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

Chimiak, L. and Eiler, J. and Sessions, A. and Blumenfeld, C. and Klatte, M. and Stoltz, B. M. (2022) Isotope effects at the origin of life: Fingerprints of the Strecker synthesis. Geochimica et Cosmochimica Acta, 321 . pp. 78-98. ISSN 0016-7037. doi:10.1016/j.gca.2022.01.015.

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Strecker synthesis creates α-amino acids from prebiotically plausible substrates (cyanide, ammonia, and aldehydes) and is widely hypothesized to be a key mechanism in the chemistry that led to life on Earth and on other planets. To better constrain the synthetic environments and precursors of abiotic α-amino acids, and to determine unique signatures of abiogenic amino acids, we measured the molecular-averaged and site-specific carbon and nitrogen isotope effects for the Strecker synthesis of alanine. The reaction steps of the Strecker synthesis can be divided into two groups: an initial series of reversible amination and nitrile-addition reactions (‘equilibration’) and a second series of irreversible hydrolysis reactions (‘hydrolysis’). The equilibration of cyanide, acetaldehyde, and ammonia with the intermediate, α-aminopropionitrile (α-APN), has a measured 55.1‰ equilibrium nitrogen isotope effect between the ¹⁵N-rich amine nitrogen in α-aminopropionitrile and the ¹⁵N-poor ammonia and a 20.0‰ equilibrium carbon isotope effect between the ¹³C-poor C-2 site in α-aminopropionitrile and the ¹³C-rich carbonyl carbon in acetaldehyde. The first irreversible hydrolysis step is inferred to have an up to 10‰ normal carbon fractionation (i.e., faster for ¹²C, slower for ¹³C) for the whole molecule, but it also has one or more side reactions that deplete the reactive α-APN reservoir by up to 15‰. The second hydrolysis step has a 15.4‰ normal kinetic isotope effect on the amide (C-1) site of alaninamide, which becomes the carboxyl site of alanine. Other α-amino acids will likely experience similar nitrogen isotope fractionations between ammonia and their amine sites, and similar carbon isotope fractionations between the carbonyl carbon in reactant aldehydes or ketones and the intermediate α-aminonitrile, and between cyanide and the carboxyl site. Therefore, these isotope effects allow us to predict the carbon and nitrogen isotopic contents and intramolecular structures of α-amino acids formed by Strecker synthesis based on their substrates’ isotopic compositions, or to infer the isotopic compositions of substrates from which amino acids formed, for example in the case of the amino-acid-rich carbonaceous chondrites. The site-specific C and N isotopic compositions of amino acids formed by Strecker chemistry contrast with those typical of terrestrial biosynthetic amino acids, so these data also provide a means of discriminating between biogenic and abiogenic α-amino acids.

Item Type:Article
Related URLs:
URLURL TypeDescription
Chimiak, L.0000-0002-5047-5421
Eiler, J.0000-0001-5768-7593
Sessions, A.0000-0001-6120-2763
Stoltz, B. M.0000-0001-9837-1528
Additional Information:© 2022 Elsevier. Received 5 August 2021, Revised 27 November 2021, Accepted 12 January 2022, Available online 20 January 2022. We would like to acknowledge Brooke Dallas for her aid in developing the Orbitrap methodology, Dr. David Vander Velde for use of the NMR facilities, and Dr. Scott Virgil for his help in determining the alaninamide intermediate. Funding: This project was supported by NASA through LARS grant number NNX17AE52G, by DOE grant DE-SC0016561, by Thermo Fisher, and by the Simons Foundations; Author contributions: LC, ALS, and JME designed methods for site-specific carbon isotope measurements. MK, CB, and LC synthesized alanine by Strecker synthesis. BS provided lab space and initial aid in finding a mentor for conducting Strecker synthesis. LC measured isotopic ratios on Strecker synthesized alanine and alaninamide, processed data, calculated concentrations and isotope ratios of intermediates, and calculated predictions of ammonia isotope ratios on meteorites. LC, ALS, and JME contributed ideas to the cause in isotopic deviations at H1; and Data and materials availability: All data is available in the main text or the Supplementary Information. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0016561
Thermo Fisher ScientificUNSPECIFIED
Simons FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20220121-870770000
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Official Citation:L. Chimiak, J. Eiler, A. Sessions, C. Blumenfeld, M. Klatte, B.M. Stoltz, Isotope effects at the origin of life: Fingerprints of the Strecker synthesis, Geochimica et Cosmochimica Acta, Volume 321, 2022, Pages 78-98, ISSN 0016-7037,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113057
Deposited By: George Porter
Deposited On:21 Jan 2022 23:23
Last Modified:15 Feb 2022 20:31

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