Mol Zn Research Articles

Zinc(II) Extraction from Hydrochloric Acid Solutions using Amberlite XAD‐7 Impregnated with Cyanex 921 (Tri‐Octyl Phosphine Oxide)

Cyanex 921 (tri‐octyl phosphine oxide) was immobilized on Amberlite XAD‐7. The extractant impregnated resin (EIR) was very efficient at removing Zn(II) from HCl solutions (optimum found for 3 M HCl). The sorption strongly depended on the Cyanex 921 concentration in the EIR, and the temperature (the reaction being exothermic). The maximum sorption capacity was close to 15 mg Zn(II) g−1 EIR (i.e. 0.19 mol Zn(II) mol−1 Cyanex 921). The uptake kinetics were controlled by intraparticle diffusion (De: 0.44 10−12 m2 s−1). Zn(II) can be easily desorbed using a number of eluents (including water and 0.1 M solution of EDTA, HNO3, H2SO4, and Na2SO4), which maintained performance levels over 5 cycles.

Development and characterization of 5% mol Zn bioceramic in granular form

Hydroxyapatite (HA) is capable of accepting substitute ions within its lattice, including zinc ions. Zinc is a trace element that activates the osteogenesis of osteoblastic cells and therefore plays an important role in the activity of alkaline phosphatase enzyme. The purpose of this work was to produce and characterize 5% mol Zn bioceramic in granular form (Zn-granules) for clinical applications and compare it with granules made from HA by using the same production route. Granules with addition of porogen agents were produced from powders of HA and zinc-containing HA by uniaxial pressing and heat treatment. The granules were subsequently ground and sieved. The results indicated that zinc contributed to the reduction of sample crystallinity and formed a biphasic structure after calcination at 1200 °C. Additionally, zinc release from granular material may have clinical applications as bone graft.

The impact of Mn oxide coatings on Zn distribution

Zinc sorption to hydrous manganese oxide (HMO)-coated clay was investigated macroscopically, kinetically, and spectroscopically. Adsorption edges and isotherms revealed that the affinity and capacity of the HMO-coated montmorillonite was greater than that of montmorillonite, and when normalized to the oxide present, the coatings behaved similarly to the discrete Mn oxide. Over two pH conditions, 5 and 6, a linear relationship was observed for the isotherms; further analysis with X-ray absorption spectroscopy (XAS) resulted in one type of sorption configuration as a function of loading and ionic strength at pH 5. However, at a surface loading of 10 −3 mol Zn g HMO - coated clay −1 when the pH increased from 5 to 7, the first shell distance decreased slightly, while the atoms and coordination numbers remained the same; this change may be attributed to an increase in electrostatic interactions. After a contact time of 4 months where an additional 60% of the sites become occupied, the slower sorption process was modeled as intraparticle surface diffusion. Best fit diffusivities ranged from 10 −18 to 10 −17 cm 2 / s , where a slower process was observed for the coated surface as compared to the discrete oxide. Interestingly, the porosity of the Mn oxide coating appears to be influenced by the substrate during its growth, as its increase and shift to a smaller pore size distribution resulted in a diffusivity between that observed for discrete HMO and montmorillonite.

Zinc sorption to biogenic hexagonal-birnessite particles within a hydrated bacterial biofilm

Biofilm-embedded Mn oxides exert important controls on trace metal cycling in aquatic and soil environments. The speciation and mobility of Zn in particular has been linked to Mn oxides found in streams, wetlands, soils, and aquifers. We investigated the mechanisms of Zn sorption to a biogenic Mn oxide within a biofilm produced by model soil and freshwater Mn II-oxidizing bacteria Pseudomonas putida. The biogenic Mn oxide is a c-disordered birnessite with hexagonal layer symmetry. Zinc adsorption isotherm and Zn and Mn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy experiments were conducted at pH 6.9 to characterize Zn sorption to this biogenic Mn oxide, and to determine whether the bioorganic components of the biofilm affect metal sorption properties. The EXAFS data were analyzed by spectral fitting, principal component analysis, and linear least-squares fitting with reference spectra. Zinc speciation was found to change as Zn loading to the biosorbent [bacterial cells, extracellular polymeric substances (EPS), and biogenic Mn oxide] increased. At low Zn loading (0.13 ± 0.04 mol Zn kg −1 biosorbent), Zn was sorbed to crystallographically well-defined sites on the biogenic oxide layers in tetrahedral coordination to structural O atoms. The fit to the EXAFS spectrum was consistent with Zn sorption above and below the Mn IV vacancy sites of the oxide layers. As Zn loading increased to 0.72 ± 0.04 mol Zn kg −1 biosorbent, Zn was also detected in octahedral coordination to these sites. Overall, our results indicate that the biofilm did not intervene in Zn sorption by the Mn-oxide because sorption to the organic material was observed only after all Mn vacancy sites were capped by Zn. The organic functional groups present in the biofilm contributed significantly to Zn removal from solution when Zn concentrations exceeded the sorption capacity of the biooxide. At the highest Zn loading studied, 1.50 ± 0.36 mol Zn kg −1 biosorbent, the proportion of total Zn sorption attributed to bioorganic material was 38 mol%. The maximum Zn loading to the biogenic oxide that we observed was 4.1 mol Zn kg −1 biogenic Mn oxide, corresponding to 0.37 ± 0.02 mol Zn mol −1 Mn. This loading is in excellent agreement with previous estimates of the content of cation vacancies in the biogenic oxide. The results of this study improve our knowledge of Zn speciation in natural systems and are consistent with those of Zn speciation in mineral soil fractions and ferromanganese nodules where the Mn oxides present are possibly biogenic.

Improvement of methane activation using n-hexane as co-reactant over Zn/HZSM-11 zeolite

Significance of effective conversion of methane (C 1) to more valuable compounds such as aromatics is studied using n-hexane (C 6) as co-reactant. AH yield was as high as 30 mol% C using the following reaction conditions: temperature, 500 °C; contact time w/ f=30 g h mol −1 and a C 1 molar fraction, X C1:=(C 1/C 1 + C 6)=0.60, was achieved. The effect of the contact time, molar fraction, and time on stream was analyzed in order to obtain more information about different species evolution. The C 1 conversion reached at 50 mol% C using Zn/HZSM-11 with 2.13 mol Zn per cell unit.

Synthesis of Zn-doped Y2O3:Eu fine-particle phosphor by the sol-gel method

Y 2 O 3 : Eu , a typical oxide phosphor, was synthesized by the sol-gel method using metal alkoxide. Effects of crystallinity, photoluminescent, and cathodoluminescent properties of Y2O3:Eu on Zn were investigated. The (222) diffraction peak of Y2O3 was shifted to a wider-angle side and crystallinity was improved by Zn addition. However, ZnO phases were observed in the case of the powders with the addition of 0.2 and 0.3 mol Zn. The emission of the D05→F27 transition peaked at around 610 nm decreased, and, the wide, blue-green broad emission of 510–520 nm caused by ZnO increased as the Zn addition increased, under He-Cd laser excitation of 325 nm. On the other hand, the blue-green emission caused by ZnO was not observed in spite of Zn addition under electron-beam excitation below 3 keV. This indicates the possibility of ZnO phase existence inside of Y2O3, rather than as a neighbor on the surface. The addition of 0.2 mol Zn to Y2O3:Eu showed about four times higher intensity compared with non-addition of Zn for cathodoluminescence under an anode voltage of 2 kV and an electron-beam density of 60 μA/cm2. Zn addition to Y2O3:Eu was quite effective for cathodoluminescent properties. Although Zn addition did not control particle size, the fine-particle phosphors below a 1 μm radius were obtained by synthesis with the sol-gel method.

Characterization of the cupin-type phosphoglucose isomerase from the hyperthermophilic archaeon Thermococcus litoralis

The gene encoding phosphoglucose isomerase was cloned from Thermococcus litoralis, and functionally expressed in Escherichia coli. The purified enzyme, a homodimer of 21.5 kDa subunits, was biochemically characterized. The inhibition constants for four competitive inhibitors were determined. The enzyme contained 1.25 mol Fe and 0.24 mol Zn per dimer. The activity was enhanced by the addition of Fe2+, but inhibited by Zn2+ and EDTA. Enzymes with mutations in conserved histidine and glutamate residues in their cupin motifs contained no metals, and showed large decreases in kcat. The circular dichroism spectra of the mutant enzymes and the wild type enzyme were essentially the same but with slight differences.

Sorptive behavior of Zn(II) on a lake sediment by sequential extraction-radiotracer technique

A sequential extraction-radiotracer technique was applied to a sediment core sample collected from lake Biwa (Japan) in order to evaluate relative importance of the fractionated solid components to sorb Zn(II) ions. The core was previously divided into three parts from the surface of the sediment; upper (0–6 cm), middle (6–12 cm) and bottom (12–18 cm). The solid residue after each chemical treatment was collected to perform a sorption experiment by using 65Zn as a tracer. A difference in the amount of Zn(II) sorption was observed among original samples without any chemical treatments at each depth. The amounts were very small (10 −5 −10 −4 mol Zn(II) 100 g −1 of dry sample) in all fractions of the sediment. Electrochemical measurements of cadmium and copper ion sorption supported the results from the radiometric sorption experiment. The effects of several potential factors on zinc sorption were investigated. Ion exchange of zinc with protons on the mineral surfaces was a significant cause of the zinc sorption.

Zinc Source Influences Zinc Retention in Hair and Hair Growth in the Dog

Zinc absorption has been shown to vary as a func tion of the source of the zinc in the diet (Ho and Hdiroglou 1977, Ashmead et al. 1985, Wedekind and Baker 1990, Wedekind et al. 1990) and, in dogs, as a function of the presence or absence of dietary antag onists (Robertson and Burns 1963). Zinc absorption also varies as a function of the ac tual quantity of zinc in the diet (Mejborn 1990), the effect being with respect to the absolute amount of zinc absorbed with increasing dietary zinc, in contrast to the percentage absorption that may remain un changed. Problems may, however, arise as a result of increas ing the zinc content of a diet in an attempt to increase zinc absorption form the gut. The increase in zinc content of the diet may result in interaction with an other mineral causing a reduction in absorption of that mineral. Increasing dietary zinc above the minimum recommended, however, remains common practice to counteract antagonist effects on zinc absorption (NRC 1985) in many commercial diets. It has been suggested that when dietary zinc is sup plied in the form of a chelate with amino acids, rather than from inorganic sources, a greater proportion of zinc is absorbed. Depending on the amino acids used to chelate the zinc, the retention of zinc in tissues may be increased (Ashmead et al. 1989) and the undesirable effects that dietary antagonists exert on zinc absorp tion may be negated. Thus the inclusion of a zinc chelate in a diet for dogs may allow for the improvement of zinc absorp tion irrespective of the presence of dietary antagonists without the need to increase the total zinc supply in the diet. The purpose of this study was to compare two sources of zinc, zinc-amino acid chelate (2 mol metgly:l mol Zn) containing 20% Zn (ZM) and a zincpolysaccharide complex consisting of zinc sulphate complexed with alkali-modified brewers wort (the liq uid portion of malted grain), 16.7% Zn (ZP) as a re placement for Zn from zinc oxide when added to a commercial diet formulation. Materials and methods. Each zinc source was added to a typical commercial diet formulation (Table 1) that contained no added zinc. An equivalent of an additional 50 mg Zn • kg'1 as either ZO, ZM or ZP was

Phytic acid-zinc ion interactions: a calorimetric and titrimetric study

Abstract Using an isoperibolic titration microcalorimeter, the ionization characteristics and associated heat changes of phytic acid (myo-inositol hexaphosphate) and phytic acid in the presence of varying Zn(II) concentrations have been examined over the pH range 2.5–11 at 25°C in 0.2 M KCl. In the absence of Zn(II), ca. 7 of the 12 ionizable protons in phytic acid are titrated in this pH range with ionization heats varying from ca. 2 to −3 kcal-mol-1. At Zn(II): phytate mol ratios of 4:1 and greater, the dissociation of all protons and complex formation of phytate with Zn(II) occurs below pH 6. From the difference titration curves of phytic acid plus Zn(II) versus Zn(II) alone, ca. 3.5 mol Zn(II) bind per mol phytate. Since Zn(II):phytate complexes are insoluble, the observed heat changes contain contributions not only from heats of precipitation but also from binding, ionization, neutralization, and hydration effects. From the heat change for the titration of (a) phytic acid, pH 2.6–10.4; (b) phytic acid + Zn(II), pH 2.6–6.1; and (c) Zn(II), pH 2.6–6.1 at Zn(II): phytate ratios of 4 to 10, the value of 24.7 ± 0.5 kcal mol−1 phytate has been obtained for the binding of 3.5 mols Zn(II). This figure also includes the heat of precipitation of the complex. In pH-drop experiments, with the initial pH at 8.65, the value of 23.9 kcal mol-1 was obtained for ΔH°. Hysteresis effects are prevalent in these reaction solutions. Time-dependent changes in pH occur with a change in pH. For the phytate-Zn(II) reactions, the time-course curves are biphasic and fit a rate equation for two simultaneous first order reactions. Hysteresis effects seen in the titration of Zn(II) fit simple first-order kinetics. These effects most probably arise from the ejection of a proton from the aqua ion or aqua ion ligand complex(es).

Trypsin activity in the small intestine of rats after application of copper and zinc

In vivo experiments with Sprague-Dawley rats were conducted in order to explore the influence of Cu(2+), Zn(2+) as well as of the combinations of both on the activity of trypsin. The solutions of the trace elements were given per os, the animals were killed 30 min after the applications, and the activity of trypsin was determined in the juice of the small intestine by usingN (α)-benzoyl-L-arginine-p-nitroanilide (L-BAPA) as the substrate. The activity of trypsin depends on the concentration of the trace elements. When Cu(2+) ions are applied, there is a minimum activity at 10(-5) mol Cu(2+)/L and a maximum at 10(-4) mol Cu(2+)/L. When giving Zn(2+) ions, a minimum of trypsin activity is found at 10(-5) mol Zn(2+)/L and a maximum at 5×10(-6) mol Zn(2+)/L. On the whole, the trypsin activity is lower when the Cu(2+)/Zn(2+) combinations are applied compared to the addition of the single trace elements. On principle, a good conformity of the in vivo results was found with in vitro results.