Three Schiff base complexes based on diethylenetriamine: synthesis, structure, DNA binding and cleavage, and in vitro cytotoxicity

Cu(II) and Zn(II) complexes with Schiff bases derived from diethylenetriamine, [Cu(C22H23N5)(H2O)(ClO4)2] (1), [Cu(C14H18N4)(ClO4)](ClO4) (2), and [Zn(C10H17N5Cl)]4[ZnCl4]2·H2O (3), have been synthesized and structurally characterized. The interactions of the complexes with CT-DNA were investigated by electronic absorption, circular dichroism (CD), and fluorescence spectroscopies. All three complexes appear to bind to DNA via groove binding modes. The order of DNA binding strength was 2 > 1 > 3. The complexes proved to be capable of efficient cleavage of pBR322 DNA at micromolar concentrations in the presence of ascorbic acid as a reducing regent. The hydroxyl radical may be the reactive species, and H2O2 may be involved in DNA strand breakage induced by these complexes. Furthermore, in vitro cytotoxicities of the complexes against four human carcinoma cell lines (HepG2, MGC-803, EC9706, and MCF-7) were screened by MTT assays. Complex 2 shows potent activity against HepG2 and MGC-803 cell lines; for all four cell lines, the activities of the complexes follow the order: 2 > 1 > 3. Hence, the different anticancer activities of the complexes may be correlated with their DNA binding abilities.