[MIS17-03] Formation of Complex Amino Acid Precursors by Cosmic Rays in Interstellar Environments
Keywords:Amino Acid Precursors, Non-Strecke-Type Reactions, Cosmic Rays, Molecular Clouds, Complex Organic Compounds, Chemical Evolution
Experiment: A gaseous mixture of CO and NH3 was sealed in a Pyrex glass tube with liquid water. The gaseous mixture was irradiated with 2.5 MeV protons from a Tandem accelerator at Tokyo Institute of Technology. Total quantity of electricity was 2 mC. The irradiation products is hereafter referred to as CAW. A mixture of CH3OH, NH3and H2O (molar ratio 1:1:2.8) was sealed in a pyrex glass tube, frozen in liquid nitrogen, and irradiated with 290 MeV/u carbon ions from HIMAC accelerator (NINS, QST, Japan). The irradiation products is hereafter referred to as MeAW.
Aminoacetonitrile, a precursor of glycine, in CAW and MeAW was determined by cation-exchange HPLC after derivatized with orthophthalaldehyde and N-actyl-L-cysrtein. Hydantoin in the both product was determined by reversed-phase HPLC. Both products were fractionated by gel filtration chromatograpy (column: Shodex OHpak SB-802.5 HQ) and/or ultrafiltration (Pall Ultrafiltration device 3K). Each fraction was acid-hydrolyzed and amino acids in the fractions were determince by the cation-exchange HPLC (shown above). Both products were also characterized by LC/Orbitrap-MS.
Results and Discussion: Both CAW and MeAW had little amino acids before hydrolysis, but various amino acids were detected after hydrolysis. Glycine was predominant in all the case. Thus, not free amino acids but amino acid precursors were formed in the simulation experiments. It was shown that neither aminoacetonitrile nor hydantoin were major glycine precursors, but complex amino acid precursors were major amino acid precursors. In the case of CAW, amino acid precursors whose molecular weights were over 3000 were predominant. Peaks of m/z = 1000 or over were detected by mass spectrometry. These results strongly suggested that complex amino acid precursors with large molecular weitghts could be directly generated from small molecules such as CO or CH3OH in interstellar environments. It was suggested that the Strecker-type reaction was not a major pathway of amino acid formation in molecular clouds: Flash-and-quench-type reactions might be important for the formation of complex molecules in space.
The present work was partly supported by JSPS KAKENHI Grant Numbers JP17H02991 and 19K21895.
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