Dinuclear cobalt(II) complexes of Schiff-base compartmental ligands: Syntheses, crystal structure and bio-relevant catalytic activities

Three dicobalt(II) complexes, namely [Co2(L1H)(H2O)2(OAc)2](OAc)2 (1), [Co2(L2)(H2O)2(OAc)2](OAc) (2) and [Co2(L3)(H2O)2(OAc)2](OAc) (3) of the p-cresol based ‘‘end-off’’ compartmental ligands 2,6-bis(R-iminomethyl)- 4-methyl-phenolato, where R = N-ethylpiperazine for L1, 2-ethylpyridine for L2 and N-ethylpiperidine for L3, have been synthesized and characterized by common physicochemical techniques, and in the case of complex 1 also by single crystal X-ray diffraction analysis. All the complexes show excellent catecholase-like activity, monitored not only with 3,5-di-tert-butylcatechol but also with tetrachlorocatechol, a substrate reluctant to be oxidized. To the best of our knowledge, to date no cobalt complex has been found in the literature to manifest such activity. The complexes are observed to interact efficiently with CT-DNA and on incubation (employing plasmid pTZ57/R/T DNA) they exhibit concentration dependent DNA cleavage activity. The mechanisms related to the DNA cleavage and catecholase-like activities have been investigated. The cytotoxicity of the complexes has also been examined through an MTT assay.