Mimicking the microbial oxidation of elemental sulfur with a biphasic electrochemical cell

The lack of an artificial system that mimics elemental sulfur (S-8) oxidation by microorganisms inhibits a deep mechanistic understanding of the sulfur cycle in the biosphere and the metabolism of sulfur-oxidising microorganisms. In this article, we present a biphasic system that mimics biochemical sulfur oxidation under ambient conditions using a liquid vertical bar liquid (L vertical bar L) electrochemical cell and gold nanoparticles (AuNPs) as an interfacial catalyst. The interface between two solvents of very different polarity is an ideal environment to oxidise S-8, overcoming the incompatible solubilities of the hydrophobic reactants (O-2 and S-8) and hydrophilic products (H+, SO32-, SO42-, etc.). Furthermore, the interfacial AuNPs provide a catalytic surface onto which O-2 and S-8 can adsorb. Control over the driving force for the reaction is provided by polarising the L vertical bar L interface externally and tuning the Fermi level of the interfacial AuNPs by the adsorption of aqueous anions. Comparison of electrochemical measurements using a 4-electrode closed bipolar electrochemical cell and a L vertical bar L electrochemical cell confirmed that electron transfer reactions are possible between O-2, gold and S-8 in biphasic systems. (C) 2021 The Author(s). Published by Elsevier Ltd.