AN ANALYTICAL STUDY OF THE REDOX BEHAVIOR OF 1,10-PHENANTHROLINE-5,6-DIONE, ITS TRANSITION-METAL COMPLEXES, AND ITS N-MONOMETHYLATED DERIVATIVE WITH REGARD TO THEIR EFFICIENCY AS MEDIATORS OF NAD(P)(+) REGENERATION

The synthesis as well as the chemical and electrochemical properties o f homoleptic and heteroleptic (trispyridyl-methylamine as coligand) tr ansition-metal complexes (Ru and Co) of 1,10-phenanthroline-5,6-dione (PD) and of its N-monomethylated derivative (PDMe+) are described. In particular, their ability to abstract hydride ions was studied. Electr ochemical investigations with cyclic voltammetry, rotating disk electr ode experiments, and spectroelectrochemical methods at different pH va lues gave an insight into the complex electrochemistry of the compound s described, which is strongly influenced by a hydration pre-equilibri um. The electrochemically active quinone form of the transition-metal complexes can be reduced to the hydroquinone state in acidic solution and to their transition-metal-stabilized semiquinone states for neutra l and basic solutions, whereas PDMe+ is reduced to the hydroquinone st ate in both acidic and neutral solutions. The compounds can also be re duced chemically, and are efficient catalysts for the indirect oxidati on of the enzymatic cofactor NAD(P)H, For the indirect aerobic NAD(P)H oxidation, up to 900 turnovers per hour can be observed, an achieveme nt yet to be reached by other catalyst systems.