Spontaneous Polymerization of Glycine under Hydrothermal Conditions

The abiotic polymerization of nucleotides and amino acids is a prerequisite for the emergence of life. It has been proposed that hydrothermal conditions might favor the polymerization of amino acids. In the present study, we analyzed by in situ Raman spectroscopy in a diamond anvil cell the fate of the simplest and most abundant amino acid, glycine, under hydrothermal conditions at 200 degrees C and pressures ranging between 50 and 3500 MPa. We also tested the effect of magnetite on the reactivity of glycine. The polymerization of glycine is highly favored under pressure and in the presence of magnetite. Linear dimers are more abundant than the cyclic ones up to a threshold pressure of 500 MPa. Above 800 MPa, amino acids stop reacting and the system is "frozen". Our findings suggest that pressure and mineral-water interface strongly favor the formation of linear peptides. The optimum conditions for polymerization obtained in the present study suggest that the prebiotic chemical evolution of amino acids was not restricted to hydrothermal vents at oceanic ridges but might also occur much deeper in the first 15-30 km of the crust, widely expanding the prebiotic reactive zone.