The tautomerization of H2NCH2C(OH)NH to H2NCH2CONH2 in the interstellar medium

Abstract

The tautomerization of H 2 NCH 2 C(OH)NH to H 2 NCH 2 CONH 2 is an important step by way of Strecker synthesis for the production of glycine in the interstellar medium (ISM) with respect to the origin of amino acids on the early Earth. Our work indicates two mechanisms for the tautomerization to occur. k CVT/SCT (rate constant) is 45.6 s −1 at 50 K, obtained with the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT), to support one mechanism assisted by quantum tunneling in the ISM. Another mechanism is through the (H 2 O) 2 -coupled proton transfer. In the (H 2 O) 2 -coupled reaction, two H 2 O molecules act as a catalyst to reduce the barrier energy by 23.7 kcal mol −1 , and cooperatively let a proton pass a hydrogen-bonded bridge composed of H 2 NCH 2 C(OH)NH with (H 2 O) 2 . k TST is 8.08×10 −4 s −1 at 100 K, calculated with TST kinetics, to demonstrate the mechanism. Therefore, the tautomerization is feasible in the ISM. H 2 NCH 2 C(OH)NH and H 2 NCH 2 CONH 2 will be detected in the ISM and found in carbonaceous chondrites. The results present new evidence for the third theory on the origin of amino acids on the early Earth.