Electrochemical Investigations of the Interaction of Metal Chelates with DNA. 3. Electrogenerated Chemiluminescent Investigation of the Interaction of Tris (1,10-phenanthroline) ruthenium (II) with DNA

The electrogenerated chemiluminescence (ECL) that results from the oxidation of tris(1,10-phenanthroline) ruthenium (II), at a gold electrode in the presence of oxalate, was used to investigate the interaction of the Ru(II) chelate with calf thymus DNA. The decrease in ECL emission from the excited state, Ru(phen)(3)(2+)*, in the presence of DNA, is ascribed to binding of the chelate to the DNA strand. An ECL titration of the metal complex with DNA allowed determination of the equilibrium constant (K) and binding-site size (s) for association of Ru(phen)(3)(2+), under the assumption that only the free metal complex contributes to the observed emission. In 25 mM Na(2)C(2)O(4), 2 mM phosphate buffer, pH 5,0.05% Tween-20, 0.05% Triton X-100, regression based on the McGhee/von Hippel model, which accounts for free base pair gaps between binding sites, yielded K = 8.1 (+/- 0.2) X 10(3) M(-1) and s = 4 bp.