彗星和陨石中的氨基酸：伽马辐射下的稳定性 和手性的保持

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摘要翻译：
太阳系天体中的氨基酸可能在导致地球生命起源的化学中发挥了关键作用。我们提出了测试氨基酸抗γ辐射光解稳定性的实验室研究。目前地球生物化学蛋白质中所用的20种左旋型手性氨基酸均被固体γ射线辐照，辐照剂量为3.2MGy，相当于彗星和小行星1.05×109年的放射性核素衰变所产生的剂量。用差示扫描量热法(DSC)和旋光色散法(ORD)测定每种氨基酸的辐解度和辐散度。根据这些测量结果，确定了每个氨基酸的辐解速率常数kdsc和辐射速率常数krac，并将其推算为14毫吉的剂量，这相当于在4.6×109年（太阳系的年龄）内天然放射性核素衰变到彗星和小行星中所有有机分子的预期总剂量。结果表明，所研究的氨基酸在14 MGy的辐射剂量下均能大量存活，但部分氨基酸在辐射分解过程中丢失。同样，伴随着辐解的辐射化过程也不会使手性消失。放射性同位素分解和放射性同位素分解速率常数的知识可以从今天在碳质球粒陨石中发现的氨基酸浓度开始，计算太阳系形成时氨基酸的原始浓度。对于某些氨基酸，太阳系前星云中的浓度可能比目前在陨石中观察到的浓度高6倍。
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英文标题：
《Amino Acids in Comets and Meteorites: Stability under Gamma Radiation
  and Preservation of Chirality》
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作者：
Susana Iglesias-Groth, Franco Cataldo, Ornella Ursini, Arturo Manchado
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最新提交年份：
2010
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分类信息：

一级分类：Physics        物理学
二级分类：Biological Physics        生物物理学
分类描述：Molecular biophysics, cellular biophysics, neurological biophysics, membrane biophysics, single-molecule biophysics, ecological biophysics, quantum phenomena in biological systems (quantum biophysics), theoretical biophysics, molecular dynamics/modeling and simulation, game theory, biomechanics, bioinformatics, microorganisms, virology, evolution, biophysical methods.
分子生物物理、细胞生物物理、神经生物物理、膜生物物理、单分子生物物理、生态生物物理、生物系统中的量子现象（量子生物物理）、理论生物物理、分子动力学/建模与模拟、博弈论、生物力学、生物信息学、微生物、病毒学、进化论、生物物理方法。
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一级分类：Physics        物理学
二级分类：Earth and Planetary Astrophysics        地球和行星天体物理学
分类描述：Interplanetary medium, planetary physics, planetary astrobiology, extrasolar planets, comets, asteroids, meteorites. Structure and formation of the solar system
行星际介质，行星物理学，行星天体生物学，太阳系外行星，彗星，小行星，陨石。太阳系的结构和形成
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一级分类：Quantitative Biology        数量生物学
二级分类：Other Quantitative Biology        其他定量生物学
分类描述：Work in quantitative biology that does not fit into the other q-bio classifications
不适合其他q-bio分类的定量生物学工作
--

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英文摘要：
  Amino acids in solar system bodies may have played a key role in the chemistry that led to the origin of life on Earth. We present laboratory studies testing the stability of amino acids against gamma radiation photolysis. All the 20 chiral amino acids in the levo form used in the proteins of the current terrestrial biochemistry have been irradiated in the solid state with gamma radiation to a dose of 3.2 MGy which is the dose equivalent to that derived by radionuclide decay in comets and asteroids in 1.05x109 years. For each amino acid the radiolysis degree and the radioracemization degree was measured by differential scanning calorimetry (DSC) and by optical rotatory dispersion (ORD) spectroscopy. From these measurements a radiolysis rate constant kdsc and a radioracemization rate constant krac have been determined for each amino acid and extrapolated to a dose of 14 MGy which corresponds to the expected total dose delivered by the natural radionuclides decay to all the organic molecules present in comets and asteroids in 4.6x109 years, the age of the Solar System. It is shown that all the amino acids studied can survive a radiation dose of 14 MGy in significant quantity although part of them are lost in radiolytic processes. Similarly, also the radioracemization process accompanying the radiolysis does not extinguish the chirality. The knowledge of the radiolysis and radioracemization rate constants may permit the calculation of the original concentration of the amino acids at the times of the formation of the Solar System starting from the concentration found today in carbonaceous chondrites. For some amino acids the concentration in the presolar nebula could have been up to 6 times higher than currently observed in meteorites.
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PDF链接：
https://arxiv.org/pdf/1007.4529

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关键词：氨基酸 稳定性 Quantitative preservation Measurements 彗星 acids 陨石 dose 同位素