Programmed Formation of HCN Oligomers through Organosulfur Catalysis

The protometabolic nature of prebiotic chemistry

The field of prebiotic chemistry has been dedicated over decades to finding abiotic routes towards the molecular components of life. There is nowadays a handful of prebiotically plausible scenarios that enable the laboratory synthesis of most amino acids, fatty acids, simple sugars, nucleotides and core metabolites of extant living organisms. The major bottleneck then seems to be the self-organization of those building blocks into systems that can self-sustain. The purpose of this tutorial review is having a close look, guided by experimental research, into the main synthetic pathways of prebiotic chemistry, suggesting how they could be wired through common intermediates and catalytic cycles, as well as how recursively changing conditions could help them engage in self-organized and dissipative networks/assemblies (i.e., systems that consume chemical or physical energy from their environment to maintain their internal organization in a dynamic steady state out of equilibrium). In the article we also pay attention to the implications of this view for the emergence of homochirality. The revealed connectivity between those prebiotic routes should constitute the basis for a robust research program towards the bottom-up implementation of protometabolic systems, taken as a central part of the origins-of-life problem. In addition, this approach should foster further exploration of control mechanisms to tame the combinatorial explosion that typically occurs in mixtures of various reactive precursors, thus regulating the functional integration of their respective chemistries into self-sustaining protocellular assemblies.

First-principles structure prediction of two-dimensional HCN polymorphs obtained via formal molecular polymerization

In the present study, ab initio evolutionary algorithms and heuristic approach were used to predict new two-dimensional (2D) hydrogen cyanide crystalline phases based on HCN and HNC molecular building blocks. Our research revealed thirty-seven 2D HCN and HNC structures within six topological families which contain N₁, N₂ dimers, N₃ trimers, infinite poly-N motifs, or zigzag C-C chains. HSE06 functional calculations indicated that 2D 1Pmn2₁ HCN, 2Pma2 HCN, 3P2₁2₁2 HCN, and 6Pbcm HNC are direct semiconductors with band gaps E_g of 5.1, 4.2, 4.3, and 2.8 eV, respectively, and isovalent element substitutions (C by Ge/Si, and H by F) were performed to tune the electronic band gaps of the resulting 2D structures (E_g = 1.2-7.4 eV). Moreover, it has been found that the high in-plane Young's modulus (330.3-445.8 N m^-1) and strong tolerance of direct band transitions (E_g = 1.2-5.3 eV) against the external biaxial strains in these four 2D HCN structures endow them with potential applications in photofunctional and flexible electronic devices. Finally, ab initio molecular dynamics simulations showed that at 50 GPa and 400 K, HCN molecules in a bulk I4mm hydrogen cyanide molecular crystal can extend to 2D HCN covalent nets.

Synthesis of CxNy-rich polycyclic oligomers from primeval monomers in aqueous media

A multichannel, non-thermolytic and efficient pathway is described toward the formation of functionalized carbon nitride-like oligomers, starting from readily available cyanamide and glyoxal (in ratios >2), in aqueous media under mild conditions. Such oligomers can be isolated as stable solids that result from structures involving cyanamide self-additions along with structures formally derived from the condensation of cyanamide, dicyandiamide or melamine with glyoxal, leading occasionally to oxygen-containing units. The oligomeric aggregates have masses up to 500 u, as inferred from mass spectra analyses, and their formation can be rationalized in terms of polyadditions of cyanamide (up to 10-mer) and glyoxal. The latter is not only a willing reaction partner, but also promotes facile condensation by enhancing the reactivity of nitrile fragments and inducing a significant lowering of the energy barriers. This mechanistic surmise is also supported by DFT calculations of the early condensation steps. As a result, melamine/triazine-type structures are obtained in aquatic environments under much milder conditions than those usually required by other synthetic procedures. Moreover, our results also help unveil the abiotic processes affording complex organic matter on celestial bodies and early earth.