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

Abstract

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 E1/2 value of −0.82 and −0.82 V, respectively. Complex 1 is oxidised as quasi‐reversible two‐electron transfer processes with oxidation potential of E1pa = 0.64 and E1pc = 0.68 V, and complex 2 with oxidation potential of E1pa = 0.62 and E1pc = 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 Kb values of 1.04 × 106 and 7.29 × 105 M−1, respectively. Chemical nuclease activity is exhibited moderately in these complexes generating singlet oxygen (1O2) 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.