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1

Luminescence of charge transfer sensitizers anchored to metal oxide nanoparticles  

Microsoft Academic Search

The photoluminescence (PL) properties of inorganic charge transfer sensitizers anchored to nanometer sized metal oxide particles are presented. The charge transfer sensitizers are inorganic coordination compounds such as ruthenium tribipyridine, Ru(bpy)2+3, which have long lived metal-to-ligand charge transfer (MLCT) excited states. The metal oxides are insulators or semiconductor materials in the form of powders, colloidal solutions, and porous nanocrystalline films.

Todd A. Heimer; Gerald J. Meyer

1996-01-01

2

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

3

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

4

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

5

High Catalytic Activity of Chiral Amino Alcohol Ligands Anchored to Polystyrene Resins.  

PubMed

Enantiomerically pure (2S,3S)-2,3-epoxy-3-phenylpropanol (3) has been anchored to Merrifield resins with different degrees of cross-linking and functionalization. The resulting epoxy-functionalized resins 4 have been submitted to completely regioselective (C-3 attack) and stereospecific ring-opening with secondary amines [piperidine (a), N-methylpiperazine (b), and cis-2,6-dimethylpiperidine (c)] in the presence of lithium perchlorate to afford (2R,3R)-3-(dialkylamino)-2-hydroxy-3-phenylpropoxy resin ethers 5a-c. The progress of these two processes has been monitored by (13)C gel-phase NMR spectroscopy. Polymer-supported amino alcohols 5a-c have been evaluated as catalytic ligands in the enantioselective addition of diethylzinc to benzaldehyde, best results being obtained with the cis-2,6-dimethylpiperidine containing ligand 5c. Analogously, (2R,3R)-3-(cis-2,6-dimethylpiperidino)-3-phenyl-1,2-propanediol (11) has been anchored to a 2-chlorotrityl chloride resin (Barlos resin) in dichloromethane in the presence of diisopropylethylamine, and the anchoring process has been also monitored by (13)C gel-phase NMR spectroscopy. The resulting resin 12 has subsequently been used as a chiral ligand in the catalytic addition at 0 degrees C of diethylzinc to a family of fourteen representative aromatic and aliphatic aldehydes 8a-n, to afford the corresponding (S)-1-substituted 1-propanols 10a-n with a mean enantiomeric excess of 92%. PMID:11672264

Vidal-Ferran, Anton; Bampos, Nick; Moyano, Albert; Pericàs, Miquel A.; Riera, Antoni; Sanders, Jeremy K. M.

1998-09-01

6

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

7

Unprecedented hybrid scorpionate/phosphine ligand able to be anchored to carbosilane dendrimers.  

PubMed

The synthesis of a novel hybrid pyrazolate/phosphine anionic ligand [CH2=CHCH2B(CH2PPh2)(pz)2]- is described. Coordination of this ligand to metals in a fac tridentate fashion occurs in the complexes [CH2=CHCH2B(CH2PPh2)(pz)2M(cod)], prepared by reactions of the lithium salt of the ligand with [M(mu-Cl)(cod)]2 (M=Rh, Ir). They are pentacoordinated, with the rhodium complex showing a distorted trigonal-bipyramidal structure in the solid state, as determined by X-ray diffraction methods. Furthermore, the ligand has been linked to the periphery of a carbosilane dendrimer, resulting in the polyanionic dendrimer [Li(TMED)]4[Si{(CH2)3SiMe2(CH2)3B(CH2PPh2)(pz)2}4], which leads further to the corresponding metallodendrimer with four rhodium atoms. PMID:16323887

Casado, Miguel A; Hack, Verena; Camerano, José A; Ciriano, Miguel A; Tejel, Cristina; Oro, Luis A

2005-12-12

8

Nitrenium ions as ligands for transition metals  

NASA Astrophysics Data System (ADS)

Unlike N-heterocyclic carbenes (NHCs), which are now used ubiquitously in metal-based chemistry, the nitrogen-derived analogue (in which a carbon is replaced with the isoelectronic nitrogen cation, a nitrenium ion) has remained elusive as a ligand for metals. This is especially intriguing, because several other main-group analogues of NHCs have been prepared, and have been shown to coordinate with transition-metal complexes. Here, we describe the preparation of several N-heterocyclic nitrenium ions that are isoelectronic and isostructural to NHCs, and study their ligand properties. The formation of relatively strong nitrenium-metal bonds is unambiguously confirmed, in solution by selective 15N-labelling experiments, and in the solid state by X-ray crystallography. Experimental and computational studies of the electronic properties of this novel type of ligand suggest that they are poor ?-donors and good ?-acceptors.

Tulchinsky, Yuri; Iron, Mark A.; Botoshansky, Mark; Gandelman, Mark

2011-07-01

9

Ligand Intermediates in Metal-Catalyzed Reactions  

SciTech Connect

The longest-running goal of this project has been the synthesis, isolation, and physical chemical characterization of homogeneous transition metal complexes containing ligand types believed to be intermediates in the metal-catalyzed conversion of CO/H{sub 2}, CO{sub 2}, CH{sub 4}, and similar raw materials to organic fuels, feedstocks, etc. In the current project period, complexes that contain unusual new types of C{sub x}(carbide) and C{sub x}O{sub y} (carbon oxide) ligands have been emphasized. A new program in homogeneous fluorous phase catalysis has been launched as described in the final report.

Gladysz, John A.

1999-07-31

10

Colloidal Stability of Gold Nanoparticles Coated with Multithiol- Poly(ethylene glycol) Ligands: Importance of Structural Constraints of the Sulfur Anchoring Groups.  

National Technical Information Service (NTIS)

Gold nanoparticles (AuNPs) coated with a series of poly(ethylene glycol) (PEG) ligands appended with four different sulfur-based terminal anchoring groups (monothiol, flexible dithiol, constrained dithiol, disulfide) were prepared to explore how the struc...

A. Johannes A. L. Huston E. Oh J. R. Deschamps K. Susumu

2013-01-01

11

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

12

Rhizofiltration of heavy metals from the tannery sludge by the anchored hydrophyte, Hydrocotyle umbellata L  

Microsoft Academic Search

The anchored hydrophyte, Hydrocotyle umbellata L., was employed for the removal of toxic metals from tannery sludge concentrations (w\\/v) from a tanneries wastewater treatment plant. Different concentrations of wet tannery sludge were prepared and plants of H. umbellata showed a good tolerance for all the prepared concentrations. Plants were retrieved after 30, 60 and 90 days and the sludge concentrations

Sheza Khilji

2008-01-01

13

Very strong metal ligand aromatic cation-? interactions in transition metal complexes: intermolecular interaction in tetraphenylborate salts  

Microsoft Academic Search

Strong intermolecular interactions between ligands in cationic metal complexes and aromatic rings of tetraphenylborate anion, so-called metal ligand aromatic cation-? (MLAC?) interactions, were found by screening Cambridge Structural Database. Distances between phenyl ring and ligand are shorter in these structures than in previously reported MLAC? interactions by 0.2 Å.

Miloš K. Mil?i?; Zoran D. Tomi?; Snežana D. Zari?

2004-01-01

14

Ligand Field Stabilization Control of Metal Ion Binding.  

National Technical Information Service (NTIS)

Specific metal ions bind to particular sites within proteins. The factors that might influence the thermodynamics of metal ion binding to proteins include metal ion radius, hard-soft acid-base effects, and ligand field stabilization energy changes. We hav...

J. M. Berg

1994-01-01

15

How to Compute Labile Metal-Ligand Equilibria  

ERIC Educational Resources Information Center

The different methods used for computing labile metal-ligand complexes, which are suitable for an iterative computer solution, are illustrated. The ligand function has allowed students to relegate otherwise tedious iterations to a computer, while retaining complete control over what is calculated.

de Levie, Robert

2007-01-01

16

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...

17

Multiple Emission in Mixed Ligand Metal Chelates.  

National Technical Information Service (NTIS)

Absorption and emission spectra, lifetimes and quantum yields are reported for mixed ligand chelates of 1,10-phenanthroline and 2,2'-dipyridyl of Rh(III). The mixed ligand complexes, (Rh(phen)2(dip))C3 and (Rh(dip)2(phen))C3, are found to possess more tha...

M. K. DeArmond W. Halper

1972-01-01

18

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

19

Influence of anchoring ligands and particle size on the colloidal stability and in vivo biodistribution of polyethylene glycol-coated gold nanoparticles in tumor-xenografted mice  

Microsoft Academic Search

Polyethylene glycol (PEG)-coated (pegylated) gold nanoparticles (AuNPs) have been proposed as drug carriers and diagnostic contrast agents. However, the impact of particle characteristics on the biodistribution and pharmacokinetics of pegylated AuNPs is not clear. We investigated the effects of PEG molecular weight, type of anchoring ligand, and particle size on the assembly properties and colloidal stability of PEG-coated AuNPs. The

Guodong Zhang; Zhi Yang; Wei Lu; Rui Zhang; Qian Huang; Mei Tian; Li Li; Dong Liang; Chun Li

2009-01-01

20

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

21

Guided ion beam studies of transition metal–ligand thermochemistry  

Microsoft Academic Search

Studies of organometallic chemistry in the gas phase can provide substantial quantitative information regarding the interactions of transition metals with a wide variety of covalently and noncovalently bound ligands. In this review, the technique of guided ion beam tandem mass spectrometry for the measurement of thermodynamic information is highlighted. Periodic trends in covalent bonds between first, second, and a few

P. B. Armentrout

2003-01-01

22

Low symmetry pyrazole-based tripodal tetraamine ligands: metal complexes and ligand decomposition reactions.  

PubMed

The new low symmetry pyrazole-based tripodal tetraamine ligands 2-(1H-pyrazol-1-yl)-N,N-bis(1H-pyrazol-1-ylmethyl)ethanamine (bmpz) and 2-(1H-pyrazol-1-yl)-N-[2-(1H-pyrazol-1-yl)ethyl]-N-(1H-pyrazol-1-ylmethyl)ethanamine (bepz) have been prepared and characterised, as have metal complexes containing these ligands. X-ray crystal structures of [Co(bmpz)Cl](2)[CoCl(4)]·H(2)O, [Co(bmpz)MeCN](ClO(4))(2)·0.13H(2)O, [Zn(bmpz)MeCN](ClO(4))(2)·0.15H(2)O, [Zn(bepz)OH(2)](ClO(4))(2)·0.5H(2)O and [(Co(bepz)Cl)(2)]Cl(2)·6H(2)O confirm coordination of the intact tripodal ligands to the metal ions through all four N atoms. However, attempts to make Cu(2+) complexes containing bmpz and bepz gave, respectively, [Cu(7)Cl(2)]·0.2H(2)O and [Cu(8)Cl(2)] (7 = 1-(1H-pyrazol-1-yl)-N-(1H-pyrazol-1-ylmethyl)ethanamine, 8 = 2-(1H-pyrazol-1-yl)-N-[2-(1H-pyrazol-1-yl)ethyl]ethanamine), complexes containing the tridentate ligands 7 and 8 which are formed by loss of a pyrazolylmethyl arm from the appropriate tripodal ligand. This decomposition reaction occurs in protic solvents both in the presence and absence of metal ions, and is ascribed to the presence of an aminal functionality in the tripodal ligands. A possible mechanism for the decomposition, based on NMR and ESMS data, is suggested. PMID:23192397

Cubanski, John R; Cameron, Scott A; Crowley, James D; Blackman, Allan G

2013-02-14

23

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

24

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

25

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

26

Transition-metal complexes with hydrosulfido and thiophene ligands  

SciTech Connect

The removal of thiophenes and dibenzothiophenes from petroleum by catalytic hydrodesulfurization is becoming increasingly important to fossil fuel processing. The reaction mechanism of this process is proposed to involve thiophene coordination to the metal surface and subsequent hydrogen transfer from a surface hydrosulfido group to the bound substate. Transitional metal complexes with SH or thiophene ligands may be thought of as molecular analogs of these proposed surface species. The reactivity of the metallothiols Cp/sub 2/M(SH)/sub 2/ (M = Ti, W) was found to differ depending on the metal center. While the titanium compound was relatively unreactive, the tungsten complex was readily alkylated with methyl iodide. Cp/sub 2/W(SH)/sub 2/ was also found to react with an isonitrile ligand in the complex (Pd(CH/sub 3/NC)/sub 2/dppe)(PF/sub 6/)/sub 2/ to afford the dithiocarbamate complex (Cp/sub 2/WS/sub 2/CN(H)CH/sub 3/)(PF/sub 6/). This reaction does not occur with uncoordinated methyl isonitrile. The compound Cp/sub 2/Ti(SH)/sub 2/ was found to function as a bidentate donor to molybdenum tetracarbonyl to form the bimetallic species Cp/sub 2/Ti(SH)/sub 2/Mo(CO)/sub 4/. The inversion of the bridging ligands was investigated by DNMR spectroscopy. The reactivity of the dimeric molecule was found to be greater than the monomeric titanium precursor, as evidenced by the ease of alkylation at sulfur.

Ruffing, C.J.

1985-01-01

27

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.

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

2013-01-01

28

Synthesis, structure and reactivity of rare-earth metal complexes containing anionic phosphorus ligands.  

PubMed

A comprehensive review of structurally characterized rare-earth metal complexes containing anionic phosphorus ligands is presented. Since rare-earth elements form hard ions and phosphorus is considered as a soft ligand, the rare-earth metal phosphorus coordination is regarded as a less favorite combination. Three classes of phosphorus ligands, (1) the monoanionic organophosphide ligands (PR2(-)) bearing one negative charge on the phosphorus atom; (2) the dianionic phosphinidene (PR(2-)) and P(3-) ligands; and (3) the pure inorganic polyphosphide ligands (Pn(x-)), are included here. Particular attention has been paid to the synthesis, structure, and reactivity of the rare-earth metal phosphides. PMID:23945727

Li, Tianshu; Kaercher, Sabrina; Roesky, Peter W

2014-01-01

29

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

30

Surface Functionalization of Magnetic Iron Oxide Nanoparticles for MRI Applications - Effect of Anchoring Group and Ligand Exchange Protocol  

PubMed Central

Hydrophobic magnetite nanoparticles synthesized from thermal decomposition of iron salts must be rendered hydrophilic for their application as MRI contrast agents. This process requires refunctionalizing the surface of the nanoparticles with a hydrophilic organic coating such as polyethylene glycol. Two parameters were found to influence the magnetic behavior and relaxivity of the resulting hydrophilic iron oxide nanoparticles: the functionality of the anchoring group and the protocol followed for the functionalization. Nanoparticles coated with PEGs via a catecholate-type anchoring moiety maintain the saturation magnetization and relaxivity of the hydrophobic magnetite precursor. Other anchoring functionalities, such as phosphonate, carboxylate, and dopamine decrease the magnetization and relaxivity of the contrast agent. The protocol for functionalizing the nanoparticles also influences the magnetic behavior of the material. Nanoparticles refunctionalized according to a direct biphasic protocol exhibit higher relaxivity than those refunctionalized according to a two-step procedure which first involves stripping the nanoparticles. This research presents the first systematic study of both the binding moiety and the functionalization protocol on the relaxivity and magnetization of water-soluble coated iron oxide nanoparticles used as MRI contrast agents.

Smolensky, Eric D.; Park, Hee-Yun E.; Berquo, Thelma S.; Pierre, Valerie C.

2011-01-01

31

The mutual influence of ligands in transition metal bis-chelates  

NASA Astrophysics Data System (ADS)

Electronic structure quantum chemical calculations of the Fe(II), Ni(II) and Cu(II) bis-chelate series are reported. The nature of the ligand mutual influence effect on these compounds is elucidated. This effect manifests itself in polarization of metal-ligand bonds. The ligands which have highly covalent bonds with the metal form bonds of even greater covalent character in mixed complexes, whereas bonds for the other ligands become more ionic.

Pilipenko, A. T.; Savransky, L. I.; Zubenko, A. I.; Kobylyashny, V. P.

32

Copper ligands isolated from estuarine water by immobilized metal affinity chromatography: temporal variability and partial characterization  

Microsoft Academic Search

Copper ligands were isolated from estuarine water using immobilized metal affinity chromatography (IMAC). Seasonal and diurnal variation of copper ligand concentrations as measured by IMAC peak areas were determined. Apparent molecular weight and UV-visible spectra of IMAC-isolated ligands were characterized. The effects of sample pH, flow rate, volume and storage (4 °C) on ligand recovery were determined. Removal of ligands

A. S. Gordon; B. J. Dyer; R. A. Kango; J. R. Donat

1996-01-01

33

Coinage metal complexes supported by the tri- and tetraphosphine ligands.  

PubMed

A series of tri- and tetranuclear phosphine complexes of d(10) metal ions supported by the polydentate ligands, bis(diphenylphosphinomethyl)phenylphosphine (PPP) and tris(diphenylphosphinomethyl)phosphine (PPPP), were synthesized. All the compounds under study, [AuM2(PPP)2](3+) (M = Au (1), Cu (2), Ag (3)), [M4(PPPP)2](4+) (M = Ag (4), Au (5)), [AuAg3(PPPP)2](4+) (6), and [Au2Cu2(PPPP)2(NCMe)4](4+) (7), were characterized crystallographically. The trinuclear clusters 1-3 contain a linear metal core, while in the isostructural tetranuclear complexes 4-6 the metal framework has a plane star-shaped arrangement. Cluster 7 adopts a structural motif that involves a digold unit bridged by two arms of the PPPP phosphines and decorated two spatially separated Cu(I) ions chelated by the remaining P donors. The NMR spectroscopic investigation in DMSO solution revealed the heterometallic clusters 2, 3, and 6 are stereochemically nonrigid and undergo reversible metal ions redistribution between several species, accompanied by their solvation-desolvation. The complexes 1-3 and 5-7 exhibit room temperature luminescence in the solid state (?em = 6-64%) in the spectral region from 450 to 563 nm. The phosphorescence observed originates from the triplet excited states, determined by the metal cluster-centered d?* ? p? transitions. PMID:24750114

Dau, Minh Thuy; Shakirova, Julia R; Karttunen, Antti J; Grachova, Elena V; Tunik, Sergey P; Melnikov, Alexey S; Pakkanen, Tapani A; Koshevoy, Igor O

2014-05-01

34

Chemical implications of incompatible ligand versus metal coordination geometry preferences.  

PubMed

Binding an electron deficient pincer ligand which strongly dictates planar, mer stereochemistry, to a metal which prefers tetrahedral structure, e.g., d(10) CuCl, is explored for possible intramolecular redox chemistry. Experiment shows that the pincer ligand 2,2'-bis-tetrazinyl pyridine, btzp, forms a complex (btzp)CuCl which is a chloride-bridged polymer in the solid state, hence with 20 valence electrons around copper. DFT calculations show that even the monomer has nonplanar copper with the tetrazinyl nitrogen lone pairs somewhat misdirected away from copper, with long Cu/N bonds, in a singlet ground state; 13.9 kcal/mol less stable is a triplet, whose electronic structure shows one electron from the ground state Cu(I) has been transferred to a pincer ?* orbital. Outer sphere electron transfer to (btzp)CuCl yields (btzp)Cu where the added electron has gone into the pincer, to leave a ligand-centered radical, characterized by EPR, chemical reactivity, and X-ray photoelectron spectroscopy. PMID:24601536

Hui, Alice K; Losovyj, Yaroslav; Lord, Richard L; Caulton, Kenneth G

2014-03-17

35

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

Microsoft Academic Search

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

Adalto Bianchini; Karl C Bowles

2002-01-01

36

Transition-metal phosphors with cyclometalating ligands: fundamentals and applications.  

PubMed

One goal of this critical review is to provide advanced methodologies for systematic preparation of transition-metal based phosphors that show latent applications in the field of organic light emitting diodes (OLEDs). We are therefore reviewing various types of cyclometalating chelates for which the favorable metal-chelate bonding interaction, on the one hand, makes the resulting phosphorescent complexes highly emissive in both fluid and solid states at room temperature. On the other hand, fine adjustment of ligand-centered pi-pi* electronic transitions allows tuning of emission wavelength across the whole visible spectrum. The cyclometalating chelates are then classified according to types of cyclometalating groups, i.e. either aromatic C-H or azolic N-H fragment, and the adjacent donor fragment involved in the formation of metallacycles; the latter is an N-containing heterocycle, N-heterocyclic (NHC) carbene fragment or even diphenylphosphino group. These cyclometalating ligands are capable to react with heavy transition-metal elements, namely: Ru(II), Os(II), Ir(III) and Pt(II), to afford a variety of highly emissive phosphors, for which the photophysical properties as a function of chelate or metal characteristics are systematically discussed. Using Ir(III) complexes as examples, the C--N chelates possessing both C-H site and N-heterocyclic donor group are essential for obtaining phosphors with emission ranging from sky-blue to saturated red, while the N--N chelates such as 2-pyridyl-C-linked azolates are found useful for serving as true-blue chromophores due to their increased ligand-centered pi-pi* energy gap. Lastly, the remaining NHC carbene and benzyl phosphine chelates are highly desirable to serve as ancillary chelates in localizing the electronic transition between the metal and remaining lower energy chromophoric chelates. As for the potential opto-electronic applications, many of them exhibit remarkable performance data, which are convincing to pave a broad avenue for further development of all types of phosphorescent displays and illumination devices (94 references). PMID:20111785

Chi, Yun; Chou, Pi-Tai

2010-02-01

37

De novo design of ligands for metal separation. 1998 annual progress report  

SciTech Connect

'Develop computer-aided molecular design technology for ligands useful in metal separations. This includes force field parameterization of different metals in various oxidation states and de novo design of ligands optimized for specific metals including constriants to certain chemical classes of ligands. This report summarizes year two of a 3-year project and focuses on force field parameterization. Work continues on the modification of algorithms to construct metal-binding ligands from molecular fragments. The lack of an appropriate theoretically derived functional form for d-orbitals in molecular mechanics has hampered efforts to utilize these programs and the efforts have focused on correcting this deficiency.'

Marshall, G.R.

1998-06-01

38

A direct anchoring of Anderson-type polyoxometalates in aqueous media with tripodal ligands especially containing the carboxyl group.  

PubMed

Polyoxometalate-based organic-inorganic hybrids were synthesized by direct modification of the parent Anderson cluster with both the traditional tripodal ligand, CH3C(CH2OH)3, and a novel one containing a carboxyl group, CH3C(CH2OH)2(COOH), which was inaccessible from the traditional self-assembly protocol. PMID:24356499

Zhang, Jiangwei; Huang, Yichao; Zhang, Jin; She, Shan; Hao, Jian; Wei, Yongge

2014-02-21

39

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

40

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

41

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

42

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.

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

2011-01-01

43

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

44

Reactions at interfaces: oxygenation of n-butyl ligands anchored on silica surfaces with methyl(trifluoromethyl)dioxirane.  

PubMed

The oxygenation of n-butyl and n-butoxy chains bonded to silica with methyl(trifluoromethyl)dioxirane (1) revealed the ability of the silica matrix to release electron density toward the reacting C(2)-H ?-bond through the Si-C(1) and Si-O(1) ?-bonds connecting the alkyl chain to the surface (silicon ?-effect). The silica surface impedes neither the alkyl chain adopting the conformation required for the silicon ?-effect nor dioxirane 1 approaching the reactive C(2) methylene group. Reaction regioselectivity is insensitive to changes in the solvation of the reacting system, the location of organic ligands on the silica surface, and the H-bonding character of the silica surface. Reaction rates are faster for those organic ligands either within the silica pores or bonded to hydrophilic silica surfaces, which evidence the enhanced molecular dynamics of confined dioxirane 1 and the impact of surface phenomena on the reaction kinetics. The oxygenation of n-butyl and n-butoxy chains carrying trimethylsilyl, trimethoxysilyl, and tert-butyl groups with dioxirane 1 under homogeneous conditions confirms the electronic effects of the silyl substituents and the consequences of steric hindrance on the reaction rate and regioselectivity. Orthosilicic acid esters react preferentially at the methylene group adjacent to the oxygen atom in clear contrast with the reactivity of the carboxylic or sulfonic acid alkyl esters, which efficiently protect this position toward oxidation with 1. PMID:22066821

Mello, Rossella; Martínez-Ferrer, Jaime; Alcalde-Aragonés, Ana; Varea, Teresa; Acerete, Rafael; González-Núñez, María Elena; Asensio, Gregorio

2011-12-16

45

New Proton-Ionizable, Calixarene-Based Ligands for Selective Metal Ion Separations  

SciTech Connect

The project objective was the discovery of new ligands for performing metal ion separations. The research effort entailed the preparation of new metal ion complexing agents and polymers and their evaluation in metal ion separation processes of solvent extraction, synthetic liquid membrane transport, and sorption. Structural variations in acyclic, cyclic, and bicyclic organic ligands were used to probe their influence upon the efficiency and selectivity with which metal ion separations can be performed. A unifying feature of the ligand structures is the presence of one (or more) side arm with a pendent acidic function. When a metal ion is complexed within the central cavity of the ligand, ionization of the side arm(s) produces the requisite anion(s) for formation of an overall electroneutral complex. This markedly enhances extraction/transport efficiency for separations in which movement of aqueous phase anions of chloride, nitrate, or sulfate into an organic medium would be required. Through systematic structural variations, new ligands have been developed for efficient and selective separations of monovalent metal ions (e.g., alkali metal, silver, and thallium cations) and of divalent metal ion species (e.g., alkaline earth metal, lead, and mercury cations). Research results obtained in these fundamental investigations provide important insight for the design and development of ligands suitable for practical metal ion separation applications.

Bartsch, Richard A.

2012-06-04

46

Coordination chemistry of transition metal complexes of a novel pentadentate ligand  

Microsoft Academic Search

The pentadentate ligand N-(2-pyridylmethyl)-3-(bis(2-pyridylmethyl)amine)-propanamide (LH) and transition metal complexes hereof were synthesised. The negative charge of the deprotonated ligand was meant to stabilise metal ions in high oxidation states thus facilitating aerobic oxidation of the metal centre. 1H NMR studies and X-ray crystallography showed that the Co(III)–OAc complex of LH (1) adopts the same structure in solution as in the

Christian Klarner Sams; Fernando Somoza; Ivan Bernal; Hans Toftlund

2001-01-01

47

Antimicrobial Activity of Metal & Metal Oxide Nanoparticles Interfaced With Ligand Complexes Of 8-Hydroxyquinoline And ?-Amino Acids  

NASA Astrophysics Data System (ADS)

Antimicrobial nanotechnology is a recent addition to the fight against disease causing organisms, replacing heavy metals and toxins. In the present work, mixed ligand complexes of metals like zinc, silver etc. and metal oxide have been synthesized using 8-hydroxyquinoline (HQ) as a primary ligand and N-and/O-donor amino acids such as L-serine, L-alanine, glycine, cysteine and histidine as secondary ligands. These complexes were characterized using different spectroscopic techniques. The complexes were tested for antifungal and antibacterial activity by using agar well diffusion bioassay.

Bhanjana, Gaurav; Kumar, Neeraj; Thakur, Rajesh; Dilbaghi, Neeraj; Kumar, Sandeep

2011-12-01

48

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

49

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

50

Weak alkali and alkaline earth metal complexes of low molecular weight ligands in aqueous solution  

Microsoft Academic Search

This work is aimed at reviewing the chemical literature dealing with thermodynamic aspects of the weak complex formation (species with logK values less than about 3) between alkali and alkaline earth metal ions with low molecular weight inorganic and organic ligands in aqueous solution. The following ligands (up to hexavalent anions) were examined in detail: (i) hydroxide, chloride, sulfate, carbonate

Pier G. Daniele; Claudia Foti; Antonio Gianguzza; Enrico Prenesti; Silvio Sammartano

2008-01-01

51

Neutral and zwitterionic group 4 metal alkyls with ancillary boroxide ligands.  

PubMed

The boroxide anion, [OB(mes)(2)](-), has been applied as an ancillary ligand to generate electron-deficient group 4 metal alkyls; however, the enhanced electrophilicity results in formation of tight ion-pairs in solution. PMID:15510256

Cole, Sarah C; Coles, Martyn P; Hitchcock, Peter B

2004-11-01

52

Synthesis and characterization of polystyrene-anchored monobasic bidentate Schiff base and its complexes with bi-, tri-, tetra- and hexavalent metal ions  

Microsoft Academic Search

A new monobasic bidentate ON donor Schiff base PS–LH2 (where PS–LH2 = polystyrene-anchored Schiff base obtained by condensation of chloromethylated polystyrene (containing 1.17 mmol of chlorine per gram of resin cross-linked with 2% divinylbenzene), 2-hydroxy-1-naphaldehyde and 4-aminosalicylic acid has been synthesized. PS–LH2 reacts with metal complexes to form polystyrene-anchored complexes: PS–LHM(CH3Coo) · DMF (where M = Cu, Zn, Cd, UO2),

D. Kumar; A. Syamal; L. K. Sharma

2008-01-01

53

Chiral induction from ligands to metal centres. A copper(II)–nitroxide complex  

Microsoft Academic Search

Copper(II) complexes of a racemic mixture of a chiral nitronyl-nitroxide are characterised. One, A, is a centro-symmetrical species where two enantiomers are coordinated to a metal centre. The second, B, is a 1D compound comprising bridging ligands through the oxyl and pyridyl donor sites. One observes that, although the crystals are racemic, within a chain, all ligands and metal centres

Victor Ovcharenko; Galina Romanenko; Yuri Shvedenkov

2001-01-01

54

A rare ether-bridged cobalt complex which gives rise to an unusual 'serpentine' metal-ligand binding motif.  

PubMed

An unusual metal-ligand binding motif is found in dimeric cobalt(II) complexes coordinated by diamidoether ligands that bridge the metals in a 'serpentine' fashion through the ether donors of the ligand backbone rather than the amido groups. PMID:12536781

Mund, Garry; Gabert, Andrea J; Batchelor, Raymond J; Britten, James F; Leznoff, Daniel B

2002-12-21

55

New homoleptic carbene transfer ligands and related coinage metal complexes  

Microsoft Academic Search

The synthesis, spectroscopic and structural characterization of the carbene ligand precursor bis(4-benzyl-1,2,4-triazol-4-ium-1-yl)dihydroborate has been described. Treatment with Ag2O leads to the silver(I) complex of the new monoanionic bis(4-benzyl-1,2,4-triazol-5-ylidene-1-yl)dihydroborate dicarbene ligand. The resulting dimetallacycle carbene complex has been used to synthesize the homoleptic gold(I) complex by transmetallation reaction.

Grazia Papini; Giuliano Bandoli; Alessandro Dolmella; Giancarlo Gioia Lobbia; Maura Pellei; Carlo Santini

2008-01-01

56

Mixed-ligand catalysts: a powerful tool in transition-metal- catalyzed cross-coupling reactions.  

PubMed

Transition-metal-catalyzed cross-coupling reactions have fundamentally revolutionized organic synthesis, empowering the otherwise difficult to achieve products with rapid and convenient accesses alongside excellent yields. Within these reactions, ligands often play a critical role in specifically and effectively advocating the corresponding catalysis. Consequently, a myriad of ligands have been created and applied to make a fine tuning of electronic and steric effect of catalysts, remarkably promoting catalytic efficiency and applicability. The "mixed-ligand" concept has recently emerged; by combining and capitalizing on the superiority of each individual ligand already available, an expedient way can be achieved to reach a larger extent of catalytic diversity and efficacy. Given the availability of a wealth of ligands, it is reasonable to have great expectations for the original application of mixed-ligand catalytic systems and their important value in organic synthesis. PMID:24677584

Fan, Yuting; Cong, Mei; Peng, Ling

2014-03-01

57

Synthesis and antimalarial activity of metal complexes of cross-bridged tetraazamacrocyclic ligands.  

PubMed

Using transition metals such as manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II), several new metal complexes of cross-bridged tetraazamacrocyclic chelators namely, cyclen- and cyclam-analogs with benzyl groups, were synthesized and screened for in vitro antimalarial activity against chloroquine-resistant (W2) and chloroquine-sensitive (D6) strains of Plasmodium falciparum. The metal-free chelators tested showed little or no antimalarial activity. All the metal complexes of the dibenzyl cross-bridged cyclam ligand exhibited potent antimalarial activity. The Mn(2+) complex of this ligand was the most potent with IC50s of 0.127 and 0.157?M against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) P. falciparum strains, respectively. In general, the dibenzyl hydrophobic ligands showed better anti-malarial activity compared to the activity of monobenzyl ligands, potentially because of their higher lipophilicity and thus better cell penetration ability. The higher antimalarial activity displayed by the manganese complex for the cyclam ligand in comparison to that of the cyclen, correlates with the larger pocket of cyclam compared to that of cyclen which produces a more stable complex with the Mn(2+). Few of the Cu(2+) and Fe(2+) complexes also showed improvement in activity but Ni(2+), Co(2+) and Zn(2+) complexes did not show any improvement in activity upon the metal-free ligands for anti-malarial development. PMID:24857776

Hubin, Timothy J; Amoyaw, Prince N-A; Roewe, Kimberly D; Simpson, Natalie C; Maples, Randall D; Carder Freeman, TaRynn N; Cain, Amy N; Le, Justin G; Archibald, Stephen J; Khan, Shabana I; Tekwani, Babu L; Khan, M O Faruk

2014-07-01

58

PREDICTING SEDIMENT METAL TOXICITY USING A SEDIMENT BIOTIC LIGAND MODEL: METHODOLOGY AND INITIAL APPLICATION  

EPA Science Inventory

An extension of the simultaneously extracted metals/acid-volatile sulfide (SEM/AVS) procedure is presented that predicts the acute and chronic sediment metals effects concentrations. A biotic ligand model (BLM) and a pore water?sediment partitioning model are used to predict the ...

59

New quadridentate ONNS ligands and their metal complexes  

Microsoft Academic Search

Summary Two new quadridentate sulphur-nitrogen chelating agents have been prepared and characterized. These ligands yield stable complexes of general formulae, M(ONNS)·xH2O (M=Ni, Cu, Zn, Cd, Pd and Pt; ONNS-2=ligand dianion; x=0, 1 or 2) and M(ONNS)X (M=Co or Fe; X=Cl or AcO). The nicke(II) complexes are diamagnetic and squareplanar. Based on magnetic and spectral data a square-planar structure is also

Mohammed Nazimuddin; Mohammed Akbar Ali; Frank E. Smith

1991-01-01

60

Terphenyl complexes of molybdenum and tungsten with quadruple metal-metal bonds and bridging carboxylate ligands.  

PubMed

Mono- and bis-terphenyl complexes of molybdenum and tungsten with general composition M2(Ar')(O2CR)3 and M2(Ar')2(O2CR)2, respectively (Ar' = terphenyl ligand), that contain carboxylate groups bridging the quadruply bonded metal atoms, have been prepared and structurally characterized. The new compounds stem from the reactions of the dimetal tetracarboxylates, M2(O2CR)4 (M = Mo, R = H, Me, CF3; M = W, R = CF3) with the lithium salts of the appropriate terphenyl groups (Ar' = Ar(Xyl2), Ar(Mes2), Ar(Dipp2), and Ar(Trip2)). Substitution of one bidentate carboxylate by a monodentate terphenyl forms a M-C ? bond and creates a coordination unsaturation at the other metal atom. Hence in M2(Ar')2(O2CR)2 complexes the two metal atoms have formally a low coordination number and an also low electron count. However, the unsaturation seems to be compensated by a weak M-Carene bonding interaction that implicates one of the aryl substituents of the terphenyl central aryl ring, as revealed by X-ray studies performed with some of these complexes and by theoretical calculations. PMID:24874837

Carrasco, Mario; Mendoza, Irene; Faust, Michelle; López-Serrano, Joaquín; Peloso, Riccardo; Rodríguez, Amor; Alvarez, Eleuterio; Maya, Celia; Power, Philip P; Carmona, Ernesto

2014-06-25

61

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

62

Oxidation of p-chlorotoluene and cyclohexene catalysed by polymer-anchored oxovanadium(IV) and copper(II) complexes of amino acid derived tridentate ligands.  

PubMed

3-Formylsalicylic acid (Hfsal), covalently bound to chloromethylated polystyrene (PS) and cross-linked with 5% divinylbenzene reacts with d,l-alanine and l-isoleucine to give the Schiff-base tridentate ligands PS-H(2)fsal-d,l-Ala and PS-H(2)fsal-l-Ile, respectively. These anchored ligands upon reaction with VOSO(4) and Cu(CH(3)COO)(2).H(2)O form the complexes PS-[VO(fsal-d,l-Ala)(H(2)O)], PS-[Cu(fsal-d,l-Ala)(H(2)O)], PS-[VO(fsal-l-Ile)(H(2)O)] and PS-[Cu(fsal-l-Ile)(H(2)O)]. The structures of these immobilized complexes have been established on the basis of scanning electron micrographs, spectroscopic (infrared, electronic and EPR), thermogravimetric and elemental analysis studies. The oxidation of p-chlorotoluene and cyclohexene has been investigated using these complexes as the catalysts in the presence of H(2)O(2) as the oxidant. Reaction conditions have been optimised by considering the concentration of the oxidant, the amount of catalyst used and the temperature of the reaction mixture. Under the optimised conditions, p-chlorotoluene gave a maximum of 14% conversion using PS-[VO(fsal-d,l-Ala)(H(2)O)] as the catalyst, with the main products having a selectivity order of: p-chlorobenzaldehyde > p-chlorobenzylalcohol > p-chlorobenzoic acid > 2-methyl-5-chlorophenol > 3-methyl-6-chlorophenol. The oxidation of cyclohexene with PS-[VO(fsal-d,l-Ala)(H(2)O)] proceeds with 79% conversion, which is followed by PS-[VO(fsal-l-Ile)(H(2)O)] with 77% conversion, and the oxidation of cyclohexene by Cu-based catalysts occurs with considerably lower conversions (29-32%). The selectivity of the products follows the order: 2-cyclohexene-1-ol > cyclohexene oxide > cyclohexane-1,2-diol > 2-cyclohexene-1-one. Recycling studies indicate that these catalysts can be reused at least three times without any significant loss in their catalytic potential. However, EPR studies indicate that while the polymer supported V(iv)O-complexes do not change after being used, the EPR spectra of the Cu-complexes show significant changes. The corresponding non-polymer bound complexes [VO(fsal-d,l-Ala)(H(2)O)], [Cu(fsal-d,l-Ala)(H(2)O)], [VO(fsal-l-Ile)(H(2)O)] and [Cu(fsal-l-Ile)(H(2)O)] have also been prepared in order to compare their spectral properties and catalytic activities. The non-polymer bound complexes exhibit lower conversion, along with lower turn-over frequency as compared to their polymer-bound analogues. Several EPR, (51)V NMR and UV-vis studies have been undertaken to detect the intermediate species, and outlines for the mechanisms of the catalytic reactions are proposed. PMID:18682861

Maurya, Mannar R; Kumar, Maneesh; Kumar, Amit; Costa Pessoa, João

2008-08-28

63

Metallo-?-lactamases withstand low Zn(II) conditions by tuning metal-ligand interactions.  

PubMed

A number of multiresistant bacterial pathogens inactivate antibiotics by producing Zn(II)-dependent ?-lactamases. We show that metal uptake leading to an active dinuclear enzyme in the periplasmic space of Gram-negative bacteria is ensured by a cysteine residue, an unusual metal ligand in oxidizing environments. Kinetic, structural and affinity data show that such Zn(II)-cysteine interaction is an adaptive trait that tunes the metal binding affinity, thus enabling antibiotic resistance at restrictive Zn(II) concentrations. PMID:22729148

González, Javier M; Meini, María-Rocío; Tomatis, Pablo E; Medrano Martín, Francisco J; Cricco, Julia A; Vila, Alejandro J

2012-08-01

64

Metallo-?-lactamases withstand low ZnII conditions by tuning metal-ligand interactions  

PubMed Central

A number of multiresistant bacterial pathogens inactivate antibiotics by producing ZnII-dependent ?-lactamases. We show that metal uptake leading to an active dinuclear enzyme in the periplasmic space of Gram-negative bacteria is ensured by a cysteine residue, an unusual metal ligand in oxidizing environments. Kinetic, structural and affinity data show that such ZnII-Cys interaction is an adaptive trait tuning the metal binding affinity, thus enabling antibiotic resistance at restrictive ZnII concentrations.

Gonzalez, Javier M.; Meini, Maria-Rocio; Tomatis, Pablo E.; Medrano Martin, Francisco J.; Cricco, Julia A.; Vila, Alejandro J.

2012-01-01

65

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.

2012-01-01

66

Ligand effects on metal-R bonding, where R is hydrogen or alkyl. A quantum chemical study  

SciTech Connect

Ligand effects on the metal-hydrogen and metal-methyl binding energies are studied by using quantum chemical methods including near degeneracy and dynamical correlation effects. The metals studied are nickel and palladium, and the ligands used are olefins (C{sub 2}H{sub 4} and C{sub 2}F{sub 4}), carbonyl, phosphine, dinitrogen, water, and chloride (Cl{sup {minus}}). These types of lone-pair ligands can have both destabilizing and stabilizing effects on the metal-R bonds. Using a valence-bond description of the bonding, they show that these ligands have a varying amount of covalent bonding to the metal and that there is a correlation between the amount of covalency in the metal-ligand bonding and the destabilizing effect of the ligand on the metal-R bond. Since the maximum number of covalent bonds is only two for nickel and palladium and these are already used in the ligand-free complexes, there will be a competition for the covalent bonding between the R groups and the ligands, which explains the observed trend. the stabilizing effects of the ligands, on the other hand, vary much less among the ligands.

Blomberg, M.R.A.; Schuele, J.; Siegbahn, P.E.M. (Institute of Theoretical Physics, Stockholm (Sweden))

1989-08-02

67

Postsynthetic ligand and cation exchange in robust metal-organic frameworks.  

PubMed

Postsynthetic ligand and metal ion exchange (PSE) processes are shown to readily occur in several "inert" metal-organic frameworks (MOFs), including zeolitic imidazolate frameworks (ZIFs). Ligand exchange can occur between solid samples, as was demonstrated under relatively mild conditions with two robust, topologically distinct MOFs, MIL-53(Al) and MIL-68(In). Interestingly, ligand PSE is not observed with MIL-101(Cr), which is attributed to the kinetic inertness of the Cr(III) ion. In addition to ligand exchange, metal ion (cation) PSE was also studied between intact MOF microcrystalline particles. Metal ion transfer between MIL-53(Al) and MIL-53(Fe) was readily observed. These PSE reactions were monitored and the products characterized by a number of techniques, including aerosol time-of-flight mass spectrometry, which permits single-particle compositional analysis. To show the potential synthetic utility of this approach, the PSE process was used to prepare the first Ti(IV) analogue of the robust UiO-66(Zr) framework. Finally, experiments to rule out mechanisms other than PSE (i.e., aggregation, dissolution/recrystallization) were performed. The results demonstrate that PSE, of either ligands or cations, is common even with highly robust MOFs such as UiO-66(Zr), MILs, and ZIFs. Furthermore, it is shown that PSE is useful in preparing novel materials that cannot be obtained via other synthetic methods. PMID:23039827

Kim, Min; Cahill, John F; Fei, Honghan; Prather, Kimberley A; Cohen, Seth M

2012-10-31

68

Phosphorescent ligand-to-metal charge-transfer excited states in the group IVB metallocene triad  

NASA Astrophysics Data System (ADS)

Long-lived ligand-to-metal charge transfer (LMCT) excited states based on a zirconium complex (ca. 2000 ?s) and a hafnium complex (ca. 300 ?s) are first characterised with use of the Cp 2Zr(IV)Cl 2 and Cp 2Hf(IV)Cl 2. The tendency in the observed photophysics (absorption and phosphorescence spectra, lifetimes, and quantum yields) in the homologous group IVB metallocenes Cp 2M(IV)Cl 2 is discussed in view of the nature of the unique metal (Ti, Zr or Hf)-ligand ?-bonding character.

Loukova, G. V.; Smirnov, V. A.

2000-10-01

69

Photoacid generating ligands for development of positive-tone directly photopatternable metal complexes.  

PubMed

Photoacid generating ligands, 4-(2-nitrobenzy-loxycarbonyl)catechol and 4-(6-nitroveratryloxycarbonyl)catechol, and indium tin and titanium complexes thereof, were synthesized. These metal complexes perform as positive-tone, directly photopatternable indium tin oxide (ITO) or titanium oxide film precursors. After exposure, acid-bearing selectively soluble complexes could be removed to give patterned films upon developing in aqueous base, which were transformable to the corresponding pattern-preserving metal oxide film. Micropatterning of ITO and titanium oxide films was accomplished with the photoreactivity of the 2-nitrobenzyloxycarbonyl (NBOC) and 6-nitroveratryloxycarbonyl (NVOC) moiety bearing ligands. PMID:21314151

Cordonier, Christopher E J; Nakamura, Akimasa; Shimada, Kazuhiko; Fujishima, Akira

2011-03-15

70

Studies on cage-type tetranuclear metal clusters with ferrocenylphosphonate ligands.  

PubMed

Reaction of FcCH(2)PO(3)H(2) [Fc=(eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))] (H(2)FMPA) and 1,10-phenanthroline (phen) with Cd(OAc)(2).2 H(2)O or ZnSO(4).7 H(2)O in methanol in the presence of triethylamine resulted in the formation of two new ferrocenylphosphonate metal-cage complexes [M(4)(fmpa)(4)(phen)(4)] 7 CH(3)OH (M=Cd 1, M=Zn 2). Both structures contain two kinds of isomeric tetranuclear metal phosphonate cages, which are linked to one another by pi-pi interactions between the phen molecules. In 1, the Cd1, Cd3, and Cd4 atoms are all pentacoordinate, while the Cd2 atom is coordinated by four oxygen atoms from three phosphonate ligands and two nitrogen atoms from the chelating phen in a distorted octahedral geometry. Four Cd atoms from each unit are interconnected through bridging phosphonate ligands with different coordination modes, such as 5.221, 4.211, and 2.11 (Harris notation), yielding a {Cd(4)} cage. In 2, each Zn atom is coordinated by three oxygen atoms from three phosphonate ligands and two nitrogen atoms from phen, leading to a distorted square-pyramidal geometry. The four Zn atoms of each isomeric unit are also interconnected through four bridging phosphonate ligands to yield a {Zn(4)} cage. Fluorescent studies indicate that ligand-to-ligand charge-transfer photoluminescence is observed for 1, while the emission bands of 2 can be assigned to an admixture of ligand-to-ligand and metal-to-ligand charge transfer. Solution-state differential pulse voltammetry indicates that the half-wave potentials of the ferrocenyl moieties in 1 and 2 have different deviations relative to the relevant H(2)FMPA ligand. This may be because the highest occupied molecular orbital (HOMO) in 1 is located in the FMPA(2-) groups, while in 2 the HOMO is located in the phen and Zn(II) groups, so the Fe(II) centers in complex 1 are more easily oxidized to Fe(III) centers than those of 2. The third-order nonlinear optical (NLO) measurements show that both 1 and 2 exhibit strong third-order NLO self-focusing effects; hence, they are promising candidates for NLO materials. By calculating the component of the lowest unoccupied molecular orbitals of 1 and 2, we confirmed that the co-planar phen rings control their optical nonlinearity, while the H(2)FMPA ligands and metal ions have only a weak influence on their NLO properties. PMID:16721869

Wu, Jie; Song, Yinglin; Zhang, Erpeng; Hou, Hongwei; Fan, Yaoting; Zhu, Yu

2006-07-24

71

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

72

The role of guest molecules in the self-assembly of metal-ligand clusters  

NASA Astrophysics Data System (ADS)

The role guest molecules play in the self-assembly of supramolecular metal-ligand clusters is examined in the context of several predictive design strategies for forming these types of assemblies. Chapter One serves as an introduction and literature survey of this topic. These large assemblies often house guest molecules which play a previously uncharacterized role in the self-assembly processes. Chapter One seeks to categorize this role: Do the guest molecules act as templates in the synthesis? Are the guest molecules necessary for cluster formation? Does the guest drive cluster assembly by forming a stable host-guest complex with the cluster? In Chapter Two a series of heterometallic-hybrid ligand clusters of stoichiometry M2M'3L6 are presented. These result from a predictive design strategy in which two different metals, one hard and one soft, supply all the symmetry elements in these C3h "mesocates." The early examples of these clusters were synthesized in a stepwise manner; however, complete self-assembly of all eleven components can be achieved using appropriate guest molecules. The self-assembly of a novel geometry for metal-ligand clusters, D3 symmetry M6L6 "cylinders," is presented in Chapter Three. This chapter presents the fortuitous synthesis of these cylinders and demonstrates the tendency for discrete clusters to form over oligomers when rigid ligands and labile metals are combined. The ligand presented was designed to assemble M4L4 tetrahedra with trivalent metal ions, however cylinders were formed in all cases examined. Guest molecules were not found to play a role in this self-assembly, but solvent molecules were found disordered within the solid state structures of these clusters. Chapter Four describes a bis-bidentate catecholamide ligand with a structure between the design for M2L3 helicate formation and M 4L6 tetrahedron formation. The two design strategies are briefly discussed, and molecular modeling studies are presented which suggested that two helicates were roughly equal in energy to one tetrahedron. The helicate was formed in the absence of any guest molecules. In the presence of suitable tetraalkylammonium cations, the helicate is quantitatively converted to the tetrahedral host-guest complex. A related dicatecholamide ligand is presented in Chapter Five. This ligand has a rigid pyrene linker between the chelating moieties and modeled as a perfect candidate to assemble M4L6 tetrahedra. The ligand indeed forms tetrahedral clusters when treated with trivalent metal ions, but only in the presence of suitable monocationic guest molecules. This guest molecule thermodynamically drives cluster synthesis through formation of a host-guest complex.

Johnson, Darren William

73

Reversible self-assembly of gels through metal-ligand interactions  

PubMed Central

Metal-ligand interactions with various proteins form in vivo metal assemblies. In recent years, metallosupramolecular approaches have been utilized to forge an assortment of fascinating two- and three-dimensional nano-architectures, and macroscopic materials, such as metal-ligand coordination polymeric materials, have promise in artificial systems. However to the best of our knowledge, the self-assembly of macroscopic materials through metal-ligand interactions has yet to be reported. Herein we demonstrate a gel assembly formed via metal-ligand interactions using polyacrylamide modified with Fe-porphyrin and L-histidine moieties. The stress values for the assembly increase as the concentration of Fe-porphyrin or L-histidine in the gels increases. Moreover, agitation of Fe-porphyrin gel, Zn-porphyrin gel, and L-histidine gel in an 80?mM Tris-acetate buffer (pH 9.0) results in selective adhesion of the Fe-porphyrin gel to the L-histidine gel based on the affinities of Fe-porphyrin and Zn-porphyrin with L-histidine.

Kobayashi, Yuichiro; Takashima, Yoshinori; Hashidzume, Akihito; Yamaguchi, Hiroyasu; Harada, Akira

2013-01-01

74

New ligand selection rule for quantum dot functionalization  

Microsoft Academic Search

Hard Soft Acid Base (HSAB) theory is introduced as a new tool to select ligands (molecules) for quantum dot covalent functionalization. According to HSAB, only soft acid-soft base bond is covalent. Since most of the transition metal semiconductor cations on the surface of the quantum dots are soft acids, the approach we propose is to select anchors which are soft

B. Serban; M. Mihaila; S. Costea; O. Buiu

2009-01-01

75

Anchoring strategies for bimetallic species in zeolites  

SciTech Connect

We explore a new approach by introducing heterobinuclear organometallic compounds for linking catalytic functions to zeolite frameworks. With two different metals present, the complexes are being anchored to the support via one oxophilic metal, ligand exchange and catalytic reactions may proceed at the second metal center. Anchoring chemistry, thermal stability and reactivity of Me[sub 3]SnMn(CO)[sub 5] in zeolite NaY and acid forms of zeolite Y was studied with X-ray absorption spectroscopy (Sn, Mn edge EXAFS) and in-situ FTIR/TPD-MS techniques. Subsequently, the tin-cobalt complex Me[sub 3]SnCo(CO)[sub 4] has been a focus of detailed synthetic and spectroscopic studies. The reactivity of tricarbonyl (cyclopentadienyl) (trimethylstannyl) molybdenum in new mesoporous hosts has been explored. A recent development is the design of vanadium oxo species in different micro- and mesoporous hosts. These are of great interest for the selective reduction of nitrogen oxides by ammonia, and selective oxidation of different hydrocarbons, such as xylenes, olefines and alkanes. Combination analytical techniques used to probe local structural changes at the molecular level, include EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy utilizing synchrotron radiation, in situ FT-IR coupled to thermodesorption/MS, UV-NIR, and CCD Raman.

Bein, T.

1993-03-01

76

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

PubMed

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 [M(2+)L]X2, where M(2+)=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. PMID:24858195

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

2014-10-15

77

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

78

Tuning of gate adsorption: modification of a flexible metal-organic framework by secondary organic ligands.  

PubMed

For realizing selective adsorption of targeted molecules, a flexible metal-organic framework (MOF) was modified with monodentate secondary ligands. Although the modified MOF retains CO2 adsorptivities with a vertical adsorption uptake, the material also shows gate adsorptivities of a specific gas molecule that the pristine MOF does not adsorb. PMID:24777049

Kondo, Atsushi; Fujii, Takuro; Maeda, Kazuyuki

2014-05-13

79

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

80

Metal d. pi. -ligand. pi. conflicts in octahedral oxo, carbyne, and carbonyl complexes  

SciTech Connect

Metal-ligand ..pi.. interactions in group VI model compounds containing oxo, carbyne, and carbonyl ligands are probed with use of the extended Hueckel method. The interplay between M double bond O ..pi.. bonding optimization and the metal sigma framework geometry in (MoO/sub 2/H/sub 4/)/sup 2 -/ is examined first. The importance of oxygen's electronegativity for housing lone pairs in monomers containing terminal oxygens is noted and later contrasted with similar model compounds containing carbyne ligands. Calculations on (W(CH)/sub 2/H/sub 4/)/sup 4 -/ confirm the qualitative expectation that a nonbonding carbon 2p orbital combination exists for both cis and trans isomers. Even though this orbital is not at particularly high energy for a filled frontier orbital, they anticipate that these carbyne carbons will be vary nucleophilic if filled or very electrophilic if vacant; i.e., they will resemble a carbanion or a carbonium ion. A mixed oxocarbyne complex, such as (W(CH)(O)H/sub 4/)/sup 3 -/ will exhibit a d..pi.. conflict with the covalency requirements of the carbyne causing electron density to build up on the terminal oxygen. Competition for d..pi.. orbitals also results when ..pi..-acid ligands are trans to ..pi..-donor ligands. Recognition of ..pi..-acid/..pi..-donor d..pi.. conflicts rationalizes the cis geometry of W(O)(CO) in d/sup 2/ M(O)(CO)L/sub 4/ octahedra.

Brower, D.C.; Templeton, J.L.; Mingos, D.M.P.

1987-08-19

81

Vibrational analysis of metal diimine dithiolate mixed ligand complexes  

NASA Astrophysics Data System (ADS)

The IR spectra of the M(mnt)(baba) where M=Ni and Pd, mnt=1,2-maleonitrile and baba=biacetylbisanyline, were recorded in the high as well in the low energy region. A complete assignment of the observed bands was performed based on well-documented references. Further, a normal coordinate analysis was carried out taking into account C2 v symmetry, and based in a simplified model in order to investigate the force field of both metal complexes and the potential energy distribution (PED) of the distinct modes of the quelate structure.

Díaz, Guillermo; Diez, Sylvia; Campos Vallette, Marcelo; Zink, Jeffrey I.

1999-05-01

82

New tri- and tetranuclear transition metal spin clusters incorporating a versatile polydentate Schiff base ligand  

Microsoft Academic Search

A trinuclear Fe(III) complex [Fe3(OAc)3L3] (1), a tetranuclear Mn(III) complex [Mn4Cl4L4] (2) and a tetranuclear Ni(II) complex [Ni4(MeOH)4L4] (3) have been synthesized from the reaction of simple metal salts with ligands derived from salicylidene-2-ethanolamine (H2L). Structural characterization of the three complexes reveals distinctly different topologies, despite the similar coordination modes of the ligand L2?. Preliminary magnetochemical studies have been performed

Colette Boskovic; Eduard Rusanov; Helen Stoeckli-Evans; Hans U. Güdel

2002-01-01

83

Preparation of macrocyclic Schiff-base ligand and antibacterial activities of transition metal complexes thereof  

Microsoft Academic Search

A macrocyclic Schiff-base (H2L) ligand is prepared via condensation of 2,6-pyridine dicarboxaldehyde with triethylene tetramine. The ligand is characterized using elemental analysis, by mass spectrometry, infrared (IR) spectroscopy, and proton nuclear magnetic resonance spectroscopy. The corresponding 1:1 metal complexes with Cr(III), Fe(III), Co(II), Ni(II), Cu(II), Cd(II), UO2(II), and Th(IV) are additionally characterized by determining their magnetic moment, molar conductance, thermal

Gehad G. Mohamed; Mohamed M. Omar; Mohsen S. Abou El-Ela; Ahmed M. M. Hindy

2011-01-01

84

Synthesis, spectral, thermal, potentiometric and antimicrobial studies of transition metal complexes of tridentate ligand  

Microsoft Academic Search

A series of metal complexes of Cu(II), Ni(II), Co(II), Fe(III) and Mn(II) have been synthesized with newly synthesized biologically active tridentate ligand. The ligand was synthesized by condensation of dehydroacetic acid (3-acetyl-6-methyl-(2H) pyran-2,4(3H)-dione or DHA), o-phenylene diamine and fluoro benzaldehyde and characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, 1H-NMR, UV–Vis spectroscopy and mass spectra.

Sarika M. Jadhav; Vinod A. Shelke; Sunil G. Shankarwar; Achut S. Munde; Trimbak K. Chondhekar

85

Anchor Modeling  

NASA Astrophysics Data System (ADS)

Maintaining and evolving data warehouses is a complex, error prone, and time consuming activity. The main reason for this state of affairs is that the environment of a data warehouse is in constant change, while the warehouse itself needs to provide a stable and consistent interface to information spanning extended periods of time. In this paper, we propose a modeling technique for data warehousing, called anchor modeling, that offers non-destructive extensibility mechanisms, thereby enabling robust and flexible management of changes in source systems. A key benefit of anchor modeling is that changes in a data warehouse environment only require extensions, not modifications, to the data warehouse. This ensures that existing data warehouse applications will remain unaffected by the evolution of the data warehouse, i.e. existing views and functions will not have to be modified as a result of changes in the warehouse model.

Regardt, Olle; Rönnbäck, Lars; Bergholtz, Maria; Johannesson, Paul; Wohed, Petia

86

Identification of an altered peptide ligand based on the endogenously presented, rheumatoid arthritis-associated, human cartilage glycoprotein-39(263-275) epitope: an MHC anchor variant peptide for immune modulation  

PubMed Central

We sought to identify an altered peptide ligand (APL) based on the endogenously expressed synovial auto-epitope of human cartilage glycoprotein-39 (HC gp-39) for modulation of cognate, HLA-DR4-restricted T cells. For this purpose we employed a panel of well-characterized T cell hybridomas generated from HC gp-39-immunized HLA-DR4 transgenic mice. The hybridomas all respond to the HC gp-39(263–275) epitope when bound to HLA-DR4(B1*0401) but differ in their fine specificities. First, the major histocompatibility complex (MHC) and T-cell receptor (TCR) contact residues were identified by analysis of single site substituted analogue peptides for HLA-DR4 binding and cognate T cell recognition using both T hybridomas and polyclonal T cells from peptide-immunized HLA-DR4 transgenic mice. Analysis of single site substituted APL by cognate T cells led to identification of Phe265 as the dominant MHC anchor. The amino acids Ala268, Ser269, Glu271 and Thr272 constituted the major TCR contact residues, as substitution at these positions did not affect HLA-DR4(B1*0401) binding but abrogated T cell responses. A structural model for visualisation of TCR recognition was derived. Second, a set of non-classical APLs, modified at the MHC key anchor position but with unaltered TCR contacts, was developed. When these APLs were analysed, a partial TCR agonist was identified and found to modulate the HC gp-39(263–275)-specific, pro-inflammatory response in HLA-DR4 transgenic mice. We identified a non-classical APL by modification of the p1 MHC anchor in a synovial auto-epitope. This APL may qualify for rheumatoid arthritis immunotherapy.

Boots, Annemieke MH; Hubers, Henk; Kouwijzer, Milou; den Hoed-van Zandbrink, Leontien; Westrek-Esselink, Bernice M; van Doorn, Cindy; Stenger, Rachel; Bos, Ebo S; van Lierop, Marie-jose C; Verheijden, Gijs F; Timmers, Cornelis M; van Staveren, Catharina J

2007-01-01

87

Synthesis and spectroscopic studies of mixed-ligand and polymeric dinuclear transition metal complexes with bis-acylhydrazone tetradentate ligands and 1,10-phenanthroline.  

PubMed

Two types of dinuclear copper(II) and nickel(II) complexes with two tetradentate N2O2 donor ligands 1,4-bis(1-anthranoylhydrazonoethyl)benzene (L1), 1,4-bis(1-salicyloylhydrazonoethyl)benzene (L2) and N,N'-bidentate heterocyclic base [1,10-phenonthroline (phen)] have been synthesized and characterized by elemental analysis, infrared spectra, UV-vis electronic absorption spectra and magnetic susceptibility measurements. The reaction of metal(II) acetates with the solution containing ligand and 1,10-phenonthroline in methanol gives mixed-ligand dinuclear metal(II) complexes with general formula [M2L(phen)2]Cl2 (L=L1 or L2), whereas, the ligands react with metal(II) acetates to form polymeric dinuclear complexes with general formula [(M2L2)n] (L=L1 or L2). In the complexes, the ligands act as dianionic tetradentate and coordination takes place in the enol tautomeric form with the enolic oxygen and azomethine nitrogen atoms while the phenolic hydroxyl and amino groups of aroylhydrazone moiety do not participate in coordination. The effect of varying pH and solvent on the absorption behavior of both ligands and complexes has been investigated. PMID:16458059

Gup, Ramazan; Kirkan, Bülent

2006-06-01

88

Extraction of metals using supercritical fluid and chelate forming ligand  

DOEpatents

A method of extracting metalloid and metal species from a solid or liquid material by exposing the material to a supercritical fluid solvent containing a chelating agent is described. The chelating agent forms chelates that are soluble in the supercritical fluid to allow removal of the species from the material. In preferred embodiments, the extraction solvent is supercritical carbon dioxide and the chelating agent is a fluorinated {beta}-diketone. In especially preferred embodiments the extraction solvent is supercritical carbon dioxide, and the chelating agent comprises a fluorinated {beta}-diketone and a trialkyl phosphate, or a fluorinated {beta}-diketone and a trialkylphosphine oxide. Although a trialkyl phosphate can extract lanthanides and actinides from acidic solutions, a binary mixture comprising a fluorinated {beta}-diketone and a trialkyl phosphate or a trialkylphosphine oxide tends to enhance the extraction efficiencies for actinides and lanthanides. The method provides an environmentally benign process for removing contaminants from industrial waste without using acids or biologically harmful solvents. The method is particularly useful for extracting actinides and lanthanides from acidic solutions. The chelate and supercritical fluid can be regenerated, and the contaminant species recovered, to provide an economic, efficient process. 7 figs.

Wai, C.M.; Laintz, K.E.

1998-03-24

89

Synthesis and anti-fungicidal activity of some transition metal complexes with benzimidazole dithiocarbamate ligand.  

PubMed

Seven transition metal complexes of benzimidazole ligand (HL) are reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analyses (TGA and DTA). From the obtained data, the complexes were proposed to have the general formulae [MX(2)(HL)(H(2)O)].yH(2)O, where M=Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cr(III); X=Cl(-), SO(4)(2-) and y=0-4. The molar conductance data revealed that all the metal chelates were non-electrolytes. From the magnetic and solid reflectance spectra, it was found that the geometrical structure of these complexes is octahedral. The thermal behaviour of these chelates showed that the hydrated complexes loss water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. Fungicidal activity of the prepared complexes and free ligand was evaluated against three soil borne fungi. Data obtained showed the higher biological activity of the prepared complexes than the parent Schiff base ligand. Formulation of the most potent complex was carried out in the form of 25% WP. Fungicidal activity of the new formulation was evaluated and compared with the standard fungicide Pencycuron (Monceren 25% WP). In most cases, the new formulation possessed higher fungicidal activity than the standard fungicide under the laboratory conditions. PMID:19119060

Mohamed, Gehad G; Ibrahim, Nasser A; Attia, Hanaa A E

2009-04-01

90

Distortions of a flexible metal-organic framework from substituted pendant ligands.  

PubMed

Four new variants of the 1,4-benzenedicarboxylate MIL-53 structure have been prepared for Co(II) under solvothermal conditions and their structures solved and refined from single-crystal X-ray data. All materials contain pendant pyridine-N-oxide ligands that bridge pairs of Co(II) atoms in the inorganic backbone of the structure via O. By the use of the ligands 3-bromopyridine-N-oxide, 4-methoxypyridine-N-oxide, isoquinoline-N-oxide and 4-phenylpyridine-N-oxide, materials are prepared with the same topology but distinct structures. These illustrate how the MIL-53 structure is able to distort to accommodate the bulk of the various substituents on the pyridine ring. The bulkiest pendant ligand, 4-phenylpyridine-N-oxide, results in a distortion of the diamond-shaped channels in an opposite sense to that seen previously in expanded forms of the parent MIL-53 structure. By comparison with published crystal structures for MIL-53 with various occluded guests, the structural distortions that take place to accommodate the pendant ligands are quantified and it is shown how a twisting of the 1,4-benzenedicarboxylate ligand, instead of a hinging about the ?(2)-carboxylate-metal connection, allows the new structures that are observed. PMID:24441123

Munn, Alexis S; Clarkson, Guy J; Walton, Richard I

2014-02-01

91

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

92

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

PubMed

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 Zn(2+) 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. PMID:24704603

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

2014-07-15

93

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

94

Immobilized metal affinity chromatography of human growth hormone Effect of ligand density  

Microsoft Academic Search

Immobilized metal affinity chromatography was examined as a method for the purification of recombinant human growth hormone, somatotropin. Cellulose-based chelating supports, Chelat-Granocel, of a different content of ligand, charged with Cu(II), were assessed for their ability to bind the protein from both crude extract and solution purified by two chromatography steps. Human growth hormone was found to exhibit high affinity

J Liesiene; K. Ra?aityt; M. Morkevi?ien; P. Valan?ius; B. Bumelis

1997-01-01

95

Anchor connector  

SciTech Connect

An anchor connector incorporating a flexible joint for securing the tension legs of a tensioned leg platform. A latch dog head engages a first recess on the fixed member of the flexible joint and a template recess to prevent disconnection when the dog heads and latch carrier are in a lower position. With the latch carrier (40) in an upper position the latch dog heads fit within a second recess (44) in the fixed member with the dog heads clearing shoulder of template recess, whereby the connector may be released.

Quigg, D.F.; Bell, J.L. Jr.; Jones, D.L.; McFerron, R.G.

1984-03-27

96

A QICAR approach for quantifying binding constants for metal-ligand complexes.  

PubMed

Relative metal-ligand complex stability is predicted by evaluating the relationships between physicochemical properties of metal ions and their experimental biotic and abiotic binding constants, K. Linear regression analysis showed that the softness index (?(p)) and the covalent index (?(2)(m) r) were especially useful in model construction for rainbow trout (Oncorhynchus mykiss), fathead minnows (Pimephales promelas) and crustaceansaquatic (Daphnia magna) based on RMSE and F-ratio criterion (F(observed)/F(critical) of ?4). The absolute value of the log of the first hydrolysis constant |logK(OH)| correlated best with logK values for barley (R(2)=0.74, p=0.02) and earthworm (R(2)=0.82, p=0.01). In contrast, the ionic index Z(2)/r explained most of the variability of logK values for the two clays kaolinite and montmorillonite, while |logK(OH)| was a better predictor of the generic NICA-Donnan parameters for HA and FA (0.67ligands and the different binding mechanisms between metal and ligands. PMID:21377206

Zhou, Dong-Mei; Li, Lian-Zhen; Peijnenburg, Willie J G M; Ownby, David R; Hendriks, A Jan; Wang, Peng; Li, Dan-Dan

2011-05-01

97

Metal Ion Complexation Studies of Novel 8-Hydroxyquinoline-Containing Diaza-18-Crown-6 Ligands and Analogues.  

National Technical Information Service (NTIS)

Interaction of some 8-hydroxyquinoline-substituted and related ligands with various metal ions was evaluated by a calorimetric titration technique at 25 deg C in MeOH. Bis-(8-hydroxyquinoline- 2-ylmethyl)- substituted ligand 13 forms a very strong complex...

J. S. Bradshaw X. X. Zhang P. B. Savage K. E. Krakowiak R. M. Izaft

1999-01-01

98

COMPLEXATION STUDIES OF ALKALINE EARTH METAL IONS WITH MACROCYCLIC LIGANDS OF THE ANTHRAQUINONE-CROWN ETHER TYPE BY ELECTROCHEMICAL METHODS  

Microsoft Academic Search

The electrochemical and complexation behaviour of synthetic ligands of the crown ether type attached to an anthraquinone unit has been studied using cyclic voltammetry. In the presence of alkaline earth metal ions the positions and type of the ligand redox waves were changed and the potentials of the respective redox couples were shifted to more positive values. These shifts in

J. M. Caridade Costa; D. Bethell

1999-01-01

99

COMPLEXATION STUDIES OF ALKALINE EARTH METAL IONS WITH MACROCYCLIC LIGANDS OF THE ANTHRAQUINONE-CROWN ETHER TYPE BY ELECTROCHEMICAL METHODS  

Microsoft Academic Search

The electrochemical and complexation behaviour of synthetic ligands of the crown ether type attached to an anthraquinone unit has been studied using cyclic voltammetry. In the presence of alkaline earth metal ions the positions and type of the ligand redox waves were changed and the potentials of the respective redox couples were shifted to more positive values. These shifts in

J. M. Caridade Costa; D. Bethell

1998-01-01

100

Evaluation of immobilized metal affinity chromatography (IMAC) for isolation and recovery of strong copper-complexing ligands from marine waters  

Microsoft Academic Search

The speciation of dissolved copper in surface seawater is dominated by complexes with at least two classes of organic ligands, L1 (the stronger) and L2 (the weaker). However, because these ligands have never been isolated, recovered, and characterized, their nature and identities are unknown. We have taken a combined approach utilizing immobilized metal affinity chromatography (IMAC) for isolation, and copper

John R. Donat; Reyaz A. Kango; Andrew S. Gordon

1997-01-01

101

Transition-Metal Fluoro Compounds Containing Carbonyl, Phosphine, Arsine and Stibine Ligands. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

This review describes the considerable variety of transition-metal fluoro compounds containing carbonyl, phosphine, arsine, and stibine ligands reported in the literature. Included are a number of stable low-valent organometallic fluorides, a class of com...

N. M. Doherty N. W. Hoffman

1991-01-01

102

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

103

Ab initio calculations in heterogeneous and homogeneous catalysis: I. Methanol to gasoline with ZSM-5. II. Carbonyl ligand effects on metal-metal bonds  

Microsoft Academic Search

This thesis is composed of two studies in catalysis. The first is an exploration, using computational techniques, of the mechanism for the first carbon-carbon bond formation in the methanol to gasoline (MTG) reaction. The second is a study of the factors important to the understanding of ligand effects on metal-metal bonds, and in particular, to metal clusters. Three possibilities were

1993-01-01

104

Ground states, excited states, and metal-ligand bonding in rare earth hexachloro complexes: a DFT-based ligand field study.  

PubMed

Metal (4f)-ligand (Cl 3p) bonding in LnCl(6)(3-) (Ln = Ce to Yb) complexes has been studied on the basis of 4f-->4f and Cl,3p-->4f charge-transfer spectra and on the analysis of these spectra within the valence bond configuration interaction model to show that mixing of Cl 3p into the Ln 4f ligand field orbitals does not exceed 1%. Contrary to this, Kohn-Sham formalism of density functional theory using currently available approximations to the exchange-correlation functional tends to strongly overestimate 4f-3p covalency, yielding, for YbCl(6)(3-), a much larger mixing of Cl 3p-->4f charge transfer into the f(13) ionic ground-state wave function. Thus, ligand field density functional theory, which was recently developed and applied with success to complexes of 3d metals in our group, yields anomalously large ligand field splittings for Ln, the discrepancy with experiment increasing from left to the right of the Ln 4f series. It is shown that eliminating artificial ligand-to-metal charge transfer in Kohn-Sham calculations by a procedure described in this work leads to energies of 4f-4f transitions in good agreement with experiment. We recall an earlier concept of Ballhausen and Dahl which describes ligand field in terms of a pseudopotential and give a thorough analysis of the contributions to the ligand field from electrostatics (crystal field) and exchange (Pauli) repulsion. The close relation of the present results with those obtained using the first-principles based and electron density dependent effective embedding potential is pointed out along with implications for applications to other systems. PMID:15819583

Atanasov, M; Daul, C; Güdel, H U; Wesolowski, T A; Zbiri, M

2005-04-18

105

An ultrafast time-resolved fluorescence spectroscopy system for metal ion complexation studies with organic ligands.  

PubMed

A dedicated spectrofluorimeter using ultrashort laser pulses as an excitation source was developed to measure the fluorescence properties of organic ligands for metal ion complexation with organic ligands. The laser system consists of an oscillator system for generation of femtosecond laser pulses, an amplifier system to increase the pulse energy of the generated pulses to about 2 mJ and an optical parametrical amplifier system to provide tunable laser pulses over a wide wavelength range (280 nm-10 microm). The laser pulses were applied to the sample and the emitted fluorescence was detected using a fast-gating intensified CCD camera-based spectrometer. To verify the performance of the laser, the well-known protonation constant [Pure Appl. Chem. 69 (1997) 329] of 2,3-dihydroxybenzoic acid was determined. The fluorescence lifetime of the excited species was determined as 375+/-32 ps in the pH range from 1.0 to 6.0, having a fluorescence emission maximum at 438 nm. The first protonation constant was determined from fluorescence data as log K(3)=3.17+/-0.05 at an ionic strength of 0.1 M and at 294 K exploiting the Stern-Volmer mechanism. The agreement of the protonation constant with literature data (log K(3)=3.10+/-0.20, I=0.1 M, T=298 K [Bull. Soc. Jpn. 44 (1971) 3459]) demonstrates the excellent performance of our system. Furthermore, we determined the complex formation constant log K(1)=-3.11+/-0.16 by measuring the fluorescence properties of the ligand for the 1:1 uranyldihydroxobenzoate complex in the pH range from 3.0 to 4.5 at ionic strength of 0.1 M and at 294 K. We also determined the complex formation constant via the fluorescence emission of the metal ion uranium(VI). The fluorescence of the uranyl ion is influenced by dynamic quenching of the non-dissociated ligand and by static quenching due to the complex formation. After correction of these effects using the determined fluorescence lifetime, the complex formation constant was calculated to be log K(1)=-3.99+/-0.44. A 1:1 metal:ligand stoichiometry was determined with both measurement methods. However, the difference of the obtained formation constants and the derived standard deviations indicate a superimposition of effects with the excited-state reactions of the ligand. PMID:14670508

Geipel, G; Acker, M; Vulpius, D; Bernhard, G; Nitsche, H; Fanghänel, Th

2004-01-01

106

Polynuclear Structures Derived from Dinuclear Metal Complex with Phenol Based Macrocyclic Ligand  

NASA Astrophysics Data System (ADS)

Dinuclear metal complex with phenol based dinucleating macrocyclic ligand (L2-) derived from the [2+2] condensation of 2,6-diformyl-4-methylphenol and 1,3-diaminopropane can act as ‘complex as metal’, since axial position of the dinuclear complex is available for accepting donation from ‘another ligand’. A tetranuclear Fe(III) complex, [{Fe2(L)(CH3COO)}2(?-O)2](PF6)2, was obtained by linking two {Fe2(L)(OAc)} units with two oxo anions. In addition, a dinuclear copper (II) complex, [Cu2(L)](ClO4)2, was reacted with [Cr(ox)3]3- and [Co(CN)6]3- as ‘complex as bridging ligand’, to afford [Cu2(L)]3[Cr(ox)3]2·6MeOH having a discrete octanuclear structure and [Cu2(L)]3[Co(CN)6]2·6MeOH·2DMF having 2-D grid structure, respectively.

Miyazato, Yuji

107

Metal dicyanamide layered coordination polymers with cyanopyridine co-ligands: Synthesis, crystal structures and magnetism  

SciTech Connect

A series of metal dicyanamide (dca) coordination polymers combined with cyanopyridine (cypy) terminal co-ligands, namely, [Co{sub 2}(dca){sub 4}(4-cypy){sub 4}] {sub n} (1), [Cd(dca){sub 2}(4-cypy){sub 2}] {sub n} (2), [Fe(dca){sub 2}(3-cypy){sub 2}] {sub n} (3) and [Co(dca){sub 2}(3-cypy){sub 2}] {sub n} (4), have been synthesized at the ambient conditions. X-ray single crystal diffraction reveals that complexes 1-4 have similar metal-dca coordination layers in which the octahedral metal centers are connected by {mu} {sub 1,5}-dca linkers. Notably, three types of 3-D packing lattices are observed for these layered arrays. The thermal stabilities of such new crystalline materials have been studied by thermogravimetric analysis of mass loss. The magnetic properties of the Co{sup II} and Fe{sup II} complexes have been investigated and discussed in detail. A discrete mononuclear molecule [Cd(dca){sub 2}(pyom){sub 2}] (5) is also described, in which the chelated ligand O-methyl picolinimidate (pyom) arises from the addition of methanol solvent across the C{identical_to}N bond of 2-cypy. - Graphical abstract: A series of new metal dicyanamide complexes with cyanopyridine terminal co-ligands have been prepared and structurally determined by X-ray single-crystal diffraction. The magnetic properties of the Co{sup II} and Fe{sup II} layered coordination polymers are also discussed.

Du Miao [College of Chemistry and Life Science, Tianjin Normal University, Tianjin 300074 (China)]. E-mail: dumiao@public.tpt.tj.cn; Wang Qian [College of Chemistry and Life Science, Tianjin Normal University, Tianjin 300074 (China); Wang Ying [College of Chemistry and Life Science, Tianjin Normal University, Tianjin 300074 (China); Zhao Xiaojun [College of Chemistry and Life Science, Tianjin Normal University, Tianjin 300074 (China); Ribas, Joan [Departament de Quimica Inorganica, Universitat de Barcelona, Diagonal, 647, 08028-Barcelona (Spain)

2006-12-15

108

Tuning main group redox chemistry through steric loading: subvalent Group 13 metal complexes of carbazolyl ligands.  

PubMed

The ability of substituted carbazol-9-yl systems to ligate in ? fashion through the amido N-donor, or to adopt alternative coordination modes through the ? system of the central five-membered ring, can be tuned by systematic variation in the steric demands of substituents in the 1- and 8-positions. The differing affinities of the two modes of coordination for hard and soft metal centres can be shown to influence not only cation selectivity, but also the redox properties of the metal centre. Thus, the highly sterically sterically demanding 1,3,6,8-tetra-tert-butylcarbazolyl ligand can be used to generate the structurally characterised amido-indium(I) complex, [{(tBu(4)carb)In}(n)], (together with its isostructural thallium counterpart) in which the metal centre interacts with the central pyrrolyl ring in ?(3) fashion [d(In-N)=2.679(3) Å; d(In-C)=2.819(3), 2.899(3) Å]. By contrast, the smaller 3,6-di-tert-butylcarbazolyl system is less able to restrict the metal centre from binding at the anionic nitrogen donor in the plane of the carbazolyl ligand (i.e. in ? fashion). Analogous chemistry with In(I) precursors therefore leads to disproportionation to the much harder In(II) [and In(0)], and the formation of the mixed-valence product, [In(2){In(2)(tBu(2)carb)(6)}], a homoleptic molecular [In(4)(NR(2))(6)] system. This chemistry reveals a flexibility of ligation for carbazolyl systems that contrasts markedly with that of the similarly sterically encumbered terphenyl ligand family. PMID:21465585

Mansaray, Hassanatu B; Kelly, Michael; Vidovic, Dragoslav; Aldridge, Simon

2011-05-01

109

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

110

Ligand and initiator effect in late and early transition metal catalyzed living radical polymerizations  

NASA Astrophysics Data System (ADS)

This thesis was concerned with the development of novel catalysts and initiators for living radical polymerization (LRP). The effect of metal, ligand and initiator was studied in the LRP of styrene using transition metal porphyrins as well as a series of 18 Ti complexes with O, N as well as substituted cyclopentadienyl ligands in conjunction with epoxide and halide initiators. The nature of the metal center was first explored in a series of tetraphenyl porphyrins containing Cu, Ni, Pb, Pd, Pt, Zn, and Ag. Styrene polymerization in the presence of these catalysts showed a linear dependence of molecular weight (Mn) on conversion but also gave broad polydisperisties (PDI). This behavior was attributed to a copolymerization of the porphyrin with styrene. Subsequently, the Cp2TiCl-catalyzed radical ring opening (RRO) of epoxides was introduced as a novel initiating reaction for LRP mediated by the unprecedented reversible end-capping of the propagating chain by Ti(III). These results were supported by a combination of NMR, GPC and reinitiation experiments and generated polymers with very narrow PDI (<1.2) and functional OH chain ends. Ti(III) was also shown to be compatible with activated and unactivated halides yielding the first halide initiated LRP which does not follow an atom transfer polymerization mechanism. Further studies of the stereoelectronic ligand effects in RRO and LRP ranked these catalysts as: L = metallocene (eta5-RCp: R = H ˜ Et ˜ iPr ˜ tBu > Ind >> Cp*) >> O-ligands (alkoxides > bisketonates) >> N ligands (hydrotris(pyrazol-1-ylborato) > phthalocyanine), while X = Cl > Br >> F ˜ Me ˜ CO and LnTiCl m > Ln-1TiClm+1. Additional experimentation examined the effect of reaction conditions and optimum results were obtained with [St]/[epoxide]/[Ti]/[Zn] = 50/1/4/8 at 60 °C--90 °C in dioxane using a 1,4-butandiol diglycidyl ether. Finally, the first example of a dual concurrent polymerization of styrene and epsilon-caprolactone was demonstrated using a single catalyst/initiator system (Ti/epoxide) and new criteria for quantifying the livingness of the process were outlined.

Moran, Isaac Webster

111

C-H functionalization: thoroughly tuning ligands at a metal ion, a chemist can greatly enhance catalyst's activity and selectivity.  

PubMed

This brief essay consists of a few "exciting stories" devoted to relations within a metal-complex catalyst between a metal ion and a coordinated ligand. When, as in the case of a human couple, the rapport of the partners is cordial and a love cements these relations, a chemist finds an ideal married couple, in other words he obtains a catalyst of choice which allows him to functionalize C-H bonds very efficiently and selectively. Examples of such lucky marriages in the catalytic world of ions and ligands are discussed here. Activity of the catalyst is characterized by turnover number (TON) or turnover frequency (TOF) as well as by yield of a target product. Introducing a chelating N,N- or N,O-ligand to the catalyst molecule (this can be an iron or manganese derivative) sharply enhances its activity. However, the activity of vanadium derivatives (with additionally added to the solution pyrazinecarboxylic acid, PCA) as well as of various osmium complexes does not dramatically depend on the nature of ligands surrounding metal ions. Complexes of these metals are very efficient catalysts in oxidations with H2O2. Osmium derivatives are record-holders exhibiting extremely high TONs whereas vanadium complexes are on the second position. Finally, elegant examples of alkane functionalization on the ions of non-transition metals (aluminium, gallium etc.) are described when one ligand within the metal complex (namely, hydroperoxyl ligand HOO(-)) helps other ligand of this complex (H2O2 molecule coordinated to the metal) to disintegrate into two species, generating very reactive hydroxyl radical. Hydrogen peroxide molecule, even ligated to the metal ion, is perfectly stable without the assistance of the neighboring HOO(-) ligand. This ligand can be easily oxidized donating an electron to its partner ligand (H2O2). In an analogous case, when the central ion in the catalyst is a transition metal, this ion changing its oxidation state can donate an electron to the coordinated H2O2 fragment. This provokes the O-O bond rupture in the hydrogen peroxide molecule as is assumed for the role of Fe(2+) ions in the Fenton system. PMID:23873447

Shul'pin, Georgiy B

2013-09-28

112

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

113

Phase-transfer catalyzed ¹⁸O labeling studies of carbonyl ligands in neutral metal carbonyl derivatives  

Microsoft Academic Search

The phase-transfer catalyzed oxygen-18 labelling of the carbon monoxide ligands bound to neutral group 6b and iron metals is reported. A biphasic reaction system was used with the organic phase consisting of the neutral carbonyl derivative in benzene and an aqueous phase. The lack of a significant secondary reaction involving COâ elimination coupled with metal hydride formation in the group

Donald J. Darensbourg; Joseph A. Froelich

1978-01-01

114

A new strategy for neurochemical photodelivery: metal-ligand heterolytic cleavage.  

PubMed

A new strategy to build caged-compounds is presented. The approach is based on heterolytic photocleavage of a metal-ligand bond in a coordination compound. A ruthenium polypyridine complex, containing the neurocompound 4-amino pyridine (4AP) is used as the core of the phototrigger. The biomolecule is released by irradiation with visible light (>480 nm). The liberated 4AP promotes the activation of a leech neuron by means of blocking its K+ channels. The syntesis, characterization, and the inherent advantages of this method are discussed. PMID:12537482

Zayat, Leonardo; Calero, Cecilia; Alborés, Pablo; Baraldo, Luis; Etchenique, Roberto

2003-01-29

115

Ultrasonic/Sonic Anchor  

NASA Technical Reports Server (NTRS)

The ultrasonic/sonic anchor (U/S anchor) is an anchoring device that drills a hole for itself in rock, concrete, or other similar material. The U/S anchor is a recent addition to a series of related devices, the first of which were reported in "Ultrasonic/Sonic Drill/Corers With Integrated Sensors"

Bar-Cohen, Yoseph; Sherrit, Stewart

2009-01-01

116

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

117

Electrochemical synthesis of zinc nanoparticles via a metal-ligand-coordinated vesicle phase.  

PubMed

Two salt-free Zn(2+)-ligand-coordinated vesicle phases were prepared from the mixtures of alkyldimethylamine oxide (C(n)DMAO, n = 14 and 16, i.e., C(14)DMAO and C(16)DMAO) and zinc laurate [(CH(3)(CH(2))(10)COO)(2)Zn] in aqueous solution. The two salt-free Zn(2+)-ligand-coordinated vesicle phases were subsequently used as the templating media for fabricating zinc nanoparticles on an indium-doped tin oxide (ITO) electrode via electrodeposition. Influence of temperature, direct current density, and composition of the surfactant mixtures on the average diameter and size distribution of Zn nanoparticles was investigated in more detail. The structure of Zn@ITO was determined by scanning electron microscope and energy-dispersive X-ray spectroscopy analysis. Monodispersed Zn nanoparticles on ITO electrode (ZnNPs@ITO) with different average diameters were obtained, and the distribution can be controlled. Finally, ZnO nanostructures on the ITO substrate were prepared from the as-synthesized Zn@ITO nanoparticles through electrochemical surface oxidation. The preparation of nanostructured Zn and ZnO particles by our established method may pave the way for a new templating route from metal-ligand-coordinated vesicles. PMID:19548656

Gao, Yue; Hao, Jingcheng

2009-07-16

118

Catechol-initiated polyethers: multifunctional hydrophilic ligands for PEGylation and functionalization of metal oxide nanoparticles.  

PubMed

Bifunctional CA-PEG (catechol-poly(ethylene glycol)) and multifunctional CA-PEG-PGA/PEVGE (poly(glycidyl amine)/poly(ethylene glycol vinyl glycidyl ether)) ligands for the functionalization and solubilization of nanoparticles are introduced. Tunable polymers with polydispersities <1.25 and molecular weights in the range 500-7700 g mol(-1) containing a catechol moiety for conjugation to metal oxide nanoparticles were prepared. The functional PEG ligands were synthesized starting from the acetonide-protected catechol initiator 2,2-dimethyl-1,3-benzodioxole-5-propanol (CA-OH) for oxyanionic polymerization. CA-OH was used both for homopolymerization of ethylene oxide (EO) as well as copolymerization with functional epoxides N,N-diallyl glycidyl amine (DAGA), releasing primary amino groups and ethylene glycol vinyl glycidyl ether (EVGE), exhibiting a double bond for click-type reactions, to generate CA-PEG and CA-PEG-PGA/PEVGE. We demonstrate the potential of the functional ligands by binding to MnO nanoparticles, rendering the PEGylated nanoparticles highly stable in aqueous environment. Furthermore, addressability of the functional groups has been proven, for example, by coupling with fluoresceine isothiocyanate (FITC), to allow for optical monitoring of the nanoparticle fate in biological systems. PMID:23210706

Wilms, Valerie S; Bauer, Heiko; Tonhauser, Christine; Schilmann, Anna-Maria; Müller, Marc-Christian; Tremel, Wolfgang; Frey, Holger

2013-01-14

119

Lead halide perovskites and other metal halide complexes as inorganic capping ligands for colloidal nanocrystals.  

PubMed

Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MXn, where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals. In particular, we show that the Lewis acid-base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20-30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50-65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface. PMID:24746226

Dirin, Dmitry N; Dreyfuss, Sébastien; Bodnarchuk, Maryna I; Nedelcu, Georgian; Papagiorgis, Paris; Itskos, Grigorios; Kovalenko, Maksym V

2014-05-01

120

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

121

Self-assembly of transition metal ion complexes of a hybrid pyrazine-terpyridine ligand.  

PubMed

A new hybrid pyrazine-terpyridine ligand L (C(34)H(22)N(8)) and its complexes with different transition metal ions, M (M = Mn(II) 1, Zn(II) 2, Fe(II) 3, Co(II) 4, Cu(II) 5 and Cd(II) 6), have been synthesised. In the presence of a nitrate counter-anion, both Cu(II) and Cd(II) give complexes in which the ratio M:L is 2:1, whereas with perchlorate, trifluoromethanesulfonate or tetrafluoroborate, the other metal ions provide solids in which this ratio is 1:1. From mass spectral measurements and a single crystal, X-ray structure determination for the Fe(II) complex 3, however, all the latter species are concluded to be 2:2 complexes. Both the Fe(II) complex 3 and the Co(II) complex 4, generated from tetrafluoroborate reactant salts, have the composition [M(2)L(2)F(2)(H(2)O)](BF(4))(2), the presence of fluoride ligands being presumed to reflect the abstraction of fluoride ions from tetrafluoroborate by the metal ions under the preparative conditions. The crystal structure of complex 3 shows the Fe(II) centres to be inequivalent, one being high-spin and heptacoordinate with a FeN(4)F(2)O coordination sphere, the other low-spin and octahedral with a FeN(6) sphere. The two ligand molecules differ markedly, one being heptadentate, the other clearly "hypodentate", with only three N-donor atoms of a terpyridine-like arm coordinated, although their conformations are similar, showing significant differences from that of C(2) symmetry found for the free ligand by a crystal structure determination. Mass spectra are consistent with the Cu(II) and Cd(II) complexes having the composition [M(2)L(H(2)O)(n)(NO(3))(4-n)](NO(3))(4-n), and the weak antiferromagnetic coupling observed for the Cu(II) complex is consistent with a preliminary crystal structure determination which indicates that the two Cu(II) centres are not bridged by a pyrazine unit. PMID:23160345

Stefankiewicz, Artur R; Wa??sa-Chorab, Monika; Harrowfield, Jack; Kubicki, Maciej; Hnatejko, Zbigniew; Korabik, Maria; Patroniak, Violetta

2013-02-01

122

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

123

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

SciTech Connect

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.

Zalis, S. [J. Heyrovsky Institute of Physical Chemistry AS CR, v. v. i., Dolejskova 3, 182 23 Prague 8 (Czech Republic); Winter, R. S.; Linseis, M. [Institut fuer Anorganische Chemie, Universitaet Regensburg, Universitaetsstrasse 31, 93040 Regensburg (Germany); Kaim, A.; Sarkar, B. [Institut fuer Anorganische Chemie, Universitaet Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany); Kratochvilova, I. [Institute of Physics, AS CR, v. v. i., Na Slovance 2, 182 21 Prague 8 (Czech Republic)

2009-08-13

124

21 CFR 872.3130 - Preformed anchor.  

... (a) Identification. A preformed anchor is a device made of austenitic alloys or alloys containing 75 percent or greater gold or metals of the platinum group intended to be incorporated into a dental appliance, such as a denture, to help...

2014-04-01

125

Deliberate design of ligand architecture yields dramatic enhancement of metal ion affinity.  

PubMed

Evaluation of the malonamide substructure with respect to binding site preorganization and complementarity for lanthanide metal ions suggests a new ligand architecture specifically designed to enhance lanthanide ion affinity. Consideration of conformational reorganization, restricted bond rotation, and donor group orientation suggests that typical malonamide structures, for example, N,N,N'N'-tetrahexylpropane-1,3-diamide (1), N,N'-dibutyl-N,N'-dimethyl-2-tetradecylpropane-1,3-diamide (2), or N,N,N'N'-tetramethylpropane-1,3-diamide (6), are poorly organized for metal ion complexation. Molecular mechanics analyses show that the unfavorable enthalpic and entropic terms are eliminated by the use of the novel bicyclic architecture found in 3,9-diaza-3,9-dimethylbicyclo[4.4.0]decane-2,10-dione (7). Diamide 7 was prepared, and the X-ray crystal structure of the complex [Eu(7)(2)(NO(3))(3)] exhibits the same chelate conformation predicted by the molecular mechanics model. A hydrophobic derivative, 3,9-diaza-3,9-dioctylbicyclo[4.4.0]decane-2,10-dione (8), was prepared, and solvent extraction studies reveal that the preorganized architecture of 8 gives a dramatic enhancement in binding affinity, exhibiting Eu(3+) distribution coefficients that are 7 orders of magnitude larger than a typical malonamide ligand, 1. PMID:12010030

Lumetta, Gregg J; Rapko, Brian M; Garza, Priscilla A; Hay, Benjamin P; Gilbertson, Robert D; Weakley, Timothy J R; Hutchison, James E

2002-05-22

126

Syntheses and spectroscopic studies of some platinum group metal complexes with oxazepam as ligand  

NASA Astrophysics Data System (ADS)

The preparation and characterization of some rhodium(III), iridium(III), palladium(II) and platinum(II) halide complexes with oxazepam, 7-chloro-1,3-dihydro-5-phenyl-3-hydroxy-2H-1,4-benzodiazepin-2-one are reported. The obtained complexes of the type ML 3X 3 (M = Rh, Ir) and ML 2X 2 (M = Pd, Pt) with the exception of the rhodium and palladium iododerivatives which have 1:6 and 1:4 metal:ligand ratios, respectively, have been studied and characterized through vibrational and electronic spectra, 1H and 13C NMR studies, conductivity measurements and magnetic susceptibility data. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of the crystal field theory and the various parameters have been calculated. The most convincing structural evidence supports an octahedral stereochemistry for the rhodium and iridium derivatives and a square planar geometry for the palladium and platinum compounds with terminal halides and terminal ligands, acting as monodentate only in all the metal complexes through the nitrogen atom in the 4-position.

Benedetti, Adriano; Preti, Carlo; Tosi, Giuseppe

1984-05-01

127

Complex-forming organic ligands in cloud-point extraction of metal ions: a review.  

PubMed

Cloud-point extraction (CPE), an easy, safe, environmentally friendly, rapid and inexpensive methodology for preconcentration and separation of trace metals from aqueous solutions has recently become an attractive area of research and an alternative to liquid-liquid extraction. Moreover, it provides results comparable to those obtained with other separation techniques and has a greater potential to be explored in improving detection limits and other analytical characteristics over other methods. A few reviews have been published covering different aspects of the CPE procedure and its relevant applications, such as the phenomenon of clouding, the application in the extraction of trace inorganic and organic materials, as well as pesticides and protein substrates from different sources, or incorporation of CPE into an FIA system. This review focuses on general properties of the most frequently used organic ligands in cloud-point extraction and on literature data (from 2000 to 2012) concerning the use of modern techniques in determination of metal ions' content in various materials. The article is divided according to the class of organic ligands to be used in CPE. PMID:23618195

Pytlakowska, K; Kozik, V; Dabioch, M

2013-06-15

128

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

129

New polymer-supported ion-complexing agents: Design, preparation and metal ion affinities of immobilized ligands  

Microsoft Academic Search

Polymer-supported reagents are comprised of crosslinked polymer networks that have been modified with ligands capable of selective metal ion complexation. Applications of these polymers are in environmental remediation, ion chromatography, sensor technology, and hydrometallurgy. Bifunctional polymers with diphosphonate\\/sulfonate ligands have a high selectivity for actinide ions. The distribution coefficient for the uranyl ion from 1M nitric acid is 70,000, compared

Spiro D. Alexandratos

2007-01-01

130

Synthesis, characterization and physiochemical information, along with antimicrobial studies of some metal complexes derived from an ON donor semicarbazone ligand  

Microsoft Academic Search

Eight new transition metal complexes of benzaldehyde-N(4)–phenylsemicarbazone have been synthesized and characterized by elemental analyses, molar conductance, electronic and infrared spectral studies. In all the complexes, the semicarbazone is coordinated as neutral bidentate ligand. 1H NMR spectrum of [Zn(HL)2(OAc)2] shows that there is no enolisation of the ligand in the complex. The magnetic susceptibility measurements indicate that Cr(III), Mn(II), Fe(III),

V. L. Siji; M. R. Sudarsana Kumar; S. Suma; M. R. Prathapachandra Kurup

2010-01-01

131

Determination of the metal complexing capacity of aqueous solutions containing ligands by titration in the presence of complexing resins  

Microsoft Academic Search

The feasibility of ligand titrations with metal ions using complexing resins as sorbing solids is evaluated. The resins considered were the iminodiacetic resin Chelex 100, the carboxilic resin Amberlite CG50, and the anion exchange resin AG1X8, whose sorbing properties for aluminium(III) and copper(II) were known from previous investigations. Synthetical solutions containing known concentrations of ligands, EDTA and IDA were titrated

Maria Pesavento; Giancarla Alberti; Antonella Profumo

2000-01-01

132

Estimation of stability constants for metal–ligand complexes containing neutral nitrogen donor atoms with applications to natural organic matter  

NASA Astrophysics Data System (ADS)

Linear free energy relationships (LFERs) were developed for estimating 1:1 metal–ligand stability constants (log KML) for small organic molecules containing neutral nitrogen donor atoms. A data set of 44 monodentate and 112 bidentate ligands for six metal ions: Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ was employed to parameterize the LFER equations. Monodentate and bidentate log KML values were adequately described using Irving–Rossotti LFERs previously developed for ligands containing negatively-charged oxygen functional groups. Modifications to the LFER equations were necessary to account for steric hindrances to metal complexation by primary, secondary, and tertiary amines. The resulting LFER equations can be used to estimate log KML values for monodentate and bidentate ligands with neutral nitrogen donor groups where such values do not currently exist in the literature. Comparison of these results to our previous work with negatively-charged oxygen donor atoms reveals that neutral nitrogen functional groups are weaker than their oxygen counterparts for metal ions classified as "hard" on the basis of Hard–Soft Acid–Base (HSAB) theory. For "soft" metals, the opposite is true. These LFERs can be used to incorporate nitrogen functional groups in models for metal ion binding to natural organic matter (NOM).

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

2013-12-01

133

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

PubMed

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) free radical scavenging and reducing power activity of superoxide anion radical generated non-enzymatic systems. Electrochemical and thermal properties of the compounds were investigated. PMID:21752697

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

2011-10-15

134

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

135

Extraction of 3d transition metals from molten cesium-sodium-potassium/acetate eutectic into dodecane using organophosphorous ligands  

SciTech Connect

Experimental results are reported for the transfer of the transition metal (TM) cations Cr/sup 3 +/, Fe/sup 2 +/, Co/sup 2 +/, Ni/sup 2 +/ from molten cesium acetate-sodium acetate-potassium acetate eutectic (50-25-25 mol%, mp approx. 90/sup 0/C) into dodecane solutions containing selected acidic and neutral organophosphorous extracting ligands. The ordering of the transition metals according to their relative extents of extraction into the dodecane phase when the ligand bis(2-ethylhexyl)-phosphinic acid, H(DEPH), is employed (and the conditions of extraction are the same for each cation) is Co/sup 2 +/ > Fe/sup 2 +/ > Cr/sup 3 +/ > Ni/sup 2 +/. Comparisons of results obtained using the acidic ligand H(DEPH) and the neutral ligand tri-n-octylphosphine oxide, TOPO, indicate that the extractible TM complex does not contain acetate as a charge neutralizing ligand, but rather requires complete displacement of inner sphere acetate ions by protonated and/or deprotonated alkylphosphinate groups. The mechanism controlling the transfer kinetics has not been elucidated, but the rates of extraction from the acetate eutectic appear to be somewhat slower than has been observed for the extraction of transition metals from molten alkali metal thiocyanate and nitrate media at comparable temperatures, i.e., 140 ..-->.. 180/sup 0/C. 13 references, 2 figures, 2 tables.

Maroni, V.A.; Philbin, C.E.; Yonco, R.M.

1983-01-01

136

Extraction of 3d transition metals from molten cesium-sodium-potassium/acetate eutectic into dodecane using organophosphorous ligands  

SciTech Connect

Measurements have been made of the transfer of the transition metal cations Cr/sup 3 +/, Fe/sup 2 +/, Co/sup 2 +/, Ni/sup 2 +/ from molten cesium acetate-sodium acetate-potassium acetate eutectic (50-25-25 mol%, mp approx. 90/sup 0/C) into dodecane solutions containing selected acidic and neutral organophosphorous extracting ligands. The ordering of the transition metals according to their relative extents of extraction into the dodecane phase when the ligand bis(2-ethylhexyl)-phosphinic acid, H(DEPH), is employed (and the conditions of extraction are the same for each cation) is Co/sup 2 +/ > Fe/sup 2 +/ > Cr/sup 3 +/ > Ni/sup 2 +/. Comparisons of results obtained using the acidic ligand H(DEPH) and the neutral ligand tri-n-octylphosphine oxide, TOPO, indicate that the extractible TM complex does not contain acetate as a charge neutralizing ligand, but rather requires complete displacement of inner sphere acetate ions by protonated and/or deprotonated alkylphosphinate groups. The mechanism controlling the transfer kinetics has not been elucidated, but the rates of extraction from the acetate eutectic appear to be somewhat slower than has been observed for the extraction of transition metals from molten alkali metal thiocyanate and nitrate media at comparable temperatures, i.e., 140 ..-->.. 180/sup 0/C. 13 references, 2 figures, 2 tables.

Maroni, V.A.; Philbin, C.E.; Yonco, R.M.

1983-01-01

137

Hydrogen migration mechanism for ligand substitution reactions in metal carbonyl hydrides  

SciTech Connect

It has been known for some time that certain transition metal carbonyl hydrides are unusually labile in ligand substitution processes. A mechanism explaining this unusual lability was offered involving a ligand migration of hydrogen to a carbonyl group, attack at the vacated coordination site y the entering ligand, loss of a CO ligand, and back-migration of H to the metal. The following recent experiments offer strong support for this hydride migration. (A) In acetone at -70/sup 0/C H/sub 2/Fe(CO)/sub 4/ reacts within 3 min with PPh/sub 3/ to give H/sub 2/Fe(CO)PPh/sub 3/ and with P(OMe)/sub 3/ to give H/sub 2/Fe(CO)/sub 3/P(OMe)/sub 3/ and H/sub 2/Fe(CO)/sub 2/(P(OMe)/sub 3/)/sub 2/. The phosphine and phosphites are cis to both hydrogens, and the hydrogens are probably cis to each other. The same results are found in methanol at room temperature. These substitutions are at least 30 times as fast as the thermal decomposition of H/sub 2/Fe(CO)/sub 4/ in methanol. H/sub 2/Fe(CO)/sub 3/PPh/sub 3/ decomposes at a rate similar to that of H/sub 2/Fe(CO)/sub 4/ and yields trans-Fe(CO)/sub 3/(PPh/sub 3/)/sub 2/ in the presence of triphenylphosphine. (B) H/sub 2/Ru(CO)/sub 4/ in acetone at -70/sup 0/C also gives H/sub 2/Ru(CO)/sub 3/P(OMe)/sub 3/ in a few minutes with the phosphite cis to hydrogen. Upon warming H/sub 2/Ru(CO)/sub 2/(P(OMe)/sub 3/)/sub 2/ is formed. (C) In methanol at 25/sup 0/C the ion HRu(CO)/sub 4//sup -/, as the PPN/sup +/ salt, is converted immediately into HRu/sub 3/(CO)/sub 11//sup -/. Adding excess sodium methoxide (about 0.4 M) slows the reaction time down to about 15 min, but the same product is formed.

Pearson, R.G.; Walker, H.W.; Mauermann, H.; Ford, P.C.

1981-08-01

138

Transition metal induced derivatisations resulting in novel coordination behaviour of bis(oxamato) ligands.  

PubMed

Two mononuclear bis(oxamato) complexes with the formula [nBu4N]2[M(2,3-acbo)] (M=Ni (), Cu (), with acbo=anthra-9,10-chinone-2,3-bis(oxamato) have been synthesized starting from symmetric diethyl N,N'-anthra-9,10-chinone-2,3-bis(oxamate) (, 2,3-acboH2Et2). The crystal structures of and have been determined, verifying that the transition metal ions are eta4(kappa2N,kappa2O) coordinated by the [2,3-acbo]4- ligands. Using the asymmetric diethyl N,N'-anthra-9,10-chinone-1,2-bis(oxamate) (, 1,2-acboH2Et2) leads, under otherwise identical reaction conditions, to the novel bis(oxamato) complex [(n)Bu4N]2[Ni(1,2-acbo)] () whereby in the case of Cu(II) the derivate [nBu4N]2[Cu(aibo)2] () (aibo=anthra[1,2-d]-(imidazole-2-carboxylato)-6,11-dione) has been obtained. The crystal structures of and have been determined, displaying that the Ni(II) ion of is eta4(kappa2N,kappa2O) coordinated by the [1,2-acbo]4- ligand. The Cu(II) ion of is coordinated by two [aibo]2- ligands, giving rise to an approximately square-planar trans-bis(aibo-N,O) arrangement. Using the symmetric diethyl N,N'-4,5-dinitro-o-phenylene-bis(oxamate) (, niboH2Et2), possessing strongly electron withdrawing NO2-groups, leads under otherwise identical reaction conditions to the bis(oxamato) complex [nBu4N]2[Ni(nibo)] (), whereby in the case of Cu(II) the derivate [nBu4N]2[Cu(niqo)2] () (niqo=7,8-dinitro-2,3-quinoxalinedionato) has been obtained. The crystal structures of and have been determined, ensuring that the Ni(II) ion of is eta(4)(kappa2N,kappa2O) coordinated by the [nibo]4- ligand. The Cu(II) ion of is coordinated by four oxygen atoms of two [niqo]2- ligands, giving rise to an approximately square-planar coordination geometry. PMID:18802625

Rüffer, Tobias; Bräuer, Björn; Meva, François Eya'ane; Walfort, Bernhard

2008-10-01

139

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

PubMed

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, (1)H NMR, (13)C 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, (1)H NMR, (13)C 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. PMID:24820326

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

2014-10-15

140

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

141

Anchoring strategies for bimetallic species in zeolites. Progress report  

SciTech Connect

We explore a new approach by introducing heterobinuclear organometallic compounds for linking catalytic functions to zeolite frameworks. With two different metals present, the complexes are being anchored to the support via one oxophilic metal, ligand exchange and catalytic reactions may proceed at the second metal center. Anchoring chemistry, thermal stability and reactivity of Me{sub 3}SnMn(CO){sub 5} in zeolite NaY and acid forms of zeolite Y was studied with X-ray absorption spectroscopy (Sn, Mn edge EXAFS) and in-situ FTIR/TPD-MS techniques. Subsequently, the tin-cobalt complex Me{sub 3}SnCo(CO){sub 4} has been a focus of detailed synthetic and spectroscopic studies. The reactivity of tricarbonyl (cyclopentadienyl) (trimethylstannyl) molybdenum in new mesoporous hosts has been explored. A recent development is the design of vanadium oxo species in different micro- and mesoporous hosts. These are of great interest for the selective reduction of nitrogen oxides by ammonia, and selective oxidation of different hydrocarbons, such as xylenes, olefines and alkanes. Combination analytical techniques used to probe local structural changes at the molecular level, include EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy utilizing synchrotron radiation, in situ FT-IR coupled to thermodesorption/MS, UV-NIR, and CCD Raman.

Bein, T.

1993-03-01

142

Connecting small ligands to generate large tubular metal-organic architectures  

NASA Astrophysics Data System (ADS)

The new metal-organic framework materials, ZnF(Am 2TAZ)·solvents and ZnF(TAZ)·solvents (Am 2TAZ=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 6F 6(ligand) 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 2TAZ)·solvents, hydrophilic -NH 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 2TAZ)·solvents are two of the most thermally stable coordination frameworks known to date.

Goforth, Andrea M.; Su, Cheng-Yong; Hipp, Rachael; Macquart, René B.; Smith, Mark D.; zur Loye, Hans-Conrad

2005-08-01

143

Multiple Photofragmentation Pathways with Different Recoil Anisotropy from a Metal-Ion Ligand Complex  

NASA Astrophysics Data System (ADS)

Spatial recoil anisotropy that is dependent upon the fragment-ion species is reported for the first time for a metal-ion ligand complex after a single photoexcitation process by linearly polarized light. Upon excitation to the lowest three excited states of Mg+-ICH3, originating from the Mg+2P states, fragment ions of MgI+ and ICH+3 are found to have clear and different angular dependences, which are also characteristic of the excited states. These are explained from the results of theoretical work in that the calculated ground-state complex has a bent structure and further in that each transition dipole moment vector of the complex almost coincides with the Mg+ 3p orbital lobe direction in each case. The fragment ions are concluded to be formed along dissociative potential surfaces which are crossed by the initially excited states, in a much faster process than the rotational period of the complex.

Misaizu, Fuminori; Furuya, Ari; Tsunoyama, Hironori; Ohno, Koichi

2004-11-01

144

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

PubMed

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 Cu(I) 3 complex and liberate two equivalents of disulfide, consistent with a four-electron four-proton process. PMID:23539341

Lionetti, Davide; Day, Michael W; Agapie, Theodor

2013-01-01

145

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

146

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.

Lionetti, Davide; Day, Michael W.

2013-01-01

147

DFT modeling and spectroscopic study of metal ligand bonding in La(III) complex of coumarin-3-carboxylic acid  

NASA Astrophysics Data System (ADS)

The binding mode of coumarin-3-carboxylic acid (HCCA) to La(III) is elucidated at experimental and theoretical level. The complexation ability of the deprotonated ligand (CCA -) to La(III) is studied using elemental analysis, DTA and TGA data as well as FTIR, 1H NMR and 13C NMR spectra. The experimental data suggest the complex formula La(CCA) 2(NO 3)(H 2O) 2. B3LYP, BHLYP, B3P86, B3PW91, PW91P86 and MPW1PW91 functionals are tested for geometry and frequency calculations of the neutral ligand and all of them show bond length deviations bellow 1%. B3LYP/6-31G(d) level combined with large quasi-relativistic effective core potential for lanthanum is selected to describe the molecular, electronic and vibrational structures as well as the conformational behavior of HCCA, CCA - and La-CCA complex. The metal-ligand binding mode is predicted through molecular modeling and energy estimation of different La-CCA structures. The calculated atomic charges and the bonding orbital polarizations point to strong ionic metal-ligand bonding in La-CCA complex and insignificant donor acceptor interaction. Detailed vibrational analysis of HCCA, CCA - and La(CCA) 2(NO 3)(H 2O) 2 systems based on both calculated and experimental frequencies confirms the suggested metal-ligand binding mode.

Mihaylov, Tz.; Trendafilova, N.; Kostova, I.; Georgieva, I.; Bauer, G.

2006-09-01

148

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

149

A fascinating new field in colloid science: small ligand-stabilized metal clusters and their possible application in microelectronics  

Microsoft Academic Search

Small metal clusters, like Au55(PPh3)12Cl6, which fall in the size regime of 1–2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors. These chemically tailored quantum dots show by the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state. The organic ligand

G. Schön; U. Simon

1995-01-01

150

A fascinating new field in colloid science: small ligand-stabilized metal clusters and possible application in microelectronics  

Microsoft Academic Search

Small metal clusters, like Au55(PPh3)12Cl6, which fall in the size regime of 1–2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors. These chemically tailored quantum dots show regarding the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state. The organic ligand

G. Schön; U. Simon

1995-01-01

151

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

152

Fabrication of highly uniform gel coatings by the conversion of surface-anchored metal-organic frameworks.  

PubMed

We report the fabrication of 3D, highly porous, covalently bound polymer films of homogeneous thickness. These surface-bound gels combine the advantages of metal-organic framework (MOF) materials, namely, the enormous flexibility and the large size of the maximum pore structures and, in particular, the possibility to grow them epitaxially on modified substrates, with those of covalently connected gel materials, namely, the absence of metal ions in the deposited material, a robust framework consisting of covalent bonds, and, most importantly, pronounced stability under biological conditions. The conversion of a SURMOF (surface-mounted MOF) yields a surface-grafted gel. These SURGELs can be loaded with bioactive compounds and applied as bioactive coatings and provide a drug-release platform in in vitro cell culture studies. PMID:24328287

Tsotsalas, Manuel; Liu, Jinxuan; Tettmann, Beatrix; Grosjean, Sylvain; Shahnas, Artak; Wang, Zhengbang; Azucena, Carlos; Addicoat, Matthew; Heine, Thomas; Lahann, Joerg; Overhage, Jörg; Bräse, Stefan; Gliemann, Hartmut; Wöll, Christof

2014-01-01

153

Photoelectric conversion at a [Ru(bpy)3](2+)-based metallic triad anchored on ITO surface.  

PubMed

A tri-metallic triad based on a [Ru(bpy)3](2+) moiety connected to Fe(ii) and Co(iii) bisterpyridine has been grafted on an ITO electrode by a stepwise procedure. Under visible light, in the presence of a sacrificial electron donor, the system produces electric current. The photo-current magnitude is compared to the one generated from a Co(iii)-Ru(ii) dyad and shows an increase of 40%. PMID:25002098

Farran, Rajaa; Jouvenot, Damien; Loiseau, Frédérique; Chauvin, Jérôme; Deronzier, Alain

2014-07-22

154

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.

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

2010-01-01

155

USE OF THE BIOTIC LIGAND MODEL TO PREDICT METAL TOXICITY TO AQUATIC BIOTA IN AREAS OF DIFFERING GEOLOGY1  

Microsoft Academic Search

This work evaluates the use of the biotic ligand model (BLM), an aquatic toxicity model, to predict toxic effects of metals on aquatic biota in areas underlain by different rock types. The chemical composition of water, soil, and sediment is largely derived from the composition of the underlying rock. Geologic source materials control key attributes of water chemistry that affect

Kathleen S. Smith

156

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

PubMed

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; Wöll, Christof; Gliemann, Hartmut

2013-01-01

157

Rock and Soil Anchor Systems  

NSDL National Science Digital Library

Williams Form Engineering manufactures one of the most diverse rock and soil anchoring product lines in the world, including mechanical anchors, resin anchors, multiple corrosion protection anchors, soil nails, sledge drive anchors and self drilling anchors. The site includes not only information on the company, but also explanation of the product and their role in the mining process.

2009-05-21

158

Immobilized triazacyclononane derivatives as selective oxidation catalysts. Final technical report of DOE Award No. DE-FG02-99ER14968 with the University of Munich [Encapsulation of metal chelate and oxocatalysts in nanoporous hosts  

SciTech Connect

This project deals with the covalent anchoring of various derivatives of triazacyclononane (TACN)ligands in the channels of period mesoporous materials and the catalytic activity of the corresponding metal complexes. Catalyst preparation, ligand immobilization, catalyst characterization, and catalyst performance in selective oxidation are discussed. A wide range of pendant variations on the TACN ligand can be synthesized, and ligands can be covalently bound to high surface area, pseudo-crystalline, silicate solids, before or after pendant addition.

Bein, Thomas

2002-10-28

159

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

160

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

161

Internal fixation strength of suture anchors--update 1997.  

PubMed

Two new areas of anchor development are biodegradable anchors and "mini" anchors. The group of biodegradable anchors tested include the Bio-Anchor, LactoSorb, Biofix, Bio-Statak, Mini Screw suture anchor, DePuy 4.5 molded, DePuy 4.5 machined, DePuy 3.5 machined, TAG Wedge 4, TAG Rod 2, TAG Wedge 3, TAG Wedge 2, and Stealth. "Mini anchors" have drill holes or minor diameters of < 2.2 mm. Those tested include the Mini Revo and Bio-Anchor, miniHarpoon, mini Mitek and Fast in 3, Statak 1.5 and 2.5, SB 2 and PeBA 3, Corkscrew 5, Corkscrew 3.5, and Fastak A2, Ogden 2.5, TAG Wedge 2, ROC 1.9, and Questus 2.5. Additional anchors tested that fit neither category include the Anspach, Questus 3.5 and 5.0, SB 3 and PeBA-C, Ogden 3.5, Fast in 4, Ultrafix, and the ROC 3.5, ROC 2.8, ROC 2.3, and ROC XS. An anchor comparison, using an established protocol in fresh porcine femurs, recorded failure strength, failure mode, eyelet size, minor and major diameters, and drill hole sizes. Except for the Bio-Anchor and TAG Wedge 2, biodegradable anchors tend to be larger to compensate for their lower strength relative to metal. Biodegradable screw anchors' predominant failure mode was eyelet cutout, whereas biodegradable nonscrew anchors failed to predominantly by anchor pullout. From an initial mechanical perspective, these biodegradable anchors perform acceptably. Both biodegradable and "mini" anchors include screw and nonscrew designs. As expected, screw designs perform well and generally fail at higher loads than nonscrew anchors. Although biodegradable anchors, as a group, are not as strong as metal anchors, they are stronger than the sutures for which they are designed. The move to smaller ("mini") and biodegradable anchors is supported by these data. Whether an anchor fails at twice the suture breaking strength or 10 times the suture breaking strength should make no difference. PMID:9195034

Barber, F A; Herbert, M A; Click, J N

1997-06-01

162

Variation in One Residue Associated with the Metal Ion-Dependent Adhesion Site Regulates ?IIb?3 Integrin Ligand Binding Affinity  

PubMed Central

The Asp of the RGD motif of the ligand coordinates with the ? I domain metal ion dependent adhesion site (MIDAS) divalent cation, emphasizing the importance of the MIDAS in ligand binding. There appears to be two distinct groups of integrins that differ in their ligand binding affinity and adhesion ability. These differences may be due to a specific residue associated with the MIDAS, particularly the ?3 residue Ala252 and corresponding Ala in the ?1 integrin compared to the analogous Asp residue in the ?2 and ?7 integrins. Interestingly, mutations in the adjacent to MIDAS (ADMIDAS) of integrins ?4?7 and ?L?2 increased the binding and adhesion abilities compared to the wild-type, while the same mutations in the ?2?1, ?5?1, ?V?3, and ?IIb?3 integrins demonstrated decreased ligand binding and adhesion. We introduced a mutation in the ?IIb?3 to convert this MIDAS associated Ala252 to Asp. By combination of this mutant with mutations of one or two ADMIDAS residues, we studied the effects of this residue on ligand binding and adhesion. Then, we performed molecular dynamics simulations on the wild-type and mutant ?IIb?3 integrin ? I domains, and investigated the dynamics of metal ion binding sites in different integrin-RGD complexes. We found that the tendency of calculated binding free energies was in excellent agreement with the experimental results, suggesting that the variation in this MIDAS associated residue accounts for the differences in ligand binding and adhesion among different integrins, and it accounts for the conflicting results of ADMIDAS mutations within different integrins. This study sheds more light on the role of the MIDAS associated residue pertaining to ligand binding and adhesion and suggests that this residue may play a pivotal role in integrin-mediated cell rolling and firm adhesion.

Wu, Xue; Xiu, Zhilong; Li, Guohui; Luo, Bing-Hao

2013-01-01

163

Extraction of 3d transition metals from molten cesium-sodium-potassium/acetate eutectic into dodecane using organophosphorous ligands  

SciTech Connect

Measurements have been made of the transfer of the transition metal cations Cr/sup 3 +/, Fe/sup 2 +/, Co/sup 2 +/, Ni/sup 2 +/ from molten cesium acetate-sodium acetate-potassium acetate eutectic (50-25-25 mol%, mp approx. 90/sup 0/C) into dodecane solutions containing selected acidic and neutral organophosphorous extracting ligands. The ordering of the relative rates and extents of extraction when the ligand bis(2-ethylhexyl)phosphinic acid, H(DEPH), is employed (and the conditions of extraction are the same for each cation) is Co/sup 2 +/ > Fe/sup 2 +/ > Cr/sup 3 +/ > Ni/sup 2 +/. Comparisons of results obtained using the acidic ligand H(DEPH) and the neutralligand Tri-n-octylphosphien oxide, TOPO, indicate that the extractible TM complex does not contain acetate as a charge neutralizing ligand, but rather requires complete displacement of inner sphere acetate ions by both protonated and deprotonated alkylphosphinate groups. In the case of Co/sup 2 +/, the extraction reaction involves the transformation of the cation from an octahedral ligand field in the acetate eutectic to a tetrahedral ligand field in the H(DEPH)/dodecane phase. The mechanism(s) controlling the transfer kinetics has not been elucidated, but it is noted that the rates of extraction from the acetate eutectic seem to be much slower than has been observed for extractions of transition metals from molten alkali metal thiocyanate and nitrate media over comparable temperature ranges (140 to 180/sup 0/C). 1 figure, 2 tables.

Maroni, V.A.; Philbin, C.E.; Yonco, R.M.

1983-04-01

164

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

165

Adjusting the stability of metal-organic frameworks under humid conditions by ligand functionalization.  

PubMed

The practical use of metal-organic frameworks (MOFs) in applications ranging from adsorption separations to controlled storage and release hinges on their stability in humid or aqueous environments. The sensitivity of certain MOFs under humid conditions is well-known, but systematic studies of water adsorption properties of MOFs are lacking. This information is critical for developing design criteria for directing future synthesis efforts. The goal of this work is to understand the influence of the extent of Zn-O bond shielding on the relative stabilities of MOFs belonging to same family of isostructural, noncatenated pillared MOFs [Zn(L)(DABCO)(0.5)], where L is the functionalized BDC (1,4-benzenedicarboxylic acid) linker. The different extent of Zn-O bond shielding is provided by incorporating a broad range of functional groups on the BDC ligand. The resulting MOFs have varying surface areas, pore sizes, and pore volumes. Stability is assessed through water vapor adsorption isotherms combined with powder X-ray diffraction (PXRD) experiments and surface area analyses. Our study demonstrates that integration of polar functional groups (e.g., nitro, bromo, chloro, hydroxy, etc.) on the dicarboxylate linker renders these MOFs water unstable compared to the parent MOF as these polar functional groups have a negative shielding effect; i.e., they facilitate hydrolysis of the Zn-O bond. On the other hand, placing nonpolar groups (e.g., methyl) on the BDC ligand results in structurally robust MOFs because the Zn-O bond is effectively shielded from attack by water molecules. Therefore, the anthracene- and tetramethyl-BDC MOFs do not lose crystallinity or surface area after water exposure, in spite of the large amount of water adsorption due to capillary condensation at ?20% relative humidity (RH). This has been observed rarely in the MOF literature. The results of this work show that by ligand functionalization it is possible to adjust the water stability of a pillared MOF in both the positive and negative directions and, thus, provide an important step toward understanding the water adsorption behavior of MOFs. PMID:23134370

Jasuja, Himanshu; Huang, You-gui; Walton, Krista S

2012-12-11

166

Complexes of divalent transition metal chlorides with the tetradentate Schiff base ligand 1,2-bis(2?-pyridylmethyleneimino)-benzene  

Microsoft Academic Search

Transition metal(II) chloro complexes of the new Schiff base ligand 1,2-bis(2'-pyridylmethyleneimino)benzene (L), derived from 2-pyridinecarboxaldehyde and 1,2-phenylenediamine, were prepared. Compounds of [MnLCl2]-H2O, [CoLCl2]·2H2O, [NiLCl2] and [Zn3L2Cl4]Cl2 were prepared. Details are given of the formation of the complex [Cu(L·EtOH)Cl2], in which one molecule of EtOH adds across only one of the Schiff base {ie531-01} groups to give the coordinated ligand L·EtOH.

Spyridoula Kasselouri; Achilleas Garoufis; George Kalkanis; Spyros P. Perlepes; Nick Hadjiliadis

1993-01-01

167

A new analysis of charge transfer and polarization for ligand-metal bonding - Model studies of Al4CO and Al4NH3  

NASA Technical Reports Server (NTRS)

The nature of the bonding of CO and NH3 ligands to Al is analyzed, and the intra-unit charge polarization and inter-unit donation for the interaction of ligands with metals are studied. The consequences of metal-to-ligand and ligand-to-metal charge transfer are separately considered by performing a constrained space orbital variation (CSOV) with the electrons of the metal member of the complex in the field of frozen ligand. The electrons of the metal atoms are then frozen in the relaxed distribution given by the CSOV SCF wave function and the ligand electrons are allowed to relax. Quantitative measures of the importance of inter-unit charge transfers and intra-unit polarization are obtained using results of SCF studies of Al4CO and Al4NH3 clusters chosen to simulate the adsorption of the ligands at an on-top side of the Al(111) surface. The electrostatic attraction of the effective dipole moments of the metal and ligand units makes an important contribution to the bond.

Bagus, P. S.; Hermann, K.; Bauschlicher, C. W., Jr.

1984-01-01

168

Reactions of aromatic N-heterocycles with d0fn-metal alkyl complexes supported by chelating diamide ligands.  

PubMed

Aromatic heterocycles are a prominent feature within natural products and pharmaceuticals and considerable efforts are directed toward their synthesis and functionalization. These molecules also appear as unwanted impurities in carbon-based fuels, and processes that fragment them are of increasing interest. Early transition metal-carbon bonds show diverse reactivity toward aromatic heterocycles: researchers have reported both functionalization, relevant to synthetic efforts, and ring opening, relevant to their removal from fuels. In particular, chelating ferrocene-diamides possess unique electronic characteristics as ancillary ligands that enable a wide range of reactivity behaviors for the resulting metal complexes. In this Account, we describe our efforts to understand the reactivity of group 3 metal and uranium alkyl complexes supported by these organometallic ligands toward aromatic N-heterocycles. Two geometrically related ancillary ligands were investigated: 1,1'-ferrocenylene-diamides and pincer-type pyridine-diamides. A substrate-dependent behavior was observed. For example, all the benzyl metal complexes cleaved 1-methylimidazole. In the case of pyridines, differences in reactivity were identified: C-H activation and C-C coupling occurred with substituted pyridines, while alkyl transfer predominated with isoquinoline and chelating pyridines. The products of the C-C coupling or the alkyl-transfer reactions underwent subsequent hydrogen transfer: within the same ring for the substituted pyridines and between two different heterocycles for isoquinoline and chelating pyridines. The comparison between yttrium and lutetium benzyl complexes supported by ferrocene- or pyridine-diamide ligands indicated that similar reactions occurred for specific substrates (1-methylimidazole, 2-picoline, and isoquinoline). A broader range of reaction types and a larger substrate scope were identified, however, for the ferrocene than for the pyridine-type complexes. Based on the reactions discussed in this Account and on isolated examples drawn from the literature, we conclude that the ferrocene-diamides represent a versatile ligand framework. We propose that iron's ability to accommodate changes in the electronic density at the metal center more readily than classical supporting ligands leads to the privileged status of these organometallic ancillary ligands. PMID:20954750

Diaconescu, Paula L

2010-10-19

169

Coordination polymers with the chiral ligand N-p-tolylsulfonyl-L-glutamic acid: Influence of metal ions and different bipyridine ligands on structural chirality  

SciTech Connect

Four new polymers, namely [Ni(-tsgluO)(2,4'-bipy){sub 2}(H{sub 2}O){sub 2}]{sub n}.5nH{sub 2}O (1), [Co(-tsgluO)(2,4'-bipy){sub 2}(H{sub 2}O){sub 2}]{sub n}.5nH{sub 2}O (2), [Ni(-tsgluO)(4,4'-bipy)]{sub n}.0.5nH{sub 2}O (3), and [Co(-tsgluO)(4,4'-bipy)]{sub n}.0.5nH{sub 2}O (4), where tsgluO{sup 2-}=(+)-N-p-tolylsulfonyl-L-glutamate dianion, 2,4'-bipy=2,4'-bipyridine, and 4,4'-bipy=4,4'-bipyridine, have been prepared and structurally characterized. Compounds 1 and 2 are isostructural and mononuclear, and crystallize in the acentric monoclinic space group Cc, forming 1D chain structures. Compound 3 is also mononuclear, but crystallizes in the chiral space group P2{sub 1}, forming a homochiral 2D architecture. In contrast to the other complexes, compound 4 crystallizes in the space group P-1 and is composed of binuclear [Co{sub 2}O{sub 6}N{sub 2}]{sub n}{sup 4-} units, which give rise to a 2D bilayer framework. Moreover, compounds 1, 2, and 4 self-assemble to form 3D supramolecular structures through {pi}-{pi} stacking and hydrogen-bonding interactions, while compound 3 is further hydrogen-bonded to form 3D frameworks. We have demonstrated the influence of the central metal and bipyridine ligands on the framework chirality of the coordination complexes. - Graphical abstract: Four novel polymers based on a chiral ligand were prepared and structurally characterized; it represents the first series of investigations about the effect of central metals and bipyridine ligands on framework chirality.

He Rong [Department of Chemistry and Material Sciences, Hebei Normal University, Shijiazhuang 050016 (China); Song Huihua, E-mail: songhuihua@mail.hebtu.edu.c [Department of Chemistry and Material Sciences, Hebei Normal University, Shijiazhuang 050016 (China); Wei Zhen [Department of Chemistry and Material Sciences, Hebei Normal University, Shijiazhuang 050016 (China); Zhang Jianjun [Experimental Center, Hebei Normal University, Shijiazhuang 050016 (China); Gao Yuanzhe [Department of Chemistry and Material Sciences, Hebei Normal University, Shijiazhuang 050016 (China)

2010-09-15

170

Comparative investigation of N donor ligand-lanthanide complexes from the metal and ligand point of view  

NASA Astrophysics Data System (ADS)

N-donor ligands such as n-Pr-BTP (2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine) studied here preferentially bind An(III) over Ln(III) in liquid-liquid separation of trivalent ac-tinides from spent nuclear fuel. The chemical and physical processes responsible for this selectivity are not yet well understood. We present systematic comparative near-edge X-ray absorption structure (XANES) spectroscopy investigations at the Gd L3 edge of [GdBTP3](NO3)3, [Gd(BTP)3](OTf)3, Gd(NO3)3, Gd(OTf)3 and N K edge of [Gd(BTP)3](NO3)3, Gd(NO3)3 complexes. The pre-edge absorption resonance in Gd L3 edge high-energy resolution X-ray absorption near edge structure spectra (HR-XANES) is explained as arising from 2p3/2 ? 4f/5d electronic transitions by calculations with the FEFF9.5 code. Experimental evidence is found for higher electronic density on Gd in [Gd(BTP)3](NO3)3 and [Gd(BTP)3](OTf)3 compared to Gd in Gd(NO3)3 and Gd(OTf)3, and on N in [Gd(BTP)3](NO3)3 compared to n-Pr-BTP. The origin of the pre-edge structure in the N K edge XANES is explained by density functional theory (DFT) with the ORCA code. Results at the N K edge suggest a change in ligand orbital occupancies and mixing upon complexation but further work is necessary to interpret observed spectral variations.

Prüßmann, T.; Denecke, M. A.; Geist, A.; Rothe, J.; Lindqvist-Reis, P.; Löble, M.; Breher, F.; Batchelor, D. R.; Apostolidis, C.; Walter, O.; Caliebe, W.; Kvashnina, K.; Jorissen, K.; Kas, J. J.; Rehr, J. J.; Vitova, T.

2013-04-01

171

GPI-anchor and GPI-anchored protein expression in PMM2-CDG patients  

PubMed Central

Background Mutations in PMM2 impair phosphomannomutase-2 activity and cause the most frequent congenital disorder of glycosylation, PMM2-CDG. Mannose-1-phosphate, that is deficient in this disorder, is also implicated in the biosynthesis of glycosylphosphatidyl inositol (GPI) anchors. Objective To evaluate whether GPI-anchor and GPI-anchored proteins are defective in PMM2-CDG patients. Methods The expression of GPI-anchor and seven GPI-anchored proteins was evaluated by flow cytometry in different cell types from twelve PMM2-CDG patients. Additionally, neutrophil CD16 and plasma hepatic proteins were studied by Western blot. Transferrin glycoforms were evaluated by HPLC. Results Patients and controls had similar surface expression of GPI-anchor and most GPI-anchored proteins. Nevertheless, patients displayed a significantly diminished binding of two anti-CD16 antibodies (3G8 and KD1) to neutrophils and also of anti-CD14 (61D3) to monocytes. Interestingly, CD16 immunostaining and asialotransferrin levels significantly correlated with patients’ age. Analysis by flow cytometry of CD14 with M?P9, and CD16 expression in neutrophils by Western blot using H-80 ruled out deficiencies of these antigens. Conclusions PMM2 mutations do not impair GPI-anchor or GPI-anchored protein expression. However, the glycosylation anomalies caused by PMM2 mutations might affect the immunoreactivity of monoclonal antibodies and lead to incorrect conclusions about the expression of different proteins, including GPI-anchored proteins. Neutrophils and monocytes are sensitive to PMM2 mutations, leading to abnormal glycosylation in immune receptors, which might potentially affect their affinity to their ligands, and contribute to infection. This study also confirms less severe hypoglycosylation defects in older PMM2-CDG patients.

2013-01-01

172

Synthesis, structural diversity and fluorescent characterisation of a series of d10 metal-organic frameworks (MOFs): reaction conditions, secondary ligand and metal effects.  

PubMed

Along with our recent investigation on the flexible ligand of H(2)ADA (1,3-adamantanediacetic acid), a series of Zn(II) and Cd(II) metal-organic frameworks, namely, [Zn(3)(ADA)(3)(H(2)O)(2)](n)·5nH(2)O (1), [Zn(ADA)(4,4'-bipy)(0.5)](n) (2), [Zn(2)(ADA)(2)(bpa)](n) (3), [Zn(2)(ADA)(2)(bpa)](n) (4), [Zn(2)(ADA)(2)(bpp)](n) (5), [Cd(HADA)(2)((4,4'-bipy)](n) (6), [Cd(3)(ADA)(3)(bpa)(2)(CH(3)OH)(H(2)O)](n) (7), and [Cd(2)(ADA)(2)(bpp)(2)](n)·7nH(2)O (8) have been synthesized and structurally characterized (where 4,4'-bipy = 4,4'-dipyridine, bpa = 1,2-bis(4-pyridyl)ethane and bpp = 1,3-bis(4-pyridyl)propane). Due to various coordination modes and conformations of the flexible dicarboxylate ligand and the different pyridyl-containing coligands, these complexes exhibit structural and dimensional diversity. Complex 1 exhibits a three-dimensional (3D) framework containing one-dimensional (1D) Zn(II)-O-C-O-Zn(II) clusters. Complex 2 exhibits a 2D structure constructed by 1D double chains based on [Zn(2)ADA(2)] units and a 4,4'-bipy pillar. Complexes 3 and 4 possess isomorphic 2D layer structures, resulting from the different coordination modes of carboxylate group of ADA ligands. Complex 5 features a 2D 4(4) layer in which ADA ligands and Zn(II) atoms construct a 1D looped chain and the chains are further connected by bpp ligands. Complex 6 is composed of 1D zig-zag chains that are entangled through hydrogen-bonding interactions to generate a 2D network. Complex 7 is a rare (3,5)-connected network. Complex 8 possesses a 3D microporous framework with lots of water molecules encapsulated in the channels. The structural diversity of the complexes perhaps mainly results from using diverse secondary ligands and different metal centre ions, and means the assistant ligand and metal centre play important roles in the design and synthesis of target metal-organic frameworks. This finding revealed that ADA could be used as an effective bridging ligand to construct MOFs and change coordination modes and conformational geometries in these complexes. The thermogravimetric analyses, X-ray powder diffraction and solid-state luminescent properties of the complexes have also been investigated. PMID:21293812

Zhang, Wei Hong; Dong, Zhe; Wang, Yao Yu; Hou, Lei; Jin, Jun Cheng; Huang, Wen Huan; Shi, Qi Zhen

2011-03-21

173

Synthesis, characterization and antimicrobial activity of 3d transition metal complexes of a biambidentate ligand containing quinoxaline moiety  

NASA Astrophysics Data System (ADS)

A new series of oxovanadium(IV), chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), and copper(II) complexes of the 3-hydrazino quinoxaline-2-one (HQO) were prepared and characterized. The ligand exhibits biambidenticity. It behaves as a bidentate ON donor in oxovanadium(IV), iron(III) and copper(II) complexes and as a bis bidentate ONNN donor in chromium(III), manganese(II), cobalt(II) and nickel(II) complexes. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, thermal, infrared, 1H NMR, electronic spectra, magnetic susceptibility and conductivity measurements. An octahedral geometry was suggested for all the complexes. All the complexes show subnormal magnetic moments. The ligand, HQO, and its complexes were tested against one strain Gram +ve bacteria ( Staphylococcus aureus), Gram -ve bacteria ( Escherichia coli). The prepared metal complexes exhibited higher antimicrobial activities than the parent ligand.

Anantha Lakshmi, P. V.; Reddy, P. Saritha; Raju, V. Jayatyaga

2009-09-01

174

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

175

Group 4 metal complexes with new chiral pincer NHC-ligands: synthesis, structure and catalytic activity.  

PubMed

Chiral group 4 NHC-metal complexes were prepared in good yields by amine elimination from M(NR2)4 (M = Ti, Zr, Hf; R = Me, Et) and chiral pincer NHC-ligands, L4(L4a and L4b), L5 and L6, which are derived from (S,S)-diphenyl-1,2-ethanediamine. Treatment of M(NR2)4 with 1 equiv. of L4 in THF gives, after recrystallization from a benzene solution, the chiral titanium amides (L4)Ti(NMe2)(Br)(THF) (7) and (L4)Ti(NMe2)(Cl)(THF) (11), zirconium amides (L4)Zr(NMe2)(Br)(THF) (8), (L4)Zr(NEt2)(Br)(THF) (10), (L4)Zr(NMe2)(Cl)(THF) (12) and (L4)Zr(NEt2)(Cl)(THF) (14), and hafnium amides (L4)Hf(NMe2)(Br)(THF) (9) and (L4)Hf(NMe2)(Cl)(THF) (13), respectively. Similarly, the reactions of L5 or L6 with 1 equiv. of M(NR2)4 yield the titanium amide (L6)Ti(NMe2)(Cl)(THF) (16), the zirconium amides (L5)Zr(NMe2)(Cl)(THF) (15), (L6)Zr(NMe2)(Cl)(THF) (17) and (L6)Zr(NEt2)(Cl)(THF) (19), and the hafnium amide (L6)Hf(NMe2)(Cl)(THF) (18), respectively. Complexes 7 - 19 were characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 10 and 14 - 19 were also established by X-ray diffraction analyses, which represent the first example of the structurally characterized group 4 chiral NHC-metal complex. Furthermore, 7 - 19 are active catalysts for the polymerization of rac-lactide in the presence of isopropanol, leading to the heterotactic-rich polylactides. PMID:24710509

Zhao, Ning; Hou, Guohua; Deng, Xuebin; Zi, Guofu; Walter, Marc D

2014-06-14

176

Assembly of three novel metal (II) complexes based on polycarboxylate and 1,10-phenanthroline ligands  

NASA Astrophysics Data System (ADS)

With the principles of crystal engineering, three novel metal(II) complexes, [Cu2(betd)(phen)4].15H2O (1), [Cd4(betd)2(phen)8]?28H2O (2) and {[Co2(betd)(phen)2(H2O)2]·2H2O}n (3) (H4betd = bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid, phen = 1,10-phenanthroline) were synthesized and structurally characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, TGA, powder XRD and fluorescent measurements. Complex 1 is a binuclear structure, novel water tapes are observed to be encapsulated in the 3D open supramolecular architecture by hydrogen bond interactions. In 2, two pairs of CdII ions joined with two (betd)4- ions to form a cyclic tetranuclear structure. The neighboring tetranuclear units are linked into 2D network through ?⋯? stacking interactions. Interestingly, the lattice H2O molecules are joined by strong hydrogen bond interactions generating a wavy water layer, which contacts the 2D network to form 3D supramolecular structure. 3 shows a 2D (4, 4) grid network, which are assembled in an ABAB sequence to 3D supramolecular structures via ?⋯? stacking interactions between two central phen ligands from two adjacent sheets and hydrogen bond interactions.

Chen, Xiaoli; Qiao, Yali; Gao, Loujun; Cui, Huali; Zhang, Meili; Lv, Junfang

2013-04-01

177

Nonlinear optical properties of metal-organic complexes with phosphorous-donor ligands  

NASA Astrophysics Data System (ADS)

Nonlinear optical materials with large intensity-induced changes in refractive index and absorption, which can be characterized by their effective third order susceptibility, are needed for numerous optical device applications. We have reported that Mo(CO)(Ph2PX) complexes exhibit strong, non-resonantly enhanced optical nonlinearities. However, the relationship between the structure of these complexes and their nonlinear optical properties is poorly understood. We have now synthesized Pd(II) and Pt(II) phosphine complexes similar to the Mo(O) complexes and have studied their nonlinear optical properties using Z-scan experiments. The Pd(II) and Pt(II) complexes have a low linear absorption at the working wavelength of 532 nm and exhibit both nonlinear optical refraction and nonlinear optical absorption effects. Our measurements indicate that the nonlinear optical properties of these complexes depend both on the nature of the phosphine ligand and on the nature of the metal center and its coordination geometry. However, this dependence is not as pronounced as we have previously observed in the Mo(CO)(Ph2PX) complexes.

Gale, David C.; Gray, Gary M.; Lawson, Christopher M.

1997-10-01

178

Synthesis, characterization and physiochemical information, along with antimicrobial studies of some metal complexes derived from an ON donor semicarbazone ligand  

NASA Astrophysics Data System (ADS)

Eight new transition metal complexes of benzaldehyde- N(4)-phenylsemicarbazone have been synthesized and characterized by elemental analyses, molar conductance, electronic and infrared spectral studies. In all the complexes, the semicarbazone is coordinated as neutral bidentate ligand. 1H NMR spectrum of [Zn(HL) 2(OAc) 2] shows that there is no enolisation of the ligand in the complex. The magnetic susceptibility measurements indicate that Cr(III), Mn(II), Fe(III), Co(II) and Cu(II) complexes are paramagnetic and Ni(II) is diamagnetic. The EPR spectrum of [Mn(HL) 2(OAc) 2] in DMF solution at 77 K shows hyperfine sextet with low intensity forbidden lines lying between each of the two main hyperfine lines. The g values calculated for the [Cu(HL) 2SO 4] complex in frozen DMF, indicate the presence of unpaired electron in the d orbital. The metal ligand bonding parameters evaluated showed strong in-plane ? bonding and in-plane ? bonding. The ligand and complexes were screened for their possible antimicrobial activities.

Siji, V. L.; Kumar, M. R. Sudarsana; Suma, S.; Kurup, M. R. Prathapachandra

2010-06-01

179

Synthesis, characterization and physiochemical information, along with antimicrobial studies of some metal complexes derived from an ON donor semicarbazone ligand.  

PubMed

Eight new transition metal complexes of benzaldehyde-N(4)-phenylsemicarbazone have been synthesized and characterized by elemental analyses, molar conductance, electronic and infrared spectral studies. In all the complexes, the semicarbazone is coordinated as neutral bidentate ligand. (1)H NMR spectrum of [Zn(HL)(2)(OAc)(2)] shows that there is no enolisation of the ligand in the complex. The magnetic susceptibility measurements indicate that Cr(III), Mn(II), Fe(III), Co(II) and Cu(II) complexes are paramagnetic and Ni(II) is diamagnetic. The EPR spectrum of [Mn(HL)(2)(OAc)(2)] in DMF solution at 77K shows hyperfine sextet with low intensity forbidden lines lying between each of the two main hyperfine lines. The g values calculated for the [Cu(HL)(2)SO(4)] complex in frozen DMF, indicate the presence of unpaired electron in the d(x)(2) - (y)(2) orbital. The metal ligand bonding parameters evaluated showed strong in-plane sigma bonding and in-plane pi bonding. The ligand and complexes were screened for their possible antimicrobial activities. PMID:20347382

Siji, V L; Kumar, M R Sudarsana; Suma, S; Kurup, M R Prathapachandra

2010-06-01

180

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

PubMed

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 (1)H 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. PMID:24892547

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

2014-11-11

181

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

182

Introduction of multiphosphonate ligand to peptide nucleic acid for metal ion conjugation  

PubMed Central

Peptide nucleic acid (PNA) is one of the most widely used synthetic DNA analogs. Conjugation of functional molecules to PNA is very effective to further widen its potential applications. For this purpose, here we report the synthesis of several ligand monomers and introduced them to PNA. These ligand-modified PNAs attract cerium ion and are useful for site-selective DNA hydrolysis. It should be noted that these ligands on PNA are also effective even under the conditions of invasion complex.

Aiba, Yuichiro; Honda, Yuta; Han, Yue; Komiyama, Makoto

2012-01-01

183

Mono- and binuclear molybdenum and tungsten complexes containing asymmetric bridging ligands: Effects of ligand conjugation and conformation on metal-metal interactions  

SciTech Connect

The authors have prepared the new monodentate ligands 4-(4-methoxyphenyl)pyridine, 1-(4-pyridyl)-2-(4-methoxyphenyl)ethene, 1-(4-pyridyl)-2-(3-methoxyphenyl)ethene, and 1-(3-pyridyl)-2-(4-methoxyphenyl)ethene (L[sup 5]-L[sup 8]); demethylation of the methoxy group in each case afforded the new bridging bidentate ligands HL[sup 1]-HL[sup 4], which contain one pyridyl and one phenolate donor. Attachment of a MoL*(NO)Cl [L* = hydrotris(3,5-dimethylpyrazolyl)borate] moiety to the pyridyl groups of L[sup 5]-L[sup 8] gave the 17-electron complexes [Mo(NO)L*ClL[prime

Das, A.; Jeffery, J.C.; Maher, J.P.; McCleverty, J.A.; Schatz, E.; Ward, M.D.; Wollermann, G. (Univ. of Bristol (United Kingdom))

1993-05-12

184

Synthesis, thermal and spectral studies of first-row transition metal complexes with girard P reagent-based ligand  

Microsoft Academic Search

A new series of first-row transition metal complexes with 1-acetylpyridinium chloride-4-benzoyl thiosemicarbazide (H2GPBzIT) have been prepared and characterized by elemental analysis, spectroscopic and magnetic measurements. The proton-ligand ionization constants were determined potentiometrically using Irving–Rossotti technique. The stability constants of complexes were also calculated and were found in agreement with the sequence of stability constants of Irving and Williams. Thermal stability

Usama El-Ayaan; I. M. Kenawy; Y. G. Abu El-Reash

2007-01-01

185

Metal-ligand cooperation on a diruthenium platform: selective imine formation through acceptorless dehydrogenative coupling of alcohols with amines.  

PubMed

Metal-metal singly-bonded diruthenium complexes, bridged by naphthyridine-functionalized N-heterocyclic carbene (NHC) ligands featuring a hydroxy appendage on the naphthyridine unit, are obtained in a single-pot reaction of [Ru2(CH3COO)2(CO)4] with 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (BIN?HBr) or 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (PIN?HBr), TlBF4, and substituted benzaldehyde containing an electron-withdrawing group. The modified NHC-naphthyridine-hydroxy ligand spans the diruthenium unit in which the NHC carbon and hydroxy oxygen occupy the axial sites. All the synthesized compounds catalyze acceptorless dehydrogenation of alcohols to the corresponding aldehydes in the presence of a catalytic amount of weak base 1,4-diazabicyclo[2.2.2]octane (DABCO). Further, acceptorless dehydrogenative coupling (ADHC) of the alcohol with amines affords the corresponding imine as the sole product. The substrate scope is examined with 1 (BIN, p-nitrobenzaldehyde). A similar complex [Ru2(CO)4(CH3COO)(3-PhBIN)][Br], that is devoid of a hydroxy arm, is significantly less effective for the same reaction. Neutral complex 1?a, obtained by deprotonation of the hydroxy arm in 1, is found to be active for the ADHC of alcohols and amines under base-free conditions. A combination of control experiments, deuterium labeling, kinetic Hammett studies, and DFT calculations support metal-hydroxyl/hydroxide and metal-metal cooperation for alcohol activation and dehydrogenation. The bridging acetate plays a crucial role in allowing ?-hydride elimination to occur. The ligand architecture on the diruthenium core causes rapid aldehyde extrusion from the metal coordination sphere, which is responsible for exclusive imine formation. PMID:24715433

Saha, Biswajit; Rahaman, S M Wahidur; Daw, Prosenjit; Sengupta, Gargi; Bera, Jitendra K

2014-05-19

186

Synthesis and spectroscopic studies of binuclear metal complexes of a tetradentate N 2O 2 Schiff base ligand derived from 4,6-diacetylresorcinol and benzylamine  

Microsoft Academic Search

A tetradentate N2O2 donor Schiff base ligand, H2L, was synthesized by the condensation of 4,6-diacetylresorcinol with benzylamine. The structure of the ligand was elucidated by elemental analyses, IR, 1H NMR, electronic and mass spectra. Reaction of the Schiff base ligand with nickel(II), cobalt(II), iron(III), cerium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded binuclear metal complexes. Also, reaction of

Magdy Shebl

2008-01-01

187

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

188

Scaling Behavioral Anchors.  

ERIC Educational Resources Information Center

Although behaviorally anchored rating scales have both intuitive and empirical appeal, they have not always yielded superior results in contrast with graphic rating scales. Results indicate that the choice of an anchoring procedure will depend on the nature of the actual rating process. (Author/JKS)

Barnes, Janet L.; Landy, Frank J.

1979-01-01

189

Metal-ligand ``multiple`` bonding: Revelations in the electronic structure of complexes of high-valent f-elements  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of this project has been to extend the understanding of the nature of interactions between f-metals and first row elements (important both in natural systems and in ceramics), as well as providing important new information regarding basic differences in the chemical nature of d- and f-metals. By developing preparative routes to novel classes of early actinide and lanthanide complexes in which metal-ligand bonding is formally unsaturated, this project has provided the means to study orbital interactions and charge distribution in these species by physical, chemical, and theoretical means. Evaluation of the physical and chemical characteristics of these species is providing dramatic evidence for the involvement of valence metal orbitals [nf and (n+1)d] in bonding, and is yielding new insights into the factors influencing stability of related species.

Burns, C.J.; Arney, D.S.J.; Schnabel, R.C.; Warner, B.P. [Los Alamos National Lab., NM (United States); Bursten, B.E. [Ohio State Univ., Columbus, OH (United States); Green, J.C. [Univ. of Oxford (United Kingdom); Marks, T.J. [Northwestern Univ., Boston, MA (United States)

1997-07-01

190

Synergistic Assembly of Heavy Metal Clusters and Luminescent Organic Bridging Ligands in Metal-Organic Frameworks for Highly Efficient X-ray Scintillation.  

PubMed

We have designed two metal-organic frameworks (MOFs) to efficiently convert X-ray to visible-light luminescence. The MOFs are constructed from M6(?3-O)4(?3-OH)4(carboxylate)12 (M = Hf or Zr) secondary building units (SBUs) and anthracene-based dicarboxylate bridging ligands. The high atomic number of Zr and Hf in the SBUs serves as effective X-ray antenna by absorbing X-ray photons and converting them to fast electrons through the photoelectric effect. The generated electrons then excite multiple anthracene-based emitters in the MOF through inelastic scattering, leading to efficient generation of detectable photons in the visible spectrum. The MOF materials thus serve as efficient X-ray scintillators via synergistic X-ray absorption by the metal-cluster SBUs and optical emission by the bridging ligands. PMID:24730683

Wang, Cheng; Volotskova, Olga; Lu, Kuangda; Ahmad, Moiz; Sun, Conroy; Xing, Lei; Lin, Wenbin

2014-04-30

191

High-Temperature Transitions in Metallopolymers Crosslinked With 2,6- bis(1'-methylbenzim idazolyl)pyridine Metal-Ligand Complex.  

National Technical Information Service (NTIS)

Metallopolymers have reversible bonding properties and strong phase separation behavior that make them useful for a variety of applications. However, relaxation processes within the polymer, specifically relaxation processes within the metal-ligand (ML) r...

A. C. Jackson B. G. Butler F. L. Beyer R. H. Lambeth V. Rodriguez-Santiago

2013-01-01

192

Characterization of Metal Ligand Mutants of Phenylalanine Hydroxylase: Insights into the Plasticity of a 2-Histidine-1-Carboxylate Triad†  

PubMed Central

The iron atom in the nonheme iron monooxygenase phenylalanine hydroxylase is bound on one face by His285, His290, and Glu330. This arrangement of metal ligands is conserved in the other aromatic amino acid hydroxylases, tyrosine hydroxylase and tryptophan hydroxylase. A similar 2-His-1-carboxylate facial triad of two histidines and an acidic residue are the ligands to the iron in other nonheme iron enzymes, including the ?-ketoglutarate dependent hydroxylases and the extradiol dioxygenases. Previous studies of the effects of conservative mutations of the iron ligands in tyrosine hydroxylase established that there is some plasticity in the nature of the ligands and that the three ligands differ in their sensitivity to mutagenesis. To determine the generality of this finding for enzymes containing a 2-His-1-carboxylate facial triad, the His285, His290, and Glu330 in rat phenylalanine hydroxylase were mutated to glutamine, glutamate, and histidine. All of the mutant proteins had low but measurable activities for tyrosine formation. In general, mutation of Glu330 had the greatest effect on activity and mutation of His290 the least. All of the mutations resulted in an excess of tetrahydropterin oxidized relative to tyrosine formation, with mutation of His285 having the greatest effect on the coupling of the two partial reactions. The H285Q enzyme had the highest activity as tetrahydropterin oxidase at 20% the wild-type value. All of the mutations greatly decreased the affinity for iron, with mutation of Glu330 the most deleterious. The results complement previous results with tyrosine hydroxylase in establishing the plasticity of the individual iron ligands in this enzyme family.

Li, Jun; Fitzpatrick, Paul F.

2008-01-01

193

Synthesis and structural characterization of group 6 transition metal complexes with terminal fluoromethylidyne (CF) ligands; a DFT/NBO/NRT comparison of bonding characteristics of terminal NO, CF and CH ligands.  

PubMed

A family of group 6 transition metal complexes M(C(5)R(5))(CO)(2)(CF) [M = Cr, Mo, W; R = H, Me] with terminal fluoromethylidyne ligands have been synthesized through the reduction of the corresponding trifluoromethyl precursors with potassium graphite or magnesium graphite. They have been characterized spectroscopically and in some cases crystallographically, although the structures show disorder between the CO and CF ligands. The M[triple bond]CF subunit reacts as a triple bond to form cluster complexes containing ?(3)-CF ligands on reaction with Co(2)(CO)(8). Computational (DFT/NBO/NRT) studies on M(C(5)H(5))(CO)(2)(CF) [M = Cr, Mo, W] and the corresponding cationic fragments M(CO)(2)(XY)(+) illustrate significant differences in the metal-ligand bonding between CF and its isoelectronic analogue NO, as well as with its hydrocarbon analogue CH. PMID:21082118

Huang, Hui; Hughes, Russell P; Rheingold, Arnold L

2011-01-01

194

Molecular squares, cubes and chains from self-assembly of bis-bidentate bridging ligands with transition metal dications.  

PubMed

The two new ligands L(fur) and L(th) consist of two chelating pyrazolyl-pyridine termini connected to furan-2,5-diyl or thiophene-2,5-diyl spacers via methylene groups. Reaction of these with a range of transition metal dications that prefer octahedral coordination affords a series of unusual structures which are all based on a 2M : 3L ratio. [M(8)(L(fur))(12)]X(16) (M = Co, Cu, X = BF(4); and M = Zn, X = ClO(4)) are octanuclear cubes with approximate D(4) symmetry in which two cyclic tetranuclear helicate M(4)L(4) units are connected by four additional 'pillar' ligands. In contrast [Ni(4)(L(fur))(6)](BF(4))(8) is a centrosymmetric molecular square consisting of two dinuclear Ni(2)L(2) units of opposite chirality that are connected by a pair of additional L(fur) ligands such that the four edges of the Ni(4) square are spanned by alternately two and one bridging ligands. [M(4)(L(th))(6)](BF(4))(8) (M = Co, Ni, Cu) are likewise molecular squares with similar structures to [Ni(4)(L(fur))(6)](BF(4))(8) with the significant difference that the two crosslinked double helicate M(2)L(2) units are now homochiral. The Cd(II) complexes both behave quite differently to the first-row metal complexes, with [Cd(L(fur))(BF(4))](BF(4)) being a simple mononuclear complex with a single ligand in which the furan oxygen atom is weakly interacting with the Cd(II) centre. In contrast, in {[Cd(2)(L(th))(3)](BF(4))(4)}(?), where this quasi-pentadentate coordination mode of the ligand is not possible because thiophene is too poor an electron donor, the ligand reverts to bis-bidentate bridging coordination to afford a one-dimensional chain consisting of an infinite sequence of crosslinked, homochiral, Cd(2)(L(th))(2) double helicate units. PMID:21519621

Stephenson, Andrew; Ward, Michael D

2011-10-28

195

De novo design of ligands for metal separation. Annual progress report, September 15, 1996--September 14, 1997  

SciTech Connect

'The specific aim of this report is to parameterize force field to reproduce geometries and relative energetics of metal-ligand complexes for cesium, strontium, plutonium, uranium, americium and other relevent alkali, transition, lanthanide and actinide metals. As an initial attempt to examine parametrization, Dr. Yasuo Takeuchi has examined parameters for iron in combination with the molecular mechanics force field. The authors realize that most of the current ad hoc methodogies used to model metal interactions in the past do not have a firm theoretical foundation for modeling the d and f orbitals. They have, therefore, started a collaboration with Prof. Anders Carlsson of the Department of Physics to provide a theoretically correct functional form for the metal force field. Prof. Carlsson has an extensive track record in the derivation of the form of angular force fields from analysis of the quantum-mechanical electronic structure. His most important related works have treated the angular forces around transition-metal (TM) atoms in an aluminum host, the angular forces in elemental bcc transition metals, and the origins of angular and torsional forces in well-bonded s-p systems. They propose to apply the basic ideas of these calculations to developing force laws for transition metal ions in biomolecules. Of particular relevance to the proposed work is his study analyzing angular forces around transition metal (TM) atoms embedded in an aluminum host. Such TM atoms have a profound effect on the host structure, often entirely reassembling the host structure in order to satisfy the angular bonding constraints around the TM atoms. For example, at a concentration of only 1 {approximately} TM to 12 {approximately} Al, the transition metals Mn, Mo, Tc, W, and Re form the Al{sup 12}W structure, in which the underlying fcc aluminum lattice is disassembled and reassembled into icosahedra which surround the transition-metal atoms. The Al{sup 12}W structure is a body-centered cubic arrangement of such icosahedra. This behavior is analogous to that of several transition metals in proteins and other potential hosts, for example the formation of square-planar or Jahn-teller distorted octahedral structure by Cu{sup 2+} ions in many proteins. In both cases, the transition metal atom or ion has strong preferences regarding its angular environment. Of course, other effects, such as steric constraints on the ligands, are also important and dominate in some cases.'

NONE

1997-01-01

196

Synthesis, spectra and DNA interactions of certain mononuclear transition metal(II) complexes of macrocyclic tetraaza diacetyl curcumin ligand  

NASA Astrophysics Data System (ADS)

A series of mononuclear transition metal(II) complexes of type [M(LL)]2+ (LL = the template condensate of orthophenylene diamine and benzilidene diacetyl curcumin (ben-diacecur) and M = Cu(II) (1) or Co(II) (2) or Ni(II) (3) or Mn(II) (4)), have been isolated and the spectral behaviors are discussed. The ligand and complexes have also been characterized by the analytical and spectral methods like UV-Visible, FT-IR, NMR and EPR. Further, the interaction of the transition metal complexes with Calf thymus (CT) DNA have also been studied by the use of physical methods like UV-Visible, emission and CD spectroscopic techniques. The electrochemical responses of these metal complexes both in presence and absence of DNA have also been demonstrated. All these findings support the hypothesis of DNA interactions of all these metal complexes through the grooves with a higher degree of interaction by complex 1 (Kb = 1.4 × 105) possibly through the interposition of the aromatic rings of the ligand compared to complexes, 2-4. The complex 1 display significant oxidative cleavage of circular plasmid pUC18 DNA in the presence of H2O2 using the singlet oxygen as a reactive species. The spectral and electrochemical response of these complexes designate that the square-planar Cu(II), Ni(II) and Co(II) complexes interact much better than the axially coordinated octahedral Mn(II) complex.

Rajesh, Jegathalaprathaban; Gubendran, Ammavasi; Rajagopal, Gurusamy; Athappan, Periyakaruppan

2012-02-01

197

Synthesis, spectral characterization, molecular modeling, thermal study and biological evaluation of transition metal complexes of a bidentate Schiff base ligand  

NASA Astrophysics Data System (ADS)

Complexes of copper(II) and nickel(II) of general composition M(L)2X2, have been synthesized [where L = 3-Bromoacetophenone thiosemicarbazone and X = CH3COO-, Cl- and NO3-]. All the complexes were characterized by elemental analysis, magnetic moments, IR, electronic and EPR spectral studies. The ligand behaved as bidentate and coordinated through sulfur of sbnd Cdbnd S group and nitrogen atoms of sbnd Cdbnd N group. The copper(II) and nickel(II) complexes were found to have magnetic moments 1.94-2.02 BM, 2.96-3.02 BM respectively which was corresponding to one and two unpaired electrons respectively. The molar conductance of the complexes in solution of DMSO lies in the range of 10-20 ?-1 cm2 mol-1 indicating their non-electrolytic behavior. On the basis of EPR, electronic and infrared spectral studies, tetragonal geometry has been assigned for copper(II) complexes and an octahedral geometry for nickel(II) complexes. The values of Nephelauxetic parameter ? lie in the range 0.19-0.37 which indicated the covalent character in metal ligand '?' bond. Synthesized ligand and its copper(II) and nickel(II) complexes have also been screened against different bacterial and fungal species which suggested that complexes are more active than the ligands in antimicrobial activities.

Chandra, Sulekh; Bargujar, Savita; Nirwal, Rita; Qanungo, Kushal; Sharma, Saroj K.

2013-09-01

198

Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited  

NASA Astrophysics Data System (ADS)

In magnetic coordination compounds and solids the magnetic orbitals are essentially located on metallic centers but present some delocalization tails on adjacent ligands. Mean field variational calculations optimize this mixing and validate a single band modelization of the intersite magnetic exchange. In this approach, due to the Brillouin's theorem, the ligand to metal charge transfer (LMCT) excitations play a minor role. On the other hand the extensive configuration interaction calculations show that the determinants obtained by a single excitation on the top of the LMCT configurations bring an important antiferromagnetic contribution to the magnetic coupling. Perturbative and truncated variational calculations show that contrary to the interpretation given in a previous article [C. J. Calzado et al., J. Chem. Phys. 116, 2728 (2002)] the contribution of these determinants to the magnetic coupling constant is not a second-order one. An analytic development enables one to establish that they contribute at higher order as a correlation induced increase in the LMCT components of the wave function, i.e., of the mixing between the ligand and the magnetic orbitals. This larger delocalization of the magnetic orbitals results in an increase in both the ferro- and antiferromagnetic contributions to the coupling constant.

Calzado, Carmen J.; Angeli, Celestino; Taratiel, David; Caballol, Rosa; Malrieu, Jean-Paul

2009-07-01

199

A series of novel 1D coordination polymers constructed from metal?quinolone complex fragments linked by aromatic dicarboxylate ligands  

NASA Astrophysics Data System (ADS)

Self-assembly of quinolones with metal salts in the presence of aromatic dicarboxylate ligands affords a series of novel 1D metal-quinolone complexes, namely [Mn(Hppa)(oba)]·3H2O (1), [Co(Hppa)(oba)]·3.25H2O (2), [Zn(Hppa)(sdba)]·1.5H2O (3), [Mn(Hcf)(bpda)(H2O)]·2H2O (4), [Mn(Hppa)2(bpdc)] (5) and [Mn(Hlome)2(bpdc)]·4H2O (6) (Hppa = Pipemidic acid, Hcf = ciprofloxacin, Hlome = lomefloxacin). The structures of compounds 1-3 consist of novel polymeric chains spanning two different directions, which display an intriguing 1D ? 3D inclined polycatenation of supramolecular ladders. Compound 4 exhibits a chain compound formed from the interconnection of [Mn2(Hcf)2(?-CO2)2] dimers with bpda ligands. Compounds 5 and 6 are similar chain compounds constructed from [Mn(Hppa)2] (or [Mn(Hlome)2]) fragments linked by bpdc ligands. The magnetic properties of 4 have been studied, which indicate the existence of antiferromagnetic interactions. Furthermore, the luminescent properties of compound 3 are discussed.

He, Jiang-Hong; Xiao, Dong-Rong; Yan, Shi-Wei; Sun, Dian-Zhen; Chen, Hai-Yan; Wang, Xin; Yang, Juan; Ye, Zhong-Li; Yuan, Ruo; Wang, En-Bo

2012-08-01

200

New two-dimensional metal-organic networks constructed from 1,2,4,5-benzenetetracarboxylate and chelate ligands.  

PubMed

Two novel nickel coordination polymers [Ni(2)(2,2'-bipy)(2)(OH)(2)(H(2)btec)](3)(n)(1) and [Ni(2)(1,10'-phen)(2)(H(2)O)(2)(btec)](n)(2) (btec = 1,2,4,5-benzenetetracarboxylate) have been hydrothermally synthesized and characterized by elemental analyses, IR and XPS spectra, TG analysis, X-ray powder diffraction, and single crystal X-ray diffraction. Crystal data for 1: C(90)H(66)N(12)O(30)Ni(6), monoclinic P2(1)/c, a = 10.905(2) A, b = 18.006(4) A, c = 20.551(4) A, beta = 94.91(3) degrees, Z = 2. Crystal data for 2: C(34)H(22)N(4)O(10)Ni(2), monoclinic P2(1)/n, a = 10.122(2) A, b = 9.3106(19) A, c = 15.690(3) A, beta = 92.03(3) degrees, Z = 2. Compound 1 exhibits a novel one-dimensional chainlike structure, in which the dinuclear Ni centers are linked by the btec ligands. Furthermore, the adjacent chains are linked into a 2-D wavelike layer via the strong OH.O hydrogen bonding interactions. Compound 2 possesses an unusual two-dimensional steplike network with interesting rhombic grids. Both compounds exhibit unprecedented metal-organic ligand construction modes in [M/btec/L] (M = transition metal; L = chelate ligands) systems. The magnetic behaviors of compounds 1 and 2 have been studied. PMID:12716210

Li, Yangguang; Hao, Na; Lu, Ying; Wang, Enbo; Kang, Zhenhui; Hu, Changwen

2003-05-01

201

Design and syntheses of electron-transfer photochromic metal-organic complexes using nonphotochromic ligands: a model compound and the roles of its ligands.  

PubMed

The model compound [Zn(HCOO)2(4,4'-bipy)] (1; 4,4'-bipy = 4,4'-bipyridine) is selected in this work to demonstrate the effectiveness of our previously proposed design strategy for electron-transfer photochromic metal-organic complexes. The electron-transfer photochromic behavior of 1 has been discovered for the first time. Experimental and theoretical data illustrate that the photochromism of 1 can be attributed to the electron transfer from formato to 4,4'-bipy and the formation of a radical photoproduct. The electron transfer prefers to occur between formato and 4,4'-bipy, which are combined directly by the Zn(II) atoms. A high-contrast (up to 8.3 times) photoluminescence switch occurs during the photochromic process. The similarity of photochromic behaviors among 1 and its analogues as well as viologen compounds has also been found. Photochromic studies of this model compound indicate that new electron-transfer photochromic metal-organic complexes can be largely designed and synthesized by the rational assembly of nonphotochromic electron-donating and electron-accepting ligands. PMID:24359084

Zhang, Cui-Juan; Chen, Zi-Wei; Lin, Rong-Guang; Zhang, Ming-Jian; Li, Pei-Xin; Wang, Ming-Sheng; Guo, Guo-Cong

2014-01-21

202

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

National Technical Information Service (NTIS)

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 unsuppor...

J. A. Gladysz

1993-01-01

203

New chiral ligands from myrtenal and caryophyllene for asymmetric oxydation of sulfides catalyzed by metal complexes  

Microsoft Academic Search

From myrtenal and caryophyllene, widespread terpene compounds, three new chiral Schiff bases were prepared suitable for ligands\\u000a in vanadium ions catalyzed sulfides oxidation to chiral sulfoxides.

T. M. Khomenko; O. V. Salomatina; S. Yu. Kurbakova; I. V. Il’ina; K. P. Volcho; N. I. Komarova; D. V. Korchagina; N. F. Salakhutdinov; A. G. Tolstikov

2006-01-01

204

Spectroscopic, and thermal studies of some new binuclear transition metal(II) complexes with hydrazone ligands containing acetoacetanilide and isoxazole  

NASA Astrophysics Data System (ADS)

A new chelating ligand, 2-(2-(5- tert-butylisoxazol-3-yl)hydrazono)- N-(2,4-dimethylphenyl)-3-oxobutanamide (HL), and its four binuclear transition metal complexes, M 2(L) 2 (?-OCH 3) 2 [M = Ni(II), Co(II), Cu(II), Zn(II)], were synthesized using the procedure of diazotization, coupling and metallization. Their structures were postulated based on elemental analysis, 1H NMR, MALDI-MS, FT-IR spectra and UV-vis electronic absorption spectra. Smooth films of these complexes on K9 glass substrates were prepared using the spin-coating method and their absorption properties were evaluated. The thermal properties of the metal(II) complexes were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Different thermodynamic and kinetic parameters namely activation energy ( E*), enthalpy of activation (? H*), entropy of activation (? S*) and free energy change of activation (? G*) are calculated using Coats-Redfern (CR) equation.

Chen, Zhimin; Wu, Yiqun; Gu, Donghong; Gan, Fuxi

2007-11-01

205

Effects of metal coordination on the ?-system of the 2,5-bis-{(pyrrolidino)-methyl}-pyrrole pincer ligand.  

PubMed

Pincer complexes of 2,5-bis{(pyrrolidino)-methyl}-pyrrole with group 14 elements such as germanium, tin, and lead were prepared and fully characterized by X-ray single-crystal analysis, NMR spectroscopy, and mass spectrometry. The structures of the complexes were analyzed and compared to the free and the lithiated ligand to gain insight into the effects of metal coordination on the aromatic system. A further aspect was to elaborate the capability of group 14 metals to interact with the pyrrole ?-system. Therefore, electronic structure calculations were carried out with group 14 complexes to better understand the bonding situation and the trends among the group. The changes in the aromaticity of the pyrrole ring upon coordination have been rationalized according to the interaction of the ?-system with the metal. The unusual short bond distance observed between germanium and the coordinated pyrrole nitrogen was also assessed. PMID:23902578

Maaß, Christian; Andrada, Diego M; Mata, Ricardo A; Herbst-Irmer, Regine; Stalke, Dietmar

2013-08-19

206

Template synthesis of a tetraazamacrocyclic ligand with two pendant pyridinyl groups: properties of the isomers of the metal-free ligand and of their first-row transition metal compounds.  

PubMed

The one-step reaction of [Cu(en)(2)](2+) (en = 1,2-diaminoethane) with formaldehyde, ethyl 2-pyridyl acetate, and base produces a mixture of [Cu(s-pypymac)](2+) and [Cu(a-pypymac)](2+) (s-pypymac = syn-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane, a-pypymac = anti-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane; syn-to-anti ratio approximately 1:9) in low yield (6%). Ion exchange chromatography is used for isomer separation, and the two isomers of the metal-free ligand are obtained by reduction of the copper(II) complexes and subsequent ion exchange chromatography. Crystal structure analyses of the metal-free a-pypymac ligand, of two isomeric copper(II) compounds of a-pypymac and one of s-pypymac, and of the cobalt(III) complexes of a- and s-pypymac and nickel(II), as well as zinc(II) complexes of a-pypymac, are reported and discussed on the basis of the expectations from force field calculations and from published experimental data of the transition metal compounds of the bis-pendant amine derivative diammac. PMID:11327910

Comba, P; Luther, S M; Maas, O; Pritzkow, H; Vielfort, A

2001-05-01

207

Axial ligand effects on the diradical characters and second hyperpolarizabilities of open-shell singlet transition-metal dinuclear complexes  

NASA Astrophysics Data System (ADS)

We investigate the axial ligand effects on the diradical character (y) dependences of the second hyperpolarizabilities (?) of transition-metal dinuclear complexes, Mo(I)2(CO)2, with different bond lengths (R) using the spin-unrestricted coupled-cluster method. Mo(I)2(CO)2 exhibits intrinsic y-? correlation and dominant d?-electron contribution to the maximum ? (?max), which are also observed in the bare dinuclear analogs. The axial-ligand coordination to Mo(I)2 is found to cause the increase of the diradical character of the d? orbital, the emergence of large negative ? for small R, and an enhancement of |?max| by a factor of ?30 as compared to the bare analogs.

Yamada, Taishi; Takamuku, Shota; Matsui, Hiroshi; Champagne, Benoît; Nakano, Masayoshi

2014-07-01

208

Radiationless decay from the ligand-to-metal charge-transfer state in the blue copper protein plastocyanin  

NASA Astrophysics Data System (ADS)

The cysteine S(p ?) ? Cu 2+d x2- y2 ligand-to-metal charge-transfer (LMCT) state in plastocyanin exhibits a time-resolved pump-probe spectrum that has excited-state absorption and stimulated-emission components to the blue and red, respectively, of the absorption maximum. The LMCT state returns to the ground state by populating the d xz+ yz ? d x2- y2 ligand-field (LF) state. The lack of hole-burned features in the time-resolved spectra implies the presence of intramolecular vibrational redistribution and/or protein-matrix solvation dynamics on a time scale that is shorter than the 125 fs lifetime of the LMCT state.

Edington, Maurice D.; Diffey, William M.; Doria, William J.; Riter, Ruth E.; Beck, Warren F.

1997-08-01

209

Synthesis and characterization of metal complexes of Schiff base ligand derived from imidazole-2-carboxaldehyde and 4-aminoantipyrine  

NASA Astrophysics Data System (ADS)

The Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from imidazole-2-carboxaldehyde and 4-aminoantipyrine were synthesized. These compounds were characterized by elemental analysis, IR, mass, 1H NMR, electronic spectra, magnetic moment, molar conductance, thermal analysis, powder XRD and SEM. The analytical data show that the metal to ligand ratio is 1:1. The IR results show that the ligand acts as a bidentate donor coordinating through the azomethine nitrogen and imidazole nitrogen atoms. From the electronic spectra and magnetic moment value predicts the geometry of the complexes. The surface morphology of the compounds was studied by SEM. The compounds were screened for their antibacterial activity and antifungal activity using Kirby Bayer disc diffusion method. The DNA cleavage and superoxide dismutase activities of the compounds were investigated. The anticancer activities of the complexes have been carried out towards HeLa and HCT116 cancer cells.

Selwin Joseyphus, R.; Shiju, C.; Joseph, J.; Justin Dhanaraj, C.; Arish, D.

2014-12-01

210

Synthesis and characterization of metal complexes of Schiff base ligand derived from imidazole-2-carboxaldehyde and 4-aminoantipyrine.  

PubMed

The Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from imidazole-2-carboxaldehyde and 4-aminoantipyrine were synthesized. These compounds were characterized by elemental analysis, IR, mass, (1)H NMR, electronic spectra, magnetic moment, molar conductance, thermal analysis, powder XRD and SEM. The analytical data show that the metal to ligand ratio is 1:1. The IR results show that the ligand acts as a bidentate donor coordinating through the azomethine nitrogen and imidazole nitrogen atoms. From the electronic spectra and magnetic moment value predicts the geometry of the complexes. The surface morphology of the compounds was studied by SEM. The compounds were screened for their antibacterial activity and antifungal activity using Kirby Bayer disc diffusion method. The DNA cleavage and superoxide dismutase activities of the compounds were investigated. The anticancer activities of the complexes have been carried out towards HeLa and HCT116 cancer cells. PMID:24934973

Selwin Joseyphus, R; Shiju, C; Joseph, J; Justin Dhanaraj, C; Arish, D

2014-12-10

211

A structure-based analysis of the vibrational spectra of nitrosyl ligands in transition-metal coordination complexes and clusters  

NASA Astrophysics Data System (ADS)

The vibrational spectra of nitrogen monoxide or nitric oxide (NO) bonded to one or to several transition-metal (M) atom(s) in coordination and cluster compounds are analyzed in relation to the various types of such structures identified by diffraction methods. These structures are classified in: (a) terminal (linear and bent) nitrosyls, [M(?-NO)] or [M(NO)]; (b) twofold nitrosyl bridges, [M 2(? 2-NO)]; (c) threefold nitrosyl bridges, [M 3(? 3-NO)]; (d) ?/?-dihaptonitrosyls or " side-on" nitrosyls; and (e) isonitrosyls (oxygen-bonded nitrosyls). Typical ranges for the values of internuclear N-O and M-N bond-distances and M-N-O bond-angles for linear nitrosyls are: 1.14-1.20 Å/1.60-1.90 Å/180-160° and for bent nitrosyls are 1.16-1.22 Å/1.80-2.00 Å/140-110°. The [M 2(? 2-NO)] bridges have been divided into those that contain one or several metal-metal bonds and those without a formal metal/metal bond (M⋯M). Typical ranges for the M-M, N-O, M-N bond distances and M-N-M bond angles for the normal twofold NO bridges are: 2.30-3.00 Å/1.18-1.22 Å/1.80-2.00 Å/90-70°, whereas for the analogous ranges of the long twofold NO bridges these are 3.10-3.40 Å/1.20-1.24 Å/1.90-2.10 Å/130-110°. In both situations the N-O vector is approximately at right angle to the M-M (or M⋯M) vector within the experimental error; i.e. the NO group is symmetrical bonded to the two metal atoms. In contrast the threefold NO bridges can be symmetrically or unsymmetrically bonded to an M 3-plane of a cluster compound. Characteristic values for the N-O and M-N bond-distances of these NO bridges are: 1.24-1.28 Å/1.80-1.90 Å, respectively. As few dihaptonitrosyl and isonitrosyl complexes are known, the structural features of these are discussed on an individual basis. The very extensive vibrational spectroscopy literature considered gives emphasis to the data from linearly bonded NO ligands in stable closed-shell metal complexes; i.e. those which are consistent with the " effective atomic number (EAN)" or "18-electron" rule. In the paucity of enough vibrational spectroscopic data from complexes with only nitrosyl ligands, it turned out to be very advantageous to use wavenumbers from the spectra of uncharged and saturated nitrosyl/carbonyl metal complexes as references, because the presence of a carbonyl ligand was found to be neutral in its effect on the ?(NO)-values. The wide wavenumber range found for the ?(NO) values of linear MNO complexes are then presented in terms of the estimated effects of net ionic charges, or of electron-withdrawing or electron-donating ligands bonded to the same metal atom. Using this approach we have found that: (a) the effect for a unit positive charge is [plus 100 cm -1] whereas for a unit negative charge it is [minus 145 cm -1]. (b) For electron-withdrawing co-ligands the estimated effects are: terminal CN [plus 50 cm -1]; terminal halogens [plus 30 cm -1]; bridging or quasi-bridging halogens [plus 15 cm -1]. (c) For electro donating co-ligands they are: PF 3 [plus 10 cm -1]; P(OPh) 3 [-30 cm -1]; P(OR) 3 (R = alkyl group) [-40 cm -1]; PPh 3 [-55 cm -1]; PR 3 (R = alkyl group) [-70 cm -1]; and ? 5-C 5H 5 [-60 cm -1]; ? 5-C 5H 4Me [-70 cm -1]; ? 5-C 5Me 5 [-80 cm -1]. These values were mostly derived from the spectra of nitrosyl complexes that have been corrected for the presence of only a single electronically-active co-ligand. After making allowance for ionic charges or strongly-perturbing ligands on the same metal atom, the adjusted 'neutral-co-ligand' ?(NO)*-values (in cm -1) are for linear nitrosyl complexes with transition metals of Period 4 of the Periodic Table, i.e. those with atomic orbitals (…4s3d4p): [ca. 1750, Cr(NO)]; [1775,Mn(NO)]; [1796,Fe(NO)]; [1817,Co(NO)]; [ca. 1840, Ni(NO)]. Period 5 (…5s4d5p): [1730 Mo(NO)]; [—, Tc(NO)]; [1745,Ru(NO)]; [1790,Rh(NO)]; [ca. 1845, Pd(NO)]. Period 6 (…6s4f5d6p), [1720,W(NO)]; [1730,Re(NO)]; [1738,Os(NO)]; [1760,Ir(NO)]; [—, Pt] respectively. Environmental differences to these values, e.g. data taken

De La Cruz, Carlos; Sheppard, Norman

2011-01-01

212

Photophysical studies of bioconjugated ruthenium metal-ligand complexes incorporated in phospholipid membrane bilayers.  

PubMed

The luminescent, mono-diimine ruthenium complexes [(H)Ru(CO)(PPh3)2(dcbpy)][PF6] (1) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridyl) and [(H)Ru(CO)(dppene)(5-amino-1,10-phen)][PF6] (2) (dppene = bis(diphenylphosphino)ethylene; phen = phenanthroline) were conjugated with 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE) and with cholesterol in the case of complex 2. Using standard conjugation techniques, compound 1 gives the bis-lipid derivative [(H)Ru(CO)(PPh3)2(dcbpy-N-DPPE2)][PF6] (3), while 2 provides the monolipid conjugate [(H)Ru(CO)(dppene)(1,10-phen-5-NHC(S)-N-DPPE)][PF6] (4) and the cholesterol derivative [(H)Ru(CO)(dppene)(1,10-phen-5-NHC(O)Ocholesteryl)][PF6] (5). These compounds were characterized by spectroscopic methods, and their photophysical properties were measured in organic solvents. The luminescence of lipid conjugates 3 and 4 is quenched in organic solvents while compound 4 shows a weak, short-lived, blue-shifted emission in aqueous solution. The cholesterol conjugate 5 shows the long-lived, microsecond-time scale emission associated with triplet metal-to-ligand charge-transfer excited states. Incorporation of conjugate 3 in lipid bilayer vesicles restores the luminescence, but with blue shifts (~80 nm) accompanied by nanosecond-time scale lifetimes. In the vesicles conjugate 4 shows a short-lived and blue-shifted emission similar to that observed in solution but with increased intensity. Conjugation of the complex [(H)Ru(CO)(PhP2C2H4C(O)O-N-succinimidyl)2(bpy)][PF6] (6") (bpy = 2,2'-bipyridyl) with DPPE gives the phosphine-conjugated complex [(H)Ru(CO)(PhP2C2H4C(O)-N-DPPE)2(bpy)][PF6] (7). Complex 7 also exhibits a short-lived and blue-shifted emission in solution and in vesicles as observed for complexes 3 and 4. We have also conjugated the complex [Ru(bpy)2(5-amino-1,10-phen)][PF6]2 (8) with both cholesterol (9) and DPPE (10). Neither complex 9 nor the previously reported complex 10 exhibited the blue shifts observed for complexes 3 and 4 when incorporated into large unilamellar vesicles (LUVs). The anisotropies of the emissions of complexes 3, 4, and 7 were also measured in LUVs, and those of complex 5 were measured in both glycerol and LUVs. High fundamental anisotropies were observed for complexes 3, 4, and 7. PMID:24063694

Sharmin, Ayesha; Salassa, Luca; Rosenberg, Edward; Ross, J B Alexander; Abbott, Geoffrey; Black, Labe; Terwilliger, Michelle; Brooks, Robert

2013-10-01

213

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

214

Synthesis and characterization of mixed ligand complexes of lomefloxacin drug and glycine with transition metals. Antibacterial, antifungal and cytotoxicity studies  

NASA Astrophysics Data System (ADS)

Mixed ligand complexes derived from lomefloxacin (LFX, L 1) as primary ligand and glycine (L 2) as secondary ligand have been prepared and characterized by conventional techniques including elemental analyses, XRD, infrared, electronic spectra, molar conductivity and thermal analyses. The elemental analyses data display the formation of 1:1:1 [M:L 1:L 2] complexes. The diffused reflectance and magnetic moment measurements reveal the presence of the complexes in an octahedral geometry. The infrared spectral data show that the chelation behavior of the ligands toward transition metal ions is through carbonyl O, and carboxylate O of LFX whereas the amino acid coordinate through the carboxylate oxygen and the amino nitrogen. The electronic spectral results display the existence of ?-?? (phenyl rings), n-?? (NH 2 and sbnd C dbnd N) and confirm the mentioned structure. The molar conductivity reveals an electrolytic nature of all chelates. The thermogravimetric analysis data of the complexes displays the existence of hydrated and coordinated water molecules. The effect of LFX, glycine and their complexes on the inhibition of bacteria or fungi growth were evaluated. The prepared complexes were found to exhibit enhanced activity on bacteria or fungi growth compared to LFX and glycine ligands. LFX, [Mn(LFX)(Gly)(H 2O) 2]·Cl, [Co(LFX)(Gly)(H 2O) 2]·Cl and [Zn(LFX)(Gly)(H 2O) 2]·Cl were found to be very active against breast cancer cells with IC50 values 14, 11.2, 13 and 16.8, respectively, while glycine and other complexes had been shown to be inactive at lower concentration than 100 ?g/ml.

Mohamed, Gehad G.; Abd El-Halim, Hanan F.; El-Dessouky, Maher M. I.; Mahmoud, Walaa H.

2011-07-01

215

Two new lead(II) diphosphonates with second ligands as an intercalated species or a multidentate metal linker  

NASA Astrophysics Data System (ADS)

Hydrothermal reactions of lead(II) acetate with N, N'-piperazinebis(methylenephosphonic acid) (H 2O 3PCH 2N(C 2H 4) 2NCH 2PO 3H 2, H 4L 1) and 5-sulfoisophalic acid monosodium salt (NaH 2SIP) or lead(II) acetate with isopropylimino-bis-(methylenephosphonic acid) ((CH 3) 2CHN (CH 2PO 3H 2) 2, H 4L 2) and succinic acid afforded two new lead(II) phosphonate hybrids, namely, Pb 4(H 2L 1)(SIP) 2(H 2O) 4·2H 2O 1 and Pb 4(L 2) 2·(HO 2CH 2CH 2CO 2H) 2. The structure of compound 1 features a 3D network formed by Pb(II) ions interconnected by H 2L 1 and the carboxylate-sulfonate SIP anions. The 3D network can be viewed as the neighboring layers of Pb 4(SIP) 2 being interconnected by H 2L 1 ligands to form a pillared layered architecture. The phosphonate groups of the diphosohonate ligands bridge the Pb(II) ions of the Pb 4(SIP) 2 layer to form a lead(II) phosphonate-sulfonate hybrid layer and the organic group of phosphonate ligand as pillars. In compound 2, the interconnection of the lead(II) ions via diphosphonate ligands lead to a <400> lead(II) diphosphonate layer. The succinic acid remains protonated and is located at interlayer space. The second ligand in compound 1 acts as a multidentate metal linker, whereas the succinic acid in compound 2 functions as an intercalated species in between the 2D layers.

Du, Zi-Yi; Ying, Shao-Ming; Mao, Jiang-Gao

2006-05-01

216

Synthesis, structure and magnetism of new polynuclear transition metal aggregates assembled with Schiff-base ligand and anionic N-donor ligands  

NASA Astrophysics Data System (ADS)

Three new polynuclear aggregates [Co 6(sae) 4(N 3) 6(MeO) 2(MeOH) 2]·0.5H 2O ( 1), [Mn 4O(sae) 4(C(CN) 3)(MeOH) 3](NO 3)·MeOH ( 2) and [NaFe 6(sae) 6(MeO) 6] (N(CN) 2)·H 2O ( 3) have been synthesized with mixed ligands of Schiff-base (salicylidene-2-ethanolamine, H 2sae) and various anionic N-donor ligands (N 3-, N(CN) 2- or C(CN) 3-) and transition metal salts in methanol solution. Crystallographic data for 1: trigonal, R3¯, a = 26.113(4) Å, b = 26.113(4) Å, c = 20.689(4) Å, ? = 120°, V = 12,218(3) Å 3, Z = 9, R1( wR2) = 0.0753(0.2176); for 2: orthorhombic, Pna2 1, a = 20.746(4) Å, b = 13.357(3) Å, c = 17.992(4) Å, V = 4985.6(2) Å 3, Z = 4, R1( wR2) = 0.0357(0.0969); for 3: monoclinic, C2/ c, a = 30.311(6) Å, b = 12.452(3) Å, c = 20.789(4) Å, ? = 94.75(3)°, V = 7820(3) Å 3, Z = 4, R1( wR2) = 0.0773(0.2299). Compound 1 exhibits a new rod-like [Co III4Co II2] structural feature. Compound 2 contains an unusual tetranuclear [Mn III4] cationic core. Compound 3 possesses a well-known circle-like [Fe III6] unit encapsulated a central sodium cation. Magnetic properties of these compounds have been studied revealing the presence of (i) intra-molecular antiferromagnetic interactions in 2 and 3 that induce an overall ST = 0 ground state and (ii) Co II-Co II ferromagnetic interactions in complex 1.

Li, Yangguang; Wu, Qiong; Lecren, Lollita; Clérac, Rodolphe

2008-11-01

217

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

218

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

NASA Astrophysics Data System (ADS)

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, 1H and 13C NMR data and spectroscopic studies. IR and 1H 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 Ndbnd N 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 (sbnd Ndbnd Nsbnd ) 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.

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

2013-12-01

219

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

220

(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.

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

2009-01-01

221

A Novel Type Half-Unit Schiff Base Ligand, 3-[o-Aminophenyliminomethyl]-4Hydroxy6Methyl2-(1H)-Quinolone and its Metal Complexes. Part IV  

Microsoft Academic Search

A novel half-unit Schiff base ligand derived from 6-methyl-3-formyl-4-hydroxy-2-(1H)-quinolone and o-phenylenediamine was prepared. The Schiff base acts as a monobasic ligand. Metal complexes of the type [MLX]2, M = Cu(II), Ni(II) or Fe(III); X = Cl or OAc were obtained by the reaction of metal acetates or chlorides with the ligand, with the ligand behaving as a terdentate. However, the

Saied M. E. Khalil; Ali Taha; Faten S. M. Abd El-Hameed

1997-01-01

222

Nitronyl nitroxide-metal complexes as metallo-ligands for the construction of hetero-tri-spin (2p-3d-4f) chains.  

PubMed

A novel approach for the preparation of hetero-tri-spin magnetic compounds is described. It consists in using preformed metal-nitronyl nitroxide complexes as metallo-ligands in an assembling process involving an additional metal centre. This is illustrated by two unprecedented radical-Cu-Ln chain compounds (Ln = Gd(3+), Tb(3+)). PMID:24409459

Zhu, Mei; Mei, Xuelan; Ma, Yue; Li, Licun; Liao, Daizheng; Sutter, Jean-Pascal

2014-02-21

223

Metal-Complexing Ligands and Metal Speciation in Sediment Porewaters: Implications for Sediment/Water Exchange and Water Column Speciation.  

National Technical Information Service (NTIS)

In this project, we determined: concentrations and benthic fluxes of total dissolved Cu (TDCu), Zn (TDZn) and Cu- and Zn-complexing ligands (L sub Cu and L sub Zn) Cu and Zn complexation and speciation in the sediment porewaters and water column of two si...

J. R. Donat D. J. Burdige

1999-01-01

224

Synthesis and characterization of divalent metal complexes containing the heteroscorpionate ligand dihydrobis(3-carboxyethyl-5-methylpyrazolyl)borate  

Microsoft Academic Search

The dihydrobis(3-carboxyethyl-5-methylpyrazolyl)borate ligand, BpCOOET,Me, reacts with divalent metals to yield complexes of general type [(BpCOOET,Me)2M], where M=Mn(II), Fe(II), Co(II), Ni(II), Zn(II), Cu(II), Pb(II) and Cd(II). All complexes have been fully characterized by elemental analyses and FT-IR in the solid state and by NMR (1H and 113Cd NMR) spectroscopy and electrospray ionization mass spectrometry in solution. A single crystal structural characterization

G. Bandoli; A. Dolmella; G. Gioia Lobbia; G. Papini; M. Pellei; C. Santini

2006-01-01

225

Synthesis, thermal and spectral studies of first-row transition metal complexes with Girard-T reagent-based ligand  

Microsoft Academic Search

The complexing behaviour of 1-acetyltrimethyl ammonium chloride-4-benzoyl thiosemicarbazide (H2GTBzIT) towards the following first-row transition metal ions namely, Cr(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) have been examined by elemental analysis, magnetic measurements, electronic, IR and 1H NMR. The proton-ligand ionization constants were determined potentiometrically using Irving–Rossotti technique. The stability constants of complexes were also calculated and were found in agreement

Usama El-Ayaan; I. M. Kenawy; Y. G. Abu El-Reash

2007-01-01

226

Synthesis, thermal and spectral studies of first-row transition metal complexes with Girard-T reagent-based ligand  

Microsoft Academic Search

The complexing behaviour of 1-acetyltrimethyl ammonium chloride-4-benzoyl thiosemicarbazide (H2GTBzIT) towards the following first-row transition metal ions namely, Cr(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) have been examined by elemental analysis, magnetic measurements, electronic, IR and 1H NMR. The proton-ligand ionization constants were determined potentiometrically using Irving Rossotti technique. The stability constants of complexes were also calculated and were found in

Usama El-Ayaan; I. M. Kenawy; Y. G. Abu El-Reash

2007-01-01

227

Synthesis, thermal and spectral studies of first-row transition metal complexes with girard P reagent-based ligand  

NASA Astrophysics Data System (ADS)

A new series of first-row transition metal complexes with 1-acetylpyridinium chloride-4-benzoyl thiosemicarbazide (H 2GPBzIT) have been prepared and characterized by elemental analysis, spectroscopic and magnetic measurements. The proton-ligand ionization constants were determined potentiometrically using Irving-Rossotti technique. The stability constants of complexes were also calculated and were found in agreement with the seq uence of stability constants of Irving and Williams. Thermal stability and degradation kinetics have been measured using thermogravimetric analyzer. Kinetic parameters were obtained for each stage of thermal degradation of complexes using Coats-Redfern method.

El-Ayaan, Usama; Kenawy, I. M.; El-Reash, Y. G. Abu

2007-10-01

228

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

229

Synthesis, structural characterization and potentiometric studies of divalent metal complexes with an octadentate tetraazamacrocyclic ligand and their DNA cleavage ability  

Microsoft Academic Search

Four new metal complexes with an octadentate macrocyclic ligand [L=1,4,7,10-tetrakis(2-carbamoylethyl)-1,4,7,10-tetraazacyclododecane] were synthesized and characterized by elemental analyses, IR and MS. These complexes have the general formula: M(L)(NO3)2·nH2O [M=Co (1), Ni (2), n=2; M=Cu (3), Zn (4), n=1]. The structures of complexes 1, 2 and 3 have been determined by X-ray diffraction. [Co(L)(NO3)](NO3)·2H2O (1) crystallizes in the triclinic space group P1?.

De-Yuan Kong; Yu-Yuan Xie

2000-01-01

230

Mono, bi- and trinuclear metal complexes derived from new benzene-1,4-bis(3-pyridin-2-ylurea) ligand. Spectral, magnetic, thermal and 3D molecular modeling studies  

NASA Astrophysics Data System (ADS)

New bis (pyridylurea) ligand, H2L, was synthesized by the reaction of ethylpyridine-2-carbamate (EPC) and p-phenylenediamine. The ligand was characterized by elemental analysis, IR, 1H NMR, electronic and mass spectra. Reaction of the prepared ligand with Co2+, Ni2+, Cu2+, Fe3+, VO2+ and UO22+ ions afforded mono, bi- and trinuclear metal complexes. Also, new mixed ligand complexes of the ligand H2L and 8-hydroxyquinoline (8-HQ) with Co2+, Ni2+, Cu2+ and Fe3+ ions were synthesized. The ligand behaves as bi- and tetradentate toward the transition metal ions, coordination via the pyridine sbnd N, the carbonyl sbnd O and/or the amidic sbnd N atoms in a non, mono- and bis-deprotonated form. The complexes were characterized by elemental and thermal analyses, IR, electronic and mass spectra as well as conductance and magnetic susceptibility measurements. The results showed that the metal complexes exhibited different geometrical arrangements such as square planar, tetrahedral, octahedral and square pyramidal arrangements. The Coats-Redfern equation was used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. 3D molecular modeling of the ligand, H2L and a representative complex were studied.

El-ghamry, Mosad A.; Saleh, Akila A.; Khalil, Saied M. E.; Mohammed, Amira A.

2013-06-01

231

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

232

New polymer-supported ion-complexing agents: design, preparation and metal ion affinities of immobilized ligands.  

PubMed

Polymer-supported reagents are comprised of crosslinked polymer networks that have been modified with ligands capable of selective metal ion complexation. Applications of these polymers are in environmental remediation, ion chromatography, sensor technology, and hydrometallurgy. Bifunctional polymers with diphosphonate/sulfonate ligands have a high selectivity for actinide ions. The distribution coefficient for the uranyl ion from 1 M nitric acid is 70,000, compared to 900 for the monophosphonate/sulfonate polymer and 200 for the sulfonic acid ion-exchange resin. A bifunctional trihexyl/triethylammonium polymer has a high affinity and selectivity for pertechnetate and perchlorate anions from groundwater. In one example, its distribution coefficient for perchlorate ions in the presence of competing anions is 3,300,000, compared to 203,180 for a commercially available anion-exchange resin. Polystyrene modified with N-methyl-D-glucamine ligands is capable of selectively complexing arsenate from groundwater. It complexes 99% of the arsenate present in a solution of 100 mg/L arsenate with 560 mg/L sulfate ions. Its selectivity is retained even in the presence of 400 mg/L phosphate. There is no affinity for arsenate above pH 9, allowing for the polymer to be regenerated with moderate alkali solution. In studies aimed at developing a Hg(II)-selective resin, simple amine resins were found to have a high Hg(II) affinity and that affinity is dependent upon the solution pH and the counterion. PMID:16762497

Alexandratos, Spiro D

2007-01-31

233

Ligating behaviour of Schiff base ligands derived from heterocyclic ?-diketone and ethanol or propanol amine with oxovanadium (IV) metal ion  

NASA Astrophysics Data System (ADS)

Synthesis and evaluation of six new oxovanadium (IV) complexes, formed by the interaction of vanadyl sulphate pentahydrate and the Schiff base, viz.; (HL 1)-(HL 3) and (HL 4)-(HL 6) such as 5-hydroxy-3-methyl-1(2-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (I), 5-hydroxy-3-methyl-1(3-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (II) and 5-hydroxy-3-methyl-1(3-sulphoamido)phenyl-1H-pyrazolone-4-carbaldehyde (III) with ethanol amine and propanol amine, respectively, in aqueous ethanol medium. The ligands and their Schiff base ligands have been characterized by elemental analyses, IR and 1H NMR. The resulting complexes have been characterized by elemental analyses, IR, 1H NMR, mass, electronic, electron spin resonance spectra, magnetic susceptibility measurement, molar conductance and thermal studies. The IR spectral data suggest that the ligand behaves as a dibasic bidentate with ON donor sequence towards metal ion. The molar conductivity data show them to be non-electrolytes. From the electronic, magnetic and ESR spectral data suggest that all the oxovanadium (IV) complexes have distorted octahedral geometry.

Thaker, B. T.; Barvalia, R. S.

2009-12-01

234

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

NASA Astrophysics Data System (ADS)

Three new zinc coordination polymers [Zn 2(btc) 2(H 2O) 2] n· n[Zn(H 2O) 6] ( 1), [Zn 3(btc) 2(2,2'-bipy) 2(H 2O) 3] n·2 nH 2O ( 2) and [Zn 3(btc) 2(H 2O) 6] n· nH 2O ( 3) (H 3btc=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 4(btc) 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 3- ligands adopt ?3, ?4 and ?5 coordination modes, respectively. The title compounds show strong blue fluorescence, which may be assigned as ?*? 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; Liu, Bing; Zheng, Fa-Kun; Guo, Guo-Cong; Huang, Jin-Shun

2005-11-01

235

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

236

Coordination polymers with the chiral ligand N- p-tolylsulfonyl- L-glutamic acid: Influence of metal ions and different bipyridine ligands on structural chirality  

NASA Astrophysics Data System (ADS)

Four new polymers, namely [Ni(-tsgluO)(2,4'-bipy) 2(H 2O) 2] n·5 nH 2O ( 1), [Co(-tsgluO)(2,4'-bipy) 2(H 2O) 2] n·5 nH 2O ( 2), [Ni(-tsgluO)(4,4'-bipy)] n·0.5 nH 2O ( 3), and [Co(-tsgluO)(4,4'-bipy)] n·0.5 nH 2O ( 4), where tsgluO 2-=(+)- N- p-tolylsulfonyl- L-glutamate dianion, 2,4'-bipy=2,4'-bipyridine, and 4,4'-bipy=4,4'-bipyridine, have been prepared and structurally characterized. Compounds 1 and 2 are isostructural and mononuclear, and crystallize in the acentric monoclinic space group Cc, forming 1D chain structures. Compound 3 is also mononuclear, but crystallizes in the chiral space group P2 1, forming a homochiral 2D architecture. In contrast to the other complexes, compound 4 crystallizes in the space group P-1 and is composed of binuclear [Co 2O 6N 2] n4- units, which give rise to a 2D bilayer framework. Moreover, compounds 1, 2, and 4 self-assemble to form 3D supramolecular structures through ?- ? stacking and hydrogen-bonding interactions, while compound 3 is further hydrogen-bonded to form 3D frameworks. We have demonstrated the influence of the central metal and bipyridine ligands on the framework chirality of the coordination complexes.

He, Rong; Song, Hui-Hua; Wei, Zhen; Zhang, Jian-Jun; Gao, Yuan-Zhe

2010-09-01

237

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.

Wang, Rongming; Zhang, Jian; Li, Lijuan

2009-01-01

238

Zinc ligands in the metal hyperaccumulator Thlaspi caerulescens as determined using X-ray absorption spectroscopy  

Microsoft Academic Search

Using the noninvasive technique of X-ray absorption spectroscopy (XAS), the authors have been able to determine the ligand environment of Zn in different tissues of the Zn-hyperaccumulator Thlaspi caerulescens. The majority of intracellular Zn in roots of T. caerulescens was found to be coordinated with histidine. In the xylem sap Zn was found to be transported mainly as the free

David E. Salt; Roger C. Prince; Alan J. M. Baker; Ilya Raskin; Ingrid J. Pickering

1999-01-01

239

Synthesis and reactivity of metal complexes with acyclic (amino)(ylide)carbene ligands.  

PubMed

No cycle required: The straightforward synthesis of acyclic (amino)(ylide)carbene gold complexes was achieved by reaction of isocyanide gold complexes with phosphorus and arsenic ylides as well as electron-rich olefins. Their ability to form bimetallic species and to act as ligand-transfer reagents has also been established. PMID:24038894

González-Fernández, Elisa; Rust, Jörg; Alcarazo, Manuel

2013-10-18

240

The electronic nature of terminal oxo ligands in transition-metal complexes: ambiphilic reactivity of oxorhenium species.  

PubMed

The synthesis of the Lewis acid-base adducts of B(C6F5)3 and BF3 with [DAAmRe(O)(X)] DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C6F5 (X = Me, 1, COCH3, 2, Cl, 3) as well as their diamidopyridine (DAP) (DAP=(2,6-bis((mesitylamino)methyl)pyridine) analogues, [DAPRe(O)(X)] (X = Me, 4, Cl, 5, I, 6, and COCH3,7), are described. In these complexes the terminal oxo ligands act as nucleophiles. In addition we also show that stoichiometric reactions between 3 and triarylphosphine (PAr3) result in the formation of triarylphosphine oxide (OPAr3). The electronic dependence of this reaction was studied by comparing the rates of oxygen atom transfer for various para-substituted triaryl phosphines in the presence of CO. From these experiments a reaction constant ? = -0.29 was obtained from the Hammett plot. This suggests that the oxygen atom transfer reaction is consistent with nucleophilic attack of phosphorus on an electrophilic metal oxo. To the best of our knowledge, these are the first examples of mono-oxo d(2) metal complexes in which the oxo ligand exhibits ambiphilic reactivity. PMID:23725588

Smeltz, Jessica L; Lilly, Cassandra P; Boyle, Paul D; Ison, Elon A

2013-06-26

241

Ambiphilic diphosphine-borane ligands: metal-->borane interactions within isoelectronic complexes of rhodium, platinum and palladium.  

PubMed

Coordination of an ambiphilic diphosphine-borane (DPB) ligand to the RhCl(CO) fragment affords two isomeric complexes. According to X-ray diffraction analysis, each complex adopts a square-pyramidal geometry with trans coordination of the two phosphine buttresses and axial RhB contacts, but the two differ in the relative orientations around the rhodium and boron centres. DFT calculations on the actual complexes provide insight into the influence of the pi-accepting CO co-ligand, compared with previously reported complexes [Rh(mu-Cl)(dpb)]2 and [RhCl(dmap)(dpb)]. In addition, comparison of the nu(CO) frequency of [RhCl(CO)(dpb)] with that of the related borane-free complex [RhCl(CO)(iPr2PPh)2] substantiates the significant electron-withdrawing effect that the sigma-accepting borane moiety exerts on the metal. Valence isoelectronic [PtCl2(dpb)] and [PdCl2(dpb)] complexes have also been prepared and characterized spectroscopically and structurally. The pronounced influence of the transition metal on the magnitude of the M-->B interaction is highlighted by geometric considerations and NBO analyses. PMID:17948327

Bontemps, Sébastien; Sircoglou, Marie; Bouhadir, Ghenwa; Puschmann, Horst; Howard, Judith A K; Dyer, Philip W; Miqueu, Karinne; Bourissou, Didier

2008-01-01

242

Structurally Diverse Metal Coordination Compounds, Bearing Imidodiphosphinate and Diphosphinoamine Ligands, as Potential Inhibitors of the Platelet Activating Factor  

PubMed Central

Metal complexes bearing dichalcogenated imidodiphosphinate [R2P(E)NP(E)R2?]? ligands (E = O, S, Se, Te), which act as (E,E) chelates, exhibit a remarkable variety of three-dimensional structures. A series of such complexes, namely, square-planar [Cu{(OPPh2)(OPPh2)N-O, O}2], tetrahedral [Zn{(EPPh2)(EPPh2)N-E,E}2], E = O, S, and octahedral [Ga{(OPPh2)(OPPh2)N-O,O}3], were tested as potential inhibitors of either the platelet activating factor (PAF)- or thrombin-induced aggregation in both washed rabbit platelets and rabbit platelet rich plasma. For comparison, square-planar [Ni{(Ph2P)2N-S-CHMePh-P, P}X2], X = Cl, Br, the corresponding metal salts of all complexes and the (OPPh2)(OPPh2)NH ligand were also investigated. Ga(O,O)3 showed the highest anti-PAF activity but did not inhibit the thrombin-related pathway, whereas Zn(S,S)2, with also a significant PAF inhibitory effect, exhibited the highest thrombin-related inhibition. Zn(O,O)2 and Cu(O,O)2 inhibited moderately both PAF and thrombin, being more effective towards PAF. This work shows that the PAF-inhibitory action depends on the structure of the complexes studied, with the bulkier Ga(O,O)3 being the most efficient and selective inhibitor.

Tsoupras, Alexandros B.; Roulia, Maria; Ferentinos, Eleftherios; Stamatopoulos, Ioannis; Demopoulos, Constantinos A.; Kyritsis, Panayotis

2010-01-01

243

Electron delocalization in the S1 and T1 metal-to-ligand charge transfer states of trans-substituted metal quadruply bonded complexes  

PubMed Central

The singlet S1 and triplet T1 photoexcited states of the compounds containing MM quadruple bonds trans-M2(TiPB)2(O2CC6H4-4-CN)2, where TiPB = 2,4,6-triisopropylbenzoate and M = Mo (I) or M = W (I?), and trans-M2(O2CMe)2((N[i Pr ])2CC ? CC6H5)2, where M = Mo (II) and M = W (II?), have been investigated by a variety of spectroscopic techniques including femtosecond time-resolved infrared spectroscopy. The singlet states are shown to be delocalized metal-to-ligand charge transfer (MLCT) states for I and I? but localized for II and II? involving the cyanobenzoate or amidinate ligands, respectively. The triplet states are MoMo??* for both I and II but delocalized 3MLCT for I? and localized 3MLCT for II?. These differences arise from consideration of the relative orbital energies of the M2? or M2?* and the ligand ?? as well as the magnitudes of orbital overlap.

Alberding, Brian G.; Chisholm, Malcolm H.; Gallucci, Judith C.; Ghosh, Yagnaseni; Gustafson, Terry L.

2011-01-01

244

Zn(II) and Cd(II) metal-organic frameworks (MOFs) constructed from a symmetric triangular semirigid multicarboxylate ligand: Synthesis, structures and luminescent properties  

NASA Astrophysics Data System (ADS)

Three transition metal coordination polymers [Zn2(H2L)(2,2'-bpy)2(H2O)]n•2nH2O (1), [Zn2(H2L)(2,2'-bpy)2]n (2), and [Cd2(H2L)(2,2'- bpy)2(H2O)2]n•2nH2O (3), have been assembled from a semirigid triangular multicarboxylate ligand 3,3',3?-(1,3,5-phenylenetri(oxy))triphthalic acid (H6L) with the help of 2,2'-bipyridine (2,2'-bpy) ligand. X-ray single crystal diffraction analysis reveals that complex 1 crystallizes in the space group of P? and displays a one-dimensional (1D) ladder chain structure constructed from 2,2'-bpy ligand and H2L ligand, which stacks together in an -ABCABC- motif, featuring a mutually embedded chained structure. In complex 2, the H2L ligands bridge the adjacent Zn(II) atoms into a complicated ribbon chain along the b axis. There is ?-? stacking interaction between the chains, which results in the formation of a 2D supramolecular structure. Complex 3 also exhibits a 1D ladder-like chain. The different molecular structures for complexes 1 and 2 formed from the same H6L and Zn(NO3)2•6H2O in different metal-to-ligand ratios in the presence of NaOH, reveals the influence of metal-ligand ratio on the structure of the coordination polymer. In contrast, a series of same reaction using Cd(NO3)2•4H2O as a starting material instead of Zn(NO3)2•6H2O only led to the formation of 3, illustrating the fact organic ligands display different coordination preferences at different metal ions. In addition, the thermal and luminescent properties of complexes 1-3 were also investigated.

Zhao, Ningning; Li, Wenjun; Sun, Changyan; Bian, Yongzhong; Wang, Hailong; Chang, Zhidong; Fan, Hongxia

2012-03-01

245

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

Microsoft Academic Search

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 1H 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

Serap Seyhan; Mehmet Çolak; Melek Merdivan; Nadir Demirel

2007-01-01

246

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.

Yernale, Nagesh Gunvanthrao; Bennikallu Hire Mathada, Mruthyunjayaswamy

2014-01-01

247

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

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, (1)H 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

248

Synthesis, spectroscopic characterization, electrochemistry and biological evaluation of some binuclear transition metal complexes of bicompartmental ONO donor ligands containing benzo[b]thiophene moiety  

NASA Astrophysics Data System (ADS)

A series of new binucleating Cu(II), Co(II), Ni(II) and Zn(II) complexes of bicompartmental ligands with ONO donor were synthesized. The ligands were obtained by the condensation of 3-chloro-6-substituted benzo[b]thiophene-2-carbohydrazides and 4,6-diacetylresorcinol. The synthesized ligands and their complexes were characterized by elemental analysis and various spectroscopic techniques. Elemental analysis, IR, 1H NMR, ESI-mass, UV-Visible, TG-DTA, magnetic measurements, molar conductance and powder-XRD data has been used to elucidate their structures. The bonding sites are the oxygen atom of amide carbonyl, azomethine nitrogen and phenolic oxygen for ligands 1 and 2. The binuclear nature of the complexes was confirmed by ESR spectral data. TG-DTA studies for some complexes showed the presence of coordinated water molecules and the final product is the metal oxide. All the complexes were investigated for their electrochemical activity, only the Cu(II) complexes showed the redox property. Cu(II) complexes were square planar, whereas Co(II), Ni(II) and Zn(II) complexes were octahedral. Powder-XRD pattern have been studied in order to test the degree of crystallinity of the complexes and unit cell calculations were made. In order to evaluate the effect of antimicrobial activity of metal ions upon chelation, both the ligands and their metal complexes were screened for their antibacterial and antifungal activities by minimum inhibitory concentration (MIC) method. The results showed that the metal complexes were found to be more active than free ligands. The DNA cleaving capacities of all the complexes were analyzed by agarose gel electrophoresis method against supercoiled plasmid DNA. Among the compounds tested for antioxidant capacity, ligand 1 displayed excellent activity than its metal complexes.

Mahendra Raj, K.; Vivekanand, B.; Nagesh, G. Y.; Mruthyunjayaswamy, B. H. M.

2014-02-01

249

A theoretical investigation into the luminescent properties of d8-transition-metal complexes with tetradentate Schiff base ligands.  

PubMed

A theoretical investigation on the luminescence efficiency of a series of d(8) transition-metal Schiff base complexes was undertaken. The aim was to understand the different photophysics of [M-salen](n) complexes (salen = N,N'-bis(salicylidene)ethylenediamine; M = Pt, Pd (n = 0); Au (n = +1)) in acetonitrile solutions at room temperature: [Pt-salen] is phosphorescent and [Au-salen](+) is fluorescent, but [Pd-salen] is nonemissive. Based on the calculation results, it was proposed that incorporation of electron-withdrawing groups at the 4-position of the Schiff base ligand should widen the (3)MLCT-(3)MC gap (MLCT = metal-to-ligand charge transfer and MC = metal centered, that is, the dd excited state); thus permitting phosphorescence of the corresponding Pd(II) Schiff base complex. Although it is experimentally proven that [Pd-salph-4E] (salph = N,N'-bis(salicylidene)-1,2-phenylenediamine; 4E means an electron-withdrawing substituent at the 4-position of the salicylidene) displays triplet emission, its quantum yield is low at room temperature. The corresponding Pt(II) Schiff base complex, [Pt-salph-4E], is also much less emissive than the unsubstituted analogue, [Pt-salph]. Thus, a detailed theoretical analysis of how the substituent and central metal affected the photophysics of [M-salph-X] (X is a substituent on the salph ligand, M = Pt or Pd) was performed. Temperature effects were also investigated. The simple energy gap law underestimated the nonradiative decay rates and was insufficient to account for the temperature dependence of the nonradiative decay rates of the complexes studied herein. On the other hand, the present analysis demonstrates that inclusions of low-frequency modes and the associated frequency shifts are decisive in providing better quantitative estimates of the nonradiative decay rates and the experimentally observed temperature effects. Moreover, spin-orbit coupling, which is often considered only in the context of radiative decay rate, has a significant role in determining the nonradiative rate as well. PMID:24715418

Tong, Glenna So Ming; Chow, Pui Keong; To, Wai-Pong; Kwok, Wai-Ming; Che, Chi-Ming

2014-05-19

250

Coordination of a Hemilabile Pincer Ligand with an Olefinic Backbone to Mid-to-Late Transition Metals.  

PubMed

The coordination chemistry of a neutral tPCH?CHP pincer (tPCH?CHP = 2,2'-bis(di-iso-propylphosphino)-trans-stilbene) with metals that form stable complexes in the +1 oxidation state was studied and (tPCH?CHP)CoCl, (tPCH?CHP)CoCl(CO), (tPCH?CHP)RhCl, (tPCH?CHP)Cu(OTf), [(tPCH?CHP)Cu][PF6], and [(tPCH?CHP)Ag][PF6] were synthesized and characterized. In order to determine whether the coordination mode is dependent on the oxidation state of the metal, some +2 metal complexes, (tPCH?CHP)CoCl2 and (tPCH?CHP)FeBr2, were also investigated. The coordination of the olefinic backbone is not observed in (tPCH?CHP)FeBr2, (tPCH?CHP)CoCl2, (tPCH?CHP)Cu(OTf), or [(tPCH?CHP)Ag][PF6], but ?(2)-coordination is present in [(tPCH?CHP)CoCl][BAr(F)4], [(tPCH?CHP)FeBr][BAr(F)4], (tPCH?CHP)CoCl, (tPCH?CHP)CoCl(CO), (tPCH?CHP)RhCl, and [(tPCH?CHP)Cu][PF6]. Cobalt(II), iron(II), and copper(I) formed complexes with the ligand in both coordination modes. All metal complexes were characterized by multinuclei NMR spectroscopy, X-ray crystallography, and elemental analysis. PMID:24959947

Barrett, Brittany J; Iluc, Vlad M

2014-07-21

251

Ligand field and density functional descriptions of the d-states and bonding in transition metal complexes.  

PubMed

The d-orbital energy sequences for low symmetry transition metal complexes derived from Kohn-Sham density functional theory and ligand field theory are different due to each model's treatment of interelectron repulsion. The implications for providing a unified description of the underlying metal-ligand bonding are analysed and illustrated using conventional and time-dependent DFT. Previous detailed spectroscopic studies have established the d orbital sequence in planar coordination complexes containing pi-donor halide ligands as dx2-y2 > dxy > dxz, dyz > dz2 while for a sigma-only system like [Pd(NH3)4]2+, ligand field approaches like the angular overlap model (AOM) or cellular ligand field (CLF) model predict dxz, dyz, and dxy, should be degenerate. However, the energies of the Kohn Sham (KS) 'd' orbitals of [PdCl4]2- and [Pd(NH3)4]2+ place dxy below the dxz/dyz pair. Direct use of the KS orbital eigenvalues in AOM or CLF analyses would imply both ligands are pi acceptors. This result is independent of the choice of functional or whether the calculation is carried out in vacuo or in a polarised continuum representing solvation by water. The origin of the difference between the KS and LFT d orbital sequences derives from their treatments of d-d interelectron repulsion. KS orbitals include interelectron repulsion contributions while LFT d orbitals do not. For a low-spin d8 complex, DFT gives less d-d interelectron repulsion in the xy plane leading to a lowering of dxy relative to dxy/dyz. This differential effect can be reversed qualitatively by progressively removing electron density from dz2 and placing it in dx2-y2. When about 0.6 electrons is rearranged, E(dxy) > E(dxz/dyz) for [PdCl4]2- and the dpi orbitals for [Pd(NH3)4]2+ are virtually degenerate. The wider ramifications of these interelectron repulsion effects are discussed for other symmetries. Excited d state energies for [PdCl4]2- are computed using both time dependent density functional theory (TDDFT) and determinant energies. The latter give the experimental sequence 1A2g < 1Eg < 1B1g while TDDFT gives 1Eg < 1A2g < 1B1g. Both give transition energies up to 30% lower than observed. A DFT analysis of the bonding energies in [PdCl4]2- indicates that the Pd-Cl pi bonding in the molecular plane is about 33% weaker than the out-of-plane pi interaction due to non-zero overlap between ligand orbitals. The normal LFT assumption of linear ligation may not always be valid. PMID:14527227

Deeth, Robert J

2003-01-01

252

Characterization of a 150 kDa accessory receptor for TGF-beta 1 on keratinocytes: direct evidence for a GPI anchor and ligand binding of the released form.  

PubMed

Transforming growth factor-beta (TGF-beta) is a key modulator of epidermal development and homeostasis, and has been shown to potently regulate keratinocyte migration and function during wound repair. There are three cloned TGF-beta receptors termed type I, type II, and type III that are found on most cell types. The types I and II are the signaling receptors, while the type III is believed to facilitate TGF-beta binding to the types I and II receptors. Recently, we reported that in addition to these receptors, human keratinocytes express a 150 kDa TGF-beta 1 binding protein (r150) which forms a heteromeric complex with the TGF-beta signaling receptors. This accessory receptor was described as glycosyl phosphatidylinositol-specific anchored based on its sensitivity to phosphatidylinositol phospholipase C (PIPLC). In the present study, we demonstrate that the GPI-anchor is contained in r150 itself and not on a tightly associated protein and that it binds TGF-beta 1 with an affinity similar to those of the types I and II TGF-beta signaling receptors. Furthermore, the PIPLC released (soluble) form of this protein is capable of binding TGF-beta 1 independently from the signaling receptors. In addition, we provide evidence that r150 is released from the cell surface by an endogenous phospholipase C. Our observation that r150 interacts with the TGF-beta signaling receptors, together with the finding that the soluble r150 binds TGF-beta 1 suggest that r150 in either its membrane anchored or soluble form may potentiate or antagonize TGF-beta signaling. Elucidating the mechanism by which r150 functions as an accessory molecule in TGF-beta signaling may be critical to understanding the molecular mechanisms underlying the regulation of TGF-beta action in keratinocytes. PMID:11596117

Tam, B Y; Larouche, D; Germain, L; Hooper, N M; Philip, A

253

Asymmetric catalysis via dynamic substrate/ligand/rare earth metal conglomerate.  

PubMed

A highly enantio- and diastereoselective catalytic asymmetric Mannich-type reaction of alpha-cyanoketones and N-Boc imines promoted by an amide ligand/Sc(OiPr)3 catalyst is described. The similar reaction outcome is obtained with/without precomplexation of catalyst, suggesting that reaction components in a non-ordered conglomerate mixture orchestrate to form an ordered transition state during the reaction. Spectroscopic data and Eyring plot are consistent with this assumption. PMID:18393416

Nojiri, Akihiro; Kumagai, Naoya; Shibasaki, Masakatsu

2008-04-30

254

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

255

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

256

New route to complexes having substituted quinoline-2-thiolate ligands through the metal-assisted coupling and cyclization of aryl isothiocyanates to alkyne ligands  

SciTech Connect

Reactions of the lightly stabilized dimetalated olefin complex Re(CO){sub 4}[trans-{mu}-HC=C(CO{sub 2}Me)]Re-(CO){sub 4}(NCMe) (1) with p-tolylisothiocyanate has yielded the complex Re(CO){sub 4}[(E)-HC=C(CO{sub 2}Me)C=N (C{sub 6}H{sub 4}-p-Me)S]Re(CO){sub 4} (2; 58% yield) by insertion of the isothiocyanate into the substituted Re-C bond. When 2 is treated with I{sub 2} in the presence of UV radiation, the tolyl ring cyclizes with the unsubstituted end of the metalated olefin to yield a new substituted quinoline-1-thiolate ligand in the complex Re{sub 2}(CO){sub 7}[{mu}-2-S-3-CO{sub 2-}Me-6-Me-NC{sub 9}H{sub 4}] ({mu}-I) (3; 18% yield). Complexes 2 and 3 were characterized by IR, {sup 1}H NMR, and single-crystal X-ray diffraction analyses. Crystal data: for 2, space group P2{sub 1}/c, a = 10.317 (1) {angstrom}, b = 15.819(2) {angstrom}, c = 15.448-(3) {angstrom}, {beta} = 103.26(1){degrees}, Z =4,2415 reflections, R = 0.027; for 3{center_dot}CH{sub 2}Cl{sub 2}, P{bar 1}, a = 10.204(4) {angstrom}, b = 13.733(6) {angstrom}, c = 9.877 (2) {angstrom}, {alpha} = 91.18(3){degrees}, {beta} = 96.17(3){degrees}, {gamma} = 74.78(3){degrees}, Z = 2,2746 reflections, R = 0.038.

Adams, R.D.; Chen, Linfeng; Wu, Wengan [Univ. of South Carolina, Columbia, SC (United States)

1993-07-01

257

Arthroscopic Lateral Meniscus Root Repair With Soft Suture Anchor Technique  

PubMed Central

Meniscus root tear leads to circumferential hoop tension loss and increases femorotibial contact force, which causes irreversible cartilage degeneration. Biomechanical studies have shown that meniscus root repair provides better femorotibial contact force than meniscectomy. Many techniques for meniscus root repair have been published in recent years. The soft suture anchor is widely used in the glenoid labral repair. It is a small low-profile soft anchor. This article presents a new and simple technique of lateral meniscus root repair using the small soft anchor, which results in an anatomic and more vertical anchor position. It avoids instrument-related complications, such as cartilage delamination, material reaction, metal retention, and hard suture anchor pullout.

Prasathaporn, Niti; Kuptniratsaikul, Somsak; Kongrukgreatiyos, Kitiphong

2013-01-01

258

Manipulating the Lateral Diffusion of Surface-Anchored EGF Demonstrates that Receptor Clustering Modulates Phosphorylation Levels  

PubMed Central

Upon activation, the epidermal growth factor (EGF) receptor becomes phosphorylated and triggers a vast signaling network that has profound effects on cell growth. The EGF receptor is observed to assemble into clusters after ligand binding and tyrosine kinase autophosphorylation, but the role of these assemblies in the receptor signaling pathway remains unclear. To address this question, we measured the phosphorylation of EGFR when the EGF ligand was anchored onto laterally mobile and immobile surfaces. We found that cells generated clusters of ligand-receptor complex on mobile EGF surfaces, and displayed a lower ratio of phosphorylated EGFR to EGF when compared to immobilized EGF that is unable to cluster. This result was verified by tuning the lateral assembly of ligand-receptor complexes on the surface of living cells using patterned supported lipid bilayers. Nanoscale metal lines fabricated into the supported membrane constrained lipid diffusion and EGF receptor assembly into micron and sub-micron scale corrals. Single cell analysis indicated that clustering impacts EGF receptor activation, and larger clusters (> 1 µm2) of ligand-receptor complex generated lower EGF receptor phosphorylation per ligand than smaller assemblies (< 1 µm2) in HCC1143 cells that were engaged to ligand-functionalized surfaces. We investigated the mechanism of EGFR clustering by treating cells with compounds that disrupt the cytoskeleton (Latrunculin-B), clathrin-mediated endocytosis (Pitstop2), and inhibit EGFR activation (Gefitinib). These results help elucidate the nature of large-scale EGFR clustering, thus underscoring the general significance of receptor spatial organization in tuning function.

Stabley, D.; Retterer, S.; Marshall, S.; Salaita, K.

2013-01-01

259

Blind-Anchor-Nut-Installation Fixture (BANIF)  

NASA Technical Reports Server (NTRS)

Blind-anchor-nut-installation fixture, BANIF, developed for replacing or installing anchor nuts in blind holes or other inaccessible places. Attachment of anchor nut to BANIF enables placement of anchor nut on blind side of component.

Willey, Norman F., Jr.; Linker, James F.

1994-01-01

260

New Metal Chelates with Sterically Hindered Azo Ligands: Synthesis and Physicochemical Properties  

Microsoft Academic Search

Metal chelates based on 3,5-di-(tert-butyl)-2-hydroxyazobenzene are synthesized and their physicochemical properties were studied. Four alternative structures and isomeric transformations between these structures were suggested on the basis of NMR data, electric dipole and magnetic moments, X-ray diffraction and quantum-chemical data. The change in stereochemistry of a complex through introduction of tert-butyl substituents was found to give unusual (for metal chelates

V. A. Kogan; S. N. Lyubchenko; I. N. Shcherbakov; A. M. Ionov; V. V. Tkachev; G. V. Shilov; S. M. Aldoshin

2005-01-01

261

Modeling toxicity of binary metal mixtures (Cu(2+) -Ag(+) , Cu(2+) -Zn(2+) ) to lettuce, Lactuca sativa, with the biotic ligand model.  

PubMed

The biotic ligand model (BLM) was applied to predict metal toxicity to lettuce, Lactuca sativa. Cu(2+) had the lowest median effective activity (EA50(M) ), compared with Ag(+) and Zn(2+) (EA50(Cu) ?= 2.60 × 10(-8) M, EA50(Ag) = 1.34 × 10(-7) ?M, EA50(Zn) = 1.06 × 10(-4) ?M). At the 50% response level, the fraction of the total number of biotic ligands occupied by ions (f50(M) ) was lowest for Ag(+) among the metals (f50(Ag) = 0.22, f50(Cu) = 0.36, f50(Zn) = 0.42). Cu(2+) had the highest affinity for biotic ligands compared with Ag(+) and Zn(2+) , as shown by stability constants of the cation-biotic ligand binding, expressed as log K(MBL) (log K(CuBL) = 7.40, log K(AgBL) = 6.39, log K(ZnBL) = 4.00). Furthermore, the BLM was combined with the toxic equivalency factor approach in predicting toxicity of mixtures of Cu(2+) -Zn(2+) and Cu(2+) -Ag(+) . The fraction of biotic ligands occupied by ions was used to determine the relative toxic potency of metals and the toxic equivalency quotient (TEQ) of mixtures. This approach allowed for including interactions in estimating mixture toxicity and showed good predictive power (r(2) = 0.64-0.84). The TEQ at the 50% response level (TEQ50, Cu(2+) equivalents) for Cu(2+) -Zn(2+) mixtures was significantly lower than the value for Cu(2+) -Ag(+) mixtures. Joint toxicity depended on both TEQ and specific composition of the mixture. The present study supports the use of the accumulation of metal ions at the biotic ligands as a predictor of toxicity of single metals and mixtures. PMID:23109233

Yen Le, T T; Vijver, Martina G; Jan Hendriks, A; Peijnenburg, Willie J G M

2013-01-01

262

Tandem postsynthetic metal ion and ligand exchange in zeolitic imidazolate frameworks.  

PubMed

Herein, we report a general postsynthetic exchange (PSE) approach to introduce a redox-active transition metal, specifically Mn(II), into "inert" zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs). It is shown that metal ion PSE occurs in ZIF-71 (RHO topology) and ZIF-8 (SOD topology) under ambient conditions. The metal exchanged ZIFs are the first porous, Mn(II)-based ZIFs and a rare example of ZIFs with two transition metal centers in a single lattice. Exchanged materials are characterized by scanning electron microscopy-energy dispersed X-ray spectroscopy (SEM-EDX), aerosol time-of-flight mass spectrometry (ATOFMS), X-ray fluorescence spectroscopy (XRF), and Brunauer-Emmett-Teller (BET) surface area analysis. In addition, stepwise "tandem" PSE strategies are described to exchange of metal ions and organic linkers consecutively in ZIFs. These findings are important for probing the chemical dynamics of ZIFs, despite their high crystallinity and robustness, and inspire the more widespread use of PSE to prepare multimetallic and multifunctional MOFs. PMID:23516974

Fei, Honghan; Cahill, John F; Prather, Kimberly A; Cohen, Seth M

2013-04-01

263

Construction of a polyhedral metal-organic framework via a flexible octacarboxylate ligand for gas adsorption and separation.  

PubMed

A flexible octacarboxylate ligand, tetrakis[(3,5-dicarboxyphenyl)oxamethyl]methane (H8X), has been used to construct a highly porous metal-organic framework (In2X)(Me2NH2)2(DMF)9(H2O)5 (1), which is comprised of octahedral and cuboctahedral cages and shows a rare (4,8)-connected scu topology. Gas adsorption studies of N2, H2 on the actived 1 at 77 K reveal a Langmuir surface area of 1707 m(2) g(-1), a BET surface area of 1555 m(2) g(-1), a total pore volume of 0.62 cm(3) g(-1), and a H2 uptake of 1.49 wt % at 1 bar and 3.05 wt % at 16 bar. CO2, CH4, and N2 adsorption studies at 195, 273, 285, and 298 K and also ideal adsorbed solution theory (IAST) calculations demonstrate that 1 has high selectivites of CO2 over CH4 and N2. The resulting framework represents a MOF with the highest gas uptakes and gas selectivities (CO2 over CH4 and N2) constructed by flexible ligands. PMID:23469758

Lin, Zu-Jin; Huang, Yuan-Biao; Liu, Tian-Fu; Li, Xiang-Ying; Cao, Rong

2013-03-18

264

Highly sensitive and selective fluorescence detection of copper (II) ion based on multi-ligand metal chelation.  

PubMed

A fluorescent probe was synthesized and demonstrated to be highly selective and sensitive in the reaction with copper (II) ion, generating a large variation of the fluorescence intensity in a dose-response manner. The probe contains a dansyl moiety as fluorophore and a multidentate ligand for copper (II) ion recognition. The reaction of the molecular probe with copper (II) ion proceeds rapidly and irreversibly in a 1 to 1 stoichiometric way, leading to the production of stable copper (II) complex, which subsequently results in the quenching of fluorescence. The detection limit for copper (II) ion was measured to be about 2ppb. It was also shown that the probe has high selectivity for copper (II) ion and good anti-interference ability against other transition metal ions. The herein reported very simple and reliable fluorescence probe could be employed for copper (II) ion detection in many aspects. PMID:24881551

Zhang, Shan; Yu, Tao; Sun, Mingtai; Yu, Huan; Zhang, Zhongping; Wang, Suhua; Jiang, Hui

2014-08-01

265

Synthesis, thermal and spectral studies of first-row transition metal complexes with Girard-T reagent-based ligand  

NASA Astrophysics Data System (ADS)

The complexing behaviour of 1-acetyltrimethyl ammonium chloride-4-benzoyl thiosemicarbazide (H 2GTBzIT) towards the following first-row transition metal ions namely, Cr(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) have been examined by elemental analysis, magnetic measurements, electronic, IR and 1H NMR. The proton-ligand ionization constants were determined potentiometrically using Irving-Rossotti technique. The stability constants of complexes were also calculated and were found in agreement with the sequence of stability constants of Irving and Williams. Thermal properties and decomposition kinetics of all complexes are investigated. The interpretation, mathematical analysis and evaluation of kinetic parameters ( E, A, ? H, ? S and ? G) of all thermal decomposition stages have been evaluated using Coats-Redfern and Horowitz-Metzger equations.

El-Ayaan, Usama; Kenawy, I. M.; Abu El-Reash, Y. G.

2007-12-01

266

Groups 5 and 6 terminal hydrazido(2-) complexes: N(?) substituent effects on ligand-to-metal charge-transfer energies and oxidation states.  

PubMed

Brightly colored terminal hydrazido(2-) (dme)MCl(3)(NNR(2)) (dme = 1,2-dimethoxyethane; M = Nb, Ta; R = alkyl, aryl) or (MeCN)WCl(4)(NNR(2)) complexes have been synthesized and characterized. Perturbing the electronic environment of the ? (NR(2)) nitrogen affects the energy of the lowest-energy charge-transfer (CT) transition in these complexes. For group 5 complexes, increasing the energy of the N(?) lone pair decreases the ligand-to-metal CT (LMCT) energy, except for electron-rich niobium dialkylhydrazides, which pyramidalize N(?) in order to reduce the overlap between the Nb?N(?) ? bond and the N(?) lone pair. For W complexes, increasing the energy of N(?) eventually leads to reduction from formally [W(VI)?N-NR(2)] with a hydrazido(2-) ligand to [W(IV)?N?NR(2)] with a neutral 1,1-diazene ligand. The photophysical properties of these complexes highlight the potential redox noninnocence of hydrazido ligands, which could lead to ligand- and/or metal-based redox chemistry in early transition metal derivatives. PMID:22506581

Tonks, Ian A; Durrell, Alec C; Gray, Harry B; Bercaw, John E

2012-05-01

267

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

268

Ligand-stabilized Au13Cu(x) (x = 2, 4, 8) bimetallic nanoclusters: ligand engineering to control the exposure of metal sites.  

PubMed

Three novel bimetallic Au-Cu nanoclusters stabilized by a mixed layer of thiolate and phosphine ligands bearing pyridyl groups are synthesized and fully characterized by X-ray single crystal analysis and density functional theory computations. The three clusters have an icosahedral Au13 core face-capped by two, four, and eight Cu atoms, respectively. All face-capping Cu atoms in the clusters are triply coordinated by thiolate or pyridyl groups. The surface ligands control the exposure of Au sites in the clusters. In the case of the Au13Cu8 cluster, the presence of 12 2-pyridylthiolate ligands still leaves open space for catalysis. All the 3 clusters are 8-electron superatoms displaying optical gaps of 1.8-1.9 eV. The thermal decomposition studies suggest that the selective release of organic ligands from the clusters is possible. PMID:23789787

Yang, Huayan; Wang, Yu; Lei, Jing; Shi, Lei; Wu, Xiaohu; Mäkinen, Ville; Lin, Shuichao; Tang, Zichao; He, Jian; Häkkinen, Hannu; Zheng, Lansun; Zheng, Nanfeng

2013-07-01

269

A theoretical study of the energy-transfer process in [Eu?bpy.bpy.bpy] 3+ cryptates: a ligand-to-metal charge-transfer state?  

NASA Astrophysics Data System (ADS)

A complete theoretical model to calculate the luminescent properties of lanthanide coordination compounds is used to analyze the emission quantum yield of the [Eu?bpy.bpy.bpy] 3+ and [Eu?bpy.bpy.bpy] 3+·2H 2O compounds. This theoretical model includes the calculation of the molecular structure, of the ligand electronic structure, of the ligand-lanthanide energy-transfer, of the temporal dependence of the ligand and lanthanide populations, which lead to the emission quantum yield, relative emission intensity and lifetime of the emitting state. In the present case, this theoretical approach was used to ascertain the presence of a ligand-to-metal charge-transfer (LMCT) state in these compounds. In addition, this approach has provided indications of the location of the LMCT state as well as of the magnitudes of the energy-transfer rates involving this state.

Longo, Ricardo; Gonçalves e Silva, Fabiana R.; Malta, Oscar L.

2000-09-01

270

Metal-ligand covalency of iron complexes from high-resolution resonant inelastic X-ray scattering.  

PubMed

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 ?-back-donation complexes: ferrous tacn [Fe(II)(tacn)2]Br2, ferrocyanide [Fe(II)(CN)6]K4, ferric tacn [Fe(III)(tacn)2]Br3 and ferricyanide [Fe(III)(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 e(g) (?*) 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 ?-back-bonding features in ferro- and ferricyanide that are significantly more intense in L-edge XAS compared to K? RIXS. This shows that two methods are complementary 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

2013-11-13

271

Bis(phosphinoselenoic amides) as versatile chelating ligands for alkaline earth metal (Mg, Ca, Sr and Ba) complexes: syntheses, structure and ?-caprolactone polymerisation.  

PubMed

We report here a series of heavier alkaline earth metal complexes with N,N'-(ethane-1,2-diyl)bis(P,P-diphenylphosphinoselenoic amide) using two synthetic routes. In the first route, the heavier alkaline earth metal bis(trimethylsilyl)amides [M{N(SiMe3)2}2(THF)n] (M = Ca, Sr, Ba), when treated with phosphinoselenoic amine [Ph2P(Se)NHCH2CH2NHPPh2(Se)] (), afforded the corresponding alkaline earth metal complexes of the composition [(THF)3M{Ph2P(Se)NCH2CH2NPPh2(Se)}] [M = Ca (), Sr (), Ba ()]. The metal complexes were also obtained from a one-pot reaction, where potassium phosphinoselenoic amide was generated in situ by the reaction of compound and [KN(SiMe3)2], followed by the addition of the respective metal diiodides in THF at room temperature. The magnesium complex [(THF)3Mg{Ph2P(Se)NCH2CH2NPPh2(Se)}] () was also prepared. The solid-state structures of alkaline earth metal complexes were established by single crystal X-ray diffraction analysis. In the solid state, all the metal complexes are monomeric but in complexes , ligand is chelated in a tetra-dentate fashion to each metal ion but in complex , ligand behaves as a bidentate ligand. Complexes were tested as catalysts for the ring-opening polymerisation of ?-caprolactone and a high level of activity for the barium complex was observed, with narrow polydispersity. We also report the synthesis and structure of the bis(amidophosphino borane) ligand [Ph2P(BH3)NHCH2CH2NHPPh2(BH3)] () and the corresponding barium complex [(THF)2Ba{Ph2P(BH3)NCH2CH2NPPh2(BH3)}]2 (). PMID:24777284

Kottalanka, Ravi K; Adimulam, Harinath; Bhattacharjee, Jayeeta; Vignesh Babu, H; Panda, Tarun K

2014-05-20

272

Excited-state equilibration: a process leading to long-lived metal-to-ligand charge transfer luminescence in supramolecular systems  

Microsoft Academic Search

A recently developed strategy to prolong the luminescence lifetime of metal polypyridine complexes is discussed, and various resulting supramolecular systems are presented. The intervening mechanism demands that certain thermodynamic and kinetic parameters are satisfied, notably rapid and reversible electronic energy transfer between lowest-lying isoenergetic triplet excited states located on an inorganic moiety, e.g., a triplet metal-to-ligand charge transfer state (3MLCT),

Nathan D. McClenaghan; Yoann Leydet; Béatrice Maubert; Maria Teresa Indelli; Sebastiano Campagna

2005-01-01

273

Ligand-centered redox activity: redox properties of 3d transition metal ions ligated by the weak-field tris(pyrrolyl)ethane trianion.  

PubMed

First-row transition metal complexes of the tris(pyrrolyl)ethane (tpe) trianion have been prepared. The tpe ligand was found to coordinate in a uniform eta(1),eta(1),eta(1)-coordination mode to the divalent metal series as revealed by X-ray diffraction studies. Magnetic and structural characterization for complexes of the type [(tpe)M(II)(py)][Li(THF)(4)] (M: Mn, Fe, Co, Ni) reveal each divalent ion to be high-spin and have a distorted trigonal-monopyramidal geometry in the solid state. The pyridine ligand binds significantly canted from the molecular C(3) axis due to a stabilizing pi-stacking interaction with a ligand mesityl substituent. Cyclic voltammetry on the [(tpe)M(II)(py)](-) series reveals a common irreversible oxidation pathway that is entirely ligand-based, invariant to the divalent metal bound. This latter observation indicates that fully populated ligand-based orbitals from the tpe construct are energetically most accessible in the electrochemical experiments, akin to their dipyrromethane analogues. Chemical oxidation of [(tpe)Fe(II)(py)](-) yields a product in which the ligand has dissociated one pyrrole (following tpe oxidation and H-atom abstraction) and binds a second equivalent of pyridine to form the neutral, tetrahedral Fe(II) species (kappa(2)-tpe)Fe(py)(2). Similarly, chemical oxidation of the Zn(II) analogue shows evidence for tpe oxidation by electron paramagnetic resonance spectroscopy (77 K, toluene glass) with an isotropic signal for the organic radical at g = 2.002. Density functional theory analysis on this family of complexes reveals that the highest lying molecular orbitals are completely ligand-based, corroborating our proposed electronic structure assignment. PMID:20102213

Sazama, Graham T; Betley, Theodore A

2010-03-01

274

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

275

Zinc ligands in the metal hyperaccumulator Thlaspi caerulescens as determined using X-ray absorption spectroscopy  

SciTech Connect

Using the noninvasive technique of X-ray absorption spectroscopy (XAS), the authors have been able to determine the ligand environment of Zn in different tissues of the Zn-hyperaccumulator Thlaspi caerulescens. The majority of intracellular Zn in roots of T. caerulescens was found to be coordinated with histidine. In the xylem sap Zn was found to be transported mainly as the free hydrated Zn{sup 2+} cation with a smaller proportion coordinated with organic acids. In the shoots, Zn coordination occurred mainly via organic acids, with a smaller proportion present as the hydrated cation and coordinated with histidine and the cell wall. Their data suggest that histidine plays an important role in Zn homeostasis in the roots, whereas organic acids are involved in xylem transport and Zn storage in shoots.

Salt, D.E. [Northern Arizona Univ., Flagstaff, AZ (United States). Chemistry Dept.] [Northern Arizona Univ., Flagstaff, AZ (United States). Chemistry Dept.; Prince, R.C. [Exxon Research and Engineering, Annandale, NJ (United States)] [Exxon Research and Engineering, Annandale, NJ (United States); Baker, A.J.M. [Univ. of Sheffield (United Kingdom). Dept. of Animal and Plant Sciences] [Univ. of Sheffield (United Kingdom). Dept. of Animal and Plant Sciences; Raskin, I. [Rutgers Univ., New Brunswick, NJ (United States)] [Rutgers Univ., New Brunswick, NJ (United States); Pickering, I.J. [Stanford Synchrotron Radiation Lab., CA (United States)] [Stanford Synchrotron Radiation Lab., CA (United States)

1999-03-01

276

Metal nanoparticles with liquid-crystalline ligands: controlling nanoparticle superlattice structure and properties.  

PubMed

Nanoparticle ordered aggregates are promising candidates for future application in a variety of sensing, optical and electronic technologies, mainly based on collective interactions between individual nano-building blocks. Physicochemical properties of such assemblies depend on nanoparticle spacing, therefore a lot of effort throughout the last years was put on development of assembly methods allowing control over aggregates structure. In this minireview we describe efficient self-assembly process based on the utilization of liquid-crystalline ligands grafted onto nanoparticle surface. We show strategies used to synthesize liquid-crystalline nanoparticles as well as discuss parameters influencing structural and thermal characteristic of aggregates. It is also demonstrated that the liquid-crystalline approach offers access to dynamic self-assembly and metamaterials with anisotropic plasmonic properties, which makes this strategy unique among others. PMID:24789440

Lewandowski, Wiktor; Wójcik, Micha?; Górecka, Ewa

2014-05-19

277

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

278

Salicylic acid and derivatives anchored on poly(styrene- co-divinylbenzene) resin and membrane via a diazo bridge: Synthesis, characterisation and application to metal extraction  

Microsoft Academic Search

New materials for chelating solid-phase extraction have been prepared by grafting of salicylic acid and derivatives on poly(styrene-co-divinylbenzene) based sorbents. These sorbents are either resin bead-shaped Amberlite® XAD-4 or membrane disk-shaped Empore™ SDB-XC. Grafting has been achieved via –NN– spacer. The grafted ligands are salicylic acid (SA), its dimer form methylenedisalicylic acid (MDSA) and trimer form aurintricarboxylic form (ATA) in

Sabrina Boussetta; Catherine Branger; André Margaillan; Jean-Luc Boudenne; Bruno Coulomb

2008-01-01

279

Synthesis of O, S and N Donor Ligands for Complexation with Some Transition Metals.  

National Technical Information Service (NTIS)

The report contains information on synthesis of Schiff bases from B-diketones, benzoin, salicylaldehyde, and macro-Schiff bases; synthesis of thio Schiff bases; metal complexes of Schiff bases; synthesis of B-polyketones; complexes of B-polyketones; b-thi...

M. M. Aslam

1985-01-01

280

Cobalt(III) complexes as functional ligands for metal (oxide) surfaces.  

PubMed

Co(III) polyamine complexes with either two or three labile coordination sites bind strongly to high surface area metal oxides such as goethite or aluminium trihydroxide, and have been shown to act as passivating agents for aluminium flake in aqueous media, in addition to providing a potential method for surface functionalisation. PMID:22908118

Cooper, Rachel J; Jane, Reuben T; Jeffs, Thomas E; Hartshorn, Richard M; Tasker, Peter A

2012-10-01

281

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...

282

First stable reduced form of [Co(5)](+10): fine tuning of linear pentacobalt(ii) complexes containing delocalized metal-metal bonds through ligand modification.  

PubMed

Pentacobalt EMACs [Co(5)(mu(5)-dpzpda)(4)X(2)] (X = Cl(-) (), NCS(-) ()) with fine-tuning of the supporting ligand based on the tripyridyldiamine ligand, N,N'-di(pyrazin-2-yl)pyridine-2,6-diamine (H(2)dpzpda), and their reduced form (Ph(4)P)[Co(5)(mu(5)-dpzpda)(4)X(2)] (X = Cl(-) (), NCS(-) ()) were first synthesized and structurally characterized. The structures of showed direct Co-Co bonds with Co-Co distances in the range 2.2385(7)-2.2888(15) A, and valence electrons delocalized through the whole metal chain with distances of longer than 9.06 A. The distances of the inner Co-Co bonds and the Co-axial ligands became longer after reduction, whereas no significant change was observed in the distances of the outer Co-Co bonds and Co-N (supporting ligand) bonds, which was consistent with the MO analysis. Electrochemical studies on both and showed one reversible oxidation and one reversible reduction at E(1/2) = +0.82 and -0.05 V for , and at E(1/2) = +0.89 and +0.02 V for , respectively. The redox reactions of the thiocyanate complex happened at higher potentials than the chloride complex . A magnetism study of revealed anomalous magnetic behaviour similar to that of heptacobalt EMACs, and a deviation from the Curie-Weiss law was observed. The chi(M)T value at 300 K is 0.84 and 1.16 emu K mol(-1) for and , respectively, suggesting spin-equilibrium or a spin-admixture between doublet and quartet states arising from the Boltzmann distribution over different energy levels. Similar results were obtained for and , showing intermediate chi(M)T values between a diamagnetic and a triplet state of 0.15-0.96 emu K mol(-1) in the temperature range 5-300 K. The structural and magnetic results were interpreted through an EHMO study. PMID:19153628

Wang, Wen-Zhen; Ismayilov, Rayyat Huseyn; Wang, Rui-Ren; Huang, Yi-Lin; Yeh, Chen-Yu; Lee, Gene-Hsiang; Peng, Shie-Ming

2008-12-21

283

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

284

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

285

Synthesis, structure and thermal stability of ternary metal complexes based on polycarboxylate and N-heterocyclic ligands  

NASA Astrophysics Data System (ADS)

The reactions of metal salts with pyrazine-2,3-dicarboxylic acid (H 2pzdc), pyridine-2,5-dicarboxylic acid (H 2pydc), pyrazine-2,3,5,6-tetracarboxylic acid (H 4pztc), 4,4'-bipyridine (bipy) and 1,10-phenanthroline (phen) afforded four new ternary complexes, namely [Co 2(pzdc) 2(bipy)(H 2O) 2] n·3 nH 2O ( 1), [Zn 2(pzdc) 2(bipy)(H 2O) 2] n·3 nH 2O ( 2), [Co(pydc) 2(H 2O) 2](H 2bipy) ( 3) and [Cu 2(pztc)(phen) 2(H 2O) 2]·2HNO 3·2H 2O ( 4). The metal centers are all six-coordinated. Compounds 1 and 2 are 2D coordination polymers exhibiting wave-like polymeric networks. The 2D layers are stacked in an interpenetrating mode to form double-layered frameworks, which possess ˜8 Å×6 Å tunnels occupied by (H 2O) 6 clusters. Compound 3 is a mononuclear supramolecular compound in which 4,4'-bipyridine is protonated and acted as a cationic building block. Compound 4 is a centro-symmetric binuclear complex. Pztc 4- as a hexadentate ligand coordinates to two Cu(II) ions to form four chelating rings. Phen are arranged in an ABAB parallel fashion to form a supramolecular architecture incorporating HNO 3 lattice molecule. The thermal stabilities of 1- 4 and luminescence of zinc complex 2 were also investigated.

Fang, Ming-Jin; Li, Ming-Xing; He, Xiang; Shao, Min; Pang, Wei; Zhu, Shou-Rong

2009-03-01

286

Enhancing gas adsorption and separation capacity through ligand functionalization of microporous metal-organic framework structures.  

PubMed

Hydroxyl- and amino- functionalized [Zn(BDC)(TED)(0.5)]·2DMF·0.2H(2)O leads to two new structures, [Zn(BDC-OH)(TED)(0.5)]·1.5DMF·0.3H(2)O and [Zn(BDC-NH(2))(TED)(0.5)]·xDMF·yH(2)O (BDC=terephthalic acid, TED=triethylenediamine, BDC-OH=2-hydroxylterephthalic acid, BDC-NH(2)=2-aminoterephthalic acid). Single-crystal X-ray diffraction and powder X-ray diffraction studies confirmed that the structures of both functionalized compounds are very similar to that of their parent structure. Compound [Zn(BDC)(TED)(0.5)]·2DMF·0.2H(2)O can be considered a 3D porous structure with three interlacing 1D channels, whereas both [Zn(BDC-OH)(TED)(0.5)]·1.5DMF·0.3H(2)O and [Zn(BDC-NH(2))(TED)(0.5)]·xDMF·yH(2)O contain only 1D open channels as a result of functionalization of the BDC ligand by the OH and NH(2) groups. A notable decrease in surface area and pore size is thus observed in both compounds. Consequently, [Zn(BDC)(TED)(0.5)]·2DMF·0.2H(2)O takes up the highest amount of H(2) at low temperatures. Interestingly, however, both [Zn(BDC-OH)(TED)(0.5)]·1.5DMF·0.3H(2)O and [Zn(BDC-NH(2))(TED)(0.5)]·xDMF·yH(2)O show significant enhancement in CO(2) uptake at room temperature, suggesting that the strong interactions between CO(2) and the functionalized ligands, indicating that surface chemistry, rather than porosity, plays a more important role in CO(2) adsorption. A comparison of single-component CO(2), CH(4), CO, N(2), and O(2) adsorption isotherms demonstrates that the adsorption selectivity of CO(2) over other small gases is considerably enhanced through functionalization of the frameworks. Infrared absorption spectroscopic measurements and theoretical calculations are also carried out to assess the effect of functional groups on CO(2) and H(2) adsorption potentials. PMID:21433121

Zhao, Yonggang; Wu, Haohan; Emge, Thomas J; Gong, Qihan; Nijem, Nour; Chabal, Yves J; Kong, Lingzhu; Langreth, David C; Liu, Hui; Zeng, Heping; Li, Jing

2011-04-26

287

Ionic Exchange in p-Sulfonatocalix[4]arene-Mediated Formation of Metal-Ligand Complexes.  

PubMed

The effect of alkali and transition metal cations in the formation of host-guest complexes with the water-soluble p-sulfonatocalix[4]arene (SC4) was studied using 2-chloropyridine and Na(+) and Cu(2+) as model guest and model cations, respectively. The results obtained from isothermal titration calorimetry and NMR experiments provide evidence for the formation of 1:1:1 ternary complexes for both cations with Cu(2+) showing positive cooperativity and Na(+) negative cooperativity. The formation of ternary complexes comprising transition metal cations has been scarcely explored but present high potential for devising catalytic systems/models or for enhancing the stability and selectivity of SC4 complexes. Because transition metal cations are usually present in solution together with other SC4 countercations (e.g., Na(+)), a general binding model that considers the dynamic formation of all possible complexes (including ionic exchange between ternary complexes) is presented. This model allows the optimization of the conditions required to selectively form target complexes. PMID:24725072

Francisco, Vitor; Basílio, Nuno; García-Río, Luis

2014-05-01

288

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.

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

2012-01-01

289

Development and Evaluation of Artificial Dental Anchors of Non-Natural Design Implanted in Miniature Swine.  

National Technical Information Service (NTIS)

Two porous materials, one ceramic and one metal, have been fabricated into cylindrical dental anchors and implanted into the mandibles of miniature swine. The ceramic alumina porcelain was formed by special slipcasting and firing techniques. The metal anc...

R. P. Marshall M. T. Karagianes J. J. Rasmussen R. E. Westerman

1973-01-01

290

Polymer pendant ligand chemistry. 3. A biomimetic approach to selective metal ion removal and recovery from aqueous solution with polymer-supported sulfonated catechol and linear catechol amide ligands  

SciTech Connect

The design of organic ligands to selectively remove and recover metal ions from aqueous solution is a new and important area of environmental inorganic chemistry. One approach to designing organic ligands for these purposes is to use biological systems as examples for selective metal ion complexation. Thus, the authors report results on 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 that are chemically bonded to modified 6% cross-linked macroporous polystyrene-divinylbenzene beads (PS-DVB) 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 was dramatically 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, while metal ion selectivity could be changed at higher pH values in the absence of Fe{sup 3+} (for example, Hg{sup 2+} at pH 3). Rates of removal and recovery of the Fe{sup 3+} ion with the PS-CATS, PS-2-6LICAMS and PS-3,3-LICAMS polymer beads were also studied as well as relative equilibrium selectivity coefficient (K{sub m}) values for all metal competition studies.

Huang, Song-Ping; Li, Wei; Franz, K.J.; Albright, R.L.; Fish, R.H. [Univ. of California, Berkeley, CA (United States)

1995-05-24

291

Synthesis and spectroscopic characterization of some transition metal complexes of a new hexadentate N 2S 2O 2 Schiff base ligand  

NASA Astrophysics Data System (ADS)

A novel interesting hexadentate dibasic N 2S 2O 2 donor Schiff base ligand, H4dcsalpte, was synthesized by the condensation of 3-formylsalicylic acid and 1,2-di( o-aminophenylthio)ethane and characterized. The reactions of the ligand with different metal(II/III)salts under varied reaction conditions afforded a series of metal complexes. The ligand, H4dcsalpte, behaves either as a dibasic or neutral hexadentate one, depending on the reaction conditions. Structural investigations on the ligand and their complexes have been made based on elemental analyses, molar conductance values, magnetic moment values, cryomagnetic and spectral (UV-vis, IR, 1H NMR, and Mössbauer) data. Based on magnetic susceptibility, Mössbauer and electronic spectral data the iron(III) complex [Fe III( H2dcsalpte)]ClO 4 ( 8), isolated in the present investigation, it is inferred that the spin states 5/2 and 1/2 are in equilibrium. Similarly a tri-iron(III) complex [Fe III3( H2dcsalpte)( H3dcsalpte)Cl 3]Cl 3 ( 7), isolated in this study, has been inferred to contain two iron(III) sites in tetrahedral environment and one in the octahedral environment. The aerial oxidation of an equimolar mixture of H4dcsalpte and Co(CH 3COO) 2·4H 2O in ethanol under reflux gave two products, [Co( H2dcsalpte)]CH 3COO ( 10) and [( Hbtcsaldm)Co( Hbvcsaldm)] ( 11), a cobalt(III) complex bound to two dissimilar tridentate NSO donor ligands formed as a result of the oxidative cleavage of the C sbnd S bond. In the complex 11, Hbtcsaldm stands for the dianion of the tridentate Schiff base ligand N-(2'-benzenethiol)-3-carboxysalicylaldimine and Hbvcsaldm stands for the mono anion of the tridentate Schiff base ligand N-(benzene-2'-S-vinyl)-3-carboxysalicylaldimine, both being formed as a result of the oxidative cleavage of H4dcsalpte.

Sarkar, Saikat; Dey, Kamalendu

2005-11-01

292

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

293

Ligand-to-metal charge-transfer dynamics in a blue copper protein plastocyanin: a molecular dynamics study.  

PubMed

Equilibrium and nonequilibrium dynamics of a blue copper protein plastocyanin in an oxidized state are studied by molecular dynamics (MD) simulation. Potential energy functions of the lowest seven electronic states, including ligand-to-metal charge-transfer (LMCT) and copper d --> d excited states, were taken from our previous work (Ando, K. J. Phys. Chem. B 2004, 108, 3940), which employed ab initio molecular orbital and density functional calculations on the active-site model. The equilibrium MD simulations in the ground state indicate that ligand motions coupled to transition from the ground state to the LMCT state are mostly represented by stretching and bending vibrations of the Cu-S(Cys) distance, Ndelta(His)-Cu-Ndelta(His) angle, and S(Cys)-Cu-[Ndelta(His)]2 trigonal pyramid structure. The nonequilibrium dynamics on the LMCT potential exhibit rapid decays in which surface crossings to the d --> d and the first excited states occur in 70-80 fs. The crossing dynamics mostly correlate with cleavage of the Cu-S(Cys) bond and the associated response in the Ndelta(His)-Cu-Ndelta(His) moiety. The average dynamics of the vertical energy gap coordinates exhibit an overdamped decay with a recurrence oscillation in 500 fs, which shows clear coherence surviving after the ensemble averaging. This oscillation stems mostly from the recoiling motion of the Ndelta(His)-Cu-Ndelta(His) part. The dynamics of the energy gaps after this coherent oscillation are randomized such that the ensemble average yields flat profiles along time, although each single trajectory exhibits fluctuations with amplitudes large enough to reach surface crossings. These indicate that the relaxation from the LMCT state first occurs via ballistic and coherent potential crossings in 70-80 and 500 fs, followed by thermally activated random transitions. PMID:18047310

Ando, Koji

2008-01-17

294

Determination of ?-hydroxy acids and their enantiomers in fruit juices by ligand exchange CE with a dual central metal ion system.  

PubMed

The content of ?-hydroxy acids and their enantiomers can be used to distinguish authentic and adulterated fruit juices. Here, we investigated the use of ligand exchange CE with two kinds of central metal ion in a BGE for the simultaneous determination of enantiomers of dl-malic, dl-tartaric and dl-isocitric acids, and citric acid. Ligand exchange CE with 100 mM d-quinic acid as a chiral selector ligand and 10 mM Cu(II) ion as a central metal ion could enantioseparate dl-tartaric acid but not dl-malic acid or dl-isocitric acid. Addition of 1.8 mM Sc(III) ion to the BGE with 10 mM Cu(II) ion to create a dual central metal ion system permitted the simultaneous determination of these ?-hydroxy acid enantiomers and citric acid. The proposed ligand exchange CE was thus well suited for detecting adulteration of fruit juices. PMID:23423790

Kodama, Shuji; Aizawa, Sen-ichi; Taga, Atsushi; Yamamoto, Atsushi; Honda, Yoshitaka; Suzuki, Kentaro; Kemmei, Tomoko; Hayakawa, Kazuichi

2013-05-01

295

Synthesis of Mononuclear Metal Complexes with Some Tetradentate Schiff Base Ligands  

Microsoft Academic Search

A series of Cu(II), Ni(II) and Co(II) complexes with N,N?-bis-[5-X-salicylidene]-2,2?-diaminodibenzyl [H2-XSalDDB (X?H, CH3, Br)] have been prepared. The metal complexes were characterized on the basis of elemental analyses, electrical conductance, magnetic susceptibility, spectral and thermal studies. All of the complexes are non-electrolytes of 1:1 (M:L) stoichiometry. The room temperature magnetic susceptibility and electronic spectral data support a pseudo-tetrahedral geometry for

N. V. Thakkar; R. M. Patil

2000-01-01

296

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

297

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

298

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

Microsoft Academic Search

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]X2 and [Ni(L)X]X compositions (where L=ligand and X=NO3?, Cl? and CH3COO?) were synthesized and characterized by physicochemical and spectral studies. The studies like elemental analyses, molar conductance measurements, magnetic susceptibility measurements,

Amit Kumar Sharma; Sulekh Chandra

2011-01-01

299

Suture anchors--update 1999.  

PubMed

New suture anchors continue to become available. Our prior reports on the pullout strength of over 50 different anchors is supplemented by a similar test conducted on 25 additional new anchors. This anchor comparison, using an established protocol in fresh porcine femurs, recorded failure strength, failure mode (anchor pullout, suture eyelet cutout, or wire breakage), eyelet size, minor and major diameters, and drill hole sizes. These new anchors were tested in diaphyseal cortex, metaphyseal cortex, and a cancellous trough. Tensile stress parallel to the axis of insertion was applied at a rate of 12.5 mm/sec by an Instron 1321 until failure and mean anchor failure strengths were calculated. Anchors tested included DePuy 4.5 prototypes D1, D2 Catera 4.5, and D3; DePuy 3.5 prototypes D4- Catera 3.5, D5, and D6; Mainstay 2.7, 3.5, 4.5; ROC EZ 2.8, EZ 3.5, and XS 3.5; Ultrafix RC and Ultrafix MiniMite; 1.3 MicroMitek, Panalok 3.5, and Tacit 2.0; Umbrella Harpoon; PeBA 2.8, 4.0, 6.5; and Stryker 1.9, 2.7, 3.4, and 4.5 prototypes. Screw anchors still tend to have higher values, but for the newer nonscrew designs this distinction is less apparent. The new biodegradable anchors were all composed of poly L-lactic acid suggesting a trend away from other polymers, and these new biodegradable anchors showed load-to-failure strengths comparable to others in their class. All anchors were stronger than the suture for which they are designed to accommodate. PMID:10524819

Barber, F A; Herbert, M A

1999-10-01

300

Complexation of metal ions with TRAP (1,4,7-triazacyclononane phosphinic acid) ligands and 1,4,7-triazacyclononane-1,4,7-triacetic acid: phosphinate-containing ligands as unique chelators for trivalent gallium.  

PubMed

Three phosphinic acid 1,4,7-triazacyclononane (TACN) derivatives bearing methylphosphinic (TRAP-H), methyl(phenyl)phosphinic (TRAP-Ph), or methyl(hydroxymethyl)phosphinic acid (TRAP-OH) pendant arms were investigated as members of a new family of efficient Ga(3+) chelators, TRAP ligands (triazacyclononane phosphinic acids). Stepwise protonation constants of ligands and stability constants of their complexes with Ga(3+), selected divalent metal, and Ln(3+) ions were determined by potentiometry. For comparison, equilibrium data for the metal ion-NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) systems were redetermined. These ligands exhibit high thermodynamic selectivity for Ga(3+) over the other metal ions (log K(GaL) - log K(ML) = 7-9) and a selective complexation of smaller Mg(2+) over Ca(2+). Stabilities of the Ga(3+) complexes are dependent on the basicity of the donor atoms: [Ga(NOTA)] (log K(GaL) = 29.6) > [Ga(TRAP-OH)] (log K(GaL) = 23.3) > [Ga(TRAP-H)] (log K(GaL) = 21.9). The [Ga(TRAP-OH)] complex exhibits unusual reversible rearrangement of the "in-cage" N(3)O(3) complex to the "out-of-cage" O(6) complex. The in-cage complex is present in acidic solutions, and at neutral pH, Ga(3+) ion binds hydroxide anion, induces deprotonation and coordination of the P-hydroxymethyl group(s), and moves out of the macrocyclic cavity; the hypothesis is supported by a combination of results from potentiometry, multinuclear nuclear magnetic resonance spectrometry, and density functional theory calculations. Isomerism of the phosphinate Ga(3+) complexes caused by a combination of the chelate ring conformation, the helicity of coordinated pendant arms, and the chirality of the coordinated phosphinate groups was observed. All Ga(3+) complexes are kinetically inert in both acidic and alkaline solutions. Complex formation studies in acidic solutions indicate that Ga(3+) complexes of the phosphinate ligands are formed quickly (minutes) and quantitatively even at pH <2. Compared to common Ga(3+) chelators (e.g., 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) derivatives), these novel ligands show fast complexation of Ga(3+) over a broad pH range. The discussed TRAP ligands are suitable alternatives for the development of (68)Ga radiopharmaceuticals. PMID:22221285

Šime?ek, Jakub; Schulz, Martin; Notni, Johannes; Plutnar, Jan; Kubí?ek, Vojt?ch; Havlí?ková, Jana; Hermann, Petr

2012-01-01

301

TRANSITION METAL COMPLEXES WITH EDDA-TYPE LIGANDS—A REVIEW  

Microsoft Academic Search

The review summarizes the results of recent studies on edda-type metal complexes. It focuses on work published during the period 1984–2001. The metals include are Co, Cr, Cu, Ni, Zn, Mn, Sn, Fe, V, Rh, Pt, Ru, whereas edda-type represents ethylenediamine-N,N?-diacetate, ethylenediamine-N,N-di-acetate, N,N?-dimethylethylenediamine-N,N?-diacetate, N,N?-diethylethylenediamine-N,N?-diacetate, 1,2-cyclo-hexanediamine-N,N?-diacetate, N,N?-dimethyl-1,2-cyclohexanediamine-N,N?-diacetate, ethylenediamine-N,N?-di-3-propionate, N,N?-dimethylethylenediamine-N,N?-di-3-propionate, ethylenediamine-N,N?-di-S-?-propionate, N,N?-dimethyl-ethylenediamine-N,N?-di-?-propionate, 1,3-propanediamine-N,N?-diacetate (trimethylenediamine-N,N?-diacetate), 1,3-propanediamine-N,N?-di-3-propionate (trimethylenediamine-N,N?-di-3-propionate), N,N?-dimethylethylenediamine-N,N?-di-?-butyrate, N,N?-diethylethylenediamine-N,N?-di-?-butyrate, 1-diethylenetriamineacetate (8-amino-3,6-diazao-ctanoate), ethylenepropylenetriamineacetate (9-amino-3,6-diazaoc-

Tibor J. Sabo; Sanja R. Grguri?-Šipka; Sre?ko R. Trifunovi?

2002-01-01

302

Bellow seal and anchor  

DOEpatents

An annular seal is made of a collapsible bellows. The bellows can function as an anchor or a seal and is easily set into position using relative component movement. The bellows folds can be slanted and their outer sealing edges can have different profiles to meet expected conditions. The bellows is expanded for insertion to reduce its outer dimension and sets by compaction as a result of relative movement. The bellows can be straight or tapered and is settable with a minimal axial force.

Mansure, Arthur J. (Albuquerque, NM)

2001-01-01

303

Use of Mitek anchoring for Bankart repair: A comparative, randomized, prospective study with traditional bone sutures.  

PubMed

The most common type of shoulder instability is posttraumatic anterior instability. Treatment is surgical. Of the several procedures used, the standard one is Bankart repair. However, this procedure is technically demanding. To simplify it a suture anchor such as Mitek anchors may be used. A prospective randomized study was conducted to compare Mitek anchors with bone sutures. The results showed that Mitek anchors shorten surgical time by making reattachment of the capsule easier. Shoulder muscle strength, range of motion, and frequency of recurrence were equally good in the anchor group and bone suture group. A roentgenographic method allowed exact measurement of placement of the anchors. This method showed at 2-year follow-up evaluation that the anchors were still in the anterior glenoid. No metal-related complications are found at the 2-year follow-up evaluation. PMID:22958842

Norlin, R

1994-11-01

304

Ab initio calculations in heterogeneous and homogeneous catalysis: I. Methanol to gasoline with ZSM-5. II. Carbonyl ligand effects on metal-metal bonds  

SciTech Connect

This thesis is composed of two studies in catalysis. The first is an exploration, using computational techniques, of the mechanism for the first carbon-carbon bond formation in the methanol to gasoline (MTG) reaction. The second is a study of the factors important to the understanding of ligand effects on metal-metal bonds, and in particular, to metal clusters. Three possibilities were considered as ways to activate a carbon in the MTG process prior to formation of C2 or higher hydrocarbons. These were a free radical mechanism, a surface ylide mechanism, and a possible defect site which might lead to steric crowding of CH[sub 2] groups. Although the free radical mechanism was found to be thermodynamically within the parameters of the MTG process, it contained a high transition state. Consideration of the molecules available prior to hydrocarbon build-up and their specific electronic structure, led to the view that the available carbon atoms (methanol, dimethyl ether, etc.) were unlikely to be activated by a free radical intermediate. The surface-stabilized ylide which has been proposed as an intermediate by many was studied to determine if in fact the ylide was stabilized. The total energy of the ylide was compared to that of the naked site on the zeolite and free methylene. Free methylene ranged, depending on the geometry of the ylide, between 50 and 80 kcal more stable. These numbers are qualitatively correct, but more electron correlation would have to be incorporated in the calculation to get an accurate value for the destabilization. Starting from a defect site, two CH[sub 2] groups were each attached to two oxygen atoms. It was thought that two CH[sub 2] groups would take up considerably more space than either than original Al atom or the four hydrogens. Molecular Mechanics calculations showed the zeolite to be sufficiently flexible to prevent crowding of the CH[sub 2]'s.

Miller, A.E.

1993-01-01

305

Synthesis of nucleosides and dNTPs bearing oligopyridine ligands linked through an octadiyne tether, their incorporation into DNA and complexation with transition metal cations.  

PubMed

Modified nucleosides (dA(R)s and dC(R)s) bearing bipyridine or terpyridine ligands attached through an octadiyne linker were prepared by single-step aqueous-phase Sonogashira cross-coupling of 7-iodo-7-deaza-2'-deoxyadenosine and 5-iodo-2'-deoxycytidine with the corresponding bipyridine- or terpyridine-octadiynes and were triphosphorylated to the corresponding nucleoside triphosphates (dA(R)TPs and dC(R)TPs). The modified dN(R)TPs were successfully incorporated into the oligonucleotides by primer extension experiment (PEX) using different DNA polymerases and the PEX products were used for post-synthetic complexation with divalent metal cations. The complexation of these DNAs containing flexibly-tethered ligands was compared with the previously reported ones bearing rigid acetylene-linked ligands suggesting the possible formation of both inter- and intra-strand complexes with Ni(2+) or Fe(2+). PMID:23090069

Kalachova, Lubica; Pohl, Radek; Bednárová, Lucie; Fanfrlík, Jind?ich; Hocek, Michal

2013-01-01

306

Synthesis, structures, and properties of two three-dimensional metal-organic frameworks, based on concurrent ligand extension.  

PubMed

A tritopic carboxylate ligand, tris(4'-carboxybiphenyl)amine (L-H(3)), has been synthesized and applied in the construction of microporous metal-organic frameworks (MOFs). Two novel metal-organic frameworks (MOFs), {[Zn(2)(L)(OH)]·2DMF·H(2)O}(?) (1) and {[Cu(L-H)(DMA)]·DMA·2H(2)O}(?) (2), have been constructed out of L-H(3), Zn(2+), and Cu(2+), respectively. 1 has a 2-fold interpenetrating three-dimensional framework formed by L connectors and the [Zn(2)(CO(2))(3)] secondary building units (SBUs). As for 1, it is worth pointing out that one ?(2)-OH group links two Zn atoms between two neighboring SBUs to produce interesting Zn-O-Zn zigzag chains in the structure. 2 has a two-dimensional grid sheet formed by L-H connectors and the typical paddle-wheel [Cu(2)(CO(2))(4)] SBUs. Two-dimensional (2D) sheets nest with each other, which finally forms a three-dimensional (3D) nested framework. Two MOFs are characterized by infrared (IR) spectroscopy, thermogravimetry, single-crystal and elemental analyses, and powder X-ray diffraction methods. Framework 1' exhibits high permanent porosity (Langmuir surface area = 848 m(2)/g), high thermal stability (up to 450 °C), highly active properties for Friedel-Crafts alkylation reaction, as well as the potential application for the CO(2) gas storage and luminescent material. The catalytic results reveal that 2' is indeed an efficient heterogeneous catalyst for olefin epoxidation reactions. PMID:22670898

Shi, Dabin; Ren, Yanwei; Jiang, Huanfeng; Cai, Bowei; Lu, Jiaxian

2012-06-18

307

Concentration, Complexation and Chemical Speciation of Zinc and Cadmium in the Western North Pacific Ocean : Exploring Sources and Transport of Trace Metals and Complexing Ligands.  

NASA Astrophysics Data System (ADS)

We determined Zn and Cd total dissolved (0.45 µm-filtered) concentrations, organic complexation and chemical speciation in surface water samples collected along the transect of the 2002 IOC Baseline Contaminant Survey expedition in the Western North Pacific and in vertical profile water samples at nine stations. The goals of this work were (1) to compare and contrast various trace metal sources, including both natural and anthropogenic atmospheric deposition, upwelling, marginal seas and others; (2) to study the organic ligand sources, generally thought to be phytoplankton; and (3) to investigate metal and ligand transport mechanisms, residence times and eventual upwelling in the Eastern North Pacific. Total dissolved (TD) Zn and Cd values were obtained using a combination of differential pulse stripping anodic voltammetry (DPASV), preconcentration with 8-HQ or APDC/DDC and quantification at ICPMS or AA. Organic complexation and chemical speciation of Zn and Cd were determined simultaneously using DPASV at a thin-mercury-film, glassy-carbon-disk-electrode. Surface transect TDZn and TDCd concentrations were low in the Subtropical Gyre (STG), in contrast with high values in the Western Subarctic Gyre (WSG). Zn and Cd were organically complexed in most surface samples: at least one ligand class was detected for Zn and Cd, whose conditional stability constants (log K') averaged 10.2 and 10.5, respectively. These ligands were found in excess of the total dissolved metal throughout the region of study except in the WSG for Cd. Vertical distributions of TDZn and TDCd exhibited nutrient-type profiles for all the STG stations. While constant Zn/Si and Cd/P values were observed throughout the water column in the WSG, some deviations were observed within the STG. In addition, the mode and intermediate water masses of the STG displayed very high concentrations of a Zn-complexing ligand (log K' 10.0) in excess of TDZn. As these water masses moved eastward, we observed that the ligand concentrations decreased. In contrast to the STG, the upper 1000m of the WSG showed elevated concentrations of both metals. Despite elevated surface (0-200m) Zn concentrations (~2nM), a Zn-complexing ligand (log K' 9.8) was found in excess of TDZn; below the photic layer, even higher TDZn concentrations might have saturated the ligand. A ligand for Cd was present in lower-than-TDCd concentrations in the same surface waters; below them, organic complexation of Cd was observed rarely in both STG and WSG regions. By studying the geographic distribution of the total dissolved metals and ligands, along with other dissolved and particulate tracers, possible sources and transport mechanisms can be contrasted and evaluated. Furthermore, the influence of these sources and transport mechanisms on the distribution of Zn and Cd chemical species and, ultimately, the bioavailability of these micronutrient metals can be studied.

Carrasco, G. G.; Morton, P. L.; Donat, J. R.

2008-12-01

308

Synthesis and characterization of new rhodium–cobalt mixed-metal octahedral linked clusters containing ? 2-diyne ligands  

Microsoft Academic Search

Six new Rh?Co mixed-metal linked cluster complexes [Rh2Co2(CO)8(?-CO)2 (?4,?2-HC?CCH2O?)]2R (R=C6H4-1,4 (1); C6H4-1,4(C(O))2 (2); (C(O)CH2)2 (3); (C(O)CH)2 (4); (C(O))2CH2 (5); (C(O))2 (6)) have been synthesized from reactions of [Rh2Co2(CO)12] (7) with the appropriate diyne compounds [(HC?CCH2CO)?]2R (R=C6H4-1,4 (8); C6H4-1,4(C(O))2 (9); (C(O)CH2)2 (10); (C(O)CH)2 (11); (C(O))2CH2 (12); (C(O))2 (13)) in n-hexane at room temperature, respectively. The acetylene moieties of diyne ligands insert

Bao-Hua Zhu; Bin Hu; Wei-Qiang Zhang; Yu-Hua Zhang; Yuan-Qi Yin; Jie Sun

2003-01-01

309

Metal-ligand interactions in perturbed blue copper sites: a paramagnetic (1)H NMR study of Co(II)-pseudoazurin.  

PubMed

Pseudoazurin is an electron transfer copper protein, a member of the cupredoxin family. The protein is frequently found in denitrifying bacteria, where it is the electron donor of nitrite reductase. The copper at the active site is coordinated to His40, Cys78, His81 and Met86 in a distorted tetragonal geometry. We have recorded and assigned the (1)H NMR spectra of Co(II)-substituted pseudoazurin from Achromobacter cycloclastes. The (1)H NMR spectrum of Co(II)-pseudoazurin closely resembles that of Co(II)-rusticyanin, reflecting an altered conformation for the Met-Co(II)-Cys moiety in both proteins, compared to Co(II)-azurin, amicyanin and stellacyanin. The electron spin density onto the Sgamma(Cys) is larger in Co(II)-pseudoazurin compared to Co(II)-rusticyanin. Instead, the Co(II)-Met interaction is similar in both derivatives. Hence, the different metal-ligand interactions might be independently modulated by the protein structure. The present work also shows that the electron spin density onto the Co(II)-S(cys) bond is sensibly smaller than the Cu(II)-S(cys). Notwithstanding, NMR data on Co(II)-substituted blue copper proteins can be safely extrapolated to native Cu(II) proteins. PMID:12459901

Fernández, Claudio O; Niizeki, Tomotake; Kohzuma, Takamitsu; Vila, Alejandro J

2003-01-01

310

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

PubMed

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; Mir?eski, Valentin; Saul, Stephanie; Pasieka, Bastian; Haeri, Haleh H; Stefova, Marina; Stanoeva, Jasmina Petreska; Mitrev, Saša; Hoth, Markus; Kappl, Reinhard

2013-01-01

311

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.

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

312

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

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

313

Metal-ligand interplay in blue copper proteins studied by 1H NMR spectroscopy: Cu(II)-pseudoazurin and Cu(II)-rusticyanin.  

PubMed

The blue copper proteins (BCPs), pseudoazurin from Achromobacter cycloclastes and rusticyanin from Thiobacillus ferrooxidans, have been investigated by (1)H NMR at a magnetic field of 18.8 T. Hyperfine shifts of the protons belonging to the coordinated ligands have been identified by exchange spectroscopy, including the indirect detection for those resonances that cannot be directly observed (the beta-CH(2) of the Cys ligand, and the NH amide hydrogen bonded to the S(gamma)(Cys) atom). These data reveal that the Cu(II)-Cys interaction in pseudoazurin and rusticyanin is weakened compared to that in classic blue sites (plastocyanin and azurin). This weakening is not induced by a stronger interaction with the axial ligand, as found in stellacyanin, but might be determined by the protein folding around the metal site. The average chemical shift of the beta-CH(2) Cys ligand in all BCPs can be correlated to geometric factors of the metal site (the Cu-S(gamma)(Cys) distance and the angle between the CuN(His)N(His) plane and the Cu-S(gamma)(Cys) vector). It is concluded that the degree of tetragonal distortion is not necessarily related to the strength of the Cu(II)-S(gamma)(Cys) bond. The copper-His interaction is similar in all BCPs, even for the solvent-exposed His ligand. It is proposed that the copper xy magnetic axes in blue sites are determined by subtle geometrical differences, particularly the orientation of the His ligands. Finally, the observed chemical shifts for beta-CH(2) Cys and Ser NH protons in rusticyanin suggest that a less negative charge at the sulfur atom could contribute to the high redox potential (680 mV) of this protein. PMID:12431099

Donaire, Antonio; Jiménez, Beatriz; Fernández, Claudio O; Pierattelli, Roberta; Niizeki, Tomotake; Moratal, José-María; Hall, John F; Kohzuma, Takamitsu; Hasnain, S Samar; Vila, Alejandro J

2002-11-20

314

Combining ligand design and photo-ligation to provide optimal quantum dot-bioconjugates for sensing and imaging  

NASA Astrophysics Data System (ADS)

We describe the design and synthesis of two metal-coordinating zwitterion ligands to promote the transfer of hydrophobic QDs to buffer media over broad range of conditions. The ligands are prepared by appending either one or two lipoic acid anchoring groups onto a zwitterion, LA-TEG200-ZW and bis(LA)- ZW. Combining these ligands with a photochemical reduction of the lipoic acid group in the presence of UV irradiation, provides an easy to implement method to transfer luminescent QDs to buffer media, while preserving their optical and spectroscopic properties intact. The resulting zwitterion-QDs have very thin capping shell, which allows their self-assembly with full size proteins via metal-to-histidine coordination. These conjugates have great potential for use in various bio-motivated applications.

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

2014-03-01

315

Metal-metal and metal-ligand bonding at a QTAIM catastrophe: a combined experimental and theoretical charge density study on the alkylidyne cluster Fe3(?-H)(?-COMe)(CO)10.  

PubMed

The charge density in the tri-iron methoxymethylidyne cluster Fe(3)(?-H)(?-COMe)(CO)(10) (1) has been studied experimentally at 100 K and by DFT calculations on the isolated molecule using the Quantum Theory of Atoms in Molecules (QTAIM). The COMe ligand acts as a nearly symmetric bridge toward two of the Fe atoms (Fe-C = 1.8554(4), 1.8608(4) Å) but with a much longer interaction to the third Fe atom, Fe-C = 2.6762(4) Å. Complex 1 provides a classic example where topological QTAIM catastrophes render an exact structure description ambiguous. While all experimental and theoretical studies agree in finding no direct metal-metal interaction for the doubly bridged Fe-Fe vector, the chemical bonding between the Fe(CO)(4) unit and the Fe(2)(?-H)(?-COMe)(CO)(6) moiety in terms of conventional QTAIM descriptors is much less clear. Bond paths implying direct Fe-Fe interactions and a weak interaction between the COMe ligand and the Fe(CO)(4) center are observed, depending on the experimental or theoretical density model examined. Theoretical studies using the Electron Localizability Indicator (ELI-D) suggest the metal-metal bonding is more significant, while the delocalization indices imply that both Fe-Fe bonding and Fe···C(alkylidyne) bonding are equally important. The source functions at various interfragment reference points are similar and highly delocalized. The potential-energy surface (PES) for the migration of the alkylidyne group from a ?(2) to a semi-?(3) coordination mode has been explored by DFT calculations on 1 and the model complexes M(3)(?-H)(?-CH)(CO)(10) (M = Fe, 2; Ru, 3; and Os, 4). These calculations confirm a semi-?(3) bridging mode for the alkylidyne ligand as the minimum-energy geometry for compounds 2-4 and demonstrate that, for 1, both Fe-Fe and Fe···C(alkylidyne) interactions are important in the cluster bonding. The PES between ?(2) and semi-?(3) alkylidyne coordination for 1 is extremely soft, and the interconversion between several topological isomers is predicted to occur with almost no energy cost. Analysis of the density ?(r) and the Laplacian of the density ?(2)?(r(b)) in the methoxymethylidyne ligand is consistent with a partial ?-bond character of the C-O bond, associated with an sp(2) hybridization for these atoms. PMID:21182291

Farrugia, Louis J; Senn, Hans Martin

2010-12-30

316

Synthesis, structures and luminescent properties of Co(II) and Ni(II) metal-organic frameworks with semirigid diphthalic ligands  

NASA Astrophysics Data System (ADS)

A series of transition metal coordination polymers [Co(H 3L) 2(4,4'- bpy)(H 2O) 2] n•n(4,4'-bpy) ( 1), [Ni(H 2L)(4,4'-bpy)(H 2O) 2] n ( 2), [Co 2(L)(phen) 2(H 2O) 4] n•(H 2O) 2n ( 3), and [Ni 2(L)(phen) 2(H 2O) 4] n•(H 2O) 2n ( 4) have been assembled from a semirigid multicarboxylate ligand 3,3'-(1,4-phenylenebis(oxy))diphthalic acid (H 4L) with the help of 4,4'-bipyridine (4,4'-bpy) ligand or 1,10-phenanthroline (phen) ligand. X-ray single crystal diffraction analysis reveals that complex 1 crystallizes in the space group of P - 1 and displays a one-dimensional (1D) chain structure constructed from 4,4'-bpy ligand and H 3L ligand, which was further interlinked to form a three-dimensional network via hydrogen bonds. In complex 2, Ni(II) atoms are coordinated by L ligand in monodentate fashion to form alternate left- and right-helices, which are further bridged together by the coordination interactions between Ni(II) atoms and 4,4'-bpy, leading to a 2-fold (4, 4)-connected interpenetrating network. Isostructural complexes 3 and 4 belong to the space group P - 1 and display a 1D chain structure constructed from phen and L ligands, which was further interlinked to form a 2D plane via ?-? interactions. In addition, their thermal and luminescent properties were also investigated.

Zhao, Ningning; Wang, Kang; Li, Wenjun; Bian, Yongzhong; Sun, Changyan; Chang, Zhidong; Fan, Hongxia

2011-11-01

317

Complexation of metal ions, including alkali-earth and lanthanide(III) ions, in aqueous solution by the ligand 2,2',6',2''-terpyridyl.  

PubMed

Some metal-ion-complexing properties of the ligand 2,2',6',2''-terpyridyl (terpy) in aqueous solution are determined by following the ?-?* transitions of 2 × 10(-5) M terpy by UV-visible spectroscopy. It is found that terpy forms precipitates when present as the neutral ligand above pH ?5, in the presence of electrolytes such as NaClO(4) or NaCl added to control the ionic strength, as evidenced by large light-scattering peaks. The protonation constants of terpy are thus determined at the ionic strength (?) = 0 to avoid precipitation and found to be 4.32(3) and 3.27(3). The log K(1) values were determined for terpy with alkali-earth metal ions Mg(II), Ca(II), Sr(II), and Ba(II) and Ln(III) (Ln = lanthanide) ions La(III), Gd(III), and Lu(III) by titration of 2 × 10(-5) M free terpy at pH >5.0 with solutions of the metal ion. Log K(1)(terpy) was determined for Zn(II), Cd(II), and Pb(II) by following the competition between the metal ions and protons as a function of the pH. Complex formation for all of these metal ions was accompanied by marked sharpening of the broad ?-?* transitions of free terpy, which was attributed to complex formation affecting ligand vibrations, which in the free ligand are coupled to the ?-?* transitions and thus broaden them. It is shown that log K(1)(terpy) for a wide variety of metal ions correlates well with log K(1)(NH(3)) values for the metal ions. The latter include both experimental log K(1)(NH(3)) values and log K(1)(NH(3)) values predicted previously by density functional theory calculation. The structure of [Ni(terpy)(2)][Ni(CN)(4)]·CH(3)CH(2)OH·H(2)O (1) is reported as follows: triclinic, P1, a = 8.644(3) Å, b = 9.840(3) Å, c = 20.162(6) Å, ? = 97.355(5)°, ? = 97.100(5)°, ? = 98.606(5)°, V = 1663.8(9) Å(3), Z = 4, and final R = 0.0319. The two Ni-N bonds to the central N donors of the terpy ligands in 1 average 1.990(2) Å, while the four peripheral Ni-N bonds average 2.107(10) Å. This difference in the M-N bond length for terpy complexes is typical of the complexes of smaller metal ions, while for larger metal ions, the difference is reversed. The significance of the metal-ion size dependence of the selectivity of polypyridyl ligands, and the greater rigidity of ligands based on aromatic groups such as pyridyl groups, is discussed. PMID:21366261

Hamilton, Joanna M; Anhorn, Michael J; Oscarson, Karen A; Reibenspies, Joseph H; Hancock, Robert D

2011-04-01

318

Vertical Breakout Behavior of the Hydrostatic Anchor.  

National Technical Information Service (NTIS)

The vertical breakout behavior of the hydrostatic anchor depends greatly upon the anchor geometry including anchor diameter and skirt length, the soil strength properties, and the pressure difference between the ambient pressure and that underneath the po...

M. C. Wang V. A. Nacci K. R. Demars

1974-01-01

319

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

320

CHEMICAL SYNTHESIS OF GLYCOSYLPHOSPHATIDYLINOSITOL ANCHORS  

PubMed Central

Many eukaryotic cell-surface proteins and glycoproteins are anchored to the plasma membrane by glycosylphosphatidylinositols (GPIs), a family of glycolipids that are post-translationally attached to proteins at their C-termini. GPIs and GPI-anchored proteins play important roles in many biological and pathological events, such as cell recognition and adhesion, signal transduction, host defense, and acting as receptors for viruses and toxins. Chemical synthesis of structurally defined GPI anchors and GPI derivatives is a necessary step toward understanding the properties and functions of these molecules in biological systems and exploring their potential therapeutic applications. In the first part of this comprehensive article on the chemical synthesis of GPIs, classic syntheses of naturally occurring GPI anchors from protozoan parasites, yeast, and mammals are covered. The second part of the article focuses on recent diversity-oriented strategies for the synthesis of GPI anchors containing unsaturated lipids, “click chemistry” tags, and highly branched and modified structures.

Swarts, Benjamin M.; Guo, Zhongwu

2013-01-01

321

Outer-sphere association of calixarenes and other macrocyclic ligands with metal complexes as the basis for the design of molecular devices  

NASA Astrophysics Data System (ADS)

The regular features of the formation of outer-sphere associates of water-soluble calixarenes with metal complexes in solutions and their structure in the solid state are analysed. A comparison with analogous data for other outer-sphere macrocyclic ligands is carried out. Some physicochemical properties of the outer-sphere associates are considered in regards to their potential use for the development of new processes and materials.

Mustafina, A. R.; Skripacheva, V. V.; Konovalov, A. I.

2007-10-01

322

Synthesis of three d 10 compounds based on N-(3-pyridylmethyl)benzimidazole, the effect of radius of metal ions on structure and the function of ligand  

NASA Astrophysics Data System (ADS)

Zn 2+, Cd 2+ and Hg 2+ complexes of L [L= N-(3-pyridylmethyl)benzimidazole] have been synthesized and characterized by single crystal X-ray analysis and fluorescence spectra as well as TGA analysis. The Zn 2+ compound is monomeric, the Cd 2+ complex is of double-bridge chain, while the Hg 2+ complex is of wave-like chain. These compounds reveal the metal radius interaction on structural types and the function of ligand.

Huang, Meihua; Liu, Ping; Chen, Yun; Wang, Jian; Liu, Zheng

2006-05-01

323

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

324

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

325

Studies with an immobilized metal affinity chromatography cassette system involving binuclear triazacyclononane-derived ligands: Automation of batch adsorption measurements with tagged recombinant proteins.  

PubMed

This study describes the determination of the adsorption isotherms and binding kinetics of tagged recombinant proteins using a recently developed IMAC cassette system and employing automated robotic liquid handling procedures for IMAC resin screening. These results confirm that these new IMAC resins, generated from a variety of different metal-charged binuclear 1,4,7-triaza-cyclononane (tacn) ligands, interact with recombinant proteins containing a novel N-terminal metal binding tag, NT1A, with static binding capacities similar to those obtained with conventional hexa-His tagged proteins, but with significantly increased association constants. In addition, higher kinetic binding rates were observed with these new IMAC systems, an attribute that can be positively exploited to increase process productivity. The results from this investigation demonstrate that enhancements in binding capacities and affinities were achieved with these new IMAC resins and chosen NT1A tagged protein. Further, differences in the binding performances of the bis(tacn) xylenyl-bridged ligands were consistent with the distance between the metal binding centres of the two tacn moieties, the flexibility of the ligand and the potential contribution from the aromatic ring of the xylenyl group to undergo ?/? stacking interactions with the tagged proteins. PMID:24891160

Petzold, Martin; Coghlan, Campbell J; Hearn, Milton T W

2014-07-18

326

Interfacial self-assembly of metal-mediated viologen-like coordination polyelectrolyte hybrids of the bisterpyridine ligand and their optical, electrochemical, and electrochromic properties.  

PubMed

Metal-mediated coordination polyelectrolyte multilayers with a bisterpyridine ligand (Bisterpy) have been self-assembled at air-water interfaces via coordination reactions of the bidentate ligand Bisterpy with inorganic salts in the subphases. To avoid dissolution of the viologen-like coordination polyelectrolyte monolayers, anionic poly(styrenesulfonic acid-o-maleic) (PSS) acid was added in the subphases as a supporting layer. The average molecular area of the ligand Bisterpy could reach 1.2-1.5 nm(2) on the surfaces of the subphases containing mixtures of inorganic salts (M) and PSS, although the ligand was unable to form a stable monolayer on the pure water surface. The Langmuir-Blodgett (LB) method was used to deposit the Bisterpy/PSS and M-Bisterpy/PSS hybrid multilayers on the substrate surfaces, which were characterized by using absorption and fluorescence spectroscopy as well as electrochemical analysis. Quasi-reversible redox waves were recorded and centered at about -0.68 and -0.92 V (vs Ag/AgCl), respectively, corresponding to the two-electron process of the ligand, Bisterpy2+ <--> Bisterpy(*+) <--> Bisterpy(0), which were slightly shifted to lower potentials in the LB films of metal-mediated coordination polymers. The film compositions were determined by using X-ray photoelectron spectroscopy. The as-prepared LB films showed strong stability and good electrochromic response upon the applied potential of -1.1 V vs Ag/AgCl and thus could act as potential materials in the development of redox-based molecular switches and display devices. PMID:20355920

Zhang, Chao-Feng; Liu, An; Chen, Meng; Nakamura, Chikashi; Miyake, Jun; Qian, Dong-Jin

2009-06-01

327

Assignment of metal-ligand modes in Pt(II) diimine complexes relevant to solar energy conversion.  

PubMed

This work describes a comprehensive assignment of the vibrational spectra of the platinum(II) diimine bisthiolate and chloride complexes as a prototype structure for a diversity of Pt(II) diimine chromophores. The dynamics and energy dissipation pathways in excited states of light harvesting molecules relies largely on the coupling between the high frequency and the low frequency modes. As such, the assignment of the vibrational spectrum of the chromophore is of utmost importance, especially in the low-frequency region, below 500 cm(-1), where the key metal-ligand framework modes occur. This region is experimentally difficult to access with infrared spectroscopy and hence frequently remains elusive. However, this region is easily accessible with Raman and inelastic neutron scattering (INS) spectroscopies. Accordingly, a combination of inelastic neutron scattering and Raman spectroscopy with the aid of computational results from periodic-DFT and the mode visualizations, as well as isotopic substitution, allowed for an identification of the modes that contain significant contributions from Pt-Cl, Pt-S, and Pt-N stretch modes. The results also demonstrate that it is not possible to assign transition energies to "pure", localized modes in the low frequency region, as a consequence of the anticipated severe coupling that occurs among the skeletal modes. The use of INS has proved invaluable in identifying and assigning the modes in the lowest frequency region, and overall the results will be of assistance in analyzing the structure of the electronic excited state in the families of chromophores containing a Pt(diimine) core. PMID:22937801

Parker, Stewart F; Refson, Keith; Bennett, Robert D; Best, Jonathan; Mel'nikov, Mikhail Ya; Weinstein, Julia A

2012-09-17

328

Synthesis, crystal structures and luminescent properties of zinc(II) metal-organic frameworks constructed from terpyridyl derivative ligand  

NASA Astrophysics Data System (ADS)

Five zinc(II) metal-organic frameworks, [Zn3(344-pytpy)2Cl6]n·n(H2O) (1), [Zn(344-pytpy)(ox)]n (2), [Zn2(344-pytpy)(bdc)2]n·1.5n(H2O) (3), [Zn2(344-pytpy)2 (sfdb)2]n·1.5n(H2O) (4) and [Zn3(344-pytpy)2(btc)2]n·2n(H2O) (5), (344-pytpy=4?-(3-pyridyl)-4,2?:6?,4?-terpyridine, H2ox=oxalic acid, H2bdc=1,4-benzenedi-carboxylic acid, H2sfdb=4,4?-sulfonyldibenzoic acid and H3btc=1,3,5-benzene-tricarboxylic acid) have been prepared by hydrothermal reactions. Compound 1 is a 1D chain structure, in which 344-pytpy ligand links three ZnII centers through three of terminal N-donors. Compound 2 is a 4-connected 3D framework with the dia topological net and the Schläfli symbol of 66. Compound 3 displays a unusual 3-fold interpenetrating 3D coordination network which exhibits a new intriguing (3,3,4)-connected topological net with the Schläfli symbol of (4.82)(4.85)(83). Compound 4 features a two-fold interpenetrating 4-connected 2D framework with the sql topological net and the Schläfli symbol of (44.62). Compound 5 is a new self-interpenetrating (3,3,4,4)-connected topological net with the Schläfli symbol of (6.82)2(62.82.10.12)(62.83.10)2(62.8)2. The luminescence properties of 1-5 have been investigated by emission spectra and they possess great thermal stabilities which can be stable up to around 400 °C.

Yang, Xiao-Le; Shangguan, Yi-Qing; Hu, Huai-Ming; Xu, Bing; Wang, Bao-Cheng; Xie, Juan; Yuan, Fei; Yang, Meng-Lin; Dong, Fa-Xin; Xue, Gang-Lin

2014-08-01

329

Development and Evaluation of Artificial Dental Anchors of Non-Natural Design Implanted in Miniature Swine.  

National Technical Information Service (NTIS)

Four porous materials, two ceramic and two forms of titanium alloy, have been fabricated into dental anchors and pins and implanted into the mandibles of miniature swine. The metal anchors, all Ti-6Al-4V alloy, have been fabricated from both Battelle-deve...

R. P. Marshall M. T. Karagianes J. J. Rasmussen R. E. Westerman

1972-01-01

330

What determines catalyst functionality in molecular water oxidation? Dependence on ligands and metal nuclearity in cobalt clusters.  

PubMed

The metal-oxo M4O4 "cubane" topology is of special significance to the field of water oxidation as it represents the merging of bioinspired structural principles derived from natural photosynthesis with successful artificial catalysts known to date. Herein, we directly compare the rates of water oxidation/O2 evolution catalyzed by six cobalt-oxo clusters including the Co4O4 cubanes, Co4O4(OAc)4(py)4 and [Co4O4(OAc)2(bpy)4](2+), using the common Ru(bpy)3(2+)/S2O8(2-) photo-oxidant assay. At pH 8, the first-order rate constants for these cubanes differ by 2-fold, 0.030 and 0.015 s(-1), respectively, reflecting the number of labile carboxylate sites that allow substrate water binding in a pre-equilibrium step before O2 release. Kinetic results reveal a deprotonation step occurs on this pathway and that two electrons are removed before O2 evolution occurs. The Co4O4 cubane core is shown to be the smallest catalytic unit for the intramolecular water oxidation pathway, as neither "incomplete cubane" trimers [Co3O(OH)3(OAc)2(bpy)3](2+) and [Co3O(OH)2(OAc)3(py)5](2+) nor "half cubane" dimers [Co2(OH)2(OAc)3(bpy)2](+) and [Co2(OH)2(OAc)3(py)4](+) were found capable of evolving O2, despite having the same ligand sets as their cubane counterparts. Electrochemical studies reveal that oxidation of both cubanes to formally Co4(3III,IV) (0.7 V vs Ag/AgCl) occurs readily, while neither dimers nor trimers are oxidized below 1.5 V, pointing to appreciably greater charge delocalization in the [Co4O4](5+) core. The origin of catalytic activity by Co4O4 cubanes illustrates three key features for water oxidation: (1) four one-electron redox metals, (2) efficient charge delocalization of the first oxidation step across the Co4O4 cluster, allowing for stabilization of higher oxidizing equivalents, and (3) terminal coordination site for substrate aquo/oxo formation. PMID:24498959

Smith, Paul F; Kaplan, Christopher; Sheats, John E; Robinson, David M; McCool, Nicholas S; Mezle, Nicholas; Dismukes, G Charles

2014-02-17

331

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

332

Development and Assessment of a New CFRP Rod Anchor System for Prestressed Concrete  

NASA Astrophysics Data System (ADS)

Design concepts and experimental assessment of a new wedge anchor system for prestressing CFRP rods are presented. This compact and reusable anchor consists of an outer cylinder (barrel), a number of wedges, and a soft metal sleeve. The contacting surfaces of the wedges and barrel have a circular profile along the length of the anchor. Tensile testing using different presetting loads, geometric configurations, and rod sizes was carried out. The relationship of the tensile load and displacement of the rod was established. Presetting was found unnecessary since the anchor system was found to be capable of carrying the full design strength of the rods.

Al-Mayah, A.; Soudki, K.; Plumtree, A.

2006-09-01

333

Diversity of metal-ligand interactions in halide (X = I, Br, Cl, F) and halide-free ambiphilic ligand rhodium complexes.  

PubMed

Reaction of the neutral ambiphilic ligand 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) with [{Rh(mu-Cl)(CO)(2)}(2)] yields [RhCl(CO)(TXPB)] (1) (Emslie et al. Organometallics 2006, 25, 5835). Complex 1 is square planar with the TXPB ligand bound to rhodium via the phosphine and thioether donors (these are features common to complexes 2-5, vide infra). Treatment of 1 with Me(3)SiBr and Me(3)SiI allowed for halide substitution to afford [RhBr(CO)(TXPB)] (2) and [RhI(CO)(TXPB)] (3), respectively. The halide co-ligands in complexes 1 and 2 form a strong bridging interaction between rhodium and the borane group in TXPB. The presence of stronger borane-halide coordination in 1 is clearly illustrated by an (11)B NMR chemical shift of 12 ppm versus 27 ppm in 2. In contrast, the iodide ligand in 3 forms only a weak bridging interaction to boron, leading to a B...I distance of 3.125(7) A, and an (11)B NMR chemical shift of 56 ppm (versus 69 ppm for free TXPB). A lower carbonyl stretching frequency in 3 (2002 cm(-1)) versus 1 or 2 (2008 and 2013 cm(-1), respectively) could be attributed to weakening of the Rh-X bond in 1 and 2 as a consequence of halide-borane coordination and/or a shorter Rh-S bond in complex 3. [Rh(CO)(TXPB-F)] (4) and the halide-free cation [Rh(CO)(TXPB)][PF(6)] (5) were accessed by reaction of 1 with [NMe(4)]F and Tl[PF(6)], respectively. Complex 4 is zwitterionic with fluoride bound to boron [(11)B NMR delta 4 ppm; B-F = 1.445(6) A; Rh...F = 3.261(3) A] and an eta(2)-interaction between the cationic rhodium center and the ipso- and ortho-carbon atoms of a B-phenyl ring in TXPB-F. By contrast, rhodium in 5 engages in an eta(2)-interaction with boron and the ipso-carbon of one B-phenyl ring; Rh-B and Rh-C(ipso) bond lengths in 5 are 2.557(3) and 2.362(2) A, respectively. The long Rh-B distance and an (11)B NMR chemical shift of 57 ppm are consistent with only a weak Rh-B interaction in 5, and a CO stretching frequency of 2028 cm(-1) (Nujol), versus 2004-2013 cm(-1) for complexes 1-4, is indicative of greatly reduced electron density in 5, relative to 1-4. PMID:20353202

Cowie, Bradley E; Emslie, David J H; Jenkins, Hilary A; Britten, James F

2010-05-01

334

Third-order NLO properties of metal complexes containing delocalized oxygen or sulphur donor ligands and mixed oxygen and sulphur donor ligands  

NASA Astrophysics Data System (ADS)

The third-order nonlinear susceptibility, (chi) (3), for a series of complexes of 3,5- ditertbutyl-o-benzoquinone (dbsq), [M(dbsq)2 where M equals Pd or Pt], o- mercaptophenol (mp), {[TBA][Ni(mp)2]}, or 1,3-dithiol- 2-thione-4,5-dithiol (dmit), {[TBA][M(dmit)2] where M equals Ni or Pd}, have been measured in CH2Cl2 solution by retroreflection DFWM technique at 1064 nm. The results indicate large (chi) (3) values of the order of 10-11 esu at concentration levels of 1018 molecules/cm3. These values are up to two orders higher than those found for other sulphur donor dithiolenes and nitrogen donor ligand systems, although the linear absorption is also higher.

Dhindsa, Ajaib S.; Underhill, Allan E.; Oliver, Stephen N.; Kershaw, Stephen V.

1995-08-01

335

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

336

New metal-anion radical framework materials: Co(II) compounds showing ferromagnetic to antiferromagnetic phase transition at about 344 K, and Zn(II) compounds exhibiting terminal anion ligand induced direct white-light-emission.  

PubMed

The preparation, X-ray crystallography, EPR, magnetic and luminescent investigation of new metal-anion radical framework materials based on a new anion radical ligand generated by in situ deprotonation of a stable zwitterionic radical are described herein. N,O,N-tripodal anion radical ligand (bipo(-)?) links metal cations, giving rise to four isostructural one-dimensional metal-organic frameworks, [M(bipo(-)?)(L)](n) [M = Zn, L = HCOO(-) (1), SCN(-) (1a), N(3)(-) (1b); M = Co, L = Br(-) (3)]. The tripodal bipo(-)? ligand and one co-ligand, 1,4-benzenedicarboxylate, coordinate to metals leading to two isostructural two-dimensional metal-organic frameworks, [M(bipo(-)?)(BDC)(0.5)](n) [M = Zn (2) and Co (4)]. The two Co(II) compounds are the first examples that exhibit unusual ferromagnetic to antiferromagnetic phase transition with transition temperature over room temperature, which can be demonstrated by the cooling and warming measurements of susceptibility. Compound 4 also exhibits long-range magnetic ordering with the critical temperature at about 44 K proved by ac susceptibility measurements. The metal-radical frameworks exhibit distinctly different fluorescence emissions. Especially, the isomorphous one-dimensional Zn(II) compounds show interesting terminal anion ligand-induced photoluminescent color changes, including direct and invariable white-light-emission with terminal SCN(-) ligand. PMID:21384049

Yong, Guo-Ping; Li, Ying-Zhou; Li, Chong-Fu; Zhang, Yi-Man; She, Wen-Long

2011-04-28

337

Synthesis and spectroscopic characterization of some transition metal complexes of a new hexadentate N(2)S(2)O(2) Schiff base ligand.  

PubMed

A novel interesting hexadentate dibasic N(2)S(2)O(2) donor Schiff base ligand, H(4)dcsalpte, was synthesized by the condensation of 3-formylsalicylic acid and 1,2-di(o-aminophenylthio)ethane and characterized. The reactions of the ligand with different metal(II/III)salts under varied reaction conditions afforded a series of metal complexes. The ligand, H(4)dcsalpte, behaves either as a dibasic or neutral hexadentate one, depending on the reaction conditions. Structural investigations on the ligand and their complexes have been made based on elemental analyses, molar conductance values, magnetic moment values, cryomagnetic and spectral (UV-vis, IR, (1)H NMR, and Mössbauer) data. Based on magnetic susceptibility, Mössbauer and electronic spectral data the iron(III) complex [Fe(III)(H(2)dcsalpte)]ClO(4) (8), isolated in the present investigation, it is inferred that the spin states 5/2 and 1/2 are in equilibrium. Similarly a tri-iron(III) complex [Fe(III)(3)(H(2)dcsalpte)(H(3)dcsalpte)Cl(3)]Cl(3) (7), isolated in this study, has been inferred to contain two iron(III) sites in tetrahedral environment and one in the octahedral environment. The aerial oxidation of an equimolar mixture of H(4)dcsalpte and Co(CH(3)COO)(2).4H(2)O in ethanol under reflux gave two products, [Co(H(2)dcsalpte)]CH(3)COO (10) and [(Hbtcsaldm)Co(Hbvcsaldm)] (11), a cobalt(III) complex bound to two dissimilar tridentate NSO donor ligands formed as a result of the oxidative cleavage of the CS bond. In the complex 11, Hbtcsaldm stands for the dianion of the tridentate Schiff base ligand N-(2'-benzenethiol)-3-carboxysalicylaldimine and Hbvcsaldm stands for the mono anion of the tridentate Schiff base ligand N-(benzene-2'-S-vinyl)-3-carboxysalicylaldimine, both being formed as a result of the oxidative cleavage of H(4)dcsalpte. PMID:16257739

Sarkar, Saikat; Dey, Kamalendu

2005-11-01

338

The Glycophosphatidylinositol Anchor of the MCMV Evasin, m157, Facilitates Optimal Cell Surface Expression and Ly49 Receptor Recognition  

PubMed Central

The murine cytomegalovirus-encoded protein m157 is a cognate ligand for both inhibitory and activating receptors expressed by natural killer cells. Additionally, m157 is expressed on the surface of infected cells by a glycophosphatidylinositol (GPI) anchor. Although endogenous GPI-anchored proteins are known to be ligands for the NK cell receptor, NKG2D, the contribution of the GPI anchor for viral m157 ligand function is unknown. To determine whether the GPI anchor for m157 is dispensable for m157 function, we generated m157 variants expressed as transmembrane fusion proteins and tested cells expressing transmembrane m157 for the capacity to activate cognate Ly49 receptors. We found that the GPI anchor is required for high-level cell surface expression of m157, and that the transmembrane m157 ligand retains the capacity to activate reporter cells and NK cells expressing Ly49H, as well as Ly49I129 reporter cells, but with reduced potency. Importantly, target cells expressing the transmembrane form of m157 were killed less efficiently and failed to mediate Ly49H receptor downregulation on fresh NK cells compared to targets expressing GPI-anchored m157. Taken together, these results show that the GPI anchor for m157 facilitates robust cell surface expression, and that NK cells are sensitive to the altered cell surface expression of this potent viral evasin.

Carlin, Lindsey E.; Guseva, Natalya V.; Shey, Michael R.; Ballas, Zuhair K.; Heusel, Jonathan W.

2013-01-01

339

Synthesis, spectroscopic, antimicrobial, DNA binding and cleavage studies of some metal complexes involving symmetrical bidentate N, N donor Schiff base ligand  

NASA Astrophysics Data System (ADS)

The Schiff base ligand, N, N'-bis-(4-isopropylbenzaldimine)-1,2-diaminoethane (L), obtained by the condensation of 4-isopropylbenzaldehyde and 1,2-diaminoethane, has been used to synthesize the complexes of the type [ML 2X 2] [M = Co(II), Ni(II) and Zn(II); X = Cl and OAc]. The newly synthesized ligand (L) and its complexes have been characterized on the basis of elemental analyses, mass, 1H and 13C-NMR, molar conductance, IR, UV-vis, magnetic moment, CV and thermal analyses, powder XRD and SEM. IR spectral data show that the ligand is coordinated to the metal ions in a bidentate manner. The geometrical structures of these complexes are found to be octahedral. Interestingly, reaction with Cu(II) ion with this ligand undergoes hydrolytic cleavage to form ethylenediamine copper(II) complex and the corresponding aldehyde. The antimicrobial results indicate that the chloro complexes exhibit more activity than the acetato complexes. The complexes bind to CT-DNA by intercalation modes. Novel chloroform soluble ZnL 2Cl 2 complex exhibits tremendous antimicrobial, DNA binding and cleaving properties.

Arish, D.; Nair, M. Sivasankaran

2011-11-01

340

Synthesis, spectroscopic, antimicrobial, DNA binding and cleavage studies of some metal complexes involving symmetrical bidentate N, N donor Schiff base ligand.  

PubMed

The Schiff base ligand, N,N'-bis-(4-isopropylbenzaldimine)-1,2-diaminoethane (L), obtained by the condensation of 4-isopropylbenzaldehyde and 1,2-diaminoethane, has been used to synthesize the complexes of the type [ML(2)X(2)] [M = Co(II), Ni(II) and Zn(II); X = Cl and OAc]. The newly synthesized ligand (L) and its complexes have been characterized on the basis of elemental analyses, mass, (1)H and (13)C-NMR, molar conductance, IR, UV-vis, magnetic moment, CV and thermal analyses, powder XRD and SEM. IR spectral data show that the ligand is coordinated to the metal ions in a bidentate manner. The geometrical structures of these complexes are found to be octahedral. Interestingly, reaction with Cu(II) ion with this ligand undergoes hydrolytic cleavage to form ethylenediamine copper(II) complex and the corresponding aldehyde. The antimicrobial results indicate that the chloro complexes exhibit more activity than the acetato complexes. The complexes bind to CT-DNA by intercalation modes. Novel chloroform soluble ZnL(2)Cl(2) complex exhibits tremendous antimicrobial, DNA binding and cleaving properties. PMID:21855399

Arish, D; Nair, M Sivasankaran

2011-11-01

341

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

PubMed

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, (1)H 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 6.14×10(5)M(-1), 1.8×10(5)M(-1), 6.7×10(4)M(-1) and 2.5×10(4)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. PMID:24835939

Raman, Natarajan; Mahalakshmi, Rajkumar; Mitu, Liviu

2014-10-15

342

Aerial Plant Guying and Anchoring.  

National Technical Information Service (NTIS)

This bulletin replaces RUS Telecommunications Engineering and Construction Manual (TE&CM) Section 650, Guys and Anchors on Wire and Cable Lines, Issue 4, dated February 1960; Addenda 1 and 2, dated October 1966, and April 1967; respectively.

1996-01-01

343

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

344

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

345

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 ?Gcrb - ?Gepx value should be an effective indicator for the catalytic activities [?Gepx: dissociation energy of ethylene oxide from the epoxide-coordinating metal complex; ?Gcrb: dissociation energy of methyl carbonate from the metal-carbonate complex]. In addition, metal complexes with a subthreshold ?Gepx value were found to show low PPC/CPC selectivity. The PPC/PPO selectivity was related to the ?Galk - ?Gepx value and steric environment around the metal center (?Galk: 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

346

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

347

Anchored Instruction and Situated Cognition Revisited.  

ERIC Educational Resources Information Center

Reviews theories of anchored instruction and addresses issues related to learning, transfer, and assessment. Highlights include video-based macrocontexts; videodisc anchors versus computer-based simulations; cooperative learning; transfer outside the classroom; authenticity; visual anchors versus verbal anchors; situated cognition; and using…

Educational Technology, 1993

1993-01-01

348

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

349

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

350

Macroporous polyacrylamide monolithic gels with immobilized metal affinity ligands: the effect of porous structure and ligand coupling chemistry on protein binding.  

PubMed

Macroporous polyacrylamide gels (MPAAG) with iminodiacetic acid (IDA) functionality were prepared by (i) chemical modification of polyacrylamide gel, (ii) co-polymerization of acrylamide with allyl glycidyl ether (AGE) and N,N'metylene-bis(acrylamide) (MBAAm) followed by coupling IDA ligand or (iii) by copolymerization of acrylamide and MBAAm with functional monomer carrying IDA-functionality (1-(N,N-bis(carboxymethyl)amino-3-allylglycerol). Screening for optimized conditions for the production of the MPAAG with required porous properties was performed in a 96-well chromatographic format that allowed parallel production and analysis of the MPAAG prepared from reaction mixtures with different compositions. Scanning electron microscopy of the fabricated MPAAG revealed two different types of the porous structures: monomodal macroporous structure with large interconnected pores separated by dense non-porous pore walls in case of plain gels or gels produced via copolymerization with AGE. The other type of the MPAAG (gel produced via co-polymerization with functional monomer carrying IDA-functionality) had bimodal pore structure with large interconnected pores separated by the pore walls pierced through with micropores. The effect of different modifications of MPAAG monoliths and of porous structure of the MPAAG (monomodal and bimodal porous structure) on protein binding has been evaluated. PMID:16703570

Plieva, Fatima; Bober, Beata; Dainiak, Maria; Galaev, Igor Yu; Mattiasson, Bo

2006-01-01

351

Synthesis, spectroscopic characterization and antimicrobial activity of binuclear metal complexes of a new asymmetrical Schiff base ligand: DNA binding affinity of copper(II) complexes.  

PubMed

The 1:1 condensation of o-acetoacetylphenol and 1,2-diaminopropane under condition of high dilution gives the mono-condensed Schiff base, (E)-3-(1-aminopropan-2-ylimino)-1-(2-hydroxyphenyl)butan-1-one. The mono-condensed Schiff base has been used for further condensation with isatin to obtain the new asymmetrical dicompartmental Schiff base ligand, (E)-3-(2-((E)-4-(2-hydroxyphenyl)-4-oxobutan-2-ylideneamino) propylimino)indolin-2-one (H3L) with a N2O3 donor set. Reactions of the ligand with metal salts give a series of new binuclear complexes. The ligand and its metal complexes were characterized by elemental analyses, IR, (1)H and (13)C NMR, electronic, ESR and mass spectra, conductivity and magnetic susceptibility measurements as well as thermal analyses. The analytical and spectroscopic tools showed that the complexes can be formulated as: [(HL)(VO)2(SO4)(H2O)]·4H2O, [(HL)Fe2Cl4(H2O)3]·EtOH, [(HL)Fe2(ox)Cl2(H2O)3]·2H2O, [(L)M2(OAc)(H2O)m]·nH2O; M=Co, Ni or Cu, m=4, 0 and n=2, 3, [(HL)Cu2Cl]Cl·6H2O and [(L)(UO2)2(OAc)(H2O)3]·6H2O. The metal complexes exhibited octahedral geometrical arrangements except copper complexes that exhibited tetrahedral geometries and uranyl complex in which the metal ion is octa-coordinated. The Schiff base and its metal complexes were evaluated for antimicrobial activity against Gram positive bacteria (Staphylococcus aureus), Gram negative bacteria (Escherichia coli) and fungi (Candida albicans and Aspergillus flavus). The ligand and some of its complexes were found to be biologically active. The DNA-binding properties of the copper complexes (6 and 7) have been investigated by electronic absorption, fluorescence and viscosity measurements. The results obtained indicate that these complexes bind to DNA via an intercalation binding mode with an intrinsic binding constant, Kb of 1.34×10(4) and 2.5×10(4) M(-1), respectively. PMID:23988527

Shebl, Magdy

2014-01-01

352

Various coordination modes of the bis(di(o-N,N-dimethylanilinyl)phosphino)methane ligand in mononuclear and binuclear complexes of group 8 and group 9 metals.  

PubMed

The synthesis and characterization of a series of compounds involving the bis(di(o-N,N-dimethylanilinyl)phosphino)methane (dmapm) ligand are described. The mononuclear complexes [MCl(CO)(P,N-dmapm)] (M = Rh, Ir) have a square-planar geometry in which the dmapm ligand chelates via a phosphine functionality and an adjacent amino group. The carbonyl ligand lies opposite the amine, while the chloro ligand is trans to the phosphine. The related complex [RhI(CO)(P,N-dmapm)] has also been prepared. All compounds are highly fluxional by at least three independent processes, as discussed for the rhodium-chloro species. A diiridium complex, [Ir(2)Cl2(CO)2(P,N,P',N'-dmapm)], and the closely related rhodium/iridium analogue, [RhIrCl2(CO)2(P,N,P',N'-dmapm)], have been prepared in which the metals are bridged by the diphosphine group while an amino group at each end of the diphosphine is also coordinating to each metal on opposite faces of the MIrP2 plane (M = Ir or Rh). For the Ir2 species, the carbonyl and chloro groups are again shown to be opposite the amine and phosphine functionalites, respectively. The mononuclear complex [Ru(CO)3(P,P'-dmapm)] has also been prepared. In contrast to the mononuclear species of rhodium and iridium, the dmapm group chelates the ruthenium center through both phosphorus atoms, occupying one axial and one equatorial site of Ru in a distorted trigonal bipyramidal geometry. Reaction of this Ru species with 1/2 equiv of the complexes [RhClL2]2 (L2 = COD, (C2H4)2, (CO)2) yields the unstable Rh/Ru product [RhRuCl(CO)3(P,N,P',N'-dmapm)]. PMID:16634605

Dennett, James N L; Bierenstiel, Matthias; Ferguson, Michael J; McDonald, Robert; Cowie, Martin

2006-05-01

353

Development and Evaluation of Artificial Dental Anchors of Non-Natural Design Implanted in Miniature Swine. 211B00402.  

National Technical Information Service (NTIS)

Two porous materials, one ceramic and one metal, have been fabricated into cylindrical dental anchors and implanted into the mandibles of miniature swine. The ceramic alumina porcelain was formed by special slipcasting and firing techniques. The metal anc...

M. T. Karagianes R. E. Westerman R. P. Marshall J. J. Rasmussen

1974-01-01

354

Metal-ligand charge-transfer-promoted photoelectronic Bergman cyclization of copper metalloenediynes: photochemical DNA cleavage via C-4' H-atom abstraction.  

PubMed

Metal-to-ligand charge-transfer (MLCT) photolyses (lambda > or = 395 nm) of copper complexes of cis-1,8-bis(pyridin-3-oxy)oct-4-ene-2,6-diyne (bpod, 1), [Cu(bpod)(2)]PF(6) (2), and [Cu(bpod)(2)](NO(3))(2) (3) yield Bergman cyclization of the bound ligands. In contrast, the uncomplexed ligand 1 and Zn(bpod)(2)(CH(3)COO)(2) compound (4) are photochemically inert under the same conditions. In the case of 4, sensitized photochemical generation of the lowest energy (3)pi-pi state, which is localized on the enediyne unit, leads to production of the trans-bpod ligand bound to the Zn(II) cation by photoisomerization. Electrochemical studies show that 1, both the uncomplexed and complexed, exhibits two irreversible waves between E(p) values of -1.75 and -1.93 V (vs SCE), corresponding to reductions of the alkyne units. Irreversible, ligand-based one-electron oxidation waves are also observed at +1.94 and +2.15 V (vs SCE) for 1 and 3. Copper-centered oxidation of 2 and reduction of 3 occur at E(1/2) = +0.15 and +0.38 V, respectively. Combined with the observed Cu(I)-to-pyridine(pi) MLCT and pyridine(pi)-to-Cu(II) ligand-to-metal charge transfer (LMCT) absorption centered near approximately 315 nm, the results suggest a mechanism for photo-Bergman cyclization that is derived from energy transfer to the enediyne unit upon charge-transfer excitation. The intermediates produced upon photolysis degrade both pUC19 bacterial plasmid DNA, as well as a 25-base-pair, double-stranded oligonucleotide. Detailed analyses of the cleavage reactions reveal 5'-phosphate and 3'-phosphoglycolate termini that are derived from H-atom abstraction from the 4'-position of the deoxyribose ring rather than redox-induced base oxidation. PMID:12785783

Benites, Pedro J; Holmberg, Rebecca C; Rawat, Diwan S; Kraft, Brian J; Klein, Lee J; Peters, Dennis G; Thorp, H Holden; Zaleski, Jeffrey M

2003-05-28

355

Anchoring International sets new water depth record  

SciTech Connect

Santa Barbara Channel has a history steeped in firsts in techniques for the production of offshore oil. Landscaped drilling and production islands, production piers, and directional drilling from land rigs to production under the channel, to name a few. The latest such project was handled by Anchoring International, Inc., a pipe line anchoring company headquartered in Houston, Texas. Contracted by Healy Tibbets Construction Company, prime contractor, Anchoring was commissioned to handle a new deep water record breaking anchoring job. The job was to anchor J-tube extensions in 820 feet of water--the deepest pipe line anchoring job ever undertaken. In most shallow water pipe line anchoring jobs, anchors and anchor installation unit placement over the pipe line is handled from a crane topside with visual assist from divers. However, due to the extreme depth of this project, the installation unit with anchors had to be modified for submersible operator-assisted placement capability. Anchoring International handled the anchor design and installation equipment, and submersible operator assistance was furnished by Oceaneering, International. WASP and JIM atmospheric diving systems were used. All ocean bottom activities were monitored topside with the JERED video-equipped remote controlled vehicle. Since the weight of the anchor sets and power installation unit are minimum, the entire operation was conducted from a small boat sufficient to carry dive equipment and the anchor installation unit power supply. A small pedestal crane was used to lower and retrieve the anchor installation unit.

Noble, H.J.

1983-07-01

356

Superoxide scavenging effects of some novel bis-ligands and their solvated metal complexes prepared by the reaction of ligands with aluminum, copper and lanthanum ions.  

PubMed

Novel antioxidants have been synthesized and characterized by their chemical properties as antioxidants with high superoxide scavenging activity. (2R,3R)-diphenylethylenediamine is a spacer in antioxidants, and we synthesized targets 11a and 11b by conjugation with o-hydroquinone and p-hydroquinone at the two N-termini, respectively. Superoxide scavenging activities of the plant flavonoid-like 11a and 11b were compared with those of known antioxidants, and shown to increase in the following order: curcumin < ascorbic acid < Trolox < (+)-epicatechin < 11a < quercetin ? 11b. Compound 11a also formed a solvated 11a-metal complex with metal ions. The 11a-Cu²? complex was shown to have higher superoxide scavenging activity than that of 11a, 11b, Cu²?, and the 11a-Al³? and 11a-La³? complexes, whereas the 11a-Al3+ complex increased rather than decreased superoxide levels. The 11a-Al³? complex did not abstract one electron from the SOMO of O??· since the HOMO and LUMO phases of Al³? do not exist in the center of the 11a-Al³? complex. However, the SOMO of the 11a-Cu²? complex distributed in the center of Cu²? may abstract one electron from the SOMO of O??·. These results suggest that 11a and 11b are powerful antioxidants. PMID:23702919

Kobayashi, Shigeki; Kanai, Sachi

2013-01-01

357

pH- and metal-dependent structural diversity from mononuclear to two-dimensional polymers based on a flexible tricarboxylate ligand  

SciTech Connect

Six complexes based on a flexible tripodal ligand H{sub 3}TTTA (2,2',2''-[1,3,5-triazine-2,4,6-triyltris(thio)]tris-acetic acid) have been hydrothermally synthesized and structurally characterized. X-ray single-crystal diffractions reveal that they have rich structural chemistry: mononuclear, [Zn(HTTTA)(2,2'-bpy)(H{sub 2}O){sub 3}]{sub n} (1); dimeric metallamacrocycle, [Zn(HTTTA)(2,2'-bipy)(H{sub 2}O)]{sub n} (2) and [Cd(HTTTA)(2,2'-bipy)(H{sub 2}O).H{sub 2}O]{sub n} (3); two-dimensional networks with binodal (3,6)-connected CdI{sub 2} topology based on linear trinuclear M{sub 3}({mu}{sup 2}-CO{sup 2}){sub 4}({mu}{sub 2}-CO{sub 2}){sub 2} SBUs (Secondary Building Units), [M{sub 3}(TTTA){sub 2}(2,2'-bipy){sub 2}(H{sub 2}O){sub m}.nH{sub 2}O]{sub n} (M=Zn.4, m=0, n=4; Cd.5 and Mn.6, m=2; n=2). The value of pH and the metal ions has large influences on the resulting structures. The flexible tricarboxylic acid exhibits four coordination modes from monodentate to {mu}{sup 6}-bridge. Fluorescence and magnetic properties of the complexes have also been investigated in details. - Graphical abstract: Six complexes based on a flexible tricarboxylate ligand exhibit rich structural chemistry from mononuclear to 2D (3,6)-connected networks. PH and metal ions have large influences on the resulting structures. Highlights: > Six complexes based on a flexible multicarboxylate ligand have been reported. > They exhibit diverse structures from mono- and binuclear molecules to 2-D layers. > pH and metal ions have large influences on the final products.

Li Chengjuan; Peng Yanqiang [School of Chemistry and Chemical Engneering, Liaocheng University, Liaocheng 252059 (China); Wang Suna, E-mail: wangsuna@lcu.edu.cn [School of Chemistry and Chemical Engneering, Liaocheng University, Liaocheng 252059 (China); State Key Laboratory of Coordination Chemistry, Nanjing 210093 (China); Zhang Xianxi [School of Chemistry and Chemical Engneering, Liaocheng University, Liaocheng 252059 (China); Li Yizhi [State Key Laboratory of Coordination Chemistry, Nanjing 210093 (China); Dou Jianmin, E-mail: jmdou@lcu.edu.cn [School of Chemistry and Chemical Engneering, Liaocheng University, Liaocheng 252059 (China); Li Dacheng [School of Chemistry and Chemical Engneering, Liaocheng University, Liaocheng 252059 (China)

2011-07-15

358

Comparing three approaches in extending biotic ligand models to predict the toxicity of binary metal mixtures (Cu-Ni, Cu-Zn and Cu-Ag) to lettuce (Lactuca sativa L.).  

PubMed

Metals are always found in the environment as mixtures rather than as solitary elements. However, effect models such as biotic ligand models (BLMs) are usually derived for toxicity prediction of single metals. Our study aimed at predicting mixture toxicity of Cu-Ni, Cu-Zn and Cu-Ag combinations to lettuce (Lactucasativa L.) by combining BLMs with three toxicity indexes: the toxic unit, the overall amounts of metal ions bound to the biotic ligands and the toxic equivalency factor. The accumulation of metal ions at the biotic ligands was used to determine the toxic potency of metals alone or in combination. On the basis of parameters derived from toxicity assessment of individual metals, these three extended BLMs appeared to be all acceptable (p<0.0001) in assessing toxicity of diverse metal mixtures. The BLM-based approaches integrated competition between metal ions in assessing mixture toxicity and showed different predictive ability for each metal combination. The outcome of modeling suggested that the combined toxicity depends on the specific components of the metal mixtures. The best developed models assist in identifying the type of underlying toxic mechanisms of diverse metal mixtures in terrestrial plants. PMID:25048917

Liu, Yang; Vijver, Martina G; Peijnenburg, Willie J G M

2014-10-01

359

Use of ligand-modified micellar-enhanced ultrafiltration in the selective removal of metal ions from water  

SciTech Connect

Ligand-modified micellar-enhanced ultrafiltration (LM-MEUF) is a membrane-based separation technique which can selectively remove specific ions from an aqueous solution containing several ions of like charge. In LM-MEUF, surfactant and amphiphilic ligand are added to the contaminated water. The surfactant forms aggregates called micelles, and the ligand is selected to complex the ion of interest and to solubilize strongly in the micelles. The result is micelles containing a high fraction of the ligand and the target ion. If the surfactant is chosen to have the same charge as the target ion, other ions in solution with this same charge will not associate with the micelles, making the retention of ions by the micelles very selective. The solution is then passed through an ultrafiltration membrane with pore sizes small enough to block the passage of micelles. In this study, divalent copper is the target ion in a solution also containing divalent calcium. A cationic surfactant is used with N-n-dodecyl-iminodiacetic acid as the copper-specific ligand. Rejections of copper of up to 99.2% are observed, with no rejection of calcium, showing that LM-MEUF has almost perfect selectively, as well as high capacity in this case.

Klepac, J.; Simmons, D.L.; Taylor, R.W.; Scamehorn, J.F.; Christian, S.D. (Univ. of Oklahoma, Norman (United States))

1991-02-01

360

Metal Complexes: Preparation, Magnetic, Spectral, and Biocidal Studies of Some Mixed?Ligand Complexes with Schiff Bases Containing NO and NN Donor Atoms  

Microsoft Academic Search

Metal complexes of the types [M(SB)2acphen] and [M(SB)2acphen] where M = Mn(II), Co(II), Ni(II), Cu(II), and Cd(II); HSB = 5?chlorosalicylidene?p?anisidine and HSB = 5?bromosalicylidene?p?anisidine have been prepared and characterized. Magnetic susceptibility measurements, elemental analyses, electro?nic, and infrared spectral data suggest six?coordinated octahedral structures for these complexes. The mixed?ligand complexes show higher activity against Saccharomyces cereuisae, Salmonella typhi, Fasarium oxysporum, and Lasiodiplodia theobromae as compared to the

Prakash P. Dholakiya; M. N. Patel

2004-01-01

361

The interplay of metal and supporting ligand in labile coordination to pincer complexes of Ag(I).  

PubMed

The bis(imino)pyridine scaffold provides support for the synthesis and characterization of unique Ag(I) pincer complexes [{ArN=CPh}(2)(NPh)]Ag(+)(OTf)(-) (Ar = 2,5-(t)Bu(2)C(6)H(3)3; 2,6-(i)Pr(2)C(6)H(3) 4). The bonding interactions between the cation-anion and between the bis(imino)pyridine ligand and the Ag centre are presented. Coordination of pyridine, toluene, 2-butyne and cyclooctene to the Ag centre led to the isolation and crystallographic characterization of labile transient adduct species. Bonding analysis of the adducts revealed conventional ligand-Ag coordination and important unconventional electron donation from the ligand to a ?*-orbital of the bis(imino)pyridine group. PMID:22301795

Jurca, Titel; Ouanounou, Sarah; Gorelsky, Serge I; Korobkov, Ilia; Richeson, Darrin S

2012-04-28

362

Chemistry of the strong electrophilic metal fragment [(99)Tc(N)(PXP)](2+) (PXP = diphosphine ligand). A novel tool for the selective labeling of small molecules.  

PubMed

Monosubstituted [M(N)Cl(2)(POP)] [M = Tc, 1; Re, 2] and [M(N)Cl(2)(PNP)] [M = Tc, 3; Re, 4] complexes were prepared by reaction of the precursors [M(N)Cl(4)](-) and [M(N)Cl(2)(PPh(3))(2)] (M = Tc, Re) with the diphosphine ligands bis(2-diphenylphosphinoethyl)ether (POP) and bis(2-diphenylphosphinoethyl)methoxyethylamine (PNP) in refluxing dichloromethane/methanol solutions. In these compounds, the diphosphine acted as a chelating ligand bound to the metal center through the two phosphorus atoms. Considering also the weak interaction of the heteroatom (N or O) located in the middle of the carbon backbone connecting the two P atoms, we found that the coordination arrangement of the diphosphine ligand could be viewed as either meridional (m) or facial (f), and the resulting geometry as pseudooctahedral. The heteroatom of the diphosphine ligand was invariably located trans to the nitrido linkage, as established by X-ray diffraction analysis of the representative compounds 2m and 4f. Density functional theoretical calculations showed that in POP-type complexes the mer form is favored by approximately 6 kcal mol(-1), whereas mer and fac isomers are almost isoenergetic in PNP-type complexes. A possible role of noncovalent interactions between the phosphinic phenyl substituents in stabilizing the fac-isomer was also highlighted. The existence of fac-mer isomerism in this class of complexes was attributed to the strong tendency of the two phosphorus atoms to occupy a reciprocal trans-position within the pseudooctahedral geometry. The switching of P atoms between cis- and trans-configurations was confirmed by the observation that the fac isomers, 1f and 2f, were irreversibly transformed, in solution, into the corresponding mer isomers, 1m and 2m, thus suggesting that fac complexes are more reactive species. Theoretical calculations supported this view by showing that the lowest unoccupied orbitals of the fac isomers are more accessible to a nucleophilic attack with respect to those of the mer ones. Furthermore, the large participation of the Cl orbitals to the HOMO, which is a metal-ligand pi* antibonding in the complex basal plane, shows that the Tc-Cl bonds are labile. As a consequence, facial isomers could be considered as highly electrophilic intermediates that were selectively reactive toward substitution by electron-rich donor ligands. Experimental evidence was in close agreement with this description. It was found that fac-[M(N)Cl(2)(PXP)] complexes easily underwent ligand-exchange reactions with bidentate donor ligands such as mercaptoacetic acid (NaHL(1)), S-methyl 2-methyldithiocarbazate (H(2)L(2)), diethyldithiocarbamate sodium salt (NaL(3)), and N-acetyl-L-cysteine (H(2)L(4)) to afford stable asymmetrical heterocomplexes of the type fac-[M(N)(L(n))(POP)](+/0) (5-8) and fac-[M(N)(L(n))(PNP)](+/0) (9-14) comprising two different polydentate chelating ligands bound to the same metal center. In these reactions, the bidentate ligand replaced the two chloride atoms on the equatorial plane of the distorted octahedron, leaving the starting fac-[M(N)(PXP)](2+) (X = O, N) moieties untouched. No formation of the corresponding symmetrical complexes containing two identical bidentate ligands was detected over a broad range of experimental conditions. Solution-state NMR studies confirmed that the structure in solution of these heterocomplexes was identical to that established in the solid state by X-ray diffraction analysis of the prototype complexes fac-[M(N)(HL(2))(POP)][BF(4)] [M = Tc, 7; Re, 8] and fac-[Tc(N)(HL(2))(PNP)][BF(4)], 11. In conclusion, the novel metal fragment fac-[M(N)(PXP)](2+) could be utilized as an efficient synthon for the preparation of a large class of asymmetrical, nitrido heterocomplexes incorporating a particular diphosphine ligand and a variety of bidentate chelating molecules. PMID:12236761

Bolzati, Cristina; Boschi, Alessandra; Uccelli, Licia; Tisato, Francesco; Refosco, Fiorenzo; Cagnolini, Aldo; Duatti, Adriano; Prakash, Sushumna; Bandoli, Giuliano; Vittadini, Andrea

2002-09-25

363

Light-induced copper(II) coordination by a bicyclic tetraaza chelator through a ligand-to-metal charge-transfer reaction.  

PubMed

To enable utilization of the broad potential of copper isotopes in nuclear medicine, rapid and robust chelation of the copper is required. Bowl adamanzanes (bicyclic tetraaza ligands) can form kinetically stable copper complexes, but they are usually formed at low rates unless high pH values and high temperatures are applied. We have investigated the effects of the variation in the pH, different anions, and UV irradiation on the chelation rate. UV spectra of mixtures of Cu(2+) and [2(4).3(1)]adz in water show the existence of a long-lived two-coordinated copper(II) intermediate (only counting coordinated amine groups) at pH above 6. These findings are supported by pH titrations of mixtures of Cu(2+) and [2(4).3(1)]adz in water. Irradiation of this complex in the ligand-to-metal charge-transfer (LMCT) band by a diode-array spectrophotometer leads to photodeprotonation and subsequently to formation of the four-coordinated copper(II) complex at a rate up to 7800-fold higher at 25 °C than in the dark. Anions in the solution were found to have three major effects: competitive inhibition due to Cu(II) binding anions, inhibition of the photoinduced transchelation from UV-absorbing anions, and photoredox inhibition from acido ligands capable of acting as electron donors in LMCT reactions. Dissolved O(2) was also found to result in photoredox inhibition. PMID:22074363

Holm-Jørgensen, Jacob R; Jensen, Mikael; Bjerrum, Morten J

2011-12-19

364

Two one-dimensional d¹?-metal coordination polymers based on polydentate Schiff-base ligand: synthesis, crystal structure and luminescent properties.  

PubMed

Two one-dimensional d(10)-metal coordination polymers {[AgL(H(2)O)](2)[AgL(NO(3))](2)(NO(3))(2)L(H(2)O)(2)}(n) (1) and [ZnLCl(2)](n) (2) (L=N,N'-bis-(1-pyridin-4-yl-ethylidene)-hydrazine) have been synthesized and characterized by IR, elemental analysis, TG technique, XRPD and X-ray crystallography. Polymer 1 contains two types of 1D Ag-double-chain units. Ag(1)-double-chain unit is formed by linking two adjacent Ag(1)-L-chains through face-to-face ??? interactions, while Ag(2)-double-chain unit is formed through the combination of coordinating NO(3)(-) anions bridging interactions and ??? interactions between two adjacent Ag(2)-L-chains. Free ligands interact with the adjacent Ag(1)-double-chain units and Ag(2)-double-chain units to form a 3D supramolecular structure through multiform hydrogen bonds. For polymer 2, each ligand acts as a bis-monodentate bridging ligand to bind adjacent Zn(II) centers forming a one-dimensional chain structure. Furthermore, 1D chain is held together with its neighboring ones via CH?? interactions. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature. PMID:22366615

Niu, Wei-Jia; Wang, Jun-Li; Bai, Yan; Dang, Dong-Bin

2012-06-01

365

Microgravity Drill and Anchor System  

NASA Technical Reports Server (NTRS)

This work is a method to drill into a rock surface regardless of the gravitational field or orientation. The required weight-on-bit (WOB) is supplied by a self-contained anchoring mechanism. The system includes a rotary percussive coring drill, forming a complete sampling instrument usable by robot or human. This method of in situ sample acquisition using micro - spine anchoring technology enables several NASA mission concepts not currently possible with existing technology, including sampling from consolidated rock on asteroids, providing a bolt network for astronauts visiting a near-Earth asteroid, and sampling from the ceilings or vertical walls of lava tubes and cliff faces on Mars. One of the most fundamental parameters of drilling is the WOB; essentially, the load applied to the bit that allows it to cut, creating a reaction force normal to the surface. In every drilling application, there is a minimum WOB that must be maintained for the system to function properly. In microgravity (asteroids and comets), even a small WOB could not be supported conventionally by the weight of the robot or astronaut. An anchoring mechanism would be needed to resist the reactions, or the robot or astronaut would push themselves off the surface and into space. The ability of the system to anchor itself to a surface creates potential applications that reach beyond use in low gravity. The use of these anchoring mechanisms as end effectors on climbing robots has the potential of vastly expanding the scope of what is considered accessible terrain. Further, because the drill is supported by its own anchor rather than by a robotic arm, the workspace is not constrained by the reach of such an arm. Yet, if the drill is on a robotic arm, it has the benefit of not reflecting the forces of drilling back to the arm s joints. Combining the drill with the anchoring feet will create a highly mobile, highly stable, and highly reliable system. The drilling system s anchor uses hundreds of microspine toes that independently find holes and ledges on a rock to create an anchor. Once the system is anchored, a linear translation mechanism moves the drill axially into the surface while maintaining the proper WOB. The linear translation mechanism is composed of a ball screw and stepper motor that can translate a carriage with high precision and applied load. The carriage slides along rails using self-aligning linear bearings that correct any axial misalignment caused by bending and torsion. The carriage then compresses a series of springs that simultaneously transmit the load to the drill along the bit axis and act as a suspension that compensates for the vibration caused by percussive drilling. The drill is a compacted, modified version of an off-the-shelf rotary percussive drill, which uses a custom carbide-tipped coring bit. By using rotary percussive drilling, the drill time is greatly reduced. The percussive action fractures the rock debris, which is removed during rotation. The final result is a 0.75-in. (.1.9- cm) diameter hole and a preserved 0.5- in. (.1.3-cm) diameter rock core. This work extends microspine technology, making it applicable to astronaut missions to asteroids and a host of robotic sampling concepts. At the time of this reporting, it is the first instrument to be demonstrated using microspine anchors, and is the first self-contained drill/anchor system to be demonstrated that is capable of drilling in inverted configurations and would be capable of drilling in microgravity.

Parness, Aaron; Frost, Matthew A.; King, Jonathan P.

2013-01-01

366

Liposome surface functionalization based on different anchoring lipids via Staudinger ligation.  

PubMed

Liposome surface functionalization facilitates numerous potential applications of liposomes, such as enhanced stability, bioactive liposome conjugates, and targeted drug, gene and image agent delivery. Anchoring lipids are needed for grafting ligands of interest and play important roles in ligand grafting density, liposome stability, and liposome chemical and physical characteristics as well. In this report, glyco-functionalized liposome systems based on two kinds of anchoring lipids, phosphatidylethanolamine (PE) and cholesterol (Chol), were prepared by post chemically selective functionalization via Staudinger ligation. The size and stability of the liposomes were confirmed by dynamic light scattering (DLS). Particularly, the impact of anchor lipids on the stability of glyco-functionalized liposomes was investigated by comparing two different anchor lipids, namely Chol-PEG2000-TP and DSPE-PEG2000-TP. In addition, the encapsulation and releasing capacity of the glycosylated liposome based on the two anchoring lipids were investigated by entrapping 5,6-carboxyfluorescein (CF) dye and monitoring the fluorescence leakage, respectively. Furthermore, the density and accessibility of grafted carbohydrate residues on the liposome surface were evaluated for the two anchoring lipid-derived liposomes with lectin binding, respectively. PMID:24413731

Vabbilisetty, Pratima; Sun, Xue-Long

2014-02-28

367

Diaza-l8-Crown-6 Ligands Containing Two Aminophenol Side Arms: New Heterobinuclear Metal Ion Receptors.  

National Technical Information Service (NTIS)

Three diaza-18-crown-6 ligands substituted with two each of 5-amino- 2-hydroxybenzyl (1), 3-amino-5-chloro-2-hydroxybenzyl (2), or 3-amino-2-hydroxy- 5-methylbenzyl (3) units (see Figure 1) were prepared as reported in our Technical Report No. 2 of August...

J. S. Bradshaw N. Su P. B. Savage X. X. Zhang R. M. Izatt

1999-01-01

368

Zn(II) metal-organic frameworks (MOFs) assembled from semirigid multicarboxylate ligands: Synthesis, crystal structures, and luminescent properties  

NASA Astrophysics Data System (ADS)

Two new coordination polymers [Zn 2L(2,2'-bpy)] n•(H 2O) 2 n ( 1) and [Zn 2L(phen)] n•(H 2O) 2 n ( 2) have been assembled from a semirigid multicarboxylate ligand 3,3'-(1,3-phenylenebis(oxy))diphthalic acid (H 4L) with the help of 2,2'-bipyridine (2,2'-bpy) or 1,10-phenanthroline (phen) as secondary ligand. Single crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the space group C2/ c and displays a one-dimensional (1D) chain structure constructed from 2,2'-bpy and L ligand, which further forms a two-dimensional (2D) plane via intermolecular ?-? interactions. Compound 2 belongs to the space group P1¯ and features a 1D ?- and ?-typed chiral chain configuration despite the racemic nature for the whole complex. The neighboring chains with the same chirality are further stacked into a 2D ???- or ???-typed supramolecular structure via intermolecular ?-? interactions because of the chiral recognition mechanism. Photophysical properties over complexes 1 and 2 have been comparatively investigated, revealing the effect of secondary ligand on the luminescent properties of these two complexes.

Wang, Kang; Wang, Hailong; Bian, Yongzhong; Li, Wenjun

2010-10-01

369

Construction of Ligand Group Orbitals for Polyatomics and Transition-Metal Complexes Using an Intuitive Symmetry-Based Approach  

ERIC Educational Resources Information Center

A molecular orbital (MO) diagram, especially its frontier orbitals, explains the bonding and reactivity for a chemical compound. It is therefore important for students to learn how to construct one. The traditional methods used to derive these diagrams rely on linear algebra techniques to combine ligand orbitals into symmetry-adapted linear…

Johnson, Adam R.

2013-01-01

370

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

371

Hydrogen-bond and metal-ligand coordination bond hybrid supramolecular capsules: identification of hemicapsular intermediate and dual control of guest exchange dynamics.  

PubMed

Hybrid supramolecular capsules self-assemble by simultaneously forming hydrogen and metal-ligand coordination bonds on mixing a C2 -symmetrical cavitand (calix[4]resorcinarene-based cavitands with ureide and terminal 4-pyridyl units) with platinum or palladium complexes ([Pt(OTf)2 ] or [Pd(OTf)2 ] with chelating bisphosphines) in 1:1 ratio. Hemicapsular assemblies formed in the presence of excess amounts of cavitand relative to the platinum or palladium complexes are identified as intermediates in the above self-assembly process by 2D-NOESY spectroscopy. External-anion-assisted encapsulation of a neutral guest, 4,4'-diiodobiphenyl, inside the hybrid supramolecular capsules accompanied conformational changes in the hydrogen-bonding moieties. The in/out exchange ratio of the encapsulated guest depends on the bite angle of the bisphosphine ligand. Addition of DMSO accelerates guest exchange by weakening the hydrogen bonds in the encapsulation complex. Therefore, variations in the structure of the metal complex and amount of polar solvent exert dual control on the dynamics of the guest exchange. PMID:24501041

Nito, Yuki; Adachi, Hirofumi; Toyoda, Naoaki; Takaya, Hikaru; Kobayashi, Kenji; Yamanaka, Masamichi

2014-04-01

372

Investigation of the electronic structures of organolanthanide sandwich complex anions by photoelectron spectroscopy: 4f orbital contribution in the metal-ligand interaction.  

PubMed

The electronic structures of lanthanide (Ln) ions sandwiched between 1,3,5,7-cyclooctatetraene (COT), Ln(COT)2(-), have been investigated by anion photoelectron spectroscopy. Complexes of 12 Ln atoms were investigated (excluding promethium (Pm), europium (Eu), and ytterbium (Yb)). The 213 nm photoelectron (PE) spectra of Ln(COT)2(-) exhibit two peaks assignable to the highest occupied molecular orbital (HOMO; e2u) and the next HOMO (HOMO-1; e2g) approximately at 2.6 and 3.6 eV, respectively, and their energy gap increases as the central metal atom progresses from lanthanum (La) to lutetium (Lu). Since lanthanide contraction shortens the distance between the Ln atom and the COT ligands, the widening energy gap represents the destabilization of the e2u orbital as well as the stabilization of the e2g orbital. Evidence for 4f orbital contribution in the metal-ligand interaction has been revealed by the Ln atom dependence in which the same e2u orbital symmetry enables an interaction between the 4f orbital of Ln atoms and the ? orbital of COT. PMID:24742246

Hosoya, Natsuki; Yada, Keizo; Masuda, Tomohide; Nakajo, Erika; Yabushita, Satoshi; Nakajima, Atsushi

2014-05-01

373

Metal-catalysed oxidation processes in thiosemicarbazones: new complexes with the ligand N-{2-([4-N-ethylthiosemicarbazone]methyl)phenyl}-p-toluenesulfonamide.  

PubMed

The coordination behaviour of a new thiosemicarbazone Schiff-base building block, N-{2-([4-N-ethylthiosemicarbazone]methyl)phenyl}-p-toluenesulfonamide, H2L1 (1), incorporating a bulky tosyl group, towards Mn II, Fe II, Co II, Ni II, Cu II, Zn II, Cd II, Ag I, Sn II, and Pb II has been investigated by means of an electrochemical preparative procedure. Most metal complexes of L1 have the general formula [M(L1)]2.nX (M=Mn, Fe, Co, Ni, Cu, Cd, Pb; n=0-4, X=H2O or CH3CN), as confirmed by the structure of [Pb(L1)]2 (15), in which the lone pair on lead is stereochemically active. This lead(II) complex shows an intense fluorescence emission with a quantum yield of 0.13. In the case of silver, the complex formed was found to possess a stoichiometry of [Ag2(L1)]2.3H2O. During reactions with manganese and copper metals, interesting catalysed processes have been found to take place, with remarkable consequences regarding the ligand skeleton structure. In synthesising the manganese complex, we obtained an unexpected dithiolate thiosemicarbazone tosyl ligand, H2L2, as a side-product, which has been fully characterised, including by X-ray diffraction analysis. In the case of copper, the solid complex has the formula [CuL1]2, but the crystallised product shows the copper atoms coordinated to a new cyclised thiosemicarbazone ligand, H2L3, as in the structures of the complexes [Cu(L3)]2.CH3CN (8) and [Cu(L3)(H2O)]2.CH3CN.H2O (9). The zinc complex [Zn(L1)]4 (12) displays a particular tetranuclear zeolite-type structure capable of hosting small molecules or ions, presumably through hydrogen bonding. PMID:17918755

Pedrido, Rosa; Romero, María J; Bermejo, Manuel R; González-Noya, Ana M; García-Lema, Iria; Zaragoza, Guillermo

2008-01-01

374

Synthesis, spectral and magnetic studies of mono- and bi-nuclear metal complexes of a new bis(tridentate NO 2) Schiff base ligand derived from 4,6-diacetylresorcinol and ethanolamine  

Microsoft Academic Search

A new bis(tridentate NO2) Schiff base ligand, H4L, was prepared by the reaction of the bifunctional carbonyl compound; 4,6-diacetylresorcinol (DAR) with ethanolamine. The ligand reacted with iron(III), cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), cerium(III) and uranyl(VI) ions, in absence and in presence of LiOH, to yield mono- and bi-nuclear complexes with different coordinating sites. The ligand and its metal complexes were

Magdy Shebl

2009-01-01

375

Cholesterol-dependent retention of GPI-anchored proteins in endosomes.  

PubMed Central

Several cell surface eukaryotic proteins have a glycosylphosphatidylinositol (GPI) modification at the Cterminal end that serves as their sole means of membrane anchoring. Using fluorescently labeled ligands and digital fluorescence microscopy, we show that contrary to the potocytosis model, GPI-anchored proteins are internalized into endosomes that contain markers for both receptor-mediated uptake (e.g. transferrin) and fluid phase endocytosis (e.g. dextrans). This was confirmed by immunogold electron microscopy and the observation that a fluorescent folate derivative bound to the GPI-anchored folate receptor is internalized into the same compartment as co-internalized horseradish peroxidase-transferrin; the folate fluorescence was quenched when cells subsequently were incubated with diaminobenzidine and H2O2. Most of the GPI-anchored proteins are recycled back to the plasma membrane but at a rate that is at least 3-fold slower than C6-NBD-sphingomyelin or recycling receptors. This endocytic retention is regulated by the level of cholesterol in cell membranes; GPI-anchored proteins are recycled back to the cell surface at the same rate as recycling transferrin receptors and C6-NBD-sphingomyelin in cholesterol-depleted cells. Cholesterol-dependent endocytic sorting of GPI-anchored proteins is consistent with the involvement of specialized lipid domains or 'rafts' in endocytic sorting. These results provide an alternative explanation for GPI-requiring functions of some GPI-anchored proteins.

Mayor, S; Sabharanjak, S; Maxfield, F R

1998-01-01

376

C?sp?3?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(CH2 SiMe3 )3 (M=Ga, In) to yield the zwitterions {ON^(CH(+) )^NO}M(-) (CH2 SiMe3 )2 (M=Ga, 2; In, 3) by abstraction of a hydride from the ligand backbone followed by elimination of dihydrogen. By contrast, with Al2 Me6 , 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?sp?3?H bond activation follows the order Al?Gametal-hydride species. DFT calculations indicate that the systems {ON^(CH2 )^NO}H2 +M(CH2 SiMe3 )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

377

Dynamic equilibria in solvent-mediated anion, cation and ligand exchange in transition-metal coordination polymers: solid-state transfer or recrystallisation?  

PubMed

The solution properties of a series of transition-metal-ligand coordination polymers [ML(X)(n)](infinity) [M=Ag(I), Zn(II), Hg(II) and Cd(II); L=4,4'-bipyridine (4,4'-bipy), pyrazine (pyz), 3,4'-bipyridine (3,4'-bipy), 4-(10-(pyridin-4-yl)anthracen-9-yl)pyridine (anbp); X=NO(3) (-), CH(3)COO(-), CF(3)SO(3) (-), Cl(-), BF(4) (-); n=1 or 2] in the presence of competing anions, metal cations and ligands have been investigated systematically. Providing that the solubility of the starting complex is sufficiently high, all the components of the coordination polymer, namely the anion, the cation and the ligand, can be exchanged on contact with a solution phase of a competing component. The solubility of coordination polymers is a key factor in the analysis of their reactivity and this solubility depends strongly on the physical properties of the solvent and on its ability to bind metal cations constituting the backbone of the coordination polymer. The degree of reversibility of these solvent-induced anion-exchange transformations is determined by the ratio of the solubility product constants for the starting and resultant complexes, which in turn depend upon the choice of solvent and the temperature. The extent of anion exchange is controlled effectively by the ratio of the concentrations of incoming ions to outgoing ions in the liquid phase and the solvation of various constituent components comprising the coordination polymer. These observations can be rationalised in terms of a dynamic equilibrium of ion exchange reactions coupled with Ostwald ripening of crystalline products. The single-crystal X-ray structures of [Ag(pyz)ClO(4)](infinity) (1), {[Ag(4,4'-bipy)(CF(3)SO(3))]CH(3)CN}(infinity) (2), {[Ag(4,4'-bipy)(CH(3)CN)]ClO(4) 0.5 CH(3)CN}(infinity) (3), metal-free anbp (4), [Ag(anbp)NO(3)(H(2)O)](infinity) (5), {[Cd(4,4'-bipy)(2)(H(2)O)(2)](NO(3))(2)4 H(2)O}(infinity) (6) and {[Zn(4,4'-bipy)SO(4)(H(2)O)(3)] 2 H(2)O}(infinity) (7) are reported. PMID:19630015

Cui, Xianjin; Khlobystov, Andrei N; Chen, Xinyong; Marsh, Dan H; Blake, Alexander J; Lewis, William; Champness, Neil R; Roberts, Clive J; Schröder, Martin

2009-09-01

378

Atomic multiplets at the L2,3 edge of 3d transition metals and the ligand K edge in x-ray absorption spectroscopy of ionic systems  

NASA Astrophysics Data System (ADS)

Experimental X-ray absorption spectra at the fluorine K and transition metal L2,3 absorption edges of the MF2 (M=Cr-Ni) family are presented. Ligand field calculations in D4h symmetry show very good agreement with the transition metal L2,3 XAS spectra. To successfully explain nominal Cr2+ L2,3 XAS spectrum in CrF2, the inclusion of Cr+ and Cr3+ was needed implying the presence of a disproportionation reaction. The multiplet calculations were then modified to remove the structure of the 2p hole in the calculated M 2p?3d absorption spectra. These results for the 3dn+1 states are in one to one correspondence with the leading edge structures found at the fluorine K edge. A direct comparison with the metal L2,3 edges also indicates that there is evidence of the metal multiplet at the fluorine K pre-edge structures.

Olalde-Velasco, P.; Jiménez-Mier, J.; Denlinger, J.; Yang, W.-L.

2013-06-01

379

Axial anchoring designed silicon-porphyrin sensitizers for efficient dye-sensitized solar cells.  

PubMed

Using silicon as a central atom of porphyrin allows the introduction of axial ligands, which are not only employed to prevent the aggregation of the macrocycles but also anchor the dyes onto the TiO2 surface. A dye-sensitized solar cell with this porphyrin sensitizer achieved a broad IPCE of around 40-60% between 380 and 670 nm. PMID:24213560

Liu, Jing; Yang, Xichuan; Sun, Licheng

2013-12-28

380

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 (), [Mn3(L)2(bib)2(H2O)4]·4H2O (), [Ni(HL)(bib)(H2O)3] () and [Ni3(bib)4(H2O)10]·2(L)·12(H2O) (), 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 , 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 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 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 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 and 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 and and antiferromagnetic properties of and 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

2014-06-24

381

Anchors Aweigh: A Demonstration of Cross-Modality Anchoring and Magnitude Priming  

ERIC Educational Resources Information Center

Research has shown that judgments tend to assimilate to irrelevant "anchors." We extend anchoring effects to show that anchors can even operate across modalities by, apparently, priming a general sense of magnitude that is not moored to any unit or scale. An initial study showed that participants drawing long "anchor" lines made higher numerical…

Oppenheimer, Daniel M.; LeBoeuf, Robyn A.; Brewer, Noel T.

2008-01-01

382

Conventional Anchor Test Results at Guam.  

National Technical Information Service (NTIS)

The results of instrumented drag embedment anchor tests in Inner Apra Harbor, Guam are presented. The Navy can use this data for selecting and sizing anchors for Guam as well as other similar sites. Test data for the Navy STOCKLESS and STATO anchors are p...

R. J. Taylor K. Rocker

1980-01-01

383

Robust conductance of dumbbell molecular junctions with fullerene anchoring groups.  

PubMed

The conductance of a molecular wire connected to metallic electrodes is known to be sensitive to the atomic structure of the molecule-metal contact. This contact is to a large extent determined by the anchoring group linking the molecular wire to the metal. It has been found experimentally that a dumbbell construction with C(60) molecules acting as anchors yields more well-defined conductances as compared to the widely used thiol anchoring groups. Here, we use density functional theory to investigate the electronic properties of this dumbbell construction. The conductance is found to be stable against variations in the detailed bonding geometry and in good agreement with the experimental value of G=3×10(-4) G(0). Electron tunneling across the molecular bridge occurs via the lowest unoccupied orbitals of C(60) which are pinned close to the Fermi energy due to partial charge transfer. Our findings support the original motivation to achieve conductance values more stable towards changes in the structure of the molecule-metal contact leading to larger reproducibility in experiments. PMID:22010695

Markussen, Troels; Settnes, Mikkel; Thygesen, Kristian S

2011-10-14

384

Evaluation of the Biotic Ligand Model for Predicting Metal Bioavailability and Toxicity in SRS Effluents and Surface Waters.  

National Technical Information Service (NTIS)

Researchers have long recognized that the toxicity of metals to aquatic life is a function of water chemistry. Metals can form organic and inorganic complexes and can also sorb onto suspended particles, all of which can reduce the bioavailability and thus...

W. L. Specht

2005-01-01

385

The interplay of catechol ligands with nanoparticulate iron oxides.  

PubMed

The unique properties exhibited by nanoscale materials, coupled with the multitude of chemical surface derivatisation possibilities, enable the rational design of multifunctional nanoscopic devices. Such functional devices offer exciting new opportunities in medical research and much effort is currently invested in the area of "nanomedicine", including: multimodal imaging diagnostic tools, platforms for drug delivery and vectorisation, polyvalent, multicomponent vaccines, and composite devices for "theranostics". Here we will review the surface derivatisation of nanoparticulate oxides of iron and iron@iron-oxide core-shells. They are attractive candidates for MRI-active therapeutic platforms, being potentially less toxic than lanthanide-based materials, and amenable to functionalisation with ligands. However successful grafting of groups onto the surface of iron-based nanoparticles, thus adding functionality whilst preserving their inherent properties, is one of the most difficult challenges for creating truly useful nanodevices from them. Functionalised catechol-derived ligands have enjoyed success as agents for the masking of superparamagnetic iron-oxide particles, often so as to render them biocompatible with medium to long-term colloidal stability in the complex chemical environments of biological milieux. In this perspective, the opportunities and limitations of functionalising the surfaces of iron-oxide nanoparticles, using coatings containing a catechol-derived anchor, are analysed and discussed, including recent advances using dopamine-terminated stabilising ligands. If light-driven ligand to metal charge transfer (LMCT) processes, and pH-dependent ligand desorption, leading to nanoparticle degradation under physiologically relevant conditions can be suppressed, colloidal stability of samples can be maintained and toxicity ascribed to degradation products avoided. Modulation of the redox behaviour of iron catecholate systems through the introduction of an electron-withdrawing substituent to the aromatic ?-system of the catechol is a promising approach towards achieving these goals. PMID:22241454

Yuen, Alexander K L; Hutton, Georgina A; Masters, Anthony F; Maschmeyer, Thomas

2012-03-01

386

Deepwater operations demand safe, stable anchoring  

SciTech Connect

The tension-leg system is characterized by the ability to suppress first-order wave-induced motions in addition to the position-keeping ability. A different philosophy is followed for the catenary system, allowing the platform to be free floating. The anchoring system affects the motion behavior of the structure only to a minor degree. A discussion is presented of excitation sources, quasistatic method, anchor design and performance, fluke anchors, pile anchors, gravity anchors, mooring lines, corrosion protection systems, and, maintenance. 10 refs.

Olsen, O.A.; Kvalstad, T.; Lereim, J.; Lohne, P.W.; Namork, J.

1982-05-01

387

DFT modeling and spectroscopic study of metal–ligand bonding in La(III) complex of coumarin-3-carboxylic acid  

Microsoft Academic Search

The binding mode of coumarin-3-carboxylic acid (HCCA) to La(III) is elucidated at experimental and theoretical level. The complexation ability of the deprotonated ligand (CCA?) to La(III) is studied using elemental analysis, DTA and TGA data as well as FTIR, 1H NMR and 13C NMR spectra. The experimental data suggest the complex formula La(CCA)2(NO3)(H2O)2. B3LYP, BHLYP, B3P86, B3PW91, PW91P86 and MPW1PW91

Tz. Mihaylov; N. Trendafilova; I. Kostova; I. Georgieva; G. Bauer

2006-01-01

388

Assembly and photocatalysis of two novel 3D Anderson-type polyoxometalate-based metal-organic frameworks constructed from isomeric bis(pyridylformyl)piperazine ligands.  

PubMed

Two novel Anderson-type polyoxometalates (POMs)-based metal-organic frameworks (MOFs), namely, H{Cu2(?2-OH)2L(1)[CrMo6(OH)6O18]}·4H2O (), {Cu2L(2)[CrMo(VI)5Mo(V)(OH)6O18](H2O)4}·4H2O () (L(1) = N,N'-bis(3-pyridinecarboxamide)-piperazine, L(2) = N,N'-bis(4-pyridinecarboxamide)-piperazine), are hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex , the hexadentate [CrMo6(OH)6O18](3-) polyoxoanion bridges the Cu(II) ions to generate a 2D Cu-POM inorganic layer, which is further extended by the ?2-bridging L(1) ligands (via ligation of pyridyl nitrogen atoms) to form a 3D MOF with a 4,6-connected {4(4)·6(10)·8}{4(4)·6(2)} topology. Complex is also a 3D POM-based MOF exhibiting a {4(2)·8(4)} topology, which is constructed from the quadridentate [CrMo(VI)5Mo(V)(OH)6O18](4-) polyoxoanions and ?4-bridging L(2) ligands (via ligation of pyridyl nitrogen and carbonyl oxygen atoms). The different coordination modes of POM polyanions and the isomeric bis(pyridylformyl)piperazine ligands play key roles in the construction of the title complexes. In addition, the photocatalytic activities of the title complexes on the degradation of methylene blue (MB) under UV, visible light and sunlight irradiation have been investigated in detail. PMID:24958084

Wang, Xiuli; Chang, Zhihan; Lin, Hongyan; Tian, Aixiang; Liu, Guocheng; Zhang, Juwen

2014-07-22