Non-energetic, Low-Temperature Formation of C_α-Glycyl Radical, a Potential Interstellar Precursor of Natural Amino Acids

The reaction of H atoms with glycine was investigated at 3.1 K inpara-H₂, a quantum-solid host. The reaction was followed by IR spectroscopy, with the spectral analysis aided by quantum chemical computations. Comparison of the experimental IR spectrum with computed anharmonic frequencies and intensities proved that, regardless of the reactant glycine conformation, C_α-glycyl radical is formed in an H-atom-abstraction process with great selectivity. The product of the second H-atom abstraction, iminoacetic acid, was also observed in a smaller amount. The C_α-glycyl radical is sensitive to UV light and decomposes to iminoacetic acid and H atom upon 280 nm radiation. Since the reactive radical center is located on the C_α-atom, it is suggested that natural α-amino acids can be formed from glycine via the C_α-glycyl radical by non-energetic mechanisms in the solid phase of the interstellar medium.