as follows: 1) simulation experiments to assess the effects of protein and peptide bond hydrolysis on the stable isotope compositions of D- and L-enantiomers of amino acids; and 2) determination of the stable nitrogen and carbon isotope compositions of D- and L-enantiomers of amino acids isolated from various molecular weight, proteinaceous fractions of fossil mollusks. At present, the isolation and stable isotope analysis of individual enantiomers of amino acids from fossil systems is a labor intensive, time consuming process. We will attempt to circumvent this problem by developing a method for the direct stable isotope analysis of quantities of amino acid enantiomers via on-line gas chromatography/stable isotope mass spectrometry (GC/SIMS). If successful, this approach will revolutionize the ability of scientists to utilize stable isotopes as probes at the molecular level (e.g., elucidation kinetic isotope effects, raceminzation processes and biosynthetic pathways for the formation of amino acids in living systems) and will open new doors with respect to furthering our understanding of 10 extraterrestrial, prebiotic organic synthesis and 2) the chemical evolution of living systems on earth.