TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 53 (No. 1), pp. 5-20, 2019

Molecular and isotopic compositions of nitrogen-containing organic molecules formed during UV-irradiation of simulated interstellar ice

Haruna Sugahara,1,2* Yoshinori Takano,1 Shogo Tachibana,3,4 Iyo Sugawara,4 Yoshito Chikaraishi,5,1 Nanako O. Ogawa,1 Naohiko Ohkouchi,1 Akira Kouchi5 and Hisayoshi Yurimoto4

1Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsushima, Yokosuka, Kanagawa 237-0061, Japan
2Institut de Chimie de Nice, Université Côte d'Azur, CNRS, UMR 7272, 06108 Nice, France
3UTokyo Organization for Planetary and Space Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
4Department of Natural History Sciences, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
5Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan

(Received July 24, 2018; Accepted November 29, 2018)

Abstract: Interstellar ice is a reaction site for molecular evolution. Gaseous molecules are frozen at low temperature (∼10 K) to form ice mantles and the energy supplied by UV photons and other energy sources can lead to the synthesis of complex organics. Nitrogen-containing organic molecules are of special interest because of their biomolecular importance and their anomalous stable nitrogen isotopic composition (15N/14N) in the interstellar dust environment. Thus, N-containing organic molecules are the keys to understanding the evolution of organic molecules and the solar system. We focused on amino acids and amines in refractory organic residues formed from ultraviolet (UV) irradiated interstellar ice analogues. We developed analytical techniques that enable the identification of the small quantities of molecules formed from the simulated interstellar ice analogues. Organic residue analysis of the UV-irradiated H2O-CH3OH-NH3 ice showed the formation of three amines (methylamine, ethylamine and propylamine) and 11 amino acids (e.g., glycine, α-alanine, β-alanine, sarcosine, α-aminobutyric acid and β-aminoisobutyric acid). Furthermore, the compound-specific isotope analysis of nitrogen within the amino acids and the bulk organic film revealed that little isotopic fractionation occurred during formation in the simulated environment.
Key words: amines and amino acids, bulk and compound-specific nitrogen isotope analysis, ice mantle, simulated interstellar ice formation, UV-irradiation

*Corresponding author E-mail: h.sugahara@jamstec.go.jp

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