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Project Progress

Prebiotic chemistry of hydrogen cyanide (dm)

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 HCN polymers under a variety of conditions and the application of modern powerful analytical methods for structure elucidation.

We have shown that analysis of HCN polymer by TMAH thermochemolysis/GC-MS has yielded considerable new structural insight. When this method is applied to the analysis of solids produced in experiments simulating Titan’s atmospheric chemistry, a large number of degradation products matching those derived from analysis of HCN polymer by this same method. These results provide evidence that N2/CH4 tholins contain HCN polymers, which could therefore be major components of Titan’s atmosphere. Along these lines, we observed the ready absorption and polymerization of HCN into nonpolar materials. When HCN gas is sealed with liquid dodecylbenzene, HCN polymer separated from this hydrocarbon liquid within a week. Also, we are examining cyano-self-addition directed by layered double hydroxide mineral surfaces. Initially pink products were formed which become darker purple with time as shown below. Recently, TMAH thermochemolysis GC-MS analysis has shown the presence of glycine, triazine, adenine and xanthine.

We have examined the polymerization reactions of HCN, aminomalononitrile (AMN, HCN trimer) and diaminomaleonitrile (DAMN, HCN tetramer) and glyconitrile under a variety of conditions. AMN and DAMN appear to be more reactive than HCN itself at equal HCN “equivalent” concentration.

Using Laser Desorption-Ionization (LDI-MS) we have found that hydrogen cyanide polymers, (HCN)n, formed from HCN monomer, showed MH+ peaks for n = 8 to 25 with the maximum occurring at n = 15 to 17. HCN polymer formed from diaminomaleonitrile (DAMN, HCN tetramer) showed a similar LDI spectra with no enhancement for peaks at n = 4, 8, 12, 16, etc., implying the breakdown of the tetramer to monomer followed by monomer repolymerization. The LDI-MS spectra of polymer formed from aminomalononitrile (HCN trimer) showed oligomers from m/z 200 to 800, but these did not match an (HCN)n series. In other studies, the water soluble products derived from stirring HCN polymer with water at room temperature for 1 to 3 days consisted primarily of two compounds, urea and a compound with formula C6H8N6 as determined by APCI-exact mass MS whose structure we are determining using NMR techniques.

Natural abundance 13C solids NMR analysis confirms previous observations of a major peak at 166 ppm. We find this same strong absorption in Titan tholin. We have now prepared (HCN)n highly enriched in 13C and 15N. Solids 13C/15N NMR analysis of this labeled polymer should provide considerable structural detail of HCN polymer.