Electrochemical characterization of redox centers organized at Hg surfaces

The electrochemical characterization of a series of redox sites absorbed at Hg surface by different interactions is reported. The redox centers, based on Fe(II) and Ru(II), are incorporated, respectively, in the molecules Fe(C5H5)(C5H4)(CH2)4SH and [Ru(NH3)5NC5H4CH2NHCO(CH2)10SH](PF6), and are anchored on the Hg surface in one component self-assembled monolayers. The electrochemical behaviour of these systems indicates that redox centers are located onto a uniform, homogeneous environment at the external surface of the monolayer. We also report the electrochemical behaviour of the positively charged redox species [Ru(NH3)6]3+ when the Hg electrode surface is functionalized with a negatively charged SAM. The SAM is formed by 11-mercaptoundecanoic acid that exposes carboxylic acid groups to solutions of different pH values. At a pH lower than 4, the cyclic voltammograms show negligible current, and pH from 5 to 9, the voltammograms are essentially identical and show a well-defined redox wave. From a study of the voltammetric responses of the View the MathML sourceRu(NH3)63+/2+ couple as a function of the electrolyte composition and concentration at pH 9, we suggest that the redox reaction takes place at the defects of the SAMs created by the repulsion of the –COO− head groups and that the current is determined by a diffusion-controlled mechanism.