Catalysis by immobilized redox enzymes. Diagnosis of inactivation and reactivation effects through odd cyclic voltammetric responses

Abstract

Odd cyclic voltammetric responses, with an inverted peak appearing on the reverse scan, have been recently reported for the catalysis of immobilized enzymes involved in a direct electron transfer at the electrode surface and implicated in a chemical inactivation/redox reactivation mechanism. In this work, it is shown that this twisted reverse trace behavior can be related rigorously and quantitatively to such a reaction scheme by means of a minimal number of dimensionless parameters. As a prelude, the requirements for ‘pure catalytic’ conditions to be achieved are established quantitatively. It is also shown that simple irreversible or reversible inactivation does not entail the appearance of twisted reverse traces. The quantitative analysis of the inactivation/reactivation mechanism does not lead to a closed form expression of the current responses, but rather requires the numerical resolution of the pertinent differential equations. This approach may be readily extended to virtually any kind of mechanism, including more complex reactions schemes, distance-dependent electron transfer kinetics, the use of immobilized or free-moving redox cosubstrates, consideration of substrate mass transport limitations, etc.