Prebiotic‐Like Condensations of Cyanamide and Glyoxal: Revisiting Intractable Biotars

Abstract

We report a detailed investigation into the nature of products that are generated by the reactions of cyanamide and glyoxal, two small molecules of astrochemical and prebiotic significance, under different experimental conditions. The experimental data suggest that the formation of oligomeric structures is related in part to the formation of insoluble tholins in the presence of oxygen-containing molecules. Although oligomerization proceeds well in water, product isolation turned out to be impractical. Instead, solid precipitates were obtained easily in acetone. Crude mixtures have been thoroughly scrutinized by spectroscopic methods, in particular NMR and mass spectroscopy (ESI mode), which are all consistent with the generation of a few functional groups that are embedded into regular chains of five- and six-membered rings, thereby pointing to a supramolecular organization. Three different models of cross-condensation and chain growth are suggested. These synthetic explorations provide further insights into the formation of complex organic matter in interstellar scenarios and extraterrestrial bodies that might have played a pivotal role in chemical evolution.

Formation of Cyanamide–Glyoxal Oligomers in Aqueous Environments Relevant to Primeval and Astrochemical Scenarios: A Spectroscopic and Theoretical Study

“…The appearance of bands at n % 3300 and 1600 cm À1 may likewise be attributedt oo ccluded water, [19] although the lower intensity of the band centereda t n = 3220 cm À1 for 2:1@water with respectt ot hose for solids isolated from acetones uggestst he presence of as mall amount of water molecules insidet he organic matrix. [5] Ab and due to the CÀOa bsorption (n = 1068 cm À1 )i s barely detectable, whereas the most intense absorptionb and at n = 2187 cm À1 may be reliably assigned to the stretching vibration of cyano groups. [5] Ab and due to the CÀOa bsorption (n = 1068 cm À1 )i s barely detectable, whereas the most intense absorptionb and at n = 2187 cm À1 may be reliably assigned to the stretching vibration of cyano groups.…”

“…[5] The peaks gatheredi nT able 2i ndicate that no structurec ould only be rationalized in terms of model I, which suggestsalow abundance of the resulting oligomers in aqueous solution,i nl ine with computation. This conclusion can also be extrapolated to the 2:1@water solid.…”

“…[5] Sinceg lyoxal hydrate( 4) can react either as ag eminal or av icinal diol, the preferred reaction site was evaluated by determining the so-called dual descriptoro ft he Fukui function, Df (for details, see the Supporting Information). Structures 5-7 are consistentw ith models previously proposed for oligomeric species isolated in acetone.…”

“…[5] Ac omparativea ssessment of elemental analyses and thermogravimetric (TG) measurements shows striking differences, even between 2:1@25 and 2:1@water (Table 1) as the latter is richer in nitrogen, while concomitantly exhibiting ad eficit in hydrogen, which remains essentially constant for the other samples. [5] Ac omparativea ssessment of elemental analyses and thermogravimetric (TG) measurements shows striking differences, even between 2:1@25 and 2:1@water (Table 1) as the latter is richer in nitrogen, while concomitantly exhibiting ad eficit in hydrogen, which remains essentially constant for the other samples.…”

“…[5] Condensations werei ntentionally conducted in acetone, as this medium forces the precipitation of white solids, thus enabling separation and analysis. We have shown that reactions of cyanamide and glyoxal in different molar ratios afford oligomeric compounds, for whichr easonable structural models could be inferred from spectroscopica nalysis and electrospray ionization mass spectra (ESI-MS).…”