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 electrode (HMDE) was studied in aqueous pH 9.18 phosphate buffer solution. At potentials positive of the formal potential (E^○′ = -0.73 V vs. SCE), bilayer formation was indicated, while at negative potentials, a less densely packed monolayer was formed. A novel differential chronoamperometric kinetic analysis, which explicitly took into account solution IR drop, indicated that a two-electron ECE pathway was followed for the cathodic reaction. The mechanism and associated kinetic parameters were also in agreement with the cyclic voltammetry. The chemical step, which was assigned to protonation of the semiquinone radical anion, was assumed to be at equilibrium. In Appendix A, the transient response of the simple Randles equivalent circuit to a potential step excitation function is derived.