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Diverse Coordinative Zinc Complexes Containing Amido-Pyridinate Ligands: Structural and Catalytic Studies.

ABSTRACT: In this work, zinc complexes containing amidopyridinate ligands substituted with different pendant arms have been described. Treatment of ligand precursors with ZnEt2 at a 1:1 ratio in THF yields zinc ethyl complexes (PyN C1Py )2(ZnEt)2 (1) and (PyN C2NMe2 )2(ZnEt)2 (2), respectively. Complexes 1 and 2 show the same geometry as a distorted tetrahedron, but adopt different coordination behaviors supported by the ligands. Complex 1 represents a rare and a non-centrosymmetric mode, which the amido group bridges two zinc centers to form a six-membered ring. However, complex 2 shows a centrosymmetric mode, which the pyridine group links to the zinc centers to form an eight-membered ring. Recrystallization of complex 2 gives an additional complex (PyN C2NMe2 )4Zn3(?3-O) (3). We attempted to prepare zinc benzyl oxide complexes but afforded only a self-assembly cubane complex Zn7Et6(OBn)8 (4). All molecular structures 1-4 are characterized depending on both single-crystal X-ray and spectroscopic data. Furthermore, their catalytic properties toward the ring opening polymerization of ?-caprolactone and L-lactide, using benzyl alcohol as the initiation reagent, are under investigation.

SUBMITTER: Chen MT

PROVIDER: S-EPMC6328485 | biostudies-other | 2018

REPOSITORIES: biostudies-other

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Diverse Coordinative Zinc Complexes Containing Amido-Pyridinate Ligands: Structural and Catalytic Studies.

Chen Ming-Tsz MT Chen Yu-Yang YY Li Guan-Lin GL Chen Chi-Tien CT

Frontiers in chemistry 20190104

In this work, zinc complexes containing amidopyridinate ligands substituted with different pendant arms have been described. Treatment of ligand precursors with ZnEt2 at a 1:1 ratio in THF yields zinc ethyl complexes (PyN C 1 Py )2(ZnEt)2 (1) and (PyN C 2 NMe 2 )2(ZnEt)2 (2), respectively. Complexes 1 and 2 show the same geometry as a distorted tetrahedron, but adopt different coordination behaviors supported ...[more]

PMID: 30662891

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Project description:The ruthenium(ii) polypyridyl complexes (RPCs), [(phen)2Ru(tatpp)]2+ (32+ ) and [(phen)2Ru(tatpp)Ru(phen)2]4+ (44+ ) are shown to cleave DNA in cell-free studies in the presence of a mild reducing agent, i.e. glutathione (GSH), in a manner that is enhanced upon lowering the [O2]. Reactive oxygen species (ROS) are involved in the cleavage process as hydroxy radical scavengers attenuate the cleavage activity. Cleavage experiments in the presence of superoxide dismutase (SOD) and catalase reveal a central role for H2O2 as the immediate precursor for hydroxy radicals. A mechanism is proposed which explains the inverse [O2] dependence and ROS data and involves redox cycling between three DNA-bound redox isomers of 32+ or 44+ . Cultured non-small cell lung cancer cells (H358) are sensitive to 32+ and 44+ with IC50 values of 13 and 15 μM, respectively, and xenograft H358 tumors in nude mice show substantial (∼80%) regression relative to untreated tumors when the mice are treated with enantiopure versions of 32+ and 44+ (Yadav et al. Mol Cancer Res, 2013, 12, 643). Fluorescence microscopy of H358 cells treated with 15 μM 44+ reveals enhanced intracellular ROS production in as little as 2 h post treatment. Detection of phosphorylated ATM via immunofluorescence within 2 h of treatment with 44+ reveals initiation of the DNA damage repair machinery due to the ROS insult and DNA double strand breaks (DSBs) in the nuclei of H358 cells and is confirmed using the γH2AX assay. The cell data for 32+ is less clear but DNA damage occurs. Notably, cells treated with [Ru(diphenylphen)3]2+ (IC50 1.7 μM) show no extra ROS production and no DNA damage by either the pATM or γH2AX even after 22 h. The enhanced DNA cleavage under low [O2] (4 μM) seen in cell-free cleavage assays of 32+ and 44+ is only partially reflected in the cytotoxicity of 32+ and 44+ in H358, HCC2998, HOP-62 and Hs766t under hypoxia (1.1% O2) relative to normoxia (18% O2). Cells treated with RPC 32+ show up to a two-fold enhancement in the IC50 under hypoxia whereas cells treated with RPC 44+ gave the same IC50 whether under hypoxia or normoxia.

Project description:Novel lanthanide (Ln) compounds [Ln(L)2]Cl.xH2O (Ln = La3+, Ce3+, Sm3+) containing aromatic N,O-chelate ligands [HL1 = 4-amino-2-(1H-benzimidazol-2-yl)phenol; HL2 = 5-amino-2-(1H-benzimidazol-2-yl)phenol] have been synthesized and structurally characterized by elemental analysis, NMR and IR spectroscopy, molar conductance measurements, and mass spectrometry (MS). The spectroscopic data suggested that the benzimidazolyl-phenol ligands act as N,O-chelate ligands through the iminic nitrogen and phenolic oxygen atoms. Elemental analysis indicated that lanthanide compounds were formed in a 1:2 stoichiometry (metal:ligand). In vitro biological evaluation was carried out using these complexes, exhibiting moderate cytotoxicity against six different human tumor cell lines (U251, human glioblastoma; HCT-15, colorectal carcinoma; MCF-7, breast epithelial adenocarcinoma; PC-3, prostate cancer; K562, myelogenous leukemia; SKLU-1, lung carcinoma) and lower toxicity against a non-cancerous cell line (COS-7, primate kidney). In addition, the antibacterial activity of the compounds was assessed against two gram-positive strains (Staphylococcus aureus ATCC 25923, Listeria monocytogenes ATCC 19115) and two gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27583) using the microdilution method. The results obtained show that the metal complexes exhibit higher biological activity than the free ligands, confirming a synergistic effect. Further benzimidazolyl-phenol derivatives were explored for the detection of bacteria using fluorescence imaging studies. Interestingly, the fluorescent properties of these compounds make them potential candidates to monitor the morphology of bacteria at different compound concentrations. Hence, the interaction of the ligand and complexes with model membranes mimicking those of bacteria was studied by using differential scanning calorimetry (DSC) and molecular dynamics (MD), showing that both compounds decreased the enthalpy of transition in two model membranes as the concentration of the compounds increased. In addition, the main transition temperature was slightly reduced as a result of these interactions.

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Diverse Coordinative Zinc Complexes Containing Amido-Pyridinate Ligands: Structural and Catalytic Studies.

Publications

Diverse Coordinative Zinc Complexes Containing Amido-Pyridinate Ligands: Structural and Catalytic Studies.

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