Structural studies and anticancer activity of a novel (N₆O ₄) macrocyclic ligand and its Cu(II) complexes

A novel (N₆O₄) macrocyclic ligand (L) and its Cu(II) complexes have been prepared and characterized by elemental analysis, spectral, thermal (TG/DTG), magnetic, and conductivity measurements. Quantum chemical calculations have also been carried out at B3LYP/6-31+G(d,p) to study the structure of the ligand and one of its complexes. The results show a novel macrocyclic ligand with potential amide oxygen atom, amide and amine nitrogen atoms available for coordination. Distorted square pyramidal ([Cu(L)Cl]Cl·2.5H₂O (1), [Cu(L)NO₃]NO ₃·3.5H₂O (2), and [Cu(L)Br]Br·3H ₂O (4) and octahedral ([Cu(L)(OAc)₂]·5H ₂O (3)) geometries were proposed. The EPR data of 1, 2, and 4 indicate d¹ x² _-y² ground state of Cu(II) ion with a considerable exchange interaction. The measured cytotoxicity for L and its complexes (1, 2) against three tumor cell lines showed that coordination improves the antitumor activity of the ligand; IC₅₀ for breast cancer cells are ≈8.5, 3, and 4 μg/mL for L and complexes (1) and (2), respectively.