title: Impact of self-assembly composition on the alternate interfacial electron transfer for electrostatically immobilized cytochrome c.
abstract: We report on the effects of self-assembled monolayer (SAM) dilution and thickness on the electron transfer (ET) event for cytochrome c (CytC) electrostatically immobilized on carboxyl terminated groups. We observed biphasic kinetic behavior for a logarithmic dependence of the rate constant on the SAM carbon number (ET distance) within the series of mixed SAMs of C(5)COOH/C(2)OH, C(10)COOH/C(6)OH, and C(15)COOH/C(11)OH that is in overall similar to that found earlier for the undiluted SAM assemblies. However, in the case of C(15)COOH/C(11)OH and C(10)COOH/C(6)OH mixed SAMs a notable increase of the ET standard rate constant was observed, in comparison with the corresponding unicomponent (omega-COOH) SAMs. In the case of the C(5)COOH/C(2)OH composite SAM a decrease of the rate constant versus the unicomponent analogue was observed. The value of the reorganization free energy deduced through the Marcus-like data analysis did not change throughout the series; this fact along with the other observations indicates uncomplicated rate-determining unimolecular ET in all cases. Our results are consistent with a model that considers a changeover between the alternate, tunneling and adiabatic intrinsic ET mechanisms. The physical mechanism behind the observed fine kinetic effects in terms of the protein-rigidifying omega-COOH/CytC interactions arising in the case of mixed SAMs are also discussed.
authors.affiliation: Institute of Molecular Biology and Biophysics, Gotua 12, Tbilisi 0160, Georgia (Republic).
authors.forename: Tina D
authors.initials: TD
authors.lastname: Dolidze
authors.forename: Sandra
authors.initials: S
authors.lastname: Rondinini
authors.forename: Alberto
authors.initials: A
authors.lastname: Vertova
authors.forename: David H
authors.initials: DH
authors.lastname: Waldeck
authors.forename: Dimitri E
authors.initials: DE
authors.lastname: Khoshtariya
mesh_terms: D000818:Animals; D045304:Cytochromes c / Q000737:chemistry*; D004563:Electrochemistry; D004579:Electron Transport; D004800:Enzymes, Immobilized / Q000737:chemistry; D006736:Horses; D007700:Kinetics; D008567:Membranes, Artificial; D009206:Myocardium / Q000201:enzymology*
chemical_list: D004800:Enzymes, Immobilized; D008567:Membranes, Artificial; D045304:Cytochromes c