Stereoisomers of isovaline in the Murchison meteorite

Pollock, Glenn E.; Cheng, Chunyang; Cronin, Sonja E.; Kvenvolden, Keith A.

doi:10.1016/0016-7037(75)90159-3

Cited by 58 publications

(35 citation statements)

References 5 publications

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“…The L-isovaline excess measured in Orgueil has not previously been reported in this or any CI meteorite and is similar to the Murchison value within error. Because isovaline is highly resistant to racemization (12), the measured D/L ratios should not have increased since the time of formation. Some radioracemization (Ϸ5%) of isovaline could have occurred based on the expected ionizing radiation dose from radioactive decay inside the Murchison and Orgueil meteorite parent bodies (24).…”

Section: Possible Sources Of Error In Lc-fd/tof-ms Amino Acid Measurementioning

confidence: 99%

“…Pizzarello et al (11) also found a possible correlation between the magnitude of the L-isovaline excesses observed in individual fragments of the Murchison meteorite and the relative abundance of hydrous silicate minerals, hinting that aqueous alteration may have played a role in amino acid asymmetry in this meteorite. These ␣-methyl amino acids are nonbiological, and unlike the ␣-hydrogen amino acids used in biochemistry, they are not prone to geologically rapid racemization under aqueous or radiogenic conditions (12). Therefore, the initial enantiomeric ratios of these ␣-methyl amino acids are much more likely to have been preserved since the time of their formation.…”

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Enrichment of the amino acid l -isovaline by aqueous alteration on CI and CM meteorite parent bodies

Glavin

Dworkin

2009

Proc. Natl. Acad. Sci. U.S.A.

273

346

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The distribution and enantiomeric composition of the 5-carbon (C5) amino acids found in CI-, 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 ␣-methyl amino acid isovaline was found in the CM meteorite Murchison (Lee ‫؍‬ 18.5 ؎ 2.6%) and the CI meteorite Orgueil (Lee ‫؍‬ 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 CI meteorite. The L-isovaline enrichments in these two carbonaceous meteorites cannot be the result of interference from other C5 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 ␣-dialkyl amino acids found in altered CI 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.enantiomeric excess ͉ homochirality ͉ origin of life ͉ carbonaceous chondrite M eteorites provide a record of the chemical processes that occurred in the early solar system before life began on the Earth. In particular, the carbonaceous chondrites are carbon-rich meteorites with up to 2 wt % organic carbon (1). The delivery of organic compounds by carbonaceous chondrites to the early Earth could have been an important source of the Earth's prebiotic organic inventory (2). The amino acid composition of carbonaceous meteorites has been characterized extensively because these prebiotic molecules are the monomers of proteins and enzymes in all life on Earth. Over 80 different amino acids have been identified in the CM meteorites Murchison and Murray, and they comprise a mixture of 2-to 8-carbon cyclic and acyclic monoamino alkanoic and alkandioic acids of nearly complete structural diversity, many of which are completely nonexistent in the terrestrial biosphere (1, 3-5). In addition, many amino acids are structurally chiral. With a few very rare exceptions, only left-handed amino acids (L) are found in biology, whereas all known abiotic syntheses of amino acids result in equal mixtures of left-and right-handed (L Ϸ D) amino acids. The origin of ''homochirality'' has been investigated for well over a century since Louis Pasteur discovered chirality, and it continues to be a topic of great importance in the origin of life field. There a...

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Section: Possible Sources Of Error In Lc-fd/tof-ms Amino Acid Measurementioning

confidence: 99%

mentioning

confidence: 99%

Enrichment of the amino acid l -isovaline by aqueous alteration on CI and CM meteorite parent bodies

Glavin

Dworkin

2009

Proc. Natl. Acad. Sci. U.S.A.

273

346

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“…with a methyl group bound to the carbon just next to the carbonyl, display higher e.e.s than their α-hydrogenated (α-H) analogs. Actually, α-H amino acids are known to racemize more efficiently than α-Me amino acids (Pollock et al 1975), because a H atom bound to a carbon close to a carbonyl is easy to remove. When an α-H amino acid loses its α-H atom, the asymmetric carbon loses its chirality.…”

Section: Comparison With Other Amino Acid Datamentioning

confidence: 99%

The effects of circularly polarized light on amino acid enantiomers produced by the UV irradiation of interstellar ice analogs

Nuevo

Meierhenrich

Muñoz

et al. 2006

A&A

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Aims. Two irradiation experiments on interstellar ice analogs at 80 K under interstellar-like conditions were performed with the LURE SU5 synchrotron beamline to assess, for the first time, the photochemical effect of circularly polarized ultraviolet light (UV CPL) at 167 nm (7.45 eV) with right and left polarizations on such ice mixtures. Methods. This effect was measured by determining the enantiomeric excesses (e.e.s) for two amino acids formed in the solid organic residues produced during the subsequent warm-up of the irradiated samples to room temperature: alanine, the most abundant chiral proteinaceous amino acid produced (both polarizations) and 2,3-diaminopropanoic acid (DAP), a non-proteinaceous amino acid (rightpolarization experiment). These excesses were compared to those measured for the same amino acids produced after unpolarized UV irradiation of the same ice mixtures (expected to be zero), in order to determine the contribution of CPL only. A careful estimate of all the associated uncertainties (statistical and systematic errors) was also developed.Results. It appears that the enantiomeric photochemical effect at this wavelength is weak, since both alanine and DAP e.e.s were found to be small, at most of the order of 1% in absolute values, and tends to be inconclusive since the effects obtained for both amino acids and both polarizations are not those expected. In light of these results, the hypothesis that CPL may be one source responsible for the e.e.s measured for such amino acids in some meteorites and, more generally, that CPL may be directly related to the origin of biomolecular homochirality on Earth is discussed.

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“…Soc. 11 6,2681 (1 994) 13. The prevousy reported compound 1 (72) has been character~zed by elemental anayss.…”

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Enantiomeric Excesses in Meteoritic Amino Acids

Cronin

Pizzarello

1997

Science

818

531

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Gas chromatographic-mass spectral analyses of the four stereoisomers of 2-amino-2,3-dimethylpentanoic acid (dl-alpha-methylisoleucine and dl-alpha-methylalloisoleucine) obtained from the Murchison meteorite show that the L enantiomer occurs in excess (7.0 and 9.1%, respectively) in both of the enantiomeric pairs. Similar results were obtained for two other alpha-methyl amino acids, isovaline and alpha-methylnorvaline, although the alpha hydrogen analogs of these amino acids, alpha-amino-n-butyric acid and norvaline, were found to be racemates. With the exception of alpha-amino-n-butyric acid, these amino acids are either unknown or of limited occurrence in the biosphere. Because carbonaceous chondrites formed 4.5 billion years ago, the results are indicative of an asymmetric influence on organic chemical evolution before the origin of life.

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Stereoisomers of isovaline in the Murchison meteorite

Cited by 58 publications

References 5 publications

Enrichment of the amino acid l -isovaline by aqueous alteration on CI and CM meteorite parent bodies

Enrichment of the amino acid l -isovaline by aqueous alteration on CI and CM meteorite parent bodies

The effects of circularly polarized light on amino acid enantiomers produced by the UV irradiation of interstellar ice analogs

Enantiomeric Excesses in Meteoritic Amino Acids

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