Monovalent Silver Ions Research Articles

Silver-exchanged CHA zeolite as a CO2-resistant adsorbent for N2/O2 separation

Zeolite Li-X is considered the best adsorbent for air separation (i.e., N 2 /O 2 one). However, this zeolite adsorbent suffers from serious limitations of preparation and process operation. Here, we report that Ag + -exchanged chabazite (Ag-CHA-6.0) with a Si/Al ratio of 6.0 shows comparable N 2 /O 2 separation performance, but higher CO 2 resistance than Li-X under N 2 /O 2 simulated conditions. The characterization results reveal that its excellent separation performance may be due to the preferential formation of partially charged silver clusters (Ag n δ+ ) within the CHA framework upon activation under a dynamic vacuum of 10 −3 Torr at 523 K. The intrazeolitic formation of these Ag n δ+ clusters, whose ability to form π-complexation with N 2 is higher than monovalent silver ions, was found to depend not only on the structure type of the zeolite support, but also its framework Si/Al ratio. • Ag + -exchanged zeolites with different framework topologies and Si/Al ratios are studied in N 2 /O 2 separation. • Ag-CHA-6.0 shows comparable N 2 /O 2 separation performance with commercial Li-X. • Ag-CHA-6.0 exhibits higher resistance to CO 2 than Li-X. • Partially charged silver clusters in Ag-CHA-6.0 contribute to its excellent N 2 /O 2 separation.

Silver ZK-5 zeolites for selective ethylene/ethane separation

The development of efficient adsorbents for olefin/paraffin separation has attracted great attention, because an alternative energy-efficient technology is required to move away from the energy intensive cryogenic distillation processes. Here, we have prepared two silver-exchanged ZK-5 (Ag-ZK-5) zeolites with low (2.9) and high (3.7) Si/Al ratios, as well as various other cation-exchanged forms, for ethylene/ethane separation and compared their separation properties with those of zeolites Na-, Ca- and Ag-A with Si/Al = 1.0 and Ag-UZM-9 with Si/Al = 3.7. Among the zeolite adsorbents tested here, Ag-ZK-5 with Si/Al = 3.7 has the highest ethylene/ethane selectivity (2.54) at 298 K in vacuum-swing adsorption mode, together with fast adsorption kinetics. While the breakthrough results hint at its applicability in concentrated ethylene/ethane streams, the outstanding performance of this Ag-ZK-5 for ethylene/ethane separation appears to be due to a combination of its unique framework topology and composition (Al content) which can stabilize monovalent silver ions.

Non-molecular monovalent metal organophosphonates and diphosphonates

The solid state chemistry of non-molecular monovalent metal organophosphonates and diphosphonates is relatively new and evolving research arena. The syntheses and structural characterization of about fifty such compounds are reported in the literature. They are a variety of mono- and di-phosphonates of inorganic monovalent cations, namely, alkali metal, thallium, cuprous, silver and mercurous ions and also ammonium ions. They have x:2 (x = 1–4) ratios of metal to phosphonate moieties and possess mostly layered and pillared-layered structures. Some of them function as solid Brönsted acids and exhibit proton conductivity.

Silver Alginate Hydrogel Micro- and Nanocontainers for Theranostics: Synthesis, Encapsulation, Remote Release, and Detection.

We have designed multifunctional silver alginate hydrogel microcontainers referred to as loaded microcapsules with different sizes by assembling them via a template assisted approach using natural, highly porous calcium carbonate cores. Sodium alginate was immobilized into the pores of calcium carbonate particles of different sizes followed by cross-linking via addition of silver ions, which had a dual purpose: on one hand, the were used as a cross-linking agent, albeit in the monovalent form, while on the other hand they have led to formation of silver nanoparticles. Monovalent silver ions, an unusual cross-linking agent, improve the sensitivity to ultrasound, lead to homogeneous distribution of silver nanoparticles. Silver nanoparticles appeared on the shell of the alginate microcapsules in the twin-structure as determined by transmission electron microscopy. Remote release of a payload from alginate containers by ultrasound was found to strongly depend on the particle size. The possibility to use such particles as a platform for label-free molecule detection based on the surface enhanced Raman scattering was demonstrated. Cytotoxicity and cell uptake studies conducted in this work have revealed that microcontainers exhibit nonessential level of toxicity with an efficient uptake of cells. The above-described functionalities constitute building blocks of a theranostic system, where detection and remote release can be achieved with the same carrier.

Giant magneto resistance and temperature coefficient of resistance in Sm0.55Sr0.30Ag0.15MnO3 perovskite

Silver ions substituted samarium strontium manganite (Sm0.55Sr0.30Ag0.15MnO3) pervoskite was synthesized by using respective oxides in stoichiometric ratio through solid state reaction. The as-prepared sample was characterized by various analytical techniques to confirm its formation and understand the effect of monovalent silver ions in pervoskite lattice. X-ray diffraction pattern confirms the single phase formation while grain morphology in SEM image indicates good connectivity among the grains. The enhancement in metal to insulator transition temperature shows quenched disorder and magnetoresistance phenomena. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) emerge from grain growth factor and homogeneity induced by Ag+ ions in the lattice. The reduction in hysteresis loss resulted from antiferromagnetic - ferromagnetic (TN) and ferromagnetic - paramagnetic (Tc) transitions reveals the removal of disorder in perovskite lattice by Ag+ ions substitution. This increases the magnetic moment across distinct ions on the applying magnetic field. The rise in MR% (~99%) with silver doping emerging from smooth spin tunneling of the grains across the boundary and suppression of the disordered magnetic fluctuations with increase in magnetic field has been reported. The present compound exhibits the first order nature of magnetism and observed first time the highest value of TCR ~ 95%.

Effect of polymer backbone chemical structure on metal ions binding by imidazolylmethyl derivatives

Sorption properties of poly(N-(5-methyl-4-imidazolyl)methylallylamine (PAA) and poly(N-(5-methyl-4-imidazolyl)methylethylenimine) (IMPEI) have been investigated and compared with those of imidazolylmethyl derivative of natural aminopolymer chitosan (IMC). We have shown that the structure of polymer backbone has a pronounced effect on sorption of both transition metal cations and noble metals by imidazolylmethyl derivatives. It was shown that sorption of Au(III) and Pt(IV) by all imidazolylmethyl derivatives is accompanied by changes in metal oxidation states. The highest content of more oxidized species – Au(III) and Pt(IV) was found in IMC, which showed the lowest sorption capacity. Efficacy of noble metals elution with HCl/thiourea solution changes in the row IMC>IMPAA>IMPEI, showing low applicability of IMPEI for recovery of gold and platinum ions in sorption/regeneration cycles despite its highest sorption capacity toward all noble metal ions.Sorption capacities toward transition metal cations change in the following row: IMPEI>IMC>IMPAA. The effect of polymer structure on sorption capacities of IMPEI, IMPAA, and IMC is much stronger for divalent cations than for monovalent silver ion. DFT calculations have shown that coordination of Ag+ ion by all derivatives occurs via formation of two Ag–N coordination bonds with N-atoms of imidazole ring and amino group of the polymer backbone, while contribution of electron–donor atoms of IMC and IMPEI backbone to coordination of divalent ions is remarkably higher.

Functional and Biochemical Characterization of Cucumber Genes Encoding Two Copper ATPases CsHMA5.1 and CsHMA5.2

Plant copper P1B-type ATPases appear to be crucial for maintaining copper homeostasis within plant cells, but until now they have been studied mostly in model plant systems. Here, we present the molecular and biochemical characterization of two cucumber copper ATPases, CsHMA5.1 and CsHMA5.2, indicating a different function for HMA5-like proteins in different plants. When expressed in yeast, CsHMA5.1 and CsHMA5.2 localize to the vacuolar membrane and are activated by monovalent copper or silver ions and cysteine, showing different affinities to Cu(+) (Km ∼1 or 0.5 μM, respectively) and similar affinity to Ag(+) (Km ∼2.5 μM). Both proteins restore the growth of yeast mutants sensitive to copper excess and silver through intracellular copper sequestration, indicating that they contribute to copper and silver detoxification. Immunoblotting with specific antibodies revealed the presence of CsHMA5.1 and CsHMA5.2 in the tonoplast of cucumber cells. Interestingly, the root-specific CsHMA5.1 was not affected by copper stress, whereas the widely expressed CsHMA5.2 was up-regulated or down-regulated in roots upon copper excess or deficiency, respectively. The copper-induced increase in tonoplast CsHMA5.2 is consistent with the increased activity of ATP-dependent copper transport into tonoplast vesicles isolated from roots of plants grown under copper excess. These data identify CsHMA5.1 and CsHMA5.2 as high affinity Cu(+) transporters and suggest that CsHMA5.2 is responsible for the increased sequestration of copper in vacuoles of cucumber root cells under copper excess.

Dental unit water treatment with hydrogen peroxide and monovalent silver ions artificially contaminated with freshly isolated pathogens.

Dental unit water (DUW) could be contaminated by human pathogens coming from biological fluids penetrated during patient treatment and by opportunistic pathogens detached from aquatic biofilm. These microorganisms could be spread to following patients. We tested the disinfectant activity of hydrogen peroxide and monovalent silver ions (H(2)O(2)-Ag(+)) into DUW artificially contaminated with freshly isolated pathogens. The tested microorganisms were Staphylococcus aureus, Enterococcus faecalis, Candida albicans, Pseudomonas aeruginosa, Legionella pneumophila, Mycobacterium chelonae, non-pathogenic Bacillus clausii spores. Bacterial suspensions were inoculated into the waterlines of pre-sterilized dental turbines. The test-turbines were connected to DUW and contaminated water was treated for 10 minutes with H(2)O(2)-Ag(+)-based disinfectant (H(2)O(2) 3% v/v, Ag(+) 0.001% w/v). The control-turbines were left untreated. Turbines were washed with sterile hard water used to assess the residual bacterial loads (expressed in colony forming units -cfu). Each strain was tested five times and the mean log loads were assessed. Following the European Standardization Committee, the disinfectant activity was evaluated as mean log load reduction, that is, the difference between the mean log load detected on the control-turbines and the mean log load detected on the test-turbines. Mean bacterial loads detected on the control-turbines ranged between 105-107 cfu. The mean log load reductions resulted 7.5 log cfu for S. aureus, E. faecalis, P. aeruginosa, 6.3 for C. albicans, 5.4 for L. pneumophila, 5.3 for M. chelonae, 2.9 for B. clausii spores. DUW disinfection with H(2)O(2)-Ag(+) could help minimize the risk that planktonic pathogens are spread to patients during dental treatment.

Synthesis of Pyridine-Based 1,3,4-Oxadiazole Derivative as Fluorescence Turn-On Sensor for High Selectivity of Ag+

An oxadiazole derivative(OXD) containing symmetrical pyridine-2-formamidophenyl-binded moiety was synthesised as fluorescence turn-on sensor OA1. Its ultraviolet-visible(UV-vis) and fluorescent spectra(FS) gave prominent fluorescence enhancement only for monovalent silver ion(Ag(+)) in HEPES buffer solution (10mM, pH = 7.0, DMF-H2O, 9:1, v/v), which indicated the photo-induced electron transfer(PET) occurred from the donor of pyridine-2-formamidophenyl group to oxadiazole fluorophore. The present study demonstrated that OA1 was a viable candidate as fluorescent receptor for a new Ag(+) sensor. And the results of fluorescent spectral titration showed this sensor formed 1:1 complex with Ag(+).

Neutralization by metal ions of the toxicity of sodium selenide.

Inert metal-selenide colloids are found in animals. They are believed to afford cross-protection against the toxicities of both metals and selenocompounds. Here, the toxicities of metal salt and sodium selenide mixtures were systematically studied using the death rate of Saccharomyces cerevisiae cells as an indicator. In parallel, the abilities of these mixtures to produce colloids were assessed. Studied metal cations could be classified in three groups: (i) metal ions that protect cells against selenium toxicity and form insoluble colloids with selenide (Ag+, Cd2+, Cu2+, Hg2+, Pb2+ and Zn2+), (ii) metal ions which protect cells by producing insoluble metal-selenide complexes and by catalyzing hydrogen selenide oxidation in the presence of dioxygen (Co2+ and Ni2+) and, finally, (iii) metal ions which do not afford protection and do not interact (Ca2+, Mg2+, Mn2+) or weakly interact (Fe2+) with selenide under the assayed conditions. When occurring, the insoluble complexes formed from divalent metal ions and selenide contained equimolar amounts of metal and selenium atoms. With the monovalent silver ion, the complex contained two silver atoms per selenium atom. Next, because selenides are compounds prone to oxidation, the stabilities of the above colloids were evaluated under oxidizing conditions. 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), the reduction of which can be optically followed, was used to promote selenide oxidation. Complexes with cadmium, copper, lead, mercury or silver resisted dissolution by DTNB treatment over several hours. With nickel and cobalt, partial oxidation by DTNB occurred. On the other hand, when starting from ZnSe or FeSe complexes, full decompositions were obtained within a few tens of minutes. The above properties possibly explain why ZnSe and FeSe nanoparticles were not detected in animals exposed to selenocompounds.

Silver Nanoparticles Compromise Neurodevelopment in PC12 Cells: Critical Contributions of Silver Ion, Particle Size, Coating, and Composition

BackgroundSilver exposures are rising because of the increased use of silver nanoparticles (AgNPs) in consumer products. The monovalent silver ion (Ag+) impairs neurodevelopment in PC12 cells and zebrafish.Objectives and methodsWe compared the effects of AgNPs with Ag+ in PC12 cells for neurodevelopmental end points including cell replication, oxidative stress, cell viability, and differentiation. First, we compared citrate-coated AgNPs (AgNP-Cs) with Ag+, and then we assessed the roles of particle size, coating, and composition by comparing AgNP-C with two different sizes of polyvinylpyrrolidone-coated AgNPs (AgNP-PVPs) or silica nanoparticles.ResultsIn undifferentiated cells, AgNP-C impaired DNA synthesis, but to a lesser extent than an equivalent nominal concentration of Ag+, whereas AgNP-C and Ag+ were equally effective against protein synthesis; there was little or no oxidative stress or loss of viability due to AgNP-C. In contrast, in differentiating cells, AgNP-C evoked robust oxidative stress and impaired differentiation into the acetylcholine phenotype. Although the effects of AgNP-PVP showed similarities to those of AgNP-C, we also found significant differences in potencies and differentiation outcomes that depended both on particle size and coating. None of the effects reflected simple physical attributes of nanoparticles, separate from composition or coating, as equivalent concentrations of silica nanoparticles had no detectable effects.ConclusionsAgNP exposure impairs neurodevelopment in PC12 cells. Further, AgNP effects are distinct from those of Ag+ alone and depend on size and coating, indicating that AgNP effects are not due simply to the release of Ag+ into the surrounding environment.

Silver Impairs Neurodevelopment: Studies in PC12 Cells

BackgroundExposure to silver is increasing because of silver nanoparticles in consumer products.Objectives and methodsMany biological effects of silver entail actions of Ag+ (monovalent silver ions), so we used neuronotypic PC12 cells to evaluate the potential for silver to act as a developmental neurotoxicant, using chlorpyrifos (CPF), a pesticide known to evoke developmental neurotoxicity, as a positive control for comparison.ResultsIn undifferentiated cells, a 1-hr exposure to 10 μM Ag+ inhibited DNA synthesis more potently than did 50 μM CPF; it also impaired protein synthesis but to a lesser extent than its effect on DNA synthesis, indicating a preferential effect on cell replication. Longer exposures led to oxidative stress, loss of viability, and reduced numbers of cells. With the onset of cell differentiation, exposure to 10 μM Ag+ evoked even greater inhibition of DNA synthesis and more oxidative stress, selectively impaired neurite formation without suppressing overall cell growth, and preferentially suppressed development into the acetylcholine phenotype in favor of the dopamine phenotype. Lowering the exposure to 1 μM Ag+ reduced the net effect on undifferentiated cells. However, in differentiating cells, the lower concentration produced an entirely different pattern, enhancing cell numbers by suppressing ongoing cell death and impairing differentiation in parallel for both neurotransmitter phenotypes.ConclusionsOur results show that silver has the potential to evoke developmental neurotoxicity even more potently than known neurotoxicants, such as CPF, and that the spectrum of effects is likely to be substantially different at lower exposures that do not show signs of outright toxicity.

Second-harmonic generation of thermally poled silver doped sodo-borophosphate glasses

Sodium niobium borophosphate glass, with a composition of 0.58(0.95NaPO3+0.05Na2B4O7)+0.42Nb2O5, has been doped with monovalent silver ions. Second harmonic generation (SHG) has been obtained from the poling treatment of this sample. The second order nonlinearity from the anode side was estimated from an analysis of transmitted polarized Maker-fringe patterns. Thanks to the original Maker fringe simulations, a value of 3 pm/V is obtained with the silver doped glass that unambiguously scales an enhancement of ∼35% with respect to the nondoped glass susceptibility. For both glasses, the nonlinear layer is found to be sodium-depleted up to 4 μm inside the anode, in accordance with quantitative energy dispersive x-ray spectroscopy characterizations. This comparative study indicates complex space-charge-migration processes during the poling treatment. The relative enhancement of the SHG signal of the silver doped glass is correlated with the increase in its linear susceptibility.

Second-harmonic generation in sodium and niobium borophosphate glasses after poling under field-assisted silver ions anodic injection

Monovalent silver ions, resulting from a thin silver layer initially deposited at the anode surface, have been introduced using the field-assisted ion-exchange technique in sodium niobium borophosphate glasses. A reproducible susceptibility χ(2) could be gained after this poling treatment, although a drop in the nonlinearity is observed due to the introduction of silver ions. From energy dispersive x-ray spectroscopy, it has been found that the nonlinear layer is characterized by a strong migration of sodium ions 4 μm deep inside the anode side, which have been partially replaced by silver ions. These results indicate a complex space-charge-migration process during the poling treatment, which is involved in the decrease in the mean second-harmonic generation signal.

Conformational Behavior of Giant DNA through Binding with Ag+ and Metallization

The conformational behavior of a long single-chain double-stranded DNA in solutions of free silver ions and silver nanoparticles generated via the reduction of AgNO3 by NaBH4 was monitored by fluorescence and electron microscopies and UV spectroscopy. The interaction of monovalent silver ions with DNA induces shrinking of a DNA-coiled polymer chain as a result of a decrease in the DNA persistence length through the complexation of Ag+ with DNA bases. In contrast, the reduction of silver ions by NaBH4 in DNA solutions triggers DNA compaction: a DNA transition from elongated coil state into a compact state. This transition is continuous, unlike the all-or-none discrete DNA compaction that is commonly seen with multications. It is suggested that the collapse of DNA is accompanied by growth aggregation of silver nanoparticles generated on the DNA template.

Introduction of Silver in Poled Sodium and Niobium Borophosphate Glasses: Characterization by Electrical Transmitted Current and SHG Measurements

Monovalent silver ions have been introduced in a sodium niobium borophosphate glass by poling the glass under heating and high voltage. A silver thin film electrode was previously deposited on the glass surface and put in contact with the anode. Second harmonic generation (SHG) has been obtained after the thermal poling treatment. The SHG signal has been studied through an analysis of transmitted polarized Maker-fringe patterns. The transmitted current curves during poling are registered and compared to the curves obtained from poling of the natural glass by the use of ndoped silicon anode. It indicates a complex space-charge-migration process during the poling treatment resulting in modification of the nonlinear SHG glasses signal profile.

Formation of the Silver Hydride Ion AgH+ upon the Reduction of Silver Ions by H· in Aqueous Solution. A Pulse Radiolysis Study

The reaction of hydrogen atoms and of alcohol radicals with monovalent silver ions is studied in aqueous solution by means of pulse radiolysis. In acidic aqueous solutions containing silver ions and an alcohol, hydrogen atoms react with silver ions to form AgH+ with a rate constant of k=1.5 × 1010dm3mol-1s-1. This complex dissociates into free silver atoms and hydrogen ions with a first order rate constant of 2 × 107s-1. A reaction of alcohol radicals with silver ions could not be observed in aqueous solutions containing either methanol, ethanol or 2-propanol during times of up to 15ms; the rate constant would therefore have to be smaller than 1 × 104dm3mol-1s-1.

Coordination geometries for monovalent and divalent metal ions in [His121]azurin--studies using perturbed angular correlations of gamma-rays from 111Ag and 111mCd.

The structural details of the metal site in the [His121]azurin mutant from Alcaligenes denitrificans where the axial methionine has been replaced by a histidine have been studied after substitution with the divalent cadmium ion and the monovalent silver ion. The studies have been carried out in solution using the technique of perturbed angular correlations of gamma-rays (PAC) of the two isotopes, 111Ag and 111mCd. In the pH range 6-9, the PAC spectra for cadmium-substituted [His121]azurin reveals a pH-independent equilibrium between two different metal-coordination geometries. Interpretation of the PAC data shows agreement between the dominating coordination geometry and that derived from X-ray diffraction on the Cu(II)[His121] azurin at high pH (Messerschmidt, A., unpublished results). Thus, it appears likely that cadmium for this geometry is four coordinated to the ligands His46, His117, Cys112, and His121. The other geometry is best interpreted as a substitution of His121 by a solvent water ligand. These interpretations stem from predictions of the experimentally determined nuclear quadrupole interactions (NQI) via the simple angular overlap model (AOM). At low pH (3.8), the concentration of the former species is reduced to 50% of its high pH value suggesting a pK of about 4 for His121. Two different coordination geometries have also been observed for the Cu(II) protein and assigned a type 1.5 and a type 1 copper site [Kroes, S. J., Hoitink, C. W. G., Andrew, C. R., Ai, J., Sanders-Loehr, J., Messerschmidt, A., Hagen, W. R. & Canters, G. W. (1996a) Eur. J. Biochem. 240, 342-351]. For silver-substituted [His121]azurin, several notable changes occur relative to the cadmium-substituted protein. At least four different metal-coordination geometries exist for silver[His121]azurin in the pH range 4-8. Changes in the population of these coordination sites occurs between pH 4 and pH 5, and pH 5 and pH 6. Furthermore, in contrast to the cadmium-substituted protein, only a single coordination geometry is present above pH 6. The change in population occurring between pH 5 and pH 6 suggests ionization of a non-coordinating histidine, here proposed as His121. The change in population at low pH could then be due to protonation of an additional coordinating histidine such as His46 or His117. The single coordination geometry existing at pH values above 6 for the silver protein cannot within our model calculations be described with His121 coordinated. However, it can be described with a coordinated water molecule but in a different angular position than for His121 in the copper protein (Messerschmidt, A., unpublished results). The reduced tendency for silver to coordinate His121 is in agreement with the general trend of lower pK values for ligands coordinating to monovalent ions relative to divalent ions. In conclusion, this work demonstrates that mutation of Met121 to other amino acid residues opens the possibility of other coordination geometries than the rigid three-coordinated structure observed for wild-type azurin, especially the possibility of increasing the coordination number by either solvent water ligands or the substituting amino acid. Furthermore, it opens up the possibility for different coordination geometries for monovalent and divalent metal ions as observed here and previously for the [Leu121]azurin mutant [Bauer, R., Danielsen, E., Hemmingsen, L., Bjerrum, M. J., Hansson, O. & Singh, K. (1997) J. Am. Chem. Soc. 119, 157-163].

Ag+center in alkaline-earth fluorides: New UV solid state lasers?

Oxygen-free strontium fluoride crystals containing single monovalent silver ions in a cubic site were grown. Our experiments showed that the Ag+ ion remained chemically stable upon optical irradiation at 222 nm (KrCl excimer). The ion exhibits a strong UV luminescence which presents no thermal quenching up to RT. At this temperature, the emitting level time-constant is 12 μs. An explanation is proposed for the silver photostability by relating it to the large electronic bandgap of the host (11.4 ev). The 222 nm absorbing level lies below the conduction band in a way such that photoionization of Ag+ is avoided, as well as other optically-induced opacity phenomena. A minimum source intensity at threshold is estimated at some 276 kW, when using a Fabry-Perot cavity. This power can normally be achieved with the excimer laser.

Copper and Silver Transport by CopB-ATPase in Membrane Vesicles of Enterococcus hirae

The P-type ATPase, CopB, of Enterococcus hirae is required for the copper resistance displayed by this organism and thus was postulated to be a copper pump. Using 64Cu+ and 110mAg+, we here show ATP-driven copper and silver accumulation catalyzed by CopB in native inside-out membrane vesicles of E. hirae. CopB ATPase exhibited an apparent Km for Cu+ and Ag+ of 1 microM and for ATP of 10 microM. Transport was maximal at pH 6 and had an apparent Vmax of 0.07 nmol.min-1.mg-1 for both copper and silver transport. Vanadate displayed a biphasic effect on transport: maximal inhibition was observed at 40 microM vanadate for copper transport and 60 microM for silver transport, respectively. At higher vanadate concentrations, these inhibitions were reversed. The CopB ATPase of E. hirae is thus a pump for the extrusion of monovalent copper and silver ions, with copper probably being the natural substrate.