Structure and spectroscopic investigations of a bi-dentate N ′-[(4-ethylphenyl)methylidene]-4-hydroxybenzohydrazide and its Co(II), Ni(II), Cu(II) and Cd(II) complexes: Insights relevant to biological properties

Bivalent Ni(II), Co(II) and Cu(II) complexes of [(E)-[(2-methyl-1,3-thiazol-5-yl)methylidene]amino]thiourea: synthesis, spectral characterization, DNA and in-vitro anti-bacterial studies

The present work describes the preparation of bivalent Ni(II), Co(II) and Cu(II) complexes of [(E)-[(2-methyl-1,3-thiazol-5-yl)methylidene]amino]thiourea (MTHC) by mixing in 1:2 ratio of corresponding metal salt and Schiff base ligand in ethanolic medium. The prepared ligand and its complexes are confirmed using elemental analysis, magnetic moments, FT-IR, NMR, electronic and ESR spectroscopy techniques. The spectroscopic data reveals that metal complexes are in square planar in nature. In DNA binding studies, the higher intrinsic binding constants (K_b) of Ni(II), Co(II) and Cu(II) complexes are 2.713 × 10⁶ M⁻¹, 5.529 × 10⁶ M⁻¹ and 2.950 × 10⁶ M⁻¹ respectively, evident that complexes are avid binder with DNA base pairs. The moderate anti-bacterial activity (in-vitro) against staphylococcus epidermidis, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli bacterial culture may be due to the high electron density of ligand which prevents the charge reduction of metal ion. In the presence and absence of H₂O_2, it is notified that there is no appreciable DNA cleavage activity of Ni(II) and Co(II) complexes except Cu(II) complex which is due to aprotonation in the medium.

Crystal structure of (E)-N'-(3,4-di-hydroxy-benzyl-idene)-4-hy-droxy-benzohydrazide

In the title benzohydrazide derivative, C14H12N2O4, the azomethine C=N double bond has an E configuration. The hydrazide connecting bridge, (C=O)-(NH)-N=(CH), is nearly planar with C-C-N-N and C-N-N=C torsion angles of -177.33 (10) and -174.98 (12)°, respectively. The 4-hy-droxy-phenyl and 3,4-di-hydroxy-phenyl rings are slightly twisted, making a dihedral angle of 9.18 (6)°. In the crystal, mol-ecules are connected by N-H⋯O and O-H⋯O hydrogen bonds into a three-dimensional network, while further consolidated via π-π inter-actions [centroid-centroid distances = 3.6480 (8) and 3.7607 (8) Å]. The conformation is compared to those of related benzyl-idene-4-hy-droxy-benzohydrazide derivatives.

Synthesis, structure, and DNA binding/cleavage of two novel binuclear Co(II) complexes

In this study, two novel binuclear Co(II) complexes, [Co₄(L₁)₂(CH₃CH₂O)₄·5.5H₂O (1) and [Co₂(L₂)₂(CH₃COO)(H₂O)]·2CH₃OH·3H₂O (2)], with the ligands H₃L₁ and H₂L₂ were synthesized and structurally characterized using single crystal X-ray diffraction. The crystal structures of complex 1 and 2 belong to a monoclinic system with space group of P2(1)/n and triclinic system with space group of P-1, respectively. Their interaction with CT-DNA was investigated using electron absorption and fluorescent spectroscopy. The apparent binding constants (K_app) of two complexes (1 and 2) were determined to be 5.34 × 10⁵ and 5.82 × 10⁵, respectively, and both exhibited a moderate intensity of insertion with 2 > 1. Fluorescence quenching studies indicated that the fluorescence quenching mechanism of complex 1 is dynamic quenching and that of complex 2 is a static quenching mechanism. The chemical nuclease activity of the complexes was studied using agarose gel electrophoresis. The results suggest that when H₂O₂ is added, complexes 1 and 2 exhibit chemical nuclease activity. The cleavage mechanisms between the complexes and plasmid DNA are the likely oxidative cleavage process of hydroxyl radical (OH) and singlet oxygen (¹O₂) as active species.