17:15 〜 18:45
[U11-P09] Bio-Inspired Catabolic Origin of Cyanide for Prebiotic Synthesis at Deep Sea Hydrothermal Vent
It is well-known that hydrogen cyanide and cyanide ions are key synthetic reagents in prebiotic chemistry, especially in the Strecker synthesis of amino acids. And multiple research groups have demonstrated cyanide not only as important reagent, such as for nucleobases, protected carbohydrates and heterocycles, but also possibly participate in metabolic pathways like TCA cycle or glyoxylate pathway. Therefore, its role in forming biological molecules is obvious and significant in understanding Origin of Life (OoL).
From geological perspective, hydrogen cyanide has been identified as an interstellar compound or an atmospheric component on certain extraterrestrial objects like Titan atmosphere, interstellar ice, and in meteorites. Previous studies also suggested that cyanide could be formed by photochemistry or high energy impact. However, physical properties of HCN (pKa = 9.3, b.p. 26℃ at 1atm) means 99% of cyanide ion is shifted to gas form in weakly acidic seawater (pH ~5). Thus, large scale of dissolution of external delivered cyanide into primordial ocean seems challenging for aqueous phase prebiotic synthesis of biological molecules.
On the contrary, hydrogenase – the only group of enzyme that uses cyanide as one of active site ligands is widely found in microorganisms like methanogens or sulfate reducers. Modern biological system utilizes amino acids especially tyrosine for in situ generation of cyanide and formation of hydrogenases. While it is unclear whether tyrosine catabolism has been verified in field of OoL, the biological pathway has inspired us to excavate possibility of an alternative origin of cyanide on Early Earth. In previous studies, glycine has been testified to be transformed into cyanide under oxidative potential at surface of platinum and gold surfaces. Relating these facts to geological relevant situations, here, we hypothesized that alkaline hydrothermal vent system (HV) is a tempting place where electricity is generated across the conductive metal sulfide mineral wall by the giant redox-potential across. Also, the alkaline condition meets thermodynamic requirement for oxidative decomposition of glycine to cyanide; in the meanwhile, solves the aforementioned solubility problem. If such scenario had been proven, the molecular hydrogen and metal sulfide rich environment might have facilitated the formation of prototype hydrogenase, therefore shed light on the origin of metabolism.
Here, we report the cyanide formation via oxidation of glycine under alkaline solutions HV minerals. Powder and bulk XRD analyses revealed the major constituents of the HV material are chalcopyrite, sphalerite and pyrite. The crystallinity and spatial distribution of minerals are highly heterogenous as indicated in 2D XRD spectroscopy, SEM and EDS mapping. We found that electrolysis of an alkaline glycine solution (pH = 12.3) by HV materials at a positive potential resulted in the oxidative C-C bond cleavage of glycine. The subsequent formation of cyanide at μM level was confirmed by UPLC-FLR, LC-MS detection with standard KCN samples as references. Notably, mineral-involved cyanide formation was also confirmed under open circuit potential condition (with no electrode potential applied) at room temperature, a finding that demonstrates applying potential is not a necessary condition for cyanide production. Time dependent investigation reveals that cyanide is formed within one day reaction scale and could maintain as long as one week. Adsorption of cyanide by HV mineral is also observed by mixing pure KCN solution with HV material. The discovery of mineral-involved cyanide formation indicates that cyanide might have been a secondary product during deep-sea HV electrochemical amino acid synthesis and adsorption might contribute to the complexation of cyanide with metal ions. In the poster presentation, detailed material characterization, chromatography data and spectra results will be discussed.
From geological perspective, hydrogen cyanide has been identified as an interstellar compound or an atmospheric component on certain extraterrestrial objects like Titan atmosphere, interstellar ice, and in meteorites. Previous studies also suggested that cyanide could be formed by photochemistry or high energy impact. However, physical properties of HCN (pKa = 9.3, b.p. 26℃ at 1atm) means 99% of cyanide ion is shifted to gas form in weakly acidic seawater (pH ~5). Thus, large scale of dissolution of external delivered cyanide into primordial ocean seems challenging for aqueous phase prebiotic synthesis of biological molecules.
On the contrary, hydrogenase – the only group of enzyme that uses cyanide as one of active site ligands is widely found in microorganisms like methanogens or sulfate reducers. Modern biological system utilizes amino acids especially tyrosine for in situ generation of cyanide and formation of hydrogenases. While it is unclear whether tyrosine catabolism has been verified in field of OoL, the biological pathway has inspired us to excavate possibility of an alternative origin of cyanide on Early Earth. In previous studies, glycine has been testified to be transformed into cyanide under oxidative potential at surface of platinum and gold surfaces. Relating these facts to geological relevant situations, here, we hypothesized that alkaline hydrothermal vent system (HV) is a tempting place where electricity is generated across the conductive metal sulfide mineral wall by the giant redox-potential across. Also, the alkaline condition meets thermodynamic requirement for oxidative decomposition of glycine to cyanide; in the meanwhile, solves the aforementioned solubility problem. If such scenario had been proven, the molecular hydrogen and metal sulfide rich environment might have facilitated the formation of prototype hydrogenase, therefore shed light on the origin of metabolism.
Here, we report the cyanide formation via oxidation of glycine under alkaline solutions HV minerals. Powder and bulk XRD analyses revealed the major constituents of the HV material are chalcopyrite, sphalerite and pyrite. The crystallinity and spatial distribution of minerals are highly heterogenous as indicated in 2D XRD spectroscopy, SEM and EDS mapping. We found that electrolysis of an alkaline glycine solution (pH = 12.3) by HV materials at a positive potential resulted in the oxidative C-C bond cleavage of glycine. The subsequent formation of cyanide at μM level was confirmed by UPLC-FLR, LC-MS detection with standard KCN samples as references. Notably, mineral-involved cyanide formation was also confirmed under open circuit potential condition (with no electrode potential applied) at room temperature, a finding that demonstrates applying potential is not a necessary condition for cyanide production. Time dependent investigation reveals that cyanide is formed within one day reaction scale and could maintain as long as one week. Adsorption of cyanide by HV mineral is also observed by mixing pure KCN solution with HV material. The discovery of mineral-involved cyanide formation indicates that cyanide might have been a secondary product during deep-sea HV electrochemical amino acid synthesis and adsorption might contribute to the complexation of cyanide with metal ions. In the poster presentation, detailed material characterization, chromatography data and spectra results will be discussed.