物理化学学报 >> 2009, Vol. 25 >> Issue (11): 2312-2318.doi: 10.3866/PKU.WHXB20091039

研究论文 上一篇    下一篇

星际媒介H2NCH2CN与H2O反应中的H2O分子偶合质子转移机理和氢隧道效应

徐四川, 马丽英, 卞富永, 史强, 葛茂发, 张兴康   

  1. 云南大学化学科学与工程技术学院生命起源研究室, 自然资源药物化学教育部重点实验室, 昆明 650091|中国科学院化学研究所, 北京分子科学国家实验室, 分子动态与稳态结构国家重点实验室, 北京 100190
  • 收稿日期:2009-05-04 修回日期:2009-07-29 发布日期:2009-10-28
  • 通讯作者: 徐四川, 史强 E-mail:sichuan@ynu.edu.cn; qshi@iccas.ac.cn

H2O-Coupled Proton Transfer Mechanism and Hydrogen Tunneling Effects in the Reaction of H2NCH2CN with H2O in the Interstellar Medium

XU Si-Chuan, MA Li-Ying, BIAN Fu-Yong, SHI Qiang, GE Mao-Fa, ZHANG Xing-Kang   

  1. Key Laboratory of Medicinal Chemistry of Natural Resource (Yunnan University), Ministry of Education, College of Chemical Science and Technology, Laboratory on the Origin of Life, Yunnan University, Kunming 650091, P. R. China|State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
  • Received:2009-05-04 Revised:2009-07-29 Published:2009-10-28
  • Contact: XU Si-Chuan, SHI Qiang E-mail:sichuan@ynu.edu.cn; qshi@iccas.ac.cn

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摘要：

H2NCH2CN+H2O→H2NCH2C(OH)NH是一个重要的反应, 涉及到星际媒介中甘氨酸的形成, 与早期地球上的氨基酸起源有关. 如果没有考虑氢隧道效应, 在MP2/6-311+G(d,p)级别上计算反应能垒是254.7 kJ·mol-1, 在星际媒介中该气相反应很难进行. 在星际媒介冰颗粒表面上, 水分子催化反应增强了该化学反应的活性. H2NCH2CN与(H2O)3反应中的两个水分子作为催化剂降低活化能77.5 kJ·mol-1和活化自由能70.9 kJ·mol-1, 并且通过氢键桥协同传递质子. 量子氢隧道对于该反应进行至关紧要,采用小弯曲隧道(SCT)近似和正则变分过渡态理论(CVT)方法研究. 温度50 K时, 速率常数kSCT/CVT为1.86×10-23 cm3·molecule-1·s-1, 表明在星际媒介中通过质子隧道机理该反应容易进行. 研究结果与地球上的氨基酸起源于地球本身物质的观点相一致.

关键词: H2NCH2CN, H2NCH2C(OH)NH, 星际媒介, 氨基酸起源, 质子转移, 氢原子隧道

Abstract:

The reaction H2NCH2CN + H2O→H2NCH2C(OH)NH is an important reaction related to the formation of glycine in the interstellar medium (ISM) and the origin of amino acids in early Earth. This reaction in the gas phase proceeds slowly and this is confirmed by its energy barrier of 254.7 kJ·mol-1 as determined at the MP2/6-311+(d,p) level without considering hydrogen tunneling in the ISM. On icy grain surfaces in the ISM, however, its reactivity may be enhanced by H2Ocatalytic reactions. The reaction of H2NCH2CNwith (H2O)3 is optimal as two H2Omolecules act as a catalyst with reducing the activation energy by 77.5 kJ·mol-1 and the activation free energy by 70.9 kJ·mol-1. A proton moves in a concerted way through a hydrogen bonded bridge. Quantum hydrogen tunneling is a crucial pathway for this reaction to proceed and was investigated using the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT). At 50 K, rate constant kSCT/CVT is 1.86×10-23 cm3·molecule-1·s-1, which demonstrates that the reaction is feasible by a hydrogen tunneling mechanism in the ISM. These results may support the theory that the origin of amino acids is fromthe materials of the Earth itself.

Key words: H2NCH2CN, H2NCH2C(OH)NH, Interstellar medium, Amino acid origin, Proton transfer, Hydrogen tunneling