ligand. This behaviour reflects slow-to-medium exchange on the NMR timescale, indicative of a strong binding event where the dissociation rate of the complex is slow in comparison to the difference in frequencies between the free and bound resonances. ligand. These results demonstrate that in the planar E form, the ligand is able to efficiently stack with the top G-tetrad, between the G4/duplex junction, whilst it does not have strong affinity for the lower G-tetrad.