Organic analysis of the Antarctic carbonaceous chondrites [microform]
- Bib ID:
- 3282701
- Format:
- Book and Microform
- Author:
- Kotra, Ramakrishna
- Description:
- 197 p.
- Summary:
-
Carbonaceous chondrites are the only natural source of prebiotic molecules available for analysis. The first unambiguous evidence for amino acids of extraterrestrial abiotic origin was obtained from the Murchison meteorite. Yet, only a small number of meteorites have been studied in detail for organic content because of the scarcity of well-preserved samples. Recent expeditions to the Antarctic have brought back more than 5000 meteorites. Some of these are carbonaceous chondrites. The relatively cold, dry and sterile environment of the Antarctic may have been an ideal place of storage for the fragile carbonaceous meteorites. Three Antarctic carbonaceous chondrites were acquired for organic analysis. These were the Allan Hills 77306 (type C2), Allan Hills 77307 (type C3) and the Yamato 74662 (type C2). Investigation of these was undertaken in an attempt to learn how well the environment preserved them and increase the knowledge of the organic components of meteorites.
The three samples were analyzed for amino acids and hydrocarbons. Samples of the well-studied Murchison meteorite (type C2) were also analyzed for comparison. A search was also made for the presence of peptides. Care was taken during the collection and subsequent handling of the meteorites to minimize the chances of adding contaminants. Samples were prepared in clean rooms prior to analysis. Great care was taken to ensure the purity of reagents, cleanliness of apparti, and procedure blanks were performed in parallel with meteorite analysis. Approximately 200 mg to 1 gram of exterior and interior portions of the meteorites were extracted sequentially with water for isolation of amino acids and peptides and then with benzene-methanol for isolation of hydrocarbons. Amino acids were determined in hydrolyzed and unhydrolyzed fractions by ion-exchange chromatography using ninhydrin and o-phthalaldehyde detection.
Portions of the extracts were also converted to the N-trifluoracetyl-isopropyl derivatives to determine the amino acid enantiomer ratios by gas chromatography and to obtain confirmation of compound identification by mass spectrometry. Hydrocarbons were analyzed by gas chromatography and gas chromatography combined with mass spectrometry. Peptides were studied by the same techniques after enzymatic and acidic hydrolysis. The amino acid analysis showed that the Yamato 74662 contained about the same quantities as the Murchison. The Allan Hills 77307 contained no extractable amino acids. The exterior and interior portions of the Antarctic meteorites contained nearly equal amounts of amino acids. Both protein and non-protein amino acids were identified. D/L ratios of several amino acids for the interior and exterior are near unity for the Antarctic meteorites. Most of the amino acids identified in this study have been detected in earlier analyses of the Murchison.
In addition, preliminary evidence for lysine, phenylalanine and tyrosine was obtained. Normal alkanes were the dominant hydrocarbons. Smaller amounts of aromatic hydrocarbons were also detected. For the alkanes neither an odd over even preference nor a bimodal distribution were observed. Small quantities of pristane and no phytane were detected. It was not possible to utilize enzymatic hydrolysis on the meteorite extracts because of the enzyme. Gas chromatographic separation of standard peptide derivatives on packed columns was plagued by sample adsorption by the column at low levels. However, with a capillary column it was possible to obtain preliminary evidence for the presence of ala-ala and gly-val. Insufficient sample prevented further analysis. The results of this first study on the Antarctic carbonaceous chondrites indicate that they have been well-preserved. The organic compounds are of extraterrestrial abiotic origin.
This detailed study of amino acids and hydrocarbons has doubled the number of well-preserved meteorites in which organic compounds have been determined. Evidence for several new compounds has also been obtained. Substantial evidence has been obtained in support of the abiotic synthesis of organic molecules in the solar system.
- Notes:
-
- (UnM)AAI8202611
- Source: Dissertation Abstracts International, Volume: 42-08, Section: B, page: 3160.
- Thesis (Ph.D.)--University of Maryland College Park, 1981.
- Reproduction:
- Microfiche. Ann Arbor, Mich.: University Microfilms International.
- Subject:
- Geochemistry
- Other authors/contributors:
- University of Maryland College Park
- Copyright:
-
In Copyright
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Copyright status was determined using the following information:
- Material type:
- Literary Dramatic Musical
- Published status:
- Unpublished
- Creation date:
- 1981
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