Presentation Information
[U17-08]Abiotic carbonyl sulfide formation in water at room temperature: a radical-mediated pathway on magnetite surfaces
*Shotaro Tagawa1, Satoshi Okada1, Norio Kitadai1 (1.JAPAN AGENCY FOR MARINE-EARTH SCIENCE AND TECHNOLOGY)
Keywords:
Origin of life,deep-sea hydrothermal systems,Carbonyl sulfide,Redox reaction,Radical formation
Carbonyl sulfide(OCS) has been regarded as an abiotic “condensing agent” capable of promoting peptide formation and, therefore, as an important molecule in prebiotic chemical evolution. However, it remains insufficiently constrained what environmental conditions were suitable for OCS production on the early Earth and how persistent that generation was. Previous scenarios have invoked volcanic gases and alkaline seafloor hydrothermal systems as plausible reaction settings, yet key limitations remain, including low reported yields, uncertainty in the sustained availability of sulfur species directly involved in OCS formation, and enhanced OCS hydrolysis under high-pH conditions.
Here we focus on the radical formation of sulfide species via single-electron oxidation on iron oxide mineral surfaces and investigate OCS formation under conditions relevant to seafloor hydrothermal environments. Because reactions between sulfide species and iron oxides are known to exhibit strong pH dependence, we systematically examined the pH range in which OCS production is maximized. Experiments were conducted under anoxic conditions using CO and NaSH as reactants and synthetic magnetite(Fe3O4) as a catalyst over pH 2–9. OCS was quantified by gas chromatography. OCS formation showed a pronounced pH dependence, and >90% yield was achieved under acidic conditions. In parallel, mineralogical analyses indicated transformation of magnetite into mackinawite(FeS) and greigite(Fe3S4). In this presentation, we report the inferred reaction processes and discuss their implications for "CO world" scenarios in early hydrothermal systems.
Here we focus on the radical formation of sulfide species via single-electron oxidation on iron oxide mineral surfaces and investigate OCS formation under conditions relevant to seafloor hydrothermal environments. Because reactions between sulfide species and iron oxides are known to exhibit strong pH dependence, we systematically examined the pH range in which OCS production is maximized. Experiments were conducted under anoxic conditions using CO and NaSH as reactants and synthetic magnetite(Fe3O4) as a catalyst over pH 2–9. OCS was quantified by gas chromatography. OCS formation showed a pronounced pH dependence, and >90% yield was achieved under acidic conditions. In parallel, mineralogical analyses indicated transformation of magnetite into mackinawite(FeS) and greigite(Fe3S4). In this presentation, we report the inferred reaction processes and discuss their implications for "CO world" scenarios in early hydrothermal systems.