Zn Bridges Research Articles

Effect of a "Zn Bridge" on the Consecutively Tunable Retention Characteristics of Volatile Random Access Memory Materials.

Polyimide memory materials with a donor-acceptor structure based on a charge-transfer mechanism exhibit great potential for next-generation information storage technology due to their outstanding high-temperature resistance and good dimensional and chemical stability. Precisely controlling memory performance by limited chemical decoration is one of core challenges in this field. Most reported work mainly focuses on designing novel and elaborate electron donors or acceptors for the expected memory behavior of polyimides; this takes a lot of time and is not always efficacious. Herein, we report a series of porphyrinated copolyimides coPI-Znx (x=5, 10, 20, 50, 80), where x represents the mole percentage of Zn ion in the central core of the porphyrin. Experimental and theoretical analysis indicate that the Zn ion could play a vital bridge role in promoting the formation and stabilization of a charge-transfer complex by enhancing the hybridization of local and charge transfer (HLCT) excitations of porphyrinated polyimides, endowing coPI-Znx with volatile random access memory performance and continuously tunable retention time. This work could provide one simple strategy to precisely regulate memory performance merely by altering the metal content in porphyrinated polyimides.

Tunable Metal Oxide Frameworks via Coordination Assembly of Preyssler-Type Molecular Clusters.

We present the synthesis of metal oxide frameworks composed of [NaP5W30O110]14- assembled with Mn, Fe, Co, Ni, Cu, or Zn bridging metal ions. X-ray diffraction shows that the frameworks adopt the same assembly regardless of bridging metal ion. Furthermore, our synthesis allows for the assembly of isostructural frameworks with mixed-metal ion bridges, or with clusters that have been doped with Mo, providing a high degree of compositional diversity. This consistent assembly enables investigation into the role of the building blocks in the properties of the metal oxide frameworks. The presence of bridging metal ions leads to increased conductivity compared to unbridged frameworks, and frameworks bridged with Fe have the highest conductivity. Additionally, Mo-doping can be used to enhance the conductivities of the frameworks. Similar structures can be obtained from clusters in which the central Na+ has been replaced withBi3+ or Sm3+. Overall, the optical and electronic properties are tunable via choice of bridging metal ion and cluster building block and reveal emergent properties in these cluster-based frameworks. These results demonstrate the promise of using polyoxometalate clusters as building blocks for tunable complex metal oxide materials with emergent properties.

Copper ion / H2O2 oxidation of Cu/Zn-Superoxide dismutase: Implications for enzymatic activity and antioxidant action

Copper ion-catalyzed oxidation of yeast SOD1 (ySOD1) was examined to determine early oxidative modifications, including oxidation of a crucial disulfide bond, and the structural and functional repercussions of these events. The study used distinct oxidative conditions: Cu2+/H2O2, Cu2+/H2O2/AscH− and Cu2+/H2O2/glucose. Capillary electrophoresis experiments and quantification of protein carbonyls indicate that ySOD1 is highly susceptible to oxidative modification and that changes can be detected within 0.1 min of the initiation of the reaction. Oxidation-induced structural perturbations, characterized by circular dichroism, revealed the formation of partially-unfolded ySOD1 species in a dose-dependent manner. Consistent with these structural changes, pyrogallol assay indicates a partial loss of enzymatic activity. ESI-MS analyses showed seven distinct oxidized ySOD1 species under mild oxidation within 0.1 min. LC/MS analysis after proteolytic digestion demonstrated that the copper-coordinating active site histidine residues, His47 and His49, were converted into 2-oxo-histidine. Furthermore, the Cu and Zn bridging residue, His64 is converted into aspartate/asparagine. Importantly, the disulfide-bond Cys58-Cys147 which is critical for the structural and functional integrity of ySOD1 was detected as being oxidized at Cys147. We propose, based on LC/MS analyses, that disulfide-bond oxidation occurs without disulfide bond cleavage. Modifications were also detected at Met85 and five surface-exposed Lys residues. Based on these data we propose that the Cys58-Cys147 bond may act as a sacrificial target for oxidants and protect ySOD1 from oxidative inactivation arising from exposure to Cu2+/H2O2 and auto-inactivation during extended enzymatic turnover.

Removal of the Fe(iii) site promotes activation of the human cystic fibrosis transmembrane conductance regulator by high-affinity Zn(ii) binding.

The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is activated by ATP binding at the interface of two cytoplasmic nucleotide binding domains (NBDs) and phosphorylation of the regulatory (R) domain by protein kinase A (PKA). The human CFTR has two functionally active thiol groups for gating regulation by chemical modification. Although modification of C832 in the R domain with N-ethylmaleimide promotes channel opening, glutathionylation of C1344 in NBD2 inhibits channel opening. Our recent studies demonstrated that the N-ethylmaleimide-induced potentiation involves a high-affinity inhibitory Fe3+ site at the interface between the R domain and intracellular loop 3 (ICL3). However, it is unknown whether the glutathionylation-evoked inhibition implies another stimulatory metal site. Here, Fe3+-insensitive mutations at the R-ICL3 interface were employed to further examine whether Zn2+ potentiated the activity of the human CFTR channel by targeting C1344 once the interfacial Fe3+ bridge was disrupted. The results showed that internal nanomolar Zn2+ increased its activity by about two- to threefold at a low level of protein kinase A, and the increase was reversed by EDTA or DTT or reduced glutathione but suppressed by a high level of protein kinase A, N-ethylmaleimide modification or a C1344A mutation. It is interesting that this Zn2+-triggered potentiation is not found in the wild type human CFTR to which endogenous Fe3+ is bound. Thus, the high-affinity binding of Zn2+ to C1344 in NBD2 may stimulate human CFTR activity in a phosphorylation-dependent manner, but the primary binding of Fe3+ to the ICL3-R interface may prohibit this stimulation.

External Zn(2+) binding to cysteine-substituted cystic fibrosis transmembrane conductance regulator constructs regulates channel gating and curcumin potentiation.

The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is activated by ATP binding-induced dimerization of nucleotide-binding domains, the interaction between the phosphorylated regulatory (R) domain and the curcumin-sensitive interface between intracellular loop (ICL) 1 and ICL4, and the resultant inward-to-'outward' reorientation of transmembrane domains. Although transmembrane helices (TM) 2 and TM11 link the ICL1-ICL4 interface with the interface between extracellular loop (ECL) 1 and ECL6, it is unknown whether both interfaces are gating-coupled during the reorientation. Herein, R334C and T1122C mutations were used to engineer two Zn(2+) bridges near and at the ECL1-ECL6 interface, respectively, and the gating effects of a Zn(2+) disturbance at the ECL1-ECL6 interface on the stimulatory ICL1/ICL4-R interaction were determined. The results showed that both Zn(2+) bridges inhibited channel activity in a dose- and Cl(-) -dependent manner, and the inhibition was reversed by a washout or suppressed by thiol-specific modification. Interestingly, their Cl(-) -dependent Zn(2+) inhibition was weakened at higher Zn(2+) concentrations, their Zn(2+) affinity was stronger in the resting state than in the activated state, and their activation current noises were decreased by external Zn(2+) binding. More importantly, the external Zn(2+) inhibition was reversed by internal curcumin in the R334C construct but not in the T1122C mutant. Therefore, although both Zn(2+) bridges may promote channel closure, external Zn(2+) may disturb the ECL1-ECL6 interface and thus prevent the stimulatory ICL1/ICL4-R interaction and curcumin potentiation via a gating coupling between these two interfaces.

ZnO quantum dots-graphene composites: Formation mechanism and enhanced photocatalytic activity for degradation of methyl orange dye

The current study demonstrates homogenous decorating of zinc oxide quantum dots (QDs) onto graphene oxide (GO) surface via simple chemical method. The AFM image exhibited that the prepared graphene was 0.8 nm thick and hence practically monolayer. Average size of the ZnO QDs was estimated by transmission electron microscopy around 3 nm. Instrumental and chemical analyses demonstrated formation of a strong bond between ZnO QDs and GO, through C–O–Zn and C–Zn bridges. The UV-visible spectra displayed that the introduction of graphene sheets to ZnO QDs resulted in higher absorption intensity of UV as well as widening of adsorption window toward visible light for ZnO-Graphene due to chemical bond between ZnO QDS and graphene surface. Results showed that adding of graphene up to 30% can improve resistance of ZnO against acids however for keeping the activity of catalyst, the recommended pH is near neutral (pH ≈ 6–7.2). In addition, the presence of graphene on the surface of the ZnO could significantly suppress the photocorrosion effect. The ZnO-Graphene hybrids indicated enhanced photocatalytic activity for degradation of methyl orange (MO) with the following order: ZnO-5% Graphene > ZnO-10% Graphene > ZnO QDs > ZnO30% -Graphene. This enhancement of photocatalytic activity may be attributed to the extended absorption of visible light, reducing of electron–hole recombination rate, and adsorption of MO molecules onto the huge surface area of graphene, where they are kept at vicinity of ZnO for decomposition.

Standing and sitting adlayers in atomic layer deposition of ZnO

The extent of reactivity of diethyl zinc (DEZ) with a hydroxylated surface during atomic layer deposition (ALD) of ZnO using DEZ and water is measured. Two adlayer configurations of DEZ are possible. The “standing” adlayer releases one ethyl group from DEZ. The “sitting” adlayer releases both ethyl groups, thus forming a Zn bridge between two O anions. Density functional theory calculations suggest the sitting configuration is more stable than the standing configuration by 790 meV. In situ quadrupole mass spectroscopy of by-product ethane generated in ALD half cycles indicate that ∼1.56 OH sites react with a DEZ molecule resulting in 71.6% of sitting sites. A simple simulation of a “ball-and-stick” DEZ molecule randomly collapsing on a neighboring site remarkably captures this adlayer behavior. It is concluded that DEZ fraction sitting is a competitive process of a standing DEZ molecule collapsing onto an available neighboring hydroxyl site, as sites vie for occupancy via adsorption and surface diffusion.

On the Origin and Structure of the Recently Observed Acetal in the Soai Reaction

Abstract Recent observation of the acetal species in the course of autoamplifying Soai reaction was analysed by the formal kinetic analysis of the experimental data and DFT computations. Kinetic analysis demonstrated convincingly that the observed species cannot be a precursor of the reaction product. Hence, it is an off-loop species that is not important for the process of the chirality amplification. DFT search for a kinetically stable acetal species resulted in the location of a Zn3 cluster stabilized with three Zn–O–Zn bridges.

Structure and properties of ZnO-containing lithium–iron–phosphate glasses

Lithium–iron–phosphate glasses with compositions of (20 − x)Li 2O· xZnO·30Fe 2O 3·50P 2O 5 ( x = 0–7.2) have been prepared. The influences of the amount of ZnO on the structure, physical and chemical properties, and crystallization behavior of the glasses were investigated using Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction techniques. The density of glass was measured according to the Archimedes principle. The chemical stability was evaluated based on the weight loss after the glass particles were boiled in water. The results indicate that Zn 2+ ions cross-linked the phosphate chains by forming P–O–Zn bridges when 2 mol% of ZnO was added. When the amount of ZnO was further increased, [ZnO 4] tetrahedra were formed and ZnO acted as a glass network former, integrating the phosphate glass network. The density, chemical stability and the activation energy of crystallization of the glasses increased with the amount of ZnO, whereas the glass transition temperature decreased. All thermally treated glasses showed surface crystallization with LiFeP 2O 7 as the crystalline phase.

Profiling the Active Site of a Copper Enzyme through Its Far‐Infrared Fingerprint

Vibrations of the metal active site of the Cu,Zn-superoxide dismutase enzyme were analyzed by far-infrared difference spectroscopy and theoretical normal mode calculation. Both electrochemically triggered Cu(I) and Cu(II) redox states show well-defined infrared vibrational modes, notably modes of the histidine ligands, the Cu(II)-His(61)-Zn(II) bridge and of the water pseudo-ligand.

A new Cu/Zn carboxylato-bridged 1D polymer: Direct synthesis, X-ray structure and magnetic properties

A new complex [Cu 2Zn(O 2CMe) 6(NH 3) 2] n was isolated as an unexpected product in an open-air synthesis of a mixed-metal compound using zero-valent copper, zinc oxide and ammonium acetate in the presence of 2-diethylaminoethanol in acetonitrile solution. Its structure consists of Cu 2(O 2CMe) 4 units situated on crystallographic inversion centres and Zn(NH 3) 2(O 2CMe) 2 units on crystallographic 2-fold axes. One O atom of each of the O 2CMe groups is attached via Zn bridges to the Cu atoms of the dimeric Cu 2(O 2CMe) 4 unit forming a 1D polymer in the bc direction. The polymer is not linear, with the dihedral angles between successive Cu–Cu vectors being 48.9°. Within the Cu 2(O 2CMe) 4 units the Cu···Cu distance is 2.675(2) Å and the angles between the O 2CMe planes are 88.8(5)°. The magnetic properties have been analyzed using the Hamiltonian Ĥ = J Ŝ 1 Ŝ 2 with J = 286 cm −1 and g = 2.13. High-field EPR spectra showed both the exchange-coupled copper pair and non-interacting copper(II) ions. The presence of the latter species was explained as an effect of zinc atoms occupying a fraction of the copper sites.

Approach to thermal properties and electronic polarizability from average single bond strength in ZnOBi 2O 3B 2O 3 glasses

The glass transition temperature ( T g), density, refractive index, Raman scattering spectra, and X-ray photoelectron spectra (XPS) for xZnO– yBi 2O 3– zB 2O 3 glasses ( x=10–65, y=10–50, z=25–60 mol%) are measured to clarify the bonding and structure features of the glasses with large amounts of ZnO. The average electronic polarizability of oxide ions ( α O2−) and optical basicity ( Λ) of the glasses estimated using Lorentz–Lorenz equation increase with increasing ZnO or Bi 2O 3 content, giving the values of α O2−=1.963 Å 3 and Λ=0.819 for 60ZnO–10Bi 2O 3–30B 2O 3 glass. The formation of BOBi and BOZn bridging bonds in the glass structure is suggested from Raman and XPS spectra. The average single bond strength ( B MO ) proposed by Dimitrov and Komatsu is applied to the glasses and is calculated using single bond strengths of 150.6 kJ/mol for ZnO bonds in ZnO 4 groups, 102.5 kJ/mol for BiO bonds in BiO 6 groups, 498 kJ/mol for BO bonds in BO 3 groups, and 373 kJ/mol for BO bonds in BO 4 groups. Good correlations are observed between T g and B MO , Λ and B MO , and T g and Λ, proposing that the average single bond strength is a good parameter for understanding thermal and optical properties of ZnOBi 2O 3B 2O 3 glasses.

Synthesis, Crystal Structure and Characterizations of New 3,4,7,8-Tetrachloro-1,10-Phenanthroline Zn(II) Complex

A novel 3,4,7,8-tetrachloro-1,10-phenanthroline (Cl4phen) Zn(II) complex has been synthesized. The complex, [Zn(Cl4phen)2(H2O)2](NO3)2·CH3CH2OH (1), has been identified and characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, thermogravimetric analysis and photoluminescence studies. Single crystal X-ray diffraction analysis reveals that complex (1) belongs to the monoclinic system, space group P2(1)/c, a = 10.061(2) A, b = 18.924(4) A, c = 18.189(4) A, β = 100.94(3)°, and Z = 4. Complex (1) consists of cationic species [Zn(Cl4phen)2(H2O)2]2+, NO3 − and CH3CH2OH. The zinc atom displays a distorted cis-N4O2 octahedral geometry. Via extended Zn–O–H···O–N–O···H–O–Zn bridge, every mononuclear unit is linked with other ones to form one-dimensional (1D) infinite chain of hydrogen bond system. Three-dimensional (3D) polymeric network arrangement was built via weak C–H···O and π-stacking interactions between Cl4phen moieties. A solvent-dependency effect of complex (1) was observed in spectroscopic properties. Three-dimensional (3D) polymeric network arrangement was built via weak C–H···O and π-stacking interactions between Cl4phen moieties.

Spectroscopic properties of guanidinium zinc sulphate [C(NH 2) 3] 2Zn(SO 4) 2 and ab initio calculations of [C(NH 2) 3] 2 and HC(NH 2) 3

Raman and FTIR spectra of guanidinium zinc sulphate [C(NH 2) 3] 2Zn(SO 4) 2 are recorded and the spectral bands assignment is carried out in terms of the fundamental modes of vibration of the guanidinium cations and sulphate anions. The analysis of the spectrum reveals distorted SO 4 2− tetrahedra with distinct S–O bonds. The distortion of the sulphate tetrahedra is attributed to Zn–O–S–O–Zn bridging in the structure as well as hydrogen bonding. The CN 3 group is planar which is expressed in the twofold symmetry along the C–N (1) vector. Spectral studies also reveal the presence of hydrogen bonds in the sample. The vibrational frequencies of [C(NH 2) 3] 2 and HC(NH 2) 3 are computed using Gaussian 03 with HF/6-31G* as basis set.

DFT characterization of adsorption and diffusion mechanisms of H, As, S, and Se on the zinc orthotitanate(0 1 0) surface

Zinc orthotitanate (ZTO) is a promising material for removal of multiple contaminant species from fuel gas streams. The ZTO(010) surface, which consists of both oxygen rich and metal rich sides, was previously predicted to be the lowest energy ZTO surface. We present density functional theory calculations examining adsorption and diffusion of atomic S, Se, As, and H on the oxygen rich and metal rich ZTO(010) surfaces. S and Se share similar bonding and diffusion mechanisms on the metal rich ZTO(010) surface, whereas As and H bind in similar ways to the oxygen rich surface. S and Se have adsorption sites involving Zn:Zn bridges whereas As and H prefer to bind at sites involving O:O bridges on the surface. H forms a hydroxyl-like bond with length of 1.0Å. Se and S have small activation energy barriers for atomic diffusion from the lowest energy adsorption site to the nearest low energy site. At temperatures around 800K we predict from our results that Se and S are approximately equal in diffusivity while being far more mobile on the surface than either H or As.

Analysis of the Fe–Zn interface of galvanized high Al–low Si TRIP steels

TRIP-assisted steels are ideal for lightweight automotive applications due to their high strength and ductility. The selective oxidation of the alloying elements Mn, Al and Si during annealing prior to galvanizing can cause poor reactive wetting during galvanizing, resulting in bare spot defects. Despite the selective oxidation of alloying elements two high Al–low Si TRIP steels were successfully galvanized. It was determined that good reactive wetting occurred by the presence of an Al-rich interfacial layer composed of Fe 2Al 5 and FeAl 3. Two mechanisms by which reactive wetting occurred were identified; (1) aluminothermic reduction of MnO by the Al in the Zn bath and (2) Zn bridging of oxide particles. When aluminothermic reduction occurred there was a localized depletion of Al in the Zn bath resulting in inhibition breakdown and the formation of Fe–Zn intermetallics at the Fe–Zn interface.

A novel O–Zn bridging polymer complex of 2,6-bis[bis(carboxylatomethyl)aminomethyl]-4-methylphenolate

A new one-dimensional coordination polymer, catena-poly[[acetatohexaaqua{mu4-2,6-bis[bis(carboxylatomethyl)aminomethyl]-4-methylphenolato}trizinc(II)] octahydrate], [Zn3(C17H17N2O9)(C2H3O2)(H2O)6] x 8 H2O, is a trinuclear complex consisting of three zinc centers joined by a phenolate bridge and Zn(H2O)4 units. In each complex polymer unit, the three Zn atoms have different coordination modes. Of the two phenolate-bridged Zn ions, one adopts a distorted octahedral coordination composed of two carboxylate ligands, one tertiary N atom, two water molecules and the bridging phenolate ligand, while the other adopts a pyramidal geometry composed of two carboxylate ligands, one tertiary N atom from another coordination arm, one acetate anion as the counter-anion and the bridging phenolate ligand. The third type of Zn centre is represented by two independent Zn atoms lying on inversion centres. They both have an octahedral coordination consisting of four O atoms from four water molecules and two acetate carbonyl O atoms from the ligand. The latter Zn atoms join the above-mentioned binuclear complex units through O atoms of the carboxylate groups into an infinite chain. Neighboring aromatic rings are distributed above and below the chain in an alternating manner. Between the coordination chains, the Zn...Zn separations are 5.750 (4) and 6.806 (4) A. The whole structure is stabilized by hydrogen bonds formed mainly by solvent water molecules.

Synthesis, crystal structure and photoluminescent properties of an aromatic bridged Schiff base ligand and its zinc complex

An aromatic bridged Schiff base ligand, N, n′-bis((4,4′-diethylamino)salicylidene)-1,2-phenylenediamine (H 2L 3), and its trinuclear Zinc(II) complex, Zn 3 L 2 3 ( CH 3 COO ) 2 , were synthesized and characterized by means of elemental analyses, FT-IR and UV–Vis absorption spectra, and single crystal X-ray crystallography. The X-ray crystal structure of the complex reveals that the zinc ion (Zn1 or Zn1A) is coordinated by two oxygen atoms in phenolate and two nitrogen atoms in imines of the ligand and one oxygen atom of the acetate, the zinc ion (Zn2) is coordinated by four oxygen atoms in phenolate of the ligands and two oxygen atoms of the acetates. Two acetates coordinate to three zinc ions through Zn–O–C–O–Zn bridges. The complex exhibits blue-green emission as the result of the fluorescence from the intraligand emission excited state. In addition, the ground-state geometries, the lowest energy transition and the UV–Vis spectrum of the ligand have been studied with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at B3LYP/6-31G(d) level, showing that the calculation outcomes are in good agreement with experimental data.

Mechanism of the MeOH/H2O Substitution in a Series of Biomimetic Bimetallo Zinc‐Based H3O2 Complexes

AbstractSmall bimetallo biomimetic zinc‐based compounds containing a bridging μ‐OH functionality can be easily hydrated to yield complexes containing an intramolecular Zn–H3O2–Zn bridge. Because such bridges are intrinsically more nucleophilic than the corresponding μ‐OH functionality, this effectively activates the complex. The Zn–H3O2–Zn unit is labile, and one can successively substitute the “water” and the “hydroxide” in the bridge for methanol and methoxide to form metal‐bound HO–H–OMe and MeO–H–OMe functionalities. We have performed an extensive density functional investigation of this substitution mechanism for a series of bimetallo zinc complexes which have been synthesised and investigated by F. Meyer et al. There are two mechanisms for water/methanol exchange – an addition–elimination and a direct exchange mechanism. If the metal ions are coordinatively unsaturated, and their ligand sphere does not sterically hinder the approach of the methanol, both pathways compete with each other. For coordinatively saturated bimetallo complexes with larger ligand spheres, only the direct exchange mechanism is possible. Regardless of the mechanism operating, the exchange is facile and is controlled by the relative thermodynamic stability of the intermediates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

An Na–O–Zn–O–Zn bridging complex of Cl-HXTA, where Cl-HXTA is 2,6-bis{[bis(carboxylatomethyl)amino]methyl}-4-chlorophenolate

In the structure of hepta­aqua-1κ3O,2κ2O,3κ2O-(μ3-2,6-bis{[bis­(carboxyl­ato­methyl)­amino]­methyl}-4-chloro­phenol­ato-1κO;2κ4O,O′,N,O1;3κ4O1,N′,O′′,O′′′)­dizinc(II)­sodium(I) pentahydrate, [NaZn2(C16H14ClN2O9)(H2O)7]·5H2O or [Zn2(Cl-HXTA)(H2O)4{Na(H2O)3}]·5H2O, the trinuclear complex unit consists of two distorted ZnNO5 octahedra bridged by a phenolate O atom and an NaO4 tetrahedron linked to one of the Zn octahedra by a carboxyl­ate O atom.