CHIRAL DISCRIMINATION IN THE BINDING OF TRIS(PHENANTHROLINE)RUTHENIUM(II) TO CALF THYMUS DNA - AN ELECTROCHEMICAL STUDY

The binding of Delta-, Lambda-, and rac-[Ru(phen)(3)](2+) (phen = 1,10 -phenanthroline) and Delta-, Lambda-, and rac-[Ru-bpy)(3)](2+). (bpy 2 ,2'-bipyridyl) with calf thymus DNA has been examined by cyclic and di fferential pulse voltammetric techniques to obtain structural insight into the noncovalent binding of the enantiomers to DNA. The insignific ant shift in Ru-II/Ru-III peak potentials on the addition of DNA sugge sts that both the oxidized and reduced forms bind to DNA to the same e xtent. Interestingly, DNA selectively decreases the peak currents of D elta-[Ru(phen)(3)](2+) but not those of the Lambda-enantiomer; rac-[Ru (phen)(3)](2+) exhibits an intermediate behavior, thus suggesting that the Delta-form exhibits significant selectivity for B-DNA. The bindin g constants (K-2+) and binding site sizes (s) have been determined fro m the decrease in the peak currents. The binding constant (K-2+) of De lta-[Ru(phen)(3)](2+) is on the order of 10(4) M(-1) which is less tha n that for proven intercalators. In contrast, the electrochemical beha vior of all three forms of [Ru(bpy)(3)](2+) remains almost unaffected in the presence of DNA, suggesting that the complexes might reside on the hydrophilic coat of the DNA helix.