A new N₃-tridentate imine ligand, 2,6-diacetylpyridinediphenylhydrazone (DAPH) (L), and its Pd(II), V(IV)O, and Ag(I) complexes were synthesized and characterized via elemental analysis, FT-IR, NMR, molar conductance, and magnetic susceptibility measurements. The obtained data confirmed geometrical structures of Pd(II), Ag(I), and V(IV)O complexes as square planar, tetrahedral, and distorted square pyramidal, respectively. Minimum inhibitory concentrations (MIC) were used to probe in vitro antimicrobial activity of DAPH ligand and metal complexes using three different bacteria. Results revealed that PdDAPH complex exhibited the highest toxicity and lowest MIC (1.25 µg/mL) toward Escherichia coli. Moreover, cytotoxic activity of the prepared complexes was evaluated via three human cancer cell lines, hepatic carcinoma (HepG2), breast carcinoma (MCF-7), and colon carcinoma (HCT-116). Among all tested complexes, PdDAPH caused a significant loss of cell viability in less time and lower dose than the reference drug vinblastine. Antioxidant activity was also measured for all complexes and compared to vitamin C. Probing the interaction of the prepared metal-DAPH chelates with calf-thymus DNA showed the Pd(II) complex displayed the strongest interaction, with a binding constant of 6.02 kcal mol⁻¹. Molecular docking was also investigated on all complexes, with PdDAPH being the most promising compound due to its facile hydrophobic interactions with the active pocket of glucose transporter (GLUT1) enzyme. Overall, the combined findings of this work clearly demonstrate that these new compounds hold promise as efficient antibiotic and anticancer agents. Graphical Abstract

In this study, four new Mn(II), Fe(III), and Cr(III) complexes with two Schiff base ligands namely, 4-bromo-2-[(E)-{[4-(2-hydroxyethyl)phenyl]imino}methyl]phenol (HL1) and 2-[(E)-{[4-(2-hydroxyethyl)phenyl]imino}methyl]-4-methoxy phenol (HL2) have been synthesized and characterized. Different analytical and spectral methods have been used to characterize the ligands and their complexes. General formulas of [M(L)Cl₂(H₂O)₂] for FeL1, CrL1 and CrL2, and [M(L)Cl(H₂O)₃] for MnL2 were proposed. HOMO and LUMO energies, as well as the electrical characteristics, have been calculated using DFT/B3LYP calculations with Gaussian 09 program. The optimized lowest energy configurations of the complexes are proven. The disc diffusion technique was used to test the pharmacological activities' antibacterial efficacy against diverse bacterial and fungus species. The MTT technique was used to assess the in vitro cytotoxicity of the ligands and their metal complexes on the Hep-G2 human liver carcinoma cell line and the MCF-7 human breast cancer cell line. All compounds displayed better activity compared to the free ligands. MnL2 complex showed predominant activity when compared to the other complexes with an IC₅₀ value of 2.6 ± 0.11 μg/ml against Hep-G2, and against MCF-7 the IC₅₀ value was 3.0 ± 0.2 μg/ml which is less than the standard drug cisplatin (4.0 μg/ml). UV–vis electronic spectrum and gel electrophoresis techniques have been used to investigate the compounds’ affinity to bind and cleavage CT-DNA. The interaction’s binding constants, or Kb, have been identified, and it was discovered that the new complexes' binding affinities are in the order of FeL1 > MnL2 > CrL2 > CrL1, and the binding mechanism has been suggested. To assess the kind of binding and binding affinity of the investigated drugs with human DNA, a molecular docking study was carried out (PDB:1bna). The acquired results supported the intercalation binding mechanism proposed in the experimental part and revealed that complexes may be inserted into the DNA molecule to stop DNA replication. According to ADMET data, the synthesized compounds have a high bioavailability profile and their physicochemical and pharmacological features remained within Lipinski's RO5 predicted limitations.

In this work, nanosized Cu and Ni Schiff-base complexes, namely ahpvCu, ahpnbCu, and ahpvNi, incorporating imine ligands derived from the condensation of 2-amino-3-hydroxypyridine, with either 3-methoxysalicylaldehyde (ahpv) or 4-nitrobenzaldehyde (ahpnb), were synthesized using sonochemical approach. The structure and properties of the new ligands and their complexes with Ni(II) and Cu(II) were determined via infrared (IR), nuclear magnetic resonance (NMR), electronic spectra (UV-Vis), elemental analysis (CHN), thermal gravimetric analysis (TGA), molar conductivity (Λ_m), and magnetic moment (μ_eff). The combined results revealed the formation of 1:1 (metal: ligand) complexes for ahpvCu and ahpvNi and 1:2 for ahpnbCu. Additionally, CuO and NiO nanoparticles were prepared by calcination of the respective nanosized Cu/Ni complexes at 500 °C, and characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Significantly, the as-prepared nanosized Schiff-base Cu/Ni complexes and their oxides showed remarkable catalytic activity towards the selective oxidation of benzyl alcohol (BzOH) in aqueous H₂O₂/ dimethylsulfoxide (DMSO) solution. Thus, catalytic oxidation of BzOH to benzaldehyde (BzH) using both ahpvCu complex and CuO nanoparticles in H₂O₂/DMSO media at 70 °C for 2 h yielded 94% and 98% BzH, respectively, with 100% selectivity.