Reply to Elsila et al.: Large enantiomeric excesses in primitive meteorites, an analytical and computational supplement

Pizzarello, Sandra; Monroe, A. A.

doi:10.1073/pnas.1213714109

Cited by 7 publications

(7 citation statements)

References 6 publications

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“…The origin of life’s homochirality, a central and still puzzling question in astrobiology, traces back probably to the origin of life itself and has been the subject of many scenarios including deterministic ones based upon the consequences of chemical or physical laws . In particular, since the discovery of a partially circularly polarized light in massive star forming region , together with the fact that l -enriched amino acids have been found in carbonaceous meteorites, a CPL-induced process has appeared as a possible asymmetric bias to which amino acids formed in the interstellar medium would have been exposed during their journey toward earth, leading to significant enantiomeric excesses (ee) that would be later amplified on earth toward homochirality. So far, most of the efforts have been targeted toward asymmetric photochemical processes simulated in the condensed matter by using UV CPL from SR, leading to significant ee in the few percent range, such as the asymmetric photolysis on thin films of the racemic amino acid leucine, and alanine induced by nonvanishing absorption anisotropy factors g, and asymmetric photochirogenesis of alanine from achiral precursors in interstellar ice analogues…”

Section: Resultsmentioning

confidence: 99%

VUV Photodynamics and Chiral Asymmetry in the Photoionization of Gas Phase Alanine Enantiomers

et al. 2014

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The valence shell photoionization of the simplest proteinaceous chiral amino acid, alanine, is investigated over the vacuum ultraviolet region from its ionization threshold up to 18 eV. Tunable and variable polarization synchrotron radiation was coupled to a double imaging photoelectron/photoion coincidence (i(2)PEPICO) spectrometer to produce mass-selected threshold photoelectron spectra and derive the state-selected fragmentation channels. The photoelectron circular dichroism (PECD), an orbital-sensitive, conformer-dependent chiroptical effect, was also recorded at various photon energies and compared to continuum multiple scattering calculations. Two complementary vaporization methods-aerosol thermodesorption and a resistively heated sample oven coupled to an adiabatic expansion-were applied to promote pure enantiomers of alanine into the gas phase, yielding neutral alanine with different internal energy distributions. A comparison of the photoelectron spectroscopy, fragmentation, and dichroism measured for each of the vaporization methods was rationalized in terms of internal energy and conformer populations and supported by theoretical calculations. The analytical potential of the so-called PECD-PICO detection technique-where the electron spectroscopy and circular dichroism can be obtained as a function of mass and ion translational energy-is underlined and applied to characterize the origin of the various species found in the experimental mass spectra. Finally, the PECD findings are discussed within an astrochemical context, and possible implications regarding the origin of biomolecular asymmetry are identified.

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Section: Resultsmentioning

confidence: 99%

VUV Photodynamics and Chiral Asymmetry in the Photoionization of Gas Phase Alanine Enantiomers

et al. 2014

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“…); and Pizzarello and coworkers concluded that l ‐isoleucine excesses were indigenous in a suite of 8 CR chondrites based on experimental and theoretical considerations (Elsila et al. ; Pizzarello and Monroe ; Pizzarello et al. ).…”

Section: Resultsmentioning

confidence: 99%

The amino acid composition of the Sutter's Mill CM2 carbonaceous chondrite

Burton

Glavin

Elsila

et al. 2014

Meteorit & Planetary Scien

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Abstract-We determined the abundances and enantiomeric compositions of amino acids in Sutter's Mill fragment #2 (designated SM2) recovered prior to heavy rains that fell April 25-26, 2012, and two other meteorite fragments, SM12 and SM51, that were recovered postrain. We also determined the abundance, enantiomeric, and isotopic compositions of amino acids in soil from the recovery site of fragment SM51. The three meteorite stones experienced terrestrial amino acid contamination, as evidenced by the low D/L ratios of several proteinogenic amino acids. The D/L ratios were higher in SM2 than in SM12 and SM51, consistent with rain introducing additional L-amino acid contaminants to SM12 and SM51. Higher percentages of glycine, b-alanine, and c-amino-n-butyric acid were observed in free form in SM2 and SM51 compared with the soil, suggesting that these free amino acids may be indigenous. Trace levels of D+L-b-aminoisobutyric acid (b-AIB) observed in all three meteorites are not easily explained as terrestrial contamination, as b-AIB is rare on Earth and was not detected in the soil. Bulk carbon and nitrogen and isotopic ratios of the SM samples and the soil also indicate terrestrial contamination, as does compound-specific isotopic analysis of the amino acids in the soil. The amino acid abundances in SM2, the most pristine SM meteorite analyzed here, are approximately 20-fold lower than in the Murchison CM2 carbonaceous chondrite. This may be due to thermal metamorphism in the Sutter's Mill parent body at temperatures greater than observed for other aqueously altered CM2 meteorites.

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“…In addition, stable isotope measurements for these amino acids were not made to firmly establish their extraterrestrial origin, and it was argued that there could have been analytical interferences that affected the enantiomeric ratios. 92,124,125 Glavin and co-workers reported an excess of L-aspartic acid of up to ∼60% in the Tagish Lake meteorite (Table 1), and stable carbon isotope measurements revealed that both enantiomers were significantly enriched in 13 C (δ 13 C = +24‰ and +29‰, respectively), confirming that the large Laspartic acid excesses in the meteorite were extraterrestrial in origin. 26 Interestingly, other proteinogenic amino acids including glutamic acid, serine, and threonine were also present with large L-enantiomeric excess in the Tagish Lake meteorite (L ee ∼ 50 to 99%, Table 1), whereas alanine, another common protein amino acid, was nearly racemic.…”

Section: Amino Acid Asymmetry and Amplification Mechanismsmentioning

confidence: 81%

“…Enantiomeric excesses of up to 50% for l -isoleucine (relative to d -isoleucine) and up to 60% for d - allo -isoleucine (relative to l - allo -isoleucine) have been reported in CR2 chondrites. , Slight d -enantiomeric excesses of the nonproteinogenic amino acids allo -isothreonine (D ee ∼ 8%) and β-aminoisobutyric acid (D ee ∼ 7%) have also been recently reported in the Murchison meteorite (Table ); however, the analytical uncertainties in these measurements were >10%, so it is not clear if these d -amino acid excesses are real. In addition, stable isotope measurements for these amino acids were not made to firmly establish their extraterrestrial origin, and it was argued that there could have been analytical interferences that affected the enantiomeric ratios. ,, …”

Section: Amino Acids In Meteorites and Lifementioning

confidence: 99%

The Search for Chiral Asymmetry as a Potential Biosignature in our Solar System

et al. 2019

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The search for evidence of extraterrestrial life in our Solar System is currently guided by our understanding of terrestrial biology and its associated biosignatures. The observed homochirality in all life on Earth, that is, the predominance of “left-handed” or l-amino acids and “right-handed” or d-sugars, is a unique property of life that is crucial for molecular recognition, enzymatic function, information storage and structure and is thought to be a prerequisite for the origin or early evolution of life. Therefore, the detection of l- or d-enantiomeric excesses (ee) of chiral amino acids and sugars could be a powerful indicator for extant or extinct life on another world. However, studies of primitive meteorites have revealed they contain extraterrestrial amino acids and sugar acids (aldonic acids) with large enantiomeric excesses of the same chirality as terrestrial biology resulting from nonbiological processes, complicating the use of chiral asymmetry by itself as a definitive biosignature. Here we review our current knowledge of the distributions and enantiomeric and isotopic compositions of amino acids and polyols found in meteorites compared to terrestrial biology and propose a set of criteria for future life detection missions that can be used to help establish the origin of chiral asymmetry.

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Reply to Elsila et al.: Large enantiomeric excesses in primitive meteorites, an analytical and computational supplement

Cited by 7 publications

References 6 publications

VUV Photodynamics and Chiral Asymmetry in the Photoionization of Gas Phase Alanine Enantiomers

VUV Photodynamics and Chiral Asymmetry in the Photoionization of Gas Phase Alanine Enantiomers

The amino acid composition of the Sutter's Mill CM2 carbonaceous chondrite

The Search for Chiral Asymmetry as a Potential Biosignature in our Solar System

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