ABSTRACT
The data were analyzed by plotting peak positions (oxidation and reduction) against scan rate, and modeling in terms of kinetic schemes incorporating a number of parameters. We have called these trumpet plots because for simple, uncoupled electron transfer, the data separate symmetrically and give a trumpet-like shape. In addition to the electron-transfer rate constant, the additional parameters include pH dependent protontransfer rate constants, participation of a base that relays the proton between solvent and cluster, and variations of the pK of both cluster and base during the reaction. Representative plots for D15N and native FdI are shown in Figure 10; in each case, the voltammograms were commenced from the oxidative limit. At high pH the plots are indeed simple, but note how their forms change dramatically as the pH is lowered. At the left (i.e., using low scan rates), the data correspond to those that might be measured in a potentiometric experiment-i.e., the system is able to equilibrate with the electrode potential. By contrast, at the right, the potential is cycled so fast that the reduction potential that is measured (average of oxidation and reduction peaks) corresponds to a snapshot of the system, recorded, in this case, on the millisecond timescale.
