Electrocatalytic oxidation of NADH at graphite electrodes modified with osmium phenanthrolinedione

We report here a detailed study concerning the electrochemical behavior of Os(4,4'-dimethyl, 2,2'-bipyridine)(2)(1,10-phenanthroline 5,6-dione) comple x, adsorbed on spectrographic graphite, and about its electrocatalytic acti vity for NADH oxidation. Cyclic voltammetric measurements, performed in aqu eous phosphate buffer solutions, at different scan rates and DH values, all owed us: (i) to relate the redox response of the o-quinone ligand (phendion e) to that of the Os(II) central ion; (ii) to confirm that, in aqueous solu tions, the phendione based redox process globally involves two electrons an d two protons; (iii) to estimate the rate constant for the heterogeneous el ectron transfer corresponding to the phendione redox couple (k(s) approxima te to 20.1 s(-1)). The second order rate constant for electrocatalytic oxid ation of NADH (k(1,[NADH]=0) = 1.9 x 10(3) M-1 s(-1), at pH 6.1) as well as its pH dependence (from pH 5.5 to 8.1) were evaluated from RDE experiments , using both Koutecky-Levich and Lineweaver-Burk data interpretations. (C) 1999 Elsevier Science S.A. All rights reserved.