ZIP8 Is an Iron and Zinc Transporter Whose Cell-surface Expression Is Up-regulated by Cellular Iron Loading

ZIP8 (SLC39A8) belongs to the ZIP family of metal-ion transporters. Among the ZIP proteins, ZIP8 is most closely related to ZIP14, which can transport iron, zinc, manganese, and cadmium. Here we investigated the iron transport ability of ZIP8, its subcellular localization, pH dependence, and regulation by iron. Transfection of HEK 293T cells with ZIP8 cDNA enhanced the uptake of ⁵⁹Fe and ⁶⁵Zn by 200 and 40%, respectively, compared with controls. Excess iron inhibited the uptake of zinc and vice versa. In RNA-injected Xenopus oocytes, ZIP8-mediated ⁵⁵Fe²⁺ transport was saturable (K_0.5 of ∼0.7 μm) and inhibited by zinc. ZIP8 also mediated the uptake of ¹⁰⁹Cd²⁺, ⁵⁷Co²⁺, ⁶⁵Zn²⁺ > ⁵⁴Mn²⁺, but not ⁶⁴Cu (I or II). By using immunofluorescence analysis, we found that ZIP8 expressed in HEK 293T cells localized to the plasma membrane and partially in early endosomes. Iron loading increased total and cell-surface levels of ZIP8 in H4IIE rat hepatoma cells. We also determined by using site-directed mutagenesis that asparagine residues 40, 88, and 96 of rat ZIP8 are glycosylated and that N-glycosylation is not required for iron or zinc transport. Analysis of 20 different human tissues revealed abundant ZIP8 expression in lung and placenta and showed that its expression profile differs markedly from ZIP14, suggesting nonredundant functions. Suppression of endogenous ZIP8 expression in BeWo cells, a placental cell line, reduced iron uptake by ∼40%, suggesting that ZIP8 participates in placental iron transport. Collectively, these data identify ZIP8 as an iron transport protein that may function in iron metabolism.     

Identification and characterization of zinc-starvation-induced ZIP transporters from barley roots

Zinc (Zn) is an essential element for plants but limited information is currently available on the molecular basis for Zn²⁺ transport in crop species. To expand the knowledge on Zn²⁺ transport in barley (Hordeum vulgare L.), a cDNA library prepared from barley roots was expressed in the yeast (Saccharomyces cerevisiae) mutant strain Δzrt1/Δzrt2, defective in Zn²⁺ uptake. This strategy resulted in isolation and identification of three new Zn²⁺ transporters from barley. All of the predicted proteins have a high similarity to the ZIP protein family, and are designated HvZIP3, HvZIP5 and HvZIP8, respectively. Complementation studies in Δzrt1/Δzrt2 showed restored growth of the yeast cells transformed with the different HvZIPs, although with different efficiency. Transformation into Fe²⁺ and Mn²⁺ uptake defective yeast mutants showed that the HvZIPs were unable to restore the growth on Fe²⁺ and Mn²⁺ limited media, respectively, indicating a specific role in Zn²⁺ transport. In intact barley roots, HvZIP8 was constitutively expressed whereas HvZIP3 and HvZIP5 were mainly expressed in ?Zn plants. These results suggest that HvZIP3, HvZIP5 and HvZIP8 are Zn²⁺ transporters involved in Zn²⁺ homeostasis in barley roots. The new transporters may facilitate breeding of barley genotypes with improved Zn efficiency and Zn content.     

Kinetic characterization of Zinc transport process and its inhibition by Cadmium in isolated rat renal basolateral membrane vesicles: In vitro and In vivo studies

We firstly characterized zinc uptake phenomenon across basolateral membrane vesicles (BLMVs) isolated from normal rat kidney. The process was found to be time, temperature, and substrate concentration dependent, and displayed saturability. Zn²⁺ uptake was competitively inhibited in the presence of 2 mM Cd with Ki of 3.9 mM. Zinc uptake was also inhibited in the presence of sulfhydryl reacting compound suggesting involvement of {–}SH groups in the transport process. Further, to elucidate the effect of in vivo Cd on zinc transport in BLMVs, Cd nephrotoxicity was induced by subcutaneous administration of CdCl₂ at dose of 0.6 mg/kg/d for 5 days in a week for 12 weeks. An indolent renal failure developed in Cd exposed rats was accompanied with a significantly high urinary excretion of Cd²⁺, Zn²⁺ and proteins. The histopathology and electron microscopy of kidneys of Cd exposed rats documented changes of proximal tubular degeneration. Notably, Cd content in renal cortex of Cd exposed rats was 215 μg/g tissue that was higher than the critical concentration of Cd in kidneys which was associated with significantly higher Zn and metallothionein (MT) contents. Zinc uptake in BLMVs isolated from kidneys of Cd exposed rats was significantly reduced. Further, kinetic studies revealed that decrease in zinc uptake synchronized with decrease in maximal velocity (V_max) and increase in affinity constant which is suggestive of decreased number of active zinc transporters. Furthermore, conformational modulation of Zn transporter in BLM was further supported by observed variation in transition temperature for zinc transport in BLMVs isolated from Cd-exposed kidney.     

The uptake of zinc by erythrocytes under near-physiological conditions

The in vitro uptake of zinc by erythrocytes was measured under near-physiological conditions, using⁶⁵Zn as a radioactive tracer. Because of the presence of serum albumin—a strong zinc ligand—a low concentration of medium free zinc was maintained. Under these conditions a high-affinity carrier for zinc transport over the cell membrane was identified. With human erythrocytes, a Michaelis constant (K _m ) of 0.2 nM with respect to free medium zinc was measured and aV _max of 4.5 nmoles Zn transported per h/g dry wt. TheK _m for medium Zn increases when the size of the internal erythrocytic Zn pool is augmented, whereasV _max remains virtually unchanged. A model to explain this phenomenon is proposed. It is suggested that this phenomenon could underlie observations, confirmed here, that the in vitro uptake of Zn by animal erythrocytes depends on the Zn status of the animal.     

The influence of protons and zinc ions on the steady-state inactivation of Kv1.3 potassium channels

Using the whole-cell patch-clamp technique, we investigated the influence of extracellular pH and zinc ions (Zn²⁺) on the steady-state inactivation of Kv1.3 channels expressed in human lymphocytes. The obtained data showed that lowering the extracellular pH from 7.35 to 6.8 shifted the inactivation midpoint (V_i) by 17.4 ± 1.12 mV (n = 6) towards positive membrane potentials. This shift was statistically significant (p < 0.05). Applying 100 μM Zn²⁺ at pH 6.8 further shifted the Vi value by 16.55 ± 1.80 mV (n = 6) towards positive membrane potentials. This shift was also statistically significant (p < 0.05). The total shift of the Vi by protons and Zn²⁺ was 33.95 ± 1.90 mV (n = 6), which was significantly higher (p < 0.05) than the shift caused by Zn²⁺ alone. The Zn²⁺-induced shift of the V_i at pH 6.8 was almost identical to the shift at pH = 7.35. Thus, the proton-and Zn²⁺-induced shifts of the V_i value were additive. The steady-state inactivation curves as a function of membrane voltage were compared with the functions of the steady-state activation. The total shift of the steady-state inactivation was almost identical to the total shift of the steady-state activation (32.01 ± 2.10 mV, n = 10). As a result, the “windows” of membrane potentials in which the channels can be active under physiological conditions were also markedly shifted towards positive membrane potentials. The values of membrane voltage and the normalised chord conductance corresponding to the points of intersection of the curves of steady-state activation and inactivation were also calculated. The possible physiological significance of the observed modulatory effects is discussed herein.     

Increased free Zn2+ correlates induction of sarco(endo)plasmic reticulum stress via altered expression levels of Zn2+‐transporters in heart failure

Zn²⁺‐homoeostasis including free Zn²⁺ ([Zn²⁺]_i) is regulated through Zn²⁺‐transporters and their comprehensive understanding may be important due to their contributions to cardiac dysfunction. Herein, we aimed to examine a possible role of Zn²⁺‐transporters in the development of heart failure (HF) via induction of ER stress. We first showed localizations of ZIP8, ZIP14 and ZnT8 to both sarcolemma and S(E)R in ventricular cardiomyocytes (H9c2 cells) using confocal together with calculated Pearson's coefficients. The expressions of ZIP14 and ZnT8 were significantly increased with decreased ZIP8 level in HF. Moreover, [Zn²⁺]_i was significantly high in doxorubicin‐treated H9c2 cells compared to their controls. We found elevated levels of ER stress markers, GRP78 and CHOP/Gadd153, confirming the existence of ER stress. Furthermore, we measured markedly increased total PKC and PKCα expression and PKCα‐phosphorylation in HF. A PKC inhibition induced significant decrease in expressions of these ER stress markers compared to controls. Interestingly, direct increase in [Zn²⁺]_i using zinc‐ionophore induced significant increase in these markers. On the other hand, when we induced ER stress directly with tunicamycin, we could not observe any effect on expression levels of these Zn²⁺ transporters. Additionally, increased [Zn²⁺]_i could induce marked activation of PKCα. Moreover, we observed marked decrease in [Zn²⁺]_i under PKC inhibition in H9c2 cells. Overall, our present data suggest possible role of Zn²⁺ transporters on an intersection pathway with increased [Zn²⁺]_i and PKCα activation and induction of HF, most probably via development of ER stress. Therefore, our present data provide novel information how a well‐controlled [Zn²⁺]_i via Zn²⁺ transporters and PKCα can be important therapeutic approach in prevention/treatment of HF.     

Novel miR-sc4 regulates the proliferation and migration of Schwann cells by targeting Cdk5r1

Clinical and experimental studies have shown an association between intracellular free Zn²⁺ ([Zn²⁺]_i)-dyshomeostasis and cardiac dysfunction besides [Ca²⁺]_i-dyshomeostasis. Since [Zn²⁺]_i-homeostasis is regulated through Zn²⁺-transporters depending on their subcellular distributions, one can hypothesize that any imbalance in Zn²⁺-homeostasis via alteration in Zn²⁺-transporters may be associated with the induction of ER stress and apoptosis in hypertrophic heart. We used a transverse aortic constriction (TAC) model to induce hypertrophy in young male rat heart. We confirmed the development of hypertrophy with a high ratio of heart to body weight and cardiomyocyte capacitance. The expression levels of ER stress markers GRP78, CHOP/Gadd153, and calnexin are significantly high in TAC-group in comparison to those of controls (SHAM-group). Additionally, we detected high expression levels of apoptotic status marker proteins such as the serine kinase GSK-3β, Bax-to-Bcl-2 ratio, and PUMA in TAC-group in comparison to SHAM-group. The ratios of phospho-Akt to Akt and phospho-NFκB to the NFκB are significantly higher in TAC-group than in SHAM-group. Furthermore, we observed markedly increased phospho-PKCα and PKCα levels in TAC-group. We, also for the first time, determined significantly increased ZIP7, ZIP14, and ZnT8 expressions along with decreased ZIP8 and ZnT7 levels in the heart tissue from TAC-group in comparison to SHAM-group. Furthermore, a roughly calculated total expression level of ZIPs responsible for Zn²⁺-influx into the cytosol (increased about twofold) can be also responsible for the markedly increased [Zn²⁺]_i detected in hypertrophic cardiomyocytes. Taking into consideration the role of increased [Zn²⁺]_i via decreased ER-[Zn²⁺] in the induction of ER stress in cardiomyocytes, our present data suggest that differential changes in the expression levels of Zn²⁺-transporters can underlie mechanical dysfunction, in part due to the induction of ER stress and apoptosis in hypertrophic heart via increased [Zn²⁺]_i- besides [Ca²⁺]_i-dyshomeostasis.     

A tetrahedral coordination of Zinc during transmembrane transport by P-type Zn2+-ATPases

Zn²⁺ is an essential transition metal required in trace amounts by all living organisms. However, metal excess is cytotoxic and leads to cell damage. Cells rely on transmembrane transporters, with the assistance of other proteins, to establish and maintain Zn²⁺ homeostasis. Metal coordination during transport is key to specific transport and unidirectional translocation without the backward release of free metal. The coordination details of Zn²⁺ at the transmembrane metal binding site responsible for transport have now been established. Escherichia coli ZntA is a well-characterized Zn²⁺-ATPase responsible for intracellular Zn²⁺ efflux. A truncated form of the protein lacking regulatory metal sites and retaining the transport site was constructed. Metrical parameters of the metal–ligand coordination geometry for the zinc bound isolated form were characterized using x-ray absorption spectroscopy (XAS). Our data support a nearest neighbor ligand environment of (O/N)₂S₂ that is compatible with the proposed invariant metal coordinating residues present in the transmembrane region. This ligand identification and the calculated bond lengths support a tetrahedral coordination geometry for Zn²⁺ bound to the TM-MBS of P-type ATPase transporters.     

65Zn2+ transport by isolated gill epithelial cells of the American lobster, Homarus americanus

Gills are the first site of impact by metal ions in contaminated waters. Work on whole gill cells and metal uptake has not been reported before in crustaceans. In this study, gill filaments of the American lobster, Homarus americanus, were dissociated in physiological saline and separated into several cell types on a 30, 40, 50, and 80% sucrose gradient. Cells from each sucrose solution were separately resuspended in physiological saline and incubated in ⁶⁵Zn²⁺ in order to assess the nature of metal uptake by each cell type. Characteristics of zinc accumulation by each kind of cell were investigated in the presence and absence of 10 mM calcium, variable NaCl concentrations and pH values, and 100 μM verapamil, nifedipine, and the calcium ionophore A23187. ⁶⁵Zn²⁺ influxes were hyperbolic functions of zinc concentration (1–1,000 μM) and followed Michaelis–Menten kinetics. Calcium reduced both apparent zinc binding affinity (K _m) and maximal transport velocity (J _max) for 30% sucrose cells, but doubled the apparent maximal transport velocity for 80% sucrose cells. Results suggest that calcium, sodium, and protons enter gill epithelial cells by an endogenous broad-specificity cation channel and trans-stimulate metal uptake by a plasma membrane carrier system. Differences in zinc transport observed between gill epithelial cell types appear related to apparent affinity differences of the transporters in each kind of cell. Low affinity cells from 30% sucrose were inhibited by calcium, while high affinity cells from 80% sucrose were stimulated. ⁶⁵Zn²⁺ transport was also studied by isolated, intact, gill filament tips. These intact gill fragments generally displayed the same transport properties as did cells from 80% sucrose and provided support for metal uptake processes being an apical phenomenon. A working model for zinc transport by lobster gill cells is presented.     

<Superscript>65</Superscript>Zn<Superscript>2+</Superscript> transport by lobster hepato-pancreatic baso-lateral membrane vesicles

The lobster (Homarus americanus) hepato-pancreatic epithelial baso-lateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph: an ATP-dependent calcium ATPase, a sodium-calcium exchanger, and a verapamil-sensitive cation channel. We used standard centrifugation methods to prepare purified hepato-pancreatic baso-lateral membrane vesicles and a rapid filtration procedure to investigate whether ⁶⁵Zn²⁺ transfer across this epithelial cell border occurs by any of these previously described transporters for calcium. Baso-lateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10–15 s and approached equilibrium by 120 s. In the absence of sodium, ⁶⁵Zn²⁺ influx was a hyperbolic function of external zinc concentration and followed the Michaelis-Menten equation for carrier transport. This carrier transport was stimulated by the addition of 150 M ATP (increase in K_m and J_max) and inhibited by the simultaneous presence of 150 mol l^–1 ATP+250 mol l^–1 vanadate (decrease in both K_m and J_max). In the absence of ATP, ⁶⁵Zn²⁺ influx was a sigmoidal function of preloaded vesicular sodium concentration (0, 5, 10, 20, 30, 45, and 75 mmol l^–1) and exhibited a Hill Coefficient of 4.03±1.14, consistent with the exchange of 3 Na⁺/1Zn²⁺. Using Dixon analysis, calcium was shown to be a competitive inhibitor of baso-lateral membrane vesicle ⁶⁵Zn²⁺ influx by both the ATP-dependent (K_i=205 nmol l^–1 Ca²⁺) and sodium-dependent (K_i=2.47 mol l^–1 Ca²⁺) transport processes. These results suggest that zinc transport across the lobster hepato-pancreatic baso-lateral membrane largely occurred by the ATP-dependent calcium ATPase and sodium-calcium exchanger carrier proteins.Communicated by: I.D. Hume     

Bioinformatic and Expression Analyses of Genes Mediating Zinc Homeostasis in Nostoc punctiforme

Zinc homeostasis was investigated in Nostoc punctiforme. Cell tolerance to Zn²⁺ over 14 days showed that ZnCl₂ levels above 22 μM significantly reduced cell viability. After 3 days in 22 μM ZnCl₂, ca. 12% of the Zn²⁺ was in an EDTA-resistant component, suggesting an intracellular localization. Zinquin fluorescence was detected within cells exposed to concentrations up to 37 μM relative to 0 μM treatment. Radiolabeled ⁶⁵Zn showed Zn²⁺ uptake increased over a 3-day period, while efflux occurred more rapidly within a 3-h time period. Four putative genes involved in Zn²⁺ uptake and efflux in N. punctiforme were identified: (i) the predicted Co/Zn/Cd cation transporter, putative CDF; (ii) the predicted divalent heavy-metal cation transporter, putative Zip; (iii) the ATPase component and Fe/Zn uptake regulation protein, putative Fur; and (iv) an ABC-type Mn/Zn transport system, putative zinc ZnuC, ZnuABC system component. Quantitative real-time PCR indicated the responsiveness of all four genes to 22 μM ZnCl₂ within 3 h, followed by a reduction to below basal levels after 24 h by putative ZIP, ZnuC, and Fur and a reduction to below basal level after 72 h by putative CDF efflux gene. These results demonstrate differential regulation of zinc transporters over time, indicating a role for them in zinc homeostasis in N. punctiforme.     

Effects of Exogenous Zinc on Cell Cycle, Apoptosis and Viability of MDAMB231, HepG2 and 293 T Cells

As a non-toxic metal to humans, zinc is essential for cell proliferation, differentiation, regulation of DNA synthesis, genomic stability and mitosis. Zinc homeostasis in cells, which is crucial for normal cellular functioning, is maintained by various protein families including ZnT (zinc transporter/SLC30A) and ZIP (Zrt-, Irt-like proteins/SLC39A) that decrease and increase cytosolic zinc availability, respectively. In this study, we investigated the influences of a specific concentration range of ZnSO₄ on cell cycle and apoptosis by flow cytometry, and cell viability by MTT method in MDAMB231, HepG2 and 293 T cell lines. Fluorescent sensors NBD-TPEA and the counterstain for nuclei Hoechst 33342 were used to stain the treated cells for observing the localisation and amount of Zn²⁺ via laser scanning confocal microscope. It was found that the influence manners of ZnSO₄ on cell cycle, apoptosis and cell viability in various cell lines were different and corresponding to the changes of Zn²⁺ content of the three cell lines, respectively. The significant increase on intracelluar zinc content of MDAMB231 cells resulted in cell death, G1 and G2/M cell cycle arrest and increased apoptotic fraction. Additionally, the mRNA expression levels of ZnT and ZIP families in the three cell lines, when treated with high concentration of ZnSO₄, increased and decreased corresponding to their functions, respectively.     

Kinetic characterization of barley root plasma membrane-bound Ca2+- and Mg2+-dependent adenosine triphosphatase activities

A plasma membrane-rich microsome fraction isolated from barley (Hordeum vulgare L. cv. Conquest) roots contained considerable divalent cation-dependent ATPase activity when assayed at 16°C. The maximal divalent cation-stimulation of the apparent basal ATPase activity varied as Ca²⁺ > Mg²⁺ > Mn²⁺= Zn²⁺ > Co²⁺ > Ni²⁺, with all other divalent cations tested being inhibitory. Double reciprocal plots of the Ca²⁺- and Mg²⁺-dependent ATPase velocities as a function of substance concentration were nonlinear, suggesting the presence of multiple catalytic sites. Both MgATP^2- and CaATP^2- served as the true substrates and apparently bind to the same catalytic sites. Free ATP and Ca²⁺ could inhibitit the Ca²⁺- and Mg²⁺-dependent ATPase. Increasing free Mg²⁺ levels enhanced the affinity of the Mg²⁺-dependent ATPase for MgATP^2-, while slightly inhibiting the V_max values. Other divalent cation-nucleoside triphosphate complexes produced maximal enzyme velocities equal to or greater than those generated by CaATP^2- and MgATP^2-. However, the ATPase had significantly higher affinities for CaATP^2- and MgATP^2-, than for the alternative substrates. The high and low affinity components of the Ca²⁺- and Mg²⁺-dependent ATPase exhibited optimal V_max values at pH 5 and 6, respectively. Analysis of the pH-dependence of the enzyme K_m values indicated enzyme-substrate binding with charge neutralization at neutral and alkaline pH's. Nonlinear double reciprocal plots were obtained at all assay temperatures. However, the complexity of the enzyme kinetics became less apparent at the higher assay temperatures. The kinetics of the barley root divalent cation-dependent ATPase activities are discussed in terms of the kinetics of ATPases from other plants and the methods used to obtain them, and compared to the kinetics of ion transport ATPases from animal membranes.     

EFFECT OF ZINC AVAILABILITY ON GROWTH,MORPHOLOGY, AND NUTRIENT INCORPORATION IN A COASTAL AND AN OCEANIC DIATOM1

We investigated the effect of Zn availability on growth rate (μ), cell morphology, and elemental stoichiometry and incorporation rate in two marine diatoms. For the coastal diatom Skeletonema costatum (Grev.) Cleve, the half‐saturation constant (K_S) for growth was 4.1 pM Zn²⁺, and growth ceased at ≤ 2.6 pM Zn²⁺, whereas for the oceanic diatom Thalassiosira oceanica Hasle, K_S was 0.5 pM Zn²⁺, and μ remained at ～40%μ_max even at 0.3 pM Zn²⁺. Under Zn‐limiting (Zn‐L) conditions, S. costatum decreased cell size significantly, leading to an 80% increase in surface area to volume ratio (SA/V) at Zn²⁺ of 3.5 pM compared to Zn‐replete (Zn‐R) conditions (at Zn²⁺ of 13.2 pM), whereas T. oceanica’s morphology did not change appreciably. Cell quotas of C, N, P, Si, and chl a significantly decreased under Zn limitation in S. costatum (at Zn²⁺ of 3.5 pM), whereas Zn limitation in T. oceanica (at Zn²⁺ of 0.3 pM) had little effect on quotas. Elemental stoichiometry was ～85C:10N:9Si:1P and 81C:9N:5Si:1P for S. costatum, and 66C:5N:2Si:1P and 52C:6N:2Si:1P for T. oceanica, under Zn‐R and Zn‐L conditions, respectively. Incorporation rates of all elements were significantly reduced under Zn limitation for both diatoms, but particularly for Si in S. costatum, and for C in T. oceanica, despite its apparent tolerance of low Zn conditions. With [Zn²⁺] in some parts of the ocean being of the same order (～0.2 to 2 pM) as our low Zn conditions for T. oceanica, our results support the hypothesis that in situ growth and C acquisition may be limited by Zn in some oceanic species.     

Free zinc concentration in bovine milk measured by analytical affinity chromatography with immobilized metallothionein

A new analytical affinity chromatography method was developed for measuring the free [Zn²⁺] concentration in bovine milk. The column was generated by immobilizing avidin and attaching biotinylated metallothionein (MT) on controlled-pore glass beads. Zinc bound to the MT column at physiological free [Zn²⁺] concentration and was dissociated again in an elution buffer of pH 2. The distributions of extrinsically added⁶⁵Zn and native zinc in different fractions of milk were virtually identical, validating the use of extrinsic labeling in studies of the free [Zn²⁺] concentration in milk. Extrinsically labeled whey fractions were mixed with standard solutions whose free [Zn²⁺] concentrations were calculated by computer model.⁶⁵Zn retained by the column provided an indication of free [Zn²⁺] concentration in the mixture, and by interpolation, in the original milk. The free [Zn²⁺] concentration measured by the affinity chromatography method in the milk of a group of six cows was 90.4±29.7 pM. This value is similar to estimates of free [Zn²⁺] concentrations in other biological fluids by entirely different methods. Measurement of free [Zn²⁺] may be helpful in understanding the physiology and biochemistry of zinc metabolism.     

H2V3O8 Nanowire/Graphene Electrodes for Aqueous Rechargeable Zinc Ion Batteries with High Rate Capability and Large Capacity

Aqueous rechargeable zinc ion batteries are considered a promising candidate for large‐scale energy storage owing to their low cost and high safety nature. A composite material comprised of H₂V₃O₈ nanowires (NWs) wrapped by graphene sheets and used as the cathode material for aqueous rechargeable zinc ion batteries is developed. Owing to the synergistic merits of desirable structural features of H₂V₃O₈ NWs and high conductivity of the graphene network, the H₂V₃O₈ NW/graphene composite exhibits superior zinc ion storage performance including high capacity of 394 mA h g^?1 at 1/3 C, high rate capability of 270 mA h g^?1 at 20 C and excellent cycling stability of up to 2000 cycles with a capacity retention of 87%. The battery offers a high energy density of 168 W h kg^?1 at 1/3 C and a high power density of 2215 W kg^?1 at 20 C (calculated based on the total weight of H₂V₃O₈ NW/graphene composite and the theoretically required amount of Zn). Systematic structural and elemental characterization confirm the reversible Zn²⁺ and water cointercalation electrochemical reaction mechanism. This work brings a new prospect of designing high‐performance aqueous rechargeable zinc ion batteries for grid‐scale energy storage.     

NaCa0.6V6O16·3H2O as an Ultra‐Stable Cathode for Zn‐Ion Batteries: The Roles of Pre‐Inserted Dual‐Cations and Structural Water in V3O8 Layer

Rechargeable aqueous batteries with Zn²⁺ as a working‐ion are promising candidates for grid‐scale energy storage because of their intrinsic safety, low‐cost, and high energy‐intensity. However, suitable cathode materials with excellent Zn²⁺‐storage cyclability must be found in order for Zinc‐ion batteries (ZIBs) to find practical applications. Herein, NaCa_0.6V₆O₁₆·3H₂O (NaCaVO) barnesite nanobelts are reported as an ultra‐stable ZIB cathode material. The original capacity reaches 347 mAh g^?1 at 0.1 A g^?1, and the capacity retention rate is 94% after 2000 cycles at 2 A g^?1 and 83% after 10 000 cycles at 5 A g^?1, respectively. Through a combined theoretical and experimental approach, it is discovered that the unique V₃O₈ layered structure in NaCaVO is energetically favorable for Zn²⁺ diffusion and the structural water situated between V₃O₈ layers promotes a fast charge‐transfer and bulk migration of Zn²⁺ by enlarging gallery spacing and providing more Zn‐ion storage sites. It is also found that Na⁺ and Ca²⁺ alternately suited in V₃O₈ layers are the essential stabilizers for the layered structure, which play a crucial role in retaining long‐term cycling stability.     

Effect of clay,organic matter and CaCO3 content on zinc adsorption by soils

Summary Zinc adsorption was studied in suspensions of six soils of different physicochemical characteristics in dilute ZnSO₄ solutions. At low concentrations, Zn²⁺ adsorption was described by the Langmuir adsorption equation. The calculated Langmuir adsorption maxima were related positively to clay and carbonate content and negatively with organic matter content of soils. Multiple regression analysis revealed that zinc adsorption maxima can be predicted with good precision from information in soil survey reports. When the added Zn²⁺ exceeded the adsorption maximum, the solid phase of zinc controlling its concentration in solution was either zinc hydroxide or carbonate so long as soil carbonates were present. The values of zinc potential also indicated that soils retain Zn²⁺ more strongly than Zn(OH)₂ or carbonate. Postgraduate student Professor of Soils. Professor of Soils.     

Reversible immobilization of invertase on Cu-chelated polyvinylimidazole-grafted iron oxide nanoparticles

Polyvinylimidazole (PVI)-grafted iron oxide nanoparticles (PVIgMNP) were prepared by grafting of telomere of PVI on the iron oxide nanoparticles. Different metal ions (Cu²⁺, Zn²⁺, Cr²⁺, Ni²⁺) ions were chelated on polyvinylimidazole-grafted iron oxide nanoparticles, and then the metal-chelated magnetic particles were used in the adsorption of invertase. The maximum invertase immobilization capacity of the PVIgMNP–Cu²⁺ beads was observed to be 142.856 mg/g (invertase/PVIgMNP) at pH 5.0. The values of the maximum reaction rate (V _max) and Michaelis–Menten constant (Km) were determined for the free and immobilized enzymes. The enzyme adsorption–desorption studies, pH effect on the adsorption efficiency, affinity of different metal ions, the kinetic parameters and storage stability of free and immobilized enzymes were evaluated.     

Effects of heavy metals on microbial activity of water and sediment communities

The effects of Cd²⁺, Cr³⁺ and Zn²⁺ on the microbial activity of water and sediment samples from a contaminated stream were studied. The maximum [¹⁴C]glucose uptake (V_max) and the mineralization (¹⁴CO₂) rates were determined. A 10% reduction in V_max was obtained at lower metal concentrations in water samples than in sediment ones. Moreover, a 10% decrease in ¹⁴CO₂ was observed at significantly minor metal levels, so ¹⁴CO₂ was more sensitive to evaluated heavy metal pollution. On the basis of MICs obtained for both communities, they were more sensitive to Cd²⁺ than to Cr³⁺ and Zn²⁺. Zinc was less inhibitory to V_max and ¹⁴CO₂ rates; Cr³⁺ showed an intermediate toxicity, and Cd²⁺ was 10–100 times more inhibitory than the other metals.