Cyanide Dynamics in Serpentinizing Systems: Implications for Prebiotic Chemistry / Ellie Katherine Hara.
While cyanide has been considered essential in some origin of life (OoL) scenarios, cyanide is notably absent from the alkaline hydrothermal vent theory (AVT) which postulates that life started from a proto-metabolism powered by a pH, temperature and chemical gradients. This thesis investigates cyan...
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| Format: | Thesis Electronic eBook |
| Language: | English |
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ProQuest Dissertations & Theses,
2023.
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| Summary: | While cyanide has been considered essential in some origin of life (OoL) scenarios, cyanide is notably absent from the alkaline hydrothermal vent theory (AVT) which postulates that life started from a proto-metabolism powered by a pH, temperature and chemical gradients. This thesis investigates cyanide storage and availability in subsurface serpentinites and how such interactions could contribute to further developing existing theories on the OoL. It has been proposed that cyanide would concentrate in the Hadean ocean as ferrocyanide complexes ([Fe(CN)6] 4-). These complexes form spontaneously when cyanide comes into contact with Fe(II), which is thought to have been present in the early Earth's ocean due to buffering with mafic and ultramafic rocks. However, once cyanide is locked into this complex it is unable to react. Further, the stability of this complex, which makes it a favorable concentration and storage mechanism, leads cyanide to be difficult to release from this complex. One suggested mechanism is thermal decomposition at temperatures upwards of 600°C produced through meteorite impacts to thermally decompose ferrocyanide salts to iron and cyanide. In chapter 2, I demonstrate that carbon monoxide can undergo a ligand exchange with ferrocyanide under alkaline and hyperalkaline conditions. This releases a cyanide that was demonstrated as free to react by adding polysulfide to the system to form thiocyanate. Further, this reaction leads to the formation of ferrocyanocarbonyl complexes, which have been noted as sharing structural similarity to [FeFe] and [FeNi] hydrogenases. It is possible that the ferrocyanocarbonyl complex itself may be a useful prebiotic reagent. This process provides a facile mechanism for cyanide release that could provide continual sources of cyanide should carbon monoxide and ferrocyanide be available. Now that a plausible mechanism for releasing cyanide from ferrocyanide in serpentinizing systems was demonstrated, I then tested how cyanide would be stored in ultramafic rock-hosted systems with abundant reactive iron minerals such as ferrous brucite. It was found that cyanide would be stored not only as aqueous ferrocyanide but also on the brucite mineral surface as an iron-cyanide complexes. Brucite is a mineral that readily precipitates at alkaline conditions and will dissolve in acidic conditions. It was found that the amount of aqueous ferrocyanide detected was controlled by the pH of the experiment. This is due to pH controlling ferroan brucite solubility, which controls the amount of aqueous Fe(II) available to form the complex. In addition, ferricyanide complexes were detected on the mineral surface through Raman spectroscopy, and a higher surface cyanide concentration was correlated with a suppression of H2(g) generation from ferroan brucite oxidation. These findings suggest that cyanide can be stored both as aqueous ferrocyanide and on mineral surfaces. Further, this indicates that ferroan brucite and by extension other iron bearing minerals commonly found in serpentinites may serve as a substantial and currently overlooked cyanide reservoir on early Earth.Finally, I assessed FeNi brucite's ability to facilitate cyanide synthesis at a low-temperature and low-pressure environment. While no cyanide synthesis occurred, FeNi brucite did demonstrate the ability to facilitate methane oxidation to methanol when it was reacted with nitrite and methane at 70°C. This is the first known example of mineral-facilitated methane oxidation at low temperatures and pressures. Further, this aligns with the first step in the proposed denitrifying methanotrophic acetogenic pathway that has been postulated as life's first metabolism.Through this thesis, I have demonstrated how cyanide could be stored and released in subsurface serpentinites, along with demonstrating that brucite, a common component of serpentinites, can facilitate methane oxidation. I propose that these findings provide sufficient evidence that cyanide is a plausible and important reagent that should be integrated into existing alkaline hydrothermal vent origin of life hypotheses. |
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| Item Description: | Source: Dissertations Abstracts International, Volume: 85-06, Section: B. Advisors: Templeton, Alexis Committee members: Wing, Boswell; Spear, John; Kopf, Sebastian; Cleland, Carol. |
| Physical Description: | 1 electronic resource (130 pages) |
| ISBN: | 9798381165005 |
| Access: | This item is not available from ProQuest Dissertations & Theses. |
| Language: | English |