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Nonracemic isovaline in the Murchison meteorite: chiral distribution and mineral association |
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| Authors: | Sandra Pizzarello Michael Zolensky |
| Institution: | 1 Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA 2 NASA Johnson Space Center, Houston, TX 77058, USA 3 NASA Ames Research Center, Moffet Field, CA 94035, USA |
| Abstract: | The enantiomeric and carbon-isotopic composition of the amino acid isovaline have been analyzed in several samples of the Murchison meteorite and one sample of the Murray meteorite. l-Enantiomeric excesses of the amino acid were found to range from 0 to 15.2%, varying significantly both between meteorite stones and at short distances within a single stone. The upper limit of this range is the largest enantiomeric excess measured to date for a biologically rare meteoritic amino acid and raises doubts that circularly polarized light irradiation could have been the sole cause of amino acids chiral asymmetry in meteorites. Individual d- and l-isovaline δ13C values ware found to be about +18‰, with no significant differences between the two enantiomers to suggest terrestrial contamination. The amino acid relative abundance also varied between samples, with isovaline/alanine ratios of 0.5 to 6.5. X-ray diffraction analyses of contiguous meteorite fragments suggest a possible correlation between isovaline and hydrous silicates abundances. |
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