Abstract/Summary

The new complexes [Ru(TAP)2(11-CN-dppz)]2+, [Ru(TAP)2(11-Br-dppz)]2+and [Ru(TAP)2(11,12-diCN-dppz)]2+ are reported. The addition of nitrile substituents to the dppz ligand of the DNA photooxidising complex [Ru(TAP)2(dppz)]2+ promote π-stacking interactions and ordered binding to DNA, as shown by X-ray crystallography. The structure of -[Ru(TAP)2(11-CN-dppz)]2+ with the DNA duplex d(TCGGCGCCGA)2 shows, for the first time with this class of complex, a closed intercalation cavity with an AT base pair at the terminus. The structure obtained is compared to that formed with the 11-Br and 11,12-dinitrile derivatives, highlighting the stabilization of syn guanine by this enantiomer when the terminal basepair is GC. In contrast the AT basepair has the normal Watson-Crick orientation, highlighting the difference in charge distribution between the two purine bases and the complementarity of the dppz-purine interaction. The asymmetry of the cavity highlights the importance of the purine-dppz-purine stacking interaction.