Consistent Scenario from Formation and Evolution of Interstellar Organic Molecules to Their Delivery to the Primitive Earth

本研究的目的是开展星际有机化合物的形成、蚀变（演化）和传递等综合实验，评估地外有机化合物在生命起源化学演化中的作用。用高能质子、γ射线或重离子照射甲醇（或一氧化碳）、氨和水的混合物。通过凝胶过滤层析和热解-气相色谱/质谱分析，证实产物为分子量达数千的“复杂有机化合物”。当产物被酸水解时，检测到各种各样的氨基酸。重离子给甘氨酸的g值（能量产率）比γ射线高。甲醇、氨和水的冷冻混合物在77 K下的g值与液体混合物在室温下的g值几乎相同。用γ射线或重离子辐照游离氨基酸和结合氨基酸（蛋白质（HSA）和非生物形成的氨基酸前体（CAW））。结合氨基酸对辐射的稳定性远高于游离氨基酸。辐照后CAW的分子量变化不大，表明星际复合有机化合物在空间环境中具有较高的稳定性。与游离氨基酸相比，CAW在轨道炮高速冲击和超临界水流反应器高温下也表现出更高的稳定性。结论是：(i)具有高分子量的复合氨基酸前体可以在星际环境中形成，（ii）它们比自由氨基酸对辐射、冲击和热更稳定，（iii）这种复杂的有机物可能是地球上产生生命的来源。我们正计划研究这种复杂星际分子在陨石基质中的可能演化。

Objectives of the present study are to perform integrated experiments including formation, alteration (evolution) and delivery of interstellar organic compounds, and to evaluate the roles of extraterrestrial organic compounds in chemical evolution toward origins of life.A mixture of methanol (or carbon monoxide), ammonia and water was irradiated with high energy protons, γ-rays, or heavy ions. It was proved that the resulting products were "complex organic compounds" with molecular weights of several thousands by gel filtration chromatography and by pyrolysis-GC/MS. A wide variety of amino acids were detected when the products were acid-hydrolyzed. Heavy ions gave higher G-values (energy yields) of glycine than γ-rays. The G-value of glycine from frozen mixture of methanol, ammonia and water at 77 K was almost the same as that from the liquid mixture at room temperature.Free amino acids and bounded amino acids (protein (HSA) and abiotically-formed amino acid precursors (CAW)) were irradiated with γ-rays or heavy ions. Bounded amino acids showed much higher stability than free amino acids against radiation. The molecular weight of CAW changed little after irradiation, which showed high stability of interstellar complex organic compounds in space environments. The CAW also showed higher stability against high-velocity impact with a rail gun, and against heat with a supercritical water flow reactor than free amino acids.It was concluded that (i)complex amino acid precursors with high molecular weight can be formed in interstellar environments, (ii)they were more stable than free amino acids against radiation, shock and heat, and (iii)such complex organics were probable sources for generation of life on the Earth. We are planning to study possible evolution of such complex interstellar molecules in meteorite matrix.