The deuterium enrichment of individual amino acids in carbonaceous meteorites: A case for the presolar distribution of biomolecule precursors

The deltaD values of over 40 amino acids and two pyridine carboxylic acids of the Murchison and Murray meteorites have been obtained by compound-specific isotopic analyses. For compounds with no known terrestrial distribution, these values range from approximately +330parts per thousand (for cyclic leucine) to +3600parts per thousand (for 2-amino-2,3-dimethylbutyric acid). The latter value is the highest ever recorded for a soluble organic compound in meteorites and nears deuterium to hydrogen ratios observed remotely in interstellar molecules. Deuterium content varies significantly between molecular species and is markedly higher for amino acids having a branched alkyl chain. The deltaD value of Murray L-isovaline. with an enantiomeric excess of similar to6%, in the meteorite. was within experimental error of that determined for the combined DL-isovaline enantiomers. Overall, the hydrogen isotope composition of meteoritic amino acids is relatively simple and their deltaD values appear to vary more with the structure of their carbon chains than with the number and relative distribution of their functionalities or C-13 content. The magnitude and extent of deuterium enrichment shared by many and varied amino acids in meteorites indicate that cosmic regimes such as those found in the interstellar medium were capable of producing. if not all the amino acids directly. at least a suite of their direct precursors that was abundant, varied. and considerably saturated. Copyright (C) 2005 Elsevier Ltd.