A team of international astronomers reported the discovery of the propionamide, the largest peptide-like molecule, in space toward Sagittarius B2(N1) at a position called N1E that is slightly offset from the continuum peak. Their study recently appeared in Arxiv.
Proteins are polymers of amino acids joined together by the peptide bond, -NHCO-. Due to the high molecular weight and extremely low gas-phase abundance, detection of proteins in the interstellar medium (ISM) at the current stage of development of observation facilities looks like a formidable task. Therefore, molecules with peptide-like bonds are of particular interest for our understanding of possible routes of protein formation in space. However, the number of peptide-like molecules found so far in space is quite limited.
Now, using the high sensitivity and high angular resolution of the ReMoCA spectral line survey conducted with ALMA toward Sgr B2(N), Chinese astronomers for the first time detected propionamide, C2H5CONH2, the next member of the interstellar amide chemical family after formamide and acetamide.
They performed a new laboratory measurements of the propionamide spectrum in the 9-461 GHz range, which provide them an opportunity to check directly for the transition frequencies of detected interstellar lines of propionamide.
“By mapping propionamide versus CH13CN, they selected a position 1.5ʹʹ to the east of the hot core Sgr B2(N1) (referred to as Sgr B2(N1E)) where they found propionamide is relatively strong while other molecular emissions are relatively weak.”— they wrote.
Their observational results indicated that propionamide emission comes from the warm, compact cores in Sagittarius B2, in which massive protostellars are forming. The column density of propionamide toward Sgr B2(N1E) was derived to be 1.5×1016 cm¯2, which is three-fifths of that of acetamide, and one-nineteenth of that of formamide.
“The detection of propionamide in Sgr B2(N) demonstrates that interstellar chemistry can reach sufficient levels of complexity to form relatively large peptide molecules and shows the possible growth of larger amide molecules from smaller ones in a massive star-forming process. It is probable that propionamide might also exist in massive star-forming regions in the Galactic disk, such as Orion KL and NGC 6334.”— they concluded.
Featured image: Generalized structure and model of propionamide © Juan Li et al.
Reference: Juan Li, Junzhi Wang, Xing Lu, Vadim Ilyushin, Roman A. Motiyenko, Qian Gou, Eugene A. Alekseev, Donghui Quan, Laurent Margules, Feng Gao, Frank J. Lovas, Yajun Wu, Edwin Bergin, Shanghuo Li, Zhiqiang Shen, Fujun Du, Meng Li, Siqi Zheng, Xingwu Zheng, “Propionamide (C2H5CONH2): The largest peptide-like molecule in space”, Arxiv, pp. 1-49, 2021.
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