The transfer of proteins by the anionic surfactant bis(2-ethylhexyl) sulfosuccinate (AOT) at a polarized 1,2-dichloroethane/water (DCE/W) interface was investigated by means of ion-transfer voltammetry. When the tetrapentylammonium salt of AOT was added to the DCE phase, the facilitated transfer of certain proteins, including cytochrome c (Cyt c), ribonuclease A, and protamine, could be controlled electrochemically, and a well-defined anodic wave for the transfer was obtained. At low pH values (e.g., pH 3.4), the anodic wave was usually well-separated from the wave for the formation of protein-free (i.e., unfilled) reverse micelles. The anodic wave for the protein transfer was analyzed by applying the theory for facilitated transfer of ions by charged ligands and then supplying information regarding the number of AOT anions reacting with one protein molecule and the total charge carried by the protein transfer. However, controlled-potential electrolyses performed for the transfer of Cyt c, which is red, revealed that the protein-AOT complexes were unstable in DCE and liable to aggregate at the interface when the pH of the W phase was 3.4. At pH 7.0, when formation of unfilled reverse micelles occurred simultaneously, the protein-AOT complexes appeared to be stabilized, probably via fusion with unfilled reverse micelles.

The reaction mechanism of electron transfer (ET) between ferrocene (Fc) in nitrobenzene (NB) and Fe(CN) 6 3-in water (W) was clarified by digital simulation of cyclic voltammograms. The voltammograms observed under various concentration conditions could not be elucidated by assuming a heterogeneous ET at the NB/W interface, whereas they were successfully elucidated in terms of the ion-transfer (IT) mechanism, in which a homogeneous ET between Fe(CN) 6 3-and Fc (partially distributed from NB) occurs in the W phase and the interfacial transfer of the resultant ferricenium ion (Fc + ) is responsible for the current passage across the interface. The validity of the IT mechanism was further supported by spectroscopic detection of Fc + produced in the W phase without electrochemical control. These results show that the homogeneous ET proceeds more advantageously than the heterogeneous ET due to a pinpoint collision of redox species at the interface. This may be ascribed to the difference in the volume of reaction field between the homogeneous and heterogeneous ETs. The reaction field for the former has a thickness of ca. 200 µm, whereas that for the latter is restricted to an interfacial layer as thin as several ångstroms. Such a large difference in the volume of the reaction field would overcome the disadvantage of the IT mechanism, i.e., the small partition of Fc into the W phase. The low possibility of the ET mechanism has also been deduced from theoretical estimation of the standard rate constant and transfer coefficient for the hypothetical heterogeneous ET.

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