Deuterium fractionation of amino acids by low-temperature atomic reactions on grain surfaces in molecular clouds

颗粒-表面反应被认为对分子云中的化学演化有重要贡献。在本研究中，我们研究了在天体物理条件下，通过颗粒-表面反应进行的氨基酸的重水分馏。最简单的氨基酸甘氨酸被气相沉积在安装在超高真空反应室中心的反应底物(12K)上。将氚原子与固体甘氨酸作用后，对反应产物进行了红外光谱和核磁共振分析。研究发现，甘氨酸通过与氢原子的反应部分实现了氢化反应。由于甘氨酸的氢化反应存在较大的活化势垒，因此必须通过量子隧穿来促进反应。本研究表明，在低温条件下，氨基酸可以通过颗粒表面反应生成重氢。

Grain-surface reactions are considered to have a significant contribution to chemical evolution in molecular clouds. In the present study, deuterium fractionation of amino acids via grain-surface reactions was investigated under astrophysically relevant conditions. The simplest amino acid glycine was vapor-deposited on a reaction substrate (12 K) mounted onto the center of an ultra-high vacuum reaction chamber. After deuterium-atom exposure to solid glycine, the reaction product was analyzed by FTIR and NMR. It was found that the glycine was partially deuterated by reactions with atomic deuterium. Since a large activation barrier is present on the deuteration of glycine, a quantum-tunneling must be required to promote the reaction. The present study demonstrated that amino acids can be deuterated by grain-surface reactions at low temperatures.