title: Thermal fluctuations determine the electron-transfer rates of cytochrome c in electrostatic and covalent complexes.
abstract: The heterogeneous electron-transfer (ET) reaction of cytochrome c (Cyt-c) electrostatically or covalently immobilized on electrodes coated with self-assembled monolayers (SAMs) of omega-functionalized alkanethiols is analyzed by surface-enhanced resonance Raman (SERR) spectroscopy and molecular dynamics (MD) simulations. Electrostatically bound Cyt-c on pure carboxyl-terminated and mixed carboxyl/hydroxyl-terminated SAMs reveals the same distance dependence of the rate constants, that is, electron tunneling at long distances and a regime controlled by the protein orientational distribution and dynamics that leads to a nearly distance-independent rate constant at short distances. Qualitatively, the same behavior is found for covalently bound Cyt-c, although the apparent ET rates in the plateau region are lower since protein mobility is restricted due to formation of amide bonds between the protein and the SAM. The experimental findings are consistent with the results of MD simulations indicating that thermal fluctuations of the protein and interfacial solvent molecules can effectively modulate the electron tunneling probability.
authors.affiliation: Technische Universität Berlin, Institut für Chemie, Str. des 17. Juni 135, Sekr. PC14, Berlin, Germany.
authors.forename: Hoang Khoa
authors.initials: HK
authors.lastname: Ly
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: Marti
authors.forename: Diego F
authors.initials: DF
authors.lastname: Martin
authors.forename: Damian
authors.initials: D
authors.lastname: Alvarez-Paggi
authors.forename: Wiebke
authors.initials: W
authors.lastname: Meister
authors.forename: Anja
authors.initials: A
authors.lastname: Kranich
authors.forename: Inez M
authors.initials: IM
authors.lastname: Weidinger
authors.forename: Peter
authors.initials: P
authors.lastname: Hildebrandt
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Murgida
mesh_terms: D045304:Cytochromes c / Q000737:chemistry*; D004566:Electrodes; D004579:Electron Transport; D055767:Immobilized Proteins / Q000737:chemistry; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D010084:Oxidation-Reduction; D013059:Spectrum Analysis, Raman; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D055767:Immobilized Proteins; D045304:Cytochromes c