Showing papers on "Zinc published in 1987"

Preparation and characterization of quantum size zinc oxide: a detailed spectroscopic study

Abstract: We report the synthesis of transparent colloidal suspensions of small zinc oxide particles in water, 2-propano1, and acetonitrile. Quantum (Q)-size effects are observed during particle growth and qualitatively interpreted by using a simple molecular orbital (MO) picture. The particles at the final stage of growth are approximately spherical in shape and consist of 2000-3000 ZnO molecules. They exhibit many of the photophysical properties of bulk zinc oxide. However, pronounced shifts in the absorption spectrum during the illumination of anoxic suspensions of ZnO reveal a distinctively different behavior of these small particles. Fluorescence spectra of the ZnO sols suggest that adsorbed electron relays are necessary to shuttle electrons from the conduction band into lower lying traps. Two fluorescence maxima are observed at the final growth stage of the ZnO particles. The bandgap fluorescence at 365 nm has an extremely short lifetime (τ < 100 ps), while the visible luminescence at 520 nm exhibits a slower biexponential decay (i.e., τ = 14 and 190 ns). The latter fluorescence is attributed to photogenerated electrons tunneling to preexisting, trapped holes. The low overall fluorescence quantum yield of Ф = 0.03 measured in these zinc oxide suspensions is indicative of radiationless transitions accompanying the emissions. A pronounced pH dependence of the Stern-Volmer constants obtained with various ionic substances, that effectively quench the 520-nm emission, is explained by specific adsorption to the charged particle surface. The zero point of charge (pH_(zpc)) of the aqueous colloidal suspension was determined to be 9.3 ± 0.2 by several independent methods.

Metal-dependent folding of a single zinc finger from transcription factor IIIA

Abstract: A 30-amino acid peptide, which corresponds to the second "zinc finger" domain of transcription factor IIIA, has been synthesized and purified. This peptide folds in the presence of zinc: adding Zn2+ significantly changes the circular dichroism spectrum, and Zn2+ protects the peptide from tryptic digestion. The peptide also binds Co2+, and the absorption spectrum of the Co2+ complex suggests that a tetrahedral binding site is formed by two cysteines and two histidines. Experiments at higher temperatures (60-75 degrees C) suggest that these folded metal-peptide complexes are quite thermostable. The peptide shows some sequence-specific effects in DNase and methylation protection experiments. However, it does not give a clear "footprint," and some effects are observed in the absence of added zinc.

Organic complexation and its control of the dissolved concentrations of copper and zinc in the Scheldt estuary

Abstract: Cathodic stripping voltammetry (CSV) is used to determine total (after UV-irradiation) and labile dissolved metal concentrations as well as complexing ligand concentrations in samples from the river Scheldt estuary. It was found that even at high added concentrations of catechol (1 mm for copper and 0·4 mm for iron) and of APDC (1 mm for zinc) only part of the dissolved metal was labile (5–58% for copper, 34–69% for zinc, 10–38% for iron); this discrepancy could be explained by the low solubility of iron which is largely present as colloidal material, and by competition for dissolved copper and zinc by organic complexing ligands. Ligand concentrations varied between 28 and 206 nm for copper and between 22 and 220 nm for zinc; part of the copper complexing ligands could be sub-divided into strong complexing sites with concentrations between 23 and 121 nm and weaker sites with concentrations between 44 and 131 nm. Values for conditional stability constants varied between (logK′ values) 13·0 and 14·8 for strong and between 11·5 and 12·1 for weaker copper complexing ligands, whereas for zinc the values were between 8·6 and 10·6. The average products of ligand concentrations and conditional stability constants (a-coefficients) were 6 × 102 for zinc and 6 × 106 for copper. The dissolved zinc concentration was found to co-vary with the zinc complexing ligand concentration throughout the estuary. It is argued that the zinc concentration is regulated, in this estuary at least, by interactions with dissolved organic complexing ligands. A similar relationship was apparent between the dissolved copper and the strong copper complexing ligand concentration. The total copper complexing ligand concentrations were much greater than the dissolved copper concentrations, suggesting that only strongly complexed copper is kept in solution. These results provide evidence for the first time that interactions of copper and zinc with dissolved organic complexing ligands determine the geochemical pathway of these metals.

Mechanism of phosphorus-induced zinc deficiency in cotton. III. Changes in physiological availability of zinc in plants Is mail

Abstract: The effect of varied supply of P (2.5× 10−5 to 6× 10−4 M) and Zn (0 to 10−6 M) on uptake and concentrations of P and Zn was studied in cotton (Gossypium hirsutum L. cv. Deltapine 15/21) grown in nutrient solution under controlled environmental conditions. At a given Zn supply, increasing levels of P had no significant effect on the concentrations of total Zn in plants. However, increasing levels of P induced or enhanced visual Zn deficiency symptoms when the Zn concentration in the nutrient solution was low. The concentrations of water-soluble Zn in roots and shoots constituted 60% of the total Zn concentrations for plants grown with low P and 30% for plants grown with high P. The concentration of water-soluble Zn in leaves, but not total Zn, was closely correlated with visual Zn deficiency symptoms, levels of chlorophyll, super oxide dismutase and membrane permeability. The critical deficiency concentration of water-soluble Zn in cotton leaves was in the range of 6 to 7 μg (g dry weight)−1 or about 1.0 μg (g fresh weight)−1. The results show that high P concentrations in plant tissue decrease the physiological availability of Zn. Water-soluble Zn in the tissue appears to be a suitable indicator for Zn nutritional status in general and phosphorus-induced Zn deficiency in particular. Also in field-grown orange trees (Citrus sinensis) visual Zn deficiency symptoms in leaves were closely related to the concentration of water-soluble Zn.

Optical constants of minerals and other materials from the millimeter to the ultraviolet

Abstract: : Reflectance spectra of near normal incidence and/or transmittance spectra of 29 materials were acquired in the ultraviolet, visible, and infrared spectra regions. Optical constants of the materials were determined primarily by use of Kramers-Kronig analysis of reflectance or extinction coefficient spectra. The materials were: Sodium chloride, Potassium chloride, Cesium iodide, Cesium bromide, Zinc sulfide, Zinc selenide, Barium fluoride, Zinc, Manganese, Molybdenum, Zirconium, Anhydrite, Dolomite, Montomorillonite, Kaolin, Illite, Composite of clays, Lanthanum hexaboride, Diesel soot, Polydimethylsiloxane, Dimethyl methylphosphonate, Diethyl sulfite, Diisopropyl methyl phosphonate, and Diethylphthalate.

Phytate × Calcium/Zinc Molar Ratios: Are They Predictive of Zinc Bioavailability?

Abstract: The utility of the phytate/zinc and phytate × calcium/zinc molar ratios for predicting zinc bioavailability from processed soybean foods was investigated Weight gain and bone zinc accumulation in rats fed various soy protein products were plotted against the calculated molar ratios The phytate × calcium/zinc ratio was a better predictor of zinc bioavailability in similarly processed products than was the phytate/ zinc ratio However, in some cases the phytate × calcium/zinc ratio was not effective since some processing procedures apparently altered binding of phytic acid to minerals and other food components

Behavior of chromium, nickel, copper, zinc, cadmium, mercury, and lead during the pyrolysis of sewage sludge.

Abstract: Raw and digested sewage sludge samples were pyrolyzed in order to investigate the partitioning of selected heavy metals during anoxic thermal treatment. Cr, Ni, Cu, Zn, and Pb were retained quantitatively in the char at temperatures up to 750 /sup 0/C. Cd compounds were reduced to Cd/sup 0/, which was volatilized at T > 600 /sup 0/C. Hg was completely evaporated at the lowest investigated pyrolysis temperature of 350 /sup 0/C. The metals contained in the char are highly immobile due to the well-buffered neutral to alkaline properties of the char. Thus for sewage sludge, which contains metals with similar chemical and physical properties such as Cr, Ni, Cu, Zn, Cd, and Pb, pyrolysis at 500-600/sup 0/C might prove suitable since no metals are released to the atmosphere and a char is produced that is well suited for disposal in an inorganic sanitary landfill. 6 figures, 5 tables.

Lubricating oil compositions containing ashless dispersant, zinc dihydrocarbyldithiophosphate, metal detergent and a copper compound

Abstract: A lubricating oil composition having improved properties comprises a major proportion by weight of a lubricating oil, a dispersant compound, from 0.01 to 0.5 wt % phosphorus and zinc and 5 to 500 parts per million of copper, and additive concentrates for blending with oil to produce such lubricating oil compositions.

Phytate:zinc and phytate X calcium:zinc millimolar ratios in self-selected diets of Americans, Asian Indians, and Nepalese.

Abstract: The literature indicates that phytate:zinc and phytate X calcium:zinc millimolar ratios of a diet may provide useful indexes of the bioavailability of dietary zinc. However, there is little information on the phytate:zinc and phytate X calcium:zinc millimolar ratios for total human diets. We have therefore determined the phytate:zinc and phytate X calcium:zinc millimolar ratios of self-selected diets of 29 American omnivores, 23 American vegetarians, 30 Asian Indian immigrant vegetarians, and 26 Nepalese lactating vegetarians. Criteria for selection of subjects were: good health, no extreme dietary habits, and no intake of nutrient supplements. According to the limited literature, the suggested critical values for phytate:zinc and phytate X calcium:zinc millimolar ratios in animal diets and retrospective calculations from human diets are greater than 10 and greater than 200, respectively. The mean phytate:zinc and phytate X calcium:zinc millimolar ratios of American omnivorous diets in the present study were less than 10 and 200, respectively. Confirmation of the critical molar ratios as indexes of the bioavailability of zinc in human diets has not been established by experimentation. However, if the data from animal studies are applicable to human diets, the present study suggests that phytate has little influence on zinc bioavailability of most American diets. In contrast, the mean phytate:zinc and phytate X calcium:zinc millimolar ratios of all vegetarian diets were above the proposed critical levels. Those data, therefore, suggest that phytate might increase the risk of impaired zinc bioavailability for vegetarians consuming a relatively high level of calcium.

Iv. the mechanism of ectomycorrhizal amelioration of zinc toxicity

Abstract: less zinc is taken up, and growth is better than in the non-mycorrhizal condition. The results also show that the metal may be adsorbed to electronegative sites in the hyphal cell walls and extra-hyphal, polysaccharide slime. The possible dual role of this slime in fungus/Betula compatibility and the amelioration mechanism is discussed.

Zinc tolerance in Betula spp. IV: The mechanism of ectomycorrhizal amelioration of zinc toxicity

Abstract: Aseptic cultures of Paxillus involutus Fr. and clones of Betula pendula Roth. and B. pubescens Ehrh. were used in experiments, involving X-ray microanalysis and split-plate culture, to investigate the mechanism of ectomycorrhizal amelioration of zinc toxicity to Betula. Results imply that as the fungal mycelium colonizes fresh soil, zinc is adsorbed to the surface of hyphae, thereby lowering the concentration of zinc in the soil solution surrounding roots. In consequence, less zinc is taken up, and growth is better than in the non-mycorrhizal condition. The results also show that the metal may be adsorbed to electronegative sites in the hyphal cell walls and extra-hyphal, polysaccharide slime. The possible dual role of this slime in fungus/Betula compatibility and the amelioration mechanism is discussed.

Characterization of impurity effects in zinc electrowinning from industrial acid sulphate electrolyte

Abstract: The individual effects of 15 impurities and their interaction with glue on zinc electrowinning from industrial acid sulphate electrolyte were characterized in terms of deposit morphology and preferred deposit orientation and in terms of current efficiency and zinc deposition polarization behaviour. The current efficiency decreased in a cyclical manner with increasing atomic number of the impurity element in each period of the periodic table. This decrease in current efficiency can be correlated to a corresponding increase in the rate of hydrogen evolution on the impurity metal. The various impurities produced four distinct zinc deposit morphologies and orientations and also produced characteristic changes in the cyclic voltammograms for the zinc deposition.

Effects of cupric and zinc ion activities on the survival and reproduction of marine copepods

Abstract: The toxicity of copper and zinc to the estuarine copepod Acartia tonsa and to the two diatom food species Thalassiosira pseudonana and T. weissflogii was measured in nitrilotriacetate-trace metal ion buffer systems at 25‰ S. Overall, A. tonsa appeared to be more sensitive to cupric and zinc ion activity than either of the diatoms; however, its sensitivity varied among the different life stages examined. Adult survival was not affected within the zinc ion activity range 10-11 to 10-8M and cupric ion activity range 10-13 to 10-11M over a 96-h period, but a cupric ion activity of 10-10M caused total mortality of adults within 72 h. Egg-laying rate was most sensitive to zinc, and was reduced at zinc ion activities ≧10-10M. Naupliar survival after 96 h was reduced by zinc ion activities ≧10-8M and by cupric ion activities ≧10-11M, and was reduced to zero at a zinc ion activity of 10-7M and at a cupric ion activity of 10-10.5M. In an interspecies comparison of 96-h adult survival, Centropages typicus was more sensitive to copper and zinc than A. tonsa and the survival of Labidocera aestiva was dependent on the ratio of cupric to zinc ion activity. A comparison of our results with estimates of zinc and cupric ion activities in estuaries suggests that ionic activities of these metals are high enough in some polluted estuaries to affect the survival and reproduction of copepods.

Neutron activation analysis techniques for identifying elemental status in Alzheimer's disease

Abstract: Brain tissue (hippocampus and cerebral cortex) from Alzheimer's disease and control individuals sampled from Eastern Canada and the United Kingdom were analyzed for Ag, Al, As, B, Br, Ca, Cd, Co, Cr, Cs, Cu, Fe, Hg, I, K, La, Mg, Mn, Mo, Ni, Rb, S, Sb, Sc, Se, Si, Sn, Sr, Ti, V and Zn. Neutron activation analysis (thermal and prompt gamma-ray) methods were used. Highly significant differences (probability less than 0.005) for both study areas were shown between Alzheimer's diesease (AD) and control (C) individuals: AD>C for Al, Br, Ca and S, and AD

Zinc tolerance in betula spp.

Abstract: SUMMARY Clones of zinc-tolerant and non-tolerant genotypes of Betula pendula Roth, and B. pubescens Ehrh. were cultured aseptically on media containing different concentrations of zinc. The location, concentration and form of zinc in root tissues of both groups of genotype were compared using various microanalytical techniques. At concentrations of zinc at which all genotypes were viable, there were no obvious differences between the tolerant and non-tolerant genotypes. When the roots were subjected to concentrations above the lethal threshold, zinc accumulated intracellularly, at the endodermis, in the form of electron-dense granules. This form of accumulation was symptomatic of tissue inundation with zinc. The results do not support the presence of cell wall binding or intracellular detoxification mechanisms of tolerance. The possibility that zinc tolerance, control of zinc uptake and zinc-induced inhibition of cell extension are all linked by common events centred on the plasma membrane are discussed.

Metal regulation and molting in the blue crab, callinectes sapidus: metallothionein function

Abstract: We recently demonstrated that zinc, copper, and hemocyanin metabolism in the blue crab varies as a function of the molt cycle. To extend these observations, and better delineate metal metabolism in marine crustaceans, we have conducted experiments to determine if environmental temperature and season of the year affect concentrations of hemocyanin and copper in the hemolymph and copper and zinc in the digestive gland. Overwintering, cold water crabs (6?C) had decreased hemocyanin and copper in the hemolymph and normal zinc and copper in the digestive gland with respect to summer crabs collected at 20-30?C. When these crabs were warmed to 20?C and fed fish for three weeks, they showed increases in the concentrations of copper in the digestive gland, and copper and hemocyanin in the hemolymph. In addition, a change from a zinc to a copper-dominated metallothionein was found in a majority of the warmed crabs, suggesting the involvement of copper metallothionein in the resynthesis of hemocyanin. Based on these observations and previous data (Engel, 1987) a conceptual model of copper and zinc partitioning in the blue crab has been constructed. In this model, metallothionein has an important role in metal regulation both during molting and in the changes related to season of the year. Metallothionein-bound copper and zinc appear to be regulated at the cellular level for the synthesis of metalloproteins, such as hemocyanin (copper) and carbonic anhydrase (zinc), both of which are necessary for normal growth and survival. Finally, we present evidence showing that copper metallothionein can directly transfer its metal to the active site ofapohemocyanin. Copper insertion seems to precede the formation of viable oxygen binding sites.

Zinc deficiency increases the osmotic fragility of rat erythrocytes

Abstract: Zinc deficiency in rats causes increased os motic fragility of their erythrocytes. This study was de signed to determine the relationship of food intake and dietary sulfur amino acid level to the effect of low zinc status on fragility. Immature rats were fed for a 3-wk period a low zinc diet (<1 mg/kg) based on isolated soybean protein or a similar control diet ( 100 mg Zn/kg diet) supplied either ad libitum or by pair feeding. Fragility was measured by the degree of hemolysis in hypotonie saline solutions. In the first experiment, zinc deficiency resulted in higher fragility than in ad libitum controls; pair-fed controls were inter mediate and not different from either. Experiment 2 in cluded two levels of methionine, 0.4 and 0.9%, and two of zinc, 0 and 100 mg Zn/kg diet. At the 0.4%, but not at the 0.9% methionine level, hemolysis of red blood cells from the zinc-deficient rats was significantly greater than those from either pair-fed or ad libitum controls. Repletion for 1 or 2 d completely alleviated the increased fragility, but in vitro addition of zinc had no effect. Restricted intake of the zinc-adequate diet reversed the fragility within 1 d as readily as did ad libitum intake. Thus, the osmotic fra gility induced by zinc deficiency was prevented by high sul fur amino acid intake and was readily reversed by dietary zinc. It is postulated that extracellular or membrane-bound zinc protects a component of the membrane that is es sential to its function, and that reversal of the defect re quires an in vivo metabolic process. J. Nutr. 117:1883- 1889, 1987.

Electrodeposition of zinc-nickel alloys from chloride solution

Abstract: Operating conditions for zinc and nickel codeposition from chloride baths were studied in order to obtain alloys containing up to 20% nickel. Satisfactory deposits were produced at 50°C using current densities ranging from 5 to 20 mA cm−2 and nickel to zinc ratios ranging from 6.8 to 37.5%.

Metal regulation and molting in the blue crab, callinectes sapidus: copper, zinc, and metallothionein

Abstract: Blue crab, Caiinectes sapidus, hemolymph and digestive glands were examined at differentstagesofthe molt cycle to determine whether molting affectedtissue and cytosolic partitioning of copper and zinc and, if so, whether metallothionein was involved. The crabs used in these determinations were not exposed to elevated con centrations ofcopper or zinc. Concentrations ofhemocyanin, copper, and zinc in the hemolymph all decreased significantly during molt. They were lowest at the soft crab stage (A2) and highest during premolt(D1—D3) and intermolt(C4). The digestive gland copper concentrations also were highest during premolt (D1-D3) and lowest in the papershellstage(B1).Zinc followed the same generalpatternin both hemolymph and digestive glands. The cytosolic distributions of copper and zinc were determined in the digestive glands using gel filtrationchromotography.The elution profilesshowed that the percentagesofcopper and zinc on metallothionein rangedfrom 10%copper/ 90%zinc at D1 to 100%copper at B1. The estimated concentrations of metallothi onein were highestduringintermolt (C1)and premolt (D1-D3) and lowest duringthe papershell(B1).The observedchanges in the tissue and cytosolic partitioningof cop per and zinc are consistent with the physiological changes occurring in the crabs. These observations support the hypothesis that metallothioneins are naturally occur ringproteinsthat are actively involved in the synthesis of hemocyanin and zinc regu lation duringthe normal processesof growthin blue crabs.