Bio-relevant cobalt(II) complexes with compartmental polyquinoline ligand: Synthesis, crystal structures and biological activities

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.

Synthesis, Magnetic Properties, and Catalytic Properties of a Nickel(II)-Dependent Biomimetic of Metallohydrolases

A dinickel(II) complex of the ligand 1,3-bis(bis(pyridin-2-ylmethyl)amino)propan-2-ol (HL1) has been prepared and characterized to generate a functional model for nickel(II) phosphoesterase enzymes. The complex, [Ni2(L1)(μ-OAc)(H2O)2](ClO4)2·H2O, was characterized by microanalysis, X-ray crystallography, UV-visible, and IR absorption spectroscopy and solid state magnetic susceptibility measurements. Susceptibility studies show that the complex is antiferromagnetically coupled with the best fit parameters J = -27.4 cm-1, g = 2.29, D = 28.4 cm-1, comparable to corresponding values measured for the analogous dicobalt(II) complex [Co2(L1)(μ-OAc)](ClO4)2·0.5 H2O (J = -14.9 cm-1 and g = 2.16). Catalytic measurements with the diNi(II) complex using the substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) demonstrated activity toward hydrolysis of the phosphoester substrate with K m ~10 mM, and k cat ~0.025 s-1. The combination of structural and catalytic studies suggests that the likely mechanism involves a nucleophilic attack on the substrate by a terminal nucleophilic hydroxido moiety.

α-N-heterocyclic thiosemicarbazone Fe(III) complex: Characterization of its antitumor activity and identification of anticancer mechanism

We synthesized an α-N-heterocyclic thiosemicarbazone ligand (L) and its Fe complex (C1) and assessed their chemical and biological properties in order to understand their marked activity. Electrochemical studies and ascorbate oxidation studies demonstrated that C1 shows considerable redox activity, and Fe(III/II) redox potentials was within the range accessible to cellular oxidants and reductants. Absorption spectral, emission spectral and viscosity analysis reveal that L and C1 interacted with DNA through intercalation and C1 exhibited a higher DNA binding ability. Agarose gel electrophoresis experiments indicated that C1 exhibited the highest pBR322 DNA cleaving ability. In vitro, C1 showed significantly more anticancer activity than the ligand alone. Moreover, C1 induces production of reactive oxygen species (ROS) and DNA damage, resulting in activation of the p53 pathway, cell cycle arrest at the S phase, and mitochondria-mediated apoptosis by regulating the expression of Bcl-2 family proteins.