Interaction of ruthenium(II)-dipyridophenazine complexes with CT-DNA: Effects of the polythioether ancillary ligands

Abstract

The complexes [Ru([9]aneSs)(dppz)Cl]Cl 1 and [Ru([12]aneS4)(dppz)]Cl2 2 ([9]aneS3=1,4,7-trithiaciclonone and [12]aneS4=1,4,7,10-tetrathiaciclododecane) were synthesised and fully characterised. These complexes belong to a small family of dipyridophenazine complexes with non-polypridyl ancillary ligands. Interaction studies of these complex with CT-DNA (UV/Vis titrations, steady-state emission and thermal denaturation) revealed their high affinity for DNA. Intercalation constants determined by UV/Vis titrations are of the same order of magnitude (106) as other dppz metallointercalators, namely [Ru(II)(bpy)2dppz]2+. Differences between 1 and 2 were identified by steady-state emission and thermal denaturation studies. Emission results are in accordance with structural data, which indicate how geometric distortions and different donor and/or acceptor ligand abilities affect luminescence. The possibility of non-covalent interactions between ancillary ligands and nucleobases by van der Waals contacts and H-bridges is discussed. Furthermore, complex 1 undergoes aquation under intra-cellular conditions and an equilibrium with the aquated form 1 is attained. This behaviour may increase the diversity of available interaction modes.