Ferrocenyl chalcone armed macrocyclic tet a-based cobalt(II) and copper(II) complexes: DNA photocleavage activity and photocytotoxicity

Ferrocenyl chalcone armed 'tet a' macrocyclic cobalt(II) and copper(II) complexes (1) and (2) were synthesised and characterised by various physico-chemical methodologies. The complexes exhibit Co(II)/Co(I) and Cu(II)/Cu(I) redox couple (quasi-reversible) with E-1/2 value of -0.82 and -0.82 V, respectively. Complex 1 is oxidised as quasi-reversible two-electron transfer processes with oxidation potential of E-pa(1) = 0.64 and E-pc(1) = 0.68 V, and complex 2 with oxidation potential of E-pa(1) = 0.62 and E-pc(1) = 0.66 V over 0.37 V of ferrocene was observed. The above scenario is indicating the positive charge destabilisation of mono- and dications originating a challenging condition for ferrocene oxidation. The DNA binding abilities of both the complexes (1 and 2) with calf thymus DNA (CT-DNA) were investigated by spectroscopic studies (absorption/fluorescence) and electrochemical methods. Absorption spectral studies revealed that complexes 1 and 2 bind with CT-DNA by partial intercalative mode of binding with K-b values of 1.04 x 10(6) and 7.29 x 10(5) M-1, respectively. Chemical nuclease activity is exhibited moderately in these complexes generating singlet oxygen (O-1(2)) species and acting as effective photocleavers of pUC19 DNA in the red light region. As irradiated by red light, their cytotoxicity toward MDA-MB-231 displays a typical increase in cytotoxicity values. In comparing the dark and red light irradiated cell, MDA-MB-231 cells that were exposed to red light exhibited significant morphological alternations. Cell morphological studies were confirmed the morphological changes with dual staining by using AO/EB, Hoechst 33342 and PI against MDA-MB-231 cells. Furthermore, complexes 1 and 2 have less toxicity on Artemia nauplii even at higher concentrations, indicating that the synthesised complexes 1 and 2 are biocompatible.

Automated summary

The synthesis and characterization of cobalt(II) and copper(II) complexes armed with ferrocenyl chalcone and a 'tet a' macrocyclic ligand were investigated. The complexes exhibited good redox properties and binding abilities to DNA, and showed potential for applications in DNA cleavage and cancer treatment.