Preparation and dielectric properties of zinc and cadmium doped barium tantalates, Ba3Zn1?xCdxTa2O9

Members of the Ba2Zn1-xCdxTa2O9 (0 less than or equal to x less than or equal to 1) series have been synthesized by solid state reactions at 1473K. Powder x-ray diffraction studies show a cubic perovskite cell with a similar to 4.1 Angstrom which increases with increase in x. Electron diffraction studies show the presence of hexagonal ordered perovskite structure in addition to the cubic structure seen by x-rays, the x = 0.5 composition showing more ordered crystallites. These samples show high dielectric constants with a maximum (epsilon(r) = 30 at 1 kHz) for the x = 0.5 member. The dielectric loss increases with increase in x at all the frequencies under study.

Metallo-beta-lactamase and phosphotriesterase activities of some zinc(II) complexes

Metallo-beta-lactamases (m beta l) and phosphotriesterase (PTE) are zinc(II) enzymes, which hydrolyze the beta-lactam antibiotics and toxic organophosphotriesters, respectively. In the present work, we have synthesized a few asymmetric phenolate-based ligands by sequential Mannich reaction and their corresponding zinc(II) complexes. These zinc(II) complexes were studied for their m beta l and PTE activities. It is shown that the zinc(II) complexes can hydrolyze oxacillin, the beta-lactam antibiotic, at much higher rates as compared to the hydrolysis of p-nitrophenyl diphenylphosphate (PNPDPP), the phosphotriester. Among the complexes studied, the binuclear asymmetric complex 1 having a water molecule coordinated to one of the zinc(II) ions exhibits much better mbl activity than the mononuclear complexes. However, the mononuclear zinc(II) complexes having labile chloride ions exhibit significant PTE activity, which can be ascribed to the replacement of chloride ions by hydroxide ions during hydrolysis reactions. (C) 2011 Elsevier B.V. All rights reserved.

Bis(acetylacetonato-kappa 2 O,O')(pyridine-kappa N)zinc(II)

In the title compound, Zn(C5H7O2)(2)(C5H5N)], the metal atom has square-pyramidal coordination geometry with the basal plane defined by the four O atoms of the chelating acetylacetonate ligands and with the axial position occupied by the pyridine N atom. The crystal packing is characterized by a C-H...O hydrogen-bonded ribbon structure approximately parallel to 10 ].

The effect of aluminosilicate on the delayed onset of upturn voltages of zinc oxide varistor ceramics

The effect of aluminosilicate (Al2SiO5) on the upturn characteristics of ZnO varistor ceramics has been investigated. Addition of Al2SiO5 shifts the point of upturn above 10(4) A cm(-2). The extended nonlinearity in the high current density region is better correlatable to the presence of higher density of trap stales and changing pattern of trap depths at the grain boundary interface as much as the grain interior conductivity. Microstructure studies show the formation and involvement of a liquid phase during sintering. The secondary phases, predominantly are antimony spinel, Zn7Sb2O12, zinc silicate, Zn2SiO4 and magnesium aluminium silicate. MgAl2Si3O10. Energy dispersive X-ray analyses (EDAX) show that Al and Si are distributed more in the grain boundaries and within the secondary phases than in the grain interiors. Capacitance-voltage analyses and dielectric dispersion studies indicate the presence of negative capacitance and associated resonance, indicative of the oscillatory charge redistribution involving increased trapping at the interface states. The admittance spectroscopy data show that the type of trap slates remains unaltered whereas the addition of Al2SiO5 increases the density of low energy traps. (C) 1997 Published by Elsevier Science S.A.

Synthesis of metastable, wurzite-based zinc oxide-cobalt(II) oxide solid solutions by spray pyrolysis

Aqueous solutions of acetates and nitrates of zinc and cobalt have been spray decomposed to study the production of extended solid solutions in the ZnO-CoO system. Examination of the products of a variety of synthesis conditions indicates that up to 70% CoO may be retained in the solid solution in the wurzite phase, even though a comparison of the equilibrium solubility in the phase diagram might be expected to favor the formation of a rock-salt-based solid solution.

Zinc-substituted alpha-nickel hydroxide as an electrode material for alkaline secondary cells

Double hydroxides of the formula, Ni1-xZn2x (OH)(2) (CO3)(x). nH(2)O (x = 0.1 to 0.25) having the same structure as that of alpha-nickel hydroxide have been synthesized by partial substitution of zinc for nickel. The hydroxide having the composition x = 0.25 exhibits prolonged stability in 6 M KOH. Pasted electrodes comprising this material are rechargeable with a stabilized reversible discharge capacity of 410 +/- 15 mAh g(-1) of nickel even under suboptimal conditions of electrode fabrication. This compares favorably with the capacity values achieved for beta-nickel hydroxide (221 mAh g(-1)', This work; 297 mAh g(-1), Delahaye-Vidal and Figlarz;(1) 456 mAh g(-1), theoretical). (C) 1999 The Electrochemical Society. S0013-4651(98)01-071-4. All rights reserved.

The design and synthesis of redox core-alpha amino acid composites based on thiol-disulfide exchange mechanism and a comparative study of their zinc abstraction potential from [CCXX] boxes in proteins

The design and synthesis of agents that can abstract zinc from their [CCXX] (C=cysteine; X=cysteine/histidine) boxes by thioldisulfide exchange-having as control, the redox parities of the core sulfur ligands of the reagent and the enzyme, has been illustrated, and their efficiency demonstrated by monitoring the inhibition of the transcription of calf thymus DNA by E. coli RNA polymerase, which harbors two zinc atoms in their [CCXX] boxes of which one is exchangeable. Maximum inhibition possible with removal of the exchangeable zinc was seen with redox-sulfanilamide-glutamate composite. In sharp contrast, normal chelating agents (EDTA, phenanthroline) even in a thousand fold excess showed only marginal inhibition, thus supporting an exchange mechanism for the metal removal. (C) 2002 Elsevier Science Ltd. All rights reserved.

A Layered Zinc Phosphate, [C6N4H22][Zn6(PO4)4(HPO4)2], Formed by One-Dimensional Tubes

An open-framework zinc phosphate, [C6N4H22][Zn6(PO4)4(HPO4)2] (I), with alternating inorganic and organic layers has been synthesized hydrothermally from a starting mixture of ZnO, HCl, H3PO4, H2C2O4, and triethylenetetramine. Single-crystal data for I: monoclinic, space GROUP =P21/c (No. 14), a=9.881(1), b=16.857(1), c=8.286(1) Å, β=96.7(1)°, V=1370.8(1) Å3, Z=2, R1=0.06, and wR2=0.13 [1408 observed reflections with I>2σ(I)]. The structure of I comprises a network of ZnO4, PO4, and PO3(OH) tetrahedra forming one-dimensional tubes. The tubes, in turn, are linked via oxygen atoms forming macroanionic inorganic layers with eight-membered apertures. The one-dimensional tube-like architecture in I is a novel feature worthy of note.

Transformations of two-dimensional layered zinc phosphates to three-dimensional and one-dimensional structures

Transformations of the layered zinc phosphates of the compositions [C6N4H22](0.5) [Zn-2 (HPO4)(3)], I, [C3N2H12][Zn-2 (HPO4)(3)], II and [C3N2OH12][Zn-2 (HPO4)(3)], III, containing triethylenetetramine, 1,3-diaminopropane, and 1,3-diamino-2-hydroxypropane, respectively, have been investigated under different conditions. On heating in water, I transforms to a one-dimensional (1-D) ladder and a three-dimensional (3-D) structure, while II gives rise to only a two-dimensional (2-D) layered structure. In the transformation reaction of I with zinc acetate, the same ladder and 3-D structures are obtained along with a tubular layer. Under similar conditions II gives a layered structure formed by the joining of two ladder motifs. III, on the other hand, is essentially unreactive when heated with water and zinc acetate, probably because the presence of the hydroxy group in the amine which hydrogen bonds to the framework. In the presence of piperazine, I, II and III give rise to a four-membered, corner-shared linear chain which is likely to be formed via the ladder structure. In addition, 2-D and 3-D structures derived from the 1-D linear chain or ladder structures are also formed. The primary result from the study is that the layers produce 1-D ladders, which then undergo other transformations. It is noteworthy that in the various transformations carried out, most of the products are single-crystalline.

Copper, Zinc-Superoxide Dismutase from Clinically Isolated Escherichia coli: Cloning, Analysis of sodC and Its Possible Role in Pathogenicity

Superoxide dismutase has been discovered within the periplasm of several Gram-negative pathogens. We studied the Cu,Zn-SOD enzyme in Escherichia coli isolated from clinical samples (stool samples) collected from patients suffering from diarrhea. Antibiogram studies of the isolates were carried out to determine the sensitive and resistant strains. The metal co-factor present in the enzyme was confirmed by running samples in native gels and inhibiting with 2 mM potassium cyanide. A 519 bp sodC gene was amplified from resistant and sensitive strains of Escherichia coli. Cloning and sequencing of the sodC gene indicated variation in the protein and amino acid sequences of sensitive and resistant isolates. The presence of sodC in highly resistant Escherichia coli isolates from diarrheal patients indicates that sodC may play role in enhancing the pathogenicity by protecting cells from exogenous sources of superoxide, such as the oxidative burst of phagocytes. The presence of SodC could be one of the factors for bacterial virulence.

One-dimensional zinc phosphates with linear chain structure

Three one-dimensional zinc phosphates, [C5N2H14][Zn(HPO4)2], I, [C10N4H26][Zn(HPO4)2].2H2O II, and [C4N2H6]2[Zn(HPO4)], III, have been prepared employing hydro/solvothermal methods in the presence of organic amines. While I and II consist of linear chains of corner-shared four-membered rings, III is a polymeric wire where the amine molecule is directly bonded to the metal center. The wire, as well as the chain in these structures, are held together by hydrogen bond interactions involving the amine and the framework oxygens. The polymeric zinc phosphate with wire-like architecture, III, is only the second example of such architecture. Crystal data: I, monoclinic, P21/c (no. 14), a=8.603(2), b=13.529(2), c=10.880(1) Å, β=94.9(1)°, V=1261.6(1) Å3, Z=4, ρcalc.=1.893 gcm−3, μ(MoKα)=2.234 mm−1, R1=0.032, wR2=0.086, [1532 observed reflections with I>2σ(I)], II, orthorhombic, Pbca (no. 61), a=8.393(1), b=15.286(1), c=22.659(1) Å, V=2906.9(2) Å3, Z=8, ρcalc.=1.794 gcm−3, μ(MoKα)=1.957 mm−1, R1=0.055, wR2=0.11, [1565 observed reflections with I>2σ(I) and III, monoclinic, P21/c (no. 14), a=8.241(1), b=13.750(2), c=10.572(1) Å, β=90.9(1)°, V=1197.7(2) Å3, Z=4, ρcalc.=1.805 gcm−3, μ(MoKα)=2.197 mm−1, R1=0.036, wR2=0.10, [1423 observed reflections with I>2σ(I)].

Synthesis from zinc oxalate, growth mechanism and optical properties of ZnO nano/micro structures

We report the synthesis of various morphological micro to nano structured zinc oxide crystals via simple precipitation technique. The growth mechanisms of the zinc oxide nanostructures such as snowflake, rose, platelets, porous pyramid and rectangular shapes were studied in detail under various growth conditions. The precursor powders were prepared using several zinc counter ions such as chloride, nitrate and sulphate along with oxalic acid as a precipitating agent. The precursors were decomposed by heating in air resulting in the formation of different shapes of zinc oxide crystals. Variations in ZnO nanostructural shapes were possibly due to the counter ion effect. Sulphate counter ion led to unusual rose-shape morphology. Strong ultrasonic treatment on ZnO rose shows that it was formed by irregular arrangement of micro to nano size hexagonal zinc oxide platelets. The X-ray diffraction studies confirmed the wurzite structure of all zinc oxide samples synthesized using different zinc counter ions. Functional groups of the zinc oxalate precursor and zinc oxide were identified using micro Raman studies. The blue light emission spectra of the various morphologies were recorded using luminescence spectrometer. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Low‐voltage varistors based on zinc antimony spinel Zn7Sb2O12

It is possible to prepare low‐voltage varistors from the zinc antimony spinel Zn7Sb2O12 with breakdown voltages in the range of 3–20 V and nonlinearity coefficient α=7–15. The varistor property is due to the formation of high ohmic potential barriers at the grain boundary regions on low‐ohmic n‐type grain interiors of the polycrystalline samples. The method of preparation of the spinel, synthesized by coprecipitation followed by annealing under restricted partial pressures of oxygen, controls the mixed valence states for antimony, namely, Sb3+ and Sb5+. This is critical in attaining high nonlinearity and lower breakdown voltages.

Catabolite repression of phosphoenolpyruvate carboxykinase by a zinc finger protein under biotin- and pyruvate carboxylase-deficient conditions in Pichia pastoris

We have identified a methanol- and biotin-starvation-inducible zinc finger protein named ROP [repressor of phosphoenolpyruvate carboxykinase (PEPCK)] in the methylotrophic yeast Pichia pastoris. When P. pastoris strain GS115 (wild-type, WT) is cultured in biotin-deficient, glucose-ammonium (Bio(-)) medium, growth is suppressed due to the inhibition of anaplerotic synthesis of oxaloacetate, catalysed by the biotin-dependent enzyme pyruvate carboxylase (PC). Deletion of ROP results in a strain (Delta ROP) that can grow under biotin-deficient conditions due to derepression of a biotin- and PC-independent pathway of anaplerotic synthesis of oxaloacetate. Northern analysis as well as microarray expression profiling of RNA isolated from WT and Delta ROP strains cultured in Bio(-) medium indicate that expression of the phosphoenolpyruvate carboxykinase gene (PEPCK) is induced in Delta ROP during biotin- or PC-deficiency even under glucose-abundant conditions. There is an excellent correlation between PEPCK expression and growth of Delta ROP in Bio(-) medium, suggesting that ROP-mediated regulation of PEPCK may have a crucial role in the biotin- and PC-independent growth of the Delta ROP strain. To our knowledge, ROP is the first example of a zinc finger transcription factor involved in the catabolite repression of PEPCK in yeast cells cultured under biotin- or PC-deficient and glucose-abundant conditions.