Characterization of HCN-Derived Thermal Polymer: Implications for Chemical Evolution

Abstract

Hydrogen cyanide (HCN)-derived polymers have been recognized as sources of relevant organic molecules in prebiotic chemistry and material sciences. However, there are considerable gaps in the knowledge regarding the polymeric nature, the physicochemical properties, and the chemical pathways along polymer synthesis. HCN might have played an important role in prebiotic hydrothermal environments; however, only few experiments use cyanide species considering hydrothermal conditions. In this work, we synthesized an HCN-derived thermal polymer simulating an alkaline hydrothermal environment (i.e., HCN (l) 0.15 M, 50 h, 100 °C, pH approximately 10) and characterized its chemical structure, thermal behavior, and the hydrolysis effect. Elemental analysis and infrared spectroscopy suggest an important oxidation degree. The thermal behavior indicates that the polymer is more stable compared to other HCN-derived polymers. The mass spectrometric thermal analysis showed the gradual release of several volatile compounds along different thermal steps. The results suggest a complicate macrostructure formed by amide and hydroxyl groups, which are joined to the main reticular chain with conjugated bonds (C=O, N=O, –O–C=N). The hydrolysis treatment showed the pH conditions for the releasing of organics. The study of the synthesis of HCN-derived thermal polymers under feasible primitive hydrothermal conditions is relevant for considering hydrothermal vents as niches of chemical evolution on early Earth.

A Lizardite–HCN Interaction Leading the Increasing of Molecular Complexity in an Alkaline Hydrothermal Scenario: Implications for Origin of Life Studies

“…This suggests that, as the second thermal stage has been associated with the decomposition of the side groups on the main chain, the polymer has no highly stable side structures. Two clear DTG peaks appear at 174 and 290 • C. Similar peaks also appear in the DTG curve for HCN-DTP (Figure 4B) [46]. In addition, a shoulder around~135 • C is detected.…”

“…Only one previous paper has reported the kinetics of the deposition of AMNderived polymers, but it did so at room temperature [59] and did not focus on the thermal stability of this new series of coatings. Phase II shows several changes related to the signals observed in the HCN-DTP control sample [46]. Figure 6B 6F).…”

“…Related to this, Takahashi and coworkers [86] described the synthesis of fatty acids from HCN using organic solvents and high temperatures (>100 • C). Likewise, Eschenmoser [87] proposed a hypothetical pathway based on the hydrolysis of diaminomaleonitrile (DAMN) and other intermediates previously detected [46] to explain the formation of fatty acids. In basic hydrolysis there was a broader spectrum of hydroxylated species in addition to the species detected by the acid hydrolysis, such as α-hydroxybutiric acid, oxalic acid, malonic acid, hydroxymalonic acid, aminomalonic acid, and other fatty acids (heptanoic acid, decanoic acid, and dodecanoic acid).…”

“…Recent papers have shown that hydrothermal fluids, during the serpentinization process, can lead to the occurrence of carbonaceous matter on mineral surfaces [ 42 , 43 , 44 ]. In addition, it has been shown that alkaline conditions and the dynamic surroundings that are present in hydrothermal systems are crucial for the transformation of cyanide species (e.g., cyanide salts and hydrogen cyanide, HCN) into other organic precursors with interesting roles in pre-RNA world scenarios [ 11 , 12 , 45 , 46 , 47 , 48 ]. Therefore, it seems necessary to study the role of serpentinite during the polymerization of HCN in order to simulate a feasible primitive geochemical scenario such as the surroundings of an alkaline hydrothermal system.…”

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

“…The chemistry of HCN and, for extension, HCN-derived polymers, are considered to play key roles in the formation of the first and primeval protometabolic and informational systems, as well as in the hypothesis of the “RNA-world” 28 , 37 , 40 – 43 . Currently, alkaline environments are proposed as a good place to develop prebiotic HCN chemistry 21 , 40 , 44 , 45 , and the HCN could have an important role in the formation of complex organic molecules under hydrothermal environments 46 – 48 . Here, the NH 4 CN oligomers/polymers synthetized under simulated hydrothermal conditions are precursors of a rich variety of bioorganics and related compounds.…”