title: Formation of Complex Amino Acid Precursors and Nucleic Acid Bases from Possible Interstellar Media

authors: Kensei Kobayashi, Hayato Tokimura, Tomoyuki Matsuda, Shingo Enomoto, Takeo Kaneko, Yoko Kebukawa, Hitoshi Fukuda, Yoshiyuki Oguri, Satoshi Yoshida, Hiromi Shibata and Ken Takayama

abstract: A wide variety of organic compounds including amino acids and nucleic acid bases have been detected in carbonaceous chondrites and comets.  The origins of such organic compounds have been not clear, but one of the possible scenarios is so-called the Greenberg model.  In this model, interstellar media in molecular clouds were irradiated with cosmic rays and UV to form complex organics.  We irradiated possible interstellar media with high-energy particles, and analyzed the products.
When a mixture of carbon monoxide, ammonia and water was irradiated with 2.5 MeV protons from a Tandem accelerator (TIT), various amino acids were detected at quite high yield after acid-hydrolysis. All of the five nucleic acid bases have also been identified in the same product by GC/MS or LC/MS.  Complex amino acid precursors were also formed when a mixture of methanol, ammonia and water was irradiated with high-energy heavy ions from HIMAC (NIRS). 
Amino acid precursors formed in the irradiation experiments had high molecular weights, and could have eneantiomeric excesses after irradiation with circularly polarized UV.  Thus it was suggested that bioorganic compounds and their enantiomeric excesses found in carbonaceous chondrites could have been prepared in prior to the formation of the solar system.