Crystallographic binding modes of octahedral transition metal complexes to duplex DNA

Octahedral transition metal complexes are increasingly recognised as useful tools for the development of complex cations that recognise and interact with specific DNA sequences and higher-order DNA topologies. The versatility and diversity of these complexes is particularly due to their rich photophysical and electrochemical properties at the octahedral metal centre, which can be modulated by changing the surrounding ligands. While X-ray crystallography provides uniquely direct structural information on metal-DNA binding, it is one of several essential approaches; solution-state methods such as NMR and complementary biophysical studies are critical for defining predominant binding modes in solution and in biologically relevant environments. Here, we present an overview of the different binding modes of some of these octahedral transition metal complexes with DNA, emphasising the structural and biophysical studies employed to understand metal complex-DNA interactions.