nai

Project Progress

The role of hydrogen cyanide polymer chemistry in the origin of life has provoked much speculation. In spite of extensive efforts by many groups, a satisfactory understanding of this polymer’s structure and mechanism of formation still eludes us. Our studies involve the synthesis of Hydrogen Cyanide (HCN) polymers under a variety of conditions and the application of modern powerful analytical methods for structure elucidation. Several significant results have been obtained in the last year.

Evidence for Peptide Bonds in (HCN)_x

Using Tetramethylammonium hydroxide (TMAH) thermochemolysis/GC-MS (Minard, 1998), dimethyldiketopiperazine is formed from di- and tri-glycine, but not glycine itself. HCN polymer, formed under various conditions, also produces substantial quantities of the same diketopiperazine, indicating it contains glycyl-glycyl or (glycyl)_x substructures. This supports the model for the structure of HCN polymer proposed by Mathews (Minard, 1975).

Surface Self-Catalyzed HCN Polymerization

HCN readily polymerizes in hydrocarbon liquids such as dodecylbenzene and toluene. It has been discovered that HCN polymerization is self-catalyzed. When neat liquid HCN or a solution of HCN in toluene is seeded with minute quantities of solid HCN polymer, the particles catalyze the slow formation of fresh HCN polymer on their surface. In most cases, 80-90% of the HCN has polymerized onto the expanding particle surface to form a large black solid mass within 20 to 30 days. It appears that traces of moisture are necessary for this autocatalysis to take place. However, this reaction does not seem to occur in water.

A Water-Soluble HCN Hexamer

Water-soluble extracts of HCN polymer yield a number of products, including diaminomaleonitrile, urea and a new compound with formula C₆H₈N_6, as determined by accurate mass measurement. Using NMR and ESI-MS-MS, it has been assigned the structure 2-cyano-3,4,5,6-tetraaminopyridine, shown below, with a reasonable mechanism of formation based on known cyanide condensation chemistry.

Synthesis of H¹³C¹⁵N polymers and solids NMR analysis

Solid-state NMR spectroscopy is a useful means by which to determine structural parameters of materials that are insoluble, thus lending itself well to the analysis of HCN polymer. Singly and doubly labeled ¹³C/¹⁵N hydrogen cyanide polymers of various enrichments have been prepared. Detection of the total signal from the observed nuclei was determined by single pulse (SP) experiments. Cross-polarization (CP) spectra were obtained to determine that those ¹³C and ¹⁵N bonded directly to a ¹H. The difference between the SP spectrum and a CP spectrum indicated the relative number of ¹⁵N or ¹³C bonded to ¹H to those that are not, as well as the various local environments of ¹⁵N or ¹³C that are bonded to ¹H. Double cross-polarization (DCP) experiments were carried out via the transfer of polarization from ¹H – ¹⁵N – ¹³C (¹³C-DCP) and from ¹H – ¹³C – ¹⁵N (¹⁵N-DCP). Work is under way to interpret these data in terms of the current structural models for (HCN)_x

References:

Minard, Robert; Yang, William; Varma, Pratibha; Nelson, John; Matthews, C.N.: 1975; Heteropolypeptides from poly-α-cyanoglycine and hydrogen cyanide. Model for the origin of proteins, Science (1975), 190(4212), 387-9