Quantum Chemical Study of the Formation of Urea in Interstellar Medium

Abstract

Background: Many observational studies have found the presence of organic molecules in interstellar medium (ISM) via spectroscopy. NH2CONH2 (urea) was first detected in ISM in 2014. Containing two NH2 groups, urea is an important biological molecule in metabolism as a carrier for waste nitrogen. The discovery of urea in ISM suggests the possibility of the formation of other biomolecules which contain peptide bonds, such as proteins. This supports the origin of life theory proposing that these biomolecules were initially formed in space and later arrived to Earth. Methods: This study investigates two possible reaction pathways for the formation of protonated urea (ureaH+) in dense molecular clouds via molecules previously observed in the ISM, formamide (HCONH2) and protonated hydroxylamine (NH2OH2+). The thermodynamics and optimized geometries were calculated for the final steps of the formation of ureaH+ using Gaussian16 at the APFD/6-31G(d,p) level of theory and a transition state was confirmed. Results: The overall mechanism, as well as the studied proton rearrangement of an intermediate to ureaH+, were found to be exothermic and exergonic processes. Conclusion: From the calculations, the conditions of ISM provide an adequate environment for the formation of ureaH+ and urea.