Divalent Zinc Ions Research Articles

Kinetics and its accompanying thermodynamics studies on simultaneous complexation of heterobimetallic neodymium (III) with zinc (II) and l-tryptophan in aquated DMF using 4f–4f absorption spectra

The 4f–4f absorption spectra of the simultaneous heterobimetallic complexation of trivalent neodymium ion with l-tryptophan and divalent zinc ion in aquated DMF (50%, v/v) at pH 6.0 was recorded at the time interval of 1h. From the observed absorption spectra, the values of intensity parameters such as oscillator strength (P) and Judd–Ofelt intensity (Tλ) parameters, kinetics and thermodynamics parameters were evaluated. The rate constant increases with an increase in the temperature along with the oscillator strengths and Judd–Ofelt intensity parameters. The positive values of the change in the standard enthalpy (ΔH°) and entropy (ΔS°) indicate that the complexation is endothermic. The negative values of the change in the standard free energy (ΔG°) in the range from 293.15K to 308.15K, indicate that the reaction occurs spontaneously and hence the formation of heterobimetallic complex in the solution is favored kinetically and thermodynamically.

Topological evolution and photoluminescent properties of a series of divalent zinc-based metal–organic frameworks tuned via ancillary ligating spacers

The combination of divalent zinc ions, 4-(4-carboxybenzamido)benzoic acid and exo-bidendate bipyridine ligands gave rise to a series of new MOFs: [ZnL(bipy)]·DMF·H2O (1), [ZnL(bpe)]·1.5H2O (2), [ZnL(bpa)]·4H2O (3) and [ZnL(bpp)]·1.75H2O (4) (MOF=metal-organic framework, bipy=4,4′-bipyridine, bpe=trans-1,2-bis(4-pyridyl)ethylene, bpa=1,2-bis(4-pyridinyl)ethane, bpp=1,3-bis(4-pyridinyl)propane, H2L=4,4′-(carbonylimino)dibenzoic acid). Fine tune over the topology of the MOFs was achieved via systematically varying the geometric length of the second ligating bipyridine ligands. Single-crystal X-ray analysis reveals that complex 1 has a triply interpenetrated three-dimensional (3D) framework with elongated primitive cubic topology, whereas isostructural complexes 2 and 3 each possesses a 6-fold interpenetrated diamondiod 3D framework. Further expansion of the length of the bipyridine ligand to bpp leads to the formation of 4, which features an interesting entangled architecture of 2D→3D parallel polycatenation. In addition, the thermogravimetric analyses and solid-state photoluminescent properties of the selected complexes are investigated.

Optical properties of ultraphosphate glasses containing mixed divalent zinc and magnesium ions

Ternary zinc magnesium ultraphosphate glasses corresponding to (ZnO)x(MgO)30−x(P2O5)70 were prepared by melt quenching technique in the range of 5⩽x⩽20mol%. The optical absorption spectra of the glasses were measured at room temperature in the wavelength range between 190 and 1100nm, and the refractive indices of the glasses were measured at room temperature at a wavelength of 632.8nm. The optical absorption spectra indicated that the electronic transition was indirect and associated with the phonon-assisted transition. From the absorption spectra, the optical energy band gap (Eopt) and Urbach energy (EU) values for all of the glass samples were calculated from their ultraviolet edges. The values of Eopt and EU were found to be in the range of 3.54–3.81eV and 0.27–0.45eV, respectively, both of which vary in a non-linear manner, with a turning point at 15mol% of ZnO. The composition-dependence of these values has been suggested and analyzed in the light of switching role of Mg2+ based on its anomalous natural behavior from network builder to modifier depending upon its concentration. The values of refractive index ranged from 1.513 to 1.534. Variations in these optical parameters, as well as variations in density and molar volume are discussed and correlated with the structural changes within the glassy matrix.

Fullerenes toxicity and electronic properties

Nanotechnology globally represents a new direction within scientific development, where the atomic and electronic properties of molecules are used in a unique fashion to produce and construct new and exotic materials and products. Fullerenes (Bucky balls, C60) constitute a particular group within the field of nanotechnology. Fullerenes find applications in medicine, industrial chemistry and electronics. However, there are several unanswered questions about fullerenes and their toxicological properties. Most toxicological studies on fullerenes evolve around the in vitro and in vivo aspects of pristine C60 along with chemically modified C60 molecules. We reviewed toxicology reports on C60. We bring a critical and challenging evaluation of the electronic and quantum properties of C60 molecules in context with the implications on cellular factors and metabolites. The evaluation shows that the reactivity and quantum chemical properties of C60 can have unexpected effects in the cell, by principally absorbing metabolites, such as OH− and H+ ions and alter its reactivity. We thus challenge the present view of C60 solely based on empirical studies, based on the electronic properties of C60 that vary considerably with their size and reaction path. A further example of this is the absorption of divalent zinc ions, which shows an increase in reactivity of the C60 that presents an important pattern of chemical state, reactivity and toxicological potential. The results evaluate the toxicological potential of C60 from a different angle than conventional, by applying a blend of critical review of the findings on C60 toxicity, their chemical and electronic properties.

The Fate of ZnO Nanoparticles Administered to Human Bronchial Epithelial Cells

A particular challenge for nanotoxicology is the evaluation of the biological fate and toxicity of nanomaterials that dissolve in aqueous fluids. Zinc oxide nanomaterials are of particular concern because dissolution leads to release of the toxic divalent zinc ion. Although zinc ions have been implicated in ZnO cytotoxicity, direct identification of the chemical form of zinc taken up by cells exposed to ZnO nanoparticles, and its intracellular fate, has not yet been achieved. We combined high resolution X-ray spectromicroscopy and high elemental sensitivity X-ray microprobe analyses to determine the fate of ZnO and less soluble iron-doped ZnO nanoparticles following exposure to cultures of human bronchial epithelial cells, BEAS-2B. We complemented two-dimensional X-ray imaging methods with atomic force microscopy of cell surfaces to distinguish between nanoparticles that were transported inside the cells from those that adhered to the cell exterior. The data suggest cellular uptake of ZnO nanoparticles is a mechanism of zinc accumulation in cells. Following uptake, ZnO nanoparticles dissolved completely generating intracellular Zn(2+) complexed by molecular ligands. These results corroborate a model for ZnO nanoparticle toxicity that is based on nanoparticle uptake followed by intracellular dissolution.

Hydroxylation mechanism of methane and its derivatives over designed methane monooxygenase model with peroxo dizinc core

The peroxo dizinc Zn(2)O(2) complex Q coordinated by imidazole and carboxylate groups for each Zn center has been designed to model the hydroxylase component of methane monooxygenase (MMO) enzyme, on the basis of the experimentally available structure information of enzyme with divalent zinc ion and the MMO with Fe(2)O(2) core. The reaction mechanism for the hydroxylation of methane and its derivatives catalyzed by Q has been investigated at the B3LYP*/cc-pVTZ, Lanl2tz level in protein solution environment. These hydroxylation reactions proceed via a radical-rebound mechanism, with the rate-determining step of the C-H bond cleavage. This radical-rebound reaction mechanism is analogous to the experimentally available MMOs with diamond Fe(2)O(2) core accompanied by a coordinate number of six for the hydroxylation of methane. The rate constants for the hydroxylation of substrates catalyzed by Q increase along CH(4) < CH(3)F < CH(3)CN ≈ CH(3)NO(2) < CH(3)CH(3). Both the activation strain ΔE(≠)(strain) and the stabilizing interaction ΔE(≠)(int) jointly affect the activation energy ΔE(≠). For the C-H cleavage of substrate CH(3)X, with the decrease of steric shielding for the substituted CH(3)X (X = F > H > CH(3) > NO(2) > CN) attacking the O center in Q, the activation strain ΔE(≠)(strain) decreases, whereas the stabilizing interaction ΔE(≠)(int) increases. It is predicted that the MMO with peroxo dizinc Zn(2)O(2) core should be a promising catalyst for the hydroxylation of methane and its derivatives.

Structural flexibility in complexes bearing a tripodal nitrogen ligand

Complexes of the divalent metal ions of zinc, cobalt and nickel and a tripodal imidazol-based ligand were investigated for their solution chemistry in protic solvents of varying steric demand. Changes in the coordination number from 4 to 6 are observed depending on solvents, temperature and ions present in solution. With bio-relevant N,O ligands, e.g. amino acids as glycine and alanine, five-coordinate complexes are formed. The solid state structures of the five-coordinate complexes [LNi(H2O)Cl]Cl (3a′) and [LZn(pic)]NO3 (L=tris(2-isopropylimidazol-4(5)-yl)phosphane, pic=picolinato) were determined.

Complexation of 1,3-Bis(tris(hydroxymethyl)methylamino)propane Systems Involving Divalent (Cobalt, Nickel, or Zinc) Ions in Aqueous Solution by Potentiometry

Protonation constants of 1,3-bis(tris(hydroxymethyl)methylamino)propane (BTP) and the complexes formed between BTP and Co(II), Ni(II), or Zn(II) metal ions have been studied by glass electrode potentiometry (GEP) in aqueous 0.1 mol·L–1 KNO3 supporting electrolyte at 25 ± 0.1 °C. The complexation model for each M(II)–BTP system was established. The proposed final model for Ni(II)–BTP system is: NiL, NiLH–1, and NiLH–2, with stability constant values, as log β, of 7.13 ± 0.02, −1.32 ± 0.04, and −10.81 ± 0.05, respectively. For Co(II)–BTP and Zn(II)–BTP systems, the proposed final model is constituted by ML, ML2, ML2H–1, and ML2H–2 complexes. For the Co(II)–BTP system, the overall refined stability constants (as log β) are 4.57 ± 0.02, 8.76 ± 0.02, 0.17 ± 0.03, and −8.73 ± 0.03, respectively, and for Zn(II)–BTP system they are 4.99 ± 0.02, 9.18 ± 0.03, 1.01 ± 0.03, and −7.91 ± 0.04, respectively. In a general way, the complex stability was found to follow the trend: Ni(II) > Zn(II) > Co(II).

Noninvasive MRI of β-cell function using a Zn 2+ -responsive contrast agent

Elevation of postprandial glucose stimulates release of insulin from granules stored in pancreatic islet β-cells. We demonstrate here that divalent zinc ions coreleased with insulin from β-cells in response to high glucose are readily detected by MRI using the Zn(2+)-responsive T(1) agent, GdDOTA-diBPEN. Image contrast was significantly enhanced in the mouse pancreas after injection of a bolus of glucose followed by a low dose of the Zn(2+) sensor. Images of the pancreas were not enhanced by the agent in mice without addition of glucose to stimulate insulin release, nor were images enhanced in streptozotocin-treated mice with or without added glucose. These observations are consistent with MRI detection of Zn(2+) released from β-cells only during glucose-stimulated insulin secretion. Images of mice fed a high-fat (60%) diet over a 12-wk period and subjected to this same imaging protocol showed a larger volume of contrast-enhanced pancreatic tissue, consistent with the expansion of pancreatic β-cell mass during fat accumulation and progression to type 2 diabetes. This MRI sensor offers the exciting potential for deep-tissue monitoring of β-cell function in vivo during development of type 2 diabetes or after implantation of islets in type I diabetic patients.

Structural and thermodynamic consequences of the replacement of zinc with environmental metals on estrogen receptor α–DNA interactions

Estrogen receptor α (ERα) acts as a transcription factor by virtue of the ability of its DNA‐binding (DB) domain, comprised of a tandem pair of zinc fingers, to recognize the estrogen response element within the promoters of target genes. Herein, using an array of biophysical methods, we probe the structural consequences of the replacement of zinc within the DB domain of ERα with various environmental metals and their effects on the thermodynamics of binding to DNA. Our data reveal that whereas the DB domain reconstituted with divalent ions of zinc, cadmium, mercury, and cobalt binds to DNA with affinities in the nanomolar range, divalent ions of barium, copper, iron, lead, manganese, nickel, and tin are unable to regenerate DB domain with DNA‐binding potential, although they can compete with zinc for coordinating the cysteine ligands within the zinc fingers. We also show that the metal‐free DB domain is a homodimer in solution and that the binding of various metals only results in subtle secondary and tertiary structural changes, implying that metal coordination may only be essential for binding to DNA. Collectively, our findings provide mechanistic insights into how environmental metals may modulate the physiological function of a key nuclear receptor involved in mediating a plethora of cellular functions central to human health and disease. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Surfactant-mediated complex formation for determination of traces amounts of zinc, cadmium, and lead with 4-(2-thiazolylazo) resorcinol and chemometric methods

The partial least squares modeling is a powerful multivariate statistical tool applied to the spectrophotometric simultaneous determination of the divalent ions of zinc, cadmium, and lead based on the formation of their complexes with 4-(2-thiazolylazo) resorcinol in surfactant media. The linear concentration range for zinc, cadmium, and lead were 0.10-1.31, 0.148-1.92, and 0.148-3.70 mg L( -1), respectively. The experimental calibration set was composed of 36 sample solutions using a mixture design for three component mixtures. The absorption spectra were recorded from 380 through 650 nm. The effect of pH on the sensitivity in determination of zinc, cadmium, and lead was studied in order to choose the optimum pH (pH = 8) for determination. The root-mean-square errors of predictions for zinc, cadmium, and lead were 0.0466, 0.0282, and 0.050, respectively. The proposed method was successfully applied for the determination of zinc, cadmium, and lead in water samples.

Phenotype detection of metallo-β-lactamase among the imipenem resistant Psudomonas and Acinetobacter in the tertiary care hospitals of Dhaka city

Metallo beta lactamases (MBL) are enzymes that have wide spread of activity and they confer a high level of resistance to all b-lactams including carbapenem, except aztreonam [1]. MBLs require divalent zinc ion for their enzymatic activity which is not diminished by serine b lactamase inhibitors like salbactam, tazobactam, clavulinic acid etc but is inhibited by metal chelators like EDTA and thiol based compounds such as 2-mercaptopropionic acid (2-MPA), 10-phenanthroline, calcium dipicholinate etc [2]. They have constant and efficient carbapenemase activity. This MBL production is typically associated with resistance to aminoglycosides and fluoroquinolones further compromising therapeutic options [3]. There are no standard methods for the detection of MBL production in gram negative organism in routine Microbiology practice. The present study was undertaken to evaluate the screening tests like double disk synergy test (DDST) and disk potentiation test (DPT) using ceftazidime (CAZ) and imipenem (IPM) disks with chelating agents like EDTA and 2-MPA. A total of 132 Pseudomonas and 76 Acinetobacter isolates were obtained from Bangabandhu Sheikh Mujib Medical University (BSMMU), Bangladesh Institute of Research and Rehabilitation for Diabetes, and Endocrine and Metabolic disorders (BIRDEM) hospitals of Dhaka city. A total of 53 and 29 IPM resistant Pseudomonas and Acinetobacter isolates respectively were selected. EDTAIPM micro dilution minimum inhibitory concentration (EDTA-IPM micro dilution MIC) method detected MBL in 44 (83%) IPM resistant Pseudomonas and 19(65.5%) Acinetobacter isolates. DDST with CAZ-0.1M EDTA and CAZ-2-MPA detected MBL in 73.6% and 67.9% of IPM resistant Pseudomonas and 55.2% and 48.3% of Acinetobacter isolates respectively. The detection rate was 67.9% and 66.1% in Pseudomonas and 51.7% and 44.8% in Acinetobacter isolates by EDTA-IPM and IPM-2MPA methods respectively. In comparison to DDST, DPT with 0.1M EDTA showed higher sensitivity (89.7%) and specificity (100%) for detection of MBL in Pseudomonas and Acinetobacter. Isolates were also tested for AmpC b lactamase by DPT using chelating agent aminophenyl boronic acid (APB) and it detected AmpC b lactamase in 6.9% and 21.1% MBL positive Pseudomonas and Acinetobacter respectively. MBL producing Pseudomonas and Acinetobacter are emerging in our country. Rapid detection of these MBLs is necessary to institute appropriate treatment and effective infection control measures. Simple screening test like DPT using CAZ/IPM with 0.1M EDTA can be introduced into the routine clinical laboratories for their early detection.

Transport of copper, nickel and zinc ions across ultrafiltration membrane based on modified polysulfone and cellulose acetate

AbstractIn this work, an attempt has been made to separate divalent copper, nickel and zinc ions from aqueous solutions by modified polymeric membranes. Membranes from polysulfone (PSf) and cellulose acetate (CA) were prepared in the absence and presence of the hydrophilic polymer, sulfonated poly ether ether ketone (SPEEK) and additive, polyethyleneglycol (PEG 600), in various compositions. Studies were carried out to find the rejection and permeate flux of Cu(II), Ni(II) and Zn(II) ions using polyethyleneimine (PEI) as the chelating ligand. On increasing concentrations of SPEEK and PEG in PSf and CA casting solution, the rejection of metal ions is decreasing while the permeate flux has an increasing trend. These effects are due to the increased pore formation in the PSf and CA membranes because of the hydrophilic polymer and additive. In general, it was found that CA/SPEEK/PEG blend membranes displayed higher permeate flux and lower rejection compared to PSf/SPEEK/PEG blend membranes at all additive concentrations. It has also been demonstrated that the extent of removal of metal ions depend on the affinity of metal ions to PEI to form macromolecular complexes and the thermodynamic stability of the formed complexes. Copyright © 2010 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Synthesis, structure, and complexing ability of a novel ligand system, 1-benzyl-2-benzimidazolylhydrazone of pyrrol-2′-carbaldehyde

A new ligand system, the product of condensation of pyrrol-2-carbaldehyde and 1-benzyl-2-hydrazinobenzimidazole is synthesized. Possible tautomers of the hetarylhydrazone are calculated and its acidebase properties studied, as well as its complexing ability with respect to divalent ions of copper, nickel, zinc, and chromium.

Fragment molecular orbital-based molecular dynamics (FMO-MD) simulations on hydrated Zn(II) ion

Abstract Recently, the method of fragment molecular orbital-based molecular dynamics (FMO-MD) was enhanced by including the three-body corrections (FMO3) [Y. Komeiji, Y. Mochizuki, T. Nakano, Chem. Phys. Lett. 484 (2010) 380]. This simulation protocol was applied to a droplet model consisting of a divalent zinc ion and 64 water molecules, in order to investigate the hydration structure in ab initio fashion. The first peak position of the Zn–O radial distribution function (RDF) was evaluated to be 2.05 A at the FMO3-HF/6-31G level of theory, which was in agreement with an X-ray value of 2.06 ± 0.02 A. The coordination number was evaluated to be 6, corresponding to an octahedral coordination.

Separation and Recovery of Zinc(II) and Cobalt(II) from a Mixed Sulfate/Thiocyanate Solution using some Commercial Organophosphorus Extractants

The separation and recovery of divalent zinc and cobalt ions from mixed sulfate and thiocyanate solutions have been carried out using CYANEX 921 (trioctylphosphine oxide), CYANEX 923 (a mixture of straight chain alkylated phosphine oxides), and CYANEX 925 (a mixture of branched chain alkylated phosphine oxides) in kerosene. Different parameters affecting the extraction equilibrium of Zn(II) and Co(II) in addition to temperature, were studied and the stoichiometry of the extracted Zn(II) and Co(II) species were postulated based on the slope analysis method. The extraction percent of the metal ions was found to increase with increasing pH and zinc was preferentially extracted over cobalt with CYANEX 925. The respective loaded organic phases were stripped with different mineral acids. The highest separation factor was obtained when using 0.015 M CYANEX 925 as extractant. Based on the obtained results, the application of the method was tested to separate Zn(II) and Co(II) from Nickel Metal Hydride batteries (Ni-MH batteries) leached by 2.0 M H2SO4 and good results were obtained.

Updated Functional Classification of β-Lactamases

Two classification schemes for beta-lactamases are currently in use. The molecular classification is based on the amino acid sequence and divides beta-lactamases into class A, C, and D enzymes which utilize serine for beta-lactam hydrolysis and class B metalloenzymes which require divalent zinc ions for substrate hydrolysis. The functional classification scheme updated herein is based on the 1995 proposal by Bush et al. (K. Bush, G. A. Jacoby, and A. A. Medeiros, Antimicrob. Agents Chemother. 39:1211-1233, 1995). It takes into account substrate and inhibitor profiles in an attempt to group the enzymes in ways that can be correlated with their phenotype in clinical isolates. Major groupings generally correlate with the more broadly based molecular classification. The updated system includes group 1 (class C) cephalosporinases; group 2 (classes A and D) broad-spectrum, inhibitor-resistant, and extended-spectrum beta-lactamases and serine carbapenemases; and group 3 metallo-beta-lactamases. Several new subgroups of each of the major groups are described, based on specific attributes of individual enzymes. A list of attributes is also suggested for the description of a new beta-lactamase, including the requisite microbiological properties, substrate and inhibitor profiles, and molecular sequence data that provide an adequate characterization for a new beta-lactam-hydrolyzing enzyme.

A Possible Role for Metallic Ions in the Carbohydrate Cluster Recognition Displayed by a Lewis Y Specific Antibody

BackgroundLewis Y (Ley) is a blood group-related carbohydrate that is expressed at high surface densities on the majority of epithelial carcinomas and is a promising target for antibody-based immunotherapy. A humanized Ley-specific antibody (hu3S193) has shown encouraging safety, pharmacokinetic and tumor-targeting properties in recently completed Phase I clinical trials.Methodology/Principal FindingsWe report the three-dimensional structures for both the free (unliganded) and bound (Ley tetrasaccharide) hu3S193 Fab from the same crystal grown in the presence of divalent zinc ions. There is no evidence of significant conformational changes occurring in either the Ley carbohydrate antigen or the hu3S193 binding site, which suggests a rigid fit binding mechanism. In the crystal, the hu3S193 Fab molecules are coordinated at their protein-protein interface by two zinc ions and in solution aggregation of Fab can be initiated by zinc, but not magnesium ions. Dynamic light scattering revealed that zinc ions could initiate a sharp transition from hu3S193 Fab monomers to large multimeric aggregates in solution.Conclusions/SignificanceZinc ions can mediate interactions between hu3S193 Fab in crystals and in solution. Whether metallic ion mediated aggregation of antibody occurs in vivo is not known, but the present results suggest that similar clustering mechanisms could occur when hu3S193 binds to Ley on cells, particularly given the high surface densities of antigen on the target tumor cells.

Influence of divalent copper, manganese and zinc ions on fibril nucleation and elongation of the amyloid-like yeast prion determinant Sup35p-NM

There is a large body of evidence that divalent metal ions, particularly copper, might play a role in several protein folding pathologies like Alzheimer's disease, Parkinson's disease or the prion diseases. However, contribution of metal ions on pathogenesis and their molecular influence on the formation of amyloid structures is not clear. Therefore, the general influence of metals on the formation of amyloids is still controversially discussed. We have utilized the well established system of yeast Sup35p-NM to investigate the role of three different metal ions, Cu(2+), Mn(2+) and Zn(2+), on amyloidogenesis. Recently, it has been shown that the prion determining region NM of the Saccharomyces cerevisiae prion protein Sup35p, which is responsible for the yeast prion phenotype [PSI(+)], specifically binds Cu(2+) ions. We further characterized the affinity of NM for Cu(2+), which were found to be comparable to that of other amyloidogenic proteins like the mammalian prion protein PrP. The specific binding sites could be located in the aminoterminal N-region which is known to initiate formation of amyloidogenic nuclei. In the presence of Cu(2+), fibril nucleation was significantly delayed, probably due to influences of copper on the oligomeric ensemble of soluble Sup35p-NM, since Cu(2+) altered the tertiary structure of soluble Sup35p-NM, while no influences on fibril elongation could be detected. The secondary structure of soluble or fibrous protein and the morphology of the fibrils were apparently not altered when assembled in presence of Cu(2+). In contrast, Mn(2+) and Zn(2+) did not bind to Sup35p-NM and did not exhibit significant effects on the formation of NM amyloid fibrils.

Estimation of Binding Constants of Cd(II), Ni(II) and Zn(II) with Polyethyleneimine (PEI) by Polymer Enhanced Ultrafiltration (PEUF) Technique

Continuous and batch processes of polymer enhanced ultrafiltration for the estimation of binding constants of divalent cadmium, nickel, and zinc ions have been elaborated. Polyethyleneimine was used as a complexation agent. Effect of pH and ionic strength on the binding ability of target metal ions to polyethyleneimine were estimated by continuous mode PEUF system. A mathematical model was developed to estimate apparent complexation constants of metal ions with PEI. The development of this model, which is in good agreement with experimental data, enables to compare the data obtained in both continuous and batch system and correlate the effect of pH and ionic strength with apparent binding constants.