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1

Uranyl ion coordination  

USGS Publications Warehouse

A review of the known crystal structures containing the uranyl ion shows that plane-pentagon coordination is equally as prevalent as plane-square or plane-hexagon. It is suggested that puckered-hexagon configurations of OH - or H2O about the uranyl group will tend to revert to plane-pentagon coordination. The concept of pentagonal coordination is invoked for possible explanations of the complex crystallography of the natural uranyl hydroxides and the unusual behavior of polynuclear ions in hydrolyzed uranyl solutions.

Evans, Jr. , H. T.

1963-01-01

2

Roles of Acetone and Diacetone Alcohol in Coordination and Dissociation Reactions of Uranyl Complexes  

SciTech Connect

Combined collision-induced dissociation mass-spectrometry experiments and DFT calculations were employed to elucidate the molecular structure of "hypercoordinated" species and the energetics of water-elimination reactions of uranyl acetone complexes observed in earlier work (Rios, D.; Rutkowski, P. X.; Van Stipdonk, M. J.; Gibson, J. K. Inorg. Chem. 2011, 50, 4781). It is shown that the "hypercoordinated" species contain diacetone alcohol ligands bonded in either bidentate or monodentate fashion, which are indistinguishable from (acetone)2 in mass spectrometry. Calculations confirm that four diacetone ligands can form stable complexes, but that the effective number of atoms coordinating with uranium in the equatorial plane does not exceed five. Diacetone alcohol ligands are shown to form mesityl oxide ligands and alkoxide species through the elimination of water, providing an explanation for the observed water-elimination reactions.

Rios, Daniel; Schoendorff, George E.; Van Stipdonk, Michael J.; Gordon, Mark S.; Windus, Theresa L.; Gibson, John K.; De Jong, Wibe A.

2012-12-03

3

On the Formation of "Hypercoordinated" Uranyl Complexes  

SciTech Connect

Recent gas phase experimental studies suggest the presence of hypercoordinated uranyl complexes. Coordination of acetone (Ace) to uranyl to form hypercoordinated species is examined using density functional theory (DFT) with a range of functionals and second order perturbation theory (MP2). Complexes with up to eight acetones were studied. It is shown that no more than six acetones can bind directly to uranium and that the observed uranyl complexes are not hypercoordinated.

Schoendorff, George E.; De Jong, Wibe A.; van Stipdonk, Michael J.; Gibson, John K.; Rios, Daniel; Gordon, Mark S.; Windus, Theresa L.

2011-09-05

4

Uranyl-glycine-water complexes in solution: comprehensive computational modeling of coordination geometries, stabilization energies, and luminescence properties.  

PubMed

Comprehensive computational modeling of coordination structures, thermodynamic stabilities, and luminescence spectra of uranyl-glycine-water complexes [UO(2)(Gly)(n)aq(m)](2+) (Gly = glycine, aq = H(2)O, n = 0-2, m = 0-5) in aqueous solution has been carried out using relativistic density functional approaches. The solvent is approximated by a dielectric continuum model and additional explicit water molecules. Detailed pictures are obtained by synergic combination of experimental and theoretical data. The optimal equatorial coordination numbers of uranyl are determined to be five. The energies of several complex conformations are competitively close to each other. In non-basic solution the most probable complex forms are those with two water ligands replaced by the bidentate carboxyl groups of zwitterionic glycine. The N,O-chelation in non-basic solution is neither entropically nor enthalpically favored. The symmetric and antisymmetric stretch vibrations of the nearly linear O-U-O unit determine the luminescence features. The shapes of the vibrationally resolved experimental solution spectra are reproduced theoretically with an empirically fitted overall line-width parameter. The calculated luminescence origins correspond to thermally populated, near-degenerate groups of the lowest electronically excited states of (3)?(g) and (3)?(g) character, originating from (U-O)?(u) ? (U-5f)?(u),?(u) configurations of the linear [OUO](2+) unit. The intensity distributions of the vibrational progressions are consistent with U-O bond-length changes around 5 1/2 pm. The unusually high intensity of the short wavelength foot is explained by near-degeneracy of vibrationally and electronically excited states, and by intensity enhancement through the asymmetric O-U-O stretch mode. The combination of contemporary computational chemistry and experimental techniques leads to a detailed understanding of structures, thermodynamics, and luminescence of actinide compounds, including those with bioligands. PMID:21341733

Su, Jing; Zhang, Kai; Schwarz, W H Eugen; Li, Jun

2011-02-22

5

Pentavalent uranyl complexes  

Microsoft Academic Search

The uranyl dication, [UO2]2+, is the most prevalent and most thermodynamically stable form of uranium and is a soluble and problematic environmental contaminant. It is also extraordinarily chemically robust due to the strongly covalent trans-UO2 bonding. In contrast, the pentavalent uranyl cation [UO2]+ is unstable in an aqueous environment with respect to disproportionation into tetravalent uranium species and [UO2]2+. Aside

Polly L. Arnold; Jason B. Love; Dipti Patel

2009-01-01

6

Isolation of a uranyl amide by "ate" complex formation.  

PubMed

The uranyl amide [{Li(DME)}(2)Cl][Li(DME)][UO(2)(NC(5)H(10))(3)](2) has been synthesised and structurally characterised. Its stability is attributed to the saturation of the uranyl coordination sphere by "ate" complex formation. PMID:20631946

Seaman, Lani A; Schnaars, David D; Wu, Guang; Hayton, Trevor W

2010-03-25

7

Uranyl Sequestration: Synthesis and Structural Characterization of Uranyl Complexes with a Tetradentate Methylterephthalamide Ligand  

SciTech Connect

Uranyl complexes of a bis(methylterephthalamide) ligand (LH{sub 4}) have been synthesized and characterized by X-ray crystallography. The structure is an unexpected [Me{sub 4}N]{sub 8}[L(UO{sub 2})]{sub 4} tetramer, formed via coordination of the two MeTAM units of L to two uranyl moieties. Addition of KOH to the tetramer gave the corresponding monomeric uranyl methoxide species [Me{sub 4}N]K{sub 2}[LUO{sub 2}(OMe)].

Ni, Chengbao; Shuh, David; Raymond, Kenneth

2011-03-07

8

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

2013-07-12

9

Mixed complexes of uranyl with oximes  

SciTech Connect

According to the authors, a distinguishing feature of hydroxylamine and its N-derivatives as ligands in the coordination chemistry of uranyl is their bidentate-cyclic coordination through the nitrogen and oxygen atoms, with the formation of a strong three-membered metallocycle. On the example of 1.2-naphthoquinone-2-oximate- and 1,2-naphthoquinone-1oximato-ligands, bidentate-cyclic coordination of the deprotonated oxime group of the ligands by uranyl with the formation of a threemembered ''hydroxylaminate'' ring was confirmed. The results of experiments presented here confirm the authors' concept of the relationship of the coordination-chemical behavior of hydroxylamines and oximes toward the uranyl ions.

Shelokov, R.N.; Ashurov, Z.R.; Beirakhov, A.G.; Mikhailov, Yu.N.; Orlova, I.M.

1986-06-01

10

Oxygen and nitrogen Lewis base adducts of [UO2(OTf)2]. Crystal structures of polypyridine complexes with out-of-plane uranyl equatorial coordination.  

PubMed

Dissolution of [UO2(OTf)2](1) in anhydrous thf, dme or py led to the formation of the complexes [UO2(OTf)2(thf)3](2), [UO2(OTf)2(dme)](3) and [UO2(OTf)2(py)3](4), respectively. Compounds 2 and 4 are neutral monomers in the solid state as well as the chloride [UO2Cl2(py)3](5) which was prepared in a similar way as for from the dimer [[UO2Cl2(thf)2]2]. Addition of 4 equivalents of triphenylphosphine oxide (tppo) to 1 afforded, in pyridine, the dicationic species [UO2(tppo)4][OTf]2 (6). The bi- or terdentate nitrogen molecules 2,2'-bipy, phen or terpy reacted with 1 in acetonitrile or pyridine to give [UO2(OTf)2(bipy)2](7), [UO2(phen)3][OTf]2(8), [UO2(OTf)2(terpy)](9) and [UO2(terpy)2][OTf]2(10), respectively. The hydroxide compound [[UO2(OH)(terpy)]2][OTf]2(11) was obtained by hydrolysis in air of 1 in a mixture of acetonitrile and ethanol in the presence of terpyridine. The X-ray crystal structures of , and reveal a novel coordination geometry for the uranyl ion, the uranium atom being in a rhombohedral environment; the six coordinating ligands atoms of the [UO2]2+ ion are separated into two parallel and staggered equilateral triangles and the UO2 axis is perpendicular to these triangles, passing through their centre. The structures of the mono(terpy) complexes 9 and 11 show the uranium atoms in a distorted pentagonal bipyramidal configuration with the nitrogen atom of the central pyridine ring of the terpy ligand significantly displaced from the equatorial plane. PMID:15514770

Berthet, Jean-Claude; Nierlich, Martine; Ephritikhine, M

2004-08-03

11

Electrospray ionization of uranyl-citrate complexes  

Microsoft Academic Search

Results presented here demonstrate the usefulness of electrospray ionization and gas-phase ion-molecule reactions to predict structural and electronic differences in complex inorganic ions. Electrospray ionization of uranyl citrate solutions generates positively and negatively charged ions that participate in further ion-molecule reactions in 3D ion trap and FT-ICR mass analyzers. Most ions observed are derived from the major solution uranyl-citrate complexes

rpd Somogyi; Sofie P. Pasilis; Jeanne E. Pemberton

2007-01-01

12

Electrospray ionization of uranyl-citrate complexes  

NASA Astrophysics Data System (ADS)

Results presented here demonstrate the usefulness of electrospray ionization and gas-phase ion-molecule reactions to predict structural and electronic differences in complex inorganic ions. Electrospray ionization of uranyl citrate solutions generates positively and negatively charged ions that participate in further ion-molecule reactions in 3D ion trap and FT-ICR mass analyzers. Most ions observed are derived from the major solution uranyl-citrate complexes and involve species of {(UO2)2Cit2}2-, (UO2)3Cit2, and {(UO2)3Cit3}3-, where Cit indicates the citrate trianion, C6H5O73-. In a 3D ion trap operated at relatively high pressure, complex adducts containing solvent molecules, alkali and ammonium cations, and nitrate or chloride anions are dominant, and proton/alkali cation (Na+, K+) exchange is observed for up to six exchangeable protons in an excess of alkali cations. Adduct formation in a FT-ICR cell that is operated at lower pressures is less dominant, and direct detection of positive and negative ions of the major solution complexes is possible. Multiply charged ions are also detected, suggesting the presence of uranium in different oxidation states. Changes in uranium oxidation state are detected by He-CID and SORI-CID fragmentation, and certain fragments undergo association reactions in trapping analyzers, forming "exotic" species such as [(UO2)4O3]-, [(UO2)4O4]-, and [(UO2)4O5]-. Ion-molecule reactions with D2O in the FT-ICR cell indicate substantial differences in H/D exchange rate and D2O accommodation for different ion structures and charge states. Most notably, the positively charged ions [H2(UO2)2Cit2(H)]+ and [(UO2)2(Cit)]+ accommodate two and three D2O molecules, respectively, which reflects well the structural differences, i.e., tighter uranyl-citrate coordination in the former ion than in the latter. The corresponding negatively charged ions accommodate zero or two D2O molecules, which can be rationalized using suggested solution phase structures and charge state distributions.

Somogyi, rpd; Pasilis, Sofie P.; Pemberton, Jeanne E.

2007-09-01

13

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

14

Identification of uranyl surface complexes on ferrihydrite: Advanced EXAFS data analysis and CD-MUSIC modeling.  

PubMed

Previous spectroscopic research suggested that uranium(VI) adsorption to iron oxides is dominated by ternary uranyl-carbonato surface complexes across an unexpectedly wide pH range. Formation of such complexes would have a significant impact on the sorption behavior and mobility of uranium in aqueous environments. We therefore reinvestigated the identity and structural coordination of uranyl sorption complexes using a combination of U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and iterative transformation factor analysis, which enhances the resolution in comparison to conventional EXAFS analysis. A range of conditions (pH, CO2 partial pressure, ionic strength) made it possible to quantify the variations in surface speciation. In the resulting set of spectral data (N=11) the variance is explained by only two components, which represent two structurally different types of surface complexes: (1) a binary uranyl surface complexwith a bidentate coordination to edges of Fe(O,OH)6 octahedra and (2) a uranyl triscarbonato surface complex where one carbonate ion bridges uranyl to the surface. This ternary type B complex differs from a type A complex where uranyl is directly attached to surface atoms and carbonate is bridged by uranyl to the surface. Both surface complexes agree qualitatively and quantitatively with predictions by a charge distribution (CD) model. According to this model the edge-sharing uranyl complex has equatorial ligands (-OH2, -OH, or one -CO3 group) that point away from the surface. The monodentate uranyl triscarbonato surface complex (type B) is relevant only at high pH and elevated pC0O. At these conditions, however, it is responsible for significant uranyl sorption, whereas standard models would predict only weak sorption. This paper presents the first spectroscopic evidence of this ternary surface complex, which has significant implications for immobilization of uranyl in carbonate-rich aqueous environments. PMID:19350910

Rossberg, Andr; Ulrich, Kai-Uwe; Weiss, Stephan; Tsushima, Satoru; Hiemstra, Tjisse; Scheinostt, Andreas C

2009-03-01

15

First principles NEXAFS simulations of N-donor Uranyl complexes  

NASA Astrophysics Data System (ADS)

The synthesis and study of soft-donor uranyl complexes can provide new insights into the coordination chemistry of non-aqueous [UO]2^+ Recently, the tunable N-donor ligand 2,6-Bis(2-benzimidazyl)pyridine (BBP) was employed to produce novel uranyl complexes in which the [UO]2^+ cation is ligated by anionic and covalent groups with discrete chemical differences. In this work we investigate the electronic structure of the three such uranyl-BBP complexes via near-edge X-ray absorption fine structure (NEXAFS) experiments and simulations using the eXcited electron and Core-Hole (XCH) approach [1]. The evolution of the structural as well as electronic properties across the three complexes is studied systematically. Computed N K-edge and O K-edge NEXAFS spectra are compared with experiment and spectral features assigned to specific electronic transitions in these complexes. Studying the variations in spectral features arising from N K-edge absorption provides a clear picture of ligand-uranyl bonding in these systems. References: [1] D. Prendergast and G. Galli, X-ray absorption spectra of water from first-principles calculations, Phys. Rev. Lett., 215502 (2006).

Pemmaraju, C. D.; Duan, R.; Copping, R.; Jeon, B.; Teat, S. J.; Janousch, M.; Tyliszczak, T.; Canning, A.; Grnbech-Jensen, N.; Shuh, D. K.; Prendergast, D.

2013-03-01

16

Infared Spectroscopy of Discrete Uranyl Anion Complexes  

SciTech Connect

The Free-Electron Laser for Infrared Experiments (FELIX) w 1 as used to study the wavelength-resolved multiple photon photodissociation of discrete, gas phase uranyl (UO2 2 2+) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO2A(S)n]+, where A was either hydroxide, methoxide, or acetate; S was water, ammonia, acetone, or acetonitrile; and n = 0-3. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO2A]+) were as low or lower than measurements for [UO2]2+ ligated with as many as five strong neutral donor ligands, and are comparable to solution phase values. This result was surprising because initial DFT calculations predicted values that were 3040 cm-1 higher, consistent with intuition but not with the data. Modification of the basis sets and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO2A]+ produced [UO2AS]+, which produced only very modest changes to the uranyl antisymmetric stretch frequency, and did not universally shift the frequency to lower values. DFT calculations for [UO2AS]+ were in accord with trends in the data, and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO2AS]+ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.

Groenewold, G. S.; Gianotto, Anita K.; McIIwain, Michael E.; Van Stipdonk, Michael J.; Kullman, Michael; Moore, David T.; Polfer, Nick; Oomens, Jos; Infante, Ivan A.; Visscher, Lucas; Siboulet, Bertrand; De Jong, Wibe A.

2008-01-24

17

Infrared Spectroscopy of Discrete Uranyl Anion Complexes  

SciTech Connect

The Free-Electron Laser for Infrared Experiments, FELIX, was used to study the wavelength-resolved multiphoton dissociation of discrete, gas phase uranyl (UO22+) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The apparent uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO2A(S)n]+, where A was either hydroxide, methoxide or acetate, S was water, ammonia, acetone or acetonitrile, and n = 0-2. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO2A]+) were as low or lower than measurements for [UO2]2+ ligated with as many as five strong neutral donor ligands, and are comparable to solution phase values. This result was surprising because initial DFT calculations using B3LYP predicted values that were 30 40 cm-1 higher, consistent with intuition but not with the data. Modification of the basis set and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO2A]+ produced [UO2AS]+, which resulted only very modest changes to the uranyl frequency, and did not universally shift values lower. DFT calculations for [UO2AS]+ were in accord with trends in the data, and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO2AS]+ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.

Gary S. Groenewold; Anita K. Gianotto; Michael E. McIlwain; Michael J. Van Stipdonk; Michael Kullman; Travis J. Cooper; David T. Moore; Nick Polfer; Jos Oomens; Ivan Infante; Lucas Visscher; Bertrand Siboulet; Wibe A. de Jong

2007-12-01

18

LUMINESCENCE SPECTRA OF THE URANYL ION IN TWO GEOMETRICALLY SIMILAR COORDINATION ENVIRONMENTS: URANYL NITRATE HEXAHYDRATE AND DI-{mu}-AQUO-BIS (DIOXODINITRA-TOURANIUM(VI) DI-IMIDAZOLE  

SciTech Connect

The luminescence spectra of the uranyl ion have been obtained at room and liquid nitrogen temperatures in the crystal hosts of uranyl nitrate hexahydrate (UNH) and di~~-aquo-bis(dioxodinitratouranium(VI)) di-imidazole (UNI). In both coordination spheres, the uranyl ion lies at the center of similar, distorted coordination hexagons consisting of two bidentate nitrate groups and two water molecules; the only difference in the coordination geometries is that the water molecules are terminal in the UNH complex and bridging in the UNI complex. The uranium-uranium "bond" distance in the UNI complex is 3.93 A. At room temperature, the emission spectra of the two compounds are essentially identical, but significant differences appear upon cooling to 77K. Vibronic structure is observed in the crystal of the UNI complex b4t not in the crystal of uranyl nitrate hexahydrate; this implies that the geom~try of the uranyl ion in the two excited states is somewhat different. An energy level sequence is presented in which the various emission lines arise from a slightly split excited state (splitting approximately 80-85 cm-1) to several vibrational levels of the ground electronic manifold. The energy spacing of the ground vibrational levels (approximately 860 cm-1) was found to vary when changing crystal systems.

Brittain, Harry G.; Perry, Dale L.

1980-02-01

19

Luminescence spectra of the uranyl ion in two geometrically similar coordination environments. Uranyl nitrate hexahydrate and di-. mu. -aquo-bis(dioxobis(nitrato)uranium(VI)) diimidazole  

SciTech Connect

The luminescence spectra of the uranyl ion have been obtained at room and liquid-nitrogen temperatures in the crystal hosts of uranyl nitrate hexahydrate (UNH) and di-..mu..-aquo-bis(dioxobis(nitrato)uranium(VI)) diimidazole (UNI). In both coordination spheres, the uranyl ion lies at the center of similar, distorted coordination hexagons consisting of two bidentate nitrate groups and two water molecules; the only difference in the coordination geometries is that the water molecules are terminal in the UNH complex and bridging in the UNI complex. The uranium-uranium bond distance in the UNI complex is 3.93 A. At room temperature, the emission spectra of the two compounds are essentially identical, but significant differences appear upon cooling to 77 K. Vibronic structure is observed in the crystal of the UNI complex but not in the crystal of uranyl nitrate hexahydrate; this implies that the geometry of the uranyl ion in the two excited states is somewhat different. An energy level sequence is presented in which the various emission lines arise from a slightly split excited state (splitting approximately 80 to 85 cm/sup -1/) to several vibrational levels of the ground electronic manifold. The energy spacing of the ground vibrational levels (approximately 860 cm/sup -1/) was found to vary when changing crystal systems.

Brittain, H.G. (Seton Hall Univ., South Orange, NJ); Perry, D.L.

1980-10-02

20

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

2007-04-07

21

Uranyl oxo activation and functionalization by metal cation coordination  

NASA Astrophysics Data System (ADS)

The oxo groups in the uranyl ion [UO2]2+-one of many oxo cations formed by metals from across the periodic table-are particularly inert, which explains the dominance of this ion in the laboratory and its persistence as an environmental contaminant. In contrast, transition metal oxo (M=O) compounds can be highly reactive and carry out difficult reactions such as the oxygenation of hydrocarbons. Here we show how the sequential addition of a lithium metal base to the uranyl ion constrained in a `Pacman' environment results in lithium coordination to the U=O bonds and single-electron reduction. This reaction depends on the nature and stoichiometry of the lithium reagent and suggests that competing reduction and C-H bond activation reactions are occurring.

Arnold, Polly L.; Pcharman, Anne-Frdrique; Hollis, Emmalina; Yahia, Ahmed; Maron, Laurent; Parsons, Simon; Love, Jason B.

2010-12-01

22

Molecular structure and electrochemical behavior of uranyl(VI) complex with pentadentate Schiff base ligand: prevention of uranyl(V) cation-cation interaction by fully chelating equatorial coordination sites.  

PubMed

The U(VI) complex with a pentadentate Schiff base ligand (N,N'-disalicylidenediethylenetriaminate = saldien(2-)) was prepared as a starting material of a potentially stable U(V) complex without any possibility of U(V)O(2)(+)...U(V)O(2)(+) cation-cation interaction and was found in three different crystal phases. Two of them had the same composition of U(VI)O(2)(saldien) x DMSO in orthorhombic and monoclinic systems (DMSO = dimethyl sulfoxide, 1a and 1c, respectively). The DMSO molecule in both 1a and 1c does not show any coordination to U(VI)O(2)(saldien), but it is just present as a solvent in the crystal structures. The other isolated crystals consisted only of U(VI)O(2)(saldien) without incorporation of solvent molecules (1b, orthorhombic). A different conformation of the coordinated saldien(2-) in 1c from those in 1a and 1b was observed. The conformers exchange each other in a solution through a flipping motion of the phenyl rings. The pentagonal equatorial coordination of U(VI)O(2)(saldien) remains unchanged even in strongly Lewis-basic solvents, DMSO and N,N-dimethylformamide. Cyclic voltammetry of U(VI)O(2)(saldien) in DMSO showed a quasireversible redox reaction without any successive reactions. The electron stoichiometry determined by the UV-vis-NIR spectroelectrochemical technique is close to 1, indicating that the reduction product of U(VI)O(2)(saldien) is [U(V)O(2)(saldien)](-), which is stable in DMSO. The standard redox potential of [U(V)O(2)(saldien)](-)/U(VI)O(2)(saldien) in DMSO is -1.584 V vs Fc/Fc(+). This U(V) complex shows the characteristic absorption bands due to f-f transitions in its 5f(1) configuration and charge-transfer from the axial oxygen to U(5+). PMID:20108945

Takao, Koichiro; Kato, Masaru; Takao, Shinobu; Nagasawa, Akira; Bernhard, Gert; Hennig, Christoph; Ikeda, Yasuhisa

2010-03-01

23

Luminescence spectra of the uranyl ion in two geometrically similar coordination environments. Uranyl nitrate hexahydrate and di-. mu. -aquo-bis(dioxobis(nitrato)uranium(VI)) diimidazole  

Microsoft Academic Search

The luminescence spectra of the uranyl ion have been obtained at room and liquid-nitrogen temperatures in the crystal hosts of uranyl nitrate hexahydrate (UNH) and di-..mu..-aquo-bis(dioxobis(nitrato)uranium(VI)) diimidazole (UNI). In both coordination spheres, the uranyl ion lies at the center of similar, distorted coordination hexagons consisting of two bidentate nitrate groups and two water molecules; the only difference in the coordination

Harry G. Brittain; Dale L. Perry

1980-01-01

24

Stability of sulfate complexes of electronically excited uranyl  

SciTech Connect

The complex formation of electronically excited uranyl ions with SO{sub 4}{sup 2-}anions in 0.1 M aqueous HClO{sub 4} has been studied by time-resolved luminescence spectroscopy. The stability constants of uranyl sulfate complexes (UO{sub 2}SO{sub 4}) (K=870 1 mol{sup -1}) and [UO{sub 2}(SO{sub 4}){sub 2}{sup 2-}](K=47000 1 mol{sup -1}) in excited state have been determined; they are more than an order of magnitude greater than those reported for complex formation of uranyl ions in the ground state. The complex formation of uranyl with sulfate ions is accompanied by the increase of the quantum yield of the uranyl lumenescence. The maxima of luminescence and absorption bands of uranyl ions are shifted with increasing the total concentration of SO{sub 4}{sup 2-} in solution, which supports the data obtained. The shift of the maxima of luminescence bands is observed at a sulfate concentration that is considerably lower than that causing the same shift of the maxima of the absorption bands. Such effect is consistent with the calculated stability constants of sulfate complexes of excited uranyl ions.

Ostakhov, S.S.; Kazakov, V.P.; Afonichev, D.D. [Inst. of Organic Chemistry, Ufa (Russian Federation)

1995-11-01

25

Water versus acetonitrile coordination to uranyl. Density functional study of cooperative polarization effects in solution.  

PubMed

Optimizations at the BLYP and B3LYP levels are reported for mixed uranyl-water/acetonitrile complexes [UO(2)(H(2)O)(5-n)(MeCN)(n)](2+) (n = 0-5), in both the gas phase and a polarizable continuum modeling acetonitrile. Car-Parrinello molecular dynamics (CPMD) simulations have been performed for these complexes in the gas phase, and for selected species (n = 0, 1, 3, 5) in a periodic box of liquid acetonitrile. According to structural and energetic data, uranyl has a higher affinity for acetonitrile than for water in the gas phase, in keeping with the higher dipole moment and polarizability of acetonitrile. In acetonitrile solution, however, water is the better ligand because of specific solvation effects. Analysis of the dipole moment of the coordinated water molecule in [UO(2)(H(2)O)(MeCN)(4)](2+) reveals that the interaction with the second-shell solvent molecules (through fairly strong and persistent O-HN hydrogen bonds) causes a significant increase of this dipole moment (by more than 1 D). This cooperative polarization of water reinforces the uranyl-water bond as well as the water solvation via strengthened (UO(2))OH(2)NCMe hydrogen bonds. Such cooperativity is essentially absent in the acetonitrile ligands that make much weaker (UO(2))NCMeNCMe hydrogen bonds. Beyond the uranyl case, this study points to the importance of cooperative polarization effects to enhance the M(n+) ion affinity for water in condensed phases involving M(n+)-OH(2)A fragments, where A is a H-bond proton acceptor and M(n+) is a hard cation. PMID:21126026

Bhl, Michael; Sieffert, Nicolas; Chaumont, Alain; Wipff, Georges

2010-12-02

26

Series of mixed uranyl-lanthanide (Ce, Nd) organic coordination polymers with aromatic polycarboxylates linkers.  

PubMed

Three series of mixed uranyl-lanthanide (Ce or Nd) carboxylate coordination polymers have been successfully synthesized by means of a hydrothermal route using either conventional or microwave heating methods. These compounds have been prepared from mixtures of uranyl nitrate, lanthanide nitrate together with phthalic acid (1,2), pyromellitic acid (3,4), or mellitic acid (5,6) in aqueous solution. The X-ray diffraction (XRD) single-crystal revealed that the phthalate complex (UO(2))(4)O(2)Ln(H(2)O)(7)(1,2-bdc)(4)NH(4)xH(2)O (Ln = Ce(1), Nd(2); x = 1 for 1, x = 0 for 2), is based on the connection of tetranuclear uranyl-centered building blocks linked to discrete monomeric units LnO(2)(H(2)O)(7) via the organic species to generate infinite chains, intercalated by free ammonium cations. The pyromellitate phase (UO(2))(3)Ln(2)(H(2)O)(12)(btec)(3)5H(2)O (Ce(3), Nd(4)) contains layers of monomeric uranyl-centered hexagonal and pentagonal bipyramids linked via the carboxylate arms of the organic molecules. The three-dimensionality of the structure is ensured by the connection of remaining free carboxylate groups with isolated monomeric units LnO(2)(H(2)O)(7). The network of the third series (UO(2))(2)(OH)Ln(H(2)O)(7)(mel)5H(2)O (Ce(5), Nd(6)) is built up from dinuclear uranyl units forming layers through connection with the mellitate ligands, which are further linked to each other through discrete monomers LnO(3)(H(2)O)(6). The thermal decomposition of the various coordination complexes led to the formation of mixed uranium-lanthanide oxide, with the fluorite-type structure at 1500 C (for 1, 2) or 1400 C for 3-6. Expected U/Ln ratio from the crystal structures were observed for compounds 1-6. PMID:22931214

Mihalcea, Ionut; Volkringer, Christophe; Henry, Natacha; Loiseau, Thierry

2012-08-29

27

Two uranylorganic frameworks with pyridinecarboxylate ligands. A novel heterometallic uranylcopper(II) complex with a cationcation interaction  

Microsoft Academic Search

Reaction of uranyl nitrate with pyridine-2-carboxylic acid (HL1) under hydrothermal conditions gives the complex [(UO2)3(L1)4(NO3)2], 1, which differs from the previously reported molecular complex, obtained at room temperature, by the absence of water, coordinated and free, and the extended carboxylate bridging. Although the trimetallic basic unit is similar in both cases, 1 crystallizes as a two-dimensional assembly. A heterometallic complex

Pierre Thury

2009-01-01

28

EXAFS determinations of uranium structures: The uranyl ion complexed with tartaric, citric, and malic acids  

SciTech Connect

Studies of the coordination chemistry of uranium in aqueous solutions are increasingly important for understanding the behavior of uranium in the environment. Actinide speciation information is essential for assessing and developing long-term strategies addressing problems such as migration in nuclear waste repositories or improvements in the processing of nuclear waste and materials. Relative to the latter, one method for removing uranium contamination from soils involves extraction using a chelating agent such as Tiron, or citrate. These types of extractants are quite efficient at binding the uranyl ion and thus are suitable for removing uranium contamination when it is in the hexavalent uranyl ion form. Martell et al. and Markovits et al. have published a series of articles detailing the complexation of the uranyl ion with tartaric, malic, and citric acids as a function of pH. Using the functional dependencies of potentiometric titration results, they showed that, in the pH range 2-4, the uranyl ion forms a 2:2 dimeric species, (UO{sub 2}){sub 2-} (L){sub 2}, where L = tartrate, malate, or citrate ligands. The authors have reinvestigated the solution structures of the uranyl complexes formed in these systems with the structural technique extended X-ray absorption fine-structure (EXAFS) spectroscopy.

Allen, P.G.; Shuh, D.K.; Bucher, J.J. [Lawrence Berkeley National Lab., CA (United States)] [and others

1996-01-31

29

Spectroscopic investigation of the structure of complexes of uranyl salts with hexamethylphosphoric triamide  

Microsoft Academic Search

Complexes of various uranyl salts with hexamethylphosphoric triamide (HMPA), whose structures were studied with the aid of IR and Raman spectroscopy, as well as a luminescence-spectroscopic analysis, have been isolated from aqueous solutions. It has been discovered that the formation of the complex UO(ClO) x 4HMPA results in the displacement of the perchlorate ions from the inner coordination sphere of

V. V. Yakshin; N. L. Khokhlova

1986-01-01

30

The catalytic role of uranyl in formation of polycatechol complexes  

PubMed Central

To better understand the association of contaminant uranium with natural organic matter (NOM) and the fate of uranium in ground water, spectroscopic studies of uranium complexation with catechol were conducted. Catechol provides a model for ubiquitous functional groups present in NOM. Liquid samples were analyzed using Raman, FTIR, and UV-Vis spectroscopy. Catechol was found to polymerize in presence of uranyl ions. Polymerization in presence of uranyl was compared to reactions in the presence of molybdate, another oxyion, and self polymerization of catechol at high pH. The effect of time and dissolved oxygen were also studied. It was found that oxygen was required for self-polymerization at elevated pH. The potential formation of phenoxy radicals as well as quinones was monitored. The benzene ring was found to be intact after polymerization. No evidence for formation of ether bonds was found, suggesting polymerization was due to formation of C-C bonds between catechol ligands. Uranyl was found to form outer sphere complexes with catechol at initial stages but over time (six months) polycatechol complexes were formed and precipitated from solution (forming humic-like material) while uranyl ions remained in solution. Our studies show that uranyl acts as a catalyst in catechol-polymerization.

2011-01-01

31

Spectroscopic investigation of the structure of complexes of uranyl salts with hexamethylphosphoric triamide  

SciTech Connect

Complexes of various uranyl salts with hexamethylphosphoric triamide (HMPA), whose structures were studied with the aid of IR and Raman spectroscopy, as well as a luminescence-spectroscopic analysis, have been isolated from aqueous solutions. It has been discovered that the formation of the complex UO/sub 2/(ClO/sub 4/)/sub 2/ x 4HMPA results in the displacement of the perchlorate ions from the inner coordination sphere of the uranyl ion by the HMPA molecules. Displacement of the anions of the acids is not observed in the case of the sulfate and nitrate complexes. The absence of water of crystallization and inner-sphere water is characteristic of all the complexes obtained. The results of the work make it possible to designate the place of HMPA in the displacement series of ligands.

Yakshin, V.V.; Khokhlova, N.L.

1986-06-01

32

Coordination trends in alkali metal crown ether uranyl halide complexes: the series [A(crown)]2[UO(2)X(4)] where A=Li, Na, K and X=Cl, Br.  

PubMed

UO(2)(C(2)H(3)O(2))(2).2H(2)O reacts with AX or A(C(2)H(3)O(2) or ClO(4)) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)](2)[UO(2)Cl(4)] (1), [K(18-crown-6)](2)[UO(2)Br(4)] (2), [Na(15-crown-5)](2)[UO(2)Cl(4)] (3), [Na(15-crown-5)](2)[UO(2)Br(4)] (4), [Li(12-crown-4)](2)[UO(2)Cl(4)] (5), and [Li(12-crown-4)](2)[UO(2)Br(4)] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO(2)X(4)](2-) ions coordinate to two [A(crown)](+) cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal nu(U-O) values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard-soft acid-base theory. PMID:11421684

Danis, J A; Lin, M R; Scott, B L; Eichhorn, B W; Runde, W H

2001-07-01

33

DFT study of uranyl peroxo complexes with H2O, F-, OH-, CO3(2-), and NO3(-).  

PubMed

The structural and electronic properties of monoperoxo and diperoxo uranyl complexes with aquo, fluoride, hydroxo, carbonate, and nitrate ligands have been studied using scalar relativistic density functional theory (DFT). Only the complexes in which the peroxo ligands are coordinated to the uranyl moiety in a bidentate mode were considered. The calculated binding energies confirm that the affinity of the peroxo ligand for the uranyl group far exceeds that of the F(-), OH(-), CO3(2-), NO3(-), and H2O ligands. The formation of the monoperoxo complexes from UO2(H2O)5(2+) and HO2(-) were found to be exothermic in solution. In contrast, the formation of the monouranyl-diperoxo, UO2(O2)2X2(4-) or UO2(O2)2X(4-/3-) (where X is any of F(-), OH(-), CO3(2-), or NO3(-)), complexes were all found to be endothermic in aqueous solution. This suggests that the monoperoxo species are the terminal monouranyl peroxo complexes in solution, in agreement with recent experimental work. Overall, we find that the properties of the uranyl-peroxo complexes conform to well-known trends: the coordination of the peroxo ligand weakens the U-O(yl) bonds, stabilizes the ?(d) orbitals and causes a mixing between the uranyl ?- and peroxo ?- and ?-orbitals. The weakening of the U-O(yl) bonds upon peroxide coordination results in uranyl stretching vibrational frequencies that are much lower than those obtained after the coordination of carbonato or hydroxo ligands. PMID:23573914

Odoh, Samuel O; Schreckenbach, Georg

2013-04-10

34

Theoretical exploration of uranyl complexes of a designed polypyrrolic macrocycle: structure/property effects of hinge size on Pacman-shaped complexes.  

PubMed

A polypyrrolic macrocycle with naphthalenyl linkers between the N(4)-donor compartments (L(2)) was designed theoretically according to its experimentally-known analogues with phenylenyl (L(1)) and anthracenyl (L(3)) linkers. The uranyl and bis(uranyl) complexes formed by this L(2) ligand have been examined using scalar-relativistic density functional theory. The calculated structural properties of the mononuclear uranyl-L(2) complexes are similar to those of their L(1) counterparts. The binuclear L(2) complexes exhibit a butterfly-like bis(uranyl) core in which a linear uranyl is coordinated in a side-by-side fashion to a cis-uranyl unit. The calculated U[double bond, length as m-dash]O bond orders in the uranyl-L(2) complexes indicate partial triple bonding character with the only exceptions being the U-O(endo) bonds in the U(2)O(4) core of the butterfly-shaped binuclear complexes. Overall, the bond orders agree with the trends in the calculated U[double bond, length as m-dash]O stretching vibrational frequencies. Regarding the bis(uranyl) L(1), L(2) and L(3) complexes, the phenylenyl-hinge L(1) complexes adopt a butterfly-like and a T-shaped isomer in the oxidation state of U(vi), but only a butterfly-like one in the U(v), which differs from that of the naphthalenyl-hinge L(2) complexes as well as the lateral twisted structure of the anthracenyl-hinge L(3) complexes. The intramolecular cation-cation interactions are found in the L(1) and L(2) complexes, but are absent in the L(3) complexes. Finally, using model uranyl transfer reactions from the L(1) complexes, the formation of the mononuclear L(2) complexes is calculated to be a slightly endothermic process. This suggests that it should be possible to synthesize the L(2) complexes using similar protocols as employed for the L(1) complexes. PMID:22714056

Pan, Qing-Jiang; Odoh, Samuel O; Schreckenbach, Georg; Arnold, Polly L; Love, Jason B

2012-06-20

35

Sulfonate complexes of actinide ions: structural diversity in uranyl complexes with 2-sulfobenzoate.  

PubMed

The reaction of uranyl nitrate hexahydrate with 2-sulfobenzoate (SB(2-)) in the presence of various amines gave the series of complexes [UO(2)(SB)(H(2)O)] (1), [UO(2)(SB)(H(2)O)](2)pyz (2), [2,2'-bipyH](2)[UO(2)(SB)(2)(H(2)O)]4H(2)O (3), [4,4'-bipyH(2)](2)[UO(2)(SB)(2)](2) (4), [4,4'-bipyH](2)[(UO(2))(2)(SB)(3)(H(2)O)]4H(2)O (5), [NMe(4)](2)[(UO(2))(2)(SB)(3)(H(2)O)(1.15)]1.35H(2)O (6), [NMe(4)](2)[(UO(2))(3)(SB)(2)O(2)] (7), and [H(2)DABCO](2)[(UO(2))(5)(SB)(4)O(2)(OH)(2)]4H(2)O (8), where pyz = pyrazine, bipy = bipyridine, and DABCO = 1,4-diazabicyclo[2.2.2]octane, with all compounds but 5 having been obtained under hydrothermal conditions. The crystal structures of these complexes display a common motif in which uranyl is chelated by the carboxylate and sulfonate groups of SB, giving a seven-membered ring. Structure-directing effects due to the amine and the presence in 7 and 8 of additional ?(3)-oxo or ?(2)-hydroxo bridges result in much structural variety, with different bridging by the carboxylate and sulfonate groups giving rise to zero- (3, 4), one- (1, 5-8), or two-dimensional (2) assemblies. Some unusual uranyl secondary building units are observed, such as the pentanuclear [(UO(2))(5)O(2)(OH)(2)] discrete motif. Addition of 3d-block metal cations (Cu(2+), Ni(2+)) in the presence of nitrogen donors gave the heterometallic molecular complex [UO(2)Cu(SB)(2)(2,2'-bipy)(2)](2)2H(2)O (9), the heterogeneous compound [Cu(4,4'-bipy)(H(2)O)(3)](2)[UO(2)(SB)(2)](2)2H(2)O (10), in which molecular uranyl dimers are encompassing copper-containing chains, and the heterometallic one-dimensional polymers [(UO(2))(2)Cu(2)(SB)(4)(bipym)(H(2)O)(4)] (11) and [UO(2)Ni(SB)(2)(bipym)(H(2)O)(2)]3H(2)O (12), where bipym = bipyrimidine. The latter two complexes display two different arrangements: in 11, bipym bridges two [UO(2)Cu(SB)(2)] chains to give a ladderlike assembly, while the uranyl cations are merely decorating species in 12. In contrast to those of phosphonates, the actinide complexes of sulfonates in the solid state have been little investigated up to now. The present results show that sulfocarboxylates such as 2-sulfobenzoate, in which sulfonate coordination is promoted by chelate effects, are of interest in the synthesis of uranyl-organic coordination polymers. PMID:23214440

Thury, Pierre

2012-12-07

36

Correlation between stabilities of uranyl ion complexes with various monocarboxylic acids and Hammett-Taft substituent constants  

SciTech Connect

A correlation has been observed between the stabilities of uranyl ion complexes (1:1 composition) and the substituent inductive constants in formic and acetic acid derivatives. For substituents which are not directly involved in couples formation the parameters of the Hammett-Taft equation log K/sub 1/ = A + B have the following values: A = 1.311, B = -2.360. For substituents which form a coordination bond with the uranyl ion, A = 7.0077 and B = - 17.321. In the case of complexes formed between the uranyl ion and salicylic acid and its derivatives, there is a correlation between complex stability and sigma/sub m/ and sigma/sub p/ substituent constants for the meta- and para-positions, respectively (A = 12.72, B = -4.41).

Poluektov, N.S.; Perfil'ev, V.A.; Meshkova, S.B.; Mishchenko, V.T.

1987-01-01

37

Evaluation of kinetic parameters of uranyl acetate complexes in ethanolic solution by cyclic voltammetry  

Microsoft Academic Search

The complexation of uranyl ion with acetate ions was investigated in 20% ethanolic solution by using cyclic voltammetry. The\\u000a uranium formed 1:1 and 1:2 complexes with acetate ions. The values of log ?1 and log ?2 for uranyl acetate complexes were 2.050.08 and 5.250.06 respectively. The diffusion coefficient and heterogeneous rate\\u000a constants for the reduction of uranyl ion at hanging

A. S. A. Khan; R. Ahmed; M. L. Mirza

2010-01-01

38

Cation-cation complexes of pentavalent uranyl: from disproportionation intermediates to stable clusters.  

PubMed

Three new cation-cation complexes of pentavalent uranyl, stable with respect to the disproportionation reaction, have been prepared from the reaction of the precursor [(UO(2)py(5))(KI(2)py(2))](n) (1) with the Schiff base ligands salen(2-), acacen(2-), and salophen(2-) (H(2)salen = N,N'-ethylene-bis(salicylideneimine), H(2)acacen = N,N'-ethylenebis(acetylacetoneimine), H(2)salophen = N,N'-phenylene-bis(salicylideneimine)). The preparation of stable complexes requires a careful choice of counter ions and reaction conditions. Notably the reaction of 1 with salophen(2-) in pyridine leads to immediate disproportionation, but in the presence of [18]crown-6 ([18]C-6) a stable complex forms. The solid-state structure of the four tetranuclear complexes, {[UO(2)(acacen)](4)[?(8)-](2)[K([18]C-6)(py)](2)} (3) and {[UO(2)(acacen)](4)[?(8)-]}?2?[K([222])(py)] (4), {[UO(2)(salophen)](4)[?(8)-K](2)[?(5)-KI](2)[(K([18]C-6)]}?2?[K([18]C-6)(thf)(2)]?2?I (5), and {[UO(2)(salen)(4)][?(8)-Rb](2)[Rb([18]C-6)](2)} (9) ([222] = [222]cryptand, py = pyridine), presenting a T-shaped cation-cation interaction has been determined by X-ray crystallographic studies. NMR spectroscopic and UV/Vis studies show that the tetranuclear structure is maintained in pyridine solution for the salen and acacen complexes. Stable mononuclear complexes of pentavalent uranyl are also obtained by reduction of the hexavalent uranyl Schiff base complexes with cobaltocene in pyridine in the absence of coordinating cations. The reactivity of the complex [U(V)O(2)(salen)(py)][Cp*(2)Co] with different alkali ions demonstrates the crucial effect of coordinating cations on the stability of cation-cation complexes. The nature of the cation plays a key role in the preparation of stable cation-cation complexes. Stable tetranuclear complexes form in the presence of K(+) and Rb(+), whereas Li(+) leads to disproportionation. A new uranyl-oxo cluster was isolated from this reaction. The reaction of [U(V)O(2)(salen)(py)][Cp*(2)Co] (Cp* = pentamethylcyclopentadienyl) with its U(VI) analogue yields the oxo-functionalized dimer [UO(2)(salen)(py)](2)[Cp*(2)Co] (8). The reaction of the {[UO(2)(salen)(4)][?(8)-K](2)[K([18]C-6)](2)} tetramer with protons leads to disproportionation to U(IV) and U(VI) species and H(2)O confirming the crucial role of the proton in the U(V) disproportionation. PMID:21053213

Mougel, Victor; Horeglad, Pawel; Nocton, Grgory; Pcaut, Jacques; Mazzanti, Marinella

2010-12-27

39

Uranyl nitrate complexes with diphenylsulfoxide and dibenzylsulfoxide: characterization, luminescence and structures  

NASA Astrophysics Data System (ADS)

Uranyl nitrate complexes with diphenylsulfoxide (DPSO) and dibenzylsulfoxide (DBSO) were synthesized and characterized by CHN elemental analyses, infrared absorption spectra, X-ray powder diffraction, visible luminescence spectra and thermal analyses (TG and DTG). The complexes present the compositions UO2(NO3)2(DPSO)2 and UO2(NO3)2(DBSO)2. Infrared spectra show a shift of /?SO to lower frequencies, indicating bonding through the sulfoxide oxygen. The nitrate bands indicate that they are coordinated as bidentate ligands. In both complexes thermal decomposition yields U3O8 as final product. Both complexes present a strong green luminescence, both at room temperature and 77K, presenting four bands with vibronic structures partially resolved at low temperature. The X-ray powder patterns of these complexes are different, therefore, both structures were determined by single-crystal X-ray diffraction. In both complexes the U(VI) occupies a symmetry center. Uranyl oxygen atoms, nitrate ions and neutral ligands are perpendicular with respect to each other.

de Almeida, K. C. S.; Martins, T. S.; Isolani, P. C.; Vicentini, G.; Zukerman-Schpector, J.

2003-02-01

40

Adsorption of uranyl onto ferric oxyhydroxides: Application of the surface complexation site-binding model  

Microsoft Academic Search

Uranyl adsorption was measured from aqueous electrolyte solutions onto well-characterized goethite, amorphous ferric oxyhydroxide, and hematite sols at 25C. Adsorption was studied at a total uranyl concentration of 10 -5 M, (dissolved uranyl 10 -5 to 10 -8 M) as a function of solution pH, ionic strength and electrolyte concentrations, and of competing cations and carbonate complexing. Solution pHs ranged

Ching-Kuo Daniel Hsi; Donald Langmuir

1985-01-01

41

Spectroscopic evidence for the direct coordination of the pertechnetate anion to the uranyl cation in [UO2(TcO4)(DPPMO2)2]+.  

PubMed

We report the synthesis and structural characterization of [UO(2)(ReO(4))(DPPMO(2))(2)][ReO(4)] and [UO(2)(Cl)(DPPMO(2))(2)][Cl] (where DPPMO(2) = bis(diphenylphosphino)methane dioxide). In both complexes, the linear uranyl dication is coordinated to two bidentate DPPMO(2) ligands in the equatorial plane with one coordinated and one non-coordinated anion (either perrhenate or chloride). We have also prepared the pertechnetate analogue, and, through (31)P and (99)Tc NMR, we have shown that the cation, [UO(2)(TcO(4))(DPPMO(2))(2)](+), is stable in solution. PMID:15332793

Sutton, Andrew D; John, Gordon H; Sarsfield, Mark J; Renshaw, Joanna C; May, Iain; Martin, Leigh R; Selvage, Andrew J; Collison, David; Helliwell, Madeleine

2004-09-01

42

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

PubMed

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. PMID:23321220

Asadi, Zahra; Shorkaei, Mohammad Ranjkesh

2012-12-28

43

Complex formation between uranyl and various thiosemicarbazide derivatives  

SciTech Connect

Complex formation between hexavalent uranium and salicylaldehyde thiosemicarbazone (H/sub 2/L), salicylaldehyde S-methyl-isothiosemicarbazone (H/sub 2/Q), S-methyl-N/sub 1/,N/sub 4/-bis(salicylidene)isothiosemicarbazide(H/sub 2/Z), and thiosemicarbazidodiacetic acid (H/sub 2/R) has been studied spectrophotometrically in solution. Stability constants for complexes having the composition UO/sub 2/A have been calculated. Solid uranyl derivatives having the composition UO/sub 2/L x 2H/sub 2/O, UO/sub 2/Q x 2H/sub 2/O, UO/sub 2/Z x 2H/sub 2/O, and UO/sub 2/R x 2H/sub 2/O have been obtained. These derivatives were isolated and their IR spectroscopic behavior and thermal properties were investigated.

Chuguryan, D.G.; Dzyubenko, V.I.

1987-01-01

44

Hydroxy- and alkoxy-bridged dinuclear uranyl-Schiff base complexes: hydrolysis, transamination and extraction studies.  

PubMed

The reaction of uranyl nitrate with 1,3-bis(salicylideneamino)-2-propanol (H(3)L1) and 1,3-bis(3,5-di-tert-butylsalicylideneamino)-2-propanol (H(3)L2) in the presence of triethylamine (Et(3)N) yielded hydroxy- and alkoxy-bridged dinuclear complexes; [(UO(2))(2)(L1)(OH)(MeOH)(2)].(MeOH)(2) (.(MeOH)(2)) and [(UO(2))(2)(L2)(OH)(MeOH)(2)].(MeOH)(2) (.(MeOH)(2)). The crystal structures of .(DMF)(2) and .(DMF)(2) exhibit an unsymmetrical central U(2)O(2) core involving bridging alkoxy- and hydroxy-oxygen atoms. The geometry around the uranium center in .(DMF)(2) and .(DMF)(2) is that of a distorted pentagonal bipyramid with the solvent molecule occupying the fifth coordination site. The flexible nature of the ligand backbone is more pronounced in .(DMF)(2) compared to .(DMF)(2), yielding two molecules per unit cell in different conformations. Under similar reaction conditions, using ethylenediamine as a base, the respective Salen-based uranyl compounds, [UO(2)(Salen)(MeOH)] () and [UO(2)(Bu(t)(2)-Salen)(MeOH)] () are obtained due to transamination of the ligand backbone. Complexes .(MeOH)(2) and .(MeOH)(2) when reacted with an excess of ethylenediamine failed to yield the respective Salen-based complexes, and , respectively. The new compounds have been characterized using solution (NMR and UV-Vis) and solid-state (IR, X-ray crystallography) techniques. Hydrolysis of .(MeOH)(2) and .(MeOH)(2) in the pH range 1-14 was studied using UV-Vis spectroscopy and compared with the hydrolysis of and [UO(2)(Salophen)(MeOH)] (). A two-phase extraction study suggests quantitative removal of uranyl ions from the aqueous phase at higher pH conditions. PMID:18493632

Bharara, Mohan S; Heflin, Kathryn; Tonks, Stephen; Strawbridge, Kara L; Gorden, Anne E V

2008-04-29

45

COMPLEXES OF URANYL ION WITH DIMETHYLFORMAMIDE AND SEMICARBAZIDE  

Microsoft Academic Search

When uranyl acetate dinydrate was refluxed with dimethyiformamide and ; cooled to 0 deg C, yellow crystals of uranyl dimethylformamide acetate, UO; (HCON(CH)) (CH(HCON(CH)(NO; (CHCOO), were precipitated. When uranyl nitrate hexahydrate was ; refluxed with dimethylformamide, was obtained. Semicarbazide underwent similar ; reactions but did not replace all of the waters in the solvation shell; UO; (HO)(NH\\/CONHNH)Cl was obtained from

N. A. Frigerio; R. F. Coley

1962-01-01

46

Structural, spectroscopic and redox properties of uranyl complexes with a maleonitrile containing ligand.  

PubMed

The reaction of uranyl nitrate hexahydrate with the maleonitrile containing Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (salmnt((Et(2)N)(2))H(2)) in methanol produces [UO(2)(salmnt((Et2N)2))(H(2)O)] (1) where the uranyl equatorial coordination plane is completed by the N(2)O(2) tetradentate cavity of the (salmnt((Et(2)N)(2)))(2-) ligand and a water molecule. The coordinated water molecule readily undergoes exchange with pyridine (py), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and triphenylphosphine oxide (TPPO) to give a series of [UO(2)(salmnt((Et(2)N)(2)))(L)] complexes (L = py, DMSO, DMF, TPPO; 2-5, respectively). X-Ray crystallography of 1-5 show that the (salmnt((Et(2)N)(2)))(2-) ligand is distorted when coordinated to the uranyl moiety, in contrast to the planar structure observed for the free protonated ligand (salmnt((Et(2)N)(2))H(2)). The Raman spectra of 1-5 only display extremely weak bands (819-828 cm(-1)) that can be assigned to the typically symmetric O=U=O stretch. This stretching mode is also observed in the infrared spectra for all complexes 1-5 (818-826 cm(-1)) predominantly caused by the distortion of the tetradentate (salmnt((Et(2)N)(2)))(2-) ligand about the uranyl equatorial plane resulting in a change in dipole for this bond stretch. The solution behaviour of 2-5 was studied using NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Complexes 2-5 exhibit intense absorptions in the visible region of the spectrum due to intramolecular charge transfer (ICT) transitions and the luminescence lifetimes (< 5 ns) indicate the emission arises from ligand-centred excited states. Reversible redox processes assigned to the {UO(2)}(2+)/{UO(2)}(+) couple are observed for complexes 2-5 (2: E(1/2) = -1.80 V; 3,5: E(1/2) = -1.78 V; 4: E(1/2) = -1.81 V : vs. ferrocenium/ferrocene {Fc(+)/Fc}, 0.1 M Bu(4)NPF(6)) in dichloromethane (DCM). These are some of the most negative half potentials for the {UO(2)}(2+)/{UO(2)}(+) couple observed to date and indicate the strong electron donating nature of the (salmnt((Et(2)N)(2)))(2-) ligand. Multiple uranyl redox processes are clearly seen for [UO(2)(salmnt((Et(2)N)(2)))(L)] in L (L = py, DMSO, DMF; 2-4: 0.1 M Bu(4)NPF(6)) indicating the relative instability of these complexes when competing ligands are present, but the reversible {UO(2)}(2+)/{UO(2)}(+) couple for the intact complexes can still be assigned and shows the position of this couple can be modulated by the solvation environment. Several redox processes were also observed between +0.2 and +1.2 V (vs. Fc(+)/Fc) that prove the redox active nature of the maleonitrile-containing ligand. PMID:21526261

Hardwick, Helen C; Royal, Drew S; Helliwell, Madeleine; Pope, Simon J A; Ashton, Lorna; Goodacre, Roy; Sharrad, Clint A

2011-04-28

47

Evaluation of the stability of uranyl peroxo-carbonato complex ions in carbonate media at different temperatures.  

PubMed

This work studied the stability of peroxide in uranyl peroxo carbonato complex ions in a carbonate solution with hydrogen peroxide using absorption and Raman spectroscopies, and evaluated the temperature dependence of the decomposition characteristics of uranyl peroxo carbonato complex ions in the solution. The uranyl peroxo carbonato complex ions self-decomposed more rapidly into uranyl tris-carbonato complex ions in higher temperature carbonate solutions. The concentration of peroxide in the solution without free hydrogen peroxide represents the concentration of uranyl peroxo carbonato complex ions in a mixture of uranyl peroxo carbonato complex and uranyl tris-carbonato complex ions. The self-decomposition of the uranyl peroxo carbonato complex ions was a first order reaction, and its activation energy was evaluated to be 7.14410(3) J mol(-1). The precipitation of sodium uranium oxide hydroxide occurred when the amount of uranyl tris-carbonato complex ions generated from the decomposition of the uranyl peroxo carbonato complex ions exceeded the solubility of uranyl tris-carbonato ions in the solution at the solution temperature. PMID:22831997

Kim, Kwang-Wook; Lee, Keun-Young; Chung, Dong-Yong; Lee, Eil-Hee; Moon, Jei-Kwon; Shin, Dong-Woo

2012-07-13

48

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

NASA Astrophysics Data System (ADS)

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 ?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 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.; Kemner, Kenneth M.; Brooks, Scott C.

2007-02-01

49

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

50

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

51

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

National Technical Information Service (NTIS)

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 ...

J. B. Briggs R. E. Rothe

1999-01-01

52

Critical Parameters of Complex Geometry Intersecting Cylinders Containing Uranyl Nitrate Solution  

Microsoft Academic Search

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 \\

Robert Emil Rothe; Joseph Blair Briggs

1999-01-01

53

Uranyl ion complexes with aminoalcoholbis(phenolate) [O,N,O,O?] donor ligands  

Microsoft Academic Search

The reaction between uranyl nitrate hexahydrate and phenolic ligand precursor N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-2-aminoethanol (H3L1) in acetonitrile without base affords the dinuclear uranyl complex [(UO2)2(H2L1)2(NO3)2] (1); in the presence of base, the mononuclear complex [UO2(H2L1)2]2H2O (2) is formed. Ligand N,N-bis(2-hydroxy-5-t-butyl-3-methylbenzyl)-2-aminoethanol (H3L2) affords a uranyl complex of formula [UO2(H2L2)2]2CH3CN (3); ligand N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-3-amino-1-propanol (H3L3) affords a uranyl complex of formula [UO2(H2L3)2] (4); whilst ligand N,N-bis(2-hydroxy-5-t-butyl-3-methylbenzyl)-3-amino-1-propanol

Harri Sopo; Jukka Sviili; Arto Valkonen; Reijo Sillanp

2006-01-01

54

Electronic Spectra and the Mechanism of Complexing of Uranyl Nitrate in WaterAcetone Solutions  

Microsoft Academic Search

Based on the analysis of electronic absorption and luminescence spectra, the processes of complexing in an aqueous solution of uranyl nitrate hexahydrate (UO2(NO3)26H2O) on gradual addition of small amounts of acetone have been investigated. In a pure aqueous solution, uranyl exists as the UO25H2O complex. It is shown that addition of acetone to the solution leads to displacement of some

A. A. Zazhogin; A. P. Zazhogin; A. I. Komyak; A. I. Serafimovich

2003-01-01

55

Spectroscopic properties of complex compounds of uranyl phosphates  

SciTech Connect

The reflection and luminescence-excitation spectra of tetracoordinated compounds of uranyl orthophosphates, metaphosphates and pyrophosphates have been studied in the 19 000--50 000-cm region. Their weak dependence on the type of ligand and second-sphere cation has been established, and their identity to the spectra of uranyl chlorides and UW impurity centers in LiF has been demonstrated. An interpretation of the observed experimental results is proposed in the framework of existing theoretical concepts of the electronic structure of uranyl compounds.

Sytko, V.V.; Krasilov, Y.I.; Kuznetsov, N.T.; Aleshkevich, N.I.; Pobedina, A.B.

1985-07-01

56

The Influence of Linker Geometry on Uranyl Complexation by Rigidly-Linked Bis(3-hydroxy-N-methyl-pyridin-2-one)  

SciTech Connect

A series of bis(3-hydroxy-N-methyl-pyridin-2-one) ligands was synthesized, and their respective uranyl complexes were characterized by single crystal X-ray diffraction analyses. These structures were inspected for high-energy conformations and evaluated using a series of metrics to measure co-planarity of chelating moieties with each other and the uranyl coordination plane, as well as to measure coordinative crowding about the uranyl dication. Both very short (ethyl, 3,4-thiophene and o-phenylene) and very long ({alpha},{alpha}{prime}-m-xylene and 1,8-fluorene) linkers provide optimal ligand geometries about the uranyl cation, resulting in planar, unstrained molecular arrangements. The planarity of the rigid linkers also suggests there is a degree of pre-organization for a planar coordination mode that is ideal for uranyl-selective ligand design. Comparison of intramolecular N{sub amide}-O{sub phenolate} distances and {sup 1}H NMR chemical shifts of amide protons supports earlier results that short linkers provide the optimal geometry for intramolecular hydrogen bonding.

Szigethy, Geza; Raymond, Kenneth

2010-04-22

57

Surface complexation model of uranyl sorption on Georgia kaolinite  

Microsoft Academic Search

The adsorption of uranyl on standard Georgia kaolinites (KGa-1 and KGa-1B) was studied as a function of pH (310), total U (1 and 10 ?mol\\/l), and mass loading of clay (4 and 40 g\\/l). The uptake of uranyl in air-equilibrated systems increased with pH and reached a maximum in the near-neutral pH range. At higher pH values, the sorption decreased

T. E Payne; J. A Davis; G. R Lumpkin; R Chisari; T. D Waite

2004-01-01

58

Electrochemical and Spectroelectrochemical Studies on Uranyl Carbonato and Aqua Complexes  

Microsoft Academic Search

The electrochemical reduction of uranyl ion has been studied by the cyclic voltammetry (CV) and the spectroelectrochemical method using optically transparent thin-layer electrode (OTTE) in basic carbonate and acidic aqueous solutions. The CV measurements showed that U(V) was formed quasireversibly by the reduction of uranyl ion in both basic carbonate and acidic Perchlorate solutions. Uranium(V) was found to be much

Kohji MIZUGUCHI; Yoon-Yul PARK; Hiroshi TOMIYASU; Yasuhisa IKEDA

1993-01-01

59

Investigation of Uranyl Nitrate Ion Pairs Complexed with Amide Ligands using Electrospray Ionization Ion Trap Mass Spectrometry and Density Functional Theory  

SciTech Connect

Ion populations formed from electrospray of uranyl nitrate solutions containing different amides vary depending on ligand nucleophilicity and steric crowding at the metal center. The most abundant species were ion pair complexes having the general formula [UO2(NO3)(amide)n=2,3]+, and complexes containing the amide conjugate base, reduced uranyl UO2+, and a 2+ charge were also formed. The formamide experiment produced the greatest diversity of species that stems from weaker amide binding leading to dissociation and subsequent solvent coordination or metal reduction. Experiments using methyl formamide, dimethyl formamide, acetamide, and methyl acetamide produced ion pair and doubly charged complexes that were more abundant, and less abundant complexes containing solvent or reduced uranyl. This pattern is reversed in the dimethylacetamide experiment, which displayed reduced doubly charged complexes and augmented reduced uranyl complexes. DFT investigations of the tris-amide ion pair complexes showed that inter-ligand repulsion distorts the amide ligands out of the uranyl equatorial plane, and that complex stabilities do not increase with increasing amide nucleophilicity. Elimination of an amide ligand largely relieves the interligand repulsion, and the remaining amide ligands become closely aligned with the equatorial plane in the structures of the bis-amide ligands. The studies show that the phenomenological distribution of coordination complexes in a metal-ligand electrospray experiment is a function of both ligand nucleophilicity and interligand repulsion, and that the latter factor begins exerting influence even in the case of relatively small ligands like the substituted methyl-formamide and acetamide ligands.

Gary S. Groenewold; Adriana Dinescu; Michael T. Benson; Garold L. Gresham; Michael J. van Stipdonk

2011-04-01

60

Photophysical studies of uranyl complexes. 2. Evidence for splitting of the luminescent excited state of the uranyl ion  

Microsoft Academic Search

High-resolution luminescence spectra have been obtained for the uranyl ion in uranyl acetate hydrate (U-O(CHO)2HO), lithium uranyl nitrate (LiUO(NO)), rubidium uranyl nitrate (RbUO(NO)), disodium uranyl bis(pyridine-2,6-dicarboxylate) (NaUO(CHNO)), zinc uranyl acetate hydrate (ZnUO(CHO)7HO), bis(iminodiacetato)dioxouranium(VI) (UO(CHNO)), and uranyl sulfate hydrate (UO(SO).3.5) at 77 K. The vibronic structure observed in the luminescence spectra has been analyzed in terms of both an unsplit emitting

Harry G. Brittain; Dale L. Perry

1981-01-01

61

Synthesis, structure, and bonding of stable complexes of pentavalent uranyl.  

PubMed

Stable complexes of pentavalent uranyl [UO(2)(salan-(t)Bu(2))(py)K](n) (3), [UO(2)(salan-(t)Bu(2))(py)K(18C6)] (4), and [UO(2)(salophen-(t)Bu(2))(thf)]K(thf)(2)}(n) (8) have been synthesized from the reaction of the complex {[UO(2)py(5)][KI(2)py(2)]}(n) (1) with the bulky amine-phenolate ligand potassium salt K(2)(salan-(t)Bu(2)) or the Schiff base ligand potassium salt K(2)(salophen-(t)Bu(2)) in pyridine. They were characterized by NMR, IR, elemental analysis, single crystal X-ray diffraction, UV-vis spectroscopy, cyclic voltammetry, low-temperature EPR, and variable-temperature magnetic susceptibility. X-ray diffraction shows that 3 and 8 are polymeric and 4 is monomeric. Crystals of the monomeric complex [U(V)O(2)(salan-(t)Bu(2))(py)][Cp*(2)Co], 6, were also isolated from the reduction of [U(VI)O(2)(salan-(t)Bu(2))(py)], 5, with Cp*(2)Co. Addition of crown ether to 1 afforded the highly soluble pyridine stable species [UO(2)py(5)]I.py (2). The measured redox potentials E(1/2) (U(VI)/U(V)) are significantly different for 2 (-0.91 and -0.46 V) in comparison with 3, 4, 5, 7 and 9 (in the range -1.65 to -1.82 V). Temperature-dependent magnetic susceptibility data are reported for 4 and 7 and give mu(eff) of 2.20 and 2.23 mu(B) at 300 K respectively, which is compared with a mu(eff) of 2.6(1) mu(B) (300 K) for 2. Complexes 1 and 2 are EPR silent (4 K) while a rhombic EPR signal (g(x) = 1.98; g(y) = 1.25; g(z) = 0.74 (at 4 K) was measured for 4. The magnetic and the EPR data can be qualitatively analyzed with a simple crystal field model where the f electron has a nonbonding character. However, the temperature dependence of the magnetic susceptibility data suggests that one or more excited states are relatively low-lying. DFT studies show unambiguously the presence of a significant covalent contribution to the metal-ligand interaction in these complexes leading to a significant lowering of the pi(u)*. The presence of a back-bonding interaction is likely to play a role in the observed solution stability of the [UO(2)(salan-(t)Bu(2))(py)K] and [UO(2)(salophen-(t)Bu(2))(py)K] complexes with respect to disproportionation and hydrolysis. PMID:20000767

Nocton, Grgory; Horeglad, Pawel; Vetere, Valentina; Pcaut, Jacques; Dubois, Lionel; Maldivi, Pascale; Edelstein, Norman M; Mazzanti, Marinella

2010-01-20

62

REVALUATION OF THE CONTINUOUS VARIATION METHOD AS APPLIED TO THE URANYL AZIDE COMPLEXES  

Microsoft Academic Search

The method of continuous variation is discussed critically, particularly ; when applied to solutions containing more than one complex. The deformations in ; the curves obtained can be interpreted by following the contours of these curves ; at different wavelengths and concentrations. The presence of mono-, di-, and tri-; azido uranyl complex ions is revealed. (auth);

F. G. Sherif; A. M. Awad

1962-01-01

63

First- and second- sphere coordination of the uranyl ion by bis[2-(2-hydroxyphenoxy)ethoxy]ethane.  

PubMed

Uranyl nitrate hexahydrate reacts with bis[2-(2-hydroxyphenoxy)ethoxy]ethane (C(18)H(22)O(6)), denoted LH(2) hereafter, in the presence of triethylamine to give triethylammonium aqua[2,2'-(3,6-dioxaoctane-1,8-diyldioxy)diphenolato-kappa(2)O,O'](nitrato-kappa(2)O,O')dioxouranium(VI), (Et(3)NH)[UO(2)(H(2)O)L(NO(3))], which possesses a symmetry plane. The uranyl ion is coordinated to the two phenoxide O atoms, a nitrate ion and a water molecule (first sphere); the water molecule is itself held in the crown ether chain by hydrogen-bonding interactions, thus ensuring second-sphere coordination by the ligand L. PMID:11828088

Thury, Pierre; Nierlich, Martine; Masci, Bernardo

2002-01-16

64

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

65

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

66

Enantiomerization of chiral uranyl-salophen complexes via unprecedented ligand hemilability: toward configurationally stable derivatives.  

PubMed

In the search for configurationally stable inherently chiral uranyl-salophen complexes, the newly synthesized compound 3 featuring a dodecamethylene chain was expected to be a promising candidate. Unexpectedly, dynamic HPLC on a enantioselective column showed that it still undergoes enantiomerization at high temperature. By comparison with the dynamic behavior of compounds 4 and 5, it was found that the enantiomerization rate is independent of the size of the ligand. This finding definitely rules out a jump rope-type mechanism for the enantiomerization process and points to reaction pathways involving preliminary rupture of one of the O...U coordinative bonds. This provides unprecedented evidence of the occurrence of ligand hemilability in metal-sal(oph)en complexes. Such findings inspired the synthesis of compound 6 endowed with a more rigid spacer, i.e., that derived from 4,4'-(1,4-phenylenediisopropylidene)bisphenol. DHPLC investigations showed that the new structural motif imparts a higher configurational stability, thus raising the half-life for the enantiomerization to more than 2 months at room temperature. This clearly establishes that this compound represents the first member of a new class of inherently chiral receptors, whose potential in chiral recognition and catalysis now can be feasibly explored. PMID:18630884

Ciogli, Alessia; Dalla Cort, Antonella; Gasparrini, Francesco; Lunazzi, Lodovico; Mandolini, Luigi; Mazzanti, Andrea; Pasquini, Chiara; Pierini, Marco; Schiaffino, Luca; Mihan, Francesco Yafteh

2008-07-16

67

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

68

Preparation of a novel uranyl- o-sulfamidobenzoate complex: its crystal and molecular structure at 150 K  

Microsoft Academic Search

The reaction of saccharinate ions with uranyl nitrate hexahydrate (2:1) has led to the opening of five-membered heterocyclic rings, and the formation of a novel uranyl complex of o-sulfamidobenzoate. This has been confirmed by determination of its crystal and molecular structure at 150 K.

Andrei S Batsanov; Clair Bilton; Robert M. K Deng; Keith B Dillon; Judith A. K Howard; Harriet Okatch-Nkala

2000-01-01

69

Isolation and epimerization kinetics of the first diastereoisomer of an inherently chiral uranyl-salophen complex.  

PubMed

The first diastereoisomeric mixture of an inherently chiral uranyl-salophen complex was prepared using (S)-naproxen as a chiral derivatizing agent. Slow crystallization from diisopropyl ether-chloroform afforded one pure diastereoisomer in 45% yield. Kinetic studies allowed the determination of the epimerization rate. [reaction--see text] PMID:15151392

Dalla Cort, Antonella; Mandolini, Luigi; Pasquini, Chiara; Schiaffino, Luca

2004-05-27

70

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

Microsoft Academic Search

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

J. B. Briggs; R. E. Rothe

1999-01-01

71

Photophysical studies of uranyl complexes. 2. Evidence for splitting of the luminescent excited state of the uranyl ion  

SciTech Connect

High-resolution luminescence spectra have been obtained for the uranyl ion in uranyl acetate hydrate (U-O/sub 2/(C/sub 2/H/sub 3/O/sub 2/)/sub 2/2H/sub 2/O), lithium uranyl nitrate (LiUO/sub 2/(NO/sub 3/)/sub 3/), rubidium uranyl nitrate (RbUO/sub 2/(NO/sub 3/)/sub 3/), disodium uranyl bis(pyridine-2,6-dicarboxylate) (Na/sub 2/UO/sub 2/(C/sub 7/H/sub 3/NO/sub 4/)/sub 2/), zinc uranyl acetate hydrate (ZnUO/sub 2/(C/sub 2/H/sub 3/O/sub 2/)/sub 4/7H/sub 2/O), bis(iminodiacetato)dioxouranium(VI) (UO/sub 2/(C/sub 4/H/sub 5/NO/sub 4/)/sub 2/), and uranyl sulfate hydrate (UO/sub 2/(SO/sub 4/)/sub 2/.3.5) at 77 K. The vibronic structure observed in the luminescence spectra has been analyzed in terms of both an unsplit emitting state and a slightly split excited state. The data can best be explained by invoking a split excited state, and arguments are presented which indicate that this splitting is due to a descent in symmetry experienced by the uranyl ion when it is placed in a crystal field.

Brittain, H.G. (Seton Hall Univ., South Orange, NJ); Perry, D.L.

1981-10-15

72

Determination of the stability constants of uranyl complex with 8-hydroxyquinolinium sulfate  

Microsoft Academic Search

8-Hydroxyquinoline (8-HOQ) is known as an important chelating agent for several metal ions. This compound is practically insoluble in water. For this reason, in this study its water soluble sulfate salt has been used for complexing uranyl ions and the stability constants of the complex have been determined. The Irving-Rosotti method computing the Calvin-Bjerrum pH-titration data, was applied. Finally, the

P. nak; D. zdemir; T. nak

1993-01-01

73

Unexpected oxidation of cis-1,3-dithiane-1,3-dioxide (cis-DTSO2) during the preparation of the uranyl nitrate complex  

NASA Astrophysics Data System (ADS)

During the preparation of the complex of hydrated uranyl nitrate with the ligand cis-DTSO2 in ethanolic solution at 50C, a molecule of the ligand suffered an unexpected oxidation giving rise to propanedisulfonate which acts both as bidentate ligand and as counterion. The uranium atom, the water molecule and the propanedisulfonate moiety are sited on a two-fold axis. The uranium atom is hepta-coordinated, in a pentagonal-bipyramidal fashion, to the uranyl oxygen atoms, one water molecule, two monodentate cis-DTSO2 moieties and the bidentate propanedisulfonate. The water molecule is hydrogen bonded to the cis-DTSO2 molecules. The supramolecular arrangement is made through a C-H...O interaction, giving rise to columns of complexes parallel to the b-axis.

Miranda, P., Jr.; Zukerman-Schpector, J.; Mduar, M. F.; Zinner, L. B.; Vicentini, G.

2003-02-01

74

Uranyl(VI) complexes of [ O, N, O, N?]-type diaminobis(phenolate) ligands: Syntheses, structures and extraction studies  

Microsoft Academic Search

The syntheses and crystal structures of four new uranyl complexes with [O,N,O,N?]-type ligands are described. The reaction between uranyl nitrate hexahydrate and the phenolic ligand [(N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N?,N?-dimethylethylenediamine)], H2L1 in a 1:2 molar ratio (M to L), yields a uranyl complex with the formula [UO2(HL1)(NO3)]CH3CN (1). In the presence of a base (triethylamine, one mole per ligand mole) with the same molar

Harri Sopo; Ari Lehtonen; Reijo Sillanp

2008-01-01

75

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

76

Complex coordinates in transformation optics  

NASA Astrophysics Data System (ADS)

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.

2011-12-01

77

Formation and characterization of the uranyl-SO2 complex, UO2(CH3SO2)(SO2)-.  

PubMed

The uranyl-SO(2) adduct, UO(2)(CH(3)SO(2))(SO(2))(-), was prepared and characterized by mass spectrometric studies as well as by density functional theory. Collision induced dissociation of UO(2)(CH(3)SO(2))(2)(-) in an ion trap resulted in the formation of UO(2)(CH(3)SO(2))(SO(2))(-), which spontaneously reacted with O(2) to give UO(2)(CH(3)SO(2))(O(2))(-), with SO(2) released. The UO(2)(CH(3)SO(2))(SO(2))(-) complex is computed to have a triplet ground state at the B3LYP level, and the SO(2) ligand is coordinated to uranium through two oxygen atoms, similar to the coordination mode of SO(2) in its complexes with hard metals. On the basis of the calculated geometric parameters and vibrational frequencies of the SO(2) ligand, the UO(2)(CH(3)SO(2))(SO(2))(-) complex can be considered as a U(V)O(2)(+) cation coordinated by SO(2)(-) and CH(3)SO(2)(-) anions. The UO(2)(CH(3)SO(2))(O(2))(-) complex is computed to have a peroxo ligand, suggesting that U(V) in UO(2)(CH(3)SO(2))(SO(2))(-) is oxidized to the U(VI) state upon O(2) substitution for SO(2). PMID:23311292

Gong, Yu; Gibson, John K

2013-01-22

78

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

2013-03-25

79

Complex formation reactions of uranyl(VI) with neutral N-donors in dimethyl sulfoxide. Influence of small amounts of water  

SciTech Connect

Quantitative information about the existence and thermodynamic stability of uranyl(VI) ion complexes based solely upon nitrogen coordination has been obtained in the solvent dimethyl sulfoxide. Calorimetric, potentiometric, and FT-IR investigations, under controlled anhydrous conditions, show that the uranyl(VI) ion can form both mono and bis chelates with the ethylenediamine ligand and only a mono chelate of rather low stability with propylenediamine. With the monodentate ligand n-butylamine only a very weak metal-ligand interaction has been detected. The stability constants and the enthalpy and entropy changes have been calculated for the identified coordinated species. All data refer to 25.0{degree}C and a tetraethylammonium perchlorate medium of ionic strength 0.1 M. All the complexes are enthalpy stabilized whereas the entropy contributions oppose the complex formation. Calorimetric and FT-IR measurements carried out to investigate the effects of small amounts of water present show that a very low water concentration, comparable to that of the coordinating metal ion, can give rise to hydrolysis reactions that may compete with complex formation. This is due to the combined action of different factors that are discussed. 39 refs., 6 figs., 1 tab.

Cassol, A.; Di Bernardo, P.; Zanonato, P. (Universita di Padova (Italy)); Portanova, R.; Tolazzi, M. (Universita di Udine (Italy) CNR, Padova (Italy))

1990-03-07

80

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

2012-12-25

81

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[double bond, length as m-dash]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[double bond, length as m-dash]O bond expansion on the charges carried by the uranyl ligand complexes. PMID:24026755

Liu, Guokui; Rao, Linfeng; Tian, Guoxin

2013-09-25

82

Raman spectroscopic study of uranyl complex in alkali chloride melts  

NASA Astrophysics Data System (ADS)

Raman spectra of alkali chloride melts containing 3 mol% U(VI) were measured at 823 K. The complexation of UO2Cl42- in binary mixtures of LiClKCl, LiClRbCl, and LiClCsCl was investigated. The spectrum of UO2Cl42- obtained was characterized by Raman active vibration modes, that is, totally symmetric stretching vibrations A1g (?1: OUO) and A1g (?2: UCl4), and bending vibration Eg (?8: UO2Cl2). The dependence of polarizing power of solvent cations on the vibrational frequencies was clarified. The ?8 frequencies were insensitive to the change in the polarizing power. On the other hand, the ?1 and ?2 frequencies increased with the rise of polarizing power. The Raman shifts suggest that the square bipyramidal structure of UO2Cl42- is kept in various binary alkali chlorides, while O2? and Cl? around U(VI) are clearly polarized by the increase of polarizing power.

Fujii, Toshiyuki; Uda, Takeshi; Iwadate, Yasuhiko; Nagai, Takayuki; Uehara, Akihiro; Yamana, Hajimu

2013-09-01

83

Experimental and theoretical studies on the fragmentation of gas-phase uranyl-, neptunyl-, and plutonyl-diglycolamide complexes.  

PubMed

Fragmentation of actinyl(VI) complexes U(VI)O2(L)2(2+), Np(VI)O2(L)2(2+), and Pu(VI)O2(L)2(2+) (L = tetramethyl-3-oxa-glutaramide, TMOGA) produced by electrospray ionization was examined in the gas phase by collision induced dissociation (CID) in a quadrupole ion trap mass spectrometer. Cleavage of the C-Oether bond was observed for all three complexes, with dominant products being U(VI)O2(L)(L-86)(+) with charge reduction, and Np(VI)O2(L)(L-101)(2+) and Pu(VI)O2(L)(L-101)(2+) with charge conservation. The neptunyl and plutonyl complexes also exhibited substantial L(+) loss to give pentavalent complexes Np(V)O2(L)(+) and Pu(V)O2(L)(+), whereas the uranyl complex did not, consistent with the comparative An 5f-orbital energies and the An(VI)O2(2+)/An(V)O2(+) (An = U, Np, Pu) reduction potentials. CID of Np(V)O2(L)2(+) and Pu(V)O2(L)2(+) was dominated by neutral ligand loss to form Np(V)O2(L)(+) and Pu(V)O2(L)(+), which hydrated by addition of residual water in the ion trap; U(V)O2(L)2(+) was not observed. Theoretical calculations of the structures and bonding of the An(VI)O2(L)2(2+) complexes using density functional theory reveal that the metal centers are coordinated by six oxygen atoms from two TMOGA ligands. PMID:24015813

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

2013-09-23

84

Uranyl adsorption and surface speciation at the imogolite water interface: Self-consistent spectroscopic and surface complexation models  

NASA Astrophysics Data System (ADS)

Macro- and molecular-scale knowledge of uranyl (U(VI)) partitioning reactions with soil/sediment mineral components is important in predicting U(VI) transport processes in the vadose zone and aquifers. In this study, U(VI) reactivity and surface speciation on a poorly crystalline aluminosilicate mineral, synthetic imogolite, were investigated using batch adsorption experiments, X-ray absorption spectroscopy (XAS), and surface complexation modeling. U(VI) uptake on imogolite surfaces was greatest at pH 7 8 (I = 0.1 M NaNO3 solution, suspension density = 0.4 g/L [U(VI)]i = 0.01 30 ?M, equilibration with air). Uranyl uptake decreased with increasing sodium nitrate concentration in the range from 0.02 to 0.5 M. XAS analyses show that two U(VI) inner-sphere (bidentate mononuclear coordination on outer-wall aluminol groups) and one outer-sphere surface species are present on the imogolite surface, and the distribution of the surface species is pH dependent. At pH 8.8, bis-carbonato inner-sphere and tris-carbonato outer-sphere surface species are present. At pH 7, bis- and non-carbonato inner-sphere surface species co-exist, and the fraction of bis-carbonato species increases slightly with increasing I (0.1 0.5 M). At pH 5.3, U(VI) non-carbonato bidentate mononuclear surface species predominate (69%). A triple layer surface complexation model was developed with surface species that are consistent with the XAS analyses and macroscopic adsorption data. The proton stoichiometry of surface reactions was determined from both the pH dependence of U(VI) adsorption data in pH regions of surface species predominance and from bond-valence calculations. The bis-carbonato species required a distribution of surface charge between the surface and ? charge planes in order to be consistent with both the spectroscopic and macroscopic adsorption data. This research indicates that U(VI)-carbonato ternary species on poorly crystalline aluminosilicate mineral surfaces may be important in controlling U(VI) mobility in low-temperature geochemical environments over a wide pH range (5 9), even at the partial pressure of carbon dioxide of ambient air (pCO2 = 10-3.45 atm).

Arai, Yuji; McBeath, M.; Bargar, J. R.; Joye, J.; Davis, J. A.

2006-05-01

85

Complexation of the uranyl ion (UO 2) 2+ with a tetraphenylimidodiphosphinate ligand: the first trinuclear uranyl complex comprising a double ? 2-oxo (UO 2) bridge  

Microsoft Academic Search

Reaction of K[(OPPh2)2N] with UO2(NO2)26H2O resulted in the formation of compound [UO2[(OPPh2)2N]2]3 (1). Single-crystal diffraction analysis of 1 reveals an elaborated and unique trinuclear uranyl compound, where the central UO2 moiety exhibits Lewis basic properties through an equatorial U?OUO?U bridging towards two outer uranyl units comprised in a six-membered ring array. The central and outer UO2 groups are also bridged

Raymundo Cea-Olivares; Graciela Canseco-Melchor; Mnica M. Moya-Cabrera; Vernica Garca-Montalvo; Jos G. Alvarado-Rodrguez; Rubn A. Toscano

2005-01-01

86

Coordination: new ways of harnessing complexity.  

PubMed

As systems evolve over time, their natural tendency is to become increasingly more complex. Studies in the field of complex systems have generated new perspectives on management in social organizations such as hospitals. Much of this research appears as a natural extension of the cross-disciplinary field of systems theory. This is the fourth of a 5-part series on applying complex systems science to the traditional management concepts of planning, organizing, directing, coordinating, and controlling. In this article, the concept of coordination is explored from a complex systems perspective. PMID:18403987

Clancy, Thomas R; Anteau, Carlene

2008-04-01

87

Electrospray ionization of uranyl-citrate complexes: Adduct formation and ion-molecule reactions in 3D ion trap and ion cyclotron resonance trapping instruments  

Microsoft Academic Search

Results presented here demonstrate the usefulness of electrospray ionization and gas-phase ion-molecule reactions to predict structural and electronic differences in complex inorganic ions. Electrospray ionization of uranyl citrate solutions generates positively and negatively charged ions that participate in further ion-molecule reactions in 3D ion trap and FT-ICR mass analyzers. Most ions observed are derived from the major solution uranyl-citrate complexes

rpd Somogyi; Sofie P. Pasilis; Jeanne E. Pemberton

2007-01-01

88

Strong anticipation: complexity matching in interpersonal coordination.  

PubMed

A subtle coordination occurs within complex systems, between multiple nested sub-systems. This intra-system coordination can be detected by the presence of 1/f fluctuations produced by the system. But coordination can occur also between systems. Interpersonal coordination has been studied from a local point of view until now, focusing on macroscopic interactions. But the recent concept of strong anticipation introduced by Dubois (Lect Notes Comput Sci 2684:110-132, 2003) suggests that interactions could occur on multiple levels between complex systems. The hypothesis is that time series in interpersonal synchronization present a matching of the complexity index (fractal exponent). Moreover, it is argued that this matching is not a consequence of short-term adaptations but reveals a global coordination between participants. Eleven pairs of participants oscillated a hand-held pendulum in the in-phase pattern for 11 min, in three conditions where the coupling strength was manipulated by the perceptual feedbacks. The results show a high correlation between fractal exponents irrespective of the coupling strength, and a very low percentage of local cross-correlations between time series appear at lag 0 and lag 1. These results suggest that interpersonal coordination, and more globally synchronization of participants with natural environments, is based on non-local time scales. PMID:22865163

Marmelat, Vivien; Delignires, Didier

2012-08-04

89

Ion exchange\\/complexation of the uranyl ion by Rhizopus biosorbent  

Microsoft Academic Search

Nonliving biomass of nine Rhizopus species effectively sequestered the uranyl ion from solution, taking up 150-250 mg U\\/g dry cells at 300 ppm U equilibrium concentration in solution, and 100-160 mg U\\/g dry cells with 100 ppm U in solution. The affinity of this biosorbent for the uranyl ion was found to be affected by timing of harvesting and medium

Margaret E. Treen-Sears; Bohumil Volesky; Ronald J. Neufeld

1984-01-01

90

Strongly coupled binuclear uraniumoxo complexes from uranyl oxo rearrangement and reductive silylation  

Microsoft Academic Search

The most common motif in uranium chemistry is the d0f0 uranyl ion [UO2]2+ in which the oxo groups are rigorously linear and inert. Alternative geometries, such as the cis-uranyl, have been identified theoretically and implicated in oxo-atom transfer reactions that are relevant to environmental speciation and nuclear waste remediation. Single electron reduction is now known to impart greater oxo-group reactivity,

Guy M. Jones; Samuel O. Odoh; Georg Schreckenbach; Nicola Magnani; Polly L. Arnold; Jason B. Love

2012-01-01

91

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...

92

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

93

Critical Parameters of Complex Geometry 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 when 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.

Rothe, Robert Emil; Briggs, Joseph Blair

1999-06-01

94

Influence of Acidity on Uranyl Nitrate Association in Aqueous Solutions: A Molecular Dynamics Simulation Study  

SciTech Connect

Uranyl ion complexation with water and nitrate is a key aspect of the uranium/plutonium extraction process. We have carried out a molecular dynamics simulation study to investigate this complexation process, including the molecular composition of the various complex species, the corresponding structure, and the equilibrium distribution of the complexes. The observed structures of the complexes suggest that in aqueous solution, uranyls are generally hydrated by 5 water molecules in the equatorial plane. When associating with nitrate ions, a water molecule is replaced by a nitrate ion, preserving the five-fold coordination and planar symmetry. Analysis of the pair correlation function between uranyl and nitrate suggests that nitrates bind to uranyl in aqueous solution mainly in a monodentate mode, although a small portion of bidentates occur. Dynamic association and dissociation between uranyls and nitrates take place in aqueous solution with a substantial amount of fluctuation in the number of various uranyl nitrate species. The average number of the uranyl mononitrate complexes shows a dependence on acid concentration consistent with equilibrium-constant analysis, namely, the concentration of [UO2NO3]+ increases with nitric acid concentration.

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

2010-01-01

95

A kinetic study of the conjugate addition of benzenethiol to cyclic enones catalyzed by a nonsymmetrical uranyl-salophen complex.  

PubMed

The Et3N-assisted addition of benzenethiol to enones in chloroform is catalyzed with high turnover efficiency by the phenyl-substituted uranyl-salophen compound 3. Catalytic data show a close adherence to a quatermolecular mechanism involving reaction of a base-activated thiol with a reversibly formed complex of enone and metal catalyst, with a complication of product inhibition due to the formation of a product-catalyst complex. The role of the binding energy made available by interactions with the aromatic sidearm of the catalyst is discussed in terms of catalyst-substrate and catalyst-transition state complementarity. PMID:17559271

van Axel Castelli, Valeria; Dalla Cort, Antonella; Mandolini, Luigi; Pinto, Valentina; Schiaffino, Luca

2007-06-09

96

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

97

INFRARED SPECTRA OF URANYL COMPOUNDS. I. URANYL NITRATES  

Microsoft Academic Search

The infra-red spectra of the di-, tri-, and hexahydrates of uranyl ; nitrate and of anhydrous potassium uranyl nitrate have been recorded. The ; results differ significantly from those of Gatehouse and Comyns but did not ; permit a decision regarding the structure of the complex anions in these ; compounds. (auth);

J. G. Allpress; A. N. Hambly

1959-01-01

98

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

National Technical Information Service (NTIS)

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...

B. E. Watkins J. H. Satcher

1995-01-01

99

Uranyl-like transitions in AnOC1\\/sup 2 -\\/ and chemical bonding in excited complexes  

Microsoft Academic Search

The authors find uranyl-like transitions in the spectrum of PuOC1\\/sup 2 -\\/ in the 5000-20000 cm⁻¹ region at 15,280, 15,498, and 15,658 cm⁻¹. The influence of the transitions of this type on the chemical bonding in the complexes AnOC1\\/sup 2 -\\/ (An= U, Np, Pu) has been discussed. Strengthening of the An-C1 bond in an excited ion in comparison to

N. G. Gorshov; L. G. Mashirov

1986-01-01

100

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

2012-07-27

101

Double-receptor sandwich supramolecule sensing method for the determination of ATP based on uranyl-salophen complex and aptamer.  

PubMed

In this study, we report a double-receptor sandwich supramolecule sensing method for the determination of adenosine triphosphate (ATP). One receptor is a uranyl-salophen complex which can bind the triphosphate group in ATP selectively, and another is an anti-adenosine aptamer which is a single-stranded oligonucleotide and can recognize the adenosine group in ATP specifically. The uranyl-salophen complex was immobilized on the surface of amino-silica gel particles and used as the solid phase receptor of ATP. The anti-adenosine aptamer was labeled with a fluorescent group and used as the labeled receptor of ATP. In the procedure of ATP detection, ATP was first combined with the solid phase receptor and then conjugated with the labeled receptor to form a sandwich-type supramolecule. The conditions of fabricating solid phase receptor and the influence of manifold variables on the determination were studied. The experimental results demonstrate that the method has a number of advantages such as high selectivity, high sensitivity, good stability and low cost. Under optimal conditions, the linear range for detection of ATP is 0.2-5.0 nmol/mL with a detection limit of 0.037 nmol/mL. The proposed method was successfully applied for the determination of ATP in real samples with the recoveries of 96.8-103.3%. PMID:22336438

Zhao, Minmin; Liao, Lifu; Wu, Minlong; Lin, Yingwu; Xiao, Xilin; Nie, Changming

2012-01-28

102

Coordinating Tectons: Bipyridyl Terminated Allenylidene Complexes  

SciTech Connect

A series of complexes with {pi}-conjugated carbon chains terminated by bipyridyl moieties has been prepared. These allenylidene complexes were derived from 9-hydroxy-9-ethynyl-4,5-diazafluorene, the preparation of which is reported; the new allenylidene complexes are highly colored with the cumulated carbon chain terminating in a bipyridyl unit providing a site for further coordination. The synthesis, characterization, and X-ray structure determination of trans-[MCl(P{intersection}P){sub 2}{sub {double_bond}}C{sub {double_bond}}C{sub {double_bond}}(4,5-diazafluoren-9-yl)]PF{sub 6} (M = Ru, P{intersection}P = bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,2-bis(dimethylphosphino)ethane (dmpe); M = Os, P{intersection}P = dppm) are described. The effect of the variation in metal and ligand on electronic and electrochemical characteristics of these complexes has been investigated by using UV-vis, solution electrochemistry, and a combination of these techniques in spectroelectrochemical experiments. DFT calculations have been performed on trans-[RuCl(P{intersection}P){sub 2}{sub {double_bond}}C{sub {double_bond}}C{sub {double_bond}}(4,5-diazafluoren-9-yl)]{sup q} (P{intersection}P = dppm, bis(dimethylphosphino)methane (dmpm); q = -1, 0, +1, +2) and subsequently solvent-corrected calculations with use of COSMO were also undertaken to examine the nature of electronic transitions in various oxidation states.

Cifuentes, Marie P.; Humphrey, Mark G.; Koutsantonis, George A.; Lengkeek, Nigel A.; Petrie, Simon; Sanford, Vanessa; Schauer, Phil A.; Skelton, Brian W.; Stranger, Robert; White, Allan H. (UWA); (ANU)

2009-01-15

103

Uranyl sequestering agents: Correlation of properties and efficacy with structure for UO{sub 2}{sup 2+} complexes of linear tetradentate 1-methyl-3-hydroxy-2(1H)-pyridinone ligands  

SciTech Connect

A rational design of uranyl sequestering agents based on 3-hydroxy-2(1H)-pyridinone ligands has resulted in the first effective agents for mammalian uranyl decorporation. In this study crystal structures of uranyl complexes with four of these agents are compared and correlated with the chemical and biological properties. These hydroxypyridinone ligands bind the uranyl ion in the equator of a pentagonal prism; a solvent molecule fills the fifth coordination site. The tetradentate ligands are composed of two hydroxypyridonate groups connected by a diamine linker via amide coupling. The dihedral angles between two pyridinone ring planes in these complexes differ as the length of linear backbone changes, giving these molecules a ruffled shape. The physical parameters (such as NMR chemical shifts) of the uranyl complexes with tetradentate Me-3,2-HOPO ligands correlate with the length of the diamine linker, as does the in vivo activity. The ligands are amides of 3-hydroxy-N-methyl-2-(1H)-4-carboxypyridone. For L{sup 1} the amine is propane amine. For the tetradentate bis-amides the linker groups are (L{sup 3}) 1,3-diaminopropane, (L{sup 4}) 1,4-diaminobutane, (L{sup 5}) 1,5-diaminopentane. Crystal data: [UO{sub 2}(L{sup 1}){sub 2}{center_dot}DMF], space group, C2/c, cell constants: a = 37.430(8) {angstrom}, b = 7.0808(14) {angstrom}, c = 26.781(5) {angstrom}, {beta} = 130.17(3){degree}, V = 5424(2) {angstrom}{sup 3}, Z = 8. [UO{sub 2}L{sup 3}{center_dot}DMSO], Pnma, a = 8.4113(1) {angstrom}, b = 16.0140(3) {angstrom}, c = 16.7339(3) {angstrom}, V = 2254.03(5) {angstrom}{sup 3}, Z = 4. [UO{sub 2}L{sup 4}{center_dot}DMSO]{center_dot}DMSO{center_dot}H{sub 2}O{center_dot}0.5C{sub 6}H{sub 12}, P2{sub 1}/n, a = 26.7382(4) {angstrom}, b = 7.4472(1) {angstrom}, c = 31.4876(2) {angstrom}, V = 6209.05(13) {angstrom}{sup 3}, Z = 8. [UO{sub 2}L{sup 5}{center_dot}DMSO]{center_dot}DMSO, Pnma, a = 7.3808(1) {angstrom}, b = 14.7403(3) {angstrom}, c = 23.134(3) {angstrom}, V = 2516.88(8) {angstrom}{sup 3}, Z = 4.

Xu, J. Raymond, K.N. [Lawrence Berkeley National Lab., CA (United States)

1999-01-25

104

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

2011-03-29

105

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

NASA Astrophysics Data System (ADS)

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.; Zhang, B.; Zhang, X.; Xu, B.

2007-03-01

106

UV-visible and infrared spectra of volatile uranyl complexes in the gas phase  

Microsoft Academic Search

The gas-phase UV-visible and infrared spectra of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)dioxouranium(VI) (UO(HFA)) were found to exhibit a marked pressure and temperature dependence which appears consistent with the monomer-dimer equilibrium previously established for this compound. The visible spectra obtained for both the monomeric and dimeric species are unusual because the vibrational structure characteristic of the spectra of many uranyl compounds is completely absent. The

A. Ekstrom; H. J. Hurst; C. H. Randall; H. Loeh

1980-01-01

107

Complex coordinate stretching as a generalized absorbing boundary condition  

Microsoft Academic Search

By complex coordinate stretching and a change ofari- ables, it is shown simply that PML is reflectionless for all frequencies and all angles. Also, Maxwell's equations for PML media reduce to ordinary Maxwell's equations with complex coordinate systems. Many closed-form solutions for Maxwell's equations map to corresponding closed-form solutions in complex coordinate systems. Numerical simulations with the closed-form solutions show

W. C. Chew; J. M. Jin; E. Michielssen

1997-01-01

108

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

109

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

2012-06-18

110

Determinacao de uranilo utilizando como reagente complexante piridilazoresorcinol pela tecnica voltametrica adsortiva com redissolucao catodica. (Uranyl determination using pyridylazoresorcinol as complexing active by adsorptive voltametry technique with cathodic redissolution).  

National Technical Information Service (NTIS)

The development method for uranyl ion determination by the optimization of chemical reaction and instrumental parameters is shown. This method is based on preconcentration stage, where in adsorptive accumulation of metallic complex in a static electrode i...

A. K. Ohara P. A. M. Farias

1990-01-01

111

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

112

Effect of nitrate, perchlorate, and water on uranyl(VI) speciation in a room-temperature ionic liquid: a spectroscopic investigation.  

PubMed

Room-temperature ionic liquids form potentially important solvents in novel nuclear waste reprocessing methods, and the solvation, speciation, and complexation behaviors of lanthanides and actinides in these solvents are of great current interest. In the study reported here, the coordination environment of uranyl(VI) in solutions of the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf(2)N]) containing perchlorate, tetrabutylammonium nitrate, and water was investigated using Raman, ATR-FTIR, and NMR spectroscopies in order to better understand the role played in uranyl(VI) solution chemistry in room-temperature ionic liquids by water and other small, weakly complexing ligands. The (2)H NMR chemical shift for water in a solution of uranyl perchlorate hexahydrate in [EMIM][Tf(2)N] appears at 6.52 ppm, indicating that water is coordinated to uranyl(VI). A broad ?(OH) stretching mode at 3370 cm(-1) in the ATR-FTIR spectrum shows that this coordinated water is engaged in hydrogen bonding with water molecules in a second coordination sphere. A significant upfield shift in the (2)H NMR signal for water and the appearance of distinct ?(as)(HOH) (at 3630 cm(-1)) and ?(s)(HOH) (at 3560 cm(-1)) vibrational bands in the ATR-FTIR spectra show that coordinated water is displaced by nitrate upon formation of the UO(2)(NO(3))(2) and UO(2)(NO(3))(3)(-) complexes. The Raman spectra indicate that perchlorate complexed to uranyl(VI) is also displaced by nitrate. Our results indicate that perchlorate and water, though weakly complexing ligands, do have a role in uranyl(VI) speciation in room-temperature ionic liquids and that Raman, infrared, and NMR spectroscopies are valuable additions to the suite of tools currently used to study the chemical behavior of uranyl(VI)-ligand complexes in these solvents. PMID:21786806

Pasilis, Sofie P; Blumenfeld, Alexander

2011-07-25

113

Exclusive transition state stabilization in the supramolecular catalysis of Diels-Alder reaction by a uranyl salophen complex.  

PubMed

Whereas the parent uranyl salophen is catalytically inactive, its phenyl derivative effectively catalyses with turnover the reaction of benzoquinone with 1,3-cyclohexadiene, while showing no appreciable affinity towards reactants and product. PMID:16041444

Dalla Cort, Antonella; Mandolini, Luigi; Schiaffino, Luca

2005-07-01

114

Determination of structural parameters of uranyl ions complexed with organic acids using EXAFS  

Microsoft Academic Search

Two compounds of known crystal structure, sodium triacetatodioxouranium(VI), Na[UO2(CH3COO)3], and dibenzoatodioxouranium(VI), UO2[C6H5(COO)]2, were studied by uranium LIII-edge extended X-ray absorption fine structure, EXAFS, spectroscopy to differentiate between bidentate and monodentate coordination of carboxylate ions on the basis of the uraniumequatorial oxygen, Oeq, bond lengths. Bidentate coordination can be verified by detecting carboxyl carbon atoms and the neighboring distal carbon atom

M. A. Denecke; T. Reich; M. Bubner; S. Pompe; K. H Heise; H Nitsche; P. G Allen; J. J Bucher; N. M Edelstein; D. K Shuh

1998-01-01

115

Fate of uranyl in a quaternary system composed of uranyl, citrate, goethite, and Pseudomonas fluorescens.  

PubMed

This study investigated the partitioning of uranyl within a quaternary system made up of uranyl, citrate, goethite, and the bacterium Pseudomonas fluorescens. In the absence of cells, uranyl was sorbed to goethite as a complex involving surface groups and/or citrate. Measurements of the evolution of CO2 indicated that the addition of bacterial cells lead to the gradual biodegradation of citrate. Throughout the biodegradation process, uranyl remained sorbed to the insoluble fraction comprised of goethite and cells. EXAFS (Extended X-ray Absorption Fine Structure) measurements showed that bacterial cells outcompeted goethite for uranyl under the experimental conditions and caused the repartitioning of uranyl from goethite to cell matter, independently from citrate degradation. Citrate degradation caused further release of uranyl from goethite surfaces, followed by subsequent association of uranyl with cells. At long equilibration times (3 months), cell lysis and phosphate release resulted in the precipitation of an autunite-like phase. This work suggests that bacterial degradation of uranyl-complexing ligands in contaminated subsurface media containing iron oxides should not necessarily lead to an increase in the mobility of uranyl. PMID:12953865

Bencheikh-Latmani, Rizlan; Leckie, James O; Bargar, John R

2003-08-15

116

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

117

The stochastic separatrix and the reaction coordinate for complex systems.  

PubMed

We present a new approach to the identification of degrees of freedom which comprise a reaction coordinate in a complex system. The method begins with the generation of an ensemble of reactive trajectories. Each trajectory is analyzed for its equicommittor position or transition state; then the transition state ensemble is identified as the stochastic separatrix. Numerical analysis of the points along the separatrix for variability of coordinate location correctly identifies the components of the reaction coordinate in a test system of a double well coupled to a promoting vibration and a bath of linearly coupled oscillators. PMID:19388729

Antoniou, Dimitri; Schwartz, Steven D

2009-04-21

118

X-ray absorption fine structures of uranyl(V) complexes in a nonaqueous solution.  

PubMed

The structures of three different U(V) complexes, [U(V)O(2)(salophen)DMSO](-), [U(V)O(2)(dbm)(2)DMSO](-), and [U(V)O(2)(saldien)](-), in a dimethyl sulfoxide (DMSO) solution were determined by X-ray absorption fine structure for the first time. PMID:19754101

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

2009-10-19

119

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

120

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

121

Automatic Method for Identifying Reaction Coordinates in Complex Systems  

Microsoft Academic Search

To interpret simulations of a complex system to determine the physical mechanism of a dynamical process, it is necessary to identify the small number of coordinates that distinguish the stable states from the transition states. We develop an automatic method for identifying these degrees of freedom from a database of candidate physical variables. In the method neural networks are used

Ao Ma; Aaron R. Dinner

2005-01-01

122

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

123

Non-centrosymmetric tetrameric assemblies of tetramethylammonium halides with uranyl salophen complexes in the solid state.  

PubMed

Ditopic salophen-UO(2) receptors 1-4 and 7 co-crystallize with tetramethylammonium (TMA) chloride and fluoride salts producing good quality crystals amenable for X-ray diffraction characterization. The arrangement of the receptor and salt units in the crystal lattice is such that tetrameric ball-shaped assemblies are formed, where an inner cluster of four TMA cations are surrounded by an outer shell of four UO(2)-bound anions. These elaborate architectures, which occur in all cases, regardless of a certain degree of structural modification on the receptors, lead to lattices that belong to non-centrosymmetric (NCS) space groups. Interestingly, the tetragonal symmetry of the tetrameric ball-shaped assemblies is either retained (I4?) or lost (R3c and I4?3d) at the lattice level, without compromising the NCS nature of the crystal lattices. The principal X-ray investigation on TMAX (X = Cl/F) co-crystals, that is, 1-(TMA)Cl, 2-(TMA)Cl, 3-(TMA)Cl, 4-(TMA)Cl, 7-(TMA)Cl, and 7-(TMA)F, is accompanied by NMR and electrospray ionization (ESI) mass spectrometry studies to gather additional insight on the modality of formation of the solid state structures observed. The important role of cation-? interactions in the receptor-salt recognition process is renewed and strengthened by comparison with NMR titration data with a novel reference compound, the salophen-UO(2) complex 8. Given the importance of NCS and polar crystalline solids in the development of functional materials, this study shows that this property can be introduced into elaborate host-guest systems, as those which assemble in the architectures described here, thus expanding its field of applicability. PMID:21090769

Cametti, Massimo; Ilander, Laura; Valkonen, Arto; Nieger, Martin; Nissinen, Maija; Nauha, Elisa; Rissanen, Kari

2010-11-23

124

Coordinating postmitotic nuclear pore complex assembly with abscission timing  

PubMed Central

Cells divide and accurately inherit genomic and cellular content through synchronized changes in cellular organization and chromosome dynamics. Although DNA segregation, nuclear reformation and cytokinesis/abscission temporally overlap, little is known about how these distinct events are coordinated to ensure accurate cell division. Recently, we found that disruption of postmitotic nuclear pore complex assembly, an essential aspect of the newly forming nuclear envelope, triggers an Aurora B-dependent delay in abscission. This delay is further characterized by mislocalized, aberrantly active Aurora B in the cytoplasm of midbody-stage cells. These results support a model in which an Aurora B-mediated abscission checkpoint provides surveillance of nuclear pore complex formation to ensure that elements of nuclear architecture are fully formed before daughter cells are physically separated. Here we discuss the process of nuclear pore complex assembly, describe potential mechanisms that may explain how this process could be coordinated with abscission and postulate why such a checkpoint mechanism may exist.

Mackay, Douglas R

2011-01-01

125

Impact of uranyl-calcium-carbonato complexes on uranium(VI) adsorption to synthetic and natural sediments.  

PubMed

Adsorption on soil and sediment solids may decrease aqueous uranium concentrations and limit its propensity for migration in natural and contaminated settings. Uranium adsorption will be controlled in large part by its aqueous speciation, with a particular dependence on the presence of dissolved calcium and carbonate. Here we quantify the impact of uranyl speciation on adsorption to both goethite and sediments from the Hanford Clastic Dike and Oak Ridge Melton Branch Ridgetop formations. Hanford sediments were preconditioned with sodium acetate and acetic acid to remove carbonate grains, and Ca and carbonate were reintroduced at defined levels to provide a range of aqueous uranyl species. U(VI) adsorption is directly linked to UO(2)(2+) speciation, with the extent of retention decreasing with formation of ternary uranyl-calcium-carbonato species. Adsorption isotherms under the conditions studied are linear, and K(d) values decrease from 48 to 17 L kg(-1) for goethite, from 64 to 29 L kg (-1) for Hanford sediments, and from 95 to 51 L kg(-1) for Melton Branch sediments as the Ca concentration increases from 0 to 1 mM at pH 7. Our observations reveal that, in carbonate-bearing waters, neutral to slightly acidic pH values ( approximately 5) and limited dissolved calcium are optimal for uranium adsorption. PMID:20058915

Stewart, Brandy D; Mayes, Melanie A; Fendorf, Scott

2010-02-01

126

Impact of uranyl-calcium-carbonato complexes on uranium(VI) adsorption to synthetic and natural sediments  

SciTech Connect

Adsorption on soil and sediment solids may decrease aqueous uranium concentrations and limit its propensity for migration in natural and contaminated settings. Uranium adsorption will be controlled in large part by its aqueous speciation, with a particular dependence on the presence of dissolved calcium and carbonate. Here we quantify the impact of uranyl speciation on adsorption to both goethite and sediments from the Hanford Clastic Dike and Oak Ridge Melton Branch Ridgetop formations. Hanford sediments were preconditioned with sodium acetate and acetic acid to remove carbonate grains, and Ca and carbonate were reintroduced at defined levels to provide a range of aqueous uranyl species. U(VI) adsorption is directly linked to UO{sub 2}{sup 2+} speciation, with the extent of retention decreasing with formation of ternary uranyl-calcium-carbonato species. Adsorption isotherms under the conditions studied are linear, and K{sub d} values decrease from 48 to 17 L kg{sup -1} for goethite, from 64 to 29 L kg{sup -1} for Hanford sediments, and from 95 to 51 L kg{sup -1} for Melton Branch sediments as the Ca concentration increases from 0 to 1 mM at pH 7. Our observations reveal that, in carbonate-bearing waters, neutral to slightly acidic pH values ({approx}5) and limited dissolved calcium are optimal for uranium adsorption.

Stewart, B.D. [Stanford University; Mayes, Melanie [ORNL; Fendorf, Scott [ORNL

2010-01-01

127

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

128

Complex formation of uranyl ion with triphenylphosphine oxide and its ligand exchange reaction in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ionic liquid.  

PubMed

Complex formation of the uranyl ion (UO(2)(2+)) with triphenylphosphine oxide (OPPh(3)) in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ([BMI][NfO]) ionic liquid was investigated by means of (31)P NMR spectroscopy. In [BMI][NfO], coordination of OPPh(3) to UO(2)(2+) was found, and its coordination number was 4.1 +/- 0.2, indicating UO(2)(OPPh(3))(4)(2+). From the [BMI][NfO] solution containing UO(2)(2+) and OPPh(3), yellow crystals of UO(2)(OPPh(3))(4)(ClO(4))(2) deposited, and its molecular and crystal structures were determined by using single-crystal X-ray analysis. An OPPh(3) exchange reaction of UO(2)(OPPh(3))(4)(2+) in [BMI][NfO] was also examined. The apparent first-order rate constant (k(obs)) showed the first-order dependence on [OPPh(3)] (k(obs) = k(4)[OPPh(3)](free)), suggesting the "associative" (A) mechanism. Its activation parameters were DeltaH(4)(++) = 55.3 +/- 2.8 kJ mol(-1) and DeltaS(4)(++) = 16.1 +/- 7.9 J mol(-1) K(-1). To compare the reactivity of UO(2)(OPPh(3))(4)(2+) in [BMI][NfO] with that in an ordinary organic solvent, the same reaction in CD(2)Cl(2) was studied. In the CD(2)Cl(2) system, an equilibrium between UO(2)(OPPh(3))(4)(2+) and UO(2)(OPPh(3))(5)(2+) was observed. The k(obs) values of the OPPh(3) exchange reactions in UO(2)(OPPh(3))(4)(2+) (k(4obs)) and UO(2)(OPPh(3))(5)(2+) (k(5obs)) in CD(2)Cl(2) are expressed as k(4obs) = k(4)[OPPh(3)](free) and k(5obs) = k(5), respectively, indicating that the exchange reactions in UO(2)(OPPh(3))(4)(2+) and UO(2)(OPPh(3))(5)(2+) are categorized in A and "dissociative" (D) mechanisms, respectively. The activation parameters of these reactions were also estimated (UO(2)(OPPh(3))(4)(2+): DeltaH(4)(++) = 7.1 +/- 0.3 kJ mol(-1) and DeltaS(4)(++) = -122 +/- 1 J mol(-1) K(-1), UO(2)(OPPh(3))(5)(2+): DeltaH(5)(++) = 62.4 +/- 1.0 kJ mol(-1) and DeltaS(5)(++) = 68.4 +/- 4.2 J mol(-1) K(-1)). A large difference in the reactivity of UO(2)(OPPh(3))(4)(2+) was found between [BMI][NfO] and CD(2)Cl(2). This was explained by the formation of a specific solvation barrier of NfO(-) around UO(2)(OPPh(3))(4)(2+) in [BMI][NfO]. PMID:19138105

Takao, Koichiro; Takahashi, Takafumi; Ikeda, Yasuhisa

2009-02-16

129

Durability of membranes containing uranyl salophenes  

Microsoft Academic Search

Potentiometric, spectroscopic and microscopic studies concerning polymer membranes based on uranyl salophenes were performed. Uranyl salophenesgroup of Schiff base complexesrevealed very good recognition abilities toward some hydrophilic anions and appeared to be very promising ionophores for phosphate-selective electrodes. The influence of the ionophore structure and polymer matrix composition on the durability and selectivity of PVC based membrane of phosphate-selective electrodes

Kamil Wojciechowski; Wojciech Wrblewski; Zbigniew Brzzka

2001-01-01

130

Synthesis and Structure of the [(UO2)S4](6-) Anion: A Cation-Stabilized Uranyl Sulfide.  

PubMed

The new uranyl sulfide anion [(UO2)S4](6-) has been synthesized and characterized as a cation-stabilized anion in the compound Na2Ba2(UO2)S4. This compound was synthesized at 873 K from the solid-state reaction of uranium, Na2O2, BaS, and sulfur. The coordination about the U(6+) center in [(UO2)S4](6-) is square bipyramidal with the uranyl O atoms 180 apart and four equatorial S atoms. The Na(+) and Ba(2+) cations form interactions with the uranyl O atoms. Despite the inherent difficulties involved in the synthesis of complex uranium oxysulfides, it is demonstrated that under the right reaction conditions the UO2(2+) species can be produced in situ and result in totally new chalcogen derivatives. PMID:24004070

Ward, Matthew D; Klingsporn, Jordan M; Ibers, James A

2013-09-05

131

Crystal structure of first- and second-sphere complexes of uranyl nitrate with 1,2- and 1,4-diols  

Microsoft Academic Search

2,3-Dimethyl-2,3-butanediol (pinacol, L1), 2,5-dimethyl-2,5-hexanediol (L2) and 2,2,7,7-tetramethyl-3,6-di-tert-butyl-3,6-octanediol (L3) were reacted with uranyl nitrate hexahydrate. Whereas L1 acts as a bidentate chelating ligand, giving the 1\\/1 anhydrous complex [UO2L1(NO3)2] in which the nitrate ions are in cis geometry, L2 and L3 are second-sphere ligands which are hydrogen bonded to the water and nitrate oxygen atoms of the [UO2(NO3)2(H2O)2] moiety. In the

Claude Villiers; Pierre Thury; Michel Ephritikhine

2004-01-01

132

EXAFS Characterization of Uranyl Interaction at the Calcite-Water Interface  

NASA Astrophysics Data System (ADS)

Recent studies using X-ray absorption and luminescence spectroscopies have demonstrated uptake and incorporation of uranyl by calcite. X-ray microprobe studies on uranyl-reacted calcite single crystals reveal that uranyl exhibits preferences for specific surface sites. These preferences are likely expressed upon adsorption of uranyl species at the calcite-water interface. We have used X-ray absorption fine structure (EXAFS), combined with luminescence spectroscopy, to characterize the interactions of uranyl carbonate species with the calcite surface in the pH range 7.4-8.3. To minimize the potential for dissolution or precipitation, solutions were pre-equilibrated with reagent calcite powder for 3 weeks, with pH stabilizing at 8.3. For other experiments, the pH was adjusted initially to achieve a final pH of 7.4 after aging for 3 weeks. Uranyl carbonate solution was added to the pre-equilibrated suspensions to achieve initial U(VI) concentrations ranging from 5 uM to 5 mM. Suspensions were filtered to recover the calcite, but were kept moist to retain the sorbed complexes at the calcite-water interface. Multiple EXAFS spectra were collected using a multi-element Ge detector at beamline 12-BM at the APS and analyzed using standard methods. Fourier transforms (FT) of the spectra contain features corresponding to two axial oxygens and a shell of equatorial oxygens, as well as weaker features at higher R. For suspensions having initial U(VI) concentrations from 5-100 uM, a shoulder is observed in the FT on the high-R side of the equatorial oxygen, and fitting suggests minor splitting of this shell. For higher initial U(VI) concentrations, including the highest U(VI) concentration, 5 mM, the splitting becomes more pronounced. Weak features in the FT at higher-R can be fitted with backscattering from carbon, oxygen, and calcium shells, although fits without calcium provide nearly the same agreement. Luminescence spectroscopy reveals the presence of multiple uranyl species sorbed on the calcite from suspensions with 100 uM U(VI) and lower concentrations. The presence of multiple species may account for the splitting of the equatorial coordination indicated by EXAFS. For higher U(VI) concentrations, the luminescence results are consistent with formation of a schoepite-like precipitate. Understanding the complex interactions of uranyl at the calcite-water interface requires complementary data from multiple techniques.

Reeder, R. J.; Elzinga, E. J.; Tait, C. D.

2002-12-01

133

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

2011-05-25

134

Determination of uranyl ion by potentiometric titration using an uranyl-selective electrode  

Microsoft Academic Search

A potentiometric titration of uranyl ion is described using an uranyl selective electrode based on a membrane containing a complex of UO2-bis[di-4-(1,1,3,3-tetra-methylbutyl)phenyl phosphate] as an ion-exchanger and tritolyl phosphate as a solvent mediator. The titrations were carried out with various titrants: sodium hydroxide, potassium fluoride and sodium salts of acetate, oxalate and citrate. The equivalence points were determined by Gran's

Nabil S. Nassory

1990-01-01

135

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

136

Probing the electronic structure and chemical bonding in tricoordinate uranyl complexes UO2X3- (X = F, Cl, Br, I): competition between Coulomb repulsion and U-X bonding.  

PubMed

While uranyl halide complexes [UO2(halogen)n](2-n) (n = 1, 2, 4) are ubiquitous, the tricoordinate species have been relatively unknown until very recently. Here photoelectron spectroscopy and relativistic quantum chemistry are used to investigate the bonding and stability of a series of gaseous tricoordinate uranyl complexes, UO2X3(-) (X = F, Cl, Br, I). Isolated UO2X3(-) ions are produced by electrospray ionization and observed to be highly stable with very large adiabatic electron detachment energies: 6.25, 6.64, 6.27, and 5.60 eV for X = F, Cl, Br, and I, respectively. Theoretical calculations reveal that the frontier molecular orbitals are mainly of uranyl U-O bonding character in UO2F3(-), but they are from the ligand valence np lone pairs in the heavier halogen complexes. Extensive bonding analyses are carried out for UO2X3(-) as well as for the doubly charged tetracoordinate complexes (UO2X4(2-)), showing that the U-X bonds are dominated by ionic interactions with weak covalency. The U-X bond strength decreases down the periodic table from F to I. Coulomb barriers and dissociation energies of UO2X4(2-) ? UO2X3(-) + X(-) are calculated, revealing that all gaseous dianions are in fact metastable. The dielectric constant of the environment is shown to be the key in controlling the thermodynamic and kinetic stabilities of the tetracoordinate uranyl complexes via modulation of the ligand-ligand Coulomb repulsions. PMID:23662677

Su, Jing; Dau, Phuong Diem; Qiu, Yi-Heng; Liu, Hong-Tao; Xu, Chao-Fei; Huang, Dao-Ling; Wang, Lai-Sheng; Li, Jun

2013-05-10

137

Coordination in complex systems: increasing efficiency in disaster mitigation and response  

Microsoft Academic Search

Coordination in multi-organisational settings is extraordinarily difficult to achieve. This article examines the problem of inter-organisational coordination in the context of public administration theory and practice. The authors present the concept of complex adaptive systems as a theoretical framework that explains the dynamic processes involved in achieving coordinated action among multiple organisations to manage complex technical operations in environments vulnerable

Louise K. Comfort; Mark Dunn; David Johnson; Robert Skertich; Adam Zagorecki

2004-01-01

138

Coordination  

NSDL National Science Digital Library

Coordination is an organized working together of muscles and groups of muscles aimed at bringing about a purposeful movement such as walking or standing. Coordination involves timing and concentration.

Olivia Worland (Purdue University;Biological Sciences)

2008-06-06

139

Preferred coordination modes in the first steps of the learning of a complex gymnastics skill  

Microsoft Academic Search

The aim of this experiment was to analyze the first coordination modes exhibited by novices in a complex gymnastics skill (the swings under parallel bars, in bent inverted hang position), compared to the coordination mode of a group of experts. Eight novices and four experts were involved in the experiment. For experts a mode of coordination was predicted which was

Didier Delignires; Dborah Nourrit; Rim Sioud; Pierre Leroyer; Maurice Zattara; Jean-Paul Micaleff

1998-01-01

140

INFRARED SPECTRA OF URANYL NITRATE HYDRATES AND RUBIDIUM URANYL NITRATE  

Microsoft Academic Search

The infrared spectra of uranyl nitrate di-, tri-, and hexahydrate have ; been examined from 3700 to 700 cm⁻¹, with nitrogen of normal isotopic ; composition and enriched in N¹⁵, and most of the bands are assigned. The ; spectrum of uranyl nitrate hexahydrate is in most respects that of a typical ; ionic nitrate. The spectra of uranyl nitrate

Bryan M. Gatehouse; Alan E. Comyns

1958-01-01

141

Batch Crystallization of Uranyl Nitrate  

Microsoft Academic Search

Batch crystallization of uranyl nitrate is carried out in order to obtain fundamental data required for the development of reprocessing involving crystallization. Particular attention is paid to the development of a method for predicting the concentrations of uranium and nitric acid in the mother liquor and the amount of uranyl nitrate crystals produced. Initial concentrations of uranyl nitrate and nitric

Takahiro CHIKAZAWA; Toshiaki KIKUCHI; Atsuhiro SHIBATA; Tomozo KOYAMA; Shunji HOMMA

2008-01-01

142

Synthesis and crystal structure of UOCl(THF): A simple preparation of an anhydrous uranyl reagent  

Microsoft Academic Search

Solid state Structures of molecular uranyl compounds are commonly described in the literature. The vast majority of these species have been isolated from aqueous media, and the presence of water often influences the resulting structures through hydrogen bonding and\\/or inner-sphere water coordination. The development of nonaqueous uranyl chemistry has demonstrated the existence of novel coordination geometries in the absence of

Marianne P. Wilkerson; Carol J. Burns; Robert T. Paine; Brian L. Scott

1999-01-01

143

Nuclear magnetic resonance and calorimetric study of the structure, dynamics, and phase behavior of uranyl ion/dipalmitoylphosphatidylcholine complexes.  

PubMed Central

The interaction of UO2(2+) with dipalmitoylphosphatidylcholine (DPPC) has been studied as a function of temperature and composition using nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), and monolayer studies. Computer simulations of the 31P-NMR powder spectra of DPPC dispersions in the presence of various concentrations of UO2(2+) are consistent with the binding stoichiometry of [UO2(2+)]/[DPPC] = 1:4 at [UO2(2+)]/[DPPC] less than 0.3. This complex undergoes a phase transition to the liquid crystalline phase at T'm = 50 +/- 3 degrees C with a breadth delta T'm = 7 +/- 3 degrees C. This broad transition gradually disappears at higher UO2(2+) concentrations, suggesting the presence of yet another UO2(2+)/DPPC complex (or complexes) whose NMR spectra are indistinguishable from those of the 1:4 UO2(2+)/DPPC species. The temperature-dependent 13C powder spectra of 2(1-13C) DPPC dispersions in the presence of 1.2 mol ratio of UO2(2+) show that this higher order complex (complexes) also undergoes a phase transition to the liquid crystalline state at T'm +/- = 58 +/- 3 degrees C with a breadth delta T"m = 15 +/- 5 degrees C. The NMR spectra indicate that exchange among these various UO2(2+)/DPPC complexes is slow. In addition, computer simulations of the 31P-, 13C-, and 2H-NMR powder spectra show that axial diffusion of the DPPC molecules about their long axes is quenched by addition of UO2(2+) and acyl chain isomerization is the dominant motional mode. The isomerization is best described as two-site hopping of the greater than C-D bond at a rate of approximately 10(6) s-1, a motional mode which is expected for a kink diffusion.

Huang, T H; Blume, A; Das Gupta, S K; Griffin, R G

1988-01-01

144

Laser-induced fluorescence of uranyl complexes in aqueous solutions: the role of diffusion-controlled excited states annihilation.  

PubMed

We present the analysis of diffusion-controlled annihilation of excited U(VI) complexes in aqueous media that leads to appearance of rapid non-exponential fluorescence decay. We show that under typical experimental conditions the impact of annihilation processes can't be neglected when determining U(VI) complexes fluorescence lifetimes: at excitation intensities between 106 W/cm2 and 108 W/cm2, the rate of excited states deactivation increases, and then an opposite trend is observed. The latter can be interpreted as the consequence of optical breakdown in water. PMID:24103925

Budylin, Gleb; Shirshin, Evgeny; Fadeev, Victor; Petrov, Vladimir; Kalmykov, Stepan

2013-09-01

145

How can the principles of complexity science be applied to improve the coordination of care for complex pediatric patients?  

PubMed

Clinical and technological advances in medicine have resulted in more patients requiring multidisciplinary care and coordination of services. This is particularly challenging in pediatrics, given the dependency of children. Coordination of care is a key ingredient of quality care; when suboptimal, clinical outcomes and satisfaction can suffer. In this article we view coordination of care through the lens of complexity science in an effort to find new solutions to this healthcare challenge. PMID:16585105

Matlow, A G; Wright, J G; Zimmerman, B; Thomson, K; Valente, M

2006-04-01

146

How can the principles of complexity science be applied to improve the coordination of care for complex pediatric patients?  

PubMed Central

Clinical and technological advances in medicine have resulted in more patients requiring multidisciplinary care and coordination of services. This is particularly challenging in pediatrics, given the dependency of children. Coordination of care is a key ingredient of quality care; when suboptimal, clinical outcomes and satisfaction can suffer. In this article we view coordination of care through the lens of complexity science in an effort to find new solutions to this healthcare challenge.

Matlow, A G; Wright, J G; Zimmerman, B; Thomson, K; Valente, M

2006-01-01

147

Influence of electrostatic effect on the stability of mixed-ligand complexes: Uranyl-complexone-phenol\\/phenolic acid ternary systems  

Microsoft Academic Search

The formation constants (logK\\u000a \\u000a \\u000a MAL\\u000a \\u000a \\u000a MA\\u000a \\u000a ) of the complexes of the type (UO2.A.L] (whereA = IMDA, NTA or EDTA;L = catechol, resorcinol, phloroglucinol, pyrogallol, ?-resorcylic acid or protocatechuic acid) have been determined potentiometrically\\u000a at 25C and ionic strength,I = 02 (mol dm?3, NaClO4) using the Irving-Rossotti approach. The formation constants of the binary complexes (logK\\u000a \\u000a \\u000a KMA\\u000a \\u000a \\u000a KM\\u000a \\u000a ) have

Anushree Samanta; S. N. Limaye; M. C. Saxena

1986-01-01

148

SOLUBILITY OF URANYL SALTS IN ORGANIC ESTERS  

Microsoft Academic Search

The relations of solubility for uranyl acetate, uranyl nitrate, and ; uranyl sulfate were investigated in dioctyl phthalate, dibutyl phthalate, dibutyl ; phosphate, and tributyl phosphate. For all the three uranyl salts, dibutyl ; phosphate proved to be the best solvent. Tributyl phosphate is an excellent ; solvent for uranyl nitrate, while it is only a mediocre solvent for the

Szilagyi

1960-01-01

149

Synthesis and Analytical Applications of Uranyl Ion Imprinted Polymer Particles  

Microsoft Academic Search

Uranyl ion imprinted polymer particles were prepared by the copolymerization of styrene monomer and a crosslinking agent divinyl benzene in the presence of -5,7-dichloroquinoline-8-ol-4-vinyl pyridine ternary complex as template where in is the imprint ion in presence of 2,2?-azo-bis-isobutyronitrile as initiator. The Uranyl ion was removed from the polymer particles by leaching with 1:1 HCl, which leaves cavities in the

Joseph Mary Gladis; Talasila Prasada Rao

2003-01-01

150

Market-based Multirobot Coordination for Complex Tasks  

Microsoft Academic Search

Current technological developments and application-driven demands are bringing us closer to the realization of au- tonomous multirobot systems performing increasingly com- plex missions. However, existing methods of distributing mis- sion subcomponents among multirobot teams do not explicitly handle the required complexity and instead treat tasks as sim- ple indivisible entities, ignoring any inherent structure and se- mantics that such complex

Robert Zlot; Anthony Stentz

2006-01-01

151

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

2012-03-08

152

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

2006-06-01

153

Proton exchange in acid-base complexes induced by reaction coordinates with heavy atom motions  

NASA Astrophysics Data System (ADS)

We extend previous work on nitric acid-ammonia and nitric acid-alkylamine complexes to illustrate that proton exchange reaction coordinates involve the rocking motion of the base moiety in many double hydrogen-bonded gas phase strong acid-strong base complexes. The complexes studied involve the biologically and atmospherically relevant glycine, formic, acetic, propionic, and sulfuric acids with ammonia/alkylamine bases. In these complexes, the magnitude of the imaginary frequencies associated with the proton exchange transition states are <400 cm-1. This contrasts with widely studied proton exchange reactions between symmetric carboxylic acid dimers or asymmetric DNA base pair and their analogs where the reaction coordinate is localized in proton motions and the magnitude of the imaginary frequencies for the transition states are >1100 cm-1. Calculations on complexes of these acids with water are performed for comparison. Variations of normal vibration modes along the reaction coordinate in the complexes are described.

Alavi, Saman; Taghikhani, Mahdi

2012-06-01

154

A Bridge to Coordination Isomer Selection in Lanthanide(III) DOTA-tetraamide Complexes  

PubMed Central

Interest in macrocyclic lanthanide complexes such as DOTA is driven largely through interest in their use as contrast agents for MRI. The lanthanide tetraamide derivatives of DOTA have shown considerable promise as PARACEST agents, taking advantage of the slow water exchange kinetics of this class of complex. We postulated that water exchange in these tetraamide complexes could be slowed even further by introducing a group to sterically encumber the space above the water coordination site, thereby hindering the departure and approach of water molecules to the complex. The ligand 8O2-bridged-DOTAM was synthesized in a 34% yield from cyclen. It was found that the lanthanide complexes of this ligand did not possess a water molecule in the inner coordination sphere of the bound lanthanide. The crystal structure of the ytterbium complex revealed that distortions to the coordination sphere were induced by the steric constraints imposed on the complex by the bridging unit. The extent of the distortion was found to increase with increasing ionic radius of the lanthanide ion, eventually resulting in a complete loss of symmetry in the complex. Because this ligand system is bicyclic, the conformation of each ring in the system is constrained by that of the other, in consequence inclusion of the bridging unit in the complexes means only a twisted square antiprismatic coordination geometry is observed for complexes of 8O2-bridged-DOTAM.

Vipond, Jeff; Woods, Mark; Zhao, Piyu; Tircso, Gyula; Ren, Jimin; Bott, Simon G.; Ogrin, Doug; Kiefer, Garry E.; Kovacs, Zoltan; Sherry, A.Dean

2008-01-01

155

Temperature programmed decomposition of uranyl nitrate hexahydrate  

Microsoft Academic Search

Temperature programmed decomposition (TPD) of uranyl nitrate hexahydrate has been studied using evolved gas analysis mass spectrometry (EGA-MS) in the temperature range 3001400 K. Thermogravimetric (TGA) investigations were performed in the temperature range 3001100 K. An attempt has been made to resolve the complexity of decomposition behaviour through suitable comparison of TGA and EGA-MS data. Kinetic control regimes for various

S. Dash; M. Kamruddin; Santanu Bera; P. K. Ajikumar; A. K. Tyagi; S. V. Narasimhan; Baldev Raj

1999-01-01

156

Different coordination modes of 2-(diphenylphosphino)azobenzenes in complexation with hard and soft metals.  

PubMed

Control of coordination modes of a ligand in metal complexes is significant because the coordination modes influence catalytic properties of transition metal catalysts. Reactions of 2-diphenylphosphinoazobenzenes, which are in equilibrium with the inner phosphonium salts, with ZnCl(2), W(CO)(5)(THF), and PtCl(2)(cod) gave three different coordination types of metal complexes with distinctive UV-vis absorptions. All the complexes were characterized by X-ray crystallographic analyses. In the zinc and tungsten complexes, the source molecule functions as an amide ligand and a phosphine ligand, respectively. In the platinum complex, the phosphorus molecule works as a tridentate ligand with formation of a carbon-platinum bond. PMID:22893026

Kano, Naokazu; Yamamura, Masaki; Meng, Xiangtai; Yasuzuka, Takaharu; Kawashima, Takayuki

2012-08-14

157

Oil spill emergency response in Norway: coordinating interorganizational complexity  

Microsoft Academic Search

Based on offshore industrial developments in the Arctic areas, strengthening the national oil spill emergency response (OSER) system has become a priority for the Norwegian government. The Norwegian OSER system, examined here, is a complex structure with private-, municipal-, and state-level actors that may be mobilized to act as one integrated national system. We first outline the main actors and

Maria Sydnes; Are Kristoffer Sydnes

2011-01-01

158

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

159

Teamwork Coordination for Realistically Complex Multi Robot Systems  

Microsoft Academic Search

In this paper we examine human tasks in controlling UAV teams by considering their computational complexity in the number of UAVs. This analysis suggests that controlling or following fine grained cooperation among many subteams of UAVs is the most difficult task and probably beyond human capabilities for most sizes of teams. We introduce Machinetta, a teamwork system that automates fine

Michael Lewis; Jijun Wang; Paul Scerri

160

Coordination polymers with carborane anions: silver dinitrile complexes.  

PubMed

Crystalline materials have been isolated and characterized from mixing the silver carborane salts Ag(CB(11)H(12)) or Ag[Co(C(2)B(9)H(11))(2)] with nitrile ligands, either terminal acetonitrile or potentially bridging alkanedinitriles. Most of the complexes showed B-H...Ag interactions between the silver center and carborane anion. [Ag(acetonitrile)(2)(CB(11)H(12))] has a hexagonal network structure. [Ag(malonitrile)(2)(CB(11)H(12))] is a discrete dimeric complex, while [Ag(4)(succinonitrile)(5)(CB(11)H(12))(4)], [Ag(glutaronitrile)(2)][Co(C(2)B(9)H(12))(2)], and [Ag(glutaronitrile)[Co(C(2)B(9)H(11))(2)

Westcott, Aleema; Whitford, Nina; Hardie, Michaele J

2004-06-14

161

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

162

Coordinating assembly and export of complex bacterial proteins  

PubMed Central

The Escherichia coli twin-arginine protein transport (Tat) system is a molecular machine dedicated to the translocation of fully folded substrate proteins across the energy-transducing inner membrane. Complex cofactor-containing Tat substrates, such as the model (NiFe) hydrogenase-2 and trimethylamine N-oxide reductase (TorA) systems, acquire their redox cofactors prior to export from the cell and require to be correctly assembled before transport can proceed. It is likely, therefore, that cellular mechanisms exist to prevent premature export of immature substrates. Using a combination of genetic and biochemical approaches including gene knockouts, signal peptide swapping, complementation, and site-directed mutagenesis, we highlight here this crucial proofreading' or quality control' activity in operation during assembly of complex endogenous Tat substrates. Our experiments successfully uncouple the Tat transport and cofactor-insertion activities of the TorA-specific chaperone TorD and demonstrate unequivocally that TorD recognises the TorA twin-arginine signal peptide. It is proposed that some Tat signal peptides operate in tandem with cognate binding chaperones to orchestrate the assembly and transport of complex enzymes.

Jack, Rachael L; Buchanan, Grant; Dubini, Alexandra; Hatzixanthis, Kostas; Palmer, Tracy; Sargent, Frank

2004-01-01

163

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

164

Recognition of alkali metal halide contact ion pairs by uranyl-salophen receptors bearing aromatic sidearms. The role of cation-pi interactions.  

PubMed

Hard anions have long been known to bind strongly to the uranium of uranyl-salophen complexes. Upon functionalization of the salophen framework with one or two benzyloxy substituents, efficient ditopic receptors for alkali metal ions are obtained. The solid-state structures of complexes formed by the two-armed receptor 1 with CsF and with the chlorides of K+, Rb+, and Cs+ reported here reveal the existence of dimeric supramolecular assemblies in which two receptor units assemble into capsules fully enclosing (MX)2 ion quartets. In addition to the strong coordinative binding of the anion to the uranyl center and to electrostatic cation-anion interactions, stabilizing interactions arise from coordination of each cation to six oxygens, three from each receptor, and most importantly, to two aromatic sidearms belonging to different receptors. There are marked differences in organization at the supramolecular level in the CsCl complex of the one-armed receptor 3, in that four uranyl-salophen units instead of two are assembled in a capsule-like arrangement housing a (CsCl)2 ion quartet. However, both receptors achieve the common goal of having each metal cation in close contact with carbon atoms of two aromatic rings. 1H NMR data provide strong evidence that cation-pi(arene) interactions with the sidearms participate in binding also in solution. PMID:15771518

Cametti, Massimo; Nissinen, Maija; Dalla Cort, Antonella; Mandolini, Luigi; Rissanen, Kari

2005-03-23

165

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

166

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

167

The role of attractive van der Waals forces in the catalysis of Michael addition by a phenyl decorated uranyl-salophen complex.  

PubMed

The Et(3)N-assisted addition of beta-ketoester 3 to MVK in chloroform is catalyzed with high turnover efficiency by the phenyl-substituted uranyl-salophen compound 2b but not by the parent compound 1b. A plausible mechanism is suggested, involving concomitant nucleophilic attack at the beta-carbon and hydrogen bonding between the Et(3)NH(+) countercation and the carbonyl oxygen of the s-cis conformation of the enone reactant. The role of the van der Waals interactions with the aromatic side arm of 2b as a crucial driving force for catalysis is discussed. PMID:18998729

Dalla Cort, Antonella; Mandolini, Luigi; Schiaffino, Luca

2008-12-01

168

Insights into metalloenzyme microenvironments: biomimetic metal complexes with a functional second coordination sphere.  

PubMed

Non-covalent interactions in the second coordination sphere of metalloenzymes play a significant role in determining activity and selectivity. The importance of these interactions is reflected in the increasing number of reports on model complexes with a functional second coordination sphere. These hybrid mimics were developed according to the strategies of modification with functional groups, combination with supramolecular hosts and coupling with polymers, to shed light on the role of non-covalent interactions in metalloenzyme catalysis. This review provides an overview of recent progress in this area. An introduction to native metalloenzymes with an emphasis on the second coordination sphere is also given. PMID:23881282

Zhao, Meng; Wang, Hai-Bo; Ji, Liang-Nian; Mao, Zong-Wan

2013-07-24

169

Localization of Crystals in Diseased Oats Treated with Uranyl Acetate 1  

PubMed Central

Uranyl acetate, a suppressor of victorin-induced electrolyte leakage in oat leaves when applied together with, or before, victorin, also suppressed victorin-induced changes in ultra-structure. Uranyl crystallized in cell walls and near the plasmalemma of vascular cells, but was excluded from the protoplasm. Fewer crystals occurred near the plasmalemma when leaves were allowed to take up uranyl and victorin simultaneously than when uranyl alone was absorbed, but deposition in cell walls was similar in the two treatments. No differences in crystal distribution were found in uranyl-treated leaves which subsequently took up either water or victorin. The most striking effect of prolonged exposure to uranyl was increased vesicular activity in the protoplasm, formation of complex concentric membranes, and tonoplast damage. Following victorin treatment, uranyl post-treatment was ineffective in suppressing electrolyte leakage or preserving normal cellular ultrastructure. More severe ultrastructural damage was found in victorintreated leaves after uranyl post-treatments than after post-treatment with water, a result of victorin-induced damage which facilitates uranyl entry into the protoplasm. Images

Easton, Carol Zeman; Hanchey, Penelope

1972-01-01

170

Multifunctionality of Organometallic Quinonoid Metal Complexes: Surface Chemistry, Coordination Polymers, and Catalysts.  

PubMed

Quinonoid metal complexes have potential applications in surface chemistry, coordination polymers, and catalysts. Although quinonoid manganese tricarbonyl complexes have been used as secondary building units (SBUs) in the formation of novel metal-organometallic coordination networks and polymers, the potentially wider applications of these versatile linkers have not yet been recognized. In this Account, we focus on these diverse new applications of quinonoid metal complexes, and report on the variety of quinonoid metal complexes that we have synthesized. Through the use of [(?(6)-hydroquinone)Mn(CO)3](+), we are able to modify the surface of Fe3O4 and FePt nanoparticles (NPs). This process occurs either by the replacement of oleylamine with neutral [(?(5)-semiquinone)Mn(CO)3] at the NP surface, or by the binding of anionic [(?(4)-quinone)Mn(CO)3](-) upon further deprotonation of [(?(5)-semiquinone)Mn(CO)3] at the NP surface. We have demonstrated chemistry at the intersection of surface-modified NPs and coordination polymers through the growth of organometallic coordination polymers onto the surface modified Fe3O4 NPs. The resulting magnetic NP/organometallic coordination polymer hybrid material exhibited both the unique superparamagnetic behavior associated with Fe3O4 NPs and the paramagnetism attributable to the metal nodes, depending upon the magnetic range examined. By the use of functionalized [(?(5)-semiquinone)Mn(CO)3] complexes, we attained the formation of an organometallic monolayer on the surface of highly ordered pyrolitic graphite (HOPG). The resulting organometallic monolayer was not simply a random array of manganese atoms on the surface, but rather consisted of an alternating "up and down" spatial arrangement of Mn atoms extending from the HOPG surface due to hydrogen bonding of the quinonoid complexes. We also showed that the topology of metal atoms on the surface could be controlled through the use of quinonoid metal complexes. A quinonoid rhodium complex showed catalytic activity in Suzuki-Miyaura type reaction. As a result of the excellent stability of the homogeneous catalyst [(quinone)Rh(COD)](-) in water, we also successfully demonstrated catalyst recycling in 1,2- and 1,4-addition reactions. The compound [(quinone)Ir(COD)](-) showed significantly poorer catalytic activity in 1,4-addition reactions. Following upon the excellent coordination ability of the quinonoid rhodium complexes to metal centers, we synthesized organometallic coordination polymer nanocatalysts and silica gel-supported quinonoid rhodium catalysts, the latter using a surface sol-gel technique. The resulting heterogeneous catalysts showed activity in the stereospecific polymerization of phenylacetylene. PMID:23745596

Kim, Sang Bok; Pike, Robert D; Sweigart, Dwight A

2013-06-01

171

Mechanics of metal-catecholate complexes: The roles of coordination state and metal types.  

PubMed

There have been growing evidences for the critical roles of metal-coordination complexes in defining structural and mechanical properties of unmineralized biological materials, including hardness, toughness, and abrasion resistance. Their dynamic (e.g. pH-responsive, self-healable, reversible) properties inspire promising applications of synthetic materials following this concept. However, mechanics of these coordination crosslinks, which lays the ground for predictive and rational material design, has not yet been well addressed. Here we present a first-principles study of representative coordination complexes between metals and catechols. The results show that these crosslinks offer stiffness and strength near a covalent bond, which strongly depend on the coordination state and type of metals. This dependence is discussed by analyzing the nature of bonding between metals and catechols. The responsive mechanics of metal-coordination is further mapped from the single-molecule level to a networked material. The results presented here provide fundamental understanding and principles for material selection in metal-coordination-based applications. PMID:24107799

Xu, Zhiping

2013-10-10

172

Mechanics of metal-catecholate complexes: The roles of coordination state and metal types  

NASA Astrophysics Data System (ADS)

There have been growing evidences for the critical roles of metal-coordination complexes in defining structural and mechanical properties of unmineralized biological materials, including hardness, toughness, and abrasion resistance. Their dynamic (e.g. pH-responsive, self-healable, reversible) properties inspire promising applications of synthetic materials following this concept. However, mechanics of these coordination crosslinks, which lays the ground for predictive and rational material design, has not yet been well addressed. Here we present a first-principles study of representative coordination complexes between metals and catechols. The results show that these crosslinks offer stiffness and strength near a covalent bond, which strongly depend on the coordination state and type of metals. This dependence is discussed by analyzing the nature of bonding between metals and catechols. The responsive mechanics of metal-coordination is further mapped from the single-molecule level to a networked material. The results presented here provide fundamental understanding and principles for material selection in metal-coordination-based applications.

Xu, Zhiping

2013-10-01

173

Mechanics of metal-catecholate complexes: The roles of coordination state and metal types  

PubMed Central

There have been growing evidences for the critical roles of metal-coordination complexes in defining structural and mechanical properties of unmineralized biological materials, including hardness, toughness, and abrasion resistance. Their dynamic (e.g. pH-responsive, self-healable, reversible) properties inspire promising applications of synthetic materials following this concept. However, mechanics of these coordination crosslinks, which lays the ground for predictive and rational material design, has not yet been well addressed. Here we present a first-principles study of representative coordination complexes between metals and catechols. The results show that these crosslinks offer stiffness and strength near a covalent bond, which strongly depend on the coordination state and type of metals. This dependence is discussed by analyzing the nature of bonding between metals and catechols. The responsive mechanics of metal-coordination is further mapped from the single-molecule level to a networked material. The results presented here provide fundamental understanding and principles for material selection in metal-coordination-based applications.

Xu, Zhiping

2013-01-01

174

Two new hybrid compounds assembled from Keggin-type polyoxometalates and transition metal coordination complexes  

SciTech Connect

Two new hybrid compounds based on Keggin-type polyoxometalates: {l_brace}[PMo{sub 12}O{sub 40}][Ni(Phen){sub 2}(H{sub 2}O)]{sub 2{r_brace}}.K.2OH{sup -} (1) and [Cd{sub 2}(Phen){sub 4}Cl{sub 2}][HPW{sub 12}O{sub 40}].H{sub 2}O (2) (Phen=1,10-phenanthroline), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Compound 1 exhibits a 1-D chain structure constructed from Pseudo-Keggin polyoxometalate bi-supported transition metal coordination complexes linked by K{sup +} ions. Compound 2 contains Pseudo-Keggin polyoxoanions [HPW{sub 12}O{sub 40}]{sup 2-} and novel metal-chloride-ligand coordination complexes [Cd{sub 2}(Phen){sub 4}Cl{sub 2}]{sup 2+}. -- Graphical abstract: Two new hybrid compounds based on different Keggin-type polyoxometalates have been hydrothermally synthesized and characterized by IR, UV-Vis, XPS, XRD, elemental analysis and single crystal X-ray diffraction analysis. Display Omitted Research highlights: {yields} Two hybrids based on Pseudo-Keggin polyanions and metal coordination complexes. {yields} 1-D structure formed by polyanion bisupported metal coordination units linked by K{sup +}. {yields} A metal-chloride-ligand coordination complex [Cd{sub 2}(Phen){sub 4}Cl{sub 2}]{sup 2+}. {yields} A hybrid based on polyanions and metal-chloride-ligand coordination complexes.

Wang Yan, E-mail: jlccwxz@163.co [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Zou, Bo, E-mail: doctorz@jlu.edu.c [College of Chemistry, Jilin University, Changchun 130023 (China); Xiao Lina, E-mail: xiaolina2009@163.co [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Jin Ning, E-mail: generalman948@163.co [China-Japan Union Hospital of Jilin University, Changchun (China); Peng Yu, E-mail: jlu5@163.co [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Wu Fengqing, E-mail: fqwu@mail.jlu.edu.c [College of Chemistry, Jilin University, Changchun 130023 (China); Ding Hong, E-mail: dinghong@jlu.edu.c [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Wang Tiegang, E-mail: Wangtg@mail.jlu.edu.c [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Gao Zhongmin, E-mail: gaozm@jlu.edu.c [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Zheng Dafang, E-mail: zhengdf@mail.jlu.edu.c [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Cui Xiaobing, E-mail: cuixb@mail.jlu.edu.c [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China); Xu Jiqing, E-mail: xjq@mail.jlu.edu.c [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023 (China)

2011-03-15

175

Role of the sodium-dependent phosphate co-transporters and of the phosphate complexes of uranyl in the cytotoxicity of uranium in LLC-PK{sub 1} cells  

SciTech Connect

Although uranium is a well-characterized nephrotoxic agent, very little is known at the cellular and molecular level about the mechanisms underlying the uptake and toxicity of this element in proximal tubule cells. The aim of this study was thus to characterize the species of uranium that are responsible for its cytotoxicity and define the mechanism which is involved in the uptake of the cytotoxic fraction of uranium using two cell lines derived from kidney proximal (LLC-PK{sub 1}) and distal (MDCK) tubule as in vitro models. Treatment of LLC-PK{sub 1} cells with colchicine, cytochalasin D, concanavalin A and PMA increased the sodium-dependent phosphate co-transport and the cytotoxicity of uranium. On the contrary, replacement of the extra-cellular sodium with N-methyl-D-glucamine highly reduced the transport of phosphate and the cytotoxic effect of uranium. Uranium cytotoxicity was also dependent upon the extra-cellular concentration of phosphate and decreased in a concentration-dependent manner by 0.1-10 mM phosphonoformic acid, a competitive inhibitor of phosphate uptake. Consistent with these observations, over-expression of the rat proximal tubule sodium-dependent phosphate co-transporter NaPi-IIa in stably transfected MDCK cells significantly increased the cytotoxicity of uranium, and computer modeling of uranium speciation showed that uranium cytotoxicity was directly dependent on the presence of the phosphate complexes of uranyl UO{sub 2}(PO{sub 4}){sup -} and UO{sub 2}(HPO{sub 4}){sub aq}. Taken together, these data suggest that the cytotoxic fraction of uranium is a phosphate complex of uranyl whose uptake is mediated by a sodium-dependent phosphate co-transporter system.

Muller, D. [IRSN, Laboratoire de Radiotoxicologie Experimentale, BP-166, 26702 Pierrelatte cedex (France)]. E-mail: dany.muller@kcl.ac.uk; Houpert, P. [IRSN, Laboratoire de Radiotoxicologie Experimentale, BP-166, 26702 Pierrelatte cedex (France)]. E-mail: pascale.houpert@irsn.fr; Cambar, J. [CEA/DEN/Valrho-Dir-CVAR, BP 17171, 30207 Bagnols sur Ceze Cedex (France)]. E-mail: jean.cambar@biocell-geppr.u-bordeaux2.fr; Henge-Napoli, M-H. [CEA/DEN/Valrho-Dir-CVAR, BP 17171, 30207 Bagnols sur Ceze Cedex (France)]. E-mail: marie-helene.napoli@cea.fr

2006-07-15

176

Determination of tetracycline in milk by using nucleotide/lanthanide coordination polymer-based ternary complex.  

PubMed

The meta-organic coordination polymers have been emerged as fascinating nanomaterials because of their tunable nature. In this work, we employed lanthanide coordination polymer self-assembled from adenosine monophosphate (AMP) and europium ion (Eu(3+)) as receptor reagent and citrate (Cit) as ancillary ligand to construct a fluorescent sensor for the detection of tetracycline (Tc) in milk. The co-coordination of Cit and Tc with Eu(3+) on the surface of the coordination polymer AMP/Eu leads to the formation of ternary complex which emitted strong fluorescence due to the removal of coordinated water molecules and an intramolecular energy transfer from Tc to Eu(3+). The fluorescent intensity of Eu(3+) displayed a good linear response to Tc concentrations in the range of 0.1-20?M with a detection limit of 60nM. This method was successfully applied to determine the levels of Tc in milk, which is the first application of coordination polymer as a fluorescent sensor in real sample. Compared with other Eu(3+)-based fluorescent methods for Tc detection, the presented method allows simple, direct analysis of Tc without requiring special reaction media or complicated prepreparation processes. This straightforward strategy could be extended to the preparation of other lanthanide coordination polymer-based fluorescent probes for applications in biosensing, imaging, drug delivery, and so on. PMID:23907076

Tan, Hongliang; Ma, Chanjiao; Song, Yonghai; Xu, Fugang; Chen, Shouhui; Wang, Li

2013-07-17

177

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

2011-11-30

178

Structural and Chiroptical Properties of the Two Coordination Isomers of YbDOTA-Type Complexes  

PubMed Central

Studies of the structural, physical, and chemical properties of the lanthanide(III) complexes of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and related ligands are often complicated by the presence of two coordination isomers in solution. Since these coordination isomers are in exchange and cannot be separated, many techniques offer information only on the weighted average of the two isomers. Lanthanide ion complexes formed with the ligands S(RRRR)NO2BnDOTMA and S(SSSS)NO2BnDOTMA preferentially adopt only one of the two common coordination isomers in solution, so the ytterbium complexes of these ligands offer a unique opportunity to study the near-infrared circular dichroism (NIR-CD) characteristics of each coordination geometry in isolation. The spectra acquired support many of the conclusions and assumptions of previous studies and demonstrate that this spectroscopy is particularly sensitive to the distortion of the coordination polyhedron. This will have particularly relevant consequences when studying achiral YbDOTA-like systems forming labile adducts with (chiral) hosts and receptors.

Di Bari, Lorenzo; Pescitelli, Gennaro; Sherry, A. Dean; Woods, Mark

2009-01-01

179

Characterization of Coordination Complexes by Desorption Electrospray Mass Spectrometry with a Capillary Target  

SciTech Connect

Metal coordination complexes were formed directly from liquid surfaces using desorption electrospray ionization (DESI) mass spectrometry. The approach is attractive because it separates complexities of ESI spray droplet formation from delivery of the analyte solution, and thereby gets around difficulty resulting from alteration of the spray process by changes in solution chemistry. Cs+, Ba2+, and La3+ coordination complexes were formed using 18-crown-6 (18c6) and triethylphosphate (TEP) as ligands (L), that had the general formula [Mn+(NO3-)n-1(L)m]+. Formation of singly charged cation complexes was preferred, with charge reduction at the metal site accomplished by attachment of nitrate. Using TEP as a model phosphoryl ligand, alkali metals coordinate with up to three ligands, with Cs+ preferring fewer than Na+. Ba2+ and La3+ are formed as ion pair complexes [Ba(NO3)]+ and [La(NO3)2]+, and both will coordinate with up to four TEP ligands. Using 18c6, Cs+ forms a bis-ligand complex. In contrast, [Ba(NO3)]+ prefers a single 18c6 ligand, while La forms mainly [La(NO3)2(18c6)]+, for which DFT calculations suggested a structure in which the nitrate ligands occupy pseudo-axial positions on opposing sides of the crown. Lower abundances of bis-18c6 complexes were also formed together with doubly charged [La(NO3)(18c6)n]2+ complexes (n = 2 4). The results suggest an alternative strategy for probing metal speciation in solution that is less perturbed by the droplet formation and ionization mechanisms operating in conventional electrospray ionization mass spectrometry.

Gary S. Groenewold; Anthony D. Appelhans; Michael E. McIlwain; Garold L. Gresham

2011-03-01

180

Infrared Spectra of Metal Chelate Compounds. IX. A Normal Coordinate Analysis of Dithiocarbamato Complexes  

Microsoft Academic Search

The infrared spectra of dithiocarbamato and N-alkyldithiocarbamato complexes with various metals have been obtained in the range between 4000 and 280 cm1. The spectra of their deuterated forms have also been obtained to confirm the band assignments. A normal-coordinate analysis has been carried out for the 1:1 (metal\\/ligand) model of the dithiocarbamato PtII complex. The results indicate that the Pt&sngbnd;S

Kazuo Nakamoto; Junnosuke Fujita; Robert A. Condrate; Yukiyoshi Morimoto

1963-01-01

181

Coordination chemistry of anticrowns: Complexation of cyclic trimeric perfluoro- o-phenylenemercury with nitro compounds  

Microsoft Academic Search

Cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 (1) is capable of reacting with nitromethane to give complex {[(o-C6F4Hg)3](CH3NO2)} (2) containing one molecule of the nitro compound per one macrocycle molecule. In this complex, the nitromethane ligand is bound to 1 by its both oxygen atoms, one of which is simultaneously coordinated to all three Hg centres of the macrocycle while the other interacts

I. A. Tikhonova; K. I. Tugashov; F. M. Dolgushin; A. A. Yakovenko; P. V. Petrovskii; G. G. Furin; A. P. Zaraisky; V. B. Shur

2007-01-01

182

Metal complexes of porphycene, corrphycene, and hemiporphycene: stability and coordination chemistry.  

PubMed

Porphyrin (P), porphycene (Pc), corrphycene (Cn), and hemiporphycene (Hpc) represent a series of well defined "4-N in" constitutional porphyrin isomers. These isomers, in the form of their octaethyl derivatives, represent a congruent set of porphyrinoids whose properties can be compared. In this study we report how variations in electronic structure and nitrogen-core size in the free-base forms of these four systems are reflected in the properties of their corresponding metal complexes. Specifically, the effects that these differences have on the axial ligation properties of the Zn(II), Mg(II), Ni(II), and Co(II) complexes of P, Pc, Cn, and Hpc in toluene using pyridine as the axial ligand are detailed. Also reported are the relative stabilities of these complexes under acidic conditions. It is shown that for the zinc, magnesium, and cobalt complexes, there are distinct differences in the ability to maintain four-, five-, or six-coordinate geometries in the presence of similar concentrations of pyridine. By contrast, no apparent differences in axial ligand binding affinity are seen for the four nickel complexes. Little difference in stability was likewise seen when these same complexes were subject to acid-mediated demetallation, with all four falling into stability class II, according to the accepted porphyrin stability ranking system. High stabilities were also seen in the case of the cobalt complexes, with the Pc and Cn complexes being of stability class III and the P and Hpc derivatives falling into stability class II. The Zn(II) and Mg(II) complexes were all far less stable than the corresponding Ni(II) and Co(II) complexes. In this case, semiquantitative analyses of the rate of acid-induced decomposition revealed the following stability sequence P>Cn>Hpc>Pc for both the Zn(II) and Mg(II) complexes. Single-crystal X-ray diffraction structures were solved for the Zn(II), Mg(II), and Ni(II) complexes of the octaethyl derivatives of Hpc, Cn, and Pc as well as a Co(II) octamethylcorrphycene and are reported as part of this study. These solid-state structures confirm four-coordinate species for the Ni(II) complexes, four- and five-coordinate species for the Mg(II) and Zn(II) complexes, and a six-coordinate species for the lone Co(II) complex. PMID:12203329

Fowler, Christopher J; Sessler, Jonathan L; Lynch, Vincent M; Waluk, Jacek; Gebauer, Andreas; Lex, Johann; Heger, Andreas; Zuniga-Y-Rivero, Fernando; Vogel, Emanuel

2002-08-01

183

Planning for Lake and Lake Shore Tourism: Complexity, Coordination and Adaptation  

Microsoft Academic Search

It may appear sensible for just one organisation to have sole responsibility for all aspects of planning for lake basins, including for tourism. In practice, however, many public agencies are often involved that have varying interests and priorities. This paper examines one instance of relatively complex governance arrangements in order to examine the coordination of its tourism planning. A relational

BILL BRAMWELL; GILL POMFRET

2007-01-01

184

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

185

Chromogenic detection of Sarin by discolouring decomplexation of a metal coordination complex.  

PubMed

An innovative chromogenic sensing concept based on decomplexation of a tris-(bipyridine)iron(ii) coordination complex has been developed for the detection of organophosphorus nerve agents. It was evaluated both on a simulant and real Sarin in vapour and liquid phases. PMID:23963476

Ordronneau, Lucie; Carella, Alexandre; Pohanka, Miroslav; Simonato, Jean-Pierre

2013-09-10

186

Analysis of Perfectly Matched Double Negative Layers Via Complex Coordinate Transformations  

Microsoft Academic Search

Complex coordinate transformations are introduced for the analysis of time-harmonic electromagnetic wave propagation in perfectly matched double negative layers. The layer is perfectly matched to free space in the sense that any incident plane wave is transmitted through the free space-material interface without reflection, irrespective of the frequency and angle of incidence of the plane wave. The material constitutive parameters

Mustafa Kuzuoglu

2006-01-01

187

Barium uranyl diphosphonates  

SciTech Connect

Three Ba{sup 2+}/UO{sub 2}{sup 2+} 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 Degree-Sign C. These compounds, Ba[UO{sub 2}[CH{sub 2}(PO{sub 3}){sub 2}]{center_dot}1.4H{sub 2}O (Ba-1), Ba{sub 3}[(UO{sub 2}){sub 4}(CH{sub 2}(PO{sub 3}){sub 2}){sub 2}F{sub 6}]{center_dot}6H{sub 2}O (Ba-2), and Ba{sub 2}[(UO{sub 2}){sub 2}(CH{sub 2}(PO{sub 3}){sub 2})F{sub 4}]{center_dot}5.75H{sub 2}O (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 UO{sub 5}F{sub 2} 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 [UO{sub 2}[CH{sub 2}(PO{sub 3}){sub 2}]{sup 2-} sheets. The interlayer space of the structures is occupied by Ba{sup 2+}, which, along with the fluoride ion, mediates the structure formed and maintains overall charge balance. - Graphical abstract: Illustration of the stacking of the layers in Ba{sub 3}[(UO{sub 2}){sub 4}(CH{sub 2}(PO{sub 3}){sub 2}){sub 2})F{sub 6}]{center_dot}6H{sub 2}O viewed along the c-axis. The structure is constructed from UO{sub 7} pentagonal bipyramidal units, U(1)O{sub 7}=gray, U(2)O{sub 7}=yellow, barium=blue, phosphorus=magenta, fluorine=green, oxygen=red, carbon=black, and hydrogen=light peach. Highlights: Black-Right-Pointing-Pointer The polymerization of the UO{sub 2}{sup 2+} sites to form uranyl dimers leads to structural variations in compounds. Black-Right-Pointing-Pointer Barium cations stitch uranyl diphosphonate anionic layers together, and help mediate structure formation. Black-Right-Pointing-Pointer HF acts as both a mineralizing agent and a ligand.

Nelson, Anna-Gay D., E-mail: nelsoa@umich.edu [Department of Civil Engineering and Geological Sciences and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556 (United States); Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109-1005 (United States); Alekseev, Evgeny V. [Institute of Energy and Climate Research (IEK-6), Forschungszentrum Juelich Wilhelm-Johnen-Strasse, Juelich 52428 (Germany); Ewing, Rodney C. [Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109-1005 (United States); Albrecht-Schmitt, Thomas E. [Department of Civil Engineering and Geological Sciences and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556 (United States)

2012-08-15

188

Coordination Chemistry of Disilylated Stannylenes with Group 10 d10 Transition Metals: Silastannene vs Stannylene Complexation  

PubMed Central

The coordination behavior of disilylated stannylenes toward zerovalent group 10 transition metal complexes was studied. This was accomplished by reactions of PEt3 adducts of disilylated stannylenes with zerovalent group 10 transition metal complexes. The thus obtained products differed between the first row example nickel and its heavier congeners. While with nickel stannylene complex formation was observed, coordination of the stannylenes to palladium and platinum compounds led to unusual silastannene complexes of these metals. A computational model study indicated that in each case metal stannylene complexes were formed first and that the disilylstannylene/silastannene rearrangement occurs only after complexation to the group 10 metal. The isomerization is a two-step process with relatively small barriers, suggesting a thermodynamic control of product formation. In addition, the results of the computational investigation revealed a subtle balance of steric and electronic effects, which determines the relative stability of the metalastannylene complex relative to its silastannene isomer. In the case of cyclic disilylstannylenes, the Pd(0) and Pt(0) silastannene complexes are found to be more stable, while with acyclic disilylstannylenes the Ni(0) stannylene complex is formed preferentially.

2013-01-01

189

The synthesis and characterization of new copper coordination complexes containing an asymmetric coordinating chelate ligand: Application to enzyme active site modeling  

SciTech Connect

A new class of ligand which produces a binuclear metal complex with coordination asymmetry has been designed and synthesized. A binuclear copper complex has been prepared and characterized including a single crystal x-ray structure analysis. The structure reveals that one copper is 5-coordinate (distorted square pyramidal) while the other copper is only 4-coordinate (distorted square planar) and are separated by an endogenous {mu}-alkoxo oxygen and a bridging acetate. Although this structural type of chelator has been found in biological systems, it has not been previously described for inorganic coordination complexes prepared by design. It is anticipated that this ligand and derivatives of it will play an important role in mimicking chemical reactivity of enzyme active sites that function by substrate interaction at only one metal of a multimetal active site.

Droege, M.W.; Satcher, J.H. Jr.; Reibold, R.A. (Lawrence Livermore National Lab., CA (United States)); Weakely, T.J.R. (Oregon Univ., Eugene, OR (United States). Dept. of Chemistry)

1992-01-01

190

Photoacoustic spectrum of a new, 12-fold-coordinated Ho(III) hydrazone complex  

Microsoft Academic Search

A new, 12-fold-coordinated holmium(III) compound [Ho(NO3)3(PBH)2]NO31.5H2O has been prepared and studied with high-resolution photoacoustic spectrometry (PAS). The spectroscopic parameters of the obtained photoacoustic lines attributed to the ff transitions were analyzed and compared with the parameters for a similar 10-fold-coordinated holmium(III) complex [Ho(NO3)2(PicBH)2]. Computer fitting of the obtained spectra allowed decomposing them into Gaussian components and calculating the spectral parameters

N. Guskos; J. Typek; J. Majszczyk; M. Maryniak; D. Paschalidis

2008-01-01

191

Molecular dynamics simulation of uranyl(VI) adsorption equilibria onto an external montmorillonite surface.  

PubMed

We used molecular dynamics simulations to study the adsorption of aqueous uranyl species (UO(2)(2+)) onto clay mineral surfaces in the presence of sodium counterions and carbonato ligands. The large system size (10,000 atoms) and long simulation times (10 ns) allowed us to investigate the thermodynamics of ion adsorption, and the atomistic detail provided clues for the observed adsorption behavior. The model system consisted of the basal surface of a low-charge Na-montmorillonite clay in contact with aqueous uranyl carbonate solutions with concentrations of 0.027 M, 0.081 M, and 0.162 M. Periodic boundary conditions were used in the simulations to better represent an aqueous solution interacting with an external clay surface. Uranyl adsorption tendency was found to decrease as the aqueous uranyl carbonate concentration was increased, while sodium adsorption remained constant. The observed behavior is explained by physical and chemical effects. As the ionic strength of the aqueous solution was increased, electrostatic factors prevented further uranyl adsorption once the surface charge had been neutralized. Additionally, the formation of aqueous uranyl carbonate complexes, including uranyl carbonato oligomers, contributed to the decreased uranyl adsorption tendency. PMID:16294234

Greathouse, Jeffery A; Cygan, Randall T

2005-09-08

192

Molecular dynamics simulation of uranyl(VI) sorption equilibria onto an external montmorillonite surface.  

SciTech Connect

We used molecular dynamics simulations to study the adsorption of aqueous uranyl species (UO22+) onto clay mineral surfaces in the presence of sodium counterions and carbonato ligands. The large system size (10 000 atoms) and long simulation times (10 ns) allowed us to investigate the thermodynamics of ion adsorption, and the atomistic detail provided clues for the observed adsorption behavior. The model system consisted of the basal surface of a low-charge Na-montmorillonite clay in contact with aqueous uranyl carbonate solutions with concentrations of 0.027 M, 0.081 M, and 0.162 M. Periodic boundary conditions were used in the simulations to better represent an aqueous solution interacting with an external clay surface. Uranyl adsorption tendency was found to decrease as the aqueous uranyl carbonate concentration was increased, while sodium adsorption remained constant. The observed behavior is explained by physical and chemical effects. As the ionic strength of the aqueous solution was increased, electrostatic factors prevented further uranyl adsorption once the surface charge had been neutralized. Additionally, the formation of aqueous uranyl carbonate complexes, including uranyl carbonato oligomers, contributed to the decreased uranyl adsorption tendency.

Cygan, Randall Timothy; Greathouse, Jeffery A.

2005-06-01

193

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

194

Multiporphyrin coordination arrays based on complexation of magnesium(II) porphyrins with porphyrinylphosphine oxides.  

PubMed

Di- and triporphyrin arrays consisting of 5,15-diphenylporphyrinatomagnesium(II) (MgDPP) coordinated to free-base and Ni(II) porphyrinyl mono- and bis-phosphine oxides, as well as the self-coordinating diphenyl[10,20-diphenylporphyrinatomagnesium(II)-5-yl]phosphine oxide [MgDPP(Ph(2)PO)], were synthesised in excellent yields and characterised by various spectroscopic techniques. Phosphine oxides stabilise Mg(II) coordination to porphyrins and the resulting complexes have convenient solubilities, while the Ni(II) complexes exhibit interesting intramolecular fluorescence quenching behaviour. The binding constant of MgDPP to triphenylphosphine oxide (5.3 +/- 0.1 x 10(5) M(-1)) and the very high self-association constant of [MgDPP(Ph(2)PO)] (5.5 +/- 0.5 x 10(8) M(-1)) demonstrate the strong affinity of phosphine oxides towards Mg(II) porphyrins. These complexes are the first strongly bound synthetic Mg(II) multiporphyrin complexes and could potentially mimic the "special pair" in the photosynthetic reaction centre. PMID:17514337

Atefi, Farzad; McMurtrie, John C; Arnold, Dennis P

2007-04-19

195

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

196

Macrocyclic hexacarboxylic acid. A highly selective host for uranyl ion  

SciTech Connect

Previously a macrocyclic hexaketone which effectively bound uranyl ion was prepared succesfully. Recently, two types of ligand of macrocyclic hexacarboxylic acid were prepared by symmetrically arranging six carboxylates on a macrocyclic skeleton in which the ring size was adjusted to give a cavity to accommodate uranyl ion comfortably. Three of six carboxylates seem to compose a binding site. One of the three additional carboxylic acid units in both ligands is amenable to attachment to a suitable polymer support. The other two probably act to make the microscopic environment around the metal binding site more hydrophilic as well as to decrease the entropy loss involved in the complexation. Compared with the previous hexaketone, the new macrocycle hexacarboxylic acids are capable of much more facile preparation in reasonable overall yields and are far more effective and selective for the binding of the uranyl ion. The preparation is a straightforward reaction between tetraethyl n-decane-1,1,-10,10-tetracarboxylate and diethyl ..cap alpha.., ..cap alpha..-bis(8-iodooctyl)malonate. The cyclization was achieved under high-dilution conditions, and the hexaethyl ester of macrocyclic hexacarboxylic acid was isolated through silica gel column chromatography. Alkaline hydrolysis yielded the hexacarboxylic acid. Similar procedures gave a hexacarboxylic acid containing an ether bridge. Uranyl ion is known to form a stable complex with carbonate (CO/sub 3//sup 2 -/). High selectivity of these ligands to uranyl was ascertained also by competition with other metal cations such as: Na/sup +/, Mg/sup 2 +/, Ni/sup 2 +/, and Zn/sup 2 +/. These results indicate that uranyl ions can be extracted efficiently from sea water using these hexacarboxylic acid ligands which are attached to a polymer completely insoluble in water.

Tabushi, I.; Kobuke, Y.; Ando, K.; Kishimoto, M.; Ohara, E.

1980-08-27

197

Coordination properties of hydralazine Schiff base Synthesis and equilibrium studies of some metal ion complexes.  

PubMed

In the present study, a new ligand is prepared by condensation of hydralazine (1-Hydralazinophthalazine) with 2-butanon-3-oxime. The acid-base equilibria of the schiff-base and the complex formation equilibria with the metal ions as Cu(II), Ni(II), Co(II), Cd(II), Mn(II) and Zn(II) are investigated potentiometrically. The stability constants of the complexes are determined and the concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties as atomic number, ionic radius, electronegativity and ionization potential are investigated. The isolated solid complexes are characterized by conventional chemical and physical methods. The potential coordination sites are assigned using the i.r. and (1)H NMR spectra. The structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies. PMID:17950027

Shoukry, Azza A; Shoukry, Mohamed M

2007-09-07

198

A Rac1-GDP Trimer Complex Binds Zinc with Tetrahedral and Octahedral Coordination, Displacing Magnesium  

SciTech Connect

The Rho family of small GTPases represent well characterized signaling molecules that regulate many cellular functions such as actin cytoskeletal arrangement and the cell cycle by acting as molecular switches. A Rac1-GDP-Zn complex has been crystallized in space group P3{sub 2}21 and its crystal structure has been solved at 1.9 {angstrom} resolution. These trigonal crystals reveal the unexpected ability of Rac1 to coordinate Zn atoms in a tetrahedral fashion by use of its biologically relevant switch I and switch II regions. Upon coordination of zinc, the switch I region is stabilized in the GDP-bound conformation and contributes to a Rac1 trimer in the asymmetric unit. Zinc coordination causes switch II to adopt a novel conformation with a symmetry-related molecule. Additionally, zinc was found to displace magnesium from its octahedral coordination at switch I, although GDP binding remained stable. This structure represents the first reported Rac1-GDP-Zn complex, which further underscores the conformational flexibility and versatility of the small GTPase switch regions.

Prehna,G.; Stebbins, E.

2007-01-01

199

Functional cooperation between FACT and MCM is coordinated with cell cycle and differential complex formation  

PubMed Central

Background Functional cooperation between FACT and the MCM helicase complex constitutes an integral step during DNA replication initiation. However, mode of regulation that underlies the proper functional interaction of FACT and MCM is poorly understood. Methods & Results Here we present evidence indicating that such interaction is coordinated with cell cycle progression and differential complex formation. We first demonstrate the existence of two distinct FACT-MCM subassemblies, FACT-MCM2/4/6/7 and FACT-MCM2/3/4/5. Both complexes possess DNA unwinding activity and are subject to cell cycle-dependent enzymatic regulation. Interestingly, analysis of functional attributes further suggests that they act at distinct, and possibly sequential, steps during origin establishment and replication initiation. Moreover, we show that the phosphorylation profile of the FACT-associated MCM4 undergoes a cell cycle-dependent change, which is directly correlated with the catalytic activity of the FACT-MCM helicase complexes. Finally, at the quaternary structure level, physical interaction between FACT and MCM complexes is generally dependent on persistent cell cycle and further stabilized upon S phase entry. Cessation of mitotic cycle destabilizes the complex formation and likely leads to compromised coordination and activities. Conclusions Together, our results correlate FACT-MCM functionally and temporally with S phase and DNA replication. They further demonstrate that enzymatic activities intrinsically important for DNA replication are tightly controlled at various levels, thereby ensuring proper progression of, as well as exit from, the cell cycle and ultimately euploid gene balance.

2010-01-01

200

Some properties of compounds of uranyl nitrate with dimethylformamide  

Microsoft Academic Search

The authors establish that in the interaction of solutions of uranyl nitrate containing excess HNO with dimethylformamide, the compound UO(N)) X 2HCON(CH) crystallizes. An analysis of the IR spectrum of the salt indicates bidentate coordination of the NO⁻ ions and a bond of the DMFA molecules to the uranium atom through the oxygen atoms. The interplane distances were calculated according

D. N. Bykhovskii; G. S. Novikov; A. N. Smirnov; L. V. Solntseva

1986-01-01

201

Oxidative decarbonylation of m-terphenyl isocyanide complexes of molybdenum and tungsten: precursors to low-coordinate isocyanide complexes.  

PubMed

Synthetic studies are presented addressing the oxidative decarbonylation of molybdenum and tungsten complexes supported by the encumbering m-terphenyl isocyanide ligand CNAr(Dipp2) (Ar(Dipp2) = 2,6-(2,6-(i-Pr)(2)C(6)H(3))(2)C(6)H(3)). These studies represent an effort to access halide or pseudohalide M/CNAr(Dipp2) species (M = Mo, W) for use as precursors to low-coordinate, low-valent group 6 isocyanide complexes. The synthesis and structural chemistry of the tetra- and tricarbonyl tungsten complexes trans-W(CO)(4)(CNAr(Dipp2))(2) and trans-W(NCMe)(CO)(3)(CNAr(Dipp2))(2) are reported. The acetonitrile adducts trans-M(NCMe)(CO)(3)(CNAr(Dipp2))(2) (M = Mo, W) react with I(2) to form divalent, diiodide complexes in which the extent of decarbonylation differs between Mo and W. In the molybdenum example, the diiodide, dicarbonyl complex MoI(2)(CO)(2)(CNAr(Dipp2))(2) is generated, which has an S = 1 ground state in solution. Paramagnetic group 6 MX(2)L(4) complexes are rare, and the structure of MoI(2)(CO)(2)(CNAr(Dipp2))(2) is discussed in relation to other diamagnetic and C(2v)-distorted MX(2)L(4) complexes. Diiodide MoI(2)(CO)(2)(CNAr(Dipp2))(2) reacts further with I(2) to effect complete decarbonylation, producing the paramagnetic tetraiodide complex trans-MoI(4)(CNAr(Dipp2))(2). The reactivity of the trans-M(NCMe)(CO)(3)(CNAr(Dipp2))(2) (M = Mo, W) complexes toward benzoyl peroxide is also surveyed, and it is shown that dicarboxylate complexes can be obtained by oxidative or salt-elimination routes. The reduction behavior of the tetraiodide complex trans-MoI(4)(CNAr(Dipp2))(2) toward Mg metal and sodium amalgam is studied. In benzene solution under N(2), trans-MoI(4)(CNAr(Dipp2))(2) is reduced by Na/Hg to the ?(6)-arene-dinitrogen complex, (?(6)-C(6)H(6))Mo(N(2))(CNAr(Dipp2))(2). The diiodide-?(6)-benzene complex (?(6)-C(6)H(6))MoI(2)(CNAr(Dipp2))(2) is an isolable intermediate in this reduction reaction, and its formation and structure are discussed in context of putative low-coordinate, low-valent molybdenum isocyanide complexes. PMID:21923128

Ditri, Treffly B; Moore, Curtis E; Rheingold, Arnold L; Figueroa, Joshua S

2011-09-16

202

Two new hybrid compounds assembled from Keggin-type polyoxometalates and transition metal coordination complexes  

NASA Astrophysics Data System (ADS)

Two new hybrid compounds based on Keggin-type polyoxometalates: {[PMo12O40][Ni(Phen)2(H2O)]2}K2OH- (1) and [Cd2(Phen)4Cl2][HPW12O40]H2O (2) (Phen=1,10-phenanthroline), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Compound 1 exhibits a 1-D chain structure constructed from Pseudo-Keggin polyoxometalate bi-supported transition metal coordination complexes linked by K+ ions. Compound 2 contains Pseudo-Keggin polyoxoanions [HPW12O40]2- and novel metal-chloride-ligand coordination complexes [Cd2(Phen)4Cl2]2+.Graphical abstractTwo new hybrid compounds based on different Keggin-type polyoxometalates have been hydrothermally synthesized and characterized by IR, UV-Vis, XPS, XRD, elemental analysis and single crystal X-ray diffraction analysis. Display Omitted

Wang, Yan; Zou, Bo; Xiao, Li-Na; Jin, Ning; Peng, Yu; Wu, Feng-Qing; Ding, Hong; Wang, Tie-Gang; Gao, Zhong-Min; Zheng, Da-Fang; Cui, Xiao-Bing; Xu, Ji-Qing

2011-03-01

203

Electrochemical synthesis and crystal structure of a penta-coordinated silver(II) macrocyclic complex  

Microsoft Academic Search

We present the electrochemical synthesis by galvanostatic electro-oxidation method and single crystal structure determination of a complex of silver(II) with a macrocyclic N donor ligand crystallized with hexafluorophosphate anions. The crystal structure analysis showed a penta-coordinated environment of silver(II) and displacement of the metal centre from the rectangular planar configuration of the macrocyclic N donor which is due to axial

Sakthivel Kandaiah; Ivan Halasz; Robert E. Dinnebier; Martin Jansen

2009-01-01

204

Cyto- and genotoxic effects of coordination complexes of platinum, palladium and rhodium in vitro  

Microsoft Academic Search

The growing industrial use of platinum group elements as catalysts, especially in automobile exhaust detoxification (trimetal\\u000a catalytic converters), is causing increasing occupational and environmental pollution. The cytotoxic and mutagenic properties\\u000a of industrially used coordination complexes of platinum, palladium and rhodium were investigated using the neutral red cytotoxicity\\u000a assay on two established cell lines and theSalmonella typhimurium\\/microsome test system (Ames test).

Jrgen Bnger; Joachim Stork; Karlheinz Stalder

1996-01-01

205

Efficient water oxidation catalysts based on readily available iron coordination complexes  

Microsoft Academic Search

Water oxidation catalysis constitutes the bottleneck for the development of energy-conversion schemes based on sunlight. To date, state-of-the-art homogeneous water oxidation catalysis is performed efficiently with expensive, toxic and earth-scarce transition metals, but 3d metal-based catalysts are much less established. Here we show that readily available, environmentally benign iron coordination complexes catalyse homogeneous water oxidation to give O2, with high

Julio Lloret Fillol; Zoel Codol; Isaac Garcia-Bosch; Laura Gmez; Juan Jos Pla; Miquel Costas

2011-01-01

206

SOME PHYSICAL PROPERTIES OF URANYL NITRATE SOLUTIONS  

Microsoft Academic Search

Boillng points, freezing points, and densities were measured in the ;\\u000a concentration range between uranyl nitrate hexahydrate and uranyl nitrate ;\\u000a dihydrate. The surface tension of molten uranyl nitrate hexahydrate was ;\\u000a determined to be approximately 45 dynes per square centimeter at 90 to 1OO icient ;\\u000a laborato C. (auth)

G. P. Lang; M. O. Nethaway

1958-01-01

207

Coronin 1B coordinates Arp2/3 complex and Cofilin activities at the leading edge  

PubMed Central

Summary Actin filament nucleation and turnover are interdependent processes in migrating cells, but the mechanisms coordinating these events are unknown. Coronin 1B influences motility, lamellipodial dynamics and actin filament architecture at the leading edge of Rat2 cells in a manner consistent with a role in coordinating filament formation and turnover. Coronin 1B interacts simultaneously with both Arp2/3 complex and Slingshot (SSH1L) phosphatase, two regulators of actin filament formation and turnover, respectively. Coronin 1B inhibits filament nucleation by Arp2/3 complex and this inhibition is attenuated by phosphorylation of Coronin 1B on Serine 2, a site targeted by SSH1L. Coronin 1B directs SSH1L to lamellipodia where it likely regulates Cofilin. Accordingly, depleting Coronin 1B increases phospho-Cofilin levels and expressing activated Cofilin partially suppresses the effects on lamellipodia dynamics of Coronin 1B depletion. Thus, Coronin 1B coordinates filament nucleation via Arp2/3 complex and turnover by Cofilin at the leading edge of migrating cells.

Cai, Liang; Marshall, Thomas W.; Uetrecht, Andrea C.; Schafer, Dorothy A.; Bear, James E.

2008-01-01

208

Thiosemicarbazone complexes of the platinum metals. A story of variable coordination modes  

Microsoft Academic Search

Salicylaldehyde thiosemicarbazone (H2saltsc) reacts with [M(PPh3)3X2] (M = Ru, Os; X = Cl, Br) to afford complexes of type [M(PPh3)2(Hsaltsc)2], in which the salicylaldehyde thiosemicarbazone ligand is coordinated to the metal as a bidentate N,S-donor forming a four-membered\\u000a chelate ring. Reaction of benzaldehyde thiosemicarbazones (Hbztsc-R) with [M(PPh3)3X2] also affords complexes of similar type, viz. [M(PPh3)2(bztsc-R)2], in which the benzaldehyde thiosemicarbazones

Indrani Pal; Falguni Basuli; Samaresh Bhattacharya

2002-01-01

209

Differences in gait complexity and variability between children with and without developmental coordination disorder.  

PubMed

We used elliptical Fourier analysis (EFA) to examine potential differences in the complexity and variability of gait of children with (N=10) and without (N=10) Developmental Coordination Disorder (DCD). Children with DCD generated movement patters with larger variability and complexity than typically developing (TD) children. In addition, children with DCD exhibited greater asymmetry in their movement patterns compared to TD children. Our results suggest that children with DCD have significantly greater difficulty producing consistent movement patterns both across their left and right legs and over repeated strides. EFA techniques show promise for distinguishing between different groups of individuals. PMID:18829321

Rosengren, Karl S; Deconinck, Frederik J A; Diberardino, Louis A; Polk, John D; Spencer-Smith, Jesse; De Clercq, Dirk; Lenoir, Matthieu

2008-10-01

210

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

211

Flexible and asymmetric ligand in constructing coordinated complexes: synthesis, crystal structures and fluorescent characterization.  

PubMed

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, [Ag(2)(L)(2)(NO(3))(2)](n) (1) and [Ag(L)(ClO(4))](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. PMID:21339976

Chen, Peng; Lin, Jianhua

2010-12-27

212

Ion pair recognition of quaternary ammonium and iminium salts by uranyl-salophen compounds in solution and in the solid state.  

PubMed

Efficient ditopic receptors for quaternary ammonium and iminium salts have been obtained upon functionalization of the uranyl-salophen unit with conformationally flexible side arms bearing phenyl or beta-naphthyl substituents. Binding affinities in chloroform solution have been measured for a large number of quaternary salts comprising tetramethylammonium (TMA), tetrabutylammonium (TBA), acetylcholine (ACh), N-methylpyridinium (NMP), and N-methylisoquinolinium (NmiQ) cations. Recognition of the anion partner is ensured by coordination to the hard Lewis acidic uranyl center, whereas cation-pi/CH-pi interactions of the quaternary ions are established with the aromatic pendants. The role of the cation-anion interactions on the dynamics of exchange between the free and complexed species is discussed. Solid-state structures have been obtained for a few salt-receptor combinations. In the solid state, side-armed receptor molecules form assemblies that enclose ion pair aggregates of varying composition and structure, including AChCl dimers, two different kinds of tetrameric (TMA)Cl clusters, and unidimentional salt strips of (NMP)Br. The lack of side arms as preferential binding sites for the polar quaternary cations prevents association patterns of the kinds formed with the side-armed receptors, as shown by the crystal structure of the complex of (TMA)Cl with the parent uranyl-salophen receptor. PMID:17338524

Cametti, Massimo; Nissinen, Maija; Cort, Antonella Dalla; Mandolini, Luigi; Rissanen, Kari

2007-03-06

213

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

PubMed

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 Ni-N bond lengths and two short ones. The enthalpies of combustion for both complexes are over 3600?kJ/mol. The N-N bond lengths in the moieties of hydrazine and azide ligands increase in the coordination process compared to those of the isolated molecules. PMID:24052834

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

2011-04-27

214

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

215

Coordination chemistry and reactivity of zinc complexes supported by a phosphido pincer ligand.  

PubMed

The preparation and characterization of new Zn(II) complexes of the type [(PPP)ZnR] in which R = Et (1) or N(SiMe(3))(2) (2) and PPP is a tridentate monoanionic phosphido ligand (PPP-H = bis(2-diphenylphosphinophenyl)phosphine) are reported. Reaction of ZnEt(2) and Zn[N(SiMe(3))(2)](2) with one equivalent of proligand PPP-H produced the corresponding tetrahedral zinc ethyl (1) and zinc amido (2) complexes in high yield. Homoleptic (PPP)(2) Zn complex 3 was obtained by reaction of the precursors with two equivalents of the proligand. Structural characterization of 1-3 was achieved by multinuclear NMR spectroscopy ((1)H, (13)C, and (31)P) and X-ray crystallography (3). Variable-temperature (1)H and (31)P?NMR studies highlighted marked flexibility of the phosphido pincer ligand in coordination at the metal center. A DFT calculation on the compounds provided theoretical support for this behavior. The activities of 1 and 2 toward the ring-opening polymerization of ?-caprolactone and of L- and rac-lactide were investigated, also in combination with an alcohol as external chain-transfer agent. Polyesters with controlled molecular parameters (M(n), end groups) and low polydispersities were obtained. A DFT study on ring-opening polymerization promoted by these complexes highlighted the importance of the coordinative flexibility of the ancillary ligand to promote monomer coordination at the reactive zinc center. Preliminary investigations showed the ability of these complexes to promote copolymerization of L-lactide and ?-caprolactone to achieve random copolymers whose microstructure reproduces the composition of the monomer feed. PMID:22267007

D'Auria, Ilaria; Lamberti, Marina; Mazzeo, Mina; Milione, Stefano; Roviello, Giuseppina; Pellecchia, Claudio

2012-01-20

216

Synthesis and activity of ruthenium alkylidene complexes coordinated with phosphine and N-heterocyclic carbene ligands.  

PubMed

This paper reports the synthesis and characterization of a variety of ruthenium complexes coordinated with phosphine and N-heterocyclic carbene (NHC) ligands. These complexes include several alkylidene derivatives of the general formula (NHC)(PR(3))(Cl)(2)Ru=CHR', which are highly active olefin metathesis catalysts. Although these catalysts can be prepared adequately by the reaction of bis(phosphine) ruthenium alkylidene precursors with free NHCs, we have developed an alternative route that employs NHC-alcohol or -chloroform adducts as "protected" forms of the NHC ligands. This route is advantageous because NHC adducts are easier to handle than their free carbene counterparts. We also demonstrate that sterically bulky bis(NHC) complexes can be made by reaction of the pyridine-coordinated precursor (NHC)(py)(2)(Cl)(2)Ru=CHPh with free NHCs or NHC adducts. Two crystal structures are presented, one of the mixed bis(NHC) derivative (H(2)IMes)(IMes)(Cl)(2)Ru=CHPh, and the other of (PCy(3))(Cl)(CO)Ru[eta(2)-(CH(2)-C(6)H(2)Me(2))(N(2)C(3)H(4))(C(6)H(2)Me(3))], the product of ortho methyl C-H bond activation. Other side reactions encountered during the synthesis of new ruthenium alkylidene complexes include the formation of hydrido-carbonyl-chloride derivatives in the presence of primary alcohols and the deprotonation of ruthenium vinylcarbene ligands by KOBu(t). We also evaluate the olefin metathesis activity of NHC-coordinated complexes in representative RCM and ROMP reactions. PMID:12603143

Trnka, Tina M; Morgan, John P; Sanford, Melanie S; Wilhelm, Thomas E; Scholl, Matthias; Choi, Tae-Lim; Ding, Sheng; Day, Michael W; Grubbs, Robert H

2003-03-01

217

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.

218

Complexation of U(VI) with dipicolinic acid: thermodynamics and coordination modes.  

PubMed

Complexation of UO2(2+) with dipicolinic acid (DPA) has been investigated in 0.1 M NaClO4. The stability constants (log ?1 and log ?2) for two successive complexes, UO2L and UO2L2(2-) where L(2-) stands for the deprotonated dipicolinate anion, were determined to be 10.7 0.1 and 16.3 0.1 by spectrophotometry. The enthalpies of complexation (?H1 and ?H2) were measured to be -(6.9 0.2) and -(28.9 0.5) kJmol(-1) by microcalorimetry. The entropies of complexation (?S1 and ?S2) were calculated accordingly to be (181 3) and (215 4) JK(-1)mol(-1). The strong complexation of UO2(2+) with DPA is driven by positive entropies as well as exothermic enthalpies. The crystal structure of Na2UO2L2(H2O)8(s) shows that, in the 1:2 UO2(2+)/DPA complex, the U atom sits at a center of inversion and the two DPA ligands symmetrically coordinate to UO2(2+) via its equatorial plane in a tridentate mode. The structural information suggests that, due to the conjugated planar structure of DPA with the donor atoms (the pyridine nitrogen and two carboxylate oxygen atoms) arranged at optimal positions to coordinate with UO2(2+), little energy is required for the preorganization of the ligand, resulting in strong UO2(2+)/DPA complexation. PMID:23421621

Xu, Chao; Tian, Guoxin; Teat, Simon J; Rao, Linfeng

2013-02-19

219

The coordination chemistry of divalent bis(pentamethylcyclopentadienyl)lanthanide complexes with non-classical ligands  

SciTech Connect

Divalent complexes (Me/sub 5/C/sub 5/)/sub 2/M (M = Eu, Sm, Yb, Ca, Sr, and Ba) have been isolated free of coordinating Lewis bases. These complexes have a ''bent-sandwich'' geometry. The bonding in the compounds is ionic. Divalent lanthanide and alkaline earth cations of similar ionic radii demonstrate similar coordination chemistry with simple Lewis bases. Isolation of the base-free species allows the synthesis of coordination compounds of weak bases, such as electron-rich olefins and acetylenes. The complexes (Me/sub 5/C/sub 5/)/sub 2/Yb(..mu..-C/sub 2/H/sub 4/)Pt(PPh/sub 3/)/sub 2/ and (Me/sub 5/C/sub 5/)/sub 2/(eta/sup 2/-MeC identical to CMe) is eta/sup 2/-coordinated to the lanthanide. Ethylene is rapidly polymerized by (Me/sub 5/C/sub 5/)/sub 2/Yb, and methylallene is catalytically isomerized to 2-butyne. Fluoro-olefins and -arenes undergo reduction followed by fluoride abstraction to give the mixed-valence compound ((Me/sub 5/C/sub 5/)/sub 2/Yb)/sub 2/(..mu..-F), which is converted thermally to the tetranuclear species (Me/sub 5/C/sub 5/)/sub 6/Yb/sub 4/(..mu..-F)/sub 4/. The reaction of (Me/sub 5/C/sub 5/)/sub 2/Yb with polar compounds such as (Me/sub 5/C/sub 5/)BeMe and BH/sub 3/ . PMe/sub 3/ results in the formation of coordination compounds. Zinc alkyl and aryl compounds are reduced to yield zincate complexes of the formula (Me/sub 5/C/sub 5/)/sub 2/Yb(..mu..-R)/sub 2/ZnR. The trimethylzincate compound displays symmetrically bridging methyl groups, while in the phenyl analog, the bridging geometry is markedly unsymmetric. Sterically demanding polar molecules such as carboranes react with (Me/sub 5/C/sub 5/)/sub 2/Yb to form inclusion compounds, with no close host-guest contacts in the solid state.

Burns, C.J.

1987-10-01

220

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

221

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

2013-03-01

222

Interfacial activity of metal ?-diketonato complexes: in situ generation of amphiphiles by water coordination.  

PubMed

Symmetric transition metal complexes of 2,4-pentanedione (acetyl acetone) are interfacially active: Spinning drop tensiometry reveals lowering of the interfacial tension at the water-organic interface, most pronounced for [Cr(acac)(3)], [Fe(acac)(3)], [Zr(acac)(4)], and [Hf(acac)(4)]. The interfacial activity is explained by the in situ generation of amphiphilic species. Based on tensiometry and (1)H and diffusion-ordered NMR spectroscopy (DOSY NMR), hydrogen bonding of the organically dissolved complexes with water, in some cases in combination with inner-sphere hydrolytic coordination, is identified as the primary origin of this amphiphilicity. The complexes are a rare example of symmetric molecules that turn amphiphilic only upon interfacial interaction with water. PMID:21639094

van den Brom, Coenraad R; Vogel, Nicolas; Hauser, Christoph P; Goerres, Sebastian; Wagner, Manfred; Landfester, Katharina; Weiss, Clemens K

2011-06-03

223

Interactions of 1-Methylimidazole with UO?(CH?CO?)? and UO?(NO?)?: Structural, Spectroscopic, and Theoretical Evidence for Imidazole Binding to the Uranyl Ion.  

SciTech Connect

The first definitive high-resolution single-crystal X-ray structure for the coordination of the 1-methylimidazole (Meimid) ligand to UO?(Ac)? (Ac ) CH?CO?) is reported. The crystal structure evidence is confirmed by IR, Raman, and UV-vis spectroscopic data. Direct participation of the nitrogen atom of the Meimid ligand in binding to the uranium center is confirmed. Structural analysis at the DFT (B3LYP) level of theory showed a conformational difference of the Meimid ligand in the free gas-phase complex versus the solid state due to small energetic differences and crystal packing effects. Energetic analysis at the MP2 level in the gas phase supported stronger Meimid binding over H?O binding to both UO?(Ac)? and UO?(NO?)?. In addition, self-consistent reaction field COSMO calculations were used to assess the aqueous phase energetics of combination and displacement reactions involving H?O and Meimid ligands to UO?R? (R ) Ac, NO?). For both UO?(NO?)? and UO?(Ac)?, the displacement of H?O by Meimid was predicted to be energetically favorable, consistent with experimental results that suggest Meimid may bind uranyl at physiological pH. Also, log(Knitrate/KAc) calculations supported experimental evidence that the binding stoichiometry of the Meimid ligand is dependent upon the nature of the reactant uranyl complex. These results clearly demonstrate that imidazole binds to uranyl and suggest that binding of histidine residues to uranyl could occur under normal biological conditions.

Gutowski, Keith E.; Cocalia, Violina A.; Griffin, Scott T.; Bridges, Nicholas J.; Dixon, David A.; Rogers, Robin D.

2007-01-24

224

Water structure and aqueous uranyl(VI) adsorption equilibria onto external surfaces of beidellite, montmorillonite, and pyrophyllite: results from molecular simulations.  

PubMed

Molecular dynamics simulations were performed to provide a systematic study of aqueous uranyl adsorption onto the external surface of 2:1 dioctahedral clays. Our understanding of this key process is critical in predicting the fate of radioactive contaminants in natural groundwaters. These simulations provide atomistic detail to help explain experimental trends in uranyl adsorption onto natural media containing smectite clays. Aqueous uranyl concentrations ranged from 0.027 to 0.162 M. Sodium ions and carbonate ions (0.027-0.243 M) were also present in the aqueous regions to more faithfully model a stream of uranyl-containing groundwater contacting a mineral system comprised of Na-smectite. No adsorption occurred near the pyrophyllite surface, and there was little difference in uranyl adsorption onto the beidellite and montmorillonite, despite the difference in location of clay layer charge between the two. At low uranyl concentration, the pentaaquouranyl complex dominates in solution and readily adsorbs to the clay basal plane. At higher uranyl (and carbonate) concentrations, the mono(carbonato) complex forms in solution, and uranyl adsorption decreases. Sodium adsorption onto beidellite occurred both as inner- and outer-sphere surface complexes, again with little effect on uranyl adsorption. Uranyl surface complexes consisted primarily of the pentaaquo cation (85%) and to a lesser extent the mono(carbonato) species (15%). Speciation diagrams of the aqueous region indicate that the mono(carbonato)uranyl complex is abundant at high ionic strength. Oligomeric uranyl complexes are observed at high ionic strength, particularly near the pyrophyllite and montmorillonite surfaces. Atomic density profiles of water oxygen and hydrogen atoms are nearly identical near the beidellite and montmorillonite surfaces. Water structure therefore appears to be governed by the presence of adsorbed ions and not by the location of layer charge associated with the substrate. The water oxygen density near the pyrophyllite surface is similar to the other cases, but the hydrogen density profile indicates reduced hydrogen bonding between adsorbed water molecules and the surface. PMID:16830554

Greathouse, Jeffery A; Cygan, Randall T

2006-06-15

225

Synthesis, structures and near-infrared luminescence properties of Ho3+ and Yb3+ coordination complexes  

NASA Astrophysics Data System (ADS)

Four Ln3+ coordination complexes with the formulas [Ln(p-toluylate)2(Ac)(H2O)]n (Ln=Ho 1, Yb 2) and {[Ln2(OOCCH2CH2COO)3(H2O)4]6H2O}n (Ln=Ho 3, Yb 4) were synthesized hydrothermally. Their structures were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are isomorphic and form infinite 2D network structures comprising p-toluylate and acetate (Ac-) moieties. Complexes 3 and 4 are also isomorphic and possess infinite 2D structures in which succinate acts as bridging ligands that are connected to a 3D hydrogen bonding network by O-HO hydrogen bonds. Solid-state IR and UV-Vis-NIR spectra, excitation and emission spectra were determined for the four complexes at room temperature. Complexes 1 and 2 exhibit characteristic NIR emission bands of Ln3+ ions but these are shifted and split relative to the theoretical positions. This is also evident for their UV-Vis-NIR spectra. The influence of ligands on enhancing the NIR luminescence of Ln3+ ions in complexes is discussed.

Chi, Yu-Xian; Liu, Tong-Shuai; Jin, Jing; Zhang, Guang-Ning; Niu, Shu-Yun

2013-12-01

226

Unusual luminescence from uranyl nitrate  

Microsoft Academic Search

Temperature-induced luminescence was observed from uranyl nitrate hexahydrate crystals. Flashes of green light were detected when the crystal was cooled with liquid nitrogen and also when the cooled crystal was allowed to return to room temperature. They mostly occurred between 77 and 100K. More and stronger flashes were observed during cooling. The intensities of these flashes and the temperatures of

R. Griffith; A. F Leung; E. Mercado; M. Morshedabbasi

2001-01-01

227

Fluorescence properties of uranyl nitrates  

Microsoft Academic Search

Fluorescence spectra of uranyl nitrate hexahydrate, trihydrate, and dihydrate at 77K were recorded. Those of the hexahydrate and trihydrate were similar but were different from that of the dihydrate. Fluorescence lifetimes of the hexahydrate, trihydrate, and dihydrate at 77K were observed to be 699, 838 and 499?s, respectively. The difference between these lifetimes was explained by considering the interaction between

A. F. Leung; L. Hayashibara; J. Spadaro

1999-01-01

228

The use of synchrotron radiation in X-ray charge density analysis of coordination complexes  

SciTech Connect

The compelling advantages of synchrotron radiation (SR) in charge density studies of coordination complexes are described and illustrated with a number of recent synchrotron studies, ordered according to the atomic number of the metal atom involved (Cr, Fe, Cu, Zr, Mo, Th). The review concludes with two studies of the Cu-containing extended solids Cu{sub 2}O and the high-temperature superconducting phase YBa{sub 2}Cu{sub 3}O{sub 6.98}, done with very high energy synchrotron radiation of about 100 keV ({approx}0.12 {angstrom}), very much beyond what is available at conventional X-ray sources.

Coppens, P.; Iversen, B.; Larsen, F.K. (Aarhus); (SUNYB)

2008-10-03

229

Stereochemistry of Tropolonato Complexes Utilizing the Higher Coordination Numbers. I. Nine-Coordinate Tetrakis(tropolonato)-N,N-dimethylformamidethorium (IV).  

National Technical Information Service (NTIS)

Molecular crystals of (DMF)ThT4 (DMF is N,N'-dimethylformamide, T(-) is the bidentate C7H5O2(-) tropolonate ion) use a two-molecule unit cell. The intensities of 7476 x-ray independent reflections were measured. The nine-coordinate (DMF)-ThT4 molecule in ...

V. W. Day J. L. Hoard

1970-01-01

230

Antitumor properties of five-coordinate gold(III) complexes bearing substituted polypyridyl ligands.  

PubMed

In an on-going effort to discover metallotherapeutic alternatives to the chemotherapy drug cisplatin, neutral distorted square pyramidal gold(III) coordination complexes possessing 2,9-disubstituted-1,10-phenanthroline ligands {[((R)phen)AuCl3]; R=n-butyl, sec-butyl} have been previously synthesized and characterized. A structurally analogous gold(III) complex bearing a 6,6'-di-methylbipyridine ligand ([((methyl)bipy)AuCl3]) has been synthesized and fully characterized to probe the effect of differing aromatic character of the ligand on solution stability and tumor cell cytotoxicity. The two compounds [((sec-butyl)phen)AuCl3] and [((methyl)bipy)AuCl3]) were subsequently assessed for their stability against the biological reductant glutathione, and it was found that the [((sec-butyl)phen)AuCl3] complex exhibits slightly enhanced stability compared to the [((methyl)bipy)AuCl3] complex and significantly higher stability than previously reported square planar gold(III) complex ions. Furthermore, these complexes were tested for cytotoxic effects against existing lung and head and neck cancer cell lines in vitro. The [((sec-butyl)phen)AuCl3] complex was found to be more cytotoxic than cisplatin against five different tumor cell lines, whereas [((methyl)bipy)AuCl3] had more limited in vitro antitumor activity. Given that [((sec-butyl)phen)AuCl3] had significantly higher antitumor activity, it was tested against an in vivo tumor model. It was found that this complex did not significantly reduce the growth of xenograft tumors in mice and initial model binding studies with bovine serum albumin indicate that interactions with serum albumin proteins may be the cause for the limited in vivo activity of this potential metallotherapeutic. PMID:23948576

Sanghvi, Chinar D; Olsen, Pauline M; Elix, Catherine; Peng, Shifang Bruce; Wang, Dongsheng; Chen, Zhuo Georgia; Shin, Dong M; Hardcastle, Kenneth I; Macbeth, Cora E; Eichler, Jack F

2013-07-17

231

Synthesis And Third-order Nonlinear Optical Studies of Four-Coordinated Copper(I) Complexes  

NASA Astrophysics Data System (ADS)

Three Cu(I) halide complexes [Cu(L)(PPh3)X] (L = 1,10-phenanthroline, X = Cl (1), Br (2) and I (3), PPh3 = triphenylphosphine) have been synthesised and characterised by spectroscopic techniques. Further structure of the complex 1 was confirmed by single crystal X-ray diffraction analysis. The nonlinear optical properties of the complexes were investigated at 532 nm using single beam Z-scan technique with nanosecond laser pulses. The complexes showed strong optical limiting behavior due to effective three-photon absorption (3PA). The values of 3PA coefficients (?) for 1, 2 and 3 were found to be 3.210-24 m3/W2, 6.010-25 m3/W2 and 1.210-23 m3/W2 respectively, which are comparable to good optical limiting materials. These studies demonstrate that the Ligand-->copper coordinative bonds facilitate the polarization of the electronic ?-system which optimizes the third-order NLO response in the reported complexes.

Kumar, H. C. Sampath; Rudresha, B. J.; Bhat, B. Ramachandra; Philip, Reji; Row, T. N. Guru

2011-10-01

232

Computation of resonances by two methods involving the use of complex coordinates  

NASA Astrophysics Data System (ADS)

We have studied two different systems producing resonances, a highly excited multielectron Coulombic negative ion (the He- 2s2p2 4P state) and a hydrogen atom in a magnetic field, via the complex-coordinate rotation (CCR) and the state-specific complex-eigenvalue Schrdinger equation (CESE) approaches. For the He- 2s2p2 4P resonance, a series of large CCR calculations, up to 353 basis functions with explicit rij dependence, were carried out to serve as benchmarks. For the magnetic-field problem, the CCR results were taken from the literature. Comparison shows that the state-specific CESE theory allows the physics of the problem to be incorporated systematically while keeping the overall size of the computation tractable regardless of the number of electrons.

Bylicki, Miros?aw; Nicolaides, Cleanthes A.

1993-11-01

233

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

PubMed

A simple synthesis of the zerovalent complex Mo[P(OCH(3))(3)](6) has been devised from a potassium reduction of MoCl(4)(tetrahydrofuran)(2) followed by reaction with trimethyl phosphite at 70 degrees . Protonation of this octahedral complex gave only low yields of the expected seven-coordinate hydride, HMo[P(OCH(3))(3)](6) (+). The major product was an octahedral nonhydridic cation, Mo[P(OCH(3))(3)](5)P(OCH(3))(2) (+), derived from proton cleavage of the P-O 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(OCH(3))(3)](5)P(OCH(3))(2) (+)-PF(6) (-). Extended reaction of trifluoroactic acid with Mo[P(OCH(3))(3)](6) yielded the seven-coordinate hydride, HMo[P(OCH(3))(3)](4)(O(2)CCF(3)), which was near pentagonal bipyramidal and was stereochemically nonrigid. PMID:16592505

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

1978-03-01

234

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

235

Utilization of IR spectral detailed analysis for coordination mode determination in novel Zn-cyclen-aminoacid complexes  

NASA Astrophysics Data System (ADS)

The infrared spectra, elemental and thermal (TG/DTG and DTA) analyses of novel [Zn(cyclen-? 4N 1,4,7,10)(HGly-? 2O,O')](ClO 4) 2 ( 1), and [Zn 2(cyclen-? 4N 1,4,7,10) 2(?-S-Ala-? 2N,O)](ClO 4) 32H 2O ( 2) complexes (cyclen - 1,4,7,10-tetraazacyclododecane) were recorded and analyzed in the relation to their structural peculiarities. IR spectral data indicate both mono- or bidentate coordination mode of a carboxylate group in the prepared complexes (at pH ? 9). The results indicate unusual bidentate carboxylate coordination mode (in complex ( 1)) toward to Zn 2+-cyclen unit. Therefore the crystal structure determination of the crystalline complex [Zn(cyclen-? 4N 1,4,7,10)(NO 3-? 2O,O')](NO 3) was attached in order to support the coordination mode assignment in complex ( 1).

Vargov, Z.; Almi, M.; Arabuli, L.; Gyryov, K.; Zele?k, V.; Kuchr, J.

2011-02-01

236

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated rhodium-dioxygen complexes.  

PubMed

Reactions of rhodium atoms with dioxygen molecules in solid argon have been investigated using matrix isolation infrared absorption spectroscopy. The rhodium-dioxygen complexes, Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO), are produced spontaneously on annealing. The Rh(eta2-O2) complex rearranges to the inserted RhO2 molecule under visible light irradiation. Experiments doped with xenon in argon show that the rhodium-dioxygen complexes are coordinated by one or two noble gas atoms in solid noble gas matrixes. Hence, the Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO) molecules trapped in solid noble gas matrixes should be regarded as the Rh(eta2-O2)(Ng)2, Rh(eta2-O2)2(Ng)2, and Rh(eta2-O2)2(eta1-OO)(Ng) (Ng = Ar or Xe) complexes. The product absorptions are identified on the basis of isotopic substitution and density functional theory calculations. PMID:17201389

Yang, Rui; Gong, Yu; Zhou, Han; Zhou, Mingfei

2007-01-11

237

EXTRACTION OF URANYL NITRATE FROM AQUEOUS SOLUTIONS  

DOEpatents

An improvement in the process is described for extracting aqueous uranyl nitrate solutions with an organic solvent such as ether. It has been found that the organic phase will extract a larger quantity of uranyl nitrate if the aqueous phase contains in addition to the uranyl nitrate, a quantity of some other soluble nitrate to act as a salting out agent. Mentioned as suitable are the nitrates of lithium, calcium, zinc, bivalent copper, and trivalent iron.

Furman, N.H.; Mundy, R.J.

1957-12-10

238

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

239

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

240

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

241

Plutonium(IV) complexation by diglycolamide ligands--coordination chemistry insight into TODGA-based actinide separations.  

PubMed

Complexation of Pu(IV) with TMDGA, TEDGA, and TODGA diglycolamide ligands was followed by vis-NIR spectroscopy. A crystal structure determination reveals that TMDGA forms a 1 : 3 homoleptic Pu(IV) complex with the nitrate anions forced into the outer coordination sphere. PMID:22914808

Reilly, Sean D; Gaunt, Andrew J; Scott, Brian L; Modolo, Giuseppe; Iqbal, Mudassir; Verboom, Willem; Sarsfield, Mark J

2012-10-01

242

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

243

Synthesis and study of cationic, two-coordinate triphenylphosphine-gold-? complexes.  

PubMed

Cationic, two-coordinate triphenylphosphine-gold(I)-? complexes of the form [(PPh?)Au(? ligand)]?SbF?? (? ligand=4-methylstyrene, 1?SbF?), 2-methyl-2-butene (3?SbF?), 3-hexyne (6?SbF?), 1,3-cyclohexadiene (7?SbF?), 3-methyl-1,2-butadiene (8?SbF?), and 1,7-diphenyl-3,4-heptadiene (10?SbF?) were generated in situ from reaction of [(PPh?)AuCl], AgSbF?, and ? ligand at -78 C and were characterized by low-temperature, multinuclear NMR spectroscopy without isolation. The ? ligands of these complexes were both weakly bound and kinetically labile and underwent facile intermolecular exchange with free ligand (?G(?) ?9 kcal mol(-1) in the case of 6?SbF?) and competitive displacement by weak ? donors, such as trifluoromethane sulfonate. Triphenylphosphine-gold(I)-? complexes were thermally unstable and decomposed above -20 C to form the bis(triphenylphosphine) gold cation [(PPh?)?Au]?SbF?? (2?SbF?). PMID:23592521

Brooner, Rachel E M; Brown, Timothy J; Widenhoefer, Ross A

2013-04-16

244

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

245

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

246

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

247

A coordination complex system for generic, ultrafast, and sensitive multimode fluorescent staining of biomolecules.  

PubMed

Gel electrophoresis staining methodologies documented thus far are largely utilized in a biomolecule context-dependent manner. We report herein the development of a generic, ultrafast, and sensitive multimode fluorescent system for the efficient identification of DNA, RNA, and proteins. Interaction between a positively charged, planar ligand-based coordination complex with partner biomolecule leads to aggregation-induced fluorescence quenching and allows for the image contrast generation within one minute. Alternatively, successive reactions of the biomolecule-loaded gel with cation and ligand, in either order of sequence, provide an equally effective staining efficacy. Image contrast reversal is accomplished through a facile washing or photobleaching procedure. The versatility in the applicable target species and signal generation modes provides a hint at the design of novel staining structures and potentially enables the high-throughput readout of biomolecules. PMID:22145885

Liu, Xingqiang; Li, Lingjuan; Sun, Jingjing; Yan, Yishu; Shu, Xin; Liu, Baoqing; Sha, Wei; Feng, Hui; Sun, Sha; Zhu, Jin

2011-12-06

248

Coordination and spin states in vanadium carbonyl complexes (V(CO)n+, n = 1-7) revealed with IR spectroscopy.  

PubMed

The vibrational spectra of vanadium carbonyl cations of the form V(CO)(n)(+), where n = 1-7, were obtained via mass-selected infrared laser photodissociation spectroscopy in the carbonyl stretching region. The cations and their argon and neon "tagged" analogues were produced in a molecular beam via laser vaporization in a pulsed nozzle source. The relative intensities and frequency positions of the infrared bands observed provide distinctive patterns from which information on the coordination and spin states of these complexes can be obtained. Density functional theory is carried out in support of the experimental spectra. Infrared spectra obtained by experiment and predicted by theory provide evidence for a reduction in spin state as the ligand coordination number increases. The octahedral V(CO)(6)(+) complex is the fully coordinated experimental species. A single band at 2097 cm(-1) was observed for this complex red-shifted from the free CO vibration at 2143 cm(-1). PMID:22486750

Ricks, Allen M; Brathwaite, Antonio D; Duncan, Michael A

2012-04-19

249

THERMAL DECOMPOSITION OF URANYL NITRATE HEXAHYDRATE  

Microsoft Academic Search

The thermal decomposition of uranyl nitrate hexahydrate was studied in ; the temperature range of 250to 400 deg C at atmospheric and at <0.1 mm pressure. ; The intermediate and final products of the decomposition were determined. The ; decomposition follows a zero-order reaction until less than half of the uranyl ; nitrate remains. The remaining portion of the decomposition

Ondrejcin

1963-01-01

250

Nanostructured manganese oxide particles from coordination complex decomposition and their catalytic properties for ethanol oxidation.  

PubMed

Novel manganese oxide particles with complex morphologies and different nanostructures (i.e., spherical/lamellar) were synthesized by initial preparation of a coordination complex of manganese with 1,4,7,10-tetraazacyclododecane (cyclen), followed by characterization of the nanostructured oxide as a catalytic material for ethanol oxidation. The samples present a bulk gamma-MnO2 structure although X-ray photoelectron spectroscopy analysis reveals that their surfaces have different chemical compositions. Some of these nanostructured particles show high catalytic activities for ethanol oxidation enabling a decrease of the reaction temperature by more than 80 degrees C as compared with traditional MnO2 particles. The high catalytic activity of the particles depends on their morphology and a relationship between morphology and specific area was established. It is proposed that these novel nanostructured manganese oxide particles may be highly active in the catalytic oxidation of other volatile organic compounds (VOCs) opening up their further development for environmental applications. PMID:23421183

Palza, Humberto; Maturana, Andrs; Gracia, Francisco; Neira, Andrnico; Fuenzalida, Victor M; Avila, Jonathan; Sanchez-Ballester, Noelia M; Elsegood, Mark R J; Teat, Simon J; Ariga, Katsuhiko; Hill, Jonathan P

2012-10-01

251

Coordination versus coupling of dicyanamide in molybdenum and manganese pyrazole complexes.  

PubMed

The reactions of cis-[MoCl(?(3)-methallyl)(CO)(2)(NCMe)(2)] (methallyl = CH(2)C(CH(3))CH(2)) with Na(NCNCN) and pz*H (pzH, pyrazole, or dmpzH, 3,5-dimethylpyrazole) lead to cis-[Mo(?(3)-methallyl)(CO)(2)(pz*H)(?-NCNCN-?(2)N,N)](2) (pzH, 1a; dmpzH, 1b), where dicyanamide is coordinated as bridging ligand. Similar reactions with fac-[MnBr(CO)(3)(NCMe)(2)] lead to the pyrazolylamidino complexes fac-[Mn(pz*H)(CO)(3)(NH?C(pz*)NCN-?(2)N,N)] (pzH, 2a; dmpzH, 2b), resulting from the coupling of pyrazol with one of the CN bonds of dicyanamide. The second CN bond of dicyanamide in 2a undergoes a second coupling with pyrazole after addition of 1 equiv of fac-[MnBr(CO)(3)(pzH)(2)], yielding the dinuclear doubly coupled complex [{fac-Mn(pzH)(CO)(3)}(2)(?-NH?C(pz)NC(pz)=NH-?(4)N,N,N,N)]Br (3). The crystal structure of 3 reveals the presence of two isomers, cis or trans, depending on whether the terminal pyrazoles are coordinated at the same or at different sides of the approximate plane defined by the bridging bis-amidine ligand. Only the cis isomer is detected in the crystal structure of the perchlorate salt of the same bimetallic cation (4), obtained by metathesis with AgClO(4). All the N-bound hydrogen atoms of the cations in 3 or 4 are involved in hydrogen bonds. Some of the C-N bonds of the pyrazolylamidino ligand have a character intermediate between single and double, and theoretical studies were carried out on 2a and 3 to confirm its electronic origin and discard packing effects. Calculations also show the essential role of bromide in the planarity of the tetradentate ligand in the bimetallic complex 3. PMID:22583336

Arroyo, Marta; Gmez-Iglesias, Patricia; Martn-Alvarez, Jose Miguel; Alvarez, Celedonio M; Miguel, Daniel; Villafae, Fernando

2012-05-15

252

A five-coordinate complex of copper chloride with 2-amino-5-ethyl-1,3,4-thiadiazole  

Microsoft Academic Search

A complex of Cu(II) chloride with 2-amino-5-ethyl-1,3,4-thiadiazole (AET) was prepared, and its structure was studied by IR\\u000a spectroscopy and single crystal X-ray diffraction. The complex has the composition CuCl2(AET)4. The coordination sphere of the copper atom includes four molecules of the heterocyclic ligand coordinated via N atoms of\\u000a thiadiazole rings and one of Cl? anions; the second Cl? anion is

Sh. A. Kadirova; M. M. Ishankhodzhaeva; N. A. Parpiev; Z. Karimov; A. Tozhiboev; B. Tashkhodzhaev

2007-01-01

253

X-ray Emission Spectroscopy to Study Ligand Valence Orbitals in Mn Coordination Complexes  

SciTech Connect

We discuss a spectroscopic method to determine the character of chemical bonding and for the identification of metal ligands in coordination and bioinorganic chemistry. It is based on the analysis of satellite lines in X-ray emission spectra that arise from transitions between valence orbitals and the metal ion 1s level (valence-to-core XES). The spectra, in connection with calculations based on density functional theory (DFT), provide information that is complementary to other spectroscopic techniques, in particular X-ray absorption (XANES and EXAFS). The spectral shape is sensitive to protonation of ligands and allows ligands, which differ only slightly in atomic number (e.g., C, N, O...), to be distinguished. A theoretical discussion of the main spectral features is presented in terms of molecular orbitals for a series of Mn model systems: [Mn(H2O)6]2+, [Mn(H2O)5OH]+, [Mn(H2O)5NH2]+, and [Mn(H2O)5NH3]2+. An application of the method, with comparison between theory and experiment, is presented for the solvated Mn2+ ion in water and three Mn coordination complexes, namely [LMn(acac)N3]BPh4, [LMn(B2O3Ph2)(ClO4)], and [LMn(acac)N]BPh4, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane, acac stands for the 2,4-pentanedionate anion, and B2O3Ph2 represents the 1,3-diphenyl-1,3-dibora-2-oxapropane-1,3-diolato dianion.

Smolentsev, Grigory; Soldatov, Alexander V; Messinger, Johannes; Merz, Kathrin; Weyhermuller, Thomas; Bergmann, Uwe; Pushkar, Yulia; Yano, Junko; Yachandra, Vittal K.; Glatzel, Pieter

2009-03-02

254

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

2009-03-27

255

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

256

Car-Parrinello molecular dynamics study of the uranyl behaviour at the gibbsite/water interface.  

PubMed

The uranyl cation UO(2)(2+) adsorption on the basal face of gibbsite is studied via Car-Parrinello molecular dynamics. In a first step, we study the water sorption on a gibbsite surface. Three different sorption modes are observed and their hydrogen bond patterns are, respectively, characterized. Then we investigate the sorption properties of an uranyl cation, in the presence of water. In order to take into account the protonation state of the (001) gibbsite face, both a neutral (001) face and a locally deprotonated (001) face are modeled. In the first case, three adsorbed uranyl complexes (1 outer sphere and 2 inner spheres) with similar stabilities are identified. In the second case, when the gibbsite face is locally deprotonated, two adsorbed complexes (1 inner sphere and 1 outer one) are characterized. The inner sphere complex appears to be the most strongly linked to the gibbsite face. PMID:23083182

Lectez, Sbastien; Roques, Jrme; Salanne, Mathieu; Simoni, Eric

2012-10-21

257

Precipitation characteristics of uranyl ions at different pHs depending on the presence of carbonate ions and hydrogen peroxide.  

PubMed

This work studied the dissolution of uranium dioxide and precipitation characteristics of uranyl ions in alkaline and acidic solutions depending on the presence of carbonate ions and H2O2 in the solutions at different pHs controlled by adding HNO3 or NaOH in the solution. The chemical structures of the precipitates generated in different conditions were evaluated and compared by using XRD, SEM, TG-DT, and IR analyses together. The sizes and forms of the precipitates in the solutions were evaluated, as well. The uranyl ions were precipitated in the various forms, depending on the solution pH and the presences of hydrogen peroxide and carbonate ions in the solution. In a 0.5 M Na2CO3 solution with H2O2, where the uranyl ions formed mixed uranyl peroxy-carbonato complexes, the uranyl ions were precipitated as a uranium peroxide of UO4(H20)4 at pH 3-4, and precipitated as a clarkeite of Na2U2Ox(OH)y(H2O)z above pH 13. In the same carbonate solution without H2O2, where the uranyl ions formed uranyl tris-carbonato complex, the uranyl ions were observed to be precipitated as a different form of clarkeite above pH 13. The precipitate of uranyl ions in a nitrate solution without carbonate ions and H2O2 at a high pH were studied together to compare the precipitate forms in the carbonate solutions. PMID:19452886

Kim, Kwang-Wook; Kim, Yeon-Hwa; Lee, Se-yoon; Lee, Jae-Won; Joe, Kih-Soo; Lee, Eil-Hee; Kim, Jong-Seung; Song, Kyuseok; Song, Kee-Chan

2009-04-01

258

Investigation of Coordinational Properties of Europium(III) Complexes with Picolinic Acid Using Eu(III) Excitation Spectroscopy  

Microsoft Academic Search

The7F0?5D0excitation spectra of Eu(III) complexed with picolinic acid were investigated using Eu(III) excitation spectroscopy. Six overlapping peaks are seen in the excitation spectra, indicating the formation of six species. The structures of the six species are proposed here and described in terms of both coordination by carboxylate and N-chelation.

Yeong Jae Park; Byoung Ho Lee; Won Ho Kim

1999-01-01

259

Long-term safety evaluation of a novel oxygen-coordinated niacin-bound chromium (III) complex  

Microsoft Academic Search

Chromium (III) is an essential micronutrient required for normal protein, fat and carbohydrate metabolism, as well as helps insulin metabolize fat, turn protein into muscle and convert sugar into energy. A broad spectrum of research investigations including in vitro, in vivo and clinical studies demonstrated the beneficial effects of novel oxygen- coordinated niacin-bound chromium (III) complex (NBC) in promoting glucose-insulin

Michael Shara; Anthony E. Kincaid; Aimee L. Limpach; Robert Sandstrom; Laura Barrett; Neil Norton; J. D. Bramble; Taharat Yasmin; Janet Tran; Archana Chatterjee; Manashi Bagchi; Debasis Bagchi

2007-01-01

260

Identification of Copper(II) Complexes in Aqueous Solution by Electron Spin Resonance: An Undergraduate Coordination Chemistry Experiment.  

ERIC Educational Resources Information Center

Background, procedures, and results are provided for an experiment which examines, through electron spin resonance spectroscopy, complex species formed by cupric and 2,6-dihydroxybenzoate ions in aqueous solutions. The experiment is illustrative of several aspects of inorganic and coordination chemistry, including the identification of species

Micera, G.; And Others

1984-01-01

261

Interactions of 1-methylimidazole with UO2(CH3CO2)2 and UO2(NO3)2: structural, spectroscopic, and theoretical evidence for imidazole binding to the uranyl ion.  

PubMed

The first definitive high-resolution single-crystal X-ray structure for the coordination of the 1-methylimidazole (Meimid) ligand to UO2(Ac)2 (Ac = CH3CO2) is reported. The crystal structure evidence is confirmed by IR, Raman, and UV-vis spectroscopic data. Direct participation of the nitrogen atom of the Meimid ligand in binding to the uranium center is confirmed. Structural analysis at the DFT (B3LYP) level of theory showed a conformational difference of the Meimid ligand in the free gas-phase complex versus the solid state due to small energetic differences and crystal packing effects. Energetic analysis at the MP2 level in the gas phase supported stronger Meimid binding over H2O binding to both UO2(Ac)2 and UO2(NO3)2. In addition, self-consistent reaction field COSMO calculations were used to assess the aqueous phase energetics of combination and displacement reactions involving H2O and Meimid ligands to UO2R2 (R = Ac, NO3). For both UO2(NO3)2 and UO2(Ac)2, the displacement of H2O by Meimid was predicted to be energetically favorable, consistent with experimental results that suggest Meimid may bind uranyl at physiological pH. Also, log(Knitrate/KAc) calculations supported experimental evidence that the binding stoichiometry of the Meimid ligand is dependent upon the nature of the reactant uranyl complex. These results clearly demonstrate that imidazole binds to uranyl and suggest that binding of histidine residues to uranyl could occur under normal biological conditions. PMID:17227015

Gutowski, Keith E; Cocalia, Violina A; Griffin, Scott T; Bridges, Nicholas J; Dixon, David A; Rogers, Robin D

2007-01-24

262

Trace detection and differentiation of uranyl(VI) ion cast films utilizing aligned Ag nanorod SERS substrates  

Microsoft Academic Search

Aligned Ag nanorod arrays prepared by oblique angle vapor deposition (OAD) were utilized to observe the SERS response for cast films of adsorbed uranyl ion complexes. These nanorod arrays consisted of preferentially aligned and tilted cylindrically shaped nanorods (average nanorod length=858nm). Routine SERS spectra of cast films of uranyl nitrate resulted in 0.87pg of material analyzed with a detection limit

Chad L. Leverette; Eliel Villa-Aleman; Slade Jokela; Zhongyue Zhang; Yongjun Liu; Yiping Zhao; Sean A. Smith

2009-01-01

263

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

264

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

265

Occurence of an octanuclear motif of uranyl isophthalate with cation-cation interactions through edge-sharing connection mode.  

PubMed

An uranyl isophthalate has been hydrothermally synthesized at 200 C for 24 h, from a mixture of uranyl nitrate, isophthalic acid, and hydrazine in water. It was characterized by single-crystal analysis [triclinic, P ?1, a = 7.3934(3) , b = 13.3296(5) , c = 15.4432(5) , ? = 111.865(2), ? = 90.637(2), ? = 104.867(2), V = 1355.49(9) (3)] and different spectroscopic techniques (Raman, IR-ATR, UV-visible). The 3D structure of the phase (UO(2))(8)O(2)(OH)(4)(H(2)O)(4)(1,3-bdc)(4)4H(2)O (1,3-bdc = 1,3-benzenedicarboxylate) reveals octanuclear units based on the association of 7-fold coordinated uranyl cations (pentagonal bipyramid) involving a rare case of cation-cation interaction together with edge-sharing polyhedral connection mode. UV-visible absorption spectroscopy confirmed that uranium was only involved in the structure as uranyl forms (excluding the presence of tetravalent or pentavalent uranium). Additionally, ?-Raman and IR-ATR experiments allowed assigning four uranyl contributions to the four types of uranyl entities in the structure, in agreement with the XRD analysis. PMID:21634393

Mihalcea, Ionut; Henry, Natacha; Clavier, Nicolas; Dacheux, Nicolas; Loiseau, Thierry

2011-06-02

266

Utilization of IR spectral detailed analysis for coordination mode determination in novel Zn-cyclen-aminoacid complexes.  

PubMed

The infrared spectra, elemental and thermal (TG/DTG and DTA) analyses of novel [Zn(cyclen-?4N1,4,7,10)(HGly-?2O,O')](ClO4)2 (1), and [Zn2(cyclen-?4N1,4,7,10)2(?-S-Ala-?2N,O)](ClO4)(3)2H2O (2) complexes (cyclen - 1,4,7,10-tetraazacyclododecane) were recorded and analyzed in the relation to their structural peculiarities. IR spectral data indicate both mono- or bidentate coordination mode of a carboxylate group in the prepared complexes (at pH?9). The results indicate unusual bidentate carboxylate coordination mode (in complex (1)) toward to Zn2+-cyclen unit. Therefore the crystal structure determination of the crystalline complex [Zn(cyclen-?4N1,4,7,10)(NO3-?2O,O')](NO3) was attached in order to support the coordination mode assignment in complex (1). PMID:21216184

Vargov, Z; Almi, M; Arabuli, L; Gyryov, K; Zele?k, V; Kuchr, J

2010-12-16

267

"yl"-Oxygen exchange in uranyl(VI) ion: a mechanism involving (UO2)2(?-OH)2(2+) via U-O(yl)-U bridge formation.  

PubMed

Szab and Grenthe (Inorg. Chem. 2007, 46, 9372-9378) suggested from NMR spectroscopy that the "yl"-oxygen exchange in dioxo uranium(VI) ion in acidic solution occurs via an OH-bridged binuclear complex (UO(2))(2)(?-OH)(2)(2+). Here, an "yl"-oxygen exchange pathway involving the (UO(2))(2)(?-OH)(2)(2+) is studied by B3LYP density functional theory calculations. The oxygen exchange takes place via an intramolecular proton shuttle between the oxygen atoms in (UO(2))(2)(?-OH)(2)(H(2)O)(6)(2+). The direct proton transfer from the hydroxo bridge or from the coordinating water to the "yl"-oxygen in (UO(2))(2)(?-OH)(2)(H(2)O)(6)(2+) appears to be negligible because of an exceedingly high activation barrier (?170 kJ mol(-1)). The exchange mechanism in (UO(2))(2)(?-OH)(2)(H(2)O)(6)(2+) can be described by a multistep pathway that leads to the formation of an oxo bridge between two uranyl(VI) centers (U-O(yl)-U bridge). The activation enthalpy ?()H of the reaction obtained at the B3LYP level is 94.7 kJ mol(-1) and is somewhat larger than the experimental value of 80 14 kJ mol(-1). However, the discrepancy between theory and experiment is at the acceptable level. The formation of an oxo bridge between the two uranyl(VI) centers was found to be the key step in proton shuttling, indicating that uranyl(VI) complexes with a stable oxo bridge (such as trinuclear (UO(2))(3)(?(3)-O)(OH)(3)(+)) may have even faster "yl"-oxygen exchange rates than (UO(2))(2)(?-OH)(2)(2+). PMID:22273491

Tsushima, Satoru

2012-01-24

268

Ions generated from uranyl nitrate solutions by electrospray ionization (ESI) and detected with Fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometry.  

PubMed

Electrospray ionization (ESI) of uranyl nitrate solutions generates a wide variety of positively and negatively charged ions, including complex adducts of uranyl ions with methoxy, hydroxy, and nitrate ligands. In the positive ion mode, ions detected by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry are sensitive to instrumental tuning parameters such as quadrupole operating frequency and trapping time. Positive ions correspond to oligomeric uranyl nitrate species that can be characterized as having a general formula of [(UO(2))(n)(A)(m)(CH(3)OH)(s)](+) or [(UO(2))(n)(O)(A)(m)(CH(3)OH)(s)](+) with n = 1-4, m = 1-7, s = 0 or 1, and A = OH, NO(3), CH(3)O or a combination of these, although the formation of NO(3)-containing species is preferred. In the negative ion mode, complexes of the form [(UO(2))(NO(3))(m)](-) (m = 1-3) are detected, although the formation of the oxo-containing ions [(UO(2))(O)(n)(NO(3))(m)](-) (n = 1-2, m = 1-2) and the hydroxy-containing ions [(UO(2))(OH)(n)(NO(3))(m)](-) (n = 1-2, m = 0-1) are also observed. The extent of coordinative unsaturation of both positive and negative ions can be determined by ligand association/exchange and H/D exchange experiments using D(2)O and CD(3)OD as neutral reaction partners in the gas-phase. Positive ions are of varying stability and reactivity and may fragment extensively upon collision with D(2)O, CD(3)OD and N(2) in sustained off-resonance irradiation/collision-induced dissociation (SORI-CID) experiments. Electron-transfer reactions, presumably occurring during electrospray ionization but also in SORI-CID, can result in reduction of U(VI) to U(V) and perhaps even U(IV). PMID:16418004

Pasilis, Sofie; Somogyi, Arpd; Herrmann, Kristin; Pemberton, Jeanne E

2006-01-18

269

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

270

Organic-inorganic hybrids constructed by Anderson-type polyoxoanions and copper coordination complexes  

NASA Astrophysics Data System (ADS)

Four organic-inorganic hybrid compounds based on Anderson-type polyoxoanions, namely, {[Cu(2,2?-bpy)(H2O)3]2[Cr(OH)6Mo6O18]}{[Cu(2,2?-bpy)(H2O)Cl][Cu(2,2?-bpy)(H2O)(NO3)][Cr(OH)6Mo6O18]}18H2O (1), [Cu(2,2?-bpy)(H2O)2Cl]{[Cu(2,2?-bpy)(H2O)2][Cr(OH)6Mo6O18]}4H2O (2), (H3O){[Cu(2,2?-bpy)(H2O)2]2[Cu(2,2?-bpy)(H2O)]2}[Cr(OH)6Mo6O18]336H2O (3), and (H3O){[Cu(2,2?-bpy)(H2O)2]2[Cu(2,2?-bpy)(H2O)]2}[Al(OH)6Mo6O18]333H2O (4), were isolated by conventional solution method, and crystal structures have been determined by single-crystal X-ray diffraction. Among them, compound 1 displays a discrete supramolecular structure, compound 2 shows a chainlike structure with chloro-copper complexes as counteranions, and compounds 3 and 4 are isomorphic and exhibit unique 3D open frameworks with lattice water molecules residing in the channels. The compounds 3 and 4 represent the first example of 3D organic-inorganic hybrid compounds in the TMs/2,2?-bpy/POMs system. Investigation of the reaction conditions reveals that the geometry and size of the anions together with its coordinating abilities to the metal centers have a decisive influence on both the composition and the dimensionality of the final compounds.

Cao, Rui-Ge; Liu, Shu-Xia; Liu, Ying; Tang, Qun; Wang, Liang; Xie, Lin-Hua; Su, Zhong-Min

2009-01-01

271

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

272

Solution interactions between the uranyl cation [UO2(2+)] and histidine, N-acetyl-histidine, tyrosine, and N-acetyl-tyrosine.  

PubMed

Complexes of the uranyl cation [UO(2)(2+)] with histidine (His), N-acetyl-histidine (NAH), tyrosine (Tyr), and N-acetyl-tyrosine (NAT) were studied by UV-visible and NMR spectroscopy, and by potentiometric titration. Protonation constants for each ligand are reported, as are cumulative formation constants for uranyl-amino acid complexes. Coupling constant data (J(CH)) for uranyl-histidine complexes indicate that inner-sphere solution interactions between histidine and uranyl cation are solely at the carboxylate site. At 25 degrees C the major uranyl-histidine complex has a cumulative formation constant of logbeta(110)=8.53, and a proposed formula of [UO(2)HisH(2)(OH)(2)](+); the stepwise formation constant, logK(UL), is estimated to be 5.6 ( approximately 8.53-(-6.1)-(-6.1)-15.15). Outer-sphere interactions, H-bonding or electrostatic interactions, are proposed as contributing a significant portion of the stability to the ternary uranyl-hydroxo-amino acid complexes. The temperature dependent protonation constants of histidine and formation constants between uranyl cation and histidine are reported from 10 to 35 degrees C; at 25 degrees C, DeltaG=-43.3 kJ/mol. PMID:18947879

Xie, Wei; Badawi, Ahmed; Huang, Huan; Van Horn, J David

2008-09-19

273

Thermal decomposition of uranyl nitrate hexahydrate  

Microsoft Academic Search

TG-DTA-EGA studies have shown that anhydrous uranyl nitrate cannot be obtained by thermal decomposition of uranyl nitrate\\u000a hexahydrate. Hydrolysis and polymerization of the salt during dehydration resulted in hydroxynitrates which decomposed in\\u000a multiple steps with the evolution of oxides of nitrogen and water. The extent of hydrolysis dependend on the sample size,\\u000a heating rate and nature of sample containment. Large

K. V. Rajagopalan; P. V. Ravindran; T. P. Radhakrishnan

1995-01-01

274

Complexation of uranium(VI) and samarium(III) with oxydiacetic acid: temperature effect and coordination modes.  

PubMed

The complexation of uranium(VI) and samarium(III) with oxydiacetate (ODA) in 1.05 mol kg(-1) NaClO(4) is studied at variable temperatures (25-70 degrees C). Three U(VI)/ODA complexes (UO(2)L, UO(2)L(2)(2-), and UO(2)HL(2)(-)) and three Sm(III)/ODA complexes (SmL(j)((3-2)(j)+) with j = 1, 2, 3) are identified in this temperature range. The formation constants and the molar enthalpies of complexation are determined by potentiometry and calorimetry. The complexation of uranium(VI) and samarium(III) with oxydiacetate becomes more endothermic at higher temperatures. However, the complexes become stronger due to increasingly more positive entropy of complexation at higher temperatures that exceeds the increase in the enthalpy of complexation. The values of the heat capacity of complexation (Delta C(p) degrees in J K(-1) mol(-1)) are 95 +/- 6, 297 +/- 14, and 162 +/- 19 for UO(2)L, UO(2)L(2)(2-), and UO(2)HL(2)(-), and 142 +/- 6, 198 +/- 14, and 157 +/- 19 for SmL(+), SmL(2)(-), and SmL(3)(3-), respectively. The thermodynamic parameters, in conjunction with the structural information from spectroscopy, help to identify the coordination modes in the uranium oxydiacetate complexes. The effect of temperature on the thermodynamics of the complexation is discussed in terms of the electrostatic model and the change in the solvent structure. PMID:12767209

Rao, Linfeng; Garnov, Alexander Yu; Jiang, Jun; Di Bernardo, Plinio; Zanonato, PierLuigi; Bismondo, Arturo

2003-06-01

275

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

2013-07-12

276

Syntheses, structures, and magnetic properties of seven-coordinate lanthanide porphyrinate or phthalocyaninate complexes with Klui's tripodal ligand.  

PubMed

A series of seven-coordinate mononuclear lanthanide(III) complexes of the general formula [(TPP)Ln(L(OEt))]0.25H2O and [(Pc)Ln(L(OEt))] (Ln(3+) = Dy(3+), Tb(3+), Ho(3+), and Gd(3+); TPP = 5,10,15,20-tetraphenylporphyrinate; Pc = phthalocyaninate; L(OEt)(-) = [(?(5)-C5H5)Co(P(=O)(OEt)2)3](-)) are synthesized on the basis of the tripodal ligand L(OEt)(-) and either porphyrin or phthalocyanine ligands. All of the complexes are characterized by X-ray crystallography and by static and dynamic magnetic measurements. The Dy and Tb complexes show the field-induced slow relaxation of magnetization, and they are interesting seven-coordinate single-lanthanide-based SMMs. The magnetic relaxation properties of these double-decker sandwich complexes are influenced by the local molecular symmetry and are sensitive to subtle distortions of the coordination geometry of the paramagnetic lanthanide ions, such as metal-to-plane distances, plane center distances, and bending angles. PMID:23692376

Gao, Feng; Yao, Min-Xia; Li, Yu-Yang; Li, Yi-Zhi; Song, You; Zuo, Jing-Lin

2013-05-21

277

Novel eight-coordinated Cd(II) complexes with two homologous pyridine alcohols. Crystal structure, spectroscopic and thermal properties  

NASA Astrophysics Data System (ADS)

Two novel cadmium(II) complexes with homologous pyridine alcohols: [Cd(2-MeOHPy)2(NO3)2] (1) and [Cd(2-EtOHPy)2(NO3)2] (2) have been prepared and characterized by elemental analysis, X-ray crystallographic studies, spectroscopic (IR, 1H and 13C NMR) and thermal properties. IR, NMR and X-ray analysis have confirmed a bidentate fashion of coordination of heteroaromatic alcohols with Cd(II) ions. 2-MeOHPy bound directly to the central ion by N, O-donor atoms giving five-membered chelate ring but 2-EtOHPy formed less stable six-membered chelate ring. In the complex (1) and (2) bidentate nitrate ligands are arranged in cis position for organic ligands. In both cases cadmium(II) ions are eight-coordinated and shape of coordination polyhedral can be described as pseudo-dodecahedron (CdN2O6 chromophore type). The crystal packing of Cd(II) complexes are stabilized by intermolecular classical hydrogen bonds of OH\\ctdot O and non-classical CH\\ctdot O type. In addition, there are ?-? stacking interactions between almost parallel-displaced pyridine rings of 2-hydroxymethylpyridine in the two neighbouring complex (1) molecules but the hydrogen interactions in (2) are formed by CH donor group of Py rings and ?-electron system of neighbouring one.

Jab?o?ska-Wawrzycka, Agnieszka; Stadnicka, Katarzyna; Masternak, Joanna; Zienkiewicz, Ma?gorzata

2012-03-01

278

New class of phosphine oxide donor-based supramolecular coordination complexes from an in situ phosphine oxidation reaction or phosphine oxide ligands.  

PubMed

A one-pot, multicomponent, coordination-driven self-assembly approach was used to synthesize the first examples of neutral bridging phosphine oxide donor-based supramolecular coordination complexes. The complexes were self-assembled from a fac-Re(CO)3 acceptor, an anionic bridging O donor, and a neutral soft phosphine or hard phosphine oxide donor. PMID:23984852

Shankar, Bhaskaran; Elumalai, Palani; Shanmugam, Ramasamy; Singh, Virender; Masram, Dhanraj T; Sathiyendiran, Malaichamy

2013-08-28

279

Inherently chiral uranyl-salophen macrocycles: computer-aided design and resolution.  

PubMed

[structure: see text] A flipping motion rapidly inverts the bent structure of uranyl-salophen compounds and, consequently, causes fast enantiomerization of nonsymmetrically substituted derivatives. This process has been previously slowed by introducing bulky substituents in the imine bond region. Since the resulting complexes dissociate upon chromatographic treatment, an alternative approach to the design and synthesis of robust, nonflipping uranyl-salophen compounds is here described. Such an approach is based on the idea that the flipping motion would be blocked by connecting the para positions with respect to the phenoxide oxygens by means of polymethylene bridges of suitable length. Analysis of a number of uranyl-salophen compounds by molecular mechanics, while showing that bulky substituents in the imine bond region cause severe distortions of the ligand backbone, suggested that the best chain lengths are those that fit the gap between the phenoxide rings without altering the natural geometry of the parent uranyl-salophen compound. Calculations showed that such chains are those composed of 12 and 13 methylene units. Accordingly, chiral uranyl-salophen macrocycles bridged with 12- and 13-methylene chains were synthesized in fairly good yields and resolved by chiral HPLC. PMID:16292810

Dalla Cort, Antonella; Mandolini, Luigi; Pasquini, Chiara; Schiaffino, Luca

2005-11-25

280

Relativistic density functional calculations for potential energy curves of uranyl nitrate hydrate  

NASA Astrophysics Data System (ADS)

Metal - ligand distances of U=O (uranyl oxygen) and U-OH2 in the uranyl nitrate dihydrate have been optimized, using the all-electron fully relativistic discrete-variational Dirac - Fock - Slater ( DV-DFS ) MO method. The calculated bond length of U=O for a free complex is larger than the experimental value for the crystal and the U---OH2 distance was in good agreement with the experimental results.The shape of the potential curves indicates individual strength of the U=O and U---OH2 bonds and reveals that the U=O bond was stronger.

Hirata, Masaru; Bastug, Turgut; Tachimori, Shoichi; Sekine, Rika; Onoe, Jun; Nakamatsu, Hirohide

281

Crystal structure of six and seven coordinate manganese(II) complexes with penta and hexadentate pyridylmethyl ligands  

Microsoft Academic Search

Two six-coordinated manganese(II) complexes [Mn(pydien)Cl](ClO4)C2H5OH (1), [Mn(pydien)NCS](ClO4) (2) and two seven-coordinated manganese(II) complexes [Mn(pydado)Cl](ClO4) (3), [Mn(pydado)NCS](ClO4) (4) have been obtained using linear penta and hexadentate ligands pydien and pydado (pydien: 1,7-bis(2-pyridylmethyl)-1,4,7-triazaheptane and pydado: 1,10-bis(pyridylmethyl)-1,10-diaza-4,7-dioxadecane). The crystal structures for all compounds have been determined. 1 and 3 crystallize in the triclinic space group P1, 2 crystallizes in the orthorhombic space group

Sanae El Ghachtouli; Aminou Mohamadou; Jean-Pierre Barbier

2005-01-01

282

A Stereodynamic Tripodal Ligand with Three Different Coordinating Arms: Synthesis and Zinc(II), Copper(I) Complexation Study  

PubMed Central

A tetradentate tripodal ligand containing a chiral center and three different coordinating arms was designed and synthesized. Its complexation properties with ZnII and CuI were studied by NMR and optical spectroscopy. NMR experiments demonstrated the formation of two diastereomers, indicating the stabilization of the central tertiary amine configuration by metal coordination. The inversion of pyramidalization of the central tertiary amine of the ligand was found to be highly dependent upon metal ion, solvent, and temperature. Dynamic NMR measurements were used to estimate the energy of activation required for nitrogen atom inversion. Finally, absorption and circular dichroism measurements confirmed the expectation that metal complexes of the ligand gave rise to circular dichroism but that such spectra were not characterized by exciton-coupling, in contrast to previously described ligands containing two identical arms with strong chromophores.

Liang, Jian; Canary, James W.

2010-01-01

283

Structural Insights into Complete Metal Ion Coordination from Ternary Complexes of B Family RB69 DNA Polymerase  

SciTech Connect

We have captured a preinsertion ternary complex of RB69 DNA polymerase (RB69pol) containing the 3' hydroxyl group at the terminus of an extendable primer (ptO3') and a nonhydrolyzable 2'-deoxyuridine 5'-{alpha},{beta}-substituted triphosphate, dUpXpp, where X is either NH or CH{sub 2}, opposite a complementary templating dA nucleotide residue. Here we report four structures of these complexes formed by three different RB69pol variants with catalytically inert Ca{sup 2+} and four other structures with catalytically competent Mn{sup 2+} or Mg{sup 2+}. These structures provide new insights into why the complete divalent metal-ion coordination complexes at the A and B sites are required for nucleotidyl transfer. They show that the metal ion in the A site brings ptO3' close to the {alpha}-phosphorus atom (P{alpha}) of the incoming dNTP to enable phosphodiester bond formation through simultaneous coordination of both ptO3' and the nonbridging Sp oxygen of the dNTP's {alpha}-phosphate. The coordination bond length of metal ion A as well as its ionic radius determines how close ptO3' can approach P{alpha}. These variables are expected to affect the rate of bond formation. The metal ion in the B site brings the pyrophosphate product close enough to P{alpha} to enable pyrophosphorolysis and assist in the departure of the pyrophosphate. In these dUpXpp-containing complexes, ptO3' occupies the vertex of a distorted metal ion A coordination octahedron. When ptO3' is placed at the vertex of an undistorted, idealized metal ion A octahedron, it is within bond formation distance to P{alpha}. This geometric relationship appears to be conserved among DNA polymerases of known structure.

Xia, Shuangluo; Wang, Mina; Blaha, Gregor; Konigsberg, William H.; Wang, Jimin (Yale)

2011-10-20

284

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

285

Functionalization of glucose at position C-3 for transition metal coordination: organo-rhenium complexes with carbohydrate skeletons.  

PubMed

Novel 3-O-[1,2;5,6-di-O-isopropylidene-alpha-D-glucofuranose] and 3-O-[D-glucose] derivatives with an iminodiacetate (N,O,O), a histidinate, and an N-(acetetyl)picolylamine (N,N,O) chelating system for tridentate coordination of the organometallic M(CO)(3)-fragment (M = Tc, Re) have been prepared. The chelates were introduced and assembled through reductive amination starting from 3-O-[1,2;5,6-di-O-isopropylidene-alpha-D-glucofuranose]-acetaldehyde. After deprotection, the pyranose derivatives were reacted with the precursor [NEt(4)](2)[ReBr(3)(CO)(3)] to afford the corresponding organometallic complexes in yields between 54% and 94%. The NMR, MS, and IR analyses corroborated the tridentate coordination of the organometallic metal center exclusively via the synthetic chelates. In the case of the N-(acetyl)picolylamine derivative, the coordinative properties were further confirmed by X-ray structure analysis of the first Re(CO)(3)-D-glucofuranose complex. All glucose complexes unveiled good stability and solubility in organic and aqueous media. PMID:15769097

Dumas, Ccile; Petrig, Jeannine; Frei, Luzia; Spingler, Bernhard; Schibli, Roger

286

Kinetics of Triscarbonato Uranyl Reduction by Aqueous Ferrous Iron: A Theoretical Study  

Microsoft Academic Search

Uranium is a pollutant whose mobility is tied to its oxidation state. While U(VI) in the form of the uranyl cation is capable of being reduced by a range of natural reductants, complexation by carbonate greatly reduces its reduction potential as well as imposing increased electron transfer (ET) distances. Very little is known about the elementary processes involved in uranium

Matthew C. F. Wander; Sebastien N. Kerisit; Kevin M. Rosso; Martin A. A. Schoonen

2006-01-01

287

A tetra-coordinate nickel(II) complex as neutral carrier for nitrate-selective PVC membrane electrode  

Microsoft Academic Search

The potentiometric response properties and applications of a tetra-coordinate nickel(II) complex with relatively high selectivity toward nitrate ion are described. The nickel(II) complex of 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,6,11,13-tetraene was used as a neutral carrier into plasticized poly(vinyl chloride) (PVC) membrane. The influence of several variables was investigated in order to optimize the potentiometric response and selectivity of the electrode. The resulting membrane electrode

Ali Reza Asghari; Mohammad Kazem Amini; Hassan Rahimi Mansour; Masoud Salavati-Niasari

2003-01-01

288

Observation of Radiolytic Field Alteration of the Uranyl Cation in Bicarbonate Solution  

SciTech Connect

In previous work we demonstrated that radiolysis of uranyl tris carbonate in near neutral pH to alkaline carbonate solutions, could be followed by 13C NMR. Radiolysis of the complex produced novel uranyl peroxo carbonate solution state species, whose structures depended on the pH and radiolytic dose rate. In this work, we investigate speciation of the uranyl carbonate trimer which is predominant in bicarbonate solution near pH 5.9. We observe radiolytically derived speciation to different mixed peroxy carbonate species than seen in the higher pH solutions. Auto radiolysis of uranium (VI) carbonate solutions between pH 5.9 and 7.2 is shown to alter the uranium speciation over relatively short periods of time and was followed by 13C NMR and visible spectrophotometry, using dissolved 233(UO2)3(CO3)6 6- both as the radiolysis source (D= 14.9 Gy/hr) and as a trap for the newly formed hydrogen peroxide. Direct addition of hydrogen peroxide to solutions of the uranyl-carbonate trimer is shown to reproduce the 13 C NMR signatures of the complexe(s) formed by radiolysis, but additionally a variety of new complexes are revealed. Ratios of H2O2/trimer < 1.5 produced a uranyl peroxo carbonate adduct, that is shown to be common to the radiolytically produced species. Ratios of H2O2/ trimer >1 resulted in formation of stable higher order peroxo carbonate complexes. The 13C NMR signatures and visible spectra of these complexes are described here. Rigorous characterization of the species is an ongoing effort.

Snow, Lanee A.; McNamara, Bruce K.; Sinkov, Sergey I.; Cho, Herman M.; Friese, Judah I.

2006-12-01

289

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

290

Synthesis, structural characterization and catalytic evaluation of the ring-opening polymerization of discrete five-coordinate alkyl aluminium complexes.  

PubMed

Five-coordinate alkyl aluminium complexes [AlR(?(2)-pbpam)2] (R = Me 1, Et 2), [AlR(?(2)-sbpam)2] (R = Me 3, Et 4) and [AlR{?(2)-(S)-mbpam}2] (R = Me 5, Et 6), -pbpam [pbpam = N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate], sbpam [sbpam = N-sec-butyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] and (S)-mbpam [(S)-mbpam = (S)-(-)-N-?-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] were obtained by an alkane elimination route involving the reaction of the previously reported acetamide heteroscorpionate precursors with 0.5 equiv. of the corresponding AlR3. In the solid state, complexes 1-6 adopt a distorted trigonal bipyramidal structure with the heteroscorpionate ligands arranged in a ?(2)-NO coordination mode. The molecular structures of 1-6 in solution were studied by VT NMR spectroscopy and a fluxional exchange between coordinated and noncoordinated pyrazole rings was observed. This process led to interconversion between the different isomers. Compounds 4 and 6 were used as precursors for the synthesis of the aryloxide aluminium compounds [Al(OR)(?(2)-sbpam)2] (7) and [Al(OR){?(2)-(S)-mbpam}2] (8) (R = 2,6-Me2C6H3O) by reaction with the corresponding 2,6-dimethylphenol. The structures of the complexes were determined by spectroscopic methods, and the X-ray crystal structures of 2, 6 and 7 were also established. Five-coordinate compounds 1-8 were evaluated as initiators in the ring-opening polymerization of rac-lactide. Compound 5 was also evaluated in the presence of a co-initiator. Finally, a study of the block and random copolymerization of ?-caprolactone and L-lactide was carried out. PMID:23396578

Castro-Osma, Jose A; Alonso-Moreno, Carlos; Mrquez-Segovia, Isabel; Otero, Antonio; Lara-Snchez, Agustn; Fernndez-Baeza, Juan; Rodrguez, Ana M; Snchez-Barba, Luis F; Garca-Martnez, Joaqun C

2013-02-08

291

Structural observations of heterometallic uranyl copper(II) carboxylates and their solid-state topotactic transformation upon dehydration.  

PubMed

The hydrothermal reactions of uranyl nitrate and metallic copper with aromatic polycarboxylic acids gave rise to the formation of five heterometallic UO(2)(2+)-Cu(2+) coordination polymers: (UO(2))Cu(H(2)O)(2)(1,2-bdc)(2) (1; 1,2-bdc = phthalate), (UO(2))Cu(H(2)O)(2)(btec)?4?H(2)O (2) and (UO(2))Cu(btec) (2'; btec = pyromellitate), (UO(2))(2)Cu(H(2)O)(4)(mel) (3; mel = mellitate), and (UO(2))(2)O(OH)(2)Cu(H(2)O)(2)(1,3-bdc)?H(2)O (4; 1,3-bdc = isophthlalate). Single-crystal X-ray diffraction (XRD) analysis of compound 1 revealed 2D layers of chains of UO(8) and CuO(4)(H(2)O)(2) units that were connected through the phthalate ligands. In compound 2, these sheets were connected to each other through the two additional carboxylate arms of the pyromellitate, thus resulting in a 3D open-framework with 1D channels that trapped water molecules. Upon heating, free and bonded water species (from Cu-OH(2)) were evacuated from the structure. This thermal transition was followed by in situ XRD and IR spectroscopy. Heating induced a solid-state topotactic transformation with the formation of a new set of Cu-O interactions in the crystalline anhydrous structure (2'), in order to keep the square-planar environment around the copper centers. The structure of compound 3 was built up from trinuclear motifs, in which one copper center, CuO(4)(OH(2))(2), was linked to two uranium units, UO(5)(H(2)O)(2). The assembly of this trimer, "U(2)Cu", with the mellitate generated a 3D network. Complex 4 contained a tetranuclear uranyl core of UO(5)(OH)(2) and UO(6)(OH) units that were linked to two copper centers, CuO(OH)(2)(H(2)O)(2), which were then connected to each other through isophthalate ligands and U=O-Cu interactions to create a 3D structure. The common structural feature of these different compounds is a bridging oxo group of U=O-Cu type, which is reflected by apical Cu-O distances in the range 2.350(3)-2.745(5)?. In the case of a shorter Cu-O distance, a slight lengthening of the uranyl bond (U=O) is observed (e.g., 1.805(3)? in complex 4). PMID:23280927

Olchowka, Jakub; Falaise, Clment; Volkringer, Christophe; Henry, Natacha; Loiseau, Thierry

2012-12-23

292

Optical Design of Reflectionless Complex Media by Finite Embedded Coordinate Transformations  

Microsoft Academic Search

Transformation optics offers an unconventional approach to the control of electromagnetic fields. The transformation optical structures proposed to date, such as electromagnetic ``invisibility'' cloaks and concentrators, are inherently reflectionless and leave the transmitted wave undisturbed. Here, we expand the class of transformation optical structures by introducing finite, embedded coordinate transformations, which allow the electromagnetic waves to be steered or focused.

Marco Rahm; Steven A. Cummer; David Schurig; John B. Pendry; David R. Smith

2008-01-01

293

Heterotopic silver-NHC complexes: from coordination polymers to supramolecular assemblies.  

PubMed

New coordination polymers based on different combinations of silver atoms and pyridyl-substituted N-heterocyclic carbene moieties are described. The addition of Zn(ii) templates leads to Ag-Zn supramolecular assemblies via selective ZnN interactions; a process that can be reverted. PMID:20445922

Rubio, Miguel; Siegler, Maxime A; Spek, Anthony L; Reek, Joost N H

2010-05-05

294

Engineering a uranyl specific binding protein from NikR  

Microsoft Academic Search

The first uranyl-selective DNA-binding protein is designed using the E. coli nickel(II)-responsive protein NikR as the template. The resulting NikR? protein binds uranyl (see picture) with a dissociation constant Kd=53?nM and selectively binds to DNA in the presence of uranyl.

Seraphine V. Wegner; Hande Boyaci; Hao Chen; Mark P. Jensen; Chuan He

2009-01-01

295

Organic-inorganic hybrids constructed by Anderson-type polyoxoanions and copper coordination complexes  

SciTech Connect

Four organic-inorganic hybrid compounds based on Anderson-type polyoxoanions, namely, {l_brace}[Cu(2,2'-bpy)(H{sub 2}O){sub 3}]{sub 2}[Cr(OH){sub 6}Mo{sub 6}O{sub 18}]{r_brace}{l_brace}[Cu(2,2'-bpy)(H{sub 2}O)Cl][Cu(2,2'-bpy) (H{sub 2}O)(NO{sub 3})][Cr(OH){sub 6}Mo{sub 6}O{sub 18}]{r_brace}.18H{sub 2}O (1), [Cu(2,2'-bpy)(H{sub 2}O){sub 2}Cl]{l_brace}[Cu(2,2'-bpy)(H{sub 2}O){sub 2}][Cr(OH){sub 6}Mo{sub 6}O{sub 18}]{r_brace}.4H{sub 2}O (2), (H{sub 3}O){l_brace}[Cu(2,2'-bpy)(H{sub 2}O){sub 2}]{sub 2}[Cu(2,2'-bpy)(H{sub 2}O)]{sub 2}{r_brace}[Cr(OH){sub 6}Mo{sub 6}O{sub 18}]{sub 3}.36H{sub 2}O (3), and (H{sub 3}O){l_brace}[Cu(2,2'-bpy)(H{sub 2}O){sub 2}]{sub 2}[Cu(2,2'-bpy)(H{sub 2}O)]{sub 2}{r_brace}[Al(OH){sub 6}Mo{sub 6}O{sub 18}]{sub 3}.33H{sub 2}O (4), were isolated by conventional solution method, and crystal structures have been determined by single-crystal X-ray diffraction. Among them, compound 1 displays a discrete supramolecular structure, compound 2 shows a chainlike structure with chloro-copper complexes as counteranions, and compounds 3 and 4 are isomorphic and exhibit unique 3D open frameworks with lattice water molecules residing in the channels. The compounds 3 and 4 represent the first example of 3D organic-inorganic hybrid compounds in the TMs/2,2'-bpy/POMs system. Investigation of the reaction conditions reveals that the geometry and size of the anions together with its coordinating abilities to the metal centers have a decisive influence on both the composition and the dimensionality of the final compounds. - Graphical Abstract: Four organic-inorganic hybrids based on Anderson-type polyoxoanions have been synthesized. Compound 1 displays a discrete structure, 2 shows a chainlike structure, 3 and 4 are isomorphic and exhibit unique 3D open frameworks with lattice waters residing in the channels. The different structures suggest that the overall structures of the compounds are influenced by the nature of the acidic anions.

Cao Ruige [Key Laboratory of Polyoxometalates Science of the Ministry of Education, College of Chemistry, Northeast Normal University, Changchun City, JiLin 130024 (China); Liu Shuxia [Key Laboratory of Polyoxometalates Science of the Ministry of Education, College of Chemistry, Northeast Normal University, Changchun City, JiLin 130024 (China)], E-mail: liusx@nenu.edu.cn; Liu Ying; Tang Qun; Wang Liang; Xie Linhua; Su Zhongmin [Key Laboratory of Polyoxometalates Science of the Ministry of Education, College of Chemistry, Northeast Normal University, Changchun City, JiLin 130024 (China)

2009-01-15

296

X-ray Crystal Structure of Trans -UO 2 (N(SiMe 3 ) 2 ) 2 (THF) 2 : One in a Series of Uranyl(VI) Complexes Supported by Bis(trimethylsilyl)amido Ligands  

Microsoft Academic Search

\\u000a AbstractThe title compound trans-UO2(N(SiMe3)2)2(THF)2 (1) was synthesized and characterized by X-ray crystallography. The complex crystallizes in the monoclinic space group C2\\/c\\u000a (#15) with lattice parameters a=16.0771(5) ?, b=13.1196(4) ?, c=16.9391(6) ?, ?=116.853(1)?, V=3187.61(18) ?3, Z=4, D\\u000a calc=1.532gcm-3. The six-coordinate uranium(VI) center adopts an all-trans octahedral geometry consisting of mutually trans oxo groups, silylamido ligands, and neutral THF donors. Structural comparisons

Anthony E. Vaughn; Charles L. Barnes; Paul B. Duval

2007-01-01

297

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

298

Two uranyl-organic frameworks with formic acid. A novel example of a uranyl-based nanotubular assemblage  

Microsoft Academic Search

Reaction of uranyl nitrate with formic acid in the presence of DABCO or NMe4OH under hydrothermal conditions gave two novel uranyl-organic frameworks. When templated by H-DABCO+ counter-ions, uranyl formate crystallizes as ribbons including ?3-oxo and ?2- and ?3-hydroxo ions. In one experiment with NMe4OH, a nanotubular material was obtained instead of the more usual two- or three-dimensional uranyl formates, with

Pierre Thury

2008-01-01

299

Complexation of uranium(VI) and samarium(III) with oxydiacetic acid: Temperature effect and coordination modes  

SciTech Connect

The complexation of uranium(VI) and samarium(III) with oxydiacetate in 1.05 mol kg{sup -1} NaClO{sub 4} is studied at variable temperatures (25-70 C). Three U(VI)/O DA complexes (UO{sub 2}L, UO{sub 2}L{sub 2}{sup 2-}, and UO{sub 2}HL{sub 2}{sup -}) and three Sm(III)/ODA complexes (SmL{sub j}{sup (3-2j)+} with j = 1, 2, 3) are identified in this temperature range. The formation constants and the molar enthalpies of complexation are determined by potentiometry and calorimetry. The complexation of uranium(VI) and samarium(III) with oxydiacetate becomes more endothermic at higher temperatures. However, the complexes become stronger due to increasingly more positive entropy of complexation at higher temperatures that exceeds the increase in the enthalpy of complexation. The values of the heat capacity of complexation ({Delta}C{sub p}{sup o} in J K{sup -1} mol{sup -1}) are 95 {+-} 6, 297 {+-} 14, and 162 {+-} 19 for UO{sub 2}L, UO{sub 2}L{sub 2}{sup 2-}, and UO{sub 2}HL{sub 2}{sup -}, and 142 {+-} 6, 198 {+-} 14 and 157 {+-} 19 for SmL{sup +}, SmL{sub 2}{sup -}, and SmL{sub 3}{sup 3-}, respectively. The thermodynamic parameters, in conjunction with the structural information from spectroscopy, help to identify the coordination modes in the uranium oxydiacetate complexes. The effect of temperature on the thermodynamics of the complexation is discussed in terms of the electrostatic model and the change in the solvent structure.

Rao, Linfeng; Garnov, Alexander Yu.; Jiang, Jun; Di Bernardo, Plinio; Zanonato, PierLuigi; Bismondo, Arturo

2003-04-01

300

Secondary Coordination Sphere Influence on the Reactivity of Nonheme Iron(II) Complexes: An Experimental and DFT Approach  

PubMed Central

The new biomimetic ligands N4Py2Ph (1) and N4Py2Ph,amide (2) were synthesized and yield the iron(II) complexes [FeII(N4Py2Ph)(NCCH3)](BF4)2 (3) and [FeII(N4Py2Ph,amide)](BF4)2 (5). Controlled orientation of the Ph substituents in 3 leads to facile triplet spin reactivity for a putative FeIV(O) intermediate, resulting in rapid arene hydroxylation. Addition of a peripheral amide substituent within hydrogen-bond distance of the iron first coordination sphere leads to stabilization of a high-spin FeIIIOOR species which decays without arene hydroxylation. These results provide new insights regarding the impact of secondary coordination sphere effects at nonheme iron centers.

2013-01-01

301

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

302

Binding optimization through coordination chemistry: CXCR4 chemokine receptor antagonists from ultra rigid metal complexes  

PubMed Central

A new copper(II) containing bis-macrocyclic CXCR4 chemokine receptor antagonist is shown to have improved binding properties to the receptor protein in comparison to the drug AMD3100 (Plerixafor, Mozobil). The interaction of the metallodrug has been optimized by using ultra rigid chelator units that offer an equatorial site for coordination to the amino acid side chains of the protein. Binding competition assays with anti-CXCR4 antibodies show that the new compound stays bound longer and it has improved anti-HIV potency in vitro (EC50 = 4.3 nM). X-ray structural studies using acetate as a model for carboxylate amino acid side chains indicate the nature of the coordination interaction.

Khan, Abid; Nicholson, Gary; Greenman, John; Madden, Leigh; McRobbie, Graeme; Pannecouque, Christophe; De Clercq, Erik; Ullom, Robert; Maples, Danny L.; Maples, Randall L.; Silversides, Jon D.; Hubin, Timothy J.; Archibald, Stephen J.

2009-01-01

303

Binuclear hexa- and pentavalent uranium complexes with a polypyrrolic ligand: a density functional study of water- and hydronium-induced reactions.  

PubMed

Binuclear uranyl (VI) and (V) complexes of a Pacman-like polypyrrolic macrocycle (H(4)L) were investigated using relativistic density functional theory. The reactivity of the bis-uranyl(VI) complex (UO(2))(2)(L) (2a) was explored computationally. Although 2a has not been obtained experimentally, its structural analogue [(UO(2))(OH)K(THF)(2)(H(2)L(Me))] has been synthesized recently. The high reactive activity of 2a originates from its unique butterfly like cation-cation structure, containing an active O center with easily broken U-O bonding and having unsaturated coordination sites of uranium(VI) along the equatorial plane. The present study indicates that 2a can react with water (Path 3) and hydronium (Path 4), which lead to the formation of a series of complexes with a triangle-like O=U=O=U=O skeleton. Path 3 results in an unusual complex containing a combined cis-uranyl/trans-uranyl cation-cation structure, (cis-UO(2))(trans-UO(2))(H(2)O)(L) (4b), where the oxo atom of the trans-uranyl coordinates the uranium center of the cis-uranyl and the water bonds to the uranium of trans-uranyl in the equatorial plane. After a process of hydrogen transfer with an extremely low energy barrier (<1.5 kcal/mol), 4b is converted into a slightly more stable isomer (U(2)O(3))(OH)(2)(L) (4a), where two hydroxyl groups link to two uranium atoms, respectively. In conjunction with previous studies, the free energies of reactions of 2a induced by isomerization (Path 1), proton (Path 2), water (Path 3), and hydronium (Path 4) were calculated in the gas phase and aqueous solution. Solvation stabilizes the free energy of the formation reactions of the neutral complexes but destabilizes that of the charged complexes. In these reactions, three pairs of isomers were obtained for binuclear uranium(VI) complexes, but only the most stable in each pair exists for the binuclear uranium(V) analogues. PMID:20557108

Pan, Qing-Jiang; Schreckenbach, Georg

2010-07-19

304

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

305

Some properties of compounds of uranyl nitrate with dimethylformamide  

SciTech Connect

The authors establish that in the interaction of solutions of uranyl nitrate containing excess HNO/sub 3/ with dimethylformamide, the compound UO/sub 2/(N)/sub 3/)/sub 2/ X 2HCON(CH/sub 3/)/sub 2/ crystallizes. An analysis of the IR spectrum of the salt indicates bidentate coordination of the NO/sup -//sub 3/ ions and a bond of the DMFA molecules to the uranium atom through the oxygen atoms. The interplane distances were calculated according to the x-ray powder patterns. The solubility of the compound was studied as a function of the composition of the liquid phase. The minimum solubility, equal to 0.013 M, is achieved at NHO/sub 3/ concentrations of about 6 M and DMFA 4-6 M. Using the electronic absorption spectra, some data were obtained on the nature of comoplex formation in solution.

Bykhovskii, D.N.; Novikov, G.S.; Smirnov, A.N.; Solntseva, L.V.

1986-05-01

306

Correlation of Relaxivity with Coordination Number in Six-, Seven-, and Eight-Coordinate Mn(II) Complexes of Pendant-Arm Cyclen Derivatives  

PubMed Central

The syntheses and characterization of several complexes of Mn(II) with cyclen derivatives having variable numbers of pendant N-acetic acid or N-acetamide arms are reported. X-ray crystallographic results are presented for Mn(DOTAM)Cl22H2O (monoclinic C2/c, a=18.5798(15), b=13.6006(11), c=10.5800(8) , ?=110.490(1), Z=4), [Mn(DO3AM)][MnCl4]EtOH (monoclinic P21/n, a=8.366(8), b=19.483(2), c=16.3627(16) , ?=99.254(2), Z=4), and Mn(H2DOTA) (monoclinic C2/c, a=16.374(3), b=6.6559(13), c=16.750(3) , ?=98.381(3), Z=4), which exhibit 8-, 7-, and 6-coordinate Mn(II), respectively. 1H relaxivity data in water at 20 MHz and 37C is presented and interpreted in terms of a mechanism involving transient binding of water in an associative intermediate. Relaxivity studies in mixed water/methanol solvents are consistent with this interpretation.

Wang, Sen; Westmoreland, T. David

2009-01-01

307

Heme-Copper/Dioxygen Complexes: Towards Understanding Ligand-Environmental Effects on Coordination Geometry, Electronic Structure and Reactivity  

PubMed Central

The nature of the ligand is an important aspect of controlling structure and reactivity in coordination chemistry. In connection with our study of heme/copper/oxygen reactivity relevant to cytochrome c oxidase O2-reduction chemistry, we compare the molecular and electronic structure of two high-spin heme-peroxo-copper [FeIII-O22--CuII]+ complexes containing N4-tetradentate (1) or N3-tridentate (2) copper ligands. Combining previously reported and new resonance Raman and EXAFS data coupled to DFT calculations we report a geometric structure and more complete electronic description of the high-spin heme-peroxo-copper complexes 1 and 2, which establish ?-(O22-) side-on to the FeIII and end-on to CuII (?-?2:?1) binding for the complex 1 but side-on/side-on (?-?2:?2) ?-peroxo coordination for the complex 2. We also compare and summarize the differences and similarities of these two complexes in their reactivity toward CO, PPh3, acid and phenols. The comparison of a new X-ray structure of ?-oxo complex 2a with the previously reported 1a X-ray structure, two thermal decomposition products respectively of 2 and 1, reveals a considerable difference in the Fe-O-Cu angle between the two ?-oxo complexes (?Fe-O-Cu = 178.2 in 1a, ?Fe-O-Cu = 149.5 in 2a). The reaction of 2 with one equivalent of exogenous N-donor axial base leads to the formation of a distinctive low-temperature stable, low-spin heme-O2-Cu complex (2b), but under the same conditions the addition of an axial base to 1 leads to the dissociation of the heme-peroxo-Cu assembly and the release of O2. 2b reacts with phenols performing hydrogen-atom (e + H+) abstraction resulting in O-O bond cleavage and the formation of high-valent ferryl [FeIV=O] complex (2c). The nature of 2c was confirmed by comparison of its spectroscopic features and reactivity with those of an independently prepared ferryl complex. The phenoxyl radical generated by the hydrogen-atom abstraction was either 1) directly detected by EPR spectroscopy using phenols that produce stable radicals or 2) indirectly by detection of the coupling product of two phenoxyl radicals.

Halime, Zakaria; Kieber-Emmons, Matthew T.; Qayyum, Munzarin F.; Mondal, Biplab; Puiu, Simona C.; Chufan, Eduardo E.; Sarjeant, Amy A. N.; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.; Karlin, Kenneth D.

2010-01-01

308

Circularly polarized luminescence of Eu(III) complexes with point- and axis-chiral ligands dependent on coordination structures.  

PubMed

Circularly polarized luminescence (CPL) of Eu(III) complexes with point- and axis-chiral ligands, [Eu((R/S)-BINAPO)(D-facam)(3)] ((R/S)-BINAPO, (R/S)-2,2'-bis(diphenylphosphoryl)-1,1'-binaphthyl; D-facam, 3-trifluoroacetyl-d-camphor), [Eu(BIPHEPO)(D-facam)(3)] (BIPHEPO, 2,2'-bis(diphenylphosphoryl)-biphenyl), [Eu(TPPO)(2)(D-facam)(3)] (TPPO, triphenylphosphine oxide), and [Eu((R)-BINAPO)(hfa)(3)] (hfa, 1,1,1,5,5,5-hexafluoropentane-2,4-dione) are reported. The photophysical properties of chiral Eu(III) complexes were characterized by circular dichroism spectra, emission spectra, emission quantum yields, emission lifetimes, and CPL spectra. The dissymmetry factors of their CPL (|g(CPL)|) at the magnetic-dipole transition of [Eu((R)-BINAPO)(D-facam)(3)], [Eu((S)-BINAPO)(D-facam)(3)], [Eu(BIPHEPO)(D-facam)(3)], and [Eu(TPPO)(2)(D-facam)(3)] were as high as 0.44, 0.34, 0.24, and 0.47, respectively, while [Eu((R)-BINAPO)(hfa)(3)] exhibited a relatively smaller dissymmetry factor (|g(CPL)| = 0.03). Their coordination structures were determined by the X-ray single-crystal analyses with shape-measure estimations. The photophysical relationship between the CPL properties and the electric transition probabilities of the chiral Eu(III) complexes is elucidated in terms of the coordination structures. PMID:19860395

Harada, Takashi; Nakano, Yoko; Fujiki, Michiya; Naito, Masanobu; Kawai, Tsuyoshi; Hasegawa, Yasuchika

2009-12-01

309

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

PubMed

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 approximately 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. PMID:18790806

Klenchin, Vadim A; Czyz, Agata; Goryshin, Igor Y; Gradman, Richard; Lovell, Scott; Rayment, Ivan; Reznikoff, William S

2008-09-12

310

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

PubMed Central

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 proteinphosphate 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 ?30-fold. X-ray crystallography indicates that transposaseDNA 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.

2008-01-01

311

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

312

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

2006-10-13

313

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

PubMed

Docking and fusion of transport vesicles/carriers with the target membrane involve a tethering factor-mediated initial contact followed by soluble N-ethylmaleimide-sensitive 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 reticulum-localized SNARE proteins. In the present study, we show that RINT-1 is also required for endosome-to-trans-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. PMID:23885118

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

2013-07-24

314

Catalytic dioxygen activation by Co(II) complexes employing a coordinatively versatile ligand scaffold.  

PubMed

The ligand bis(2-isobutyrylamidophenyl)amine has been prepared and used to stabilize both mononuclear and dinuclear cobalt(II) complexes. The nuclearity of the cobalt product is regulated by the deprotonation state of the ligand. Both complexes catalytically oxidize triphenylphosphine to triphenylphosphine oxide in the presence of O(2). PMID:21180730

Sharma, Savita K; May, Philip S; Jones, Matthew B; Lense, Sheri; Hardcastle, Kenneth I; MacBeth, Cora E

2010-12-22

315

An organicinorganic hybrid compound constructed by Strandberg-type polyoxoanions and transition metal coordination complexes  

Microsoft Academic Search

An organicinorganic hybrid compound formulated as {[Cu(2,2?-bpy)(H2O)2]5[Cu(2,2?-bpy)(H2O)]}[P2Mo5O23]210H2O (1) has been isolated by conventional solution method and characterized by elemental analyses, IR, thermal stability analysis, magnetic susceptibility measurement and single-crystal X-ray diffraction analysis. The compound is a 1D chain structure built from Strandberg-type polyoxoanions [P2Mo5O23]6? and secondary copper coordination complexes along c axis. Extensive ?? interactions of the 2,2?-bpy ligands and

Ruige Cao; Shuxia Liu; Jianfang Cao; Liang Wang; Qun Tang; Ying Liu; Yuanhang Ren

2008-01-01

316

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

317

[Hg{sub 5}O{sub 2}(OH){sub 4}][(UO{sub 2}){sub 2}(AsO{sub 4}){sub 2}]: A complex mercury(II) uranyl arsenate  

SciTech Connect

Under mild hydrothermal conditions UO{sub 2}(NO{sub 3}){sub 2}.6H{sub 2}O, Hg{sub 2}(NO{sub 3}){sub 2}.2H{sub 2}O, and Na{sub 2}HAsO{sub 4}.7H{sub 2}O react to form [Hg{sub 5}O{sub 2}(OH){sub 4}][(UO{sub 2}){sub 2}(AsO{sub 4}){sub 2}] (HgUAs-1). Single crystal X-ray diffraction experiments reveal that HgUAs-1 possesses a pseudo-layered structure consisting of two types of layers: {sub i}nfinity{sup 2}[Hg{sub 5}O{sub 2}(OH){sub 4}]{sup 2+} and {sub i}nfinity{sup 2}[(UO{sub 2}){sub 2}(AsO{sub 4}){sub 2}]{sup 2-}. The {sub i}nfinity{sup 2}[Hg{sub 5}O{sub 2}(OH){sub 4}]{sup 2+} layers are complex, and contain three crystallographically unique Hg centers. The coordination environments and bond-valence sum calculations indicate that the Hg centers are divalent. The {sub i}nfinity{sup 2}[(UO{sub 2}){sub 2}(AsO{sub 4}){sub 2}]{sup 2-} layers belong to the Johannite topological family. The {sub i}nfinity{sup 2}[Hg{sub 5}O{sub 2}(OH){sub 4}]{sup 2+} and {sub i}nfinity{sup 2}[(UO{sub 2}){sub 2}(AsO{sub 4}){sub 2}]{sup 2-} layers are linked to each other through mu{sub 2}-O bridges that include Hg...O=U=O interactions. - Graphical abstract: A depiction of the coordination environments for mercury in [Hg{sub 5}O{sub 2}(OH){sub 4}][(UO{sub 2}){sub 2}(AsO{sub 4}){sub 2}] (HgUAs-1).

Yu Yaqin; Jiang, Kai [Department of Chemistry and Biochemistry, and Center for Actinide Science, Auburn University, Auburn, Alabama 36849 (United States); Albrecht-Schmitt, Thomas E., E-mail: albreth@auburn.ed [Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Department of Chemistry and Biochemistry, and Center for Actinide Science, Auburn University, Auburn, Alabama 36849 (United States)

2009-07-15

318

Structural and Electrochemical Studies on Uranium(VI) Nitrato Complex with n-Octyl(phenyl)-N,N-Diisobutylcarbamoylmethylphosphine Oxide in Nonaqueous Solvents  

Microsoft Academic Search

The structure of uranyl nitrato complex with CMPO [n-Octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide] in solid state and in non-aqueous solvents without containing free CR\\/IPO has been studied by using IR spectrophotometer, C- and P-NMR. The carbonyl(vcO) and phosphoryl(vpO) stretching bands of coordinated CMPO were observed at lower wavenumber than the corresponding bands of free CMPO in both the states. The C and P

Seong-Yun KIM; Koh HATAKEYAMA; Hiroshi TOMIYASU; Yasuhisa IKEDA

1998-01-01

319

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

320

Uranyl complexation by chloride ions. Formation of a tetrachlorouranium(VI) complex in room temperature ionic liquids [Bmim][Tf2N] and [MeBu3N][Tf2N].  

PubMed

The tetrachlorouranium(VI) complex is formed in [Bmim][Tf2N] and [MeBu3N][Tf2N] from a uranium(VI) solution in the presence of a stoichiometric quantity of chloride ions. The [UVIO2Cl4]2- absorption and emission spectra show bands splitting in comparison with the [UVIO2]2+ spectra, as observed in the solid state, organic solvents, and chloroaluminate-based ionic liquids. The fluorescence lifetime of [UO2Cl4]2- in [MeBu3N][Tf2N] is 0.7 +/- 0.1 mus. The reduction potential of this complex is -1.44 and -1.8 V vs Ag/Ag+ respectively in [Bmim][Tf2N] and [MeBu3N][Tf2N] and does not depend on the chloride concentration. The mechanism proposed for the redox process is a monoelectronic reduction to form [UVO2Cl4]3-, followed by a chemical reaction. The tetrachlorouranium(V) complex seems more stable in [Bmim][Tf2N] than in [MeBu3N][Tf2N]. The electrochemical analysis put in evidence specific interactions of the ionic liquid cation with the uranium anionic species. PMID:17173389

Sornein, M-O; Cannes, C; Le Naour, C; Lagarde, G; Simoni, E; Berthet, J-C

2006-12-25

321

Precursor-directed assembly of complex oxide nanobeads: the role of strongly coordinated inorganic anions.  

PubMed

The use of an inorganic perrhenate ligand in the structure of early-transition-metal alkoxide precursors permits to achieve uniform self-assembly of the primary nanoparticles produced by their hydrolysis. The latter has been carried out in a hydrocarbon reaction medium by the addition of water with vigorous stirring, either in the pure form or in solutions in parent alcohols. The self-assembly is guided by the surface charge enhanced by the presence of strongly coordinated anions as determined by zeta potential measurements. The aggregation process has been followed in real time by nanoparticle tracking analysis (NanoSight technique). The reaction products are spherical aggregates with a size that can be efficiently controlled through the polarity of the reaction medium. The produced nanobeads have been characterized by TEM, SEM-EDS, DLS, nitrogen adsorption, and FTIR. The coordination of metal centers has been investigated using EXAFS spectroscopy. The aggregates remain amorphous on thermal treatment of up to 700 C (24 h treatment) but crystallize when treated at 1000 C. This latter process is associated with the total loss of rhenium content and offers early-transition-metal oxides as products. PMID:21830800

Nikonova, Olesya A; Nedelec, Jean-Marie; Kessler, Vadim G; Seisenbaeva, Gulaim A

2011-08-17

322

Stereodynamic Coordination Complexes. Dependence of Exciton Coupled Circular Dichroism Spectra on Molecular Conformation and Shape  

Microsoft Academic Search

Summary. Chiral amino alcohols, amino ethers, and amino thioethers were converted to tetradentate ligands by alkylation with a variety of chromophore-bearing alkyl heterocycles. Copper(II) complexes of the ligands display conformational diastereomerism in solution. The resultant propeller-shaped compounds were characterized by a variety of techniques, including exciton coupled circular dichroism (ECCD). Three X-ray crystal structures of complexes are described that partially

Andrea E. Holmes; Samuel A. Simpson; James W. Canary

2005-01-01

323

Anion recognition in water with use of a neutral uranyl-salophen receptor.  

PubMed

A new water-soluble uranyl-salophen complex incorporating two glucose units has been synthesized. This neutral derivative shows noteworthy binding affinity for fluoride in water thanks to the Lewis acid-base interaction occurring between the metal and the anion. Such interaction is strong enough to overcome the high hydration enthalpy of fluoride. Moreover this complex effectively binds hydrogen phosphate and exhibits remarkably strong association for nucleotide polyanions ADP(3-) and ATP(4-). PMID:21812437

Dalla Cort, Antonella; Forte, Gianpiero; Schiaffino, Luca

2011-08-22

324

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

325

Effect of the benzyl groups on the binding of H2 by three-coordinated Ti complexes  

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we investigate the adsorption of H2 molecules on a three-coordinated benzyl-decorated titanium complex suggested in a recent experiment [A. Hamaed , J. Am. Chem. Soc. 130, 6992 (2008)10.1021/ja710288g]. Unlike the interpretation of the experimental results that the Ti(III) complex can bind five H2 molecules via the Kubas interaction, the Ti(III) complex cannot adsorb H2 molecules via the Kubas interaction. In contrast, a benzyl-released Ti(III) complex can adsorb up to two H2 molecules with a binding energy of 0.25eV/H2 via the Kubas interaction, in good agreement with the measurement of 0.2eV . The calculated occupation number of H2 molecules at 25C and -78C under 60 atm is 0.9 and 1.9, respectively, in good agreement with the measurement of 1.1 and 2.4 near the conditions, respectively. Our results suggest that the Ti complex in experiment might be a benzyl-released form.

Lee, Hoonkyung

2010-07-01

326

Coordination features of a terpyridine-containing polyamine receptor. Effect of protonation on the photophysical properties of the complexes.  

PubMed

The synthesis of the new terpyridine-containing macrocycle 2,6,10,14-tetraaza[15](6,6'')cyclo(2,2':6',2'')terpyridinophane (L) is reported. The ligand contains a tetraamine chain linking the 6,6'' positions of a terpyridine unit. A potentiometric, (1)H NMR, UV-vis spectrophotometric and fluorescence emission study on the basicity properties of in aqueous solutions shows that the first four protonation steps occur on the polyamine chain, while the terpyridine nitrogens are involved in proton binding only in the last protonation step at strongly acidic pH values. Cu(II), Zn(II), Cd(II) and Pb(II) complexation was studied in aqueous solution by means of potentiometric, spectrophotometric and spectrofluorimetric measurements. Cu(II) and Zn(II) can form both mono- and dinuclear complexes in solution, while the larger Cd(II) and Pb(II) give only mononuclear complexes. In the [ML](2+) complexes (M = Zn(II) or Cd(II)) the metal is unequivocally bound to the terpyridine unit. Some amine groups are not coordinated and can quench the fluorescence emission of the terpyridine unit thanks to an electron transfer process. Protonation of the unbound amine groups inhibits the eT process, affording fluorescent [MLH(x)]((2+x)+) complexes. PMID:17146539

Bazzicalupi, Carla; Bencini, Andrea; Bianchi, Antonio; Borsari, Lucia; Danesi, Andrea; Giorgi, Claudia; Mariani, Palma; Pina, Fernando; Santarelli, Samuele; Valtancoli, Barbara

2006-10-04

327

Synthesis, characterization and crystal structures of some four coordinated nickel(II) complexes with tridentate Schiff base ligands  

Microsoft Academic Search

A number of Ni(II) complexes with tridentate Schiff base ligands with a N2O donor set and coordinating NNN? and SCN? anions have been synthesized and characterized by analytical, spectroscopic and electrochemical techniques. X-ray structure analyses of three of these complexes [L1Ni(NNN)] (1), [L2Ni(NNN)] (2) and [L3Ni(NCS)] (6) [HL1=Me2NCH2CH2N(Me)C6H4OH, HL2=Et2NCH2CH2N(H)C6H4OH, HL3=Et2NCH2CH2N(H)C6H3BrOH] show that the nickel atom has a square planar geometry.

Nijhuma Mondal; Volker Gramilich; S. Ozra Ghodsi

2001-01-01

328

Coordination of 1,4-Diazabutadiene Ligands to Decamethylytterbocene: Additional Examples of Spin Coupling in Ytterbocene Complexes  

SciTech Connect

The paramagnetic 1:1 coordination complexes of (C5Me5)2Yb with a series of diazabutadiene ligands, RN=C(R')C(R')=NR, where R= CMe3, CHMe2, adamantyl, p-tolyl, p-anisyl, and mesityl when R'=H, and R= p-anisyl when R'= Me, have been prepared. The complexes are paramagnetic, but their magnetic moments are less than expected for the two uncoupled spin carriers, (C5Me5)2Yb(III, 4f13) and the diazabutadiene radical anions (S=1/2), which implies exchange coupling between the spins. The variable temperature 1H NMR spectra show that rotation about the R-N bond is hindered and these barriers are estimated. The barriers are largely determined by steric effects but electronic effects are not unimportant.

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

2006-11-04

329

Field-induced slow magnetic relaxation in a six-coordinate mononuclear cobalt(II) complex with a positive anisotropy.  

PubMed

The novel mononuclear Co(II) complex cis-[Co(II)(dmphen)(2)(NCS)(2)]0.25EtOH (1) (dmphen = 2,9-dimethyl-1,10-phenanthroline) features a highly rhombically distorted octahedral environment that is responsible for the strong positive axial and rhombic magnetic anisotropy of the high-spin Co(II) ion (D = +98 cm(-1) and E = +8.4 cm(-1)). Slow magnetic relaxation effects were observed for 1 in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co(II) complex with a transverse anisotropy energy barrier. PMID:22963111

Vallejo, Julia; Castro, Isabel; Ruiz-Garca, Rafael; Cano, Joan; Julve, Miguel; Lloret, Francesc; De Munno, Giovanni; Wernsdorfer, Wolfgang; Pardo, Emilio

2012-09-14

330

Two new copper(II) complexes with the shortest (N N) diazine based rigid ligand: Example of unusual tridentate coordination mode  

NASA Astrophysics Data System (ADS)

Two new five coordinated Cu(II) complexes, Cu(L)Cl2,CH3OH (1) and Cu(L)Br2 (2) derived from the flexidentate ligand (L), 2-pyridinealdazine, have been synthesised and characterised by spectroscopic and electrochemical studies. Single crystal structures of the complexes were determined. Crystal structures of both the complexes contain monomeric entities of five coordinated copper(II) ions where the Schiff base ligand, 2-pyridinealdazine, acts in a tridentate fashion. The central part of the ligand in complex 2 is disordered over two positions: N8N9 make up the major position and N8AN9A make up the minor position.

Karmakar, Ruma; Choudhury, Chirantan Roy; Batten, Stuart R.; Mitra, Samiran

2007-01-01

331

Synthesis and crystal structures of the distorted pentagonal bipyramidal seven-coordinate acetylacetonate complexes [MI(acac)(CO) 2(PEt 3) 2] (M = Mo or W)  

Microsoft Academic Search

Equimolar quantities of [MI2(CO)3(PEt3)2] (M = Mo or W) and Na[acac] react in a Et2O\\/CH2Cl2\\/EtOH mixture at room temperature to give high yields of the seven-coordinate complexes [MI(acac)(CO)2(PEt3)2] (1 and 2). The crystal structures of 1 and 2, while not isomorphous, show similar seven-coordination geometries with the acetylacetonate ligand coordinating in a bidentate manner. The geometry around these complexes can

Paul K. Baker; Alec I. Clark; Michael G. B. Drew; Marcus C. Durrant; Raymond L. Richards

1997-01-01

332

Fluxional interconversion of divalent palladium complexes having NSNSN ligands between flexible SNS and rigid NNN-coordinated structures.  

PubMed

Mono- and dicationic divalent palladium complexes having 2,6-bis(N-heteroarylsulfanylmethyl)pyridine ligands (NSNSN ligands) were synthesized and characterized. The NSNSN ligands were fixed in a rac-SNS tridentate coordination mode in the solid state, while the equilibria among meso-SNS, rac-SNS, and NNN isomers were observed in solution. The equilibrium between the SNS and NNN isomers could be modulated by temperature, as well as by the steric and electronic factors of the NSNSN and monodentate ligands. Lowering the temperature tended to make NNN isomers more predominant compared with SNS isomers. On the other hand, the steric demand between the ligands in the complexes shifted the equilibrium from NNN to SNS isomers. Introduction of pyridyl groups instead of pyrimidyl groups as N-heteroarenes also shifted the equilibrium to SNS isomers. DFT calculation indicated rapid ring inversion of the metallacycle moieties and relatively slow S-inversion in the SNS isomers, a result that was in good agreement with the experimentally observed dynamic behaviors. Both the experimental and theoretical results revealed that the SNS isomers had flexible structures in solution, whereas the NNN isomers were rigid and less dynamic. The mechanistic pathways for interconversion between SNS and NNN isomers were also calculated. Such calculations indicated that a pathway featuring a relatively unstable, distorted ax-SNN intermediate was plausible. The intermediate had an N-heteroarene on the coordinated sulfur atom at an axial position. PMID:23989193

Kawada, Yumi; Kataoka, Yasutaka; Ura, Yasuyuki

2013-10-01

333

p21-Activated Kinases 1 and 3 Control Brain Size through Coordinating Neuronal Complexity and Synaptic Properties?  

PubMed Central

The molecular mechanisms that coordinate postnatal brain enlargement, synaptic properties, and cognition remain an enigma. Here, we demonstrate that neuronal complexity controlled by p21-activated kinases (PAKs) is a key determinant for postnatal brain enlargement and synaptic properties. We showed that double-knockout (DK) mice lacking both PAK1 and PAK3 were born healthy, with normal brain size and structure, but severely impaired in postnatal brain growth, resulting in a dramatic reduction in brain volume. Remarkably, the reduced brain size was accompanied by minimal changes in total cell count, due to a significant increase in cell density. However, the DK neurons have smaller soma, markedly simplified dendritic arbors/axons, and reduced synapse density. Surprisingly, the DK mice had elevated basal synaptic responses due to enhanced individual synaptic potency but were severely impaired in bidirectional synaptic plasticity. The actions of PAK1 and PAK3 are possibly mediated by cofilin-dependent actin regulation, because the activity of cofilin and the properties of actin filaments were altered in the DK mice. These results reveal an essential in vivo role of PAK1 and PAK3 in coordinating neuronal complexity and synaptic properties and highlight the critical importance of dendrite/axon growth in dictating postnatal brain growth and attainment of normal brain size and function.

Huang, Wayne; Zhou, Zikai; Asrar, Suhail; Henkelman, Mark; Xie, Wei; Jia, Zhengping

2011-01-01

334

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

2009-07-18

335

GRAPHITE PRODUCTION UTILIZING URANYL NITRATE HEXAHYDRATE CATALYST  

Microsoft Academic Search

ABS>The graphitizing of a mixture composed of furfuryl alcohol binder ; and uranyl nitrate hexahydrate hardener and the subsequent curing, baking, and ; graphitizing with pressure being initially applied prior to curing are described. ; The pressure step may be carried out by extrusion, methyl cellulose being added ; to the mixture before the completion of extrusion. Uranium oxide may

H. Sheinberg; J. R. Armstrong; D. H. Schell

1964-01-01

336

Regulation of CTnDOT Conjugative Transfer Is a Complex and Highly Coordinated Series of Events  

PubMed Central

ABSTRACT CTnDOT is a 65-kb conjugative transposon that is found in Bacteroides spp., which are one of the more abundant members within the lower human gastrointestinal tract. CTnDOT encodes resistance to the antibiotics erythromycin and tetracycline (Tc). An interesting feature of CTnDOT is that exposure to low levels of Tc induces a cascade of events that ultimately results in CTnDOT conjugative transfer. However, Tc is apparently not a switch that activates transfer but rather a signal that appears to override a series of negative regulators that inhibit premature excision and transfer of CTnDOT. In this minireview, we summarize over 20years of research that focused on elucidating the highly coordinated regulation of excision, mobilization, and transfer of CTnDOT.

Waters, Jillian L.; Salyers, Abigail A.

2013-01-01

337

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

PubMed

The complex [Nb(NMe2)2{(NMe2)C[double bond, length as m-dash]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

2013-08-29

338

Ions generated from uranyl nitrate solutions by electrospray ionization (ESI) and detected with fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometry  

Microsoft Academic Search

Electrospray ionization (ESI) of uranyl nitrate solutions generates a wide variety of positively and negatively charged ions,\\u000a including complex adducts of uranyl ions with methoxy, hydroxy, and nitrate ligands. In the positive ion mode, ions detected\\u000a by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry are sensitive to instrumental tuning parameters such\\u000a as quadrupole operating frequency and trapping time. Positive

Sofie Pasilis; rpd Somogyi; Kristin Herrmann; Jeanne E. Pemberton

2006-01-01

339

Physical and electrochemical interactions within hybrid nanocomposites of ruthenium coordination complexes and single-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

The research presented in this dissertation is a study of the interaction of ruthenium coordination complexes with single-walled carbon nanotubes (SWCNTs), a pursuit ultimately leading to the development of composite SWCNT materials. The work comprising this dissertation includes three major accomplishments: the synthesis and characterization of two new dinuclear ruthenium coordination complexes, the development of isothermal titration calorimetry (ITC) to thermodynamically quantify interactions with SWCNTs, and the fabrication and characterization of ruthenium complex---SWCNT hybrid nanocomposite electrodes. The work leading to these major accomplishments is inspired by the goal of attaining control over assembly of nanoscale building blocks, i.e. SWCNTs. The first step towards this goal is the development of appropriate molecules that can nondestructively link two SWCNTs together without damaging the physical structure of the tube. [Cl(trpy)Ru(tpphz)Ru(trpy)Cl](PF6) 2 and [(phen)2Ru(tpphz)Ru(trpy)Cl](PF6)3 are the two ruthenium dimer molecules synthesized and discussed herein. They possess a rigid nanoscale pocket that contains conjugated pi-electron density capable of interacting with the walls of SWCNTs. During the work to synthesize these complexes significant improvements were made to synthetic procedures to produce important precursors. The synthesis of the two complexes and the new synthetic procedures were novel. The second step required the development of a new tool (ITC) to study the interaction thermodynamics of dispersions of SWCNTs. ITC is a well established tool to measure binding thermodynamics of biological proteins and enzymes. Based on the analogy that can drawn between SWCNTs in solution and proteins, I developed ITC methods and protocols for measuring interactions of solvents with SWCNTs as well as the binding of the ruthenium dimer complexes with SWCNTs. I have established that ITC can be an important nanoscale science and materials development tool which can provide detailed insight into the thermodynamic interactions of nanomaterials in solution. I combined SWCNTs and ruthenium complexes, and developed procedures to fabricate nanocomposite films. The films produced by our method improve on previously reported techniques by avoiding surfactants and binders which retard the properties of SWCNT films. I was able to transfer these films to various substrates and they were shown to have enhanced capacitance versus pristine SWCNT films when used as an electrode in an electrochemical cell. Augmenting SWCNT electrodes in this way has not been reported and the technique is a promising vehicle for photo-induced charge transfer as well as cheaper and lighter capacitor devices.

Alston, Jeffrey Resing

340

Luminescent, magnetic and ferroelectric properties of noncentrosymmetric chain-like complexes composed of nine-coordinate lanthanide ions.  

PubMed

Reaction of the chiral ligand (-)-4,5-pinenepyridyl-2-pyrazine (L) with Ln(hfac)32H2O precursors [hfac(-) = 1,1,1,5,5,5-hexafluoroacetylacetonate, Ln = Sm(3+) (), Eu(3+) (), Tb(3+) () and Dy(3+) ()] in methanol solution led to the formation of four noncentrosymmetric lanthanide complexes with the general formula [Ln(hfac)3L]nH2O. The single-crystal X-ray diffraction analyses revealed that they are isostructural and take a one-dimensional (1D) chain structure based on the Ln(hfac)3L repeating units, in which the nine-coordinate Ln(3+) ions reside in a tricapped trigonal prism (TTP) environment never reported in previous 1D chain lanthanide complexes. The investigations of their photophysical properties showed that complexes , and exhibit characteristic emissions of Sm(3+), Eu(3+) and Tb(3+) ions with respective luminescent lifetime values of 0.065, 1.066 and 0.129 ms, while complex does not display any emission. The different luminescent intensities and lifetimes among them were further discussed in detail. Moreover, the magnetic properties of complexes were assessed with a special emphasis on the Dy(3+) complex . Alternating-current (ac) magnetic susceptibility measurements indicated that field-induced two-step slow magnetic relaxation processes were observed in , indicating the single-molecule magnet (SMM) behavior of . In addition, the noncentrosymmetric complexes crystallizing in the same polar point group (Cs) exhibit both ferroelectric and nonlinear optical properties at room temperature. All these features make them multifunctional crystalline molecule materials. PMID:24002651

Li, Xi-Li; Chen, Chun-Lai; Xiao, Hong-Ping; Wang, Ai-Ling; Liu, Cai-Ming; Zheng, Xianjun; Gao, Li-Jun; Yang, Xiao-Gang; Fang, Shao-Ming

2013-10-15

341

Oxoboryl Complexes: Boron-Oxygen Triple Bonds Stabilized in the Coordination Sphere of Platinum  

Microsoft Academic Search

Monomeric oxoboranes have hitherto been detected only as short-lived species in gas-phase or low-temperature matrix experiments. Here, we report formation of the oxoboryl complex trans-[(Cy3P)2BrPt(B?O)] (Cy being cyclohexyl) by means of reversible liberation of trimethylsilylbromide from the boron-bromine oxidative addition product of dibromo(trimethylsiloxy)borane and [Pt(PCy3)2] in room-temperature toluene solution. The platinum complex is inert toward oligomerization, even under photolytic conditions

Holger Braunschweig; Krzysztof Radacki; Achim Schneider

2010-01-01

342

Synthesis and characterization of Tetrakis(Alkylisocyanide) Bis(Triarylphosphine)Cobalt(III) complexes by Labile ligand substitution in intermediate-spin six-coordinate Co(III) complexes  

Microsoft Academic Search

Three intermediate-spin six-coordinate Co(III) complexes, [Co(CNCH2Ph)4{OAs(C6H4Me-p)3}2](BF4)3 (1), [Co(CNC6H11)4(OSbPh3)2](ClO4)3 (2), and [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 (3), undergo rapid ligand substitution with selected triarylphosphines at 0C. Complexes 1, 2, and 3 react with P(C6H4OMe-p)3, 1 and 2 react with PPh3, and 2 reacts with P(C6H4Me-p)3, to produce trans-[Co(CNR)4(PR?3)2]X3 complexes in very high yields. Attempted reaction with P(C6H4Cl-p)3 yields a Co(I) complex. The triarylphosphine-alkylisocyanide Co(III) complexes

Clifford A. L. Becker; Edward Eddie Mmatli

2004-01-01

343

Functionally distinct Gata3/Chd4 complexes coordinately establish T helper 2 (Th2) cell identity  

PubMed Central

GATA binding protein 3 (Gata3) is a GATA family transcription factor that controls differentiation of nave CD4 T cells into T helper 2 (Th2) cells. However, it is unknown how Gata3 simultaneously activates Th2-specific genes while repressing those of other Th lineages. Here we show that chromodomain helicase DNA-binding protein 4 (Chd4) forms a complex with Gata3 in Th2 cells that both activates Th2 cytokine transcription and represses the Th1 cytokine IFN-?. We define a Gata3/Chd4/p300 transcriptional activation complex at the Th2 cytokine loci and a Gata3/Chd4nucleosome remodeling histone deacetylase repression complex at the Tbx21 locus in Th2 cells. We also demonstrate a physiological role for Chd4 in Th2-dependent inflammation in an in vivo model of asthmatic inflammation. Thus, Gata3/Chd4 forms functionally distinct complexes, which mediate both positive and negative gene regulation to facilitate Th2 cell differentiation.

Hosokawa, Hiroyuki; Tanaka, Tomoaki; Suzuki, Yutaka; Iwamura, Chiaki; Ohkubo, Shuichi; Endoh, Kanji; Kato, Miki; Endo, Yusuke; Onodera, Atsushi; Tumes, Damon John; Kanai, Akinori; Sugano, Sumio; Nakayama, Toshinori

2013-01-01

344

Coordination of Engineering Design Agents for High Assurance in Complex Dynamic System Design  

Microsoft Academic Search

This paper presents a hierarchical architecture for an innovative self-adaptive design network for physics-based modeling of complex systems dynamics in order to assess and control its behavior characteristics. Each structural component of the system is simulated by an engineering design agent (EDA) which models the conceptual design parameters of the component in its operational environment. The objective here is to

Shashi Phoha; Eugene Eberbach; Eileen Peluso; Atilla P. Kiraly

1998-01-01

345

Variable coordination of redox-active TCNB in discrete and polymeric ferrocenylcopper(i) complexes: structures and spectroelectrochemical behaviour.  

PubMed

1,2,4,5-Tetracyanobenzene (TCNB) was reacted with [Cu(dppf)(CH3CN)2](BF4) and [Cu(dchpf)(CH3CN)](BF4), dppf = 1,1'-bis(diphenylphosphino)ferrocene and dchpf = 1,1'-bis(dicyclohexylphosphino)ferrocene, to produce a heterotetranuclear metallamacrocycle 1, {[Cu(dppf)(?-TCNB)](BF4)}2, and a heterooctanuclear complex 2, [{Cu(dchpf)}4(?4-TCNB)](BF4)4. Complex 1 is the first example of a structurally characterised discrete transition metal complex of TCNB. Upon crystallisation attempts, compound 2 formed the structurally identified coordination polymer 3, {[Cu(dchpf)(?-TCNB)]2(BF4)2}n. Structural and spectroscopic analyses confirmed the redox-innocent behaviour of TCNB in 1, 2 and 3. However, the soluble compounds 1 and 2 could be oxidised and reduced spectroelectrochemically (UV-vis, IR, and EPR). The oxidation occurs invariably at the ferrocene sites without notable splitting of redox potentials. Reduction involves the TCNB bridging ligands to produce radical complexes. As a variably bridging acceptor component of supramolecular structures the TCNB ligand thus adopts an intermediate position between the highly electron transfer-active TCNE, TCNQ and TCNQF4 systems and the numerous redox-innocent bridges. PMID:24022668

Jana, Rajkumar; Mobin, Shaik M; Schwederski, Brigitte; Fiedler, Jan; Kaim, Wolfgang

2013-09-10

346

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

347

Regulation of CTnDOT Conjugative Transfer Is a Complex and Highly Coordinated Series of Events.  

PubMed

ABSTRACT CTnDOT is a 65-kb conjugative transposon that is found in Bacteroides spp., which are one of the more abundant members within the lower human gastrointestinal tract. CTnDOT encodes resistance to the antibiotics erythromycin and tetracycline (Tc). An interesting feature of CTnDOT is that exposure to low levels of Tc induces a cascade of events that ultimately results in CTnDOT conjugative transfer. However, Tc is apparently not a switch that activates transfer but rather a signal that appears to override a series of negative regulators that inhibit premature excision and transfer of CTnDOT. In this minireview, we summarize over 20years of research that focused on elucidating the highly coordinated regulation of excision, mobilization, and transfer of CTnDOT. IMPORTANCE Bacteroides spp. are abundant commensals in the human colon, but they are also considered opportunistic pathogens, as they can cause life-threatening infections if they should escape the colon. Bacteroides spp. are the most common cause of anaerobic infections and are rather difficult to treat due to the prevalence of antibiotic resistance within this genus. Today over 80% of Bacteroides are resistant to tetracycline (Tc), and a study looking at both clinical and community isolates demonstrated that this resistance was specifically due to the conjugative transposon CTnDOT. PMID:24169574

Waters, Jillian L; Salyers, Abigail A

2013-10-29

348

Syntheses and characterization of novel lanthanide adamantine-dicarboxylate coordination complexes  

SciTech Connect

Hydrothermal reactions of 1,10-phenanthroline (phen), 1,3-adamantanedicarboxylic acid (H{sub 2}L) and lanthanide chlorides yielded six compounds: [Ln(L)(HL)(phen)] (Ln=Pr, 1; Nd, 2), [Ln(L)(HL)(phen)(H{sub 2}O)] (Sm, 3; Eu, 4), [Tb(L)(HL)(phen)(H{sub 2}O)]{sub 2}.2H{sub 2}O (5), [Er{sub 3}(L){sub 4}(OH)(phen)]{sub 2} (6). Compounds 1-4 are structurally featured by one-dimensional polymeric chains; 5 hold binuclear structure constructed from eight-coordinated lanthanide center LnN{sub 2}O{sub 6} of distorted bicapped trigonal prism bridged by dicarboxylate ligands; 6 shows that erbium ions are in mono and bicapped trigonal prismatic geometries, respectively, which are further connected by {mu}{sub 3}-OH to give rise to trinuclear structure. Thermogravimetric analyses of 1, 3 and 5 were performed. Fluorescent measurements of 4 and 5 were carried out, respectively. - Grapical Abstract: Hydrothermal reactions of 1,10-phenanthroline, 1,3-adamantanedicarboxylic acid and lanthanide choloride yielded a novel supramolecular architectures constructed from polyhedral LnN{sub 2}O{sub 6} of distorted bicapped trigonal prism bridged by dicarboxylate.

Li Xing; Wei Danyi; Huang Shijie [Institute of Solid Materials Chemistry, State Key Laboratory Base of Novel Functional Materials and Preparation Science, Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo, Zhejiang 315211 (China); Zheng Yueqing [Institute of Solid Materials Chemistry, State Key Laboratory Base of Novel Functional Materials and Preparation Science, Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo, Zhejiang 315211 (China)], E-mail: zhengyueqing@nbu.edu.cn

2009-01-15

349

Observation of Radiolytic Field Alteration of the Uranyl Cation in Bicarbonate Solution  

SciTech Connect

Auto radiolysis of uranium (VI) carbonate solutions between pH 5.9 and 7.2 is shown to alter the uranium speciation over relatively short periods of time and was followed by {sup 13}C NMR and visible spectrophotometry, using dissolved [({sup 233}UO{sub 2}){sub 3}(CO{sub 3}){sub 6}]{sup 6-} both as the radiolysis source (D 14.9 Gy/hr) and as a trap for the newly formed hydrogen peroxide. The speciation is different than the uranyl mixed peroxy carbonate species that have been reported for higher pH carbonate solutions. Direct addition of hydrogen peroxide to solutions of the uranyl-carbonate trimer is shown to reproduce the {sup 13}C, {sup 17}O NMR signatures of the complex(es) formed by radiolysis, but additionally a variety of new complexes are revealed. Ratios of H{sub 2}O{sub 2}/trimer <1.5 produced uranyl peroxo carbonate adducts that are shown to be common to the radiolytically produced species. Ratios of H{sub 2}O{sub 2}/trimer >1.5 resulted in formation of stable higher order peroxo carbonate complexes. The {sup 13}C, {sup 17}O NMR signatures and visible spectra of these complexes are described here. Rigorous characterization of the species is an ongoing effort. (authors)

Snow, Lanee; McNamara, Bruce; Sinkov, Sergei; Cho, Herman; Friese, Judah [Pacific Northwest National Laboratory, Mail Stop, P.O. Box 999, Richland, WA 99352 (United States)

2007-07-01

350

Synthetic and structural studies on amine coordination to Pd-N-heterocyclic carbene complexes.  

PubMed

The reaction between 2-chlorobenzylamine or 2-chlorobenzylalcohol and Pd(I(t)Bu)(2) (I(t)Bu = 1,3-di-tert-butylimidazol-2-ylidene) in benzene affords the dimeric complexes [Pd(I(t)Bu)(mu-NH{2-CH(2)C(6)H(4)})](2) and [Pd(I(t)Bu)(mu-O{2-CH(2)C(6)H(4)})](2); the latter has been structurally characterised. The syntheses, structural characterisation and reactivity of the Pd-NHC amine complexes [(I(t)Bu)Pd(R-4-C(6)H(4))(morpholine)Cl] (R = Me, OMe, CO(2)Me), intermediates in the Buchwald-Hartwig aryl amination reaction, are also reported. PMID:20449153

de K Lewis, Alexandra K; Caddick, Stephen; Esposito, Oriana; Cloke, F Geoffrey N; Hitchcock, Peter B

2009-07-21

351

Pyro without fire: synthesis, structure, and reactivity of a dimeric vanadyl pyrophosphate coordination complex.  

PubMed

The complex {[(V(IV)O)bipy(H(2)O)](2)(?-P(2)O(7))}3H(2)O (2) was readily obtained as a nanocrystalline powder by one-pot synthesis under mild conditions. Single crystals of 2 were grown at room temperature over 2 months, and its structure was determined. Fundamental catalytic activity was proven for this species by testing for oxidation of benzyl alcohol in air. PMID:22974202

Marino, Nadia; Hanson, Susan K; Mller, Peter; Doyle, Robert P

2012-09-13

352

Aerobic intramolecular oxidative amination of alkenes catalyzed by NHC-coordinated palladium complexes.  

PubMed

[reaction: see text] Palladium(II) complexes bearing a single N-heterocyclic carbene ligand serve as effective catalysts for the aerobic oxidative cyclization of alkenes with pendant sulfonamides. The use of carboxylic acid cocatalysts (AcOH and PhCO(2)H) often leads to significant improvements in catalyst stability and product yield and enables catalytic turnover to be achieved with air, rather than pure oxygen gas, as the source of O(2). PMID:16706500

Rogers, Michelle M; Wendlandt, Johanna E; Guzei, Ilia A; Stahl, Shannon S

2006-05-25

353

Synthesis and Studies of Semicarbazonato Lantianum(III) and Samarium(III) Coordination Complexes  

Microsoft Academic Search

Synthesis and characterization of lanthanum(III) and samarium(III) semicarbazonato complexes are reported. These derivatives of the type (OR)Ln(SCZ), Ln2(SCZ)3 and Ln(SCZ)(SCZH) [where Ln = La(III) or Sm(III), R = isopropyl or tertiary butyl and SCZ = anion of the aldimine or ketimine semicarbazones viz. salicylidinesemicarbazone, 2-hydroxy-1-naphthalidinesemicarbazone and 2-hydroxy-1-acetophenoneiminesemicarbazone] are obtained in the form of coloured solids by the reactions of tris(isopropoxy)

S. P. Mital; R. V. Singh; J. P. Tandon

1982-01-01

354

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

355

Cobalt, zinc, and nickel complexes of a diatopic heteroscorpionate ligand: building blocks for coordination polymers.  

PubMed

New binuclear complexes of Co(II), Zn(II), and Ni(II) derived from a diatopic heteroscorpionate ligand, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L4c), have been synthesized and characterized by X-ray diffraction, ESI-MS, IR, UV-vis spectroscopy, and magnetic susceptibility. These building blocks have been subsequently used for the construction of higher order metallosupramolecular architectures. PMID:18186625

Santillan, Guillermo A; Carrano, Carl J

2008-01-11

356

Coordination of DNA replication and histone modification by the Rik1-Dos2 complex.  

PubMed

Histone modification marks have an important role in many chromatin processes. During DNA replication, both heterochromatin and euchromatin are disrupted ahead of the replication fork and are then reassembled into their original epigenetic states behind the fork. How histone marks are accurately inherited from generation to generation is still poorly understood. In fission yeast (Schizosaccharomyces pombe), RNA interference (RNAi)-mediated histone methylation is cell cycle regulated. Centromeric repeats are transiently transcribed in the S phase of the cell cycle and are processed into short interfering RNAs (siRNAs) by the complexes RITS (RNA-induced initiation of transcriptional gene silencing) and RDRC (RNA-directed RNA polymerase complex). The small RNAs together with silencing factors-including Dos1 (also known as Clr8 and Raf1), Dos2 (also known as Clr7 and Raf2), Rik1 and Lid2-promote heterochromatic methylation of histone H3 at lysine 9 (H3K9) by a histone methyltransferase, Clr4 (refs 8-13). The methylation of H3K9 provides a binding site for Swi6, a structural and functional homologue of metazoan heterochromatin protein 1 (HP1). Here we characterize a silencing complex in fission yeast that contains Dos2, Rik1, Mms19 and Cdc20 (the catalytic subunit of DNA polymerase-?). This complex regulates RNA polymerase II (RNA Pol II) activity in heterochromatin and is required for DNA replication and heterochromatin assembly. Our findings provide a molecular link between DNA replication and histone methylation, shedding light on how epigenetic marks are transmitted during each cell cycle. PMID:21725325

Li, Fei; Martienssen, Rob; Cande, W Zacheus

2011-07-03

357

The influence of the magnetic field on the photosubstitution reaction of coordination complexes  

NASA Astrophysics Data System (ADS)

Photolyses of rhodium(III) complexes, Rh(NH 3) 5X 2+ (X = Cl - and Br -), under intense magnetic fields, e.g. ? excit = 360 nm and H = 24 kG, have been investigated. The magnetic field quenches the photoaquation of the ammonia and enhances the photoaquation of the acido ligand, X = Cl - or Br - by 10% for H = 24 kG. The implication of two different precursors in the formation of the photoproducts is discussed.

Ferraudi, G.; Pacheco, M.

1984-11-01

358

Coordination of DNA Replication and Histone Modification by the Rik1-Dos2 Complex  

PubMed Central

Histone modification marks play an important role in many chromatin processes1,2. During DNA replication, both heterochromatin and euchromatin are disrupted ahead of the replication fork and then reassembled into their original epigenetic states behind the fork3,4. How the histone marks are faithfully inherited during each generation is still poorly understood. In fission yeast RNA interference (RNAi)-mediated histone methylation is cell-cycle regulated. Centromere repeats are transiently transcribed at S phase and processed into small interference RNAs (siRNAs) by RITS and RDRC complexes5-7. The small RNAs, in concert with silencing factors, including Dos1/Clr8, Dos2/Clr7, Rik1 and Lid2, promote heterochromatic H3K9 methylation by a histone methyltransferase, Clr48-13. H3K9 methylation serves as a binding site for Swi6, a structural and functional homolog of metazoan Heterochromatin Protein 1 (HP1)14. Here we characterize a silencing complex, which contains Dos2, Rik1, Mms19, and Cdc20 (DNA polymerase epsilon). The complex regulates RNA Pol II activity in heterochromatin, and is required for DNA replication and heterochromatin assembly. Our findings provide a molecular link between DNA replication and histone methylation, shedding light on how epigenetic marks are transmitted during each cell cycle.

Li, Fei; Martienssen, Rob; Cande, W. Zacheus

2011-01-01

359

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

2012-04-04

360

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

2011-06-15

361

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

362

Preparation and coordination complex of the first imine-bridged tetrathiafulvalene-pyridine donor ligand.  

PubMed

The first imine-bridged pyridyltetrathiafulvalene building block (TTF-CH=N-Py, 1) has been synthesized via the Schiff base condensation of formyltetrathiafulvalene and 2-aminopyridine. The preparation, X-ray crystal structure, electrochemical and magnetic characterization of a 1:1 copper complex [CuII(hfac)2(TTF-CH=N-Py)] (2) are reported. The crystal structure reveals that the imine N atom participates in chelation to the paramagnetic center, thus making this ligand an attractive precursor for the assembly of pi-d systems. PMID:17439207

Chahma, M'hamed; Hassan, Nasser; Alberola, Antonio; Stoeckli-Evans, Helen; Pilkington, Melanie

2007-04-18

363

Synthesis and crystal structure of UO{sub 2}Cl{sub 2}(THF){sub 3}: A simple preparation of an anhydrous uranyl reagent  

SciTech Connect

Solid state Structures of molecular uranyl compounds are commonly described in the literature. The vast majority of these species have been isolated from aqueous media, and the presence of water often influences the resulting structures through hydrogen bonding and/or inner-sphere water coordination. The development of nonaqueous uranyl chemistry has demonstrated the existence of novel coordination geometries in the absence of these effects. Further studies are required to examine the potentially unique electrochemical and spectroscopic properties of these products. Until recently, the development of nonaqueous uranyl chemistry has been inhibited by a lack of appropriate starting materials. Several thermal routes for the synthesis of anhydrous UO{sub 2}Cl{sub 2} have been reported. However, they are generally unsuitable for the generation of reagents because of difficulties encountered separating precursors and/or side products from UO{sub 2}Cl{sub 2}, the unavailability of a commercial source for starting materials, e.g., UCl{sub 4}, or the limited scale of preparation. The authors have been interested in the development of nonaqueous uranyl chemistry in order to examine physical properties of uranyl species unstable to hydrolysis. The expansion of this chemistry has been facilitated by the development of a simple one-pot dehydration of UO{sub 2}Cl{sub 2}{center{underscore}dot}x(H{sub 2}O) (x = 1,3) for the preparation of UO{sub 2}Cl{sub 2}(THF){sub 3} (1). The previously reported dimeric derivative, [UO{sub 2}Cl{sub 2}(THF){sub 2}]{sub 2} (2), may be isolated upon desolvation of 1. Compound 2 is an excellent starting material for the further synthesis of uranyl alkoxides and uranyl amides.

Wilkerson, M.P.; Burns, C.J.; Paine, R.T.; Scott, B.L.

1999-09-06

364

[Study of the mechanisms of cytotoxic effect of uranyl nitrate].  

PubMed

The mechanisms of cytotoxic effect of uranyl nitrate were studied. It was shown that uranyl nitrate induced HEp-2 cell death, mainly by necrotic way. In the experiments in vitro, uranyl nitrate caused an appearance of 8-oxoguanine in DNA, indicating the induction of oxidative stress. The experiments with isolated rat liver mitochondria revealed that 1 mM uranyl nitrate decreased the respiration rates of mitochondria in state 3 and DNP-induced respiration. At the same time, uranyl nitrate had no influence on the opening of the mitochondrial permeability transition pore and decreased the rate of formation of H2O2 by mitochondria. Possible molecular mechanisms of uranyl-induced necrosis are discussed. PMID:23136770

Belosludtsev, K N; Garmash, S A; Belosludtseva, N V; Belova, S P; Berezhnov, A V; Gudkov, S V

365

Oxoboryl complexes: boron-oxygen triple bonds stabilized in the coordination sphere of platinum.  

PubMed

Monomeric oxoboranes have hitherto been detected only as short-lived species in gas-phase or low-temperature matrix experiments. Here, we report formation of the oxoboryl complex trans-[(Cy3P)2BrPt(B[triple bond]O)] (Cy being cyclohexyl) by means of reversible liberation of trimethylsilylbromide from the boron-bromine oxidative addition product of dibromo(trimethylsiloxy)borane and [Pt(PCy3)2] in room-temperature toluene solution. The platinum complex is inert toward oligomerization, even under photolytic conditions and at elevated temperatures. The bromide was substituted by thiophenolate, and spectral parameters of both products as well as results of computational and x-ray diffraction studies are in agreement with the formulation of a triple bond between boron and oxygen. The boron-oxygen distance of 120.5(7) picometers shows a bond shortening of 7.2% as compared with a double bond, which is similar to the shortening observed in carbon-carbon analogs. PMID:20395506

Braunschweig, Holger; Radacki, Krzysztof; Schneider, Achim

2010-04-16

366

Studies of the Antiproliferative Activity of Ruthenium (II) Cyclopentadienyl-Derived Complexes with Nitrogen Coordinated Ligands  

PubMed Central

Four cationic ruthenium(II) complexes with the formula [Ru(?5-C5H5)(PPh3)2]+, with L = 5-phenyl-1H-tetrazole (TzH) 1, imidazole (ImH) 2, benzo[1,2-b;4,3-b?] dithio-phen-2-carbonitrile (Bzt) 3, and [5-(2-thiophen-2-yl)-vinyl]-thiophene-2-carbonitrile] (Tvt) 4 were prepared and characterized in view to evaluate their potentialities as antitumor agents. Studies by Circular Dichroism indicated changes in the secondary structure of ct-DNA. Changes in the tertiary structure of pBR322 plasmid DNA were also observed in gel electrophoresis experiment and the images obtained by atomic force microscopy (AFM) suggest strong interaction with pBR322 plasmid DNA; the observed decreasing of the viscosity with time indicates that the complexes do not intercalate between DNA base pairs. Compounds 1, 2, and 3 showed much higher cytotoxicity than the cisplatin against human leukaemia cancer cells (HL-60 cells).

Moreno, Virtudes; Lorenzo, Julia; Aviles, Francesc X.; Garcia, M. Helena; Ribeiro, Joao P.; Morais, Tania S.; Florindo, Pedro; Robalo, M. Paula

2010-01-01

367

Arabidopsis FLC clade members form flowering-repressor complexes coordinating responses to endogenous and environmental cues  

PubMed Central

The developmental transition to flowering is timed by endogenous and environmental signals through multiple genetic pathways. In Arabidopsis, the MADS-domain protein FLOWERING LOCUS C is a potent flowering repressor. Here, we report that the FLOWERING LOCUS C clade member MADS AFFECTING FLOWERING3 acts redundantly with another clade member to directly repress expression of the florigen FLOWERING LOCUS T and inhibit flowering. FLOWERING LOCUS C clade members act in partial redundancy in floral repression and mediate flowering responses to temperature, in addition to their participation in the flowering-time regulation by vernalization and photoperiod. We show that FLOWERING LOCUS C, MADS AFFECTING FLOWERING3 and three other clade members can directly interact with each other and form nuclear complexes, and that FLOWERING LOCUS C-dependent floral repression requires other clade members. Our results collectively suggest that the FLOWERING LOCUS C clade members act as part of several MADS-domain complexes with partial redundancy, which integrate responses to endogenous and environmental cues to control flowering.

Gu, Xiaofeng; Le, Chau; Wang, Yizhong; Li, Zicong; Jiang, Danhua; Wang, Yuqi; He, Yuehui

2013-01-01

368

Linear and nonlinear two-coordinate vanadium complexes: synthesis, characterization, and magnetic properties of V(II) amides.  

PubMed

The synthesis and characterization of the first stable two-coordinate vanadium complexes are described. The vanadium(II) primary amido derivative V{N(H)Ar(iPr6)}2 [Ar(iPr6) = C6H3-2,6-(C6H2-2,4,6-iPr3)2] (1) was synthesized via the reaction of LiN(H)Ar(iPr6) with the V(III) complex VCl32NMe3 or the V(II) salt [V2Cl3(THF)6](+)I(-) in a 2:1 and 4:1 stoichiometry, respectively. Reaction of the less crowded LiN(H)Ar(Me6) with [V2Cl3(THF)6](+)I(-) afforded V{N(H)Ar(Me6)}2 [Ar(Me6) = C6H3-2,6-(C6H2-2,4,6-Me3)2] (2), which has a nonlinear [N-V-N = 123.47(9)] vanadium coordination. Magnetometry studies showed that V{N(H)Ar(iPr6)}2 and V{N(H)Ar(Me6)}2 have ambient temperature magnetic moments of 3.41 and 2.77 ?B, respectively, which are consistent with a high-spin d(3) electron configuration. These values suggest a significant spin orbital angular momentum contribution that leads to a magnetic moment that is lower than their spin-only value of 3.87 ?B. DFT calculations showed that the major absorptions in their UV-vis spectra were due to ligand to metal charge transfer transitions. Exposure of the reaction mixture for 2 to dry O2 resulted in the formation of the diamagnetic V(V) oxocluster [V{N(H)Ar(Me6)}2]2(?-O-Li-O)2 (3). PMID:23782062

Boynton, Jessica N; Guo, Jing-Dong; Fettinger, James C; Melton, Christopher E; Nagase, Shigeru; Power, Philip P

2013-07-10

369

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

2012-05-04

370

Coulomb explosion upon electron attachment to a four-coordinate monoanionic metal complex.  

PubMed

Electron capture to monoanionic metal complexes in high-energy collisions with sodium vapor is shown to occur with the formation of dianions. In this way, we prepared the small dianions Cr(SCN)42-, Fe(CN)42-, Pt(NO2)22-, and Pt(C2O4)22- in the gas phase. The Cr(SCN)42- dianion Coulomb explodes into Cr(SCN)3- and SCN- with a release of kinetic energy (3.2 +/- 0.4 eV) into translational energy of the fragments. The scheme provides a way to study charge dissociation reactions of molecular dianions that are too short-lived to survive extraction from the ion source. PMID:12904017

Nielsen, Anders Baardseth; Hvelplund, Preben; Liu, Bo; Nielsen, Steen Brndsted; Tomita, Shigeo

2003-08-13

371

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

372

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

373

Organicinorganic hybrids constructed by Anderson-type polyoxoanions and copper coordination complexes  

Microsoft Academic Search

Four organicinorganic hybrid compounds based on Anderson-type polyoxoanions, namely, {[Cu(2,2?-bpy)(H2O)3]2[Cr(OH)6Mo6O18]}{[Cu(2,2?-bpy)(H2O)Cl][Cu(2,2?-bpy)(H2O)(NO3)][Cr(OH)6Mo6O18]}18H2O (1), [Cu(2,2?-bpy)(H2O)2Cl]{[Cu(2,2?-bpy)(H2O)2][Cr(OH)6Mo6O18]}4H2O (2), (H3O){[Cu(2,2?-bpy)(H2O)2]2[Cu(2,2?-bpy)(H2O)]2}[Cr(OH)6Mo6O18]336H2O (3), and (H3O){[Cu(2,2?-bpy)(H2O)2]2[Cu(2,2?-bpy)(H2O)]2}[Al(OH)6Mo6O18]333H2O (4), were isolated by conventional solution method, and crystal structures have been determined by single-crystal X-ray diffraction. Among them, compound 1 displays a discrete supramolecular structure, compound 2 shows a chainlike structure with chloro-copper complexes as counteranions, and compounds 3 and 4 are

Rui-Ge Cao; Shu-Xia Liu; Ying Liu; Qun Tang; Liang Wang; Lin-Hua Xie; Zhong-Min Su

2009-01-01

374

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

375

Two-coordinate first row transition metal complexes with short unsupported metal-metal bonds.  

PubMed

A series of first row transition metal complexes with unsupported M-Fe bonds, (3,5-(i)Pr2-Ar*)MFe(?(5)-C5H5)(CO)2 (M = Fe (1), Mn (2), Cr (3), 3,5-(i)Pr2-Ar* = -C6H-2,6-(C6H2-2,4,6-(i)Pr3)2-3,5-(i)Pr2), was synthesized by salt metathesis. They were characterized by (1)H NMR, UV-vis spectroscopy, X-ray crystallography, and SQUID magnetic measurements. Two distinct Fe atoms in 1 were confirmed by Mssbauer spectroscopy. All three compounds feature short metal-metal bond distances (Fe-Fe, 2.3931(8) (1); Mn-Fe, 2.4512(5) (2); Cr-Fe, 2.4887(5) (3)). Their DFT computed structures were in excellent agreement with the experimental data and revealed a dative bonding interaction between the metals. PMID:21090630

Lei, Hao; Guo, Jing-Dong; Fettinger, James C; Nagase, Shigeru; Power, Philip P

2010-11-19

376

XPS Studies of Planar Four-Coordinate Copper(II) and Copper(III) Complexes  

NASA Astrophysics Data System (ADS)

X-ray photoelectron spectra of some planar CuS4 copper N,N-dialkyl dithiocarbamate compounds in the formal +2 and +3 oxidation states and the CuO4 complex carbonate, Na2[Cu(CO3)2], have been recorded. Cu(2p3/2) binding energies for the copper(II) dithiocarbamate and carbonate compounds are similar although the shakeup satellite structure for the dithiocarbamate compounds is relatively less intense. The modified Auger parameter, ?', for the two sets of compounds is also similar but ca. 1-2 eV lower than the value reported for the most Cu(II) compounds. The copper binding and kinetic energy parameters for the Cu(III) compounds have been found to correspond to values found for the Cu(II) compounds with, however, an absence of secondary satellite structure. Differences between the compounds in the two oxidation states are also found in the ligand sulphur 2p binding energies which are ca. 1 eV higher in the Cu(III) compounds.

Healy, Peter C.; Myhra, Sverre; Stewart, Andrew M.

1987-11-01

377

THE MECHANISM OF THE EXTRACTION OF SEVERAL URANYL SALTS BY TRI-n-BUTYL PHOSPHATE  

Microsoft Academic Search

The extraction of several uranyl salts (nitrate, chloride, perchlorate, ; sulfate, acetate, and phosphate) by TBP was studied. The formation of the ; complexes UO(NO)(TBP), and UO(ClO)\\/sub ; 2\\/(TBP) was confirmed by partition study and infrared study. The ; influence of acid concentration on uranium extraction was discussed, especially ; for the system UO(ClO)-HClOTBP. The order of the ; extractabilities

Keiji Naito; Toshio Suzuki

1962-01-01

378

GRAPHITE PRODUCTION UTILIZING URANYL NITRATE HEXAHYDRATE CATALYST  

DOEpatents

ABS>The graphitizing of a mixture composed of furfuryl alcohol binder and uranyl nitrate hexahydrate hardener and the subsequent curing, baking, and graphitizing with pressure being initially applied prior to curing are described. The pressure step may be carried out by extrusion, methyl cellulose being added to the mixture before the completion of extrusion. Uranium oxide may be added to the graphitizable mixture prior to the heating and pressure steps. The graphitizable mixture may consist of discrete layers of different compositions. (AEC)

Sheinberg, H.; Armstrong, J.R.; Schell, D.H.

1964-03-10

379

Pillared and open-framework uranyl diphosphonates  

NASA Astrophysics Data System (ADS)

The hydrothermal reactions of uranium trioxide, uranyl acetate, or uranyl nitrate with 1,4-benzenebisphosphonic acid in the presence of very small amount of HF at 200 C results in the formation of three different uranyl diphosphonate compounds, [H 3 O] 2 {(UO 2 ) 6 [C 6 H 4 (PO 3 )(PO 2 OH)] 2 [C 6 H 4 (PO 2 OH) 2 ] 2 [C 6 H 4 (PO 3 ) 2 ]}(H 2 O) 2 ( Ubbp-1 ), [H 3 O] 4 {(UO 2 ) 4 [C 6 H 4 (PO 3 ) 2 ] 2 F 4 }H 2 O ( Ubbp-2 ), and {(UO 2 )[C 6 H 2 F 2 (PO 2 OH) 2 (H 2 O)} 2 H 2 O ( Ubbp-3 ). The crystal structures of these compounds were determined by single crystal X-ray diffraction experiments. Ubbp-1 consists of UO 7 pentagonal bipyramids that are bridged by the phosphonate moieties to form a three-dimensional pillared structure. Ubbp-2 is composed of UO 5 F 2 pentagonal bipyramids that are bridged through the phosphonate oxygen atoms into one-dimensional chains that are cross-linked by the phenyl spacers into a pillared structure. The structure of Ubbp-3 is a three-dimensional open-framework with large channels containing water molecules with internal dimensions of approximately 10.910.9 . Ubbp-1 and Ubbp-2 fluoresce at room temperature.

Adelani, Pius O.; Albrecht-Schmitt, Thomas E.

2011-09-01

380

The uranyl ion revisited: the electric field gradient at U as a probe of environmental effects  

NASA Astrophysics Data System (ADS)

The experimental electric field gradient (EFG) at the U nucleus in uranyl is positive. It has been pointed out by Pyykk that this could be a signature of a hole in the 6p shell induced by the strong bonding to the axial O atoms. We have revisited this issue with the help of relativistic density functional calculations, including accurate ZORA-4 calculations of the EFG. We confirm the existence of a 6p hole, with a positive contribution to the EFG, but we still find the EFG in the free uranyl ion to be negative due to the non-spherical electron distribution in the valence 5f shell caused by the bonding to the oxygens. A positive EFG only results in our calculations from the effect of the crystal environment of the uranyl ion, i.e. the coordination of three nitrate groups in the equatorial plane. Again the extended nature of 6p plays a key role, with an important positive contribution to the EFG coming from 6p tails in the high-lying electron pair orbitals of the closed shell nitrate ligands due to the orthogonality requirement. A further contribution comes from electron donation by the nitrate groups into the U 5? and 6d? orbitals which both have their lobes in the equatorial plane. Our findings highlight the sensitivity of the EFG to the environment, through effects on the upper valence electronic structure.

Belanzoni, Paola; Baerends, Evert Jan; van Lenthe, Erik

381

Engineering and Coordination of Regulatory Networks and Intracellular Complexes to Maximize Hydrogen Production by Phototrophic Microorganisms  

SciTech Connect

This project is a collaboration with F. R. Tabita of Ohio State. Our major goal is to understand the factors and regulatory mechanisms that influence hydrogen production. The organisms to be utilized in this study, phototrophic microorganisms, in particular nonsulfur purple (NSP) bacteria, catalyze many significant processes including the assimilation of carbon dioxide into organic carbon, nitrogen fixation, sulfur oxidation, aromatic acid degradation, and hydrogen oxidation/evolution. Our part of the project was to develop a modeling technique to investigate the metabolic network in connection to hydrogen production and regulation. Organisms must balance the pathways that generate and consume reducing power in order to maintain redox homeostasis to achieve growth. Maintaining this homeostasis in the nonsulfur purple photosynthetic bacteria is a complex feat with many avenues that can lead to balance, as these organisms possess versatile metabolic capabilities including anoxygenic photosynthesis, aerobic or anaerobic respiration, and fermentation. Growth is achieved by using H{sub 2} as an electron donor and CO{sub 2} as a carbon source during photoautotrophic and chemoautotrophic growth, where CO{sub 2} is fixed via the Calvin-Benson-Bassham (CBB) cycle. Photoheterotrophic growth can also occur when alternative organic carbon compounds are utilized as both the carbon source and electron donor. Regardless of the growth mode, excess reducing equivalents generated as a result of oxidative processes, must be transferred to terminal electron acceptors, thus insuring that redox homeostasis is maintained in the cell. Possible terminal acceptors include O{sub 2}, CO{sub 2}, organic carbon, or various oxyanions. Cells possess regulatory mechanisms to balance the activity of the pathways which supply energy, such as photosynthesis, and those that consume energy, such as CO{sub 2} assimilation or N{sub 2} fixation. The major route for CO{sub 2} assimilation is the CBB reductive pentose phosphate pathway, whose key enzyme is ribulose 1,5-biphosphate carboxylase/oxygenase (RubisCO). In addition to providing virtually all cellular carbon during autotrophic metabolism, RubisCO-mediated CO{sub 2} assimilation is also very important for nonsulfur purple photosynthetic bacteria under photoheterotrophic growth conditions since CO{sub 2} becomes the major electron sink under these conditions. In this work, Ensemble Modeling (EM) was developed to examine the behavior of CBB-compromised RubisCO knockout mutant strains of the nonsulfur purple photosynthetic bacterium Rhodobacter sphaeroides. Mathematical models of metabolism can be a great aid in studying the effects of large perturbations to the system, such as the inactivation of RubisCO. Due to the complex and highly-interconnected nature of these networks, it is not a trivial process to understand what the effect of perturbations to the metabolic network will be, or vice versa, what enzymatic perturbations are necessary to yield a desired effect. Flux distribution is controlled by multiple enzymes in the network, often indirectly linked to the pathways of interest. Further, depending on the state of the cell and the environmental conditions, the effect of a perturbation may center around how it effects the carbon flow in the network, the balancing of cofactors, or both. Thus, it is desirable to develop mathematical models to describe, understand, and predict network behavior. Through the development of such models, one may gain the ability to generate a set of testable hypotheses for system behavior.

James C. Liao

2012-05-22

382

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

383

Expanding the crystal chemistry of actinyl peroxides: open sheets of uranyl polyhedra in Na5[(UO2)3(O2)4(OH)3](H2O)13.  

PubMed

A uranyl peroxide, Na5[(UO2)3(O2)4(OH)3](H2O)13, with an open sheet of uranyl polyhedra has been synthesized under ambient conditions and structurally characterized. The structure (orthorombic, Cmca, a = 23.632(1) A, b = 15.886(1) A, c = 13.952(1) A, V = 5237.7 A(3), and Z = 8) consists of sheets composed of two symmetrically unique uranyl (UO2)2+ ions that are coordinated equatorially by two peroxide groups and two OH(-) groups, forming distorted uranyl hexagonal bipyramids of composition (UO2)(O2)2(OH)2(4-). The uranyl bipyramids are connected into sheets with openings with dimensions 13.7 A along [010] and 15.9 A along [100]. The shortest dimension of the cavity is 8.08 A. Sheets of two-dimensionally polymerized uranyl polyhedra are the most common structural type of inorganic uranyl phases; however, such an open topology has never been observed. PMID:16878908

Kubatko, Karrie-Ann; Burns, Peter C

2006-08-01

384

Noble gas-transition-metal complexes: coordination of VO2 and VO4 by Ar and Xe atoms in solid noble gas matrixes.  

PubMed

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that vanadium oxides, VO2 and VO4, coordinate noble gas atoms in forming noble gas complexes. The results showed that VO2 coordinates two Ar or Xe atoms and that VO4 coordinates one Ar or Xe atom in solid noble gas matrixes. Hence, the VO2 and VO4 molecules trapped in solid noble gas matrixes should be regarded as the VO2(Ng)2 and VO4(Ng) (Ng = Ar or Xe) complexes. The total V-Ng binding energies were predicted to be 12.8, 18.2, 5.0, and 7.3 kcal/mol, respectively, for the VO2(Ar)2, VO2(Xe)2, VO4(Ar), and VO4(Xe) complexes at the CCSD(T)//B3LYP level of theory. PMID:16451016

Zhao, Yanying; Gong, Yu; Chen, Mohua; Zhou, Mingfei

2006-02-01

385

A tetra-coordinate nickel(II) complex as neutral carrier for nitrate-selective PVC membrane electrode.  

PubMed

The potentiometric response properties and applications of a tetra-coordinate nickel(II) complex with relatively high selectivity toward nitrate ion are described. The nickel(II) complex of 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,6,11,13-tetraene was used as a neutral carrier into plasticized poly(vinyl chloride) (PVC) membrane. The influence of several variables was investigated in order to optimize the potentiometric response and selectivity of the electrode. The resulting membrane electrode incorporating 31.0% PVC, 61.0% dioctyl phthalate (DOP) as plasticizer, 3% methyltrioctylammonium chloride (MTOAC) as a cationic additive and 5% carrier (all w/w) demonstrates a Nernstian response slope of -59.6 mV per decade over the concentration range of 5 x 10(-6)-1 x 10(-1) M NO(3)(-). The electrode exhibits a fast response time (< or =10 s), a detection limit of 2.5x10(-6) M, and can be used over a wide pH range of 4-12. The electrode shows improved selectivity in comparison to most of the previously reported nitrate-selective electrodes. It was successfully applied to the determination of nitrate ion in natural water samples. PMID:18969218

Asghari, Ali Reza; Amini, Mohammad Kazem; Mansour, Hassan Rahimi; Salavati-Niasari, Masoud

2003-11-12

386

Behaviors of acrylamide/itaconic acid hydrogels in uptake of uranyl ions from aqueous solutions  

SciTech Connect

In this study, adsorptions of uranyl ions from two different aqueous uranyl solutions by acrylamide-itaconic acid hydrogels were investigated by a spectroscopic method. The hydrogels were prepared by irradiating with {gamma}-radiation. In the experiment of uranyl ions adsorption, Type II adsorption was found. One gram of acrylamide-itaconic acid hydrogels sorbed 178-219 mg uranyl ions from the solutions of uranyl acetate, 42-76 mg uranyl ions from the aqueous solutions of uranyl nitrate, while acrylamide hydrogel did not sorb any uranyl ion. For the hydrogel containing 40 mg of itaconic acid and irradiated to 3.73 kGy, swelling of the hydrogels was observed in water (1660%), in the aqueous solution of uranyl acetate (730%), and in the aqueous solution of uranyl nitrate (580%). Diffusions of water onto hydrogels were a non-Fickian type of diffusion, whereas diffusions of uranyl ions were a Fickian type of diffusion.

Karadag, E.; Saraydin, D. [Cumhuriyet Univ., Sivas (Turkey); Gueven, O. [Hacettepe Univ., Ankara (Turkey)

1995-12-01

387

Syntheses and structures of uranyl ethylenediphosphonates: from layers to elliptical nanochannels.  

PubMed

A family of uranium diphosphonates have been hydrothermally synthesized through the reaction of ethylenediphosphonic acid (EDP, H4L) and uranyl nitrate/zinc uranyl acetate in the presence of organic templates, such as tetraethyl ammonium (NEt4(+)), 4,4'-bipyridine (bipy), and 1,10-phenanthroline (phen). The UO2(2+) in UO2(H2O)(H2L)(EDP-U1) is equatorially five-coordinated by four phosphonate groups and one aqua ligand, forming a pentagonal bipyramid. Each EDP ligand is doubly protonated and chelates three UO2(2+), resulting in a layered structure. Compounds (NEt4)2(UO2)3(HL)2(H2L)4H2O (EDP-U2) and (H2bipy)UO2L (EDP-U3) have the same layered structure in which NEt4(+) and protonated bipy fill in the uranyl-phosphonate interlayers, respectively, and play a role to balance the negative charges. Different from that in EDP-U1, the UO2(2+) exists in the form of a UO6 tetragonal bipyramid and is surrounded by four different EDP ligands in EDP-U2 and EDP-U3. (Hphen)2(UO2)2(H2L)3 (EDP-U4) features a three-dimensional framework structure with large elliptical channels along the c axis (1.3 1.1 nm(2)). Monoprotonated phen molecules fill in these channels and hold together through strong ?? interactions. All of the four compounds have been characterized by IR and photoluminescent spectroscopy. Their characteristic emissions have been attributed as transition properties of uranyl cations. The ion-exchange study indicates that [Co(en)3](3+) could partially replace the protonated phen molecules. PMID:23701415

Tian, Tao; Yang, Weiting; Wang, Hao; Dang, Song; Pan, Qing-Jiang; Sun, Zhong-Ming

2013-05-23

388

Complex Frequency Shifted PML Auxiliary Differential Equation Implementation for Seismic Wave Modeling in Cartesian, Spherical and General Curvilinear Coordinates  

NASA Astrophysics Data System (ADS)

The perfectly matched layer (PML) has been widely used in seismic wave modeling to absorb waves at nonphysical boundaries surrounding the computational domain. The traditional PML performs poorly in absorbing low-frequency waves, evanescent waves or waves at grazing incidence. By using a complex frequency-shifted (CFS) stretching function, the Convolutional-PML (C-PML) has proven to be more efficient under these circumstances. However, updating the auxiliary memory variables in the CFS C-PML involves convolution operators and needs an algorithm different from the numerical scheme used in the interior domain. We propose an alternative unsplit-field CFS PML implementation using auxiliary differential equations (ADE) to update the auxiliary memory variables. Equations of the CFS ADE-PML are all first-order differential equations and do not involve convolution or integral terms. The same numerical scheme used in the interior domain can be used to solve the CFS ADE-PML equations, and is thus straightforward to use with a higher-order time matching scheme. The memory requirement is the same as the CFS C-PML, one memory variable for each derivative. The CFS ADE-PML can be implemented as a perturbation to the original wave equations on each face of the computational domain and does not require tracking the indexes of the edges or corners. At the free surface, the CFS ADE-PML equations are derived taking the free surface boundary condition into account, which is crucial to effectively absorb surface waves when the free surface coincides with the normal stress components in the staggered-grid finite-difference method. The parameters of the CFS stretching function contribute to an effective wave speed decrease in the normal direction of the PML layer and a frequency dependent damping in the PML layer. Our numerical tests indicate the optimal parameters lead to the effective shortest wavelength in the PML layer to twice or triple the cell size. In spherical and general curvilinear coordinates, the ADE CFS-PML can be implemented by mapping to a local orthogonal coordinate and correct the original equations along normal direction. Numerical tests indicate the efficacy of the ADE CFS-PML and stable solution can be obtained in spherical and general curvilinear coordinates.

Zhang, W.; Shen, Y.

2009-12-01

389

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

390

Macrocyclic hexacarboxylic acid. A highly selective host for uranyl ion  

Microsoft Academic Search

Previously a macrocyclic hexaketone which effectively bound uranyl ion was prepared succesfully. Recently, two types of ligand of macrocyclic hexacarboxylic acid were prepared by symmetrically arranging six carboxylates on a macrocyclic skeleton in which the ring size was adjusted to give a cavity to accommodate uranyl ion comfortably. Three of six carboxylates seem to compose a binding site. One of

Iwao Tabushi; Yoshiaki Kobuke; Kiyoto Ando; Masanari Kishimoto; Eiichi Ohara

1980-01-01

391

Bases for DOT exemption uranyl nitrate solution shipments  

Microsoft Academic Search

Uranyl nitrate solutions from a Savannah River Plant reprocessing facility have been transported in cargo tank trailers for more than 20 years without incident during transit. The solution is shipped to Oak Ridge for further processing and returned to SRP in a solid metal form for recycle. This solution, called uranyl nitrate hexahydrate (UNH) solution in Department of Transportation (DOT)

1982-01-01

392

Conformations, structural transitions and visible near-infrared absorption spectra of four-, five- and six-coordinated Cu(II) aqua complexes.  

PubMed

We have performed Car-Parrinello molecular dynamics simulations at ambient conditions for four-, five- and six-coordinated Cu(II) aqua complexes. The molecular geometry has been investigated in terms of Cu-O, Cu-H bond lengths and O-Cu-O bond angles and compared with earlier experimental measurement results and theoretical calculations. We find that the average Cu-O and Cu-H bond lengths increase with increasing coordination number. We have also observed relatively faster structural transition in the case of five-coordinated complex between trigonal bipyramidal and square pyramidal geometry. This result deviates from the findings of the earlier report (A. Pasquarello et al., Science, 2001, 291, 856) on copper(II) in aqueous solution and we attribute these differences to the neglect of solvent environment in our calculations. The averaged absorption spectra for the copper(II) aqua complexes have been computed using spin-restricted density functional linear response formalism taking 100 snap shots from a trajectory of 0.48 ps. We find that the calculated spectra are significantly different, showing clear features that distinguish each coordination model. Comparison with the experimentally reported absorption spectra is made wherever it is possible and the results obtained favor the distorted fivefold-coordination arrangement for the molecular structure of the Cu(II) ion in aqueous solution. PMID:19283268

de Almeida, Katia Jlia; Murugan, N Arul; Rinkevicius, Zilvinas; Hugosson, Hkan Wilhelm; Vahtras, Olav; Agren, Hans; Cesar, Amary

2008-11-06

393

Role of the uranyl oxo group as a hydrogen bond acceptor.  

PubMed

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(2)(OH(2))(5)](2+) species, they are attracted to the oxo groups in [UO(2)(OH(2))(2)(NO(3))(2)](0), [UO(2)(NO(3))(3)](-), and [UO(2)Cl(4)](2-) species. Hydrogen bond strength depends on the equatorial ligation and can exceed 15 kcal mol(-1). The results also reveal the existence of directionality at the uranyl oxo acceptor, with a weak preference for linear U?O---H angles. PMID:21291200

Watson, Lori A; Hay, Benjamin P

2011-02-03

394

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

395

MOLECULAR SPECTROSCOPY OF ANHYDROUS URANYL SALTS. III. SPECTROSCOPIC CHARACTERISTICS OF ANHYDROUS AND HEXAHYDRATE URANYL NITRATE  

Microsoft Academic Search

A comparison was made of the absorption spectra of hexahydrate and ; anhydrous uranyl nitrate in dioxane, acetone, and formamide, and it was found ; that the transition energies change in a characteristic manner. Hypsochromic ; shifts occurred in going from the hydrated to the anhydrous salt, the largest in ; dioxane amounting to 538 cm⁻¹. The vibrational structure was

B. Jezowska-Trzebiatowska; A. Bartecki; B. Kedzia

1962-01-01

396

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

2013-01-01

397

Kinetics of triscarbonato uranyl reduction by aqueous ferrous iron: a theoretical study.  

PubMed

Uranium is a pollutant whose mobility is strongly dependent on its oxidation state. While U(VI) in the form of the uranyl cation is readily reduced by a range of natural reductants, by contrast complexation of uranyl by carbonate greatly reduces its reduction potential and imposes increased electron transfer (ET) distances. Very little is known about the elementary processes involved in uranium reduction from U(VI) to U(V) to U(IV) in general. In this study, we examine the theoretical kinetics of ET from ferrous iron to triscarbonato uranyl in aqueous solution. A combination of molecular dynamics (MD) simulations and density functional theory (DFT) electronic structure calculations is employed to compute the parameters that enter into Marcus' ET model, including the thermodynamic driving forces, reorganization energies, and electronic coupling matrix elements. MD simulations predict that two ferrous iron atoms will bind in an inner-sphere fashion to the three-membered carbonate ring of triscarbonato uranyl, forming the charge-neutral ternary Fe(2)UO(2)(CO(3))(3)(H(2)O)(8) complex. Through a sequential proton-coupled electron-transfer mechanism (PCET), the first ET step converting U(VI) to U(V) is predicted by DFT to occur with an electronic barrier that corresponds to a rate on the order of approximately 1 s(-1). The second ET step converting U(V) to U(IV) is predicted to be significantly endergonic. Therefore, U(V) is a stabilized end product in this ET system, in agreement with experiment. PMID:16884201

Wander, Matthew C F; Kerisit, Sebastien; Rosso, Kevin M; Schoonen, Martin A A

2006-08-10

398

Coordination chemistry of heterocycle-functionalized diazamesocycles: tuning the productive Ni II complexes through altering the pendants of ligands  

Microsoft Academic Search

In order to further understand the coordination chemistry of diazamesocyclic systems, a series of mononuclear NiII complexes with 1,4-diazacycloheptane (DACH) functionalized by additional imidazole or pyridine donor pendants, including [NiL1](ClO4)2H2O (1), [NiL1Cl](ClO4) (2), [NiL2Cl](ClO4)CH3OH (3), [NiL2Cl][NiL2](ClO4)3 (4) and [NiL3](ClO4)2 (5), where L1=1,4-bis(N-1-methylimidazol-2-yl-methyl)-1,4-diazacycloheptane, L2=1,4-bis(pyridyl-2-yl-methyl)-1,4-diazacycloheptane, and L3=1,4-bis-(imidazol-4-yl-methyl)-1,4-diazacycloheptane, have been prepared and characterized. A detailed study on the solid structures and solution spectra

Ya-Mei Guo; Miao Du; Xian-He Bu

2005-01-01

399

Arf6 coordinates actin assembly through the WAVE complex, a mechanism usurped by Salmonella to invade host cells.  

PubMed

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 Arf1-WRC 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. PMID:24085844

Humphreys, Daniel; Davidson, Anthony C; Hume, Peter J; Makin, Laura E; Koronakis, Vassilis

2013-10-01

400

Paramagnetic 3d coordination complexes involving redox-active tetrathiafulvalene derivatives: an efficient approach to elaborate multi-properties materials.  

PubMed

The elaboration of multifunctional materials is a great challenge for the physical chemistry community and the studies of molecular materials exhibiting coexistence or synergy between two or more properties are very active. In particular, molecular compounds displaying electrical conductivity and magnetic interactions are currently the subject of intensive studies. Two approaches are now well-known and are explored. On the one hand, the interactions between mobile electrons of the organic network (? electrons) and localized electrons of paramagnetic transition metal (d electrons) take place through space. On the other hand, these interactions take place through covalent chemical bonds. In the latter, the probability to have significant interaction between ? and d electrons is enhanced compared to the first approach. In this perspective article, we will give an overview of the known coordination complexes involving tetrathiafulvalene derivatives as ligands for paramagnetic 3d ions and we will describe their physical properties. If necessary, the coexistence or synergy between electrical conductivity, magnetism and other properties will be highlighted. PMID:23208602

Pointillart, Fabrice; Golhen, Stphane; Cador, Olivier; Ouahab, Lahcne

2013-02-14

401

Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation  

NASA Astrophysics Data System (ADS)

In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, '2-line' Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0-50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH) 6 octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe-O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 for Fe-O, 3.03 for Fe-Fe1, and 3.45 for Fe-Fe2. Likewise, citrate had no effect on the As-Fe (3.31 ) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear ( 2C) As(V) surface complexes and (ii) combinations of 2C, monodentate mononuclear ( 1V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing 1V/ 2C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3-6.6, I 0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios ?25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.

Mikutta, Christian; Frommer, Jakob; Voegelin, Andreas; Kaegi, Ralf; Kretzschmar, Ruben

2010-10-01

402

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

2013-03-25

403

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

404

A New Family of Multiferrocene Complexes with Enhanced Control of Structure and Stoichiometry via Coordination-Driven Self-Assembly and their Electrochemistry  

PubMed Central

The design and synthesis of a new family of multiferrocene complexes with enhanced control of structure and stoichimetry via coordination-driven self-assembly is described. Insight into the structure and electronic properties of all supramolecules was obtained by electrochemical studies. The collective results provide an enhanced understanding of the influence of structural factors on the electrochemistry of multifunctional electroactive supramolecular architectures.

Yang, Hai-Bo; Ghosh, Koushik; Zhao, Yue; Northrop, Brian H.; Lyndon, Matthew M.; Muddiman, David C.; White, Henry S.; Stang, Peter J.

2008-01-01

405

Influence of carbonate complexes on uranium migration through abyssal red clays  

SciTech Connect

Diffusion experiments have been conducted to study the interactions between uranyl carbonate complexes and abyssal red clays. Experimental results indicate that in pH 8.8 solutions containing high concentrations of bicarbonate, uranyl carbonate complexes migrate rapidly through the clay samples. At lower pH values and bicarbonate concentrations, the uranyl carbonate complexes are converted to uranyl hydroxide complexes which are strongly sorbed by the clays and do not migrate. A competitive equilibrium model has been developed which explains these results, and which can be used to define the chemical environments in which uranium migration through the red clays should be rapid. 10 references.

Bunker, B.C.; Erickson, K.L.

1983-09-01

406

SEPARATION OF URANYL NITRATE BY EXTRACTION  

DOEpatents

A process is presented for obtaining U/sup 233/ from solutions containing Pa/sup 233/. A carrier precipitate, such as MnO/sub 2/, is formed in such solutions and carries with it the Pa/sup 233/ present. This precipitate is then dissolved in nitric acid and the solution is aged to allow decay of the Pa/ sup 233/ into U/sup 233/. After a sufficient length of time the U/sup 233/ bearing solution is made 2.5 to 4.5 Molar in manganese nitrate by addition thereof, and the solution is then treated with ether to obtain uranyl nitrate by solvent extraction techniques.

Stoughton, R.W.; Steahly, F.L.

1958-08-26

407

Cryoscopic Studies of the Uranyl SulfateWater, Uranyl NitrateWater, and Uranyl NitrateNitric AcidWater Systems  

Microsoft Academic Search

Freezing point lowerings of aqueous solutions of uranyl sulfate in the concentration range m = 0.40 mol-kg-1 and the activity and osmotic coefficients, which were calculated using the Pitzer equations for 2:2 electrolytes, are presented. Crystallization temperatures are reported for 0 to 13 molar nitric acid and 10150 g uranium per liter uranyl nitratenitric acidwater solutions.

Alexander Apelblat

1999-01-01

408

Carbonate formation within a nickel dimer: synthesis of a coordinatively unsaturated bis(mu-hydroxo) dinickel complex and its reactivity toward carbon dioxide.  

PubMed

The tridentate aminopyridine ligand bearing a bulky tert-butyl substituent at the amine nitrogen, tert-butyl-dipicolylamine (tBuDPA), occupies three coordination sites in six-coordinate complexes of nickel(ii), leaving the remaining three sites available for additional ligand binding and activation. New crystallographically characterized complexes include two mononuclear species with 1:1 metal:ligand complexation: a trihydrate solvate (1.3H(2)O) and a monohydrate biacetonitrile solvate (1.H(2)O.2CH(3)CN). Complexation in the presence of sodium hydroxide results in a bis(mu-hydroxo) complex (2), the bridging hydroxide anions of which are labile and become displaced by methoxide anions in methanol solvent, affording bis-methoxo-bridged (4). Nickel(II) centers in 2 are five-coordinate and antiferromagnetically coupled (with J = -31.4(5) cm(-1), H = -2JS(1)S(2), in agreement with Ni-O-Ni angle of 103.7 degrees). Bridging hydroxide or alkoxide anions in coordinatively unsaturated dinuclear nickel(II) complexes with tBuDPA react as active nucleophiles. 2 readily performs carbon dioxide fixation, resulting in the formation of a bis(mu-carbonato) tetrameric complex (3), which features a novel binding geometry in the form of an inverted butterfly-type nickel-carbonate core. Temperature-dependent magnetic measurements of tetranuclear carbonato-bridged revealed relatively weak antiferromagnetic coupling (J(1) = -3.1(2) cm(-1)) between the two nickel centers in the core of the cluster, as well as weak antiferromagnetic pairwise interactions (J(2) = J(3) = -4.54(5) cm(-1)) between central and terminal nickel ions. PMID:20179843

Wikstrom, Jeffrey P; Filatov, Alexander S; Mikhalyova, Elena A; Shatruk, Michael; Foxman, Bruce M; Rybak-Akimova, Elena V

2010-01-20

409

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

2013-06-07

410