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

本研究的目的是进行包括星际有机化合物的形成、变化(演化)和输送在内的综合实验，并评估外星有机化合物在迈向生命起源的化学演化中的作用。高能质子、γ射线或重离子辐照了甲醇(或一氧化碳)、氨和水的混合物。经凝胶过滤层析和裂解-GC/MS鉴定，产物为分子量几千的复杂有机化合物，酸解产物中含有多种氨基酸。重离子对甘氨酸的G值(能量产额)高于γ射线。用γ-射线或重离子辐照游离氨基酸和结合氨基酸(蛋白质和非生物形成的氨基酸前体)，得到77K下冷冻的甲醇、氨和水混合物中甘氨酸的G值与室温下液体混合物中甘氨酸的G值基本相同。结合氨基酸表现出比游离氨基酸更高的抗辐射稳定性。辐照后CAW的相对分子质量变化不大，表明星际有机络合物在空间环境中具有较高的稳定性。CAW还表现出比游离氨基酸更高的稳定性，在轨道炮下抵抗高速撞击，在超临界水流反应堆中抵抗热。结论是：(I)高相对分子质量的复合氨基酸前体可以在星际环境中形成，(Ii)它们比游离氨基酸更稳定，不受辐射、冲击和热的影响，(Iii)这种复杂有机物可能是地球上生命产生的来源。我们正计划研究陨石基质中这种复杂星际分子的可能演化。

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.