由于软X射线引起的稠密分子云内气相和固相生物分子的光稳定性
Photostability of gas- and solid-phase biomolecules within dense molecular clouds due to soft X-rays
摘要：
在软X射线下进行了涉及气相和固相氨基酸（甘氨酸，DL-缬氨酸，DL-脯氨酸）和核碱基（腺嘌呤和尿嘧啶）的实验光化学研究。其目的是测试基本生物分子对密集分子云和原恒星盘类似物内电离光子场的分子稳定性。在这些环境中，主要的能量来源是宇宙射线和软X射线。这些测量是在巴西同步加速器光实验室（LNLS）进行的，使用150 eV光子。通过飞行时间质谱仪（TOF-MS）和傅里叶变换红外（FTIR）光谱仪分别进行气相和固相分析。固相氨基酸的半衰期，假设存在于谷物地幔，是至少3E 5年和3E 8年内致密的分子云和原行星盘，分别。我们估计，对于气相化合物，这些值增加一个数量级，因为甘氨酸的解离截面在气相比在固相相同的光子能量。固相核碱基的半衰期比氨基酸高约2-3个数量级。结果表明，核碱基比氨基酸更能抵抗电离辐射。我们认为这些影响的生存和转移的生物分子在空间环境中。
英文摘要：
An experimental photochemistry study involving gas- and solid-phase amino acids (glycine, DL-valine, DL-proline) and nucleobases (adenine and uracil) under soft X-rays was performed. The aim was to test the molecular stabilities of essential biomolecules against ionizing photon fields inside dense molecular clouds and protostellar disks analogs. In these environments, the main energy sources are the cosmic rays and soft X-rays. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing 150 eV photons. In-situ sample analysis was performed by Time-of-flight mass spectrometer (TOF-MS) and Fourier transform infrared (FTIR) spectrometer, for gas- and solid- phase analysis, respectively. The half-life of solid phase amino acids, assumed to be present at grain mantles, is at least 3E5 years and 3E8 years inside dense molecular clouds and protoplanetary disks, respectively. We estimate that for gas-phase compounds these values increase one order of magnitude since the dissociation cross section of glycine is lower at gas-phase than at solid phase for the same photon energy. The half-life of solid phase nucleobases is about 2-3 orders of magnitude higher than found for amino acids. The results indicate that nucleobases are much more resistant to ionizing radiation than amino acids. We consider these implications for the survival and transfer of biomolecules in space environments.
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