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Abstract: In this work, we studied interfacial proton transfer of the self-assembled monolayer (SAM) of 1-(12-mercaptododecyl)imidazole on a gold electrode by faradaic impedance titration method with Fe(CN)6 3− as an anionic redox probe molecule. The surface pK 1/2 was found to be 7.3, which was nearly the same as that of 1-alkylimidazole in solution. We also investigated the electrochemical properties of the SAM-modified electrode by cyclic voltammetry. Cyclic voltammetry was performed (1) in the solution containing Fe(CN)6 3− with repeated alternation of pH values to investigate the electrostatic interaction of the protonated or deprotonated imidazole with Fe(CN)6 3− and (2) in the acidic or basic electrolyte containing Ru(NH3)6 3+ as a cationic redox probe to verify the effect of the polarity of a redox probe. We observed the reversible adsorption/desorption of Fe(CN)6 3− and concluded that the adsorbed Fe(CN)6 3− catalyzed the electron transfer of both Fe(CN)6 3− itself and cationic Ru(NH3)6 3+. [Copyright &y& Elsevier]