Chronoamperometry of surface-confined redox couples. Application to daunomycin adsorbed on hanging mercury drop electrodes

The electrochemistry of daunomycin adsorbed on a hanging mercury drop elect rode (HMDE) was studied in aqueous pH 9.18 phosphate buffer solution. At po tentials positive of the formal potential (E-o' = -0.73 V vs. SCE), bilayer formation was indicated, while at negative potentials, a less densely pack ed monolayer was formed. A novel differential chronoamperometric kinetic an alysis, which explicitly took into account solution IR drop, indicated that a two-electron ECE pathway was followed for the cathodic reaction. The mec hanism and associated kinetic parameters were also in agreement with the cy clic voltammetry. The chemical step, which was assigned to protonation of t he semiquinone radical anion, was assumed to be at equilibrium. In Appendix A, the transient response of the simple Randles equivalent circuit to a po tential step excitation function is derived. (C) 1999 Elsevier Science Ltd. All rights reserved.