Inhibition of Electrocatalytic O2 Reduction of Functional CcO Models by Competitive, Non-Competitive, and Mixed Inhibitors

Electrocatalytic reduction of O-2 by functional cytochrome C Oxidase (CcO) models is studied in the presence of several known inhibitors like CO, N-3(-), CN-, and NO2-. These models successfully reproduce the inhibitions observed in CcO at similar concentrations reported for these inhibitors. Importantly, the data show very different electrochemical responses depending on the nature of the inhibitor, that is, competitive, non-competitive and mixed. Chemical models have been provided for these observed differences in the electrochemical behavior. Using the benchmark electrochemical behaviors for known inhibitors, the inhibition by NO2- is investigated. Electrochemical data suggests that NO2- acts as a competitive inhibitor at high concentrations. Spectroscopic data suggests that NO released during oxidation of the reduced catalyst in presence of excess NO2- is the source of the competitive inhibition by NO2- Presence of the distal Cu-B lowers the inhibitory effect of CN- and NO2-. While for CN- it weakens its binding affinity to the reduced complex by similar to 4.5 times, for NO2-, it allows regeneration of the active catalyst from a catalytically inactive, air stable ferrous nitrosyl complex via a proposed superoxide mediated pathway.