2-Phenylpyridine ruthenacycles as effectors of glucose oxidase activity: inhibition by RuII and activation by RuIII

Cyclometalated Ru II derivatives of 2-phenylpyridine (Hphpy) [Ru(phpy)(bpy) 2 ]Cl ( 1a ) and [Ru(phpy)(phen) 2 ]Cl ( 1b ) (bpy is 2,2′-bipyridine, phen is 1,10-phenanthroline) behave as noncompetitive inhibitors of glucose oxidase from Aspergillus niger in the enzyme-catalyzed oxidation of d -glucose by O 2 into the corresponding lactone at pH 5.0 and 25 °C. The enzymatic activity has been measured by monitoring the O 2 consumption. The inhibition constants K i are 0.036 and 0.017 M for 1a and 1b , respectively, indicating that 1b inhibits the enzymatic activity more efficiently than 1a . The well-known coordination compound [Ru(bpy) 3 ]Cl 2 ( 2 ) behaves, in contrast, as a competitive inhibitor, with K i = 0.018 M under the same conditions. The monophasic consumption of O 2 in the case of 1a , 1b , and 2 is replaced by a distinct two-phase kinetics in the presence of the cyclometalated Ru III compound [Ru(phpy)(bpy) 2 ]Cl 2 ( 3 ), which was obtained from 1a in the presence of a large excess of H 2 O 2 and the iron TAML activator. Interestingly, the rates of the first and the second phases are influenced by 3 in a different way. The rate of the first phase is noticeably higher in the presence of Ru III , although the dependence is nonmonotonic and maximal acceleration is observed at the lowest loadings of 3 . The rate of the second phase decreases monotonically on increasing the concentration of the ruthenium complex in solution. The nonmonotonic action of 3 was confirmed by using the doubly cyclometalated Ru III derivative [Ru(phpy) 2 (bpy)]Cl. The diverse rate variations induced by 3 accounted for acceleration by Ru III of the O 2 reduction by the reduced form of glucose oxidase during the first phase, which ceases after the enzymatic reduction of Ru III to the Ru II species, the latter behaving similarly to 1a as the inhibitor of the enzyme.