2002 Annual Science Report
Pennsylvania State University Reporting | JUL 2001 – JUN 2002
Environment of Prebiotic Earth and the Origin of Life: Chemistry of Hydrogen Cyanide
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
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 C6H8N6, 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
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
PROJECT MEMBERS:Robert Minard
RELATED OBJECTIVES:Objective 1.0
Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous matter were significant sources of organic matter.
Develop and test plausible pathways by which ancient counterparts of membrane systems, proteins and nucleic acids were synthesized from simpler precursors and assembled into protocells.
Determine the presence of life's chemical precursors and potential habitats for life in the outer solar system.