Salphen metal complexes as tunable G-quadruplex binders and optical probes

A series of seven new metal complexes (metal = NiII, CuII, PtII and VO2+) with substituted salphen ligands have been prepared and their duplex and G-quadruplex DNA affinities determined. The selectivity of the complexes towards a given DNA topology is dictated by several factors including geometry, overall charge and substitution pattern of the complex. We also show that the two platinum(II)–salphen complexes developed as part of this series are emissive. Confocal microscopy studies were carried out with these two complexes using four different cell lines (CHO, HeLa, U2OS and HepG2). These studies showed that the cell permeability and localization are different for the two probes and highly dependent on the cell line used.