Cationic porphyrin–anthraquinone dyads: Modes of interaction with G-quadruplex DNA

The interaction of a parallel, guanine quadruplex DNA with four, cationic porphyrin–anthraquinone dyads which comprise bridging linkages of differing lengths, was investigated for the first time. Using a combination of absorption and fluorescence titration, surface-enhanced Raman spectroscopy and induced circular dichroism spectroscopy as well as Job plot, it was found that the porphyrin and anthraquinone moieties in the dyads equipped with long linkages are able to bis-intercalate with the G4 structure whereas dyads that contain short linkages were unable to undergo such interaction. In addition, cationic dyads that contain long linkages are able to stabilize the quadruplex structure to a greater extent than dyads with shorter linkages.