Binding of Cd2+, Ni2+, Cu2+ and Zn2+ by isolated envelopes of Pseudomonas fluorescens

Abstract Cell envelopes of Pseudomonas fluorescens , cytoplasmic membrane, peptidoglycan and outer membrane were obtained from a fractionation procedure and tested for their metal binding capacity. Isolated envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) were chemically modified and functional carboxyl groups transformed to electropositive amine groups, using carbodiimide ethylenediamine. Transformation of carboxyl groups was evaluated by measuring total amine groups in all fractions (modified or not). Using equilibrium dialysis and Scatchard plots for the data, we have established that isolated unmodified cell envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) possess at least two types of metal binding sites with different association constants ( K _a and K '_a). Introduction of positive charges into the bacterial envelopes resulted in the disappearance of one type of metal binding site which had the highest association constant value for Ni²⁺, Cu²⁺ and Zn²⁺. All fractions, modified or not, always presented at least two types of binding sites with different association constants for Cd²⁺.     

Tunable Broadband Optical Responses of Substrate-Supported Metal/Dielectric/Metal Nanospheres

Using the image charge theory and finite element methods, we present the first comprehensive study on the optical properties of substrate-supported, three-layer, metal/dielectric/metal nanospheres. By adopting dipolar and quadrupolar approximations of the quasistatic image charge theory, we derive analytical expressions for the polarization-dependent polarizabilities of a three-layer nanosphere near a substrate and use them to find the nanosphere’s plasmon resonance wavelengths as functions of the geometric and material parameters of the nanosphere–substrate system. By calculating the resonance wavelength of substrate-supported gold/silica/gold nanosphere over a sufficiently large domain of the nanosphere’s dimensions, we show that this wavelength can be tuned from visible to infrared regions by altering only the size of the nanosphere’s core. We also show that the resonance position as well as the enhancement and confinement of the near-field can be dynamically tuned over broad ranges by changing the polarization of the excitation light. Of significance for the applicability of our results in practice is that we employ size-dependent permittivity of gold, which allows experimentalists to readily produce these substrate-supported nanospheres with desired optical responses. Upon comparing our analytical results with the results of numerical simulations, we reveal the range of the nanospheres’ outer radii within which the dipolar and quadrupolar approximations adequately describe the nanosphere–substrate interaction. Since majority of the optical functions are realized with light polarized parallel to the substrate, our results allow one to readily engineer the broadband optical responses of substrate-supported metal/dielectric/metal nanospheres for applications in resonance-enhanced sensing, in light harvesting, and in biomedicine.     

Crystal structure based design of functional metal/protein hybrids

Preparation of metal/protein hybrids is growing into important topics in the field of bioinorganic chemistry. X-ray crystal structure analyses of them provide direct information on unique interactions of metal cations or metal cofactors to understand and design enzymatic functions. In this mini review, the authors focus on the recent studies on the metal/protein hybrids concerning crystal structure analyses since 2002 and our related works. The precise structural determination promise us to deeply understand coordination chemistry in protein scaffold and shows intriguing suggestions on rational design and application use for biocatalysts, metal drugs and so on.     

Structural basis for copper transfer by the metallochaperone for the Menkes/Wilson disease proteins

The Hah1 metallochaperone protein is implicated in copper delivery to the Menkes and Wilson disease proteins. Hah1 and the N-termini of its target proteins belong to a family of metal binding domains characterized by a conserved MT/HCXXC sequence motif. The crystal structure of Hah1 has been determined in the presence of Cu(I), Hg(II), and Cd(II). The 1.8 A resolution structure of CuHah1 reveals a copper ion coordinated by Cys residues from two adjacent Hah1 molecules. The CuHah1 crystal structure is the first of a copper chaperone bound to copper and provides structural support for direct metal ion exchange between conserved MT/HCXXC motifs in two domains. The structures of HgHah1 and CdHah1, determined to 1.75 A resolution, also reveal metal ion coordination by two MT/HCXXC motifs. An extended hydrogen bonding network, unique to the complex of two Hah1 molecules, stabilizes the metal binding sites and suggests specific roles for several conserved residues. Taken together, the structures provide models for intermediates in metal ion transfer and suggest a detailed molecular mechanism for protein recognition and metal ion exchange between MT/HCXXC containing domains.     

Interaction of divalent metal ions with the NADP+-malic enzyme from maize leaves

The effect of several metal ions on NADP⁺-malic enzyme (EC 1.1.1.40) purified from Zea mays L. leaves was studied Mg²⁺, Mn²⁺, Co²⁺ and Cd²⁺ were all active metal cofactors. The malic enzyme from maize has a moderately high intrinsic preference for Mn²⁺ relative to Mg²⁺ at pH 7.0 and 8.0 Negative cooperativity detected in the binding of Mg²⁺ at pH 7.0 and 8.0 and in the binding of Mn²⁺ at pH 7.0 suggests the existence of at least two binding sites with different affinity. All of the activating metal ions have preference for octahedral coordination geometry and have ionic radii of 0.86–1.09 Å. The ions that act as inhibitors are outside this range and/or are incapable of octahedral coordination. Ba²⁺, Sr²⁺, Cd²⁺, Ca²⁺, Be²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Co²⁺, Hg²⁺ showed mixed-type inhibition. The reciprocal of their K₁ values follow the order of their apparence in the Irving-Williams series of stability that derives in part from size effects. It is suggested that the size of the ions may play a partial role in determining the strength of the metal interaction.     

Metal ion requirement of bifunctional UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase from rat liver

The metal ion requirement for both enzymatic activitiesof the bifunctional UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosaminekinase (E.C. 5.1.3.14/ 2.7.1.60), the key enzyme of N-acetylneuraminic acidbiosynthesis in ratliver, was investigated. UDP-N-acetylglucosamine 2-epimerase was active inimida-zole/HCl buffer in the complete absence of any metal ion. 200 mM Na + , K + , Rb + and Cs +activated enzymeactivity up to five-fold, whereas lower concentrations of thesemonovalent metal ions showed only a small effect on UDP-N-acetylglucosamine 2-epimeraseactivity. In sodium phosphate buffer the enzyme activitywas increased by 0.5 mM Mg , Sr , Ba and Mn , while in the presence of 200 mM NaCl UDP-N-acetyl-glucosamine2-epimerase activity showed astronger activation by these divalent metal ions. In imidazole/HClbuffer, UDP-N-acetylglucosamine2-epimerase activity was partially inhibited by 0.5 mM Be , Mg , Ba ,Mn , Sn and Fe , and completely inhibited by 0.5 mM Zn and Cd . Divalent metal ions were essen-tialforN-acetylmannosamine kinase activity, the most effective being Mg , followed byMn and Co .The optimal concentration of these metal ions was 3 mM. Less effective were Ni and Cd , whereas Ca ,Ba , Cu , Fe and Zn showed no effect on enzyme activity.     

Volume regulation by Amphiuma red blood cells: strategies for identifying alkali metal/H+ transport

The regulation of cell volume in response to anisotonic media, and in a broader perspective electroneutral alkali/metal H+ exchange transport, are currently areas of general interest to transport physiologists. In this paper I outline the basic features of volume-sensitive ion fluxes as studied with Amphiuma red blood cells. As has been shown in previous studies the alkali metal ion fluxes that are responsible for volume regulation by these cells are electroneutral by virtue of obligatory counter coupling with H+. The criteria for establishing the existence of electroneutral alkali metal/H+ exchange in these cells will be reviewed and expanded on. In the process, behavior and phenomena consistent with, as well as those unique to, electroneutral alkali metal/H+ exchange will be introduced, illustrated with experimental data, and discussed. Finally, based on thermodynamic considerations, kinetic behavior will be evaluated in terms of electroneutral alkali metal/H+ transport.     

High Activity Hydrogen Evolution Catalysis by Uniquely Designed Amorphous/Metal Interface of Core–shell Phosphosulfide/N‐Doped CNTs

A cost effective hydrogen evolution reaction (HER) catalyst that does not use precious metallic elements is a crucial demand for environment‐benign energy production. The family of earth‐abundant transition metal compounds of nitrides, carbides, chalcogenides, and phosphides is one of the promising candidates for such a purpose, particularly in acidic conditions. However, its catalytic performance is still needed to be enhanced through novel material designs and crystalline engineering. Herein, a chemically and electronically coupled transition metal phosphosulfide/N‐doped carbon nanotubes (NCNT) hybrid electrocatalyst is fabricated via a two‐step synthesis. The uniquely designed synthesis leads to the material morphology featuring a core–shell structure, in which the crystalline metal phosphide core is surrounded by an amorphous phosphosulfide nanoshell. Notably, due to the favorable modification of chemical composition and surface properties, core–shell CoP@PS/NCNT exhibits the noticeable HER activity of approximately ?80 mV @ ?10 mA cm^?2 with excellent durability, which is one of the highest active nonnoble metal electrocatalysts ever reported thus far.     

Tamm Plasmon Polariton as Refractive Index Sensor Excited by Gyroid Metals/Porous Ta2O5 Photonic Crystal

In this paper, a novel refractive index sensor in terahertz region is proposed. The proposed structure is prism/(sample/porousTa₂O₅)¹⁵/sample/gyroid metal/substrate. The sensor is based on the Tamm plasmon polariton at the interface between porous one-dimensional photonic crystal and gyroidal metal. The gyroidal metal has been used as an alternative metal and its refraction index can be tuned by the gyroid parameters. The effects of the metal volume fraction and sample refractive index on the performance are studied to improve the ability of the sensor. The proposed sensor achieves high sensitivity of 6.7 THz/RIU, a high figure of merit 6*10³ RIU^?1, a high-quality factor of 3*10³, and a low detection limit of 9*10^?6 RIU. The proposed device can be a good candidate for fabricating gyroid metal and porous material-based biosensors, active optoelectronic and polaritonic devices.

     

Nano-viewpoint in Modeling and Investigation of the D/M/D Transparent-Conductive Layer

Plasmonics - A transparent-conductive film (TCF) is widely used in various electro-optical devices. The dielectric/metal/dielectric (D/M/D) as one type of TCF has been highly considered due to more...     

Molecular Mechanisms and Genetic Basis of Heavy Metal Tolerance/Hyperaccumulation in Plants

Phytoremediation has gained increased attention as a cost-effective method for the remediation of heavy metal-contaminated sites. Because some plants possess a range of potential mechanisms that may be involved in the detoxification of heavy metals, they manage to survive under metal stresses. High tolerance to heavy metal toxicity could rely either on reduced uptake or increased plant internal sequestration,which is manifested by an interaction between a genotype and its environment. The growing application of molecular genetic technologies has led to increased understanding of mechanisms of heavy metal tolerance/accumulation in plants and, subsequently, many transgenic plants with increased heavy metal resistance,as well as increased uptake of heavy metals, have been developed for the purpose of phytoremediation. In the present review, our major objective is to concisely evaluate the progress made so far in understanding the molecular/cellular mechanisms and genetic basis that control the uptake and detoxification of metals by plants.     

Effective switch-on fluorescence sensing of zinc(II) ion by 8-aminoquinolino-beta-cyclodextrin/adamantaneacetic acid system in water

A water-soluble 8-aminoquinolino-beta-cyclodextrin/1-adamantaneacetic acid (1/ADA) system is prepared in situ and exhibits a unique switch-on fluorescence response to Zn(2+) over other common metal ions. Spectrophotometric studies demonstrate that this system can strongly coordinate Zn(2+) through a cyclodextrin/substrate/metal triple recognition mode, and the resulting 1/ADA/Zn(2+) ternary complex emits the blue-green fluorescence (lambda=490nm) that can be easily distinguished by eyes in aqueous solution. Significantly, the switch-on fluorescence response of 1/ADA to Zn(2+) is barely affected by various metal ions except Cu(2+). As a result, this system can behave as an efficient supramolecular fluorescence sensor for Zn(2+) in water.     

Iron uptake and Nramp2/DMT1/DCT1 in human bronchial epithelial cells

The capacity of natural resistance-associated macrophage protein-2 [Nramp2; also called divalent metal transporter-1 (DMT1) and divalent cation transporter-1 (DCT1)] to transport iron and its ubiquitous expression make it a likely candidate for transferrin-independent uptake of iron in peripheral tissues. We tested the hypothesis that non-transferrin-bound iron uptake by airway epithelial cells is associated with Nramp2/DMT1/DCT1 and that exposure to iron can increase Nramp2/DMT1/DCT1 mRNA and protein expression and transport of this metal. Exposure of BEAS-2B cells to ferric ammonium citrate (FAC) resulted in a decrease in Fe(3+) concentration in the supernatant that was dependent on time and initial iron concentration. In the presence of internalized calcein, FAC quenched the fluorescent signal, indicating intracellular transport of the metal. The Nramp2/DMT1/DCT1 mRNA isoform without an iron-response element (IRE) increased with exposure of BEAS-2B cells to FAC. RT-PCR demonstrated no change in the mRNA for the isoform with an IRE. Similarly, Western blot analysis for the isoform without an IRE confirmed an increased expression of this protein after FAC exposure, whereas the isoform with an IRE exhibited no change. Finally, immunohistochemistry revealed an increase in the isoform without an IRE in the rat lung epithelium after instillation of FAC. Comparable to mRNA and protein increases, iron transport was elevated after pretreatment of BEAS-2B cells with iron-containing compounds. We conclude that airway epithelial cells increase mRNA and expression of the Nramp2/DMT1/DCT1 without an IRE after exposure to iron. The increase results in an elevated transport of iron and its probable detoxification by these cells.     

Metalloenzymes and signal transduction: the protein serine/threonine phosphatases,a novel class of binuclear metal-containing enzymes

The serine/threonine protein phosphatases are important regulatory enzymes involved in signal transduction pathways in eukaryotic organisms. These enzymes include protein phosphatases 1, 2A, and 2B (also known as calcineurin). Recent structural data have indicated that the serine/threonine protein phosphatases are novel metalloenzymes containing a dinuclear metal ion cofactor at the active site. The dinuclear metal site is situated in a unique protein fold, a β-α-β-α-β motif which provides the majority of ligands to the metal ions. A similar fold is also seen in plant purple acid phosphatases, which also contain a dinuclear iron–zinc cofactor. In these enzymes, the two metal ions are bridged by a solvent molecule and a carboxylate group from an aspartic acid residue, juxtaposing the two metal ions to within 3.0–4.0?Å of each other. A similar motif has been identified in a number of other enzymes which exhibit phosphoesterase activity, implicating several of them as metalloenzymes which contain dinuclear metal ion cofactors.     

Cross Talk between Transition Metal Cathode and Li Metal Anode: Unraveling Its Influence on the Deposition/Dissolution Behavior and Morphology of Lithium

Lithium metal batteries (LMBs) combining a Li metal anode with a transition metal (TM) cathode can achieve higher practical energy densities (Wh L^?1) than Li/S or Li/O₂ cells. Research for improving the electrochemical behavior of the Li metal anode by, for example, modifying the liquid electrolyte is often conducted in symmetrical Li/Li or Li/Cu cells. This study now demonstrates the influence of the TM cathode on the Li metal anode, thus full cell behavior is analyzed in a way not considered so far in research with LMBs. Therefore, the deposition/dissolution behavior of Li metal and the resulting morphology is investigated with three different cathode materials (LiNi_0.5Mn_1.5O₄, LiNi_0.6Mn_0.2Co_0.2O₂, and LiFePO₄) by post mortem analysis with a scanning electron microscope. The observed large differences of the Li metal morphology are ascribed to the dissolution and crossover of TMs found deposited on Li metal and in the electrolyte by X‐ray photoelectron spectroscopy, energy‐dispersive X‐ray spectroscopy, and total reflection X‐ray fluorescence analysis. To support this correlation, the TM dissolution is simulated by adding Mn salt to the electrolyte. This study offers new insights into the cross talk between the Li metal anodes and TM cathodes, which is essential, when investigating Li metal electrodes for LMB full cells.     

Electrochemically Stable Sodium Metal‐Tellurium/Carbon Nanorods Batteries

Electrochemical metal cells utilizing tellurium and sodium chemistry are being extensively explored for developing advanced high‐performance batteries. The daunting challenges, however, still remain with low rate capability/volumetric capacity, unclear redox reaction processes, and the notorious sodium dendrites. Here, a cell design that features a novel Te/carbon nanorods cathode and a tailored ether‐based electrolyte is reported. It is the first report of Na metal‐Te full batteries with performance comparable to those of reported Na‐S and Na‐Se batteries at low ratings. By using the semimetal Te instead of the insulating S or Se, the Na‐Te batteries actually outperform reported Na‐S and Na‐Se batteries at high ratings. Ab initio molecular dynamics simulations, UV–vis spectrum, ex situ X‐ray photoelectron spectroscopy, and scanning electron microscopy results clearly reveal a three‐step redox process and stability of the Na metal‐Te cells. These comprehensive results demonstrate the feasibility of practical Na metal‐Te batteries with high volumetric energy density and a viable cell fabrication cost.     

芒属植物重金属耐性及其在矿山废弃地植被恢复中的应用潜力

芒属植物重金属耐性强,并且是重要的能源植物,其在矿山废弃地植被恢复中的应用备受关注.芒属植物对多种重金属耐性强,但不属于重金属超累积植物.目前的研究认为,根系代谢能力强、根际存在多种共生微生物及抗氧化和光合作用能力强是芒属植物重金属耐性强的重要原因,但更为全面的耐性机理需要深入研究.芒属植物在矿山废弃地植被恢复的应用潜力大,可以清除土壤重金属、改善土壤性质和促进生物多样性发展.本文总结分析了芒属植物生物学特性、重金属耐性特点、机理及其在矿山废弃地植被恢复中的应用潜力,提出了应用芒属植物进行矿山废弃地植被恢复的基本思路,并对芒属植物的重金属耐性机理及应用的未来研究方向进行展望,以期为利用芒属植物开展矿山废弃地植被恢复提供借鉴.     

Potentiation of 45Ca Uptake and Acute Toxicity Mediated by the N-Methyl-D-Aspartate Receptor: The Effect of Metal Binding Agents and Transition Metal Ions

Abstract: The activities mediated by the N -methyl-D-aspartate (NMDA) receptor were studied in cultured rat cerebellar granule cells. Micromolar concentrations of the metal binding compounds, EDTA, cysteine, and histidine, as well as serum albumin strongly potentiated receptor activity in the presence of millimolar concentrations of Ca²⁺ and Mg²⁺. The findings indicated that these agents remove an endogenous metal, probably Zn²⁺, which attenuates NMDA receptor-mediated ⁴⁵Ca uptake and toxicity. Several added metal ions were therefore tested at low micromolar concentrations. Zn²⁺ was found to be the most potent inhibitor of NMDA-induced ⁴⁵Ca uptake, followed by Cu²⁺ and Fe²⁺. Co²⁺, Cd²⁺, Fe³⁺, and AI³⁺ had no significant effect, whereas Ni²⁺ potentiated the ⁴⁵Ca uptake but inhibited at much higher concentrations. The potentiating agents that remove the endogenous metal had a particularly dramatic effect in the presence of Mg²⁺, the voltage-dependent suppressor of the NMDA receptor. Mg²⁺ also played an important role in the inhibitory effect of added Zn²⁺. Much lower concentrations of Zn²⁺ were needed to achieve inhibition of NMDA-induced ⁴⁵Ca uptake in the presence of Mg²⁺. Under a variety of conditions, a very good correlation was found between NMDA receptor-mediated ⁴⁵Ca uptake and the magnitude of acute neurotoxicity.