Voltammetric studies in the absence of added supporting electrolyte are presently dominated by the use of near-steady-state microelectrode techniques and millimolar or lower depolarizer concentrations. However, with this methodology, large departures from conventional migration-diffusion theory have been reported for the [Fe(CN)6](3-/4-) process at both carbon fiber and platinum microdisk electrodes. In contrast, data obtained in the present study reveal that use of the transient cyclic voltammetric technique at glassy carbon, gold, or platinum macrodisk electrodes and K4[Fe(CN)6] or K3[Fe(CN)6] concentrations of 50 mM or greater provides an approximately reversible response in the absence of added electrolyte. It is suggested that the use of very high [Fe(CN)6](3-) and [Fe(CN)6](4-) concentrations overcomes problems associated with a diffuse double layer and that large electrode surface areas and faster potential sweep rates minimize electrode blockage and passivating phenomena that can plague voltammetric studies at microelectrodes. The cyclic voltammetry of the [Fe(CN)6](3-/4-) couple at a range of concentrations at macroelectrodes in the absence of added inert electrolyte is compared with that obtained in the presence of 1 M KCl. The enhanced influences of uncompensated resistance, migration, and natural convection arising from density gradients under transient conditions at macrodisk electrodes also are considered.

The voltammetric behavior of the [Fe(CN) 6 ] 3-/4couple at a glassy carbon rotating macrodisk electrode without added supporting electrolyte is shown to be in close to ideal agreement with the theory presented over a wide range of electrode rotation and scan rates when the concentration of electroactive species used is 50 mM. The influences of migration, uncompensated resistance, heterogeneous charge-transfer kinetics, and inhomogeneous diffusion are shown to be well modeled by a finite difference simulation scheme that affords excellent agreement between experiment and theory. The use of the rotating disk electrode, even when only moderate rotation rates are employed, is shown to eliminate the problem with natural convection that exists when using stationary electrodes (macro-or microdisk) and that is enhanced in the absence of added supporting electrolyte. Consequently, it has been concluded that the rotating disk electrode method represents an almost ideal technique for conducting studies without added supporting electrolyte.

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The reversible formal potentials of auracyanin A and auracyanin B, two closely related "blue" copper proteins from the photosynthetic bacterium Chloroflexus aurantiacus, have been determined by protein film voltammetry in the range 4