Mechanisms of glycine formation from aminoacetonitrile in space

The potential energy surfaces for the formation of glycine (Gly) or its precursors, such as Gly radical cation and deprotonated Gly, starting from aminoacetonitrile (NH₂CH₂CN) or deprotonated aminoacetonitrile were determined by CBS-QB3 calculation. The reaction of NH₂CH₂CN + H₂O⁺˙ + H₂O gave mainly unwanted products other than Gly or its precursors. The reactions of ˙NHCH₂CN + 2H₂O, NH₂˙CHCN + 2H₂O, or NH₂CH₂CN + ˙OH + H₂O, led to Gly or its precursors as one of the main products. The overall activation barriers were 229 kJ mol⁻¹, 216 kJ mol⁻¹, and 118 kJ mol⁻¹, respectively. A barrierless pathway for the formation of Gly from the reaction of NH₂CH₂CN + ˙OH + H₂O with a catalytic H₂O was found, strongly suggesting that Gly can be formed thermally from NH₂CH₂CN and ˙OH on icy grain surfaces in the interstellar medium.