Cobalt(II) and cobalt(III) dipicolinate complexes: solid state, solution, and in vivo insulin-like properties

In vitro biological activity of cobalt(II) complexes with salicylaldimine ligands in microbial and cancer cells

Background: More studies using cobalt complexes as drugs are needed. Results: The drug action of two cobalt salicylaldimines was determined. The complexes and amphotericin B (20 mg/ml) inhibited Candida albicans at 9-15 and 21 mm. This concentration of both ligands inhibited Staphylococcus aureus at 10 mm and one ligand inhibited Escherichia coli at 9 mm, but the complexes and ampicillin inhibited four bacteria at 9-20 and 21-26 mm. The ligands were inactive against cancer and normal cells, but the complexes and doxorubicin provided IC50 values of 28.18-54.19 and 9.66 μM against MCF-7 cells and 15.76-20.49 and 36.42 μM against BHK cells. Conclusion: The ligands' activity was much improved by complexation, although they remained substandard.

(NH4)2[Co(H2O)6]2V10O28·4H2O Vs. (NH4)2[Ni(H2O)6]2V10O28·4H2O: Structural, Spectral and Thermal Analyses and Evaluation of Their Antibacterial Activities

This paper presents the synthesis of two cluster compounds {(NH4)2[Co(H2O)6]2V10O28·4H2O (C1) and (NH4)2[Ni(H2O)6]2V10O28·4H2O (C2)} which were obtained as single crystals suitable for XRD analysis that revealed their crystallization in the monoclinic (C2/c) and triclinic (P-1) space groups, respectively. Additionally, C1 and C2 were characterized using CHN analysis and FT-IR spectroscopy and their thermal decomposition mechanisms were investigated. The antibacterial activities of both compounds were determined against three human pathogenic bacterial strains {Bacillus cereus ATCC 33,018, Escherichia coli O157:H7 and Pseudomonas aeruginosa ATCC 9027} and one phytopathogenic bacterial strain {Ralstonia solanacearum}, while drug standards {chloramphenicol and streptomycin} were used as control. The inhibitory activity and the minimum inhibitory concentration (MIC) values of the tested compounds clearly indicated higher antibacterial activities of the nickel compound against B. cereus ATCC 33,018, E. coli O157 and R. solanacearum with MIC values of 3.150, 3.150 and 6.300 mg/ml, respectively. On the other hand, (NH4)2[Co(H2O)6]2V10O28·4H2O exhibited higher antibacterial activity against P. aeruginosa ATCC 9027 (MIC value of 6.300 mg/ml) in comparison to the nickel analog. In general, the measured activities are lower than that obtained for the standards except for the higher activity given by C2 in comparison to streptomycin against the R. solanacearum strain.

Recent advances in heteroleptic multiple-stranded metallosupramolecules

Well-ordered combination of defined coordination spheres and multiple types of ligands (heteroleptic) in a given structure can expand the structural complexity and functional diversity of the resulting metallosupramolecules. Such heteroleptic metallosupramolecular architectures are expected to afford advanced utility in a variety of applications. In this concise review article, recent advances in the development of multi-nuclear-cluster-based heteroleptic multiple-stranded (HLMS) metallosupramolecules are summarized and demonstrated. To construct HLMS metallosupramolecules, one type of multitopic ligands can be employed for building up multiple strands, while another type of ligands can be utilized to construct multi-nuclear clusters. Most HLMS metallosupramolecules adopt helical geometries and have high molecular symmetry, which can be key factors for the structural completion. HLMS metallosupramolecules can be used as basic building blocks for the fabrication of higher-order polymeric or discrete assembly architectures with well-defined geometries.

Changes in the proportions of an active pharmaceutical through cocrystals

In this study, the modulation of amounts sulfathiazolium cations in different 2,6-pyridinedicarboxylates is demonstrated. An uncommon monoionic sulfathiazolium zinc 2,6-pyridinedicarboxylate (1:1 electrolyte) complex was characterized. Conventional sulfathiazolium zinc-bis-2,6-pyridinedicarboxylate dianionic complexes (2:1 electrolyte) were formed when hydroxyaromatic compounds such as 1,3-dihydroxybenzene or 3-nitrophenol were used as guest components. Thus, with the aid of the hydroxyaromatic molecules the zinc-bis-2,6-pyridinedicarboxylate complexes were stabilized with the relatively large sized sulfathiazolium cations. It was a consequence of domain expansion by the phenolic compounds. Sandwiched aromatic guests between the 2,6-pyridinedicarboxylates provided appropriate packing to accommodate the two large cations in the self-assemblies, which helped to modulate the amounts of sulfathiazole in different formulations. Antibacterial activities with E. coli DH5α have shown that the salt and the complexes have lower g/ml antibacterial activity than the parent drug.

Cooperative Effects of Heterodinuclear IrIII-MII Complexes on Catalytic H2 Evolution from Formic Acid Dehydrogenation in Water

Novel heterodinuclear Ir^III-M^II complexes (M = Co, Ni, or Cu) with two adjacent reaction sites were synthesized by using 3,5-bis(2-pyridyl)-pyrazole (Hbpp) as a structure-directing ligand and employed as catalysts for H₂ evolution through formic acid dehydrogenation in water. A cooperative effect of the hetero-metal centers was observed in the H₂ evolution in comparison with the corresponding mononuclear Ir^III and M^II complexes as the components of the Ir^III-M^II complexes. The H₂ evolution rate for the Ir^III-M^II complexes was at most 350-fold higher than that of the mononuclear Ir^III complex. The catalytic activity increased in the following order: Ir^III-Cu^II complex < Ir^III-Co^II complex < Ir^III-Ni^II complex . The Ir^III-H intermediates of the Ir^III-M^II complexes were successfully detected by ultraviolet-visible, ¹H nuclear magnetic resonance, and ESI-TOF-MS spectra. The catalytic enhancement of H₂ evolution by the Ir^III-M^II complexes indicates that the Ir^III-H species formed in the Ir^III moiety act as reactive species and the M^II moieties act as acceleration sites by the electronic effect from the M^II center to the Ir^III center through the bridging bpp^- ligand. The Ir^III-M^II complexes may also activate H₂O at the 3d M^II centers as a proton source to facilitate H₂ evolution. In addition, the affinity of formate for the Ir^III-M^II complexes was investigated on the basis of Michaelis-Menten plots; the Ir^III-Co^II and Ir^III-Ni^II complexes exhibited affinities that were relatively higher than that of the Ir^III-Cu^II complex. The catalytic mechanism of H₂ evolution by the Ir^III-M^II complexes was revealed on the basis of spectroscopic detection of reaction intermediates, kinetic analysis, and isotope labeling experiments.

Role of biologically important imidazole moiety on the antimicrobial and anticancer activity of Fe(III) and Mn(II) complexes

Currently, most pathogens influencing a number of epidemics outline a notable warning to human health. It has pushed researchers to design new antimicrobial drugs using transition metals that are studied in proceeding fewer years for their antimicrobial properties. Henceforth, in this work, two mononuclear complexes [Imz-H][Fe(pda)₂]⋅1⋅3H₂O (1) and [Mn(Imz)₆]⋅2Cl^-⋅2H₂O (2) [Imz = imidazole and H₂pda = 2,6 pyridine dicarboxylic acid] are isolated and characterized systematically by various spectral and single-crystal XRD studies. The antimicrobial activity of the present hexadentate complexes of Fe(III) and Mn(II) against Gram-positive as well as Gram-negative bacteria is also assessed. Augmented activity against standard isolates of Staphylococcus aureus with a minimum inhibitory concentration (MIC) is observed. Similar activity was also observed toward Escherichia coli, Klebsiella pneumoniae and Listeria monocytogenes. 1 and 2 have excellent bactericidal activity, and no resistant mutant for S. aureus was seen. The compound also unveiled antibiofilm activity and was capable to disrupt significantly the pre-formed biofilms and this property was confirmed by XTT assay experiment. The MTT assay data indicate that 1 and 2 can be used as anticancer agents toward the RAW 64.7 (human macrophage/monocyte) cell line. Further, the molecular docking study reveals that the role of imidazole is very important in the biological activity of these complexes. Moreover, our results suggest that 1 and 2 with its effective anti-microbial, anti-biofilm and cytotoxicity activity can be used to treat bacterial and fungal infections and could be appraised clinically for further applications.Communicated by Ramaswamy H. Sarma.

In vitro assessment of cobalt oxide particle dissolution in simulated lung fluids for identification of new decorporating agents

Inhalation of ⁶⁰Co₃O₄ particles may occur at the work place in nuclear industry. Their low solubility may result in chronic lung exposure to γ rays. Our strategy for an improved therapeutic approach is to enhance particle dissolution to facilitate cobalt excretion, as the dissolved fraction is rapidly eliminated, mainly in urine. In vitro dissolution of Co₃O₄ particles was assessed with two complementary assays in lung fluid surrogates to mimic a pulmonary contamination scenario. Twenty-one molecules and eleven combinations were selected through an extensive search in the literature, based on dissolution studies of other metal oxides (Fe, Mn, Cu) and tested for dissolution enhancement of cobalt particles after 1-28 days of incubation. DTPA, the recommended treatment following cobalt contamination did not enhance ⁶⁰Co₃O₄ particles dissolution when used alone. However, by combining molecules with different properties, such as redox potential and chelating ability, we greatly improved the efficacy of each drug used alone, leading for the highest efficacy, to a 2.7 fold increased dissolution as compared to controls. These results suggest that destabilization of the particle surface is an important initiating event for a good efficacy of chelating drugs, and open new perspectives for the identification of new therapeutic strategies.

Stereochemistry of Hexacoordinated Zn(II), Cu(II), Ni(II), and Co(II) Complexes with Iminodiacetamide Ligands

Metal complexes of iminodiacetamide (imda) ligands and metal ions Zn(II), Cu(II), Ni(II), and Co(II) were prepared using eight imda ligands (L1-L8) substituted with groups of different steric and electronic properties on the central amine N atom (H atom, methyl, isopropyl, and benzyl) and the para position of the phenyl rings (nitro and dimethylamino). The effect of these substituents on the stoichiometry (ML and ML₂), geometry, and stereochemistry (mer, trans-fac, cis-fac) of the complexes was studied in the solid state, in solution, and by density functional theory calculations. Single-crystal and powder X-ray diffraction, thermogravimetry, and IR spectroscopy showed that in the solid state imda ligands preferentially form trans-fac ML₂ complexes, with the exception of the cis-fac complex 7_Zn. NMR spectroscopy of diamagnetic Zn(II) and paramagnetic Co(II) complexes revealed the formation of both ML and ML₂ complexes in solution, which was also confirmed by UV-vis titrations. Variable-temperature NMR was used to study the effect of the substituent on the central amine N atom on the Zn-N bond strength and nitrogen inversion. The relative stabilities of the isomers were rationalized by computations and the optimized structures used for geometry analysis.

Mechanistic Insight into Synergistic Catalysis of Olefin Hydrogenation by a Hetero-Dinuclear RuII-CoII Complex with Adjacent Reaction Sites

We have designed and synthesized a hetero-dinuclear Ru^II-Co^II complex with a dinucleating ligand inspired by hetero-dinuclear active sites of metalloenzymes. A synergistic effect between the adjacent Ru^II and Co^II sites has been confirmed in catalytic olefin hydrogenation by the complex, exhibiting a much higher turnover number than those of mononuclear Ru^II or Co^II complexes as the components. A Ru^II-hydrido species was detected by ¹H NMR and electrospray ionization (ESI)-time-of-flight (TOF)-MS measurements as an intermediate to react with olefins, and Co^II-bound methanol was suggested to act as a proton source.

ONS donor entwined iron(iii) and cobalt(iii) complexes with exemplary safety profile as potent anticancer and glucose uptake agents

Highly safe, efficacious iron(iii) and cobalt(iii) complexes are found to be effective in vitro anticancer and antidiabetic agents.

New complexes of Cu(II) with dipicolinate and pyridyl-based ligands: An experimental and DFT approach

The three novel mononuclear copper(II) complexes with dipicolinate and pyridyl-based ligands [Cu(dipic)(L)(OH₂)] (L=4-picoline, vinylpyridine, 4-styrylpyridine; dipic^2-=dipicolinate) were afforded and structurally characterized. X-ray diffraction studies accounted for slight distorted square-pyramidal structures in which the dianion dipic^2- acts as a tridentate ligand in a mer-fashion, the N-donor species occupy an in-plane position, and a water molecule was detected apically coordinated. To assess the effect of the nature of the pyridyl-substituent (para position) on electronic properties, other complexes were also synthesized: [Cu(dipic)(py)(OH₂)], [{Cu(dipic)(OH₂)}₂(μ-pyz)] and [{Cu(dipic)(OH₂)}(μ-pypy){Cu(dipic)}] (py=pyridine, pyz=pyrazine, pypy=(E)-1,2-bis(pyridine-4-yl)ethane). Absorptive behavior in the UV-VIS region was studied in solution and in the solid state (reflectance measurements). Additionally, geometry and population analyses were conducted by means of DFT calculations. Electronic UV-VIS spectra were simulated for both dinuclear complexes in the framework of the TD-DFT methodology to assign the origin of the absorption bands.

In vitro studies on the pleotropic antidiabetic effects of zinc oxide nanoparticles

Aim: Our earlier study demonstrated antidiabetic activity of zinc oxide nanoparticles (ZON) in diabetic rats. The present study was performed to elucidate its mechanism of antidiabetic action. Methods: Protein tyrosine phosphatase 1B, protein kinase B and hormone sensitive lipase phosphorylation; glucose transporter 4 translocation and glucose uptake; glucose 6 phosphatase, phosphoenol pyruvate carboxykinase and glucokinase expression; and pancreatic beta cell proliferation were evaluated after ZON treatment to cells. Result: ZON treatment resulted in PKB activation, protein tyrosine phosphatase 1B inactivation, increased glucose transporter 4 translocation and enhanced glucose uptake, decreased glucose 6 phosphatase and phosphoenol pyruvate carboxykinase expression, hormone sensitive lipase inactivation and pancreatic beta cell proliferation. Conclusion: To the best of our knowledge, we report for the first time, pleiotropic antidiabetic effects of ZON viz. improved insulin signaling, enhanced glucose uptake, decreased hepatic glucose output, decreased lipolysis and enhanced pancreatic beta cell mass.

A tetranuclear ruthenium complex with bridging pyridine-2,4-dicarboxylato ligands forming a square metallamacrocycle

Treatment of [RuCl2(PPh3)3] with equimolar amounts of 2,4-pyridinedicarboxylic acid (2,4-dipicH2) in the presence of Et3N afforded a tetranuclear complex [Ru(μ-2,4-dipic)(PPh3)2]4 (1) as red crystals. The crystal and molecular structure of [Ru(μ-2,4-dipic)(PPh3)2]4·CHCl3·8H2O (1·CHCl3·8H2O) was determined by single-crystal X-ray diffraction. Each ruthenium center in 1 is six-coordinated with two phosphorus atoms from triphenylphosphine ligands, one nitrogen atom from a pyridyl moiety and three oxygen atoms from two 2,4-dipic2– ligands. 2,4-Pyridinedicarboxylate dianions (2,4-dipic2–) act as bridging ligands to form the stable tetranuclear metallamacrocyclic compound. The electrochemical properties of 1 were also investigated.

Combined experimental-theoretical characterization of chelidamate nickel complex with 4-methylpyrimidine

A new chelidamate complex of nickel(II) ion, [Ni(chel)(H2O)2(mpd)]·2H2O [chel: chelidamate or 4-hydroxypyridine-2,6-dicarboxylate, mpd: 4-methylpyrimidine] was synthesized and characterized by single-crystal X-ray diffraction, UV-Vis and FT-IR spectroscopy. Intermolecular O-H⋯O and O-H⋯N hydrogen bonds and π-π stacking interactions appear to be effective in the stabilization of the crystal structure. Theoretical calculations have been carried out by using Hartree-Fock (HF)/6-31G (d) and Density Functional Theory (DFT)/6-31+G (d). Molecular geometry from X-ray experiment of Ni(II) complex in the ground state was compared using unrestricted hybrid density functional B3LYP. HOMO-LUMO energies, absorption wavelengths and excitation energy were computed by time dependent DFT (TD-DFT) method with polarizable continuum model. The observed FT-IR vibrational frequencies are analyzed and compared with theoretically predicted vibrational frequencies. The natural charges on the atoms and second-order interaction energies were derived from natural bond orbital analysis (NBO).

Two new chelidamate complexes with the 4-methoxypyridine: A combined theoretical and experimental study

Two new mixed chelidamate complexes, [M(chel)(mhpOCH3)·2H2O]·2H2O [M=Ni(II) (1); Co(II) (2); chel: chelidamate or 4-hydroxypyridine-2,6-dicarboxylate; mhp: 4-methoxypyridine], were prepared and characterized through a combination of X-ray diffraction method, FT-IR and UV-Vis spectroscopy. The central M(II) ion in complex (1) and (2) is coordinated by the mhp nitrogen atom, the chel nitrogen and oxygen atoms and aqua oxygen atoms, forming the distorted octahedral geometry. Intra and intermolecular hydrogen bonds and π-π stacking interactions appear to be effective in the stabilization of the crystal structures. Also, the fully optimized geometries and vibrational frequencies have been calculated using density functional theory (DFT)-B3LYP with 6-31G (d) basis set. The vibrational frequencies were interpreted by means of potential energy distribution (PED). The energetic behaviors of the complexes in methanol solvent were examined using by time-dependent DFT (TD-DFT) method by applying the polarizable continuum model (PCM). The molecular stability and charge delocalization were analyzed using natural bond orbital (NBO) analysis.

Structures and multiple properties of two polar metal–organic frameworks based on achiral N,O-coordinated ligands: toward multifunctional materials

Reported here are two polar MOFs with combined PL and SHG response or combined antiferromagnetism and photocatalysis properties.