Emergence of Order in Origin-of-Life Scenarios on Mineral Surfaces: Polyglycine Chains on Silica

The polymerization of amino acids (AAs) to peptides on oxide surfaces has attracted interest owing to its high importance in biotechnology, prebiotic chemistry, and origin of life theories. However, its mechanism is still poorly understood. We tried to elucidate the reactivity of glycine (Gly) from the vapor phase on the surface of amorphous silica under controlled atmosphere at 160 degrees C. Infrared (IR) spectroscopy reveals that Gly functionalizes the silica surface through the formation of ester species, which represent, together with the weakly interacting silanols, crucial elements for monomers activation and polymerization. Once activated, beta-turns start to form as initiators for the growth of long linear polypeptides (poly-Gly) chains, which elongate into ordered structures containing both beta-sheet and helical conformations. The work also points to the role of water vapor in the formation of further self-assembled beta-sheet structures that are highly resistant to hydrolysis.