title: Correcting for electrocatalyst desorption and inactivation in chronoamperometry experiments.
abstract: Chronoamperometric experiments with adsorbed electrocatalysts are commonly performed either for analytical purposes or for studying the catalytic mechanism of a redox enzyme. In the context of amperometric sensors, the current may be recorded as a function of time while the analyte concentration is being increased to determine a linearity range. In mechanistic studies of redox enzymes, chronoamperometry proved powerful for untangling the effects of electrode potential and time, which are convoluted in cyclic voltammetric measurements, and for studying the energetics and kinetics of inhibition. In all such experiments, the fact that the catalyst's coverage and/or activity decreases over time distorts the data. This may hide meaningful features, introduce systematic errors, and limit the accuracy of the measurements. We propose a general and surprisingly simple method for correcting for electrocatalyst desorption and inactivation, which greatly increases the precision of chronoamperometric experiments. Rather than subtracting a baseline, this consists in dividing the current, either by a synthetic signal that is proportional to the instant electroactive coverage or by the signal recorded in a control experiment. In the latter, the change in current may result from film loss only or from film loss plus catalyst inactivation. We describe the different strategies for obtaining the control signal by analyzing various data recorded with adsorbed redox enzymes: nitrate reductase, NiFe hydrogenase, and FeFe hydrogenase. In each case we discuss the trustfulness and the benefit of the correction. This method also applies to experiments where electron transfer is mediated, rather than direct, providing the current is proportional to the time-dependent concentration of catalyst.
authors.affiliation: Unité de Bioénergétique et Ingénierie des Protéines, IMM, UPR 9036, CNRS, 31 Chemin Joseph Aiguier, F-13402 Marseille Cedex 20, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Fourmond
authors.forename: Thomas
authors.initials: T
authors.lastname: Lautier
authors.forename: Carole
authors.initials: C
authors.lastname: Baffert
authors.forename: Fanny
authors.initials: F
authors.lastname: Leroux
authors.forename: Pierre-Pol
authors.initials: PP
authors.lastname: Liebgott
authors.forename: Sébastien
authors.initials: S
authors.lastname: Dementin
authors.forename: Marc
authors.initials: M
authors.lastname: Rousset
authors.forename: Pascal
authors.initials: P
authors.lastname: Arnoux
authors.forename: David
authors.initials: D
authors.lastname: Pignol
authors.forename: Isabelle
authors.initials: I
authors.lastname: Meynial-Salles
authors.forename: Phillippe
authors.initials: P
authors.lastname: Soucaille
authors.forename: Patrick
authors.initials: P
authors.lastname: Bertrand
authors.forename: Christophe
authors.initials: C
authors.lastname: Léger
mesh_terms: D000327:Adsorption; D016477:Artifacts; D055162:Biocatalysis; D004553:Electric Conductivity; D055664:Electrochemical Techniques / Q000379:methods*; D004798:Enzymes / Q000737:chemistry / Q000378:metabolism; D012984:Software
chemical_list: D004798:Enzymes