N-substitution in isatin thiosemicarbazones decides nuclearity of Cu(II) complexes – Spectroscopic, molecular docking and cytotoxic studies

The mono- (1) and bi-nuclear (2) copper(II) complexes containing N-substituted isatin thiosemicarbazone(s) were synthesized, and characterized by analytical and spectroscopic (UV–Visible, FT-IR and EPR) techniques. Bimetallic nature of complex 2 was confirmed by single crystal X-ray crystallography. The structures predicted by spectroscopic and crystallographic methods were validated by computational studies. From the spectroscopic, crystallographic and computational data, the structures were found to be distorted square planar for 1 and distorted square pyramidal for 2. Molecular docking studies showed hydrogen bonding and hydrophobic interactions of the complexes with tyrosinase kinase receptors. Complex 1 exhibited promising cytotoxic activity against Jurkat (leukemia) cell line, and complex 2 displayed more activity against HeLa S3 (cervical) and Jurkat cell lines with the IC₅₀ values of 3.53 and 3.70 μM, respectively. Cytotoxicity of 1 (Jurkat) and 2 (Jurkat and HeLa S3) was better than that of cisplatin. Morphological changes in A549 (lung), HeLa S3 and Jurkat cell lines were examined in presence of the active complexes with the co-staining of Hoechst, AO (acridine orange) and EB (ethidium bromide) by fluorescence microscope.