Interaction of Cr(diimine)33+ complexes with DNA

Luminescence spectroscopy coupled with capillary electrophoresis (CE) provides insight into the nature and stereoselectivity of Cr(diimine)(3)(3+) interactions with polynucleotides. Photoluminescence measurements on Cr(phen)(3)(3+) and Cr(bpy)(3)(3+) in air or N-2-saturated solution demonstrate strong B-DNA quenching of Cr(diimine)(3)(3+) emission intensities and lifetimes. Both dynamic and static quenching are observed, the latter being attributed to DNA bound Cr(diimine)(3)(3+). Very rapid quenching is also observed with deoxyguanosine monophosphate (dGMP), while no bimolecular quenching is observed with other mononucleotides. Likewise, poly(dG-dC).poly(dG-dC) causes rapid quenching, while only minor quenching is observed for poly(dA-dT).poly(dA-dT). These emission results are consistent with a DNA quenching mechanism involving guanine base oxidation. The electropherogram resulting from the co-injection of rac-Cr(phen)(3)(3+) and rac-Ru(phen)(3)(2+) into a capillary containing B-DNA indicates a similar binding constant for the two complexes, while the enantiomeric stereoselectivities are reversed. CE studies for Ru(phen)(3)(2+) with distamycin A (an AT selective minor groove binder) reveal a significant reduction in complex migration times and a complete loss of enantiomeric discrimination. These results are consistent with a literature model where nonelectrostatic binding for both isomers occurs in the minor groove. Analogous distamycin studies with Cr(phen)(3)(3+) are also in accord with minor groove binding.