Two zinc(II) and cadmium(II) complexes based on the V-shaped ligand 2,6-bis(2-benzimidazolyl)pyridine: Synthesis, crystal structure, DNA-binding properties and antioxidant activities

Zn(ii), Cd(ii) and Hg(ii) saccharinate complexes with 2,6-bis(2-benzimidazolyl)pyridine as promising anticancer agents in breast and lung cancer cell lines via ROS-induced apoptosis

New Zn(ii), Cd(ii) and Hg(ii) complexes of saccharinate (sac) and 2,6-bis(2-benzimidazolyl)pyridine (bzimpy), [Zn(bzimpy)2](sac)2·2H2O (Zn), [Cd(sac)2(bzimpy)] (Cd) and [Hg(sac)2(bzimpy)] (Hg), were prepared and fully characterized by spectroscopic methods and X-ray crystallography. In vitro anticancer screening in A549 (lung), MCF-7 (breast) and HT29 (colon) cell lines showed that Zn was highly cytotoxic against A549 and MCF-7 cells with IC50 values of 1.74 ± 0.06 and 3.15 ± 0.10 μM, respectively, and Hg demonstrated potent cytotoxic activity in MCF-7 cells (8.61 ± 0.98 μM), while Cd and bzimpy exhibited moderate growth inhibitory activities in all of the cell lines. In addition, they showed significantly lower toxicity towards normal human breast epithelial MCF10A cells. Moreover, the complexes exhibited significantly high nuclease activity towards plasmid DNA and their interactions with DNA were assessed by gel electrophoresis and DNA docking. Zn and Hg induced G0/G1 cell arrest and apoptotic cell death detected via typical DNA condensation/fragmentation, annexin V staining and caspase 3/7 activity in A549 and MCF-7 cells. These complexes further caused depolarization of mitochondria and oxidative damage of genomic DNA following excessive production of reactive oxygen species (ROS).

Thermally Stable Fluorogenic Zn(II) Sensor Based on a Bis(benzimidazole)pyridine-Linked Phenyl-Silsesquioxane Polymer

A 2,6-bis(2-benzimidazolyl) pyridine-linked silsesquioxane-based semi-branched polymer was synthesized, and its photophysical and metal-sensing properties have been investigated. The polymer is thermally stable up to 285 °C and emits blue in both solid and solution state. The emission of the polymer is sensitive to pH and is gradually decreased and quenched upon protonation of the linkers. The initial emission color is recoverable upon deprotonation with triethylamine. The polymer also shows unique spectroscopic properties in both absorption and emission upon long-term UV irradiation, with red-shifted absorption and emission not present in a simple blended system of phenylsilsesquioxane and linker, suggesting that a long-lived energy transfer or charge separated state is present. In addition, the polymer acts as a fluorescence shift sensor for Zn(II) ions, with red shifts observed from 464 to 528 nm, and reversible binding by the introduction of a competitive ligand such as tetrahydrofuran. The ion sensing mechanism can differentiate Zn(II) from Cd(II) by fluorescence color shifts, which is unique because they are in the same group of the periodic table and possess similar chemical properties. Finally, the polymer system embedded in a paper strip acts as a fluorescent chemosensor for Zn(II) ions in solution, showing its potential as a solid phase ion extractor.

Cu(I) complexes regulated by N-heterocyclic ligands: Syntheses, structures, fluorescence and electrochemical properties

Three mononuclear Cu(I) complexes, namely, [Cu(2-PBO)(PPh₃)₂]·ClO₄·2CH₂Cl₂ (1), [Cu(3-PBO)(PPh₃)₂(ClO₄)]·CH₂Cl₂ (2) and [Cu(PBM)(PPh₃)₂]·ClO₄ (3) (2-PBO = 2-(2'-Pyridyl)benzoxazole, 3-PBO = 2-(3'-Pyridyl)benzoxazole, PBM = 2-(2'-Pyridyl)benzimidazole, PPh₃ = triphenylphosphine) have been synthesized and characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR, X-ray single crystal diffraction and thermal analysis. Photoluminescent investigation shows that complexes 1-3 exhibit distinct tunable light green (512 nm)-to-yellow (557 nm) photoluminescence by varying the N-heterocyclic ligands. Three complexes show intense 2-PBO-based yellow, 3-PBO-based light green and intense PBM-based bright green luminescence upon irradiation with a standard UV lamp (λ_ex = 254 nm) at room temperature. Moreover, the electrochemical properties of 1-3 have been investigated by cyclic voltammetry. The results suggest the frontier molecular orbits and the HOMO-LUMO energy gaps of these cuprous complexes are effectively adjusted through the introduction of different N-heterocyclic ligands, thus achieving the selective luminescence of the cuprous complexes.

Zinc complexes of flufenamic acid: Characterization and biological evaluation

The reaction of ZnCl2 with the non-steroidal anti-inflammatory drug flufenamic acid (Hfluf) led to the formation of complex [Zn(fluf-O)2(MeOH)4], 1. When the reaction takes places in the presence of a N,N'-donor heterocyclic ligand such as 2.2'-bipyridylamine (bipyam), 2.2'-bipyridine (bipy), 1.10-phenanthroline (phen) and 2.2'-dipyridylketone oxime (Hpko), the complexes [Zn(fluf)2(bipyam)], 2, [Zn(fluf)2(bipy)], 3, [Zn(fluf)(phen)2(H2O)](fluf)·0.2MeOH, 4·0.2MeOH and [Zn(fluf)2(Hpko)2], 5 were isolated, respectively. The complexes were characterized by physicochemical and spectroscopic techniques and the crystal structures of complexes 2 and 4 were determined by X-ray crystallography. The ability of the complexes to scavenge 1.1-diphenyl-picrylhydrazyl, 2.2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) and hydroxyl radicals and to inhibit soybean lipoxygenase was evaluated; the complexes were more active than free Hfluf. The interaction of the complexes with serum albumins was investigated by fluorescence emission spectroscopy and the corresponding binding constants were calculated. UV-vis spectroscopy, viscosity measurements and fluorescence emission spectroscopy for the competitive studies of the complexes with ethidium bromide were the techniques employed to monitor the interaction of the complexes with calf-thymus DNA and revealed intercalation as the most possible mode of binding.

Sol-gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure-activity correlations in hybrid materials targeting Zn(II) antibacterial use

In the emerging issue of enhanced multi-resistant properties in infectious pathogens, new nanomaterials with optimally efficient antibacterial activity and lower toxicity than other species attract considerable research interest. In an effort to develop such efficient antibacterials, we a) synthesized acid-catalyzed silica-gel matrices, b) evaluated the suitability of these matrices as potential carrier materials for controlled release of ZnSO4 and a new Zn(II) binary complex with a suitably designed well-defined Schiff base, and c) investigated structural and textural properties of the nanomaterials. Physicochemical characterization of the (empty-loaded) silica-nanoparticles led to an optimized material configuration linked to the delivery of the encapsulated antibacterial zinc load. Entrapment and drug release studies showed the competence of hybrid nanoparticles with respect to the a) zinc loading capacity, b) congruence with zinc physicochemical attributes, and c) release profile of their zinc load. The material antimicrobial properties were demonstrated against Gram-positive (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus) and negative (Escherichia coli, Pseudomonas aeruginosa, Xanthomonas campestris) bacteria using modified agar diffusion methods. ZnSO4 showed less extensive antimicrobial behavior compared to Zn(II)-Schiff, implying that the Zn(II)-bound ligand enhances zinc antimicrobial properties. All zinc-loaded nanoparticles were less antimicrobially active than zinc compounds alone, as encapsulation controls their release, thereby attenuating their antimicrobial activity. To this end, as the amount of loaded zinc increases, the antimicrobial behavior of the nano-agent improves. Collectively, for the first time, sol-gel zinc-loaded silica-nanoparticles were shown to exhibit well-defined antimicrobial activity, justifying due attention to further development of antibacterial nanotechnology.

Antioxidant capacity and DNA-interaction studies of zinc complexes with a non-steroidal anti-inflammatory drug, mefenamic acid

Zinc(II) complexes of a non-steroidal anti-inflammatory drug, mefenamic acid(=Hmef) in the absence or presence of the nitrogen donor heterocyclic ligands 2,2'-bipyridine(=bipy), 2,2'-bipyridylamine(=bipyam), 2,2'-dipyridylketone oxime(=Hpko) or 1,10-phenanthroline(=phen) have been synthesized and characterized. The crystal structures of [Zn(mef-O,O')2(bipy)], 2, [Zn(mef-O)2(Hpko-N,N')2]·EtOH, 4 and [Zn(mef-O)(mef-O,O')(phen)(H2O)], 5, have been determined by X-ray crystallography showing distinct binding modes of mefenamato carboxylato group, bidentate in 2, monodentate in 4 or both in 5. Interaction studies of the complexes with calf-thymus DNA (CT DNA) have shown that complexes can bind to CT DNA with [Zn(mef-O)2(Hpko)2] exhibiting the highest binding constant to CT DNA (Kb = 1.93(±0.04) × 10(7) M(-1)). The complexes can bind to CT DNA via intercalation as concluded by DNA solution viscosity measurements. Competitive studies with ethidium bromide (EB) have shown that the complexes can displace the DNA-bound EB. The complexes exhibit good binding affinity to serum albumin proteins with [Zn(mef-O)2(H2O)4], 1 exhibiting the highest quenching ability (kq = 1.46 × 10(15) M(-1) s(-1) for human and 5.55 × 10(15) M(-1) s(-1) for bovine serum albumin). All compounds have been tested for their antioxidant and free radical scavenging activity as well as for their in vitro inhibitory activity against soybean lipoxygenase. The scavenging activity is low to moderate against 1,1-diphenyl-picrylhydrazyl (DPPH) radicals and high against hydroxyl and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(+·)) radicals, with [Zn(mef-O)2(H2O)4], 1 (ABTS%, 0.1 mM: 94.75(±1.06)%; (·)OH%, 0.1mM: 96.69(±0.27)%; LOX: IC50 = 27.34(±0.90) μM) exhibiting the highest scavenging activity of the ABTS radical cation among the complexes. Additionally, the complexes exhibit higher scavenging and LOX inhibitory activity than free mefenamic acid (ABTS%, 0.1 mM: 66.32(±0.38)%; (·)OH%, 0.1 mM: 92.51(±0.44)%; LOX: IC50 = 48.52(±0.88) μM).