Showing papers on "Zinc published in 1980"

Trace Elements in Soils and Plants

Abstract: Fifteen or more elements present in rocks and soils normally in very small amounts are essential for plant and/or animal nutrition. By the nature of their low abundance in natural uncontaminated earth materials or plants, they are known as trace elements, minor elements or micro-nutrients. Boron, copper, iron, manganese, molybdenum, silicon, vanadium and zinc are required by plants; copper, cobalt, iodine, iron, manganese, molybdenum, selenium and zinc by animals. In addition essential roles of arsenic, fluorine, nickel, silicon, tin and vanadium have in recent years been established in animal nutrition.

The adsorption of lead and other heavy metals on oxides of manganese and iron

Abstract: Measurements were made of the adsorption of cobalt, copper, manganese, nickel, lead, and zinc on nine synthetic manganese oxides and three synthetic iron oxides, to determine the mechanism by which lead accumulates in the manganese oxides in soils. Adsorption of lead by the manganese oxides was up to 40 times greater than that by the iron oxides, and lead was adsorbed more strongly than any of the other ions studied by all of the oxides except goethite. This is considered to be the reason for the accumulation of lead in the manganese oxides in soils. No evidence was found for the oxidation of lead, nor for the formation of specific lead-manganese minerals.

Structure of the metal clusters in rabbit liver metallothionein.

Abstract: Cadmium-113 nuclear magnetic resonance (113Cd NMR) has been used to determine the structures of the multiple cadmium binding sites in the two major isoproteins of rabbit liver metallothionein The isotopically 113Cd-labeled metallothionein used in these studies was isolated from the livers of rabbits that had been subjected to repeated injections of 113CdCl2 The native protein isolated from these livers contains an appreciable amount of Zn in addition to Cd, ranging from 2-3 mol per mol of protein out of a total metal content of 7 mol per mol of protein The 113Cd NMR spectrum of Cd, Zn-containing metallothionein is quite complex, reflecting the fact that the native protein is a heterogeneous mixture of species containing different relative amounts of Zn and Cd Replacement of the native Zn with 113Cd in vitro gave a protein whose 113Cd NMR spectrum was much simpler, containing eight distinct multiplets with chemical shifts ranging from 611-670 ppm The origin of the multiplet structures has been shown to be 113Cd-113Cd scalar coupling arising from two-bond interactions between 113Cd ions linked to one another by bridging cysteine thiolate ligands The size and structures of the metal clusters in the protein were determined by the application of selective homonuclear 113Cd decoupling techniques Analysis of these data showed that rabbit liver metallothionein contains two separate metal clusters, one containing four Cd2+ ions and the other containing three These two clusters, whose structures are the same in both isoproteins, have been designated “cluster A” and “cluster B,” respectively Structures for the clusters are proposed that account for the 113Cd spin coupling data and the participation of all 20 of the cysteine residues in metal ligation, 11 in cluster A and 9 in cluster B The appearance in the spectrum of eight multiplets rather than the seven that would be expected on the basis of the number of metal binding sites in the protein is an indication of some residual heterogeneity in the 113Cd-labeled metallothionein sample The origin of this heterogeneity is suggested to be the presence of a protein species that lacks metal ions at its cluster B binding sites

Porphyrins. 40. Electronic spectra and four-orbital energies of free-base, zinc, copper, and palladium tetrakis(perfluorophenyl)porphyrins

Abstract: Absorption and emission spectra and emission quantum yields are given for free-base (H/sub 2/), Zn, Cu, and Pd derivatives of tetrakis(perfluorophenyl)porphyrin (TFPP). The four-orbital model is used to rationalize differences in the optical properties among the derivatives of TFPP and the same derivatives of porphine (P), octaethylporphyrin (OEP), and tetraphenylporphyrin (TPP). It is concluded from absorption data that the energy difference between the two excited singlets, i.e., /sup 1/E(a/sub 2u/,e/sug g/) - /sup 1/E(a/sub 1u/,e/sub g/), decreases along the series Pd > Cu > Zn > H/sub 2/ and also along the series OEP > P > TFPP > TPP. The theory and date are reviewed, and it is concluded that the energy difference between the two excited triplets, i.e., /sup 3/E(a/sub 2u/,e/sub g/) - /sup 3/E(a/sub 1u/,e/sub g/), also decreases along these series. However the condition of degeneracy, e.g., /sup 1/E(a/sub 2u/,e/sub g/) - /sup 1/E(a/sub 1u/,e/sub g/) = 0, occurs for different molecules in the singlet and triplet cases. Theory also suggests that if /sup 3/E(a/sub 2u/,e/sub g/) > /sup 3/E(a/sub 1u/,e/sub g), the molecule should form a /sup 2/A/sub 1u/ cation radical and if /sup 3/E(a/sub 2u/,e/sub g/) < /sup 3/E(a/sub 1u/,e/sub g/) the molecule should formmore » a /sup 2/A/sub 2u/ radical. 4 figures, 2 tables.« less

Reactivation in vitro of zinc-requiring apo-enzymes by rat liver zinc-thionein

Abstract: The ability of rat liver zinc-thionein to donate its metal to the apo-enzymes of the zinc enzymes horse liver alcohol dehydrogenase, yeast aldolase, thermolysin, Escherichia coli alkaline phosphatase and bovine erythrocyte carbonic anhydrase was investigated. Zinc-thionein was as good as, or better than, ZnSO4, Zn(CH3CO2)2 or Zn(NO3)2 in donating its zinc to these apo-enzymes. Apo-(alcohol dehydrogenase) could not be reactivated by zinc salts or by zinc-thionein. Incubation of the other apo-enzymes with near-saturating amounts of zinc as ZnSO4, Zn(CH3CO2)2, Zn(NO3)2, or zinc-thionein resulted in reactivation of the apo-enzymes. With apo-aldolase zinc-thionein gave 100% reactivation within 30min. Reactivation by ZnSO4 and Zn(CH3CO2)2 was complete and instantaneous. Zinc-thionein was somewhat better than Zn(NO3)2 in completely reactivating apo-thermolysin. With apo-(alkaline phosphatase) 43% reactivation was obtained with Zn(CH3CO2)2 and 18% with zinc-thionein. With apo-(carbonic anhydrase) zinc-thionein was better than ZnSO4, Zn(CH3CO2)2 or Zn(NO3)2, with a maximal reactivation of 54%. That zinc was really being transferred from zinc-thionein to apo-(carbonic anhydrase) was shown by the fact that 2,6-pyridine dicarboxylic acid and 1,10-phenanthroline had minimal effects on the reactivation of apo-(carbonic anhydrase) when added after the incubation {[apo-(carbonic anhydrase)+zinc thionein]+chelator}, but inhibited reactivation when added before the incubation {apo-(carbonic anhydrase)+[zinc-thionein+chelator]}. These observations support the idea that zinc-thionein can function in zinc homeostasis as a reservoir of zinc, releasing the metal to zinc-requiring metalloenzymes according to need.

Zinc Lowers High-Density Lipoprotein-Cholesterol Levels

Abstract: Zinc administration in rats is associated with a rise in serum cholesterol level. This study examined the effect of zinc administration on serum lipoprotein values in man. Twelve healthy adult men ingested 440 mg of zinc sulfate per day for five weeks. High-density lipoprotein-cholesterol concentration decreased 25% below baseline values (40.5 to 30.1 mg/dL). Total cholesterol, triglyceride, and low-density lipoprotein-cholesterol levels did not change throughout the study. The sharp fall of the "antiatherogenic" lipoprotein, high-density lipoprotein, associated with zinc administration supports the concept that zinc ingestion may be atherogenic in man.

Influence of defects on the electronic structure of zinc oxide surfaces

Abstract: Intrinsic point defects were produced on ZnO ($10\overline{1}0$) surfaces by thermal treatment, uv illumination, and CO exposure. Electronic structure and thermodynamics of surface defects as well as their influence on charge-transfer reactions are discussed.

Ligand substitution reactions of metallothioneins with EDTA and apo-carbonic anhydrase.

Abstract: The reactions of Zn-, Zn,Cd-, and Cd-thioneins with EDTA and apo-carbonic anhydrase have been studied. The ligand substitution reaction of zinc with EDTA is multiphasic, having both associative and dissociative components in the rate expression. The cadmium sites are about 2 orders of magnitude less reactive. In contrast, apo-carbonic anhydrase abstracts zinc from Zn-thionein and Zn,Cd-thionein in second-order processes that are 2-3 orders of magnitude more rapid than those involving EDTA and approach the rate for unligated Zn2+ with the apo-protein. In comparison with other zinc proteins, Zn-thionein contains unusually reactive metal sites, suggesting that this protein may be a physiological zinc transfer protein, able to donate zinc to zinc-requiring apo macromolecules.

On the sensitivity of metallothioneins to oxidation during isolation

Abstract: It is demonstrated that the distribution of metals among the Sephadex G-75 fractions of rat liver and horse kidney supernatant is altered by exposure to oxidizing conditions. In particular, the metals bound to metallothionein are displaced into high-molecular-weight fractions and, to a lesser extent, into the low-molecular-weight forms, under aerobic conditions. In this process, metallothionein zinc is much more labile than cadmium. An appreciable proportion of the thionein is also found in the high-molecular-weight fractions and can be recovered along with the metals by treatment with mercaptoethanol. This result shows that the distributions obtained aerobically with large cadmium content in the high-molecular-weight fractions are an artefact due to metallothionein oxidation and suggests that 'spillage' of metals such as cadmium may be due in large part to oxidative processes rather than saturation effects. Evidence is presented that disulphide-bond formation occurs as thionein becomes bound in the high-molecular-weight region and that chemical reduction is necessary to restore its normal elution behaviour. Mercaptoethanol added to the homogenates maintains the reducing conditions normally found in the cellular milieu and prevents the oxidation of the metallothionein redistribution of the metals during isolation. Under these conditions the rat liver metallothionein isolated from animals exposed to chronic low concentrations of cadmium in drinking water contains appreciable quantities of copper as well as zinc and contains much of the zinc that is present in horse kidney supernatants. Metallothionein can also be extracted from a 40 000g pellet after sonication of the pellet. Thus careful analytical studies of the sites of cadmium deposition in rat liver indicate that greater than 95% is bound to metallothionein.

Metabolism of zinc in the mussel, Mytilus edulis (L): a combined ultrastructural and biochemical study.

Abstract: The uptake, transport, storage and excretion of zinc has been studied in Mytilus edulis. Zinc accumulates in the soft tissues in proportion to its concentration in sea water whilst the concentration in the haemolymph is little above that in the environment. Uptake is via the gut, mantle and gills. The zinc is transported from the gills and gut (t½ ≈ 8 days) via the haemolymph, either as a high molecular weight complex or in the granular amoebocytes, to the kidney. Most of the body zinc is present in the granular amoebocytes (which are found in all the body tissues) or in the gut and kidney. The kidney forms the major storage organ for many trace metals, containing 30% of the body zinc and a concentration of about 1000 μg/g. Zinc is localized as insoluble granules in membranelimited vesicles occupying some 20% of the cell volume. Excretion of zinc is by defaecation, exocytosis of the kidney granules into the urine and diapedesis of the amoebocytes. A multicompartmental model for zinc metabolism which correlates the ultrastructural and kinetic data is proposed.

Photoelectron study of the interaction of carbon monoxide with zinc oxide

Abstract: Ultraviolet photoelectron spectroscopy (UPS) has been used to study the chemisorption of CO on four low-index surfaces of ZnO, an active methanol catalyst. These surfaces have significant differences with respect to their coordination unsaturation; thus, a correlation between the adsorption behavior and the surface structure enables the geometric requirements for chemisorption to be determined. The He II photoelectron peak associated with the 4 sigma molecular orbital of the CO molecule serves as a probe of the amount of adsorbed CO. The adsorption is found to be reversible, and measurements of the equilibrium coverage as a function of temperature and pressure demonstrate that the bonding interactions are very similar on all four surfaces, with an initial heat of adsorption of 12.0 +- 0.4 kcal/mol, which decreases approximately linearly with coverage. Chemisorbed CO is readily displaced by NH/sub 3/, indicating the involvement of zinc ions in the bonding of CO to the surface. This is strongly supported by the relative CO coverage of the four surfaces under equivalent conditions, which generally correlates with the availability of unsaturated zinc sites. Angle-resolved measurements of the 4 sigma intensity are used to confirm this binding mode. The bonding of CO to ZnO is cominated bymore » the sigma donor interaction of the carbon end of the molecule with the zinc ion as determined from the observed decrease in the splitting of the energies of the 4 sigma and 5 sigma molecular orbitals. The lack of significant ..pi.. back-bonding is supported by the increase of the dipole moment of the coordinated CO molecule to approximately 0.6 D as determined from He I photoelectron work function measurements. This mode of binding of CO is consistent with the observed increase in the CO stretching frequency relative to the gas-phase value and suggests possible relevance to catalysis.« less

Characterization and Quantitation of a Zinc-Binding Ligand in Human Milk

Abstract: A low-molecular-weight zinc-binding ligand from human milk has been isolated and characterized. The ligand was isolated by chromatography on Dowex 50, Dowex 1, and Sephadex G-15 equilibrated with 0.153 mM Zn(NO3)2. Mass spectroscopy, thin-layer chromatography, and infrared spectroscopy proved that the zinc-binding ligand isolated by this method from human milk is pyridine-2-carboxylic acid, commonly known as picolinic acid. The concentration of picolinic acid in human milk was 308 microM, the concentration in one brand of processed cow's milk was 20 microM, but picolinic acid was undetectable in a second brand of cow's milk and in four different infant formulas. Weanling rats fed supplemental picolinic acid absorbed significantly more dietary zinc and gained significantly more weight than rats fed an unsupplemented diet. The results suggest that the high bioavailability of zinc in human milk results from the presence of picolinic acid, a bidentate chelating ligand which facilitates zinc absorption from the intestine.

Effect of Dietary Phytate/Zinc Molar Ratio on Growth and Bone Zinc Response of Rats Fed Semipurified Diets

Abstract: In rats fed semipurified diets, bioavailability of dietary zinc was tested at different phytate/zinc molar ratios; growth and zinc in femurs were the criteria of adequacy. On diets with 10--12 ppm zinc, the growth of rats was not affected by phytate/zinc molar ratios of 12 or less if the level of dietary calcium was 0.75% but was depressed at ratios greater than 6 if the level of calcium was 1.75%. Phytate/zinc molar ratios greater than these did not depress growth if the dietary zinc concentration was at least 2.5 and 5 times the minimal requirement for growth at dietary calcium levels of 0.75 and 1.75%, respectively. At the maximum phytate/zinc molar ratio that did not depress growth, accumulation of zinc in femurs was depressed. Small increases in dietary calcium (from 0.75 to 0.87%) depressed growth of rats fed diets with 12 ppm zinc and a phytate/zinc molar ratio of 25. Preformed Zn3 and Zn6 phytate preparations were equivalent to ZnSO4.7H2O as dietary zinc sources. The data indicated that high dietary calcium per se reduced zinc bioavailability. The maximum phytate/zinc molar ratio that did not depress growth of young rats was greatly influenced by dietary calcium level and somewhat influenced by total dietary zinc concentration.

Total true efficiency of zinc utilization: determination and homeostatic dependence upon the zinc supply status in young rats.

Abstract: Total true efficiency of zinc utilization and its component factors, true absorption and metabolic efficiency, were studied in relation to dietary zinc supply in a 15-day experiment with 36 weanling rats in six groups. After day 3, the initial supply of 18.2 ppm zinc in the diet for all groups was changed to 5.6, 10.6, 18.2, 39, 70 and 141 ppm. in groups 1 to 6, respectively. During the 6-day balance period after day 9, zinc in take was proportional to dietary zinc concentration. Mean daily rates of weight gain and apparent zinc retention increased from a near zero level in group 1 to a high plateau from group 4 to 6. True absorption rate steadily rose and reached about twice that of apparent absorption in group 6. This difference in rates was due to endogenous zinc excretion. Percent total utili zation and percent true absorption steadily declined from a mean of about 100 in groups 1 and 2 to nearly 15 and 30, respectively, in group 6. Meta bolic efficiency, reflecting true retention of absorbed zinc, similarly de clined as percent true absorption did. The major conclusion was that not only the absorptive but also the metabolic efficiency greatly contributed to zinc homeostasis and total true efficiency of zinc utilization. J. Nutr. 110: 469-480, 1980.

Bromine Complexation in Zinc‐Bromine Circulating Batteries

Abstract: Upon electrolysis of aqueous zinc bromide solutions containing unsymmetrically substituted, cyclic quaternary ammonium bromides, both zinc metal and a bromine‐rich liquid are produced. Data, reported for N‐ethyl, N‐methylmorpholinium (1), N‐methoxymethyl, N‐methylpiperidinium (2), and N‐chloromethyl, N‐methylpyrrolidinium (3) bromides suggest that the bromine‐rich liquid is a fused salt and separates from the aqueous solution because of insolubility and density differences. The separation process of the bromine fused salt from the aqueous solution is represented as a partitioning of bromine between two phases and is dependent upon electrolysis state‐of‐charge, quaternary ammonium bromide, bromide ion concentration, and temperature. The bromine‐fused salts have properties dependent on composition. Selected examples of densities, specific resistances, viscosities, and polarization are given. Bromine, in the form of a dense, stable, conductive liquid, is useful in circulating zinc‐bromine batteries.

Wittig-type Reaction of Dimetallated Carbodianion Species as Produced by Zinc Reduction of gem-Polyhalogen Compounds in the Presence of Lewis Acids

Abstract: Treatment of R1COR2 with a suspension prepared from diiodomethane, trimethylaluminum and excess zinc in tetrahydrofuran at room temperature affords olefins R1R2C=CH2 in fair (R1,R2=alkyl) to good (R1=alkyl, R2=H) yields. The ketone methylenation is better carried with another system consisting of CH2Br2–Zn–TiCl4. Ketones and aldehydes are transformed into α-chloro α,β-unsaturated esters or α,β-unsaturated esters in good yields on treatment with methyl trichloroacetate or t-butyl dichloroacetate (ethyl dibromoacetate) in the presence of diethylaluminum chloride and zinc.

Comparison of extractants for plant-available zinc, cadmium, nickel, and copper in contaminated soils.

Abstract: The objective of this study was to find a suitable extractant(s) for plant-available metals in metal contaminated soils. Swiss chard (Beta vulgaris L. Fordhook Giant) was grown in greenhouse pots on 46 Ontario soils varying in degree of contamination with metals. The soils had been contaminated with metals to varying degrees over a period of years. After 40 days, the plants were harvested and Zn, Cd, Ni, and Cu concentrations were measured. Each soil was extracted with nine different extractants: aqua regia, 0.01M EDTA, 0.005M DTPA, 0.02M NTA, 0.5N CH/sub 3/COOH, 1N CH/sub 3/COONH/sub 4/, 0.6N HCl + 0.05N AlCl/sub 3/, (COOH)/sub 2/ + (COONH/sub 4/)/sub 2/, and H/sub 2/O. Zinc, cadmium, nickel, and copper concentrations in Swiss chard were correlated with the amounts of soil Zn, Cd, Ni, and Cu removed by each extractant. Of the nine soil extractants, CH/sub 3/COONH/sub 4/ was the best predictor of plant-available Zn if only extractable Zn and soil pH were included as independent variables in a regression equation. Acetic acid was the best extractant for prediction of both plant-available Cd and Ni when soil pH was included in the equation. Attempts to find a suitable soil extractant for plant-available Cu were unsuccessful.