Carbon isotope evidence for the substrates and mechanisms of prebiotic synthesis in the early solar system

Abstract

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Isotope effects at the origin of life: Fingerprints of the Strecker synthesis

“…Recent site-specific isotope ratio (SSIR) measurements of an alanine sample from the Murchison meteorite identified a pronounced 13 C enrichment that the α-carbon (i.e., HO 2 C-HCNH 2 -CH 3 ), a pattern consistent with derivation by Strecker chemistry from acetaldehyde with a 13 C-rich carbonyl carbon (Chimiak et al, 2020). The evidence that Strecker synthesis created α-amino acids in meteorite parent bodies -rocky bodies containing water, simple organics, and (presumably) no life-bolsters its potential as a pathway to form amino acids on early Earth and other planets.…”

“…It has been previously suggested that Strecker synthesis could be an abiotic route to amino acid formation on carbonaceous chondrite parent bodies and other planetary bodies (Cronin et al, 1993;Pizzarello and Shock, 2010;Burton et al, 2012). This suggestion was recently supported by a study of the site-specific carbon isotope structure of alanine (Chimiak et al, 2020). If this interpretation is correct, we can combine the experimental constraints on N isotope fractionations of the Strecker synthesis presented here with prior measurements of δ 15 N values of alanine recovered from the carbonaceous chondrites (Pizzarello et al, 1994;Pizzarello and Holmes, 2009;Pizzarello et al, 2011;Elsila et al, 2012) to estimate a range of δ 15 N values for ammonia from which alanine formed (Figure 8a).…”

“…As explained in Eiler et al (2017) and Chimiak et al (2020), all samples are derivatized with the same reagents and methods, so the derivative-sourced carbons are assumed to have identical δ 13 C values between samples and standards and thus only dilute differences in 13 C content between a given molecular or fragment species of alanine samples and standards. This assumption was verified by analysis of the differences in isotopic contents between the VWR, Alfa Aesar, and Strecker-synthesis standards by both the mass spectrometric method described here (Appendix A) and previously established values determined by combining EA-IRMS and ninhydrin decarboxylation data for the molecule and C-1, respectively (Eiler et al, 2017;Chimiak et al, † i F j is related to i R j by the formula: i F j = and i R j is related to δ h X as described in footnote *.…”

“…On meteorites, aldehydes, ammonia, and their potential Strecker synthesis products, α-amino acids, have higher compound-specific H, N and C isotope abundance ratios (i.e., D/H, 13 C/ 12 C and 15 N/ 14 N) than those observed in common terrestrial materials and in the bulk average (i.e., at hand-sample scale) meteoritic organic matter. These 13 C-enrichments decrease with increasing carbon number among the C2+ aldehydes and α-amino acids (Elsila et al, 2012;Aponte et al, 2017;Chimiak et al, 2020). The shared heavy-isotope enrichment and correlation of 13 C/ 12 C with carbon number have been interpreted as evidence that the meteoritic α-amino acids are derived from the co-occurring Strecker reagents and thus plausibly formed by the Strecker mechanism (Pizzarello et al, 1994;Elsila et al, 2012;Aponte et al, 2017;Simkus et al, 2019).…”

Position‐specific carbon isotope analysis of serine by gas chromatography/Orbitrap mass spectrometry, and an application to plant metabolism

“…High-resolution mass spectrometry provides an alternative path for PSIA of amino acids, as has been illustrated using the Thermo Scientific™ Q Exactive™ GC and HF Orbitrap™ platforms. 11,14,25,26 Analytes are fragmented in the ion source and can be subjected to additional fragmentation in a collision cell if needed. The resulting fragment ions retain structural information and may sample different combinations of atoms from the original molecule.…”