Permalink : http://hdl.handle.net/2115/34708

炭素質コンドライトや彗星中に種々の複雑有機物が検出されていることから，地球外有機物が生命の誕生に重要な役割を果たした可能性が議論されている．隕石・彗星中有機物の起源としては，分子雲中の星間塵アイスマントル中で宇宙線・紫外線エネルギーにより生成したとするモデルが提案されて いる．われわれは模擬星間物質に重粒子線を照射することにより高分子状の複雑有機物に結合したアミノ酸前駆体が生成することを見いだした．このような高分子状結合型アミノ酸は遊離アミノ酸と比較して宇宙環境で安定であること，円偏光照射によりアミノ酸エナンチオ過剰を生じうることなどが わかった．これらの知見をもとに生命の起源にいたる新たな化学進化シナリオを提案する．
Complex organic compounds were detected in carbonaceous chondrites and comets, and their relevance to origins of life has been discussed. It was suggested that these extraterrestrial organics were originally formed in ice mantles of interstellar dusts (ISDs) in molecular clouds. It was reported that amino acid precursors were formed from ice mixtures simulating ISD ice mantles by irradiation with UV or high-energy particles, but the nature of the precursors before hydrolysis were unknown. We irradiated a frozen mixture of possible interstellar molecules (methanol, ammonia and water) with high-energy heavy ions. The products were complex precursors of amino acids with large molecular weights. Such “complex amino acid precursors” were much more stable than free amino acids against irradiation with γ-rays or heavy ions. Irradiation of simulated interstellar complex organics with circular polarized light gave an enantiomeric excess of amino acid. These results suggested that formation of complex organics-bound amino acids and seeds of homochirality of amino acids were originally formed in interstellar cold environments. We propose a novel scenario of chemical evolution from interstellar organics to the first life on the Earth.