Note: This page contains sample records for the topic metal ligand anchored from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

A robust protein host for anchoring chelating ligands and organocatalysts.  

PubMed

In order to put the previously proposed concept of directed evolution of hybrid catalysts (proteins that harbor synthetic transition-metal catalysts or organocatalysts) into practice, several prerequisites must be met. The availability of a robust host protein that can be expressed in sufficiently large amounts, and that can be purified in a simple manner is crucial. The thermostable enzyme tHisF from Thermotoga maritima, which constitutes the synthase subunit of a bi-enzyme complex that is instrumental in the biosynthesis of histidine, fulfills these requirements. In the present study, fermentation has been miniaturized and parallelized, as has purification of the protein by simple heat treatment. Several mutants with strategically placed cysteines for subsequent bioconjugation have been produced. One of the tHisF mutants, Cys9Ala/Asp11Cys, was subjected to bioconjugation by the introduction of a variety of ligands for potential metal ligation, of a ligand/metal moiety, and of several organocatalytic entities that comprise a flavin or thiazolium salts. Characterization by mass spectrometry and tryptic digestion was achieved. As a result of this study, a platform for performing future directed evolution of these hybrid catalysts is now available. PMID:18273849

Reetz, Manfred T; Rentzsch, Martin; Pletsch, Andreas; Taglieber, Andreas; Hollmann, Frank; Mondière, Régis J G; Dickmann, Norbert; Höcker, Birte; Cerrone, Simona; Haeger, Michaela C; Sterner, Reinhard

2008-03-01

2

Photoconductivity of PbSe quantum-dot solids: dependence on ligand anchor group and length.  

PubMed

The assembly of quantum dots is an essential step toward many of their potential applications. To form conductive solids from colloidal quantum dots, ligand exchange is required. Here we study the influence of ligand replacement on the photoconductivity of PbSe quantum-dot solids, using the time-resolved microwave conductivity technique. Bifunctional replacing ligands with amine, thiol, or carboxylic acid anchor groups of various lengths are used to assemble quantum solids via a layer-by-layer dip-coating method. We find that when the ligand lengths are the same, the charge carrier mobility is higher in quantum-dot solids with amine ligands, while in quantum-dot solids with thiol ligands the charge carrier lifetime is longer. If the anchor group is the same, the charge carrier mobility is ligand length dependent. The results show that the diffusion length of charge carriers can reach several hundred nanometers. PMID:23078408

Gao, Yunan; Aerts, Michiel; Sandeep, C S Suchand; Talgorn, Elise; Savenije, Tom J; Kinge, Sachin; Siebbeles, Laurens D A; Houtepen, Arjan J

2012-10-31

3

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

SciTech Connect

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

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

2005-06-01

4

Binding constants of membrane-anchored receptors and ligands depend strongly on the nanoscale roughness of membranes.  

PubMed

Cell adhesion and the adhesion of vesicles to the membranes of cells or organelles are pivotal for immune responses, tissue formation, and cell signaling. The adhesion processes depend sensitively on the binding constant of the membrane-anchored receptor and ligand proteins that mediate adhesion, but this constant is difficult to measure in experiments. We have investigated the binding of membrane-anchored receptor and ligand proteins with molecular dynamics simulations. We find that the binding constant of the anchored proteins strongly decreases with the membrane roughness caused by thermally excited membrane shape fluctuations on nanoscales. We present a theory that explains the roughness dependence of the binding constant for the anchored proteins from membrane confinement and that relates this constant to the binding constant of soluble proteins without membrane anchors. Because the binding constant of soluble proteins is readily accessible in experiments, our results provide a useful route to compute the binding constant of membrane-anchored receptor and ligand proteins. PMID:24006364

Hu, Jinglei; Lipowsky, Reinhard; Weikl, Thomas R

2013-09-04

5

Strategies for the anchoring of metal complexes, clusters, and colloids inside nanoporous alumina membranes.  

PubMed

Two complementary strategies are presented for the anchoring of molecular palladium complexes, of cobalt or platinum clusters or of gold colloids inside the nanopores of alumina membranes. The first consists in the one step condensation of an alkoxysilyl functional group carried by the metal complex with the hydroxy groups covering the surface of the membrane pores. Thus, using the short-bite alkoxysilyl-functionalized diphosphane ligands (Ph2P)2N(CH2)3Si(OMe)3 (1) and (Ph2P)2N(CH2)4SiMe2(OMe)] (2) derived from (Ph2P)2NH (dppa) (dppa bis(diphenylphosphanyl)amine), the palladium complexes [Pd(dmba)(kappa2-P,P-(Ph2P)2N(CH2)3Si(OMe)3)] Cl (3) and [Pd(dmba)[kappa2-P,P-(Ph2P)2N(CH2)4SiMe2(OMe)

Braunstein, P; Kormann, H P; Meyer-Zaika, W; Pugin, R; Schmid, G

2000-12-15

6

CCMR: Biological Ligands and Metal Transport  

NSDL National Science Digital Library

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

Powell, Alanna

2005-08-17

7

Anchor Side Chains of Short Peptide Fragments Trigger Ligand-Exchange of Class II MHC Molecules  

PubMed Central

Class II MHC molecules display peptides on the cell surface for the surveillance by CD4+ T cells. To ensure that these ligands accurately reflect the content of the intracellular MHC loading compartment, a complex processing pathway has evolved that delivers only stable peptide/MHC complexes to the surface. As additional safeguard, MHC molecules quickly acquire a ‘non-receptive’ state once they have lost their ligand. Here we show now that amino acid side chains of short peptides can bypass these safety mechanisms by triggering the reversible ligand-exchange. The catalytic activity of dipeptides such as Tyr-Arg was stereo-specific and could be enhanced by modifications addressing the conserved H-bond network near the P1 pocket of the MHC molecule. It affected both antigen-loading and ligand-release and strictly correlated with reported anchor preferences of P1, the specific target site for the catalytic side chain of the dipeptide. The effect was evident also in CD4+ T cell assays, where the allele-selective influence of the dipeptides translated into increased sensitivities of the antigen-specific immune response. Molecular dynamic calculations support the hypothesis that occupation of P1 prevents the ‘closure’ of the empty peptide binding site into the non-receptive state. During antigen-processing and -presentation P1 may therefore function as important “sensor” for peptide-load. While it regulates maturation and trafficking of the complex, on the cell surface, short protein fragments present in blood or lymph could utilize this mechanism to alter the ligand composition on antigen presenting cells in a catalytic way.

Gupta, Shashank; Hopner, Sabine; Rupp, Bernd; Gunther, Sebastian; Dickhaut, Katharina; Agarwal, Noopur; Cardoso, M. Cristina; Kuhne, Ronald; Wiesmuller, Karl-Heinz; Jung, Gunther; Falk, Kirsten; Rotzschke, Olaf

2008-01-01

8

Metal ion ligands in hyperaccumulating plants  

Microsoft Academic Search

Metal-hyperaccumulating plants have the ability to take up extraordinary quantities of certain metal ions without succumbing\\u000a to toxic effects. Most hyperaccumulators select for particular metals but the mechanisms of selection are not understood at\\u000a the molecular level. While there are many metal-binding biomolecules, this review focuses only on ligands that have been reported\\u000a to play a role in sequestering, transporting

Damien L. Callahan; Alan J. M. Baker; Spas D. Kolev; Anthony G. Wedd

2006-01-01

9

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

10

Anchoring strategies for bimetallic species in zeolites. Progress report.  

National Technical Information Service (NTIS)

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 exc...

T. Bein

1993-01-01

11

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

12

Design and synthesis of a novel anchoring ligand for highly efficient thin film dye-sensitized solar cells.  

PubMed

A novel ligand, 5,5'-(2,2'-bipyridine-4,4'-diyl)-bis(thiophene-2-carboxylic acid) (BTC), and its Ru(II) complex (BTC-1) in which the anchoring group is attached to the thiophene units were developed. Using a low-volatility electrolyte and 3.3 mum mesoporous TiO2 films BTC-1 achieved a solar-to-electricity conversion efficiency of 6.1%, compared to 4.8% for N719 under the same experimental conditions. PMID:19921011

Mishra, Amaresh; Pootrakulchote, Nuttapol; Fischer, Markus K R; Klein, Cedric; Nazeeruddin, Md K; Zakeeruddin, Shaik M; Bäuerle, Peter; Grätzel, Michael

2009-10-29

13

Metal nanoparticles functionalized with metal-ligand covalent bonds  

NASA Astrophysics Data System (ADS)

Metal-organic contact has been recognized to play important roles in regulation of optical and electronic properties of nanoparticles. In this thesis, significant efforts have been devoted into synthesis of ruthenium nanoparticles with various metal-ligand interfacial linkages and investigation of their electronic and optical properties. Ruthenium nanoparticles were prepared by the self-assembly of functional group onto bare Ru colloid surface. As to Ru-alkyne nanoparticles, the formation of a Ru-vinylidene (Ru=C=CH--R) interfacial bonding linkage was confirmed by the specific reactivity of the nanoparticles with imine derivatives and olefin at the metal-ligand interface, as manifested in NMR, photoluminescence, and electrochemical measurements. Interestingly, it was found the electronic coupling coefficient (beta)for strongly depend upon such metal-ligand interfacial bonding. Next, such metal-ligand interfacial bonding was extended to ruthenium-nitrene pi bonds on ruthenium colloids, which were investigated by XPS. The nanoparticles exhibited a 1:1 atomic ratio of nitrogen to sulfur, consistent with that of sulfonyl nitrene fragments. In addition, the nanoparticle-bound nitrene moieties behaved analogously to azo derivatives, as manifested in UV-vis and fluorescence measurements. Further testimony of the formation of Ru=N interfacial linkages was highlighted in the unique reactivity of the nanoparticles with alkenes by imido transfer. Extensive conjugation between metal-ligand interfacial bond results in remarkable intraparticle charge delocalization on Ru-alkynide nanoparticles, which was manipulated by simple chemical reduction or oxidation. Charging of extra electrons into the nanoparticle cores led to an electron-rich metal core and hence red-shift of the triple bond stretching mode, lower binding energy of sp hybridized C 1s and dimmed fluorescence of nanoparticles. Instead, chemical oxidation resulted in the opposite impacts on these properties. By taking advantage of such extensively conjugated metal-ligand bonding and effective intraparticle charge delocalization of ruthenium nanoparticles, Ru=carbene nanoparticles functionalized with multiple moieties by olefin metathesis reactions was further exploited for metal ion sensing. When the nanoparticles were co-functionalized with 1-vinylpyrene and 4-vinylbenzo-18-crown-6, upon the binding of metal ions into the crown ether cavity, the emission intensity of the nanoparticle fluorescence from the conjugation of vinylpyrene was found to diminish, with the most significant effects observed with K+ ions. In the case of ruthenium nanoparticles co-functionalized with pyrene and histidine derivative moieties through Ru=carbene pi bonds. The selective complexation of the histidine moiety with transition metal ions led to marked diminishment of the emission intensity from conjugation of pyrene. Of all the metal ions tested, the impacts were much more drastic with Pb2+ , Co2+ and Hg2+ than with Li +, K+, Rb+, Mg2+ Ca 2+ and Zn2+ ions. These were ascribed to the selective binding of 18-crown-6 to potassium ions or complexation of histidine derivative to transition metal ions, where the metal ions led to polarization of the nanoparticle core electrons to the metal surface and hence impeded intraparticle charge delocalization. Functionalization of semiconductor with metal nanoparticles could be exploited to remarkably enhance their photo catalytic performance. Before this exploration, in the last chapter, the impacts of the TiO2 nanocrystalline structure on the photocatalytic activity were then examined by using the reduction of methylene blue in water. It was found that in the presence of anatase and brookite crystalline phase, TiO2 nanotube arrays exhibited the highest photo catalytic activity. This is ascribed to synergistic coupling of the anatase and brookite crystalline domains, which led to effective charge separation upon photoirradiation.

Kang, Xiongwu

14

(Ligand intermediates in metal-catalyzed reactions)  

SciTech Connect

This report consists of sections on sigma bond complexes of alkenes, a new carbon-hydrogen bond activation reaction of alkene complexes, carbon-hydrogen bond migrations in alkylidene complexes, carbon- hydrogen bond migrations in alkyne complexes, synthesis, structure and reactivity of C{sub x} complexes, synthesis and reactivity of alcohol and ether complexes, new catalysts for the epimerization of secondary alcohols; carbon-hydrogen bond activation in alkoxide complexes, pi/sigma equilibria in metal/O=CXX' complexes, and other hydrocarbon ligands; miscellaneous.(WET)

Not Available

1992-01-01

15

Ligand-Metal Exchange Effects in Paramagnetic Transition Metal Complexes . Ligand-Metall-Wechselwirkungen in Paramagnetischen Uebergangsmetallkomplexen.  

National Technical Information Service (NTIS)

Spectroscopic analysis of the electron delocalization mechanism of a large number of paramagnetic transition metal complexes was conducted. Various substances were treated as novel, two-toothed ligands in a pseudo-octahedral complex of cobalt 2 and nickel...

H. Biedermann

1971-01-01

16

A GPI anchor explains the unique biological features of the common NKG2D-ligand allele MICA*008.  

PubMed

The human MICA (MHC I-related chain A) gene, encoding a ligand for the NKG2D (NKG2-D type II integral membrane protein) receptor, is highly polymorphic. A group of MICA alleles, named MICA 5.1 (prototype, MICA*008), produce a truncated protein due to a nucleotide insertion in the transmembrane domain. These alleles are very frequent in all of the human populations studied and they have different biological properties, compared with full-length alleles, e.g. recruitment into exosomes, which makes them very potent for down-modulating the NKG2D receptor in effector immune cells. Moreover, MICA*008 is not affected by viral immune evasion mechanisms that target other MICA alleles. In the present study, we demonstrate that MICA*008 acquires a GPI (glycosylphosphatidylinositol) anchor and that this modification is responsible for many of the distinct biological features of the truncated MICA alleles, including recruitment of the protein to exosomes. MICA*008 processing is also unusual as it is observed in the endoplasmic reticulum as a Triton™ X-114 soluble protein, partially undergoing GPI modification while the rest is exocytosed, suggesting a new model for MICA*008 release. This is the first report of a GPI-anchored MICA allele. The finding that this modification occurs in both families of human NKG2D ligands, as well as in the murine system, suggests positive pressure to maintain this biochemical feature. PMID:23772752

Ashiru, Omodele; López-Cobo, Sheila; Fernández-Messina, Lola; Pontes-Quero, Samuel; Pandolfi, Rachele; Reyburn, Hugh T; Valés-Gómez, Mar

2013-09-01

17

Anchoring platinum on graphene using metallic adatoms: a first principles investigation.  

PubMed

First principles calculations based on spin-polarized density functional theory were used to identify metallic adatoms that would strengthen the Pt(111)/graphene interface (with a low work of separation of 0.009 J m(-2)), when the adatom was placed between the Pt(111) and the graphene. It was shown that the strength of the Pt-adatom bond, which had a metallic character, increased with the amount of charge transferred from the adatom to the Pt. The carbon-adatom bond, on the other hand, had a mixed ionic and covalent character and was weaker than the Pt-adatom bond for each of the 25 elements considered. Consequently, the total Pt(111)/graphene interface strength and, hence, the anchoring effect of the adatom were controlled by the carbon-adatom bond strength. Metals with unfilled d orbitals increased the Pt/graphene interface strength to above 0.5 J m(-2). The carbon-adatom bond strength was proportional to the ratio between the charge transferred from the adatom to the graphene (?Z(C)) and the charge transferred to the Pt surface (?Z(Pt)); i.e., the ?Z(C)/?Z(Pt) ratio defined the ability of an adatom to anchor Pt to graphene. For Ir, Os, Ru, Rh and Re, ?Z(C)/?Z(Pt) > 1.0, making these elements the most effective adatoms for anchoring Pt to graphene. PMID:22534238

Sen, F G; Qi, Y; Alpas, A T

2012-04-26

18

Influence of ligands on metals leachability from landfilling bottom ashes  

Microsoft Academic Search

After municipal solid waste is incinerated, its bottom ash used to be disposed by landfill. Although the leachate quality is less polluted, some heavy metals in the bottom ashes are affected by ligands, which raise their release potential. Concerned by the bottom ashes landfilling, this research explored the influence strengths of ligands in leaching heavy metals, by rotary extraction and

Sue-huai Gau; Wen-chin Jeng

1998-01-01

19

Synthesis and structures of the first bismuth-ester complexes using heterobifunctional thiolate anchored ligands and mass spectrometric identification of ligand-bridged derivatives.  

PubMed

The first systematic series of bismuth complexes involving ester donors, Bi(SCH(2)C(O)OCH(2)CH(3))Cl(2), Bi(SCH(2)C(O)OCH(3))(2)Cl, and Bi(SCH(2)COOCH(3))(3), has been isolated and characterized by spectroscopic (IR, Raman) and X-ray crystallographic data. In addition, these and other species have been identified by electron-impact, electrospray, and atmospheric pressure chemical ionization mass spectometry. The generally applicable synthetic methodology involves the use of heterobifunctional ligands containing a thiolate moiety as an anchor to facilitate coordinate interactions between weak donors (carbonyls) and weak acids (bismuth). The bifunctional nature of the ligands is manifested in both chelating and bridging roles. Important comparisons can be made with the pharmaceutical agent "colloidal bismuth subcitrate" (CBS). The observations allow for a new appreciation of bioactive bismuth compounds, by providing an approach to study the interaction of biorelevant functional groups with bismuth. PMID:12716213

Briand, Glen G; Burford, Neil; Eelman, Melanie D; Cameron, T Stanley; Robertson, Katherine N

2003-05-01

20

Chelation ion chromatography of trace metal ions using metallochromic ligands  

Microsoft Academic Search

Hydrophobic metallochromic ligands can be used to coat high-performance reversed-phase substrates producing chelating stationary phases with the capacity to separate metal ions. To date the main approaches have been to `pre-coat' the substrate with the ligand and use it with a mobile phase containing an inorganic salt or alternatively to include the ligand itself within the mobile phase, where the

Paul R Haddad

1999-01-01

21

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

22

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

PubMed

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

Campbell, Charles T; Sellers, Jason R V

2013-01-01

23

Ammonia formation by metal-ligand cooperative hydrogenolysis of a nitrido ligand  

NASA Astrophysics Data System (ADS)

Bioinspired hydrogenation of N2 to ammonia at ambient conditions by stepwise nitrogen protonation/reduction with metal complexes in solution has experienced remarkable progress. In contrast, the highly desirable direct hydrogenation with H2 remains difficult. In analogy to the heterogeneously catalysed Haber-Bosch process, such a reaction is conceivable via metal-centred N2 splitting and unprecedented hydrogenolysis of the nitrido ligands to ammonia. We report the synthesis of a ruthenium(IV) nitrido complex. The high nucleophilicity of the nitrido ligand is demonstrated by unusual N-C coupling with ?-acidic CO. Furthermore, the terminal nitrido ligand undergoes facile hydrogenolysis with H2 at ambient conditions to produce ammonia in high yield. Kinetic and quantum chemical examinations of this reaction suggest cooperative behaviour of a phosphorus-nitrogen-phosphorus pincer ligand in rate-determining heterolytic hydrogen splitting.

Askevold, Bjorn; Nieto, Jorge Torres; Tussupbayev, Samat; Diefenbach, Martin; Herdtweck, Eberhardt; Holthausen, Max C.; Schneider, Sven

2011-07-01

24

Predictive gold nanocluster formation controlled by metal-ligand complexes.  

PubMed

The formation of ligand-protected gold nanoclusters during size-selective syntheses is seemingly driven by the inherent properties of the protecting ligands, but a general description of the product formation has not been presented. This study uses diphosphine-protected Au clusters as a model system to examine i) control of metal-ligand complex distributions in methanol-chloroform solutions, ii) role of solution perturbations, e.g., oxidation, and iii) nanocluster formation through reduction of characterized complex distributions. By selectively reducing complexes and monitoring cluster formation with electrospray ionization mass spectrometry and UV-vis, data show the distribution of complexes can be controlled through ligand exchange, and the reduction of specific complexes produce characteristic ligated gold clusters based on ligand class. Specifically, 1,n-bis(diphenylphosphino)n-alkane ligands, L(n), where n = 1 through 6, are classified into two distinct sets. The classes represent ligands that either form mainly [AuL(n)(2)](+) (Class I, n = 1-3) or bridged [Au(2)L(n)(2)](2+) (Class II, n = 4-6) complexes after complete ligand exchange with AuClPPh(3). Selectively reducing gold-phosphine ligand complexes allows mapping of product formation, resulting collectively in a predictive tool for ligated gold cluster production by simply monitoring the initial complex distribution prior to reduction. PMID:22228703

Pettibone, John M; Hudgens, Jeffrey W

2012-01-09

25

IDENTIFICATION OF CATALYTIC METAL ION LIGANDS IN RIBOZYMES  

PubMed Central

Site-bound metal ions participate in the catalytic mechanisms of many ribozymes. Understanding these mechanisms therefore requires knowledge of the specific ligands on both substrate and ribozyme that coordinate these catalytic metal ions. A number of different structural and biochemical strategies have been developed and refined for identifying metal ion binding sites within ribozymes, and for assessing the catalytic contributions of the metal ions bound at those sites. We review these approaches and provide examples of their application, focusing in particular on metal ion rescue experiments and their roles in the construction of the transition state models for the Tetrahymena group I and RNase P ribozymes.

Frederiksen, John K.; Piccirilli, Joseph A.

2012-01-01

26

Long-Lifetime Metal–Ligand pH Probe  

Microsoft Academic Search

We describe the synthesis and fluorescence spectral characterization of a pH-sensitive metal–ligand complex, [Ru(deabpy)(bpy)2]2+, where deabpy is 4,4?-diethylaminomethyl-2,2?-bipyridine. This metal–ligand complex (MLC) was found to display pH-dependent intensities, emission spectra, and decay times, with the changes centered near the physiological useful pH value of 7.5. The apparent pKavalues were not found to be dependent on ionic strength. The compound was

Zakir Murtaza; Qing Chang; Govind Rao; Harriet Lin; Joseph R. Lakowicz

1997-01-01

27

Synthesis of porphyrinoids with silane anchors and their covalent self-assembling and metallation on solid surface.  

PubMed

We have synthesized a set of porphyrin and phthalocyanine compounds with two different silane anchors. Syntheses of the anchor-substituted chromophores have been carried out via hydrosilylation of alkene derivatives, catalyzed by platinum complexes. The reduction side-process was suppressed using specific anchor/catalyst pairs, and the silane-containing compounds were successfully isolated from hydrogenated by-products in pure form with good yields. The target porphyrinoids having stable reactive silane anchors possess the ability to self-assemble on metal oxides and quartz surfaces and optical fibers. Covalent attachment is done in one-step, which makes the bonding process fast and easy. Immobilized chromophores were further converted by on-surface reactions into Zn(II) and Mg(II) metal complexes. The metallation time was found to be as fast as 1 min for Zn ion. Bonding densities calculated from the absorbances of the deposited layers give rough estimations for packing of the molecules on various substrates and evidence for monomolecular layers formation. PMID:22230214

Sariola-Leikas, Essi; Hietala, Matti; Veselov, Alexey; Okhotnikov, Oleg; Semjonov, Sergei L; Tkachenko, Nikolai V; Lemmetyinen, Helge; Efimov, Alexander

2011-12-28

28

Electroactive films of polypyrroles containing complexing cavities preformed by entwining ligands on metallic centers  

SciTech Connect

New functionalized polypyrrole films containing transition metal complexes have been prepared and studied. The strategy is based on the three-dimensional template effect of a metal center (Cu{sup 1}, Co{sup II}, Zn{sup II}, Ag{sup I}) able to entwine two end-functionalized chelating ligands before polymerization. The ligands used consist of a 2,9-diphenyl-1,10-phenanthroline subunit (dpp) bearing two pyrrole nuclei. The pseudotetrahedral geometry of the precursor complex is such that after polylmerization of the N-anchored pyrrole rings, a highly entangled network is obtained. The rigidity of the polymer matrix is sufficient to allow demetalation of the template center (by CN{sup {minus}} or SCN{sup {minus}}) without collapse of the three-dimensional structure. Such a property is related to the expected complex topology of the material prepared. The organic backbone certainly contains interlocking rings and various network substructures. The free ligand polymer film can be recomplexed using an appropriate metal source. The polymer matrix thus keeps a memory of the templating metal used for building it. Copper (I) turned out to be the most convenient template during the polymer electrosynthesis and seemed to lead to the most structured network. The various complexes obtained using the electrosynthesis method display electrochemical properties analogous to those of the corresponding catenates in solution. Here again, low oxidation states like copper (I), cobalt(I), formal zinc(I), and silver (0) are remarkably stabilized by the entwined and entangled system. Conductivity measurements and detailed electrochemical and spectroelectrochemical studies on several films have been carried out. 31 refs., 10 figs., 3 tabs.

Bidan, G.; Divisia-Blohorn, B.; Lapkowski, M. [Centre d`Etudes Nuclearires de Grenoble (France)] [and others

1992-07-15

29

Polymer-anchored vanadium(IV), molybdenum(VI) and copper(II) complexes of bidentate ligand as catalyst for the liquid phase oxidation of organic substrates  

Microsoft Academic Search

Monobasic bidentate ligand 2-(2?-hydroxyphenyl)benzimidazole (Hhpbmz) has been covalently bonded to the chloromethylated polystyrene cross-linked with 5% divinylbenzene. Treatment of the resulted chelating resin, abbreviated as PS-Hhpbmz, with [VO(acac)2], [MoO2(acac)2] (Hacac=acetylacetone) and Cu(CH3COO)2·H2O, gave polymer-anchored complexes PS-[VO(hpbmz)2], PS-[MoO2(hpbmz)2] and PS-[Cu(hpbmz)2], respectively. The corresponding neat complexes with Hhpbmz have also been prepared similarly. Structures of these complexes have been established on the

Mannar R. Maurya; Maneesh Kumar; Umesh Kumar

2007-01-01

30

Hypersensitivity to suture anchors.  

PubMed

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

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

2013-07-11

31

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

32

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

33

Potential uses of silica-bonded macrocyclic ligands for separation of metal ions from nuclear waste  

Microsoft Academic Search

This paper explores the potential of a relatively new separation material that is obtained by covalently binding macrocyclic ligands to silica gel. Fortunately, neutral macrocyclic ligands can be bound to silica gel such that metal binding constants do not differ significantly from the binding constants of the free ligands so that selectivities of free macrocyclic ligands can be used in

R. L. Bruening; D. M. Camaioni; N. G. Colton; J. R. Morrey

1991-01-01

34

Incorporation of glycosylphosphatidylinositol-anchored granulocyte- macrophage colony-stimulating factor or CD40 ligand enhances immunogenicity of chimeric simian immunodeficiency virus-like particles.  

PubMed

The rapid worldwide spread of human immunodeficiency virus (HIV) mandates the development of successful vaccination strategies. Since live attenuated HIV is not accepted as a vaccine due to safety concerns, virus-like particles (VLPs) offer an attractive safe alternative because they lack the viral genome yet they are perceived by the immune system as a virus particle. We hypothesized that adding immunostimulatory signals to VLPs would enhance their efficacy. To accomplish this we generated chimeric simian immunodeficiency virus (SIV) VLPs containing either glycosylphosphatidylinositol (GPI)-anchored granulocyte-macrophage colony-stimulating factor (GM-CSF) or CD40 ligand (CD40L) and investigated their biological activity and ability to enhance immune responses in vivo. Immunization of mice with chimeric SIV VLPs containing GM-CSF induced SIV Env-specific antibodies as well as neutralizing activity at significantly higher levels than those induced by standard SIV VLPs, SIV VLPs containing CD40L, or standard VLPs mixed with soluble GM-CSF. In addition, mice immunized with chimeric SIV VLPs containing either GM-CSF or CD40L showed significantly increased CD4(+)- and CD8(+)-T-cell responses to SIV Env, compared to standard SIV VLPs. Taken together, these results demonstrate that the incorporation of immunostimulatory molecules enhances humoral and cellular immune responses. We propose that anchoring immunostimulatory molecules into SIV VLPs can be a promising approach to augmenting the efficacy of VLP antigens. PMID:17108046

Skountzou, Ioanna; Quan, Fu-Shi; Gangadhara, Sailaja; Ye, Ling; Vzorov, Andrei; Selvaraj, Periasamy; Jacob, Joshy; Compans, Richard W; Kang, Sang-Moo

2006-11-15

35

Studies on charge distribution and valence tautomerism in transition metal complexes of catecholate and semiquinonate ligands  

Microsoft Academic Search

Transition metal complexes containing first row metal ions chelated by catecholate (Cat) and semiquinonate (SQ) ligands have been found to have localized electronic structures with quinone ligands bonded in both SQ and Cat electronic forms. In exceptional cases the balance of metal and quinone orbital energies is sufficiently close as to permit magnetic and spectroscopic observations on isomers differing in

Cortlandt G. Pierpont

2001-01-01

36

trans effect and trans influence: importance of metal mediated ligand-ligand repulsion.  

PubMed

The trans effect and trans influence were investigated and rationalized in the aminolysis, a typical nucleophilic substitution reaction, of trans-TPtCl2NH3 complexes (T = NH3, PH3, CO and C2H4) using energy decomposition analysis, both along the reaction paths and on the stationary points, and Natural Orbital for Chemical Valence analysis. In order to scrutinize the underlying principles and the origin of the kinetic trans effect, plausible structural constraints were introduced in the decomposition analysis, which allowed eliminating the distance dependence of the interaction energy components. It was established that the trans effect can be rationalized with the interaction of the TPtCl2 and NH3 fragments in the reactant state and TPtCl2 and (NH3)2 fragments in the transition state. It was evinced quantitatively that the ?-donor ability of T indeed controls the stability of the reactant, whereas in the case of ?-acids, backdonation stabilizes the transition state, for which conceptually two mechanisms are available: intrinsic and induced ?-backdonation. In the destabilization of the reactant and also in the labilization of the leaving group (trans influence) repulsion plays a more important role than orbital sharing effects, which are the cornerstones of the widely accepted interpretations of the trans influence, such as competition for donation or limitation of the donation of the leaving group by the trans ligand T. This repulsive interaction was rationalized both in terms of donated electron density and also in the molecular orbital framework. NOCV orbitals indeed clearly show that the ?-trans effect can be envisioned as a donation from the trans ligand not only to the metal but also to the ?* orbital of the metal-leaving group bond, which manifests as a repulsion between the metal and the leaving group. PMID:24022294

Pinter, Balazs; Van Speybroeck, Veronique; Waroquier, Michel; Geerlings, Paul; De Proft, Frank

2013-09-25

37

Anchor stores  

Microsoft Academic Search

Planned shopping malls usually have one or more department (anchor) stores and multiple specialized retailers selling substitutable commodities in each commodity category. If consumers know their taste for the anchor's commodity and its price, but learn about a retailer's commodity only by costly search, collocation may benefit both store types. Intra-mall competition reduces markups, but anchors guarantee a minimum surplus

Hideo Konishi; Michael T. Sandfort

2003-01-01

38

Novel vitamin D receptor ligands having a carboxyl group as an anchor to arginine 274 in the ligand-binding domain.  

PubMed

Vitamin D3 is metabolized into the hormonally active form, 1alpha,25-dihydroxyvitamin D3 (1), via 25-hydroxyvitamin D3 (2) which is the most abundant circulating metabolite. Introduction of the 1alpha-hydroxyl group into 25-hydroxyvitamin D3 (2) to produce 1alpha,25-dihydroxyvitamin D3 (1) increases the VDR binding affinity by approximately 1000-fold. The X-ray crystal structure of human VDR in complex with 1alpha,25-dihydroxyvitamin D3 (1) shows that, together with Ser-237, the 1alpha-hydroxyl group of 1alpha,25-dihydroxyvitamin D3 (1) makes hydrogen bonds with Arg-274, single mutation of which results in impaired ligand recognition. In 2002, lithocholic acid, which possesses a carboxyl group at position C24, was demonstrated to be a weak VDR ligand. We speculated that the carboxylic acid of lithocholic acid could be recognized by Arg-274 in the ligand-binding domain of VDR. In view of the significance of Arg-274 to direct the 1alpha-hydroxyl group, as well as the results with lithocholic acid and its derivatives, we designed the C2 modified analogues of 25-hydroxylvitamin D3 (2) having a carboxyl group, instead of the 1-hydroxyl group, for better electrostatic interaction to the guanidinium side-chain of arginine. PMID:20435140

Fujishima, Toshie; Tsuji, Genichiro; Tanaka, Chika; Harayama, Hiroshi

2010-05-06

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

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

41

Biological activity studies on metal complexes of novel tridentate Schiff base ligand. Spectroscopic and thermal characterization  

Microsoft Academic Search

Metal complexes of novel Schiff base (HL) ligand, prepared via condensation of 4-aminoantipyrine and 2-aminophenol, are prepared. The ligand is characterized based on elemental analysis, mass, IR and 1H NMR spectra. Metal complexes are reported and characterized based on elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, ESR spectra and thermal analyses (TG, DTG and DTA). From

Gehad G. Mohamed; M. M. Omar; Amr A. Ibrahim

2009-01-01

42

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

43

Evaluation of Metal-Mediated DNA Binding of Benzoazole Ligands by Electrospray Ionization Mass Spectrometry  

PubMed Central

The binding of a series of benzoxazole analogs with different amide- and ester-linked side chains to duplex DNA in the absence and presence of divalent metal cations is examined. All ligands were found to form complexes with Ni2+, Cu2+, and Zn2+, with 2:1 ligand/metal cation binding stoichiometries dominating for ligands containing shorter side chains (2, 6, 7, and 8), while 1:1 complexes were the most abundant for ligands with long side chains (9, 10 and 11). Ligand binding with duplex DNA in the absence of metal cations was assessed, and the long side-chain ligands were found to form low abundance complexes with 1:1 ligand/DNA binding stoichiometries. The ligands with the shorter side chains only formed DNA complexes in the presence of metal cations, most notably for 7 and 8 binding to DNA in the presence of Cu2+. The binding of long side-chain ligands was enhanced by Cu2+ and to a lesser degree by Ni2+ and Zn2+. The cytotoxicities of all of the ligands against the A549 lung cancer and MCF7 breast cancer cell lines were also examined. The ligands exhibiting the most dramatic metal-enhanced DNA binding also demonstrated the greatest cytotoxic activity. Both 7 and 8 were found to be the most cytotoxic against the A549 lung cancer cell line and 8 demonstrated moderate cytotoxicity against MCF7 breast cancer cells. Metal ions also enhanced the DNA binding of the ligands with the long side-chains, especially for 9, which also exhibited the highest level of cytotoxicity of the long side-chain compounds.

Mazzitelli, Carolyn L.; Rodriguez, Mireya; Kerwin, Sean; Brodbelt, Jennifer S.

2008-01-01

44

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

45

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

46

Low molecular weight metal ligands: Indicators of metal-induced stress  

SciTech Connect

The authors have used EDTA-based metal chelate buffer system to control the speciation of Cd in seawater in order to examine the relationships between free Cd ion activity (Cd{sup +2}) and Cd bioavailability, accumulation and toxicity in the errant polychaete, Neanthes arenceodentata. At external concentrations of (Cd{sup +2}) below 10{sup {minus}10} M, the accumulated dose of Cd in the organism at steady state condition is proportional to the concentrations of metal in the media. An order of magnitude increase in total body load of Cd is observed for each order of magnitude increase in (Cd{sup +2}) in the seawater. At (Cd{sup +2}) greater than 10{sup {minus}9} M, however, the accumulation of Cd by the organisms exceeded proportionality relative to the (Cd{sup +2}) in the seawater. Subcellular fractionation studies show that this increase in accumulation in total body load is due to the combined effects of increased metal accumulation in two cytosolic ligand pools. At 10{sup {minus}9} M (Cd{sup +2}), there is elevated levels of Cd in the metallothionein pool (MT) which appears to reflect induction of the protein. At Cd{sup +2} higher than 10{sup {minus}8} M, there is no further accumulation of Cd on MT, but there is a dramatic increase of Cd in the low molecular weight ligand pool.

Mason, A.Z.; Jenkins, K.D. (California State Univ., Long Beach (USA))

1988-09-01

47

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

48

Determination of Compositions of Some Metal-Ligand Complexes by Hptlc-Densitometry  

Microsoft Academic Search

The well known methods of Job's continuous variations and mole-ratio were used for the determination of the compositions of some metal-N,N-diethyl-N?-benzoyl-thiourea complexes chromatographically using HPTLC-densitometry. A different and a simple application of these two methods makes the determination of the composition of metal-ligand complexes possible even when the maximum absorption wavelengths of ligand and complexes are close to each other.

M. Merdivan; R. S. Aygün; N. Külcü

1998-01-01

49

Electroactive films of polypyrroles containing complexing cavities preformed by entwining ligands on metallic centers  

Microsoft Academic Search

New functionalized polypyrrole films containing transition metal complexes have been prepared and studied. The strategy is based on the three-dimensional template effect of a metal center (Cu¹, Co{sup II}, Zn{sup II}, Ag{sup I}) able to entwine two end-functionalized chelating ligands before polymerization. The ligands used consist of a 2,9-diphenyl-1,10-phenanthroline subunit (dpp) bearing two pyrrole nuclei. The pseudotetrahedral geometry of the

Gerard Bidan; Bernadette Divisia-Blohorn; Mieczyslaw Lapkowski; Jean Marc Kern; Jean Pierre Sauvage

1992-01-01

50

Direct assembly synthesis of metal complex-semiconductor hybrid photocatalysts anchored by phosphonate for highly efficient CO2 reduction.  

PubMed

Hybrid photocatalysts consisting of a ruthenium complex and p-type photoactive N-doped Ta(2)O(5) anchored with an organic group were successfully synthesized by a direct assembly method. The photocatalyst anchored by phosphonate exhibited excellent photoconversion activity of CO(2) to formic acid under visible-light irradiation with respect to the reaction rate and stability. PMID:21713249

Suzuki, Tomiko M; Tanaka, Hiromitsu; Morikawa, Takeshi; Iwaki, Masayo; Sato, Shunsuke; Saeki, Shu; Inoue, Masae; Kajino, Tsutomu; Motohiro, Tomoyoshi

2011-06-28

51

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

SciTech Connect

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

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

2008-03-13

52

Direct synthesis of coordination compounds from zerovalent metals and organic ligands  

NASA Astrophysics Data System (ADS)

Data on the direct synthesis of coordination compounds from zerovalent metals and organic ligands are surveyed and described systematically. The preparation of metal complexes in the gas and liquid phases is considered. It is shown that the direct syntheses are single-stage processes and make it possible to obtain all types of coordination compounds — molecular and ?-complexes, metal chelates, and dinuclear and polynuclear structures. Problems of competitive reactions in the course of the direct synthesis of complexes of ambident ligand systems are discussed. The bibliography includes 289 references.

Garnovskii, Alexander D.; Kharisov, B. I.; Gojon-Zorrilla, G.; Garnovskii, D. A.

1995-03-01

53

Heterogeneous processes affecting metal ion transport in the presence of organic ligands: Reactive transport modeling  

NASA Astrophysics Data System (ADS)

The development of models to accurately simulate metal ion transport through saturated systems under variable chemical conditions, e.g., in systems containing organic ligands (L) such as natural organic matter (NOM), has two essential aspects: (1) establishing the ability to simulate metal ion sorption to aquifer solids over a range of metal/ligand ratios; and (2) to incorporate this ability to simulate metal speciation over a range in chemical conditions (e.g., pH, ligand activity) into mass transport models. Modeling approaches to evaluate metal ion sorption and transport in the presence of NOM include: (1) isotherm-based transport models, and (2) multicomponent (MC) transport models. The accuracy of transport models depends on how well the chemical interactions affecting metal ion transport in the presence of organic ligands (e.g., metal/ligand complexation) are described in transport equations. The isotherm-based transport models often fail to accurately describe metal ion transport in the presence of NOM since these models treat NOM as a single solute despite the fact that NOM is a multicomponent mixture of subcomponents with different chemical and polyfunctional behavior. On the other hand, the calculations presented in this study suggest that a multicomponent reactive transport model, in conjunction with a mechanistic modeling approach for the description of metal ion binding by NOM in a manner conducive to the application of surface complexation modeling (SCM), can effectively be used as an important predictive tool in simulating metal ion sorption and transport under variable chemical conditions in the presence of NOM.

Kantar, Cetin

2007-04-01

54

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

55

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

56

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

57

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

2012-10-18

58

Theoretical Modeling of Hydrogen Bonded and Metal-Ligand Associating Polymers  

NASA Astrophysics Data System (ADS)

Applying analytical modeling in combination with Monte Carlo simulations we have studied the association behavior and properties of two types of supramolecular polymers employing 1) hydrogen bonded and 2) metal-ligand associative motifs. In the first case association between the hydrogen bonded arrays results in numerous donor-acceptor interactions between the complementary end groups of linear oligomers leading primarily to formation of linear chains or rings. Similar architectures of self-assembled polymers can also be obtained by reversible 1:2 complex formation between metal ions (such as Zn(+2), Cd(+2), Co (+2), etc.) and ligands of end-functionalized oligomers. In this case the association is strongly influenced by metal- ligand ratio. We analyze the chain-ring equilibrium and study the influence of the strength and type of association, rigidity of the complex and solution composition on the degree of association and the average molecular weight of the supramolecular polymers. For metal ions (such as La(+3), Nd(+3), Eu(+3), etc) capable of 1:3 complex formation with the ligands, self-assembly results in reversible polymers of more complex architecture, in particular a reversible network (in the percolation limit). Since the coordination sites of the metal possess unequal reactivity (having different energies of association with the first, second and third ligand) and due to the cooperativity of binding, network formation is influenced by different factors such as metal/ligand ratio, oligomer length and concentration. Predictions of an analytical model based on the equilibrium among different associating species and classical percolation theory compare favorably with simulation results for gel fraction and average molecular weight. Simulation results and theoretical predictions will be compared with available experimental data.

Dormidontova, Elena

2006-03-01

59

Biological activity studies on metal complexes of novel tridentate Schiff base ligand. Spectroscopic and thermal characterization.  

PubMed

Metal complexes of novel Schiff base (HL) ligand, prepared via condensation of 4-aminoantipyrine and 2-aminophenol, are prepared. The ligand is characterized based on elemental analysis, mass, IR and (1)H NMR spectra. Metal complexes are reported and characterized based on elemental analyses, IR, (1)H NMR, solid reflectance, magnetic moment, molar conductance, ESR spectra and thermal analyses (TG, DTG and DTA). From the elemental analyses, 1:1 [M]:[ligand] complexes are prepared with the general formulae [M(L)Cl(H(2)O)(2)] x yH(2)O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), y = 3-4), [Fe(L)Cl(2)(H(2)O)] x 3 H(2)O and [Th(L)Cl(H(2)O)(2)]Cl(2) x 3 H(2)O. The molar conductance data reveal that all the metal chelates are non-electrolytes (except Th(IV) complex, it is 2:1 electrolyte). IR spectra show that HL is coordinated to the metal ions in a uninegatively tridentate manner with NNO donor sites of the azomethine-N, amino N and deprotonated phenolic-O. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral. 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 are calculated from the DTG curves using Coats-Redfern method. The synthesized ligand, in comparison to its metal complexes is screened for its antibacterial activity against bacterial species, Escherichia coli, Pseudomonas putida, Exiguobacterium acetylicum and Bacillus simplex. The activity data show that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species. PMID:19758728

Mohamed, Gehad G; Omar, M M; Ibrahim, Amr A

2009-08-06

60

Complications of Bioabsorbable Suture Anchors in the Shoulder  

Microsoft Academic Search

The development of the suture anchor has played a pivotal role in the transition from open to arthroscopic techniques of the shoulder. Various suture anchors have been manufactured that help facilitate the ability to create a soft tissue to bone repair. Because of reported complications of loosening, migration, and chondral injury with metallic anchors, bioabsorbable anchors have become increasingly used

Aman Dhawan; Neil Ghodadra; Vasili Karas; Michael J. Salata; Brian J. Cole

2012-01-01

61

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

62

Metal Complexes of Macrocyclic Schiff-Base Ligand: Preparation, Characterisation, and Biological Activity  

PubMed Central

A new macrocyclic multidentate Schiff-base ligand Na4L consisting of two submacrocyclic units (10,21-bis-iminomethyl-3,6,14,17-tricyclo[17.3.1.18,12]tetracosa-1(23),2,6,8,10,12(24),13,17,19,21,-decaene-23,24-disodium) and its tetranuclear metal complexes with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) are reported. Na4L was prepared via a template approach, which is based on the condensation reaction of sodium 2,4,6-triformyl phenolate with ethylenediamine in mole ratios of 2?:?3. The tetranuclear macrocyclic-based complexes were prepared from the reaction of the corresponding metal chloride with the ligand. The mode of bonding and overall geometry of the compounds were determined through physicochemical and spectroscopic methods. These studies revealed tetrahedral geometries about Mn, Co, and Zn atoms. However, square planar geometries have been suggested for NiII and CuII complexes. Biological activity of the ligand and its metal complexes against Gram positive bacterial strain Staphylococcus aureus and Gram negative bacteria Escherichia coli revealed that the metal complexes become more potentially resistive to the microbial activities as compared to the free ligand. However, these metal complexes do not exhibit any effects on the activity of Pseudomonas aeruginosa bacteria. There is therefore no inhibition zone.

Ahmed, Riyadh M.; Yousif, Enaam I.; Hasan, Hasan A.; Al-Jeboori, Mohamad J.

2013-01-01

63

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

Microsoft Academic Search

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)

Ramazan Gup; Bülent Kirkan

2006-01-01

64

Potential uses of silica-bonded macrocyclic ligands for separation of metal ions from nuclear waste  

SciTech Connect

This paper explores the potential of a relatively new separation material that is obtained by covalently binding macrocyclic ligands to silica gel. Fortunately, neutral macrocyclic ligands can be bound to silica gel such that metal binding constants do not differ significantly from the binding constants of the free ligands so that selectivities of free macrocyclic ligands can be used in designing silica-bound materials with appropriate selectivities. Accordingly, macrocyclic ligands known to have selectivities for Pd{sup +2}, Ag{sup +}, Ru{sup +3}, Sr{sup +2}, and Cs{sup +} were covalently bound to silica gel. These materials were then tested for their ability to separate these ions from a synthetic test solution representative of a nuclear process waste stream. Cs{sup +} and Sr{sup +2} are of interest because their radioactive isotopes are major radioactive constituents of defense nuclear wastes accumulated at the Hanford site. Removal of precious metals such as Pd{sup +2}, Ag{sup +} and Ru{sup +3} present in nuclear defense waste are of interest not just because of their obvious economic value, but also because these metals may hinder the waste vitrification process for confining radionuclides.

Bruening, R.L. (IBC Advanced Technologies, Inc., Provo, UT (United States)); Camaioni, D.M.; Colton, N.G.; Morrey, J.R. (Pacific Northwest Lab., Richland, WA (United States))

1991-11-01

65

Spectroscopic characterization of tetradentate macrocyclic ligand: it's transition metal complexes  

NASA Astrophysics Data System (ADS)

Manganese(II), cobalt(II), nickel(II) and copper(II) complexes are synthesized with a novel tetradentate ligand viz. 1,3,9,11-tetraaza-4,8,12,16-tetraoxo-2,6,10,14-tetrathiacyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, electron impact mass, 1H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes. Thus these complexes may be formulated as [M(L)X 2] and [Ni(L)]X 2 (where M: Mn(II), Co(II), and Cu(II) and X = Cl - and NO 3-). On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.

Chandra, Sulekh; Gupta, Lokesh Kumar

2004-10-01

66

DITHIOPHOSPHONATES AND RELATED P\\/S-TYPE LIGANDS OF GROUP 11 METALS  

Microsoft Academic Search

Within the phosphor-1,1,-dithiolate class of compounds, the dithiophosphonato ligand [S2PAr(OR?)] (typically Ar = aryl or ferrocenyl; R? = alkyl) has emerged as an interesting choice for the preparation of a variety of new metal complexes. This review focuses on the dithiophosphonates and certain related thio species of the group 11 coinage metals, copper, silver and gold, with particular emphasis on structure and coordination modes.

Werner E. Van Zyl

2010-01-01

67

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

Microsoft Academic Search

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

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

2011-01-01

68

Structural and Electronic Comparison of 1st Row Transition Metal Complexes of a Tripodal Iminopyridine Ligand.  

PubMed

We report the preparation and characterization of a series of divalent 3d transition metal complexes (Cr to Zn, 1-7), featuring the multidentate, tripodal iminopyridine Schiff-base ligand trimethyl 6,6',6?-((1E,1'E,1?E)-((nitrilotris(ethane-2,1-diyl))tris(azanylylidene))tris-(methanylylidene))trinicotinate (L(5-OOMe)). X-ray structural studies carried out on 1-5 and 7 reveal complex geometries ranging from local octahedral coordination to significant distortion toward trigonal prismatic geometry to heptacoordinate environments. Regardless of coordination mode, magnetic and spectroscopic studies show the ligand to provide moderately strong ligand fields: the Fe complex is low-spin, while the Co and Mn complexes are high-spin at all temperatures probed. Cyclic voltammograms exhibit multiple reversible ligand-based reductions, which are relatively consistent throughout the series; however, the electrochemical behavior of the Cr complex 1 is fundamentally different from those of the other complexes. Time-dependent (TD) density functional theory (DFT) and natural transition orbital (NTO) computational analyses are presented for the ligand, its anion, and complexes 1-7: the computed spectra reproduce the major differential features of the observed visible absorption spectra, and NTOs provide viable interpretations for the observed features. The combined studies indicate that all complexes contain neutral ligands bound to M(II) ions, except for the Cr complex 1, which is best described as a Cr(III) species bound to a radical anionic ligand. PMID:23136902

McDaniel, Ashley M; Rappé, Anthony K; Shores, Matthew P

2012-11-01

69

RELATIONSHIPS OF ACTIVITIES OF METAL-LIGAND SPECIES TO AQUATIC TOXICITY  

EPA Science Inventory

Water quality criteria for toxicity of metal-ligand species to aquatic life are investigated by computer modeling. The speciation calculations are performed using REDEQL2. Correlations of toxicity to concentrations (or activities) of particular species or types of species are dis...

70

Early-transition-metal catalysts with phenoxy-imine-type ligands for the oligomerization of ethylene.  

PubMed

Early-transition-metal complexes incorporating phenoxy-imine-type bidentate and tridentate ligands, after activation, can achieve selective as well as nonselective ethylene oligomerization to produce 1-hexene, linear ?-olefins, and vinyl-terminated low-molecular-weight polyethylenes, all with high efficiency. PMID:21254407

Kinoshita, Shinsuke; Kawamura, Kazumori; Fujita, Terunori

2011-01-11

71

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

72

Borane-mediated silylation of a metal-oxo ligand.  

PubMed

The addition of 1 equiv of HSiPh(3) to UO(2)((Ar)acnac)(2) ((Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3)), in the presence of 1 equiv of B(C(6)F(5))(3), results in the formation of U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2) (1), via silylation of an oxo ligand and reduction of the uranium center. The addition of 1 equiv of Cp(2)Co to 1 results in a reduction to uranium(IV) and the formation of [Cp(2)Co][U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2)] (2) in 78% yield. Complexes 1 and 2 have been characterized by X-ray crystallography, while the solution-phase redox properties of 1 have been measured with cyclic voltammetry. PMID:21553868

Schnaars, David D; Wu, Guang; Hayton, Trevor W

2011-05-09

73

Novel lanthanide–transition-metal coordination polymer materials: Crystal engineering challenges and a ligand-directed assembly strategy  

Microsoft Academic Search

The challenge on lanthanide–transition-metal (Ln–M) coordination polymer crystals and a corresponding ligand-directed assembly strategy of crystal engineering were studied. The multifunctional isonicotinate with mixed donor sites was selected as the directing ligand to link lanthanide and transition-metal ions on the basis of the coordination nature of both different types of metal ions. A new three-dimensional (3D) Ln–M heterometallic coordination polymer

Wanyan Xiao; Xiaojun Gu; Dongfeng Xue

2009-01-01

74

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

75

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

NASA Astrophysics Data System (ADS)

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

Hoch, Cortney Leigh

76

Electrophilic metal alkyl chemistry in new ligand environments  

SciTech Connect

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

Jordan, Richard F.

2002-09-11

77

De Novo Design of Ligands for Metal Separation - Final Report - 09/15/1996 - 09/14/2000  

SciTech Connect

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 (structure-based design), including the prediction of affinity. Adaptation of the algorithms to place donor atoms at appropriate geometrical locations surrounding the metal of interest, rather than filling up a cavity with donor/acceptor atoms placed optimally to interact with a protein active site, is straightforward. Appropriate geometrical parameters for metals can be derived from crystal structures and force constants adapted from recent advances in theories of metal-ligand interactions. The practical goal is computer-aided design of ligands which would be selective for one metal over another with a predicted selectivity ratio and affinity.

Marshall, Garland, R.

2001-09-14

78

Differentially ligand-functionalized microcantilever arrays for metal ion identification and sensing.  

PubMed

A microcantilever array sensor with cantilevers differentially functionalized with self-assembled monolayers (SAMs) of thiolated ligands is prepared by simultaneous capillary coating. This array is described for the detection of metal ions including Li+, Cs+, Cu2+, Co2+, Fe3+, and Al3+. Binding of the charged metal cations to the surface of the microcantilever sensors produces surface stress that causes bending of the cantilevers that is detected as tip deflection using an array of vertical cavity surface emitting lasers and a position-sensitive detector. Optimization studies of the nanostructured dealloyed surface were performed for SAMs based on their response to Cu2+ cations. Sensor performance experiments demonstrate good sensitivity toward metal ions, with limits of detection as low as 10(-8) molar. A multiplex capillary coating method for cantilever array creation is demonstrated and validated based on surface-enhanced Raman spectra obtained from adjacent cantilevers that were functionalized with different thiolated SAMs. The cantilever array coated with a range of thiolated ligands was exposed to the group of metal ions. The response characteristics of each metal ion show substantial diversity, varying not only in response magnitude, but response kinetics. A pattern recognition algorithm based on a combination of independent component analysis and support vector machines was able to validate that the sensor array response profiles produced enough information content that metal ions could be reliably classified with probabilities as high as 89%. PMID:17705449

Chapman, Peter J; Long, Zhou; Datskos, Panos G; Archibald, Richard; Sepaniak, Michael J

2007-08-18

79

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

80

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

Microsoft Academic Search

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

Brian C. Peoples; René S. Rojas

81

Theoretical curves in indicator photometric titration of monodentate polyatomic ligands by metal ions  

SciTech Connect

On the basis of the law of mass action and material balance conditions, theoretical equations have been derived for the curves obtained in indicator photometric titration of anionic ligands by metal ions for the cases of formation of complexes ML, M/sub 2/L, and ML/sub 2/. Correspondence between theoretical and experimental titration curves has been demonstrated, thus making it possible to explain the factual material and to use reactions of low-stability complex formation in photometric titrations.

Kuznetsov, V.V.; Shamanskii, V.A.

1986-03-20

82

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

PubMed Central

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

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

2011-01-01

83

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

Microsoft Academic Search

In this study, we prepared the Schiff base ligand (L) and its Cu(II), Co(II) and Ni(II) complexes. The compounds were characterized by the analytical and spectroscopic methods. The ligand (L) behaves as a bidentate ligand and coordinates to the metal ions via the nitrogen atoms. The complexes have the mononuclear structures. The analytical and spectroscopic results indicated that the chloride

Mustafa Dolaz; Vickie McKee; Serhan Urus; Necmettin Demir; Ali E. Sabik; Aysegül Gölcü; Mehmet Tümer

2010-01-01

84

Ligand interchange controls many oxidations of divalent first-row transition metal ions by free radicals  

SciTech Connect

These studies suggest that the rate-determining step in the oxidation of a large variety of transition metal complexes by free radicals is the ligand exchange step. In other words it is proposed that free radicals behave in many reactions with transition metal complexes as incoming nucleophilic ligands. It seemed of interest to investigate this speculative statement in more detail. It was decided therefore to study the interaction of various Mn(II), Fe(II), and Co(II) complexes with a variety of free radicals. These ions were selected as it was shown that Mn(II) ligand exchange processes processed usually via the I[sub a] mechanism, whereas those of Fe(II) and Co(II) proceed usually via the I[sub d] mechanism. The selected reactions are such that they were all suggested to proceed via the inner-sphere mechanism as their rates of reaction are nearly independent of the nature of the free radical and can therefore be considered as typical complex formation reactions as shown earlier. The pressure dependence of the studied reactions enables a detailed comparison with the volumes of activation for solvent exchange and complex formation reactions of these divalent first-row transition elements. Futhermore, it allows the authors to comment on the general behavior of free radicals during complex formation reactions with different metal centers.

Eldik, R. van (Univ. of Witten/Herdecke, Witten (Germany)); Cohen, H. (Nuclear Research Centre Negev, Beer-Sheva (Israel)); Meyerstein, D. (R. Bloch Coal Research Center and Chemistry Department, Beer-Sheva (Israel))

1994-03-30

85

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

SciTech Connect

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

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

2008-02-11

86

Calorimetric Study of Ligand Interactions with Protons and Metal Ions in the 100 to 400 deg C Range.  

National Technical Information Service (NTIS)

The thermodynamic quantities (log K, delta H, delta S, and delta Cp) associated with the interactions of protons and metal ions with ligands in aqueous solutions are strongly influenced by the structure and properties of water. These quantities, especiall...

R. M. Izatt J. L. Oscarson S. E. Gillespie X. Chen P. Wang

1995-01-01

87

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

NASA Astrophysics Data System (ADS)

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 UO 2(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.

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

2011-01-01

88

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

2010-06-11

89

Thermoanaerobacter brockii alcohol dehydrogenase: characterization of the active site metal and its ligand amino acids.  

PubMed Central

The active-site metal ion and the associated ligand amino acids in the NADP-linked, tetrameric enzyme Thermoanaerobacter brockii alcohol dehydrogenase (TBADH) were characterized by atomic absorption spectroscopy analysis and site-directed mutagenesis. Our preliminary results indicating the presence of a catalytic zinc and the absence of a structural metal ion in TBADH (Peretz & Burstein. 1989. Biochemistry 28:6549-6555) were verified. To determine the role of the putative active-site zinc, we investigated whether exchanging the zinc for other metal ions would affect the structural and/or the enzymatic properties of the enzyme. Substituting various metal ions for zinc either enhanced or diminished enzymatic activity, as follows: Mn2+ (240%); Co2+ (130%); Cd2+ (20%); Cu2+ or V3+ (< 5%). Site-directed mutagenesis to replace any one of the three putative zinc ligands of TBADH, Cys 37, His 59, or Asp 150, with the non-chelating residue, alanine, abolished not only the metal-binding capacity of the enzyme but also its catalytic activity, without affecting the overall secondary structure of the enzyme. Replacing the three putative catalytic zinc ligands of TBADH with the respective chelating residues serine, glutamine, or cysteine damaged the zinc-binding capacity of the mutated enzyme and resulted in a loss of catalytic activity that was partially restored by adding excess zinc to the reaction. The results imply that the zinc atom in TBADH is catalytic rather than structural and verify the involvement of Cys 37, His 59, and Asp 150 of TBADH in zinc coordination.

Bogin, O.; Peretz, M.; Burstein, Y.

1997-01-01

90

Conjugated ligands modulated sandwich structures and luminescence properties of lanthanide metal-organic frameworks.  

PubMed

A conjugated ligand, 2-(carboxylic acid)-6-(2-benzimidazolyl) pyridine (Hcbmp), and a series of Lanthanide metal-organic frameworks (MOFs) [Ln(2)(cbmp)(ox)(3)(H(2)O)(2)](2)·2H(3)O(+)·7H(2)O (Ln = Sm (3), Eu (4), and Gd (5), H(2)ox = oxalic acid) have been designed and assembled. To elucidate how the conjugated ligands modulate the structures and luminescence properties, we carried out the structural characterizations and luminescence studies of complexes 3 and 4, and their corresponding oxalate complexes [Ln(ox)(1.5)(H(2)O)(3)]·2H(2)O (Ln = Sm (1) and Eu (2)) were also investigated for comparison. The changes of luminescence behaviors upon dehydration and D(2)O-rehydration processes are presented and discussed in detail. The results indicated that, the cbmp(-) ligands distribute on both sides of the ox(-)-Ln bilayer network to construct a sandwich structure. Moreover, the lowest triplet state of cbmp(-) ligands can match well the energy levels of the Sm(3+) and Eu(3+) cations which allow the preparation of new Ln-MOF materials with enhanced luminescence properties. Meanwhile, the crystallinity of solid states produces more substantial change in the luminescence behaviors than removal or replacement of effective nonradiative relaxers. PMID:21553823

Liu, Tian-Fu; Zhang, Wenjuan; Sun, Wen-Hua; Cao, Rong

2011-05-09

91

Metal-ligand complexes as a new class of long-lived fluorophores for protein hydrodynamics.  

PubMed Central

We describe the use of asymmetric Ru-ligand complexes as a new class of luminescent probes that can be used to measure rotational motions of proteins. These complexes are known to display luminescent lifetimes ranging from 10 to 4000 ns. In this report, we show that the asymmetric complex Ru(bpy)2(dcbpy) (PF6)2 displays a high anisotropy value when excited in the long wavelength absorption band. For covalent linkage to proteins, we synthesized the N-hydroxy succinimide ester of this metal-ligand complex. To illustrate the usefulness of these probes, we describe the intensity and anisotropy decays of [Ru(bpy)2(dcbpy)] when covalently linked to human serum albumin, concanavalin A (ConA), human immunoglobulin G (IgG), and Ferritin, and measured in solutions of increased viscosity. These data demonstrate that the probes can be used to measure rotational motions on the 10 ns to 1.5 microseconds timescale, which so far has been inaccessible using luminescence methods. The present probe [Ru(bpy)2(dcbpy)] can be regarded as the first of a class of metal-ligand complexes, each with different chemical reactivity and spectral properties, for studies of macromolecular dynamics. Images FIGURE 5 FIGURE 7

Terpetschnig, E; Szmacinski, H; Malak, H; Lakowicz, J R

1995-01-01

92

Alkali metal cation-ligand affinities: Basis set superposition correction for the Gaussian protocols  

NASA Astrophysics Data System (ADS)

The effect of basis set superposition error (BSSE) on Gaussian-2 and Gaussian-3 calculated alkali metal cation-ligand affinities has been studied. For these systems, we found that the standard Boys-Bernadi full counterpoise (CP) method often leads to correction terms that are physically incorrect. This problem may be rectified by using the geometry corrected counterpoise (GCP) method. The relationship between CP, GCP corrections, and deformation energy is discussed. In order to yield good agreement with existing experimental Li+ and Na+ ligand affinities, we recommend the adoption of either the G3 (with GCP correction) or the G2(MP2,SVP)-FC (without GCP correction) protocols. In the case of K+, the GCP correction is of negligible magnitude, and hence GCP corrections may be omitted in the G2(MP2,SVP)-ASC affinity calculations for these complexes.

Siu, F. M.; Ma, N. L.; Tsang, C. W.

2001-04-01

93

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

PubMed

In this study, the Schiff base ligand trans-N,N'-bis[(2,4-dichlorophenyl) methylidene] cyclohexane-1,2-diamine (L) and its copper(II), nickel(II) and palladium(II) transition metal complexes were prepared and characterized by the analytical and spectroscopic methods. The (1)H((13)C) NMR spectra of the ligand and its diamagnetic complexes were recorded in DMSO-d(6) solvent and obtained data confirm that the nitrogen atoms of the imine groups coordinated to the metal ions. Electrochemical properties of the ligand and its metal complexes were investigated in the DMF solvent at the 100 and 250 mVs(-1) scan rates. The ligand and metal complexes showed both reversible and irreversible processes at these scan rates. The single crystal of the ligand (L) was obtained from MeOH solution, and its crystal structure was determined by X-ray diffraction. The C-Hcdots, three dots, centeredCl hydrogen bonding interactions in the molecule were seen which increase the stability of the crystal structure. The antimicrobial activity studies of the ligand and its metal complexes were carried out by using the various bacteria and fungi. PMID:19646919

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

2009-07-15

94

Decontamination of solutions containing Cu(II) and ligands tartrate, glycine and quadrol using metallic iron.  

PubMed

Decontamination of solutions containing Cu(II) complexes with tartrate, glycine and quadrol (N,N,N'N'-tetrakis(2-hydroxypropyl)ethylenediamine) using metallic iron depends on pH and proceeds best in mildly acidic solutions. Cu(II) is completely removed from all solutions containing the ligands investigated. The degree of ligand removal from solutions considerably differs. Tartrate is relatively rapidly and completely removed from solutions. A complete removal of glycine is prolonged. The removal of quadrol from solutions using metallic iron is negligible. Electrochemical investigations showed that tartrate and glycine have inhibitory influence on anodic dissolution of iron at pH 2 and enhance it at pH 4. Quadrol does not exhibit any significant influence on iron dissolution. Chemical analysis and FT-IR investigations have shown that the content of organic compounds is the greatest in the precipitate formed in solutions containing tartrate, while it is considerably lower in glycine containing solutions. The precipitate formed in quadrol-containing solutions during the treatment with metallic iron contains only negligible amount of organics. PMID:19896768

Gyliene, Ona; Vengris, Tomas; Nivinskiene, Ona; Binkiene, Rima

2009-11-06

95

Phosphorescent properties of metal-free diphosphine ligands and effects of copper binding.  

PubMed

We studied the luminescence properties of copper(i) complexes containing bis[2-(diphenylphosphino)phenyl]ether (DPEphos), [Cu(DPEphos)(CH3CN)]PF6 (1), [Cu(DPEphos)2]PF6 (2), and copper(i) complexes with 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos), [Cu(xantphos)(CH3CN)2]PF6 (3), [Cu(xantphos)2]PF6 (4) in the solid state. The metal-free xantphos ligand shows weak phosphorescent emission at around 455 nm with an emission lifetime in the sub-microsecond range in the solid state at room temperature. When xantphos forms complex 4, it results in a nearly 4-fold increase in the emission quantum yield and emission lifetime, with a small shift in the emission maximum. In contrast, no such enhancement in the luminescence or increment in the emission lifetime was observed in complexes 1-3. The X-ray structural analysis of complexes 1-4 reveals a large vacant space in complexes 1-3 and in contrast, close packing of the ligands in complex 4 around the metal center. This indicates that the decrease in the free-space around the metal center results in a decrease in the geometric relaxation, suppressing the excited-state deactivation pathway. PMID:23996045

Yuasa, Junpei; Dan, Misato; Kawai, Tsuyoshi

2013-08-30

96

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

97

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

2013-07-19

98

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

99

[Ligand intermediates in metal-catalyzed reactions]. Progress report, July 1, 1989--June 30, 1992  

SciTech Connect

This report consists of sections on sigma bond complexes of alkenes, a new carbon-hydrogen bond activation reaction of alkene complexes, carbon-hydrogen bond migrations in alkylidene complexes, carbon- hydrogen bond migrations in alkyne complexes, synthesis, structure and reactivity of C{sub x} complexes, synthesis and reactivity of alcohol and ether complexes, new catalysts for the epimerization of secondary alcohols; carbon-hydrogen bond activation in alkoxide complexes, pi/sigma equilibria in metal/O=CXX` complexes, and other hydrocarbon ligands; miscellaneous.(WET)

Not Available

1992-08-01

100

Ligand-directed metal(II) coordination polymers: Unusual disorder, and photoluminescence  

Microsoft Academic Search

2,6-Dimethyl-4-phenylpyridine-3,5-dicarboxylic acid (H2mppdc, H2L) is firstly employed in coordination chemistry. Two metal-organic coordination polymers with a general formula of M2L2(4,4?-bpy)x(H2O)4?2x (M=Zn or Co, x=1 or 2) are assembled from H2L, 4,4?-bipyridine, zinc and cobalt salt under hydrothermal conditions, and characterized by single-crystal X-ray diffraction analyses. Of the crystal structures of title compounds, L ligands, limited in the environment from 4,4?-bipyridine,

Kun-Lin Huang

2008-01-01

101

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

102

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

NASA Astrophysics Data System (ADS)

Pyrazolyl diazine (?-NN) bridged late first row transition metal(II) complexes have been prepared by the interaction of metal(II) chlorides with an 'end-off' compartmental Schiff base ligand. The ligand system has a strong diazine bridging component and obtained as a condensation product between 1 H-pyrazole-3,5-dicarbohydrazide and 3-acetylcoumarin in absolute ethanol. All synthesized compounds are characterized on the basis of various spectral and analytical techniques. Complexes are found to be non-electrolytes and monomeric in nature. The magnetic exchange interactions are very weak because of the more electronegative exogenous chloride, though diazine bridging group bring metal centers in a close proximity.

Budagumpi, Srinivasa; Revankar, Vidyanand K.

2010-09-01

103

Utilizing Metal to Ligand Charge Transfer States of MM Quadruply Bonded Complexes for Photovoltaic Applications  

NASA Astrophysics Data System (ADS)

In this contribution, we report two examples of our efforts to develop MM quadruply bonded complexes for photovoltaic applications. In the first example, evidence, based on femtosecond transient absorption and time resolved infrared spectroscopy, is presented for photoinduced charge transfer from the Mo_{2}? orbital of the quadruply bonded molecule trans-Mo_{2}(TiPB)_{2}BTh)_{2}, where TiPB = 2,4,6-triisopropyl benzoate and BTh = 2,2'-bithienylcarboxylate, to di-n-octyl perylene diimide and di-n-hexylheptyl perylene diimide in thin films and solutions of the mixtures. In the second example, the structural and photophysical properties of the new compounds trans-M_{2}(TiPB)_{2}(L)_{2} and trans-M_{2}(TiPB)_{2}(L')_{2}, where M=Mo or W and L and L' are triphenylamine-cyanoacrylate ligands are presented. These ligands promote intense metal to ligand charge transfer transitions that span the range 550 to 1100 nm. The excited states have been studied by transient absorption and time resolved infrared spectroscopy

Lewis, Sharlene A.; Brown-Xu, Samantha E.; Chisholm, Malcolm H.; Epstein, Arthur J.

2013-06-01

104

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

2012-12-20

105

Metal-ligand multiple bonds as frustrated Lewis pairs for C-H functionalization  

PubMed Central

Summary The concept of frustrated Lewis pairs (FLPs) has received considerable attention of late, and numerous reports have demonstrated the power of non- or weakly interacting Lewis acid–base pairs for the cooperative activation of small molecules. Although most studies have focused on the use of organic or main-group FLPs that utilize steric encumbrance to prevent adduct formation, a related strategy can be envisioned for both organic and inorganic complexes, in which "electronic frustration" engenders reactivity consistent with both nucleophilic (basic) and electrophilic (acidic) character. Here we propose that such a description is consistent with the behavior of many coordinatively unsaturated transition-metal species featuring metal–ligand multiple bonds, and we further demonstrate that the resultant reactivity may be a powerful tool for the functionalization of C–H and E–H bonds.

2012-01-01

106

Indicator ligands in metal complexation studies: role of 4-(2-pyridylazo)resorcinol in europium carbonate equilibrium investigations  

Microsoft Academic Search

Spectrophotometric procedures utilizing the strongly complexing indicator 4-(2-pyridylazo)resorcinol (PAR) permit determination of 1:2 metal-ligand formation constants while substantially promoting metal solubility. The intricacies inherent in competitive equilibria involving PAR can be well-managed through use of low total metal-total indicator (PAR) ratios and observations of comparative complexation at constant pH. The influences of carbonate and oxalate complexation on the adsorbance of

Shannon W. Thompson; Robert H. Byrne

1988-01-01

107

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

PubMed

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

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

2010-03-18

108

Anchor Design and Bone Mineral Density Affect the Pull-Out Strength of Suture Anchors in Rotator Cuff RepairWhich Anchors Are Best to Use in Patients With Low Bone Quality?  

Microsoft Academic Search

Background: Different metal and biodegradable suture anchors are available for rotator cuff repair. Poor bone quality may result in anchor loosening and tendon rerupture.Hypotheses: Higher bone mineral density is associated with higher pull-out strength of suture anchors. Depending on anchor placement, pull-out strengths of anchors are different within the greater tuberosity.Study Design: Cadaveric biomechanical study.Methods: Trabecular and cortical bone mineral

Markus J. Tingart; Maria Apreleva; Janne Lehtinen; David Zurakowski; Jon J. P. Warner

2004-01-01

109

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

110

XAFS studies of metal-ligand interactions at organic surfaces and in solution  

NASA Astrophysics Data System (ADS)

X-ray absorption fine structure spectroscopy (XAFS) was used as a structural probe to determine the mechanism of metal adsorption to organic surfaces. Two specific systems were investigated, Pb adsorption to heneicosanoic acid Langmuir monolayers (CH3(CH2)19COOH), and Cd adsorption to isolated cell walls of the Bacillus subtilis bacterium. Although the study of these systems is important for quite different reasons, the goal in both is metal binding site speciation and structural characterization of the surface complex. The adsorption of aqueous Cd to B. subtilis was studied as a function of pH by fluorescence mode bulk XAFS. Samples were prepared at six pH values in the range 3.4 to 7.8, and the bacterial functional groups responsible for the adsorption were identified under each condition. Under the experimental Cd and bacterial concentrations, the spectroscopy results indicate that Cd binds predominantly to protonated phosphoryl ligands below pH 4.4, while at higher pH adsorption to carboxyl groups becomes increasingly important. At pH 7.8 we observe the activation of an additional binding site, which we tentatively ascribe to deprotonated phosphoryl ligands. A quantitative Cd speciation diagram for the pH range is presented. Grazing-incidence Pb L3 edge XAFS was used in situ to determine the adsorption complex structure in the Pb-Langmuir monolayer study. The results indicate covalent binding of the Pb cations to the carboxyl headgroups, and the observed Pb-Pb coordination suggests that the metal is adsorbed as a hydrolysis polymer, rather than as individual Pb 2+ ions. The data suggest a bidentate binding mechanism and a one Pb atom to one carboxyl headgroup binding stoichiometry. We discuss how this adsorption model can explain the peculiarities observed with Pb in previous metal-Langmuir monolayer studies. A systematic study of the metal local environment in aqueous solutions was conducted and used in the above analyses. Perchlorate and acetate salt solutions of Cd, Pb, Mn, Cr, and Cu were characterized as standards of hydrated ions and metal-carboxyl complexes. The utility of XAFS in differentiating between the ionic, monodentate, bridging-bidentate, and bidentate metal-carboxyl complexes through C-C multiple scattering effects and XANES features is demonstrated.

Boyanov, Maxim I.

111

Metal-substituted protein MRI contrast agents engineered for enhanced relaxivity and ligand sensitivity.  

PubMed

Engineered metalloproteins constitute a flexible new class of analyte-sensitive molecular imaging agents detectable by magnetic resonance imaging (MRI), but their contrast effects are generally weaker than synthetic agents. To augment the proton relaxivity of agents derived from the heme domain of cytochrome P450 BM3 (BM3h), we formed manganese(III)-containing proteins that have higher electron spin than their native ferric iron counterparts. Metal substitution was achieved by coexpressing BM3h variants with the bacterial heme transporter ChuA in Escherichia coli and supplementing the growth medium with Mn3+-protoporphyrin IX. Manganic BM3h variants exhibited up to 2.6-fold higher T1 relaxivities relative to native BM3h at 4.7 T. Application of ChuA-mediated porphyrin substitution to a collection of thermostable chimeric P450 domains resulted in a stable, high-relaxivity BM3h derivative displaying a 63% relaxivity change upon binding of arachidonic acid, a natural ligand for the P450 enzyme and an important component of biological signaling pathways. This work demonstrates that protein-based MRI sensors with robust ligand sensitivity may be created with ease by including metal substitution among the toolkit of methods available to the protein engineer. PMID:21171606

Lelyveld, Victor S; Brustad, Eric; Arnold, Frances H; Jasanoff, Alan

2011-02-01

112

Scaling Behavioral Anchors  

Microsoft Academic Search

Although behaviorally anchored rating scales (BARS) have both intuitive and empirical appeal, they have not always yielded superior results in contrast with graphic rating scales. The present study examined the issue of how behavioral descrip tions are anchored. Subjects scaled anchors describ ing teaching performance in a college classroom using either a graphic rating procedure or a pair- comparison procedure.

Frank J. Landy; Janet L. Barnes

1979-01-01

113

Reversible Ligand Exchange in a Metal-Organic Framework (MOF): Toward MOF-Based Dynamic Combinatorial Chemical Systems.  

PubMed

Reversible benzene dicarboxylate/2-bromobenzene dicarboxylate ligand exchange has been studied in the cubic metal-organic framework MOF-5. Significant exchange (up to ?50%), with continuous compositional variation, was observed using ex-situ (1)H NMR following treatment over ?6 h at ?85 °C in 10-40 mM ligand solutions. Exchange occurred without significant structural degradation as characterized by X-ray diffraction, nitrogen adsorption, and scanning electron microscopy. Solid-state (13)C NMR was used to show that exchanged ligands were incorporated into the framework lattice and not simply adsorbed within the pores. Exchange was found to be sensitive to the small free energy changes caused by the ligand concentration in the exchanging solution indicating that exchange is energetically nearly degenerate. This demonstration of reversible, nearly isoenergetic exchange indicates that mixed ligand MOFs could be developed as dynamic combinatorial chemical systems. PMID:23586479

Gross, Adam F; Sherman, Elena; Mahoney, Sky L; Vajo, John J

2013-05-01

114

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

Microsoft Academic Search

The analysis presented below suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms with no distinction between phenolic, carboxylic or inorganic hydroxide functional groups: logKML=?O logKHL+?O; where KML is the metal–ligand formation constant, KHL is the corresponding proton–ligand formation constant, and ?O and ?O are termed the Irving–Rossotti slope and intercept, respectively. Linear free energy relationships

Richard F. Carbonaro; Dominic M. Di Toro

2007-01-01

115

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

Microsoft Academic Search

The analysis presented below suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms with no distinction between phenolic, carboxylic or inorganic hydroxide functional groups: log KML = alphaO log KHL + betaO; where KML is the metal ligand formation constant, KHL is the corresponding proton ligand formation constant, and alphaO and betaO are termed the Irving

Richard F. Carbonaro; Dominic M. di Toro

2007-01-01

116

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

NASA Astrophysics Data System (ADS)

Using the chiral ligand N-acetyl-L-tyrosine (Hacty) and maintaining identical reaction conditions, Zn(II), Co(II), and Cd(II) salts provided four novel homochiral coordination polymers {[Zn(acty)(bipy)2(H2O)2]·NO3·2H2O}n1, {[Co(acty)(bipy)2(H2O)2]·NO3·2H2O}n2, {[Cd(acty)2(bipy)H2O]·H2O}n3, and {[Cd(acty)(bpe)2(Ac)]·6H2O}n4 (bipy=4,4?-bipyridine; bpe=1,2-di(4-pyridyl)ethane) in the presence of ancillary ligands. Compounds 1 and 2 are isostructural 1D chain structures. The neighboring chains are further linked into a 3D supramolecular structure via ?⋯? stacking and hydrogen bond interactions. Compound 3 shows a 2D network and 4 generates 1D infinite chains along the c-axis. Compounds 3 and 4 are further connected into 3D supramolecular network by hydrogen bond interactions. More importantly, coordination in acyl oxygen atoms and ancillary ligands (bpe) as monodentate decorating ligands in 4 are rarely reported. Ancillary ligands and metal cations significantly influence the structure of the complexes. The photoluminescence properties of 1, 3, and 4 were studied at room temperature. Circular dichroism (CD) of the complexes have been investigated.

Li, Meng-Li; Song, Hui-Hua

2013-10-01

117

SPECTRAL, ANTIMICROBIAL AND THERMAL STUDIES OF SOME TRANSITION METAL COMPLEXES DERIVED FROM BIDENTATE LIGANDS CONTAINING N AND S DONOR ATOMS  

Microsoft Academic Search

Bidentate ligands have been synthesized by the reaction of 2,4-dichlorobenzaldehyde with 4-amino-5-mercapto-1,2,4-triazole and 4-amino-5-mercapto-3-propyl-1,2,4-triazole. The ligands react with acetates of Co(II), Ni(II), Cu(II) and Zn(II) to yield 1:2 [metal: ligand] complexes. The newly synthesized compounds were characterized by elemental analyses, spectral (UV-Vis, IR, H NMR, fluorescence, ESR) studies, thermal techniques and magnetic measurements. Thermal studies of the complexes showed a

Kiran Singh; Yogender Kumar; Parvesh Puri; Chetan Sharma; Kamal Rai Aneja

2012-01-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

119

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

120

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

2011-06-21

121

Supramolecular isomers of metal-organic frameworks: the role of a new mixed donor imidazolate-carboxylate tetradentate ligand.  

PubMed

Five new metal-organic frameworks prepared from the ligand 5-bis(3-(1-imidazolyl)propylcarbamoyl)terephthalate (bipta(2-)) and transition metal salts, Zn(2+) (1), Co(2+) (2), Mn(2+) (3, 4) and Cu(2+) (5), are reported. Single crystal X-ray studies reveal that the bipta(2-) ligand acts as a tetradentate ligand and combines with four-coordinate cationic metal nodes to give four-connected framework structures. Whilst reaction of bipta(2-) with Zn(II) gives rise to a framework of diamondoid topology 1, the analogous frameworks with Co(II), Mn(II) and Cu(II) afford frameworks that incorporate square-planar nodes. Whereas 2 and 5 form frameworks of Cd(SO(4)) (cds) and square 4(4) nets (sql), respectively, reaction of Mn(II) with bipta(2-) forms two supramolecular isomers of topology cds for 3 and sql for 4. PMID:22301665

Richards, Victoria J; Argent, Stephen P; Kewley, Adam; Blake, Alexander J; Lewis, William; Champness, Neil R

2012-02-03

122

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

123

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

124

Density functional analysis of ancillary ligand electronic contributions to metal-mediated enediyne cyclization.  

PubMed

Density functional theory (DFT) has been used to study electronic perturbations induced by ancillary halogen ligation within metalloenediyne constructs, and the subsequent affect upon thermal Bergman cyclization temperatures. To isolate electronic from geometric components of Bergman cyclization thermodynamics, model diamine- and diphosphine-enediynes (L = 1,6-diamino- or 1,6-diphosphino-cis-1,5-hexadiyne-3-ene) of Mn(II), Cu(II), Zn(II), and Pd(II) with ancillary chloride ligands have been examined computationally and compared to more complex ethylenediamine-based metalloenediyne frameworks of the form MLX(2) (X = Cl, Br, I; L = 1,4-dibenzyl-1,4-diaza-cyclododec-8-ene-6,10-diyne) with distorted square-planar (Cu(II)), T(d) (Zn(II)), and D(4h) (Pd(II)) geometries. In the latter systems, the ethylenediamine linkage restricts the conformation of the enediyne backbone, causing the alkyne termini separation to be nearly independent of metal geometry (3.75-3.82 A). Within the Zn(II) family, steric effects are shown to induce conformational changes on the cyclization potential energy surface (PES) prior to the Bergman transition state, introducing distinct electron-electron repulsive interactions. Multiple metal and ligand conformations are also observed on the Cu(II) metalloenediyne cyclization PES. In contrast, square-planar Pd(II) compounds exhibit overlap between the out-of-plane halogen lone pairs and metal d orbitals, as well as the enediyne pi system, reminiscent of an organometallic "push-pull" reaction mechanism. These systems have significantly higher predicted activation barriers toward cycloaromatization due to enhanced electron repulsion. PMID:18759428

Clark, Aurora E; Bhattacharryya, Sibaprasad; Zaleski, Jeffrey M

2009-05-01

125

Interaction of anchors with soil and anchor design  

NASA Astrophysics Data System (ADS)

The report provides a practical up-to-date guide that enables the practicing engineer to select and size common anchor types, including direct-embedment anchors, deadweight anchors, drag-embedment anchors, and pile anchors. For each anchor type, the report includes site survey recommendations, a brief description of various anchors within each anchor category, methods for determining anchor performance, and, in certain cases, suggestions for improving poor anchor behavior. Sources for additional information are suggested where the treatment of a broad topic is necessarily limited.

Taylor, R. J.

1982-04-01

126

Spectroscopic investigations and physico-chemical characterization of newly synthesized mixed-ligand complexes of 2-methylbenzimidazole with metal ions  

Microsoft Academic Search

Some mixed ligand complexes containing 2-methylbenzimidazole and thiocyanate ion were synthesized. Free ligands and their\\u000a metal complexes were characterized using elemental analysis, determination of metal, magnetic susceptibility, molar conductivity,\\u000a infrared, UV-VIS, and (1H, 13C) NMR spectra, and X-ray structure analysis. The results suggest that the Ag(I) complex has linear geometry, Fe(II), Co(II),\\u000a Ni(II), Cu(II), Zn(II), and Cd(II) have tetrahedral geometry,

Shayma A. Shaker; Hamid Khaledi; Hapipah Mohd Ali

2011-01-01

127

Immobilized tris(hydroxymethyl)aminomethane as a scaffold for ion-selective ligands: the auxiliary group effect on metal ion binding at the phosphate ligand.  

PubMed

The metal ion affinities of a ligand in a polymer-supported reagent can be enhanced by the presence of a proximate group capable of hydrogen bonding. A new polymer-supported reagent has been synthesized by immobilizing tris(hydroxymethyl)aminomethane (Tris) onto cross-linked poly(vinylbenzyl chloride) and then phosphorylating the -OH moieties. The -NH- acts as the auxiliary group to increase the extent of complexation by the phosphate ligand. Additionally, Tris acts as a scaffold, wherein the phosphate ligands are in a known stereochemical arrangement. The Tris resin is mono-, di-, and triphosphorylated, depending on the concentration of the phosphorylating agent. The highest metal ion affinities are found with the resin having a phosphorus-to-nitrogen ratio of 2.36, consistent with one-third of the ligands being triphosphorylated and the remainder being diphosphorylated. The unphosphorylated Tris and phosphonate diester resins have no ionic affinities under the same conditions. Trivalent ions (Fe(III), Al(III), La(III), Eu(III), Lu(III)) are preferred over divalent ions (Pb(II), Cd(II), Cu(II), Zn(II)) from solutions at pH 2. The distribution coefficients of the divalent ions correlate with the Misono softness parameters, indicating that the polarizability of the phosphoryl oxygen is important to binding of the metal ions. The mechanism of complexation is probed with Fe(III) in 0.01-5 M HNO3 and HCl. The high affinities are ascribed to activation of the P=O ligand toward metal ion binding by the N-H moieties acting as auxiliary groups, coupled with intraligand cooperation among the phosphate moieties at a given site. FTIR spectra show that the P=O band at 1261 cm-1 shifts as a function of the extent of hydrogen bonding. Binding at the P=O requires a balance between activation by hydrogen bonding and availability of the lone pair electrons to the metal ions. PMID:17298055

Alexandratos, Spiro D; Zhu, Xiaoping

2007-02-14

128

The ligand-promoted mobilisation of metal ions from mineral surfaces  

NASA Astrophysics Data System (ADS)

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

Putnis, C. V.

2003-04-01

129

Direct observation of a bent carbonyl ligand in a 19-electron transition metal complex.  

PubMed

The photochemistry of [CpRu(CO)2]2 in P(OMe)3/CH2Cl2 solution has been studied using picosecond time-resolved infrared (TRIR) spectroscopy. Photolysis at 400 nm leads to the formation of 17-electron CpRu(CO)2(•) radicals, which react on the picosecond time scale to form 19-electron CpRu(CO)2P(OMe)3(•) adducts. The TRIR spectra of this adduct display an unusually low CO stretching frequency for the antisymmetric CO stretching mode, suggesting that one carbonyl ligand adopts a bent configuration to avoid a 19-electron count at the metal center. This spectral assignment is supported by analogous experiments on [CpFe(CO)2]2 in the same solvent, combined with DFT studies on the structures of the 19-electron adducts. The DFT results predict a bent CO ligand in CpRu(CO)2P(OMe)3(•), whereas approximately linear Fe-C-O bond angles are predicted for CpFe(CO)2P(OMe)3(•). The observation of a bent CO ligand in the 19-electron ruthenium adduct is a surprising result, and it provides new insight into the solution-phase behavior of 19-electron complexes. TRIR spectra were also collected for [CpRu(CO)2]2 in neat CH2Cl2, and it is interesting to note that no singly bridged [CpRu(CO)]2(?-CO) photoproduct was observed to form following 400- or 267-nm excitation, despite previous observations of this species on longer time scales. PMID:23448247

Lomont, Justin P; Nguyen, Son C; Harris, Charles B

2013-03-12

130

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

2012-11-26

131

Indicator ligands in metal complexation studies: role of 4-(2-pyridylazo)resorcinol in europium carbonate equilibrium investigations  

SciTech Connect

Spectrophotometric procedures utilizing the strongly complexing indicator 4-(2-pyridylazo)resorcinol (PAR) permit determination of 1:2 metal-ligand formation constants while substantially promoting metal solubility. The intricacies inherent in competitive equilibria involving PAR can be well-managed through use of low total metal-total indicator (PAR) ratios and observations of comparative complexation at constant pH. The influences of carbonate and oxalate complexation on the adsorbance of Eu-PAR complexes are quantitatively described in terms of Eu(CO/sub 3/)/sub 2//sup -/, Eu(OX)/sub 2//sup -/, and ternary (Eu-PAR-ligand) complexes. Since PAR is a nonspecific colorimetric complexant, the spectrophotometric procedures outlined in this work are applicable to a wide variety of metals.

Thompson, S.W.; Byrne, R.H.

1988-01-01

132

Novel linear transition metal clusters of a heptadentate bis-beta-diketone ligand.  

PubMed

The synthesis and the structure of the new potentially heptadentate ligand 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene (H5L) is described. The reaction in pyridine or DMF of this ligand with various M(AcO)2 salts (M = NiII, CoII, MnII) leads to very different products depending on the metal. Thus, the dinuclear complexes [M2(H3L)2(py)4] (M = NiII, 1; CoII, 2) or the linear zigzag tetranuclear clusters [Mn4(H2L)2(AcO)2(py)5] (3) and [Mn4(H2L)2(AcO)2(dmf)4] (4) have been synthesized and characterized crystallographically. Slow oxidation of complex 3 leads to the formation of the novel mixed-valence linear complex [Mn3(HL)2(py)6] (5), displaying an unprecedented asymmetric MnIIIMnIIIMnII topology. The coordination geometry of complexes 1 to 5 has been analyzed and discussed by means of continuous shape measures. Magnetic measurements of 3 and 5 demonstrate that the metals within these complexes weakly interact magnetically with coupling constants of J1 = -1.13 cm-1 and J2 = -0.43 cm-1 (S = 0) for complex 3 and J1 = -5.4 cm-1 and J2 = -0.4 cm-1 (S = 5/2) for complex 5 (using the H = -Sigma2JijSiSj convention). These results are consistent with X-band EPR measurements on these compounds. PMID:17326626

Aromí, Guillem; Gamez, Patrick; Krzystek, J; Kooijman, Huub; Spek, Anthony L; MacLean, Elizabeth J; Teat, Simon J; Nowell, Harriott

2007-02-28

133

Synthesis and structural chemistry of alkali metal tris(HMDS) magnesiates containing chiral diamine donor ligands.  

PubMed

Six alkali metal tris(HMDS) magnesiate complexes (HMDS, 1,1,1,3,3,3,-hexamethyldisilazide) containing chiral diamine ligands have been prepared and characterised in both the solid- and solution-state. Four of the complexes have a solvent-separated ion pair composition of the form [{M·(chiral diamine)(2)}(+){Mg(HMDS)(3)}(-)] [M = Li for 1 and 3, Na for 2 and 4; chiral diamine = (-)-sparteine for 1 and 2, (R,R)-TMCDA for 3 and 4, (where (R,R)-TMCDA is N,N,N',N'-(1R,2R)-tetramethylcyclohexane-1,2-diamine)] and two have a contacted ion pair composition of the form [{K·chiral diamine}(+){Mg(HMDS)(3)}(-)](n) [chiral diamine = (-)-sparteine for 5 and (R,R)-TMCDA for 6]. In the solid-state, complexes 1-4 are essentially isostructural, with the lithium or sodium cation sequestered by the respective chiral diamine and the previously reported anion consisting of three HMDS ligands coordinated to a magnesium centre. As such, complexes 1-4 are the first structurally characterised complexes in which the alkali metal is sequestered by two molecules of either of the chiral diamines (-)-sparteine (1 and 2) or (R,R)-TMCDA (3 and 4). In addition, complex 4 is a rare (R,R)-TMCDA adduct of sodium. In the solid state, complexes 5 and 6 exist as polymeric arrays of dimeric [{K·chiral diamine}(+){Mg(HMDS)(3)}(-)](2) subunits, with 5 adopting a two-dimensional net arrangement and 6 a linear arrangement. As such, complexes 5 and 6 appear to be the only structurally characterised complexes in which the chiral diamines (-)-sparteine (5) or (R,R)-TMCDA (6) have been incorporated within a polymeric framework. In addition, prior to this work, no (-)-sparteine or (R,R)-TMCDA adducts of potassium had been reported. PMID:21455502

García-Álvarez, Pablo; Kennedy, Alan R; O'Hara, Charles T; Reilly, Kieran; Robertson, Gemma M

2011-03-31

134

Linear Free Energy Relationships for Metal-Ligand Complexation: Bidentate Binding to Negatively-Charged Oxygen Donor Atoms  

PubMed Central

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 pKa values), and ?O is the Irving-Rossotti slope. The parameter ?OO is metal specific and has slightly different values for 5 and 6 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.

2011-01-01

135

Anti-Inflammatory Compounds as Ligands in Metal Complexes as Revealed in X-Ray Structural Studies  

Microsoft Academic Search

The papers which report on the crystal structures of the metal complexes containing anti-inflammatory drugs used to cure humans and other animals are critically reviewed and analyzed to search for the major structural-characteristics both for the coordination spheres and the ligand moieties. Even though this is not an exhaustive review, it appears that metal complexes of non-steroidal anti-inflammatory drugs (NSAID)

Renzo Cini

2000-01-01

136

Effects of different metal ions on the fluorescence of CdSe/ZnS quantum dots capped with various thiolate ligands.  

PubMed

In this report, we systematically studied the effects of different metal ions on the fluorescence of common thiolate ligand capped quantum dots. Generally, heavy metal ions exhibited much more significant fluorescence quenching. Also, the coordination capability and steric hindrance of the ligand jointly affect the quenching efficiency. PMID:24071802

Zeng, Tao; Hu, Yanxi; Wang, Na; Xia, Chuanqin; Li, Shoujian; Zu, Yan; Liu, Lei; Yao, Zhiyi; Zhao, Yuliang; Wu, Hai-Chen

2013-10-01

137

Supramolecular detection of metal ion binding: ligand conformational control of cholesteric induction in nematic liquid crystalline phases.  

PubMed

Tripodal tetradentate ligands may act as chemosensor molecules. Their ability to torque a nematic into a cholesteric phase increases upon complexation with copper ion. Moreover, changes in overall shape of the complexes induced by different metals and counter ions were transferred sensitively to the supramolecular level, observed by proportionate changes in the degree of twisting. Modification of the oxidation state of the metal center also gave large changes in twisting power; this suggests potential application in electrochemical molecular switches. The handedness of the induced cholesteric phase is related to the stereochemistry of the ligand: The small amount of chiral dopant needed for the LC technique (less than 2 nmol) suggests the possible determination of the absolute configuration of the parent primary amines of the ligands. PMID:11205030

Zahn, S; Proni, G; Spada, G P; Canary, J W

2001-01-01

138

Synthesis and characterization of the ligand based on benzoxazole and its transition metal complexes: DNA-binding and antitumor activity.  

PubMed

A new ligand 2-((2-((benzo[d]oxazol-2-yl)methoxy)phenoxy)methyl)benzoxazole (L) and its four transition metal complexes M(NO(3))(2)L (M=Cu, Co, Ni, Zn), have been synthesized and investigated. The single crystal structures of the complexes show that all of them have similar molecular structure and the ligand exhibits good coplanarity after coordination with the metal ions. Further investigation of DNA binding indicates that both the ligand L and the complexes can bond to DNA by intercalation mode, and the latter possesses much stronger binding affinity. Antitumor activity of these compounds tested on the four cancer cell lines, follows the order: Cu-L>Ni-L approximately Co-L>Zn-L>L, which are thought to be related with their DNA-binding affinity. PMID:20202687

Jiang, Jie; Tang, Xiaoliang; Dou, Wei; Zhang, Huihui; Liu, Weisheng; Wang, Chenxuan; Zheng, Jiangrong

2010-02-11

139

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

140

Cooperation between metal and ligand in oxygen atom transport by N-confused porphyrin oxorhenium(V) complexes.  

PubMed

N-Confused porphyrin oxorhenium(V) complexes were prepared and their X-ray structures were elucidated. The oxorhenium(V) complexes can transfer oxygen atom from pyridine N-oxide to triphenylphosphine, in which unique cooperation between metal and ligand was observed. PMID:22653414

Yamamoto, Takaaki; Toganoh, Motoki; Furuta, Hiroyuki

2012-06-01

141

Solvent nuclear quantum effects in electron transfer reactions. III. Metal ions in water. Solute size and ligand effects  

Microsoft Academic Search

Solvent nuclear quantum effects in redox electron transfer (ET) reactions between metal ions in aqueous solution are studied via a molecular dynamics simulation analysis. The impacts of the solute size and charge variations together with the solvent ligand effects are examined by comparing with our previous study on a moderate size donor-acceptor system that assumed typical organic fluorescer-quencher molecules [J.

Koji Ando

2001-01-01

142

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

PubMed

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

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

2012-09-01

143

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

PubMed

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

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

2011-06-22

144

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

145

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

146

Helical hexaazamacrocyclic ligands containing pyridyl and (+ or ?)- trans-diaminocyclohexyl groups: effect of ligand constraints upon metal ion binding  

Microsoft Academic Search

The synthesis of 2(R),7(R),18(R),23(R), 1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene (rrrr-Cy2PYAN) and its 2(S),7(S),18(S),23(S) enantiomer (ssss-Cy2PYAN) from enantiomerically pure starting materials is reported. The ligands were isolated by precipitation in their tetraprotonated form as bromide salts. Circular dichroism spectra of the tetraprotonated, diprotonated, and neutral macrocyclic ligands in aqueous solution were obtained, as well as of the enantiomeric pairs of the [Cu(Cy2PYAN)]2+ and [Zn(Cy2PYAN)]2+ complexes.

P. Michelle Fitzsimmons; Susan C. Jackels

1996-01-01

147

Metal complexes with tetrapyrrole ligands. 71. Heteroaggregation of cationic metal mono- and bisporphyrinates with anionic metal porphyrinates or indigosulfonates  

Microsoft Academic Search

The formation of binary or ternary porphyrin heteroaggregates of the type AB, BC, BC2 or ABC is investigated by UV-Vis spectrophotometry (1:1 mixtures and Job's method of continuous variation), precipitation and electrophoresis. Components ae: A = anionic acceptor molecule, e.g. indigotetrasulfonate, (inds4)4?; B = cationic metal monoporphyrinate, e.g. the tetrakis (trimethylammoniophenyl)porphyrin derivative [Cu(ttm4ap)]4+ (2h-Cu), or cationic metal bisporphyrinate, e.g.[Ce(tm4pyp)2]7+ (3d,

Johann W. Buchler; Michaela Nawra

1996-01-01

148

Rational design, characterization and catalytic application of metal clusters functionalized with hydrophilic, chiral ligands: a proof of principle study.  

PubMed

A proof of principle is presented for the rational design of metal clusters functionalized with hydrophilic, chiral ligands. A colloidal method is used to prepare "unprotected" metal clusters of well-defined size that are subsequently functionalized in a separate step with hydrophilic, chiral ligands. As clusters from the same batch are functionalized with different organic molecules while the cluster size is maintained, the approach allows for systematic investigations and the differences in the observed properties to be related to the influence of the functionalizing ligand. Within this work cysteine and two cysteine derivatives (glutathione and N-acetyl-cysteine) are used as functionalizing ligands for Pt clusters. The materials are characterized using various methods allowing for the determination of ligand coverage, binding mode and chiro-optical properties. Finally, 2-butanone hydrogenation is used as a simple model reaction to demonstrate that these systems exhibit the potential to be used as asymmetric, heterogeneous catalysts. The observed differences in selectivity and reactivity are discussed based on the knowledge gained from the characterization. PMID:24113576

Kunz, Sebastian; Schreiber, Patrick; Ludwig, Martin; Maturi, Mark M; Ackermann, Olaf; Tschurl, Martin; Heiz, Ueli

2013-10-23

149

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

150

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

PubMed

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 Ala(252) 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 Ala(252) 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. PMID:24116162

Raborn, Joel; Fu, Ting; Wu, Xue; Xiu, Zhilong; Li, Guohui; Luo, Bing-Hao

2013-10-08

151

Anchors for Education Reforms  

ERIC Educational Resources Information Center

|Education reforms, considering their significance, deserve better methods than mere "trial and error." This article conceptualizes a network of six anchors for education reforms: education policy, education system, curriculum, pedagogy, assessment, and teacher education. It establishes the futility to reform anchors in isolation and anticipates…

Alok, Kumar

2012-01-01

152

Designing Effective Interdisciplinary Anchors.  

ERIC Educational Resources Information Center

|A curricular anchor is a complex problem that students acknowledge as worth solving and that validates learning a set of relevant skills and concepts. To motivate students, anchors must capture the imagination, be perceived as important by learners, legitimize the disciplinary content they integrate, and accommodate a variety of learning…

Barab, Sasha A.; Landa, Anita

1997-01-01

153

Polymeric Coordination Compounds Derived from Transition Metal (II) with Bis-dentate Ligand: Synthesis, Spectroscopic, Magnetic and Thermal Studies  

Microsoft Academic Search

Polymeric compounds have been synthesized using the ligand [(5,5?-(3,3?-((4-Hydroxyphenyl)methylene)bis(1H-indole-3,1-diyl)bis(methylene)diquinolin-8-ol)] (HMBIQ) with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The ligand has been characterized by H and C-NMR spectroscopy. The coordination polymers have been characterized by elemental analyses, magnetic measurements, thermogravimetric analyses, electronic and infrared spectra. The coordination compounds are colored and the central metal ions are octahedrally coordinated with two water

Darshana J. Patel; Hasmukh S. Patel

2012-01-01

154

Synthesis, Structural Characterization, and Antibacterial Studies of Some Mixed?Ligand First Row d?Transition Metal Complexes  

Microsoft Academic Search

Some mixed?ligand complexes of the transition metal ions Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) with the potassium salt of salicylideneglycine and 2,2??bipyridylamine or di(benzylidene)?1,8?diaminonaphthalene have been prepared. The coordination behavior of the mixed?ligand complexes was characterized on the basis of elemental analyses, IR, and electronic spectra. The magnetic measurements have been obtained by a vibrating sample magnetometer. It is

Pragnesh K. Panchal; M. N. Patel

2004-01-01

155

Intramolecular energy transfer between the triplet of ancillary ligand and the metal to ligand charge transfer state existed in heterocyclometalated iridium (III) complexes  

NASA Astrophysics Data System (ADS)

Higher efficiency red organic light emitting devices (OLEDs) were obtained by employing Ir (III) complexes with 1-phenylbutane-1, 3-dione (ba) as the second ligand than that with acetylacetone (acac) as the second ligand, which were attributed to the intramolecular energy transfer existed in these complexes. The reason were attributed to the intramolecular energy transfer existed in these complexes and were approved by their photoluminescence characteristics at 77 K, as well the phosphorescence decay lifetime. Because of the lower triplet energy level of ba (Tba,19 230 cm-1) whose energy was suitable to transfer to the triplet of the metal to ligand charge transfer (MLCT) (3MLCT,16 260 cm-1) state compared to Tacac (25 500 cm-1), more efficient OLEDs were obtained (7.0 cd/A) using Ir[2-(4'-methanoxy-styryl)-benzothiazole]2ba (ba-2) than Ir[2-(4'-methanoxy-styryl)-benzothiazole]2acac acac-2 (6.1 cd/A).

Han, Liangliang; Yang, Dongfang; Li, Wenlian; Chu, Bei; Chen, Yiren; Su, Zisheng; Zhang, Dongyu; Yan, Fei; Wu, Shuanghong; Wang, Junbo; Hu, Zhizhi; Zhang, Zhiqiang

2009-04-01

156

Experimental and DFT characterization of metal-to-ligand charge-transfer excited states of (rutheniumammine)(monodentate aromatic ligand) chromophores.  

PubMed

The heretofore unknown emission properties of the metal-to-ligand charge-transfer (MLCT) excited states of several complexes with (ruthenium)(monodentate aromatic ligand, MDA) chromophores are given. Emission spectra and lifetimes in 77 K glasses are reported for several monometallic complexes of the type [Ru(NH3)(5-n)(L)(n)(MDA)](2+) and two bimetallic pyrazine (pz)-bridged [{Ru(NH3)(4-n)(L)(n)}2pz](4+) complexes (L = pz, pyridine, or a multipyridine ligand; MDA = pz or a substituted pyridine, Y-py). The emission maxima occur in the visible and near-IR spectral regions and have much more poorly resolved vibronic sidebands than do related complexes with Ru-bpy chromophores, and the excited-state lifetimes are characteristic of Ru-bpy MLCT excited states in this energy range. The emission yields of trans-[Ru(NH3)4(MDA)(pz)](2+) (MDA = py or pz) are less than 0.2%, and combined with the other observations, this implies that most of the excited-state quenching occurs in high-energy excited states whose population precedes that of the lowest-energy (3)MLCT excited state. The pz-bridged, bimetallic complexes have mixed-valence excited states, and they absorb and emit at lower energies than their monometallic analogues do. PMID:23952527

Tsai, Chia Nung; Tian, Yi-Han; Shi, Xuetao; Lord, Richard L; Schlegel, H Bernhard; Chen, Yuan Jang; Endicott, John F

2013-08-16

157

Hydrothermal syntheses, structures, and properties of four metal–organic coordination polymers assembled from V-shaped tetracarboxylate ligands and N-donor ancillary ligands  

Microsoft Academic Search

A series of four metal–organic frameworks, namely, [Cu(sdpa)0.5(2,2?-bpy)]·H2O (1), [Zn2(sdpa)(2,2?-bpy)2(H2O)2]·3H2O (2), [Zn2(sdpa)(4,4?-bpy)]·3H2O (3), [Cd2(sdpa)(4,4?-bpy)1.5(H2O)2](4), have been hydro(solvo)thermally synthesized through the reaction of 2,3,2?,3?-sulfonyldiphthalic acid (H4sdpa) with divalent copper, zinc and cadmium salts in the presence of ancillary nitrogen ligands (4,4?-bpy=4,4?-bipyridine, 2,2?-bpy=2,2?-bipyridine) and structurally characterized by elemental analysis, IR and X-ray diffraction. Both complex 1 and 2 show metal–organic chain structure,

Shuang-Quan Zang; Jia-Bin Li; Qi-Yao Li; Hong-Wei Hou; Thomas C. W. Mak

2010-01-01

158

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

159

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

2011-02-04

160

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

161

Sugars to control ligand shape in metal complexes: conformationally constrained glycoligands with a predetermination of stereochemistry and a structural control.  

PubMed

In coordination chemistry, ligand shape can be used to tune properties, such as metal selectivity, coordination number, electronic structure, redox potential, and metal center stereochemistry including coordination helicates formation, and also to generate cavities for encapsulation. The results presented in this article indicate that two epimeric glycoligands (3 and 4) based on the conformationally restrained xylo- and ribo-1,2-O-isopropylidenefurano scaffolds are preorganized in water through pi-pi stacking due to hydrophobic interactions, as evidenced from excimer observation. The structure obtained in the solid state for one of the Cu(II) complexes (5) is chiral, with an original helical chirality arising from the coiling of the two ligands around the Cu-Cu axis. It shows an unusual double-deck type structure, with pi-pi interaction between two triazoyl-pyridyl rings and with a small cavity between the two Cu(II) ions able to host a bridging water molecule, as suggested by electron paramagnetic resonance. The Cu(II) complex from the epimeric ligand (6) shows similar properties with a mirror-image CD spectrum in the d-d region of the Cu(II). There is a predetermination of chirality at the metal center by the glycoligand induced by the C3 configuration, 6 and 5 being pseudoenantiomers. Interestingly, the stereochemistry at the metal center is here controlled by the combination of pi-stacking and chiral backbone. PMID:20690737

Garcia, Ludivine; Maisonneuve, Stéphane; Xie, Juan; Guillot, Régis; Dorlet, Pierre; Rivière, Eric; Desmadril, Michel; Lambert, François; Policar, Clotilde

2010-08-16

162

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

PubMed

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

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

2012-07-20

163

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 ?\\ctdot ? 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 ?\\ctdot ? 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

164

Synthesis and thermal studies of tetraaza macrocylic ligand and its transition metal complexes. DNA binding affinity of copper complex.  

PubMed

A Tetraaza Macrocylic Ligand (H2L) and its complexes, [Cd(H2L)(OH2)2](NO3)(2)·1/2OH2 (I), [Co(H2L)(OH2)](NO3)(2)·1/2OH2 (II), [Cu(H2L)(NO3)2]·3/2OH2 (III) and [Ni(H2L)(NO3)(OH2)]NO3·OH2 (IV), have been synthesized and characterized on the basis of elemental analysis, molar conductivity, 1H NMR, UV-vis, FT-IR and mass spectroscopy. All results confirm that the prepared compounds have 1:1 metal-to-ligand stoichiometry, octahedral configuration and the ligand behaves as a neutral tetradendate towards the metal ions. [CdL(OH2)2] (V), [CoL(OH2)2] (VI), [CuL(OH2)2] (VII) and [Ni(H2L)(NO3)2] (VIII) were synthesized pyrolytically in solid state from corresponding compounds (I-IV). Analytical results of complexes (V-VIII) show that the ligand behaves either as a neutral tetradendate or dianionic tetradentate ligand towards the metal ions. The binding of H2L and its copper complex (III) to DNA has been investigated by ultraviolet absorption spectroscopy. The experiments indicate that H2L and its copper complex (III) can bind to DNA through an intercalative mode. The H2L and its copper complex (III) exhibited anti-tumor activity against Ehrlich Acites Carcinoma (E.A.C) at the concentration of 100 ?g/ml. PMID:21684198

Saif, M; Mashaly, Mahmoud M; Eid, Mohamed F; Fouad, R

2011-05-31

165

Synthesis and thermal studies of tetraaza macrocylic ligand and its transition metal complexes. DNA binding affinity of copper complex  

NASA Astrophysics Data System (ADS)

A Tetraaza Macrocylic Ligand (H 2L) and its complexes, [Cd(H 2L)(OH 2) 2](NO 3) 2·1/2OH 2 (I), [Co(H 2L)(OH 2)](NO 3) 2·1/2OH 2 (II), [Cu(H 2L)(NO 3) 2]·3/2OH 2 (III) and [Ni(H 2L)(NO 3)(OH 2)]NO 3·OH 2 (IV), have been synthesized and characterized on the basis of elemental analysis, molar conductivity, 1H NMR, UV-vis, FT-IR and mass spectroscopy. All results confirm that the prepared compounds have 1:1 metal-to-ligand stoichiometry, octahedral configuration and the ligand behaves as a neutral tetradendate towards the metal ions. [CdL(OH 2) 2] (V), [CoL(OH 2) 2] (VI), [CuL(OH 2) 2] (VII) and [Ni(H 2L)(NO 3) 2] (VIII) were synthesized pyrolytically in solid state from corresponding compounds (I-IV). Analytical results of complexes (V-VIII) show that the ligand behaves either as a neutral tetradendate or dianionic tetradentate ligand towards the metal ions. The binding of H 2L and its copper complex (III) to DNA has been investigated by ultraviolet absorption spectroscopy. The experiments indicate that H 2L and its copper complex (III) can bind to DNA through an intercalative mode. The H 2L and its copper complex (III) exhibited anti-tumor activity against Ehrlich Acites Carcinoma (E.A.C) at the concentration of 100 ?g/ml.

Saif, M.; Mashaly, Mahmoud M.; Eid, Mohamed F.; Fouad, R.

2011-09-01

166

Vertically moored platform anchoring  

SciTech Connect

An improved system is disclosed for anchoring a floating vessel which is anchored only by parallel and essentially vertical conduits. The anchoring load is carried by units of concentric pipes including an outer riser pipe and inner strings of casing. Drilling wells and/or production of oil and gas or like operations are conducted through these casings. The tension of the inner casing string is transmitted to the floating vessel through the upper end of the outer riser pipe. The system prevents excessive buildup of stresses in the upper end of the inner casing due to the bending caused by excursions caused by the waves, the wind and the current.

Blenkarn, K.A.; Beynet, P.A.

1984-02-14

167

Complications of bioabsorbable suture anchors in the shoulder.  

PubMed

The development of the suture anchor has played a pivotal role in the transition from open to arthroscopic techniques of the shoulder. Various suture anchors have been manufactured that help facilitate the ability to create a soft tissue to bone repair. Because of reported complications of loosening, migration, and chondral injury with metallic anchors, bioabsorbable anchors have become increasingly used among orthopaedic surgeons. In this review, the authors sought to evaluate complications associated with bioabsorbable anchors in or about the shoulder and understand these in the context of the total number of bioabsorbable anchors placed. In 2008, 10 bioabsorbable anchor-related complications were reported to the US Food and Drug Administration. The reported literature complications of bioabsorbable anchors implanted about the shoulder include glenoid osteolysis, synovitis, and chondrolysis. These potential complications should be kept in mind when forming a differential diagnosis in a patient in whom a bioabsorbable anchor has been previously used. These literature reports, which amount to but a fraction of the total bioabsorbable anchors implanted in the shoulder on a yearly basis, underscore the relative safety and successful clinical results with use of bioabsorbable suture anchors. Product development continues with newer composites such as PEEK (polyetheretherketone) and calcium ceramics (tricalcium phosphate) in an effort to hypothetically create a mechanically stable construct with and improve biocompatibility of the implant. Bioabsorbable anchors remain a safe, reproducible, and consistent implant to secure soft tissue to bone in and about the shoulder. Meticulous insertion technique must be followed in using bioabsorbable anchors and may obviate many of the reported complications found in the literature. The purpose of this review is to provide an overview of the existing literature as it relates to the rare complications seen with use of bioabsorbable suture anchors in the shoulder. PMID:21856927

Dhawan, Aman; Ghodadra, Neil; Karas, Vasili; Salata, Michael J; Cole, Brian J

2011-08-19

168

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

169

Mutagenesis studies of the ? I domain metal ion binding sites on integrin ?V?3 ligand binding affinity.  

PubMed

Three divalent cation binding sites in the integrin ? I domain have been shown to regulate ligand binding and adhesion. However, the degree of ligand binding and adhesion varies among integrins. The ?L?2 and ?4?7 integrins show an increase in ligand binding affinity and adhesion when one of their ADMIDAS (adjacent to MIDAS, or the metal ion-dependent adhesion site) residues is mutated. By contrast, the ?2?1, ?5?1, and ?IIb?3 integrins show a decrease in binding affinity and adhesion when their ADMIDAS is mutated. Our study here indicated that integrin ?V?3 had lower affinity when the ADMIDAS was mutated. By comparing the primary sequences of these integrin subunits, we propose that one residue associated with the MIDAS (?3 Ala(252)) may account for these differences. In the ?1 integrin subunit, the corresponding residue is also Ala, whereas in both ?2 and ?7 integrin subunits, it is Asp. We mutated the ?3 residue Ala(252) to Asp and combined this mutant with mutations of one or two ADMIDAS residues. The mutant A252D showed reduced ligand binding affinity and adhesion. The ligand binding affinity and adhesion were increased when this A252D mutant was paired with mutations of one ADMIDAS residue. But when paired with mutations of two ADMIDAS residues the mutant nearly abolished ligand-binding ability, which was restored by the activating glycosylation mutation. Our study suggests that the variation of this residue contributes to the different ligand binding affinities and adhesion abilities among different integrin families. PMID:22095620

Raborn, Joel; Luo, Bing-Hao

2012-04-01

170

Synthesis of Crosslinked Chitosan with Epichlorohydrin Possessing Two Novel Polymeric Ligands and Its Use in Metal Removal  

Microsoft Academic Search

One of the major applications of chitosan and its derivatives is based on its ability to bind strongly toxic metal ions. In\\u000a this work, two novel polymeric ligands were synthesized to investigate the adsorption properties of Cu(II), Pb(II), Zn(II)\\u000a and Ni(II) ions in an aqueous solution. To prevent the reaction between as the C2 amine group of chitosan and ECH,

Mustafa Sahin; Nuriye Kocak; Gulsin Arslan; Halil Ismet Ucan

2011-01-01

171

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

Microsoft Academic Search

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

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

2011-01-01

172

Potential importance of metal-ligand interactions in enzyme assays demonstrated with the assay cocktail for phosphoenolpyruvate carboxylase  

SciTech Connect

Assay cocktail modification such as addition of effector can cause inadvertent changes in the concentration of other metal-ligand and free species. In some cases, e.g. in the assay for phosphoenolpyruvate carboxylase under a limiting-substrate condition, unintentional changes in substrate concentration are significant and confound an interpretation based solely on the total concentration of each component. A cautionary argument is developed on the basis of examples from the current literature.

Outlaw, W.H. Jr. (Florida State Univ., Tallahassee (USA))

1990-02-01

173

Structural Investigations of Silica Polyamine Composites: Surface Coverage, Metal Ion Coordination, and Ligand Modification  

SciTech Connect

Silanization of the silica gel surface in the synthesis of silica gel polyamine composites uses (chloropropyl)-trichlorosilane (CPTCS). It is possible to substitute a molar fraction of reagent CPTCS with methyltrichlorosilane (MTCS), creating a mixed silane surface layer. Two types of silica gels were modified with a series of MTCS:CPTCS molar ratios. Solid-state CP/MAS 29Si and 13C NMR spectroscopies were used to evaluate the surface silane composition. Surface silane coverage was markedly improved for the resulting gels. When polyamines were grafted to the resultant MTCS:CPTCS silane layers, it was shown that the decrease in the number of propyl attachments to the polyamine resulted in increased quantities of ''free amines''. Optimum MTCS:CPTCS ratios were determined for three polyamines grafted onto one silica gel. A substantial free amine increase was observed for poly(allylamine) (PAA). Metal uptake studies show increases in Cu(II) capacity and/or an improvement in Cu(II) mass-transfer kinetics. The effect of polymer molecular weight upon Cu(II) capacity was investigated for each polyamine. Substantial differences in Cu(II) capacity between 50,000 MW poly(vinylamine) (PVA) and >1000 MW PVA were evident. Similar differences between 25,000 MW poly(ethyleneimine) (PEI) and 1200 MW PEI were found. The mass-transfer kinetics was shown to be improved for composites prepared using a large fraction of MTCS in the reagent silane mixture. This resulted in substantial improvements in the 10% breakthrough Cu(II) capacity for PVA (50 000 MW). PEI composites were further modified to form an amino-acetate ligand. The impact of the MTCS:CPTCS silane ratio on the acetate ligand loading and ultimately on the Cu(II) capacity at pH 2 was investigated. A ratio of 12.5:1 was shown to result in an acetate modified PEI composite with a Cu(II) capacity 140% of the Cu(II) capacity of the same composite prepared with ''CPTCS only''.

Hughes, Mark; Nielsen, Daniel; Rosenberg, Edward; Gobetto, Roberto; Viale, Alessandra; Burton, Sarah D.; Ferel, Joseph

2006-09-13

174

Determining the magnitude and direction of photoinduced ligand field switching in photochromic metal-organic complexes: molybdenum-tetracarbonyl spirooxazine complexes.  

PubMed

The ability to optically switch or tune the intrinsic properties of transition metals (e.g., redox potentials, emission/absorption energies, and spin states) with photochromic metal-ligand complexes is an important strategy for developing "smart" materials. We have described a methodology for using metal-carbonyl complexes as spectroscopic probes of ligand field changes associated with light-induced isomerization of photochromic ligands. Changes in ligand field between the ring-closed spirooxazine (SO) and ring-opened photomerocyanine (PMC) forms of photochromic azahomoadamantyl and indolyl phenanthroline-spirooxazine ligands are demonstrated through FT-IR, (13)C NMR, and computational studies of their molybdenum-tetracarbonyl complexes. The frontier molecular orbitals (MOs) of the SO and PMC forms differ considerably in both electron density distributions and energies. Of the multiple ?* MOs in the SO and PMC forms of the ligands, the LUMO+1, a pseudo-b(1)-symmetry phenanthroline-based MO, mixes primarily with the Mo(CO)(4) fragment and provides the major pathway for Mo(d)?phen(?*) backbonding. The LUMO+1 is found to be 0.2-0.3 eV lower in energy in the SO form relative to the PMC form, suggesting that the SO form is a better ?-acceptor. Light-induced isomerization of the photochromic ligands was therefore found to lead to changes in the energies of their frontier MOs, which in turn leads to changes in ?-acceptor ability and ligand field strength. Ligand field changes associated with photoisomerizable ligands allow tuning of excited-state and ground-state energies that dictate energy/electron transfer, optical/electrical properties, and spin states of a metal center upon photoisomerization, positioning photochromic ligand-metal complexes as promising targets for smart materials. PMID:21524110

Paquette, Michelle M; Patrick, Brian O; Frank, Natia L

2011-06-09

175

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

176

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

177

Simulated annealing and density functional theoretical prediction of macrocyclic ligand conformations, protonation sites and complex metal-ligand exchange reaction directions.  

PubMed

The prediction of conformations and protonation sites for the macrocyclic ligands H2DO2A (1,4,7,10-tetraazacyclododecane-1,7-diacetic acid) and H2ODO2A (1-oxa-4,7,10-triazacyclododecane-4,10-diacetic acid) has been performed employing the simulated annealing (SA) method and density functional theory (DFT) calculations using the B3LYP/6-31G* method in a vacuum and aqueous solution. These SA method/DFT calculations reveal that, in contrast to the H2ODO2A ligand system, the H2DO2A ligand system is (i) pre-organized for trivalent lanthanide (Ln) and other metal ion complexation, (ii) structurally more symmetrical and slightly more compact in aqueous solution (i.e. more and/or shorter intra-molecular hydrogen bonds), and (iii) with a greater degree of partial positive charge accumulation on the hydrogen atoms bonded to macrocyclic ring nitrogen atoms when protonated. The H2ODO2A ligand system is not pre-organized. These observations are in accord with the experimental findings that the LnODO2A(+) complexes are less thermodynamically stable and kinetically more labile as compared to those of the corresponding LnDO2A(+) complexes. The results on the prediction of the ligand protonation sites are consistent with those experimentally obtained via NMR spectroscopy. The calculations of the first and second protonation constants are, however, not as accurate as compared to those experimentally determined using either the thermodynamic cycle (TC) or the isodesmic reaction (IRn) methodology, although the latter gave relatively better results. The lowest energy structures of the LnL(+) and ZnL (Ln = Eu, Y; L = DO2A, ODO2A) complexes are also calculated using the same method. The Gibb's free energies (?Gaq) for a number of ligand and/or metal ion exchange reactions such as LnDO2A(+) + HnODO2A((2-n)-) -->/<-- LnODO2A(+) + HnDO2A((2-n)-) (Ln = Eu, Y; n = 0, 1, 2), LnDO2A(+) + Ln'ODO2A(+) -->/<-- LnODO2A(+) + Ln'DO2A(+) (Ln = Eu, Ln' = Y), LnDO2A(+) + Ln'(3+) -->/<-- Ln'ODO2A(+) + Ln(3+) (Ln = Eu, Ln' = Y) and LnDO2A(+) + ZnODO2A -->/<-- LnODO2A(+) + ZnDO2A (Ln = Eu, Y) have been calculated in aqueous phase and the reaction directions in some cases could be predicted to be consistent with experimental or expected results. The errors between the calculated and experimental Gibb's free energy data are in the range ?G(aq,calc) - ?G(aq,exp) = -1.89 to +7.00 kcal mol(-1) in seven selected cases involving LnDO2A(+), LnODO2A(+) (Ln = Eu, Y), ZnDO2A and ZnODO2A complexes. The predicted reaction directions with the small core effective core potential (ECP) data are not necessarily better than those using large core ECP. However, the former takes much longer computer time to obtain the energy data. PMID:23462882

Chang, C Allen; Lee, Hwa Yu; Chen, Cheng-Lung

2013-05-14

178

Role of dynamical polarization of the ligand-to-metal charge transfer excitations in ab initio determination of effective exchange parameters  

Microsoft Academic Search

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits us to suggest a variant of the difference dedicated configuration interaction (DDCI) method, presently one of the

Alain Gellé; Markéta L. Munzarová; Marie-Bernadette Lepetit; Francesc Illas

2003-01-01

179

The role of dynamical polarization of the ligand to metal charge transfer excitations in ab initio determination of effective exchange parameters  

Microsoft Academic Search

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits to suggest a new variant of the Difference Dedicated Configuration Interaction (DDCI) method, presently one of the

Alain Gelle; Marketa L. Munzarova; Marie-Bernadette Lepetit; Francesc Illas

2003-01-01

180

New metal organic framework structures based on 2,5-pyridinedicarboxylate ligands and Zn2+ ions  

NASA Astrophysics Data System (ADS)

Structural characteristics and adsorption properties of new heteroaromatic framework structures based on Zn2+ ions and 2,5-pyridinedicarboxylate ligands are investigated. A comparative study of the aromatic framework structure MOF-5 based on Zn4O clusters and 1,4-benzenedicarboxylate ligands is also performed in order to reveal the effect of the nature of the organic fragment.

Isaeva, V. I.; Tkachenko, O. P.; Brueva, T. R.; Nissenbaum, V. D.; Mishin, I. V.; Grünert, W.; Kustov, L. M.

2011-03-01

181

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

182

Kinetics of brucite dissolution at 25°C in the presence of organic and inorganic ligands and divalent metals  

NASA Astrophysics Data System (ADS)

Brucite (Mg(OH) 2) dissolution rate was measured at 25°C in a mixed-flow reactor at various pH (5 to 11) and ionic strengths (0.01 to 0.03 M) as a function of the concentration of 15 organic and 5 inorganic ligands and 8 divalent metals. At neutral and weakly alkaline pH, the dissolution is promoted by the addition of the following ligands ranked by decreasing effectiveness: EDTA ? H 2PO 4- > catechol ? HCO 3- > ascorbate > citrate > oxalate > acetate ˜ lactate and it is inhibited by boric acid. At pH >10.5, it decreases in the presence of PO 43-, CO 32-, F -, oxine, salicylate, lactate, acetate, 4-hydroxybenzoate, SO 42- and B(OH) 4- with orthophosphate and borate being the strongest and the weakest inhibitor, respectively. Xylose (up to 0.1 M), glycine (up to 0.05 M), formate (up to 0.3 M) and fulvic and humic acids (up to 40 mg/L DOC) have no effect on brucite dissolution kinetics. Fluorine inhibits dissolution both in neutral and alkaline solutions. From F sorption experiments in batch and flow-through reactors and the analysis of reacted surfaces using X-ray Photoelectron Spectroscopy (XPS), it is shown that fluorine adsorption is followed by its incorporation in brucite lattice likely via isomorphic substitution with OH. The effect of eight divalent metals (Sr, Ba, Ca, Pb, Mn, Fe, Co and Ni) studied at pH 4.9 and 0.01 M concentration revealed brucite dissolution rates to be correlated with the water molecule exchange rates in the first hydration sphere of the corresponding cation. The effect of investigated ligands on brucite dissolution rate can be modelled within the framework of the surface coordination approach taking into account the adsorption of ligands on dissolution-active sites and the molecular structure of the surface complexes they form. The higher the value of the ligand sorption constant, the stronger will be its catalyzing or inhibiting effect. As for Fe and Al oxides, bi- or multidentate mononuclear surface complexes, that labilize Mg-O bonds and water coordination to Mg atoms at the surface, enhance brucite dissolution whereas bi- or polynuclear surface complexes tend to inhibit dissolution by bridging two or more metal centers and extending the cross-linking at the solid surface. Overall, results of this study demonstrate that very high concentrations of organic ligands (0.01-0.1 M) are necessary to enhance or inhibit brucite dissolution. As a result, the effect of extracellular organic products on the weathering rate of Mg-bearing minerals is expected to be weak.

Pokrovsky, Oleg S.; Schott, Jacques; Castillo, Alain

2005-02-01

183

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

184

Synthesis, characterization, and lactide polymerization activity of group 4 metal complexes containing two bis(phenolate) ligands.  

PubMed

A series of group 4 metal complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2), Zr-(5)(2), Hf-(1)(2), and Hf-(4)(2) containing two bridged bis(phenolate) ligands of the (OSSO)-type were prepared by the reaction of the corresponding bis(phenol) and group 4 metal precursor MX(4) (X = O(i)Pr, CH(2)Ph) and isolated as robust, colorless crystals. NMR spectra indicate D(2) symmetry, in agreement with the solid state structure determined by single crystal X-ray diffraction study of the complexes Zr-(1)(2), Hf-(1)(2), Zr-(3)(2), Zr-(4)(2), and Zr-(5)(2). The complexes with the 1,4-dithiabutanediyl bridged ligands exhibit a highly symmetric coordination around the metal center. The introduction of the rigid trans-1,2-cyclohexanediyl bridged ligands led to a distorted coordination around the metal center in Zr-(4)(2) and Zr-(5)(2) when the ortho substituent is tert-butyl and the para substituent is larger than methyl. The complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2) as well as Hf-(1)(2) and Hf-(4)(2) initiated the ring-opening polymerization of meso-lactide at 100 °C to give heterotactic polylactide with pronounced heterotacticity (>70%) and varying polydispersity (1.05 < M(w)/M(n) < 1.61). As shown by kinetic studies, zirconium complex Zr-(1)(2) polymerized meso-lactide faster than the homologous hafnium complex Hf-(1)(2). PMID:22571415

Sauer, Andreas; Buffet, Jean-Charles; Spaniol, Thomas P; Nagae, Haruki; Mashima, Kazushi; Okuda, Jun

2012-05-09

185

Synthesis and properties of metal-ligand complexes with endohedral amine functionality.  

PubMed

A series of tetracationic M(2)L(4) palladium-pyridyl complexes with endohedral amine functionality have been synthesized. The complexes were analyzed by NMR techniques (including Diffusion NMR and 2D NOESY), electrospray ionization (ESI) mass spectrometry, and X-ray crystallography. The solid state analysis shows a large change in crystal morphology upon introduction of the endohedral amine groups, caused by deleterious interactions between the amines and the triflate counterions from the coordination process. Combination of different ligands allows analysis of ligand exchange rates via NMR analysis, with half-lives on the order of 3 h, independent of the donor properties of the ligand. Self-sorting behavior is observed, with more electron-rich ligands being favored. The amine-containing and extended complexes are strongly fluorescent, giving quantum yields of up to 83%. PMID:21902178

Johnson, Amber M; Moshe, Orly; Gamboa, Ana S; Langloss, Brian W; Limtiaco, John F K; Larive, Cynthia K; Hooley, Richard J

2011-09-08

186

Uranium(III) Complexes with Bulky Aryloxide Ligands Featuring Metal-Arene Interactions and Their Reactivity Toward Nitrous Oxide.  

PubMed

We report the synthesis and use of an easy-to-prepare, bulky, and robust aryloxide ligand starting from inexpensive precursor materials. Based on this aryloxide ligand, two reactive, coordinatively unsaturated U(III) complexes were prepared that are masked by a metal-arene interaction via ?-backbonding. Depending on solvent and uranium starting material, both a tetrahydrofuran (THF)-bound and Lewis-base-free U(III) precursor can easily be prepared on the multigram scale. The reaction of these trivalent uranium species with nitrous oxide, N2O, was studied and an X-ray diffraction (XRD) study on single crystals of the product revealed the formation of a five-coordinate U(V) oxo complex with two different molecular geometries, namely, square pyramidal and trigonal bipyramidal. PMID:23987649

Franke, Sebastian M; Tran, Ba L; Heinemann, Frank W; Hieringer, Wolfgang; Mindiola, Daniel J; Meyer, Karsten

2013-08-30

187

Binuclear transition metal complexes of bicompartmental SNO donor ligands: synthesis, characterization, and electrochemistry  

Microsoft Academic Search

A series of new binucleating Co, Ni, Cu, and Zn complexes of bicompartmental ligands with SNO donors was prepared. The Schiff bases were obtained by the condensation of 4,6-diacetylresorcinol and mercapto-substituted 1,2,4-triazoles. The ligands and their complexes were characterized by elemental analysis, infrared, H-NMR, UV-Vis, FAB-mass, and ESR spectral studies, magnetic susceptibility, and conductivity measurements. All the complexes were monomeric

Naveen V. Kulkarni; M. P. Sathisha; Srinivasa Budagumpi; Gurunath S. Kurdekar; Vidyanand K. Revankar

2010-01-01

188

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

189

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

PubMed

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, [M2(?2-NO)]; (c) threefold nitrosyl bridges, [M3(?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 ?/1.60-1.90 ?/180-160° and for bent nitrosyls are 1.16-1.22 ?/1.80-2.00 ?/140-110°. The [M2(?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 ?/1.18-1.22 ?/1.80-2.00 ?/90-70°, whereas for the analogous ranges of the long twofold NO bridges these are 3.10-3.40 ?/1.20-1.24 ?/1.90-2.10 ?/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 M3-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 ?/1.80-1.90 ?, 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: PF3 [plus 10 cm(-1)]; P(OPh)3 [-30 cm(-1)]; P(OR)3 (R=alkyl group) [-40 cm(-1)]; PPh3 [-55 cm(-1)]; PR3 (R=alkyl group) [-70 cm(-1)]; and ?5-C5H5 [-60 cm(-1)]; ?5-C5H4Me [-70 cm(-1)]; ?5-C5Me5 [-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 in polar solu

De La Cruz, Carlos; Sheppard, Norman

2010-08-17

190

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

191

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

2013-09-24

192

Strap anchor system and method  

US Patent & Trademark Office Database

In accordance with the teachings of the present invention, a strap anchor system and method are provided. In a particular embodiment of the present invention, the system includes a helmet body, a support structure substantially disposed within the helmet body, and a strap anchor housing coupled to the support structure and substantially disposed within the helmet body. The strap anchor housing is operable to receive a strap anchor after formation of the helmet body. The strap anchor is operable to couple a strap to the strap anchor housing so that a load on the strap is transferred to the support structure before being transferred to the helmet body.

2011-09-20

193

Construction of metal–organic frameworks with transitional metals based on the 3,5-bis(4-pyridyl)-1 H-1,2,4-triazole ligand  

Microsoft Academic Search

Based on the versatile ligand 3,5-bis(4-pyridyl)-1H-1,2,4-triazole (Hbpt) derived from an in situ metal\\/ligand reaction, a series of coordination compounds CoCl4(H3bpt)(H2O) (1), Cu(H2bpt)2(SO4)2(H2O)6 (2), [Ag(bpt)]n (3), [Co(Hbpt)(pa)]n (4), [Co(Hbpt)(pda)]n (5) and [Cu(Hbpt)(pda)(H2O)]n (6) have been constructed (pa=phthalate, pda=1,3-phenylenediacetate). The structures of these targeted complexes have been characterized by X-ray single-crystal diffraction techniques. Structural analysis reveals that Hbpt adopts versatile coordination modes

Xiao-Feng Xie; San-Ping Chen; Zheng-Qiang Xia; Sheng-Li Gao

2009-01-01

194

Application of Trianionic Pincer Ligands to Reactions Involving Group VI Alkylidynes, Metal-Metal Multiple Bonds, and Group IV Amides.  

National Technical Information Service (NTIS)

In an effort to isolate a pincer-support tungsten alkylidyne, several new tungsten alkylidenes and a ditungsten compound have been isolated, supported by the previously reported OCO3- pincer ligand 3,3 -di-tert-butyl-2, 2 -di-(hydroxy-kappaO)-1,1 :3 ,1 -(...

A. J. Peloquin

2008-01-01

195

A newly Synthesis and characterization of metal complexes of 3-(N- phenyl) thiourea-pentanone-2 as ligand  

NASA Astrophysics Data System (ADS)

Present communication deals with the synthesis of copper and cobalt complexes derived from 3-(N- phenyl) thiourea-pentanone-2 as the ligand. Structure of all the compounds was characterized by elemental, XRD, FTIR, UV-VIS, SEM and 1HNMR spectroanalytical studies. The X-ray diffraction studies indicate that 3-(N- phenyl) thiourea-pentanone-2 and their complexation with copper and cobalt metals are crystalline in nature. The FTIR spectroscopic data were used to assign the characteristic vibrational frequencies of various groups present in the compounds. Scanning electron Micrograms were used to assign the morphology and particle size of the compounds.

Mishra, A.; Ninama, S.; Sharma, P.; Soni, N.; Awate, R.

2012-05-01

196

A base-stabilized silylene with a tricoordinate silicon atom as a ligand for a metal complex.  

PubMed

Treatment of base stabilized silylene [PhC(NtBu)(2)]SiOtBu (1) with a tricoordinate silicon atom and diiron nonacarbonyl [Fe(2)(CO)(9)] in tetrahydrofuran led to the formation of {[PhC(NtBu)(2)]SiOtBu}Fe(CO)(4) (2), the first stable metal complex derived from a base-stabilized tricoordinate silylene ligand. The solid-state structure and bonding situation of 2 were investigated with single-crystal X-ray diffraction and quantum chemical calculations. PMID:19456135

Yang, Wei; Fu, Hao; Wang, Haijun; Chen, Mingqing; Ding, Yuqiang; Roesky, Herbert W; Jana, Anukul

2009-06-15

197

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

198

Oxidatively induced abstraction reactions. A synthetic approach to low-coordinate and reactive early transition metal complexes containing metal-ligand multiple bonds.  

PubMed

A library of low-coordinate titanium and vanadium complexes containing terminal metal-ligand multiply bonded functionalities such as alkylidenes, alkylidynes, and imides have been prepared by one-electron oxidatively induced alpha-hydrogen abstraction reactions. In the case of the alkylidene motif, the nucleophilic nature of the M-C multiple bond permits subsequent reactions such as alpha-hydrogen migration to generate other rare functionalities such as phosphinidene-alkyl and imide-alkyls. Identifying and fine-tuning of the supporting ancillary ligand on the metal has allowed the isolation of kinetically stable titanium alkylidene and phosphinidene systems. The former is a key functionality to generate transient titanium alkylidynes, which readily engage in intermolecular C-H activation reactions of arenes and alkanes, and the ring-opening metathesis of aromatic substrates such as pyridines. In this Account, we describe several synthetic strategies to achieve reactive functionalities, functionalities that were previously portrayed as "incompatible" or "too kinetically reactive" with 3d early transition metals. PMID:17115721

Mindiola, Daniel J

2006-11-01

199

(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

200

Characteristics of Anchor Tests.  

ERIC Educational Resources Information Center

|The purpose of this study was twofold: to investigate to what extent characteristics of anchor tests may affect precision of item calibration, and to estimate to what extent precision of item calibration may be affected by removal of persons whose response patterns deviate from those normally expected from the Rasch one-parameter logistic model.…

Chang, S. Tai; Bashaw, W. L.

201

Science Sampler: Anchor activities  

NSDL National Science Digital Library

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

Corlett, Cindy

2003-03-01

202

AMIDES AS LIGANDS. I. METALLIC COMPLEXES OF N,N-DIMETHYLACETAMIDE  

Microsoft Academic Search

The preparation of 26 metallic complexes of 14 different metals with N,N-; dimethylacetamide (DMA) is reported. The complexes were characterized by their ; melting points, infrared spectra in the 2 to 15 mu region, electrical ; conductance in DMA, and magnetic moments. The infrared spectra suggest that ; coordination through the oxygen of DMA occurs for all the metals investigated.

William E. Bull; Stanley K. Madan; Joseph E. Willis

1963-01-01

203

Tetranuclear group 7/8 mixed-metal and open trinuclear group 7 metal carbonyl clusters bearing bridging 2-mercapto-1-methylimidazole ligands.  

PubMed

The reactivity of group 7 metal dinuclear carbonyl complexes [M(2)(CO)(6)(mu-SN(2)C(4)H(5))(2)] (1, M = Re; 2, M = Mn) toward group 8 metal trinuclear carbonyl clusters were examined. Reactions of 1 and 2 with [Os(3)(CO)(10)(NCMe)(2)] in refluxing benzene furnished the tetranuclear mixed-metal clusters [Os(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (3) and [Os(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (4), respectively. Similar treatment of 1 and 2 with Ru(3)(CO)(12) yielded the ruthenium analogs [Ru(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (5), and [Ru(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (6), but in the case of 2 a secondary product [Mn(3)(CO)(10)(mu-Cl)(mu(3)-SN(2)C(4)H(5))(2)] (7) was also formed. Compounds have a butterfly core of four metal atoms with the M (Mn or Re) at a wingtip of the butterfly and containing a noncrystallographic mirror plane of symmetry. This result provides a potential method for the synthesis of a series of new group 7/8 mixed metal complexes containing a bifunctional heterocyclic ligand. Compound 7 is a unique example of a 54-electron trimanganese complex having bridging 2-mercapto-1-methylimidazolate and chloride ligands. Interestingly, the reaction of 1 with Fe(3)(CO)(12) at 70-75 degrees C furnished the tri- and dirhenium complexes [Re(3)(CO)(10)(mu-H)(mu(3)-SN(2)C(4)H(5))(2)] (8) and [Re(2)(CO)(6)(N(2)C(4)H(5))(mu-SN(2)C(4)H(5))(2)] (9), respectively instead of the expected formation of the mixed-metal clusters. The former is an interesting example of a 52-electron trirhenium-hydridic complex containing bridging 2-mercapto-1-methylimidazolate ligand, while the latter can be viewed as a 1-methylimidazole adduct of 1 . No mixed Fe-Re complexes were produced in this reaction. The molecular structures of the new compounds and were established by single-crystal X-ray diffraction analyses and the DFT studies of compounds , and are reported. PMID:19381413

Ghosh, Shishir; Kabir, Shariff E; Pervin, Salina; Raha, Arun K; Golzar Hossain, G M; Haworth, Daniel T; Lindeman, Sergey V; Bennett, Dennis W; Siddiquee, Tasneem A; Salassa, Luca; Roesky, Herbert W

2009-03-23

204

Incorporation of active metal sites in MOFs via in situ generated ligand deficient metal-linker complexes.  

PubMed

Two novel 3D MOFs, namely MOF-647A and MOF-648 (previously unknown trinodal 4-connected net), comprised of Cu ions and pyrazole-3,5-dicarboxylate were synthesized and characterized. A strategy for incorporating open metal sites in MOFs was investigated by utilizing an in situ generated metal-linker complex as a precursor to construct MOF-648. PMID:21983899

Barman, Samir; Furukawa, Hiroyasu; Blacque, Olivier; Venkatesan, Koushik; Yaghi, Omar M; Jin, Guo-Xin; Berke, Heinz

2011-10-10

205

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

2013-09-03

206

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

PubMed

Five new Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) mixed ligand complexes have been synthesized using a Schiff base precursor (obtained by the condensation of N-(4-aminophenyl)acetamide and 4-chlorobenzaldehyde) as main ligand and 1,10-phenanthroline as co-ligand. They have been characterized by microanalytical data, IR, UV-Vis, magnetic moment values, conductivity and electrochemical measurements. The spectral data reveal that all the complexes exhibit octahedral geometry. The high electrical conductance of the complexes supports their electrolytic nature. The monomeric nature of the complexes has been assessed from their magnetic susceptibility values. These complexes are better antimicrobial active agents than the free ligands. DNA (CT) binding properties of these complexes have been explored by UV-Vis., viscosity measurements, cyclic voltammetry, and differential pulse voltammetry measurements. The oxidative cleavage activity of the complexes has been studied using supercoiled pUC19 DNA by gel electrophoresis. The experimental results show that the complexes are good intercalators. PMID:23666355

Mahalakshmi, Rajkumar; Raman, Natarajan

2013-04-22

207

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

NASA Astrophysics Data System (ADS)

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

Mahalakshmi, Rajkumar; Raman, Natarajan

2013-08-01

208

Potential cross-linking transition metal complexes (M = Ni, Cu, Zn) in the ligand-modified LNA duplexes.  

PubMed

Options for interstrand DNA duplex linkages have been studied by incorporating transition metal ions in the ligand-functionalized LNA (locked nucleic acid) duplexes. The effect of first-row transition metal ions (M = Ni(2+), Cu(2+), and Zn(2+)) on the geometries and formation energies of mono- and dimetallic model complexes was calculated by DFT methods, and the results were compared with available experimental data. The results showed a clear preference for the formation of copper complexes over the corresponding nickel and zinc complexes, in agreement with the trends observed in the denaturation temperatures of the ligand-functionalized LNA duplexes. In addition, dichloride bridged dimeric complex, [L(LNA)Cu(?-Cl)(2)CuL(LNA)](2+), in which L(LNA) is N,N-bis(2-pyridylmethyl)-?-alanyl functionalized LNA, was found energetically very stable, providing a potential structural option for an interstrand duplex linkage. The model complex and its simpler structural analogues were synthesized and structurally characterized. Comparison of the dimeric linker introduced into duplex tetramer strands, which provided a computational model for a double helix with two closely located LNA units, with a similar model for mononuclear Cu(L(LNA))(2)(2+) linker also showed a clear preference of the dichloride-bridged option, suggesting that the [L(LNA)Cu(?-Cl)(2)CuL(LNA)](2+) complex produced a chemically realistic model to explain duplex stabilization in the presence of Cu(2+) and excess Cl(-). PMID:20726539

Hirva, Pipsa; Nielsen, Anne; Bond, Andrew D; McKenzie, Christine J

2010-09-16

209

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

2013-06-13

210

Differences in actinide metal-ligand orbital interactions: comparison of U(IV) and Pu(IV) ?-ketoiminate N,O donor complexes.  

PubMed

Syntheses and characterization of UCl(2)((Ar)acnac)(2), UI(2)((Ar)acnac)(2), and PuI(2)((Ar)acnac)(2) are reported ((Ar)acnac denotes a bis-phenyl ?-ketoiminate ligand where Ar = 3,5-(t)Bu(2)C(6)H(3)). Structural analyses and computations show significant metal-ligand orbital interaction differences in U(IV) vs. Pu(IV) bonding. PMID:21655591

Schnaars, David D; Batista, Enrique R; Gaunt, Andrew J; Hayton, Trevor W; May, Iain; Reilly, Sean D; Scott, Brian L; Wu, Guang

2011-06-08

211

Poly(L-cysteine) as an electrochemically modifiable ligand for trace metal chelation.  

PubMed

The short-chain (n approximately equal to 50) homopolymer poly(L-cysteine) (PLC) has been previously studied for use as a novel metal chelator. PLC exhibits reversible oxidation-reduction chemistry involving the thiol groups of the cysteine (Cys) residues. Previously, chemical oxidation of the PLC immobilized on silica showed that metal binding capacity was minimal in the oxidized state. In this study, Cys and PLC are immobilized on a glassy carbon disk electrode (GCE) to study these redox processes and how they impact metal binding and release. Voltammetric and chronoamperometric methods were employed to demonstrate nearly monolayer coverage of both immobilized Cys monomer and immobilized PLC on GCE. The PLC-GCE exhibited a maximum metal binding capacity for Cd2+ of approximately 11 Cd2+ ions/chain. No detectable metal binding capacity was observed for oxidized PLC. The bound metals were capable of being efficiently released through disulfide bond formation and tertiary structure changes by means of repetitive oxidative pulses. The Cys-modified electrode exhibited a metal binding capacity for Cd2+ of approximately 1 Cd2+/Cys. Oxidized Cys did retain a significant capacity following oxidation, likely as a result of complexation with the terminal carboxylate site and unoxidized thiols. A glycine (Gly)-modified electrode was also evaluated as an amino acid control. Minimal Cd2+ binding was observed. Further metal binding studies were conducted using PLC-GCE with single metal solutions of Co2+, Cu2+, Ni2+, and Pb2+, as well as a multimetal solution composed of equal concentrations of all five target metals. The observed metal binding trend was as follows: Cu2+ > Cd2+ > Ni2+ > Pb2+ > Co2+. All metals were quantitatively released upon oxidation of PLC using the same anodic potential, 600 mV vs Ag/AgCl. PMID:15623275

Johnson, Ashley M; Holcombe, James A

2005-01-01

212

The effect of hexaaza-and hexathia–macrocyclic ligands on transition metal cytotoxicity in human hepatoma-derived cultured cells  

Microsoft Academic Search

The effect of macrocyclic ligands on cytotoxic concentrations of the transition metal ions of copper, zinc, and cadmium was investigated. For this purpose, a hexaaza-[3,6,9,17,20,23-hexaazatricyclo[23.3.1.111,15] triaconta–1(29),11(30),12,14,25,27–hexaene (L2)] and hexathia-chelating ligand [1,4,7,10,13,16-hexathiacyclooctadecane (L3)] were used in the human hepatoma-derived HepG2 cell line. The cytotoxicity was measured by the neutral red uptake inhibition assay. First, the NI50 of the ligands, i.e., the

P W Smet; T F Pauwels; P J Dierickx

2002-01-01

213

Pipe initiation anchor  

SciTech Connect

In a pipe initiation anchor for forming a fixed anchor point for use in laying underwater pipelines, this patent described the combination of: a frame; a ground engaging member; means for attaching the frame to the ground engaging member; and socket means carried in the frame defining a socket for receiving and retaining the end portion of the pipeline within the socket. The socket means include first and second generally horizontal bars, with the first bar mounted in the frame and with the second bar mounted on a pivoting member in the frame and spaced from the first bar, and a counter-balance weight carried on the pivoting member urging the second bar toward the first bar.

Morris, G.A.

1987-10-27

214

Role of the central metal ion and ligand charge in the DNA binding and modification by metallosalen complexes.  

PubMed

Several metal complexes of three different functionalized salen derivatives have been synthesized. The salens differ in terms of the electrostatic character and the location of the charges. The interactions of such complexes with DNA were first investigated in detail by UV-vis absorption titrimetry. It appears that the DNA binding by most of these compounds is primarily due to a combination of electrostatic and other modes of interactions. The melting temperatures of DNA in the presence of various metal complexes were higher than that of the pure DNA. The presence of additional charge on the central metal ion core in the complex, however, alters the nature of binding. Bis-cationic salen complexes containing central Ni(II) or Mn(III) were found to induce DNA strand scission, especially in the presence of co-oxidant as revealed by plasmid DNA cleavage assay and also on the basis of the autoradiogram obtained from their respective high-resolution sequencing gels. Modest base selectivity was observed in the DNA cleavage reactions. Comparisons of the linearized and supercoiled forms of DNA in the metal complex-mediated cleavage reactions reveal that the supercoiled forms are more susceptible to DNA scission. Under suitable conditions, the DNA cleavage reactions can be induced either by preformed metal complexes or by in situ complexation of the ligand in the presence of the appropriate metal ion. Also revealed was the fact that the analogous complexes containing Cu(II) or Cr(III) did not effect any DNA strand scission under comparable conditions. Salens with pendant negative charges on either side of the precursor salicylaldehyde or ethylenediamine fragments did not bind with DNA. Similarly, metallosalen complexes with net anionic character also failed to induce any DNA modification activities. PMID:9404652

Mandal, S S; Varshney, U; Bhattacharya, S

215

Synthesis and reactivity of a transition metal complex containing exclusively TEMPO ligands: Ni(?2-TEMPO)2.  

PubMed

The reaction of Ni(COD)(2) with two equivalents of the TEMPO radical at 68 °C affords the 16 e(-) "bow-tie" complex Ni(?(2)-TEMPO)(2), 1, in 78% yield. Compound 1 reacts with tert-butyl isocyanide and phenylacetylene at room temperature to yield the 16 e(-) distorted square planar nickel complexes Ni(?(2)-TEMPO)(?(1)-TEMPO)(CN(t)Bu), 2, and Ni(?(2)-TEMPO)(?(1)-TEMPOH)(CCPh), 4, respectively. The facile reactivity of 1 is aided by the transition of the TEMPO ligand from an ?(2) to ?(1) binding mode. Complex 4 is an unusual example of hydrogen atom transfer from phenylacetylene to a coordinated TEMPO ligand. PMID:21591738

Isrow, Derek; Captain, Burjor

2011-05-18

216

Coordination compounds of a number of d and f metals with amide ligands  

SciTech Connect

Several physiocochemical properties of amide coordination compounds of metals and the types of coordination of amides with complex-forming metal ions have been summarized in this review. The results of thermal investigations, including the intermediate and final products, and the structure of monosemicarbazidatozinc chloride have been presented, and the prospects of the practical utilization of the compounds have been considered.

Murzubralmov, B.

1986-10-01

217

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

PubMed

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

Prince, Bruce M; Cundari, Thomas R

2013-09-11

218

Late first-row transition metal complexes of a tetradentate pyridinophane ligand: electronic properties and reactivity implications.  

PubMed

The synthesis and structural comparison are reported herein for a series of late first-row transition metal complexes using a macrocyclic pyridinophane ligand, N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane ((tBu)N4). The (tBu)N4 ligand enforces a distorted octahedral geometry in complexes [((tBu)N4)M(II)(MeCN)2](OTf)2 (M = Fe(II), Co(II), Ni(II), Cu(II)), [((tBu)N4)Zn(II)(MeCN)(OTf)](OTf), and [((tBu)N4)Fe(III)(OMe)2](OTf), with elongated axial M-N(amine) distances compared to the equatorial M-N(py) distances. The geometry of [((tBu)N4)Cu(I)(MeCN)](OTf) is pentacoordinate with weak axial interactions with the amine N-donors of (tBu)N4. Complexes [((tBu)N4)M(MeCN)2](OTf)2 (M = Fe, Co) exhibit magnetic properties that are intermediate between those expected for high spin and low spin complexes. Electrochemical studies of ((tBu)N4)M complexes suggest that (tBu)N4 is suitable to stabilize Co(I), Ni(I), Co(III), Fe(III) solvato-complexes, while the electrochemical oxidation of ((tBu)N4)NiCl2 complex leads to formation of a Ni(III) species, supporting the ability of the (tBu)N4 ligand to stabilize first row transition metal complexes in various oxidation states. Importantly, the [((tBu)N4)M(II)(MeCN)2](2+) complexes exhibit two available cis coordination sites and thus can mediate reactions involving exogenous ligands. For example, the [((tBu)N4)Cu(II)(MeCN)2](2+) species acts as an efficient Lewis acid and promotes an uncommon hydrolytic coupling of nitriles. In addition, initial UV-vis and electron paramagnetic resonance (EPR) studies show that the [((tBu)N4)Fe(II)(MeCN)2](2+) complex reacts with oxidants such as H2O2 and peracetic acid to form high-valent Fe transient species. Overall, these results suggest that the ((tBu)N4)M(II) systems should be able to promote redox transformations involving exogenous substrates. PMID:23517006

Khusnutdinova, Julia R; Luo, Jia; Rath, Nigam P; Mirica, Liviu M

2013-03-21

219

Transition metal complexes of the novel hexadentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine.  

PubMed

The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine, bimptz, has been synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the 1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray diffraction. Upon reaction of bimptz with two equivalents of MnCl(2)·4H(2)O, CoCl(2)·6H(2)O and [Ru(dmso)(4)Cl(2)], the dinuclear complexes [Mn(2)(bimptz)(µ-Cl)(2)Cl(2)] (1), [Co(2)(bimptz)(CH(3)OH)(2)(µ-Cl)(2)](PF(6))(2) (3) and [Ru(2)(bimptz)(dmso)(2)(µ-Cl)(2)](PF(6))(2) (4), respectively, were isolated. The latter were found to have similar solid state structures with octahedrally coordinated metal centers bridged by the phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as PF(6)(-) salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)(2)](PF(6))(4) (6) was obtained from the reaction of two equivalents bimptz with [Ru(dmso)(4)Cl(2)]. In complex 6, three donor sites per ligand molecule are used for coordination of the Ru(ii) center. In each bimptz ligand, one of the remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the unprotonated N-methylimidazole ring of the other bimptz ligand. PMID:21409278

Roggan, Stefan; Limberg, Christian; Knispel, Christina; Tilley, T Don

2011-03-16

220

Metal-ligand cooperation in catalytic intramolecular hydroamination: a computational study of iridium-pyrazolato cooperative activation of aminoalkenes.  

PubMed

The present study comprehensively explores diverse mechanistic pathways for intramolecular hydroamination of prototype 2,2-dimethyl-4-penten-1-amine by Cp*Ir chloropyrazole (1; Cp*=pentamethylcyclopentadienyl) in the presence of KOtBu base with the aid of density functional theory (DFT) calculations. The most accessible mechanistic pathway for catalytic turnover commences from Cp*Ir pyrazolato (Pz) substrate adduct 2?S, representing the catalytically competent compound and proceeds via initial electrophilic activation of the olefin C=C bond by the metal centre. It entails 1) facile and reversible anti nucleophilic amine attack on the iridium-olefin linkage; 2) Ir-C bond protonolysis via stepwise transfer of the ammonium N-H proton at the zwitterionic [Cp*IrPz-alkyl] intermediate onto the metal that is linked to turnover-limiting, reductive, cycloamine elimination commencing from a high-energy, metastable [Cp*IrPz-hydrido-alkyl] species; and 3) subsequent facile cycloamine liberation to regenerate the active catalyst species. The amine-iridium bound 2?a?S likely corresponds to the catalyst resting state and the catalytic reaction is expected to proceed with a significant primary kinetic isotope. This study unveils the vital role of a supportive hydrogen-bonded network involving suitably aligned ?-basic pyrazolato and cycloamido moieties together with an external amine molecule in facilitating metal protonation and reductive elimination. Cooperative hydrogen bonding thus appears pivotal for effective catalysis. The mechanistic scenario is consonant with catalyst performance data and furthermore accounts for the variation in performance for [Cp*IrPz] compounds featuring a ?- or ?-basic pyrazolato unit. As far as the route that involves amine N-H bond activation is concerned, a thus far undocumented pathway for concerted amidoalkene ? cycloamine conversion through olefin protonation by the pyrazole N-H concurrent with N-C ring closure is disclosed as a favourable scenario. Although not practicable in the present system, this pathway describes a novel mechanistic variant in late transition metal-ligand bifunctional hydroamination catalysis that can perhaps be viable for tailored catalyst designs. The insights revealed herein concerning the operative mechanism and the structure-reactivity relationships will likely govern the rational design of late transition metal-ligand bifunctional catalysts and facilitate further conceptual advances in the area. PMID:22549963

Tobisch, Sven

2012-04-30

221

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

222

Antifungal activity of ?-methyl trans cinnamaldehyde, its ligand and metal complexes: promising growth and ergosterol inhibitors  

Microsoft Academic Search

Antifungal effectivity and utility of cinnamaldehyde is limited because of its high MIC and skin sensitivity. In this study,\\u000a ?-methyl trans cinnamaldehyde, a less irritating derivative, have been self coupled and complexed with Co(II) and Ni(II) to\\u000a generate N, N?–Bis (?-methyl trans cinnamadehyde) ethylenediimine [C22H24N2], [Co(C44H48N4)Cl2] and [Ni(C44H48N4)Cl2]. Ligand and complexes were characterized on the basis of FTIR, ESI–MS, IR

Sheikh Shreaz; Rayees A. Sheikh; Rimple Bhatia; Khan Neelofar; Sheikh Imran; Athar A. Hashmi; Nikhat Manzoor; Seemi F. Basir; Luqman A. Khan

223

One-step purification of rabbit histidine rich glycoprotein by dye-ligand affinity chromatography with metal ion requirement.  

PubMed

A simple method for purification of the histidine rich glycoprotein (rHRG) from rabbit sera was developed. The rHRG was purified by one-step affinity chromatography using the triphenylmethane dye "acid fuchsin" as a specific ligand, which gave an overall yield above 80%. Interestingly, the binding of rHRG to the ligand required the divalent transition-metal ions such as Zn2+, Ni2+, and Co2+ at pH 9.5. In the presence of 0.5 mM ZnCl2, the binding was enhanced 15 times compared with that in the absence of ZnCl2. Bound rHRG was efficiently eluted from the affinity absorbent with 100 mM imidazole or histidine. Purified rHRG was homogeneous with an Mr of 94 kDa when analyzed by SDS-PAGE, whereas isoelectric focusing revealed microheterogeniety with pI values ranging from 6.3 to 6.8. Blotting analysis with lectins specific for carbohydrate moieties and treatment with glycosidases demonstrated that rHRG is a highly N-glycosylated protein with diverse carbohydrate structures. PMID:11185553

Mori, S; Nishibori, M; Yamaoka, K; Okamoto, M

2000-11-15

224

[Os(bpy)2(CO)(enIA)][OTf]2: a novel sulfhydryl-specific metal-ligand complex.  

PubMed

The synthesis and physical-chemical characterization of the metal-ligand complex [Os(bpy)2(CO)(enIA)][OTf]2 (where enIA = ethylenediamine iodoacetamide) with a sulfhydryl-specific functional group is described. The UV and visible absorption and luminescence emission, including lifetime and steady-state anisotropy, are reported for the free probe and the probe covalently linked to two test proteins. The spectroscopic properties of the probe are unaffected by chemical modification and subsequent covalent linkage to the proteins. The luminescence lifetime in aqueous buffer is approximately 200 ns and the limiting anisotropy is greater than 0.125, suggesting a potentially useful probe for biophysical investigations. PMID:15907113

Garino, Claudio; Ghiani, Simona; Gobetto, Roberto; Nervi, Carlo; Salassa, Luca; Ancarani, Valentina; Neyroz, Paolo; Franklin, Laurie; Alexander Ross, J B; Seibert, Eleanore

2005-05-30

225

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

226

Transition metal(II) complexes of vitamin B13 with monodentate orotate(1-) ligands  

NASA Astrophysics Data System (ADS)

The formation of bisorotate(1-) complexes of the type [M(C5H3N2O4)2(H2O)4]·nH2O (M=Co, Ni, Zn and n=2, 4) was achieved by the reaction of ammonium orotate with the corresponding M(II) ions. The crystal structure of [Co(C5H3N2O4)2(H2O)4]·2H2O was determined by single crystal X-ray diffraction analysis. Each Co(II) ion in the monomeric Co(C5H3N2O4)2(H2O)4 units adapts a slightly distorted octahedral geometry comprised of two monodentate orotate anions and four H2O ligands. Columnar packing of pyrimidine rings along the c axis leads to the formation of layers that propagate parallel to the b axis and the adjacent layers are linked by hydrogen bonds forming a 3D lattice. Complexes of nickel and zinc were assumed to contain monodentate bound orotate ligands as well on the basis of physical and spectroscopic data.

Köse, Dursun Ali; Zümreoglu-Karan, Birgül; ?ahin, Onur; Büyükgüngör, Orhan

2006-05-01

227

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

228

Reversal of the hydrogen bond to zinc ligand histidine-119 dramatically diminishes catalysis and enhances metal equilibration kinetics in carbonic anhydrase II.  

PubMed

Direct metal ligands to transition metals in metalloproteins exert a profound effect on protein-metal affinity and function. Indirect ligands, i.e., second-shell residues that hydrogen bond to direct metal ligands, typically exert more subtle effects on the chemical properties of the protein-metal complex. However, E117 of human carbonic anhydrase II (CAII), which is part of the E117-119-Zn(2+) triad, is a notable exception: E117-substituted CAIIs exhibit dramatically increased kinetics of zinc complexation, and the E117Q variant exhibits enormously diminished catalytic activity and sulfonamide affinity. The three-dimensional structures of zinc-bound and zinc-free E117Q CAII reveal no discrete structural changes in the active site that are responsible for enhanced zinc equilibration kinetics and decreased activity. Additionally, the structure of the acetazolamide complex is essentially identical to that of the wild-type enzyme despite the 10(4)-fold loss of enzyme-inhibitor affinity. We conclude, therefore, that the functional differences between E117Q and wild-type CAIIs arise from electrostatic and not structural differences in the active site. We propose that the E117Q substitution reverses the polarity of the residue 117-H119 hydrogen bond, thereby stabilizing H119 as a histidinate anion in the E117Q CAII holoenzyme. The additional negative charge in the first coordination sphere of the metal ion increases the pK(a) of the zinc-water ligand, destabilizes the transition state for CO(2) hydration, and facilitates the exchange of a zinc-histidine ligand with an additional water molecule by decreasing the stability of the tetrahedral zinc complex. These novel properties engineered into E117Q CAII facilitate the exploitation of CAII as a rapid and sensitive Zn(2+) biosensor. PMID:8639494

Huang, C C; Lesburg, C A; Kiefer, L L; Fierke, C A; Christianson, D W

1996-03-19

229

Dynamical processes in the lowest-excited triplet metal-to-ligand charge transfer states of ruthenium and osmium diimine complexes in crystals  

NASA Astrophysics Data System (ADS)

This review presents a detailed description of the lowest-excited states in ruthenium(II) and osmium(II) diimine complexes, based on extensive studies of their optical spectra in crystalline environments. Deuteration, and Zeeman and Stark effects provide a wealth of incisive results. The transferred charge in the lowest-excited triplet metal-to-ligand charge transfer states is localized on a single ligand in ruthenium(II) diimine complexes and the excitation exchange interaction between equivalent metal-ligand subunits is 0 5 cm . Localization gives rise to subtle effects, such as small Stokes shifts, in spectra. The lowest-excited states of osmium(II) diimine complexes in crystals with low inhomogeneous broadening are well described as coherent intramolecular excitons with excitation exchange interactions in the range from 2 to 30 cm .

Riesen, Hans; Wallace, Lynne; Krausz, Elmars

230

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

PubMed

A series of tetraaza (N(4) donor) macrocyclic ligands (L(1)-L(4)) were derived from the condensation of o-phthalaldehyde (OPA) with some substituted aromatic amines/azide, and subsequently used to synthesize the metal complexes of Ru(II), Pd(II) and Pt(II). The structures of macrocyclic ligands and their metal complexes were characterized by elemental analyses, IR, (1)H &(13)C NMR, mass and electronic spectroscopy, thermal, magnetic and conductance measurements. Both the ligands and their complexes were screened for their antibacterial activities against Gram positive and Gram negative bacteria by MIC method. Besides, these macrocyclic complexes were investigated as catalysts in the oxidation of pharmaceutical drug didanosine. The oxidized products were further treated with sulphanilic acid to develop the colored products to determine by spectrophotometrically. The current oxidation method is an environmentally friendly, simple to set-up, requires short reaction time, produces high yields and does not require co-oxidant. PMID:22750687

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

2012-06-06

231

Isospecific polymerization of 1-hexene by C1-symmetric half-metallocene dimethyl complexes of group 4 metals with bidentate N-substituted iminomethylpyrrolyl ligands.  

PubMed

Non-bridged half-metallocene dimethyl complexes of group 4 metals 2a-4a with an N-4-methoxyphenyl(iminomethyl)pyrrolyl ligand 1a were synthesized and characterized by NMR spectroscopy and X-ray analysis. Upon activation with [Ph3C][B(C6F5)4], these complexes became active catalysts for the polymerization of 1-hexene. A series of hafnium complexes with various N-substituents on the imine group of ligands 1b-1g were also prepared and applied as catalysts for 1-hexene polymerization. The activation parameters for the exchange process between the two methyl groups bound to the metal for Cp*MMe2(R-pyr) complexes were estimated by NMR shape analysis at various temperatures. The findings indicated that the transition state of the ligand flipping process might be associated with the isoselectivity of the polymerization reaction. PMID:23235804

Yasumoto, Takahiro; Yamamoto, Keishi; Tsurugi, Hayato; Mashima, Kazushi

2012-12-12

232

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

PubMed

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

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

1988-01-12

233

Syntheses and structural characterization of two metal-organic frameworks from tripodal and dipodal ligands  

Microsoft Academic Search

Two isomorphic metal–organic frameworks, {[M3(nbtb)2(bpe)3(H2O)2]?·?2H2O}n (M?=?Co for (1) and Ni for (2)), have been synthesized by the combination of an extended linker 1,2-bi(4-pyridyl)ethene(bpe) and tripodal tecton 5-nitro-1,2,3-benzenetricarboxylic acid. Single-crystal X-ray diffraction studies indicate that 1 and 2 are (4,?5)-connected motifs containing (4?·?6?·?8) (4?·?6?·?8) (6?·?8) (4?·?6) topologies. The magnetic behavior of 1 exhibits weak antiferromagnetic interaction between metal centers.

Jian-Qiang Liu

2011-01-01

234

Heterobimetallic metal-complex assemblies constructed from the flexible arm-like ligand 1,1'-bis[(3-pyridylamino)carbonyl]ferrocene: structural versatility in the solid state.  

PubMed

The bidentate ferrocenyl sandwich molecule 1,1'-bis[(3-pyridylamino)carbonyl]ferrocene (3-BPFA) has been employed as an organometallic ligand in reactions with a series of transition metal salts to construct heterobimetallic architectures. X-ray crystallographic characterization reveals that the crystal packing of free ligand 3-BPFA induces spontaneous resolution of helical chains via intermolecular hydrogen bonds. By combining the flexibility from the arm-like molecule (3-BPFA) with the variation of the coordination property from different metal ions and/or the different counteranions, five different types of architectures are prepared: one octahedral coordination cage (copper(II) complex 1); two discrete pseudocapsules for combination of chlorine anions (nickel(II) complex 2 and cobalt(II) complex 3); two dimers with metal-metal interactions (silver(I) complexes 4 and 5); one macrocyclic complex (mercury(II) complex 6); and five two-dimensional mixed-metal-organic frameworks (M'-MOFs) (zinc(II), cadmium(II), and mercury(II) complexes 7-11). The structures of all complexes are characterized in detail by IR, elementary analysis, and single-crystal X-ray diffraction analysis. The factors inducing the structure variation among the complexes are discussed by taking account of the coordination geometry of different metal ions, the span angle between the two "arms", and the coordination mode of the 3-BPFA ligand. PMID:20095640

Wei, Kai-Ju; Ni, Jia; Liu, Yangzhong

2010-02-15

235

A strategy toward constructing a bifunctionalized MOF catalyst: post-synthetic modification of MOFs on organic ligands and coordinatively unsaturated metal sites.  

PubMed

A new strategy toward constructing bifunctionalized MOFs has been developed based on post-synthetic modification of MOFs on organic ligands and coordinatively unsaturated metal sites, respectively. Based on this strategy, an organo-bifunctionalized MOF catalyst has been synthesized for the first time and successfully applied in one-pot tandem reaction. PMID:22588474

Li, Baiyan; Zhang, Yiming; Ma, Dingxuan; Li, Lu; Li, Guanghua; Li, Guodong; Shi, Zhan; Feng, Shouhua

2012-05-15

236

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

237

Towards longer-lived metal-to-ligand charge transfer states of iron(II) complexes: an N-heterocyclic carbene approach.  

PubMed

A 9 ps (3)MLCT lifetime was achieved by a Fe(II) complex based on C(NHC)^N(py)^C(NHC) pincer ligands. This is the longest known so far for any kind of complexes of this abundant metal, and increased by almost two orders of magnitude compared to the reference Fe(II) bis-terpyridine complex. PMID:23752944

Liu, Yizhu; Harlang, Tobias; Canton, Sophie E; Chábera, Pavel; Suárez-Alcántara, Karina; Fleckhaus, André; Vithanage, Dimali A; Göransson, Erik; Corani, Alice; Lomoth, Reiner; Sundström, Villy; Wärnmark, Kenneth

2013-07-21

238

A tetranuclear Cu4(?3-OH)2-based metal-organic framework (MOF) with sulfonate-carboxylate ligands for proton conduction.  

PubMed

A new tetranuclear Cu4(?3-OH)2-based metal-organic framework (MOF) with sulfonate-carboxylate ligands features large hydrophilic channels. This MOF exhibits proton conductivity over 10(-3) S cm(-1) at 85-100 °C and 98% relative humidity and colossal dielectric constant. PMID:24092457

Dong, Xi-Yan; Wang, Rui; Li, Jia-Bin; Zang, Shuang-Quan; Hou, Hong-Wei; Mak, Thomas C W

2013-10-17

239

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...

240

Yttrium-89 NMR: A Possible Spin Relaxation Probe for Studying Metal Ion Interactions with Organic Ligands.  

National Technical Information Service (NTIS)

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-r...

G. C. Levy P. L. Rinaldi J. T. Bailey

1979-01-01

241

Versatile chemical transformations of benzoxazole based ligands on complexation with 3d-metal ions.  

PubMed

Two benzoxazoles derivative ligands were synthesized from the condensation of 3,5-di-tert-butyl-o-benzoquinone (DTBBQ) with ethanolamine or 1,3-diamino-2-hydroxypropane in methanol. Condensation of DTBBQ with ethanolamine gives the expected 5,7-di-tert-butyl-2-methylenhydroxylbenzoxazole (HL1) while with 1,3-diamino-2-hydroxypropane it gives (2-hydroxyethyl-2-{2,4-bis(1,1-dimethylethyl)-1-phenol-6 amino}-2{5,7-di-tert-butyl-benzoxazole}) (H(2)L2) with only one benzoxazole ring instead of the symmetric bis-benzoxazole derivative. The structure of HL1 and H(2)L2 were confirmed by NMR-spectroscopy and X-ray diffraction on a single crystal for HL1. The reaction of HL1 with CuCl(2) gives a mononuclear [Cu(II)(HL1)(2)Cl(2)] (1) complex for which the crystal structure shows that HL1 is preserved. In contrast, upon reaction with nickel(II), cobalt(II), and manganese(II) H(2)L2 is further oxidized and transformed in new ligands HL3 in mononuclear complexes [M(II)(L3)(2)] (M = Ni(II) (2); M = Co(II) (3)) and H(2)L4 in tetranuclear complex [Mn(II)(4)(HL4)(4)Cl(4)] (4) as found from the crystal structures of complexes 2-4. Electrochemical studies for complexes 2 and 3 evidence complicated redox properties. [Mn(II)(4)(HL4)(4)Cl(4)] (4) has a cubane-like structure with a "4 + 2" fashion The magnetic susceptibility of 4 is well fitted considering one Mn---Mn interaction J(a)(Mn(II)-Mn(II)) = -0.50(1) cm(-1) with g = 2.00(7). PMID:22233278

Iasco, Olga; Novitchi, Ghenadie; Jeanneau, Erwann; Tommasino, Jean Bernard; Roques, Nans; Luneau, Dominique

2012-01-10

242

Metal-organic complexes in geochemical processes: Estimation of standard partial molal thermodynamic properties of aqueous complexes between metal cations and monovalent organic acid ligands at high pressures and temperatures  

NASA Astrophysics Data System (ADS)

Regression of standard state equilibrium constants with the revised Helgeson-Kirkham-Flowers (HKF) equation of state allows evaluation of standard partial molal entropies ( overlineSo) of aqueous metal-organic complexes involving monovalent organic acid ligands. These values of overlineSo provide the basis for correlations that can be used, together with correlation algorithms among standard partial molal properties of aqueous complexes and equation-of-state parameters, to estimate thermodynamic properties including equilibrium constants for complexes between aqueous metals and several monovalent organic acid ligands at the elevated pressures and temperatures of many geochemical processes which involve aqueous solutions. Data, parameters, and estimates are given for 270 formate, propanoate, n-butanoate, n-pentanoate, glycolate, lactate, glycinate, and alanate complexes, and a consistent algorithm is provided for making other estimates. Standard partial molal entropies of association ( ? -Sro) for metal-monovalent organic acid ligand complexes fall into at least two groups dependent upon the type of functional groups present in the ligand. It is shown that isothermal correlations among equilibrium constants for complex formation are consistent with one another and with similar correlations for inorganic metal-ligand complexes. Additional correlations allow estimates of standard partial molal Gibbs free energies of association at 25°C and 1 bar which can be used in cases where no experimentally derived values are available.

Shock, Everetr L.; Koretsky, Carla M.

1995-04-01

243

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

244

Influence of vanadium-organic ligands treatment on selected metal levels in kidneys of STZ rats.  

PubMed

The objective of the study was to investigate the effects of five organic vanadium complexes supplement and a small dose of insulin injection on V, Fe, Cu, Zn, Mn, Ca, and K level in the streptozotocin diabetic rat's kidney during a 5-week treatment with the tested complexes. In all groups of animals, metal level in the lyophilized kidney organs was investigated by means of the proton induced X-ray emission method. Tissue vanadium level was naturally higher in vanadium-treated rats. The maximum level of vanadium was observed in the kidney (x(mean) = 16.6 ?g/g). The influence of vanadium administration on other metal level in rat's tissue was also investigated. Spectacular influence of vanadium action was observed on copper and zinc level in examined tissue. PMID:23661329

Kro?niak, Miros?aw; Kowalska, Joanna; Francik, Renata; Grybo?, Ryszard; Blusz, Magdalena; Kwiatek, Wojciech M

2013-05-11

245

A high voltage organic-inorganic hybrid photovoltaic cell sensitized with metal-ligand interfacial complexes.  

PubMed

A thin solid-state photovoltaic cell of organic-inorganic hetero junctions was fabricated by forming a dye-metal charge-transfer complex as the sensitizer monolayer at the interface of crystalline state organic and inorganic semiconductors. The organic-inorganic hybrid thin-film photocell generates a high photovoltage of 1.2 V, yielding an energy conversion efficiency of up to 1.5%. PMID:22932690

Ishii, Ayumi; Miyasaka, Tsutomu

2012-08-30

246

Protein Interaction with Immobilized Metal Ion Affinity Ligands under High Ionic Strength Conditions  

Microsoft Academic Search

An investigation into the adsorption behavior under batch equilibrium binding conditions of hen egg white lysozyme (HEWL) with the immobilized metal ion affinity chromatographic adsorbent, Cu2+–IDA Sepharose CL-4B, in the presence of high concentrations of NaCl or KCl has been undertaken. When the concentration of NaCl or KCl in the adsorption buffer was ?0.2M, the adsorption data correlated with predictions

Wei Jiang; Milton T. W. Hearn

1996-01-01

247

Binuclear organo-rare-earth-metal complexes containing silicon-linked cyclopentadienyl ligands in either a chelating or metal-bridging fashion: A mass spectrometric study  

SciTech Connect

Four chloride-bridged, binuclear bis(cyclopentadienyl) rare-earth-metal complexes have been subjected to detailed mass spectrometric studies adopting exhaustively the B/E-linked scan technique: (Me{sub 2}Si(C{sub 5}H{sub 4}){sub 2}Yb({mu}-Cl)){sub 2} (1), ((Me{sub 3}SiC{sub 5}H{sub 4}){sub 2}Yb({mu}-Cl)){sub 2} (2), (Me{sub 2}Si(C{sub 5}H{sub 4}){sub 2}Y({mu}-Cl)){sub 2} (3), and Me{sub 2}Si(C{sub 5}H{sub 4}){sub 2}Yb({mu}-Cl){sub 2}Y(C{sub 5}H{sub 4}){sub 2}SiMe{sub 2} (5). The strict dominance of binuclear fragments in the spectrum of pure 1 indicates, in excellent accordance with a previous crystallographic X-ray study, the presence of metal-bridging Me{sub 2}Si(C{sub 5}H{sub 4}){sub 2} ligands in the vapor state. The existence of the new complex 5, which could not be separated chemically from admixtures of 1 and 3 (i.e., from sample 4), has been confirmed unambiguously by deducing its individual fragmentation pattern from a systematic B/E-linked scan analysis.

Qiao, Ke; Fischer, R.D. (Universitaet Hamburg (West Germany)); Paolucci, G. (Universita di Venezia (Italy)); Traldi, P. (Servizio di Spettrometria di Massa del CNR Padova (Italy)); Celon, E. (Universita di Padova (Italy))

1990-05-01

248

Dinuclear silver(I) complexes for the design of metal-ligand networks based on triazolopyrimidines.  

PubMed

Silver(I) coordination complexes with the versatile and biomimetic ligands 1,2,4-triazolo[1,5-a]pyrimidine (tp), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) and 7-amine-1,2,4-triazolo[1,5-a]pyrimidine (7atp) all feature dinuclear [Ag(2)(?-tp)(2)](2+) building units (where tp is a triazolopyrimidine derivative), which are the preferred motif, independently of the counter-anion used. According to AIM (atoms in molecules) and ELF (electron localization function) analyses, this fact is due to the great stability of these dinuclear species. The complexes structures range from the dinuclear entities [Ag(2)(?-tp)(2)(CH(3)CN)(4)](BF(4))(2) (1), [Ag(2)(?-tp)(2)(CH(3)CN)(4)](ClO(4))(2) (2), [Ag(2)(?-7atp)(2)](ClO(4))(2) (3) and [Ag(2)(?-dmtp)(2)(CH(3)CN)](PF(6))(ClO(4)) (4) over the 1D polymer chain [Ag(2)(?-CF(3)SO(3))(2)(?-dmtp)(2)](n) (5) to the 3D net {[Ag(2)(?(3)-tp)(2)](PF(6))(2)·?6H(2)O}(n) (6) with NbO topology. PMID:21971399

Caballero, Ana B; Maclaren, Jana K; Rodríguez-Diéguez, Antonio; Vidal, Isaac; Dobado, Jose A; Salas, Juan M; Janiak, Christoph

2011-10-05

249

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

250

Crystal and molecular structure of manganese(II) lapacholate, a novel polymeric species undergoing temperature-reversible metal to ligand electron transfer.  

PubMed

Lapachol (2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphtoquinone) (HLap, C(15)H(14)O(3)) reacts with Mn(2+) producing a novel polymeric complex with formula: [Mn(Lap)(2)](n). Two ligands chelate the metal through their ortho oxygen (O1, O2) moiety while two para oxygens, from other Lap ligands, complete the octahedral coordination sphere. Thus far, all reported Lap metal complexes are mononuclear, lack the metal-trans-quinonic (para) oxygen binding and have Lap as a bidentate ligand. Synthesis, X-ray diffraction, IR, and UV-visible spectroscopic properties, thermogravimetric analysis, and differential thermal analysis of this complex are reported along with a density functional theory study describing electron transfer from the Mn to the Lap ligand at low temperature. X-ray structure determinations at 125, 197, and 300 K describe the progressive trend of a Mn contribution to the Mn-O1 bond length as a function of T. The Mn-O1 bond distance increases with temperature and may be therefore associated with a semiquinonate action at low T by the carbonyl O1 donor (and corresponding to Mn(III)). It transforms to a more classical coordinative bond at room T and stabilizes a Mn(II) species; this is a reversible phenomenon involving Mn(II)-Mn(III) oxidation states. PMID:19281193

Caruso, Francesco; Martínez, Miguel A; Rossi, Miriam; Goldberg, Alexander; Chacón Villalba, M Elizabeth; Aymonino, Pedro J

2009-04-20

251

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

2013-04-12

252

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

253

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

254

Vibrational modeling of copper-histamine complexes: metal-ligand IR modes investigation.  

PubMed

Recent reports on proteins and related models show that vibrational spectroscopy in the far-infrared domain is a promising technique to characterize metal sphere coordination in proteins. The low-frequency modes are however complex, and there is a need to develop the analysis of metal sites by means of quantum chemical calculations as a support for useful interpretation of the far-IR data. In this study, we determined vibrational properties for systems containing Cu(II)-N(Imidazole) interactions present in many biological complexes by means of quantum chemical calculations and confronted the normal mode description with available experimental data. Analysis of the [Cu(histamine)]2+ complex led us to conclude that the anharmonic contributions are negligible in the far-IR domain. Geometry optimizations and vibrational frequency calculations of [Cu(hm)]2+ and [Cu(hm)2(ClO4)2] complexes were compared using various hybrid DFT functionals and basis sets. These investigations stressed the need of potential energy distribution calculations (PED) to assign the vibrational modes, to obtain an overall description of the vibration modes, and to efficiently compare the methods. Comparison of calculation methods with the B3LYP/6-31+G(d,p) and B3LYP/6-311+G(2d,2p) methods and with available experimental data showed that the B3LYP/6-31G(d,p) level of theory provides accurate predictions of the normal mode frequencies and assignments. These comparisons also enlighten that theoretical investigations of 2H- and 65Cu-labeled [Cu(hm)2(ClO4)2] complexes give with a very good accuracy the band shifts of the labeled copper-histamine derivatives. The theoretical calculations combined with experimental data allowed us to predict and calculate with good accuracy the values and assignments of the low-frequency IR modes, notably those involving metal contribution. PMID:19831393

Xerri, Bertrand; Flament, Jean-Pierre; Petitjean, Hugo; Berthomieu, Catherine; Berthomieu, Dorothee

2009-11-12

255

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

PubMed

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±0.1K 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 ?logK, logX and logX' 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)5-FU(A)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. PMID:23416916

Shobana, Sutha; Dharmaraja, Jeyaprakash; Selvaraj, Shanmugaperumal

2013-01-23

256

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

257

Preparation, structure, and ethylene (co)polymerization behavior of Group IV metal complexes with an [OSSO]-carborane ligand.  

PubMed

The synthesis of Group IV metal complexes that contain a tetradentate dianionic [OSSO]-carborane ligand [(HOC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2 (B(10)H(10))] (1a) is described. Reactions of TiCl(4) and Ti(OiPr)(4) with the [OSSO]-type ligand 1a afford six-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2)] (2a) and four-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))(OiPr)(2)] (2b), respectively. ZrCl(4) and HfCl(4) were treated with 1a to give six-coordinated zirconium complex [Zr(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2) (thf)(2)] (2c) and six-coordinated hafnium complex [Hf(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2)] (2d). All the complexes were fully characterized by IR, NMR spectroscopy, and elemental analysis. In addition, X-ray structure analyses were performed on complexes 2a and 2b and reveal the expected different coordination geometry due to steric hindrance effects. Extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on complexes 2c and 2d to describe the coordination chemistry of this ligand around Zr and Hf. Six-coordinated titanium complex 2a showed good activity toward ethylene polymerization as well as toward copolymerization of ethylene with 1-hexene in the presence of methylaluminoxane (MAO) as cocatalyst (up to 1060 kg[mol(Ti)](-1) h(-1) in the case of 10 atm of ethylene pressure). PMID:21695738

Hu, Ping; Wang, Jian-Qiang; Wang, Fosong; Jin, Guo-Xin

2011-06-21

258

1,3-Diboraheterocycles as ligands in metal complexes involving endo-C–H bonds  

Microsoft Academic Search

Pentaalkyl-2,3-dihydro-1,3-diboroles possess unique properties in [LnM(C3B2HR5)] complexes because the neutral heterocycle functions as 4e donor toward metal complex fragments e.g. CpM (M=Co, Rh), (arene)Fe, and others. The specific feature of these complexes is its MeC–H group with methyl in the exo- and hydrogen in an endo-position, forming a bridging 3c,2e C–H–B or an axial M–C–H bonding. This reduces the strength

Walter Siebert

2009-01-01

259

Aromatizing Olefin Metathesis by Ligand Isolation inside a Metal- Organic Framework.  

PubMed

The aromatizing ring-closing metathesis has been shown to take place inside an extended porous framework. Employing a combination of solvent-assisted linker exchange and postsynthesis modification using olefin metathesis, the noninterpenetrated SALEM-14 was formed and converted catalytically into PAH-MOF-1 with polycyclic aromatic hydrocarbon (PAH) pillars. The metal-organic framework in SALEM-14 prevents "intermolecular" olefin metathesis from occurring between the pillars in the presence of the first generation Hoveyda-Grubbs catalyst, while favoring the production of a PAH, which can be released from the framework under acidic conditions in dimethylsulfoxide. PMID:24047342

Vermeulen, Nicolaas A; Karagiaridi, Olga; Sarjeant, Amy A; Stern, Charlotte L; Hupp, Joseph T; Farha, Omar K; Stoddart, J Fraser

2013-09-26

260

Formation of metal complex ions from amino acid in the presence of Li+, Na+ and K+ by electrospray ionization: metal replacement of hydrogen in the ligands.  

PubMed

Alkali metal cations easily form complexes with proteins in biological systems; understanding amino acid clusters with these cations can provide useful insight into their behaviors at the molecular level including diagnosis and therapy of related diseases. For the purpose of characterization of basic interaction between amino acids and alkali metal, each of the 20 naturally occurring amino acids were ionized in the presence of lithium, sodium and potassium cations by electrospray ionization, and the resulting product ions were analyzed. We focus our attention on the gas phase alkali metal ion-proton exchanged complexes in current study, specifically complexes with serine, threonine, asparagine and glutamine, which share characteristic pattern unlike other amino acids. All amino acids generated [M + H](+) and [M + Na](+) ions, where M stands for the neutral amino acid. Serine, threonine, asparagine and glutamine generated cluster ions of [nM - nH + (n + 1)Na](+) and [nM - (n - 1)H + (n - 1)Na + K](+) , where n = 1-7. While the (M - H + Li) and (M - H + K) species were not observed, the neutral (M - H + Na) species formed by proton-sodium cation exchange had a highly stable cyclic structure with ketone and amine ligand sites, suggesting that (M - H + Na) serves as a building block in cluster ion formation. Cluster ion intensity distributions of [nM - nH + (n + 1)Na](+) and [nM - (n - 1)H + (n - 1)Na + K](+) showed a magic number at n = 3 and 4, respectively. Extensive B3LYP-DFT quantum mechanical calculations were carried out to elucidate the geometry and energy of the cluster ions, and they provided a reasonable explanation for the stability and structure of the cluster ions. PMID:21500307

Jang, Soonmin; Song, Min Ju; Kim, Hyunsik; Choi, Sung-Seen

2011-05-01

261

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

262

Role of the [2Fe-2S]2+ cluster in biotin synthase: mutagenesis of the atypical metal ligand arginine 260.  

PubMed

Biotin synthase (BS) is an S-adenosylmethionine (AdoMet)-dependent radical enzyme that catalyzes the addition of sulfur to dethiobiotin. Like other AdoMet radical enzymes, BS contains a [4Fe-4S] cluster that is coordinated by a highly conserved CxxxCxxC sequence motif and by the methionyl amine and carboxylate of AdoMet. The close association of the [4Fe-4S]+ cluster with AdoMet facilitates reductive cleavage of the sulfonium and the generation of transient 5'-deoxyadenosyl radicals, which are then proposed to sequentially abstract hydrogen atoms from the substrate to produce carbon radicals at C9 and C6 of dethiobiotin. BS also contains a [2Fe-2S]2+ cluster located approximately 4-5 A from dethiobiotin, and we have proposed that a bridging sulfide of this cluster quenches the substrate radicals, leading to formation of the thiophane ring of biotin. In BS from Escherichia coli, the [2Fe-2S]2+ cluster is coordinated by cysteines 97, 128, and 188, and the atypical metal ligand, arginine 260. The evolutionary conservation of an arginine guanidinium as a metal ligand suggests a novel role for this residue in tuning the reactivity or stability of the [2Fe-2S]2+ cluster. In this work, we explore the effects of mutagenesis of Arg260 to Ala, Cys, His, and Met. Although perturbations in a number of characteristics of the [2Fe-2S]2+ cluster and the proteins are noted, the reconstituted enzymes have in vitro single-turnover activities that are 30-120% of that of the wild type. Further, in vivo expression of each mutant enzyme was sufficient to sustain growth of a bioB- mutant strain on dethiobiotin-supplemented medium, suggesting the enzymes were active and efficiently reconstituted by the in vivo iron-sulfur cluster (ISC) assembly system. Although we cannot exclude an as-yet-unidentified in vivo role in cluster repair or retention, we can conclude that Arg260 is not essential for the catalytic reaction of BS. PMID:17115711

Broach, Robyn B; Jarrett, Joseph T

2006-11-28

263

Solid-state transition metal chemistry with quinolin-4-yl-methyl-[N-(n-butyl)amino]-diphenylphosphine oxide (4-qmape): Crystal structure of the 4-qmape ligand  

NASA Astrophysics Data System (ADS)

A series of three perchlorate coordination compounds of bioactive diethyl quinolin-4-yl-methyl(N-butylamino)diphenylphosphine oxide (4-qmape) ligand, with the following stoichiometries [M(2-qmape)2](ClO4)2 MCu and Ni and [Co(2-qmape)2](ClO4)2, were obtained and studied. Stoichiometry and stereochemistry of the compounds was confirmed by spectroscopic and magnetic studies as well as by elemental analyses. In particular, the crystal structure of the free ligand was determined. The 4-qmape ligand has a potential capacity to coordinate to metal ions by following atoms: phosphoryl oxygen, amino nitrogen and quinolyl nitrogen. In studied compounds, 4-qmape adopts the didentate N,O-coordination mode, bonding metal centers through the phosphoryl oxygen and amino nitrogen. Quinoline nitrogen atom does not participate in coordination. The all complexes are monomeric with tetrahedral environment of metal ions. Magnetic studies (1.8-300 K) indicate existence of a very weak exchange coupling between metal centers in crystal lattice.

?urowska, Bogumi?a; Brzuszkiewicz, Anna; Boduszek, Bogdan

2012-11-01

264

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

2010-12-07

265

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

2012-06-06

266

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

267

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

268

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

269

4-{[(2-Hydroxyphenyl)imino]methyl}-1,2-benzenediol (HIMB) anchored Amberlite XAD-16: Preparation and applications as metal extractants.  

PubMed

Amberlite XAD-16 was loaded with 4-{[(2-hydroxyphenyl)imino]methyl}-1,2-benzenediol (HIMB) via azo linker and the resulting resin AXAD-16-HIMB explored for enrichment of Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II) in the pH range 5.0-8.0. The sorption capacity was found between 56 and 415mumolg(-1) and the preconcentration factors from 150 to 300. Tolerance limits for foreign species are reported. The kinetics of sorption is not slow, as t(1/2) is metal ion ions in river and synthetic water samples, Co in vitamin tablets and Zn in powdered milk samples. PMID:19071301

Venkatesh, Gopalan; Singh, Ajai K

2006-05-09

270

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

271

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

272

Mechanistic Inferences from the Binding of Ligands to LpxC, A Metal-Dependent Deacetylase  

SciTech Connect

The metal-dependent deacetylase LpxC catalyzes the first committed step of lipid A biosynthesis in Gram-negative bacteria. Accordingly, LpxC is an attractive target for the development of inhibitors that may serve as potential new antibiotics for the treatment of Gram-negative bacterial infections. Here, we report the 2.7 Angstroms resolution X-ray crystal structure of LpxC complexed with the substrate analogue inhibitor TU-514 and the 2.0 Angstroms resolution structure of LpxC complexed with imidazole. The X-ray crystal structure of LpxC complexed with TU-514 allows for a detailed examination of the coordination geometry of the catalytic zinc ion and other enzyme-inhibitor interactions in the active site. The hydroxamate group of TU-514 forms a bidentate chelate complex with the zinc ion and makes hydrogen bond interactions with conserved active site residues E78, H265, and T191. The inhibitor C-4 hydroxyl group makes direct hydrogen bond interactions with E197 and H58. Finally, the C-3 myristate moiety of the inhibitor binds in the hydrophobic tunnel of the active site. These intermolecular interactions provide a foundation for understanding structural aspects of enzyme-substrate and enzyme-inhibitor affinity. Comparison of the TU-514 complex with cacodylate and imidazole complexes suggests a possible substrate diphosphate binding site and highlights residues that may stabilize the tetrahedral intermediate and its flanking transition states in catalysis. Evidence of a catalytic zinc ion in the native zinc enzyme coordinated by H79, H238, D242, and two water molecules with square pyramidal geometry is also presented. These results suggest that the native state of this metallohydrolase may contain a pentacoordinate zinc ion, which contrasts with the native states of archetypical zinc hydrolases such as thermolysin and carboxypeptidase A.

Gennadios,H.; Whittington, D.; Li, X.; Fierke, C.; Christianson, D.

2006-01-01

273

Metal-assisted in situ formation of a tridentate acetylacetone ligand for complexation of fac-Re(CO)3+ for radiopharmaceutical applications.  

PubMed

Reaction of [NEt4]2[ReBr3(CO)3] with 2,4-pentanedione (acac) yields a complex of the type fac-Re(acac)(OH2)(CO)3 (1) under aqueous conditions. 1 was further reacted with a monodentate ligand (pyridine) to yield a fac-Re(acac)(pyridine)(CO)3 complex (2). Complex 1 was found to react with primary amines to generate a Schiff base (imine) in aqueous solutions. When a mixed-nitrogen donor bidentate ligand, 2-(2-aminoethyl)pyridine, that has different coordination affinities for fac-Re(acac)(OH2)(CO)3 was utilized, a unique tridentate ligand was formed in situ utilizing a metal-assisted Schiff base formation to yield a complex fac-Re(CO)3(3[(2-phenylethyl)imino]-2-pentanone) (3). Tridentate ligand formation was found to occur only with the Re-coordinated acac ligand. Reactions of acac with fac-Re(CO)3Br(2-(2-aminoethyl)pyridine) (4) or a mixture of [NEt4]2[ReBr3(CO)3], acac, and 2-(2-aminoethyl)pyridine did not yield the formation of complex 3 in water. PMID:18298058

Benny, Paul D; Fugate, Glenn A; Barden, Adam O; Morley, Jennifer E; Silva-Lopez, Elsa; Twamley, Brendan

2008-02-26

274

Highly porous and robust ionic MOFs with nia topology constructed by connecting an octahedral ligand and a trigonal prismatic metal cluster.  

PubMed

Two non-interpenetrated and isomorphous MOFs with nia topology, cationic JUC-101 and anionic JUC-102, are synthesized by connecting a trigonal prismatic metal cluster with an octahedral organic ligand. JUC-101 obtains a BET surface area of 3742 m(2) g(-1) and can absorb 4.18 wt% of H(2) at 30 atm and 77 K, while JUC-102 can absorb cationic dye molecules and release them under the triggering of ions. PMID:22576860

Jia, Jiangtao; Sun, Fuxing; Borjigin, Tsolmon; Ren, Hao; Zhang, Tingting; Bian, Zheng; Gao, Lianxun; Zhu, Guangshan

2012-05-10

275

Solvent tuning of the excited-state properties of (2,2'-bipyridine)tetracyanoferrate(II): direct observation of a metal-to-ligand charge-transfer excited state of iron(II)  

Microsoft Academic Search

In contrast to Ru(bpy)â\\/sup 2 +\\/ and Os(bpy)â\\/sup 2 +\\/ (bpy = 2,2'-bipyridine) the lowest excited state of Fe(bpy)â\\/sup 2 +\\/ is LF (ligand field) rather than MLCT (metal-to-ligand charge transfer) in character. Replacement of a bpy by two stronger field CN⁻ ligands to give Fe(bpy)â(CN)â does not alter this ordering. Here the authors report observations that show that in

Jay R. Winkler; Carol Creutz; Norman Sutin

1987-01-01

276

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

277

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

278

Two-dimensional self-assembly of a porphyrin-polypyridyl ruthenium(II) hybrid on hopg surface through metal-ligand interactions.  

PubMed

The synthesis and self-assembly behavior of porphyrin-polypyridyl ruthenium(II) hybrid, which consists of a flexible alkyl chain attached with two conjugated moieties is described. The electronic absorption spectrum and emission spectra show that the [C(8)-TPP-(ip)Ru(phen)(2)](ClO(4))(2), abbreviated as (C(8)ip)TPPC has optical properties. Scanning tunneling microscopy (STM) studies found that the pi-pi interaction and metal-ligand interaction allow (C(8)ip)TPPC to form self-assembled structure and have an edge-on orientation on the highly oriented pyrolytic graphite (HOPG) surface. The multidentate structure in (C(8)ip)TPPC molecules act as linkers between the molecules and form metal-ligand coordination, which forces the assembly process in the direction of stable columnar arrays. In addition, although the sample was stored for two months in ambient conditions, STM experiments showed that the order of (C(8)ip)TPPC self-assembly only slightly decreased which indicates that the self-assembled monolayer is stable. This work demonstrates that introducing a metal-ligand in the porphyrin-polypyridyl compound is a useful strategy to obtain novel surface assemblies. PMID:20401895

Gao, Aimei; Miao, Xinrui; Liu, Jie; Zhao, Ping; Huang, Jinwang; Deng, Wenli

2010-06-21

279

The ligand, the metal and the ?Holey?-host: Synthesis, structural and magnetic characterisation of Co(ii), Ni(ii) and Mn(ii) metal?organic frameworks incorporating 4,4?-dicarboxy-2,2?-bipyridine  

Microsoft Academic Search

We report herein the single crystal structures of four metal-organic framework complexes incorporating the 4,4?- dicarboxy-2,2?-bipyridine ligand, H2dcbp: a-(Co(dcbp)(H2O)2), 1; b-(Co(dcbp)(H2O)2), 2, (Ni(dcbp)(H2O)2), 3 and {(Mn(dcbp))·1?2DEF}, 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1 : 1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the

Eithne Tynan; Paul Jensen; Niamh R. Kelly; Paul E. Kruger; Anthea C. Lees; Boujemaa Moubaraki; Keith S. Murray

2004-01-01

280

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

281

Zeolitic polyoxometalates metal organic frameworks (Z-POMOF) with imidazole ligands and epsilon-Keggin ions as building blocks; computational evaluation of hypothetical polymorphs and a synthesis approach.  

PubMed

We investigate here a new family of zeolitic Metal Organic Frameworks (MOFs) based on imidazole (im) as the ligand and epsilon-type Keggin PolyOxoMetalates (POMs) as building units. The POM used in this study is the epsilon-{PMo(12)O(40)} Keggin isomer capped by four Zn(ii) ions (noted epsilon-Zn) in tetrahedral coordination. We describe here our methods to first construct and then evaluate the stability of hypothetical 3-D POMOFs possessing a tetrahedral network, typified by dense silica polymorphs and zeotypes and referred here to as Z-POMOFs. We use the analogy between the connectivity of silicon ion in dense minerals or zeolites and the epsilon-Zn, using imidazolate ligands to mimic the role of oxygen atoms in zeolites. Handling the epsilon-Keggin and imidazole as the constitutive building-blocks, a selection of 40 polymorphs were constructed and their relative stabilities computed. Among these Z-POMOFs, the cristobalite-like and zni-structure were identified as the most stable candidates. In parallel, we have attempted to synthesize Z-POMOF structures with epsilon-Zn POMs, synthesized in situ under hydrothermal conditions, and imidazole ligands. We present our first experimental result, the extended material [NBu(4)][PMo(V)(8)Mo(VI)(4)O(37)(OH)(3)Zn(4)(im)(Him)], named epsilon(im)(2). The structure of the hybrid framework is built by the connection of dimerized epsilon-Zn POMs to imidazole ligands in two directions. The obtaining of the first POMOF based on imidazole ligand is an encouraging step towards the synthesis of a new family of POMOFs. PMID:20593072

Rodriguez Albelo, L Marleny; Ruiz-Salvador, A Rabdel; Lewis, Dewi W; Gómez, Ariel; Mialane, Pierre; Marrot, Jérome; Dolbecq, Anne; Sampieri, Alvaro; Mellot-Draznieks, Caroline

2010-06-30

282

Group 3 metal initiators with an [OSSO]-type bis(phenolate) ligand for the stereoselective polymerization of lactide monomers.  

PubMed

A series of 1,?-dithiaalkanediyl-bridged bis(phenols) of the general type [OSSO]H(2) with variable steric properties and various bridges were prepared. The stoichiometric reaction of the bis(phenols) 1,3-dithiapropanediyl-2,2'-bis(4,6-di-tert-butylphenol), 1,3-dithiapropanediyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-propanediyl-1,4-dithiabutanediyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-butanediyl-1,4-dithiabutane diyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-hexanediyl-1,4-dithiabutanediyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], 1,3-dithiapropanediyl-2,2'-bis[6-(1-methylcyclohexyl)-4-methylphenol] (C(1), R=1-methylcyclohexyl), and 1,4-dithiabutanediyl-2,2'-bis[6-(1-methylcyclohexyl)-4-methylphenol] with rare-earth metal silylamido precursors [Ln{N(SiHMe(2))(2)(3)(thf)(x)] (Ln=Sc, x=1 or Ln=Y, x=2; thf=tetrahydrofuran) afforded the corresponding scandium and yttrium bis(phenolate) silylamido complexes [Ln(OSSO){N(SiHMe(2))(2)}(thf)] in moderate to good yields. The monomeric nature of these complexes was shown by an X-ray diffraction study of one of the yttrium complexes. The complexes efficiently initiated the ring-opening polymerization of rac- and meso-lactide to give heterotactic-biased poly(rac-lactides) and highly syndiotactic poly(meso-lactides). Variation of the ligand backbone and the steric properties of the ortho substituents affected the level of tacticity in the polylactides. PMID:22367758

Kapelski, Andreas; Buffet, Jean-Charles; Spaniol, Thomas P; Okuda, Jun

2012-02-24

283

The tunable coordination architectures of a flexible multicarboxylate N-(4-carboxyphenyl)iminodiacetic acid via different metal ions, pH values and auxiliary ligand  

SciTech Connect

{l_brace}[Pb{sub 3}(CPIDA){sub 2}(H{sub 2}O){sub 3}].H{sub 2}O{r_brace}{sub n}1, {l_brace}[Cd{sub 3}(CPIDA){sub 2}(H{sub 2}O){sub 4}].5H{sub 2}O{r_brace}{sub n}2, [Cd(HCPIDA)(bpy)(H{sub 2}O)]{sub n}3 (bpy=4,4'-bipyridine) and {l_brace}[Co{sub 3}(CPIDA){sub 2}(bpy){sub 3}(H{sub 2}O){sub 4}].2H{sub 2}O{r_brace}{sub n}4 were synthesized with N-(4-carboxyphenyl) iminodiacetic acid (H{sub 3}CPIDA). In 1, the CPIDA{sup 3-} ligands adopt chelating and bridging modes with Pb(II) to possess a 3D porous framework. In 2D-layer 2, the CPIDA{sup 3-} ligands display a simple bridging mode with Cd(II). The 2D layers have parallelogram-shaped channels along a axis. With bpy ligands, the HCPIDA{sup 2-} ligands in 3 show more abundant modes, but 3 still displays a 2D sheet on bc plane for the unidentate bpy molecules. However, in 3D-framework 4, the bpy ligands adopt bridging bidentate at a higher pH value and the CPIDA{sup 3-} ligands show bis-bidentate modes with Co(II). Additionally, 2D correlation analysis of FTIR was introduced to ascertain the characteristic adsorptions location of the carboxylate groups with different coordination modes in 4 with thermal and magnetic perturbation. Compounds 1, 2 and 4 exhibit the fluorescent emissions at room temperature. - Graphical abstract: A series of coordination polymers were synthesized with H{sub 3}CPIDA and transition metal ions at lower pH values. The figure displays a 3D porous framework with three parallel channels in compound 1.

Chai Xiaochuan [Department of Chemistry, Fuzhou University, Fuzhou, Fujian 350108 (China); Zhang Hanhui, E-mail: zhanghh1840@hotmail.co [Department of Chemistry, Fuzhou University, Fuzhou, Fujian 350108 (China); State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Zhang Shuai; Cao Yanning; Chen Yiping [Department of Chemistry, Fuzhou University, Fuzhou, Fujian 350108 (China)

2009-07-15

284

2,3-Di(2-pyridyl)-5-phenylpyrazine: a NN-CNN-type bridging ligand for dinuclear transition-metal complexes.  

PubMed

A new bridging ligand, 2,3-di(2-pyridyl)-5-phenylpyrazine (dpppzH), has been synthesized. This ligand was designed so that it could bind two metals through a NN-CNN-type coordination mode. The reaction of dpppzH with cis-[(bpy)2RuCl2] (bpy = 2,2'-bipyridine) affords monoruthenium complex [(bpy)2Ru(dpppzH)](2+) (1(2+)) in 64?% yield, in which dpppzH behaves as a NN bidentate ligand. The asymmetric biruthenium complex [(bpy)2Ru(dpppz)Ru(Mebip)](3+) (2(3+)) was prepared from complex 1(2+) and [(Mebip)RuCl3] (Mebip = bis(N-methylbenzimidazolyl)pyridine), in which one hydrogen atom on the phenyl ring of dpppzH is lost and the bridging ligand binds to the second ruthenium atom in a CNN tridentate fashion. In addition, the RuPt heterobimetallic complex [(bpy)2Ru(dpppz)Pt(C?CPh)](2+) (4(2+)) has been prepared from complex 1(2+), in which the bridging ligand binds to the platinum atom through a CNN binding mode. The electronic properties of these complexes have been probed by using electrochemical and spectroscopic techniques and studied by theoretical calculations. Complex 1(2+) is emissive at room temperature, with an emission ?max = 695?nm. No emission was detected for complex 2(3+) at room temperature in MeCN, whereas complex 4(2+) displayed an emission at about 750?nm. The emission properties of these complexes are compared to those of previously reported Ru and RuPt bimetallic complexes with a related ligand, 2,3-di(2-pyridyl)-5,6-diphenylpyrazine. PMID:23640789

Wu, Si-Hai; Zhong, Yu-Wu; Yao, Jiannian

2013-05-02

285

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

2013-09-04

286

Formation of a metal-to-nitrogen bond of normal length by a neutral sufonamide group within a tridentate ligand. A new approach to radiopharmaceutical bioconjugation.  

PubMed

We demonstrate that a tertiary sulfonamide group, N(SO2R)R'2, can rehybridize to form a M-N bond of normal length even when the group is in a linear tridentate ligand, such as in the new tridentate N(SO2R)dpa ligands derived from di-(2-picolyl)amine (N(H)dpa). N(SO2R)dpa ligands were used to prepare fac-[Re(CO)3(N(SO2R)dpa)](PF6 or BF4) complexes. Structural characterization of the new complexes established that the tertiary sulfonamide nitrogen atom binds to Re with concomitant sp(2)-to-sp(3) rehybridization, facilitating facial coordination. The new fac-[Re(CO)3(N(SO2R)dpa)]X structures provide the only examples for any metal with the sulfonamide as part of a noncyclic linear tridentate ligand and with a normal metal-to-nitrogen(tertiary sulfonamide) bond length. Rare previous examples of such normal M-N bonds have been found only in more constrained situations, such as with tripodal tetradentate ligands. Our long-term objectives for the new tridentate N(SO2R)dpa ligands are to develop the fundamental chemistry relevant to the eventual use of the fac-[M(I)(CO)3](+) core (M = (99m)Tc, (186/188)Re) in imaging and therapy. The sulfonamide group uniquely contributes to two of our goals: expanding ways to conjugate the fac-[M(I)(CO)3](+) core to biological molecules and also developing new symmetrical tridentate ligands that can coordinate facially to this core. Tests of our conjugation method, conducted by linking the fac-[Re(I)(CO)3](+) core to a new tetraarylporphyrin (T(N(SO2C6H4)dpa)P) as well as to a dansyl (5-(dimethylamino)naphthalene-1-sulfonyl) group, demonstrate that large molecular fragments can be tethered via a coordinated tertiary sulfonamide linkage to this core. PMID:23421481

Perera, Theshini; Abhayawardhana, Pramuditha; Marzilli, Patricia A; Fronczek, Frank R; Marzilli, Luigi G

2013-02-19

287

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

288

Glycosylphosphatidylinositol anchors regulate glycosphingolipid levels[S  

PubMed Central

Glycosylphosphatidylinositol (GPI) anchor biosynthesis takes place in the endoplasmic reticulum (ER). After protein attachment, the GPI anchor is transported to the Golgi where it undergoes fatty acid remodeling. The ER exit of GPI-anchored proteins is controlled by glycan remodeling and p24 complexes act as cargo receptors for GPI anchor sorting into COPII vesicles. In this study, we have characterized the lipid profile of mammalian cell lines that have a defect in GPI anchor biosynthesis. Depending on which step of GPI anchor biosynthesis the cells were defective, we observed sphingolipid changes predominantly for very long chain monoglycosylated ceramides (HexCer). We found that the structure of the GPI anchor plays an important role in the control of HexCer levels. GPI anchor-deficient cells that generate short truncated GPI anchor intermediates showed a decrease in very long chain HexCer levels. Cells that synthesize GPI anchors but have a defect in GPI anchor remodeling in the ER have a general increase in HexCer levels. GPI-transamidase-deficient cells that produce no GPI-anchored proteins but generate complete free GPI anchors had unchanged levels of HexCer. In contrast, sphingomyelin levels were mostly unaffected. We therefore propose a model in which the transport of very long chain ceramide from the ER to Golgi is regulated by the transport of GPI anchor molecules.

Loizides-Mangold, Ursula; David, Fabrice P. A.; Nesatyy, Victor J.; Kinoshita, Taroh; Riezman, Howard

2012-01-01

289

Synthesis, structure and anion-exchange property of the first example of self-penetrated three-dimensional metal-organic framework with flexible three-connecting ligand and nickel(II) perchlorate  

Microsoft Academic Search

Novel polymeric coordination complex [Ni(timpt)2](ClO4)21 was synthesized by solvothermal reaction of 2,4,6-tris[4-(imidazol-1-ylmethyl)phenyl]-1,3,5-triazine (timpt) ligand with Ni(ClO4)2·6H2O and characterized by X-ray crystallography. Each Ni(II) is coordinated by six imidazolyl N atoms from six different timpt ligands with an octahedral geometry and each timpt ligand connects three metal atoms to generate a three-dimensional (3D) metal-organic framework with self-penetration. The uncoordinated perchlorate anions

Shuang-Yi Wan; Yu-Ting Huang; Yi-Zhi Li; Wei-Yin Sun

2004-01-01

290

Metal (Mg, Fe, Co, Zr and Ti) complexes derived from aminosilyl substituted aminopyridinato ligand: synthesis, structures and ethylene polymerization behaviors of the group 4 complexes.  

PubMed

Lithium N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamidate (2) was prepared from the reaction of new compound N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamine (1) and LiBu(n). Treatment of the lithium salt (2) with an equal equivalent of MgBr(2)(THF)(2), FeCl(2) and CoCl(2) afforded the corresponding dinuclear complexes , , and , in which metal atoms possess similar trigonal bipyramidal geometries and each ligand functions as a bimetallic bridging binding aminopyridinato moiety with N-donation from the dimethylamino group. While the stoichiometric reaction of with ZrCl(4) gave the mononuclear zirconium complex (6); the seven coordinated zirconium atom adopts a distorted pentagonal bipyramid geometry and the ligand acts as monoanionic ?(2)-aminopyridinato moiety with the pendant arm coordinated via N(CH(3))(2). The reaction of with one equivalent of TiCl(4)(THF)(2) produced the interesting dinuclear titanium complex (7) owing to the elimination of a (N,N-dimethylamino)dimethylsilyl group from the original ligand, and the two titanium centers present different coordination geometries. The molecular structures of the crystalline metal complexes have been confirmed by X-ray single crystal diffraction analysis. Upon activation with methylaluminoxane (MAO), both complexes and exhibited moderate catalytic activities toward ethylene polymerization and produced high molecular weight polyethylenes with broad molecular weight distributions. PMID:22806137

Duan, Xin-E; Yuan, Shi-Fang; Tong, Hong-Bo; Bai, Sheng-Di; Wei, Xue-Hong; Liu, Dian-Sheng

2012-08-21

291

Synthesis and DNA binding studies of Ni(II), Co(II), Cu(II) and Zn(II) metal complexes of N 1,N 5-bis[pyridine-2-methylene]-thiocarbohydrazone Schiff-base ligand  

NASA Astrophysics Data System (ADS)

The thiocarbohydrazone Schiff-base ligand with a nitrogen and sulphur donor was synthesized through condensation of pyridine-2-carbaldehyde and thiocarbohydrazide. Schiff-base ligands have the ability to conjugate with metal salts. A series of metal complexes with a general formula [MCl 2(H 2L)]· nH 2O (M dbnd Ni, Co, Cu and Zn) were synthesized by forming complexes of the N 1,N 5-bis[pyridine-2-methylene]-thiocarbohydrazone (H 2L) Schiff-base ligand. These metal complexes and ligand were characterized by using ultraviolet-visible (UV-Vis), Fourier Transform Infrared (FT-IR), 1H and 13C NMR spectroscopy and mass spectroscopy, physicochemical characterization, CHNS and conductivity. The biological activity of the synthesized ligand was investigated by using Escherichia coli DNA as target. The DNA interaction of the synthesized ligand and complexes on E. coli plasmid DNA was investigated in the aqueous medium by UV-Vis spectroscopy and the binding constant ( Kb) was calculated. The DNA binding studies showed that the metal complexes had an improved interaction due to trans-geometrical isomers of the complexes than ligand isomers in cis-positions.

Tiwari, A. D.; Mishra, A. K.; Mishra, S. B.; Mamba, B. B.; Maji, B.; Bhattacharya, S.

2011-09-01

292

Anchored in the Florida Current  

NASA Astrophysics Data System (ADS)

I once spent a week aboard a vessel anchored in the Florida current, in water 830 m deep, far from the sight of land. We were there to measure transport variations, and I recall the numbing hourly routine of profiling the current with an instrument that traveled down a weighted line suspended from the ship. In much sharper focus I remember the mighty current that ceaselessly swept past the vessel. The current raised a foaming bow wave and strummed the anchor cable with a note that permeated the quiet ship, giving the strange experience of being underway with silent engines while going nowhere.

Brooks, David A.

293

Wells Dawson anion, a useful building block to construct one-dimensional chain as a chelate ligand coordinating with transition metal cations  

NASA Astrophysics Data System (ADS)

Two composite compounds, [{Cu(PPD)2}(As2W18O60)]·2H2PPD·14H2O 1 (PPD = p-phenylenediamine) and [Cu4(Hen)2As2W18O68]·4H2en·18H2O 2 (en = ethylenediamine) have been prepared under mild hydrothermal conditions with difference in pH values of the initial reaction solutions and structurally characterized by single-crystal X-ray diffraction. Compound 1 exhibits a one-dimensional chain constructed from Wells Dawson anions and Cu(II) coordination complex. It is the first example of a one-dimensional chain based on Wells Dawson anions that act as chelate ligands to coordinate with transition metal. Compound 2 is constructed from trivacant Keggin polyanions linked through tetrameric copper unit, which coordinates with organonitrogen ligands.

Fan, Linlin; Wang, Enbo; Li, Yangguang; An, Haiyan; Xiao, Dongrong; Wang, Xinlong

2007-09-01

294

Controlled assembly of zero-, one- and two-dimensional metal-organic frameworks involving in situ ligand synthesis under different reaction pH  

Microsoft Academic Search

Five cadmium(II) metal-organic frameworks, namely [Cd(BIPA)(daf)(H2O)3]·2H2O (1), Cd2(BDC)2(pdon)2(H2O)2 (2), Cd(BIPA)(pdon) (3), Cd(BIPA)(daf) (4) and [Cd2(BIPA)2(pdon)2]·H2O (5) (H2BIPA=5-bromoisophthalic acid, H2BDC=terephthalic acid, pdon=1,10-phenanthroline-5,6-dione, daf=4,5-diaza-fluoren-9-one), have been constructed from cadmium(II) salts with multi-carboxylate ligands and pdon ligands under different reaction pH. The framework structures of these polymeric complexes have been determined by the X-ray single crystal diffraction technique. The differences of the five

Guang-Xiang Liu; Rong-Yi Huang; Heng Xu; Xue-Jun Kong; Liang-Fang Huang; Kun Zhu; Xiao-Ming Ren

2008-01-01

295

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

296

Change of the magnetic coupling of a metal-organic complex with the substrate by a stepwise ligand reaction.  

PubMed

The surface-assisted intramolecular ligand reaction of a porphyrin molecule adsorbed on Au(111) is studied by scanning tunneling microscopy and spectroscopy. The temperature-induced stepwise transformation of iron octaethylporphyrin proceeds via a concentric electrocyclic ring closure, with the final product iron tetrabenzoporphyrin being identified by its characteristic Kondo resonance. Along with the transformation of the organic ligand, changes in the magnetic fingerprint are observed, indicating an increasing coupling of the iron spin with the substrate electrons. PMID:23985020

Heinrich, Benjamin W; Ahmadi, Gelavizh; Müller, Valentin L; Braun, Lukas; Pascual, José I; Franke, Katharina J

2013-09-04

297

Synthesis and characterization of a new thiohydrazone ligand, 3-carboxy-2-hydroxybenzaldehydemorpholine N-thiohydrazone and its metal complexes  

Microsoft Academic Search

The reaction of 3-formylsalicylic acid with morpholine N-thiohydrazide in ethanol leading to the formation of a new thiohydrazone, 3-carboxy-2-hydroxybenzaldehydemorpholine N-thiohydrazone (H2chbmth) is described. This thiohydrazone ligand remained as the thio-keto form in the solid state. However, thioketo- and a small amount of the thiol-tautomeric forms (H2chbmth and H3chbmthol, respectively) remain in equilibrium in solution. The reactions of the ligand with

Kamalendu Dey; Saikat Sarkar; Sanjib Mukhopadhyay; Alok Kumar Mallik; Susobhan Biswas; Bijali Bikash Bhaumik

2006-01-01

298

Synthesis of new late transition metal P,P-, P,N-, and P,O- complexes using phosphonium dimers as convenient ligand precursors.  

PubMed

The phosphonium dimer [-Cy2PCH(OH)CH2-]2(X)2, X = Cl(-), Br(-) was used to synthesize and characterize a variety of late transition metal complexes containing chelating phosphino-enolate (PCy2CH?CHO(-)), imine (PCy2CH2CH?NR, R = Ph, (S)-CHMePh), and oxime (PCy2CH2CH?NOH) ligands. The phosphonium dimer, when deprotected with base, generates the phosphine aldehyde PCy2CH2CHO in situ, which, in the presence of [M(COD)Cl]2, M = Rh, Ir, and a PF6(-) salt, or [Ni(H2O)6][BF4]2, facilitates a condensation reaction with an amine or hydroxylamine to form phosphino-imine or phosphino-oxime metal complexes [M(COD)(P-N)][PF6] or [Ni(P-N)2][X]2, X = ClO4(-), BF4(-), respectively. In the absence of an amine, phosphino-enolate containing complexes are formed. A neutral Ni(II) complex Ni(PCy2CH?CHO)2 with trans-bis(phosphino-enolate) ligands which resemble ligands used on nickel for olefin oligomerization, as well as neutral Rh(I) and Ir(I) 1,5-cyclooctadiene complexes M(COD)(PCy2CH?CHO) are characterized. Both the rhodium and iridium complexes are active olefin hydrogenation catalysts. Reaction of the phosphino-aldehyde with Pt(COD)Cl2 results in the formation of trans-PtCl2(PCy2CH2CHO)2 with pendant aldehyde groups, and under certain conditions, they undergo an intraligand aldol condensation to form a disphosphine ligand. PMID:23570571

Park, Kanghee; Lagaditis, Paraskevi O; Lough, Alan J; Morris, Robert H

2013-04-09

299

Anchoring in lie detection revisited  

Microsoft Academic Search

Previous research has shown that the human lie detector tends to interpret messages as truthful rather than as deceptive (the truthfulness bias) and to infer attitudes congruent with the content of the (sometimes deceptive) messages (over-attribution). It was hypothesized that these effects are moderated by the extent to which receivers are anchored to the verbal content of the message; that

Miron Zuckerman; Scott A. Fischer; Roger W. Osmun; Beatrice A. Winkler; Lauren R. Wolfson

1987-01-01

300

Spatial and temporal lightness anchoring  

Microsoft Academic Search

Research in the area of lightness perception has not adequately addressed the influence of previously viewed visual fields on perceived surface reflectance. In the spatial realm, a spot-in-a-void will appear darker when a second surface of higher intensity is placed adjacent to it. The brighter surface takes the role of white, the anchor, and the dimmer is scaled accordingly. We

Joseph Cataliotti; Frederick Bonato

2003-01-01

301

Anchored phosphatases modulate glucose homeostasis.  

PubMed

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

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

2012-08-31

302

Ligand K-edge and metal L-edge X-ray absorption spectroscopy and density functional calculations of oxomolybdenum complexes with thiolate and related ligands: Implications for sulfite oxidase  

SciTech Connect

X-ray absorption spectra have been measured at the S K-, Cl K-, and Mo L{sub 3}- and L{sub 2}-edges for the d{sup 0} dioxomolybdenum(VI) complexes LMoO{sub 2}(SCH{sub 2}Ph), LMoO{sub 2}Cl, and LMoO{sub 2}(OPh) (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) to investigate ligand-metal covalency and its effects on oxo transfer reactivity. Two dominant peaks are observed at the S K-edge (2,470.5 and 2,472.5 eV) for LMoO{sub 2}(SCH{sub 2}Ph) and at the Cl K-edge (2,821.9 and 2,824.2 eV) for LMoO{sub 2}Cl, demonstrating two major covalent contributions from S and Cl to the Mo d orbitals.Density functional calculations were performed on models of the three Mo complexes, and the energies and characters of the Mo 4d orbitals were interpreted in terms of the effects of two strong cis-oxo bonds and additional perturbations due to the thiolate, chloride, or alkoxide ligand. The major perturbation effects are for thiolate and Cl{sup {minus}} {pi} mixed with the d{sub xz} orbital and {sigma} mixed with the d{sub z}{sup 2} orbital. The calculated 4d orbital energy splittings for models of these two major contributions to the bonding of thiolate and Cl ligands (2.47 and 2.71 eV, respectively) correspond to the splittings observed experimentally for the two dominant ligand K-edge peaks for LMoO{sub 2}(SCH{sub 2}Ph) and LMoO{sub 2}Cl (2.0 and 2.3 eV, respectively) after consideration of final state electronic relaxation. Quantification of the S and Cl covalencies in the d orbital manifold from the pre-edge intensity yields, {approximately} 42% and {approximately} 17% for LMoO{sub 2}(SCH{sub 2}Ph) and LMoO{sub 2}Cl, respectively. The Mo L{sub 2}-edge spectra provide a direct probe of metal 4 d character for the three Mo complexes. The spectra contain a strong, broad peak and two additional sharp peaks at higher energy, which are assigned to 2p transitions to the overlapping t{sub 2g} set and to the d{sub z}{sup 2} and d{sub xy} levels, respectively. The total peak intensities of the Mo L{sub 2}-edges for LMoO{sub 2}(OPh) and LMoO{sub 2}Cl are similar to and larger than those for LMoO{sub 2}(SCH{sub 2}Ph), which agrees with the calculated trend in ligand-metal covalency. The theoretical and experimental description of bonding developed from these studies provides insight into the relationship of electronic structure to the oxo transfer chemistry observed for the LMoO{sub 2}X complexes. These results imply that anisotropic covalency of the Mo-S{sub cys} bond in sulfite oxidase may promote preferential transfer of one of the oxo groups during catalysis.

Izumi, Yasuo; Glaser, T.; Rose, K.; McMaster, J.; Basu, P.; Enemark, J.H.; Hedman, B.; Hodgson, K.O.; Solomon, E.I.

1999-11-03

303

A Highly Porous and Robust (3,3,4)-Connected Metal?Organic Framework Assembled with a 90° Bridging-Angle Embedded Octacarboxylate Ligand  

SciTech Connect

A dicopper(II)-paddle-wheel-based metal-organic framework (PCN-80, see picture) with a rare (3,3,4)-connected topology has been synthesized by using a unique octatopic ligand featuring 90{sup o} bridging-angle dicarboxylate moieties. PCN-80 has Brunauer-Emmett-Teller (BET) and Langmuir surface areas of 3850 and 4150 m{sup 2}g{sup -1}, respectively. It exhibits high gas-uptake capacity for H{sub 2} and large adsorption selectivity of CO{sub 2} over N{sub 2}.

Lu, Weigang; Yuan, Daqiang; Makal, Trevor A.; Li, Jian-Rong; Zhou, Hong-Cai (TAM)

2012-03-15

304

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

305

Robust conductance of dumbbell molecular junctions with fullerene anchoring groups  

NASA Astrophysics Data System (ADS)

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 C60 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 G0. Electron tunneling across the molecular bridge occurs via the lowest unoccupied orbitals of C60 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.

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

2011-10-01

306

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

307

Anchoring and adjustment in software estimation  

Microsoft Academic Search

Anchoring and adjustment is a form of cognitive bias that affects judgments under uncertainty. If given an initial answer, the respondent seems to use this as an 'anchor', adjusting it to reach a more plausible answer, even if the anchor is obviously incorrect. The adjustment is frequently insufficient and so the final answer is biased. In this paper, we report

Jorge Aranda; Steve Easterbrook

2005-01-01

308

Anchoring structure for marine riser assembly  

Microsoft Academic Search

This patent describes an anchor system for anchoring the lower end of a marine riser, lower marine riser package (LMRP) assembly and drill string to the ocean floor, it comprises: an anchor assembly secured to the ocean floor, the assembly including a tubular member extending into the ocean bottom; a guide means, an elongated weight means disposed in the tubular

Ritter; P. B. Jr

1992-01-01

309

Anchoring structure for marine riser assembly  

SciTech Connect

This patent describes an anchor system for anchoring the lower end of a marine riser, lower marine riser package (LMRP) assembly and drill string to the ocean floor, it comprises: an anchor assembly secured to the ocean floor, the assembly including a tubular member extending into the ocean bottom; a guide means, an elongated weight means disposed in the tubular member.

Ritter, P.B. Jr.

1992-09-15

310

Synthesis and solid-state NMR structural characterization of polysiloxane-immobilized amine ligands and their metal complexes  

Microsoft Academic Search

Polysiloxane-immobilized amine and diamine ligand systems have been made by hydrolytic condensation of Si(OEt)4 with (EtO)3Si(CH2)3NH2 or (MeO)3Si(CH2)3NH(CH2)2NH2. The corresponding triamine ligand was made from the reaction of 3-chloropropylpolysiloxane with diethylenetriamine (H2NCH2CH2NHCH2CH2NH2); solid-state 13C and 15N nuclear magnetic resonance (NMR) spectra can identify the structure of the product of this reaction. 29Si, 15N, 13C and 1H NMR spectra are in

Jane Jie Yang; Issa M El-Nahhal; I-Ssuer Chuang; Gary E Maciel

1997-01-01

311

Intrazeolite anchoring of [HRuCo3(CO)9(?2-CO)3]: Synthesis and reversible decarbonylation  

NASA Astrophysics Data System (ADS)

The synthesis of intrazeolite anchoring of [HRuCo3(CO)9(?2-CO)3] involves the adsorption of metal carbonyl species into zeolite cages followed by reductive carbonylation under a mixed CO and H2 atmosphere. The physicochemical characterization of the samples was based on a multianalytical approach, including Fourier transform-infrared, extended x-ray absorption fine structure spectroscopies, and CO/H2 gas chemisorption. The research encomassed several key points as follows: (a) The generation process of bimetallic carbonyl clusters was considered to occur through the interaction of [Ru-Co], Co(CO)4- and RuI carbonyls, and conversion into [HRuCo3(CO)9(?3-CO)3] and further to [HRuCo3(CO)9(?2-CO)3] isomer. (b) There is significant bimetallic interaction. (c) Internal and external confinement of [HRuCo3(CO)9(?2-CO)3] were compared. (d) The intrazeolite anchoring of [RuCo3] carbonyl clusters shows a strong reaction with the extraframework Na+ ?-cage cations, through involvement of the oxygen end of the bridging carbonyl ligands.

Shen, James G. C.; Ichikawa, Masaru

1999-03-01

312

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

2012-02-01

313

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

2011-11-10

314

Electrochemically induced FTIR difference spectroscopy in the mid- to far infrared (200 microm) domain: a new setup for the analysis of metal-ligand interactions in redox proteins.  

PubMed

We report the setup of an electrochemical cell with chemical-vapor deposition diamond windows and the use of a Bruker 66 SX FTIR spectrometer equipped with DTGS and Si-bolometer detectors and KBr and mylar beam splitters, to record on the same sample, FTIR difference spectra corresponding to the structural changes associated with the change in redox state of active sites in proteins in the whole 1800-50 cm(-1) region. With cytochrome c we show that reliable reduced-minus-oxidized FTIR difference spectra are obtained, which correspond to single molecular vibrations. Redox-sensitive IR modes of the cytochrome c are detected until 140 cm(-1) with a good signal to noise. This new setup is promising to analyze the infrared spectral region where metal-ligand vibrations are expected to contribute and to extend the analysis of vibrational properties to metal sites or redox states not accessible to (resonance) Raman spectroscopy. PMID:16453337

Berthomieu, Catherine; Marboutin, Laure; Dupeyrat, François; Bouyer, Pierre

2006-07-01

315

New metal-organic precursors for MOCVD applications: Synthesis, characterization, crystal structure and thermal properties of mixed-ligand Mg(II) complexes  

NASA Astrophysics Data System (ADS)

In an effort to develop new MOCVD precursors, mixed-ligand metal-organic complexes, bis (acetylacetonato-k2O,O?) (2,2?-bipyridine-k2N,N?) magnesium(II), and bis (acetylacetonato-k2O,O?) (1,10-phenanthroline-k2N,N?) magnesium(II) were synthesized. Spectroscopic characterization and crystal structures confirmed them to be monomeric and stable complexes. Crystal structure analysis suggests in each of the magnesium(II) complexes, the metal center has a distorted octahedral coordination geometry. Thermo-gravimetric analysis (TGA/DTA) suggests that these complexes are volatile and thermally stable. The thermal characteristics of newly designed complexes make them attractive precursors for MOCVD applications.

Brahma, Sanjaya; Srinidhi, M.; Shivashankar, S. A.; Narasimhamurthy, T.; Rathore, R. S.

2013-03-01

316

Artificial metalloenzymes based on protein cavities: Exploring the effect of altering the metal ligand attachment position by site directed mutagenesis  

Microsoft Academic Search

In an effort to construct catalysts with enzyme-like properties, we are employing a small, cavity-containing protein as a scaffold for the attachment of catalytic groups. In earlier work we demonstrated that a phenanthroline ligand could be introduced into the cavity of the protein ALBP and used to catalyze ester hydrolysis. To examine the effect of positioning the phenanthroline catalyst at

Ronald R. Davies; Hao Kuang; Dongfeng Qi; Aram Mazhary; Evelyn Mayaan; Mark D. Distefano

1999-01-01

317

Tensile tests of micro anchors anodically bonded between Pyrex glass and aluminum thin film coated on silicon wafer  

Microsoft Academic Search

Micro anchor is a kind of typical structures in micro\\/nano electromechanical systems (MEMS\\/NEMS), and it can be made by anodic bonding process, with thin films of metal or alloy as an intermediate layer. At the relative low temperature and voltage, specimens with actually sized micro anchor structures were anodically bonded using Pyrex 7740 glass and patterned crystalline silicon chips coated

Yu-Qun Hu; Ya-Pu Zhao; Tongxi Yu

2008-01-01

318

Octupole anchor for tandem mirrors  

SciTech Connect

The octupole anchor is a very promising alternative to the usual quadrupole designs. The most critical unsolved problem is stabilization of the trapped particle mode. The anchor magnetic field is low because MHD stabilization is by hot electrons, thus permitting relatively small magnet currents and conductor cross sections. Increasing the field to a sufficient level to permit operation of the thermal barrier and electrostatic plug required for trapped particle mode stabilization would require much more massive magnets, higher ECRH power, and the much more complex operating scenario associated with standard quadrupole operation. Despite these complications, the absence of a long transition (with an axial minimum in B) between the central cell and the octupole makes the option attractive.

Hopper, E.B. Jr.

1984-03-21

319

Anchoring bias in online voting  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

320

Octahedral Group 4 Metal Complexes That Contain Amine, Amido, and Aminopyridinato Ligands: Synthesis, Structure, and Application in alpha-Olefin Oligo- and Polymerization.  

PubMed

The reaction of trimethylsilyl-substituted 2-aminopyridines with mixed chloro(dialkylamido)metal complexes (titanium and zirconium) leads via amine elimination to octahedral group 4 metal complexes that contain amine, amido, and aminopyridinato ligands. The X-ray crystal structure analyses of (4-Me-TMS-APy)(NMe(2))(HNMe(2))TiCl(2) (1) (crystallographic data: P2(1)/c (No. 14), monoclinic, a = 16.754(2) Å, b = 14.395(2) Å, c = 17.890(3) Å, beta = 110.28(1) degrees, Z = 8) and (6-Me-TMS-APy)(NEt(2))(HNEt(2))ZrCl(2) (2) (crystallographic data: P2(1)/n (No. 14) monoclinic, a = 10.125(1) Å, b = 16.331(1) Å, c = 15.276(2) Å, beta = 93.90(1), Z = 4) prove the compounds to be mononuclear with a cisoid arrangement of the two chloro ligands embedded in a reactive pocket determined by the steric demand of the three nitrogen containing ligands. Oligo- and polymerization studies with propene and 1-butene reveal the following results. First, 1 is a remarkably active precatalyst in contrast to the very low activity of 2. Second, MAO, a 1:1 mixture of i-Bu(3)Al/B(C(6)F(5))(3) (homogeneous polymerization) and ethylaluminum sesquichloride (if 1 is incorporated in a MgCl(2)-matrix) have shown to be the most active cocatalysts. Third, the polymers and oligomers are atactic. PMID:11666837

Fuhrmann, Hans; Brenner, Simon; Arndt, Perdita; Kempe, Rhett

1996-11-01

321

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

322

Independent control of polar and azimuthal anchoring  

NASA Astrophysics Data System (ADS)

Monte Carlo simulation, experiment, and continuum theory are used to examine the anchoring exhibited by a nematic liquid crystal at a patterned substrate comprising a periodic array of rectangles that, respectively, promote vertical and planar alignment. It is shown that the easy axis and effective anchoring energy promoted by such surfaces can be readily controlled by adjusting the design of the pattern. The calculations reveal rich behavior: for strong anchoring, as exhibited by the simulated system, for rectangle ratios ?2 the nematic aligns in the direction of the long edge of the rectangles, the azimuthal anchoring coefficient changing with pattern shape. In weak anchoring scenarios, however, including our experimental systems, preferential anchoring is degenerate between the two rectangle diagonals. Bistability between diagonally aligned and edge-aligned arrangement is predicted for intermediate combinations of anchoring coefficient and system length scale.

Anquetil-Deck, C.; Cleaver, D. J.; Bramble, J. P.; Atherton, T. J.

2013-07-01

323

[Bone-anchored auricular prosthesis].  

PubMed

During the period February 1989-September 1991, 15 patients with absent or defective pinna were treated with a bone-anchored auricular prosthesis at the ENT-department, Rigshospitalet, Copenhagen. These patients were followed up from the hospital records and by means of a questionnaire. Altogether 40 titanium implants have been inserted, of which one implant was found not to be integrated at the time of the second-stage surgery. Five patients underwent additional surgery, one patient because of non-integration of a screw, and four patients on account of soft-tissue reactions. From the questionnaire replies it appears that all patients found the cosmetic result and the technique concerning mounting of the prosthesis very satisfactory. Nearly half the patients found that the care of the skin around the abutments caused considerable problems. Three patients had experienced unintended losses of the prosthesis. In conclusion, treatment with a bone anchored auricular prosthesis has considerable advantages compared to treatment with a prosthesis attached by adhesive. Furthermore the use of a bone-anchored prosthesis should be considered a viable alternative to surgical reconstruction because of the outstanding aesthetic result and because the surgical procedure puts less strain on the patient. The disadvantage of the method is the lifelong daily care of the skin and the dependence on the health services. PMID:7985274

Bille, M; Homøe, P; Vesterhauge, S; Rixen, M; Bretlau, P

1994-10-01

324

Electrostatically anchored branched brush layers.  

PubMed

A novel type of block copolymer has been synthesized. It consists of a linear cationic block and an uncharged bottle-brush block. The nonionic bottle-brush block contains 45 units long poly(ethylene oxide) side chains. This polymer was synthesized with the intention of creating branched brush layers firmly physisorbed to negatively charged surfaces via the cationic block, mimicking the architecture (but not the chemistry) of bottle-brush molecules suggested to be present on the cartilage surface, and contributing to the efficient lubrication of synovial joints. The adsorption properties of the diblock copolymer as well as of the two blocks separately were studied on silica surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry. The adsorption kinetics data highlight that the diblock copolymers initially adsorb preferentially parallel to the surface with both the cationic block and the uncharged bottle-brush block in contact with the surface. However, as the adsorption proceeds, a structural change occurs within the layer, and the PEO bottle-brush block extends toward solution, forming a surface-anchored branched brush layer. As the adsorption plateau is reached, the diblock copolymer layer is 46-48 nm thick, and the water content in the layer is above 90 wt %. The combination of strong electrostatic anchoring and highly hydrated branched brush structures provide strong steric repulsion, low friction forces, and high load bearing capacity. The strong electrostatic anchoring also provides high stability of preadsorbed layers under different ionic strength conditions. PMID:23046176

Liu, Xiaoyan; Dedinaite, Andra; Rutland, Mark; Thormann, Esben; Visnevskij, Ceslav; Makuska, Ricardas; Claesson, Per M

2012-10-26

325

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

326

Anchoring Au and Pt Nanoparticles on Multiwalled Carbon Nanotubes via Electron Beam Induced Amorphous Carbon Encapsulation  

Microsoft Academic Search

Au and Pt nanoparticles (NPs) were anchored on multiwalled carbon nanotubes (MWCNTs) via electron beam induced amorphous carbon encapsulation by energy-tunable MeV electron beam irradiation (MEBI) under ambient conditions. MEBI allowed the formation of size-homogeneous Au and Pt NPs on MWCNTs, as observed by transmission electron microscopy. Anchoring of metal NPs was achieved by MEBI-induced amorphous carbon encapsulation. The chemical

Wooseok Song; Sung Hwan Kim; Yooseok Kim; Soo Youn Kim; Cheolho Jeon; Won Chel Choi; Byung Cheol Lee; Chong-Yun Park

2011-01-01

327

Synthesis, structural characterization and anion-sensing studies of metal(II) complexes based on 3,3',4,4'-oxydiphthalate and N-donor ligands.  

PubMed

Using a multicarboxylate ligand, 3,3',4,4'-oxydiphthalic acid (H(4)ODPA), and N-donor ligands, five metal(II)-ODPA complexes formulated as Cu(4)(ODPA)(2)(L1)(4)(H(2)O)(10)·2H(2)O (L1 = 4-(2-(pyridin-4-yl)vinyl)pyridine) (1), Co(H(2)ODPA) (L1)(H(2)O) (2), Zn(2)(ODPA)(2)(H(2)PIP)(2)·H(2)O (PIP = 1,3-bis(4-piperidinyl)propane) (3), Mn(2)(ODPA)(phen)(H(2)O)(2) (phen = phenanthroline) (4) and Cu(2)(H(2)ODPA)(2)(phen)(4)·H(2)O (5) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 shows a three dimensional (3D) framework with an unprecedented (4.6(4).8)(2)(4(2).6(4)) topology generated by the polycatenation of 2D layers. Complex 2 exhibits a uninodal 4-connected 3D architecture with 6(5)8-cds topology. Complex 3 shows a uninodal 2D layer with 4(4)-sql topology. Complex 4 has a binodal (4,6)-connected non-interpenetrated 3D architecture with (3.4(3).5.6)(3(2).4(3).5(4).6(4).7(2)) topology. Complex 5 is a mononuclear Cu(II) complex. Complexes 1 and 5 can irreversibly and reversibly detect SCN(-), Cl(-), Br(-) and I(-) in water, respectively. Complexes 2-4 are not feasible candidates for colorimetric detection of anions in aqueous solution. The metal(II) species and the structure of the metal complex play important roles in the colorimetric detection. PMID:22169819

Gong, Yun; Qin, JianBo; Wu, Tao; Li, JingHua; Yang, Li; Cao, Rong

2011-12-15

328

Solution extraction of transition and post-transition heavy and precious metals by chelate and macrocyclic ligands  

Microsoft Academic Search

This review focuses on compounds and methods that can be used for the extraction and separation from solution of two classes of elements that we define as heavy metals and precious metals. These elements are often targeted because they are toxic, costly, and their coordination chemistry has already been well studied, and because there is a need to develop methods

Alexander T Yordanov; D. Max Roundhill

1998-01-01

329

Metal vs ligand reduction in complexes of dipyrido[3,2-a:2',3'-c]phenazine and related ligands with [(C5Me5)ClM]+ (M = Rh or Ir): evidence for potential rather than orbital control in the reductive cleavage of the metal-chloride bond.  

PubMed

Complexes between the chlorometal(III) cations [(C5Me5)ClM]+, M = Rh or Ir, and the 1,10-phenanthroline-derived alpha-diimine (N--N) ligands dipyrido[3,2-a:2',3'-c]phenazine (dppz), 1,4,7,10-tetraazaphenanthrene (tap), or 1,10-phenanthroline-5,6-dione (pdo) were investigated by cyclic voltammetry, EPR, and UV-vis-NIR spectroelectrochemistry with respect to either ligand-based or metal-centered (and then chloride-dissociative) reduction. Two low-lying unoccupied molecular orbitals (MOs) are present in each of these three N wedge N ligands; however, their different energies and interface properties are responsible for different results. Metal-centered chloride-releasing reduction was observed for complexes of the DNA-intercalation ligands dppz and tap to yield compounds [(N--N)(C5Me5)M] in a two-electron step. The separation of alpha-diimine centered optical orbitals and phenazine-based redox orbitals is apparent from the EPR and UV-vis-NIR spectroelectrochemistry of [(dppz)(C5Me5)M](0/*-/2-). In contrast, the pdo complexes undergo a reversible one-electron reduction to yield o-semiquinone radical complexes [(pdo)(C5Me5)ClM]* before releasing the chloride after the second electron uptake. The fact that the dppz complexes undergo a Cl(-)-dissociative two-electron reduction despite the presence of a lowest lying pi* MO (b1(phz)) with very little overlap to the metal suggests that an unoccupied metal/chloride-based orbital is lower in energy. This assertion is confirmed both by the half-wave reduction potentials of the ligands (tap, -1.95 V; dppz, -1.60 V; pdo, -0.85 V) and by the typical reduction peak potentials of the complexes [(L)(C5Me5)ClM](PF6) (tap, -1.1 V; dppz, -1.3 V; pdo, -0.6 V; all values against Fc(+/0)). PMID:14966991

Berger, Sascha; Fiedler, Jan; Reinhardt, Ralf; Kaim, Wolfgang

2004-02-23

330

Inorganic-organic hybrid compounds based on octamolybdates and metal-organic fragments with flexible multidentate ligand: syntheses, structures and characterization.  

PubMed

Six polyoxometalate-based (POM) hybrid materials based on octamolybdate building blocks and metal-organic fragments with flexible multidentate ligand, namely [Cu(II)(2)(ttb)(2)(?-Mo(8)O(26))(H(2)O)(2)]·2H(2)O (1), Cu(I)(4)(ttb)(2)(?-Mo(8)O(26))(H(2)O) (2), [Cu(I)(4)(ttb)(3)(?-Mo(8)O(26))] (3), [Ni(2)(ttb)(2)(?-Mo(8)O(26))(H(2)O)(6)]·2H(2)O (4), [Zn(2)(ttb)(2)(?-Mo(8)O(26))(H(2)O)(2)] (5), and [Ag(4)(ttb)(2)(?-Mo(8)O(26))] (6), where ttb = 1,3,5-tris(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethyl benzene, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, TGA, IR spectra, and electrochemistry. Compounds 1 and 2 exhibit three-dimensional (3D) 2-fold interpenetrating frameworks with (3,6)-connected (4(1)·6(2))(4(2)·6(10)·10(3)) and (3,4)-connected (6(2)·8(1))(2)(6(2)·8(4)) topologies, respectively. We are not aware of any other examples of interpenetrating (3,6)- and (3,4)-connected frameworks which involves the octamolybdates. Compound 3 shows a rare two-dimensional (2D) 2-fold interpenetrating network structure. In compound 4, a 3D supramolecular framework with the channels is constructed by the hydrogen-bonding interactions between (?-Mo(8)O(26))(4-) polyanions and the Ni-ttb double layers, in which the guest (?-Mo(8)O(26))(4-) anions are included. If ZnO interactions are considered, the structure of 5 is a 3D (3,4)-connected framework with (4·8(2))(4·8(2)·10(3)) topology. In 6, the ttb ligand as a tetradentate ligand links the Ag atoms to yield a 2D POM-based network. By careful inspection of the structures of 1-6, it can be seen that the ttb ligand, the metal ion and the coordination mode of the octamolybdate anion play important roles in the formation of the POM-based MOFs. PMID:21125130

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

2010-12-02

331

Thermodynamic, spectroscopic, and structural studies of complexation of phenol- and pyridine-armed macrocyclic ligands with univalent metal ions  

SciTech Connect

Log K, {Delta}H, and {Delta}S values for interactions of a series of pyridinoazacrown ethers each bearing a phenol arm (2-6) and two macrocycles each bearing a pyridine arm (7, 8) with Na{sup +}, K{sup +}, Tl{sup +}, and Ag{sup +} have been determined in absolute methanol at 25{degrees}C by calorimetric titration. In each case, the complex stability has the sequence Na{sup +} < K {sup +} < Tl{sup +} {much_lt} Ag{sup +}. The phenol-armed macrocycles exhibit selectivity of more than 4 orders of magnitude for Ag{sup +} over Na{sup +}, K{sup +}, and Tl{sup +}. Attachment of a pendant phenol arm having various substituents to parent macrocycle 1 increases the binding abilities of the resulting ligands. Substituents on the para position of the phenol arm have an appreciable effect on cation-binding constants. Good Hammett correlations are found by plotting log K values vs {sigma}{sub p} for interactions of five phenol-armed macrocyclic ligands (2-6) with Na{sup +}, K{sup +}, and Tl{sup +}. The complexation has been characterized by means of {sup 1}H NMR and UV-visible spectroscopic, and X-ray crystallographic methods. The study indicates that the phenol OH group of 2-6 is capable of forming an intramolecular hydrogen bond with the macroring nitrogen atom and that the complexation in absolute methanol generally does not deprotonate these phenols. In the crystal structure of the Na{sup +} -3 complex, the Na{sup +} is coordinated to all seven of the donor atoms of the ligand and two Na{sup +} -3 complexes join together to form a dimer. The dimer contains an intermolecular hydrogen bond formed between the phenol hydrogen atom of one ligand and the phenolate group of a centrosymmetrically related ligand and two {pi}-{pi} stacking interactions between the electron-deficient pyridine ring of one molecule and the electron-rich phenol ring of the other. 36 refs., 5 figs., 6 tabs.

Zhang, Xian Xin; Bordunov, A.V.; Dalley, N.K. [Brigham Young Univ., Provo, UT (United States)] [and others

1997-06-04

332

Strong metal ion size based selectivity of the highly preorganized ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) with trivalent metal ions. A crystallographic, fluorometric, and thermodynamic study.  

PubMed

The selectivity of the rigid ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) for some M(III) (M = metal) ions is presented. The structure of [Fe(PDA(H)(1/2))(H(2)O)(3)] (ClO(4))(2).3H(2)O.(1)/(2)H(5)O(2) (1) is reported: triclinic, P1, a = 7.9022(16) A, b = 12.389(3) A, c = 13.031(3) A, alpha = 82.55(3) degrees , beta = 88.41(3) degrees , gamma = 78.27(3) degrees , V = 1238.6(4) A(3), Z = 2, R = 0.0489. The coordination geometry around the Fe(III) is close to a regular pentagonal bipyramid, with Fe-N lengths averaging 2.20 A, which is normal for a 1,10-phenanthroline type of ligand coordinated to seven-coordinate Fe(III). The Fe-O bonds to the carboxylate oxygens average 2.157 A, which is rather long compared to the average Fe-O length of 2.035 A to carboxylates in seven-coordinate Fe(III) complexes. The structure of 1 supports the idea that the Fe(III) is too small for ideal coordination in the cleft of PDA, and the structure shows that the Fe(III) adapts to this by inducing numerous small distortions in the structure of the PDA ligand. The log K(1) values for PDA at 25 degrees C in 0.1 M NaClO(4) were determined by UV spectroscopy with Al(III) (log K(1) = 6.9), Ga(III) (log K(1) = 9.7), In(III) (log K(1) = 19.7), Fe(III) (log K(1) = 20.0), and Bi(III) (log K(1) = 26.2). The low values of log K(1) for PDA with Al(III) and Ga(III) are because these ions are too small for the cleft in PDA, which requires a large metal ion with an ionic radius (r(+)) of 1.0 A. In(III) and Fe(III) (r(+) = 0.86 and 0.72 A for a coordination number (CN) of 7) are somewhat too small for the cleft in PDA but may adapt by increasing the coordination number, which increases the metal ion size, and have high log K(1) values. Very large log K(1) values are found, as expected, for Bi(III) (r(+) = 1.17 A, CN = 8), which fits the cleft quite well. Fluorescence studies show that Y(III) produces the largest CHEF (chelation enhanced fluorescence) effects, followed by La(III) and Lu(III), in the PDA complexes. Metal ions with nonfilled d or f subshells produce very large quenching of the fluorescence, as do heavy-metal ions such as In(III) and Bi(III), which have large spin-orbit coupling effects. The Al(III)/PDA complex produced an intense broad band at longer wavelength than the pi*-pi emissions of the PDA ligand, which is at a maximum at pH 6, and the possibility that this might reflect an exciplex, where one PDA ligand in the Al(III) complex pi-stacks with the excited state of a second PDA ligand, is discussed. PMID:19603801

Williams, Neil J; Dean, Nolan E; VanDerveer, Donald G; Luckay, Robert C; Hancock, Robert D

2009-08-17

333

Metal flux and dynamic speciation at (bio)interfaces. Part VI: The roles of simple, fulvic and aggregate complexes on computed metal flux in freshwater ligand mixtures; comparison of Pb, Zn and Ni at planar and microspherical interfaces  

NASA Astrophysics Data System (ADS)

The computations of metal flux in aquatic systems, at consuming interfaces like microorganism surfaces are of major importance in ecotoxicology and dynamic risk assessment. In this paper, the flux of Zn(II) and Ni(II), at a planar consuming interface in a typical natural freshwater, are studied. The system includes (a) simple ligands (OH -, CO32-); (b) fulvics; (c) aggregates, as complexants, i.e., those which play the major roles in controlling the metal distribution and/or metal flux in aquatic media. The above two metals are chosen because they participate, respectively, to intermediate and very slow chemical reactions with complexing sites, and are thus complementary to Pb(II) and Cu(II) (two metals with very fast reactions) studied in Parts III-V of this series. The effects of the various physico-chemical factors, in particular, the diffusion layer thickness, the stability constants and complexing site distribution of fulvics and the size distribution of aggregates, are studied in details. The contribution to the flux, of each complex type, is computed. This paper also compares the dynamic behaviour of Pb(II), Zn(II) and Ni(II) as well as the labilities and flux contributions of their various complexes at planar and microspherical interfaces. This enables to make predictions on biouptake by microorganisms.

Zhang, Zeshi; Buffle, Jacques

2009-03-01

334

Triazoles as complexing agents: Synthesis and structural studies of some bivalent metal ion complexes with Bi and tridentate ligands  

Microsoft Academic Search

Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of 4-amino-5-mercapto-3-trifluoromethyl-s-triazole (AMTT) and 5-mercapto-4-salicylideneamino-3-trifluoromethyl-s-triazole (MSTT) have been synthesized and characterized on the basis of elemental analyses, magnetic measurements, infrared and electronic spectral data. The ligandsAMTT andMSTT were characterized by elemental analyses, infrared and1H NMR spectral studies.AMTT, involving N and S as donor atoms, andMSTT, involving N, O and S as donor atoms,

S. N. Dubey; R. N. Handa; B. K. Vaid

1994-01-01

335

Sorption of precious metals from acid solutions by functionalised vinylbenzyl chloride–acrylonitryle–divinylbenzene copolymers bearing amino and guanidine ligands  

Microsoft Academic Search

New functional resins with long functional ligands were synthesised by modification of poly(vinylbenzylchloride–acrylonitryle–divinylbenzene) matrix with ethylenediamine, bis(aminopropyl)amine, bis(aminohexyl)triamine or tris(2-aminoethyl)amine. The derivatives were reacted with S-methylthiourea to obtain resins with 2.8–5.0mmol of amino group per 1g of dry resin. Sorption efficiency of resin towards Au(III), Pt(IV), Pd(II) chlorocomplexes was determined in a batch mode multicomplexes solutions of Cu(II), Ni(II) and

D. Jermakowicz-Bartkowiak; B. N. Kolarz; A. Serwin

2005-01-01

336

Volatility and high thermal stability in mid-to-late first-row transition-metal complexes containing 1,2,5-triazapentadienyl ligands.  

PubMed

Treatment of first-row transition-metal MCl(2) (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the potassium 1,2,5-triazapentadienyl salts K(tBuNNCHCHNR) (R = tBu, NMe(2)) afforded M(tBuNNCHCHNR)(2) in 18-73% isolated yields after sublimation. The X-ray crystal structures of these compounds show monomeric, tetrahedral molecular geometries, and magnetic moment measurements are consistent with high-spin electronic configurations. Complexes with R = tBu sublime between 155 and 175 °C at 0.05 Torr and have decomposition temperatures that range from 280 to 310 °C, whereas complexes with R = NMe(2) sublime at 105 °C at 0.05 Torr but decompose between 181 and 225 °C. This work offers new nitrogen-rich ligands that are related to widely used ?-diketiminate and 1,3,5-triazapentadienyl ligands and demonstrates new complexes with properties suitable for use in atomic-layer deposition. PMID:23343413

Kalutarage, Lakmal C; Heeg, Mary Jane; Martin, Philip D; Saly, Mark J; Kuiper, David S; Winter, Charles H

2013-01-23

337

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

338

Dehydrogenation of secondary amines: synthesis, and characterization of rare-earth metal complexes incorporating imino- or amido-functionalized pyrrolyl ligands.  

PubMed

The dehydrogenation of pyrrolyl-functionalized secondary amines initiated by rare-earth metal amides was systematically studied. Reactions of the rare-earth metal amides [(Me(3)Si)(2)N](3)RE(?-Cl)Li(THF)(3) with pyrrolyl-functionalized secondary amines 2-(t)BuNHCH(2)-5-R-C(4)H(2)NH (R = H (1), R = (t)Bu (2)) led to dehydrogenation of the secondary amines with isolation of imino-functionalized pyrrolyl rare-earth metal complexes [2-(t)BuN=CH-5-R-C(4)H(2)N](2)REN(SiMe(3))(2) (R = H, RE = Y (3a), Dy (3b), Yb (3c), Eu (3d); R = (t)Bu, RE = Y (4a), Dy (4b), Er (4c)). The mixed ligands erbium complex [2-(t)BuNCH(2)-5-(t)Bu-C(4)H(2)N]Er[2-(t)BuN=CH-5-(t)BuC(4)H(2)N](2)ClLi(2)(THF) (4c') was isolated in a short reaction time for the synthesis of complex 4c. Reaction of the deuterated pyrrolyl-functionalized secondary amine 2-((t)BuNHCHD)C(4)H(3)NH with yttrium amide [(Me(3)Si)(2)N](3)Y(?-Cl)Li(THF)(3) further proved that pyrrolyl-amino ligands were transferred to pyrrolyl-imino ligands. Treatment of 2-((t)BuNHCH(2))C(4)H(3)NH (1) with excess (Me(3)Si)(2)NLi gave the only pyrrole deprotonated product {[?(5):?(2):?(1)-2-((t)BuNHCH(2))C(4)H(3)N]Li(2)N(SiMe(3))(2)}(2) (5), indicating that LiN(SiMe(3))(2) could not dehydrogenate the secondary amines to imines and rare-earth metal ions had a decisive effect on the dehydrogenation. The reaction of the rare-earth metal amides [(Me(3)Si)(2)N](3)RE(?-Cl)Li(THF)(3) with 1 equiv. of more bulky pyrrolyl-functionalized secondary amine 2-[(2,6-(i)Pr(2)C(6)H(3))NHCH(2)](C(4)H(3)NH) (6) in toluene afforded the only amine and pyrrole deprotonated dinuclear rare-earth metal amido complexes {(?-?(5):?(1)):?(1)-2-[(2,6-(i)Pr(2)C(6)H(3))NCH(2)]C(4)H(3)N]LnN(SiMe(3))(2)}(2) (RE = Nd (7a), Sm (7b), Er (7c)), no dehydrogenation of secondary amine to imine products were observed. On the basis of experimental results, a plausible mechanism for the dehydrogenation of secondary amines to imines was proposed. PMID:23238708

Li, Qinghai; Zhou, Shuangliu; Wang, Shaowu; Zhu, Xiancui; Zhang, Lijun; Feng, Zhijun; Guo, Liping; Wang, Fenhua; Wei, Yun

2013-02-28

339

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

SciTech Connect

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

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

2009-10-15

340

Synthesis, spectral and biological studies of nitrogen-sulphur donor macrocyclic ligands and their transition metals complexes.  

PubMed

Mn(II), Co(II), Ni(II) and Cu(II) complexes have been synthesized with 22 and 24 membered tetramide macrocyclic ligands viz; 1,9,12,20-tetraaza-2,8,13,19-tetraone-5,16-dithiacyclodocosane [L(1)] and 1,9,13,21-tetraaza-2,8,14,20-tetraone-5,17-dithiacyclotetracosane [L(2)] and characterized by elemental analysis, molar conductance, magnetic susceptibility measurements, mass, IR, electronic EPR spectral studies and electrochemical properties. The molar conductance of all the complexes in DMSO solution is corresponding to 1:2 electrolyte. Thus these complexes may be formulated as [M(L')]Cl(2) [where M = Mn(II), Co(II), Ni(II) and Cu(II) L' = L(1) and L(2)]. On the basis of spectral studies a distorted octahedral geometry has been assigned for all the complexes. The ligands and their complexes were also screened in vitro against two pathogenic fungi (F. moniliformae and R. solani) to assess their growth inhibiting potential. PMID:19589720

Verma, Shweta; Chandra, Sulekh; Dev, Usha; Joshi, Nidhi

2009-06-17

341

Synthesis, spectral and biological studies of nitrogen-sulphur donor macrocyclic ligands and their transition metals complexes  

NASA Astrophysics Data System (ADS)

Mn(II), Co(II), Ni(II) and Cu(II) complexes have been synthesized with 22 and 24 membered tetramide macrocyclic ligands viz; 1,9,12,20-tetraaza-2,8,13,19-tetraone-5,16-dithiacyclodocosane [L 1] and 1,9,13,21-tetraaza-2,8,14,20-tetraone-5,17-dithiacyclotetracosane [L 2] and characterized by elemental analysis, molar conductance, magnetic susceptibility measurements, mass, IR, electronic EPR spectral studies and electrochemical properties. The molar conductance of all the complexes in DMSO solution is corresponding to 1:2 electrolyte. Thus these complexes may be formulated as [M(L')]Cl 2 [where M = Mn(II), Co(II), Ni(II) and Cu(II) L' = L 1 and L 2]. On the basis of spectral studies a distorted octahedral geometry has been assigned for all the complexes. The ligands and their complexes were also screened in vitro against two pathogenic fungi ( F.moniliformae and R.solani) to assess their growth inhibiting potential.

Verma, Shweta; Chandra, Sulekh; Dev, Usha; Joshi, Nidhi

2009-10-01

342

Mass, EPR, IR and electronic spectroscopic studies on newly synthesized macrocyclic ligand and its transition metal complexes  

NASA Astrophysics Data System (ADS)

Manganese(II), cobalt(II), nickel(II) and copper(II) complexes have been synthesized with a new tetradentate ligand viz. 1,3,7,9-tetraaza-2,4,8,10-tetraketo-6,12-diphenyl-cyclododecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMF correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes. Thus, these complexes may be formulated as [M(L)X 2] and [Ni(L)]X 2 (where M = Mn(II), Co(II) and Cu(II) and X = Cl - and NO 3-). On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.

Chandra, Sulekh; Gupta, Lokesh Kumar

2005-12-01

343

Two 2D metal-organic frameworks based on N-heterocyclic and polycarboxylates ligands: Syntheses, structures, and photoluminescent properties  

NASA Astrophysics Data System (ADS)

Two novel complexes constructed from aromatic acid and N-heterocyclic ligands have been synthesized by hydrothermal reaction: {[Mn(dipt)(BDC)3?H2O]n (1) [dipt = 2-(2,4-dichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, BDC = terephthalic acid] and [Pb(dnpt)(BDC)2]n (2) [dnpt = 2-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline]. Complexes 1 and 2 were characterized by elemental analysis, IR, single crystal X-ray diffraction and thermogravimetric analysis (TGA). The results suggest that complexes 1-2 exhibit 1D chain structure. The intermolecular C-H\\ctdot O and N-H\\ctdot O interactions extend the complexes into 2D networks, and the existing H-bonds further stabilized the title complexes, which can be proved by TGA experiment. Furthermore, the solid-state fluorescence spectrum of complexes 1 and 2 were also investigated, as well as the ligands dipt and dnpt.

Yan, Li; Li, Chuanbi; Zhu, Dongsheng

2013-02-01

344

Ir Spectroscopy of Au-...(CO2)n Clusters: Strong Cluster Size Dependence of Metal-Ligand Interaction  

NASA Astrophysics Data System (ADS)

Gold is a widely used catalyst in many reactions. For example, negatively charged gold clusters have been shown to catalyze the oxidation of CO to CO2 [1], although the precise role of negative charge has not been understood. A previous study from our laboratory has shown that the binary complex [AuCO2]- has the CO2 ligand covalently bound to the gold, leading to significant charge transfer onto the CO2 unit and concomitant decrease of the OCO bond angle and weakening of the CO bonds [2]. The structure of this aurylformate anion is reminiscent of structural motifs assumed to play a role in a recent approach towards production of solar fuels using reductive activation of CO2 [3]. We report infrared spectra of Au-...(CO2)n clusters highlighting solvation mediated changes in the infrared signatures of the ligands. These results are discussed in the framework of quantum chemistry calculations. 1. U. Heiz and W.D. Schneider, J. Phys. D - Appl. Phys., 33 (2000) R85- R102. 2. A.D. Boese, H. Schneider, A.N. Gloess, and J.M. Weber, J. Chem. Phys., 122 (2005) 154301. 3. E.E. Barton, D.M. Rampulla, and A.B. Bocarsly, J. Am. Chem. Soc., 130 (2008) 6342.

Knurr, Benjamin J.; Weber, J. Mathias

2012-06-01

345

[MAGUKs: beyond ionic channel anchoring].  

PubMed

A family of anchoring proteins named MAGUK (for membrane associated guanylate kinase) has emerged as a key element in the organization of protein complexes in specialized membrane regions. These proteins are characterized by the presence of multipe protein-protein interaction domains including PDZ and SH3 domains. The MAGUK family comprises the post-synaptic density 95 (PSD-95) protein and closely related molecules such as chapsyn-110, synapse-associated protein 102 (SAP-102), and SAP-97. These are located either on the pre- and/or post-synaptic sides of synapses or at cell-cell adhesion sites of epithelial cells. MAGUK proteins interact with glutamate receptors and various ionic channels. For instance, an interaction has been reported between the first two PDZ domains of MAGUK proteins and several channels via a consensus sequence Thr/Ser-X-Val/Leu usually located at their carboxy terminus. The role of these anchoring proteins in channel function is not fully understood. MAGUK proteins enhance the current density by increasing the number of functional channels to the sarcolemma. They can also facilitate signaling between channels and several enzymes or G protein-dependent signaling pathways. In the heart also, MAGUK proteins are abundantly expressed and they interact with various channels including Shaker Kv1.5 and connexins. PMID:14770369

Godreau, David; Neyroud, Nathalie; Vranckx, Roger; Hatem, Stéphane

2004-01-01

346

Tautomeric switching and metal-cation sensing of ligand-equipped 4-hydroxy-/4-oxo-1,4-dihydroquinolines.  

PubMed

Novel 4-hydroxyquinoline (4HQ) based tautomeric switches are reported. 4HQs equipped with coordinative side arms (8-arylimino and 3-piperidin-1-ylmethyl groups) were synthesized to access O- or N-selective chelation of Zn(2+) and Cd(2+) ions by 4HQ. In the case of the monodentate arylimino group, O chelation of metal ions induces concomitant switching of phenol tautomer to the keto form in nonpolar or aprotic media. This change is accompanied by selective and highly sensitive fluorometric sensing of Zn(2+) ions. In the case of the bidentate 8-(quinolin-8-ylimino)methyl side arm, NMR studies in CD(3) OD indicated that both Cd(2+) and Zn(2+) ions afford N chelation for 4HQ, coexisting with tautomeric switching from quinolin-4(1H)-one to quinolin-4-olate. In corroboration, UV/Vis-monitored metal-ion titrations in toluene and methanol implied similar structural changes. Additionally, fluorescence measurements indicated that the metal-triggered tautomeric switching is associated with compound signaling properties. The results are supported by DFT calculations at the B3LYP 6-31G* level. Several X-ray structures of metal-free and metal-chelating 4HQ are presented to support the solution studies. PMID:22517539

Todorov, Aleksandar R; Nieger, Martin; Helaja, Juho

2012-04-19

347

A Homologous Series of First-Row Transition-Metal Complexes of 2,2'-Bipyridine and their Ligand Radical Derivatives: Trends in Structure, Magnetism, and Bonding.  

PubMed

The organometallic first-row transition-metal complexes [M(2,2'-bipy)(mes)(2)] (M = Cr (1), Mn (2), Co (4), Ni (5); 2,2'-bipy = 2,2'-bipyridine; mes = 2,4,6-Me(3)C(6)H(2)) were reacted with potassium and a suitable alkali-metal sequestering agent to yield salts of the anionic species [M(2,2'-bipy)(mes)(2)](-). The neutral parent compounds and their corresponding anionic congeners were characterized by single-crystal X-ray diffraction in [Cr(2,2'-bipy)(mes)(2)]·1.5C(6)H(6), [Mn(2,2'-bipy)(mes)(2)], [Co(2,2'-bipy)(mes)(2)]·THF, [Ni(2,2'-bipy)(mes)(2)], [K(dibenzo-18-crown-6)·THF][Cr(2,2'-bipy)(mes)(2)]·2THF, [K(18-crown-6)][Mn(2,2'-bipy)(mes)(2)]·2THF, [K(18-crown-6)][Mn(2,2'-bipy)(mes)(2)]·0.67py·0.67tol, [K(2,2,2-crypt)][Co(2,2'-bipy)(mes)(2)], and [K(2,2,2-crypt)][Ni(2,2'-bipy)(mes)(2)]. These species, along with the previously reported neutral and anionic iron complexes [Fe(2,2'-bipy)(mes)(2)](0/-) (3/3(-)), form a homologous series of compounds which allow for an in-depth study of the interactions between metals and ligands. Single-crystal X-ray diffraction data, DFT calculations, and various spectroscopic and magnetic measurements indicate that the anionic complexes (1(-)-5(-)) can be best formulated as M(II) complexes of the 2,2'-bipyridyl radical anion. These findings complement recent studies which indicate that bond metric data from single-crystal X-ray diffraction may be employed as an important diagnostic tool in determining the oxidation states of bipyridyl ligands in transition-metal complexes. PMID:23110751

Irwin, Mark; Doyle, Laurence R; Krämer, Tobias; Herchel, Radovan; McGrady, John E; Goicoechea, Jose M

2012-10-30

348

Anchors Away: Media Framing of Broadcast Television Network Evening News Anchors  

Microsoft Academic Search

Between 2002 and 2006, six newcomers took the anchor chairs at the evening news programs of ABC, CBS, and NBC. Collectively, they received extensive news coverage. This study uses content analysis to examine how three national newspapers framed the new anchors. A frame casting the anchors as competitors in a ratings game was especially common. At the same time, the

Paul R. Brewer; Timothy Macafee

2007-01-01

349

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

350

Synthesis and Spectral Characterization of 14- and 16-membered tetraazamacrocyclic Schiff base ligands and their transition metal complexes and a comparative study of interaction of calf thymus DNA with copper(II) complexes  

NASA Astrophysics Data System (ADS)

14 and 16 membered Schiff base macrocyclic ligands, 7,14-dimethyl-5,12-di(N-amino)-2-methylphenyl-1,4,8,11-tetraaza-cyclotetradecane-4,7,11,14-tetraene (L 1) and 8,16-dimethyl-6,14-di(N-amino)-2-methylphenyl-1,5,9,13-tetraaza-cyclohexadecane-5,8,13,16-tetraene (L 2) were synthesized by condensation reaction between 2'-methyleacetoacetanilide and aliphatic diamines. The metal complexes of the types, [ML 1](NO 3) 2 and [ML 2(NO 3) 2] [M = Co(II), Ni(II), Cu(II) and Zn(II)] were prepared by interaction of ligands, L 1 or L 2 with hydrated metal(II) nitrates. The ligands and their complexes were characterized by elemental analysis, IR, 1H and 13C NMR, EPR, UV-Vis spectroscopy, magnetic susceptibility, conductivity measurements and ESI-mass spectral studies. The results of elemental analyses, ESI-mass and conductivity measurements confirmed the stoichiometry of ligands and their complexes while the characteristic absorption bands and resonance peaks in IR and NMR spectra confirmed the formation of ligand frameworks around the metal ions. The square planar geometry for complexes derived from ligand L 1 and octahedral environment for complexes derived from ligand L 2 with distortion in Cu(II) complex have been confirmed on the basis of results of electronic and electron spin resonance spectral studies and magnetic moment measurements. Absorption and fluorescence spectral studies revealed different binding mode for complex, [CuL 1](NO 3) 2 as compared with [CuL 2(NO 3) 2] on interaction with calf thymus DNA.

Khan, Tahir Ali; Naseem, Sultana; Khan, Shahper N.; Khan, Asad U.; Shakir, Mohammad

2009-08-01

351

Synthesis and spectral characterization of 14- and 16-membered tetraazamacrocyclic Schiff base ligands and their transition metal complexes and a comparative study of interaction of calf thymus DNA with copper(II) complexes.  

PubMed

14 and 16 membered Schiff base macrocyclic ligands, 7,14-dimethyl-5,12-di(N-amino)-2-methylphenyl-1,4,8,11-tetraaza-cyclotetradecane-4,7,11,14-tetraene (L(1)) and 8,16-dimethyl-6,14-di(N-amino)-2-methylphenyl-1,5,9,13-tetraaza-cyclohexadecane-5,8,13,16-tetraene (L(2)) were synthesized by condensation reaction between 2'-methyleacetoacetanilide and aliphatic diamines. The metal complexes of the types, [ML(1)](NO(3))(2) and [ML(2)(NO(3))(2)] [M = Co(II), Ni(II), Cu(II) and Zn(II)] were prepared by interaction of ligands, L(1) or L(2) with hydrated metal(II) nitrates. The ligands and their complexes were characterized by elemental analysis, IR, (1)H and (13)C NMR, EPR, UV-Vis spectroscopy, magnetic susceptibility, conductivity measurements and ESI-mass spectral studies. The results of elemental analyses, ESI-mass and conductivity measurements confirmed the stoichiometry of ligands and their complexes while the characteristic absorption bands and resonance peaks in IR and NMR spectra confirmed the formation of ligand frameworks around the metal ions. The square planar geometry for complexes derived from ligand L(1) and octahedral environment for complexes derived from ligand L(2) with distortion in Cu(II) complex have been confirmed on the basis of results of electronic and electron spin resonance spectral studies and magnetic moment measurements. Absorption and fluorescence spectral studies revealed different binding mode for complex, [CuL(1)](NO(3))(2) as compared with [CuL(2)(NO(3))(2)] on interaction with calf thymus DNA. PMID:19403328

Khan, Tahir Ali; Naseem, Sultana; Khan, Shahper N; Khan, Asad U; Shakir, Mohammad

2009-03-31

352

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

DOEpatents

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

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

2011-01-04

353

Rare-earth-metal-hydrocarbyl complexes bearing linked cyclopentadienyl or fluorenyl ligands: synthesis, catalyzed styrene polymerization, and structure-reactivity relationship.  

PubMed

A series of rare-earth-metal-hydrocarbyl complexes bearing N-type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH(2)SiMe(3))(3)(thf)(2)] with equimolar amount of the electron-donating aminophenyl-Cp ligand C(5)Me(4)H-C(6)H(4)-o-NMe(2) afforded the corresponding binuclear monoalkyl complex [({C(5)Me(4)-C(6)H(4)-o-NMe(?-CH(2))}Y{CH(2)SiMe(3)})(2)] (1a) via alkyl abstraction and C-H activation of the NMe(2) group. The lutetium bis(allyl) complex [(C(5)Me(4)-C(6)H(4)-o-NMe(2))Lu(?(3)-C(3)H(5))(2)] (2b), which contained an electron-donating aminophenyl-Cp ligand, was isolated from the sequential metathesis reactions of LuCl(3) with (C(5)Me(4)-C(6)H(4)-o-NMe(2))Li (1 equiv) and C(3)H(5)MgCl (2 equiv). Following a similar procedure, the yttrium- and scandium-bis(allyl) complexes, [(C(5)Me(4)-C(5)H(4)N)Ln(?(3)-C(3)H(5))(2)] (Ln=Y (3a), Sc (3b)), which also contained electron-withdrawing pyridyl-Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl-Flu ligand (C(13)H(9)-C(5)H(4)N) by [Ln(CH(2)SiMe(3))(3)(thf)(2)] generated the rare-earth-metal-dialkyl complexes, [(?(3)-C(13)H(8)-C(5)H(4)N)Ln(CH(2)SiMe(3))(2)(thf)] (Ln=Y (4a), Sc (4b), Lu (4c)), in which an unusual asymmetric ?(3)-allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium-trisalkyl complex [Y(CH(2)C(6)H(4)-o-NMe(2))(3)], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(?(3)-C(13)H(8)-C(5)H(4)N)Y(CH(2)C(6)H(4)-o-NMe(2))(2)] (5). Complexes 1-5 were fully characterized by (1)H and (13)C NMR and X-ray spectroscopy, and by elemental analysis. In the presence of both [Ph(3)C][B(C(6)F(5))(4)] and AliBu(3), the electron-donating aminophenyl-Cp-based complexes 1 and 2 did not show any activity towards styrene polymerization. In striking contrast, upon activation with [Ph(3)C][B(C(6)F(5))(4)] only, the electron-withdrawing pyridyl-Cp-based complexes 3, in particular scandium complex 3b, exhibited outstanding activitiy to give perfectly syndiotactic (rrrr >99%) polystyrene, whereas their bulky pyridyl-Flu analogues (4 and 5) in combination with [Ph(3)C][B(C(6)F(5))(4)] and AliBu(3) displayed much-lower activity to afford syndiotactic-enriched polystyrene. PMID:22282393

Jian, Zhongbao; Cui, Dongmei; Hou, Zhaomin

2012-01-26

354

Extraction of 3D Transition Metals from Molten Cesium-Sodium-Potassium/Acetate Eutectic into Dodecane Using Organophosphorous Ligands.  

National Technical Information Service (NTIS)

Measurements have been made of the transfer of the transition metal cations Cr exp 3+ , Fe exp 2+ , Co exp 2+ , Ni exp 2+ from molten cesium acetate-sodium acetate-potassium acetate eutectic (50-25-25 mol%, mp approx. 90 exp 0 C) into dodecane solutions c...

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

1983-01-01

355

Simple ligand-field theory of d4 and d6 transition metal complexes with a C3 symmetry axis.  

PubMed

There have been a number of recent studies reporting high-spin d(4,6) complexes with three- and four-coordinate geometry, which exhibit roughly trigonal symmetry. These include complexes of Fe(II) with general formula L(3)FeX, where L = thioether or dialkylphosphine donors of a tripodal chelating ligand and X is a monodentate ligand on the C(3) axis. In these systems, there is unquenched orbital angular momentum, which has significant consequences on the electronic/magnetic properties of the complexes, including magnetic susceptibility, EPR spectra, and magnetic Mössbauer spectra. We describe here a simple model using a description of the d orbitals with trigonal symmetry that along with the application of the spin-orbit interaction successfully explains the magnetic properties of such systems. These d orbitals with 3-fold symmetry are complex orbitals with a parameter, a, that is determined by the bond angle, ?, of LFeX. We demonstrate that the E symmetry states in such systems with S > 1/2 cannot be properly "simulated by" or be "represented by" the Zeeman and second-order zero-field spin Hamiltonian alone because by definition the parameters D and E are second-order terms. One must include the first-order spin-orbit interaction. We also find these systems to be very anisotropic in all their magnetic properties. For example, the perpendicular values of g and the hyperfine interaction parameter are essentially zero for the ground-state doublet. For illustrative purposes, the discussion focuses primarily on two specific Fe(II) complexes: one with the bond angle ? greater than tetrahedral and another with the bond angle ? less than tetrahedral. The nature of the EPR spectra and hyperfine interaction of (57)Fe are discussed. PMID:22583045

McGarvey, Bruce R; Telser, Joshua

2012-05-14

356

Anchors of Religious Commitment in Adolescents  

ERIC Educational Resources Information Center

This study explores adolescent religious commitment using qualitative data from a religiously diverse (Jewish, Christian, Muslim) sample of 80 adolescents. A new construct, "anchors of religious commitment," grounded in interview data, is proposed to describe what adolescents commit to as a part of their religious identity. Seven anchors of…

Layton, Emily; Dollahite, David C.; Hardy, Sam A.

2011-01-01

357

Anchoring International sets new water depth record  

Microsoft Academic Search

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

1983-01-01

358

Anchors of Religious Commitment in Adolescents  

Microsoft Academic Search

This study explores adolescent religious commitment using qualitative data from a religiously diverse (Jewish, Christian, Muslim) sample of 80 adolescents. A new construct, anchors of religious commitment, grounded in interview data, is proposed to describe what adolescents commit to as a part of their religious identity. Seven anchors of religious commitment are discussed: (a) religious traditions, rituals, and laws; (b)

Emily Layton; David C. Dollahite; Sam A. Hardy

2011-01-01

359

Anchors of Religious Commitment in Adolescents  

ERIC Educational Resources Information Center

|This study explores adolescent religious commitment using qualitative data from a religiously diverse (Jewish, Christian, Muslim) sample of 80 adolescents. A new construct, "anchors of religious commitment," grounded in interview data, is proposed to describe what adolescents commit to as a part of their religious identity. Seven anchors of…

Layton, Emily; Dollahite, David C.; Hardy, Sam A.

2011-01-01

360

Explaining Forward Discount Bias: Is It Anchoring?  

Microsoft Academic Search

Anchoring is a well-documented behaviour pattern. It occurs when agents form their expectations of an objective variable by only partially adjusting from some given starting value. We present a model of the foreign exchange market in which there are two types of traders: those who are fully rational and those whose expectations are anchored to the forward exchange rate. Under

David W. R. Gruen; Marianne C. Gizycki

1993-01-01

361

Anchor Text Extraction for Academic Search  

Microsoft Academic Search

Anchor text plays a special important role in improving the performance of general Web search, due to the fact that it is relatively ob- jective description for a Web page by poten- tially a large number of other Web pages. Academic Search provides indexing and search functionality for academic articles. It may be desirable to utilize anchor text in aca-

Shuming Shi; Fei Xing; Mingjie Zhu; Zaiqing Nie; Ji-Rong Wen

2009-01-01

362

76 FR 30301 - Commercial Acquisition; Anchor Tenancy  

Federal Register 2010, 2011, 2012, 2013

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

2011-05-25

363

Pile anchoring method and apparatus. [offshore drilling  

Microsoft Academic Search

A method and the apparatus are described for the pile anchoring of a structure in a relatively shallow or underconsolidated substratum. The method includes the initial introduction of an anchoring pile to a desired depth into the normally incompetent substratum. A seires of longitudinally spaced peripheral projections is then formed in the substratum adjacent to the pile external wall, at

I. C. Pogonowski; P. D. Carmichael; R. H. Griswold

1972-01-01

364

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2013 CFR

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

2013-04-01

365

Ligand Substitution Dynamics.  

National Technical Information Service (NTIS)

This article presents a review of recent progress in the study of the dynamics of the replacement of one ligand by another on metal ions in solution. The subject is organized according to the A-I-D scheme of Langford and Gray. After a brief introduction a...

C. H. Langford T. R. Stengle

1968-01-01

366

Five novel transition metal coordination polymers with 2D/3D framework structure based on flexible H{sub 2}tzda and ancillary ligand bpe  

SciTech Connect

Five new transition metal coordination polymers based on H{sub 2}tzda and co-ligand bpe, {l_brace}[M(tzda)(bpe)].H{sub 2}O{r_brace}{sub n} [M=Zn(1), Cd(2), Mn(3), Co(4)] and [Ni{sub 2}(tzda){sub 2}(bpe){sub 2}(H{sub 2}O)]{sub n} (5) [H{sub 2}tzda=(1,3,4-thiadiazole-2,5-diyldithio)diacetic acid, bpe=1,2-bis(4-pyridyl)ethane], have been hydrothermally synthesized and structurally characterized. Compounds 1-4 feature a 2D-layered architecture generated from [M(tzda)]{sub n} moiety with double-chain structure cross-linking bpe spacers. However, the conformations bpe adopts in 3 and 4 are different from those in 1 and 2 due to the rotation of C-C single bond in bpe. Polymer 5 exhibits an interesting 3D porous framework with 2-fold interpenetration, in which intriguing 1D double helix chains are observed. The photoluminescence properties of 1 and 2 in the solid-state at room temperature are investigated. In addition, variable-temperature magnetic data show weak antiferromagnetic behavior in 3-5. - Graphical abstract: Five new transition metal coordination polymers based on flexible H{sub 2}tzda and bpe have been hydrothermally synthesized and characterized by X-ray diffraction, luminescent emission spectra and low-temperature magnetic measurements, respectively.

Wang Yuting [Department of Chemistry, Henan Institute of Education, Henan 450014 (China); Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052 (China); Xu Yan [Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052 (China); Fan Yaoting, E-mail: yt.fan@zzu.edu.c [Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052 (China); Hou Hongwei [Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052 (China)

2009-10-15

367

Ligand-solvent interactions in a highly reduced metal chelate complex: medium dependence of the one-electron reduction of the bis(maleonitriledithiolato)gold dianion.  

PubMed

The one-electron reduction of [Au(mnt)(2)](2-) (mnt = [S(2)C(2)(CN)(2)](2-), maleonitriledithiolate), 1(2-), stands out in the rich redox chemistry of metal-mnt complexes as a chemically reversible but electrochemically irreversible process. Although the E(1/2) value of the primary redox reaction 1(2-)/1(3-) is only slightly medium dependent (ca. -1.36 V to -1.53 V vs FcH in several nonaqueous solvents and supporting electrolytes), its chemical reversibility is dramatically solvent dependent. A quasi-Nernstian process was observed only in tetrahydrofuran (THF) at low supporting electrolyte concentrations. Fast reversible follow-up reactions, ascribed to formation of solvento-complexes [Au(mnt)(2).Solv](3-), were observed through cyclic voltammetry (CV) studies in dichloromethane and acetonitrile. The specifically solvated trianion reverts to "unsolvated" 1(2-) when reoxidized, accounting for the overall chemical reversibility of the process. Owing to the fact that the ligands in 1(3-) are highly negatively charged, the strong specific solvation is likely to involve H-bonding interactions between the solvent and the sulfur atoms of the trianion. Ion-pairing interactions between 1(3-) and electrolyte cations were also shown to have a discernible effect on the 1(2-)/1(3-) couple in THF. The heterogeneous electron-transfer (ET) rate constant (k(s)) for this couple was sufficiently low (k(s) = approximately 10(-3) cm s(-1)) to suggest a square-planar to quasi-tetrahedral structural rearrangement being intrinsic to the 1(2-)/1(3-) ET process. The E(1/2) separation between the 1(-)/1(2-) and 1(2-)/1(3-) couples (ca. 220 mV) is much smaller than any of those previously reported for metal-mnt complexes. The behavior of the gold-mnt trianion is a rare example of a ligand-based solvento-complex, which contrasts with the well-known metal-based solvento-complexes that are commonly observed between electron-deficient complexes and strong donor solvents. PMID:19894771

LeSuer, Robert J; Geiger, William E

2009-11-16

368

Guyline anchor design keys rig stability  

SciTech Connect

Inadequate design and field installation of ground anchors at lease well sites have frequently led to the collapse of well service rigs operating in high surface wind conditions (>50 mph). Such catastrophes incur significant equipment damage and injury to operating personnel. Although collapse of a well service rig can be attributed to inadequate strength in the guyline connection to the mast or anchor or to deformed or inadequate wire rope strength in the guyline itself, most failures result from improperly placed anchors not meeting API specifications to withstand 14,000 lb of force in tension. This article defines the length, diameter, and depth necessary (based on soil conditions) for a buried guyline anchor to meet API specifications. Deficiencies in guyline connection and strength can be alleviated by following the manufacturer's guidance on size of wire rope, its inspection, and size connection criteria in mounting guyline connectors to the mast and anchor.

Murphy, R.J.; Laguros, J.G.

1983-09-01

369

Deepwater Propellant Embedded Anchor having Emergency Release Mechanism.  

National Technical Information Service (NTIS)

This improved propellant embedded marine anchor includes an emergency release device used to safely separate the anchor projectile from the gun assembly for the purpose of disarming the system when a misfire occurs. The anchor projectile is connected to a...

M. Stern D. G. True

1981-01-01

370

Synthesis and characterization of group 6 and cobalt metal complexes containing nitrogen-rich donor ligands for metal nitride nanoparticles and thin films  

Microsoft Academic Search

Metalorganic and organometallic group 6 source compounds for the growth of MNx and MNxCy thin films for application as diffusion barriers in integrated circuits by Atomic Layer Deposition (ALD) are limited to a few compounds. In addition, group 6 metal nitride nanoparticles and their use as diffusion barriers have not been explored. Accordingly, the work described entailed the synthesis and

Oussama M El-Kadri

2006-01-01

371

Hindsight bias as a function of anchor distance and anchor plausibility.  

PubMed

This study explored the influence of anchor distance on hindsight bias and how the subjective plausibility of different anchors moderates this relation. In addition to the standard memory design used in hindsight bias research, participants were asked to indicate the range of values for possible answers to difficult almanac questions. Varying anchor distance on the basis of each participant's individual range of possible answers showed (1) that anchor plausibility decreased with increasing anchor distance following a non-linear monotone function, (2) that size of hindsight bias initially increased with increasing anchor distance but, from a certain distance, started to decrease, and (3) that hindsight bias was found to be always higher for plausible than for implausible anchors. PMID:14562869

Hardt, Oliver; Pohl, Rüdiger F

372

Metal-Ligand Interplay in Strongly Correlated Oxides: A Parametrized Phase Diagram for Pressure-Induced Spin Transitions  

Microsoft Academic Search

We investigate the magnetic properties of archetypal transition-metal oxides MnO, FeO, CoO, and NiO under very high pressure by x-ray emission spectroscopy at the Kbeta line. We observe a strong modification of the magnetism in the megabar range in all the samples except NiO. The results are analyzed within a multiplet approach including charge-transfer effects. The spectral changes are well

Aleksi Mattila; Jean-Pascal Rueff; James Badro; György Vankó; Abhay Shukla

2007-01-01

373

Functionalized adamantane tectons used in the design of mixed-ligand copper(II) 1,2,4-triazolyl/carboxylate metal-organic frameworks.  

PubMed

Bistriazoles, 1,3-bis(1,2,4-triazol-4-yl)propane (tr(2)pr) and 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr(2)ad), were examined in combination with the rigid tetratopic 1,3,5,7-adamantanetetracarboxylic acid (H(4)-adtc) platform for the construction of neutral heteroleptic copper(II) metal-organic frameworks. Two coordination polymers, [{Cu(4)(OH)(2)(H(2)O)(2)}{Cu(4)(OH)(2)}(tr(2)pr)(2)(H-adtc)(4)]·2H(2)O (1) and [Cu(4)(OH)(2)(tr(2)ad)(2)(H-adtc)(2)(H(2)O)(2)]·3H(2)O (2), were synthesized and structurally characterized. In complexes 1 and 2, the N(1),N(2)-1,2,4-triazolyl (tr) and ?(3)-OH(-) groups serve as complementary bridges between adjacent metal centers supporting the tetranuclear dihydroxo clusters. The structure of 1 represents a unique association of two different kinds of centrosymmetrical {Cu(4)(OH)(2)} units in a tight 3D framework, while in compound 2, another configuration type of acentric tetranuclear metal clusters is organized in a layered 3,6-hexagonal motif. In both cases, the {Cu(4)(OH)(2)} secondary building block and trideprotonated carboxylate H-adtc(3-) can be viewed as covalently bound six- and three-connected nodes that define the net topology. The tr ligands, showing ?(3)- or ?(4)-binding patterns, introduce additional integrating links between the neighboring {Cu(4)(OH)(2)} fragments. A variable-temperature magnetic susceptibility study of 2 demonstrates strong antiferromagnetic intracluster coupling (J(1) = -109 cm(-1) and J(2) = -21 cm(-1)), which combines for the bulk phase with a weak antiferromagnetic intercluster interaction (zj = -2.5 cm(-1)). PMID:23294097

Senchyk, Ganna A; Lysenko, Andrey B; Krautscheid, Harald; Rusanov, Eduard B; Chernega, Alexander N; Krämer, Karl W; Liu, Shi-Xia; Decurtins, Silvio; Domasevitch, Konstantin V

2013-01-07

374

Synthesis, reactivity, and characterization of sodium and rare-earth metal complexes bearing a dianionic N-aryloxo-functionalized beta-ketoiminate ligand.  

PubMed

The synthesis and reactivity of a series of sodium and rare-earth metal complexes stabilized by a dianionic N-aryloxo-functionalized beta-ketoiminate ligand were presented. The reaction of acetylacetone with 1 equiv of 2-amino-4-methylphenol in absolute ethanol gave the compound 4-(2-hydroxy-5-methylphenyl)imino-2-pentanone (LH2, 1) in high yield. Compound 1 reacted with excess NaH to afford the novel sodium cluster [LNa2(THF)2]4 (2) in good isolated yield. Structure determination revealed that complex 2 has the 22-vertex cage structure. Reactions of complex 2 with anhydrous LnCl3 in a 1:4 molar ratio, after workup, gave the desired lanthanide chlorides [LLnCl(DME)]2 [Ln = Y (3), Yb (4), Tb (5)] as dimers. A further study revealed that complexes 3-5 are inert for chlorine substitution reactions. (ArO)3Ln(THF) (ArO = 2,6-Bu(t)2-4-MeC6H2O) reacted with compound 1 in a 1:1 molar ratio in tetrahydrofuran (THF), after workup, to give the desired rare-earth metal aryloxides as dimers [LLn(OAr)(THF)]2 [Ln = Nd (6), Sm (7), Yb (8), Y (9)] in high isolated yields. All of these complexes are well characterized, and the definitive molecular structures of complexes 2 and 4-6 were determined. It was found that complexes 6-9 can be used as efficient initiators for L-lactide polymerization, and the ionic radii of the central metals have a significant effect on the catalytic activity. PMID:18828586

Peng, Hongmei; Zhang, Zhenqin; Qi, Ruipeng; Yao, Yingming; Zhang, Yong; Shen, Qi; Cheng, Yanxiang

2008-10-02

375

A study of the removal of heavy metals from aqueous solutions by Moringa oleifera seeds and amine-based ligand 1,4-bis[N,N-bis(2-picoyl)amino]butane.  

PubMed

Uptake for lead, copper, cadmium, nickel and manganese from aqueous solution using the Moringa oleifera seeds biomass (MOSB) and amine-based ligand (ABL) was investigated. Experiments on two synthetic multi-solute systems revealed that MOSB performed well in the biosorption and followed the decreasing orders Pb(II)>Cu(II)>Cd(II)>Ni(II)>Mn(II) and Zn(II)>Cu(II)>Ni(II). The general trend of the heavy metal ions uptake by the amine-based ligand followed decreased in the order Mn>Cd>Cu>Ni>Pb, which is the reverse trend for what was observed for MOSB. Comparing the single- and multi-metal solutions, there was no clear effect in the biosorption capacity of MOSB suggesting the presence of sufficient active binding sites for all metal ions studied. The MOSB performance is also not affected by pH in the range 3.5-8. PMID:22632049

Obuseng, Veronica; Nareetsile, Florence; Kwaambwa, Habauka M

2012-02-06

376

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

PubMed Central

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

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

2012-01-01

377

"Directed" assembly of metallacalix[n]arenes with pyrimidine nucleobase ligands of low symmetry: interchanging metals in mixed-metal metallacalix[4]arenes and incorporating additional metals at the exocyclic groups.  

PubMed

The pyrimidine (pym) nucleobase cytosine (H(2)C) forms cyclic ring structures ("metallacalix[n]arenes") when treated with square-planar cis-a(2)M(II) entities (M=Pt, Pd; a=NH(3) or a(2)=diamine). The number of possible linkage isomers for a given n and the number of possible rotamers can be substantially reduced if a "directed" approach is pursued. Hence, two cytosine ligands are bonded in a defined way to a kinetically robust platinum corner stone. In the accompanying paper (Part I: A. Khutia, P. J. Sanz?Miguel, B. Lippert, Chem. Eur. J. 2010, 17, DOI: 10.1002/chem.2010002722) we have demonstrated this principle by allowing cis-[Pta(2)(H(2)C-N3)(2)](2+) to react with (en)Pd(II) to give cycles of (N1,N3?N3,N1?)(x) (with x=2 or 3; ? represents Pt(II) and ? represents Pd(II)). In an extension of this work we have now prepared cis-[Pta(2)(HC-N1)(2)] (1; HC=monoanion of cytosine) and treated it with (bpy)Pd(II) (bpy=2,2'-bipyridine) to give the Pt(2) Pd(2) cycle cis-[{Pt(NH(3))(2)(N1-HC-N3)(2)Pd(bpy)}(2)](NO(3))(4) ?13H(2)O (5) with the coordination sites of the metals inverted; hence, platinum is bonded to N1 and palladium is bonded to N3 sites. Again, not only the expected single linkage isomer is formed, but at the same time the solid-state structure and (1)H?NMR spectroscopy reveal the preferential occurrence of a single rotamer (1,3-alternate). The addition of (bpy)Pd(II) to 5 led to the formation of Pd(6) Pt(2) complex 6 in which the exocyclic N4H(2) groups of the cytosine ligands have undergone deprotonation and chelate four more (bpy)Pd(II) entities through the O2 and N4H sites. With a large excess of (bpy)Pd(II) over 5 (4:1), cis-(NH(3))(2) Pt(II) is eventually substituted by (bpy)Pd(II) to give the Pd(8) complex 7. In both 6 and 7 stacks of three (bpy)Pd(II) entities occur. The linkage isomer of 5,cis-[{Pt(NH(3))(2)(N3-HC-N1)(2)Pd(bpy)}(2)](NO(3))(4) ?9H(2)O (8), has been structurally characterized and the two complexes compared. The acid/base properties of cis-[Pt(NH(3))(2)(H(2)C-N1)(2)] (1) have been determined and compared with those of the corresponding N3 isomer. The complexation of AgCl by 1 is reported. PMID:21387424

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

2011-03-08

378

Synthesis, molecular and electronic structures of six-coordinate transition metal (Mn, Fe, Co, Ni, Cu, and Zn) complexes with redox-active 9-hydroxyphenoxazin-1-one ligands.  

PubMed

A series of pseudo-octahedral metal (M = Mn, Fe, Co, Ni, Cu, Zn) complexes 4 of a new redox-active ligand, 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 3, have been synthesized, and their molecular structures determined with help of X-ray crystallography. The effective magnetic moments of complexes 4 (M = Mn, Fe, Co, and Ni) measured in the solid state and toluene solution point to the stabilization of their high-spin electronic ground states. Detailed information on the electronic structure of the complexes and their redox-isomeric forms has been obtained using density functional theory (DFT) B3LYP*/6-311++G(d,p) calculations. The energy disfavored low-spin structures of manganese, iron, and cobalt complexes have been located, and based on the computed geometries and distribution of spin densities identified as Mn(IV)[(Cat-N-SQ)](2), Fe(II)[Cat-N-BQ)](2), and Co(II)[Cat-N-BQ)](2) compounds, respectively. It has been shown that stabilization of the high-spin structures of complexes 4 (M = Mn, Fe, Co) is caused by the rigidity of the molecular framework of ligands 3 that sterically inhibits interconversions between the redox-isomeric forms of the complexes. The calculations performed on complex 4 (M = Co) predict that a suitable structural modification that might provide for stabilization of the low-spin electromeric forms and create conditions for the valence tautomeric rearrangement via stabilization of the low-spin electromer and narrowing energy gap between the low-spin ground state tautomer and the minimal energy crossing point on the intersection of the potential energy surfaces of the interconverting structures consists in the replacement of an oxygen in the oxazine ring by a bulkier sulfur atom. PMID:21718042

Ivakhnenko, Eugeny P; Starikov, Andrey G; Minkin, Vladimir I; Lyssenko, Konstantin A; Antipin, Mikhail Yu; Simakov, Vladimir I; Korobov, Mikhail S; Borodkin, Gennady S; Knyazev, Pavel A

2011-06-30

379

Unraveling principles of lead discovery: from unfrustrated energy landscapes to novel molecular anchors.  

PubMed

The search for novel leads is a critical step in the drug discovery process. Computational approaches to identify new lead molecules have focused on discovering complete ligands by evaluating the binding affinity of a large number of candidates, a task of considerable complexity. A new computational method is introduced in this work based on the premise that the primary molecular recognition event in the protein binding site may be accomplished by small core fragments that serve as molecular anchors, providing a structurally stable platform that can be subsequently tailored into complete ligands. To fulfill its role, we show that an effective molecular anchor must meet both the thermodynamic requirement of relative energetic stability of a single binding mode and its consistent kinetic accessibility, which may be measured by the structural consensus of multiple docking simulations. From a large number of candidates, this technique is able to identify known core fragments responsible for primary recognition by the FK506 binding protein (FKBP-12), along with a diverse repertoire of novel molecular cores. By contrast, absolute energetic criteria for selecting molecular anchors are found to be promiscuous. A relationship between a minimum frustration principle of binding energy landscapes and receptor-specific molecular anchors in their role as "recognition nuclei" is established, thereby unraveling a mechanism of lead discovery and providing a practical route to receptor-biased computational combinatorial chemistry. PMID:8799133

Rejto, P A; Verkhivker, G M

1996-08-20

380

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

SciTech Connect

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

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

2008-08-15

381

Bromination and nitration reactions of metallated (Ru and Os) multiaromatic ligands and crystal structures of selected products  

Microsoft Academic Search

Three nitrogen-containing aromatic heterocycles, 2-(1?-naphthyl)pyridine, 2-phenylquinoline, and 2,3-diphenylquinoxaline, have been mercurated in the naphthyl or phenyl ring 2-position and then symmetrised to form the mercury compounds Ar2Hg (Ar=Nppy (3), Phqn (1) or Dpqx (5), respectively). These reagents are suitable for trans-metallation and reaction with MHCl(CO)(PPh3)3 affords the complexes M(?2-C,N?Ar)Cl(CO)(PPh3)2, (6, M=Ru, Ar=Nppy; 7, M=Os, Ar=Nppy; 8, M=Ru, Ar=Phqn; 9, M=Os,

Alex M Clark; Clifton E. F Rickard

2000-01-01

382

Regulatory consideration of bioavailability for metals: simplification of input parameters for the chronic copper biotic ligand model.  

PubMed

The chronic Cu biotic ligand model (CuBLM) provides a means by which the bioavailability of Cu can be taken into account in assessing the potential chronic risks posed by Cu at specific freshwater locations. One of the barriers to the widespread regulatory application of the CuBLM is the perceived complexity of the approach when compared to the current systems that are in place in many regulatory organizations. The CuBLM requires 10 measured input parameters, although some of these have a relatively limited influence on the predicted no-effect concentration (PNEC) for Cu. Simplification of the input requirements of the CuBLM is proposed by estimating the concentrations of the major ions Mg2+, Na+, K+, SO4(2-), Cl- , and alkalinity from Ca concentrations. A series of relationships between log10 (Ca, mg?l(-1)) and log10 (major ion, mg?l(-1)) was established from surface water monitoring data for Europe, and applied in the prediction of Cu PNEC values for some UK freshwater monitoring data. The use of default values for major ion concentrations was also considered, and both approaches were compared to the use of measured major ion concentrations. Both the use of fixed default major ion concentrations, and major ion concentrations estimated from Ca concentrations, provided Cu PNEC predictions which were in good agreement with the results of calculations using measured data. There is a slight loss of accuracy when using estimates of major ion concentrations compared to using measured concentration data, although to a lesser extent than when fixed default values are applied. The simplifications proposed provide a practical evidence-based methodology to facilitate the regulatory implementation of the CuBLM. PMID:21082669

Peters, Adam; Merrington, Graham; de Schamphelaere, Karel; Delbeke, Katrien

2011-03-23

383

Metal–organic coordination polymers based on imidazolyl- and benzimidazolyl-containing 4,4?-bipy type ligands  

NASA Astrophysics Data System (ADS)

Two new semirigid ligands 2,2?-bis(imidazol-1-ylmethyl)-4,4?-bis(4-pyridyl)biphenyl(L1) and 2,2?-bis(benzimidazol-1-ylmethyl)-4,4?-bis(4-pyridyl)biphenyl(L2) were designed and synthesized. Six new coordination compounds, {Cd(L1)Br2}n (1), {Cd(L1)(1,2-bdc)(H2O)?H2O}n (2), {Zn(L1) (1,3-bdc)?2.7H2O}n (3), {Co(L1)(1,3-bdc)?H2O}n (4), (1,2-bdc = 1,2-benzenedicarboxylate, 1,3-bdc = 1,3-benzenedicarboxylate, {Cd(L2)2(NO3)2?2H2O}n (5) and, [Ni(L2)2(H2O)2](ClO4)2?3H2O (6) based on them were obtained and characterized by single-crystal X-ray diffraction methods. 1 is a 2D infinite spongy cushion-like network. In 2, two bridging 1,2-bdc anions chelate two neighboring Cd(II) atoms with their carboxylate groups to form a 1D double chain. 3 displays a 2D network in which the wavelike {Zn(1,3-bdc2?)}n chains are linked to each other by bidentate L1. 4 adopts a unique 3D framework, in which the coplanar {Co(1,3-bdc2?)}n chains are connected to each other through tridentate L1. 5 features a 1D double chain motif composed of a square bimetallic ring as the building block. 6 is mononuclear nickel complex. The photoluminescence properties of L1–L2, 1–3 and 5 were investigated, and all of them exhibit intense fluorescent emissions in the solid state at room temperature.

Jin, Guo-Xia; Ma, Jian-Ping; Dong, Yu-Bin

2013-11-01

384

Inflammatory Response with Osteolysis Related to a Bioabsorbable Anchor in the Finger: a Case Report  

PubMed Central

Soft tissue fixation of ligaments and tendons in the hand can be achieved by the use of metal or bioabsorbable suture anchors. Advantages of bioabsorbable suture anchors include lack of interference in magnetic resonance imaging, resorption of anchor, replacement by bone, and no need for hardware removal. However, complications of these bioabsorbable implants include inflammatory response to the material use. We present what we believe to be the first case in the hand of a poly(l-lactide-co-d,l-lacitide) suture anchor causing an inflammatory response leading to significant osteolysis 4 months postoperatively after repair of a ring finger flexor digitorum profundus avulsion. Exploration of the distal phalanx revealed an intact implant and repair, no signs of infection, and an extensive bone defect. Pathology showed chronically inflamed tissue. This case has led us to reconsider the use of bioabsorbable anchor sutures in the hand. Further research is necessary to better define the contraindications to bioabsorbable suture anchor use in the hand.

Galano, Gregory J.; Strauch, Robert J.; Rosenwasser, Melvin P.; Tang, Peter

2009-01-01

385

Proton transport facilitating water-oxidation: the role of second sphere ligands surrounding the catalytic metal cluster.  

PubMed

The ability of PSII to extract electrons from water, with molecular oxygen as a by-product, is a remarkable biochemical and evolutionary innovation. From an evolutionary perspective, the invention of PSII approximately 2.7 Ga led to the accelerated accumulation of biomass in the biosphere and the accumulation of oxygen in the atmosphere, a combination that allowed for the evolution of a much more complex and extensive biosphere than would otherwise have been possible. From the biochemical and enzymatic perspective, PSII is remarkable because of the thermodynamic and kinetic obstacles that needed to have been overcome to oxidize water as the ultimate photosynthetic electron donor. This article focuses on how proton release is an integral part of how these kinetic and thermodynamic obstacles have been overcome: the sequential removal of protons from the active site of H2O-oxidation facilitates the multistep oxidation of the substrate water at the Mn4CaO x , the catalytic heart of the H2O-oxidation reaction. As noted previously, the facilitated deprotonation of the Mn4CaO x cluster exerts a redox-leveling function preventing the accumulation of excess positive charge on the cluster, which might otherwise hinder the already energetically difficult oxidation of water. Using recent results, including the characteristics of site-directed mutants, the role of the second sphere of amino acid ligands and the associated network of water molecules surrounding the Mn4CaO x is discussed in relation to proton transport in other systems. In addition to the redox-leveling function, a trapping function is assigned to the proton release step occurring immediately prior to the dioxygen chemistry. This trapping appears to involve a yet-to-be clarified gating mechanism that facilitates to coordinated release of a proton from the neighborhood of the active site thereby insuring that the backward charge-recombination reaction does not out-compete the forward reaction of dioxygen chemistry during this final step of H2O-oxidation. PMID:23975203

Bao, Han; Dilbeck, Preston L; Burnap, Robert L

2013-08-24

386

The v-sis protein retains biological activity as a type II membrane protein when anchored by various signal-anchor domains, including the hydrophobic domain of the bovine papilloma virus E5 oncoprotein  

PubMed Central

Membrane-anchored forms of the v-sis oncoprotein have been previously described which are oriented as type I transmembrane proteins and which efficiently induce autocrine transformation. Several examples of naturally occurring membrane-anchored growth factors have been identified, but all exhibit a type I orientation. In this work, we wished to construct and characterize membrane-anchored growth factors with a type II orientation. These experiments were designed to determine whether type II membrane-anchored growth factors would in fact exhibit biological activity. Additionally, we wished to determine whether the hydrophobic domain of the E5 oncoprotein of bovine papilloma virus (BPV) can function as a signal-anchor domain to direct type II membrane insertion. Type II derivatives of the v-sis oncoprotein were constructed, with the NH2 terminus intracellular and the COOH terminus extracellular, by substituting the NH2 terminal signal sequence with the signal-anchor domain of a known type II membrane protein. The signal-anchor domains of neuraminidase (NA), asialoglycoprotein receptor (ASGPR) and transferrin receptor (TR) all yielded biologically active type II derivatives of the v-sis oncoprotein. Although transforming all of the type II signal/anchor-sis proteins exhibited a very short half-life. The short half-life exhibited by the signal/anchor-sis constructs suggests that, in some cases, cellular transformation may result from the synthesis of growth factors so labile that they activate undetectable autocrine loops. The E5 oncoprotein encoded by BPV exhibits amino acid sequence similarity with PDGF, activates the PDGF beta-receptor, and thus resembles a miniature membrane-anchored growth factor with a putative type II orientation. The hydrophobic domain of the E5 oncoprotein, when substituted in place of the signal sequence of v-sis, was indistinguishable compared with the signal-anchor domains of NA, TR, and ASGPR, demonstrating its ability to function as a signal-anchor domain. NIH 3T3 cells transformed by the signal/anchor-sis constructs exhibited morphological reversion upon treatment with suramin, indicating a requirement for ligand/receptor interactions in a suramin- sensitive compartment, most likely the cell surface. In contrast, NIH 3T3 cells transformed by the E5 oncoprotein did not exhibit morphological reversion in response to suramin.

1993-01-01

387

Rare-earth metal alkyl, amido, and cyclopentadienyl complexes supported by imidazolin-2-iminato ligands: synthesis, structural characterization, and catalytic application.  

PubMed

The rare earth metal dichlorides [(1)MCl(2)(THF)(3)] (2a, M = Sc; 2b, M = Y; 2c, M = Lu) and the gadolinium complex [(1)GdCl(2)(THF)(2)] x [LiCl(THF)(2)] (2d), containing the 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato ligand 1, proved to be versatile starting materials for the preparation of trimethylsilylmethyl ("neosilyl") and bis(trimethylsilyl)amido complexes [(1)M(CH(2)SiMe(3))(2)(THF)(2)] (3a-3d) and [(1)M(HMDS)(2)(THF)] [4a-4d, HMDS = hexamethyldisilazide, N(SiMe(3))(2)] and for the preparation of the benzyl complex [(1)Lu(CH(2)Ph)(2)(THF)(2)] (5c) by the reaction with LiCH(2)SiMe(3), Na[N(SiMe(3))(2)], and KCH(2)Ph, respectively. Treatment of 2a-2c with KCp* afforded the mono(pentamethylcyclopentadienyl) complexes [(1)Sc(Cp*)Cl(THF)] (6a), [(1)Y(Cp*)Cl(THF)(2)] (6b), and [(1)Lu(Cp*)Cl(THF)] (6c). In contrast, the gadolinocene complex [(1)Gd(Cp*)(2)(THF)] (7) was isolated from the reaction of 2d with 2 equiv of KCp*. The molecular structures of 3a-3d, 4b.THF, 4d, 5c, 6a, 6c, and 7 x THF were determined by X-ray diffraction analyses, revealing the presence of exceptionally short metal-nitrogen bonds. The neosilyl complexes 3b and 3c showed high catalytic activity in the intramolecular hydroamination of aminoalkenes and aminoalkynes and in the hydrosilylation of 1-hexene and 1-octene with PhSiH(3). PMID:20102173

Trambitas, Alexandra G; Panda, Tarun K; Jenter, Jelena; Roesky, Peter W; Daniliuc, Constantin; Hrib, Cristian G; Jones, Peter G; Tamm, Matthias

2010-03-01

388

Covalent Anchor Positions Play an Important Role in Tuning Catalytic Properties of a Rationally Designed MnSalen-containing Metalloenzyme.  

PubMed

Two questions important to the success in metalloenzyme design are how to attach or anchor metal cofactors inside protein scaffolds, and in what way such positioning affects enzymatic properties. We have previously reported a dual anchoring method to position a nonnative cofactor, MnSalen (1), inside the heme cavity of apo sperm whale myoglobin (Mb) and showed that the dual anchoring can increase both the activity and enantioselectivity over the single anchoring methods, making this artificial enzyme an ideal system to address the above questions. Here we report systematic investigations of the effect of different covalent attachment or anchoring positions on reactivity and selectivity of sulfoxidation by the MnSalen-containing Mb enzymes. We have found that changing the left anchor from Y103C to T39C has an almost identical effect of increasing rate by 1.8-fold and increasing selectivity by +14% for S, whether the right anchor is L72C or S108C. At the same time, regardless of the identity of the left anchor, changing the right anchor from S108C to L72C increases rate by 4-fold and selectivity by +66%. The right anchor site was observed to have a greater influence than the left anchor site on the reactivity and selectivity in sulfoxidation of a wide scope of other ortho-, meta- and para- substituted substrates. The 1•Mb(T39C/L72C) showed the highest reactivity (TON up to 2.31 min(-1)) and selectivity (ee% up to 83%) among the different anchoring positions examined. Molecular dynamic simulations indicate that these changes in reactivity and selectivity may be due to the steric effects of the linker arms inside the protein cavity. These results indicate that small differences in the anchor positions can result in significant changes in reactivity and enantioselectivity, probably through steric interactions with substrates when they enter the substrate-binding pocket, and that the effects of right and left anchor positions are independent and additive in nature. The finding that the anchoring arms can influence both the positioning of the cofactor and steric control of substrate entrance will help design better functional metalloenzymes with predicted catalytic activity and selectivity. PMID:22013554

Garner, Dewain K; Liang, Lei; Barrios, David A; Zhang, Jun-Long; Lu, Yi

2011-09-01

389

Chemistry of Marine Ligands and Siderophores  

PubMed Central

Marine microorganisms are presented with unique challenges to obtain essential metal ions required to survive and thrive in the ocean. The production of organic ligands to complex transition metal ions is one strategy to both facilitate uptake of specific metals, such as iron, and to mitigate the potential toxic effects of other metal ions, such as copper. A number of important trace metal ions are complexed by organic ligands in seawater, including iron, cobalt, nickel, copper, zinc, and cadmium, thus defining the speciation of these metal ions in the ocean. In the case of iron, siderophores have been identified and structurally characterized. Siderophores are low molecular weight iron-binding ligands produced by marine bacteria. Although progress has been made toward the identity of in situ iron-binding ligands, few compounds have been identified that coordinate the other trace metals. Deciphering the chemical structures and production stimuli of naturally produced organic ligands and the organisms they come from is fundamental to understanding metal speciation and bioavailability. The current evidence for marine ligands, with an emphasis on siderophores, and discussion of the importance and implications of metal-binding ligands in controlling metal speciation and cycling within the world’s oceans are presented.

Vraspir, Julia M.; Butler, Alison

2011-01-01

390

Nuclear migration: Cortical anchors for cytoplasmic dynein  

Microsoft Academic Search

Nuclear migration in yeast provides a model system for studying how a cell polarizes the actin and microtubule cytoskeletons toward sites of cell growth. Recent findings indicate that cortical anchors are necessary for directing microtubule-based processes.

Kerry Bloom

2001-01-01

391

Design of chiral ligands for asymmetric catalysis: From C2-symmetric P,P- and N,N-ligands to sterically and electronically nonsymmetrical P,N-ligands  

PubMed Central

For a long time, C2-symmetric ligands have dominated in asymmetric catalysis. More recently, nonsymmetrical modular P,N-ligands have been introduced. These ligands have been applied successfully in various metal-catalyzed reactions and, in many cases, have outperformed P,P- or N,N-ligands.

Pfaltz, Andreas; Drury, William J.

2004-01-01

392

Syntheses, structures, photoluminescence, and magnetic properties of (3,6)- and 4-connected lanthanide metal-organic frameworks with a semirigid tricarboxylate ligand.  

PubMed

Lanthanide coordination polymers [LnL(DMF)(2)]·0.25H(2)O [Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), and Tm (12)], and [GdL(H(2)O)(3)] (7') (H(3)L = 5-(4-carboxy-2-nitrophenoxy)-isophthalic acid), have been synthesized under hydro- and solvothermal conditions, respectively. Compounds 1-12 exhibit the same three-dimensional (3D) architecture, which is built up from binuclear paddle-wheel building blocks, and their resulting frameworks can be rationalized as rarely reported flu-3,6-C2/c topology. Compound 7' crystallizes in the monoclinic system, space group P2(1)/c. The ligands (L) bridge the Gd(III) centers to form 3D frameworks featuring a zeolite BCT topology, which have been unreported based on rare earth metals until now. Moreover, compound 6 exhibits characteristic red luminescent properties of Eu(III) complexes. The magnetic susceptibilities, over a temperature range of 2.0-300 K, of 7 and 7' have also been investigated. PMID:22374318

Su, Shengqun; Wang, Song; Song, Xuezhi; Song, Shuyan; Qin, Chao; Zhu, Min; Hao, Zhaomin; Zhao, Shuna; Zhang, Hongjie

2012-02-29

393

Five novel transition metal coordination polymers with 2D/3D framework structure based on flexible H2tzda and ancillary ligand bpe  

NASA Astrophysics Data System (ADS)

Five new transition metal coordination polymers based on H2tzda and co-ligand bpe, {[M(tzda)(bpe)]·H2O}n [M=Zn(1), Cd(2), Mn(3), Co(4)] and [Ni2(tzda)2(bpe)2(H2O)]n (5) [H2tzda=(1,3,4-thiadiazole-2,5-diyldithio)diacetic acid, bpe=1,2-bis(4-pyridyl)ethane], have been hydrothermally synthesized and structurally characterized. Compounds 1-4 feature a 2D-layered architecture generated from [M(tzda)]n moiety with double-chain structure cross-linking bpe spacers. However, the conformations bpe adopts in 3 and 4 are different from those in 1 and 2 due to the rotation of C-C single bond in bpe. Polymer 5 exhibits an interesting 3D porous framework with 2-fold interpenetration, in which intriguing 1D double helix chains are observed. The photoluminescence properties of 1 and 2 in the solid-state at room temperature are investigated. In addition, variable-temperature magnetic data show weak antiferromagnetic behavior in 3-5.

Wang, Yu-Ting; Xu, Yan; Fan, Yao-Ting; Hou, Hong-Wei

2009-10-01

394

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

NASA Astrophysics Data System (ADS)

Six complexes based on a flexible tripodal ligand H3TTTA (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)(H2O)3]n (1); dimeric metallamacrocycle, [Zn(HTTTA)(2,2?-bipy)(H2O)]n (2) and [Cd(HTTTA)(2,2?-bipy)(H2O)·H2O]n (3); two-dimensional networks with binodal (3,6)-connected CdI2 topology based on linear trinuclear M3(?2-CO2)4(?2-CO2)2 SBUs (Secondary Building Units), [M3(TTTA)2(2,2?-bipy)2(H2O)m·nH2O]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 ?6-bridge. Fluorescence and magnetic properties of the complexes have also been investigated in details.

Li, Chengjuan; Peng, Yanqiang; Wang, Suna; Zhang, Xianxi; Li, Yizhi; Dou, Jianmin; Li, Dacheng

2011-07-01

395

Versatile frameworks constructed from divalent metals with 4,4?-methylenedibenzoic acid and imidazole derivative ligands: Syntheses, crystal structures and physical properties  

NASA Astrophysics Data System (ADS)

Seven coordination polymers, namely, [Zn(DBA)(Hpyim)]n·nH2O (1), [Cd(DBA)(Hpyim)]n (2), [Zn(DBA)(bix)]n·2nH2O (3), [Co(DBA)(bix)]n (4), [Ni(DBA)(bix)]n (5), [Co(DBA)(mbix)]n (6), and [Ni(DBA)(mbix)(H2O)2]n·nH2O (7), where H2DBA=4,4?-methylenedibenzoic acid, Hpyim=2-(2-pyridyl)imidazole, bix=1,4-bis(imidazol-1-ylmethyl) benzene and mbix=1,3-bis(imidazol-1-yl-methyl) benzene, were synthesized. Complex 1 is a one-dimensional (1D) infinite chain. Complex 2 has a two-dimensional (2D) 4-connected (4,4) network based on dinuclear units. Complex 3 features a 2D sheet constructed from mononuclear center. Complexes 4 and 5 exhibit similar 2D layers, which are further linked into 3D supramolecular frameworks through ?-? interactions. Complex 6 possesses a 3D 5-fold interpenetrating diamond framework, while complex 7 shows a 1D double-strand chain. The results indicate that the coordination modes of DBA, auxiliary ligands and metal ions play important roles in the formation of the final framework. Moreover, the luminescent properties of 1-3 and nonlinear optical and ferroelectric properties of 1 were also investigated.

Liu, Guang-Xiang; Wang, Xiao-Feng; Zhou, Hong

2013-03-01

396

Physiochemical characterization and antimicrobial evaluation of phenylthiourea-formaldehyde polymer (PTF) based polymeric ligand and its polymer metal complexes  

NASA Astrophysics Data System (ADS)

Phenylthiourea-formaldehyde polymer (PTF) has been synthesized via polycondensation of phenylthiourea and formaldehyde in basic medium and its corresponding metal complexes [PTF-M(II)] were prepared with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions. The synthesized polymers have been characterized by elemental analysis, magnetic susceptibility, UV-visible, FT-IR, 1H NMR, 13C NMR, ESR spectroscopy and thermogravimetric analysis (TGA). Elemental analysis, electronic spectra and magnetic moment measurement indicate that PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) show octahedral geometry, while PTF-Cu(II) and PTF-Zn(II) show square planar and tetrahedral geometry, respectively. The results of TGA ascribed that all the PTF-M(II) showed better heat-resistance properties than PTF resin. In vitro antimicrobial activities were performed against several bacteria and fungi using agar well diffusion method. The results of microbial activity were compared with Kanamycin and Miconazole as standard antibiotics for antibacterial and antifungal activities respectively.

Ahamad, Tansir; Alshehri, Saad M.

2013-05-01