Formation of the Simplest Amide in Molecular Clouds: Formamide (NH₂CHO) and Its Derivatives in H₂O-rich and CO-rich Interstellar Ice Analogs upon VUV Irradiation

Abstract

The astronomical detection of formamide (NH2CHO) toward various star-forming regions and in cometary material implies that the simplest amide might have an early origin in dark molecular clouds at low temperatures. Laboratory studies have proven the efficient NH2CHO formation in interstellar CO:NH3 ice analogs upon energetic processing. However, it is still under debate, whether the proposed radical–radical recombination reactions forming complex organic molecules remain valid in an abundant H2O environment. The aim of this work was to investigate the formation of NH2CHO in H2O- and CO-rich ices under conditions prevailing in molecular clouds. Therefore, different ice mixtures composed of H2O:CO:NH3 (10:5:1), CO:NH3 (4:1), and CO:NH3 (0.6:1) were exposed to vacuum ultraviolet photons in an ultra-high vacuum chamber at 10 K. Fourier-transform infrared spectroscopy was utilized to monitor in situ the initial and newly formed species as a function of photon fluence. The infrared spectral identifications are complementarily secured by a temperature-programmed desorption experiment combined with a quadrupole mass spectrometer. The energetic processing of CO:NH3 ice mixtures mainly leads to the formation of NH2CHO, along with its chemical derivatives such as isocyanic acid (HNCO) and cyanate ion (OCN−). The formation kinetics of NH2CHO shows an explicit dependency on ice ratios and compositions; the highest yield is found in H2O-rich ice. The astronomical relevance of the resulting reaction network is discussed.

Substituent effects in the tautomerization of imidic acids R−C(OH)=NH → R−C(O)NH2: Kinetic implications for the formation of peptide bonds in the interstellar medium

“…18 A detailed examination of the various gas-phase and solid-state formation routes of formamide has been carried out by Chuang et al in combination with VUV photolysis experiments on water and carbon monoxide-rich ices doped with ammonia. 19 They conclude that despite the numerous studies the validity of the proposed chemistry that leads to complex species like formamide is still open to debate. Another discussion of possible formation routes for formamide both in the gas-phase and on dust grains has been given.…”

Peptide Bonds in the Interstellar Medium: Facile Catalytic Formation from Nitriles on Water–Ice Grains

“…Vacuum ultraviolet (VUV) irradiation of water-rich and CO-rich ammonia ices at 10 K with compositions H 2 O:CO:NH 3 = 10:5:1, CO:NH 3 = 4:1 and CO:NH 3 = 0.6:1 have shown that formamide is preferentially formed, although mechanistically the situation is complicated with no clear indication as to actual formation routes. 13 Indirect evidence for the formation routes of formamide based on the stratified distribution of the molecules HNCO and H 2 CO, putative parents of HCONH 2 , in the atmosphere of the HH 212 protostellar disk, appears to rule out HNCO as a parent. 14 Most recently Marks et al have carried out experiments involving acetaldehyde (ethanal) ammonia mixtures undergoing irradiation with simulated galactic cosmic rays.…”

“…A comprehensive summary has been given recently by Chuang et al during the course of their laboratory work on the formation of formamide in water- and carbon monoxide-rich water ices with ammonia as the substrate. Vacuum ultraviolet (VUV) irradiation of water-rich and CO-rich ammonia ices at 10 K with compositions H 2 O:CO:NH 3 = 10:5:1, CO:NH 3 = 4:1 and CO:NH 3 = 0.6:1 have shown that formamide is preferentially formed, although mechanistically the situation is complicated with no clear indication as to actual formation routes . Indirect evidence for the formation routes of formamide based on the stratified distribution of the molecules HNCO and H 2 CO, putative parents of HCONH 2 , in the atmosphere of the HH 212 protostellar disk, appears to rule out HNCO as a parent …”

Direct Synthesis of Formamide from CO2 and H2O with Nickel–Iron Nitride Heterostructures under Mild Hydrothermal Conditions

“…C–N coupling reaction that produces nitrogenous compounds including amides is one of the most fundamental reactions in the chemical industry. − In life, amide functional groups are ubiquitous moieties in amino acids and the peptide bond . Formamide, the simplest amide, consists of the most common elements (C, H, N, and O) in the universe and is widely used for the synthesis of prebiotic molecules. , Formamide can be considered as a multifunctional tool for prebiotic chemistry since its condensation and degradation products generatein the presence of minerals and metal oxidesbiologically relevant molecules including amino acids, cofactors, nucleobases, and carboxylic acids. ,, Formamide produces the nucleosides adenine, purine, hypoxanthine, cytosine, thymine, and uracil . In 2008, Saladino et al reported that the interaction of formamide with the hydrothermal vent mineral pyrite (FeS 2 ) yields purine and adenine, which are basic components of nucleic acids. , Formamide was also reported to serve as a solvent for the phosphorylation of nucleosides to nucleotides .…”