Showing papers on "Zinc published in 1988"

Reaction kinetics of the adsorption and desorption of nickel, zinc and cadmium by goethite. I. Adsorption and diffusion of metals

Abstract: SUMMARY The reactions of Ni, Zn and Cd with goethite were studied over a range of initial metal concentrations (10−6 to 10−4M), pH values (4 to 8), reaction times (2h to 42d) and temperatures (5 to 35°C). The adsorption of metals increased with pH, reaction time and temperature. Adsorption of Ni increased relative to Zn and Cd with increasing time and temperature. The initially rapid adsorption of metals within a few hours was followed by a much slower reaction linearly related to time1/2, interpreted as diffusion–controlled penetration of goethite. The pH–dependent relative diffusion rates (Ni > Zn > Cd) were influenced by both affinity for goethite surfaces and by ionic radius. Diffusion coefficients of the three metals ranged from about 10−19to 10−20cm2s−1. The corresponding activation energies of diffusion were also calculated (Ni 35, Cd 55, Zn 90 kJ mol−1). Our view about the reactions of heavy metals with goethite involves (i) adsorption of metals on external surfaces, (ii) solid–state diffusion of metals from external to internal binding sites, and (iii) metal binding and fixation at positions inside the goethite particles. The general parameters of these processes are related to the hydrolytic properties (pK values) and the ionic radii of the metals. The results show that goethite may be an efficient sink for trace metals.

Serum thymulin in human zinc deficiency

Abstract: The activity of thymulin (a thymic hormone) is dependent on the presence of zinc in the molecule. We assayed serum thymulin activity in three models of mildly zinc-deficient (ZD) human subjects before and after zinc supplementation: (a) two human volunteers in whom a specific and mild zinc deficiency was induced by dietary means; (b) six mildly ZD adult sickle cell anemia (SCA) subjects; and (c) six mildly ZD adult non-SCA subjects. Their plasma zinc levels were normal and they showed no overt clinical manifestations of zinc deficiency. The diagnosis of mild zinc deficiency was based on the assay of zinc in lymphocytes, granulocytes, and platelets. Serum thymulin activity was decreased as a result of mild zinc deficiency and was corrected by in vivo and in vitro zinc supplementation, suggesting that this parameter was a sensitive indicator of zinc deficiency in humans. An increase in T101-, sIg-cells, decrease in T4+/T8+ ratio, and decreased IL 2 activity were observed in the experimental human model during the zinc depletion phase, all of which were corrected after repletion with zinc. Similar changes in lymphocyte subpopulation, correctable with zinc supplementation, were also observed in mildly ZD SCA subjects. Inasmuch as thymulin is known to induce intra- and extrathymic T cell differentiation, our studies provide a possible mechanism for the role of zinc on T cell functions.

Partitioning of arsenic and metals in reducing sulfidic sediments

Abstract: The sediment in a reservoir on the Clark Fork River in western Montana is contaminated with arsenic, copper, zinc, and other elements. This sediment is the source of groundwater contamination in the adjacent alluvial aquifer, and this study elucidates the processes transferring arsenic to the groundwater by the formation of diagenetic sulfides in the sediment. Vertical trends in a core through oxidized surface sediment into reducing sediment below show that concentration and partitioning of metals and arsenic are controlled by the redox interface. Solid phases of arsenic, copper, and zinc change from dominantly oxyhydroxide and organic phases to sulfide phases across the interface. Arsenic, copper, zinc, manganese, and iron in the pore water are controlled by the solubility of iron and manganese oxyhydroxides in the oxidized zone and metal sulfides in the reduced zone. The change in redox conditions upon burial results in a system where the growth of diagenetic copper, zinc, and arsenic sulfides controls the distribution and partitioning of metals and arsenic in the sediment and the speciation and release of arsenic to the adjacent groundwater system.

Zinc-dependent structure of a single-finger domain of yeast ADR1.

Abstract: In the proposed "zinc finger" DNA-binding motif, each repeat unit binds a zinc metal ion through invariant Cys and His residues and this drives the folding of each 30-residue unit into an independent nucleic acid-binding domain. To obtain structural information, we synthesized single and double zinc finger peptides from the yeast transcription activator ADR1, and assessed the metal-binding and DNA-binding properties of these peptides, as well as the solution structure of the metal-stabilized domains, with the use of a variety of spectroscopic techniques. A single zinc finger can exist as an independent structure sufficient for zinc-dependent DNA binding. An experimentally determined model of the single finger is proposed that is consistent with circular dichroism, one- and two-dimensional nuclear magnetic resonance, and visual spectroscopy of the single-finger peptide reconstituted in the presence of zinc.

Removal of lead, cadmium and zinc by waste tea leaves

Abstract: The solid waste of commercially available tea leaves of local produce were found to be good sorbents of metal ions, especially Pb(II), Cd(II) and Zn(II) ions. The extent of adsorption depends on pH, ionic strength, metal concentration, substrate concentration, and the presence of interfering ions and surfactants. Among the various types of surfactants studied, cetyl trimethylammonium bromide severely hindered the metal uptake while Triton XlOO interfered mildly. Initial enhancement of Pb(II) and Zn(II) uptake was observed in the presence of small amount of sodium dodecyl sulphate. The enhancement effect decreased as the anionic surfactant concentration increased. Metal concentration dependence curves can be described by a Langmuir isotherm. Adsorption capacities of tea leaves were found to be 0.38, 0.28 and 0.18 mmole/g for Pb, Cd and Zn respectively.Column experiments revealed near 100% efficiency for metal removal of as much as 100 ppm Pb(ll) ion at pH 6, using 1.8 g waste tea leaves and flow r...

Characterization of deep levels in zinc oxide

Abstract: An electron trap of 0.3 eV depth was characterized in hydrothermally grown, single‐crystal zinc oxide using deep‐level transient spectroscopy. Specimens were fabricated with Ag Schottky contacts on (0001) surfaces. The capture cross section was determined to be 2.6×10−14 cm2. The defect is a native donor and is attributed to a singly ionized oxygen vacancy V•O.

X-ray standing waves: a molecular yardstick for biological membranes

Abstract: Structural information on an atomic scale has been obtained for a Langmuir-Blodgett (LB) trilayer system by means of long-period x-ray standing waves. The LB trilayer of zinc and cadmium arachidate was deposited on a layered synthetic microstructure (LSM) consisting of 200 tungsten/silicon layer pairs with a 25 A period. A 30 A thermally induced inward collapse of the zinc atom layer that was initially located in the LB trilayer at 53 A above the LSM surface has been observed. The mean position and width of the zinc atom layer was determined with a precision of +/- 0.3 A.

Distinct binding sites for zinc and double-stranded RNA in the reovirus outer capsid protein sigma 3.

Abstract: By atomic absorption analysis, we determined that the reovirus outer capsid protein sigma 3, which binds double-stranded RNA (dsRNA), is a zinc metalloprotein. Using Northwestern blots and a novel zinc blotting technique, we localized the zinc- and dsRNA-binding activities of sigma 3 to distinct V8 protease-generated fragments. Zinc-binding activity was contained within an amino-terminal fragment that contained a transcription factor IIIA-like zinc-binding sequence, and dsRNA-binding activity was associated with a carboxy-terminal fragment. By these techniques, new zinc- and dsRNA-binding activities were also detected in reovirus core proteins. A sequence similarity was observed between the catalytic site of the picornavirus proteases and the transcription factor IIIA-like zinc-binding site within sigma 3. We suggest that the zinc- and dsRNA-binding activities of sigma 3 may be important for its proposed regulatory effects on viral and host cell transcription and translation.

Metallothionein gene expression in rats: tissue-specific regulation by dietary copper and zinc.

Abstract: Regulation of metallothionein gene expression by dietary zinc and copper was examined in rat liver, kidney, intestine and brain using a 3 X 3 factorial design. Purified diets containing 5, 30 and 180 mg Zn/kg and 1, 6 and 36 mg Cu/kg were fed for 2 wk. Serum concentrations of copper and zinc were lower at the lowest intakes of either metal than at normal or supplemental levels. Kidney metallothionein levels were proportional to dietary zinc, being 50% less in the 5 mg Zn/kg group than in those fed the highest zinc intake. Metallothionein mRNA was measured by dot blot hybridization to a 32P-labeled oligonucleotide DNA probe representing the terminal 5' sequence of the metallothionein gene. In kidney the number of metallothionein mRNA molecules per cell increased four- to five-fold (from 4 to 29 molecules per cell) with increasing dietary zinc. A less pronounced effect on metallothionein mRNA was observed in response to dietary copper. At the lowest copper intake level and highest intake of zinc intestinal metallothionein mRNA was sevenfold greater than in any other group. Liver and brain did not respond appreciably to the dietary levels of copper and zinc that were fed. Chromatography showed that copper and zinc content of renal metallothionein was directly related to the dietary levels fed. In kidney, both metallothionein-1 and -2 genes were expressed.

A controlled trial on utility of oral zinc supplementation in acute dehydrating diarrhea in infants.

Abstract: A controlled, randomized trial was conducted in 50 infants with acute dehydrating diarrhea to evaluate the effect of oral zinc supplementation in acute diarrhea. After completion of rehydration, 25 infants in Group A received oral zinc sulfate (20 mg elemental zinc twice daily) and an equal number in Group B were given placebo (glucose). Both groups were comparable with respect to various initial characteristics including nutritional status, diarrheal disease, serum alkaline phosphatase, and serum and rectal mucosal zinc content. During therapy all the assessed parameters of zinc status (serum alkaline phosphatase and serum and rectal zinc) recorded significant elevation and reduction in Groups A and B, respectively. At recovery the zinc status of Group A was significantly better and was nearer that of healthy controls. The diarrheal duration and frequency in the zinc-supplemented group were lower, but the differences were not significant (0.05 less than p less than 0.1). However, when only subjects with relatively severe initial zinc depletion (rectal zinc lower than the 15th percentile of healthy controls; 11 in Group A and 14 in Group B) were considered, the diarrheal duration and frequency were significantly (p less than 0.05 and p less than 0.01, respectively) lower in the zinc-supplemented cases. Weight gain in both groups was similar. It is concluded that oral zinc administration in acute diarrhea can replenish body zinc status and this may shorten the diarrheal duration and frequency in children with relatively severe zinc depletion.

Zinc-manganese dioxide galvanic cell using zinc sulphate as electrolyte. Rechargeability of the cell

Abstract: The discharge capacity of the Zn|ZnSo4(aq)|MnO2 galvanic cell increases with increase in the concentration of ZnSO4; use of a 2 M aqueous solution of ZnSO4 gives 65% utilization of MnO2. When the cell is charged after discharging, X-ray diffraction analysis of the positive electrode material indicates regeneration of γ-MnO2 during the charging. Repeated charging and discharging under various modes reveals that the cell is rechargeable more than 30 times. When the cell is charged to 1.70V and discharged to 0.9V, the cell shows about 100% coulombic efficiency with an average discharging voltage of about 1.3V (energy efficiency=83%) and 57% utilization of MnO2. The cell is rechargeable after discharging to 0V.

Zinc electrode and rechargeable zinc-air battery

Abstract: An improved zinc electrode is disclosed for a rechargeable zinc-air battery comprising an outer frame and a porous foam electrode support within the frame which is treated prior to the deposition of zinc thereon to inhibit the formation of zinc dendrites on the external surface thereof. The outer frame is provided with passageways for circulating an alkaline electrolyte through the treated zinc-coated porous foam. A novel rechargeable zinc-air battery system is also disclosed which utilizes the improved zinc electrode and further includes an alkaline electrolyte within said battery circulating through the passageways in the zinc electrode and an external electrolyte circulation means which has an electrolyte reservoir external to the battery case including filter means to filter solids out of the electrolyte as it circulates to the external reservoir and pump means for recirculating electrolyte from the external reservoir to the zinc electrode.

Electroreduction of nitrate ions in concentrated sodium hydroxide solutions at lead, zinc, nickel and phthalocyanine-modified electrodes

Abstract: The electrochemical reduction of nitrate in strongly alkaline solution has been studied using nickel, lead, zinc and iron cathodes. Intermediate formation of nitrite ion and ammonia product was observed for all electrode materials. Coating a nickel sponge electrode with phthalocyanine renders it less active toward nitrate reduction, while iron electrodes appear to be activated. Electrolysis between a lead cathode and a nickel anode is an efficient means of removing nitrate from strongly alkaline solutions.

Distribution and Forms of Copper, Iron, Manganese, and Zinc in Calcareous Soils of India

Abstract: The distribution of trace metals among various chemical forms may vary significantly in response to changing soil properties. Therefore, we conducted a study to investigate the distribution of Cu, Fe, Mn, and Zn among soil fractions for 11 soils that varied in physical and chemical properties. A sequential extraction scheme was used that fractionated Cu, Fe, Mn, and Zn into exchangeable (EX), carbonates-bound (CARB), organically bound (OM), Mn-oxide-bound (MnOX), amorphous Fe-oxide-bound (AFeOX), crystalline Fe-oxide-bound (CFeOX), and residual (RES) forms. A sequential fractionation showed that about 62, 52, 53, and 82% of the total soil Cu, Fe, Mn, and Zn, respectively, was present in RES fraction; about 17, 41, 11, and 7% of the total soil Cu, Fe, Mn, and Zn, respectively, was associated with the CFeOX fraction. The AFeOX fraction averaged to 12, 6, 9, and 5% of the total soil Cu, Fe, Mn, and Zn, respectively. The amounts of metals in the OM fraction were generally <1.0%. Metals associated with the MnOX fraction amounted to 0.7, <0.1, 22, and 2% of the total soil Cu, Fe, Mn, and Zn, respectively. Carbonates-bound Cu, Fe, Mn, and Zn accounted for 6, <0.1, 4, and 2%, respectively, of the total present in soils. EX-Cu or EX-Zn averaged to 2%, whereas EX-Fe or EX-Mn were nonsignificant fractions averaging to <0.1% of the total present. Exchangeable metals did not show significant correlations with any soil properties except EX-Zn and free Fe. In general, such soil properties as sand, silt, clay, free Fe, and free Mn were significantly correlated with metals in AFeOX, CFeOX, and RES fractions. No consistent correlations were observed between soil properties and metals associated with CARB, OM and MnOX fractions.

Selective conversion of methanol into aromatic hydrocarbons over zinc-exchanged ZSM-5 zeolites

Abstract: The conversion of methanol into hydrocarbons over ZSM-5 zeolites has been studied with a special emphasis on improving the selectivity to aromatic hydrocarbons. The introduction of zinc or gallium cations to ZSM-5 appreciably increased the yield of or selectivity for aromatic hydrocarbons. Thus, under the reaction conditions of 700 K, methanol pressure of 40 kPa and W/F= 9.0 g h mol–1, the yields of aromatic hydrocarbons over H-ZSM-5, Ga-ZSM-5, and Zn-ZSM-5 were 40.3, 48.2 and 67.4%, respectively. Over Zn-ZSM-5 the distribution of aromatic products on a molar basis was as follows; benzene (5.8%), toluene (28.0%), xylenes + ethylbenzene (45.6%) and C9+(20.6%). The reaction conditions were optimized to obtain the highest yield of aromatic hydrocarbons over Zn-ZSM-5. The yield of aromatics increased with temperature up to 700 K, but a further temperature increase led to the decomposition of methanol to carbon oxides. The selectivity for aromatics gave a maximum of 70% at a methanol partial pressure of 22 kPa. The yield of aromatic hydrocarbons increased with the degree of cation-exchange of H-ZSM-5 with Zn-cations, indicating the essential role of zinc species in the enhancement of the selectivity to aromatics. It is concluded that the zinc species has a capability of efficiently converting alkene intermediates to aromatic hydrocarbons.

Sorption and Sorptive Interaction of Cadmium and Zinc on Hydrous Manganese Oxide

Abstract: Adsorption of Zn, Cd, and Ca by was measured at pH 4, 6, and 8 by a batch technique at steady-state conditions. Fitting the data to Langmuir and Freundlich expressions suggested that there were two or more mechanisms or sites of sorption for both Zn and Ca. The "higher energy" site(s) (first to fill) showed preference for Cd over Zn, whereas the reverse was true for the lower energy site(s). Simultaneous addition of both Cd and Zn reduced adsorption of both ions. Cadmium and Zn adsorption diminished somewhat when Ca was present at higher Zn and Cd loadings but competition from Ca was minimal at low metal loadings. It is proposed that the high energy binding is an exchange sorption on the negatively charged oxide sites by displacement of surface and diffuse layer cations and protons, which binds Cd more strongly than Zn. On a relative basis at pH 6 and 8, Zn is more strongly bound than Cd. The higher surface charge density and greater proportion of Zn hydroxy solution phase species at higher pH may favor Zn sorption. Competition between Cd, Zn, and Ca was observed at pH 4, 6, and 8, suggesting that solution bulk precipitation was not controlling solution metal