Multifaceted insights into Cu(II) complexes with bis(benzimidazole) ligands: Structural investigation, theoretical studies, cytotoxicity evaluation, and antioxidant summarizing

In this study, the synthesized two new ligands, namely bis(1H-benzo[d]imidazole-1-yl) methane [L1] and 1,2-bis(1H-benzo[d]imidazole-1-yl) ethane [L2], from benzimidazole. They chose 1,2-dibromomethane and 1,2-dibromoethane as they are widely used in environmental catalysis and as ligands in conjugated configurations. The researchers were able to synthesize the Cu(II) complexes, [Cu(L1)₂]Cl₂ or [1] and [Cu(L2)₂]Cl₂ or [2], at room temperature. They used several analytical techniques, including elemental analysis, magnetic moment measurement, UV–visible spectroscopy, FT-IR spectroscopy, FT-Raman spectroscopy, NMR spectroscopy (including ¹H, ¹³C, DEPT-135, HSQC, and HMBC techniques), ESI-MS analysis, thermogravimetric analysis, and ESR spectroscopy, to characterize the synthesized compounds. They found that the ESR spectra of complexes [1] and [2] suggest that both metal complexes have square planar coordination spheres. In the DFT study of the geometrical optimization of both complexes, the central plane consists of the Cu metal atom connected to four nitrogen atoms. The Cu–N bond lengths are measured at 2.194 Å for [1] and 2.176 Å for [2] whereas the FMO theory's slight reduction in the HOMO-LUMO gap for [2] suggests that it is more reactive and less stable compared to [1]. In addition, the researchers tested the effect of these compounds on human cervical cancer cell lines (HeLa) which showed significant cytotoxic effects under laboratory conditions. Complex [2] had a significant inhibitory impact on the growth of cancer cells. The researchers also assessed the antioxidant effects of the ligands and metal complexes using DPPH, OH, and NO assays and found that [2] had the most potent inhibitory effect on the radicals, with IC₅₀ values of 36.11 μM (DPPH), 28.18 μM (OH), and 26.20 μM (NO).