Pathways to Glycine and Other Amino Acids in Ultraviolet-irradiated Astrophysical Ices Determined via Quantum Chemical Modeling

A recent experimental study reported that glycine and other amino acids were formed when cryogenic H2O ice containing small amounts of CH3OH, NH3, and HCN was subjected to ultraviolet (UV) irradiation. Quantum chemical calculations were employed to evaluate the viability of various pathways to the formation of glycine, alanine, and serine in dilute H2O ice containing CH3OH and HCN. Under the experimental processing conditions of deposition and UV irradiation at 15 K followed by heating to room temperature, amino acids can form by recombining radicals produced by dehydrogenating H2O and CH3OH and subsequently hydrogenating HCN. The study indicates that isotopic substitution experiments would identify CH3OH as the source of the C atom in the COOH carboxylic acid group of the amino acids observed in the irradiation experiments, with the CO+OH reaction playing an important role. The remaining C and N atoms in glycine are predicted to originate from HCN via sequential hydrogenation to yield CH2NH2. Formation pathways for alanine and serine are also discussed.

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