High Field ESR Characterization of the Catalytic Copper Center of Laccase in Biofunctionalized Fuel Cell Electrode

The scientific community is constantly striving towards more environmentally friendly and lower cost routes to chemical syntheses and energy production. One such push is for an fuel cell that emits little to no toxic byproducts. To do this, there is a focus on developing strategies to attach enzymes to electrodes in order to create biofunctionalized fuel cells. In our work, we have focused on laccase, a copper‐ containing oxidase found in many plants, fungi, and microorganisms, which catalyzes the clean four‐electron reduction of oxygen gas to water and can therefore mediate the cathode reaction in fuel cells.. Laccase's catalytic site contains 4 copper ions:one Type 1 (T1) copper, and a trinuclear cluster (TNC) consisting of one T2, and two T3 coppers. The TNC forms the oxygen binding site and carries out the reduction reaction, while the T1 copper transfers electrons from an organic substrate to the TNC, turning over 4 times during the oxygen reduction cycle. We describe a new experiment in which the catalytic cycle of the TNC may be investigated by observing the electron spin resonance (ESR) spectrum of the T2 copper in situ in an electrochemical cell. A locally constructed high‐frequency ESR spectrometer is used to resolve and characterize new spectroscopic feature in the different states of the TNC catalytical cycle, which in turn reflect changes in the electronic structure associated with catalysis.