Substituent Effects on the Biological Properties of Zn-Salophen Complexes

The synthesis, characterization, and luminescent properties of a series of 5,5′-X-substituted salophen ligands, X= OCH₃, Br, and NO₂, and the corresponding Zn­(II) complexes are reported here. Their biological activity has been analyzed and related to the different Lewis acid character of the complexes. In vitro studies (AFM and absorption and emission titrations) show that the strongest interaction with free plasmid DNA is observed for 5,5′-dinitro-substituted Zinc-salophen complex 3b. Semiempirical theoretical calculations together with redox potential measurements suggest that this might be interpreted as a direct consequence of this compound having the hardest Lewis acid character. Cellular uptake and cytotoxicity studies undertaken with these metal complexes show that they enter the cells but are not cytotoxic.