First Glycine Isomer Detected in the Interstellar Medium: Glycolamide (NH₂C(O)CH₂OH)

Abstract

We report the first detection in the interstellar medium (ISM) of a C2H5O2N isomer: syn-glycolamide (NH2C(O)CH2OH). The exquisite sensitivity at sub-mK levels of an ultradeep spectral survey carried out with the Yebes 40 m and IRAM 30 m telescopes toward the G+0.693–0.027 molecular cloud has allowed us to unambiguously identify multiple transitions of this species. We derived a column density of (7.4 ± 0.7) × 1012 cm−2, which implies a molecular abundance with respect to H2 of 5.5 × 10−11. The other C2H5O2N isomers, including the higher-energy anti conformer of glycolamide and two conformers of glycine, were not detected. The upper limit derived for the abundance of glycine indicates that this amino acid is surely less abundant than its isomer glycolamide in the ISM. The abundances of the C2H5O2N isomers cannot be explained in terms of thermodynamic equilibrium; thus, chemical kinetics need to be invoked. While the low abundance of glycine might not be surprising, based on the relative low abundances of acids in the ISM compared to other compounds (e.g., alcohols, aldehydes, or amines), several chemical pathways can favor the formation of its isomer glycolamide. It can be formed through radical–radical reactions on the surface of dust grains. The abundances of these radicals can be significantly boosted in an environment affected by a strong ultraviolet field induced by cosmic rays, such as that expected in G+0.693–0.027. Therefore, as shown by several recent molecular detections toward this molecular cloud, it stands out as the best target to discover new species with carbon, oxygen, and nitrogen with increasing chemical complexity.

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS+

“…We searched for both HOCS + and HSCO + isomers toward the molecular cloud G+0.693-0.027 (hereafter G+0.693), located in the Central Molecular Zone of the Milky Way. This astronomical source has been established as one of the prime targets for unraveling new interstellar complex organic molecules (or COMs, defined as carbon-based molecules comprising six or more atoms, Herbst et al 2020), based on the first detection of a deluge of C-, O-, N-, and also S-bearing species (see, e.g., Rivilla et al 2019Rivilla et al , 2020Rivilla et al , 2021aRivilla et al , 2021bRivilla et al , 2022aRivilla et al , 2022bRivilla et al , 2023Bizzocchi et al 2020;Rodríguez-Almeida et al 2021aZeng et al 2021Zeng et al , 2023Jiménez-Serra et al 2022;Fatima et al 2023;Sanz-Novo et al 2023).…”

“…We used Yebes 40 m observations to cover the Q band (31.075-50.424 GHz), and IRAM 30 m observations to cover three frequency windows: GHz. More detailed information on the ultradeep spectral survey (e.g., resolution and noise levels of the spectra), including the new Yebes 40 m (project 21A014; PI: Rivilla) and IRAM 30 m observations (project 123-22; PI: Jiménez-Serra), can be found in Rivilla et al (2023) and Sanz-Novo et al (2023). Note that the sensitivity of this molecular line survey has seen a significant improvement compared to previous works (e.g., Rivilla et al 2021b;Rodríguez-Almeida et al 2021a;Jiménez-Serra et al 2022), reaching now sub-mK noise levels.…”

“…Hence, these results are an additional example against the minimum energy principle (MEP; Lattelais et al 2011), which proposes that the thermodynamically favored (most stable) isomer is expected to be predominant in the ISM. This fact is not striking, since the MEP has been proven to fail to predict the relative abundances of a plethora of structural isomers (e.g., the C 3 H 2 O, C 2 H 4 O 2 , or C 2 H 5 O 2 N isomeric families; Shingledecker et al 2019;Mininni et al 2020;Rivilla et al 2023). Thus, the identification of HOCS + provides clear observational evidence to argue that the MEP does not apply to the interstellar [H, C, S, O] + isomeric family either.…”

A Vision for the Future of Astrochemistry in the Interstellar Medium by 2050

“…This discrepancy between their presence in solar system bodies from in situ measurements and a lack of gas phase, remote observation almost certainly points to shortcomings in the latter. Claims for remote amino acid detections have already been given without confirmation from the community while other searches have turned up empty-handed, but several prebiotic precursors have been observed directly , including an isomer of glycine giving reason to believe that amino acids should be present and potentially observable in various astrophysical regions.…”

Vacuum Ultraviolet Single Photon Ionization and Decomposition of 2-Aminopropionitrile in Astrophysical Objects

“…Nevertheless, the search for this amino acid and its isomers is still a very active field. Very recently, Rivilla et al (2023) successfully detected glycolamide (H 2 NC(O)CH 2 OH), an isomer of glycine. They deduced a molecular abundance of glycolamide with respect to H 2 of 5.5 × 10 −11 .…”