Zinc Metal Ions Research Articles

Coordination chemistry of two new tetraaza Ni(II) and Cu(II) macrocyclic and two new Co(II) and Zn(II) macroacyclic Schiff base complexes containing piperazine moiety: X-ray crystal structures of Ni(II) and Zn(II) complexes

A new potentially tetradentate (N4) Schiff base ligand (L), 1,9,12,20-tetraazatetracyclo[18.2.2.02,7.014,19]tetracosa-2(7),3,5,8,12,14(19),15,17-octaene containing a piperazine moiety is described. Macrocyclic Schiff base complexes, [NiL](ClO4)2 (1) and [CuL](ClO4)2 (2) have been obtained from equimolar amounts of ligand (L) with nickel(II) and copper(II) metal ions. While the equilibrium reaction in the presence of cobalt(II) and zinc(II) metal ions with ligand L in a 1:1 molar ratio yielded the open-chain Schiff base complexes, [CoL′](ClO4)2 (3) and [ZnL′](ClO4)2 (4) containing two terminal primary amino groups. The ligand L′ is 1,4-bis(2-(2-aminoethyliminomethyl)phenyl)piperazine. The crystal structures of (1) and (4) have been also determined by X-ray diffraction. It was shown that the Ni(II) is coordinated to the ligand L by two nitrogen atoms of piperazine group and two nitrogen atoms of the imine groups, in a slightly distorted square-planar geometry. Also single crystal X-ray analysis of (4) confirmed a distorted octahedral arrangement in the vicinity of Zn atom with N6 donor set. The spectroscopic characterization of all complexes is consistent with their crystal structures.

Adsorption of zinc (Zn 2+) from aqueous solution on natural bentonite

The adsorptive properties of natural bentonite in the removal of zinc (Zn 2+) from aqueous solution were studied. The results show that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, and solution pH but decreases with the amount of adsorbent and temperature of the system. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn 2+) on bentonite is a two step process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreasing intraparticle diffusion in the interior of the adsorbent which has also been confirmed by intraparticle diffusion model. Overall the kinetic studies showed that the zinc adsorption process followed pseudo-second-order kinetic model. The different kinetic parameters including rate constant, half adsorption time, and diffusion coefficient are determined at different physicochemical conditions. The equilibrium adsorption results are fitted better with Langmuir isotherm compared to Freundlich models. The value of separation factor, R L from Langmuir equation and Freundlich constant, n both give an indication of favorable adsorption. Finally in thermodynamic studies, it has been found that the adsorption process is exothermic due to negative ∆ H 0 accompanied by a decrease in entropy change and Gibbs free energy change (∆ G 0).

The use of Apatite II™ to remove divalent metal ions zinc(II), lead(II), manganese(II) and iron(II) from water in passive treatment systems: Column experiments

The conventional passive treatments for remediation of acid mine drainage using calcite are not totally efficient in the removal of certain heavy metal ions. Although pH increases to 6–7 and promotes the precipitation of trivalent and some divalent metals as hydroxides and carbonates, the remaining concentrations of some divalent metals ions do not fulfill the environmental regulations. In this study, Apatite II™, a biogenic hydroxyapatite, is used as an alternative reactive material to remove Zn(II), Pb(II), Mn(II) and Fe(II). Apatite II™ reacted with acid water releasing phosphate and increasing pH up to 6.5–7, inducing metals to precipitate mainly as metal–phosphates: zinc precipitated as hopeite, Zn3(PO4)2·4H2O, lead as pyromorfite, Pb5(PO4)3OH, manganese as metaswitzerite, Mn3(PO4)2·4H2O and iron as vivianite, Fe3(PO4)2·8H2O. Thus, metal concentrations from 30 to 75mgL−1 in the inflowing water were depleted to values below 0.10mgL−1. Apatite II™ dissolution is sufficiently fast to treat flows as high as 50m/a. For reactive grain size of 0.5–3mm, the treatment system ends due to coating of the grains by precipitates, especially when iron and manganese are present in the solution.

Study of mango biomass (Mangifera indica L) as a cationic biosorbent

Unfertilizable fruiting buds of mango plant Mangifera Indica L, an agrowaste, is used as a biomass in this study. The efficacy of the biosorbent was tested for the removal of lead, copper, zinc and nickel metal ions using batch experiments in single and binary metal solution under controlled experimental conditions. It is found that metal sorption increases when the equilibrium metal concentration rises. At highest experimental solution concentration used (150 mg/L), the removal of metal ions were 82.76 % for lead, 76.60 % for copper, 63.35 % for zinc and 59.35 % for nickel while at lowest experimental solution concentration (25 mg/L), the removal of metal ions were 92.00% for lead, 86.84 % for copper, 83.96 % for zinc and 82.29 % for nickel. Biosorption equilibrium isotherms were plotted for metal uptake capacity (q) against residual metal concentrations (Cf) in solution. The q versus Cf sorption isotherm relationship was mathematically expressed by Langmuir and Freundlich models. The values of separation factor were between zero and one indicating favourable sorption for four tested metals on the biosorbent. The surface coverage values were approaching unity with increasing solution concentration indicating effectiveness of biosorbent under investigation. The non-living biomass of Mangifera indica L present comparable biosorption capacity for lead, copper, zinc and nickel metal ions with other types of biosorbent materials found in literature and is effective to remove metal ions from single metal solutions as well as in the presence of other co-ions with the main metal of solution.

Selective adsorption of chromium(VI) from zinc(II) and other metal ions using persimmon waste gel

An adsorption gel was prepared from persimmon waste, a cellulosic material, rich in polyphenolic compounds, which exhibits a high affinity for chromium(VI). It was prepared by cross-linking persimmon waste with concentrated sulphuric acid. Adsorption tests for different metal ions such as Cr(VI), Cr(III), Fe(III), Zn(II), Cd(II) and Pb(II) from aqueous solution at pH values ranging from (pH 1 to 5) found Cr(VI) to be selectively adsorbed on the cross-linked gel over the other metal ions studied. The adsorption isotherm of Cr(VI) followed the Langmuir type of adsorption and exhibited a maximum loading capacity of 7.18 mol kg − 1 at pH 1. Selective removal of Cr(VI) from Zn(II) was successfully demonstrated by using a column packed with the persimmon waste gel.

Synthesis and characterization of Ni(II), Cu(II) and Zn(II) complexes with new macrocyclic Schiff base ligands containing piperazine moiety

Two new macrocyclic Schiff base ligands L 1 and L 2 from [1 + 1] and [2 + 2] condensation reaction, respectively, have been obtained in a one-pot synthesis starting from 1,4-bis(2-formylphenyl)piperazine and 2,2-dimethyl-propylendiamine. Unfortunately, because of the low solubility of two products, we were unable to separate them effectively. Macrocyclic Schiff base complexes [NiL 1](ClO 4) 2, [CuL 1](ClO 4) 2 and [ZnL 1](ClO 4) 2 were prepared from the reaction of a mixture of L 1 and L 2 in the presence of nickel(II), copper(II) and zinc(II) metal ions, respectively. In all cases, only [1 + 1] condensation products were obtained and no metal complexes were isolated with the L 2 macrocycle. All of complexes have been characterized by elemental analysis, IR spectra, FAB-MS, conductivity measurements and in the case of Zn(II) complex by 1H and 13C NMR spectroscopy. Crystal structures of [NiL 1](ClO 4) 2 and [NiL 1′](ClO 4) 2 complexes have been also determined. The Ni(II) is coordinated to the ligand L 1 and L 1′ by two nitrogen atoms of piperazine group and two nitrogen atoms of the imine groups, in a slightly distorted square-planar geometry.

Synthesis and Characterization of Novel Thermoplastic Films for Removal of Heavy Metal Ions

The main objective of this study is to establish the applicability of novel thermoplastic films based on extracted gelatins from bovine (Gb) and bird (Gc) bones in addition to hide powder (HP), which blended with modified polyethylene (MPE) for the removal of heavy metal ions such as copper (II), chromium (VI), nickel (II) and zinc (II) from aqueous media. The chemical reaction between 2-oxoglutaric acid with furfural in presence of methyl amine, via Mannich reaction mechanism, resulted in chemical compound I. The chemical structure of product I was confirmed by different spectroscopic tools such as: nuclear magnetic resonance (13C- and 1H-NMR) and Fourier transform infrared spectroscopy (FT-IR). The synthesized chemical product I was used as compatibilizing agent for blending Gb, Gc and Hp with MPE to obtain thermoplastic films using a polymer melting technique. The efficiency of the prepared films for absorption of different heavy metal ions from aqueous solution was investigated. The results indicated that the compatibilized films (MPE/I/HP) illustrated a maximum removal of zinc metal ions (∼100%) under conditions of initial metal concentration about 240 mg/l. While, at initial metal concentration of about 150 mg/l, they exhibited excellent efficiency for removal of mixed metal ions of about 97–100% relative to the uncompatibilized ones (MPE/HP) 0%.

Computational design and elaboration of a de novo heterotetrameric alpha-helical protein that selectively binds an emissive abiological (porphinato)zinc chromophore.

The first example of a computationally de novo designed protein that binds an emissive abiological chromophore is presented, in which a sophisticated level of cofactor discrimination is pre-engineered. This heterotetrameric, C(2)-symmetric bundle, A(His):B(Thr), uniquely binds (5,15-di[(4-carboxymethyleneoxy)phenyl]porphinato)zinc [(DPP)Zn] via histidine coordination and complementary noncovalent interactions. The A(2)B(2) heterotetrameric protein reflects ligand-directed elements of both positive and negative design, including hydrogen bonds to second-shell ligands. Experimental support for the appropriate formulation of [(DPP)Zn:A(His):B(Thr)](2) is provided by UV/visible and circular dichroism spectroscopies, size exclusion chromatography, and analytical ultracentrifugation. Time-resolved transient absorption and fluorescence spectroscopic data reveal classic excited-state singlet and triplet PZn photophysics for the A(His):B(Thr):(DPP)Zn protein (k(fluorescence) = 4 x 10(8) s(-1); tau(triplet) = 5 ms). The A(2)B(2) apoprotein has immeasurably low binding affinities for related [porphinato]metal chromophores that include a (DPP)Fe(III) cofactor and the zinc metal ion hemin derivative [(PPIX)Zn], underscoring the exquisite active-site binding discrimination realized in this computationally designed protein. Importantly, elements of design in the A(His):B(Thr) protein ensure that interactions within the tetra-alpha-helical bundle are such that only the heterotetramer is stable in solution; corresponding homomeric bundles present unfavorable ligand-binding environments and thus preclude protein structural rearrangements that could lead to binding of (porphinato)iron cofactors.

Isolation and purification of superoxide dismutase from garlic using two-stage ultrafiltration

The objective of this work is to develop a membrane-based cost-effective process for the separation and purification of superoxide dismutase (SOD) from garlic. It was found that a two-stage ultrafiltration process using a 100 kDa MWCO regenerated cellulose membrane and a 50 kDa MWCO polyethersulfone membrane could successfully be employed to isolate SOD by removing the bigger macromolecules and smaller molecules from the crude feedstock. The effects of solution pH and ionic strength on the transmission of SOD and the presence of impurity proteins with molecular weights close to SOD were quantified using the pulsed sample injection ultrafiltration technique. The effect of other parameters including system hydrodynamics and mass transfer, in terms of stirring speed, and permeate flux on the separation of SOD was also studied using parameter scanning ultrafiltration. Under optimized conditions, the purity of SOD obtained was greater than 98.0% after two-stage ultrafiltration process and the recovery of SOD from the feedstock was close to 90%. The resulting SOD product was analyzed by isoelectric focusing (IEF), SDS-PAGE and circular dichroism (CD), to confirm its isoelectric point, molecular weight and molecular secondary structure of the garlic SOD. The purity and activity as well as effects of metal ions (copper and zinc ions) on SOD specific activities were experimentally determined.

On the metal ion (Zn2+, Cu2+) coordination with beta-amyloid peptide: DFT computational study

As is widely accepted, the crucial event of the progress of Alzheimer's disease is the formation of extracellular neurotoxic amyloid plaques, consisting mainly of 40 or 42 amino acid residues, in the brain. Zinc and copper metal ions are involved in this process, since they enhance the amyloid beta aggregation and are incorporated into plaques. In this paper we have analyzed theoretically the energetics implied in the formation of some complexes of both cations, adopting a number of models that take into account various coordination environments. The aim was to determine which among the coordination patterns examined is the favoured one in order to give better insight in the controversy concerning the metal binding site of amyloid beta peptide.

Zinc(II) complexes of 2-acetyl pyridine 1-(4-fluorophenyl)-piperazinyl thiosemicarbazone: Synthesis, spectroscopic study and crystal structures – Potential anticancer drugs

2-Acetyl pyridine thiosemicarbazone containing an 1-(4-fluorophenyl)-piperazinyl ring incorporated at N(4)-position, HAcPipPheF (1) and the zinc(II) complexes [Zn(AcPipPheF)(2)] (2) and [Zn(OAc)(AcPipPheF)](2) (3) have been prepared and structurally characterized by means of vibrational and NMR ((1)H and (13)C) spectroscopy. The crystal structures of the compounds 1-3 have been determined by X-ray crystallography. The metal coordination geometry of [Zn(AcPipPheF)(2)] is described as distorted octahedral configuration in a trans-N-cis-N-cis-S configuration. In [Zn(OAc)(AcPipPheF)](2) one of the acetato group exhibits monoatomic bridge and the other bridges in a bidentate manner. The zinc(1) metal ion is coordinated in a distorted octahedral configuration while the metal coordination of Zn(2) is described as distorted square pyramidal. Biomedical studies revealed that, compounds 1-3 displayed potent anticancer activity. The antiproliferative activity of 1-3 was found to be considerably stronger than that of cis-platin. The IC(50) values range from 26 to 90nM, against all cell lines tested, while for cis-platin the IC(50) values range from 2 to 17microM and for the zinc salt, ZnCl(2), the IC(50) values range from 81 to 93microM. The complex 3 shows the highest activity against all four cancer cell lines and the highest selectivity against K562 and MDA-MB-453 cancer cell lines. The compounds inhibited tumor cell proliferation by arresting the cell cycle progression at the S phase.

Synthetic Peptides as Structural Maquettes of Angiotensin‐I Converting Enzyme Catalytic Sites

The rational design of synthetic peptides is proposed as an efficient strategy for the structural investigation of crucial protein domains difficult to be produced. Only after half a century since the function of ACE was first reported, was its crystal structure solved. The main obstacle to be overcome for the determination of the high resolution structure was the crystallization of the highly hydrophobic transmembrane domain. Following our previous work, synthetic peptides and Zinc(II) metal ions are used to build structural maquettes of the two Zn-catalytic active sites of the ACE somatic isoform. Structural investigations of the synthetic peptides, representing the two different somatic isoform active sites, through circular dichroism and NMR experiments are reported.

Syntheses, characterization and antitumor activities of transition metal complexes with isoflavone

Five new complexes were synthesized by the reaction of 4'-methoxy-5,7-dihydroxy-isoflavone ligand (a) with transition metal ions zinc (Zn(2+)) (complex b), manganese (Mn(2+)) (complex c), copper (Cu(2+)) (complex d), cobalt (Co(2+)) (complex e) and nickel (Ni(2+)) (complex f). The composition of the complexes has been characterized by elemental analysis, IR, mass spectrometry (MS) and (1)H NMR spectrometric techniques. Their antitumor properties were evaluated against five human cancer cell lines using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. The results indicated that the complexes possess higher growth inhibitory effects than free isoflavone and corresponding metal ions. Complex c and f showed greater antitumor activity and selectivity than other described complexes, even more effective than the positive control cisplatin against the selected cell lines. In addition, DNA flow cytometric analysis demonstrated that complexes display a significant G(2)/M phase arrest, which then progressed to early apoptosis as detected by flow cytometry after double-staining with annexin V and propidium iodide (PI).

A comparative analysis of the fluorescence properties of the wild-type and active site mutants of the hepatitis C virus autoprotease NS2-3

Hepatitis C virus encodes an autoprotease, NS2-3, which is required for processing of the viral polyprotein between the non-structural NS2 and NS3 proteins. This protease activity is vital for the replication and assembly of the virus and therefore represents a target for the development of anti-viral drugs. The mechanism of this auto-processing reaction is not yet clear but the protease activity has been shown to map to the C-terminal region of NS2 and the N-terminal serine protease region of NS3. The NS2-3 precursor can be expressed in Escherichia coli as inclusion bodies, purified as denatured protein and refolded, in the presence of detergents and the divalent metal ion zinc, into an active form capable of auto-cleavage. Here, intrinsic tryptophan fluorescence has been used to assess refolding in the wild-type protein and specific active site mutants. We also investigate the effects on protein folding of alterations to the reaction conditions that have been shown to prevent auto-cleavage. Our data demonstrate that these active site mutations do not solely affect the cleavage activity of the HCV NS2-3 protease but significantly affect the integrity of the global protein fold.

Novel role for theSaccharomyces cerevisiaeoligopeptide transporter Opt2 in drug detoxificationIn memory of Ghassan Belhadj.

Saccharomyces cerevisiae Opt2 is a member of the oligopeptide transporter family that was initially identified to transport tetra- and pentapeptides. Mutants deleted for the OPT2 gene exhibit no growth defects under normal culture conditions. We identified OPT2 from a high-throughput screen that when deleted results in mutants that displayed sensitivity to the anticancer agent bleomycin. The opt2Delta mutant was also reisolated in two additional genome-wide screens designed to identify mutants that are sensitive to the immunosuppressant rapamycin and the divalent metal ion zinc. However, the role of Opt2 in protecting cells against these agents was not investigated. Herein, we show that opt2Delta mutants are also sensitive to a wide variety of toxic agents that are typically detoxified by the vacuoles. Mutants lacking two other related oligopeptide transporters, Opt1 and Ygl114w, showed no significant sensitivities to these drugs, indicating a specific role for Opt2 in drug detoxification. The sensitivities of the opt2Delta mutants were not related to an increased drug uptake but rather to the presence of several small vesicles instead of a functional large vacuole. We propose that Opt2 has a novel function involving the fusion of vesicles to form a mature vacuole.

Removal of zinc metal ion (Zn 2+) from its aqueous solution by kaolin clay mineral: A kinetic and equilibrium study

A laboratory batch study has been performed to study the effect of various physic-chemical factors such as initial metal ion concentration, solution pH, and amount of adsorbent, contact time and temperature on the adsorption characteristics of zinc (Zn 2+) metal ions onto kaolin. It has been found that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, solution pH but decreases with the amount of adsorbent and temperature of the system. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn 2+) on kaolin is a two steps process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreasing intra-particle diffusion in the interior of the adsorbent which has also been confirmed by intra-particle diffusion model. The equilibrium time is found to be in the order of 60 min. Overall the kinetic studies showed that the zinc adsorption process followed pseudo-second-order kinetics among pseudo-first-order and intra-particle diffusion model. The different kinetic parameters including rate constant are determined at different initial metal ion concentration, solution pH, amount of adsorbent and temperature respectively. The equilibrium adsorption results are analyzed by both Langmuir and Freundlich models to determine the mechanistic parameters associated with the adsorption process. The value of separation factor, R L from Langmuir equation also gives an indication of favorable adsorption. Finally thermodynamic parameters are determined at three different temperatures and it has been found that the adsorption process is exothermic due to negative Δ H° accompanied by decrease in entropy change and Gibbs free energy change (Δ G°).

Amyloid plaques in PSAPP mice bind less metal than plaques in human Alzheimer's disease

Amyloid beta (Aβ) is the primary component of Alzheimer's disease (AD) plaques, a key pathological feature of the disease. Metal ions of zinc (Zn), copper (Cu), iron (Fe), and calcium (Ca) are elevated in human amyloid plaques and are thought to be involved in neurodegeneration. Transgenic mouse models of AD also exhibit amyloid plaques, but fail to exhibit the high degree of neurodegeneration observed in humans. In this study, we imaged the Zn, Cu, Fe, and Ca ion distribution in the PSAPP transgenic mouse model representing end-stage AD (N=6) using synchrotron X-ray fluorescence (XRF) microprobe. In order to account for differences in density in the plaques, the relative protein content was imaged with synchrotron Fourier transform infrared microspectroscopy (FTIRM) on the same samples. FTIRM results revealed a 61% increase in protein content in the plaques compared to the surrounding tissue. After normalizing to protein density, we found that the PSAPP plaques contained only a 29% increase in Zn and there was actually less Cu, Fe, and Ca in the plaque compared to the surrounding tissue. Since metal binding to Aβ is thought to induce redox chemistry that is toxic to neurons, the reduced metal binding in PSAPP mice is consistent with the lack of neurodegeneration in these animals. These findings were in stark contrast to the high metal ion content observed in human AD plaques, further implicating the role of metal ions in human AD pathology.

Synthesis, Spectroscopic and Biological Activity of New Mononuclear Transition Metal Complexes of Macrocyclic Schiff Bases Derived from 1,1′-Diacetylferrocin

Two series of mono-nuclear complexes with tetradentate macrocyclic Schiff base ligands, derived from the condensation of 1,1′-diacetylferrocene with 1,3-diaminopropanein in the molar ratio 1:1 and 1:2 have been prepared. The structures of these ligands were elucidated by different spectroscopic methods. The two Schiff base ligands react with copper(II), nickel(II), cobalt(II), and Zinc(II) metal ions in the molar ratio 1:1. The structures of complexes were identified by elemental analyses, infrared, electronic spectra, 1 H-NMR, 13 C-NMR, magnetic susceptibility, conductivity measurement and TGA analysis. The ligands and the complexes show growth inhibitory activity against pathogenic bacteria and plant pathogenic fungi.

Micro-solvation of the Zn2+ ion—a case study

The structures and thermodynamic parameters of hydrated zinc ion clusters incorporating a single zinc ion and up to eighteen water molecules have been determined with a quantum mechanical hybrid density functional, namely B3LYP using cc-PVDZ basis functions for H and O and a split valence 6-31G (d, p) basis function for Zn. The geometries for all the zinc ion water clusters are optimized with several initial guess structures and without imposing any initial symmetry restriction. Zinc metal ion is found to be preferably four coordinated for smaller sizes of hydrated cluster but attains an octahedral coordination for larger sizes (n >or= 11) of hydrated cluster. Structures with seven or more than seven water molecules attached directly to the central zinc ion are not found. The calculated gas phase coordination number in the first solvation sphere of a large hydrated zinc metal ion is found to be six and the same is also confirmed in the force field based classical molecular dynamics simulation study for an aqueous zinc ion and thus confirms the experimental findings. The equilibrium zinc-oxygen distance of 2.09328 A at the present B3LYP level of study is in excellent agreement with the X-ray diffraction result of 2.093 +/- 0.002 A for a hexahydrated zinc cluster.

Potentiometric studies on nickel(II), copper(II) and zinc(II) metal complexes with new schiff bases containing cyclobutane and thiazole groups in 60% dioxane-water mixture

The acid-base equilibria of Schiff bases containing cyclobutane and thiazole functional groups and their copper(II), nickel(II) and zinc(II) complexes were investigated potentiometrically in 60% dioxane-water media at 25. 0 ± 0. 1 oC and I = 0. 10 mol L-1 NaClO4. The values of the protonation constants determined in this study, logKOH, logKNH(1) and logKNH(2), are related to the protonation of the phenolate oxygen atom, the nitrogen atom on the thiazole ring and the imine nitrogen atom, respectively. The variation of the protonation constants of the Schiff bases was interpreted on the basis of structural factors. The Schiff bases form stable complexes with copper(II), nickel(II) and zinc(II) metal ions. There was not a meaningful correlation between the basicity of the Schiff bases and the stability constants of their complexes. Complex stabilities follow the trend copper(II) > nickel(II) > zinc(II), which is in agreement with the Irving-Williams series.