The Electron-Providing Effect of a Schiff Base Copper(II) Complex Mediator and Lignin for Laccase

In biofuel cells using laccase, the electron supply to the type 1 (T1) site is inefficient, constituting a major bottleneck for the overall reaction. To solve this problem, the use of mediator molecules that mediate electron transfer is being studied. Furthermore, lignin is known to be oxidized by laccase and can donate electrons, which indicates the potential application of this reaction in biofuel cells. Therefore, in this study, docking calculations were performed to clarify the interactions between a copper(II) complex mediator and laccase. At the same time, a copper complex mediator was selected, and cyclic voltammetry (CV) measurements were performed to evaluate its electrochemical properties. In the CV measurements, the differences in current responses with and without the mediator and lignin (an oxidized substrate of laccase) were compared. As a result, based on the docking calculations, it was proposed that the synthesized copper complex mediator binds relatively strongly to laccase. Moreover, CV measurements confirmed that the current tended to increase upon the addition of the mediator and/or lignin. This current enhancement explicitly demonstrates the efficient electron-providing effect of the mediator and lignin to the laccase-based system.