Ab initio study of the formation of glycine via amino acetonitrile and amino-cyano-acetic acid

Ab initio theoretical calculations were carried out to study the hydrolysis of amino acetonitrile (NH₂CH₂CN) and amino-cyano-acetic acid (NH₂(CN)CHCOOH). Each of the proposed schemes was considered to be one of the possible reaction paths by which the simplest amino acid, glycine, may be synthesized by nature. The optimized structures of the species on the potential energy surfaces were calculated at both the HF and MP2 levels. We found that the direct hydrolysis of the nitrile group of amino acetonitrile required a higher energy barrier (52.38 kcal/mol) compared to the barrier for the hydrolysis of amino-cyano-acetic acid (46.11 kcal/mol). Our calculated potential energy profiles revealed that this glycine evolution would not occur as easily in an anhydrous atmosphere as in moist surroundings. (The difference in the barriers may be more than 30 kcal/mol.) Molecular orbital interaction between H₂O and the amino acetonitrile was also studied, and we found that the crucial part of this hydrolysis process was the transfer of the hydrogen atom of H₂O to the N atom of the nitrile group rather than the formation of the C-O bond between the O atom of H₂O and the C atom of the nitrile group. The schematic processes with calculated lower energy barriers in the proposed schemes might be considered to be possible mechanisms in the prebiotic chemical evolution on the primitive earth.