New approaches to coupling infrared spectroscopy and electrochemistry

We have developed IR spectroelectrochemical methods to address catalysts supported on carbon particles assembled into high surface area 3D electrodes. This research is supported by a major ERC Starting Grant.^ref

-Understanding active site chemistry of hydrogenase enzymes

A wide range of micro-organisms express hydrogenases - highly active enzymes for oxidation of H₂, or reduction of H⁺ to produce H₂. The efficiency of H₂/H⁺ interconversion by hydrogenases is providing inspiration for development of new catalysts for fuel cells or clean H₂ production built from abundant metals, but this requires an intimate knowledge of how H₂ is activated at hydrogenase active sites. The Vincent group are using a combination of electrochemical and spectroscopic methods to understand hydrogenase active site chemistry.

Direct electrochemical methods, in which hydrogenases are adsorbed as a sub-monolayer film onto a graphite electrode, provide precise control over active site chemistry. In this approach called (protein film electrochemistry), adsorbed enzyme molecules exchange electrons directly with the electrode so that no electron-transfer mediators are required. The current at the electrode reports on the catalytic activity of the adsorbed hydrogenase at each applied potential. Protein film electrochemistry has provided much insight into the chemistry of hydrogenases.

The Vincent group has established a method for combining protein film electrochemistry at carbon electrodes with infrared spectroscopy. We call this approach 'protein film infrared electrochemistry' (PFIRE), and we are using this to reveal structural details of enzyme active site chemistry during catalytic turnover on an electrode. The active sites of hydrogenases incorporate ligands that are unusual in biology: carbon monoxide (CO) and cyanide (CN^-). These ligands provide a useful spectroscopic handle for studying structural changes at the metal centre because vibrational transitions associated with CO and CN^- give rise to relatively intense absorption bands in the infrared. Using the PFIRE approach we have obtained strong evidence for the role of a Ni(I) active site called Ni-L in catalytic turnover of E. coli NiFe hydrogenase I.^ref

We are studying the binding of small molecule ligands at a range of other biological metal centres. One area of study involves the reactions of nitric oxide with protein-bound iron sulphur clusters, with relevance to bacterial sensing of NO. Work on this topic has recently been published in J. Am. Chem. Soc. Another system of interest is the enzyme nitrogenase (in collaboration with Lance Seefeldt at Utah State University).

We are applying IR spectroelectrochemistry to examine surface chemistry and poisoning of supported nanoparticles of platinum and other precious metals in fuel cell electrocatalysis, under fuel flow conditions.

Recycling biological cofactors NAD⁺ and NADH: Applications of enzyme catalysis

We have developed a system for recycling the biological cofactors NAD⁺ and NADH with H₂ / H⁺ as electron source / sink using graphite particles modified with a hydrogenase and a diaphorase moiety. This work is carried out in collaboration with Dr Oliver Lenz and Lars Lauterbach at Humboldt University of Berlin/ Technical University of Berlin and has been supported by ERC Proof of Concept funding. Preliminary results are published in Chemical Communications. The developments have been protected by a patent application and further information on commercial opportunities is available from Oxford University's Technology Transfer company, Isis Innovation.

We are also using protein film electrochemistry to study electrocatalytic NAD⁺ reduction and NADH oxidation by the diaphorase moiety of Ralstonia eutropha soluble hydrogenase in collaboration with Oliver Lenz and Lars Lauterbach. This research is published in PLoS ONE.