Interactions of glucose oxidase with various metal polypyridine complexes as mediators of glucose oxidation

The interaction between glucose oxidase (GOx) and a typical metal complex, which is chemically stable in both oxidized and reduced forms, has been investigated by a voltammetric method. The evaluation of an electron-transfer mediator useful for glucose oxidation is discussed from thermodynamic and kinetic points of view, i.e. the redox potentials of various metal complexes and the second-order rate constants for the electron transfer between GOx in reduced form and the metal complexes in oxidized form. No mediation of glucose oxidation by [Co(bpy)(3)](2+) (bpy=2,2'-bipyridine) or [Cu(bpy)(2)](2+) occurred, in spite of their appropriate redox potentials. This was attributed mainly to the lower electron-self-exchange rates of the mediator and the reaction with GOx. All three types of osmium(II) complexes, [Os(PP) (n)](2+) ( n=2 or 3; PP=polypyridine), [OsL(2)(PP)(2)](2+) (L=imidazole and its derivatives), and [OsClL(bpy)(2)](+), acted as excellent electron-transfer mediators for the glucose oxidation. Mixed ligand complexes, [OsL(2)(PP)(2)](2+) and [OsClL(bpy)(2)](+), have been concluded to be more efficient electron-transfer mediators. The electron-transfer rates between the mediator and GOx have been found to be accelerated by intermolecular electrostatic interactions or hydrogen bonds.