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1

Crown Ether Complexes of Uranyl, Neptunyl, and Plutonyl: Hydration Differentiates Inclusion versus Outer Coordination.  

PubMed

The structures of actinyl-crown ether complexes are key to their extraction behavior in actinide partitioning. Only UO2(18C6)(2+) and NpO2(18C6)(+) (18C6 = 18-Crown-6) have been structurally characterized. We report a series of complexes of uranyl, neptunyl, and plutonyl with 18-Crown-6, 15-Crown-5 (15C5), and 12-Crown-4 (12C4) produced in the gas phase by electrospray ionization (ESI) of methanol solutions of AnO2(ClO4)2 (An = U, Np, or Pu) and crown ethers. The structures of 1:1 actinyl-crown ether complexes were deduced on the basis of their propensities to hydrate. Hydration of a coordinated metal ion requires that it be adequately exposed to allow further coordination by a water molecule; the result is that hydrates form for outer-coordination isomers but not for inclusion isomers. It is demonstrated that all the actinyl 18C6 complexes exhibit fully coordinated inclusion structures, while partially coordinated outer-coordination structures are formed with 12C4. Both inclusion and outer-coordination isomers were observed for actinyl-15C5 complexes, depending on whether they resulted from ESI or from collision-induced dissociation. Evidence for the formation of 1:2 complexes of actinyls with 15C5 and 12C4, which evidently exhibit bis-outer-coordination structures, is presented. PMID:24828467

Gong, Yu; Gibson, John K

2014-06-01

2

Polymer complexes: XLX. Novel supramolecular coordination modes of structure and bonding in polymeric hydrazone sulphadrugs uranyl complexes  

NASA Astrophysics Data System (ADS)

Novel five binuclear polymeric dioxouranium(VI) of azosulphadrugs [(azodrug substances) azobenzene sulphonamides] were prepared for the first time. The infrared spectra of the samples were recorded and their fundamental vibration wave number was obtained. The resulting polymeric uranyl complexes were characterized on the basis of their elemental analyses, conductance and spectral (IR, NMR, and electronic spectra) data. The ligation modes of the azosulphadrugs ligands towards uranyl(II) ions were critically assigned and addressed properly on the basis of their IR and their uranyl(II) complexes. The theoretical aspects are described in terms of the well-known theory of 5d-4f transitions. The coordination geometries and electronic structures are determined from a framework for the modeling of novel polymer complexes. The values of ?3 of the prepared complexes containing UO 22+ were successfully used to calculate the force constant, FUO (1n 10 -8 N/) and the bond length RUO of the U-O bond. Wilson's, matrix method, Badger's formula, and Jones and El-Sonbati equations were used to calculate the U-O bond distances from the values of the stretching and interaction force constants. The most probable correlations between U-O force constant to U-O bond distance were satisfactorily discussed in terms of "Badger's rule", "Jones" and "El-Sonbati equations".

El-Sonbati, A. Z.; Diab, M. A.; El-Shehawy, M. S.; Moqbal, M.

2010-01-01

3

Uranyl-copper(II) heterometallic oxalate complexes: coordination polymers and frameworks.  

PubMed

Five oxalate complexes containing both uranyl and copper(II) ions and 2,2?-bipyridine (bipy), 2,2?-bipyrimidine (bipym) or 1,10-phenanthroline (phen) as co-ligands have been synthesized under hydrothermal conditions and their crystal structures were determined. [UO2Cu(C2O4)(NO3)2(bipy)(H2O)] (1) is a molecular complex in which the two cations are connected by the bis-chelating oxalate. A one-dimensional uranyl oxalate ribbon is formed in [UO2Cu(C2O4)2(bipym)(H2O)] (2), with uranyl ions bound to two chelating anions and to a third, monodentate oxalate which holds the decorating [Cu(bipym)(H2O)]2+ groups. Complex [(UO2)2Cu2(C2O4)2(bipym)3(OH)2]2NO3 (3) is a two-dimensional assembly in which uranyl oxalate chains are linked to one another by [Cu2(bipym)3]4+ dinuclear units through bridging hydroxide ions. Finally, [UO2Cu(C2O4)2(bipy)] (4) and [UO2Cu(C2O4)2(phen)] (5) display identical three-dimensional arrangements containing uranyl oxalate sheets connected to one another by copper oxalate dinuclear units. The magnetic properties of compounds 2 and 4 have been investigated. Weak inter-chain antiferromagnetic interactions between copper(II) atoms are present in 2, while 4 displays strong oxalate-mediated antiferromagnetic exchange (J = -335 cm(-1)). These complexes are the first uranyl-d block metal oxalate complexes to be reported. PMID:23760346

Thury, Pierre; Rivire, Eric

2013-08-01

4

Probing the local coordination environment and nuclearity of uranyl(VI) complexes in non-aqueous media by emission spectroscopy.  

PubMed

We describe the synthesis, solid state and solution properties of two families of uranyl(VI) complexes that are ligated by neutral monodentate and anionic bidentate P=O, P=NH and As=O ligands bearing pendent phenyl chromophores. The uranyl(VI) ions in these complexes possess long-lived photoluminescent LMCT (3)?(u) excited states, which can be exploited as a sensitive probe of electronic structure, bonding and aggregation behaviour in non-aqueous media. For a family of well defined complexes of given symmetry in trans-[UO(2)Cl(2)(L(2))] (L = Ph(3)PO (1), Ph(3)AsO (2) and Ph(3)PNH (3)), the emission spectral profiles in CH(2)Cl(2) are indicative of the strength of the donor atoms bound in the equatorial plane and the uranyl bond strength; the uranyl LMCT emission maxima are shifted to lower energy as the donor strength of L increases. The luminescence lifetimes in fluid solution mirror these observations (0.87-3.46 ?s) and are particularly sensitive to vibrational and bimolecular deactivation. In a family of structurally well defined complexes of the related anion, tetraphenylimidodiphosphinate (TPIP), monometallic complexes, [UO(2)(TPIP)(thf)] (4), [UO(2)(TPIP)(Cy(3)PO)] 5), a bimetallic complex [UO(2)(TPIP)(2)](2) (6) and a previously known trimetallic complex, [UO(2)(TPIP)(2)](3) (7) can be isolated by variation of the synthetic procedure. Complex 7 differs from 6 as the central uranyl ion in 7 is orthogonally connected to the two peripheral ones via uranyl ? uranium dative bonds. Each of these oligomers exhibits a characteristic optical fingerprint, where the emission maxima, the spectral shape and temporal decay profiles are unique for each structural form. Notably, excited state intermetallic quenching in the trimetallic complex 7 considerably reduces the luminescence lifetime with respect to the monometallic counterpart 5 (from 2.00 ?s to 1.04 ?s). This study demonstrates that time resolved and multi-parametric luminescence can be of value in ascertaining solution and structural forms of discrete uranyl(VI) complexes in non-aqueous solution. PMID:21264387

Redmond, Michael P; Cornet, Stephanie M; Woodall, Sean D; Whittaker, Daniel; Collison, David; Helliwell, Madeleine; Natrajan, Louise S

2011-04-21

5

Uranyl-oxo coordination directed by non-covalent interactions.  

PubMed

Directed coordination of weakly Lewis acidic K(+) ions to weakly Lewis basic uranyl oxo ligands is accomplished through non-covalent cation-? and cation-F interactions for the first time. Comparison of a family of structurally related diarylamide ligands highlights the role that the cation-? and cation-F interactions play in guiding coordination. Cation binding to uranyl is demonstrated in the solid state and in solution, providing the shortest reported crystallographic uranyl-oxo to potassium distance. UV-Vis, TD-DFT calculations, and electrochemical measurements show that cation coordination directly impacts the electronics at the uranium(vi) cation. PMID:24894554

Lewis, Andrew J; Yin, Haolin; Carroll, Patrick J; Schelter, Eric J

2014-06-24

6

Uranyl complexes of alkyl-bridged ditopic diaminotetraphenol ligands and their use as uranyl ion extractors.  

PubMed

The coordination chemistry of uranyl ions was studied using long n-alkyl chain (n = 5-8) bridged by N,N,N',N'-tetrakis(2-hydroxy-3-methyl-5-tert-butylbenzyl)diaminoalkanes (H4L1-H4L4) as ligands. All ligands formed 2:1 (U-to-L ratio) complexes with uranyl ions, but in addition 1:1 complexes could be characterized using ligands H4L2 and H4L3. The complexes were characterized by elemental analysis, spectroscopy (IR and NMR), and X-ray diffraction. The 2:1 complexes are of two types: [(UO2)2(H2Lm)(NO3)2(solvent)2] (m = 1 and 2; solvent = ethanol or propanol) or (cation)2[(UO2)2(H2Lm)(NO3)2(anion)2]xsolvent (m = 2 and 4; cation = triethylammonium, anion = nitrate or thiocyanate, and solvent = dichloromethane and acetonitrile; x = 1 or 2). The 1:1 complexes have the formula [(UO2)2(H2Lm)2] (m = 2 and 3). In the solid state, 2:1 complexes are almost in a linear conformation with the uranyl ion at both ends of the ligand. The 1:1 complexes are cyclic dinuclear molecules. Preliminary studies of the ligands as uranyl ion extractors from water to dichloromethane were also performed. A high extraction efficiency was observed with H4L3 for uranyl ions, and in the presence of Cu(II), Ni(II), Co(II), and Zn(II) ions, a good extraction selectivity for uranyl ions was found with H4L1. PMID:23848559

Riisi, Antti; Visnen, Ari; Sillanp, Reijo

2013-08-01

7

Uranyl coordination environment in hydrophobic ionic liquids: an in situ investigation.  

PubMed

Different inner-sphere coordination environments are observed for the uranyl nitrate complexes formed with octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide and tributyl phosphate in dodecane and in the hydrophobic ionic liquids (ILs) [C(4)mim][PF(6)] and [C(8)mim][N(SO(2)CF(3))(2)]. Qualitative differences in the coordination environment of the extracted uranyl species are implied by changes in peak intensity patterns and locations for uranyl UV-visible spectral bands when the solvent is changed. EXAFS data for uranyl complexes in dodecane solutions is consistent with hexagonal bipyramidal coordination and the existence of UO(2)(NO(3))(2)(CMPO)(2). In contrast, the complexes formed when uranyl is transferred from aqueous nitric acid solutions into the ILs exhibit an average equatorial coordination number of approximately 4.5. Liquid/liquid extraction results for uranyl in both ILs indicate a net stoichiometry of UO(2)(NO(3))(CMPO)(+). The concentration of the IL cation in the aqueous phase increases in proportion to the amount of UO(2)(NO(3))(CMPO)(+) in the IL phase, supporting a predominantly cation exchange mechanism for partitioning in the IL systems. PMID:12665350

Visser, Ann E; Jensen, Mark P; Laszak, Ivan; Nash, Kenneth L; Choppin, Gregory R; Rogers, Robin D

2003-04-01

8

Density Functional Studies on the Complexation and Spectroscopy of Uranyl Ligated with Acetonitrile and Acetone Derivatives  

SciTech Connect

The coordination of nitrile (acetonitrile, propionitrile, and benzonitrile) and carbonyl (formaldehyde, ethanal, and acetone) ligands to the uranyl dication (UO22+) has been examined using density functional theory (DFT) utilizing relativistic effective core potentials (RECPs). Complexes containing up to six ligands have been modeled for all ligands except formaldehyde, for which no minimum could be found. A comparison of relative binding energies indicates that five coordinate complexes are predominant while a six coordinate complex involving propionitrile ligands might be possible. Additionally, the relative binding energy and the weakening of the uranyl bond is related to the size of the ligand and, in general, nitriles bind more strongly to uranyl than carbonyls.

Schoendorff, George E.; Windus, Theresa L.; De Jong, Wibe A.

2009-12-12

9

Comparative study of uranyl(VI) and -(V) carbonato complexes in an aqueous solution.  

PubMed

Electrochemical, complexation, and electronic properties of uranyl(VI) and -(V) carbonato complexes in an aqueous Na2CO3 solution have been investigated to define the appropriate conditions for preparing pure uranyl(V) samples and to understand the difference in coordination character between UO22+ and UO2+. Cyclic voltammetry using three different working electrodes of platinum, gold, and glassy carbon has suggested that the electrochemical reaction of uranyl(VI) carbonate species proceeds quasi-reversibly. Electrolysis of UO22+ has been performed in Na2CO3 solutions of more than 0.8 M with a limited pH range of 11.7 < pH < 12.0 using a platinum mesh electrode. It produces a high purity of the uranyl(V) carbonate solution, which has been confirmed to be stable for at least 2 weeks in a sealed glass cuvette. Extended X-ray absorption fine structure (EXAFS) measurements revealed the structural arrangement of uranyl(VI) and -(V) tricarbonato complexes, [UO2(CO3)3]n- [n = 4 for uranyl(VI), 5 for uranyl(V)]. The bond distances of U-Oax, U-Oeq, U-C, and U-Odist are determined to be 1.81, 2.44, 2.92, and 4.17 A for the uranyl(VI) complex and 1.91, 2.50, 2.93, and 4.23 A for the uranyl(V) complex, respectively. The validity of the structural parameters obtained from EXAFS has been supported by quantum chemical calculations for the uranyl(VI) complex. The uranium LI- and LIII-edge X-ray absorption near-edge structure spectra have been interpreted in terms of electron transitions and multiple-scattering features. PMID:17417836

Ikeda, Atsushi; Hennig, Christoph; Tsushima, Satoru; Takao, Koichiro; Ikeda, Yasuhisa; Scheinost, Andreas C; Bernhard, Gert

2007-05-14

10

Stereognostic coordination chemistry. 1. The design and synthesis of chelators for the uranyl ion  

SciTech Connect

A new approach to the molecular recognition of metal oxo cations is introduced based on a ligand design strategy that provides at least one hydrogen bond donor for interaction with oxo group(s) as well as conventional electron pair donor ligands for coordination to the metal center. This concept of stereognostic coordination of oxo metal ions is exemplified in the design of four tripodal ligands-tris[2-(2-carboxyphenoxy)ethyl]amine[NEB],tris[3-(2-carboxyphenoxy)propyl]amine[NPB], tris[3-(2-carboxynaphthyl-3-oxy)propyl]amine [NPN], and tris[3-(2-carboxy=4octadecylphenoxy)propyl]amine[NPodB] - for sequestration of the uranyl ion. The ligands NEB, NPB, and NPN form 1:1 complexes with UO{sub 2}{sup 2+}. The bidentate coordination of carboxyl groups of these compounds is indicated by the infrared spectra, which offer some support for the presence of a hydrogen bond to the uranyl group. Mass spectral data corroborate CPK model predictions that more than five intervening atoms between the tertiary nitrogen atom and the carboxylate groups are required for metal ion incorporation and monomeric complex formation. Solvent extractions of aqueous UO{sub 2}{sup 2+} into chloroform solutions of the ligands have shown them to be powerful extractants. In the case of the very hydrophobic ligand NPodB the stoichiometry of the complexation reaction is shown to be 1:1 UO{sub 2}/ligand complex formed by the release of 3 protons. The extraction is quantitative at pH 2.5, and an effective extraction coefficient of about 10{sup 11} is estimated for neutral aqueous solutions of UO{sub 2}{sup 2+}. 81 refs., 13 figs., 2 tabs.

Franczyk, T.S.; Czerwinski, K.R.; Raymond, K.N. [Univ. of Caifornia, Berkeley, CA (United States)

1992-10-07

11

Intercalative Ion Exchange of Polyamine Transition Metal Complexes into Hydrogen Uranyl Phosphate.  

PubMed

A series of derivatives of hydrogen uranyl phosphate (HUP) was prepared by displacing the butylammonium ions of butylammonium uranyl phosphate with the transition metal complexes Cu(en)(2)(2+), Cu(pn)(2)(2+), Cu(trien)(2+), Cu(14-ane)(2+), Cu(15-ane)(2+), Ni(trien)(2+), Ni(14-ane)(2+), and Ni(diene)(2+). X-ray powder patterns proved that the original tetragonal structure of the UP layers remained intact in all derivatives. The extent of the ion exchange and the interlamellar distances were found to depend mainly on the size and on the shape of a particular coordinating ligand. Electronic absorption spectra indicated that the intercalated complexes had four-coordinate square-planar geometry inside the UP lattice. Extents of hydration of the intercalates varied significantly, and they depended mostly on the shapes of the coordinating ligands and on their abilities to regularly pack between the UP layers. Results of the above-mentioned characteristics allow one to divide these transition metal complexes into two groups which differ from each other in their abilities to efficiently fill up the space between the UP layers. The steady-state luminescence spectra of intercalates showed a very weak uranyl emission which was partly due to quenching by the Cu(2+) and Ni(2+) guest complexes and partly to self-absorption. PMID:11670016

Grohol, Daniel; Blinn, Elliott L.

1997-07-30

12

Complexes of vanadyl and uranyl ions with the chelating groups of humic matter.  

PubMed

The uranyl and vanadyl complexes formed with salicylic, phthalic and 3,4-dihydroxybenzoic acids have been studied by potentiometry in order to determine the stability constants of the M(m)L(n) species formed in solution, and the constants for the hydrolysis and polymeric complexes, at 25.0 degrees , in 0.10, 0.40 and 0.70M sodium perchlorate. MINIQUAD was used to process the data to find the best models for the species in solution, and calculate the formation constants. The uranyl-salicylic acid system was also studied by spectrophotometry and the program SQUAD used to process the data obtained. The best models for these systems show that co-ordination of the uranyl ion by carboxylate groups is easier than for the vanadyl ion, whereas the vanadyl ion seems to form more stable complexes with phenolate groups. Both oxo-cations seem to tend to hydrolyse rather than form complexes when the L:M ratios are greater than unity. Although the change in the constants with ionic strength is small, the activity coefficients of the salicylate and phthalate species have been calculated at ionic strengths 0.40 and 0.70M, along with the interaction parameters with Na(+), from the stability constants found for the species ML and H(2)L, according to the Brnsted-Guggenheim expression. PMID:18964417

Gonalves, M L; Mota, A M

1987-10-01

13

Experimental and Theoretical Approaches to Redox Innocence of Ligands in Uranyl Complexes: What Is Formal Oxidation State of Uranium in Reductant of Uranyl(VI)?  

PubMed

Redox behavior of [UO2(gha)DMSO](-)/UO2(gha)DMSO couple (gha = glyoxal bis(2-hydroxanil)ate, DMSO = dimethyl sulfoxide) in DMSO solution was investigated by cyclic voltammetry and UV-vis-NIR spectroelectrochemical technique, as well as density functional theory (DFT) calculations. [UO2(gha)DMSO](-) was found to be formed via one-electron reduction of UO2(gha)DMSO without any successive reactions. The observed absorption spectrum of [UO2(gha)DMSO](-), however, has clearly different characteristics from those of uranyl(V) complexes reported so far. Detailed analysis of molecular orbitals and spin density of the redox couple showed that the gha(2-) ligand in UO2(gha)DMSO is reduced to gha(3-) to give [UO2(gha)DMSO](-) and the formal oxidation state of U remains unchanged from +6. In contrast, the additional DFT calculations confirmed that the redox reaction certainly occurs at the U center in other uranyl(V/VI) redox couples we found previously. The noninnocence of the Schiff base ligand in the [UO2(gha)DMSO](-)/UO2(gha)DMSO redox couple is due to the lower energy level of LUMO in this ligand relative to those of U 5f orbitals. This is the first example of the noninnocent ligand system in the coordination chemistry of uranyl(VI). PMID:24848497

Takao, Koichiro; Tsushima, Satoru; Ogura, Toshinari; Tsubomura, Taro; Ikeda, Yasuhisa

2014-06-01

14

Synthesis, X-ray crystallography, thermal studies, spectroscopic and electrochemistry investigations of uranyl Schiff base complexes  

NASA Astrophysics Data System (ADS)

Some tetradentate salen type Schiff bases and their uranyl complexes were synthesized and characterized by UV-Vis, NMR, IR, TG, C.H.N. and X-ray crystallographic studies. From these investigations it is confirmed that a solvent molecule occupied the fifth position of the equatorial plane of the distorted pentagonal bipyramidal structure. Also, the kinetics of complex decomposition by using thermo gravimetric methods (TG) was studied. The thermal decomposition reactions are first order for the studied complexes. To examine the properties of uranyl complexes according to the substitutional groups, we have carried out the electrochemical studies. The electrochemical reactions of uranyl Schiff base complexes in acetonitrile were reversible.

Asadi, Zahra; Shorkaei, Mohammad Ranjkesh

2013-03-01

15

Theoretical analysis of optical spectra of uranyl in complexes  

NASA Astrophysics Data System (ADS)

A theoretical model is developed for simulating optical spectra of uranyl in complexes. The spectral profiles of electronic and vibronic transitions of UO22+ bonded to equatorial ligands are evaluated based on the Huang-Rhys theory of vibronic coupling in solids. This model assumes that only the symmetric O dbnd U dbnd O stretching mode exhibits multi-phonon progression, whereas all other local modes are not Franck-Condon allowed and treated as false origins of the progressing mode. A simulation of vibronic transitions in the UO 2(NO 3) 2(TBP) 2 complex is compared with absorption spectrum to determine the excited state energy levels, frequencies of local vibration modes and vibronic coupling strength.

Liu, G. K.; Jensen, M. P.

2010-10-01

16

Interfacial Complex Formation in Uranyl Extraction by Tributyl-Phosphate in Dodecane Diluent: A Molecular Dynamics Study  

SciTech Connect

Atomistic simulations have been carried out in a multicomponent two-phase system (aqueous and organic phases in direct contact) to investigate the interfacial molecular mechanisms leading to uranyl extractionfrom the aqueous to organic phase. The aqueous phase consists of the dissolved ions UO2^2+ and nitrate NO3-,with or without H3O+, in water to describe acidic or neutral condition; the organic phase consists of tributyl phosphate, the extractant, in dodecane as the diluent. We find that the interface facilitates the formation of various uranyl complexes, with a general formula UO2^2+(NO3-)n mTBP kH2O, with n + m + k ) 5, suggesting a 5-fold coordination. The coordination for all three molecular entities has the common feature that they all bind to the uranyl at the uranium atom with an oxygen atom in the equatorial plane perpendicular to the molecular axis of the uranyl, forming a 5-fold symmetry plane. Nitric acid has a strong effect in enhancing the formation of extractable species, which is consistent with experimental findings.

de Almeida, Valmor F [ORNL; Cui, Shengting [ORNL; Ye, Xianggui [ORNL; Khomami, Bamin [ORNL

2009-01-01

17

X-ray Absorption Spectroscopy Identifies Calcium-Uranyl-Carbonate Complexes at Environmental Concentrations  

SciTech Connect

Current research on bioremediation of uranium-contaminated groundwater focuses on supplying indigenous metal-reducing bacteria with the appropriate metabolic requirements to induce microbiological reduction of soluble uranium(VI) to poorly soluble uranium(IV). Recent studies of uranium(VI) bioreduction in the presence of environmentally relevant levels of calcium revealed limited and slowed uranium(VI) reduction and the formation of a Ca-UO2-CO3 complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO2-CO3 complex. Such a complex might exist even at high calcium concentrations, as some UO2-CO3 complexes will still be present. The number of calcium and/or sodium atoms coordinated to a uranyl carbonate complex will determine the net charge of the complex. Such a change in aqueous speciation of uranium(VI) in calcareous groundwater may affect the fate and transport properties of uranium. In this paper, we present the results from X-ray absorption fine structure (XAFS) measurements of a series of solutions containing 50 lM uranium(VI) and 30 mM sodium bicarbonate, with various calcium concentrations of 0-5 mM. Use of the data series reduces the uncertainty in the number of calcium atoms bound to the UO2-CO3 complex to approximately 0.6 and enables spectroscopic identification of the Na-UO2-CO3 complex. At nearly neutral pH values, the numbers of sodium and calcium atoms bound to the uranyl triscarbonate species are found to depend on the calcium concentration, as predicted by speciation calculations.

Kelly, Shelly D [Argonne National Laboratory (ANL); Kemner, Kenneth M [Argonne National Laboratory (ANL); Brooks, Scott C [ORNL

2007-01-01

18

X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations.  

SciTech Connect

Current research on bioremediation of uranium-contaminated groundwater focuses on supplying indigenous metal-reducing bacteria with the appropriate metabolic requirements to induce microbiological reduction of soluble uranium(VI) to poorly soluble uranium(IV). Recent studies of uranium(VI) bioreduction in the presence of environmentally relevant levels of calcium revealed limited and slowed uranium(VI) reduction and the formation of a Ca-UO{sub 2}-CO{sub 3} complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO{sub 2}-CO{sub 3} complex. Such a complex might exist even at high calcium concentrations, as some UO{sub 2}-CO{sub 3} complexes will still be present. The number of calcium and/or sodium atoms coordinated to a uranyl carbonate complex will determine the net charge of the complex. Such a change in aqueous speciation of uranium(VI) in calcareous groundwater may affect the fate and transport properties of uranium. In this paper, we present the results from X-ray absorption fine structure (XAFS) measurements of a series of solutions containing 50 {micro}M uranium(VI) and 30 mM sodium bicarbonate, with various calcium concentrations of 0-5 mM. Use of the data series reduces the uncertainty in the number of calcium atoms bound to the UO{sub 2}-CO{sub 3} complex to approximately 0.6 and enables spectroscopic identification of the Na-UO{sub 2}-CO{sub 3} complex. At nearly neutral pH values, the numbers of sodium and calcium atoms bound to the uranyl triscarbonate species are found to depend on the calcium concentration, as predicted by speciation calculations.

Kelly, S. D.; Kemner, K. M.; Brooks, S. C.; Biosciences Division; ORNL

2007-01-01

19

Syntheses and crystal structures of two novel alkaline uranyl chromates A{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2} (A=Rb, Cs) with bidentate coordination mode of uranyl ions by chromate anions  

SciTech Connect

Single crystals of Cs{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2} and Rb{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2} were prepared by solid state reactions. The structures are based upon the [(UO{sub 2})(CrO{sub 4}){sub 2}]{sup 2-} chains. Within the chains, UrO{sub 5} pentagonal bipyramids (Ur=uranyl) form Ur{sub 2}O{sub 8} dimers, which are linked via CrO{sub 4} tetrahedra into one-dimensional chains. The CrO{sub 4} tetrahedra coordinate uranyl ions in both mono- and bidentate fashion, which is unusual for uranyl chromates. The bidentate coordination has a strong influence upon geometrical parameters of both U and Cr coordination polyhedra. The conformation of the chains in 1 and 2 is different due to the different size of the Cs{sup +} and Rb{sup +} cations. - Graphical abstract: Uranyl chromate chain with monodentate and bidentate coordination mode of uranyl cations by CrO{sub 4} tetrahedra in Cs{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2}. Highlights: Black-Right-Pointing-Pointer Single crystals of novel uranyl chromates were prepared by solid state reactions. Black-Right-Pointing-Pointer The CrO{sub 4} tetrahedra coordinate uranyl ions in both mono- and bidentate fashion. Black-Right-Pointing-Pointer The bidentate coordination has a strong influence upon geometrical parameters.

Siidra, Oleg I., E-mail: siidra@mail.ru [Department of Crystallography, St. Petersburg State University, University Emb. 7/9, 199034 St.Petersburg (Russian Federation); Nazarchuk, Evgeny V.; Krivovichev, Sergey V. [Department of Crystallography, St. Petersburg State University, University Emb. 7/9, 199034 St.Petersburg (Russian Federation)

2012-03-15

20

Surface complexation modeling of uranyl adsorption on corrensite from the Waste Isolation Pilot Plant Site  

SciTech Connect

Corrensite is the dominant clay mineral in the Culebra Dolomite at the Waste Isolation Pilot Plant. The surface characteristics of corrensite, a mixed chlorite/smectite clay mineral, have been studied. Zeta potential measurements and titration experiments suggest that the corrensite surface contains a mixture of permanent charge sites on the basal plane and SiOH and AlOH sites with a net pH-dependent charge at the edge of the clay platelets. Triple-layer model parameters were determined by the double extrapolation technique for use in chemical speciation calculations of adsorption reactions using the computer program HYDRAQL. Batch adsorption studies showed that corrensite is an effective adsorbent for uranyl. The pH-dependent adsorption behavior indicates that adsorption occurs at the edge sites. Adsorption studies were also conducted in the presence of competing cations and complexing ligands. The cations did not affect uranyl adsorption in the range studied. This observation lends support to the hypothesis that uranyl adsorption occurs at the edge sites. Uranyl adsorption was significantly hindered by carbonate. It is proposed that the formation of carbonate uranyl complexes inhibits uranyl adsorption and that only the carbonate-free species adsorb to the corrensite surface. The presence of the organic complexing agents EDTA and oxine also inhibits uranyl sorption.

Park, Sang-Won; Leckie, J.O. [Stanford Univ., CA (United States)] [Stanford Univ., CA (United States); Siegel, M.D. [Sandia National Labs., Albuquerque, NM (United States)] [Sandia National Labs., Albuquerque, NM (United States)

1995-09-01

21

Complexation or uranyl ion. II. Complexation of uranyl ion in the VP-IAp anion exchanger phase during sorption from carbonate media  

SciTech Connect

The complicated process of increased uranium sorption from carbonate medium by the strongly basic anion exchanger VP-1Ap after additional treatment with alkaline solution was studied by IR spectroscopy. The process is related to the formation of certain complex forms of uranyl, differing in degree of polymerization, in which polynuclear forms predominate.

Stupin, N.P.; Kakhaeva, T.V.; Buskina, I.A.; Rodionov, V.V.; Vodolazov, L.I.; Zhukova, N.G.

1987-11-01

22

The Stereochemistry and Chemical Composition of Interstitial Complexes in Uranyl-Oxysalt Minerals  

NASA Astrophysics Data System (ADS)

The crystal structures and chemical compositions of uranyl-oxysalt minerals (primarily with sheet structural units) are interpreted in terms of the binary-representation/bond-valence approach to the structure and chemistry of oxysalts. There is a coherent relation between the average basicity of the structural unit and [CN]in, the average number of bonds to O-atoms of the structural unit from the interstitial complex and adjacent structural units. This relation allows calculation of the range of Lewis basicity for specific structural units. The Lewis acidity of an interstitial complex is expressed graphically as a function of the amounts and coordination numbers of monovalent, divalent and trivalent interstitial cations and the amount of interstitial transformer (H2O) groups. The range in Lewis basicity for a specific structural unit may also be expressed graphically, and where there is overlap of the Lewis acidity and Lewis basicity, the valence- matching principle is satisfied and the details of the possible interstitial complexes can be derived. The number and types of (H2O) groups in the interlayer are predicted. The ratio between the number of anions in the structural unit and the number of bonds emanating from interstitial cations and (OH) groups of the structural unit is the major factor controlling the number and type of (H2O) groups in the interstitial complex. This ratio is named the bond-valence distribution factor (D). There are three distinct types of interstitial (H2O) groups: transformer, non-transformer and inverse-transformer (H2O) groups. There are positive correlations between transformer and transformer plus non-transformer (H2O) groups and the bond-valence distribution factors in uranyl-oxy-salt minerals with sheet structural-units. Inverse-transformer (H2O) groups accept three bonds from cations, other (H2O) groups and (OH) groups of the structural unit. Their occurrence is rare and is limited to minerals with low bond-valence distribution factors. Detailed predictions of the number of transformer, non-transformer and inverse transformer (H2O) groups in the minerals of the meta-autunite, uranophane, phosphuranylite, carnotite, zippeite and uranyl-hydroxy-hydrate groups (and synthetic analogues) are in good agreement with the observed chemical compositions.

Hawthorne, F. C.; Schindler, M.

2006-05-01

23

Oxo-functionalization and reduction of the uranyl ion through lanthanide-element bond homolysis: synthetic, structural, and bonding analysis of a series of singly reduced uranyl-rare earth 5f1-4f(n) complexes.  

PubMed

The heterobimetallic complexes [{UO2Ln(py)2(L)}2], combining a singly reduced uranyl cation and a rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle (Pacman) and bridged through a uranyl oxo-group, have been prepared for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds are formed by the single-electron reduction of the Pacman uranyl complex [UO2(py)(H2L)] by the rare-earth complexes Ln(III)(A)3 (A = N(SiMe3)2, OC6H3Bu(t)2-2,6) via homolysis of a Ln-A bond. The complexes are dimeric through mutual uranyl exo-oxo coordination but can be cleaved to form the trimetallic, monouranyl "ate" complexes [(py)3LiOUO(?-X)Ln(py)(L)] by the addition of lithium halides. X-ray crystallographic structural characterization of many examples reveals very similar features for monomeric and dimeric series, the dimers containing an asymmetric U2O2 diamond core with shorter uranyl U?O distances than in the monomeric complexes. The synthesis by Ln(III)-A homolysis allows [5f(1)-4f(n)]2 and Li[5f(1)-4f(n)] complexes with oxo-bridged metal cations to be made for all possible 4f(n) configurations. Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies on the complexes are utilized to provide a basis for the better understanding of the electronic structure of f-block complexes and their f-electron exchange interactions. Furthermore, the structures, calculated by restricted-core or all-electron methods, are compared along with the proposed mechanism of formation of the complexes. A strong antiferromagnetic coupling between the metal centers, mediated by the oxo groups, exists in the U(V)Sm(III) monomer, whereas the dimeric U(V)Dy(III) complex was found to show magnetic bistability at 3 K, a property required for the development of single-molecule magnets. PMID:23451865

Arnold, Polly L; Hollis, Emmalina; Nichol, Gary S; Love, Jason B; Griveau, Jean-Christophe; Caciuffo, Roberto; Magnani, Nicola; Maron, Laurent; Castro, Ludovic; Yahia, Ahmed; Odoh, Samuel O; Schreckenbach, Georg

2013-03-13

24

Syntheses and crystal structures of two novel alkaline uranyl chromates A2(UO2)(CrO4)2 (A=Rb, Cs) with bidentate coordination mode of uranyl ions by chromate anions  

NASA Astrophysics Data System (ADS)

Single crystals of Cs2(UO2)(CrO4)2 and Rb2(UO2)(CrO4)2 were prepared by solid state reactions. The structures are based upon the [(UO2)(CrO4)2]2- chains. Within the chains, UrO5 pentagonal bipyramids (Ur=uranyl) form Ur2O8 dimers, which are linked via CrO4 tetrahedra into one-dimensional chains. The CrO4 tetrahedra coordinate uranyl ions in both mono- and bidentate fashion, which is unusual for uranyl chromates. The bidentate coordination has a strong influence upon geometrical parameters of both U and Cr coordination polyhedra. The conformation of the chains in 1 and 2 is different due to the different size of the Cs+ and Rb+ cations.

Siidra, Oleg I.; Nazarchuk, Evgeny V.; Krivovichev, Sergey V.

2012-03-01

25

Density Functional Theory Study of the Complexation of the Uranyl Dication with Anionic Phosphate Ligands with and without Water Molecules  

SciTech Connect

The structures, vibrational frequencies and energetics of anhydrous and hydrated complexes of UO2 2+ with the phosphate anions H2PO4 ?, HPO4 2?, and PO4 3? were predicted at the density functional theory (DFT) and MP2 molecular orbital theory levels as isolated gas phase species and in aqueous solution by using self-consistent reaction field (SCRF) calculations with different solvation models. The geometries and vibrational frequencies of the major binding modes for these complexes are compared to experiment where possible and good agreement is found. The uranyl moiety is nonlinear in many of the complexes, and the coordination number (CN) 5 in the equatorial plane is the predominant binding motif. The phosphates are found to bind in both monodentate and bidentate binding modes depending on the charge and the number of water molecules. The SCRF calculations were done with a variety of approaches, and different SCRF approaches were found to be optimal for different reaction types. The acidities of HxPO4 3?x in HxPO4 3?x(H2O)4, x = 0?3 complexes were calculated with different SCRF models and compared to experiment. Phosphate anions can displace water molecules from the first solvation shell at the uranyl exothermically. The addition of water molecules can cause the bonding of H2PO4 ? and HPO4 2? to change from bidentate to monodentate exothermically while maintaining CN 5. The addition of water can generate monodentate structures capable of cross-linking to other uranyl phosphates to form the types of structures found in the solid state. [UO2(HPO4)(H2O)3] is predicted to be a strong base in the gas phase and in aqueous solution. It is predicted to be a much weaker acid than H3PO4 in the gas phase and in solution.

Jackson, Virgil E.; Gutowski, Keith E.; Dixon, David A.

2013-09-12

26

Coordination Complexes of Cobalt.  

ERIC Educational Resources Information Center

Described is an experiment involving the synthesis and spectral studies of cobalt complexes that not only give general chemistry students an introduction to inorganic synthesis but allows them to conduct a systematic study on the effect of different ligands on absorption spectra. Background information, procedures, and experimental results are

Williams, Gregory M.; And Others

1989-01-01

27

Mixed Ligand Uranyl(VI) Complexes of 2,6-Dipicolinic Acid  

Microsoft Academic Search

The mixed ligand uranyl(VI) complexes of pyridine-2,6-dicarboxylic acid (H2PDC) of the type [UO2(PDC) (N-N)], where N-N stands for a bidentate ligand, such as ethylenediamine, 2,2?-bipyridyl, 1,10-phenanthroline, o- and m-phenylenediamines, have been described. The complexes have been characterised on the basis of elemental analysis, electrical conductance and spectral (infrared and electronic) data.

V. Kumari; S. K. Sahni; S. Kher; R. N. Kapoor

1979-01-01

28

Trace level uranyl complexation with phenylphosphonic acid in aqueous solution: direct speciation by high resolution mass spectrometry.  

PubMed

The complexation of U(VI) by organic P-containing ligands in humic substances (HS) is an important issue of uranyl mobility in soil. We have investigated the complexation of uranyl by a model ligand for aromatic phosphorus functionalities in HS, phenylphosphonic acid, by using ultrahigh resolution electrospray ionization-mass spectrometry (ESI-MS). The high sensitivity permitted to investigate the complexation of trace level uranyl and to explore directly in the native aqueous solutions the nature of the uranyl-phenylphosphonate complexes. Positive identification of the complexes coexisting in solutions with low pH and varying ligand-to-metal ratio was achieved thanks to the high resolving power, high mass accuracy, and reliability of ion abundance of the technique. The positively charged and neutral uranyl species were detected simultaneously on negative ion mass spectra, evidencing formation of three types of U(VI)-phenylphosphonate complexes. Two complexes with a metal-to-ligand stoichiometry of 1:1 (in the monoprotonated and nonprotonated forms) existed in solutions at pH 3-5, and a 1:2 complex was additionally formed at relatively high ligand-to-metal ratio. A strategy based on the use of uranyl-phosphate solution complexes as internal standards was developed to determine from the ESI(-)MS results the stability constants of the complexes, which were calculated to be log K111 = 3.4 0.2 for UO2(HPhPO3)(+), log K101 = 7.1 0.1 for UO2PhPO3, and log K112 = 7.2 0.2 for UO2(HPhPO3)2. The speciation model presented here suggests that organic P existing at low concentration in HS is involved significantly in binding by humic and fulvic acids of trace level uranyl in soil. PMID:23527599

Galindo, Catherine; Del Nero, Mirella

2013-04-15

29

Complex coordinates in transformation optics  

SciTech Connect

We show that complex coordinates used in conjunction with transformation optics offer an extra degree of freedom that allows control over not only the propagation direction of electromagnetic waves but also their amplitude. We illustrate this idea in two applications. First, we show that in an n-dimensional space one can manipulate the field amplitude for up to n different amplitude distributions in regions that are critical to the performance of the device under consideration, and thus reduce the device's sensitivity to design imperfections in these regions. Second, we expand previous work on reflectionless perfectly matched layers and show how complex coordinates and transformation optics are a natural choice for designing perfectly matched layers of arbitrary shape.

Popa, Bogdan-Ioan; Cummer, Steven A. [Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708 (United States)

2011-12-15

30

Citrate Enhanced Uranyl Adsorption on Geothite: An EXAFS Analysis  

SciTech Connect

Citric acid promotes the adsorption of uranyl (U(VI) as UO22+) on goethite (a-FeOOH) at pH=5. Enhanced adsorption does not appear to follow a simple stoichiometric relationship between total citrate and total uranyl. An excess of citric acid relative to uranyl, or a high concentration of surface-bound citrate is required. An extended X-ray absorption fine structure spectroscopy (EXAFS) study was conducted to help understand the surface interactions between citrate, UO22+, and goethite between pH 3.5 and pH 5.5. Two principal surface species were found to be necessary and sufficient to describe the uranyl EXAFS spectra for the range of adsorbed citrate concentrations studied. (The possibility of additional minor surface species has not been eliminated, but inherent uncertainties in the data do not permit their clear identification.) One species is identified as an inner-sphere, uranylgoethite complex, which exists at pH 5.5 in the absence of citrate. A second species is interpreted to be an adsorbed uranyl + citrate complex, which displaces the binary uranylgoethite complex as the concentration of adsorbed citrate increases. The EXAFS spectra from samples with intermediate adsorbed citrate concentrations were reproduced using linear combinations of the spectra from these two end-member species. The uranyl + citrate surface complex appears to dominate adsorbed uranyl speciation at ligand : metal ratios of 10 : 1, or when the total surface-bound citrate approaches saturation. Although the exact structural configuration for the uranyl + citrate surface complex cannot be identified at this time, coordination between uranyl and one or more citrate molecules appears to involve both a bidentate bond (four-membered ring structure) and a putative eight-membered ring structure. The distribution and type of surface species should provide useful constraints on the development of model simulations of surface complexation behavior in this system.

Redden, George Dean; Bargar, J.; Bencheikh-Latmani, R.

2001-12-01

31

Uranyl complexation with selenate at variable temperatures studied by affinity capillary electrophoresis.  

PubMed

The uranyl-selenate system is studied in aqueous acid solutions (pH 2.5) at different values of the ionic strength (from 0.02 to 0.1 molL(-1)) in the temperature range from 15C to 55C by affinity capillary electrophoresis. Hydrodynamic transfer of the sample through the non-thermostated inlet into the thermostated region of capillary is used to avoid the influence of non efficiently thermostated short inlet. The formation of two complex species UO(2)SeO(4) and UO(2)(SeO(4))(2)(2-) is observed. Thermodynamic parameters (the molar Gibbs energy of reaction (?(r)G(m)), the molar enthalpy of reaction (?(r)H(m)) and the molar entropy of reaction (?(r)S(m))) are calculated and extrapolated to zero ionic strength with aid of specific ion interaction theory. Results show that complex species of uranyl with selenate become stronger as the temperature is increased. The complexation is endothermic and entropy-driven, showing typical characteristics of inner-sphere complexation between hard acceptor and hard donor. PMID:23312556

Sladkov, Vladimir

2013-02-01

32

Theoretical analysis and quantification of the absorption spectra of uranyl complexes with structurally-related tridentate ligands.  

PubMed

A semi-empirical model of vibronic coupling was developed in the present work to provide a quantitative analysis of partially resolved vibronic structure in uranyl absorption spectra. The studied uranyl complexes share a similar structure but bear different electric charges in the equatorial ligands. Their optical absorption spectra exhibit the common characteristics of charge transfer vibronic transitions of uranyl complexes but fine structures arising from specific vibrational modes are obscured. Accordingly, in application of the Franck-Condon principle of vibronic coupling, our model takes a mode-degenerate approximation. The absorption spectra of uranyl in various ligand environments were calculated and fitted to the experimental data. The semi-empirical approach enabled quantitative evaluation of the electronic energy levels, vibrational frequencies, and vibronic coupling strength. Moreover, the expansion of the U=O bond in the excited states was calculated from the values of the vibronic coupling parameters determined in simulation of the experimental spectra. The calculated results agree very well with the experimentally observed trends in thermodynamic binding constants and structural parameters. A theoretical interpretation is given to the dependence of the U=O bond expansion on the charges carried by the uranyl ligand complexes. PMID:24026755

Liu, Guokui; Rao, Linfeng; Tian, Guoxin

2013-10-28

33

Multiphoton dissociation of some volatile uranyl complexes. I. The phenomena of reversible and permanent dissociation  

NASA Astrophysics Data System (ADS)

Bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato) dioxo uranium (VI) is stable and volatile at ?120C, particularly with a ligand such as ammonia or trimethyl phosphate, and susceptible to multiphoton dissociation (mpd) via tle uranyl asymmetric vibration at ?950 cm -1. There are two dissociation paths: (i) detachment of the ligand at fluences below 0.2 J cm -2; (ii) permanent dissociation Of UO 2(hfacac) 2 into UO 2F 2 and a furanone C 5F 5O 2H at fluences above 0.6 J cm -2. Ligand detachment appears to be a conventional unimolecular mpd reaction describable by master equations in spite of the remarkably low fluence threshold. Permanent dissociation shows much greater chemical complexity.

Eberhardt, J. E.; Hoare, I. E.; Johnson, D. A.; Knott, R. B.; Pryor, A. W.; Waugh, A. B.

1982-11-01

34

Structure of a uranyl peroxo complex in aqueous solution from first-principles molecular dynamics simulations.  

PubMed

Static ab initio and density-functional computations, as well as Car-Parrinello molecular dynamics simulations in aqueous solution are reported for [UO2(OH)(?(2)-O2)(H2O)2](-) and [UO2(OH)2(?(1)-O2H)(H2O)](-). Whereas the ?(1)-hydroperoxo isomer is found to be more stable than the ?(2)-peroxo form in the gas phase, the order of stability is reversed in explicit bulk solution. Based on free energies from thermodynamic integration (BLYP functional), the peroxo form is favoured by ca. 32 kJ mol(-1) in water. This stabilisation is discussed in terms of the hydration shells about the individual ligands and dipole moments of the complexes in water, and highlights the importance of explicit solute-solvent interactions and bulk solvation for the speciation of uranyl(vi) compounds. PMID:24310370

Bhl, Michael; Sieffert, Nicolas; Wipff, Georges

2014-08-01

35

COPPER(II), NICKEL AND URANYL COMPLEXES OF SOME AMINO ACIDS  

Microsoft Academic Search

The formation constants of copper(II) and nickel complexes of ; hydroxyproline, asparagine and N,Ndimethylglycine have been obtained. The pK\\/; sub 2\\/ of asparagine and the formation constants of its complexes are independeut ; of the optical configanration. The nickel complexes of serine methyl ester and ; glycine methyl ester are equally stable, indicating that the serine ester ; coordinates to

N. C. Li; B. E. Doody; J. M. White

1958-01-01

36

Citrate Enhanced Adsorption of U(VI) on Goethite: Characterization of Uranyl Speciation Using EXAFS  

SciTech Connect

Citric acid promotes the adsorption of uranyl (U(VI) as UO22+) on goethite (a-FeOOH) at pH=5. Enhanced adsorption does not appear to follow a simple stoichiometric relationship between total citrate and total uranyl. An excess of citric acid relative to uranyl, or a high concentration of surface-bound citrate is required. An extended X-ray absorption fine structure spectroscopy (EXAFS) study was conducted to help understand the surface interactions between citrate, UO22+, and goethite between pH 3.5 and pH 5.5. Two principal surface species were found to be necessary and sufficient to describe the uranyl EXAFS spectra for the range of adsorbed citrate concentrations studied. (The possibility of additional minor surface species has not been eliminated, but inherent uncertainties in the data do not permit their clear identification.) One species is identified as an inner-sphere, uranylgoethite complex, which exists at pH 5.5 in the absence of citrate. A second species is interpreted to be an adsorbed uranyl + citrate complex, which displaces the binary uranylgoethite complex as the concentration of adsorbed citrate increases. The EXAFS spectra from samples with intermediate adsorbed citrate concentrations were reproduced using linear combinations of the spectra from these two end-member species. The uranyl + citrate surface complex appears to dominate adsorbed uranyl speciation at ligand : metal ratios of 10 : 1, or when the total surface-bound citrate approaches saturation. Although the exact structural configuration for the uranyl + citrate surface complex cannot be identified at this time, coordination between uranyl and one or more citrate molecules appears to involve both a bidentate bond (four-membered ring structure) and a putative eight-membered ring structure. The distribution and type of surface species should provide useful constraints on the development of model simulations of surface complexation behavior in this system.

Redden, George Dean; Bargar, J.; Bencheikh-Latmani, R.

2001-12-01

37

Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments  

SciTech Connect

Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on the temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.

Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.; Zachara, John M.; Zhu, Weihuang

2013-03-15

38

Structural/electronic properties and reaction energies of a series of mono- and bis-uranyl dihalides equatorially coordinated by N/O ligands.  

PubMed

Monometallic (UO2)(X)2(L)3 (L?=?pyridine (py), X?=?F (1), Cl (2), Br (3) and I (4); L?=?tetrahydrofuran (thf), X?=?Cl (5); L?=?pyrrole (pl), X?=?Cl (6)) as well as bimetallic [(UO2)(?2-X)(X)(L)2]2 (L?=?py, X?=?F (7), Cl (8), Br (9) and I (10); L?=?thf, X?=?Cl (11); L?=?pl, X?=?Cl (12); ? 2?=?doubly bridged) were examined using relativistic density functional theory. With changing from F, Cl, Br to I irregardless of in mono- or bis-uranyl complexes, bond lengths of U?=?O were calculated to be decreasing, resulting from strengthening of axial U?=?O bonds while weakening equatorial X???U coordination. This is further evidenced by calculated bond orders of U?=?O and stretching vibrational frequencies. A similar situation was is found in 2, 5 and 6 as well as in 8, 11 and 12, where N/O ligands are varied but the chlorine atoms are retained. The present study reveals that all these complexes have U(f)-character low-lying unoccupied orbitals, and their ?*(U?=?O) antibonds are located on higher-energy orbitals. Complex 1 was calculated to show ?(U?=?O) bonding character for HOMO, and pyridine-character for other occupied orbitals; the fluorine ligand occurs in a relatively low-energy region. In contrast, the ?(p) characters of heavier halogen atoms significantly contribute to most frontier molecular orbitals of 2, 3 and 4. Unlike this electronic feature of 2, complexes 5 and 6 exhibit mainly thf and pyrrole characters, respectively, for their high-lying occupied orbitals. Electronic structures of bisuranyl complexes 7-12, albeit a little more complicated, are revealed to be similar to those of the corresponding monouranyl complexes. Finally, energies of formation reactions of the above complexes were calculated and compared with available experimental results. PMID:24869781

Yao, Jun; Wang, Yong-Ming; Pan, Qing-Jiang; Guo, Yuan-Ru; Zhang, Hong-Xing

2014-06-01

39

Critical Parameters of Complex Geometries of Intersecting Cylinders Containing Uranyl Nitrate Solution  

SciTech Connect

About three dozen previously unreported critical configurations are presented for very complex geometries filled with high concentration enriched uranyl nitrate solution. These geometries resemble a tall, thin Central Column (or trunk of a ''tree'') having long, thin arms (or ''branches'') extending up to four directions off the column. Arms are equally spaced from one another in vertical planes, and that spacing ranges from arms in contact to quite wide spacings. Both the Central Column and the many different arms are critically safe by themselves with each, alone, is filled with fissile solution; but, in combination, criticality occurs due to the interactions between arms and the column. Such neutronic interactions formed the principal focus of this study. While these results are fresh to the nuclear criticality safety industry and to those seeking novel experiments against which to validate computer codes, the experiments, themselves, are not recent. Over 100 experiments were performed at the Rocky Flats Critical Mass Laboratory between September, 1967, and February of the following year.

J. B. Briggs (INEEL POC); R. E. Rothe

1999-06-14

40

Free energy study of uranyl complexes across water-oil and water-oil+tri-butyl phosphate (TBP) interfaces  

NASA Astrophysics Data System (ADS)

Free energy profiles of heavy metal ion complexes, UO2 (NO3)2, UO2 (NO3)2TBP2, and TBP, across the water-hexane and water hexane+TBP (50%/50%) interfaces, were calculated from molecular dynamics simulations. These complexes and interfaces are relevant to recently developed heavy-ion separation techniques. The solute complex with TBP, UO2 (NO3)2TBP2, shows strong interfacial activity in contrast to the free energy barrier for UO2 (NO3)2 at the water-hexane interface. Increased TBP concentration in the oil phase reduces the interfacial activity and better solvates the ion complexes and their ligands. The solute complex with TBP oriented parallel to the water-hexane+TBP interface binds more strongly to the hexane+TBP phase than to the pure hexane phase. The (un-complexed) TBP orientational probability distribution shows the polar head buried in water, while the nonpolar tails are buried in the oil phase, and hence TBP exhibits interfacial activity. The calculated density profiles at the interface show that TBP acts not only as a carrier for uranyl transport across the interface, but also as an ``interface modifier''. Our simulation results are in agreement with the recent study of uranyl transport across chemically modified membranes with TBP based metal ion carriers.

Jayasinghe, Manori; Beck, Thomas L.

2007-03-01

41

COMPLEXANTS FOR ACTINIDE ELEMENT COORDINATION AND IMMOBILIZATION  

EPA Science Inventory

We propose that inorganic clusters known as polyoxoanions (POAs) can be exploited as complexants for actinide (An) ion coordination and immobilization. Our objective is to develop rugged, stoichiometrically well-defined POAs that act as molecular containers of An elements. Poly...

42

Uranyl complexes with diamide ligands: a quantum mechanics study of chelating properties in the gas phase.  

PubMed

We report a quantum mechanical study on the complexes of UO(2)(2+) with diamide ligands L of malonamide and succinamide type, respectively, forming 6- and 7-chelate rings in their bidentate coordination to uranium. The main aims are to (i) assess how strong the chelate effect is (i.e., the preference for bi- versus monodentate binding modes of L), (ii) compare these ligands as a function of the chelate ring size, and (iii) assess the role of neutralizing counterions. For this purpose, we consider UO(2)L(2+), UO(2)L(2)(2+), UO(2)L(3)(2+), and UO(2)X(2)L type complexes with X(-) = Cl(-) versus NO(3)(-). Hartree-Fock and DFT calculations lead to similar trends and reveal the importance of saturation and steric repulsions ("strain") in the first coordination sphere. In the unsaturated UO(2)L(2+), UO(2)L(2)(2+), and UO(2)Cl(2)L complexes, the 7-ring chelate is preferred over the 6-ring chelate, and bidentate coordination is preferred over the monodentate one. However, in the saturated UO(2)(NO(3))(2)L complexes, the 6- and 7-chelating ligands have similar binding energies, and for a given ligand, the mono- and bidentate binding modes are quasi-isoenergetic. These conclusions are confirmed by the calculations of free energies of complexation in the gas phase. In condensed phases, the monodentate form of UO(2)X(2)L complexes should be further stabilized by coordination of additional ligands, as well as by interactions (e.g., hydrogen bonding) of the "free" carbonyl oxygen, leading to an enthalpic preference for this form, compared to the bidentate one. We also considered an isodesmic reaction exchanging one bidentate ligand L with two monoamide analogues, which reveals that the latter are clearly preferred (by 23-14 kcal/mol at the HF level and 24-12 kcal/mol at the DFT level). Thus, in the gas phase, the studied bidentate ligands are enthalpically disfavored, compared to bis-monodentate analogues. The contrast with trends observed in solution hints at the importance of "long range" forces (e.g., second shell interactions) and entropy effects on the chelate effect in condensed phases. PMID:12767210

Coupez, Bernard; Wipff, Georges

2003-06-01

43

3D-supermolecular structure and electronic absorption of uranyl ?-diketone [UO 2(tfa) 2(L)] (L = H 2O, OHCH 2CH 3) complex  

NASA Astrophysics Data System (ADS)

Uranyl ?-diketone complex UO 2(tfa) 2H 2O ( 3) (tfa = deprotonated 4,4,4,-trifluoro-1-(2-furyl)-1,3-butanedione) has been successfully prepared by reacting UO 2(OAc) 22H 2O (OAc = O 2CMe) with two equivalents of 4,4,4,-trifluoro-1-(2-furyl)-1,3-butanedione ( H-tfa: 1) in ethanol. Complex 3 was characterized by elemental analysis and FT-IR. Dissolving 3 in ethanol gave during several days single crystals of [UO 2(tfa) 2(OHCH 2CH 3)] ( 4), wherein one ethanol molecule replaces aqua ligand. The solid-state structure of 4 was determined by a single X-ray analysis. Crystal data of C 18H 14F 6O 9U: a = 13.7163(7), b = 20.7528(10), c = 7.4664(4) , ? = 90.818(4), space group P2(1)/c, Z = 4 and dcalc = 2.270 mg/m 3. Complex 4 adopted a distorted pentagonal bipyramidal geometry. The coordinated oxygen atoms of tfa ( deprotonated- 1) ligands are occupying equatorial positions, while the oxygen atoms of UO22+ are still in the axial positions. The formation of the ?-? interactions together with hydrogen bonded result in the set up a 3D-supramolecular architecture. The electronic absorption of 3 is reported and discussed.

Al-Anber, Mohammed A.; Daoud, Haneen M.; Rffer, Tobias; Lang, Heinrich

2011-06-01

44

The Complexes of Bisphosphonate and Magnetite Nanoparticles to Remove Uranyl Ions from Aqueous Phase  

SciTech Connect

Using tetraethyl-3-amino-propane-1,1-bisphosphonate (BP) as the functional molecule, we functionalized Fe3O4 magnetic nanoparticles via dopamine (DA) linkage to create a system with an Fe3O4-DA-BP nanostructure, which possesses high specificity for removing uranyl ions from water or blood. This work demonstrates that magnetic nanoparticles, combined with specific receptor-ligand interactions, promise a sensitive and rapid platform for the detection, recovery, and decorporation of radioactive metal toxins from biological environment.

Wang, L.; Yang, Z.; Gao, J.; Xu, K.; Gu, H.; Xu, B. [Department of Chemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China); Zhang, B.; Zhang, X. [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China)

2007-03-20

45

Homoleptic pnictogen-chalcogen coordination complexes.  

PubMed

The synthesis and structural characterization of dicationic selenium and tellurium analogues of the carbodiphosphorane and triphosphenium families of compounds are reported. These complexes, [Ch(dppe)][OTf](2) [Ch = Se, Te; dppe = 1,2-bis(diphenylphosphino)ethane; OTf = trifluoromethanesulfonate], are formed using [Ch](2+) reagents via a ligand-exchange protocol and represent extremely rare examples of homoleptic pnictogen ? chalcogen coordination complexes. The corresponding arsenic compounds were also prepared, [Ch(dpAse)][OTf](2) [Ch = Se, Te; dpAse = 1,2-bis(diphenylarsino)ethane], exhibiting the first instance of an arsenic ? chalcogen dative bond. The electronic structures of these unique compounds were determined and compared to previously reported chalcogen dications. PMID:22839766

Dube, Jonathan W; Hnninen, Mikko M; Dutton, Jason L; Tuononen, Heikki M; Ragogna, Paul J

2012-08-20

46

Effect of the TBP and water on the complexation of uranyl nitrate and the dissolution of nitric acid into supercritical CO2. A Theoretical Study.  

PubMed

We report theoretical studies on the complexation of uranyl nitrate and the dissolution of nitric acid in supercritical CO2 by TBP. According to quantum mechanical calculations, TBP (modeled by trimethyl phosphate TMP) displays stronger hydrogen-bonding interactions with HNO3 than with H2O, and this has been modeled in force-field calculations. Different combinations of water, TBP, and acid are compared in SC-CO2 and simulated by molecular dynamics (MD), demonstrating the importance of TBP and water concentrations. In MD simulations, which started from "random" mixtures of water, TBP, nitric acid, and uranyl nitrate, complexation of uranyl by TBP is observed and the yield increases with the TBP concentration. TBP molecules are also necessary to dissolve nitric acid in the supercritical phase. Indeed, without TBP, nitric acid alone self aggregates via hydrogen-bonding interactions. Adding water to this solution leads to the formation of water microdomains containing the acid and uranyl salts. The simulations show that a high TBP/nitric acid ratio is needed to fully dissolve the acid in the supercritical phase and to form CO2-philic UO2(NO3)2(TBP)2 complexes. The resulting hydrogen-bonding and solvation patterns are analyzed. The results are consistent with experimental observations and provide microscopic views of this important extraction system. PMID:16833878

Schurhammer, R; Wipff, G

2005-06-16

47

Coordination equilibria between seven- and five-coordinate iron(II) complexes.  

PubMed

Octahedral, tetrahedral, and square planar geometries are the most often encountered coordination geometries for transition metal complexes. In certain cases, coordination equilibria can exist between different geometries, such as between six- and four-coordinate geometries in nickel(II) complexes, which were discovered half a century ago. Here, we present the first examples of a seven-five coordination equilibrium. Extensive spectroscopic studies in solution have provided evidence for a dynamic equilibrium between two iron(II) complexes, one with a seven-coordinate pentagonal bipyramidal geometry and one with a five-coordinate trigonal bipyramidal geometry. PMID:24111485

Grau, Michaela; England, Jason; Torres Martin de Rosales, Rafael; Rzepa, Henry S; White, Andrew J P; Britovsek, George J P

2013-10-21

48

Structural and electrochemical studies on uranyl(VI) complex with pentadentate Schiff base ligand: A guide to stable uranyl(V)  

NASA Astrophysics Data System (ADS)

A U(VI) complex with N,N'-disalicylidenediethylenetriaminate (saldien2-) was characterized by single crystal X-ray analysis and X-ray absorption fine structure (XAFS) spectroscopy, and its electrochemical behavior in a DMSO solution was studied. The obtained U(VI)-saldien2- complex recrystallized from DMSO was identified as orthorhombic UVIO2(saldien)DMSO. All coordination sites in the equatorial plane of UO22+ are occupied by coordinating O and N atoms of saldien2-. Comparing a k3-weighted U LIII-edge EXAFS spectra of UVIO2(saldien) in DMSO and DMF solutions with that in solid state, the molecular structure of UVIO2(saldien) remains even in the solutions. Quasi-reversible redox waves of UVIO2(saldien) were observed at E' = -1.582 0.005 V vs. Fc/Fc+ (?Ep = 0.080-0.170 V at v = 0.010-0.500 Vs-1) in DMSO. UV-Vis-NIR absorption spectral change with the electrochemical reduction of UVIO2(saldien) using the spectroelectrochemical technique shows isosbestic points clearly, indicating that the electrochemical reaction of UVIO2(saldien) is only present. Using the absorbance change and the Nernstian equation, the electron stoichiometry in the reduction of UVIO2(saldien) in DMSO was determined as 0.929. This quantity close to unity reveals a redox reaction, UVIO2(saldien) + e- = [UVO2(saldien)]-, i.e., UVIO2(saldien) without unidentate ligands results in the stable U(V) complex, [UVO2(saldien)]-, in DMSO. This U(V) species also shows the characteristic absorption bands of U(V) at 630, 700, 830, 1390, and 1890 nm as well as other U(V) complexes.

Takao, Koichiro; Kato, Masaru; Takao, Shinobu; Nagasawa, Akira; Scheinost, Andreas C.; Bernhard, Gert; Hennig, Christoph; Ikeda, Yasuhisa

2010-03-01

49

Polytypism and oxo-tungstate polyhedra polymerization in novel complex uranyl tungstates.  

PubMed

Three new uranyl tungstates, ?-, ?-Cs(2)[(UO(2))(2)(W(2)O(9))], and Rb(6)[(UO(2))(7)(WO(5))(2)(W(3)O(13))O(2)], have been obtained by high temperature solid state reactions. All three compounds display novel structure topologies: ?- and ?-Cs(2)[(UO(2))(2)(W(2)O(9))] are based upon layers with a new topology that can be related to the uranophane topology; Rb(6)[(UO(2))(7)(WO(5))(2)(W(3)O(13))O(2)] is a rare example of a non-molecular inorganic phase with layers containing oxo-tungstate trimers. The structural relationship between ?- and ?-Cs(2)[(UO(2))(2)(W(2)O(9))] can be assigned to polytypism. PMID:22710950

Seliverstov, Andrey N; Suleimanov, Evgeny V; Chuprunov, Evgeny V; Somov, Nikolay V; Zhuchkova, Elena M; Lelet, Maxim I; Rozov, Konstantin B; Depmeier, Wulf; Krivovichev, Sergey V; Alekseev, Evgeny V

2012-07-28

50

Uranium dioxide in ionic liquid with a tri-n-butylphosphate-HNO3 complex--dissolution and coordination environment.  

PubMed

Uranium dioxide can be dissolved directly in an imidazolium-based ionic liquid (IL) at room temperature with a tri-n-butylphosphate(TBP)-HNO(3) complex. The dissolution process follows pseudo first-order kinetics initially. Raman spectroscopic studies show the dissolved uranyl ions are coordinated with TBP in the IL phase with a molar ratio of (UO(2))(2+) : TBP = 1 : 2. The dissolved uranyl species can be effectively transferred to a supercritical fluid carbon dioxide (sc-CO(2)) phase. No aqueous phase is formed in either the IL dissolution or the supercritical fluid extraction process. Absorption spectra of the extracted uranyl species in the sc-CO(2) phase suggests the presence of a UO(2)(TBP)(2)(NO(3))(2) and HNO(3) adduct probably of the form UO(2)(TBP)(2)(NO(3))(2)HNO(3). The adduct dissociates in a water-dodecane trap solution during pressure reduction resulting in UO(2)(TBP)(2)(NO(3))(2) collected in the dodecane phase. PMID:21445434

Wai, Chien M; Liao, Yu-Jung; Liao, Weisheng; Tian, Guoxin; Addleman, Raymond S; Quach, Donna; Pasilis, Sofie P

2011-05-14

51

Synthesis, structure, and thermolysis of compounds of uranyl acetate with some amides  

SciTech Connect

The present investigation was devoted to studying the changes in the structure of the intial uranyl carboxylate UO/sub 2/(CH/sub 3/COO)/sub 2/.2H/sub 2/O connected with the introduction of neutral nitrogen-containing ligands into the coordination sphere of the uranyl group, and also the nature of the coordination and the composition of the additional ligands on the course of the thermal decomposition of the complex. Complex compounds of uranyl acetate with dimethylacetamide and urea that have been described previously have been synthesized. On the basis of x-ray structural results the following formulas have been established for the compounds obtained: (UO/sub 2/(CH/sub 3/COO)/sub 2/.DMAA)/sub 2/ and (UO/sub 2/(CH/sub 3/COO)Ur/sub 3/)(UO/sub 2/(CH/sub 3/COO)/sub 3/). As the result of thermal analysis (polythermal and isothermal conditions) of bisdiacetato(dimethylacetamide)uranyl (VI) and the acetatoureauranyl(VI) triacetatodioxouranate(VI) it has been shown that the course of the thermal decomposition of the amide complexes of uranyl acetate, and also the composition of the oxide formed in this process are determined by the presence of the H atoms in the amide grouping which participate in the formation of hydrogen bonds in the compounds and lead to an increased mobility of the nitrogen atoms.

Spitysn, V.I.; Kolesnik, V.V.; Mistryukov, V.E.; Yuranov, I.A.; Mikhailov, Y.N.; Dunaeva, K.M.

1982-04-01

52

Gas-Phase Coordination Complexes of UVIO{2/2+}, NpVIO{2/2+}, and PuVIO{2/2+} with Dimethylformamide  

NASA Astrophysics Data System (ADS)

Electrospray ionization of actinyl perchlorate solutions in H2O with 5% by volume of dimethylformamide (DMF) produced the isolatable gas-phase complexes, [AnVIO2(DMF)3(H2O)]2+ and [AnVIO2(DMF)4]2+, where An = U, Np, and Pu. Collision-induced dissociation confirmed the composition of the dipositive coordination complexes, and produced doubly- and singly-charged fragment ions. The fragmentation products reveal differences in underlying chemistries of uranyl, neptunyl, and plutonyl, including the lower stability of Np(VI) and Pu(VI) compared with U(VI).

Rutkowski, Philip X.; Rios, Daniel; Gibson, John K.; van Stipdonk, Michael J.

2011-11-01

53

The synthesis and characterization of new iron coordination complexes utilizing an asymmetric coordinating chelate ligand  

SciTech Connect

A binuclear, unsymmetric coordinating ligand that is an effective metal chelator has been designed and synthesized. The new ligand has been shown to react readily with iron(II)/(III) forming a variety of coordination complexes. The binuclear complexes are of significant interest since they represent proof-of-principle for the development of coordinatively asymmetric, binuclear metal chelate compounds. Although this structural type of chelator now appears to be common in biological systems, it has not been previously described for inorganic coordination chemistry. The isolation of oxidation products will be helpful in establishing reaction mechanism(s) of these complexes with molecular oxygen. It is expected that this ligand and derivatives of it will play an important role in the development of bioinorganic complexes that aim to mimic enzyme active sites that function by substrate interaction at only one metal site of a multimetal active site.

Watkins, B.E.; Satcher, J.H.

1995-07-01

54

Development and Application of an Assay for Uranyl Complexation by Fungal Metabolites, Including Siderophores  

Microsoft Academic Search

An assay to detect UO2 2 complexation was developed based on the chrome azurol S (CAS) assay for siderophores (B. Schwyn and J. B. Neilands, Anal. Biochem. 160:47-56, 1987) and was used to investigate the ability of fungal metabolites to complex actinides. In this assay the discoloration of two dyed agars (one containing a CAS-Fe3 dye and the other containing

Joanna C. Renshaw; Verity Halliday; Geoffrey D. Robson; Anthony P. J. Trinci; Marilyn G. Wiebe; Francis R. Livens; David Collison; Robin J. Taylor

2003-01-01

55

A low complexity demodulator for coordinate interleaved modulation schemes  

Microsoft Academic Search

This paper discusses techniques to reduce the demodulation complexity at the receiver of systems that use coordinate interleaving (CI) with N2-QAM constellations. CI is a method used to increase the diversity order of any modulation scheme on fading channels, but has a high demodulation complexity. The techniques described reduce the complexity required to calculate the maximum likelihood and log likelihood

G. Anand Srinivas; D. N. Rohith; M. Z. Ali Khan

2008-01-01

56

QM/MM study of aqueous solvation of the uranyl fluoride [UO2F4(2-)] complex.  

PubMed

The aqueous solvation of the uranylfluoride complex [UO(2)F(4) (2-)] was studied using full quantum mechanical (QM) and hybrid QM/molecular mechanics (MM) methods. Inclusion of a complete first solvation shell was found necessary to reproduce the experimentally observed heptacoordination of uranium. An efficient and accurate computational model is proposed that consists of structure optimization of the coordinated uranium complex as QM region, followed by single-point full QM calculations to compute relative energies. This method is proven feasible for studies of large solvated actinide complexes. PMID:14696073

Infante, Ivan; Visscher, Lucas

2004-02-01

57

Structural and thermal characterization of ternary complexes of piroxicam and alanine with transition metals: Uranyl binary and ternary complexes of piroxicam. Spectroscopic characterization and properties of metal complexes  

NASA Astrophysics Data System (ADS)

Ternary Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO 2(II) complexes with piroxicam (Pir) drug (H 2L 1) and dl-alanine (Ala) (HL 2) and also the binary UO 2(II) complex with Pir were studied. The structures of the complexes were elucidated using elemental, IR, molar conductance, magnetic moment, diffused reflectance and thermal analyses. The UO 2(II) binary complex was isolated in 1:2 ratio with the formula [UO 2(H 2L) 2](NO 3) 2. The ternary complexes were isolated in 1:1:1 (M:H 2L 1:L 2) ratios. The solid complexes were isolated in the general formulae [M(H 2L)(L 2)(Cl) n(H 2O) m] yH 2O (M = Fe(III) ( n = 2, m = 0, y = 1), Co(II) ( n = 1, m = 1, y = 2) and Ni(II) ( n = 1, m = 1, y = 0)); [M(H 2L)(L 2)](X) z yH 2O (M = Cu(II) (X = AcO, z = 1, y = 0), Zn(II) (X = AcO, z = 1, y = 3) and UO 2(II) (X = NO 3, z = 1, y = 2)). Pir behaves as a neutral bidentate ligand coordinated to the metal ions via the pyridine-N and carbonyl-O groups, while Ala behaves as a uninegatively bidentate ligand coordinated to the metal ions via the deprotonated carboxylate-O and amino-N. The magnetic and reflectance spectral data show that the complexes have octahedral geometry except Cu(II) and Zn(II) complexes have tetrahedral structures. The thermal decomposition of the complexes was discussed in relation to structure, and the thermodynamic parameters of the decomposition stages were evaluated.

Mohamed, Gehad G.

2005-12-01

58

SYNTHESIS, CHARACTERIZATION, AND STRUCTURE OF A URANYL COMPLEX WITH A DISULFIDE LIGAND, BIS(DI-n-PROPYLAMMONIUM) DISULFIDOBIS (DI-n-PROPYLMONOTHIOCARBAMATO) DIOXOURANATE(VI)  

SciTech Connect

Olive-green crystals of the title compound, [({underline n}-C{sub 3}H{sub 7}){sub 2}NH{sub 2}{sup +}]{sub 2} [UO(({underline n}-C{sub 3}H{sub 7}){sub 2}NCOS){sub 2}(S{sub 2}){sup -2}, are orthorhombic, space group Pcan, with {underline a}= 15.326(6) {Angstrom}, {underline b} = 17.474(6) {Angstrom}, {underline C} = 14.728(6) {Angstrom}, and Z = 4, (d{sub X} = 1.45 g/cm{sup 3}). For 1833 data, I >{sigma}, R = 0.052, and R{sub w} = 0.069. The structure was revealed by single-crystal x-ray diffraction studies to consist of [(n-C{sub 3}H{sub 7}){sub 2}NH{sub 2}]+ cations and [UO{sub 2}(({underline n|-C{sub 3}H{sub 7}){sub 2}NCOS){sub 2}(S{sub 2}){sup -2} anions with the uranium atom at the center of an irregular hexagonal bipyramid. The uranyl oxygen atoms occupy the axial positions. The equatorial coordination plane contains the disulfide (S{sub 2}{sup -2}) group bonded in a "side-on" fashion, and two oxygen and two sulfur donor atoms from the monothiocarbamate ligands. Interatomic distances are S-S = 2.05(1) {Angstrom}, U-S= 2.714(3) {Angstrom} (disulfide); U-S= 2.871(3) {Angstrom} and U-O = 2.46(1) {Angstrom} (thiocarbamate); U-O = 1.81(1) {Angstrom} (uranyl), The nitrogen atom in the dipropylammonium cation is hydrogen bonded to the uranyl oxgyen atoms,

Perry, Dale L.; Zalkin, Allan; Ruben, Helena; Templeton, David H.

1981-05-01

59

Photoconversion and photocatalytic activity of uranyl in acetone solutions  

NASA Astrophysics Data System (ADS)

We have studied the effect of irradiation on the uranyl nitrate acetone and uranyl perchlorate acetone systems. We have established that when the uranyl perchlorate acetone system is irradiated, polymerization of the acetone occurs and the catalyst for the process is excited uranyl complexes. In the polymer, uranium is found in the form of nanoclusters of pentavalent and tetravalent uranium, formed as a result of photochemical reactions. Polymerization does not occur in the uranyl nitrate acetone system. We consider possible factors responsible for the noted differences.

Zazhogin, A. P.; Zazhogin, A. A.; Komyak, A. I.; Umreiko, D. S.

2007-09-01

60

Behavior of formylphenol derivative complexes of uranyl ion in alcoholic media  

SciTech Connect

The reaction of 2,6-diformyl-4-methylphenol, H(MDA), with boiling ethanol yields the acetalated species 2-diethylacetal-4-methyl-6-formylphenol, H(EAC). Consequently the dioxouranium(VI) complexes (UO/sub 2/(EAC)/sub 2/) and ((C/sub 2/H/sub 5/O)/sub 2/CH-OC/sub 6/H/sub 2/CH/sub 3/-HC=N(CH/sub 2/))/sub 2/XUO/sub 2/ /X = NH, (UO/sub 2/(NEAC)); X = S, (UO/sub 2/(SEAC)/ have been isolated. When condensation is carried out in boiling methanol, the complex ((CH/sub 3/O)/sub 2/CH-OC/sub 6/H/sub 2/CH/sub 3/-HC=N(CH/sub 2/)/sub 2/)/sub 2/NHUO/sub 2/, (UO/sub 2/(NMAC)), is obtained. The compounds bearing the NH group in the chain under substitution of one of the acetal groups with the formyl group, yielding the species (Y/sub 2/CH-OC/sub 6/H/sub 2/CH/sub 3/-HC=N(CH/sub 2/)/sub 2/-NH-N(CH/sub 2/)/sub 2/-NH-N(CH/sub 2/)/sub 2/=CH-CH/sub 3/C/sub 6/H/sub 2/O-CHO) UO/sub 2/(Y=OEt and OMe). Ligands and complexes have been characterized by infrared, /sup 1/H and /sup 13/C NMR spectroscopy and by thermogravimetric measurements.

Sitran, S.; Fregona, D.; Faraglia, G.

1988-01-01

61

Colloidal nanocrystals fluoresced by surface coordination complexes.  

PubMed

Colloidal Nanocrystals (NCs) with fluorescence originating from surface complexes are successfully prepared. The components of these NCs range from insulator, semiconductor to metal, with either pure phase, doped or core/shell structures. The photoluminescence of these NCs can be reversibly tuned across the visible to infrared spectrum, and even allow multi-color emission. A light emitting device is fabricated and a new in vivo cell imaging method is performed to demonstrate the power of this technology for emerging applications. PMID:24970242

Wang, Guan; Ji, Jianwei; Zhang, Xinwen; Zhang, Yan; Wang, Qiangbin; You, Xiaozeng; Xu, Xiangxing

2014-01-01

62

Colloidal Nanocrystals Fluoresced by Surface Coordination Complexes  

PubMed Central

Colloidal Nanocrystals (NCs) with fluorescence originating from surface complexes are successfully prepared. The components of these NCs range from insulator, semiconductor to metal, with either pure phase, doped or core/shell structures. The photoluminescence of these NCs can be reversibly tuned across the visible to infrared spectrum, and even allow multi-color emission. A light emitting device is fabricated and a new in vivo cell imaging method is performed to demonstrate the power of this technology for emerging applications.

Wang, Guan; Ji, Jianwei; Zhang, Xinwen; Zhang, Yan; Wang, Qiangbin; You, Xiaozeng; Xu, Xiangxing

2014-01-01

63

Development and Application of an Assay for Uranyl Complexation by Fungal Metabolites, Including Siderophores  

PubMed Central

An assay to detect UO22+ complexation was developed based on the chrome azurol S (CAS) assay for siderophores (B. Schwyn and J. B. Neilands, Anal. Biochem. 160:47-56, 1987) and was used to investigate the ability of fungal metabolites to complex actinides. In this assay the discoloration of two dyed agars (one containing a CAS-Fe3+ dye and the other containing a CAS-UO22+ dye) caused by ligands was quantified. The assay was tested by using the siderophore desferrioxamine B (DFO), and the results showed that there was a regular, reproducible relationship between discoloration and the amount of siderophore added. The ratio of the discoloration on the CAS-UO22+ agar to the discoloration on the CAS-Fe3+ agar was independent of the amount of siderophore added. A total of 113 fungi and yeasts were isolated from three soil samples taken from the Peak District National Park. The fungi were screened for the production of UO22+ chelators by using the CAS-based assay and were also tested specifically for hydroxamate siderophore production by using the hydroxamate siderophore auxotroph Aureobacterium flavescens JG-9. This organism is highly sensitive to the presence of hydroxamate siderophores. However, the CAS-based assay was found to be less sensitive than the A. flavescens JG-9 assay. No significant difference between the results for each site for the two tests was found. Three isolates were selected for further study and were identified as two Pencillium species and a Mucor species. Our results show that the new assay can be effectively used to screen fungi for the production of UO22+ chelating ligands. We suggest that hydroxamate siderophores can be produced by mucoraceous fungi.

Renshaw, Joanna C.; Halliday, Verity; Robson, Geoffrey D.; Trinci, Anthony P. J.; Wiebe, Marilyn G.; Livens, Francis R.; Collison, David; Taylor, Robin J.

2003-01-01

64

Uranyl peroxide oxalate cage and core-shell clusters containing 50 and 120 uranyl ions.  

PubMed

Cage clusters built from uranyl hexagonal bipyramids and oxalate ligands crystallize from slightly acidic aqueous solution under ambient conditions, facilitating structure analysis. Each cluster contains uranyl ions coordinated by peroxo ligands in a bidentate configuration. Uranyl ions are bridged by shared peroxo ligands, oxalate ligands, or through hydroxyl groups. U(50)Ox(20) contains 50 uranyl ions and 20 oxalate groups and is a topological derivative of the U(50) cage cluster that has a fullerene topology. U(120)Ox(90) contains 120 uranyl ions and 90 oxalate groups and is the largest and highest mass cluster containing uranyl ions that has been reported. It has a core-shell structure, in which the inner shell (core) consists of a cluster of 60 uranyl ions and 30 oxalate groups, identical to U(60)Ox(30), with a fullerene topology. The outer shell contains 12 identical units that each consist of five uranyl hexagonal bipyramids that are linked to form a ring (topological pentagon), with each uranyl ion also coordinated by a side-on nonbridging oxalate group. The five-membered rings of the inner and outer shells (the topological pentagons) are in correspondence and are linked through K cations. The inner shell topology has therefore templated the location of the outer shell rings, and the K counterions assume a structure-directing role. Small-angle X-ray scattering data demonstrated U(50)Ox(20) remains intact in aqueous solution upon dissolution. In the case of clusters of U(120)Ox(90), the scattering data for dissolved crystals indicates the U(60)Ox(30) core persists in solution, although the outer rings of uranyl bipyramids contained in the U(120)Ox(90) core-shell cluster appear to detach from the cluster when crystals are dissolved in water. PMID:22296269

Ling, Jie; Qiu, Jie; Burns, Peter C

2012-02-20

65

The application of novel hydrophobic ionic liquids to the extraction of uranium(VI) from nitric acid medium and a determination of the uranyl complexes formed.  

PubMed

Novel ammonium based hydrophobic ionic liquids (ILs) have been synthesised and characterised, and their use in the liquid-liquid extraction of uranium(VI) from an aqueous nitric acid solution using tri-n-butyl phosphate (TBP), studied. On varying the nitric acid concentration, each IL was found to give markedly different results. Relatively hydrophilic ILs showed high uranium(VI) extractability at 0.01 M nitric acid solution which progressively decreased from 0.01 to 2 M HNO(3) and then increased again as the nitric acid concentration was increased to 6 M. An analysis of the mechanisms involved for one such IL, pointed to cationic-exchange being the predominant route at low nitric acid concentrations whilst at high nitric acid concentrations, anionic-exchange predominated. Strongly hydrophobic ILs showed low extractability for nitric acid concentrations below 0.1 M but increasing extractability from 0.1 M to 6 M nitric acid. The predominant mechanism in this case involved the partitioning of a neutral uranyl complex. The uranyl complexes were found to be UO(2)(2+)(TBP)(3) for the cationic exchange mechanism, UO(2)(NO(3))(2)(TBP)(2) for the neutral mechanism and UO(2)(NO(3))(3)(-)(TBP) for the anionic exchange mechanism. PMID:21887434

Bell, Thomas James; Ikeda, Yasuhisa

2011-10-21

66

The Reactivity Patterns of Low-Coordinate Iron Hydride Complexes  

PubMed Central

We report a survey of the reactivity of the first isolable iron-hydride complexes with a coordination number less than five. The high-spin iron(II) complexes [(?-diketiminate)Fe(?-H)]2 react rapidly with representative cyanide, isocyanide, alkyne, N2, alkene, diazene, azide, CO2, carbodiimide and Brnsted acid containing substrates. The reaction outcomes fall into three categories: (1) addition of Fe-H across a multiple bond of the substrate, (2) reductive elimination of H2 to form iron(I) products, and (3) protonation of the hydride to form iron(II) products. The products include imide, isocyanide, vinyl, alkyl, azide, triazenido, benzo[c]cinnoline, amidinate, formate, and hydroxo complexes. These results expand the range of known bond transformations at iron complexes. Additionally, they give insight into the elementary transformations that may be possible at the iron-molybdenum cofactor of nitrogenases, which may have hydride ligands on high-spin, low coordinate metal atoms.

Yu, Ying; Sadique, Azwana R.; Smith, Jeremy M.; Dugan, Thomas R.; Cowley, Ryan E.; Brennessel, William W.; Flaschenriem, Christine J.; Bill, Eckhard; Cundari, Thomas R.; Holland, Patrick L.

2008-01-01

67

Two-Electron Three-Centered Bond in Side-On (?2) Uranyl(V) Superoxo Complexes  

SciTech Connect

Mononuclear dioxygen-metal compounds, such as FeO2 complexes with Schiff base and porphyrin ligands, play an essential role in chemistry ranging from oxyhemoglobin to cytochrome P-450 and cytochrome oxidase. It is well known that the superoxo complexes involved in these systems have end-on (?1) coordination geometries with OO bond lengths of ~1.30 , FeOO bond angles of ~135o, and vibrational frequencies of ~1150 cm-1,1 which reflects a formal change of the oxidation state from Mn+ to Mn+1. In addition, there are side-on (?2) peroxospecies, such as [Fe(porphyrin)(O2)], in which the OO bond lengths is ~1.46 and vibrational frequencies of ~820 cm-1.1 These reflect a formal change of the oxidation state from Mn+ to Mn+2.

Bryantsev, Vyacheslav; De Jong, Wibe A.; Cossel, Kevin C.; Diallo, Mamadou S.; Goddard III, W. A.; Groenewold, G. S.; Chien, Winnie; Van Stipdonk, Michael J.

2008-06-10

68

Coordination complexes in conducting and magnetic molecular materials  

Microsoft Academic Search

In this paper we present organicinorganic molecular materials investigated in our group during the last decade. These materials result from the chemical and electrochemical molecular assemblies of coordination complexes such as tetracyanometallates, hexacyanometallates, metal bis-(dithiolates), metal bis-(dithiolenes), metallocenium complexes and polyoxometalates and organic precursors such as TTF and BEDT-TTF derivatives and paramagnetic nitronyl nitroxide radicals. Taking advantage of the fascinating

Lahcne Ouahab

1998-01-01

69

Memory for Negation in Coordinate and Complex Sentences  

ERIC Educational Resources Information Center

Two experiments were run to test memory for the negation morpheme "not" in coordinate sentences (e.g., The ballerina had twins and the policewoman did not have triplets) and complex sentences (e.g., The ghost scared Hamlet into not murdering Shakespeare). (Editor)

Harris, Richard J.

1976-01-01

70

Coordinating complex problem-solving among distributed intelligent agents  

NASA Technical Reports Server (NTRS)

A process-oriented control model is described for distributed problem solving. The model coordinates the transfer and manipulation of information across independent networked applications, both intelligent and conventional. The model was implemented using SOCIAL, a set of object-oriented tools for distributing computing. Complex sequences of distributed tasks are specified in terms of high level scripts. Scripts are executed by SOCIAL objects called Manager Agents, which realize an intelligent coordination model that routes individual tasks to suitable server applications across the network. These tools are illustrated in a prototype distributed system for decision support of ground operations for NASA's Space Shuttle fleet.

Adler, Richard M.

1992-01-01

71

The synthesis and characterization of new iron coordination complexes utilizing an asymmetric coordinating chelate ligand  

SciTech Connect

We are investigating the structure/activity relationships of the bacterial enzyme methane monooxygenase, which catalyzes the specific oxidation of methane to methanol. We then utilize this information to design and synthesize inorganic coordination complexes that mimic the function of the native enzyme but are more robust and have higher catalytic site density. We envision these catalysts to be useful in process catalytic reactors in the conversion of methane in natural gas to liquid ethanol.

Watkins, B.E.; Satcher, J.H.

1995-03-01

72

Composition and structure of complexes formed in the reaction of uranyl di(2-ethylhexyl)phosphate and tributyl phosphate or di-n-octyl sulfoxide in benzene solutions  

SciTech Connect

This paper reports on {sup 31}P NMR and IR studies of the interaction of tributyl phosphate (TBP) and di-n-octyl sulfoxide (DOSO) with polymer molecules of uranyl di-2-ethylhexyl phosphate (UO{sub 2}X{sub 2})p (I) in C{sub 6}H{sub 6} solutions. Detailed interpretations of the {sup 31}P NMR spectra and the v{sub as}(POO) IR bands and determination of the fraction of nonequivalent phosphorus atoms of X{sup -} anions and uranium (VI) atoms as well as the concentration of U(VI)-bonded TBP in I have shown that only a single TBP or DOSO molecule is coordinated to the uranium atoms of polymer I at C{sub TBP} = 0.1-2 M or C{sub DOSO}=0.1-0.5 M. In the case of 100% TBP, two TBP molecules are coordinated to some U(VI) atoms. Distribution of TBP (DOSO) molecules along the polymer chain agrees with the mean statistical value. The portion of terminal chelate POO-groups of X{sup -} anions is determined. The dependence of the degree of (UO{sub 2}X{sub 2})p{center_dot}nL (L = TBP, DOSO) polymerization on C{sub L} is obtained. Saturation of solutions with water only slightly affects the terminal POO-groups and has no effect on the distribution of L along the polymer chain of I.

Stoyanov, E.S.; Mikhailov, V.A.; Torgov, V.G. [and others

1995-05-01

73

Energetic lanthanide complexes: coordination chemistry and explosives applications  

NASA Astrophysics Data System (ADS)

Metals are generally added to organic molecular explosives in a heterogeneous composite to improve overall heat and energy release. In order to avoid creating a mixture that can vary in homogeneity, energetic organic molecules can be directly bonded to high molecular weight metals, forming a single metal complex with Angstrom-scale separation between the metal and the explosive. To probe the relationship between the structural properties of metal complexes and explosive performance, a new series of energetic lanthanide complexes has been prepared using energetic ligands such as NTO (5-nitro-2,4-dihydro-1,2,4-triazole-3-one). These are the first examples of lanthanide NTO complexes where no water is coordinated to the metal, demonstrating novel control of the coordination environment. The complexes have been characterized by X-ray crystallography, NMR and IR spectroscopies, photoluminescence, and sensitivity testing. The structural and energetic properties are discussed in the context of enhanced blast effects and detection. Cheetah calculations have been performed to fine-tune physical properties, creating a systematic method for producing explosives with 'tailor made' characteristics. These new complexes will be benchmarks for further study in the field of metalized high explosives.

Manner, V. W.; Barker, B. J.; Sanders, V. E.; Laintz, K. E.; Scott, B. L.; Preston, D. N.; Sandstrom, M.; Reardon, B. L.

2014-05-01

74

Dinuclear copper complexes: coordination of Group 14 heteroborates.  

PubMed

Dicopper(i) complexes with the chelating dmapm ligand [dmapm = 1,1-bis{di(o-N,N-dimetylanilinyl)phosphino}methane] have been synthesized and characterized structurally. Synthesis of the acetonitrile adduct [Cu2(?-dmapm)(CH3CN)2][BF4]2 () has been presented and the dicopper electrophile has been used as the starting material in reaction with Group 14 heteroborates. Coordination of the closo-borates at the dicopper moiety resulted in different molecular structures with varying CuCu distances. In the case of the side on coordinated stanna-closo-dodecaborate the tin vertex has been characterized by (119)Sn Mssbauer spectroscopy and the nucleophilicity at the tin was established in reaction with a molybdenum carbonyl complex. PMID:24964388

Scheel, Holger; Wiederkehr, Jessica; Eichele, Klaus; Mayer, Hermann A; Winter, Florian; Pttgen, Rainer; Wesemann, Lars

2014-07-15

75

Structure sensitive normal coordinate analysis of metal-diethyldithiocarbamate - complexes  

NASA Astrophysics Data System (ADS)

Symmetry changes in the course of dissolution are assumed to produce frequency shifts in molecular spectra of N, N-Disubstituted Dithiocarbamates. Using (mass-weighted) cartesian coordinates it is possible to calculate eigenvalues both for the site- and the molecular symmetry. Calculated shifts for Cu- and Zn- complexes are of the same order of magnitude as experimental results and calculation of frequencies even for assumed structures is possible.

Mikosch, H.; Bauer, G.; Kellner, R.; Trendafilova, N. S.; St. Nikolov, G.

1986-03-01

76

Stable eight-coordinate iron(III/II) complexes.  

PubMed

The chemistry of unusual coordination numbers of transition-metal complexes has been of interest because of their presence in biology and catalytic systems. Herein we describe a systematic and predictable approach toward isolation of stable eight-coordinate (8C) iron(III/II) systems. The 8C (S = 2; high-spin, HS) complex [Fe(L(N4))(2)](BF(4))(2) (1) has been synthesized and characterized, displaying a distorted square-antiprism structure. Complex 1 is a unique 8C iron complex that exhibits remarkable stability in solution under various unfavorable conditions. The E(1/2) value of 1 (0.430 V vs Ag/AgCl, MeCN) supports the Fe(II) oxidation state; however, the corresponding HS (S = 5/2) 8C Fe(III) analogue [Fe(L(N4))(2)](NO(3))(3) (3) has also been synthesized via the chemical oxidation of 1. The structural, spectroscopic, and theoretical descriptions of these 8C iron complexes are reported in this work. PMID:20108928

Patra, Ashis K; Dube, Koustubh S; Papaefthymiou, Georgia C; Conradie, Jeanet; Ghosh, Abhik; Harrop, Todd C

2010-03-01

77

Extended structures and physicochemical properties of uranyl-organic compounds.  

PubMed

The ability of uranium to undergo nuclear fission has been exploited primarily to manufacture nuclear weapons and to generate nuclear power. Outside of its nuclear physics, uranium also exhibits rich chemistry, and it forms various compounds with other elements. Among the uranium-bearing compounds, those with a uranium oxidation state of +6 are most common and a particular structural unit, uranyl UO(2)(2+) is usually involved in these hexavalent uranium compounds. Apart from forming solids with inorganic ions, the uranyl unit also bonds to organic molecules to generate uranyl-organic coordination materials. If appropriate reaction conditions are employed, uranyl-organic extended structures (1-D chains, 2-D layers, and 3-D frameworks) can be obtained. Research on uranyl-organic compounds with extended structures allows for the exploration of their rich structural chemistry, and such studies also point to potential applications such as in materials that could facilitate nuclear waste disposal. In this Account, we describe the structural features of uranyl-organic compounds and efforts to synthesize uranyl-organic compounds with desired structures. We address strategies to construct 3-D uranyl-organic frameworks through rational selection of organic ligands and the incorporation of heteroatoms. The UO(2)(2+) species with inactive U?O double bonds usually form bipyramidal polyhedral structures with ligands coordinated at the equatorial positions, and these polyhedra act as primary building units (PBUs) for the construction of uranyl-organic compounds. The geometry of the uranyl ions and the steric arrangements and functionalities of organic ligands can be exploited in the the design of uranyl--organic extended structures, We also focus on the investigation of the promising physicochemical properties of uranyl-organic compounds. Uranyl-organic materials with an extended structure may exhibit attractive properties, such as photoluminescence, photocatalysis, photocurrent, and photovoltaic responses. In particular, the intriguing, visible-light photocatalytic activities of uranyl-organic compounds are potentially applicable in decomposition of organic pollutants and in water-splitting with the irradiation of solar light. We ascribe the photochemical properties of uranyl-organic compounds to the electronic transitions within the U?O bonds, which may be affected by the presence of organic ligands. PMID:21612214

Wang, Kai-Xue; Chen, Jie-Sheng

2011-07-19

78

In vacuo formation of peptide-metal coordination complexes  

PubMed Central

Here we report on the reaction of rhenate anions (ReO3?) with multiply protonated peptide cations in a quadrupole linear ion trap mass spectrometer. These reactions effect the formation of an anioncation complex that, upon collisional activation, dissociates along the peptide backbone rather than by displacement of the anion. Cleavage of the peptide backbone, with anion retention, leads us to conclude the anioncationcomplexmust be tightly bound, most probably through coordination chemistry. We describe this chemistry and detail the possible application of such ion attachment reactions to the characterization of intact proteins.

McAlister, Graeme C.; Kiessel, Sharon E.B.; Coon, Joshua J.

2009-01-01

79

Giant regular polyhedra from calixarene carboxylates and uranyl  

PubMed Central

Self-assembly of large multi-component systems is a common strategy for the bottom-up construction of discrete, well-defined, nanoscopic-sized cages. Icosahedral or pseudospherical viral capsids, built up from hundreds of identical proteins, constitute typical examples of the complexity attained by biological self-assembly. Chemical versions of the so-called 5 Platonic regular or 13 Archimedean semi-regular polyhedra are usually assembled combining molecular platforms with metals with commensurate coordination spheres. Here we report novel, self-assembled cages, using the conical-shaped carboxylic acid derivatives of calix[4]arene and calix[5]arene as ligands, and the uranyl cation UO22+ as a metallic counterpart, which coordinates with three carboxylates at the equatorial plane, giving rise to hexagonal bipyramidal architectures. As a result, octahedral and icosahedral anionic metallocages of nanoscopic dimensions are formed with an unusually small number of components.

Pasquale, Sara; Sattin, Sara; Escudero-Adan, Eduardo C.; Martinez-Belmonte, Marta; de Mendoza, Javier

2012-01-01

80

Charge transfer vibronic transitions in uranyl tetrachloride compounds.  

PubMed

The electronic and vibronic interactions of uranyl (UO(2))(2+) in three tetrachloride crystals have been investigated with spectroscopic experiments and theoretical modeling. Analysis and simulation of the absorption and photoluminescence spectra have resulted in a quantitative understanding of the charge transfer vibronic transitions of uranyl in the crystals. The spectra obtained at liquid helium temperature consist of extremely narrow zero-phonon lines (ZPL) and vibronic bands. The observed ZPLs are assigned to the first group of the excited states formed by electronic excitation from the 3? ground state into the f(?,?) orbitals of uranyl. The Huang-Rhys theory of vibronic coupling is modified successfully for simulating both the absorption and luminescence spectra. It is shown that only vibronic coupling to the axially symmetric stretching mode is Franck-Condon allowed, whereas other modes are involved through coupling with the symmetric stretching mode. The energies of electronic transitions, vibration frequencies of various local modes, and changes in the O?U?O bond length of uranyl in different electronic states and in different coordination geometries are evaluated in empirical simulations of the optical spectra. Multiple uranyl sites derived from the resolution of a superlattice at low temperature are resolved by crystallographic characterization and time- and energy-resolved spectroscopic studies. The present empirical simulation provides insights into fundamental understanding of uranyl electronic interactions and is useful for quantitative characterization of uranyl coordination. PMID:22148434

Liu, Guokui; Deifel, Nicholas P; Cahill, Christopher L; Zhurov, Vladimir V; Pinkerton, A Alan

2012-01-19

81

Design of magnetic coordination complexes for quantum computing.  

PubMed

A very exciting prospect in coordination chemistry is to manipulate spins within magnetic complexes for the realization of quantum logic operations. An introduction to the requirements for a paramagnetic molecule to act as a 2-qubit quantum gate is provided in this tutorial review. We propose synthetic methods aimed at accessing such type of functional molecules, based on ligand design and inorganic synthesis. Two strategies are presented: (i) the first consists in targeting molecules containing a pair of well-defined and weakly coupled paramagnetic metal aggregates, each acting as a carrier of one potential qubit, (ii) the second is the design of dinuclear complexes of anisotropic metal ions, exhibiting dissimilar environments and feeble magnetic coupling. The first systems obtained from this synthetic program are presented here and their properties are discussed. PMID:21818467

Arom, Guillem; Aguil, David; Gamez, Patrick; Luis, Fernando; Roubeau, Olivier

2012-01-21

82

Structure and dynamics of complexes of the uranyl ion with nonamethylimidodiphosphoramide (NIPA). 2. NMR studies of complexes (UO/sub 2/(NIPA)/sub 2/X)(CIO/sub 4/)/sub 2/ with X = H/sub 2/O, MeOH, EtOH, or Me/sub 2/CO  

SciTech Connect

The /sup 31/P and /sup 1/H spectra at -90/sup 0/C of the title uranyl complex ions (prepared as solutions of the solid perchlorates in inert anhydrous organic solvents (CH/sub 3/NO/sub 2/, CH/sub 2/Cl/sub 2/)) reveal a pentacoordinated arrangement of two symmetrically doubly bonded NIPA molecules and one solvent molecule about the uranyl group. In the case of (UO/sub 2/(NIPA)/sub 2/(EtOH))(ClO/sub 4/)/sub 2/, an intermolecular exchange between bound and free ethanol molecules is observed above -75/sup 0/C upon addition of ethanol to a solution of the complex. The observed rate law, k/sub inter/ = kK(EtOH)/(1 + K(EtOH) is accounted for by the existence of an outer-sphere complex (UO/sub 2//sup 2 +/(NIPA)/sub 2/(EtOH))EtOH in fast equilibrium (K) with the initial complex and free ethanol. The rate-determining step (k) consists of an outer-sphere to inner-sphere interchange of ethanol molecules. The thermodynamic and kinetic parameters are K(25/sup 0/C) = 15.8 dm/sup 3/ mol/sup -1/, k(25/sup 0/C) = 1.0 x 10/sup 4/s/sup -1/, ..delta..H and ..delta..H/sub inter//sup + +/ = -4.8 and 7.6 kcal mol/sup -1/, and ..delta..S and ..delta..S/sub inter//sup + +/ = 10.7 and -14.7 eu. A second exchange takes place at higher temperatures (above -30/sup 0/C) yielding full dynamic equivalence of the phosphorus nuclei of the coordinated NIPA molecules. The observed rate law k/sub intra/ = k/sub ex/(1 + K(EtOH)) reveals that the internal rearrangement of NIPA molecules occurs on the complex ion (UO/sub 2/(NIPA)/sub 2/(EtOH))/sup 2 +/ but not on the outer-sphere complex: k/sub ex/(25/sup 0/C) = 0.91 x 10/sup 3/s/sup -1/, ..delta..H/sub intra//sup + +/ = 10.6 kcal mol/sup -1/ and ..delta..S/sub intra//sup + +/ = -9.4 eu. Possible mechanisms for this exchange are discussed. 5 figures, 2 tables.

Rodehueser, L.; Rubini, P.R.; Bokolo, K.; Delpuech, J.J.

1982-03-01

83

Molecular biosensor based on a coordinated iron complex  

NASA Astrophysics Data System (ADS)

A sensor model based on the porphyrin nucleus of the soluble guanylate cyclase enzyme is modeled and tested with nitric oxide and carbon monoxide. Molecular oxygen is tested as a possible interferer. Geometries and electronic structures of the model are assessed by density functional theory. Vibrational circular dichroism (VCD), infrared, and Raman spectra are obtained for the iron complexes uncoordinated and coordinated with the gas moieties. The sensor is capable of detecting the ligands to different extents. Carbon monoxide is less detectable than nitric oxide due to the adopted position of the molecule in the sensor; carbon oxide is aligned with the iron atom, while nitric oxide and molecular oxygens bend with an angle detectable by the VCD. It is suggested that pollutants may be detected and measured with the proposed biosensors

Salazar-Salinas, Karim; Jauregui, Luis A.; Kubli-Garfias, Carlos; Seminario, Jorge M.

2009-03-01

84

{sup 13}C and {sup 17}O NMR binding constant studies of uranyl carbonate complexes in near-neutral aqueous solution. Yucca Mountain Project Milestone Report 3351  

SciTech Connect

Valuable structural information, much of it unavailable by other methods, can be obtained about complexes in solution through NMR spectroscopy. From chemical shift and intensity measurements of complexed species, NMR can serve as a species-specific structural probe for molecules in solution and can be used to validate thermodynamic constants used in geochemical modeling. Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy has been employed to study the speciation of uranium(VI) ions in aqueous carbonate solutions as a function of pH, ionic strength, carbonate concentration, uranium concentration, and temperature. Carbon-13 and oxygen-17 NMR spectroscopy were used to monitor the fractions, and hence thermodynamic binding constants of two different uranyl species U0{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} and (UO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6{minus}} in aqueous solution. Synthetic buffer solutions were prepared under the ionic strength conditions used in the NMR studies in order to obtain an accurate measure of the hydrogen ion concentration, and a discussion of pH = {minus}log(a{sub H}{sup +}) versus p[H] = {minus}log[H+] is provided. It is shown that for quantitative studies, the quantity p[H] needs to be used. Fourteen uranium(VI) binding constants recommended by the OECD NEA literature review were corrected to the ionic strengths employed in the NMR study using specific ion interaction theory (SIT), and the predicted species distributions were compared with the actual species observed by multinuclear NMR. Agreement between observed and predicted stability fields is excellent. This establishes the utility of multinuclear NMR as a species-specific tool for the study of the actinide carbonate complexation constants, and serves as a means for validating the recommendations provided by the OECD NEA.

Clark, D.L.; Newton, T.W.; Palmer, P.D.; Zwick, B.D.

1995-01-01

85

Coordinates  

NSDL National Science Digital Library

This introduction to the labeling of points on a plane by their Cartesian coordinates can optionally be extended to coordinates in 3-dimensional space, to plane polar coordinates and to 3-dimensional polar coordinates. Students should learn to use Cartesian coordinates (x,y) for defining the position of a point in two dimensions and to use Cartesian coordinates (x,y,z) in 3-dimensional space and learn to appreciate the two ways of defining the z axis. Students should also become familiar with some of the tools and terms used by surveyors such as theodolite, azimuth, elevation, and zenith. Optional items for students familiar with trigonometry and with the theorem of Pythagoras are polar coordinates (r,f ) on the plane, Converting (r,f) to (x,y) and vice versa, at least for r, and Spherical polar coordinates (r,q, f) in 3-dimensional space.

Stern, David

86

Investigation of the interaction between organic compounds and uranyl ions by raman spectroscopy  

NASA Astrophysics Data System (ADS)

Raman spectra of uranyl oxalate, salinate, salicylate, terephthalate and humate have been measured. The O=U=O symmetric stretching frequency of uranyl oxalate, malonate, terephthalate and humate had similar values, suggesting the same number of ligands co-ordinating to central uranium atom, i.e. one carboxyl group is co-ordinated to one uranium atom. The smaller frequency was observed in uranyl salicylate, suggesting the co-ordination of both carboxyl and phenyl groups, under the formation of a 6-membered chelate ring. Ab initio MO calculation supported this idea.

Tsushima, S.; Nagasaki, S.; Tanaka, S.; Suzuki, A.

1999-01-01

87

Polymer complexes. LIII. Supramolecular coordination modes and structural of novel sulphadrug complexes  

NASA Astrophysics Data System (ADS)

Novel polymer complexes of copper(II), palladium(II), platinum(II) and cadmium(II) containing homopolymer [4-acrylamido benzene sulphonyl guanidine; (HL)] and various anions (SO 42-, CH 3COO -, NO 3-, Br - or Cl -) have been designed and carried out. Their structures were investigated by elemental analyses, spectral (IR, UV-vis, 1H NMR and ESR) and magnetic moments. The modes of interactions between the ligand and the metals were discussed, where oxygen (of O dbnd S dbnd O group) and nitrogen atom [of imino nitrogen (NH/N) of the guanidine group] are involved in chelation. The homopolymer shows two types of coordination behaviour. In mononuclear polymer complexes 4 and 6- 10, it acts as a neutral bidentate ligand chelated through the NH and O atoms, whereas in the polymer complexes 1- 3, 5 and 11, monobasic bidentate ligand is coordinated through the -N and -O atoms. The poly-chelates are of 1:1/1:2 (metal-homopolymer) stoichiometry and exhibit four coordination. On the basis of electronic spectral data and magnetic susceptibility measurement square planar geometry has been proposed. The ESR spectral data provided information about their structure on the basis Hamiltonian parameters and degree of covalency. From the electron paramagnetic resonance and spectral data, the orbital reduction factors were calculated.

Diab, M. A.; El-Sonbati, A. Z.; Mohamed, R. H.

2010-11-01

88

Synthesis and characterization of new iron coordination complexes utilizing an asymmetric coordinating chelate ligand.  

National Technical Information Service (NTIS)

The authors are investigating the structure/activity relationships of the bacterial enzyme, methane monooxygenase, which catalyzes the specific oxidation of methane to methanol. They then utilize this information to design and synthesize inorganic coordin...

D. Baldwin B. E. Watkins J. H. Satcher

1993-01-01

89

Synthesis and characterization of new iron coordination complexes utilizing an asymmetric coordinating chelate ligand.  

National Technical Information Service (NTIS)

We are investigating the structure/activity relationships of the bacterial enzyme methane monooxygenase, which catalyzes the specific oxidation of methane to methanol. We then utilize this information to design and synthesize inorganic coordination comple...

B. E. Watkins J. H. Satcher

1995-01-01

90

Structure determination of a complex tubular uranyl phenylphosphonate, (UO{sub 2}){sub 3}(HO{sub 3}PC{sub 6}H{sub 5}){sub 2}(O{sub 3}PC{sub 6}H{sub 5}){sub 2}{center_dot}H{sub 2}O, from conventional x-ray powder diffraction data  

SciTech Connect

The three-dimensional structure of a complex tubular uranyl phosphonate, (UO{sub 2}){sub 3}(HO{sub 3}PC{sub 6}H{sub 5}){sub 2}(O{sub 3}PC{sub 6}H{sub 5}){sub 2}(O{sub 3}PC{sub 6}H{sub 5}){sub 2} {center_dot} H{sub 2}O, was determined ab initio from laboratory X-ray powder diffraction data and refined by the Rietveld method. The crystals belong to the space group P2{sub 1}2{sub 1}2{sub 1}, with {alpha} = 17.1966(2) {Angstrom}, b = 7.2125(2) {Angstrom}, c = 27.8282(4) {Angstrom}, and Z = 4. The structure consists of three independent uranium atoms, among which two are seven-coordinated and the third is eight-coordinated. These metal atoms are connected by four different phosphonate groups to form a one-dimensional channel structure along the b axis. The phenyl groups are arranged on the outer periphery of the channels, and their stacking forces keep the channels intact in the lattice. The determination of this structure which contains 50 non-hydrogen atoms in the asymmetric unit, from conventional X-ray powder data, represents significant progress in the application of powder techniques to structure of complex inorganic compounds, including organometallic compounds.

Poojary, D.M. [Texas A& M Univ. College Station, TX (United States)] [Texas A& M Univ. College Station, TX (United States); Cabeza, A.; Aranda, A.G. [Universidad de Malaga (Spain)] [and others] [Universidad de Malaga (Spain); and others

1996-03-13

91

Lactide polymerization by well-defined calcium coordination complexes: comparisons with related magnesium and zinc chemistry.  

PubMed

Amide and alkoxide coordination complexes of calcium supported by beta-diiminato and bulky trispyrazolylborate complexes are reported together with their activity in lactide ring-opening polymerization; some are amongst the most active systems discovered to date. PMID:12610959

Chisholm, Malcolm H; Gallucci, Judith; Phomphrai, Khamphee

2003-01-01

92

Coordination Chemistry of Metal Surfaces and Metal Complexes.  

National Technical Information Service (NTIS)

The coordination chemistry of two isomeric molecules, acetonitrile and methyl isocyanide, has been characterized for (A) single crystal nickel surfaces as a function of crystallography and surface composition, (B) nickel catalyst surfaces and (C) molecula...

E. L. Muetterties

1979-01-01

93

DNA conformational analysis in solution by uranyl mediated photocleavage.  

PubMed Central

Uranyl mediated photocleavage of double stranded DNA is proposed as a general probing for DNA helix conformation in terms of minor groove width/electronegative potential. Specifically, it is found that A/T-tracts known to constitute strong distamycin binding sites are preferentially photocleaved by uranyl in a way indicating strongest uranyl binding at the center of the minor groove of the AT-region. The A-tracts of kinetoplast DNA show the highest reactivity at the 3'-end of the tract--as opposed to cleavage by EDTA/Fell--in accordance with the minor groove being more narrow at this end. Finally, uranyl photocleavage of the internal control region (ICR) of the 5S-RNA gene yields a cleavage modulation pattern fully compatible with that obtained by DNase I which also--in a more complex way--senses DNA minor groove width. Images

Nielsen, P E; M?llegaard, N E; Jeppesen, C

1990-01-01

94

Uranyl adsorption on solvated edge surfaces of pyrophyllite: a DFT model study.  

PubMed

In a computational study we addressed the adsorption of uranyl UO(2)(2+) on solvated (110) and (010) edge surfaces of pyrophyllite, applying a density functional approach to periodic slab models. We explored bidentate adsorption complexes on various partially deprotonated adsorption sites: octahedral Al(O,OH), tetrahedral Si(O,OH), and mixed AlO-SiO. Aluminol sites were determined to be most favorable on the (110) surface of pyrophyllite, while on the (010) surface mixed AlO-SiO sites are preferred. The structural parameters of all low-energy complexes on both surfaces agree rather well with EXAFS results for the structurally similar mineral montmorillonite. We calculate the average U-O distance to surface and aqua ligand oxygen atoms to increase with the increasing coordination number of uranyl whereas EXAFS results indicate the opposite trend. According to our results, several adsorption species, with different coordination numbers on different edge faces, may coexist on clay minerals. This computational finding rationalizes why earlier spectroscopic studies indicated the existence of more than one adsorption species, whereas a single type of adsorption complex was suggested from most EXAFS results. PMID:22402675

Kremleva, Alena; Martorell, Benjam; Krger, Sven; Rsch, Notker

2012-04-28

95

Highly Distorted Uranyl Ion Coordination and One/Two-Dimensional Structural Relationship in the Ba2[UO2(TO4)2] (T = P, As) System: An Experimental and Computational Study.  

PubMed

Uranium compounds ?-Ba2[UO2(PO4)2] (1), ?-Ba2[UO2(PO4)2] (2), and Ba2[UO2(AsO4)2] (3) were synthesized by H3BO3/B2O3 flux reactions, though boron is not incorporated into the structures. Phases 1 and 2 are topologically identical, but 1 is heavily distorted with respect to 2. An unusual UO7 pentagonal bipyramid occurs in 1, exhibiting a highly distorted equatorial configuration and significant bending of the uranyl group, due to edge-sharing with one neighboring PO4(3-) tetrahedron. Compound 2 contains more normal square bipyramids that share corners with four neighboring PO4(3-) tetrahedra, but the uranyl cation UO2(2+) is tilted relative to the equatorial plane. Experimental evidence as well as density functional theory (DFT) calculations suggest that 1 is more stable than 2. In theory, 1 and 2 can interconvert by forming/releasing the shared edge between the uranyl polyhedron and the phosphate tetrahedron. Similar fundamental building blocks in ?-Ba2[UO2(PO4)2] and Ba2[UO2(AsO4)2] indicate a possible evolution of uranyl-based structures from chain to layer type and formation of an accretional series. PMID:24991981

Wu, Shijun; Kowalski, Piotr M; Yu, Na; Malcherek, Thomas; Depmeier, Wulf; Bosbach, Dirk; Wang, Shuao; Suleimanov, Evgeny V; Albrecht-Schmitt, Thomas E; Alekseev, Evgeny V

2014-07-21

96

Recent advances on technetium complexes: coordination chemistry and medical applications  

Microsoft Academic Search

Current literature (19902005) on methods for synthesizing technetium (Tc) complexes is presented. The development and design of Tc complexes for imaging of different organic tissues, of special interest for their medical applications, are also reviewed.

Miguel A. Mndez-Rojas; Boris I. Kharisov; Aslan Yu. Tsivadze

2006-01-01

97

Distributed detection of communities in complex networks using synthetic coordinates  

NASA Astrophysics Data System (ADS)

Various applications like finding Web communities, detecting the structure of social networks, and even analyzing a graphs structure to uncover Internet attacks are just some of the applications for which community detection is important. In this paper, we propose an algorithm that finds the entire community structure of a network, on the basis of local interactions between neighboring nodes and an unsupervised distributed hierarchical clustering algorithm. The novelty of the proposed approach, named SCCD (standing for synthetic coordinate community detection), lies in the fact that the algorithm is based on the use of Vivaldi synthetic network coordinates computed by a distributed algorithm. The current paper not only presents an efficient distributed community finding algorithm, but also demonstrates that synthetic network coordinates could be used to derive efficient solutions to a variety of problems. Experimental results and comparisons with other methods from the literature are presented for a variety of benchmark graphs with known community structure, derived from varying a number of graph parameters and real data set graphs. The experimental results and comparisons to existing methods with similar computation cost on real and synthetic data sets demonstrate the high performance and robustness of the proposed scheme.

Papadakis, H.; Panagiotakis, C.; Fragopoulou, P.

2014-03-01

98

Bidentate and tridentate metal-ion coordination states within ternary complexes of RB69 DNA polymerase  

SciTech Connect

Two divalent metal ions are required for primer-extension catalyzed by DNA polymerases. One metal ion brings the 3'-hydroxyl of the primer terminus and the {alpha}-phosphorus atom of incoming dNTP together for bond formation so that the catalytically relevant conformation of the triphosphate tail of the dNTP is in an {alpha},{beta},{gamma}-tridentate coordination complex with the second metal ion required for proper substrate alignment. A probable base selectivity mechanism derived from structural studies on Dpo4 suggests that the inability of mispaired dNTPs to form a substrate-aligned, tridentate coordination complex could effectively cause the mispaired dNTPs to be rejected before catalysis. Nevertheless, we found that mispaired dNTPs can actually form a properly aligned tridentate coordination complex. However, complementary dNTPs occasionally form misaligned complexes with mutant RB69 DNA polymerases (RB69pols) that are not in a tridentate coordination state. Here, we report finding a {beta},{gamma}-bidentate coordination complex that contained the complementary dUpNpp opposite dA in the structure of a ternary complex formed by the wild type RB69pol at 1.88 {angstrom} resolution. Our observations suggest that several distinct metal-ion coordination states can exist at the ground state in the polymerase active site and that base selectivity is unlikely to be based on metal-ion coordination alone.

Xia, Shuangluo; Eom, Soo Hyun; Konigsberg, William H.; Wang, Jimin (Yale); (Gwangju)

2012-02-21

99

Coordination mode of dihydroxybenzoic acids in oxorhenium(V) complexes  

Microsoft Academic Search

Trans-ReOCl3(PPh3)2 reacts with 2,3- and 2,6-dihydroxybenzoic acid (H2dhb) in an equimolar ratio in benzene to give the products [ReOCl(2,3-dhb)(PPh3)2] (1) and [ReOCl(2,6-dhb)(PPh3)2] (2), respectively. Elemental analysis, infrared, NMR and X-ray crystallographic results indicate that the ligand 2,3-dhb coordinates via the catecholato mode to the metal centre in 1, but 2,6-dhb functions as a salicylato-type chelate in 2.

Giuliano Bandoli; Alessandro Dolmella; Thomas I. A. Gerber; Joanne Perils; Jan G. H. du Preez

1999-01-01

100

An octahedral coordination complex of iron(VI).  

PubMed

The hexavalent state, considered to be the highest oxidation level accessible for iron, has previously been found only in the tetrahedral ferrate dianion, FeO4(2-). We report the photochemical synthesis of another Fe(VI) compound, an octahedrally coordinated dication bearing a terminal nitrido ligand. Mssbauer and x-ray absorption spectra, supported by density functional theory, are consistent with the octahedral structure having an FeN triple bond of 1.57 angstroms and a singlet d2(xy) ground electronic configuration. The compound is stable at 77 kelvin and yields a high-spin Fe(III) species upon warming. PMID:16741074

Berry, John F; Bill, Eckhard; Bothe, Eberhard; George, Serena DeBeer; Mienert, Bernd; Neese, Frank; Wieghardt, Karl

2006-06-30

101

Synthesis, characterization, and structure of a uranyl complex with a disulfide ligand, Bis(di-n-propylammonium) Disulfidobis(di-n-propylthiocarbamato)dioxouranate(VI)  

SciTech Connect

Olive green crystals of the title compound, ((n-C/sub 3/H/sub 7/)/sub 2/NH/sub 2//sup +/)/sub 2/(UO/sub 2/((n-C/sub 3/H/sub 7/)/sub 2/NCOS)/sub 2/(S/sub 2/))/sup 2 -/, are orthorhombic, space group Pcan, with a = 15.326 (6) A, b = 17.474 (6) A, c = 14.728 (6) A, and Z = 4 (d/sub x/ = 1.45 g/cm/sup 3/). For 1833 data, I > sigma/sub I/, R = 0.052, and R/sub w/ = 0.069. The structure was revealed by single-crystal x-ray diffraction studies to consist of ((n-C/sub 3/H/sub 7/)/sub 2/NH/sub 2/)/sup +/ cations and (UO/sub 2/((n-C/sub 3/H/sub 7/)/sub 2/NCOS)/sub 2/(S/sub 2/))/sup 2 -/ anions with the uranium atom at the center of an irregular hexagonal bipyramid. The uranyl oxygen atoms occupy the axial positions. The equatorial coordiantion plane contains the disulfide (S/sub 2//sup 2 -/) group bonded in a side-on fashion and two oxygen and two sulfur donor atoms from the monothiocarbamate ligands. Interatomic distances are S-S = 2.05 (1) A and U-S = 2.711 (3) A (disulfide), U-S = 2.873 (3) A and U-O = 2.48 (1) A (thiocarbamate), and U-0 = 1.82 (1) A (uranyl). The nitrogen atom in the dipropylammonium cation is hydrogen bonded to the uranyl oxygen atoms.

Perry, D.L.; Zalkin, A.; Ruben, H.; Templeton, D.H.

1982-01-01

102

Trinuclear complexes of four-coordinate iron and cobalt  

Microsoft Academic Search

The mononuclear, tetrahedral iron and cobalt complexes, FeCl2(Hhpp)2, I, and CoCl2(Hhpp)2, II, are readily formed by the reaction of the metal (II) chloride with Hhpp. Compound II crystallized as blue blocks in the space group Fdd2. The reaction of I with LiMe yielded the trinuclear complex Fe3Cl2(hpp)4, III, which crystallized as colorless blocks in the space group P21\\/n. A cobalt

F. Albert Cotton; Carlos A Murillo; Daren J Timmons

1998-01-01

103

Investigation on coordination number and geometrical conformation of rare earth complexes with catenulate aminopolycarboxylic acid ligands  

Microsoft Academic Search

This article gives an overview on the molecular and crystal structures of rare earth metal (REM) complexes with a series of aminopolycarboxylic acid (APCA) ligands, nitrilotriacetic acid (NTA), ethylenediamine-N,N,N?,N?-tetraacetic acid (EDTA), diethylenetriamine-N,N,N?,N?,N?-pentaacetic acid (DTPA), and triethylenetetramine-N,N,N?,N?,N???,N???-hexaacetic acid (TTHA). Among the REM complexes with the same APCA ligand, the coordination law of coordination numbers and geometrical conformation are discussed. The research

Jun Wang; Ping Hu; Bin Liu; Xudong Jin; Yumei Kong; Jingqun Gao; Dan Wang; Baoxin Wang; Rui Xu; Xiangdong Zhang

2010-01-01

104

Four coordinate tin complexes: synthesis, characterization, thermodynamic and theoretical calculations.  

PubMed

In this work, two new Sn(IV) complexes, [SnL(x)]Cl2 where (L(x))(2-) is the deprotonated form of 5-A-salabza-H2=N,N'-bis(salicylidene)-2-aminobenzylamine and A=5-OMe, 5-H, 5-NO2, 5-Br, were synthesized and fully characterized by UV-Vis, FT-IR, (1)H NMR, (13)C NMR, (119)Sn NMR spectroscopies, mass spectrometry and elemental analysis. The thermodynamic formation constants of the complexes were determined spectrophotometrically at 25 C in acetonitrile. The trend of formation constants of the complexes are as: 5-OMe>5-H>5-NO2>5-Br and Ph2SnCl2>Me2SnCl2>n-Bu2SnCl2. DFT/B3LYP molecular orbital calculations were carried out for the 5-H substituent isomer, [SnL(2)](2+), in an attempt to explain the structure of complexes. The optimized resulting geometries, vibrational frequencies and the NMR resonances of the complexes are discussed. PMID:23988534

Mohammadikish, Maryam

2014-01-01

105

The coordination and atom transfer chemistry of titanium porphyrin complexes  

SciTech Connect

Preparation, characterization, and reactivity of ({eta}{sup 2}- alkyne)(meso-tetratolylpoprphrinato)titanium(II) complexes are described, along with inetermetal oxygen atom transfer reactions involving Ti(IV) and Ti(III) porphyrin complexes. The {eta}{sup 2}- alkyne complexes are prepared by reaction of (TTP)TiCl{sub 2} with LiAlH{sub 4} in presence of alkyne. Structure of (OEP)Ti({eta}{sup 2}-Ph-C{triple_bond}C-Ph) (OEP=octaethylporphryin) was determined by XRD. The compounds undergo simple substitution to displace the alkyne and produce doubly substituted complexes. Structure of (TTP)Ti(4-picoline){sub 2} was also determined by XRD. Reaction of (TTP)Ti{double_bond}O with (OEP)Ti-Cl yields intermetal O/Cl exchange, which is a one-electron redox process mediated by O atom transfer. Also a zero-electron redox process mediated by atom transfer is observed when (TTP)TiCl{sub 2} is reacted with (OEP)Ti{double_bond}O.

Hays, J.A.

1993-11-05

106

Assessment of accidental intakes of uranyl acetylacetonate (UAA)  

Microsoft Academic Search

Uranyl acetylacetonate (UAA) is an organic complex of uranium used for military applications as a chemical catalyst in high explosives. It is prepared from depleted uranium metal (in lots of 5 kg to 7 kg) by dissolution in nitric acid, neutralization, and complexation with 2,4-pentanedione; the precipitate is dissolved in benzene and recrystallized, dried, ground, and packaged. About six workers

D. R. Fisher; J. K. Briant

1993-01-01

107

Probing the Molecular Geometry of Five-Coordinate Vanadyl Complexes with Pulsed ENDOR.  

PubMed

The pulsed electron paramagnetic resonance (EPR) technique of (51)V electron spin echo-electron nuclear double resonance (ESE-ENDOR) has been used to measure the nuclear quadrupole coupling constants of a series of five-coordinate vanadyl complexes containing Schiff base ligands with geometries ranging from distorted square pyramidal to distorted trigonal bipyramidal. Vanadium nuclear quadrupole coupling constants are sensitive to the coordination geometry of the vanadyl ion, and thus sensitive to the structural distortions within this series of complexes. (51)V ESE-ENDOR has been shown to be a probe of the coordination geometry of vanadyl complexes. Such a spectroscopic probe should prove useful in the investigation of vanadyl of unknown coordination geometry, such as may be found in the interaction of the vanadyl ion with biomolecules. PMID:11671345

Grant, Christopher V.; Geiser-Bush, Katherine M.; Cornman, Charles R.; Britt, R. David

1999-12-27

108

Pointing errors in strabismics: complex patterns of distorted visuomotor coordination.  

PubMed

Monocular eye-hand coordination was tested in a pointing experiment in the central and peripheral visual field of each eye of strabismic and anisometropic amblyopes, strabismic alternators and normal controls. In the normal controls, pointing was accurate in the central visual field. Towards the periphery, normal observers showed a varying amount of undershoot as well as increasing uncertainty. The pointing pattern was similar in the two eyes of these subjects. Increased uncertainty of pointing responses was found in most amblyopic eyes as compared to the dominant eyes. Three strabismic amblyopes and one strabismic alternator also had systematic pointing errors (i.e. systematic differences between pointing under the control of the dominant as compared to the nondominant eye). The pointing pattern was not uniform across the visual field in some of the strabismics, but was composed of areas of larger and smaller pointing errors. Larger pointing errors (i.e. larger differences between the dominant and nondominant eyes) were usually found in the central visual field. These errors were not closely related to the angle of squint. The clinical history of the strabismics seems to be an important factor for the occurrence of pointing errors. PMID:8160386

Fronius, M; Sireteanu, R

1994-03-01

109

Solvent-extraction complexes of the uranyl ion. 2. Crystal and molecular structures of catena-bis(. mu. -di-n-butyl phosphato-O,O')dioxouranium(VI) and bis(. mu. -di-n-butyl phosphato-O,O')bis((nitrato)(tri-n-butylphosphine oxide)dioxouranium(VI))  

Microsoft Academic Search

Two complexes of the uranyl ion with organophosphus extractants have been analyzed by single-crystal x-ray diffraction methods. A polymeric complex, UO((CH)PO), is formed with dibutylphosphoric acid; and with a mixture of this acid and tributylphosphine oxide a dimeric complex having the composition (UO((CH)PO)((CH)PO)NO) is formed. The first of these is Trinclinic, P1, with a = 8.402 (6) A, b =

1983-01-01

110

Coordination Complexes of p-Hydroxybenzoate on Fe Oxides  

Microsoft Academic Search

Adsorption ofp-hydroxybenzoate anion on synthetic Fe oxides, hydroxides, and oxyhydroxides (hereafter referred to as oxides) was measured at pH 5.5, and the organic-oxide interaction was charac- terized using diffuse-reflectance Fourier-transform infrared (DRIFT) spectroscopy. Surface complexes with ferrihydrite, hematite, goethite, and noncrystalline Fe oxide were investigated. Infrared (IR) spectra of the oxides after separation from p-hydroxybenzoate solutions showed the organic to

King-Hsi Kung; MURRAY B. McBRIDE

1989-01-01

111

Supramolecular coordination and antimicrobial activities of constructed mixed ligand complexes.  

PubMed

A novel series of copper(II) and palladium(II) with 4-derivatives benzaldehyde pyrazolone (L(n)) were synthesized. The mixed ligand complexes were prepared by using 1,10-phenanthroline (Phen) as second ligand. The structure of these complexes was identified and confirm by elemental analysis, molar conductivity, UV-Vis, IR and (1)H NMR spectroscopy and magnetic moment measurements as well as thermal analysis. The ligand behaves as a neutral bidentate ligand through ON donor sites. ESR spectra show the simultaneous presence of a planar trans and a nearly planar cis isomers in the 1:2 ratio for all N,O complexes [Cu(L(n))(2)]Cl(2)?2H(2)O. Schiff bases (L(n)) were tested against bacterial species; namely two Gram positive bacteria (Staphylococcus aureus and Bacillus cereus) and two Gram negative bacteria (Escherichia coli and Klebsiella pneumoniae) and fungal species (Aspergillus niger, Fusarium oxysporium, Penicillium italicum and Alternaria alternata). The tested compounds have antibacterial activity against S. aureus, B. cereus and K. pneumoniae. PMID:23268204

El-Sonbati, A Z; Diab, M A; El-Bindary, A A; Abou-Dobara, M I; Seyam, H A

2013-03-01

112

Supramolecular coordination and antimicrobial activities of constructed mixed ligand complexes  

NASA Astrophysics Data System (ADS)

A novel series of copper(II) and palladium(II) with 4-derivatives benzaldehyde pyrazolone (Ln) were synthesized. The mixed ligand complexes were prepared by using 1,10-phenanthroline (Phen) as second ligand. The structure of these complexes was identified and confirm by elemental analysis, molar conductivity, UV-Vis, IR and 1H NMR spectroscopy and magnetic moment measurements as well as thermal analysis. The ligand behaves as a neutral bidentate ligand through ON donor sites. ESR spectra show the simultaneous presence of a planar trans and a nearly planar cis isomers in the 1:2 ratio for all N,O complexes [Cu(Ln)2]Cl2?2H2O. Schiff bases (Ln) were tested against bacterial species; namely two Gram positive bacteria (Staphylococcus aureus and Bacillus cereus) and two Gram negative bacteria (Escherichia coli and Klebsiella pneumoniae) and fungal species (Aspergillus niger, Fusarium oxysporium, Penicillium italicum and Alternaria alternata). The tested compounds have antibacterial activity against S. aureus, B. cereus and K. pneumoniae.

El-Sonbati, A. Z.; Diab, M. A.; El-Bindary, A. A.; Abou-Dobara, M. I.; Seyam, H. A.

2013-03-01

113

Synthesis and Characterization of Templated Ion Exchange Resins for the Selective Complexation of Actinide Ions  

SciTech Connect

The purpose of this research is to develop a polymeric extractant for the selective complexation of uranyl ions (and subsequently other actinyl and actinide ions) from aqueous solutions (lakes, streams, waste tanks and even body fluids). Chemical insights into what makes a good complexation site will be used to synthesize reagents tailor-made for the complexation of uranyl and other actinide ions. These insights, derived from studies of molecular recognition include ion coordination number and geometry, ionic size and ionic shape, as well as ion to ligand thermodynamic affinity. Selectivity for a specific actinide ion will be obtained by providing the polymers with cavities lined with complexing ligands so arranged as to match the charge, coordination number, coordination geometry, and size of the actinide metal ion. These cavity-containing polymers will be produced by using a specific ion (or surrogate) as a template around which monomeric complexing ligands will be polymerized. The complexing ligands will be ones containing functional groups known to form stable complexes with a specific ion and less stable complexes with other cations. Prior investigator's approaches for making templated resins for metal ions have had marginal success. We have extended and amended these methodologies in our work with Pb(II) and uranyl ion, by changing the order of the steps, by the inclusion of sonication, by using higher complex loading, and the selection of functional groups with better complexation constants. This has resulted in significant improvements to selectivity. The unusual shape of the uranyl ion suggests that this approach will result in even greater selectivities than already observed for Pb(II). Preliminary data obtained for uranyl templated polymers shows unprecedented selectivity and has resulted in the first ion selective electrode for uranyl ion.

Murray, George M.; Uy, O. Manual murragm1@aplcomm.jhuapl.edu; uyom1@aplmsg.jhuapl.edu

2001-03-01

114

Composition for detecting uranyl  

DOEpatents

The present invention relates to an indicator composition for use in spectrophotometric detection of a substance in a solution, and a method for making the composition. Useful indicators are sensitive to the particular substance being measured, but are unaffected by the fluid and other chemical species that may be present in the fluid. Optical indicators are used to measure the uranium concentration of process solutions in facilities for extracting uranium from ores, production of nuclear fuels, and reprocessing of irradiated fuels. The composition comprises an organohalide covalently bonded to an indicator for the substance, in such a manner that the product is itself an indicator that provides increased spectral resolution for detecting the substance. The indicator is preferably arsenazo III and the organohalide is preferably cyanuric chloride. These form a composition that is ideally suited for detecting uranyl.

Baylor, L.C.; Stephens, S.M.

1994-01-01

115

A Convergent Coordination Chemistry-Based Approach to Dissymmetric Macrocyclic Cofacial Porphyrin Complexes  

SciTech Connect

We report a highly convergent and modular approach for the synthesis of dissymmetric cofacial porphyrin complexes, which is based upon the weak-link approach to supramolecular coordination chemistry. Specifically, we have utilized a halide-induced ligand rearrangement reaction, which is capable of providing heteroligated mixed-metal porphyrin complexes in quantitative yield. Significantly, the adoption of a coordination chemistry based approach for the synthesis of these complexes allows for facile in situ regulation of the porphyrin-porphyrin interactions through the addition of external chemical stimuli.

Oliveri, Christopher G.; Heo, Jungseok; Nguyen, SonBinh T.; Mirkin, Chad A.; Wawrzak, Zdzislaw (NWU)

2010-12-03

116

Ligand Dependence of Binding to Three-Coordinate Fe(II) Complexes  

PubMed Central

A series of three- and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sulfur ligands is presented. The electronic variation is explored by measuring the association constant of the neutral ligands, and the reduction potential of the iron(II) complexes. Varying the neutral ligand gives large changes in Keq, which decrease in the order CNtBu > pyridine > 2-picoline > DMF > MeCN > THF > PPh3. These differences can be attributed to a mixture of steric effects and electronic effects (both ? and ?). The binding constants and the reduction potentials are surprisingly insensitive to changes in an anionic spectator ligand. This suggests that three-coordinate iron(II) complexes may have similar binding trends as proposed three-coordinate iron(II) intermediates in the FeMoco of nitrogenase, even though the anionic spectator ligands in the synthetic complexes differ from the sulfides in the FeMoco.

Chiang, Karen P.; Barrett, Pamela M.; Ding, Feizhi; Smith, Jeremy M.; Kingsley, Savariraj; Brennessel, William W.; Clark, Meghan M.; Lachicotte, Rene J.; Holland, Patrick L.

2009-01-01

117

Site-specific mapping of transition metal oxygen coordination in complex oxides  

NASA Astrophysics Data System (ADS)

We demonstrate site-specific mapping of the oxygen coordination number for transition metals in complex oxides using atomically resolved electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope. Pb2Sr2Bi2Fe6O16 contains iron with a constant Fe3+ valency in both octahedral and tetragonal pyramidal coordination and is selected to demonstrate the principle of site-specific coordination mapping. Analysis of the site-specific Fe-L2,3 data reveals distinct variations in the fine structure that are attributed to Fe in a six-fold (octahedron) or five-fold (distorted tetragonal pyramid) oxygen coordination. Using these variations, atomic resolution coordination maps are generated that are in excellent agreement with simulations.

Turner, S.; Egoavil, R.; Batuk, M.; Abakumov, A. A.; Hadermann, J.; Verbeeck, J.; Van Tendeloo, G.

2012-12-01

118

Modeling and Simulation of Complex Network Attributes on Coordinating Large Multiagent System  

PubMed Central

With the expansion of distributed multiagent systems, traditional coordination strategy becomes a severe bottleneck when the system scales up to hundreds of agents. The key challenge is that in typical large multiagent systems, sparsely distributed agents can only communicate directly with very few others and the network is typically modeled as an adaptive complex network. In this paper, we present simulation testbed CoordSim built to model the coordination of network centric multiagent systems. Based on the token-based strategy, the coordination can be built as a communication decision problem that agents make decisions to target communications and pass them over to the capable agents who will potentially benefit the team most. We have theoretically analyzed that the characters of complex network make a significant difference with both random and intelligent coordination strategies, which may contribute to future multiagent algorithm design.

Li, Xiang; Liu, Ming

2014-01-01

119

Spin-labelled cyclometallated palladium complexes. EPR study of dynamic processes in coordination sphere.  

PubMed

New four-, five- and six-coordinated cyclometallated o-semiquinonato palladium complexes were obtained and characterized in solution by EPR. Interaction of square-planar azaphenyl palladium semiquinonate with mono and bidentate phosphane donors leads to formation of five- and six-coordinated adducts. Typical values of HFC constants on apical and basal phosphorouses are observed for such compounds. In one case the reversible addition of tri-phenyl-phosphane was observed. The coordination mode of pincer ligand (bi- or tridentate) in o-semiquinonato pincer complexes depends on the nature of linker between coordinating group and pincer aryl ring. In the case of CH(2) linker five coordinated complexes are formed. The "swing" and "fan" oscillations are observed for these compounds. Complexes with -O- linker are the first examples of compounds with bidentate bonded phosphorous-based pincer ligand. Most of complexes are unstable and decompose during some hours. Only the application of o-semiquinones as spin labels and using the EPR technique made possible to observe and interpret their structure. PMID:23143010

Kozhanov, K A; Bubnov, M P; Abakumov, G A; Cherkasov, V K

2012-12-01

120

Surprising Coordination Geometry Differences in Ce(IV)- and Pu(IV)-Maltol Complexes  

SciTech Connect

As part of a study to characterize the detailed coordination behavior of Pu(IV), single crystal X-ray diffraction structures have been determined for Pu(IV) and Ce(IV) complexes with the naturally-occurring ligand maltol (3-hydroxy-2-methyl-pyran-4-one) and its derivative bromomaltol (5-bromo-3-hydroxy-2-methyl-pyran-4-one). Although Ce(IV) is generally accepted as a structural analog for Pu(IV), and the maltol complexes of these two metals are isostructural, the corresponding bromomaltol complexes are strikingly different with respect to ligand orientation about the metal ion: All complexes exhibit trigonal dodecahedral coordination geometry but the Ce(IV)-bromomaltol complex displays an uncommon ligand arrangement not mirrored in the Pu(IV) complex, although the two metal species are generally accepted to be structural analogs.

Lawrence Berkeley National Laboratory; Raymond, Kenneth; Szigethy, Geza; Xu, Jide; Gorden, Anne E.V.; Teat, Simon J.; Shuh, David K.; Raymond, Kenneth N.

2008-02-12

121

Syntheses, crystal structures and photophysical properties of Ag(I) coordination complexes  

NASA Astrophysics Data System (ADS)

Three Ag(I) coordination complexes, [Ag(pyzca)]n (1) (Hpyzca = pyrazine-2-carboxylic acid), Ag[(HNA)(NA)(H2O)4] (2) (HNA = nicotinic acid) and [Ag1Ag2-(2,3-pydc)]n (3) (H2pydc = pyridine-2, 3-dicarboxylic acid) have been synthesized by the hydrothermal method. Their structures are determined by single-crystal X-ray diffractometer. Complex 1 possesses the 3D infinite structure. Complex 2 is a mononuclear coordination complex and exhibits one 3D infinite network by a large number of hydrogen bonds. In complex 3, two crystallographic independent Ag(I) ions exist, i.e., Ag1 is three-coordinate and Ag2 is two-coordinate, forming the 2D layer structure. At room temperature in the solid state, the IR, FP and UV-Vis spectra of all complexes were measured and investigated in detail. The emission and absorption spectra of the three complexes and their corresponding ligands are compared and analyzed.

Chi, Yu-Xian; Dai, Hui-Ping; Li, Shu-Mei; Jin, Jing; Niu, Shu-Yun; Zhang, Guang-Ning

2013-04-01

122

Characterization and elucidation of coordination requirements of adenine nucleotides complexes with Fe(II) ions.  

PubMed

In spite of the significant role of iron ions-nucleotide complexes in living cells, these complexes have been studied only to a limited extent. Therefore, we fully characterized the ATP:Fe(II) complex including stoichiometry, geometry, stability constants, and dependence of Fe(II)-coordination on pH. A 1:1 stoichiometry was established for the ATP:Fe(II) complex based on volumetric titrations, UV and SEM/EDX measurements. The coordination sites of ferrous ions in the complex with ATP, established by 1H-, 31P-, and 15N-NMR, involve the adenine N7 as well as P(alpha), P(beta), and P(gamma). Coordination sites remain the same within the pH range of 3.1-8.3. By applying fluorescence monitored Fe(II)-titration, we established a logK value of 5.13 for the Fe(ATP)2- complex, and 2.31 for the Fe(HATP)-complex. Ferrous complexes of ADP3- and AMP2- were less stable (log K 4.43 and 1.68, respectively). The proposed major structure for the Fe(ATP)2- complex is the 'open' structure. In the minor 'closed' structure N7 nitrogen is probably coordinated with Fe(II) through a bridging water molecule. The electronic and stereochemical requirements for Fe(II)-coordination with ATP4- were probed using a series of modified-phosphate or modified-adenine ATP analogues. We concluded that: Fe(II) coordinates solely with the phosphate-oxygen atom, and not with sulfur, amine, or borane in the cases of phosphate-modified analogues of ATP; a high electron density on N7 and an anti conformation of the adenine-nucleotide are required for enhanced stability of ATP analogues:Fe(II) complexes as compared to ATP complexes (up to more than 100-fold); there are no stereochemical preferences for Fe(II)-coordination with either Rp or Sp isomers of ATP-alpha-S or ATP-alpha-BH3 analogues. PMID:14533880

Richter, Yael; Fischer, Bilha

2003-09-01

123

Increasing phonological complexity reveals heightened instability in inter-articulatory coordination in adults who stutter  

PubMed Central

The potential role of phonological complexity in destabilizing the speech motor systems of adults who stutter was explored by assessing the performance of 17 adults who stutter and 17 matched control participants on a nonword repetition task. The nonwords varied in length and phonological complexity. Behavioral results revealed no differences between the stuttering and normally fluent groups on accuracy of nonword repetition. In contrast, dramatic differences between groups were observed in the kinematic data. Indices of the consistency of inter-articulator coordination revealed that adults who stutter were much less consistent in their coordinative patterns over repeated productions. With increasing length and complexity of the nonwords, between-group differences in coordinative consistency were more pronounced. Coordination consistency measures revealed that adults who stutter (but not normally fluent adults) showed within-session practice effects; their coordinative consistency improved in five later compared to five earlier productions. Adults who stutter produced the nonwords at a slower rate, but both groups showed increased rates of production on the later trials, indicating a practice effect for duration for both groups. We conclude that, though the adults who stutter performed behaviorally with the same accuracy as normally fluent adults, the nonword repetition task reveals remarkable differences in the speech motor dynamics underlying fluent speech production in adults who stutter compared to their normally fluent peers. These results support a multifactorial, dynamic model of stuttering in which linguistic complexity and utterance length are factors that contribute to the probability of breakdown of the speech motor system.

Smith, Anne; Sadagopan, Neeraja; Walsh, Bridget; Weber-Fox, Christine

2010-01-01

124

Coordination and Redox Isomerization in the Reduction of a Uranium(III) Monoarene Complex.  

PubMed

Synthetic studies on the redox chemistry of trivalent uranium monoarene complexes were undertaken with a complex derived from the chelating tris(aryloxide)arene ligand ((Ad,Me) ArO)3 mes(3-) . Cyclic voltammetry of [{((Ad,Me) ArO)3 mes}U(III) ] (1) revealed a nearly reversible and chemically accessible reduction at -2.495?V vs. Fc/Fc(+) -the first electrochemical evidence for a formally divalent uranium complex. Chemical reduction of 1 indicates that reduction induces coordination and redox isomerization to form a uranium(IV) hydride, and addition of a crown ether results in hydride insertion into the coordinated arene to afford uranium(IV) complexes. This stoichiometric reaction sequence provides structural insight into the mechanism of arene functionalization at diuranium inverted sandwich complexes. PMID:24889470

La Pierre, Henry S; Kameo, Hajime; Halter, Dominik P; Heinemann, Frank W; Meyer, Karsten

2014-07-01

125

Barium uranyl diphosphonates  

NASA Astrophysics Data System (ADS)

Three Ba2+/UO22+ methylenediphosphonates have been prepared from mild hydrothermal treatment of uranium trioxide, methylendiphosphonic acid (C1P2) with barium hydroxide octahydrate, barium iodate monohydrate, and small aliquots of HF at 200 C. These compounds, Ba[UO2[CH2(PO3)2]1.4H2O (Ba-1), Ba3[(UO2)4(CH2(PO3)2)2F6]6H2O (Ba-2), and Ba2[(UO2)2(CH2(PO3)2)F4]5.75H2O (Ba-3) all adopt layered structures based upon linear uranyl groups and disphosphonate molecules. Ba-2 and Ba-3 are similar in that they both have UO5F2 pentagonal bipyramids that are bridged and chelated by the diphosphonate moiety into a two-dimensional zigzag anionic sheet (Ba-2) and a one-dimensional ribbon anionic chain (Ba-3). Ba-1, has a single crystallographically unique uranium metal center where the C1P2 ligand solely bridges to form [UO2[CH2(PO3)2]2- sheets. The interlayer space of the structures is occupied by Ba2+, which, along with the fluoride ion, mediates the structure formed and maintains overall charge balance.

Nelson, Anna-Gay D.; Alekseev, Evgeny V.; Ewing, Rodney C.; Albrecht-Schmitt, Thomas E.

2012-08-01

126

Electrochemically fabricated polypyrrole-cobalt-oxygen coordination complex as high-performance lithium-storage materials.  

PubMed

Current lithium-ion battery (LIB) technologies are all based on inorganic electrode materials, though organic materials have been used as electrodes for years. Disadvantages such as limited thermal stability and low specific capacity hinder their applications. On the other hand, the transition metal oxides that provide high lithium-storage capacity by way of electrochemical conversion reaction suffer from poor cycling stability. Here we report a novel high-performance, organic, lithium-storage material, a polypyrrole-cobalt-oxygen (PPy-Co-O) coordination complex, with high lithium-storage capacity and excellent cycling stability. Extended X-ray absorption fine structure and Raman spectroscopy and other physical and electrochemical characterizations demonstrate that this coordination complex can be electrochemically fabricated by cycling PPy-coated Co(3)O(4) between 0.0 V and 3.0 V versus Li(+)/Li. Density functional theory (DFT) calculations indicate that each cobalt atom coordinates with two nitrogen atoms within the PPy-Co coordination layer and the layers are connected with oxygen atoms between them. Coordination weakens the C-H bonds on PPy and makes the complex a novel lithium-storage material with high capacity and high cycling stability. PMID:22127820

Guo, Bingkun; Kong, Qingyu; Zhu, Ying; Mao, Ya; Wang, Zhaoxiang; Wan, Meixiang; Chen, Liquan

2011-12-23

127

Selective extraction of uranyl ions using ion-imprinted chelating microspheres.  

PubMed

In this work, uranyl complex with Schiff base derived from condensation of p-aminostyrene and salicyaldehyde (HASS) was synthesized. Both ligand and uranyl complex were characterized using elemental analysis, FTIR, (1)H and (13)C NMR spectra. The complex was then copolymerized with styrene and divinylbenzene cross-linker using potassium persulfate free radical initiator through emulsion polymerization technique. The uranyl ions were then leached out from the cross-linked network to finally produce uranyl ion-imprinted microspheres (U-PASS), which were investigated using SEM and FTIR. The effect of various significant parameters such as pH, temperature, contact times and initial uranyl concentration on the removal of uranyl from aqueous solution was examined and the results indicated that the adsorption was exothermic in nature and the kinetics of adsorption fit with the second-order kinetic model. Also, Langmuir adsorption isotherm exhibited the best fit with the experimental results with maximum adsorption capacity 147.8 mg/g. Moreover, the selectivity studies revealed that the ion-imprinted microspheres resin exhibited an obvious affinity toward the uranyl ions in presence of other interfering metal ions compared to the non-imprinted resin. PMID:24703676

Monier, M; Elsayed, Nadia H

2014-06-01

128

Coordination chemistry, thermodynamics and DFT calculations of copper(II) NNOS Schiff base complexes.  

PubMed

Synthesis, magnetic and spectroscopy techniques are described for five copper(II) containing tetradentate Schiff bases are synthesized from methyl-2-(N-2'-aminoethane), (1-methyl-2'-aminoethane), (3-aminopropylamino)cyclopentenedithiocarboxylate. Molar conductance and infrared spectral evidences indicate that the complexes are four-coordinate in which the Schiff bases are coordinated as NNOS ligands. Room temperature ?eff values for the complexes are 1.71-1.80B.M. corresponding to one unpaired electron respectively. The formation constants and free energies were measured spectrophotometrically, at constant ionic strength 0.1M (NaClO4), at 25?C in DMF solvent. Also, the DFT calculations were carried out to determine the structural and the geometrical properties of the complexes. The DFT results are further supported by the experimental formation constants of these complexes. PMID:24992917

Esmaielzadeh, Sheida; Azimian, Leila; Shekoohi, Khadijeh; Mohammadi, Khosro

2014-12-10

129

Synthesis and reactivity of two-coordinate Ni(I) alkyl and aryl complexes.  

PubMed

Reaction of [(IPr)Ni(?-Cl)]2 (1-Cl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with ClMg{CH(SiMe3)2}Et2O affords (IPr)Ni{CH(SiMe3)2} (2), a two-coordinate Ni(I) alkyl complex. An analogous two-coordinate aryl derivative, (IPr)Ni(dmp) (dmp = 2,6-dimesitylphenyl), can be similarly prepared from Li(dmp) and 1-Cl. Reaction of 2 with alkyl bromides gives the three-coordinate Ni(II) alkyl halide complex (IPr)Ni{CH(SiMe3)2}Br. Evidence for a radical mechanism is presented to explain the reaction of 2 with alkyl halides. PMID:24237257

Laskowski, Carl A; Bungum, Donald J; Baldwin, Steven M; Del Ciello, Sarah A; Iluc, Vlad M; Hillhouse, Gregory L

2013-12-11

130

Synthesis and Base Hydrolysis of a Cobalt(III) Complex Coordinated by a Thioether Ligand  

ERIC Educational Resources Information Center

A two-week laboratory experiment for students in advanced inorganic chemistry is described. Students prepare and characterize a cobalt(III) complex coordinated by a thioether ligand during the first week of the experiment and then study the kinetics of Co-S bond cleavage in basic solution during the second week. The synthetic portion of the

Roecker, Lee

2008-01-01

131

Complex-coordinate calculation of 1D(e) resonances using Hylleraas functions  

NASA Technical Reports Server (NTRS)

The lowest 1D(e) resonances below the n = 2 and n = 3 thresholds are calculated using a method of complex-coordinate rotation. The results, obtained with the use of Hylleraas functions, are believed to be of high accuracy. This work should serve as a useful reference for other investigations.

Bhatia, A. K.; Ho, Y. K.

1990-01-01

132

Room-temperature magnetic anisotropy of lanthanide complexes: A model study for various coordination polyhedra  

Microsoft Academic Search

The dependence of the room-temperature magnetic anisotropy ?? of lanthanide complexes on the type of the coordination polyhedron and on the nature of the lanthanide ion is quantitatively analyzed in terms of a model approach based on numerical calculations. The aim of this study is to establish general regularities in the variation of the sign and magnitude of the magnetic

Vladimir S. Mironov; Yury G. Galyametdinov; Arnout Ceulemans; Koen Binnemans

2002-01-01

133

Room-temperature magnetic anisotropy of lanthanide complexes: A model study for various coordination polyhedra  

Microsoft Academic Search

The dependence of the room-temperature magnetic anisotropy Deltachi of lanthanide complexes on the type of the coordination polyhedron and on the nature of the lanthanide ion is quantitatively analyzed in terms of a model approach based on numerical calculations. The aim of this study is to establish general regularities in the variation of the sign and magnitude of the magnetic

Vladimir S. Mironov; Yury G. Galyametdinov; Arnout Ceulemans; Christiane Grller-Walrand; Koen Binnemans

2002-01-01

134

Analogies Among Active Sites of Coordinatively-Unsaturated Transition-Metal Complexes, Surfaces and Supported Catalysts.  

National Technical Information Service (NTIS)

It has been shown by Ugo et al. that the coordinatively-unsaturated transition-metal complex (PPh3)2Pt (bistriphenylphosphine-platinum(0))- exhibits a chemical reactivity and binding stability with respect to the molecules O2, CO, SO2, C2H2, C2H4, H2, and...

K. H. Johnson A. C. Balazs H. J. Kolari

1977-01-01

135

A Tetrahomodioxacalix[6]arene as a Ditopic Ligand for Uranyl Ions with Carbonate or Carbamate Bridges  

Microsoft Academic Search

The first crystal structures of a p-tert-butyltetrahomodioxacalix[6]arene comprising two tri-phenolic subunits separated by two ether bridges and two of its complexes with uranyl ions are reported. The doubly deprotonated macrocycle assumes a much elongated, cone-like conformation including two organic species. Two binuclear uranyl complexes are described. In both, each cation is bound to the three phenoxide oxygen atoms of a

Bernardo Masci; Pierre Thury

2003-01-01

136

Influence of topology in the evolution of coordination in complex networks under information diffusion constraints  

NASA Astrophysics Data System (ADS)

In this paper, we study the influence of the topological structure of social systems on the evolution of coordination in them. We simulate a coordination game ("Stag-hunt") on four well-known classes of complex networks commonly used to model social systems, namely scale-free, small-world, random and hierarchical-modular, as well as on the well-mixed model. Our particular focus is on understanding the impact of information diffusion on coordination, and how this impact varies according to the topology of the social system. We demonstrate that while time-lags and noise in the information about relative payoffs affect the emergence of coordination in all social systems, some topologies are markedly more resilient than others to these effects. We also show that, while non-coordination may be a better strategy in a society where people do not have information about the payoffs of others, coordination will quickly emerge as the better strategy when people get this information about others, even with noise and time lags. Societies with the so-called small-world structure are most conducive to the emergence of coordination, despite limitations in information propagation, while societies with scale-free topologies are most sensitive to noise and time-lags in information diffusion. Surprisingly, in all topologies, it is not the highest connected people (hubs), but the slightly less connected people (provincial hubs) who first adopt coordination. Our findings confirm that the evolution of coordination in social systems depends heavily on the underlying social network structure.

Kasthurirathna, Dharshana; Piraveenan, Mahendra; Harr, Michael

2014-01-01

137

Spectroscopic and theoretical studies on axial coordination of bis(pyrrol-2-ylmethyleneamine)phenyl complexes  

NASA Astrophysics Data System (ADS)

Metal (M = Zn(II), Ni(II), Cu(II)) complexes with tetradentate Schiff base ligand, bis(pyrrol-2-ylmethyleneamine)phenyl, has been synthesized and characterized by elemental analyses, 1H NMR, mass spectra and UV-vis spectra. The standard association constants ( K?) and the thermodynamic parameters (?Hm?, ?Sm?, ?Gm?) for axial coordination of imidazole derivatives with these Shiff base complexes were measured with UV-vis spectrophotometric titration. The decrease of enthalpy is found to be the drive of the axial coordination. Our Schiff base complexes can incorporate two axial ligands, except 2-Et-4-MeIm with two big substituents of great steric bulk according to stoichiometry of 1:1. ZnL displays high selectively binding to imidazole due to the steric bulk effect. Supporting density functional theory (DFT) calculations have been undertaken on B3LYP/6-31G(d) level.

Chen, Jia-Mei; Ruan, Wen-Juan; Meng, Liang; Gao, Feng; Zhu, Zhi-Ang

2008-11-01

138

Spectroscopic and theoretical studies on axial coordination of bis(pyrrol-2-ylmethyleneamine)phenyl complexes.  

PubMed

Metal (M = Zn(II), Ni(II), Cu(II)) complexes with tetradentate Schiff base ligand, bis(pyrrol-2-ylmethyleneamine)phenyl, has been synthesized and characterized by elemental analyses, 1H NMR, mass spectra and UV-vis spectra. The standard association constants (Ktheta) and the thermodynamic parameters (Delta(r)Hmtheta,Delta(r)Smtheta,Delta(r)Gmtheta) for axial coordination of imidazole derivatives with these Shiff base complexes were measured with UV-vis spectrophotometric titration. The decrease of enthalpy is found to be the drive of the axial coordination. Our Schiff base complexes can incorporate two axial ligands, except 2-Et-4-MeIm with two big substituents of great steric bulk according to stoichiometry of 1:1. ZnL displays high selectively binding to imidazole due to the steric bulk effect. Supporting density functional theory (DFT) calculations have been undertaken on B3LYP/6-31G(d) level. PMID:18243780

Chen, Jia-Mei; Ruan, Wen-Juan; Meng, Liang; Gao, Feng; Zhu, Zhi-Ang

2008-11-01

139

Pi-accepting-pincer rhodium complexes: an unusual coordination mode of PCP-type systems.  

PubMed

The novel pi-accepting, pincer-type ligand, dipyrrolylphoshinoxylene (DPyPX), is introduced. This ligand has the strongest pi-accepting phosphines used so far in the PCP family of ligands and this results in some unusual coordination chemistry. The rhodium(I) complex, [(DPyPX)Rh(CO)(PR3)] (4, R=Ph, Et, pyrrolyl) is prepared by treating the relevant [(DPyPX)Rh(PR3)] (3) complex with CO and is remarkably resistant to loss of either ligand. X-ray crystallographic analysis of complex 4 b (R=Et) reveals an unusual cisoid coordination of the PCP phosphine ligands. These observations are supported by density functional theory (DFT) calculations. PMID:15643661

Kossoy, Elizaveta; Iron, Mark A; Rybtchinski, Boris; Ben-David, Yehoshoa; Shimon, Linda J W; Konstantinovski, Leonid; Martin, Jan M L; Milstein, David

2005-04-01

140

Structural properties of the inner coordination sphere of indium chloride complexes in organic and aqueous solutions.  

PubMed

The nature of the inner coordination sphere of In(3+) present in both the organic and aqueous solutions during the solvent extraction of In(3+) from an aqueous HCl solution with tri-n-octyl amine (TOA) was investigated by In K-edge XAFS. This information was then used to clarify the details of the extraction properties of indium chloride anion complexes with TOA. In aqueous HCl solution (0.1-10 M), In(3+) exists as octahedral anion complexes, [InCln(H2O)6-n](3-n) (n ? 4); the [InCl6](3-) complex is dominant at 10 M HCl. The extraction of In(3+) from HCl solution with TOA was performed using two kinds of diluents: nitrobenzene (NB) or n-dodecane (DD), which contained 20 vol% of 2-ethylhexanol as an additive. The stoichiometric composition of the extracted complexes, which is estimated from the distribution ratios of In(3+), is affected by the diluents and the HCl concentration of the aqueous phase; the apparent values of TOA/In(3+) in the extracted complex are 3 for DD-1 M HCl (diluent-aqueous phase) and DD-5 M HCl, 2 for NB-1 M HCl and NB-5 M HCl, and 1 for NB-10 M HCl. The EXAFS analysis of these extracted complexes shows that the In(3+) has ?4 Cl(-) at ?2.336 and no H2O in the inner coordination sphere; additionally, the shape of the XANES suggests that their coordination geometry is tetrahedral. Therefore, the same tetrahedral [InCl4](-) complex is formed during the extraction in spite of the variation in the stoichiometric composition (TOA/In(3+) = 1-3) of the extracted complexes. PMID:24217005

Narita, Hirokazu; Tanaka, Mikiya; Shiwaku, Hideaki; Okamoto, Yoshihiro; Suzuki, Shinichi; Ikeda-Ohno, Atsushi; Yaita, Tsuyoshi

2014-01-28

141

Three-Coordinate Terminal Imidoiron(III) Complexes: Structure, Spectroscopy, and Mechanism of Formation  

PubMed Central

Reaction of 1-adamantyl azide with iron(I) diketiminate precursors gives metastable but isolable imidoiron(III) complexes LFe=NAd (L = bulky ?-diketiminate ligand; Ad = 1-adamantyl). This paper addresses: (1) the spectroscopic and structural characterization of the Fe=N multiple bond in these interesting three-coordinate iron imido complexes, and (2) the mechanism through which the imido complexes form. The iron(III) imido complexes have been examined by 1H NMR and EPR spectroscopies and temperature-dependent magnetic susceptibility (SQUID), and structurally characterized by crystallography and/or X-ray absorption (EXAFS) measurements. These data show that the imido complexes have quartet ground states and short (1.68 0.01 ) iron-nitrogen bonds. The formation of the imido complexes proceeds through unobserved ironRN3 intermediates, which are indicated by QM/MM computations to be best described as iron(II) with an RN3 radical anion. The radical character on the organoazide bends its NNN linkage to enable easy N2 loss and imido complex formation. The product distribution between imidoiron(III) products and hexazene-bridged diiron(II) products is solvent-dependent, and the solvent dependence can be explained by coordination of certain solvents to the iron(I) precursor prior to interaction with the organoazide.

Cowley, Ryan E.; DeYonker, Nathan J.; Eckert, Nathan A.; Cundari, Thomas R.; DeBeer, Serena; Bill, Eckhard; Ottenwaelder, Xavier; Flaschenriem, Christine; Holland, Patrick L.

2010-01-01

142

Ligand dependence of binding to three-coordinate Fe(II) complexes.  

PubMed

A series of three- and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sulfur ligands is presented. The electronic variation is explored by measuring the association constant of the neutral ligands and the reduction potential of the iron(II) complexes. Varying the neutral ligand gives large changes in K(eq), which decrease in the order CN(t)Bu > pyridine >2-picoline > DMF > MeCN > THF > PPh(3). These differences can be attributed to a mixture of steric effects and electronic effects (both sigma-donation and pi-backbonding). The binding constants and the reduction potentials are surprisingly insensitive to changes in an anionic spectator ligand. This suggests that three-coordinate iron(II) complexes may have similar binding trends as proposed three-coordinate iron(II) intermediates in the FeMoco of nitrogenase, even though the anionic spectator ligands in the synthetic complexes differ from the sulfides in the FeMoco. PMID:19438179

Chiang, Karen P; Barrett, Pamela M; Ding, Feizhi; Smith, Jeremy M; Kingsley, Savariraj; Brennessel, William W; Clark, Meghan M; Lachicotte, Rene J; Holland, Patrick L

2009-06-15

143

Zinc(II)-Coordination Complexes as Membrane Active Fluorescent Probes and Antibiotics  

PubMed Central

Molecular probes with zinc(II)-(2,2-dipicolylamine) coordination complexes associate with oxyanions in aqueous solution and target biomembranes that contain anionic phospholipids. This study examines a new series of coordination complexes with 2,6-bis(zinc(II)-dipicolylamine) phenoxide as the molecular recognition unit. Two lipophilic analogues are observed to partition into the membranes of zwitterionic and anionic vesicles and induce the transport of phospholipids and hydrophilic anions (carboxyfluorescein). These lipophilic zinc complexes are moderately toxic to mammalian cells. A more hydrophilic analogue does not exhibit mammalian cell toxicity (LD50 >50 g/mL), but it is highly active against the Gram-positive bacteria Staphylococcus aureus (MIC of 1 g/mL). Furthermore, it is active against clinically important S. aureus strains that are resistant to various antibiotics including vancomycin and oxacillin. The antibiotic action is attributed to its ability to depolarize the bacterial cell membrane. The intense bacterial staining exhibited by a fluorescent conjugate suggests that this family of zinc coordination complexes can be used as molecular probes for the detection and imaging of bacteria.

DiVittorio, Kristy M.; Leevy, W. Matthew; O'Neil, Edward J.; Johnson, James R.; Vakulenko, Sergei; Morris, Joshua D.; Rosek, Kristine D.; Serazin, Nathan; Hilkert, Sarah; Hurley, Scott; Marquez, Manuel; Smith, Bradley D.

2010-01-01

144

Reactivity pathways for nitric oxide and nitrosonium with iron complexes in biologically relevant sulfur coordination spheres.  

PubMed

The interaction of nitric oxide (NO) with iron-sulfur cluster proteins results in the formation of dinitrosyl iron complexes (DNICs) coordinated by cysteine residues from the peptide backbone or with low molecular weight sulfur-containing molecules like glutathione. Such DNICs are among the modes available in biology to store, transport, and deliver NO to its relevant targets. In order to elucidate the fundamental chemistry underlying the formation of DNICs and to characterize possible intermediates in the process, we have investigated the interaction of NO (g) and NO(+) with iron-sulfur complexes having the formula [Fe(SR)(4)](2-), where R=(t)Bu, Ph, or benzyl, chosen to mimic sulfur-rich iron sites in biology. The reaction of NO (g) with [Fe(S(t)Bu)(4)](2-) or [Fe(SBz)(4)](2-) cleanly affords the mononitrosyl complexes (MNICs), [Fe(S(t)Bu)(3)(NO)](-) (1) and [Fe(SBz)(3)(NO)](-) (3), respectively, by ligand displacement. Mononitrosyl species of this kind were previously unknown. These complexes further react with NO (g) to generate the corresponding DNICs, [Fe(SPh)(2)(NO)(2)](-) (4) and [Fe(SBz)(2)(NO)(2)](-) (5), with concomitant reductive elimination of the coordinated thiolate donors. Reaction of [Fe(SR)(4)](2-) complexes with NO(+) proceeds by a different pathway to yield the corresponding dinitrosyl S-bridged Roussin red ester complexes, [Fe(2)(mu-S(t)Bu)(2)(NO)(4)] (2), [Fe(2)(mu-SPh)(2)(NO)(4)] (7) and [Fe(2)(mu-SBz)(2)(NO)(4)] (8). The NO/NO(+) reactivity of an Fe(II) complex with a mixed nitrogen/sulfur coordination sphere was also investigated. The DNIC and red ester species, [Fe(S-o-NH(2)C(6)H(4))(2)(NO)(2)](-) (6) and [Fe(2)(mu-S-o-NH(2)C(6)H(4))(2)(NO)(4)] (9), were generated. The structures of 8 and 9 were verified by X-ray crystallography. The MNIC complex 1 can efficiently deliver NO to iron-porphyrin complexes like [Fe(TPP)Cl], a reaction that is aided by light. Removal of the coordinated NO ligand of 1 by photolysis and addition of elemental sulfur generates higher nuclearity Fe/S clusters. PMID:17618690

Harrop, Todd C; Song, Datong; Lippard, Stephen J

2007-11-01

145

Flexible and Asymmetric Ligand in Constructing Coordinated Complexes: Synthesis, Crystal Structures and Fluorescent Characterization  

PubMed Central

Flexible and asymmetric ligand L [L = 1-((pyridin-3-yl)methyl)-1H-benzotriazole], is used as a basic backbone to construct complicated metal-organic frameworks. Two new polymers, namely, [Ag2(L)2(NO3)2]n (1) and [Ag(L)(ClO4)]n (2), were synthesized and characterized by X-ray structure analysis and fluorescent spectroscopy. The complex 1 gives an S type double helical conformation, whereas complex 2 exhibits a 1D zigzag configuration. Different anions affect the silver coordination geometry and crystal packing topology.

Chen, Peng; Lin, Jianhua

2011-01-01

146

SIDEROPHILIN METAL COORDINATION. 1. COMPLEXATION OF THORIUM BY TRANSFERRIN: STRUCTURE-FUNCTION IMPLICATIONS  

SciTech Connect

As part of a program to develop actinide-specific sequestering agents, the coordination of actinide ions by human transferrin is being investigated. Therapeutically useful synthetic ligands must be able to compete with this iron-transport protein for the bound actinide ion. As in the Fe(III) complex of the native protein, two Th(IV) ions bind at pH 7. This coordination has been monitored at several pH values by using difference ultraviolet spectroscopy. The corresponding coordination of a phenolic ligand, ethylene-bis-(o-hydroxyphenylglycine) [EHPG], has been used to determine {Delta}{epsilon} for a tyrosyl group coordinated to Th(IV), in contrast to the common practice of assuming the {Delta}{epsilon} for protons and all metal ions is the same. This in turn is used to determine, from the observed {Delta}{epsilon} upon protein coordination, the number of transferrin tyrosine residues that coordinate. Maxima in the Th(IV) + EHPG difference UV spectra occur at 292 and 238 nm, with corresponding {Delta}{epsilon} values per phenolic group of 2330 and 8680 cm{sup -1} M{sup -1}, respectively. At pH 7.2, the Th(IV) transferrin spectrum is closely similar to the TH(IV) EHPG spectrum, with maxima at 292 and 240 nm. The {Delta}{epsilon} at 240 nm reaches a maximum of 24700 cm{sup -1} M{sup -1}, which corresponds to coordination of three tyrosine residues in the dithorium-transferrin complex; the stronger binding site (A or C-terminal) coordinates via two tyrosines and the weaker (B or N-terminal) via one. There is evidence suggesting that the N-terminal site is slightly smaller than the C-terminal site; while Th(IV) easily fits into the C-terminal site, the large ionic radius of Th(IV) makes this ion of borderline size to fit into the N-terminal site. This may be an important biological difference between Th(IV) and the slightly smaller Pu(IV), which should easily fit into both sites. At pH values below 7, the complexation of Th(IV) by transferrin decreases rapidly. At pH 6 and a Th(IV)/transferrin ratio of 2, only ~0.3 Th(IV) are bound per protein ([Th] = 10{sup -5}M). The N-terminal site is more rapidly affected by lowering the pH, so that coordination is entirely at the C-terminal site at low pH. Above pH 9, the conformation at the C-terminal site (two tyrosines) changes such that only one tyrosine is bound, the same that pertains at the N-terminal site at neutral pH. In addition to the three protons released by the coordinating tyrosine residues, the complexation of two Th(IV) ions releases two more protons at pH 8.6, which are ascribed to hydrolysis, so that the metal is bound as a monohydroxo species. It is suggested that diferric transferrin undergoes a similar reaction, and the other implications of these results for the structure and function of the native ferric transferrin are discussed.

Harris, Wesley R.; Carrano, Carl J.; Pecoraro, Vincent L.; Raymond, Kenneth N.

1980-08-01

147

Synthesis of 1,3Diphenyl4,5-bis(hydroxyimino)imidazolidine and Its Complexes with Nickel(II), Cobalt(II), Copper(II), Palladium(II), and Uranyl(VI)  

Microsoft Academic Search

1, 3-Dipheny1-4, 5-bis(hydroxyimino)imidazolidine (LH2) has been prepared from anti-dichloroglyoxime, N,N?-diphenylmethylenediamine, and sodium bicarbonate in ethanol. Complexes of Cu(II), Ni(II), Co(II), Pd(II), and UO2(VI) and LH2 give a metal-ligand ratio of 1:2. A tetrahedral complex is obtained for the Ni(II) complex by coordination through N and O atoms. The (LH2)Co. H2O complex is squarepyramidal while the Cu(II), Pd(II) and UO2(VI) complexes

Vefa Ahsen; zer Bek?ro?lu

1985-01-01

148

Density functional theory and molecular dynamics study of the uranyl ion (UO?)?.  

PubMed

The detection of uranium is very important, especially in water and, more importantly, in the form of uranyl ion (UO?)?, which is one of its most abundant moieties. Here, we report analyses and simulations of uranyl in water using ab initio modified force fields for water with improved parameters and charges of uranyl. We use a TIP4P model, which allows us to obtain accurate water properties such as the boiling point and the second and third shells of water molecules in the radial distribution function thanks to a fictitious charge that corrects the 3-point models by reproducing the exact dipole moment of the water molecule. We also introduced non-bonded interaction parameters for the water-uranyl intermolecular force field. Special care was taken in testing the effect of a range of uranyl charges on the structure of uranyl-water complexes. Atomic charges of the solvated ion in water were obtained using density functional theory (DFT) calculations taking into account the presence of nitrate ions in the solution, forming a neutral ensemble. DFT-based force fields were calculated in such a way that water properties, such as the boiling point or the pair distribution function stand. Finally, molecular dynamics simulations of a water box containing uranyl cations and nitrate anions are performed at room temperature. The three peaks in the oxygen-oxygen radial distribution function for water were found to be kept in the presence of uranyl thanks to the improvement of interaction parameters and charges. Also, we found three shells of water molecules surrounding the uranyl ion instead of two as was previously thought. PMID:24573498

Rodrguez-Jeangros, Nicols; Seminario, Jorge M

2014-03-01

149

An MRAS, SHOC2, and SCRIB complex coordinates ERK pathway activation with polarity and tumorigenic growth.  

PubMed

SHOC2 is mutated in Noonan syndrome and plays a key role in the activation of the ERK-MAPK pathway, which is upregulated in the majority of human cancers. SHOC2 functions as a PP1-regulatory protein and as an effector of MRAS. Here we show that SHOC2 and MRAS form a complex with SCRIB, a polarity protein with tumor suppressor properties. SCRIB functions as a PP1-regulatory protein and antagonizes SHOC2-mediated RAF dephosphorylation through a mechanism involving competition for PP1 molecules within the same macromolecular complex. SHOC2 function is selectively required for the malignant properties of tumor cells with mutant RAS, and both MRAS and SHOC2 play a key role in polarized migration. We propose that MRAS, through its ability to recruit a complex with paradoxical components, coordinates ERK pathway spatiotemporal dynamics with polarity and that this complex plays a key role during tumorigenic growth. PMID:24211266

Young, Lucy C; Hartig, Nicole; Muoz-Alegre, Marta; Oses-Prieto, Juan A; Durdu, Sevi; Bender, Sabine; Vijayakumar, Vineetha; Vietri Rudan, Matteo; Gewinner, Christina; Henderson, Stephen; Jathoul, Amit P; Ghatrora, Rupinder; Lythgoe, Mark F; Burlingame, Alma L; Rodriguez-Viciana, Pablo

2013-12-12

150

Computational Study of Coordinated Ni(II) Complex with High Nitrogen Content Ligands  

PubMed Central

Density functional computations were performed on two tetracoordinated Ni(II) complexes as high nitrogen content energetic materials (1: dinickel bishydrazine ter[(1H-Tetrazol-3-yl)methan-3yl]-1H-tetrazole and 2: dinickel tetraazide ter[(1H-Tetrazol-3-yl)methan-3yl]-1H-tetrazolate). The geometrical structures, relative stabilities and sensitivities, and thermodynamic properties of the complexes were investigated. The energy gaps of frontier molecular orbital (HOMO and LUMO) and vibrational spectroscopies were also examined. There are minor Jahn-Teller distortions in both complexes 1 and 2, with two long NiN bond lengths and two short ones. The enthalpies of combustion for both complexes are over 3600?kJ/mol. The NN bond lengths in the moieties of hydrazine and azide ligands increase in the coordination process compared to those of the isolated molecules.

Tang, Bo; Ye, Jia-Hai; Ju, Xue-Hai

2011-01-01

151

Bivalent and trivalent iron complexes of acyclic hexadentate ligands providing pyridyl/pyrazine-amide-thioether coordination.  

PubMed

Acyclic pyridine-2-carboxamide- and thioether-containing hexadentate ligand 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpctb), in its deprotonated form, has afforded purple low-spin (S = 0) iron(II) complex [Fe(bpctb)] (1). A new ligand, the pyrazine derivative of H(2)bpctb, 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpzctb), has been synthesized which has furnished the isolation of purple iron(II) complex [Fe(bpzctb)].CH(2)Cl(2) (4) (S = 0). Chemical oxidation of 1 by [(eta(5)-C(5)H(5))(2)Fe][PF(6)] or [Ce(NO(3))(6)][NH(4)](2) led to the isolation of low-spin (S = 1/2) green Fe(III) complexes [Fe(bpctb)][PF(6)] (2) or [Fe(bpctb)][NO(3)].H(2)O (3), and oxidation of 4 by [Ce(NO(3))(6)][NH(4)](2) afforded [Fe(bpzctb)][NO(3)].H(2)O (5) (S = 1/2). X-ray crystal structures of 1 and 4 revealed that (i) in each case the ligand coordinates in a hexadentate mode and (ii) bpzctb(2-) binds more strongly than bpctb(2-), affording distorted octahedral M(II)N(2)(pyridine/pyrazine)N'(2)(amide)S(2)(thioether) coordination. To the best of our knowledge, 1 and 4 are the first examples of six-coordinate low-spin Fe(II) complexes of deprotonated pyridine/pyrazine amide ligands having appended thioether functionality. The Fe(III) complexes display rhombic EPR spectra. Each complex exhibits in CH(2)Cl(2)/MeCN a reversible to quasireversible cyclic voltammetric response, corresponding to the Fe(III)-Fe(II) redox process. The E(1/2) value of 4 is more anodic by approximately 0.2 V than that of 1, attesting that compared to pyridine, pyrazine is a better stabilizer of iron(II). Moreover, the E(1/2) value of 1 is significantly higher (approximately 1.5 V) than that reported for six-coordinate Fe(II)/Fe(III) complexes of the tridentate pyridine-2-carboxamide ligand incorporating thiolate donor site. PMID:16060634

Singh, Akhilesh Kumar; Mukherjee, Rabindranath

2005-08-01

152

The Runge-Lenz vector for quantum Kepler problem in the space of positive constant curvature and complex parabolic coordinates  

Microsoft Academic Search

By analogy with the Lobachevsky space H_{3}, generalized parabolic\\u000acoordinates (t_{1},t_{2},\\\\phi) are introduced in Riemannian space model of\\u000apositive constant curvature S_{3}. In this case parabolic coordinates turn out\\u000ato be complex valued and obey additional restrictions involving the complex\\u000aconjugation. In that complex coordinate system, the quantum-mechanical Coulomb\\u000aproblem is stu- died: separation of variables is carried out and

A. A. Bogush; V. S. Otchik; V. M. Red'kov

2006-01-01

153

Investigating the pharmacodynamic and magnetic properties of pyrophosphate-bridged coordination complexes  

NASA Astrophysics Data System (ADS)

The multidentate nature of pyrophosphate makes it an attractive ligand for complexation of metal cations. The participation of pyrophosphate in a variety of biological pathways and its metal catalyzed hydrolysis has driven our investigation into its coordination chemistry. We have successfully synthesized a library of binuclear pyrophosphate bridge coordination complexes. The problem of pyrophosphate hydrolysis to phosphate in the presence of divalent metal ions was overcome by incorporating capping ligands such as 1,10-phenanthroline and 2,2'-bipyridine prior to the addition of the pyrophosphate. The magnetic properties of these complexes was investigated and magneto-structural analysis was conducted. The biological abundance of pyrophosphate and the success of metal based drugs such as cisplatin, prompted our investigation of the cytotoxic properties of M(II) pyrophosphate dimeric complexes (where M(II) is CoII, CuII, and NiII) in adriamycin resistant human ovarian cancer cells. Thess compounds were found to exhibit toxicity in the nanomolar to picomolar range. We conducted in vitro stability studies and the mechanism of cytoxicity was elucidated by performing DNA mobility and binding assays, enzyme inhibition assays, and in vitro oxidative stress studies.

Ikotun, Oluwatayo (Tayo) F.

154

Versatile reactivity of a four-coordinate scandium phosphinidene complex: reduction, addition, and CO activation reactions.  

PubMed

The four-coordinate scandium phosphinidene complex, [LSc(?-PAr)]2 (L = (MeC(NDIPP)CHC(Me)(NCH2CH2N((i)Pr)2)), DIPP = 2,6-((i)Pr)2C6H3; Ar = 2,6-Me2C6H3) (1), has been synthesized in good yield, and its reactivity has been investigated. Although 1 has a bis(?-phosphinidene)discandium structural unit, this coordinatively unsaturated complex shows high and versatile reactivity toward a variety of substrates. First, two-electron reduction occurs when substrates as 2,2'-bipyridine, elemental selenium, elemental tellurium, Me3P?S, or Ph3P?E (E = S, Se) is used, resulting in the oxidative coupling of two phosphinidene ligands 2[PAr](2-) into a diphosphene ligand [ArP-PAr](2-). Complex 1 easily undergoes nucleophilic addition reactions with unsaturated substrates, such as benzylallene, benzonitrile, tert-butyl isocyanide, and CS2. This complex also shows a peculiar reactivity to CO and Mo(CO)6, that includes C-P bond formation, C-C coupling and C-O bond cleavage of CO, to afford novel phosphorus-containing products. In the last two types of reactivity, reaction profiles have been computed (for the insertion of (t)BuNC and the CO activation by 1) at the DFT level. The unexpected/surprising sequence of steps in the latter case is also revealed. PMID:24004243

Lv, Yingdong; Kefalidis, Christos E; Zhou, Jiliang; Maron, Laurent; Leng, Xuebing; Chen, Yaofeng

2013-10-01

155

The Cbp3-Cbp6 complex coordinates cytochrome b synthesis with bc1 complex assembly in yeast mitochondria  

PubMed Central

Respiratory chain complexes in mitochondria are assembled from subunits derived from two genetic systems. For example, the bc1 complex consists of nine nuclear encoded subunits and the mitochondrially encoded subunit cytochrome b. We recently showed that the Cbp3Cbp6 complex has a dual function for biogenesis of cytochrome b: it is both required for efficient synthesis of cytochrome b and for protection of the newly synthesized protein from proteolysis. Here, we report that Cbp3Cbp6 also coordinates cytochrome b synthesis with bc1 complex assembly. We show that newly synthesized cytochrome b assembled through a series of four assembly intermediates. Blocking assembly at early and intermediate steps resulted in sequestration of Cbp3Cbp6 in a cytochrome bcontaining complex, thereby making Cbp3Cbp6 unavailable for cytochrome b synthesis and thus reducing overall cytochrome b levels. This feedback loop regulates protein synthesis at the inner mitochondrial membrane by directly monitoring the efficiency of bc1 complex assembly.

Gruschke, Steffi; Rompler, Katharina; Hildenbeutel, Markus; Kehrein, Kirsten; Kuhl, Inge; Bonnefoy, Nathalie

2012-01-01

156

Aluminium coordination complexes in copolymerization reactions of carbon dioxide and epoxides.  

PubMed

Al complexes are widely used in a range of polymerization reactions (ROP of cyclic esters and cationic polymerization of alkenes). Since the discovery in 1978 that an Al porphyrin complex could copolymerize propylene oxide with carbon dioxide, Al coordination compounds have been studied extensively as catalysts for epoxide-carbon dioxide copolymerizations. The most widely studied catalysts are Al porphyrin and Al salen derivatives. This is partially due to their ability to act as mechanistic models for more reactive, paramagnetic Cr catalysts. However, this in depth mechanistic understanding could be employed to design more active Al catalysts themselves, which would be beneficial given the wide availability of this metal. Polymerization data (% CO3 linkages, M(n), M(w)/M(n) and TON) for these complexes are presented and mechanisms discussed. In most cases, especially those employing square-based pyramidal Al complexes, co-catalysts are required to obtain high levels of carbon dioxide incorporation. However, in some cases, the use of co-catalysts inhibits the copolymerization reaction. Lewis acidic Al phenolate complexes have been used as activators in CHO-carbon dioxide copolymerizations to increase TOF and this has recently led to the development of asymmetric copolymerization reactions. Given the ready availability of Al, the robustness of many complexes (e.g. use in immortal polymerizations) and opportunity to prepare block copolymers and other designer materials, Al complexes for copolymerization of carbon dioxide are surely worth a second look. PMID:23450228

Ikpo, Nduka; Flogeras, Jenna C; Kerton, Francesca M

2013-07-01

157

Modal method based on subsectional Gegenbauer polynomial expansion for nonperiodic structures: complex coordinates implementation.  

PubMed

In this paper we present an extension of the modal method by Gegenbauer expansion (MMGE) [J. Opt. Soc. Am. A28, 2006 (2011)], [Progress Electromagn. Res.133, 17 (2013)] to the study of nonperiodic problems. The nonperiodicity is introduced through the perfectly matched layers (PMLs) concept, which can be introduced in an equivalent way either by a change of coordinates or by the use of a uniaxial anisotropic medium. These PMLs can generate strong irregularities of the electromagnetic fields that can significantly alter the convergence and stability of the numerical scheme. This is the case, e.g., for the famous Fourier modal method, especially when using complex stretching coordinates. In this work, it will be shown that the MMGE equipped with PMLs is a robust approach because of its natural immunity against spurious modes. PMID:23595322

Edee, Kofi; Guizal, Brahim

2013-04-01

158

Synthesis, crystal structures and magnetic properties of transition metal dicyanamide complexes coordinated with pyridyl nitronyl nitroxides  

Microsoft Academic Search

Two novel complexes Ni(NITpPy)2[N(CN)2]2 ? 2H2O (I) and Zn(NITpPy)2[N(CN)2]2 ? 2H2O (II) (NITpPy = 2-(p-pyridyl)-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide) were synthesized and characterized by infrared spectra, elemental\\u000a analyses, and UV-Vis techniques. The crystal structures of both complexes have been determined by X-ray diffraction analysis.\\u000a Both complexes are of centrosymmetric distorted octahedral co-ordination geometry in which metal ions are bound to two dicyanamide\\u000a anions,

Q. H. Zhao; D. Y. Tang; L. Du; R. B. Fang

2007-01-01

159

A Codeposition Route to CuI-Pyridine Coordination Complexes for OLEDs  

PubMed Central

We demonstrate a new approach to utilize copper(I) iodide coordination complexes as emissive layers in organic light-emitting diodes (OLEDs), by in situ codeposition of copper(I) iodide and 3,5-bis(carbazol-9-yl)pyridine (mCPy). With a simple three-layer device structure, pure green electroluminescence at 530 nm from a copper(I) complex was observed. Maximum luminance and external quantum efficiency (EQE) of 9700 cd/m2 and 4.4% have been achieved, respectively. The luminescent species has been identified as [CuI(mCPy)2]2 based on photophysical studies of model complexes and X-ray absorption spectroscopy (XAS).

Liu, Zhiwei; Qayyum, Munzarin F.; Wu, Chao; Whited, Matthew T.; Djurovich, Peter I.; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.; Thompson, Mark E.

2011-01-01

160

Influence of water molecule coordination on the magnetic properties of polyamine copper dinitrate complexes  

NASA Astrophysics Data System (ADS)

The magnetic properties of two biogenic polyamine copper complexes were investigated by dc magnetization and electron paramagnetic resonance (EPR) measurements. The variation in temperature of the low field magnetization reveals that the absence or presence of water molecules in the copper coordination sphere results, respectively, in the enhancement or suppression of antiferromagnetic interactions between Cu2+ ions. Analysis of the EPR spectra shows considerable temperature dependence of both the g values and EPR linewidths that persist in the paramagnetic regime for both complexes. Such variation of EPR parameters is attributed to the interplay of demagnetizing field effects, pertinent to the purely paramagnetic compound, and to the presence of short-range magnetic order that applies to the antiferromagnetic polyamine complex.

Guskos, N.; Glenis, S.; Likodimos, V.; Typek, J.; Fuks, H.; Wabia, M.; Szymczak, R.; Lin, C. L.; Perkowska, T. A.

2003-06-01

161

Synthesis, structure and reactivity of novel pyridazine-coordinated diiron bridging carbene complexes.  

PubMed

[{mu-(Pyridazine-N(1):N(2))}Fe(2)(mu-CO)(CO)(6)](1) reacts with aryllithium reagents, ArLi (Ar = C(6)H(5), m-CH(3)C(6)H(4)) followed by treatment with Me(3)SiCl to give the novel pyridazine-coordinated diiron bridging siloxycarbene complexes [(C(4)H(4)N(2))Fe(2){mu-C(OSiMe(3))Ar}(CO)(6)](2, Ar = C(6)H(5); 3, Ar =m-CH(3)C(6)H(4)). Complex 2 reacts with HBF(4).Et(2)O at low temperature to yield a cationic bridging carbyne complex [(C(4)H(4)N(2))Fe(2)(mu-CC(6)H(5))(CO)(6)]BF(4)(4). Cationic 4 reacts with NaBH(4) in THF at low temperature to afford the diiron bridging arylcarbene complex [(C(4)H(4)N(2))Fe(2){mu-C(H)C(6)H(5)}(CO)(6)](5). Unexpectedly, the reaction of 4 with NaSCH(3) under similar conditions gave the bridging arylcarbene complex 5 and a carbonyl-coordinated diiron bridging carbene complex [Fe(2){mu-C(SCH(3))C(6)H(5)}(CO)(7)](6), while the reaction of NaSC(6)H(4)CH(3)-p with 4 affords the expected bridging arylthiocarbene complex [(C(4)H(4)N(2))Fe(2){mu-C(SC(6)H(4)CH(3)-p)C(6)H(5)}(CO)(6)](7), which can be converted into a novel diiron bridging carbyne complex with a thiolato-bridged ligand, [Fe(2)(mu-CC(6)H(5))(mu-SC(6)H(4)CH(3)-p)(CO)(6)](8). Cationic can also react with the carbonylmetal anionic compound Na(2)[Fe(CO)(4)] to yield complex 5, while the reactions of 4 with carbonylmetal anionic compounds Na[M(CO)(5)(CN)](M = Cr, Mo, W) produce the diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [(C(4)H(4)N(2))Fe(2)-{mu-C(C(6)H(5))NCM(CO)(5)}(CO)(6)](9, M = Cr; 10, M = Mo; 11, M = W). The structures of complexes 2, 5, 6, 8, and 9 have been established by X-ray diffraction studies. PMID:16172652

Xiao, Nu; Xu, Qiang; Sun, Jie; Chen, Jiabi

2005-10-01

162

Characterization of inorganic coordination complexes by matrix-assisted laser desorption/ionization mass spectrometry.  

PubMed

We report the direct laser desorption/ionization (LDI) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis of four inorganic coordination complexes: monometallic [Ir(dpp)(2)Cl(2)](PF(6)), homonuclear trimetallic ([(bpy)(2)Ru(dpp)](2)RuCl(2))- (PF(6))(4), and heteronuclear [(tpy)Ru(tpp)Ru(tpp)RhCl(3)](PF(6))(4) and ([(bpy)(2)Ru(dpp)](2)IrCl(2))(PF(6))(5) (dpp = 2,3-bis-(2'-pyridyl)pyrazine, bpy = 2,2'-bipyridine, tpy = 2,2',6',2"-terpyradine, tpp = 2,3,5,6,-tetrakis-(2'-pyridyl)pyrazine). Spectral intensities and fragmentation patterns are compared and evaluated for instrument parameters, matrix selection, and matrix-to-analyte ratio. Direct LDI and MALDI mass spectra of the monometallic complex showed the same ion peaks and differed only in the relative peak intensities. Direct LDI of the trimetallic complexes produced only low-mass fragments containing one metal at most. MALDI spectra of the trimetallic complexes exhibited little fragmentation in the high-mass region (>1500 Da) and less fragmentation in the low-mass region compared to direct LDI. Significant fragments of the molecules were detected and identified, including ligand fragments, intermediate-mass fragments such as [Ru(tpy)](+), and molecular ions with varying degrees of PF(6)(-) loss ([M - n(PF(6))](+), where n = 1-3). A correlation exists between the solution-phase electrochemistry and the observed [M - n(PF(6))](+) series of peaks for the trimetallic complexes. Proper matrix selection for MALDI analysis was vital, as was an appropriate matrix-to-analyte ratio. The results demonstrate the applicability of MALDI-TOFMS for the structural characterization of labile inorganic coordination complexes. PMID:11466794

Hunsucker, S W; Watson, R C; Tissue, B M

2001-01-01

163

An interesting coordination complex formed between the azo dye Sudan Red G and cobalt ion  

NASA Astrophysics Data System (ADS)

In this study, the synthesis, spectroscopic analysis (Raman and infrared) and crystal structure of compound denominated [Co(SRG)2]CH3CH2OH have been investigated, were SRG is 1-(2-methoxyphenyl-azo)-2-naphthol or simply Sudan Red G and CH3CH2OH is one molecule of ethanol. The repeating unit is formed by the presence of an adduct complex constituted by two SRG ligands coordinated to the cobalt ion in a slightly distorted octahedral geometry. The other building block consists of a molecule of ethanol, which was used as the reaction solvent. The spectroscopic analysis provided important information related to coordination and formation of molecular complex through its mains bands. In the Raman spectrum the presence of marker bands as in at 1224 cm-1 ascribed to the binder SRG [?(NH) + ?(COC) + ?(CH) + ?(CC)] were displaced in the complex formed to 1232 cm-1 due to the loss of the proton from the azo group and the formation of a bond between the oxygen of the ether group with the metal ion. In the infrared spectrum the bands at 653/489 cm-1 and 622/528 cm-1 were attributed to [?(CoO) + ?CC)] and [?CoN + ?CC] characteristic of the metal-ligand bond.

Garcia, Humberto C.; Ferreira, Gilson Rodrigues; de Oliveira, Luiz Fernando C.

2014-03-01

164

Talking about the institutional complexity of the integrated rehabilitation system--the importance of coordination  

PubMed Central

Rehabilitation in Finland is a good example of functions divided among several welfare sectors, such as health services and social services. The rehabilitation system in Finland is a complex one and there have been many efforts to create a coordinated entity. The purpose of this study is to open up a complex welfare system at the upper policy level and to understand the meaning of coordination at the level of service delivery. We shed light in particular on the national rehabilitation policy in Finland and how the policy has tried to overcome the negative effects of institutional complexity. In this study we used qualitative content analysis and frame analysis. As a result we identified four different welfare state frames with distinct features of policy problems, policy alternatives and institutional failure. The rehabilitation policy in Finland seems to be divided into different components which may cause problems at the level of service delivery and thus in the integration of services. Bringing these components together could at policy level enable a shared view of the rights of different population groups, effective management of integration at the level of service delivery and also an opportunity for change throughout the rehabilitation system.

Miettinen, Sari; Ashorn, Ulla; Lehto, Juhani

2013-01-01

165

Synthesis of coordinatively unsaturated mesityliron thiolate complexes and their reactions with elemental sulfur.  

PubMed

The reactions of Fe(2)Mes(4) (1; Mes = mesityl) with bulky thiols, namely, HSDmp (Dmp = 2,6-dimesitylphenyl), HSDxp (Dxp = 2,6-dixylylphenyl), and HSBtip [Btip = 2,6-(2,4,6-(i)Pr(3)C(6)H(2))(2)C(6)H(3)], provided a series of iron(II) mesityl complexes bearing bulky thiolate ligands. These iron complexes are the thiolate-bridged dinuclear complexes Fe(2)Mes(2)(mu-SAr)(mu-Mes) (2a, Ar = Dmp; 2b, Ar = Dxp), the 1,2-dimethoxyethane (DME) adducts (DME)Fe(SAr)(Mes) (3a, Ar = Dmp; 3b, Ar = Dxp), the mixed-valence Fe(I)-Fe(II) dinuclear complexes (Mes)Fe(mu-SAr)(mu-S Ar) Fe (4a, Ar = Dmp; 4b, Ar = Dxp), and a low-coordinate mononuclear complex (B tipS) Fe(Mes) (5). An [Fe(8)S(7)] cluster [Fe(4)S(3)(SDmp)](2)(mu-SDmp)(2)(mu-SMes)(mu(6)-S) (6), the core structure of which is topologically relevant to that of the FeMo-cofactor of nitrogenase, was obtained from the reaction of 3a or 4a with S(8). The mu-SMes ligand in 6 is formed via insertion of a sulfur atom into the Fe-C(Mes) bond. The formation of cluster 6 from 3a or 4a demonstrates that organoiron complexes are applicable as precursors for iron-sulfur clusters. PMID:20527790

Hashimoto, Takayoshi; Ohki, Yasuhiro; Tatsumi, Kazuyuki

2010-07-01

166

Identification and geometrical modelling of complex shape surfaces using coordinate measuring machine and CAD\\/CAM systems  

Microsoft Academic Search

Two similar methods for the geometric identification of complex shape surfaces using the scanning measurement technique on a coordinate measuring machine (CMM) will be presented in this work. The first method employs the surfaces defined by the CAD system parametric technique based on the set of measurement points. The coordinates of points in space are determined by measurement in successive

K. Skalski; R. Filipowski; W. ?wi?szkowski; K. K?dzior; A. D?browski; J. Zawora

1998-01-01

167

Ferromagnetic interactions in zinc(II) coordination complex containing nitronyl nitroxide radicals  

Microsoft Academic Search

A novel complex Zn(NIT2-py)3(ClO4)2(NIT2-py=2-(2?-pyridyl)-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl-3-oxide) (1) has been synthesized and characterized structurally and magnetically. The metal coordination sphere is fully occupied by three chelating nitroxide ligands, showing a distorted octahedral geometry. Temperature dependence of susceptibility measurements shows a weak ferromagnetic coupling between NIT2-py radicals with J=2.13cm?1. The field dependence of the magnetization further confirms that the ground state of the compound

Liya Wang; Lufang Ma; Yufang Wang; Bin Zhao; Zonghui Jiang; Daizheng Liao; Shiping Yan

2007-01-01

168

Novel pincer complexes of Ag(I), coordination of toluene and their comparison with indium analogues.  

PubMed

The bis(imino)pyridine scaffold provides for the synthesis and characterization of the unique Ag(I) pincer complexes [{ArN=CPh}(2)(NPh)]Ag(+)(OTf)(-) (Ar = 2,5-(t)Bu(2)C(6)H(3); 2,6-(i)Pr(2)C(6)H(3)). The similar covalent radii of Ag(I) and In(I), prompted a bonding comparison of these species with their In(I) analogues. Coordination of toluene to the Ag center revealed the stronger Lewis acidity of the metal site in these compounds relative to In(I) analogues. PMID:21445395

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

2011-05-01

169

Polymeric coordination complexes based on cobalt, nickel, and ruthenium that exhibit synergistic thermal properties  

SciTech Connect

d-Block transition-metal-containing polymer blends which form coordination complexes are the focus of this research. The model compounds are Co chloride hexahydrate, Ni acetate tetrahydrate, and the dimer of dichlorotricarbonylruthenium (II). The ligand is poly (4-vinylpyridine), P4VP, or copolymers that contain 4-vinylpyridine repeat units. Differential scanning calorimetry suggests that the glass transition temperature (gtt) of the polymeric ligand(s) is enhanced by these d-block metal salts in binary and ternary blends. Co and Ni salts function as transition-metal compatibilizers for two immiscible copolymers of styrene with 4-vinylpyridine and butyl methacrylate with 4-vinylpyridine. At the molecular level, FTIR of P4VP-Ru precipitates reveals that the pyridine nitrogen lone pair coordinates to the metal center and strengthens Ru-carbonyl bonds in the polymeric complex. IR absorption frequencies of the CO ligands are consistent with {pi}-backbonding between the t{sub 2g} molecular orbitals of the metal in the octahedral point group and the {pi}* antibonding orbitals of CO. High-resolution C-13 solid-state NMR spectroscopy identifies at least two, and possibly three, carbonyl signals in the undiluted pseudooctahedral Ru dimer via the Bloch-decay pulse sequence. In the polymeric complex, carbonyl C-13 magnetization unique to the Ru salt is generated via intermolecular polarization transfer from the proton spin manifold of poly(4-vinylpyridine) using a cross-polarization thermal mixing time of 2 ms. Since there are no protons in the Ru dimer, the observation of energy-conserving H-1/C-13 spin diffusion between dissimilar molecules under matched Hartmann-Hahn spin-lock conditions argues convincingly that heteronuclear dipolar distances are small enough for the proposed polymeric complex to form. Thermodynamic interpretation of ligand field stabilization energies appropriate to tetrahedral Co complexes is employed to estimate the synergistic enhancement of the gtt.

Belfiore, L.A.; McCurdie, M.P.; Ueda, E. [Colorado State Univ., Fort Collins, CO (United States). Dept. of Chemical Engineering

1993-12-06

170

Challenging conventional f-element separation chemistry - reversing uranyl(vi)/lanthanide(iii) solvent extraction selectivity.  

PubMed

The water soluble tetradentate Schiff base, N,N'-bis(5-sulfonatosalicylidene)-diaminoethane (H2salen-SO3), will readily coordinate to the uranyl(vi) cation, but not to the same extent to trivalent lanthanide cations. This allows for the reversal of conventional solvent extraction properties and opens the possibility for novel separation processes. PMID:24958394

Hawkins, C A; Bustillos, C G; Copping, R; Scott, B L; May, I; Nilsson, M

2014-08-14

171

Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method.  

PubMed

The formation constants of ternary complexes (MUO2(CO3)3(2-) and M2UO2(CO3)3(0)) of uranyl and carbonate with alkaline earth metals (M2+ denotes Mg2+, Ca2+, Sr2+, and Ba2+) were determined with an anion exchange method by varying the metal concentrations (0.1-5 mmol/L) at pH 8.1 and a constant ionic strength (0.1 mol/L NaNO3) under equilibrium with atmospheric CO2. The results indicate that the complexes of MUO2(CO3)3(2-) and M2UO2(CO3)3 are simultaneously formed for Ca2+ and Ba2+, while Mg2+ and Sr2+ form only the MUO2(CO3)3(2-) complex under our experimental conditions. The cumulative stability constants for the MUO2(CO3)3(2-) complex obtained at / = 0 are as follows: logbeta113 = 26.11 +/- 0.04, 27.18 +/- 0.06, 26.86 +/- 0.04, and 26.68 +/- 0.04 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively. For M2UO2(CO3)3(0), the value of logbeta213 at / = 0 was measured to be 30.70 +/- 0.05 and 29.75 +/- 0.07 for Ca2+ and Ba2+, respectively. Based on the formation constants obtained in this study, speciation calculations indicate that at low Ca2+ concentration (e.g., <2.2 mmol/L), CaUO2(CO3)3(2-) is more important than Ca2UO2(CO3)3 and that the Ca2UO2(CO3)3 distribution increased with increasing Ca2+ concentration. Uranium sorption onto anion-exchange resins is inhibited by the formation of the neutral Ca2UO2(CO3)3(0) species. PMID:16913125

Dong, Wenming; Brooks, Scott C

2006-08-01

172

Time-domain solver in curvilinear coordinates for outdoor sound propagation over complex terrain.  

PubMed

The current work aims at developing a linearized Euler equations solver in curvilinear coordinates to account for the effects of topography on sound propagation. In applications for transportation noise, the propagation environment as well as the description of acoustic sources is complex, and time-domain methods have proved their capability to deal with both atmospheric and ground effects. First, equations in curvilinear coordinates are examined. Then time-domain boundary conditions initially proposed for a Cartesian coordinate system are implemented in the curvilinear solver. Two test cases dealing with acoustic scattering by an impedance cylinder in a two-dimensional geometry and by an impedance sphere in a three-dimensional geometry are considered to validate the boundary conditions. Accurate solutions are obtained for both rigid and impedance surfaces. Finally, the solver is used to examine a typical outdoor sound propagation problem. It is shown that it is well-suited to study coupled effects of topography, mixed impedance ground and meteorological conditions. PMID:23742330

Dragna, Didier; Blanc-Benon, Philippe; Poisson, Franck

2013-06-01

173

Exploring chemical reactivity of complex systems with path-based coordinates: Role of the distance metric.  

PubMed

Path-based reaction coordinates constitute a valuable tool for free-energy calculations in complex processes. When a reference path is defined by means of collective variables, a nonconstant distance metric that incorporates the nonorthonormality of these variables should be taken into account. In this work, we show that, accounting for the correct metric tensor, these kind of variables can provide iso-hypersurfaces that coincide with the iso-committor surfaces and that activation free energies equal the value that would be obtained if the committor function itself were used as reaction coordinate. The advantages of the incorporation of the variable metric tensor are illustrated with the analysis of the enzymatic reaction catalyzed by isochorismate-pyruvate lyase. Hybrid QM/MM techniques are used to obtain the free energy profile and to analyze reactive trajectories initiated at the transition state. For this example, the committor histogram is peaked at 0.5 only when a variable metric tensor is incorporated in the definition of the path-based coordinate. 2014 Wiley Periodicals, Inc. PMID:24986052

Zinovjev, Kirill; Tun, Iaki

2014-09-01

174

Characterization of Ce SUP 3+-tributyl phosphate coordination complexes produced by fused droplet electrospray ionization with a target capillary  

Microsoft Academic Search

Coordination complexes containing Ce(III) and tri-n-butyl phosphate (TBP) in the 1+, 2+ and 3+ charge states were generated using desorption electrospray ionization (DESI) mass spectrometry, in which the analyte solutions were supplied via a target capillary orthogonally situated with respect to the electrospray. Comparison with direct electrospray (ESI) showed that the same coordination complexes were produced in each experiment, and

Gary S. Groenewold; Jean-Jacques Gaumet

2011-01-01

175

Hybrid uranyl-carboxyphosphonate cage clusters.  

PubMed

Two new hybrid uranyl-carboxyphosphonate cage clusters built from uranyl peroxide units were crystallized from aqueous solution under ambient conditions in approximately two months. The clusters are built from uranyl hexagonal bipyramids and are connected by employing a secondary metal linker, the 2-carboxyphenylphosphonate ligand. The structure of cluster A is composed of a ten-membered uranyl polyhedral belt that is capped on either end of an elongated cage by five-membered rings of uranyl polyhedra. The structure of cluster B consists of 24 uranyl cations that are arranged into 6 four-membered rings of uranyl polyhedra. Four of the corresponding topological squares are fused together to form a sixteen-membered double uranyl pseudobelt that is capped on either end by 2 topological squares. Cluster A crystallizes over a wide pH range of 4.6-6.8, while cluster B was isolated under narrower pH range of 6.9-7.8. Studies of their fate in aqueous solution upon dissolution of crystals by electrospray ionization mass spectrometry (ESI-MS) and small-angle X-ray scattering (SAXS) provide evidence for their persistence in solution. The well-established characteristic fingerprint from the absorption spectra of the uranium(VI) cations disappears and becomes a nearly featureless peak; nonetheless, the two compounds fluoresce at room temperature. PMID:23763595

Adelani, Pius O; Ozga, Michael; Wallace, Christine M; Qiu, Jie; Szymanowski, Jennifer E S; Sigmon, Ginger E; Burns, Peter C

2013-07-01

176

QM and QM/MM Studies of Uranyl Fluorides in the Gas and Aqueous Phases and in the Hydrophobic Cavities of Tetrabrachion  

SciTech Connect

The structural properties and electronic structures of pentacoordinated uranyl complexes belonging to the [UO?Fn(H?O)??n]?? series have been studied in the gas and aqueous phases using density functionals with relativistic pseudopotentials and all-electron basis sets in the gas-phase calculations in combination with COSMO in the aqueous phase. In addition, the conformational orientation and structural and electronic properties of [UO?F?] in the hydrophobic cavities of the right-handed coiled-coil (RHCC) protein of tetrabrachion have been determined using the hybrid QM/MM method. Although there is good agreement between the available experimental geometrical parameters and the values obtained in the aqueous phase using pseudopotentials or all-electron basis sets, variation of the uranyl U?O bond with the number of fluoride ligands is only truly captured after the inclusion of five water molecules in the second coordination sphere around the molecules. The docking procedure used in this work shows that there are only two possible orientations of the uranyl group of [UO?F?] embedded in the hydrophobic cavities of the RHCC protein. The two orientations are exclusively along the axes perpendicular to the protein axial channel with no possible orientation of the uranyl group along the axial channel because of both steric effects and interaction with the alkyl chain of the isoleucine residues pointing into the axial channel. In addition, the embedded complex is always positioned nearer to the isoleucine residues at the N-terminal ends of the hydrophobic cavities. Energy analysis, however, reveals that both conformations can only be observed in cavity 2, the largest hydrophobic cavity. The structural and electronic properties of the ligand embedded in this cavity are very similar to those of the gas-phase structure. A comparable study of [Pt(CN)?] and the anticancer drug cisplatin, [PtCl?(NH?)?], in cavity 2, revealed the existence of just two orientations for the former, similar to the uranyl complex, and multiple orientations for the latter.

Odoh, Samuel O.; Walker, Sean M.; Meier, Markus; Stetefeld, Jorg; Schreckenbach, Georg

2011-04-04

177

The activation of sulfur hexafluoride at highly reduced low-coordinate nickel dinitrogen complexes.  

PubMed

The greenhouse gas sulfur hexafluoride is the common standard example in the literature of a very inert inorganic small molecule that is even stable against O2 in an electric discharge. However, a reduced ?-diketiminate nickel species proved to be capable of converting SF6 into sulfide and fluoride compounds at ambient standard conditions. The fluoride product complex features an unprecedented [NiF](+) unit, where the Ni atom is only three-coordinate, while the sulfide product exhibits a rare almost linear [Ni(?-S)Ni](2+) moiety. The reaction was monitored applying (1)H?NMR, IR and EPR spectroscopic techniques resulting in the identification of an intermediate nickel complex that gave insight into the mechanism of the eight-electron reduction of SF6. PMID:24481669

Holze, Patrick; Horn, Bettina; Limberg, Christian; Matlachowski, Corinna; Mebs, Stefan

2014-03-01

178

A tricky water molecule coordinated to a verdazyl radical-iron(II) complex: a multitechnique approach.  

PubMed

The first iron complexes of high-spin iron(II) species directly coordinated to verdazyl radicals, [Fe(II)(vdCOO)2(H2O)2]2H2O (1; vdCOO(-) = 1,5-dimethyl-6-oxo-verdazyl-3-carboxylate) and [Fe(II)(vdCOO)2(D2O)2]2D2O (2), were synthesized. The crystal structure of 1 was investigated by single-crystal X-ray diffraction at room temperature and at 90 K. The compound crystallizes in the P1 space group with no phase transition between 300 and 90 K. The crystals are composed of discrete [Fe(II)(vdCOO)2(H2O)2] complexes and crystallization water molecules. In the complex, two vdCOO(-) ligands coordinate to the iron(II) ion in a head-to-tail arrangement and two water molecules complete the coordination sphere. The Fe-X (X = O, N) distances vary in the 2.069-2.213 range at 300 K and in the 2.0679-2.2111 range at 90 K, indicating that the iron(II) ion is in its high-spin (HS) state at both temperatures. At 300 K, one of the coordinated water molecules is H-bonded to two crystallization water molecules whereas the second one appears as loosely H-bonded to the two oxygen atoms of the carboxylate group of two neighboring complexes. At 90 K, the former H-bonds remain essentially the same whereas the second coordinated water molecule reveals a complicated behavior appearing simultaneously as tightly H-bonded to two oxygen atoms and non-H-bonded. The (57)Fe Mssbauer spectra, recorded between 300 K and 10 K, give a clue to this situation. They show two sets of doublets typical of HS iron(II) species whose intensity ratio varies smoothly with temperature. It demonstrates the existence of an equilibrium between the high temperature and low temperature forms of the compounds. The solid-state magic angle spinning (2)H NMR spectra of 2 were recorded between 310 K and 193 K. The spectra suggest the existence of a strongly temperature-dependent motion of one of the coordinated water molecules in the whole temperature range. Variable-temperature magnetic susceptibility measurements indicate an antiferromagnetic interaction (J(Fe-vd) = -27.1 cm(-1); H = -J(ij)S(i)S(j)) of the HS iron(II) ion and the radical spins with high g(Fe) and D(Fe) values (g(Fe) = 2.25, D(Fe) = +3.37 cm(-1)) for the HS iron(II) ion. Moreover, the radicals are strongly antiferromagnetically coupled through the iron(II) center (J(vd-vd) = -42.8 cm(-1)). These last results are analysed based on the framework of the magnetic orbitals formalism. PMID:24695973

Kamebuchi, Hajime; Okubo, Masashi; Okazawa, Atsushi; Enomoto, Masaya; Harada, Jun; Ogawa, Keiichiro; Maruta, Goro; Takeda, Sadamu; Kojima, Norimichi; Train, Cyrille; Verdaguer, Michel

2014-05-21

179

Two-dimensional coordination polymeric structures in caesium complexes with ring-substituted phenoxyacetic acids.  

PubMed

The two-dimensional polymeric structures of the caesium complexes with the phenoxyacetic acid analogues (4-fluorophenoxy)acetic acid, (3-chloro-2-methylphenoxy)acetic acid and the herbicidally active (2,4-dichlorophenoxy)acetic acid (2,4-D), namely poly[[?5-(4-fluorophenoxy)acetato][?4-(4-fluorophenoxy)acetato]dicaesium], [Cs2(C8H6FO3)2]n, (I), poly[aqua[?5-(3-chloro-2-methylphenoxy)acetato]caesium], [Cs(C9H8ClO3)(H2O)]n, (II), and poly[[?7-(2,4-dichlorophenoxy)acetato][(2,4-dichlorphenoxy)acetic acid]caesium], [Cs(C8H5Cl2O3)(C8H6Cl2O3)]n, (III), are described. In (I), the Cs(+) cations of the two individual irregular coordination polyhedra in the asymmetric unit (one CsO7 and the other CsO8) are linked by bridging carboxylate O-atom donors from the two ligand molecules, both of which are involved in bidentate chelate Ocarboxy,Ophenoxy interactions, while only one has a bidentate carboxylate O,O'-chelate interaction. Polymeric extension is achieved through a number of carboxylate O-atom bridges, with a minimum Cs...Cs separation of 4.3231?(9)?, giving layers which lie parallel to (001). In hydrated complex (II), the irregular nine-coordination about the Cs(+) cation comprises a single monodentate water molecule, a bidentate Ocarboxy,Ophenoxy chelate interaction and six bridging carboxylate O-atom bonding interactions, giving a Cs...Cs separation of 4.2473?(3)?. The water molecule forms intralayer hydrogen bonds within the two-dimensional layers, which lie parallel to (100). In complex (III), the irregular centrosymmetric CsO6Cl2 coordination environment comprises two O-atom donors and two ring-substituted Cl-atom donors from two hydrogen bis[(2,4-dichlorophenoxy)acetate] ligand species in a bidentate chelate mode, and four O-atom donors from bridging carboxyl groups. The duplex ligand species lie across crystallographic inversion centres, linked through a short O-H...O hydrogen bond involving the single acid H atom. Structure extension gives layers which lie parallel to (001). The present set of structures of Cs salts of phenoxyacetic acids show previously demonstrated trends among the alkali metal salts of simple benzoic acids with no stereochemically favourable interactive substituent groups for formation of two-dimensional coordination polymers. PMID:24898967

Smith, Graham; Lynch, Daniel E

2014-06-15

180

New water oxidation chemistry of a seven-coordinate ruthenium complex with a tetradentate polypyridyl ligand.  

PubMed

The mononuclear ruthenium(II) complex [Ru](2+) (Ru = Ru(dpp)(pic)2, where dpp is the tetradentate 2,9-dipyrid-2'-yl-1,10-phenanthroline ligand and pic is 4-picoline) reported by Thummel's group (Inorg. Chem. 2008, 47, 1835-1848) that contains no water molecule in its primary coordination shell is evaluated as a catalyst for water oxidation in artificial photosynthesis. A detailed theoretical characterization of the energetics, thermochemistry, and spectroscopic properties of intermediates allowed us to interpret new electrochemical and spectroscopic experimental data, and propose a mechanism for the water oxidation process that involves an unprecedented sequence of seven-coordinate ruthenium complexes as intermediates. This analysis provides insights into a mechanism that generates four electrons and four protons in the solution and a gas-phase oxygen molecule at different pH values. On the basis of the calculations and corroborated substantially by experiments, the catalytic cycle goes through [(2)Ru(III)](3+) and [(2)Ru(V)(O)](3+) to [(1)Ru(IV)(OOH)](3+) then [(2)Ru(III)((3)O2)](3+) at pH 0, and through [(3)Ru(IV)(O)](2+), [(2)Ru(V)(O)](3+), and [(1)Ru(IV)(OO)](2+) at pH 9 before reaching the same [(2)Ru(III)((3)O2)](3+) species, from which the liberation of the weakly bound O2 might require an additional oxidation to form [(3)Ru(IV)(O)](2+) to initiate further cycles involving all seven-coordinate species. PMID:24911180

Muckerman, James T; Kowalczyk, Marta; Badiei, Yosra M; Polyansky, Dmitry E; Concepcion, Javier J; Zong, Ruifa; Thummel, Randolph P; Fujita, Etsuko

2014-07-01

181

Optical apparatus and method for sensing uranyl  

DOEpatents

An optical sensing device for uranyl and other substances, a method for making an optical sensing device and a method for chemically binding uranyl and other indicators to glass, quartz, cellulose and similar substrates. The indicator, such as arsenazo III, is immobilized on the substrate using a chemical binding process. The immobilized arsenazo III causes uranyl from a fluid sample to bind irreversibly to the substrate at its active sites, thus causing absorption of a portion of light transmitted through the substrate. Determination of the amount of light absorbed, using conventional means, yields the concentration of uranyl present in the sample fluid. The binding of uranyl on the substrate can be reversed by subsequent exposure of the substrate to a solution of 2,6-pyridinedicarboxylic acid. The chemical binding process is suitable for similarly binding other indicators, such as bromocresol green.

Baylor, L.C.; Buchanan, B.R.

1994-01-01

182

Chemistry of low-valent molybdenum phosphite complexes: Models of seven-coordinate reaction intermediates  

PubMed Central

A simple synthesis of the zerovalent complex Mo[P(OCH3)3]6 has been devised from a potassium reduction of MoCl4(tetrahydrofuran)2 followed by reaction with trimethyl phosphite at 70. Protonation of this octahedral complex gave only low yields of the expected seven-coordinate hydride, HMo[P(OCH3)3]6+. The major product was an octahedral nonhydridic cation, Mo[P(OCH3)3]5P(OCH3)2+, derived from proton cleavage of the PO phosphite ester bond. This octahedral cation was stereochemically nonrigid, apparently through facile methoxy group migration. Close packing by methoxy groups in this fluxional cation was established through an x-ray crystallographic study of Mo[P(OCH3)3]5P(OCH3)2+-PF6-. Extended reaction of trifluoroactic acid with Mo[P(OCH3)3]6 yielded the seven-coordinate hydride, HMo[P(OCH3)3]4(O2CCF3), which was near pentagonal bipyramidal and was stereochemically nonrigid.

Muetterties, E. L.; Kirner, J. F.; Evans, W. J.; Watson, P. L.; Abdel-Meguid, S.; Tavanaiepour, I.; Day, V. W.

1978-01-01

183

Structures and luminescent properties of new uranyl-based hybrid materials  

NASA Astrophysics Data System (ADS)

Six uranyl coordination compounds, UO 2(OH)(PYCA) ( 1), UO 2(PYCA) 2(H 2O)2H 2O ( 2), UO 2(PIC) 2 ( 3), UO 2(H 2O) 2(NIC) 2 ( 4), UO 2(OH)(HINIC)(INIC) ( 5), and UO 2(PYTAC) 2(H 2O) 2 ( 6) were grown as single crystals via hydrothermal synthesis (PYCA = pyrazine-2-carboxylate, PIC = picolinate, NIC = nicotinate, INIC = isonicotinate, and PYTAC = 2-(pyridin-4-yl)thiazole-5-carboxylate) to study their optical properties. All six compounds have been identified via single crystal X-ray diffraction and fully characterized via powder X-ray diffraction, infrared spectroscopy, UV-Vis spectroscopy, and fluorescence spectroscopy. Three of the complexes, 1, 3, and 6, represent new structures, and their synthesis and structural characterization is detailed within. The structures of 2, 4, and 5 have previously been reported in the literature. Coordination polymer 1 crystallizes in the orthorhombic space group Pca21 ( a = 13.5476(5) , b = 6.6047(2) , c = 8.3458(3) ), and forms infinite 1-D chains of corner-sharing uranium polyhedra connected into 2-D layers by bridging ligands. Coordination polymer 3 crystallizes in the monoclinic space group Cc ( a = 8.4646(8) , b = 13.0357(11) , c = 11.8955(10) , ? = 96.815(2)), and forms ligand-bridged 1-D chains. Complex 6 crystallizes in the triclinic space group P-1 ( a = 5.6272(7) , b = 8.9568(10) , c = 10.4673(12) , ? = 90.508(2), ? = 104.194(2), ? = 91.891(2)), and consists of isolated uranyl complexes connected via hydrogen bonds. The structures and luminescent properties of UO 2(OH)(PYCA) ( 1), UO 2(PYCA) 2(H 2O)2H 2O ( 2), UO 2(PIC) 2 ( 3), UO 2(H 2O) 2(NIC) 2 ( 4), UO 2(OH)(HINIC)(INIC) ( 5), and UO 2(PYTAC) 2(H 2O) 2 ( 6) are discussed.

Severance, Rachel C.; Vaughn, Shae Anne; Smith, Mark D.; zur Loye, Hans-Conrad

2011-06-01

184

Combination of optically measured coordinates and displacements for quantitative investigation of complex objects  

NASA Astrophysics Data System (ADS)

Holographic interferometry makes it possible to measure high precision displacement data in the range of the wavelength of the used laser light. However, the determination of 3D- displacement vectors of objects with complex surfaces requires the measurement of 3D-object coordinates not only to consider local sensitivities but to distinguish between in-plane deformation, i.e. strains, and out-of-plane components, i.e. shears, too. To this purpose both the surface displacement and coordinates have to be combined and it is advantageous to make the data available for CAE- systems. The object surface has to be approximated analytically from the measured point cloud to generate a surface mesh. The displacement vectors can be assigned to the nodes of this surface mesh for visualization of the deformation of the object under test. They also can be compared to the results of FEM-calculations or can be used as boundary conditions for further numerical investigations. Here the 3D-object coordinates are measured in a separate topometric set-up using a modified fringe projection technique to acquire absolute phase values and a sophisticated geometrical model to map these phase data onto coordinates precisely. The determination of 3D-displacement vectors requires the measurement of several interference phase distributions for at least three independent sensitivity directions depending on the observation and illumination directions as well as the 3D-position of each measuring point. These geometric quantities have to be transformed into a reference coordinate system of the interferometric set-up in order to calculate the geometric matrix. The necessary transformation can be realized by means of a detection of object features in both data sets and a subsequent determination of the external camera orientation. This paper presents a consistent solution for the measurement and combination of shape and displacement data including their transformation into simulation systems. The described procedure will be demonstrated on an automotive component. Thus more accurate and effective measurement techniques make it possible to bring experimental and numerical displacement analysis closer.

Andrae, Peter; Beeck, Manfred-Andreas; Jueptner, Werner P.; Nadeborn, Werner; Osten, Wolfgang

1996-09-01

185

Actinide immobilization in the subsurface environment by in-situ treatment with a hydrolytically unstable organophosphorus complexant: Uranyl uptake by calcium phytate  

SciTech Connect

In addition to naturally occurring uranium and thorium, actinide ions exist in the subsurface environment as a result of accidental releases and intentional disposal practices associated with nuclear weapons production. These species present a significant challenge to cost-effective remediation of contaminated environments. An attractive approach to decreasing the probability of actinide migration in the subsurface is to transform the ions into a less mobile form by remote treatment. We have under development a process which relies on a polyfunctional organophosphorus complexant to sequester the mobile metal ions by complexation/cation exchange in the near term, and to subsequently decompose, transforming the actinides into insoluble phosphate mineral forms in the long term. Studies to date include identification of a suitable organophosphorus reagent, profiling of its decomposition kinetics, verification of the formation of phosphate mineral phases upon decomposition of the reagent, and extensive comparison of the actinide uptake ability of the calcium salt of the reagent as compared with hydroxyapatite. In this report, we briefly describe the process with focus on the cation exchange behavior of the calcium salt of the organophosphorus sequestrant.

Nash, K.L.; Jensen, M.P.; Schmidt, M.A.

1997-12-31

186

A two-coordinate manganese(0) complex with an unsupported mn-mg bond: allowing access to low coordinate homo- and heterobimetallic compounds.  

PubMed

This study details the synthesis and characterization of an unprecedented two-coordinate, high-spin manganese(0) complex that incorporates an unsupported Mn-Mg bond, viz. L()MnMg((Mes)Nacnac) (L() = -N(Ar())(SiPr(i)3), Ar() = C6H2{C(H)Ph2}2Pr(i)-2,6,4; (Mes)Nacnac = [(MesNCMe)2CH](-); Mes = mesityl). This compound has been utilized as an "inorganic Grignard reagent" in the preparation of the first two-coordinate manganese(I) dimer, L()MnMnL* (L* = -N(Ar*)(SiMe3), Ar* = C6H2{C(H)Ph2}2Me-2,6,4), and the related mixed valence, bis(amido)-hetereobimetallic complex, Mn(II)(?-L())(?-L*)Cr(0). It is also shown to act as a two-electron reducing agent in reactions with unsaturated substrates. PMID:24660853

Hicks, Jamie; Hoyer, Chad E; Moubaraki, Boujemaa; Manni, Giovanni Li; Carter, Emma; Murphy, Damien M; Murray, Keith S; Gagliardi, Laura; Jones, Cameron

2014-04-01

187

Integrated complex care coordination for children with medical complexity: A mixed-methods evaluation of tertiary care-community collaboration  

PubMed Central

Background Primary care medical homes may improve health outcomes for children with special healthcare needs (CSHCN), by improving care coordination. However, community-based primary care practices may be challenged to deliver comprehensive care coordination to complex subsets of CSHCN such as children with medical complexity (CMC). Linking a tertiary care center with the community may achieve cost effective and high quality care for CMC. The objective of this study was to evaluate the outcomes of community-based complex care clinics integrated with a tertiary care center. Methods A before- and after-intervention study design with mixed (quantitative/qualitative) methods was utilized. Clinics at two community hospitals distant from tertiary care were staffed by local community pediatricians with the tertiary care center nurse practitioner and linked with primary care providers. Eighty-one children with underlying chronic conditions, fragility, requirement for high intensity care and/or technology assistance, and involvement of multiple providers participated. Main outcome measures included health care utilization and expenditures, parent reports of parent- and child-quality of life [QOL (SF-36, CPCHILD, PedsQL)], and family-centered care (MPOC-20). Comparisons were made in equal (up to 1 year) pre- and post-periods supplemented by qualitative perspectives of families and pediatricians. Results Total health care system costs decreased from median (IQR) $244 (981) per patient per month (PPPM) pre-enrolment to $131 (355) PPPM post-enrolment (p=.007), driven primarily by fewer inpatient days in the tertiary care center (p=.006). Parents reported decreased out of pocket expenses (p<.0001). Parental QOL did not significantly change over the course of the study. Child QOL improved between baseline and 6 months in two PedsQL domains [Social (p=.01); Emotional (p=.003)], and between baseline and 1 year in two CPCHILD domains [Health Standardization Section (p=.04); Comfort and Emotions (p=.03)], while total CPCHILD score decreased between baseline and 1 year (p=.003). Parents and providers reported the ability to receive care close to home as a key benefit. Conclusions Complex care can be provided in community-based settings with less direct tertiary care involvement through an integrated clinic. Improvements in health care utilization and family-centeredness of care can be achieved despite minimal changes in parental perceptions of child health.

2012-01-01

188

Coordination of motilin and ghrelin regulates the migrating motor complex of gastrointestinal motility in Suncus murinus.  

PubMed

Motilin and ghrelin are the gastrointestinal (GI) hormones released in a fasting state to stimulate the GI motility of the migrating motor complex (MMC). We focused on coordination of the ghrelin/motilin family in gastric contraction in vivo and in vitro using the house musk shrew (Suncus murinus), a ghrelin- and motilin-producing mammal. To measure the contractile activity of the stomach in vivo, we recorded GI contractions either in the free-moving conscious or anesthetized S. murinus and examined the effects of administration of motilin and/or ghrelin on spontaneous MMC in the fasting state. In the in vitro study, we also studied the coordinative effect of these hormones on the isolated stomach using an organ bath. In the fasting state, phase I, II, and III contractions were clearly recorded in the gastric body (as observed in humans and dogs). Intravenous infusion of ghrelin stimulated gastric contraction in the latter half of phase I and in the phase II in a dose-dependent manner. Continuous intravenous infusion of ghrelin antagonist (d-Lys3-GHRP6) significantly suppressed spontaneous phase II contractions and prolonged the time of occurrence of the peak of phase III contractions. However, intravenous infusion of motilin antagonist (MA-2029) did not inhibit phase II contractions but delayed the occurrence of phase III contractions of the MMC. In the in vitro study, even though a high dose of ghrelin did not stimulate contraction of stomach preparations, ghrelin administration (10(-10)-10(-7) M) with pretreatment of a low dose of motilin (10(-10) M) induced gastric contraction in a dose-dependent manner. Pretreatment with 10(-8) M ghrelin enhanced motilin-stimulated gastric contractions by 10 times. The interrelation of these peptides was also demonstrated in the anesthetized S. murinus. The results suggest that ghrelin is important for the phase II contraction and that coordination of motilin and ghrelin are necessary to initiate phase III contraction of the MMC. PMID:22383491

Mondal, Anupom; Xie, Zuoyun; Miyano, Yuki; Tsutsui, Chihiro; Sakata, Ichiro; Kawamoto, Yoichi; Aizawa, Sayaka; Tanaka, Toru; Oda, Sen-ichi; Sakai, Takafumi

2012-05-15

189

Coordination Complexes as Catalysts: The Oxidation of Anthracene by Hydrogen Peroxide in the Presence of VO(acac)[subscript 2  

ERIC Educational Resources Information Center

A laboratory experiment aimed at students who are studying coordination chemistry of transition-metal complexes is described. A simple vanadyl acetylacetonate complex can be used as a catalyst in the hydrogen peroxide oxidation of anthracene to produce anthraquinone. The reaction can be performed under a variety of reaction conditions, ideally by

Charleton, Kimberly D. M.; Prokopchuk, Ernest M.

2011-01-01

190

Coordination Complexes of Decamethylytterbocene with4,4'-Disubstituted Bipyridines: An Experimental Study of Spin Coupling inLanthanide Complexes  

SciTech Connect

The paramagnetic 1:1 coordination complexes of (C5Me5)2Ybwith a series of 4,4'-disubstituted bipyridines, bipy-X, where X is Me,tert-Bu, OMe, Ph, CO2Me, and CO2Et have been prepared. All of thecomplexes are paramagnetic and the values of the magnetic susceptibilityas a function of temperature show that these values are less thanexpected for the cation, [(C5Me5)2Yb(III)(bipy-X)]+, which have beenisolated as the cation-anion ion-pairs[(C5Me5)2Yb(III)(bipy-X)]+[(C5Me5)2YbI2]f fnfn where X is CO2Et, OMe andMe. The 1H NMR chemical shifts (293 K) for the methine resonances locatedat the 6,6' site in the bipy-X ring show a linear relationship with thevalues of chiT (300 K) for the neutral complexes which illustrates thatthe molecular behavior does not depend upon the phase with one exception,viz., (C5Me5)2Yb(bipy-Me). Single crystals of the 4,4'-dimethylbipyridinecomplex undergo an irreversible, abrupt first order phase change at 228 Kthat shatters the single crystals. The magnetic susceptibility,represented in a delta vs. T plot, on this complex, in polycrystallineform undergoes reversible abrupt changes in the temperature regime 205 -212 K, which is suggested to be due to the way the individual molec ularunits pack in the unit cell. A qualitative model is proposed thataccounts for the sub-normal magnetic moments in theseytterbocene-bipyridine complexes.

Walter, Marc D.; Berg, David J.; Andersen, Richard A.

2005-12-08

191

Synthesis, crystal structures and magnetic properties of transition metalazide complexes coordinated with pyridyl nitronyl nitroxides  

Microsoft Academic Search

Two novel complexes Co(N3)2(PNN)4 (I) and Mn(N3)2(PNN)2(CH3OH)(C2H5OH) (II) (PNN=2-(p-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3oxide) were synthesized and characterized by infrared spectra, elemental analyses and UVVis techniques. The crystal structures of both complexes have been determined by X-ray diffraction analysis. Complex I is a neutral five-spin system and adopts a centrosymmetric tetragonally compressed octahedral coordination geometry in which Co(II) ion is coordinated to four radicals through

Lei Zhang; Li-Cun Li; Dai-Zheng Liao; Zong-Hui Jiang; Shi-Ping Yan; Pan-Wen Shen

2001-01-01

192

A two-coordinate nickel imido complex that effects C?H amination.  

PubMed

An exceptionally low coordinate nickel imido complex, (IPr*)Ni?N(dmp) (2) (dmp = 2,6-dimesitylphenyl), has been prepared by the elimination of N2 from a bulky aryl azide in its reaction with (IPr*)Ni(?6-C7H8) (1). The solid-state structure of 2 features two-coordinate nickel with a linear C?Ni?N core and a short Ni?N distance, both indicative of multiple-bond character. Computational studies using density functional theory showed a Ni?N bond dominated by Ni(d?)?N(p?) interactions, resulting in two nearly degenerate singly occupied molecular orbitals (SOMOs) that are Ni?N ?* in character. Reaction of 2 with CO resulted in nitrene-group transfer to form (dmp)NCO and (IPr*)Ni(CO)3 (3). Net C?H insertion was observed in the reaction of 2 with ethene, forming the vinylamine (dmp)NH(CH?CH2) (5) via an azanickelacyclobutane intermediate, (IPr*)Ni{N,C:?2-N(dmp)CH2CH2} (4). PMID:21175213

Laskowski, Carl A; Miller, Alexander J M; Hillhouse, Gregory L; Cundari, Thomas R

2011-02-01

193

Synthesis and Characterization of Three-Coordinate Ni(III)-Imide Complexes  

PubMed Central

A new family of low-coordinate nickel imides supported by 1,2-bis(di-tert-butylphosphino)ethane was synthesized. The oxidation of nickel(II) complexes led to the formation of both aryl- and alkyl-substituted nickel(III) imides, and examples of both types have been isolated and fully characterized. The aryl substituent that proved most useful in stabilizing the Ni(III)-imide moiety was the bulky 2,6-dimesitylphenyl. The two nickel(III)-imide compounds showed different variable-temperature magnetic properties, but analogous EPR spectra at low temperatures. In order to account for this discrepancy, a low-spin/high-spin equilibrium was proposed to take place for the alkyl-substituted imide nickel(III) complex. This proposal was supported by DFT calculations. DFT calculations also indicated that the unpaired electron is mostly localized on the imide nitrogen for the nickel(III) complexes. The results of reactions carried out in the presence of hydrogen donors supported the findings from DFT calculations that the adamantyl substituent was a significantly more reactive hydrogen-atom abstractor. Interestingly, the steric properties of the 2,6-dimesitylphenyl substituent are important not only in protecting the Ni=N core but also in favoring one rotamer of the resulting nickel(III) imide, by locking in the phenyl ring in a perpendicular orientation with respect to the NiPP plane.

Iluc, Vlad M.; Miller, Alexander J. M.; Anderson, John S.; Monreal, Marisa J.; Mehn, Mark P.; Hillhouse, Gregory L.

2011-01-01

194

Coordinated regulation of polycomb group complexes through microRNAs in cancer.  

PubMed

Polycomb Repressive Complexes (PRC1 and PRC2)-mediated epigenetic regulation is critical for maintaining cellular homeostasis. Members of Polycomb Group (PcG) proteins including EZH2, a PRC2 component, are upregulated in various cancer types, implicating their role in tumorigenesis. Here, we have identified several microRNAs (miRNAs) that are repressed by EZH2. These miRNAs, in turn, regulate the expression of PRC1 proteins BMI1 and RING2. We found that ectopic overexpression of EZH2-regulated miRNAs attenuated cancer cell growth and invasiveness, and abrogated cancer stem cell properties. Importantly, expression analysis revealed an inverse correlation between miRNA and PRC protein levels in cell culture and prostate cancer tissues. Taken together, our data have uncovered a coordinate regulation of PRC1 and PRC2 activities that is mediated by miRNAs. PMID:21840484

Cao, Qi; Mani, Ram-Shankar; Ateeq, Bushra; Dhanasekaran, Saravana M; Asangani, Irfan A; Prensner, John R; Kim, Jung H; Brenner, J Chad; Jing, Xiaojun; Cao, Xuhong; Wang, Rui; Li, Yong; Dahiya, Arun; Wang, Lei; Pandhi, Mithil; Lonigro, Robert J; Wu, Yi-Mi; Tomlins, Scott A; Palanisamy, Nallasivam; Qin, Zhaohui; Yu, Jindan; Maher, Christopher A; Varambally, Sooryanarayana; Chinnaiyan, Arul M

2011-08-16

195

Mesomorphism of Four-Coordinated Four-Chained Metal Complexes Based on Pyrazolylpyridine Derivatives  

Microsoft Academic Search

A homologous series of four-chained silver(I) and zinc(II) metal complexes based on the coordination of two NN?-bidentate ligands pzpy 2-[3,5-bis(4-alkyloxy)phenyl]pyrazol-1-yl]pyridine (R=C6H4OCnH2n+1, n=16, 18) have been synthesised. All compounds [M(pzpy)2][A]m (M=Ag, m=1, n=16, 18, (1,2), (3,4), CF3 (OTf) (5,6), (7,8); M=Zn, m=2, n=16, 18, (9,10)) exhibit liquid crystal properties showing enantiotropic SmA phases, independently of the starting pzpy ligands (non-mesomorphism for

Paloma Ovejero; M. Jos Mayoral; Mercedes Cano; Jos A. Campo; Jos V. Heras; Paula Fernndez-Tobar; Marta Valin; Elena Pinilla; M. Rosario Torres

2008-01-01

196

Regulation and coordination of nuclear envelope and nuclear pore complex assembly  

PubMed Central

In metazoans with open mitosis, cells undergo structural changes involving the complete disassembly of the nuclear envelope (NE). In post-mitosis, the dividing cell faces the difficulty to reassemble NE structures in a highly regulated fashion around separated chromosomes. The de novo formation of nuclear pore complexes (NPCs), which are gateways between the cytoplasm and nucleoplasm across the nuclear membrane, is an archetype of macromolecular assembly and is therefore of special interest. The reformation of a functional NE further involves the reassembly and organization of other NE components, the nuclear membrane and NE proteins, around chromosomes in late mitosis. Here, we discuss the function of NE components, such as lamins and INM proteins, in NE reformation and highlight recent results on coordination of NPC and NE assembly.

Clever, Michaela; Mimura, Yasuhiro; Funakoshi, Tomoko; Imamoto, Naoko

2013-01-01

197

Three-coordinate copper(I) amido and aminyl radical complexes  

PubMed Central

A three-coordinate Cu-NR2 system (R = p-tolyl) supported by the anionic bis(phosphino)borate ligand [Ph2B(CH2PtBu2)2]? has been isolated and structurally characterized in both its anionic CuI and neutral (formally) CuII oxidation states. A rapid rate constant kS ? 107 M?1 s?1 for the self-exchange electron transfer reaction makes this system a functional model for the type-1 active sites in blue copper proteins. Multi-edge XAS, multi-frequency EPR, and DFT analyses collectively indicate that the oxidized form is best regarded as a CuI-aminyl radical complex rather than a CuII-amido species, with about 70% localization of the unpaired electron on the NR2 unit. Hydrogen atom transfer and C-C coupling reactions are presented as examples of chemical reactivity manifested by this unusual electronic structure.

Mankad, Neal P.; Antholine, William E.; Szilagyi, Robert K.; Peters, Jonas C.

2011-01-01

198

Cation-cation interactions and cation exchange in a series of isostructural framework uranyl tungstates  

NASA Astrophysics Data System (ADS)

The isotypical compounds (UO2)3(WO6)(H2O)5 (1), Ag(UO2)3(WO6)(OH)(H2O)3 (2), K(UO2)3(WO6)OH(H2O)4 (3), Rb(UO2)3(WO6)(OH)(H2O)3.5 (4), and Cs(UO2)3(WO6)OH(H2O)3 (5) were synthesized, characterized, and their structures determined. Each crystallizes in space group Cc. (1): a=12.979 (3), b=10.238 (2), c=11.302 (2), ?=102.044 (2); (2): a=13.148 (2), b=9.520 (1), c=11.083 (2), ?=101.568 (2); (3): a=13.111 (8), b=9.930 (6), c=11.242 (7), ?=101.024 (7); (4): a=12.940 (2), b=10.231 (2), c=11.259(2), ?=102.205 (2); (5): a=12.983 (3), b=10.191 (3), c=11.263 (4), ?=101.661 (4). Compounds 1-5 are a framework of uranyl and tungsten polyhedra containing cation-cation interactions. The framework has three symmetrically distinct U(VI) cations, one tungsten, sixteen to eighteen oxygen atoms, and in 2-5, one monovalent cation. Each atom occupies a general position. Each U(VI) cation is present as a typical (UO2)2+ uranyl ion in an overall pentagonal bipyramidal coordination environment. Each pentagonal bipyramid shares two equatorial edges with two other pentagonal bipyramids, forming a trimer. Trimers are connected into chains by edge-sharing with WO6 octahedra. Chains are linked through cation-cation interactions between two symmetrically independent uranyl ions. This yields a remarkably complex system of intersecting channels that extend along [0 0 1] and [-1 1 0]. The cation exchange properties of 2 and 3 were characterized at room temperature and at 140 C.

Balboni, Enrica; Burns, Peter C.

2014-05-01

199

Polymer complexes. XXXX. Supramolecular assembly on coordination models of mixed-valence-ligand poly[1-acrylamido-2-(2-pyridyl)ethane] complexes.  

PubMed

The build-up of polymer metallic supramolecules based on homopolymer (1-acrylamido-2-(2-pyridyl)ethane (AEPH)) and ruthenium, rhodium, palladium as well as platinum complexes has been pursued with great interest. The homopolymer shows three types of coordination behaviour. In the mixed valence paramagnetic trinuclear polymer complexes [(11)+(12)] in the paper and in mononuclear polymer complexes (1)-(5) it acts as a neutral bidentate ligand coordinating through the N-pyridine and NH-imino atoms, while in the mixed ligand diamagnetic poly-chelates, which are obtained from the reaction of AEPH with PdX2 and KPtCl4 in the presence of N-heterocyclic base consisting of polymer complexes (9)+(10), and in monouclear compounds (6)-(8), it behaves as a monobasic bidentate ligand coordinating through the same donor atoms. In mononuclear compounds (13)+(14) it acts as a monobasic and neutral bidentate ligand coordinating only through the same donor atoms. Monomeric distorted octahedral or trimeric chlorine-bridged, approximately octahedral structures are proposed for these polymer complexes. The poly-chelates are of 1:1, 1:2 and 3:2 (metal-homopolymer) stoichiometry and exhibit six coordination. The values of ligand field parameters were calculated. The homopolymer and their polymer complexes have been characterized physicochemically. PMID:12524114

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

2003-02-01

200

Polymer complexes.. XXXX. Supramolecular assembly on coordination models of mixed-valence-ligand poly[1-acrylamido-2-(2-pyridyl)ethane] complexes  

NASA Astrophysics Data System (ADS)

The build-up of polymer metallic supramolecules based on homopolymer (1-acrylamido-2-(2-pyridyl)ethane (AEPH)) and ruthenium, rhodium, palladium as well as platinum complexes has been pursued with great interest. The homopolymer shows three types of coordination behaviour. In the mixed valence paramagnetic trinuclear polymer complexes [( 11)+( 12)] in the paper and in mononuclear polymer complexes ( 1)-( 5) it acts as a neutral bidentate ligand coordinating through the N-pyridine and NH-imino atoms, while in the mixed ligand diamagnetic poly-chelates, which are obtained from the reaction of AEPH with PdX 2 and KPtCl 4 in the presence of N-heterocyclic base consisting of polymer complexes ( 9)+( 10), and in monouclear compounds ( 6)-( 8), it behaves as a monobasic bidentate ligand coordinating through the same donor atoms. In mononuclear compounds ( 13)+( 14) it acts as a monobasic and neutral bidentate ligand coordinating only through the same donor atoms. Monomeric distorted octahedral or trimeric chlorine-bridged, approximately octahedral structures are proposed for these polymer complexes. The poly-chelates are of 1:1, 1:2 and 3:2 (metal-homopolymer) stoichiometry and exhibit six coordination. The values of ligand field parameters were calculated. The homopolymer and their polymer complexes have been characterized physicochemically.

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

2003-02-01

201

The HITECH Act and Electronic Health Records' Limitation in Coordinating Care for Children with Complex Chronic Conditions.  

PubMed

While the HITECH Act was implemented to promote the use of electronic health records to improve the quality and coordination of healthcare, the limitations established to the setting of the hospital or physician's office affect the care coordination for those who utilize many health-related services outside these settings, including children with complex and chronic conditions. Incentive-based support or nationally supported electronic health record systems for allied and other healthcare professionals are necessary to see the full impact that electronic health records can have on care coordination for individuals who utilize many skilled healthcare services that are not associated with a hospital or physician's office. PMID:24925039

Cook, Jason E

2014-01-01

202

Effects of solvent systems on two silver coordination complexes: From discrete structure to 2D sheet  

NASA Astrophysics Data System (ADS)

Two mixed-ligand silver(I) coordination complexes (CCs), [Ag4(mpyz)(npt)2(H2O)2]n (1) and [Ag4(mpyz) (npt)2]n (2) were synthesized with reactions of methyl-pyrazine(mpyz) and 3-nitro-1,2-benzenedicarboxylic acid (H2npt) with silver nitrate in different solvent systems and were structurally characterized by single-crystal X-ray crystallography. Structural differences of CCs are due to the effects of solvent systems and the intricacy of the self-assembly process for these systems. For 1, the Ag4 unit which is like Y letter which stand upside and down and repeat to form a 1D-63-silver-ring which shares Ag1 and Ag2 only with npt ligands. The eight Ag ions of complex 2 are in a shape like the branches of a tree which repeat to form a 1D silver chain. Effects of solvents on the structures, as well as the intricacy of the self-assembly process were discussed. The photoluminescence, infrared spectroscopy (IR) and thermogravimetric analyses (TGA) behaviors of the compounds were also discussed.

Wang, Dan-Feng; Wang, Zhan-Hui; Lu, Bo-Wei; Chen, Shu-Fen; Zhang, Ting; Huang, Rong-Bin; Zheng, Lan-Sun

2014-02-01

203

Thermal Analysis Studies of Ammonium Uranyl Carbonate.  

National Technical Information Service (NTIS)

The simultaneous thermogravimetry and differential thermal analysis of the ammonium uranyl carbonate powder were performed with heat balance in the following atmosphers: Air, Ar and Ar-8%H/sub 2/. The thermogravimetry and differential thermal analysis cur...

X. Cao X. Ma F. Wang N. Liu C. Ji

1988-01-01

204

U(VI)-kaolinite surface complexation in absence and presence of humic acid studied by TRLFS.  

PubMed

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the U(VI) surface complexes on kaolinite in the presence and absence of humic acid (HA). Two uranyl surface species with fluorescence lifetimes of 5.9 +/- 1.4 and 42.5 +/- 3.4 micros and 4.4 +/- 1.2 and 30.9 +/- 7.2 micros were identified in the binary (U(VI)-kaolinite) and ternary system (U(VI)-HA-kaolinite), respectively. The fluorescence spectra of adsorbed uranyl surface species are described with six and five fluorescence emission bands in the binary and ternary system, respectively. The positions of peak maxima are shifted significantly to higher wavelengths compared to the free uranyl ion in perchlorate medium. HA has no influence on positions of the fluorescence emission bands. In the binary system, both surface species can be attributed to adsorbed bidentate mononuclear surface complexes, which differ in the number of water molecules in their coordination environment. In the ternary system, U(VI) prefers direct binding on kaolinite rather than via HA, but it is sorbed as a uranyl-humate complex. Consequently, the hydration shell of the U(VI) surface complexes is displaced with complexed HA, which is simultaneously distributed between kaolinite particles. Aluminol binding sites are assumed to control the sorption of U(VI) onto kaolinite. PMID:17937294

Krepelova, Adela; Brendler, Vinzenz; Sachs, Susanne; Baumann, Nils; Bernhard, Gert

2007-09-01

205

Normal-to-abnormal rearrangement and NHC activation in three-coordinate iron(II) carbene complexes.  

PubMed

The 'normal' three-coordinate iron-NHC complex [(IPr)Fe(N'')2] (N? = N(SiMe3)2) rearranges to its abnormal NHC analogue [(aIPr)Fe(N?)2] (6) on heating, providing a rare abnormal iron-aNHC complex, and the first such three-coordinate complex. The tert-butyl-substituted complex [(I(t)Bu)Fe(N?)2] (4) undergoes a thermal decomposition that has not previously been observed in iron-NHC chemistry, resulting in the bis(imidazole) complex [((t)BuIm)2Fe(N?)2] (7). A mechanism that involves consecutive C-H and C-N activation is proposed to account for the formation of 7. PMID:23978294

Day, Benjamin M; Pugh, Thomas; Hendriks, Danil; Guerra, Clia Fonseca; Evans, David J; Bickelhaupt, F Matthias; Layfield, Richard A

2013-09-11

206

Long patch base excision repair proceeds via coordinated stimulation of the multienzyme DNA repair complex.  

PubMed

Base excision repair, a major repair pathway in mammalian cells, is responsible for correcting DNA base damage and maintaining genomic integrity. Recent reports show that the Rad9-Rad1-Hus1 complex (9-1-1) stimulates enzymes proposed to perform a long patch-base excision repair sub-pathway (LP-BER), including DNA glycosylases, apurinic/apyrimidinic endonuclease 1 (APE1), DNA polymerase beta (pol beta), flap endonuclease 1 (FEN1), and DNA ligase I (LigI). However, 9-1-1 was found to produce minimal stimulation of FEN1 and LigI in the context of a complete reconstitution of LP-BER. We show here that pol beta is a robust stimulator of FEN1 and a moderate stimulator of LigI. Apparently, there is a maximum possible stimulation of these two proteins such that after responding to pol beta or another protein in the repair complex, only a small additional response to 9-1-1 is allowed. The 9-1-1 sliding clamp structure must serve primarily to coordinate enzyme actions rather than enhancing rate. Significantly, stimulation by the polymerase involves interaction of primer terminus-bound pol beta with FEN1 and LigI. This observation provides compelling evidence that the proposed LP-BER pathway is actually employed in cells. Moreover, this pathway has been proposed to function by sequential enzyme actions in a "hit and run" mechanism. Our results imply that this mechanism is still carried out, but in the context of a multienzyme complex that remains structurally intact during the repair process. PMID:19329425

Balakrishnan, Lata; Brandt, Patrick D; Lindsey-Boltz, Laura A; Sancar, Aziz; Bambara, Robert A

2009-05-29

207

Uranyl fluoride luminescence in acidic aqueous solutions  

SciTech Connect

Luminescence emission spectra and decay rates are reported for uranyl species in acidic aqueous solutions containing HF or added NaF. The longest luminescence lifetime, 0.269 {+-} 0.006 ms, was observed from uranyl in 1 M HF + 1 M HClO{sub 4} at 296 K and decreased with increasing temperature. Based on a luminescence dynamics model that assumes equilibrium among electronically excited uranyl fluoride species and free fluoride ion, this long lived uranyl luminescence in aqueous solution is attributed primarily to UO{sub 2}F{sub 2}. Studies on the effect of added LiNO{sub 3} or Na{sub 2}WO{sub 4}{center_dot}2H{sub 2}O showed relatively weak quenching of uranyl fluoride luminescence which suggests that high sensitivity determination of the UF{sub 6} content of WF{sub 6} gas should be feasible via uranyl luminescence analysis of hydrolyzed gas samples of impure WF{sub 6}.

Beitz, J.V.; Williams, C.W. [Argonne National Lab., IL (United States). Chemistry Div.

1996-08-01

208

Self-assembly of three new coordination complexes: Formation of 2-D square grid, 1-D chain and tape structures  

NASA Astrophysics Data System (ADS)

Three distinct coordination complexes, viz., [Co(imi) 2(tmb) 2] ( 1) [where imi = imidazole], {[Ni(tmb) 2(H 2O) 3]2H 2O} n ( 2) and [Cu 2(?-tmb) 4(CH 3OH) 2] ( 3), have been synthesized hydrothermally by the reactions of metal acetates, 2,4,6-trimethylbenzoic acid (Htmb) and with or without appropriate amine. The Ni analogue of 1 and the Co analogue of 2 have also been synthesized. X-ray single-crystal diffraction suggests that complex 1 represents discrete mononuclear species and complex 2 represents a 1D chain coordination polymer in which the Ni(II) ions are connected by the bridging water molecules. Complex 3 represents a neutral dinuclear complex. In 1, the central metal ions are associated by the carboxylate moiety and imidazole ligands, whereas the central metal atom is coordinated to the carboxylate moiety and the respective solvent molecules in 2 and 3. In 3, the four 2,4,6-trimethylbenzoate moieties act as a bridge connecting two copper (II) ions and the O atoms of methanol coordinate in an anti arrangement to form a square pyramidal geometry, with the methanol molecule at the apical position. In all the three structures the central metal atom sits on a crystallographic inversion centre. In all the cases, the coordination entities are further organized via hydrogen bonding interactions to generate multifarious supramolecular networks. Complexes 1, 2 and 3 have also been characterized by spectroscopic (UV/Vis and IR) and thermal analysis (TGA). In addition, the complexes were found to exhibit antimicrobial activity.The magnetic susceptibility measurements, measured from 8 to 300 K, revealed antiferromagnetic interactions between the Co(II) ions in compound 1 and the Ni(II) ions in 1a, respectively.

Indrani, Murugan; Ramasubramanian, Ramasamy; Fronczek, Frank R.; Vasanthacharya, N. Y.; Kumaresan, Sudalaiandi

2009-08-01

209

Characterization of Ce(3+) -tributyl phosphate coordination complexes produced by fused droplet electrospray ionization with a target capillary.  

PubMed

Coordination complexes containing Ce(III) and tri-n-butyl phosphate (TBP) in the 1+, 2+ and 3+ charge states were generated using both direct infusion electrospray ionization (ESI) and fused droplet (FD) ESI using a target capillary, in which the analyte solutions are impinged by the ESI droplets. The same coordination complexes were produced in each experiment, and their relative abundances were also very close, suggesting that similar processes are occurring in both experiments. The ion species formed in both experiments have the general formula [Ce(NO(3) )(m=0-2) (TBP)(n=3-7) ]((3-m)+) . The appearance of abundant 1+ and 2+ ion pair complexes indicated that the ESI process was modifying the ion populations in the original solutions, which contain predominantly 3+ and 2+ species. The FD ESI experiments were less sensitive for coordination complexes compared to direct infusion ESI; however, mid-picomolar quantities of coordination complexes were measured using the target capillary, indicating that sensitivity would be sufficient for measuring species in many industrial separations processes. PMID:22223419

Groenewold, G S; Gaumet, J-J

2011-12-01

210

Enhanced environmental detection of uranyl compounds based on luminescence characterization  

NASA Astrophysics Data System (ADS)

Uranium (U) contamination can be introduced to the environment as a result of mining and manufacturing activities related to nuclear power, detonation of U-containing munitions (DoD), or nuclear weapons production/processing (DOE facilities). In oxidizing environments such as surface soils, U predominantly exists as U(VI), which is highly water soluble and very mobile in soils. U(VI) compounds typically contain the UO22+ group (uranyl compounds). The uniquely structured and long-lived green luminescence (fluorescence) of the uranyl ion (under UV radiation) has been studied and remained a strong topic of interest for two centuries. The presented research is distinct in its objective of improving capabilities for remotely sensing U contamination by understanding what environmental conditions are ideal for detection and need to be taken into consideration. Specific focuses include: (1) the accumulation and fluorescence enhancement of uranyl compounds at soil surfaces using distributed silica gel, and (2) environmental factors capable of influencing the luminescence response, directly or indirectly. In a complex environmental system, matrix effects co-exist from key soil parameters including moisture content (affected by evaporation, temperature and humidity), soil texture, pH, CEC, organic matter and iron content. Chapter 1 is a review of pertinent background information and provides justification for the selected key environmental parameters. Chapter 2 presents empirical investigations related to the fluorescence detection and characterization of uranyl compounds in soil and aqueous samples. An integrative experimental design was employed, testing different soils, generating steady-state fluorescence spectra, and building a comprehensive dataset which was then utilized to simultaneously test three hypotheses: The fluorescence detection of uranyl compounds is dependent upon (1) the key soil parameters, (2) the concentration of U contamination, and (3) time of analysis, specifically following the application of silica gel enhancing material. A variety of statistical approaches were employed, including the development of multiple regression models for predicting both intensity and band structure responses. These statistical models validated the first two listed hypotheses, while the third hypothesis was not supported by this dataset. The combination of inadequate moisture levels and reaction times (? 24 hrs) greatly limited the detection of varying levels of U, depending on the soil.

Nelson, Jean Dennis

211

Characterization of Ce SUP 3+-tributyl phosphate coordination complexes produced by fused droplet electrospray ionization with a target capillary  

SciTech Connect

Coordination complexes containing Ce(III) and tri-n-butyl phosphate (TBP) in the 1+, 2+ and 3+ charge states were generated using desorption electrospray ionization (DESI) mass spectrometry, in which the analyte solutions were supplied via a target capillary orthogonally situated with respect to the electrospray. Comparison with direct electrospray (ESI) showed that the same coordination complexes were produced in each experiment, and could be described by the general formula [Ce(NO3)m=0-2(TBP)n](3-m)+. This result indicates that DESI has utility for measuring metal speciation for metal ligand solutions where the gas-phase complexes generated by ESI have been correlated with solution speciation. Such an application would be useful for analyses where it is desirable to limit the total amount of metal being handled, or that have solvent systems that are not readily amenable to ESI. Both the direct ESI and DESI mass spectra showed similar trends with respect to the TBP:Ce ratio, viz. high values tend to favor formation of a larger fraction of the 1+ species, and the 2+ and 3+ species become relatively more important as the ratio is decreased. Within individual charge state ion envelopes, lower TBP:Ce ratios produce coordination complexes with fewer ligands, a trend also seen using both approaches. These trends again point toward strong similarity between the direct ESI and DESI analyses of the metal-ligand solutions. The DESI experiments were less sensitive for measuring the coordination complexes compared to the direct ESI experiments, by a factor of 10 - 100 depending on whether minimum detectable concentration or absolute ion abundances were considered. Nevertheless, mid-picomolar quantities of coordination complexes were measured using the target capillary, indicating that sensitivity would be sufficient for measuring species in many industrial separations processes.

Gary S. Groenewold; Jean-Jacques Gaumet

2011-12-01

212

Coordination of tRNA transcription with export at nuclear pore complexes in budding yeast.  

PubMed

tRNAs are encoded by RNA polymerase III-transcribed genes that reside at seemingly random intervals along the chromosomes of budding yeast. Existing evidence suggests that the genes congregate together at the nucleolus and/or centromeres. In this study, we re-examined spatial and temporal aspects of tRNA gene (tDNA) expression. We show that tDNA transcription fluctuates during cell cycle progression. In M phase, when tRNA synthesis peaks, tDNAs localize at nuclear pore complexes (NPCs). Docking of a tDNA requires the DNA sequence of the contacted gene, nucleoporins Nup60 and Nup2, and cohesin. Characterization of mutants that block NPC localization revealed that docking is a consequence of elevated tDNA transcription. NPC-tDNA contact falters in the absence of the principal exportin of nascent tRNA, Los1, and genetic assays indicate that gating of tDNAs at NPCs favors cytoplasmic accumulation of functional tRNA. Collectively, the data suggest that tDNAs associate with NPCs to coordinate RNA polymerase III transcription with the nuclear export of pre-tRNA. The M-phase specificity of NPC contact reflects a regulatory mechanism that may have evolved, in part, to avoid collisions between DNA replication forks and transcribing RNA polymerase III machinery at NPCs. PMID:24788517

Chen, Miao; Gartenberg, Marc R

2014-05-01

213

Mononuclear and binuclear iron(III) complexes incorporating N 4O 3 coordinating heptadentate ligand: Synthesis, structure and magnetic properties  

Microsoft Academic Search

The N4O3 coordinating heptadentate ligand afforded the mononuclear [FeIII(HL)][BPh4] (1) and binuclear [Fe2IIIL(OAc)2][BPh4] (2) complexes. In complex 1, the ligand binds in a trianionic N2O3 fashion whereas in the case of 2 the ligand binds in the trianionic N4O3 form in which the iron ions are held together by ?-phenoxo and bis ?-acetato bridges. In 1, the Fe(III) center has

Reena Singh; Coen de Graaf; Enrique Colacio; Kajal Krishna Rajak

2008-01-01

214

Vibrational Spectroscopy of Mass-Selected [UO2(ligand)n]2+ Complexes in the Gas Phase: Comparison with Theory  

SciTech Connect

The gas-phase infrared spectra of discrete uranyl ([UO2]2+) complexes ligated with acetone and/or acetonitrile were used to evaluate systematic trends of ligation on the position of the OdUdO stretch and to enable rigorous comparison with the results of computational studies. Ionic uranyl complexes isolated in a Fourier transform ion cyclotron resonance mass spectrometer were fragmented via infrared multiphoton dissociation using a free electron laser scanned over the mid-IR wavelengths. The asymmetric OdUdO stretching frequency was measured at 1017 cm-1 for [UO2(CH3COCH3)2]2+ and was systematically red shifted to 1000 and 988 cm-1 by the addition of a third and fourth acetone ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. In contrast to the uranyl frequency shifts, the carbonyl frequencies of the acetone ligands were progressively blue shifted as the number of ligands increased from two to four and approached that of free acetone. This observation was consistent with the formation of weaker noncovalent bonds between uranium and the carbonyl oxygen as the extent of ligation increases. Similar trends were observed for [UO2(CH3CN)n]2+ complexes, although the uranyl asymmetric stretching frequencies were greater than those measured for acetone complexes having equivalent coordination, which is consistent with the fact that acetonitrile is a weaker nucleophile than is acetone. This conclusion was confirmed by the uranyl stretching frequencies measured for mixed acetone/acetonitrile complexes, which showed that substitution of one acetone for one acetonitrile produced a modest red shift of 3-6 cm-1.

Gary S. Groenewold; Anita K. Gianotto

2006-03-01

215

Electronic Transitions as a Probe of Tetrahedral versus Octahedral Coordination in Nickel(II) Complexes: An Undergraduate Inorganic Chemistry Experiment.  

ERIC Educational Resources Information Center

Discusses procedures, theoretical considerations, and results of an experiment involving the preparation of a tetrahedral nickel(II) complex and its transformation into an octahedral species. Suggests that fundamental aspects of coordination chemistry can be demonstrated by simple experiments performed in introductory level courses. (Author/JN)

Filgueiras, Carlos A. L.; Carazza, Fernando

1980-01-01

216

Ga(III) complexes--the effect of metal coordination on potential systemic absorption after topical exposure.  

PubMed

The handling of elemental gallium is not thought to be harmful, but this assumption does not consider metal coordination which readily occurs in physiological fluids. The aim of this work was to determine Ga(III) coordination behaviour in simple solutions and assess the effects of complex formation upon skin permeation in vitro. Ga(III) coordination was modelled using metal-ligand stability constants in silico and the permeation of the metal through human and porcine skin determined using four test conditions. Ga(III) was presented to the skin as: (1) Ga+ ions; (2) a -ve citrate complex (Ga(neg)); (3) a mixture of +ve and -ve complexes (Ga(mix)) and (4) a mixture of +ve hydroxide complexes (Ga(pos)). The permeability coefficient (Kp) of Ga(III) through human skin increased by almost 2 orders of magnitude when applied as free Ga+ ions or a Ga(neg) complex (the two most water soluble complexes), compared to Ga(mix) or Ga(pos). This trend was not well modelled by porcine skin which proved to be less of a barrier to Ga(III) permeation compared to human skin (Kp=2 x 10? 2 x 10?? cm h?). Given the significant transdermal bioavailablity of Ga(III) demonstrated by this study, it would appear prudent to re-evaluate the dermal toxicity of this metal. PMID:21315140

Staff, Kirsten; Brown, Marc B; Chilcott, Robert P; Hider, Robert C; Jones, Stuart A; Kong, Xiao L

2011-05-10

217

Neutral six-coordinate and cationic five-coordinate silicon(IV) complexes with two bidentate monoanionic N,S-pyridine-2-thiolato(-) ligands.  

PubMed

A series of neutral six-coordinate silicon(IV) complexes (4-11) with two bidentate monoanionic N,S-pyridine-2-thiolato ligands and two monodentate ligands R(1) and R(2) was synthesized (4, R(1) = R(2) = Cl; 5, R(1) = Ph, R(2) = Cl; 6, R(1) = Ph, R(2) = F; 7, R(1) = Ph, R(2) = Br; 8, R(1) = Ph, R(2) = N3; 9, R(1) = Ph, R(2) = NCO; 10, R(1) = Ph, R(2) = NCS; 11, R(1) = Me, R(2) = Cl). In addition, the related ionic compound 12 was synthesized, which contains a cationic five-coordinate silicon(IV) complex with two bidentate monoanionic N,S-pyridine-2-thiolato ligands and one phenyl group (counterion: I(-)). Compounds 4-12 were characterized by elemental analyses, NMR spectroscopic studies in the solid state and in solution, and crystal structure analyses (except 7). These structural investigations were performed with a special emphasis on the sophisticated stereochemistry of these compounds. These experimental investigations were complemented by computational studies, including bonding analyses based on relativistic density functional theory. PMID:24011307

Baus, Johannes A; Burschka, Christian; Bertermann, Rdiger; Guerra, Clia Fonseca; Bickelhaupt, F Matthias; Tacke, Reinhold

2013-09-16

218

Coordination and conformational isomers in mononuclear iron complexes with pertinence to the [FeFe] hydrogenase active site.  

PubMed

A series of six mononuclear iron complexes of the type [Fe(X-bdt)(P(R)2N(Ph)2)(CO)] (P(R)2N(Ph)2 = 1,5-diaza-3,7-diphosphaoctane, bdt = benzenedithiolate with X = H, Cl2 or Me and R = Ph, Bn, Cyc or tert-Bu) was prepared. This new class of penta-coordinate iron complexes contains a free coordination site and a pendant base as essential structural features of the [FeFe]-hydrogenase active site. The bidentate nature of the P(R)2N(Ph)2 ligands was found to be crucial for the preferential formation of coordinatively unsaturated penta-coordinate complexes, which is supported by first principle calculations. IR-spectroscopic data suggest the presence of coordination isomers around the metal center, as well as multiple possible conformers of the P(R)2N(Ph)2 ligand. This finding is further corroborated by X-ray crystallographic and computational studies. (31)P{(1)H}-NMR- and IR-spectroscopic as well as electrochemical measurements show that the electronic properties of the complexes are strongly, and independently, influenced by the P-substituents at the P(R)2N(Ph)2 ligand as well as by modifications of the bdt bridge. These results illustrate the advantages of this modular platform, which allows independent and selective tuning through site specific modifications. Potential catalytic intermediates, namely singly reduced and protonated complexes, have been further investigated by spectroscopic methods and exhibit remarkable stability. Finally, their general capacity for electro-catalytic reduction of protons to molecular hydrogen was verified. PMID:24457903

Orthaber, Andreas; Karnahl, Michael; Tschierlei, Stefanie; Streich, Daniel; Stein, Matthias; Ott, Sascha

2014-03-21

219

Structural Studies of Copper(I) Complexes of Amyloid-Beta Peptide Fragments: Formation of Two-Coordinate Bis(Histidine) Complexes  

SciTech Connect

The beta bind: Copper(I) binds to amyloid {beta}-peptide fragments (see structure) as a stable bis(histidine), two-coordinate, near-linear complex, even in the presence of potential additional ligands. As has been proposed or assumed in other studies, the copper(I)-peptide complexes react with dioxygen to form the reactive oxygen species H{sub 2}O{sub 2}, without the need for a third histidine ligand to promote the chemistry.

Himes, R.A.; Park, G.Young.; Siluvai, G.Sutha.; Blackburn, N.J.; Karlin, K.D.

2009-05-18

220

Improving robustness against the coordinated attack by removing crashed hub nodes in complex network  

Microsoft Academic Search

Recently, several distributed attacks based on local information have been emerged threating network security. The coordinated attack is one of the most destructive attacks, with an important property to identify the next-step target through coordinating all crashed nodes. It has been ignored in most of existing researches that the crashed nodes network size will become larger and larger along with

Yue Zhuo; Yunfeng Peng; Keping Long

2009-01-01

221

Photochemical reduction of uranyl nitrate  

SciTech Connect

The photochemical reduction of uranyl nitrate solutions to tetravalent uranium was investigated as a means of producing uranium dioxide feed for the saltless direct oxide reduction (SDOR) process. At high uranium concentrations, reoxidation of U{sup +4} occurs rapidly. The kinetics of the nitric oxidation of tetravalent uranium depend on the concentrations of hydrogen ion, nitrate ion, nitrous acid, and tetravalent uranium in the same manner as was reported elsewhere for the nitrate oxidation of PU{sup +3}. Reaction rate data were successfully correlated with a mechanism in which nitrogen dioxide is the reactive intermediate. Addition of a nitrous acid scavenger suppresses the reoxidation reaction. An immersion reactor employing a mercury vapor lamp gave reduction times fast enough for routine production usage. Precipitation techniques for conversion of aqueous U(NO{sub 3}){sub 4} to hydrous UO{sub 2} were evaluated. Prolonged dewatering times tended to make the process time consuming. Use of 3- to 4-M aqueous NaOH gave the best dewatering times observed. Reoxidation of the UO{sub 2} by water of hydration was encountered, which required the drying process to be carried out under a reducing atmosphere.

Duerksen, W.K.

1993-10-20

222

Carbynes and carbenes in coordination chemistry: A new class of pentaammine and tetraammine complexes of osmium(II)  

SciTech Connect

Since their discovery by Fischer and co-workers in 1973, the study of transition-metal carbyne complexes and their role in alkyne metathesis has rapidly developed into a mature field. Although carbyne complexes are known for a diverse set of early- and mid-transition metals, the vast majority of these complexes contain carbon or phosphine [pi]-acids, or bulky alkoxide ligands, which limit the coordination number. We wish to report the first example of a carbyne species, as well as several heteroatom-carbene derivatives, in which the metal fragment, Os[sup II](NH[sub 3])[sub 5], provides a classical octahedral coordination environment. The carbyne [Os(NH[sub 3])[sub 5]([equivalent to]CPh)](OTf)[sub 3] (2) is synthesized in two steps from Os(NH[sub 3])[sub 5](OTf)[sub 3] and benzaledhyde dimethyl acetal.

Hodges, L.M.; Sabat, M.; Harman, W.D. (Univ. of Virginia, Charlottesville (United States))

1993-02-17

223

How Does a Coordinated Radical Ligand Affect the Spin Crossover Properties in an Octahedral Iron(II) Complex?  

PubMed

The influence of a coordinated ?-radical on the spin crossover properties of an octahedral iron(II) complex was investigated by preparing and isolating the iron(II) complex containing the tetradentate N,N'-dimethyl-2,11-diaza[3.3](2,6)pyridinophane and the radical anion of N,N'-diphenyl-acenaphtene-1,2-diimine as ligands. This spin crossover complex was obtained by a reduction of the corresponding low-spin iron(II) complex with the neutral diimine ligand, demonstrating that the reduction of the strong ?-acceptor ligand is accompanied by a decrease in the ligand field strength. Characterization of the iron(II) radical complex by structural, magnetochemical, and spectroscopic methods revealed that spin crossover equilibrium occurs above 240?K between an S=1/2 ground state and an S=3/2 excited spin state. The possible origins of the fast spin interconversion observed for this complex are discussed. PMID:24810415

Schmitz, Markus; Seibel, Manuel; Kelm, Harald; Demeshko, Serhiy; Meyer, Franc; Krger, Hans-Jrg

2014-06-01

224

Correlated coordination and redox activity of a hemilabile noninnocent ligand in nickel complexes.  

PubMed

The compound [Ni(QM )2 ], QM =4,6-di-tert-butyl-N-(2-methylthiomethylphenyl)-o-iminobenzoquinone, is a singlet diradical species with approximately planar configuration at the tetracoordinate metal atom and without any Ni?S bonding interaction. One-electron oxidation results in additional twofold Ni?S coordination (dNi?S ?2.38?) to produce a complex cation of [Ni(QM )2 ](PF6 ) with hexacoordinate Ni(II) and two distinctly different mer-configurated tridentate ligands. The O,O'-trans arrangement in the neutral precursor is changed to an O,O'-cis configuration in the cation. The EPR signal of [Ni(QM )2 ](PF6 ) has a very large g anisotropy and the magnetic measurements indicate an S=3/2 state. The dication was structurally characterized as [Ni(QM )2 ](ClO4 )2 to exhibit a similar NiN2 O2 S2 framework as the monocation. However, the two tridentate (O,N,S) ligands are now equivalent according to the formulation [Ni(II) (QM (0) )2 ](2+) . Cyclic voltammetry reflects the qualitative structure change on the first, but not on the second oxidation of [Ni(QM )2 ], and spectroelectrochemistry reveals a pronounced dependence of the 800-900?nm absorption on the solvent and counterion. Reduction of the neutral form occurs in an electrochemically reversible step to yield an anion with an intense near-infrared absorption at 1345?nm (?=10400?M(-1) ?cm(-1) ) and a conventional g factor splitting for a largely metal-based spin (S=1/2), suggesting a [(QM (.) (-) )Ni(II) (QM (2-) )](-) configuration with a tetracoordinate metal atom with antiferromagnetic Ni(II) -(QM (.) (-) ) interactions and symmetry-allowed ligand-to-ligand intervalence charge transfer (LLIVCT). Calculations are used to understand the Ni?S binding activity as induced by remote electron transfer at the iminobenzoquinone redox system. PMID:24665084

Paretzki, Alexa; Bubrin, Martina; Fiedler, Jan; Zli, Stanislav; Kaim, Wolfgang

2014-04-25

225

Oxa1-Ribosome Complexes Coordinate the Assembly of Cytochrome c Oxidase in Mitochondria*  

PubMed Central

The terminal enzyme of the respiratory chain, cytochrome c oxidase, consists of a hydrophobic reaction center formed by three mitochondrially encoded subunits with which 910 nuclear encoded subunits are associated. The three core subunits are synthesized on mitochondrial ribosomes and inserted into the inner membrane in a co-translational reaction facilitated by the Oxa1 insertase. Oxa1 consists of an N-terminal insertase domain and a C-terminal ribosome-binding region. Mutants lacking the C-terminal region show specific defects in co-translational insertion, suggesting that the close contact of the ribosome with the insertase promotes co-translational insertion of nascent chains. In this study, we inserted flexible linkers of 100 or 200 amino acid residues between the insertase domain and ribosome-binding region of Oxa1 of Saccharomyces cerevisiae. In the absence of the ribosome receptor Mba1, these linkers caused a length-dependent decrease in mitochondrial respiratory activity caused by diminished levels of cytochrome c oxidase. Interestingly, considerable amounts of mitochondrial translation products were still integrated into the inner membrane in these linker mutants. However, they showed severe defects in later stages of the biogenesis process, presumably during assembly into functional complexes. Our observations suggest that the close proximity of Oxa1 to ribosomes is not only used to improve membrane insertion but is also critical for the productive assembly of the subunits of the cytochrome c oxidase. This points to a role for Oxa1 in the spatial coordination of the ribosome with assembly factors that are critical for enzyme biogenesis.

Keil, Melanie; Bareth, Bettina; Woellhaf, Michael W.; Peleh, Valentina; Prestele, Martin; Rehling, Peter; Herrmann, Johannes M.

2012-01-01

226

Inner shells do not cause grave difficulties in resonance studies for atoms with the direct complex-coordinate method  

NASA Astrophysics Data System (ADS)

Many papers in the 1970s and 1980s state that inner shells cause considerable difficulties in resonance studies with the direct complex-coordinate method, especially for high-Z systems. However, our studies show that after rotating the Hamiltonian into complex space, inner-shell orbitals for atoms are not highly oscillatory. Because of an overall exponential decay, they do not cause grave difficulties in resonance studies. The results depend greatly on the choice of basis set. To demonstrate this, the doubly excited 2s2 1S states of He and He-like Ne (Ne8+) are examined with a complex-scaled multireference configuration-interaction method.

Zhang, Song Bin; Yeager, Danny L.

2012-05-01

227

Use of metalloligands [CuL] (H2L = salen type di-Schiff bases) in the formation of heterobimetallic copper(II)-uranyl complexes: photophysical investigations, structural variations, and theoretical calculations.  

PubMed

Five heterobimetallic copper(II)-uranium(VI) complexes [(CuL(1))UO2(NO3)2] (1), [{CuL(1)(CH3CN)}UO2(NO3)2] (2), [{CuL(1)(CH3COCH3)}UO2(NO3)2] (3), [{CuL(2)(CH3CN)}UO2(NO3)2](4), and [{CuL(2)(CH3COCH3)}UO2(NO3)2][{CuL(2)}UO2(NO3)2] (5) have been synthesized by reacting the Cu(II)-derived metalloligands [CuL(1)] and [CuL(2)] (where, H2L(1) = N,N'-bis(?-methylsalicylidene)-1,3-propanediamine and H2L(2) = N,N'-bis(salicylidene)-1,3-propanediamine) with UO2(NO3)26H2O in 1:1 ratio by varying the reaction temperature and solvents. Absorption and fluorescence quenching experiments (steady-state and time-resolved) indicate the formation of 1:1 ground-state charge transfer copper(II)-uranium(VI) complexes in solution. X-ray single-crystal structure reveals that each complex contains diphenoxido bridged Cu(II)-U(VI) dinuclear core with two chelated nitrato coligands. The complexes are solvated (acetonitrile or acetone) in the axial position of the Cu(II) in different manner or desolvated. The supramolecular interactions that depend upon the co-ordinating metalloligands seem to control the solvation. In complexes 2 and 3 a rare NO3(-)NO3(-) weak interaction plays an important role in forming supramolecular network whereas an uncommon U?ONO3(-) weak interaction helps to self-assemble heterobinuclear units in complex 5. The significance of the noncovalent interactions in terms of energies and geometries has been analyzed using theoretical calculations. PMID:23786416

Ghosh, Soumavo; Biswas, Saptarshi; Bauz, Antonio; Barcel-Oliver, Miquel; Frontera, Antonio; Ghosh, Ashutosh

2013-07-01

228

Conformational isomerism in monomeric, low-coordinate group?12 complexes stabilized by a naphthyl-substituted m-terphenyl ligand.  

PubMed

The synthesis and characterization of the first series of low-coordinate bis(terphenyl) complexes of the Group?12 metals, [Zn(2,6-Naph2 C6 H3 )2 ] (1), [Cd(OEt2 )(2,6-Naph2 C6 H3 )2 ] (2) and [Hg(OEt2 )(2,6-Naph2 C6 H3 )2 ] (3) (Naph=1-C10 H7 ) are described. The naphthyl substituents of the terphenyl ligands confer considerable steric bulk, and as a result of limited flexibility introduce multiple conformations to these unusual systems. In the solid state, complex 1 features a two-coordinate Zn centre with the ligands oriented in a syn/anti conformation, whereas the three-coordinate distorted T-shaped complexes 2 and 3 feature the ligands in the syn/syn configurations. The results of DFT calculations are in good agreement with the solid-state configurations for these complexes and support the spectroscopic measurements, which indicate several conformers in solution. PMID:23852994

Gridley, Benjamin M; Moxey, Graeme J; Lewis, William; Blake, Alexander J; Kays, Deborah L

2013-08-19

229

Hydrothermal syntheses and structures of the uranyl tellurates AgUO 2(HTeO 5) and Pb 2UO 2(TeO 6)  

NASA Astrophysics Data System (ADS)

Two uranyl tellurates, AgUO 2(HTeO 5) ( 1) and Pb 2UO 2(TeO 6) ( 2), were synthesized under hydrothermal conditions and were structurally, chemically, and spectroscopically characterized. 1 crystallizes in space group Pbca, a=7.085(2) , b=11.986(3) , c=13.913(4) , V=1181.5(5) 3, Z=8; 2 is in P2(1)/ c, a=5.742(1) , b=7.789(2) , c=7.928(2) , V=90.703(2) 3, and Z=2. These are the first structures reported for uranyl compounds containing tellurate. The U 6+ cations are present as (UO 2) 2+ uranyl ions that are coordinated by O atoms to give pentagonal and square bipyramids in compounds 1 and 2, respectively. The structural unit in 1 is a sheet consisting of chains of edge-sharing uranyl pentagonal bipyramids that are one bipyramid wide, linked through the dimers of TeO 6 octahedra. In 2, uranyl square bipyramids share each of their equatorial vertices with different TeO 6 octahedra, giving a sheet with the autunite-type topology. Sheets in 1 and 2 are connected through the low-valence cations that are located in the interlayer region. The structures of 1 and 2 are compared to those of uranyl compounds containing octahedrally coordinated cations.

Ling, Jie; Ward, Matthew; Burns, Peter C.

2011-02-01

230

THE COMPLEXING INTO METAL-CONTAINING GELATIN-IMMOBILIZED MATRICES AS NOVEL PERSPECTIVE METHOD OF COORDINATION POLYMERS SYNTHESIS. UNCHELATED COORDINATION POLYMERS OF NICKEL (II) AND COPPER(II) WITH DITHIOOXAMIDE  

Microsoft Academic Search

The novel unchelates coordination polymers of Ni(II) and Cu(II) with dithiooxamide have been synthesized under specific complexing conditions which have not been used in coordination chemistry before, namely into a nickel(II)- and copper(II)hexacyanoferrate(II) gelatin-immobilized matrices in contact with the aqueous solution of above organic compound.

Oleg V. Mikhailov

1997-01-01

231

Pyrophosphate-mediated magnetic interactions in Cu(II) coordination complexes.  

PubMed

The reaction in water of Cu(NO(3))(2)2.5H(2)O with 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), or 1,10-phenanthroline-5-amine (phenam), and sodium pyrophosphate (Na(4)P(2)O(7)), at various pHs, afforded three new copper(II)-pyrophosphate complexes, namely, {[Cu(bipy)(cis-H(2)P(2)O(7))](2)}3H(2)O (1a), {[Cu(phen)(H(2)O)](4)(HP(2)O(7))(2)}(ClO(4))(2)4H(2)O (2), and {[Cu(2)(phenam)(2)(P(2)O(7))](2)25H(2)O}(n) (3). A solvent free crystalline phase of 1a was also isolated with formula {[Cu(bipy)(trans-H(2)P(2)O(7))](2)} (1b), which can be regarded as a pseudo-polymorph of 1a. Single crystal X-ray analyses revealed these compounds to have uncommon molecular architectures, with 3 being an unprecedented pyrophosphate-containing two-dimensional (2D) polymer. Compounds 1a/1b and 2 are discrete di- and tetra-nuclear complexes, respectively. The cationic {[Cu(phen)(H(2)O)](4)(HP(2)O(7))(2)}(2+) unit in 2 presents a unique quasi-flat structure, held together by solely in-plane pyrophosphate bridging modes (short O(eq)-P-O(eq) and long O(eq)-P-O-P-O(eq) pathways), a coordination arrangement also not previously reported. A different tetranuclear copper(II)-pyrophosphate arrangement is found in 3, with two classically bridged dimers (O(eq)-P-O(eq) pathway) joined together by auxiliary equatorial-axial ?-O pyrophosphate bridges. Here, the bidimensionality is reached through bridging phenam ligands, which provide further inter-"tetramer" metal-metal connections [(N,N')(eq)-(N'')(ax) pathway], leading to the formation of an expanded covalent network based on the [Cu(2)(phenam)(2)(P(2)O(7))](2) moiety. Variable-temperature magnetic susceptibility measurements on polycrystalline samples of 2 and 3 revealed net antiferromagnetic coupling between metal centers with J(2a) = -7.9(2) cm(-1), J(2b) = -46.9(3) cm(-1), J(2c) = 0 cm(-1) in 2 (H = -J(2a)[S(Cu(1))S(Cu(2)) + S(Cu(1a))S(Cu(2a))] - J(2b)[S(Cu(1))S(Cu(2a)) + S(Cu(1a))S(Cu(2))] - J(2c)S(Cu(2))S(Cu(2a))), and J(3a) = -87.9(2) cm(-1), J(3b) = -5(1) cm(-1) and J(3c) = +5(3) cm(-1) in 3 (H = -J(3a)[S(Cu(1))S(Cu(2)) + S(Cu(1a))S(Cu(2a))] - J(3b)[S(Cu(1))S(Cu(2a)) + S(Cu(1a))S(Cu(2))] - J(3c)S(Cu(2))S(Cu(2a))). For 1a, a net ferromagnetic coupling is observed with J(1a) = +0.86(1) cm(-1) (H = -J S(A)S(B) + S(A)D S(B) + ?H (g(A)S(A) + g(B)S(B)). This is the first example of ferromagnetic coupling in pyrophosphate-complexes reported to date. A structure-function correlation study focusing on magnetic exchange across the observed diverse pyrophosphate-bridges is described with density functional theory (DFT) calculations included to support the stated observations. PMID:21114311

Marino, Nadia; Ikotun, Oluwatayo F; Julve, Miguel; Lloret, Francesc; Cano, Juan; Doyle, Robert P

2011-01-01

232

Nitrogen-rich compounds of the actinoids: dioxouranium(VI) 5,5'-azobis[tetrazolide] pentahydrate and its unusually small uranyl angle.  

PubMed

Uranyl(VI) 5,5'-azobis[tetrazolide] pentahydrate was synthesized and characterized using X-ray crystallography, elemental analysis, UV/vis, MIR, FIR, and Raman spectroscopy. It is the second-most nitrogen rich compound of uranium (26.72 wt % N) and only the second structurally characterized uranium complex with a tetrazole ligand described in the literature. The compound's structure is characterized by an exceptionally small uranyl angle of 172.4(1), which provides information on the coordination properties of tetrazole ligands as they affect the donor's environment by strong steric and perhaps electrostatic repulsion. The compound showed luminescence under excitation with a near UV laser. The mean lifetime of its excited state was shorter than in the case of UO(2)(NO(3))(2)6H(2)O, indicating quenching by the ligand. Despite its high nitrogen content (and thus potentially explosive character), the title compound proved to be stable even under neutron radiation causing induced fission processes. PMID:22651244

Steinhauser, Georg; Giester, Gerald; Wagner, Christoph; Weinberger, Peter; Zachhuber, Bernhard; Ramer, Georg; Villa, Mario; Lendl, Bernhard

2012-06-18

233

Recovering Ga(III) from coordination complexes using pyridine 2,6-dicarboxylic acid chelation ion chromatography.  

PubMed

Ion exchange chelation chromatography is an effective means to extract metals from coordination complexes and biological samples; however there is a lack of data to verify the nature of metal complexes that can be successfully analysed using such a procedure. The aim of this study was to assess the capability of pyridine 2,6-dicarboxylic acid (PDCA) to extract and quantify Ga(III) from a range of environments using standard liquid chromatography apparatus. The PDCA chelation method generated a single Ga(III) peak with a retention time of 2.55 +/- 0.02 min, a precision of <2% and a limit of detection of 110 microM. Ga(III) hydroxide complexes (highest stability constant 15.66) were used to successfully cross-validate the chelation method with inductively coupled plasma mass spectrometry. The PDCA assay extracted 96.9 +/- 1.2% of the spiked Ga(III) from porcine mucus and 100.7 +/- 2.7% from a citrate complex (stability constant 10.02), but only ca 50% from an EDTA complex (stability constant 22.01). These data suggest that PDCA chelation can be considered a suitable alternative to inductively coupled plasma mass spectrometry for Ga(III) quantification from all but the most strongly bound coordinated complexes i.e. a stability constant of <15. PMID:20700886

Staff, K; Brown, M B; Hider, R C; Kong, X L; Friden, P; Jones, S A

2010-09-01

234

Vibrational Spectroscopy of Mass Selected [UO2(ligand)n]2+ Complexes in the Gas Phase  

SciTech Connect

The gas-phase infrared spectra of discrete uranyl ([UO2]2+) complexes ligated with acetone and/or acetonitrile were used to evaluate systematic trends of ligation on the position of the O=U=O stretch, and to enable rigorous comparison with the results of computational studies. Ionic uranyl complexes isolated in a Fourier transform ion cyclotron resonance mass spectrometer were fragmented via infrared multiphoton dissociation using a free electron laser scanned over the mid-IR wavelengths. The asymmetric O=U=O stretching frequency was measured at 1017 cm-1 for [UO2(CH3COCH3)2]2+, and was systematically red shifted to 1000 and 988 cm-1 by the addition of a third and fourth acetone ligands, respectively, which was consistent with more donation of electron density to the uranium center in complexes with higher coordination number. The experimental measurements were in good agreement with values generated computationally using LDA, B3LYP, and ZORA-PW91 approaches. In contrast to the uranyl frequency shifts, the carbonyl frequencies of the acetone ligands were progressively blue shifted as the number of ligands increased from 2 to 4, and approached that of free acetone. This observation was consistent with the formation of weaker noncovalent bonds between uranium and the carbonyl oxygen as the extent of ligation increases. Similar trends were observed for [UO2(CH3CN)n]2+ complexes although the magnitude of the red shift in the uranyl frequency upon addition more acetonitrile ligands was smaller than for acetone, consistent with the more modest nucleophilic nature of acetonitrile. This conclusion was amplified by the uranyl stretching frequencies measured for mixed acetone/acetonitrile complexes, which showed that substitution of one acetone for one acetonitrile produced a modest red shift of 3 to 6 cm-1.

Gary S. Groenewold; Anita Gianotto; Michael Vanstipdonk; Kevin C. Cossel; David T. Moore,; Nick Polfer; Jos Oomens

2006-03-01

235

The Numerical Complex-Coordinate Hartree-Fock Method and the Calculation of Atomic Quasi-Bound States  

Microsoft Academic Search

The numerical multi-configuration Hartree-Fock program of C. Froese Fischer (Comp.Phys.Comm. 14,145(1978)), has been modified for performance of self-consistent field (SCF) calculations on atomic quasi-bound states using the complex-coordinate (dilation) technique. Such states are commonly observed as resonances in electron-atom and photon -atom reactions, appearing as localized fluctuations in the scattering cross section. These structures are approximately described by Breit-Wigner profiles

Murry D. Bentley

1990-01-01

236

Synthesis and Characterization of Some Novel Hepta-Coordinated Mixed-Ligand Cyanonitrosyl Complexes of Vanadium Having {VNO} Electron Configuration  

Microsoft Academic Search

A new series of hepta-coordinated mixed-ligand cyanonitrosyl complexes of vanadium (having {VNO} electron configuration), formed by the interaction of potassium hexa-cyanonitrosylvanadate(I) monohydrate with some heterocyclic organic bases like 2, 3-, 2, 4-, 2, 6- and 3, 5- lutidines, 2, 3, 6- and 2, 4, 6- collidines and nicotine in aqueous methanol has been isolated in the solid state. The products,

R. C. Maurya; R. K. Shukla; D. C. Gupta; M. Agrawal

1987-01-01

237

Raman spectroscopic study of the molecular structure of the uranyl mineral zippeite from Jchymov (Joachimsthal), Czech Republic.  

PubMed

Raman spectra at 298 and 77K and infrared spectra of the uranyl sulfate mineral zippeite from Jchymov (Joachimsthal), Czech Republic, K(0.6)(H(3)O)0.4[(UO(2))6(SO(4))3(OH)7].8H2O, were studied. Observed bands were tentatively attributed to the (UO(2))2+ and (SO(4))2- stretching and bending vibrations, the OH stretching vibrations of water molecules, hydroxyls and oxonium ions, and H(2)O, oxonium, and delta U-OH bending vibrations. Empirical relations were used for the calculation of U-O bond lengths in uranyl R (A)=f(nu(3) or nu(1)(UO(2))2+). Calculated U-O bond lengths are in agreement with U-O bond lengths from the single crystal structure analysis and those inferred for uranyl anion sheet topology of uranyl pentagonal dipyramidal coordination polyhedra. The number of observed bands supports the conclusion from single crystal structure analysis that at least two symmetrically distinct U6+ (in uranyls) and S6+ (in sulfates), water molecules and hydroxyls may be present in the crystal structure of the zippeite studied. Strong to very weak hydrogen bonds present in the crystal structure of zippeite studied were inferred from the IR spectra. PMID:17113344

Frost, Ray L; Cejka, Jir; Bostrom, Thor; Weier, Matt; Martens, Wayde

2007-08-01

238

Raman spectroscopic study of the molecular structure of the uranyl mineral zippeite from Jchymov (Joachimsthal), Czech Republic  

NASA Astrophysics Data System (ADS)

Raman spectra at 298 and 77 K and infrared spectra of the uranyl sulfate mineral zippeite from Jchymov (Joachimsthal), Czech Republic, K 0.6(H 3O) 0.4[(UO 2) 6(SO 4) 3(OH) 7]8H 2O, were studied. Observed bands were tentatively attributed to the (UO 2) 2+ and (SO 4) 2- stretching and bending vibrations, the OH stretching vibrations of water molecules, hydroxyls and oxonium ions, and H 2O, oxonium, and ? U-OH bending vibrations. Empirical relations were used for the calculation of U-O bond lengths in uranyl R () = f( ?3 or ?1(UO 2) 2+). Calculated U-O bond lengths are in agreement with U-O bond lengths from the single crystal structure analysis and those inferred for uranyl anion sheet topology of uranyl pentagonal dipyramidal coordination polyhedra. The number of observed bands supports the conclusion from single crystal structure analysis that at least two symmetrically distinct U 6+ (in uranyls) and S 6+ (in sulfates), water molecules and hydroxyls may be present in the crystal structure of the zippeite studied. Strong to very weak hydrogen bonds present in the crystal structure of zippeite studied were inferred from the IR spectra.

Frost, Ray L.; ?ejka, Ji?; Bostrom, Thor; Weier, Matt; Martens, Wayde

2007-08-01

239

The Pcdp1 complex coordinates the activity of dynein isoforms to produce wild-type ciliary motility  

PubMed Central

Generating the complex waveforms characteristic of beating cilia requires the coordinated activity of multiple dynein isoforms anchored to the axoneme. We previously identified a complex associated with the C1d projection of the central apparatus that includes primary ciliary dyskinesia protein 1 (Pcdp1). Reduced expression of complex members results in severe motility defects, indicating that C1d is essential for wild-type ciliary beating. To define a mechanism for Pcdp1/C1d regulation of motility, we took a functional and structural approach combined with mutants lacking C1d and distinct subsets of dynein arms. Unlike mutants completely lacking the central apparatus, dynein-driven microtubule sliding velocities are wild type in C1d- defective mutants. However, coordination of dynein activity among microtubule doublets is severely disrupted. Remarkably, mutations in either outer or inner dynein arm restore motility to mutants lacking C1d, although waveforms and beat frequency differ depending on which isoform is mutated. These results define a unique role for C1d in coordinating the activity of specific dynein isoforms to control ciliary motility.

DiPetrillo, Christen G.; Smith, Elizabeth F.

2011-01-01

240

Synthesis, Crystal Structure and NLO Properties of a Novel Ruthenium(II) Complex with Unusual Coordination Mode  

Microsoft Academic Search

A new Schiff base 4-[N-hydroxyethyl-N-(methyl)amino]benzaldehyde S-methyl dithiocarbazate (HL, where H is a dissociable proton) and the ruthenium complex [Ru(bpy)2L]PF6 (bpy=2,2?-bipyridine) have been synthesized. The structural determinations of the ligand and its ruthenium complex, by X-ray crystallography, show that the ligand is coordinated as a monoanionic bidentate N, S-donor, forming a four-member chelate ring with a bite angle of 65.91. The

Yu-Peng Tian; Ming-Liang Zhang; Zhang-Jun Hu; Han-Mei Hu; Jie-Ying Wu; Xuan-Jun Zhang; Sheng-Yi Zhang; Xu-Tang Tao; Min-Hua Jiang; He-Ping Chen; Suchada Chantrapromma; Hoong-Kun Fun

2005-01-01

241

A tetradentate metalloligand: synthesis and coordination behaviour of a 2-pyridyl-substituted cyclobutadiene iron complex.  

PubMed

The salt [K([18]crown-6){Cp*Fe(?(4)-C4py4)}] (K1, py = 2-pyridyl, Cp* = C5Me5) is accessible by the reaction of an iron(0) naphthalene precursor and bis(2-pyridyl)acetylene. Cyclic voltammetry and preparative investigations demonstrate the electron-rich nature of K1, which is reversibly oxidized to neutral [Cp*Fe(?(4)-C4py4)] (1) at a low potential. The first coordination studies with iron(II) and zinc(II) chloride show that all four 2-pyridyl units may be employed for metal coordination. PMID:24302434

Rezaei Rad, Babak; Herrmann, Dirk; Lescop, Christophe; Wolf, Robert

2014-03-21

242

Three-coordinate gold(I) N-heterocyclic carbene complexes: a new class of strongly luminescent derivatives.  

PubMed

A selected group of cationic three-coordinate Au(I)-NHC complexes of the form [Au(NHC)(dppbz)]OTf have been prepared from a commercially available bidentate phosphine. All complexes have been fully characterised by NMR and mass spectroscopy. The [Au(NHC)](+) fragment shows a pronounced tendency to form linear complexes which is confirmed by the molecular structure of [Au(IPr)(dppbz)]OTf in the solid state. The complexes are brightly luminescent and present very high quantum yield values in the solid state. The assignments of the electronic transitions involved in the emissions are of a phosphorescent nature and it is proposed that the origin of the emissions is derived from the ligand (dppbz) to metal-ligand (Au-NHC) charge-transfer (LML'CT) transition. PMID:24105255

Visbal, Renso; Lpez-de-Luzuriaga, Jos M; Laguna, Antonio; Gimeno, M Concepcin

2014-01-01

243

Solid-state dynamics of uranyl polyoxometalates.  

PubMed

Understanding fundamental uranyl polyoxometalate (POM) chemistry in solution and the solid state is the first step to defining its future role in the development of new actinide materials and separation processes that are vital to every step of the nuclear fuel cycle. Many solid-state geometries of uranyl POMs have been described, but we are only beginning to understand their chemical behavior, which thus far includes the role of templates in their self-assembly, and the dynamics of encapsulated species in solution. This study provides unprecedented detail into the exchange dynamics of the encapsulated species in the solid state through Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy. Although it was previously recognized that capsule-like molybdate and uranyl POMs exchange encapsulated species when dissolved in water, analogous exchange in the solid state has not been documented, or even considered. Here, we observe the extremely high rate of transport of Li(+) and aqua species across the uranyl shell in the solid state, a process that is affected by both temperature and pore blocking by larger species. These results highlight the untapped potential of emergent f-block element materials and vesicle-like POMs. PMID:24889825

Alam, Todd M; Liao, Zuolei; Zakharov, Lev N; Nyman, May

2014-07-01

244

Modulation of electronics and thermal stabilities of photochromic phosphino-aminoazobenzene derivatives in weak-link approach coordination complexes.  

PubMed

A series of d(8) transition-metal (Pt(II) and Pd(II)) coordination complexes incorporating phosphine-functionalized aminoazobenzene derivatives as hemilabile phosphino-amine (P,N) ligands were synthesized and studied as model weak-link approach (WLA) photoresponsive constructs. The optical and photochemical properties of these complexes were found to be highly influenced by various tunable parameters in WLA systems, which include type of metal, coordination mode, type of ancillary ligand, solvent, and outer-sphere counteranions. In dichloromethane, reversible chelation and partial displacement of the P,N coordinating moieties allow for toggling between aminoazobenzene- or pseudostilbene- and azobenzene-type derivatives. The reversible switching between electronic states of azobenzene can be controlled through either addition or extraction of chloride counterions and is readily visualized in the separation between ?-?* and n-?* bands in the complexes' electronic spectra. In acetonitrile solution, the WLA variables inherent to semiopen complexes have a significant impact on the half-lives of the corresponding cis isomers, allowing one to tune their half-lives from 20 to 21000 s, while maintaining photoisomerization behaviors with visible light. Therefore, one can significantly increase the thermal stability of a cis-aminoazobenzene derivative to the extent that single crystals for X-ray diffraction analysis can be grown for the first time, uncovering an unprecedented edge-to-face arrangement of the phenyl rings in the cis isomer. Overall, the azobenzene-functionalized model complexes shed light on the design parameters relevant for photocontrolled WLA molecular switches, as well as offer new ways of tuning the properties of azobenzene-based, photoresponsive materials. PMID:24187977

Park, Jung Su; Lifschitz, Alejo M; Young, Ryan M; Mendez-Arroyo, Jose; Wasielewski, Michael R; Stern, Charlotte L; Mirkin, Chad A

2013-11-13

245

Human Balance System: A Complex Coordination of Central and Peripheral Systems  

MedlinePLUS

... and maintained by a complex set of sensorimotor control systems that include sensory input from vision (sight), proprioception ( ... balance system involves a complex set of sensorimotor-control systems. Its interlacing feedback mechanisms can be disrupted by ...

246

Synthesis, characterization, and crystal structures of uranyl compounds containing mixed chromium oxidation states  

NASA Astrophysics Data System (ADS)

The mixed-valence chromium uranyl compounds Li5[(UO2)4(Cr(V)O5)(Cr(VI)O4)4](H2O)17 (1), (Mg(H2O)6)5[(UO2)8(Cr(V)O5)2(Cr(VI)O4)8] (2) and (NH4)5[(UO2)4(Cr(V)O5)(Cr(VI)O4)2]H2O11 (3) have been synthesized and characterized. Each contains an identical sheet of cation-centered polyhedra. Central to the connectivity of the sheet are four uranyl pentagonal bipyramids that share some of their equatorial vertices, giving a four-membered ring. The Cr(V) cation located near the center of this ring is coordinated by O atoms in a square pyramidal arrangement. The Cr(VI) is tetrahedrally coordinated by O atoms, and these tetrahedra link the four-membered rings of bipyramids. The mixed-valence nature of the sheet was verified by XANES, an EPR spectrum, and bond-valence analysis. Low-valence cations and H2O groups reside between the sheets of uranyl and chromate polyhedra, where they provide linkages between adjacent sheets.

Unruh, Daniel K.; Quicksall, Andrew; Pressprich, Laura; Stoffer, Megan; Qiu, Jie; Nuzhdin, Kirill; Wu, Weiqiang; Vyushkova, Mariya; Burns, Peter C.

2012-07-01

247

Three-Coordinate Nickel(II) and Nickel(I) Thiolate Complexes Based on the ?-Diketiminate Ligand System.  

PubMed

Mononuclear nickel(II) thiolate complexes [L(tBu)Ni(SEt)] (1) and [L(tBu)Ni(aet)] (2, aet = (-)S(CH2)2NH2) (L(tBu) = [HC(C((t)Bu)NC6H3((i)Pr)2)2](-)), supported by a bulky nacnac ligand, were synthesized by treatment of the nickel(II) bromide precursor [L(tBu)Ni(Br)] (I) with the potassium salts of ethanethiol and cysteamine, respectively. The nickel atom in 1 features a planar T-shaped environment, while the Ni ion within 2 shows a distorted square planar coordination geometry, as the aminoethanethiolate (aet) is coordinated as a chelating ligand. In 2 the ?-diketiminate ligand binds in a rarely observed ?(2)C,N coordination mode. Reduction of complex 1 or its benzenethiolate analogue [L(tBu)Ni(SPh)] (II) by KC8 resulted in the formation of dinuclear Ni(I) thiolates (KOEt2)(K)[L(tBu)Ni(SEt)]2 (3) and (KOEt2)2[L(tBu)Ni(SPh)]2 (4), respectively. In these compounds [L(tBu)Ni(SR)](-) units are held together by potassium cations produced in the reduction process. All compounds mentioned were structurally characterized by single-crystal X-ray crystallography. PMID:24914615

Horn, Bettina; Limberg, Christian; Herwig, Christian; Braun, Beatrice

2014-07-01

248

Temporary changes in macrophages and MHC class-II molecule-expressing cells in the tubulointerstitium in response to uranyl acetate-induced acute renal failure in rats  

Microsoft Academic Search

The present study was designed to asses the dynamic changes in macrophages (Ms) with or without expression of major histocompatibility complex (MHC) class-II molecule in response to uranyl acetate-induced acute renal failure (ARF) in rats. ED1+ monocytes\\/Ms infiltrated into the interstitium as early as day2, peaked in number on day5 after uranyl acetate-induced ARF. ED1+ cells did not correlate with

Yoshihide Fujigaki; Di Fei Sun; Tetsuo Goto; Akira Hishida

2003-01-01

249

Multiagent Coordination Techniques for Complex Environments: The Case of a Fleet of Combat Ships  

Microsoft Academic Search

The use of agent and multiagent techniques to assist humans in their daily routines has been increasing for many years, notably in Command and Control (C2) systems. In this context, we propose using multiagent planning and coordination techniques for resources management in real-time C2 systems. The particular problem we studied is the design of a decision-support for Anti-Air Warfare (AAW)

Patrick Beaumont; Brahim Chaib-draa

2007-01-01

250

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

PubMed

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

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

2012-04-28

251

Photoinduced single-molecule magnet properties in a four-coordinate iron(II) spin crossover complex.  

PubMed

The four-coordinate Fe(II) complex, PhB(MesIm)3Fe-N?PPh3 (1) has been previously reported to undergo a thermal spin-crossover (SCO) between high-spin (HS, S = 2) and low-spin (LS, S = 0) states. This complex is photoactive below 20 K, undergoing a photoinduced LS to HS spin state change, as determined by optical reflectivity and photomagnetic measurements. With continuous white light irradiation, 1 displays slow relaxation of the magnetization, i.e. single-molecule magnet (SMM) properties, at temperatures below 5 K. This complex provides a structural template for the design of new photoinduced mononuclear SMMs based on the SCO phenomenon. PMID:24313622

Mathonire, Corine; Lin, Hsiu-Jung; Siretanu, Diana; Clrac, Rodolphe; Smith, Jeremy M

2013-12-26

252

Jahn-Teller distortion in the phosphorescent excited state of three-coordinate Au(I) phosphine complexes.  

PubMed

DFT calculations were used to optimize the phosphorescent excited state of three-coordinate [Au(PR3)3]+ complexes. The results indicate that the complexes rearrange from their singlet ground-state trigonal planar geometry to a T-shape in the lowest triplet luminescent excited state. The optimized structure of the exciton contradicts the structure predicted based on the AuP bonding properties of the ground-state HOMO and LUMO. The rearrangement to T-shape is a Jahn-Teller distortion because an electron is taken from the degenerate e' (5dxy, 5dx2-y2) orbital upon photoexcitation of the ground-state D3h complex. The calculated UV absorption and visible emission energies are consistent with the experimental data and explain the large Stokes' shifts while such correlations are not possible in optimized models that constrained the exciton to the ground-state trigonal geometry. PMID:14624542

Barakat, Khaldoon A; Cundari, Thomas R; Omary, Mohammad A

2003-11-26

253

Coordination Polymer: Synthesis, Spectral Characterization and Thermal Behaviour of Starch-Urea Based Biodegradable Polymer and Its Polymer Metal Complexes  

PubMed Central

A starch-urea-based biodegradable coordination polymer modified by transition metal Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) was prepared by polycondensation of starch and urea. All the synthesized polymeric compounds were characterized by Fourier transform-infrared spectroscopy (FT-IR), 1H-NMR spectroscopy, 13C-NMR spectroscopy, UV-visible spectra, magnetic moment measurements, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). The results of electronic spectra and magnetic moment measurements indicate that Mn(II), Co(II), and Ni(II) complexes show octahedral geometry, while Cu(II) and Zn(II) complexes show square planar and tetrahedral geometry, respectively. The thermogravimetric analysis revealed that all the polymeric metal complexes are more thermally stable than the parental ligand. In addition, biodegradable studies of all the polymeric compounds were also carried out through ASTM standards of biodegradable polymers by CO2 evolution method.

Malik, Ashraf; Parveen, Shadma; Ahamad, Tansir; Alshehri, Saad M.; Singh, Prabal Kumar; Nishat, Nahid

2010-01-01

254

Metal complexes with N-(2-pyridylmethyl)iminodiacetate: from discrete polynuclear compounds to 1D coordination polymers.  

PubMed

The reactions of M(ClO(4))(2).6H(2)O (M = Mn(2+), Co(2+) and Ni(2+)) with N-(2-pyridylmethyl)-iminodiacetic acid (H(2)pmida) gave three discrete polynuclear complexes {Na[Mn(3)(pmida)(3)(H(2)O)(3)]}ClO(4) (), {Na[Co(3)(pmida)(3)(H(2)O)(3)](H(2)O)}ClO(4) () and [Co(H(2)O)(6)][Co(3)(pmida)(3)(H(2)O)(3)](2)(ClO(4))(2).4H(2)O () and two 1D polymers {[Co(pmida)(H(2)O)].H(2)O}(n) () and {[Ni(pmida)(H(2)O)].H(2)O}(n) (). All complexes were characterized by elemental analysis, infrared (IR) spectroscopy and single-crystal X-ray diffraction analysis. Complexes and show similar structures with an unprecedented trinuclear unit [M(3)(pmida)(3)(H(2)O)(3)] in which the three six-coordinated divalent metal ions are joined by three coplanar syn-anti bridging carboxylate groups of three ligands into a closed planar twelve-membered ring with one Na(+) ion located on the C(3) axis. Complex possesses two kinds of coordination units: mononuclear cation [Co(H(2)O)(6)](2+) and trinuclear unit [Co(3)(pmida)(3)(H(2)O)(3)]. The Co(2+) and Ni(2+) ions in complexes and , respectively, present distorted octahedral geometries and are bridged by anti-anti bridging carboxylate groups of the ligands to form 1D chains. Compounds display a structure variation from discrete polynuclear to 1D coordination polymer along Mn(ii), Co(ii) to Ni(ii), and a dependence of the formation of discrete compound or coordination polymer on the identity of the metal ion. The magnetic investigations of were also carried out. The negative Weiss constants and coupling constants obtained from two kinds of fitting models indicate the presence of dominant antiferromagnetic exchanges mediated by the syn-anti bridging carboxylate groups between the metal centers of three compounds. PMID:19565081

Chen, Zilu; Li, Yan; Jiang, Chunfang; Liang, Fupei; Song, You

2009-07-21

255

Vibrational Spectroscopy of Mass-Selected [UO?(ligand)n]? Complexes in the Gas Phase: Comparison with Theory  

SciTech Connect

The gas-phase infrared spectra of discrete uranyl ([UO?]?) complexes ligated with acetone and/or acetonitrile were used to evaluate systematic trends of ligation on the position of the O=U=O stretch, and to enable rigorous comparison with the results of computational studies. Ionic uranyl complexes isolated in a Fourier transform ion cyclotron resonance mass spectrometer were fragmented via infrared multiphoton dissociation using a free electron laser scanned over the mid-IR wavelengths. The asymmetric O=U=O stretching frequency was measured at 1017 cm? for [UO?(CH?COCH?)?]? and was systematically red shifted to 1000 and 988 cm? by the addition of a third and fourth acetone ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. In contrast to the uranyl frequency shifts, the carbonyl frequencies of the acetone ligands were progressively blue shifted as the number of ligands increased from 2 to 4, and approached that of free acetone. This observation was consistent with the formation of weaker noncovalent bonds between uranium and the carbonyl oxygen as the extent of ligation increases. Similar trends were observed for [UO?(CH?CN)n]? complexes, although the magnitude of the red shift in the uranyl frequency upon addition of more acetonitrile ligands was smaller than for acetone, consistent with the more modest nucleophilic nature of acetonitrile. This conclusion was confirmed by the uranyl stretching frequencies measured for mixed acetone/acetonitrile complexes, which showed that substitution of one acetone for one acetonitrile produced a modest red shift of 3 to 6 cm?.

Groenewold, G. S.; Gianotto, Anita K.; Cossel, Kevin C.; Van Stipdonk, Michael J.; Moore, David T.; Polfer, Nick; Oomens, Jos; De Jong, Wibe A.; Visscher, Lucas

2006-03-18

256

Phosphate coordination and movement of DNA in the Tn5 synaptic complex: role of the (R)YREK motif  

SciTech Connect

Bacterial DNA transposition is an important model system for studying DNA recombination events such as HIV-1 DNA integration and RAG-1-mediated V(D)J recombination. This communication focuses on the role of protein-phosphate contacts in manipulating DNA structure as a requirement for transposition catalysis. In particular, the participation of the nontransferred strand (NTS) 5' phosphate in Tn5 transposition strand transfer is analyzed. The 5' phosphate plays no direct catalytic role, nonetheless its presence stimulates strand transfer {approx}30-fold. X-ray crystallography indicates that transposase-DNA complexes formed with NTS 5' phosphorylated DNA have two properties that contrast with structures formed with complexes lacking the 5' phosphate or complexes generated from in-crystal hairpin cleavage. Transposase residues R210, Y319 and R322 of the (R)YREK motif coordinate the 5' phosphate rather than the subterminal NTS phosphate, and the 5' NTS end is moved away from the 3' transferred strand end. Mutation R210A impairs the 5' phosphate stimulation. It is posited that DNA phosphate coordination by R210, Y319 and R322 results in movement of the 5' NTS DNA away from the 3'-end thus allowing efficient target DNA binding. It is likely that this role for the newly identified RYR triad is utilized by other transposase-related proteins.

Klenchin, Vadim A.; Czyz, Agata; Goryshin, Igor Y.; Gradman, Richard; Lovell, Scott; Rayment, Ivan; Reznikoff, William S. (UW); (Polish)

2009-01-15

257

Effect of ligand substituent coordination on the geometry and the electronic structure of Cu(II)-diradical complexes.  

PubMed

Two organic moieties, known as ligands, having -OMe and -SePh as the ortho substituent attached to the aniline moiety of the parent 2-anilino-4,6-di-tert-butylphenol ligand, were synthesized. The ligands reacted with CuCl22H2O in a 2:1 ratio in CH3CN in the presence of Et3N and provided the corresponding mononuclear Cu(II)-diradical complexes 1 (-OMe) and 2 (-SePh). Complex 1 was square planar, while complex 2 was in distorted square planar geometry due to the secondary coordination between the Se atom and the central Cu(II) center. Both complexes were comprised of multi-paramagnetic centers and exhibited an St = 1/2 ground state as established by variable-temperature magnetic susceptibility measurements. X-band electron paramagnetic resonance measurements indicated the presence of an unpaired electron at the Cu(II) center in complex 1 and at the ligand center (?-radical) in complex 2. The extent of the secondary interaction was found to be dependent on the "softness" of the donor atom belonging to the ortho substituent. PMID:24654914

Rakshit, Richa; Ghorai, Samir; Biswas, Soumava; Mukherjee, Chandan

2014-04-01

258

Raman spectra and normal coordinate analyses of low-frequency vibrations of oxo-bridged manganese complexes.  

PubMed

The active sites of certain metalloenzymes involved in oxygen metabolism, such as manganese catalase and the oxygen-evolving complex of photosystem II, contain micro -oxo-bridged Mn clusters with ligands that include H(2)O and micro (1,3)-carboxylato bridges provided by protein side chains. In order to understand better the vibrational spectra of such clusters, the low-frequency resonance Raman spectra of a series of structurally characterized Mn-oxo model complexes were examined. The series includes complexes of the type [Mn(2)(O)(OAc)(2)(bpy)(2)(L)(2)] and [Mn(2)(O)(2)(OAc)(bpy)(2)(L)(2)], where bpy=2,2'-bipyridine, OAc=acetate and L=H(2)O or Cl(-). Complexes containing the isotopomers OAc- d(3) and D(2)O, as well as those containing both isotopomers, were also examined. Normal coordinate analyses (NCA) were performed on the various complexes using theGF matrix method. Selected vibrational modes in the 200-600 cm(-1) region were assigned based on the spectra and NCA, which identify vibrational modes arising from the metal-ligand bonds. These results will be useful in interpreting the vibrational spectra obtained from metalloproteins containing Mn-oxo complexes in their active sites. PMID:12761665

Cua, Agnes; Vrettos, John S; de Paula, Julio C; Brudvig, Gary W; Bocian, David F

2003-04-01

259

Synthesis, spectroscopic, coordination and biological activities of some organometallic complexes derived from thio-Schiff base ligands.  

PubMed

Two series of mono- and binuclear complexes cyclic or acyclic thio-ferocine Schiff base ligands, derived from the condensation of 2-aminobenzenthiol (L) with monoacetyl ferrocene in the molar ratio 1:1 or in the molar ratio 1:2 for diacetyl ferocine have been prepared. The condensation reactions yield the corresponding Schiff Base ligands, HLa-Maf and H2Lb-Daf. The chelation of the ligands to metal ions occurs through the sulfur of the thiol group as well as the nitrogen atoms of the azomethine group of the ligands. HLa-Maf acts as monobasic bidentate or dibasic tetradentate, while H2Lb-Daf behaves as twice negatively cargend tetradentate ligand. The structures of these ligands were elucidated by elemental analysis, infrared, ultraviolet-visible spectra, as well as (1)H NMR spectra. Reactions of the Schiff bases ligands with ruthenium(III), oxovanadium(IV) and dioxouranium(VI) afforded the corresponding transition metal complexes. The properties of the newly prepared complexes were analyse by elemental analyses, infrared, electronic spectra, (1)H NMR as well as the magnetic susceptibility and conductivity measurement. The metal complexes exhibits different geometrical arrangements such as octahedral and square pyramidal coordination. Schiff base ligands and their metal complexes were tested against two pathogenic bacteria as Gram-positive and Gram-negative bacteria as well as one kind of fungi to study their biological activity. All the complexes exhibit antibacterial and antifungal activities against these organisms. PMID:24070648

Abou-Hussein, Azza A; Linert, Wolfgang

2014-01-01

260

A new role for RINT-1 in SNARE complex assembly at the trans-Golgi network in coordination with the COG complex  

PubMed Central

Docking and fusion of transport vesicles/carriers with the target membrane involve a tethering factormediated initial contact followed by soluble N-ethylmaleimidesensitive factor attachment protein receptor (SNARE)catalyzed membrane fusion. The multisubunit tethering CATCHR family complexes (Dsl1, COG, exocyst, and GARP complexes) share very low sequence homology among subunits despite likely evolving from a common ancestor and participate in fundamentally different membrane trafficking pathways. Yeast Tip20, as a subunit of the Dsl1 complex, has been implicated in retrograde transport from the Golgi apparatus to the endoplasmic reticulum. Our previous study showed that RINT-1, the mammalian counterpart of yeast Tip20, mediates the association of ZW10 (mammalian Dsl1) with endoplasmic reticulumlocalized SNARE proteins. In the present study, we show that RINT-1 is also required for endosome-totrans-Golgi network trafficking. RINT-1 uncomplexed with ZW10 interacts with the COG complex, another member of the CATCHR family complex, and regulates SNARE complex assembly at the trans-Golgi network. This additional role for RINT-1 may in part reflect adaptation to the demand for more diverse transport routes from endosomes to the trans-Golgi network in mammals compared with those in a unicellular organism, yeast. The present findings highlight a new role of RINT-1 in coordination with the COG complex.

Arasaki, Kohei; Takagi, Daichi; Furuno, Akiko; Sohda, Miwa; Misumi, Yoshio; Wakana, Yuichi; Inoue, Hiroki; Tagaya, Mitsuo

2013-01-01

261

Coordination complexes of Ph?Sb? and Ph?Bi?: beyond pnictonium cations.  

PubMed

The syntheses of salts containing ligand-stabilized Ph3Sb(2+) and Ph3Bi(2+) dications have been realized by in?situ formation of Ph3Pn(OTf)2 (Pn=Sb or Bi) and subsequent reaction with OPPh3, dmap and bipy. The solid-state structures demonstrate diversity imposed by the steric demands and nature of the ligands. The synthetic method has the potential for broad application enabling widespread development of the coordination chemistry for Pn(V) acceptors. PMID:24616180

Robertson, Alasdair P M; Burford, Neil; McDonald, Robert; Ferguson, Michael J

2014-03-24

262

Hydrodesulfurization model complexes: nucleophilic addition to. pi. -coordinated benzo(b)thiophenes and thiophene  

SciTech Connect

The ..pi..-bound thiophene (T) and benzo(b)thiophene (BT) complexes (CpRu(BT))/sup +/, (Cp*Ir(BT))/sup 2 +/, and (Cp*Ir(T)/sup 2 +/, models for the adsorption of thiophenic compounds to hydrodesulfurization (HDS) catalysts surfaces, react with a variety of nucleophiles (H/sup -/, MeO/sup -/, (MeO/sub 2/C)/sub 2/CH/sup -/, EtS/sup -/, and phosphines). The BT complexes yield the first isolable transition-metal cyclohexadienyl complexes derived from fused ring aromatic ligands; four isomers of each cyclohexadienyl complex are produced. The isomers results from addition at the four carbons on the benzene ring; for the nucleophiles studied, addition occurs preferentially at the carbon closest to the sulfur atom, C7. This isomer of CpRu(BT x H) has been characterized by an X-ray structure determination. The T complex reacts with phosphines to produce (Cp*Ir(eta/sup 4/-T x PR/sub 3/))/sup 2 +/. Double nucleophilic addition reactions (H/sup -/ and MeO/sup -/) of (Cp*Ir(BT))/sup 2 +/ are also discussed. Reaction of either NaBet/sub 3/H or Cp/sub 2/CO with (Cp*Ir(T))/sup 2 +/ results in a 2e reduction of the Ir complex. On the basis of /sup 1/H NMR data and by analogy to related complexes, this product is formulated as Cp*Ir(eta/sup 4/-T).

Huckett, S.C.; Angelici, R.J.

1988-07-01

263

Five-coordinate M(II)-semiquinonate (M = Fe, Mn, Co) complexes: reactivity models of the catechol dioxygenases.  

PubMed

A series of five-coordinate M(II)-semiquinonate (M = Fe, Mn, Co) complexes were synthesized and characterized, including the first example of a mononuclear Fe(II)-semiquinonate. Intermediates were observed in the reactions of M(II)-phenSQ (M = Fe, Co) with O2. Evidence for the relevance of these intermediates to the intradiol catechol dioxygenases was obtained by characterization of the oxidized semiquinone-derived product, muconic anhydride, resulting from the reaction of [PhTt(tBu)]Co(II)(3,5-DBSQ) with O2. PMID:24756105

Wang, Peng; Yap, Glenn P A; Riordan, Charles G

2014-05-01

264

Dynamic Resectorization and Coordination Technology: An Evaluation of Air Traffic Control Complexity  

NASA Technical Reports Server (NTRS)

The work described in this report is done under contract with the National Aeronautics and Space Administration (NASA) to support the Advanced Air Transportation Technology (AATR) program. The goal of this program is to contribute to and accelerate progress in Advanced Air Transportation Technologies. Wyndemere Incorporated is supporting this goal by studying the complexity of the Air Traffic Specialist's role in maintaining the safety of the Air Transportation system. It is envisioned that the implementation of Free Flight may significantly increase the complexity and difficulty of maintaining this safety. Wyndemere Incorporated is researching potential methods to reduce this complexity. This is the final report for the contract.

Brinton, Christopher R.

1996-01-01

265

Synthesis of Some Nickel(II) Diphosphine Complexes Having Coordinated Carboxylates  

Microsoft Academic Search

Treatment of aminobis(methylphosphine) complexes of nickel(II) with carboxylic acids in the presence of silver(I) salts in dichloromethane gives the corresponding nickel(II) complexes of the type [NiA(P-P] where A = CO3 (carbonate), (2),2- OC6H4CO2 (salicylate, Sal), (3),O2CCH2CH2 CH(NH2)CO2 (glutamate, Glu), (4), O2 CCH2CH2CO2 (succinicate, Suc), (5); P-P = (Cy2PCH2)2NMe (dcpam), (Ph2PCH2)2NMe (dppam). The complexes have been characterized by spectroscopic techniques such

Osman Serindag; Mustafa Keles

2008-01-01

266

Synthesis of Some Nickel(II) Diphosphine Complexes Having Coordinated Carboxylates  

Microsoft Academic Search

Treatment of aminobis(methylphosphine) complexes of nickel(II) with carboxylic acids in the presence of silver(I) salts in dichloromethane gives the corresponding nickel(II) complexes of the type [NiA(P-P] where A = CO3 (carbonate), (2), 2-OC6H4CO2 (salicylate, Sal), (3), O2CCH2CH2CH(NH2)CO2 (glutamate, Glu), (4), O2CCH2CH2CO2 (succinicate, Suc), (5); P-P = (Cy2PCH2)2NMe (dcpam), (Ph2PCH2)2NMe (dppam). The complexes have been characterized by spectroscopic techniques such as

Osman Serindag; Mustafa Keles

2008-01-01

267

Control of size in losartan/copper(II) coordination complex hydrophobic precipitate.  

PubMed

Reaction of highly soluble orally active, non-peptide antihypertensive drug losartan with copper(II) leads to the spontaneous formation of a very insoluble 2:1 covalent complex, which self assembles in a hydrophobic supramolecular structure of nanometric dimensions. Thermal analysis showed that Los/Cu(II) complex presents intermediate stability in comparison with its precursors KLos and Cu(OAc)2H2O. Isothermal titration calorimetry indicated complexation to be a stepwise process, driven by enthalpy and entropy. Zeta potential and DLS measurements showed that it is possible to control the size and charge of nanoprecipitates by adjusting the relative concentration of Los(-) and Cu(II). PMID:23910296

Denadai, ngelo M L; Da Silva, Jeferson G; Guimares, Pedro P G; Gomes, Leonardo Bertolini S; Mangrich, Antonio S; de Rezende, Edivaltrys I P; Daniel, Izabela M P; Beraldo, Helosa; Sinisterra, Rubn D

2013-10-01

268

A novel type of coordination mode of chloranilic acid leading to the formation of polymeric coordination ribbon in the series of mixed-ligand copper(II) complexes with 1,10-phenanthroline.  

PubMed

A series of four novel mixed-ligand complexes of copper(II) with 3,6-dichloro-2,6-dihydroxy-1,4-benzoquinone (chloranilic acid) and 1,10-phenanthroline was prepared and characterised by X-ray structure analysis and IR spectroscopy. Three complexes exhibit square-pyramidal coordination, whereas one exhibits octahedral coordination. The ligand 1,10-phenanthroline acts in a bidentate chelating mode with N,N-metal binding. The chloranilate dianion coordinates to the Cu(II) atom in a terminal bidentate ortho-quinone-like mode, forming a mononuclear complex species. However, in one structure a novel type of coordination mode of chloranilate is observed. In addition to the bidentate mode, a monodentate bridging mode through a carboxy oxygen of a symmetry-related dianion leads to the formation of polymeric coordination ribbon. The crystal packing of penta-coordinated species, in addition to hydrogen bonding, involves less common stacking interactions of chelate rings with the ?-systems of the ligands. PMID:24676311

Mol?anov, Kreimir; Juri?, Marijana; Koji?-Prodi?, Biserka

2014-05-21

269

Overcoming Spontaneous Patterns of Coordination During the Acquisition of a Complex Balancing task  

Microsoft Academic Search

Learning in complex tasks is usually conceived as the problem of mastering the multiple and redundant degrees of freedom of the system. To reduce control requirements, two different strategies are conceivable. The first one consists of a \\

N. Caillou; D. Nourrit; T. Deschamps; B. Lauriot; Didier Delignieres

2002-01-01

270

Complexation of Lanthanides with Nitrate at Variable Temperatures: Thermodynamics and Coordination Modes  

SciTech Connect

Complexation of neodymium(III) with nitrate was studied at variable temperatures (25, 40, 55 and 70 C) by spectrophotometry and microcalorimetry. The NdNO{sub 3}{sup 2+} complex is weak and becomes slightly stronger as the temperature is increased. The enthalpy of complexation at 25 C was determined by microcalorimetry to be small and positive, (1.5 {+-} 0.2) kJ {center_dot} mol{sup -1}, in good agreement with the trend of the stability constant at variable temperatures. Luminescence emission spectra and lifetime of Eu(III) in nitrate solutions suggest that inner-sphere and bidentate complexes form between trivalent lanthanides (Nd{sup 3+} and Eu{sup 3+}) and nitrate in aqueous solutions. Specific Ion Interaction approach (SIT) was used to obtain the stability constants of NdNO{sub 3}{sup 2+} at infinite dilution and variable temperatures.

Rao, Linfeng; Tian, Guoxin

2008-12-10

271

Coordination chemistry of transition metal complexes of a novel pentadentate ligand  

Microsoft Academic Search

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

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

2001-01-01

272

Coordinate MicroRNA-Mediated Regulation of Protein Complexes in Prostate Cancer  

PubMed Central

MicroRNAs are a class of small non-coding regulatory RNA molecules that regulate mRNAs post-transcriptionally. Recent evidence has shown that miRNAs target entire functionally related proteins such as protein complexes and biological pathways. However, characterizing the influence of miRNAs on genes whose encoded proteins are part of protein complexes has not been studied in the context of disease. We propose an entropy-based framework to identify miRNA-mediated dysregulation of functionally related proteins during prostate cancer progression. The proposed framework uses experimentally verified miRNA-target interactions, functionally related proteins and expression data to identify miRNA-influenced protein complexes in prostate cancer, and identify genes that are dysregulated as a result. The framework constructs correlation matrixes between functionally related proteins and miRNAs that have targets in the complex, and assesses the changes in the Shannon entropy of the modules across different stages of prostate cancer. Results reveal that SMAD4 and HDAC containing protein complexes are highly affected and disrupted by miRNAs, particularly miRNA-1 and miRNA-16. Using biological pathways to define functionally related proteins reveals that NF-kB-, RAS-, and Syndecan-mediated pathways are dysregulated due to miRNA-1- and miRNA-16-mediated regulation. These results suggest that miRNA-1 and miRNA-16 are important master regulators of miRNA-mediated regulation in prostate cancer. Moreover, results reveal that miRNAs with high-influence on the disrupted protein complexes are diagnostic and prognostic biomarker candidates for prostate cancer progression. The observation of miRNA-mediated protein complex regulation and miRNA-mediated pathway regulation, with partial experimental verification from previous studies, demonstrates that our framework is a promising approach for the identification of novel miRNAs and protein complexes related to disease progression.

Alshalalfa, Mohammed; D. Bader, Gary; Bismar, Tarek A.; Alhajj, Reda

2013-01-01

273

Effects of bidentate coordination on the molecular properties rapta-C based complex using theoretical approach.  

PubMed

In this work several quantum properties including the NEDA and QTAIM are computed on three models of rapta-C complexes using DFT with hybrid functional and basis set with ECP and without ECP. Several interesting correlations within the observed properties and also with the reported experimental behaviors of these complexes including their biological activities are presented. The study shows that the stability of the two complexes with bidentate ligands is associated with their high hydrogen bonding stability and existence of stronger non-covalent metal-ligand bonds. The energy decomposition analysis indicated that inter-atomic interactions in the three forms of rapta-C complexes and their stability are governed by the charge transfer term with significant contributions from polarization and electrostatic terms. The higher stability of complex 1 and 2 over 3 comes from the lower exchange repulsion and higher polarization contributions to their stability which agrees perfectly with the experimental observation. Our results provide insight into the nature of intramolecular forces that influence the structural stability of the three complexes. PMID:23187687

Adeniyi, Adebayo A; Ajibade, Peter A

2013-03-01

274

Observation of Pade summability in divergent L/sup 2/ complex coordinate calculations of t-matrix amplitudes in the presence of long-range forces  

SciTech Connect

The method of complex coordinates has been long been known to allow L/sup 2/ calculations of t-matrix amplitudes for short-range potentials, but to yield divergent results for long-range forces. Using a spherical long-range potential as an example, it is shown here that the Pade method of summation can be used in conjunction with the diverging complex-coordinate calculations to obtain accurate values of the scattering amplitude.

Johnson, B.R.; Reinhardt, W.P.

1984-05-01

275

Factors that regulate the conformation of m-benziporphodimethene complexes: agostic metal-arene interaction, hydrogen bonding, and ?2,? coordination.  

PubMed

Group?12 and silver(I) tetramethyl-m-benziporphodimethene (TMBPDM) complexes with phenyl, methylbenzoate, or nitrophenyl groups as meso substituents were synthesized and fully characterized. The dimeric silver(I) complex displays an unusual ?(2),? coordination from the ?-pyrrolic C=C bond to the silver ion. All of the complexes displayed a close contact between the metal ion and the inner C(22)-H(22) on the m-phenylene ring. The downfield chemical shifts of H(22) and large coupling constants between Cd(II) and H(22) strongly support the presence of an agostic interaction between the metal ion and inner C(22)-H(22). Crystal structures revealed that the syn form is the predominant conformation for TMBPDM complexes. This is distinctively different from the exclusive anti conformation observed in m-benziporphyrin and tetraphenyl-m-benziporphodimethene (TPBPDM) complexes. Evidently, intramolecular hydrogen-bonding interactions between axial chloride and methyl groups stabilize syn conformations. Unlike the merely syn conformation observed in the solid-state structures of TMBPDM complexes that contain an axial chloride, in solution these complexes display highly solvent- and temperature-dependent syn/anti ratio changes. The observation of dynamic (1)H NMR spectroscopic scrambling between syn and anti conformations from the titration of chloride ion into the solution of the TMBPDM complex suggests that axial ligand exchange is a likely pathway for the conversion between syn and anti forms. Theoretical calculations revealed that intermolecular hydrogen-bonding interactions between the axial chloride and CHCl(3) stabilizes the anti conformation, which explains the increased ratio for the anti form when dichloromethane or chloroform was used as the solvent. PMID:21922564

Chang, Gao-Fong; Wang, Chun-Hung; Lu, Hung-Chieh; Kan, Lou-Sing; Chao, Ito; Chen, Wei Hao; Kumar, Anil; Lo, Liyang; dela Rosa, Mira Anne C; Hung, Chen-Hsiung

2011-09-26

276

The Drosophila Enhancer of split Gene Complex: Architecture and Coordinate Regulation by Notch, Cohesin, and Polycomb Group Proteins  

PubMed Central

The cohesin protein complex functionally interacts with Polycomb group (PcG) silencing proteins to control expression of several key developmental genes, such as the Drosophila Enhancer of split gene complex [E(spl)-C]. The E(spl)-C contains 12 genes that inhibit neural development. In a cell line derived from the central nervous system, cohesin and the PRC1 PcG protein complex bind and repress E (spl)-C transcription, but the repression mechanisms are unknown. The genes in the E(spl)-C are directly activated by the Notch receptor. Here we show that depletion of cohesin or PRC1 increases binding of the Notch intracellular fragment to genes in the E(spl)-C, correlating with increased transcription. The increased transcription likely reflects both direct effects of cohesin and PRC1 on RNA polymerase activity at the E(spl)-C, and increased expression of Notch ligands. By chromosome conformation capture we find that the E(spl)-C is organized into a self-interactive architectural domain that is co-extensive with the region that binds cohesin and PcG complexes. The self-interactive architecture is formed independently of cohesin or PcG proteins. We posit that the E(spl)-C architecture dictates where cohesin and PcG complexes bind and act when they are recruited by as yet unidentified factors, thereby controlling the E(spl)-C as a coordinated domain.

Schaaf, Cheri A.; Misulovin, Ziva; Gause, Maria; Koenig, Amanda; Dorsett, Dale

2013-01-01

277

Rare tautomers of 1-methyluracil and 1-methylthymine: tuning relative stabilities through coordination to PtII complexes.  

PubMed

We have computationally explored how the relative stabilities of 1-methyluracil (1-MeUH) tautomers can be tuned through coordination of these tautomers to Pt(II) complexes with a particular set of ligands. This has been done using density functional theory at the BP86/TZ2P level. Thus, we have examined the water/1-MeUH exchange reactions of [Pt(II)(A)(B)(C)(OH(2))](q) + 1-MeUH to uncover: i) which tautomers are best stabilized by the Pt(II) complex, and ii) how the net charge q in the complex affects the reaction energy. The net charge q depends on the ligands A, B, and C, which can be the neutral NH(3) or anionic Cl(-). To reveal the effect of solvation, all reaction systems are studied both in the gas phase and in water. Also the stabilization of tautomers of 1-methylthymine (1-MeTH) by cisplatin is investigated. The calculations reveal that relative energies of the metal (here: Pt(II))-complexed forms of the various tautomers (here: of 1-MeUH and 1-MeTH) do not parallel those of the free tautomers. Rather, a rare nucleobase tautomer, despite its low natural abundance, may become favored over the predominant one when complexed to a metal ion. PMID:19058265

van der Wijst, Tushar; Fonseca Guerra, Clia; Swart, Marcel; Bickelhaupt, F Matthias; Lippert, Bernhard

2009-01-01

278

The Drosophila enhancer of split gene complex: architecture and coordinate regulation by notch, cohesin, and polycomb group proteins.  

PubMed

The cohesin protein complex functionally interacts with Polycomb group (PcG) silencing proteins to control expression of several key developmental genes, such as the Drosophila Enhancer of split gene complex [E(spl)-C]. The E(spl)-C contains 12 genes that inhibit neural development. In a cell line derived from the central nervous system, cohesin and the PRC1 PcG protein complex bind and repress E (spl)-C transcription, but the repression mechanisms are unknown. The genes in the E(spl)-C are directly activated by the Notch receptor. Here we show that depletion of cohesin or PRC1 increases binding of the Notch intracellular fragment to genes in the E(spl)-C, correlating with increased transcription. The increased transcription likely reflects both direct effects of cohesin and PRC1 on RNA polymerase activity at the E(spl)-C, and increased expression of Notch ligands. By chromosome conformation capture we find that the E(spl)-C is organized into a self-interactive architectural domain that is co-extensive with the region that binds cohesin and PcG complexes. The self-interactive architecture is formed independently of cohesin or PcG proteins. We posit that the E(spl)-C architecture dictates where cohesin and PcG complexes bind and act when they are recruited by as yet unidentified factors, thereby controlling the E(spl)-C as a coordinated domain. PMID:23979932

Schaaf, Cheri A; Misulovin, Ziva; Gause, Maria; Koenig, Amanda; Dorsett, Dale

2013-10-01

279

Spectroscopic characterization of alkaline earth uranyl carbonates  

SciTech Connect

A series of alkaline uranyl carbonates, M[UO{sub 2}(CO{sub 3}){sub 3}].nH{sub 2}O (M=Mg{sub 2}, Ca{sub 2}, Sr{sub 2}, Ba{sub 2}, Na{sub 2}Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). The molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba{sub 2}[UO{sub 2}(CO{sub 3}){sub 3}].6H{sub 2}O was obtained for the first time. The EXAFS analysis showed that this compound consists of (UO{sub 2})(CO{sub 3}){sub 3} clusters similar to the other alkaline earth uranyl carbonates. The average U-Ba distance is 3.90+/-0.02A.Fluorescence wavelengths and life times were measured using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The U-O bond distances determined by EXAFS, TRLFS, XPS, and Raman spectroscopy agree within the experimental uncertainties. The spectroscopic signatures observed could be useful for identifying uranyl carbonate species adsorbed on mineral surfaces.

Amayri, Samer [Institute of Nuclear Chemistry, Johannes Gutenberg-Universitaet Mainz, Fritz-Strassmann-Weg 2, 55128 Mainz (Germany); Reich, Tobias [Institute of Nuclear Chemistry, Johannes Gutenberg-Universitaet Mainz, Fritz-Strassmann-Weg 2, 55128 Mainz (Germany)]. E-mail: tobias.reich@uni-mainz.de; Arnold, Thuro [Forschungszentrum Rossendorf e.V., Institute of Radiochemistry, P.O. Box 510119, 01314 Dresden (Germany); Geipel, Gerhard [Forschungszentrum Rossendorf e.V., Institute of Radiochemistry, P.O. Box 510119, 01314 Dresden (Germany); Bernhard, Gert [Forschungszentrum Rossendorf e.V., Institute of Radiochemistry, P.O. Box 510119, 01314 Dresden (Germany)

2005-02-15

280

Synthesis, structures and properties of a series of manganese coordination complexes constructed from dicarboxylic fluorene derivatives  

SciTech Connect

Assembly reactions of 9,9-diethylfluorene-2,7-dicarboxylic acid (H{sub 2}DFDC) and Mn(CH{sub 3}COO){sub 2}{center_dot}4H{sub 2}O or MnCl{sub 2}{center_dot}4H{sub 2}O by tuning of various secondary ligands such as 2,2 Prime -bipyridine (2,2 Prime -bpy), 4,4 Prime -bipyridine (4,4 Prime -bpy) or 1,3-bis(4-pyridyl)propane) (bpp), gave rise to four complexes {l_brace} [Mn{sub 2}(DFDC){sub 2}(DMF){sub 2}]{center_dot}H{sub 2}O{r_brace} {sub n} (1), [Mn(DFDC)(2,2 Prime -bpy)]{sub n} (2), {l_brace} [Mn{sub 2}(DFDC){sub 2}(4,4 Prime -bpy){sub 2}]{center_dot}2CH{sub 3}OH{r_brace} {sub n} (3), and {l_brace} [Mn{sub 4}(DFDC){sub 4}(bpp){sub 2}(CH{sub 3}OH){sub 3} (H{sub 2}O){sub 3}]{center_dot}3(CH{sub 3}OH){center_dot}3(H{sub 2}O){r_brace} {sub n} (4). Single crystal X-ray diffraction analysis reveal that complex 1 is three dimensional structure with rhombic channels filled by guest water molecules; 2 presents a close-packed structure with high thermal stability; 3 exhibits a three dimensional framework with micro-porous channels filled by guest methanol molecules and 4 is a two-dimensional structure. The photoluminescent properties of 1-4 have been studied, respectively, showing that the Mn(II) ions, accessorial organic ligands or crystal structures exert important influences on the photoluminescence emissions of H{sub 2}DFDC ligands. Thermogravimetric analysis show that the complexes have remarkably high thermal stability. Magnetic susceptibility measurements have been finished and discussed for the complexes. - Graphical abstract: Assembly of 9,9-diethylfluorene-2,7-dicarboxylic acid and Mn(II) salts by tuning of various accessorial ligands resulted in four manganese complexes with different topological frameworks. Highlights: Black-Right-Pointing-Pointer Four manganese complexes based on 9,9-diethylfluorene-2,7-dicarboxylic acid were obtained. Black-Right-Pointing-Pointer The complexes were structurally characterized by single-crystal X-ray diffraction. Black-Right-Pointing-Pointer The complexes 1-4 display different topological structures. Black-Right-Pointing-Pointer Thermogravimetric analysis show the complexes have remarkably high thermal stability.

Li Xing, E-mail: lixing@nbu.edu.cn [State Key Laboratory Base of Novel Functional Materials and Preparation Science, Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo, Zhejiang, 315211 (China); Zhao Xiuhua; Bing Yue; Zha Meiqin; Xie Hongzhen; Guo Zhiyong [State Key Laboratory Base of Novel Functional Materials and Preparation Science, Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo, Zhejiang, 315211 (China)

2013-01-15

281

CORVET and HOPS tethering complexes - coordinators of endosome and lysosome fusion.  

PubMed

Protein and lipid transport along the endolysosomal system of eukaryotic cells depends on multiple fusion and fission events. Over the past few years, the molecular constituents of both fission and fusion machineries have been identified. Here, we focus on the mechanism of membrane fusion at endosomes, vacuoles and lysosomes, and in particular on the role of the two homologous tethering complexes called CORVET and HOPS. Both complexes are heterohexamers; they share four subunits, interact with Rab GTPases and soluble NSF attachment protein receptors (SNAREs) and can tether membranes. Owing to the presence of specific subunits, CORVET is a Rab5 effector complex, whereas HOPS can bind efficiently to late endosomes and lysosomes through Rab7. Based on the recently described overall structure of the HOPS complex and a number of in vivo and in vitro analyses, important insights into their function have been obtained. Here, we discuss the general function of both complexes in yeast and in metazoan cells in the context of endosomal biogenesis and maturation. PMID:23645161

Balderhaar, Henning J kleine; Ungermann, Christian

2013-03-15

282

User centered design in complex healthcare workflows: the case of care coordination and care management redesign  

PubMed Central

We present the User Need Analysis process for the Integrated Care Coordination Information System (ICCIS) research project at Oregon Health & Science University (OHSU). The primary goal of the process was to select a mix of methodologies to perform user need analysis which would lead to generation of system requirements. The ICCIS Team developers would use these prioritized requirements to build the next generation of the ICCIS software that would help meet the overall goals of the care model. First, semi-structured User Discussion Guides and structured questioners were used to collect raw needs from Physicians, Nurses, IT and Administrative personal. Later Conjoint Analysis (CA) and Dimensional Analysis (DA) were used to generate emerging concepts and priorities from the discussions with the end-user community.

Behkami, Nima A.; Dorr, David A.

2009-01-01

283

Oxidation state delineation via U L(III)-edge XANES in a series of isostructural uranium coordination complexes.  

PubMed

We present an X-ray absorption near-edge structure (XANES) study of a series of uranium coordination complexes that possess nearly identical first coordination spheres and geometries in a range of oxidation states from U(III) to U(VI). These compounds were obtained through the activation of small molecules, such as ketones, azides, and carbon dioxide, and upon oxidation of a high-valent U(V)?O to [U(VI)?O](+). Most of the compounds have been reported previously. All of them are fully characterized and their oxidation states have been confirmed by various spectroscopic methods (SQUID, (1)H NMR, and UV/vis/near-IR). Each uranium complex consists of a triazacyclononane anchor bearing three aryloxide side arms with bulky tert-butyl (t-Bu) or adamantyl (Ad) ortho substituents. All complexes have approximate C(3) symmetry and possess an axial cavity that is either empty (U(III)) or occupied by a seventh ligand, namely, terminal oxygen (U(V) and U(VI)) or an oxygen-containing ligand (U(IV)). The only exception is [(((t-Bu)ArO)(3)tacnU(VI)(O)][SbF(6)], which is the rare case of a complex that shows a strong inverse trans influence. The determined correlation between the uranium oxidation state and the U L(III)-edge XANES absorption in this series includes a single terminal oxo ligand bonded uranium(V,VI), for which data are essentially nonexistent. The correct assignment of the uranium valence in a U(IV)-L(-) compound (L(-) = ketyl radical) is shown to be only possible by a comparison to structurally similar compounds. PMID:22765506

Kosog, Boris; La Pierre, Henry S; Denecke, Melissa A; Heinemann, Frank W; Meyer, Karsten

2012-07-16

284

A novel hemilabile calix[4],quinoline-based P,N-ligand: coordination chemistry and complex characterisation.  

PubMed

The synthesis of the calix[4]arene-based P,N-ligand 3 (5,11,17,23-tetra-tert-butyl-25-[(2-quinolylmethyl)oxy]-26,27,28-(mu3-phosphorustrioxy)calix[4]arene), in which the nitrogen atom-containing moiety has been introduced at the lower rim of the cavity prior to P-functionalisation, is described and its coordination properties investigated. In the crystal structure, the calix[4]-cavity adopts a cone conformation with an exo orientation of the phosphorus lone pair enabling P-N chelation. 1H, 13C, 31P and 1H{15N} HMQC NMR spectra indicated that, in complexes [PdCl(CH3)(3)] (4) and [Rh(CO)Cl(3)] (5), ligand 3 coordinates in a chelating fashion, while in cis-[PtC12(3)2] (6) and [Rh(acac)(CO)(3)] (7) it behaves as a monodentate ligand, coordinating via the phosphorus atom only. X-Ray crystal structure determinations were performed for [PdCl(CH3)(3)] (4) and cis-[PtCl2(3)2] (6). The cationic Pd complex [Pd(CH3)(CH3CN)(3)][PF5] (8) was found to be active in a CO/ethylene copolymerisation reaction. Good selectivities were observed for the Pd-catalysed allylic alkylation of cinnamyl acetate with in situ prepared catalysts. [Rh(acac)(CO)2] modified with ligand 3 catalyses the hydroformylation of 1-octene with low selectivities towards linear aldehydes. High-pressure NMR experiments on the hydrido carbonyl rhodium(3) were inconclusive, different species were formed. PMID:19378555

Marson, Angelica; Ernsting, Johanneke E; Lutz, Martin; Spek, Anthony L; van Leeuwen, Piet W N M; Kamer, Paul C J

2009-01-28

285

Importance of dynamical processes in the coordination chemistry and redox conversion of copper amyloid-beta complexes.  

PubMed

Interaction of Cu ions with the amyloid-beta (Abeta) peptide is linked to the development of Alzheimer's disease; hence, determining the coordination of Cu(I) and Cu(II) ions to Abeta and the pathway of the Cu(I)(Abeta)/Cu(II)(Abeta) redox conversion is of great interest. In the present report, we use the room temperature X-ray absorption near edge structure to show that the binding sites of the Cu(I) and Cu(II) complexes are similar to those previously determined from frozen-solution studies. More precisely, the Cu(I) is coordinated by the imidazole groups of two histidine residues in a linear fashion. However, an NMR study unravels the involvement of all three histidine residues in the Cu(I) binding due to dynamical exchange between several set of ligands. The presence of an equilibrium is also responsible for the complex redox process observed by cyclic voltammetry and evidenced by a concentration-dependent electrochemical response. PMID:19618220

Hureau, Christelle; Balland, Vronique; Coppel, Yannick; Solari, Pier Lorenzo; Fonda, Emiliano; Faller, Peter

2009-09-01

286

Aging induced loss of complexity and dedifferentiation: consequences for coordination dynamics within and between brain, muscular and behavioral levels  

PubMed Central

Growing evidence demonstrates that aging not only leads to structural and functional alterations of individual components of the neuro-musculo-skeletal system (NMSS) but also results in a systemic re-organization of interactions within and between the different levels and functional domains. Understanding the principles that drive the dynamics of these re-organizations is an important challenge for aging research. The present Hypothesis and Theory paper is a contribution in this direction. We propose that age-related declines in brain and behavior that have been characterized in the literature as dedifferentiation and the loss of complexity (LOC) are: (i) synonymous; and (ii) integrated. We argue that a causal link between the aforementioned phenomena exists, evident in the dynamic changes occurring in the aging NMSS. Through models and methods provided by a dynamical systems approach to coordination processes in complex living systems, we: (i) formalize operational hypotheses about the general principles of changes in cross-level and cross-domain interactions during aging; and (ii) develop a theory of the aging NMSS based on the combination of the frameworks of coordination dynamics (CD), dedifferentiation, and LOC. Finally, we provide operational predictions in the study of aging at neural, muscular, and behavioral levels, which lead to testable hypotheses and an experimental agenda to explore the link between CD, LOC and dedifferentiation within and between these different levels.

Sleimen-Malkoun, Rita; Temprado, Jean-Jacques; Hong, S. Lee

2014-01-01

287

Synthesis and preliminary evaluation of radiolabeled bis(zinc(II)-dipicolylamine) coordination complexes as cell death imaging agents  

PubMed Central

The aim of this study was the development of 99mTc labeled bis(zinc(II)-dipicolylamine) (Zn2+-DPA) coordination complexes, and the in vivo evaluation of their usefulness as radiotracers for the detection of cell death. DPA ligand 1 was labeled with 99mTc via the 99mTc-tricarbonyl core ([99mTc(CO)3-1]3+) or via HYNIC (99mTc-HYNIC-1) in good radiochemical yields. Highest in vitro stabilities were demonstrated for [99mTc(CO)3-1]3+. A mouse model of hepatic apoptosis (anti-Fas mAb) was used to demonstrate binding to apoptotic cells. 99mTc-HYNIC-1 showed the best targeting of apoptotic hepatic tissue with a 2.2 times higher liver uptake in anti-Fas treated mice as compared to healthy animals. A rat model of ischemia-reperfusion injury was used to further explore the ability of the 99mTc-labeled Zn2+-DPA coordination complexes to target cell death. Selective accumulation could be detected for both tracers in the area at risk, correlating with histological proof of cell death. Area at risk to normal tissue uptake ratios were 3.82 for [99mTc(CO)3-1]3+ and 5.45 for 99mTc-HYNIC-1.

wyffels, Leonie; Gray, Brian D.; Barber, Christy; Woolfenden, James M.; Pak, Koon Y.; Liu, Zhonglin

2011-01-01

288

Unexpected mild C-N bond cleavage mediated by guanidine coordination to a niobium iminocarbamoyl complex.  

PubMed

The complex [Nb(NMe2)2{(NMe2)C=N(t)Bu}{N(2,6-(i)Pr2C6H3)}] reacts with trialkylguanidines and undergoes a room temperature C-N bond cleavage of the iminocarbamoyl moiety. This reaction affords the guanidinate complexes [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NH(i)Pr)}] or [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NH(n)Bu)}] and free isocyanide. The first crystal structure of a niobium iminocarbamoyl complex is reported. PMID:23955374

Elorriaga, David; Carrillo-Hermosilla, Fernando; Antiolo, Antonio; Lpez-Solera, Isabel; Fernndez-Galn, Rafael; Villaseor, Elena

2013-10-01

289

Dihydrogen complexes as prototypes for the coordination chemistry of saturated molecules  

PubMed Central

The binding of a dihydrogen molecule (H2) to a transition metal center in an organometallic complex was a major discovery because it changed the way chemists think about the reactivity of molecules with chemically inert strong bonds such as HH and CH. Before the seminal finding of side-on bonded H2 in W(CO)3(PR3)2(H2), it was generally believed that H2 could not bind to another atom in stable fashion and would split into two separate H atoms to form a metal dihydride before undergoing chemical reaction. Metal-bound saturated molecules such as H2, silanes, and alkanes (?-complexes) have a chemistry of their own, with surprisingly varied structures, bonding, and dynamics. H2 complexes are of increased relevance for H2 production and storage in the hydrogen economy of the future.

Kubas, Gregory J.

2007-01-01

290

Eight-coordinate stereochemistries of U(IV) catecholate and aquo complexes  

SciTech Connect

An extended MM3 model has been used to identify all low energy configurations for U(IV) complexes with catecholate and aquo ligands. Both stochastic and systematic conformational analyses of[U(cat)n(OH2)8-n]4-2n complexes, n= 1 - 4, establish that 20 of the 67 possible stereochemistries are minima on the MM3 potential surface. The stable stereochemistries are reported for each stoichiometry and, where possible, the results are compared with experimental data and with the predictions from prior repulsion energy calculations.

Hay, Benjamin P.; Uddin, Jamal; Firman, Timothy K.

2004-01-01

291

Neutral, seven-coordinate dioxime complexes of technetium(III): Synthesis and characterization  

Microsoft Academic Search

The tin-capped complexes ⁹⁹Tc(oxime)(μ-OH)SnCl (oxime = dimethylglyoxime (DMG) or cyclohexanedione dioxime (CDO)) can be prepared by the reduction of NHTcO with 2 equiv of SnCl in the presence of dioxime and HCl. These tin-capped complexes can be readily converted into a new class of uncapped Tc-dioxime compounds, TcCl(oxime), by treatment with HCl. This reaction is reversible. Both the tin-capped and

Karen E. Linder; Mary F. Malley; Jack Z. Gougoutas; Steve E. Unger; Adrian D. Nunn

1990-01-01

292

Mechanistic studies on monodentateligand substitution of five-coordinate trigonal-bipyramidal platinum (II) complexes with tris[2-(diphenylphosphino)ethyl]phosphine  

Microsoft Academic Search

Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp3)](BF4) (pt=1-propanethiolate, pp3=tris[2-(diphenylphosphino)ethyl]phosphine), with I? in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp3)]++I??[PtI(pt) (pp3)], and the kinetic parameters for the chemical exchange were obtained as follows: Kex298=7.510-1mol-1kg,

Sen-ichi Aizawa; Tadashi Kobayashi; Tatsuya Kawamoto

2005-01-01

293

Sub-Grid Reactive Diffusion and Apparent Uranyl Adsorption/Desorption Rates  

NASA Astrophysics Data System (ADS)

Adsorption/desorption is an important process affecting contaminant fate and transport in subsurface sediments. This presentation will discuss the importance of sub-grid reactive diffusion in both intragranular and inter-grain domains that affect the apparent rates of uranyl adsorption/desorption at the macroscopic scale. Uranyl[U(VI)]-contaminated site at Hanford 300A where U(VI) resides in intragranular domains as surface-complexed species is used as an example in this presentation. Molecular dynamics calculations revealed that uranyl surface complexation reactions are a fast process with a first-order rate constant of 100 per second. Consequently U(VI) adsorption/desorption is treated as an equilibrium process. An equilibrium, Kd-based model, however, significantly over-predicted the historical migration of the uranyl plume at the site. Sub-grain pore-scale simulations and stirred-flow cell experiments indicated that the coupling of intragranular diffusion with surface complexation reactions decreased the apparent rate of U(VI) adsorption/desorption over 4 order of magnitude. The apparent rate of U(VI) adsorption/desorption decreased further over 1 order of magnitude due to the sub-grid pore-scale coupling of diffusive mass transfer and grain-scale U(VI) adsorption/desorption as revealed by column experiments and pore-scale simulations. Field-scale reactive transport models that incorporate the complexity of sub-grid reactive diffusion in the apparent rate of U(VI) adsorption/desorption were consistent with the slow migration of the U(VI) plume at the site.

Liu, C.; Kerisit, S.; Ma, R.; Zheng, C.; Zachara, J. M.

2011-12-01

294

Tracking excited-state charge and spin dynamics in iron coordination complexes.  

PubMed

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2'-bipyridine)3](2+), where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)3](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes. PMID:24805234

Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe; Bressler, Christian; Chollet, Matthieu; Galler, Andreas; Gawelda, Wojciech; Hadt, Ryan G; Hartsock, Robert W; Kroll, Thomas; Kjr, Kasper S; Kubi?ek, Katharina; Lemke, Henrik T; Liang, Huiyang W; Meyer, Drew A; Nielsen, Martin M; Purser, Carola; Robinson, Joseph S; Solomon, Edward I; Sun, Zheng; Sokaras, Dimosthenis; van Driel, Tim B; Vank, Gyrgy; Weng, Tsu-Chien; Zhu, Diling; Gaffney, Kelly J

2014-05-15

295

Complex-coordinate calculation of D-(1,3) resonances in two-electron systems  

NASA Technical Reports Server (NTRS)

Feshbach-type D-(1,3)resonances in two-electron systems, Z = 2-10, have been investigated using the method of complex rotation. These states lie below the n = 2 and 3 thresholds of hydrogenic systems. Wave functions containing up to 1230 Hylleraas functions have been used, giving accurate results for positions and widths. Comparisons between various calculations are given.

Ho, Y. K.; Bhatia, A. K.

1991-01-01

296

Tracking excited-state charge and spin dynamics in iron coordination complexes  

NASA Astrophysics Data System (ADS)

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2'-bipyridine)3]2+, where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)3]2+ on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes.

Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe; Bressler, Christian; Chollet, Matthieu; Galler, Andreas; Gawelda, Wojciech; Hadt, Ryan G.; Hartsock, Robert W.; Kroll, Thomas; Kjr, Kasper S.; Kubi?ek, Katharina; Lemke, Henrik T.; Liang, Huiyang W.; Meyer, Drew A.; Nielsen, Martin M.; Purser, Carola; Robinson, Joseph S.; Solomon, Edward I.; Sun, Zheng; Sokaras, Dimosthenis; van Driel, Tim B.; Vank, Gyrgy; Weng, Tsu-Chien; Zhu, Diling; Gaffney, Kelly J.

2014-05-01

297

Coordination modes, spectral, thermal and biological evaluation of hetero-metal copper containing 2-thiouracil complexes  

NASA Astrophysics Data System (ADS)

Mononuclear copper complex [CuL(NH3)4]Cl20.5H2O and three new hetero-metallic complexes: [Cu2Ni(L)2(NH3)2Cl26H2O] 2H2O, [Cu3Co(L)48H2O]Cl45H2O, and [Cu4Co2Ni(L)3(OH)4(NH3)Cl43H2O]4H2O where L is 2-thiouracil, were prepared and characterized by elemental analyses, molar conductance, room-temperature magnetic susceptibility, spectral (IR, UV-Vis and ESR) studies and thermal analyses techniques (TG, DTG and DTA). The molar conductance data revealed that [CuL(NH3)4]Cl20.5H2O and [Cu3Co(L)48H2O]Cl4.5H2O are electrolytes, while, [Cu2Ni(L)2(NH3)2Cl26H2O]2H2O and [Cu4Co2Ni(L)3(OH)4(NH3)Cl43H2O]4H2O are non-electrolytes. IR spectra showed, that 2-thiouracil ligand behaves as a bidentate or tetradentate ligand. The geometry around the metal atoms is octahedral in all the prepared complexes except in [Cu4Co2Ni(L)3(OH)4(NH3)Cl43H2O]4H2O complex where square planar environment around Co(II), Ni(II) and Cu(II) were suggested. Thermal decomposition study of the prepared complexes was monitored by TG, DTG and DTA analyses under N2 atmosphere. The decomposition course and steps were analyzed. The order of chemical reactions (n) was calculated via the peak symmetry method and the activation parameters of the non- isothermal decomposition were computed from the thermal decomposition data. The negative values of ?S? deduced the ordered structures of the prepared complexes compared to their starting reactants. The antimicrobial activity of the prepared complexes were screened in vitro against a Gram positive, a Gram negative bacteria, a filamentous fungi and a yeast. The antimicrobial screening data showed that the studied compounds exhibited a good level of activity against Escherichia coli, Staphylococcus aureus and Candida albicans but have no efficacy against Aspergillus flavus. It was observed that [Cu4Co2Ni(L)3(OH)4(NH3)Cl43H2O]4H2O complex showed the most intensive activity against the tested microorganisms. Trials to prepare single crystals from complexes were failed.

Masoud, Mamdouh S.; Soayed, Amina A.; El-Husseiny, Amel F.

2012-12-01

298

A-kinase anchoring protein Lbc coordinates a p38 activating signaling complex controlling compensatory cardiac hypertrophy.  

PubMed

In response to stress, the heart undergoes a remodeling process associated with cardiac hypertrophy that eventually leads to heart failure. A-kinase anchoring proteins (AKAPs) have been shown to coordinate numerous prohypertrophic signaling pathways in cultured cardiomyocytes. However, it remains to be established whether AKAP-based signaling complexes control cardiac hypertrophy and remodeling in vivo. In the current study, we show that AKAP-Lbc assembles a signaling complex composed of the kinases PKN, MLTK, MKK3, and p38? that mediates the activation of p38 in cardiomyocytes in response to stress signals. To address the role of this complex in cardiac remodeling, we generated transgenic mice displaying cardiomyocyte-specific overexpression of a molecular inhibitor of the interaction between AKAP-Lbc and the p38-activating module. Our results indicate that disruption of the AKAP-Lbc/p38 signaling complex inhibits compensatory cardiomyocyte hypertrophy in response to aortic banding-induced pressure overload and promotes early cardiac dysfunction associated with increased myocardial apoptosis, stress gene activation, and ventricular dilation. Attenuation of hypertrophy results from a reduced protein synthesis capacity, as indicated by decreased phosphorylation of 4E-binding protein 1 and ribosomal protein S6. These results indicate that AKAP-Lbc enhances p38-mediated hypertrophic signaling in the heart in response to abrupt increases in the afterload. PMID:23716597

Prez Lpez, Irene; Cariolato, Luca; Maric, Darko; Gillet, Ludovic; Abriel, Hugues; Diviani, Dario

2013-08-01

299

Synthesis and characterization of oxo-bridged, trinuclear, six-coordinate mixed-carboxylato complexes of chromium (III)  

NASA Astrophysics Data System (ADS)

Mixed-carboxylato ?-diketonato complexes of chromium (III) (R=C 13H 27, C 15H 31 or C 17H 35 and L=CH 3OH) [Cr 3O(OOCR) 3(dike) 3L 3] + have been synthesized by enforced substitution reactions of [Cr 3O(OOCCH 3) 7(H 2O)] first with straight chain fatty acids (myristic, palmitic or stearic acid) and then with ?-diketones (H?-dike) like acetylacetone(Hacac) or benzoylacetone(Hbzac) in toluene under reflux. These are new type of oxo-bridged chromium(III) complexes in which one ligand is a fatty acid while the other one is a ?-diketone. The complexes were characterized by elemental analyses, spectral (infrared, electronic, FAB mass and powder XRD) studies, molar conductance and magnetic susceptibility measurements. Bridging coordination modes for both carboxylate and ?-diketonate anions were indicated by presence of ?asym(Cr 3O) vibrations in the infrared spectra. Trinuclear nature of the complexes and their structural features have been discussed on the basis of physicochemical studies.

Baranwal, B. P.; Fatma, Talat

2005-08-01

300

Synthesis and coordination behavior of a bipyridine platinum(II) complex with thioglucose.  

PubMed

A mononuclear platinum(II) complex with two monodentate-S H4tg(-) ligands, [Pt(H4tg-?S)2(bpy)] (1), was newly synthesized by the reaction of [PtCl2(bpy)] (bpy = 2,2'-bipyridyl) with NaH4tg (NaH4tg =1-thio-?-d-glucose sodium salt) in water. Complex 1 reacted with additional [PtCl2(bpy)] in water to give an S-bridged dinuclear complex, [Pt2(?2-H4tg-?(1)S:?(1)S)2(bpy)2](2+) ([2](2+)), in which a square-planar [Pt(H4tg)2(bpy)] unit binds to a [Pt(bpy)](2+) moiety through two thiolato groups. Treatments of 1 with Cu(2+) and Ni(2+) in water in the presence of bpy produced S-bridged dinuclear complexes [PtCu(?2-H4tg-?(1)S:?(2)O,S)2(bpy)2](2+) ([3](2+)) and [PtNi(?2-H4tg-?(1)S:?(2)O,S)2(bpy)2](2+) ([4](2+)), respectively, in which a square-planar [Pt(H4tg)2(bpy)] unit binds to a [M(bpy)](2+) (M = Cu(II), Ni(II)) moiety through two thiolato and two hydroxyl groups to form a chiral [M(N)2(O)2(S)2] octahedron with the ? configuration. On the other hand, similar treatment with Cd(2+) in the presence of bpy resulted in the formation of an S-bridged trinuclear complex, [Cd{Pt(?2-H4tg-?(1)S:?(2)O,S)(?2-H4tg-?(1)S:?(1)S)(bpy)}2](2+) ([5](2+)), in which each of two square-planar [Pt(H4tg)2(bpy)] units binds to a Cd(II) ion through two thiolato groups and one hydroxyl group to form a chiral [Cd(O)2(S)4] octahedron with the ? configuration. Of two geometrical configurations, syn and anti, which arise from the relative arrangement of two ?-D-pyranose moieties, [2](2+) adopts the syn configuration with symmetric bridging sulfur atoms, while [3](2+), [4](2+), and [5](2+) all have the anti configuration with R configurational bridging sulfur atoms. All of the complexes were fully characterized by electronic absorption, CD, and NMR spectroscopies, along with single-crystal X-ray crystallography. PMID:23577632

Tsuji, Takaaki; Kuwamura, Naoto; Yoshinari, Nobuto; Konno, Takumi

2013-05-01

301

Lanthanide complexes with oda, ida, and nta: From discrete coordination compounds to supramolecular assemblies  

NASA Astrophysics Data System (ADS)

Lanthanide metal-organic frameworks have been receiving special attention for the last decade. The use of polydentate organic ligands has allowed the construction of interesting network topologies with many potential applications, based on the special characteristics of the 4f electrons. In this paper, the structural and thermodynamic properties of Ln(III) complexes with oxydiacetate, iminodiacetate, and nitrilotriacetate are critically reviewed. The presence of ligands able to act as a bridge promotes the formation of Ln-M polynuclear complexes with fascinating 3D structures, whose study is also included. Equilibrium data of these systems in aqueous solution have been collected, showing the relationship between the composition of the species in solution and the nuclearity in the solid state.

Kremer, Carlos; Torres, Julia; Domnguez, Sixto

2008-05-01

302

Synthesis and coordination chemistry of organotin(IV) complexes of 2,3-methylenedioxyphenylpropenoic acid  

Microsoft Academic Search

The synthesis, spectroscopy, and antitumor behavior of organotin(IV) complexes of 2,3-methylenedioxyphenylpropenoic acid are described. The spectroscopic data indicate 1 : 2 and 1 : 1 metal to ligand stoichiometry in case of di- and trioganotin(IV) compounds and hypervalency of Sn(IV) in trigonal bipyramidal and octahedral modes. Mass spectrometric and elemental analysis data support the solid and solution spectroscopic results. The

Mukhtiar Hussain; Muhammad Hanif; Saqib Ali; Saira Shahzadi; Muhammad Sheeraz Ahmad; Bushra Mirza; Helen S. Evans

2009-01-01

303

Coordination Chemistry of the Imino Nitroxides. Ferromagnetic Behavior of Some First Row Transition Metal Complexes  

Microsoft Academic Search

\\u000a The structural and magnetic properties of discrete adducts of imino nitroxides with first row transition metal ions are described.\\u000a The striking result of this study is the large metal-radical ferromagnetic interactions in the Cu(II), Ni(II), Co(II) complexes\\u000a induced by the bonding geometry of the imino nitrogen atom of the free radical to the metal. On the other hand, the Mn(II)

P. Rey; D. Luneau; A. Cogne

304

The MRN complex: coordinating and mediating the response to broken chromosomes  

Microsoft Academic Search

The MRE11RAD50NBS1 (MRN) protein complex has been linked to many DNA metabolic events that involve DNA double-stranded breaks (DSBs). In vertebrate cells, all three components are encoded by essential genes, and hypomorphic mutations in any of the human genes can result in genome-instability syndromes. MRN is one of the first factors to be localized to the DNA lesion, where it

Michael van den Bosch; Ronan T. Bree; Noel F. Lowndes

2003-01-01

305

Synthesis, structures and properties of a series of manganese coordination complexes constructed from dicarboxylic fluorene derivatives  

NASA Astrophysics Data System (ADS)

Assembly reactions of 9,9-diethylfluorene-2,7-dicarboxylic acid (H2DFDC) and Mn(CH3COO)24H2O or MnCl24H2O by tuning of various secondary ligands such as 2,2'-bipyridine (2,2'-bpy), 4,4'-bipyridine (4,4'-bpy) or 1,3-bis(4-pyridyl)propane) (bpp), gave rise to four complexes {[Mn2(DFDC)2(DMF)2]H2O}n (1), [Mn(DFDC)(2,2'-bpy)]n (2), {[Mn2(DFDC)2(4,4'-bpy)2]2CH3OH}n (3), and {[Mn4(DFDC)4(bpp)2(CH3OH)3 (H2O)3]3(CH3OH)3(H2O)}n (4). Single crystal X-ray diffraction analysis reveal that complex 1 is three dimensional structure with rhombic channels filled by guest water molecules; 2 presents a close-packed structure with high thermal stability; 3 exhibits a three dimensional framework with micro-porous channels filled by guest methanol molecules and 4 is a two-dimensional structure. The photoluminescent properties of 1-4 have been studied, respectively, showing that the Mn(II) ions, accessorial organic ligands or crystal structures exert important influences on the photoluminescence emissions of H2DFDC ligands. Thermogravimetric analysis show that the complexes have remarkably high thermal stability. Magnetic susceptibility measurements have been finished and discussed for the complexes.

Li, Xing; Zhao, Xiuhua; Bing, Yue; Zha, Meiqin; Xie, Hongzhen; Guo, Zhiyong

2013-01-01

306

Tetradentate N2S2 vanadyl(IV) coordination complexes: synthesis, characterization, and reactivity studies.  

PubMed

The versatile N(2)S(2) tetradentate ligands (bme-daco)(2-), (bme-dach)(2-), and (ema)(4-) are known to accommodate many divalent transition-metal ions (M = Ni(II), Pd(II), Pt(II), Pb(II), Zn(II), Cd(II), Cu(II), and Fe(II)) while maintaining reactivity at the S-thiolate sites of the respective N(2)S(2)M complexes. The vanadyl ion, of interest for its pharmacological possibilities and its spin-label reporter properties for bioinorganic studies, also shows an affinity for such mixed nitrogen/sulfur-donor environments. Thus, (V?O)(2+) analogues of a well-characterized series of N(2)S(2)Ni complexes have been prepared as mimics of possible N(2)S(2)(V?O) formed from in vivo binding sites of the tripeptide motif, Cys-X-Cys. The nucleophilicity of the S-thiolate in these systems is explored with alkylating agents. IR [?(VO)], electronic spectral, and electron paramagnetic resonance measurements are presented. X-ray diffraction studies of (bme-daco)(V?O), (bme-dach)(V?O), and [Et(4)N](2)[(ema)(V?O)] further characterize the vanadyl complexes. A comparison of the spectral properties with the product of vanadyl interaction with the CGC tripeptide, the biological analogue of the tetraanionic N(2)S(2) ligand, is given. PMID:21299197

Jenkins, Roxanne M; Pinder, Tiffany A; Hatley, Michelle L; Reibenspies, Joseph H; Darensbourg, Marcetta Y

2011-03-01

307

Uranyl and arsenate cosorption on aluminum oxide surface  

NASA Astrophysics Data System (ADS)

In this study, we examined the effects of simultaneous adsorption of aqueous arsenate and uranyl onto aluminum oxide over a range of pH and concentration conditions. Arsenate was used as a chemical analog for phosphate, and offers advantages for characterization via X-ray absorption spectroscopy. By combining batch experiments, speciation calculations, X-ray absorption spectroscopy, and X-ray diffraction, we investigated the uptake behavior of uranyl, as well as the local and long-range structure of the final sorption products. In the presence of arsenate, uranyl sorption was greatly enhanced in the acidic pH range, and the amount of enhancement is positively correlated to the initial arsenate and uranyl concentrations. At pH 4-6, U L III- and As K-edge EXAFS results suggest the formation of surface-sorbed uranyl and arsenate species as well as uranyl arsenate surface precipitate(s) that have a structure similar to trgerite. Uranyl polymeric species or oxyhydroxide precipitate(s) become more important with increasing pH values. Our results provide the basis for predictive models of the uptake of uranyl by aluminum oxide in the presence of arsenate and (by analogy) phosphate, which can be especially important for understanding phosphate-based uranium remediation systems.

Tang, Yuanzhi; Reeder, Richard J.

2009-05-01

308

EB1-recruited microtubule +TIP complexes coordinate protrusion dynamics during 3D epithelial remodeling  

PubMed Central

SUMMARY Background Epithelial remodeling, in which apical-basal polarized cells switch to a migratory phenotype, plays a central role in development and disease of multicellular organisms. Although dynamic microtubules (MTs) are required for directed migration on flat surfaces, how MT dynamics are controlled or contribute to epithelial remodeling in a more physiological three-dimensional (3D) environment is not understood. We use confocal live cell imaging to analyze MT function and dynamics during 3D epithelial morphogenesis and remodeling of polarized Madin-Darby canine kidney (MDCK) epithelial cells that undergo partial epithelial-to-mesenchymal transition (EMT) in response to hepatocyte growth factor (HGF). Results We find that HGF treatment increases MT growth rate before morphological changes are evident, and that large numbers of MTs grow into HGF-induced cell extensions independent of centrosome reorientation. Using lentivirus-mediated shRNA, we demonstrate that EB1, an adaptor protein that mediates recruitment of numerous other +TIP proteins to growing MT plus ends, is required for this HGF-induced MT reorganization. We further show that protrusion and adhesion dynamics are disorganized, and that vesicular trafficking to the tip of HGF-induced cell extensions is disrupted in EB1-depleted cells. Conclusions We conclude that EB1-mediated interactions with growing MTs are important to coordinate cell shape changes and directed migration into the surrounding extracellular matrix during epithelial remodeling in a physiological 3D environment. In contrast, EB1 is not required for the establishment or maintenance of apical-basal cell polarity, suggesting different functions of +TIPs and MTs in different types of cell polarity.

Gierke, Sarah; Wittmann, Torsten

2012-01-01

309

Ruthenium bidentate phosphine complexes for the coordination and catalytic dehydrogenation of amine- and phosphine-boranes.  

PubMed

Addition of the amine-boranes H(3)B?NH(2)tBu, H(3)B?NHMe(2) and H(3)B?NH(3) to the cationic ruthenium fragment [Ru(xantphos)(PPh(3))(OH(2))H][BAr(F)(4)] (2; xantphos=4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; BAr(F)(4)=[B{3,5-(CF(3))(2)C(6)H(3)}(4)](-)) affords the ?(1)-B-H bound amine-borane complexes [Ru(xantphos)(PPh(3))(H(3)B?NH(2)tBu)H][BAr(F)(4)] (5), [Ru(xantphos)(PPh(3))(H(3) B?NHMe(2))H][BAr(F)(4)] (6) and [Ru(xantphos)(PPh(3))(H(3)B?NH(3))H][BAr(F)(4)] (7). The X-ray crystal structures of 5 and 7 have been determined with [BAr(F)(4)] and [BPh(4)] anions, respectively. Treatment of 2 with H(3)B?PHPh(2) resulted in quite different behaviour, with cleavage of the B-P interaction taking place to generate the structurally characterised bis-secondary phosphine complex [Ru(xantphos)(PHPh(2))(2)H][BPh(4)] (9). The xantphos complexes 2, 5 and 9 proved to be poor precursors for the catalytic dehydrogenation of H(3)B?NHMe(2). While the dppf species (dppf=1,1'-bis(diphenylphosphino)ferrocene) [Ru(dppf)(PPh(3))HCl] (3) and [Ru(dppf)(?(6)-C(6)H(5)PPh(2))H][BAr(F)(4)] (4) showed better, but still moderate activity, the agostic-stabilised N-heterocyclic carbene derivative [Ru(dppf)(ICy)HCl] (12; ICy=1,3-dicyclohexylimidazol-2-ylidene) proved to be the most efficient catalyst with a turnover number of 76 h(-1) at room temperature. PMID:21678503

Ledger, Araminta E W; Ellul, Charles E; Mahon, Mary F; Williams, Jonathan M J; Whittlesey, Michael K

2011-07-25

310

Coordination of lanthanides by two polyamino polycarboxylic macrocycles: formation of highly stable lanthanide complexes  

Microsoft Academic Search

The formation constants of a few lanthanide complexes with DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) and TETA (1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid) have been measured by potentiometric and competition methods. The ligand DOTA forms the most stable lanthanide chelates known so far (log K\\/sub ML\\/ = 28.2-29.2) while the stability of the TETA compounds at 80 °C (log K\\/sub ML\\/ = 14.5-16.5) is comparable to the

M. F. Loncin; J. F. Desreux; E. Merciny

1986-01-01

311

New nine and ten coordinated complexes of lanthanides with bidentate 2-pyrazinecarboxylate containing hydrazinium cation  

Microsoft Academic Search

The new hydrazinium lanthanide metal complexes of 2-pyrazinecarboxylic acid of the formulae (N2H5)2[Ln(pyzCOO)5]2H2O (1), where Ln=La or Ce and (N2H5)3[Ln(pyzCOO)4(H2O)]2NO3 (2), where Ln=Pr, Nd, Sm or Dy have been synthesized by the addition of an aqueous solution of corresponding metal nitrate hydrates to an aqueous mixture of carboxylic acid and hydrazine hydrate in an appropriate ratios. The structure of (N2H5)2[La(pyzCOO)5]2H2O

Thathan Premkumar; Subbaiah Govindarajan; Nigam P. Rath; Vadivelu Manivannan

2009-01-01

312

Catching gaseous SO2 in cone-type lanthanide complexes: an unexpected coordination mode for SO2 in f-element chemistry.  

PubMed

Easy come, easy go: the first molecular SO(2) complexes of the lanthanides (Ln=Sm, Eu) have been prepared. The compounds can reversibly coordinate gaseous SO(2). Concomitant with the addition and removal of SO(2), the color of the complexes changes reversibly. The structures of the SO(2) compounds could be confirmed in solution and in the solid state. PMID:22473788

Benndorf, Paul; Schmitt, Sophia; Kppe, Ralf; Oa-Burgos, Pascual; Scheurer, Andreas; Meyer, Karsten; Roesky, Peter W

2012-05-14

313

Pro-oxidative, genotoxic and cytotoxic properties of uranyl ions.  

PubMed

It is demonstrated that hydroxyl radicals and hydrogen peroxide are formed under the action of uranyl ions in aqueous solutions containing no reducing agents. In the presence of uranyl ions, formation of 8-oxoguanine in DNA and long-lived protein radicals are observed invitro. It is shown that the pro-oxidant properties of uranyl at micromolar concentrations mostly result from the physico-chemical nature of the compound rather than its radioactive decay. Uranyl ions lead to damage in DNA and proteins causing death of HEp-2 cells by necrotic pathway. It is revealed that the uranyl ions enhance radiation-induced oxidative stress and significantly increase a death rate of mice exposed to sublethal doses of X-rays. PMID:23312590

Garmash, S A; Smirnova, V S; Karp, O E; Usacheva, A M; Berezhnov, A V; Ivanov, V E; Chernikov, A V; Bruskov, V I; Gudkov, S V

2014-01-01

314

Coordinated regulation of transcriptional repression by the RBP2 H3K4 demethylase and Polycomb-Repressive Complex 2  

PubMed Central

Polycomb group (PcG) proteins regulate important cellular processes such as embryogenesis, cell proliferation, and stem cell self-renewal through the transcriptional repression of genes determining cell fate decisions. The Polycomb-Repressive Complex 2 (PRC2) is highly conserved during evolution, and its intrinsic histone H3 Lys 27 (K27) trimethylation (me3) activity is essential for PcG-mediated transcriptional repression. Here, we show a functional interplay between the PRC2 complex and the H3K4me3 demethylase Rbp2 (Jarid1a) in mouse embryonic stem (ES) cells. By genome-wide location analysis we found that Rbp2 is associated with a large number of PcG target genes in mouse ES cells. We show that the PRC2 complex recruits Rbp2 to its target genes, and that this interaction is required for PRC2-mediated repressive activity during ES cell differentiation. Taken together, these results demonstrate an elegant mechanism for repression of developmental genes by the coordinated regulation of epigenetic marks involved in repression and activation of transcription.

Pasini, Diego; Hansen, Klaus H.; Christensen, Jesper; Agger, Karl; Cloos, Paul A.C.; Helin, Kristian

2008-01-01

315

Investigating CN- cleavage by three-coordinate M[N(R)Ar]3 complexes.  

PubMed

Three-coordinate Mo[N((t)Bu)Ar]3 binds cyanide to form the intermediate [Ar((t)Bu)N]3Mo-CN-Mo[N((t)Bu)Ar]3 but, unlike its N2 analogue which spontaneously cleaves dinitrogen, the C-N bond remains intact. DFT calculations on the model [NH2]3Mo/CN- system show that while the overall reaction is significantly exothermic, the final cleavage step is endothermic by at least 90 kJ mol(-1), accounting for why C-N bond cleavage is not observed experimentally. The situation is improved for the [H2N]3W/CN- system where the intermediate and products are closer in energy but not enough for CN- cleavage to be facile at room temperature. Additional calculations were undertaken on the mixed-metal [H2N]3Re+/CN- /W[NH2]3 and [H2N]3Re+/CN-/Ta[NH2]3 systems in which the metals ions were chosen to maximise the stability of the products on the basis of an earlier bond energy study. Although the reaction energetics for the [H2N]3Re+/CN /W[NH2]3 system are more favourable than those for the [H2N]3W/CN- system, the final C-N cleavage step is still endothermic by 32 kJ mol(-1) when symmetry constraints are relaxed. The resistance of these systems to C-N cleavage was examined by a bond decomposition analysis of [H2N]M-L1[triple bond]L2-M[NH2]3 intermediates for L1[triple bond]L2 = N2, CO and CN which showed that backbonding from the metal into the L1[triple bond]L2 pi* orbitals is significantly less for CN than for N2 or CO due to the negative charge on CN- which results in a large energy gap between the metal d(pi), and the pi* orbitals of CN-. This, combined with the very strong M-CN- interaction which stabilises the CN intermediate, makes C-N bond cleavage in these systems unfavourable even though the C[triple bond]N triple bond is not as strong as the bond in N2 or CO. PMID:18411843

Christian, Gemma; Stranger, Robert; Yates, Brian F; Cummins, Christopher C

2008-01-21

316

Role of the Uranyl Oxo Group as a Hydrogen Bond Acceptor  

SciTech Connect

Density functional theory calculations have been used to evaluate the geometries and energetics of interactions between a number of uranyl complexes and hydrogen bond donor groups. The results reveal that although traditional hydrogen bond donors are repelled by the oxo group in the [UO{sub 2}(OH{sub 2}){sub 5}]{sup 2+} species, they are attracted to the oxo groups in [UO{sub 2}(OH{sub 2}){sub 2}(NO{sub 3}){sub 2}]{sup 0}, [UO{sub 2}(NO{sub 3}){sub 3}]{sup -}, and [UO{sub 2}Cl{sub 4}]{sup 2-} species. Hydrogen bond strength depends on the equatorial ligation and can exceed 15 kcal mol{sup -1}. The results also reveal the existence of directionality at the uranyl oxo acceptor, with a weak preference for linear U=O---H angles.

Watson, Lori A [ORNL; Hay, Benjamin [ORNL

2011-01-01

317

Low coordinate germanium(II) and tin(II) hydride complexes: efficient catalysts for the hydroboration of carbonyl compounds.  

PubMed

This study details the first use of well-defined low-valent p-block metal hydrides as catalysts in organic synthesis. That is, the bulky, two-coordinate germanium(II) and tin(II) hydride complexes, L()(H)M: (M = Ge or Sn, L() = -N(Ar())(SiPr(i)3), Ar() = C6H2{C(H)Ph2}2Pr(i)-2,6,4), are shown to act as efficient catalysts for the hydroboration (with HBpin, pin = pinacolato) of a variety of unactivated, and sometimes very bulky, carbonyl compounds. Catalyst loadings as low as 0.05 mol % are required to achieve quantitative conversions, with turnover frequencies in excess of 13?300 h(-1) in some cases. This activity rivals that of currently available catalysts used for such reactions. PMID:24524219

Hadlington, Terrance J; Hermann, Markus; Frenking, Gernot; Jones, Cameron

2014-02-26

318

Well-Defined Four-Coordinate Iron(II) Complexes For Intramolecular Hydroamination of Primary Aliphatic Alkenylamines.  

PubMed

Despite the growing interest in iron catalysis and hydroamination reactions, iron-catalyzed hydroamination of unprotected primary aliphatic amines and unactivated alkenes has not been reported to date. Herein, a novel well-defined four-coordinate ?-diketiminatoiron(II) alkyl complex is shown to be an excellent precatalyst for the highly selective cyclohydroamination of primary aliphatic alkenylamines at mild temperatures (70-90?C). Both empirical kinetic analyses and the reactivity of an isolated iron(II) amidoalkene dimer, [LFe(NHCH2 CPh2 CH2 CH?CH2 )]2 favor a stepwise ?-insertive mechanism that entails migratory insertion of the pendant alkene into an iron-amido bond associated with a rate-determining aminolysis step. PMID:24692368

Bernoud, Elise; Ouli, Pascal; Guillot, Rgis; Mellah, Mohamed; Hannedouche, Jrme

2014-05-01

319

Influence of the ?-coordinated arene on the anticancer activity of ruthenium(II) carbohydrate organometallic complexes  

PubMed Central

The synthesis and in vitro cytotoxicity of a series of RuII(arene) complexes with carbohydrate-derived phosphite ligands and various arene co-ligands is described. The arene ligand has a strong influence on the in vitro anticancer activity of this series of compounds, which correlates fairly well with cellular accumulation. The most lipophilic compound bearing a biphenyl moiety and a cyclohexylidene-protected carbohydrate is the most cytotoxic with unprecedented IC50 values for the compound class in three human cancer cell lines. This compound shows reactivity to the DNA model nucleobase 9-ethylguanine, but does not alter the secondary structure of plasmid DNA, indicating that other biological targets are responsible for its cytotoxic effect.

Hanif, Muhammad; Meier, Samuel M.; Nazarov, Alexey A.; Risse, Julie; Legin, Anton; Casini, Angela; Jakupec, Michael A.; Keppler, Bernhard K.; Hartinger, Christian G.

2013-01-01

320

Coordination complexes as molecular glue for immobilization of antibodies on cyclic olefin copolymer surfaces.  

PubMed

A novel metal-based chelating method has been used to provide an order of magnitude increase in immunoassay performance on cyclic olefin copolymer (COC) plastics compared with passive binding. COCs are hydrophobic, and without surface modification they are often unsuitable for applications where protein adhesion is desired. When interacting with the bare plastic, the majority of the bound proteins will be denatured and become nonfunctional. Many of the surface modification techniques reported to date require costly equipment setup or the use of harsh reaction conditions. Here, we have successfully demonstrated the use of a simple and quick metal chelation method to increase the sensitivity, activity, and efficiency of protein binding to COC surfaces. A detailed analysis of the COC surfaces after activation with the metal complexes is presented, and the immunoassay performance was studied using three different antibody pairs. PMID:24721294

Ooi, Huey Wen; Cooper, Shaun J; Huang, Chang-Yi; Jennins, Dean; Chung, Emma; Maeji, N Joe; Whittaker, Andrew K

2014-07-01

321

Binding of molecular oxygen and alkenes to coordinatively unsaturated bipyridinium metal complexes in the gas phase  

NASA Astrophysics Data System (ADS)

Unsaturated metal complexes have vacant sites for binding and may promote insertion reactions. Rate coefficients were determined for the formation of adduct ions in ion-molecule reactions between M(bipy)22+ (M = Cr, Ru, or Os; bipy = bipyridine) and dioxygen, propane, ethene, propene, and 1-butene in the cell of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Together with estimated capture rate coefficients, these lead to efficiencies for adduct formation. Efficiencies for O2 adduct formation are small, which is indicative of a weak binding between the metal and dioxygen. The efficiency was independent of pressure, and consequently radiative emission must be responsible for cooling of the excited adducts, M(bipy)2(O2)2+*. The efficiency for addition of alkenes to Ru(bipy)22+ is higher. Reactions between Ru(bipy)2(alkene)2+ and alkene were investigated. In the case of ethene, simple addition occurred to give the Ru(bipy)2(ethene)22+ ion. In contrast, reactions with propene and 1-butene produced the ions Ru(bipy)2(C2H3)(alkene)2+ and Ru(bipy)2(C3H5)(alkene)2+ which are indicative of alkene activation. In the ion-molecule reaction between Ru(bipy)22+ and propene, a small abundance of the bis(allyl) complex, Ru(bipy)(allyl)22+, was also observed. The assignment of the products and elucidation of the detailed reaction mechanisms is based on collisional activation and supported by experiments with deuterium-labeled propene.

Nielsen, Steen Brndsted; iestad, se Marit L.; Bojesen, Gustav; Uggerud, Einar

2005-06-01

322

Dinuclear formation, oxygen atom transfer, and intramolecular coordination isomerization in oxotechnetium complexes  

SciTech Connect

Dinuclear, asymmetric and dissymmetric, mixed-valent (III-IV), {mu}-oxo complexes of technetium spontaneously form in both neat pyridine and pyridine solutions in dichlorobenzene from higher valent, mononuclear species, with which they reach an equilibrium. When (OX{sub 4}Tc{sup V}){sup {minus}} is used as the starting material and only the neat pyridine ligand is present, the formation of the dinuclear species is second-order in Tc{sup V} and occurs with concomitant production of pyridine N-oxide, indicating that oxygen atom transfer occurs in the technetium reduction process. K{sub eq} for the formation of the dinuclear species in picoline solution is 193 {plus minus} 8 M{sup {minus}1} with k = (1.46 {plus minus} 0.1) {times} 10{sup {minus}2} M{sup {minus}1} s{sup {minus}1}. The asymmetric and dissymmetric dinuclear species spontaneously interconvert. In o-dichlorobenzene, this process is first-order in chloride ion and requires a minimum concentration ({approximately}0.1 M) of the pyridine ligand to prevent decomposition of the dinuclear starting material. With picoline as the ligand, at 140{degree}C the reaction proceeds with a specific rate of (3.12 {plus minus} 0.08) {times} 10{sup {minus}3} M{sup {minus}1} s{sup {minus}1} to approach an equilibrium between the asymmetric and dissymmetric complexes with K{sub eq} = 2.83 {plus minus} 0.12. Activation parameters are {Delta}H* = 144 {plus minus} 2 kJ/mol and {Delta}S* = 53.5 {plus minus} 1 J/(mol K). Minor changes in the ligands generate marked differences in K{sub eq} and K{sub iso}.

Lu, Jun; Clarke, M.J. (Boston College, Chestnut Hill, MA (USA))

1988-12-28

323

Reversible switching of the coordination modes of a pyridine-functionalized quinonoid zwitterion; its di- and tetranuclear palladium complexes.  

PubMed

The coordination chemistry of a new functional quinonoid zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(?-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(?-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(?-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the [Pd(dmba)](+) moieties, from the NPy sites in 3, to the N,O donor sites of the quinonoid core in 4, respectively. This switch modifies the extent of ?-delocalization involving the potentially antiaromatic quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(?-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(?-L){Pd(dmba)}2(?-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2-5 and 7. PMID:24813619

Ghisolfi, Alessio; Waldvogel, Audrey; Routaboul, Lucie; Braunstein, Pierre

2014-06-01

324

Effect of High Pressure on Uranyl Nanocages  

NASA Astrophysics Data System (ADS)

Uranyl nanocages U24Py12, U60, and U24 were studied in situ at high pressure in order to understand the response of these structures to pressure. Single crystals of the nanocage structures were analyzed by in situ Raman spectroscopy, synchrotron X-ray diffraction and small angle X-Ray scattering in diamond anvil cells, as well as electrospray ionization mass spectrometry. At ambient pressure conditions, U24Py12 is tetragonal (P42/mnm: a = 22.746(2) , c = 30.426(4) ), U60 is isometric (Fm-3: a=37.884(2) ), and U24 is triclinic (P1-: a=19.2111(11), b=31.003(2), c=32.252(2), ?=102.404(4), ?=99.506(4) , ?=95.362(4) ). Pressures ranged from ambient to 50 GPa; single crystals less than 200 microns in diameter were used. Two symmetric stretch modes of the uranyl ion are evident in the Raman spectra of all three nanocages with Raman shifts of 810 and 830 cm-1. The modes are clearly evident at pressures ranging from ambient to 4-8 GPa. At pressures higher than this range, the uranyl ion vibrational mode broadens further and shifts to higher stretching frequencies. The signal for U60 is irreversibly lost at 17 GPa, but for U24 and U24Py12, the signal persists and continues to broaden at pressures up to 50 GPa. After pressure quenching, there was still no signal from the U60, but U24 and U24Py12 both show one broad Raman mode at 840 cm-1. High pressure synchrotron X-ray diffraction measurements were completed at Argonne National Laboratory to quantify structural unit cell changes over the pressure ranges investigated. U24Py12 undergoes a phase transition to higher symmetry at approximately 5 GPa, and eventually partially amorphizes at 17 GPa, irreversibly. U60 undergoes a phase transition from isometric to tetragonal at 4.4 GPa, and amorphizes irreversibly at 10 GPa. Small angle X-ray scattering measurements show that the cluster topology is maintained even after amorphization of U24Py12 and U60. Mass spectrometry data indicate that these clusters remain intact at high pressures, despite the loss of long-range periodicity. These experiments provide insight into the stability of different types of uranyl nanocages, as well the relation between cluster topology and stability with increasing pressure.

Turner, K. M.; Zhang, F.; Pellegrini, K.; McGrail, B. T.; Burns, P. C.; Ewing, R. C.

2013-12-01

325

Coordination of alkenes and alkynes to a cationic d(0) zirconocene alkoxide complex.  

PubMed

This paper describes the synthesis of base-free (C5R5)2Zr(OtBu)+ cations, the direct observation of nonchelated alkene and alkyne adducts of these cations, and studies of the thermodynamic and dynamic properties of these novel species. Reaction of %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%ZrMe%@sb@%2%@sbx@%%@mx@% (Cp' = C5H4Me) with tert-butyl alcohol followed by [Ph3C][B(C6F5)4] in benzene yields [%@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@mx@% ][B(C6F5)4] (1), which exists as %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%ClR%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% solvent adducts in C6D5Cl and CD2Cl2 solutions. Addition of ligands L (L = ethylene, propylene, propyne, 2-butyne, CO, phenylacetylene, allene, 1-hexene, cis-2-butene) to 1 in CD2Cl2 at -89 degrees C results in reversible formation of %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%L%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% adducts. NMR data for %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%H%@sb@%2%@sbx@%C=%@/bd@%CHMe%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% (4) indicate that the propylene coordinates unsymmetrically and is polarized with positive charge buildup at Cint. Equilibrium constants, defined by Keq = [Zr-L][1]-1[L]-1, vary in the order CO > propyne > 2-butyne > phenylacetylene > ethylene > allene > propylene > 1-hexene > cis-2-butene > vinyl chloride. Loss of L from %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%L%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% to give 1 appears to proceed via associative displacement by CD2Cl2 in most cases. PMID:12630871

Stoebenau, Edward J; Jordan, Richard F

2003-03-19

326

New near-wall models with dynamic subgrid scale closure for large eddy simulation in curvilinear coordinates for complex geometries  

NASA Astrophysics Data System (ADS)

This dissertation presents modifications and improvements to the dynamic subgrid scale model and introduces a new wall model. These are applied to the large eddy simulation technique in curvilinear coordinates. They are then validated and tested in three-dimensional complex geometries. The large eddy simulation method captures many scales of turbulence up to the grid size. A closure model is used to simulate subgrid turbulence. The Smagorinsky and dynamic subgrid models are presented and tested. The dynamic model overcomes many of the deficiencies of the Smagorinsky subgrid scale model. Spatial and temporal low-pass filters have been introduced in the dynamic subgrid scale model for numerical stability. No practical differences have been observed between the Smagorinsky and dynamic models. Several near-wall models are considered for the large eddy simulation technique. A local averaging technique makes these models applicable to complex geometries. A new model is introduced which overcomes planar averaging near the wall and captures ejection and sweep effects. Special treatment of inlet boundary conditions was introduced. These models have been implemented in a large eddy simulation computer program that uses a strongly conservative curvilinear coordinate formulation. The covariant projections are used as the dependent variables in a staggered methodology. The body fitted grids are advantageous in complex geometry descriptions. Results are validated in a lid driven cavity flow at Reynolds number of 10000. A single tube in a channel is simulated to show the applicability of the models to complex geometries with attachment and separation as well as end-wall effects. The shedding effect was captured and turbulence characteristics were acceptable. One million nodes were used in a large eddy simulation of a three-dimensional tube bundle at Reynolds number of 21700. Results are presented in the form of visualization and compared with available experimental data. The 'flapping' effect in the tube wake is captured. This dissertation shows the large eddy simulation technique may be used as a tool in predicting the unsteady behavior of flow in industrial applications.

Barsamian, Hagop Raffi

2000-10-01

327

Care coordination for children with complex special health care needs: the value of the advanced practice nurse's enhanced scope of knowledge and practice.  

PubMed

Efficiency and effectiveness of care coordination depends on a match between the needs of the population and the skills, scope of practice, and intensity of services provided by the care coordinator. Existing literature that addresses the relevance of the advanced practice nurse (APN) role as a fit for coordination of care for children with special health care needs (SHCN) is limited. The objective of this article is to describe the value of the APN's enhanced scope of knowledge and practice for relationship-based care coordination in health care homes that serve children with complex SHCN. The TeleFamilies project is provided as an example of the integration of an APN care coordinator in a health care home for children with SHCN. PMID:22560803

Looman, Wendy S; Presler, Elizabeth; Erickson, Mary M; Garwick, Ann W; Cady, Rhonda G; Kelly, Anne M; Finkelstein, Stanley M

2013-01-01

328

Tuberous sclerosis complex and Myc coordinate the growth and division of Drosophila intestinal stem cells  

PubMed Central

Intestinal stem cells (ISCs) in the adult Drosophila melanogaster midgut can respond to damage and support repair. We demonstrate in this paper that the tuberous sclerosis complex (TSC) plays a critical role in balancing ISC growth and division. Previous studies have shown that imaginal disc cells that are mutant for TSC have increased rates of growth and division. However, we report in this paper that loss of TSC in the adult Drosophila midgut results in the formation of much larger ISCs that have halted cell division. These mutant ISCs expressed proper stem cell markers, did not differentiate, and had defects in multiple steps of the cell cycle. Slowing the growth by feeding rapamycin or reducing Myc was sufficient to rescue the division defect. The TSC mutant guts had a thinner epithelial structure than wild-type tissues, and the mutant flies were more susceptible to tissue damage. Therefore, we have uncovered a context-dependent phenotype of TSC mutants in adult ISCs, such that the excessive growth leads to inhibition of division.

Amcheslavsky, Alla; Ito, Naoto; Jiang, Jin

2011-01-01

329

Low valent and hydride complexes of NHC coordinated gallium and indium.  

PubMed

The reactions of the N-heterocyclic carbene 1,3-dimesitylimidazol-2-ylidene (IMes) with Ga[GaCl(4)], "GaI", InCl(2) and GaBr(3) have been examined. All reactions using a low valent gallium or indium starting material led to species of the form [{MX(2)(IMes)}(2)], where M = Ga, X = Cl (1), I (2); M = In, X = Cl (3), with disproportionation and loss of gallium metal in the case of 2. Reaction of IMes with gallium tribromide yields the air and moisture stable complex [GaBr(3)(IMes)] (4), which has been used as a precursor to the mixed bromohydrides [GaBrH(2)(IMes)] (5) and [GaBr(2)H(IMes)] (6) by (i) ligand redistribution with [GaH(3)(IMes)], (ii) hydride-bromide exchange with triethylsilane, and (iii) alkylation with (n)butyllithium followed by ?-hydride elimination (6 only). Attempts to prepare 1, or monovalent analogues such as [{GaCl(IMes)}(n)], by thermally induced reductive elimination of dihydrogen from the chlorohydride congeners of 5 and 6 resulted in isolation of the known compounds [IMesCl][Cl] (IMesCl = 1,3-dimesityl-2-chloroimidazolium), and/or 1,3-dimesityl-2-dihydroimidazole, and gallium metal. Preliminary photochemical NMR spectroscopy and catalytic studies of 5 and 6 aimed at reductive dehydrogenation under milder conditions are reported. Compounds 1 and 4 have been characterised by single crystal X-ray structure determination. PMID:22080333

Ball, Graham E; Cole, Marcus L; McKay, Alasdair I

2012-01-21

330

Coordinated Regulation of Retinoic Acid Signaling Pathway by KDM5B and Polycomb Repressive Complex 2.  

PubMed

Polycomb repressive complex 2 (PRC2) is a critical epigenetic regulator in many biological processes, including maintenance of cell identity, stem cell self-renewal, differentiation, and deregulation of PRC2 is often observed in human cancers and diseases. Here we report that KDM5B (PLU-1/JARID1B), a histone lysine demethylase of Jumonji family, associates with PRC2 and colocalizes with PRC2 in nuclear bodies, and their physical association is dependent on direct interaction between KDM5B and the SUZ12 component of PRC2. Interestingly, co-occupancy of KDM5B and PRC2 was evidenced at the conserved cis-regulatory DNA element on retinoic acid (RA) responsive genes. Transcription readout and in vitro pull-down experiments suggest that KDM5B is an essential co-activator, but not a co-repressor, for the RA signaling, and the interface between KDM5B's JMJC domain and retinoic acid receptor ? (RAR?) is crucial for RA-mediated gene expression. Detailed chromatin immunoprecipitation assays addressed the seemingly paradox by revealing a biphasic effect of KDM5B on RA-induced gene activation through decoupled H3K4me3 demethylation and PRC2-antagonizing activities. These results demonstrate that KDM5B and PRC2 regulate RA signaling cascade in a cooperative and orchestrated fashion. J. Cell. Biochem. 115: 1528-1538, 2014. 2014 Wiley Periodicals, Inc. PMID:24619877

Zhang, Yu; Liang, Jing; Li, Qian

2014-09-01

331

Novel dimetal bridging carbene complexes derived from a terminal carbonyl dimetal compound. Syntheses, structures and reactivities of 7H-indene-coordinated diiron bridging carbene complexes.  

PubMed

Pentacarbonyl-7H-indenediiron, [Fe2(CO)5(eta3,eta5-C9H8)] (1), reacts with aryllithium, ArLi (Ar = C6H5, p-C6H5C6H4), followed by alkylation with Et3OBF4 to give novel 7H-indene-coordinated diiron bridging alkoxycarbene complexes [Fe2{mu-C(OC2H5)Ar}(CO)4(eta4,eta4-C9H8)] (2, Ar = C6H5; 3, Ar = p-C6H5C6H4). Complexes 2 and 3 react with HBF4.Et2O at low temperature to yield cationic bridging carbyne complexes [Fe2(mu-CAr)(CO)4(eta4,eta4-C9H8)]BF4 (4, Ar = C6H5; 5, Ar = p-C6H5C6H4). Cationic 4 and 5 react with NaBH4 in THF at low temperature to afford diiron bridging arylcarbene complexes [Fe2{mu-C(H)Ar}(CO)4(eta4,eta4-C9H8)] (6, Ar = C6H5; 7, Ar = p-C6H5C6H4). The similar reactions of 4 and 5 with NaSC6H4CH3-p produce the bridging arylthiocarbene complexes [Fe2{mu-C(Ar)SC6H4CH3-p}(CO)4(eta4,eta4-C9H8)] (8, Ar = C6H5; 9, Ar = p-C6H5C6H4). Cationic 4 and 5 can also react with anionic carbonylmetal compounds Na[M(CO)5(CN)] (M = Cr, Mo, W) to give the diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [Fe2{mu-C(Ar)NCM(CO)5}(CO)4(eta4,eta4-C9H8)] (10, Ar = C6H5, M = Cr; 11, Ar = p-C6H5C6H4, M = Cr; 12, Ar = C6H5, M = Mo; 13, Ar = p-C6H5C6H4, M = Mo; 14, Ar = C6H5, M = W; 15, Ar = p-C6H5C6H4, M = W). Interestingly, in CH2Cl2 solution at room temperature complexes 10-15 were transformed into the isomerized 7H-indene-coordinated monoiron complexes [Fe(CO)2(eta5-C9H8)C(Ar)NCM(CO)5] (16, Ar = C6H5, M = Cr; 17, Ar = p-C6H5C6H4, M = Cr; 18, Ar = C6H5, M = Mo; 19, Ar = p-C6H5C6H4, M = Mo; 20, Ar = C6H5, M = W; 21, Ar = p-C6H5C6H4, M = W), while complex 3 was converted into a novel ring addition product [Fe2{C(OC2H5)C6H4C6H5-p-(eta2,eta5-C9H8)}(CO)5] (22) under the same conditions. The structures of complexes 2, 6, 8, 14, 18 and 22 have been established by X-ray diffraction studies. PMID:16967119

Zhang, Lei; Sun, Jie; Zhu, Huping; Xu, Qiang; Tsumori, Nobuko; Chen, Jiabi

2006-09-28

332

Investigations of iron coordination and redox reactions in seawater using 59Fe radiometry and ion-pair solvent extraction of amphiphilic iron complexes  

Microsoft Academic Search

Hudson, R.J.M., Covault, D.T. and Morel, F.M.M., 1992. Investigations of iron coordination and redox reactions in seawater using 59Fe radiometry and ion-pair solvent extraction of amphiphilic iron complexes. Mar. Chem., 38: 209-235. Iron coordination and redox reactions in synthetic and coastal seawater were investigated at na- nomolar concentrations using 59Fe radiometry and ion-pair solvent extraction of iron chelated by sulfoxine

Robert J. M. Hudson; Dianne T. Covault; Francois M. M. Morel

1992-01-01

333

Complexation of Mercury(II) in Soil Organic Matter: EXAFS Evidence for Linear Two-Coordination with Reduced Sulfur Groups  

SciTech Connect

The chemical speciation of inorganic mercury (Hg) is to a great extent controlling biologically mediated processes, such as mercury methylation, in soils, sediments, and surface waters. Of utmost importance are complexation reactions with functional groups of natural organic matter (NOM), indirectly determining concentrations of bioavailable, inorganic Hg species. Two previous extended X-ray absorption fine structure (EXAFS) spectroscopic studies have revealed that reduced organic sulfur (S) and oxygen/nitrogen (O/N) groups are involved in the complexation of Hg(II) to humic substances extracted from organic soils. In this work, covering intact organic soils and extending to much lower concentrations of Hg than before, we show that Hg is complexed by two reduced organic S groups (likely thiols) at a distance of 2.33 Angstroms in a linear configuration. Furthermore, a third reduced S (likely an organic sulfide) was indicated to contribute with a weaker second shell attraction at a distance of 2.92-3.08 Angstroms. When all high-affinity S sites, corresponding to 20-30% of total reduced organic S, were saturated, a structure involving one carbonyl-O or amino-N at 2.07 Angstroms and one carboxyl-O at 2.84 Angstroms in the first shell, and two second shell C atoms at an average distance of 3.14 Angstroms, gave the best fit to data. Similar results were obtained for humic acid extracted from an organic wetland soil. We conclude that models that are in current use to describe the biogeochemistry of mercury and to calculate thermodynamic processes need to include a two-coordinated complexation of Hg(II) to reduced organic sulfur groups in NOM in soils and waters.

Skyllberg,U.; Bloom, P.; Qian, J.; Lin, C.; Bleam, W.

2006-01-01

334

Controlling Magnetism by Light in Nanoscaled Heterostructures of Cyanometallate Coordination Networks: the role of increased complexity  

NASA Astrophysics Data System (ADS)

Nanometer-sized heterostructures of the Prussian blue analogues AjCok[Fe(CN)6]l.nH2O (Co-Fe PBA, with A = K, Rb) and RbaNib[Cr(CN)6]c.mH2O (Ni-Cr PBA) have been investigated, and new phenomena, not observed for the constituent bulk phases, have been observed.footnotetext D.M. Pajerowski, M.J. Andrus, J.E. Gardner, E.S. Knowles, M.W. Meisel, D.R. Talham, J. Am. Chem. Soc. 132 (2010) 4058.^,footnotetext M.F. Dumont, E.S. Knowles, A. Guiet, D.M. Pajerowski, A. Gomez, S.W. Kycia, M.W. Meisel, D.R. Talham, Inorg. Chem. 50 (2011) 4295.^,footnotetext D.M. Pajerowski, J.E. Gardner, M.J. Andrus, S. Datta, A. Gomez, S.W. Kycia, S. Hill, D.R. Talham, M.W. Meisel, Phys. Rev. B 82 (2010) 214405.^,footnotetext E.S. Knowles, M.F. Dumont, M.K. Peprah, M.W. Meisel, C.H. Li, M.J. Andrus, D.R. Talham, arxiv:1207.2623 (2012). A crucial aspect of the ability to photocontrol the persistent magnetism up to 70 K is the role of the strain coupling present at the interfaces between the nanoscaled regions of the constituents. Increasing the morphological complexity of the samples has the potential to provide materials possessing novel combinations of properties. In parallel, the interplay between long-range magnetic order and structural coherence is an important consideration in our attempts to design new systems. Open, unresolved issues will be discussed, and potential future paths will be sketched.

Meisel, Mark W.

2013-03-01

335

Parahydrogen derived illumination of pyridine based coordination products obtained from reactions involving rhodium phosphine complexes.  

PubMed

The reactions of RhCl(PBz3)3 with H2 and pyridine or 4-methylpyridine yield RhCl(H)2(PBz3)2(py) and RhCl(H)2(PBz3)2(4-Me-py), respectively. These species undergo hydride site exchange via the loss of the pyridyl donor and formation of RhCl(H)2(PBz3)2 which contains equivalent hydride ligands; for the py system the activation free energy, deltaG++300, is 57.4 +/- 0.1 kJ mol(-1) while for 4-Me-py the value is 59.6 +/- 0.3 kJ mol(-1). These products only showed parahydrogen enhancement in the corresponding hydride resonances when a sacrificial substrate was added to promote hydrogen cycling. When RhCl(PPh3)3 was used as the precursor similar observations were made, while when RhCl(PCy3)2(C2H4) was examined, H2 addition led to the formation of the binuclear complex (H)2Rh(PCy3)2(micro-Cl)2Rh(H)2(PCy3)2 which was differentiated from RhCl(H)2(PCy3)2 on the basis of the similarity in diffusion coefficient (5.5 x 10(-9) m2 s(-1)) to that of (H)2Rh(PPh3)2(micro-Cl)2Rh(PPh3)2 (5.3 x 10(-9) m2 s(-1)). The detection of RhCl(H)2(PCy3)2(py) was facilitated when pyridine was added to a solution of RhCl(PCy3)2(C2H4) before the introduction of H2. During these reactions trace amounts of the double substitution products, RhCl(H)2(phosphine)(py)2, were also detected. PMID:16471059

Zhou, Rongrong; Aguilar, Juan A; Charlton, Adrian; Duckett, Simon B; Elliott, Paul I P; Kandiah, Rathika

2005-12-01

336

Photoinduced Intercalation and Coordination of a Dirhodium Complex to DNA: Dual DNA Binding.  

PubMed

Two new complexes, cis-H,H-[Rh2 (OCCH3 NH)2 (LL)(CH3 CN)2 ](2+) , where LL=bpy (2, bpy=2,2'-bipyridine) and dppz (3, dppz=dipyrido[3,2-a:2',3'-c]phenazine), were prepared from the reaction of cis-H,H-[Rh2 (OCCH3 NH)2 (CH3 CN)6 ](2+) (1) with the corresponding bidentate ligand. The bpy and dppz ligands chelate to the same rhodium atom and are positioned trans to the amidato N?atoms, as determined by the single crystal X-ray structure of 2. Irradiation of 2 and 3 with visible light in water results in the exchange of one CH3 CNeq ligand for an H2 O molecule with quantum yields, ?400 , of 0.040 and 0.044, respectively (?irr =400?nm). The identities of the photoproducts of 2 and 3 were determined to be cis-H,H-[Rh2 (OCCH3 NH)2 (L)(H2 O)(CH3 CN)](2+) , where L is bpy (4) and dppz (5), respectively. Mobility shift assays show that 4 crosslinks double-stranded DNA, and ESI-MS experiments indicate that both 4 and 5 form covalent adducts with single-stranded DNA. In addition, relative viscosity and 2D?NMR experiments show that the dppz ligand of 5 also intercalates into DNA upon irradiation, making 3 a dual-binding agent that both intercalates and covalently binds to DNA upon the absorption of visible light. PMID:24753463

Palmer, Alycia M; Burya, Scott J; Gallucci, Judith C; Turro, Claudia

2014-06-01

337

Dinitrogen cleavage by three-coordinate molybdenum(III) complexes: Mechanistic and structural data  

SciTech Connect

The synthesis and characterization of the complexes Mo[N(R)Ar]{sub 3} (R = C(CD{sub 3}){sub 2}CH{sub 3}, Ar = 3.5-C{sub 6}H{sub 3}Me{sub 2}), ({mu}-N{sub 2})[C@Mo[N(R)Ar]{sub 3}]C{sub 2}, ({mu}-{sup 15}N{sub 2})[C@Mo[N(R)Ar]{sub 3}]C{sub 2}, NMo[N(R)Ar]{sub 3}, {sup 15}NMo[N(R)Ar]{sub 3}, Mo[N(t-Bu)Ph]{sub 3}, ({mu}-N{sub 2})[C@Mo[N(t-Bu)Ph]{sub 3}]C{sub 2}, and NMo[N(t-Bu)Ph]{sub 3} are described. Temperature-dependent magnetic susceptibility data indicate a quartet ground state for Mo[N(R)Ar]{sub 3}. Single-crystal X-ray diffraction studies for Mo[N(R)Ar]{sub 3} and NMo[N(t-Bu)Ph]{sub 3} are described. Extended X-ray absorption fine structure (EXAFS) structural studies for Mo[N(R)Ar]{sub 3}({mu}-N{sub 2})[C@Mo[N(R)Ar]{sub 3}] RTBC{sub 2}, and NMo[N(R)Ar]{sub 3} are reported. Temperature-dependent kinetic data are given for the unimolecular fragmentation of ({mu}-N{sub 2})[C@Mo[N(R)Ar]{sub 3}]{sub 2} to 2 equiv of NMo[N(R)Ar]{sub 3} and for the fragmentation of ({mu}-{sup 15}N{sub 2})[C@Mo[N(R)Ar]{sub 3}]{sub 2} to 2 equiv of {sup 15}NMo[N(R)Ar]{sub 3}. The temperature dependence of the {sup 15}N{sub 2} isotope effect for the latter N{sub 2} cleavage process was fitted to a simple harmonic model, leading to a prediction for the difference in NN stretching frequencies for the two isotopomers. 35 refs., 14 figs., 2 tabs.

Laplaza, C.E.; Johnson, M.J.A.; Peters, J.C.; Odom, A.L.; Kim, E.; Cummins, C.C. [Massachusetts Inst. of Technology, Cambridge, MA (United States)] [Massachusetts Inst. of Technology, Cambridge, MA (United States); George, G.N.; Pickering, I.J. [Stanford Univ., CA (United States)] [Stanford Univ., CA (United States)

1996-09-11

338

Yttrium and lanthanide complexes of ?-dialdehydes: synthesis, characterization, luminescence and electrochemistry of coordination compounds with the conjugate base of bromomalonaldehyde.  

PubMed

Novel yttrium, europium and terbium coordination compounds having formulae [AsPh4][Ln(BrMA)4] (), Ln(BrMA)3(bipyO2) (), Ln(NMA)3(phen) () and Ln(NMA)3(terpy) () (Ln = Y, Eu, Tb; BrMA = conjugate base of bromomalonaldehyde; bipyO2 = 2,2'-bipyridine-N,N'-dioxide; phen = 1,10-phenantroline; terpy = 2,2':6',2''-terpyridine) were synthesized and characterized by using spectroscopic and electrochemical techniques. Uncharged europium and, to a lesser extent, terbium complexes showed appreciable luminescence in the solid state upon excitation with UV light. Polymeric materials and ionic liquids containing BrMA and lanthanides were prepared and photoluminescence measurements were carried out. From an electrochemical point of view, europium(iii) BrMA-complexes showed a quasi-reversible one-electron reduction process. The one electron transfer reaction Eu(iii) to Eu(ii) allowed the photoluminescence tuning of deposited on the surface of a glassy carbon electrode. PMID:24819039

Bortoluzzi, Marco; Battistel, Dario; Roppa, Stefania; Daniele, Salvatore; Perosa, Alvise; Enrichi, Francesco

2014-05-28

339

Cdk1 Coordinates Timely Activation of MKlp2 Kinesin with Relocation of the Chromosome Passenger Complex for Cytokinesis.  

PubMed

The chromosome passenger complex (CPC) must relocate from anaphase chromosomes to the cell equator for successful cytokinesis. Although this landmark event requires the mitotic kinesin MKlp2, the spatiotemporal mechanistic basis remains elusive. Here, we show that phosphoregulation of MKlp2 by the mitotic kinase Cdk1/cyclin B1 coordinates proper mitotic transition with CPC relocation. We identified multiple Cdk1/cyclin B1 phosphorylation sites within the stalk and C-terminal tail that inhibit microtubule binding and bundling, oligomerization/clustering, and chromosome targeting ofMKlp2. Specifically, inhibition of these abilities byCdk1/cyclin B1 phosphorylation is essential for proper early mitotic progression. Upon anaphase onset, however, reversal of Cdk1/cyclin B1 phosphorylation promotes MKlp2-CPC complex formation and relocates the CPC from anaphase chromosomes for successful cytokinesis. Thus, we propose that phosphoregulation of MKlp2 by Cdk1/cyclin B1ensures that activation of MKlp2 kinesin and relocation of the CPC occur at the appropriate time and space for proper mitotic progression and genomic stability. PMID:24656812

Kitagawa, Mayumi; Fung, Suet Yin Sarah; Hameed, Umar Farook Shahul; Goto, Hidemasa; Inagaki, Masaki; Lee, Sang Hyun

2014-04-10

340

Radical generating coordination complexes as tools for rapid and effective fragmentation and fluorescent labeling of nucleic acids for microchip hybridization.  

SciTech Connect

DNA microchip technology is a rapid, high-throughput method for nucleic acid hybridization reactions. This technology requires random fragmentation and fluorescent labeling of target nucleic acids prior to hybridization. Radical-generating coordination complexes, such as 1,10-phenanthroline-Cu(II) (OP-Cu) and Fe(II)-EDTA (Fe-EDTA), have been commonly used as sequence nonspecific 'chemical nucleases' to introduce single-strand breaks in nucleic acids. Here we describe a new method based on these radical-generating complexes for random fragmentation and labeling of both single- and double-stranded forms of RNA and DNA. Nucleic acids labeled with the OP-Cu and the Fe-EDTA protocols revealed high hybridization specificity in hybridization with DNA microchips containing oligonucleotide probes selected for identification of 16S rRNA sequences of the Bacillus group microorganisms.We also demonstrated cDNA- and cRNA-labeling and fragmentation with this method. Both the OP-Cu and Fe-EDTA fragmentation and labeling procedures are quick and inexpensive compared to other commonly used methods. A column-based version of the described method does not require centrifugation and therefore is promising for the automation of sample preparations in DNA microchip technology as well as in other nucleic acid hybridization studies.

Kelly, J. J.; Chernov, B. N.; Mirzabekov, A. D.; Bavykin, S. G.; Biochip Technology Center; Northwestern Univ.; Engelhardt Inst. of Molecular Biology

2002-01-01

341

Significant Influence of Coligands Toward Varying Coordination Modes of 2,2'-Bipyridine-3,3'-diol in Ruthenium Complexes.  

PubMed

The varying coordination modes of the ambidentate ligand 2,2'-bipyridine-3,3'-diol (H2L) in a set of ruthenium complexes were demonstrated with special reference to the electronic features of the coligands, including ?-donating acac(-) (= acetylacetonate) in Ru(III)(acac)2(HL(-)) (1), strongly ?-accepting pap (= 2-phenylazopyridine) in Ru(II)(pap)2(L(2-)) (2)/[(pap)2Ru(II)(?-L(2-))Ru(II)(pap)2](ClO4)2 ([4](ClO4)2), and reported moderately ?-accepting bpy (= 2,2'-bypiridine) in [Ru(II)(bpy)2(HL(-))]PF6 ([5]PF6)/[(bpy)2Ru(?-L(2-))Ru(bpy)2](PF6)2 ([7](PF6)2). The single-crystal X-ray structures reveal that, in paramagnetic and electron paramagnetic resonance active 1 and reported diamagnetic [5]PF6, nearly planar monoanionic HL(-) coordinates to the metal ion via the N,N donors forming a five-membered chelate ring with hydrogen-bonded O-HO function at the backbone of the ligand framework, as has also been reported in other metal complexes. However, structurally characterized diamagnetic 2 represents O(-),O(-) bonded seven-membered chelate of fully deprotonated but twisted L(2-). The nonplanarity of the coordinated L(2-) in 2 does not permit the second metal fragment {Ru(pap)2} or {Ru(bpy)2} or {Ru(acac)2} to bind with the available N,N donors at the back face of L(2-). Further, the deprotonated form of the model ligand 2,2'-biphenol (H2L') yields Ru(II)(pap)2(L'(2-)) (3); its crystal structure establishes the expected O(-),O(-) bonded seven-membered chelate of nonplanar L'(2-) as in reported Ru(II)(bpy)2(L'(2-)) (6), although {Ru(acac)2} metal precursor altogether fails to react with H2L'. All attempts to make diruthenium complex from {Ru(acac)2} and H2L failed; however, the corresponding {Ru(pap)2(2+)} derived dimeric [4](ClO4)2 was structurally characterized. It establishes the symmetric N,O(-)/N,O(-) bridging mode of nonplanar L(2-) as in reported [7](PF6)2. Besides structural and spectroscopic characterization of the newly developed complexes, the ligand (HL(-), L(2-), L'(2-), pap)-, metal-, or mixed metal-ligand-based accessible redox processes in 1(n) (n = +2, +1, 0, -1), 2(n)/3(n) (n = +2, +1, 0, -1, -2), and 4(n) (n = +4, +3, +2, +1, 0, -1) were analyzed in conjunction with density functional theory calculations. PMID:24853947

Ghosh, Prabir; Mondal, Prasenjit; Ray, Ritwika; Das, Ankita; Bag, Sukdev; Mobin, Shaikh M; Lahiri, Goutam Kumar

2014-06-16

342

Liquid-liquid extraction of uranyl by an amide ligand: interfacial features studied by MD and PMF simulations.  

PubMed

We report a molecular dynamics study of biphasic systems involved in the liquid-liquid extraction of uranyl nitrate by a monoamide ligand (L = N,N-di(2-ethylhexyl)isobutyramide, DEHiBA) to hexane, from pH neutral or acidic (3 M nitric acid) aqueous solutions. We first describe the neat interfaces simulated with three electrostatic models, one of which including atomic polarizabilities. The free energy profiles for crossing the water/hexane interface by L or its UO2(NO3)2L2 complex are then investigated by PMF (potential of mean force) calculations. They indicate that the free ligand and its complex are surface active. With the polarizable force field, however, the complexes have a lower affinity for the interface than without polarization. When DEHiBA gets more concentrated and in acidic conditions, their surface activity diminishes. Surface activity of UO2(NO3)2L2 complexes is further demonstrated by demixing simulations of randomly mixed DEHiBA, hexane, and neutral or acidic water. Furthermore, demixing of randomly mixed solvents, L molecules, UO2(NO3)2 salts, and nitric acid shows in some cases complexation of L to form UO2(NO3)2L2 and UO2(NO3)2L complexes that adsorb at the aqueous interfaces. These features suggest that uranyl complexation by amide ligands occurs "right at the interface", displaying marked analogies with the liquid-liquid extraction of uranyl by TBP (tri-n-butyl phosphate). Regarding the positive effect of nitric acid on extraction, the simulations point to several facets involving enhanced ion pairing of uranyl nitrate, decreased affinity of the complex for the interface, and finally, stabilization of the complex in the organic phase. PMID:23746355

Benay, G; Wipff, G

2013-06-20

343

Uranyl Incorporation in Organic-Bearing Soil Calcite  

NASA Astrophysics Data System (ADS)

Phosphor imaging and fission track maps reveal a close correlation between uranium and organic-rich calcite that lines roots in an ancient caliche soil. Concordant U-Pb ages show that this uranium has not been mobilized since the soil calcite formed 298 1 Ma ago. Luminescence spectroscopic analysis of the organic-rich calcite demonstrates that uranium is present in the oxidized state. More or less comparable luminescence spectra were collected using a CW lamp at room temperature and at liquid nitrogen (LN2) temperature. Spectra for inorganic U species are generally greatly enhanced at liquid nitrogen temperatures over room temperature and thus the similarity may suggest that the U is bound to organic matter. UV-excitation Raman spectroscopy of the calcite samples reveals a vibrational signature that is, in addition to the calcite peaks, essentially identical to that of sodium humate, acquired under similar conditions and consistent with those reported previously for humate substances. Since these spectra are dominated by the carbon backbone structure, the persistence of a carbon backbone structure is noted, but persistence of the ligating functional groups cannot be proven directly. We suggest that this sample records a snapshot of the process of uranium complexation with organic acids in natural systems. In our model organic acids with active functional groups that complex uranyl are sorbed onto the calcite surface and then incorporated as humate into the mineral with further calcite precipitation. Further, the uranyl complex is preserved through near-surface reducing conditions and temperatures to the conditions associated with 2700 meters burial depths. These combined observations suggest that the encapsulating calcite not only prevents reduction of uranium in the surface environment, but also inhibits the breakdown of the humate with burial. Due to the long time scale of immobilization of uranium, evidenced by the age of the calcite, this study has profound implications for understanding sampling for U-series and U-Pb dating of carbonates as well as for developing strategies for nuclear waste management. This study also has implications for any other deposits where uranium is associated with organic matter.

Rasbury, E.; Tait, C.; Donohoe, R. J.

2003-12-01

344

Coordination effects on electron distributions for rhodium complexes of the redox-active bis(3,5-di-tert-butyl-2-phenolate)amide ligand.  

PubMed

New rhodium complexes of bis(3,5-di-tert-butyl-2-phenol)amine ([ONO(cat)]H(3)) were synthesized, and their electronic properties were investigated. These compounds were prepared by combining [ONO(q)]K and [(cod)Rh(?-Cl)](2) in the presence of an auxiliary donor ligand to yield complexes of the type [ONO]RhL(n) (n = 3, L = py (1); n = 2, L = PMe(3) (2a), L = PMe(2)Ph (2b), PMePh(2) (2c), PPh(3) (2d)). Single-crystal X-ray diffraction studies on [ONO]Rh(py)(3) (1) revealed a six-coordinate, octahedral rhodium complex. In the case of [ONO]Rh(PMe(3))(2) (2a), X-ray diffraction showed a five-coordinate, distorted square-pyramidal coordination environment around the rhodium center. While 1 is static on the NMR time scale, complexes 2a-d are fluxional, displaying both rapid isomerization of the square-pyramidal structure and exchange of coordinated and free phosphine ligands. UV-vis spectroscopy shows stark electronic differences between 1 and 2a-d. Whereas 1 displays a strong absorbance at 380 nm with a much weaker band at 585 nm in the absorption spectrum, complexes 2a-d display an intense (? > 10(4) M(-1) cm(-1)), low-energy absorption band in the region 580-640 nm; however, in the cases of 2a and 2b, the addition of excess phosphine resulted in changes to the UV-vis spectrum indicating the formation of six-coordinate adducts [ONO]Rh(PMe(3))(3) (3a) and [ONO]Rh(PMe(2)Ph)(3) (3b), respectively. The experimental and DFT computational data for the six-coordinate complexes 1, 3a, and 3b are consistent with their formulation as classical, d(6), pseudo-octahedral, coordination complexes. In the five-coordinate complexes 2a-2d, ?-bonding between the rhodium center and the [ONO] ligand leads to a high degree of covalency and metal-ligand electron distributions that are not accurately described by formal oxidation state assignments. PMID:22482509

Szigethy, Gza; Shaffer, David W; Heyduk, Alan F

2012-12-01

345

Coordination chemistry of phosphanyl amino acids: solid state and solution structures of neutral and cationic rhodium complexes.  

PubMed

Copper phosphide or arsenide complexes, [Cu(EPh(2))(neo)] (E = P, As, neo = 2,9-dimethyl-1,10-phenanthroline; trivial name: neocuprine) react selectively with the N-protected brominated serine derivatives, 2-(S)-(alkoxycarbonylamino)-3-bromomethylpropionates ((ROCO)SerBr, : R = PhCH(2), : tBu, : Me) to give the corresponding phosphanylated or arsanylated amino acids, (ROCO)SerPhos (: Phos = PPh(2)) and (Z)SerArs (Ars = AsPh(2), Z = PhCH(2)OCO). The dipeptide (Z)AlaSerPhos was likewise prepared. The phosphanes , and the arsane reacted cleanly with [Rh(2)(micro-Cl)(2)(cod)(2)] to give the rhodium(I) complexes [RhCl(cod)((Z)SerPhos)] , [RhCl(cod)((Boc)SerPhos)] (Boc = tBuOCO), [RhCl(cod)((Z)AlaSerPhos)] , and [RhCl(cod)((Z)SerArs)] which were characterized by X-ray diffraction studies. A common structural feature is an intramolecular (N)H[dot dot dot]Cl(Rh)-hydrogen bridge which according to NMR investigations remains intact in solution. The abstraction of chloride from the coordination sphere of Rh(I) in or has a profound structural impact. While in and , the ligands bind in a monodentate fashion, via the phosphorus atom only, they serve as bidentate ligands via the phosphorus centre and the peptidic C=O group in [Rh(cod)(kappa(2)-(Z)SerPhos)]PF(6) and [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6). This causes also the amino acid residue structures to change from alpha-helix type in and to a beta-sheet type in both. Addition of chloride to and fully re-establishes the structures of both. The complexes [RhCl(cod)((Z)SerPhos)] and [RhCl(cod)((Boc)SerPhos)] show good activities in homogeneously catalyzed hydrogenations of olefins while the dipeptide complex is less active. Phosphane addition to greatly diminishes the catalytic activity. The cationic complex [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6) shows low activity which, however, is greatly increased by addition of one equivalent of phosphane. PMID:16357969

Meyer, Christian; Scherer, Markus; Schnberg, Hartmut; Regger, Heinz; Loss, Sandra; Gramlich, Volker; Grtzmacher, Hansjrg

2006-01-01

346

Solvent-mediated crystal-to-crystal interconversion between discrete lanthanide complexes and one-dimensional coordination polymers and selective sensing for small molecules.  

PubMed

Two isostructural 1D coordination polymers {[Ln(OAc)2(H2O)(OBPT)]3H2O}n (HOBPT = 4,6-bis(2-pyridyl)-1,3,5-triazin-2-ol, Ln = Eu(3+), 1; Tb(3+), 3) and two discrete complexes [Ln(OAc)2(DMF)2(OBPT)] (Ln = Eu(3+), 2; Tb(3+), 4) have been synthesized in H2O-MeOH or DMF solvents, respectively. Their structures were identified by powder X-ray diffraction. Single-crystal X-ray studies for complexes 1 and 2 revealed that the coordination geometries of the Eu(3+) ions are similar and can be described as a distorted tricapped trigonal prism with six oxygen atoms and three nitrogen atoms. The difference between them is that one aqua ligand and one oxygen atom from the OBPT ligand complete the coordination sphere in complex 1, whereas two DMF molecules complete the coordination sphere in complex 2. Interestingly, the solvent-mediated, reversible crystal-to-crystal transformation between them was achieved by immersing the crystalline samples in the corresponding solvent (H2O or DMF) or by exposing them to solvent vapor. Complex 1 shows a highly selective luminescence enhancement in response to DMF in comparison to that observed in response to other examined solvents such as acetone, ethyl acetate, ethanol, acetonitrile, methanol, and THF. PMID:23697967

Wu, Jin-Ji; Ye, Yu-Xin; Qiu, Ying-Yu; Qiao, Zheng-Ping; Cao, Man-Li; Ye, Bao-Hui

2013-06-01

347

Synthesis and structural characterization of a new heterobimetallic coordination complex of barium and cobalt for use as a precursor for chemical vapor deposition.  

PubMed

Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex. PMID:16323901

Tahir, Asif A; Molloy, Kieran C; Mazhar, Muhammad; Kociok-Khn, Gabriele; Hamid, Mazhar; Dastgir, Sarim

2005-12-12

348

Assessment of accidental intakes of uranyl acetylacetonate (UAA)  

SciTech Connect

Uranyl acetylacetonate (UAA) is an organic complex of uranium used for military applications as a chemical catalyst in high explosives. It is prepared from depleted uranium metal (in lots of 5 kg to 7 kg) by dissolution in nitric acid, neutralization, and complexation with 2,4-pentanedione; the precipitate is dissolved in benzene and recrystallized, dried, ground, and packaged. About six workers at a small chemical company were exposed over a period of time to UAA powders during routine preparation and packaging of the uranium catalyst. The dissolution characteristics of the inhaled material were unknown and could not be determined from the published scientific literature. A 1.05-g sample of UAA powder was obtained from the responsible regulatory authority for further study to determine its chemical composition, and for dissolution in simulated lung fluid. We found the solubility of UAA to be equivalent to a mixture of 52% ICRP class D and 48% ICRP class W material. The annual limit on intake and the derived air concentration for radiological protection were estimated from this result for airborne exposure to UAA. A recycling biokinetic model was used to estimate both material-specific variations in urinary excretion rates and lung retention with time after accidental intakes. This study provides new information for evaluating future exposures to UAA.

Fisher, D.R.; Briant, J.K.

1993-12-01

349

Spectrophotometric determination of uranium through uranyl/azide system  

SciTech Connect

An alternative method for the determination of uranium has been established by spectrophotometry. The procedure is based on the products of reaction between uranyl and azide ions (excess). This system furnishes yellowish complexes and the reaction was explored in water-acetonitrile medium (60% v/v), at 311 m. The resulting solution has a good stability and precision of measurements about 0.4% (standard deviation). The system obeys the Beer`s law over concentration range from 5.0 to 40 ppm. The molar absorptivity and Sandell`s sensitivity of the complexes are 9.23 x 10{sup 3} 1 mol{sup -1}cm{sup -1} and 0.0292 {mu}g cm{sup -2}, respectively. Effect of some diverse ions has been studied and several anions and cations do not interfere. The method was tested for a natural sample (uraninite), after different carbonate treatments. The results for uranium were compared with a conventional spectrophotometric (arsenazo) and inductively coupled plasma (ICP) methods. The possibility of the simultaneous spectrophotometric determination of uranium(VI) and iron(III) was also verified. This methodology showed good accuracy, precision, selectivity and simplicity.

Carmo, D.R. do; Andrade, J.F. de [FFCLRP-USP, Ribeirao Preto (Brazil); Guimaraes, O.M. [UFPR, Curitiba (Brazil)

1995-07-01

350

Interaction of uranyl with calcite in the presence of EDTA.  

PubMed

Adsorption of uranyl at the surface of calcite was investigated by using batch sorption experiments and synchrotron X-ray standing wave (XSW) measurements. Aqueous solutions containing 236U(VI) (4.5 x 10(-7) to 1.0 x 10(-4) M) and EDTA (5.0 x 10(-7) to 1.1 x 10(-4) M) were reacted for 90 s to 60 min with freshly cleaved calcite (104) surfaces and calcite powders. Surface exchange coefficients, sorption kinetics, and influence of powder surface area/solution volume (SA/V) ratio were investigated by alpha-counting of 236U. Powder sorption results at SA/V = 870 cm2/mL fit a Freundlich isotherm [log [U]surface (in monolayers) = log K + n log [U]aq (in moles/L)], where K = 1.9+/-0.5 and n = 0.9+/-0.1, consistent with uptake of U(VI) by a specific surface reaction where the availability of sorption sites is nonlimiting in the U concentration range measured. Measured U(VI) coverages along this isotherm, based on the calcite (104) surface Ca site density, ranged from 0.04% to 5.4% of a monolayer. Steady state surface coverages were obtained within 90 s. Sorption of U(VI) on calcite (104) single-crystal cleavage surfaces using identical solutions yielded higher coverages, because of increased step density induced by dissolution at the relatively low SA/V ratio (approximately 1) of these measurements. The crystallographic location of the sorbed U(VI) was examined with the synchrotron XSW technique. Measurements were performed at the Advanced Photon Source on fresh calcite (104) cleavage surfaces reacted for 90 s with U(VI) solutions. Coherent fractions for sorbed U ranged from 0.14 to 0.62, and the mean value of the U coherent position was 0.84+/-0.02. This position was independent of dissolved U(VI) concentration and corresponds to a distance between the U atom and the calcite (104) plane of 2.55+/-0.06 A. These results are consistent with U(VI) adsorption atthe calcite surface as an inner-sphere uranyl-carbonate surface complex bonded with the outer oxygen atom(s) of a single surface carbonate group. Steric considerations allow this observed U(VI) surface complex to occur both at step sites ((441)_ and (481)_) and on terrace areas adjacent to Ca vacancies. PMID:15506202

Rihs, Sophie; Sturchio, Neil C; Orlandini, Kent; Cheng, Likwan; Teng, Henry; Fenter, Paul; Bedzyk, Michael J

2004-10-01

351

Different coordination behavior of a catechol phosphine and its sulfide: Formation of an unprecedented dinuclear rhodium complex with a non-coordinated P S unit  

Microsoft Academic Search

Sulfurization of 3-[(diphenylphosphinyl)methyl]benzene-1,2-diol 1 produced phosphine sulfide 3. Both ligands reacted easily to form gold(I) and rhodium(I) complexes which were characterized by analytical and spectroscopic data, and single-crystal X-ray diffraction studies. Whereas the phosphine prefers to form complexes with a metal-to-ligand ratio of 1:2 with both metals, the phosphine sulfide exhibits a reduced donor power and yields only a 1:1

Gernot Bauer; Cornelia Englert; Martin Nieger; Dietrich Gudat

2011-01-01

352

A complex regulatory network coordinating cell cycles during C. elegans development is revealed by a genome-wide RNAi screen.  

PubMed

The development and homeostasis of multicellular animals requires precise coordination of cell division and differentiation. We performed a genome-wide RNA interference screen in Caenorhabditis elegans to reveal the components of a regulatory network that promotes developmentally programmed cell-cycle quiescence. The 107 identified genes are predicted to constitute regulatory networks that are conserved among higher animals because almost half of the genes are represented by clear human orthologs. Using a series of mutant backgrounds to assess their genetic activities, the RNA interference clones displaying similar properties were clustered to establish potential regulatory relationships within the network. This approach uncovered four distinct genetic pathways controlling cell-cycle entry during intestinal organogenesis. The enhanced phenotypes observed for animals carrying compound mutations attest to the collaboration between distinct mechanisms to ensure strict developmental regulation of cell cycles. Moreover, we characterized ubc-25, a gene encoding an E2 ubiquitin-conjugating enzyme whose human ortholog, UBE2Q2, is deregulated in several cancers. Our genetic analyses suggested that ubc-25 acts in a linear pathway with cul-1/Cul1, in parallel to pathways employing cki-1/p27 and lin-35/pRb to promote cell-cycle quiescence. Further investigation of the potential regulatory mechanism demonstrated that ubc-25 activity negatively regulates CYE-1/cyclin E protein abundance in vivo. Together, our results show that the ubc-25-mediated pathway acts within a complex network that integrates the actions of multiple molecular mechanisms to control cell cycles during development. PMID:24584095

Roy, Sarah H; Tobin, David V; Memar, Nadin; Beltz, Eleanor; Holmen, Jenna; Clayton, Joseph E; Chiu, Daniel J; Young, Laura D; Green, Travis H; Lubin, Isabella; Liu, Yuying; Conradt, Barbara; Saito, R Mako

2014-05-01

353

Coordinated rearrangements between cytoplasmic and periplasmic domains of the membrane protein complex ExbB-ExbD of Escherichia coli.  

PubMed

Gram-negative bacteria rely on the ExbB-ExbD-TonB system for the import of essential nutrients. Despite decades of research, the stoichiometry, subunit organization, and mechanism of action of the membrane proteins of the Ton system remain unclear. We copurified ExbB with ExbD as an ?240kDa protein-detergent complex, measured by light scattering and by native gels. Quantitative Coomassie staining revealed a stoichiometry of ExbB4-ExbD2. Negative stain electron microscopy and 2D analysis showed particles of ?10nm diameter in multiple structural states. Nanogold labeling identified the position of the ExbD periplasmic domain. Random conical tilt was used to reconstruct the particles in three structural states followed by sorting of the single particles and refinement of each state. The different states are interpreted by coordinated structural rearrangements between the cytoplasmic domain and the periplasmic domain, concordant with invivo predictions. PMID:24657092

Sverzhinsky, Aleksandr; Fabre, Lucien; Cottreau, Andrew L; Biot-Pelletier, Damien M P; Khalil, Sofia; Bostina, Mihnea; Rouiller, Isabelle; Coulton, James W

2014-05-01

354

Arf6 coordinates actin assembly through the WAVE complex, a mechanism usurped by Salmonella to invade host cells  

PubMed Central

ADP ribosylation factor (Arf) 6 anchors to the plasma membrane, where it coordinates membrane trafficking and cytoskeleton remodelling, but how it assembles actin filaments is unknown. By reconstituting membrane-associated actin assembly mediated by the WASP family veroprolin homolog (WAVE) regulatory complex (WRC), we recapitulated an Arf6-driven actin polymerization pathway. We show that Arf6 is divergent from other Arf members, as it was incapable of directly recruiting WRC. We demonstrate that Arf6 triggers actin assembly at the membrane indirectly by recruiting the Arf guanine nucleotide exchange factor (GEF) ARNO that activates Arf1 to enable WRC-dependent actin assembly. The pathogen Salmonella usurped Arf6 for host cell invasion by recruiting its canonical GEFs EFA6 and BRAG2. Arf6 and its GEFs facilitated membrane ruffling and pathogen invasion via ARNO, and triggered actin assembly by generating an Arf1WRC signaling hub at the membrane in vitro and in cells. This study reconstitutes Arf6-dependent actin assembly to reveal a mechanism by which related Arf GTPases orchestrate distinct steps in the WRC cytoskeleton remodelling pathway.

Humphreys, Daniel; Davidson, Anthony C.; Hume, Peter J.; Makin, Laura E.; Koronakis, Vassilis

2013-01-01

355

Coordinated control of senescence by lncRNA and a novel T-box3 co-repressor complex  

PubMed Central

Cellular senescence is a crucial tumor suppressor mechanism. We discovered a CAPER?/TBX3 repressor complex required to prevent senescence in primary cells and mouse embryos. Critical, previously unknown roles for CAPER? in controlling cell proliferation are manifest in an obligatory interaction with TBX3 to regulate chromatin structure and repress transcription of CDKN2A-p16INK and the RB pathway. The IncRNA UCA1 is a direct target of CAPER?/TBX3 repression whose overexpression is sufficient to induce senescence. In proliferating cells, we found that hnRNPA1 binds and destabilizes CDKN2A-p16INK mRNA whereas during senescence, UCA1 sequesters hnRNPA1 and thus stabilizes CDKN2A-p16INK. Thus CAPER?/TBX3 and UCA1 constitute a coordinated, reinforcing mechanism to regulate both CDKN2A-p16INK transcription and mRNA stability. Dissociation of the CAPER?/TBX3 co-repressor during oncogenic stress activates UCA1, revealing a novel mechanism for oncogene-induced senescence. Our elucidation of CAPER? and UCA1 functions in vivo provides new insights into senescence induction, and the oncogenic and developmental properties of TBX3. DOI: http://dx.doi.org/10.7554/eLife.02805.001

Kumar P, Pavan; Emechebe, Uchenna; Smith, Richard; Franklin, Sarah; Moore, Barry; Yandell, Mark; Lessnick, Stephen L; Moon, Anne M

2014-01-01

356

Separation performance of cucurbit[8]uril and its coordination complex with cadmium (II) in capillary gas chromatography.  

PubMed

Here we report the investigation of using cucurbit[8]uril (CB8) and its coordination complex with cadmium (II) (CB8-Cd) as stationary phases for capillary gas chromatography (GC). The prepared capillary columns of CB8 and CB8-Cd stationary phases achieved column efficiency of 2200plates/m and 1508plates/m, respectively, and showed weak polarity based on the measured McReynolds constants. Their separation performance was investigated by GC separation of mixtures of different types while a commercial column was used for comparison. The CB8 stationary phase achieved high resolution for a wide range of analytes from nonpolar to polar while the CB8-Cd stationary phase exhibited good separation mainly for nonpolar to weak polar analytes. The CB stationary phases differ from the commercial one in terms of retention behaviors and resolving ability due to their different molecular interactions with analytes. Moreover, energy effect on the retention of analytes on CB8 and CB8-Cd stationary phases was examined, showing that retention on CB8 column was determined mainly by enthalpy change for polar analytes and by both enthalpy change and entropy change for weak polar analytes whereas retention on CB8-Cd column was mainly controlled by entropy change. This work demonstrates the great potential of CB8 and CB8-Cd stationary phases as a new type of GC stationary phases in GC analysis. PMID:24745846

Sun, Tao; Ji, Ningning; Qi, Meiling; Tao, Zhu; Fu, Ruonong

2014-05-23

357

A Complex Regulatory Network Coordinating Cell Cycles During C. elegans Development Is Revealed by a Genome-Wide RNAi Screen  

PubMed Central

The development and homeostasis of multicellular animals requires precise coordination of cell division and differentiation. We performed a genome-wide RNA interference screen in Caenorhabditis elegans to reveal the components of a regulatory network that promotes developmentally programmed cell-cycle quiescence. The 107 identified genes are predicted to constitute regulatory networks that are conserved among higher animals because almost half of the genes are represented by clear human orthologs. Using a series of mutant backgrounds to assess their genetic activities, the RNA interference clones displaying similar properties were clustered to establish potential regulatory relationships within the network. This approach uncovered four distinct genetic pathways controlling cell-cycle entry during intestinal organogenesis. The enhanced phenotypes observed for animals carrying compound mutations attest to the collaboration between distinct mechanisms to ensure strict developmental regulation of cell cycles. Moreover, we characterized ubc-25, a gene encoding an E2 ubiquitin-conjugating enzyme whose human ortholog, UBE2Q2, is deregulated in several cancers. Our genetic analyses suggested that ubc-25 acts in a linear pathway with cul-1/Cul1, in parallel to pathways employing cki-1/p27 and lin-35/pRb to promote cell-cycle quiescence. Further investigation of the potential regulatory mechanism demonstrated that ubc-25 activity negatively regulates CYE-1/cyclin E protein abundance in vivo. Together, our results show that the ubc-25-mediated pathway acts within a complex network that integrates the actions of multiple molecular mechanisms to control cell cycles during development.

Roy, Sarah H.; Tobin, David V.; Memar, Nadin; Beltz, Eleanor; Holmen, Jenna; Clayton, Joseph E.; Chiu, Daniel J.; Young, Laura D.; Green, Travis H.; Lubin, Isabella; Liu, Yuying; Conradt, Barbara; Saito, R. Mako

2014-01-01

358

Uranyl photofootprinting of triple helical DNA.  

PubMed Central

Two triple helix structures (15-mers containing only T.A-T triplets or containing mixed T.A-T and C.G-C triplets) have been studied by uranyl mediated DNA photocleavage to probe the accessibility of the phosphates of the DNA backbone. Whereas the phosphates of the pyrimidine strand are at least as accessible as in double stranded DNA, in the phosphates of the purine strand are partly shielded and more so at the 5'-end of the strand. With the homo A/T target increased cleavage is observed towards the 3'-end on the pyrimidine strand. These results show that the third strand is asymmetrically positioned along the groove with the tightest triple strand double strand interactions at the 5'-end of the third strand. The results also indicate that homo-A versus mixed A/G 'Hoogsteen-triple helices' have different structures. Images

Nielsen, P E

1992-01-01

359

ESI-MS and theoretical study on the coordination structures and reaction modes of the diperoxovanadate complexes containing histidine-like ligands  

NASA Astrophysics Data System (ADS)

In order to study the coordination structures and the reaction modes of diperoxovanadate complexes in the gas phase, the interaction between K3[OV(O2)2(C2O4)]H2O and a series of histidine-like ligands has been investigated by the combination of the electrospray ionization-mass spectrometry (ESI-MS) and the density functional theory (DFT) calculations. The experimental results proved the formation of both [OV(O2)2L]- (L = all histidine-like ligands) and [OV(O2)2L'2]- (L' = histidine and carnosine only) species. DFT calculations at the level of B3LYP/6-31+G* showed that [OV(O2)2L'2]- is a hexa-coordinated complex, instead of a hepta-coordinated complex as proposed before. The unique coordination mode in the gas phase is for one ligand to bind to the oxygen atoms via hydrogen binding, rather than both ligands to the metal center. The L'2 dimer formation and the maintenance of the hydrogen bonding within the dimer during the complex formation are two important factors that enhance the abundance of the [OV(O2)2L'2]- species. The calculated bonding enthalpy and free energy changes provided an explanation on the reaction modes of the interaction systems, in agreement with the observations of the ESI-MS experiments.

Yu, Xian-Yong; Xu, Xin; Chen, Zhong

2008-01-01

360

Efficient quenching of TGA-capped CdTe quantum dot emission by a surface-coordinated europium(III) cyclen complex.  

PubMed

Extremely efficient quenching of the excited state of aqueous CdTe quantum dots (QDs) by photoinduced electron transfer to a europium cyclen complex is facilitated by surface coordination to the thioglycolic acid capping ligand. The quenching dynamics are elucidated using steady-state emission and picosecond transient absorption. PMID:23527563

Gallagher, Shane A; Comby, Steve; Wojdyla, Michal; Gunnlaugsson, Thorfinnur; Kelly, John M; Gun'ko, Yurii K; Clark, Ian P; Greetham, Gregory M; Towrie, Michael; Quinn, Susan J

2013-04-15

361

Intramolecular N-HCl hydrogen bonds in the outer coordination sphere of a bipyridyl bisurea-based ligand stabilize a tetrahedral FeLCl2 complex.  

PubMed

A bipyridyl-based anion receptor is utilized as a ligand in a tetrahedral FeCl2 complex and demonstrates secondary coordination sphere influence through intramolecular hydrogen bonding to the chloride ligands as evidenced by X-ray crystallography. PMID:24854889

Gavette, Jesse V; Klug, Christina M; Zakharov, Lev N; Shores, Matthew P; Haley, Michael M; Johnson, Darren W

2014-06-10

362

Durable phosphate-selective electrodes based on uranyl salophenes  

Microsoft Academic Search

Lipophilic uranyl salophenes derivatives were used as ionophores in durable phosphate-selective electrodes. The influence of the ionophore structure and membrane composition (polarity of plasticizer, the amount of incorporated ionic sites) on the electrode selectivity and long-term stability were studied. The highest selectivity for H2PO4? over other anions tested was obtained for lipophilic uranyl salophene III (with t-butyl substituents) in poly(vinylchloride)\\/o-nitrophenyl

Wojciech Wrblewski; Kamil Wojciechowski; Artur Dybko; Zbigniew Brzzka; Richard J. M. Egberink; Bianca H. M. Snellink-Rul; David N. Reinhoudt

2001-01-01

363

Water exchange on seven-coordinate Mn(II) complexes with macrocyclic pentadentate ligands: insight in the mechanism of Mn(II) SOD mimetics.  

PubMed

Seven-coordinate manganese(II) complexes [Mn(L)(H2O)2]2+, where L represents an equatorial pentadentate macrocyclic ligand with five nitrogen donor atoms, were studied with regard to their acid-base properties, water-exchange rate constants, and corresponding activation parameters (DeltaH, DeltaS, and DeltaV). Three of the studied complexes without imine bonds in the macrocyclic ligand are proven superoxide dismutase (SOD) mimetics. Their water-exchange parameters were compared with those of the imino groups containing complex [Mn(L1)(Cl)2] (dichloro-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]-octadeca-1(18),2,12,14,16-pentaenemanganese(II)), which does not show SOD activity. In addition the X-ray crystal structure of a new complex, dichloro-2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]pyridine-manganese(II) [Mn(L2)(Cl)2], which is the acyclic analog of [Mn(L1)(Cl)2], is reported. Stability constants of the complexes and the pKa values of the ligands were measured by potentiometric titration. The titrations of [Mn(L1)(H2O)2]2+ and [Mn(L2)(H2O)2]2+ led to complicated species distribution curves because of their ligands containing imine bonds. Water exchange was measured by temperature- and pressure-dependent 17O NMR techniques. In addition to the measurements on [Mn(EDTA)(H2O)]2- and its derivatives, this is the only study of water exchange on seven-coordinate manganese complexes. The water exchange rate constants vary between 1.6 x 107 s-1 and 5.8 x 107 s-1 at 25 degrees C and are mainly controlled by the pi-acceptor abilities of the ligands. The exchange rate constant of the diaqua-1,4,7,10,13-pentaazacyclopentadecanemanganese(II) [Mn([15]aneN5)(H2O)2]2+ complex seems to be even higher but could not be exactly determined. On the basis of the obtained activation parameters, the exchange mechanism of the studied seven-coordinate manganese(II) complexes follows a dissociative pathway (Id mechanism). DFT calculations (UB3LYP/LANL2DZp) were performed to obtain the energy required for the dissociation of the coordinated water molecule, that is, the energy difference between the starting seven-coordinate complex and a six-coordinate intermediate. The results have been discussed in terms of the catalytic mechanism of the proven SOD mimetics. PMID:17326621

Dees, Anne; Zahl, Achim; Puchta, Ralph; Hommes, Nico J R van Eikema; Heinemann, Frank W; Ivanovi?-Burmazovi?, Ivana

2007-04-01

364

Copper(II) complexes containing a CuN4O2 coordination sphere assembled via pyridine-imine-amide coordination: Synthesis, structure and properties  

Microsoft Academic Search

Copper(II) complexes [CuL2] of pyridine-N, imine-N and amide-O donor Schiff bases (HL) are reported. The Schiff bases Hpabh, Hpamh and Hpadh were prepared by condensation of 2-pyridinecarboxaldehyde with benzhydrazide, 4-methoxybenzhydrazide and 4-dimethylaminobenzhydrazide, respectively. The complexes were synthesised in MeOH media by reacting Cu(OAc)2 H2O with HL in a 1:2 mole ratio. The X-ray structure of [Cu(pabh)2] was determined. The

Satyanarayan Pal; Jally Pushparaju; Nimma Rajaiah Sangeetha; Samudranil Pal

2000-01-01

365

Reduction and selective oxo group silylation of the uranyl dication.  

PubMed

Uranium occurs in the environment predominantly as the uranyl dication [UO2]2+. Its solubility renders this species a problematic contaminant which is, moreover, chemically extraordinarily robust owing to strongly covalent U-O bonds. This feature manifests itself in the uranyl dication showing little propensity to partake in the many oxo group functionalizations and redox reactions typically seen with [CrO2]2+, [MoO2]2+ and other transition metal analogues. As a result, only a few examples of [UO2]2+ with functionalized oxo groups are known. Similarly, it is only very recently that the isolation and characterization of the singly reduced, pentavalent uranyl cation [UO2]+ has been reported. Here we show that placing the uranyl dication within a rigid and well-defined molecular framework while keeping the environment anaerobic allows simultaneous single-electron reduction and selective covalent bond formation at one of the two uranyl oxo groups. The product of this reaction is a pentavalent and monofunctionalized [O = U...OR]+ cation that can be isolated in the presence of transition metal cations. This finding demonstrates that under appropriate reaction conditions, the uranyl oxo group will readily undergo radical reactions commonly associated only with transition metal oxo groups. We expect that this work might also prove useful in probing the chemistry of the related but highly radioactive plutonyl and neptunyl analogues found in nuclear waste. PMID:18202653

Arnold, Polly L; Patel, Dipti; Wilson, Claire; Love, Jason B

2008-01-17

366

Complexes of Ag(I), Hg(I) and Hg(II) with multidentate pyrazolyl-pyridine ligands: From mononuclear complexes to coordination polymers via helicates, a mesocate, a cage and a catenate.  

PubMed

The coordination chemistry of a series of di- and tri-nucleating ligands with Ag(I), Hg(I) and Hg(II) has been investigated. Most of the ligands contain two or three N,N'-bidentate chelating pyrazolyl-pyridine units pendant from a central aromatic spacer; one contains three binding sites (2 + 3 + 2-dentate) in a linear sequence. A series of thirteen complexes has been structurally characterised displaying a wide range of structural types. Bis-bidentate bridging ligands react with Ag(I) to give complexes in which Ag(I) is four-coordinate from two bidentate donors, but the complexes can take the form of one-dimensional coordination polymers, or dinuclear complexes (mesocate or helicate). A tris-bidentate triangular ligand forms a complicated two-dimensional coordination network with Ag(I) in which Ag...Ag contacts, as well as metal-ligand coordination bonds, play a significant role. Three dinuclear Hg(I) complexes were isolated which contain an {Hg2}2+ metal-metal bonded core bound to a single bis-bidentate ligand which can span both metal ions. Also characterised were a series of Hg(II) complexes comprising a simple mononuclear four-coordinate Hg(II) complex, a tetrahedral Hg(II)4 cage which incorporates a counter-ion in its central cavity, a trinuclear double helicate, and a trinuclear catenated structure in which two long ligands have spontaneously formed interlocked metallomacrocyclic rings thanks to cyclometallation of two of the Hg(II) centres. PMID:17060986

Argent, Stephen P; Adams, Harry; Riis-Johannessen, Thomas; Jeffery, John C; Harding, Lindsay P; Clegg, William; Harrington, Ross W; Ward, Michael D

2006-11-14

367

Hybrid scorpionate/cyclopentadienyl magnesium and zinc complexes: synthesis, coordination chemistry, and ring-opening polymerization studies on cyclic esters.  

PubMed

The reaction of the hybrid scorpionate/cyclopentadienyl lithium salt [Li(bpzcp)(THF)] [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl] with 1 equiv of RMgCl proceeds cleanly to give very high yields of the corresponding monoalkyl kappa(2)-NN-eta(5)-C(5)H(4) magnesium complexes [Mg(R)(kappa(2)-eta(5)-bpzcp)] (R = Me 1, Et 2, (n)Bu 3, (t)Bu 4, CH(2)SiMe(3) 5, CH(2)Ph 6). Hydrolysis of the hybrid lithium salt [Li(bpzcp)(THF)] with NH(4)Cl/H(2)O in ether cleanly affords the two previously described regioisomers: (bpzcpH) 1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene (a) and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene (b). Subsequent reaction of the bpzcpH hybrid ligand with ZnR(2) quantitatively yields the monoalkyl kappa(2)-NN-eta(1)(pi)-C(5)H(4) zinc complexes [Zn(R){kappa(2)-eta(1)(pi)-bpzcp}] (R = Me 7, Et 8, (t)Bu 9, CH(2)SiMe(3) 10). Additionally, magnesium alkyls 1, 2, 4, and 5 can act as excellent cyclopentadienyl and alkyl transfers to the zinc metal center and yield zinc alkyls 7-10 in good yields. The single-crystal X-ray structures of the derivatives 4, 5, 7, and 10 confirm a 4-coordinative structure with the metal center in a distorted tetrahedral geometry. Interestingly, whereas alkyl magnesium derivatives 4 and 5 present a eta(5) coordination mode for the cyclopentadienyl fragment, zinc derivatives 7 and 10 feature a peripheral eta(1)(pi) arrangement in the solid state. Furthermore, the reaction of the hybrid lithium salt [Li(bpzcp)(THF)] with 1 equiv of ZnCl(2) in tetrahydrofuran (THF) affords very high yields of the chloride complex [ZnCl{kappa(2)-eta(1)(pi)-bpzcp}] (11). Compound 11 was used as a convenient starting material for the synthesis of the aromatic amide zinc compound [Zn(NH-4-MeC(6)H(4)){kappa(2)-eta(1)(pi)-bpzcp}] (12), by reaction with the corresponding aromatic primary amide lithium salt. Alternatively, aliphatic amide and alkoxide derivatives were only accessible by protonolysis of the bis(amide) complexes [M{N(SiMe(3))(2)}(2)] (M = Mg, Zn) and the mixed ligand complex [EtZnOAr)] with the hybrid ligand bpzcpH to afford [Zn(R){kappa(2)-eta(1)(pi)-bpzcp}] (R = N(SiMe(3))(2) 13, R = 2,4,6-Me(3)C(6)H(2)O 14) and [Mg{N(SiMe(3))(2)}(kappa(2)-eta(5)-bpzcp)] (15). Finally, alkyl and alkoxide-containing complexes 1-10 and 14 can act as highly effective single-component living initiators for the ring-opening polymerization of epsilon-caprolactone and lactides over a wide range of temperatures. Epsilon-caprolactone is polymerized within minutes to give high molecular weight polymers with medium-broad polydispersities (M(n) > 10(5), M(w)/M(n) = 1.45). Lactide afforded poly(lactide) materials with medium molecular weights and polydispersities as narrow as M(w)/M(n) = 1.02. Additionally, polymerization of L-lactide occurred without racemization in the propagation process and offered highly crystalline, isotactic poly(L-lactides) with very high melting temperatures (T(m) = 165 degrees C). Microstructural analysis of poly(rac-lactide) by (1)H NMR spectroscopy revealed that propagations occur without appreciable levels of stereoselectivity. Polymer end group analysis showed that the polymerization process is initiated by alkyl transfer to the monomer. PMID:20146427

Garcs, Andrs; Snchez-Barba, Luis F; Alonso-Moreno, Carlos; Fajardo, Mariano; Fernndez-Baeza, Juan; Otero, Antonio; Lara-Snchez, Agustn; Lpez-Solera, Isabel; Rodrguez, Ana Mara

2010-03-15

368

Towards the Rational Design of MRI Contrast Agents: Electron Spin Relaxation Is Largely Unaffected by the Coordination Geometry of Gadolinium(III)-DOTA-Type Complexes  

PubMed Central

Electron-spin relaxation is one of the determining factors in the efficacy of MRI contrast agents. Of all the parameters involved in determining relaxivity it remains the least well understood, particularly as it relates to the structure of the complex. One of the reasons for the poor understanding of electron-spin relaxation is that it is closely related to the ligand-field parameters of the Gd3+ ion that forms the basis of MRI contrast agents and these complexes generally exhibit a structural isomerism that inherently complicates the study of electron spin relaxation. We have recently shown that two DOTA-type ligands could be synthesised that, when coordinated to Gd3+, would adopt well defined coordination geometries and are not subject to the problems of intramolecular motion of other complexes. The EPR properties of these two chelates were studied and the results examined with theory to probe their electron-spin relaxation properties.

Bean, Jonathan F.; Clarkson, Robert B.; Helm, Lothar; Moriggi, Loick; Sherry, A. Dean

2009-01-01

369

First examples of ternary lanthanide 5-aminoisophthalate complexes: Hydrothermal syntheses and structures of lanthanide coordination polymers with 5-aminoisophthalate and oxalate  

NASA Astrophysics Data System (ADS)

Two new lanthanide coordination polymers with mixed-carboxylates, [Ln(OX)(HAPA)(H 2O)] n[Ln = Eu ( 1), Ho ( 2); H 2APA = 5-aminoisophthalic acid; OX = oxalate] were obtained by hydrothermal reactions, and characterized by single crystal X-ray diffraction, elemental analysis and IR spectra. Complexes 1 and 2 are both 3-D supramolecular structure, in which lanthanide ions are bridged by oxalate and 5-aminoisophthalate ligands forming 2-D metal-organic framework, and 2-D networks are further architectured to form 3-D supramolecular structures by hydrogen bonds. The two carboxylate groups of H 2APA ligand are all deprotonated and exhibit chelating and bridging bidentate coordination modes, respectively, and the amino group in HAPA presents - NH3+ in the titled complexes. The thermogravimetric analysis was carried out to examine the thermal stability of the titled complexes. And the photoluminescence property of 1 was investigated.

Liu, Chong-Bo; Wen, Hui-Liang; Tan, Sheng-Shui; Yi, Xiu-Guang

2008-05-01

370

Uranyl(VI) nitrate salts: modeling thermodynamic properties using the binding mean spherical approximation theory and determination of "fictive" binary data.  

PubMed

This work is aimed at a description of the thermodynamic properties of highly concentrated aqueous solutions of uranyl nitrate at 25 degrees C. A new resolution of the binding mean spherical approximation (BIMSA) theory, taking into account 1-1 and also 1-2 complex formation, is developed and used to reproduce, from a simple procedure, experimental uranyl nitrate osmotic coefficient variation with concentration. For better consistency of the theory, binary uranyl perchlorate and chloride osmotic coefficients are also calculated. Comparison of calculated and experimental values is made. The possibility of regarding the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O as a "simple" solution (in the sense of Zdanovskii, Stokes, and Robinson) is examined from water activity and density measurements. Also, an analysis of existing uranyl nitrate binary data is proposed and compared with our obtained data. On the basis of the concept of "simple" solution, values for density and water activity for the binary system UO(2)(NO(3))(2)/H(2)O are proposed in a concentration range on which uranyl nitrate precipitates from measurements on concentrated solutions of the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O. This new set of binary data is "fictive" in the sense that the real binary system is not stable chemically. Finally, a new, interesting predictive capability of the BIMSA theory is shown. PMID:16494358

Ruas, Alexandre; Bernard, Olivier; Caniffi, Barbara; Simonin, Jean-Pierre; Turq, Pierre; Blum, Lesser; Moisy, Philippe

2006-02-23

371

Coordinated Leading and Lagging Strand DNA Synthesis by Using the Herpes Simplex Virus 1 Replication Complex and Minicircle DNA Templates ?  

PubMed Central

The origin-specific replication of the herpes simplex virus 1 genome requires seven proteins: the helicase-primase (UL5-UL8-UL52), the DNA polymerase (UL30-UL42), the single-strand DNA binding protein (ICP8), and the origin-binding protein (UL9). We reconstituted these proteins, excluding UL9, on synthetic minicircular DNA templates and monitored leading and lagging strand DNA synthesis using the strand-specific incorporation of dTMP and dAMP. Critical features of the assays that led to efficient leading and lagging stand synthesis included high helicase-primase concentrations and a lagging strand template whose sequence resembled that of the viral DNA. Depending on the nature of the minicircle template, the replication complex synthesized leading and lagging strand products at molar ratios varying between 1:1 and 3:1. Lagging strand products (?0.2 to 0.6 kb) were significantly shorter than leading strand products (?2 to 10 kb), and conditions that stimulated primer synthesis led to shorter lagging strand products. ICP8 was not essential; however, its presence stimulated DNA synthesis and increased the length of both leading and lagging strand products. Curiously, human DNA polymerase ? (p70-p180 or p49-p58-p70-p180), which improves the utilization of RNA primers synthesized by herpesvirus primase on linear DNA templates, had no effect on the replication of the minicircles. The lack of stimulation by polymerase ? suggests the existence of a macromolecular assembly that enhances the utilization of RNA primers and may functionally couple leading and lagging strand synthesis. Evidence for functional coupling is further provided by our observations that (i) leading and lagging strand synthesis produce equal amounts of DNA, (ii) leading strand synthesis proceeds faster under conditions that disable primer synthesis on the lagging strand, and (iii) conditions that accelerate helicase-catalyzed DNA unwinding stimulate decoupled leading strand synthesis but not coordinated leading and lagging strand synthesis.

Stengel, Gudrun; Kuchta, Robert D.

2011-01-01

372

Extraction of uranyl, La(III), and Y(III) nitrates with a composite solid extractant based on a polymeric support impregnated with trialkylamine  

Microsoft Academic Search

Extraction of uranyl, La(III), and Y(III) nitrates from aqueous solutions containing 04 M sodium nitrate with a composite\\u000a solid extractant based on a polymeric support impregnated with trialkylamine (C7-C9) was studied. The extraction isotherms were analyzed assuming that La(III), Y(III), and uranyl nitrates are extracted with\\u000a the solid extractant in the form of complexes (R3NH)3[Ln(NO3)6] and (R3NH)2[UO2(NO3)4], respectively. The extraction

A. K. Pyartman; V. V. Lishchuk; V. A. Keskinov

2007-01-01

373

Extraction of uranyl, La(III), and Y(III) nitrates with a composite solid extractant based on a polymeric support impregnated with trialkylmethylammonium nitrate  

Microsoft Academic Search

Extraction of uranyl, La(III), and Y(III) nitrates from aqueous solutions containing 04 M sodium nitrate with a composite\\u000a solid extractant based on a polymeric support impregnated with trialkylmethylammonium nitrate (Aliquat-336) was studied. The\\u000a extraction isotherms were analyzed assuming that uranyl, La(III), and Y(III) nitrates are extracted with the solid extractant\\u000a in the form of complexes (R4N)2[Ln(NO3)5] and (R4N)2[UO2(NO3)4], respectively. The

A. K. Pyartman; V. A. Keskinov; V. V. Lishchuk; A. V. Konstantinova; V. V. Belova

2007-01-01

374

Uranyl Nitrate and HgCl2-Induced Alterations in Ion Transport.  

National Technical Information Service (NTIS)

The present studies were de, *Mercury chloride, *Uranyl nitratesigned to characterize the effects on epithelial ion transport function of mercuric chloride (HgCl2) and uranyl nitrate, two heavy metals salts which have been demonstrated to induce nephrotox...

J. H. Schwartz W. Flamenbaum

1976-01-01

375

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

376

A redox-active porous coordination network film based on a Ru complex as a building block on an ITO electrode.  

PubMed

The combination of self-assembled monolayer (SAM) and layer-by-layer (LbL) growth methods for the construction of a surface porous film has the potential to incorporate a wide range of chemical functionalities on a solid surface. A novel redox-active Ru complex with 2,6-bis(N-pyridylbenzimidazolyl)-pyridine ligands (Ru complex 1), in which four peripheral pyridine groups act as coordination sites, was used as a building block for a porous coordination network film. By using (4-pyridyl)phenylphosphonic acid as a SAM primer layer on an ITO surface, the Ru complex 1 was immobilized by the successive reaction of PdCl2 on the ITO electrode in the LbL growth method. Multilayer growth was monitored by UV-vis spectra and cyclic voltammetry, in which the linear increases of both absorbance and the peak current were observed. This result indicated that the regular accumulation of Ru complex 1 onto the ITO surface took place. The permselectivity of the present porous coordination network structure was examined using redox-active molecular probes with different sizes and charges such as ferrocene, trimethylaminomethylferrocene, the Os bis(2,6-bis(N-methylbenzimidazolyl)-pyridine) complex, and tetrathiofulvarene (TTF). With the Os complex and cationic ferrocene, only the catalytic peak was observed as a prewave of the adsorbed Ru(II/III) peak at +0.73 V. On the other hand, the oxidation peak of ferrocene was observed around 0 V vs. Fc(+)/Fc even for nine-layered films in addition to the adsorbed Ru(II/III) peak. From these results, not only molecular size but also electrostatic interaction plays an important role in the permeation into the Ru complex 1 porous network film. PMID:24030849

Shinomiya, Takuya; Ozawa, Hiroaki; Mutoh, Yuichiro; Haga, Masa-Aki

2013-12-01

377

Exploratory studies on coordination chemistry of a redox-active bridging ligand: synthesis, properties and solid state structures of the complexes.  

PubMed

The explorative coordination chemistry of the bridging ligand TTF-PPB is presented. Its strong binding ability to Co(II) and then to Ni(II) or Cu(II) in the presence of hexafluoroacetylacetonate (hfac(-)), forming new mono- and dinuclear complexes 1-3, is described. X-ray crystallographic studies have been conducted in the case of the free ligand TTF-PPB as well as its complexes [Co(TTF-PPB)(hfac)(2)] (1) and [Co(hfac)(2)(?-TTF-PPB)Ni(hfac)(2)] (2). Each metal ion is bonded to two bidentate hfac(-) anions through their oxygen atoms and two nitrogen atoms of the PPB moiety with a distorted octahedral coordination geometry. Specifically, nitrogen donor atoms of TTF-PPB adopt a cis-coordination but not in the equatorial plane, which is quite rare. Electronic absorption, photoinduced intraligand charge transfer ((1)ILCT), and electrochemical behaviour of 1-3 have been investigated. UV-Vis spectroscopy shows very strong bands in the UV region consistent with ligand centred ?-?* transitions and an intense broad band in the visible region corresponding to a spin-allowed ?-?* (1)ILCT transition. Upon coordination, the (1)ILCT band is bathochromically shifted by 3100, 6100 and 5900 cm(-1) on going from 1 to 3. The electrochemical studies reveal that all of them undergo two reversible oxidation and one reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the PPB unit, respectively. PMID:21725556

Ran, Ying-Fen; Liu, Shi-Xia; Sereda, Olha; Neels, Antonia; Decurtins, Silvio

2011-08-28

378

Ezrin-anchored Protein Kinase A Coordinates Phosphorylation-dependent Disassembly of a NHERF1 Ternary Complex to Regulate Hormone-sensitive Phosphate Transport*  

PubMed Central

Congenital defects in the Na/H exchanger regulatory factor-1 (NHERF1) are linked to disordered phosphate homeostasis and skeletal abnormalities in humans. In the kidney, these mutations interrupt parathyroid hormone (PTH)-responsive sequestration of the renal phosphate transporter, Npt2a, with ensuing urinary phosphate wasting. We now report that NHERF1, a modular PDZ domain scaffolding protein, coordinates the assembly of an obligate ternary complex with Npt2a and the PKA-anchoring protein ezrin to facilitate PTH-responsive cAMP signaling events. Activation of ezrin-anchored PKA initiates NHERF1 phosphorylation to disassemble the ternary complex, release Npt2a, and thereby inhibit phosphate transport. Loss-of-function mutations stabilize an inactive NHERF1 conformation that we show is refractory to PKA phosphorylation and impairs assembly of the ternary complex. Compensatory mutations introduced in mutant NHERF1 re-establish the integrity of the ternary complex to permit phosphorylation of NHERF1 and rescue PTH action. These findings offer new insights into a novel macromolecular mechanism for the physiological action of a critical ternary complex, where anchored PKA coordinates the assembly and turnover of the Npt2a-NHERF1-ezrin complex.

Wang, Bin; Means, Chris K.; Yang, Yanmei; Mamonova, Tatyana; Bisello, Alessandro; Altschuler, Daniel L.; Scott, John D.; Friedman, Peter A.

2012-01-01

379

Syntheses, structures, photoluminescence of four dicarboxylate-controlled Zn(II) coordination complexes incorporating flexible 1-(4-pyridylmethyl)-benzimidazole ligand  

NASA Astrophysics Data System (ADS)

Four Zn(II) coordination complexes, namely {[Zn(pmbm)2(tpa)]H2O}n (1), {[Zn(pmbm)(phda)]2(H2O)}n (2), [Zn(pmbm)(aze)]n (3), {[Zn(pmbm)(1,4-ndc)]2(CH3OH)}n (4) [pmbm = 1-(4-pyridylmethyl)-benzimidazole, H2tpa = terephthalic acid, H2phda = phenylenediacetic acid, H2aze = azelaic acid, 1,4-ndcH2 = 1,4-naphthalenedicarboxylic acid] have been synthesized by solution phase ultrasonic reactions of Zn(AC)22H2O with pmbm and various dicarboxylates ligands under the ammoniacal condition. All the complexes have been characterized by elemental analyses, IR spectra and X-ray diffraction. Complexes 1 and 2 exhibit one-dimensional chains structure and complex 3 and 4 are two-dimensional sheets structure with (4,4) topology. Complexes 14 spanning from one-dimensional chains to two-dimensional sheets suggest that dicarboxylates play significant roles in the formation of such coordination architectures. The photoluminescences of the complexes were also investigated in the solid state at room temperature.

Hao, Hong-Jun; Du, Ming-Yue; Wang, Dan-Feng; Sun, Cheng-Jie; Wang, Zhan-Hui; Huang, Rong-Bin; Zheng, Lan-Sun

2013-09-01

380

Spectroscopic, kinetic, and mechanistic study of a new mode of coordination of indole derivatives to platinum(II) and palladium(II) ions in complexes.  

PubMed

Binding of tryptophan residue to intrinsic metal ions in proteins is unknown, and very little is known about the coordinating abilities of indole. Indole-3-acetamide displaces the solvent ligands from cis-[Pt(en)(sol)2]2+, in which sol is acetone or H2O, in acetone solution and forms the complex cis-[Pt(en)(indole-3-acetamide)]2+ (3) of spiro structure, in which the new bidentate ligand coordinates to the Pt(II) atom via the C(3) atom of the indolyl group and the amide oxygen atom. This structure is supported by 1H, 13C, 15N, and 195Pt NMR spectra and by UV, IR, and mass spectra. Molecular mechanical simulations by Hyperchem and CHARMM methods give consistent structural models; the latter is optimized by density-functional quantum chemical calculations. Dipeptide-like molecules N-(3-indolylacetyl)-L-amino acid in which amino acid is alanine, leucine, isoleucine, valine, aspartic acid, or phenylalanine also displace the solvent ligands in acetone solution and form complexes cis-[Pt(en) N-(3-indolylacetyl)-L-amino acid)]2+ (6), which structurally resemble 3 but exist as two diastereomers, detected by 1H NMR spectroscopy. The bulkier the amino acid moiety, the slower the coordination of these dipeptide-like ligands to the Pt(II) atom. The indolyl group does not coordinate as a unidentate ligand; a second donor atom is necessary for bidentate coordination of this atom and the indolyl C(3) atom. The solvent-displacement reaction is of first and zeroth orders with respect to indole-3-acetamide and cis-[Pt(en)(sol)2]2+, respectively. A mechanism consisting of initial unidentate coordination of the ligand via the amide oxygen atom followed by closing of the spiro ring is supported by 1H NMR data, the kinetic effects of acid and water, and the activation parameters for the displacement reaction. In the case of N-(3-indolylacetyl)-L-phenylalanine, the bulkiest of the entering ligands, the reaction is of first order with respect to both reactants. The bidentate indole-3-acetamide ligand in 3 is readily displaced by (CH3)2SO and 2-methylimidazole, but not by CNO-, CH3COO-, and CH3CN. Complexes cis-[Pd(en)(sol)2]2+ and cis-[Pd(dtco)(sol)2]2+ react with indole-3-acetamide more rapidly than their Pt(II) analogues do and yield complexes similar to 3. This study augments our recent discovery of selective, hydrolytic cleavage of tryptophan-containing peptides by Pd(II) and Pt(II) complexes. PMID:11233196

Kaminskaia, N V; Ullmann, G M; Fulton, D B; Kostic, N M

2000-10-30

381

Hydrothermal Phase Relations Among Uranyl Minerals at the Nopal I Analog Site  

SciTech Connect

Uranyl mineral paragenesis at Nopal I is an analog of spent fuel alteration at Yucca Mountain. Petrographic studies suggest a variety of possible hydrothermal conditions for uranium mineralization at Nopal I. Calculated equilibrium phase relations among uranyl minerals show uranophane stability over a broad range of realistic conditions and indicate that uranyl mineral variety reflects persistent chemical potential heterogeneity. (author)

Murphy, William M. [Geological and Environmental Sciences, California State University, Chico, CA, 95929 (United States)

2007-07-01

382

DETERMINATION OF URANYL NITRATE IN FREE NITRIC ACID BY MEANS OF ACIDIMETRIC TITRATION  

Microsoft Academic Search

A method based on the quantitative reaction of uranyl nitrate with ; hydrogen peroxide to release nitric acid is presented for the determination of ; uranyl nitrate in nitric acid solution. The hydrogen peroxide is added to the ; uranyl nitrate solution and the total nitric acid determined by visual or ; potentiometric titration with sodium hydroxide. The free nitric

J. Cepelak; Maly; V. J. f Vesely

1959-01-01

383

Five coordinate M(II)-diphenolate [M = Zn(II), Ni(II), and Cu(II)] Schiff base complexes exhibiting metal- and ligand-based redox chemistry.  

PubMed

Five-coordinate Zn(II), Ni(II), and Cu(II) complexes containing pentadentate N(3)O(2) Schiff base ligands [1A](2-) and [1B](2-) have been synthesized and characterized. X-ray crystallographic studies reveal five coordinate structures in which each metal ion is bound by two imine N-donors, two phenolate O-donors, and a single amine N-donor. Electron paramagnetic resonance (EPR) spectroscopic studies suggest that the N(3)O(2) coordination spheres of [Cu(1A)] and [Cu(1B)] are retained in CH(2)Cl(2) solution and solid-state superconducting quantum interference device (SQUID) magnetometric studies confirm that [Ni(1A)] and [Ni(1B)] adopt high spin (S = 1) configurations. Each complex exhibits two reversible oxidation processes between +0.05 and +0.64 V vs [Fc](+)/[Fc]. The products of one- and two-electron oxidations have been studied by UV/vis spectroelectrochemistry and by EPR spectroscopy which confirm that each oxidation process for the Zn(II) and Cu(II) complexes is ligand-based with sequential formation of mono- and bis-phenoxyl radical species. In contrast, the one-electron oxidation of the Ni(II) complexes generates Ni(III) products. This assignment is supported by spectroelectrochemical and EPR spectroscopic studies, density functional theory (DFT) calculations, and the single crystal X-ray structure of [Ni(1A)][BF(4)] which contains Ni in a five-coordinate distorted trigonal bipyramidal geometry. PMID:23297765

Franks, Mark; Gadzhieva, Anastasia; Ghandhi, Laura; Murrell, David; Blake, Alexander J; Davies, E Stephen; Lewis, William; Moro, Fabrizio; McMaster, Jonathan; Schrder, Martin

2013-01-18

384

The Retromer Coat Complex Coordinates Endosomal Sorting and Dynein-Mediated Transport, with Carrier Recognition by the trans-Golgi Network  

Microsoft Academic Search

Early endosome-to-trans-Golgi network (TGN) transport is organized by the retromer complex. Consisting of cargo-selective and membrane-bound subcomplexes, retromer coordinates sorting with membrane deformation and carrier formation. Here, we describe four mammalian retromers whose membrane-bound subcomplexes contain specific combinations of the sorting nexins (SNX), SNX1, SNX2, SNX5, and SNX6. We establish that retromer requires a dynamic spatial organization of the endosomal

Thomas Wassmer; Naomi Attar; Martin Harterink; Jan R. T. van Weering; Colin J. Traer; Jacqueline Oakley; Bruno Goud; David J. Stephens; Paul Verkade; Hendrik C. Korswagen; Peter J. Cullen

2009-01-01

385

Seven-coordinate anion complex with a tren-based urea: Binding discrepancy of hydrogen sulfate in solid and solution states  

SciTech Connect

Structural characterization of a hydrogen sulfate complex with a tren-based urea suggests that the anion is coordinated with sixNH Obonds (dN O = 2.857 (3) to 3.092 (3)A ) and one OH O bond (dO O = 2.57 (2) A ) from three receptors; however, in solution the anion is bound within the pseudocavity of one receptor.

Pramanik, Avijit [Jackson State University; Thompson, Bethtrice [Jackson State University; Hayes, Trina [Jackson State University; Tucker, Kimberly [Jackson State University; Powell, Douglas R. [University of Oklahoma, Norman; Bonnesen, Peter V [ORNL; Ellis, Erick D [Jackson State University; Lee, Ken S. [Jackson State University; Yu, Hongtau [Jackson State University; Hossain, Md. Alamgir [Jackson State University

2011-01-01

386

Bioreduction of hydrogen uranyl phosphate: mechanisms and U(IV) products.  

PubMed

The mobility of uranium (U) in subsurface environments is controlled by interrelated adsorption, redox, and precipitation reactions. Previous work demonstrated the formation of nanometer-sized hydrogen uranyl phosphate (abbreviated as HUP) crystals on the cell walls of Bacillus subtilis, a non-U(VI)-reducing, Gram-positive bacterium. The current study examined the reduction of this biogenic, cell-associated HUP mineral by three dissimilatory metal-reducing bacteria, Anaeromyxobacter dehalogenans strain K, Geobacter sulfurreducens strain PCA, and Shewanella putrefaciens strain CN-32, and compared it to the bioreduction of abiotically formed and freely suspended HUP of larger particle size. Uranium speciation in the solid phase was followed over a 10- to 20-day reaction period by X-ray absorption fine structure spectroscopy (XANES and EXAFS) and showed varying extents of U(VI) reduction to U(IV). The reduction extent of the same mass of HUP to U(IV) was consistently greater with the biogenic than with the abiotic material under the same experimental conditions. A greater extent of HUP reduction was observed in the presence of bicarbonate in solution, whereas a decreased extent of HUP reduction was observed with the addition of dissolved phosphate. These results indicate that the extent of U(VI) reduction is controlled by dissolution of the HUP phase, suggesting that the metal-reducing bacteria transfer electrons to the dissolved or bacterially adsorbed U(VI) species formed after HUP dissolution, rather than to solid-phase U(VI) in the HUP mineral. Interestingly, the bioreduced U(IV) atoms were not immediately coordinated to other U(IV) atoms (as in uraninite, UO2) but were similar in structure to the phosphate-complexed U(IV) species found in ningyoite [CaU(PO4)2H2O]. This indicates a strong control by phosphate on the speciation of bioreduced U(IV), expressed as inhibition of the typical formation of uraninite under phosphate-free conditions. PMID:23634690

Rui, Xue; Kwon, Man Jae; O'Loughlin, Edward J; Dunham-Cheatham, Sarrah; Fein, Jeremy B; Bunker, Bruce; Kemner, Kenneth M; Boyanov, Maxim I

2013-06-01