Direct Electron Transfer to Cytochrome c Induced by a Conducting Polymer

The direct electron transfer (DET) to redox proteins has become a central topic in the development of biotechnological devices. The present work explores the mechanisms of the direct electrochemistry between cytochrome c (cyt c) and a conducting polymer, poly(3,4ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT PSS). This polymer has been electrosynthesized from its monomers in aqueous solution on gold electrodes, and its capabilities for DET to cyt c have been examined by electrochemical and spectroelectrochemical methods. The polymer was electrodeposited with controlled thickness, and we determined that the electron transfer rate constant for cyt c oxidation was about 2 orders of magnitude higher than those obtained at conventional electrodes. Spectroelectrochemical measurements allowed us to evaluate the redox state of the polymer as a function of the potential and, in addition, the observation of intrinsic cyt c redox activity upon electron transfer from the conducting polymer. During the oxidation process of this protein, lysine residues placed near the heme crevice interact electrostatically with the anionic polyelectrolyte PSS. This interaction favors the orientation of the heme group toward the chains of the PEDOT backbone, which is eventually responsible for the electron transfer to the protein.