Electric-field effects on the interfacial electron transfer and protein dynamics of cytochrome c

Surface‐enhanced vibrational spectroscopy for probing transient interactions of proteins with biomimetic interfaces: electric field effects on structure, dynamics and function of cytochrome c

“…The reorganization energy derived from these studies is distinctly lower than that determined for cytochrome c in solution [39], indicating a strongly reduced contribution of the solvent reorganization in the immobilized state [38]. However, much weaker overpotential dependencies, corresponding to physically meaningless low values for the reorganization energy, are obtained for SAMcoated Au and Au-Ag hybrid instead of Ag electrodes [40]. In an attempt to reconcile these conflicting results, it has been proposed that, also in the low-field regime, the local electric field at the SAM-cytochrome c interface affects the electron transfer step.…”

“…3. Rate constants for reorientation (red) and reduction (blue) of cytochrome c immobilised on Ag electrodes coated with carboxylterminated SAMs of different chain lengths, determined by timeresolved SERR spectroscopy [25,28,40]. The bottom axis indicates the electric field strength at the SAM-cytochrome c interface as estimated on the basis of an electrostatic model [23].…”

“…Assuming that the local electric field strength is proportional to the difference between the actual electrode potential and the metal-specific potential of zero charge, an empirical linear correction has been included in the free-energy term of the Marcus equation, in analogy to previous approaches employed for describing field effects on intramolecular electron transfer reactions [41]. This rather simple approximation allows for a consistent description of the overpotential dependencies on Ag, Au-Ag hybrid and Au electrodes by TR-SERR and TR-SEIRA experiments [40], but further experimental studies and a refinement of the theoretical model are required.…”

“…Thus, the heterogeneous electron transfer is a convolution of the orientation-dependent electron tunnelling and the orientational distribution of the immobilized protein, and is thus characterized by an apparent electron transfer rate constant, k app . In addition, the electric field effect on electron tunnelling itself, which is not negligible even in the low-field regime, is expected to play a dominant role at high electric fields, and may account for the decrease in k app when the SAM thickness is reduced below that of a C5-SAM [40], or when the charge density in the interface is increased [16]. Under these extreme conditions, k app displays a kinetic isotope effect that is tentatively attributed to the field-dependent reorganization of the hydrogen bond network in the protein-SAM interface [40].…”

High Performance Reduction of H2O2 with an Electron Transport Decaheme Cytochrome on a Porous ITO Electrode

“…23,24 The dominating species with marker bands located at 1375, 1506, and 1639 cm –1 in the ferric and 1359, 1491, and 1621 cm –1 in the ferrous state for ν 4 , ν 3 , and ν 10 , respectively, is assigned to hexacoordinated hemes with bis-histidine axial ligation as anticipated from the crystal structure (Table S1). 19,23,25 For these spectral features, the relative concentration of ferric ( c ox ) with respect to the ferrous form was calculated and plotted versus the applied potential (Figure 4a, inset).…”