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1

Cobalt and nickel macrocycles anchored to nanocrystalline titanium dioxide thin films: Sensitization, catalysis, and ligand association  

NASA Astrophysics Data System (ADS)

The global demand for renewable, clean electricity and fuel has compelled efforts to utilize the immense power incident upon the Earth from the Sun. Photovoltaic systems could power the planet's electrical demands with only moderate efficiencies. However, mitigation of fossil fuels used for transportation and night-time electricity requires the storage of photon energy, for example, in the form of chemical bonds. Mesoporous, nanocrystalline TiO2 thin films provide a manifold for anchoring molecular species that absorb and utilize photons to catalyze fuel-generating reactions. The overarching theme of this thesis is to improve understanding of the semiconductor/molecule interface utilizing earth abundant first-row transition metal coordination compounds. Chapter 2 presents the non-ideal redox behavior of cobalt porphyrins anchored to semiconductor surfaces. Additionally, CoI porphyrins were utilized as photocatalysts for the 2e- reduction of organobromides to yield a CoIII-R intermediate. The cobalt-carbon bond of CoIII-R was photodissociated with visible light to yield Co II and R·. The organic radical dimerized to form R-R. Light excitation of CoI compounds was found to result in electron transfer to TiO2, Chapter 3. Cobalt porphyrins, phthalocyanines, glyoximes, and corrins were all observed to exhibit this behavior. Electron transfer was demonstrated to primarily occur via excitation into the large extinction coefficient metal-to-ligand charge transfer absorption bands of CoI complexes. Chapter 4 focuses on the unique coordination chemistry of cobalt porphyrins anchored to a TiO2 thin film. Notably, pyridine axially ligated a CoII porphyrin following excited-state electron transfer of the CoI porphyrin to the TiO2. The rate constant for recombination of an electron in the TiO2 with CoII was observed to decrease with increasing pyridine concentration, behavior attributed primarily to a negative shift of the CoII/I potential in the presence of pyridine. Finally, Chapter 5 reports a comparative study of the kinetic and thermodynamic properties of the equilibrium between a 4-coordinate, low spin and a 6-coordinate, high spin nickel porphyrin, both in solution and anchored to TiO2. The mesoporous TiO2 thin film was found to influence the enthalpy and entropy of axial ligation while also altering the dissociative activation energy of axial ligation.

Achey, Darren Craig

2

Preparation and characterization of Ag nanoparticle-embedded blank and ligand-anchored silica gels.  

PubMed

Ag nanoparticles, used for halogen (especially iodine) adsorption and an evaluation of halogen behavior, were embedded in synthesized inorganic-organic hybrid gels. In particular, an irradiation method using an electron beam plays a part in introducing Ag nanoparticles to the organofunctionalized silica gels from AgNO3 solutions in a simple way at atmospheric pressure and room temperature. For preparation of the Ag nanoparticle-embedded inorganic-organic hybrid gels, ligands of ethylenediamine (NH2CH2CH2NH-, TMSen) and mercapto (HS-) functionalized three-dimensional porous SiO2 sol-gels were first synthesized through hydrolysis and condensation reactions, and Ag nanoparticles were then embedded into the ethylenediamine- and mercapto-anchored silica gels each, through electron-beam irradiation. The addition of ligands yielded larger average pore sizes than the absence of any ligand. Moreover, the ethylenediamine ligand led to looser structures and better access of the Ag nanoparticles to the ethylenediamine-anchored gel. As a result, more Ag nanoparticles were introduced into the ethylenediamine-anchored gel. The preparation and characterization of Ag nanoparticle-embedded blank and ligand-anchored silica gels are discussed in detail. PMID:24245307

Im, Hee-Jung; Lee, Byung Cheol; Yeon, Jei-Won

2013-11-01

3

The Membrane-anchoring Domain of Epidermal Growth Factor Receptor Ligands Dictates Their Ability to Operate in Juxtacrine Mode  

SciTech Connect

All ligands of the epidermal growth factor receptor (EGFR) are synthesized as membrane-anchored precursors. Previous work has suggested that some ligands, such as EGF, must be proteolytically released to be active, whereas others, such as heparin binding EGF-like growth factor (HB-EGF) can function while still anchored to the membrane (i.e., juxtacrine signaling). To explore the structural basis for these differences in ligand activity, we engineered a series of membrane-anchored ligands in which the core, receptor-binding domain of EGF was combined with different domains of both EGF and HB-EGF. We found that ligands having the N-terminal extension of EGF could not bind to the EGFR, even when released from the membrane. Ligands lacking an N-terminal extension, but possessing the membrane-anchoring domain of EGF still required proteolytic release for activity, whereas ligands with the membrane anchoring domain of HB-EGF could elicit full biological activity while still membrane anchored. Ligands containing the HB-EGF membrane anchor, but lacking an N-terminal extension, activated EGFR during their transit through the Golgi apparatus . However, cell-mixing experiments and fluorescence resonance energy transfer (FRET) studies showed that juxtacrine signaling typically occurred in trans at the cell surface, at points of cell-cell contact. Our data suggest that the membrane-anchoring domain of ligands selectively controls their ability to participate in juxtacrine signaling and thus, only a subclass of EGFR ligands can act in a juxtacrine mode.

Dong, Jianying; Opresko, Lee; Chrisler, William B.; Orr, Galya; Quesenberry, Ryan D.; Lauffenburger, Douglas A.; Wiley, H S.

2005-06-01

4

CCMR: Biological Ligands and Metal Transport  

NSDL National Science Digital Library

Aluminum toxicity is a major inhibitor in plant root growth on acidic soils. Plants have evolved defense mechanism in the root apex that counteract these metal cation harmful effects, and allow plant growth. Aluminum tolerant species are known to secrete organic acids from the roots in the presence of the toxin. Aluminum triggers unique responses in the rhizosphere to release ligands, such as citrate or malate for example that combine with aluminum to form metal-ligand complexes. This project involved developing new methods for characterizing and quantifying aqueous metal-ligand complexes. The focus of this project was to first determine the binding capacity of aluminum to the resin. At a later date we will then add ligands to the system determining the binding capacity of aluminum to the ligand. This will aid in a better understanding of how complex formations and organic acids control the behavior and toxicity of aluminum in the environment.

Powell, Alanna

2005-08-17

5

Ligand intermediates in metal-catalyzed reactions; Annual technical report, August 1, 1992--August 1, 1993  

SciTech Connect

Achievements are reported for the following 4 areas: {pi}/{sigma} equillibria in aldehyde and ketone complexes; thermodynamic ligand binding affinities ({alpha},{beta} unsaturated organic carbonyl compounds); (a new form of coordinated carbon) an unsupported C{sub 3} chain that spans two different transition metals; and (a new form of coordinated carbon) an C{sub 3} chain that is anchored by a metal on each end and spanned by a third.

Gladysz, J.A.

1993-08-10

6

Ligand coordination and spin crossover in a nickel porphyrin anchored to mesoporous TiO2 thin films.  

PubMed

The coordination and spin equilibrium of a Ni(II) meso-tetra(4-carboxyphenyl)porphyrin compound, NiP, was quantified both in fluid solution and when anchored to mesoporous, nanocrystalline TiO2 thin films. This comparison provides insights into the relative rate constants for excited-state injection and ligand field population. In the presence of pyridine, the spectroscopic data were consistent with the presence of equilibrium concentrations of a 4-coordinate low-spin S = 0 ((1)A1g) Ni(II) compound and a high-spin S = 1 ((3)B1g) 6-coordinate compound. Temperature-dependent equilibrium constants were consistently smaller for the surface-anchored NiP/TiO2, as were the absolute values of ?H and ?S. In the presence of diethylamine (DEA), the ground-state 6-coordinate compound was absent, but evidence for it was present after pulsed light excitation of NiP. Arrhenius analysis of data, measured from -40 to -10 °C, revealed activation energies for ligand dissociation that were the same for the compound in fluid solution and anchored to TiO2, Ea = 6.6 kcal/mol, within experimental error. At higher temperatures, a significantly smaller activation energy of 3.5 kcal/mol was found for NiP(DEA)2/TiO2. A model is proposed wherein the TiO2 surface sterically hinders ligand coordination to NiP. The lack of excited-state electron transfer from Ni(II)P*/TiO2 indicates that internal conversion to ligand field states was at least 10 times greater than that of excited-state injection into TiO2. PMID:23914901

Achey, Darren; Meyer, Gerald J

2013-08-19

7

Adsorption of heavy metal ions onto dithizone-anchored poly (EGDMA-HEMA) microbeads  

Microsoft Academic Search

The dithizone-anchored poly (EGDMA-HEMA) microbeads were prepared for the removal of heavy metal ions (i.e. cadmium, mercury, chromium and lead) from aqueous media containing different amounts of these ions (25–500 ppm) and at different pH values (2.0–8.0). The maximum adsorptions of heavy metal ions onto the dithizone-anchored microbeads from their solutions was 18.3, Cd(II); 43.1, Hg(II); 62.2, Cr(III) and 155.2

B Salih; A Denizli; C Kavakl?; R Say; E Pi?kin

1998-01-01

8

Compensatory mechanisms allow undersized anchor-deficient class I MHC ligands to mediate pathogenic autoreactive T cell responses.  

PubMed

Self-reactive T cells must escape thymic negative selection to mediate pathogenic autoimmunity. In the NOD mouse model of autoimmune diabetes, several ? cell-cytotoxic CD8 T cell populations are known, with the most aggressive of these represented by AI4, a T cell clone with promiscuous Ag-recognition characteristics. We identified a long-elusive ? cell-specific ligand for AI4 as an unusually short H-2D(b)-binding 7-mer peptide lacking a C-terminal anchor residue and derived from the insulin A chain (InsA14-20). Crystallography reveals that compensatory mechanisms permit peptides lacking a C-terminal anchor to bind sufficiently to the MHC to enable destructive T cell responses, yet allow cognate T cells to avoid negative selection. InsA14-20 shares two solvent-exposed residues with previously identified AI4 ligands, providing a structural explanation for AI4's promiscuity. Detection of AI4-like T cells, using mimotopes of InsA14-20 with improved H-2D(b)-binding characteristics, establishes the AI4-like T cell population as a consistent feature of the islet infiltrates of NOD mice. Our work establishes undersized peptides as previously unrecognized targets of autoreactive CD8 T cells and presents a strategy for their further exploration as Ags in autoimmune disease. PMID:25063871

Lamont, Deanna; Mukherjee, Gayatri; Kumar, P Rajesh; Samanta, Dibyendu; McPhee, Caroline G; Kay, Thomas W H; Almo, Steven C; DiLorenzo, Teresa P; Serreze, David V

2014-09-01

9

Sorption of Heavy Metal Ions on New Metal-Ligand Complexes Chemically Derived from Lycopodium clavatum  

Microsoft Academic Search

Sorption of heavy metal ions from aqueous solution has been investigated as a function of pH using a novel exchanger system whereby Lycopodium clavatum is functionalized with carboxylate and glyoxime metal-ligand complexes. The new ligand exchangers were prepared using a reaction of diaminosporopollenin with various metal-ligand complexes of glyoxime and monocarboxylic acid. The sorptive behavior of these metal-ligand exchangers and

Erol Pehlivan; Mustafa Ersoz; Salih Yildiz; Harry J. Duncan

1994-01-01

10

Selective removal of metal-ligand complexes using synthetic sorbents  

SciTech Connect

When dissolved heavy metals are accompanied by ligands (organic and inorganic) in a wastewater stream, conventional removal methods, such as precipitation, become hindered. Heavy metals remain in solution due to complexation with ligands. Non-conventional methods such as selective ion-exchange also do not work because of reduced selectivity when strong ligands are present in a system. As industry forges ahead improving purification processes used in the metal plating and electronics sectors, the removal of metals in the presence of strong ligands becomes more of a problem. Heavy metals that would have normally precipitated out, using past purification methods, are remaining in solution because of complexation with heavy metals. Trace levels are approaching or surpassing, the Environmental Protection Agencies (EPA) maximum concentration limits (MCL). The primary objective of this project is to characterize some new and tailored polymeric sorbents for the selective sorption of anionic metal-ligand complexes. The basic concept of the process the authors are developing is to tailor a resin in such a way that it will have a high affinity for an array of predefined target ions (metal (2) ions, ligands and metal-ligand complexes) present in trace concentrations, all at the same time.

Kney, A.; Sengupta, A. [Lehigh Univ., Bethlehem, PA (United States). Civil and Environmental Engineering Dept.

1995-12-31

11

DE NOVO DESIGN OF LIGANDS FOR METAL SEPARATION  

EPA Science Inventory

This application focuses on the development of appropriate computation tools and parameters for the de novo design of selective metal ligands. We have developed a successful suite of tools for computer-aided design of ligands for receptors of known three-dimensional structure (st...

12

Sorption of heavy metal ions on new metal-ligand complexes chemically derived from Lycopodium clavatum  

SciTech Connect

Sorption of heavy metal ions from aqueous solution has been investigated as a function of pH using a novel exchanger system whereby Lycopodium clavatum is functionalized with carboxylate and glyoxime metal-ligand complexes. The new ligand exchangers were prepared using a reaction of diaminosporopollenin with various metal-ligand complexes of glyoxime and monocarboxylic acid. The sorptive behavior of these metal-ligand exchangers and the possibilities to remove and to recover selectively heavy metal cations using these systems are discussed on the basis of their chemical natures and their complexing properties.

Pehlivan, E.; Ersoz, M.; Yildiz, S. [Univ. of Selcuk, Konya (Turkey); Duncan, H.J. [Univ. of Glasgow, Scotland (United Kingdom)

1994-08-01

13

A Modified Metallic Coil Embolization Technique for Pulmonary Arteriovenous Malformations Using Coil Anchors and Occlusion Balloon Catheters  

SciTech Connect

Purpose. To evaluate the feasibility and efficacy of a modified metallic coil embolization technique for pulmonary arteriovenous malformations (PAVMs) using coil anchors and occlusion balloon catheters. Methods. Five consecutive female patients with 6 PAVMs were included in the present study. One of the 6 PAVMs was of the complex type with four feeding arteries. An occlusion balloon catheter was inserted into the feeding artery as close to the venous sac as possible. The coil anchor, which was a simple W-shaped bent stainless steel wire with two markers at each end, was deployed prior to embolization to prevent the systemic migration of embolic materials. Then, metallic coils were deployed around the coil anchors under inflow stoppage using the inflated occlusion balloon catheter. In the complex-type PAVM, the main feeder was occluded by this technique and the other three small feeders were embolized with metallic coils only. Results. In all 5 cases, occlusion balloon catheters could be inserted into the feeding arteries just proximal to the venous sacs, coil anchors were easily deployed, and complete occlusion was achieved without any migration of metallic coils or paradoxical embolism during the procedure. Conclusions. The modified metallic coil embolization technique with coil anchors and occlusion balloon catheters was feasible and considered to be useful in preventing procedure-related complications.

Mori, Kensaku [Institute of Clinical Medicine, University of Tsukuba, Department of Diagnostic and Interventional Radiology (Japan)], E-mail: moriken@md.tsukuba.ac.jp; Shiigai, Masanari [Tsukuba Medical Center Hospital, Department of Radiology (Japan); Saida, Tsukasa; Anno, Izumi [Institute of Clinical Medicine, University of Tsukuba, Department of Diagnostic and Interventional Radiology (Japan); Wada, Mitsuyoshi [Seinan Medical Center Hospital, Department of Radiology (Japan); Minami, Manabu [Institute of Clinical Medicine, University of Tsukuba, Department of Diagnostic and Interventional Radiology (Japan)

2008-05-15

14

Anchored metal nanoparticles: effects of support and size on their energy, sintering resistance and reactivity.  

PubMed

Many catalysts consist of metal nanoparticles anchored to the surfaces of oxide supports. These are key elements in technologies for the clean production and use of fuels and chemicals. We show here that the chemical reactivity of the surface metal atoms on these nanoparticles is closely related to their chemical potential: the higher their chemical potential, the more strongly they bond to small adsorbates. Controlling their chemical potential by tuning the structural details of the material can thus be used to tune their reactivity. As their chemical potential increases, this also makes the metal surface less noble, effectively pushing its behavior upwards and to the left in the periodic table. Also, when the metal atoms are in a nanoparticle with higher chemical potential, they experience a larger thermodynamic driving force to sinter. Calorimetric measurements of metal vapor adsorption energies onto clean oxide surfaces in ultrahigh vacuum show that the chemical potential increases with decreasing particle size below 6 nm, and, for a given size, decreases with the adhesion energy between the metal and its support, Eadh. The structural factors that control the metal/oxide adhesion energy are thus also keys for tuning catalytic performance. For a given oxide, Eadh increases with (deltaHsub,M--deltaHf,MOx)/OmegaM2/3 for the metal, where deltaHsub,M is its heat of sublimation, deltaHf,MOx is the standard heat of formation of that metal's most stable oxide (per mole of metal), and OmegaM is the atomic volume of the bulk solid metal. The value deltaHsub,M--deltaHf,MOx equals the heat of formation of that metal's oxide from a gaseous metal atom plus O2(g), so it reflects the strength of the chemical bonds which that metal atom can make to oxygen, and OmegaM2/3 simply normalizes this energy to the area per metal atom, since Eadh is the adhesion energy per unit area. For a given metal, Eadh to different clean oxide surfaces increases as: MgO(100) approximately TiO2(110) < or = alpha-Al2O3(0001) < CeO2-x(111) < or = Fe3O4(111). Oxygen vacancies also increase Eadh, but surface hydroxyl groups appear to decrease Eadh, even though they increase the initial heat of metal adsorption. PMID:24015573

Campbell, Charles T; Sellers, Jason R V

2013-01-01

15

The connection between metal ion affinity and ligand affinity in integrin I domains  

E-print Network

The connection between metal ion affinity and ligand affinity in integrin I domains Thomas Vorup in regulating ligand binding has been reported, the relationship between metal ion binding affinity and ligand binding affinity has not been elucidated. Metal and ligand binding by several I domain mutants

Springer, Timothy A.

16

Multidentate oligomeric ligands to enhance the biocompatibility of iron oxide and other metal nanoparticles  

NASA Astrophysics Data System (ADS)

We prepared a set of multi-coordinating and reactive amphiphilic polymer ligands and used them for surface-functionalizing magnetic iron oxide nanoparticles. The amphiphilic oligomers were prepared by coupling (via one step nucleophilic addition) several dopamine anchoring groups, polyethylene glycol moieties and reactive groups onto a poly(isobutylene-alt-maleic anhydride) chain. The availability of several anchoring groups in the same ligand greatly enhances the ligand affinity to the nanoparticle surfaces, via multiplecoordination, while the hydrophilic and reactive groups promote colloidal stability in buffer media and allow subsequent conjugation to target biomolecules. The hydrophilic nanoparticles capped with these polymers maintain compact size and exhibit great long term colloidal stability.

Wang, Wentao; Palui, Goutam; Ji, Xin; Aldeek, Fadi; Mattoussi, Hedi

2014-03-01

17

Ligand directed self-assembly vs. metal ion coordination algorithm-when does the ligand or the metal take control?  

PubMed

Polyfunctional hydrazone ligands with multidentate terminal donor groups offer metal ions many donor choices, and the coordination outcome depends mainly on the identity of the metal ion. Co(ii) and Ni(ii) prefer to adopt largely undistorted, six-coordinate geometries, while Cu(ii) can easily adapt to a variety of coordination situations (e.g. CN 4-6), and will optimize its coordination number and stereochemistry based on all the available donors. Ni(ii) and Co(ii) form simple [2 x 2] [M(4)-(micro(2)-O)(4)] square grids with such ditopic hydrazone ligands, and ignore other coordination options, while Cu(ii) tries to bind to all the available donors, and forms extended and 2D structures based on linked Cu(ii) triads rather than grids. Ni(ii) is also reluctant to compromise its desire to maximize its crystal field stabilization energy (CFSE) by binding to 'weak' ligands, and with a tetratopic pyrazole bis-hydrazone ligand it ignores the oxygen donors in favour of nitrogen, forming a novel trinuclear, triangular cluster. Also, reaction of a linear Ni(ii)(3) complex of a tetratopic pyridazine bis-hydrazone ligand with NiN(6) coordination spheres with Cu(ii), leads exclusively to a square Cu(12) grid based complex, and complete displacement of nickel. Structural and magnetic properties are highlighted, and metal-ligand interactions are discussed in detail. PMID:19352520

Shuvaev, Konstantin V; Abedin, Tareque S M; McClary, Corey A; Dawe, Louise N; Collins, Julie L; Thompson, Laurence K

2009-04-28

18

Functional metal-organic frameworks via ligand doping: influences of ligand charge and steric demand.  

PubMed

Doping a functional ligand into a known crystalline system built from ligands of similar shape and length provides a powerful strategy to construct functional metal-organic frameworks (MOFs) with desired functionality and structural topology. This mix-and-match approach mimics the widely applied metal ion doping (or solid solution formation) in traditional inorganic materials, such as metal oxides, wherein maintaining charge balance of the doped lattice and ensuring size match between doped metal ions and the parent lattice are key to successful doping. In this work, we prepared three sterically demanding dicarboxylate ligands based on Ir/Ru-phosphors with similar structures and variable charges (-2 to 0), [Ir(ppy)3]-dicarboxylate (L1, ppy is 2-phenylpyridine), [Ir(bpy)(ppy)2](+)-dicarboxylate (L2, bpy is 2,2'-bipyridine), and Ru(bpy)3](2+)-dicarboxylate (L3), and successfully doped them into the known IRMOF-9/-10 structures by taking advantage of matching length between 4,4'-biphenyl dicarboxylate (BPDC) and L1-L3. We systematically investigated the effects of size and charge of the doping ligand on the MOF structures and the ligand doping levels in these MOFs. L1 carries a -2 charge to satisfy the charge requirement of the parent Zn4O(BPDC)3 framework and can be mixed into the IRMOF-9/-10 structure in the whole range of H2L1/H2BPDC ratios from 0 to 1. The steric bulk of L1 induces a phase transition from the interpenetrated IRMOF-9 structure to the non-interpenetrated IRMOF-10 counterpart. L2 and L3 do not match the dinegative charge of BPDC in order to maintain the charge balance for a neutral IRMOF-9/-10 framework and can only be doped into the IRMOF-9 structure to a certain degree. L2 and L3 form a charge-balanced new phase with a neutral framework structure at higher doping levels (>8% For L2 and >6% For L3). This systematic investigation reveals the influences of steric demand and charge balance on ligand doping in MOFs, a phenomenon that has been well-established in metal ion doping in traditional inorganic materials. PMID:24422471

Wang, Cheng; Liu, Demin; Xie, Zhigang; Lin, Wenbin

2014-02-01

19

A new ligand field approach to linear transition metal dihalides  

NASA Astrophysics Data System (ADS)

We have performed theoretical multiconfigurational calculations of the molecular energy levels based on two axial ligand field models and determined the model parameters to reproduce ab initio energies of TiCl2, TiF2, VCl2, and VF2. We develop two extensions to ligand field theory (LFT) for linear transition metal dihalides, which are incorrectly described by standard LFT. The standard LFT is augmented (1) by including the ligand induced hybridization of the d(?) orbital with the 4s orbital or (2) by using a different radial part for the d(?) orbital. Both models reproduce the energies of the first electronic states in very good agreement with numerical multireference configuration interaction results. Furthermore the model parameters are very close to experimental known Racah parameters describing the term energies of Ti2+ and V2+.

Vogel, M.; Weber, W.; Wenzel, W.

2006-07-01

20

Alternatives to pyridinediimine ligands: syntheses and structures of metal complexes supported by donor-modified alpha-diimine ligands.  

PubMed

This report describes the synthesis and characterization of metal halide complexes (M = Mn, Fe, Co) supported by a new family of pendant donor-modified alpha-diimine ligands. The donor (N, O, P, S) substituent is linked to the alpha-diimine by a short hydrocarbon spacer forming a tridentate, mer-coordinating ligand structure. The tridentate ligands are assembled from monoimine precursors, the latter being synthesized by selective reaction with one carbonyl group of the alpha-dione. While attempts to separately isolate tridentate ligands in pure form were unsuccessful, metal complexes supported by the tridentate ligand are readily synthesized in-situ, by forming the ligand in the presence of the metal halide, resulting in a metal complex which subsequently crystallizes out of the reaction mixture. Metal complexes with NNN, NNO, NNP and NNS donor sets have been prepared and examples supported by NNN, NNP and NNS ligands have been structurally characterized. In the solid state, NNN and NNP ligands coordinate in a mer fashion and the metal complexes possess distorted square pyramidal structures and high spin (S = 2) electronic configurations. Compounds with NNS coordination environments display a variety of solid state structures, ranging from those with unbound sulfur atoms, including chloride bridged and solvent ligated species, to those with sulfur weakly bound to the metal center. The extent of sulfur ligation depends on the donor ability of the crystallization solvent and the substitution pattern of the arylthioether substituent. PMID:17563791

Schmiege, Benjamin M; Carney, Michael J; Small, Brooke L; Gerlach, Deidra L; Halfen, Jason A

2007-06-28

21

Synthesis and NMR characterization of ligand-capped metal and metal-oxide nanoparticles  

NASA Astrophysics Data System (ADS)

Ligand-capped metal and metal-oxide nanoparticles (NPs) have some interesting and useful physical properties that are not present in their respective bulk materials. These properties are of research interest in many applications such as catalysis, drug delivery, biological imaging, and plasmonics. In such applications, it is critical to understand the surface structure of NPs and the roles played by the surface bound ligands. To characterize surface environment, ligand dynamics, and exchange kinetics, ligand-capped metal and metal-oxide NPs are synthesized and studied by multinuclear NMR. Phosphines and phosphonic acids are used to passivate metal (gold and silver) and metal-oxide (tin dioxide) NPs in different sizes (1-5 nm) by following published procedures or original synthesis methods. In both solution and solid state NMR, the 31P chemical shift of surface-bound ligands are distinctly different from those observed for free ligands. Additionally, NMR line widths in surface-bound ligands are highly broadened compared to those of free ligands. The lines are broadened due to both homogeneous and inhomogeneous broadening mechanisms, determined through hole burning NMR and spin-spin relaxation measurements. In small particles (< 2 nm), the main source of line broadening is inhomogeneous and originates due to structural heterogeneity and underlying chemical shift distributions. In large particles (> 2 nm), both inhomogeneous and homogeneous line broadening mechanisms are present. When the particles' sizes increase from small to large, the homogeneous broadening mechanism becomes dominant due to strong nuclear-electron interaction and reintroduction of residual dipolar coupling as shown by a combination of 1H, 13C and 31P NMR. Results from a series of ligand exchange experiments in silver and gold NPs further indicate the presence of Au(I) and Ag(I) on the particle surfaces.

Sharma, Ramesh

22

Selective transformations of cyclopentadienyl ligands of transition-metal and rare-earth metal complexes.  

PubMed

Cyclopentadienyl and substituted cyclopentadienyl ligands are observed in a wide range of organometallic complexes. In addition to serving as ancillary ligands, these ligands have come into their own as intermediates in organometallic reactions, and shown many unique reaction modes involving ring C-H, C-C and C=C bond cleavages. This feature article summarizes the progressive development of cyclopentadienyl-based reactions of metallocene complexes of transition metals and rare-earth metals, with the aim of further developing the fundamental modes of reactivity of such systems together with their synthetic applications. PMID:23323264

Liu, Ruiting; Zhou, Xigeng

2013-04-21

23

Hypersensitivity to Suture Anchors  

PubMed Central

Hypersensitivity to suture anchor is extremely rare. Herein, we present a case in which hypersensitivity to suture anchor was strongly suspected. The right rotator cuff of a 50-year-old woman was repaired with a metal suture anchor. Three weeks after the surgery, she developed erythema around her face, trunk, and hands, accompanied by itching. Infection was unlikely because no abnormalities were detected by blood testing or by medical examination. Suspicious of a metallic allergy, a dermatologist performed a patch testing 6 months after the first surgery. The patient had negative reactions to tests for titanium, aluminum, and vanadium, which were the principal components of the suture anchor. The anchor was removed 7 months after the first surgery, and the erythema disappeared immediately. When allergic symptoms occur and persist after the use of a metal anchor, removal should be considered as a treatment option even if the patch test result is negative. PMID:23956902

Goto, Masafumi; Gotoh, Masafumi; Mitsui, Yasuhiro; Tanesue, Ryo; Okawa, Takahiro; Higuchi, Fujio; Shiba, Naoto

2013-01-01

24

Zwitterionic Group VIII transition metal initiators supported by olefin ligands  

DOEpatents

A zwitterionic Group VIII transition metal complex containing the simple and relatively small 3-(arylimino)-but-1-en-2-olato ligand that catalyzes the formation of polypropylene and high molecular weight polyethylene. A novel feature of this catalyst is that the active species is stabilized by a chelated olefin adduct. The present invention also provides methods of polymerizing olefin monomers using zwitterionic catalysts, particularly polypropylene and high molecular weight polyethylene.

Bazan, Guillermo C. (Goleta, CA); Chen, Yaofeng (Shanghai, CN)

2011-10-25

25

Electrophilic Metal Alkyl Chemistry in New Ligand Environments  

SciTech Connect

The goals of this project were to design new electrophilic metal alkyl complexes and to exploit these systems in fundamental studies of olefin polymerization and other important and new catalytic reactions. A key target reaction is insertion copolymerization of olefins and polar CH2=CHX vinyl monomers such as vinyl halides and vinyl ethers. During the period covered by this report we (i) investigated the properties of ortho-alkoxy-arylphosphine ligands in Ni-based olefin polymerization catalysts, (ii) studied the synthesis of double-end-capped polyethylene using group 4 metal catalysts that contain tris-pyrazolylborate ligands, (iii) explored the ethylene insertion reactivity of group 4 metal tris-pyrazolyl-borate complexes, (iv) showed that (?-diimine)PdMe{sup +} species undergo multiple insertion of silyl vinyl ethers, (v) synthesized and explored the reactivity of base-free Ni benzyl complexes that contain ortho-phosphino-arene sulfonate ligands, (vi) established the mechanism of the reaction of vinyl chloride with (?-diimine)PdMe{sup +} catalysts, (vii) explored the role of cationic polymerization and insertion chemistry in the reactions of vinyl ethers with (?-diimine)PdMe{sup +} species, (viii) discovered a new class of self-assembled tetranuclear Pd catalysts that produce high molecular weight linear polyethylene and copolymerize ethylene and vinyl fluoride, and (ix) developed model systems that enabled investigation of cis-trans isomerization of {phosphine-sulfonate}Pd(II) complexes.

Jordan, Richard F. [University of Chicago] University of Chicago

2013-06-30

26

Long-lifetime metal-ligand pH probe.  

PubMed

We describe the synthesis and fluorescence spectral characterization of a pH-sensitive metal-ligand complex, [Ru(deabpy)(bpy)2]2., where deabpy is 4,4'-diethylaminomethyl-2,2'-bipyridine. This metal-ligand complex (MLC) was found to display pH-dependent intensities, emission spectra, and decay times, with the changes centered near the physiological useful pH value of 7.5. The apparent pKa values were not found to be dependent on ionic strength. The compound was found to be useful for lifetime-based sensing by phase-modulation fluorometry. Global analysis of the intensity decays over a range of pH values revealed two decay times of 235 and 380 ns, associated with the protonated and unprotonated forms, respectively. Because of its long decay time, optical pH measurements could be accomplished by phase-modulation fluorometry with a conveniently low modulation frequency of 700 kHz. The lifetime data were obtained with either a amplitude-modulated laser or with an amplitude-modulated blue-light-emitting diode. This pH-sensitive complex also displays a modest spectral shift with change in pH, allowing its use as a wavelength-ratiometric MLC probe. One can imagine lifetime sensors for a variety of blood cations and point-of-care assays based on long-lifetime metal-ligand complexes and simple solid-state light sources and detectors. PMID:9177680

Murtaza, Z; Chang, Q; Rao, G; Lin, H; Lakowicz, J R

1997-05-01

27

The effect of two nonresorbable suture types on the mechanical performance over a metal suture anchor eyelet.  

PubMed

An understanding of the mechanical properties of different suture materials is valuable when selecting the most appropriate suture and repair technique. Sutures should be strong, easy to handle and have high knot security. The introduction of suture anchors adds an additional variable regarding the effect of stress risers over the eyelet. Improving the mechanical properties of a suture may be a possible method to help avoid failure over stress risers such as the eyelet of suture anchor. This study examined the static and viscoelastic properties of a new polyethylene based non-resorbable suture (Fibrewire) over the eyelet of a standard anchor compared to braid polyester non-resorbable suture (Ethibond). Fibrewire had superior ultimate load properties compared to Ethibond (360.2 N+/-23.8 vs 191.9 N+/-17.3) as well as greater stiffness (61.3 N/mm+/-9.7 vs 8.1 N/mm+/-0.4) when tested in uniaxial tension through a metal anchor eyelet (Mitek) ( p<0.001). Fibrewire demonstrated greater stress relaxation than Ethibond ( p<0.05). Differences in the static and viscoelastic properties of suture may have implications in the post-operative period or during rehabilitation. PMID:13680105

Acton, D; Perry, A; Evans, R; Butler, A; Stephens, P; Bruce, W; Goldberg, J; Sonnabend, D; Walsh, W R

2004-03-01

28

The Interactions and Exchanges of Metal-bound Sulfur Containing Ligands with Various Transition Metals  

E-print Network

....... 26 Figure 4-1 The zinc-platinum adduct (a) and the metal exchange product (b) ... 29 Figure 4-2 Previously studied reactions of zinc and nickel biomimetic pathways 31 Figure 4-3 The ligand cannibalism of Zn-1?-Ac to form the diacetate... species and the starting dimer ........................................................................ 32 Figure 4-4 Reaction pathways to address the mechanism for ligand cannibalism and reformulation...

Foley, William

2011-02-22

29

Introduction of functionalized mesopores to metal-organic frameworks via metal-ligand-fragment coassembly.  

PubMed

Introduction of functionalized mesopores into microporous metal-organic frameworks (MOFs) can endow them with suitable properties for applications in gas storage, separation, catalysis, and drug delivery. However, common methods for functionalization (including pre- and post-synthetic modifications) of the internal surface of a MOF reduce the pore size of the MOF because the additional functional groups fill up the pores. We present a metal-ligand-fragment coassembly strategy for the introduction of (meso)pores functionalized with various substituent groups on the ligand fragments. Astonishingly, this new functionalization strategy increases the pore volume of a MOF instead of reducing it. Since the ligand fragments are often readily available or easily prepared, the new procedure for synthesis of the modified MOFs becomes much easier and more applicable than existing approaches. Remarkably, mesopores can be generated conveniently and controllably by the coassembly of a ligand and its fragment containing the desired functional groups. The fragment/ligand ratio has been optimized to preserve the parent structure and to promote maximum mesopore introduction, which has led to a systematic evaluation of the effectiveness of a series of functional groups for the adsorption of guest molecules. PMID:23157426

Park, Jinhee; Wang, Zhiyong U; Sun, Lin-Bing; Chen, Ying-Pin; Zhou, Hong-Cai

2012-12-12

30

Metal-Ligand Cooperation in H2 Activation with Iron Complexes Bearing Hemilabile Bis(diphenylphosphino)amine Ligands.  

PubMed

The octahedral transition-metal complex [(dppa)Fe(Ph2P-N-PPh2)2] (1) [dppa = bis(diphenylphosphino)amine] with homofunctional bidentate ligands is described. The ligand exhibits hemilability due to its small bite angle and the steric repulsion of the coordinated donor groups. As the {Ph2P-N-PPh2}(-) ligand can act as an internal base, heterolytic cleavage of dihydrogen by complex 1 leads to the formation of the hydride complex [(dppa)(Ph2P-N-PPh2)Fe(H)(?(1)-Ph2P-NH-PPh2)2] (2), representing an example of cooperative bond activation with a homofunctional hemilabile ligand. This study demonstrates that hemilability of homofunctionalized ligands can be affected by careful adjustment of geometric parameters. PMID:25290535

Frank, Nicolas; Hanau, Katharina; Langer, Robert

2014-10-20

31

A quantitative approach of the interaction between metal triflates and organic ligands using electrospray mass spectrometry.  

PubMed

The interaction between two Lewis "superacid" catalysts Zn(OTf)(2) and In(OTf)(3) and series of amide and phosphate ligands is quantitatively characterized by electrospray ionization mass spectrometry (ESI-MS). A specific feature of the ESI-MS spectra of the mixture of metal triflates and Lewis bases is the formation of ionic adducts resulting from the displacement of one triflate anion by two neutral ligands. A ligand competition model is developed, which describes the relative intensities of the ionic adducts as a function of relative ligand concentrations. The relative affinities deduced from the ligand competition method are combined in an affinity scale for the metal triflate. PMID:23055073

Gal, Jean-François; Iacobucci, Claudio; Monfardini, Ilaria; Massi, Lionel; Duñach, Elisabet; Olivero, Sandra

2012-12-01

32

A Quantitative Approach of the Interaction between Metal Triflates and Organic Ligands Using Electrospray Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The interaction between two Lewis "superacid" catalysts Zn(OTf)2 and In(OTf)3 and series of amide and phosphate ligands is quantitatively characterized by electrospray ionization mass spectrometry (ESI-MS). A specific feature of the ESI-MS spectra of the mixture of metal triflates and Lewis bases is the formation of ionic adducts resulting from the displacement of one triflate anion by two neutral ligands. A ligand competition model is developed, which describes the relative intensities of the ionic adducts as a function of relative ligand concentrations. The relative affinities deduced from the ligand competition method are combined in an affinity scale for the metal triflate.

Gal, Jean-François; Iacobucci, Claudio; Monfardini, Ilaria; Massi, Lionel; Duñach, Elisabet; Olivero, Sandra

2012-12-01

33

Phthalocyaninato complexes with peripheral alkylthio chains: disk-like adsorbate species for the vertical anchoring of ligands on gold surfaces  

PubMed Central

Thin metalorganic films were prepared on gold by self-assembly of thioether-functionalised phthalocyaninato complexes from solution. The phthalocyaninato ligands used contain eight peripheral, ?-positioned, alkylthio substituents SR (1a: R = n-C8H17, 1b: R = n-C12H25), which serve as headgroups for surface binding and promote lateral assembly, while the disk-like phthalocyaninato core offers the scope for the attachment of axial ligands to the adsorbed molecules. This process was mimicked by coordination of pyridine (Py) to [Zn(1a)] and [Zn(1b)], respectively. The crystal structures of the products [Zn(1a)(Py)] and [Zn(1b)(Py)] were determined. The crystal structures of 4,5-bis(octylthio)phthalodinitrile and 4,5-bis(dodecylthio)phthalodinitrile were also determined. The films fabricated from [Mn(1a)Cl] and [Mn(1b)Cl] on gold were characterised by XPS, ToF-SIMS and NEXAFS spectroscopy, which revealed the presence of well-defined and homogeneous self-assembled monolayers (SAMs), whose constituents are bound to the substrate by thioether–gold linkages. The orientation of the macrocycles is predominantly parallel to the surface. Strong electronic interaction of the manganese(III) centre with the substrate leads to Cl loss upon adsorption and its reduction to MnII. PMID:21857743

Siemeling, Ulrich; Schirrmacher, Christian; Glebe, Ulrich; Bruhn, Clemens; Baio, Joe E.; Arnadottir, Liney; Castner, David G.; Weidner, Tobias

2011-01-01

34

Phthalocyaninato Complexes with Peripheral Alkylthio Chains: Disk-like Adsorbate Species for the Vertical Anchoring of Ligands onto Gold Surfaces  

SciTech Connect

Thin metalorganic films were prepared on gold by self-assembly of thioether-functionalized phthalocyaninato complexes from solution. The phthalocyaninato ligands used contain eight peripheral, {beta}-positioned, alkylthio substituents SR (1a: R = n-C{sub 8}H{sub 1}7, 1b: R = n-C{sub 12}H{sub 25}), which serve as headgroups for surface binding and promote lateral assembly, while the disk-like phthalocyaninato core offers the scope for the attachment of axial ligands to the adsorbed molecules. This process was mimicked by coordination of pyridine (Py) to [Zn(1a)] and [Zn(1b)], respectively. The crystal structures of the products [Zn(1a)(Py)] and [Zn(1b)(Py)] were determined. The crystal structures of 4,5-bis(octylthio)phthalodinitrile and 4,5-bis(dodecylthio)phthalodinitrile were also determined. The films fabricated from [Mn(1a)Cl] and [Mn(1b)Cl] on gold were characterized by XPS, ToF-SIMS and NEXAFS spectroscopy, which revealed the presence of well-defined and homogeneous self-assembled monolayers (SAMs), whose constituents are bound to the substrate by thioether-gold linkages. The orientation of the macrocycles is predominantly parallel to the surface. Strong electronic interaction of the manganese(III) centre with the substrate leads to Cl loss upon adsorption and its reduction to MnII.

U Siemeling; C Schirrmacher; U Glebe; C Bruhn; J Baio; L Arnadottir; D Castner; T Weidner

2011-12-31

35

Metal-ligand redox interaction in the multielectron chemistry of porphyrinogen coordination compounds  

E-print Network

Metal complexes of the macrocycle porphyrinogen (calix[4]pyrrole) are studied with an emphasis on the redox activity ("non-innocence") of the ligand (Chapter I). Porphyrinogen complexes of spherical, redox-inert metal ...

Bachmann, Julien

2006-01-01

36

The Study Of The Successive Metal-Ligand Binding Energies For Fe+, Fe-, V+ and Co+  

NASA Technical Reports Server (NTRS)

The successive binding energies of CO and H2O to Fe(+), CO to Fe(-), and H2 to Co(+) and V(+) are presented. Overall the computed results are in good agreement with experiment. The trends in binding energies are analyzed in terms of metal to ligand donation, ligand to metal donation, ligand-ligand repulsion, and changes in the metal atom, such as hybridization, promotion, and spin multiplicity. The geometry and vibrational frequencies are also shown to be directly affected by these effects.

Bauschicher, Charles W., Jr.; Ricca, Alessandra; Maitre, Philippe; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

37

The Study of the Successive Metal-ligand Binding Energies for Fe(+), Fe(-), V(+) and Co(+)  

NASA Technical Reports Server (NTRS)

The successive binding energies of CO and H2O to Fe(+), CO to Fe(-), and H2 to Co(+) and V(+) are presented. Overall the computed results are in good agreement with experiment. The trends in binding energies are analyzed in terms of metal to ligand donation, ligand to metal donation, ligand-ligand repulsion, and changes in the metal atom, such as hybridization, promotion, and spin multiplicity. The geometry and vibrational frequencies are also shown to be directly affected by these effects.

Bauschlicher, Charles W., Jr.; Ricca, Alessandra; Maitre, Philippe; Langhoff, Stephen R. (Technical Monitor)

1994-01-01

38

Mononuclear, oligonuclear and polynuclear metal coordination compounds with 1,2,4-triazole derivatives as ligands  

Microsoft Academic Search

1,2,4-Triazole and its derivatives have gained great attention as ligands to transition metals by the fact that they unite the coordination geometry of both pyrazoles and imidazoles, and in addition exhibit a strong and typical property of acting as bridging ligands between two metal centres. In this bridging capacity, the 1,2,4-triazole ligands show a great coordination diversity, especially when the

Jaap G. Haasnoot

2000-01-01

39

Determination of binding constants of labile ligands in metal–ligand complexes containing carboxylic groups bound polymer by using breakthrough technique  

Microsoft Academic Search

This study was conducted to confirm the possibilities of determining the binding constants of ligands in metal–ligand complexes containing carboxylic groups bound polymer by using breakthrough technique. Aniline and o-anisidine were selected as model ligands. A mini column apparatus was used to study sorption of ligands onto ligand exchange resin. The experiments were conducted in a constant temperature at 25°C.

Ahmet Ayar; A. Ihsan Pekacar; Bedrettin Mercimek

2003-01-01

40

Metal sulfides in oxygenated aquatic systems: implications for the biotic ligand model.  

PubMed

The Biotic Ligand Model (BLM) attempts to predict metal toxicity to aquatic organisms on the basis of metal speciation and effects at the cell surface. Current versions of the BLM for silver and copper consider metal binding by inorganic ligands, dissolved organic matter (DOM) and also competition at the cell surface from calcium and protons (pH). Recent studies reported in the geochemical and ecotoxicological literature have indicated the importance of sulfide as a ligand, even in fully oxygenated aquatic systems. Speciation calculations for oxygenated waters do not currently include reduced sulfur as a ligand and as a consequence, no version of the BLM model has been published including reduced sulfur. This reflects the limitations on our knowledge regarding reduced sulfur in aquatic systems. In this paper we highlight the need to include reduced sulfur in the Biotic Ligand Model, with the interaction between silver and inorganic metal sulfides as a specific example. The geochemical importance of metal sulfides as ligands for silver and the effect of 'dissolved' metal sulfide and other ligands on metal toxicity and accumulation are described and reviewed. Recommendations are made for future work needed to incorporate sulfide ligands into the BLM's modeling framework. PMID:12356516

Bianchini, Adalto; Bowles, Karl C

2002-09-01

41

Synthesis, cytotoxic and hydrolytic studies of titanium complexes anchored by a tripodal diamine bis(phenolate) ligand.  

PubMed

The reactivity, cytotoxic studies and hydrolytic behaviour of diamine bis(phenolate) titanium complexes are reported. The reactions of [Ti((tBu2)O2NN')Cl]2(?-O) () with LiO(i)Pr or HO(i)Pr in the presence of NEt3, aiming at the synthesis of the alkoxido derivative of led to no reaction or to the synthesis of the monomeric complex [Ti((tBu2)O2NN')(O(i)Pr)2] (), respectively. A small amount of the alkoxidotitanium dimer [Ti((tBu2)O2NN')(O(i)Pr)]2(?-O) () crystallized out of a solution of and DFT calculations showed that the transformation of into is a thermodynamically favorable process in the presence of a base (NEt3) (?G = -14.7 kcal mol(-1)). was quantitatively obtained through the direct reaction of the ligand precursor H2((tBu2)O2NN') with titanium tetra(isopropoxido). Further reaction of with an excess of TMSCl was revealed to be the most suitable method for the preparation of [Ti((tBu2)O2NN')Cl2] (). and disclosed cytotoxic activity towards HeLa, Fem-x, MDA-MB-361 and K562 cells and exhibited moderate binding affinity to FS-DNA. (1)H NMR hydrolysis studies attested the fast decomposition of in the presence of D2O. The hydrolysis of is slower and proceeds through the formation of [Ti((tBu2)O2NN')(OH)]2(?-O) () that was crystallographically characterized. Upon D2O addition immediately forms complex new species, stable in solution for long periods (weeks). PMID:25338018

Barroso, Sónia; Coelho, Ana M; Gómez-Ruiz, Santiago; Calhorda, Maria José; Zižak, Zeljko; Kalu?erovi?, Goran N; Martins, Ana M

2014-11-01

42

Modelling of trace metal uptake by roots taking into account complexation by exogenous organic ligands  

NASA Astrophysics Data System (ADS)

The context of this study is phytoextraction of soil trace metals such as Cd, Pb or Zn. Trace metal transfer from soil to plant depends on physical and chemical processes such as minerals alteration, transport, adsorption/desorption, reactions in solution and biological processes including the action of plant roots and of associated micro-flora. Complexation of metal ions by organic ligands is considered to play a role on the availability of trace metals for roots in particular in the event that synthetic ligands (EDTA, NTA, etc.) are added to the soil to increase the solubility of the contaminants. As this role is not clearly understood, we wanted to simulate it in order to quantify the effect of organic ligands on root uptake of trace metals and produce a tool which could help in optimizing the conditions of phytoextraction.We studied the effect of an aminocarboxilate ligand on the absorption of the metal ion by roots, both in hydroponic solution and in soil solution, for which we had to formalize the buffer power for the metal. We assumed that the hydrated metal ion is the only form which can be absorbed by the plants. Transport and reaction processes were modelled for a system made up of the metal M, a ligand L and the metal complex ML. The Tinker-Nye-Barber model was adapted to describe the transport of solutes M, L and ML in the soil and absorption of M by the roots. This allowed to represent the interactions between transport, chelating reactions, absorption of the solutes at the root surface, root growth with time, in order to simulate metal uptake by a whole root system.Several assumptions were tested such as i) absorption of the metal by an infinite sink and according to a Michaelis-Menten kinetics, solutes transport by diffusion with and without ii) mass flow and iii) soil buffer power for the ligand L. In hydroponic solution (without soil buffer power), ligands decreased the trace metal flux towards roots, as they reduced the concentration of hydrated metal ion. In soil, depending on the L/M ratio, the presence of metal complexes could increase the metal flux taken up by roots since the ligand desorbed the metal on soil solid phase while the complex dissociated and provided metal ions to the solution in the vicinity of the root.The model enabled to surround the conditions in which phytoextraction is thus optimized. In addition of complexation by organic ligands added to the soil, we expect to integrate complexation by roots organic exudates and by soil organic matter, as well as the competition of the metal ions with Ca2+ et H+.

Jean-Marc, Custos; Christian, Moyne; Sterckeman, Thibault

2010-05-01

43

Effect of vacancy defects in graphene on metal anchoring and hydrogen adsorption  

NASA Astrophysics Data System (ADS)

The dispersion of transition and alkaline-earth metals on defective graphenes is studied using first-principles calculations. The effect of vacancy defects on binding properties of metal atoms to the graphene and with hydrogen molecules is particularly investigated. It is shown that vacancy defects enhance efficiently the metal binding energy and thus its dispersion, particularly for alkaline-earth metals. Mg on vacancy defects shows a substantial increase in its binding energy and hydrogen uptake capacity. Among metals considered, Ca-vacancy complexes are found to exhibit the most favorable hydrogen adsorption characteristics in terms of the binding energy and the capacity.

Kim, Gyubong; Jhi, Seung-Hoon; Lim, Seokho; Park, Noejung

2009-04-01

44

Ligand effect on the adsorption of heavy metals: The sulfate — Cadmium — Goethite case  

Microsoft Academic Search

Complexing ligands may alter the adsorption behaviour of heavy metals compared to a ligand free system, either by changes in solution speciation, or by interactions at the adsorbing mineral surface. In this paper the effect of sulfate on the adsorption of cadmium onto goethite has been studied. Adsorption experiments under defined conditions revealed the following effects: Cadmium adsorption from sulfate

Ulrich Hoins; Laurent Charlet; Hans Sticher

1993-01-01

45

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

SciTech Connect

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW{sub 12}O{sub 40}]{sub 2}[Cu{sub 2}(Phen){sub 4}Cl](H{sub 2}4, 4 Prime -bpy){sub 4}{center_dot}H{sub 3}O{center_dot}5H{sub 2}O (1) and [HPW{sub 12}O{sub 40}][Cd{sub 2}(Phen){sub 4}Cl{sub 2}](4, 4 Prime -bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW{sub 12}O{sub 40}]{sup 5-}, metal halide clusters [Cu{sub 2}(Phen){sub 4}Cl]{sup +}and 4, 4 Prime -bpy ligands, while compound 2 is constructed from [PW{sub 12}O{sub 40}]{sup 3-}, metal halide cluster [Cd{sub 2}(Phen){sub 4}Cl{sub 2}]{sup 2+} and 4, 4 Prime -bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. - Graphical Abstract: Two new compounds have been synthesized and characterized. Structure analyses revealed that the two compounds are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Highlights: Black-Right-Pointing-Pointer First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Two different kinds of metal halide clusters. Black-Right-Pointing-Pointer Supramolecular structures based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Hybridization of three different of building blocks.

Wang Lamei; Fan Yong; Wang Yan; Xiao Lina; Hu Yangyang; Peng Yu; Wang Tiegang; Gao Zhongmin; Zheng Dafang [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Cui Xiaobing, E-mail: cuixb@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Xu Jiqing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China)

2012-07-15

46

Metallophore mapping in complex matrices by metal isotope coded profiling of organic ligands.  

PubMed

Metal isotope coded profiling (MICP) introduces a universal discovery platform for metal chelating natural products that act as metallophores, ion buffers or sequestering agents. The detection of cation and oxoanion complexing ligands is facilitated by the identification of unique isotopic signatures created by the application of isotopically pure metals. PMID:25298978

Deicke, Michael; Mohr, Jan Frieder; Bellenger, Jean-Philippe; Wichard, Thomas

2014-12-01

47

The ligand-promoted mobilisation of metal ions from mineral surfaces  

Microsoft Academic Search

Many metals such as Fe, Mo, Cu, Zn etc have been identified as essential micronutrients for plants and microorganisms. These metals have to be mobilised from mineral surfaces in contact with crustal fluids in order to be available to living cells. Many studies have shown the importance of chelation in the mobilisation of metal ions into these fluids. The ligand-promoted

C. V. Putnis

2003-01-01

48

Actinide(III) and lanthanide(III) complexes with nitrogen ligands: Counterions and ligand substituent effects on the metal–ligand bond  

Microsoft Academic Search

Relativistic density functional theory calculations are reported for actinide(III) (An=U, Am, Cm) and lanthanide(III) (Ln=La, Nd) complexes with tridentate aromatic nitrogen ligands. Calculations have been performed on 2,2?:6?,2?-terpyridine (Terpy) complexes with various species in the first coordination sphere of the metal ion besides one Terpy ligand (H2O, Cl? and NO3?) and on bis(1,2-4-triazin-3-yl)pyridine (Btp) complexes with various susbtituents attached to

Dominique Guillaumont

2006-01-01

49

Metal-metal bonding in low-coordinate dicobalt complexes supported by phosphinoamide ligands.  

PubMed

Homobimetallic dicobalt complexes featuring metal centers in different coordination environments have been synthesized, and their multielectron redox chemistry has been investigated. Treatment of CoX(2) with MesNKP(i)Pr(2) leads to self-assembly of [(THF)Co(MesNP(i)Pr(2))(2)(?-X)CoX] [X = Cl (1), I (2)], with one Co center bound to two amide donors and the other bound to two phosphine donors. Upon two-electron reduction, a ligand rearrangement occurs to generate the symmetric species (PMe(3))Co(MesNP(i)Pr(2))(2)Co(PMe(3)) (3), where each Co has an identical mixed P/N donor set. One-electron oxidation of 3 to generate a mixed valence species promotes a ligand reararrangement back to an asymmetric configuration in [(THF)Co(MesNP(i)Pr(2))(2)Co(PMe(3))][PF(6)] (4). Complexes 1-4 have been structurally characterized, and their metal-metal interactions are discussed in the context of computational results. PMID:23298415

Mathialagan, Ramyaa; Kuppuswamy, Subramaniam; De Denko, Alexandra T; Bezpalko, Mark W; Foxman, Bruce M; Thomas, Christine M

2013-01-18

50

Organophosphorus Ligands in Studies of Metal Complexes. Investigations of Ligand Exchange and Multielement Trace Analysis using Dithiophosphinic Ligands  

Microsoft Academic Search

On mixing organic solutions of [Et2PS2]M\\/n and [Prop2PS2]M\\/n [M=Pd(II), Pt(II), Rh(III), lr(III), Cr(III)] an equilibrium is obtained containing statistical amounts of the corresponding mixed ligand complexes as can be shown by 31P{H}-NMR, HPLC and FD-MS. With Pt(II)- and Pd(II)-chelates the kinetics of ligand exchange was determined by HPLC. Mixed complexes ML2L? and MLL?2 were isolated from the equilibrium solutions in

W. Kuchen; E. Lehnert; Peter Panster; Peter Kleinschmit

1987-01-01

51

Design and Formation of a Large, Tetrahedral, Metal-ligand Cluster Using 1,1'-Binaphthyl Ligands  

SciTech Connect

Many chemists have been fascinated with the development of discrete supramolecular structures that encapsulate guest molecules. These structures can be assembled through covalent or hydrogen bonds, electrostatic or metal-ligand interactions. These host structures have provided valuable insight into the forces involved in small molecule recognition. Our work has focused on the design and study of metal-ligand clusters of varying sizes. The naphthalene [M{sub 4}L{sub 6}]{sup 12-} cluster 1, shown in Figure 1, has demonstrated diastereoselective guest binding and chiral induction properties as well as the ability to catalyze reactions carried out inside the cavity in an enzyme-like manner. However, the size of the cavity (ca. 300-500 {angstrom}{sup 3}) has often limited the scope of substrates for these transformations.

Biros, Shannon M.; Yeh, Robert M.; Raymond, Kenneth N.

2008-03-13

52

Metal effects on ligand non-innocence in Group 5 complexes of the redox-active [ONO] pincer ligand.  

PubMed

Isostructural vanadium, niobium and tantalum complexes of bis(3,5-di-tert-butyl-2-phenol)amine ([ONO]H3), were prepared and characterized to evaluate the impact of the metal ion on redox-activity of the ligand platform. New vanadium and niobium complexes with the general formula, [ONO]MCl2L (M = V, L = THF, 1-V; M = Nb, L = Et2O, 1-Nb) were prepared and structurally analysed by X-ray crystallography. The solid-state structures indicate that the niobium derivative is electronically analogous to the tantalum analog 1-Ta, containing a reduced (ONO) ligand and a niobium(v) metal ion, [ONO(cat)]Nb(V)Cl2(OEt2); whereas, the vanadium derivative is best described as a vanadium(iv) complex, [ONO(sq)]V(IV)Cl2(THF). One-electron oxidation was carried out on all three metal complexes to afford [ONO]MCl3 derivatives (3-V, 3-Nb, 3-Ta). For all three derivatives, oxidation occurs at the (ONO) ligand. In the cases of niobium and tantalum, electronically similar complexes characterized as [ONO(sq)]M(V)Cl3 were obtained and for vanadium, ligand-based oxidation led to the formation of a complex best described as [ONO(q)]V(IV)Cl3. All complexes were characterized by spectroscopic and electrochemical methods. DFT and TD-DFT calculations were used to probe the electronic structure of the complexes and help verify the different electronic structures stemming from changes to the coordinated metal ion. PMID:25352212

Hananouchi, Steven; Krull, Brandon T; Ziller, Joseph W; Furche, Filipp; Heyduk, Alan F

2014-11-18

53

A mixed-valence copper coordination polymer generated by hydrothermal metal/ligand redox reactions  

E-print Network

A mixed-valence copper coordination polymer generated by hydrothermal metal/ligand redox reactions A novel coordination polymer of mixed-valence copper(I,II) with 4,4A-bipyridine and in situ oxidized frameworks of coordination polymers, based on complexes of transition metals and multifunctional bridging

Li, Jing

54

Cationic and neutral transition metal complexes with a tetramethylfulvene or trimethylallyldiene ligand  

Microsoft Academic Search

Published data on the synthesis and chemical properties of complexes of Group 4-10 transition metals (d elements) with eta 6-tetramethylfulvene and eta7-trimethylallyldiene ligands, formed from the pentamethylcyclopentadienyl complexes of these metals, are described systematically. A description of the structures of these complexes in terms of a \\

Arkadii Z. Kreindlin; Margarita I. Rybinskaya

2004-01-01

55

Unusual metal coordination chemistry from an amino-amide derivative of 4-nitrophenol, a surprising ligand.  

PubMed

The simple ligand N-(2-aminoethyl)-2-hydroxy-5-nitrobenzamide () exhibits several coordination modes depending on the reaction conditions, acting as a zwitterion on its own or being ionic in the presence of acid and depending on the concentration of metal present in a reaction, it can coordinate to the metal in either a 1:1 or a 1:2 metal:ligand mode. Furthermore, the role of solvent plays an important role in these complexation reactions with both four and six coordinate copper complexes being obtained using water as solvent but only six coordinate copper complexes obtained using acetonitrile as solvent. PMID:19789795

McGinley, John; McKee, Vickie; Toftlund, Hans; Walsh, John M D

2009-10-21

56

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

NASA Astrophysics Data System (ADS)

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW12O40]2[Cu2(Phen)4Cl](H24, 4'-bpy)4·H3O·5H2O (1) and [HPW12O40][Cd2(Phen)4Cl2](4, 4'-bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW12O40]5-, metal halide clusters [Cu2(Phen)4Cl]+and 4, 4'-bpy ligands, while compound 2 is constructed from [PW12O40]3-, metal halide cluster [Cd2(Phen)4Cl2]2+ and 4, 4'-bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands.

Wang, La-Mei; Fan, Yong; Wang, Yan; Xiao, Li-Na; Hu, Yang-Yang; Peng, Yu; Wang, Tie-Gang; Gao, Zhong-Min; Zheng, Da-Fang; Cui, Xiao-Bing; Xu, Ji-Qing

2012-07-01

57

The Effect of Substrates / Ligands on Metal Nanocatalysts Investigated By Quantitative Z-Contrast Imaging and High Resolution Electron Microscopy  

E-print Network

The Effect of Substrates / Ligands on Metal Nanocatalysts Investigated By Quantitative Z- Contrast of the cluster-substrates relationship for consideration in real applications. INTRODUCTION Nanocatalysts we

Frenkel, Anatoly

58

Structure simulation into a lamellar supramolecular network and calculation of the metal ions/ligands ratio  

PubMed Central

Background Research interest in phosphonates metal organic frameworks (MOF) has increased extremely in the last two decades, because of theirs fascinating and complex topology and structural flexibility. In this paper we present a mathematical model for ligand/metal ion ratio of an octahedral (Oh) network of cobalt vinylphosphonate (Co(vP)·H2O). Results A recurrent relationship of the ratio between the number of ligands and the number of metal ions in a lamellar octahedral (Oh) network Co(vP)·H2O, has been deducted by building the 3D network step by step using HyperChem 7.52 package. The mathematical relationship has been validated using X ray analysis, experimental thermogravimetric and elemental analysis data. Conclusions Based on deducted recurrence relationship, we can conclude prior to perform X ray analysis, that in the case of a thermogravimetric analysis pointing a ratio between the number of metal ions and ligands number around 1, the 3D network will have a central metal ion that corresponds to a single ligand. This relation is valid for every type of supramolecular network with divalent metal central ion Oh coordinated and bring valuable information with low effort and cost. PMID:22932493

2012-01-01

59

Supercritical carbon dioxide-soluble ligands for extracting actinide metal ions from porous solids (EMSP Project Number 64965)  

SciTech Connect

The objective of this project is to develop novel, substituted diphosphonic acid ligands that can be used for supercritical carbon dioxide extraction (SCDE) of actinide ions from solid wastes. Specifically, selected diphosphonic acids, which are known to form extremely stable complexes with actinides in aqueous and organic solution, are to be rendered carbon dioxide-soluble by the introduction of appropriate alkyl- or silicon-containing substituents. The metal complexation chemistry of these new ligands in SC-CO{sub 2} will then be investigated and techniques for their use in actinide extraction from porous solids developed. This report summarizes the work performed during the first 1.3 years of a 3-year program. Because the planned studies of metal complexation and the development of techniques for actinide removal from solids are dependent on the availability of suitable ligands, efforts to date have focused primarily on the synthesis of selected alkyl- or silicon-containing diphosphonic acids. The authors' principal targets have been derivatives in which the silicon-containing groups either serve as the ester function or are attached to the anchor carbon of the diphosphonic acid. Because methylenediphosphonic acid (MDPA) is commercially available and because its esterification with simple alcohols to yield symmetrical diesters is well-established, their initial studies have focused on this ligand and its reactions with silyl alcohols. Success has been achieved in the reaction of MDPA and its ethylene, propylene, and butylene analogs with 3-(trimethylsilyl)-1-propanol. Using a procedure similar to that previously employed for the synthesis of C-8 dialkylmethylenediphosphonic acids, this series of alkylenediphosphonic acids has been esterified in good yield (ca. 60%) to the symmetrically-substituted diesters. Vapor phase osmometric and cryoscopic studies of these compounds in toluene and 1-decanol, respectively, indicate that their aggregation properties closely parallel those of the dialkyl-substituted alkylenediphosphonic acids, specifically, the P,P{prime}-bis(2-ethylhexyl)alkylenediphosphonic acids, H{sub 2}DEH[ADP]. Infrared spectroscopy and molecular mechanics methods have been employed to obtain information about the structures of the dimers of P,P{prime}-di-[3-(trimethylsilyl)-1-propylene]methylenediphosphonic acid, H{sub 2}TMSP[MDP], and its propylene analog. Infrared spectroscopy has also been employed to provide qualitative information on the binding of various metal ions by H{sub 2}TMSP[MDP]. The metal complexation properties of this ligand have been found to be similar to those of di-(2-ethylhexyl)methylenediphosphonic acid, examined previously. Studies of the extraction of various cations (e.g., Fe(III), Th(IV), Am(III)) by H{sub 2}TMSP[MDP] and its ethylene analog in conventional organic diluents (e.g., o-xylene) indicate that the extraction behavior of the silyl-derivatized diphosphonic acids closely mimics that of conventional alkylenediphosphonic acids. Thus, derivatization has no adverse impact on the complexation or extraction properties of the diphosphonic acids.

Dietz, M. L.; Barrans, Jr., R. E.; Herlinger, A. W.; Brennecke, J. F.

2000-04-24

60

The Calculation of Accurate Metal-Ligand Bond Energies  

NASA Technical Reports Server (NTRS)

The optimization of the geometry and calculation of zero-point energies are carried out at the B3LYP level of theory. The bond energies are determined at this level, as well as at the CCSD(T) level using very large basis sets. The successive OH bond energies to the first row transition metal cations are reported. For most systems there has been an experimental determination of the first OH. In general, the CCSD(T) values are in good agreement with experiment. The bonding changes from mostly covalent for the early metals to mostly electrostatic for the late transition metal systems.

Bauschlicher, Charles W.; Partridge, Harry, III; Ricca, Alessandra; Arnold, James O. (Technical Monitor)

1997-01-01

61

Tuning the topology and functionality of metal-organic frameworks by ligand design.  

PubMed

Metal-organic frameworks (MOFs)-highly crystalline hybrid materials that combine metal ions with rigid organic ligands-have emerged as an important class of porous materials. The organic ligands add flexibility and diversity to the chemical structures and functions of these materials. In this Account, we summarize our laboratory's experience in tuning the topology and functionality of MOFs by ligand design. These investigations have led to new materials with interesting properties. By using a ligand that can adopt different symmetry conformations through free internal bond rotation, we have obtained two MOFs that are supramolecular stereoisomers of each other at different reaction temperatures. In another case, where the dimerized ligands function as a D(3)-Piedfort unit spacer, we achieve chiral (10,3)-a networks. In the design of MOF-based materials for hydrogen and methane storage, we focused on increasing the gas affinity of frameworks by using ligands with different geometries to control the pore size and effectively introduce unsaturated metal centers (UMCs) into the framework. Framework interpenetration in PCN-6 (PCN stands for porous coordination network) can lead to higher hydrogen uptake. Because of the proper alignment of the UMCs, PCN-12 holds the record for uptake of hydrogen at 77 K/760 Torr. In the case of methane storage, PCN-14 with anthracene-derived ligand achieves breakthrough storage capacity, at a level 28% higher than the U.S. Department of Energy target. Selective gas adsorption requires a pore size comparable to that of the target gas molecules; therefore, we use bulky ligands and network interpenetration to reduce the pore size. In addition, with the help of an amphiphilic ligand, we were able to use temperature to continuously change pore size in a 2D layer MOF. Adding charge to an organic ligand can also stabilize frameworks. By ionizing the amine group within mesoMOF-1, the resulting electronic repulsion keeps the network from collapsing, giving rise to the first case of mesoporous MOF that demonstrates the type IV isotherm. We use dendritic hexacarboxylate ligands to synthesize an isoreticular series of MOFs with (3,24)-connected network topology. The cuboctahedral cages serve as building blocks that narrow the opening of the mesocavities into microwindows and stabilize these MOFs. The resulting materials have exceptionally high surface areas and hydrogen uptake capacities. Despite the many achievements in MOF development, there is still ample opportunity for further exploration. We will be continuing our efforts and look forward to contributing to this blossoming field in the next decade. PMID:21126015

Zhao, Dan; Timmons, Daren J; Yuan, Daqiang; Zhou, Hong-Cai

2011-02-15

62

Metal complexes of ONO donor Schiff base ligand as a new class of bioactive compounds; Synthesis, characterization and biological evolution  

NASA Astrophysics Data System (ADS)

Present work reviews that, the synthesis of (E)-N";-((7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)benzohydrazide [L] ligand and their metal complexes. The colored complexes were prepared of type [M2+L]X2, where M2+ = Mn, Co, Ni, Cu, Sr and Cd, L = (7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)benzohydrazide, X = Cl-. Ligand derived from the condensation of 8-formyl-7-hydroxy-4-methylcoumarin and benzohydrazide in the molar ratio 1:1 and in the molar ratio 1:2 for metal complexes have been prepared. The chelation of the ligand to metal ions occurs through the both oxygen groups, as well as the nitrogen atoms of the azomethine group of the ligand. Reactions of the Schiff base ligand with Manganese(II), Cobalt(II), Nickel(II), Copper(II), Strontium(II), and Cadmium(II) afforded the corresponding metal complexes. The structures of the obtained ligand and their respective metal complexes were elucidated by infra-red, elemental analysis, Double beam UV-visible spectra, conductometric measurements, magnetic susceptibility measurements and also thermochemical studies. The metal complex exhibits octahedral coordination geometrical arrangement. Schiff base ligand and their metal complexes were tested against antioxidants, antidiabetic and antimicrobial activities have been studied. The Schiff base metal complexes emerges effective ?-glucosidase inhibitory activity than free Schiff base ligand.

Kumar Naik, K. H.; Selvaraj, S.; Naik, Nagaraja

2014-10-01

63

Estimating the acidity of transition metal hydride and dihydrogen complexes by adding ligand acidity constants.  

PubMed

A simple equation (pKa(THF) = ?AL + Ccharge + Cnd + Cd6) can be used to obtain an estimate of the pKa of diamagnetic transition metal hydride and dihydrogen complexes in tetrahydrofuran, and, by use of conversion equations, in other solvents. It involves adding acidity constants AL for each of the ligands in the 5-, 6-, 7-, or 8-coordinate conjugate base complex of the hydride or dihydrogen complex along with a correction for the charge (Ccharge = -15, 0 or 30 for x = +1, 0 or -1 charge, respectively) and the periodic row of the transition metal (Cnd = 0 for 3d or 4d metal, 2 for 5d metal) as well as a correction for d(6) octahedral acids (Cd6 = 6 for d(6) metal ion in the acid, 0 for others) that are not dihydrogen complexes. Constants AL are provided for 13 commonly occurring ligand types; of these, nine neutral ligands are correlated with Lever's electrochemical ligand parameters EL. This method gives good estimates of the over 170 literature pKa values that range from less than zero to 50 with a standard deviation of 3 pKa units for complexes of the metals chromium to nickel, molybdenum, ruthenium to palladium, and tungsten to platinum in the periodic table. This approach allows a quick assessment of the acidity of hydride complexes found in nature (e.g., hydrogenases) and in industry (e.g., catalysis and hydrogen energy applications). The pKa values calculated for acids that have bulky or large bite angle chelating ligands deviate the most from this correlation. The method also provides an estimate of the base strength of the deprotonated form of the complex. PMID:24410025

Morris, Robert H

2014-02-01

64

Chirality control of quadruple helixes of metal strings by peripheral chiral ligands.  

PubMed

Chirality control of helixes with the ? (P) or ? (M) form is interesting in various fields such as extended metal atom chains (EMACs), in which the metal backbones are helically wrapped by four ligands. Herein, we report two EMACs, ?-[Ni5 ((-)camnpda)4 ] and ?-[Ni5 ((+)camnpda)4 ], whose chiralities are controlled by chiral ligands with naphthyridine and camphorsulfonyl groups. There is a large energy difference (108?kcal?mol(-1) ) between the two helical structures with one chiral ligand. Furthermore, the electron communication between [Ni2 ](3+) units is more pronounced than in [Ni5 (bna)4 Cl2 ](2+) (bna=binaphthyridylamido). The results demonstrate control of small-scale helical structure and set the stage for future development of chiral controlled base and nanoelectronic devices. PMID:25146243

Yu, Chung-Han; Kuo, Min-Shiang; Chuang, Ching-Yi; Lee, Gene-Hsiang; Hua, Shao-An; Jin, Bih-Yaw; Peng, Shie-Ming

2014-11-01

65

Theoretical dynamical studies of metal clusters and cluster-ligand systems  

SciTech Connect

In what follows we use the term cluster to designate a cohesive group of like atoms (molecules), i.e., bare ({open_quotes}neet{close_quotes} {open_quotes}naked{close_quotes}) clusters. More generally, the term is also used for organo- and inorganometallic compounds, i.e., ligated clusters. Although the approaches and techniques used by the various disciplines to study metal-ligand interactions are quite different, many of the central subjects and issues are common for them. The common subjects include possible geometric structures and isomeric forms, structural (isomerization) transitions, stability, fluxionality, structure-reactivity correlation (or lack of it), role of coordination, etc. However, the precise interpretation of these issues and the details emphasized by the different disciplines are dictated by the nature of the objects studied and may not, therefore, be identical. For example, questions regarding structures, isomerization transitions, fluxionality or even melting of metal clusters refer to the state and properties of the metal network itself. The same questions, when asked in connection with organo- and inorganometallic compounds, often refer to the arrangements and rearrangements of the ligands attached to a metal framework of a fixed structure. Of course, when required, the state of and changes in the metal framework are considered as well. The fields of metal-containing molecular compounds, surface science, and physics and chemistry of clusters furnish complementary information on a broad variety of metal-ligand systems. A comprehensive understanding of the nature and properties of these systems, as defined by the type and number of metal atoms and ligands involved, can be achieved only through a mutual awareness of and continuing progress in all of these research areas.

Jellinek, J.

1995-06-01

66

Metal-to-ligand and ligand-to-metal charge transfer in thin films of Prussian blue analogues investigated by X-ray absorption spectroscopy.  

PubMed

A series of thin films of Prussian blue analogues is investigated by X-ray absorption spectroscopy (XAS) at the Fe, Co and Mn L(2,3)-edges. The ligand field multiplet theory enables us to examine accurately the electronic structure of these materials. Experimental XAS spectra of CoFe Prussian blue analogues are successfully reproduced using a ground state configuration including metal-to-ligand (MLCT) and ligand-to-metal charge transfer (LMCT) at the Co and Fe L(2,3)-edges. In particular, a huge improvement is achieved for satellite peaks at the Co(iii) L(2,3)-edges compared to previous calculations in the literature based on LMCT effects only. On the other hand, XAS spectra of MnFe analogues synthesized for the first time, can be reproduced conveniently by taking into account either MLCT or LMCT depending on the conditions of the sample preparation. For each thin film, the proportion of the different oxidation states of Co, Fe and Mn is evaluated. Unexpectedly, this analysis reveals the presence of a significant amount of a reduced phase, which turns out to be strongly dependent on the sample synthesis and storage conditions. PMID:18818842

Bonhommeau, Sébastien; Pontius, Niko; Cobo, Saioa; Salmon, Lionel; de Groot, Frank M F; Molnár, Gábor; Bousseksou, Azzedine; Dürr, Hermann A; Eberhardt, Wolfgang

2008-10-14

67

Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin  

E-print Network

-CNISM, Universita della Tuscia, I-01100 Viterbo, Italy 2 Institute of Agro-environmental and Forest Biology-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light. The capability of controlling electron transfer processes through light pulses opens interesting perspectives

Tuscia, Università Degli Studi Della

68

Metal-humate interactions. 1. Discrete ligand and continuous distribution models  

SciTech Connect

In this paper the authors examine critically the theory underlying discrete and continuous multiligand models for metal-humate binding. The concepts and equations that unify the various models are presented, and a general solution to the fundamental integral equation for ion binding in a multiligand system is given. Particular attention is paid to the continuous distribution models (normal distribution, affinity spectrum, and continuous stability function) which are relatively new tools in the field of metal-humate complexation. It is shown that the lower half and extreme right of the Gaussian ligand distribution assumed in the normal distribution model never affect metal speciation measurably and hence are not knowable. It is also shown that an affinity spectrum does not correspond to an actual distribution of ligands; rather, each peak in the spectrum indicates the most probable stability constant controlling metal binding in a particular region of the experimental formation function. Application of the affinity spectrum model leads to a set of discrete ligands. A close examination of the continuous stability function model shows that it contains implicitly the same assumption as the affinity spectrum approach and thus leads also to discrete ligands.

Dzombak, D.A.; Fish, W.; Morel, F.M.M.

1986-07-01

69

Supramolecular assembly of metal-ligand chromophores for sensing and phosphorescent OLED applications.  

PubMed

The exploration of phosphorescent materials based on transition metal-ligand chromophoric complexes represents an important area of research in molecular materials. The knowledge and fundamental understanding of their photophysical properties offer a possible fine-tuning of their electronic absorption and luminescence properties. The strong propensity of d(8) transition metal compounds to form non-covalent metal···metal interactions facilitates supramolecular assembly and the formation of supramolecular nanostructures with interesting photophysical properties. The introduction of supramolecular assembly with hierarchical complexity involving non-covalent interactions could lead to research dimensions of unlimited possibilities and opportunities. This article briefly summarizes the latest progress on the use of d(8) metal-ligand chromophores as chemosensors, as exemplified by alkynylplatinum(II) complexes with emphasis on supramolecular assembly involving non-covalent interactions, and the recent advances in the utilization of d(8) metal-ligand phosphors, as exemplified by alkynylgold(III) system, for the exploration and development of phosphorescent OLEDs. PMID:24777887

Wong, Keith Man-Chung; Chan, Maggie Mei-Yee; Yam, Vivian Wing-Wah

2014-08-20

70

Excited state evolution towards ligand loss and ligand chelation at group 6 metal carbonyl centres.  

PubMed

The photochemistry and photophysics of three model "half-sandwich" complexes (?(6)-benzophenone)Cr(CO)3, (?(6)-styrene)Cr(CO)3, and (?(6)-allylbenzene)Cr(CO)3 were investigated using pico-second time-resolved infrared spectroscopy and time-dependent density functional theory methods. The (?(6)-benzophenone)Cr(CO)3 complex was studied using two excitation wavelengths (470 and 320 nm) while the remaining complexes were irradiated using 400 nm light. Two independent excited states were detected spectroscopically for each complex, one an unreactive excited state of metal-to-arene charge-transfer character and the other with metal-to-carbonyl charge transfer character. This second excited state leads to an arrested release of CO on the pico-second time-scale. Low-energy excitation (470 nm) of (?(6)-benzophenone)Cr(CO)3 populated only the unreactive excited state which simply relaxes to the parent complex. Higher energy irradiation (320 nm) induced CO-loss. Irradiation of (?(6)-styrene)Cr(CO)3, or (?(6)-allylbenzene)Cr(CO)3 at 400 nm provided evidence for the simultaneous population of both the reactive and unreactive excited states. The efficiency at which the unreactive excited state is populated depends on the degree of conjugation of the substituent with the arene ?-system and this affects the efficiency of the CO-loss process. The quantum yield of CO-loss is 0.50 for (?(6)-allylbenzene)Cr(CO)3 and 0.43 for (?(6)-styrene)Cr(CO)3. These studies provide evidence for the existence of two photophysical routes to CO loss, a minor ultrafast route and an arrested mechanism involving the intermediate population of a reactive excited state. This reactive excited state either relaxes to reform the parent species or eject CO. Thus the quantum yield of the CO-loss is strongly dependent on the excitation wavelength. Time-dependent density functional theory calculations confirm that the state responsible for ultrafast CO-loss has significant metal-centred character while the reactive state responsible for the arrested CO-loss has significant metal-to-carbonyl charge-transfer character. The CO-loss product (?(6)-allylbenzene)Cr(CO)2 formed following irradiation of (?(6)-allylbenzene)Cr(CO)3 reacts further with the pendent alkenyl group to form the chelate product (?(6),?(2)-allylbenzene)Cr(CO)2. PMID:25093429

Manton, Jennifer C; Amirjalayer, Saeed; Coleman, Anthony C; McMahon, Suzanne; Harvey, Emma C; Greetham, Gregory M; Clark, Ian P; Buma, Wybren Jan; Woutersen, Sander; Pryce, Mary T; Long, Conor

2014-11-12

71

Cell surface-anchored SR-PSOX\\/CXC chemokine ligand 16 mediates firm adhesion of CXC chemokine receptor 6-expressing cells  

Microsoft Academic Search

Direct contacts between dendritic cells (DCs) and T cells or natural killer T (NKT) cells play important roles in primary and secondary im- mune responses. SR-PSOX\\/CXC chemokine ligand 16 (CXCL16), which is selectively expressed on DCs and macrophages, is a scavenger receptor for oxidized low-density lipoprotein and also the che- mokine ligand for a G protein-coupled receptor CXC chemokine receptor

Takeshi Shimaoka; Takashi Nakayama; Noriko Fukumoto; Noriaki Kume; Shu Takahashi; Junko Yamaguchi; Manabu Minami; Kazutaka Hayashida; Toru Kita; Jun Ohsumi; Osamu Yoshie; Shin Yonehara

2003-01-01

72

Synthesis and metal complexes of chiral c(2)-symmetric diamino-bisoxazoline ligands.  

PubMed

A synthetic route to tetradentate chiral N(4) ligands has been developed with the aim to study the potential of corresponding iron and manganese complexes as catalysts for enantioselective epoxidation. These ligands, which contain two oxazoline rings and two trialkylamino groups as coordinating units, are readily prepared in enantiomerically pure form by the reaction of chiral 2-chloromethyloxazolines with achiral N,N'-dimethylethane-1,2-diamine or chiral (R,R)-N,N'-dimethylcyclohexane-1,2-diamine. The ligands derived from N,N'-dimethylethane-1,2-diamine reacted with anhydrous metal halides MnCl(2) and FeCl(2) in a stereoselective manner to give octahedral mononuclear complexes that have the general formula Delta-[(L)MCl(2)]. In contrast, the ligands derived from N,N'-dimethylcyclohexane-1,2-diamine formed complexes with different coordination modes depending on the diastereomer employed: in one case the metal ion was found to be pentacoordinate, in the other case a hexacoordinated complex was observed. The structure of a series of Fe and Mn complexes was determined by X-ray analysis. The coordination chemistry of these ligands was further studied by X-ray and NMR analyses of the diamagnetic isostructural complexes [(L)ZnCl(2)]. Analogous ionic complexes, which were prepared by removing chloride with silver trifluoromethanesulfonate or hexafluoroantimonate, were tested as catalysts for the epoxidation of olefins. PMID:17721893

Guillemot, Geoffroy; Neuburger, Markus; Pfaltz, Andreas

2007-01-01

73

Metal coordination architectures of triazole-based ligands: Effect of the backbone of bridging ligands on the construction of polymers  

NASA Astrophysics Data System (ADS)

In our efforts to investigate the influence of the backbone of different triazole-based bridging ligands on the structure of their metal complexes, four new coordination polymers, {[Cu(L1)2(H2O)2]Cl2}n (1), [Cu(L2)2Cl2]n (2), [Co(L2)2(SCN)2]n (3), and [Cu(L3)2(NO3)2]n (4), (L1 = 1,2-bis(triazol-1-ylmethyl)benzene, L2 = 1,3-bis(triazol-1-ylmethyl)benzene, L3 = 1,4-bis(triazol-1-ylmethyl)benzene), have been synthesized. All the complexes have been structurally characterized by IR, elemental analysis and single-crystal X-ray diffraction. Structural analyses show that 1 and 4 possess 2D coordination networks with (4,4) topology, and 1 shows a diagonal-diagonal inclined interpenetration. 2 and 3 are isostructural and feature 1D double chain, which further connected by C-H···Cl or ?···? weak interactions to form 2D supramolecular frameworks. The results show that the structures of ligands (with different non-coordination backbone spacers) play important roles in the formation of such coordination architectures. Furthermore, EPR (Electron Paramagnetic Resonance) spectra of CuII complexes (1, 2, and 4) have been investigated in the solid state at room temperature.

Du, Jian-Long; Hu, Tong-Liang; Bu, Xian-He

2012-04-01

74

Polyimido Sulfur(VI) Phosphanyl Ligand in Metal Complexation.  

PubMed

Herein, new complexes containing the [Ph2 PCH2 S(NtBu)3 ](-) anion are presented, supplying three imido nitrogen atoms and a remote phosphorus atom as potential donor sites to main group and transition-metal cations. The lithiated complex [(tmeda)Li{(NtBu)3 SCH2 PPh2 }] (1) is an excellent starting material in transmetalation reactions. Herein, the transition-metal complexes [M{(NtBu)3 SCH2 PPh2 }2 ] (M=Mn (2), Ni (3), Zn (4)) were synthesized and structurally characterized. Their isotypical molecules show SN2 chelation and no employment of the adjacent phosphorus atom in coordination. The third pendent imido group is always twisted toward the vacant face of the tetrahedrally coordinated sulfur atom. PMID:25284488

Carl, Elena; Stalke, Dietmar

2014-11-24

75

Synthesis and characterization of novel nitrogen-containing ligands for metal ion separations  

NASA Astrophysics Data System (ADS)

A serious limiting factor in the continued development of nuclear power is the disposal of high-level radioactive waste from spent nuclear fuel. The PUREX process can be used for the recovery of U and Pu, but it does not separate the products of fission which are potentially useful, but currently cause most of our problems with radioactive waste. An important complicating factor is the presence of large amounts of lanthanides in dissolved spent nuclear fuel. The separation of lanthanides (Ln) from actinides (An) is therefore critical to the future of nuclear power. One approach to recovering these materials and decreasing the volume of the radioactive waste is the development of novel, highly selective organic ligands for the lanthanide and actinide ions. The focus of this dissertation is to design and synthesize new tridentate polyaza-ligands expected to exhibit affinity for first-row transition metals, lanthanides and actinides. In general, these chelating agents are structurally and functionally related to the pyridine and bipyridine bis-triazinyl compounds that have been investigated for potential application as separations agents for radioactive materials. Selected 1,2,3-triazoles have been synthesized using Sharpless' "Click Chemistry". Variation of the backbone and substituents on the triazole ring allows for facile modification of the cation binding pocket and phase compatibility properties of the new compounds. Characterization of the new ligands was performed using conventional analytical methods. Overall, the studies with three different ligands revealed useful information about the continuing effort of ligand design for actinide (III)/lanthanide (III) separations. Crystal structures established the purity of the organic molecules by showing that the PTMP and BDTP ligands are able to bind transition metals. Also, it was shown that the BDTB ligand was able to bind to Nd 3+ as observed from the spectrophotometric titrations and the calculated binding constant. To increase the lipophilicity of the ligand, the addition of an alkyl chain on the 4-position of the pyridine ring could be made. This confirms that scientists are advancing in the area of ligand design and hopefully one day the ligand with all of the desired characteristics will be used to close the nuclear fuel cycle.

Hoch, Cortney Leigh

76

Electrophilic metal alkyl chemistry in new ligand environments  

SciTech Connect

Cationic group 4 and actinide Cp{sub 2}MR{sup +} metallocenes, and isolobal neutral group 3 and lanthanide Cp{sub 2}MR analogs, are exceptionally reactive in insertion and {sigma}-bond metathesis processes, and have been exploited extensively in catalysis and synthesis, most notably single-site olefin polymerization. The objectives of recent work were to design new electrophilic metal alkyls based on non-Cp{sub 2}M structures, and to exploit these systems in fundamental and applied studies related to olefin polymerization and other catalytic reactions. Key results are reported in the following areas: discrete non-metallocene cationic group 4 alkyls, activation of non-metallocene compounds with methylalumoxane, and cationic aluminum alkyl compounds. Numerous structural formulas are included.

Jordan, Richard F.

2002-09-11

77

Metal and ligand effects on bonding in group 6 complexes of redox-active amidodiphenoxides.  

PubMed

Group 6 complexes M(ONO)2 (M = Cr, Mo, W; ONO = bis(2-oxy-3,5-di-tert-butylphenyl)amide) are prepared by the reaction of divalent metal halide precursors with Pb(ONO(Q))2. Analogous complexes containing the 2,4,6,8-tetra-tert-butyl-1,9-dioxophenoxazinate ligand (DOPO) are prepared by protonolysis of chromocene with H(DOPO(Q)) or by reaction of Pb(DOPO(Q))2 with M2Br4(CO)8 (M = Mo, W). The molybdenum and tungsten complexes are symmetrical, octahedral compounds for which spectroscopic data are consistent with M(VI) complexes with fully reduced [L(Cat)](3-) ligands. Quantitative analysis of the intraligand bond lengths, by comparison with literature standards, allows calculation of metrical oxidation states (MOS) for the ONO ligands. The MOS values of the tungsten and molybdenum complexes indicate that ? donation from the ligand is weak and that differences between the ONO and DOPO ligands are small. In both the solid state and in solution, Cr(DOPO)2 is paramagnetic with localized quinone and semiquinone ligands bound to Cr(III). The geometry and electronic structure of Cr(ONO)2 differ in the solid state and in solution, as determined by crystallography, magnetic measurements, and Cr K-edge X-ray absorption spectroscopy. In solution, the structure resembles that of the DOPO analogue. In contrast, solid Cr(ONO)2 is a singlet, and X-ray absorption near-edge spectroscopy indicates that the chromium is significantly more oxidized in the solid state than in solution. An electronic description compounds to that of the tungsten and molybdenum analogues, but with considerably more charge transfer from the ligand to chromium via ? donation, is in agreement with the experimental observations. PMID:25247396

Ranis, Leila G; Werellapatha, Kalpani; Pietrini, Nicholas J; Bunker, Bruce A; Brown, Seth N

2014-10-01

78

III-V nanocrystals capped with molecular metal chalcogenide ligands: high electron mobility and ambipolar photoresponse.  

PubMed

In this work, we synthesized InP and InAs nanocrystals (NCs) capped with different inorganic ligands, including various molecular metal chalcogenide complexes (MCCs) and chalcogenide ions. We found that MCCs and chalcogenide ions can quantitatively displace organic ligands from the surface of III-V NCs and serve as the inorganic capping groups for III-V NC surfaces. These inorganic ligands stabilize colloidal solutions of InP and InAs NCs in polar solvents and greatly facilitate charge transport between individual NCs. Charge transport studies revealed high electron mobility in the films of MCC-capped InP and InAs NCs. For example, we found that bridging InAs NCs with Cu(7)S(4)(-) MCC ligands can lead to very high electron mobility exceeding 15 cm(2)/(V s). In addition, we observed unprecedented ambipolar (positive/negative) photoresponse of MCC-capped InAs NC solids that changed sign depending on the ligand chemistry, illumination wavelength, and doping of the NC solid. For example, the sign of photoconductance of InAs NCs capped with Cu(7)S(4)(-) or Sn(2)S(6)(4-) ions converted from positive at 0.80 and 0.95 eV to negative at 1.27 and 1.91 eV. We propose an explanation of this unusually complex photoconductivity of InAs NC solids. PMID:23267673

Liu, Wenyong; Lee, Jong-Soo; Talapin, Dmitri V

2013-01-30

79

Synthesis of new microbial pesticide metal complexes derived from coumarin-imine ligand  

NASA Astrophysics Data System (ADS)

A series of metal complexes of zinc(II), cadmium(II), copper(II), nickel(II) and palladium(II) have been synthesized from coumarin-imine ligand, 8-[(1E)-1-(2-aminophenyliminio)ethyl]-2-oxo-2H-chromen-7-olate, [HL]. The structures of the complexes were proposed in the light of their spectroscopic, molar conductance, magnetic and thermal studies. The ligand coordinated in a tridentate manner through the azomethine nitrogen, the phenolic oxygen and the amine nitrogen and all complexes were non-electrolytes with different geometrical arrangements around the central metal ion. Photoluminescence data unambiguously showed remarkable fluorescence enhancement to Zn2+ over other cations. The antimicrobial screening tests revealed that copper(II) complex exhibited the highest potency and its minimum inhibitory concentration on the enzymatic activities of the tested microbial species was determined. No toxin productivity was detected for all tested toxigenic species upon the exposure of copper complex.

Elhusseiny, Amel F.; Aazam, Elham S.; Al-Amri, Huda M.

2014-07-01

80

Cooperative thermodynamic control of selectivity in the self-assembly of rare earth metal-ligand helices.  

PubMed

Metal-selective self-assembly with rare-earth cations is possible with suitable rigid, symmetrical bis-tridentate ligands. Kinetically controlled formation is initially observed, with smaller cations preferentially incorporated. Over time, the more thermodynamically favorable complexes with larger metals are formed. This thermodynamic control is a cooperative supramolecular phenomenon and only occurs upon multiple-metal-based self-assembly: single-metal ML3 analogues do not show reversible selectivity. The selectivity is dependent on small variations in lanthanide ionic radius and occurs despite identical coordination-ligand coordination geometries and minor size differences in the rare-earth metals. PMID:24206215

Johnson, Amber M; Young, Michael C; Zhang, Xing; Julian, Ryan R; Hooley, Richard J

2013-11-27

81

Development of Imine Derivative Ligands for the Exocyclic Activation of Late Transition Metal Polymerization Catalysts  

Microsoft Academic Search

\\u000a Transition metal complexes bearing imine and imine derivative ligands represent a growing number of polymerization catalysts\\u000a in development. The ease of synthesis and large number of structural variations which are readily accessible make these systems\\u000a of great interest both academically and industrially. One subset of imine-based complexes are those which bear exocyclic functionality\\u000a which can interact with Lewis acids. These

Brian C. Peoples; René S. Rojas

82

Strong ferromagnetic metal-ligand exchange in a nickel bis(3,5-dipyridylverdazyl) complex  

PubMed Central

A new 1,5-dipyridyl verdazyl, synthesized from the corresponding dipyridyl hydrazone, coordinates nickel(II) to form a structurally characterized, pseudooctahedral complex analogous to Ni(terpy)22+. The unusually short Ni-verdazyl distance results in strong ferromagnetic exchange (JNi-rad=+300, Jrad-rad=+160 cm?1) between all three paramagnetic species along with a metal-ligand charge transfer band in the electronic spectrum. PMID:20697644

Brook, David J. R.; Richardson, Cardius; Haller, Benjamin C.; Hundley, Michael; Yee, Gordon

2011-01-01

83

Rare-Earth Metal Complexes Supported by Nitrogen-Containing Ligands in Olefin Polymerization  

Microsoft Academic Search

\\u000a In this review the recent developments in the synthesis of rare-earth metal complexes active in catalysis of olefin polymerization\\u000a are summarized. Alkyl (neutral and ate), cationic alkyl and hydrido complexes supported by nitrogen-containing ligands are\\u000a considered. The polymerization-active complexes are classified according to monomer (ethylene, ?-olefin, styrene), type of\\u000a compound (neutral alkyl, cationic alkyl, ate-alkyl, hydrido) and the number of

Alexander A. Trifonov

84

Dinuclear metal(II) complexes of polybenzimidazole ligands as carriers for DNA delivery  

Microsoft Academic Search

A metal-based nonviral carrier for DNA-transfer in gene therapy was synthesized and characterized. The strong intermolecular ?–? contacts are common in the observed dinuclear Cu2+ and Co2+ complexes of polybenzimidazole ligands. The affinity assays indicated that the strong binding of the complexes to DNA is driven by both electrostatic attractions between the complexes and DNA and the intercalation of the

Liang Liu; Hang Zhang; Xianggao Meng; Jun Yin; Dongfeng Li; Changlin Liu

2010-01-01

85

An evolutionarily conserved alternate metal ligand is important for activity in ?-isopropylmalate synthase from Mycobacterium tuberculosis.  

PubMed

Members of the DRE-TIM metallolyase superfamily rely on an active-site divalent cation to catalyze various reactions involving the making and breaking of carbon-carbon bonds. While the identity of the metal varies, the binding site is well-conserved at the superfamily level with an aspartic acid and two histidine residues acting as ligands to the metal. Previous structural and bioinformatics results indicate that the metal can adopt an alternate architecture through the addition of an asparagine residue as a fourth ligand. This asparagine residue is strictly conserved in all members of the DRE-TIM metallolyase superfamily except fungal homocitrate synthase (HCS-lys) where it is replaced with isoleucine. The role of this additional metal ligand in ?-isopropylmalate synthase from Mycobacterium tuberculosis (MtIPMS) has been investigated using site-directed mutagenesis. Substitution of the asparagine ligand with alanine or isoleucine results in inactive enzymes with respect to ?-isopropylmalate formation. Control experiments suggest that the substitutions have not drastically affected the enzyme's structure indicating that the asparagine residue is essential for catalysis. Interestingly, all enzyme variants retained acetyl CoA hydrolysis activity in the absence of ?-ketoisovalerate, similar to the wild-type enzyme. In contrast to the requirement of magnesium for ?-isopropylmalate formation, hydrolytic activity could be inhibited by the addition of magnesium chloride in wild-type, D81E, and N321A MtIPMS, but not in the other variants studied. Attempts to rescue loss of activity in N321I MtIPMS by mimicking the fungal HCS active site through the D81E/N321I double variant were unsuccessful. This suggests epistatic constraints in evolution of function in IPMS and HCS-lys enzymes. PMID:25064783

Frantom, Patrick A; Birman, Yuliya; Hays, Brittani N; Casey, Ashley K

2014-10-01

86

Synthesis, characterization and antimicrobial activities of mixed ligand transition metal complexes with isatin monohydrazone Schiff base ligands and heterocyclic nitrogen base.  

PubMed

Mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with various uninegative tridentate ligands derived from isatin monohydrazone with 2-hydroxynapthaldehyde/substituted salicylaldehyde and heterocyclic nitrogen base 8-hydroxyquinoline have been synthesized and characterized by elemental analysis, conductometric studies, magnetic susceptibility and spectroscopic techniques (IR, UV-VIS, NMR, mass and ESR). On the basis of these characterizations, it was revealed that Schiff base ligands existed as monobasic tridentate ONO bonded to metal ion through oxygen of carbonyl group, azomethine nitrogen and deprotonated hydroxyl oxygen and heterocyclic nitrogen base 8-hydroxyquinoline existed as monobasic bidentate ON bonded through oxygen of hydroxyl group and nitrogen of quinoline ring with octahedral or distorted octahedral geometry around metal ion. All the compounds have been tested in vitro against various pathogenic Gram positive bacteria, Gram negative bacteria and fungi using different concentrations (25, 50, 100, 200 ?g/mL) of ligands and their complexes. Comparative study of antimicrobial activity of ligands, and their mixed complexes indicated that complexes exhibit enhanced activity as compared to free ligands and copper(II) Cu(LIV)(Q)?H2O complex was found to be most potent antimicrobial agent. PMID:25129626

Devi, Jai; Batra, Nisha

2015-01-25

87

Highly Fluorescent Group 13 Metal Complexes with Cyclic, Aromatic Hydroxamic Acid Ligands  

SciTech Connect

The neutral complexes of two ligands based on the 1-oxo-2-hydroxy-isoquinoline (1,2-HOIQO) motif with group 13 metals (Al, Ga, In) show bright blue-violet luminescence in organic solvents. The corresponding transition can be attributed to ligand-centered singlet emission, characterized by a small Stokes shifts of only a few nm combined with lifetimes in the range between 1-3 ns. The fluorescence efficiency is high, with quantum yields of up to 37% in benzene solution. The crystal structure of one of the indium(III) complexes (trigonal space group R-3, a = b = 13.0384(15) {angstrom}, c = 32.870(8) {angstrom}, ? = {beta} = 90{sup o}, {gamma} = 120{sup o}, V = 4839.3(14) {angstrom}{sup 3}, Z = 6) shows a six-coordinate geometry around the indium center which is close to trigonal-prismatic, with a twist angle between the two trigonal faces of 20.7{sup o}. Time-dependent density functional theory (TD-DFT) calculations (Al and Ga: B3LYP/6-31G(d)); In: B3LYP/LANL2DZ of the fac and mer isomers with one of the two ligands indicate that there is no clear preference for either one of the isomeric forms of the metal complexes. In addition, the metal centers do not have a significant influence on the electronic structure, and as a consequence, on the predominant intraligand optical transitions.

Seitz, Michael; Moore, Evan G.; Raymond, Kenneth N.

2008-02-11

88

Surface Ligand Effects on Metal-Affinity Coordination to Quantum Dots: Implications for Nanoprobe Self-Assembly  

E-print Network

Surface Ligand Effects on Metal-Affinity Coordination to Quantum Dots: Implications for Nanoprobe strategy would be quick and facile with high affinity, would not require subsequent purification, and would exploiting ligand-receptor affinities such as biotin-avidin binding (8), and more general affinity

89

Four homochiral coordination polymers contain N-acetyl-L-tyrosine and different N-donor ligand: Influence of metal cations, ancillary ligands and coordination modes  

SciTech Connect

Using the chiral ligand N-acetyl-L-tyrosine (Hacty) and maintaining identical reaction conditions, Zn(II), Co(II), and Cd(II) salts provided four novel homochiral coordination polymers ([Zn(acty)(bipy){sub 2}(H{sub 2}O){sub 2}]·NO{sub 3}·2H{sub 2}O){sub n}1, ([Co(acty)(bipy){sub 2}(H{sub 2}O){sub 2}]·NO{sub 3}·2H{sub 2}O){sub n}2, ([Cd(acty){sub 2}(bipy)H{sub 2}O]·H{sub 2}O){sub n}3, and ([Cd(acty)(bpe){sub 2}(Ac)]·6H{sub 2}O){sub n}4 (bipy=4,4?-bipyridine; bpe=1,2-di(4-pyridyl)ethane) in the presence of ancillary ligands. Compounds 1 and 2 are isostructural 1D chain structures. The neighboring chains are further linked into a 3D supramolecular structure via ??? stacking and hydrogen bond interactions. Compound 3 shows a 2D network and 4 generates 1D infinite chains along the c-axis. Compounds 3 and 4 are further connected into 3D supramolecular network by hydrogen bond interactions. More importantly, coordination in acyl oxygen atoms and ancillary ligands (bpe) as monodentate decorating ligands in 4 are rarely reported. Ancillary ligands and metal cations significantly influence the structure of the complexes. The photoluminescence properties of 1, 3, and 4 were studied at room temperature. Circular dichroism (CD) of the complexes have been investigated. - Graphical abstract: Four new homochiral coordination polymers were prepared and structurally characterized, which investigate the influence of the ancillary ligands and metal ions on the design and synthesis of coordination polymers. Display Omitted - Highlights: • It is rarely reported that the chiral coordination polymers prepared with N-acetyl-L-tyrosine ligands. • The alkalescent acetyl oxygen atom is difficult to participate in coordination but it is happened in the N-acetyl-L-tyrosine ligands. • The ancillary ligands (4,4?-bipy and bpe) are present in an unusual coordination modes, monodentate decorating ligands in 1, 2 and 4. • Structure comparative analyses results indicate that the secondary ligands and metal ions influence the fabrication of these inorganic–organic arrangements.

Li, Meng-Li; Song, Hui-Hua, E-mail: flower9486@163.com

2013-10-15

90

Synthesis, structural, thermal studies and biological activity of a tridentate Schiff base ligand and their transition metal complexes.  

PubMed

Schiff base (L) ligand is prepared via condensation of pyridine-2,6-dicarboxaldehyde with -2-aminopyridine. The ligand and its metal complexes are characterized based on elemental analysis, mass, IR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). The molar conductance reveals that all the metal chelates are non-electrolytes. IR spectra shows that L ligand behaves as neutral tridentate ligand and bind to the metal ions via the two azomethine N and pyridine N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Th(IV)) and tetrahedral (Mn(II), Cd(II), Zn(II), and UO2(II)). The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as, E*, ?H*, ?S* and ?G* are calculated from the DTG curves using Coats-Redfern method. The synthesized ligand, in comparison to their metal complexes also was screened for its antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus pyogones and Fungi (Candida). The activity data shows that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species. PMID:21130026

Abd El-halim, Hanan F; Omar, M M; Mohamed, Gehad G

2011-01-01

91

Stereochemistry of complexes with double and triple metal-ligand bonds: a continuous shape measures analysis.  

PubMed

To each coordination polyhedron we can associate a normalized coordination polyhedron that retains the angular orientation of the central atom-ligand bonds but has all the vertices at the same distance from the center. The use of shape measures of these normalized coordination polyhedra provides a simple and efficient way of discriminating angular and bond distance distortions from an ideal polyhedron. In this paper we explore the applications of such an approach to analyses of several stereochemical problems. Among others, we discuss how to discern the off-center displacement of the metal from metal-ligand bond shortening distortions in families of square planar biscarbene and octahedral dioxo complexes. The normalized polyhedron approach is also shown to be very useful to understand stereochemical trends with the help of shape maps, minimal distortion pathways, and ligand association/dissociation pathways, illustrated by the Berry and anti Berry distortions of triple-bonded [X?ML4] complexes, the square pyramidal geometries of Mo coordination polyhedra in oxido-reductases, the coordination geometries of actinyl complexes, and the tetrahedricity of heavy atom-substituted carbon centers. PMID:25365476

Alvarez, Santiago; Menjón, Babil; Falceto, Andrés; Casanova, David; Alemany, Pere

2014-11-17

92

Guanidinates: a new class of ligands for dimetal units with multiple metal-metal bonds  

E-print Network

This dissertation concerns the discovery of the ability of the guanidinate ligand hpp (hpp = anion of 1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) to stabilize high oxidation states of dimetal units (particularly dimolybdenum species...

Wilkinson, Chad C.

2009-05-15

93

Anchoring of palladium onto surface of porous metal-organic framework through post-synthesis modification and studies on Suzuki and Stille coupling reactions under heterogeneous condition.  

PubMed

An ecofriendly solid catalyst has been synthesized by anchoring palladium(II) into post synthetically modified metal organic framework IRMOF-3. The pore of IRMOF-3 was first modified with pyridine-2-aldehyde. The amine group of IRMOF-3 upon condensation with pyridine-2-aldehyde afforded a bidentate Schiff base moiety in the porous matrix. The Schiff base moieties were used to anchor palladium(II) ions. The prepared catalyst has been characterized by UV-vis, IR spectroscopy, X-ray powder diffraction, and nitrogen sorption measurements. Framework structure of the catalyst is not being destroyed in the multistep synthesis procedure as evidenced in X-ray powder diffraction studies. The catalyst has shown high activity toward the Suzuki and Stille cross-coupling reaction in 20% H2O/EtOH and EtOH medium, respectively, at 80 °C. The immobilized complex did not leach or decompose during the catalytic reactions, showing practical advantages over the homogeneous catalysis. PMID:23373729

Saha, Debraj; Sen, Rupam; Maity, Tanmoy; Koner, Subratanath

2013-03-01

94

Metal-pyrazolyl diazine interaction: Synthesis, structure and electrochemistry of binuclear transition metal(II) complexes derived from an ‘end-off’ compartmental Schiff base ligand  

Microsoft Academic Search

Pyrazolyl diazine (?-NN) bridged late first row transition metal(II) complexes have been prepared by the interaction of metal(II) chlorides with an ‘end-off’ compartmental Schiff base ligand. The ligand system has a strong diazine bridging component and obtained as a condensation product between 1H-pyrazole-3,5-dicarbohydrazide and 3-acetylcoumarin in absolute ethanol. All synthesized compounds are characterized on the basis of various spectral and

Srinivasa Budagumpi; Vidyanand K. Revankar

2010-01-01

95

Synthesis, spectroscopic, structural characterization, electrochemical and antimicrobial activity studies of the Schiff base ligand and its transition metal complexes  

NASA Astrophysics Data System (ADS)

In this study, the Schiff base ligand trans-N,N'-bis[(2,4-dichlorophenyl) methylidene] cyclohexane-1,2-diamine (L) and its copper(II), nickel(II) and palladium(II) transition metal complexes were prepared and characterized by the analytical and spectroscopic methods. The 1H( 13C) NMR spectra of the ligand and its diamagnetic complexes were recorded in DMSO-d 6 solvent and obtained data confirm that the nitrogen atoms of the imine groups coordinated to the metal ions. Electrochemical properties of the ligand and its metal complexes were investigated in the DMF solvent at the 100 and 250 mV s -1 scan rates. The ligand and metal complexes showed both reversible and irreversible processes at these scan rates. The single crystal of the ligand (L) was obtained from MeOH solution, and its crystal structure was determined by X-ray diffraction. The C-H⋯Cl hydrogen bonding interactions in the molecule were seen which increase the stability of the crystal structure. The antimicrobial activity studies of the ligand and its metal complexes were carried out by using the various bacteria and fungi.

Aslanta?, Mehmet; Kendi, Engin; Demir, Necmettin; ?abik, Ali E.; Tümer, Mehmet; Kertmen, Metin

2009-10-01

96

Oxy-functionalization of Group 9 and 10 transition metal methyl ligands: use of pyridine-based hemi-labile ligands.  

PubMed

Hemi-labile ligands (HLLs) are intriguing candidates for catalysts since they may facilitate bond activation and bond formation through facile ligand dissociation/association. DFT studies are reported of hemi-labile ligands in conjunction with Group 9 and 10 metals for oxygen atom insertion into metal-methyl bonds. Analysis of the reaction of pyridine-N-oxide with d(8)-[LnM (Me)(THF)](q+) (M = Co, Rh, Ir, Ni, Pd, Pt; Ln = 2-(CH3OCH2)Py; q = 0 and +1 for Group 9 and 10 metals, respectively; Py = pyridine; THF = tetrahydrofuran) indicates that oxy-insertion for Group 9 complexes occurs with lower free energy barriers than their Group 10 congeners. Analysis of structural changes along the reaction coordinate suggests that the initial oxygen atom transfer and subsequent methyl migration steps are favored by a reduction and increase, respectively, in coordination number. This emphasizes that HLLs could be uniquely positioned to assist both transformations within a single complex. Additionally, such ligands are worthy of experimental study due to their ability to meet the disparate coordination demands for two-step, redox-based oxy-insertion. PMID:24699887

Prince, Bruce M; Gunnoe, T Brent; Cundari, Thomas R

2014-05-28

97

Linear free energy relationships for metal-ligand complexation: Bidentate binding to negatively-charged oxygen donor atoms  

NASA Astrophysics Data System (ADS)

Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log KML = ?OO( ?O log KHL,1 + ?O log KHL,2) where KML is the metal-ligand stability constant for a 1:1 complex, KHL,1 and KHL,2 are the proton-ligand stability constants (the ligand p Ka values), and ?O is the Irving-Rossotti slope. The parameter ?OO is metal specific and has slightly different values for five and six membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, ?-hydroxycarboxylic acids, and ?-ketocarboxylic acids, a modification of the LFER where log KHL,2 is set equal to zero is required. The chemical interpretation of ?OO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log KML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log KML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems.

Carbonaro, Richard F.; Atalay, Yasemin B.; Di Toro, Dominic M.

2011-05-01

98

Metal- and Ligand-Accelerated Catalysis of the Baylis-Hillman Reaction.  

PubMed

The Baylis-Hillman reaction, the coupling of an unsaturated carbonyl compound/nitrile with aldehydes, is a valuable reaction but is limited in its practicality by poor reaction rates. We have endeavored to accelerate the reaction using Lewis acids and found that while conventional Lewis acids gave reduced rates group III, and lanthanide triflates (5 mol %) gave increased rates. The optimum metal salts were La(OTf)(3) and Sm(OTf)(3), which gave rate accelerations (k(rel)) of approximately 4.7 and 4.9, respectively, in reactions between tert-butyl acrylate and benzaldehyde when using stoichiometric amounts of DABCO. At low loadings of DABCO (up to 10 mol %), no reaction occurred due to association of DABCO with the metal. Use of additional ligands to displace the DABCO from the metal was studied, and the rate of reaction was found to increase further in most cases. Of the ligands tested, at 5 mol %, (+)-binol gave one of the largest rate accelerations (3.4-fold) and was studied in more detail. It was found that reactions occurred even at low DABCO concentration so that here the Lewis base and Lewis acid were able to promote the reaction without interference from each other. While the (+)-binol (and other chiral ligands) failed to provide any significant asymmetric induction, a substantial nonlinear effect was observed with binol. Thus, use of racemic binol gave no effect on the rate. In seeking to maximize the rate attainable, more soluble (liquid) ligands were studied. Diethyl tartrate and triethanolamine gave rate enhancements of 5.2x and 3.5x at 50 mol %, respectively, versus 1.5x and 2.3x at 5 mol %. The best protocol was to use 100 mol % DABCO, 50 mol % triethanolamine, and 5 mol % La(OTf)(3). This gave overall rate accelerations of between 23-fold and 40-fold depending on the acrylate and approximately 5-fold for acrylonitrile. A simple acid wash removed the reagents, leaving the product in the organic phase. While triethanolamine accelerated the reaction without the lanthanum triflate (18-22-fold at 80 mol %), the reaction in the presence of the metal salt was faster. The system was tested synthetically on various substrates and found to give good rate accelerations with both activated (benzaldehyde and p-nitrobenzaldehyde) and less activated aldehydes (anisaldehyde and cyclohexanecarboxaldehyde) with acrylates. The limited amount of dimerized acrylate in the latter reactions is noteworthy and should extend the range of substrates that can be made by the Baylis-Hillman reaction using our optimum conditions. PMID:11672359

Aggarwal, Varinder K.; Mereu, Andrea; Tarver, Gary J.; McCague, Ray

1998-10-16

99

Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: spectroscopic observation of facile metal-carboxylate displacement and binding.  

PubMed

We demonstrate that metal carboxylate complexes (L-M(O2CR)2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N',N'-tetramethylbutylene-1,4-diamine, pyridine, N,N,N',N'-tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by (1)H NMR spectroscopy and depends most strongly on geometric factors such as sterics and chelation, although also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L-M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface-bound Cd(O2CR)2 from CdSe and CdS nanocrystals decreases the Cd/Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1S(e)-2S(3/2h) absorption, and decreases the photoluminescence quantum yield (PLQY) from 10% to <1% (CdSe) and from 20% to <1% (CdS). These changes are partially reversed upon rebinding of M(O2CR)2 at room temperature (?60%) and fully reversed at elevated temperature. A model is proposed in which electron-accepting M(O2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals, leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed. PMID:24199846

Anderson, Nicholas C; Hendricks, Mark P; Choi, Joshua J; Owen, Jonathan S

2013-12-11

100

Effects of ligand modification and protonation on metal oxime hydrogen evolution electrocatalysts.  

PubMed

The design of hydrogen-evolving electrocatalysts that operate at modest overpotentials is important for solar energy devices. The M(II/I) reduction potential for metal diimine-dioxime and diglyoxime electrocatalysts is often related to the overpotential required for hydrogen evolution. Herein the impact of ligand modification and protonation on the M(II/I) reduction potentials for cobalt, nickel, and iron diimine-dioxime and diglyoxime complexes is investigated with computational methods. The calculations are consistent with experimental data available for some of these complexes and additionally provide predictions for complexes that have not yet been synthesized. The calculated pKa's imply that ligand protonation is likely to occur at the O-H-O bridge but not at other ligand sites for these complexes. Moreover, the calculations imply that a ligand-protonated Co(III)-hydride intermediate is formed along the H2 production pathway for catalysts containing an O-H-O bridge in the presence of sufficiently strong acid. The calculated M(II/I) reduction potentials indicate that the anodic shift due to protonation of the O-H-O bridge is greater than that due to replacing the O-H-O bridge with an O-BF2-O bridge for cobalt and nickel but not for iron complexes. Experiments suggest degradation for complexes with two O-H-O bridges and alternative mechanisms for certain iron complexes with two O-BF2-O bridges. Asymmetric cobalt, nickel, and strongly electron withdrawing substituted iron diimine-dioxime and diglyoxime complexes containing a single O-H-O bridge are proposed to be effective hydrogen evolution electrocatalysts with relatively low overpotentials in acetonitrile and water. These insights are important for the design of efficient aqueous-based hydrogen-evolving catalysts. PMID:23701462

Solis, Brian H; Yu, Yinxi; Hammes-Schiffer, Sharon

2013-06-17

101

Synthesis, structural characterization, catalytic, thermal and electrochemical investigations of bidentate Schiff base ligand and its metal complexes.  

PubMed

In this study, we prepared the Schiff base ligand (L) and its Cu(II), Co(II) and Ni(II) complexes. The compounds were characterized by the analytical and spectroscopic methods. The ligand (L) behaves as a bidentate ligand and coordinates to the metal ions via the nitrogen atoms. The complexes have the mononuclear structures. The analytical and spectroscopic results indicated that the chloride ions coordinate to the metal ions. The complexes have the general formulae [M(L)(Cl)(2)] (M: Cu(II), Co(II) and Ni(II) metal ions). Electrochemical properties were investigated as ligand and metal centres in the different solvents and at the scan rates, respectively. The thermal properties of the metal complexes were studied in the N(2) atmosphere. We investigated the improved catalytic activity of the Cu(II), Co(II) and Ni(II) complexes on the cyclohexane as a substrate. Obtained data showed that the best catalyst is the Cu(II) complex. The single crystal of the ligand (L) was obtained from CH(3)CN solution. There is a C-H...N H-bond linking the molecules into chains (C6)...N(2) 3.4415(18)A under symmetry operation (x+1,y,z) as well as pi-pi stacking on the outside of the "V" shape--nothing on the inside. PMID:20409747

Dolaz, Mustafa; McKee, Vickie; Uru?, Serhan; Demir, Necmettin; Sabik, Ali E; Gölcü, Ay?egül; Tümer, Mehmet

2010-07-01

102

Using a Combination of Experimental and Computational Methods to Explore the Impact of Metal Identity and Ligand Field Strength on the Electronic Structure of Metal Ions  

ERIC Educational Resources Information Center

In this exercise, students apply a combination of techniques to investigate the impact of metal identity and ligand field strength on the spin states of three d[superscript 5] transition-metal complexes: Fe(acac)[subscript 3], K[subscript 3][Fe(CN)[subscript 6

Pernicone, Naomi C.; Geri, Jacob B.; York, John T.

2011-01-01

103

Dinuclear metal(II) complexes of polybenzimidazole ligands as carriers for DNA delivery.  

PubMed

A metal-based nonviral carrier for DNA-transfer in gene therapy was synthesized and characterized. The strong intermolecular pi-pi contacts are common in the observed dinuclear Cu(2+) and Co(2+) complexes of polybenzimidazole ligands. The affinity assays indicated that the strong binding of the complexes to DNA is driven by both electrostatic attractions between the complexes and DNA and the intercalation of the ligands between DNA base pairs. The typical in vitro studies showed that micromolar doses of each complex tested can efficiently and rapidly condense free DNA, either in linear or circular state, from solutions into well defined and globular nanoparticles with varied sizes. Therefore, the formation and dissociation of the DNA condensates were explored in detail under different conditions, indicating that the sizes of DNA condensates can be regulated by changing both doses and incubation time for the different dinuclear complexes. Since the intermolecular pi-pi interactions in the DNA-bound complexes may be a key force to drive DNA condensation, we propose a new DNA condensation model that is essentially distinct from that proposed for the most studied multivalent cationic reagents used in DNA condensation. The cellular uptake experiments successfully performed with the DNA condensates including plasmid pGL3 control vector that strongly expresses luciferase in many types of mammalian cells, as well as cytotoxicity evaluation, demonstrated the potentiality of the dinuclear metal(II) complexes as a new nonviral gene carrier. Finally, the dinuclear Co(2+) complexes of polybenzimidazole ligands are suggested to be the most potential nonviral gene carriers that are not impacted by serum proteins. PMID:19906419

Liu, Liang; Zhang, Hang; Meng, Xianggao; Yin, Jun; Li, Dongfeng; Liu, Changlin

2010-02-01

104

Aspects of C-H Activation in Metal Complexes Containing Sulfur Ligands  

SciTech Connect

The research project proposed to synthesize new metal complexes with sulfido, disulfido and other types of reactive sulfur ligands, and to explore the joint reactivity of metal and sulfur ligands with hydrogen and organic molecules. The overall objective was to investigate reaction pathways relevant to those observed for the heterogeneous metal sulfide catalysts which promote hydrogen activation, hydrogenation-dehydrogenation of organic substrates, and hydrogenolysis of carbon-heteroatom bonds. Particular emphasis was placed on CpRe derivatives (where Cp might be C5H5 or alkylated versions) so that comparisons could be made with the previously studied CpMo complexes, which showed extensive reactivity at the sulfur ligands. Heterogeneous rhenium sulfides generally show higher catalytic activity than molybdenum sulfides, and this is attributed, in part, to the weaker Re-S bond strength, relative to the moybdenum-sulfur bond. In our studies of discrete Re-sulfide complexes, we have also observed evidence for weaker Re-S bonds relative to the molybdenum systems. In addition we have characterized novel hydrogen activation by rhenium sulfido complexes, as well as carbon-hydrogen, carbon-sulfur and metal sulfur bond cleavage reactions. Hydrogen Activation. The complex Cp{prime}ReCl2S3 was synthesized in ca 70% yield and characterized by an X-ray diffraction study which confirms that the complex contains a {eta}2-trisulfide ligand. The cyclic voltammogram of Cp{prime}ReCl2S3 shows a wide window of redox stability with an irreversible reduction wave at -0.97 V and an irreversible oxidation at +1.03 V vs Fc. Nevertheless, the complex undergoes a facile reaction with hydrogen at 50 C to form H2S and a new dinuclear sulfido bridged rhenium complex. This reaction is of interest because it is the first example of the hydrogenolysis of a discrete metal polysulfide complex to produce H2S, a reaction also observed for heterogeneous rhenium sulfides. The reaction contrasts with those of related Cp-molybdenum complexes with sulfide ligands, which also activate hydrogen, but generally form hydrosulfido products without H2S elimination. C-H and C-S Cleavage Reactions. New mononuclear Cp{prime}Re(dithiolate) complexes such as Cp{prime}ReCl2(SC2H4S), 1, have been prepared and characterized and have been found to display a very interesting range of reactions. The thermal reaction of 1 involves the dehydrogenation of the alkanedithiolate ligand to form Cp{prime}ReCl2(SCH=CHS), 2 as well as a competing elimination of olefin from the dithiolate ligand in 1. On the basic of kinetic and related studies, the mechanism is proposed to involve a sequential series of reactions. In the first reaction, the olefin extrusion is proposed to produce a reactive Re-disulfide or Re-bis(sulfido) intermediate, CpReCl2S2 which serves as an oxidant for the dithiolate complex 1. The ability of the bis sulfido complex to dehydrogenate hydrocarbons is a unique feature and several additional dehydrogenation reactions with this system have been characterized, including the oxidation of other dithiolate complexes, of tetrahydro-naphthalene and of cyclohexadiene. Precedents for the role of metal sulfides in dehydrogenation reactions have been reported for heterogeneous metal sulfide surfaces. This work has begun to provide information about the electronic and structural features necessary for such reactivity. Carbon Sulfur Bond Formation. When the thermal reaction of 1 was carried out in the presence of excess dry ethene a new reaction was observed in which the dithiolate ligand is displaced by incoming olefin to form the cyclic organic product, 1,4-dithiane. The Re product is identified as Cp{prime}Re(alkene)Cl2 on the basis of NMR and mass spectroscopic data. Similar reactions with alkynes have been found to form unsaturated 6-membered rings and reactions with 1,3 dithiolate complexes form the organic 7-membered rings. To our knowledge the formation of cyclic bis-thioethers by the reactions of an alkene or alkyne with a discrete dithiolate metal complex has not been repor

Rakowski-DuBois, Mary C.

2004-10-08

105

Supported Molecular Iridium Catalysts: Resolving Effects of Metal Nuclearity and Supports as Ligands  

SciTech Connect

The performance of a supported catalyst is influenced by the size and structure of the metal species, the ligands bonded to the metal, and the support. Resolution of these effects has been lacking because of the lack of investigations of catalysts with uniform and systematically varied catalytic sites. We now demonstrate that the performance for ethene hydrogenation of isostructural iridium species on supports with contrasting properties as ligands (electron-donating MgO and electron-withdrawing HY zeolite) can be elucidated on the basis of molecular concepts. Spectra of the working catalysts show that the catalytic reaction rate is determined by the dissociation of H{sub 2} when the iridium, either as mono- or tetra-nuclear species, is supported on MgO and is not when the support is the zeolite. The neighboring iridium sites in clusters are crucial for activation of both H{sub 2} and C{sub 2}H{sub 4} when the support is MgO but not when it is the zeolite, because the electron-withdrawing properties of the zeolite support enable even single site-isolated Ir atoms to bond to both C{sub 2}H{sub 4} and H{sub 2} and facilitate the catalysis.

Lu, Jing; Serna, Pedro; Aydin, Cerem; Browning, Nigel D.; Gates, Bruce C. (UCD)

2012-02-07

106

DFT modeling of Spectral and Redox Properties of Di-and Tetranuclear Ruthenium Transition Metal Complexes with Bridging Ligands  

NASA Astrophysics Data System (ADS)

The electronic structures of di-and tetranuclear transition metal complexes with bridging ligands (tetracyanoethene, tetracyano-p-quinodimethane, divinylphenylene and tetrakis(4-styryl)ethene) were calculated by density functional (DFT) method. DFT method was used for calculations of IR frequencies in different oxidation states and EPR parameters of radical ions. The observed electronic transitions of closed shell systems were assigned by TD DFT. The different aspects of bridge mediated metal-metal interaction are discussed.

Záliš, S.; Winter, R. S.; Linseis, M.; Kaim, A.; Sarkar, B.; Kratochvílová, I.

2009-08-01

107

Bioinspired hydrogen bond motifs in ligand design: the role of noncovalent interactions in metal ion mediated activation of dioxygen.  

PubMed

Hydrogen bonds influence secondary coordination spheres around metal ions in many proteins. To duplicate these features of molecular architecture in synthetic systems, urea-based ligands have have been developed that create rigid organic frameworks when bonded to metal ions. These frameworks position hydro-gen bond donors proximal to metal ion(s) to form specific chem-ical microenvironments. Iron(II) and manganese(II) complexes with constrained cavities activate O(2), yielding M(III) (M(III) = Fe and Mn) complexes with terminal oxo ligands. Installation of anionic sites within the cavity assists the formation of complexes with M(II/III)-OH and M(III)-O units derived directly from water. Opening the cavity promotes M(mu-O)(2)M rhombs, as illustrated by isolation of a cobalt(III) analogue, the stability of which is promoted by the hydrogen bonds surrounding the bridging oxo ligands. PMID:15654737

Borovik, A S

2005-01-01

108

Synthesis, characterization and biological activity of ferrocene-based Schiff base ligands and their metal (II) complexes  

NASA Astrophysics Data System (ADS)

Metal (II) complexes derived from S-benzyl-N-(1-ferrocenyl-3-(4-methylbenzene)acrylketone) dithiocarbazate; HL1, S-benzyl-N-(1-ferrocenyl-3-(4-chlorobenzene)acrylketone)dithiocarbazate; HL2, all the compounds were characterized using various spectroscopic techniques. The molar conductance data revealed that the chelates were non-electrolytes. IR spectra showed that the Schiff bases were coordinated to the metal ions in a bidentate manner with N, S donor sites. The ligands and their metal complexes have been screened for in vitro antibacterial, antifungal properties. The result of these studies have revealed that zinc (II) complexes 6 and 13 of both the ligands and copper (II) complexes 9 of the HL2 were observed to be the most active against all bacterial strains, antifungal activity was overall enhanced after complexation of the ligands.

Liu, Yu-Ting; Lian, Gui-Dan; Yin, Da-Wei; Su, Bao-Jun

109

Antioxidant, electrochemical, thermal, antimicrobial and alkane oxidation properties of tridentate Schiff base ligands and their metal complexes  

NASA Astrophysics Data System (ADS)

In this study, two Schiff base ligands (HL 1 and HL 2) and their Cu(II), Co(II), Ni(II), Pd(II) and Ru(III) metal complexes were synthesized and characterized by the analytical and spectroscopic methods. Alkane oxidation activities of the metal complexes were studied on cyclohexane as substrate. The ligands and their metal complexes were evaluated for their antimicrobial activity against Corynebacterium xerosis, Bacillus brevis, Bacillus megaterium, Bacillus cereus, Mycobacterium smegmatis, Staphylococcus aureus, Micrococcus luteus and Enterococcus faecalis (as Gram-positive bacteria) and Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Yersinia enterocolitica, Klebsiella fragilis, Saccharomyces cerevisiae, and Candida albicans (as Gram-negative bacteria). The antioxidant properties of the Schiff base ligands were evaluated in a series of in vitro tests: 1,1-diphenyl-2-picrylhydrazyl (DPPH rad ) free radical scavenging and reducing power activity of superoxide anion radical generated non-enzymatic systems. Electrochemical and thermal properties of the compounds were investigated.

Ceyhan, Gökhan; Çelik, Cumali; Uru?, Serhan; Demirta?, ?brahim; Elmasta?, Mahfuz; Tümer, Mehmet

2011-10-01

110

On the dielectric and optical properties of surface-anchored metal-organic frameworks: A study on epitaxially grown thin films  

NASA Astrophysics Data System (ADS)

We determine the optical constants of two highly porous, crystalline metal-organic frameworks (MOFs). Since it is problematic to determine the optical constants for the standard powder modification of these porous solids, we instead use surface-anchored metal-organic frameworks (SURMOFs). These MOF thin films are grown using liquid phase epitaxy (LPE) on modified silicon substrates. The produced SURMOF thin films exhibit good optical properties; these porous coatings are smooth as well as crack-free, they do not scatter visible light, and they have a homogenous interference color over the entire sample. Therefore, spectroscopic ellipsometry (SE) can be used in a straightforward fashion to determine the corresponding SURMOF optical properties. After careful removal of the solvent molecules used in the fabrication process as well as the residual water adsorbed in the voids of this highly porous solid, we determine an optical constant of n = 1.39 at a wavelength of 750 nm for HKUST-1 (stands for Hong Kong University of Science and Technology-1; and was first discovered there) or [Cu3(BTC)2]. After exposing these SURMOF thin films to moisture/EtOH atmosphere, the refractive index (n) increases to n = 1.55-1.6. This dependence of the optical properties on water/EtOH adsorption demonstrates the potential of such SURMOF materials for optical sensing.

Redel, Engelbert; Wang, Zhengbang; Walheim, Stefan; Liu, Jinxuan; Gliemann, Hartmut; Wöll, Christof

2013-08-01

111

Synthesis, crystal structures and properties of three new mixed-ligand d{sup 10} metal complexes constructed from pyridinecarboxylate and in situ generated amino-tetrazole ligand  

SciTech Connect

Three new metal-organic frameworks, [Zn(atz)(nic)]{sub n}(1), [Zn(atz)(isonic)]{sub n}.nHisonic(2) and [Cd(atz)(isonic)]{sub n}(3) (Hnic=nicotinic acid, Hisonic=isonicotinic acid), have been firstly synthesized by employing mixed-ligand of pyridinecarboxylate with the in situ generated ligand of 5-amino-tetrazolate(atz{sup -}), and characterized by elemental analysis, IR spectroscopy, TGA and single crystal X-ray diffraction. The results revealed that 1 presents a two-dimensional (2D) 'sql' topological network constructed from the linear chain subunit of Zn(nic){sub 2} and atz{sup -} ligand. A remarkable feature of 2 is a 2-fold interpenetrated diamondoid network with free Hisonic molecules locating in the channels formed by the zigzag chain subunits of Zn(isonic){sub 2}. Complex 3 is a 3D non-interpenetrated pillared framework constructed from the double chain subunits of Cd-COO{sup -}Cd. It possesses a rarely observed (4,6)-connected 'fsc' topology. The thermal stabilities and fluorescent properties of the complexes were investigated. All of these complexes exhibited intense fluorescent emissions in the solid state at room temperature. - Graphical abstract: Three new mixed-ligand d{sup 10} metal complexes have been synthesized by employing mixed-ligand synthetic approach. Complex 1 presents a 2D 'sql' topological network. Complex 2 is a 2-fold interpenetrated diamondoid network with microporous channels. Rarely observed (4,6)-connected 'fsc' topological network was found in complex 3.

Liu Dongsheng [State Key Laboratory Breeding Base of Photocatalysis, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108 (China); College of Chemistry and Chemical Engineering, Jinggangshan University, Ji'an, Jiangxi 343009 (China); Huang, Xihe [State Key Laboratory Breeding Base of Photocatalysis, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108 (China); Huang Changcang, E-mail: changcanghuang@hotmail.co [State Key Laboratory Breeding Base of Photocatalysis, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108 (China); Huang Gansheng [State Key Laboratory Breeding Base of Photocatalysis, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108 (China); College of Chemistry and Chemical Engineering, Jinggangshan University, Ji'an, Jiangxi 343009 (China); Chen Jianzhong, E-mail: j.z.chen@fzu.edu.c [State Key Laboratory Breeding Base of Photocatalysis, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108 (China)

2009-07-15

112

A periodic walk: a series of first-row transition metal complexes with the pentadentate ligand PY5.  

PubMed

A series of transition metal complexes derived from the pentadentate ligand PY5, 2,6-(bis-(bis-2-pyridyl)methoxymethane)pyridine, illustrates the intrinsic propensity of this ligand to complex metal ions. X-ray structural data are provided for six complexes (1-6) with cations of the general formula [M(II)(PY5)(Cl)](+), where M = Mn, Fe, Co, Ni, Cu, Zn. In complexes 1-4 and 6, the metal ions are coordinated in a distorted-octahedral fashion; the four terminal pyridines of PY5 occupy the equatorial sites while the axial positions are occupied by the bridging pyridine of PY5 and a chloride anion. Major distortions from an ideal octahedral geometry arise from displacement of the metal atom from the equatorial plane toward the chloride ligand and from differences in pyridine-metal-pyridine bond angles. The series of complexes shows that M(II) ions are consistently accommodated in the ligand by displacement of the metal ion from the PY5 pocket, a tilting of the axial pyridine subunit, and nonsymmetrical pyridine subunit ligation in the equatorial plane. The displacement from the ligand pocket increases with the ionic radius of M(II). The axial pyridine tilt, however, is approximately the same for all complexes and appears to be independent of the electronic ground state of M(II). In complex 5, the Cu(II) ion is coordinated by only four of the five pyridine subunits of the ligand, resulting in a square-pyramidal complex. The overall structural similarity of 5 with the other complexes reflects the strong tendency of PY5 to enforce a distorted-octahedral coordination geometry. Complexes 1-6 are further characterized in terms of solution magnetic susceptibility, electrochemical behavior, and optical properties. These show the high-spin nature of the complexes and the anticipated stabilization of the divalent oxidation state. PMID:12206686

Klein Gebbink, Robertus J M; Jonas, Robert T; Goldsmith, Christian R; Stack, T Daniel P

2002-09-01

113

Research Dialogue Anchoring unbound  

E-print Network

) different types of anchors that exert their influence through different underlying mechanisms, 2) important of anchors that are likely to influence judgment, suggesting four potentially distinct types into the moderators and consequences of anchoring effects in everyday life. � 2009 Society for Consumer Psychology

114

Synthesis of metal complexes involving Schiff base ligand with methylenedioxy moiety: Spectral, thermal, XRD and antimicrobial studies  

NASA Astrophysics Data System (ADS)

Metal complexes of Zn(II), Cd(II), Ni(II), Cu(II), Fe(III), Co(II), Mn(II) Hg(II), and Ag(I) have been synthesized from Schiff base ligand, prepared by the condensation of 3,4-(methylenedioxy)aniline and 5-bromo salicylaldehyde. All the compounds have been characterized by using elemental analysis, molar conductance, FT-IR, UV-Vis, 1H NMR, 13C NMR, mass spectra, powder XRD and thermal analysis (TG/DTA) technique. The elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). The FT-IR, 1H NMR, 13C NMR and UV-Vis spectral data suggest that the ligand coordinate to the metal atom by imino nitrogen and phenolic oxygen as bidentate manner. Mass spectral data further support the molecular mass of the compounds and their structure. Powder XRD indicates the crystalline state and morphology of the ligand and its metal complexes. The thermal behaviors of the complexes prove the presence of lattice as well as coordinated water molecules in the complexes. Melting point supports the thermal stability of all the compounds. The in vitro antimicrobial effects of the synthesized compounds were tested against five bacterial and three fungal species by well diffusion method. Antioxidant activities have also been performed for all the compounds. Metal complexes show more biological activity than the Schiff base.

Sundararajan, M. L.; Jeyakumar, T.; Anandakumaran, J.; Karpanai Selvan, B.

2014-10-01

115

Two Ce-containing 3D metal-organic frameworks: In situ formation of ligand (DDPD)  

NASA Astrophysics Data System (ADS)

Hydrothermal reactions of cerium nitrate and 5-hydroxyisophthalic acid (OH-H2BDC) produce two new metal-organic frameworks (MOFs), {[Ce(DDPD)1.5(H2O)2.5]·4H2O}n (1) and {[Ce(OH-BDC)(OH-HBDC)(H2O)2]·2H2O]n (2) (DDPD(II)=5,10-dioxo-5,10-dihydro-4,9-dioxapyrene-2,7-dicarboxylate(II)}. These two complexes have been characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction. It was remarkable that the in situ reaction of OH-H2BDC to DDPD(II) was found in complex 1. In 1, Ce(III) ions are bridged by DDPD ligands to form infinite 1D chain, which is further connected via DDPD ligands to form 3D structure. Complex 2 possesses a neutral noninterpenetrating 2D layer structure. Furthermore, the fluorescence properties and magnetic behavior of 1 and 2 have been investigated.

Cao, Xinyu; Yu, Liqiong; Huang, Rudan

2014-02-01

116

Multicomponent assembly of fluorescent-tag functionalized ligands in metal-organic frameworks for sensing explosives.  

PubMed

Detection of trace amounts of explosive materials is significantly important for security concerns and pollution control. Four multicomponent metal-organic frameworks (MOFs-12, 13, 23, and 123) have been synthesized by employing ligands embedded with fluorescent tags. The multicomponent assembly of the ligands was utilized to acquire a diverse electronic behavior of the MOFs and the fluorescent tags were strategically chosen to enhance the electron density in the MOFs. The phase purity of the MOFs was established by PXRD, NMR spectroscopy, and finally by single-crystal XRD. Single-crystal structures of the MOFs-12 and 13 showed the formation of three-dimensional porous networks with the aromatic tags projecting inwardly into the pores. These electron-rich MOFs were utilized for detection of explosive nitroaromatic compounds (NACs) through fluorescence quenching with high selectivity and sensitivity. The rate of fluorescence quenching for all the MOFs follows the order of electron deficiency of the NACs. We also showed the detection of picric acid (PA) by luminescent MOFs is not always reliable and can be misleading. This attracts our attention to explore these MOFs for sensing picryl chloride (PC), which is as explosive as picric acid and used widely to prepare more stable explosives like 2,4,6-trinitroaniline from PA. Moreover, the recyclability and sensitivity studies indicated that these MOFs can be reused several times with parts per billion (ppb) levels of sensitivity towards PC and 2,4,6-trinitrotoluene (TNT). PMID:25164426

Gole, Bappaditya; Bar, Arun Kumar; Mukherjee, Partha Sarathi

2014-10-01

117

Linkage isomerism in transition-metal complexes of mixed (arylcarboxamido)(arylimino)pyridine ligands.  

PubMed

The synthesis of a series of asymmetric mixed 2,6-disubstituted (arylcarboxamido)(arylimino)pyridine ligands and their coordination chemistry toward a series of divalent first-row transition metals (Cu, Co, and Zn) have been explored. Complexes featuring both anionic N,N',N?-carboxamido and neutral O,N,N'-carboxamide coordination have been prepared and characterized by X-ray crystallography, cyclic voltammetry, and UV-visible and EPR spectroscopy. Specifically, (R)LM(X) (M = Cu; X = Cl(-), OAc(-)) and (R)L(H)MX2 (M = Cu, Co, Zn; X = Cl(-), SbF6(-)) complexes that feature N,N',N?- or O,N,N'-coordination are presented. Base-induced linkage isomerization from O,N,N'-carboxamide to N,N',N?-carboxamido coordination is also confirmed by multiple forms of spectroscopy. PMID:24819403

Boyce, David W; Salmon, Debra J; Tolman, William B

2014-06-01

118

Metal-Templated Ligand Architectures for Trinuclear Chemistry: Tricopper Complexes and Their O2 Reactivity  

PubMed Central

A trinucleating framework was assmbled by templation of a heptadentate ligand around yttrium and lanthanides. The generated complexes orient three sets of two or three N-donors each for binding additional metal centers. Addition of three equivalents of copper(I) leads to the formation of tricopper(I) species. Reactions with dioxygen at low temperatures generate species whose spectroscopic features are consistent with a ?3,?3-dioxo-tricopper complex. Reactivity studies were performed with a variety of substrates. The dioxo-tricopper species deprotonates weak acids, undergoes oxygen atom transfer with one equivalent of triphenylphosphine to yield triphenylphosphine oxide, and abstracts two hydrogen atom equivalents from tetramethylpiperidine-N-hydroxide (TEMPO-H). Thiophenols reduce the oxygenated species to a CuI3 complex and liberate two equivalents of disulfide, consistent with a four-electron four-proton process. PMID:23539341

Lionetti, Davide; Day, Michael W.

2013-01-01

119

The Study of the Successive Metal-Ligand Binding Energies for Fe(sup +), Fe(sup -), V(sup +) and Co(sup +)  

NASA Technical Reports Server (NTRS)

The successive binding energies of CO and H2O to Fe(sup +), CO to Fe(sup -), and H2 to Co(sup +) and V(sup +) are presented. Overall the computed results are in good agreement with experiment. The trends in binding energies are analyzed in terms of metal to ligand donation, ligand to metal donation, ligand-ligand repulsion, and changes in the metal atom, such as hybridization, promotion, and spin multiplicity. The geometry and vibrational frequencies are also shown to be directly affected by these effects.

Bauschlicher, Charles W., Jr.; Ricca, Alessandra; Maitre, Philippe; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

120

The ligand-promoted mobilisation of metal ions from mineral surfaces  

NASA Astrophysics Data System (ADS)

Many metals such as Fe, Mo, Cu, Zn etc have been identified as essential micronutrients for plants and microorganisms. These metals have to be mobilised from mineral surfaces in contact with crustal fluids in order to be available to living cells. Many studies have shown the importance of chelation in the mobilisation of metal ions into these fluids. The ligand-promoted dissolution of minerals enables elements essential to life to be accessible. Organic acids with chelating properties are widely present on the surface of the earth (both anthropogenic and those produced naturally such as siderophores) and as well as releasing metal ions into solution for bioavailability, they control processes such as metal ion transport and adsorption and thereby are important in the understanding of toxicity and contamination. In this study we have compared mineral dissolution using a strong industrial chelator (DTPA -- diethylene triamine penta-acetic acid) and dissoluton using a synthetically produced naturally occurring siderophore, 2,3-dihydroxybenzoic acid produced by Azotobacter vinelandii. The dissolution kinetics of a number of minerals (barite, chalcopyrite, malachite) by DTPA solution has been studied as a function of DTPA concentration in the range 0.001--0.5 M. Batch experiments were carried out at pH 12 where the DTPA is effectively de-protonated and over a range of temperatures (22--90C^o) to investigate the factors controlling the dissolution rate.. Although the dissolution mechanism involves the chelation of one metal ion by each molecule of DTPA, the dissolution rate was found to be inversely related to the DTPA concentration in solution and not dependent on the initial grain size of the mineral. The high activation energy for the dissolution process suggests that the rate is controlled by a surface desorption process rather than diffusion in the solution. The inverse dependence on the DTPA concentration suggests steric hindrance associated with the metal-DTPA surface complex formation. Dissolution kinetics of the natural siderophore, known to be specfic to Fe chelation, was observed under similar conditions and comparisons made with the strong industrial chelator in an attempt to understand the dissolution process. The results have important applications to many aspects of mineral dissolution and therefore metal ion mobility as well as raising fundamental questions regarding the nature of the crystal-solution interface at an atomic level.

Putnis, C. V.

2003-04-01

121

Anchoring of a Single Molecular Rotor and Its Array on Metal Surfaces using Molecular Design and Self-Assembly  

PubMed Central

Functionalizing of single molecules on surfaces has manifested great potential for bottom-up construction of complex devices on a molecular scale. We discuss the growth mechanism for the initial layers of polycyclic aromatic hydrocarbons on metal surfaces and we review our recent progress on molecular machines, and present a molecular rotor with a fixed off-center axis formed by chemical bonding. These results represent important advances in molecular-based nanotechnology. PMID:20386659

Gao, Li; Du, Shi-Xuan; Gao, Hong-Jun

2010-01-01

122

Metal-ligand cooperation by aromatization-dearomatization: a new paradigm in bond activation and "green" catalysis.  

PubMed

In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on "cooperating" ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation. We have discovered a new mode of metal-ligand cooperation, involving aromatization-dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H-H, C-H (sp(2) and sp(3)), O-H, and N-H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H(2) and light-induced liberation of O(2), using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique "long-range" metal-ligand cooperation in the activation of H(2) and in reaction with ammonia. In this Account, we begin by providing an overview of the metal-ligand cooperation based on aromatization-dearomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal-ligand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcohols to ketones, (2) acceptorless dehydrogenative coupling of alcohols to esters, (3) acylation of secondary alcohols by esters with dihydrogen liberation, (4) direct coupling of alcohols and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides with H(2) liberation, (6) selective synthesis of imines from alcohols and amines, (6) facile catalytic hydrogenolysis of esters to alcohols, (7) hydrogenolysis of amides to alcohols and amines, (8) hydrogenation of ketones to secondary alcohols under mild hydrogen pressures, (9) direct conversion of alcohols to acetals and dihydrogen, and (10) selective synthesis of primary amines directly from alcohols and ammonia. These reactions are efficient, proceed under neutral conditions, and produce no waste, the only byproduct being molecular hydrogen and/or water, providing a foundation for new, highly atom economical, green synthetic processes. PMID:21739968

Gunanathan, Chidambaram; Milstein, David

2011-08-16

123

Site-selective growth of surface-anchored metal-organic frameworks on self-assembled monolayer patterns prepared by AFM nanografting  

PubMed Central

Summary Surface anchored metal-organic frameworks, SURMOFs, are highly porous materials, which can be grown on modified substrates as highly oriented, crystalline coatings by a quasi-epitaxial layer-by-layer method (liquid-phase epitaxy, or LPE). The chemical termination of the supporting substrate is crucial, because the most convenient method for substrate modification is the formation of a suitable self-assembled monolayer. The choice of a particular SAM also allows for control over the orientation of the SURMOF. Here, we demonstrate for the first time the site-selective growth of the SURMOF HKUST-1 on thiol-based self-assembled monolayers patterned by the nanografting technique, with an atomic force microscope as a structuring tool. Two different approaches were applied: The first one is based on 3-mercaptopropionic acid molecules which are grafted in a 1-decanethiolate SAM, which serves as a matrix for this nanolithography. The second approach uses 16-mercaptohexadecanoic acid, which is grafted in a matrix of an 1-octadecanethiolate SAM. In both cases a site-selective growth of the SURMOF is observed. In the latter case the roughness of the HKUST-1 is found to be significantly higher than for the 1-mercaptopropionic acid. The successful grafting process was verified by time-of-flight secondary ion mass spectrometry and atomic force microscopy. The SURMOF structures grown via LPE were investigated and characterized by atomic force microscopy and Fourier-transform infrared microscopy. PMID:24205458

Ladnorg, Tatjana; Welle, Alexander; Heissler, Stefan; Woll, Christof

2013-01-01

124

Factors affecting the removal of metals during activated sludge wastewater treatment I. The role of soluble ligands  

Microsoft Academic Search

Samples of mixed liquor were withdrawn from a laboratory-scale activated sludge simulation operated at a range of sludge ages from 3 to 12 days in order to examine the difference in metal uptake by the mixed liquor biomass in the absence and presence of soluble ligands. One half of the samples were centrifuged, washed, and resuspended in physiological saline solution,

P. S. Lawson; R. M. Sterritt; J. N. Lester

1984-01-01

125

Preparation, spectral and biological investigation of formaldehyde-based ligand containing piperazine moiety and its various polymer metal complexes  

NASA Astrophysics Data System (ADS)

A novel tetradentate salicylic acid-formaldehyde ligand containing piperazine moiety (SFP) was synthesized by condensation of salicylic acid, formaldehyde and piperazine in presence of base catalyst, which was subjected for the preparation of coordination polymers with metal ions like manganese(II), cobalt(II), copper(II), nickel(II) and zinc(II). All the synthesized polymeric compounds were characterized by elemental analysis, IR, 1H NMR and electronic spectral studies. The thermal stability was determined by thermogravimetric analysis and thermal data revealed that all the polymer metal complexes show good thermal stability than their parent ligand. Electronic spectral data and magnetic moment values revealed that polymer metal complexes of Mn(II), Co(II) and Ni(II) show an octahedral geometry while Cu(II) and Zn(II) show distorted octahedral and tetrahedral geometry respectively. The antimicrobial screening of the ligand and coordination polymers was done by using Agar well diffusion method against various bacteria and fungi. It was evident from the data that antibacterial and antifungal activity increased on chelation and all the polymer metal complexes show excellent antimicrobial activity than their parent ligand.

Khan, Shamim Ahmad; Nishat, Nahid; Parveen, Shadma; Rasool, Raza

2011-10-01

126

Preparation, spectral and biological investigation of formaldehyde-based ligand containing piperazine moiety and its various polymer metal complexes.  

PubMed

A novel tetradentate salicylic acid-formaldehyde ligand containing piperazine moiety (SFP) was synthesized by condensation of salicylic acid, formaldehyde and piperazine in presence of base catalyst, which was subjected for the preparation of coordination polymers with metal ions like manganese(II), cobalt(II), copper(II), nickel(II) and zinc(II). All the synthesized polymeric compounds were characterized by elemental analysis, IR, (1)H NMR and electronic spectral studies. The thermal stability was determined by thermogravimetric analysis and thermal data revealed that all the polymer metal complexes show good thermal stability than their parent ligand. Electronic spectral data and magnetic moment values revealed that polymer metal complexes of Mn(II), Co(II) and Ni(II) show an octahedral geometry while Cu(II) and Zn(II) show distorted octahedral and tetrahedral geometry respectively. The antimicrobial screening of the ligand and coordination polymers was done by using Agar well diffusion method against various bacteria and fungi. It was evident from the data that antibacterial and antifungal activity increased on chelation and all the polymer metal complexes show excellent antimicrobial activity than their parent ligand. PMID:21757398

Khan, Shamim Ahmad; Nishat, Nahid; Parveen, Shadma; Rasool, Raza

2011-10-15

127

Synthesis, characterization, biological activity and equilibrium studies of metal(II) ion complexes with tridentate hydrazone ligand derived from hydralazine.  

PubMed

In the present study, a new hydrazone ligand (2-((2-phthalazin-1-yl)hydrazono)methyl)phenol) prepared by condensation of hydralazine (1-Hydralazinophthalazine) with salicylaldehyde (SAH). The synthesized SAH-hydrazone and its metal complexes have been characterized by elemental analyses, IR, (1)H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV-vis and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:1 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated hydrazone ligand. IR spectra show that SAH is coordinated to the metal ions in a tridentate manner through phthalazine-N, azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. Proton-ligand association constants of (SAH) and the stepwise stability constants of its metal complexes are determined potentiometrically in 0.1 M NaNO(3) at different temperatures and the corresponding thermodynamic parameters were derived and discussed. The order of -?G° and -?H° were found to obey Mn(2+)

El-Sherif, Ahmed A; Shoukry, Mohamed M; Abd-Elgawad, Mohamed M A

2012-12-01

128

Metal oxide nanocrystals: Spatial control via polydimethylsiloxane ligands and quantitative composition analysis by XPS  

NASA Astrophysics Data System (ADS)

Metal oxide nanoparticles have been widely used as catalysts and sensors because of their unique surface and interface properties. However, because of the scale, it is still a challenge to control the spatial distribution and to characterize the composition of these metal oxide nanoparticles. In the first part of this dissertation, we were able to control and to vary the interparticle spacing among gamma-Fe2O3 nanoparticles on the surface or in the solution by grafting different molecular weight of carboxylic acid terminated polydimethylsiloxane (PDMS-COON) onto the nanoparticles. The phase behavior of the PDMS grafted gamma-Fe2O3 nanoparticles in the bulk PDMS homopolymer blends was also studied. It was found the dispersion of Fe2O3-PDMS colloids in the PDMS homopolymer is strongly depended on the ratio of grafted ligand length to the blend homopolymer length. The Fe2O3-PDMS complexes can be further converted to Fe2O3-SiO x membranes by treating with UV/ozone. These composite oxide membranes were successfully used as the catalysts to grow carbon nanotubes under CVD with several advantages over other techniques. In the second part of this dissertation, we used X-ray Photoelectron Microscopy (XPS) to quantitatively analyze the core-shell structure of Cu2O nanoparticles, i.e. the amorphous CuO shell and the crystalline Cu2O core. Although copper oxides are not stable under the X-ray irradiation, we were able to overcome this difficulty and the CuO shell is estimated to be 0.5 nm by this procedure. This characterization is very important as the catalytic properties of metal oxide nanoparticles are strongly depending on the metal ion state and their composition.

Wu, Chun-Kwei

129

Metal chelates anchored to poly-l-peptides and linear d,l-?-peptides with promising nanotechnological applications  

NASA Astrophysics Data System (ADS)

Regular configurationally alternating amino acid sequences generate cyclic and linear helical peptides with a local ?-conformation able to self-assemble in nanowires and nanoscaffolds directed and stabilized by hydrogen bonds. The possibility of modulating the chemical profile of the various amino acid residues containing reactive side chains means that peptides could be flexible templates for creating various building blocks. A method for the design of molecules with potential spintronic properties is described. Peptides containing lysine residues, the side chains of which are bridged through the formation of metal chelates via Schiff bases, could provide stable molecular channels. When metal chelates with high electron spin states are used, their coupling could generate materials that are interesting due to their magnetic properties as well as for the patterning of nanometric lattices driven by their orientation under a magnetic field. With this aim, three alternating d- and l-lysine-containing octapeptides are synthesized and the formation of their bis(pyridoxalaldimine) copper(II) chelate derivatives is shown by absorption and circular dichroism spectroscopies.

Punzi, P.; Giordano, C.; Marino, F.; Morosetti, S.; De Santis, P.; Scipioni, A.

2012-10-01

130

Anchored nanostructure materials and method of fabrication  

DOEpatents

Anchored nanostructure materials and methods for their fabrication are described. The anchored nanostructure materials may utilize nano-catalysts that include powder-based or solid-based support materials. The support material may comprise metal, such as NiAl, ceramic, a cermet, or silicon or other metalloid. Typically, nanoparticles are disposed adjacent a surface of the support material. Nanostructures may be formed as anchored to nanoparticles that are adjacent the surface of the support material by heating the nano-catalysts and then exposing the nano-catalysts to an organic vapor. The nanostructures are typically single wall or multi-wall carbon nanotubes.

Seals, Roland D; Menchhofer, Paul A; Howe, Jane Y; Wang, Wei

2012-11-27

131

Solid phase extractive preconcentration of trace metals using p-tert-butylcalix[4]arene-1,2-crown-4-anchored chloromethylated polymeric resin beads.  

PubMed

5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-dihydroxy-27,28-crown-4-calix[4]arene in the cone conformation was synthesized. This p-tert-butylcalix[4]arene-1,2-crown-4 compound was then anchored with Merrifield chloromethylated resin beads. The modified polymeric resin was characterized by (1)H NMR, FT-IR and elemental analysis and used successfully for the separation and preconcentration of Cu(II), Cd(II), Co(II), Ni(II) and Zn(II) prior to their determination by FAAS. Effective extraction conditions were optimized in both batch and column methods. The resin exhibits good separating ability with maximum between pH 6.0-7.0 for Cu(II), pH 6.0 for Cd(II), pH 5.0 for Co(II), pH 4.0-4.5 for Ni(II), and pH 4.5 for Zn(II). The elution studies were carried out with 0.5 mol L(-1) HCl for Cu(II), Co(II) and Co(II), 1.0 mol L(-1) HCl for Cd(II) and Zn(II). The sorption capacity, preconcentration factor and distribution coefficient of each metal ion were determined. The detection limits were 1.10, 1.25, 1.83, 1.68 and 2.01 microg L(-1) for Cu(II), Cd(II), Co(II), Ni(II) and Zn(II). The influence of several ions on the resin performance was also investigated. The validity of the proposed method was checked for these metal ions in NIST standard reference material 2709 (San Joaquin Soil) and 2711 (Montana Soil). PMID:17386638

Seyhan, Serap; Colak, Mehmet; Merdivan, Melek; Demirel, Nadir

2007-02-19

132

Three-component entanglements consisting of three crescent-shaped bidentate ligands coordinated to an octahedral metal centre.  

PubMed

3,3'-biisoquinoline ligands (biiq) L, bearing aromatic substituents on their 8 and 8' positions, have been used to generate interwoven systems consisting of three crescent-shaped ligands disposed around an octahedral metal centre. Mono-ligand complexes of the type [ReL(CO)3py]+ (py: pyridine) have also been prepared, leading to sterically non-hindering complexes in spite of the endotopic nature of the chelate used. The three-component entanglements have been prepared by using either FeII or RuII as gathering metal centre. The synthetic procedure is simple and efficient, affording fully characterised complexes as their PF6 or SbCl6 salts. X-ray crystallography clearly shows that the crescent-shaped ligands do not repel each other in the tris-chelate complexes. In an analogous way, the ReI complexes show open structures with no steric repulsion between the L ligand and the ancillary CO or py groups. The FeL3 or RuL3 compounds are very unusual in the sense that, contrary to all the other tris-bidentate chelate complexes made till now, the three organic components are tangled up, in a situation which will be very favourable to the formation of new non trivial topologies of the catenane type. PMID:17639547

Durola, Fabien; Russo, Luca; Sauvage, Jean-Pierre; Rissanen, Kari; Wenger, Oliver S

2007-01-01

133

Synthesis, crystal structures and properties of three new mixed-ligand d10 metal complexes constructed from pyridinecarboxylate and in situ generated amino-tetrazole ligand  

NASA Astrophysics Data System (ADS)

Three new metal-organic frameworks, [Zn(atz)(nic)] n(1), [Zn(atz)(isonic)] n· nHisonic(2) and [Cd(atz)(isonic)] n(3) (Hnic=nicotinic acid, Hisonic=isonicotinic acid), have been firstly synthesized by employing mixed-ligand of pyridinecarboxylate with the in situ generated ligand of 5-amino-tetrazolate(atz -), and characterized by elemental analysis, IR spectroscopy, TGA and single crystal X-ray diffraction. The results revealed that 1 presents a two-dimensional (2D) "sql" topological network constructed from the linear chain subunit of Zn(nic) 2 and atz - ligand. A remarkable feature of 2 is a 2-fold interpenetrated diamondoid network with free Hisonic molecules locating in the channels formed by the zigzag chain subunits of Zn(isonic) 2. Complex 3 is a 3D non-interpenetrated pillared framework constructed from the double chain subunits of Cd-COO --Cd. It possesses a rarely observed (4,6)-connected " fsc" topology. The thermal stabilities and fluorescent properties of the complexes were investigated. All of these complexes exhibited intense fluorescent emissions in the solid state at room temperature.

Liu, Dongsheng; Huang, Xihe; Huang, Changcang; Huang, Gansheng; Chen, Jianzhong

2009-07-01

134

Alkali metal cation-induced destabilization of gas-phase protein-ligand complexes: consequences and prevention.  

PubMed

Electrospray ionization, now a well established technique for studying noncovalent protein-ligand interactions, is prone to production of alkali metal adducts. Here it is shown that this adduction significantly destabilizes the interactions between two model proteins and their ligands and that destabilization correlates with cation size. For both the [FKBP·FK506] and [lysozyme·NAG(n)] systems, dissociation of the metalated complex occurs at markedly lower collision energies than their purely protonated equivalents. Dependency upon size of the metal(+) demonstrates the importance of electrostatic charge density during the dissociation process. Differences in the gas phase basicities (GBapp) of the multiply charged protein ions and proton and sodium affinities of the ligands explain the observed charge partitioning during dissociation of the complexes. Ion mobility-mass spectrometry measurements demonstrate that metal cation adduction does not induce a significant increase in unfolding of the polypeptides, indicating that this is not the principal mechanism responsible for destabilization. Destabilizing effects can be largely reduced by exposing the electrospray to solvent (e.g., acetonitrile) vapor, a method that acts to reduce the amount of adduct formation as well as decrease the charge states of the resulting ions. This approach leads to more accurate determination of apparent K(D)s in the presence of trace alkali metals. PMID:21863818

Hopper, Jonathan T S; Oldham, Neil J

2011-10-01

135

Connecting small ligands to generate large tubular metal-organic architectures  

SciTech Connect

The new metal-organic framework materials, ZnF(Am{sub 2}TAZ).solvents and ZnF(TAZ).solvents (Am{sub 2}TAZ=3,5-diamino-1,2,4-triazole, TAZ=1,2,4-triazole), have been synthesized solvothermally and structurally characterized by either Rietveld refinement from powder XRD data or by single crystal X-ray diffraction. The three-dimensional structures of the compounds display open-ended, tubular channels, which are constituted of covalently bonded hexanuclear metallamacrocycles (Zn{sub 6}F{sub 6}(ligand){sub 6}). The tubular channels are subsequently covalently joined into a honeycomb-like hexagonal array to generate the three-dimensional porous framework. In the case of ZnF(Am{sub 2}TAZ).solvents, hydrophilic -NH{sub 2} groups point into the channels, effectively reducing their inner diameter relative to ZnF(TAZ).solvents. The present compounds are isostructural to one another and to the previously reported ZnF(AmTAZ).solvents (AmTAZ=3-amino-1,2,4-triazole), illustrative of the fact that the internal size and chemical properties of the framework may be altered by modification of the small, heterocyclic ligand. In addition to demonstrating the ability to modify the basic framework, ZnF(TAZ).solvents and ZnF(Am{sub 2}TAZ).solvents are two of the most thermally stable coordination frameworks known to date. - Graphical abstract: Top view of the open-ended, honeycomb tubular architecture of ZnF(Am{sub 2}TAZ)

Goforth, Andrea M. [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Su, Cheng-Yong [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Hipp, Rachael [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Macquart, Rene B. [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Smith, Mark D. [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Loye, Hans-Conrad zur [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States)]. E-mail: zurloye@mail.chem.sc.edu

2005-08-15

136

Immunoglobulin G adsorption behavior of l-histidine ligand attached and Lewis metal ions chelated affinity membranes  

Microsoft Academic Search

Immobilized metal affinity membranes were prepared by chelating Cu(II) and Fe(III) ions on poly(2-hydroxyethyl methacrylate-glycidyl methacrylate), poly(HEMA-GMA) membranes using l-histidine as a chelating ligand. To achieve this goal, the poly(HEMA-GMA) membrane was prepared via UV initiated photopolymerization. A spacer-arm (i.e., 1,6-diaminohexane) was introduced through the epoxy groups of the membrane (poly(HEMA-GMA)-SA). A chelating ligand (i.e., l-histidine amino acid) was covalently

Gülay Bayramoglu; Gökce Celik; M. Yakup Arica

2006-01-01

137

Investigation of the ligand shells of homo-ligand and mixed-ligand monolayer protected metal nanoparticles : a scanning tunneling microscopy study  

E-print Network

Monolayer Protected Metal Nanoparticles have recently found widespread use in and are the focus of intensive study in many areas of scientific research ranging from biology to physics to medicine. Consisting of a nanoscale, ...

Jackson, Alicia M

2007-01-01

138

Essentially Molecular Metal Complexes Anchored to Zeolite: Synthesis and Characterization of Rhodium Complexes and Ruthenium Complexes Prepared from Rh(acac)(2-C2H4)2 and cis-Ru(acac)2( -C2H4)2  

SciTech Connect

Mononuclear complexes of rhodium and of ruthenium, Rh(acac)({eta}{sup 2}-C{sub 2}H{sub 4}){sub 2} and cis-Ru(acac)2({eta}{sup 2}-C{sub 2}H{sub 4}){sub 2} (acac = C{sub 5}H{sub 7}O{sub 2}{sup -}), were used as precursors to synthesize metal complexes bonded to zeolite {beta}. Infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectra show that the species formed from Rh(acac)({eta}{sup 2}-C{sub 2}H{sub 4}){sub 2} was Rh({eta}{sup 2}-C{sub 2}H{sub 4}){sub 2}{sup +}, which was bonded to the zeolite at aluminum sites via two Rh-O bonds. Reaction of this supported rhodium complex with CO gave the supported rhodium gem-dicarbonyl Rh(CO){sub 2}{sup +}, which was characterized by two {nu}{sub CO} bands in the IR spectrum, at 2048 and 2115 cm{sup -1}, that were sharp (fwhm of 2115-cm{sup -1} band = 5 cm{sup -1}), indicating a high degree of uniformity of the supported species. Nearly the same result was observed (Liang, A. et al. J. Am. Chem. Soc. 2009, 131, 8460) for the isostructural rhodium complex supported on dealuminated HY zeolite, which was characterized by frequencies of the {nu}{sub CO} bands that were 4 and 2 cm{sup -1}, respectively, greater than those characterizing the zeolite {beta}-supported complex. This comparison indicates that the Rh atoms in Rh({eta}{sup 2}-C{sub 2}H{sub 4}){sub 2}{sup +} anchored on zeolite {beta} were slightly more electron-rich than those on zeolite Y. This inference is supported by EXAFS results showing shorter Rh-C bonds in the zeolite {beta}-supported rhodium ethene complex than in the zeolite Y-supported rhodium ethene complex. In contrast to these supported rhodium complexes, the zeolite {beta}-supported ruthenium samples were shown by IR and EXAFS spectroscopies to consist of mixtures of mononuclear ruthenium complexes with various numbers of acac ligands; when CO reacted with the supported ruthenium complexes, the resultant ruthenium carbonyls were characterized by {nu}{sub CO} spectra characteristic of both ruthenium dicarbonyls and ruthenium tricarbonyls.

Ogino, I.; Gates, B

2010-01-01

139

Three-Way Cooperativity in d(8) Metal Complexes with Ligands Displaying Chemical and Redox Non-Innocence.  

PubMed

Reversible proton- and electron-transfer steps are crucial for various chemical transformations. The electron-reservoir behavior of redox non-innocent ligands and the proton-reservoir behavior of chemically non-innocent ligands can be cooperatively utilized for substrate bond activation. Although site-decoupled proton- and electron-transfer steps are often found in enzymatic systems, generating model metal complexes with these properties remains challenging. To tackle this issue, we present herein complexes [(cod-H )M(?-L(2-) )?M(cod-H )] (M=Pt(II) , [1] or Pd(II) , [2], cod=1,5-cyclooctadiene, H2 L=2,5-di-[2,6-(diisopropyl)anilino]-1,4-benzoquinone), in which cod acts as a proton reservoir, and L(2-) as an electron reservoir. Protonation of [2] leads to an unusual tetranuclear complex. However, [1] can be stepwise reversibly protonated with up to two protons on the cod-H ligands, and the protonated forms can be stepwise reversibly reduced with up to two electrons on the L(2-) ligand. The doubly protonated form of [1] is also shown to react with OMe(-) leading to an activation of the cod ligands. The site-decoupled proton and electron reservoir sources work in tandem in a three-way cooperative process that results in the transfer of two electrons and two protons to a substrate leading to its double reduction and protonation. These results will possibly provide new insights into developing catalysts for multiple proton- and electron-transfer reactions by using metal complexes of non-innocent ligands. PMID:25251147

Deibel, Naina; Hohloch, Stephan; Schweinfurth, David; Weisser, Fritz; Grupp, Anita; Sarkar, Biprajit

2014-11-10

140

Syntheses, structures and physical properties of transition metal-organic frameworks assembled from trigonal heterofunctional ligands.  

PubMed

Six novel metal-organic frameworks (MOFs), {Mn(bpydb)(bpyHdbH)}(n) (1) {[Co(2)(bpydb)(2)](H(2)O)(0.5)}(n) (2), {[Ni(0.5)(bpydbH)(H(2)O)](DMF)(2)}(n) (3), {[Cu(2)(bpydb)(2)](H(2)O)(0.5)}(n) (4), {Zn(bpyHdb)(2)}(n) (5) and {[Cd(0.5)(bpydb)(0.5)(DMF)](H(2)O)}(n) (6), were successfully synthesized by assembling transition metal salts with trigonal heterofunctional ligand 4,4'-(4,4'-bipyridine-2,6-diyl) dibenzoic acid (bpydbH(2)) under hydrothermal and/or solvothermal conditions. Compound 1 features a rare 4-fold interpenetrating (3,5)-connected framework with hms-type topology. Isostructural compounds 2 and 4, constructed by M(2)(COO)(4) secondary building units, exhibit a robust 3D framework with alb topological type in 2-fold interpenetrating mode. Compound 3 consists of 2D (4,4) networks, which are further assembled into the new topological framework with the symbol (5(3)·6(2)·8)(5(3)·6(3))(2) through O-HO interactions. Compound 5 manifests a novel 4-connected interpenetrating framework, constructed by 2D (4,4) layers and interbedded N-HO interactions. Non-interpenetrating honeycomb networks are observed in compound 6, and further packed into a 3D framework featuring 1D channels. The magnetic susceptibility of compound 2 indicates antiferromagnetic interactions between cobalt ions. The photoluminescent properties of 5 and 6 were investigated in the solid state at room temperature. PMID:22814798

Song, Shu-Yan; Song, Xue-Zhi; Zhao, Shu-Na; Qin, Chao; Su, Sheng-Qun; Zhu, Min; Hao, Zhao-Min; Zhang, Hong-Jie

2012-09-14

141

Dynamics of tRNAtyr probed with long-lifetime metal-ligand complexes.  

PubMed

The metal-ligand complexes, [Ru(bpy)(2)(dppz)](2+) (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine) (RuBD) and [Ru(phen)(2)(dppz)](2+) (phen = 1,10-phenanthroline) (RuPD), display favorable photophysical properties including long lifetime, polarized emission, and very little background fluorescence. To check if RuBD and RuPD reflect the overall rotational mobility of small nucleic acid, we measured the intensity and anisotropy decays of RuBD and RuPD when intercalated into tRNA(tyr) using pBC SK(+) phagemid as a control. We used frequency-domain fluorometry with a blue light-emitting diode (LED) as the modulated light source. We observed shorter lifetimes for tRNA(tyr) than those for the pBC SK(+) phagemid for both probes, however, RuPD showed much larger decrease in the mean lifetime values (64%). The slow rotational correlation time of RuBD (31.3 ns) and the fast rotational correlation time of RuPD (26.0 ns) reflected the overall rotational mobility of tRNA(tyr). In addition, the steady-state anisotropy and time-resolved anisotropy decay data showed a clear difference between tRNA(tyr) and pBC SK(+) phagemid. This suggests the possibility of a homogeneous assay for identifying target nucleic acids and/or nucleic acid binding proteins. PMID:20730479

Hwang, Woo Suk; Jung, Yun Hong; Son, Woo Sung; Son, Byeng Wha; Kang, Jung Sook

2011-01-01

142

Influences of metal-ligand complexes on the cadmium and zinc biokinetics in the marine bacterium, Bacillus firmus.  

PubMed

Uptake kinetics of cadmium and zinc in gram-positive bacteria, Bacillus firmus, isolated from Hong Kong sediments were examined in the present study. The metal uptake by the bacteria was measured at different ambient free metal ion concentrations (10(-12)-10(-6) M Cd(2+) and 10(-10)-10(-6) M Zn(2+)) by adding different concentrations of total dissolved Cd and Zn and hydrophilic organic ligands (ethylenedinitrilotetraacetic acid, nitrilotriacetic acid, and citrate). Our data suggest that Cd and Zn uptake by B. firmus is best predicted by Cd(2+) and Zn(2+) activities. Free metal ions were complexed with the active sites on the bacterial surface, and an equilibrium between the free metal ion and surface-metal complex was reached quickly. After binding, the metal ions were then biologically transported into the bacteria. In addition, with the presence of lipophilic organic ligands (diethyldithiocarbamate and oxine), the lipophilic metal complex was internalized rapidly into B. firmus by passive diffusion through the bacterial plasma membrane. The uptake of the lipophilic metal complex could not be predicted by the free ion activity model because the mass transport through plasma membrane was the most important metal uptake pathway. Furthermore, the efflux of Cd and Zn by B. firmus was determined in the present study. The calculated efflux rate constants of Cd and Zn were (5.55 +/- 1.96) x 10(-4)/min and (3.75 +/- 1.04) x 10(-4)/min, respectively. The present study helps us to understand the process of bioaccumulation of metals in marine bacteria, which remains a poorly studied area. PMID:18092855

Keung, Chung Fai; Guo, Feng; Qian, Peiyuan; Wang, Wen-Xiong

2008-01-01

143

Transition metal complexes of a new 15-membered [N5] penta-azamacrocyclic ligand with their spectral and anticancer studies  

NASA Astrophysics Data System (ADS)

Novel penta-azamacrocyclic 15-membered [N5] ligand [L] i.e. 1,5,8,12-tetetraaza-3,4: 9,10-dibenzo-6-ethyl-7-methyl-1,12-(2,6-pyrido)cyclopentadecan-5,7 diene-2,11-dione and its transition metal complexes with Co(II), Ni(II), Cu(II), Ru(III) and Pd(II) have been synthesized and structurally characterized by elemental analysis, spectral, thermal as well as magnetic and molar conductivity measurements. On basis of IR, MS, UV-Vis 1H NMR and EPR spectral studies an octahedral geometry has been proposed for all complexes except Co(II), Cu(II) nitrate complexes and Pd(II) chloride complex that adopt tetrahedral, square pyramidal and square planar geometries, respectively. The antitumor activity of the synthesized ligand and some complexes against human breast cancer cell lines (MCF-7) and human hepatocarcinoma cell lines (HepG2) has been studied. The complexes (IC50 = 2.04-9.7, 2.5-3.7 ?g/mL) showed potent antitumor activity comparable with their ligand (IC50 = 11.7, 3.45 ?g/mL) against the above mentioned cell lines, respectively. The results evidently show that the activity of the ligand becomes more pronounced and significant when coordinated to the metal ion.

El-Boraey, Hanaa A.; Serag El-Din, Azza A.

2014-11-01

144

Chromotropism Behavior and Biological Activity of some Schiff Base-Mixed Ligand Transition Metal Complexes  

Microsoft Academic Search

We report about a series of mono-nuclear and bi-nuclear complexes with acyclic as well as macro-cyclic ligands, which have been synthesized with Schiff base ligands in tri- tetra and pentadentate forms. The bonding sites on complex formation are mainly the azomethine groups and\\/or imide nitrogen, ketonic oxygen or sulphur atoms. Complexes of two series of Schiff base ligands, H2La and

Azza A. A. Abou-Hussen; Wolfgang Linert

2009-01-01

145

Rare earth metal bis(alkyl) complexes bearing a monodentate arylamido ancillary ligand: Synthesis, structure, and Olefin polymerization catalysis  

Microsoft Academic Search

The reaction of Ln(CH2SiMe3)3(thf)2 with 1 equiv. of the amine ligand 2,6-iPr2C6H3NH(SiMe3) gave the corresponding amido-ligated rare earth metal bis(alkyl) complexes [2,6-iPr2C6H3N(SiMe3)]Ln(CH2SiMe3)2(thf) (Ln=Sc (1), Y (2), Ho (3), Lu (4)), which represent rare examples of bis(alkyl) rare earth metal complexes bearing a monodentate anionic ancillary ligand. In the case of Gd, a similar reaction gave the bimetallic complex Gd2(?-CH2SiMe2NC6H3iPr2-2,6)3(thf)3 (5)

Yunjie Luo; Masayoshi Nishiura; Zhaomin Hou

2007-01-01

146

Synthesis of Imine-Naphthol Tripodal Ligand and Study of Its Coordination Behaviour towards Fe(III), Al(III), and Cr(III) Metal Ions  

PubMed Central

A hexadentate Schiff base tripodal ligand is synthesized by the condensation of tris (2-aminoethyl) amine with 2-hydroxy-1-naphthaldehyde and characterized by various spectroscopic techniques like UV-VIS, IR, NMR, MASS, and elemental analysis. The solution studies by potentiometric and spectrophotometric methods are done at 25 ± 1°C, µ = 0.1?M KCl, to calculate the protonation constants of the ligand and formation constants of metal complexes formed by the ligand with Fe(III), Al(III), and Cr(III) metal ions. The affinity of the ligand towards Fe(III) is compared with deferiprone (a drug applied for iron intoxication) and transferrin (the main Fe(III) binding protein in plasma). Structural analysis of the ligand and the metal complexes was done using semiempirical PM6 method. Electronic and IR spectra are calculated by semiempirical methods and compared with experimental one. PMID:25294978

Kaur, Kirandeep

2014-01-01

147

Preparation, spectral and biological investigation of formaldehyde-based ligand containing piperazine moiety and its various polymer metal complexes  

Microsoft Academic Search

A novel tetradentate salicylic acid–formaldehyde ligand containing piperazine moiety (SFP) was synthesized by condensation of salicylic acid, formaldehyde and piperazine in presence of base catalyst, which was subjected for the preparation of coordination polymers with metal ions like manganese(II), cobalt(II), copper(II), nickel(II) and zinc(II). All the synthesized polymeric compounds were characterized by elemental analysis, IR, 1H NMR and electronic spectral

Shamim Ahmad Khan; Nahid Nishat; Shadma Parveen; Raza Rasool

2011-01-01

148

Ligand effect and cooperative role of metal ions on the DNA cleavage efficiency of mono and binuclear Cu(II) macrocyclic ligands complexes.  

PubMed

Two binuclear Cu(II) complexes of N-functionalized macrocycle ligands, namely 1,3-bis(1,4,7-triaza-1-cyclonomyl)propane and 1-(3-(1,4,7-triazonan-1-yl)propyl)-1,4,7,10-tetraazacyclo-dodecane, were synthesized and their ability to hydrolyze the cleavage of supercoiled plasmid DNA (pBR322) was compared with that of structurally related non-functionalized mononuclear Cu(II) complexes. The former, binuclear Cu(II) complex with the symmetrical ligand exhibited enhanced double-strand cleavage activity compared to the other three complexes at the same [Cu(2+)] concentration. In contrast, the latter binuclear complex with unsymmetrical macrocylic ligand did not give rise to double-strand DNA cleavage. The linear DNA formation induced by the mononuclear Cu(II) 1,4,7,10-tetraazacyclo-dodecane complex was realized via a non-random double-stranded scission process. The differential cleavage activity is discussed in relation to dimer formation, effective cooperation and coordination environment of the metal center. The hydrolytic cleavage by the copper complexes without H2O2 is supported by evidence from an anaerobic reaction, free radical quenching, and nitro blue tetrazolium assay. In contrast, both the binuclear complexes cleaved supercoiled DNA efficiently to Form III (linearized DNA) in the presence of H2O2, indicating that nuclearity is a crucial parameter in oxidative cleavage. The radical scavenger inhibition study and nitro blue tetrazolium assay suggested the involvement of H2O2 and superoxide ions in the oxidative cleavage of DNA by the binuclear complexes. PMID:25108187

Chitrapriya, Nataraj; Wang, Wei; Jang, Yoon Jung; Kim, Seog K; Kim, Jung Hee

2014-11-01

149

Review: Formation of Peptide Radical Ions Through Dissociative Electron Transfer in Ternary Metal-Ligand-Peptide Complexes  

SciTech Connect

The formation and fragmentation of odd-electron ions of peptides and proteins is of interest to applications in biological mass spectrometry. Gas-phase redox chemistry occurring during collision-induced dissociation of ternary metal-ligand-peptide complexes enables the formation of a variety of peptide radicals including the canonical radical cations, M{sup +{sm_bullet}}, radical dications, [M{sup +}H]{sup 2+{sm_bullet}}, radical anions, [M-2H]{sup -{sm_bullet}}. In addition, odd-electron peptide ions with well-defined initial location of the radical site are produced through side chain losses from the radical ions. Subsequent fragmentation of these species provides information on the role of charge and the location of the radical site on the competition between radical-induced and proton-driven fragmentation of odd-electron peptide ions. This account summarizes current understanding of the factors that control the efficiency of the intramolecular electron transfer (ET) in ternary metal-ligand-peptide complexes resulting in formation of odd-electron peptide ions. Specifically, we discuss the effect of the metal center, the ligand and the peptide structure on the competition between the ET, proton transfer (PT), and loss of neutral peptide and neutral peptide fragments from the complex. Fundamental studies of the structures, stabilities, and the energetics and dynamics of fragmentation of such complexes are also important for detailed molecular-level understanding of photosynthesis and respiration in biological systems.

Chu, Ivan K.; Laskin, Julia

2011-12-31

150

Bio-mimetic metal-ligand crosslinks yield self-healing polymer networks with near-covalent elastic moduli  

NASA Astrophysics Data System (ADS)

Growing evidence supports a load-bearing role for metal-polymer interactions in biological protein networks. In particular, the strength of the coordinate bonds in metal-ligand coordination complexes combined with their capacity to reform after breaking has been proposed as a source of the high toughness and potential self-healing in certain natural materials. Some of the highest stabilities among metal-ligand coordination complexes are found between Fe3+ and catechol ligands at alkaline pH where the tris-catecholato-Fe3+ stoichiometry prevails, yet the effect of such crosslinks on material properties has not been fully characterized due to the low solubility of Fe3+ at high pH. Inspired by the pH jump experienced by marine biomaterials during secretion, we have developed a simple method to control catechol-Fe3+ inter-polymer crosslinking via pH. The resulting gels display elastic moduli (G') that approach covalently crosslinked gels as well as self-healing properties.

Holten-Andersen, Niels; Harrington, Matthew; Birkedal, Henrik; Lee, Bruce; Messersmith, Phillip; Waite, Herbert; Lee, Ka Yee

2011-03-01

151

Synthesis and spectral studies on metal complexes of s-triazine based ligand and non linear optical properties  

NASA Astrophysics Data System (ADS)

A series of transition metal complexes of type [ML] and [ML2]Cl2 (where M = Cu(II), Ni(II), Co(II) have synthesized from 2-phenylamino-4,6-dichloro-s-triazine and 3,5-dimethyl pyrazole; their characteristics have been investigated by means of elemental analyses, magnetic susceptibility, molar conductance, IR, UV-Vis, Mass, NMR and ESR spectra. The electrochemical behavior of copper(II) complexes we have studied, by using cyclic voltammetry. The ESR spectra of copper(II) complexes are recorded at 300 K and 77 K and their salient features are appropriately reported. Spectral datas, we found, show that the ligand acts as a neutral tridentate, and coordinates through the triazine ring nitrogen and pyrazolyl ring nitrogen atoms to the metal ion. Evident from our findings, the metal(II) complexes of [ML] type exhibit square pyramidal geometry, and that of [ML2]Cl2 exhibit octahedral geometry. The in vitro antimicrobial activities of the ligand and its complexes are evaluated against Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mutans, Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Proteus vulgaris, Cryptococcus neoformans, Pseudomonas aeruginosa, Salmonella typhi, Serratia marcescens, Shigella flexneri, Vibrio cholera, Vibris parahaemolyticus, Aspergillus niger, Candida albicans and Penicillium oxalicum by well-diffusion method. The second harmonic generation efficiency of the ligand and its complexes are determined and compared with urea and KDP.

Shanmugakala, R.; Tharmaraj, P.; Sheela, C. D.

2014-11-01

152

Metal-Humate Interactions. 1. Discrete Ligand and Continuous Distribution David A. Dzombak, Wllllam Fish,+and Franqols M. M. Morel"  

E-print Network

Metal-Humate Interactions. 1. Discrete Ligand and Continuous Distribution Models David A. Dzombak and continuous multiligand models for metal- humate binding. The concepts and equations that unify the various of metal-humate com- plexation. It is shown that the lower half and extremeright of the Gaussianligand

Morel, François M. M.

153

Non-localized ligand-to-metal charge transfer excited states in (Cp)2Ti(IV)(NCS)2.  

PubMed

The bent d(0) titanium metallocene (Cp)(2)Ti(NCS)(2) exhibits an intense phosphorescence from a ligand-to-metal charge transfer triplet excited state at 77 K in an organic glass substrate and a poly(methyl methacrylate) plastic substrate. Quantum chemical calculations and spectroscopic studies show that the orbital parentage of this triplet state arises from the promotion of an electron from an essentially nonbonding symmetry adapted pi molecular orbital located on the NCS(-) ligands to a d(z)2-(y)2 orbital located on the Ti metal. Standard infrared spectroscopy of (Cp)(2)Ti(NCS)(2) in its ground electronic state at 77 K reveals a pair of closely spaced absorptions at (2072 cm(-1), 2038 cm(-1))(glass) and (2055 cm(-1), 2015 cm(-1))(plastic) that are assigned, respectively, to the symmetric and antisymmetric CN stretching modes of the two coordinated NCS(-) ligands. Low-temperature (77 K) time-resolved infrared spectroscopy that accesses the phosphorescing triplet excited state on the ns time scale shows an IR bleach that is coincident with the two ground state CN stretching bands and an associated grow-in of a pair of new IR bands at slightly lower energies (2059 cm(-1), 2013 cm(-1))(glass) and (2049 cm(-1), 1996 cm(-1))(plastic) that are assigned, respectively, to the symmetric and antisymmetric CN stretches in the emitting triplet state. These transient IR bands decay with virtually identical lifetimes to those observed for the phosphorescence decays when measured under identical experimental conditions. Singular value decomposition analysis of the time-resolved infrared data shows that the observed transient IR features arise from the same electronic manifold as measured through luminescence studies. The close similarity between the ground state and excited-state CN stretching bands in (Cp)(2)Ti(NCS)(2) indicates that symmetry breaking does not occur in forming the charge-transfer triplet excited-state manifold; i.e., electron density is withdrawn from a delocalized pi MO spread across both NCS(-) ligands. Calculations at several levels of theory reveal a delocalized ligand-to-metal charge transfer excited triplet manifold. These calculations closely reproduce the relative intensity ratios and frequencies of the symmetric and antisymmetric transient infrared vibrations in the CN region. This study is the first time-resolved infrared investigation of a ligand-to-metal charge-transfer excited state and the first to be performed at cryogenic temperatures in thin-film organic glass and plastic substrates. PMID:12720460

Patrick, Elizabeth L; Ray, Chad J; Meyer, Grant D; Ortiz, Theodore P; Marshall, Jason A; Brozik, James A; Summers, Melissa A; Kenney, John W

2003-05-01

154

Rigid versus flexible: how important is ligand "preorganization" for metal ion recognition by lower rim-functionalized calix[4]arenes?  

PubMed

For an assessment of the outcomes from use of an appropriately "preorganized" calixarene-based ionophore versus its conformationally mobile prototype, solvent extraction propensities of flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] for alkali, alkaline earth metal cations, Pb2+, Ag+ and Hg2+ are compared with those for seven new rigid analogs fixed in the cone, partial cone and 1,3-alternate conformations. For each of the metal ions, the preferred calix[4]arene conformation was determined from the NMR spectra for the metal salt of the flexible ligand. Except for Ag+, flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] were found to provide greater metal ion extraction efficiency and better selectivity than the corresponding "preorganized" ionophores. PMID:15351822

Talanova, Galina G; Talanov, Vladimir S; Hwang, Hong-Sik; Park, Chunkyung; Surowiec, Kazimierz; Bartsch, Richard A

2004-09-21

155

Influence of connectivity and porosity on ligand-based luminescence in zinc metal-organic frameworks.  

PubMed

Applications of metal-organic frameworks (MOFs) require close correlation between their structure and function. We describe the preparation and characterization of two zinc MOFs based on a flexible and emissive linker molecule, stilbene, which retains its luminescence within these solid materials. Reaction of trans-4,4'-stilbene dicarboxylic acid and zinc nitrate in N,N-dimethylformamide (DMF) yielded a dense 2-D network, 1, featuring zinc in both octahedral and tetrahedral coordination environments connected by trans-stilbene links. Similar reaction in N,N-diethylformamide (DEF) at higher temperatures resulted in a porous, 3-D framework structure, 2. This framework consists of two interpenetrating cubic lattices, each featuring basic zinc carboxylate vertices joined by trans-stilbene, analogous to the isoreticular MOF (IRMOF) series. We demonstrate that the optical properties of both 1 and 2 correlate with the local ligand environments observed in the crystal structures. Steady-state and time-resolved spectroscopic measurements reveal that the stilbene linkers in the dense structure 1 exhibit a small degree of interchromophore coupling. In contrast, the stilbenoid units in 2 display very little interaction in this low-density 3-D framework, with excitation and emission spectra characteristic of monomeric stilbenes, similar to the dicarboxylic acid in dilute solution. In both cases, the rigidity of the stilbene linker increases upon coordination to the inorganic units through inhibition of torsion about the central ethylene bond, resulting in luminescent crystals with increased emission lifetimes compared to solutions of trans-stilbene. The emission spectrum of 2 is found to depend on the nature of the incorporated solvent molecules, suggesting use of this or related materials in sensor applications. PMID:17503820

Bauer, Christina A; Timofeeva, Tatiana V; Settersten, Thomas B; Patterson, Brian D; Liu, Vincent H; Simmons, Blake A; Allendorf, Mark D

2007-06-01

156

The wooden anchor  

E-print Network

'Archeologie Subaquatique Corpus Inscriptionum Atticarum / Comptes rendus de 1'Academic des inscriptiones et belles lettres Greek Papyri Greek Papyri in the British Museum IG Inscriptiones Graecae I JNA International Journal of Nautical Archaeology and Underwater..., to Eupalamus and Anacharsis; and Pausanias, to Nidas (738-696 B. C. ). The earliest certain evidence of wooden anchors is the employment of the Greek word ankura, "anchor", or "bent", by Alcaeus (c. 620-580) around the end of the seventh century B. C...

Haldane, David Douglas

2012-06-07

157

The Resolution of Chiral, Tetrahedral M4L6 Metal-LigandHosts  

SciTech Connect

The supramolecular metal-ligand assemblies of M{sub 4}1{sub 6} stoichiometry are chiral (M = Ga{sup III}, Al{sup III}, In{sup III}, Fe{sup III}, Ti{sup IV}, or Ge{sup IV}, H{sub 4}1 = N,N'-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene). The resolution process of {Delta}{Delta}{Delta}{Delta}- and {Lambda}{Lambda}{Lambda}{Lambda}-[M{sub 4}1{sub 6}]{sup 12-} by the chiral cation s-nicotinium (S-nic{sup +}) is described for the Ga{sup III}, Al{sup III}, and Fe{sup III} assemblies, and the resolution is shown to be proton dependent. From a methanol solution of M(acac){sub 3}, H{sub 4}1, S-nicI, and KOH, the {Delta}{Delta}{Delta}{Delta}-KH{sub 3}(S-nic){sub 7}[(S-nic) {contained_in}M{sub 4}1{sub 6}] complexes precipitate, and the {Lambda}{Lambda}{Lambda}{Lambda}-K{sub 6}(S-nic){sub 5}[(S-nic) {contained_in} M{sub 4}1{sub 6}] complexes subsequently can be isolated from the supernatant. Ion exchange enables the isolation of the (NEt{sub 4}{sup +}){sub 12}, (NMe{sub 4}{sup +}){sub 12} and K{sub 12}{sup +} salts of the resolved structures, which have been characterized by CD and NMR spectroscopies. Resolution can also be accomplished with one equivalent of NEt{sub 4}{sup +} blocking the cavity interior, demonstrating that external binding sites are responsible for the difference in S-nic{sup +} enantiomer interactions. Circular dichroism data demonstrate that the (NMe{sub 4}{sup +}){sub 12} and (NEt{sub 4}{sup +}){sub 12} salts of the resolved [Ga{sub 4}1{sub 6}]{sup 12-} and [Al{sub 4}1{sub 6}]{sup 12-} structures retain their chirality over extended periods of time (>20 d) at room temperature; heating the (NEt{sub 4}{sup +}){sub 12}[Ga{sub 4}1{sub 6}] assembly to 75 C also had no effect on its CD spectrum. Finally, experiments with the resolved K{sub 12}[Ga{sub 4}1{sub 6}] assemblies point to the role of a guest in stabilizing the resolved framework.

Davis, Anna V.; Fiedler, Dorothea; Ziegler, Marco; Terpin,Andreas; Raymond, Kenneth N.

2007-08-28

158

Red electroluminescence of ruthenium sensitizer functionalized by sulfonate anchoring groups.  

PubMed

We have synthesized five novel Ru(ii) phenanthroline complexes with an additional aryl sulfonate ligating substituent at the 5-position [Ru(L)(bpy)2](BF4)2 (1), [Ru(L)(bpy)(SCN)2] (2), [Ru(L)3](BF4)2 (3), [Ru(L)2(bpy)](BF4)2 (4) and [Ru(L)(BPhen)(SCN)2] (5) (where L = 6-one-[1,10]phenanthroline-5-ylamino)-3-hydroxynaphthalene 1-sulfonic, bpy = 2,2'-bipyridine, BPhen = 4,7-diphenyl-1,10-phenanthroline), as both photosensitizers for oxide semiconductor solar cells (DSSCs) and light emitting diodes (LEDs). The absorption and emission maxima of these complexes red shifted upon extending the conjugation of the phenanthroline ligand. Ru phenanthroline complexes exhibit broad metal to ligand charge transfer-centered electroluminescence (EL) with a maximum near 580 nm. Our results indicated that a particular structure (2) can be considered as both DSSC and OLED devices. The efficiency of the LED performance can be tuned by using a range of ligands. Device (2) has a luminance of 550 cd m(-2) and maximum efficiency of 0.9 cd A(-1) at 18 V, which are the highest values among the five devices. The turn-on voltage of this device is approximately 5 V. The role of auxiliary ligands in the photophysical properties of Ru complexes was investigated by DFT calculation. We have also studied photovoltaic properties of dye-sensitized nanocrystalline semiconductor solar cells based on Ru phenanthroline complexes and an iodine redox electrolyte. A solar energy to electricity conversion efficiency (?) of 0.67% was obtained for Ru complex (2) under standard AM 1.5 irradiation with a short-circuit photocurrent density (Jsc) of 2.46 mA cm(-2), an open-circuit photovoltage (Voc) of 0.6 V, and a fill factor (ff) of 40%, which are all among the highest values for ruthenium sulfonated anchoring groups reported so far. Monochromatic incident photon to current conversion efficiency was 23% at 475 nm. Photovoltaic studies clearly indicated dyes with two SCN substituents yielded a higher Jsc for the cell than dyes with a tris-homoleptic anchor substituent. PMID:24818219

Shahroosvand, Hashem; Abbasi, Parisa; Mohajerani, Ezeddin; Janghouri, Mohammad

2014-06-28

159

(S)-5-(p-Nitrobenzyl)-PCTA, a Promising Bifunctional Ligand with Advantageous Metal Ion Complexation Kinetics  

PubMed Central

A bifunctional version of PCTA (3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9,-triacetic acid) that exhibits fast complexation kinetics with the trivalent lanthanide(III) ions was synthesized in reasonable yields starting from N, N?, N?-tristosyl-(S)-2-(p-nitrobenzyl)-diethylenetriamine. pH-potentiometric studies showed that the basicities of p-nitrobenzyl-PCTA and the parent ligand PCTA were similar. The stability of M(NO2-Bn-PCTA) (M = Mg2+, Ca2+, Cu2+, Zn2+) complexes was similar to that of the corresponding PCTA complexes while the stability of Ln3+ complexes of the bifunctional ligand is somewhat lower than that of PCTA chelates. The rate of complex formation of Ln(NO2-Bn-PCTA) complexes was found to be quite similar to that of PCTA, a ligand known to exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid catalyzed decomplexation kinetic studies of the selected Ln(NO2-Bn-PCTA) complexes showed that the kinetic inertness of the complexes was comparable to that of Ln(DOTA) chelates making the bifunctional ligand NO2-Bn-PCTA suitable for labeling biological vectors with radioisotopes for nuclear medicine applications. PMID:19220012

Tircso, Gyula; Benyo, Eniko Tircsone; Suh, Eul Hyun; Jurek, Paul; Kiefer, Garry E.; Sherry, A. Dean; Kovacs, Zoltan

2009-01-01

160

Supramolecular spectral studies on metal-ligand bonding of novel quinoline azodyes.  

PubMed

A series of novel bidentate azodye quinoline ligands were synthesized with various p-aromatic amines like p-(OCH3, CH3, H, Cl and NO2). All ligands and their complexes have been characterized on the basis of elemental analysis, IR, (1)H and (13)C NMR data and spectroscopic studies. IR and (1)H NMR studies reveal that the ligands (HLn) exists in the tautomeric azo/hydrazo form in both states with intramolecular hydrogen bonding. The ligands obtained contain NN and phenolic functional groups in different positions with respect to the quinoline group. IR spectra show that the azo compounds (HLn) act as monobasic bidentate ligand by coordinating via the azodye (NN) and oxygen atom of the phenolic group. The ESR (g|| and g ) and bonding ?(2) parameters of the copper ion were greatly affected by substituting several groups position of ring of quinoline and p-aromatic ring. The ESR spectra of copper complexes in powder form show a broad signal with values in order g|| >g > ge > 2.0023. The value of covalency factor ? and orbital reduction factor K accounts for the covalent nature of the complexes. All complexes possessed an octahedral and square planar geometry. The thermal properties of the complexes were investigated using TGA and DSC. It is found that the change of substituent affects the thermal properties of complexes. PMID:23973590

Diab, M A; El-Sonbati, A Z; El-Bindary, A A; Barakat, A M

2013-12-01

161

Stereoselective synthesis of cobalt(III) anionic complexes with chiral pyruvylaminoacid oximes and metal–ligand interactions in aqueous solution  

Microsoft Academic Search

A series of cobalt(III) anionic complexes with hydroxyimino analogs of dipeptides – oximes of pyruvylglycine, pyruvyl-l-alanine, pyruvyl-l-methionine and pyruvyl-l-phenylalanine (H2pamaco, amac=amino acid) of composition Cat3[Co(H?1pamaco)2]·nH2O (Cat – a monovalent metal cation) has been synthesized and investigated by UV–Vis, CD and 1H NMR spectroscopy. It was established that for the two latter ligands, non-racemic mixtures of two diastereomeric complexes were formed

Aleksander Kufelnicki; Igor O. Fritsky; Tatiana Yu. Sliva; Inna F. Golovaneva; Rostislav D. Lampeka

2007-01-01

162

Quest for highly porous metal?metalloporphyrin framework based upon a custom-designed octatopic porphyrin ligand  

SciTech Connect

A porous metal-metalloporphyrin framework, MMPF-2, has been constructed from a custom-designed octatopic porphyrin ligand, tetrakis(3,5-dicarboxyphenyl)porphine, that links a distorted cobalt trigonal prism secondary building unit. MMPF-2 possesses permanent microporosity with the highest surface area of 2037 mg{sup 2} g{sup -1} among reported porphyrin-based MOFs, and demonstrates a high uptake capcity of 170 cm{sup 3} g{sup -1} CO{sub 2} at 273 K and 1 bar.

Wang, Xi-Sen; Chrzanowski, Matthew; Kim, Chungsik; Gao, Wen-Yang; Wojtas, Lukasz; Chen, Yu-Sheng; Zhang, X. Peter; Ma, Shengqian (USF); (UC)

2012-12-13

163

A New Rare-Earth Metal Coordination Polymer Constructed from N -hetero Aromatic Multicarboxylate Ligand  

Microsoft Academic Search

\\u000a Abstract  The hydrothermal reaction of Gd(NO3)3·6H2O with 2,2?-bipyridyl-4,4?-dicarboxylic acid(H2BPDC) ligand results in the formation of a new Gd(III) polymer: {[Gd2(BPDC)3(H2O)3]·H2O}\\u000a n..(1). The central gadolinium ion is coordinated by eight oxygen atoms to give a dicapped triangular prism geometry. Based on\\u000a the versatile coordination modes of BPDC2? ligand, together with hydrogen bonds and ?···? stacking interactions, a 3-D network is presented. DFT

Hai-Jun DongMin; Min Wang; Shu-Wei Huang; Yan-Ling Wu; Hao-Hong Li; Zhi-Rong Chen

2010-01-01

164

Blue fluorescence of three metal-organic zinc polymers containing tetrazinc units and asymmetric ligand of btc{sup 3-}  

SciTech Connect

Three new zinc coordination polymers [Zn{sub 2}(btc){sub 2}(H{sub 2}O){sub 2}] {sub n} .n[Zn(H{sub 2}O){sub 6}] (1), [Zn{sub 3}(btc){sub 2}(2,2'-bipy){sub 2}(H{sub 2}O){sub 3}] {sub n} .2nH{sub 2}O (2) and [Zn{sub 3}(btc){sub 2}(H{sub 2}O){sub 6}] {sub n} .nH{sub 2}O (3) (H{sub 3}btc=1,2,4-benzenetricarboxylic acid, 2,2'-bipy=2,2'-bipyridine) were obtained by the diffusion method and their crystal structures were determined by single-crystal X-ray diffraction. Compounds 1-3 have the similar tetrametallic unit [Zn{sub 4}(btc){sub 2}] SBUs and these SBUs are further connected into stair-like structure, 2-D layer and 3-D framework for 1, 2 and 3, in which the btc{sup 3-} ligands adopt {mu} {sub 3}, {mu} {sub 4} and {mu} {sub 5} coordination modes, respectively. The title compounds show strong blue fluorescence, which may be assigned as {pi}*{sup {yields}}n transition of the ligand mixed with the ligand-to-metal change transfer (LMCT), indicating the fluorescence, indicates the title compounds may be good candidates for blue-light photoactive materials.

Xu Ling [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China); Liu Bing [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Zheng Fakun [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Guo Guocong [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)]. E-mail: gcguo@ms.fjirsm.ac.cn; Huang Jinshun [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)

2005-11-15

165

[2]Catenanes built around octahedral transition-metal complexes that contain two intertwined endocyclic but non-sterically hindering tridentate ligands.  

PubMed

Sterically hindering bidentate chelates, such as 2,9-diphenyl-1,10-phenanthroline, form entwined complexes with copper(I) and other tetrahedrally coordinated transition-metal centres. To prepare octahedral complexes containing two entwined tridentate ligands and thus apply a strategy similar to that used for making catenanes with tetrahedral metal centres, the use of the classical terpy ligand (terpy=2,2':6',2''-terpyridine) appears to be attractive. In fact, 6,6''-diphenyl-2,2':6',2''-terpyridine (dp-terpy) is not appropriate due to strong "pinching" of the organic backbone by coordination to the metal and thus stable entwined complexes with this ligand cannot be obtained. Herein, we report the synthesis and coordination properties of a new family of tridentate ligands, the main features of which are their endocyclic nature and non-sterically hindering character. The coordinating fragment consists of two 8'-phenylisoquinolin-3'-yl groups attached at the 2 and 6 positions of a pyridine nucleus. Octahedral complexes containing two such entangled ligands around an octahedral metal centre, such as Fe(II) , Ru(II) or Co(III) , are highly stable, with no steric congestion around the metal. By using functionalised ligands bearing terminal olefins, double ring-closing metathesis leads to [2]catenanes in good yield with Fe(II) or Co(III) as the templating metal centre. The X-ray crystallography structures of the Fe(II) precursor and the Fe(II) catenane are also reported. These show that although significant pinching of the ligand is observed in both Fe(II) complexes, the system is very open and no steric constraints can be detected. PMID:22431359

Ayme, Jean-François; Lux, Jacques; Sauvage, Jean-Pierre; Sour, Angélique

2012-04-27

166

Conformation Preference of a Flexible Cyclohexanetetracarboxylate Ligand in Three New Metal-Organic Frameworks: Structures, Magnetic and Luminescent Properties  

PubMed Central

Three novel complexes of formula [Co5(OH)2(cht)2(H2O)10]n · 2nH2O (1) (H4cht = cyclohexane-1,2,4,5-tetracarboxylic acid), [Zn2(cht)(H2O)3]n · nH2O (2), and [Cd2(cht)(H2O)5]n · 2nH2O (3) were synthesized by a hydrothermal reaction of cyclohexane-1,2,4,5-tetracarboxylic acid in the presence of sodium hydroxide with Co(NO3)2 · 6H2O, Zn(NO3)2 · 6H2O, and Cd(NO3)2 · 4H2O, respectively. These complexes were obtained by controlling the molar ratios of starting materials and the pH values of reaction mixtures with an initial pH of 5.87 for 1, 5.50 for 2, and 5.57 for 3, respectively. The single-crystal X-ray investigations reveal that the cht ligands change their conformations exclusively to the a,e,e,a form in all three complexes. Complex 1 features a two-dimensional (2D) metal-organic framework (MOF) with an axis surrounded by two zigzag structures, a rectangular channel surrounded by two a-carboxylate-metal-a-carboxlate and two e-carboxylate-metal-e-carboxylate chains, and two smaller distorted square-pyramidal channels surrounded by hydroxyl oxygen, cyclohexane, and its two a-carboxylates. Each cht ligand connects five cobalt atoms and each cobalt atom is six-coordinated with carboxylate-oxygen, hydroxyl, and water molecules. Complex 2 possesses a three-dimensional (3D) MOF structure that consists of the cht ligands and two types of cobalt; one is four-coordinated with carboxylate-oxygens and the other is six-coordinated with carboxylate-oxygens and water molecules. Each cht ligand is bonded to seven zinc atoms. Complex 3 is also a 2DMOF structure constructed by seven-coordinated cadmium atoms and the cht ligands. The e-carboxylates of two parallel cht ligands are connected to a type of cadmium atoms to form 1D chains, and these chains are further connected through a-carboxylates of the ligands and another type of cadmium atoms to give the 2D structure. Extensive hydrogen bonding interactions involving carboxylate-oxygen atoms and crystallization water molecules afford 3D supramolecular networks in complexes 1 and 2. Magnetic susceptibility measurement of 1 confirmed a six-coordinated high-spin cobalt(II) ion and the presence of magnetic exchange coupling among the three hydroxyl-oxygen bridged cobalt ions. Fluorescent spectra of complexes 2 and 3 show strong fluorescent emissions in the blue region. PMID:19586018

Wang, Rongming; Zhang, Jian; Li, Lijuan

2009-01-01

167

Effect of metal complexation on the conductance of single-molecular wires measured at room temperature.  

PubMed

The present work aims to give insight into the effect that metal coordination has on the room-temperature conductance of molecular wires. For that purpose, we have designed a family of rigid, highly conductive ligands functionalized with different terminations (acetylthiols, pyridines, and ethynyl groups), in which the conformational changes induced by metal coordination are negligible. The single-molecule conductance features of this series of molecular wires and their corresponding Cu(I) complexes have been measured in break-junction setups at room temperature. Experimental and theoretical data show that no matter the anchoring group, in all cases metal coordination leads to a shift toward lower energies of the ligand energy levels and a reduction of the HOMO-LUMO gap. However, electron-transport measurements carried out at room temperature revealed a variable metal coordination effect depending on the anchoring group: upon metal coordination, the molecular conductance of thiol and ethynyl derivatives decreased, whereas that of pyridine derivatives increased. These differences reside on the molecular levels implied in the conduction. According to quantum-mechanical calculations based on density functional theory methods, the ligand frontier orbital lying closer to the Fermi energy of the leads differs depending on the anchoring group. Thereby, the effect of metal coordination on molecular conductance observed for each anchoring could be explained in terms of the different energy alignments of the molecular orbitals within the gold Fermi level. PMID:24831452

Ponce, Julia; Arroyo, Carlos R; Tatay, Sergio; Frisenda, Riccardo; Gaviña, Pablo; Aravena, Daniel; Ruiz, Eliseo; van der Zant, Herre S J; Coronado, Eugenio

2014-06-11

168

The development of N2S2 metal complexes as bidentate ligands for organometallic chemistry  

E-print Network

Electronic and steric parameters for square planar NiN2S2 complexes as bidentate, S-donor ligands have been established. According to the (CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of (NiN2S2)W(CO)4 adducts...

Rampersad, Marilyn Vena

2007-04-25

169

A Tetrapositive Metal Ion in the Gas Phase: Thorium(IV) Coordinated by Neutral Tridentate Ligands  

SciTech Connect

ESI of 1:1 mixtures of Th(ClO?)? and ligand TMOGA in acetonitrile resulted in the observation of the TMOGA supported tetracation, Th(L)???, in the gas phase. Three TMOGA ligands are necessary to stabilize the tetrapositive thorium ion; no Th(L)??? or Th(L)??? was observed. Theoretical calculations reveal that the Th(L)??? complex possesses C? symmetry with the thorium center coordinated by nine oxygen atoms from three ligands, which forms a twisted TPP geometry. Actinide compounds with such a geometry feature a nine-coordinate chiral actinide center. The Th-L binding energy and bond orders of Th(L)n?? decrease as the coordination number increases, consistent with the trend of concurrently increasing Th-O distances. The Th-O bonding is mainly electrostatic in nature, but the covalent interactions are not negligible. CID of the Th(L)??? complex mainly resulted in charge reduction to form Th(L)?(L-86)³?oss of neutral TMOGA was not observed. The protic ligand methanol stabilized only tri- and dications of ligated thorium. The intensity of the Th(L)??? peak was reduced as the percentage of water increased in the Th(ClO?)?/TMOGA solution.

Gong, Yu; Hu, Han-Shi; Tian, Guoxin; Rao, Linfeng; Li, Jun; Gibson, John K.

2013-07-01

170

Cluster Synthesis via Ligand-Arrested Solid Growth: Triethylphosphine-Capped Fragments of Binary Metal Chalcogenides  

E-print Network

generated in the gas phase by laser ablation.1 Typically, these clusters are produced only in very small intermediates. Triethylphosphine was selected as a volatile ligand expected to have an affinity for the soft walls melted to give a darkly colored solution. Unreacted triethylphosphine was then removed by vacuum

171

Enthused research on DNA-binding and DNA-cleavage aptitude of mixed ligand metal complexes  

NASA Astrophysics Data System (ADS)

Five new Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) mixed ligand complexes have been synthesized using a Schiff base precursor (obtained by the condensation of N-(4-aminophenyl)acetamide and 4-chlorobenzaldehyde) as main ligand and 1,10-phenanthroline as co-ligand. They have been characterized by microanalytical data, IR, UV-Vis, magnetic moment values, conductivity and electrochemical measurements. The spectral data reveal that all the complexes exhibit octahedral geometry. The high electrical conductance of the complexes supports their electrolytic nature. The monomeric nature of the complexes has been assessed from their magnetic susceptibility values. These complexes are better antimicrobial active agents than the free ligands. DNA (CT) binding properties of these complexes have been explored by UV-Vis., viscosity measurements, cyclic voltammetry, and differential pulse voltammetry measurements. The oxidative cleavage activity of the complexes has been studied using supercoiled pUC19 DNA by gel electrophoresis. The experimental results show that the complexes are good intercalators.

Mahalakshmi, Rajkumar; Raman, Natarajan

2013-08-01

172

Ligand effects on the dimensionality of oxamato-bridged mixed-metal open-framework magnets.  

PubMed

Increasing dimensionality [from 2D (1) to 3D (2)] and T(C) [from 10 (1) to 20 K (2)] in two new oxamato-bridged heterobimetallic Mn(II)(2)Cu(II)(3) open-frameworks result from the steric hindrance provided by the different alkyl substituents of the N-phenyloxamate bridging ligands. PMID:22378323

Ferrando-Soria, Jesús; Grancha, Thais; Julve, Miguel; Cano, Joan; Lloret, Francesc; Journaux, Yves; Pasán, Jorge; Ruiz-Pérez, Catalina; Pardo, Emilio

2012-04-11

173

Heavy metal complexation with naturally occurring organic ligands in wetland ecosystems  

Microsoft Academic Search

The mode, rate, and extent of heavy metal uptake by freshwater wetlands were investigated as well as heavy metal complexation by a variety of soluble organics. One study involved adding Cd, Cu, Mn, and Zn to septage from Waldo, Florida, and pumping the wastewater through a 10 x 40-m corridor in a cypress swamp. Soluble concentrations of all four metals

Tuschall; J. R. Jr

1981-01-01

174

Fatigue testing of suture anchors.  

PubMed

In a porcine tibia model, we subjected widely used anchor-suture combinations to a fatigue-testing protocol. The Ethibond No. 2 suture was the weakest part of the anchor-suture combinations when they were loaded to failure by a single pull. Under cyclic-loading conditions, fixation strength was decreased compared with single-pull tests. The suture/anchor interface was identified as the weakest link in the Mitek GII/No. 2 combination and in the Zimmer Statak 3.5/No. 2 combination. In most cases the suture was worn through at the eyelet. Threading the GII anchor with a No. 5 suture and use of larger anchors in combination with No. 2 sutures increased the fatigue strength. Suture breakage at the knot was the predominant failure mode for biodegradable anchors inserted into cortical bone. The highest fatigue strength was seen for the Super Anchor/No. 5 combination when the anchor was inserted in cortical bone. Fatigue testing is crucial for evaluation of suture anchors and should be performed along with single-pull testing. The mechanical performance of a suture anchor threaded with a defined suture depends on several key factors: the pullout strength of the anchor, the tensile strength of the suture, and the interaction of anchor and suture at the eyelet (suture/anchor interface). PMID:11912095

Rupp, Stefan; Georg, Thomas; Gauss, Christian; Kohn, Dieter; Seil, Romain

2002-01-01

175

Coordination properties of 2,5-dimesitylpyridine: an encumbering and versatile ligand for transition-metal chemistry.  

PubMed

To overcome the unfavorable steric pressures associated with 2,6-disubstitution in encumbering pyridine ligands, the coordination chemistry of a 2,5-disubstituted variant, namely, 2,5-dimesitylpyridine (2,5-Mes(2)py), is reported. This diaryl pyridine shows good binding ability to a range of transition-metal fragments with varying formal oxidation states and coligands. Treatment of 2.0 equiv of 2,5-Mes(2)py with monovalent Cu and Ag triflate sources generates complexes of the type [M(2,5-Mes(2)py)(2)]OTf (M = Cu, Ag; OTf = OSO(2)CF(3)), which feature long M-OTf distances and a substrate-accessible primary coordination sphere. Combination of 2,5-Mes(2)py with Cu(OTf)(2) and Pd(OAc)(2) produces four-coordinate complexes featuring cis- and trans-2,5-Mes(2)py orientations, respectively. The four-coordinate palladium complex Pd(OAc)(2)(2,5-Mes(2)py)(2) is found to resist py-ligand dissociation at room temperature in solution, but functions as a precatalyst for the aerobic C-H bond olefination of benzene at elevated temperatures. This C-H bond activation chemistry is compared with a similar Pd-based system featuring 2,6-disubstituted pyridines. 2,5-Mes(2)py also readily supports mono- and dinuclear divalent Co complexes, and the solution-phase equilibria between such species are detailed. The coordination studies presented highlight the potential of 2,5-Mes(2)py to function as an encumbering ancillary for the stabilization of low-coordinate complexes and as a supporting ligand for metal-mediated transformations. PMID:21710998

Stauber, Julia M; Wadler, Andrew L; Moore, Curtis E; Rheingold, Arnold L; Figueroa, Joshua S

2011-08-01

176

Molecular Architectures Derived from Metal Ions and the Flexible 3,3?-Bipyridine Ligand: Unexpected Dimer with Hg(II)  

PubMed Central

The flexible ditopic ligand 3,3?-bipyridine (3,3?-bpy) has been reacted with a series of transition metal species (Ag+, Hg2+, cis-a2M2+ (a = NH3 or a2 = en; M = Pt, Pd), trans-a2Pt2+ (a = NH3)) in an attempt to produce discrete cyclic constructs. While Ag+ gave a polymeric structure {[Ag(3,3?-bpy)](ClO4)?·?H2O}n (1), with all other metal entities cyclic structures were formed. Interestingly, Hg(CH3COO)2 produced a dinuclear complex [Hg(3,3?-bpy)(CH3COO)2]2?·?3H2O (2), in which the two 3,3?-bpy ligands adopt a cis-orientation of the coordinating pyridyl entities. With cis-(NH3)2Pt2+, a cyclic complex 4 was isolated in crystalline form which, according to HRMS, is a trimer. With trans-(NH3)2Pt2+, different species are formed according to 1H NMR spectroscopy, the nature of which was not established. PMID:20631837

Khutia, Anupam; Sanz Miguel, Pablo J.; Lippert, Bernhard

2010-01-01

177

Anchoring the Deficit of the Anchor Deficit: Dyslexia or Attention?  

ERIC Educational Resources Information Center

In the anchoring deficit hypothesis of dyslexia ("Trends Cogn. Sci.", 2007; 11: 458-465), it is proposed that perceptual problems arise from the lack of forming a perceptual anchor for repeatedly presented stimuli. A study designed to explicitly test the specificity of the anchoring deficit for dyslexia is presented. Four groups, representing all…

Willburger, Edith; Landerl, Karin

2010-01-01

178

Science Sampler: Anchor activities  

NSDL National Science Digital Library

What's the best way to keep students occupied when they have finished their work? An Anchor Activity Learning Station provides high-interest, educational options for students who have finished with required class assignments, labs, or investigations. A list of ideas is included.

Corlett, Cindy

2003-03-01

179

Synthesis, Characterization, Antimicrobial, DNA Cleavage, and In Vitro Cytotoxic Studies of Some Metal Complexes of Schiff Base Ligand Derived from Thiazole and Quinoline Moiety  

PubMed Central

A novel Schiff base ligand N-(4-phenylthiazol-2yl)-2-((2-thiaxo-1,2-dihydroquinolin-3-yl)methylene)hydrazinecarboxamide (L) obtained by the condensation of N-(4-phenylthiazol-2-yl)hydrazinecarboxamide with 2-thioxo-1,2-dihydroquinoline-3-carbaldehyde and its newly synthesized Cu(II), Co(II), Ni(II), and Zn(II) complexes have been characterized by elemental analysis and various spectral studies like FT-IR, 1H NMR, ESI mass, UV-Visible, ESR, TGA/DTA, and powder X-ray diffraction studies. The Schiff base ligand (L) behaves as tridentate ONS donor and forms the complexes of type [ML(Cl)2] with square pyramidal geometry. The Schiff base ligand (L) and its metal complexes have been screened in vitro for their antibacterial and antifungal activities by minimum inhibitory concentration (MIC) method. The DNA cleavage activity of ligand and its metal complexes were studied using plasmid DNA pBR322 as a target molecule by gel electrophoresis method. The brine shrimp bioassay was also carried out to study the in vitro cytotoxicity properties for the ligand and its metal complexes against Artemia salina. The results showed that the biological activities of the ligand were found to be increased on complexation. PMID:24729778

Yernale, Nagesh Gunvanthrao; Bennikallu Hire Mathada, Mruthyunjayaswamy

2014-01-01

180

Metalloprotease-Mediated Ligand Release Regulates Autocrine Signaling Through the Epidermal Growth Factor Receptor  

Microsoft Academic Search

Ligands that activate the epidermal growth factor receptor (EGFR) are synthesized as membrane-anchored precursors that appear to be proteolytically released by members of the ADAM family of metalloproteases. Because membrane-anchored EGFR ligands are thought to be biologically active, the role of ligand release in the regulation of EGFR signaling is unclear. To investigate this question, we used metalloprotease inhibitors to

Jianying Dong; Lee K. Opresko; Peter J. Dempsey; Douglas A. Lauffenburger; Robert J. Coffey; H. Steven Wiley

1999-01-01

181

Preorganized and immobilized ligands for metal ion separations. Final report, June, 1994--May, 1997  

SciTech Connect

Historically, much of the interest shown in f-element ion coordination chemistry has been driven by practical needs to devise separation schemes for lanthanide (Ln) and actinide (An) ions. However, few of the separations are completely satisfactory, and the basic chemical framework needed to achieve improvements is still poorly developed. As a result, studies of the fundamental aspects of f-element coordination chemistry are still pertinent not only to the evolution of improved separations, but also waste remediation, biological and medical applications of Ln ions, biochemistry of An ion decorporation, and new solid state materials preparations. The research objectives during the present grant period were to (1) synthesize new bifunctional and trifunctional chelating ligands, particularly in the class of new phosphonopyridine N-oxides; (2) characterize the structural features of the Ln and An coordination complexes formed by these ligands; (3) determine the extraction efficacy of these ligands; and (4) explore synthetic approaches for formation of dendritic polymers containing phosphoryl terminating groups. Some highlights of recently accomplished work and still-in-progress research are outlined.

Paine, R.T.

1997-12-01

182

Protonation of metal-bound ?-hydroxycarboxylate ligand and implication for the role of homocitrate in nitrogenase: Computational study of the oxy-bidentate chelate ring opening  

NASA Astrophysics Data System (ADS)

Protonation of the metal-bound oxy-bidentate ligand in the model complexes of [(HS)3(NH3)M(OCH2COO)]q (M = Mo, Fe, V, Co; q = -2, -1) in the gas phase and in solutions of water and acetonitrile has been explored by the density functional approach. Calculations show that protonation of the carboxyl oxygen can open the ?-hydroxycarboxylate chelate ring ligated to a transition-metal center under specific oxidation and spin states. The feasibility of the chelate ring opening by protonation depends on the electronic nature of the metal site in tune with conversion of a six-coordinate with a five-coordinate metal atom. Such selective dissociation of the metal-bound chelate ligand manipulates the availability of an empty site at the metal center and significantly affects reactivity of the metal-mediated chemical processes. Protonation changes the stability of species with different spin multiplicities and impels spin transition at the metal center in dissociation of the oxy-bidentate ligand. Solvent environments of water and acetonitrile play an important role in stabilizing the negatively charged species.

Cao, Zexing; Jin, Xi; Zhou, Zhaohui; Zhang, Qianer

183

Methane C-H bond activation by "naked" alkali metal imidyl and alkaline earth metal imide complexes. The role of ligand spin and nucleophilicity.  

PubMed

High accuracy correlation consistent Composite Approach (ccCA) calculations have been used to investigate methane C-H bond activation with alkali metal imidyl and alkaline earth metal imide complexes. Alkali metals (Li, Na) and alkaline earth metals (Be, Mg) are used in this research given their redox innocence, namely, M(+) and M(2+), respectively. The ccCA calculations for methane activation by imidyl radical NH(•-) and triplet nitrene NH(••) show a thermodynamic (??H = 13.2 kcal/mol) and kinetic (??H(‡) = 15.9 kcal/mol) preference for the former. Methane activation by LiNH(•) and MgNH proceeds via hydrogen atom abstraction (HAA) and [2 + 2] transition states; only HAA pathways are isolated for NaNH and BeNH. The ccCA computed enthalpies lead to the hypothesis that the nucleophilicity of the nitrogen of the activating ligand (NR) is the key ingredient in activating the strongest sp(3) C-H bonds like that of methane. PMID:23978308

Prince, Bruce M; Cundari, Thomas R

2013-09-26

184

Using low-frequency IR spectra for the unambiguous identification of metal ion-ligand coordination sites in purpose-built complexes.  

PubMed

One of the aims of our long-term research is the identification of metal ion-ligand coordination sites in bioinspired metal ion-C- or N-protected amino acid (histidine, tyrosine, cysteine or cystine) complexes immobilised on the surface of chloropropylated silica gel or Merrifield resin. In an attempt to reach this goal, structurally related, but much simpler complexes have been prepared and their metal ion-ligand vibrations were determined from their low-frequency IR spectra. The central ions were Mn(II), Co(II), Ni(II) or Cu(II) and the ligands (imidazole, isopropylamine, monosodium malonate) were chosen to possess only one-type of potential donor group. The low-frequency IR spectra were taken of the complexes for each ion-ligand combination and the typical metal ion-functional group vibration bands were selected and identified. The usefulness of the obtained assignments is demonstrated on exemplary immobilised metal ion-protected amino acid complexes. PMID:24316539

Varga, Gábor; Csendes, Zita; Peintler, Gábor; Berkesi, Ottó; Sipos, Pál; Pálinkó, István

2014-03-25

185

Asymmetric Catalysis Mediated by the Ligand Sphere of Octahedral Chiral-at-Metal Complexes.  

PubMed

Due to the relationship between structure and function in chemistry, access to novel chemical structures ultimately drives the discovery of novel chemical function. In this light, the formidable utility of the octahedral geometry of six-coordinate metal complexes is founded in its stereochemical complexity combined with the ability to access chemical space that might be unavailable for purely organic compounds. In this Minireview we wish to draw attention to inert octahedral chiral-at-metal complexes as an emerging class of metal-templated asymmetric "organocatalysts" which exploit the globular, rigid nature and stereochemical options of octahedral compounds and promise to provide new opportunities in the field of catalysis. PMID:25156957

Gong, Lei; Chen, Liang-An; Meggers, Eric

2014-10-01

186

High-valent transition metal centers versus noninnocent ligands in metallocorroles: insights from electrochemistry and implications for high-valent heme protein intermediates.  

PubMed

For relatively electron-rich corrole ligands, the halfwave potentials for oxidation of Cu(III), Sn(IV)Ph, Fe(IV)Ph, and Fe(IV)-O-Fe(IV) complexes are significantly lower than those of Sn(IV)Cl, Fe(IV)Cl, Mn(IV)Cl, and Cr(V)(O) complexes, suggesting that the corrole ligand is relatively electron-rich or 'innocent' in the former group of complexes and that it is relatively electron-deficient or 'noninnocent' in the latter group. Both the formal charge of the central metal ion and the nature of the axial ligand, if any, appear to be key determinants of the electronic character of the corrole ligand in metallocorrole complexes, a theme that has interesting resonances with recent findings on high-valent heme protein intermediates. However, for very strongly electron-deficient ligands such as meso-tris(pentafluorophenyl)corrole (TPFPC) and beta-octabromo-meso-tris(pentafluorophenyl)corrole (Br(8)TPFPC), which cannot sustain significant radical character, the various metal complexes all exhibit comparable halfwave potentials for oxidation and the ligand may be considered to be relatively innocent. PMID:12175935

Ghosh, Abhik; Steene, Erik

2002-08-30

187

Trace metals in the brain: allosteric modulators of ligand-gated receptor channels, the case of ATP-gated P2X receptors.  

PubMed

Zinc and copper are indispensable trace metals for life with a recognized role as catalysts in enzyme actions. We now review evidence supporting the role of trace metals as novel allosteric modulators of ionotropic receptors: a new and fundamental physiological role for zinc and copper in neuronal and brain excitability. The review is focussed on ionotropic receptor channels including nucleotide receptors, in particular the P2X receptor family. Since zinc and copper are stored within synaptic vesicles in selected brain regions, and released to the synaptic cleft upon electrical nerve ending depolarization, it is plausible that zinc and copper reach concentrations in the synapse that profoundly affect ligand-gated ionic channels, including the ATP-gated currents of P2X receptors. The identification of key P2X receptor amino acids that act as ligands for trace metal coordination, carves the structural determinants underlying the allosteric nature of the trace metal modulation. The recognition that the identified key residues such as histidines, aspartic and glutamic acids or cysteines in the extracellular domain are different for each P2X receptor subtype and may be different for each metal, highlights the notion that each P2X receptor subtype evolved independent strategies for metal coordination, which form upon the proper three-dimensional folding of the receptor channels. The understanding of the molecular mechanism of allosteric modulation of ligand-operated ionic channels by trace metals is a new contribution to metallo-neurobiology. PMID:17972073

Huidobro-Toro, J Pablo; Lorca, Ramón A; Coddou, Claudio

2008-03-01

188

Can an electron-shell closing model explain the structure and stability of ligand-stabilized metal clusters?  

PubMed

We investigated the structure and stability of several aluminum hydride complexes to understand the essence of "superatom chemistry" and to gain a right perspective on the ligand (L)-stabilized metal (M) clusters. We successfully interpret the structure and stability using molecular orbital analysis, which clearly shows the failure of an electron-shell closing model (or a superatom model) to explain it. The structure and stability of Al(m)H(n) are closely associated with the molecular orbital stabilization owing to the effective orbital overlap between Al(m) (M(m)) and nH (nL). The importance of retaining the electronic structural integrity of M(m) in M(m)L(n)-within an electron-shell closing model-has been underestimated or even disregarded, and this has created the current controversies in the scientific community. PMID:21443223

Jung, Jaehoon; Kim, Hyemi; Han, Young-Kyu

2011-04-20

189

An Isoreticular Series of Metal?Organic Frameworks with Dendritic Hexacarboxylate Ligands and Exceptionally High Gas-Uptake Capacity  

SciTech Connect

Metal-organic frameworks (MOFs) are newly emerging porous materials. Owing to their large surface area and tunable pore size and geometry, they have been studied for applications in gas storage and separation, especially in hydrogen and methane storage and carbon dioxide capture. It has been well established that the high-pressure gravimetric hydrogen-adsorption capacity of an MOF is directly proportional to its surface area. However, MOFs of high surface areas tend to decompose upon activation. In our previous work, we described an approach toward stable MOFs with high surface areas by incorporating mesocavities with microwindows. To extend this work, we now present an isoreticular series of (3,24)-connected MOFs made from dendritic hexacarboxylate ligands, one of which has a Langmuir surface area as high as 6033 m{sup 2} g{sup -1}. In addition, the gas-adsorption properties of this new isoreticular MOF series have been studied.

Yuan, Daqiang; Zhao, Dan; Sun, Daofeng; Zhou, Hong-Cai (TAM); (Shandong)

2010-10-01

190

Assembly of metal ions and ligands with adaptable coordinative tendencies as a route to functional metal-organic solids  

SciTech Connect

The majority of efforts on metal-organic frameworks (MOFs) concern their rational design and, intuitively, researchers are drawn to assembly units with well-defined, reliable coordinating tendencies. Assembly units with less well-defined properties are generally less employed. This concept paper discusses the merits of using adaptable components for the assembly of functional MOFs. 'Adaptable' components, whether for the metal ion or for the ligating group, are defined as those having several coordination modes within a narrow energetic range. Use of these assembly units can lead to new solids with: (i) highly dynamic properties; (ii) new inorganic structural motifs; and possibly (iii) high thermal stabilities. The article, to facilitate comparison, considers a framework on the basis of metal ion, coordinating functionality, and organic spacer. Networks with one, two and three 'adaptable' units are then discussed. Ultimately, the illustration that less well-defined properties does not necessarily translate to less functional materials will be made.

Shimizu, George K.H. [Department of Chemistry, University of Calgary, Calgary, Alta., T2N 1N4 (Canada)]. E-mail: gshimizu@ucalgary.ca

2005-08-15

191

Synthesis, spectral and thermal studies of some transition metal mixed ligand complexes: Modeling of equilibrium composition and biological activity  

NASA Astrophysics Data System (ADS)

Several mixed ligand Ni(II), Cu(II) and Zn(II) complexes of 2-amino-3-hydroxypyridine (AHP) and imidazoles viz., imidazole (him), benzimidazole (bim), histamine (hist) and L-histidine (his) have been synthesized and characterized by elemental and spectral (vibrational, electronic, 1H NMR and EPR) data as well as by magnetic moment values. On the basis of elemental analysis and molar conductance values, all the complexes can be formulated as [MAB]Cl except histidine complexes as MAB. Thermogravimetric studies reveal the presence of coordinated water molecules in most of the complexes. From the magnetic measurements and electronic spectral data, octahedral structure was proposed for Ni(II) and Cu(II)-AHP-his, tetrahedral for Cu(II)-AHP-him/bim/hist, but square planar for the Cu(II)-AHP complex. The g?/ A? calculated supports tetrahedral environment around the Cu(II) in Cu(II)-AHP-him/bim/hist and distorted octahedral for Cu(II)-AHP-his complexes. The morphology of the reported metal complexes was investigated by scanning electron micrographs (SEM). The potentiometric study has been performed in aqueous solution at 37 °C and I = 0.15 mol dm -3 NaClO 4. MABH, MAB and MAB 2 species has been identified in the present systems. Proton dissociation constants of AHP and stability constants of metal complexes were determined using MINIQUAD-75. The most probable structure of the mixed ligand species is discussed based upon their stability constants. The in vitro biological activity of the complexes was tested against the Gram positive and Gram negative bacteria, fungus and yeast. The oxidative DNA cleavage studies of the complexes were performed using gel electrophoresis method. Cu(II) complexes have been found to promote DNA cleavage in presence of biological reductant such as ascorbate and oxidant like hydrogen peroxide.

Neelakantan, M. A.; Sundaram, M.; Nair, M. Sivasankaran

2011-09-01

192

Metal-ligand Covalency of Iron Complexes from High-Resolution Resonant Inelastic X-ray Scattering  

PubMed Central

Data from K? resonant inelastic X-ray scattering (RIXS) have been used to extract electronic structure information, i.e., the covalency of metal-ligand bonds, for four iron complexes using an experimentally based theoretical model. K? RIXS involves resonant 1s ? 3d excitation and detection of the 2p ? 1s (K?) emission. This two-photon process reaches similar final states as single-photon L-edge (2p ? 3d) X-ray absorption spectroscopy (XAS), but involves only hard X-rays and can therefore be used to get high-resolution L-edge-like spectra for metal proteins, solution catalysts and their intermediates. To analyze the information content of K? RIXS spectra, data have been collected for four characteristic ?-donor and ?-backdonation complexes; ferrous tacn [FeII(tacn)2]Br2, ferrocyanide [FeII(CN)6]K4, ferric tacn [FeIII(tacn)2]Br3 and ferricyanide [FeIII(CN)6]K3. From these spectra metal-ligand covalencies can be extracted using a charge-transfer multiplet model, without previous information from the L-edge XAS experiment. A direct comparison of L-edge XAS and K? RIXS spectra show that the latter reaches additional final states, e.g., when exciting into the eg (?*) orbitals, and the splitting between final states of different symmetry provides an extra dimension that makes K? RIXS a more sensitive probe of ?-bonding. Another key difference between L-edge XAS and K? RIXS is the ?-backbonding features in ferro- and ferricyanide that are significantly more intense in L-edge XAS compared to K? RIXS. This shows that two methods are complimentary in assigning electronic structure. The K? RIXS approach can thus be used as a stand-alone method, in combination with L-edge XAS for strongly covalent systems that are difficult to probe by UV/Vis spectroscopy, or as an extension to conventional absorption spectroscopy for a wide range of transition metal enzymes and catalysts. PMID:24131028

Lundberg, Marcus; Kroll, Thomas; DeBeer, Serena; Bergmann, Uwe; Wilson, Samuel A.; Glatzel, Pieter; Nordlund, Dennis; Hedman, Britt; Hodgson, Keith O.; Solomon, Edward I.

2013-01-01

193

Ligand functionalization and its effect on CO2 adsorption in microporous metal-organic frameworks.  

PubMed

We report two new 3D structures, [Zn3(bpdc)3(2,2'-dmbpy)] (DMF)x(H2O)y (1) and [Zn3(bpdc)3(3,3'-dmbpy)]·(DMF)4(H2O)0.5 (2), by methyl functionalization of the pillar ligand in [Zn3(bpdc)3(bpy)] (DMF)4·(H2O) (3) (bpdc=biphenyl-4,4'-dicarboxylic acid; z,z'-dmbpy=z,z'-dimethyl-4,4'-bipyridine; bpy=4,4'-bipyridine). Single-crystal X-ray diffraction analysis indicates that 2 is isostructural to 3, and the power X-ray diffraction (PXRD) study shows a very similar framework of 1 to 2 and 3. Both 1 and 2 are 3D porous structures made of Zn3(COO)6 secondary building units (SBUs) and 2,2'- or 3,3'-dmbpy as pillar ligand. Thermogravimetric analysis (TGA) and PXRD studies reveal high thermal and water stability for both compounds. Gas-adsorption studies show that the reduction of surface area and pore volume by introducing a methyl group to the bpy ligand leads to a decrease in H2 uptake for both compounds. However, CO2 adsorption experiments with 1' (guest-free 1) indicate significant enhancement in CO2 uptake, whereas for 2' (guest-free 2) the adsorbed amount is decreased. These results suggest that there are two opposing and competitive effects brought on by methyl functionalization: the enhancement due to increased isosteric heats of CO2 adsorption (Q(st)), and the detraction due to the reduction of surface area and pore volume. For 1', the enhancement effect dominates, which leads to a significantly higher uptake of CO2 than its parent compound 3' (guest-free 3). For 2', the detraction effect predominates, thereby resulting in reduced CO2 uptake relative to its parent structure 3'. IR and Raman spectroscopic studies also present evidence for strong interaction between CO2 and methyl-functionalized ? moieties. Furthermore, all compounds exhibit high separation capability for CO2 over other small gases including CH4, CO, N2, and O2. PMID:23362024

Liu, Hui; Zhao, Yonggang; Zhang, Zhijuan; Nijem, Nour; Chabal, Yves J; Peng, Xiangfang; Zeng, Heping; Li, Jing

2013-04-01

194

Functionalization of large-pore periodic mesoporous silicas: metal silylamide and isopropoxide molecular grafting and secondary surface ligand exchange.  

PubMed

Divalent metal silylamide complexes of zinc and cobalt and trivalent aluminium isopropoxide were successfully grafted onto large-pore hexagonal channel-like SBA-15 and cubic MCM-48-like periodic mesoporous silica (PMS) KIT-6, to afford hybrid materials Zn[N(SiMe3)2]2@SBA-15, Co[N(SiMe3)2]2(thf)@SBA-15/KIT-6 and {Al(OCHMe2)3}@SBA-15 with well-defined surface species (?SiO)2M(thf)x, ?SiOM[N(SiMe3)2](THF)x (x = 0, M = Zn; x = 1, M = Co), ?SiOSiMe3 and (?SiO)2Al(OCHMe2) and ?SiOAl(OCHMe2)2, respectively. Surface silylamido ligand exchange with 1,4-benzenediol, 1,4-benzenedicarboxylic acid, and biphenyl-4,4'-dicarboxylic acid gave hybrid materials of type ?SiOML(solvent)x and (?SiO)2M(solvent)x (L = O(C6H4)OSiMe3, O2C(C6H4)CO2SiMe3, O2C(C6H4)2CO2SiMe3; M = Zn and Co) revealing in situ ligand silylation as a side reaction. Surface isopropoxide/carboxylato ligand exchange generated species (?SiO)2AlL(DMF)x and ?SiOAl(OCHMe2)(2-y)L(y) (L = O2C(C6H4)CO2H, y ? 2) devoid of any secondary functionalization (such as formation of ester groups), offering a potential approach to PMS-encapsulated metal-organic frameworks. All featured surface species were verified by (1)H, (13)C and (29)Si magic angle spinning (MAS) NMR and diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy as well as elemental analysis. Additionally, preservation of the long-range ordered mesostructures was proven by powder X-ray diffraction (PXRD), nitrogen physisorption, and transmission electron microscopy (TEM). PMID:23503675

Liang, Yucang; Erichsen, Egil Sev; Anwander, Reiner

2013-05-21

195

An unprecedented 2D ? 3D metal-organic polyrotaxane framework constructed from cadmium and a flexible star-like ligand.  

PubMed

An unprecedented 2D ? 3D metal-organic polyrotaxane framework, based on a new star-like tri(4-imidazolylphenyl)amine ligand, has been synthesized and characterized, which represents the first example of 2D ? 3D polyrotaxane entangled in a parallel fashion. PMID:21135935

Wu, Hua; Liu, Hai-Yan; Liu, Ying-Ying; Yang, Jin; Liu, Bo; Ma, Jian-Fang

2011-02-14

196

Structural, spectral and biological studies of binuclear tetradentate metal complexes of N 3O Schiff base ligand synthesized from 4,6-diacetylresorcinol and diethylenetriamine  

NASA Astrophysics Data System (ADS)

The binuclear Schiff base, H 2L, ligand was synthesized by reaction of 4,6-diacetylresorcinol with diethylenetriamine in the molar ratio 1:2. The coordination behavior of the H 2L towards Cu(II), Ni(II), Co(II), Zn(II), Fe(III), Cr(III), VO(IV) and UO 2(VI) ions has been investigated. The elemental analyses, magnetic moments, thermal studies and IR, electronic, 1H NMR, ESR and mass spectra were used to characterize the isolated ligand and its metal complexes. The ligand acts as dibasic with two N 3O-tetradentate sites and can coordinate with two metal ions to form binuclear complexes. The bonding sites are the nitrogen atoms of the azomethine and amine groups and the oxygen atoms of the phenolic groups. The metal complexes exhibit either square planar, tetrahedral, square pyramid or octahedral structures. The Schiff base ligand and its metal complexes were tested against four pathogenic bacteria ( Staphylococcus aureus and Streptococcus pyogenes) as Gram-positive bacteria, and ( Pseudomonas fluorescens and Pseudomonas phaseolicola) as Gram-negative bacteria and two pathogenic fungi ( Fusarium oxysporum and Aspergillus fumigatus) to assess their antimicrobial properties. Most of the complexes exhibit mild antibacterial and antifungal activities against these organisms.

Emara, Adel A. A.

2010-09-01

197

Paramagnetic metal effect on the ligand localized S/sub 1/. -->. T/sub 1/ intersystem crossing in the rare-earth-metal complexes and methyl salicylate  

SciTech Connect

The electronic relaxation processes in the chelates of La/sup 3 +/, Gd/sup 3 +/, Tb/sup 3 +/, and Lu/sup 3 +/ with methyl salicylate have been investigated by measurements of picosecond fluorescence, nanosecond transient absorptions, and quantum yields. The quantum yields of the S/sub 1/ ..-->.. T/sub 1/ intersystem crossing are not appreciably altered by a change in the central metal ions. However, the fluorescence lifetimes are decreased dramatically in the paramagnetic Gd/sup 3 +/ (240 ps) and Tb/sup 3 +/ (<10 ps) complexes compared with those in the diamagnetic La/sup 3 +/ (2.2 ns) and Lu/sup 3 +/ (2.4 ns) complexes. The rate constants derived from these results for the S/sub 1/ ..-->.. T/sub 1/ intersystem crossing, k/sub TM/, in ligands are 5.5 x 10/sup 7/, 7.5 x 10/sup 8/, and 7.9 x 10/sup 7/ s/sup -1/ for the La/sup 3 +/, Gd/sup 3 +/, and Lu/sup 3 +/ complexes, respectively. A large increase of k/sub TM/ is observed in the paramagnetic Gd/sup 3 +/ complexes, which can be attributed to the electron exchange mechanism with ligand ..pi.. electrons. 27 references, 8 figures, 3 tables.

Tobita, S.; Arakawa, M.; Tanaka, I.

1985-01-01

198

Identification of nonprotein ligands to the metal ions bound to glutamine synthetase.  

PubMed

Electron paramagnetic resonance (EPR) was used to study the environment of Mn2+ bound to the tight (n1) metal ion binding site of glutamine synthetase in the presence of analogues of the tetrahedral adduct, L-methionine (S)-sulfoximine [Met(O)(NH)-S] and L-methionine (R)-sulfoximine [Met(O)(NH)-R]. The Mn2+ EPR spectrum in the presence of Met(O)(NH)-S is identical with the previously published spectrum obtained from a mixture of isomers [Met(O)(NH)-RS] [Villafranca, J. J., Ash, D. E., & Wedler, F. C. (1976) Biochemistry 15, 544] and is characteristic of a highly octahedral metal ion environment with a small zero field splitting. The presence of Met(O)(NH)-R produces an EPR spectrum that appears characteristic of a more distorted metal ion environment, with a larger zero field splitting. These data demonstrate that the two isomers interact differently with the enzyme-bound Mn2+. Broadening of the Mn2+ EPR spectrum in the presence of Met(O)(NH) is observed in 17O-enriched water due to superhyperfine coupling of water to the metal ion. Deconvolution of the spectrum demonstrates the presence of at least a single water molecule in the inner coordination sphere of the metal ion. Superhyperfine coupling due to the 14N nucleus of the imine nitrogen of the sulfoximine moiety of Met(O)(NH)-S but not of Met(O)(NH)-R has been detected by electron spin-echo envelope modulation spectroscopy. Two intense peaks are evident in the presence of Met(O)(NH)-S with frequencies at 1.7 and 3.3 MHz. These peaks are absent when [15N]imine-labeled Met(O)(NH) is used, indicating the presence of the sulfoximine nitrogen of Met(O)(NH)-S in the inner coordination sphere of the metal ion.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2894845

Eads, C D; LoBrutto, R; Kumar, A; Villafranca, J J

1988-01-12

199

YTTRIUM-89 NMR: A POSSIBLE SPIN RELAXATION PROBE FOR STUDYING METAL ION INTERACTIONS WITH ORGANIC LIGANDS  

EPA Science Inventory

The spin-lattice relaxation mechanisms for aqueous and dimethyl sulfoxide solutions of Y(NO3)3 have been found to be mainly spin-rotation and dipolar relaxation with solvent protons, unlike most heavy spin=1/2 metal ions which are relaxed mainly by spin-rotation and chemical shif...

200

Immobilization and chelation of metal complexes with bifunctional phosphine ligands: a solid-state NMR study  

E-print Network

, suspension NMR spectroscopy3can be applied routinely. Since most transition metals form stable phosphine com to bonding via one, two, or three siloxane bridges and there is also the possibility of cross- linking.' Therefore, we used the monoethoxy phosphine PPh2(C6H4)SiMe20Et1 that forms just one siloxane bridge when

Bluemel, Janet

201

Metal-humate interactions. 1. Discrete ligand and continuous distribution models  

Microsoft Academic Search

In this paper the authors examine critically the theory underlying discrete and continuous multiligand models for metal-humate binding. The concepts and equations that unify the various models are presented, and a general solution to the fundamental integral equation for ion binding in a multiligand system is given. Particular attention is paid to the continuous distribution models (normal distribution, affinity spectrum,

David A. Dzombak; William Fish; Francois M. M. Morel

1986-01-01

202

Self-assembly of metal-organic coordination networks using on-surface synthesized ligands.  

PubMed

Supramolecular assembly and on-surface synthesis are two widely-used methods for constructing low-dimensional molecular nanostructures on surfaces. Here we describe an approach that combines both methods to create two-dimensional metal-organic networks with exceptionally large pores. PMID:25347223

Lin, Tao; Kuang, Guowen; Shang, Xue Song; Liu, Pei Nian; Lin, Nian

2014-12-18

203

Antimicrobial and toxicological studies of some metal complexes of 4-methylpiperazine-1-carbodithioate and phenanthroline mixed ligands  

PubMed Central

A few mixed ligand transition metal carbodithioate complexes of the general formula [M(4-MPipzcdt)x(phen)y]Y (M = Mn(II), Co(II), Zn(II); 4-MPipzcdt = 4-methylpiperazine-1-carbodithioate; phen = 1,10-phenanthroline; x = 1 and y = 2 when Y = Cl; x = 2 and y = 1 when Y = nil) were synthesized and screened for their antimicrobial activity against Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecalis by disk diffusion method. All the complexes exhibited prominent antimicrobial activity against tested pathogenic strains with the MIC values in the range <8-512 gmL-1. The complexes [Mn(4-MPipzcdt)2(phen)] and [Co(4-MPipzcdt)(phen)2]Cl inhibited the growth of Candida albicans at a concentration as low as 8 µgmL-1. The complexes were also evaluated for their toxicity towards human transformed rhabdomyosarcoma cells (RD cells). Moderate cell viability of the RD cells was exhibited against the metal complexes. PMID:24031441

Kalia, S.B.; Kaushal, G.; Kumar, M.; Cameotra, S.S.; Sharma, A.; Verma, M.L.; Kanwar, S.S.

2009-01-01

204

Room temperature C-N bond cleavage of anionic guanidinate ligand in rare-earth metal complexes.  

PubMed

The dissociation of the anionic guanidinate ligand N=C(NMe2)2 promoted by rare-earth metal complexes at room temperature is described. Treatment of CpLnCl2(THF)3 with two equiv. of Li[N=C(NMe2)2] in THF at room temperature affords [Cp2Ln(?-?(1):?(2)-L2)]2 (Ln = Y; L = N=C(NMe2)N=C(NMe2)2) and CpLn[N=C(NMe2)2](?-?(1):?(2)-L)2LnCp2 (Ln = Dy) in moderated yields, respectively. YCl3 reacts with three equiv. of Li[N=C(NMe2)2] under the same conditions to give a trinuclear yttrium guanidinate [(Me2N)2C=N]5Y3[?-N=C(NMe2)2]2(?-?(1):?(2)-L)2 in 63% yield. These reactions show that rare-earth metals can promote a C-N bond cleavage of the guanidine anion [N=C(NMe2)2](-) at room temperature. All new complexes were characterized by elemental analysis and spectroscopic properties, and their solid-state structures were determined through single-crystal X-ray diffraction analysis. PMID:23456152

Zhang, Jie; Yi, Weiyin; Chen, Zhenxia; Zhou, Xigeng

2013-04-28

205

Assessing electronic structure approaches for gas-ligand interactions in metal-organic frameworks: the CO2-benzene complex.  

PubMed

Adsorption of gas molecules in metal-organic frameworks is governed by many factors, the most dominant of which are the interaction of the gas with open metal sites, and the interaction of the gas with the ligands. Herein, we examine the latter class of interaction in the context of CO2 binding to benzene. We begin by clarifying the geometry of the CO2-benzene complex. We then generate a benchmark binding curve using a coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)] at the complete basis set (CBS) limit. Against this ?CCSD(T)/CBS standard, we evaluate a plethora of electronic structure approximations: Hartree-Fock, second-order Møller-Plesset perturbation theory (MP2) with the resolution-of-the-identity approximation, attenuated MP2, and a number of density functionals with and without different empirical and nonempirical van der Waals corrections. We find that finite-basis MP2 significantly overbinds the complex. On the other hand, even the simplest empirical correction to standard density functionals is sufficient to bring the binding energies to well within 1 kJ/mol of the benchmark, corresponding to an error of less than 10%; PBE-D in particular performs well. Methods that explicitly include nonlocal correlation kernels, such as VV10, vdW-DF2, and ?B97X-V, perform with similar accuracy for this system, as do ?B97X and M06-L. PMID:24628196

Witte, Jonathon; Neaton, Jeffrey B; Head-Gordon, Martin

2014-03-14

206

Assessing electronic structure approaches for gas-ligand interactions in metal-organic frameworks: The CO2-benzene complex  

NASA Astrophysics Data System (ADS)

Adsorption of gas molecules in metal-organic frameworks is governed by many factors, the most dominant of which are the interaction of the gas with open metal sites, and the interaction of the gas with the ligands. Herein, we examine the latter class of interaction in the context of CO2 binding to benzene. We begin by clarifying the geometry of the CO2-benzene complex. We then generate a benchmark binding curve using a coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)] at the complete basis set (CBS) limit. Against this ?CCSD(T)/CBS standard, we evaluate a plethora of electronic structure approximations: Hartree-Fock, second-order Møller-Plesset perturbation theory (MP2) with the resolution-of-the-identity approximation, attenuated MP2, and a number of density functionals with and without different empirical and nonempirical van der Waals corrections. We find that finite-basis MP2 significantly overbinds the complex. On the other hand, even the simplest empirical correction to standard density functionals is sufficient to bring the binding energies to well within 1 kJ/mol of the benchmark, corresponding to an error of less than 10%; PBE-D in particular performs well. Methods that explicitly include nonlocal correlation kernels, such as VV10, vdW-DF2, and ?B97X-V, perform with similar accuracy for this system, as do ?B97X and M06-L.

Witte, Jonathon; Neaton, Jeffrey B.; Head-Gordon, Martin

2014-03-01

207

Mixed ligand complexation of some transition metal ions in solution and solid state: Spectral characterization, antimicrobial, antioxidant, DNA cleavage activities and molecular modeling  

NASA Astrophysics Data System (ADS)

Equilibrium studies of Ni(II), Cu(II) and Zn(II) mixed ligand complexes involving a primary ligand 5-fluorouracil (5-FU; A) and imidazoles viz., imidazole (him), benzimidazole (bim), histamine (hist) and L-histidine (his) as co-ligands(B) were carried out pH-metrically in aqueous medium at 310 ± 0.1 K with I = 0.15 M (NaClO4). In solution state, the stoichiometry of MABH, MAB and MAB2 species have been detected. The primary ligand(A) binds the central M(II) ions in a monodentate manner whereas him, bim, hist and his co-ligands(B) bind in mono, mono, bi and tridentate modes respectively. The calculated ? log K, log X and log X' values indicate higher stability of the mixed ligand complexes in comparison to binary species. Stability of the mixed ligand complex equilibria follows the Irving-Williams order of stability. In vitro biological evaluations of the free ligand(A) and their metal complexes by well diffusion technique show moderate activities against common bacterial and fungal strains. Oxidative cleavage interaction of ligand(A) and their copper complexes with CT DNA is also studied by gel electrophoresis method in the presence of oxidant. In vitro antioxidant evaluations of the primary ligand(A), CuA and CuAB complexes by DPPH free radical scavenging model were carried out. In solid, the MAB type of M(II)sbnd 5-FU(A)sbnd his(B) complexes were isolated and characterized by various physico-chemical and spectral techniques. Both the magnetic susceptibility and electronic spectral analysis suggest distorted octahedral geometry. Thermal studies on the synthesized mixed ligand complexes show loss of coordinated water molecule in the first step followed by decomposition of the organic residues subsequently. XRD and SEM analysis suggest that the microcrystalline nature and homogeneous morphology of MAB complexes. Further, the 3D molecular modeling and analysis for the mixed ligand MAB complexes have also been carried out.

Shobana, Sutha; Dharmaraja, Jeyaprakash; Selvaraj, Shanmugaperumal

2013-04-01

208

Reduction reactions of water soluble cyano-cobalt(III)-porphyrins: Metal versus ligand centered processes  

SciTech Connect

Reduction reactions of dicyano-cobalt(III)-porphyrins (potential in vivo cyanide scavenger drugs) were studied by radiolytic and electrochemical methods using the water soluble tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP). For ((CN)2CoIIITPPS)-, reduction occurs stepwise to the CoII, CoI, and finally to the phlorin anion. This behavior is similar to that of the cobalt porphyrins in the absence of cyanide, except that the cyanide ligand shifts the reduction potentials to much more negative values. On the other hand, under radiolytic conditions, ((CN)2CoIIITMPyP)- is reduced on the porphyrin macrocycle by one electron to give the CoIII pi-radical anion, which disproportionates into the initial complex and the two-electron ring reduced CoIII phlorin. The radical anion is also formed by intramolecular electron transfer subsequent to the reaction of CoIITMPyP and cyanide. The results are compared with the chemistry of Vitamin B-12.

Mosseri, S.; Neta, P.; Harriman, A.; Hambright, P. (National Institute of Standards and Technology, Gaithersburg, MD (USA))

1990-06-01

209

Reaction of Metal Binding Ligands with the Zinc Proteome: Zinc Sensors and TPEN  

PubMed Central

The commonly used Zn2+ sensors, TSQ and Zinquin, have been shown to image Zn-proteins as a result of the formation for sensor-Zn-protein ternary adducts not Zn(TSQ)2 or Zn(Zinquin)2 complexes. The powerful, cell permeant chelating agent TPEN is also used in conjunction with these and other Zn2+ sensors to validate that the observed fluorescence enhancement seen with the sensors depends on intracellular interaction with Zn2+. We demonstrated that the kinetics of reaction of TPEN with cells pretreated with TSQ or Zinquin was not consistent with its reaction with Zn(TSQ)2 or Zn(Zinquin)2. Instead, TPEN and other chelating agents extract between 25–35% of the Zn2+ bound to the proteome, including Zn2+ from Zn-metallothionein, and, thereby, quench some but not all of the sensor-Zn-protein fluorescence. Another mechanism in which TPEN exchanges with TSQ or Zinquin to form TP EN-Zn-protein adducts found support in the reactions of TPEN with Zinquin-Zn-alcohol dehydrogenase. TPEN also removed one of the two Zn2+ ions per monomer from Zn-alcohol dehydrogenase and Zn-alkaline phosphatase, consistent with its ligand substitution reactivity with the Zn-proteome. PMID:22380934

Meeusen, Jeffrey W.; Nowakowski, Andrew; Petering, David H.

2012-01-01

210

Nano-sized, quaternary titanium(IV) metal-organic frameworks with multidentate ligands.  

PubMed

Some mononuclear nano-sized, quaternary titanium(IV) complexes having the general formula [Ti(acac)(OOCR)2(SB)] (where Hacac=acetylacetone, R=C15H31 or C17H35, HSB=Schiff bases) have been synthesized using different multidentate ligands. These were characterized by elemental analyses, molecular weight determinations and spectral (FTIR, 1H NMR and powder XRD) studies. Conductance measurement indicated their non-conducting nature which may behave like insulators. Structural parameters like the values of limiting indices h, k, l, cell constants a, b, c, angles ?, ?, ? and particle size are calculated from powder XRD data for complex 1 which indicated nano-sized triclinic system in them. Bidentate chelating nature of acetylacetone, carboxylate and Schiff base anions in the complexes was established by their infrared spectra. Molecular weight determinations confirmed mononuclear nature of the complexes. On the basis of physico-chemical studies, coordination number 8 was assigned for titanium(IV) in the complexes. Transmission electron microscopy (TEM) and the selected area electron diffraction (SAED) studies indicated spherical particles with poor crystallinity. PMID:20863747

Baranwal, Balram Prasad; Singh, Alok Kumar

2010-12-01

211

Organoantimony Lewis Acid as Flouride Receptors and Ligands towards Transition Metals  

E-print Network

that the redox state of the metal could be used to control anion binding at antimony. Reaction of (o-(Ph_(2)P)C_(6)H_(4))_(2)SbPh with (Et_(2)S)_(2)PtCl_(2) affords [ClSb(Ph)PtCl(o-dppp)_(2)] (o-dppp = o-(Ph_(2)P)C_(6)H_(4)) which further reacts with PhICl_(2...

Ke, Iou-Sheng

2013-08-08

212

Dual Anchoring of the GRASP Membrane Tether Promotes trans Pairing*  

PubMed Central

GRASP proteins share an N-terminal GRASP domain and mediate homotypic tethering of Golgi cisternae to form extended Golgi ribbons. The golgin GM130 is thought to bind the C-terminal side of the GRASP domain to recruit GRASP65 onto the Golgi whereas stable membrane association appears to also depend on anchoring of the N terminus by myristoylation. Here, we examine the nature of the GM130/GRASP65 interaction and test whether the dual membrane contacts of the GRASP domain have a role in tethering beyond membrane recruitment. GM130 was found to contain a C-terminal PDZ ligand that binds the putative groove of the second PDZ-like domain in GRASP65. To test tethering activity independent of targeting, we took advantage of a tethering assay carried out on the mitochondrial membrane in which the GRASP membrane attachment points were individually or simultaneously substituted with mitochondrially targeted transmembrane sequences. N-terminally anchored constructs tethered only if the C terminus was also anchored; and likewise, C-terminally anchored constructs tethered only if the N terminus was anchored. One explanation for the role of this dual anchoring is that it orients the GRASP domain to prevent cis interactions within the same membrane thereby favoring trans interactions between adjacent membranes. Indeed, singly anchored GRASP constructs, although nonfunctional in tethering, interacted with one another and also bound and inhibited dually anchored constructs. This work thus elucidates the GM130/GRASP65 interaction and supports a novel orientation-based model of membrane tether regulation in which dual membrane contact orients the tethering interaction interface to favor trans over cis interactions. PMID:20228057

Bachert, Collin; Linstedt, Adam D.

2010-01-01

213

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 ligands in cone and 1,2-alternate conformations: synthesis and metal ion extraction.  

PubMed

Novel di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 ligands in cone and 1,2-alternate conformations were prepared as potential metal ion extractants. Selective bridging of proximal hydroxyl groups of the calix[4]arene platform by a crown-3 polyether unit was achieved under Mitsunobu reaction conditions. In addition to the carboxylic acid group, the acidity tunable N-(X)sulfonyl oxyacetamide functions [OCH(2)C(O)NHSO(2)X] with X group variation from methyl to phenyl to p-nitrophenyl to trifluomethyl were used as the proton-ionizable groups. Conformations and regioselectivities of the new ligands were established by (1)H and (13)C NMR spectroscopy. Competitive solvent extractions of alkali metal cations and of alkaline earth metal cations from aqueous solutions into chloroform were performed, as were single species extractions of lead(ii) and mercury(ii). PMID:17406724

Zhang, Dongmei; Cao, Xiaodan; Purkiss, David W; Bartsch, Richard A

2007-04-21

214

Multiply Bonded Metal(II) Acetate (Rhodium, Ruthenium, and Molybdenum) Complexes with the trans-1,2-Bis(N-methylimidazol-2-yl)ethylene Ligand.  

PubMed

The synthesis and structural characterization of new coordination polymers with the N,N-donor ligand trans-1,2-bis(N-methylimidazol-2-yl)ethylene (trans-bie) are reported. It was found that the acetate-bridged paddlewheel metal(II) complexes [M2(O2CCH3)4(trans-bie)]n with M = Rh, Ru, Mo, and Cr are linked by the trans-bie ligand to give a one-dimensional alternating chain. The metal-metal multiple bonds were analyzed with density functional theory and CASSCF/CASPT2 calculations (bond orders: Rh, 0.8; Ru, 1.7; Mo, 3.3). PMID:25393757

Fritsch, Nico; Wick, Christian R; Waidmann, Thomas; Dral, Pavlo O; Tucher, Johannes; Heinemann, Frank W; Shubina, Tatyana E; Clark, Timothy; Burzlaff, Nicolai

2014-12-01

215

The effect of the nature of peripheral platinated and bridging mercapto ligands on the optical and electrochemical properties of binuclear Pt(II) complexes with a metal-metal chemical bond  

NASA Astrophysics Data System (ADS)

The effect of heterocyclic metalated and bridging ligands on the optical and electrochemical properties of [Pt(C^N)(?-N^S)]2 complexes ((C^N)- and (N^S)- are the deprotonated forms of 1-phenylpyrazole, 2-tolylpyridine, benzo[h]quinoline, 2-phenylbenzothiazole and 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptopyridine) is studied by 1H NMR, electronic absorption, and emission spectroscopy, as well as by voltammetry. The long-wavelength spin-allowed (415-540 nm) absorption bands of the complexes are attributed to the metal-metal-to-ligand charge transfer (MMLCT) optical transitions. It is shown that the interaction of the d Z2 and ?{(C^N/*)} orbitals of two {Pt(C^N)} fragments of binuclear complexes leads to a cathodic shift (0.5-1.0 V) of their metal-centered oxidation potential and to an anodic shift (0.1-0.2 V) of their ligand-centered reduction potential with respect to [Pt(C^N)En]+ complexes. The luminescence of binuclear complexes in solutions at room temperature is assigned to the spin-forbidden MMLCT transition. It is shown that, in frozen (77 K) solutions, in addition to the MMLCT optical transitions, spin-forbidden radiative processes occur from the intraligand (?(C^N)-?{(C^N)/*}) and metal-to-ligand charge transfer (dPt-?{(C^N)/*}) excited states.

Katlenok, E. A.; Balashev, K. P.

2014-09-01

216

Polymer-supported sulfonated catechol and linear catechol amide ligands and their use in selective metal ion removal recovery from aqueous solutions  

DOEpatents

The present invention concerns the synthesis of several biomimetically important polymer-supported, sulfonated catechol (PS-CATS), sulfonated bis-catechol linear amide (PS-2-6-LICAMS) and sulfonated 3,3-linear tris-catechol amide (PS-3,3-LICAMS) ligands, which chemically bond to modified 6% crosslinked macroporous polystyrene-divinylbenzene beads (PS-DVB). These polymers are useful for the for selective removal and recovery of environmentally and economically important metal ions from aqueous solution, as a function of pH. The Fe.sup.3+ ion selectivity shown for PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads in competition with a similar concentration of Cu.sup.2+, Zn.sup.2+, Mn.sup.2+, Ni.sup.2+, Mg.sup.2+, Al.sup.3+, and Cr.sup.3+ ions at pH 1-3. Further, the metal ion selectivity is changed at higher pH values in the absence of Fe.sup.3+ (for example, Hg.sup.2+ at pH 3). The rates of selective removal and recovery of the trivalent metal ions, e.g. Fe.sup.3+ Al.sup.3+ ion etc. with the PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads used determined are useful as well as equilibrium selectivity coefficient (K.sub.m) values for all metal competition studies. The chelate effect for the predisposed octahedral PS-3,3-LICAMS polymer pendant ligand is the reason that this ligand has a more pronounced selectivity for Fe.sup.3+ ion in comparison to the PS-CATS polymer beads. The predisposed square planar PS-2,6-LICAMS series of polymer pendant ligands are more selective to divalent metal ions Cu.sup.2+, Zn.sup.2+, Mn.sup.2+, Ni.sup.2+, and Mg.sup.2+, than either PS-CATS or PS-3,3-LICAMS. However, Fe.sup.3+ ion still dominates in competition with other divalent and trivalent metal ions. In the absence of Fe.sup.3+, the polymer ligand is selective for Al.sup.3+, Cu.sup.2+ or Hg.sup.2+. The changing of the cavity size from two CH.sub.2 groups to six CH.sub.2 groups in the PS-2-6-LICAMS polymer pendant ligand series does not effect the order of metal ion selectivity.

Fish, Richard H. (Berkeley, CA)

1998-01-01

217

Polymer-supported sulfonated catechol and linear catechol amide ligands and their use in selective metal ion removal recovery from aqueous solutions  

DOEpatents

The present invention concerns the synthesis of several biomimetically important polymer-supported, sulfonated catechol (PS-CATS), sulfonated bis-catechol linear amide (PS-2-6-LICAMS) and sulfonated 3,3-linear tris-catechol amide (PS-3,3-LICAMS) ligands, which chemically bond to modified 6% crosslinked macroporous polystyrene-divinylbenzene beads (PS-DVB). These polymers are useful for the for selective removal and recovery of environmentally and economically important metal ions from aqueous solution, as a function of pH. The Fe{sup 3+} ion selectivity shown for PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads in competition with a similar concentration of Cu{sup 2+}, Zn{sup 2+}, Mn{sup 2+}, Ni{sup 2+}, Mg{sup 2+}, Al{sup 3+}, and Cr{sup 3+} ions at pH 1--3. Further, the metal ion selectivity is changed at higher pH values in the absence of Fe{sup 3+} (for example, Hg{sup 2+} at pH 3). The rates of selective removal and recovery of the trivalent metal ions, e.g. Fe{sup 3+}, Al{sup 3+} ion etc. with the PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads used determined are useful as well as equilibrium selectivity coefficient (K{sub m}) values for all metal competition studies. The chelate effect for the predisposed octahedral PS-3,3-LICAMS polymer pendant ligand is the reason that this ligand has a more pronounced selectivity for Fe{sup 3+} ion in comparison to the PS-CATS polymer beads. The predisposed square planar PS-2,6-LICAMS series of polymer pendant ligands are more selective to divalent metal ions Cu{sup 2+}, Zn{sup 2+}, Mn{sup 2+}, Ni{sup 2+}, and Mg{sup 2+}, than either PS-CATS or PS-3,3-LICAMS. However, Fe{sup 3+} ion still dominates in competition with other divalent and trivalent metal ions. In the absence of Fe{sup 3+}, the polymer ligand is selective for Al{sup 3+}, Cu{sup 2+} or Hg{sup 2+}. The changing of the cavity size from two CH{sub 2} groups to six CH{sub 2} groups in the PS-2-6-LICAMS polymer pendant ligand series does not effect the order of metal ion selectivity. 9 figs.

Fish, R.H.

1998-11-10

218

The mechanism of metal incorporation into the cavity of macrocyclic ligands: a molecular mechanical analysis  

NASA Astrophysics Data System (ADS)

The subtle structural difference between meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacy-clotetradecane (tet-a) (L 1) and c-rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (tet-b) (L 2) is responsible for different methods of metal binding. Conformational studies show that steric interactions limit the flexibility of tet-a (L 1) thus increasing the strain energy of the folded forms of the macrocycle. Conformational searches are not normally undertaken in inorganic molecular mechanical calculations but this work shows them to be of vital importance.

Canales, Carmen R.; Zimmer, Marc

1991-05-01

219

Recognition of some lanthanides, actinides, and transition- and heavy-metal cations by N-donor ligands: thermodynamic and kinetic aspects.  

PubMed

The remarkable actinide(III) selectivity of the polyaromatic N-donors bis-triazine-pyridines (BTPs), hemi-bis-triazine-pyridines (hemi-BTPs) and bis-triazine-bipyridines (BTBPs) make these ligands the most promising candidates in partitioning and transmutation processes developed so far to better manage nuclear waste. The interactions of n-Pr-BTP, C(5)-hemi-BTP, and the two most extensively investigated BTBPs (C(5)-BTBP and CyMe(4)-BTBP) have been studied with some representative lanthanide(III), uranyl, thorium, and transition- and other heavy-metal cations in methanol. The formation of complexes of different stoichiometries, the stability of which depended on both the ligands and the cations, was shown using UV absorption spectrophotometry. Study of the complexation reactions of La(3+), Eu(3+) and Yb(3+) with these four ligands by stopped-flow spectrophotometry allowed determination of the rate constants and postulation of possible complexation mechanisms. PMID:20055507

Hubscher-Bruder, Véronique; Haddaoui, Jaouad; Bouhroum, Saliha; Arnaud-Neu, Françoise

2010-02-15

220

System with Potential Dual Modes of Metal-Ligand Cooperation: Highly Catalytically Active Pyridine-Based PNNH-Ru Pincer Complexes.  

PubMed

Metal-ligand cooperation (MLC) plays an important role in catalysis. Systems reported so far are generally based on a single mode of MLC. We report here a system with potential for MLC by both amine-amide and aromatization-dearomatization ligand transformations, based on a new class of phosphino-pyridyl ruthenium pincer complexes, bearing sec-amine coordination. These pincer complexes are effective catalysts under unprecedented mild conditions for acceptorless dehydrogenative coupling of alcohols to esters at 35?°C and hydrogenation of esters at room temperature and 5?atm H2 . The likely actual catalyst, a novel, crystallographically characterized monoanionic de-aromatized enamido-Ru(II) complex, was obtained by deprotonation of both the N?H and the methylene proton of the N-arm of the pincer ligand. PMID:25331061

Fogler, Eran; Garg, Jai Anand; Hu, Peng; Leitus, Gregory; Shimon, Linda J W; Milstein, David

2014-11-24

221

Spectroscopic, cyclic voltammetric and biological studies of transition metal complexes with mixed nitrogen-sulphur (NS) donor macrocyclic ligand derived from thiosemicarbazide.  

PubMed

The complexation of new mixed thia-aza-oxa macrocycle viz., 2,12-dithio-5,9,14,18-tetraoxo-7,16-dithia-1,3,4,10,11,13-hexaazacyclooctadecane containing thiosemicarba-zone unit with a series of transition metals Co(II), Ni(II) and Cu(II) has been investigated, by different spectroscopic techniques. The structural features of the ligand have been studied by EI-mass, (1)H NMR and IR spectral techniques. Elemental analyses, magnetic moment susceptibility, molar conductance, IR, electronic, and EPR spectral studies characterized the complexes. Electronic absorption and IR spectra of the complexes indicate octahedral geometry for chloro, nitrato, thiocyanato or acetato complexes. The dimeric and neutral nature of the sulphato complexes are confirmed from magnetic susceptibility and low conductance values. Electronic spectra suggests square-planar geometry for all sulphato complexes. The redox behaviour was studied by cyclic voltammetry, show metal-centered reduction processes for all complexes. The complexes of copper show both oxidation and reduction process. The redox potentials depend on the conformation of central atom in the macrocyclic complexes. Newly synthesized macrocyclic ligand and its transition metal complexes show markedly growth inhibitory activity against pathogenic bacterias and plant pathogenic fungi under study. Most of the complexes have higher activity than that of the metal free ligand. PMID:16174565

Chandra, Sulekh; Gupta, Lokesh Kumar; Sangeetika

2005-11-01

222

Intelligent Educational Systems for Anchored Instruction?  

ERIC Educational Resources Information Center

Explores the potential for using Intelligent Educational Systems (IES) for anchoring instruction in macro contexts in science education. Topics include anchored instruction; situated cognition; problem solving; cognitivism; interactive video environments; and examples of combining IES and anchored instruction. (LRW)

Kumar, David D.

1995-01-01

223

Two-dimensional metal-organic frameworks (MOFs) constructed from heterotrinuclear coordination units and 4,4'-biphenyldicarboxylate ligands.  

PubMed

Three novel metal-organic frameworks (MOFs) formulated as [Zn(2)M(BPDC)(3)(DMF)(2)].4DMF (M = Co(II), Ni(II) or Cd(II); BPDC = 4,4'-biphenyldicarboxylate; DMF = N,N'-dimethylformamide) have been prepared via solvothermal synthesis from mixtures of the corresponding transition metal salts and 4,4'-biphenyldicarboxylic acid (H(2)BPDC). The framework structures are characterized by single-crystal X-ray diffraction analysis, IR and UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis (TGA), and X-ray powder diffraction (XRPD). All three compounds possess essentially the same 2-D layered coordination framework consisting of linear heterotrinuclear secondary building units (SBUs) connected by rigid bridging BPDC ligands. Crystal data: for (C(60)H(66)CoN(6)O(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1348.86, a = 20.463(4), b = 14.819(3), c = 23.023(5) A, beta = 111.75(3) degrees , V = 6484(2) A(3), Z = 4, D(c) = 1.382 Mg m(-3). For (C(60)H(66)N(6)NiO(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1348.64, a = 11.670(2), b = 14.742(3), c = 19.391(4) A, beta = 102.29(3) degrees , V = 3259.5(11) A(3), Z = 2, D(c) = 1.374 Mg m(-3). For (C(60)H(66)CdN(6)O(18)Zn(2)): monoclinic, space group P2(1)/n, M = 1402.33, a = 11.491(2), b = 14.837(3), c = 19.386(4) A, beta = 101.53(3) degrees , V = 3238.3(11) A(3), Z = 2, D(c) = 1.438 Mg m(-3). PMID:17268603

Wang, Yonghui; Bredenkötter, Björn; Rieger, Bernhard; Volkmer, Dirk

2007-02-14

224

Novel metal complexes containing a chiral trinitrogen isoindoline-based pincer ligand: in situ synthesis and structural characterization.  

PubMed

The first synthesis and characterization of metal coordinated complexes containing in situ prepared chiral trinitrogen 1,3-bis(4,5-dihydrooxazol-2-ylimino)isoindoline-based pincer ligands are reported. Two zinc complexes, isolated as Zn(L)(2), where L = 1,3-bis(4,5-dihydro-4-(R)-phenyloxazol-2-ylimino)isoindoline ((R,R)-5) or 1,3-bis(4,5-dihydro-4-(S)-iso-propyloxazol-2-ylimino)isoindoline ((S,S)-6), respectively, are reported. Complexes Zn((R,R)-5)(2) and Zn((S,S)-6)(2) were prepared in situ through the condensation of phthalonitrile with enantiopure 2-amino-4-(R)-phenyloxazoline ((R)-3) or 2-amino-4-(S)-iso-propyloxazoline ((S)-4) in the presence of ZnCl(2) at 80 °C in dry toluene over 3-4 days. The characterizations of Zn((R,R)-5)(2) and Zn((S,S)-6)(2) in both the solid (X-ray crystallography) and solution (multinuclear NMR spectroscopy) states are reported. PMID:20927427

Cryder, Jessica L; Killgore, Andrew J; Moore, Curtis; Golen, James A; Rheingold, Arnold L; Daley, Christopher J A

2010-11-28

225

Extraction of uranium and lead from mixed waste debris using a variety of metal/ligand complexes  

SciTech Connect

To ensure the safety of our Nation`s nuclear stockpile, Los Alamos National Laboratory is in the process of constructing the DARHT (Dual Axis Radiographic Hydrodynamic Test) facility. DARHT will examine the effects of aging and the stability of our stockpile. Contained testing will be phased in to reduce the impact of these tests, which contain depleted uranium, on our environment. The main focus of this research is to develop a treatment scheme for the recovery of depleted uranium and lead from shot debris that will result from these tests. The goals of this research are to optimize the conditions on a bench scale using a commercially available water soluble polymer to bind the lead and a variety of metal/ligand complexes such as 4,5-dihydroxy-1,3-benzene-disulfonic acid, dithionite, sodium carbonate/bicarbonate, and sodium hypochlorite to bind the uranium. Studies were conducted on a mixture of debris, such as wood, cable, paper towels, and tubing that contained both uranium and lead ranging in concentration from 10-1000`s of ppm of contaminants. Experiments were done varying combinations and successions of extractant solutions as well as a number of sequential extractions. Studies show that a mixture of sodium hypochlorite and carbonate removed 90+% of both uranium and lead. We then focused on a separation scheme for the lead and uranium.

Needham, D.A.; Duran, B.L.; Ehler, D.S.; Sauer, N.N. [Los Alamos National Lab., NM (United States)

1997-12-31

226

Dynamics of bacteriophage R17 probed with a long-lifetime Ru(II) metal-ligand complex.  

PubMed

The metal-ligand complex, [Ru(2,2'-bipyridine)(2)(4,4'-dicarboxy-2,2'-bipyridine)](2+) (RuBDc), was used as a spectroscopic probe for studying macromolecular dynamics. RuBDc is a very photostable probe that possesses favorable photophysical properties including long lifetime, high quantum yield, large Stokes' shift, and highly polarized emission. To further show the usefulness of this luminophore for probing macromolecular dynamics, we examined the intensity and anisotropy decays of RuBDc when conjugated to R17 bacteriophage using frequency-domain fluorometry with a blue light-emitting diode (LED) as the modulated light source. The intensity decays were best fit by a sum of two exponentials, and we obtained a longer mean lifetime at 4 degrees C ( = 491.8 ns) as compared to that at 25 degrees C ( = 435.1 ns). The anisotropy decay data showed a single rotational correlation time, which is typical for a spherical molecule, and the results showed a longer rotational correlation time at 4 degrees C (2,574.9 ns) than at 25 degrees C (2,070.1 ns). The use of RuBDc enabled us to measure the rotational correlation time up to several microseconds. These results indicate that RuBDc has significant potential for studying hydrodynamics of biological macromolecules. PMID:20195712

Kim, Myung Sup; Kim, Jae Hui; Son, Beng Whwa; Kang, Jung Sook

2010-05-01

227

Hydroxylated derivatives of dimethoxy-1,4-benzoquinone as redox switchable earth-alkaline metal ligands and radical scavengers  

PubMed Central

Benzoquinones (BQ) have important functions in many biological processes. In alkaline environments, BQs can be hydroxylated at quinoid ring proton positions. Very little is known about the chemical reaction leading to these structural transformations as well as about the properties of the obtained hydroxyl benzoquinones. We analyzed the behavior of the naturally occurring 2,6-dimethoxy-1,4-benzoquinone under alkaline conditions and show that upon substitution of methoxy-groups, poly-hydroxyl-derivatives (OHBQ) are formed. The emerging compounds with one or several hydroxyl-substituents on single or fused quinone-rings exist in oxidized or reduced states and are very stable under physiological conditions. In comparison with the parent BQs, OHBQs are stronger radical scavengers and redox switchable earth-alkaline metal ligands. Considering that hydroxylated quinones appear as biosynthetic intermediates or as products of enzymatic reactions, and that BQs present in food or administered as drugs can be hydroxylated by enzymatic pathways, highlights their potential importance in biological systems. PMID:23689559

Gulaboski, Rubin; Bogeski, Ivan; Mirceski, Valentin; Saul, Stephanie; Pasieka, Bastian; Haeri, Haleh H.; Stefova, Marina; Stanoeva, Jasmina Petreska; Mitrev, Sasa; Hoth, Markus; Kappl, Reinhard

2013-01-01

228

Single-atom ligand changes affect breathing in an extended metal-organic framework.  

PubMed

2-Phenylpyridine-5,4'-dicarboxylic acid (1, dcppy), a derivative of 4,4'-biphenyldicarboxylic (2, bpdc) was used as the organic linking component for several metal-organic frameworks (MOFs). The pyridine component of 1 does not interfere with the solvothermal synthetic procedure, and hence both 1 and 2 form similar isoreticular MOFs. Zr(4+)-based UiO-67-dcppy, Al(3+)-based DUT-5-dcppy, Zn(2+)-based DMOF-1-dcppy, and interpenetrated Zn(2+)-based BMOF-1-dcppy were readily synthesized from 1. Similarly, isostructural frameworks from 2 were prepared (UiO-67, DUT-5, DMOF-1-bpdc, and interpenetrated BMOF-1-bpdc). The structures and physical properties of these frameworks were characterized by powder X-ray diffraction (PXRD), single X-ray diffraction (XRD), thermogravimetric analysis (TGA), and gas sorption analysis. Generally, frameworks prepared from 1 or 2 displayed similar properties; however, gas sorption data showed that BMOF-1-dcppy displayed a very large hysteresis with N(2) and CO(2) suggestive of possible framework flexibility. In contrast, the analogous framework prepared from 2 (BMOF-1-bpdc) showed low uptake of N(2) and CO(2). The substantial difference in the gas sorption behavior of these MOFs is attributed to the pyridine nature of 1 that results in weakened ?-? interactions between the interpenetrated nets. PMID:22545717

Dau, Phuong V; Kim, Min; Garibay, Sergio J; Münch, Frédéric H L; Moore, Curtis E; Cohen, Seth M

2012-05-21

229

Extreme metal carbonyl back bonding in cyclopentadienylthorium carbonyls generates bridging C2O2 ligands by carbonyl coupling.  

PubMed

Laboratory studies of the interaction of carbon monoxide with organoactinides result in the formation of isolable complexes such as Cp3UCO derivatives (Cp = cyclopentadienyl) as well as coupling reactions to give derivatives of the oligomeric anions C(n)O(n)(2-) (n = 2, 3, 4). To gain some insight into actinide carbonyl chemistry, binuclear cyclopentadienylthorium carbonyls Cp2Th2(CO)n (n = 2 to 5) as model compounds have been investigated using density functional theory. The most favorable such structures in terms of energy and thermochemistry are the tricarbonyl Cp2Th2(?(2)-?-CO)3 having three four-electron donor bridging carbonyl groups and the tetracarbonyl Cp2Th2(?(4)-?-C2O2)(?(2)-?-CO)2 having not only two four-electron donor bridging carbonyl groups but also a bridging ethynediolate ligand formed by coupling two CO groups through C-C bond formation. The bridging infrared ?(CO) frequencies ranging from 1140 to 1560 cm(-1) in these Cp2Th2(CO)n (n = 3, 4) derivatives indicate extremely strong Th?CO back bonding in these structures, corresponding to formally dianionic CO(2-) and C2O2(2-) ligands and the favorable +4 thorium oxidation state. A characteristic of the Cp2Th2(?(2)-?-CO)3 and Cp2Th2(?(4)-?-C2O2)(?(2)-?-CO)2 structures is their ability to add terminal CO groups, preferably to the thorium atom bonded to the fewest oxygen atoms. These terminal CO groups exhibit ?(CO) frequencies in a similar range as terminal CO groups in d-block metal carbonyls. However, these terminal CO groups are relatively weakly bonded to the thorium atoms as indicated by predicted CO dissociation energies of 14 kcal/mol for Cp2Th2(CO)5. Two low energy structures for the dicarbonyl Cp2Th2(CO)2 are found with two separate four-electron donor bridging CO groups and relatively short Th-Th distances of 3.3 to 3.4 Å suggesting formal single bonds and +3 thorium formal oxidation states. However, a QTAIM analysis of this formal Th-Th bond does not reveal a bond critical point thus suggesting a multicenter bonding model involving the bridging CO groups. PMID:23721544

Li, Huidong; Feng, Hao; Sun, Weiguo; King, R Bruce; Schaefer, Henry F

2013-06-17

230

Polymer-supported sulfonated catechol and linear catechol amide ligands and their use in selective metal ion removal and recovery from aqueous solutions  

DOEpatents

The present invention concerns the synthesis of several biomimetically important polymer-supported, sulfonated catechol (PS-CATS), sulfonated bis-catechol linear amide (PS-2-6-LICAMS) and sulfonated 3,3-linear tris-catechol amide (PS-3,3-LICAMS) ligands, which chemically bond to modified 6% crosslinked macroporous polystyrene-divinylbenzene beads (PS-DVB). These polymers are useful for the for selective removal and recovery of environmentally and economically important metal ions from aqueous solution, as a function of pH. The Fe{sup 3+} ion selectivity shown for PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads in competition with a similar concentration of Cu{sup 2+}, Zn{sup 2+}, Mn{sup 2+}, Ni{sup 2+}, Mg{sup 2+}, Al{sup 3+}, and Cr{sup 3+} ions at pH 1--3. Further, the metal ion selectivity is changed at higher pH values in the absence of Fe{sup 3+} (for example, Hg{sup 2+} at pH 3). The rates of selective removal and recovery of the trivalent metal ions, e.g. Fe{sup 3+}, Al{sup 3+} ion etc. with the PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads use determined are useful as well as equilibrium selectivity coefficient (K{sub m}) values for all metal competition studies. The chelate effect for the predisposed octahedral PS-3,3-LICAMS polymer pendant ligand is the reason that this ligand has a more pronounced selectivity for Fe{sup 3+} ion in comparison to the PS-CATS polymer beads. The predisposed square planar PS-2-6-Mn{sup 2+}, Ni{sup 2+}, and Mg{sup 2+}, than either PS-CATS or PS-3,3-LICAMS. However, Fe{sup 3+} ion still dominates in competition with other divalent and trivalent metal ions. In the absence of Fe{sup 3+}, the polymer ligand is selective for Al{sup 3+}, Cu{sup 2+} or Hg{sup 2+}. The changing of the cavity size from two CH{sub 2} groups to six CH{sub 2} groups in the PS-2-6-LICAMS polymer pendant ligand series does not effect the order of metal ion selectivity. 9 figs.

Fish, R.H.

1997-04-22

231

Polymer-supported sulfonated catechol and linear catechol amide ligands and their use in selective metal ion removal and recovery from aqueous solutions  

DOEpatents

The present invention concerns the synthesis of several biomimetically important polymer-supported, sulfonated catechol (PS-CATS), sulfonated bis-catechol linear amide (PS-2-6-LICAMS) and sulfonated 3,3-linear tris-catechol amide (PS-3,3-LICAMS) ligands, which chemically bond to modified 6% crosslinked macroporous polystyrene-divinylbenzene beads (PS-DVB). These polymers are useful for the for selective removal and recovery of environmentally and economically important metal ions from aqueous solution, as a function of pH. The Fe.sup.3+ ion selectivity shown for PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads in competition with a similar concentration of Cu.sup.2+, Zn.sup.2+, Mn.sup.2+, Ni.sup.2+,Mg.sup.2+, Al.sup.3+, and Cr.sup.3+ ions at pH 1-3. Further, the metal ion selectivity is changed at higher pH values in the absence of Fe.sup.3+ (for example, Hg.sup.2+ at pH 3). The rates of selective removal and recovery of the trivalent metal ions, e.g. Fe.sup.3+ Al.sup.3+ ion etc. with the PS-CATS, PS-2-6-LICAMS, and PS-3,3-LICAMS polymer beads use determined are useful as well as equilibrium selectivity coefficient (K.sub.m) values for all metal competition studies. The chelate effect for the predisposed octahedral PS-3,3-LICAMS polymer pendant ligand is the reason that this ligand has a more pronounced selectivity for Fe.sup.3+ ion in comparison to the PS-CATS polymer beads. The predisposed square planar PS-2-6-Mn.sup.2+, Ni.sup.2+, and Mg.sup.2+, than either PS-CATS or PS-3,3-LICAMS. However, Fe.sup.3+ ion still dominates in competition with other divalent and trivalent metal ions. In the absence of Fe.sup.3+, the polymer ligand is selective for Al.sup.3+, Cu.sup.2+ or Hg.sup.2+. The changing of the cavity size from two CH.sub.2 groups to six CH.sub.2 groups in the PS-2-6-LICAMS polymer pendant ligand series does not effect the order of metal ion selectivity.

Fish, Richard H. (Berkeley, CA)

1997-01-01

232

Multidentate zwitterionic ligands provide compact and highly biocompatible quantum dots.  

PubMed

Hydrophilic functional semiconductor nanocrystals that are also compact provide greatly promising platforms for use in bioinspired applications and are thus highly needed. To address this, we designed a set of metal coordinating ligands where we combined two lipoic acid groups, bis(LA)-ZW, (as a multicoordinating anchor) with a zwitterion group for water compatibility. We further combined this ligand design with a new photoligation strategy, which relies on optical means instead of chemical reduction of the lipoic acid, to promote the transfer of CdSe-ZnS QDs to buffer media. In particular, we found that the QDs photoligated with this zwitterion-terminated bis(lipoic) acid exhibit great colloidal stability over a wide range of pHs, to an excess of electrolytes, and in the presence of growth media and reducing agents, in addition to preserving their optical and spectroscopic properties. These QDs are also stable at nanomolar concentrations and under ambient conditions (room temperature and white light exposure), a very promising property for fluorescent labeling in biology. In addition, the compact ligands permitted metal-histidine self-assembly between QDs photoligated with bis(LA)-ZW and two different His-tagged proteins, maltose binding protein and fluorescent mCherry protein. The remarkable stability of QDs capped with these multicoordinating and compact ligands over a broad range of conditions and at very small concentrations, combined with the compatibility with metal-histidine conjugation, could be very useful for a variety of applications, ranging from protein tracking and ligand-receptor binding to intracellular sensing using energy transfer interactions. PMID:24003892

Zhan, Naiqian; Palui, Goutam; Safi, Malak; Ji, Xin; Mattoussi, Hedi

2013-09-18

233

New ?-SnTe4 and ?-Sn2Te6 ligands to transition metal: Solvothermal syntheses and characterizations of zinc tellurostannates containing polyamine ligands  

NASA Astrophysics Data System (ADS)

Zinc tellurostannates [{Zn(teta)}2(?-1?:2?-SnTe4)] (1), [{Zn(teta)}3(?3-1?:2?:3?-SnTe4)]I2 (2), [{Zn(tren)}2(?-1?:2?-Sn2Te6)] (3), and [Zn(dien)2]4(Sn2Te6)1.75(Sn2Te8)0.25·dien (4) were prepared by the reactions of Zn, Sn, and Te with iodine ion assistant in teta and dien. The tetrahedral [SnTe4]4- anion coordinates to two [Zn(teta)]2+ units as a bidentate ?-1?:2?-SnTe4 ligand to form the neutral complex 1. It coordinates to three [Zn(teta)]2+ units with a tridentate ?3-1?:2?:3? coordination modes, generating a complex cation [{Zn(teta)}3(?3-1?:2?:3?- SnTe4)]2+ in 2. In 3, the [Sn2Te6]4- anion joins two [Zn(tren)]2+cations with the trans terminal Te atoms, forming neutral complex 3. The ?-1?:2?-SnTe4, ?3-1?:2?:3?-SnTe4, and ?-1?:2?-Sn2Te6 ligands to TM centers in 1-3 have not been observed before. Compound 4 contains a normal [Sn2Te6]4- and an abnormal [(Sn2Te6)0.75(Sn2Te8)0.25]4- anions. Compounds 1-4 exhibit narrow band gaps in the range of 1.47-1.98 eV, and a distinct red-shift of the band gaps is observed from 4 to 1-3.

Lu, Jialin; Wang, Fang; Shen, Yali; Tang, Chunying; Zhang, Yong; Jia, Dingxian

2014-08-01

234

Mechanical testing of absorbable suture anchors  

Microsoft Academic Search

Purpose: Absorbable suture anchors offer great advantages but are made of mechanically weak material. The weakest link in the fixation of soft tissue to bone may therefore be the anchor itself. In this study, several commercially available anchors were mechanically tested in vitro. Type of study: Biomechanical bench study. Methods: Twelve absorbable suture anchor models were implanted into an artificial

Dominik C. Meyer; Sandro F. Fucentese; Kurt Ruffieux; Hilaire A. C. Jacob; Christian Gerber

2003-01-01

235

A fluorescent ligand rationally designed to be selective for zinc(II) over larger metal ions. The structures of the zinc(II) and cadmium(II) complexes of N, Nbis(2-methylquinoline)-2-(2-aminoethyl)pyridine  

Microsoft Academic Search

The metal ion coordinating properties of the ligands N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine (DQPEA) and N,N-bis(2-methylquinoline)-2-(2-aminomethyl)pyridine (DQPMA) are presented. DQPEA and DQPMA differ only in that DQPEA forms six-membered chelate rings that involve the pyridyl group, whereas DQPMA forms analogous five-membered chelate rings.These two ligands illustrate the application of a ligand design principle, which states that increase of chelate ring size in a ligand

Wei Gan; S. Bart Jones; Joseph H. Reibenspies; Robert D. Hancock

2005-01-01

236

Highly dispersed palladium nanoparticles anchored on UiO-66(NH2) metal-organic framework as a reusable and dual functional visible-light-driven photocatalyst  

NASA Astrophysics Data System (ADS)

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed Pd nanoparticles of about 3-6 nm in diameter are immobilized in the metal-organic framework (MOF) UiO-66(NH2) via a facile one-pot hydrothermal method. The resulting Pd@UiO-66(NH2) nanocomposite exhibits an excellent reusable and higher visible light photocatalytic activity for reducing Cr(vi) compared with UiO-66(NH2) owing to the high dispersion of Pd nanoparticles and their close contact with the matrix, which lead to the enhanced light harvesting and more efficient separation of photogenerated electron-hole pairs. More significantly, the Pd@UiO-66(NH2) could be used for simultaneous photocatalytic degradation of organic pollutants, like methyl orange (MO) and methylene blue (MB), and reduction of Cr(vi) with even further enhanced activity in the binary system, which could be attributed to the synergetic effect between photocatalytic oxidation and reduction by individually consuming photogenerated holes and electrons. This work represents the first example of using the MOFs-based materials as dual functional photocatalyst to remove different categories of pollutants simultaneously. Our finding not only proves great potential for the design and application of MOFs-based materials but also might bring light to new opportunities in the development of new high-performance photocatalysts.Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed Pd nanoparticles of about 3-6 nm in diameter are immobilized in the metal-organic framework (MOF) UiO-66(NH2) via a facile one-pot hydrothermal method. The resulting Pd@UiO-66(NH2) nanocomposite exhibits an excellent reusable and higher visible light photocatalytic activity for reducing Cr(vi) compared with UiO-66(NH2) owing to the high dispersion of Pd nanoparticles and their close contact with the matrix, which lead to the enhanced light harvesting and more efficient separation of photogenerated electron-hole pairs. More significantly, the Pd@UiO-66(NH2) could be used for simultaneous photocatalytic degradation of organic pollutants, like methyl orange (MO) and methylene blue (MB), and reduction of Cr(vi) with even further enhanced activity in the binary system, which could be attributed to the synergetic effect between photocatalytic oxidation and reduction by individually consuming photogenerated holes and electrons. This work represents the first example of using the MOFs-based materials as dual functional photocatalyst to remove different categories of pollutants simultaneously. Our finding not only proves great potential for the design and application of MOFs-based materials but also might bring light to new opportunities in the development of new high-performance photocatalysts. Electronic supplementary information (ESI) available: XRD patterns of Pd@UiO-66(NH2) before and after the photocatalytic reduction of Cr(vi) reaction; XPS patterns of Pd@UiO-66(NH2) before and after the photocatalytic reduction of Cr(vi) reaction; BET adsorption-desorption isotherms of UiO-66(NH2) (a) and Pd@UiO-66(NH2) (b); Mott-Schottky plot of UiO-66(NH2) in 0.2 M Na2SO4 aqueous solution (pH = 6.8); a schematic drawing of the structure of UiO-66(NH2) based on the structure of UiO-66. Zirconium-oxygen clusters (green part); N of the free amino groups (blue dots). See DOI: 10.1039/c3nr03153e

Shen, Lijuan; Wu, Weiming; Liang, Ruowen; Lin, Rui; Wu, Ling

2013-09-01

237

Bio-sensitive activities of coordination compounds containing 1,10-phenanthroline as co-ligand: Synthesis, structural elucidation and DNA binding properties of metal(II) complexes  

NASA Astrophysics Data System (ADS)

Present work reports the DNA binding and cleavage characteristics of a series of mixed-ligand complexes having the composition [M(L)(phen)2]Cl2 (where M = Cu(II), Ni(II), Co(II) and Zn(II) and phen as co-ligand) in detail. Their structural features and other properties have been deduced from their elemental analyses, magnetic susceptibility and molar conductivity as well as from IR, UV-Vis, 1H NMR and EPR spectral studies. The UV-Vis, magnetic susceptibility and EPR spectral data of metal complexes suggest an octahedral geometry. The binding properties of these complexes with calf thymus DNA (CT-DNA) have been explored using electronic absorption spectroscopy, viscosity measurement, cyclic voltammetry and differential pulse voltammetry. The DNA-binding constants for Cu(II), Ni(II), Co(II), and Zn(II) complexes are 6.14 × 105 M-1, 1.8 × 105 M-1, 6.7 × 104 M-1 and 2.5 × 104 M-1 respectively. Detailed analysis reveals that these complexes interact with DNA through intercalation binding. Nuclease activity has also been investigated by gel electrophoresis. Moreover, the synthesized Schiff base and its mixed-ligand complexes have been screened for antibacterial and antifungal activities. The data reveal that the complexes exhibit higher activity than the parent ligand.

Raman, Natarajan; Mahalakshmi, Rajkumar; Mitu, Liviu

2014-10-01

238

Ligand-Thickness Effect Leads to Enhanced Preference for Large Anions in Alkali Metal Extraction by Crown Ethers  

SciTech Connect

Jean-Marie Lehn (Nobel laureate, 1987) suggested ligand thickness to be an important consideration in the design of host molecules for cation recognition. We have recently expanded the role of this simple ligand property by demonstrating a case in which ligand thickness contributes significantly to anion discrimination. It was found that in the extraction of sodium nitrate and perchlorate by a simple crown ether, bis(t-octylbenzo)-14-crown-4 (BOB 14C4), the normal preference for perchlorate is almost completely lost when the complex cation has the open-face sandwich vs. the sandwich structure.

Haverlock, T.J.; Moyer, B.A.; Sachleben, R.A.

1999-07-11

239

Investigation of group 12 metal complexes with a tridentate SNS ligand by X-ray crystallography and 1H NMR spectroscopy.  

PubMed

Two series of zinc triad complexes containing the ligand 2,6-bis(methylthiomethyl)pyridine (L1) were synthesized and characterized by X-ray crystallography and solution-state 1H NMR spectroscopy. The distorted meridional octahedral M(L1)2(ClO4)2 series includes the first structurally characterized Zn(II) and Cd(II) complexes with N2(SR2)4 coordination spheres. Coordination of HgCl2 and ZnCl2 with 1 equiv of ligand afforded mononuclear, five-coordinate species Hg(L1)Cl2 and Zn(L1)Cl2, respectively, with distorted square-pyramidal and trigonal-bipyramidal geometries. With CdCl2, the dimeric [Cd(L1)Cl(mu-Cl)]2 complex was obtained. The distorted octahedral coordination geometry of each Cd(II) center in this complex is formed by one tridentate ligand, two bridging chloride ions, and one terminal chloride ion. NMR spectra indicate that the intermolecular ligand-exchange rate of [M(L1)2](2+) decreased in the order Cd(II) > Zn(II) > Hg(II). Slow intermolecular ligand-exchange conditions on the chemical-shift time scale were found for 1:2 metal-to-ligand complexes of L(1) with Hg(II) and Zn(II) but not Cd(II). Slow intermolecular ligand-exchange conditions in acetonitrile-d(3) solutions permitting detection of (3-5)J(199Hg1H) were found for 1:1 and 1:2 Hg(ClO4)2/L1 complexes, but not for the related Cd(ClO4)2) complexes. The magnitudes of J(199Hg1H) for equivalent protons were smaller in [Hg(L1)2](2+) than in [Hg(L1)(NCCH3)x](2+). The relative intermolecular ligand-exchange rates of the zinc triad complexes investigated here suggest that the toxicity of Hg(II) is accentuated by the relative difficulty of displacing it from the coordination sites encountered. PMID:16411692

Lai, Wei; Berry, Steven M; Bebout, Deborah C; Butcher, Raymond J

2006-01-23

240

Crystal structure of nonadentate tricompartmental ligand derived from pyridine-2,6-dicarboxylic acid: Spectroscopic, electrochemical and thermal investigations of its transition metal(II) complexes  

NASA Astrophysics Data System (ADS)

The coordinating behavior of a new dihydrazone ligand, 2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine towards manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been described. The metal complexes were characterized by magnetic moments, conductivity measurements, spectral (IR, NMR, UV-Vis, FAB-Mass and EPR) and thermal studies. The ligand crystallizes in triclinic system, space group P-1, with ? = 98.491(10)°, ? = 110.820(10)° and ? = 92.228(10)°. The cell dimensions are a = 10.196(7) Å, b = 10.814(7) Å, c = 10.017(7) Å, Z = 2 and V = 1117.4(12). IR spectral studies reveal the nonadentate behavior of the ligand. All the complexes are neutral in nature and possess six-coordinate geometry around each metal center. The X-band EPR spectra of copper(II) complex at both room temperature and liquid nitrogen temperature showed unresolved broad signals with giso = 2.106. Cyclic voltametric studies of copper(II) complex at different scan rates reveal that all the reaction occurring are irreversible.

Vadavi, Ramesh S.; Shenoy, Rashmi V.; Badiger, Dayananda S.; Gudasi, Kalagouda B.; Devi, L. Gomathi; Nethaji, Munirathinam

2011-07-01

241

Assemblies of a new flexible multicarboxylate ligand and d10 metal centers toward the construction of homochiral helical coordination polymers: structures, luminescence, and NLO-active properties.  

PubMed

Hydro(solvo)thermal reactions between a new flexible multicarboxylate ligand of 2,2',3,3'-oxydiphthalic acid (2,2',3,3'-H(4)ODPA) and M(NO(3))(2).xH(2)O (M = Zn, x = 6; M = Cd, x = 4) in the presence of 4,4'-bipyridine (bpy) afford two novel homochiral helical coordination polymers [[Zn(2)(2,2',3,3'-ODPA)(bpy)(H(2)O)(3)].(H(2)O)(2) for 1 and [Cd(2)(2,2',3,3'-ODPA)(bpy)(H(2)O)(3)].(H(2)O)(2) for 2]. Though having almost the same chemical formula, they have different space groups (P2(1)2(1)2(1) for 1 and P2(1) for 2) and different bridging modes of the 2,2',3,3'-ODPA ligand. Two kinds of homochiral helices (right-handed) are found in both 1 and 2, each of which discriminates only one kind of crystallographical nonequivalent metal atom. 1 has a 2D metal-organic framework and can be seen as the unity of two parallel homochiral Zn1 and Zn2 helices, in which the nodes are etheric oxygen atoms. In contrast, 2 has a 3D metal-organic framework and consists of two partially overlapped homochiral Cd1 and Cd2 helices in the two dimensions. Moreover, metal-ODPA helices give a 2D chiral herringbone structural motif in both 1 and 2 in the two dimensions, which are further strengthened by the second ligand of bpy. Bulk materials for 1 and 2 all have good second-harmonic generation activity, approximately 1 and 0.8 times that of urea. PMID:16390053

Zang, Shuangquan; Su, Yang; Li, Yizhi; Ni, Zhaoping; Meng, Qingjin

2006-01-01

242

Facile estimation of catalytic activity and selectivities in copolymerization of propylene oxide with carbon dioxide mediated by metal complexes with planar tetradentate ligand.  

PubMed

Mechanistic studies were conducted to estimate (1) catalytic activity for PPC, (2) PPC/CPC selectivity, and (3) PPC/PPO selectivity for the metal-catalyzed copolymerization of propylene oxide with carbon dioxide [PPC: poly(propylene carbonate); CPC = cyclic propylene carbonate; PPO: poly(propylene oxide)]. Density functional theory (DFT) studies demonstrated that the ?G(crb) - ?G(epx) value should be an effective indicator for the catalytic activities [?G(epx): dissociation energy of ethylene oxide from the epoxide-coordinating metal complex; ?G(crb): dissociation energy of methyl carbonate from the metal-carbonate complex]. In addition, metal complexes with a subthreshold ?G(epx) value were found to show low PPC/CPC selectivity. The PPC/PPO selectivity was related to the ?G(alk) - ?G(epx) value and steric environment around the metal center (?G(alk): dissociation energy of alkoxide ligand from the metal center). Based on the mechanistic studies, two metal complexes were designed and applied to the copolymerization to support validity of these indicators. The results presented here should be useful for brand-new catalyst candidates since these indicators can be easily calculated by DFT method without computing transition states. PMID:25025746

Ohkawara, Takahiro; Suzuki, Kohei; Nakano, Koji; Mori, Seiji; Nozaki, Kyoko

2014-07-30

243

Synthesis of ligand-stabilized metal oxide nanocrystals and epitaxial core/shell nanocrystals via a lower-temperature esterification process.  

PubMed

The properties of metal oxide nanocrystals can be tuned by incorporating mixtures of matrix metal elements, adding metal ion dopants, or constructing core/shell structures. However, high-temperature conditions required to synthesize these nanocrystals make it difficult to achieve the desired compositions, doping levels, and structural control. We present a lower temperature synthesis of ligand-stabilized metal oxide nanocrystals that produces crystalline, monodisperse nanocrystals at temperatures well below the thermal decomposition point of the precursors. Slow injection (0.2 mL/min) of an oleic acid solution of the metal oleate complex into an oleyl alcohol solvent at 230 °C results in a rapid esterification reaction and the production of metal oxide nanocrystals. The approach produces high yields of crystalline, monodisperse metal oxide nanoparticles containing manganese, iron, cobalt, zinc, and indium within 20 min. Synthesis of tin-doped indium oxide (ITO) can be accomplished with good control of the tin doping levels. Finally, the method makes it possible to perform epitaxial growth of shells onto nanocrystal cores to produce core/shell nanocrystals. PMID:24369702

Ito, Daisuke; Yokoyama, Shun; Zaikova, Tatiana; Masuko, Keiichiro; Hutchison, James E

2014-01-28

244

The effect of thermal motion on the electron localization in metal-to-ligand charge transfer excitations in [Fe(bpy)3](2+).  

PubMed

Accurate electronic structure calculations of the lowest excited states have been performed on twenty snapshots of a molecular dynamics simulation of [Fe(bpy)3](2+) dissolved in water. The thermal motion distorts the structure of the complex from its average D3 symmetry, causing the localization on one bipyridine ligand of the excited electron in the metal-to-ligand charge transfer (MLCT) state. The excitation energy is about 0.25 eV lower than that for the delocalized description of the MLCT state and is in good agreement with experiments. The composition of the MLCT band is carefully analyzed and the effect of thermal motion on the mechanism of light-induced spin crossover is discussed. PMID:25360630

Domingo, Alex; Sousa, Carmen; de Graaf, Coen

2014-11-12

245

Complexation of nitrogen and sulphur donor Schiff's base ligand to Cr(III) and Ni(II) metal ions: Synthesis, spectroscopic and antipathogenic studies  

NASA Astrophysics Data System (ADS)

2,6-Diacetyl pyridine based ligand was synthesized by the reaction of 2,6-diacetyl pyridine with thiocarbohydrazide in presence of acetic acid. The coordination compounds with Cr(III) and Ni(II) metal ions having [Cr(L)X]X 2 and [Ni(L)X]X compositions (where L = ligand and X = NO 3-, Cl - and CH 3COO -) were synthesized and characterized by physicochemical and spectral studies. The studies like elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, UV-Vis, NMR, mass and EPR reveal that the complexes are octahedral. The compounds were examined against the pathogenic fungal and bacterial strains like Alternaria brassicae, Aspergillus niger, Fusarium oxysporum, Xanthomonas compestris and Pseudomonas aeruginosa. A. niger causes the diseases Apergillosis and Otomycosis in humans.

Sharma, Amit Kumar; Chandra, Sulekh

2011-01-01

246

Trifluoropropynyl as a surrogate for the cyano ligand and intense, room-temperature, metal-centered emission from its Rh(III) complex.  

PubMed

The trifluoropropynyl ligand -C?CCF(3) was studied as a possible surrogate for the cyano ligand. Complexes of the type trans-[M(cyclam)(C?CCF(3))(2)]OTf (where M = Cr(3+), Co(3+), and Rh(3+); OTf = trifluoromethanesulfonate) were prepared and then characterized by electronic spectroscopy and by cyclic voltammetry for the Co(3+) complex. The UV-vis spectra for all three bear a remarkable similarity to that of the trans-M(cyclam)(CN)(2)(+) cations. The trifluoropropynyl complex of Co(3+) shows electrochemical behavior nearly identical with that of its dicyano analogue. Metal-centered phosphorescence from the Rh(III) complex in room-temperature aqueous solution has a quantum yield of 0.12 and a lifetime of 73 ?s, nearly 10 times higher than those of its dicyano analogue. PMID:23013542

Sun, Chivin; Thakker, Parth U; Khulordava, Levan; Tobben, Daniel J; Greenstein, Seth M; Grisenti, David L; Kantor, Andrew G; Wagenknecht, Paul S

2012-10-15

247

Reduction of an electronically unsaturated transition-metal. eta. sup 2 -acyl complex. Arene formation from deoxygenative acyl coupling with a cyclopentadienyl ligand  

SciTech Connect

{eta}{sup 2}-Acyl ligands are common products from carbonylation of early-transition-metal, lanthanide, and actinide alkyls and have been studied primarily from a synthetic or structural rather than a reactivity perspective. Our interests in mid-valent, mono({eta}-C{sub 5}R{sub 5}) early-metal chemistry and in the comparative structure/reactivity of organometallic functional groups in complexes with different metal valencies led us to examine whether an electronically unsaturated {eta}{sup 2}-acyl complex would deinsert, rearrange to a ketene hydride, have altered {eta}{sup 2}-interaction and reactivity, or undergo structural rearrangement upon reduction. We have discovered an example of the latter, specifically that {eta}{sup 2}-acyl reduction can lead to deoxygenative coupling with a cyclopentadienyl C{sub ring}-C{sub ring} bond.

Meyer, T.Y.; Messerle, L. (Univ. of Iowa, Iowa City (USA))

1990-05-23

248

Anchoring the deficit of the anchor deficit: dyslexia or attention?  

PubMed

In the anchoring deficit hypothesis of dyslexia (Trends Cogn. Sci., 2007; 11: 458-465), it is proposed that perceptual problems arise from the lack of forming a perceptual anchor for repeatedly presented stimuli. A study designed to explicitly test the specificity of the anchoring deficit for dyslexia is presented. Four groups, representing all combinations of reading skills (high or low) and attention (high or low), were given a time estimation task in which a standard tone was compared with tones of varying length. Poor readers showed problems only if they had limited attentional skills as well, while poor readers with good attention were unaffected. It is concluded that a single deficit in time estimation is not sufficient to cause reading deficits. PMID:20440745

Willburger, Edith; Landerl, Karin

2010-05-01

249

Synthesis and characterization of metal complexes containing tetrazolate, poly(tetrazolyl)borate, and poly(azolyl)aluminate ligands as high energy density materials  

NASA Astrophysics Data System (ADS)

A series of heavy alkaline earth metal tetrazolate complexes has been synthesized that contain metal ions saturated by aqua ligands. Tetrazolates with small ring-core carbon substituents favor formation of two dimensional polymers with micro3-coordination of the tetrazolate to the metal centers. Tetrazolates with bulkier groups block coordination to the 1- and 4-nitrogen atoms, resulting in monomer formation. The first example of a trihydro(tetrazolyl)borate was prepared, and its bonding is heavily influenced by the basic BH3 moiety. 18-Crown-6 adducts of dihydrobis(tetrazolyl)borate complexes have been prepared that contain B-N bonding to the 2-nitrogen atoms, due to bulky ring-core atom substituents. A series of alkali metal hydrotris(tetrazolyl)borate complexes has been prepared by closely monitoring the reactions by electrospray ionization-mass spectrometry. The lithium hydrotris(tetrazolyl)borate complex contains kappa3-N,N,N bonding that is analgous to the bonding mode of hydrotris(pyrazolyl)borate ligands. The 18-crown-6 adducts of the sodium and potassium hydrotris(tetrazolyl)borate salts adopt eta 2-N,N and kappa2-N,H coordination modes, respectively, due to steric hindrances between the 18-crown-6 and hydrotris(tetrazolyl)borate ligands. The bonding modes of the hydrotris(tetrazolyl)borate complexes are stabilized by many hydrogen-bonding and dihydrogen-bonding contacts between the hydrotris(tetrazolyl)borate ligand and the ancillary ligand on the metal center. A series of poly(pyrazolyl)aluminate complexes containing aluminum-hydrogen bonds has been prepared, and these complexes exhibit similar coordination modes to their poly(pyrazolyl)borate analogues. Pyrazolyl exchange processes occur at room temperature in solution due to the weak Al-N and Al-H bonds. Salt metathesis of the new complexes with metal(II) halides yielded ligand, hydride, or pyrazolate transfer, depending on the metal and reaction conditions. The reactivity of 5-substituted tetrazoles with lithium aluminum hydride was investigated in an attempt to prepare tetrakis(tetrazolyl)aluminate salts at low temperatures to avoid thermal decomposition of the parent tetrazoles. The reactions yielded complex reaction mixtures that were only soluble in polar solvents. A lithium tetrazolate was isolated from one of the reaction mixtures, which may be due to an equilibrium between the lithium tetrakis(tetrazolyl)aluminate complex and lithium and aluminum tetrazolate complexes in solution. All tetrazolate and poly(tetrazolyl)borate complexes presented herein are thermally stable above 200 °C, are insensitive to shock, friction, and electrical discharge, and can be handled safely. The tetrazolate complexes described herein deflagrate or explode upon exposure to a flame, and therefore may serve as secondary energetic materials or colorants in pyrotechnics. The poly(tetrazolyl)borate complexes are insensitive to the flame test, with the exception of the lithium hydrotris(tetrazolyl)borate, which explodes upon exposure to a flame.

Snyder, Christopher James

250

Enhanced selectivity for actinides over lanthanides with CMPO ligands secured to a C(3)-symmetric triphenoxymethane platform.  

PubMed

A ligand system containing three preorganized carbamoylmethylphosphine oxide (CMPO) moieties anchored onto a rigid C(3)-symmetric triphenoxymethane platform has been developed for facile metal complexation and subsequent extraction from aqueous acidic nuclear waste streams. Intended to mimic the 3:1 CMPO-actinide stoichiometry of the extracted species in the TRUEX nuclear waste treatment process, the CMPO arms on this ligand are oriented such that all three CMPO moieties can cooperatively bind a metal ion. Extractions of simulated nuclear waste streams (10(-4) M metal in 1 M nitric acid) with solutions of this ligand in methylene chloride (10(-3) M) reveal a high affinity for the actinide thorium and a very low, but constant, affinity for the lanthanides across the series. Thorium and five lanthanide (lanthanum, cerium, neodymium, europium, and ytterbium) nitrate complexes of this ligand have been synthesized and fully characterized by X-ray crystallography, (1)H and (31)P NMR spectra, and FT-ICR-MS to elucidate the mechanism of this unique actinide selectivity. All six oxygen donors from the three CMPO arms of the ligand and one or two nitrate counterions coordinate these metals to afford 2+ cationic complexes in every case. Because of the large size of the ligand, both the thorium and lanthanide complexes present similarly charged and sized surfaces to the extraction solvents, but the thorium complex is extracted quantitatively over the lanthanide complexes. A possible rationale for this extraction behavior difference is presented and further illustrated by the extraction properties of this ligand system for the alkali metals (lithium, sodium, potassium, rubidium, and cesium) as picrate salts and by the solid- and solution-state structures of its lithium picrate complex. PMID:11925161

Peters, Matthew W; Werner, Eric J; Scott, Michael J

2002-04-01

251

Solvent effects on the metal-to-ligand charge transfer transition of the complex [Ru(NH3)5(Pyrazine)]2+  

NASA Astrophysics Data System (ADS)

In this work the solvent effects on the structure and metal-to-ligand charge transfer (MLCT) transition of the complex [Ru(NH3)5(Pyrazine)]2+ was investigated in aqueous solution, using the hybrid Density Functional Theory/Effective Fragment Potential Hamiltonian (DFT/EFP/MD) approach. The MLCT transition causes a large charge separation in the complex and produces a dipole moment variation of 8.3 ± 1.1 Debye upon excitation in solution and causes a large red-shift of 0.55 ± 0.15 eV. The solvatochromic shift can be attributed to the large charge separation accompanying the MLCT transition in solution.

Chagas, Marcelo A.; Rocha, Willian R.

2014-09-01

252

Anchor Callback Ask the rendering canvas for an anchor and  

E-print Network

anchor callback: [ self someAction ]; with: `Some Action' The callback-block won't be evaluated right-input field: html textInput value: self text; callback: [ :value | self text: value ] Render a password-input field: html passwordInput callback: [ :value | self text: value ] #12;Text Area Render a text-area field

Nierstrasz, Oscar

253

A 2D Metal-Organic Framework with a Flexible Cyclohexane-1,2,5,6-tetracarboxylic Acid Ligand: Synthesis, Characterization and Photoluminescent Property  

PubMed Central

A novel metal-organic framework, [Zn2(OH)(Hcht)(4,4?-bpy)]n·4nH2O (1) (H4cht = cyclohexane-1,2,4,5-tetracarboxylic acid and 4,4?-bpy = 4,4?-bipyridine), was synthesized by the hydrothermal reaction of Zn(NO3)2.6H2O, 4,4?-bipyridine, and cyclohexane-1,2,4,5-tetracarboxylic acid in the presence of sodium carbonate. The complex was obtained by controlling the ratio of the starting materials and a reaction temperature at 120°C and was characterized by IR, X-ray powder diffraction, thermogravimetric analysis, fluorescent spectrum, and single crystal X-ray diffraction. Single-crystal X-ray investigation reveals that the structure features a two-dimensional framework with novel coordination mode of Hcht ligand and all Hcht ligands exclusively convert to a sole conformation in the complex. IR spectrum reveals the characteristic absorption peaks of asymmetric stretching vibrations that result from the protonated and deprotonated carboxyl groups,. Thermogravimetric analysis shows four clear courses of weight loss, which corresponds to the decomposition of different ligands. Fluorescent spectrum displays that complex 1 is a potential blue-luminescent material. PMID:20383315

Wang, Rongming; Zhang, Jian; Li, Lijuan

2009-01-01

254

Formation of mixed-ligand complexes of pd2+ with nucleoside 5'-monophosphates and some metal-ion-binding nucleoside surrogates.  

PubMed

Formation of mixed-ligand Pd2+ complexes between canonical nucleoside 5'-monophosphates and five metal-ion-binding nucleoside analogs has been studied by 1H-NMR spectroscopy to test the ability of these nucleoside surrogates to discriminate between unmodified nucleobases by Pd2+-mediated base pairing. The nucleoside analogs studied included 2,6-bis(3,5-dimethylpyrazol-1-yl)-, 2,6-bis(1-methylhydrazinyl)- and 6-(3,5-dimethylpyrazol-1-yl)-substituted 9-(?-d-ribofuranosyl)purines 1-3, and 2,4-bis(3,5-dimethylpyrazol-1-yl)- and 2,4-bis(1-methylhydrazinyl)-substituted 5-(?-d-ribofuranosyl)-pyrimidines 4-5. Among these, the purine derivatives 1-3 bound Pd2+ much more tightly than the pyrimidine derivatives 4, 5 despite apparently similar structures of the potential coordination sites. Compounds 1 and 2 formed markedly stable mixed-ligand Pd2+ complexes with UMP and GMP, UMP binding favored by 1 and GMP by 2. With 3, formation of mixed-ligand complexes was retarded by binding of two molecules of 3 to Pd2+. PMID:25340302

Golubev, Oleg; Lönnberg, Tuomas; Lönnberg, Harri

2014-01-01

255

Anchored phosphatases modulate glucose homeostasis.  

PubMed

Endocrine release of insulin principally controls glucose homeostasis. Nutrient-induced exocytosis of insulin granules from pancreatic ?-cells involves ion channels and mobilization of Ca(2+) and cyclic AMP (cAMP) signalling pathways. Whole-animal physiology, islet studies and live-?-cell imaging approaches reveal that ablation of the kinase/phosphatase anchoring protein AKAP150 impairs insulin secretion in mice. Loss of AKAP150 impacts L-type Ca(2+) currents, and attenuates cytoplasmic accumulation of Ca(2+) and cAMP in ?-cells. Yet surprisingly AKAP150 null animals display improved glucose handling and heightened insulin sensitivity in skeletal muscle. More refined analyses of AKAP150 knock-in mice unable to anchor protein kinase A or protein phosphatase 2B uncover an unexpected observation that tethering of phosphatases to a seven-residue sequence of the anchoring protein is the predominant molecular event underlying these metabolic phenotypes. Thus anchored signalling events that facilitate insulin secretion and glucose homeostasis may be set by AKAP150 associated phosphatase activity. PMID:22940692

Hinke, Simon A; Navedo, Manuel F; Ulman, Allison; Whiting, Jennifer L; Nygren, Patrick J; Tian, Geng; Jimenez-Caliani, Antonio J; Langeberg, Lorene K; Cirulli, Vincenzo; Tengholm, Anders; Dell'Acqua, Mark L; Santana, L Fernando; Scott, John D

2012-10-17

256

Anchored phosphatases modulate glucose homeostasis  

E-print Network

EMBO open Anchored phosphatases modulate glucose homeostasis Simon A Hinke1 , Manuel F Navedo2 principally controls glucose homeostasis. Nutrient-induced exocytosis of insulin granules from pancreatic b signalling events that facilitate insulin secretion and glucose homeostasis may be set by AKAP150 associated

Scott, John D.

257

Topotactic elimination of water across a C-C ligand bond in a dense 3-D metal-organic framework.  

PubMed

Upon heating, lithium l-malate undergoes topotactic dehydration to form a phase containing the unsaturated fumarate ligand, in which the original 3-D framework remains intact. Insight into this unusual transformation has been obtained by single crystal X-ray diffraction, MAS-NMR, in situ powder X-ray diffraction and DFT calculations. PMID:25232700

Yeung, Hamish H-M; Kosa, Monica; Griffin, John M; Grey, Clare P; Major, Dan T; Cheetham, Anthony K

2014-11-11

258

Nanopatterned anchoring layers for liquid crystals  

E-print Network

This thesis describes the theory and fabrication of inhomogeneous Liquid Crystal anchoring layers. While chemical anchoring techniques have proved useful for many applications, especially Liquid Crystal Displays, they have ...

Gear, Christopher S. (Christopher Stanwood)

2014-01-01

259

Encapsulation of the 4-mercaptobenzoate ligand by macrocyclic metal complexes: conversion of a metallocavitand to a metalloligand.  

PubMed

Complexation of the ambidentate ligand 4-mercaptobenzoate (4-SH-C6H4CO2H, H2mba) by the macrocyclic complex [Ni2L(?-Cl)]ClO4 (L(2-) represents a 24-membered macrocyclic hexaazadithiophenolate ligand) has been examined. The monodeprotonated Hmba(-) ligand reacts with the Ni2 complex in a selective manner by substitution of the bridging chlorido ligand to produce ?1,3-carboxylato-bridged complex [Ni2L(Hmba)](+) (2(+)), which can be isolated as an air-sensitive perchlorate (2ClO4) or tetraphenylborate (2BPh4) salt. The reactivity of the new mercaptobenzoate complex is reminiscent of that of a "free" thiophenolate ligand. In the presence of air, 2ClO4 dimerizes via a disulfide bond to generate tetranuclear complex [{Ni2L}2(O2CC6H4S)2](2+) (3(2+)). The auration of 2ClO4 with [AuCl(PPh3)], on the other hand, leads to monoaurated complex [Ni(II)2L(mba)Au(I)PPh3](+) (4(+)). The bridging thiolate functions of the N6S2 macrocycle are deeply buried and are unaffected/unreactive under these conditions. The complexes were fully characterized by electrospray ionization mass spectrometry, IR and UV/vis spectroscopy, density functional theory, cyclic voltammetry, and X-ray crystallography [for 3(BPh4)2 and 4BPh4]. Temperature-dependent magnetization and susceptibility measurements reveal an S = 2 ground state that is attained by ferromagnetic coupling between the spins of the Ni(II) ions in 2ClO4 (J = +22.3 cm(-1)) and 4BPh4 (J = +20.8 cm(-1); H = -2JS1S2). Preliminary contact-angle and X-ray photoelectron spectroscopy measurements indicate that 2ClO4 interacts with gold surfaces. PMID:25299133

Lach, Jochen; Jeremies, Alexander; Breite, Daniel; Abel, Bernd; Mahns, Benjamin; Knupfer, Martin; Matulis, Vitaly; Ivashkevich, Oleg A; Kersting, Berthold

2014-10-20

260

In situ synthesis of trisubstituted methanol ligands and their potential as one-pot generators of cubane-like metal complexes.  

PubMed

Two different one pot routes to a variety of metal cubane compounds are reported; one route is based on an in situ benzilic acid type rearrangement and the other involves in situ nucleophilic attack at a ketone. Diketosuccinic acid in basic solution in the presence of certain divalent metal ions undergoes a benzilic acid type rearrangement to generate the carbon oxyanion, C(CO(2) (-))(3)O(-), which serves as a cubane-forming bridging ligand in a series of octanuclear complexes of composition [M(8){C(CO(2))(3)O}(4)](H(2)O)(12) (M=Mg, Mn, Fe, Co, Ni, Zn). At the heart of each of these highly symmetrical aggregates is an M(4)O(4) cubane core, each oxygen component of which is provided by the alkoxo centre of a C(CO(2) (-))(3)O(-) ligand. Reaction of 2,2'-pyridil, (2-C(5)H(4)N)COCO(2-C(5)H(4)N), and calcium nitrate in basic alcoholic solution, which proceeds by a similar benzilic acid type rearrangement, gives the cubane compounds, [Ca(4)L(4)(NO(3))(4)] in which L=(2-C(5)H(4)N)(2)C(COOR)O(-) (R=Me or Et). Nucleophilic attack by bisulfite ion at the carbonyl carbon atom of 2,2'-dipyridyl ketone in the presence of certain divalent metals generates the electrically neutral complexes, [{(C(5)H(4)N)(2)SO(3)C(OH)}(2)M] (M=Mn, Fe, Co, Ni, Zn and Cd). Cubane-like complexes [M(4){(C(5)H(4)N)(2)SO(3)C(O)}(4)] (M=Zn, Mn) can be obtained directly from 2,2'-dipyridyl ketone in one-pot reaction systems (sealed tube, 120 degrees C) if a base as weak as acetate ion is present to deprotonate the OH group of the initial [(C(5)H(4)N)(2)SO(3)C(OH)](-) bisulfite addition compound; the [(C(5)H(4)N)(2)SO(3)C(O)](2-) ligand in this case plays the same cubane-forming role as the ligands C(COO(-))(3)O(-) and (2-C(5)H(4)N)(2)C(COOR)O(-) above. When excess sodium sulfite is used in similar one-pot reaction mixtures, the monoanionic complexes, [M(3)Na{(C(5)H(4)N)(2)SO(3)C(O)}(4)](-) (M=Zn, Mn, Co) with an M(3)NaO(4) cubane core, are formed directly from 2,2'-dipyridyl ketone. PMID:16835854

Abrahams, Brendan F; Hudson, Timothy A; Robson, Richard

2006-09-18

261

Nestin Modulates Glucocorticoid Receptor Function by Cytoplasmic Anchoring  

PubMed Central

Nestin is the characteristic intermediate filament (IF) protein of rapidly proliferating progenitor cells and regenerating tissue. Nestin copolymerizes with class III IF-proteins, mostly vimentin, into heteromeric filaments. Its expression is downregulated with differentiation. Here we show that a strong nestin expression in mouse embryo tissue coincides with a strong accumulation of the glucocorticoid receptor (GR), a key regulator of growth and differentiation in embryonic development. Microscopic studies on cultured cells show an association of GR with IFs composed of vimentin and nestin. Cells lacking nestin, but expressing vimentin, or cells expressing vimentin, but lacking nestin accumulate GR in the nucleus. Completing these networks with an exogenous nestin, respectively an exogenous vimentin restores cytoplasmic anchoring of GR to the IF system. Thus, heteromeric filaments provide the basis for anchoring of GR. The reaction pattern with phospho-GR specific antibodies and the presence of the chaperone HSC70 suggest that specifically the unliganded receptor is anchored to the IF system. Ligand addition releases GR from IFs and shifts the receptor into the nucleus. Suppression of nestin by specific shRNA abolishes anchoring of GR, induces its accumulation in the nucleus and provokes an irreversible G1/S cell cycle arrest. Suppression of GR prior to that of nestin prevents entry into the arrest. The data give evidence that nestin/vimentin specific anchoring modulates growth suppression by GR. We hypothesize that expression of nestin is a major determinant in suppression of anti-proliferative activity of GR in undifferentiated tissue and facilitates activation of this growth control in a precise tissue and differentiation dependent manner. PMID:19562035

Szalay, Beata; Hagel, Christian; Hohenberg, Heinrich; Deppert, Wolfgang; Bohn, Wolfgang

2009-01-01

262

Steady-state distribution of metals among metallothionein and other cytosolic ligands and links to cytotoxicity in bivalves living along a polymetallic gradient.  

PubMed

The present study was designed to assess the environmental effects of metals in a field setting. We explored exposure-->bioaccumulation-->effects relationships in freshwater molluscs exposed to metals in their natural habitat. Indigenous floater mussels (Pyganodon grandis) were collected from ten limnologically similar lakes located along a Cd, Cu and Zn gradient. Ambient free-metal ion concentrations were estimated as a measure of metal exposure. Metallothionein (MT) was measured in mussel gills and metal partitioning among the various cytosolic protein pools was determined by size exclusion chromatography. Various biomarkers were also measured, including malondialdehyde (MDA) concentrations in the gills and in the digestive gland, glutathione-peroxidase and glutathione-reductase activities in the digestive gland, and lipid concentrations in the gonad. Cadmium and MT concentrations in the gill cytosol increased along the contamination gradient, but Cu and Zn levels were independent of the ambient free-metal ion concentrations. The distribution of Cd among the various cytosolic complexes remained quite constant: 80% in the MT-like pool, 7% in the low molecular weight pool (LMW<1.8 kDa) and 13% in the high molecular weight pool (HMW>18 kDa). For these chronically exposed molluscs there was thus no threshold exposure concentration above which spillover of Cd occurred from the MT pool to other cytosolic ligands. However, the presence of Cd in the LMW and HMW fractions suggests that metal detoxification was imperfect, i.e. that P. grandis was subject to some Cd-related stress at low chronic exposure concentrations. Consistent with this suggestion, MDA concentrations, an indicator of oxidative stress, increased with gill cytosolic Cd. In the digestive gland, MDA concentrations were unrelated to any of the measured metals, but glutathione-peroxidase and glutathione-reductase activities increased with gill cytosolic copper. We speculate that cytosolic Cu catalyses the production of reactive oxygen species, to which the organism reacts by increasing activities of the two enzymes, thus preventing the accumulation of reactive oxygen species. Lipid concentrations in the gonad did not decrease with any of the measured toxicological parameters, suggesting that energy reserves for reproduction were not compromised in the metal-contaminated mussels. The results of the present study, where chronically exposed bivalves were collected from their natural habitat along a metal contamination gradient, contrast markedly with what would have been predicted on the basis of experimental metal exposures, and clearly demonstrate the need to study metal exposure-->bioaccumulation-->effects relationships in natural populations. PMID:12799111

Giguère, Anik; Couillard, Yves; Campbell, Peter G C; Perceval, Olivier; Hare, Landis; Pinel-Alloul, Bernadette; Pellerin, Jocelyne

2003-07-16

263

Synthesis, characterization, and antipathogenic studies of some transition metal complexes with N,O-chelating Schiff's base ligand incorporating azo and sulfonamide Moieties  

NASA Astrophysics Data System (ADS)

Chromium(III), Manganese(II), Cobalt(II), nickel(II), copper(II) and cadmium(II) complexes of 4-[4-hydroxy-3-(phenyliminomethyl)-phenylazo]benzenesulfonamide, were prepared and characterized on the basis of elemental analyses, spectral, magnetic, molar conductance and thermal analysis. Square planar, tetrahedral and octahedral geometries have been assigned to the prepared complexes. Dimeric complexes are obtained with 2:2 molar ratio except chromium(III) complex is monomeric which is obtained with 1:1 molar ratios. The IR spectra of the prepared complexes were suggested that the Schiff base ligand(HL) behaves as a bi-dentate ligand through the azomethine nitrogen atom and phenolic oxygen atom. The crystal field splitting, Racah repulsion and nepheloauxetic parameters and determined from the electronic spectra of the complexes. Thermal studies suggest a mechanism for degradation of HL and its metal complexes as function of temperature supporting the chelation modes. Also, the activation thermodynamic parameters, such as ?E*, ?H*, ?S* and ?G* for the different thermal decomposition steps of HL and its metal complexes were calculated. The pathogenic activities of the synthesized compounds were tested in vitro against the sensitive organisms Staphylococcus aureus (RCMB010027), Staphylococcus epidermidis (RCMB010024) as Gram positive bacteria, Klebsiella pneumonia (RCMB 010093), Shigella flexneri (RCMB 0100542), as Gram negative bacteria and Aspergillus fumigates (RCMB 02564), Aspergillus clavatus (RCMB 02593) and Candida albicans (RCMB05035) as fungus strain, and the results are discussed.

Alaghaz, Abdel-Nasser M. A.; Bayoumi, Hoda A.; Ammar, Yousry A.; Aldhlmani, Sharah A.

2013-03-01

264

Limited coordination number and competitive coordination in ammonia-water mixed-ligand complexes of monopositive metal ions as studied by the laser-ablation-molecular beam method: Experiment and simulation  

Microsoft Academic Search

Ammonia-water mixed-ligand complexes of monopositive metal ions M+ (M=Mg, Al, Mn, and Co) were prepared in the gas phase by reactions of metal ions laser-ablated from a metal substrate in vacuum with ammonia-water binary clusters in a molecular beam injected nearby [the laser-ablation-molecular beam (LAMB) method]. Relative abundances of M+(NH3)m(H2O)n are characterized by intensity gaps which indicate limited (typically 2

Hiroyasu Sato; Akiyoshi Matsuzaki; Satoru Nishio; Osamu Ito; Koji Furukawa; Takashi Kawasaki

1998-01-01

265

Group 11 Metal Compounds with Tripodal Bis(imidazole) Thioether Ligands. Applications as Catalysts in the Oxidation of Alkenes and as Antimicrobial Agents  

PubMed Central

New group 11 metal complexes have been prepared using the previously described tripodal bis(imidazole) thioether ligand (N-methyl-4,5-diphenyl-2-imidazolyl)2C(OMe)C(CH3)2S(tert-Bu) ({BITOMe,StBu}, 2). The pincer ligand offers a N2S donor atom set that can be used to coordinate the group 11 metals in different oxidation states [AuI, AuIII, AgI, CuI and CuII]. Thus the new compounds [Au{BITOMe,StBu}Cl][AuCl4]2 (3), [Au{BITOMe,StBu}Cl] (4), [Ag{BITOMe,StBu}X] (X = OSO2CF3 ? 5, PF6 ? 6) and [Cu{BITOMe,StBu}Cl2] (7) have been synthesized from reaction of 2 with the appropriate metal precursors, and characterized in solution. While attempting characterization in the solid state of 3, single crystals of the neutral dinuclear mixed AuIII-AuI species [Au2{BITOMe,S}Cl3] (8) were obtained and its crystal structure was determined by X-ray diffraction studies. The structure shows a AuIII center coordinated to the pincer ligand through one N and the S atom. The soft AuI center coordinates to the ligand through the same S atom that has lost the tert-butyl group, thus becoming a thiolate ligand. The short distance between the AuI–AuIII atoms (3.383 Å) may indicate a weak metal-metal interaction. Complexes 2–7 and the previously described CuI compound [Cu{BITOMe,StBu}]PF6 (9) have been evaluated in the oxidation of biphenyl ethylene with tert-butyl hydrogen peroxide (TBHP) as the oxidant. Results have shown that the AuI and AgI complexes 4 and 6 (at 10 mol % loading) are the more active catalysts in this oxidative cleavage. The antimicrobial activity of compounds 2–5, 7 and 9 against Gram-positive and Gram-negative bacteria and yeast has also been evaluated. The new gold and silver compounds display moderate to high antibacterial activity, while the copper derivatives are mostly inactive. The gold and silver complexes were also potent against fungi. Their cytotoxic properties have been analyzed in vitro utilizing HeLa human cervical carcinoma cells. The compounds displayed a very low cytotoxicity on this cell line (5 to 10 times lower than cisplatin) and on normal primary cells derived from C57B6 mouse muscle explants, which may make them promising candidates as potential antimicrobial agents and safer catalysts due to low toxicity in human and other mammalian tissues. PMID:25134773

Liu, Fangwei; Anis, Reema; Hwang, Eunmi; Ovalle, Rafael; Varela-Ramirez, Armando; Aguilera, Renato J.; Contel, Maria

2011-01-01

266

C(sp?)-H bond activation with triel metals: indium and gallium zwitterions through internal hydride abstraction in rigid salan ligands.  

PubMed

The hydropyrimidine salan (salan=N,N'-dimethyl-N,N'-bis[(2-hydroxyphenyl)methylene]-1,2-diaminoethane) proteo-ligands with a rigid backbone {ON^(CH2)^NO}H2 react with M(CH2SiMe3)3 (M=Ga, In) to yield the zwitterions {ON^(CH(+))^NO}M(-)(CH2SiMe3)2 (M=Ga, 2; In, 3) by abstraction of a hydride from the ligand backbone followed by elimination of dihydrogen. By contrast, with Al2Me6, the neutral-at-metal bimetallic complex [{ON^(CH2)^NO}AlMe]2 ([1]2) is obtained quantitatively. The formation of indium zwitterions is also observed with sterically more encumbered ligands containing o-Me substituents on the phenolic rings, or an N?(CHPh)?N moiety in the heterocyclic core. Overall, the ease of C(sp3)-H bond activation follows the order Al?Gametal-hydride species. DFT calculations indicate that the systems {ON^(CH2)^NO}H2+M(CH2SiMe3)3 (M=Al, Ga, In) all initially lead to the formation of the neutral monophenolate dihydrocarbyl species through a single protonolysis. From here, the thermodynamic product, the model neutral-at-metal complex 1, is formed in the case of aluminum after a second protonolysis. On the other hand, lower activation energy pathways lead to the generation of zwitterionic complexes 2 and 3 in the cases of gallium and indium, and the formation of these zwitterions obeys a strict kinetic control; the computations suggest that, as inferred from the experimental data, the reaction proceeds through an instable metal-hydride species, which could not be isolated synthetically. PMID:24842493

Maudoux, Nicolas; Fang, Jian; Roisnel, Thierry; Dorcet, Vincent; Maron, Laurent; Carpentier, Jean-François; Sarazin, Yann

2014-06-16

267

Self-assembly of NIR luminescent 30-metal drum-like and 12-metal rectangular d-f nanoclusters with long-chain Schiff base ligands.  

PubMed

Two classes of heterobimetallic d-f nanoclusters [Ln6Cd24(L(1))11(OAc)43(OH)] and [Ln4Zn8(L(2))2(OAc)20(OH)4] (Ln = Nd and Yb) were prepared using flexible long-chain Schiff base ligands which have (CH2)6 backbones. Their NIR luminescence properties were determined. PMID:25358081

Yang, Xiaoping; Li, Zongping; Wang, Shiqing; Huang, Shaoming; Schipper, Desmond; Jones, Richard A

2014-12-21

268

Synthesis, characterization and thermal study of some transition metal complexes of an asymmetrical tetradentate Schiff base ligand  

Microsoft Academic Search

Complexes of Cu(II), Ni(II), Co(II), Mn(II) and Fe(III) with an asym- metric tetradentate Schiff base ligand derived from dehydroacetic acid, 4-me- thyl-o-phenylenediamine and salicylic aldehyde were synthesized and charac- terized by elemental analysis, conductometry, magnetic susceptibility, UV-Vis, IR, 1 H-NMR spectroscopy, X-ray diffraction analysis of powdered samples and thermal analysis, and screened for antimicrobial activity. The IR spectral data suggested

ACHUT S. MUNDE; AMARNATH N. JAGDALE; SARIKA M. JADHAV; TRIMBAK K. CHONDHEKAR

2010-01-01

269

Anchoring Bias in Online Voting  

E-print Network

Voting online with explicit ratings could largely reflect people's preferences and objects' qualities, but ratings are always irrational, because they may be affected by many unpredictable factors like mood, weather, as well as other people's votes. By analyzing two real systems, this paper reveals a systematic bias embedding in the individual decision-making processes, namely people tend to give a low rating after a low rating, as well as a high rating following a high rating. This so-called \\emph{anchoring bias} is validated via extensive comparisons with null models, and numerically speaking, the extent of bias decays with interval voting number in a logarithmic form. Our findings could be applied in the design of recommender systems and considered as important complementary materials to previous knowledge about anchoring effects on financial trades, performance judgements, auctions, and so on.

Yang, Zimo; Zhou, Tao

2012-01-01

270

Anchoring bias in online voting  

NASA Astrophysics Data System (ADS)

Voting online with explicit ratings could largely reflect people's preferences and objects' qualities, but ratings are always irrational, because they may be affected by many unpredictable factors like mood, weather and other people's votes. By analyzing two real systems, this paper reveals a systematic bias embedding in the individual decision-making processes, namely people tend to give a low rating after a low rating, as well as a high rating following a high rating. This so-called anchoring bias is validated via extensive comparisons with null models, and numerically speaking, the extent of bias decays with voting interval in a logarithmic form. Our findings could be applied in the design of recommender systems and considered as important complementary materials to previous knowledge about anchoring effects on financial trades, performance judgments, auctions, and so on.

Yang, Zimo; Zhang, Zi-Ke; Zhou, Tao

2012-12-01

271

Metal ions and solvents ratio co-regulate four new magnetic coordination polymers based upon an unsymmetric tricarboxylate acid ligand.  

PubMed

Four new coordination polymers (CPs), [Co3(L)2(bib)3(EtOH)2]·2H2O (1), [Mn3(L)2(bib)2(H2O)4]·4H2O (2), [Ni(HL)(bib)(H2O)3] (3) and [Ni3(bib)4(H2O)10]·2(L)·12(H2O) (4), were synthesized under solvothermal conditions with an unsymmetrical tricarboxylic acid ligand [biphenyl-3,3',5-tricarboxylic acid (H3L)] in the presence of the 1,4-bis(1H-imidazol-4-yl)benzene (bib) ligand. In compound 1, tricarboxylate acid ligands (H3L) link Co centers to generate two-dimensional (2D) layers which are further connected by bib ligands to exhibit a three-dimensional (3D) framework with a (4,4,5)-connected (4(2)·6(3)·8)2(4(2)·6(7)·8)2(6(4)·8·10) topology. The three-dimensional (3D) framework of 2 is defined as a (3,3,4)-connected topology with the point symbol of (6·8(2))2(6(2)·8)2(8·10(4)·12). Compound 3 contains a one-dimensional (1D) left-hand helix chain along the a direction and further extends into a 2D supramolecular network and a 3D supramolecular framework via hydrogen bonds. Compound 4 displays a one-dimensional (1D) molecular ladder, which is further combined with each other through ?···? stacking to extend into 2D supramolecular sheets. The supramolecular networks of 3 and 4 resulted from the different solvent ratios [V(H2O)-V(EtOH)] in the reaction. All the CPs are characterized by single-crystal X-ray diffraction analyses, powder X-ray diffraction (PXRD), elemental analyses, IR spectroscopy, and TGA analyses. Moreover, the weak ferromagnetic properties of 2 and 3 and antiferromagnetic properties of 1 and 4 have also been investigated. PMID:24905184

Li, Yuan-Pu; Chai, Ying; Yang, Guo-Ping; Miao, Hui-Hui; Cui, Lin; Wang, Yao-Yu; Shi, Qi-Zhen

2014-07-28

272

Synthesis, spectroscopic characterization and thermal studies of some rare earth metal complexes of unsymmetrical tetradentate Schiff base ligand  

Microsoft Academic Search

The solid complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III) and Gd(III) with 4-hydroxy-3-(1-{2-(2-hydroxy-benzylidene)-aminophenylimino}-thyl)-6-methy-pyran-2-one (H2L) derived from o-phenylenediamine, 3-acetyl-6-methyl-(2H)pyran,2,4(3H)-dione (dehydroacetic acid or DHA) and salicylic aldehyde have been synthesized and characterized by elemental analysis, conductometry, magnetic susceptibility, UV–visible, FTIR, 1H NMR spectra, X-ray diffraction, and thermal analysis and screened for antimicrobial activity. The FTIR spectral data suggest that the ligand behaves

V. A. Shelke; S. M. Jadhav; V. R. Patharkar; S. G. Shankarwar; A. S. Munde; T. K. Chondhekar

273

The use of Acufex wedge tag tissue anchors in hand surgery.  

PubMed

Over a period of 4 years, in various circumstances commonly seen in hand surgery, 100 patients underwent 127 soft tissue attachments to bone using the Acufex wedge tag system (Acufex Microsurgical, Inc, Mansfield, MA), a non-metallic bone anchor. No failures to maintain the attachment of the desired soft tissue to bone were identified. While less robust than the Mitek anchor, the other commonly available system of bone anchoring, and therefore possibly inappropriate for general orthopaedics, the Acufex wedge tag proved adequate for the smaller forces of hand surgery. PMID:14734064

Khandwala, A R; Khan, I U; Elliot, D

2004-02-01

274

Unique (3,8)-connected lanthanide arenedisulfonate metal-organic frameworks containing benzimidazole-5,6-dicarboxylic acid co-ligand: Syntheses, structures and luminescence  

NASA Astrophysics Data System (ADS)

Two isostructural 3D lanthanide arenedisulfonate metal-organic frameworks (MOFs) [Ln(Hbidc)(nds)0.5(H2O)]n(Ln=Eu(1), La(2)) have been successfully synthesized by the hydrothermal reaction of lanthanide oxide with 2,6-naphthalenedisulfonate sodium (Na2nds) and an auxiliary ligand, 1H-benzimidazole-5,6-dicarboxylic acid (H3bidc). The two complexes are both constructed from 2D [Ln(Hbidc)]+ double layers pillared by nds2- ligands to generate 3D (3, 8)-connected open-framework structures with 1D long narrow channels running along the a axis. From topological point of view, the 3D framework is a (3, 8)-connected tfz-d net. The weak interactions including N-H⋯O, O-H⋯O hydrogen bonds and ?-? stacking are observed in 1. The 2D IR correlation spectroscopy was applied to study the molecular interactions induced by thermal perturbation. The emission spectra of 1 exhibit the characteristic transition of 5D0?7FJ(J=0-4) of Eu(III).

Sun, Yan-Qiong; Liu, Qi; Zhong, Jie-Cen; Pan, Qun-Feng; Chen, Yi-Ping

2013-10-01

275

Synthesis, structure and catalytic activity of alkali metal-free bent-sandwiched lanthanide amido complexes with calix[4]-pyrrolyl ligands.  

PubMed

Simple silylamine elimination reactions of calix[4]-pyrrole [R(2)C(C(4)H(2)NH)](4) (R = Me (1), {-(CH(2))(5)-}(0.5) (2)) with 2 equiv. of [(Me(3)Si)(2)N](3)Ln(?-Cl)Li(THF)(3) (Ln = Nd, Sm, Dy) in reflux toluene, afforded the novel dinuclear alkali metal-free trivalent lanthanide amido complexes (?(5):?(1):?(5):?(1)-R(8)-calix[4]-pyrrolyl){LnN(SiMe(3))(2)}(2) (R = Me, Ln = Nd (3), Sm (4), Dy (5); R = {-(CH(2))(5)-}(0.5), Ln = Nd (6), Sm(7)). The complexes were fully characterized by elemental analyses, spectroscopic analyses and single-crystal X-ray analyses. X-ray diffraction studies showed that each lanthanide metal was supported by bispyrrolyl anions in an ?(5) fashion and along with three nitrogen atoms from N(SiMe(3))(2) and two other pyrroyl rings in ?(1) modes formed the novel bent-sandwiched lanthanide amido bridged trivalent lanthanide amido complexes, similar to ansa-cyclopentadienyl ligand-supported lanthanide amides with respect to each metal center. The catalytic activities of these organolanthanide complexes as single component l-lactide polymerization catalysts were studied. PMID:21850293

Zhou, Shuangliu; Wu, Shihong; Zhu, Hong; Wang, Shaowu; Zhu, Xiancui; Zhang, Lijun; Yang, Gaosheng; Cui, Daohui; Wang, Hengyu

2011-10-01

276

Gas adsorption and gas mixture separations using mixed-ligand MOF material  

DOEpatents

A method of separating a mixture of carbon dioxiode and hydrocarbon gas using a mixed-ligand, metal-organic framework (MOF) material having metal ions coordinated to carboxylate ligands and pyridyl ligands.

Hupp, Joseph T. (Northfield, IL); Mulfort, Karen L. (Chicago, IL); Snurr, Randall Q. (Evanston, IL); Bae, Youn-Sang (Evanston, IL)

2011-01-04

277

Metal-organic coordination architectures of azole heterocycle ligands bearing acetic acid groups: Synthesis, structure and magnetic properties  

SciTech Connect

Four new coordination complexes with azole heterocycle ligands bearing acetic acid groups, [Co(L{sup 1}){sub 2}]{sub n} (1), [CuL{sup 1}N{sub 3}]{sub n} (2), [Cu(L{sup 2}){sub 2}.0.5C{sub 2}H{sub 5}OH.H{sub 2}O]{sub n} (3) and [Co(L{sup 2}){sub 2}]{sub n} (4) (here, HL{sup 1}=1H-imidazole-1-yl-acetic acid, HL{sup 2}=1H-benzimidazole-1-yl-acetic acid) have been synthesized and structurally characterized. Single-crystal structure analysis shows that 3 and 4 are 2D complexes with 4{sup 4}-sql topologies, while another 2D complex 1 has a (4{sup 3}){sub 2}(4{sup 6})-kgd topology. And 2 is a 3D complex composed dinuclear mu{sub 1,1}-bridging azido Cu{sup II} entities with distorted rutile topology. The magnetic properties of 1 and 2 have been studied. - Graphical Abstract: The synthesis, crystal structure, and magnetic properties of the new coordination complexes with azole heterocycle ligands bearing acetic acid groups are reported.

Hu Bowen; Zhao Jiongpeng; Yang Qian; Hu Tongliang; Du Wenping [Department of Chemistry, Nankai University, Tianjin 300071 (China); Bu Xianhe, E-mail: buxh@nankai.edu.c [Department of Chemistry, Nankai University, Tianjin 300071 (China)

2009-10-15

278

Metal coordination and in situ S-C bond cleavage of the bis(2-pyridylthio)methane ligand.  

PubMed

The compound [2bpytmH](2)[I(3)](2)[I(2)], which contains protonated 2bpytm, and four neutral monomeric complexes [CoCl(2)(2bpytm)]·H(2)O (1), [CoBr(2)(2bpytm)] (2), [CoI(2)(2bpytm)]·1/2H(2)O (3) and [NiBr(2)(2bpytm)]·H(2)O (4) have been obtained during a study into the reactivity of the bis(2-pyridylthio)methane (2bpytm) ligand towards cobalt(II) and nickel(II) halides. Furthermore, a cyclic dimer [CuBr(2)(2bpytm)](2) (5) and a 1D polymer [CuBr(2)(2bpytm)](n)·CH(3)CN (6) have been obtained from copper(II)/(I) bromide salts. An unprecedented S-CH(2)-S activation and cleavage in 2bpytm has been observed on using copper(II) salts with organic and voluminous inorganic anions. The cleavage of 2bpytm enabled the isolation of copper(II) complexes containing the in situ generated ligands 2-pyridinethiolate, 2-pyridinesulfenate or 2-pyridinesulfonate. PMID:20882242

Belén Lago, Ana; Amoedo, Almudena; Carballo, Rosa; García-Martínez, Emilia; Vázquez-López, Ezequiel M

2010-11-14

279

Rare-earth metal alkyl and hydride complexes stabilized by a cyclen-derived [NNNN] macrocyclic ancillary ligand.  

PubMed

A trinuclear rare-earth metal hydride complex was synthesized from the dialkyl complex supported by a monoanionic [NNNN] macrocycle and shown to catalyze the hydrosilylation of olefins efficiently. PMID:18461944

Ohashi, Masato; Konkol, Marcin; Del Rosal, Iker; Poteau, Romuald; Maron, Laurent; Okuda, Jun

2008-06-01

280

Synthesis of N4 donor macrocyclic Schiff base ligands and their Ru (II), Pd (II), Pt (II) metal complexes for biological studies and catalytic oxidation of didanosine in pharmaceuticals  

NASA Astrophysics Data System (ADS)

A series of tetraaza (N4 donor) macrocyclic ligands (L1-L4) were derived from the condensation of o-phthalaldehyde (OPA) with some substituted aromatic amines/azide, and subsequently used to synthesize the metal complexes of Ru(II), Pd(II) and Pt(II). The structures of macrocyclic ligands and their metal complexes were characterized by elemental analyses, IR, 1H &13C NMR, mass and electronic spectroscopy, thermal, magnetic and conductance measurements. Both the ligands and their complexes were screened for their antibacterial activities against Gram positive and Gram negative bacteria by MIC method. Besides, these macrocyclic complexes were investigated as catalysts in the oxidation of pharmaceutical drug didanosine. The oxidized products were further treated with sulphanilic acid to develop the colored products to determine by spectrophotometrically. The current oxidation method is an environmentally friendly, simple to set-up, requires short reaction time, produces high yields and does not require co-oxidant.

Ravi krishna, E.; Muralidhar Reddy, P.; Sarangapani, M.; Hanmanthu, G.; Geeta, B.; Shoba Rani, K.; Ravinder, V.

2012-11-01

281

Innocence and noninnocence of the ligands in bis(pyrazine-2,3-dithiolate and -diselonate) d?-metal complexes. A theoretical and experimental study for the Cu(III), Au(III) and Ni(II) cases.  

PubMed

In this paper we present an experimental and theoretical study to investigate the electronic structures of [ML?]? (M(III) = Cu, L = pdt and pds, pyrazine-2,3-dithiolate and -diselonate; M(III) = Au, L = pds) with the aim of elucidating the nature of the bonding and to establish the innocent-noninnocent character of the ligand in these complexes. Calculations based on DFT methods have been performed to obtain geometry optimizations, harmonic frequencies, IR intensities and Raman scattering activities. The experimental vibrational spectra are accurately reproduced by the calculations, which show that CC, CN, and CX (X = S, Se) vibrations are extensively mixed with other modes, and thus unsuitable to work as vibrational markers. Geometry optimization performed at the DFT level provides geometrical parameters in good agreement with the available structural data. The energetic sequence and nature of the redox-active molecular orbitals help to elucidate the observed electrochemical behaviour. Accordingly, the quasi-reversible redox couple for the reduction processes exhibited by [ML?]²? (L = pdt and pds), that appears at negative values and depends both on the ligand and on the metal, is related to the LUMO which is a ? antibonding combination of the ligand orbitals (sulfur or selenium atoms) and the 3d(xy) (Cu) and 5d(xy) (Au) metal orbitals. The HOMO is a ?-orbital with a b(2g) symmetry, predominantly ligand in character with a small contribution of the nd(xz) atomic orbitals in antibonding combination with chalcogen atom orbitals. The low energy of the metal d-orbitals compared to the ligand orbitals, due to the high effective nuclear charge of the metals, explains their small participation to this orbital. Thus in [ML?]? the metals approach the oxidation state 3+ and the ligand a dichalcogenolate description and thus a prevalent innocent character. However the same ligand shows a noninnocent character in complexes with a different d? metal such as Ni(II) whose d-orbitals lie at higher energies and mix at a higher extent with the ligand orbitals in the HOMO. PMID:20383385

Bruno, Giuseppe; Almeida, Manuel; Artizzu, Flavia; Dias, João C; Mercuri, Maria Laura; Pilia, Luca; Rovira, Concepció; Ribas, Xavi; Serpe, Angela; Deplano, Paola

2010-05-21

282

Complexation- and ligand-induced metal release from 316L particles: importance of particle size and crystallographic structure.  

PubMed

Iron, chromium, nickel, and manganese released from gas-atomized AISI 316L stainless steel powders (sized <45 and <4 ?m) were investigated in artificial lysosomal fluid (ALF, pH 4.5) and in solutions of its individual inorganic and organic components to determine its most aggressive component, elucidate synergistic effects, and assess release mechanisms, in dependence of surface changes using atomic absorption spectroscopy, Raman, XPS, and voltammetry. Complexation is the main reason for metal release from 316L particles immersed in ALF. Iron was mainly released, while manganese was preferentially released as a consequence of the reduction of manganese oxide on the surface. These processes resulted in highly complexing media in a partial oxidation of trivalent chromium to hexavalent chromium on the surface. The extent of metal release was partially controlled by surface properties (e.g., availability of elements on the surface and structure of the outermost surface) and partially by the complexation capacity of the different metals with the complexing agents of the different media. In general, compared to the coarse powder (<45 ?m), the fine (<4 ?m) powder displayed significantly higher released amounts of metals per surface area, increased with increased solution complexation capacity, while less amounts of metals were released into non-complexing solutions. Due to the ferritic structure of lower solubility for nickel of the fine powder, more nickel was released into all solutions compared with the coarser powder. PMID:21691833

Hedberg, Yolanda; Hedberg, Jonas; Liu, Yi; Wallinder, Inger Odnevall

2011-12-01

283

Metal-organic coordination architectures of azole heterocycle ligands bearing acetic acid groups: Synthesis, structure and magnetic properties  

NASA Astrophysics Data System (ADS)

Four new coordination complexes with azole heterocycle ligands bearing acetic acid groups, [Co( L1) 2] n ( 1) , [Cu L1N 3] n ( 2), [Cu( L2) 2·0.5C 2H 5OH·H 2O] n ( 3) and [Co( L2) 2] n ( 4) (here, H L1=1H-imidazole-1-yl-acetic acid, H L2=1H-benzimidazole-1-yl-acetic acid) have been synthesized and structurally characterized. Single-crystal structure analysis shows that 3 and 4 are 2D complexes with 4 4-sql topologies, while another 2D complex 1 has a (4 3) 2(4 6)-kgd topology. And 2 is a 3D complex composed dinuclear ?1,1-bridging azido Cu II entities with distorted rutile topology. The magnetic properties of 1 and 2 have been studied.

Hu, Bo-Wen; Zhao, Jiong-Peng; Yang, Qian; Hu, Tong-Liang; Du, Wen-Ping; Bu, Xian-He

2009-10-01

284

Ab initio and density functional theoretical design and screening of model crown ether based ligand (host) for extraction of lithium metal ion (guest): effect of donor and electronic induction.  

PubMed

The structures, energetic and thermodynamic parameters of model crown ethers with different donor, cavity and electron donating/ withdrawing functional group have been determined with ab initio MP2 and density functional theory in gas and solvent phase. The calculated values of binding energy/ enthalpy for lithium ion complexation are marginally higher for hard donor based aza and oxa crown compared to soft donor based thia and phospha crown. The calculated values of binding enthalpy for lithium metal ion with 12C4 at MP2 level of theory is in good agreement with the available experimental result. The binding energy is altered due to the inductive effect imparted by the electron donating/ withdrawing group in crown ether, which is well correlated with the values of electron transfer. The role of entropy for extraction of hydrated lithium metal ion by different donor and functional group based ligand has been demonstrated. The HOMO-LUMO gap is decreased and dipole moment of the ligand is increased from gas phase to organic phase because of the dielectric constant of the solvent. The gas phase binding energy is reduced in solvent phase as the solvent molecules weaken the metal-ligand binding. The theoretical values of extraction energy for LiCl salt from aqueous solution in different organic solvent is validated by the experimental trend. The study presented here should contribute to the design of model host ligand and screening of solvent for metal ion recognition and thus can contribute in planning the experiments. PMID:22318713

Boda, Anil; Ali, Sk Musharaf; Rao, Hanmanth; Ghosh, Sandip K

2012-08-01

285

Mechanismic investigation on the cleavage of phosphate monoester catalyzed by unsymmetrical macrocyclic dinuclear complexes: the selection of metal centers and the intrinsic flexibility of the ligand.  

PubMed

The hydrolysis mechanisms of phosphor-monoester monoanions NPP(-) (p-nitrophenyl phosphate) catalyzed by unsymmetrical bivalent dinuclear complexes are explored using DFT calculations in this report. Four basic catalyst-substrate binding modes are proposed, and two optional compartments for the location of the nucleophile-coordinated metal center are also considered. Five plausible mechanisms are examined in this computational study. Mechanisms 1, 2, and 3 employ an unsymmetrical dizinc complex. All three mechanisms are based on concerted SN2 addition-substitution pathways. Mechanism 1, which involves more electronegative oxygen atoms attached to the imine nitrogen atoms in the nucleophile-coordinated compartment, was found to be more competitive compared to the other two mechanisms. Mechanisms 4 and 5 are based on consideration of the substitution of the bivalent metal centers and the intrinsic flexibility of the ligand. Both mechanisms 4 and 5 are based on stepwise SN2-type reactions. Magnesium ions with hard base properties and more available coordination sites were found to be good candidates as a substitute in the M(II) dinuclear phosphatases. The reaction energy barriers for the more distorted complexes are lower than those of the less distorted complexes. The proper intermediate distance and a functional second coordination sphere lead to significant catalytic power in the reactions studied. More importantly, the mechanistic differences between the concerted and the stepwise pathways suggest that a better nucleophile with more available coordination sites (from either the metal centers or a functional second coordination sphere) favors concerted mechanisms for the reactions of interest. The results reported in the paper are consistent with and provide a reasonable interpretation for experimental observations in the literature. More importantly, our present results provide some practical suggestions for the selection of the metal centers and how to approach the design of a catalyst. PMID:24649877

Zhang, Xuepeng; Zhu, Yajie; Zheng, Xiaowei; Phillips, David Lee; Zhao, Cunyuan

2014-04-01

286

A lunar/Martian anchor emplacement system  

NASA Astrophysics Data System (ADS)

On the Moon or Mars, it is necessary to have an anchor, or a stable, fixed point able to support the forces necessary to rescue a stuck vehicle, act as a stake for a tent in a Martian gale, act as a fulcrum in the erection of general construction poles, or support tent-like regolith shields. The anchor emplacement system must be highly autonomous. It must supply the energy and stability for anchor deployment. The goal of the anchor emplacement system project is to design and build a prototype anchor and to design a conceptual anchor emplacement system. Various anchors were tested in a 1.3 cubic meter test bed containing decomposed granite. A simulated lunar soil was created by adjusting the moisture and compaction characteristics of the soil. We conducted tests on emplacement torque, amount of force the anchor could withstand before failure, anchor pull out force at various angles, and soil disturbances caused by placing the anchor. A single helix auger anchor performed best in this test bed based on energy to emplace, and the ultimate holding capacity. The anchor was optimized for ultimate holding capacity, minimum emplacement torque, and minimum soil disturbance in sandy soils yielding the following dimensions: helix diameter (4.45 cm), pitch (1.27 cm), blade thickness (0.15 cm), total length (35.56 cm), shaft diameter (0.78 cm), and a weight of 212.62 g. The experimental results showed that smaller diameter, single-helix augers held more force than larger diameter augers for a given depth. The emplacement system consists of a flywheel and a motor for power, sealed in a protective box supported by four legs. The flywheel system was chosen over a gear system based on its increased reliability in the lunar environment.

Clinton, Dustin; Holt, Andrew; Jantz, Erik; Kaufman, Teresa; Martin, James; Weber, Reed

287

Cyclopendant ligands  

Microsoft Academic Search

The numerous cyclopendant ligands are described in the review. These contain a cyclic fragment, with donor atoms, with groups added which are capable of coordinating cations. An attempt has been made to systematise the literature data on the methods of synthesis and the properties of cyclopendant ligands. Fundamental results of authors on the application of a quantitative method of assessing

F I Belskii; Yu M Polikarpov; Martin I Kabachnik

1992-01-01

288

10094 Biochemistry 1995,34, 10094-10100 Characterization of Metal Binding by a Designed Protein: Single Ligand  

E-print Network

10094 Biochemistry 1995,34, 10094-10100 Characterization of Metal Binding by a Designed Protein of Molecular Biophysics 13Biochemistry, Yale University, 266 Whitney Avenue, New Haven, Connecticut 06520)-binding site in the de novo designed protein ZQ [Regan, L., & Clarke, N. D. (1990) Biochemistry 29, 108781

Mochrie, Simon

289

Resin reinforced expansion anchor system  

SciTech Connect

An expansion anchor assembly is described in combination with a dual compartment resin and cartridge inserted into a mine roof opening, the anchor assembly including: (a) an elongated bolt having a head at one end and threaded for a portion of its length at the other end; (b) an expansion member engaged with the threaded end of the bolt; (c) the expansion member including an expansion shell having a plurality of leaf segments; (d) a first means for engaging the expansion shell with the elongated bolt; (e) a wedge threaded on the elongated bolt for engagement with the expansion shell to urge the latter into gripping engagement with the mine roof; (f) a first resin passageway means on the outer surface of the wedge for permitting resin to gravitate therethrough; (g) the leaf segments of the expansion shell being separated to form a second resin passageway means aligned with the first resin passageway means, whereby resin may gravitate downwardly through substantially the entire length of the assembly, and (h) a second means within the first passageway and engageable with one of the leaf segments to prevent relative rotation of the wedge member with respect to the expansion shell; (i) the resin being mixed upon rotation of the bolt and expansion member and gravitating downwardly through the first and second passageway means into engagement with that portion of the mine roof defining the mine roof opening.

Clark, C.A.; Wright, R.L.

1988-08-16

290

Investigation of immobilized catalysts. XVII. Study of three-dimensional structure in catalytic properties of anchored mononuclear and binuclear chelates of nickel  

SciTech Connect

Polymeric supports with chelate-forming groups of the diketone, diacylamine, aminovinyl ketone, and acylsalicylamide types were treated with Ni(II) acetate in alcoholic medium in order to synthesize a series of mononuclear and binuclear chelates of nickel. An octahedral configuration was established for the coordinating unit in the synthesized nickel complexes, and the splitting parameters and degree of covalency of the planar sigma-bond between the metal and ligand were calculated. It was shown that the anchored nickel chelates have high, stable activities in the dimerization of ethylene to butenes. The nature of the coordination unit and of the metallocycle of the immobilized complexes has a considerable influence of the dimerizing activity of the catalyst. An increase in the number of nickel ions in the complex molecule lowers the specific catalytic activity of the immobilized systems.

Uflyand, I.E.; Pomogailo, A.D.; Gorbunova, M.O.; Starikov, A.G.; Sheinker, V.N.

1987-11-01

291

Metal and ligand binding to the HIV-RNase H active site are remotely monitored by Ile556  

PubMed Central

HIV-1 reverse transcriptase (RT) contains a C-terminal ribonuclease H (RH) domain on its p66 subunit that can be expressed as a stable, although inactive protein. Recent studies of several RH enzymes demonstrate that substrate binding plays a major role in the creation of the active site. In the absence of substrate, the C-terminal helix E of the RT RNase H domain is dynamic, characterized by severe exchange broadening of its backbone amide resonances, so that the solution characterization of this region of the protein has been limited. Nuclear magnetic resonance studies of 13C-labeled RH as a function of experimental conditions reveal that the ?1 methyl resonance of Ile556, located in a short, random coil segment following helix E, experiences a large 13C shift corresponding to a conformational change of Ile556 that results from packing of helix E against the central ?-sheet. This shift provides a useful basis for monitoring the effects of various ligands on active site formation. Additionally, we report that the RNase H complexes formed with one or both divalent ions can be individually observed and characterized using diamagnetic Zn2+ as a substitute for Mg2+. Ordering of helix E results specifically from the interaction with the lower affinity binding to the A divalent ion site. PMID:22941642

Zheng, Xunhai; Mueller, Geoffrey A.; DeRose, Eugene F.; London, Robert E.

2012-01-01

292

Unique (3,8)-connected lanthanide arenedisulfonate metal-organic frameworks containing benzimidazole-5,6-dicarboxylic acid co-ligand: Syntheses, structures and luminescence  

SciTech Connect

Two isostructural 3D lanthanide arenedisulfonate metal-organic frameworks (MOFs) [Ln(Hbidc)(nds){sub 0.5}(H{sub 2}O)]{sub n}(Ln=Eu(1), La(2)) have been successfully synthesized by the hydrothermal reaction of lanthanide oxide with 2,6-naphthalenedisulfonate sodium (Na{sub 2}nds) and an auxiliary ligand, 1H-benzimidazole-5,6-dicarboxylic acid (H{sub 3}bidc). The two complexes are both constructed from 2D [Ln(Hbidc)]{sup +} double layers pillared by nds{sup 2?} ligands to generate 3D (3, 8)-connected open-framework structures with 1D long narrow channels running along the a axis. From topological point of view, the 3D framework is a (3, 8)-connected tfz-d net. The weak interactions including N–H?O, O–H?O hydrogen bonds and ?–? stacking are observed in 1. The 2D IR correlation spectroscopy was applied to study the molecular interactions induced by thermal perturbation. The emission spectra of 1 exhibit the characteristic transition of {sup 5}D{sub 0}?{sup 7}F{sub J}(J=0–4) of Eu(III). - Graphical abstract: Two isostructural 3D (3,8)-connected lanthanide arenedisulfonates were hydrothermally synthesized. The 2D IR correlation spectroscopy was applied to study the molecular interactions induced by thermal perturbation. Display Omitted - Highlights: • The first lanthanide arenedisulfonates incorporating fused-ring aromatic carboxylic acid. • Three-dimensional (3,8)-connected framework with tfz-d network topology. • The emission spectra of 1 exhibit the characteristic transition of {sup 5}D{sub 0}?{sup 7}F{sub J} (J=0–4) of Eu(III). • The 2D IR correlation spectroscopy was applied to study the molecular interactions.

Sun, Yan-Qiong, E-mail: sunyq@fzu.edu.cn [College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou 350002 (China); State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Liu, Qi; Zhong, Jie-Cen; Pan, Qun-Feng; Chen, Yi-Ping [College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou 350002 (China)

2013-10-15

293

Dynamics of supercoiled and linear pTZ18U plasmids observed with a long-lifetime metal-ligand complex.  

PubMed

The metal-ligand complex, [Ru(bpy)2(dppz)]2+ (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine) (Ru-BD), was used as a spectroscopic probe for studying nucleic acid dynamics. The Ru-BD complex displays a long lifetime of over 100 ns and a molecular light switch property upon DNA binding due to shielding of its dppz ligand from water. To further show the usefulness of this luminophore (Ru-BD) for probing DNA dynamics, we examined its intensity and anisotropy decays when intercalated into supercoiled and linear pTZ18U plasmids using frequency-domain fluorometry with a light-emitting diode (LED) as the modulated light source. Compared to the supercoiled plasmids with an average intensity decay time of 120.8 ns at 25 degrees C, we obtained somewhat longer lifetimes for the linear plasmids ((tau) = 141.4 ns at 25 degrees C), suggesting a more efficient shielding from water by the linear plasmids. The anisotropy decay data also showed longer rotational correlation times for the linear plasmids (495 and 35 ns at 25 degrees C) as compared to the supercoiled plasmids (412 and 27 ns at 25 degrees C). The slow and fast rotational correlation times appear to be consistent with the bending and torsional motions of the plasmids, respectively. The anisotropy values were quite similar, although the values of the supercoiled plasmids were slightly higher in both the steady-state and anisotropy decay measurements. These results indicate that Ru-BD can be applied in the study of both bending and torsional dynamics of nucleic acids. PMID:12073934

Kang, Jung Sook; Abugo, Omoefe O; Lakowicz, Joseph R

2002-01-01

294

Synthesis and structural characterization of two-coordinate low-valent 14-group metal complexes bearing bulky bis(amido)silane ligands.  

PubMed

A series of germylene, stannylene and plumbylene complexes [?(2)(N,N)-Me(2)Si(DippN)(2)Ge:] (3a), [?(2)(N,N)-Ph(2)Si(DippN)(2)Ge:] (3b), [?(2)(N,N)-Me(2)Si(DippN)(2)Sn:] (4), [?(2)(N,N)-Me(2)Si(DippN)(2)Pb:](2) (5a), and [?(2)(N,N)-Ph(2)Si(DippN)(2)Pb:] (5b) (Dipp = 2,6-iPr(2)C(6)H(3)) bearing bulky bis(amido)silane ligands were readily prepared either by the transamination of M[N(SiMe(3))(2)](2) (M = Sn, Pb) and [Me(2)Si(DippNH)(2)] or by the metathesis reaction of bislithium bis(amido)silane [?(1)(N),?(1)(N)-R(2)Si(DippNLi)(2)] (R = Me, Ph) with the corresponding metal halides GeCl(2)(dioxane), SnCl(2), and PbCl(2), respectively. Preliminary atom-transfer chemistry involving [?(2)(N,N)-Me(2)Si(DippN)(2)Ge:] (3a) with oxygen yielded a dimeric oxo-bridged germanium complex [?(2)(N,N)-Me(2)Si(DippN)(2)Ge(?-O)](2) (6). All complexes were characterized by (1)H, (13)C, (119)Sn NMR, IR, and elemental analysis. X-ray single crystal diffraction analysis revealed that the metal centres in 3b, 4, and 5b are sterically protected to prevent interaction between the metal centre and the nitrogen donors of adjacent molecules while complex 5a shows a dimeric feature with a strong intermolecular Pb···N interaction. PMID:22218706

Yang, Dongming; Guo, Jianmei; Wu, Haishun; Ding, Yuqiang; Zheng, Wenjun

2012-02-21

295

Four Zn(II)/Cd(II)-3-amino-1,2,4-triazolate frameworks constructed by in situ metal/ligand reactions: Structures and fluorescent properties  

SciTech Connect

Four Cd(II) and Zn(II) complexes with the in situ-generated ligand of 3-amino-1,2,4-triazolate (AmTAZ{sup -}) were isolated from the solvothermal reactions of the corresponding Cd(II) or Zn(II) salts with 5-amino-1H-1,2,4-triazole-3-carboxylic acid (AmTAZAc). Their structures were determined by single-crystal X-ray diffraction analysis. [Zn(AmTAZ)(CH{sub 3}COO)] (1) presents a two-dimensional framework constructed from Zn(II) ions and {mu}{sub 3}-AmTAZ{sup -} ligands. A remarkable feature of [Zn{sub 4}(AmTAZ){sub 4}(SO{sub 4})(OH)(C{sub 2}O{sub 4}){sub 0.5}].2H{sub 2}O (2) is the construction of the building units of octagonal cylinders which interact with each other by sharing one face or overlapping, resulting in the formation of a three-dimensional framework with three kinds of 1D channels. [Cd(AmTAZ)Br] (3) crystallizes in a chiral space group P2{sub 1}2{sub 1}2{sub 1}, giving a homochiral three-dimensional framework with two types of helical channels (left- and right-handed). Different from the others, the 3-amino-1,2,4-triazole molecules in [Cd(AmTAZH)SO{sub 4}] (4) behave as neutral {mu}{sub 2}-2,4-bridges to connect the two-dimensional CdSO{sub 4} sheets into a three-dimensional framework. Of all, 2 and 3 display different fluorescent properties probably due to different metal ions, coordination environments and structural topologies. - Graphical abstract: The solvothermal reactions of Cd(II) and Zn(II) salts bearing different anions with 5-amino-1H-1,2,4-triazole-3-carboxylic acid (AmTAZAc) produced four Cd(II) and Zn(II) MOFs with the in situ-generated 3-amino-1,2,4-triazolate (AmTAZ{sup -}) ion as ligand, which display different structural topologies and fluorescent properties. Display Omitted.

Chen Zilu; Li Xiaoling [College of Chemistry and Chemical Engineering, Guangxi Normal University, Yucai Road 15, Guilin 541004 (China); Liang Fupei [College of Chemistry and Chemical Engineering, Guangxi Normal University, Yucai Road 15, Guilin 541004 (China)], E-mail: fliangoffice@yahoo.com

2008-08-15

296

Anchored Instruction in a Situated Learning Environment.  

ERIC Educational Resources Information Center

The purpose of this study was to design and develop a multimedia-based anchored program and to examine the effects of students' and group characteristics on the problem-solving process in anchored instruction with the multimedia program in a situated learning environment. Sixty-eight students were assigned to small groups via a stratified random…

Lee, Miwha

297

24 CFR 3285.401 - Anchoring instructions.  

...INSTALLATION STANDARDS Anchorage Against Wind § 3285.401 Anchoring instructions...manufactured home must be secured against the wind by use of anchor assembly type installations...require the home to be secured against the wind, as described in this section....

2014-04-01

298

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2013 CFR

...INSTALLATION STANDARDS Anchorage Against Wind § 3285.401 Anchoring instructions...manufactured home must be secured against the wind by use of anchor assembly type installations...require the home to be secured against the wind, as described in this section....

2013-04-01

299

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2011 CFR

...INSTALLATION STANDARDS Anchorage Against Wind § 3285.401 Anchoring instructions...manufactured home must be secured against the wind by use of anchor assembly type installations...require the home to be secured against the wind, as described in this section....

2011-04-01

300

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2012 CFR

...INSTALLATION STANDARDS Anchorage Against Wind § 3285.401 Anchoring instructions...manufactured home must be secured against the wind by use of anchor assembly type installations...require the home to be secured against the wind, as described in this section....

2012-04-01

301

76 FR 30301 - Commercial Acquisition; Anchor Tenancy  

Federal Register 2010, 2011, 2012, 2013

...of 1992. NASA may enter into multi-year anchor...under the heading ``Enter keyword or ID'' and selecting ``Search.'' Select the link...authorization for NASA to enter into multi- year anchor...5) The long-term viability of the...

2011-05-25

302

Anchor-free NEMS non-volatile memory cell for harsh environment data storage  

NASA Astrophysics Data System (ADS)

This work demonstrates a novel anchor-free nano-electromechanical (NEMS) based non-volatile memory cell, suitable for high temperature (T ? 300?°C) and radiation prone harsh environment applications. The anchor-free circular metal beam is actuated by electrostatic force and is held in one of the bi-stable memory states by adhesion force between two smooth metal surfaces in contact. Smooth metal layers form strong van der Waals stiction between two surfaces in contact and memory detection (Logic-‘1’ / Logic-‘0’) is obtained by detecting the conductance between two fixed contacts. This anchor-free design offers highest density (9F2 footprint) compared to other mechanical memory devices reported to date.

Singh, Pushpapraj; Li Chua, Geng; Liang, Ying Shun; Gopal Jayaraman, Karthik; Do, Anh Tuan; Tae-Hyoung Kim, Tony

2014-11-01

303

Transition-metal complexes containing parent phosphine or phosphinyl ligands and their use as precursors for phosphide nanoparticles.  

PubMed

P-H functional transition-metal complexes were synthesized without using hazardous PH3 gas in good yields by photolysis of the transition-metal carbonyl complexes M(CO)6-x (M = Cr, W, Fe; x = 0, 1) in tetrahydrofuran followed by reaction with P2(SiMe3)4 and subsequent methanolysis to give the bridging complexes [(CO)xM(?-PH2)]2 (M = Fe, x = 3 (1), M = Cr, x = 4 (2a), M = W, x = 4 (2b)). The photolysis of [(CO)4M(?-PH2)]2 (M = Cr (2a), M = W (2b)) with P(SiMe3)3 was applied followed by methanolysis to synthesize the PH2 bridging transition-metal binuclear complexes with terminal PH3 groups. The products [(CO)4M(?-PH2)2M(CO)3(PH3)] (M = Cr (3a), M = W (3b)) and [(CO)4W(?-PH2)2W(CO)2(PH3)2] (4b) were isolated in moderate yield. Another synthetic approach to this type of compounds is the direct photolysis of the complexes [(CO)3M(PH3)3] (M = Cr (5a), M = W (5b)). The products were comprehensively characterized by (31)P NMR and IR spectroscopy as well as by X-ray structural analysis. Additionally, the relevancy of 2a as single source precursor for the synthesis of stoichiometry-controlled CrP nanoparticles has been demonstrated. PMID:25329878

Bauer, Susanne; Hunger, Cornelia; Bodensteiner, Michael; Ojo, Wilfried-Solo; Cros-Gagneux, Arnaud; Chaudret, Bruno; Nayral, Céline; Delpech, Fabien; Scheer, Manfred

2014-11-01

304

Ruthenium, osmium and rhodium complexes of polypyridyl ligands: Metal-promoted activities, stereochemical aspects and electrochemical properties  

Microsoft Academic Search

This article presents a brief overview of the reactions of2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in presence of rhodium(III), ruthenium(II) and osmium(II) under various experimental conditions.\\u000a Under certain experimental conditions tptz exhibits metal-assisted hydrolysis\\/hydroxylation at the triazine ring. However,\\u000a synthetic methods have also been developed to prepare complexes with intact tptz. Molecular structures of some of the complexes,\\u000a especially stereoisomers of the hydroxylated products,

Parimal Paul; G B Marg

2002-01-01

305

An equilibrium model for ligand-modified micellar-enhanced ultrafiltration, selective separation of metal ions using iminoacetic substituted polyamines and a theoretical model for the titration behavior of polyamines  

SciTech Connect

This thesis consists of three chapters. Chapter 1, An equilibrium model for ligand-modified micellar-enhanced ultrafiltration, describes a theoretical model and experimental investigations which used the semi-equilibrium-dialysis method with N-n-dodecyl iminodiacetic acid as the ligand. In Chapter 2, Selective separation of metal ions using iminoacetic substituted polyamines, polyamines with a substituted ligand group are synthesized and used in investigating selective separation of copper ions from aqueous solution. In Chapter 3, A theoretical model for the titration behavior of polyamines, a novel approach to explain the titration behavior of polymeric amines based on the binding behavior of counterions is described. The application of this study is to the investigation of inexpensive and efficient methods of industrial waste water treatment.

Dharmawardana, U.R.

1992-12-31

306

Calculated Hydride Donor Abilities of Five-Coordinate Transition Metal Hydrides [HM(diphosphine)2]+ (M = Ni, Pd, Pt) as a Function of the Bite Angle and Twist Angle of Diphosphine Ligands  

SciTech Connect

Density functional theory (BLYP and B3LYP) and the polarized continuum model (PCM-UA0) for solvation have been used to investigate the effect of bite angle (P-M-P) of diphosphine ligands and the dihedral or twist angle between diphosphine ligands on the hydride donor abilities of Ni, Pd, and Pt [HM(diphosphine)2]+ complexes. It is found that an increased bite angle for a given transition metal atom results in poorer hydride donor abilities. However, hydride donor abilities for these complexes also decrease as the size of the alkyl side groups on the phosphorus atom increase (Et > Me > H) and with the length of the metal phosphorus bond (Ni > Pd = Pt). These trends correlate with an increase in the twist angle between the two diphosphine ligands, which increases from 0° for a square-planar configuration to 90° for a tetrahedral geometry. Shorter M-P bonds, larger substituents on the diphosphine ligands, and larger bite angles all result in increased steric interactions between diphosphine ligands and larger dihedral or twist angles between the diphosphine ligands. The twist angle correlates much more strongly with hydride donor abilities than do bite angles alone. As the twist angle increases, the hydride donor ability decreases in a linear fashion. A frontier orbital analysis has been carried out, and it is shown that the hydride donor ability of [HM(diphosphine)2]+ complexes is largely determined by the energy of the lowest unoccupied molecular orbital of the corresponding [M(diphosphine)2]2+ complex. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Nimlos, Mark; Chang, Christopher H.; Curtis, Calvin J.; Miedaner, Alex; Pilath, H. M.; DuBois, Daniel L.

2008-06-23

307

Calculated Hydride Donor Abilities of Five-Coordinate Transition Metal Hydrides [HM(diphosphine)2] (+) (M = Ni, Pd, Pt) as a Function of the Bite Angle and Twist Angle of Diphosphine Ligands  

SciTech Connect

Density functional theory (BLYP and B3LYP) and the polarized continuum model (PCM-UA0) for solvation have been used to investigate the effect of bite angle (P-M-P) of diphosphine ligands and the dihedral or twist angle between diphosphine ligands on the hydride donor abilities of Ni, Pd, and Pt [HM(diphosphine)2]+ complexes. It is found that an increased bite angle for a given transition metal atom results in poorer hydride donor abilities. However, hydride donor abilities for these complexes also decrease as the size of the alkyl side groups on the phosphorus atom increase (Et > Me > H) and with the length of the metal phosphorus bond (Ni > Pd = Pt). These trends correlate with an increase in the twist angle between the two diphosphine ligands, which increases from 0° for a square-planar configuration to 90° for a tetrahedral geometry. Shorter M-P bonds, larger substituents on the diphosphine ligands, and larger bite angles all result in increased steric interactions between diphosphine ligands and larger dihedral or twist angles between the diphosphine ligands. The twist angle correlates much more strongly with hydride donor abilities than do bite angles alone. As the twist angle increases, the hydride donor ability decreases in a linear fashion. A frontier orbital analysis has been carried out, and it is shown that the hydride donor ability of [HM(diphosphine)2]+ complexes is largely determined by the energy of the lowest unoccupied molecular orbital of the corresponding [M(diphosphine)2]2+ complex. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Nimlos, Mark R.; Chang, Christopher H.; Curtis, Calvin J.; Miedaner, Alex; Pilath, H. M.; DuBois, Daniel L.

2008-07-07

308

Amino Acid Complexes of Metal Carbonyls: Mechanistic Aspects of the CO-Labilizing Ability of Glycinate Ligands in Zero-Valent Chromium and Tungsten Derivatives.  

PubMed

The amino and phosphino acid derivatives of chromium(0) and tungsten(0), [Et(4)N][Cr(CO)(4)(O(2)CCH(2)NH(2))] (1), [Et(4)N][Cr(CO)(4)(O(2)CCH(2)NHMe)] (2), [Et(4)N][Cr(CO)(4)(O(2)CCH(2)NMe(2))] (3), [Et(4)N][W(CO)(4)(O(2)CCH(C(CH(3))(3))NH(2))] (4), [Et(4)N][W(CO)(4)(O(2)CCH(C(6)H(5))NH(2))], [Et(4)N][W(CO)(4)(O(2)CCH(2)PPh(2))] (5), and [Et(4)N][Cr(CO)(4)(O(2)CCH(2)PPh(2))] have been synthesized from the reaction of the M(CO)(5)THF adduct with the tetraethylammonium salt of the corresponding amino or phosphino acid in THF solution. The complexes have been characterized in solution by (13)C NMR and infrared spectroscopies and in the solid state by X-ray crystallography. The geometry of the metal anion is, in each case, that of a distorted octahedron consisting of four carbonyl ligands and a puckered five-membered glycinate chelate ring, bound through the nitrogen atom and one of its oxygen atoms. Notable about complex 1 is that the crystal obtained exhibited both a different morphology and a different space group than its tungsten analogue. Examination of the packing diagram reveals that this change is due to the different orientation of the chelate ring in 1 relative to the corresponding orientation in the W(CO)(4)(O(2)CCH(2)NH(2))(-) anion. Complexes 1 and 2 exhibit intermolecular hydrogen-bonding interactions between the amine N-H group and the distal oxygen on an adjacent molecule, with N.O distances of 2.828 and 2.821 Å, respectively. Investigations of the lability of the carbonyl ligands have been carried out. The lability is proposed to be due to base-assisted removal of a proton from the amine ligand leading to a substitutionally labile amide transient species. The tungsten analogue of complex 1 was used to obtain evidence in support of this mechanism. The isotope effect (k(H)/k(D)) was measured for W(CO)(4)(O(2)CCH(2)NH(2))(-) using d(5)-glycine and was found to be 2.34. The activation parameters for the intermolecular exchange of CO in the [Et(4)N][W(CO)(4)(O(2)CCH(2)NH(2))] salt were determined and found to be DeltaH() = 15.4 +/- 1.0 kcal/mol and DeltaS() = -23.2 +/- 3.2 eu, values consistent with the proposed mechanism. In addition, the effect of substitution of electron-donating (C(CH(3))(3)) and electron-withdrawing (C(6)H(5)) substituents on the methylene carbon was evaluated. There was little change in the rate of CO exchange observed for W(CO)(4)(O(2)CCH(C(CH(3))(3))NH(2))(-) (5) and W(CO)(4)(O(2)CCH(C(6)H(5))NH(2))(-) vs W(CO)(4)(O(2)CCH(2)NH(2))(-), showing that steric or electronic effects away from the N center are not responsible for the observed CO lability. As anticipated on the basis of the proposed substitutional pathway, the phosphino acid metal carbonyl derivatives did not exhibit facile intermolecular CO exchange. PMID:11670056

Darensbourg, Donald J.; Draper, Jennifer D.; Reibenspies, Joseph H.

1997-08-13

309

Metal-organic frameworks based on the [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid ligand: syntheses, structures and magnetic properties.  

PubMed

The solvothermal reactions of [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid (H4TPTA) with transition metal cations afforded five novel coordination polymers in the presence of three pyridine ligands (4,4'-bipy = 4,4'-bipyridine, 2,2'-bipy = 2,2'-bipyridine and phen = 1,10-phenanthroline), namely [M(TPTA)0.5(4,4'-bpy)0.5(H2O)2]n (M = Co for (), Ni for ()), {[Mn2(TPTA)(2,2'-bpy)H2O]·1.5H2O}n (), and [M(H2TPTA)(phen)]n (M = Mn for (), Co for ()). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Polymers and are isomorphous and exhibit 3D 4-fold interpenetrated networks with the point Schläfli symbol of (4(2)·10(4)) (4·10(2)). Polymer shows a 2D layer framework. Polymers and are also isomorphous and each displays a one-dimensional (1D) chain, which further forms a 2D supramolecular architecture via inter-chain ?? interactions. Moreover, variable-temperature magnetic susceptibilities of polymers exhibit overall weak antiferromagnetic coupling between the adjacent M(ii) ions. PMID:25189532

Lv, Xiaofeng; Liu, Lu; Huang, Chao; Guo, Li'an; Wu, Jie; Hou, Hongwei; Fan, Yaoting

2014-09-30

310

Neutral ligand induced methane elimination from rare-earth metal tetramethylaluminates up to the six-coordinate carbide state.  

PubMed

The reaction of 1,3,5-trimethyl-1,3,5-triazacyclohexane (TMTAC) with [La{Al(CH(3))(4)}(3)] resulted in C-H activation, leading to the formation of [(TMTAC)La{Al(CH(3))(4)}{(mu(3)-CH(2))[Al(CH(3))(2)(mu(2)-CH(3))](2)}] (1) containing a bis(aluminate) dianion and subsequent extrusion of methane. A similar reaction with [Y{Al(CH(3))(4)}(3)] led to the formation of CH(4), [TMTAC{Al(CH(3))(3)}(2)] (2) and {[(TMTAC)Y][Y(2)(mu(2)-CH(3))][{(mu(6)-C)[Al(mu(2)-CH(3))(2)(CH(3))](3)}{(mu(3)-CH(2))(mu(2)-CH(3))Al(CH(3))(2)}(2)] (3), containing a six-coordinate carbide ion and two [CH(2)Al(CH(3))(3)](2)(-) anions. Compound 3 is a product of multiple C-H activation. This reaction was monitored by in situ(1)H NMR spectroscopy. The analogous reaction with [Sm{Al(CH(3))(4)}(3)] led to the formation of 2, of [(TMTAC)Sm{(mu(2)-CH(3))(CH(3))(2)Al}(2){(mu(3)-CH(2))(2)Al(CH(3))(2)}(2)] (4), which contains a tris(aluminate) trianion, and [{(TMTAC)Sm}{Sm(2)(mu(2)-CH(3))}{(mu(6)-C)[Al(mu(2)-CH(3))(2)(CH(3))](3)}{(mu(3)-CH(2))(mu(2)-CH(3))Al(CH(3))(2)}(2)] (5), which is isostructural to 3. The products were characterised by elemental analyses (except 4, 5), 1 by multinuclear NMR spectroscopy and compounds 1, 2, 3, 4 and 5 by X-ray crystallography. Quantumchemical calculations were undertaken to support the crystallographic data analysis and confirm the structure of 3 and to compare it with an analogous compound where the central six-coordinate carbon has been replaced by oxygen. The investigations point to a mechanism of sterically induced condensation of [Al(CH(3))(4)](-) groups in close proximity in the coordination spheres of the rare-earth metal atoms, which is dependent on the size of these metal atoms. PMID:20449090

Venugopal, Ajay; Kamps, Ina; Bojer, Daniel; Berger, Raphael J F; Mix, Andreas; Willner, Alexander; Neumann, Beate; Stammler, Hans-Georg; Mitzel, Norbert W

2009-08-01

311

Biomechanical testing of a new knotless suture anchor compared with established anchors for rotator cuff repair.  

PubMed

Various suture anchors are available for rotator cuff repair. For arthroscopic application, a knotless anchor was developed to simplify the intra-operative handling. We compared the new knotless anchor (BIOKNOTLESStrade mark RC; DePuy Mitek, Raynham, MA) with established absorbable and titanium suture anchors (UltraSorbtrade mark and Super Revo 5mmtrade mark; ConMed Linvatec, Utica, NY). Each anchor was tested on 6 human cadaveric shoulders. The anchors were inserted into the greater tuberosity. An incremental cyclic loading was performed. Ultimate failure loads, anchor displacement, and mode of failure were recorded. The anchor displacement of the BIOKNOTLESStrade mark RC (15.3 +/- 5.3 mm) after the first cycle with 75 N was significantly higher than with the two other anchors (Super Revo 2.1 +/- 1.6 mm, UltraSorb: 2.7 +/- 1.1 mm). There was no significant difference in the ultimate failure loads of the 3 anchors. Although the Bioknotlesstrade mark RC indicated comparable maximal pullout strength, it bares the risk of losing contact between the tendon-bone-interface due to a significantly higher system displacement. Therefore, gap formation between the bone and the soft tissue fixation jeopardizes the repair. Bioknotlesstrade mark RC should be used in the lateral row only when a double row technique for rotator cuff repair is performed, and is not appropriate for rotator cuff repair if used on its own. PMID:18396417

Pietschmann, Matthias F; Froehlich, Valerie; Ficklscherer, Andreas; Wegener, Bernd; Jansson, Volkmar; Müller, Peter E

2008-01-01

312

Soluble precursors for CuInSe2, CuIn(1-x)Ga(x)Se2, and Cu2ZnSn(S,Se)4 based on colloidal nanocrystals and molecular metal chalcogenide surface ligands.  

PubMed

We report a new platform for design of soluble precursors for CuInSe(2) (CIS), Cu(In(1-x)Ga(x))Se(2) (CIGS), and Cu(2)ZnSn(S,Se)(4) (CZTS) phases for thin-film potovoltaics. To form these complex phases, we used colloidal nanocrystals (NCs) with metal chalcogenide complexes (MCCs) as surface ligands. The MCC ligands both provided colloidal stability and represented essential components of target phase. To obtain soluble precursors for CuInSe(2), we used Cu(2-x)Se NCs capped with In(2)Se(4)(2-) MCC surface ligands or CuInSe(2) NCs capped with {In(2)Cu(2)Se(4)S(3)}(3-) MCCs. A mixture of Cu(2-x)Se and ZnS NCs, both capped with Sn(2)S(6)(4-) or Sn(2)Se(6)(4-) ligands was used for solution deposition of CZTS films. Upon thermal annealing, the inorganic ligands reacted with NC cores forming well-crystallized pure ternary and quaternary phases. Solution-processed CIS and CZTS films featured large grain size and high phase purity, confirming the prospects of this approach for practical applications. PMID:22329720

Jiang, Chengyang; Lee, Jong-Soo; Talapin, Dmitri V

2012-03-21

313

Novel transition-metal (M=Cr, Mo, W, Fe) carbonyl complexes with bis(guanidinato)silicon(II) ligands.  

PubMed

The donor-stabilized silylene 2 (the first bis(guanidinato)silicon(II) complex) reacts with the transition-metal carbonyl complexes [M(CO)6 ] (M=Cr, Mo, W) to form the respective silylene complexes 7-10. In the reactions with [M(CO)6 ] (M=Cr, Mo, W), the bis(guanidinato)silicon(II) complex 2 behaves totally different compared with the analogous bis(amidinato)silicon(II) complex 1, which reacts with [M(CO)6 ] as a nucleophile to replace only one of the six carbonyl groups. In contrast, the reaction of 2 leads to the novel spirocyclic compounds 7-9 that contain a four-membered SiN2 C ring and a five-membered MSiN2 C ring with a M?Si and M?N bond (nucleophilic substitution of two carbonyl groups). Compounds 7-10 were characterized by elemental analyses (C, H, N), crystal structure analyses, and NMR spectroscopic studies in the solid state and in solution. PMID:25042407

Mück, Felix M; Kloss, Dorit; Baus, Johannes A; Burschka, Christian; Tacke, Reinhold

2014-07-28

314

Hydrothermal synthesis and structure characterization of two six-connected metal-organic frameworks based on the mixed ligands  

NASA Astrophysics Data System (ADS)

Two metal-organic frameworks, namely, [Ni2(BIMB)2(ndd)2·H2O]n (1) and [Zn3(ndd)2.5(?3-OH)(1,3-dpp)]n (2) (H2ndd = 2,2?-(naphthalene-1,5-diylbis(oxy))diacetic acid, BIMB = 1,4-bis[(1H-imidazol-1-ly)methyl]benzene, 1,3-dpp = 1,3-di(pyridin-4-yl)propane) have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction and thermogravimetric analysis. Compound 1 presents a two-dimensional network with point symbol of (36·46·53)-hxl topology. Moreover, compound 2 displays a novel 2-fold interpenetrated structure with the point symbol of (412·63)-pcu topology based on the hexanuclear [Zn6(CO2)10(N)4] unit as a six-connected node. Meanwhile, compound 2 shows good fluorescence property in the solid state at room temperature.

Li, Lian-Jie; Wang, Xin-Long; Shao, Kui-Zhan; Su, Zhong-Min; Xie, Hai-Ming

2014-08-01

315

Spectroscopic studies and biological evaluation of some transition metal complexes of azo Schiff-base ligand derived from (1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one) and 5-((4-chlorophenyl)diazenyl)-2-hydroxybenzaldehyde.  

PubMed

A series of metal(II) complexes of VO(II), Co(II), Ni(II), Cu(II) and Zn(II) have been synthesized from the azo Schiff base ligand 4-((E)-4-((E)-(4-chlorophenyl)diazenyl)-2-hydroxybenzylideneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (CDHBAP) and characterized by elemental analysis, spectral (IR, UV-Vis, (1)H NMR, ESR and EI-mass), magnetic moment measurements, molar conductance, DNA, SEM, X-ray crystallography and fluorescence studies. The electronic absorption spectra and magnetic susceptibility measurements of the complexes indicate square pyramidal geometry for VO(II) and octahedral geometry for all the other complexes. The important infrared (IR) spectral bands corresponding to the active groups in the ligand and the solid complexes under investigation were studied and implies that CDHBAP is coordinated to the metal ions in a neutral tridentate manner. The redox behavior of copper(II) and vanadyl(II) complexes have been studied by cyclic voltammetry. The nuclease activity of the above metal(II) complexes shows that the complexes cleave DNA. All the synthesized complexes can serve as potential photoactive materials as indicated from their characteristic fluorescence properties. The antibacterial and antifungal activities of the synthesized ligand and its metal complexes were screened against bacterial species (Staphylococcus aureus, Salmonella typhi, Escherichia coli, Bacillus subtilis, Shigella sonnie) and fungi (Candida albicans, Aspergillus niger, Rhizoctonia bataicola). Amikacin and Ketoconozole were used as references for antibacterial and antifungal studies. The activity data show that the metal complexes have a promising biological activity comparable with the parent Schiff base ligand against bacterial and fungal species. The second harmonic generation (SHG) efficiency of the ligand was measured and the NLO (non-linear optical) properties of the ligand are expected to result in the realization of advanced optical devices in optical fiber communication (OFC) and optical computing. The SEM image of the copper(II) complex implies that the size of the particles is 1 ?m. PMID:22728967

Anitha, C; Sheela, C D; Tharmaraj, P; Sumathi, S

2012-10-01

316

New concept to remove heavy metals from liquid waste based on electrochemical pH-switchable immobilized ligands  

NASA Astrophysics Data System (ADS)

Absorption on resins is often used as secondary step in the treatment of water-based effluents, in order to reach very low concentrations. The separation of the trapped effluents from the resins and the regeneration of the resins for further use create wide volumes of secondary effluents coming from the washings of the resins with chemical reagents. We propose an alternative solution based on a "surface strategy" through adsorption phenomena and electrical control of the expulsion stage. The final goal is to limit or ideally to avoid the use of chemical reagents at the expulsion (or regeneration) stage of the depolluting process. Heavy metal ions were captured on active filters composed by a conducting surface covered by poly-4-vinylpyridine (P 4VP). Due to pyridine groups those polymer films have chelating properties for copper ions. Our strategy for electrical triggering of the copper expulsion in aqueous medium is based on pH sensitive chelating groups. Applying moderate electro-oxidizing conditions generates acidic conditions in the vicinity of the electrode, i.e. "inside" the polymer film. This allows a "switch-off" of the complexing properties of the film from the basic form of pyridine to pyridinium. Interestingly, no buffer washing is necessary to restore (or "switch-on") the complexing properties of the polymer film because the pH of the external medium is left unchanged by the electrochemical effect that affects only the vicinity of the electrode. Switch-on/switch-off cycles are followed and attested by IR spectroscopy and EQCM method.

Pascal, Viel; Laetitia, Dubois; Joël, Lyskawa; Marc, Sallé; Serge, Palacin

2007-01-01

317

Inflammatory Response with Osteolysis Related to a Bioabsorbable Anchor in the Finger: a Case Report  

PubMed Central

Soft tissue fixation of ligaments and tendons in the hand can be achieved by the use of metal or bioabsorbable suture anchors. Advantages of bioabsorbable suture anchors include lack of interference in magnetic resonance imaging, resorption of anchor, replacement by bone, and no need for hardware removal. However, complications of these bioabsorbable implants include inflammatory response to the material use. We present what we believe to be the first case in the hand of a poly(l-lactide-co-d,l-lacitide) suture anchor causing an inflammatory response leading to significant osteolysis 4 months postoperatively after repair of a ring finger flexor digitorum profundus avulsion. Exploration of the distal phalanx revealed an intact implant and repair, no signs of infection, and an extensive bone defect. Pathology showed chronically inflamed tissue. This case has led us to reconsider the use of bioabsorbable anchor sutures in the hand. Further research is necessary to better define the contraindications to bioabsorbable suture anchor use in the hand. PMID:19898759

Galano, Gregory J.; Strauch, Robert J.; Rosenwasser, Melvin P.; Tang, Peter

2009-01-01

318

Anchored Mobilities: Mobile Technology and Transnational Migration  

E-print Network

Anchored Mobilities: Mobile Technology and Transnational Migration Amanda Williams Donald Bren.m [Information Systems]: miscellaneous General Terms Design, Human Factors. Keywords Mobilility, mobile technology, transnational, aging, ethnography 1. INTRODUCTION Researchers in Human Computer Interaction have

Dourish,Paul

319

A comparison of soft-tissue anchors in tendo achilles reattachment.  

PubMed

This prospective study evaluated four soft-tissue fixation modalities, used in seven different combinations, to reattach the tendo Achilles in 34 cadaveric specimens. Ultimate loads, elastic moduli, and modes of failure were evaluated by loading the specimen in a cantilevered fashion on an Instron. Mann-Whitney U tests were performed to compare the failure load data for statistical significance. Although the use of two Mitek SuperAnchors showed better load resistance than one anchor (p < .01), there was no significant improvement between using two or three anchors (one anchor 116 +/- 24 N, two anchors 234 +/- 21 N, three anchors 277 +/- 80 N). Two Bionx Bankart Tacks demonstrated no significant difference over using a single tack (one tack 178 +/- 57 N, two tacks 214 +/- 86 N). No statistical difference was observed between the screw and washer systems (screw with polyacetal resin washer 307 +/- 80 N, screw with metal washer 290 +/- 81 N). Both screw and washer systems did show greater stability when compared with a single Mitek SuperAnchor (p < .01) or a single Bionx Bankart Tack (p < .05). Similar analyses using the Mann-Whitney U tests were performed on the elastic modulus data. Analysis of the displacement data among all groups showed no statistical difference. Observations of the mode of failure exhibited 86% of Mitek SuperAnchor failed secondary to suture, and 70% of the Bionx Bankart Tack and 90% of the screw and washer systems failed because of the tendon shearing around the fixation. The comparisons of cost-effectiveness among the fixations showed the Synthes screw and polyacetal resin spiked washer to have the lowest cost to load ratio ($0.15/N). PMID:11924680

Janis, L; Lam, A T; Espiritu, T; Ploot, E; Husain, Z S

2001-01-01

320

SOLVENT EXTRACTION OF THE RARE-EARTH METAL IONS BY A CONE-SHAPED CALDC[4]ARENE SUBSTITUTED AT THE LOWER RTM BY FOUR CH2P(O)Ph2 LIGANDS  

Microsoft Academic Search

The extraction properties of cone-5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis(diphenylphosphinoylmethoxy)calix[4]arene (1) in 1,2-dichloroethane towards rare-earth metal ions at 25 °C have been investigated. The slope analysis showed a 1:1 metal\\/ligand ratio for the extracted species (La, Eu, Er and Y). The distribution coefficients increase with the polarity of the diluents : chloroform ? dichioromethane ? 1,2-dichloroethane ? nitrobenzene. In the competitive extraction of 11 rare-earth

M. R. Yaftian; M. Burgard; D. Matt; C. B. Dieleman; F. Rastegar

1997-01-01

321

Photoswitching of cell surface receptors using tethered ligands.  

PubMed

Optical probing and manipulation of cellular signaling has revolutionized biological studies ranging from isolated cells to intact tissues in the live animal. A promising avenue of optical manipulation is Chemical Optogenetics (or Optogenetic Pharmacology), an approach for engineering specific proteins to be rapidly and reversibly switched on and off with light. The approach employs synthetic photoswitched ligands, which can be reversibly photo-isomerized to toggle back and forth between two conformations in response to two wavelengths of light. We focus here on the photoswitched tethered ligand (PTL) approach in which the PTL is covalently attached in a site-directed manner to a signaling protein. For this a ligand anchoring site is introduced at a location which allows the ligand to dock only in one of the light-controlled conformations, thus enabling liganding to be rapidly switched. The ligand can be an agonist, antagonist or an active site (or pore) blocker. In principle, orthogonal chemistries of attachment would make PTL anchoring completely unique. However, extremely high specificity of remote control is also obtained by cysteine attachment because of the ligand specificity and precise geometric requirements for liganding. We describe here the design of light-gated ionotropic and metabotropic glutamate receptors, the selection of a site for cysteine placement, the method for PTL attachment, and a detailed protocol of photoswitching experiments in cultured cells. These descriptions can guide applications of Chemical Optogenetics to other receptors and serve as a starting point for use in more complex preparations. PMID:24718794

Reiner, Andreas; Isacoff, Ehud Y

2014-01-01

322

The Use of Comics-Based Cases in Anchored Instruction  

ERIC Educational Resources Information Center

The primary purpose of this research was to understand how comics fulfill the role of anchor in an anchored instruction learning environment. Anchored instruction addresses the inert knowledge problem through the use of realistic multimedia stories, or "anchors," that embed a problem and the necessary data to solve it within the narrative. In the…

Kneller, Matthew F.

2009-01-01

323

The adsorption and simulated separation of light hydrocarbons in isoreticular metal-organic frameworks based on dendritic ligands with different aliphatic side chains.  

PubMed

Three isoreticular metal-organic frameworks, JUC-100, JUC-103 and JUC-106, were synthesized by connecting six-node dendritic ligands to a [Zn4O(CO2)6] cluster. JUC-103 and JUC-106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC-100. The uptake measurements of the three MOFs for CH4, C2H4, C2H6 and C3H8 were carried out. At 298?K, 1?atm, JUC-103 has relatively high CH4 uptake, but JUC-100 is the best at 273?K, 1?atm. JUC-100 and JUC-103 have similar C2H4 absorption ability. In addition, JUC-100 has the best absorption capacity for C2H6 and C3H8. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C3H8/CH4 and C2H6/CH4 selectivities for an equimolar quaternary CH4/C2H4/C2H6/C3H8 gas mixture maintained at isothermal conditions at 298?K, and JUC-106 has the best C2H6/CH4 selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH4/C2 H4/C2H6/C3H8 mixture into three different fractions of C1, C2 and C3 hydrocarbons. PMID:24919582

Jia, Jiangtao; Wang, Lei; Sun, Fuxing; Jing, Xiaofei; Bian, Zheng; Gao, Lianxun; Krishna, Rajamani; Zhu, Guangshan

2014-07-14

324

Synthesis and characterization of d10 metal complexes with mixed 1,3-di(1H-imidazol-4-yl)benzene and multicarboxylate ligands  

NASA Astrophysics Data System (ADS)

Seven new coordination polymers [Zn(H2L)(mbdc)] (1), [Zn(H3L)(btc)] (2), [Zn(H2L)(Hbtc)] (3), [Zn(H2L)(Hbtc)]·H2O (4), [Zn2(H2L)(btc)(?2-OH)] (5), [Cd(H2L)(mbdc)] (6) and [Cd3(H2L)2(btc)2(H2O)]·5H2O (7) were synthesized by reactions of the corresponding metal salt with rigid ligand 1,3-di(1H-imidazol-4-yl)benzene (H2L) and different carboxylic acids of 1,3-benzenedicarboxylic acid (H2mbdc) and benzene-1,3,5-tricarboxylic acid (H3btc), respectively. The results of X-ray crystallographic analysis indicate that complex 1 is 1D chain while 2 is a (3,3)-connected 2D network with Point (Schläfli) symbol of (4,82). Complexes 3 and 6 are 2D networks, 4 is a 3-fold interpenetrating 3D framework with Point (Schläfli) symbol of (65,8) and 5 is a (3,8)-connected 2D network with Point (Schläfli) symbol of (3,42)2(34,46,56,68,73,8), while 7 is a (3,10)-connected 3D net with Schläfli symbol of (3,4,5)2(34,48,518,612,72,8). The thermal stability and photoluminescence of the complexes were investigated. Furthermore, DFT calculations were performed for 2-4 to discuss the temperature controlled self-assembly of the complexes.

Chen, Zhi-Hao; Zhao, Yue; Chen, Shui-Sheng; Wang, Peng; Sun, Wei-Yin

2013-06-01

325

Photo- and electrocatalytic H2 production by new first-row transition-metal complexes based on an aminopyridine pentadentate ligand.  

PubMed

The synthesis and characterisation of the pentadentate ligand 1,4-di(picolyl)-7-(p-toluenesulfonyl)-1,4,7-triazacyclononane (Py2(Ts)tacn) and their metal complexes of general formula [M(CF3SO3)(Py2(Ts)tacn)][CF3SO3], (M = Fe (1Fe), Co (1Co) and Ni (1Ni)) are reported. Complex 1Co presents excellent H2 photoproduction catalytic activity when using [Ir(ppy)2(bpy)]PF6 (PSIr) as photosensitiser (PS) and Et3N as electron donor, but 1Ni and 1Fe result in a low activity and a complete lack of it, respectively. On the other hand, all three complexes have excellent electrocatalytic proton reduction activity in acetonitrile, when using trifluoroacetic acid (TFA) as a proton source with moderate overpotentials for 1Co (0.59?V vs. SCE) and 1Ni (0.56?V vs. SCE) and higher for 1Fe (0.87?V vs. SCE). Under conditions of CH3CN/H2O/Et3N (3:7:0.2), 1Co (5??M), with PSIr (100??M) and irradiating at 447?nm gives a turnover number (TON) of 690 (n?H2/n1Co) and initial turnover frequency (TOF) (TON×t(-1)) of 703?h(-1) for H2 production. It should be noted that 1Co retains 25?% of the catalytic activity for photoproduction of H2 in the presence of O2. The inexistence of a lag time for H2 evolution and the absence of nanoparticles during the first 30?min of the reaction suggest that the main catalytic activity observed is derived from a molecular system. Kinetic studies show that the reaction is -0.7 order in catalyst, and time-dependent diffraction light scattering (DLS) experiments indicate formation of metal aggregates and then nanoparticles, leading to catalyst deactivation. By a combination of experimental and computational studies we found that the lack of activity in photochemical water reduction by 1Fe can be attributed to the 1Fe (II/I) redox couple, which is significantly lower than the PSIr (III/II) , while for 1Ni the pKa value (-0.4) is too small in comparison with the pH (11.9) imposed by the use of Et3N as electron donor. PMID:24692261

Call, Arnau; Codolà, Zoel; Acuña-Parés, Ferran; Lloret-Fillol, Julio

2014-05-12

326

GPI-Anchored Proteins in Health and Disease  

Microsoft Academic Search

\\u000a Covalently linked to the C-terminus of many proteins, the glycosyl-phosphatidylinositol (GPI) anchor provides a means to anchor\\u000a the attached protein to the cell membrane. Whilst the GPI anchor of mature proteins may be extensively modified, all GPI anchors\\u000a possess a common core structure comprising of a phosphoethanolamine linker and a phosphatidylinositol lipid tail, separated\\u000a by a glycan core. GPI-anchored proteins

David R. Taylor; Nigel M. Hooper

327

Insertion of Guest Molecules into a Mixed Ligand Metal-Organic Framework via Single-Crystal-to-Single Crystal Guest Exchange.  

National Technical Information Service (NTIS)

Metal organic frameworks (MOFs) are constructed from metal ions or metal ion clusters and bridging organic linkers, which provide diverse structural topologies with porous architectures. They have potential to be applied to molecular sieving, storage, ion...

L. Giri, N. J. Trivedi, R. Pesce-Rodriguez, S. P. Karna

2014-01-01

328

Acetylacetonate anchors for robust functionalization of TiO2 nanoparticles with Mn(II)-terpyridine complexes.  

PubMed

A novel class of derivatized acetylacetonate (acac) linkers for robust functionalization of TiO2 nanoparticles (NPs) under aqueous and oxidative conditions is reported. The resulting surface adsorbate anchors are particularly relevant to engineering photocatalytic and photovoltaic devices since they can be applied to attach a broad range of photosensitizers and photocatalytic complexes and are not affected by humidity. Acac is easily modified by CuI-mediated coupling reactions to provide a variety of scaffolds, including substituted terpy complexes (terpy = 2,2':6,2''-terpyridine), assembled with ligands coordinated to transition-metal ions. Since Mn-terpy complexes are known to be effective catalysts for oxidation chemistry, functionalization with Mn(II) is examined. This permits visible-light sensitization of TiO2 nanoparticles due to interfacial electron transfer, as evidenced by UV-vis spectroscopy of colloidal thin films and aqueous suspensions. The underlying ultrafast interfacial electron injection is complete on a subpicosecond time scale, as monitored by optical pump-terahertz probe transient measurements and computer simulations. Time-resolved measurements of the Mn(II) EPR signal at 6 K show that interfacial electron injection induces Mn(II) --> Mn(III) photooxidation, with a half-time for regeneration of the Mn(II) complex of ca. 23 s. PMID:18831585

McNamara, William R; Snoeberger, Robert C; Li, Gonghu; Schleicher, James M; Cady, Clyde W; Poyatos, Macarena; Schmuttenmaer, Charles A; Crabtree, Robert H; Brudvig, Gary W; Batista, Victor S

2008-10-29

329

Scapholunate ligament repair using suture anchors.  

PubMed

Background. This article describes the surgical repair of scapholunate ligament injury using Mitek suture anchors. Material and methods. 3 patients with neglected injuries of the scapholunate ligament were operated from 8 weeks to 5 months after trauma. The authors found that using the Mitek anchor suture simplifies the operative technique, obviates the technical difficulties involved in guiding the tendon through the bone tunnel, and reduces the possibility of the complications seen in the standard ligament repair techniques. Results and Conclusions. The operative technique used in the Clinic of Hand Surgery at the Medical University of Gdansk combines reduction of the displaced scaphoid bone from the dorsal approach and temporary scaphocapitate fixation with K wires, bringing the ruptured ligament closer with capsulodesis using Mitek suture anchors. PMID:17603433

Baczkowski, Bogus?aw; Lorczy?ski, Adam; Kabu?a, Jaros?aw; Camilleri, Rafa?

2006-04-28

330

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2''-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning.  

PubMed

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'?:?6',2''-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands. PMID:22729349

Lewis, Frank W; Harwood, Laurence M; Hudson, Michael J; Drew, Michael G B; Sypula, Michal; Modolo, Giuseppe; Whittaker, Daniel; Sharrad, Clint A; Videva, Vladimira; Hubscher-Bruder, Véronique; Arnaud-Neu, Françoise

2012-08-14

331

Strong metal-metal coupling in mixed-valent intermediates [Cl(L)Ru(?-tppz)Ru(L)Cl]+, L = ?-diketonato ligands, tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine.  

PubMed

Five diruthenium(II) complexes [Cl(L)Ru(?-tppz)Ru(L)Cl] (1-5) containing differently substituted ?-diketonato derivatives (1: L = 2,4-pentanedionato; 2: L = 3,5-heptanedionato; 3: L = 2,2,6,6-tetramethyl-3,5-heptanedionato; 4: L = 3-methyl-2,4-pentanedionato; 5: L = 3-ethyl-2,4-pentanedionato) as ancillary ligands (L) were synthesized and studied by spectroelectrochemistry (UV-Vis-NIR, electron paramagnetic resonance (EPR)). X-ray structural characterisation revealed anti (1, 2, 5) or syn (3) configuration as well as non-planarity of the bis-tridentate tppz bridge and strong d?(Ru(II)) ? ?*(pyrazine, tppz) back-bonding. The widely separated one-electron oxidation steps, Ru(II)Ru(II)/Ru(II)Ru(III) and Ru(II)Ru(III)/Ru(III)Ru(III), result in large comproportionation constants (K(c)) of ?10(10) for the mixed-valent intermediates. The syn-configurated (n) exhibits a particularly high K(c) of 10(12) for n = 1+, accompanied by density functional theory (DFT)-calculated minimum Ru-N bond lengths for this Ru(II)Ru(III) intermediate. The electrogenerated mixed-valent states 1(+)-5(+) exhibit anisotropic EPR spectra at 110 K with average values of 2.304-2.234 and g anisotropies ?g = g(1)-g(3) of 0.82-0.99. Metal-to-metal charge transfer (MMCT) absorptions occur for 1(+)-5(+) in the NIR region at 1660 nm-1750 nm (? ? 2700 dm(3) mol(-1) cm(-1), ??(1/2) ? 1800 cm(-1)). DFT calculations of 1(+) and 3(+) yield comparable Mulliken spin densities of about 0.60 for the metal ions, corresponding to valence-delocalised situations (Ru(2.5))(2). Rather large spin densities of about -0.4 were calculated for the tppz bridges in 1(+) and 3(+). The calculated electronic interaction values (V(AB)) for 1(+)-5(+) are about 3000 cm(-1), comparable to that for the Creutz-Taube ion at 3185 cm(-1). The DFT calculations predict that the Ru(III)Ru(III) forms in 1(2+)-5(2+) prefer a triplet (S = 1) ground state with ?E (S = 0 - S = 1) ?5000 cm(-1). One-electron reduction takes place at the tppz bridge which results in species [Cl(L)Ru(II)(?-tppz?(-))Ru(II)(L)Cl](-) (1?(-)-3?(-), 5?(-)) which exhibit free radical-type EPR signals and NIR transitions typical of the tppz radical anion. The system 4(n) is distinguished by lability of the Ru-Cl bonds. PMID:23007666

Kundu, Tanaya; Schweinfurth, David; Sarkar, Biprajit; Mondal, Tapan Kumar; Fiedler, Jan; Mobin, Shaikh M; Puranik, Vedavati G; Kaim, Wolfgang; Lahiri, Goutam Kumar

2012-11-21

332

Illuminating Metal Ion Sensors - Benzimidazolesulfonamide Metal Complexes  

PubMed Central

The synthesis, structure, and solution spectroscopy of several 2-sulfonamidophenylbenzimidazole metal complexes is reported. These ligands, which have been reported as selective molecular sensors for Zn2+, readily form complexes with Co2+, Ni2+, Cu2+, and Zn2+. Surprisingly, the ligand adopts different binding modes depending on the metal ion. The work here provides insight into the coordination chemistry of these ligands that may allow for the development of improved metal ion sensors and metalloprotein inhibitors. PMID:20942382

Martin, David; Rouffet, Matthieu

2010-01-01

333

Complexes With Biologically Active Ligands. Part 91 Metal Complexes of 5-Benzoylamino- and 5-(3-Nitrobenzoyl-Amino)-1,3,4-Thiadiazole-2-Sulfonamide as Carbonic Anhydrase Inhibitors  

PubMed Central

Complexes containing the anions of 5-benzoylamido-1,3,4-thiadiazole-2-sulfonamide and 5-(3-nitro-benzoylamido)-1,3,4-thiadiazole-2-sulfonamid as ligands, and V(IV); Cr(III); Fe(III); Co(II); Ni(II); Cu(II) and Ag(I) were synthesized and characterized by standard procedures (elemental analysis; IR, electronic, and EPR spectroscopy; TG, magnetic and conductimetric measurements). The original sulfonamides and their metal complexes are strong inhibitors of two carbonic anhydrase (CA) isozymes, CA I and II. PMID:18475759

Jitianu, Andrei; llies, Marc A.; Briganti, Fabrizio; Scozzafava, Andrea

1997-01-01

334

Use of bone anchors in female urology  

Microsoft Academic Search

Stress urinary incontinence remains one of the most prevalent conditions encountered by urologists. In many cases, surgical correction of this condition is carried out using a pubovaginal sling procedure. Bone anchors were initially used in transvaginal needle suspension procedures to improve stabilization of the bladder neck. This technology has been extended to sling procedures, allowing completion of these procedures by

J. Christian Winters; Harriette M Scarpero; Rodney A Appell

2000-01-01

335

Simple suture and anchor in rabbit hips  

PubMed Central

Objective Using biomechanical studies, this research aims to compare hip capsulorrhaphy in rabbits, carried out with two different techniques: capsulorrhaphy with simple sutures and with anchors. Method Thirteen New Zealand Albino (Oryctolaguscuniculus) male rabbits, twenty-six hip joints, were used. First, a pilot project was performed with three rabbits (six hip joints). This experiment consisted of ten rabbits divided into two groups: group 1 underwent capsulorrhaphy on both right and left hips with simple suture using polyglycolic acid absorbable thread, and group 2 underwent capsulorrhaphy with titanium anchors. After a four-week postoperative period, the animals were euthanized and the hip joints were frozen. On the same day of the biomechanical studies, after the hip joints were previously unfrozen, the following parameters were evaluated: rigidity, maximum force, maximum deformity and energy. Results There was no relevant statistical difference in rigidity, maximum force, maximum deformity and energy between the simple suture and anchor groups. Conclusion Through biomechanical analyses, using parameters of rigidity, maximum force, maximum deformity and energy, it has been shown that capsulorrhaphy with simple suture and with anchors has similar results in rabbit hip joints. Level of Evidence II, Prospective Comparative Study. PMID:24453618

Garcia Filho, Fernando Cal; Guarniero, Roberto; de Godoy Junior, Rui Maciel; Pereira, Cesar Augusto Martins; Matos, Marcos Almeida; Garcia, Lucas Cortizo

2012-01-01

336

The first example of calix[4]pyrrole functionalized vic-dioxime ligand: Synthesis, characterization, spectroscopic studies and redox properties of the mononuclear transition metal complexes  

Microsoft Academic Search

Novel calix[4]pyrrole bearing vic-dioxime ligand (LH2) of the general formula, R1R2C2N2O2H2 (where, R1=C6H5- and R2=C39H50N5-) has been synthesized by the reaction of anti-chlorophenylglyoxime with 3-aminophenylcalix[4]pyrrole at room temperature. The mononuclear Cu(II), Ni(II) and Co(II)complexes of this vic-dioxime ligand were prepared and their structures were confirmed by elemental analysis, FT-IR, TGA and magnetic susceptibility measurements; the HMBC, DEPT, 1H and 13C

Bilge Taner; Pervin Deveci; Soner Bereket; Ali Osman Solak; Emine Özcan

2010-01-01

337

Undrained behavior of plate anchors subjected to general loading  

E-print Network

that withstands significant lateral and uplift loads imposed on floating structures. Plate anchors are a common anchoring system which is cost-effective and geotechnically efficient compared to other types of anchors such as anchor piles, suction caissons.... The study explores the effect of the flap on the performance of the SEPLA and provides a theoretical basis for the design of the SEPLA 10 plate configuration including the flap. 1.3 Outline of Research This research consists of two parts...

Yang, Ming

2010-01-14

338

Incorporation of Membrane-Anchored Flagellin into Influenza Virus-Like Particles Enhances the Breadth of Immune Responses  

Microsoft Academic Search

We have designed a membrane-anchored form of the Toll-like receptor 5 ligand flagellin, the major proinflammatory determinant of enteropathogenic Salmonella, which was found to be glycosylated and ex- pressed on cell surfaces. A chimeric influenza virus-like particle (cVLP) vaccine candidate containing A\\/PR8\\/34 (H1N1) hemagglutinin (HA), matrix protein (M1), and the modified flagellin as a molecular adjuvant was produced. The immunogenicity,

Bao-Zhong Wang; Fu-Shi Quan; Sang-Moo Kang; Jadranka Bozja; Ioanna Skountzou; Richard W. Compans

2008-01-01

339

Coordination of Aza Heterocycles with Macroheterocyclic Metal Complexes in Amphiprotic Media: II. Kinetics of Outer-Sphere Ligand Exchange in Chromium(III) Tetrphenylporphyrinate  

Microsoft Academic Search

Rate constants and activation parameters for substitution of alcohols with aza heterocycles in the chromium(III) (acetate)tetraphenylporphyrinate complex were calculated. The nature of the leaving ligand significantly affects the activation parameters. Increased strength of the H bond in the outer coordination sphere of the macrocyclic complex decreases the substitution rate constant. The logarithms of the reaction rate constants linearly vary with

I. P. Trifonova; V. A. Burmistrov; A. S. Ocheretovyi; O. I. Koifman

2005-01-01

340

Effect of para-substituents on alkaline earth metal ion extraction by proton di-ionizable calix[4]arene-crown-6 ligands in cone, partial-cone and 1,3-alternate conformations.  

PubMed

Two carboxylic acid or N-(X)sulfonyl carboxamide groups were incorporated into calix[4]arene-crown-6 compounds to afford di-ionizable ligands for use in divalent metal ion separations. Acidities of the N-(X)sulfonyl carboxamide groups were tuned by variation of the electron-withdrawing properties of X. Cone, partial-cone and 1,3-alternate conformations were obtained by different synthetic strategies and their structures verified by NMR spectroscopy. Competitive solvent extractions of alkaline earth metal cations from aqueous solutions into chloroform were performed and the results compared with those reported previously for di-ionizable p-tert-butylcalix[4]arene-crown-6 analogues to probe the influence of the para-substituent on the calix[4]arene scaffold on extraction selectivity and efficiency. PMID:17205177

Zhou, Hui; Liu, Dazhan; Gega, Jerzy; Surowiec, Kazimierz; Purkiss, David W; Bartsch, Richard A

2007-01-21

341

Metal flux and dynamic speciation at (bio)interfaces. Part V: The roles of simple, fulvic and aggregate complexes on Pb flux in freshwater ligand mixtures, computed at planar consuming interfaces  

NASA Astrophysics Data System (ADS)

The computations of metal flux in aquatic systems, at consuming interfaces like oganism membranes are of major importance in ecotoxicology and dynamic risk assessment. In this paper, the flux of Pb(II), at a planar consuming interface in natural waters, is studied. The system includes (a) simple ligands (OH -, CO32-); (b) fulvics and (c) aggregates, as complexants, i.e. those which may play the major roles in controlling the metal flux in aquatic media. The effects of various physico-chemical factors, in particular, the diffusion layer thickness, the stability constants of fulvic and aggregate complexes, the complexing site distribution of fulvics and the size distribution of aggregates, are studied in details.

Zhang, Zeshi; Buffle, Jacques

2009-03-01

342

Synthesis, characterization, reactivity and antibacterial activity of new peroxovanadium(V) complexes anchored to soluble polymers  

Microsoft Academic Search

New peroxovanadate (pV) complexes anchored to soluble polymers of the type, Na3[V2O2(O2)4(carboxylate)]–PA [PA=poly(acrylate)] (PAV) and Na2[VO(O2)2(carboxylate)]–PMA [PMA=Poly(methacrylate)] (PMAV) have been synthesized from the reaction of V2O5 with H2O2 and the sodium salts of the respective macromolecular ligands at pH ca. 6. The compounds were characterized by elemental analysis, SEM, EDX, TGA and spectral studies. In PMAV, the pV moieties are

Diganta Kalita; Swapnalee Sarmah; Siva Prasad Das; Diganta Baishya; Ashok Patowary; Sashi Baruah; Nashreen S. Islam

2008-01-01

343

Chiral rhodium complexes covalently anchored on carbon nanotubes for enantioselective hydrogenation.  

PubMed

Chiral rhodium hybrid nanocatalysts have been prepared by covalent anchorage of pyrrolidine-based diphosphine ligands onto functionalized CNTs. This work constitutes the first attempt at covalent anchoring of homogeneous chiral catalysts on CNTs. The catalysts, prepared with two different chiral phosphines, were characterized by ICP, XPS, N2 adsorption and TEM, and have been tested in the asymmetric hydrogenation of two different substrates: methyl 2-acetamidoacrylate and ?-acetamidocinnamic acid. The hybrid nanocatalysts have shown to be active and enantioselective in the hydrogenation of ?-acetamidocinnamic acid. A good recyclability of the catalysts with low leaching and without loss of activity and enantioselectivity was observed. PMID:24590206

Gheorghiu, C C; Machado, B F; Salinas-Martínez de Lecea, C; Gouygou, M; Román-Martínez, M C; Serp, P

2014-05-28

344

Synthesis, structural, photophysical and electrochemical studies of various d-metal complexes of btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] ligands that give rise to the formation of metallo-supramolecular gels.  

PubMed

2,6-Bis(1,2,3-triazol-4-yl)pyridine (btp) is a terdentate binding motif that is synthesised modularly via the CuAAC reaction. Herein, we present the synthesis of ligands 1 and 2 and the investigation of the coordination chemistry, photophysical behaviour and electrochemistry of complexes of these with a number of d-metal ions (e.g. Ru(II), Ir(III), Ni(II) and Pt(II)). The X-ray crystal structures of ligand 1 and the complexes [Ru·2(2)](PF6)Cl, [Ni·1(2)](PF6)Cl and [Ir·1Cl3] are also presented. All of the complexes displayed non-classical triazolyl C-H···Cl(-) hydrogen bonding. All but one complex showed no metal-based luminescence at room temperature, while all of the Pt(ii) complexes displayed luminescence at 77 K. The electrochemistry of the Ru(II) complexes was also studied and these complexes were found to have higher oxidation potentials than analogous compounds. The redox behaviour of [RuL2](2+) complexes with both 1 and 2 was nearly identical, while [Ru·1Cl2(DMSO)] was oxidised at significantly lower potential. We also show that the Ru(II) complex of 2, [Ru·2(2)](PF6)Cl, gave rise to the formation of a metallo-supramolecular gel, the morphology of which was studied using scanning electron and helium ion microscopy. PMID:24149846

Byrne, Joseph P; Kitchen, Jonathan A; Kotova, Oxana; Leigh, Vivienne; Bell, Alan P; Boland, John J; Albrecht, Martin; Gunnlaugsson, Thorfinnur

2014-01-01

345

Selectivity of the highly preorganized tetradentate ligand 2,9-di(pyrid-2-yl)-1,10-phenanthroline for metal ions in aqueous solution, including lanthanide(III) ions and the uranyl(VI) cation.  

PubMed

Some metal ion complexing properties of DPP (2,9-Di(pyrid-2-yl)-1,10-phenanthroline) are reported with a variety of Ln(III) (Lanthanide(III)) ions and alkali earth metal ions, as well as the uranyl(VI) cation. The intense ?-?* transitions in the absorption spectra of aqueous solutions of 10(-5) M DPP were monitored as a function of pH and metal ion concentration to determine formation constants of the alkali-earth metal ions and Ln(III) (Ln = lanthanide) ions. It was found that log K(1)(DPP) for the Ln(III) ions has a peak at Ln(III) = Sm(III) in a plot of log K(1) versus 1/r(+) (r(+) = ionic radius for 8-coordination). For Ln(III) ions larger than Sm(III), there is a steady rise in log K(1) from La(III) to Sm(III), while for Ln(III) ions smaller than Sm(III), log K(1) decreases slightly to the smallest Ln(III) ion, Lu(III). This pattern of variation of log K(1) with varying size of Ln(III) ion was analyzed using MM (molecular mechanics) and DFT (density functional theory) calculations. Values of strain energy (?U) were calculated for the [Ln(DPP)(H(2)O)(5)](3+) and [Ln(qpy)(H(2)O)(5)](3+) (qpy = quaterpyrdine) complexes of all the Ln(III) ions. The ideal M-N bond lengths used for the Ln(III) ions were the average of those found in the CSD (Cambridge Structural Database) for the complexes of each of the Ln(III) ions with polypyridyl ligands. Similarly, the ideal M-O bond lengths were those for complexes of the Ln(III) ions with coordinated aqua ligands in the CSD. The MM calculations suggested that in a plot of ?U versus ideal M-N length, a minimum in ?U occurred at Pm(III), adjacent in the series to Sm(III). The significance of this result is that (1) MM calculations suggest that a similar metal ion size preference will occur for all polypyridyl-type ligands, including those containing triazine groups, that are being developed as solvent extractants in the separation of Am(III) and Ln(III) ions in the treatment of nuclear waste, and (2) Am(III) is very close in M-N bond lengths to Pm(III), so that an important aspect of the selectivity of polypyridyl type ligands for Am(III) will depend on the above metal ion size-based selectivity. The selectivity patterns of DPP with the alkali-earth metal ions shows a similar preference for Ca(II), which has the most appropriate M-N lengths. The structures of DPP complexes of Zn(II) and Bi(III), as representative of a small and of a large metal ion respectively, are reported. [Zn(DPP)(2)](ClO(4))(2) (triclinic, P1, R = 0.0507) has a six-coordinate Zn(II), with each of the two DPP ligands having one noncoordinated pyridyl group appearing to be ?-stacked on the central aromatic ring of the other DPP ligand. [Bi(DPP)(H(2)O)(2)(ClO(4))(2)](ClO(4)) (triclinic, P1, R = 0.0709) has an eight-coordinate Bi, with the coordination sphere composed of the four N donors of the DPP ligand, two coordinated water molecules, and the O donors of two unidentate perchlorates. As is usually the case with Bi(III), there is a gap in the coordination sphere that appears to be the position of a lone pair of electrons on the other side of the Bi from the DPP ligand. The Bi-L bonds become relatively longer as one moves from the side of the Bi containg the DPP to the side where the lone pair is thought to be situated. A DFT analysis of [Ln(tpy)(H(2)O)(n)](3+) and [Ln(DPP)(H(2)O)(5)](3+) complexes is reported. The structures predicted by DFT are shown to match very well with the literature crystal structures for the [Ln(tpy)(H(2)O)(n)](3+) with Ln = La and n = 6, and Ln = Lu with n = 5. This then gives one confidence that the structures for the DPP complexes generated by DFT are accurate. The structures generated by DFT for the [Ln(DPP)(H(2)O)(5)](3+) complexes are shown to agree very well with those generated by MM, giving one confidence in the accuracy of the latter. An analysis of the DFT and MM structures shows the decreasing O--O nonbonded distances as one progresses from La to Lu, with these distances being much less than the sum of the van der Waals radii for the smaller Ln(III) ions. The effect t

Carolan, Ashley N; Cockrell, Gregory M; Williams, Neil J; Zhang, Gang; VanDerveer, Donald G; Lee, Hee-Seung; Thummel, Randolph P; Hancock, Robert D

2013-01-01

346

Perfluorinated Taddol Phosphoramidite as an L,Z-Ligand on Rh(I) and Co(-I): Evidence for Bidentate Coordination via Metal-C6F5 Interaction  

PubMed Central

Perfluorinated Taddol-based phosphoramidite, CKphos, is a highly selective ligand for formation of the vinylogous amide cycloadduct in the Rh(I) catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and alkynes. CKphos overrides substrate bias of product selectivity in the cycloaddition, providing indolizinones in excellent product and enantioselectivities. Excellent selectivities are attributed to a shortened Rh-P bond and coordination of one C6F5 to rhodium via a Z-type interaction, making the phosphoramidite a bidentate L,Z-ligand on rhodium. Evidence for the shortened Rh-P and C6F5 coordination is provided by X-ray, NMR and DFT computation analyses. Additionally, an anionic cobalt complex with CKphos was synthesized and two Co-C6F5 interactions are seen. Rh(C2H4)Cl•CKphos catalyst in the [2+2+2] cycloaddition of alkenyl isocyanates and alkynes represents a rare example of metal-C6F5 Z-type interaction affecting selectivity in transition metal catalysis. PMID:23671790

Dalton, Derek M.; Rappe, Anthony K.

2013-01-01

347

Synthesis and spectroscopic studies of homo-binuclear, alkoxo bridged homo- and hetero-tetranuclear metal complexes of a bis-N2O4 Schiff base ligand derived from ethanolamine and macroacyclic tetranaphthaldehyde.  

PubMed

Three new homo-binuclear Ni(II), Cu(II), Zn(II) complexes (2-4), homo-tetranuclear Cu(II) complex (5), and hetero-tetranuclear Cu(II)-Ni(II) complex (6) of a macroacyclic potentially bis-hexadentate N2O4 Schiff base have been synthesized. The imino-alcohol ligand, H4L was obtained by the condensation of ethanolamine with 2,2'-[2,3-bis(1-formyl-2-naphthyloxymethyl)-but-2-ene-1,4-diyldioxy]bis(naphthalene-1-carbaldehyde). The structures of both the Schiff base and its complexes have been proposed by elemental analyses, spectroscopic data i.e. IR, 1H and 13C NMR, UV-vis, electrospray ionisation mass spectra, molar conductivities and magnetic susceptibility measurements. The ligand has two similar compartments to bind first primary two metal ions, and acts bi- or tetra-negative, bis-tetradentate forming five membered chelate ring. However, secondary two metal ions (either Cu2+ or Ni2+) are ligated with dianionic oxygen atoms of the alcohol groups and are linked to the 1,10-phenanthroline-nitrogen atoms in the tetranuclear complexes (5 and 6). PMID:21550297

Karao?lu, Kaan; Baran, Talat; De?irmencio?lu, Ismail; Serbest, Kerim

2011-09-01

348

Behavior of 10 full-scale ground anchors installed in stiff clay  

E-print Network

Anchors 2. 3 Ground Anchor Design Practice 2, 4 Load Testing of Ground Anchors 2. 4. 1 Testing Equipment 2. 4. 2 Components of Ground Anchor Movements 2. 4. 3 Proof Tests. . . . . . . . . . . . . . . . . . 2. 4. 4 Performance Tests 2. 4. 5 Creep... Tests 3 GROUND ANCHOR BEHAVIOR 3. 1 Load Distribution in Ground Anchors 3. 2 Creep Behavior of Ground Anchors. . . . . . . . . . . . . . 3. 3 Mechanisms Contributing to Ground Anchor Failure 3. 3. 1 Failure of the Grout-Tendon Bond...

Powers, William Francis

2012-06-07

349

Monitoring of stress distribution along a ground anchor using BOTDA  

NASA Astrophysics Data System (ADS)

For the understanding of the bearing behavior of a loaded ground anchor, the measuring and monitoring of the stress distribution in the anchor tendon is essential. This paper proposes a novel monitoring ground anchor using embedded optical fibers for the continuous strain assessment along the anchor tendon. In a first step, optical sensors have been integrated into short tendons using different methods and laboratory strain testing was performed on these instrumented tendons. The evaluation of the laboratory testing enabled the design and development of an 8m long monitoring ground anchor for field application. In 2009, this anchor has been placed into a wall supporting an excavation pit and subsequently, anchor pullout test was carried out. The anchor was loaded stepwise up to 470kN, almost reaching its ultimate bearing capacity. Optical measurements were taken successfully at each load step. Comparison of the optical data with data acquired using conventional methods indicated good consistency of the results. To a geotechnical engineer, this proposed monitoring anchor provides a powerful tool for the measuring of the pullout load, the anchor head displacement and the load distribution in the anchor tendon.

Iten, Michael; Puzrin, Alexander M.

2010-04-01

350

Robust parylene-to-silicon mechanical anchoring  

Microsoft Academic Search

This paper describes a new technique for strongly anchoring parylene (poly-para-xylylene) layers on a silicon substrate. Parylene has gained interest for MEMS applications due to its excellent properties. More specifically, because of its flexibility (Young's modulus of 4 GPa), its chemical barrier properties, its conformal deposition and its biocompatibility, parylene is of great interest for microfluidics and BioMEMS. One of

Matthieu Liger; Damien C. Rodger; Yu-Chong Tai

2003-01-01

351

Assembly of CdI2-type coordination networks from triangular ligand and octahedral metal center: topological analysis and potential framework porosity.  

PubMed

Reaction of a rigid triangular ligand 2,4,6-tris[4-(1H-imidazole-1-yl)phenyl]-1,3,5-triazine (TIPT) with Cd2+ ions affordedrare non-interpenetrating CdI2-type networks which display high thermostability and potential porosity; the topological character of the CdI2-type networks have been analyzed in comparison with three common uniform (4,4), (6,3) and (3,6) plane nets. PMID:18399206

Zheng, Sheng-Run; Yang, Qing-Yuan; Liu, Yong-Ru; Zhang, Jian-Yong; Tong, Ye-Xiang; Zhao, Cun-Yuan; Su, Cheng-Yong

2008-01-21

352

Current state of laser synthesis of metal and alloy nanoparticles as ligand-free reference materials for nano-toxicological assays  

PubMed Central

Summary Due to the abundance of nanomaterials in medical devices and everyday products, toxicological effects related to nanoparticles released from these materials, e.g., by mechanical wear, are a growing matter of concern. Unfortunately, appropriate nanoparticles required for systematic toxicological evaluation of these materials are still lacking. Here, the ubiquitous presence of surface ligands, remaining from chemical synthesis are a major drawback as these organic residues may cause cross-contaminations in toxicological studies. Nanoparticles synthesized by pulsed laser ablation in liquid are a promising alternative as this synthesis route provides totally ligand-free nanoparticles. The first part of this article reviews recent methods that allow the size control of laser-fabricated nanoparticles, focusing on laser post irradiation, delayed bioconjugation and in situ size quenching by low salinity electrolytes. Subsequent or parallel applications of these methods enable precise tuning of the particle diameters in a regime from 4–400 nm without utilization of any artificial surface ligands. The second paragraph of this article highlights the recent progress concerning the synthesis of composition controlled alloy nanoparticles by laser ablation in liquids. Here, binary and ternary alloy nanoparticles with totally homogeneous elemental distribution could be fabricated and the composition of these particles closely resembled bulk implant material. Finally, the model AuAg was used to systematically evaluate composition related toxicological effects of alloy nanoparticles. Here Ag+ ion release is identified as the most probable mechanism of toxicity when recent toxicological studies with gametes, mammalian cells and bacteria are considered. PMID:25247135

Rehbock, Christoph; Jakobi, Jurij; Gamrad, Lisa; van der Meer, Selina; Tiedemann, Daniela; Taylor, Ulrike; Kues, Wilfried; Rath, Detlef

2014-01-01

353

Complexes possessing rare "tertiary" sulfonamide nitrogen-to-metal bonds of normal length: fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes with hydrophilic sulfonamide ligands.  

PubMed

Tertiary sulfonamide nitrogen-to-metal bonds of normal length are very rare. We recently discovered such a bond in one class of fac-[Re(CO)3(N(SO2R)(CH2Z)2)](n) complexes (Z = 2-pyridyl) with N(SO2R)dpa ligands derived from di-(2-picolyl)amine (N(H)dpa). fac-[M(CO)3(N(SO2R)(CH2Z)2)](n) agents (M = (186/188)Re, (99m)Tc) could find use as radiopharmaceutical bioconjugates when R is a targeting moiety. However, the planar, electron-withdrawing 2-pyridyl groups of N(SO2R)dpa destabilize the ligand to base and create relatively rigid chelate rings, raising the possibility that the rare M-N(sulfonamide) bond is an artifact of a restricted geometry. Also, the hydrophobic 2-pyridyl groups could cause undesirable accumulation in the liver, limiting future use in radiopharmaceuticals. Our goal is to identify a robust, hydrophilic, and flexible N(CH2Z)2 chelate framework. New C2-symmetric ligands, N(SO2R)(CH2Z)2 with (Z = CH2NH2; R = Me, dmb, or tol), were prepared by treating N(H)dien(Boc)2, a protected diethylenetriamine (N(H)dien) derivative, with methanesulfonyl chloride (MeSO2Cl), 3,5-dimethylbenzenesulfonyl chloride (dmbSO2Cl), and 4-methylbenzenesulfonyl chloride (tolSO2Cl). Treatment of fac-[Re(CO)3(H2O)3](+) with these ligands, designated as N(SO2R)dien, afforded new fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes. Comparing the fac-[Re(CO)3(N(SO2Me)dien)]PF6 and fac-[Re(CO)3(N(SO2Me)dpa)]PF6 complexes, we find that the Re(I)-N(sulfonamide) bonds are normal in length and statistically identical and that the methyl (13)C NMR signal has an unusually upfield shift compared to that in the free ligand. We attribute this unusual upfield shift to the fact that the sulfonamide N undergoes an sp(2)-to-sp(3) rehybridization upon coordination to Re(I) in both complexes. Thus, the sulfonamide N of N(SO2R)dien ligands is a good donor, even though the chelate rings are conformationally flexible. Addition of the strongly basic and potentially monodentate ligand, 4-dimethylaminopyridine, did not affect the fac-[Re(CO)3(N(SO2tol)dien)]PF6 complex, even after several weeks. This complex is also stable to heat in aqueous solution. These results indicate that N(SO2R)dien ligands form fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes sufficiently robust to be utilized for radiopharmaceutical development. PMID:24400928

Abhayawardhana, Pramuditha L; Marzilli, Patricia A; Fronczek, Frank R; Marzilli, Luigi G

2014-01-21

354

Steady-state distribution of metals among metallothionein and other cytosolic ligands and links to cytotoxicity in bivalves living along a polymetallic gradient  

Microsoft Academic Search

The present study was designed to assess the environmental effects of metals in a field setting. We explored exposure?bioaccumulation?effects relationships in freshwater molluscs exposed to metals in their natural habitat. Indigenous floater mussels (Pyganodon grandis) were collected from ten limnologically similar lakes located along a Cd, Cu and Zn gradient. Ambient free-metal ion concentrations were estimated as a measure of

Anik Giguère; Yves Couillard; Peter G. C Campbell; Olivier Perceval; Landis Hare; Bernadette Pinel-Alloul; Jocelyne Pellerin

2003-01-01

355

Spectroscopic and biological studies of new binuclear metal complexes of a tridentate ONS hydrazone ligand derived from 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one and 4,6-diacetylresorcinol  

NASA Astrophysics Data System (ADS)

The binuclear hydrazone, H2L, ligand derived from 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one and 4,6-diacetylresorcinol, in the molar ratio 2:1, and its copper(II), nickel(II), cobalt(II), zinc(II), cadmium(II), cerium(III), iron(III), oxovanadium(IV) and dioxouranium(VI) complexes have been synthesized. Structures of the ligand and its metal complexes were characterized by elemental analyses, spectral (infrared, electronic, mass, 1H NMR and ESR) data, magnetic susceptibility, molar conductivity measurements and thermal gravimetric analysis (TGA). The ligand acts as dibasic with two ONS tridentate sites. The bonding sites are the azomethine nitrogen, phenolate oxygen and sulfur atoms. The metal complexes exhibit different geometrical arrangements such as square planer, tetrahedral and octahedral. The Coats-Redfern equation was used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. The ligand and its metal complexes showed antimicrobial activity towards Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), Gram-negative bacteria (Salmonella typhimurium and Escherichia coli), yeast (Candida albicans) and fungus (Aspergillus fumigatus). Structural parameters of the ligand and its metal complexes were theoretically computed on the basis of semiempirical PM3 level, and the results were correlated with their experimental data.

Adly, Omima M. I.; Emara, Adel A. A.

2014-11-01

356

The biotic ligand model: a historical overview  

Microsoft Academic Search

During recent years, the biotic ligand model (BLM) has been proposed as a tool to evaluate quantitatively the manner in which water chemistry affects the speciation and biological availability of metals in aquatic systems. This is an important consideration because it is the bioavailability and bioreactivity of metals that control their potential to cause adverse effects. The BLM approach has

Paul R. Paquin; Joseph W. Gorsuch; Simon Apte; Graeme E. Batley; Karl C. Bowles; Peter G. C. Campbell; Charles G. Delos; Dominic M. Di Toro; Robert L. Dwyer; Fernando Galvez; Robert W. Gensemer; Gregory G. Goss; Christer Hogstrand; Colin R. Janssen; James C. McGeer; Rami B. Naddy; Richard C. Playle; Robert C. Santore; Uwe Schneider; William A. Stubblefield; Chris M. Wood; Kuen Benjamin Wu

2002-01-01

357

Two new metal-organic coordination polymers of lead with O-, N-donor ligands: Synthesis, characterization, luminescence and thermal behavior  

SciTech Connect

The synthesis of two new lead(II) coordination polymers, [Pb{sub 2}(picOH){sub 4}]{center_dot}H{sub 2}O (1) and [Pb{sub 3}(Sip){sub 2}(H{sub 2}O){sub 2}]{center_dot}H{sub 2}O (2) has been reported, where HpicOH=3-hydroxypicolinic acid and NaH{sub 2}Sip=5-sulfoisophthalic acid monosodium salt. Both the complexes were structurally characterized by X-ray single crystal diffraction analysis. Complex 1, where the 3-hydroxypicolinate ligand is used for the first time in conjunction with Pb(II), revealed to be a 1D polymeric array. Complex 2 showed a 3D structure with 5-sulfoisophthalate ligand adopting two novel binding modes of high denticity ({eta}{sup 6}{mu}{sub 6} and {eta}{sup 7}{mu}{sub 7}). The photoluminescence and thermal properties of the two complexes have been studied. - Graphical abstract: 1D and 3D inorganic organic hybrid luminescent material of Pb(II) have been synthesized by using 3-hydroxypicolinate and 5-sulfoisophthalate anions. The 5-sulfoisophthalate ligand shows two novel binding modes with high denticity. Highlights: Black-Right-Pointing-Pointer 3-hydroxypicolinic acid is used for first time with Pb{sup 2+} in a MOF. Black-Right-Pointing-Pointer 5-sulfoisophthalic acid displays two novel binding modes of high denticity. Black-Right-Pointing-Pointer Complex 1 shows high thermal stability (up to 167 Degree-Sign C). Black-Right-Pointing-Pointer MLCT is present in both the complexes.

Rana, Abhinandan; Kumar Jana, Swapan; Bera, Madhusudan; Hazari, Debdoot; Sankar Chowdhuri, Durga [Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore 721 102, West Bengal (India); Zangrando, Ennio [Dipartimento di Scienze Chimiche e Farmaceutiche, University of Trieste, 34127 Trieste (Italy); Dalai, Sudipta, E-mail: sudipta@mail.vidyasagar.ac.in [Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore 721 102, West Bengal (India)

2013-01-15

358

Coordination chemistry of two heavy metals: I, Ligand preferences in lead(II) complexation, toward the development of therapeutic agents for lead poisoning: II, Plutonium solubility and speciation relevant to the environment  

SciTech Connect

The coordination chemistry and solution behavior of the toxic ions lead(II) and plutonium(IV, V, VI) have been investigated. The ligand pK{sub a}s and ligand-lead(II) stability constants of one hydroxamic acid and four thiohydroaxamic acids were determined. Solution thermodynamic results indicate that thiohydroxamic acids are more acidic and slightly better lead chelators than hydroxamates, e.g., N-methylthioaceto-hydroxamic acid, pK{sub a} = 5.94, log{beta}{sub 120} = 10.92; acetohydroxamic acid, pK{sub a} = 9.34, log{beta}{sub l20} = 9.52. The syntheses of lead complexes of two bulky hydroxamate ligands are presented. The X-ray crystal structures show the lead hydroxamates are di-bridged dimers with irregular five-coordinate geometry about the metal atom and a stereochemically active lone pair of electrons. Molecular orbital calculations of a lead hydroxamate and a highly symmetric pseudo octahedral lead complex were performed. The thermodynamic stability of plutonium(IV) complexes of the siderophore, desferrioxamine B (DFO), and two octadentate derivatives of DFO were investigated using competition spectrophotometric titrations. The stability constant measured for the plutonium(IV) complex of DFO-methylterephthalamide is log{beta}{sub 110} = 41.7. The solubility limited speciation of {sup 242}Pu as a function of time in near neutral carbonate solution was measured. Individual solutions of plutonium in a single oxidation state were added to individual solutions at pH = 6.0, T = 30.0, 1.93 mM dissolved carbonate, and sampled over intervals up to 150 days. Plutonium solubility was measured, and speciation was investigated using laser photoacoustic spectroscopy and chemical methods.

Neu, M.P. [Lawrence Berkeley Lab., CA (United States)

1993-11-01

359

Potentiometric and Blood Plasma Simulation Studies of Nickel(II) Complexes of Poly(amino)amido Pentadentate Ligands: Computer Aided Metal-Based Drug Design  

PubMed Central

The thermodynamic equilibria of nickel(II) with N,N?-di(aminoethylene)-2,6-pyridinedicarbonylamine (L1), Bis-(N,N-dimethylethyl)-2,6-pyridinedicarboxamide (L2), and N,N?-bis[2(2-pyridyl)-methyl]pyridine-2,6-dicarboxamide (L3) have been studied at 25°C and an ionic strength of 0.15?mol?dm?3 by glass electrode potentiometry. The protonation and formation constants added to blood plasma model predict that Cu(II) competes effectively against Ni(II), Zn(II), and Ca(II) for these ligands in vivo. PMID:25371660

Jackson, Graham E.

2014-01-01

360

Homoleptic Nickel(II) Complexes of Redox-Tunable Pincer-type Ligands.  

PubMed

Different synthetic methods have been developed to prepare eight new redox-active pincer-type ligands, H(X,Y), that have pyrazol-1-yl flanking donors attached to an ortho-position of each ring of a diarylamine anchor and that have different groups, X and Y, at the para-aryl positions. Together with four previously known H(X,Y) ligands, a series of 12 Ni(X,Y)2 complexes were prepared in high yields by a simple one-pot reaction. Six of the 12 derivatives were characterized by single-crystal X-ray diffraction, which showed tetragonally distorted hexacoordinate nickel(II) centers. The nickel(II) complexes exhibit two quasi-reversible one-electron oxidation waves in their cyclic voltammograms, with half-wave potentials that varied over a remarkable 700 mV range with the average of the Hammett ?p parameters of the para-aryl X, Y groups. The one- and two-electron oxidized derivatives [Ni(Me,Me)2](BF4)n (n = 1, 2) were prepared synthetically, were characterized by X-band EPR, electronic spectroscopy, and single-crystal X-ray diffraction (for n = 2), and were studied computationally by DFT methods. The dioxidized complex, [Ni(Me,Me)2](BF4)2, is an S = 2 species, with nickel(II) bound to two ligand radicals. The mono-oxidized complex [Ni(Me,Me)2](BF4), prepared by comproportionation, is best described as nickel(II) with one ligand centered radical. Neither the mono- nor the dioxidized derivative shows any substantial electronic coupling between the metal and their bound ligand radicals because of the orthogonal nature of their magnetic orbitals. On the other hand, weak electronic communication occurs between ligands in the mono-oxidized complex as evident from the intervalence charge transfer (IVCT) transition found in the near-IR absorption spectrum. Band shape analysis of the IVCT transition allowed comparisons of the strength of the electronic interaction with that in the related, previously known, Robin-Day class II mixed valence complex, [Ga(Me,Me)2](2+). PMID:25222027

Hewage, Jeewantha S; Wanniarachchi, Sarath; Morin, Tyler J; Liddle, Brendan J; Banaszynski, Megan; Lindeman, Sergey V; Bennett, Brian; Gardinier, James R

2014-10-01

361

C(sp3)-H activation without a directing group: regioselective synthesis of N-ylide or N-heterocyclic carbene complexes controlled by the choice of metal and ligand.  

PubMed

N-Ylide complexes of Ir have been generated by C(sp(3))-H activation of ?-pyridinium or ?-imidazolium esters in reactions with [Cp*IrCl2]2 and NaOAc. These reactions are rare examples of C(sp(3))-H activation without a covalent directing group, which-even more unusually-occur ? to a carbonyl group. For the reaction of the ?-imidazolium ester [3H]Cl, the site selectivity of C-H activation could be controlled by the choice of metal and ligand: with [Cp*IrCl2]2 and NaOAc, C(sp(3))-H activation gave the N-ylide complex 4; in contrast, with Ag2O followed by [Cp*IrCl2]2, C(sp(2))-H activation gave the N-heterocyclic carbene complex 5. DFT calculations revealed that the N-ylide complex 4 was the kinetic product of an ambiphilic C-H activation. Examination of the computed transition state for the reaction to give 4 indicated that unlike in related reactions, the acetate ligand appears to play the dominant role in C-H bond cleavage. PMID:25164979

Cross, Warren B; Razak, Sunnah; Singh, Kuldip; Warner, Andrew J

2014-10-01

362

Pro-porous coordination polymers of the 1,4-bis((3,5-dimethyl-1H-pyrazol-4-yl)-methyl)benzene ligand with late transition metals.  

PubMed

Solvothermal reactions of the flexible, pyrazole-based 1,4-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)benzene ligand (H(2)BDMPX) with late transition metal ions allowed the isolation of the four coordination compounds M(x)(BDMPX) (x = 1 for M = Zn, 1; Co, 2; Cd, 3; x = 2 for M = Cu, 4). The investigation of the thermal behavior assessed the high thermal robustness of these materials, which are stable in air at least up to 300 °C, with the Cd(II) derivative starting to decompose only around 500 °C. As retrieved by ab initio X-ray powder diffraction, the isomorphous compounds 1-3 possess a dense 3-D network featuring rhombic motifs hinged about rigid and parallel chains of tetrahedral MN(4) chromophores. As demonstrated by thermodiffractometric measurements, temperature increase triggers framework flexibility. The latter is at work also when N(2) adsorption is assayed at 77 K: 1 and 2 show permanent porosity, with BET and Langmuir specific surface areas of 515, 667 m(2)/g and 209, 384 m(2)/g, respectively. 1 and 2 thus represent an intriguing example of "porosity without pores", their pro-porous nature being explained in terms of the flexibility of the rhombic motifs, stimulated by the gas probe and facilitated by the nature of the ligand. PMID:22010946

T?b?caru, Aurel; Pettinari, Claudio; Masciocchi, Norberto; Galli, Simona; Marchetti, Fabio; Angjellari, Mariglen

2011-11-21

363

Anti-inflammatory drugs interacting with Zn (II) metal ion based on thiocyanate and azide ligands: Synthesis, spectroscopic studies, DFT calculations and antibacterial assays  

NASA Astrophysics Data System (ADS)

Zinc (II) complexes with non-steroidal anti-inflammatory drugs (NSAIDs) naproxen (nap) and ibuprofen (ibu) were synthesized in the presence of nitrogen donor ligands (thiocyanate or azide). The complexes were characterized by elemental analysis, FT-IR, 1H NMR and UV-Vis spectroscopes. The binding modes of the ligands in complexes were established by means of molecular modeling of the complexes, and calculation of their IR, NMR and absorption spectra at DFT (TDDFT)/B3LYP level were studied. The experimental and calculated data verified monodentate binding through the carboxylic oxygen atoms of anti-inflammatory drugs in the zinc complexes. The calculated 1H, FT-IR and UV-Vis data are in better agreement with the experimental results, and confirm the predicted tetrahedral structures for the Zn (II) complexes. In addition to DFT calculations of complexes, natural bond orbital (NBO) was performed at B3LYP/6-31+G(d,p) level of theory. Biological studies showed the antibacterial activity of zinc complexes against Gram-positive and Gram-negative bacterial strains.

Chiniforoshan, Hossein; Tabrizi, Leila; Hadizade, Morteza; Sabzalian, Mohammad R.; Chermahini, Alireza Najafi; Rezapour, Mehdi

2014-07-01

364

Interplay of metalloligand and organic ligand to tune micropores within isostructural mixed-metal organic frameworks (M'MOFs) for their highly selective separation of chiral and achiral small molecules.  

PubMed

Four porous isostructural mixed-metal-organic frameworks (M'MOFs) have been synthesized and structurally characterized. The pores within these M'MOFs are systematically tuned by the interplay of both the metalloligands and organic ligands which have enabled us not only to direct their highly selective separation of chiral alcohols 1-phenylethanol (PEA), 2-butanol (BUT), and 2-pentanol (2-PEN) with the highest ee up to 82.4% but also to lead highly selective separation of achiral C(2)H(2)/C(2)H(4) separation. The potential application of these M'MOFs for the fixed bed pressure swing adsorption (PSA) separation of C(2)H(2)/C(2)H(4) has been further examined and compared by the transient breakthrough simulations in which the purity requirement of 40 ppm in the outlet gas can be readily fulfilled by the fixed bed M'MOF-4a adsorber at ambient conditions. PMID:22545712

Das, Madhab C; Guo, Qunsheng; He, Yabing; Kim, Jaheon; Zhao, Cong-Gui; Hong, Kunlun; Xiang, Shengchang; Zhang, Zhangjing; Thomas, K Mark; Krishna, Rajamani; Chen, Banglin

2012-05-23

365

Nonrotating, self-centering anchor assembly for anchoring a bolt in a borehole  

SciTech Connect

An expandable anchor assembly is provided for anchoring the threaded end portion of an elongated roof bolt in a borehole. The anchoring assembly includes a hollow outer sleeve in the form of a plurality of symmetrically arranged, longitudinal segmented wall portions with exterior gripping teeth and an inner expander sleeve in the form of a corresponding plurality of longitudinal wall portions symmetrically arranged about a central axis to define an inner threaded cylindrical section. The inner sleeve is captured within and moveable axially relative to the outer sleeve. As the threaded end portion of the elongated bolt is inserted into the inner threaded cylindrical section of the inner sleeve from the trailing end to the leading end thereof, the inner sleeve expands over and clamps around the threaded end portion of the elongated bolt. Thereafter, partial withdrawal of the elongated bolt from the borehole causes the inner sleeve to axially move relative to the outer sleeve from the leading end toward the trailing end of the outer sleeve in a wedging action to cause the outer sleeve to radially expand and force engagement of the gripping teeth against the sidewall of the borehole to thereby secure the expandable anchor assembly and therewith the threaded end portion of the elongated bolt within the borehole.

Bevan, John E.; King, Grant W.

1997-12-01

366

Use of lug anchors to related pavement movement  

NASA Astrophysics Data System (ADS)

Minnesota Department of Transporatation's policy is that grades in the 3 to 5 percent and greater range are steep and may require lug anchors. Standard lug anchor spacing varies from 150 feet, center to center, for 3 percent grades to 75 feet, center to center, for 5 percent and greater grades. Conclusions are: (1) that lug anchors do prevent the downhill movement of the concrete pavement; (2) that when lug anchors are used a perforated pipe system also be built to collect the surface water that enters the pavement structure thus eliminating the anticipated base pumping and pavement settlement.

Oakey, S. A.

1980-04-01

367

Functional convergence of signalling by GPI-anchored and anchorless forms of a salamander protein implicated in limb regeneration.  

PubMed

The GPI-anchor is an established determinant of molecular localisation and various functional roles have been attributed to it. The newt GPI-anchored three-finger protein (TFP) Prod1 is an important regulator of cell behaviour during limb regeneration, but it is unclear how it signals to the interior of the cell. Prod1 was expressed by transfection in cultured newt limb cells and activated transcription and expression of matrix metalloproteinase 9 (MMP9) by a pathway involving ligand-independent activation of epidermal growth factor receptor (EGFR) signalling and phosphorylation of extracellular regulated kinase 1 and 2 (ERK1/2). This was dependent on the presence of the GPI-anchor and critical residues in the ?-helical region of the protein. Interestingly, Prod1 in the axolotl, a salamander species that also regenerates its limbs, was shown to activate ERK1/2 signalling and MMP9 transcription despite being anchorless, and both newt and axolotl Prod1 co-immunoprecipitated with the newt EGFR after transfection. The substitution of the axolotl helical region activated a secreted, anchorless version of the newt molecule. The activity of the newt molecule cannot therefore depend on a unique property conferred by the anchor. Prod1 is a salamander-specific TFP and its interaction with the phylogenetically conserved EGFR has implications for our view of regeneration as an evolutionary variable. PMID:21118959

Blassberg, Robert A; Garza-Garcia, Acely; Janmohamed, Azara; Gates, Phillip B; Brockes, Jeremy P

2011-01-01

368

Image compression quality rating using anchored scales  

NASA Astrophysics Data System (ADS)

Traditional image quality rating schemes use descriptive scales applicable to wide ranges of quality. These scales, based on equal interval verbal descriptors, cannot be used for restricted ranges of quality now encountered in image compression studies. Although numerical category scales have been successfully used in some studies for quantifying small variations in quality arising from lossy image compression, problems arise in more general image coding applications. In this work, we propose a double anchored numerical category scale based on a 3-context visual assessment scheme for image coding applications. The goal is to devise a common subjective scale applicable to a set of images produced from multiple scenes compressed by multiple coding algorithms. Therefore, the contexts are in the use of distinct coders and distinct images. The first two contexts, using a specific image scene, are the visibility of specific coder induced artifacts and the visibility of artifacts arising from different coders. In the third context, the artifact visibility is in terms of the content of different image scenes. Separate scales are obtained for images differing in scene content and for each coding algorithm, using numerical category scaling with explicit high and low anchors. These scales are linked using pairwise matching techniques to obtain a robust image quality sale.

Avadhanam, Niranjan; Algazi, V. Ralph

1998-04-01

369

Self-assembly of three d10 metal coordination polymers based on a flexible bis(2-methylbenzimidazole) and dicarboxylate co-ligands  

NASA Astrophysics Data System (ADS)

Hydrothermal self-assembly of zinc nitrate with 1,1?-(1,3-propane)bis-(2-methylbenzimidazole) (pbmb) and different dicarboxylic acid ligands gave rise to three new coordination polymers [Zn(pbmb)(hmph)]n (1), {[Zn2(pbmb)(chdc)2]?0.5H2O}n (2), [Zn(pbmb)(mip)]n (3) (H2hmph = homophthalic acid, H2chdc = 1,4-cyclohexanedicarboxylic acid and H2mip = 5-methylisophthalic acid). Both complexes 1 and 3 possess 2D {63} framework and further extend into 3D supramolecular network via Csbnd H⋯O hydrogen bonding or ?-? stack interactions. While 2 is a 1D double loop-like chain structure, which arranged into a 2D network through Csbnd H⋯O hydrogen bonding interactions. Three compounds all exhibit strong photoluminescence at room temperature in solid state and may be good candidates for potential luminescence materials.

Hao, Jin-ming; Zhao, Ying-na; Yang, Rui; Cui, Guang-hua

2014-07-01

370

The history and development of English anchors ca. 1550- to 1850  

E-print Network

technology, there were radical changes in the design of anchors. These anchors were different in their design, being stockless anchors made of cast iron, instead of the earlier wrought iron anchors.This thesis examines the small changes that the anchor...

Jobling, Harold James Williamson

2012-06-07

371

Experimental and Theoretical Investigations of Anion-pi Interactions Metallacyclic Architectures of First-Row Transition Metals and N-Heteroaromatic Ligands  

E-print Network

metallacycles. The extension of metallacycles of bptz to CoII and FeII demonstrates the ability to tune the size of the metallacyclic cavity by simply changing the metal ion and results in the surprising encapsulation of two [SbF6]- anions in [Fe5(bptz)5(NCCH3...

Giles, Ian

2012-07-16

372

Ferrocene phosphane-heteroatom/carbon bidentate ligands in asymmetric catalysis.  

PubMed

Chiral ferrocene derivatives belong to privileged ligand classes for asymmetric transition metal catalysed reactions. Hetero-bidentate phosphane ligands are hybrid ligands, which combine the properties of phosphorus with those of other donor atoms. This feature creates further asymmetry around the metal centre, which may be helpful for increasing the stereoinduction. Therefore, hetero-bidentate ligands are useful alternatives to homo-bidentate ligands. Ligands featuring phosphorus and nitrogen or sulphur are quite common. From among ferrocene catalysts, ferrocenyl amino phosphanes and phosphane oxazolines serve as excellent examples. Fesulphos and ThioClickFerrophos are notable P,S-ligand examples. On the other hand, combinations of phosphorus with oxygen or carbon are only beginning to show their potential in asymmetric catalysis. Another useful feature in ligands of this type is the markedly different coordination properties of donor atoms, resulting in interesting opportunities for catalysis. Ferrocenyl MOP-analogues or a fascinating combination of phosphane and secondary phosphane-oxide would represent this ligand class. The last section of the review focuses on phosphanes combined with carbon-based donor atoms that are phosphane-alkene and phosphane-carbene ligands. This review focuses on the applications of these hetero-bidentate ferrocene ligands in asymmetric catalysis with a special emphasis on the most recent and influential literature reports. PMID:25307172

Toma, Stefan; Csizmadiová, Jana; Me?iarová, Mária; Sebesta, Radovan

2014-10-22

373

Stability and structure of mixed-ligand metal ion complexes that contain Ni2+, Cu2+, or Zn2+, and Histamine, as well as adenosine 5'-triphosphate (ATP4-) or uridine 5'-triphosphate (UTP(4-): an intricate network of equilibria.  

PubMed

With a view on protein-nucleic acid interactions in the presence of metal ions we studied the "simple" mixed-ligand model systems containing histamine (Ha), the metal ions Ni(2+), Cu(2+), or Zn(2+) (M(2+)), and the nucleotides adenosine 5'-triphosphate (ATP(4-)) or uridine 5'-triphosphate (UTP(4-)), which will both be referred to as nucleoside 5'-triphosphate (NTP(4-)). The stability constants of the ternary M(NTP)(Ha)(2-) complexes were determined in aqueous solution by potentiometric pH titrations. We show for both ternary-complex types, M(ATP)(Ha)(2-) and M(UTP)(Ha)(2-), that intramolecular stacking between the nucleobase and the imidazole residue occurs and that the stacking intensity is approximately the same for a given M(2+) in both types of complexes: The formation degree of the intramolecular stacks is estimated to be 20 to 50%. Consequently, in protein-nucleic acid interactions imidazole-nucleobase stacks may well be of relevance. Furthermore, the well-known formation of macrochelates in binary M(2+) complexes of purine nucleotides, that is, the phosphate-coordinated M(2+) interacts with N7, is confirmed for the M(ATP)(2-) complexes. It is concluded that upon formation of the mixed-ligand complexes the M(2+)-N7 bond is broken and the energy needed for this process corresponds to the stability differences determined for the M(UTP)(Ha)(2-) and M(ATP)(Ha)(2-) complexes. It is, therefore, possible to calculate from these stability differences of the ternary complexes the formation degrees of the binary macrochelates: The closed forms amount to (65±10)%, (75±8)%, and (31±14)?% for Ni(ATP)(2-), Cu(ATP)(2-), and Zn(ATP)(2-), respectively, and these percentages agree excellently with previous results obtained by different methods, confirming thus the internal validity of the data and the arguments used in the evaluation processes. Based on the overall results it is suggested that M(ATP)(2-) species, when bound to an enzyme, may exist in a closed macrochelated form only, if no enzyme groups coordinate directly to the metal ion. PMID:21465580

Knobloch, Bernd; Mucha, Ariel; Operschall, Bert P; Sigel, Helmut; Je?owska-Bojczuk, Ma?gorzata; Koz?owski, Henryk; Sigel, Roland K O

2011-05-01

374

Tether-supported biomembranes with ?-helical peptide-based anchoring constructs.  

PubMed

The strict requirement of constructing a native lipid environment to preserve the structure and functionality of membrane proteins is the starting constraint when building biomaterials and sensor systems from these biomolecules. To enhance the viability of supported biomembranes systems and build new ligand display interfaces, we apply rationally designed peptides partitioned into the lipid bilayer interface. Peptides designed to form membrane-spanning ?-helical anchoring domains are synthesized using solid-phase peptide synthesis. K(3)A(4)L(2)A(7)L(2)A(3)K(2)-FITC is synthesized on the 100 mg scale for use as a biomembrane anchoring molecule, where orthogonal side-chain modifications allow us to introduce probes enabling peptide localization within supported bilayers. The peptides are found to form ?-helical domains within liposomes as assessed with circular dichroism spectroscopy. These peptides are designed to be incorporated into lipid bilayers supported by microspheres and serve as biomembrane anchoring moieties to amino-terminated surfaces. Here, the silica bead surface (4.7 ?m diameter) is activated with homobifunctional NHS-PEG(3000)-NHS as "polymer cushion" spacers. This tethering to a subset of the K(3)A(4)L(2)A(7)L(2)A(3)K(2)-FITC molecules present in the bilayer is achieved by the fusion of liposomes followed by coupling of the peptide amino groups to the NHS presented from the silica microsphere surfaces. The biomembrane distributions of tethered and untethered K(3)A(4)L(2)A(7)L(2)A(3)K(2)-FITC are probed with confocal microscopy and are found to give 3D reconstructions consistent with largely homogeneous supported biomembranes. The fluidity of the untethered fraction of peptides within supported membranes is quantified using the fluorescence recovery after photobleaching (FRAP) technique. The presence of the PEG(3000) polymer cushion facilitated a 28.9% increase in peptide diffusivity over untethered bilayers at the lowest peptide to lipid ratio we examined. We show that rationally designed peptide-based anchors can be used to tether lipid bilayers, creating a polymer-cushioned lipid microenvironment on surfaces with high lateral mobility and facilitating the development of a new platform for ligand displays. PMID:23190371

Zhong, Lina; Tu, Raymond; Gilchrist, M Lane

2013-01-01

375

Comprehensive Analysis of Glycosylphosphatidylinositol-Anchored Proteins in Candida albicans  

Microsoft Academic Search

There are two types of membrane proteins: the integral membrane proteins and the lipid-anchored proteins. Integral membrane proteins contain one or several transmembrane do- mains that allow for the formation of hydrophobic -helices, which ultimately embed the protein in a lipid bilayer. We count four types of lipid-anchored proteins divided into two groups: one group generally links the proteins to

Mathias L. Richard; Armel Plaine

2007-01-01

376

Pubovaginal Sling Using Polypropylene Mesh and Vesica Bone Anchors  

Microsoft Academic Search

Objectives. To report preliminary results from a modified pubovaginal sling procedure using polypropylene mesh as the sling suspended by nonabsorbable sutures anchored to the pubic tubercle with Vesica bone anchors.Methods. Thirty-five women with type III stress urinary incontinence (SUI) (with or without associated urethral hypermobility) or type II SUI with additional risk factors such as obesity, chronic obstructive pulmonary disease,

David Hom; Michael G Desautel; Jeffrey H Lumerman; Roy E Feraren; Gopal H Badlani

1998-01-01

377

A-kinase-anchoring Lorene K. Langeberg and John  

E-print Network

A-kinase-anchoring proteins Lorene K. Langeberg and John D. Scott* Howard Hughes Medical Institute of proteins known as A-kinase- anchoring proteins (AKAPs). AKAPs provide a framework for the coordination of phosphorylation and dephosphorylation events by sequestering enzymes such as protein kinases and phosphatases

Scott, John D.

378

Moody experts --- How mood and expertise influence judgmental anchoring  

Microsoft Academic Search

Anchoring effects, the assimilation of numerical estimates to previously considered standards, are highly robust. Two studies examined whether mood and expertise jointly moderate the magnitude of anchoring. Previous research has demonstrated that happy mood induces judges to process information in a less thorough manner than sad mood, which means that happy judges tend to be more susceptible to unwanted influences.

Birte Englich; Kirsten Soder

2009-01-01

379

Bearing area: a new indication for suture anchor pullout strength?  

PubMed

Studies performed to quantify the pullout strength of suture anchors have not adequately defined the basic device parameters that control monotonic pullout. The bearing area of a suture anchor can be used to understand and predict anchor pullout strength in a soft-bone model. First, conical-shaped test samples were varied in size and shape and tested for pullout in 5, 8, and 10 pcf sawbone models. Next, bearing area and pullout strength relationships developed from the test samples were validated against nine commercially available suture anchors, including the Mitek QuickAnchor and SpiraLok, Opus Magnum(2), ArthroCare ParaSorb, and Arthrex BioCorkscrew. The samples showed a direct correlation between bearing area and pullout strength. Increased insertion depth was a secondary condition that also increased pullout strength. The pullout strength for the suture anchors followed the predicted trends of conical devices based on their individual bearing areas. For the 5 and 8 pcf models, only two and three devices, respectively, fell outside the predicted pullout strength range by more than a standard deviation. The use of a synthetic sawbone model was validated against the pullout strength of an Arthrex Corkscrew in five fresh-frozen cadaver humeral heads. The bearing area of a suture anchor can be used to predict the pullout strength independent of design in a soft-bone model. This work helps provide a foundation to understand the principles that affect the pullout strength of suture anchors. PMID:19226593

Yakacki, Christopher Michael; Griffis, Jack; Poukalova, Mariya; Gall, Ken

2009-08-01

380

Electrically insulated MLI and thermal anchor  

NASA Astrophysics Data System (ADS)

The thermal shield of JT-60SA is kept at 80 K and will use the multilayer insulation (MLI) to reduce radiation heat load to the superconducting coils at 4.4 K from the cryostat at 300 K. Due to plasma pulse operation, the MLI is affected by eddy current in toroidal direction. The MLI is designed to suppress the current by electrically insulating every 20 degree in the toroidal direction by covering the MLI with polyimide films. In this paper, two kinds of designs for the MLI system are proposed, focusing on a way to overlap the layers. A boil-off calorimeter method and temperature measurement has been performed to determine the thermal performance of the MLI system. The design of the electrical insulated thermal anchor between the toroidal field (TF) coil and the thermal shield is also explained.

Kamiya, Koji; Furukawa, Masato; Hatakenaka, Ryuta; Miyakita, Takeshi; Murakami, Haruyuki; Kizu, Kaname; Tsuchiya, Katsuhiko; Koidea, Yoshihiko; Yoshida, Kiyoshi

2014-01-01

381

Silver(I)-directed growth of metal-organic complex nanocrystals with bidentate ligands of hydroquinine anthraquinone-1,4-diyl diethers as linkers at the water-chloroform interface  

NASA Astrophysics Data System (ADS)

Immiscible liquid-liquid interfaces provide unique double phase regions for the design and construction of nanoscale materials. Here, we reported Ag(I)-directed growth of metal-organic complex nanocrystals by using AgNO3 as a connector in the aqueous solution and bidentate ligand of 1,4-bis(9-O-dihydroquininyl)anthraquinone [(DHQ)2AQN] and its enantiomer of (DHQD)2AQN in the chloroform solutions as linkers. The Ag-(DHQ)2AQN and Ag-(DHQD)2AQN complex nanocrystals were formed at the liquid-liquid interfaces and characterized by using UV-vis absorption and fluorescence spectroscopy and X-ray photoelectron spectroscopy, as well as by using scanning electron microscopy. Screw-like nanocrystals were formed at the initial 30 min after the interfacial coordination reaction started, then they grew into nanorods after several days, and finally became cubic microcrystals after 2 weeks. The pure ligand showed two emission bands centered at about 363 and 522 nm in the methanol solution, the second one of which was quenched and shifted to about 470 nm in the Ag-complex nanocrystals. Two couples of reversible redox waves were recorded for the Ag-complex nanocrystals; one centered at about -0.25 V (vs. Ag/AgCl) was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag - (DHQ)2AQN+, and the other one centered at about 0.2 V was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag+ - (DHQ)2AQN.

Tang, Ying; Wang, Hui-Ting; Chen, Meng; Qian, Dong-Jin; Zhang, Li; Liu, Minghua

2014-09-01

382

A set of alkali and alkaline-earth coordination polymers based on the ligand 2-(1H-benzotriazol-1-yl) acetic acid: Effects the radius of metal ions on structures and properties  

NASA Astrophysics Data System (ADS)

Four new metal coordination complexes, namely, [Na(BTA)]n (1), [K2(BTA)2(?2-H2O)]n (2), and [M(BTA)2(H2O)2]n (M=Ca(II) and Sr(II) for 3 and 4, respectively) [BTA=2-(1H-benzotriazol-1-yl) acetic anion], have been obtained under hydrothermal condition, by reacting the different alkali and alkaline-earth metal hydroxides with HBTA. Complexes 1-4 were structurally characterized by X-ray single-crystal diffraction, EA, IR, PXRD, and thermogravimetry analysis (TGA). These complexes display low-dimensional features displaying various two-dimensional (2D) and one-dimensional (1D) coordination motifs. Complex 1 displays a 2D layer with the thickness of 1.5 nm and possesses a topologic structure of a 11 nodal net with Schläfli symbol of {318}. Complex 2 also shows a thick 2D sheet and its topologic structure is a 9 nodes with Schläfli symbol of {311×42}. Complexes 3 and 4 possess a 1D linear chain and further stack via hydrogen bonding interactions to generate a three-dimensional supramolecular architecture. These results suggest that both the coordination preferences of the metal ions and the versatile nature of this flexible ligand play a critical role in the final structures. The luminescent spectra show strong emission intensities in complexes 1-4, which display violet photoluminescence. Additionally, ferroelectric, dielectric and nonlinear optic (NLO) second-harmonic generation (SHG) properties of 2 are discussed in detail.

Wang, Jin-Hua; Tang, Gui-Mei; Qin, Ting-Xiao; Yan, Shi-Chen; Wang, Yong-Tao; Cui, Yue-Zhi; Weng Ng, Seik

2014-11-01

383

Group 3 metal complexes supported by tridentate pyridine- and thiophene-linked bis(naphtholate) ligands: synthesis, structure, and use in stereoselective ring-opening polymerization of racemic lactide and beta-butyrolactone.  

PubMed

Scandium, yttrium and lanthanum amido complexes supported by tridentate bis(ortho-silyl-substituted naphtholate)-donor ligands ({ONO(SiPh3)}(2-) and {ONO(SitBuMe2)}(2-), donor = 2,6-pyridine; {OSO(SiPh3)}(2-), donor = 2,5-thiophene) have been prepared in high yields (72-96%) by reaction of the corresponding pro-ligand {OZO(SiR3)}H(2) and Ln[N(SiHMe(2))(2)](3)(THF)(n) precursor. The solid-state structures of {ONO(SiPh3)}La[N(SiHMe(2))(2)](THF) (3), {ONO(SitBuMe2)}Ln[N(SiHMe(2))(2)](THF) (Ln = Sc, 4; Y, 5) and {OSO(SiPh3)}Ln[N(SiHMe(2))(2)](THF) (Ln = Sc, 7; La, 9) have been determined by single-crystal X-ray diffraction studies. In all five complexes, the naphtholate rings twist in the same direction from the plane of the pyridine or thiophene linker, to give rise to C(s)-symmetric (non crystallographic) structures. Compounds are 1-9 single-site initiators for the ring-opening polymerization (ROP) of racemic lactide (rac-LA) at 20 degrees C, affording poly(lactides)s (PLAs) with relatively narrow polydispersities and molecular weights in good agreement with calculated values. When carried out in THF, the polymerizations afforded heterotactic-enriched PLAs (P(r) up to 0.93), while atactic polymers are formed in toluene. Compounds 1-3 and 7-9, having o-SiPh(3) substituents on the naphtholate rings, are also active for the ROP of racemic beta-butyrolactone at 20-50 degrees C, to form syndiotactic-enriched poly(3-hydroxybutyrate)s (PHBs) (P(r) up to 0.87) when using toluene as the solvent, whereas atactic polymers were obtained in THF. The nature of the metal center (Sc, Y, La), the central linker in the ligand framework (pyridine, thiophene), and the ortho-silyl substituent (SiPh(3), SiMe(2)tBu) significantly affect the degree of stereocontrol in those polymerizations. PMID:20631952

Grunova, Ekaterina; Kirillov, Evgueni; Roisnel, Thierry; Carpentier, Jean-François

2010-08-01

384

Synthesis and chemistry of (Os/sub 3/(CO)/sub 9/(. mu. /sub 3/-CCO))/sup 2 -/. Metal ensemble effects on the reactions of the CCO ligand  

SciTech Connect

The acylation of (Os/sub 3/(CO)/sub 11/)/sup 2 -/ followed by reductive CO cleavage produces (Os/sub 3/(CO)/sub 9/(CCO))/sup 2 -/ (1) which undergoes a variety of reactions on the metal centers or the CCO ligand. Protonation yields (HOs/sub 3/(CO)/sub 9/(CCO))/sup -/ and the previously reported H/sub 2/Os/sub 3/(CO)/sub 9/(CCO). The CCO ligand-centered reactions of 1 are dependent on the presence or absence of CO in the reaction. Hence under a CO atmosphere 1 is attacked by 2 equiv of CH/sub 3/OSO/sub 2/CF/sub 3/ to give the acetylene cluster Os/sub 3/(C-O)/sub 10/(CH/sub 3/C identical with COCH/sub 3/) (4) while in the absence of CO the alkylidyne cluster Os/sub 3/(CO)/sub 9/(..mu../sub 3/-COCH/sub 3/) (3) along with a small amount of 4, is produced. The origins of the reactivity differences between the (M/sub 3/(CO)/sub 9/(CCO))/sup 2 -/ clusters (M = Fe, Ru, Os) were explored from the standpoint of electronic structure and steric accessibility. A single-crystal X-ray structure determination of 1 reveals that the CCO ligand is tilted 26/sup 0/ away from the normal to the Os/sub 3/ plane toward one of the Os atoms. Thus it is structurally similar to (Fe/sub 3/(CO)/sub 9/(CCO))/sup 2 -/ but quite different from (Ru/sub 3/(CO)/sub 9/(CCO))/sup 2 -/. (PPh/sub 4/)/sub 2/(Os/sub 3/(CO)/sub 9/(CCO)) crystallizes in the triclinic space group, P anti 1, with a = 12.762 (2) A, b = 20.447 (5) A, c = 10.779 (2) A, ..cap alpha.. = 97.68 (2)/sup 0/, ..beta.. = 110.33 (2)/sup 0/, and ..gamma.. = 89.27 (2)/sup 0/.

Went, M.J.; Sailor, M.J.; Bogdan, P.L.; Brock, C.P.; Shriver, D.F.

1987-09-30

385

Genetic characterization of the silkworm Bombyx mori by simple sequence repeat (SSR)-anchored PCR  

Microsoft Academic Search

Thirteen diverse strains of the silkworm Bombyx mori were analysed using the simple sequence repeat anchored polymerase chain reaction (SSR-anchored PCR) or Inter-SSR-PCR (ISSR-PCR). A set of four 5¢-anchored and two 3¢-anchored repeat primers amplified a total of 239 bands out of which 184 (77%) were polymorphic. The 5¢-anchored primers revealed more distinct polymorphic markers than the 3¢-anchored primers and

K. DAMODAR REDDY; J. NAGARAJU; E. G. ABRAHAM

1999-01-01

386

Transition Metal Complexes of Cr, Mo, W and Mn Containing {eta}{sup 1}(S)-2,5-Dimethylthiophene, Benzothiophene and Dibenzothiophene Ligands  

SciTech Connect

The UV photolysis of hexanes solutions containing the complexes M(CO){sub 6} (M=Cr, Mo, W) or CpMn(CO){sub 3} (Cp={eta}{sup 5}-C{sub 5}H{sub 5}) and excess thiophene (T{sup *}) (T{sup *}=2,5-dimethylthiophene (2,5-Me{sub 2}T), benzothiophene (BT), and dibenzothiophene (DBT)) produces the {eta}{sup 1}(S)-T{sup *} complexes (CO){sub 5}M({eta}{sup 1}(S)-T{sup *}) 1-8 or Cp(CO){sub 2}Mn({eta}{sup 1}(S)-T{sup *})9-11, respectively. However, when T{sup *}=DBT, and M=Mo, a mixture of two products result which includes the {eta}{sup 1}(S)-DBT complex (CO){sub 5}Mo({eta}{sup 1}(S)-DBT) 4a and the unexpected {pi}-complex (CO){sub 3}Mo({eta}{sup 6}-DBT) 4b as detected by {sup 1}H NMR. The liability of the {eta}{sup 1}(S)-T{sup *} ligands is illustrated by the rapid displacement of DBT in the complex (CO){sub 5}W({eta}{sup 1}(S)-DBT) (1) by THF, and also in the complexes (CO){sub 5}Cr({eta}{sup 1}(S)-DBT) (5) and CpMn(CO){sub 2}({eta}{sup 1}(S)-DBT) (9) by CO (1 atm) at room temperature. Complexes 1-11 have been characterized spectroscopically ({sup 1}H NMR, IR) and when possible isolated as analytically pure solids (elemental analysis, EIMS). Single crystal, X-ray structural determinations are reported for (CO){sub 5}W({eta}{sup 1}(S)-DBT) and Cp(CO){sub 2}Mn({eta}{sup 1}(S)-DBT).

Reynolds, M.

2000-09-21

387

First Principles Density Functional Investigation of Supported Tungsten Cluster (Wn; n = 1 TO 6) on Anchored Graphite (0001) Surface  

NASA Astrophysics Data System (ADS)

Size-selected Wn clusters can be deposited firmly on a graphite (0001) surface using a novel technique, where the positive ions (of the same metal atom species) embedded on the graphite surface by ion implantation, act as anchors. The size selected metal clusters can then soft land on this anchored surface m [Hayakawa et al., 2009]. We have carried out a systematic theoretical study of the adsorption of Wn (n = 1-6) clusters on anchored graphite (0001) surface, using state-of-art spin-polarized density functional approach. In our first-principles calculations, the graphite (0001) surface has been suitably modeled as a slab separated by large vacuum layers. Wn clusters bond on clean graphite (0001) surface with a rather weak Van-der-Waals interaction. However, on the anchored graphite (0001) surface, the Wn clusters get absorbed at the defect site with a much larger adsorption energy. We report here the results of our first-principles investigation of this supported Wn cluster system, along with their reactivity trend as a function of the cluster size (n).

Barman, Sonali; Das, G. P.; Kawazoe, Y.

2013-12-01

388

Transition metal cation separations with a resorcinarene-based amino acid stationary phase.  

PubMed

A resorcinarene-based macrocyclic ligand functionalized with alanine and undecyl groups (AUA) was synthesized and applied to ion chromatographic separations. The selectivity and separation of transition metal ions on a column packed with AUA adsorbed onto 55% cross-linked styrene-divinylbenzene resin are presented. The upper and lower rims of the resorcinarene were modified with amino acids and -C(11)H(23) alkyl chains, respectively. The four carboxylic acid groups on the upper rim act as cation-exchangers while the four -C(11)H(23) alkyl chains serve to anchor the ligand to the resin surface by the hydrophobic effect. A systematic study of the effect of different eluent components including non-metal-chelating (HNO(3)) and chelating acids (oxalic acid, succinic acid, dipicolinic acid, and citric acid) on the retention of transition metal ions was investigated. Six metal ions (Mn(2+), Co(2+), Ni(2+), Cd(2+), Cu(2+), and Zn(2+)) were separated on the AUA column within a reasonable time with a single eluent gradient using oxalic acid. The separation is compared to that obtained using a commercial column containing carboxylic acid functional groups. The AUA column containing four preorganized carboxylic acid groups showed selectivity for Cu(2+) when no chelating eluent was present, a selectivity which was not observed with the comparison column. PMID:23324944

Li, Na; Allen, Lee J; Harrison, Roger G; Lamb, John D

2013-03-01

389

Rational design of class I MHC ligands  

NASA Astrophysics Data System (ADS)

From the knowledge of the three-dimensional structure of a class I MHC protein, several non natural peptides were designed in order to either optimize the interactions of one secondary anchor amino acid with its HLA binding pocket or to substitute the non interacting part with spacer residues. All peptides were synthesized and tested for binding to the class I MHC protein in an in vitro reconstitution assay. As predicted, the non natural peptides present an enhanced binding to the HLA-B27 molecule with respect to their natural parent peptides. This study constitutes the first step towards the rational design of non peptidic MHC ligands that should be very promising tools for the selective immunotherapy of autoimmune diseases.

Rognan, D.; Scapozza, L.; Folkers, G.; Daser, Angelika

1995-04-01

390

Arthroscopic transosseous suture anchor technique for rotator cuff repairs.  

PubMed

The skin is incised 1 to 2 cm distal to the lateral portal. A transosseous tunnel is created through the greater tuberosity by a sharp penetrator, entering 1.5 to 2 cm distal to the top of the greater tuberosity. The penetrator exits medially, between the tip of the greater tuberosity and the articular surface of the humeral head, in the middle of the footprint. The first anchor, a 5-mm Spiralok (DePuy Mitek, Norwood, MA) is placed at the penetrator's exit site on the footprint. Using a specially designed suture leader, the lateral limb of the suture in the anchor, which passes through the previously created transosseous tunnel, is taken from the anchor and pulled out. The other suture end is passed through the supraspinatus tendon. The second suture, placed superficially in the anchor, is passed from the anchor through the supraspinatus tendon, as a mattress suture. If more anchors are required, the procedure should be repeated. The transosseous suture limb and the suture limb that is passed through the supraspinatus tendon are tied through the lateral portal. The knot tying is then performed with a sliding Delimar knot. The mattress suture, passing through the supraspinatus tendon, is tied through the anterior lateral portal. The knot tying procedure is repeated depending on the number of anchors. PMID:16651169

Cicak, Nikola; Klobucar, Hrvoje; Bicanic, Goran; Trsek, Denis

2006-05-01