Development of benzoxazole-2-yl-guanidine based Cu (II), Co (II), and Ni (II) complexes: Structural features, physicochemical aspects underpinning their pharmaceutical potential supported with theoretical approaches.

In this study, novel bioactive metal complexes of Cu (II), Co (II), and Ni (II) were synthesized using a guanidine-based ligand, 1,3-benzoxazole-2-yl-guanidine (L). The resulting coordination compounds [Cu(L)(CH₃COO)₂(H₂O)]·2H₂O, [Co(L)(NO₃)₂(H₂O)]·3H₂O, and [Ni(L)(NO₃)₂(H₂O)]·H₂O were comprehensively characterized using a range of physicochemical and spectroscopic techniques, including UV-visible spectrophotometry, FT-IR spectroscopy, elemental analysis, molar conductance, MS analysis, TGA, and magnetic measurements. The collected data support the formation of octahedral geometries around the metal centers, highlighting the ligand's flexible coordination behavior. Density functional theory (DFT) calculations were employed to optimize the molecular structures and support the experimental findings. Solution characterization established stoichiometric relationships, equilibrium constants, and pH-dependent properties, indicating their robustness in aqueous environments. The biological potential of the synthesized compounds was further evaluated through in vitro cytotoxicity assays (MTT) against HepG2 (liver), MCF-7 (breast), and HCT-116 (colon) cancer cell lines. Among the tested compounds, the Cu (II)-L complex exhibited the most pronounced antiproliferative activity, particularly against MCF-7 cells. Antioxidant capacity, assessed via DPPH radical scavenging assay, confirmed the strong free-radical neutralizing potential of the metal chelates. Antimicrobial investigations demonstrated broad-spectrum activity against various pathogenic strains, including S. marcescens, M. luteus, E. coli, C. albicans, A. flavus, and F. oxysporum. Notably, the copper complex exhibited significant antibacterial activity against M. luteus and potent antifungal effects against F.oxysporum. These effects highlight the therapeutic promise of guanidine-derived metal chelates as multifunctional agents with potential applications in anticancer, antioxidant, and antimicrobial therapies.