DNA binding of an organic dppz-based intercalator

An improved synthesis of a water-soluble derivative of dipyrido[3,2-a:2',3'-c]phenazine (dppz) is reported. The structures of both dppz and the cation ethylene-bipyridyidiylium-phenazine dinitrate {[1][(PF6)(2)]} have been obtained via X-ray crystallography. Metal complex derivatives of dppz are very well studied. However, using the water soluble [1][(NO3)(2)], the nature of the interaction of a simple dppz unit with duplex DNA has been investigated for the first time. In both organic solvents and water, 1 displays unstructured luminescence, assigned to an intramolecular charge transfer. The emission is quenched on binding to natural and synthetic duplex DNA, including poly(dA)(.)poly(dT). A variety of techniques reveal that the cation binds to DNA with an affinity comparable to those of many metal dppz complexes, via an intercalative binding mode.