The stability of hydrogen cyanide and cyanoacetylene under a wide range of planetary conditions

Understanding the origin of life on early Earth is challenging, as it requires work across several different disciplines like astrophysics, astrobiology, chemistry, geology etc.^[1]Despite these complexities, the research in this field is progressing steadily. Several chemical pathways have been proposed to understand the formation of biologically significant molecules on early Earth, with lessons for the exploration of life’s origins on other rocky planets. One promising scenario for the synthesis of many of life’s building blocks is the cyanosulfidic scenario, where the major building blocks of life  –  lipids, sugars and nucleotides – can be synthesised using hydrogen cyanide (HCN) and cyanoacetylene (HC₃N).^[2]However, research has just begun to discover the feasibility of these reactions under prebiotic conditions and the physical factors influencing their efficiency in a planetary context

     In this presentation, I will show empirical constraints of the stability of HCN and HC₃N. My results constrain the prebiotic environment in which the prebiotic synthesis of amino acids, nucleotides and phospholipids could have occurred. I measure the hydrolysis of cyanide at different temperature, pH and in the presence of salts like sulphate, sulfite, sulfide and phosphate, and provide a degradation rate for this in wide range of conditions. I find that the hydrolysis rates are significantly influenced by pH and temperature with variations observed depending on the nature of salts. Phosphate and sulphate do not measurably affect the degradation rate of cyanide. The lifetime of HCN in the presence of sulfide is 10x shorter due to the formation of products like thioformamide and thioformate in addition of formate. I also show how the presence of sulfite affects the lifetime of cyanide.

Finally, I observe the hydrolysis of cyanoacetylene at different temperature and pH. My preliminary results show that the lifetime of HC₃N is 100x shorter in alkaline solution than the neutral solution at 30°C, consistent with literature values.^[6] I will present the first-ever measurements of cyanoacetylene lifetimes as a function of both pH and temperature. These observations provide new insights into the effect of physical parameters on cyanide and cyanoacetylene stability, providing firm constraints for environments where prebiotic chemistry involving cyanide and cyanoacetylene can take place.

Fig 1: Hydrolysis of HCN at 80 °C, pH-8 to form formate ion (a) Quantitative ¹H NMR showing the increase in the concentration of formate ion with time and (b) Kinetics of formation of formate ion fitted to a kinetic model to estimate the rate of formation of formate ion.

References:

1. Sutherland, J.D., The Origin of Life—Out of the Blue. Angewandte Chemie International Edition, 2016. 55(1): p. 104-121.

2. Patel, B.H., et al., Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism. Nat Chem, 2015. 7(4): p. 301-7.

3. Miyakawa, S., H. James Cleaves, and S.L. Miller, The Cold Origin of Life: A. Implications Based On The Hydrolytic Stabilities Of Hydrogen Cyanide And Formamide. Origins of life and evolution of the biosphere, 2002. 32(3): p. 195-208.

4. Todd, Z.R., N.F. Wogan, and D.C. Catling, Favorable Environments for the Formation of Ferrocyanide, a Potentially Critical Reagent for Origins of Life. ACS Earth and Space Chemistry, 2024. 8(2): p. 221-229.

5. White, S.B., P.B. Rimmer, and Z. Liu, Shedding Light on the Kinetics of the Carboxysulfitic Scenario. ACS Earth and Space Chemistry, 2024. 8(11): p. 2133-2144.

6. Ferris, J.P., R.A. Sanchez, and L.E. Orgel, Studies in prebiotic synthesis. 3. Synthesis of pyrimidines from cyanoacetylene and cyanate. J Mol Biol, 1968. 33(3): p. 693-704.