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

Abstract

The reaction of H atoms with glycine was investigated at 3.1 K in para-H 2 , 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.

Computational studies on the possible formation of glycine via open shell gas-phase chemistry in the interstellar medium

“…Furthermore, our results corroborate with those of Ioppolo 48 et al and Joshi 79 et al , who showed that glycine by non-energetic glycine mechanisms can be formed in the presence of H atoms in dark clouds and in a similar manner very recently, Tarczay 80 et al have shown that “natural α-amino acids can be formed from glycine via the Cα-glycyl radical by non-energetic mechanisms in the solid phase of the interstellar medium. Moreover, our paper highlights the complementarity between gas-phase interstellar chemistry – a reaction pathway studied by Rimola et al in ref.…”

Hydrogen‐atom tunneling reactions in solid para‐hydrogen and their applications to astrochemistry

“…We have investigated reactions of H atoms with astronomically relevant species such as methanol CH 3 OH, [ 62 ] formamide HC(O)NH 2 , [ 80 ] methyl formate HC(O)OCH 3, [ 57 ] acetamide CH 3 C(O)NH 2 , [ 81 ] acetic acid CH 3 C(O)OH, [ 82 ] glycine NH 2 CH 2 C(O)OH, [ 83 ] methyl amine CH 3 NH 2 , [ 84 ] and N‐methyl formamide HC(O)NHCH 3 [ 85 ] ; as discussed previously, these species are building blocks of peptides, as illustrated in Figure 5. The UV/IR irradiated matrix was typically maintained in darkness for more than 10 h to facilitate H‐atom tunneling reactions.…”

“…[ 109,110 ] In collaboration with Tarczay's group in Hungary, we investigated reaction H + NH 2 CH 2 C(O)OH. [ 83 ] The spectrum of deposited glycine in p ‐H 2 reveals three isomers, Ip (0.0), IIn (3.8), and IIIn (7.2); values in parentheses represent the relative energies in kJ mol −1 with respect to most stable isomer Ip. UV/IR irradiation of Cl 2 ‐doped NH 2 CH 2 C(O)OH/ p ‐H 2 matrices formed C α ‐glycyl radical, H 2 N•CHC(O)OH (referred to as In CH ) after H‐abstraction on the methylene moiety of Ip; lines of In CH were unambiguously assigned according to quantum‐chemical computations.…”

Potential Catalytic Role of Small Heterocycles in Interstellar H2 Formation: A Laboratory Astrochemistry Study on Furan and Its Hydrogenated Forms

“…Among the possible molecules that can act as catalysts in these reactions, polyaromatic hydrocarbons (PAHs) 8−12 and small organic molecules 13,14 were investigated by theoretical and experimental methods. The role of PAHs in H 2 formation can be especially important in photon-dominated regions (PDRs).…”

“…Although H 2 is the smallest and the most abundant molecule of the interstellar medium (ISM), its formation in the present universe is still not fully understood. Due to the low-pressure conditions in the ISM, and due to the lack of a dipole moment for H 2 , its gas-phase formation rate from H atoms both by three-body collision (eq ) and by radiative association (eq ) mechanisms is practically zero. − …”