Laccase voltammetry

In-situ STM of laccase has so far been attempted using only basal-plane pyrolytic graphite surfaces [54]. No adsotption could be detected. This is perhaps not surprising as laccase voltammetry requires edge-plane graphite and/or pre-adsorption of promoters. Low-resolution ex-situ micron-scale laccase structures coidd be recorded during evaporation of laccase solution where individual molecular-size structures, possibly dislodged by mechanical tip contact, could also be observed. 

Figures 5.4 and 5.5 summarize results of a recent study of P. versicolor laccase electrochemistry based on cyclic and rotating disk voltammetry [60]. Figure 5.4 shows unequivocally that this laccase is voltammetrically active and gives a kinetically controlled, unpromoted four-electron peak at edge-plane pyrolytic graphite. Electrochemical reduction of 02 catalyzed by an immobilized laccase monolayer is close to reversible, and unrestricted by mass transport. The electrocatalysis follows, moreover, a Michaelis-Menten pattern (Fig. 5.5). Finally, there is a characteristic bell-shaped functional pH-profile with a pronounced maximum at pH 3.1.

Methylene blue acted as a mediator of electrons providing electrical contact between the electrode and the solution-resident enzyme laccase (Fig. 10.5.7) catalyzing reduction of oxygen to water [46], The catalytic effect is revealed by the wave shape of the cyclic voltammetry curve in the oxygen-saturated solutions and its increased limiting current. 

The in situ XAS analyses deseribed herein were performed using X-ray absorption near-edge structure (XANES) analysis and extended X-ray absorption fine strueture (EXAFS) analysis and analyzed in conjunction with FEFF8.0 modeling to investigate changes to the active site as a function of potential and presenee of O2. Fundamental electrochemical methods sueh as cyclic voltammetry (CV), chronoamperometry, and ORR polarization measurements were then compared to illustrate the electrocatalytic activity of laccase. Finally, an in-depth analysis of the A //FFFF8 results lead to a new proposed mechanism for the laccase-catalyzed ORR. 

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