Acta Phys. -Chim. Sin. ›› 2009, Vol. 25 ›› Issue (11): 2312-2318.doi: 10.3866/PKU.WHXB20091039

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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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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

MSC2000: 

  • O641