Redox Mediation and Photomechanical Oscillations Involving Photosensitive Cyclometalated Ru(II) Complexes, Glucose Oxidase, and Peroxidase

摘要

Intact photosensitive cyclometalated Ru~II derivatives of 2-phenylpwidine or N,N-dimethylbenZylamine cis-[Ru(C~N)(LL)X_2]PF_6 [C~N = o-C_6H_4-py or o-C_6H_4CH_2NMe_2; LL = 1,10-phenanththroline (phen), 2,2'-bipyrindine (bpy), or 4,4'-Me_2-2,2'-bipyridine (Me_2bpy); X = MeCN or pyridine (py)] are efficient mediators of glucose oxidase (GO) from Aspergillus niger and horseradish perotidase (HRP). Their redox potentials in an aqueous buffer are in the range 0.15--0.35 V versus SCE, and the rate constants for the oxidation GO(red) (where red indicates reduced) by the electrochemically generated Ru~III species equal (1.7--2.5) x 10~6 M~-1 s~-1 at pH 7 and 25 deg C. The redox potentials of all complexes decrease cathodically by 0.4--0.6 V upon irradiation by visible light because of the photoinduced solvolysis Of acetonitrile or py ligands. These in situ generated species display an even better mediating performance the HRP, although their behavior toward GO is different. The loading of a ruthenium unit into the protein interior brings about large catalytic currents in a self-assembled system GO--Ru--D-glucose. The estimated rate constant for intramolecular electron transfer from FADH_2 of the active site at Ru~III, k_intra, equals 4.4 x 10~3 s~-1. This suggests that the distance between the redox partners is around 19 A. The value of 21 A was obtained through the docking analysis of a possible closest-to-FAD localization of a Ru-containing fragment derived from the irradiated complex cis-[Ru(o-C_6H_4-py)(phen)(MeCN)_2]PF_6. The operational stability of the GO-Ru assemblies depends on the nature of complex used, the highest being observed for cis-[Ru(o-C_6H_4-py)(Me_2-bpy)(MeCN)_2]PF_6 (2). UV-vis studies of interaction of 2 with GO revealed photomechanical oscillations in the system GO--Ru--D-glucose. When irradiated complex 2 is mixed with GO and D-glucose, the absorbance at 510 nm increases because of the enzymatic reduction of Ru~III to Ru~II.