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Zn2+
Terms modified by Zn2+ Selected AbstractsCrystallization kinetics of ZnS precipitation; an experimental study using the mixed-suspension-mixed-product-removal (MSMPR) methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2004Mousa Al-Tarazi Abstract The precipitation kinetics of zinc sulfide were studied using a lab scale mixed-suspension-mixed-product-removal (MSMPR) precipitation reactor. The vessel was operated at different feed concentrations, molar ratios, stirrer speeds, pH-values, feed injection positions and residence times. Primary nucleation and volume average crystal growth rates as well as agglomeration kernel were determined. Relationships were found between the rates of the different crystallization steps on the one hand and supersaturation, stirrer speeds, pH-values, Zn2+ to S2- ratio, feed positions on the other. These show that larger crystals are obtained at high supersaturation, moderate stirrer speeds, small residence times, a pH-value of around 5 and high Zn2+ to S2- ratios. One should realize though that the applied MSMPR method is not the most optimal technique for examining fast precipitation reactions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Calixarene/Nafion-Modified Bismuth-Film Electrodes for Adsorptive Stripping Voltammetric Determination of LeadELECTROANALYSIS, Issue 17-18 2009Ferenc Torma Abstract This paper presents an enhanced adsorptive stripping voltammetric procedure (AdSV) for the determination of Pb2+, which relies on the accumulation of the metals at a calixarene-based chemically modified bismuth-film electrode on glassy carbon substrate. Following the accumulation of the target metals at open circuit and a medium exchange, both the square wave anodic stripping detection of the metal ions and the in situ bismuth-film formation was performed simultaneously in a Bi3+ containing supporting electrolyte. The analysis of Pb2+ under optimized conditions resulted in stripping responses with good linearity (in the range 0.05,0.6,,M) and precision (RSD=1.12% at 0.2,,M Pb2+; n=10) and low detection limit (0.02,,g/L at 10,min preconcentration). The determination of Pb2+ (0.4,,M) at 100-fold excess of interfering ions (Cd2+, Cu2+ and Zn2+) yielded well resolved lead signal. The analytical utility of the method elaborated was tested in the analysis of trace Pb2+ in environmental water samples. [source] Voltammetric Investigation of Zinc Release from Metallothioneins Modulated by the Glutathione Redox Couple and Separated with a Porous MembraneELECTROANALYSIS, Issue 20 2008Lin Liu Abstract Glutathione (GSH), in addition to serving as a redox buffer in cellular environment, has been suggested as a modulator in metal regulation and homeostasis by metallothioneins (MTs). The interactions of MTs with both GSH and its oxidized form GSSG have been shown to govern the direction of metal transfer. Common methods for the determination of zinc release from MTs modulated by GSH/GSSG either involve radioactive species or enzymes or are labor-intensive. In this study, upon separation of Zn2+ from the reaction mixture of MTs and GSH with a centrifugal filter membrane, differential pulse voltammetry (DPV) was used for the Zn2+ quantification. The same approach is extended to the studies of metal transfer between Zn7MT with a GSH/GSSG mixture and that between Zn7MT with GSSG. The concomitant conversion between the free thiol and disulfide bonds was confirmed with UV-vis spectrophotometry. The results demonstrate that GSSG, GSH, and the GSH/GSSG mixture all modulate zinc release from Zn7MT. The percentage of zinc release increases in the order of GSH, GSSG, and the GSH/GSSG mixture. The new approach is demonstrated to be well suited for investigation of redox regulation of MT and its reaction with zinc-containing enzymes. [source] Silver(I)-Selective PVC Membrane Potentiometric Sensor Based on a Recently Synthesized Calix[4]areneELECTROANALYSIS, Issue 10 2006Ayça Demirel Abstract A new PVC membrane potentiometric sensor for Ag(I) ion based on a recently synthesized calix[4]arene compound of 5,11,17,23-tetra- tert -butyl-25,27-dihydroxy-calix[4]arene-thiacrown-4 is developed. The electrode exhibits a Nernstian response for Ag(I) ions over a wide concentration range (1.0×10,2,1.0×10,6 M) with a slope of 53.8±1.6,mV per decade. It has a relatively fast response time (5,10,s) and can be used for at least 2 months without any considerable divergence in potentials. The proposed electrode shows high selectivity towards Ag+ ions over Pb2+, Cd2+, Co2+, Zn2+, Cu2+, Ni2+, Sr2+, Mg2+, Ca2+, Li+, K+, Na+, NH4+ ions and can be used in a pH range of 2,6. Only interference of Hg2+ is found. It is successfully used as an indicator electrode in potentiometric titration of a mixture of chloride, bromide and iodide ions. [source] Capillary electrophoretic study of the binding of zinc(II) ion to bacitracin A1 in water-2,2,2-trifluoroethanolELECTROPHORESIS, Issue 10 2003Massimo Castagnola Abstract Binding of Zn2+ to bacitracin A1 was studied by capillary electrophoresis in water/2,2,2-trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A1 in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn2+ ion, as pointed out by the strong increase of the association constant measured in water/2,2,2-trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn2+ ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro-organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A1 towards its biologically active structure.* [source] Chromosomal antioxidant genes have metal ion-specific roles as determinants of bacterial metal toleranceENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Joe J. Harrison Summary Microbiological metal toxicity involves redox reactions between metal species and cellular molecules, and therefore, we hypothesized that antioxidant systems might be chromosomal determinants affecting the susceptibility of bacteria to metal toxicity. Here, survival was quantified in metal ion-exposed planktonic cultures of several Escherichia coli strains, each bearing a mutation in a gene important for redox homeostasis. This characterized ,250 gene,metal combinations and identified that sodA, sodB, gor, trxA, gshA, grxA and marR have distinct roles in safeguarding or sensitizing cells to different toxic metal ions (Cr2O72,, Co2+, Cu2+, Ag+, Zn2+, AsO2,, SeO32, or TeO32,). To shed light on these observations, fluorescent sensors for reactive oxygen species (ROS) and reduced thiol (RSH) quantification were used to ascertain that different metal ions exert oxidative toxicity through disparate modes-of-action. These oxidative mechanisms of metal toxicity were categorized as involving ROS and thiol-disulfide chemistry together (AsO2,, SeO32,), ROS predominantly (Cu2+, Cr2O72,) or thiol-disulfide chemistry predominantly (Ag+, Co2+, Zn2+, TeO32,). Corresponding to this, promoter- luxCDABE fusions showed that toxic doses of different metal ions up- or downregulate the transcription of gene sets marking distinct pathways of cellular oxidative stress. Altogether, our findings suggest that different metal ions are lethal to cells through discrete pathways of oxidative biochemistry, and moreover, indicate that chromosomally encoded antioxidant systems may have metal ion-specific physiological roles as determinants of bacterial metal tolerance. [source] Toxicity of manufactured zinc oxide nanoparticles in the nematode Caenorhabditis elegansENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2009Hongbo Ma Abstract Information describing the possible impacts of manufactured nanoparticles on human health and ecological receptors is limited. The objective of the present study was to evaluate the potential toxicological effects of manufactured zinc oxide nanoparticles (ZnO-NPs; 1.5 nm) compared to aqueous zinc chloride (ZnCl2) in the free-living nematode Caenorhabditis elegans. Toxicity of both types of Zn was investigated using the ecologically relevant endpoints of lethality, behavior, reproduction, and transgene expression in a mtl-2::GFP (gene encoding green fluorescence protein fused onto the metallothionein-2 gene promoter) transgenic strain of C. elegans. Zinc oxide nanoparticles showed no significant difference from ZnCl2 regarding either lethality or reproduction in C. elegans, as indicated by their median lethal concentrations (LC50s; p = 0.29, n = 3) and median effective concentrations (EC50s; Z = 0.835, p = 0.797). Also, no significant difference was found in EC50s for behavioral change between ZnO-NPs (635 mg Zn/L; 95% confidence interval [CI], 477,844 mg Zn/L) and ZnCl2 (546 mg Zn/L; 95% CI, 447,666 mg Zn/L) (Z = 0.907, p = 0.834). Zinc oxide nanoparticles induced transgene expression in the mtl-2::GFP transgenic C. elegans in a manner similar to that of ZnCl2, suggesting that intracellular biotransformation of the nanoparticles might have occurred or the nanoparticles have dissolved to Zn2+ to enact toxicity. These findings demonstrate that manufactured ZnO-NPs have toxicity to the nematode C. elegans similar to that of aqueous ZnCl2. [source] Biokinetics of cadmium and zinc in a marine bacterium: Influences of metal interaction and pre-exposureENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2008Dongshi Chen Abstract The uptake kinetics of Cd and Zn, as influenced by metal interaction and metal pre-exposure, was examined in the gram-positive marine bacterium Bacillus firmus over a wide range of ambient free-Cd and -Zn concentrations. Bacteria were exposed to experimental media with different concentrations of Cd and Zn over a short, 15-min period. Zinc was found to be an effective competitive inhibitor of Cd uptake when the Zn2+ concentration ([Zn2+]) was increased to 10,8 M, whereas the Cd concentration (ranging from 10,9 to 10,6 M) did not affect Zn uptake. Inhibition of Cd uptake was dependent on [Zn2+] instead of the [Zn2+] to Cd2+ concentration ratio. Cadmium uptake at different [Zn2+] was significantly inhibited by a sulfur ligand (SH) blocker (N -ethylmaleimide) and a Ca-channel blocker (lanthanum), suggesting that competition between Cd and Zn most likely occurred via binding to the same transport sites. Cadmium efflux also was determined in the presence of different [Zn2+]. A biphasic depuration of Cd was found when [Zn2+] was greater than 10,8 M, whereas the calculated Cd efflux rate was independent of [Zn2+]. We further exposed B. firmus at different Cd or Zn concentrations for 24 h, then determined the metal uptake and efflux kinetics as well as the metallothionein (MT) induction. Both the Cd and Zn cellular concentrations increased with greater exposed metal concentration, but the MT levels and efflux were little affected by the elevated metal concentration. To some extent, however, the Cd uptake was reduced with an elevated intracellular Zn concentration, suggesting that at high Cd concentrations, intracellular Zn can suppress the Cd uptake in B. firmus. These results help to understand the interactions of metals in the marine environments. [source] Competition among zinc, manganese, and cadmium uptake in the freshwater alga Scenedesmus vacuolatusENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2007Stefanie Töpperwien Abstract In the present study, Zn and Mn competition with Cd uptake was investigated in the freshwater alga Scenedesmus vacuolatus. Scenedesmus vacuolatus was exposed to experimental media with Cd and either Zn or Mn in short-term experiments; long-term experiments were undertaken to investigate the effect of growth on Cd accumulation. Cadmium accumulation in S. vacuolatus could be detected at very low exposure concentrations (free Cd2+, 2 × 10,14 to 1 × 10,11 M), and uptake was proportional to the free-Cd2+ concentration. Zinc was an effective competitive inhibitor of Cd uptake when the Zn2+ to Cd2+ ratio was greater than 14 in the exposure medium, whereas Mn competed with Cd for uptake above a Mn2+ to Cd2+ ratio of greater than 10,000. Binding constants for Cd and Zn affinity to the transport sites were determined (KZn and KCd). Values for KZn were slightly higher (log K = 9.4,9.8) than values for KCd (log K = 8.9,9.8). In contrast, Cd seemed not to compete with the Mn-binding sites for uptake over the Mn concentration range from 1 × 10,10 to 1 × 10,8 M. Determined values for the binding constants of Zn and Cd show that a simple model can be applied to predict Cd uptake at known Zn and Cd concentrations. The environmental implications of these results are discussed with respect to potential Cd toxicity for aquatic organisms. [source] Development of a coupled metal speciation-fate model for surface aquatic systemsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2004Satyendra P. Bhavsar Abstract A coupled metal transport and speciation model (TRANSPEC) has been developed for surface aquatic systems that explicitly considers the influence of metal speciation on fate. The TRANSPEC, which is general to most metal and surface aquatic systems, is constructed by sequentially coupling the speciation/complexation module (in this application MINEQL+) with the fugacity/aquivalence approach for the fate calculations. This model formulation increases the mechanistic detail, predictive power, and fidelity to reality of current fugacity-aquivalence fate models for metals by estimating aqueous speciation and complexation, rather than relying on empirically derived partition coefficients. A pseudo-steady state version of TRANSPEC was used to simulate Zn dynamics in Ross Lake (Flin Flon, MB, Canada) that received elevated metal and organic matter inputs for over 50 years. Field studies revealed that ZnS forms soluble ZnL, Zn2+, and ZnSO40 increasing pore water concentrations when surficial sediments turn oxic during fall. The model results for three seasonal scenarios suggest that Zn remobilization is driven by resuspension of insoluble ZnS and the contribution of diffusion is negligible, even during fall when ZnS dissolves to increase the concentration of soluble species under oxic conditions in the sediments. The low diffusive flux is due to the binding of Zn to colloidal dissolved organic matter (DOM) for which sediment-water diffusion is relatively slow, a result that was obtained as a result of considering metal speciation in the fate calculations. [source] Toward an Allosteric Metallated ContainerEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2009Helga Szelke Abstract Polytopic ligands L1 and L2 in which three 2,2,-bipyridine units are linked to a central tris(pyrid-2-yl)amine (L1) or tris(pyrid-2-yl)methanol (L2) moiety by alkyl spacers were prepared by multistep organic syntheses. The parent tris(pyrid-2-yl)-type ligands were shown to be modest-to-good chelators for Zn2+ and Cu2+ ions in solution, and bi- and tridentate N-coordination was confirmed by crystal structures of CuII and RuII complexes, respectively. FeII and RuII smoothly form stable, cage-like 1:1 complexes with L1 and L2, in which the metal ion is coordinated to the tris(bpy) site of the ligands. The vacant tris(pyrid-2-yl) site of these complexes is, however, a poor donor site for Zn2+ and Cu2+ ions. In addition, FeII modulates the coordination behaviour of the tris(pyrid-2-yl) site toward Zn2+: Whereas tris(5-methylpyrid-2-yl)amine forms a 2:1 complex with Zn2+ in CH2Cl2, [Fe(L1)]2+ forms a 1:1 Zn complex. Spectrophotometric titrations suggest that [Fe(L2)]2+ forms a polynuclear Zn2+ complex in CH2Cl2, possibly involving bridging coordination of the alcohol OH group, which contrasts the smooth formation of a 2:1 complex of the parent tris(pyrid-2-yl)-type ligand with Zn. FeII might therefore be considered as an allosteric effector, which modulates the metal binding properties of the second tris(pyrid-2-yl) site of L1 and L2. Contrary to expectation, Zn2+ and Cu2+ appear to associate weakly with donor atoms directed toward the exterior of the cage-like complexes [Fe(Ln)]2+ and [Ru(L1)]2+, rather than locating in the interior of the container by tripodal coordination to the tris(pyrid-2-yl) site.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Stability Constants and Dissociation Rates of the EDTMP Complexes of Samarium(III) and Yttrium(III)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2008Ferenc Krisztián Kálmán Abstract The stability constants of Sm(EDTMP) (log,KML = 20.71) and Y(EDTMP) (log,KML = 19.19) were determined by a competition reaction between the Ln3+ ion (Ln3+ = Sm3+ or Y3+) and Cu2+ for the EDTMP ligand by spectrophotometry at pH , 10, in the presence of an excess amount of citrate (0.15 M NaCl, 25 °C). For determining the stability constants of Cu(EDTMP) (log,KML = 19.36) and Ca(EDTMP) (log,KML = 8.71) pH,potentiometry was used. In the pH range 4,9 the EDTMP complexes are present in the form of nonprotonated and mono-, di- and triprotonated species. The Ca2+ ion forms a dinuclear complex with Ln(EDTMP). In a simplified blood plasma model consisting of Sm3+, Ca2+ and Zn2+ metal ions, EDTMP, citrate, cysteine and histidine ligands, Sm3+ is practically present in the form of [Sm(HEDTMP)Ca]2,, whereas Zn2+ predominantly forms [Zn(HEDTMP)]5, and [Zn(H2EDTMP)]4, complexes. For studying the dissociation rates of the complexes, the kinetics of the metal exchange (transmetallation) reactions between the Ln(EDTMP) complexes and Cu2+,citrate were investigated in the pH range 7,9 by the stopped-flow method. The rates of the exchange reactions are independent of the Cu2+ concentration and increase with the H+ concentration. The rate constants, characterizing the proton-assisted dissociation of the Ln(EDTMP) complexes, are several orders of magnitude higher than those of the similar Ln(EDTA) complexes, because the protonation constants of Ln(EDTMP) are high and the protonated Ln(HEDTMP) and Ln(H2EDTMP) species are present in higher concentration. The half-times of dissociation of Sm(EDTMP) and Y(EDTMP) at pH = 7.4 and 25 °C are 4.9 and 7.5 s, respectively. These relatively short dissociation half-time values do not predict the deposition of Ln3+ ions in bones in the form of intact Ln(EDTMP) complexes. It is more probable that sorption of the EDTMP ligand and Sm3+ or Y3+ ions occurs independently after the dissociation of complexes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Different Morphological Organic,Inorganic Hybrid Nanomaterials as Fluorescent Chemosensors and Adsorbents for CuII IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2008Soo Jin Lee Abstract Functionalized silica nanotubes (FSNT), functionalized mesoporous silica (FMS), and functionalized silica nanoparticles (FSNP-15) with an immobilized phenanthroline moiety as a fluorescent receptor were fabricated by a sol,gel reaction, and their binding abilities with metal ions were evaluated by fluorophotometry in water/acetonitrile (8:2, v/v) at pH 7. They selectively recognized Cu2+ ions among other metal cations such as Co2+, Cd2+, Hg2+, Ni2+, Fe3+, Ag+, Pb2+, and Zn2+, because the Cu2+ ion selectively binds to the nitrogen atoms of the phenanthroline moiety. Among the three silica nanomaterials with the immobilized receptor 1, the sensitivity of FSNT for Cu2+ ions is better than those of FMS and FSNP-15, indicating that the adsorption capacity for metal ions is dependent on the shape and surface area of the supporting nanomaterials. FSNT (10 mg) adsorb 75,% of the Cu2+ ions (2.0,×,10,4 mM) while FSNP-15 (10 mg) adsorb only 36,%. The detection limit of FSNT for Cu2+ ions was ca. 3.0,×,10,8M. FSNT and FMS can be easily renewed by treatment with a solution of HCl and tetrabutylammonium hydroxide. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] (Benzimidazolylmethyl)cyclen: A Potential Sensitive Fluorescent PET Chemosensor for ZincEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 32 2007Abir El Majzoub Abstract A new fluorescent probe for Zn2+, methylbenzimidazole-pendant cyclen [LH: 1-(benzimidazol-2-ylmethyl)-1,4,7,10-tetraazacyclododecane] was designed and synthesized. The protonation constants of (benzimidazolylmethyl)cyclen and the stability constants of the corresponding zinc complex were determined by potentiometric titrations. The single-crystal X-ray diffraction analysis showed that LH and Zn2+ form a 1:1 complex [ZnLH]2+. The results of potentiometric, 1H NMR and UV titrations indicated that above pH 8, [ZnLH]2+ mainly deprotonates into [ZnL]+. On addition of successive amounts of Zn2+ at pH 10.4 (2,×,10,2 mol,L,1 CAPS, 25 °C), the fluorescence emission of cyclen(methylbenzimidazole) increases linearly by a factor of 3.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Highly Organosoluble Metal-Free Phthalocyanines and Metallophthalocyanines: Synthesis and CharacterizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2007Ahmet Bilgin Abstract The syntheses and characterization of metal-free and metal-containing (Zn and Ni) derivatives of a symmetrically octa-substituted phthalocyanine derived from 4,5:12,13-bis(4,- tert -butylbenzo)-8,9-(4,,5,-dicyanobenzo)-6,11-ditosyl-6,11-diaza-2,15-dithiacyclohexadeca-4,8,12-triene and CuPc from 4,5:12,13-bis(4,- tert -butylbenzo)-8,9-(4,,5,-dibromobenzo)-6,11-ditosyl-6,11-diaza-2,15-dithiacyclohexadeca-4,8,12-triene were carried out. Pentanuclear silver(I) and palladium(II) complexes have also been prepared from nickel(II) phthalocyaninate derivatives. The prepared phthalocyanines were semiconducting materials in the range of 10,5 to10,10 S,cm,1 in vacuo and under atmospheric pressure. The extraction abilities of NiPc and detosylated phthalocyanines were evaluated in chloroform/water by using several heavy-metal picrates such as Ag+, Cd2+, Cu2+, Hg2+, Pb2+, Pd2+, and Zn2+. The extraction affinities of NiPc and detosylated phthalocyanines for Ag+ were found to be the highest in solvent extraction experiments. The new compounds were characterized by using elemental analysis, UV/Vis, FTIR, NMR, MS spectroscopic data and DTA/TG. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Complexes of the Bicyclic Multifunctional Sulfur-Nitrogen Ligand F3CCN5S3 with Co2+, Zn2+, Cu2+, and Cd,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2005Carsten Knapp Abstract The ability of the sulfur-nitrogen-carbon bicycle F3CCN5S3 to act as a donor towards transition metal cations has been investigated. F3CCN5S3 forms complexes with [M(SO2)2](AsF6)2 [M = Co, Cu, Zn, Cd] in the ratio 2:1 of the composition [M(F3CCN5S3)2(OSO)2(FAsF5)2] [M = Co (1), Zn (3)], [Cu(F3CCN5S3)2(,-F)(,-F2AsF4)]2 (4), and [Cd(F3CCN5S3)(,-F3CCN5S3)(,2 -F2AsF4)2]2 (5) in liquid sulfur dioxide. In the octahedral Co and Zn complexes F3CCN5S3 coordinates as a monodentate ligand through the bridging nitrogen atom N5, which carries the highest negative charge according to theoretical calculations. With Cu2+ a dinuclear structure with a central planar, four-membered Cu2F2 ring is formed, which has the shortest Cu···Cu distance of all structurally characterized Cu2F2 units. Similar to the Co and Zn complexes, F3CCN5S3 acts as a terminal monodentate ligand in the Cu compound. The reaction with the larger and softer Cd2+ cation results in a dinuclear complex that contains terminal and bridging F3CCN5S3 ligands. The bridging ligands coordinate through N5 and a nitrogen atom neighboring the carbon atom. In addition, a third weak bonding interaction between one fluorine atom of the trifluoromethyl substituent and the Cd2+ center is observed. The formation of the different structures and the versatile coordination modes of the F3CCN5S3 ligand are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Serum or target deprivation-induced neuronal death causes oxidative neuronal accumulation of Zn2+ and loss of NAD+EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2010Christian T. Sheline Abstract Trophic deprivation-mediated neuronal death is important during development, after acute brain or nerve trauma, and in neurodegeneration. Serum deprivation (SD) approximates trophic deprivation in vitro, and an in vivo model is provided by neuronal death in the mouse dorsal lateral geniculate nucleus (LGNd) after ablation of the visual cortex (VCA). Oxidant-induced intracellular Zn2+ release ([Zn2+]i) from metallothionein-3 (MT-III), mitochondria or ,protein Zn2+', was implicated in trophic deprivation neurotoxicity. We have previously shown that neurotoxicity of extracellular Zn2+ required entry, increased [Zn2+]i, and reduction of NAD+ and ATP levels causing inhibition of glycolysis and cellular metabolism. Exogenous NAD+ and sirtuin inhibition attenuated Zn2+ neurotoxicity. Here we show that: (1) Zn2+ is released intracellularly after oxidant and SD injuries, and that sensitivity to these injuries is proportional to neuronal Zn2+ content; (2) NAD+ loss is involved , restoration of NAD+ using exogenous NAD+, pyruvate or nicotinamide attenuated these injuries, and potentiation of NAD+ loss potentiated injury; (3) neurons from genetically modified mouse strains which reduce intracellular Zn2+ content (MT-III knockout), reduce NAD+ catabolism (PARP-1 knockout) or increase expression of an NAD+ synthetic enzyme (Wlds) each had attenuated SD and oxidant neurotoxicities; (4) sirtuin inhibitors attenuated and sirtuin activators potentiated these neurotoxicities; (5) visual cortex ablation (VCA) induces Zn2+ staining and death only in ipsilateral LGNd neurons, and a 1 mg/kg Zn2+ diet attenuated injury; and finally (6) NAD+ synthesis and levels are involved given that LGNd neuronal death after VCA was dramatically reduced in Wlds animals, and by intraperitoneal pyr vate or nicotinamide. Zn2+ toxicity is involved in serum and trophic deprivation-induced neuronal death. [source] Routes of zinc entry in mouse cortical neurons: role in zinc-induced neurotoxicityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2000Philippe Marin Abstract Exposure of central neurons to Zn2+ triggers neuronal death. The routes of Zn2+ entry were investigated in living cortical neurons from the mouse using the specific Zn2+ fluorescent dye N-(6-methoxy-8-quinolyl)-p-toluene sulphonamide (TSQ), which preferentially detects membrane-bound Zn2+. Exposure of cortical neurons to increasing concentrations of Zn2+ (1,100 ,m) induced a progressive increase in the fluorescence of TSQ. This fluorescence signal was not attenuated by the permeation of plasma membrane with digitonin. Accordingly, the major part of TSQ fluorescence (two-thirds) was associated to the particulate fraction of cortical neurons exposed to Zn2+. These results suggest that Zn2+ detected with TSQ in neurons is mainly bound to membranes. TSQ fluorescence measured in neurons exposed to 3 ,m Zn2+ was enhanced by Na+ -pyrithione, a Zn2+ ionophore, ,-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), N-methyl- d -aspartate (NMDA) or KCl-induced depolarization. However, in the absence of any treatment, TSQ labelling of neurons exposed to 3 ,m Zn2+ was only decreased by NMDA receptor antagonists, whereas it remained unaltered in the presence of antagonists of AMPA receptors or L-type voltage-gated Ca2+ channels. Zn2+ entry through NMDA receptors did not contribute to Zn2+ -induced neuronal death, as it was prevented by antagonists of NMDA receptors only when they were added after the Zn2+ exposure. Finally, Zn2+ induced a delayed accumulation of extracellular glutamate which might be responsible for the delayed NMDA receptor activation that leads to neuronal death. [source] Specific Ca2+ Fluorescent Sensor: Signaling by Conformationally Induced PET Suppression in a Bichromophoric AcridinedioneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 34 2009Pichandi Ashokkumar Abstract A series of acridinedione-based bichromophoric podand systems 1a,c were synthesized and characterized. Among these, bichromophore 1c shows specific binding of Ca2+ in the presence of other biologically important metal ions like Na+, K+, Mg2+, and Zn2+. The selective complexation was proved by steady-state emission, time-resolved emission, and 1H NMR titration. Signaling of the binding event was achieved by Ca2+ -induced folding of the bichromophore, resulting in PET suppression in the acridinedione chromophore. Involvement of a PET process in the optical signaling was confirmed by comparing bichromophores 1a,c with non-PET compound 2 and monochromophore model compound 3. Non-PET compound 2 failed to give optical response upon Ca2+ binding as a result of the absence of a PET process in the Ca2+ -bound complex. Monochromophore 3 shows a similar optical response, which is the same as that in 1c. Titration of the metal-ion-bound complex of 1c with EDTA released the metal ion from the complex, thereby regaining the original photophysical properties of the bichromophore.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Metal-Assisted Hybridization of Oligonucleotides, Evaluation of Circular 2,- O -Me RNA as Ligands for the TAR RNA TargetEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2003Laurence Zapata Abstract Two complementary oligonucleotides were conjugated with terpyridine ligands at their nearby 5,- and 3,-ends. Addition of a stoichiometric amount of a transition metal (Zn2+, Fe2+) resulted in a large increase in the melting temperature of the duplex. The conjugation of TPY to stem-loop oligomers provided an efficient procedure for the cyclisation of the oligomer after the addition of metal ions. Such a short stem-loop oligomer was designed to target the HIV-1 TAR RNA through loop,loop interactions. The addition of Zn2+ ions yielded a good ligand (Kd = 30 nM) for this RNA structural element. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Fate of airborne metal pollution in soils as related to agricultural management.EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007Summary The fate of airborne metal pollutants in soils is still relatively unknown. We studied the incorporation of such airborne metal pollution in two soils under long-term permanent pasture (PP) and conventional arable land (CA). Both soils were located at an almost equal distance from a former zinc smelter complex and developed under comparable pedogenetic conditions. Profiles of total concentrations of Zn, chosen as a mobile, and Pb as a little- or non-mobile element, were examined and compared with macro- and micromorphological soil characteristics (soil colour, biological activity). The two soils showed different profiles of total Zn and Pb concentrations, with a marked decrease of concentrations of both elements under the plough layer in CA, whereas the decrease was more progressive in PP. However, the stocks of Zn and Pb for the 1-m soil profiles of CA and PP were comparable. Correlation of Zn and Pb concentration at different depths with total Fe contents and comparison with estimated data for the local geochemical background (LGCB), suggests transport of Zn from the surface to depth in CA and PP, and Pb movement in PP. In CA, 53% of Zn and 92.5% of Pb stocks derived from airborne metal pollution were located at depths < 26 cm. In PP, only 40% of Zn and 82% of Pb, derived from airborne pollution, were found in the A11 and A12 horizons (< 26 cm), the remaining 18% of the Pb stock being incorporated until 50 cm depth; one-third of total Zn stock ascribed to airborne pollution was found at depths > 50 cm. Studies of the composition of gravitational water collected in soils from the same study area suggest two mechanisms for metal movement. First, mobile metal ions (Zn2+) move in the soil solution and are intercepted by iron-clay complexes in deeper soil horizons. Second, observed only in PP, simultaneous movement of Zn and Pb is ascribed to bioturbation by earthworms. [source] Interaction of copper and zinc with allophane and organic matter in the B horizon of an AndosolEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2003C. Latrille Summary Andosols developed on basaltic material are naturally rich in metals. Organic matter and allophane, the key colloids of these soils, have a strong affinity for trace metals, but are intimately mixed so that speciation of trace metal is difficult to determine. We used three complementary approaches, namely physical fractionation, chemical extraction and potentiometric measurement, to distinguish them. Physical particle-size separations and chemical selective dissolution of allophanes and organic matter were combined to demonstrate relations between the occurrence of colloids and contents of Cu and Zn in an andic B horizon. About 22% of total soil Cu and 7% of total soil Zn were present in the < 5-,m fraction, associated with organic or amorphous mineral constituents. To support this association further, the affinity of soil colloids for Cu and Zn in a mimicked system was demonstrated. An Al-rich allophane was synthesized, and a portion of the organic matter was extracted from the clay fraction, and their reactivities towards Cu2+ or Zn2+ were studied by potentiometry. The two metallic cations displayed specific affinity towards allophane or soluble organic matter. Furthermore, the behaviour of copper and zinc in the ternary system, allophane + soluble organic matter + trace element, revealed a synergy in the surface complexation. The use of these three speciation approaches highlighted the linkage between metals and constituents, and showed how important the colloidal constituents are in the behaviour of Cu and Zn in Andosols. [source] Methods for determining labile cadmium and zinc in soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2000S. D. Young Summary Isotopically exchangeable cadmium and zinc (,E values') were measured on soils historically contaminated by sewage sludge and ones on zinc-rich mine spoil. The E -value assay involves determining the distribution of an added metal isotope, e.g. 109Cd, between the solid and solution phases of a soil suspension. The E values for both metals were found to be robust to changes in the position of the metal solid,solution equilibrium, even though the concentration of dissolved metal varied substantially with electrolyte composition and soil:solution ratio. Concentration of labile metal was also invariant over isotope equilibration times of 2,6 days. The use of a submicron filtration procedure, in addition to centrifuging at 2200 g, proved unnecessary if 0.1 m Ca electrolyte was used to suspend the soils. The proportion of ,fixed' metal, in non-labile forms, apparently increased with increasing pH, although there was considerable variation in both sets of contaminated soil. Zinc and cadmium in the sludged soils were similarly labile. Several possible methods for the measurement of chemically reactive metal were explored for comparison with E values, including single extraction with 1 m CaCl2 and a ,pool depletion' (PD) method. The latter involves comparing solid,solution metal equilibria in two electrolytes with differing degrees of (solution) complex formation, 0.1 m Ca(NO3)2 and CaCl2. Both the single extraction and the PD method gave good estimates of E value for Cd, although the single extraction was more consistent. Neither technique was a useful substitute for determining labile Zn, because of weak chloro-complexation of Zn2+. We therefore suggest that 1 m CaCl2 extraction of Cd alone be used as an alternative to E values to avoid the inconvenience of isotopic dilution procedures. [source] Determination of the metal ion dependence and substrate specificity of a hydratase involved in the degradation pathway of biphenyl/chlorobiphenylFEBS JOURNAL, Issue 4 2005Pan Wang BphH is a divalent metal ion-dependent hydratase that catalyzes the formation of 2-keto-4-hydroxypentanoate from 2-hydroxypent-2,4-dienoate (HPDA). This reaction lies on the catabolic pathway of numerous aromatics, including the significant environmental pollutant, polychlorinated biphenyls (PCBs). BphH from the PCB degrading bacterium, Burkholderia xenoverans LB400, was overexpressed and purified to homogeneity. Atomic absorption spectroscopy and Scatchard analysis reveal that only one divalent metal ion is bound to each enzyme subunit. The enzyme exhibits the highest activity when Mg2+ was used as cofactor. Other divalent cations activate the enzyme in the following order of effectiveness: Mg2+ > Mn2+ > Co2+ > Zn2+ > Ca2+. This differs from the metal activation profile of the homologous hydratase, MhpD. UV-visible spectroscopy of the Co2+,BphH complex indicates that the divalent metal ion is hexa-coordinated in the enzyme. The nature of the metal ion affected only the kcat and not the Km values in the BphH hydration of HPDA, suggesting that cation has a catalytic rather than just a substrate binding role. BphH is able to transform alternative substrates substituted with methyl- and chlorine groups at the 5-position of HPDA. The specificity constants (kcat/Km) for 5-methyl and 5-chloro substrates are, however, lowered by eight- and 67-fold compared with the unsubstituted substrate. Significantly, kcat for the chloro-substituted substrate is eightfold lower compared with the methyl-substituted substrate, showing that electron withdrawing substituent at the 5-position of the substrate has a negative influence on enzyme catalysis. [source] Inhibition of pea ferredoxin,NADP(H) reductase by Zn-ferrocyanideFEBS JOURNAL, Issue 22 2004Daniela L. Catalano Dupuy Ferredoxin,NADP(H) reductases (FNRs) represent a prototype of enzymes involved in numerous metabolic pathways. We found that pea FNR ferricyanide diaphorase activity was inhibited by Zn2+ (Ki 1.57 µm). Dichlorophenolindophenol diaphorase activity was also inhibited by Zn2+ (Ki 1.80 µm), but the addition of ferrocyanide was required, indicating that the inhibitor is an arrangement of both ions. Escherichia coli FNR was also inhibited by Zn-ferrocyanide, suggesting that inhibition is a consequence of common structural features of these flavoenzymes. The inhibitor behaves in a noncompetitive manner for NADPH and for artificial electron acceptors. Analysis of the oxidation state of the flavin during catalysis in the presence of the inhibitor suggests that the electron-transfer process between NADPH and the flavin is not significantly altered, and that the transfer between the flavin and the second substrate is mainly affected. Zn-ferrocyanide interacts with the reductase, probably increasing the accessibility of the prosthetic group to the solvent. Ferredoxin reduction was also inhibited by Zn-ferrocyanide in a noncompetitive manner, but the observed Ki was about nine times higher than those for the diaphorase reactions. The electron transfer to Anabaena flavodoxin was not affected by Zn-ferrocyanide. Binding of the apoflavodoxin to the reductase was sufficient to overcome the inhibition by Zn-ferrocyanide, suggesting that the interaction of FNRs with their proteinaceous electron partners may induce a conformational change in the reductase that alters or completely prevents the inhibitory effect. [source] Characterization of the Cph1 holo-phytochrome from Synechocystis sp.FEBS JOURNAL, Issue 7 2001PCC 680 The cph1 gene from the unicellular cyanobacterium Synechoycstis sp. PCC 6803 encodes a protein with the characteristics of plant phytochromes and histidine kinases of two-component phospho-relay systems. Spectral and biochemical properties of Cph1 have been intensely studied in vitro using protein from recombinant systems, but virtually nothing is known about the situation in the natural host. In the present study, His6 -tagged Cph1 was isolated from Synechocystis cells. The cph1,his gene was expressed either under the control of the natural cph1 promoter or over-expressed using the strong promoter of the psbA2 gene. Upon purification with nickel affinity chromatography, the presence of Cph1 in extracts was confirmed by immunoblotting and Zn2+ -induced fluorescence. The Cph1 extracts exhibited a red/far-red photoactivity characteristic of phytochromes. Difference spectra were identical with those of the phycocyanobilin adduct of recombinant Cph1, implying that phycocyanobilin is the chromophore of Cph1 in Synechocystis. [source] Purification and characterization of the single-strand-specific and guanylic-acid-preferential deoxyribonuclease activity of the extracellular nuclease from Basidiobolus haptosporusFEBS JOURNAL, Issue 16 2000Neelam A. Desai An extracellular nuclease from Basidiobolus haptosporus (designated as nuclease Bh1) was purified to homogeneity by ammonium sulfate precipitation, heat treatment, negative adsorption on DEAE-cellulose, and chromatography on phenyl-Sepharose followed by FPLC on phenyl-Superose. The overall yield was 26%. The Mr of the purified enzyme, determined by gel filtration, was 41 000 whereas by SDS/PAGE (after deglycosylation) it was 30 000. It is a glycoprotein with a pI of 6.8. The optimum pH and temperature for DNA hydrolysis were 8.5 and 60 °C, respectively. Nuclease Bh1 is a metalloprotein but has no obligate requirement for metal ions to be active, nor is its activity stimulated in the presence of metal ions. The enzyme was inhibited by Zn2+, Ag2+, Hg2+, Fe3+ and Al3+, inorganic phosphate, pyrophosphate, dithiothreitol, 2-mercaptoethanol, NaCl and KCl. It was stable to high concentrations of organic solvents and urea but susceptible to low concentrations of SDS and guanidine hydrochloride. Nuclease Bh1 is a multifunctional enzyme and its substrate specificity is in the order of ssDNA , 3,AMP , RNA > dsDNA. Studies on its mode of action showed that it cleaved supercoiled pUC 18 DNA and phage M13 DNA, endonucleolytically, generating single base nicks. The enzyme hydrolyzed DNA with preferential liberation of 5,dGMP, suggesting it to be a guanylic acid preferential endoexonuclease. 5,dGMP, the end product of hydrolysis, was a competitive inhibitor of the enzyme. The absence of 5,dCMP as a hydrolytic product, coupled with the resistance of (dC)10 and deoxyribodinucleoside monophosphates having cytosine either at the 3, or the 5, end, indicates that C-linkages are resistant to cleavage by nuclease Bh1. [source] Divalent metal cation binding properties of human prothymosin ,FEBS JOURNAL, Issue 15 2000Nina V. Chichkova The divalent cation binding properties of human prothymosin ,, an abundant nuclear protein involved in cell proliferation, were evaluated. By using prothymosin , retardation on a weak cation chelating resin charged with various divalent cations, specific binding of Zn2+ ions by prothymosin , was observed. This finding was further confirmed by the equilibrium dialysis analysis which demonstrated that, within the micromolar range of Zn2+ concentrations, prothymosin , could bind up to three zinc ions in the presence of 100 mm NaCl and up to 13 zinc ions in the absence of NaCl. Equilibrium dialysis analysis also revealed that prothymosin , could bind Ca2+, although the parameters of Ca2+ binding by prothymosin , were less pronounced than those of Zn2+ binding in terms of the number of metal ions bound, the KD values, and the resistance of the bound metal ions to 100 mm NaCl. The effects of Zn2+ and Ca2+ on the interaction of prothymosin , with its putative partners, Rev of HIV type 1 and histone H1, were examined. We demonstrated that Rev binds prothymosin ,, and that prothymosin , binding to Rev but not to histone H1 was significantly enhanced in the presence of zinc and calcium ions. Our data suggest that the modes of prothymosin , interaction with Rev and histone H1 are distinct and that the observed zinc and calcium-binding properties of prothymosin , might be functionally relevant. [source] Phytase activity in Cryptococcus laurentii ABO 510FEMS YEAST RESEARCH, Issue 3 2007Jason Van Staden Abstract Ten Cryptococcus strains were screened for phytase activity, of which the Cryptococcus laurentii ABO 510 strain showed the highest level of activity. The cell wall-associated enzyme displayed temperature and pH optima of 62°C and 5.0, respectively. The enzyme was thermostable at 70°C, with a loss of 40% of its original activity after 3 h. The enzyme was active on a broad range of substrates, including ATP, d -glucose 6-phosphate, d -fructose 1,6-diphosphate and p -nitrophenyl phosphate (p -NPP), but its preferred substrate was phytic acid (Km of 21 ,M). The enzyme activity was completely inhibited by 0.5 mM inorganic phosphate or 5 mM phytic acid, and moderately inhibited in the presence of Hg2+, Zn2+, Cd2+ and Ca2+. These characteristics suggest that the Cry. laurentii ABO 510 phytase may be considered for application as an animal feed additive to assist in the hydrolysis of phytate complexes to improve the bioavailability of phosphorus in plant feedstuff. [source] Chlorotoxin-sensitive Ca2+ -activated Cl, channel in type R2 reactive astrocytes from adult rat brainGLIA, Issue 4 2003Stanislava Dalton Abstract Astrocytes express four types of Cl, or anion channels, but Ca2+ -activated Cl, (ClCa) channels have not been described. We studied Cl, channels in a morphologically distinct subpopulation (, 5% of cells) of small (10,12 ,m, 11.8 ± 0.6 pF), phase-dark, GFAP-positive native reactive astrocytes (NRAs) freshly isolated from injured adult rat brains. Their resting potential, ,57.1 ± 4.0 mV, polarized to ,72.7 ± 4.5 mV with BAPTA-AM, an intracellular Ca2+ chelator, and depolarized to ,30.7 ± 6.1 mV with thapsigargin, which mobilizes Ca2+ from intracellular stores. With nystatin-perforated patch clamp, thapsigargin activated a current that reversed near the Cl, reversal potential, which was blocked by Cl, channel blockers, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) and Zn2+, by I, (10 mM), and by chlorotoxin (EC50 = 47 nM). With conventional whole-cell clamp, NPPB- and Zn2+ -sensitive currents became larger with increasing [Ca2+]i (10, 150, 300 nM). Single-channel recordings of inside-out patches confirmed Ca2+ sensitivity of the channel and showed open-state conductances of 40, 80, 130, and 180 pS, and outside-out patches confirmed sensitivity to chlorotoxin. In primary culture, small phase-dark NRAs developed into small GFAP-positive bipolar cells with chlorotoxin-sensitive ClCa channels. Imaging with biotinylated chlorotoxin confirmed the presence of label in GFAP-positive cells from regions of brain injury, but not from uninjured brain. Chlorotoxin-tagged cells isolated by flow cytometry and cultured up to two passages exhibit positive labeling for GFAP and vimentin, but not for prolyl 4-hydroxylase (fibroblast), A2B5 (O2A progenitor), or OX-42 (microglia). Expression of a novel chlorotoxin-sensitive ClCa channel in a morphologically distinct subpopulation of NRAs distinguishes these cells as a new subtype of reactive astrocyte. GLIA 42:325,339, 2003. © 2003 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||