Fungi are fantastic recyclers. Their enzymes let them decompose vast quantities of plant matter. One such enzyme, laccase, can split oxygen molecules and use them to degrade stubborn materials like lignin. This exergonic reaction powers fungi and it would be interesting to couple a catalyst that splits oxygen with one that splits an energy carrier, like hydrogen. Such a fuel cell could use laccase but the enzyme is sensitive to pH and temperature so we are instead keen to make small-molecule copper complexes as models for the laccase active site. We aim to develop models that are fast electrocatalysts for oxygen reduction, while having a greater robustness and smaller footprint than the enzymes that inspired them.
The laccase active site features four copper centers: three of these ‘gang up’ on an oxygen molecule to cooperatively split it, as pictured. A fourth copper center is able to oxidize plant matter and relay the electrons to the other three coppers. We focus on synthetic models of the tricopper portion, which resides in a histidine-rich region of the protein. Thus, our project sees us prepare multinucleating nitrogen-donor ligands to support a cooperative trio of catalytic copper sites.