Surface plasmon enhanced interfacial electron transfer and resonance Raman, surface-enhanced resonance Raman studies of cytochrome c mutants

Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO₂ were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO₂, large photoelectrocatalytic effect for the reduction of CO₂ was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO₂ in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.; Resonance Raman studies of cytochrome c and its mutants demonstrate the sensitivity of the spectra to mutations that affect the interactions of the heme peripheral substituents with the protein matrix. The most dramatic differences in the spectra of the mutant cytochromes, as compared with that of wild-type cytochrome c, occurred in the low-wavenumber region. The bands that are most strongly affected include bending modes of the thioether linkages and propionic acid side-chains. Oxidation state dependent axial ligand switching of heme iron in yeast iso-1-cytochrome c mutant F82H was determined by UV-visible, circular dichroism and resonance Raman spectra. From the analysis of the spectra, it was concluded that in the oxidized F82H axial ligands to the heme iron are His-18 and His-82 whereas in the reduced form the sixth ligand switches from His-82 to Met-80. The mutant possesses less distorted porphyrin macrocycle and more opened conformation relative to that of wild type protein. The comparisons of the surface-enhanced resonance Raman scattering spectra and cyclic voltammetries of the proteins reveal that F82H mutant has more stable conformation and negative redox reaction potential.