Molecular distribution, 13C-isotope, and enantiomeric compositions of carbonaceous chondrite monocarboxylic acids

The water-soluble organic compounds in carbonaceous chondrite meteorites constitute a record of the synthetic reactions occurring at the birth of the solar system and those taking place during parent body alteration and may have been important for the later origins and development of life on Earth. In this present work, we have developed a novel methodology for the simultaneous analysis of the molecular distribution, compound-specific delta C-13, and enantiomeric compositions of aliphatic monocarboxylic acids (MCA) extracted from the hot-water extracts of 16 carbonaceous chondrites from CM, CR, CO, CV, and CK groups. We observed high concentrations of meteoritic MCAs, with total carbon weight percentages which in some cases approached those of carbonates and insoluble organic matter. Moreover, we found that the concentration of MCAs in CR chondrites is higher than in the other meteorite groups, with acetic acid exhibiting the highest concentration in all samples. The abundance of MCAs decreased with increasing molecular weight and with increasing aqueous and/or thermal alteration experienced by the meteorite sample. The delta C-13 isotopic values of MCAs ranged from -52 to +27 parts per thousand, and aside from an inverse relationship between delta C-13 value and carbon straight-chain length for C-3-C-6 MCAs in Murchison, the C-13-isotopic values did not correlate with the number of carbon atoms per molecule. We also observed racemic compositions of 2-methylbutanoic acid in CM and CR chondrites. We used this novel analytical protocol and collective data to shed new light on the prebiotic origins of chondritic MCAs.