TY - DATA T1 - Charge-Transfer Mechanism for Cytochrome c Adsorbed on Nanometer Thick Films. Distinguishing Frictional Control from Conformational Gating PY - 2003/06/03 AU - Dimitri E. Khoshtariya AU - Jianjun Wei AU - Haiying Liu AU - Hongjun Yue AU - David H. Waldeck UR - https://acs.figshare.com/articles/journal_contribution/Charge-Transfer_Mechanism_for_Cytochrome_i_c_i_Adsorbed_on_Nanometer_Thick_Films_Distinguishing_Frictional_Control_from_Conformational_Gating/3650367 DO - 10.1021/ja034719t.s001 L4 - https://ndownloader.figshare.com/files/5739231 KW - electron tunneling probability KW - SAM KW - plateau KW - polarization relaxation processes KW - alkane KW - separation KW - COOH KW - transition KW - dependence KW - Nanometer Thick Films KW - D 2 O KW - terthiophene KW - H 2 O KW - Distinguishing Frictional Control KW - Cytochrome c Adsorbed KW - mechanism KW - conclusion KW - viscosity KW - cytochrome c KW - pyridine N2 - Using nanometer thick tunneling barriers with specifically attached cytochrome c, the electron-transfer rate constant was studied as a function of the SAM composition (alkane versus terthiophene), the ω-terminating group type (pyridine, imidazole, nitrile), and the solution viscosity. At large electrode−reactant separations, the pyridine terminated alkanethiols exhibit an exponential decline of the rate constant with increasing electron-transfer distance. At short separations, a plateau behavior, analogous to systems involving −COOH terminal groups to which cytochrome c can be attached electrostatically, is observed. The dependence of the rate constant in the plateau region on system properties is investigated. The rate constant is insensitive to the mode of attachment to the surface but displays a significant viscosity dependence, change with spacer composition (alkane versus terthiophene), and nature of the solvent (H2O versus D2O). Based on these findings and others, the conclusion is drawn that the charge-transfer rate constant at short distance is determined by polarization relaxation processes in the structure, rather than the electron tunneling probability or large-amplitude conformational rearrangement (gating). The transition in reaction mechanism with distance reflects a gradual transition between the tunneling and frictional mechanisms. This conclusion is consistent with data from a number of other sources as well. ER -