Electrocatalysis at a conducting composite electrode doped with a ruthenium(II) metallodendrimer

A pentaerythritol-based metallodendrimer with Ru(II)terpyridine units was synthesized and tested as a mediator for the electrochemical oxidation of methionine (L-Met), cystine (L-Cys), and As-III. A reversible oxidation of Ru-II was observed with the metallodendrimer as a solute in mixed acetonitrile-water solvents and as a component of carbon-based conducting composite electrodes. Mediated oxidation of the test species was observed. In aqueous solution, the composite electrode yielded a cyclic voltammetric peak current for the oxidation of L-Met in a 0.1 M phosphate buffer (pH 7.0) at 1.1 V vs Ag/AgCl. This anodic process was employed for amperometric detection in a now system. Linear calibration curves were obtained over the range 1.0-10 mu M Met and Cys. Using the criterion of the concentration yielding a signal 3 times the uncertainty of a blank, detection limits of 0.6 and 0.5 mu M were calculated for Met and Cys, respectively. The slopes with three nominally identical electrodes varied by 10%.