Enhanced Synthesis of Alkyl Amino Acids in Miller’s 1958 H2S Experiment
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Stanley Miller’s 1958 H2S-containing experiment, which included a simulated prebiotic atmosphere of methane (CH4), ammonia (NH3), carbon dioxide (CO2), and hydrogen sulfide (H2S) produced several alkyl amino acids, including the α-, β-, and γ-isomers of aminobutyric acid (ABA) in greater relative yields than had previously been reported from his spark discharge experiments. In the presence of H2S, aspartic and glutamic acids could yield alkyl amino acids via the formation of thioimide intermediates. Radical chemistry initiated by passing H2S through a spark discharge could have also enhanced alkyl amino acid synthesis by generating alkyl radicals that can help form the aldehyde and ketone precursors to these amino acids. We propose mechanisms that may have influenced the synthesis of certain amino acids in localized environments rich in H2S and lightning discharges, similar to conditions near volcanic systems on the early Earth, thus contributing to the prebiotic chemical inventory of the primordial Earth.
KeywordsStanley Miller Spark discharge Hydrogen sulfide
We thank Mandeville Special Collections in the UC San Diego Geisel Library for making Miller’s original laboratory notebooks accessible. The authors thank the National Aeronautics and Space Administration (NASA) Astrobiology Institute (NAI) and the Goddard Center for Astrobiology for grant support. M.P.C. and H.J.C. acknowledge support from the NAI Postdoctoral Program administered by Oak Ridge Associated Universities. A.L. is grateful for support provided by CONACYT Mexico (Project 50520-Q), and by a DGAPA-UNAM and a UC Mexus-CONACYT Fellowship. We also thank Jamie Elsila and Facundo Fernandez for additional analytical support. J.L.B. and H.J.C. are affiliated with the Center for Chemical Evolution at the Georgia Institute of Technology, supported by the National Science Foundation (NSF) and the NASA Astrobiology Program, under NSF Grant CHE-1004570.
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