Hydrothermal treatment of glycine and adiabatic expansion cooling: implications for prebiotic synthesis of biopolymers

There have been several studies on biopolymer synthesis under hydrothermal conditions. The conventional hydrothermal methods make it possible to synthesize only a dipeptide and short oligopeptides as well as cyclo-dimer, from amino acids. As these studies that were applied with various quenching methods suggested the importance of quenching rate from hydrothermal conditions, rapid quenching could avoid hydrolysis of the oligomers that had already been synthesized under hydrothermal conditions. In this study, therefore, we designed a novel hydrothermal flow reactor adopted with adiabatic expansion cooling system from the reason that it was thought to be one of the most rapid quenching methods. It mimics geysers, fumaroles, hot springs, and volcanic eruptions. Once aqueous solutions of monomers were treated at high temperature and pressure, the solutions were released into the atmosphere through an orifice to be depressurized and cooled down simultaneously with the Joule–Thomson effect. We demonstrated oligomerization of glycine up to decamer (Gly10) by using the flow reactor, which had never been yielded with any other quenching methods. This suggests that rapid quenching methods under non-equilibrium conditions such as adiabatic expansion cooling is an efficient way to produce long oligomers connected by covalent bonds via dehydration condensation