Ab Initio Study of Glycine Formation in the Condensed Phase: Carbon Monoxide, Formaldimine, and Water Are Enough

Abstract

Glycine is considered to be crucial in the formation of proteins and prebiotic substances. Nevertheless, the mechanism of spontaneous glycine formation under prebiotic Earth conditions or within the interstellar medium (ISM) remains a topic of debate, given the changing geochemical environment over Earth’s history and the difficulty of detecting it within the ISM. Yet it is believed that its formation could be possible in interstellar water-rich ice. In this study, using molecular dynamics (MD) simulations at the ab initio level of theory enhanced with modern free energy calculations, we modeled the chemical reaction between carbon monoxide, formaldimine, and water to produce glycine. We estimated under what conditions, in condensed phase at 50, 70, 100, and 300 K, glycine is formed. We also explored the effect of different electric fields on this process. Our results show that glycine could be formed with energy barriers as low as 0.5 kcal mol−1 at 50 K. We discuss whether this reaction could be a suitable candidate for explaining the mechanism of glycine formation under conditions that resemble various astrophysical environments, such as planets, exoplanets, and Earth. This study is relevant to finding a consensus among various proposals for glycine formation. Moreover, it highlights the importance of metadynamics and Car–Parrinello MD methods as tools in finding unknown complex, multistep reaction mechanism pathways, possibly important to the astronomical phenomena.