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1

The Use of Anchors in Shoulder Surgery: A Shift From Metallic to Bioabsorbable Anchors  

Microsoft Academic Search

With major advances in arthroscopy, suture anchors became the primary devices used to assist in fixing soft tissues to bone. Metallic anchors were first produced and used in soft tissue fixation around the shoulder. However, their use resulted in some reported complications, including articular surface damage from migrating implants and distortion and artifact production in postoperative magnetic resonance imaging. Bioabsorbable

Mehmet Ozbaydar; Bassem Elhassan; Jon J. P. Warner

2007-01-01

2

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

SciTech Connect

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

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

2005-06-01

3

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

PubMed

Correction for 'Synthesis, cytotoxic and hydrolytic studies of titanium complexes anchored by a tripodal diamine bis(phenolate) ligand' by Snia Barroso et al., Dalton Trans., 2014, 43, 17422-17433. PMID:25526919

Barroso, Snia; Coelho, Ana M; Gmez-Ruiz, Santiago; Calhorda, Maria Jos; iak, eljko; Kalu?erovi?, Goran N; Martins, Ana M

2015-01-20

4

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

5

Exploration of non-destructive testing of anchorage quality of metal anchored bar system with ultrasonic guided wave  

Microsoft Academic Search

This paper manages to perform non-destructive testing of anchored integrity of metal bar in anchored bar system by use of ultrasonic guided wave through theoretical analysis, simulation analysis and experimental study of the properties of guided wave propagating in the metal bar of anchored bar system. The theoretical models of free bar and end anchored bar are established for anchored

Hu Yang

2011-01-01

6

Optimization of Asymmetric Catalysts Using Achiral Ligands: Metal  

E-print Network

by Katsuki2,3 in the asymmetric epoxidation with achiral manganese salen complexes resulted in highOptimization of Asymmetric Catalysts Using Achiral Ligands: Metal Geometry-Induced Ligand Asymmetry becomes asymmetric, a concept termed Metal Geometry-Induced Ligand Asymmetry. The enantioselectivity

Walsh, Patrick J.

7

Metal nanoparticles functionalized with metal-ligand covalent bonds  

NASA Astrophysics Data System (ADS)

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

Kang, Xiongwu

8

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

9

PARTITIONING-SEPARATION OF METAL IONS USING HETEROCYCLIC LIGANDS  

Microsoft Academic Search

Some guidelines are proposed for the effective design of heterocylic ligands for partitioning because there is no doubt that the correct design of a molecular extractant is required for the effective separation of metal ions such as actinides(III) from lanthanides(III). Heterocyclic ligands with aromatic ring systems have a rich chemistry, which is only now becoming sufficiently well understood in relation

Michael J. Hudson; Michael G. B. Drew; Peter B. Iveson; Charles Madic; Mark L. Russell

10

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

PubMed

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

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

2012-06-01

11

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

Microsoft Academic Search

Class II MHC molecules display peptides on the cell surface for the surveillance by CD4+ T cells. To ensure that these ligands accurately reflect the content of the intracellular MHC loading compartment, a complex processing pathway has evolved that delivers only stable peptide\\/MHC complexes to the surface. As additional safeguard, MHC molecules quickly acquire a 'non-receptive' state once they have

Shashank Gupta; Sabine Hpner; Bernd Rupp; Sebastian Gnther; Katharina Dickhaut; Noopur Agarwal; M. Cristina Cardoso; Ronald Khne; Karl-Heinz Wiesmller; Gnther Jung; Kirsten Falk; Olaf Rtzschke

2008-01-01

12

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

Microsoft Academic Search

Class II MHC molecules display peptides on the cell surface for the surveillance by CD4+ T cells. To ensure that these ligands accurately reflect the content of the intracellular MHC loading compartment, a complex processing pathway has evolved that delivers only stable peptide\\/MHC complexes to the surface. As additional safeguard, MHC molecules quickly acquire a non-receptive state once they have

Shashank Gupta; Sabine Hpner; Bernd Rupp; Sebastian Gnther; Katharina Dickhaut; Noopur Agarwal; M. Cristina Cardoso; Ronald Khne; Karl-Heinz Wiesmller; Gnther Jung; Kirsten Falk; Olaf Rtzschke; Mauricio Martins Rodrigues

2008-01-01

13

Metrical oxidation states of 2-amidophenoxide and catecholate ligands: structural signatures of metal-ligand ? bonding in potentially noninnocent ligands.  

PubMed

Catecholates and 2-amidophenoxides are prototypical "noninnocent" ligands which can form metal complexes where the ligands are best described as being in the monoanionic (imino)semiquinone or neutral (imino)quinone oxidation state instead of their closed-shell dianionic form. Through a comprehensive analysis of structural data available for compounds with these ligands in unambiguous oxidation states (109 amidophenolates, 259 catecholates), the well-known structural changes in the ligands with oxidation state can be quantified. Using these correlations, an empirical "metrical oxidation state" (MOS) which gives a continuous measure of the apparent oxidation state of the ligand can be determined based on least-squares fitting of its C-C, C-O, and C-N bond lengths to this single parameter (a simple procedure for doing so is provided via a spreadsheet in the Supporting Information). High-valent d(0) metal complexes, particularly those of vanadium(V) and molybdenum(VI), have ligands with unexpectedly positive, and generally nonintegral, MOS values. The structural effects in these complexes are attributed not to electron transfer, but rather to amidophenoxide- or catecholate-to-metal ? bonding, an interpretation supported by the systematic variation of the MOS values as a function of the degree of competition with the other ?-donating groups in the structures. PMID:22260321

Brown, Seth N

2012-02-01

14

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 13-37nm with the average size of 23nm. 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?molL(-1) and 1.14-1120?molL(-1) with detection limits of 0.85 and 0.27?molL(-1) H2O2, sensitivities of 3545 and 11,293?Ammol(-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

15

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

16

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

SciTech Connect

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

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

2008-05-15

17

Spectroscopic investigations of new metallic complexes with leucine as ligand  

NASA Astrophysics Data System (ADS)

The [Cu(L) 2] H 2O ( 1), [Co(L) 2] 2H 2O ( 2) and [Zn(L) 2] H 2O ( 3) complexes with leucine (L) as ligand, were synthesized in water solution and analyzed by physical-chemical and spectroscopic means (UV-VIS, FT-IR, ESR). The comparative analysis of the IR spectra for the ligand and the complexes indicate the coordination of the metallic centre to the carboxylic oxygen atom and the nitrogen atom of the amino group due to the shift of the ?s(C dbnd O) and ?s(NH) stretching vibrations. Spectral UV-VIS and ESR data confirmed the covalent metal-ligand bonds, the pseudotetrahedral symmetry around the copper and zinc ions and the octahedral environment for the cobalt ion.

Stanila, A.; Nagy, Cs.; Marcu, A.; Cozma, D.; Rusu, D.; David, L.

2009-01-01

18

Adsorbate-induced anchoring transitions of liquid crystals on surfaces presenting metal salts with mixed anions.  

PubMed

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 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 the increase in the 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

2014-02-26

19

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

20

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

PubMed

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

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

2014-01-01

21

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

22

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

E-print Network

A mixed-valence copper coordination polymer generated by hydrothermal metal/ligand redox reactions in preparing highly stable, infinite metal­ligand frameworks.2 It has been found that in situ reactions,3 such as ligand oxidative coupling, hydrolysis, substitution and redox process of copper, can occur under hydro

Li, Jing

23

Hypersensitivity to suture anchors.  

PubMed

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

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

2013-01-01

24

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

25

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

NASA Astrophysics Data System (ADS)

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

Gal, Jean-Franois; Iacobucci, Claudio; Monfardini, Ilaria; Massi, Lionel; Duach, Elisabet; Olivero, Sandra

2012-12-01

26

Open layers based on metal-oxide chains linked by cyclohexanedicarboxylate ligands  

E-print Network

Open layers based on metal-oxide chains linked by cyclohexanedicarboxylate ligands Inn Hoe Kim a]. The coordination polymers, or metal organic frame- works (MOFs), are composed of isolated metal atoms or clusters of the inorganic units. We have been interested in MOOFs based on infinite metal-oxide chains cross

Wang, Xiqu

27

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

28

Eugenic metal-free sensitizers with double anchors for high performance dye-sensitized solar cells.  

PubMed

A series of new phenothiazine-based dyes (HL5-HL7) with double acceptors/anchors have been synthesized and used as the sensitizers for highly efficient dye-sensitized solar cells (DSSCs). Among them, the HL7-based cell exhibits the best efficiency of 8.32% exceeding the N719-based cell (7.35%) by ?13%. PMID:25555237

Hung, Wei-I; Liao, You-Ya; Lee, Ting-Hui; Ting, Yu-Chien; Ni, Jen-Shyang; Kao, Wei-Siang; Lin, Jiann T; Wei, Tzu-Chien; Yen, Yung-Sheng

2015-02-01

29

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

30

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 thioethergold 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.; rnadttir, Lney; Castner, David G.; Weidner, Tobias

2011-01-01

31

Cubes, squares, and books: a simple transition metal/bridging ligand combination can lead to a surprising range of structural types with the same metal/ligand proportions.  

PubMed

Reaction of two structurally related bridging ligands L(26Py) and L(13Ph), in which two bidentate chelating pyrazolyl-pyridine units are connected to either a 2,6-pyridine-diyl or 1,3-benzene-diyl central group via methylene spacers, with first-row transition metal dications, results in a surprising variety of structures. The commonest is that of an octanuclear coordination cage [M(8)L(12)]X(16) [M = Co(II) or Zn(II); X = perchlorate or tetrafluoroborate] in which a metal ion is located at each of the eight vertices of an approximate cube, and one bis-bidentate bridging ligand spans each edge. The arrangement of fac and mer tris-chelate metal centers around the inversion center results in approximate (non-crystallographic) S(6) symmetry. Another structural type observed in the solid state is a hexanuclear complex [Co(6)(L(13Ph))(9)](ClO(4))(12) in which the six metal ions are in a rectangular array (two rows of three), folded about the central Co-Co vector like a partially open book, with each metal-metal edge containing one bridging ligand apart from the two outermost metal-metal edges which are spanned by a pair of bridging ligands in a double helical array. The final structural type we observed is a tetranuclear square [Ni(4)(L(26Py))(6)](BF(4))(8), with the four Ni-Ni edges spanned alternately by one and two bridging ligand such that it effectively consists of two dinuclear double helicates cross-linked by additional bridging ligands. A balance between the "cube" and "book" forms, which varied from compound to compound, was observed in solution in many cases by (1)H NMR and ES mass spectrometry studies. PMID:19924896

Najar, Adel M; Tidmarsh, Ian S; Adams, Harry; Ward, Michael D

2009-12-21

32

Tetrachelate porphyrin chromophores for metal oxide semiconductor sensitization: effect of the spacer length and anchoring group position.  

PubMed

Four Zn(II)-tetra(carboxyphenyl)porphyrins in solution and bound to metal oxide (TiO2, ZnO, and ZrO2) nanoparticle films were studied to determine the effect of the spacer length and anchoring group position (para or meta) on their binding geometry and photoelectrochemical and photophysical properties. The properties of three types of anchoring groups (COOH and COONHEt3) for four Zn(II)-porphyrins (Zn(II)-5,10,15,20-tetra(4-carboxyphenyl)porphyrin (p-ZnTCPP), Zn(II)-5,10,15,20-tetra(3-carboxyphenyl)porphyrin (m-ZnTCPP), Zn(II)-5,10,15,20-tetra(3-(4-carboxyphenyl)phenyl)porphyrin (m-ZnTCP2P), and Zn(II)-5,10,15,20-tetra(3-ethynyl(4-carboxyphenyl)phenyl)porphyrin (m-ZnTC(PEP)P)) were compared. In m-ZnTCPP, m-ZnTCP2P, and m-ZnTC(PEP)P the four anchoring groups are in the meta position on the meso-phenyl rings of the porphyrin macrocycle, thus favoring a planar binding mode to the metal oxide surfaces. The three meta-substituted porphyrin salts have rigid spacer units of increasing length (phenyl (P), biphenyl (P2), and diphenylethynyl (PEP)) between the porphyrin ring and the carboxy anchoring groups, thus raising the macrocycle from the metal oxide surface. All porphyrins studied here, when bound to TiO2 and ZnO, exhibited quenching of the fluorescence emission, consistent with electron injection into the conduction band of the semiconductor. Steady-state UV-vis and fluorescence studies of p-ZnTCPP on insulating ZrO2 showed evidence of aggregation and exciton coupling. This was not observed in any of the meta-substituted porphyrins. The photoelectrochemical properties (IPCE, Voc, and Isc) of the porphyrins bound to TiO2 films in solar cells have been measured and rationalized with respect to the sensitizer binding geometry and distance from the surface. PMID:17385856

Rochford, Jonathan; Chu, Dorothy; Hagfeldt, Anders; Galoppini, Elena

2007-04-18

33

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

34

Metal-ligand binding interactions in rhodium/palladium-catalyzed synthesis of dihydroquinolines.  

PubMed

A domino Rh- and Pd-catalyzed synthesis of dihydroquinolines is disclosed. Two metals and two ligands are placed in one reaction vessel along with the two reactive reagents to afford selective sequential coupling despite the potential for side reactions. In this report, we describe mechanistic investigations attempting to discern the catalyst-ligand interactions occurring in this domino reaction. Through these studies, the reactivity and relative catalyst ligand loadings were successfully tuned to efficiently access the heterocyclic products. PMID:25337795

Zhang, Lei; Panteleev, Jane; Lautens, Mark

2014-12-19

35

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

SciTech Connect

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

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

2012-07-15

36

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

PubMed

The reactivity, cytotoxic studies and hydrolytic behaviour of diamine bis(phenolate) titanium complexes are reported. The reactions of [Ti((tBu2)O2NN')Cl]2(?-O) (1) with LiO(I)Pr or HO(I)Pr in the presence of NEt3, aiming at the synthesis of the alkoxido derivative of 1 led to no reaction or to the synthesis of the monomeric complex [Ti((tBu2)O2NN')(O(i)Pr)2] (3), respectively. A small amount of the alkoxidotitanium dimer [Ti((tBu2)O2NN')(O(i)Pr)]2(?-O) (2) crystallized out of a solution of 3 and DFT calculations showed that the transformation of 1 into 3 is a thermodynamically favorable process in the presence of a base (NEt3) (?G = -14.7 kcal mol(-1)). 2 was quantitatively obtained through the direct reaction of the ligand precursor H2((tBu2)O2NN') with titanium tetra(isopropoxido). Further reaction of 2 with an excess of TMSCl was revealed to be the most suitable method for the preparation of [Ti((tBu2)O2NN')Cl2] (4). 1 and 3 disclosed cytotoxic activity towards HeLa, Fem-x, MDA-MB-361 and K562 cells and 1 exhibited moderate binding affinity to FS-DNA. (1)H NMR hydrolysis studies attested the fast decomposition of 4 in the presence of D2O. The hydrolysis of 3 is slower and proceeds through the formation of [Ti((tBu2)O2NN')(OH)]2(?-O) (5) that was crystallographically characterized. Upon D2O addition 1 immediately forms complex new species, stable in solution for long periods (weeks). PMID:25338018

Barroso, Snia; Coelho, Ana M; Gmez-Ruiz, Santiago; Calhorda, Maria Jos; Ziak, Zeljko; Kalu?erovi?, Goran N; Martins, Ana M

2014-12-14

37

Metal-organic frameworks based on flexible ligands (FL-MOFs): structures and applications.  

PubMed

Metal-organic frameworks (MOFs), also known as coordination polymers (CPs), are crystalline materials constructed from metal ions or clusters bridged by organic ligands to form one-, two-, or three-dimensional infinite networks. In contrast with the prolific production of MOFs based on rigid ligands (RL-MOFs), the design, syntheses and applications of MOFs based on flexible ligands (FL-MOFs) are somewhat overlooked. Although sacrificing a measure of control, the use of flexible ligands may provide unique opportunities to obtain novel crystalline framework materials exhibiting desirable attributes. In this review, emphasis has been placed on the design and the structural diversity of FL-MOFs. Homochiral FL-MOFs and dynamic frameworks induced by flexible ligands are also briefly outlined. An overview is also shown for the applications of FL-MOFs as platforms for gas adsorption, heterogeneous catalysis, proton conduction etc. PMID:24699533

Lin, Zu-Jin; L, Jian; Hong, Maochun; Cao, Rong

2014-08-21

38

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

39

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

PubMed

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

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

2009-10-21

40

Isotopic studies of the metal-ligand vibrations in histamine complexes with Copper(II)  

NASA Astrophysics Data System (ADS)

Two known copper complexes of the formulae Cu(hm) 2(ClO 4) 2, Cu(hm)Cl 2 and new, Cu(hm)Br 2 (hm=histamine) have been investigated in the 600-50 cm -1 far-infrared region. Assignments of vibrations related to metal-ligand bonds have been made based on metal isotope substitution, partial deuteration and halogen sensitivity. Copper-hm stretching vibrations have been localised at 420, 417 and 411 cm -1 for modes involving amine nitrogen and at 282, 270, 259 cm -1 for those of imidazole nitrogen. Vibrational coupling between some metal-ligand modes has been postulated.

Dro?d?ewski, Piotr; Kordon, Ewa

2000-06-01

41

Metal extraction from the artificially contaminated soil using supercritical CO2 with mixed ligands.  

PubMed

Supercritical fluids have good penetrating power with a high capacity to dissolve certain solutes in the fluid itself, making it applicable for soil cleaning. Supercritical CO2 along with mixed ligands has been used for cleaning artificially contaminated soil. The extraction of metal from the soil was successful, and the molar ratio of ligands to the extracted metal was as low as 3. Complicated structures with a large surface area of the real soil seemed to cause the lower efficiency. Reduced efficiency was also observed over time after the sample preparation, indicating the possibility of chemisorption of the metal ion onto the soil. The use of supercritical CO2 with dissolved mixed ligands was sufficient to extract metal from the soil. PMID:23347618

Park, Kwangheon; Lee, Jeongken; Sung, Jinhyun

2013-04-01

42

30 CFR 57.7032 - Anchoring.  

Code of Federal Regulations, 2013 CFR

...NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Drilling and Rotary Jet Piercing Drilling-Underground Only 57.7032 Anchoring. Columns and the drills mounted on them shall be anchored...

2013-07-01

43

30 CFR 57.7032 - Anchoring.  

...NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Drilling and Rotary Jet Piercing Drilling-Underground Only 57.7032 Anchoring. Columns and the drills mounted on them shall be anchored...

2014-07-01

44

30 CFR 57.7032 - Anchoring.  

Code of Federal Regulations, 2011 CFR

...NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Drilling and Rotary Jet Piercing Drilling-Underground Only 57.7032 Anchoring. Columns and the drills mounted on them shall be anchored...

2011-07-01

45

30 CFR 57.7032 - Anchoring.  

Code of Federal Regulations, 2012 CFR

...NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Drilling and Rotary Jet Piercing Drilling-Underground Only 57.7032 Anchoring. Columns and the drills mounted on them shall be anchored...

2012-07-01

46

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)4H3O5H2O (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

47

Polydiacetylene vesicles functionalized with N-heterocyclic ligands for metal cation binding.  

PubMed

Self assembled poly diacetylene (PDA) based blue vesicles LS-Terpy, LS-DPA, LS-DP and LS-DEA with metal chelating sites have been prepared and characterized. Their response to the presence of metal cations in buffered aqueous solution has been investigated by monitoring changes of colour, UV-Vis absorption and emission. The addition of zinc, manganese, cadmium, mercury or silver salts to solutions of the vesicles induces a colour change from blue to red observable by the naked eye, while the addition of other metal salts, containing ions like Li(+), Na(+), K(+), Mg(2+), Ca(2+), Cr(2+), Ni(2+), Fe(2+), Co(2+), Cu(2+) or Pb(2+), failed to show any changes. The metal ion coordination selectivity of the ligands is slightly different for the vesicle surface immobilized ligands compared to the reported metal cation binding of the corresponding ligands in solution, which may be due to the special environment at the lipid-solution interface. The vesicles aggregate upon metal ion coordination to the embedded ligands as shown by dynamic light scattering (DLS) particle size analysis. The functionalized PDA vesicles retain their response to the presence of aqueous solutions of metal ions if immobilized in transparent polyvinyl alcohol films or on paper. PMID:20090984

Jose, D Amilan; Knig, Burkhard

2010-02-01

48

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

PubMed

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

Gonzlez, Javier M; Meini, Mara-Roco; Tomatis, Pablo E; Medrano Martn, Francisco J; Cricco, Julia A; Vila, Alejandro J

2012-08-01

49

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

PubMed Central

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

Gonzlez, Javier M.; Meini, Mara-Roco; Tomatis, Pablo E.; Medrano Martn, Francisco J.; Cricco, Julia A.; Vila, Alejandro J.

2012-01-01

50

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

PubMed

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

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

2012-10-31

51

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

52

Mononuclear MetalO2 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 metalsuperoxo and peroxo species, and the OO bond cleavage of metalhydroperoxo complexes to form high-valent metal-oxo oxidants. Because these mononuclear metaldioxygen (MO2) 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 MO2 complexes bearing the macrocyclic N-tetramethylated cyclam (TMC) ligand. This Account describes the synthesis, structural and spectroscopic characterization, and reactivity studies of MO2 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 metalO2 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 metalO2 complexes, resulting in the end-on metalsuperoxo versus side-on metalperoxo structures. Reactivity studies performed with the isolated metal-superoxo complexes reveal that they can conduct electrophilic reactions such as oxygen atom transfer and CH bond activation of organic substrates. The metalperoxo 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 metalO2 intermediates that are relevant in biology and in biomimetic reactions. PMID:22612523

CHO, JAEHEUNG; SARANGI, RITIMUKTA; NAM, WONWOO

2013-01-01

53

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

NASA Astrophysics Data System (ADS)

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

Johnson, Darren William

54

Simulation of metal-ligand self-assembly into spherical complex M6L8.  

PubMed

Molecular dynamics simulations were performed to study the self-assembly of a spherical complex through metal-ligand coordination interactions. M(6)L(8), a nanosphere with six palladium ions and eight pyridine-capped tridentate ligands, was selected as a target system. We successfully observed the spontaneous formation of spherical shaped M(6)L(8) cages over the course of our simulations, starting from random initial placement of the metals and ligands. To simulate spontaneous coordination bond formations and breaks, the cationic dummy atom method was employed to model nonbonded metal-ligand interactions. A coarse-grained solvent model was used to fill the gap between the time scale of the supramolecular self-assembly and that accessible by common molecular dynamics simulation. The simulated formation process occurred in the distinct three-stage (assembly, evolution, fixation) process that is well correlated with the experimental results. We found that the difference of the lifetime (or the ligand exchange rate) between the smaller-sized incomplete clusters and the completed M(6)L(8) nanospheres is crucially important in their supramolecular self-assembly. PMID:22889247

Yoneya, Makoto; Yamaguchi, Tomohiko; Sato, Sota; Fujita, Makoto

2012-09-01

55

Ligand influence on metal aggregation: a unique bonding mode for pyridylpyrrolides.  

PubMed

The synthesis and characterization of a Cu(I) complex with a cis-bidentate monoanionic nitrogenous ligand, 2-pyridylpyrrolide, L, is reported. This shows binding of one base B = MeCN or CO per copper in a species LCu(B), but this readily releases the volatile ligand under vacuum with aggregation of transient LCu to a mixture of two enantiomers of a chiral trimer: a zwitterion containing inequivalent Cu(I) centers, possible via a new bonding mode of pyridylpyrrolide, and one with nitrogen lone pairs donating to two different metals. Density functional theory calculations show the energetics of both ligand binding and aggregation (including dimer and monomer alternatives), as well as the ability of this ligand to rotate away from planarity to accommodate a bridging structural role. The trimer serves as a synthon for the simple fragment LCu. PMID:20687530

Andino, Jos G; Flores, Jaime A; Karty, Jonathan A; Massa, Joseph P; Park, Hyunsoo; Tsvetkov, Nikolay P; Wolfe, Robert J; Caulton, Kenneth G

2010-09-01

56

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

57

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

58

The second-shell metal ligands of human arginase affect coordination of the nucleophile and substrate.  

PubMed

The active sites of eukaryotic arginase enzymes are strictly conserved, especially the first- and second-shell ligands that coordinate the two divalent metal cations that generate a hydroxide molecule for nucleophilic attack on the guanidinium carbon of l-arginine and the subsequent production of urea and l-ornithine. Here by using comprehensive pairwise saturation mutagenesis of the first- and second-shell metal ligands in human arginase I, we demonstrate that several metal binding ligands are actually quite tolerant to amino acid substitutions. Of >2800 double mutants of first- and second-shell residues analyzed, we found more than 80 unique amino acid substitutions, of which four were in first-shell residues. Remarkably, certain second-shell mutations could modulate the binding of both the nucleophilic water/hydroxide molecule and substrate or product ligands, resulting in activity greater than that of the wild-type enzyme. The data presented here constitute the first comprehensive saturation mutagenesis analysis of a metallohydrolase active site and reveal that the strict conservation of the second-shell metal binding residues in eukaryotic arginases does not reflect kinetic optimization of the enzyme during the course of evolution. PMID:21053939

Stone, Everett M; Chantranupong, Lynne; Georgiou, George

2010-12-14

59

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 metalmetal 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

60

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.; Garca-Granda, Santiago

2015-01-01

61

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

PubMed

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

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

2014-12-21

62

Alkali metal salts of formazanate ligands: diverse coordination modes as a result of the nitrogen-rich [NNCNN] ligand backbone.  

PubMed

Alkali metal salts of redox-active formazanate ligands were prepared, and their structures in the solid-state and in solution are determined. The nitrogen-rich [NNCNN] backbone of formazanates results in a varied coordination chemistry, with both the internal and terminal nitrogen atoms available for bonding with the alkali metal. The potassium salt K[PhNNC(p-tol)NNPh]2THF (1-K) is dimeric in the solid state and even in THF solution, as a result of the K atom bridging via interaction with a terminal N atom and the aromatic ring of a second unit. Conversely, for the compounds Na[MesNNC(CN)NNMes]2THF (2-Na) and Na[PhNNC((t)Bu)NNPh] (3-Na) polymeric and hexameric structures are found in the solid state respectively. The preference for binding the alkali metal through internal N atoms (1-K and 2-Na) to give a 4-membered chelate, or via internal/external N atoms (5-membered chelate in 3-Na), contrasts with the 6-membered chelate mode observed in our recently reported formazanate zinc complexes. PMID:25351633

Travieso-Puente, Raquel; Chang, Mu-Chieh; Otten, Edwin

2014-12-28

63

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

64

Heavy metal uptake by lignin: comparison of biotic ligand models with an ion-exchange process.  

PubMed

Metal uptake by kraft lignin, hereafter referred to as lignin, occurs by displacement of protons or bound metals with equilibrium constants K(ex)H and K(ex), respectively. Values calculated for wide ranges of initial concentrations are reasonably constant, thereby demonstrating the validity of these displacement processes and proving that uptake in these systems is not simple adsorption. It was found that the stoichiometry for Sr and Cd uptake by Ca-loaded lignin is 1 mol of metal for 1 mol of Ca released. This observation for metals of very different binding strengths is difficult to rationalize with the biotic ligand model as generally applied but is in complete agreement with an ion-exchange process. Binding strengths to lignin, which contains only oxygen ligands, follow the order Pb > Cu > Zn > Cd > Ca (strongest to weakest). For proton displacement, only more tightly bound metals such as Pb, Cu, Zn, and Cd can compete with protons for anion-binding sites at low pH, but at high pH, uptake of Ca, Sr, and Li can occur. An observed logarithmic decrease of K(ex)H with pH can be explained by having only weaker acids available for proton displacement under more basic conditions. The advantages and disadvantages of using adsorption and biotic ligand models for an ion-exchange process are discussed. PMID:11999055

Crist, Ray H; Martin, J Robert; Crist, Delanson R

2002-04-01

65

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

NASA Astrophysics Data System (ADS)

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

Hoch, Cortney Leigh

66

Radiosensitization of mammalian cells by transition metal complexes containing nitroimidazole ligands  

SciTech Connect

Various transition metal complexes containing nitroimidazoles as ligands have been shown to act as radiosensitizers of hypoxic cells in vitro. Sensitization by cis-Pt(II)Cl/sub 2/ (nitroimidazole)/sub 2/ complexes is no greater than that which can be demonstrated by the free nitroimidazole ligand alone. These results differ from those previously described for the compound FLAP where an ER of 2.4 was obtained at a concentration of 50 ..mu..M. The authors report that, even using the same treatment technique, the maximum ER that can be achieved is 1.2. Further, the sensitizing efficiency of FLAP cannot be imporved when cells are kept in contact with the compound for 12 hours in air prior to deoxygenation and irradiation. In contrast, Rh(II) complexes show much greater sensitization than can be obtained with the free ligand and these compounds are in turn more efficient sensitizers than the comparable Pt(II) complexes.

Chibber, R.; Stratford, I.J.; Ahmed, I.; Robbins, A.B.; Goodgame, D.; Lee, B.

1984-08-01

67

Redox-induced reversible metal assembly through translocation and reversible ligand coupling in tetranuclear metal sandwich frameworks  

NASA Astrophysics Data System (ADS)

Sandwich structures formed by metal atoms intercalated between sp2-carbon planes can be found either in metal-graphite-based materials or discrete multinuclear sandwich complexes. Their reactivity, and in particular their dynamic behaviour, has recently attracted interest both from a structural and a practical aspect, for example in catalysis. However, progress in this area has been rather slow, and it remains difficult to elucidate their structure and behaviour at the molecular level. Here, we report two sandwich complexesin which four palladium centres are incorporated between two ?-conjugated ligandswhich exhibit two modes of redox-switchable structural changes. In the first complex, the tetrapalladium chain is split by oxidation into two well-separated dipalladium units. This motion is reversed on reduction. In the second complex, reversible carbon-carbon coupling occurs between the ligands during the redox process.

Murahashi, Tetsuro; Shirato, Katsunori; Fukushima, Azusa; Takase, Kohei; Suenobu, Tomoyoshi; Fukuzumi, Shunichi; Ogoshi, Sensuke; Kurosawa, Hideo

2012-01-01

68

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

69

S K-edge XAS as a Probe of Ligand-Metal Bond Covalency: Metal vs Ligand Oxidation in Cu and Ni Dithiolene Complexes  

PubMed Central

A combination of Cu L-edge and S K-edge X-ray absorption data and density functional theory (DFT) calculations have been correlated with 33S EPR superhyperfine results to obtain the dipole integral (Is) for the S 1s?3p transition for the dithiolene ligand MNT (maleonitriledithiolate) in (TBA)2[Cu(MNT)2]. The results have been combined with the Is of sulfide derived from XPS studies to experimentally obtain a relation between the S 1s?4p transition energy (which reflects the charge on the S atom (QmolS)) and the dipole integral over a large range of QmolS. The results show that for high charges on S, Is can vary from the previously reported Is calculated using data over a limited range of QmolS. A combination of S K-edge and Cu K and L-edge X-ray absorption data and DFT calculations have been used to investigate the one-electron oxidation of [Cu(MNT)2]2- and [Ni(MNT)2]2-. The conversion of [Cu(MNT)2]2- to [Cu(MNT)2]- results in a large change in the charge on the Cu atom in the molecule (QmolCu) and is consistent with a metal-based oxidation. This is accompanied by extensive charge donation from the ligands to compensate the high charge on the Cu in [Cu(MNT)2]- based on the increased S K-edge and decreased Cu L-edge intensity, respectively. In contrast, the oxidation of [Ni(MNT)2]2- to [Ni(MNT)2]- results in a small change in QmolNi indicating a ligand-based oxidation consistent with oxidation of a molecular orbital, ?SOMO? (singly occupied molecular orbital), with predominant ligand character. PMID:17269767

Sarangi, Ritimukta; George, Serena DeBeer; Rudd, Deanne Jackson; Szilagyi, Robert K.; Ribas, Xavi; Rovira, Concepci; Almeida, Manuel; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.

2010-01-01

70

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

71

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.

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

2009-05-01

72

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

NASA Astrophysics Data System (ADS)

Seven transition metal complexes of benzimidazole ligand (HL) are reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analyses (TGA and DTA). From the obtained data, the complexes were proposed to have the general formulae [MX 2(HL)(H 2O)] yH 2O, where M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cr(III); X = Cl -, SO 42- and y = 0-4. The molar conductance data revealed that all the metal chelates were non-electrolytes. From the magnetic and solid reflectance spectra, it was found that the geometrical structure of these complexes is octahedral. The thermal behaviour of these chelates showed that the hydrated complexes loss water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. Fungicidal activity of the prepared complexes and free ligand was evaluated against three soil borne fungi. Data obtained showed the higher biological activity of the prepared complexes than the parent Schiff base ligand. Formulation of the most potent complex was carried out in the form of 25% WP. Fungicidal activity of the new formulation was evaluated and compared with the standard fungicide Pencycuron (Monceren 25% WP). In most cases, the new formulation possessed higher fungicidal activity than the standard fungicide under the laboratory conditions.

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

2009-04-01

73

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, Jos A; Pereira, Cludia C L; Vilela, Srgio M F; Tom, Joo P C; Maralo, Joaquim; Almeida Paz, Filipe A

2014-02-01

74

Identification of an altered peptide ligand based on the endogenously presented, rheumatoid arthritis-associated, human cartilage glycoprotein-39(263275) epitope: an MHC anchor variant peptide for immune modulation  

PubMed Central

We sought to identify an altered peptide ligand (APL) based on the endogenously expressed synovial auto-epitope of human cartilage glycoprotein-39 (HC gp-39) for modulation of cognate, HLA-DR4-restricted T cells. For this purpose we employed a panel of well-characterized T cell hybridomas generated from HC gp-39-immunized HLA-DR4 transgenic mice. The hybridomas all respond to the HC gp-39(263275) epitope when bound to HLA-DR4(B1*0401) but differ in their fine specificities. First, the major histocompatibility complex (MHC) and T-cell receptor (TCR) contact residues were identified by analysis of single site substituted analogue peptides for HLA-DR4 binding and cognate T cell recognition using both T hybridomas and polyclonal T cells from peptide-immunized HLA-DR4 transgenic mice. Analysis of single site substituted APL by cognate T cells led to identification of Phe265 as the dominant MHC anchor. The amino acids Ala268, Ser269, Glu271 and Thr272 constituted the major TCR contact residues, as substitution at these positions did not affect HLA-DR4(B1*0401) binding but abrogated T cell responses. A structural model for visualisation of TCR recognition was derived. Second, a set of non-classical APLs, modified at the MHC key anchor position but with unaltered TCR contacts, was developed. When these APLs were analysed, a partial TCR agonist was identified and found to modulate the HC gp-39(263275)-specific, pro-inflammatory response in HLA-DR4 transgenic mice. We identified a non-classical APL by modification of the p1 MHC anchor in a synovial auto-epitope. This APL may qualify for rheumatoid arthritis immunotherapy. PMID:17645792

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

2007-01-01

75

Crystal structures of transition metal complexes with an asymmetrical tridentate Schiff-base ligand  

NASA Astrophysics Data System (ADS)

The asymmetrical tridentate Schiff base ( H 2L = (E)-N'-(2-hydroxybenzylidene)-4-hydroxybenzohydrazide) has been designed and synthesized. The four transition metal complexes with this ligand [Cu(HL)(NO 3)](H 2O) ( 1), [Zn 2(HL) 2(bipy)(H 2O) 2](NO 3) 2 ( 2), [Cu(HL)(H 2O)] 2(NO 3) 2 ( 3) and [Cu(HL)(Me 2NCO)] 2 ( 4) have been studied. The unsaturated coordination site of metal ion in complexes 1 and 2 is occupied by secondary ligand of nitrate and 4,4'-bipyridine. The crystal structure of complex 1 exhibits supramolecular framework with homochirality. Complexes 3 and 4 are dinuclear complexes bridged by the phenol oxygen atoms and the fifth coordination is occupied by H 2O molecular and DMF anion respectively. Hydrogen bonding and ?-? stacking exist in all four complexes to construct supramolecular architecture.

Tang, Bei-bei; Sun, Xiao-ping; Liu, Gui-lei; Li, Hui

2010-12-01

76

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

77

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

PubMed

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

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

2014-10-01

78

Metal-ligand binding affinity vs reactivity: qualitative studies in Rh(I)-catalyzed asymmetric ring-opening reactions.  

PubMed

Rh(I)-catalyzed asymmetric ring opening (ARO) of oxabenzonorbornadiene is used as a model system to qualitatively study reactions involving multiple metal-ligand interactions. The key feature of this approach is the use of product ee as an indicator to quickly gain important information such as the relative ligand binding affinity and relative reactivity of catalysts. PMID:23683143

Tsui, Gavin Chit; Dougan, Patrick; Lautens, Mark

2013-06-01

79

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

80

Anchoring of a Fully Covered Self-Expandable Metal Stent With a 5F Double-Pigtail Plastic Stent to Prevent Migration in the Management of Benign Biliary Strictures  

Microsoft Academic Search

OBJECTIVES:Fully covered self-expandable metal stents (FCSEMSs) can be effectively placed in patients with benign biliary stricture (BBS). However, stent migration is an inherent problem of FCSEMSs. We evaluated the efficacy of anchoring with a 5F double-pigtail plastic stent (anchoring stent) to prevent migration of an FCSEMS in patients with BBS.METHODS:Between January 2007 and December 2009, 33 of 37 consecutive patients

Jong Kyu Park; Jong Ho Moon; Hyun Jong Choi; Seul Ki Min; Tae Hoon Lee; Gab Jin Cheon; Young Koog Cheon; Young Deok Cho; Sang-Heum Park; Sun-Joo Kim

2011-01-01

81

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 inorganicorganic arrangements.

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

2013-10-15

82

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

PubMed Central

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 metalligand recognition events. Synthetic bipyridine lipoligands Bn bearing a bipyridine unit as head group were prepared and incorporated into large unilamellar vesicles. The addition of Ni2+ or Co2+ metal ions led to the formation of complexes MBn and MBn2 followed by spontaneous fusion to generate giant multilamellar vesicles. The metal ion complexation was followed by UV spectroscopy and the progressive fusion could be visualized by optical dark-field and fluorescence microscopies. Vesicle fusion occurred without leakage of the aqueous compartments and resulted in the formation of multilamellar giant vesicles because of the stacking of the lipoligands Bn. The fusion process required a long enough oligoethylene glycol spacer and a minimal concentration of lipoligand within the vesicle membrane. Metallosupramolecular systems such as the present one offer an attractive way to induce selective intervesicular processes, such as vesicle fusion, under the control of molecular recognition between specific metal ions and lipoligands incorporated in the bilayer membrane. They provide an approach to the design of artificial tissue-mimetics through the generation of polyvesicular arrays of defined architecture and to the control of their functional properties. PMID:15492229

Richard, Antoine; Marchi-Artzner, Valrie; Lalloz, Marie-Nolle; Brienne, Marie-Josphe; Artzner, Franck; Gulik-Krzywicki, Thadde; Guedeau-Boudeville, Marie-Alice; Lehn, Jean-Marie

2004-01-01

83

Design of supported membranes tethered via metal-affinity ligand-receptor pairs.  

PubMed Central

Model lipid layers are very promising in investigating the complex network of recognition, transport and signaling processes at membranes. We have developed a novel and generic approach to create supported lipid membranes tethered by metal-affinity binding. By self-assembly we have generated various interfaces that display histidine sequences (6xHis) via polymer spacers. These histidine-functionalized interfaces are designed to allow specific docking and fusion of vesicles containing metal-chelating lipids. By means of surface plasmon resonance and atomic force microscopy we analyzed the formation and subsequently the structure of these solid-supported membranes. Although the affinity constant of single ligand-receptor pairs is only in the micromolar range, very stable immobilization of these membranes was observed. This behavior can be explained by multivalent interactions resembling many features of cell adhesion. The process is highly specific, because vesicle docking and bilayer formation are strictly dependent on the presence of metal-affinity ligand-receptor pairs. The surface accessibility and geometry of these tethered membranes were probed by binding of histidine-tagged polypeptides. The supported membranes show adsorption kinetics and values similar to planar supported monolayers. Using various combinations of metal-chelating and histidine-tagged lipids or thiols these metal-affinity-tethered membranes should make a great impact on probing and eventually understanding the dynamic dialog of reconstituted membrane proteins. PMID:11106619

Rdler, U; Mack, J; Persike, N; Jung, G; Tamp, R

2000-01-01

84

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, Ivn; Stylianou, Kyriakos C; Imaz, Inhar; Maspoch, Daniel

2014-11-18

85

Ion-molecule reaction chemistry of ionic transition-metal carbonyl clusters fragments. 1. Ligand-exchange reactions of Cr sub 2 (CO) sub y sup + ions  

SciTech Connect

The ligand-exchange ion-molecule reaction chemistry of Cr{sub 2}(CO){sub y}{sup +} ionic transition metal cluster fragments has been investigated by using a two-section ion cell Fourier transform ion cyclotron resonance mass spectrometer. Simple ligand-exchange reactions involving ligand (L) addition followed by metal-ligand (M---CO) bond cleavage (i.e., an associative ligand-exchange mechanism) as well as ligand exchange involving metal-metal cleavage (i.e. addition of L to Cr{sub 2}(CO){sub y}{sup +} followed by metal-metal bond cleavage) are observed. The branching ratios for reactions involving metal-metal bond cleavage increase as the metal-to-ligand ratio decreases. In addition, the ratio for simple ligand exchange to metal-metal bond cleavage is strongly dependent upon the nature of the reacting ligand (L). These data combined with collision-induced dissociation data for Cr{sub 2}(CO){sub y}{sup +} ionic cluster fragments suggest that the Cr-Cr bond strength decreases as y is increased; i.e., the Cr---Cr bond order is strongly dependent upon the ligand environment.

Sellers-Hahn, L.; Russell, D.H. (Texas A and M Univ., College Station (USA))

1990-08-01

86

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; Menjn, Babil; Falceto, Andrs; Casanova, David; Alemany, Pere

2014-11-17

87

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.

88

Anchor connector  

SciTech Connect

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

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

1984-03-27

89

Mononuclear and three-dimensional metal complexes based on a multidentate hydrazone ligand.  

PubMed

A potentially pentadentate hydrazone ligand, N'-[1-(pyrazin-2-yl)ethylidene]nicotinohydrazide (HL), was prepared from the condensation reaction of nicotinohydrazide and acetylpyrazine. Reactions of HL with MnCl2, Mn(CH3COO)2 and Cd(CH3COO)2 afforded three metal complexes, namely dichlorido{N'-[1-(pyrazin-2-yl-?N(1))ethylidene]nicotinohydrazide-?(2)N',O}manganese(II), [MnCl2(C12H11N5O)], (I), bis{N'-[1-(pyrazin-2-yl-?N(1))ethylidene]nicotinohydrazidato-?(2)N',O]manganese(II), [Mn(C12H10N5O)2], (II), and poly[[(acetato-?(2)O,O'){?3-N'-[1-(pyrazin-2-yl-?(2)N(1):N(4))ethylidene]nicotinohydrazidato-?(3)N',O:N(1)}cadmium(II)] chloroform disolvate], {[Cd(C12H10N5O)(CH3COO)]2CHCl3}n, (III), respectively. Complex (I) has a mononuclear structure, the Mn(II) centre adopting a distorted square-pyramidal coordination. Complex (II) also has a mononuclear structure, with the Mn(II) centre occupying a special position (C2 symmetry) and adopting a distorted octahedral coordination environment, which is defined by two O atoms and four N atoms from two N'-[1-(pyrazin-2-yl)ethylidene]nicotinohydrazidate (L(-)) ligands related via a crystallographic twofold axis. Complex (III) features a unique three-dimensional network with rectangular channels, and the L(-) ligand also serves as a counter-anion. The coordination geometry of the Cd(II) centre is pentagonal bipyramidal. This study demonstrates that HL, which can act as either a neutral or a mono-anionic ligand, is useful in the construction of interesting metal-organic compounds. PMID:25652278

Liu, Yan Fei; Liu, Ya Ping; Zhang, Ke Ke; Ren, Qing Ling; Qin, Jie

2015-02-01

90

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

NASA Astrophysics Data System (ADS)

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

Moran, Isaac Webster

91

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

PubMed

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

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

2010-03-15

92

Adsorption of heavy metals on vermiculite: influence of pH and organic ligands.  

PubMed

The sorption behaviour of vermiculite has been studied with respect to cadmium, copper, lead, manganese, nickel, and zinc as a function of pH and in the presence of different ligands. The continuous column method was used in order to evaluate the feasibility to use the clay in wastewater purification systems. The total capacity of vermiculite was found to decrease in the following order: Mn > Ni > Zn > Cd > Cu > Pb. The adsorption of metal ions on vermiculite decreases with decreasing pH and increasing ionic strength. In general, the metal uptake on the clay was hindered by the presence of strong complexing agents in solution and it decreases with increasing of the complexation constants of the ligands with exception of cysteine and tiron. It is necessary, hence, to consider all these factors to effectively predict the uptake efficiency of this sorbent. However, it is possible to conclude that the vermiculite has good potentialities for cost-effective treatments of metal-contaminated wastewaters. PMID:16581085

Malandrino, M; Abollino, O; Giacomino, A; Aceto, M; Mentasti, E

2006-07-15

93

Single-chain self-folding of synthetic polymers induced by metal-ligand complexation.  

PubMed

The controlled folding of a single polymer chain is for the first time realized by metal- complexation. ?,?-Bromine functional linear polymers are prepared via activators regenerated by electron transfer (ARGET) ATRP (Mn,SEC = 5900 g mol(-1) , ? = 1.07 and 12 000 g mol(-1) , ? = 1.06) and the end groups of the polymers are subsequently converted to azide functionalities. A copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is carried out in the presence of a novel triphenylphosphine ligand and the polymers to afford homotelechelic bis-triphenylphosphine polymeric-macroligands (MLs) (Mn,SEC = 6600 g mol(-1) , ? = 1.07, and 12 800 g mol(-1) , ? = 1.06). Single-chain metal complexes (SCMCs) are formed in the presence of Pd(II) ions in highly diluted solution at ambient temperature. The results derived via (1) H and (31) P{(1) H} NMR experiments, SEC, and DLS unambiguously evidence the efficient formation of SCMCs via metal ligand complexation. PMID:24123407

Willenbacher, Johannes; Altintas, Ozcan; Roesky, Peter W; Barner-Kowollik, Christopher

2014-01-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

95

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

PubMed

We 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 data set. The biotic ligand model used in the present study hypothesizes that metals inhibit an essential cation (calcium) and organisms die due to its deficiency, leading to an assumption that the proportion of metal binding to available sites on the 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, we statistically modeled the survival effects of single metals separately (i.e., f-survival relationship) by using 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. We 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 make predictions for effects of metal mixtures. Environ Toxicol Chem 2014 SETAC. PMID:25323464

Iwasaki, Yuichi; Kamo, Masashi; Naito, Wataru

2014-10-16

96

Predicting sediment metal toxicity using a sediment biotic ligand model: methodology and initial application.  

PubMed

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 sediment concentration that is in equilibrium with the biotic ligand effects concentration. This initial application considers only partitioning to sediment particulate organic carbon. This procedure bypasses the need to compute the details of the pore-water chemistry. Remarkably, the median lethal concentration on a sediment organic carbon (OC)-normalized basis, SEM*(x,OC), is essentially unchanged over a wide range of concentrations of pore-water hardness, salinity, dissolved organic carbon, and any other complexing or competing ligands. Only the pore-water pH is important. Both acute and chronic exposures in fresh- and saltwater sediments are compared to predictions for cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) based on the Daphnia magna BLM. The SEM*(x,OC) concentrations are similar for all the metals except cadmium. For pH = 8, the approximate values (micromol/gOC) are Cd-SEM*(xOC) approximately equal to 100, Cu-SEM*(x,OC) approximately equal to 900, Ni-SEMoc approximately equal to 1,100, Zn-SEM*(x,OC) approximately equal to 1,400, and Pb-SEM*(x,OC) approximately equal to 2,700. This similarity is the explanation for an empirically observed dose-response relationship between SEM and acute and chronic effects concentrations that had been observed previously. This initial application clearly demonstrates that BLMs can be used to predict toxic sediment concentrations without modeling the pore-water chemistry. PMID:16268143

Di Toro, Dominic M; McGrath, Joy A; Hansen, David J; Berry, Walter J; Paquin, Paul R; Mathew, Rooni; Wu, Kuen Benjamin; Santore, Robert C

2005-10-01

97

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, Universit 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, Universit della Tuscia, I-01100 Viterbo (Italy)

2014-03-03

98

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

PubMed

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

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

2013-12-11

99

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

100

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

PubMed

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

101

Novel supramolecular assembly of symmetrical mixed-metal-ligand complexes of dioxouranium(VI).  

PubMed

Some binary and ternary novel complexes of dioxouranium(VI) with 8-hydroxy-7-quinolinecarboxaldehyde (OXH) have been prepared and characterized by elemental analyses, magnetic susceptibility measurements and spectral studies. Coordination effects on the vibrational spectra of the ligands have been investigated. The amine exchange reactions of coordinated Schiff bases in these complexes have been also studied, which reveal symmetrical tetradentate Schiff base complexes. Metal exchange reaction of dioxouranium(VI) complexes was obtained when reacted with tetradentate Schiff base complexes of Cu(II) with ZrCl(4)/UO(2)(CH(3)COO)(2) giving heterobinuclear complexes. Magnetic, electronic and IR spectral data suggest the configurations of distorted square planar ligand field copper(II) complexes. The ligands behave as bi-(O,O) and tetradentate (N(2),O(2)) donors. El-Sonbati equation has been used to evaluate the symmetric stretching frequency from which the F(U-O) and F(UO,UO)(-) were calculated. The bond distances of these complexes were also investigated. PMID:16843709

Mubarak, Ahmed T

2006-12-01

102

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

103

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

104

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

NASA Astrophysics Data System (ADS)

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

Dolaz, Mustafa; McKee, Vickie; Uru?, Serhan; Demir, Necmettin; Sabik, Ali E.; Glc, Ay?egl; Tmer, Mehmet

2010-07-01

105

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

PubMed

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

Dolaz, Mustafa; McKee, Vickie; Uru?, Serhan; Demir, Necmettin; Sabik, Ali E; Glc, Ay?egl; Tmer, Mehmet

2010-07-01

106

Ligand-controlled syntheses of copper(I) complexes with metal-metal interactions: crystal structure and relativistic density functional theory investigation.  

PubMed

A family of di-, tri-, and tetranuclear copper(I) complexes supported by length-controlled silaamidinate ligands have been synthesized to show short Cu(I)-Cu(I) distances (2.43-2.62 ) and feature a linear or bent metal-metal arrangement, which is elucidated by a relativistic density functional theory calculation. PMID:25278439

Liu, Jun-Feng; Min, Xue; Lv, Jin-Yu; Pan, Fu-Xing; Pan, Qing-Jiang; Sun, Zhong-Ming

2014-10-20

107

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

108

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

PubMed

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

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

2013-03-01

109

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

E-print Network

positions (cis isomer, Figure 1(c)). In addition to the proposal of novel structures now known as Werner compounds, Werner also developed new concepts like primary and secondary valence, which correspond to oxidation state and coordination number... to ligand field theory. 5 The qualitative MO diagram of [Co(NH3)6] 3+ (Figure 3) is used to illustrate some important concepts of the MO approach. In general, we only need to consider MOs constructed by the valence orbitals of each atom because...

Xu, Zhenggang

2014-07-25

110

Metalligand multiple bonds as frustrated Lewis pairs for CH functionalization  

PubMed Central

Summary The concept of frustrated Lewis pairs (FLPs) has received considerable attention of late, and numerous reports have demonstrated the power of non- or weakly interacting Lewis acidbase pairs for the cooperative activation of small molecules. Although most studies have focused on the use of organic or main-group FLPs that utilize steric encumbrance to prevent adduct formation, a related strategy can be envisioned for both organic and inorganic complexes, in which "electronic frustration" engenders reactivity consistent with both nucleophilic (basic) and electrophilic (acidic) character. Here we propose that such a description is consistent with the behavior of many coordinatively unsaturated transition-metal species featuring metalligand multiple bonds, and we further demonstrate that the resultant reactivity may be a powerful tool for the functionalization of CH and EH bonds. PMID:23209486

2012-01-01

111

Two Ce-containing 3D metalorganic 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 metalorganic 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

112

Porosity tuning of carborane-based metalorganic frameworks (MOFs) via coordination chemistry and ligand design  

Microsoft Academic Search

Two new metalorganic framework (MOF) materials based on boron-rich cluster struts (p-carborane) are reported herein. Cu(I) catalyzed coupling chemistry was used to synthesize carboxylate-based ligands, which are substantially longer than the previously studied dicarboxylated p-carborane, leading to structures with greater porosity. Solvothermal syntheses involving these ligands and Zn salts were used to prepare two new Zn(II)-based MOFs with 2D and

Alexander M. Spokoyny; Omar K. Farha; Karen L. Mulfort; Joseph T. Hupp; Chad A. Mirkin

2010-01-01

113

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

114

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

115

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

116

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

SciTech Connect

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

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

2012-02-07

117

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

PubMed

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

Pytlakowska, K; Kozik, V; Dabioch, M

2013-06-15

118

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

NASA Astrophysics Data System (ADS)

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

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

119

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, Gkhan; elik, Cumali; Uru?, Serhan; Demirta?, ?brahim; Elmasta?, Mahfuz; Tmer, Mehmet

2011-10-01

120

Synthesis and catalytic activity of heterogeneous rare-earth metal catalysts coordinated with multitopic Schiff-base ligands.  

PubMed

Four multitopic Schiff-base ligand precursors were synthesized via condensation of 4,4'-diol-3,3'-diformyl-1,1'-diphenyl or 1,3,5-tris(4-hydroxy-5-formylphenyl)benzene with 2,6-diisopropylaniline or 2,6-dimethylaniline. Amine elimination reactions of Ln[N(SiMe(3))(2)](3) (Ln = La, Nd, Sm or Y) with these multitopic ligand precursors gave ten heterogeneous rare-earth metal catalysts. These heterogeneous rare-earth metal catalysts are active for intramolecular hydroalkoxylation of alkynols, and the catalytic activities are influenced by the ligand and metal ion. The recycling experiment on the most active heterogeneous catalyst showed the catalyst has a good reusability. PMID:22782285

Sun, Yilin; Wu, Guangming; Cen, Dinghai; Chen, Yaofeng; Wang, Limin

2012-08-28

121

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

122

Validation of the biotic ligand model in metal mixtures: bioaccumulation of lead and copper.  

PubMed

The biotic ligand model (BLM) has the potential to predict biological effects and bioaccumulation in metal mixtures. Pb and Cu uptake by the green alga Chlamydomonas reinhardtii have been quantified in single-metal exposures and in metal mixtures in order to test some of the key assumptions of the BLM. Stability constants for the interaction of the metals with biological uptake sites were determined from measured short-term internalization fluxes. In the absence of competition, a value of 10(5.8) M(-1) was obtained for Cu, while 10(5.9) M(-1) was obtained for Pb. Competition experiments did not show a straightforward antagonistic competition as would be predicted by the BLM. Only at high Cu(2+) concentrations (>1 microM) did Cu behave as a competitive inhibitor of Pb transport. Surprisingly, low concentrations of Cu(2+) had a synergistic effect on Pb uptake. Furthermore, Cu uptake was independent of Pb when Cu concentrations were below 10(-7) M. In order to explain the observed discrepancies with the BLM, membrane permeability and Cu transporter expression levels were probed. The expression of ctr2, a gene coding for a Cu transporter, increased significantly in the presence of Pb, indicating that bioaccumulation is much more dynamic than assumed in the equilibrium models. PMID:20384345

Chen, Zhongzhi; Zhu, Lin; Wilkinson, Kevin J

2010-05-01

123

Isolation of naturally occurring aluminium ligands using immobilized metal affinity chromatography for analysis by ESI-MS.  

PubMed

Aluminium (iii) is one of the most abundant metal ions found in soil. Typically, Al(+3) is bound to minerals, but its bioavailability and toxicity toward vascular plants increases with increasing soil acidity. Ectomycorrhizal fungi, which live symbiotically on the roots of numerous woody plants, often confer Al(+3) resistance to host plants by reducing metal availability to the plant by unknown mechanisms. A potential mechanism of detoxification is binding of the Al(+3) by organic compounds that are exuded by the fungi into the surrounding soil and solution. A novel method has been developed to purify and characterize Al(+3) binding ligands from Pisolithus tinctorius exudate solutions using Al(+3) immobilized metal affinity chromatography (IMAC), reversed phase chromatography, and mass spectrometry. Fungal exudates produced by P. tinctorius exhibit a strong binding capacity for Al(+3), allowing their selective enrichment and collection using this IMAC method. Elution of the ligands requires the use of high pH. RP-HPLC separation and elemental analysis of the IMAC elutent indicates that the Al(+3) and the exudate ligands both elute from the column but are not bound in a complex. Thus, reversed phase HPLC at pH 10 is used for separation of the ligands and Al(+3) prior to MS analysis. The strongest binding IMAC fraction is analyzed by electrospray ionization mass spectrometry in positive and negative ion modes. This report provides new methods for the direct purification and analysis of naturally occurring ligands that bind hard metal ions. PMID:15724160

Baldwin, Carson; Cumming, Jonathan; Timperman, Aaron T

2005-03-01

124

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

SciTech Connect

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

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

2009-07-15

125

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

126

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

127

Synthesis, structural characterization, electrochemistry and spectroelectrochemistry of dinuclear copper(II) metal complexes stabilized by a tetradentate NOOO salicylaldimine ligands  

NASA Astrophysics Data System (ADS)

The synthesis, structure, spectroscopic and electro-spectrochemical properties of salicylaldimine Schiff-base ligands (L nH) ( n = 1, 2, and 3) (L 1H = N-[2-amino-8-hydroxyquinoline]-salicylaldimine, L 2H = N-[2-amino-8-hydroxyquinoline]-5-bromosalicylaldimine and L 3H = N-[2-amino-8-hydroxyquinoline]-5-methoxysalicylaldimine), respectively, and their dinuclear copper(II) complexes [Cu 2(L n) 2] are described. Three new dissymmetric tetradentate salicylaldimine ligands containing a donor set of NOOO were prepared by reaction of 2-amino-8-hydroxyquinoline with different salicylaldehydes. The dinuclear copper(II) metal complexes of these ligands were synthesized by treating an ethanolic solution of the appropriate ligand with an equimolar amount of Cu(Ac) 2H 2O. The ligands and their copper complexes were characterized by FT-IR, UV-vis, 1H NMR, elemental analysis, molar conductivity, mass spectra and thermal analysis methods in addition to magnetic susceptibility and spectroelectrochemical techniques. The reaction of these ligands in a 1:1 mole ratio with copper(II) acetate afforded dinuclear Cu(II) metal complexes. The room temperature magnetic moments of [Cu 2(L n) 2] complexes are found between 1.12 and 1.28 BM for per Cu(II) molecule.

Tas, E.; Onal, I. H.; Yilmaz, I.; Kilic, A.; Durgun, M.

2009-06-01

128

Competitive metal-ligand binding between CdTe quantum dots and EDTA for free Ca(2+) 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 0.80-3.20mgL(-1), and a detection limit of 0.66mgL(-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, Joo A V; Santos, Joo L M

2015-03-01

129

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

130

The ligand-promoted mobilisation of metal ions from mineral surfaces  

NASA Astrophysics Data System (ADS)

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

Putnis, C. V.

2003-04-01

131

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

PubMed

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

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

2011-05-21

132

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

PubMed Central

Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log KML = ?OO(?O log KHL,1 + ?O log KHL,2) where KML is the metal-ligand stability constant for a 1:1 complex, KHL,1 and KHL,2 are the proton-ligand stability constants (the ligand pKa values), and ?O is the Irving-Rossotti slope. The parameter ?OO is metal specific and has slightly different values for 5 and 6 membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, ?-hydroxycarboxylic acids, and ?-ketocarboxylic acids, a modification of the LFER where log KHL,2 is set equal to zero is required. The chemical interpretation of ?OO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log KML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log KML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems. PMID:21833149

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

2011-01-01

133

A photoluminescent interpenetrating metal-organic frame work based on Cu4I4 and novel azino-quinoline ligand  

NASA Astrophysics Data System (ADS)

Synthesis of a novel, triply-interpenetrating metal-organic framework 1.H2O is described here. The coordination polymer was synthesized by simple reaction of Cu2I2 with an azino-quinoline ligand (L1). The X-ray crystal structure analysis reveals that the complex 1.H2O is a 2-D coordination polymer having (4,4?) grid network architecture. The ligand L1 possesses quinoline group and the 2-D structure of 1.H2O contains distorted cubane type Cu4I4 SBU unit. Each of the four Cu(I) ions posses tetrahedral coordination environment. Metal-organic framework in 1.H2O shows strong photoluminescence property at room temperature in solid state and emission spectra shows a blue shift of the peak in comparison to the free azino-quinoline ligand (L1). The coordination polymer 1.H2O was found to be stable up to 290 C.

Pal, Pankaj K.; Mukherjee, Anindita; Ghosh, Anindya; Patra, Goutam K.

2014-02-01

134

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

Microsoft Academic Search

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

Renzo Cini

2000-01-01

135

One and two-photon induced growth of ligand coated nanoparticles for 2 &3D metal patterning  

Microsoft Academic Search

Ligand-coated metallic nanoparticles are powerful new materials for nano-electronic and photonics applications. They can be readily synthesized and their stability and solubility allows them to be cast in complex composite materials or self-assembled into quasi-ordered films. We demonstrate that, in the presence of reducing dyes with a large two-photon cross-section and metal salts, it is possible to induce the growth

Francesco Stellacci; Christina A. Bauer; Timo Meyer-Friedrichsen; Wim Wenseleers; Valrie Alain; Stephen M. Kuebler; Stephanie J. Pond; Yadong Zhang; Seth R. Marder; Joseph W. Perry

2002-01-01

136

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

137

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

Microsoft Academic Search

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

Kathleen S. Smith

138

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)] () 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

2015-01-15

139

The Role of Symmetry and Spatial Shielding of Metal by Ligands in the Biological Activity of Organometallic and Coordination Compounds  

Microsoft Academic Search

Previously, we demonstrated the importance of spatial shielding of the metal atom by ligands in the stability, volatility, and reactivity [1?3] of organometallic and coordination compounds R n M. Interest in predicting the physiological action of these compounds [4, 5] and systematic analysis of the biological activities of known organometallic and coordination compounds prompted us to the conclusion that these

G. A. Domrachev; Yu. A. Shevelev; L. N. Zakharov; L. G. Domracheva; E. G. Domracheva

2003-01-01

140

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

141

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

NASA Astrophysics Data System (ADS)

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

Wu, Chun-Kwei

142

Anchoring noble metal nanoparticles on CeO2 modified reduced graphene oxide nanosheets and their enhanced catalytic properties.  

PubMed

The strategy of structurally integrating noble metal, metal oxide, and graphene is expected to offer prodigious opportunities toward emerging functions of graphene-based nanocomposites. In this study, we develop a facile two-step approach to disperse noble metal (Pt and Au) nanoparticles on the surface of CeO2 functionalized reduced graphene oxide (RGO) nanosheets. It is shown that Pt and Au with particle sizes of about 5 and 2nm are well dispersed on the surface of RGO/CeO2. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 was used as a model reaction to quantitatively evaluate the catalytic properties of the as-synthesized RGO/Pt/CeO2 and RGO/Au/CeO2 ternary nanocomposites. In such triple-component catalysts, CeO2 nanocrystals provide unique and critical roles for optimizing the catalytic performance of noble metallic Pt and Au, allowing them to express enhanced catalytic activities in comparison with RGO/Pt and RGO/Au catalysts. In addition, a possible mechanism for the enhanced catalytic activities of the RGO/Pt/CeO2 and RGO/Au/CeO2 ternary catalysts in the reduction of 4-NP is proposed. It is expected that our prepared graphene-based triple-component composites, which inherit peculiar properties of graphene, metal oxide, and noble metal, are attractive candidates for catalysis and other applications. PMID:25080384

Ji, Zhenyuan; Shen, Xiaoping; Xu, Yuling; Zhu, Guoxing; Chen, Kangmin

2014-10-15

143

A flexible ligand-based wavy layered metal-organic framework for lithium-ion storage.  

PubMed

A substantial challenge for direct utilization of metal-organic frameworks (MOFs) as lithium-ion battery anodes is to maintain the rigid MOF structure during lithiation/delithiation cycles. In this work, we developed a flexible, wavy layered nickel-based MOF (C20H24Cl2N8Ni, designated as Ni-Me4bpz) by a solvothermal approach of 3,3',5,5'-tetramethyl-4,4'-bipyrazole (H2Me4bpz) with nickel(II) chloride hexahydrate. The obtained MOF materials (Ni-Me4bpz) with metal azolate coordination mode provide 2-dimensional layered structure for Li(+) intercalation/extraction, and the H2Me4bpz ligands allow for flexible rotation feature and structural stability. Lithium-ion battery anodes made of the Ni-Me4bpz material demonstrate excellent specific capacity and cycling performance, and the crystal structure is well preserved after the electrochemical tests, suggesting the potential of developing flexible layered MOFs for efficient and stable electrochemical storage. PMID:25638743

An, Tiance; Wang, Yuhang; Tang, Jing; Wang, Yang; Zhang, Lijuan; Zheng, Gengfeng

2015-05-01

144

Self-assembly molecular squares with metal complexes as bridging ligands  

SciTech Connect

Polynuclear transition metal complexes containing multichromophoric units, such as metal polypyridyl complexes, are of considerable current interest. Much attention has been paid to the synthesis of multicomponent systems that exhibit photoinduced intercomponent electron and/or energy-transfer processes and to their potential applications for photonic and electronic devices. Systems incorporating Re(I)- Ru(II)-, and Os(II)-based polypyridyl chromophores are the most commonly studied because of their favorable redox and spectroscopic characteristics. In this communication, the authors combine the concepts of self-assembly and complexes as ligands and report the preparation of a series of molecular squares with the general molecular formula [fac-Br(CO){sub 3}Re({mu}-(pyterpy){sub 2}M)]{sub 4}(PF{sub 6}){sub 8}, where pyterpy is 4{prime}-(4{prime}{double_prime}-pyridyl)-2,2{prime}:6{prime}2{double_prime}-terpyridine and M = Fe, Ru, or Os. The spectroscopic properties and a preliminary anion binding study of these novel octanuclear molecular squares are also presented.

Sun, S.S.; Silva, A.S.; Brinn, I.M.; Lees, A.J.

2000-04-03

145

Sandwich transitional metal complexes with tungstobismuthates and 1-methylimidazole ligands: Syntheses, structures and magnetic properties  

NASA Astrophysics Data System (ADS)

Two novel sandwich-type coordination compounds of tungstobismuthate Na 9[{Na(H 2O) 2} 3{Co II(mim)} 3(Bi IIIW VI9O 33) 2]36H 2O ( 1) and Na 7H 2[{Na(H 2O) 2} 3{Mn II(mim)} 3(Bi IIIW VI9O 33) 2]21H 2O ( 2) (mim = 1-methylimidazole) have been synthesized in alkaline aqueous solution. Their composition and structures were established by elemental analyses, IR spectra, and single crystal X-ray diffraction. These two complexes consist of two tri-vacant [?-B-Bi IIIW VI9O 33] 9- moieties linked through three Cu II or Mn II and three Na + ions. These Na + cations around the complex anion were bonded with some terminal and bridging oxo atoms from the complex anion and water molecules. In addition to tungstobismuthate ligands, 1-methylimidazoles also coordinate to sandwich transitional metal ions. Magnetic measurement indicates the existence of antiferromagnetic interaction between the trimeric transitional metal ions for 1 and 2.

Liu, Hong; Xu, Lin; Gao, Guanggang; Li, Fengyan; Jiang, Ning

2008-04-01

146

Cytotoxic behavior and spectroscopic characterization of metal complexes of ethylacetoacetate bis(thiosemicarbazone) ligand.  

PubMed

Reaction of Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) ion with 2,4-dihydrazino-thioamido-1-ethoxybutane led to the formation of mono and binuclear complexes. These complexes have been characterized by elemental analyses, IR, UV-Vis spectra, magnetic moments, molar conductances, (1)H NMR and mass spectra (ligand and its Zn(II) complex), thermal analyses (DTA and TGA) and ESR measurements. The IR data suggest the involvement of sulfur and azomethane nitrogen atoms in coordination to the central metal ion .The Molar conductances of the complexes in DMF are commensurate with their non-ionic character. The ESR spectra of Cu(II) complexes show axial type symmetry (d(x2-y2)) ground state with covalent bond character. On the basis of spectral studies, octahedral or tetrahedral geometry has been assigned to the metal complexes. Complexes have been tested invitro against tumor cells and number of microorganisms in order to assess their antitumor and antimicrobial properties. PMID:24011929

El-Tabl, Abdou Saad; El-wahed, Moshira Mohamed Abd; Rezk, Ahmed Mahmoud Salah Mahmoud

2014-01-01

147

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

148

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; Gmez-Garca, Carlos J; Desplanches, Cdric; Mitra, Samiran

2014-11-14

149

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

150

Photoemission mechanism of water-soluble silver nanoclusters: ligand-to-metal-metal charge transfer vs strong coupling between surface plasmon and emitters.  

PubMed

Using carboxylate-protected silver nanoclusters (Ag-carboxylate NCs) as a model, we separately investigated the contribution of the ligand shell and the metal core to understand the nature of photoluminescence of Ag NCs. A new Ag(0)NCs@Ag(I)-carboxylate complex core-shell structural model has been proposed. The emission from the Ag-carboxylate NCs could be attributed to ligand-to-metal-metal charge transfer from Ag(I)-carboxylate complexes (the oxygen atom in the carboxylate ligands to the Ag(I) ions) to the Ag atoms and subsequent radiative relaxation. Additionally, we found that the emission wavelength of the Ag NCs depends on the excitation wavelength implying a strong coupling between surface plasmon and emitter in Ag NCs. The strong coupling between the surface plasmon and the emitter determines the quantum yield and lifetime. The emission mechanism of Ag NCs and its relation to the organic templates and metal cores were clearly clarified. The results should stimulate additional experimental and theoretical research on the molecular-level design of luminescent metal probes for optoelectronics and other applications. PMID:24437963

Chen, Yuting; Yang, Taiqun; Pan, Haifeng; Yuan, Yufeng; Chen, Li; Liu, Mengwei; Zhang, Kun; Zhang, Sanjun; Wu, Peng; Xu, Jianhua

2014-02-01

151

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

PubMed

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

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

2014-01-01

152

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

PubMed Central

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

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

2010-01-01

153

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

154

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; Heiler, Stefan; Wll, Christof

2013-01-01

155

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.

156

Microwave Assisted Synthesis, Spectral and Antifungal Studies of 2-Phenyl-N,N?-bis(pyridin-4-ylcarbonyl)butanediamide Ligand and Its Metal Complexes  

PubMed Central

2-Phenyl-N,N?-bis(pyridin-4-ylcarbonyl)butanediamide ligand with a series of transition metal complexes has been synthesized via two routes: microwave irradiation and conventional heating method. Microwave irritation method happened to be the efficient and versatile route for the synthesis of these metal complexes. These complexes were found to have the general composition M(L)Cl2/M(L)(CH3COO)2 (where M = Cu(II), Co(II), Ni(II), and L = ligand). Different physical and spectroscopic techniques were used to investigate the structural features of the synthesized compounds, which supported an octahedral geometry for these complexes. In vitro antifungal activity of the ligand and its metal complexes revealed that the metal complexes are highly active compared to the standard drug. Metal complexes showed enhanced activity compared to the ligand, which is an important step towards the designing of antifungal drug candidates. PMID:24772018

Shiekh, Rayees Ahmad; Malik, Maqsood Ahmad; Al-Thabaiti, Shaeel Ahmed; Nabi, Arshid

2014-01-01

157

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

158

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

NASA Astrophysics Data System (ADS)

A Tetraaza Macrocylic Ligand (H 2L) and its complexes, [Cd(H 2L)(OH 2) 2](NO 3) 21/2OH 2 (I), [Co(H 2L)(OH 2)](NO 3) 21/2OH 2 (II), [Cu(H 2L)(NO 3) 2]3/2OH 2 (III) and [Ni(H 2L)(NO 3)(OH 2)]NO 3OH 2 (IV), have been synthesized and characterized on the basis of elemental analysis, molar conductivity, 1H NMR, UV-vis, FT-IR and mass spectroscopy. All results confirm that the prepared compounds have 1:1 metal-to-ligand stoichiometry, octahedral configuration and the ligand behaves as a neutral tetradendate towards the metal ions. [CdL(OH 2) 2] (V), [CoL(OH 2) 2] (VI), [CuL(OH 2) 2] (VII) and [Ni(H 2L)(NO 3) 2] (VIII) were synthesized pyrolytically in solid state from corresponding compounds (I-IV). Analytical results of complexes (V-VIII) show that the ligand behaves either as a neutral tetradendate or dianionic tetradentate ligand towards the metal ions. The binding of H 2L and its copper complex (III) to DNA has been investigated by ultraviolet absorption spectroscopy. The experiments indicate that H 2L and its copper complex (III) can bind to DNA through an intercalative mode. The H 2L and its copper complex (III) exhibited anti-tumor activity against Ehrlich Acites Carcinoma (E.A.C) at the concentration of 100 ?g/ml.

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

2011-09-01

159

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

PubMed

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

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

2014-06-14

160

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

PubMed

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

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

2008-01-01

161

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

162

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

163

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

164

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 1C, = 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

165

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

166

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

167

Quest for highly porous metalmetalloporphyrin framework based upon a custom-designed octatopic porphyrin ligand  

Microsoft Academic Search

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 mg² g⁻¹ among reported porphyrin-based MOFs, and demonstrates a high uptake capcity of 170 cm³ g⁻¹ CO at 273 K and 1 bar.

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

2012-01-01

168

N-heterocyclic carbene (NHC) ligands annulated to free-base porphyrins: modulation of the electronic properties of the NHC upon protonation or metallation of the porphyrin.  

PubMed

NHC ligands annulated to free-base porphyrins can be reversibly switched between electron-poor and electron-rich states upon protonation and deprotonation of the inner nitrogen atoms of the porphyrin. Metallation of the macrocycle with nickel(II) locks the peripheral NHC ligand in its electron-rich state. PMID:21249236

Lefebvre, Jean-Franois; Lo, Mamadou; Leclercq, Dominique; Richeter, Sbastien

2011-03-14

169

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

170

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

171

Synthesis and properties of a twistophane ion sensor: a new conjugated macrocyclic ligand for the spectroscopic detection of metal ions.  

PubMed

The synthesis of a structurally new type of conjugated macrocyclic ligand (1) is reported that comprises a dehydroannulene framework incorporating two 2,2'-bipyridine units. Modeling studies showed the ligand to possess an unusual chirally twisted and relatively rigid architecture capable of binding metal ions in an enforced tetrahedral coordination geometry. The macrocycle was prepared in seven steps from (2-bromophenylethynyl)-trimethylsilane (2) and characterized by spectroscopic techniques. The pyridine H3 protons in the 1H NMR spectrum of 1 showed a marked temperature dependencey that may be related to conformational opening and closing motions of the macrocyclic ring. Ligand 1 was found to spectroscopically detect the presence of Co2+, Ni2+, Cu2+, and Zn2+ and, in particular, to function as a multiple readout sensor, giving different sequences of signal output depending upon the type of metal ion analyte with which the system was addressed. Macrocycle 1 also gave a highly characteristic and specific visual output response in the presence of Zn2+ consisting of a bright turquoise fluorescence and in this respect may find applications in the sensing of this biologically important metal ion. PMID:11397150

Baxter, P N

2001-06-15

172

The effects of phosphorous donor ligand substitution on the reactivity of anionic group 6 transition metal carbonyl hydrides  

E-print Network

W(p-H)(CO)4{L)(PPh )] Bridging Hydride in THF Solution 35 37 47 A Comparison of Selectivity in the Reduction of Linear and Branched RBr by Anionic Group 6 Metal Hydrides 57 VI GC Yields for Reductions Using Various Acids with the Hydrides PPN HM(CO)4L... region of Na HW(CO)4P(OMe) in THF solution at 22'C Infrared spectrum of the car bonyl region of bridging hydride [AuW(rr-H)(CO)?(P(OMe) }(PPh )] 34 48 CHAPTER I INTRODUCTION The P-donor ligand substituted hydrides of the gnoup 6 transition metals...

Lusk, Richard Jay

2012-06-07

173

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

174

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

SciTech Connect

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

Ogino, I.; Gates, B

2010-01-01

175

NMR shielding calculations across the periodic table: diamagnetic uranium compounds. 2. Ligand and metal NMR.  

PubMed

In this and a previous article (J. Phys. Chem. A 2000, 104, 8244), the range of application for relativistic density functional theory (DFT) is extended to the calculation of nuclear magnetic resonance (NMR) shieldings and chemical shifts in diamagnetic actinide compounds. Two relativistic DFT methods are used, ZORA ("zeroth-order regular approximation") and the quasirelativistic (QR) method. In the given second paper, NMR shieldings and chemical shifts are calculated and discussed for a wide range of compounds. The molecules studied comprise uranyl complexes, [UO(2)L(n)](+/-)(q); UF(6); inorganic UF(6) derivatives, UF(6-n)Cl(n), n = 0-6; and organometallic UF(6) derivatives, UF(6-n)(OCH(3))(n), n = 0-5. Uranyl complexes include [UO(2)F(4)](2-), [UO(2)Cl(4)](2-), [UO(2)(OH)(4)](2-), [UO(2)(CO(3))(3)](4-), and [UO(2)(H(2)O)(5)](2+). For the ligand NMR, moderate (e.g., (19)F NMR chemical shifts in UF(6-n)Cl(n)) to excellent agreement [e.g., (19)F chemical shift tensor in UF(6) or (1)H NMR in UF(6-n)(OCH(3))(n)] has been found between theory and experiment. The methods have been used to calculate the experimentally unknown (235)U NMR chemical shifts. A large chemical shift range of at least 21,000 ppm has been predicted for the (235)U nucleus. ZORA spin-orbit appears to be the most accurate method for predicting actinide metal chemical shifts. Trends in the (235)U NMR chemical shifts of UF(6-n)L(n) molecules are analyzed and explained in terms of the calculated electronic structure. It is argued that the energy separation and interaction between occupied and virtual orbitals with f-character are the determining factors. PMID:12470051

Schreckenbach, Georg

2002-12-16

176

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

Schdle, Dorothea; Maichle-Mssmer, Ccilia; Schdle, Christoph; Anwander, Reiner

2015-01-01

177

Kinetics of brucite dissolution at 25C 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 25C 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

178

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

179

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

PubMed Central

Peptide nucleic acid (PNA) is one of the most widely used synthetic DNA analogs. Conjugation of functional molecules to PNA is very effective to further widen its potential applications. For this purpose, here we report the synthesis of several ligand monomers and introduced them to PNA. These ligand-modified PNAs attract cerium ion and are useful for site-selective DNA hydrolysis. It should be noted that these ligands on PNA are also effective even under the conditions of invasion complex. PMID:22772037

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

2012-01-01

180

Molecular order in Langmuir-Blodgett monolayers of metal-ligand surfactants probed by sum frequency generation.  

PubMed

Molecular organization of Langmuir-Blodgett (LB) monolayers of novel copper-containing metal-ligand surfactants was characterized by the surface-selective vibrational sum frequency generation (SFG) spectroscopy. The orientational and conformational order inferred from the SFG peak amplitudes and line shapes were correlated with the two-dimensional phases of the monolayers observed in the compression isotherms. The octadecyl-pyridin-2-ylmethyl-amine (L(PyC18)) ligand by itself shows good amphiphilic properties, as indicated by the high monolayer collapse pressure at the air/water interface, but its LB films transferred onto fused silica exhibit a high degree of trans-gauche conformational disorder in the alkyl tails. Coordination of copper(II) ions to the chelating head group enhances the molecular alignment and reduces the fraction of gauche defects of the alkyl chains. Monolayers of single-tail (L(PyC18)Cu(II)Cl(2)) and double-tail [(L(PyC18))(2)Cu(II)]Cl(2) metallosurfactants show distinctly different behavior of their molecular organization as a function of the area per molecule. Our observations suggest metal-ligand interactions as a pathway to induce molecular order in LB monolayer films. PMID:19505159

Jayathilake, Himali D; Driscoll, Jeffery A; Bordenyuk, Andrey N; Wu, Libo; da Rocha, Sandro R P; Verani, Claudio N; Benderskii, Alexander V

2009-06-16

181

Synthesis and catalytic activity of group 5 metal amides with chiral biaryldiamine-based ligands.  

PubMed

A new series of group 5 metal amides have been prepared from the reaction between V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) and chiral ligands, (R)-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (1H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (2H(2)), (R)-6,6'-dimethyl-2,2'-bis(mesitoylamino)-1,1'-biphenyl (3H(2)), (R)-2,2'-bis(mesitylenesulfonylamino)-6,6'-dimethyl-1,1'-biphenyl (4H(2)), (R)-2,2'-bis(diphenylthiophosphoramino)-1,1'-binaphthyl (5H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (6H(2)), (R)-2,2'-bis[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (7H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-1,1'-binaphthyl (8H(2)), (S)-2-(mesitoylamino)-2'-(dimethylamino)-1,1'-binaphthyl (9H), and (R)-2-(mesitoylamino)-2'-(dimethylamino)-6,6'-dimethyl-1,1'-biphenyl (10H), which are derived from (R) or (S)-2,2'-diamino-1,1'-binaphthyl, and (R)-2,2'-diamino-6,6'-dimethyl-1,1'-biphenyl, respectively. Treatment of V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) with 1 equiv of C(2)-symmetric amidate ligands 1H(2), 2H(2), 3H(2), 4H(2), and 5H(2), or Schiff base ligands 6H(2), 7H(2) and 8H(2) at room temperature gives, after recrystallization from a benzene, toluene or n-hexane solution, the vanadium amides (1)V(NMe(2))(2) (11), (2)V(NMe(2))(2) (14), (3)V(NMe(2))(2) (17), (5)V(NMe(2))(2) (22), (6)V(NMe(2))(2) (23) and (7)V(NMe(2))(2) (24), and niobium amides (1)Nb(NMe(2))(3) (12), (2)Nb(NMe(2))(3) (15), (3)Nb(NMe(2))(3) (18), (4)Nb(NMe(2))(3) (20) and [2-(3-Me(3)C-2-O-C(6)H(3)CHN)-2'-(N)-C(20)H(12)][2-(Me(2)N)(2)CH-6-CMe(3)-C(6)H(3)O]NbNMe(2)C(7)H(8) (25C(7)H(8)), and tantalum amides (1)Ta(NMe(2))(3) (13), (2)Ta(NMe(2))(3) (16), (3)Ta(NMe(2))(3) (19) and (4)Ta(NMe(2))(3) (21) respectively, in good yields. Reaction of V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) with 2 equiv of C(1)-symmetric amidate ligands 9H or 10H at room temperature gives, after recrystallization from a toluene or n-hexane solution, the chiral bis-ligated vanadium amides (9)(2)V(NMe(2))(2)3C(7)H(8) (273C(7)H(8)) and (10)V(NMe(2))(2) (28), and chiral bis-ligated metallaaziridine complexes (10)(2)M(NMe(2))(?(2)-CH(2)NMe) (M = Nb (29), Ta (30)) respectively, in good yields. The niobium and tantalum amidate complexes are stable in a toluene solution at or below 160 C, while the vanadium amidate complexes degrade via diemthylamino group elimination at this temperature. For example, heating the complex (2)V(NMe(2))(2) (14) in toluene at 160 C for four days leads to the isolation of the complex [(2)V](2)(?-NMe(2))(2) (26) in 58% yield. These new complexes have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 12, 13, and 15-30 have further been confirmed by X-ray diffraction analyses. The vanadium amides are active chiral catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to good yields with good ee values (up to 80%), and the tantalum amides are outstanding chiral catalysts for the hydroaminoalkylation, giving chiral secondary amines in good yields with excellent ee values (up to 93%). PMID:21218246

Zhang, Furen; Song, Haibin; Zi, Guofu

2011-02-21

182

Measurement of complexation properties of metal ions in natural conditions by ultrafiltration: measurement of equilibrium constants for complexation of zinc by synthetic and natural ligands  

SciTech Connect

A new ultrafiltration method is described to measure complexation properties (stability constants) of trace metal ions with natural aquatic ligands. The determination of stability constants is described theoretically and the best operational conditions are discussed theoretically and experimentally. Theory is tested with Zn, known synthetic ligands, and pedogenic fulvic acids of natural waters. The results obtained by this method compare well with the literature data. In particular, for natural mixture of complexing sites like fulvic acids, this method permits the determination of the detailed equilibrium function to be carried out instead of its average value, over a given range of metal to ligand ratio. The most important advantages of this method are the fact that there is no limitation with regard to the nature of metal ions and little for that of the ligands.

Buffle, J.; Staub, C.

1984-12-01

183

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

PubMed

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

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

2013-08-19

184

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

PubMed

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

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

2014-12-10

185

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

186

Synthesis and cytotoxic activities of group 3 metal complexes having monoanionic tridentate ligands.  

PubMed

Complexes of scandium, yttrium, samarium and neodymium bearing monoanionic tridentate ancillary ligands have been synthesized and characterized. The cytotoxic activities of novel compounds, as well as that of similar compounds previously reported have been evaluated on rat glioma (C6), murine fibrosarcoma (WHEI-164) and human embryonic kidney (HEK-293) cell lines. Scandium complex with quinolinephenoxyamine (NNHO) ligand showed very interesting activity against C6 cell line. PMID:20591537

Saturnino, Carmela; Napoli, Mariagrazia; Paolucci, Gino; Bortoluzzi, Marco; Popolo, Ada; Pinto, Aldo; Longo, Pasquale

2010-09-01

187

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 /1.60-1.90 /180-160 and for bent nitrosyls are 1.16-1.22 /1.80-2.00 /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 /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 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 /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: 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

188

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

189

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

190

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 (pH11.5). 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

191

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

192

The synthesis, characterization, antimicrobial and antimutagenic activities of hydroxyphenylimino ligands and their metal complexes of usnic acid isolated from Usnea longissima.  

PubMed

Novel multifunctional hydroxyphenylimino ligands (L1, L2 and L3) were synthesized by the condensation of 2-aminophenol, 3-aminophenol and 4-aminophenol with usnic acid, a lichen metabolite. The synthesized ligands and their Cu(II), Co(II), Ni(II) and Mn(II) complexes were characterized using FT-IR, UV-Vis, (1)H-NMR, (13)C-NMR, 1D- and 2D NMR (DEPT, COSY, HMQC and HMBC), LC-MS and TGA. In addition, the metal complexes of the novel ligands were prepared with high yields using Cu(II), Co(II), Ni(II) and Mn(II) salts and were characterized using the FT-MIR/FAR, UV-Vis, elemental analysis, ICP-OES and TG/DTA techniques. The ligands and their complexes were tested against ten important pathogen microorganisms using the disc diffusion method and the metal complexes of the ligands were more active against all of the microorganisms tested with a broad spectrum than the ligands exhibiting 1132 mm inhibition zones. On the other hand, a broad spectrum of the strongest antimicrobial activity was determined for the Mn(II) and Cu(II) complexes of the hydroxyphenylimino ligand with usnic acid (L3). In addition, the antimutagenic activities of all of the ligands and their metal complexes were determined using the Ames-Salmonella and E. coli WP2 microbial assay systems and they showed varied and strong antimutagenic effects. In general, it has been found that the Co and Mn complexes of the ligands possess potent antimutagenic activity. In view of these results, it can be concluded that some metal complexes can be used as antimicrobial and anticancer agents. PMID:24589530

Koer, Sibel; Uru?, Serhan; ak?r, Ahmet; Gllce, Medine; D??rak, Metin; Alan, Yusuf; Aslan, Ali; Tmer, Mehmet; Karaday?, Mehmet; Kazaz, Cavit; Dal, Hakan

2014-04-28

193

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, Stphane; Dagorne, Samuel; Dmpelmann, Ralf; Steffanut, Pascal

2014-01-01

194

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

PubMed Central

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

Tircs, Gyula; Beny, Enik? Tircsn; Suh, Eul Hyun; Jurek, Paul; Kiefer, Garry E.; Sherry, A. Dean; Kovcs, Zoltn

2009-01-01

195

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

196

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

SciTech Connect

Upon activation, the epidermal growth factor (EGF) receptor becomes phosphorylated and triggers a vast signaling network that has profound effects on cell growth. The EGF receptor is observed to assemble into clusters after ligand binding and tyrosine kinase autophosphorylation, but the role of these assemblies in the receptor signaling pathway remains unclear. To address this question, we measured the phosphorylation of EGFR when the EGF ligand was anchored onto laterally mobile and immobile surfaces. We found that cells generated clusters of ligand-receptor complex on mobile EGF surfaces, and generated a lower ratio of phosphorylated EGFR to EGF than when compared to immobilized EGF that is unable to cluster. This result was verified by tuning the lateral assembly of ligand-receptor complexes on the surface of living cells using patterned supported lipid bilayers. Nanoscale metal lines fabricated into the supported membrane constrained lipid diffusion and EGF receptor assembly into micron and sub-micron scale corrals. Single cell analysis indicated that clustering impacts EGF receptor activation, and larger clusters (> 1 m2) of ligand-receptor complex generated lower EGF receptor phosphorylation per ligand than smaller assemblies (< 1 m2) in HCC1143 cells that were engaged to ligand-functionalized surfaces. We investigated EGFR clustering by treating cells with compounds that disrupt the cytoskeleton (Latrunculin-B), clathrin-mediated endocytosis (Pitstop2), and inhibit EGFR activation (Gefitinib). These results help elucidate the nature of large-scale EGFR clustering, thus underscoring the general significance of receptor spatial organization in tuning function.

Stabley, Daniel [Emory University; Retterer, Scott T [ORNL; Marshal, Stephen [Emory University; Salaita, Khalid [Emory University

2013-01-01

197

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

PubMed

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

Alexandratos, Spiro D

2007-01-31

198

Obtaining chiral metal-organic frameworks via a prochirality synthetic strategy with achiral ligands step-by-step.  

PubMed

Although some achievements of constructing chiral metal-organic frameworks (MOFs) with diverse achiral ligands have been made, there is still a lack of full understanding of the origin and formation mechanism of chirality, as well as the reasonable principles for the design and construction of chiral frameworks. The concept of prochirality in organic molecules and complex systems inspires us to explore the synthetic strategy of chiral MOFs based on achiral sources. Here, an achiral compound [Cu(en)][(VO3)2] (1) was isolated in the CuCl2/NH4VO3/en system, while further chiral frameworks [Cu(en)(Im)2][(VO3)2] (2a and 2b) were obtained by the reaction between compound 1 and another achiral ligand Im (ethanediamine = en and imidazole = Im). In the present system, compound 1 has the characteristic of a quasi-plane structure unit. Further reaction of compound 1 and the achiral ligand (Im) induced the formation of chiral ?/? Cu centers, and then a pair of chiral frameworks containing one-dimensional (1D) helical chains was formed. The chiral symmetry breaking phenomenon of compounds 2a and 2b can also be expected and explained based on this kind of prochirality synthetic strategy. PMID:24611962

Dong, Huan; Hu, Hailiang; Liu, Yang; Zhong, Jun; Zhang, Guangju; Zhao, Fangfang; Sun, Xuhui; Li, Youyong; Kang, Zhenhui

2014-04-01

199

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

SciTech Connect

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

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

2005-11-15

200

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] n5 nH 2O ( 1), [Co(-tsgluO)(2,4'-bipy) 2(H 2O) 2] n5 nH 2O ( 2), [Ni(-tsgluO)(4,4'-bipy)] n0.5 nH 2O ( 3), and [Co(-tsgluO)(4,4'-bipy)] n0.5 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

201

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

PubMed Central

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

Wang, Rongming; Zhang, Jian; Li, Lijuan

2009-01-01

202

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

E-print Network

produce more efficient catalysts as the electron-rich character of the NiN2S2 ligand favors the resting state of the catalyst, [(Ni-1)Pd(C(O)CH3)(CO)]+, over the reactive form (Ni-1)Pd(C(O)CH3)(2-C2H4)]+. An exploratory investigation with the Ni...

Rampersad, Marilyn Vena

2007-04-25

203

Evaluation of stability constants of metal complexes with sulphonated azo-ligands.  

PubMed

An ion-exchange procedure is described for the determination of the stability constants for cadmium, copper, nickel and manganese complexes with three sulphonated azo ligands: calmagite, alizarin violet N and palatine chrome black. The results, log K values, show a good agreement with those obtained by a spectrophotometric technique. PMID:18966044

Abollino, O; Sarzanini, C; Mentasti, E; Liberatori, A

1994-07-01

204

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

205

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

206

21 CFR 872.3130 - Preformed anchor.  

Code of Federal Regulations, 2010 CFR

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

2010-04-01

207

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

208

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

209

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

PubMed

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

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

2014-05-19

210

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

211

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, 68), 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 MCl 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

212

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

PubMed

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

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

1997-01-01

213

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-HS 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-HO 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

214

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

NASA Astrophysics Data System (ADS)

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

Varga, Gbor; Csendes, Zita; Peintler, Gbor; Berkesi, Ott; Sipos, Pl; Plink, Istvn

2014-03-01

215

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

PubMed

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

Prince, Bruce M; Cundari, Thomas R

2013-09-26

216

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

PubMed Central

Upon activation, the epidermal growth factor (EGF) receptor becomes phosphorylated and triggers a vast signaling network that has profound effects on cell growth. The EGF receptor is observed to assemble into clusters after ligand binding and tyrosine kinase autophosphorylation, but the role of these assemblies in the receptor signaling pathway remains unclear. To address this question, we measured the phosphorylation of EGFR when the EGF ligand was anchored onto laterally mobile and immobile surfaces. We found that cells generated clusters of ligand-receptor complex on mobile EGF surfaces, and displayed a lower ratio of phosphorylated EGFR to EGF when compared to immobilized EGF that is unable to cluster. This result was verified by tuning the lateral assembly of ligand-receptor complexes on the surface of living cells using patterned supported lipid bilayers. Nanoscale metal lines fabricated into the supported membrane constrained lipid diffusion and EGF receptor assembly into micron and sub-micron scale corrals. Single cell analysis indicated that clustering impacts EGF receptor activation, and larger clusters (> 1 m2) of ligand-receptor complex generated lower EGF receptor phosphorylation per ligand than smaller assemblies (< 1 m2) in HCC1143 cells that were engaged to ligand-functionalized surfaces. We investigated the mechanism of EGFR clustering by treating cells with compounds that disrupt the cytoskeleton (Latrunculin-B), clathrin-mediated endocytosis (Pitstop2), and inhibit EGFR activation (Gefitinib). These results help elucidate the nature of large-scale EGFR clustering, thus underscoring the general significance of receptor spatial organization in tuning function. PMID:23416883

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

2013-01-01

217

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

PubMed

A new chelating ligand, 2-(2-(5-tert-butylisoxazol-3-yl)hydrazono)-N-(2,4-dimethylphenyl)-3-oxobutanamide (HL), and its four binuclear transition metal complexes, M(2)(L)(2) (micro-OCH(3))(2) [M=Ni(II), Co(II), Cu(II), Zn(II)], were synthesized using the procedure of diazotization, coupling and metallization. Their structures were postulated based on elemental analysis, (1)H NMR, MALDI-MS, FT-IR spectra and UV-vis electronic absorption spectra. Smooth films of these complexes on K9 glass substrates were prepared using the spin-coating method and their absorption properties were evaluated. The thermal properties of the metal(II) complexes were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Different thermodynamic and kinetic parameters namely activation energy (E*), enthalpy of activation (DeltaH*), entropy of activation (DeltaS*) and free energy change of activation (DeltaG*) are calculated using Coats-Redfern (CR) equation. PMID:17307385

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

2007-11-01

218

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

219

Schiff base ligands and their transition metal complexes in the mixtures of ionic liquid + organic solvent: a thermodynamic study.  

PubMed

Schiff bases and their metal complexes in the mixtures of ionic liquid (IL) + organic solvent have shown great potential in attractive oxidation catalytic processes. The efficiency of such a process is strongly dependent on the various molecular interactions occurring between components. Thermodynamic properties of these systems can provide valuable information about structural interactions. Therefore, in this work, the interactions of the IL 1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) with Schiff bases in organic solvents were studied through the measurements of density, viscosity, and electrical conductivity. The effect of solvent on the interactions was examined by the solutions of IL + BPIC Schiff base + solvent (C2H6O-C3H8O-C4H10O). Moreover, the influence of Schiff base ligand and Schiff base complex structures was probed by the solutions of IL + DMA + ligand (salcn/salpr/salen) and IL + DMA + complex (VO(3-OMe-salen)/VO(salophen)/VO(salen)), respectively. Using the experimental data, some important thermodynamic properties, such as standard partial molar volume (V), experimental slope (Sv), viscosity B-coefficient, solvation number (B/V), and limiting molar conductivity (?0) were calculated and discussed in terms of solute-solvent (IL-DMF/alcohol) and solute-cosolute (IL-Schiff base) interactions. PMID:25482659

Shekaari, Hemayat; Kazempour, Amir; Khoshalhan, Maryam

2015-01-21

220

Synthesis of arene-soluble mixed-metal uranium/zirconium complexes using the dizirconium nonaisopropoxide ligand.  

PubMed

The utility of polydentate monoanionic [Zr(2)(O(i)Pr)(9)](-) (dzni) in generating arene-soluble, mixed-metal Zr/U complexes is described. K[Zr(2)(O(i)Pr)(9)] reacts readily with UI(3)(THF)(4) to form [Zr(2)(O(i)Pr)(9)]UI(2)(THF), 1, in >90% yield. The integrity of the [[Zr(2)(O(i)Pr)(9)]U](2+) unit in 1 was examined by the reaction of 1 with K(2)C(8)H(8), which formed the organometallic complex [Zr(2)(O(i)Pr)(9)]U(C(8)H(8)), 2. In contrast, the reaction of K[Zr(2)(O(i)Pr)(9)] with UCl(4) did not form U(IV)-dzni complexes, and only the ligand exchange product, [UCl(2)(O(i)Pr)(2)(DME)](2), 3, was isolated. The effect of the dzni ligand on the electrochemistry and near-infrared spectroscopy of U(III) is also described. PMID:11735484

Evans, W J; Nyce, G W; Greci, M A; Ziller, J W

2001-12-17

221

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 EC1020 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; Schnrch, Michael; Ernst, Margot; Mihovilovic, Marko D.

2015-01-01

222

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

PubMed

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; Schnrch, Michael; Ernst, Margot; Mihovilovic, Marko D

2015-01-15

223

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

224

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

225

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

PubMed

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

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

2013-07-01

226

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

PubMed

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

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

2013-11-13

227

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

228

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

Microsoft Academic Search

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

Jian-Qiang Liu

2011-01-01

229

Embryogenesis: anchors away!  

PubMed

It has long been appreciated that the oocyte cortex plays a key role in regulating fertilization and establishing embryonic polarity. Recent studies have identified the anti-phosphatase EGG-3 as a cortical anchor for regulatory proteins required for launching embryogenesis in Caenhorhabditis elegans. PMID:17956750

Govindan, J Amaranath; Greenstein, David

2007-10-23

230

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

PubMed

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

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

2012-10-01

231

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...

232

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 Mller-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

233

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 Mller-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

234

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

235

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

236

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

PubMed

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

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

2014-12-01

237

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

PubMed

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

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

2013-05-01

238

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

239

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

PubMed

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

Baranwal, Balram Prasad; Singh, Alok Kumar

2010-12-01

240

Metal Complexation with Different types of Soluble and Adsorbed Freshwater Ligands Followed by DPASV  

Microsoft Academic Search

In order to understand metal speciation in a polluted river (Este River, Northern Portugal) filtrate, freeze dried particles\\u000a and organics desorbed from surfaces were titrated with Cd(II) and Zn(II), followed by differential pulse anodic stripping\\u000a voltammetry (DPASV). The obtained results are compared with those previously published for Pb(II) and Cu(II). Due to the heterogeneity\\u000a of the system, a continuous and

Cidlia Maria Sousa Botelho; Rui Alfredo Rocha Boaventura; Maria de Lurdes Sadler Simes Gonalves

2007-01-01

241

Extended biotic ligand model for prediction of mixture toxicity of Cd and Pb using single metal toxicity data.  

PubMed

The combined toxic effects of Cd and Pb in the presence of different concentrations of Ca(2+) were predicted using the biotic ligand model (BLM), with the parameters derived from the Cd-only and Pb-only toxicity data. The BLM-based toxic unit (TU) approach and the proposed BLM-based f(mix) approach were used for prediction. The predicted mixture toxic effects using the BLM-based f(mix) approach were closer to the observed mixture effects (root mean square error [RMSE]?= 9.7 at 25 mM Ca(2+) ) than that using the BLM-based TU approach (RMSE?= 25.6 at 25 mM Ca(2+) ). This can be attributed to the fact that the BLM-based TU approach only considers the competition between Ca(2+) and Cd or Pb, whereas the BLM-based f(mix) approach considers both the competition between Cd and Pb and the competition between Ca(2+) and Cd or Pb for biotic ligand sites. In addition, the parameters derived from the Cd-only and Pb-only solutions in the presence of the background Ca(2+) concentration (0.025 mM) could be used to predict the mixture toxic effects at higher Ca(2+) concentrations. The BLM-based f(mix) approach proposed in the current study suggests a new way of predicting the Cd-Pb mixture toxicity from the single metal toxicity data by adopting the f(mix) values. PMID:21538486

Jho, Eun Hea; An, Jinsung; Nam, Kyoungphile

2011-07-01

242

Effects of tethered ligands and of metal oxidation state on the interactions of cobalt complexes with the 26S proteasome  

PubMed Central

In this paper we report on the synthesis and characterization of three cobalt complexes described as [CoII(L1)2] (1), [CoII(L2)] (2), and [CoIII(L1)2]ClO4 (3). These complexes contain the deprotonated forms of the [NN?O] tridentate ligand HL1 and its newly synthesized [N2N?2O2] hexadentate counterpart H2L2, namely, 2,4-diiodo-6-((pyridine-2-ylmethylamino)methyl)phenol and 6,6?-((ethane-1,2-diylbis((pyridin-2-ylmethyl) azanediyl))bis(methylene))bis(2,4-diiodophenol). Characterizations for 13 include electrospray ionization (ESI) spectrometry, infrared, and UVvisible spectroscopies, and elemental analyses. A detailed 1H-NMR study was conducted for 3 and X-ray structural data was obtained for 2. The viability of this series as potential agents for proteasome inhibition and cell apoptotic induction involving PC-3 cancer cells is presented comparing the behavior of the untethered [NN?O]2 six-coordinate 1 and 3 and the tethered counterpart 2 with a 1:1 metal-to-ligand ratio. It is observed that the tethering in 2 decreases inhibition activity. When 1 and 3 are compared, the most inert, but redox-active, cobalt(III) species shows the highest chymotrypsin-like activity inhibition on purified proteasome and PC-3 cancer cells. A hypothesis based on the role of oxidation states for proteasome inhibition is offered. PMID:22056177

Tomco, Dajena; Schmitt, Sara; Ksebati, Bashar; Heeg, Mary Jane; Dou, Q. Ping; Verani, Cludio N.

2013-01-01

243

A series of transition and non-transition metal complexes from a N?O? hexadentate Schiff base ligand: Synthesis, spectroscopic characterization and efficient antimicrobial activities.  

PubMed

Some transition and non-transition metal complexes of the hexadentate N?O? donor Schiff base ligand 1,8-N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine, abbreviated to H?fsatrien, have been synthesized. All the 14 metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic (UV-Vis, IR, NMR, ESR) data. The analytical data helped to elucidate the structures of the metal complexes. The Schiff base, H?fsatrien, is found to act as a dibasic hexadentate ligand using N?N?O? donor set of atoms (leaving the COOH group uncoordinated) leading to an octahedral geometry for the complexes around all the metal ions except VO(+) and UO?(+). However, surprisingly the same ligand functions as a neutral hexadentate and neutral tetradentate one towards UO?(+) and VO(+), respectively. In case of divalent metal complexes they have the general formula [M(H?fsatrien)] (where M stands for Cu, Co, Hg and Zn); for trivalent metal complexes it is [M(H?fsatrien)]XnH?O (where M stands for Cr, Mn, Fe, Co and X stands for CH?COO, Cl, NO?, ClO?) and for the complexes of VO(+) and UO?(+), [M(H?fsatrien)]Y (where M=VO and Y=SO?); M=UO? and Y=2 NO?). The Schiff base ligand and most of the complexes have been screened in vitro to judge their antibacterial (Escherichia coli and Staphylococcus aureus) and antifungal (Aspergillus niger and Pencillium chrysogenum) activities. PMID:20801711

Sarkar, Saikat; Dey, Kamalendu

2010-11-01

244

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

245

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

246

Anchoring groups for dye-sensitized solar cells.  

PubMed

The dyes in dye-sensitized solar cells (DSSCs) require one or more chemical substituents that can act as an anchor, enabling their adsorption onto a metal oxide substrate. This adsorption provides a means for electron injection, which is the process that initiates the electrical circuit in a DSSC. Understanding the structure of various DSSC anchors and the search for new anchors are critical factors for the development of improved DSSCs. Traditionally, carboxylic acid and cyanoacrylic acid groups are employed as dye anchors in DSSCs. In recent years, novel anchor groups have emerged, which make a larger pool of materials available for DSSC dyes, and their associated physical and chemical characteristics offer interesting effects at the interface between dye and metal oxide. This review focuses especially on the structural aspects of these novel dye anchors for TiO2-based DSSCs, including pyridine, phosphonic acid, tetracyanate, perylene dicarboxylic acid anhydride, 2-hydroxylbenzonitrile, 8-hydroxylquinoline, pyridine-N-oxide, hydroxylpyridium, catechol, hydroxamate, sulfonic acid, acetylacetanate, boronic acid, nitro, tetrazole, rhodanine, and salicylic acid substituents. We anticipate that further exploration and understanding of these new types of anchoring groups for TiO2 substrates will not only contribute to the development of advanced DSSCs, but also of quantum dot-sensitized solar cells, water splitting systems, and other self-assembled monolayer-based technologies. PMID:25594514

Zhang, Lei; Cole, Jacqueline M

2015-02-18

247

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

248

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

PubMed

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

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

2009-11-12

249

LIQUID-LIQUID EXTRACTION OF TRANSITION METAL CATIONS BY CALIXARENE-BASED CYCLIC LIGANDS  

Microsoft Academic Search

The selective liquid-liquid extraction of various alkali and transition metal cations from the aqueous phase to the organic phase was carried out by using p-tert-butylcalix[4]arene (L1), p-tert-butylcalix[6]arene (L2), tetra-ethyl p-tert-butylcalix[4]arene-tetra-acetate (L3), tetra-methyl-p-tert-butyl-calix[4]arene-tetra-ketone (L4), calix[n]arenes (n=4 and 6) bearing oxime groups on the lower rim (L5, L6 ) and a polymeric calix[4]arene. It was found that compounds L5 and L6, showed

Hasalettin Deligz; Mustafa Yilmaz

1995-01-01

250

Versatile tuning of supramolecular hydrogels through metal complexation of oxidation-resistant catechol-inspired ligands  

PubMed Central

The mussel byssal cuticle employs DOPA-Fe3+ complexation to provide strong, yet reversible crosslinking. Synthetic constructs employing this design motif based on catechol units are plagued by oxidation-driven degradation of the catechol units and the requirement for highly alkaline pH conditions leading to decreased performance and loss of supramolecular properties. Herein, a platform based on a 4-arm poly(ethylene glycol) hydrogel system is used to explore the utility of DOPA analogues such as the parent catechol and derivatives, 4-nitrocatechol (nCat) and 3-hydroxy-4-pyridinonone (HOPO), as structural crosslinking agents upon complexation with metal ions. HOPO moieties are found to hold particular promise, as robust gelation with Fe3+ occurs at physiological pH and is found to be largely resistant to oxidative degradation. Gelation is also shown to be triggered by other biorelevant metal ions such as Al3+, Ga3+ and Cu2+ which allows for tuning of the release and dissolution profiles with potential application as injectable delivery systems. PMID:24285981

Menyo, Matthew S.

2013-01-01

251

Anchoring of semiotic symbols  

Microsoft Academic Search

Abstract: This paper presents arguments for approaching the anchoring problem using semiotic symbols. Semiotic symbols are dened by a triadic relation between forms,meanings and referents, thus having an implicit relation to the real world. Anchorsare formed between these three elements rather than between `traditional'symbols and sensory images. This allows an optimization between the form (i.e.the `traditional' symbol) and the referent.

Paul Vogt

2003-01-01

252

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

PubMed

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

Hubscher-Bruder, Vronique; Haddaoui, Jaouad; Bouhroum, Saliha; Arnaud-Neu, Franoise

2010-02-15

253

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

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

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

256

N-aryl pyrrolo-tetrathiafulvalene based ligands: synthesis and metal coordination.  

PubMed

A straightforward general synthetic access to N-aryl-1,3-dithiolo[4,5-c]pyrrole-2-thione derivatives 6 from acetylenedicarbaldehyde monoacetal is depicted. In addition to their potentiality as precursors to dithioalkyl-pyrrole derivatives, thiones 6 are key building blocks to N-aryl monopyrrolo-tetrathiafulvalene (MPTTF) derivatives 10. X-ray structures of four of these thiones intermediates, reminiscent of the corresponding MPTTF derivatives, are provided. When the aryl group is a binding pyridyl unit, the MPTTF derivative 10a can coordinate M(II) salts (M = Pt, Pd). The first examples of metal-directed orthogonal MPTTF-based dimers 11-14, obtained through coordination of 10a to cis-blocked square planar Pt or Pd complexes are described. Studies on the parameters influencing the dimer construction are presented, as well as first recognition properties of the resulting electron-rich clip for C(60). PMID:20143799

Balandier, Jean-Yves; Chas, Marcos; Dron, Paul I; Goeb, Sbastien; Canevet, David; Belyasmine, Ahmed; Allain, Magali; Sall, Marc

2010-03-01

257

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

PubMed

A tritopic carboxylate ligand, tris(4'-carboxybiphenyl)amine (L-H(3)), has been synthesized and applied in the construction of microporous metal-organic frameworks (MOFs). Two novel metal-organic frameworks (MOFs), {[Zn(2)(L)(OH)]2DMFH(2)O}(?) (1) and {[Cu(L-H)(DMA)]DMA2H(2)O}(?) (2), have been constructed out of L-H(3), Zn(2+), and Cu(2+), respectively. 1 has a 2-fold interpenetrating three-dimensional framework formed by L connectors and the [Zn(2)(CO(2))(3)] secondary building units (SBUs). As for 1, it is worth pointing out that one ?(2)-OH group links two Zn atoms between two neighboring SBUs to produce interesting Zn-O-Zn zigzag chains in the structure. 2 has a two-dimensional grid sheet formed by L-H connectors and the typical paddle-wheel [Cu(2)(CO(2))(4)] SBUs. Two-dimensional (2D) sheets nest with each other, which finally forms a three-dimensional (3D) nested framework. Two MOFs are characterized by infrared (IR) spectroscopy, thermogravimetry, single-crystal and elemental analyses, and powder X-ray diffraction methods. Framework 1' exhibits high permanent porosity (Langmuir surface area = 848 m(2)/g), high thermal stability (up to 450 C), highly active properties for Friedel-Crafts alkylation reaction, as well as the potential application for the CO(2) gas storage and luminescent material. The catalytic results reveal that 2' is indeed an efficient heterogeneous catalyst for olefin epoxidation reactions. PMID:22670898

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

2012-06-18

258

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

PubMed

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

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

2013-01-01

259

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

SciTech Connect

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

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

1997-12-31

260

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

261

Novel chiral N4S2- and N6S3-donor macrocyclic ligands: synthesis, protonation constants, metal-ion binding and asymmetric catalysis in the Henry reaction.  

PubMed

New hydrophobic chiral macrocyclic ligands L1-L3 with chiral diamino and thiophene moieties have been synthesized by the Schiff base condensation approach. Protonation constants of L1 and L2 were determined by potentiometry titration. Metal-ion binding experiments exhibited that L1 and L3 are pronounced in selective recognition, Ag+, Cu2+ and Ca2+ ions among the surveyed metal ions (Cu2+, Co2+, Ni2+, Zn2+, Cd2+, Pb2+, Ag+, Li+, Na+, K+, and Ca2+). L1 was found to spectroscopically detect the presence of Cu2+ and Ca2+ to function as a multiple readout sensor. The detection limit for Ca2+ ions was found to be 9.8 x 10(-5) M in CH2Cl2-MeOH solution. The trimeric chiral ligand L3 has been shown to be an efficient auxiliary in a Zn(II)-mediated enantioselective Henry reaction. PMID:12948208

Gao, Jian; Martell, A E

2003-08-01

262

Performance of embedded anchor chains and consequences for anchor design  

SciTech Connect

With the growth in popularity of floating systems for offshore oil production, there has been an increased focus on the design of permanent mooring systems. It is widely acknowledged that the anchor chain plays an important part in the total mooring system by developing frictional load and introducing an inclination of the load at the subseabed anchorage. By making a simple and valid assumption, the force equilibrium equations of the chain are simplified to produce closed form expressions for both the force distribution and the geometric profile of the anchor chain. This paper then shows how these equations can be applied to simplify the design of anchor piles and drag anchors.

Neubecker, S.R.; Randolph, M.F. [Univ. of Western Australia, Nedlands (Australia)

1995-12-01

263

A highly stable 3D acentric zinc metal-organic framework based on two symmetrical flexible ligands: high second-harmonic-generation efficiency and tunable photoluminescence.  

PubMed

A 3D metal-organic framework (MOF), [Zn(BPHY)(SA)]n (1; BPHY = 1,2-bis(4-pyridyl)hydrazine, H2SA = succinic acid), which crystallizes in a noncentrosysmmetric space group (Cc), has been solvothermally obtained and testified to be a good nonlinear-optical material with the largest second-harmonic-generation response among the known MOFs based on sysmmetric ligands and high stability. Ultraviolet-to-visible tunable emission for 1 is observed. PMID:24731069

Guo, Jin-Shuang; Xu, Gang; Jiang, Xiao-Ming; Zhang, Ming-Jian; Liu, Bin-Wen; Guo, Guo-Cong

2014-05-01

264

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

265

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

266

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

267

Metal complexes of a new potentially heptadentate(N 7) tripodal Schiff base ligand. Synthesis, NMR studies and ab initio calculations  

Microsoft Academic Search

Tris(3-aminopropyl)amine, 2-pyridinecarboxaldehyde and a number of metal ions were used to prepare metal complexes of a new fully condensed potentially heptadentate(N7) tripodal Schiff base ligand (L333). The resulting complexes, [M(L333)](ClO4)2 {M= Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II); L333=[N(CH2CH2CH2NCH(C5H4N))3]}, were characterized by microanalysis, IR and electronic spectra in all cases and by NMR spectra in the case of Zn(II)

Sadegh Salehzadeh; Seyed Amrollah Javarsineh; Hassan Keypour

2006-01-01

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

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

Microsoft Academic Search

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

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

2004-01-01

270

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...

271

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

NASA Astrophysics Data System (ADS)

Five zinc(II) metal-organic frameworks, [Zn3(344-pytpy)2Cl6]nn(H2O) (1), [Zn(344-pytpy)(ox)]n (2), [Zn2(344-pytpy)(bdc)2]n1.5n(H2O) (3), [Zn2(344-pytpy)2 (sfdb)2]n1.5n(H2O) (4) and [Zn3(344-pytpy)2(btc)2]n2n(H2O) (5), (344-pytpy=4?-(3-pyridyl)-4,2?:6?,4?-terpyridine, H2ox=oxalic acid, H2bdc=1,4-benzenedi-carboxylic acid, H2sfdb=4,4?-sulfonyldibenzoic acid and H3btc=1,3,5-benzene-tricarboxylic acid) have been prepared by hydrothermal reactions. Compound 1 is a 1D chain structure, in which 344-pytpy ligand links three ZnII centers through three of terminal N-donors. Compound 2 is a 4-connected 3D framework with the dia topological net and the Schlfli symbol of 66. Compound 3 displays a unusual 3-fold interpenetrating 3D coordination network which exhibits a new intriguing (3,3,4)-connected topological net with the Schlfli symbol of (4.82)(4.85)(83). Compound 4 features a two-fold interpenetrating 4-connected 2D framework with the sql topological net and the Schlfli symbol of (44.62). Compound 5 is a new self-interpenetrating (3,3,4,4)-connected topological net with the Schlfli symbol of (6.82)2(62.82.10.12)(62.83.10)2(62.8)2. The luminescence properties of 1-5 have been investigated by emission spectra and they possess great thermal stabilities which can be stable up to around 400 C.

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

2014-08-01

272

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 6.1410(5)M(-1), 1.810(5)M(-1), 6.710(4)M(-1) and 2.510(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

273

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

PubMed

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

Arish, D; Nair, M Sivasankaran

2011-11-01

274

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

Microsoft Academic Search

Novel polymeric coordination complex [Ni(timpt)2](ClO4)21 was synthesized by solvothermal reaction of 2,4,6-tris[4-(imidazol-1-ylmethyl)phenyl]-1,3,5-triazine (timpt) ligand with Ni(ClO4)26H2O and characterized by X-ray crystallography. Each Ni(II) is coordinated by six imidazolyl N atoms from six different timpt ligands with an octahedral geometry and each timpt ligand connects three metal atoms to generate a three-dimensional (3D) metal-organic framework with self-penetration. The uncoordinated perchlorate anions

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

2004-01-01

275

Anchored phosphatases modulate glucose homeostasis  

E-print Network

/phosphatase anchoring protein AKAP150 impairs insulin secretion in mice. Loss of AKAP150 impacts L-type Ca2 þ currents, and attenuates cytoplasmic accumulation of Ca2 þ and cAMP in b-cells. Yet surprisingly AKAP150 null animals analyses of AKAP150 knock-in mice unable to anchor protein kinase A or protein phosphatase 2B uncover

Scott, John D.

276

Anchored phosphatases modulate glucose homeostasis  

E-print Network

/phospha- tase anchoring protein AKAP150 impairs insulin secretion in mice. Loss of AKAP150 impacts L-type Ca2 þ currents, and attenuates cytoplasmic accumulation of Ca2þ and cAMP in b-cells. Yet surprisingly AKAP150. More refined analyses of AKAP150 knock- in mice unable to anchor protein kinase A or protein phos

Scott, John D.

277

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

278

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

PubMed

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

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

2014-07-30

279

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

Microsoft Academic Search

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

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

2008-01-01

280

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

PubMed

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

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

2014-12-21

281

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

PubMed

2,6-diacetyl pyridine based ligand was synthesized by the reaction of 2,6-diacetyl pyridine with thiocarbohydrazide in presence of acetic acid. The coordination compounds with Cr(III) and Ni(II) metal ions having [Cr(L)X]X2 and [Ni(L)X]X compositions (where L=ligand and X=NO3-, Cl- and CH3COO-) were synthesized and characterized by physicochemical and spectral studies. The studies like elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, UV-Vis, NMR, mass and EPR reveal that the complexes are octahedral. The compounds were examined against the pathogenic fungal and bacterial strains like Alternaria brassicae, Aspergillus niger, Fusarium oxysporum, Xanthomonas compestris and Pseudomonas aeruginosa. A. niger causes the diseases Apergillosis and Otomycosis in humans. PMID:21094079

Sharma, Amit Kumar; Chandra, Sulekh

2011-01-01

282

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

283

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

PubMed Central

The murine cytomegalovirus-encoded protein m157 is a cognate ligand for both inhibitory and activating receptors expressed by natural killer cells. Additionally, m157 is expressed on the surface of infected cells by a glycophosphatidylinositol (GPI) anchor. Although endogenous GPI-anchored proteins are known to be ligands for the NK cell receptor, NKG2D, the contribution of the GPI anchor for viral m157 ligand function is unknown. To determine whether the GPI anchor for m157 is dispensable for m157 function, we generated m157 variants expressed as transmembrane fusion proteins and tested cells expressing transmembrane m157 for the capacity to activate cognate Ly49 receptors. We found that the GPI anchor is required for high-level cell surface expression of m157, and that the transmembrane m157 ligand retains the capacity to activate reporter cells and NK cells expressing Ly49H, as well as Ly49I129 reporter cells, but with reduced potency. Importantly, target cells expressing the transmembrane form of m157 were killed less efficiently and failed to mediate Ly49H receptor downregulation on fresh NK cells compared to targets expressing GPI-anchored m157. Taken together, these results show that the GPI anchor for m157 facilitates robust cell surface expression, and that NK cells are sensitive to the altered cell surface expression of this potent viral evasin. PMID:23840655

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

2013-01-01

284

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

285

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

286

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

SciTech Connect

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

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

2011-07-15

287

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

NASA Astrophysics Data System (ADS)

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

Chagas, Marcelo A.; Rocha, Willian R.

2014-09-01

288

Synthesis and characterization of group 5 metal complexes containing pyrazolate, amidate, and related ligands as potential precursors for thin film growth by Atomic Layer Deposition  

NASA Astrophysics Data System (ADS)

Atomic Layer Deposition (ALD) is an advanced variant of Chemical Vapor Deposition (CVD) and is used to deposit smooth and conformal thin films for applications in the microelectronics industry. ALD requires metal precursors that are sufficiently volatile and thermally stable at elevated temperatures. Several group 5 ALD and CVD precursors were reported in the literature, which have been used to deposit TaN, NbN, Nb2O5, and Ta 2O5 thin films. Synthesis of low and mid valent group 5 metal ALD precursors might give us access to deposit NbO2, Nb2O 3, Ta2O3, and TaO2 thin films by low temperature ALD pathways upon applying mild oxidation conditions. To this end, attempts were made to synthesize niobium(IV) and tantalum(IV) complexes from pyrazolate, amidate, and ?-iminoketone ligand systems. Pyrazolate compounds undergo reductive N-N bond cleavage on Nb(IV) and Ta(IV) metal centers and afford six membered metallacycles that are analogous to metallapyrimidines and metallapyrimidiniums. Two other pyrazolate ligands are found to be intact and the final oxidation state of the complexes were +5. Those metallacycles are nearly planer, conjugated, have 6 ?-electrons, and follow the Hckel formalism, hence formally aromatic. In order to estimate the aromaticity of those metallacycles against pyrazoles and pyrimidines, NICS calculations were performed. The metallacycles were found to be aromatic but only weakly aromatic than that of pyrimidines and pyrazoles. In order to synthesize metal complexes that are in the +4 oxidation state, a novel class of Ta(IV) and Nb(IV) amidate compounds with a variety of substituent groups were synthesized and structurally characterized. All the compounds are monomeric and isolated by sublimation at temperatures between 110-160 C/0.05 Torr. Several compounds were crystallized in solution and X-ray crystal structures were obtained to address the structural features. TGA/DTA traces, melting points, and decomposition temperatures were used for the thermal stability assessment and preparative sublimation experiments were carried out to estimate the volatility properties. We have identified several compounds that are sufficiently volatile and thermally stable, which can be used as precursors for ALD to deposit group 5 metal oxide thin films. Due to the fact that the limited availability of group 5 ALD precursors, we have synthesized niobium and tantalum compounds from ?-iminoketonate ligands. The six-coordinate niobium and tantalum ?-iminoketonate complexes were structurally characterized by X-ray crystallography and found that one of the ?-iminoketone ligands undergo hydrogen abstraction at the ?-carbon atom. Further evidence of hydrogen atom abstraction was obtained by 1H NMR experiments. In order to understand the reaction mechanism DFT calculations were performed on those compounds, several putative intermediates, and hypothetical gallium ?-iminoketone analogs. The bond lengths of the possible intermediates and the experimental bond distances were compared and identified a plausible intermediate for the reaction. The resulted complexes were found out to be in the +5 oxidation state and contain two fully reduced ?-iminoketone ligands and one iminoalkoxi ligand, which is a formal ?-radical monoanion.

Perera, Thuduwage Hiran

289

Cell Reports AKAP-Anchored PKA Maintains  

E-print Network

Cell Reports Article AKAP-Anchored PKA Maintains Neuronal L-type Calcium Channel Activity and NFAT to the channel by A-kinase anchoring protein 79/150 (AKAP79/150). AKAP79/150 anchoring of CaN also promotes LTCC report here that the basal activity of AKAP79/150-anchored PKA maintains neuronal LTCC coupling to Ca

Scott, John D.

290

Subliminal anchoring: Judgmental consequences and underlying mechanisms  

Microsoft Academic Search

Judgmental anchoringthe assimilation of a numeric estimate towards a previously considered standardis an exceptionally ubiquitous effect that influences human judgment in a variety of domains and paradigms. Three studies examined whether anchoring effects even occur, if anchor values are presented subliminally, outside of judges awareness. Studies 1 and 2 demonstrate such subliminal anchoring effects: judges assimilated target estimates towards the

Thomas Mussweiler; Birte Englich

2005-01-01

291

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

292

A 2D metal-organic framework with a flexible cyclohexane-1,2,5,6-tetracarboxylic acid ligand: Synthesis, characterization and photoluminescent property  

NASA Astrophysics Data System (ADS)

A novel metal-organic framework, [Zn 2(OH)(Hcht)(4,4'-bpy)] n4nH 2O ( 1) (H 4cht = cyclohexane-1,2,4,5-tetracarboxylic acid and 4,4'-bpy = 4,4'-bipyridine), was synthesized by the hydrothermal reaction of Zn(NO 3) 26H 2O, 4,4'-bipyridine, and cyclohexane-1,2,4,5-tetracarboxylic acid in the presence of sodium carbonate. The complex was obtained by controlling the ratio of the starting materials and a reaction temperature at 120 C and was characterized by IR, X-ray powder diffraction, thermogravimetric analysis, fluorescent spectrum, and single crystal X-ray diffraction. Single-crystal X-ray investigation reveals that the structure features a two-dimensional framework with novel coordination mode of Hcht ligand and all Hcht ligands exclusively convert to a sole conformation in the complex. IR spectrum reveals the characteristic absorption peaks of asymmetric stretching vibrations that result from the protonated and deprotonated carboxyl groups. Thermogravimetric analysis shows four clear courses of weight loss, which corresponds to the decomposition of different ligands. Fluorescent spectrum displays that complex 1 is a potential blue-luminescent material.

Wang, Rongming; Zhang, Jian; Li, Lijuan

2010-04-01

293

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

294

The first example of a zirconium-oxide based metal-organic framework constructed from monocarboxylate ligands.  

PubMed

This work reports the first example of a Zr-based MOF which is exclusively constructed from the monocarboxylate ligand formate. Despite the low surface area, the new material exhibits an unexpectedly favourable affinity for carbon dioxide over nitrogen at room temperature. PMID:25482606

Liang, Weibin; Babarao, Ravichandar; Murphy, Michael J; D'Alessandro, Deanna M

2014-12-23

295

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

296

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

297

5-MERCAPTOTETRAZOLE-1-ACETIC Acid as a Novel Capping Ligand for Stabilization of Metal Nanoparticles in Water  

NASA Astrophysics Data System (ADS)

The novel stabilizing ligand, 5-mercaptotetrazole-1-acetic acid, has been applied for synthesis of silver and palladium nanoparticles in aqueous media. The morphology of the synthesized particles and some properties were determined by TEM, FTIR and UV-visible spectroscopy, thermogravimetric analysis and quantum-chemical calculations.

Nichick, M. N.; Voitekhovich, S. V.; Matulis, V. E.; Komsa, D. N.; Lesnikovich, A. I.; Ivashkevich, O. A.

2013-05-01

298

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

299

Spectroscopic and electrochemical properties of organic framework of macrocylic OONNOO-donor ligand with its metal organic framework: Host/guest stability measurements  

NASA Astrophysics Data System (ADS)

In this study, we synthesized 1,2-di( o-aminophenoxy)ethane, as the starting material, used in the preparation of a novel hexadentate OONNOO-donor macrocyclic ligand-1,4,11,14-tetraoxo-7,8-diaza-5,6:9,10;15,16:19,20-terabezocyclododeca-8,17-iene. It has twenty membered organic framework (OF), which has been designed, synthesized and characterized. Our main findings of this paper are related to the organic framework of ligand, its capacity to digest the metal ions and the stability of metal organic framework (MOFs) with cobalt(II), nickel(II) and manganese(II). The authenticity of the used organic framework and its metal complexes have been detected and observed in solid state as well as in aqueous solutions. The main observations were made on the basis of physiochemical measurements viz.: elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, 1H NMR, 13C NMR, mass spectroscopy, electronic, ESR spectroscopy. In addition, the magnetic susceptibility and electrochemistry measurements have been made. The 1H NMR spectra suggest stereochemistry and proton movement interaction. Considering the used organic framework there are a lot of carbon atoms in the molecule reflected by the 13C NMR spectrum. All these observations gave a clear view to confirming the encapsulation; arrive at the composition, structure and geometry of encapsulated complexes. In simple words, it confirms the host/guest coordination and its stability. Electrochemical properties of the complexes have been investigated to confirm the various changes in oxidation state of metals with change in potentials with respect to current at different scan rate.

Kumar, Rajiv; Singh, R. P.; Singh, R. P.

2008-11-01

300

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 AuIAuIII atoms (3.383 ) may indicate a weak metal-metal interaction. Complexes 27 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 25, 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-Ramrez, Armando; Aguilera, Renato J.; Contel, Mara

2011-01-01

301

Phosphonate-anchored thin films on titanium and niobium oxide surfaces: Fabrication and characterization  

Microsoft Academic Search

Phosphonate-anchored thin films form on various metal oxide substrates. This paper compares structural details of these covalently anchored films on the oxidized surfaces of titanium, niobium and a Ti45Nb alloy. This is made possible by a sample configuration wherein the alkylphosphonates are coated onto a thin film of metal which is sputtered onto a double-side-polished silicon wafer and then oxidized.

Racheli Adadi; Gilad Zorn; Reuven Brener; Irena Gotman; Elazar Y. Gutmanas; Chaim N. Sukenik

2010-01-01

302

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.; Jimnez-Mier, J.; Denlinger, J.; Yang, W.-L.

2013-06-01

303

Ligand-enabled multiple absolute stereocontrol in metal-catalysed cycloaddition for construction of contiguous all-carbon quaternary stereocentres  

NASA Astrophysics Data System (ADS)

The development of a general catalytic method for the direct and stereoselective construction of contiguous all-carbon quaternary stereocentres remains a formidable challenge in chemical synthesis. Here, we report a highly enantio- and diastereoselective [3+2] annulation reaction of 5-vinyloxazolidinones and activated trisubstituted alkenes catalysed by a palladium complex bearing a newly devised phosphine ligand with a chiral ammonium salt component, which enables the single-step construction of three contiguous stereocentres, including vicinal all-carbon quaternary stereocentres, in a five-membered heterocyclic framework. This stereoselective cycloaddition protocol relies on the remarkable ability of the chiral ligand to rigorously control the absolute stereochemistry of each chiral centre associated with the multiple bond-forming events, and provides a reliable catalytic process for the asymmetric synthesis of densely functionalized pyrrolidines.

Ohmatsu, Kohsuke; Imagawa, Naomichi; Ooi, Takashi

2014-01-01

304

Ligand-enabled multiple absolute stereocontrol in metal-catalysed cycloaddition for construction of contiguous all-carbon quaternary stereocentres.  

PubMed

The development of a general catalytic method for the direct and stereoselective construction of contiguous all-carbon quaternary stereocentres remains a formidable challenge in chemical synthesis. Here, we report a highly enantio- and diastereoselective [3+2] annulation reaction of 5-vinyloxazolidinones and activated trisubstituted alkenes catalysed by a palladium complex bearing a newly devised phosphine ligand with a chiral ammonium salt component, which enables the single-step construction of three contiguous stereocentres, including vicinal all-carbon quaternary stereocentres, in a five-membered heterocyclic framework. This stereoselective cycloaddition protocol relies on the remarkable ability of the chiral ligand to rigorously control the absolute stereochemistry of each chiral centre associated with the multiple bond-forming events, and provides a reliable catalytic process for the asymmetric synthesis of densely functionalized pyrrolidines. PMID:24345946

Ohmatsu, Kohsuke; Imagawa, Naomichi; Ooi, Takashi

2014-01-01

305

Synthesis of phosphinoferrocene amides and thioamides from carbamoyl chlorides and the structural chemistry of Group 11 metal complexes with these mixed-donor ligands.  

PubMed

The reaction of in situ generated 1'-(diphenylphosphino)-1-lithioferrocene with carbamoyl chlorides, ClC(E)NMe2, affords the corresponding (thio)amides, Ph2PfcC(E)NMe2 (E = O (), S (); fc = ferrocene-1,1'-diyl). These compounds as well as their analogues, Ph2PfcC(O)NHMe () and Ph2PfcC(O)NH2 (), prepared from 1'-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) were studied as ligands for the Group 11 metal ions. In the reactions with [Cu(MeCN)4][BF4], the amides give rise to bis-chelate complexes of the type [Cu(L-?(2)O,P)2][BF4]. Similar products, [Ag(L-?(2)O,P)2]ClO4, are obtained from silver(i) perchlorate and , or . In contrast, the reaction of AgClO4 with produces a unique molecular dimer [Ag()(ClO4-?O)]2, where the metal centres are bridged by the sulfur atoms of the P,S-chelating thioamides. The reactions of with [AuCl(tht)] (tht = tetrahydrothiophene) afford the expected gold(i)-phosphine complexes, [AuCl(L-?P)], containing uncoordinated (thio)amide moieties. Hemilabile coordination of the phosphinoamide ligands in complexes with the soft Group 11 metal ions is established by the crystal structure of a solvento complex, [Cu(-?(2)O,P)(-?P)(CHCl3-?Cl)][BF4], which was isolated serendipitously during an attempted crystallisation of [Cu(-?(2)O,P)2][BF4]. All of the compounds are characterised by spectroscopic methods, and the structures of several representatives of both the free phosphinoamides and their complexes are determined by X-ray diffraction analysis and further studied by DFT calculations and cyclic voltammetry. PMID:25572958

Fernandes, Tiago A; Sola?ov, Hana; Csa?ov, Ivana; Uhlk, Filip; tcha, Martin; t?pni?ka, Petr

2015-02-01

306

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

307

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

308

Rare-earth metal bis(alkyl)s that bear a 2-pyridinemethanamine ligand: dual catalysis of the polymerizations of both isoprene and ethylene.  

PubMed

New pyridinemethanamido-ligated rare-earth metal bis(alkyl) complexes [C(5)H(4)N-CH(Me)-NC(6)H(3)((i)Pr)(2)]Ln(CH(2)SiMe(3))(2)(THF) (Ln = Sc (1), Y (2), Lu (3)) have been prepared at 0 C via a protonolysis reaction between rare-earth metal tris(alkyl)s and the corresponding 2-pyridinemethanamine ligand and fully characterized by NMR and X-ray diffraction analysis. Bis(alkyl) complexes 1-3 are analogous monomers of THF solvate, where the ligand bonds to the metal center in a ?N:?N-bidentate mode. Complexes 1-3, in combination with [Ph(3)C][B(C(6)F(5))(4)], showed a good activity towards isoprene polymerization to give polyisoprene with a main 3,4-selectivity (60%-66%); in particular the yttrium catalyst system, 2/[Ph(3)C][B(C(6)F(5))(4)], displayed a living mode. By contrast, only the precatalyst 2 exhibited activity for isoprene polymerization in the presence of [PhNMe(2)H][B(C(6)F(5))(4)]. The influence of alkylaluminium (AlR(3), R = Me, Et, (i)Bu) and the metal center on the polymerization of isoprene was also studied, and it was found that addition of AlMe(3) to the catalyst systems could lead to a dramatic change in the microstructure of the polymer from 3,4-specific to 1,4-selective (89%-95%), but the ionic radius of the central metal had little influence on the selectivity. In addition, by using the 1(Sc)/[Ph(3)C][B(C(6)F(5))(4)]/10 Al(i)Bu(3), the polymerization of ethylene was also achieved with moderate activity (up to 3.2 10(5) g (PE) mol(Sc)(-1) h(-1) bar(-1)) and narrow polydispersity (M(w)/M(n) = 1.19-1.28); while the effect of temperature on the activity was discussed. Such dual catalysis for the polymerizations of both isoprene and ethylene is rare. PMID:22214996

Jian, Zhongbao; Cui, Dongmei

2012-02-28

309

An investigation of chlorine ligands in transition-metal complexes via ?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, Rgis; Trbosc, Julien; Delevoye, Laurent; Popoff, Nicolas; Taoufik, Mostafa; Oudatchin, Konstantin; Schurko, Robert W

2014-09-15

310

Functionalization of robust Zr(iv)-based metal-organic framework films via a postsynthetic ligand exchange.  

PubMed

A facile and efficient fabrication approach for homogeneous, crack-free UiO-66 films with exceptionally high crystallinity and tunable thickness on a transparent and conductive glass substrate is reported. Two functionalized species, a catechol ligand and a Fe2 complex with structural resemblance to the active site of [FeFe] hydrogenase, were introduced into the MOF films via a postsynthetic exchange. Voltammetric studies show the [FeFe] complex in the thinner UiO-66 films (2-5 ?m) can be reduced electrochemically. PMID:25364799

Fei, Honghan; Pullen, Sonja; Wagner, Andreas; Ott, Sascha; Cohen, Seth M

2015-01-01

311

Zinc(II) and cadmium(II) metal-organic frameworks with 4-imidazole containing tripodal ligand: sorption and anion exchange properties.  

PubMed

The use of a 4-imidazole containing tripodal ligand 1,3,5-tri(1H-imidazol-4-yl)benzene (H3L) enabled isolation of two three-dimensional (3D) porous metal-organic frameworks (MOFs) [Zn(HL)] solvent (1) and [Cd(H3L)2](ClO4)2 10.5H2O (2) featuring 4,4- and 3,6-connected nets related to the structures of ecl and pyrite, respectively. Framework 1 has 3D channels based on Zn-Im(-) (Im(-) = imidazolate) moieties due to partial deprotonation of the 1H-imidazol-4-yl groups of H3L while porous framework 2 is constructed by the coordination of neutral H3L ligands with Cd(II). Desolvated solid 1' showed remarkable uptake for CO2, N2, H2, CH4 gases as well as the volatile organic vapor of MeOH, EtOH, i-PrOH and C6H6, significantly, exhibiting temperature dependent selective gas sorption for CO2 over N2. Grand Canonical Monte Carlo (GCMC) simulations were performed to elucidate the mechanism of the selective gas adsorption. Cage-like motifs are found in pyrite-net 2, in which ClO4(-) anions are hosted, and the results of IR, elemental analysis and PXRD measurements confirm that 2 has a reversible anion exchange property among perchlorate, nitrate and nitrite anions. PMID:24534873

Chen, Shui-Sheng; Wang, Peng; Takamizawa, Satoshi; Okamura, Taka-Aki; Chen, Min; Sun, Wei-Yin

2014-04-28

312

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

313

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

314

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

SciTech Connect

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

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

2009-10-15

315

How anchoring proteins shape pain.  

PubMed

Cellular responsiveness to external stimuli can be altered by extracellular mediators which activate membrane receptors, in turn signalling to the intracellular space via calcium, cyclic nucleotides, membrane lipids or enzyme activity. These signalling events trigger a cascade leading to an effector which can be a channel, an enzyme or a transcription factor. The effectiveness of these intracellular events is enhanced when they are maintained in close proximity by anchoring proteins, which assemble complexes of signalling molecules such as kinases together with their targets, and in this way enhance both the speed and the precision of intracellular signalling. The A kinase anchoring protein (AKAP) family are adaptor proteins originally named for their ability to associate Protein Kinase A and its targets, but several other enzymes bound by AKAPs have now been found and a wide variety of target structures has been described. This review provides an overview of anchoring proteins involved in pain signalling. The key anchoring proteins and their ion channel targets in primary sensory neurons responding to painful stimuli (nociceptors) are discussed. PMID:24727631

Fischer, Michael J M; McNaughton, Peter A

2014-09-01

316

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

NASA Astrophysics Data System (ADS)

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

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

2009-08-01

317

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

318

Identification of non-classical C-HM interactions in early and late transition metal complexes containing the CH(ArO)3 ligand.  

PubMed

The fully optimised DFT structure of the d(0) complex [{CH(ArO)3}Ti(NEt2)] (2) at the B3LYP level compares well with the distorted tetrahedral geometry shown by the X-ray crystal structure. QTAIM analysis of the electron density associated with the C-HTi interaction shows a well defined bond critical point, a bond path between the hydrogen and titanium centres and a negative value for the energy density indicative of covalency. A natural bond orbital (NBO) picture of the interaction shows that the C-H ? bond electron density donates to a d hybrid orbital on the metal in a linear fashion. Calculated IR and NMR data for the components of the interaction are consistent with experiment. The computed structures for [{CH(ArO)3}Ti(OPh)] (3), [{CH(ArO)3}Zr(NEt2)] (4), [{CH(ArO)3}Hf(NEt2)] (5), show tetrahedral geometries and QTAIM and NBO properties similar to (2). [{CH(ArO)3}Mo(NEt2)] (6) shows distortion of the tripodal ligand and a reduced C-HM bond angle with properties more consistent with a C-HM side-on donor interaction. In [{CH(ArO)3}Fe(NEt2)] (7) the C-HM bond angle is linear and involves a donor interaction. An energy minimised structure maintaining the three fold coordination to the tripodal ligand was not obtained for [{CH(ArO)3}Ni(NEt2)](2-) but changing from a diethyl amide ligand to phenolato gave energy minimised [{CH(ArO)3}Ni(OPh)](2-) (8). This structure shows a distorted square planar geometry with a substantially bent phenoxo ligand and a near linear C-HM covalent interaction with donor and back bonding properties. The work shows that linear C-HM interactions can have both agostic and weak hydrogen bond-like covalency. PMID:23788028

Lein, Matthias; Harrison, John A; Nielson, Alastair J

2013-08-14

319

Robust conductance of dumbbell molecular junctions with fullerene anchoring groups  

NASA Astrophysics Data System (ADS)

The conductance of a molecular wire connected to metallic electrodes is known to be sensitive to the atomic structure of the molecule-metal contact. This contact is to a large extent determined by the anchoring group linking the molecular wire to the metal. It has been found experimentally that a dumbbell construction with C60 molecules acting as anchors yields more well-defined conductances as compared to the widely used thiol anchoring groups. Here, we use density functional theory to investigate the electronic properties of this dumbbell construction. The conductance is found to be stable against variations in the detailed bonding geometry and in good agreement with the experimental value of G=3 10^{-4} G_0. Electron tunneling across the molecular bridge occurs via the lowest unoccupied orbitals of C60 which are pinned close to the Fermi energy due to partial charge transfer. Our findings support the original motivation to achieve conductance values more stable towards changes in the structure of the molecule-metal contact leading to larger reproducibility in experiments.

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

2011-10-01

320

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

321

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

322

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

323

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

324

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

PubMed

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

McGarvey, Bruce R; Telser, Joshua

2012-06-01

325

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 Mller-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

326

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

327

Independent control of polar and azimuthal anchoring.  

PubMed

Monte Carlo simulation, experiment, and continuum theory are used to examine the anchoring exhibited by a nematic liquid crystal at a patterned substrate comprising a periodic array of rectangles that, respectively, promote vertical and planar alignment. It is shown that the easy axis and effective anchoring energy promoted by such surfaces can be readily controlled by adjusting the design of the pattern. The calculations reveal rich behavior: for strong anchoring, as exhibited by the simulated system, for rectangle ratios ?2 the nematic aligns in the direction of the long edge of the rectangles, the azimuthal anchoring coefficient changing with pattern shape. In weak anchoring scenarios, however, including our experimental systems, preferential anchoring is degenerate between the two rectangle diagonals. Bistability between diagonally aligned and edge-aligned arrangement is predicted for intermediate combinations of anchoring coefficient and system length scale. PMID:23944468

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

2013-07-01

328

Comparative DNA binding abilities and phosphatase-like activities of mono-, di-, and trinuclear Ni(II) complexes: the influence of ligand denticity, metal-metal distance, and coordinating solvent/anion on kinetics studies.  

PubMed

Six novel Ni(II) complexes, namely, [Ni2(HL(1))(OAc)2] (1), [Ni3L(1)2]H2O2CH3CN (2), [Ni2(L(2))(L(3))(CH3CN)] (3), [Ni2(L(2))2(H2O)2] (4), [Ni2(L(2))2(DMF)2]22H2O (5), and [Ni(HL(2))2]H2O (6), were synthesized by reacting nitrophenol-based tripodal (H3L(1)) and dipodal (H2L(2)) Schiff base ligands with Ni(II) metal salts at ambient conditions. All the complexes were fully characterized with different spectroscopic techniques such as elemental analyses, IR, UV-vis spectroscopy, and electrospray ionization mass spectrometry. The solid-state structures of 2, 3, 5, and 6 were determined using single-crystal X-ray crystallography. The compounds 1, 3, 4, and 5 are dinuclear complexes where the two Ni(II) centers have octahedral geometry with bridging phenoxo groups. Compound 2 is a trinuclear complex with two different types of Ni(II) centers. In compound 3 one of the Ni(II) centers has a coordinated acetonitrile molecule, whereas in compound 4, a water molecule has occupied one coordination site of each Ni(II) center. In complex 5, the coordinated water of complex 4 was displaced by the dimethylformamide (DMF) during its crystallization. Complex 6 is mononuclear with two amine-bis(phenolate) ligands in scissorlike fashion around the Ni(II) metal center. The single crystals of 1 and 4 could not be obtained; however, from the spectroscopic data and physicochemical properties (electronic and redox properties) it was assumed that the structures of these complexes are quite similar to other analogues. DNA binding abilities and phosphatase-like activities of all characterized complexes were also investigated. The ligand denticity, coordinated anions/solvents (such as acetate, acetonitrile, water, and DMF), and cooperative action of two metal centers play a significant role in the phosphate ester bond cleavage of 2-hydroxypropyl-p-nitropenylphosphate by transesterification mechanism. Complex 3 exhibits highest activity among complexes 1-6 with 3.86 10(5) times greater rate enhancement than uncatalyzed reaction. PMID:25226493

Bhardwaj, Vimal K; Singh, Ajnesh

2014-10-01

329

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

330

Development of a membrane-anchored chemerin receptor agonist as a novel modulator of allergic airway inflammation and neuropathic pain.  

PubMed

The chemerin receptor (CMKLR1) is a G protein-coupled receptor found on select immune, epithelial, and dorsal root ganglion/spinal cord neuronal cells. CMKLR1 is primarily coupled to the inhibitory G protein, G?i, and has been shown to modulate the resolution of inflammation and neuropathic pain. CMKLR1 is activated by both lipid and peptide agonists, resolvin E1 and chemerin, respectively. Notably, these ligands have short half-lives. To expedite the development of long acting, stable chemerin analogs as candidate therapeutics, we used membrane-tethered ligand technology. Membrane-tethered ligands are recombinant proteins comprised of an extracellular peptide ligand, a linker sequence, and an anchoring transmembrane domain. Using this technology, we established that a 9-amino acid-tethered chemerin fragment (amino acids 149-157) activates both mouse and human CMKLR1 with efficacy exceeding that of the full-length peptide (amino acids 21-157). To enable in vivo delivery of a corresponding soluble membrane anchored ligand, we generated lipidated analogs of the 9-amino acid fragment. Pharmacological assessment revealed high potency and wash resistance (an index of membrane anchoring). When tested in vivo, a chemerin SMAL decreased allergic airway inflammation and attenuated neuropathic pain in mice. This compound provides a prototype membrane-anchored peptide for the treatment of inflammatory disease. A parallel approach may be applied to developing therapeutics targeting other peptide hormone G protein-coupled receptors. PMID:24659779

Doyle, Jamie R; Krishnaji, Subrahmanian T; Zhu, Guangli; Xu, Zhen-Zhong; Heller, Daniel; Ji, Ru-Rong; Levy, Bruce D; Kumar, Krishna; Kopin, Alan S

2014-05-01

331

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

332

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

333

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

SciTech Connect

Two isostructural 3D lanthanide arenedisulfonate metal-organic frameworks (MOFs) [Ln(Hbidc)(nds){sub 0.5}(H{sub 2}O)]{sub n}(Ln=Eu(1), La(2)) have been successfully synthesized by the hydrothermal reaction of lanthanide oxide with 2,6-naphthalenedisulfonate sodium (Na{sub 2}nds) and an auxiliary ligand, 1H-benzimidazole-5,6-dicarboxylic acid (H{sub 3}bidc). The two complexes are both constructed from 2D [Ln(Hbidc)]{sup +} double layers pillared by nds{sup 2?} ligands to generate 3D (3, 8)-connected open-framework structures with 1D long narrow channels running along the a axis. From topological point of view, the 3D framework is a (3, 8)-connected tfz-d net. The weak interactions including NH?O, OH?O hydrogen bonds and ?? stacking are observed in 1. The 2D IR correlation spectroscopy was applied to study the molecular interactions induced by thermal perturbation. The emission spectra of 1 exhibit the characteristic transition of {sup 5}D{sub 0}?{sup 7}F{sub J}(J=04) of Eu(III). - Graphical abstract: Two isostructural 3D (3,8)-connected lanthanide arenedisulfonates were hydrothermally synthesized. The 2D IR correlation spectroscopy was applied to study the molecular interactions induced by thermal perturbation. Display Omitted - Highlights: The first lanthanide arenedisulfonates incorporating fused-ring aromatic carboxylic acid. Three-dimensional (3,8)-connected framework with tfz-d network topology. The emission spectra of 1 exhibit the characteristic transition of {sup 5}D{sub 0}?{sup 7}F{sub J} (J=04) of Eu(III). The 2D IR correlation spectroscopy was applied to study the molecular interactions.

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

2013-10-15

334

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

SciTech Connect

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

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

2008-08-15

335

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

SciTech Connect

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

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

1987-11-01

336

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

PubMed

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

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

2014-11-01

337

CMPO-functionalized C{sub 3}-symmetric tripodal ligands in liquid/liquid extractions : efficient, selective recognition of Pu(IV) with low affinity for 3+ metal ions.  

SciTech Connect

Structural modifications of carbamoylmethylphosphine oxide (CPMO)-functionalized triphenoxymethane platforms are described, and the influence of these changes on the ability of the ligand to extract actinides from simulated acidic nuclear waste streams has been evaluated. The ligand system has been shown to have excellent binding efficiency and a selectivity for An(IV) in comparison to the a simple monomeric CMPO ligand under analogous conditions. Both the extraction efficiency and selectivity are strongly dependent on the flexibility and electronic properties of the ligating units in the triphenoxymethane construct. The Tb(III) and Bi(III) nitrate complexes of tris-CMPO derivatives have been isolated, and their structures were elucidated by NMR, ESI FT-ICR MS, and X-ray analysis, providing information on the interactions between metal ions and the tris-CMPO molecules.

Matloka, K.; Sah, A. K.; Peters, M. W.; Srinivasan, P.; Gelis, A. V.; Regalbuto, M.; Scott, M. J.; Univ. of Florida

2007-12-10

338

Induced chirality-at-metal and diastereoselectivity at ?/?-configured distorted square-planar copper complexes by enantiopure Schiff base ligands: combined circular dichroism, DFT and X-ray structural studies.  

PubMed

Bidentate enantiopure Schiff base ligands, (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminato-?(2)N,O, diastereoselectively yield ?/?-chiral four-coordinated, non-planar Cu(N^O)2 complexes [Ar = C6H5 R/S-L1, m-C6H4OMe R-L2, p-C6H4OMe R/S-L3, and p-C6H4Br R/S-L4]. Two N,O-chelate ligands coordinate to the copper(II) atom in distorted square-planar mode, and induce metal-centered ?/?-chirality at the copper atom in the C2-symmetric complexes. In the solid state, the R-L1 (or R-L4) ligand chirality diastereoselectively induces a ?-Cu configuration in ?-Cu-R-L1 (or ?-Cu-R-L4), the S-L1 ligand a ?-Cu configuration in ?-Cu-S-L1, forming enantiopure crystals upon crystallization. Conversely, the R-L2 ligand combines both ?/?-Cu-R-L2 as a diastereomeric pair in the crystals. In solution, electronic circular dichroism (CD) spectra show full or partial diastereoselectivity towards ?-Cu for R ligands and towards ?-Cu for S ligands. The electronic CD spectra measured on all complexes obtained from R ligands (or S ligands), e.g. Cu-R-L1, Cu-R-L2, Cu-R-L3, and Cu-R-L4 (or Cu-S-L1, Cu-S-L3, and Cu-S-L4), show consistent spectral features. TDDFT calculations of the electronic CD spectra for the diastereomers ?-Cu-R-L1 and ?-Cu-R-L1 suggest that the CD spectra are largely dominated by the configuration at the metal center (? vs. ?). The experimental CD spectrum of Cu-R-L1 agrees well with the one calculated for the ?-Cu-R-L1 configuration. Cyclic voltammetry of Cu-R-L1 reveals a quasi-reversible redox wave corresponding to one-electron transfer for the [Cu(II)L2](0)/[Cu(I)L2](-1) couple in acetonitrile. DSC analyses for the complexes show an exothermic peak between 377 and 478 K (?H = -12 to -43 kJ mol(-1)), corresponding to a phase transformation from distorted square-planar/tetrahedral to regular tetrahedral geometry on heating. PMID:24366532

Enamullah, Mohammed; Uddin, A K M Royhan; Pescitelli, Gennaro; Berardozzi, Roberto; Makhloufi, Gamall; Vasylyeva, Vera; Chamayou, Anne-Christine; Janiak, Christoph

2014-02-28

339

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

SciTech Connect

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

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

2008-07-07

340

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

SciTech Connect

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

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

2008-06-23

341

Bis{phenyl[di(methoxyethyloxy)phosphoryl]methyl}amine as a new ligand for metal ions and cationic organic molecules  

NASA Astrophysics Data System (ADS)

The bis(phenylphosphorylmethyl)amine containing binding units based on "crown-ether like" ester moiety was tested as a supramolecular host molecule. The complexation properties towards metal ions (Li +, Na +, K +, Rb +, Cs +, Mg 2+, Ca 2+, Ba 2+) and hydrochlorides of amino acids (Lys, Arg), diethylenetriamine (2EN3A) and pentaethylenehexaamine (5EN6A) were studied. In order to assess the binding affinities of the receptor to selected guest molecules in various solvents, the ESI-MS and NMR techniques were applied. The results were also supported by theoretical studies. The ESI-MS studies revealed the selective binding of Cs + and 5EN6 by the phosphonate molecule, whereas NMR investigation in solution indicated tighter association of the host-guest system obtained for Mg 2+ and Arg. The discrepancies between the results originating from both used methods are most likely caused by influence of the solvent on intermolecular interactions.

M?ynarz, Piotr; Ptak, Tomasz; Czernicka, Anna; Pankiewicz, Rados?aw; Gluza, Karolina; Zarzecza?ska, Dorota

2011-04-01

342

Synthesis and characterization of amine-functionalized mixed-ligand metal-organic frameworks of UiO-66 topology.  

PubMed

A series of amine-functionalized mixed-linker metal-organic frameworks (MOFs) of idealized structural formula Zr6O4(OH)4(BDC)(6-6X)(ABDC)6X (where BDC = benzene-1,4-dicarboxylic acid, ABDC = 2-aminobenzene-1,4-dicarboxylic acid) has been prepared by solvothermal synthesis. The materials have been characterized by thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and Fourier transform infrared (FTIR) spectroscopy with the aim of elucidating the effect that varying the degrees of amine functionalization has on the stability (thermal and chemical) and porosity of the framework. This work includes the first application of ultraviolet-visible light (UV-vis) spectroscopy in the quantification of ABDC in mixed-linker MOFs. PMID:25148242

Chavan, Sachin M; Shearer, Greig C; Svelle, Stian; Olsbye, Unni; Bonino, Francesca; Ethiraj, Jayashree; Lillerud, Karl Petter; Bordiga, Silvia

2014-09-15

343

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

344

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

PubMed

The solvothermal reactions of [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid (H4TPTA) with transition metal cations afforded five novel coordination polymers in the presence of three pyridine ligands (4,4'-bipy = 4,4'-bipyridine, 2,2'-bipy = 2,2'-bipyridine and phen = 1,10-phenanthroline), namely [M(TPTA)0.5(4,4'-bpy)0.5(H2O)2]n (M = Co for (1), Ni for (2)), {[Mn2(TPTA)(2,2'-bpy)H2O]1.5H2O}n (3), and [M(H2TPTA)(phen)]n (M = Mn for (4), Co for (5)). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Polymers 1 and 2 are isomorphous and exhibit 3D 4-fold interpenetrated networks with the point Schlfli symbol of (4(2)10(4)) (410(2)). Polymer 3 shows a 2D layer framework. Polymers 4 and 5 are also isomorphous and each displays a one-dimensional (1D) chain, which further forms a 2D supramolecular architecture via inter-chain ?? interactions. Moreover, variable-temperature magnetic susceptibilities of polymers 3-5 exhibit overall weak antiferromagnetic coupling between the adjacent M(II) ions. PMID:25189532

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

2014-11-01

345

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

PubMed

A series of metal(II) complexes of VO(II), Co(II), Ni(II), Cu(II) and Zn(II) have been synthesized from the azo Schiff base ligand 4-((E)-4-((E)-(4-chlorophenyl)diazenyl)-2-hydroxybenzylideneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (CDHBAP) and characterized by elemental analysis, spectral (IR, UV-Vis, (1)H NMR, ESR and EI-mass), magnetic moment measurements, molar conductance, DNA, SEM, X-ray crystallography and fluorescence studies. The electronic absorption spectra and magnetic susceptibility measurements of the complexes indicate square pyramidal geometry for VO(II) and octahedral geometry for all the other complexes. The important infrared (IR) spectral bands corresponding to the active groups in the ligand and the solid complexes under investigation were studied and implies that CDHBAP is coordinated to the metal ions in a neutral tridentate manner. The redox behavior of copper(II) and vanadyl(II) complexes have been studied by cyclic voltammetry. The nuclease activity of the above metal(II) complexes shows that the complexes cleave DNA. All the synthesized complexes can serve as potential photoactive materials as indicated from their characteristic fluorescence properties. The antibacterial and antifungal activities of the synthesized ligand and its metal complexes were screened against bacterial species (Staphylococcus aureus, Salmonella typhi, Escherichia coli, Bacillus subtilis, Shigella sonnie) and fungi (Candida albicans, Aspergillus niger, Rhizoctonia bataicola). Amikacin and Ketoconozole were used as references for antibacterial and antifungal studies. The activity data show that the metal complexes have a promising biological activity comparable with the parent Schiff base ligand against bacterial and fungal species. The second harmonic generation (SHG) efficiency of the ligand was measured and the NLO (non-linear optical) properties of the ligand are expected to result in the realization of advanced optical devices in optical fiber communication (OFC) and optical computing. The SEM image of the copper(II) complex implies that the size of the particles is 1 ?m. PMID:22728967

Anitha, C; Sheela, C D; Tharmaraj, P; Sumathi, S

2012-10-01

346

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

347

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

348

Bioabsorbable suture anchor migration to the acromioclavicular joint: how far can these implants go?  

PubMed

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

Medina, Giovanna; Garofo, Guilherme; D'Elia, Caio O; Bitar, Alexandre C; Castropil, Wagner; Schor, Breno

2014-01-01

349

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.

350

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)2H2O]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 (364653)-hxl topology. Moreover, compound 2 displays a novel 2-fold interpenetrated structure with the point symbol of (41263)-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

351

Synthesis and structural studies of metal complexes of the biological ligand 2-quinaldic acid: Utilization of the polymer pendant analog PS2QA for selective aluminum ion removal from aqueous solution  

Microsoft Academic Search

The synthetic reactions of quinaldic acid (2-QA, 1), a ligand with potential implications in Al{sup 3+} ion biological transport and in pharmaceutical applications and of use for the removal and recovery of Al{sup 3+} ions from environmental waste sites, were studied with tri- and divalent metal ions that encompass Al{sup 3+}, Fe{sup 3+}, Ga{sup 3+}, Zn{sup 2+}, Ni{sup 2+}, Mn{sup

Wei Li; Marilyn M. Olmstead; Dana Miggins; Richard H. Fish

1996-01-01

352

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 510(-7)M of free metal at 30C and pH 6. Nickel internalization fluxes (Jint) were measured in the presence of various concentrations of lead or copper from 510(-8)M to 510(-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 510(-7)M. However, a maximum value of Ni uptake was observed at 510(-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

353

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

354

Zero-phonon transitions and the Stokes shift of Mn2+-doped perovskites: Dependence on the metal-ligand distance  

NASA Astrophysics Data System (ADS)

This work reports the excitation and luminescence spectra at T=9 K of the Mn2+-doped RbCdF3, RbCaF3, and CsCaF3 fluoroperovskites. A Mn2+ concentration down to 400 ppm has been detected. The present data together with those available for KMgF3:Mn2+, KZnF3:Mn2+, KMnF3, and RbMnF3, allow us to explore the variations of the zero-phonon line (ZPL) and the Stokes shift [associated with the Mn2+ luminescent 4T1g(G)-->6A1g(S) transition] along the whole series of cubic fluoroperovskites doped with Mn2+ in order to investigate their dependence with the Mn-F distance, R. The experimental variation of the ZPL energy measured in the 206-215 pm range is EZPL=-21 305+187R (pm). This strong dependence of ZPL upon R allows one to measure Mn-F distances along the series of fluoroperovskites with accuracies of better than 0.001 , thus improving by more than one order of magnitude the extended x-ray-absorption fine structure resolution. Furthermore, this sensitivity is extended down to 10-4 when we analyze the variations ?R induced by pressure in a given system. As regards ?Es, the present results on Mn2+-doped fluoroperovskites demonstrate an increase of the Stokes shift when R increases. This behavior is explained to be related to a Grneisen constant ?(a1g) corresponding to the symmetric mode of the complex. The value of the constant is greater than 1.9, in agreement with calculations on divalent transition-metal complexes like MnF4-6 and VF4-6. The importance of the present results for the observation of luminescence through the full series of Mn2+-doped fluoroperovskites is also discussed.

Marco de Lucas, M. C.; Rodrguez, F.; Moreno, M.

1994-08-01

355

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

356

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.

Baghelani, Masoud; Ghavifekr, Habib Badri; Ebrahimi, Afshin

2013-01-01

357

Thermodynamics of the interaction of Pd(dmen)(H2O)22+ with bio-relevant ligands with reference to the deactivation of metal-based drug by thiol ligands  

NASA Astrophysics Data System (ADS)

Pd(dmen)Cl2 complex was synthesized and characterized, where dmen = N,N-dimethylethylenediamine. Stoichiometry and stability constants of the complexes formed between [Pd(dmen)(H2O)2]2+ and various biologically relevant ligands such as amino acids, peptides and dicarboxylic acids are investigated at 25 C and at constant 0.1 M ionic strength. The concentration distribution diagrams of the various species formed are evaluated. The equilibrium constants for the displacement of coordinated ligands as inosine, glycine or methionine by cysteine are calculated. The results are expected to contribute to the chemistry of tumour therapy.

Shehata, Mohamed R.; Shoukry, Mohamed M.; Ali, Sara

2012-06-01

358

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))]66H2O (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, Lusa M D R S; Pettinari, Claudio; Pombeiro, Armando J L

2014-09-15

359

OMNI-Maxtrade anchor development and technology  

Microsoft Academic Search

As a result of Mobile Offshore Drilling Unit (MODU) temporary mooring failures during mainly hurricanes Ivan in 2004 and Katrina and Rita in 2005, the need for new and improved anchor technology is ever so present. Currently, self-deployed high holding capacity (HHC) drag embedment anchors are widely used for catenary mooring systems. The majority of these mooring systems that failed

J. T. Shelton

2007-01-01

360

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

361

Anchor Text Extraction for Academic Search  

Microsoft Academic Search

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

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

2009-01-01

362

DSSC anchoring groups: a surface dependent decision.  

PubMed

Electrodes in dye sensitised solar cells are typically nanocrystalline anatase TiO2 with a majority (1?0?1) surface exposed. Generally the sensitising dye employs a carboxylic anchoring moiety through which it adheres to the TiO? surface. Recent interest in exploiting the properties of differing TiO? electrode morphologies, such as rutile nanorods exposing the (1?1?0) surface and anatase electrodes with high percentages of the (0?0?1) surface exposed, begs the question of whether this anchoring strategy is best, irrespective of the majority surface exposed. Here we address this question by presenting density functional theory calculations contrasting the binding properties of two promising anchoring groups, phosphonic acid and boronic acid, to that of carboxylic acid. Anchor-electrode interactions are studied for the prototypical anatase (1?0?1) surface, along with the anatase (0?0?1) and rutile (1?1?0) surfaces. Finally the effect of using these alternative anchoring groups to bind a typical coumarin dye (NKX-2311) to these TiO? substrates is examined. Significant differences in the binding properties are found depending on both the anchor and surface, illustrating that the choice of anchor is necessarily dependent upon the surface exposed in the electrode. In particular the boronic acid is found to show the potential to be an excellent anchor choice for electrodes exposing the anatase (0?0?1) surface. PMID:24762339

O'Rourke, C; Bowler, D R

2014-05-14

363

Anchoring of proteins to lactic acid bacteria  

Microsoft Academic Search

The anchoring of proteins to the cell surface of lactic acid bacteria (LAB) using genetic techniques is an exciting and emerging research area that holds great promise for a wide variety of biotechnological applications. This paper reviews five different types of anchoring domains that have been explored for their efficiency in attaching hybrid proteins to the cell membrane or cell

Kees Leenhouts; Girbe Buist; Jan Kok

1999-01-01

364

Guyline anchor design keys rig stability  

SciTech Connect

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

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

1983-09-01

365

Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds.  

PubMed

The photophysical properties of singlet and triplet metal-to-ligand charge transfer (MLCT) states of [Cu(I)(diimine)(2)](+), where diimine is 2,9-dimethyl-1,10-phenanthroline (dmphen), 2,9-dibutyl-1,10-phenanthroline (dbphen), or 6,6'-dimethyl-2,2'-bipyridine (dmbpy), were studied. On 400 nm laser excitation of [Cu(dmphen)(2)](+) in CH(2)Cl(2) solution, prompt (1)MLCT fluorescence with a quantum yield of (2.8 +/- 0.8) x 10(-5) was observed using a picosecond time-correlated single photon counting technique. The quantum yield was dependent on the excitation wavelength, suggesting that relaxation of the Franck-Condon state to the lowest (1)MLCT competes with rapid intersystem crossing (ISC). The fluorescence lifetime of the copper(I) compound was 13-16 ps, unexpectedly long despite a large spin-orbit coupling constant of 3d electrons in copper (829 cm(-1) ). Quantum chemical calculations using a density functional theory revealed that the structure of the lowest (1)MLCT in [Cu(dmphen)(2)](+) (1(1)B(1)) was flattened due to the Jahn-Teller effect in 3d(9) electronic configuration, and the dihedral angle between the two phenanthroline planes (dha) was about 75 degrees with the dha around 90 degrees in the ground state. Intramolecular reorganization energy for the radiative transition of 1(1)B(1) was calculated as 2.1 x 10(3) cm(-1), which is responsible for the large Stokes shift of the fluorescence observed (5.4 x 10(3) cm(-1)). To understand the sluggishness of the intersystem crossing (ISC) of (1)MLCT of the copper(I) compounds, the strength of the spin-orbit interaction between the lowest (1)MLCT (1(1)B(1)) and all (3)MLCT states was calculated. The ISC channels induced by strong spin-orbit interactions (ca. 300 cm(-1)) between the metal-centered HOMO and HOMO - 1 were shown to be energetically unfavorable in the copper(I) compounds because the flattening distortion caused large splitting (6.9 x 10(3) cm(-1)) between these orbitals. The possible ISC is therefore induced by weak spin-orbit interactions (ca. 30 cm(-1)) between ligand-centered molecular orbitals. Further quantum mechanical study on the spin-orbit interaction between the lowest (3)MLCT (1(3)A) and all (1)MLCT states indicated that the phosphorescence borrows intensity from 2(1)B(1). The radiative rate of the phosphorescence was also structure-sensitive. The flattening distortion reduced the transition dipole moment of 2(1)B(1) --> the ground state, and decreased the extent of mixing between 1(3)A and 2(1)B(1), thereby considerably reducing the phosphorescence radiative rate at the MLCT geometry compared to that at the ground state geometry. The theoretical calculation satisfactorily reproduced the radiative rate of ca. 10(3) s(-1) and accounted for the structure-sensitive phosphorescence intensities of copper(I) bis(diimine) compounds recently demonstrated by Felder et al. (Felder, D.; Nierengarten, J. F.; Barigelletti, F.; Ventura, B.; Armaroli, N. J. Am. Chem. Soc. 2001, 123, 6291). PMID:14514312

Siddique, Zainul Abedin; Yamamoto, Yuichi; Ohno, Takeshi; Nozaki, Koichi

2003-10-01

366

[Bone anchored hearing aids (BAHA)].  

PubMed

Bone anchored hearing aids (BAHA) achieve optimal acoustic coupling by means of direct bone conduction via an osseointegrated percutaneous titanium implant. Currently this system has a record of over 30 years of clinical application and reliability. Patients with bilateral hearing loss with air-bone gaps will benefit from bilateral BAHA fitting. Likewise, unilateral conductive hearing loss with normal hearing on the other side can be treated with a BAHA. New developments in this field include the BAHA Intenso and also novel implant systems, such as the Epiplating system by Medicon, the alpha system by Otomag and the OBC system by Otorix. Due to the advantages of the BAHA system (possibility of preoperative testing, simple surgery without the risk of inner ear damage, MRI compatibility, etc.), the BAHA will keep its important role in hearing rehabilitation even in the era of other partially and totally implantable hearing devices. PMID:19343390

Federspil, P A

2009-03-01

367

The adsorption and simulated separation of light hydrocarbons in isoreticular metal-organic frameworks based on dendritic ligands with different aliphatic side chains.  

PubMed

Three isoreticular metal-organic frameworks, JUC-100, JUC-103 and JUC-106, were synthesized by connecting six-node dendritic ligands to a [Zn4O(CO2)6] cluster. JUC-103 and JUC-106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC-100. The uptake measurements of the three MOFs for CH4, C2H4, C2H6 and C3H8 were carried out. At 298?K, 1?atm, JUC-103 has relatively high CH4 uptake, but JUC-100 is the best at 273?K, 1?atm. JUC-100 and JUC-103 have similar C2H4 absorption ability. In addition, JUC-100 has the best absorption capacity for C2H6 and C3H8. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C3H8/CH4 and C2H6/CH4 selectivities for an equimolar quaternary CH4/C2H4/C2H6/C3H8 gas mixture maintained at isothermal conditions at 298?K, and JUC-106 has the best C2H6/CH4 selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH4/C2 H4/C2H6/C3H8 mixture into three different fractions of C1, C2 and C3 hydrocarbons. PMID:24919582

Jia, Jiangtao; Wang, Lei; Sun, Fuxing; Jing, Xiaofei; Bian, Zheng; Gao, Lianxun; Krishna, Rajamani; Zhu, Guangshan

2014-07-14

368

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

369

Probing pore constriction in a ligand-gated ion channel by trapping a metal ion in the pore upon agonist dissociation.  

PubMed

Eukaryotic pentameric ligand-gated ion channels (pLGICs) are receptors activated by neurotransmitters to rapidly transport ions across cell membranes, down their electrochemical gradients. Recent crystal structures of two prokaryotic pLGICs were interpreted to imply that the extracellular side of the transmembrane pore constricts to close the channel (Hilf, R. J., and Dutzler, R. (2009) Nature 457, 115-118; Bocquet, N., Nury, H., Baaden, M., Le Poupon, C., Changeux, J. P., Delarue, M., and Corringer, P. J. (2009) Nature 457, 111-114). Here, we utilized a eukaryotic acetylcholine (ACh)-serotonin chimeric pLGIC that was engineered with histidines to coordinate a metal ion within the channel pore, at its cytoplasmic side. In a previous study, the access of Zn(2+) ions to the engineered histidines had been explored when the channel was either at rest (closed) or active (open) (Paas, Y., Gibor, G., Grailhe, R., Savatier-Duclert, N., Dufresne, V., Sunesen, M., de Carvalho, L. P., Changeux, J. P., and Attali, B. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 15877-15882). In this study, the interactions of Zn(2+) with the pore were probed upon agonist (ACh) dissociation that triggers the transition of the receptor from the active conformation to the resting conformation (i.e. during deactivation). Application of Zn(2+) onto ACh-bound open receptors obstructed their pore and prevented ionic flow. Removing ACh from its extracellular binding sites to trigger deactivation while Zn(2+) is still bound led to tight trapping of Zn(2+) within the pore. Together with single-channel recordings, made to explore single pore-blocking events, we show that dissociation of ACh causes the gate to shut on a Zn(2+) ion that effectively acts as a "foot in the door." We infer that, upon deactivation, the cytoplasmic side of the pore of the ACh-serotonin receptor chimera constricts to close the channel. PMID:20466725

Pittel, Ilya; Witt-Kehati, Dvora; Degani-Katzav, Nurit; Paas, Yoav

2010-08-20

370

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) and 10.522(1) , 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, Joaqun; Alonso, Javier; Barandiaran, Jose Manuel; Janiak, Christoph

2014-08-21

371

EphB receptors and ephrinB ligands: regulators of vascular assembly and homeostasis  

Microsoft Academic Search

Eph receptors comprise the largest family of receptor tyrosine kinases consisting of eight EphA receptors (with five corresponding glycosyl-phosphatidyl-inositol-anchored ephrinA ligands) and six EphB receptors (with three corresponding transmembrane ephrinB ligands). Originally identified as neuronal pathfinding molecules, genetic loss of function experiments have identified EphB receptors and ephrinB ligands as crucial regulators of vascular assembly, orchestrating arteriovenous differentiation and boundary

Hellmut G. Augustin; Yvonne Reiss

2003-01-01

372

Coordinatively Unsaturated Derivatives of Group 6 Metal Carbonyls Containing the pi-Donating Ligand 3,5-Di-tert-butylcatecholate.  

PubMed

The series of group 6 metal tricarbonyl derivatives of di-tert-butylcatecholate have been synthesized from the reactions of M(CO)(5)THF (M = Cr, Mo, W) with 2 equiv of [Et(4)N][3,5-(t)Bu(2)OC(6)H(2)OH]. Subsequent removal of the free catechol was achieved by the addition of NaOMe. The complexes were shown by X-ray crystallography to exhibit coordinatively unsaturated M degrees centers. These metal dianions which have formally 16e(-) configurations are stabilized by pi-donation from the oxygen atoms of the catecholate ligand. This is evident from the short M-O bond distances, e.g., for M = W, 2.059(6) vs 2.151(4) for a single bond. The structures of these five-coordinate dianions can be loosely defined as trigonal bipyramidal with the more electron-rich oxygen donor of the catecholate (ortho to the electron-releasing tert-butyl substituent) occupying an equatorial site as indicated by a shorter M-O bond length. The tungsten derivative was shown to reversibly react with CO or phosphines to afford the 18e(-), saturated complexes. Although the molybdenum tricarbonyl derivative reacts with CO to partially provide the tetracarbonyl complex, the analogous process involving chromium did not occur. That is, the formation of an O-->M pi bond vs an additional M-CO bond is favored for M = chromium. Complex 2, [Et(4)N](2)[W(CO)(4)DTBCat], crystallizes in the monoclinic space group P2(1)/c with a = 10.013(5) , b = 43.921(14) , c = 9.113(4) , beta = 115.76(3) degrees, V = 3609(3) (3), and d(calc) = 1.429 g/cm(3), for Z = 4. Complex 4, [Et(4)N](2)[Mo(CO)(3)DTBCat], crystallized in the monoclinic space group C2 with a = 18.255(7) , b = 8.596(3) , c = 22.369(7) , beta = 91.05(6) degrees, V = 3510(2) (3), and d(calc) = 1.251 g/cm(3), for Z = 4. Similarly, complex 5, [Et(4)N](2)[Cr(CO)(3)DTBCat], crystallized in the monoclinic space group C2 with a = 18.09(2) , b = 8.553(3) , c = 21.927(11) , beta = 91.09(8) degrees, V = 3393(4) (3), and d(calc) = 1.208 g/cm(3), for Z = 4. PMID:11666368

Darensbourg, Donald J.; Klausmeyer, Kevin K.; Reibenspies, Joseph H.

1996-03-13

373

Photo- and electrocatalytic H2 production by new first-row transition-metal complexes based on an aminopyridine pentadentate ligand.  

PubMed

The synthesis and characterisation of the pentadentate ligand 1,4-di(picolyl)-7-(p-toluenesulfonyl)-1,4,7-triazacyclononane (Py2(Ts)tacn) and their metal complexes of general formula [M(CF3SO3)(Py2(Ts)tacn)][CF3SO3], (M = Fe (1Fe), Co (1Co) and Ni (1Ni)) are reported. Complex 1Co presents excellent H2 photoproduction catalytic activity when using [Ir(ppy)2(bpy)]PF6 (PSIr) as photosensitiser (PS) and Et3N as electron donor, but 1Ni and 1Fe result in a low activity and a complete lack of it, respectively. On the other hand, all three complexes have excellent electrocatalytic proton reduction activity in acetonitrile, when using trifluoroacetic acid (TFA) as a proton source with moderate overpotentials for 1Co (0.59?V vs. SCE) and 1Ni (0.56?V vs. SCE) and higher for 1Fe (0.87?V vs. SCE). Under conditions of CH3CN/H2O/Et3N (3:7:0.2), 1Co (5??M), with PSIr (100??M) and irradiating at 447?nm gives a turnover number (TON) of 690 (n?H2/n1Co) and initial turnover frequency (TOF) (TONt(-1)) of 703?h(-1) for H2 production. It should be noted that 1Co retains 25?% of the catalytic activity for photoproduction of H2 in the presence of O2. The inexistence of a lag time for H2 evolution and the absence of nanoparticles during the first 30?min of the reaction suggest that the main catalytic activity observed is derived from a molecular system. Kinetic studies show that the reaction is -0.7 order in catalyst, and time-dependent diffraction light scattering (DLS) experiments indicate formation of metal aggregates and then nanoparticles, leading to catalyst deactivation. By a combination of experimental and computational studies we found that the lack of activity in photochemical water reduction by 1Fe can be attributed to the 1Fe (II/I) redox couple, which is significantly lower than the PSIr (III/II) , while for 1Ni the pKa value (-0.4) is too small in comparison with the pH (11.9) imposed by the use of Et3N as electron donor. PMID:24692261

Call, Arnau; Codol, Zoel; Acua-Pars, Ferran; Lloret-Fillol, Julio

2014-05-12

374

Incorporating single molecules into electrical circuits. The role of the chemical anchoring group.  

PubMed

Constructing electronic circuits containing singly wired molecules is at the frontier of electrical device miniaturisation. When a molecule is wired between a pair of electrodes, the two points of contact are determined by the chemical anchoring groups, located at the ends of the molecule. At this point, when a bias is applied, electrons are channelled from a metallic environment through an extremely narrow constriction, essentially a single atom, into the molecule. The fact that this is such an abrupt change in the electron pathway makes the nature of the chemical anchoring groups critically important regarding the propagation of electrons from the electrode across the molecule. A delicate interplay of phenomena can occur when a molecule binds to the electrodes, which can produce profound differences in conductance properties depending on the anchoring group. This makes answering the question "what is the best anchoring group for single molecule studies" far from straight forward. In this review, we firstly take a look at techniques developed to 'wire-up' single molecules, as understanding their limitations is key when assessing a molecular wire's performance. We then analyse the various chemical anchoring groups, and discuss their merits and disadvantages. Finally we discuss some theoretical concepts of molecular junctions to understand how transport is affected by the nature of the chemical anchor group. PMID:25522058

Leary, Edmund; La Rosa, Andrea; Gonzlez, M Teresa; Rubio-Bollinger, Gabino; Agrat, Nicols; Martn, Nazario

2015-02-10

375

A comparison of soft-tissue anchors in tendo achilles reattachment.  

PubMed

This prospective study evaluated four soft-tissue fixation modalities, used in seven different combinations, to reattach the tendo Achilles in 34 cadaveric specimens. Ultimate loads, elastic moduli, and modes of failure were evaluated by loading the specimen in a cantilevered fashion on an Instron. Mann-Whitney U tests were performed to compare the failure load data for statistical significance. Although the use of two Mitek SuperAnchors showed better load resistance than one anchor (p < .01), there was no significant improvement between using two or three anchors (one anchor 116 +/- 24 N, two anchors 234 +/- 21 N, three anchors 277 +/- 80 N). Two Bionx Bankart Tacks demonstrated no significant difference over using a single tack (one tack 178 +/- 57 N, two tacks 214 +/- 86 N). No statistical difference was observed between the screw and washer systems (screw with polyacetal resin washer 307 +/- 80 N, screw with metal washer 290 +/- 81 N). Both screw and washer systems did show greater stability when compared with a single Mitek SuperAnchor (p < .01) or a single Bionx Bankart Tack (p < .05). Similar analyses using the Mann-Whitney U tests were performed on the elastic modulus data. Analysis of the displacement data among all groups showed no statistical difference. Observations of the mode of failure exhibited 86% of Mitek SuperAnchor failed secondary to suture, and 70% of the Bionx Bankart Tack and 90% of the screw and washer systems failed because of the tendon shearing around the fixation. The comparisons of cost-effectiveness among the fixations showed the Synthes screw and polyacetal resin spiked washer to have the lowest cost to load ratio ($0.15/N). PMID:11924680

Janis, L; Lam, A T; Espiritu, T; Ploot, E; Husain, Z S

2001-01-01

376

The first tritopic bridging ligand 1,3,5-tris(4-carboxyphenyl)-benzene (H3BTB) functionalized porous polyoxometalate-based metal-organic framework (POMOF): from design, synthesis to electrocatalytic properties.  

PubMed

Replacing the metal ions (or metal clusters) in routine MOFs with size-matched polyoxoanions to construct POM-based MOF materials (POMOF) combining well-defined crystalline structures, high surface area, regular and tunable cavities is the great challenge in the current POM chemistry area. In this work, we report a 2-fold interpenetrated porous POMOF, [TBA]6[H3PMo12O40]2[Zn8(BTB)2](?35H2O), which exhibits effective catalytic activity towards bromate reduction, using the methodology of extension for the reduced transition-metal-grafted ?-Keggin polyoxoanions with an expanded tripodal bridging ligand of H3BTB. The simultaneous TGA/DSC-MS technique was applied in this work to identify the evolved gases and was proved to be an effective method for analysing the decomposition process. PMID:25428699

Dong, Bao-Xia; Chen, Lu; Zhang, Shi-Yang; Ge, Jun; Song, Liang; Tian, Hui; Teng, Yun-Lei; Liu, Wen-Long

2015-01-21

377

Synthesis of two new tripodal ligands and their cyclocondensation with 2-[2-(2-formylphenoxy)ethoxy]benzaldehyde in the presence of manganese(II) and cadmium(II) metal ions  

Microsoft Academic Search

Two new asymmetric tripodal tetraamine ligands, 2-((bis(2-aminoethyl)amino)methyl)benzenamine (L2) and 2-(((2-aminoethyl)(3-aminopropyl)amino)methyl)benzenamine (L3) were synthesized and characterized. [1+1] Macrocyclic Schiff-base complexes containing 1,2-diphenoxyethane head units and a 2-aminobenzyl pendant arm, were synthesized as [MnL4(MeOH)](ClO4)2 (1), [MnL5(MeOH)](ClO4)2 (2), [CdL4(H2O)](NO3)2 (3) and [CdL5(H2O)](NO3)2 (4) from the metal ion templated cyclocondensation reactions of 2-[2-(2-formylphenoxy)ethoxy]benzaldehyde with the (L2) or (L3) tripodal tetraamine ligands. The crystal structure

Hassan Keypour; Reza Azadbakht; Sadegh Salehzadeh; Hamid Khanmohammadi; Hamidreza Khavasi; Harry Adams

2008-01-01

378

Syntheses, structures, and properties of two new zinc(II) metal-organic frameworks based on flexible 1,6-bis(2-methyl-imidazole-1-yl)hexane ligand  

NASA Astrophysics Data System (ADS)

Two new zinc(II) metal-organic compounds of [Zn(ADC)(bimh)]n (1) and [Zn(ADA)(bimh)]n (2) (H2ADC = 1,3-adamantanedicarboxylic acid, H2ADA = 1,3-adamantanediacetic acid, bimh = 1,6-bis(2-methyl-imidazole-1-yl)-hexane, have been structurally characterized by X-ray diffraction analysis. In compound 1, the zinc(II) ions are bridged by ADC and bimh ligands to form a 1D looped chain. In compound 2, the ADA molecules alternately bridge Zn(II) atoms to form infinite chains, and then the 1D chain is connected through the bimh ligand resulting in an undulating infinite two-dimensional (2D) polymeric network. Additionally, TG analysis, XRPD and fluorescent properties for compounds 1 and 2 are also measured and discussed.

Jin, Jun-Cheng; Fu, Ai-Yun; Li, Dian; Chang, Wen-Gui; Wu, Ju; Yang, Mei; Xie, Cheng-Gen; Xu, Guang-Nian; Cai, An-Xing; Wu, Ai-Hua

2014-11-01

379

Synthesis, thermolysis and pyrolysis of group IV metal pinacolates: The impact of a vicinal diol as a supporting ligand for molecular precursors  

NASA Astrophysics Data System (ADS)

In an effort to investigate the suitability of an alternative ligand class for molecular precursors, the following studies were carried out: (1) New zirconium species were obtained by reaction of zirconium isopropoxide alcoholate, Zr2(OiPr)8(HOiPr) 2, with pinacol (HOCMe2CMe2OH). Control of reaction stoichiometries followed by azeotropic distillation of evolved isopropanol led to the successful preparation of a range of homo- and heteroleptic trinuclear species, Zr3(OCMe2CMe2O)2(O iPr)8(HOiPr)2, Zr3(OCMe 2CMe2O)4(OCMe2CMe2OH) 2(OiPr)2, and Zr3(OCMe2CMe 2O)4(OCMe2CMe2OH)4. Dinuclear products could be obtained by carrying out the reactions at room temperature or by addition of excess pinacol (in which case Zr2(OCMe2 CMe2O)2(OCMe2CMe2OH) 4 was the product). (2) Similar reactions between Ti(Oi Pr)4 and pinacol gave dinuclear products under all conditions. Both homo- (Ti2(OiPr)2(OCMe2CMe 2O)2(OCMe2CMe2OH)2) and heterometallic complexes (Ti2(OCMe2CMe2O) 2(OCMe2CMe2OH)4) were characterized. (3) Controlled addition of water to either of the isolated titanium pinacolates gave Ti3(mu3-O)(OCMe2CMe2O) 4(OCMe2CMe2OH)2. (4) Reaction of zirconium pinacolates with water led to the isolation of Zr4(mu 2-O)(OCMe2CMe2O)4(OCMe2CMe 2OH)6 and Zr6(mu3-O)4(H 2O)2(OCMe2CMe2O)5(OCMe 2CMe2OH)5. 17O NMR studies aided in the investigation of active equilibria and reversibility of hydrolysis. (5) The thermolysis of Zr2(OCMe2CMe2O) 2(OCMe2CMe2OH)4 gave ZrO2 in a mixture of crystalline phases. GC-MS and NMR analysis of the volatiles revealed 4 C6 products as well as two ligand coupled products. Isotope-labeling studies were carried out to probe the mechanisms by which the organic products were formed. (6) Reaction of Zr2(OCMe 2CMe2O)2(OCMe2CMe2OH) 4 with Ti(OiPr)4 gives (OiPr) 2TiZr2(OCMe2CMe2O)4(OCMe 2CMe2OH)2 which reacts with a second equivalent of Ti(OiPr)4 to give (OiPr) 4Ti2Zr2(OCMe2CMe2O) 6. (7) Reaction of Li{N(SiMe3)2}Et 2O or Na{N(SiMe3)2}x THF with Zr2(OCMe2CMe2O)2(OCMe 2CMe2OH)4 gave (THF)LiZr2(OCMe 2CMe2O)3(OCMe2CMe2OH) 3 or (HOCMe2CMe2OH)2Na2Zr 2(OCMe2CMe2O)4(OCMe2CMe 2OH)2 respectively. Similar reactions with larger +1 or +2 metals led to the formation of insoluble precipitates.

Zechmann, Cecilia A.

380

Rhodium complexes of a chelating ligand with imidazol-2-ylidene and pyridin-2-ylidene donors: the effect of C-metalation of nicotinamide groups on uptake of hydride ion.  

PubMed

Rhodium complexes of the imidazolylidene (C-im) N-heterocyclic carbene (NHC) ligand, C-im-pyH(+), bearing a nicotinamide cation substituent (pyH(+)) have been targeted for ligand-centered uptake and delivery of hydride ion. This work reveals that rhodium(I) complexes such as [Rh(C-im-pyH(+))(COD)X][PF(6)] (1, a: X = Cl, b: X = I) undergo facile C-metalation of the nicotinamide ring to afford rhodium complexes of a novel chelate ligand, C,C'-im-py, with coordinated imidazolylidene (C(im)) and pyridylidene (C(py)) NHC-donors. Seven examples were characterized and include rhodium(III) monomers of the general formula [Rh(C,C'-im-py)L(x)I(2)](z+) (2: z = 1, L = H(2)O or solvent, x = 2; 3, 5, 7: z = 0, L = carboxylate, x = 1) and novel rhodium(II) dimers, the anti/syn-isomers of [Rh(2)(C,C'-im-py)(2)(?OAc)(2)I(2)] (4-anti/syn). The NMR data, backed by DFT calculations, is consistent with attribution of the C,C'-im-py ligand as a bis(carbene) donor. Single crystal X-ray diffraction studies are reported for 2, 3, 4-anti, 4-syn and 7. Consistently, within the each complex, the Rh-C(im) bond length is shorter than the Rh-C(py) bond length, which is the opposite trend to that expected based on simple electronic considerations. It is proposed that intramolecular steric interactions imposed by different rings in the rigid C,C'-im-py chelate ligand dictate the observed Rh-C(NHC) bond lengths. Attempts to add hydride to the C-metalated nicotinamide ring in 3 were unsuccessful. The redox behavior of 3 and 4 and, for comparison, an analogous bis(imidazolylidene)rhodium(III) monomer (8), were characterized by cyclic voltammetry, electron paramagnetic resonance (EPR), and UV-vis spectroelectrochemistry. In 3 and 4, the C-metalated nicotinamide ring is found to exhibit a one-electron reduction process at far lower potential (-2.34 V vs. Fc(+)/Fc in acetonitrile) than the two-electron nicotinamide cation-dihydronicotinamide couple found for the corresponding nonmetalated ring (-1.24 V). The C,C'-ligand is electrochemically silent over a large potential range (from -2.3 V to the anodic solvent limit), thus for both 3 and 4 the first reduction processes are metal-centered. For 4-anti, the cyclic voltammetry and UV-vis spectrochemical results are consistent with a diamagnetic [Rh(I)Rh(II)](2) tetrameric reduction product. Density functional theory (DFT) calculations were used to further probe the uptake of hydride ion by the nicotinamide ring, both before and after C-metalation. It is found that C-metalation significantly decreases the ability of the nicotinamide ring to take up hydride ion, which is attributed to the "carbene-like" character of a C-metalated pyridylidene ring. PMID:22309370

McSkimming, Alex; Ball, Graham E; Bhadbhade, Mohan M; Colbran, Stephen B

2012-02-20

381

Dinuclear Rare-Earth Metal Alkyl Complexes Supported by Indolyl Ligands in ?-?(2) :?(1) :?(1) Hapticities and their High Catalytic Activity for Isoprene 1,4-cis-Polymerization.  

PubMed

Two series of new dinuclear rare-earth metal alkyl complexes supported by indolyl ligands in novel ?-?(2) :?(1) :?(1) hapticities are synthesized and characterized. Treatment of [RE(CH2 SiMe3 )3 (thf)2 ] with 1?equivalent of 3-(tBuN?CH)C8 H5 NH (L1 ) in THF gives the dinuclear rare-earth metal alkyl complexes trans-[(?-?(2) :?(1) :?(1) -3-{tBuNCH(CH2 SiMe3 )}Ind)RE(thf)(CH2 SiMe3 )]2 (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L1 is deprotonated by the metal alkyl species and the imino C?N group is transferred to the amido group by alkyl CH2 SiMe3 insertion, affording a new dianionic ligand that bridges two metal alkyl units in ?-?(2) :?(1) :?(1) bonding modes, forming the dinuclear rare-earth metal alkyl complexes. When L1 is reduced to 3-(tBuNHCH2 )C8 H5 NH (L2 ), the reaction of [Yb(CH2 SiMe3 )3 (thf)2 ] with 1?equivalent of L2 in THF, interestingly, generated the trans-[(?-?(2) :?(1) :?(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (major) and cis-[(?-?(2) :?(1) :?(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (minor) complexes. The catalytic activities of these dinuclear rare-earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio- and stereoselectivities for isoprene 1,4-cis-polymerization. PMID:25490879

Zhang, Guangchao; Wei, Yun; Guo, Liping; Zhu, Xiancui; Wang, Shaowu; Zhou, Shuangliu; Mu, Xiaolong

2015-02-01

382

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2''-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning.  

PubMed

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'?:?6',2''-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands. PMID:22729349

Lewis, Frank W; Harwood, Laurence M; Hudson, Michael J; Drew, Michael G B; Sypula, Michal; Modolo, Giuseppe; Whittaker, Daniel; Sharrad, Clint A; Videva, Vladimira; Hubscher-Bruder, Vronique; Arnaud-Neu, Franoise

2012-08-14

383

Synthesis, characterization and magnetism of metal-organic compounds: role of the positions of the coordinating groups of a meso-flexible ligand in placing anisotropy to exhibit spin-canting behaviour.  

PubMed

In continuation of our recent investigation on flexible ligands, three new metal-organic coordination framework containing compounds, formulated as {Co2()2(px3ampy)2}nnpx3ampy (), {Co()(px3ampy)0.5}n () and {Co2() (px3ampy)2(H2O)}n3nH2O () have been synthesized using three structurally different meso-flexible polycarboxylate ligands, (4,4'-methylenebis-(oxy)dibenzoic acid), (3,3'-methylenebis-(oxy)dibenzoic acid) and (5,5'-methylene-bis(oxy)diisophthalic acid) bearing the flexible spacer in the middle of the skeleton, along with a long flexible pyridyl ligand px3ampy (1,4-bis(3-pyridylaminomethyl)benzene). Compounds have been characterized by single crystal X-ray diffraction analysis, IR spectroscopy and thermogravimetric (TG) studies including elemental analysis. The crystal structure determinations reveal that compound has a 1D ladder-like structure and compounds and are characterized by 3D frameworks. Compound possesses a tiling of a snz net and compound has a 3D interpenetrated motif with a (4,4) connecting 2-nodal net. The variable temperature magnetic susceptibility measurements demonstrate the dominating antiferromagnetic nature of all three title compounds; interestingly, however, compounds and exhibit ferromagnetic interactions due to the uncompensated magnetic moment of the system at low temperatures. Compound illustrates the occurrence of spin canted antiferromagnetic ordering at Tc ? 25 K with a coercive field (Hc) of 900 Oe at 10 K due to the inclusion of magnetic anisotropy caused by the twisting of the concerned ligand skeleton. Compound shows comparatively weak ferromagnetic ordering with Tc ? 9.5 K, for which weak magnetic anisotropy is present because of two different coordination environments (octahedral and tetrahedral) between two cobalt centers. A structure-function relationship has been described based on the position of the coordinating groups with respect to the flexible center of the ligand skeleton as well as the coordination angle between the ligand and the metal ion. PMID:25562803

Manna, Paulami; Tripuramallu, Bharat Kumar; Bommakanti, Suresh; Das, Samar K

2015-01-28

384

Histologic and morphologic evaluation of explanted bone anchors from bone-anchored hearing aids  

Microsoft Academic Search

Bone-anchored hearing aids are a standard option in rehabilitation of patients with conductive or mixed hearing loss, and\\u000a also CROS fitting. However, the skin-penetrating bone anchor repeatedly gives reason for discussion about the risk of infection\\u000a of surrounding tissues as a major cause of malfunction. In the present study, explanted bone anchors with surrounding bone\\u000a and soft tissue were examined

Robert Mlynski; Eva Goldberg; Joerg Ebmeyer; Matthias Scheich; Stefan Gattenlhner; Konrad Schwager; Rudolf Hagen; Wafaa Shehata-Dieler

2009-01-01

385

Tightening procedures for large diameter anchor bolts  

E-print Network

judgment concerning how tight to tighten the nuts on the anchor bolt system. Recent bolt failures have raised concerns about nut tightening procedures. When the nuts of a double nut system are not tightened sufficiently, fatigue loading, and even impact...

Abraham, Ryan Charles

1997-01-01

386

Adhesion of membranes via receptor-ligand complexes: Domain formation, binding cooperativity, and active processes  

E-print Network

Cell membranes interact via anchored receptor and ligand molecules. Central questions on cell adhesion concern the binding affinity of these membrane-anchored molecules, the mechanisms leading to the receptor-ligand domains observed during adhesion, and the role of cytoskeletal and other active processes. In this review, these questions are addressed from a theoretical perspective. We focus on models in which the membranes are described as elastic sheets, and the receptors and ligands as anchored molecules. In these models, the thermal membrane roughness on the nanometer scale leads to a cooperative binding of anchored receptor and ligand molecules, since the receptor-ligand binding smoothens out the membranes and facilitates the formation of additional bonds. Patterns of receptor domains observed in Monte Carlo simulations point towards a joint role of spontaneous and active processes in cell adhesion. The interactions mediated by the receptors and ligand molecules can be characterized by effective membrane adhesion potentials that depend on the concentrations and binding energies of the molecules.

Thomas R. Weikl; Mesfin Asfaw; Heinrich Krobath; Bartosz Rozycki; Reinhard Lipowsky

2009-06-09

387

Metal-binding loop length is a determinant of the pKa of a histidine ligand at a type 1 copper site.  

PubMed

The type 1 copper site of a cupredoxin involves coordination by cysteine, histidine, and methionine residues from a single loop. Dissociation and protonation of the histidine ligand on this loop is observed in only certain reduced cupredoxins and can regulate electron-transfer reactivity. This effect is introduced in azurin (AZ) (the wild-type protein has an estimated pKa of <2) by mutating the native copper-binding loop (C(112)TFPGH(117)SALM(121), ligands numbered). In this work, we have investigated the influence of loop length alone on histidine ligand protonation by determining the pKa value in AZ variants with ligand-containing polyalanine loops of different length. Crystal structures of the Cu(I)-variant with the loop sequence C(112)AAH(115)AAM(118) (AZ2A2A) demonstrate that at pH 4.2 His115 is protonated and no longer coordinated, and the imidazole ring is rotated by 180. The influence of pH on the reduction potential allows a pKa of 5.2 0.1 for His115 in Cu(I)-AZ2A2A to be determined. In the reduced AZ variants in which the loop sequences C(112)AAAAH(117)AAAM(121) (AZ4A3A) and C(112)AAAAH(117)AAAAM(122) (AZ4A4A) have been introduced, pKa values of 4.5 0.1 and 4.4 0.1, respectively, are obtained for the His117 ligand. Consistent with these data, the crystal structure of Cu(I)-AZ4A4A at pH 5.3 shows no sign of His117 protonation (crystals were unstable at lower pH values). The loop length range studied matches that which occurs naturally and these investigations indicate that length alone can alter the pKa of the coordinating histidine by approximately 1 pH unit. The pKa for this histidine ligand varies in native cupredoxins by >5 pH units. Other structural and electronic features, governed primarily by the second-coordination sphere, to which the ligand-binding loop is a major contributor, also alter this important feature. A longer ligand-containing loop made of residues whose side chains are larger and more complex than a methyl group increases the second coordination sphere providing additional scope for tuning the pKa of the histidine ligand and other active site properties. PMID:21141901

Li, Chan; Sato, Katsuko; Monari, Stefano; Salard, Isabelle; Sola, Marco; Banfield, Mark J; Dennison, Christopher

2011-01-17

388

Hydrothermal synthesis, structure and rare ferromagnetic property of a 3-D Nd(III) metalorganic framework based on mixed pyridine-2,5-dicarboxylic acid\\/nicotinic acid ligands  

Microsoft Academic Search

A novel 3-D metalorganic framework Nd(2,5-pydc)(nic)(H2O) (1, 2,5-pydc=pyridine-2,5-dicarboxylic acid, nic=nicotinic acid) has been hydrothermally synthesized and characterized by elemental analyses, IR, and X-ray single-crystal diffraction. Compound 1 is the first MOF based on mixed 2,5-pydc\\/nic ligands. The title compound displays an interseting 3-D (6,3)-connected network with the topology of (4.62)2(4261083). Magnetic susceptibility measurements show that compound1 presents a rare ferromagnetic

Dao-Jun Zhang; Tian-You Song; Li Wang; Jing Shi; Jia-Ning Xu; Ying Wang; Kui-Rong Ma; Wei-Rong Yin; Li-Rong Zhang; Yong Fan

2009-01-01

389

Dicarbollylamine ligand as a tunable template for sigma,sigma- and pi,sigma-bonding modes: syntheses, structures, and theoretical studies of eta5:eta1-coordinated constrained-geometry group 13 metal complexes.  

PubMed

A series of group 13 main group complexes with pi,sigma-type bonding interaction of the formula [{(eta (5)-RC 2B 9H 9)(CH 2)(eta (1)-NMe 2)}MMe] (M = Al, R = H 5, Me 6; Ga, R = H 7, Me 8; In, R = H 9, Me 10) was produced by the reaction of group 13 metal alkyls (MMe 3; M = Al, Ga, In) with the dicarbollylamine ligands, nido-8-R-7,8-C 2B 9H 10-7-(CH 2)NHMe 2 (R = H 1, Me 2). The reactions of 1 and 2 with AlMe 3 in toluene initially afforded tetra-coordinated aluminum complexes with sigma,sigma-type bonding interaction, [{(eta (1)-RC 2B 9H 10)(CH 2)(eta (1)-NMe 2)}AlMe 2] (R = H 3, Me 4), which readily underwent further methane elimination to yield the corresponding constrained geometry complexes (CGCs, 5 and 6) of aluminum with pi,sigma-bonding interaction. However, the reactions between 1 and 2 and MMe 3 (M = Ga, In) in toluene produced gallium and indium pi,sigma-CGCs of 7 and 10 directly, not proceeding through sigma,sigma-intermediates. The structures of group 13 metal CGCs were established by X-ray diffraction studies of 5, 6, and 8, which authenticated a characteristic eta (5):eta (1)-coordination mode of the dicarbollylamino ligand to the group 13 metals. A similar pi,sigma-bondi