Ketene and Ammonia Forming Acetamide in the Interstellar Medium

Abstract

Background: Peptide bonds are among the fundamental building blocks of life, polymerizing amino acids to form proteins that make up the structural components of living cells and regulate biochemical processes. The detection of glycine by NASA in comet Wild 2 in 2009 suggests the possibility of the formation of biomolecules in extraterrestrial environments through the interstellar medium. Detected in the dense molecular cloud Sagittarius B2, acetamide is the largest molecule containing a peptide bond and is hypothesized to be the precursor to all amino acids; as such, viability of its formation is of important biological relevance. Methods: Under a proposed mechanism of ammonia and ketene reactants, which have also been detected in dense molecular clouds in the ISM, the reaction pathway for the formation of acetamide was modelled using quantum chemical calculations in Gaussian16, using Austin-Frisch-Petersson functional with dispersion density functional theory at a 6-31G(d) basis set level of theory to optimize geometries and determine the thermodynamic properties for the reaction. Stability of the reactants, transition states, and products were examined to establish a reasonable mechanism. Conclusion: Product formation of acetamide was found to be highly exergonic and exothermic with a low energy barrier, suggesting a mechanism that is viable in the extreme density and temperature conditions found in ISM.