HCN polymers characterized by solid state NMR: Chains and sheets formed in the neat liquid

Abstract

Hydrogen cyanide polymerizes readily under a variety of conditions and significant prebiotic roles have been suggested for these polymers due to the abundance of HCN in universe. However, the structures of HCN polymers have been more speculative than grounded in experimental data. Here we show that 13 C and 15 N solid state NMR spectra of polymers formed in neat HCN are inconsistent with the previously proposed structures and suggest instead that the polymers are formed by simple monomer addition, first in head-to-tail fashion to form linear, conjugated chains, and then laterally to form saturated two-dimensional networks. This interpretation of the NMR spectra finds support in other information about the polymerization of neat HCN, including the presence of free radicals. As expected from the literature, formation of the HCN tetramer, diaminomaleonitrile, is also observed, but only when the reaction is catalyzed exclusively by base and then in crystalline form.

TGA–FT-IR study of pyrolysis of poly(hydrogen cyanide) synthesized from thermal decomposition of formamide. Implications in cometary emissions

“…Very recently Mamajanov and Herzfeld [28,29] using solid state 13 C and 15 N NMR spectra have investigated the chemical structure of the PHC prepared by a free radical and a base-catalyzed reaction and also obtained by heating the HCN tetramer. Unfortunately, the spectra reported by these authors are different from the solid state 13 C NMR CP-MAS reported in Fig.…”

HCN polymers characterized by SSNMR: Solid state reaction of crystalline tetramer (diaminomaleonitrile)

“…Taken together, the results suggest that each HCN tetramer loses one HCN monomer per molecule upon polymerization. Figure 3 compares 13 C CPMAS spectra of DAMN, DAMN polymer, and conventional HCN polymer ͑prepared as described previously 6 ͒. In all cases, the narrow signals are due to crystalline DAMN and the broad signals are due to polymer.…”

“…[1][2][3][4][5] One of most intriguing proposals, 2 based on observations of ␣-amino acids in polymer hydrolysates, suggests the formation of protopeptides by acid-base polymerization of the HCN trimer, aminomalononitrile. However, our previous NMR study 6 showed that protopeptide is not formed in the polymerization of neat HCN. On the other hand, the same study showed that crystalline HCN tetramer, diaminomaleonitrile ͑DAMN͒ ͓Figs.…”

“…Mixed-labeled DAMN was extracted with hot isobutyl alcohol from the mixture of DAMN and polymer that was formed by the base-catalyzed reaction of a 1:1 mixture of H 13 CN and HC 15 N described previously. 6 Recrystallized DAMN was sealed in a pressure tube under argon and incubated at 125°C for 12 h to assure complete conversion to polymer. For electrical conductivity measurements, the polymer was doped by exposure to iodine vapor for varying periods of time at room temperature.…”

Prebiotic-chemistry inspired polymer coatings for biomedical and material science applications

“…Hydrolysis experiments of the polymers result in the observation of amino acids with particularly significant amounts of glycine and polycyclic nitrogenous compounds such as purines and imidazole derivatives (Supplementary Figure S1). 9,11,[24][25][26][27][28][29][30] Because of these properties, we investigated the AMN polymer as a candidate for a new generic coating method that may be particularly useful in biomedical applications such as cell culture tools, providing high cell attachment and surface coatings on implantable medical devices providing enhanced tissue integration.…”