Showing papers on "Zinc published in 1991"

The Secondary Alkaline Zinc Electrode

Abstract: Zinc is the most commonly used battery electrode, and zinc primary batteries have found numerous applications. The zinc electrode is electrochemically reversible in alkaline electrolytes, and there is a strong incentive to develop a practical secondary battery based on this metal. However, secondary batteries that use zinc electrodes typically exhibit short lifetimes, because of problems with zinc material redistribution and undesirable zinc morphologies that form during recharge. There has been a worldwide effort to develop a long‐lived secondary alkaline zinc electrode, and marked improvements in cell lifetimes have resulted. This article reviews these efforts, paying particular attention to research and development during the period 1975–1990.

Atomic structure of adenosine deaminase complexed with a transition-state analog: understanding catalysis and immunodeficiency mutations

Abstract: The crystal structure of a murine adenosine deaminase complexed with 6-hydroxyl-1,6-dihydropurine ribonucleoside, a nearly ideal transition-state analog, has been determined and refined at 2.4 angstrom resolution. The structure is folded as an eight-stranded parallel alpha/beta barrel with a deep pocket at the beta-barrel COOH-terminal end wherein the inhibitor and a zinc are bound and completely sequestered. The presence of the zinc cofactor and the precise structure of the bound analog were not previously known. The 6R isomer of the analog is very tightly held in place by the coordination of the 6-hydroxyl to the zinc and the formation of nine hydrogen bonds. On the basis of the structure of the complex a stereoselective addition-elimination or SN2 mechanism of the enzyme is proposed with the zinc atom and the Glu and Asp residues playing key roles. A molecular explanation of a hereditary disease caused by several point mutations of an enzyme is also presented.

A physiological role for endogenous zinc in rat hippocampal synaptic neurotransmission.

Abstract: The mammalian central nervous system (CNS) contains an abundance of the transition metal zinc, which is highly localized in the neuronal parenchyma. Zinc is actively taken up and stored in synaptic vesicles in nerve terminals, and stimulation of nerve fibre tracts that contain large amounts of zinc, such as the hippocampal mossy fibre system, can induce its release, suggesting that it may act as a neuromodulator. The known interaction of zinc with the major excitatory and inhibitory amino-acid neurotransmitter receptors in the CNS supports this notion. That zinc has a role in CNS synaptic transmission, however, has so far not been shown. Here we report a physiological role for zinc in the young rat hippocampus (postnatal, P3-P14 days). Our results indicate that naturally occurring spontaneous giant depolarizing synaptic potentials (GDPs) in young CA3 pyramidal neurones, mediated by the release of GABA (gamma-aminobutyric acid), are induced by endogenously released zinc. These synaptic potentials are inhibited by specific zinc-chelating agents. GDPs are apparently generated by an inhibitory action of zinc on both pre- and postsynaptic GABAB receptors in the hippocampus. Our study implies that zinc modulates synaptic transmission in the immature hippocampus, a finding that may have implications for understanding benign postnatal seizures in young children suffering with acute zinc deficiency.

Structural biology of zinc.

Abstract: The biological function of zinc is governed by the composition of its tetrahedral coordination polyhedron in the metalloprotein, and each ligand group that coordinates to the metal ion does so with a well-defined stereochemical preference. Consequently, protein-zinc recognition and discrimination requires proper chemical composition and proper stereochemistry of the metal-ligand environment. However, it should be noted that the entire protein behaves as the "zinc ligand," since residues that are quite distant from the metal affect recognition and function by through-space (either solvent or the protein milieu) or through-hydrogen bond coulombic interactions. Additionally, long-range interactions across hydrogen bonds serve to orient ligands and therefore minimize the entropy loss incurred on metal binding. Since zinc is not subject to ligand field stabilization effects, it is easy for the tetrahedral protein-binding site to discriminate zinc from other first-row transition metal ions: It is only for Zn2+ that the change from an octahedral to a tetrahedral ligand field is not energetically disfavored. Structural considerations such as these must illuminate the engineering of de novo zinc-binding sites in proteins. Zinc serves chemical, structural, and regulatory roles in biological systems. In biological chemistry zinc serves as an electrophilic catalyst; that is, it stabilizes negative charges encountered during an enzyme-catalyzed reaction. The coordination polyhedron of catalytic zinc is usually dominated by histidine side chains. In biological structure zinc is typically sequestered from solvent, and its coordination polyhedron is almost exclusively dominated by cysteine thiolates. Structural or regulatory zinc is found as either a single metal ion or as part of a cluster of two or more metals. In multinuclear clusters cysteine thiolates either bridge two metal ions or serve as terminal ligands to a single metal ion. Even in complex multinuclear clusters, Zn2+ displays tetrahedral coordination. The structural biology of zinc continues to receive attention in catalytic and regulatory systems such as leucine aminopeptidase, alkaline phosphatase, transcription factors, and steroid receptors. For example, zinc-mediated hormone-receptor association has recently been demonstrated in the binding of human growth hormone to the extracellular binding domain of the human prolactin receptor (Cunningham et al., 1990). To be sure, structural studies of zinc in biology will continue to be a fruitful source of bioinorganic advances, as well as surprises, in the future.

The direct formation of functionalized alkyl(aryl)zinc halides by oxidative addition of highly reactive zinc with organic halides and their reactions with acid chlorides, .alpha.,.beta.-unsaturated ketones, and allylic, aryl, and vinyl halides

Abstract: Highly reactive zinc, prepared by the lithium naphthalenide reduction of ZnCl 2 , readily undergoes oxidative addition to alkyl, aryl, and vinyl halides under mild conditions to generate the corresponding organozinc compounds in excellent yields. Significantly, the reaction will tolerate a spectrum of functional groups on the organic halides. Accordingly, this approach can now be used to prepare a wide variety of highly functionalized organozinc compounds. In the presence of Cu(I) salts, the organozinc compounds cross-couple with acid chlorides, conjugatively add to α,β-unsaturated ketones, and regioselectively undergo S N 2' substitution reactions with allylic halides. They also cross-couple with aryl or vinyl halides with Pd(O) catalysts

Zinc fingers, zinc clusters, and zinc twists in DNA-binding protein domains

Abstract: We now recognize three distinct motifs of DNA-binding zinc proteins: (i) zinc fingers, (ii) zinc clusters, and (iii) zinc twists. Until very recently, x-ray crystallographic or NMR three-dimensional structure analyses of DNA-binding zinc proteins have not been available to serve as standards of reference for the zinc binding sites of these families of proteins. Those of the DNA-binding domains of the fungal transcription factor GAL4 and the rat glucocorticoid receptor are the first to have been determined. Both proteins contain two zinc binding sites, and in both, cysteine residues are the sole zinc ligands. In GAL4, two zinc atoms are bound to six cysteine residues which form a "zinc cluster" akin to that of metallothionein; the distance between the two zinc atoms of GAL4 is approximately 3.5 A. In the glucocorticoid receptor, each zinc atom is bound to four cysteine residues; the interatomic zinc-zinc distance is approximately 13 A, and in this instance, a "zinc twist" is represented by a helical DNA recognition site located between the two zinc atoms. Zinc clusters and zinc twists are here recognized as two distinctive motifs in DNA-binding proteins containing multiple zinc atoms. For native "zinc fingers," structural data do not exist as yet; consequently, the interatomic distances between zinc atoms are not known. As further structural data become available, the structural and functional significance of these different motifs in their binding to DNA and other proteins participating in the transmission of the genetic message will become apparent.

Study of the Kinetics of Hydrogen Evolution Reaction on Nickel‐Zinc Alloy Electrodes

Abstract: The mechanism and kinetics of the hydrogen evolution reaction were studied in on nickel‐zinc alloy electrodes prepared by electrodeposition at controlled potential A series of electrodes containing 70 to 28% Ni was prepared Before the measurements, zinc was leached in alkaline solution Using the ac impedance technique, it was found that the reaction proceeds via the Volmer‐Heyrovsky mechanism, and the kinetic parameters of the process were determined With a decrease in the nickel content, the electrode becomes more active, and an increase in the real surface area is observed The surface morphology was studied using SEM and optical microscopy

A consensus zinc finger peptide: design, high-affinity metal binding, a pH-dependent structure, and a His to Cys sequence variant

Abstract: A single zinc finger peptide, ProTyrLysCysProGluCysGlyLysSerPheSerGlnLysSerAspLeuValLysHisGlnAr~ ThrHisThrGly, has been designed with the use of a data base of 131 zinc finger sequences. Studies indicated that this peptide binds metal ions such as Zn2+ and Co2+ and folds in their presence. The affinity of this peptide for metal ions is greater than that demonstrated for any other zinc finger peptide characterized to date. Nuclear magnetic resonance studies revealed that the zinc complex of this peptide adopts a structure similar to that predicted and observed for other zinc finger domains. In addition, these studies led to the discovery that the latter of the histidine residues can be protonated and dissociated from the metal center with only local loss of structure. This histidine residue can also be replaced with a cysteine residue to yield a peptide that has a (Cy~)~(His) rather than a (Cys)*(Hi~)~ metal binding site. Introduction In recent years, a large class of proteins has been discovered that is characterized by the presence of one or more sequences that closely approximate the form (Tyr,Phe)-X-Cys-X2,4-CysX3-Phe-X,-Leu-X2-His-XS,,-His where X represents relatively variable amino acids.' Each of these sequences appears to form a small domain (often termed a 'zinc finger" domain2) organized around a zinc ion tetrahedrally coordinated by the cysteine and histidine residues. Where it has been determined, proteins that contain these domains have been shown to be specific nucleic acid binding proteins. Peptides corresponding to single domains of this type have been used to characterize the folding, metal-binding, and structural properties of such domains although these peptides have been found to be incapable of site-specific interactions with DNA.s1o It has been demonstrated that these peptides are largely unfolded in the absence of appropriate metal ions but fold to unique three-dimensional structures in their presence. These peptides have been very useful for structural studies of zinc finger domains by two-dimensional nuclear magnetic resonance (NMR) methods, as they are small (approximately 30 amino acids) yet fold in aqueous solution. Such N M R studies on several different zinc finger peptides have revealed structures that are quite similar to although not identical with one a n ~ t h e r . ~ ~ ~ , ' * ~ J ~ Moreover, the experimentally determined structures are strikingly similar to a structure predicted for the zinc finger domains on the basis of the observation of recurring metal-chelating substructures in crystallographically characterized metalloproteins.lI The structure, which consists of two strands and a helix, is shown schematically in Figure 1. The number of zinc finger sequences that are known is large and growing rapidly.' This is true for several reasons. First, as noted above, these sequences often occur as large tandem arrays, with as many as 37 such sequences being found in a single deduced protein sequence. Second, a large number of genes involved in developmental control are being cloned and sequenced and many of these are found to contain zinc finger sequences. Third, it has been possible to intentionally clone zinc finger encoding regions on the basis of hybridization to other zinc finger encoding DNA fragments. Finally, methods based on the polymerase chain reaction are being developed that may make detection and characterization of zinc finger sequences even more facile.I2 When the project described herein was initiated, a total of 131 sequences from 18 protein^,'^-^* tabulated in Table I, were known. *To whom correspondence should be addressed at The Johns Hopkins University School of Medicine. This sequence data base contains a great deal of information. As one illustration of this point, consider the distribution of proline (1) Berg, J. M. Annu. Rev. Biophys. Biophys. Chem. 1990,19,405 and (2) Miller, J.; McLachlan, A. D.; Klug, A. EMBO J . 1985, 4, 1609. (3) Frankel, A. D.; Berg, J. M.; Pabo, C. 0. Proc. Natl. Acad. Sci. U.S.A. (4) Pirraga, G.; Horvath, S. J.; Eisen, A,; Taylor, W. E.; Hood, L.; Young, references therein.

Crystal structure of Penicillium citrinum P1 nuclease at 2.8 A resolution.

Abstract: P1 nuclease from Penicillium citrinum is a zinc dependent glyco-enzyme consisting of 270 amino acid residues which cleaves single-stranded RNA and DNA into 5'-mononucleotides. The X-ray structure of a tetragonal crystal form of the enzyme with two molecules per asymmetric unit has been solved at 3.3 and refined at 2.8 A resolution to a crystallographic R-factor of 21.6%. The current model consists of 269 amino acid residues, three Zn ions and two N-acetyl glucosamines per subunit. The enzyme is folded very similarly to phospholipase C from Bacillus cereus, with 56% of the structure displaying an alpha-helical conformation. The three Zn ions are located at the bottom of a cleft and appear to be rather inaccessible for any phosphate group in double-stranded RNA or DNA substrates. A crystal soaking experiment with a dinucleotide gives clear evidence for two mononucleotide binding sites separated by approximately 20 A. One site shows binding of the phosphate group to one of the zinc ions. At both sites there is a hydrophobic binding pocket for the base, but no direct interaction between the protein and the deoxyribose. A cleavage mechanism is proposed involving nucleophilic attack by a Zn activated water molecule.

Synthesis of Optically Active Bis(2-oxazolines): Crystal Structure of a 1,2-Bis(2-oxazolinyl)benzene ZnCl2 Complex

Abstract: Dinitriles (5–7, 12, 13) react with enantiomerically pure β-amino alcohols (8 – 11,17) under zinc chloride catalysis to give optically active C2-symmetric bis(oxazolines). 1,2-Bis(2-oxazolin-2-yl)benzenes 1a – e are obtained under mild reaction conditions. 1H-NMR spectroscopy indicates the formation of 1:1 complexes 23 of these compounds with ZnCl2. The energy required for a conformational interconversion of zinc dichloride complex 23e was determined by variable-temperature 1H-NMR studies. An X-ray structure analysis was performed with the substituted [1,2-bis(2-oxazolinyl)benzene]zinc dichloride complex 23a.

III-V solar cells and doping processes

Abstract: Zinc diffusion procedures applicable for large scale manufacture of GaAs and GaSb cells used in tandem solar cells having a high energy conversion efficiency. The zinc doping and carrier concentration are restricted to be less than about 10 19 /cm 3 to obtain good light generated carrier collection and hence good short circuit currents. The amount of zinc that is available for diffusion during a drive-in heating step is restricted. Confinement of zinc and arsenic vapors during the heating step may be effected by use of a proximity source wafer or by an encapsulant layer. The zinc diffusion of GaSb is obtained by a homogeneous light diffusion that is followed by a patterned heavy diffusion to give low ohmic contact with the grid lines. Texture etching of the GaSb solar cell is also compatible with this diffusion process.

Sexual lubricants containing zinc as an anti-viral agent

Abstract: This invention relates to an article of manufacture comprising an aqueous gel containing a selected zinc salt contained within a deformable plastic-walled tubular container, for convenient and consistent use as a topical genital lubricant during acts of sexual intercourse. The zinc salt must be organic, water-soluble, and have substantial dissociation rates to release divalent zinc ions. Suitable zinc salts include zinc acetate, zinc propionate, zinc butyrate, zinc formate, zinc gluconate, zinc glycerate, zinc glycolate, and zinc lactate. The gel must also contain a thickening agent (such as chemically treated cellulose) and a lubricating agent (such as glycerin), and it must be free of heparin, dextran sulfate, or any other anti-coagulant or other component which poses a substantial risk of adverse effects if the lubricant is used frequently and repeatedly over a period of months or years. The zinc-containing lubricants described herein can reduce the risk that a previously uninfected person will become infected by genital herpes viruses, and possibly by HIV, hepatitis, or papilloma viruses or other sexually transmitted pathogens, during or after intercourse with an infected partner.

Biosorption of zinc by fungal mycelial wastes

Abstract: Waste mycelia from several industrial fermentation plants (Aspergillus niger, Penicillium chrysogenum, Claviceps paspali) were used as a biosorbent for zinc ions from aqueous environments, both batchwise as well as in a column mode. With all mycelia testes, biosorption per biomass dry weight was a function of pH (increasing with increasing pH between 1.0 and 9.0), biomass concentration (decreasing at high biomass concentrations) and the zinc concentration. Under optimized conditions, A. niger and C. paspali were superior to P. chrysogenum. Treatment of A. niger biomass with NaOH further increased its biosorbent capacity. Desorption of biosorbed zinc was achieved by elution with 0.1 m HCl, best results being obtained with NaOH-treated A. niger. Such treatment did not affect the capacity for biosorption in repeated experiments. NaOH-treated A. niger mycelia were also successfully used in removal of zinc from polluted waters in Austria, thereby showing that the simultaneous presence of other naturally occurring ions does not affect biosorption.

Grain Growth of Zinc Oxide During the Sintering of Zinc Oxide—Antimony Oxide Ceramics

Abstract: On a ajoute de 0,29 a 2,38% de Sb 2 O 3 a ZnO de haute purete. On examine la croissance de grain lors du frittage dans l'air a 1106-1400 o C. On compare les resultats avec ceux de ceramiques de ZnO pur et additionne de Bi 2 O 3

Intracellular free zinc and zinc buffering in human red blood cells.

Abstract: Zn2+ has been allowed to equilibrate across the red cell membrane using two agents that increase membrane permeability to this ion: the ionophore A23187 and the specific carrier ethylmaltol. Extracellular free Zn2+ was controlled with EGTA (1,2-di(2-aminoethoxy)ethane-NNN′N′tetra-acetic acid)) buffers, except in the case of ethylmaltol, which itself acts as a buffer. Measurement of cellular zinc content at different levels of free Zn2+ facilitated the study of intracellular Zn2+ binding. It was also possible to estimate intracellular free Zn2+ concentration in untreated cells using a “null-point” technique. Intracellular zinc was found to consist of an inexchangeable component of about 129 μmol/1013 cells and an exchangeable component of 6.7±1.5 μmol/1013 cells, with a free concentration of about 2.4×10−11 m. The main component of Zn2+ buffering is hemoglobin, with a dissociation constant of about 2×10−8 m.

Ion-pair extraction and determination of copper(II) and zinc(II) in environmental and pharmaceutical samples

Abstract: Copper and zinc were extracted from salicylate solution into Aliquat 336 dissolved in toluene and determined in the organic phase spectrophotometrically using 1-(2-pyridylazo)-2-naphthol. The determination of copper and zinc was also carried out titrimetrically or by atomic absorption spectrometry after stripping the metal ions from the organic phase. The method permits the determination of copper and zinc in environmental and pharmaceutical samples. The standard deviation and relative standard deviation are 0.052 µg and 0.69%, respectively, for copper and 0.041 µg and 0.60%, respectively, for zinc.

Release of zinc mobilizing root exudates in different plant species as affected by zinc nutritional status

Abstract: The effect of zinc nutritional status of the plant on the release of zinc mobilizing root exudates was studied in various dicotyledonous (apple, bean, cotton, sunflower, tomato) and graminaceous (barley, wheat) plant species grown in nutrient solutions. In all species, zinc deficiency increased root exudation of amino acids, sugars and phenolics. However, the root exudates of zinc deficient dicotyledonous species did not enhance zinc mobilization from a synthetic resin (Zn chelite), or a calcareous soil, although mobilization of iron from FeIII hydroxide was increased. By contrast in the graminaceous species, root exudates from zinc deficient plants greatly increased mobilization of both zinc and iron from the various sources. These differences in capability of mobilization of zinc and iron between the plant species are the result of an enhanced release of phytosiderophores with zinc deficiency in the graminaceous species.

The Behavior of Zinc Electrode in Alkaline Electrolytes II . A Kinetic Analysis of Anodic Dissolution

Abstract: A model for the kinetics of active zinc dissolution is developed taking into account the presence of an interfacial layer. From electrode impedance spectroscopy, it is shown that the metal dissolution takes place essentially at the base of pores in a conductive layer of oxidation products which is progressively degraded by the anodic current

Effects of dietary calcium and available phosphorus concentration on digesta pH and on the availability of calcium, iron, magnesium and zinc from the intestinal contents of meat chickens.

Abstract: 1. The effects of high calcium intakes on the pH and availability of calcium, iron, magnesium and zinc in the gastrointestinal tract (GIT) contents of meat chickens were studied in two experiments. 2. A high dietary concentration of calcium (25.3 vs 10.7 g/kg) increased the pH of crop and ileum contents, but did not influence the pH of the contents of other segments of the GIT. 3. The solubilities of minerals in GIT contents were reduced and the size of dissolved mineral complexes were increased as the digesta moved from the duodenum and jejunum to the ileum. 4. After feeding diets with calcium and available phosphorus concentrations (15.3 and 4.3 g vs 21.8 and 4.3 g vs 22.6 and 8.3 g/kg), centrifugation of GIT contents showed that most (70-92%) of the calcium, iron, magnesium and zinc was in an insoluble form. High calcium diets reduced the proportion of soluble zinc associated with small complexes, and high calcium and available phosphorus diets reduced the proportions of soluble magnesium and zinc associated with small complexes. 5. These findings explain the mechanism of the reduced availability of zinc and magnesium in high calcium and high available phosphorus diets.

Metals biosorption by sodium alginate immobilized Chlorella homosphaera cells

Abstract: Cadmium and zinc biosorption, alone or in combination, was investigated with sodium alginate immobilizedChlorella homosphaera cells. Concentrations ranging from 20.0 to 41.0mg/l cadmium, 75.0 and 720.0mg/l zinc were tested and, in all cases, the metal removal achieved values near 100%. When these metals were put in combination a decrease in the rate of absorption was detected. Gold was also tested in the immobilized system and 90% of the initial metal added was recovered in a solution containing 213.0mg/l of the metal, the alginic matrix being responsible for 40% gold uptake.