Water-assisted transamination of glycine and formaldehyde

A computational study on the transamination reaction of molecular complexes that consist of NH2CH2COOH + CH2O + nH2O, where n = 0, 1, 2, is presented. This work has allowed the description of the geometries of all the intermediates and transition states of the reactions, which can be described by five steps: carbinolamine formation, dehydration, 1,3 proton transfer, hydrolysis, and carbinolamine elimination. Among the five steps of the reaction, hydrolysis and elimination occur with the existence of general acid catalysis related to the carboxylic group. The water molecules can be involved in the reaction by performing as a proton-transfer carrier and a stabilizing zwitterion. It can be predicted from our calculations that in the transamination between alpha-amino acids and alpha-keto acids, the carbinolamine is formed with small barrier or even barrierless while the dehydration occurs easily at room temperature. However, without heating the 1,3 proton transfer could not occur as the barrier is 26.7 kcal/mol relative to the reactant complex when including two water molecules. Our results are in good agreement with experimental conclusions.