Distribution of Metal Complexes Bound to DNA Determined by Normal Pulse Voltammetry

The effects of DNA binding on the normal pulse voltammetry of metal complexes have been investigated. Studies were performed both for oxidation of OsL32+/3+ and for reduction of CoL33+/2+ (L is bpy = 2,2‘-bipyridine or phen = 1,10-phenanthroline). The diffusive current obtained from voltammograms at potentials well past E1/2 gives an accurate measure of the extent to which the complexes codiffuse with DNA or are free in solution, and this response is not affected by kinetic factors resulting from slow heterogeneous electron transfer. Analysis of the diffusion-limited current using the appropriate binding isotherm provides binding constants in good agreement with those measured by other methods. For the bpy complexes, the ionic strength dependence, the relative binding constants for the 2+ and 3+ forms, and the associated change in E1/2 upon DNA binding are in good agreement with the predictions of polyelectrolyte theory where the 3+ ion binds more strongly. For the phen complexes, the reverse trend is obs...