Synthesis, properties, and biosensor applications of cycloruthenated 2-phenylimidazoles

Abstract

The cycloruthenation of 2-phenylimidazole (phim) by [Ru(η 6-C 6H 6)(μ-Cl)Cl] 2 in acetonitrile in the presence of NaOH has been carried out. The unstable intermediate [Ru(phim)(MeCN) 4]PF 6 formed has been converted into the complexes [Ru(phim)(4,4′-Me 2bpy)(MeCN) 2]PF 6 ( 2) and [Ru(phim)(LL) 2]PF 6 ( 3, LL=phen ( a), bpy, 4,4′-Me 2bpy), which were characterized by the mass-spectrometry, 1H-NMR spectroscopy, UV–vis spectrophotometry, and cyclic voltammetry. The Ru II/III redox potentials of complexes 3 equal 130–250 mV (vs. Ag–AgCl) at pH 7 (0.01 M phosphate). Such potential range is favorable for fast exchange of electrons with the active sites of redox enzymes. In fact, the second-order rate constant for the oxidation of reduced glucose oxidase (GO) from Aspergillus niger by the electrochemically generated Ru III derivative of complex 3a equals (8.1×10 6 M −1 s −1). The second-order rate constant for the oxidation of 3a by the Compound II of horseradish peroxidase is 9.3×10 7 M −1 s −1. Complexes 3 were used as mediators for the fabrication of enzyme electrodes by simple co-adsorbing with GO or horseradish peroxidase on graphite electrodes. These electrodes were tested in flow-injection systems and showed linear responses in the range of d-glucose and H 2O 2 concentrations 0.1–30 mM and 1–200 μM, respectively. The new mediators reported herein seem promising for the construction of amperometric biosensors based on GO, horseradish peroxidase, and similar enzymes.