Electrochemical and DNA-binding properties of dipyridophenazine complexes of osmium(II)

A transition metal complex as an electrochemical probe of a DNA sensor must have an applicable redox potential, high binding affinity and chemical sta bility. Some complexes with the dipyrido[3,2-a:2 ' ,3 ' -c]phenazine (DPPZ) ligand have been reported to have high binding affinity for DNA. However, it was difficult to detect the targeted DNA electrochemically using these c omplexes because of the relatively high redox potential. In this work, a co mbination of bipyridine ligands with functional groups (-NH2, -CH3 and -COO H) and the DPPZ ligand were studied. The introduction of electron-donating groups was effective for controlling the redox potential of the DPPZ-type o smium complex. The [Os(DA-bPY)(2)DPPZ](2+) complex (DA-bpy; 4,4 ' -diamino- 2,2 ' -bipyridine) had a lower half-wave potential (E-1,E-2) of 147 mV (vs. Ag\AgCl) and higher binding affinity with DNA {binding constant, K = 3.1 x 10(7) M-1 in 10 mmol dm(-3) Tris-HCl buffer with 50 mmol dm(-3) NaCl (pH 7 .76)} than those of other complexes. With the single stranded DNA (ssDNA) m odified gold electrode, the hybridization signal (DeltaI) of the [Os(DA-bpy )(2)DPPZ](2+) complex was linear in the concentration range of 1.0 pg ml(-1 )-0.12 mug ml(-1) for the targeted DNA with a regression coefficient of 0.9 99. The detection limit was 0.1 pg ml(-1). (C) 2001 Elsevier Science B.V. A ll rights reserved.