Web Release Date: January 25,
Multiple Sites for Electron Tunneling between Cytochrome c and Mixed Self-Assembled Monolayers
and
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, and Department of Chemistry, Saint Francis University, Loretto, Pennsylvania 15940
Received: August 23, 2007
In Final Form: October 26, 2007
Abstract:
The electron-tunneling pathway between an electrode and the protein cytochrome c was studied on mixed C15-carboxylic acid/hydroxyl-terminated SAMs and C16-pyridine/alkane-terminated SAMs as a function of the surface concentration and the length of the diluent alkanethiol. It was found that by increasing the concentration of shorter-chain hydroxyl diluent thiol in the SAM the rate constant increased in a systematic way. When the diluent composition is high, the k0 increases exponentially with decreasing chain length of the diluent molecules until the chain length of the diluent molecule reaches a length of about eight methylene groups. These results indicate that short-chain diluent molecules contribute to the electronic coupling between the protein and electrode, and that shortening of the diluent decreases the effective tunneling distance.
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