Elemental sulfur, hydrogen sulfide, and carbon monoxide-driven dimerization of glycine at sub-millimolar concentrations: Implications for the origin of life

The life's origin in submarine hydrothermal systems is a long-standing scenario supported by diverse sci-entific disciplines, while verification of its chemical plausibility remains a major bottleneck. Most scenar-ios of hydrothermal origin postulate peptides as key players in prebiotic chemistry; nevertheless, it remains unknown how peptides were formed from geochemically available amino acids that must be low in concentration. Here we show that a simple mixing with elemental sulfur (S0), hydrogen sulfide (HS-), and carbon monoxide (CO) enables an effective dimerization of glycine (Gly) at micro to several millimolar concentrations. Incubation of 1 mM Gly with the three inorganic compounds in a warm alka -line solution (pH 9.3 and 35 or 50 degrees C) led up to 18% conversion of Gly to glycylglycine (GlyGly). Dimerization of 0.01 mM Gly was also discerned in the yield far exceeding the thermodynamic equilib-rium (0.4% yield). In this reaction, CO is oxidized to CO2 concomitant with the reduction of S0 to polysul-fides, serving as the driving force for the Gly-to-GlyGly conversion. Although the formation of CO2 as a byproduct suppressed the formation of GlyGly, its adverse effect was mitigated by carbonate precipita-tion upon adding Mg2+ and Ca2+. To our knowledge, 0.01 mM is the lowest concentration of amino acid oligomerized experimentally in the prebiotic context. Given the ubiquity of S0, HS-, and CO in primordial ocean hydrothermal systems, and the abundance of Mg2+ and Ca2+ in seawater, our demonstrated favor-able condition for amino acid dimerization is likely to have occurred on the Hadean seafloor. This possi-bility supports an abiotic appearance of peptides and thereby facilitates the hydrothermal origin of life.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Automated summary

The origin of life in submarine hydrothermal systems has been supported by diverse scientific disciplines for a long time, but the chemical plausibility of this scenario remains uncertain. Many hypotheses propose peptides as important molecules in the prebiotic chemistry, but it is still unknown how peptides were formed from amino acids that were present in low concentrations. In this study, it was shown that a simple mix of elemental sulfur, hydrogen sulfide, and carbon monoxide enabled efficient dimerization of glycine at low concentrations. This finding supports the possibility of abiotic peptide formation and facilitates the hydrothermal origin of life.