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

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Abstract
Cyclic voltammetric and electrogenerated chemiluminescent data were used to study the binding of tris(2,2''-bipyridine)-osmium(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.degree.'' 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 NaCl, 10 mM Tris pH 7, K2+ = (7.3 .+-. 0.4) .times. 103 M-1 and s = 3 based pairs (mobile) and K2+ = (5.0 .+-. 0.2) .times. 103 M-1 and S = 3 base pairs (static). Electrogenerated chemiluminescence 9ecl0 was produced upon oxiation of Os(bpy)32+ at a Pt 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) .times. 103 M-1 and s = base pairs. The osmium complex produced ECL when bound to the DNA molecule with an efficiency of 30% that of the unbound chelate.