Ab initio study of hydrolysis of amino malononitrile: Formation of amino acetonitrile

Ab initio theoretical calculation was carried out to study the hydrolysis of amino malononitrile. The proposed scheme was considered as one of the possible reaction paths that the simplest amino acid, glycine, may be synthesized by the nature. Several other probable schemes based on the potential reaction sites of amino malononitrile were also examined. The optimized structures of the species on the reaction potential energy surfaces in addition to the activation energies were calculated at both HF and MP2 levels. The basis set superposition error (BSSE) for the correction of calculated energy was also performed. It came out that one of the proposed reactions had the lower potential energy profile in the sequential processes to form the amino acetonitrile. Most of the calculated barriers in this scheme were below 60 kcal/mol. The first added H₂O in the hydrolysis of amino malononitrile was calculated to be at lower barrier (49.00 kcal/mol) on attacking one of the nitrile group of amino malononitrile and successively forming an amide, rather than attacking on the amino group of amino malononitrile (82.24 kcal/mol). Further frontier orbital analysis also proved the same fact. The second H₂O molecule was added to hydrolyze the forming amide and produced carboxylic acid, which then underwent decarboxylation to form amino acetonitrile. Direct decarboxylation needs around 61 kcal/mol to cross the barrier, the highest one in all the processes derived in Scheme 1. Of course, it may be assisted by the third molecule such as H₂O to lower the barrier (around 20 kcal/mol). From the calculated low barriers the proposed processes in Scheme 1 may be considered as one of the acceptable mechanisms in prebiotic chemical evolution on the primitive earth.