ELECTROCHEMICAL STUDIES OF THE INTERACTION OF METAL-CHELATES WITH DNA .4. VOLTAMMETRIC AND ELECTROGENERATED CHEMILUMINESCENT STUDIES OF THE INTERACTION OF TRIS(2,2'-BIPYRIDINE)OSMIUM(II) WITH DNA

Cyclic voltammetric and electrogenerated chemiluminescentdata were used to study the binding of trls(2,2′-blpyrldlne)-osmkim(II), Os(bpy)32+, an electrostatic binder, to calf thymus DNA. The oxidized form of the osmium complex, Os-(bpy)33+, has a stronger association to DNA than the reduced form, Os(bpy)32+, as indicated by the negative shift of E° of the CV waves (k3+/k2+ = 3.35). The calculated binding constant, K2+, and binding site size, s, for the Os(bpy)32+− DNA system depended slightly on whether a mobile or a static equilibrium was assumed. In 10 mM NaCI, 10 mM Tris pH 7, K2+ = (7.3 ± 0.4) × 103 M−1 and s = 3 base pairs (mobile) and K2+ = (5.0 ± 0.2) × 103 M−1 and s = 3 base pairs (static). Electrogenerated chemiluminescence (ECL) was produced upon oxidation of Os(bpy)32+ at a Pl electrode in a solution containing 10 mM C2O42− and 10 mM phosphate at pH 5. Addition of DNA caused a decrease in the emission intensity (I); a plot of I vs relative DNA concentration yielded K2+ = (6.5 ± 0.5) × 103 M−1 and s = 3 base pairs. The osmium complex produced ECL when bound to the DNA molecule with an efficiency of 30% that of the unbound chelate. © 1990, American Chemical Society. All rights reserved.