Thermal Fluctuations Determine the Electron Trasfer Rates of Cytochrome c in Electrostatic and Covalent Complexes

LY, H. K.; MARTÍ, M.A.; MARTIN, D.F.; ALVAREZ PAGGI, D.; MEISTER, W.; KRANICH, A.; WEIDINGER, I. M.; HILDEBRANDT , P.; MURGIDA, D.H.

Chemphyschem

WILEY-V C H VERLAG GMBH

Año: 2010 vol. 11 p. 1225 - 1235

1439-4235

The heterogeneous electron-transfer (ET) reaction of cytochrome c (Cyt-c) electrostatically or covalently immobilized on electrodes coated with self-assembled monolayers (SAMs) of wfunctionalized 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 dynamicsthat leads to a nearly distance-independent rate constant at short distances. Qualitatively, the same behavior is found forcovalently 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 theSAM. The experimental findings are consistent with the results of MD simulations indicating that thermal fluctuations of the protein and interfacial solvent molecules can effectively modulatethe electron tunneling probability.