Synthesis, spectral, X-ray diffraction, antimicrobial studies, and DNA binding properties of binary and ternary complexes of pentadentate N2O3 carbohydrazone ligands

Abstract

Two pentadentate carbohydrazone ligands, H2L1 and H2L2, were prepared by the reaction of the bifunctional compound carbohydrazide with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde, respectively. Reactions of the ligands with oxovanadium(IV), cerium(III), thorium(IV), and dioxouranium(VI) ions yielded binary complexes. Reactions of the ligands with the dioxouranium(VI) ion in the presence of secondary ligands (8-hydroxyquinoline, glycine, salicylaldehyde, or benzoylacetone) yielded ternary complexes. The ligands and metal complexes were characterized by different techniques such as elemental and thermal analyses, IR, 1H and 13C NMR, electronic, ESR, mass spectra, and powder XRD as well as magnetic susceptibility and conductivity measurements. The coordinating sites are phenolic oxygen, azomethine nitrogen, and carbonyl oxygen. In complexes, the ligands act as dibasic pentadentate except ternary dioxouranium(VI) complexes, obtained using glycine or benzoylacetone, in which the ligands act as monobasic pentadentate. The XRD patterns for the H2L1 ligand, its binary dioxouranium(VI) complex, and its 8-hydroxyquinoline ternary complex indicate crystalline nature and the grain size was estimated. The H2L1 ligand and its binary complex have triclinic systems while the ternary complex has a monoclinic system with different unit-cell parameters. The ligands and some of their metal complexes showed antimicrobial activity toward some Gram-positive and Gram-negative bacteria, yeast (Candida albicans), and fungus (Aspergillus fumigatus), and MIC values were determined. The DNA binding properties of the oxovanadium(IV) complexes of H2L1 and H2L2 ligands were investigated by electronic absorption spectroscopy and viscosity measurements. The results indicated that these complexes bind to DNA via an intercalation binding mode with an intrinsic binding constant K b of 2.55 × 104 and 3 × 104 M−1, respectively.