A Reaction Network for Triglycine Synthesis under Hydrothermal Conditions

Abstract

Abstract It has been hypothesized that chemical evolution leading to the origin of life might have occurred in hydrothermal environments on primitive Earth. To examine this hypothesis, we investigated how the polymerization of amino acids proceeds under high-temperature and high-pressure conditions. We investigated a reaction network consisting of glycine and oligoglycines up to trimer, and the condensation/hydrolysis reactions among these molecules. We determined the rate constants of these reactions in experiments employing a flow reactor at 200 °C and 25 MPa. We found that two condensation reactions of glycine, which yield diglycine and diketopiperazine as products, have larger equilibrium constants under these conditions than at 25 °C. This result supports the hypothesis that hydrothermal conditions are thermodynamically favorable for chemical evolution. We also found that triglycine formation is mediated by diketopiperazine at 200 °C and 25 MPa. This implies that diketopiperazine acts as an important intermediate in the polymerization process of amino acids, which might have occurred in hydrothermal environments on primitive Earth.