| Using a variety of octahedral transition metal complexes DNA charge transport (CT) has been probed. Interactions with DNA by a family of ruthenium(II) complexes bearing the dipyridophenazine (dppz) ligand or its derivatives have been examined. A direct correlation between the amount of guanine oxidation and the strength of intercalative binding was observed. Electronic access to the DNA base pairs, provided by intercalation of the oxidant, is a prerequisite for efficient CT through the DNA pi-stack.; The flash/quench technique was applied in probing CT in DNA assemblies containing a tethered ruthenium intercalator and methylindole (M), a low potential nucleobase analog, where radical formation could be examined both by laser spectroscopy and biochemical methods. Hole injection and subsequent formation of the M radical cation were observed at a distance of over 30 A at rates ≥107 s-1 in assemblies containing no guanine bases intervening the ruthenium intercalator and M. Critical is the sequence at the injection site; this sequence determines initial hole localization and hence the probability of hole propagation.; DNA assemblies containing a pendant Ru(II)-dppz complex along with two oxidative traps, a site containing M and a 5'-GGG-3 ' site, were constructed to explore charge equilibration across the duplex. The 5'-GGG-3' site is effective in competing for the migrating charge; importantly, switching the orientation of the two trapping sites does not affect the yield of oxidized products at either site. Therefore, in DNA both forward and reverse charge transport occur so as to provide equilibration across the duplex on a time scale that is fast compared to trapping at a particular site.; DNA conjugates containing adjacent duplex and guanine quadruplex assemblies have been designed to explore CT into quadruplex architectures. Using an intercalating rhodium photooxidant oxidizing radicals are found to be trapped in the folded quadruplex. The data indicate that in the conjugates examined, the guanine quadruplex provides a more effective trap than a 5'-GG-3 ' guanine doublet within duplex DNA. |
