ADSORPTION DEPOSITION OF THE LIGANDS 9,10-PHENANTHROLINE-5,6-DIONE AND 9,10-PHENANTHROLINE-5,6-DIOL AND THEIR METAL-COMPLEXES ON PYROLYTIC-GRAPHITE ELECTRODES/
Ml. Shi et Fc. Anson, ADSORPTION DEPOSITION OF THE LIGANDS 9,10-PHENANTHROLINE-5,6-DIONE AND 9,10-PHENANTHROLINE-5,6-DIOL AND THEIR METAL-COMPLEXES ON PYROLYTIC-GRAPHITE ELECTRODES/, Analytical chemistry, 70(8), 1998, pp. 1489-1495
Metal complexes of the electroactive ligand 9,10-phenanthroline-5,6-di
one (pdon) are receiving extensive study because of their demonstrated
potential as electrocatalysts for the oxidation of NADH and other sub
strates. In aqueous media, the reduced ligand, 9,10-phenanthroline-5,6
-diol (pdol), and its complexes with transition metals are only slight
ly soluble and tend to accumulate on the surfaces of electrodes, where
they are generated by reduction of pdon. The adsorbed (or precipitate
d) molecular layers can interfere with the continued electroreduction
of the more soluble, oxidized precursors from which they are generated
. The use of freshly cleaved basal plane pyrolytic graphite electrodes
allowed the surface coordination chemistry and electrochemistry of pd
on, pdol, and their complexes to be inspected in more detail than in p
revious studies. The results revealed several general trends: (i) Coor
dination of pdon to transition metals shifts its reduction potential t
o more positive values. (ii) The affinity of the dipositive form of tr
ansition metal redox couples for pdon is greater than that of the trip
ositive form by a factor that exceeds the corresponding affinities for
9,10-phenanthroline. (iii) Pdol and its complexes are much less solub
le in aqueous media than are pdon and its complexes. (iv) Complexes of
pdon are much less strongly adsorbed on graphite than is the free lig
and in both its protonated and unprotonated forms.