From Anodic Oxidation of Aliphatic α-Amino Acids to Polypeptides by Quantum Electrochemistry Approach: Beyond Miller-Urey Experiments

For years, polypeptide formation has fascinated the scientific world because its understanding could lead to one of the possible explanations for the origin of life. Anodic oxidation of aliphatic alpha-amino acids in aqueous electrolytes can result either in their decomposition or in their polymerization into polypeptide. This behavior depends experimentally on both amino acid concentration and pH. The elucidation of the involved mechanisms remains a challenge because of the multitude of products which can be obtained. In this context, the electrochemical behavior of glycine and alanine on a biased platinum surface was examined at the nanoscale by quantum electrochemistry via the effective screening medium method. Several electrochemical systems with different concentrations and pH values have been explored. Simulations of the anodic oxidation of the amino acids have not only confirmed their electropolymerization and decomposition at high and low concentrations, respectively, but also have revealed unsuspected mechanisms at the origin of polypeptide formation. This sheds new light on electrochemistry of a-amino acids, on occurrence of polypeptides, and more generally on organic electrochemistry.