A Comparative Study on HCN Polymers Synthesized by Polymerization of NH₄CN or Diaminomaleonitrile in Aqueous Media: New Perspectives for Prebiotic Chemistry and Materials Science

Abstract

HCN polymers are a group of complex and heterogeneous substances that are widely known in the fields of astrobiology and prebiotic chemistry. In addition, they have recently received considerable attention as potential functional material coatings. However, the real nature and pathways of formation of HCN polymers remain open questions. It is well established that the tuning of macromolecular structures determines the properties and practical applications of a polymeric material. Herein, different synthetic conditions were explored for the production of HCN polymers from NH4CN or diaminomaleonitrile in aqueous media with different concentrations of the starting reactants and several reaction times. By using a systematic methodology, both series of polymers were shown to exhibit similar, but not identical, spectroscopic and thermal fingerprints, which resulted in a clear differentiation of their morphological and electrochemical properties. New macrostructures are proposed for HCN polymers, and promising insights are discussed for prebiotic chemistry and materials science on the basis of the experimental results.

A dual perspective on the microwave-assisted synthesis of HCN polymers towards the chemical evolution and design of functional materials

“…Moreover, when the polymerization time is fixed (10 min) and the initial concentration is increased from 0.25 M to 1 M (inset in Fig. 1a), the conversion values are also increasing, as was expected 10 . Therefore, under microwave radiation conditions in the range of the times considered here, the kinetic tendency of NH 4 CN polymerization qualitatively resembles classical polymerizations when air is present in the reaction environment.…”

“…2d. For details about the assignment of these bands, please see 9,10,12,31 ). The intensity of the nitrile bands (close to 2200 cm −1 ) is lower in reactions under the presence of air; conversely, the intensity of the bands related to unsaturated bonds (1645 cm −1 , C=C and/or C=N) is lower in the anoxic series.…”

“…A comparative analysis of bands at 1645 and 3330 cm −1 results from the following equation to determine the extension of conjugation (EOC) in this macromolecular system, EOC = [I 1645 /(I 1645 + I 3330 )]•100 (bottom part of Fig. 2e) 10 . Samples obtained in the presence of air present slightly higher EOC values than HCN polymers produced under anoxic conditions.…”

“…FT-IR spectroscopy and powder XRD were performed using the same measuring equipment and parameters reported previously in reference 10 . The parameter records of the UV-vis spectra are described in references 9…”

“…Moreover, these prebiotic polymers have recently inspired new coatings for potential biomedical and materials science applications [2][3][4] , such as bone contacting 5 , antibacterial coatings 6 or passive filtration for stormwater/greywater disinfection 7 , and a new family of photocatalysers for the purification of wastewater 8 . On the other hand, the structural properties of these HCN polymers (and hence their potential applications) as well as the single biomolecules and related organics found in them via chromatographic analysis all depend directly on the synthetic conditions used for their production [9][10][11][12][13] . However, despite the considerable developments in the area of microwave-assisted organic synthesis and polymerization in recent decades [14][15][16][17] , only one report describes the production of HCN-derived polymers from formamide using microwave radiation 18 .…”