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enrichment of the amino acid l-isovaline by aqueous alteration on ci and cm meteorite parent bodiesThe distribution and enantiomeric composition of the 5-carbon (C(sub 5)) amino acids found in Cl-, CM-, and CR-type carbonaceous meteorites were investigated by using liquid chromatography fluorescence detection/TOF-MS coupled with o-phthaldialdehyde/Nacetyl- l-cysteine derivatization. A large L-enantiomeric excess (ee) of the a-methyl amino acid isovaline was found in the CM meteorite Murchison (L(sub ee) = 18.5 +/- 2.6%) and the Cl meteorite Orguell (L(sub ee) = 15.2 +/- 4.0%). The measured value for Murchison is the largest enantiomeric excess in any meteorite reported to date, and the Orgueil measurement of an isovaline excess has not been reported previously for this or any Cl meteorite. The L-isovaline enrichments in these two carbonaceous meteorites cannot be the result of interference from other C(sub 5) amino acid isomers present in the samples, analytical biases, or terrestrial amino acid contamination. We observed no L-isovaline enrichment for the most primitive unaltered Antarctic CR meteorites EET 92042 and QUE 99177. These results are inconsistent with UV circularly polarized light as the primary mechanism for L-isovaline enrichment and indicate that amplification of a small initial isovaline asymmetry in Murchison and Orgueil occurred during an extended aqueous alteration phase on the meteorite parent bodies. The large asymmetry in isovaline and other alpha-dialkyl amino acids found in altered Ct and CM meteorites suggests that amino acids delivered by asteroids, comets, and their fragments would have biased the Earth's prebiotic organic inventory with left-handed molecules before the origin of life.
Document ID
20090042743
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Glavin, Daniel P.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Dworkin, Jason P.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 24, 2013
Publication Date
April 7, 2009
Publication Information
Publication: Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Volume: 106
Issue: 14
Subject Category
Lunar and Planetary Science and Exploration
Distribution Limits
Public
Copyright
Other