Electrocatalytic oxidation of NADH at glassy carbon electrodes modified with transition metal complexes containing 1,10-phenanthroline-5,6-dione ligands

The preparation and electrochemical characterization of glassy carbon electrodes modified with 1,10-phenanthroline-5,6-dione (phen-dione) complexes of transition metals including [M(phen-dione)(3)](2+) (M = Fe, Ru, Co, Cr, Ni), [Re(phen-dione)(CO)(3)Cl], and [Ru(v-bpy)(2)(phen-dione)](PF6)(2) (v-bpy is 4 vinyl-4'-methyl-2,2'-bipyridine) as well as their behavior as electrocatalysts toward the oxidation of NADH are described, The above-mentioned materials could be deposited by electrochemical deposition or electropolymerization. The resulting modified electrodes exhibited redox responses very similar to those of the complexes in solution, including the ps-dependent response ascribed to the pendant o-quinone groups. ?he deposited films also showed potent and persistent electrocatalytic activity toward NADH oxidation, In all cases, NADH oxidation took place at potentials around 0.0 V vs SSCE, which represents a dramatic diminution in the overpotential, In addition, interference effects due to ascorbate could be significantly decreased. Of all the materials tested, the [Fe(phen-dione)(3)](2+) complex was found to have the highest activity toward NADH oxidation, The kinetics of the catalytic reaction were characterized by using cyclic voltammetry and rotated disk electrode techniques, and a value of (6.2 +/- 0.6) x 10(3) M(-1) s(-1) was obtained for electrodes modified with this complex. Moreover, this complex exhibited the best stability as determined from the time dependency of the decay of its redox activity. Using these observations as a point of departure, we have developed an ethanol biosensor based on the enzymatic activity of immobilized (on a nylon mesh) alcohol dehydrogenase, coupled with the electrocatalytic oxidation of NADH.