George U. Yuen

Isotopic and molecular analyses of hydrocarbons and monocarboxylic acids of the Murchison meteorite

The monocarboxylic acids and hydrocarbons of the Murchison meteorite (CM2) were isolated for isotopic analysis. The nonvolatile hydrocarbons were analyzed as crude methanol and benzene-methanol extracts and also after separation by silica gel chromatography into predominantly aliphatic, aromatic, and polar hydrocarbon fractions. The volatile hydrocarbons were obtained after progressive decomposition of the meteorite matrix by freeze-thaw, hot water, and acid treatment. Molecular analyses of the aromatic hydrocarbons showed them to comprise a complex suite of compounds in which pyrene, fluoranthene, phenanthrene, and acenaphthene were the most abundant components, a result similar to earlier analyses. The polar hydrocarbons also comprise a very complex mixture in which aromatic ketones, nitrogen, and sulfur heterocycles were identified. Both delta 13C and delta D values were obtained for all preparations. The monocarboxylic acids, aliphatic, aromatic, and polar hydrocarbons, and the indigenous volatile hydrocarbons were found to be D-rich with delta D values ranging from about +100 to +1000. The delta 13C values ranged overall from -13 to +17. The deuterium enrichment observed in these compounds is suggestive of a relationship to interstellar organic compounds. In two separate analyses, the delta D values of the nonvolatile hydrocarbons were observed to increase in the following order: aliphatic < aromatic < polar. This finding is consistent with an early solar system or parent body conversion of aromatic to aliphatic compounds as well as the earlier suggestion of pyrolytic formation of aromatic from aliphatic compounds.

Amino acids of the Murchison meteorite. II - Five carbon acyclic primary beta-, gamma-, and delta-amino alkanoic acids

All ten of the possible five-carbon acyclic primary beta-, gamma-, and delta-amino alkanoic acids (amino position isomers of the valines) have been positively identified in hot-water extracts of the Murchison meteorite using combined gas chromatography-mass spectrometry (GC-MS) and ion exchange chromatography. With the exception of delta-aminovaleric acid, none of these amino acids has been previously reported to occur in meteorites or in any other natural material. The gamma-amino acids (4-aminopentanoic acid, 4-amino-2-methlybutanoic acid, and 4-amino-3-methylbutanoic acid) are present at higher concentrations (about 5 nmol g-1)than are the beta-amino isomers (3-aminopentanoic acid, 3-amino-2-methylbutanoic acid, allo-3-amino-2-methylbutanoic acid, 3-amino-3-methylbutanoic acid, 3-amino-2-ethylpropanoic acid, and 3-amino-2,2-dimethylpropanoic acid) which are present at concentrations of 1-2 nmol g-1. These amino acids are less abundant in the meteorite than either the corresponding alpha-amino acids or the four-carbon homologues. Thirty-six amino acids have now been positively identified in the Murchison meteorite, 17 of which are apparently unique to carbonaceous chondrites. The fact that the meteorite contains all possible five-carbon acyclic primary alpha-, beta-, gamma-, and delta-amino alkanoic acids is consistent with a synthetic process involving random combination of single-carbon precursors.

Quantification of monocarboxylic acids from a spark discharge synthesis

SummaryA suite of sixteen monocarboxylic acids having carbon numbers 2 to 7, formed by the Miller-Urey spark discharge process, were identified and quantified by gas chromatography and mass fragmentography using a deuterium spiking technique. The molar concentration and isomeric distribution of these laboratory synthesized monocarboxylic acids are compared to those previously reported for the Murchison meteorite. They show similar trends, namely, decreasing molar concentration with increasing molecular weight, and, the ratio of normal/branched isomers tend toward smaller with increasing carbon numbers.

Gas chromatographic-mass spectral analysis of the five-carbon β-, γ-, and δ-amino alkanoic acids

Abstract A gas chromatographic separation method and electron impact mass spectra obtained by gas chromatography-mass spectrometry are presented for N-trifluoroacetyl-2-butyl esters of the nine possible five-carbon β-, γ-, and δ-amino alkanoic acids. Mass spectral fragmentation patterns are rationalized in terms of amino acid struture, and general criteria are described for distinguishing between amino position and chain isomers of aliphatic amino acids based on mass spectra of their N-trifluoroacetyl-2-butyl esters.