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1

Distearoyl anchor-painted erythrocytes with prolonged ligand retention and circulation properties in vivo  

PubMed Central

Red blood cells (RBCs) attract significant interest as carriers of biomolecules, drugs and nanoparticles. In this regard, versatile technologies to attach molecules and ligands to the RBC surface are of great importance. Reported here is a fast and efficient surface painting strategy to attach ligands to the surface of RBCs, and the factors that control the stability and circulation properties of the modified RBCs in vivo. Distearoyl phosphatidylethanolamine anchor-conjugated immunoglobulin (IgG) efficiently incorporates in the RBC membrane following 15–30 min incubation. The optimized RBCs show prolonged circulation in vivo (70% of the injected dose after 48h) and efficient retention of IgG in the membrane with terminal half-life of 73 hours. The IgG construct is gradually lost from the RBCs mainly due to the transfer to plasma components, liver endothelial cells and Kupffer cells. The ligand retention efficiency is partially dictated by ligand type, anchor type, and ligand concentration in the membrane, while RBC half-life is determined by initial concentration of the ligand in the membrane and presence of PEG linker between the ligand and the anchor. This work provides important guidance for non-covalent surface painting of RBCs as well as other types of blood borne cells for in vivo therapeutic and targeting applications. PMID:23798381

Shi, Guixin; Mukthavaram, Rajesh; Kesari, Santosh

2014-01-01

2

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

PubMed

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

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

2013-11-01

3

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

Microsoft Academic Search

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

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

2005-01-01

4

Anchoring group effects of surface ligands on magnetic properties of Fe? O? nanoparticles: towards high performance MRI contrast agents.  

PubMed

The effect of the anchoring group of surface ligands on the magnetic properties, especially relaxometric properties, of PEGylated Fe? O? nanoparticles is investigated. Systematic experimental results together with in-depth theoretical analysis reveal that the ligand binding affinity can largely vary the saturation magnetization, whereas conjugated anchoring groups can remarkably enhance the transverse relaxivity, which highlights a novel approach for achieving high-performance MRI contrast agents. PMID:24615901

Zeng, Jianfeng; Jing, Lihong; Hou, Yi; Jiao, Mingxia; Qiao, Ruirui; Jia, Qiaojuan; Liu, Chunyan; Fang, Fang; Lei, Hao; Gao, Mingyuan

2014-05-01

5

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

6

Folate ligand anchored liquid crystal microdroplets emulsion for in vitro detection of KB cancer cells.  

PubMed

A KB cancer cell-selective, liquid crystal microdroplets emulsion is prepared using folic acid-conjugated block copolymers (PS-b-PAA-FA) and sodium dodecyl sulfate (SDS) as a mediator to induce configurational transitions in 4-cyano-4'-pentylbiphenyl (5CB) liquid crystal microdroplets emulsion. The prepared liquid crystal microdroplets emulsion has shown a configurational transition from radial to bipolar on interacting with KB cancer cells, but no transition from radial to bipolar configuration is observed when liquid crystal microdroplets emulsion was allowed to interact with other normal cells such as fibroblast and osteoblast. The KB cancer cell selectivity of liquid crystal microdroplets emulsion has been considered due to the presence of KB cancer cell folate receptor-specific ligand (FA) at the surface of liquid crystal microdroplets, which allowed liquid crystal microdroplets to interact specifically with KB cancer cells. The ligand-receptor interactions have been considered responsible for triggering the configurational transitions from radial to bipolar in liquid crystal microdroplets emulsion. Thus, folate ligand anchored liquid crystal microdroplets emulsion has shown a potential to be used for in vitro detection of KB cancer cells in the early stage of tumor development. PMID:25121826

Yoon, Seong H; Gupta, Kailash C; Borah, Jyoti S; Park, Soo-Young; Kim, Young-Kyoo; Lee, Joon-Hyung; Kang, Inn-Kyu

2014-09-01

7

Ligand Intermediates in Metal-Catalyzed Reactions  

SciTech Connect

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

Gladysz, John A.

1999-07-31

8

Photoreactivity of metal-to-ligand charge transfer excited states  

Microsoft Academic Search

Generally, transition metal complexes in metal-to-ligand charge transfer (MLCT) excited states are considered to be less reactive than in other states (e.g. ligand field, ligand-to-metal charge transfer) because the orbitals which participate in MLCT transitions are frequently of the ? type and, thus, less involved in strong bonding interactions. However, contrary to these expectations, numerous complexes, in particular the organometallic

Arnd Vogler; Horst Kunkely

1998-01-01

9

Theoretical studies on effective metal-to-ligand charge transfer characteristics of novel ruthenium dyes for dye sensitized solar cells.  

PubMed

The development of ruthenium dye-sensitizers with highly effective metal-to-ligand charge transfer (MLCT) characteristics and narrowed transition energy gaps are essential for the new generation of dye-sensitized solar cells. Here, we designed a novel anchoring ligand by inserting the cyanovinyl-branches inside the anchoring ligands of selected highly efficient dye-sensitizers and studied their intrinsic optical properties using theoretical methods. Our calculated results show that the designed ruthenium dyes provide good performances as sensitizers compared to the selected efficient dyes, because of their red-shift in the UV-visible absorption spectra with an increase in the absorption intensity, smaller energy gaps and thereby enhancing MLCT transitions. We found that, the designed anchoring ligand acts as an efficient "electron-acceptor" which boosts electron-transfer from a -NCS ligand to this ligand via a Ru-bridge, thus providing a way to lower the transition energy gap and enhance the MLCT transitions. PMID:24743972

Wang, Huei-Tang; Taufany, Fadlilatul; Nachimuthu, Santhanamoorthi; Jiang, Jyh-Chiang

2014-05-01

10

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

Microsoft Academic Search

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

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

1994-01-01

11

How to Compute Labile Metal-Ligand Equilibria  

ERIC Educational Resources Information Center

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

de Levie, Robert

2007-01-01

12

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

SciTech Connect

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

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

1994-08-01

13

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

14

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

PubMed

Bioinspired hydrogenation of N(2) 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 H(2) remains difficult. In analogy to the heterogeneously catalysed Haber-Bosch process, such a reaction is conceivable via metal-centred N(2) 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 H(2) 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. PMID:21697873

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

2011-07-01

15

Synthesis of new copper nanoparticle-decorated anchored type ligands: applications as non-enzymatic electrochemical sensors for hydrogen peroxide.  

PubMed

In this work, copper nanoparticles (CuNPs) decorated on two new anchored type ligands were utilized to prepare two electrochemical sensors. These ligands are made from bonding amine chains to silica support including SiO2-pro-NH2 (compound I) and SiO2-pro-NH-cyanuric-NH2 (compound II). The morphology of synthesized CuNPs was characterized by transmission electron microscopy (TEM). The nano-particles were in the range of 13-37 nm with the average size of 23 nm. These materials were used to modify carbon paste electrode. Different electrochemical techniques, including cyclic voltammetry, electrochemical impedance spectroscopy and hydrodynamic chronoamperometry, were used to study the sensor behavior. These electrochemical sensors were used as a model for non-enzymatic detection of hydrogen peroxide (H2O2). To evaluate the abilities of the modified electrodes for H2O2 detection, the electrochemical signals were compared in the absence and presence of H2O2. From them, two modified electrodes showed significant responses vs. H2O2 addition. The amperograms illustrated that the sensors were selective for H2O2 sensing with linear ranges of 5.14-1250 ?mol L(-1) and 1.14-1120 ?mol L(-1) with detection limits of 0.85 and 0.27 ?mol L(-1) H2O2, sensitivities of 3545 and 11,293 ?A mmol(-1)L and with response times less than 5s for I/CPE and II/CPE, respectively. As further verification of the selected sensor, H2O2 contained in milk sample was analyzed and the obtained results were comparable with the ones from classical control titration method. PMID:25492200

Ensafi, Ali A; Zandi-Atashbar, N; Ghiaci, M; Taghizadeh, M; Rezaei, B

2015-02-01

16

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

17

Glenoid damage from articular protrusion of metal suture anchor after arthroscopic rotator cuff repair.  

PubMed

Arthroscopic repair of rotator cuff tears has been shown to be effective and safe. The use of suture anchors has increased the ability to perform rotator cuff repairs arthroscopically. However, the use of suture anchors for any surgery around the shoulder can result in complications if the devices are not used and inserted properly. Complications that have been reported with the use of suture anchors for rotator cuff surgery include prominent anchors in the tuberosities, dislodged anchors secondary to pull-out or improper insertion, and osteolysis around the anchors. We report a case of articular cartilage damage secondary to a suture anchor protruding through the humeral head because of improper anchor insertion. Our patient's case reminds surgeons not only to be careful of the depth of insertion of suture anchors when performing rotator cuff surgery but also to obtain radiographs to evaluate the anchor position if patients continue to have symptoms after rotator cuff repair using these devices. PMID:25750956

Kim, Yang-Soo; Ok, Ji-Hoon; Garzon-Muvdi, Juan; McFarland, Edward G

2015-03-01

18

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

Microsoft Academic Search

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

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

2011-01-01

19

Ligand design for functional metal-organic frameworks.  

PubMed

Metal-organic frameworks (MOFs), also known as coordination polymers, are formed by the self-assembly of metallic centres and bridging organic linkers. In this critical review, we review the key advances in the field and discuss the relationship between the nature and structure of specifically designed organic linkers and the properties of the products. Practical examples demonstrate that the physical and chemical properties of the linkers play a decisive role in the properties of novel functional MOFs. We focus on target materials suitable for the storage of hydrogen and methane, sequestration of carbon dioxide, gas separation, heterogeneous catalysis and as magnetic and photoluminescent materials capable of both metal- and ligand-centred emission, ion exchangers and molecular sieves. The advantages of highly active discrete complexes as metal-bearing ligands in the construction of MOFs are also briefly reviewed (128 references). PMID:21918788

Paz, Filipe A Almeida; Klinowski, Jacek; Vilela, Sérgio M F; Tomé, João P C; Cavaleiro, José A S; Rocha, João

2012-02-01

20

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

PubMed

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

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

2013-02-14

21

Surface anchored metal-organic frameworks as stimulus responsive antifouling coatings.  

PubMed

Surface-anchored, crystalline and oriented metal organic frameworks (SURMOFs) have huge potential for biological applications due to their well-defined and highly-porous structure. In this work we describe a MOF-based, fully autonomous system, which combines sensing, a specific response, and the release of an antimicrobial agent. The Cu-containing SURMOF, Cu-SURMOF 2, is stable in artificial seawater and shows stimulus-responsive anti-fouling properties against marine bacteria. When Cobetia marina adheres on the SURMOF, the framework's response is lethal to the adhering microorganism. A thorough analysis reveals that this response is induced by agents secreted from the microbes after adhesion to the substrate, and includes a release of Cu ions resulting from a degradation of the SURMOF. The stimulus-responsive antifouling effect of Cu-SURMOF 2 demonstrates the first application of Cu-SURMOF 2 as autonomous system with great potential for further microbiological and cell culture applications. PMID:24706148

Sancet, Maria Pilar Arpa; Hanke, Maximilian; Wang, Zhengbang; Bauer, Stella; Azucena, Carlos; Arslan, Hasan K; Heinle, Marita; Gliemann, Hartmut; Wöll, Christof; Rosenhahn, Axel

2013-12-01

22

Adsorbate-Induced Anchoring Transitions of Liquid Crystals on Surfaces Presenting Metal Salts with Mixed Anions  

PubMed Central

We report that metal salts composed of mixtures of anions of differing coordination strength can be used to increase the sensitivity and selectivity of adsorbate-induced anchoring transitions of liquid crystals (LCs) supported on surfaces decorated with the metal salts. Specifically, the dynamics of anchoring transitions triggered by the adsorbate dimethyl methylphosphonate (DMMP) on surfaces of aluminum (III) salts were analyzed within the framework of a model for mass transport to reveal that the sensitivity of a nitrile-containing nematic LC to DMMP increased from 250 parts-per- billion (ppb) to 25 ppb when the composition of the (counter) anion was changed from 100% perchlorate to 90% nitrate and 10% perchlorate (by mole percent). To provide insight into these observations, Polarization-Modulation Infrared Reflectance-Absorbance Spectroscopy (PM-IRRAS) was used to show that the intensity of the absorption band in the IR spectrum corresponding to the coordinated state of the nitrile group (but not the position of the peak) decreased with increase in mole fraction of the strongly coordinating anion (nitrate) in the anion mixture, thus suggesting that the addition of the strongly coordinating anion decreased the number of coordination interactions (per unit area of the interface) but not the strength of the individual coordination interactions between the metal cation and the LC. We also measured the incorporation of the nitrate anion into the metal salt to decrease the effect of humidity on the dynamic response of the LC to DMMP, a result that is consistent with weaker interactions between the nitrate anion and water as compared to the perchlorate anion and water. Finally, the bidentate anion acetylacetonate was measured to cause a similar increase in sensitivity to DMMP when mixed with perchlorate in a 1:1 ratio (the resulting sensitivity of the system to DMMP was 100 ppb). Overall, these results suggest that tailoring the identity of the anion represents a general and facile approach for tuning the orientational response of LCs supported on metal salts to targeted analytes. PMID:24369715

Hunter, Jacob T.; Abbott, Nicholas L.

2014-01-01

23

Transition metal-ligand bonding. II  

NASA Technical Reports Server (NTRS)

The nature of the bonding of CO, H2O, and NH3 to transition metal atoms is analyzed using the constrained-space-orbital-variation (CSOV) technique. The cooperative effects for Ni(CO)2 are found to be different than those for Ni(H2O)2. The bonding between neutral systems and the positive ions is found to be quite different; NiCO(+) has little pi bonding, while NiCO has strong pi bonding. The positive ion of NiH2O is far more strongly bound than the neutral, while for NiCO the positive ion and neutral are bound by about the same energy.

Bauschlicher, C. W., Jr.

1986-01-01

24

Zwitterionic Group VIII transition metal initiators supported by olefin ligands  

DOEpatents

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

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

2011-10-25

25

Enhancement of interface anchoring and densification of Y2O3 coating by metal substrate manipulation in aerosol deposition process  

NASA Astrophysics Data System (ADS)

The interface anchoring and densification of Y2O3 coatings prepared by aerosol deposition (AD) process were systematically investigated for various types of metal substrates. At initial anchoring stage in AD process, the kinetic energy of impacted particles is converted to the heat energy, which instantly elevates the interface temperature between coating layer and substrate. Thus, the Sn substrate with low melting temperature (˜505 K) results in strong impact anchoring by local interface melting during AD process. On the other hand, the continuous collision and fracture of impacted particles lead to solid consolidation and densification of deposited coating layers. Thus, the SUS substrate with high hardness (˜173 Hv) leads to a highly densified coating layer. Indeed, the bulk metallic glass (BMG) substrates, which have unique low processable temperature (<800 K) called supercooled liquid region and ultra-high hardness (>500 Hv), give rise to both excellent interface anchoring and densification of thick Y2O3 layers with a nano-crystalline structure by AD process. These advantages of the BMG substrates can be used more widely by forming metallic glass buffer layer on various substrates applied to AD process.

Kim, Jinwoo; Lee, Je In; Park, Dong Soo; Park, Eun Soo

2015-01-01

26

Electrophilic Metal Alkyl Chemistry in New Ligand Environments  

SciTech Connect

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

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

2013-06-30

27

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

28

df-METAL COMPLEXES SUPPORTED BY FERROCENE-BASED CHELATING LIGANDS  

Microsoft Academic Search

Ferrocene is widely incorporated in pharmaceutical candidates, materials, and redox agents. In addition, ligand scaffolds make use of ferrocene groups because of their steric, electronic, and redox properties. In some cases, ferrocene is involved directly in the reactivity of a metal center even when it is part of the supporting ligand. While metal-ligand cooperation plays an important role in enzymatic

Paula L. Diaconescu

2010-01-01

29

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

PubMed

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

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

2014-05-01

30

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

E-print Network

-dach in the production and subsequent transfer of the same ligand to exogenous metal ion sources was investigated. Cu2+ and Cd2+ analogs to the Zn-1’-Ac2 were synthesized and their properties investigated with IR, elemental analysis, and UV-vis spectroscopy....

Foley, William

2011-02-22

31

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

E-print Network

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

Bachmann, Julien

2006-01-01

32

Surface engineered and ligand anchored nanobioconjugate: An effective therapeutic approach for oral insulin delivery in experimental diabetic rats.  

PubMed

The present study was designed to enhance intestinal absorption of insulin by nanobioconjugate formulated with PEGylation and Concanavalin A based targeted synergistic approach. The attempts were aimed at maximizing bioavailability and therapeutic efficacy of insulin by incorporating it in Concanavalin A anchored PEGylated nanoconstructs. The Con A anchored PEGylated PLGA diblock copolymer was synthesized by modified surface functionalization method, and was then characterized by FTIR and (1)H NMR spectrum analysis. The nanoparticles from synthesized polymers were prepared and characterized for mean size and distribution by laser diffraction spectroscopy. The physicochemically characterized (by SEM and TEM) formulations were evaluated for optimum particle size, polydispersity index, zeta potential and entrapment efficiency 196.3±4.5nm, 0.15±0.04, -25.6±1.68 and 44.6±3.5% respectively. The insulin encapsulation efficiency and in vitro release were assessed by bicinchoninic protein assay (BCA). The in vitro results corroborated in vivo studies carried out in experimentally created diabetic albino rats. The nano-encapsulated insulin was discovered to meet the requirements by achieving better stability, improved absorption and enhanced oral bioavailability elucidated by in vivo and in vitro bioassays. PMID:25679489

Sharma, Rajeev; Gupta, Umesh; Garg, Neeraj K; Tyagi, Rajeev K; Jain, N K

2015-03-01

33

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

34

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

35

Fusogenic supramolecular vesicle systems induced by metal ion binding to amphiphilic ligands  

Microsoft Academic Search

The incorporation of lipophilic ligands into the bilayer membrane of vesicles offers the possibility to induce, upon binding of suitable metal ions, a variety of processes, in particular vesicle aggregation and fusion and generation of vesicle arrays, under the control of specific metal-ligand recognition events. Synthetic bipyridine lipoligands Bn bearing a bipyridine unit as head group were prepared and incorporated

Antoine Richard; Valérie Marchi-Artzner; Marie-Noëlle Lalloz; Marie-Josèphe Brienne; Franck Artzner; Thaddée Gulik-Krzywicki; Marie-Alice Guedeau-Boudeville; Jean-Marie Lehn

2004-01-01

36

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

37

New Coordination Polymers Based on Transition Metal Squarates and Pyrazine Ligands  

Microsoft Academic Search

Three new coordination polymers have been prepared by hydrothermal reaction of squaric acid, pyrazine and the metal halides FeCl2· 4H 2O, CoBr2 and NiBr2. In their crystal structures the metal atoms are coordinated by four water molecules and two pyrazine ligands within slightly distorted octahedra. The pyrazine ligands connect the metal atoms via µ-N,N'-coordination to linear chains which are connected

Christian Näther; Jan Greve

2003-01-01

38

Metal ion and ligand binding of integrin ?5?1.  

PubMed

Integrin ?5?1 binds to an Arg-Gly-Asp (RGD) motif in its ligand fibronectin. We report high-resolution crystal structures of a four-domain ?5?1 headpiece fragment, alone or with RGD peptides soaked into crystals, and RGD peptide affinity measurements. The headpiece crystallizes in a closed conformation essentially identical to that seen previously for ?5?1 complexed with a Fab that allosterically inhibits ligand binding by stabilizing the closed conformation. Soaking experiments show that binding of cyclic RGD peptide with 20-fold higher affinity than a linear RGD peptide induces conformational change in the ?1-subunit ?I domain to a state that is intermediate between closed (low affinity) and open (high affinity). In contrast, binding of a linear RGD peptide induces no shape shifting. However, linear peptide binding induces shape shifting when Ca(2+) is depleted during soaking. Ca(2+) bound to the adjacent to metal ion-dependent adhesion site (ADMIDAS), at the locus of shape shifting, moves and decreases in occupancy, correlating with an increase in affinity for RGD measured when Ca(2+) is depleted. The results directly demonstrate that Ca(2+) binding to the ADMIDAS stabilizes integrins in the low-affinity, closed conformation. Comparisons in affinity between four-domain and six-domain headpiece constructs suggest that flexible integrin leg domains contribute to conformational equilibria. High-resolution views of the hybrid domain interface with the plexin-semaphorin-integrin (PSI) domain in different orientations show a ball-and-socket joint with a hybrid domain Arg side chain that rocks in a PSI domain socket lined with carbonyl oxygens. PMID:25475857

Xia, Wei; Springer, Timothy A

2014-12-16

39

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

PubMed Central

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

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

2011-01-01

40

Dinuclear first-row transition metal complexes with a naphthyridine-based dinucleating ligand.  

PubMed

A series of dinuclear and tetranuclear first-row transition metal complexes were synthesized with the dinucleating ligand 2,7-bis(di(2-pyridyl)fluoromethyl)-1,8-naphthyridine (DPFN). The coordination pocket and rigidity of the DPFN ligand enforces pseudo-octahedral geometries about the metal centers that contain chloro, hydroxo, and aqua bridging ligands forming a "diamond" shaped configuration with metal-metal distances varying from 2.7826(5) to 3.2410(11) Å. Each metal center in the dinuclear complexes has an additional open coordination site that accommodates terminal ligands in a syn geometry of particular interest in catalyst design. The complexes are characterized by electronic spectroscopy, electrochemistry and potentiometric titration methods. PMID:25420206

Davenport, T C; Tilley, T D

2014-11-24

41

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

Microsoft Academic Search

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

Custos Jean-Marc; Moyne Christian; Thibault Sterckeman

2010-01-01

42

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

E-print Network

The connection between metal ion affinity and ligand affinity in integrin I domains Thomas Vorup Abstract Integrins are cell-surface heterodimeric proteins that mediate cell­cell, cell­matrix, and cell­pathogen interactions. Half of the known integrin subunits contain inserted domains (I domains) that coordinate ligand

Springer, Timothy A.

43

The Electronic Structure of Transition Metal Cluster Complexes with Weak and Strong-field Ligands  

Microsoft Academic Search

A systematic account and a survey of the results of quantum-chemical and spectroscopic studies of the electronic structure of transition metal cluster complexes are presented. In terms of the theory of canonical molecular orbitals and the theory of weak- and strong-field ligands, the concept of the structure and stability of the clusters taking into account the influence of the ligands

Galina P. Kostikova; Dimitrii V. Korol'kov

1985-01-01

44

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

Microsoft Academic Search

A dedicated spectrofluorimeter using ultrashort laser pulses as an excitation source was developed to measure the fluorescence properties of organic ligands for metal ion complexation with organic ligands. The laser system consists of an oscillator system for generation of femtosecond laser pulses, an amplifier system to increase the pulse energy of the generated pulses to about 2 mJ and an

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

2004-01-01

45

Uncommon cis configuration of a metal-metal bridging noninnocent Nindigo ligand.  

PubMed

In contrast to several reported coordination compounds of trans-Nindigo ligands [Nindigo = indigo-bis(N-arylimine) = LH2] with one or two six-membered chelate rings involving one indole N and one extracyclic N for metal binding, the new diruthenium complex ion [(acac)2Ru(?,?(2):?(2)-L)Ru(bpy)2](2+) = 2(2+) exhibits edge-sharing five- and seven-membered chelate rings in the first documented case of asymmetric bridging by a Nindigo ligand in the cis configuration [L(2-) = indigo-bis(N-phenylimine)dianion]. The dication in compound [2](ClO4)2 displays one Ru(?-diimine)3 site and one ruthenium center with three negatively charged chelate ligands. Compound [2](ClO4)2 is obtained from the [Ru(bpy)2](2+)-containing cis precursor [(LH)Ru(bpy)2]ClO4 = [1]ClO4, which exhibits intramolecular H-bonding in the cation. Four accessible oxidation states each were characterized for the 1(n) and 2(n) redox series with respect to metal- or ligand-centered electron transfer, based on X-ray structures, electron paramagnetic resonance, and ultraviolet-visible-near-infrared spectroelectrochemistry in conjunction with density functional theory calculation results. The structural asymmetry in the Ru(III)/Ru(II) system 2(2+) is reflected by the electronic asymmetry (class I mixed-valence situation), leaving the noninnocent Nindigo bridge as the main redox-active site. PMID:25137231

Mondal, Prasenjit; Plebst, Sebastian; Ray, Ritwika; Mobin, Shaikh M; Kaim, Wolfgang; Lahiri, Goutam Kumar

2014-09-01

46

The effect of metal binding on the characteristic infrared band intensities of ligands of biological interest  

NASA Astrophysics Data System (ADS)

Since ˜40% of all proteins contain metal ions that perform a wide variety of functions indispensable for life processes, a plethora of experimental and theoretical methods have probed the interactions between metal ions and protein residues. Notably, previous studies have focused on how metal binding affects the protein ligands' vibrational frequencies, but not the corresponding intensities (to the best of our knowledge), even though the latter are generally much more sensitive to structural and environmental alterations than the former. Hence, we have systematically evaluated how metal binding affects not only the protein ligands' vibrational frequencies, but also the corresponding intensities and how these IR parameters depend on properties of the metal and its host ligand using density functional calculations. The results reveal that for a given protein ligand, the IR intensities, particularly those corresponding to bands without vibrational mode mixing, are quite sensitive to metal binding, and their changes are dictated by the metal's charge-accepting ability and the ligand's denticity. The results suggest that IR band intensities, along with vibrational frequencies, may be used to help interpret the IR spectra of protein binding sites in the metal-free and metal-bound states.

Dudev, Todor; Lim, Carmay

2012-02-01

47

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

48

On the dual roles of ligands in the synthesis of colloidal metal nanostructures.  

PubMed

Eloquent routes to colloidal metal nanostructures have emerged in recent years, and a central component to any successful nanosynthesis is the initial selection of metal complexes with an appropriate ligand environment. This local ligand environment may be predetermined by the coordination complex selected as the metal precursor; however, recent studies reveal that the ligand environment of coordination complexes can be modified through exchange with other components for the synthesis that include solvent molecules, capping agents, anions, and even reducing agents. Importantly, ligands can often play multiple roles in a synthesis and direct the outcome by manipulating the rates of precursor reduction and particle coalescence, providing colloidal and facet stabilization and even serving as reducing agents themselves. This Feature Article highlights examples in which the ligand environments of metal precursors and nanoparticles contribute to product formation in multiple ways. Acknowledgment of the dual roles of ligands in nanomaterial synthesis will enable new strategies for nanostructures by decoupling the often contradictory roles of ligands. PMID:24446902

Ortiz, Nancy; Skrabalak, Sara E

2014-06-17

49

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

PubMed

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

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

2014-12-28

50

Why Are There No Terminal Oxo Complexes of the Late Transition Metals? or The Importance of Metal–Ligand ? Antibonding Interactions  

Microsoft Academic Search

? antibonding interactions result from the overlap of a filled ? symmetry ligand orbital with a filled metal d orbital. This antibonding plays an important role in the chemistry of ? donor ligands such as oxo and alkoxide. It is in large part responsible for the lack of late transition metal complexes with terminal oxo ligands, and can explain some

James M. Mayer

1988-01-01

51

Photophysical studies of metal to ligand charge transfer involving quadruply bonded complexes of molybdenum and tungsten.  

PubMed

Photoinduced metal-to-ligand charge transfer transitions afford numerous applications in terms of photon energy harvesting. The majority of metal complexes studied to date involve diamagnetic systems of d(6), d(8), and d(10) transition metals. These typically have very short-lived, ?100 fs, singlet metal to ligand charge transfer ((1)MLCT) states that undergo intersystem crossing to triplet metal to ligand charge transfer ((3)MLCT) states that are longer lived and are responsible for much of the photophysical studies. In contrast, the metal-metal quadruply bonded complexes of molybdenum and tungsten supported by carboxylate, O2CR, and related amidinate ligands (RN)2C(R') have relatively long-lived (1)MLCT states arising from M2? to L?* transitions. These have lifetimes in the range 1-20 ps prior to intersystem crossing to T1 states that may be (3)MLCT or (3)MM??* with lifetimes of 1-100 ns and 1-100 ?s, respectively. The M2 quadruply bonded complexes take the form M2L4 or M2L4-nL'n where n = 1-3. Thus, in their photoexcited MLCT states, these compounds pose the question of how the charge resides on the ligands. This Account reviews the current knowledge of how charge is positioned with time in S1 and T1 states with the aid of active IR reported groups located on the ligands, for example, C?X multiple bonds (X = C, N, or O). Several examples of localized and delocalized charge distributions are noted along with kinetic barriers to the interconversion of MLCT and ??* states. On the 50th anniversary of the recognition of the MM quadruple bond, these complexes are revealing some remarkable features in the study of the photophysical properties of metal-ligand charge transfer states. PMID:25695495

Chisholm, Malcolm H; Brown-Xu, Samantha E; Spilker, Thomas F

2015-03-17

52

A pyridine-thiol ligand with multiple bonding sites for heavy metal precipitation.  

PubMed

There are immediate concerns with current commercial ligands that are used for heavy metal precipitation, especially the limited arrays of bonding sites. Previous research has indicated that not only do commercial reagents lack sufficient bonding criteria, but they also fail to provide long-term stability as ligand-metal complexes. For this reason, we have developed a pyridine-based thiol ligand (DTPY) which not only offers multiple bonding sites for heavy metals but also should form stable metal-ligand precipitates. In this study, we used the divalent metals cadmium and copper to model the reactivity and pH stability of divalent metal complexes with the DTPY ligand. Using inductively-coupled plasma spectrometry (ICP), results indicate that a 50.00ppm (parts per million) copper solution, pH of 4.5, can be reduced to below the ICP detection limits of 0.00093ppm (>99.99% removal), and a 50.00ppm cadmium solution, pH of 6.0, can be reduced to 0.06ppm (99.88%). PMID:11165061

Matlock, M M; Howerton, B S; Henke, K R; Atwood, D A

2001-03-19

53

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

EPA Science Inventory

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

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

Defect self-doped TiO? for visible light activity and direct noble metal anchoring.  

PubMed

A facile approach was developed for preparing defective, self-doped TiO2, which shows remarkable visible light activity in the photocatalytic degradation of RhB and hydrogen liberation from water. Moreover, noble metal was directly deposited onto the TiO2 surface via an in situ redox reaction between surficial Ti(3+) and metal salt. The lack of involvement of foreign reducing agents or stabilizers permits intimate contact between metal nanoparticles and the TiO2 substrate, which ensures the facilitated interfacial charge transfer. The strategy presented in this work may be applied to design other defect and noble metal mediated visible-light-active photocatalysts. PMID:25203901

Pei, Zengxia; Ding, Luyao; Feng, Wenhui; Weng, Sunxian; Liu, Ping

2014-10-21

56

Nonlinear absorption reversing between an electroactive ligand and its metal complexes.  

PubMed

We present the nonlinear absorption investigation of an electroactive ligand and two ruthenium and iron metal complexes under 532 nm, 30 ps laser excitation, by the "open aperture" Z-scan technique. Significant nonlinear optical parameters have in all cases been measured, while the nonlinear attribute has been found to change from saturable to reverse saturable absorption between the initial ligand and its complexes. PMID:23187347

Iliopoulos, Konstantinos; El-Ghayoury, Abdelkrim; El Ouazzani, Hasnaa; Pranaitis, Mindaugas; Belhadj, Esmah; Ripaud, Emilie; Mazari, Miloud; Sallé, Marc; Gindre, Denis; Sahraoui, Bouchta

2012-11-01

57

Using metal-ligand binding characteristics to predict metal toxicity: quantitative ion character-activity relationships (QICARs).  

PubMed

Ecological risk assessment can be enhanced with predictive models for metal toxicity. Modelings of published data were done under the simplifying assumption that intermetal trends in toxicity reflect relative metal-ligand complex stabilities. This idea has been invoked successfully since 1904 but has yet to be applied widely in quantitative ecotoxicology. Intermetal trends in toxicity were successfully modeled with ion characteristics reflecting metal binding to ligands for a wide range of effects. Most models were useful for predictive purposes based on an F-ratio criterion and cross-validation, but anomalous predictions did occur if speciation was ignored. In general, models for metals with the same valence (i.e., divalent metals) were better than those combining mono-, di-, and trivalent metals. The softness parameter (sigma p) and the absolute value of the log of the first hydrolysis constant ([symbol: see text] log KOH [symbol: see text]) were especially useful in model construction. Also, delta E0 contributed substantially to several of the two-variable models. In contrast, quantitative attempts to predict metal interactions in binary mixtures based on metal-ligand complex stabilities were not successful. PMID:9860900

Newman, M C; McCloskey, J T; Tatara, C P

1998-12-01

58

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

PubMed Central

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

2012-01-01

59

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

SciTech Connect

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

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

2000-04-24

60

Self-healing multiphase polymers via dynamic metal-ligand interactions.  

PubMed

A new self-healing multiphase polymer is developed in which a pervasive network of dynamic metal-ligand (zinc-imidazole) interactions are programmed in the soft matrix of a hard/soft two-phase brush copolymer system. The mechanical and dynamic properties of the materials can be tuned by varying a number of molecular parameters (e.g., backbone/brush degree of polymerization and brush density) as well as the ligand/metal ratio. Following mechanical damage, these thermoplastic elastomers show excellent self-healing ability under ambient conditions without any intervention. PMID:25348857

Mozhdehi, Davoud; Ayala, Sergio; Cromwell, Olivia R; Guan, Zhibin

2014-11-19

61

Mononuclear Metal–O2 Complexes Bearing Macrocyclic N-Tetramethylated Cyclam Ligands  

PubMed Central

CONSPECTUS Metalloenzymes activate dioxygen to carry out a variety of biological reactions, including the biotransformation of naturally occurring molecules, oxidative metabolism of xenobiotics, and oxidative phosphorylation. The dioxygen activation at the catalytic sites of the enzymes occurs through several steps, such as the binding of O2 at a reduced metal center, the generation of metal–superoxo and –peroxo species, and the O–O bond cleavage of metal–hydroperoxo complexes to form high-valent metal-oxo oxidants. Because these mononuclear metal–dioxygen (M–O2) adducts are implicated as key intermediates in dioxygen activation reactions catalyzed by metalloenzymes, studies of the structural and spectroscopic properties and reactivities of synthetic biomimetic analogues of these species have aided our understanding of their biological chemistry. One particularly versatile class of biomimetic coordination complexes for studying dioxygen activation by metal complexes is M–O2 complexes bearing the macrocyclic N-tetramethylated cyclam (TMC) ligand. This Account describes the synthesis, structural and spectroscopic characterization, and reactivity studies of M–O2 complexes bearing tetraazamacrocyclic n-TMC ligands, where M = Cr, Mn, Fe, Co, and Ni and n = 12, 13, and 14, based on recent results from our laboratory. We have used various spectroscopic techniques, including resonance Raman and X-ray absorption spectroscopy, and density functional theory (DFT) calculations to characterize several novel metal–O2 complexes. Notably, X-ray crystal structures had shown that these complexes are end-on metal-superoxo and side-on metal-peroxo species. The metal ions and the ring size of the macrocyclic TMC ligands control the geometric and electronic structures of the metal–O2 complexes, resulting in the end-on metal–superoxo versus side-on metal–peroxo structures. Reactivity studies performed with the isolated metal-superoxo complexes reveal that they can conduct electrophilic reactions such as oxygen atom transfer and C–H bond activation of organic substrates. The metal–peroxo complexes are active oxidants in nucleophilic reactions, such as aldehyde deformylation. We also demonstrate a complete intermolecular O2-transfer from metal(III)–peroxo complexes to a Mn(II) complex. The results presented in this Account show the significance of metal ions and supporting ligands in tuning the geometric and electronic structures and reactivities of the metal–O2 intermediates that are relevant in biology and in biomimetic reactions. PMID:22612523

CHO, JAEHEUNG; SARANGI, RITIMUKTA; NAM, WONWOO

2013-01-01

62

The Calculation of Accurate Metal-Ligand Bond Energies  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

64

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

PubMed

Present work reviews that, the synthesis of (E)-N'-((7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)benzohydrazide [L] ligand and their metal complexes. The colored complexes were prepared of type [M(2+)L]X2, where M(2+)=Mn, Co, Ni, Cu, Sr and Cd, L=(7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)benzohydrazide, X=Cl(-). Ligand derived from the condensation of 8-formyl-7-hydroxy-4-methylcoumarin and benzohydrazide in the molar ratio 1:1 and in the molar ratio 1:2 for metal complexes have been prepared. The chelation of the ligand to metal ions occurs through the both oxygen groups, as well as the nitrogen atoms of the azomethine group of the ligand. Reactions of the Schiff base ligand with Manganese(II), Cobalt(II), Nickel(II), Copper(II), Strontium(II), and Cadmium(II) afforded the corresponding metal complexes. The structures of the obtained ligand and their respective metal complexes were elucidated by infra-red, elemental analysis, Double beam UV-visible spectra, conductometric measurements, magnetic susceptibility measurements and also thermochemical studies. The metal complex exhibits octahedral coordination geometrical arrangement. Schiff base ligand and their metal complexes were tested against antioxidants, antidiabetic and antimicrobial activities have been studied. The Schiff base metal complexes emerges effective ?-glucosidase inhibitory activity than free Schiff base ligand. PMID:24858195

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

2014-10-15

65

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

PubMed

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

Morris, Robert H

2014-02-01

66

Outlook of application of aberration corrected-electron microscopy in the ligand-protected metal clusters  

E-print Network

Outlook of application of aberration corrected-electron microscopy in the ligand- protected metal microscopy(HREM) and high angle annular dark field (HAADF) -scanning transmission EM (STEM) imaging clusters has been observed. For example, both Fresnel fringes around the particles and strong phase

Frenkel, Anatoly

67

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

PubMed

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

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

2014-08-20

68

A comparative topological study of different metal-metal and metal-ligand interactions in polynuclear organometallic clusters  

NASA Astrophysics Data System (ADS)

The existence and characterization of a bond between the Zn atoms in the recently synthesized complex [Zn2(?5- C5Me5)2] (I), as well as between two of the three Ru atoms in [Ru3(?- H )2(?3- MeImCH )( CO9] (Me2Im = 1,3-dimethylimidazolin-2-ylidene) (II), are firmly based on low temperature X-ray synchrotron diffraction experiments. The multipolar refinement of the experimental electron densities and their topological analyses by means of the Atoms in Molecules (AIM) theory reveal the details of the Zn-Zn and Ru-Ru bonds, such as their open-shell intermediate character. The results are consistent with a typical metal-metal single ? bond for the former, whereas a delocalized kind of bond involving 5c-6e is present in the latter. In addition, experimental results are compared with theoretical ab initio calculations of the DFT (density functional theory) and MP2 (Mo/ller-Plesset perturbation theory) electron densities, giving a coherent view of the bonding in both complexes. Many other topological properties of both compounds are also studied, in particular the different metal-ligand interactions.

Van der Maelen, Juan F.; García-Granda, Santiago

2015-01-01

69

MetalLigand-Containing Polymers: Terpyridine as the Supramolecular Unit  

E-print Network

will be successfully mimicked by materials created through supramolecular design principles. In fact, the properties-assemble molecules into supramolecular materials including hydrogen and metal bonds, p­p and donor­acceptor associations, electrostatics, hydrophilic-hydrophobic, and van der Waals forces.[1] In contrast to the field

Tew, Gregory N.

70

The concept of mixed organic ligands in metal-organic frameworks: design, tuning and functions.  

PubMed

The research on metal-organic frameworks (MOFs) has been developing at an extraordinary pace in its two decades of existence, as judged by the exponential growth of novel structures and the constant expansion of its applicability and research scope. A major part of the research and its success are due to the vital role of the concept of mixed organic ligands in the design, tuning and functions. This perspective, therefore, reviews the recent advances in MOFs based on this concept, which is generally based on employing a small polydentate ligand (here labelled as "nodal ligand") to form either clusters, rods or layers, which are then connected by a second ditopic linker ligand to form the framework. The structures of the materials can be grouped into the following three categories: layer-spacer (usually known as pillared-layer), rod-spacer, and cluster-spacer based MOFs. Depending on the size and geometry of the spacer ligands, interpenetrations of frameworks are occasionally found. These MOFs show a wide range of properties such as (a) crystal-to-crystal transformations upon solvent modifications, post-synthetic metal exchange or ligand reactions, (b) gas sorption, solvent selectivity and purification, (c) specific catalysis, (d) optical properties including colour change, luminescence, non-linear optic, (e) short- and long range magnetic ordering, metamagnetism and reversible ground-state modifications and (f) drug and iodine carriers with controlled release. In the following, we will highlight the importance of the above concept in the design, tuning, and functions of a selection of existing MOFs having mixed organic ligands and their associated structures and properties. The results obtained so far using this concept look very promising for fine-tuning the pore size and shape for selective adsorption and specificity in catalytic reactions, which appears to be one way to propel the advances in the application and commercialization of MOFs. PMID:25687325

Yin, Zheng; Zhou, Yan-Ling; Zeng, Ming-Hua; Kurmoo, Mohamedally

2015-03-10

71

Functional and computational studies of the ligand-associated metal binding site of beta3 integrins.  

PubMed

A combination of experimental and computational approaches was used to provide a structural context for the role of the beta3 integrin subunit ligand-associated metal binding site (LIMBS) in the binding of physiological ligands to beta3 integrins. Specifically, we have carried out (1) adhesion assays on cells expressing normal alphaIIbeta3, normal alphaVbeta3, or the corresponding beta3 D217A LIMBS mutants; and (2) equilibrium and nonequilibrium (steered) molecular dynamics (MD) simulations of eptifibatide in complex with either a fully hydrated normal alphaIIbeta3 integrin fragment (alphaIIb beta-propeller and the beta3 betaA (I-like), hybrid, and PSI domains) or the equivalent beta3 D217A mutant. Normal alphaIIbeta3 expressing cells adhered to immobilized fibrinogen and echistatin, whereas cells expressing the alphaIIbeta3 D217A LIMBS mutant failed to adhere to either ligand. Similarly, the equivalent alphaVbeta3 mutant was unable to support adhesion to vitronectin or fibrinogen. The alphaIIbeta3 D217A mutation increased the binding of mAb AP5, which recognizes a ligand-induced binding site (LIBS) in the beta3 PSI domain, indicating that this mutation induced allosteric changes in the protein. Steered MD simulating the unbinding of eptifibatide from either normal alphaIIbeta3 or the equivalent beta3 D217A mutant suggested that the reduction in ligand binding caused by the LIMBS mutant required the loss of both the LIMBS and the metal ion-dependent adhesion site (MIDAS) metal ions. Our computational results indicate that the LIMBS plays a crucial role in ligand binding to alphaIIbeta3 by virtue of its effects on the coordination of the MIDAS. PMID:18175315

Murcia, Marta; Jirouskova, Marketa; Li, Jihong; Coller, Barry S; Filizola, Marta

2008-06-01

72

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

NASA Astrophysics Data System (ADS)

Published data on the synthesis and chemical properties of complexes of Group 4-10 transition metals (d elements) with ? 6-tetramethylfulvene and ?7-trimethylallyldiene ligands, formed from the pentamethylcyclopentadienyl complexes of these metals, are described systematically. A description of the structures of these complexes in terms of a "specific" resonance hybrid of fulvene and methylenecyclopentadienyl (or allyldiene and dimethylenecyclopentadienyl) structures is proposed. It is noted that similar properties or behaviours of the fulvene and allyldiene complexes can be followed both for compounds formed by metals of the same Group and for compounds of elements of the same transition row with identical electron configurations.

Kreindlin, Arkadii Z.; Rybinskaya, Margarita I.

2004-05-01

73

Dual-Functionalized Metal-Organic Frameworks Constructed from Hexatopic Ligand for Selective CO2 Adsorption.  

PubMed

A ligand design approach, which requires rational design of ligand based on the knowledge of specific target, was applied for the synthesis of two interesting and robust MOFs 1 and 2 containing unusual several types of copper(II) secondary building units (SBUs). Thanks to unsaturated metal centers (UMCs) and azo group, microporous material 1 exhibited not only high CO2 uptake but also an impressive selective adsorption of CO2 over CH4 and N2. Moreover, a high H2 uptake of 1 was also observed. PMID:25695730

Zhang, Shi-Yuan; Zhang, Xiaoping; Li, Huimin; Niu, Zheng; Shi, Wei; Cheng, Peng

2015-03-01

74

Ligand Kedge x-ray absorption spectroscopy as a probe of ligand-metal bonding: Charge donation and covalency in copper-chloride systems  

Microsoft Academic Search

X-ray absorption spectra (XAS) have been measured at the chloride K-edge for a series of complexes containing chloride ligands bound to open shell d⁹ copper ions in order to probe ligand-metal bonding. The intensity of the pre-edge feature in these spectra reflects the covalency in the half-occupied dâ²⁻{sub y}²⁻ derived molecular orbital (HOMO) of the complex. The energy of the

Susan E. Shadle; Britt Hedman; E. I. Solomon; K. O. Hodgson

1994-01-01

75

Comparison of the Electronic Properties of Diarylamido-Based PNZ Pincer Ligands: Redox Activity at the Ligand and Donor Ability Toward the Metal.  

PubMed

This paper presents the synthesis and characterization of a series of pincer ligands and their Ni, Pd, Pt, and Rh complexes. The ligands under examination are based on a diarylamine which is modified either by two phosphino (-PR2) substituents in the ortho-positions (PNP ligands) or by a combination of a phosphino and an iminyl (-CH?NX) substituent (PNN ligands). The ligands can be broken down into three groups: (a) C2v-symmetric PNP ligands with identical side -PR2 donors, (b) Cs-symmetric PNP' ligands with different -PR2 side donors, and (c) PNN ligands containing a -P(i)Pr2 side donor. All of the ligands under study readily formed square-planar complexes of the types (PNZ)PdCl, (PNZ)Pd(OAc), and (PNZ)RhCO, where PNZ is the corresponding anionic tridentate pincer ligand. For select PNP ligands, (PNP)NiCl and (PNP)PtCl were also studied. The (PNZ)MCl complexes (M = Ni, Pd, Pt) underwent quasireversible oxidation in cyclic voltammetry experiments. Based on the close similarity of formal potentials for Ni, Pd, and Pt analogs, and based on the previous literature evidence, these oxidation events are ascribed primarily to the PNZ ligand, and the E1/2 values can be used to compare the ease of oxidation of different ligands. A (PNP)PdCl complex containing methoxy substituents para- to the central nitrogen underwent two quasireversible oxidations. Two mono-oxidized complexes were isolated and structurally characterized in comparison to their neutral analog, revealing minimal changes in the bond distances and angles. Several other neutral complexes were also structurally characterized. The carbonyl stretching frequency in (PNZ)RhCO complexes was used to gauge the donating ability of the various pincer ligands toward the metal. Comparison of E1/2 values for (PNZ)PdCl and ?CO values for (PNZ)RhCO revealed that the two are not consistently correlated across all the studied ligands and can be tuned to different degrees through judicious ligand alteration. PMID:25714352

Davidson, Jillian J; DeMott, Jessica C; Douvris, Christos; Fafard, Claudia M; Bhuvanesh, Nattamai; Chen, Chun-Hsing; Herbert, David E; Lee, Chun-I; McCulloch, Billy J; Foxman, Bruce M; Ozerov, Oleg V

2015-03-16

76

Metal ion oxidation state assignment based on coordinating ligand hyperfine interaction.  

PubMed

In exchange-coupled mixed-valence spin systems, the magnitude and sign of the effective ligand hyperfine interaction (HFI) can be useful in determining the formal oxidation state of the coordinating metal ion, as well as provide information about the coordination geometry. This is due to the fact that the observed ligand HFI is a function of the projection factor (Clebsch-Gordon coefficient) that maps the site spin value S i of the local paramagnetic center onto the total spin of the exchange-coupled system, S T. Recently, this relationship has been successfully exploited in identifying the oxidation state of the Mn ion coordinated by the sole nitrogenous ligand to the oxygen-evolving complex in certain states of photosystem II. The origin and evolution of these efforts is described. PMID:25663565

Oyala, Paul H; Stich, Troy A; Britt, R David

2015-04-01

77

Supramolecular polymers constructed by orthogonal self-assembly based on host-guest and metal-ligand interactions.  

PubMed

Supramolecular polymers constructed by orthogonal self-assembly based on host-guest and metal-ligand interactions are attracting increasing attention currently because of their interesting properties and potential applications. Host-guest interactions impart these polymers with good selectivity and convenient enviro-responsiveness, and metal-ligand interactions endow them with various coordination geometries, strong yet tunable coordination binding abilities, as well as magnetic, redox, photophysical, and electrochromic properties. Therefore, supramolecular polymers constructed by orthogonal host-guest and metal-ligand interactions have wide applications in the fields of soft matter, fluorescence sensing, heterocatalysis, electronics, gas storage, etc. In this critical review, we will address the recent development of supramolecular polymeric systems involving metal-ligand interactions and host-guest molecular recognition. Specifically, we classify the related supramolecular polymers depending on the types of macrocyclic hosts, and highlight their intriguing properties originating from the elegant combination of host-guest complexation and metal centers. PMID:25423355

Wei, Peifa; Yan, Xuzhou; Huang, Feihe

2015-02-01

78

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

79

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

80

Physico-Chemical and Spectroscopic Investigations of New Metallic Complexes with Phenylalanine as Ligand  

NASA Astrophysics Data System (ADS)

The [Cu(L)2]?H2O (1), [Co(L)2]?2H2O (2) and [Zn(L)2]?H2O (3) metallic complexes with phenylalanine as ligand were synthesized in aqueous solution and characterized by means of atomic absorption, elemental analysis, differential scanning calorimetry, FT-IR, UV-VIS and ESR spectroscopies. The comparative analysis of the FT-IR spectra for the ligand and the complexes indicate the coordination of the metallic centre to the carboxylic oxygen atom and to the nitrogen atom of the amino group. In the ligand spectrum the ?s(N-H) stretching vibration appears splitted at 3078 cm-1 and 3030 cm-1 and is shifted at 3320 cm-1 and 3256 cm-1 in the copper complex, at 3220 cm-1 in the cobalt spectrum and at 3256 cm-1 and 3334 cm-1 for the zinc complex proving the involvement of the -NH2- group in the complex formation. The ?s(C=O) stretching vibration emerge in the ligand spectrum at 1623 cm-1 and appears to be shifted toward higher wave numbers with 4 cm-1 and 10 cm-1 for Cu and Co complexes and with 9 cm-1 toward lower wave numbers for Zn complex. The n??* characteristic band in the UV spectra assigned to the C=O bond appear at 231 nm for phenylalanine and is shifted toward lower wave lengths in the complexes spectra proving the covalent nature of the metal-ligand bond. Powder ESR spectra at room temperature are typically for monomeric species with pseudotetrahedral symmetry around the copper ions and octahedral environment for the cobalt ion.

Hübner, Maria; Stanila, Adriana; Marcu, Anca; Cozar, Ionu? B.; David, Leontin

2009-05-01

81

K? mainline X-ray emission spectroscopy as an experimental probe of metal-ligand covalency.  

PubMed

The mainline feature in metal K? X-ray emission spectroscopy (XES) has long been recognized as an experimental marker for the spin state of the metal center. However, even within a series of metal compounds with the same nominal oxidation and spin state, significant changes are observed that cannot be explained on the basis of overall spin. In this work, the origin of these effects is explored, both experimentally and theoretically, in order to develop the chemical information content of K? mainline XES. Ligand field expressions are derived that describe the behavior of K? mainlines for first row transition metals with any d(n) count, allowing for a detailed analysis of the factors governing mainline shape. Further, due to limitations associated with existing computational approaches, we have developed a new methodology for calculating K? mainlines using restricted active space configuration interaction (RAS-CI) calculations. This approach eliminates the need for empirical parameters and provides a powerful tool for investigating the effects that chemical environment exerts on the mainline spectra. On the basis of a detailed analysis of the intermediate and final states involved in these transitions, we confirm the known sensitivity of K? mainlines to metal spin state via the 3p-3d exchange coupling. Further, a quantitative relationship between the splitting of the K? mainline features and the metal-ligand covalency is established. Thus, this study furthers the quantitative electronic structural information that can be extracted from K? mainline spectroscopy. PMID:24914450

Pollock, Christopher J; Delgado-Jaime, Mario Ulises; Atanasov, Mihail; Neese, Frank; DeBeer, Serena

2014-07-01

82

Bridging-ligand-substitution strategy for the preparation of metal-organic polyhedra  

SciTech Connect

Metal–organic polyhedra—discrete molecular architectures constructed through the coordination of metal ions and organic linkers—have recently attracted considerable attention due to their intriguing structures, their potential for a variety of applications and their relevance to biological self-assembly. Several synthetic routes have been investigated to prepare these complexes. However, to date, these preparative methods have typically been based on the direct assembly of metal ions and organic linkers. Although these routes are convenient, it remains difficult to find suitable reaction conditions or to control the outcome of the assembly process. Here, we demonstrate a synthetic strategy based on the substitution of bridging ligands in soluble metal–organic polyhedra. The introduction of linkers with different properties from those of the initial metal–organic polyhedra can thus lead to new metal–organic polyhedra with distinct properties (including size and shape). Furthermore, partial substitution can also occur and form mixed-ligand species that may be difficult to access by means of other approaches.

Li, Jian-Rong; Zhou, Hong-Cai

2010-01-01

83

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

PubMed

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

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

2013-11-27

84

Competitive metal-ligand binding between CdTe quantum dots and EDTA for free Ca2+ determination.  

PubMed

In this work, a fluorometric approach for the selective determination of calcium by using CdTe nanocrystals as chemosensors, was developed. The quantum dots interacted not with the metal, but with a ligand that also bonded the metal. The fluorescence response was modulated by the extension of the competitive metal-ligand binding, and therefore the amount of free ligand. CdTe quantum dots (QDs) with different capping layers were evaluated, as the QDs surface chemistry and capping nature affected recognition, thus the magnitude of the ensuing fluorescence quenching. The developed procedure was automated by using a multipumping flow system. Upon optimization, thioglycolic acid (TGA) and EDTA were selected as capping and ligand, respectively, providing a linear working range for calcium concentrations between 0.80-3.20 mg L(-1), and a detection limit of 0.66 mg L(-1). A quenching mechanism relying on nanocrystal destabilization upon detachment of surface Cd by the ligand was proposed. PMID:25618655

Rodrigues, S Sofia M; Prieto, Diego R; Ribeiro, David S M; Barrado, Enrique; Prior, João A V; Santos, João L M

2015-03-01

85

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

Microsoft Academic Search

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

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

2003-01-01

86

Photoinduced charge, ion & energy transfer processes at transition-metal coordination compounds anchored to mesoporous, nanocrystalline metal-oxide thin films  

NASA Astrophysics Data System (ADS)

Photovoltaics provide a direct means of converting photons into useful, electric power; however traditional silicon-based technologies are too expensive for global commercialization. Dye-sensitized mesoporous semiconducting thin films, when utilized in regenerative photoelectrochemical cells, are one category of next generation photovoltaics that could eventually circumvent this issue. In fact, their architecture also affords a clear platform for implementation of a direct, solar fuel-forming system. The mechanisms involved in the myriad of molecular processes that occur in these molecular--solid-state hybrid materials are poorly understood. Thus, the overriding goal of this dissertation was to evaluate sensitized mesoporous, nanocrystalline metal-oxide thin films critically so as to elucidate mechanistic phenomena. Using transient and steady-state absorption and emission spectroscopies as well as (photo)electrochemistry, various previously unobserved processes have been identified. Chapter 2 demonstrates for the first time that the electric fields emanating from these charged thin films affect surface-anchored molecular sensitizers via a Stark effect. In most cases, further, but incomplete, ionic screening of the charged nanoparticles from the sensitizers, as non-Faradaic electrolyte redistribution, was spectroscopically inferred after rapid semiconductor charging. Chapter 3 highlights the reactivity of Co(I) coordination-compound catalysts anchored to anatase TiO2 thin-film electrodes. Visible-light excitation resulted in prompt excited-state electron injection into TiO2 while introduction of benzylbromide into the fluid solution surrounding the thin film led to a 2e--transfer, oxidative-addition reaction to Co1 forming a stable Co--benzyl product. Subsequent visible-light excitation initiated a photocatalytic cycle for C--C bond formation. Unique to the nanocrystalline thin films employed here, Chapter 4 demonstrates that traditional time-resolved polarization spectroscopy can be employed to monitor lateral self-exchange energy- and hole-transfer reactions across the sensitized TiO2 surface. Under conditions of poor excited-state injection, support for Ru*/II self exchange was obtained, while subsequent to electron injection, the resulting RuIII state of the sensitizer was often capable of RuIII/II self-exchange reactions. The kinetics for many processes associated with mesoporous, nanocrystalline TiO2 thin films can be modeled by a stretched-exponential function, which possesses an underlying distribution of rate constants. In Chapter 5, we provide the first implementation of an Arrhenius analysis for the temperature dependence of these distributions.

Ardo, Shane

87

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

88

Metal-organic frameworks based on uranyl and phosphonate ligands.  

PubMed

Three new crystalline metal-organic frameworks have been prepared from the reaction of uranyl nitrate with nitrilotris(methylphosphonic acid) [H6nmp, N(CH2PO3H2)3], 1,4-phenylenebis(methylene)diphosphonic acid [H4pmd, C6H4(PO3H2)2], and (benzene-1,3,5-triyltris(methylene))triphosphonic acid [H6bmt, C6H3(PO3H2)3]. Compound [(UO2)2F(H3nmp)(H2O)]·4H2O (I) crystallizes in space group C2/c, showing two crystallographically independent uranyl centres with pentagonal bipyramidal coordination geometries. While one metal centre is composed of a {(UO2)O3(?-F)}2 dimer, the other comprises an isolated {(UO2)O5} polyhedron. Compound [(UO2)(H2pmd)] (II) crystallizes in space group P21/c, showing a centrosymmetric uranyl centre with an octahedral {(UO2)O4} coordination geometry. Compound [(UO2)3(H3bmt)2(H2O)2]·14H2O (III) crystallizes in space group P\\bar 1, showing two crystallographically independent uranyl centres. One uranyl centre is a {(UO2)O5} pentagonal bipyramid similar to that in (I), while the other is a {(UO2)O4} centrosymmetric octahedron similar to that in (II). Compounds (I) and (III) contain solvent-accessible volumes accounting for ca 23.6 and 26.9% of their unit-cell volume, respectively. In (I) the cavity has a columnar shape and is occupied by disordered water molecules, while in (III) the cavity is a two-dimensional layer with more ordered water molecules. All compounds have been studied in the solid state using FT-IR spectroscopy. Topological studies show that compounds (I) and (III) are trinodal, with 3,6,6- and 4,4,6-connected networks, respectively. Compound (II) is instead a 4-connected uninodal network of the type cds. PMID:24441125

Monteiro, Bernardo; Fernandes, José A; Pereira, Cláudia C L; Vilela, Sérgio M F; Tomé, João P C; Marçalo, Joaquim; Almeida Paz, Filipe A

2014-02-01

89

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

90

Activation of a metal-axial ligand bond in aluminum porphyrin by visible light  

SciTech Connect

Irradiation with visible light induced a remarkable effect on the reactivity of a metal-carbon bond in (tetraphenylporphinato)aluminum methyl in the nucleophilic substitution reaction with protic compounds such as phenol. A similar photoacceleration effect was also observed in the reversible ligand exchange of (tetraphenylporphinato)aluminum phenoxide with phenol. As for the former reaction, comparable quantum yields were observed upon irradiation at the Soret band and at the Q-band. 22 refs., 5 figs.

Hirai, Yasuhiro; Murayama, Hideki; Aida, Takuzo; Inoue, Shohei (Univ. of Tokyo (Japan))

1988-10-26

91

Versatile functionalization of carbon electrodes with a polypyridine ligand: metallation and electrocatalytic H(+) and CO2 reduction.  

PubMed

A strategy is proposed for immobilization of homogeneous catalysts whereby a glassy carbon electrode is functionalized by electro-grafting of a ligand, terpyridine. The modified electrode can easily be metallated with cobalt and shows activity towards catalytic proton and CO2 reduction. The metal can be removed and the electrode re-metallated at will. PMID:25597872

Elgrishi, Noémie; Griveau, Sophie; Chambers, Matthew B; Bedioui, Fethi; Fontecave, Marc

2015-02-18

92

Evidence for metal-ligand cooperation in a Pd-PNF pincer-catalyzed cross-coupling.  

PubMed

The first Pd-pincer complex bearing a halogen (fluorine) arm has been prepared via the base-assisted dearomatization of a phosphine-quinoline (P~N) ligand. This dearomatization is reversible and has been used to facilitate catalytic Sonogashira-type cross-coupling that, contrary to the typical mechanistic approach, is based on a metal-ligand cooperation mode. PMID:23256879

Scharf, Adam; Goldberg, Israel; Vigalok, Arkadi

2013-01-23

93

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

94

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

PubMed

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

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

2011-05-01

95

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

NASA Astrophysics Data System (ADS)

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

Devi, Jai; Batra, Nisha

2015-01-01

96

Electrophilic metal alkyl chemistry in new ligand environments. Annual report, January 1, 1992--September 15, 1992  

SciTech Connect

Methods have been worked out for efficient synthesis of various N{sub 4}{sup 2{minus}} macrocyclic ligands, neutral group 4 metal (e.g., Zr) (N{sub 4})MR{sub 2} complexes, and cationic mono-alkyl (N{sub 4})M(R){sup +} species. Intital indications are that the latter will be highly reactive in base-free form. Objective is to develop new types of electrophilic metal alkyl complexes for study of olefin polymerization and C-H activation catalysis.

Jordan, R.F.

1992-12-31

97

The influence of the enantiomeric ratio of an organic ligand on the structure and chirality of metal-organic frameworks.  

PubMed

We have prepared three distinct polyamino acid-based metal-organic frameworks (MOFs) with different chiralities and porosities using the same chemistry, by simply modifying the enantiomeric ratio of the chiral organic ligand used. PMID:25253285

Burneo, Iván; Stylianou, Kyriakos C; Imaz, Inhar; Maspoch, Daniel

2014-11-18

98

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

SciTech Connect

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

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

2013-10-15

99

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

100

Group 4 metal complexes bearing new tridentate (NNO) ligands: Benzyl migration and formation of unusual C–C coupled products  

Microsoft Academic Search

Group 4 metal complexes bearing new phenoxy(benzimidazolyl)-imine, -amine and -amide ligands have been synthesized. A series of metal chloride derivatives has been prepared via treatment of MCl4(THF)2 (M=Ti, Zr, Hf) with the in situ generated sodium salt of the (benzimidazolyl)imine phenol 1. Reaction of the pro-ligand 2 with TiCl4(THF)2 afforded the corresponding complex 8 in which the amine proton remains

Renan Cariou; Vernon C. Gibson; Atanas K. Tomov; Andrew J. P. White

2009-01-01

101

Bond Activation by Metal-Ligand Cooperation: Design of “Green” Catalytic Reactions Based on Aromatization-Dearomatization of Pincer Complexes  

Microsoft Academic Search

\\u000a We have developed a new mode of bifunctional catalysis based on metal–ligand cooperation, involving aromatization–dearomatization\\u000a of pyridine- and acridine-derived pincer complexes. This type of metal–ligand cooperation is involved in the recently discovered\\u000a environmentally benign reactions of alcohols, catalyzed by PNP and PNN pincer complexes of ruthenium, including: (a) dehydrogenation\\u000a of secondary alcohols to ketones, (b) dehydrogenative coupling of primary alcohols

Chidambaram Gunanathan; David Milstein

102

Electronic states and metal-ligand bonding of gadolinium complexes of benzene and cyclooctatetraene.  

PubMed

Gadolinium (Gd) complexes of benzene (C(6)H(6)) and (1,3,5,7-cyclooctatetraene) (C(8)H(8)) were produced in a laser-vaporization supersonic molecular beam source and studied by single-photon pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy. Adiabatic ionization energies and metal-ligand stretching frequencies were measured for the first time from the ZEKE spectra. Metal-ligand bonding and electronic states of the neutral and cationic complexes were analyzed by combining the spectroscopic measurements with ab initio calculations. The ground states of Gd(C(6)H(6)) and [Gd(C(6)H(6))](+) were determined as (11)A(2) and (10)A(2), respectively, with C(6v) molecular symmetry. The ground states of Gd(C(8)H(8)) and [Gd(C(8)H(8))](+) were identified as (9)A(2) and (8)A(2), respectively, with C(8v) molecular symmetry. Although the metal-ligand bonding in Gd(C(6)H(6)) is dominated by the covalent interaction, the bonding in Gd(C(8)H(8)) is largely electrostatic. The bonding in the benzene complex is much weaker than that in the cyclooctatetraene species. The strong bonding in Gd(C(8)H(8)) arises from two-electron transfer from Gd to C(8)H(8), which creates a strong charge-charge interaction and converts the tub-shaped ligand into a planar form. In both systems, Gd 4f orbitals are localized and play little role in the bonding, but they contribute to the high electron spin multiplicities. PMID:22200405

Roudjane, Mourad; Kumari, Sudesh; Yang, Dong-Sheng

2012-01-19

103

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

PubMed

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

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

2014-11-17

104

Determination of the metal complexation capacity of natural waters by ligand titration in the presence of complexing resins  

NASA Astrophysics Data System (ADS)

The complexation properties of some drinking waters for U(VI), Al(III) and Cu(II) are determined by ligand titration (LT) with the metal ions, using a new method for monitoring, i.e. the sorpion of metal ion on complexing resins. The concentration of the free metal ion in solution is evaluated from the concentration of sorbed metal ion and from the quantity K^*, which is the ratio of the concentration of the metal ion sorbed on the resin to the concentration of free metal ion in solution, and can be independently evaluated. The concentration of the ligands in solution (c_I) and the conditional stability constant (K_M(I)) are obtained by the Ruzic linearization. Different resins, i.e. the iminodiacetic resin Chelex 100, the carboxylic resin Amberlite CG 50 and the anion exchange resin AGIX8 were used for monitoring the titration, since they have different sorbing properties, and in principe they allow the detection of different ligands. Ligands at low concentration and with very high complexation constants were detected in the considered samples. Particularly in the case of U(VI), they are able to complex the metal ion much more strongly than the ligands that are usually considered in aqueous solution, i.e. carbonate and hydroxyl.

Pesavento, M.; Biesuz, R.; Alberti, G.

2003-05-01

105

BIG METALS, SMALL LIGANDS: CHARACTERIZATION OF THE 15-COORDINATE COMPLEX THORIUM AMINODIBORANATE [Th(H3BN(CH3)2BH3)4  

E-print Network

BIG METALS, SMALL LIGANDS: CHARACTERIZATION OF THE 15- COORDINATE COMPLEX THORIUM AMINODIBORANATE aminodiboranate ligands coordinate to the thorium center. The Werner coordination number of 15 in the solid state

Girolami, Gregory S.

106

Ligand K-edge x-ray absorption spectroscopy as a probe of ligand-metal bonding: Charge donation and covalency in copper-chloride systems  

SciTech Connect

X-ray absorption spectra (XAS) have been measured at the chloride K-edge for a series of complexes containing chloride ligands bound to open shell d{sup 9} copper ions in order to probe ligand-metal bonding. The intensity of the pre-edge feature in these spectra reflects the covalency in the half-occupied d{sub x}{sup 2-}{sub y}{sup 2-} derived molecular orbital (HOMO) of the complex. The energy of the pre-edge feature as well as the energy of the rising absorption edge provides quantitative information about the covalency of the ligand-metal interaction, the charge donated by the chloride, and the energy of the copper d-manifold. The results demonstrate that ligand K-edge XAS features can be used to obtain information about ligand-metal bonding. The results also identify the chemical basis for trends in the XAS data for the following complexes: D{sub 4h} CuCl{sub 4}{sup 2-}, D{sub 2d} CuCl{sub 4}{sup 2-}, planar trans-CuCl{sub 2-} (pdmp){sub 2} (pdmp = N-phenyl-3,5-dimethylpyrazole), square pyramidal CuCl{sub 5}{sup 3-}, the planar dimer KCuCl{sub 3}, the distorted tetrahedral dimer (Ph{sub 4}P)CuCl{sub 3}, and two dimers with mixed ligation, one containing a bridging chloride, and the other, containing terminally bound chloride. Several of these results are supported by independent spectral data or by basic ligand field concepts. A geometric distortion from square planar to distorted tetrahedral results in a decrease in the chloride-copper HOMO covalency but an increase in the total charge donation by the chlorides. While the geometry can maximize the overlap for a highly covalent HOMO, this does not necessarily reflect the overall charge donation.

Shadle, S.E.; Hedman, B.; Solomon, E.I.; Hodgson, K.O. [Stanford Univ., CA (United States)

1994-09-14

107

The use of polymer-ligands vs bioindicators in heavy metal monitoring  

SciTech Connect

Major problems involved in using bio-indicators to monitor heavy metals in the marine environment include standardizing a great variety of physical and biological factors which have a significant effect on metal accumulation. The fact that different species may have different accumulation strategies for different metals; and also limits of natural distribution of indicator species often prevent comparison between monitoring results in different geographic areas and hydrographic conditions. Environmental effects on the uptake and deputation of the metals in the biological indicators are generally poorly understood. In the present study, uptake of Cd, Cr, Cu, Ni, Pb and Zn by four polymer-ligands (i.e. Chelex 100, poly(4-vinylpyridine), Sephadex Sp C-J5 and Amberlite IR-122) were studied. Laboratory results showed that Chelex 100 was most effective in taking up the soluble fractions of these three metals at low ambient concentrations (0.1 to 10 mg/L). Equilibrium at low concentrations was reached at about 21 days. Concentration factors after 21 days` exposure ranged from 2,500 to 5,500, depending upon the metal species and ambient concentration. Both uptake and release of metals by Chelex are directly responsive to ambient concentrations and exposure time. Results of field transplantation of Chelex and mussels (P. virvidis) also showed that Chelex accumulated significantly higher levels of Cd, Cr and Pb; similar levels of Cu, and a lower level of Zn than those of mussels under natural field conditions. Coefficients of variations of metal uptake of Chelex were also much smaller. The suitability of using Chelex 100 as a novel chemical device for monitoring metal pollution in the aquatic environment is evaluated against selection criteria established for metal bioindicators.

Wu, R.S.S.; Lau, T.C. [City Univ. of Hong Kong, Kowloon (Hong Kong). Dept. of Biology and Chemistry

1995-12-31

108

Advances in Quantitative Ion Character-Activity Relationships (QICARs): Using Metal-Ligand Binding Characteristics to Predict  

E-print Network

; QICAR ± Quantitative Ion Character Activity Relationship; HSAB ± Hard and Soft Acid Base Theory; HOMO developed to predict metal toxicity. The QICAR approach, based on metal-ligand binding tendencies, has been were based on atomic size and electrode potentials. Pharmacologists and mammalian toxicologists

Newman, Michael C.

109

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

SciTech Connect

Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

2014-03-03

110

Porous coordination polymers with ubiquitous and biocompatible metals and a neutral bridging ligand  

PubMed Central

The design of inexpensive and less toxic porous coordination polymers (PCPs) that show selective adsorption or high adsorption capacity is a critical issue in research on applicable porous materials. Although use of Group II magnesium(II) and calcium(II) ions as building blocks could provide cheaper materials and lead to enhanced biocompatibility, examples of magnesium(II) and calcium(II) PCPs are extremely limited compared with commonly used transition metal ones, because neutral bridging ligands have not been available for magnesium(II) and calcium(II) ions. Here we report a rationally designed neutral and charge-polarized bridging ligand as a new partner for magnesium(II) and calcium(II) ions. The three-dimensional magnesium(II) and calcium(II) PCPs synthesized using such a neutral ligand are stable and show selective adsorption and separation of carbon dioxide over methane at ambient temperature. This synthetic approach allows the structural diversification of Group II magnesium(II) and calcium(II) PCPs. PMID:25592677

Noro, Shin-ichiro; Mizutani, Junya; Hijikata, Yuh; Matsuda, Ryotaro; Sato, Hiroshi; Kitagawa, Susumu; Sugimoto, Kunihisa; Inubushi, Yasutaka; Kubo, Kazuya; Nakamura, Takayoshi

2015-01-01

111

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

112

Metal complexes containing allenylidene and higher cumulenylidene ligands: a theoretical perspective.  

PubMed

Transition metal complexes containing unsaturated carbenes have enjoyed a recent surge in research interest. In addition to showing potential as molecular wires and as components of opto-electronic materials, they provide multifaceted reactive sites for organic synthesis. In this Account, we describe results of recent theoretical studies that delineate the main features of electronic structure and bonding in allenylidenes and higher cumulenylidene complexes, [L(m)M]?C(?C)(n)?CR(1)R(2) (where L represents the ligand, M the metal, and n ? 1). Although free cumulenylidene ligands, :C(?C)(n)?CR(1)R(2), are extremely unstable and reactive species, they can be stabilized by coordination to a transition metal. The ?-donation of the electron lone pair on the terminal carbon atom to an empty metal d-orbital, together with the simultaneous ? back-donation from filled metal d(?)-orbitals to empty cumulene ?* system orbitals, leads to the formation of a strong M?C bond with multiple character. Density functional theory studies on the model systems [(CO)(5)Cr(?C)(n)CH(2)] and [trans-Cl(PH(3))(4)Ru(?C)(n)CH(2)](+) (where n = 1-9) have been useful in interpreting the structural and spectroscopic properties and the reactivity of this class of complexes. Geometry optimizations significantly contributed to the generalization of the sparse structural data available for allenylidene, butatrienylidene, and pentatetraenylidene complexes to higher cumulenylidene complexes (with up to eight carbon atoms in the chain), which show a clear structural trend. In particular, the geometries of all even-chain cumulenes are consistent with an almost purely cumulenic structure, whereas the geometries of odd-chain cumulenes present a significant polyyne-like carbon-carbon bond length alternation. The calculated bond dissociation energies (BDEs) of the cumulenylidene ligand remain almost constant on lengthening the cumulene chain. These BDEs indicate that there is no thermodynamic upper limit to the cumulene chain length and suggest that the synthetic difficulties in preparing higher cumulenylidenes are due to an increase in reactivity. The calculated charges on the carbon atoms show no significant polarization along the cumulene chain, indicating that charge distribution is not important in determining the regioselectivity of either electrophilic or nucleophilic attack, which is instead determined by frontier orbital factors. The breakdown of the contributions from the metal and the carbon atoms along the chain to the HOMO and LUMO shows that the HOMO has contributions mainly from the metal and the carbon atoms in even positions along the chain (C(2), C(4), C(6), and higher). In contrast, the LUMO has contributions mainly from the carbon atoms in odd positions along the chain (C(1), C(3), C(5), and higher), thus explaining the experimentally observed regioselectivity of electrophilic and nucleophilic attacks, which are directed, respectively, to even and odd positions of the cumulenylidene chain. The study of the electronic structure of cumulenylidenes has allowed us not only to give a consistent rationale for the main structural and spectroscopic properties and for the reactivity of this emerging class of compounds but also to predict the effect of ancillary ligands on the metal center or substituents on the carbon end. The result is a useful guide to new developments in the still-underexplored fields of this fascinating class of compounds. PMID:21899273

Coletti, Cecilia; Marrone, Alessandro; Re, Nazzareno

2012-02-21

113

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

SciTech Connect

Hydrothermal reactions of cerium nitrate and 5-hydroxyisophthalic acid (OH-H{sub 2}BDC) produce two new metal–organic frameworks (MOFs), ([Ce(DDPD){sub 1.5}(H{sub 2}O){sub 2.5}]·4H{sub 2}O){sub n} (1) and ([Ce(OH-BDC)(OH-HBDC)(H{sub 2}O){sub 2}]·2H{sub 2}O]{sub n} (2) (DDPD(II)=5,10-dioxo-5,10-dihydro-4,9-dioxapyrene-2,7-dicarboxylate(II)). These two complexes have been characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction. It was remarkable that the in situ reaction of OH-H{sub 2}BDC to DDPD(II) was found in complex 1. In 1, Ce(III) ions are bridged by DDPD ligands to form infinite 1D chain, which is further connected via DDPD ligands to form 3D structure. Complex 2 possesses a neutral noninterpenetrating 2D layer structure. Furthermore, the fluorescence properties and magnetic behavior of 1 and 2 have been investigated. - Graphical abstract: In complex 1, the in situ reaction of OH-H{sub 2}BDC to DDPD(II) was found. Complex 1 features a 3D network structure. Adjacent Ce(III) ions are bridged by two carboxylate groups to form a 1D infinite inorganic chain, and further linked by the DDPD(II) ligands. Display Omitted - Highlights: • Complexes 1 and 2 was synthesized via hydrothermal methods. • In situ reaction of OH-H{sub 2}BDC to DDPD(II) was found in complex 1. • Ce(III) ions are bridged by the DDPD(II) ligands to generate a 3D structure in complex 1. • Complex 2 possesses a neutral noninterpenetrating 2D layer structure. • Fluorescent properties and magnetic behavior of 1 and 2 have been studied.

Cao, Xinyu; Yu, Liqiong; Huang, Rudan, E-mail: huangrd@bit.edu.cn

2014-02-15

114

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

PubMed

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

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

2013-06-17

115

Room temperature rapid functionalization of E-H bonds (E = O, N, S) via the metal-ligand cooperation mechanism.  

PubMed

An arylpalladium PNF-type pincer complex reacts with water and anilines under very mild conditions, providing access to new PNO- and PNN-pincer complexes with concomitant hydrogen transfer to the ligand core. Such a metal-ligand cooperation mode allows for the irreversible double activation of even highly sterically hindered aniline molecules. With thiols, the activation mode depends on the nature of the substituent at the sulfur atom, with thiophenols giving products of C-S elimination. PMID:24344770

Scharf, Adam; Goldberg, Israel; Vigalok, Arkadi

2014-01-01

116

Removal of Heavy Metals from Aqueous Solutions by Precipitation-Filtration Using Novel OrganoPhosphorus Ligands  

Microsoft Academic Search

An organophosphorus mixture of sodium mono- and di-(n-hexa-decyl) phosphinate was synthesized and purified, and then used as a ligand to remove heavy metals by precipitation from aqueous nitrate, chloride, and sulfate solutions. The new ligand offers more advantages over the previously studied sodium dioctyl and dodecyl phosphinates. The sodium form of the mono- and di-(n-hexa-decyl) phosphinate has a much lower

Jamaleddin Esalah; Maen M. Husein

2008-01-01

117

New metal complexes of N3 tridentate ligand: Synthesis, spectral studies and biological activity  

NASA Astrophysics Data System (ADS)

New tridentate ligand 3-amino-4-{1,5-dimethyl-3-[2-(5-methyl-1H-indol-3-yl)-ethylimino]-2phenyl-2,3-dihydro-1H-pyrazol-4-ylazo}-phenol L was synthesized from the reaction of 1,5-dimethyl-3-[2-(5-methyl-1H-indol-3-yl)-ethylimino]-2-phenyl-2,3-dihydro-1H-pyrazol-4-ylamine and 3.4-amino phenol. A complexes of these ligand [Ni(II)(L)(H2O)2 Cl]Cl, [pt(IV)(L)Cl3]Cl and [M(II)(L)Cl]Cl (M = Pd (II), Zn (II), Cd (II) and Hg (II) were synthesized. The complexes were characterized by spectroscopic methods and magnetic moment measurements, elemental analysis, metal content, Chloride containing and conductance. These studies revealed octahedral geometries for the Ni (II), pt (IV) complexes, square planar for Pd (II) complex and tetrahedral for the Zn (II), Cd(II) and Hg (II) complexes. The study of complexes formation via molar ratio and job method in DMF solution has been investigated and results were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1). The thermodynamic parameters, such as ?E*, ?H*, ?S* ?G* and K are calculated from the TGA curve using Coats-Redfern method. Hyper Chem-8 program has been used to predict structural geometries of compounds in gas phase. The synthesized ligand and its metal complexes were screened for their biological activity against bacterial species, two Gram positive bacteria (Bacillus subtilis and Staphylococcus aureus) and two Gram negative bacteria (Escherichia coli and Pseudomonasaeruginosa).

Al-Hamdani, Abbas Ali Salih; Al Zoubi, Wail

2015-02-01

118

New metal complexes of N3 tridentate ligand: synthesis, spectral studies and biological activity.  

PubMed

New tridentate ligand 3-amino-4-{1,5-dimethyl-3-[2-(5-methyl-1H-indol-3-yl)-ethylimino]-2phenyl-2,3-dihydro-1H-pyrazol-4-ylazo}-phenol L was synthesized from the reaction of 1,5-dimethyl-3-[2-(5-methyl-1H-indol-3-yl)-ethylimino]-2-phenyl-2,3-dihydro-1H-pyrazol-4-ylamine and 3.4-amino phenol. A complexes of these ligand [Ni(II)(L)(H2O)2 Cl]Cl, [pt(IV)(L)Cl3]Cl and [M(II)(L)Cl]Cl (M=Pd (II), Zn (II), Cd (II) and Hg (II) were synthesized. The complexes were characterized by spectroscopic methods and magnetic moment measurements, elemental analysis, metal content, Chloride containing and conductance. These studies revealed octahedral geometries for the Ni (II), pt (IV) complexes, square planar for Pd (II) complex and tetrahedral for the Zn (II), Cd(II) and Hg (II) complexes. The study of complexes formation via molar ratio and job method in DMF solution has been investigated and results were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1). The thermodynamic parameters, such as ?E(*), ?H(*), ?S(*) ?G(*) and K are calculated from the TGA curve using Coats-Redfern method. Hyper Chem-8 program has been used to predict structural geometries of compounds in gas phase. The synthesized ligand and its metal complexes were screened for their biological activity against bacterial species, two Gram positive bacteria (Bacillus subtilis and Staphylococcus aureus) and two Gram negative bacteria (Escherichia coli and Pseudomonasaeruginosa). PMID:25203213

Al-Hamdani, Abbas Ali Salih; Al Zoubi, Wail

2015-02-25

119

Deliberate Design of Ligand Architecture Yields Dramatic Enhancement of Metal Ion Affinity  

SciTech Connect

Evaluation of the malonamide substructure with respect to binding site preorganization and complementarity for lanthanide metal ions suggests a new ligand architecture specifically designed to enhance lanthanide ion affinity. Consideration of conformational reorganization, restricted bond rotation, and donor group orientation suggest that typical malonamide structures, for example, N,N,N?N?-tetrahexylpropane-1,3-diamide (1), N,N?-dibutyl-N,N?-dimethyl-2-tetradecylpropane-1,3-diamide (2), or N,N,N?N?-tetramethylpropane-1,3-diamide (6), are poorly organized for metal ion complexation. Molecular mechanics analyses show that the unfavorable enthalpic and entropic terms are eliminated by the use of the novel bicyclic architecture found in 3,9-diaza-3,9-dimethylbicyclo[4.4.0]decane-2,10-dione (7). Diamide 7 was prepared and the X-ray crystal structure of the complex[Eu(7)2(NO3)3] exhibits the same chelate conformation predicted by the molecular mechanics model. A hydrophobic derivative, 3,9-diaza-3,9-dioctylbicyclo[4.4.0]decane-2,10-dione (8), was prepared and solvent extraction studies reveal that the preorganized architecture of 8 gives a dramatic enhancement in binding affinity, exhibiting Eu3+ distribution coefficients that are 107 times larger than a typical malonamide ligand, 1.

Lumetta, Gregg J. (BATTELLE (PACIFIC NW LAB)); Rapko, Brian M. (BATTELLE (PACIFIC NW LAB)); Garza, Priscilla A. (BATTELLE (PACIFIC NW LAB)); Hay, Benjamin P. (BATTELLE (PACIFIC NW LAB)); Gilbertson, Robert D. (Oregon, Univ Of); Weakley, T J. (Other); Hutchison, James E. (Oregon, Univ Of)

2001-12-01

120

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

SciTech Connect

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

Rakowski-DuBois, Mary C.

2004-10-08

121

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

NASA Astrophysics Data System (ADS)

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

Benedetti, Adriano; Preti, Carlo; Tosi, Giuseppe

1984-05-01

122

Synthesis, Characterization and Cytotoxic Activity on MCF7 Cell line of some novel Metal Complexes with substituted Benzimidazole ligands  

Microsoft Academic Search

A series of novel metal complexes with the Schiff base ligands 4-((((1H-benzo[d]imidazol-2-yl)methyl)imino)methyl)benzene-1,3-diol, H3L, and (((1H-benzo[d]imidazol-2-yl)methyl)thio)propanenitrile, HL, have been synthesized and identified by elemental and spectral (UV-Vis, IR, 1H NMR, mass) analyses, molar conductivities, as well as magnetic moment measurements technique. The ligands behave either as neutral tridentate or bidentate ligand. The antitumor activity of the new compounds was tested against

Nabil S. Youssef; Ahmed M. A. El-Seidy; Eman El-Zahany; Shadia A. Galal; Sayed A. Drweesh; Atiat S. Barakat

2012-01-01

123

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

124

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

125

Ultrasonic/Sonic Anchor  

NASA Technical Reports Server (NTRS)

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

Bar-Cohen, Yoseph; Sherrit, Stewart

2009-01-01

126

Electric relaxation processes in chemodynamics of aqueous metal complexes: from simple ligands to soft nanoparticulate complexants.  

PubMed

The chemodynamics of metal complexes with nanoparticulate complexants can differ significantly from that for simple ligands. The spatial confinement of charged sites and binding sites to the nanoparticulate body impacts on the time scales of various steps in the overall complex formation process. The greater the charge carried by the nanoparticle, the longer it takes to set up the counterion distribution equilibrium with the medium. A z+ metal ion (z > 1) in a 1:1 background electrolyte will accumulate in the counterionic atmosphere around negatively charged simple ions, as well as within/around the body of a soft nanoparticle with negative structural charge. The rate of accumulation is often governed by diffusion and proceeds until Boltzmann partition equilibrium between the charged entity and the ions in the medium is attained. The electrostatic accumulation proceeds simultaneously with outer-sphere and inner-sphere complex formation. The rate of the eventual inner-sphere complex formation is generally controlled by the rate constant of dehydration of the metal ion, k(w). For common transition metal ions with moderate to fast dehydration rates, e.g., Cu(2+), Pb(2+), and Cd(2+), it is shown that the ionic equilibration with the medium may be the slower step and thus rate-limiting in their overall complexation with nanoparticles. PMID:22126743

van Leeuwen, Herman P; Buffle, Jacques; Town, Raewyn M

2012-01-10

127

Ligand and metal-ion effects in metal-ion clusters used for chiral analysis of alpha-hydroxy acids by the kinetic method.  

PubMed

Chiral recognition of alpha-hydroxy acids has been achieved, and mixtures of enantiomers have been quantified in the gas phase, by using the kinetics of competitive unimolecular dissociation of singly-charged transition metal ion-bound trimeric complexes, [M(II)(A)(ref*)(2)-H](+) (M(II)=divalent transition metal ion; A=alpha-hydroxy acid; ref*=chiral reference ligand), to form the dimeric complexes [M(II)(A)(ref*)-H](+) and [M(II)(ref*)(2)-H](+). Chiral selectivity, the ratio of these two fragment ion abundances for the complex containing the analyte in one enantiomeric form expressed relative to that for the fragments of the corresponding complex containing the other enantiomer, ranges from 0.65 to 7.32. Chiral differentiation is highly dependent on the choice of chiral reference compound and central metal ion. The different coordination geometry of complexes resulting from the different d-orbital electronic configurations of these transition metal ions plays a role in chiral discrimination. Of all the transition metal ions examined chiral recognition is lowest for Cu(II), because of large distortion of the coordination complexes, and hence weak metal-ligand interactions and small stereochemical effects. It seems that two independent pi-cation interactions occur when N-acetyl-substituted aromatic amino acids used as the reference ligands and this accounts for improved chiral discrimination. If both metal-ligand and ligand-ligand interactions are optimized, large chiral selectivity is achieved. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, which are intrinsic to the kinetic method, enable mixtures to be analyzed for small enantiomeric excess ( ee) by simply recording the ratios of fragment ion abundances in a tandem mass spectrum. PMID:12185574

Wu, Lianming; Tao, W Andy; Cooks, R G

2002-08-01

128

Structures and Reactivity of Transition-Metal Compounds Featuring Metal-Ligand Multiple Bonds  

E-print Network

to the formation of transition metal imido compound (M=NR). In the second system a cationic oxorhenium(V) complex reacts with a series of arylazides (N_(3)Ar) to give cationic cis-rhenium(VII) oxo imido complexes. Inductive effect is found in the reaction rates...

Xu, Zhenggang

2014-07-25

129

Testing an application of a biotic ligand model to predict acute toxicity of metal mixtures to rainbow trout.  

PubMed

The authors tested the applicability of a previously developed biotic ligand model (BLM) to predict acute toxicity of single metals and metal mixtures (cadmium, lead, and zinc) to rainbow trout fry (Oncorhynchus mykiss) from a single available dataset. The BLM used in the present study hypothesizes that metals inhibit an essential cation (calcium) and organisms die as a result of its deficiency, leading to an assumption that the proportion of metal-binding ligand (f) is responsible for the toxic effects of metals on the survival of rainbow trout. The f value is a function of free-ion concentrations of metals computed by a chemical speciation model, and the function has affinity constants as model parameters. First, the survival effects of single metals were statistically modeled separately (i.e., f-survival relationship) by using the generalized linear mixed model with binomial distribution. The modeled responses of survival rates to f overlapped reasonably irrespective of metals tested, supporting the theoretical prediction from the BLM that f-survival relationships are comparable regardless of metal species. The authors thus developed the generalized linear mixed model based on all data pooled across the single-metal tests. The best-fitted model well predicted the survival responses observed in mixture tests (r?=?0.97), providing support for the applicability of the BLM to predict effects of metal mixtures. Environ Toxicol Chem 2015;34:754-760. © 2014 SETAC. PMID:25323464

Iwasaki, Yuichi; Kamo, Masashi; Naito, Wataru

2015-04-01

130

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

131

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

PubMed

Metal complexes of Zn(II), Cd(II), Ni(II), Cu(II), Fe(III), Co(II), Mn(II) Hg(II), and Ag(I) have been synthesized from Schiff base ligand, prepared by the condensation of 3,4-(methylenedioxy)aniline and 5-bromo salicylaldehyde. All the compounds have been characterized by using elemental analysis, molar conductance, FT-IR, UV-Vis, (1)H NMR, (13)C NMR, mass spectra, powder XRD and thermal analysis (TG/DTA) technique. The elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). The FT-IR, (1)H NMR, (13)C NMR and UV-Vis spectral data suggest that the ligand coordinate to the metal atom by imino nitrogen and phenolic oxygen as bidentate manner. Mass spectral data further support the molecular mass of the compounds and their structure. Powder XRD indicates the crystalline state and morphology of the ligand and its metal complexes. The thermal behaviors of the complexes prove the presence of lattice as well as coordinated water molecules in the complexes. Melting point supports the thermal stability of all the compounds. The in vitro antimicrobial effects of the synthesized compounds were tested against five bacterial and three fungal species by well diffusion method. Antioxidant activities have also been performed for all the compounds. Metal complexes show more biological activity than the Schiff base. PMID:24820326

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

2014-10-15

132

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

133

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

PubMed

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

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

2014-10-01

134

Coordination dimers constructed from metal(II) halides and the organic ligand 1,2-dimethoxy- 4,5-bis(2-pyridylethynyl)benzene  

Microsoft Academic Search

A series of new coordination compounds has been synthesized using the organic ligand 1,2-dimethoxy-4,5-bis(2-pyridylethynyl)benzene (dmpeb). The compounds all form dimers consisting of two metal cations bridged by two ligand molecules. Charge balance is provided by halide ligands, and the four-coordinate metal centers are distorted from the ideal tetrahedral environment. [CoCl2(dmpeb)]2 (1) crystallizes in the monoclinic space group P21\\/n with a

Jeffrey E. Fiscus; Sandra Shotwell; Ralph C. Layland; Rachael E. Hipp; Andrea M. Goforth; Craig T. Chapman; Mark D. Smith; Uwe H. F. Bunz; Hans-Conrad zur Loye

2005-01-01

135

Discovery of Environmentally Benign Catalytic Reactions of Alcohols Catalyzed by Pyridine-Based Pincer Ru Complexes, Based on Metal–Ligand Cooperation  

Microsoft Academic Search

We have developed a new mode of metal–ligand cooperation, based on aromatization–dearomatization of pyridine-based pincer-type\\u000a ligands, and have demonstrated it in the activation of H2 and C–H bonds by PNP Ir complexes. This type of metal–ligand cooperation plays a key role in the recently discovered environmentally\\u000a benign reactions of alcohols, catalyzed by PNP and PNN pincer complexes of ruthenium, including

David Milstein

2010-01-01

136

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

137

A metal-ligand cooperative pathway for intermolecular oxa-Michael additions to unsaturated nitriles.  

PubMed

An unprecedented catalytic pathway for oxa-Michael addition reactions of alcohols to unsaturated nitriles has been revealed using a PNN pincer ruthenium catalyst with a dearomatized pyridine backbone. The isolation of a catalytically competent Ru-dieneamido complex from the reaction between the Ru?catalyst and pentenenitrile in combination with DFT?calculations supports a mechanism in which activation of the nitrile through metal-ligand cooperativity is a key step. The nitrile-derived Ru-N?moiety is sufficiently Brønsted basic to activate the alcohol and initiate conjugate addition of the alkoxide to the ?,?-unsaturated fragment. This reaction proceeds in a concerted manner and involves a six-membered transition state. These features allow the reaction to proceed at ambient temperature in the absence of external base. PMID:25663451

Perdriau, Sébastien; Zijlstra, Douwe S; Heeres, Hero J; de Vries, Johannes G; Otten, Edwin

2015-03-27

138

Infrared Spectroscopy of Metal Ion Complexes: Models for Metal Ligand Interactions and Solvation  

NASA Astrophysics Data System (ADS)

Weakly bound complexes of the form M^+-Lx (M=Fe, Ni, Co, etc.; L=CO2, C2H2, H2O, benzene, N2) are prepared in supersonic molecular beams by laser vaporization in a pulsed-nozzle cluster source. These species are mass analyzed and size-selected in a reflectron time-of-flight mass spectrometer. Clusters are photodissociated at infrared wavelengths with a Nd:YAG pumped infrared optical parametric oscillator/amplifier (OPO/OPA) laser or with a tunable infrared free-electron laser. M^+-(CO2)x complexes absorb near the free CO2 asymmetric stretch near 2349 cm-1 but with an interesting size dependent variation in the resonances. Small clusters have blue-shifted resonances, while larger complexes have additional bands due to surface CO2 molecules not attached to the metal. M^+(C2H2)n complexes absorb near the C-H stretches in acetylene, but resonances in metal complexes are red-shifted with repect to the isolated molecule. Ni^+ and Co^+ complexes with acetylene undergo intracluster cyclization reactions to form cyclobutadiene. Transition metal water complexes are studied in the O-H stretch region, and partial rotational structure can be measured. M^+(benzene) and M^+(benzene)2 ions (M=V, Ti, Al) represent half-sandwich and sandwich species, whose spectra are measured near the free benzene modes. These new IR spectra and their assignments will be discussed as well as other new IR spectra for similar complexes.

Duncan, Michael

2006-03-01

139

Metal-free inorganic ligands for colloidal nanocrystals: S2-, HS-, Se2-, HSe-, Te2-, HTe-, TeS3(2-), OH-, and NH2- as surface ligands.  

PubMed

All-inorganic colloidal nanocrystals were synthesized by replacing organic capping ligands on chemically synthesized nanocrystals with metal-free inorganic ions such as S(2-), HS(-), Se(2-), HSe(-), Te(2-), HTe(-), TeS(3)(2-), OH(-) and NH(2)(-). These simple ligands adhered to the NC surface and provided colloidal stability in polar solvents. The versatility of such ligand exchange has been demonstrated for various semiconductor and metal nanocrystals of different size and shape. We showed that the key aspects of Pearson's hard and soft acids and bases (HSAB) principle, originally developed for metal coordination compounds, can be applied to the bonding of molecular species to the nanocrystal surface. The use of small inorganic ligands instead of traditional ligands with long hydrocarbon tails facilitated the charge transport between individual nanocrystals and opened up interesting opportunities for device integration of colloidal nanostructures. PMID:21682249

Nag, Angshuman; Kovalenko, Maksym V; Lee, Jong-Soo; Liu, Wenyong; Spokoyny, Boris; Talapin, Dmitri V

2011-07-13

140

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

PubMed

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

Gunanathan, Chidambaram; Milstein, David

2011-08-16

141

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

142

Metal-organic complexes in geochemical processes: temperature dependence of the standard thermodynamic properties of aqueous complexes between metal cations and dicarboxylate ligands  

NASA Astrophysics Data System (ADS)

By combining results from regression and correlation methods, standard state thermodynamic properties for aqueous complexes between metal cations and divalent organic acid ligands (oxalate, malonate, succinate, glutarate, and adipate) are evaluated and applied to geochemical processes. Regression of experimental standard-state equilibrium constants with the revised Helgeson-Kirkham-Flowers (HKF) equation of state yields standard partial molal entropies (S¯°) of aqueous metal-organic complexes, which allow determination of thermodynamic properties of the complexes at elevated temperatures. In cases where S¯° is not available from either regression or calorimetric measurement, the values of S¯° can be estimated from a linear correlation between standard partial molal entropies of association (?S¯°r) and standard partial molal entropies of aqueous cations (S¯°M). The correlation is independent of cation charge, which makes it possible to predict S¯° for complexes between divalent organic acids and numerous metal cations. Similarly, correlations between standard Gibbs free energies of association of metal-organic complexes (??°r) and Gibbs free energies of formation (??°f) for divalent metal cations allow estimates of standard-state equilibrium constants where experimental data are not available. These correlations are found to be a function of ligand structure and cation charge. Predicted equilibrium constants for dicarboxylate complexes of numerous cations were included with those for inorganic and other organic complexes to study the effects of dicarboxylate complexes on the speciation of metals and organic acids in oil-field brines. Relatively low concentrations of oxalic and malonic acids affect the speciation of cations more than similar concentrations of succinic, glutaric, and adipic acids. However, the extent to which metal-dicarboxylate complexes contribute to the speciation of dissolved metals depends on the type of dicarboxylic acid ligand; relative concentration of inorganic, mono-, and dicarboxylate ligands; and the type of metal cation. As an example, in the same solution, dicarboxylic acids have a greater influence on the speciation of Fe+2 and Mg+2 than on the speciation of Zn+2 and Mn+2.

Prapaipong, Panjai; Shock, Everett L.; Koretsky, Carla M.

1999-10-01

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

2011-10-15

144

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

145

Tandem isomerization-decarboxylation of unsaturated fatty acids to olefins via ruthenium metal-as-ligand catalysts  

Technology Transfer Automated Retrieval System (TEKTRAN)

A new facile Ru-catalyzed route to bio-olefins3 from unsaturated fatty acids via readily accessible metal-as-ligand type catalyst precursors, [Ru(CO)2RCO2]n and Ru3(CO)12, will be described. The catalyst apparently functions in a tandem mode by dynamically isomerizing the positions of double bonds i...

146

Reevaluation of metal bioaccumulation and chronic toxicity in Hyalella azteca using saturation curves and the biotic ligand model  

Microsoft Academic Search

Bioaccumulation by Hyalella of all metals studied so far in our laboratory was re-evaluated to determine if the data could be explained satisfactorily using saturation models. Saturation kinetics are predicted by the biotic ligand model (BLM), now widely used in modelling acute toxicity, and are a pre-requisite if the BLM is to be applied to chronic toxicity. Saturation models provided

U. Borgmann; W. P. Norwood; D. G. Dixon

2004-01-01

147

A luminescent metal-organic framework constructed using a tetraphenylethene-based ligand for sensing volatile organic compounds.  

PubMed

By using a tetraphenylethene (TPE)-based ligand, tetrakis[4-(4-carboxyphenyl)phenyl]ethene (H4TCPPE), a porous metal-organic framework [Zn2(TCPPE)] (1) is synthesized, which exhibits strong fluorescence and is capable of gas adsorption and sensing volatile organic compounds. PMID:25502496

Liu, Xun-Gao; Wang, Hui; Chen, Bin; Zou, Yang; Gu, Zhi-Guo; Zhao, Zujin; Shen, Liang

2015-01-31

148

Carbonyl substitution chemistry of some trimetallic transition metal cluster complexes with polyfunctional ligands  

SciTech Connect

The trimetallic clusters [Ru{sub 3}(CO){sub 10}(dppm)], [Ru{sub 3}(CO){sub 12}] and [RuCo{sub 2}(CO){sub 11}] react with a number of multifunctional secondary phosphine and tertiary arsine ligands to give products consequent on carbonyl substitution and, in the case of the secondary phosphines, PH activation. The reaction with the unresolved mixed P/S donor, 1-phenylphosphino-2-thio(ethane), HSCH{sub 2}CH{sub 2}PHPh ({double_bond}LH{sub 2}), gave two products under various conditions which have been characterized by spectroscopic and crystallographic means. These two complexes [Ru{sub 3}({mu}dppm)(H)(CO){sub 7}(LH)] and [Ru{sub 3}({mu}-dppm)(H)(CO){sub 8}(LH)Ru{sub 3}({mu}-dppm)(CO){sub 9}], show the versatility of the ligand, with it chelating in the former and bridging two Ru{sub 3} units in the latter. The stereogenic centres in the molecules gave rise to complicated spectroscopic data which are consistent with the presence of diastereoisomers. In the case of [Ru{sub 3}(CO){sub 12}] the reaction with LH{sub 2} gave a poor yield of a tetranuclear butterfly cluster, [Ru{sub 4}(CO){sub 10}(L){sub 2}], in which two of the ligands bridge opposite hinge wingtip bonds of the cluster. A related ligand, HSCH{sub 2}CH{sub 2}AsMe(C{sub 6}H{sub 4}CH{sub 2}OMe), reacted with [RuCo{sub 2}(CO){sub 11}] to give a low yield of the heterobimetallic Ru-Co adduct, [RuCo(CO){sub 6}(SCH{sub 2}CH{sub 2}AsMe(C{sub 6}H{sub 4}CH{sub 2}OMe))], which appears to be the only one of its type so far structurally characterized. The secondary phosphine, HPMe(C{sub 6}H{sub 4}(CH{sub 2}OMe)) and its oxide HP(O)Me(C{sub 6}H{sub 4}(CH{sub 2}OMe)) also react with the cluster [Ru{sub 3}(CO){sub 10}(dppm)] to give carbonyl substitution products, [Ru{sub 3}(CO){sub 5}(dppm)({mu}{sub 2}-PMe(C{sub 6}H{sub 4}CH{sub 2}OMe)){sub 4}], and [Ru{sub 3}H(CO){sub 7}(dppm)({mu}{sub 2},{eta}{sup 1}P({double_bond}O)Me(C{sub 6}H{sub 4}CH{sub 2}OMe))]. The former consists of an open Ru{sub 3} triangle with four phosphide ligands bridging the metal-metal bonds; the latter has the O atom symmetrically bridging one Ru-Ru bond, the P atom being attached to a non-bridged Ru atom.

Byrne, Lindsay T.; Hondow, Nicole S.; Koutsantonis, George A.; Skelton, Brian W.; Torabi, A. Asgar; White, Allan H.; Wild, S. Bruce (UWA); (ANU)

2008-11-03

149

Increased Diversity of the HLA-B40 Ligandome by the Presentation of Peptides Phosphorylated at Their Main Anchor Residue*  

PubMed Central

Human leukocyte antigen (HLA) class I molecules bind peptides derived from the intracellular degradation of endogenous proteins and present them to cytotoxic T lymphocytes, allowing the immune system to detect transformed or virally infected cells. It is known that HLA class I–associated peptides may harbor posttranslational modifications. In particular, phosphorylated ligands have raised much interest as potential targets for cancer immunotherapy. By combining affinity purification with high-resolution mass spectrometry, we identified more than 2000 unique ligands bound to HLA-B40. Sequence analysis revealed two major anchor motifs: aspartic or glutamic acid at peptide position 2 (P2) and methionine, phenylalanine, or aliphatic residues at the C terminus. The use of immobilized metal ion and TiO2 affinity chromatography allowed the characterization of 85 phosphorylated ligands. We further confirmed every sequence belonging to this subset by comparing its experimental MS2 spectrum with that obtained upon fragmentation of the corresponding synthetic peptide. Remarkably, three phospholigands lacked a canonical anchor residue at P2, containing phosphoserine instead. Binding assays showed that these peptides bound to HLA-B40 with high affinity. Together, our data demonstrate that the peptidome of a given HLA allotype can be broadened by the presentation of peptides with posttranslational modifications at major anchor positions. We suggest that ligands with phosphorylated residues at P2 might be optimal targets for T-cell-based cancer immunotherapy. PMID:24366607

Marcilla, Miguel; Alpízar, Adán; Lombardía, Manuel; Ramos-Fernandez, Antonio; Ramos, Manuel; Albar, Juan Pablo

2014-01-01

150

Inter-ligand azo (N[double bond, length as m-dash]N) unit formation and stabilization of a Co(ii)-diradical complex via metal-to-ligand d?-p?* back donation: synthesis, characterization, and theoretical study.  

PubMed

An azide (-N3) group attached at the -ortho carbon atom to the aniline moiety of 2-anilino-4,6-di-tert-butylphenol formed a diradical-containing Co(ii) complex via inter-ligand azo (N[double bond, length as m-dash]N) bond formation. Metal-to-ligand (azo), d?-to-p?* back donation stabilized the metal in its lower oxidation state. PMID:25623286

Rakshit, Richa; Ghorai, Samir; Sarmah, Amrit; Tiwari, Archana; Roy, Ram Kinkar; Mukherjee, Chandan

2015-02-10

151

Synthesis, characterization, DNA binding, DNA cleavage and antimicrobial studies of schiff base ligand and its metal complexes.  

PubMed

A series of Cu(II) , Ni(II) , Co(II) , Mn(II) and Zn(II) complexes have been synthesized from the Schiff base ligand L. The Schiff base ligand 4-chloro-2-((4-oxo-4H-chromen-3yl) methylene amino) benzoic acid (L) has been synthesized by the reaction between chromone-3-carbaldehyde and 4-chloro-2-amino benzoic acid. The nature of bonding and geometry of the transition metal complexes as well as ligand L have been deduced from elemental analysis, FT-IR, UV-vis, (1)H NMR, (13)C NMR, ESR spectral studies, mass, magnetic susceptibility and molar conductance measurements. The complexes are found to have ML2 composition and are neutral in DMSO. Based on elemental, conductance and spectral studies, six-coordinated geometry was assigned for these complexes. The ligand L acts as tridentate and coordinates through nitrogen atom of azomethine group, hydroxyl of the carboxyl group and oxygen atom of keto group of ?-pyrone ring. The interaction of Cu(II) complex with CT- DNA was carried out by UV-vis, fluorescence titrations and viscosity measurements. The complex binds to DNA through intercalative binding mode. The nuclease activity of the above metal complexes shows that Cu(II) and Co(II) complexes cleave DNA through redox chemistry. The biological activity of the ligand and its complexes have been studied on four bacteria E.coli, B.subtilis, pseudomonas and Edwardella and two fungi penicillium and trichoderma by well disc and fusion method and found that the metal complexes are more active than the free Schiff base ligand. PMID:25663196

Mendu, Padmaja; Kumari, C Gyana; Ragi, Rajesh

2015-03-01

152

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

153

Synthesis, spectral, thermal and antimicrobial studies of transition metal complexes of 14-membered tetraaza[N4] macrocyclic ligand.  

PubMed

A series of metal complexes of Mn(II), Co(II), Ni(II), Cu(II), have been synthesized with newly synthesized biologically active macrocyclic ligand. The ligand was synthesized by condensation of ?-diketone 1-(4-chlorophenyl)-3-(2-hydroxyphenyl)propane-1,3-dione and o-phenylene diamine. All the complexes were characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, (1)H-NMR, UV-Vis spectroscopy and mass spectroscopy. From the analytical data, stoichiometry of the complexes was found to be 1:2 (metal:ligand). Thermal behavior (TG/DTA) and kinetic parameters suggest more ordered activated state in complex formation. All the complexes are of high spin type and six coordinated. On the basis of IR, electronic spectral studies and magnetic behavior, an octahedral geometry has been assigned to these complexes. The antibacterial and antifungal activities of the ligand and its metal complexes, has been screened in vitro against Staphylococcus aureus, Escherichia coli and Aspergillus niger, Trichoderma respectively. PMID:25775943

Shankarwar, Sunil G; Nagolkar, Bhagwat B; Shelke, Vinod A; Chondhekar, Trimbak K

2015-06-15

154

How a redox-innocent metal promotes the formal reductive elimination of biphenyl using redox-active ligands.  

PubMed

One of the most compelling strategies for utilizing redox-active ligands is to perform redox events at the ligands to avoid accessing prohibitively high energy oxidation states at the metal center. This has been demonstrated experimentally in many systems, yet there is little understanding of the fundamental electronic structures involved with these transformations or how to control them. Here, the reductive elimination of biphenyl from [M(isq)2 Ph2 ] (M=Ti, Zr, and Hf and isq=2,4-di-tert-butyl-6-tert-butyliminosemiquinone) was studied computationally. It was found that the metal remains in the +IV oxidation state and all redox chemistry was mediated by the redox-active ligands. Two types of electron-transfer mechanisms were identified, an asymmetric unpaired electron transfer (UET) and a symmetric pairwise electron transfer (PET), the former always being lower in energy. The energetic differences between these two mechanisms were explained through simple molecular orbital theory arguments. Despite the metal's redox-inactivity, it still has a marked influence on the calculated energetics of the reaction, with the Ti systems being much more reactive than the Zr/Hf systems. This primarily originates from the shorter Ti?Ph bond, which leads to a stronger filled-filled interaction between these ligands at the reactant state. This greater reactant destabilization leads to the lower activation energies. PMID:25653096

Ashley, Daniel Charles; Baik, Mu-Hyun

2015-03-01

155

Studies on antimicrobial effects of four ligands and their transition metal complexes with 8-mercaptoquinoline and pyridine terminal groups.  

PubMed

Four types of ligands (Q1-Q4) and their complexes (1-36) with transition metal ions have been synthesized, in which two new complexes (15 and 20) have been prepared and tested. In vitro antimicrobial activities of the ligands and their complexes were investigated against a representative panel of strains including two Gram positive bacteria (Sarcina ureae, Staphylococcus aureus), two Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and three fungi (Aspergillus niger, Saccharomyces cerevisiae, Fusarium oxysporum f. sp. cubense). The relationship between the structure and the antibacterial activities was discussed. Our study results indicated that some compounds have preferred antibacterial activities that may have potential pharmaceutical applications. PMID:25791454

Zhang, Li-Jie; Zhang, Jing-An; Zou, Xun-Zhong; Liu, Ya-Jie; Li, Ning; Zhang, Zi-Jie; Li, Yu

2015-04-15

156

Switching and redox isomerism in first-row transition metal complexes containing redox active Schiff base ligands.  

PubMed

The reversible redox isomerisms in first row transition metal complexes of the type ML2 were studied. The six ML2 complexes (M = Mn(III) (), Fe(II) (), Co(III) (), Ni(II) (), Cu(II) () and Zn(II) ()) were synthesized with a redox active Schiff base ligand [2-(3,5-di-tert-butyl-2-hydroxyphenylamino)-4-chlorophenol] (H3L) presenting different oxidation states from -2 to 0 (L(2-), L(-) and L(0)). EPR spectra and magnetic susceptibility measurements indicate the presence of complexes of the type [Mn(III)(L(2-))(L(-))] () with S = 1/2, [Fe(II)(L(-))2] () with S = 2, [Co(III)(L(2-))(L(-))] () with S = 1/2, [Ni(II)(L(-))2] () with S = 1, [Cu(II)(L(-))2] () with S = 1/2 and [Zn(II)(L(-))2] () with S = 0 at high temperatures. Temperature and solvents influence the electronic structures of the species and give several valence tautomers. At low temperatures these complexes present thermally induced metal-to-ligand (, , ) or ligand-to-ligand (in , ) electron transfer (partial or total), resulting in compounds of the type [Mn(IV)(L(2-))2] () with S = 1/2, [Fe(III)(L(-))(L(2-))] () with S = 1, [Ni(III)(L(2-))(L(-))] () with S = 0, [Cu(II)(L(2-))(L(0))] () with S = 1/2 and [Zn(II)(L(2-))(L(0))] () with S = 1. This electron transfer is in agreement with the general trend in the redox potentials of the first row transition metal ions from Mn(ii) to Zn(ii), and it allows us to prepare and stabilize reversibly switchable tautomeric forms in transition metal complexes with redox-active ligands. PMID:25233051

Sasmal, Ashok; Garribba, Eugenio; Gómez-García, Carlos J; Desplanches, Cédric; Mitra, Samiran

2014-11-14

157

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

PubMed Central

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

Ladnorg, Tatjana; Welle, Alexander; Heißler, Stefan; Wöll, Christof

2013-01-01

158

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.

159

Bioabsorbable anchors in glenohumeral shoulder surgery.  

PubMed

The use of implants to provide glenohumeral soft tissue fixation has changed dramatically over the past few decades, from point tack fixation to metallic suture anchors to bioabsorbable suture anchors. Bioabsorbable suture anchors have largely replaced metallic anchors because of concerns of implant loosening, migration, and chondral injury. Although the safety and efficacy of bioabsorbable anchors has been well documented, there are numerous reports regarding the early failure related to implant bioabsorbable implant breakage or premature degradation. Patients with anchor-related complications generally present with pain and/or stiffness, and the surgeon should have a high index of suspicion if a patient does not progress as expected. Glenohumeral synovitis, glenoid osteolysis, loose bodies, and chondral injury are some of the notable complications that have been reported. Careful attention to proper anchor insertion techniques can limit the potential for complications. Newer materials, such as polyetheretherketone and other composites, have recently been introduced. These materials may address concerns of biocompatibility and material strength, but additional rigorous in vitro and in vivo trials need to be conducted before their use becomes widespread. PMID:19560644

Nho, Shane J; Provencher, Matthew T; Seroyer, Shane T; Romeo, Anthony A

2009-07-01

160

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

E-print Network

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

Jackson, Alicia M

2007-01-01

161

Anchored nanostructure materials and method of fabrication  

DOEpatents

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

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

2012-11-27

162

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

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

163

Complexes of aminosquarate ligands with first-row transition metals and lanthanides: new insights into their hydrolysis.  

PubMed

Attempts at synthesizing first-row transition-metal complexes of the 3-hydroxy-4-[(1'S,2'R)-(2-hydroxy-1',2'-diphenylethyl)amino]-3-cyclobutene-1,2-dione ligand in alcoholic solutions resulted in the formation of the monomers [M(NH(2)C(4)O(3))(2)(H(2)O)(4)] [M = Mn (1), Co (2), Ni (3), Cu (4), Zn (5)] instead, as a result of the hydrolysis of the ligand. 1, 2, and 3 are isomorphous (C2/c), with the metal atoms octahedrally coordinated to four aqua and two cis aminosquarate ligands. The copper and zinc complexes (4 and 5) have the same molecular formula as 1-3 but belong to the C2/m and P2(1)/c space groups respectively. 4 has square-pyramidal geometry with trans-oriented aminosquarate ligands in the basal plane; aqua ligands complete the coordination sphere. 5 has octahedral geometry, with four aqua and two trans-oriented aminosquarate ligands. Reaction of aqueous solutions of the anilinosquarate ligand with Ln(NO(3))(3) x xH(2)O produced the eight-coordinate complexes {Sm(mu-C(6)H(5)NHC(4)O(3))(3)(H(2)O)(4) x 3H(2)O}n (6), {[M(mu(2)-C(4)O(4))(H(2)O)(6)][C(6)H(5)NHC(4)O(3)] x 4H(2)O}n [M = Er (7), Yb (8)], {Sm(C(6)H(5)NHC(4)O(3)) (mu(3)-C(4)O(4))(H(2)O)(4) x H(2)O}(n) (9), and {[{(C(6)H(5)NHC(4)O(3))(2)(H(2)O)(5)Yb}(2)(mu-C(4)O(4))] x 4H(2)O}n (10). 7 and 8 are isomorphous with the previously reported analogues Eu, Gd, and Tb ionic polymers. The presence of the squarate ligand in 7-10 is indicative of some form of hydrolysis of the anilinosquarate ligand during their syntheses. However, hydrolysis was not evident in the synthesis of 6. The mechanism for the hydrolysis in the syntheses of 1-5 is apparently different from that for 7-10. PMID:17523629

Piggot, Patrice M T; Seenarine, Shireen; Hall, Lincoln A

2007-06-25

164

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

165

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

PubMed

Novel penta-azamacrocyclic 15-membered [N5] ligand [L] i.e. 1,5,8,12-tetetraaza-3,4: 9,10-dibenzo-6-ethyl-7-methyl-1,12-(2,6-pyrido)cyclopentadecan-5,7 diene-2,11-dione and its transition metal complexes with Co(II), Ni(II), Cu(II), Ru(III) and Pd(II) have been synthesized and structurally characterized by elemental analysis, spectral, thermal as well as magnetic and molar conductivity measurements. On basis of IR, MS, UV-Vis 1H NMR and EPR spectral studies an octahedral geometry has been proposed for all complexes except Co(II), Cu(II) nitrate complexes and Pd(II) chloride complex that adopt tetrahedral, square pyramidal and square planar geometries, respectively. The antitumor activity of the synthesized ligand and some complexes against human breast cancer cell lines (MCF-7) and human hepatocarcinoma cell lines (HepG2) has been studied. The complexes (IC50=2.04-9.7, 2.5-3.7 ?g/mL) showed potent antitumor activity comparable with their ligand (IC50=11.7, 3.45 ?g/mL) against the above mentioned cell lines, respectively. The results evidently show that the activity of the ligand becomes more pronounced and significant when coordinated to the metal ion. PMID:24892547

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

2014-11-11

166

New 15-membered tetraaza (N4) macrocyclic ligand and its transition metal complexes: spectral, magnetic, thermal and anticancer activity.  

PubMed

Novel tetraamidemacrocyclic 15-membered ligand [L] i.e. naphthyl-dibenzo[1,5,9,12]tetraazacyclopentadecine-6,10,11,15-tetraoneand its transition metal complexes with Fe(II), Co(II), Ni(II), Cu(II), Ru(III) and Pd(II) have been synthesized and characterized by elemental analysis, spectral, thermal as well as magnetic and molar conductivity measurements. On the basis of analytical, spectral (IR, MS, UV-Vis, (1)H NMR and EPR) and thermal studies distorted octahedral or square planar geometry has been proposed for the complexes. The antitumor activity of the synthesized ligand and some complexes against human breast cancer cell lines (MCF-7) and human hepatocarcinoma cell lines (HepG2) has been studied. The complexes (IC50=2.27-2.7, 8.33-31.1?g/mL, respectively) showed potent antitumor activity, towards the former cell lines comparable with their ligand (IC50=13, 26?g/mL, respectively). The results show that the activity of the ligand towards breast cancer cell line becomes more pronounced and significant when coordinated to the metal ion. PMID:25531404

El-Boraey, Hanaa A; EL-Gammal, Ohyla A

2015-03-01

167

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

168

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

PubMed Central

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

Kaur, Kirandeep

2014-01-01

169

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

170

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

PubMed Central

Background Mutations in PMM2 impair phosphomannomutase-2 activity and cause the most frequent congenital disorder of glycosylation, PMM2-CDG. Mannose-1-phosphate, that is deficient in this disorder, is also implicated in the biosynthesis of glycosylphosphatidyl inositol (GPI) anchors. Objective To evaluate whether GPI-anchor and GPI-anchored proteins are defective in PMM2-CDG patients. Methods The expression of GPI-anchor and seven GPI-anchored proteins was evaluated by flow cytometry in different cell types from twelve PMM2-CDG patients. Additionally, neutrophil CD16 and plasma hepatic proteins were studied by Western blot. Transferrin glycoforms were evaluated by HPLC. Results Patients and controls had similar surface expression of GPI-anchor and most GPI-anchored proteins. Nevertheless, patients displayed a significantly diminished binding of two anti-CD16 antibodies (3G8 and KD1) to neutrophils and also of anti-CD14 (61D3) to monocytes. Interestingly, CD16 immunostaining and asialotransferrin levels significantly correlated with patients’ age. Analysis by flow cytometry of CD14 with M?P9, and CD16 expression in neutrophils by Western blot using H-80 ruled out deficiencies of these antigens. Conclusions PMM2 mutations do not impair GPI-anchor or GPI-anchored protein expression. However, the glycosylation anomalies caused by PMM2 mutations might affect the immunoreactivity of monoclonal antibodies and lead to incorrect conclusions about the expression of different proteins, including GPI-anchored proteins. Neutrophils and monocytes are sensitive to PMM2 mutations, leading to abnormal glycosylation in immune receptors, which might potentially affect their affinity to their ligands, and contribute to infection. This study also confirms less severe hypoglycosylation defects in older PMM2-CDG patients. PMID:24139637

2013-01-01

171

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

Microsoft Academic Search

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

Azza A. A. Abou-Hussen; Wolfgang Linert

2009-01-01

172

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

SciTech Connect

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

Ogino, I.; Gates, B

2010-01-01

173

Unsymmetrical Schiff base (ON) ligand on complexation with some transition metal ions: synthesis, spectral characterization, antibacterial, fluorescence and thermal studies.  

PubMed

A series of eight metal Schiff base complexes were synthesized by the thermal reaction of Cu(II), Ni(II), Fe(III), Co(II), Zn(II), Hg(II), La(III) or Sm(III) with a Schiff base "L" produced by the condensation of furfuraldehyde and 1,2-diaminobenzene. These compounds were characterized by elemental analysis, UV-Vis, FT-IR, molar conductance, mass spectrometry, thermal and fluorescence studies. The studies suggested the coordination of the ligand L to metal through azomethine imine nitrogen and furan oxygen atoms of Schiff base moiety. Thermogravimetric (TG/DTG) analyses data were studied and indicated high stability for all complexes and suggested the presence of lattice and/or coordinated water molecules in the complexes. Coats-Redfern method has been used to calculate the kinetic and thermodynamic parameters of the metal complexes. The spectral and thermal analysis reveal that all complexes have octahedral geometry except Cu(II) and Ni(II) complexes which can attain a square planner arrangements. The ligand and its complexes exhibited intraligand (?-?(?)) fluorescence and can potentially serve as photoactive materials. Both the ligand and its complexes have been screened for antibacterial activities. PMID:25448965

Ali, Omyma A M; El-Medani, Samir M; Abu Serea, Maha R; Sayed, Abeer S S

2015-02-01

174

Unsymmetrical Schiff base (ON) ligand on complexation with some transition metal ions: Synthesis, spectral characterization, antibacterial, fluorescence and thermal studies  

NASA Astrophysics Data System (ADS)

A series of eight metal Schiff base complexes were synthesized by the thermal reaction of Cu(II), Ni(II), Fe(III), Co(II), Zn(II), Hg(II), La(III) or Sm(III) with a Schiff base "L" produced by the condensation of furfuraldehyde and 1,2-diaminobenzene. These compounds were characterized by elemental analysis, UV-Vis, FT-IR, molar conductance, mass spectrometry, thermal and fluorescence studies. The studies suggested the coordination of the ligand L to metal through azomethine imine nitrogen and furan oxygen atoms of Schiff base moiety. Thermogravimetric (TG/DTG) analyses data were studied and indicated high stability for all complexes and suggested the presence of lattice and/or coordinated water molecules in the complexes. Coats-Redfern method has been used to calculate the kinetic and thermodynamic parameters of the metal complexes. The spectral and thermal analysis reveal that all complexes have octahedral geometry except Cu(II) and Ni(II) complexes which can attain a square planner arrangements. The ligand and its complexes exhibited intraligand (?-??) fluorescence and can potentially serve as photoactive materials. Both the ligand and its complexes have been screened for antibacterial activities.

Ali, Omyma A. M.; El-Medani, Samir M.; Abu Serea, Maha R.; Sayed, Abeer S. S.

2015-02-01

175

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

SciTech Connect

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

Chu, Ivan K.; Laskin, Julia

2011-12-31

176

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

177

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

SciTech Connect

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

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

1993-05-12

178

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

PubMed

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

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

2014-11-01

179

Computational Modeling of the Triplet Metal-to-Ligand Charge-Transfer Excited-State Structures of Mono-Bipyridine-Ruthenium(II)  

E-print Network

of Mono-Bipyridine-Ruthenium(II) Complexes and Comparisons to their 77 K Emission Band Shapes Richard L in the lowest energy triplet metal to ligand charge-transfer (3 MLCT = T0) excited states of ruthenium

Schlegel, H. Bernhard

180

Synergistic assembly of heavy metal clusters and luminescent organic bridging ligands in metal-organic frameworks for highly efficient X-ray scintillation.  

PubMed

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

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

2014-04-30

181

Quadruple metal-metal bonds with strong donor ligands. Ultraviolet photoelectron spectroscopy of Mâ(form)â (M = Cr, Mo, W; form = N,Nâ²-diphenylformamidinate)  

Microsoft Academic Search

The He I photoelectron spectra of Mâ(form)â(M = Cr, Mo, W; form - N,Nâ²-diphenylformamidinate) and Moâ(cyform)â (cyform = N,Nâ²-dicyclohexylformamidinate) are presented. For comparison, the Ne I, He I, and He II photoelectron spectra of Moâ(p-CHâ-form)â have also been obtained. The valence ionization features of these molecules are interpreted based on (1) the changes that occur with the metal and ligand

Dennis L. Lichtenberger; Matthew A. Lynn; Malcolm H. Chisholm

1999-01-01

182

Tin, Antimony, Bismuth, and Tellurium Lewis Acids in sigma-Accepting Ligands for Transition Metals  

E-print Network

shown to activate small molecules such as H2, CO2, and CHCl3. Further, the concept of Z-ligand has been extended to s- and d-block Lewis acids. In spite of these achievements, Z-ligands that contain Group 14-16 elements as Lewis acids remain scarce...

Lin, Tzu-Pin

2012-10-19

183

Rare-earth-metal methyl, amide, and imide complexes supported by a superbulky scorpionate ligand.  

PubMed

The reaction of monomeric [(Tp(tBu,Me) )LuMe2 ] (Tp(tBu,Me) =tris(3-Me-5-tBu-pyrazolyl)borate) with primary aliphatic amines H2 NR (R=tBu, Ad=adamantyl) led to lutetium methyl primary amide complexes [(Tp(tBu,Me) )LuMe(NHR)], the solid-state structures of which were determined by XRD analyses. The mixed methyl/tetramethylaluminate compounds [(Tp(tBu,Me) )LnMe({?2 -Me}AlMe3 )] (Ln=Y, Ho) reacted selectively and in high yield with H2 NR, according to methane elimination, to afford heterobimetallic complexes: [(Tp(tBu,Me) )Ln({?2 -Me}AlMe2 )(?2 -NR)] (Ln=Y, Ho). X-ray structure analyses revealed that the monomeric alkylaluminum-supported imide complexes were isostructural, featuring bridging methyl and imido ligands. Deeper insight into the fluxional behavior in solution was gained by (1) H and (13) C?NMR spectroscopic studies at variable temperatures and (1) H-(89) Y HSQC NMR spectroscopy. Treatment of [(Tp(tBu,Me) )LnMe(AlMe4 )] with H2 NtBu gave dimethyl compounds [(Tp(tBu,Me) )LnMe2 ] as minor side products for the mid-sized metals yttrium and holmium and in high yield for the smaller lutetium. Preparative-scale amounts of complexes [(Tp(tBu,Me) )LnMe2 ] (Ln=Y, Ho, Lu) were made accessible through aluminate cleavage of [(Tp(tBu,Me) )LnMe(AlMe4 )] with N,N,N',N'-tetramethylethylenediamine (tmeda). The solid-state structures of [(Tp(tBu,Me) )HoMe(AlMe4 )] and [(Tp(tBu,Me) )HoMe2 ] were analyzed by XRD. PMID:25392940

Schädle, Dorothea; Maichle-Mössmer, Cäcilia; Schädle, Christoph; Anwander, Reiner

2015-01-01

184

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

185

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

186

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

187

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

189

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

190

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

2011-01-01

191

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

2012-06-01

192

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

193

Photophysical Studies of Bioconjugated Ruthenium Metal-Ligand Complexes Incorporated in Phospholipid Membrane Bilayers  

PubMed Central

Luminescent, mono-diimine, ruthenium complexes, [(H)Ru(CO)(PPh3)2(dcbpy)][PF6] (1, dcbpy = 4,4?-dicarboxy bipyridyl) and [(H)Ru(CO)(dppene)(5-amino-1,10-phen)][PF6] (2, dppene = bis diphenylphosphino-ethylene, phen = 9,10-phenanthroline), have been conjugated with 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE) and with cholesterol in the case of 2. Compound 1 gives the bis-lipid derivative [(H)Ru(CO)(PPh3)2(dcbpy-N-DPPE2)][PF6] (3), while 2 provides the mono-lipid 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)OChol)][PF6] (5, Chol = cholesteryl), using standard conjugation techniques. These compounds were characterized by spectroscopic methods, and their photophysical properties were measured in organic solvents. The luminescence of lipid conjugates 3 and is quenched in organic solvents while compound 4 a weak, short-lived, blue-shifted emission in solution. The cholesterol conjugate shows the long-lived, microsecond-timescale emission associated with triplet metal-to-ligand charge-transfer (3MLCT) excited states. Incorporation of conjugate 3 in lipid bilayer vesicles restores the luminescence, but with blue shifts (~80 nm) accompanied by nanosecond-timescale lifetimes. In the vesicles conjugate 4 shows a similar short-lived and blue-shifted emission 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”) 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 3 and 4. We have also conjugated the complex [Ru(bpy)2(5-amino-1,10-phenanthroline)][PF6]2 (8) with both cholesterol (9) and DPPE (10). Neither 9 nor the previously reported 10 exhibited the blue shifts observed for 3 and 4 when incorporated into LUVs. The anisotropies of the emissions of 3, 4 and 7 were also measured in LUVs and of 5 in both glycerol and LUVs. High fundamental anisotropies were observed for 3 and 4 and 7. PMID:24063694

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

2013-01-01

194

Removal of heavy metal species from industrial sludge with the aid of biodegradable iminodisuccinic acid as the chelating ligand.  

PubMed

High level of heavy metals in industrial sludge was the obstacle of sludge disposal and resource recycling. In this study, iminodisuccinic acid (IDS), a biodegradable chelating ligand, was used to remove heavy metals from industrial sludge generated from battery industry. The extraction of cadmium, copper, nickel, and zinc from battery sludge with aqueous solution of IDS was studied under various conditions. It was found that removal efficiency greatly depends on pH, chelating agent's concentration, as well as species distribution of metals. The results showed that mildly acidic and neutral systems were not beneficial to remove cadmium. About 68 % of cadmium in the sample was extracted at the molar ratio of IDS to heavy metals 7:1 without pH adjustment (pH 11.5). Copper of 91.3 % and nickel of 90.7 % could be removed by IDS (molar ratio, IDS: metals?=?1:1) with 1.2 % phosphoric acid effectively. Removal efficiency of zinc was very low throughout the experiment. Based on the experimental results, IDS could be a potentially useful chelant for heavy metal removal from battery industry sludge. PMID:25115899

Wu, Qing; Duan, Gaoqi; Cui, Yanrui; Sun, Jianhui

2015-01-01

195

Synthesis, spectroscopic studies and inhibitory activity against bactria and fungi of acyclic and macrocyclic transition metal complexes containing a triamine coumarine Schiff base ligand.  

PubMed

Two series of new mono and binuclear complexes with a Schiff base ligand derived from the condensation of 3-acetylcoumarine and diethylenetriamine, in the molar ratio 2:1 have been prepared. The ligand was characterized by elemental analysis, IR, UV-visible, (1)H-NMR and mass spectra. The reaction of the Schiff base ligand with cobalt(II), nickel(II), copper(II), zinc(II) and oxovanadium(IV) lead to mono or binuclear species of cyclic or macrocyclic complexes, depending on the mole ratio of metal to ligand and as well as on the method of preparation. The Schiff base ligand behaves as a cyclic bidentate, tetradendate or pentaentadentae ligand. The formation of macrocyclic complexes depends significantly on the dimension of the internal cavity, the rigidity of the macrocycles, the nature of its donor atoms and on the complexing properties of the anion involved in the coordination. Electronic spectra and magnetic moments of the complexes indicate that the geometries of the metal centers are either square pyramidal or octahedral for acyclic or macro-cyclic complexes. The structures are consistent with the IR, UV-visible, ESR, (1)H-NMR, mass spectra as well as conductivity and magnetic moment measurements. The Schiff base ligand and its metal complexes were tested against two pathogenic bacteria as Gram-positive and Gram-negative bacteria as well as one kind of fungi. Most of the complexes exhibit mild antibacterial and antifungal activities against these organisms. PMID:25681806

Abou-Hussein, A A; Linert, Wolfgang

2015-04-15

196

Combining NHC bis-phenolate ligands with oxophilic metal centers: a powerful approach for the development of robust and highly effective organometallic catalysts.  

PubMed

The present paper describes an overview of a novel family of tridentate NHC pincer ligand in which two phenoxide moieties are directly connected to the nitrogen atoms of a central N-heterocyclic carbene. It was envisioned that such a structure might be suitable for coordination to a variety of metal centers across the periodic table, including oxophilic metals. Various metal complexes bearing such ligand are indeed readily accessible in high yields via straightforward routes. Interestingly, a robust zirconium-NHC complex was found to polymerize rac-lactide in a highly controlled, living and stereoselective manner to afford heterotactic PLA. PMID:25437390

Bellemin-Laponnaz, Stéphane; Dagorne, Samuel; Dümpelmann, Ralf; Steffanut, Pascal

2014-01-01

197

Ligand(s)-to-metal charge transfer as a factor controlling the equilibrium constants of late first-row transition metal complexes: revealing the Irving-Williams thermodynamical series.  

PubMed

A unified relationship between the experimental formation constants and the ligand(s)-to-metal charge transfer values of versatile ligand complexes of late transition series first-row bivalent metal ions is uncovered. The latter property not only explicates the Irving-Williams series but also rationalizes quantitatively Pearson's concept of hard and soft acids and bases by correlating the gas-phase to aqueous solution-phase chemistry in a broad sense. PMID:25414118

Varadwaj, Pradeep R; Varadwaj, Arpita; Jin, Bih-Yaw

2015-01-14

198

Transition metal complexes of quadridentate pyrazolo-based ligands with two thiolato and two imine donor atoms  

Microsoft Academic Search

The copper(II), nickel(II) and cobalt(II) complexes of new S2N2 ligands on Schiff bases of 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-thione and various diamines were prepared and characterized. Using different diamines it is possible to control the geometry around the central metal atom. An X-ray structure determination of a Cu(II) S2N2 complex showed the (N?Cu?S, N?Cu?S) dihedral angle to be 52.11° and the following distances: Cu?S1

L. Hennig; R. Kirmse; O. Hammerich; S. Larsen; H. Frydendahl; H. Toftlund; J. Becher

1995-01-01

199

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

SciTech Connect

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

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

2012-12-13

200

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

201

(S)-5-(p-nitrobenzyl)-PCTA, a promising bifunctional ligand with advantageous metal ion complexation kinetics.  

PubMed

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(NO(2)-Bn-PCTA) (M = Mg(2+), Ca(2+), Cu(2+), Zn(2+)) complexes was similar to that of the corresponding PCTA complexes, while the stability of Ln(3+) complexes of the bifunctional ligand is somewhat lower than that of PCTA chelates. The rate of complex formation of Ln(NO(2)-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(NO(2)-Bn-PCTA) complexes showed that the kinetic inertness of the complexes was comparable to that of Ln(DOTA) chelates making the bifunctional ligand NO(2)-Bn-PCTA suitable for labeling biological vectors with radioisotopes for nuclear medicine applications. PMID:19220012

Tircsó, Gyula; Benyó, Eniko Tircsóné; Suh, Eul Hyun; Jurek, Paul; Kiefer, Garry E; Sherry, A Dean; Kovács, Zoltán

2009-03-18

202

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

PubMed

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

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

2012-04-27

203

Red electroluminescence of ruthenium sensitizer functionalized by sulfonate anchoring groups.  

PubMed

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

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

2014-06-28

204

"Long-range" metal-ligand cooperation in H2 activation and ammonia-promoted hydride transfer with a ruthenium-acridine pincer complex.  

PubMed

The acridine-based pincer complex 1 exhibits an unprecedented mode of metal-ligand cooperation involving a "long-range" interaction between the distal acridine C9 position and the metal center. Reaction of 1 with H(2)/KOH results in H(2) splitting between the Ru center and C9 with concomitant dearomatization of the acridine moiety. DFT calculations show that this process involves the formation of a Ru dihydride intermediate bearing a bent acridine ligand in which C9 is in close proximity to a hydride ligand followed by through-space hydride transfer. Ammonia induces transfer of a hydride from the Ru center of 1 to C9 of the flexible acridine pincer ligand, forming an unusual dearomatized fac-acridine PNP complex. PMID:20925343

Gunanathan, Chidambaram; Gnanaprakasam, Boopathy; Iron, Mark A; Shimon, Linda J W; Milstein, David

2010-10-27

205

DNA binding, anti-inflammatory and analgesic evaluation of metal complexes of N/S/O donor ligands; Synthesis, spectral characterization.  

PubMed

Transition metal complexes containing tri-dentate NSN donor ligands i.e., 5-((1(aminomethyl)cyclohexyl)methyl)-1,3,4-thiadiazol-2-amine (AMTA) (2) and 5-(2-aminophenyl)-1,3,4-thiadiazol-2-amine (ATA) (4i-ii) have been synthesized. The newly synthesized ligands and their respective complexes were characterized by elemental analysis, molar conductance measurement and various spectral studies [infrared (IR), electronic, and NMR (for ligands only)]. Metal complexes are like [M(AMTA)2], [M(ATA)2] type, where M=Mn(II), Co(II) and Cu(II). The proposed geometries of the complexes are octahedral in nature. The synthesized ligands and their complexes were exhibits effective anti-inflammatory, analgesic and DNA binding activities. All the tested compounds exhibited significant analgesic activity, whereas the compound 4i, 4(ia) and 4(iib) is equipotent with Diclofenac sodium. PMID:25666328

Kumar Naik, K H; Ashok, B; Naik, Nagaraja; Mulla, Jameel Ahmed S; Prakasha, Avinash

2015-04-15

206

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

207

Intraconfigurational transitions in tetrahedral d 2 ions: on the expediency of the ligand field model for transition metal ions in high-oxidations states  

Microsoft Academic Search

A ligand field analysis of intraconfigurational transitions in tetrahedral MnO43? and FeO43? is shown to give rather anomalous B values for the ground state configuration e2. A model taking explicit account of interactions between d2 (ionic) multiplets and singly excited (ligand to metal) charge transfer configurations is used to show that for low charge transfer energies each state of e2

M. Atanasov

1995-01-01

208

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

209

The design of new ligands and transition metal compounds for the oxidation of organic compounds  

E-print Network

..................................... 2 1.3 Epoxidation of ?,?-unsaturated carboxylic acids with catalytic sodium tungstate and hydrogen peroxide ........................................ 3 1.4 The Sharpless asymmetric epoxidation reaction.............................. 4 1....5 Salen ligands .................................................................................. 6 1.6 Jacobsen?s epoxidation catalyst, 1-3 ............................................... 7 1.7 Gilheany's epoxidation catalyst...

Grill, Joseph Michael

2009-06-02

210

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

SciTech Connect

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

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

2013-07-01

211

Cages with tetrahedron-like topology formed from the combination of cyclotricatechylene ligands with metal cations.  

PubMed

Cage the elephant: anionic tetrahedral assemblies, formed from the combination of cyclotricatechylene anions with transition metal ions, such as vanadium, contain large internal cavities that can act as hosts for alkali metal ions and solvent molecules. With appropriate metal centers, the anionic units can be linked together to form highly symmetric coordination polymers (V?blue, O?red, C?black). PMID:20229559

Abrahams, Brendan F; FitzGerald, Nicholas J; Robson, Richard

2010-04-01

212

Metal-ligand complexes as a new class of long-lived fluorophores for protein hydrodynamics and fluorescence polarization immunoassay  

NASA Astrophysics Data System (ADS)

We describe the use of asymmetric Ru-ligand complexes as a new class of luminescent probes. These complexes are known to display luminescent lifetimes ranging from 10 to 4000 ns. We show that the asymmetric complex Ru(bpy)2(dcbpy) (PF6)2 displays a high anisotropy value near 0.26 when excited in the long wavelength absorption band, and an intensity decay time near 400 ns. For covalent linkage to proteins, we synthesized the N- hydroxy succinimide ester. We measured the intensity and anisotropy decays of [Ru(bpy)2(dcbpy)] when covalently linked to proteins and in solutions of increasing viscosity. These data demonstrated that the probes can be used to measure rotational motions on the microsecond(s) timescale, which so far has been inaccessible using luminescence methods. We also used this probe in a fluorescence polarization immunoassay of HSA. We found that the steady-state polarization of labeled HSA was sensitive to binding of anti-HSA, resulting in a 200% increase in polarization. The labeled HSA was also used in a competitive format with unlabeled HSA as the antigen. The time-resolved anisotropy decays demonstrate increased correlation times for labeled HSA in the presence of anti-HSA, an effect which was partially reversed in the presence of unlabeled HSA. These results demonstrate the potential of the metal-ligand complexes to be used in the fluorescence polarization immunoassay of high molecular weight analytes. The use of such metal-ligand complexes enable fluorescence polarization immunoassays which bypass the usual limitation to low molecular weight antigens.

Lakowicz, Joseph R.; Terpetschnig, Ewald A.; Szmacinski, Henryk; Malak, Henryk M.

1995-05-01

213

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

PubMed Central

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

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

2010-01-01

214

Systematic ligand modulation enhances the moisture stability and gas sorption characteristics of quaternary metal-organic frameworks.  

PubMed

Complex metal-organic frameworks (MOFs) that maintain high structural order promise sophisticated and tunable properties. Here, we build on our strategy of using combinations of structurally distinct ligands to generate a new isoreticular series of ordered quaternary Zn4O-carboxylate MOFs. Rational design of the framework components steers the system toward multicomponent MOFs and away from competing phases during synthesis. Systematic ligand modulation led to the identification of a set of frameworks with unusually high stability toward water vapor. These frameworks lose no porosity after 100 days' exposure to ambient air or 20 adsorption-desorption cycles up to 70% relative humidity. Across this series of frameworks, a counterintuitive relationship between the length of pendant alkyl groups and framework stability toward water vapor emerges. This phenomenon was probed via a series of gas and vapor adsorption experiments together with Grand Canonical Monte Carlo (GCMC) simulations, and could be rationalized on the basis of the propensity of the frameworks to adsorb water vapor and the proximity of the adsorbed water molecules to the water-sensitive metal clusters. Systematic variation of the pore volume and topography also tunes the CO2 and CH4 gas adsorption behavior. Certain of these materials display increases in their adsorption capacities of 237% (CO2) and 172% (CH4) compared to the parent framework. PMID:25740632

Liu, Lujia; Telfer, Shane G

2015-03-25

215

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

PubMed

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

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

2013-06-26

216

Spectroscopic and biological studies of new mononuclear metal complexes of a bidentate NN and NO hydrazone-oxime ligand derived from egonol.  

PubMed

A novel ligand, vicinal dioxime ligand (egonol-hydrazone glyoxime) (LH2) was synthesized and characterized using (1)H NMR, (13)C NMR, MS, AAS, infrared spectroscopy, and magnetic susceptibility measurements. Mononuclear nickel (II), copper (II) and cobalt (II) complexes with a metal:ligand ratio of 1:2 for LH2 were also synthesized. Zn(II) forms complex [Zn(LH)Cl2] with a metal to ligand ratio of 1:1. IR spectrum shows that the ligand act in a bidentate manner and coordinates N4 donor groups of the ligands to Ni(II), Cu(II), Co(II) and Zn(II) ions. The detection of H-bonding (OH?O) in the [M(LH)2] metal complexes by IR spectra supported the square-planar MN4 coordination of Ni(II), Cu(II) and Co(II) complexes. The antimicrobial activities of compounds LH2 and their Ni(II), Cu(II), Co(II) and Zn(II) complexes were evaluated using the disc diffusion method against 16 bacteria and 5 yeasts. The minimal inhibitory concentrations (MICs) against all the bacteria and yeasts were also determined. Among the attempted test compounds, it is showed that all the compounds (L, LH2, [Ni(LH)2], [Cu(LH)2], [Co(LH)2(H2O)2], [Zn(LH)Cl2]) were effective against used test microorganisms. PMID:25686861

Babahan, Ilknur; Emirda?-Öztürk, Safiye; Poyrazo?lu-Çoban, Esin

2015-04-15

217

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

PubMed Central

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

Yernale, Nagesh Gunvanthrao; Bennikallu Hire Mathada, Mruthyunjayaswamy

2014-01-01

218

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

219

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

PubMed

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

Deeth, Robert J

2003-01-01

220

Synthesis, Characterization, and Theoretical Studies of Metal Complexes Derived from the Chiral Tripyridyldiamine Ligand Bn-CDPy3  

PubMed Central

Synthesis and characterization of metal complexes of the chiral tripyridyldiamine ligand Bn-CDPy3 (1), derived from trans-1,2-diaminocyclohexane, are described, along with theoretical studies that support the experimental data. These studies confirm that a single coordination geometry, out of five possible, is favored for octahedral complexes of the type [M(Bn-CDPy3)Cl], where M equals Co(III), Fe(II), and Zn(II). A combination of X-ray crystallographic and NMR spectroscopic methods was used to define the structures of the complexes [Co(Bn-CDPy3)Cl]Cl2 (5), [Fe(Bn-CDPy3)Cl]X (X = FeCl4, Cl, ClO4, 6–8), and [Zn(Bn-CDPy3)Cl]2ZnCl4 (9) in the solid state and in solution. Experimental and theoretical data indicate that the most stable coordination geometry for all complexes possesses the Cl group trans to a basic amine donor and three pyridyl donors adopting the mer geometry, with two pyridyl N-donors adopting a coplanar geometry with respect to the M–Cl bond and the third pyridyl donor perpendicular to that axis. Calculations indicate that the ability to favor a single geometry is born from the chiral ligand, which prefers to be in a single conformation in metal complexes due to steric interactions and electronic factors. Calculated structures of the complexes were used to locate key interactions among the various diastereomeric complexes that are proposed to create an energetic preference for the coordination geometry observed in the metal complexes of 1. PMID:20459127

Abouelatta, Ahmed I.; Sonk, Jason A.; Hammoud, Mirvat M.; Zurcher, Danielle M.; McKamie, Joshua J.; Schlegel, H. Bernhard; Kodanko, Jeremy J.

2015-01-01

221

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

SciTech Connect

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

Paine, R.T.

1997-12-01

222

Syntheses, crystal structures, and optical properties of five metal complexes constructed from a V-shaped thiophene-containing ligand and different dicarboxylate ligands.  

PubMed

Five new metal complexes, {[Ni(DIDP)(m-bdc)(H2O)]·5H2O}n (1), {[Zn(DIDP)(hfipbb)]·2DMA}n (2), {[Zn(DIDP)(4,4'-sdb)]·H2O}n (3), {[Co(DIDP)(p-bdc)]}n (4), and {[Co2(DIDP)(hfipbb)2]·H2O}n (5), have been synthesized by reactions of the corresponding metal ions with a V-shaped ligand 2,8-di(1H-imidazol-1-yl)dibenzothiophene (DIDP) and different aromatic dicarboxylic acids, namely isophthalic acid (m-H2bdc), terephthalic acid (p-H2bdc), 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (H2hfipbb), and 4,4'-sulfonyldicarboxylic acid (4,4'-H2sdb), respectively. The structures of the complexes were determined by X-ray single-crystal diffraction. Complex 1 is a 1D chain structure containing a one-dimensional channel along the a direction and is further extended via O-H···S hydrogen bonds and C-H···? stacking interactions into a 3D framework. Complex 2 exhibits a quasi 2D + 2D ? 2D with parallel polycatenation of 2D (4, 4) nets. Complex 3 displays an unusual 2D + 2D ? 3D parallel polycatenated framework based on a 2D 6(3)-hcb network. Complex 4 shows a 2D 4-connected {4(4)·6(2)}-sql network containing a one-dimensional channel along the b direction. The adjacent 2D networks are further extended via C-H···O hydrogen bonds into a 3D supramolecular framework. Complex 5 features a 2-fold interpenetrating 3D framework with a 6-connected {4(12)·6(3)} pcu topology. Furthermore, the thermal stability for 1-5 and luminescence properties of 2 and 3 have been studied. Moreover, the solid-state UV-visible spectroscopy experiments show that complexes 1-5 are all optical semiconductors with band gaps of 3.06, 3.18, 3.23, 2.98, and 3.17 eV, respectively. PMID:25050987

Shi, Zhi-Qiang; Guo, Zi-Jian; Zheng, He-Gen

2014-09-21

223

Study of the ligands involved in metal binding to alfalfa biomass  

SciTech Connect

Previously performed studies have shown that the alfalfa shoot biomass can bind an appreciable amount of copper(II), nickel(II), cadmium(II), chromium(III), lead(II), and zinc(II) ions from aqueous solution. Of the seven different alfalfa populations studied, Malone and African demonstrated the highest capacity for metal binding. Laboratory experiments were performed to determine the pH profiles, time dependency, capacity for metal binding, as well as the recovery of the metals bound. For most of the metal ions studied, the biomass showed a high affinity for metal binding around pH 5.0 within a short time period. Binding capacity experiments revealed the following amounts of metal ions bound per gram of biomass: 19.7 mg Cu(II), 4.11 mg Ni(II), 7.1 mg Cd(II), 7.7 mg Cr(III), 43 mg Pb(II), and 4.9 mg Zn(II). Most of these metals were recovered from the biomass by treatment with 0.1 M HCl with the exception of Cr(III). Because no Cr(VI) binding occurred, none was recovered. Direct and indirect approaches were applied to study the possible mechanisms involved in metal binding by the alfalfa biomass. The direct approach involves investigations of the alfalfa shoot biomass by X-ray absorption spectroscopy analysis (XANES and EXAFS), which were performed at Brookhaven National Laboratory.

Tiemann, K.J.; Gardea-Torresdey, J.L.; Sias, S.; Gamez, G.; Rodriguez, O. [Univ. of Texas, El Paso, TX (United States). Dept. of Chemistry; Renner, M.W.; Furenlid, L.R. [Brookhaven National Lab., Upton, NY (United States)

1997-12-31

224

High current density electrodeposition of silver from silver-containing liquid metal salts with pyridine-N-oxide ligands.  

PubMed

New cationic silver-containing ionic liquids were synthesized and used as non-aqueous electrolytes for the electrodeposition of silver layers. In the liquid state of these ionic liquids, a silver (i) cation is coordinated by pyridine-N-oxide (py-O) ligands in a 1?:?3 metal-to-ligand ratio, although in some cases a different stoichiometry of the silver center crystallized out. As anions, bis(trifluoromethanesulfonyl)imide (Tf2N), trifluoromethanesulfonate (OTf), methanesulfonate (OMs) and nitrate were used, yielding compounds with the formulae [Ag(py-O)3][Tf2N], [Ag(py-O)3][OTf], [Ag(py-O)3][OMs] and [Ag(py-O)3][NO3], respectively. The compounds were characterized by CHN analysis, FTIR, NMR, DSC, TGA and the electrodeposition of silver was investigated by cyclic voltammetry, linear potential scans, scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). With the exception of [Ag(py-O)3][Tf2N], which melts at 108 °C, all the silver(i) compounds have a melting point below 80 °C and were tested as electrolytes for silver electrodeposition. Interestingly, very high current densities were observed at a potential of -0.5 V vs. Ag/Ag(+) for the compounds with fluorine-free anions, i.e. [Ag(py-O)3][NO3] (current density of -10 A dm(-2)) and [Ag(py-O)3][OMs] (-6.5 A dm(-2)). The maximum current density of the compound with the fluorinated anion trifluoromethanesulfonate, [Ag(py-O)3][OTf], was much lower: -2.5 A dm(-2) at -0.5 V vs. Ag/Ag(+). Addition of an excess of ligand to [Ag(py-O)3][OTf] resulted in the formation of the room-temperature ionic liquid [Ag(py-O)6][OTf]. A current density of -5 A dm(-2) was observed at -0.5 V vs. Ag/Ag(+) for this low viscous silver salt. The crystal structures of several silver complexes could be determined by X-ray diffraction, and it was found that several of them had a stoichiometry different from the 1?:?3 metal-to-ligand ratio used in their synthesis. This indicates that the compounds form crystals with a composition different from that of the molten state. The electrochemical properties were measured in the liquid state, where the metal-to-ligand ratio was 1?:?3. Single crystal X-ray diffraction measurements showed that silver(i) is six coordinate in [Ag(py-O)3][Tf2N] and [Ag(py-O)3][OTf], while it is five coordinate in the other complexes. In [Ag3(py-O)8][OTf]3, there are two different coordination environments for silver ions: six coordinate central silver ions and five coordinate for the outer silver ions. In some of the silver(i) complexes, silver-silver interactions were observed in the solid state. PMID:24217798

Sniekers, Jeroen; Brooks, Neil R; Schaltin, Stijn; Van Meervelt, Luc; Fransaer, Jan; Binnemans, Koen

2014-01-28

225

Effective removal of heavy metals from industrial sludge with the aid of a biodegradable chelating ligand GLDA.  

PubMed

Tetrasodium of N,N-bis(carboxymethyl) glutamic acid (GLDA), a novel readily biodegradable chelating ligand, was employed for the first time to remove heavy metals from industrial sludge generated from a local battery company. The extraction of cadmium, nickel, copper, and zinc from battery sludge with the presence of GLDA was studied under different experimental conditions such as contact times, pH values, as well as GLDA concentrations. Species distribution of metals in the sludge sample before and after extraction with GLDA was also analyzed. Current investigation showed that (i) GLDA was effective for Cd extraction from sludge samples under various conditions. (ii) About 89% cadmium, 82% nickel and 84% copper content could be effectively extracted at the molar ratio of GLDA:M(II)=3:1 and at pH=4, whereas the removal efficiency of zinc was quite low throughout the experiment. (iii) A variety of parameters, such as contact time, pH values, the concentration of chelating agent, stability constant, as well as species distribution of metals could affect the chelating properties of GLDA. PMID:25464318

Wu, Qing; Cui, Yanrui; Li, Qilu; Sun, Jianhui

2015-02-11

226

Reactivity of Transition-Metal Borylene Complexes: Recent Advances in B-C and B-B Bond Formation via Borylene Ligand Coupling.  

PubMed

Terminal borylene complexes of group 6-10 metals have been prepared through a number of synthetic strategies, displaying a wide structural diversity with numerous coordination modes of the borylene ligand [:BR]. Earlier, amino-substituted borylenes were found to serve as borylene ligand transfer reagents to a range of organic and organometallic substrates. In contrast, aryl- and alkyl-substituted borylenes display metathesis behavior when combined with ketones. Recent studies on these complexes revealed new reactivity patterns involving borylene-borylene and carbonyl-borylene ligand coupling. Herein a brief account on the recent progress of these borylene ligand coupling reactions made in our laboratories is provided. These reactions offer unprecedented alternative methods for electron-precise B-B and B-C bond formation. PMID:25760461

Braunschweig, Holger; Shang, Rong

2015-04-01

227

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

PubMed

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

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

2014-08-01

228

Metal-assisted synthesis of unsymmetrical magnolol and honokiol analogs and their biological assessment as GABAA receptor ligands  

PubMed Central

We present the synthesis of new derivatives of natural products magnolol (1) and honokiol (2) and their evaluation as allosteric ligands for modulation of GABAA receptor activity. New derivatives were prepared via metal assisted cross-coupling reactions in two consecutive steps. Compounds were tested by means of two-electrode voltage clamp electrophysiology at the ?1?2?2 receptor subtype at low GABA concentrations. We have identified several compounds enhancing GABA induced current (IGABA) in the range similar or even higher than the lead structures. At 3 ?M, compound 8g enhanced IGABA by factor of 443, compared to 162 and 338 of honokiol and magnolol, respectively. Furthermore, 8g at EC10–20 features a much bigger window of separation between the ?1?2?2 and the ?1?1?2 subtypes compared to honokiol, and thus improved subtype selectivity. PMID:25510374

Rycek, Lukas; Puthenkalam, Roshan; Schnürch, Michael; Ernst, Margot; Mihovilovic, Marko D.

2015-01-01

229

Zwitterionic late transition metal alkene polymerisation catalysts containing aminofulvene-aldiminate (AFA) ligands   

E-print Network

Over recent years significant progress has been made in the design and development of late transition metal cationic catalysts for olefin polymerisation. Never-the-less, the activation of catalyst precursors and generation ...

Rahman, Mohammed Mahmudur

2010-01-01

230

Lewis acidic metal complexes with polydentate ligands for the preparation of biorenewable polymers   

E-print Network

Due to the ever increasing necessity to reduce our dependence on fossil fuels as feedstocks for polymeric materials, the work presented herein describes the investigation of new metal complexes as initiators for the ...

Gamboa Martinez, Sergio Aaron; Gamboa, Sergio Aaron M.; Martinez, Sergio Aaron Gamboa

2014-06-28

231

Metal-to-ligand alkyl migration inducing carbon-sulfur bond cleavage in dialkyl yttrium complexes supported by thiazole-containing amidopyridinate ligands: synthesis, characterization, and catalytic activity in the intramolecular hydroamination reaction.  

PubMed

Neutral Y(III) dialkyl complexes supported by tridentate N(-) ,N,N monoanionic methylthiazole- or benzothiazole-amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole-containing system through an unprecedented metal-to-ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N(-) ,N,N(-) ,S(-) ligand as the result of metal-to-ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual Y?H group to the imino fragment of a second equivalent of the ring-opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph3 C(+) [B(C6 F5 )4 ](-) , were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed. PMID:24616174

Lyubov, Dmitry M; Luconi, Lapo; Rossin, Andrea; Tuci, Giulia; Cherkasov, Anton V; Fukin, Georgy K; Giambastiani, Giuliano; Trifonov, Alexander A

2014-03-17

232

Group 13 ligand supported heavy-metal complexes: first structural evidence for gallium-lead and gallium-mercury bonds.  

PubMed

Heavy-metal complexes of lead and mercury stabilized by Group 13 ligands were derived from the oxidative addition of Ga(ddp) (ddp=HC(CMeNC(6)H(3)-2,6-iPr(2))(2), 2-diisopropylphenylamino-4-diisopropyl phenylimino-2-pentene) with corresponding metal precursors. The reaction of Me(3)PbCl and Ga(ddp) afforded compound [{(ddp)Ga(Cl)}PbMe(3)] (1) composed of Ga-Pb(IV) bonds. In addition, the monomeric plumbylene-type compound [{(ddp)Ga(OSO(2)CF(3))}(2)Pb(thf)] (2a) with an unsupported Ga-Pb(II)-Ga linkage was obtained by the reaction of [Pb(OSO(2)CF(3))(3)] with Ga(ddp) (2 equiv). Compound 2a falls under the rare example of a discrete plumbylene-type compound supported by a nonclassical ligand. Interesting structural changes were observed when [Pb(OSO(2)CF(3))(3)]2.H(2)O was treated with Ga(ddp) in a 1:2 ratio to yield [{(ddp)Ga(mu-OSO(2)CF(3))}(2)(OH(2))Pb] (2b) at below -10 degrees C. Compound 2b consists of a bent Ga-Pb-Ga backbone with a bridging triflate group between the Ga-Pb bond and a weakly interacting water molecule at the gallium center. Similarly, the reaction of mercury thiolate Hg(SC(6)F(5)) with Ga(ddp) (2 equiv) produced the bimetallic homoleptic compounds anti-[{(ddp)Ga(SC(6)F(5))}(2)Hg] (3a) and gauche-[{(ddp)Ga(SC(6)F(5))}(2)Hg] (3b), respectively, with a linear Ga-Hg-Ga linkage. Compounds 1-3 were structurally characterized and these are the first examples of compounds comprised of Ga-Pb(II), Ga-Pb(IV), and Ga-Hg bonds. PMID:20391574

Prabusankar, Ganesan; Gemel, Christian; Winter, Manuela; Seidel, Rüdiger W; Fischer, Roland A

2010-05-25

233

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

234

A new mode of activation of CO2 by metal-ligand cooperation with reversible C-C and M-O bond formation at ambient temperature.  

PubMed

Team work: Although CO(2) binding to metal centers usually involves ? coordination to a C=O group or ? bonds to the carbon or oxygen atom of the CO(2) molecule, a new mode of metal-ligand cooperative activation of CO(2) to a ruthenium PNP pincer complex involving aromatization/dearomatization steps is presented in experimental and theoretical studies (see scheme). PMID:22736579

Vogt, Matthias; Gargir, Moti; Iron, Mark A; Diskin-Posner, Yael; Ben-David, Yehoshoa; Milstein, David

2012-07-23

235

Structural diversity in the self-assembly of various macrocyclic metallic tectons and 4,4?-biphenyldicarboxylic acid ligand  

NASA Astrophysics Data System (ADS)

Five new nickel(II) coordination complexes based on macrocyclic metallic tectons and 4,4?-biphenyldicarboxylic acid ligand, namely, [(NiL1)2(4,4?-bpdc)(CH3CN)2]?(ClO4)2?2CH3CN (1), {[(NiL1)(4,4?-bpdc)]?DMF?4H2O}n (2) and [(NiL1)2(4,4?-bpdc)(H2O)2][(NiL1)2(4,4?-bpdc)3]?14H2O (3), {(NiL2)(4,4?-bpdc)}n (4) and {[(NiL3)(4,4?-bpdc)]?8H2O}n (5) (L1 = 1,3,6,8,12,15-hexaazatricycloeicosane, L2 = 1,3,6,9,11,14-hexaazatricyclooctadecane and L3 = 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradeca) have been synthesized and characterized by single-crystal X-ray diffraction. Each nickel(II) atom in complex 1 shows a [NiN5O] octahedral coordination geometry, where four nitrogen atoms from the hexaazamacrocycle ligand, one nitrogen atom from acetonitrile and one oxygen atom from the 4,4?-biphenyldicarboxylic acid ligand. However, all nickel(II) atoms in complexes 2-5 are six-coordinated with four nitrogen atoms from the hexaazamacrocycle ligand and two oxygen atoms from the 4,4?-biphenyldicarboxylic acid, resulting a [NiN4O2] octahedral coordination geometry. Complex 1 possesses an extended framework structure based on a discrete 0D fragment. Complex 2 contains a 3D supramolecular structure based on two 1D chains arraying uniformly in an ABAB manner. Hydrogen-bonded 1D chains in complex 3 rise to 3D frameworks with ABCABC fashion. Complex 4 features rare plywood structure based on 1D chain. Complex 5 has a 3D framework structure bearing 1D water hexamers chains. In addition, the solid states UV-Vis for complexes 1-5 have been investigated.

Yan, Ge; Zhou, Gangxiang; Yu, Xiaoli; Jiang, Xiang; Xia, Hua

2014-09-01

236

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

PubMed Central

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

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

2013-01-01

237

Arthroscopic Lateral Meniscus Root Repair With Soft Suture Anchor Technique  

PubMed Central

Meniscus root tear leads to circumferential hoop tension loss and increases femorotibial contact force, which causes irreversible cartilage degeneration. Biomechanical studies have shown that meniscus root repair provides better femorotibial contact force than meniscectomy. Many techniques for meniscus root repair have been published in recent years. The soft suture anchor is widely used in the glenoid labral repair. It is a small low-profile soft anchor. This article presents a new and simple technique of lateral meniscus root repair using the small soft anchor, which results in an anatomic and more vertical anchor position. It avoids instrument-related complications, such as cartilage delamination, material reaction, metal retention, and hard suture anchor pullout. PMID:24892012

Prasathaporn, Niti; Kuptniratsaikul, Somsak; Kongrukgreatiyos, Kitiphong

2013-01-01

238

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

239

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.

Cindy Corlett

2003-03-01

240

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

SciTech Connect

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

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

1999-03-01

241

A new nanomaterial synthesized from size-selected, ligand-free metal clusters  

NASA Astrophysics Data System (ADS)

Thins films are synthesized by deposition of size-selected Mon- cluster anions on an inert substrate. Scanning tunneling microscopy pictures indicate that the deposited material consists of individual particles with diameters corresponding to the size of the preformed clusters from the gas phase. Previous attempts to manufacture cluster materials from metals failed since these clusters coalesced at room temperature. Our data suggest the possibility to synthesize new nanomaterials from clusters of high fusing metals. This may prove to be the key to harness size-dependent and tuneable properties of clusters for creating novel classes of functional tailor-made materials.

Li, X.; Wepasnick, K.; Tang, X.; Fairbrother, D. H.; Bowen, K. H.; Dollinger, A.; Strobel, C. H.; Huber, J.; Mangler, T.; Luo, Y.; Proch, S.; Gantefoer, G.

2014-03-01

242

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

PubMed

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

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

2014-03-14

243

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

244

Photophysical characterization of fluorescent metal nanoclusters synthesized using oligonucleotides, proteins and small molecule ligands  

NASA Astrophysics Data System (ADS)

The size transition from bulk conducting metals to insulating nanoparticles and eventually to single atoms passes through the relatively unexplored few-atom nanocluster region. With dimensions close to the Fermi wavelength, these nanoclusters demonstrate molecule-like properties distinct from bulk metals or atoms, such as discrete and size-tunable electronic transitions which lead to photoluminescence. Current research aims to elucidate the fundamental photophysical properties of metal nanoclusters made by different means and based on different encapsulation agents. Here, we report the study of the photophysical properties, including quantum yields, lifetimes, extinction coefficients, blinking dynamics and sizes, of silver and gold nanoclusters synthesized using oligonucleotides, a protein (bovine serum albumin) and a Good's buffer molecule (MES, 2-(N-morpholino) ethanesulfonic acid) as encapsulation agents. We also investigate the change of photoluminescence as a function of temperature. Furthermore, we show that the fluorescent metal clusters can be used as a donor in forming a resonance energy transfer pair with a commercial organic quencher. These new fluorophores have great potential as versatile tools for a broad range of applications in biological and chemical detection.

Yeh, Hsin-Chih; Sharma, Jaswinder; Yoo, Hyojong; Martinez, Jennifer S.; Werner, James H.

2010-02-01

245

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...

246

Reaction under ball-milling: solvent-, ligand-, and metal-free synthesis of unsymmetrical diaryl chalcogenides.  

PubMed

A convenient, efficient, and general procedure for the synthesis of diaryl chalcogenides including sulfides, selenides and tellurides has been developed by the reaction of diazonium tetrafluoroborates and diaryl dichalcogenides on the surface of alumina under ball-milling without any solvent or metal. A wide range of functionalized diaryl chalcogenides are obtained in high purity by this procedure. PMID:24116379

Mukherjee, Nirmalya; Chatterjee, Tanmay; Ranu, Brindaban C

2013-11-01

247

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

248

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

249

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

250

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

251

Enhanced association for C70 over C60 with a metal complex with corannulene derivate ligands.  

PubMed

The geometry imposed by the coordination sphere around the metal, together with the choice of the "arms" can be advantageously used to build corannulene-based molecular tweezers, which show great affinities for C60 and C70, as revealed by NMR titration experiments, mass spectroscopy, DFT calculations and the single crystal X-ray structural analysis of the compound C60 ?1. PMID:25181755

Álvarez, Celedonio M; García-Escudero, Luis A; García-Rodríguez, Raúl; Martín-Álvarez, Jose M; Miguel, Daniel; Rayón, Víctor M

2014-11-14

252

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

Microsoft Academic Search

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

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

2008-01-01

253

Synthesis, spectroscopic characterization, electrochemistry and biological evaluation of some metal (II) complexes with ONO donor ligand containing benzo[b]thiophene and coumarin moieties  

NASA Astrophysics Data System (ADS)

Schiff base ligand 3-chloro-N?-((7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)benzo[b]thiophene-2-carbohydrazide and its Cu(II), Co(II), Ni(II) and Zn(II) complexes were synthesized, characterized by elemental analysis and various physico-chemical techniques like, IR, 1H NMR, ESI-mass, UV-Visible, thermogravimetry - differential thermal analysis, magnetic measurements and molar conductance. Spectral analysis indicates octahedral geometry for all the complexes. Cu(II) complex have 1:1 stoichiometry of the type [M(L)(Cl)(H2O)2], whereas Co(II), Ni(II) and Zn(II) complexes have 1:2 stoichiometric ratio of the type [M(L)2]. The bonding sites are the oxygen atom of amide carbonyl, nitrogen of azomethine function and phenolic oxygen of the Schiff base ligand via deprotonation. The thermogravimetry - differential thermal analysis studies gave evidence for the presence of coordinated water molecules in the composition of Cu(II) complex which was further supported by IR measurements. All the complexes were investigated for their electrochemical activity, but only the Cu(II) complex showed the redox property. In order to evaluate the effect of antimicrobial potency of metal ions upon chelation, ligand and its metal complexes along with their respective metal chlorides were screened for their antibacterial and antifungal activities by minimum inhibitory concentration (MIC) method. The results showed that the metal complexes were found to be more active than free ligand. Ligand and its complexes were screened for free radical scavenging activity by DPPH method and DNA cleavage activity using Calf-thymus DNA (Cat. No-105850).

Mahendra Raj, K.; Mruthyunjayaswamy, B. H. M.

2014-09-01

254

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

255

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

256

Design of a humidity-stable metal-organic framework using a phosphonate monoester ligand.  

PubMed

Phosphonate monoesters are atypical linkers for metal-organic frameworks, but they offer potentially added versatility. In this work, a bulky isopropyl ester is used to direct the topology of a copper(II) network from a dense to an open framework, CALF-30. CALF-30 shows no adsorption of N2 or CH4 however, using CO2 sorption, CALF-30 was found to have a Langmuir surface area of over 300 m(2)/g and to be stable to conditions of 90% relative humidity at 353 K owing to kinetic shielding of the framework by the phosphonate ester. PMID:25646642

Gelfand, Benjamin S; Lin, Jian-Bin; Shimizu, George K H

2015-02-16

257

C60 fullerene as an ?6 ligand in ? complexes of transition metals  

NASA Astrophysics Data System (ADS)

The possible existence of complexes formed by the C60 fullerene or its derivatives with transition metals interacting with the carbon cage via ?6-? type bonding is discussed. The derivatives C60 R 6 of the C60 fullerene ( R = -, H, F, Cl, Br, CN) are analyzed using the density functional method within the Perdew-Burke-Ernzerhof approximation. In these molecules, the R groups are attached to carbon atoms located in the ? positions with respect to the common hexagon of the C60 fullerene. The structure and electron configuration of complexes formed by these molecules with Cr(C6H6), Cr(CO)3, MoC6H6, and Mo(CO)3 particles are modeled. The “dimer” systems C60R6- M- R 6C60 ( M = Cr, Mo, R =-, H, F) are investigated in which two fullerene molecules interact via a transition-metal atom. It is found that the introduction of six R groups in the ? sites with respect to the common hexagon of C60 favors the formation of complexes of these derivatives of the C60 fullerene with the Cr(C6H6), Cr(CO), Mo(C6H6), and Mo(CO)3 particles in which ?6-? type bonds arise between the metal and the atoms of the hexagon fringed with the R groups. It is also demonstrated that analogous complexes with a “bare” C60 fullerene are possible, but they are significantly less stable. The (C6H6) M- R 6C60 R 6- M (C6H6) complexes of particles M(C6H6) ( M= Cr, Mo) and derivatives R 6C60 R 6 ( R =-, H, F, Cl, Br) are studied. In the R 6C60 R 6 molecule, six R groups are located in the ? sites with respect to the common hexagon of the C60 fullerene and six other groups fringe the opposite hexagon. The obtained results can be applied to planning synthesis of new complexes that C60 fullerene derivatives can form with transition metals.

Gal'Pern, E. G.; Sabirov, A. R.; Stankevich, I. V.

2007-12-01

258

System with potential dual modes of metal-ligand cooperation: highly catalytically active pyridine-based PNNH-Ru pincer complexes.  

PubMed

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

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

2014-11-24

259

Solution pH effects on arsenic removal by drinking water treatment residuals in presence of metals and ligands  

NASA Astrophysics Data System (ADS)

Arsenic (As) is a Group A carcinogen whose presence in soils in higher than background concentrations has become a serious concern with increasing suburban encroachment on former agricultural lands. One of the most promising methods to decrease the mobility of As in soil and water environments is by promoting its adsorption onto amorphous Fe/Al hydroxides. Drinking water treatment residuals (WTRs) are cost-effective sources of such Fe/Al hydroxides, and generated during the drinking water treatment process as a byproduct. Preliminary work in our laboratory showed that the WTRs are characterized by large specific surface and a net positive charge, ideal for retention of oxyanions such as those of As. However, the overall magnitude of As retention by the WTRs is a function of solution factors such as pH, presence of competing ions and complexing metals. A comprehensive understanding of the aforementioned parameters is, therefore, needed to quantify As mobility and bioaccessibility. The primary objective of the studying progress is to determine the effect of solution pH (range: 3-10) on the amount of As sorbed by the WTRs in the presence of competing ligands such as phosphate, sulfate and silicate as well as complexing metals (e.g., calcium and lead). Experiments are being conducted at 3 solid/solution ratios- 1:5, 1:10 and 1:20 and four initial As loads (375, 750, 1500 and 3000 mgAs L-1). Sodium arsenate is used as the As source. Arsenate adsorption is expected to decrease with increasing pH because generally when solution pH is less than pH of the zero point of charge, the positively charged surface on the soil prefers to complex with the negatively charged arsenate oxyanions. Furthermore, phosphate, sulfate and silicate are expected to compete with arsenate for sorption sites because like arsenate, these ions are typically sorbed via formation of inner-sphere complexes with suface functional groups. On the other hand, the presence of metals like lead and calcium are expected to decrease As mobility due to their tendency to complex with As oxyanions, thereby promoting precipitation when the ion activity product (IAP) is equal to or higher then the solubility equilibrium constant (Ksp) of the respective mineral precipitate. Keywords: Adsorption, arsenic, water treatment residuals, oxyanions, complexing metals, competing ions.

Nagar, R.; Sarkar, D.; Datta, R.; Makris, K.

2006-05-01

260

Group 12 metal complexes of tetradentate N 2O 2–Schiff-base ligands incorporating pyrazole  

Microsoft Academic Search

New [M(Q)2(X)] derivatives (where M=Zn, Cd or Hg; Q=1-phenyl-3-methyl-4-R(C=O)-pyrazolon-5-ato; in detail: QL, R=C6H5; QB, R=CH2C(CH3)3; QS, R=CH(C6H5)2; X=EtOH or H2O) have been synthesised and characterised. These compounds undergo a condensation reaction with the appropriate diamine in ethanol, affording novel Schiff-base metal derivatives [M(diaquo)bis(1-phenyl-3methyl-4-R(C=N)-pyrazolone)(CH2)ndiimmine] (LnH2, R=C6H5, n=2, 3 or 4; BnH2, R=CH2C(CH3)3, n=2, 3 or 4; SnH2, R=CH(C6H5)2, n=2 or 3;

Fabio Marchetti; Claudio Pettinari; Riccardo Pettinari; Augusto Cingolani; Dante Leonesi; Adriana Lorenzotti

1999-01-01

261

Dual Anchoring of the GRASP Membrane Tether Promotes trans Pairing*  

PubMed Central

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

Bachert, Collin; Linstedt, Adam D.

2010-01-01

262

Carbon dioxide adsorption in amine-functionalized mixed-ligand metal-organic frameworks of UiO-66 topology.  

PubMed

A series of mixed-ligand [1,4-benzenedicarboxylic acid (BDC)/2-amino-1,4-benzenedicarboxylic acid (ABDC)] UiO-66 metal-organic frameworks (MOFs) synthesized through two different methods (low (LT) and high temperature (HT)) have been investigated for their carbon dioxide adsorption properties from 0 to 1?bar to clarify the role of amino loading on carbon dioxide uptake. Volumetric CO2 isotherms show that the CO2 capacity (normalized to the Langmuir surface area) increases with a degree of functionalization of about 46%; for similar NH2 contents, the same values are found for both synthetic procedures. Microcalorimetric isotherms reveal that amino-functionalized materials have a larger differential heat of adsorption (q(diff) ) towards CO2 ; reaching 27(25) and 20(22)?kJ?mol(-1) on HT(LT)-UiO-66-NH2 and UiO-66, respectively, at the lowest equilibrium pressures used in this study. All experimental results are supported by values obtained through quantum mechanical calculations. PMID:25302675

Ethiraj, Jayashree; Albanese, Elisa; Civalleri, Bartolomeo; Vitillo, Jenny G; Bonino, Francesca; Chavan, Sachin; Shearer, Greig C; Lillerud, Karl Petter; Bordiga, Silvia

2014-12-01

263

Syntheses, structures and properties of three metal-organic complexes containing 2,2?-dipyridyl-5,5?-dicarboxylate ligands  

NASA Astrophysics Data System (ADS)

Three new metal-organic complexes Cu[Hbpdc]2 (1), [Ni(bpdc)(H2O)]·H2O (2) and [Ni(H2bpdc)(H2O)2]SO4 (3) (H2bpdc=2,2?-bipyridyl-5,5?-dicarboxylic acid) have been hydrothermally prepared and structurally characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. 1 is a 3-D supramolecular architecture formed by hydrogen bonding interactions between carboxyl O atoms and strong face-to-face ?⋯? stacking interactions between bipyridyl rings of Hbpdc- ligands, 2 exhibits an intriguing 2-D sheet constructed from [Ni(bpdc)(H2O)] units and 3 displays an infinite 1-D chain built by {[Ni(H2bpdc)(H2O)2]2+} fragments through SO42-. Moreover, thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses of 3 have been conducted and the TG curve shows two-stage weight loss between 300 and 950 K and the corresponding apparent activation energies are calculated by Ozawa-Flynn-Wall (OFW) method and Friedman method. The most probable kinetic model function of the dehydration reaction of 3 has been estimated by Coats-Redfern integral method and Achar-Bridly-Sharp differential method.

Liu, Jiancai; Zhang, Yudong; Shang, Sensen; Li, Yanzhou; Chen, Lijuan; Zhao, Junwei

2015-01-01

264

Chromatographic behaviour of trace metal ions on a strong base anion exchange resin functionalized by azo ligands.  

PubMed

A model which allows the evaluation of the elution volume V(E) and the central point V(C) of the breakthrough curve of a metal ion at trace level on a chromatographic column containing a chelating resin is presented. V(E) and V(C) mainly depend on the complexation properties of the active groups, and on the acidity and composition of the aqueous solution, according to the Gibbs-Donnan model for the resin. The model has been tested in the case of strong base anion exchange resins in chloride form functionalized with two different sulphonated azo ligands (T-azo-C, T-azo-R). The chromatographic behaviour of copper(II) and thorium(IV) is as expected from the formation of a complex with the azo dye in the resin, while that of zinc(II) and cadmium(II) is fully described by also taking into account the formation of anionic chloro complexes inside the resin. PMID:18966122

Pesavento, M; Profumo, A; Sastre, A

1994-10-01

265

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

PubMed

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

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

2011-04-01

266

New isostructural transition metal complexes with a non-innocent dithiolate ligand.  

PubMed

Three new complexes with 3,6-dichlorobenzene-1,2-dithiol (bdtCl2), namely methyltriphenylphosphonium bis(3,6-dichlorobenzene-1,2-dithiolato-?(2)S,S')cobaltate(1-), (C19H18P)[Co(C6H2Cl2S2)2], (I), bis(methyltriphenylphosphonium) bis(3,6-dichlorobenzene-1,2-dithiolato-?(2)S,S')cuprate(2-) dimethyl sulfoxide disolvate, (C19H18P)2[Cu(C6H2Cl2S2)2]·2C2H6OS, (II), and methyltriphenylphosphonium bis(3,6-dichlorobenzene-1,2-dithiolato-?(2)S,S')cuprate(1-), (C19H18P)[Cu(C6H2Cl2S2)2], (III), have been synthesized and characterized by single-crystal X-ray diffraction. The X-ray structure analyses of all three complexes confirm that the four donor S atoms form a slightly distorted square-planar coordination arrangement around the central metal atom. An interesting finding for both the Cu(II) and Cu(III) complexes, i.e. (II) and (III), respectively, is that the coordination polyhedra are principally the same and differ only slightly with respect to the interatomic distances. PMID:25652286

Herich, Peter; Fronc, Marek; Ko?íšek, Jozef

2015-02-01

267

Fluorescence Polarization Immunoassay of a High-Molecular-Weight Antigen Using a Long Wavelength-Absorbing and Laser Diode-Excitable Metal–Ligand Complex  

Microsoft Academic Search

We describe a fluorescence polarization immunoassay (FPI) based on an osmium metal–ligand complex, Os(bpy)2(dcbpy). The Os complex was selected for its long wavelength absorption, which allows excitation with wavelengths up to 720 nm. At these wavelengths tissue absorbance and autofluorescence are minimal, and excitation can be accomplished with LEDs or laser diodes. The Os complex displays a lifetime of 19

Ewald Terpetschnig; Henryk Szmacinski; Joseph R. Lakowicz

1996-01-01

268

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

269

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

270

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

271

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

PubMed

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

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

2014-07-18

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

Hydrothermal synthesis of an ortho-metallated Co(III) complex anchored by a carboxylate group with a selective oxidation catalytic property.  

PubMed

An air-stable and water-tolerant ortho-metallated complex [Co(tfb)(bpy)(2)](NO(3))·3H(2)O was obtained via hydrothermal synthesis. The mechanism for the formation of Co-C bond was studied using both DFT calculations and experimental analysis. This highly stable complex exhibits good catalytic performance for the selective oxidation of cyclohexane. PMID:23348750

Zhang, Shi-Yuan; Shi, Wei; Ma, Jian-Gong; Zhang, Yu-Qi; Zhang, Zhen-Jie; Cheng, Peng

2013-03-28

274

Extraction of Micronutrient Metals from Peat-based Media Using Various Chelate-ligand and Iron-source Extractants  

Technology Transfer Automated Retrieval System (TEKTRAN)

Objectives of the study were to determine effects of chelate-ligand (experiment 1) and iron-source (experiment 2) unbuffrered extractant solutions on substrate pH and Cu, Fe, Mn, and Zn extraction from peat-based media. Chelate-ligand extractants consisted of 5 mM solutions of ethylenediaminedisucc...

275

A new ONO3- trianionic pincer-type ligand for generating highly nucleophilic metal-carbon multiple bonds.  

PubMed

Appending an amine to a C?C double bond drastically increases the nucleophilicity of the ?-carbon atom of the alkene to form an enamine. In this report, we present the synthesis and characterization of a novel CF(3)-ONO(3-) trianionic pincer-type ligand, rationally designed to mimic enamines within a metal coordination sphere. Presented is a synthetic strategy to create enhanced nucleophilic tungsten-alkylidene and -alkylidyne complexes. Specifically, we present the synthesis and characterization of the new CF(3)-ONO(3-) trianionic pincer tungsten-alkylidene [CF(3)-ONO]W?CH(Et)(O(t)Bu) (2) and -alkylidyne {MePPh(3)}{[CF(3)-ONO]W?C(Et)(O(t)Bu)} (3) complexes. Characterization involves a combination of multinuclear NMR spectroscopy, combustion analysis, DFT computations, and single crystal X-ray analysis for complexes 2 and 3. Exhibiting unique nucleophilic reactivity, 3 reacts with MeOTf to yield [CF(3)-ONO]W?C(Me)(Et)(O(t)Bu) (4), but the bulkier Me(3)SiOTf silylates the tert-butoxide, which subsequently undergoes isobutylene expulsion to form [CF(3)-ONO]W?CH(Et)(OSiMe(3)) (5). A DFT calculation performed on a model complex of 3, namely, [CF(3)-ONO]W?C(Et)(O(t)Bu) (3'), reveals the amide participates in an enamine-type bonding combination. For complex 2, the Lewis acids MeOTf, Me(3)SiOTf, and B(C(6)F(5))(3) catalyze isobutylene expulsion to yield the tungsten-oxo complex [CF(3)-ONO]W(O)((n)Pr) (6). PMID:22681641

O'Reilly, Matthew E; Ghiviriga, Ion; Abboud, Khalil A; Veige, Adam S

2012-07-11

276

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

2013-03-01

277

CHEMICAL SYNTHESIS OF GLYCOSYLPHOSPHATIDYLINOSITOL ANCHORS  

PubMed Central

Many eukaryotic cell-surface proteins and glycoproteins are anchored to the plasma membrane by glycosylphosphatidylinositols (GPIs), a family of glycolipids that are post-translationally attached to proteins at their C-termini. GPIs and GPI-anchored proteins play important roles in many biological and pathological events, such as cell recognition and adhesion, signal transduction, host defense, and acting as receptors for viruses and toxins. Chemical synthesis of structurally defined GPI anchors and GPI derivatives is a necessary step toward understanding the properties and functions of these molecules in biological systems and exploring their potential therapeutic applications. In the first part of this comprehensive article on the chemical synthesis of GPIs, classic syntheses of naturally occurring GPI anchors from protozoan parasites, yeast, and mammals are covered. The second part of the article focuses on recent diversity-oriented strategies for the synthesis of GPI anchors containing unsaturated lipids, “click chemistry” tags, and highly branched and modified structures. PMID:22794184

Swarts, Benjamin M.; Guo, Zhongwu

2013-01-01

278

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

NASA Astrophysics Data System (ADS)

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

Raman, Natarajan; Mahalakshmi, Rajkumar; Mitu, Liviu

2014-10-01

279

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

PubMed

Present work reports the DNA binding and cleavage characteristics of a series of mixed-ligand complexes having the composition [M(L)(phen)2]Cl2 (where M=Cu(II), Ni(II), Co(II) and Zn(II) and phen as co-ligand) in detail. Their structural features and other properties have been deduced from their elemental analyses, magnetic susceptibility and molar conductivity as well as from IR, UV-Vis, (1)H NMR and EPR spectral studies. The UV-Vis, magnetic susceptibility and EPR spectral data of metal complexes suggest an octahedral geometry. The binding properties of these complexes with calf thymus DNA (CT-DNA) have been explored using electronic absorption spectroscopy, viscosity measurement, cyclic voltammetry and differential pulse voltammetry. The DNA-binding constants for Cu(II), Ni(II), Co(II), and Zn(II) complexes are 6.14×10(5)M(-1), 1.8×10(5)M(-1), 6.7×10(4)M(-1) and 2.5×10(4)M(-1) respectively. Detailed analysis reveals that these complexes interact with DNA through intercalation binding. Nuclease activity has also been investigated by gel electrophoresis. Moreover, the synthesized Schiff base and its mixed-ligand complexes have been screened for antibacterial and antifungal activities. The data reveal that the complexes exhibit higher activity than the parent ligand. PMID:24835939

Raman, Natarajan; Mahalakshmi, Rajkumar; Mitu, Liviu

2014-10-15

280

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

281

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

282

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

PubMed

The murine cytomegalovirus-encoded protein m157 is a cognate ligand for both inhibitory and activating receptors expressed by natural killer cells. Additionally, m157 is expressed on the surface of infected cells by a glycophosphatidylinositol (GPI) anchor. Although endogenous GPI-anchored proteins are known to be ligands for the NK cell receptor, NKG2D, the contribution of the GPI anchor for viral m157 ligand function is unknown. To determine whether the GPI anchor for m157 is dispensable for m157 function, we generated m157 variants expressed as transmembrane fusion proteins and tested cells expressing transmembrane m157 for the capacity to activate cognate Ly49 receptors. We found that the GPI anchor is required for high-level cell surface expression of m157, and that the transmembrane m157 ligand retains the capacity to activate reporter cells and NK cells expressing Ly49H, as well as Ly49I(129) reporter cells, but with reduced potency. Importantly, target cells expressing the transmembrane form of m157 were killed less efficiently and failed to mediate Ly49H receptor downregulation on fresh NK cells compared to targets expressing GPI-anchored m157. Taken together, these results show that the GPI anchor for m157 facilitates robust cell surface expression, and that NK cells are sensitive to the altered cell surface expression of this potent viral evasin. PMID:23840655

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

2013-01-01

283

Nanoscaled Copper Metal-Organic Framework (MOF) Based on Carboxylate Ligands as an Efficient Heterogeneous Catalyst for Aerobic Epoxidation of Olefins and Oxidation of Benzylic and Allylic Alcohols.  

PubMed

Aerobic epoxidation of olefins at a mild reaction temperature has been carried out by using nanomorphology of [Cu3 (BTC)2 ] (BTC=1,3,5-benzenetricarboxylate) as a high-performance catalyst through a simple synthetic strategy. An aromatic carboxylate ligand was employed to furnish a heterogeneous copper catalyst and also serves as the ligand for enhanced catalytic activities in the catalytic reaction. The utilization of a copper metal-organic framework catalyst was further extended to the aerobic oxidation of aromatic alcohols. The shape and size selectivity of the catalyst in olefin epoxidation and alcohol oxidation was investigated. Furthermore, the as-synthesized copper catalyst can be easily recovered and reused several times without leaching of active species or significant loss of activity. PMID:25430789

Qi, Yue; Luan, Yi; Yu, Jie; Peng, Xiong; Wang, Ge

2015-01-19

284

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

NASA Astrophysics Data System (ADS)

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

Snyder, Christopher James

285

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

NASA Astrophysics Data System (ADS)

The 1:1 condensation of o-acetoacetylphenol and 1,2-diaminopropane under condition of high dilution gives the mono-condensed Schiff base, (E)-3-(1-aminopropan-2-ylimino)-1-(2-hydroxyphenyl)butan-1-one. The mono-condensed Schiff base has been used for further condensation with isatin to obtain the new asymmetrical dicompartmental Schiff base ligand, (E)-3-(2-((E)-4-(2-hydroxyphenyl)-4-oxobutan-2-ylideneamino) propylimino)indolin-2-one (H3L) with a N2O3 donor set. Reactions of the ligand with metal salts give a series of new binuclear complexes. The ligand and its metal complexes were characterized by elemental analyses, IR, 1H and 13C NMR, electronic, ESR and mass spectra, conductivity and magnetic susceptibility measurements as well as thermal analyses. The analytical and spectroscopic tools showed that the complexes can be formulated as: [(HL)(VO)2(SO4)(H2O)]·4H2O, [(HL)Fe2Cl4(H2O)3]·EtOH, [(HL)Fe2(ox)Cl2(H2O)3]·2H2O, [(L)M2(OAc)(H2O)m]·nH2O; M = Co, Ni or Cu, m = 4, 0 and n = 2, 3, [(HL)Cu2Cl]Cl·6H2O and [(L)(UO2)2(OAc)(H2O)3]·6H2O. The metal complexes exhibited octahedral geometrical arrangements except copper complexes that exhibited tetrahedral geometries and uranyl complex in which the metal ion is octa-coordinated. The Schiff base and its metal complexes were evaluated for antimicrobial activity against Gram positive bacteria (Staphylococcus aureus), Gram negative bacteria (Escherichia coli) and fungi (Candida albicans and Aspergillus flavus). The ligand and some of its complexes were found to be biologically active. The DNA-binding properties of the copper complexes (6 and 7) have been investigated by electronic absorption, fluorescence and viscosity measurements. The results obtained indicate that these complexes bind to DNA via an intercalation binding mode with an intrinsic binding constant, Kb of 1.34 × 104 and 2.5 × 104 M-1, respectively.

Shebl, Magdy

2014-01-01

286

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

PubMed

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

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

2002-04-01

287

Chemical biology of glycosylphosphatidylinositol anchors.  

PubMed

Glycosylphosphatidylinositols (GPIs) are complex glycolipids that are covalently linked to the C-terminus of proteins as a posttranslational modification. They anchor the attached protein to the cell membrane and are essential for normal functioning of eukaryotic cells. GPI-anchored proteins are structurally and functionally diverse. Many GPIs have been structurally characterized but comprehension of their biological functions, beyond the simple physical anchoring, remains largely speculative. Work on functional elucidation at a molecular level is still limited. This Review focuses on the roles of GPI unraveled by using synthetic molecules and summarizes the structural diversity of GPIs, as well as their biological and chemical syntheses. PMID:23086912

Tsai, Yu-Hsuan; Liu, Xinyu; Seeberger, Peter H

2012-11-12

288

Building complexity in O2-binding copper complexes. Site-selective metalation and intermolecular O2-binding at dicopper and heterometallic complexes derived from an unsymmetric ligand.  

PubMed

A novel unsymmetric dinucleating ligand (L(N3N4)) combining a tridentate and a tetradentate binding sites linked through a m-xylyl spacer was synthesized as ligand scaffold for preparing homo- and dimetallic complexes, where the two metal ions are bound in two different coordination environments. Site-selective binding of different metal ions is demonstrated. L(N3N4) is able to discriminate between Cu(I) and a complementary metal (M' = Cu(I), Zn(II), Fe(II), Cu(II), or Ga(III)) so that pure heterodimetallic complexes with a general formula [Cu(I)M'(L(N3N4))](n+) are synthesized. Reaction of the dicopper(I) complex [Cu(I)2(L(N3N4))](2+) with O2 leads to the formation of two different copper-dioxygen (Cu2O2) intermolecular species (O and (T)P) between two copper atoms located in the same site from different complex molecules. Taking advantage of this feature, reaction of the heterodimetallic complexes [CuM'(L(N3N4))](n+) with O2 at low temperature is used as a tool to determine the final position of the Cu(I) center in the system because only one of the two Cu2O2 species is formed. PMID:25424176

Serrano-Plana, Joan; Costas, Miquel; Company, Anna

2014-12-15

289

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

PubMed

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

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

2014-10-01

290

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

291

50 CFR 622.432 - Anchoring restriction.  

Code of Federal Regulations, 2014 CFR

...system that recovers the anchor by its crown, thereby preventing the anchor from...rode to reverse and slip back toward the crown. For a fluke- or plow-type anchor, a trip line consisting of a line from the crown of the anchor to a surface buoy would...

2014-10-01

292

50 CFR 622.432 - Anchoring restriction.  

Code of Federal Regulations, 2013 CFR

...system that recovers the anchor by its crown, thereby preventing the anchor from...rode to reverse and slip back toward the crown. For a fluke- or plow-type anchor, a trip line consisting of a line from the crown of the anchor to a surface buoy would...

2013-10-01

293

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

294

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

295

Highly Efficient Heterogeneous Hydroformylation over Rh-Metalated Porous Organic Polymers: Synergistic Effect of High Ligand Concentration and Flexible Framework.  

PubMed

A series of diphosphine ligand constructed porous polymers with stable and flexible frameworks have been successfully synthesized under the solvothermal conditions from polymerizing the corresponding vinyl-functionalized diphosphine monomers. These insoluble porous polymers can be swollen by a wide range of organic solvents, showing similar behavior to those of soluble analogues. Rather than just as immobilizing homogeneous catalysts, these porous polymers supported with Rh species demonstrate even better catalytic performance in the hydroformylations than the analogue homogeneous catalysts. The sample extraordinary performance could be attributed to the combination of high ligand concentration and flexible framework of the porous polymers. Meanwhile, they can be easily separated and recycled from the reaction systems without losing any activity and selectivity. This excellent catalytic performance and easy recycling heterogeneous catalyst property make them be very attractive. These diphosphine ligand constructed porous polymers may provide new platforms for the hydroformylation of olefins in the future. PMID:25848868

Sun, Qi; Dai, Zhifeng; Liu, Xiaolong; Sheng, Na; Deng, Feng; Meng, Xiangju; Xiao, Feng-Shou

2015-04-22

296

Preparation of core-shell coordination molecular assemblies via the enrichment of structure-directing "codes" of bridging ligands and metathesis of metal units.  

PubMed

A series of molybdenum- and copper-based MOPs were synthesized through coordination-driven process of a bridging ligand (3,3'-PDBAD, L(1)) and dimetal paddlewheel clusters. Three conformers of the ligand exist with an ideal bridging angle between the two carboxylate groups of 0° (H2?-L(1)), 120° (H2?-L(1)), and of 90° (H2?-L(1)), respectively. At ambient or lower temperature, H2L(1) and Mo2(OAc)4 or Cu2(OAc)4 were crystallized into a molecular square with ?-L(1) and Mo2/Cu2 units. With proper temperature elevation, not only the molecular square with ?-L(1) but also a lantern-shaped cage with ?-L(1) formed simultaneously. Similar to how Watson-Crick pairs stabilize the helical structure of duplex DNA, the core-shell molecular assembly possesses favorable H-bonding interaction sites. This is dictated by the ligand conformation in the shell, coding for the formation and providing stabilization of the central lantern shaped core, which was not observed without this complementary interaction. On the basis of the crystallographic implications, a heterobimetallic cage was obtained through a postsynthetic metal ion metathesis, showing different reactivity of coordination bonds in the core and shell. As an innovative synthetic strategy, the site-selective metathesis broadens the structural diversity and properties of coordination assemblies. PMID:25384026

Park, Jinhee; Chen, Ying-Pin; Perry, Zachary; Li, Jian-Rong; Zhou, Hong-Cai

2014-12-01

297

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

Microsoft Academic Search

Synthesis and evaluation of six new oxovanadium (IV) complexes, formed by the interaction of vanadyl sulphate pentahydrate and the Schiff base, viz.; (HL1)–(HL3) and (HL4)–(HL6) such as 5-hydroxy-3-methyl-1(2-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (I), 5-hydroxy-3-methyl-1(3-chloro)phenyl-1H-pyrazolone-4-carbaldehyde (II) and 5-hydroxy-3-methyl-1(3-sulphoamido)phenyl-1H-pyrazolone-4-carbaldehyde (III) with ethanol amine and propanol amine, respectively, in aqueous ethanol medium. The ligands and their Schiff base ligands have been characterized by elemental analyses, IR and

B. T. Thaker; R. S. Barvalia

2009-01-01

298

Interactions of algal ligands, metal complexation and availability, and cell responses of the diatom Ditylum brightwellii with a gradual increase in copper.  

PubMed

A continuous culture experiment was conducted to study interactions between copper-binding ligands released by light-limited Ditylum brightwellii, and toxic effects of Cu on this diatom. Over 6 months, the Cu concentration in the medium has been increased in seven steps (3-173 nM). At each Cu addition, Cu speciation, characteristics of Cu sorption to cellular binding sites, and cell characteristics were determined. Physiological effects of Cu were studied, using indicators for metal detoxification (thiols) and lipid peroxidation (malondialdehyde). Minor amounts of Cu (<1.4%) were chelated by a minimum amount of EDTA (57 nM), required to maintain a stable long-term continuous culture. The responses of D. brightwellii to Cu were monitored. (1) From 3 to 47 nM added Cu, decreasing pools of glutathione, increasing malondialdehyde contents, an increased release of lipophilic ligands, and cell lysis indicated the enhancement of lipid peroxidation. (2) From 47 to 94 nM Cu, a 16-fold increase in high-affinity (strong) hydrophilic ligands was measured (conditional stability constants K' approximately 10(12)) that complexed most Cu (maximum 97%); sexual reproduction was stimulated and cell volumes increased. (3) From 126 nM Cu, glutathione pools increased again, whereas cell division rates decreased slightly. (4) At 142 nM Cu, the number of lysed cells reached a maximum, as did the production of lipophilic compounds that complexed approximately 2% Cu. As the binding sites of the strong ligands became Cu-saturated above 142 nM Cu, larger amounts of Cu were bound to low-affinity (weak) dissolved ligands (3-30%) and cellular binding sites (0.2-2.5%). Probably due to saturation of organic complexes at 142 nM Cu, the MINEQL-calculated Cu2+ concentrations increased markedly; pCu values decreased from >11 to approximately 10; division rates were further inhibited; gamma-glutamylcysteine (phytochelatin precursor) was produced. (5) At 157 nM Cu, phytochelatin synthesis started, and Cu-sorption capacities (cell walls and internal binding sites) increased. (6) At 173 nM Cu, the phytochelatin pool sizes and the number of cellular Cu-binding sites increased further. These results suggest that ligands released by a dense bloom of D. brightwellii, either by active excretion or lysis, would have lower affinities for Cu (K' approximately 10(9)-10(12)) and moderate the availability of Cu less effectively than ligands in natural environments (10(13)-10(14)). In this diatom, the concurring release of ligands, enhanced malondialdehyde production, increasing numbers of presexual cells and cell enlargement may serve as early-warning signals for Cu toxicity, rather than metal-specific phytochelatins that appeared at a stage when cell division was already clearly inhibited. PMID:11755700

Rijstenbil, J W; Gerringa, L J A

2002-01-01

299

Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands  

PubMed Central

We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date. PMID:25788358

Holby, Edward F.; Taylor, Christopher D.

2015-01-01

300

Ag(I) and Tl(I) precursors as transfer agents of a pyrrole-based pincer ligand to late transition metals.  

PubMed

A PNP ligand, PN(pyr)P ((PN(pyr)P)H = 2,5-bis((di-iso-propylphosphino)methyl)pyrrole), which employs a pyrrole unit as a central anionic nitrogen donor, was designed. The corresponding group 10 metal chlorides as well as iridium and ruthenium compounds were isolated. In order to conduct this work, [(PN(pyr)P)Tl] and [(PN(pyr)P)Ag]2 were synthesized and characterized. The thallium and silver species were paramount in the formation of the iridium and ruthenium complexes, which could not be isolated using (PN(pyr)P)H or the corresponding lithium pyrrolide salt. Interestingly, the solid state molecular structure of [(PN(pyr)P)Tl] indicates that the metal center engages in an ?(2) intermolecular interaction with the backbone of a neighboring pyrrole molecule instead of the expected bonding to the phosphine arms. PMID:25386700

Kessler, Julie A; Iluc, Vlad M

2014-12-01

301

Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands.  

PubMed

We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date. PMID:25788358

Holby, Edward F; Taylor, Christopher D

2015-01-01

302

Co(II\\/III) coordinated pyridine alcoholate ligand generated through metal assisted nucleophilic addition to a C O function: Temperature dependent synthesis of a mononuclear complex and a neutral cubane cluster  

Microsoft Academic Search

The synthesis and characterization of pyridine alcoholate ligand coordinated Co(II\\/III) metal complexes are reported. The characterization includes elemental analysis, spectral, magnetism, and X-ray crystallographic studies. Water readily shows nucleophilic addition to the CO group upon coordination of the 2-pyridyl ring of the ligands, forming a gem-diol form of (2-py)2CO. By coordinating through the two pyridine nitrogen atoms and one oxygen

Sumanta Kumar Padhi; Rojalin Sahu

2008-01-01

303

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

Microsoft Academic Search

The objective of this project is to develop novel, substituted diphosphonic acid ligands that can be used for supercritical carbon dioxide extraction (SCDE) of actinide ions from solid wastes. Specifically, selected diphosphonic acids, which are known to form extremely stable complexes with actinides in aqueous and organic solution, are to be rendered carbon dioxide-soluble by the introduction of appropriate alkyl-

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

2000-01-01

304

Achiral and chiral PNP-pincer ligands with a carbazole backbone: coordination chemistry with d8 transition metals.  

PubMed

Two new monoanionic PNP pincer type ligands have been synthesized, the achiral 3,6-di-tert-butyl-1,8-bis((diphenyl-phosphino)methyl)-9H-carbazole CbzdiphosH (5) and the chiral 3,6-di-tert-butyl-1,8-bis(((2R,5R)-2,5-diphenylphospholan-1-yl)methyl)-9H-carbazole CbzdipholH (7), both of which were initially prepared as their borane complexes. The synthesis of CbzdiphosH is based on the reaction between the key intermediate 1,8-bis(bromomethyl)-3,6-di-tert-butyl-9H-carbazole (3) and lithium diphenylphosphide-borane complex. The chiral ligand CbzdipholH was prepared by treating 3 with lithium (2R,5R)-2,5-diphenylphospholanide-borane complex and subsequent deprotection with diethylamine. The complexation of the two ligands with nickel, palladium and rhodium was investigated, for which the conformational behavior of the ligands was found to be different. Although the arrangement of the donor atoms in all crystallographically characterized complexes is approximately square planar, the carbazole plane in Cbzdiphos complexes is inclined relative to the coordination plane. On the other hand, a helical twist is observed in Cbzdiphol complexes. PMID:23363395

Grüger, Nora; Rodríguez, Lara-Isabel; Wadepohl, Hubert; Gade, Lutz H

2013-02-18

305

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

ERIC Educational Resources Information Center

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

Johnson, Adam R.

2013-01-01

306

Chiral crystallization and optical properties of three metal complexes based on two non-centrosymmetric tripodal ligands.  

PubMed

Chiral coordination polymers have attracted much attention due to their special properties and significant applications. In this work, we synthesized two non-centrosymmetric ligands, N,N-bis(4-(1H-imidazol-1-yl)phenyl)-4-(pyridin-4-yl)aniline (DIMPPA) and N-(4-(1H-imidazol-1-yl)phenyl)-4-(pyridin-4-yl)-N-(4-(pyridin-4-yl)phenyl)aniline (MIDPPA), via structural modification of two reported centrosymmetric ligands; after that achiral ? chiral induction occurred in the construction of three coordination polymers namely {[Cd(DIMPPA)(5-OH-bdc)](H2O)}n (), {[Co(DIMPPA)(5-OH-bdc)](H2O)}n () and {[Cd2(MIDPPA)2(d-ca)2(H2O)2](H2O)5}n (), when replacing the reported centrosymmetric ligands with non-centrosymmetric ligands (5-OH-H2bdc = 5-hydroxyisophthalic acid, d-H2ca = d-camphoric acid). Isostructural complexes and exhibit chiral 2D ? 3D frameworks with the coexistence of polyrotaxane and parallel polycatenation features. Complex shows two-fold interpenetrating 3D chiral architecture with cds-type topology. The luminescence emissions of both complexes and are mostly assignable to the internal ???* electron transition in DIMPPA and MIDPPA, respectively. Complex can satisfy the fundamental requirement of second-order nonlinear optical materials. PMID:25715030

Zhang, Ming-Dao; Shi, Zhi-Qiang; Chen, Min-Dong; Zheng, He-Gen

2015-03-10

307

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

PubMed

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

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

2014-05-01

308

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

309

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

PubMed

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

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

2014-10-20

310

Liposome Surface Functionalization Based on Different Anchoring Lipids via Staudinger Ligation  

PubMed Central

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

Vabbilisetty, Pratima; Sun, Xue-Long

2014-01-01

311

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

PubMed Central

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

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

2011-01-01

312

Chelating fibers prepared with a wet spinning technique using a mixture of a viscose solution and a polymer ligand for the separation of metal ions in an aqueous solution.  

PubMed

Chelating fibers containing polymer ligands such as carboxymethylated polyallylamine, carboxymethylated polyethyleneimine, and a copolymer of diallylamine hydrochloride/maleic acid were prepared with a wet spinning technique using mixtures of a viscose solution and the polymer ligands. The chelating fibers obtained effectively adsorbed various metal ions, including Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Ti(IV), and Zn(II). The metal ions adsorbed could be readily desorbed using 0.1 or 0.5 mol L(-1) HNO(3). The chelating fiber containing carboxymethylated polyallylamine was available for the separation of some metal ions in synthetic wastewater containing a large amount of Na(2)SO(4). The wet spinning technique using a solution containing a base polymer and a polymer ligand was quite simple and effective and would be applicable for preparing various chelating fibers. PMID:22209589

Kagaya, Shigehiro; Miyazaki, Hiroyuki; Inoue, Yoshinori; Kato, Toshifumi; Yanai, Hideyuki; Kamichatani, Waka; Kajiwara, Takehiro; Saito, Mitsuru; Tohda, Koji

2012-02-15

313

Role of spin state and ligand charge in coordination patterns in complexes of 2,6-diacetylpyridinebis(semioxamazide) with 3d-block metal ions: a density functional theory study.  

PubMed

We report here a systematic computational study on the effect of the spin state and ligand charge on coordination preferences for a number of 3d-block metal complexes with the 2,6-diacetylpyridinebis(semioxamazide) ligand and its mono- and dianionic analogues. Our calculations show excellent agreement for the geometries compared with the available X-ray structures and clarify some intriguing experimental observations. The absence of a nickel complex in seven-coordination is confirmed here, which is easily explained by inspection of the molecular orbitals that involve the central metal ion. Moreover, we find here that changes in the spin state lead to completely different coordination modes, in contrast to the usual situation that different spin states mainly result in changes in the metal-ligand bond lengths. Both effects result from different occupations of a combination of ?- and ?-antibonding and nonbonding orbitals. PMID:24252122

Stepanovi?, Stepan; Andjelkovi?, Ljubica; Zlatar, Matija; Andjelkovi?, Katarina; Gruden-Pavlovi?, Maja; Swart, Marcel

2013-12-01

314

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

315

Metal-ligand complexes as a new class of long-lived fluorophores for protein hydrodynamics and fluorescence polarization immunoassay  

Microsoft Academic Search

We describe the use of asymmetric Ru-ligand complexes as a new class of luminescent probes. These complexes are known to display luminescent lifetimes ranging from 10 to 4000 ns. We show that the asymmetric complex Ru(bpy)2(dcbpy) (PF6)2 displays a high anisotropy value near 0.26 when excited in the long wavelength absorption band, and an intensity decay time near 400 ns.

Joseph R. Lakowicz; Ewald A. Terpetschnig; Henryk Szmacinski; Henryk Malak

1995-01-01

316

Comparison of Interfacial Electron Transfer through Carboxylate and Phosphonate Anchoring Groups  

E-print Network

directly connected to the bipyridine ligands. The injection kinetics, as measured by subpicosecond IR in many molecule-based devices such as molecular electronics1 and dye-sensitized solar cells.2 Although of anchoring group on the efficiency of dye-sensitized solar cells (DSSCs) has also been investigated. So far

317

Microgravity Drill and Anchor System  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

318

Ligand displacement for fixing manganese: relevance to cellular metal ion transport and synthesis of polymeric coordination complexes.  

PubMed

A dinuclear manganese(III) complex (1) of an N-(carboxymethyl)-N-[3,5-bis(?,?-dimethylbenzyl-2-hydroxybenzyl)]glycine (HDA) ligand (L) binds a manganese(II) species through displacement of its solvating ligands by appropriately dispositioned carbonyl groups of a dinuclear complex {[Mn(2)(L)(2)(OH)(OCH(3))][Mn(H(2)O)(3)(CH(3)OH)(3)], 2, triclinic P1, a = 13.172(3) Å, b = 15.897(3) Å, c = 19.059(4) Å, V = 3461.9(13) Å(3)} leading to a trinuclear complex {3, monoclinic P21/n, a = 11.7606(8) Å, b = 21.3505(8) Å, c = 26.7827(17) Å, V = 6722.7(7) Å(3)} with cyclization of two of the carboxy groups through the doubly-carboxy group coordinated Mn(2+) ion. The reaction is discussed in terms of its significance as an illustration of how Mn(2+) ions might be sequestered in biological systems. A similar solvato-ligand displacement reaction was used to synthesise coordination polymers of an HDA iron(III) complex involving polymerization through a bridging carboxylato group. Several isostructural polymers (5-7; for 5: orthorhombic Pbca, a = 9.411(5) Å, b = 16.390(8) Å, c = 37.968(19) Å, V = 5856(5) Å(3)) with different coordinated alcohols could be prepared indicating the potential synthetic uses of this method. PMID:23238775

Sanchez-Ballester, Noelia M; Shrestha, Lok Kumar; Elsegood, Mark R J; Schmitt, Wolfgang; Ariga, Katsuhiko; Anson, Christopher E; Hill, Jonathan P; Powell, Annie K

2013-02-28

319

Nematic Anchoring on Carbon Nanotubes  

E-print Network

A dilute suspension of carbon nanotubes (CNTs) in a nematic liquid crystal (LC) does not disturb the LC director. Due to a strong LC-CNT anchoring energy and structural symmetry matching, CNT long axis follows the director field, possessing enhanced dielectric anisotropy. This strong anchoring energy stabilizes local pseudo-nematic domains, resulting in non-zero dielectric anisotropy in the isotropic phase. These anisotropic domains respond to external electric fields and show intrinsic frequency response. The presence of these domains makes the isotropic phase field-responsive, giving rise to a large dielectric hysteresis effect.

Rajratan Basu; Germano S. Iannacchione

2009-09-28

320

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

321

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

PubMed

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

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

2014-08-28

322

An investigation of chlorine ligands in transition-metal complexes via ³?Cl solid-state NMR and density functional theory calculations.  

PubMed

Chlorine ligands in a variety of diamagnetic transition-metal (TM) complexes in common structural motifs were studied using (35)Cl solid-state NMR (SSNMR), and insight into the origin of the observed (35)Cl NMR parameters was gained through first-principles density functional theory (DFT) calculations. The WURST-CPMG pulse sequence and the variable-offset cumulative spectrum (VOCS) methods were used to acquire static (35)Cl SSNMR powder patterns at both standard (9.4 T) and ultrahigh (21.1 T) magnetic field strengths, with the latter affording higher signal-to-noise ratios (S/N) and reduced experimental times (i.e., <1 h). Analytical simulations were performed to extract the (35)Cl electric field gradient (EFG) tensor and chemical shift (CS) tensor parameters. It was found that the chlorine ligands in various bonding environments (i.e., bridging, terminal-axial, and terminal-equatorial) have drastically different (35)Cl EFG tensor parameters, suggesting that (35)Cl SSNMR is ideal for characterizing chlorine ligands in TM complexes. A detailed localized molecular orbital (LMO) analysis was completed for NbCl5. It was found that the contributions of individual molecular orbitals must be considered to fully explain the observed EFG parameters, thereby negating simple arguments based on comparison of bond lengths and angles. Finally, we discuss the application of (35)Cl SSNMR for the structural characterization of WCl6 that has been grafted onto a silica support material. The resulting tungsten-chloride surface species is shown to be structurally distinct from the parent compound. PMID:25162702

O'Keefe, Christopher A; Johnston, Karen E; Sutter, Kiplangat; Autschbach, Jochen; Gauvin, Régis; Trébosc, Julien; Delevoye, Laurent; Popoff, Nicolas; Taoufik, Mostafa; Oudatchin, Konstantin; Schurko, Robert W

2014-09-15

323

Nanopatterned anchoring layers for liquid crystals  

E-print Network

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

Gear, Christopher S. (Christopher Stanwood)

2014-01-01

324

21 CFR 872.3130 - Preformed anchor.  

Code of Federal Regulations, 2014 CFR

... FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3130 Preformed anchor. (a) Identification. A preformed anchor is a device made of...

2014-04-01

325

1,2-Distanna-closo-dodecaborate--a rare example of a 1,2-distannylene ligand in transition metal chemistry.  

PubMed

The coordination chemistry of the novel bidentate tin ligand 1,2-distanna-closo-dodecaborate is illustrated for the first time by reactions with molybdenum, platinum and gold metal complexes. Up to three clusters coordinate two metal centers in close proximity. For all these metal complexes the typical ?-bridging coordination mode was observed exclusively. Furthermore, two cluster anions react with dichloromethane via substitution of the chloride ions. The carbon functionalized tin cluster [Et(4)N](2)[CH(2)(Sn(2)B(10)H(10))(2)] and the coordination complexes [Et(3)NMe](6)[Mo(2)(CO)(6)(Sn(2)B(10)H(10))(3)], [Et(3)NMe](2)[{HPt(PEt(3))(2)(Sn(2)B(10)H(10))}(2)], [Et(4)N](2)[{HPt(PPh(3))(2)(Sn(2)B(10)H(10))}(2)] and [{(TP)Au}(2)(Sn(2)B(10)H(10))] (TP = PhP(o-Ph(2)PC(6)H(4))(2)) are fully characterized by multinuclear NMR spectroscopy, elemental analyses and crystal structure analyses. PMID:22095111

Nickl, Claudia; Eichele, Klaus; Wesemann, Lars

2012-01-01

326

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli  

PubMed Central

Growing evidence supports a critical role of metal-ligand coordination in many attributes of biological materials including adhesion, self-assembly, toughness, and hardness without mineralization [Rubin DJ, Miserez A, Waite JH (2010) Advances in Insect Physiology: Insect Integument and Color, eds Jérôme C, Stephen JS (Academic Press, London), pp 75–133]. Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle of mussel byssal threads and proposed to endow self-healing properties [Harrington MJ, Masic A, Holten-Andersen N, Waite JH, Fratzl P (2010) Science 328:216–220]. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol-Fe3+ interpolymer cross-linking via pH. The resonance Raman signature of catechol-Fe3+ cross-linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli (G?) that approach covalently cross-linked gels as well as self-healing properties. PMID:21278337

Holten-Andersen, Niels; Harrington, Matthew J.; Birkedal, Henrik; Lee, Bruce P.; Messersmith, Phillip B.; Lee, Ka Yee C.; Waite, J. Herbert

2011-01-01

327

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli.  

PubMed

Growing evidence supports a critical role of metal-ligand coordination in many attributes of biological materials including adhesion, self-assembly, toughness, and hardness without mineralization [Rubin DJ, Miserez A, Waite JH (2010) Advances in Insect Physiology: Insect Integument and Color, eds Jérôme C, Stephen JS (Academic Press, London), pp 75-133]. Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle of mussel byssal threads and proposed to endow self-healing properties [Harrington MJ, Masic A, Holten-Andersen N, Waite JH, Fratzl P (2010) Science 328:216-220]. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol-Fe(3+) interpolymer cross-linking via pH. The resonance Raman signature of catechol-Fe(3+) cross-linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli (G') that approach covalently cross-linked gels as well as self-healing properties. PMID:21278337

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

2011-02-15

328

Coordination mode of pentadentate ligand derivative of 5-amino-1,3,4-thiadiazole-2-thiol with nickel(II) and copper(II) metal ions: Synthesis, spectroscopic characterization, molecular modeling and fungicidal study  

NASA Astrophysics Data System (ADS)

Complexes of nickel(II), and copper(II) were synthesized with pantadentate ligand i.e. 3,3?-thiodipropionicacid-bis(5-amino-1,3,4-thiadiazole-2-thiol) (L). The ligand was synthesized by the condensation of thiodipropionic acid and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio, respectively. Synthesized ligand was characterized by elemental analysis, mass, 1H NMR, IR, and molecular modeling. All the complexes were characterized by elemental analysis, molar conductance, magnetic moment, IR, electronic spectra, ESR, and molecular modeling. The newly synthesized complexes possessed general composition [M(L)X2] where M = Ni(II), Cu(II), L = pantadentate ligand and X = Cl-, CH3COO-. The IR spectral data indicated that the ligand behaved as a pantadentate ligand and coordinated to the metal ion through N2S3 donor atoms. The molar conductance value of Ni(II), and Cu(II) complexes in DMSO corresponded to their electrolytic behavior. On the basis of spectral study, octahedral and tetragonal geometry was assigned for Ni(II) and Cu(II) complexes, respectively. In vitro fungicidal study of ligand and its complexes was investigated against fungi Candida albicans, Candida parapsilosis, Candidia krusei, and Candida tropicalis by means of well diffusion method.

Chandra, Sulekh; Gautam, Seema; Kumar, Amit; Madan, Molly

2015-02-01

329

Coordination mode of pentadentate ligand derivative of 5-amino-1,3,4-thiadiazole-2-thiol with nickel(II) and copper(II) metal ions: synthesis, spectroscopic characterization, molecular modeling and fungicidal study.  

PubMed

Complexes of nickel(II), and copper(II) were synthesized with pantadentate ligand i.e. 3,3'-thiodipropionicacid-bis(5-amino-1,3,4-thiadiazole-2-thiol) (L). The ligand was synthesized by the condensation of thiodipropionic acid and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio, respectively. Synthesized ligand was characterized by elemental analysis, mass, (1)H NMR, IR, and molecular modeling. All the complexes were characterized by elemental analysis, molar conductance, magnetic moment, IR, electronic spectra, ESR, and molecular modeling. The newly synthesized complexes possessed general composition [M(L)X2] where M = Ni(II), Cu(II), L = pantadentate ligand and X = Cl(-), CH3COO(-). The IR spectral data indicated that the ligand behaved as a pantadentate ligand and coordinated to the metal ion through N2S3 donor atoms. The molar conductance value of Ni(II), and Cu(II) complexes in DMSO corresponded to their electrolytic behavior. On the basis of spectral study, octahedral and tetragonal geometry was assigned for Ni(II) and Cu(II) complexes, respectively. In vitro fungicidal study of ligand and its complexes was investigated against fungi Candida albicans, Candida parapsilosis, Candidia krusei, and Candida tropicalis by means of well diffusion method. PMID:25448967

Chandra, Sulekh; Gautam, Seema; Kumar, Amit; Madan, Molly

2015-02-01

330

Anchored phosphatases modulate glucose homeostasis  

E-print Network

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

Scott, John D.

331

Anchored phosphatases modulate glucose homeostasis  

PubMed Central

Endocrine release of insulin principally controls glucose homeostasis. Nutrient-induced exocytosis of insulin granules from pancreatic ?-cells involves ion channels and mobilization of Ca2+ 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 Ca2+ currents, and attenuates cytoplasmic accumulation of Ca2+ 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

2012-01-01

332

ATHLETE : Double Auger Anchoring Mechanism  

NASA Technical Reports Server (NTRS)

The All-Terrain Hex-Legged Extra-Terrestrial Explorer (ATHLETE) is a six-limbed robot designed to support surface explorations on Near Earth Objects, the Moon and Mars. ATHLETE can carry large payloads on its top deck and can carry a fully equipped pressurized habitat in low gravity. The robot has wheels on each of its six articulated limbs, allowing it to actively conform to terrain while driving and to walk when driving is impractical. With the use of a tool adapter, ATHLETE limbs can be equipped with end effectors to support various mission objectives. For work on Near Earth Objects and other microgravity environments, an anchoring mechanism is needed to keep the ATHLETE from floating off the surface. My goal for this spring session at JPL was to design and build a counter rotating, double auger, anchoring mechanism. The mechanism mates to the tool adapter and is driven off the wheel motor. The double auger anchoring mechanism will be tested in a regolith simulant that will determine the uplift capacity of the anchoring mechanism.

Shin, Joseph

2011-01-01

333

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

334

Anchored phosphatases modulate glucose homeostasis  

E-print Network

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

Scott, John D.

335

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

336

A B3LYP-DBLOC empirical correction scheme for ligand removal enthalpies of transition metal complexes: parameterization against experimental and CCSD(T)-F12 heats of formation.  

PubMed

Average ligand removal enthalpies of 30 differently coordinated mono-nuclear fourth-row transition metal complexes taken from a database recently considered by Johnson and Becke [Can. J. Chem., 2009, 8, 1369] have been computed in the gas phase using unrestricted pseudo-spectral (LACV3P) and fully analytic (qzvp(-g)) B3LYP including a recently developed empirical dispersion correction. Heats of formation of neutral singlet reactants and neutral, potentially high spin, products have been taken from NIST's Organometallic Thermochemistry Database. Comparison of B3LYP-MM//qzvp(-g) and experimental average ligand removal enthalpies reveals a systematic error in the reported experimental enthalpies for manganese-containing complexes which is verified with high-level, CCSD(T)-F12//family of cc-pVTZ, explicitly correlated coupled-cluster methods. Other B3LYP-MM//qzvp(-g) error patterns give rise to a d-block localized orbital correction (DBLOC) scheme containing six transferable parameters that correct the functional's description of metal-ligand bonding, cation-?, and dispersion interactions as well as metal and/or ligand multi-reference effects. Metal-ligand cation-? and dispersion interactions have been fit to the monopole/induced-dipole, C(4)/R(4), and induced-dipole/induced-dipole, C(6)/R(6), interaction functions, respectively. This DBLOC model has been built upon a previously determined set of metal atom parameters which are necessary to properly describe the free metal atom reaction products. The final DBLOC model brings the mean unsigned error of B3LYP-MM//qzvp(-g) from 3.74 ± 3.51 kcal/mol to 0.94 ± 0.68 kcal/mol and corrects the functional's under binding in nearly every case. Several important connections among DBLOC parameters have been made. PMID:22513477

Hughes, Thomas F; Harvey, Jeremy N; Friesner, Richard A

2012-06-01

337

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

338

31P Solid State NMR Studies of Metal Selenophosphates Containing [P2Se6]4-, [P4Se10]4-, [PSe4]3-, [P2Se7]4-, and [P2Se9]4-Ligands  

E-print Network

31P Solid State NMR Studies of Metal Selenophosphates Containing [P2Se6]4-, [P4Se10]4-, [PSe4]3-, [P2Se7]4-, and [P2Se9]4- Ligands Christian G. Canlas, Mercouri G. Kanatzidis, and David P. Weliky P solid-state nuclear magnetic resonance (NMR) spectra of 12 metal-containing selenophosphates have

Weliky, David

339

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

PubMed

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

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

2012-08-01

340

Synthesis and characterization of d{sup 10} metal complexes with mixed 1,3-di(1H-imidazol-4-yl)benzene and multicarboxylate ligands  

SciTech Connect

Seven new coordination polymers [Zn(H{sub 2}L)(mbdc)] (1), [Zn(H{sub 3}L)(btc)] (2), [Zn(H{sub 2}L)(Hbtc)] (3), [Zn(H{sub 2}L)(Hbtc)]·H{sub 2}O (4), [Zn{sub 2}(H{sub 2}L)(btc)(?{sub 2}-OH)] (5), [Cd(H{sub 2}L)(mbdc)] (6) and [Cd{sub 3}(H{sub 2}L){sub 2}(btc){sub 2}(H{sub 2}O)]·5H{sub 2}O (7) were synthesized by reactions of the corresponding metal salt with rigid ligand 1,3-di(1H-imidazol-4-yl)benzene (H{sub 2}L) and different carboxylic acids of 1,3-benzenedicarboxylic acid (H{sub 2}mbdc) and benzene-1,3,5-tricarboxylic acid (H{sub 3}btc), respectively. The results of X-ray crystallographic analysis indicate that complex 1 is 1D chain while 2 is a (3,3)-connected 2D network with Point (Schläfli) symbol of (4,8{sup 2}). Complexes 3 and 6 are 2D networks, 4 is a 3-fold interpenetrating 3D framework with Point (Schläfli) symbol of (6{sup 5},8) and 5 is a (3,8)-connected 2D network with Point (Schläfli) symbol of (3,4{sup 2}){sub 2}(3{sup 4},4{sup 6},5{sup 6},6{sup 8},7{sup 3},8), while 7 is a (3,10)-connected 3D net with Schläfli symbol of (3,4,5){sub 2}(3{sup 4},4{sup 8},5{sup 18},6{sup 12},7{sup 2},8). The thermal stability and photoluminescence of the complexes were investigated. Furthermore, DFT calculations were performed for 2–4 to discuss the temperature controlled self-assembly of the complexes. - Graphical abstract: Seven new coordination polymers with multicarboxylate and rigid ditopic 4-imidazole containing ligands have been obtained and found to show different structures and topologies. - Highlights: • Metal complexes with diverse structures of 1D chain, 2D network and 3D framework. • Mixed ligands of 1,3-di(1H-imidazol-4-yl)benzene and multicarboxylate. • Photoluminescence property.

Chen, Zhi-Hao; Zhao, Yue; Chen, Shui-Sheng; Wang, Peng; Sun, Wei-Yin, E-mail: sunwy@nju.edu.cn

2013-06-15

341

Ligand-based carbon-nitrogen bond forming reactions of metal dinitrosyl complexes with alkenes and their application to C-H bond functionalization.  

PubMed

Over the past few decades, researchers have made substantial progress in the development of transition metal complexes that activate and functionalize C-H bonds. For the most part, chemists have focused on aliphatic and aromatic C-H bonds and have put less effort into complexes that activate and functionalize vinylic C-H bonds. Our groups have recently developed a novel method to functionalize vinylic C-H bonds that takes advantage of the unique ligand-based reactivity of a rare class of metal dinitrosyl complexes. In this Account, we compare and discuss the chemistry of cobalt and ruthenium dinitrosyl complexes, emphasizing alkene binding, C-H functionalization, and catalysis. Initially discovered in the early 1970s by Brunner and studied more extensively in the 1980s by the Bergman group, the cyclopentadienylcobalt dinitrosyl complex CpCo(NO)2 reacts reversibly with alkenes to give, in many cases, stable and isolable cobalt dinitrosoalkane complexes. More recently, we found that treatment with strong bases, such as lithium hexamethyldisilazide, Verkade's base, and phosphazene bases, deprotonates these complexes and renders them nucleophilic at the carbon ? to the nitroso group. This conjugate anion of metal dinitrosoalkanes can participate in conjugate addition to Michael acceptors to form new carbon-carbon bonds. These functionalized cobalt complexes can further react through alkene exchange to furnish the overall vinylic C-H functionalized organic product. This stepwise sequence of alkene binding, functionalization, and retrocycloaddition represents an overall vinylic C-H functionalization reaction of simple alkenes and does not require directing groups. We have also developed an asymmetric variant of this reaction sequence and have used this method to synthesize C1- and C2-symmetric diene ligands with high enantioinduction. Building upon these stepwise reactions, we eventually developed a simple one-pot procedure that uses stoichiometric amounts of a cobalt dinitrosoalkane complex for both inter- and intramolecular C-H functionalization. We can achieve catalysis in one-pot intramolecular reactions with a limited range of substrates. Our groups have also reported an analogous ruthenium dinitrosyl complex. In analogy to the cobalt complex, this ruthenium complex reacts with alkenes in the presence of neutral bidentate ligands, such as TMEDA, to give octahedral dinitrosoalkane complexes. Intramolecular functionalization or cyclization of numerous ruthenium dinitrosoalkane complexes proceeds under mild reaction conditions to give the functionalized organic products in excellent yields. However, despite extensive efforts, so far we have not been able to carry out intermolecular reactions of these complexes with a variety of electrophiles or C-H functionalization reactions. Although additional work is necessary to further boost the catalytic capabilities of both cobalt and ruthenium dinitrosyl complexes for vinylic C-H functionalization of simple alkenes, we believe this ligand-based vinylic C-H functionalization reaction has provided chemists with a useful set of tools for organic synthesis. PMID:24359109

Zhao, Chen; Crimmin, Mark R; Toste, F Dean; Bergman, Robert G

2014-02-18

342

Spectroscopic and magnetic investigations of some transition metal complexes with N-4-methoxyphenyl- N-4-chlorobenzoyl hydrazide as ligand  

NASA Astrophysics Data System (ADS)

The preparation, spectroscopic and magnetic properties of ML 2Cl 2 (M=Cu(II), Mn(II), Ni(II)) and [ML 3]Cl 3 (M=Fe(III), Cr(III)), L= N-4-methoxyphenyl- N-4-chlorobenzoyl hydrazide are reported. In all the studied complexes the N-4-methoxyphenyl- N-4-chlorobenzoyl hydrazide acts as a neutral bidentate chelating ligand with coordination involving the carbonyl oxygen and nitrogen atom of the secondary hydrazide group. The complexes appear to have an pseudo-octahedral stereochemistry. ESR parameters ( g1=4.432, g2=1.991, D=0.096 cm -1) and ?eff=3.55 ?B obtained for [CrL 3]Cl 3 also suggest the possibilities of magnetic dipole-dipole coupling interactions between Cr(III) ions.

David, L.; Rusu, M.; Cozar, O.; Rusu, D.; Todica, M.; Balan, C.

1999-05-01

343

Hydrothermal Synthesis of Two Ni(II) MetalOrganic Coordination Polymers Constructed from Dicarboxylate and Nitrogen-contained Ligands  

Microsoft Academic Search

Two new coordination polymers[Ni(2,4?-oba)(1,10-phen)]n (1) and {[Ni(2,4?-Hoba)2 (4,4?- bipy)(H2O)2]·2H2O}n (2) have been synthesized [2,4?-H2oba = 2-(4-carboxyphenoxy)benzoic acid, 1,10- phen = 1,10-phenanthroline and 4,4?-bipy = 4,4?-bipyridine]. The framework structures of these polymeric complexes have been determined by single-crystal X-ray diffraction studies. Complex 1 exhibits double-helical chains formed by ?-? stacking interactions from the phenyl rings of the 1,10-phen ligands. Complex 2

Feng Guo; Jian-Jun Li; Xian-Jiang Li; Bao-Yong Zhu; Xiu-Ling Zhang

2012-01-01

344

Liquid Injection Field Desorption Ionization Mass Spectrometry of Cyclic Metal Carbonyl Complexes with Tetra-Antimony Ligands  

NASA Astrophysics Data System (ADS)

Reactions of (norbornadiene)Cr(CO)4 or cis-(piperidine)2Mo(CO)4 with R2Sb-SbR2, and cyclo-(R'Sb)n (R' = Et, n-Pr; n = 4, 5) give the complexes cyclo-[M(CO)4(R2Sb-SbR'- SbR'-SbR2)] ( 1: M = Cr, R = Me, R'= Et; 2: M = Mo, R = Et, R' = Et; 3: M = Mo, R = Et, R' = n-Pr). Not accessible to established characterization methods, the oily, extremely reactive unpurified mixture of 3 with scrambled ligands was characterized by mass spectrometry using liquid injection field desorption ionization (LIFDI). [Figure not available: see fulltext.

Breunig, Hans J.; Linden, H. Bernhard; Moldovan, Ovidiu

2013-01-01

345

Tuning the stability and reactivity of metal-bound alkylperoxide by remote site substitution of the ligand.  

PubMed

An alkylperoxonickel(II) complex with hydrotris(3,5-diisopropyl-4-bromo-1-pyrazolyl)borate, [Ni(II)(OOtBu)(Tp(iPr2,Br))] (3 a), is synthesized, and its chemical properties are compared with those of the prototype non-brominated ligand derivative [Ni(II)(OOtBu)(Tp(iPr2))] (3 b; Tp(iPr2)=hydrotris(3,5-diisopropyl-1-pyrazolyl)borate). Same synthetic procedures for the prototype 3 b and its precursors can be employed to the synthesis of the Tp(iPr2,Br) analogues. The dimeric nickel(II)-hydroxo complex, [(Ni(II)Tp(iPr2,Br))(2)(mu-OH)(2)] (2 a), can be synthesized by the base hydrolysis of the labile complexes [Ni(II)(Y)(Tp(iPr2,Br))] (Y=NO(3) (1 a), OAc (1 a')), which are obtained by the metathesis of NaTp(iPr2,Br) with the corresponding nickel(II) salts, and the following dehydrative condensation of 2 a with the stoichiometric amount of tert-butylhydroperoxide yields 3 a. The unique structural characteristics of the prototype 3 b, that is, highly distorted geometry of the nickel center and intermediate coordination mode of the O--O moiety between eta(1) and eta(2), are kept in the brominated ligand analogue 3 a. The introduction of the electron-withdrawing substitutents on the distal site of Tp(R) affects the thermal stability and reactivity of the nickel(II)-alkylperoxo species. PMID:20589827

Hikichi, Shiro; Kobayashi, Chiho; Yoshizawa, Michito; Akita, Munetaka

2010-09-01

346

Reactivity of ligand-swapped mutants of the SCO protein from Bacillus subtilis. Isomers of the CCH metal binding motif.  

PubMed

The Synthesis of Cytochrome Oxidase protein, or SCO protein, is required for the assembly of cytochrome c oxidase in many mitochondrial and bacterial respiratory chains. SCOs have been proposed to deliver copper to the CuA site of cytochrome c oxidase. We have reported that Bacillus subtilis SCO (i.e., BsSCO) binds Cu(II) with high-affinity via a two-step process mediated by three conserved residues (i.e., two cysteines and one histidine, or the CCH motif). A remarkable feature in the reaction of reduced (i.e., di-thiol) BsSCO with copper is that it does not generate any of the disulfide form of BsSCO. This molecular aversion is proposed to be a consequence of a binding mechanism in which the initial copper complex of BsSCO does not involve cysteine, but instead involves nitrogen ligands. We test this proposal here by constructing two isomers of BsSCO in which the conserved copper binding residues (i.e., the CCH-motif) are retained, but their positions are altered. In these variants the two cysteines are exchanged with histidine, and both react transiently with copper (II) with distinct kinetic profiles. The reaction generates Cu(I) and the protein is oxidized to its disulfide form. EPR analysis supports a copper binding model in which cysteine, which is at the "histidine position" in the mutant, is part of an initial encounter complex with copper. When cysteine is the initial ligating residue an oxidation reaction ensues. In contrast initial binding to native BsSCO uses nitrogen-based ligands, and thereby avoids the opportunity for thiol oxidation. PMID:25192666

Yao, Xin; Andrews, Diann; Hill, Bruce C

2014-09-01

347

Phosphonate-anchored monolayers for antibody binding to magnetic nanoparticles.  

PubMed

Targeted delivery of magnetic iron oxide nanoparticles (IONPs) to a specific tissue can be achieved by conjugation with particular biological ligands on an appropriately functionalized IONP surface. To take best advantage of the unique magnetic properties of IONPs and to maximize their blood half-life, thin, strongly bonded, functionalized coatings are required. The work reported herein demonstrates the successful application of phosphonate-anchored self-assembled monolayers (SAMs) as ultrathin coatings for such particles. It also describes a new chemical approach to the anchoring of antibodies on the surface of SAM-coated IONPs (using nucleophilic aromatic substitution). This anchoring strategy results in stable, nonhydrolyzable, covalent attachment and allows the reactivity of the particles toward antibody binding to be activated in situ, such that prior to the activation the modified surface is stable for long-term storage. While the SAMs do not have the well-packed crystallinity of other such monolayers, their structure was studied using smooth model substrates based on an iron oxide layer on a double-side polished silicon wafer. In this way, atomic force microscopy, ellipsometry, and contact angle goniometry (tools that could not be applied to the nanoparticles' surfaces) could contribute to the determination of their monomolecular thickness and uniformity. Finally, the successful conjugation of IgG antibodies to the SAM-coated IONPs such that the antibodies retain their biological activity is verified by their complexation to a secondary fluorescent antibody. PMID:21863873

Benbenishty-Shamir, Helly; Gilert, Roni; Gotman, Irena; Gutmanas, Elazar Y; Sukenik, Chaim N

2011-10-01

348

Assessing electronic structure approaches for gas-ligand interactions in metal-organic frameworks: The CO{sub 2}-benzene complex  

SciTech Connect

Adsorption of gas molecules in metal-organic frameworks is governed by many factors, the most dominant of which are the interaction of the gas with open metal sites, and the interaction of the gas with the ligands. Herein, we examine the latter class of interaction in the context of CO{sub 2} binding to benzene. We begin by clarifying the geometry of the CO{sub 2}–benzene complex. We then generate a benchmark binding curve using a coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)] at the complete basis set (CBS) limit. Against this ?CCSD(T)/CBS standard, we evaluate a plethora of electronic structure approximations: Hartree-Fock, second-order Møller-Plesset perturbation theory (MP2) with the resolution-of-the-identity approximation, attenuated MP2, and a number of density functionals with and without different empirical and nonempirical van der Waals corrections. We find that finite-basis MP2 significantly overbinds the complex. On the other hand, even the simplest empirical correction to standard density functionals is sufficient to bring the binding energies to well within 1 kJ/mol of the benchmark, corresponding to an error of less than 10%; PBE-D in particular performs well. Methods that explicitly include nonlocal correlation kernels, such as VV10, vdW-DF2, and ?B97X-V, perform with similar accuracy for this system, as do ?B97X and M06-L.

Witte, Jonathon [Department of Chemistry, University of California, Berkeley, California 94720 (United States) [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Neaton, Jeffrey B., E-mail: jbneaton@lbl.gov [Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States); Head-Gordon, Martin, E-mail: mhg@cchem.berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States) [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2014-03-14

349

In situ metal imaging and Zn ligand-speciation in a soil-dwelling sentinel: complementary electron microprobe and synchrotron microbeam X-ray analyses.  

PubMed

Understanding the relationships between accumulated metal speciation in cells and tissues of ecologically significant taxa such as earthworms will improve risk assessments. Synchrotron-based ?-focus X-ray spectroscopy was used to detect, localize, and determine ligand-speciation of Zn and Pb in thin sections of two epigeic earthworm species collected from a Pb/Zn-mine soil. The findings indicated that Zn and Pb partition predominantly as typical hard acids (i.e., strong affinities for O-donors) within liverlike chloragocytes. Moreover, Zn speciation was very similar in the chloragog and intestinal epithelia but differed subtly in the kidneylike nephridial tubules; neither Zn nor Pb was detectable in the ventral nerve cord. High resolution X-ray mapping of high pressure-frozen, ultrathin, freeze-substituted sections in a transmission electron microscope (TEM), combined with conventional TEM structural analysis, identified a new cell type packed with highly organized rough endoplasmic reticulum and containing deposits of Cd (codistributed with S); there was no evidence that these cells are major depositories of Zn or Pb. These data may be used in a systems biology approach to assist in the interpretation of metal-evoked perturbations in whole-worm transcriptome and metabolome profiles. PMID:23198708

Morgan, A J; Mosselmans, J F W; Charnock, J M; Bennett, A; Winters, C; O'Reilly, M; Fisher, P; Andre, J; Turner, M; Gunning, P; Kille, P

2013-01-15

350

Synthesis, thermal and optical properties of metal(II) complexes with a novel ligand derived from pyrazolone-5  

NASA Astrophysics Data System (ADS)

Three novel metal(II) complexes, CoL2, NiL2 and CuL2 (L = (Z)-4-(2-(1,3-dimethyl-5-oxo-1H-pyrazol-4(5H)-ylidene)hydrazinyl)-1,5-dimethyl-2-phenyl-1,2-dihydropyrazol-3-one were synthesized. Their structures were postulated based on elemental analyses, 1H NMR, ESI-MS, FT-IR spectra and UV-vis spectra. The effect of different central metal(II) ions on absorption bands of the metal(II) complexes in CHCl3 solutions was researched. The result indicates that the bathochromic shift is CuL2 > NiL2 > CoL2. The absorption properties of thin films and thermal stability of these complexes are also discussed. In addition, the optical constants (complex refractive index N= n+ ik) and thickness of the complex thin films on polished single-crystal silicon substrates were measured by spectroscopic ellipsometry. Results indicate that the metal(II) complexes would be a promising recording medium candidate for blu-ray recordable optical storage system due to good absorption at 405 nm, high thermal stability and sharp thermal decomposition, and a high n values of 1.35-1.45 and a low k values of 0.33-0.39.

Li, Xiaoyi; Wu, Yiqun; Gu, Donghong; Gan, Fuxi

2011-03-01

351

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

E-print Network

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

Mochrie, Simon

352

Exact ligand cone angles.  

PubMed

Many properties of transition-metal complexes depend on the steric bulk of bound ligands, usually quantified by the Tolman (?) and solid (?) cone angles, which have proven utility but suffer from various limitations and coarse approximations. Here, we present an improved, mathematically rigorous method to determine an exact cone angle (?°) by solving for the most acute right circular cone that contains the entire ligand. The procedure is applicable to any ligand, planar or nonplanar, monodentate or polydentate, bound to any metal center in any environment, and it is ideal for analyzing structures from quantum chemical computations as well as X-ray crystallography experiments. Exact cone angles were evaluated for a wide array of phosphine and amine ligands bound to palladium, nickel, or platinum by optimizing structures using B3LYP/6-31G* density functional theory with effective core potentials for the transition metals. The mean absolute deviations of the standard ? and ? parameters from the exact cone angles were 15-25°, mostly caused by distortions from the assumed idealized structures. PMID:23408559

Bilbrey, Jenna A; Kazez, Arianna H; Locklin, Jason; Allen, Wesley D

2013-05-30

353

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

2012-11-01

354

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. PMID:15069193

Pfaltz, Andreas; Drury, William J.

2004-01-01

355

X-ray absorption edge spectroscopy of ligands bound to open-shell metal ions: Chlorine K-edge studies of covalency in CuCl sub 4 sup 2 minus  

SciTech Connect

Information on electronic structure can be obtained from analysis of x-ray absorption edge spectra. This approach has been used to obtain information from edges of transition metals like Cu, Fe, Ni, and Mo. It is also possible to directly study the absorption edge of ligands such as Cl and S bound to the metal. These edges fall in the 2-3-keV energy region where edge features are very well resolved. We report here the observation of an intense preedge transition associated with ligands bound to open-shell central atoms. We further show that the properties of these preedge features can be used to probe covalency in metal-ligand bonding. We have studied the ligand K edge of chlorine complexes of Cu and Zn: Cs{sub 2}CuCl{sub 4}, bis(creatininium)CuCl{sub 4}, and Cs{sub 2}ZnCl{sub 4}. The Cu site in Cs{sub 2}CuCl{sub 4} is distorted tetrahedral (D{sub 2d}), and the Zn site in Cs{sub 2}ZnCl{sub 4} is isostructural. Bis(creatininium)CuCl{sub 4} has a square-planar (D{sub 4h}) geometry. X-ray absorption spectroscopy (XAS) edge data were measured at the Stanford Synchrotron Radiation Laboratory by using methodology that has been previously described.

Hedman, B.; Hodgson, K.O.; Solomon, E.I. (Stanford Univ., CA (USA))

1990-02-14

356

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

PubMed

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

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

2012-02-21

357

Synthesis, crystal structures, luminescence properties of two metal coordination polymers derived from 5-substituted isophthalate and flexible bis (triazole) ligands  

NASA Astrophysics Data System (ADS)

Two new metal complexes, [Ni(btx)(nip)(H2O)]n (1), {[Cd(btx)(mip)(H2O)]·H2O}n (2) (btx = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene, H2nip = 5-nitroisophthalic acid, H2mip = 5-methyisophthalic acid) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction methods, IR spectroscopy, TGA and elemental analysis. Complex 1 features a 3D metal-organic framework with three-fold interpenetrating CdSO4-type topology. Complex 2 exhibits a 2D network with square grid units, which is further extended into a rare 3,5T1 three-dimensional supramolecular network via three modes of classical Osbnd H⋯O hydrogen bonds. In addition, luminescence properties of 1 and 2 have also been investigated in the solid state.

Ming, Chun-lun; Wang, Li-na; Hecke, Kristof Van; Cui, Guang-hua

2014-08-01

358

Synthesis, crystal structures, luminescence properties of two metal coordination polymers derived from 5-substituted isophthalate and flexible bis (triazole) ligands.  

PubMed

Two new metal complexes, [Ni(btx)(nip)(H2O)]n (1), {[Cd(btx)(mip)(H2O)]·H2O}n (2) (btx=1,4-bis(1,2,4-triazol-1-ylmethyl)benzene, H2nip=5-nitroisophthalic acid, H2mip=5-methyisophthalic acid) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction methods, IR spectroscopy, TGA and elemental analysis. Complex 1 features a 3D metal-organic framework with three-fold interpenetrating CdSO4-type topology. Complex 2 exhibits a 2D network with square grid units, which is further extended into a rare 3,5T1 three-dimensional supramolecular network via three modes of classical OH?O hydrogen bonds. In addition, luminescence properties of 1 and 2 have also been investigated in the solid state. PMID:24727171

Ming, Chun-lun; Wang, Li-na; Van Hecke, Kristof; Cui, Guang-hua

2014-08-14

359

Turn-on phosphorescence by metal coordination to a multivalent terpyridine ligand: a new paradigm for luminescent sensors.  

PubMed

A hexathiobenzene molecule carrying six terpyridine (tpy) units at the periphery has been designed to couple the aggregation induced phosphorescence, displayed by the core in the solid state, to the metal binding properties of the tpy units. Upon Mg(2+) complexation in THF solution, phosphorescence of the hexathiobenzene core is turned on. Metal ion coordination yields the formation of a supramolecular polymer which hinders intramolecular rotations and motions of the core chromophore, thus favoring radiative deactivation of the luminescent excited state. Upon excitation of the [Mg(tpy)2](2+) units of the polymeric structure, sensitization of the core phosphorescence takes place with >90% efficiency. The light-harvesting polymeric antenna can be disassembled upon fluoride ion addition, thereby switching off luminescence and offering a new tool for fluoride ion sensing. This unique system can, thus, serve as cation or anion sensor. PMID:24725096

Fermi, Andrea; Bergamini, Giacomo; Roy, Myriam; Gingras, Marc; Ceroni, Paola

2014-04-30

360

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

PubMed Central

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

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

2012-01-01

361

Synthesis, crystal structures, luminescence and catalytic properties of two d(10) metal coordination polymers constructed from mixed ligands.  

PubMed

Two new coordination polymers [Cd(bmb)(hmph)]n (1), {[Ag(bmb)]·H2btc}n (2) (bmb=1,4-bis(2-methylbenzimidazol-1-ylmethyl)benzene, H2hmph=homophthalic acid, H3btc=1,3,5-benzenetetracarboxylic acid) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction methods, IR spectroscopy, TGA, XRPD and elemental analysis. Complex 1 features a 3D threefold interpenetrating dia array with a 4-connected 6(6) topology. Complex 2 shows a 1D helix chain structure connected by L1 ligands, which is finally extended into a rarely 2D 4L2 supramolecular network via C-H?O hydrogen bond interactions. In addition, the luminescence and catalytic properties of the two complexes for the degradation of the methyl orange azo dye in a Fenton-like process were presented. The degradation efficiency of the methyl orange azo dye for 1 and 2 are 56% and 96%, respectively. PMID:25576941

Wang, Xiao-Xiao; Zhang, Ming-Xi; Yu, Baoyi; Van Hecke, Kristof; Cui, Guang-Hua

2015-03-15

362

Heterolytic Cleavage of Dihydrogen by an Iron(II) PNP Pincer Complex via Metal–Ligand Cooperation  

PubMed Central

The bis-carbonyl Fe(II) complex trans-[Fe(PNP-iPr)(CO)2Cl]+ reacts with Zn as reducing agent under a dihydrogen atmosphere to give the Fe(II) hydride complex cis-[Fe(PNP-iPr)(CO)2H]+ in 97% isolated yield. A crucial step in this reaction seems to be the reduction of the acidic NH protons of the PNP-iPr ligand to afford H2 and the coordinatively unsaturated intermediate [Fe(PNPH-iPr)(CO)2]+ bearing a dearomatized pyridine moiety. This species is able to bind and heterolytically cleave H2 to give cis-[Fe(PNP-iPr)(CO)2H]+. The mechanism of this reaction has been studied by DFT calculations. The proposed mechanism was supported by deuterium labeling experiments using D2 and the N-deuterated isotopologue of trans-[Fe(PNP-iPr)(CO)2Cl]+. While in the first case deuterium was partially incorporated into both N and Fe sites, in the latter case no reaction took place. In addition, the N-methylated complex trans-[Fe(PNPMe-iPr)(CO)2Cl]+ was prepared, showing no reactions with Zn and H2 under the same reaction conditions. An alternative synthesis of cis-[Fe(PNP-iPr)(CO)2H]+ was developed utilizing the Fe(0) complex [Fe(PNP-iPr)(CO)2]. This compound is obtained in high yield by treatment of either trans-[Fe(PNP-iPr)(CO)2Cl]+ or [Fe(PNP-iPr)Cl2] with an excess of NaHg or a stoichiometric amount of KC8 in the presence of carbon monoxide. Protonation of [Fe(PNP-iPr)(CO)2] with HBF4 gave the hydride complex cis-[Fe(PNP-iPr)(CO)2H]+. X-ray structures of both cis-[Fe(PNP-iPr)(CO)2H]+ and [Fe(PNP-iPr)(CO)2] are presented. PMID:23990692

2013-01-01

363

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

364

Cubane-type Cu(II)4 and Mn(II)2Mn(III)2 complexes based on pyridoxine: a versatile ligand for metal assembling.  

PubMed

By using Vitamin B6 in its monodeprotonated pyridoxine form (PN-H) [PN = 3-hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridine], two tetranuclear compounds of formula [Mn4(PN-H)4(CH3CO2)3Cl2]Cl·2CH3OH·2H2O (1) and [Cu4(PN-H)4Cl2(H2O)2]Cl2 (2) have been synthesized and magneto-structurally characterized. 1 crystallizes in the triclinic system with space group P1 whereas 2 crystallizes in the orthorhombic system with Fdd2 as space group. They exhibit Mn(II)2Mn(III)2 (1) and Cu(II)4 (2) cubane cores containing four monodeprotonated pyridoxine groups simultaneously acting as chelating and bridging ligands (1 and 2), three bridging acetate ligands in the syn-syn conformation (1), and two terminally bound chloride anions (1 and 2) plus two coordinated water molecules (2). The electroneutrality is achieved by the presence of chloride counterions in both compounds. Tri- [Mn(1) and Mn(3)] and divalent [Mn(2) and Mn(4)] manganese centers coexist in 1, all being six-coordinate with distorted Mn(1/3)O6 and Mn(2/4)O5Cl octahedral surroundings, respectively, the equatorial Mn-O bonds being about 0.2 Å shorter at the former ones. The two crystallographically independent copper(II) ions in 2 are five-coordinate in somewhat distorted CuO5 [Cu(1)] and CuO4Cl [Cu(2)] square pyramidal geometries. The values of the intracore metal-metal separation cover the ranges 3.144(1)-3.535(1) (1) and 2.922(6)-3.376(1) Å (2). The magnetic properties of 1 and 2 were investigated in the temperature range 1.9-300 K, and they correspond to an overall antiferromagnetic behavior with susceptibility maxima at 5.0 (1) and 65.0 K (2). The analysis of the magnetic susceptibility data showed the coexistence of intracore antiferro- and ferromagnetic interactions in the two compounds. Their values compare well with those existing in the literature for the parent systems. PMID:24074249

Marino, Nadia; Armentano, Donatella; Mastropietro, Teresa F; Julve, Miguel; De Munno, Giovanni; Martínez-Lillo, José

2013-10-21

365

The effects of phosphorous donor ligand substitution on the reactivity of anionic group 6 transition metal carbonyl hydrides  

E-print Network

substituted anionic gr oup 6 transition metal hydrides, HW(CO) P (M Cr and W), has further defined the nature of these compounds. This group has been expanded such that it now includes P(OCH ) , P(C6H ) P(CH3)(C6H&) , P(CH3)3, P(OC6H ) , and As(C6H... ) substituted hydr zdes. In several cases, the reactivity of these compounds has been examined relative to that of their all-car bonyl relatives, HM(CO ) . They have been characterized by infrared spectroscopy studies that exhibit, v(CO) band frequencies...

Lusk, Richard Jay

1986-01-01

366

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

SciTech Connect

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

Dharmawardana, U.R.

1992-12-31

367

Excited State Properties of Paddlewheel Complexes Involving Metal-Metal (m = MO, w) Quadruple Bonds Supported by Amidinate and Carboxylate Ligands  

Microsoft Academic Search

Spectroscopic studies of the trans-substituted compounds M2(O2CCH3)2[(NiPr)2CCCR]2 (where M = Mo or W and R = aromatic hydrocarbon) have been carried out. These complexes have been shown to possess optically active excited states in both the singlet and triplet manifolds that can be classified as either charge transfer or metal centered in character. The nature of the excited states has

Brian G. Alberding; Malcolm H. Chisholm; Terry L. Gustafson

2010-01-01

368

Tightening procedures for large diameter anchor bolts  

E-print Network

anchor bolt failures in Michigan in January and February of 1990, one of which resulted in a motorist fatality, have emphasized these concerns. Michigan DOT, in reaction to these two failures, initiated a study of their practice in designing... procedures. Another source of laboratory data on the fatigue strength of anchor bolts was a series of reports from the Michigan Department of Transportation (MDOT). The static and dynamic properties of anchor bolts were tested by the Materials...

Abraham, Ryan Charles

1997-01-01

369

A lunar/Martian anchor emplacement system  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

370

Transformation of metal-organic framework to polymer gel by cross-linking the organic ligands preorganized in metal-organic framework.  

PubMed

Until now, seamless fusion of metal-organic frameworks (MOFs) and covalently cross-linked polymer gels (PG) at molecular level has been extremely rare, since these two matters have been regarded as opposite, that is, hard versus soft. In this report, we demonstrate transformation of cubic MOF crystals to PG via inner cross-linking of the organic linkers in the void space of MOF, followed by decomposition of the metal coordination. The obtained PG behaved as a polyelectrolyte gel, indicating the high content of ionic groups inside. Metal ions were well adsorbed in the PG due to its densely packed carboxylate groups. A chimera-type hybrid material consisting of MOF and PG was obtained by partial hydrolysis of resulting cross-linked MOF. The shape of resulting PG network well reflected the crystal structure of MOF employed as a template. Our results will connect the two different network materials that have been ever studied in the two different fields to provide new soft and hard hybrid materials, and the unique copolymerization in the large void space of the MOF will open a new horizon toward "ideal network polymers" never prepared before now. PMID:23472763

Ishiwata, Takumi; Furukawa, Yuki; Sugikawa, Kouta; Kokado, Kenta; Sada, Kazuki

2013-04-10

371

Heterolytic Cleavage of Dihydrogen by an Iron(II) PNP Pincer Complex via Metal-Ligand Cooperation.  

PubMed

The bis-carbonyl Fe(II) complex trans-[Fe(PNP-iPr)(CO)2Cl](+) reacts with Zn as reducing agent under a dihydrogen atmosphere to give the Fe(II) hydride complex cis-[Fe(PNP-iPr)(CO)2H](+) in 97% isolated yield. A crucial step in this reaction seems to be the reduction of the acidic NH protons of the PNP-iPr ligand to afford H2 and the coordinatively unsaturated intermediate [Fe(PNP(H)-iPr)(CO)2](+) bearing a dearomatized pyridine moiety. This species is able to bind and heterolytically cleave H2 to give cis-[Fe(PNP-iPr)(CO)2H](+). The mechanism of this reaction has been studied by DFT calculations. The proposed mechanism was supported by deuterium labeling experiments using D2 and the N-deuterated isotopologue of trans-[Fe(PNP-iPr)(CO)2Cl](+). While in the first case deuterium was partially incorporated into both N and Fe sites, in the latter case no reaction took place. In addition, the N-methylated complex trans-[Fe(PNP(Me)-iPr)(CO)2Cl](+) was prepared, showing no reactions with Zn and H2 under the same reaction conditions. An alternative synthesis of cis-[Fe(PNP-iPr)(CO)2H](+) was developed utilizing the Fe(0) complex [Fe(PNP-iPr)(CO)2]. This compound is obtained in high yield by treatment of either trans-[Fe(PNP-iPr)(CO)2Cl](+) or [Fe(PNP-iPr)Cl2] with an excess of NaHg or a stoichiometric amount of KC8 in the presence of carbon monoxide. Protonation of [Fe(PNP-iPr)(CO)2] with HBF4 gave the hydride complex cis-[Fe(PNP-iPr)(CO)2H](+). X-ray structures of both cis-[Fe(PNP-iPr)(CO)2H](+) and [Fe(PNP-iPr)(CO)2] are presented. PMID:23990692

Bichler, Bernhard; Holzhacker, Christian; Stöger, Berthold; Puchberger, Michael; Veiros, Luis F; Kirchner, Karl

2013-08-12

372

Bioabsorbable Suture Anchor Migration to the Acromioclavicular Joint: How Far Can These Implants Go?  

PubMed Central

Few complications regarding the use of bioabsorbable suture anchors in the shoulder have been reported. What motivated this case report was the unusual location of the anchor, found in the acromioclavicular joint which, to our knowledge, has never been reported so far. A 53-year old male with previous rotator cuff (RC) repair using bioabsorbable suture anchors presented with pain and weakness after 2 years of surgery. A suspicion of retear of the RC led to request of a magnetic resonance image, in which the implant was found located in the acromioclavicular joint. The complications reported with the use of metallic implants around the shoulder led to the development of bioabsorbable anchors. Advantages are their absorption over time, minimizing the risk of migration or interference with revision surgery, less artifacts with magnetic resonance imaging, and tendon-to-bone repair strength similar to metallic anchors. Since the use of bioabsorbable suture anchors is increasing, it is important to know the possible complications associated with these devices. PMID:25114822

Garofo, Guilherme; D'Elia, Caio O.; Bitar, Alexandre C.

2014-01-01

373

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

374

Mixed ligand chelate therapy for plutonium and toxic metals from energy power production. Final report, April 15, 1977-October 14, 1980. [Mice  

SciTech Connect

The results of experiments are summarized on the ability of combinations of chelating agents to modify the genotoxicity or tissue distributions. The mutagenicities of Cr and of chelating agents were determined. The metals described in the report are Pu(IV), Cd(II), Cr(III), and Cr(VI). Accurate measurements were made of the ability of CaNa/sub 2/EDTA, CaNa/sub 3/DTPA, and DMPS to reduce mortality in mice given doses (i.p.) of CdCl/sub 2/ well above the 100% lethal level. The efficacy in terms of the mmoles/kg needed to reduce the mortality was: DTPA > EDTA > DMPS. The combination of DTPA + DMPS proved most promising though little evidence for mixed complex formation was noted. Potentiometric titration studies the case of Pu(IV) a few combinations proved effective, but only when given shortly after Pu administration and then only in the liver but not the skeleton. It is recommended that metabolically stable chelating agents be used in combinations, especially for those combinations which may form very stable mixed ligand chelates.

Schubert, J.

1980-10-14

375

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

NASA Astrophysics Data System (ADS)

Five new transition metal coordination polymers based on H 2tzda and co-ligand bpe, {[ M(tzda)(bpe)]·H 2O} n [ M=Zn( 1), Cd( 2), Mn( 3), Co( 4)] and [Ni 2(tzda) 2(bpe) 2(H 2O)] n ( 5) [H 2tzda=(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

376

The research of acoustic wave non-destructive examination technology for anchoring quality of anchored bolt  

Microsoft Academic Search

The key factor to the evaluation of bolt performance is its length embedded in cement mortar and the saturation between the bolt and mortar. Therefore, the main task of testing the quality of anchored bolt is to evaluate these two technical specifications. The earlier means of anchoring test is to test the anchor pullout resistance. But there are many flaws

Ji-min Zhao; Shi-feng Yang; Pei-cheng Tang; Xiu-qing Wang

2010-01-01

377

Anchored Instruction and Anchored Assessment: An Ecological Approach to Measuring Situated Learning.  

ERIC Educational Resources Information Center

Anchored instruction and anchored assessment are described and illustrated through a mathematics problem from the Jasper problem solving series developed at Vanderbilt University in Nashville (Tennessee). Anchored instruction is instruction situated in a context complex enough to provide meaning and reasons for why information is useful. Problems…

Young, Michael F.; Kulikowich, Jonna M.

378

Excited State Properties of Paddlewheel Complexes Involving Metal-Metal (m = MO, w) Quadruple Bonds Supported by Amidinate and Carboxylate Ligands  

NASA Astrophysics Data System (ADS)

Spectroscopic studies of the trans-substituted compounds M2(O2CCH3)2[(NiPr)2CCCR]2 (where M = Mo or W and R = aromatic hydrocarbon) have been carried out. These complexes have been shown to possess optically active excited states in both the singlet and triplet manifolds that can be classified as either charge transfer or metal centered in character. The nature of the excited states has been assigned based on steady state absorbance and emission studies and supported by electronic structure calculations. Furthermore, excited state dynamics have been determined from both ns- and fs-transient absorption spectroscopies. Comparisons will be made between molybdenum and tungsten.

Alberding, Brian G.; Chisholm, Malcolm H.; Gustafson, Terry L.

2010-06-01

379

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

NASA Astrophysics Data System (ADS)

A series of metal(II) complexes of VO(II), Co(II), Ni(II), Cu(II) and Zn(II) have been synthesized from the azo Schiff base ligand 4-((E)-4-((E)-(4-chlorophenyl)diazenyl)-2-hydroxybenzylideneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (CDHBAP) and characterized by elemental analysis, spectral (IR, UV-Vis, 1H NMR, ESR and EI-mass), magnetic moment measurements, molar conductance, DNA, SEM, X-ray crystallography and fluorescence studies. The electronic absorption spectra and magnetic susceptibility measurements of the complexes indicate square pyramidal geometry for VO(II) and octahedral geometry for all the other complexes. The important infrared (IR) spectral bands corresponding to the active groups in the ligand and the solid complexes under investigation were studied and implies that CDHBAP is coordinated to the metal ions in a neutral tridentate manner. The redox behavior of copper(II) and vanadyl(II) complexes have been studied by cyclic voltammetry. The nuclease activity of the above metal(II) complexes shows that the complexes cleave DNA. All the synthesized complexes can serve as potential photoactive materials as indicated from their characteristic fluorescence properties. The antibacterial and antifungal activities of the synthesized ligand and its metal complexes were screened against bacterial species (Staphylococcus aureus, Salmonella typhi, Escherichia coli, Bacillus subtilis, Shigella sonnie) and fungi (Candida albicans, Aspergillus niger, Rhizoctonia bataicola). Amikacin and Ketoconozole were used as references for antibacterial and antifungal studies. The activity data show that the metal complexes have a promising biological activity comparable with the parent Schiff base ligand against bacterial and fungal species. The second harmonic generation (SHG) efficiency of the ligand was measured and the NLO (non-linear optical) properties of the ligand are expected to result in the realization of advanced optical devices in optical fiber communication (OFC) and optical computing. The SEM image of the copper(II) complex implies that the size of the particles is 1 ?m.

Anitha, C.; Sheela, C. D.; Tharmaraj, P.; Sumathi, S.

2012-10-01

380

The maximal affinity of ligands  

PubMed Central

We explore the question of what are the best ligands for macromolecular targets. A survey of experimental data on a large number of the strongest-binding ligands indicates that the free energy of binding increases with the number of nonhydrogen atoms with an initial slope of ??1.5 kcal/mol (1 cal = 4.18 J) per atom. For ligands that contain more than 15 nonhydrogen atoms, the free energy of binding increases very little with relative molecular mass. This nonlinearity is largely ascribed to nonthermodynamic factors. An analysis of the dominant interactions suggests that van der Waals interactions and hydrophobic effects provide a reasonable basis for understanding binding affinities across the entire set of ligands. Interesting outliers that bind unusually strongly on a per atom basis include metal ions, covalently attached ligands, and a few well known complexes such as biotin–avidin. PMID:10468550

Kuntz, I. D.; Chen, K.; Sharp, K. A.; Kollman, P. A.

1999-01-01

381

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

PubMed

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

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

2009-08-01

382

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

383

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

384

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

PubMed

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

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

2014-07-28

385

Role of Cu and pb on Ni bioaccumulation by Chlamydomonas reinhardtii: Validation of the biotic ligand model in binary metal Mixtures.  

PubMed

Ni, Pb and Cu uptake by Chlamydomonas reinhardtii has been quantified in single and binary metal systems in order to test some of the key assumptions of the biotic ligand model (BLM). Experiments were performed in solutions containing 5×10(-7)M of free metal at 30°C and pH 6. Nickel internalization fluxes (Jint) were measured in the presence of various concentrations of lead or copper from 5×10(-8)M to 5×10(-6)M at pH 6.0. Competition experiments did not show a straightforward antagonistic competition, as would be predicted by BLM. Synergistic and antagonistic effects were observed in binary metal systems which implies that bioaccumulation process is much more dynamic than assumed in the equilibrium models. Ni uptake decreased significantly in the presence of Cu(2+) concentrations higher than 5×10(-7)M. However, a maximum value of Ni uptake was observed at 5×10(-7)M Pb(2+). Cu(2+) was shown to compete strongly with Ni for uptake, having a higher binding affinity to Ni transport sites (KCu-Rs=10(6.95)M(-1)) than to Cu transport sites (KCu-Rs'=10(6.22)M(-1)). In contrast, the effect of Pb(2+) on Ni uptake could not be explained by a simple competitive equilibrium with the transport sites of Ni such as the BLM. On the other hand, internalization fluxes of Cu and Pb were nearly constant in the absence and in the presence of Ni, implying that nickel had no effect on the uptake of copper or lead. The calculated affinity constant of Cu to Ni transport sites in the presence of Ni was similar to that obtained in the absence of Ni (K'Cu-Rs'=10(6.22)M(-1)). It was further concluded that Cu and Pb did not interact with the same active sites on the cell surface. Ni and Cu were shown to interfere with Mg and Na transporters, while Pb uptake was thought to occur by the Ca pathway. PMID:25483376

Flouty, Roula; Khalaf, Gaby

2015-03-01

386

Enhancing CO(2) separation ability of a metal-organic framework by post-synthetic ligand exchange with flexible aliphatic carboxylates.  

PubMed

A series of porous metal-organic frameworks having flexible carboxylic acid pendants in their pores (UiO-66-ADn: n=4, 6, 8, and 10, where n denotes the number of carbons in a pendant) has been synthesized by post-synthetic ligand exchange of terephthalate in UiO-66 with a series of alkanedioic acids (HO2 C(CH2 )n-2 CO2 H). NMR, IR, PXRD, TEM, and mass spectral data have suggested that a terephthalate linker in UiO-66 was substituted by two alkanedioate moieties, resulting in free carboxyl pendants in the pores. When post-synthetically modified UiO-66 was partially digested by adjusting the amount of added HF/sample, NMR spectra indicated that the ratio of alkanedioic acid/terephthalic acid was increased with smaller amounts of acid, implying that the ligand substitution proceeded from the outer layer of the particles. Gas sorption studies indicated that the surface areas and the pore volumes of all UiO-66-ADns were decreased compared to those of UiO-66, and that the CO2 adsorption capacities of UiO-66-ADn (n=4, 8) were similar to that of UiO-66. In the case of UiO-66-AD6, the CO2 uptake capacity was 34?% higher at 298?K and 58?% higher at 323?K compared to those of UiO-66. It was elucidated by thermodynamic calculations that the introduction of flexible carboxyl pendants of appropriate length has two effects: 1)?it increases the interaction enthalpy between the host framework and CO2 molecules, and 2)?it mitigates the entropy loss upon CO2 adsorption due to the formation of multiple configurations for the interactions between carboxyl groups and CO2 molecules. The ideal adsorption solution theory (IAST) selectivity for CO2 adsorption over that of CH4 was enhanced for all of the UiO-66-ADns compared to that of UiO-66 at 298?K. In particular, UiO-66-AD6 showed the most strongly enhanced CO2 uptake capacity and significantly increased selectivity for CO2 adsorption over that of CH4 at ambient temperature, suggesting that it is a promising material for sequestering CO2 from landfill gas. PMID:24390910

Hong, Dae Ho; Suh, Myunghyun Paik

2014-01-01

387

Crossed ring anchored disk resonator for self-alignment of the anchor  

PubMed Central

Misalignment is a problematic challenge in RF MEMS resonators. It causes asymmetry in the ultra symmetric radial contour mode disk resonators and degrades their performance by increasing the insertion loss and decreasing their quality factors (Q). Self-alignment method seems to be a good solution for misalignment problem, but it cannot be directly applied on high performance ring shape anchored resonators. This paper discusses misalignment effects for the ring shape anchored resonators and proposes a method for reconfiguring its anchor to be compatible with self-alignment process. Simulation results validate that the crossed ring anchor structure has the same resonance characteristics with the complete ring shape anchored resonator. PMID:25685477

Baghelani, Masoud; Ghavifekr, Habib Badri; Ebrahimi, Afshin

2013-01-01

388

New concept to remove heavy metals from liquid waste based on electrochemical pH-switchable immobilized ligands  

NASA Astrophysics Data System (ADS)

Absorption on resins is often used as secondary step in the treatment of water-based effluents, in order to reach very low concentrations. The separation of the trapped effluents from the resins and the regeneration of the resins for further use create wide volumes of secondary effluents coming from the washings of the resins with chemical reagents. We propose an alternative solution based on a "surface strategy" through adsorption phenomena and electrical control of the expulsion stage. The final goal is to limit or ideally to avoid the use of chemical reagents at the expulsion (or regeneration) stage of the depolluting process. Heavy metal ions were captured on active filters composed by a conducting surface covered by poly-4-vinylpyridine (P 4VP). Due to pyridine groups those polymer films have chelating properties for copper ions. Our strategy for electrical triggering of the copper expulsion in aqueous medium is based on pH sensitive chelating groups. Applying moderate electro-oxidizing conditions generates acidic conditions in the vicinity of the electrode, i.e. "inside" the polymer film. This allows a "switch-off" of the complexing properties of the film from the basic form of pyridine to pyridinium. Interestingly, no buffer washing is necessary to restore (or "switch-on") the complexing properties of the polymer film because the pH of the external medium is left unchanged by the electrochemical effect that affects only the vicinity of the electrode. Switch-on/switch-off cycles are followed and attested by IR spectroscopy and EQCM method.

Pascal, Viel; Laetitia, Dubois; Joël, Lyskawa; Marc, Sallé; Serge, Palacin

2007-01-01

389

MFR PAPER 1070 Anchor tags show ment  

E-print Network

a high retention rate. be nonlethal. and quicl-. to apply. The recently developed Floy anchor taggi ng spines. The T bar po rtion of the tag was insert ed through the carapace into the anterior portion of the right branchial cavity . The anchor po rti on of th e tag often failed to return to its norm al shape

390

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2011 CFR

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

2011-04-01

391

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2010 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....

2010-04-01

392

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2012 CFR

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

2012-04-01

393

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

394

24 CFR 3285.401 - Anchoring instructions.  

Code of Federal Regulations, 2014 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....

2014-04-01

395

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

396

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

397

Case Type, Anchoring Errors, and Counselor Education.  

ERIC Educational Resources Information Center

Graduate students (N=28) in counseling read client information that was nonemotive and factual, indicative of well-adjustment, or suggestive of need for psychological help, then rated mental health of clients. Results revealed anchoring errors for all cases regardless of severity; presence of anchoring errors was restricted to those made as result…

Pain, Michelle D.; Sharpley, Christopher F.

1988-01-01

398

76 FR 30301 - Commercial Acquisition; Anchor Tenancy  

Federal Register 2010, 2011, 2012, 2013, 2014

...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

399

SOLVENT EXTRACTION OF THE RARE-EARTH METAL IONS BY A CONE-SHAPED CALDC[4]ARENE SUBSTITUTED AT THE LOWER RTM BY FOUR CH2P(O)Ph2 LIGANDS  

Microsoft Academic Search

The extraction properties of cone-5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis(diphenylphosphinoylmethoxy)calix[4]arene (1) in 1,2-dichloroethane towards rare-earth metal ions at 25 °C have been investigated. The slope analysis showed a 1:1 metal\\/ligand ratio for the extracted species (La, Eu, Er and Y). The distribution coefficients increase with the polarity of the diluents : chloroform ? dichioromethane ? 1,2-dichloroethane ? nitrobenzene. In the competitive extraction of 11 rare-earth

M. R. Yaftian; M. Burgard; D. Matt; C. B. Dieleman; F. Rastegar

1997-01-01

400

Bonding Interactions Generated by Halogen Oxidation of Zirconium(IV) Redox-Active Ligand Complexes  

E-print Network

of frontier orbital mixing between the ligand-based orbitals and the metal-based d-orbital manifold of transition metal ions provide an archetype for understanding the interplay of ligand-based and metal-type ligands coordinated to transition metals, the dianionic catecholate form, the monoanionic semi

Baik, Mu-Hyun

401

Cooperative metal-ligand assisted E/Z isomerization and cyano activation at Cu(II) and Co(II) complexes of arylhydrazones of active methylene nitriles.  

PubMed

New (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzoic acid (H2L(4)) and known sodium 2-(2-(dicyanomethylene)hydrazinyl)benzenesulfonate (NaHL(1)), 2-(2-(dicyano-methylene)hydrazinyl)benzoic acid (H2L(2)), and sodium (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzenesulfonate (NaHL(3)) were used in the template synthesis of a series of Cu(II) and Co(II) complexes [Cu(H2O)2L(1a)]·H2O (1), [Cu(H2O)(3-pyon)L(1b)]·H2O (2), [Cu(H2O)(4-pyon)L(1b)] (3), [Co(H2O)((CH3)2NCHO)(?-L(2a))]2·(CH3)2NCHO (4), [Cu3(?3-OH)(NO3)(CH3OH)(?2-X)3(?2-HL(3))] (5), [Cu(H2O)(py)L(3)]·H2O (6), [Cu(H2O)2(?-L(4))]6·6H2O (7), [Cu(2-cnpy(b))2(L(1b))2]·2H2O (8), [Cu(2-cnpy(a))2(L(1a))2]·2H2O (9), and [Cu(H2O)(4-cnpy)(L(1a))2] (10), where 3-pyon = 1-(pyridin-3-yl)ethanone, 4-pyon = 1-(pyridin-4-yl)ethanone, py = pyridine, HX = syn-2-pyridinealdoxime, 4-cnpy = 4-cyanopyridine; 2-cnpy(a), 2-cnpy(b), L(1a), L(1b), L(2a) are the ligands derived from nucleophilic attack of methanol (a) or water (b) on a cyano group of 2-cyanopyridine (2-cnpy), L(1) or L(2), respectively, giving the corresponding iminoesters (2-cnpy(a), L(1a) or L(2a)) or carboxamides (2-cnpy(b) or L(1b)). An auxiliary ligand, namely syn-2-pyridinealdoxime or pyridine, acting cooperatively with the metal ion (Cu(II) in this case), induced an E/Z isomerization of the H2L(4) ligand; the E- and Z-isomers were isolated separately and fully characterized (compounds 9 and 10, respectively). A one-pot activation of nitrile groups in different molecules was achieved in the syntheses of 8 and 9. Complexes 1-10 are catalyst precursors for the solvent-free microwave (MW)-assisted selective oxidation of secondary alcohols to the corresponding ketones, with typical yields in the 29-99% range (TOFs up to 4.94 × 10(3) h(-1)) after 30 min of MW irradiation. PMID:25148569

Mahmudov, Kamran T; Kopylovich, Maximilian N; Sabbatini, Alessandra; Drew, Michael G B; Martins, Luísa M D R S; Pettinari, Claudio; Pombeiro, Armando J L

2014-09-15

402

Heteronuclear, mixed-metal Ag(I)-Mn(II) coordination polymers with bridging N-pyridinylisonicotinohydrazide ligands: synthesis, crystal structures, magnetic and photoluminescence properties.  

PubMed

Mixed-metal dicyanoargentate-bridged coordination polymers of Ag(i)-Mn(ii) have been prepared and their structure and magnetic properties were determined. Reaction of manganese(ii) chloride and potassium dicyanoargentate(i) with (X)(pyridin-2-ylmethylene)isonicotinohydrazide ligands (HL(1) X = Ph, HL(2) X = Me, HL(3) X = H) produced the coordination polymer 2D-[Mn(?-L(1))(Cl)(?-NCAgCN)Mn0.5(CH3OH)]n (), 1D-{[Mn(L(2))(Cl)(?-NCAgCN)Mn0.5(CH3OH)]CH3OH}n () and [Mn(L(3))(Cl)(?-NCAgCN)Mn0.5(CH3OH)]n () in good yields. Trinuclear {Mn(?-L(1))Mn(?-L(1))Mn} and [Ag(CN)2](-) building units form a two-dimensional slab in and 1D strands in . Variable temperature magnetic susceptibility measurements showed that despite the long distance among the high spin Mn(ii) ions [10.4676(12) Å and 10.522(1) Å, for and , respectively], weak antiferromagnetic coupling takes place through the long NC-Ag-CN bridge. The best fit parameters to the model led to the magnetic coupling constant of J = -0.1 and J = -0.47 cm(-1) for and , respectively. The photoluminescence behaviour of compounds and was studied. The spectrum of compound shows a broad emission centered at about 450 nm and two excitation maxima at 270 and 310 nm. PMID:24967880

Bikas, Rahman; Hosseini-Monfared, Hassan; Vasylyeva, Vera; Sanchiz, Joaquín; Alonso, Javier; Barandiaran, Jose Manuel; Janiak, Christoph

2014-08-21

403

Synthesis and characterization of d10 metal complexes with mixed 1,3-di(1H-imidazol-4-yl)benzene and multicarboxylate ligands  

NASA Astrophysics Data System (ADS)

Seven new coordination polymers [Zn(H2L)(mbdc)] (1), [Zn(H3L)(btc)] (2), [Zn(H2L)(Hbtc)] (3), [Zn(H2L)(Hbtc)]·H2O (4), [Zn2(H2L)(btc)(?2-OH)] (5), [Cd(H2L)(mbdc)] (6) and [Cd3(H2L)2(btc)2(H2O)]·5H2O (7) were synthesized by reactions of the corresponding metal salt with rigid ligand 1,3-di(1H-imidazol-4-yl)benzene (H2L) and different carboxylic acids of 1,3-benzenedicarboxylic acid (H2mbdc) and benzene-1,3,5-tricarboxylic acid (H3btc), respectively. The results of X-ray crystallographic analysis indicate that complex 1 is 1D chain while 2 is a (3,3)-connected 2D network with Point (Schläfli) symbol of (4,82). Complexes 3 and 6 are 2D networks, 4 is a 3-fold interpenetrating 3D framework with Point (Schläfli) symbol of (65,8) and 5 is a (3,8)-connected 2D network with Point (Schläfli) symbol of (3,42)2(34,46,56,68,73,8), while 7 is a (3,10)-connected 3D net with Schläfli symbol of (3,4,5)2(34,48,518,612,72,8). The thermal stability and photoluminescence of the complexes were investigated. Furthermore, DFT calculations were performed for 2-4 to discuss the temperature controlled self-assembly of the complexes.

Chen, Zhi-Hao; Zhao, Yue; Chen, Shui-Sheng; Wang, Peng; Sun, Wei-Yin

2013-06-01

404

FTIR studies of metal ligands, networks of hydrogen bonds, and water molecules near the active site Mn?CaO? cluster in Photosystem II.  

PubMed

The photosynthetic conversion of water to molecular oxygen is catalyzed by the Mn?CaO? cluster in Photosystem II and provides nearly our entire supply of atmospheric oxygen. The Mn?CaO? cluster accumulates oxidizing equivalents in response to light-driven photochemical events within Photosystem II and then oxidizes two molecules of water to oxygen. The Mn?CaO? cluster converts water to oxygen much more efficiently than any synthetic catalyst because its protein environment carefully controls the cluster's reactivity at each step in its catalytic cycle. This control is achieved by precise choreography of the proton and electron transfer reactions associated with water oxidation and by careful management of substrate (water) access and proton egress. This review describes the FTIR studies undertaken over the past two decades to identify the amino acid residues that are responsible for this control and to determine the role of each. In particular, this review describes the FTIR studies undertaken to characterize the influence of the cluster's metal ligands on its activity, to delineate the proton egress pathways that link the Mn?CaO? cluster with the thylakoid lumen, and to characterize the influence of specific residues on the water molecules that serve as substrate or as participants in the networks of hydrogen bonds that make up the water access and proton egress pathways. This information will improve our understanding of water oxidation by the Mn?CaO? catalyst in Photosystem II and will provide insight into the design of new generations of synthetic catalysts that convert sunlight into useful forms of storable energy. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. PMID:25038513

Debus, Richard J

2015-01-01

405