Novel Mononuclear Cu(II), Ni(II), and Co(II) Complexes of Coumarinyl-Pyrazolyl-Thiazole Thiosemicarbazone: Synthesis, Characterization, and Biological Evaluation

Cu(II), Ni(II), and Co(II) acetates reacted with a thiosemicarbazone ligand (CPPTSC; HL) to produce novel solid complexes with the general formula [M(L)(H₂O)_m]·nH₂O, m = 2 or nil, n = 1 or nil, M = Cu(II), Ni(II), and Co(II). Several analytical and spectroscopic techniques have been efficiently used to characterize the synthesized chelates. The investigated CPPTSC ligand functions as a monoanionic tridentate in all chelates. Measurements of molar conductivity showed that all chelates behaved in a non-electrolytic manner. In contrast to nickel-CPPTSC and cobalt-CPPTSC complexes, which showed tetrahedral geometries, the copper-CPPTSC complex showed a distorted octahedral geometry. The thermal decomposition behaviors of CPPTSC complexes were examined using TG. To assess the molecular structural characteristics of CPPTSC and its complexes, density functional theory (DFT) was applied at the B3LYP/6-311G(d,p) and LanL2dz levels. The antiproliferative properties of CPPTSC and its chelates against two human cancer cell lines, HepG-2 (hepatic) and MCF-7 (breast), were evaluated. The Cu-CPPTSC and Ni-CPPTSC complexes displayed the superior IC₅₀ values compared with doxorubicin, suggesting a potentially improved therapeutic index. The bioactive Cu-CPPTSC and Ni-CPPTSC complexes markedly increased the late apoptosis of all studied tumor cells. The Cu-CPPTSC and Ni-CPPTSC complexes showed great cell cycle arrest in the G2 phase and moderate cell cycle arrest in the S phase. The discovered Cu-CPPTSC and Ni-CPPTSC complexes were then subjected to a molecular docking experiment and displayed good interactions with CDK-2 receptor.