A comparative study of cytotoxicity and interaction with DNA/protein of five transition metal complexes with Schiff base ligands

•Five transition metal complexes were synthesized and characterized.•In vitro cytotoxicities of all compounds were tested against five cancer cell lines.•DNA/BSA interactions of all compounds were studied.

Five transition metal complexes NiL12 (1), CuL12 (2), ZnL12 (3), [MnL12(N3)]n·nCH2Cl2 (4), CuL22 (5) {HL1 = 3-{[2-(2-hydroxy-ethoxy)-ethylimino]-methyl}-naphthalen-2-ol, HL2 = 2-{[2-(2-hydroxy-ethoxy)-ethylimino]-methyl}-phenol} have been synthesized and fully characterized. In all of the complexes, the ligands coordinated to the metal ion in a negative fashion via O and N donor atoms. The X-ray structures of nickel complex 1 and copper complexes 2 and 5 are four-coordinated monomers and show slightly distorted square-planar geometry in the vicinity of the central metal atom. Zinc complex 3 exhibits a four-coordinated tetrahedral structure. Differently, manganese complex 4 reveals a six-coordinated octahedral structure, one-dimensional chain is linked by azide in the end-to-end mode. In vitro cytotoxicity of these complexes to various tumor cell lines was assayed by the MTT method. The results showed that most of these metal-Schiff base complexes exhibited enhanced cytotoxicity than Schiff base ligands, which clearly implied a positive synergistic effect. Moreover, these complexes appeared to be selectively active against certain cell lines. The interactions of these metal complexes with CT-DNA were investigated by UV–vis, fluorescence and CD spectroscopy, the results indicated that these complexes are metallointercalators and can interact with CT-DNA. The study of interaction between complexes and BSA indicated that all of the complexes could quench the intrinsic fluorescence of BSA in a static quenching process.