Abstract
Hydrogen cyanide (HCN) is known to react with complex organic materials and is a key reagent in the formation of various prebiotic building blocks, including amino acids and nucleobases. Here, we explore the possible first step in several such processes, the dimerization of HCN into iminoacetonitrile. Our study combines steered ab initio molecular dynamics and quantum chemistry to evaluate the kinetics and thermodynamics of base-catalyzed dimerization of HCN in the liquid state. Simulations predict a formation mechanism of iminoacetonitrile that is consistent with experimentally observed time scales for HCN polymerization, suggesting that HCN dimerization may be the rate-determining step in the assembly of more complex reaction products. The predicted kinetics permits for iminoacetonitrile formation in a host of astrochemical environments, including on the early Earth, on periodically heated subsurfaces of comets, and following heating events on colder bodies, such as Saturn’s moon Titan.
Highlights
In this work, we use steered ab initio molecular dynamics to unveil the reaction mechanism for base-catalyzed formation of iminoacetonitrile (Figure 1, compound 2), a suspected key prebiotic reaction intermediate, in liquid hydrogen cyanide (HCN).[1,2] HCN is one of the most ubiquitous small molecules in the universe, having been observed in the interstellar medium,[3] in the coma of several comets,[4] in the atmosphere of the giant planets,[5,6] on Pluto,[7] as well as on Saturn’s moon Titan.[8]
Our study of this condensed phase chemistry relies on molecular dynamics simulations
The use of dynamics simulations allows for the explicit consideration and sampling of the solvent environment and is important for three reasons: first, HCN is an exceptionally polar molecule
Summary
We use steered ab initio molecular dynamics to unveil the reaction mechanism for base-catalyzed formation of iminoacetonitrile (Figure 1, compound 2), a suspected key prebiotic reaction intermediate, in liquid hydrogen cyanide (HCN).[1,2] HCN is one of the most ubiquitous small molecules in the universe, having been observed in the interstellar medium,[3] in the coma of several comets,[4] in the atmosphere of the giant planets,[5,6] on Pluto,[7] as well as on Saturn’s moon Titan.[8]. The potential importance of this molecule has since been pointed out by many (e.g., refs 19, 22) and it has been proposed as an early intermediate in the HCN-based synthesis of various biologically relevant molecules, such as purines, pyrimidines, pterins, and amino acids.[1,23−25] HCN-derived polymers are of interest as functional materials, e.g., in catalysis or as adhesives and coatings for biomedical applications.[13,22] Given the presumed key role of iminoacetonitrile in prebiotic chemistry, it is important to answer the questions: where can this molecule form and how?
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