Transition Metal Binding Research Articles

Phosphine Oxide Porous Organic Polymers Incorporating Cobalt(II) Ions: Synthesis, Characterization, and Investigation of H2 Production.

Suitably functionalized porous matrices represent versatile platforms to support well-dispersed catalytic centers. In the present study, porous organic polymers (POPs) containing phosphine oxide groups were fabricated to bind transition metals and to be investigated for potential electrocatalytic applications. Cross-linking of mono- and di-phosphine monomers with multiple phenyl substituents was subject to the Friedel–Crafts (F-C) reaction and the oxidation process, which generated phosphine oxide porous polymers with pore capacity up to 0.92 cm3/g and a surface area of about 990 m2/g. The formation of the R3P·BH3 borohydride adduct during synthesis allows to extend the library of phosphine-based monomeric entities when using FeCl3. The porous polymers were loaded with 0.8–4.2 w/w % of cobalt(II) and behaved as hydrogen evolution reaction (HER) catalysts with a Faradaic efficiency of up to 95% (5.81 × 10–5 mol H2 per 11.76 C) and a stable current density during repeated controlled potential experiments (CPE), even though with high overpotentials (0.53–0.68 V to reach a current density of 1 mA·cm–2). These studies open the way to the effectiveness of tailored phosphine oxide POPs produced through an inexpensive and ecofriendly iron-based catalyst and for the insertion of transition metals in a porous architecture, enabling electrochemically driven activation of small molecules.

Study on metal binding capacity of the freshwater crab Sinopotamon henanense's recombinant copper specific binding metallothionein expressed in Escherichia coli.

The copper specific binding metallothionein (CuMT) is a type of cysteine-rich, metal-binding, small protein which plays an important role in Cu2+ metabolism in vertebrates. In this study, we investigated the metal tolerance and removing ability of recombinant strains harboring CuMT obtained in vivo from the freshwater crab Sinopotamon henanense (ShCuMT) in order to study its physiological functions and metal binding capacity. We performed a 3D modeling of ShCuMT and created its structural and functional models using the I-TASSER program. The shCumt gene was inserted into a pGEX-4t-1 vector and recombinant soluble ShCuMT was expressed in Escherichia coli. In addition, in order to characterize the tolerance and removing ability of heavy metals in E. coli with ShCuMT expression, the recombinant strains harboring ShCuMT were exposed to various concentrations of Cd2+, Cu2+ and Zn2+, respectively. The results showed that ShCuMT contains transition metal binding sites. In addition, E. coli cells expressing ShCuMT exhibited enhanced metal tolerance and higher removing ability of metal ions than control cells. However, compared with Cd2+ and Zn2+, E. coli cells expressing ShCuMT have stronger tolerance and higher removing ability of Cu2+. In general, ShCuMT contains multiple transition metal binding sites, and it could enhance tolerance and removing ability of metal ions. Therefore, ShCuMT can provide potential candidates for heavy metal bioremediation. This research on the metal binding properties of ShCuMT provides a scientific basis for bioremediation of heavy metal pollution by the recombinant strains.

Accelerated Molecular Dynamics to Explore the Binding of Transition Metals to Amyloid-β.

We report the accelerated molecular dynamics (aMD) simulation of amyloid-β (Aβ) peptides of four different lengths (16, 28, 40, and 42 residues) and their complexes when bound to Cu(II), Fe(II), or Zn(II). 600 ns equilibrated trajectory data were analyzed for each structure from three independent 200 ns aMD simulations, generating 16 aMD trajectories. We show that the presence of a metal ion leads to reduced size and decreased mobility relative to the free peptide due to the anchoring effect of the ions. The reduced mobility was shown largely to be due to the restricted movement in N-terminal residues, most notably Asp1 and His6 that are involved in the metal-ion coordination in all cases. Significant disruption of the secondary structure and patterns of salt bridge interactions arise on the coordination of metal ions. In this regard, similarities were noted between results for Zn(II) and Fe(II), whereas results for Cu(II) are more comparable to that of the free peptides. Reweighting of free energy surfaces was carried out from aMD data to identify the properties and descriptions of local minima structures.

Multifunctional Redox Modulators Protect Auditory, Visual, and Cognitive Function.

Significance: Oxidative stress contributes to vision, hearing and neurodegenerative disorders. Currently, no treatments prevent these disorders; therefore, there is an urgent need for redox modulators that can prevent these disorders. Recent Advances: Oxidative stress is associated with the generation of reactive oxygen species (ROS) and reactive nitrogen species, metal dyshomeostasis, and mitochondrial dysfunction. Here, we discuss the role that oxidative stress and metal dyshomeostasis play in hearing loss, visual impairments, and neurodegeneration and discuss the benefits of a new class of multifunctional redox modulators (MFRMs) that suppress sensory and neural degeneration. MFRMs not only reduce free radicals but also independently bind transition metals associated with the generation of hydroxyl radicals. The MFRMs redistribute zinc from neurotoxic amyloid beta zinc (Aβ:Zn) complexes to the cytoplasm, facilitating the degradation of Aβ plaques by matrix metalloprotease-2 (MMP-2). Although MFRMs bind copper (Cu1+, Cu2+), iron (Fe2+, Fe3+), zinc (Zn2+), and manganese (Mn2+), they do not deplete free cytoplasmic Zn+2 and they protect mitochondria from Mn+2-induced dysfunction. Oral administration of MFRMs reduce ROS-induced cataracts, protect the retina from light-induced degeneration, reduce neurotoxic Aβ:Zn plaque formation, and protect auditory hair cells from noise-induced hearing loss. Critical Issues: Regulation of redox balance is essential for clinical efficacy in maintaining sensory functions. Future Directions: Future use of these MFRMs requires additional pharmacokinetic, pharmacodynamics, and toxicological data to bring them into widespread clinical use. Additional animal studies are also needed to determine whether MFRMs can prevent neurodegeneration, dementia, and other forms of vision and hearing loss.

A Nanocrystal Catalyst Incorporating a Surface Bound Transition Metal to Induce Photocatalytic Sequential Electron Transfer Events.

Heterogeneous photocatalysis is less common but can provide unique avenues for inducing novel chemical transformations and can also be utilized for energy transductions, i.e., the energy in the photons can be captured in chemical bonds. Here, we developed a novel heterogeneous photocatalytic system that employs a lead-halide perovskite nanocrystal (NC) to capture photons and direct photogenerated holes to a surface bound transition metal Cu-site, resulting in a N-N heterocyclization reaction. The reaction starts from surface coordinated diamine substrates and requires two subsequent photo-oxidation events per reaction cycle. We establish a photocatalytic pathway that incorporates sequential inner sphere electron transfer events, photons absorbed by the NC generate holes that are sequentially funneled to the Cu-surface site to perform the reaction. The photocatalyst is readily prepared via a controlled cation-exchange reaction and provides new opportunities in photodriven heterogeneous catalysis.

Dynamic electrochromic play via “mix-and-match” reversible metal-ligand interactions

In this issue of Chem, Zhang and co-workers report on the development of a novel methodology for creating electrochromic materials based on dynamic metal-ligand interactions. The proposed approach for the search of new systems is interesting and could allow fast developments in the area of electrochromic materials for non-emissive displays.

Metal Affinity/Selectivity of Monophosphate-Containing Signaling/Lipid Molecules.

Monophosphate, an essential component of nucleic acids, as well as cell membranes and signaling molecules, is often bound to metal cations. Despite the biological importance of monophosphate-containing cell-signaling or lipid molecules, their propensity to bind the two most abundant cellular dications, Mg2+ and Ca2+, in a particular mode (inner/outer shell, mono/bidentate) is not well understood. Whether they prefer binding to Mg2+ than to Ca2+ and if they can outcompete the carboxylates of excitatory Asp/Glu and inhibitory gamma-aminobutyric acid (GABA) neurotransmitters in binding to Mg2+/Ca2+ remain unclear. To address these questions, we modeled cyclic adenosine/guanosine monophosphate (cAMP/cGMP), nucleoside 2',3'-cyclic phosphate, phosphatidylinositol (PI), phosphatidylserine (PS), and phosphatidylethanolamine (PEA) and determined their most stable metal-binding modes, including those of Asp/Glu and GABA, as well as their selectivity for Mg2+/Ca2+ using density functional theory combined with the polarizable continuum model. The results obtained, which are consistent with the available experimental findings, reveal that the structurally and functionally diverse monophosphate-containing ligands studied prefer monodentate coordination of Mg2+ because of the greater strain encountered upon bidentate coordination, whereas the larger Ca2+ imposes less strain upon bidentate binding and has reduced/no preference for monodentate coordination. We further show that in a low-dielectric environment, negatively charged monophosphate-containing ligands favor the better charge-accepting dication, that is, Mg2+ rather than Ca2+. By promoting Mg2+ over Ca2+ binding, signaling monophosphates (cAMP/cGMP) do not entrap cellular Ca2+ and interfere with signal transduction processes employing Ca2+ as a second messenger. In regions with high glutamate cytoplasmic concentration, glutamate may sequester Mg2+ bound to isolated five-/six-membered ring phosphates, PI, or neutral PEA, but not anionic phospholipids constituting the inner leaflet of the cell membrane.

Isolation Strategy towards Earth-Abundant Single-Site Co-Catalysts for Photocatalytic Hydrogen Evolution Reaction

Achieving efficient photocatalytic water splitting remains one of the most vital challenges in the photocatalysis field, as the performance of contemporary heterogeneous catalysts is still limited by their insufficient activity and low predictability. To address this challenge, this work takes inspiration from the concept of heterogeneous single-metal-site catalysts (HSMSCs) and follows the idea of site-isolation, aiming towards single-site co-catalyst species and a higher atom-utilization efficiency. We synthesized a set of photocatalysts through an adsorption-limited wet impregnation process using bare and phosphate-modified TiO2 as model supports and earth-abundant metals (Cu and Ni) with various loadings (0.008–5 wt.%) as co-catalyst species. The catalysts are characterized by TXRF for the determination of the real co-catalyst loadings, UV-vis and FTIR spectroscopes for semi-quantitative analysis of the metal state and binding modes to the substrate, and HRTEM for resolving the morphology of the sample’s surface. All samples were then evaluated towards the photocatalytic hydrogen evolution reaction (HER). We show that much higher turnover frequencies (TOFs) are obtained for both Cu- and Ni-based systems when lower co-catalyst loadings are used, which indicates an improved atom-utilization efficiency that reaches performances comparable to the noble Au co-catalyst. We also introduce a structural model to explain the observed TOF trends, which confirms that both earth-abundant systems undergo a strong structural reconstruction upon site-isolation towards smaller, perhaps even single-site-like species.

Synthesis, crystallography, spectroscopy, and kinetics involving the fluorimetric detection of metal ions by internal imine derivatives of anthraquinone-18-crown-5 in aqueous media

We have selectively synthesized and characterized several aliphatic internal imine isomers which show selectivity towards various transition metal ions with large shifts in the UV–Vis and OFF-ON switching of fluorescence in solution. The stoichiometry with different transition metals has been determined to be 1:1, with the 1,2-ethlenediamine dimer showing the best selectivity towards Hg(II). Selectivity in different solvent media and the varying kinetics of transition metal binding with the macrocycle has been presented along with the crystallography of the ligands and their metal complexes.

Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate.

Metalation of covalent organic frameworks (COFs) is a critical strategy to functionalize COFs for advanced applications yet largely relies on the pre-installed specific metal docking sites in the network, such as porphyrin, salen, 2,2′-bipyridine, etc. We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) via cyclometalation, which has not been explored before. The iridacycle decorated COF exhibited more than 10-fold efficiency enhancement in (photo)catalytic hydrogen evolution from aqueous formate solution than its molecular counterpart under mild conditions. This work will inspire more functional cyclometallated COFs to be explored beyond catalysis considering the large imine COF library and the rich metallacycle chemistry.

Assembling triazolated calix[4]semitubes by means of copper(i)-catalyzed azide–alkyne cycloaddition

Calix[4]arene-based bis(alkynes) and bis(azides) react with each other under thoroughly tuned CuAAC conditions and produce diverse biscalixarene semitube assemblies linked by two triazole units, which are capable of binding transition metal cations.

Mimicking the graphene oxide structure in solutions by interaction of Fe(III) and Gd(III) with model small-size ligands. The NMR relaxation study

Despite long history and recent progress, the chemical behavior of graphene oxide (GO) is not fully understood. One of the remaining open questions is an extremely high cation exchange capacity, which cannot be explained in the frames of the commonly accepted Lerf-Klinowski structural model. The interaction of GO with metals, termed as sorption, is usually considered as physisorption, or as non-specific electrostatic attraction. Recently, we demonstrated that in fact this interaction has the coordinate-covalent bonding nature. In this work, by the means of the NMR relaxation, we investigated the interaction of Fe(III) and Gd(III) ions with several small molecule size chelators and with linear polymers in order to possibly mimic the GO structure. The experiments were conducted in the broad pH range, and at the different metal/chelator ratios. From the two tested metal ions, Fe(III) has the stronger affinity toward GO due to its higher charge density. GO binds Fe(III) with formation of strong high-relaxivity complexes, which do not undergo hydrolysis even in basic conditions. Numerous model small-size molecules, tested to mimic the GO structure, did not demonstrate the same effect on the relaxation of the Fe(III) and Gd(III) solutions, as does interaction with GO. From the tested linear polymers, only polyacrylic acid (PAA) can bind Fe(III), however, even PAA, consisting from carboxyl groups, cannot prevent Fe(III) from hydrolysis already in neutral solutions. Subsequently, carboxyl groups were excluded from the species in GO structure, responsible for the strong binding of meatal ions. We conclude that there are no preexisting sites or functional group fragments in GO structure, capable to strongly bind transition metal cations. The binding sites are formed from the existing structure upon the reaction with metal cations, to afford formation of the metal/GO coordination compounds. The most probable change in the GO structure is the formation of enolates from tertiary alcohols with rupture of the CC bonds. The newly reported data provide additional experimental evidence for the Dynamic Structural Model of GO and broadens the areas of its applicability.

Theoretical investigation of the interaction of gas molecules with Pt-adsorbed arsenene monolayers

Using density functional theory calculations, we investigated the binding of transition metals (Co, Cu and Pt) on pristine arsenene monolayers and adsorption behavior of Pt-functionalized arsenene (Pt-Arsenene) monolayer upon various gas molecules. It is found that the Pt adatom prefers to be located at the hollow site of pristine arsenene monolayer with the highest adsorption energy. The considered adsorption energies and charge transfers indicated that all the gas molecules are stably chemisorbed on the surface of Pt-Arsenene monolayer. The projected density of states and charge density analyses verify the strong chemical interaction between Pt adatom and interacting atoms in the gas molecules. The density of states plots also describe the sensing mechanism of Pt-Arsenene based chemical sensor for recognition of gas molecules. Our theoretical results can provide useful guidance to search for the novel gas sensors based on Pt-functionalized arsenene nanosheets.

Tuning the redox potential of the primary electron donor in bacterial reaction centers by manganese binding and light-induced structural changes

The influence of transition metal binding on the charge storage ability of native bacterial reaction centers (BRCs) was investigated. Binding of manganous ions uniquely prevented the light-induced conformational changes that would yield to long lifetimes of the charge separated state and the drop of the redox potential of the primary electron donor (P). The lifetimes of the stable charge pair in the terminal conformations were shortened by 50-fold and 7-fold upon manganous and cupric ion binding, respectively. Nickel and zinc binding had only marginal effects. Binding of manganese not only prevented the drop of the potential of P/P+ but also elevated it by up to 117 mV depending on where the metal was binding. With variable conditions, facilitating either manganese binding or light-induced structural changes a controlled tuning of the potential of P/P+ in multiple steps was demonstrated in a range of ~200 mV without the need of a mutation or synthesis. Under the selected conditions, manganese binding was achieved without its photochemical oxidation thus, the energized but still native BRCs can be utilized in photochemistry that is not reachable with regular BRCs. A 42 Å long hydrophobic tunnel was identified that became obstructed upon manganese binding and its likely role is to deliver protons from the hydrophobic core to the surface during conformational changes.

Polyphenol oxidase activities by cobalt (II) complex with Benzopyran Derivatives, Synthetic, Characterization, Kinetics Study and Molecular Modeling Studies

The Cobalt complex of 2-Amino-4-(2-chloro-5-nitrophenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo- 4H-chromene-3-carbonitrile)( CNB) was synthesized. The organic ligand CNB was previously synthesized using an environment friendly method using microwave irradiation. The cobalt complex cobalt (II)-CNB was characterized by different tools such as IR, electronic spectroscopy, elemental analysis, Thermal analysis and mass spectroscopy. The mode of metal binding shows that the cobalt binds with the ligand through the nitrogen atoms of the amino and cyanide groups. The cobalt complex cobalt (II)-CNB has been used in the homogenous oxidation of polyphenol 1, 2, 3-trihydroxybenzene in presence of a green oxidant H2O2 as biomimetic metalloenzymes. Kinetic parameters were calculate kcat 1.0971×10-5S-1, KM1.412 ×10-2 M, Vmax 7.68×10-4MS−1 and catalytic efficiency 7.769×10-7 .The oxidation reaction is inhibited by competitive inhibition by kojic acid with IC50 = 200 μM and molecular modeling studies geometrical optimization ,(HOMOs) ,(LUMOs and electrostatic potentials (ESP).

Computational study of Cu2+, Fe2+, Fe3+, Mn2+ and Mn3+ binding sites identification on HSA 4K2C

This research aims to computationally characterize HSA 4K2C protein and describe as well as its ability to bind transition metal ions. Data mining is performed to obtain HSA 4K2C from PDB and transition metal ions such as Cu2+ (ID: 27099), Fe2+ (ID: 27284), Mn2+ (ID: 27854), Mn3+ (ID: 105130) and Fe3+ (ID: 29936) from PubChem. The analysis consists of ProtParam, Motif Search, CFSSP, DLP-SVM, and docking. Docking used PyRx Autodock Vina. Analysis of receptor-ligand interactions used DS 2016. The results of the ProtParam analysis provide some information on HAS 4K2C, which is it has 585 amino acids with an isoelectric point (pI) of 5.67, an index of protein instability of 38.85, then total amino acids (aa) residues of negatively charged (Asp + Glu) are 98 while the positively charged ones (Arg + Lys) are 83. Motive Search shows that there are three HSA motifs namely motif 1 (aa. 551-575), motif 2 (aa. 353-377), and motif 3 (aa. 61-185). CFSP shows α -helix structure is the dominant structure compared to β-sheet, turn and coil in 4K2C. DLP-SVM shows two domain linkers where DL-1 (aa. 410-451) and DL-2 (aa. 96-122). Docking shows the ability of HSA 4K2C in binding metal ions such as Cu2+, Fe2+, Mn2+, Mn3+ and Fe3+.

Characteristics and potential inhalation exposure risks of PM2.5–bound environmental persistent free radicals in Nanjing, a mega–city in China

PM2.5–bound toxic elements and organic pollutants have been extensively investigated, while limited information is available for environmental persistent free radicals (EPFRs) associated with PM2.5, which may lead to oxidative stress in the human lung when exposed to PM2.5. In this study, the levels and types of PM2.5–bound EPFRs present in Nanjing, a mega–city in China, were analyzed. PM2.5–bound EPFRs were found to mainly be a mixture of carbon– and oxygen–centered radicals. The concentration of PM2.5–bound EPFRs ranged from 2.78 × 1012 to 1.72 × 1013 spins m−3, with an average value of 7.61 × 1012 spins m−3. The half–life of the PM2.5–bound EPFRs was calculated to be an average of 83.5 days when stored at room temperature, with only weak correlations observed between EPFRs and conventional air pollutants (NO2, O3, CO and PM2.5)/PM2.5–bound transition metals (Cu, Zn, Cr, Mn, V, Cd, and Ni) and significant correlations between EPFRs and SO2/PM2.5–bound Fe. PM2.5–bound EPFRs can induce the formation of reactive oxygen species (ROS) in both water and a H2O2 solution, which are used to simulate lung solution of a healthy person and patient, respectively. Therefore, PM2.5–bound EPFRs can lead to potential oxidative stress in humans. Overall, PM2.5–bound EPFRs show an obvious temporal variation and can pose potential health risks to humans via the induction of ROS in the lung solution.

Naturally present metal ions in plants could interfere with common antioxidant assays

Most of the commonly applied assays used to assess antioxidant properties of plant extracts exploit the ability of some biologically active metabolites to participate in oxidation-reduction reactions with metal ions. On the other hand, most plants contain different chelated metal ions whose levels depend on the geographic origin, soil, and environmental pollutions. In this study the levels of redox-active metal ions in three plant sources were measured and extracts of these botanicals were treated with ChelexⓇ – an ion exchanger that is noteworthy for its ability to bind transition metal ions. The original and chelated extracts were subjected to three antioxidant assays based on single electron transfer. The results obtained showed statistically significant differences between the original and Chelex-treated extracts suggesting that the naturally present metal ions could interfere with the results of the three most commonly applied antioxidant methods.•The proposed pre-analytical procedure is simple and does not require special instrumental equipment.•Preliminary depletion of redox active metal ions, namely iron and copper ions could improve reproducibility of the analytical methods.•The method allows a more reliable comparison of antioxidant properties of particular botanical species from different geographic regions.

Avian MRP126 Restricts Microbial Growth through Ca(II)-Dependent Zn(II) Sequestration.

The calgranulins form a class of S100 proteins in higher vertebrates that innate-immune cells release in abundance at infection sites. These proteins function by binding transition metal ions to prevent microbial pathogens from obtaining those essential nutrients. Mammals express three distinct members of this family: S100A8 (calgranulin A), S100A9 (calgranulin B, which heterooligomerizes with S100A8 to form calprotectin), and S100A12 (calgranulin C), that exhibit Ca(II)-dependent transition metal binding properties. Human calprotectin effectively sequesters Mn(II), Fe(II), Ni(II), and Zn(II), whereas human S100A12 selectively sequesters Zn(II) over these other metal ions. Birds and reptiles express a single calgranulin homologue named MRP126, which we reasoned could have properties more similar to those of either calprotectin or S100A12. Here we present the purification and biophysical characterization of recombinant chicken MRP126 and, to the best of our knowledge, provide the first assessment of the metal binding and antimicrobial properties of an avian MRP126. We show that MRP126 is a homodimer that selectively sequesters Zn(II) and restricts the growth of certain microbes. MRP126 binds Zn(II) at two canonical His3Asp sites. The presence of excess Ca(II) increases the affinity of the His3Asp sites from the low-nanomolar to the low-picomolar range, thereby enhancing antimicrobial activity. Chicken MRP126 also binds additional Zn(II) equivalents with low-nanomolar affinity at two nonconserved dicysteine sites and with high-nanomolar affinity using a histidine-rich C-terminal tail that is a hallmark of this clade of calgranulins. Our results with chicken MRP126 suggest that Ca(II)-dependent Zn(II) sequestration was a role of the last common ancestor of calgranulin proteins, with mammalian calprotectin subsequently evolving a broader metal binding repertoire.

Biological Applications of Thiocarbohydrazones and Their Metal Complexes: A Perspective Review.

Although organic compounds account for more than 99% of currently approved clinical drugs, the established clinical use of cisplatin in cancer or auranofin in rheumatoid arthritis have paved the way to several research initiatives to identify metal-based drugs for a wide range of human diseases. Nitrogen and sulfur donor ligands, characterized by different binding motifs, have been the subject in recent years of one of the main research areas in coordination chemistry. Among the nitrogen/sulfur compounds, very little is known about thiocarbohydrazones (TCH), the higher homologues of the well-known thiosemicarbazones (TSC), and their metal complexes. The extra hydrazine moiety provides the ligands of variable metal binding modes, structural diversity and promising biological implications. The interesting coordination chemistry of TCH has mainly been focused on symmetric derivatives, which are relatively simple to synthesize while few examples of asymmetric ligands have been reported. This informative review on TCHs and their metal complexes will be helpful for improving the design of metal-based pharmaceuticals for applications ranging from anticancer to antinfective therapy.