CHLOROPHYLEPHOTOSENSITIZED ELECTRON TRANSFER BETWEEN CYTOCHROME c AND A LIPID-MODIFIED TRANSPARENT INDIUM OXIDE ELECTRODE

Both direct and chlorophyll-photosensitized electron transfer reactions between cytochrome c and a lipid-modified indium oxide electrode have been studied by cyclic voltammetry and photoelectrochemistry. The lipid films consisted of egg phosphatidylcholine (PC), either alone or in combination with the negatively charged surfactant dihexadecylphosphate (DHP-), and contained varying amounts of chlorophyll. The photocurrents were either ca-thodic, when cytochrome c was used in its oxidized form in the supporting electrolyte, or anodic when the reduced form of cytochrome c was present, with a magnitude that depended on the PC concentration and the applied voltage. Quantum efficiencies of the anodic and cathodic photocurrents reached their maxima (5% and 10/o, respectively), at an intermediate PC concentration (5 mg/mL in the membrane-forming solution), conditions under which the diffusion-controlled electrochemical response of cytochrome c was also maximal. Incorporation of DHP^- into the PC film increased both the direct and chlorophyll-photosensitized currents, presumably due to electrostatic binding of the positively charged cytochrome c to the electrode surface.