The Proton-Coupled Proton Transfer Mechanism, H2O Catalysis, and Hydrogen Tunneling Effects in the Reaction of HNCH2 with HCOOH in the Interstellar Medium

The reaction HNCH2 + HCOOH -> H2NCH2COOH is supposed to be an important reaction related to the possible origin of amino acids on the early Earth. We find that it has an energy barrier of 87.37 kcal mol(-1) obtained with MP2/6-311+G** in the gas phase, but it is likely enhanced to occur in the interstellar medium (ISM) through a proton-coupled proton transfer reaction, initiated by HNCH2 coupled with H-2(+), H-3(+), or H3+O. H-2(+) H-3(+), and H3+O serve as a donor of energy in the coupled reactions. H+, which is a key species to the coupled reactions, further, plays a catalytic role in reducing a barrier up to 14.14 kcal mol(-1). In the coupled reaction with H3+O, H2O, which can seize, transport, and deliver a proton from HCOOH to H2NCH2+, reduces a barrier up to 14.96 kcal mol(-1). A significant hydrogen-tunneling pathway is predicted by the temperature dependences of k(H)(CVT/SCT), calculated using the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT). Hydrogen tunneling is another important mechanism to make the reaction happen in the ISM. The achieved results can be applied to discuss the origin of amino acids from the materials of the Earth itself. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 2671-2682, 2010