Metal Ion Sites Research Articles

Efficient Removal of Metals from Synthetic and Real Galvanic Zinc-Containing Effluents by Brewer's Yeast Saccharomyces cerevisiae.

The performance of the brewer’s yeast Saccharomyces cerevisiae to remove metal ions from four batch systems, namely Zn(II), Zn(II)-Sr(II)-Cu(II), Zn(II)-Ni(II)-Cu(II), and Zn(II)-Sr(II)-Cu(II)-Ba(II), and one real effluent was evaluated. Yeast biosorption capacity under different pH, temperature, initial zinc concentration, and contact time was investigated. The optimal pH for removal of metal ions present in the analyzed solution (Zn, Cu, Ni, Sr, and Ba) varied from 3.0 to 6.0. The biosorption process for zinc ions in all systems obeys Langmuir adsorption isotherm, and, in some cases, the Freundlich model was applicable as well. The kinetics of metal ions biosorption was described by pseudo-first-order, pseudo-second-order, and Elovich models. Thermodynamic calculations showed that metal biosorption was a spontaneous process. The two-stage sequential scheme of zinc ions removal from real effluent by the addition of different dosages of new sorbent allowed us to achieve a high efficiency of Zn(II) ions removal from the effluent. FTIR revealed that OH, C=C, C=O, C–H, C–N, and NH groups were the main biosorption sites for metal ions.

Structure, magnetic and thermodynamic properties of heterometallic ludwigites: Cu2GaBO5 and Cu2AlBO5

We present an extensive study of the structural, magnetic and thermodynamic properties of high-quality monocrystals of two heterometallic oxyborates from the ludwigite family: Cu2GaBO5 and Cu2AlBO5 in the temperature range above 2 K. The distinctive feature of the investigated structures is the selective distribution of Cu and Ga/Al cations. The unit cell of Cu2GaBO5 and Cu2AlBO5 contains four nonequivalent crystallographic sites of metal ions. Two sites in the structure of Cu2GaBO5 are fully occupied by Cu atoms which form the quasi one-dimensional chains along the a-axis. For Cu2AlBO5 all sites are partially occupied by Al and Cu atoms. The joint analysis of low-temperature data on magnetic susceptibility and magnetic contribution to the specific heat showed that Cu2AlBO5 and Cu2GaBO5 exhibit an antiferromagnetic transition at TN=2.4 and 4.1 K, respectively. The magnetic response below TN can be represented as the sum of two contributions: the ordered component and the paramagnetic contribution from defects of the same relative weight. It is shown that the external magnetic field above 2.5T and 2.8T for Cu2GaBO5 and Cu2AlBO5, respectively, leads to a broadening of the magnetic phase transition indicating suppression of the long-range antiferromagnetic order.

Underpinning the conductivity mechanism in wide bandgap metal organic framework through chemical sensing

Metal organic frameworks are an emerging class of materials with a broad range of electronic properties with diverse applications such as sensors, catalysts, and permeable membranes. Here, three isostructural wide bandgap (WB) zeolitic imidazole frameworks (ZIFs) are synthesized having metal ion sites occupied by Zn (ZIF-8, Eg = 5.3 eV), Co (ZIF-67, Eg = 4.3 eV), and both Zn and Co (50%–50% mixture). The conductivity mechanism in these WB ZIFs involves the Mott variable range hopping of charge carriers from one metal site to the other. The hopping probability in the mixture is governed by the constitute having a lesser activation energy. Thus, it reveals that the incorporation of a different metal ion (Co in place of Zn) in the lattice forms a parallel low resistance path through hopping at Co sites and hence reduces the sensor response as well as selectivity toward ammonia. This parallel resistance path of the Co channel does not get affected by ammonia since it is found that ammonia has high affinity toward Zn ions and not toward Co ions. Thus, the incorporation of new metal ions hinders the hopping charge transport mechanisms in ZIFs.

Comparative adsorption of heavy metal ions in wastewater on monolayer molybdenum disulfide

To maximize the potential of monolayer molybdenum disulfide (MoS2) sheet in the disposal of heavy metal ions in wastewater, we compared the adsorption of several common heavy metal ions (including Cr3+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+) in wastewater on the monolayer MoS2 sheet through first-principles calculation. Our simulation results show that the monolayer MoS2 sheet is a potential heavy metal adsorption material because of the attractive interaction between them. The most negative adsorption energy determines that the TMo site is the most stable adsorption site for the heavy metal ions. The attractive interaction is considered as chemical adsorption, and it is closely related to charge transfer. The orbital hybridization between S p and heavy metal ions p and d states electrons contributes to the adsorption, except the orbital hybridization between S p and Pb p states electrons contributes to the Pb2+ adsorption. All the results show that the monolayer MoS2 sheet is most suitable for removing Ni2+ and Cr3+ ions from wastewater, followed by Cu2+ and Pb2+. For the ions Cd2+, Zn2+, and Hg2+, its adsorption strength remains to be improved.

Adsorption of Cu (II)and Co (II) from aqueous solution using lignosulfonate/chitosan adsorbent

In practical application, the adsorption capacity, adsorption kinetics, recycling and production cost of adsorbent affect the application of adsorbent. In this study, porous lignosulfonate/chitosan adsorbent was prepared by simple radical polymerization of acrylic acid in the mixed solution of lignosulfonate and chitosan. The porous and large surface area of adsorbent provides more adsorption sites for heavy metal ions. A variety of characterization methods were used to characterize the appearance and structure of the adsorbent. Adsorbent can effectively adsorb heavy metal ions in aqueous solution, and has the best removal effect for Cu2+ and Co2+. The adsorption capacity of adsorbent for Co2+ is 386 mg g−1, and for Cu2+ is 283 mg g−1. 0.01 g adsorbent was used to adsorb 100 mg L−1 Cu2+, and the adsorption equilibrium was reached within 60 min. When the amount of adsorbent reaches 0.03 g, the removal rate of heavy metal ions of 100 mg L−1 can reach 99%. In this study, an adsorbent based on acrylic resin was developed.

COFBTLP-1/three-dimensional macroporous carbon electrode for simultaneous electrochemical detection of Cd2+, Pb2+, Cu2+ and Hg2+

The indissolubility or poor dissolubility of covalent-organic frameworks (COFs) limits their wide applications. Here, the COFBTLP-1 which were prepared by the aminaldehyde condensation between 1,4-benzenedithiol-2,5-diamino-hydrochloride and 1,3,5-triformylbenzene was controllably grown on kenaf stem-derived macroporous carbon (3D-KSC). Compared with COFBTLP-1 powder, the COFBTLP-1 grown on 3D-KSC avoided their random orientation effectively. The results showed that the amount of COFBTLP-1 could be effectively controlled by adjusting the concentration of monomers and growing time. Each unit of COFBTLP-1 has 12 adsorption sites (6 sulfur atoms and 6 nitrogen atoms) for heavy metal ions (HMIs) and regular holes to facilitate the transfer of HMIs. A large number of adsorption sites of HMIs could identify and captured HMIs selectively, and accordingly Cd2+, Pb2+, Cu2+ and Hg2+ could be detected simultaneously by using the COFBTLP-1/3D-KSC electrode. The detection limits for Cd2+, Pb2+, Cu2+ and Hg2+ are 12.3 nM, 11.8 nM, 18.6 nM and 21.4 nM, respectively. The sensitivities are up to 1337.4 μA/μM cm2, 1389.0 μA/μM cm2 and 886.2 μA/μM cm2, 770.0 μA/μM cm2, respectively. The COFBTLP-1/3D-KSC may be also applied in other fields of electroanalytical chemistry.

Iminodiacetic acid-functionalized porous polymer for removal of toxic metal ions from water

The design of efficient adsorbent with abundant binding sites for heavy metal ions is crucial for developing innovative materials that will remove pollutant metal ions. The high uptake capacity, kinetics, and affinity towards the toxic metals are the key requirements that the materials under invesigation should accomplish. Here we report the synthesis of iminodiacetic acid-functionalized hypercrosslinked polymer (IDA-HCP) for purification of water polluted by toxic metal ions via coordination of carboxylate and amino active sites on the surface of porous polymer. The obtained porous polymer is stable under harsh conditions and the structural features on the polymer work together to help the removal of Pb(II) with 1138 mg g–1 uptake capacity. In the meanwhile, the IDA-HCP reveals reuseability and very promising capture efficiency not only for Pb2+, but also for Hg2+ and Cd2+ from a mixture of Pb2+, Hg2+, Cd2+, Co2+, Fe3+, Zn2+, Mg2+, and Na+ metal ions. This result gives us confidence that the polymer material can solve the pollution problem caused by various metal ions.

Dynamer and Metallodynamer Interconversion: An Alternative View to Metal Ion Complexation.

A bifunctional molecule containing both a bidentate binding site for metal ions and an aminopyrimidine H-bond donor-acceptor site has been synthesized, and its properties, in its free and coordinated forms, have been established in solution and in the solid state by analytical and spectroscopic methods as well as by X-ray structure determinations. Structural characterization has shown that it forms a one-dimensional H-bonded polymeric assembly in the solid state, while spectroscopic measurements indicate that it also aggregates in solution. The reaction of a simple Fe(II) salt with this assembly results in the emergence of two geometrical isomers of the complex: [FeL3](BF4)2·9H2O-C1 (meridional, mer) and [FeL3]2(SiF6)(BF4)2·12H2O-C2 (facial, fac). While, complex C1 in the solid state generates a one-dimensional H-bonded polymer involving just two ligands on each Fe center, with the chirality of the complex units alternating along the polymer chain, the structure of complex C2 shows NH···N interactions seen in both the ligand and mer complex (C1) structures to be completely absent. Physicochemical properties of the free and complexed ligand differ substantially.

How does the active site in the MoSe2 surface affect its electrochemical performance as anode material for metal-ion batteries?

In this work, we implement density functional theory (DFT) simulations to study how active sites in the MoSe2 surface affect its electrochemical performance as anode material for metal-ion batteries (metal ions including Li, Na, K, Mg, and Al ions). Se vacancy MoSe2 (0 0 1) and MoSe2 (1 1 0) are considered to provide active sites for metal ions. The adsorption energies, diffusion energy barriers, electronic conductivity and open circuit voltage profile (OCV) are evaluated. According to our calculations, MoSe2 (0 0 1) with Se vacancy occupied by Mg ion shows similar diffusion energy barriers and comparable OCV to the pristine MoSe2 (0 0 1). Moreover, Mg ion shows much lower diffusion barriers than the other ions. Besides that, MoSe2 (1 1 0) shows much higher adsorption energies than the (0 0 1) section, indicating its high capacity for metal-ion batteries. However, MoSe2 (1 1 0) also exhibits much higher diffusion energy barriers, which would inhibit its rate capability. Comparatively, MoSe2 (0 0 1) with Se vacancies can improve the conductivity of MoSe2, and the conductivity increases with the number of Se vacancies increases. Consequently, MoSe2 (0 0 1) with single Se vacancy has comprehensive electrochemical performance for Mg-ion battery anode, including low Mg-ion diffusion energy, comparable OCV, and high electronic conductance.

Atomic deciphering of cation exchange mechanism in upconversion nanoparticles

Transition metal ion doping in upconversion nanoparticles (UCNPs) provides an effective way to enhance the luminescence for their wide array of applications. However, the doping sites of transition metal ions have not been comprehensively explored, and commonly assumed that transition metal ions replace the trivalent lanthanides within the lattice. Here we report that cation exchange of transition metal (Mn2+) in β-NaYF4:Yb3+/Er3+ UCNPs occurs through alkaline metal (Na+) replacement, via 2Na+↔ Mn2+ + Vacancy reaction. This process distorts the LnF9 polyhedrons and tailors the surrounding environment around the trivalent lanthanides, thereby improving the upconversion intensity from active lanthanides. Further confirmed by core-shell design and spectroscopic study, we prove that the transition–alkaline metal exchange enables both the emission enhancement and transition probability variation of activators.

Elucidating the role of the axial cysteine residue in NHase catalysis and the enzyme maturation

Nitrile hydratases are metalloenzymes that contain trivalent Fe/or Co ions in their active site, coordinated in an N2S3 ligand environment. The sulfur atoms are post‐translationally modified and have three different oxidation states (αCys, Cys‐SOH and Cys‐SOO−) while backbone amines account for the nitrogen ligands and are deprotonated. Theoretical calculations assume that the αCys ligand is a thiolate, making it a strong π‐donor ligand and a good a nucleophile. A critical outstanding mechanistic question is whether the formation of a transient disulfide bond is essential for catalytic turnover. Such a transient disulfide bond was proposed based on QM/MM calculations between the αCys sulfur and the sulfur of the proposed sulfenic acid cyclic intermediate. However, more recent theoretical studies is self‐inconsistent in its conclusions regarding a transient disulfide formation. To examine the role of the αCys108 ligand in catalysis, it was mutated to A, M, S, and H in the Co‐type NHase from Pseudonocardia thermophila JCM 3095 (PtNHase). ICP‐MS demonstrated reduced metal ion content for each mutant: <5% (αC108A), ~44% (αC108M), ~50% (αC108S) and ~55% ( αC108H) and catalytic activity also decreased to ~0.3%, ~0.8%, ~1.6%, and ~6.7%, respectively, towards acrylonitrile. The X‐ray crystal structure of αC108A confirmed the mutation and the decreased active site metal content. Therefore, the axial thiolate is important to properly tune the electronic properties of the active site metal ion, but is not essential to catalysis. These data provide insight into the critical mechanistic question of whether the axial αCys ligand forms a transient disulfide bond during turnover.Support or Funding InformationThis work was supported by (CHE‐1808711, RCH; CHE‐1308672, BB; CHE‐1532168 BB & RCH), the Todd Wehr Foundation, Bruker Biospin, and the National Institutes of Health/NIBIB National Biomedical EPR Center (P41‐EB001980)

Covalent modification of Nanocellulose (NCC) by functionalized Graphene oxide (GO) and the study of adsorption mechanism

ABSTRACT In this study, nanocellulose/graphene oxide composites (NCC/GO) were prepared by dissolving NCC with AmimCl ionic liquid, and covalently modifying NCC with functionalized GO via esterification reaction, which weakened the hydrogen bonding of molecules and reduced chemical inertness. The morphology of modified NCC was characterized by SEM. The structure between NCC and GO was analyzed by FTIR. The crystalline phase of NCC and NCC/GO composites was investigated by XRD. The results revealed that NCC/GO composites were successfully prepared, and GO was uniformly dispersed in the NCC matrix. Because of the introduction of GO, it greatly increased the proportion of functional groups in composites. In addition, taking heavy metal ions-Ni2+ as an example, the adsorption rate of NCC and NCC/GO composites on Ni2+ was studied, and the adsorption mechanism also was explored. The experimental results showed that the adsorption rate of Ni2+ by NCC/GO composites was 95.8% higher than that of pure NCC. Furthermore, the composites had multiple adsorption sites (–COOH, –OH, –C = O, pore structure) for heavy metal ions because of the grafting of GO onto NCC.–

Enhancement of Oxidative Reaction by the Intramolecular Electron Transfer between the Coordinated Redox-Active Metal Ions in SOD1

The denatured Cu, Zn superoxide dismutase (SOD1) has the pro-oxidant activity that is suggested to be related with the pathogenesis of amyotrophic lateral sclerosis (ALS). We showed from the changes in the coordinated metal ions that the Cu ion in the Cu-binding site is the catalytic site of the pro-oxidant activity, and a redox-active metal ion in the Zn-binding site has the auxiliary function to enhance the pro-oxidant activity. The auxiliary function is suggested to arise from the intramolecular electron transfer between the coordinated metal ions in the denatured SOD1. The oxidation/reduction cycle of Cu in the Cu-binding site is assisted with changing the oxidation state of a metal ion in the Zn-binding site. The magnitude of the toxicity of the denatured SOD1 is discussed based on the ability of the auxiliary function.

Paramagpy: software for fitting magnetic susceptibility tensors using paramagnetic effects measured in NMR spectra.

Paramagnetic metal ions with fast-relaxing electrons generate pseudocontact shifts (PCSs), residual dipolar couplings (RDCs), paramagnetic relaxation enhancements (PREs) and cross-correlated relaxation (CCR) in the nuclear magnetic resonance (NMR) spectra of the molecules they bind to. These effects offer long-range structural information in molecules equipped with binding sites for such metal ions. Here we present the new open-source software Paramagpy, which has been written in Python 3 with a graphic user interface. Paramagpy combines the functionalities of different currently available programs to support the fitting of magnetic susceptibility tensors using PCS, RDC, PRE and CCR data and molecular coordinates in Protein Data Bank (PDB) format, including a convenient graphical user interface. Paramagpy uses efficient fitting algorithms to avoid local minima and supports corrections to back-calculated PCS and PRE data arising from cross-correlation effects with chemical shift tensors. The source code is available from 10.5281/zenodo.3594568 .

Partial Metal Ion Saturation of C2 Domains Primes Synaptotagmin 1-Membrane Interactions

Synaptotagmin 1 (Syt1) is an integral membrane protein whose phospholipid-binding tandem C2 domains, C2A and C2B, act as Ca2+ sensors of neurotransmitter release. Our objective was to understand the role of individual metal-ion binding sites of these domains in the membrane association process. We used Pb2+, a structural and functional surrogate of Ca2+, to generate the protein states with well-defined protein-metal ion stoichiometry. NMR experiments revealed that binding of one divalent metal ion per C2 domain results in loss of conformational plasticity of the loop regions, potentially pre-organizing them for additional metal-ion and membrane-binding events. In C2A, a divalent metal ion in site 1 is sufficient to drive its weak association with phosphatidylserine-containing membranes, whereas in C2B, it enhances the interactions with the signaling lipid phosphatidylinositol-4,5-bisphosphate. In full-length Syt1, both Pb2+-complexed C2 domains associate with phosphatidylserine-containing membranes. Electron paramagnetic resonance experiments show that the extent of membrane insertion correlates with the occupancy of the C2 metal ion sites. Together, our results indicate that upon partial metal ion saturation of the intra-loop region, Syt1 adopts a dynamic, partially membrane-bound state. The properties of this state, such as conformationally restricted loop regions and positioning of C2 domains in close proximity to anionic lipid headgroups, “prime” Syt1 for cooperative binding of a full complement of metal ions and deeper membrane insertion.

One‐Step Synthesis of Nanostructured CoS2 Grown on Titanium Carbide MXene for High‐Performance Asymmetrical Supercapacitors

AbstractMXene (2D titanium carbide) as the electrode material for supercapacitors has been studied extensively and deeply in recent years. In order to enhance the electrochemical performance of MXene, CoS2 nanoparticles grown on MXene surface are constructed by a simple one‐step solvent thermal method. CoS2 nanoparticles play a crucial part in increasing the active sites of metal ions on the surface of MXene. In three‐electrode system, the obtained MXene/CoS2 composite delivers high performance. Its specific capacitance can be up to 1320 F g−1 at a current density of 1 A g−1 and it shows remarkable cycle performance with 78.4% after 3000 cycles at 10 A g−1. Moreover, the asymmetric supercapacitors (ASCs) with reduced graphene oxide as the negative electrode and MXene/CoS2 composite as the positive electrode exhibit a wide potential window of 1.6 V and high energy density (28.8 Wh kg−1) at a power density of 800 W kg−1. After 5000 cycles, the ASCs maintain 98% of initial specific capacitance at 5 A g−1. These results can effectively promote the application in the supercapacitor materials.

Role of the B′-site metal ion in the framework structures and dielectric transitions in host–guest type cyanometalates (HIm)2[B′Co(CN)6] (HIm = imidazolium cation)

The B′-site alkali metal ion in (HIm)2[B′Co(CN)6] plays a key role in the change of the framework structures and the dynamic behaviours of the guest.

User-Friendly Quantum Mechanics: Applications for Drug Discovery.

Quantum mechanics (QM) methods provide a fine description of receptor-ligand interactions and of chemical reactions. Their use in drug design and drug discovery is increasing, especially for complex systems including metal ions in the binding sites, for the design of highly selective inhibitors, for the optimization of bi-specific compounds, to understand enzymatic reactions, and for the study of covalent ligands and prodrugs. They are also used for generating molecular descriptors for predictive QSAR/QSPR models and for the parameterization of force fields. Thanks to the continuous increase of computational power offered by GPUs and to the development of sophisticated algorithms, QM methods are becoming part of the standard tools used in computer-aided drug design (CADD). We present the most used QM methods and software packages, and we discuss recent representative applications in drug design and drug discovery.

Tuning of Emission by Eu3+ Concentration in a Pyrophosphate: the Effect of Local Symmetry.

The local symmetry of a Eu3+ ion has a crucial effect on its luminescence properties. In this work, we show that the red/orange ratio in the emission of Eu3+-doped MgIn2P4O14 phosphors is tunable by adjusting the Eu3+ concentrations, due to the change in the local symmetry of metal ions. The substitution of Eu3+ for In3+ lowers the distortion in the lattice of monoclinic MgIn2P4O14, and an increase in Eu3+ doping concentration causes the metal ion sites to shift closer to an inverse center, leading to a reversal of the relative emission intensity of a magnetic dipole transition to an electric dipole transition. Meanwhile, the higher asymmetry of metal ion sites occupied by Eu3+ in MgIn2P4O14 makes the luminescence less thermally stable than that in Mg3In4P6O24.

Binding and Reactivity of Copper to R1 and R3 Fragments of tau Protein.

Tau protein is present in significant amounts in neurons, where it contributes to the stabilization of microtubules. Insoluble neurofibrillary tangles of tau are associated with several neurological disorders known as tauopathies, among which is Alzheimer's disease. In neurons, tau binds tubulin through its microtubule binding domain which comprises four imperfect repeats (R1-R4). The histidine residues contained in these fragments are potential binding sites for metal ions and are located close to the regions that drive the formation of amyloid aggregates of tau. In this study, we present a detailed characterization through potentiometric and spectroscopic methods of the binding of copper in both oxidation states to R1 and R3 peptides, which contain one and two histidine residues, respectively. We also evaluate how the redox cycling of copper bound to tau peptides can mediate oxidation that can potentially target exogenous substrates such as neuronal catecholamines. The resulting quinone oxidation products undergo oligomerization and can competitively give post-translational peptide modifications yielding catechol adducts at amino acid residues. The presence of His-His tandem in the R3 peptide strongly influences both the binding of copper and the reactivity of the resulting copper complex. In particular, the presence of the two adjacent histidines makes the copper(I) binding to R3 much stronger than in R1. The copper-R3 complex is also much more active than the copper-R1 complex in promoting oxidative reactions, indicating that the two neighboring histidines activate copper as a catalyst in molecular oxygen activation reactions.