The interaction of Schiff Base complexes of nickel(II) and zinc(II) with duplex and G-quadruplex DNA

The duplex and G-quadruplex DNA-binding of six nickel(II) and zinc(II) complexes of three salphen-like ligands (salphen = N,N′-bis-salicylidene-1,2-phenylenediaminato) was investigated by UV–visible absorption and circular dichroism spectroscopy. The results obtained, in particular the values of the DNA-binding constants, Kb, point out that the nickel(II) complexes show a higher affinity toward both duplex and G-quadruplex DNA, compared to the analogous zinc(II) complexes. Interestingly, the zinc(II) complexes possess high selectivity toward G-quadruplex DNA, being negligible their binding with duplex DNA. Molecular dynamics (MD) simulations provided atomistic models for the interpretation of the binding of the zinc(II) complexes with G-quadruplex DNA, allowing a structural comparison of the three salphen-like ligands, due to the presence of different substituents (H, F, CF3) on the position 4 of the phenyl ring on the N,N′ bridge.