Figure 2. The 1 Q agarose ethidium bromide gels showing the elcctrophoresis of solutions containing 60 p M pSport1 DNA with (A) no ruthenium and with 20 p M [R~"(tpy)(bipy)OH~](CIO~)~ electrolyzed a t 0.8, V for (B) 15 min, (C) 30 min, and (D) 1.5 h, (E) shows 60 p M pSport1 with no ruthenium, and (F) shows 60 pM pSport1 that has been electrolyzed at 0.8 V in the absence of metal complex for 2 h, (G) shows 60 p M pSportl incubated at 25 " C with 0.2 mM [Ru"(tpy)(bipy)-OH2](C10,)2 for 1 h, and (H) shows 60 p M pSport1 incubated with 0.2 m M [R~'~(tpy)(bipy)O](ClO~)~ for 1 h. Molecular weight markers are from DRIgest 111 (A DNA-Hind III/&YI74-Hae 111 digest) purchased from Pharmacia. mograms with and without DNA are given in the supplementary material)?JO In oxidations of small molecules, controlled potential electrolysis at 0.8 V of R~"(tpy)(bipy)OH~~+ leads to electrocatalytic conversions mediated by the Ru(IV) form.' Similarly, controlled potential electrolysis at 0.8 V of solutions containing DNA and Rd1(tpy)(bipy)OHz2+ leads to nearly complete conversion of the supercoiled DNA to the nicked circular form in 1.5 h (Figure 2, lane D).IlJ2 Addition of Ru'"(tpy)(bipy)@+ directly to the DNA effects conversion to form I1 (lane H). In control (9) Cyclic voltammetry was performed at 0.32 cm2 tindoped indium oxide working electrodes as previously described (Thorp, H. H.; Brudvig, G. W.; Bowden, E. F. J. Electrwnal. Chem. 1990, 290. 293) with a PAR 273A potentiatat and PAR Model 270 software. (IO) The addition of DNA to solutions of Ru"(tpy)(bipy)OH?+ causes decreases in peak currents in the cyclic voltammogram indicative of binding of the complex to the DNA. Importantly, peak currents in the cyclic voltammograms taken with and without DNA exhibit a linear dependence on the square root of the sweep rate, showing that adsorption of the complex or the DNA on the electrode dots not occur. For detailed discussions of the effects of DNA binding on the cyclic voltammetry of metal complexes, see: (a) Carter, M. T.; Rodriguez, M.; Bard, A. J. J. Am. Chem.Sm. 1989,III,8901. (b) Carter, M. T.; Bard, A. J. J. Am. Chem. Sm. 1987,109,7528. (c) Carter, M. T.; Bard, A. J. Biuconjugate Chem. 1990, I , 257.(1 1) Solutions were electrolyzed in the same cell used for cyclic voltammetry and stirred by bubbling buffer-saturated N2 through the solution. Fractions were loaded onto 1 % agarose gels containing ethidium bromide and