Electrochemical studies of Ru(II) diimine bioconjugates

The electrochemical behavior of the ruthenium(II) diimine complexes [Ru(CO)(CF₃CO₂)(dppene)(5-R-phen)][PF₆] (dppene = 1,2-diphenylphosphinoethene; phen = 1,10-phenanthroline; R = H, 1; R = NH₂, 2; R = cholestoryl carbamate, 3; R = 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, 4), [Ru(CO)(H)(4,4′-R-bpy)(R′Ph₂P)₂][PF₆] (bpy = 2,2′-bipyridine; R = H, R′ = Ph, 5; R = H, R′ = 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, 6; R = 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, R′ = Ph, 7), [Ru(bpy)₂(5-R-phen)][PF₆]₂ (R = NH₂, 8; R = cholestoryl carbamate, 9; R = 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, 10) is reported. Complexes 1-6 give cyclovoltammetric (CV) responses with multiple ill-defined reduction waves and one oxidation wave, all of which were chemically irreversible. Complexes 5 and 7, containing axially coordinating phosphines, showed reversible oxidation and reduction CV responses, while 6 showed redox waves similar to 3. Complexes 8-10 show a metal-centered irreversible oxidation around +1.4 V that, in the case of 8 and 9, is heavily modified by adsorption phenomena. In the negative part of the CV, 9 and 10 show a single chemically and electrochemically reversible 1e^- reduction both at E°′ = -1.29 V, about 500 mV cathodically shifted with respect to 8. The interactions of complexes 1 and 2 with bovine serum albumin (BSA) and double stranded DNA (ds-DNA) were also studied by electrochemical methods. Both complexes showed strong binding to BSA. Evidence for intercalation of both complexes with DNA is presented, with 1 showing a stronger interaction than 2.