Guanine synthesis from 4-aminoimidazole-5-carbonitrile: A computational mechanistic study

The potential energy surface (PES) for guanine formation from 4-aminoimidazole-5-carbonitrile (AICN) after adding H₂O and cyanogen (NCCN) was determined from quantum chemical calculations using the CBS-QB3 method. Its activation energy was too high for the reaction to occur in the interstellar medium. The PES for the formation of a protonated guanine from AICN by adding H₃O⁺ and NCCN was also determined. Although its overall activation energy was zero, its occurrence in the interstellar gas phase is not likely due to unstable intermediates. When H₂O was added to some reaction steps as a catalyst, their activation barriers were significantly reduced.