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1

Variable Denticity in Carboxylate Binding to the Uranyl Coordination Complexes  

SciTech Connect

Tris-carboxylate complexes of the uranyl [UO2]2+ cation with acetate and benzoate were generated using electrospray ionization mass spectrometry, and then isolated in a Fourier transform ion cyclotron resonance mass spectrometer. Wavelength-selective infrared multiple photon dissociation (IRMPD) of the tris-acetatouranyl anion resulted in a redox elimination of an acetate radical, which was used to generate an IR spectrum that consisted of six prominent absorption bands. These were interpreted with the aid of density functional theory calculations in terms of a symmetric and antisymmetric CO2 stretches of both the monodentate and bidentate acetate, CH3 bending and umbrella vibrations, and a uranyl OUO asymmetric stretch. The comparison of the calculated and measured IR spectra indicated that the tris-acetate complex contained two acetate ligands bound in a bidentate fashion, while the third acetate was monodentate. In similar fashion, the tris-benzoate uranyl anion was formed and photodissociated by loss of a benzoate radical, enabling measurement of the infrared spectrum that was in close agreement with that calculated for a structure containing one monodentate, and two bidentate benzoate ligand.

G. S. Groenewold; W. A. de Jong; J. Oomens; M. J. van Stipdonk

2010-05-01

2

Variable Denticity in Carboxylate Binding to the Uranyl Coordination Complexes  

SciTech Connect

Tris-carboxylate complexes of the uranyl [UO2]2+ cation with acetate and benzoate were generated using electrospray ionization mass spectrometry, and then isolated in a Fourier transformion cyclotron resonance mass spectrometer. Wavelength-selective infrared multiple photon dissociation (IRMPD) of the tris-acetatouranyl anion resulted in a redox elimination of an acetate radical, which was used to generate an IR spectrum that consisted of six prominent absorption bands. These were interpreted with the aid of density functional theory calculations in terms of symmetric and antisymmetric -CO2 stretches of both the monodentate and bidentate acetate, CH3 bending and umbrella vibrations, and a uranyl O-U-O asymmetric stretch. The comparison of the calculated and measured IR spectra indicated that the tris-acetate complex contained two acetate ligands bound in a bidentate fashion, while the third acetate was monodentate. In similar fashion, the tris-benzoate uranyl anion was formed and photodissociated by loss of a benzoate radical, enabling measurement of the infrared spectrum that was in close agreement with that calculated for a structure containing one monodentate, and two bidentate benzoate ligands.

Groenewold, G. S.; De Jong, Wibe A.; Oomens, Jos; Van Stipdonk, Michael J.

2010-05-01

3

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

4

Alkali-metal ion coordination in uranyl(VI) poly-peroxide complexes in solution. Part 1: the Li?, Na? and K?--peroxide-hydroxide systems.  

PubMed

The alkali metal ions Li(+), Na(+) and K(+) have a profound influence on the stoichiometry of the complexes formed in uranyl(VI)-peroxide-hydroxide systems, presumably as a result of a templating effect, resulting in the formation of two complexes, M[(UO2)(O2)(OH)]2(-) where the uranyl units are linked by one peroxide bridge, ?-?(2)-?(2), with the second peroxide coordinated "end-on", ?(2), to one of the uranyl groups, and M[(UO2)(O2)(OH)]4(3-), with a four-membered ring of uranyl ions linked by ?-?(2)-?(2) peroxide bridges. The stoichiometry and equilibrium constants for the reactions: M(+) + 2UO2(2+) + 2HO2(-) + 2H2O ? M[(UO2)(O2)(OH)]2(-) + 4H(+) (1) and M(+) + 4UO2(2+) + 4HO2(-) + 4H2O ? M[(UO2)(O2)(OH)]4(3-) + 8H(+) (2) have been measured at 25 C in 0.10 M (tetramethyl ammonium/M(+))NO3 ionic media using reaction calorimetry. Both reactions are strongly enthalpy driven with large negative entropies of reaction; the observation that ?H(2) ? 2?H(1) suggests that the enthalpy of reaction is approximately the same when peroxide is added in bridging and "end-on" positions. The thermodynamic driving force in the reactions is the formation of strong peroxide bridges and the role of M(+) cations is to provide a pathway with a low activation barrier between the reactants and in this way "guide" them to form peroxide bridged complexes; they play a similar role as in the synthesis of crown-ethers. Quantum chemical (QC) methods were used to determine the structure of the complexes, and to demonstrate how the size of the M(+)-ions affects their coordination geometry. There are several isomers of Na[(UO2)(O2)(OH)]2(-) and QC energy calculations show that the ones with a peroxide bridge are substantially more stable than the ones with hydroxide bridges. There are isomers with different coordination sites for Na(+) and the one with coordination to the peroxide bridge and two uranyl oxygen atoms is the most stable one. PMID:25286234

Zanonato, Pier Luigi; Di Bernardo, Plinio; Vallet, Valerie; Szab, Zoltn; Grenthe, Ingmar

2015-01-28

5

Sterically congested uranyl complexes with seven-coordination of the UO2 unit: the peculiar ligation mode of nitrate in [UO2(NO3)2(Rbtp)] complexes.  

PubMed

Addition of 1 or 2 molar equiv of Rbtp [Rbtp = 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine; R = Me, Pr ( n )] to UO 2(OTf) 2 in anhydrous acetonitrile gave the neutral compounds [UO 2(OTf) 2(Rbtp)] [R = Me ( 1), ( n )Pr ( 2)] and the cationic complexes [UO 2(Rbtp) 2][OTf] 2 [R = Me ( 3), Pr ( n ) ( 4)], respectively. No equilibrium between the mono and bis(Rbtp) complexes or between [UO 2(Rbtp) 2][OTf] 2 and free Rbtp in acetonitrile was detected by NMR spectroscopy. The crystal structures of 1 and 3 resemble those of their terpyridine analogues, and 3 is another example of a uranyl complex with the uranium atom in the unusual rhombohedral environment. In the presence of 1 molar equiv of Rbtp in acetonitrile, UO 2(NO 3) 2 was in equilibrium with [UO 2(NO 3) 2(Rbtp)] and the formation of the bis adduct was not observed, even with an excess of Rbtp. The X-ray crystal structures of [UO 2(NO 3) 2(Rbtp)] [R = Me ( 5), Pr ( n ) ( 6)] reveal a particular coordination geometry with seven coordinating atoms around the UO 2 fragment. The large steric crowding in the equatorial girdle forces the bidentate nitrate ligands to be almost perpendicular to the mean equatorial plane, inducing bending of the UO 2 fragment. The dinuclear oxo compound [U(CyMe 4btbp) 2(mu-O)UO 2(NO 3) 3][OTf] ( 7), which was obtained fortuitously from a 1:2:1 mixture of U(OTf) 4, CyMe 4btbp, and UO 2(NO 3) 2 [CyMe 4btbp = 6,6'-bis-(3,3,6,6-tetramethyl-cyclohexane-1,2,4-triazin-3-yl)-2,2'-bipyridine] is a very rare example of a mixed valence complex involving covalently bound U (IV) and U (VI) ions; its crystal structure also exhibits a seven coordinate uranyl moiety, with one bidentate nitrate group almost parallel to the UO 2 fragment. The distinct structural features of [UO 2(kappa (2)-NO 3) 2(Mebtp)], with its high coordination number and a noticeable bending of the UO 2 fragment, and of [UO 2(kappa (2)-NO 3)(kappa (1)-NO 3)(terpy)], which displays a classical geometry, were analyzed by Density Functional Theory, considering the bonding energy components and the molecular orbitals involved in the interaction between the uranyl, nitrate, and Mebtp or terpy moieties. The unusual geometry of the Mebtp derivative with the seven coordinating atoms around the UO 2 fragment was found very stable. In both the Mebtp and terpy complexes, the origin of the interaction appears to be primarily steric (Pauli repulsion and electrostatic); this term represents 62-63% of the total bonding energy while the orbital term contributes to about 37-38%. PMID:18582036

Berthet, Jean-Claude; Thury, Pierre; Dognon, Jean-Pierre; Guillaneux, Denis; Ephritikhine, Michel

2008-08-01

6

Synthesis of thorium (uranyl) sulfoxide complexes and crystal structure of novel thorium complex containing both 10 and 12 coordinated thorium  

NASA Astrophysics Data System (ADS)

Two complexes [Th(NO 3) 3(dchso) 4][Th(NO 3) 5(dchso) 2] ( 1) and [UO 2(NO 3) 2(dchso) 2] ( 2) (dchso=dicyclohexyl sulfoxide) have been synthesized and characterized. The crystal structure of [Th(NO 3) 3(dchso) 4][Th(NO 3) 5(dchso) 2] ( 1) has been determined. The X-ray analysis reveals that 1 contains [Th(NO 3) 3(dchso) 4] + cations and [Th(NO 3) 5(dchso) 2] - anions. In the cations, the Th atom has a coordination number 10 with irregular polyhedron involving six oxygen atoms from three bidentate nitrate groups and four oxygen atoms from the four dchso ligands. In the anions, the Th atoms have a coordination number 12 with icosahedron involving 10 oxygen atoms from five bidentate nitrate groups and two oxygen atoms from the two dchso ligands.

Zhu, Liming; Zhu, Xia; Zhang, Yuping; Li, Baolong; Cao, Zhengbai; Zhang, Yong

2003-09-01

7

Synthesis of thorium (uranyl) sulfoxide complexes and crystal structure of novel thorium complex containing both 10 and 12 coordinated thorium  

Microsoft Academic Search

Two complexes [Th(NO3)3(dchso)4][Th(NO3)5(dchso)2] (1) and [UO2(NO3)2(dchso)2] (2) (dchso=dicyclohexyl sulfoxide) have been synthesized and characterized. The crystal structure of [Th(NO3)3(dchso)4][Th(NO3)5(dchso)2] (1) has been determined. The X-ray analysis reveals that 1 contains [Th(NO3)3(dchso)4]+ cations and [Th(NO3)5(dchso)2]? anions. In the cations, the Th atom has a coordination number 10 with irregular polyhedron involving six oxygen atoms from three bidentate nitrate groups and four

Liming Zhu; Xia Zhu; Yuping Zhang; Baolong Li; Zhengbai Cao; Yong Zhang

2003-01-01

8

Uranyl-halide complexation in N,N-dimethylformamide: halide coordination trend manifests hardness of [UO2]2+.  

PubMed

Complexation of [UO2](2+) with Cl(-), Br(-), and I(-) in N,N-dimethylformamide (DMF) was studied by UV-vis absorption spectroscopy and extended X-ray absorption fine structure (EXAFS) to clearly differentiate halide coordination strengths to [UO2](2+). In the Cl(-) system, it was clarified that the Cl(-) coordination to [UO2](2+) in DMF proceeds almost quantitatively. The coordination number of Cl(-) almost quantitatively increases up to 4, i.e., the limiting complex is [UO2Cl4](2-). Logarithmic gross stability constants of [UO2Cl(x)](2-x) (x = 1-4) were evaluated as log ?1 = 9.67, log ?2 = 15.49, log ?3 = 19.89, and log ?4 = 24.63 from UV-vis titration experiments. The EXAFS results well demonstrated not only the Cl(-) coordination, but also the DMF solvation in the equatorial plane of [UO2](2+). The interaction of Br(-) and I(-) with [UO2](2+) in DMF was also investigated. As a result, the Br(-) coordination to [UO2](2+) stops at the second step, i.e., only [UO2Br](+) and UO2Br2 were observed. The molecular structure of each occurring species was confirmed by EXAFS. The evaluated log ?x values of [UO2Br(x)](2-x) (x = 1, 2) are 3.45 and 5.42, respectively. The much smaller log ?x than those of [UO2Cl(x)](2-x) indicates that Br(-) is a much weaker ligand to [UO2](2+) than Cl(-). The EXAFS experiments revealed that the presence of I(-) in the test solution does not modify any coordination structure around [UO2](2+). Thus, I(-) does not form any stable [UO2](2+) complexes in DMF. Consequently, the stability of the halido complexes of [UO2](2+) in DMF is exactly in line with the hardness order of halides. PMID:23877093

Takao, Koichiro; Takao, Shinobu; Ikeda, Yasuhisa; Bernhard, Gert; Hennig, Christoph

2013-09-28

9

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

PubMed

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

Riisi, Antti; Visnen, Ari; Sillanp, Reijo

2013-08-01

10

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

SciTech Connect

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

Visser, A. E.; Jensen, M. P.; Laszak, I.; Nash, K. L.; Choppin, G. R.; Roers, R. D.; Chemistry; Univ. of Alabama; Flordia State Univ.

2003-01-01

11

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

12

Thermolysis of Urea Complexes of Uranyl Nitrate  

Microsoft Academic Search

Quantitative parameters of thermolysis of uranyl nitrate urea complexes, [UO2(NO3)2{(NH2)2CO}2], [UO2(H2O){(NH2)2CO}4](NO3)2, and [UO2(H2O){(NH2)2CO}5](NO3)2 at 175, 200, and 225C were measured. Thermolysis of [UO2(NO3)2{(NH2)2CO}2] at 200C affords the biuret complex of uranyl nitrate in a 90% yield. The urea ligands in the hydrated complexes completely\\u000a transform into biuret at 175C. Thermolysis of [UO2(H2O){(NH2)2CO}5](NO3)2 yields the biuret-cyanurate complexes of uranyl nitrate. The

N. N. Kostyuk

2005-01-01

13

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

14

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

15

Photochemical water oxidation and origin of nonaqueous uranyl peroxide complexes.  

PubMed

Sunlight photolysis of uranyl nitrate and uranyl acetate solutions in pyridine produces uranyl peroxide complexes. To answer longstanding questions about the origin of these complexes, we conducted a series of mechanistic studies and demonstrate that these complexes arise from photochemical oxidation of water. The peroxo ligands are easily removed by protonolysis, allowing regeneration of the initial uranyl complexes for potential use in catalysis. PMID:24635209

McGrail, Brendan T; Pianowski, Laura S; Burns, Peter C

2014-04-01

16

Complexes of Uranyl Nitrate, Uranyl Acetate, Uranyl Thiocyanate and Uranyl Chloride with Benzoyl, Salicyloyl and Isonicotinoyl Hydrazines  

Microsoft Academic Search

Some uranyl complexes of benzoylhydrazine (BH), sali-cyloylhydrazine (MSH) and isonicotinoylhydrazine (ISH) of the type UO2 LX2nH2O (where L = BH, MSH and ISH, X = NO3, CH3COO, SCN, Cl and n = 0,1 or 2) have been prepared and characterized by analytical data, decomposition temperature, molar conductance and infrared spectral measurements down to 200 cm. The molar conductance data in

Ram A. Lal; Manindra N. Singh; Sujit Das

1986-01-01

17

Identification of Uranyl Surface Complexes an Ferrihydrite: Advanced EXAFS Data Analysis and CD-MUSIC Modeling  

Microsoft Academic Search

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

Andre? Rossberg; Kai-Uwe Ulrich; Stephan Weiss; Satoru Tsushima; Tjisse Hiemstra; Andreas C. Scheinost

2009-01-01

18

Preparation and characterization of uranyl complexes with phosphonate ligands  

Microsoft Academic Search

The preparation, spectroscopic characterization and thermal stability of neutral complexes of uranyl ion, UO2\\u000a 2+, with phosphonate ligands, such as diphenylphosphonic acid (DPhP), diphenyl phosphate (DPhPO) and phenylphosphonic acid (PhP)\\u000a are described. The complexes were prepared by a reaction of hydrated uranyl nitrate with appropriate ligands in methanolic\\u000a solution. The ligands studied and their uranyl complexes were characterized using thermogravimetric

Z. Hnatejko; S. Lis; Z. Stry?a

2010-01-01

19

Nonaqueous chemistry of uranyl complexes with tripodal ligands  

Microsoft Academic Search

The trans dioxo uranyl(VI) ion (UO22+) is remarkably stable with respect to the U=O bond, which dominates the stereochemistry of its coordination compounds in both aqueous and non-aqueous solutions. The linear O=U=O unit directs all other ligands to coordinate in an equatorial plane perpendicular to the O=U=O axis. In aqueous solution, uranyl coordination chemistry has been developed with a wide

Carol J. Burns; David L. Clark; Paul B. Duval; Brian L. Scott

2000-01-01

20

Nonaqueous chemistry of uranyl complexes with tripodal ligands  

Microsoft Academic Search

The trans dioxo uranyl(VI) ion (UO22+) is remarkably stable with respect to the U&dblbnd;O bond, which dominates the stereochemistry of its coordination compounds in both aqueous and non-aqueous solutions. The linear O&dblbnd;U&dblbnd;O unit directs all other ligands to coordinate in an equatorial plane perpendicular to the O&dblbnd;U&dblbnd;O axis. In aqueous solution, uranyl coordination chemistry has been developed with a wide

Carol J. Burns; David L. Clark; Paul B. Duval; Brian L. Scott

2000-01-01

21

Reaction of uranyl nitrate with carboxylic diacids under hydrothermal conditions. Crystal structure of complexes with l(+)-tartaric and oxalic acids  

Microsoft Academic Search

l(+)-tartaric acid reacts with uranyl nitrate in the presence of KOH, under mild hydrothermal conditions, to give the complex [UO2(C4H4O6)(H2O)] (1), the first uranyl tartrate to be crystallographically characterized. Each tartrate ligand bridges three uranyl ions, one of them in chelating fashion through proximal carboxylate and hydroxyl groups. The resulting assemblage is two-dimensional, with the uranyl pentagonal bipyramidal coordination polyhedra

Pierre Thury

2007-01-01

22

The gas-phase bis-uranyl nitrate complex [(UO2)2(NO3)5]-: infrared spectrum and structure  

SciTech Connect

The infrared spectrum of the bis-uranyl nitrate complex [(UO2)2(NO3)5]- was measured in the gas phase using multiple photon dissociation (IRMPD). Intense absorptions corresponding to the nitrate symmetric and asymmetric vibrations, and the uranyl asymmetric vibration were observed. The nitrate v3 vibrations indicate the presence of nitrate in a bridging configuration bound to both uranyl cations, and probably two distinct pendant nitrates in the complex. The coordination environment of the nitrate ligands and the uranyl cations were compared to those in the mono-uranyl complex. Overall, the uranyl cation is more loosely coordinated in the bis-uranyl complex [(UO2)2(NO3)5]- compared to the mono-complex [UO2(NO3)3]-, as indicated by a higher O-U-O asymmetric stretching (v3) frequency. However, the pendant nitrate ligands are more strongly bound in the bis-complex than they are in the mono-uranyl complex, as indicated by the v3 frequencies of the pendant nitrate, which are split into nitrosyl and O-N-O vibrations as a result of bidentate coordination. These phenomena are consistent with lower electron density donation per uranyl by the nitrate bridging two uranyl centers compared to that of a pendant nitrate in the mono-uranyl complex. The lowest energy structure predicted by density functional theory (B3LYP functional) calculations was one in which the two uranyl molecules bridged by a single nitrate coordinated in a bis-bidentate fashion. Each uranyl molecule was coordinated by two pendant nitrate ligands. The corresponding vibrational spectrum was in excellent agreement with the IRMPD measurement, confirming the structural assignment.

Groenewold, G. S.; van Stipdonk, Michael J.; Oomens, Jos; De Jong, Wibe A.; McIIwain, Michael E.

2011-12-01

23

The gas-phase bis-uranyl nitrate complex [(UO2)(2)(NO3)(5)](-): infrared spectrum and structure  

SciTech Connect

The infrared spectrum of the bis-uranyl nitrate complex [(UO{sub 2}){sub 2}(NO{sub 3}){sub 5}]{sup -} was measured in the gas phase using multiple photon dissociation (IRMPD). Intense absorptions corresponding to the nitrate symmetric and asymmetric vibrations, and the uranyl asymmetric vibration were observed. The nitrate nu3 vibrations indicate the presence of nitrate in a bridging configuration bound to both uranyl cations, and probably two distinct pendant nitrates in the complex. The coordination environment of the nitrate ligands and the uranyl cations were compared to those in the mono-uranyl complex. Overall, the uranyl cation is more loosely coordinated in the bis-uranyl complex [(UO{sub 2}){sub 2}(NO{sub 3}){sub 5}]{sup -} compared to the mono-complex [UO{sub 2}(NO{sub 3}){sub 3}]{sup -}, as indicated by a higher O-U-O asymmetric stretching (nu3) frequency. However, the pendant nitrate ligands are more strongly bound in the bis-complex than they are in the mono-uranyl complex, as indicated by the {nu}{sub 3} frequencies of the pendant nitrate, which are split into nitrosyl and O-N-O vibrations as a result of bidentate coordination. These phenomena are consistent with lower electron density donation per uranyl by the nitrate bridging two uranyl centers compared to that of a pendant nitrate in the mono-uranyl complex. The structure was calculated using density functional theory (B3LYP functional), which produced a structure in which the two uranyl molecules bridged by a single nitrate coordinated in a bis-bidentate fashion. Each uranyl molecule was coordinated by two pendant nitrate ligands. The corresponding vibrational spectrum was in excellent agreement with the IRMPD measurement, confirming the structural assignment.

Gary S. Groenewold; Michael J. van Stipdonk; Jos Oomens; Wibe de Jong; Michael E. McIlwain

2011-12-01

24

A Spectrophotometric Study on Uranyl Nitrate Complexation to 150?C  

Microsoft Academic Search

The formation constant of the mononitratouranyl complex was studied spectrophotometrically at temperatures of 25, 40, 55,\\u000a 70, 100 and 150?C (298, 313, 328, 343, 373 and 423 K). The uranyl ion concentration was fixed at approximately 0.008 mol?kg?1 and the ligand concentration was varied from 0.05 to 3.14 mol?kg?1. The uranyl nitrate complex, UO2NO3+, is weak at 298 K but

O. M. Suleimenov; T. M. Seward; J. K. Hovey

2007-01-01

25

Bonding and charge transfer in nitrogen-donor uranyl complexes: insights from NEXAFS spectra.  

PubMed

We investigate the electronic structure of three newly synthesized nitrogen-donor uranyl complexes [(UO2)(H2bbp)Cl2], [(UO)2(Hbbp)(Py)Cl], and [(UO2)(bbp)(Py)2] using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments and simulations. The complexes studied feature derivatives of the tunable tridentate N-donor ligand 2,6-bis(2-benzimidazyl)pyridine (bbp) and exhibit discrete chemical differences in uranyl coordination. The sensitivity of the N K-edge X-ray absorption spectrum to local bonding and charge transfer is exploited to systematically investigate the evolution of structural as well as electronic properties across the three complexes. A thorough interpretation of the measured experimental spectra is achieved via ab initio NEXAFS simulations based on the eXcited electron and Core-Hole (XCH) approach and enables the assignment of spectral features to electronic transitions on specific absorbing sites. We find that ligand-uranyl bonding leads to a signature blue shift in the N K-edge absorption onset, resulting from charge displacement toward the uranyl, while changes in the equatorial coordination shell of the uranyl lead to more subtle modulations in the spectral features. Theoretical simulations show that the flexible local chemistry at the nonbinding imidazole-N sites of the bbp ligand is also reflected in the NEXAFS spectra and highlights potential synthesis strategies to improve selectivity. In particular, we find that interactions of the bbp ligand with solvent molecules can lead to changes in ligand-uranyl binding geometry while also modulating the K-edge absorption. Our results suggest that NEXAFS spectroscopy combined with first-principles interpretation can offer insights into the coordination chemistry of analogous functionalized conjugated ligands. PMID:25330350

Pemmaraju, C D; Copping, Roy; Wang, Shuao; Janousch, Markus; Teat, Simon J; Tyliszcak, Tolek; Canning, Andrew; Shuh, David K; Prendergast, David

2014-11-01

26

EXAFS Study of Uranyl Complexation at Pseudomonas fluorescens Cell Surfaces  

NASA Astrophysics Data System (ADS)

Little is known about the roles of microbial biomass as a sink and source for uranium in contaminated aquifers, nor of the impact of bacterial biochemistry on uranium speciation in the subsurface. A significant role is implied by the high affinities of both Gram positive and Gram negative cells for binding uranyl (UO2{ 2+}). In the present study, Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy was used to identify membrane functional groups involved in uranyl binding to the Gram negative bacterium Pseudomonas fluorescens from pH 3 to pH 8. Throughout this pH-range, EXAFS spectra can be described primarily in terms of coordination of carboxylic groups to uranyl. U-C distances characteristic of 4-, 5- and 8- membered rings were observed, as well as the possibility of phosphato groups. Both shell-by-shell fits and principle component analyses indicate that the functional groups involved in binding of uranyl to the cell surface do not vary systematically across the pH range investigated. This result contrasts with EXAFS results of uranyl sorbed to Gram positive bacteria, and suggests an important role for long-chain carboxylate-terminated membrane functional groups in binding uranyl.

Bencheikh, R.; Bargar, J. R.; Tebo, B. M.

2002-12-01

27

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

2012-09-17

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] [Lawrence Berkeley National Lab., CA (United States); and others

1996-01-31

29

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. PMID:21396112

2011-01-01

30

Density functional study of uranyl (VI) amidoxime complexes  

NASA Astrophysics Data System (ADS)

Uranyl (VI) amidoxime complexes are investigated using relativistic density functional theory. The equilibrium structures, bond orders, and Mulliken populations of the complexes have been systematically investigated under a generalized gradient approximation (GGA). Comparison of (acet) uranyl amidoxime complexes ([UO2(AO)n]2-n, 1 <= n <= 4) with available experimental data shows an excellent agreement. In addition, the U-O(1), U-O(3), C(1)-N(2), and C(3)-N(4) bond lengths of [UO2(CH3AO)4]2- are longer than experimental data by about 0.088, 0.05, 0.1, and 0.056 . The angles of N(3)-O(3)-U, O(2)-N(1)-C(1), N(3)-C(3)-N(4), N(4)-C(3)-C(4), and C(4)-C(3)-N(3) are different from each other, which is due to existing interaction between oxygen in uranyl and hydrogen in amino group. This interaction is found to be intra-molecular hydrogen bond. Studies on the bond orders, Mulliken charges, and Mulliken populations demonstrate that uranyl oxo group functions as hydrogen-bond acceptors and H atoms in ligands act as hydrogen-bond donors forming hydrogen bonds within the complex.

Chi, Fang-Ting; Li, Peng; Xiong, Jie; Hu, Sheng; Gao, Tao; Xia, Xiu-Long; Wang, Xiao-Lin

2012-09-01

31

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

2013-05-01

32

Steric effects on uranyl complexation: synthetic, structural, and theoretical studies of carbamoyl pyrazole compounds of the uranyl(VI) ion.  

PubMed

New bifunctional pyrazole based ligands of the type [C(3)HR(2)N(2)CONR'] (where R = H or CH(3); R' = CH(3), C(2)H(5), or (i)C(3)H(7)) were prepared and characterized. The coordination chemistry of these ligands with uranyl nitrate and uranyl bis(dibenzoyl methanate) was studied with infrared (IR), (1)H NMR, electrospray-mass spectrometry (ES-MS), elemental analysis, and single crystal X-ray diffraction methods. The structure of compound [UO(2)(NO(3))(2)(C(3)H(3)N(2)CON{C(2)H(5)}(2))] (2) shows that the uranium(VI) ion is surrounded by one nitrogen atom and seven oxygen atoms in a hexagonal bipyramidal geometry with the ligand acting as a bidentate chelating ligand and bonds through both the carbamoyl oxygen and pyrazolyl nitrogen atoms. In the structure of [UO(2)(NO(3))(2)(H(2)O)(2)(C(5)H(7)N(2)CON {C(2)H(5)}(2))(2)], (5) the pyrazole ligand acts as a second sphere ligand and hydrogen bonds to the water molecules through carbamoyl oxygen and pyrazolyl nitrogen atoms. The structure of [UO(2)(DBM)(2)C(3)H(3)N(2)CON{C(2)H(5)}(2)] (8) (where DBM = C(6)H(5)COCHCOC(6)H(5)) shows that the pyrazole ligand acts as a monodentate ligand and bonds through the carbamoyl oxygen to the uranyl group. The ES-MS spectra of 2 and 8 show that the ligand is similarly bonded to the metal ion in solution. Ab initio quantum chemical studies show that the steric effect plays the key role in complexation behavior. PMID:22471744

Das, Debasish; Kannan, Shanmugaperumal; Maity, Dilip K; Drew, Michael G B

2012-04-16

33

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

2013-01-01

34

Spectroscopic study on uranyl carboxylate complexes formed at the surface layer of Sulfolobus acidocaldarius.  

PubMed

The complexation of U(vi) at the proteinaceous surface layer (S-layer) of the archaeal strain Sulfolobus acidocaldarius was investigated over a pH range from pH 1.5 to 6 at the molecular scale using time-resolved laser-induced fluorescence spectroscopy (TRLFS) and U L(III)-edge extended X-ray absorption fine structure (EXAFS). The S-layer, which represents the interface between the cell and its environment, is very stable against high temperatures, proteases, and detergents. This allowed the isolation and purification of S-layer ghosts (= empty cells) that maintain the size and shape of the cells. In contrast to many other microbial cell envelope compounds the studied S-layer is not phosphorylated, enabling the investigation of uranyl carboxylate complexes formed at microbial surfaces. The latter are usually masked by preferentially formed uranyl phosphate complexes. We demonstrated that at highly acidic conditions (pH 1.5 to 3) no uranium was bound by the S-layer. In contrast to that, at moderate acidic pH conditions (pH 4.5 and 6) a complexation of U(vi) at the S-layer via deprotonated carboxylic groups was stimulated. Titration studies revealed dissociation constants for the carboxylic groups of glutamic and aspartic acid residues of pK(a) = 4.78 and 6.31. The uranyl carboxylate complexes formed at the S-layer did not show luminescence properties at room temperature, but only under cryogenic conditions. The obtained luminescence maxima are similar to those of uranyl acetate. EXAFS spectroscopy demonstrated that U(vi) in these complexes is mainly coordinated to carboxylate groups in a bidentate binding mode. The elucidation of the molecular structure of these complexes was facilitated by the absence of phosphate groups in the studied S-layer protein. PMID:25387060

Reitz, Thomas; Rossberg, Andre; Barkleit, Astrid; Steudtner, Robin; Selenska-Pobell, Sonja; Merroun, Mohamed L

2015-02-14

35

Vibrational spectroscopic studies of uranyl complexes in aqueous and non-aqueous solutions  

NASA Astrophysics Data System (ADS)

Vibrational spectra have been obtained for aqueous solution of uranyl-perchlorates, -fluorides, -chlorides, -acetates and -sulphates over a range of solution composition with added anions. We have prepared [Bu n4N][UO 2Cl 4], [Me 4N][UO 2Cl 4], [Pr n4N][[UO 2(NO 3) 3], [Bu n4N][UO 2(NO 3) 3], with the expectation that the large cation would give a better approximation to vibrational frequencies of the free anion and would allow measurements in non-coordinating solvents. As the perchlorate is not coordinated to [UO 2] 2+ in aqueous solution the expected structure is a solvated cation [UO 2(OH 2) 5] 2+ with characteristic infrared 962.5, 253 and 160 cm -1 and Raman 874 and 198 cm -1 bands. The formation of weak, solvated [UO 2X] + complexes (X=F, Cl) has been established with frequencies at 908, 827, 254, 380 cm -1 and 956, 871, 254 and 222 cm -1 for [UO 2F] + and [UO 2Cl] +, respectively. Bidentate NO 3 coordination has been established for solid and dissolved (in CH 2Cl 2) [R 4N][UO 2(NO 3) 3] (R=Pr n, Bu n). Aqueous solutions of UO 2(NO 3) 2 and Cs[UO 2(NO 3) 3] show no clear evidence that bidentate or monodentate nitrate is present. Both unidentate and bidentate linkage of acetate-uranyl were established for acetate complexes in aqueous solutions. For the uranyl sulphate system, monodentate sulphate coordination is the major mode at low SO 4:U ratios, and even at a ratio of 3:1 there is very little free sulphate.

Gl, M.; Goggin, P. L.; Mink, J.

1992-01-01

36

New uranyl complex with imidazolidine-2-one [UO 2 (Imon) 4 (H 2 O)](ClO 4 ) 2 : Structure and some properties  

Microsoft Academic Search

A complex of uranyl perchlorate with imidazolidine-2-one as the molecular ligand, [UO2(Imon)4(H2O)](ClO4)2 (I), was synthesized and structurally characterized by X-ray diffraction analysis. The coordination number of the uranium atom is 7. The nearest environment of the uranyl ion includes four O atoms of the imidazolidine-2-one molecules and one O atom of the water molecule. The perchlorate anions are outer-sphere ligands.

G. B. Andreev; M. Yu. Antipin; N. A. Budantseva; E. V. Tuchina; L. B. Serezhkina; A. M. Fedoseev; A. B. Yusov

2004-01-01

37

Kinetic behavior of carbonate ligands with different coordination modes: Equilibrium dynamics for uranyl(2+) carbonato complexes in aqueous solution. A {sup 13}C and {sup 17}O NMR study  

SciTech Connect

Exchange processes (proton transfer and carbonate transfer) between uranyl and carbonate in solutions of uranyl carbonate were studied over the ranges 6 < pH < 9, and -5{degrees}C < t < 85{degrees}C. NMR methods were utilized in these studies including the 2D-EXSY technique. Rate constants for various reaction pathways are presented.

Banyai, I.; Micskei, K.; Toth, I.; Zekany, L. [Kossuth Univ., Debrecen (Hungary); Glaser, J. [Royal Inst. of Technology, Stockholm (Sweden)

1995-07-05

38

Tetraalkylammonium uranyl isothiocyanates.  

PubMed

Three tetraalkylammonium uranyl isothiocyanates, [(CH(3))(4)N](3)UO(2)(NCS)(5) (1), [(C(2)H(5))(4)N](3)UO(2)(NCS)(5) (2), and [(C(3)H(7))(4)N](3)UO(2)(NCS)(5) (3), have been synthesized from aqueous solution and their structures determined by single-crystal X-ray diffraction. All of the compounds consist of the uranyl cation equatorially coordinated to five N-bound thiocyanate ligands, UO(2)(NCS)(5)(3-), and charge-balanced by three tetraalkylammonium cations. Raman spectroscopy data have been collected on compounds 1-3, as well as on solutions of uranyl nitrate with increasing levels of sodium thiocyanate. By tracking the Raman signatures of thiocyanate, the presence of both free and bound thiocyanate is confirmed in solution. The shift in the Raman signal of the uranyl symmetric stretching mode suggests the formation of higher-order uranyl thiocyanate complexes in solution, while the solid-state Raman data support homoleptic isothiocyanate coordination about the uranyl cation. Presented here are the syntheses and crystal structures of 1-3, pertinent Raman spectra, and a discussion regarding the relationship of these isothiocyanates to previously described uranyl halide phases, UO(2)X(4)(2-). PMID:23072277

Rowland, Clare E; Kanatzidis, Mercouri G; Soderholm, L

2012-11-01

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 UO 2(NO 3) 2(DPSO) 2 and UO 2(NO 3) 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 U 3O 8 as final product. Both complexes present a strong green luminescence, both at room temperature and 77 K, 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

Intrinsic Hydration of Uranyl-Hydroxide, -Nitrate and -Acetate Complexes  

SciTech Connect

The intrinsic hydration of three monopositive uranyl-anion complexes (UO2A)+ (where A = acetate, nitrate, or hydroxide) was investigated using ion-trap mass spectrometry (IT-MS). The relative rates for the formation of the monohydrates [(UO2A)(H2O)]+, with respect to the anion, followed the trend: Acetate = nitrate >> hydroxide. This finding was rationalized in terms of the donation of electron density by the strongly basic OH- to the uranyl metal center, thereby reducing the Lewis acidity of U and its propensity to react with incoming nucleophiles, viz., H2O. An alternative explanation is that the more complex acetate and nitrate anions provide increased degrees of freedom that could accommodate excess energy from the hydration reaction. The monohydrates also reacted with water, forming dihydrates and then trihydrates. The rates for formation of the nitrate and acetate dihydrates [(UO2A)(H2O)2]+ were very similar to the rates for formation of the monohydrates; the presence of the first H2O ligand had no influence on the addition of the second. In contrast, formation of the [(UO2OH)(H2O)2]+ was nearly three times faster than the formation of the monohydrate.

Winnie Chien; Dorothy Hanna; Victor Anbalagan; Garold Gresham; Gary Groenewold; Michael Van Stipdonk

2004-06-01

42

Experimental and theoretical approaches to redox innocence of ligands in uranyl complexes: what is formal oxidation state of uranium in reductant of uranyl(VI)?  

PubMed

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

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

2014-06-01

43

Complexation of the Carbonate, Nitrate, and Acetate Anions with the Uranyl Dication: Density Functional Studies with Relativistic Effective Core Potentials  

Microsoft Academic Search

The structures and vibrational frequencies of uranyl carbonates, [UO?(CO?)n](?- ??) and [(UO?)?(CO?)?]??, uranyl nitrates, [UO? (NO?)n](?-?), and uranyl acetates, [UO?(CH?COO)n](?-?) (n = 1,2,3) have been calculated by using local density functional theory (LDFT). Only bidentate ligand coordination modes to the uranyl dication have been modeled. The calculated structures and frequencies are compared to available experimental data, including IR, Raman, X-ray

Wibe A. De Jong; Edoardo Apra; Theresa L. Windus; Jeffrey A. Nichols; Robert J. Harrison; Keith E. Gutowski; David A. Dixon

2005-01-01

44

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

SciTech Connect

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

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

2009-01-01

45

Complexation of the Carbonate, Nitrate, and Acetate Anions with the Uranyl Dication: Density Functional Studies with Relativistic Effective Core Potentials  

SciTech Connect

The structures and vibrational frequencies of uranyl carbonates, [UO?(CO?)n](?- ??) and [(UO?)?(CO?)?]??, uranyl nitrates, [UO? (NO?)n](?-?), and uranyl acetates, [UO?(CH?COO)n](?-?) (n = 1,2,3) have been calculated by using local density functional theory (LDFT). Only bidentate ligand coordination modes to the uranyl dication have been modeled. The calculated structures and frequencies are compared to available experimental data, including IR, Raman, X-ray diffraction, and EXAFS solution and crystal structure data. The energetics of ligand binding have been calculated using the B3LYP hybrid functional. In general, the structural and vibrational results at the LDFT level are in good agreement with experimental results and provide realistic pictures of solution phase and solid state behavior. For the [UO? (CO?)?]?? anion, calculations suggest that complexity in the CO??? stretching signature upon complexation is due to the formation of C=O and C-O domains, the latter of which can split by as much as 300 cm??. Assessment of the binding energies indicate that the [UO? (CO?)?]?? anion is more stable than the [UO?(CO?)?]?? anion due to the accumulation of excess charge, whereas the tri-ligand species are the most stable in the nitrate and acetate anions.

De Jong, Wibe A.; Apra, Edoardo; Windus, Theresa L.; Nichols, Jeffrey A.; Harrison, Robert J.; Gutowski, Keith E.; Dixon, David A.

2005-12-22

46

Complexation of the carbonate, nitrate, and acetate anions with the uranyl dication: density functional studies with relativistic effective core potentials.  

PubMed

The structures and vibrational frequencies of uranyl carbonates, [UO2(CO3)n](2-2n) and [(UO2)3(CO3)6]6-, uranyl nitrates, [UO2(NO3)n](2-n), and uranyl acetates, [UO2(CH3COO)n](2-n) (n = 1,2,3) have been calculated by using local density functional theory (LDFT). Only bidentate ligand coordination modes to the uranyl dication have been modeled. The calculated structures and frequencies are compared to available experimental data, including IR, Raman, X-ray diffraction, and EXAFS solution and crystal structure data. The energetics of ligand binding have been calculated using the B3LYP hybrid functional. In general, the structural and vibrational results at the LDFT level are in good agreement with experimental results and provide realistic pictures of solution phase and solid-state behavior. For the [UO2(CO3)3]6- anion, calculations suggest that complexity in the CO3(2-) stretching signature upon complexation is due to the formation of C=O and C-O domains, the latter of which can split by as much as 300 cm(-1). Assessment of the binding energies indicate that the [UO2(CO3)2]2- anion is more stable than the [UO2(CO3)3]4- anion due to the accumulation of excess charge, whereas the tri-ligand species are the most stable in the nitrate and acetate anions. PMID:16354049

de Jong, Wibe A; Apr, Edoardo; Windus, Theresa L; Nichols, Jeffrey A; Harrison, Robert J; Gutowski, Keith E; Dixon, David A

2005-12-22

47

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

2011-06-14

48

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

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-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

50

Uranyl sensitization of samarium(III) luminescence in a two-dimensional coordination polymer.  

PubMed

Heterometallic carboxyphosphonates UO(2)(2+)/Ln(3+) have been prepared from the hydrothermal reaction of uranyl nitrate, lanthanide nitrate (Ln = Sm, Tb, Er, Yb), and phosphonoacetic acid (H(3)PPA). Compound 1, (UO(2))(2)(PPA)(HPPA)(2)Sm(H(2)O)2H(2)O (1) adopts a two-dimensional structure in which the UO(2)(2+) metal ions bind exclusively to the phosphonate moiety, whereas the Ln(3+) ions are coordinated by both phosphonate and carboxylate functionalities. Luminescence studies of 1 show very bright visible and near-IR samarium(III)-centered emission upon direct excitation of the uranyl moiety. The Sm(3+) emissive state exhibits a double-exponential decay with lifetimes of 67.2 6.5 and 9.0 1.3 ?s as measured at 594 nm, after excitation at both 365 and 420 nm. No emission is observed in the region typical of the uranyl cation, indicating that all energy is either transferred to the Sm(3+) center or lost to nonradiative processes. Herein we report the synthesis, crystal structure, and luminescent behavior of 1, as well as those of the isostructural terbium, erbium, and ytterbium analogues. PMID:22171660

Knope, Karah E; de Lill, Daniel T; Rowland, Clare E; Cantos, Paula M; de Bettencourt-Dias, Ana; Cahill, Christopher L

2012-01-01

51

Effect of the TBP and Water on the Complexation of Uranyl Nitrate and the Dissolution of Nitric Acid into Supercritical CO2. A Theoretical Study  

E-print Network

Effect of the TBP and Water on the Complexation of Uranyl Nitrate and the Dissolution of Nitric report theoretical studies on the complexation of uranyl nitrate and the dissolution of nitric acid started from "random" mixtures of water, TBP, nitric acid, and uranyl nitrate, complexation of uranyl

Boyer, Edmond

52

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

SciTech Connect

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

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

1995-09-01

53

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

SciTech Connect

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

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

2012-03-15

54

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

55

The structure of monomeric and dimeric uranyl adsorption complexes on gibbsite: A combined DFT and EXAFS study  

NASA Astrophysics Data System (ADS)

We investigated the structure of uranyl sorption complexes on gibbsite (pH 5.6-9.7) by two independent methods, density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) spectroscopy at the U-L III edge. To model the gibbsite surface with DFT, we tested two Al (hydr)oxide clusters, a dimer and a hexamer. Based on polarization, structure, and relaxation energies during geometry optimization, the hexamer cluster was found to be the more appropriate model. An additional advantage of the hexamer model is that it represents both edges and basal faces of gibbsite. The DFT calculations of (monomeric) uranyl sorption complexes show an energetic preference for the corner-sharing versus the edge-sharing configuration on gibbsite edges. The energy difference is so small, however, that possibly both surface species may coexist. In contrast to the edge sites, sorption to basal sites was energetically not favorable. EXAFS spectroscopy revealed in all investigated samples the same interatomic distances of the uranyl coordination environment ( R ? 1.80 , R ? 2.40 ), and towards the gibbsite surface ( RU-O ? 2.87 , RU-Al ? 3.38 ). In addition, two U-U distances were observed, 3.92 at pH 9.7 and 4.30 at pH 5.6, both with coordination numbers of 1. The short U-U distance is close to that of the aqueous uranyl hydroxo dimer, UO 2(OH) 2, reported as 3.875 in the literature, but significantly longer than that of aqueous trimers (3.81-3.82 ), suggesting sorption of uranyl dimers at alkaline pH. The longer U-U distance (4.30 ) at acidic pH, however, is not in line with known aqueous uranyl polymer complexes. Based on the EXAFS findings we further refined dimeric surface complexes with DFT. We propose two structural models: in the acidic region, the observed long U-U distance can be explained with a distortion of the uranyl dimer to form both a corner-sharing and an edge-sharing linkage to neighboring Al octahedra, leading to RU-U = 4.150 . In the alkaline region, a corner-sharing uranyl dimer complex is the most favorable. The U-O path at 2.87 in the EXAFS spectra arises from the oxygen atom linking two Al cations in corner-sharing arrangement. The adsorption structures obtained by DFT calculations are in good agreement with the structural parameters from EXAFS analysis: U-Al (3.394 ), U-U (3.949 ), and U-O (2.823 ) for the alkaline pH model, and U-Al (3.279 ), U-U (4.150 ), and U-O (2.743 ) for the acidic pH model. This work shows that by combining EXAFS and DFT, consistent structural models for uranyl sorption complexes can be obtained, which are relevant to predict the migration behavior of uranium at nuclear facilities.

Hattori, Tatsuya; Saito, Takumi; Ishida, Keisuke; Scheinost, Andreas C.; Tsuneda, Takao; Nagasaki, Shinya; Tanaka, Satoru

2009-10-01

56

Investigation of uranyl nitrate ion pairs complexed with amide ligands using electrospray ionization ion trap mass spectrometry and density functional theory.  

PubMed

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 [UO(2)(NO(3))(amide)(n=2,3)](+); however, singly charged complexes containing the amide conjugate base and reduced uranyl UO(2)(+) were also formed as were several doubly charged species. The formamide experiment produced the greatest diversity of species resulting 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 lower abundance doubly charged complexes, but augmented reduced uranyl complexes. DFT investigations of the tris-amide ion pair complexes showed that interligand 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 methyl-acetamide ligands. PMID:21449598

Gresham, Garold L; Dinescu, Adriana; Benson, Michael T; Van Stipdonk, Michael J; Groenewold, Gary S

2011-04-21

57

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

58

Uranyl and uranyl-3d block cation complexes with 1,3-adamantanedicarboxylate: crystal structures, luminescence, and magnetic properties.  

PubMed

The reaction of 1,3-adamantanedicarboxylic acid (LH2) with uranyl nitrate under solvo-hydrothermal conditions, either alone or in the presence of additional metal cations (Co(2+), Ni(2+), or Cu(2+)) gives a series of nine complexes displaying a wide range of architectures. While [UO2(L)(H2O)]1.25CH3CN (1) and [UO2(L)(DMF)] (2) are one-dimensional (1D) species analogous to that previously known, [H2NMe2]2[(UO2)2(L)3]1.5H2O (3), which includes dimethylammonium counterions generated in situ, is a three-dimensional (3D) framework, and [UO2(L)(NMP)] (4) (NMP = N-methyl-2-pyrrolidone) is a braid-shaped 1D polymer. When 3d block metal ions are present and bound to 2,2'-bipyridine (bipy) coligands, their role is reduced to that of decorating species attached to uranyl-containing 1D polymers, as in [UO2M(L)2(bipy)2]0.5H2O with M = Co (5) or Ni (6), and [(UO2)2Cu2(L)3(NO3)2(bipy)2]0.5H2O (9), or of counterions, as in [Ni(bipy)3][(UO2)4(O)2(L)3]3H2O (7), in which a two-dimensional (2D) assembly is built from tetranuclear uranyl-containing building units. In contrast, the heterometallic 3D framework [UO2Cu(L)2] (8) can be isolated in the absence of bipy. The emission spectra measured in the solid state display the usual uranyl vibronic fine structure, with various degrees of resolution and quenching, except for that of complex 7, which shows emission from the nickel(II) centers. The magnetic properties of complexes 5, 6, 8, and 9 were investigated, showing, in particular, the presence of zero-field splitting effects in 6 and weak antiferromagnetic interactions in 9. PMID:25710676

Thury, Pierre; Rivire, Eric; Harrowfield, Jack

2015-03-16

59

Uranyl nitrate complex extraction into TBP/dodecane organic solutions: a molecular dynamics study.  

PubMed

Liquid-liquid extraction of uranyl is studied by conducting atomistic molecular dynamics simulation using quantum chemistry calibrated force fields via restrained electrostatic potential fitting of atomic forces. The simulations depict the migration of uranyl nitrate complexes from the aqueous-organic interface into the tri-n-butyl phosphate (TBP)/dodecane organic phase, in the form of UO(2)(NO(3))(2)H(2)O2TBP and UO(2)(NO(3))(2)3TBP. The migration process is characterized by the gradual breaking of all the hydrogen bonds between the complex and the water molecules at the interface. Moreover, our simulation results suggest that the experimentally observed complex UO(2)(NO(3))(2)2TBP is formed after the migration of the aforementioned complexes into the organic phase by means of a reorganization of the nitrate binding mode from mono to bidentate which removes the excess oxygen atoms bound to uranyl. PMID:20967313

Ye, Xianggui; Cui, Shengting; de Almeida, Valmor F; Hay, Benjamin P; Khomami, Bamin

2010-12-21

60

Binding constant determination of uranyl-citrate complex by ACE using a multi-injection method.  

PubMed

The binding constant determination of uranyl with small-molecule ligands such as citric acid could provide fundamental knowledge for a better understanding of the study of uranyl complexation, which is of considerable importance for multiple purposes. In this work, the binding constant of uranyl-citrate complex was determined by ACE. Besides the common single-injection method, a multi-injection method to measure the electrophoretic mobility was also applied. The BGEs used contained HClO4 and NaClO4 , with a pH of 1.98 0.02 and ionic strength of 0.050 mol/L, then citric acid was added to reach different concentrations. The electrophoretic mobilities of the uranyl-citrate complex measured by both of the two methods were consistent, and then the binding constant was calculated by nonlinear fitting assuming that the reaction had a 1:1 stoichiometry and the complex was [(UO2 )(Cit)](-) . The binding constant obtained by the multi-injection method was log K = 9.68 0.07, and that obtained by the single-injection method was log K = 9.73 0.02. The results provided additional knowledge of the uranyl-citrate system, and they demonstrated that compared with other methods, ACE using the multi-injection method could be an efficient, fast, and simple way to determine electrophoretic mobilities and to calculate binding constants. PMID:25598434

Zhang, Yiding; Li, Linnan; Huang, Hexiang; Xu, Linnan; Li, Ze; Bai, Yu; Liu, Huwei

2015-04-01

61

Formation of bare UO2(2+) and NUO(+) by fragmentation of gas-phase uranyl-acetonitrile complexes.  

PubMed

In a prior study [Van Stipdonk; et al. J. Phys. Chem. A 2006, 110, 959-970], electrospray ionization (ESI) was used to generate doubly charged complex ions composed of the uranyl ion and acetonitrile (acn) ligands. The complexes, general formula [UO2(acn)n](2+), n = 0-5, were isolated in an 3-D quadrupole ion-trap mass spectrometer to probe intrinsic reactions with H2O. Two general reaction pathways were observed: (a) the direct addition of one or more H2O ligands to the doubly charged complexes and (b) charge-exchange reactions. For the former, the intrinsic tendency to add H2O was dependent on the number and type of nitrile ligand. For the latter, charge exchange involved primarily the formation of uranyl hydroxide, [UO2OH](+), presumably via a collision with gas-phase H2O and the elimination of a protonated nitrile ligand. Examination of general ion fragmentation patterns by collision-induced dissociation, however, was hindered by the pronounced tendency to generate hydrated species. In an update to this story, we have revisited the fragmentation of uranyl-acetonitrile complexes in a linear ion-trap (LIT) mass spectrometer. Lower partial pressures of adventitious H2O in the LIT (compared to the 3-D ion trap used in our previous study) minimized adduct formation and allowed access to lower uranyl coordination numbers than previously possible. We have now been able to investigate the fragmentation behavior of these complex ions completely, with a focus on tendency to undergo ligand elimination versus charge reduction reactions. CID can be used to drive ligand elimination to completion to furnish the bare uranyl dication, UO2(2+). In addition, fragmentation of [UO2(acn)](2+) generated [UO2(NC)](+), which subsequently fragmented to furnish NUO(+). Formation of the nitrido by transfer of N from cyanide was confirmed using precursors labeled with (15)N. The observed formation of [UO2(NC)](+) and NUO(+) was modeled by density functional theory. PMID:25121574

Van Stipdonk, Michael J; Michelini, Maria del Carmen; Plaviak, Alexandra; Martin, Dean; Gibson, John K

2014-09-11

62

New uranyl nitrate complex with N-cyclohexyl-2-pyrrolidone: a promising candidate for nuclear fuel reprocessing  

Microsoft Academic Search

Bis(N-cyclohexyl-2-pyrrolidone) uranyl nitrate complex was prepared from uranyl nitrate and N-cyclohexyl-2-pyrrolidone (NCP) in 7 M aqueous nitric acid solution with a yield of 68%. The yellow UO2(NO3)2(NCP)2 complex was precipitated from this highly acidic media and was characterized by NMR, IR and UV-vis spectroscopies.

T. R Varga; M Sato; Zs Fazekas; M Harada; Y Ikeda; H Tomiyasu

2000-01-01

63

The gas-phase bis-uranyl nitrate complex [(UO 2) 2(NO 3) 5] ?: Infrared spectrum and structure  

Microsoft Academic Search

The infrared spectrum of the bis-uranyl nitrate complex [(UO2)2(NO3)5]? was measured in the gas phase using multiple photon dissociation (IRMPD). Intense absorptions corresponding to the nitrate symmetric and asymmetric vibrations, and the uranyl asymmetric vibration were observed. The nitrate ?3 vibrations indicate the presence of nitrate in a bridging configuration bound to both uranyl cations, and probably two distinct pendant

Gary S. Groenewold; Michael J. van Stipdonk; Jos Oomens; Wibe A. de Jong; Michael E. McIlwain

2011-01-01

64

Structure and dynamics of the uranyl tricarbonate complex in aqueous solution: insights from quantum mechanical charge field molecular dynamics.  

PubMed

This investigation presents the characterization of structural and dynamical properties of uranyl tricarbonate in aqueous solution employing an extended hybrid quantum mechanical/molecular mechanical (QM/MM) approach. It is shown that the inclusion of explicit solvent molecules in the quantum chemical treatment is essential to mimic the complex interaction occurring in an aqueous environment. Thus, in contrast to gas phase cluster calculations on a quantum chemical level proposing a 6-fold coordination of the three carbonates, the QMCF MD simulation proposes a 5-fold coordination. An extensive comparison of the simulation results to structural and dynamical data available in the literature was found to be in excellent agreement. Furthermore, this work is the first theoretical study on a quantum chemical level of theory able to observe the conversion of carbonate (CO??) to bicarbonate (HCO??) in the equatorial coordination sphere of the uranyl ion. From a comparison of the free energy ?G values for the unprotonated educt [UO?(CO?)?]?? and the protonated [UO?(CO?)?(HCO?)]?, it could be concluded that the reaction equilibrium is strongly shifted toward the product state confirming the benignity for the observed protonation reaction. Structural properties and the three-dimensional arrangement of carbonate ligands were analyzed via pair-, three-body, and angular distributions, the dynamical properties were evaluated by hydrogen-bond correlation functions and vibrational power spectra. PMID:25157847

Tirler, Andreas O; Hofer, Thomas S

2014-11-13

65

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

PubMed

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

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

2013-03-13

66

The effect of coordinated solvent ligands on the solid-state structures of compounds involving uranyl nitrate and Schiff bases  

Microsoft Academic Search

A range of solvent adducts of uranyl complexes of the Schiff base ligands salen (salen?N,N?-ethylenebis(salicylidenimine)) and salpn (?N,N?-propylenebis(salicylidenimine)) have revealed similar morphologies about the uranium centre. Subtle differences in hydrogen bonding arrays, types of solvents and conformation of the Schiff base ligands result in vastly different crystal packing motifs.

David J Evans; Peter C Junk; Matthew K Smith

2002-01-01

67

Density functional theory study of the complexation of the uranyl dication with anionic phosphate ligands with and without water molecules.  

PubMed

The structures, vibrational frequencies and energetics of anhydrous and hydrated complexes of UO2(2+) with the phosphate anions H2PO4(-), HPO4(2-), and PO4(3-) were predicted at the density functional theory (DFT) and MP2 molecular orbital theory levels as isolated gas phase species and in aqueous solution by using self-consistent reaction field (SCRF) calculations with different solvation models. The geometries and vibrational frequencies of the major binding modes for these complexes are compared to experiment where possible and good agreement is found. The uranyl moiety is nonlinear in many of the complexes, and the coordination number (CN) 5 in the equatorial plane is the predominant binding motif. The phosphates are found to bind in both monodentate and bidentate binding modes depending on the charge and the number of water molecules. The SCRF calculations were done with a variety of approaches, and different SCRF approaches were found to be optimal for different reaction types. The acidities of HxPO4(3-x) in HxPO4(3-x)(H2O)4, x = 0-3 complexes were calculated with different SCRF models and compared to experiment. Phosphate anions can displace water molecules from the first solvation shell at the uranyl exothermically. The addition of water molecules can cause the bonding of H2PO4(-) and HPO4(2-) to change from bidentate to monodentate exothermically while maintaining CN 5. The addition of water can generate monodentate structures capable of cross-linking to other uranyl phosphates to form the types of structures found in the solid state. [UO2(HPO4)(H2O)3] is predicted to be a strong base in the gas phase and in aqueous solution. It is predicted to be a much weaker acid than H3PO4 in the gas phase and in solution. PMID:23905705

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

2013-09-12

68

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

SciTech Connect

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

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

2013-09-12

69

Anion-dependent electron paramagnetic resonance of uranium(V) intermediates in photo- and electrolytic reductions of uranyl complexes in organic solution  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) and optical spectra of uranium(V) were observed in both photo- and electrolytic reductions of uranyl-TIBP (triisobutylphosphate) and uranyl-CMPO (octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide) complexes with the counter-ions NO3(-) and ClO4 in several organic solutions. In addition, IR spectra and cyclic voltammograms were measured. The EPR signals of all these complexes during the electrolytic reduction and of the uranylperchlorate complexes during the photoreduction are broad and the values of the g factor are larger than 2.0. On the other hand, sharp signals were recorded for the uranylnitrate complexes during the photoreduction and the values of the g factor are smaller than 2.0. These results are explained on the basis of crystal field theory by considering the difference in the coordination states around uranium(V) in the two reductions.

Miyake, C.; Sano, Y.

1994-10-01

70

Preparation and characterization of uranyl complexes with three isomeric methyl-pyridine-N-oxide ligands  

Microsoft Academic Search

The synthesis and characterization of complexes of uranyl nitrate with methyl-pyridine-N-oxide isomers (picoline-N-oxide (2-picNO), 3-picoline-N-oxide (3-picNO) and 4-picoline-N-oxide (4-picNO)) as ligands (L) are described. They were prepared by reaction of hydrated uranyl nitrate with ligands in ethanolic solution (molar ratio 1:2). The compounds were characterized by CHN microanalytical procedures, infrared spectroscopy, X-ray powder diffraction, and TG\\/DTG. The analytical results suggest

M. G Alvarenga; L. B Zinner; C. A Fantin; J. R Matos; G Vicentini

2004-01-01

71

Near-infrared-induced electron transfer of an uranyl macrocyclic complex without energy transfer to dioxygen.  

PubMed

Photoexcitation of dichloromethane solutions of an uranyl macrocyclic complex with cyclo[1]furan[1]pyridine[4]-pyrrole () at the near-infrared (NIR) band (1177 nm) in the presence of electron donors and acceptors resulted in NIR-induced electron transfer without producing singlet oxygen via energy transfer. PMID:25791126

Davis, Christina M; Ohkubo, Kei; Ho, I-Ting; Zhang, Zhan; Ishida, Masatoshi; Fang, Yuanyuan; Lynch, Vincent M; Kadish, Karl M; Sessler, Jonathan L; Fukuzumi, Shunichi

2015-04-01

72

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

73

Competitive complexation of nitrates and chlorides to uranyl in a room temperature ionic liquid.  

PubMed

By coupling EXAFS, UV-vis spectroscopy, and molecular dynamics and quantum mechanical calculations, we studied the competitive complexation of uranyl cations with nitrate and chloride ions in a water immiscible ionic liquid (IL), C(4)mimTf(2)N (C(4)mim(+): 1-butyl-3-methyl-imidazolium; Tf(2)N(-) = (CF(3)SO(2))(2)N)(-): bis(trifluoromethylsulfonyl)imide). Both nitrate and chloride are stronger ligands for uranyl than the IL Tf(2)N(-) or triflate anions and when those anions are simultaneously present, neither the limiting complex UO(2)(NO(3))(3)(-) nor UO(2)Cl(4)(2-) alone could be observed. At a U/NO(3)/Cl ratio of 1/2/2, the dominant species is likely UO(2)Cl(NO(3))(2)(-). When chloride is in excess over uranyl with different nitrate concentrations (U/NO(3)/Cl ratio of 1/2/6, 1/4/4, and 1/12/4) the solution contains a mixture of UO(2)Cl(4)(2-) and UO(2)Cl(3)(NO(3))(2-) species. Furthermore, it is shown that the experimental protocol for introducing these anions to the solution (either as uranyl counterion, as added salt, or as IL component) influences the UV-vis spectra, pointing to the formation of different kinetically equilibrated complexes in the IL. PMID:20557035

Gaillard, C; Chaumont, A; Billard, I; Hennig, C; Ouadi, A; Georg, S; Wipff, G

2010-07-19

74

Laws of the complexation of uranyl salts with neutral bases in nonaqueous media  

SciTech Connect

The complexation of nonaqueous uranyl chloride with neutral oxygen-containing organic bases in an acetone medium has been discussed with reference to the donor ability of the neutral molecules. It has been shown that the dissociation constants of the 1:1 complexes do not show any correlation with the donor ability of the neutral bases. At the same time, the stability constants of the complexes increased as the donor ability of the ligands is increased. However, the dependence has a complicated character and is determined by the nature of the neutral molecules. The contributions of uranyl chloride and O donors to the values of the stability constants and the heats of formation of the complexes have been evaluated.

Kobets, L.B.; Buchikhin, E.P.

1987-12-01

75

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

Microsoft Academic Search

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 \\/nuSO to lower frequencies, indicating bonding through the sulfoxide oxygen. The nitrate bands indicate

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

2003-01-01

76

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

Microsoft Academic Search

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

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

2003-01-01

77

Molecular dynamics simulations of uranyl and uranyl carbonate adsorption at aluminosilicate surfaces.  

PubMed

Adsorption at mineral surfaces is a critical factor controlling the mobility of uranium(VI) in aqueous environments. Therefore, molecular dynamics (MD) simulations were performed to investigate uranyl(VI) adsorption onto two neutral aluminosilicate surfaces, namely, the orthoclase (001) surface and the octahedral aluminum sheet of the kaolinite (001) surface. Although uranyl preferentially adsorbs as a bidentate inner-sphere complex on both surfaces, the free energy of adsorption on the orthoclase surface (-15 kcal mol(-1)) is significantly more favorable than that at the kaolinite surface (-3 kcal mol(-1)), which is attributed to differences in surface functional groups and the ability of the orthoclase surface to release a surface potassium ion upon uranyl adsorption. The structures of the adsorbed complexes compare favorably with X-ray absorption spectroscopy results. Simulations of the adsorption of uranyl complexes with up to three carbonate ligands revealed that uranyl complexes coordinated to up to two carbonate ions are stable on the orthoclase surface whereas uranyl carbonate surface complexes are unfavored at the kaolinite surface. Combining the MD-derived equilibrium adsorption constants for orthoclase with aqueous equilibrium constants for uranyl carbonate species indicates the presence of adsorbed uranium complexes with one or two carbonates under alkaline conditions, in support of current uranium(VI) surface complexation models. PMID:24580048

Kerisit, Sebastien; Liu, Chongxuan

2014-04-01

78

Unexpected oxidation of cis-1,3-dithiane-1,3-dioxide ( cis-DTSO 2) 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-DTSO 2 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-DTSO 2 moieties and the bidentate propanedisulfonate. The water molecule is hydrogen bonded to the cis-DTSO 2 molecules. The supramolecular arrangement is made through a C-HO 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

79

Importance of charge transfer and polarization effects for the modeling of uranyl-cation complexes  

SciTech Connect

The structures, energies, and charges of uranyl cation complexes with water molecules, nitrate ion, and carbonate ions were determined using Hartree-Fock, second-order Moeller-Plesset (MP2) perturbation theory, and density functional theory (DFT) ab initio quantum chemical methods. Reasonable agreement with experimentally determined structures was found. Significant polarization of the ligands as well as charge transfer to the uranyl ion was observed in the complexes. The dissociation energy curves for the complexes were also determined at the MP2 level of theory. Attempts to reproduce these curves with molecular mechanical models with fixed atomic point charges failed, showing that an appropriate force field for these systems must include polarization and charge-transfer effects.

Hemmingsen, L.; Amara, P.; Ansoborlo, E.; Field, M.J.

2000-05-04

80

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

81

Thermal stability of uranyl complexes with neutral oxygen-containing organic bases  

SciTech Connect

The thermal stability of uranyl chloride, nitrate, and oxalate with a series of neutral oxygen-containing organic ligands is discussed. It was found that the temperatures of removal of chlorine are higher than the stripping of the first molecule of the base in complexes UO/sub 2/Cl/sub 2/ x 2L. This is an indication of greater strength of the bonds of the Cl/sup -/ ions to the uranyl group in comparison with the investigated bases. It was shown that the temperatures of removal of a mole of neutral ligands depend little on the nature of the anions and exhibit a correlation with the donor capacity of the bases: Ac < TBP < DMFA similarly ordered DMSO < TBPO similarly ordered PyO. The chemistry of the decomposition of the complexes and the strength of the binding of the acido- and neutral ligands in them are discussed.

Kobets, L.V.

1987-03-01

82

Thermal stability of uranyl complexes with neutral oxygen-containing organic bases  

Microsoft Academic Search

The thermal stability of uranyl chloride, nitrate, and oxalate with a series of neutral oxygen-containing organic ligands is discussed. It was found that the temperatures of removal of chlorine are higher than the stripping of the first molecule of the base in complexes UOCl x 2L. This is an indication of greater strength of the bonds of the Cl⁻ ions

Kobets

1987-01-01

83

Characterization of uranyl(VI) nitrate complexes in a room temperature ionic liquid using attenuated total reflection-Fourier transform infrared spectrometry.  

PubMed

Room temperature ionic liquids form potentially important solvents in novel nuclear waste reprocessing methods, and the solvation, speciation, and complexation behaviors of actinides and lanthanides in room temperature ionic liquids is of current interest. In this study, the coordination environment of uranyl(VI) in solutions of the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide containing either tetrabutylammonium nitrate or nitric acid was characterized using attenuated total reflection-Fourier transform infrared spectrometry. Both UO(2)(NO(3))(2) and UO(2)(NO(3))(3)(-) species were detected in solutions containing tetrabutylammonium nitrate. ?(as)(UO(2)) for these two species were found to lie at 951 and 944 cm(-1), respectively, while ?(as)(UO(2)) arising from uranyl(VI) coordinated by bis(trifluoromethylsulfonyl)imide anions in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was found to lie at 968 cm(-1). In solutions containing nitric acid, only UO(2)(NO(3))(2) was detected, due to the high water content. The UO(2)(NO(3))(+) species was not detected under the conditions used in this study. From the results shown here, we conclude that infrared spectroscopy forms a valuable addition to the suite of tools currently used to study the chemical behavior of uranyl(VI) in room temperature ionic liquids. PMID:20722398

Quach, Donna L; Wai, Chien M; Pasilis, Sofie P

2010-09-20

84

Fluorescent uranyl ion lidded cucurbit[5]uril capsule.  

PubMed

A novel fluorescent complex {(UO(2))(2)(CB5)}(NO(3))(4)4HNO(3).3H(2)O (U2CB5) is obtained from cucurbit[5]uril (CB5) and uranyl nitrate under ambient temperature conditions. The crystal structure revealed that two uranyl ions are coordinated to the two open portals of CB5 giving a closed molecular capsule, which further connected through CB5 molecules to give two-dimensional frameworks. The U2CB5 complex was further investigated by NMR, FTIR and TGA techniques. The Fluorescence of uranyl ion was found to be enhanced due to complexation with cucurbituril. PMID:22129203

Kushwaha, S; Rao, Srinivas A; Sudhakar, Padmaja P

2012-01-01

85

Thermodynamics of lanthanide and uranyl complexes with tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA).  

SciTech Connect

We present the results of an investigation of the thermochemistry of the complexation of La{sup 3+} Nd{sup 3+}, Eu{sup 3+}, Dy{sup 3+}, Tm{sup 3+}, and UO{sub 2}{sup 2+} by tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA). This predisposed structural analog to oxydiacetic acid (ODA) has been previously shown both to exhibit greater sensitivity to lanthanide cation radius than complexes with the unconstrained ODA and to form anomalously weak complexes with UO{sub 2}{sup 2+}. Our purpose is to interpret these observations in terms of the balance between enthalpy and entropy contributions to the overall complexation thermodynamics. Enthalpies have been calculated from titration calorimetry experiments both for the protonation of the free ligand and for the formation of selected 1:1 and 1:2 complexes in pH 2-3 acidic media (I = 0.1 M). The complexation entropies for the lanthanide complexes have been calculated using the previously reported stability constants for the MH{sub 2}L{sup +}, MHL, and M(H{sub 2}L){sup 2-}. The stability constants for the uranyl complexes have been determined by potentiometric titration and these values used to calculate the thermodynamic parameters. Complexation enthalpies for the 1:1 lanthanide-THFTCA complexes (MH{sub 2}L{sup +} species) are nearly identical to those of the lanthanide ODA complexes. Therefore, the size-selectivity observed in the lanthanide-THFTCA complexes arises from the complexation entropy. The comparative weakness of the uranyl complexes with THFTCA also is accounted for thermodynamically in the entropy term. Calculations based on an electrostatic model for complexation entropy and molecular mechanics modeling are used to help interpret the experimental results.

Morss, L. R.; Nash, K. L.; Tennessee Technological Univ.

2000-01-01

86

Structural units in three uranyl perrhenates.  

PubMed

Three uranyl perrhenates have been synthesized, and their structures have been determined. (UO2)2(ReO4)4(H2O)3 (1) is triclinic, space group P, a=5.2771(7), b=13.100(2), c=15.476(2) A, alpha=107.180(2), beta=99.131(3), gamma=94.114(2) degrees, V=1001.12 A3, Z=2. [(UO2)4(ReO4)2O(OH)4(H2O)7](H2O)5 (2) is also triclinic, space group P, a=7.884(1), b=11.443(2), c=16.976(2) A, alpha=83.195(4), beta=89.387(4), gamma=85.289(4) degrees, V=1515.70 A3, Z=2. Na(UO2)(ReO4)3(H2O)2 (3) is monoclinic, space group C2/m, a=12.311(3), b=22.651(6), c=5.490(1) A, beta=109.366(6) degrees, V=1444.24 A3, Z=4. These compounds are the first structurally characterized uranyl perrhenates that do not contain organic ligands. In each structure, perrhenate groups coordinate uranyl ions at the equatorial vertices of pentagonal bipyramids. 1 contains complex chains of uranyl pentagonal bipyramids that are bridged by vertex sharing with perrhenate groups. The structural units in 2 and 3 consist of three novel finite clusters that include the coordination of uranyl ions with perrhenate. In general, weakly coordinating ligands such as perchlorate, perrhenate, and pertechnetate are assumed not to form stable complexes with uranyl in solutions or solids. The current findings, together with other recently reported studies, indicate each of these ligands can coordinate uranyl, and novel structure types result. PMID:17973369

Karimova, Oxana V; Burns, Peter C

2007-11-26

87

Composition for detecting uranyl  

DOEpatents

A composition for detecting the presence and concentration of a substance such as uranyl, comprising an organohalide covalently bonded to an indicator for said substance. The composition has at least one active OH site for forming a complex with the substance to be detected. The composition is made by reacting equimolar amounts of the indicator and the organohalide in a polar organic solvent. The absorbance spectrum of the composition-uranyl complex is shifted with respect to the absorbance spectrum of the indicator-uranyl complex, to provide better spectral resolution for detecting uranyl.

Baylor, Lewis C. (North Augusta, SC); Stephens, Susan M. (Athens, GA)

1995-01-01

88

Study of kinetics of thermal decomposition of uranyl nitrate complexes with N-alkylcaprolactams by means of non-isothermal gravimetry  

Microsoft Academic Search

The kinetics of thermal decomposition of a series of uranyl nitrate complexes with N-alkylcaprolactams (alkyl=C2H5, C4H9, C6H13, C8H17, C10H21 or C12H25) was studied by means of non-isothermal gravimetry under a nitrogen atmosphere. From the TG-DTG curves, the kinetic parameters\\u000a relating to the loss of two molecules of coordinated ligand were obtained by employing two groups of methods: (I) a group

Z. Lu; L. Yang; J. Sun

1995-01-01

89

Toward equatorial planarity about uranyl: synthesis and structure of tridentate nitrogen-donor {UO2}2+ complexes.  

PubMed

The reaction of UO2Cl23THF with the tridentate nitrogen donor ligand 2,6-bis(2-benzimidazolyl)pyridine (H2BBP) in pyridine leads to the formation of three different complexes: [(UO2)(H2BBP)Cl2] (1), [(UO)2(HBBP)(Py)Cl] (2), and [(UO2)(BBP)(Py)2] (3) after successive deprotonation of H2BBP with a strong base. Crystallographic determination of 1-3 reveals that increased charge through ligand deprotonation and displacement of chloride leads to equatorial planarity about uranyl as well as a more compact overall coordination geometry. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectra of 1-3 at the U-4d edges have been recorded using a soft X-ray Scanning Transmission X-ray Microscope (STXM) and reveal the uranium 4d5/2 and 4d3/2 transitions at energies associated with uranium in the hexavalent oxidation state. First-principles Density Functional Theory (DFT) electronic structure calculations for the complexes have been performed to determine and validate the coordination characteristics, which correspond well to the experimental results. PMID:24528285

Copping, Roy; Jeon, Byoungseon; Pemmaraju, C Das; Wang, Shuao; Teat, Simon J; Janousch, Markus; Tyliszczak, Tolek; Canning, Andrew; Grnbech-Jensen, Niels; Prendergast, David; Shuh, David K

2014-03-01

90

Gas-Phase Reactions of Molecular Oxygen with Uranyl(V) Anionic Complexes-Synthesis and Characterization of New Superoxides of Uranyl(VI).  

PubMed

Gas-phase complexes of uranyl(V) ligated to anions X(-) (X = F, Cl, Br, I, OH, NO3, ClO4, HCO2, CH3CO2, CF3CO2, CH3COS, NCS, N3), [UO2X2](-), were produced by electrospray ionization and reacted with O2 in a quadrupole ion trap mass spectrometer to form uranyl(VI) anionic complexes, [UO2X2(O2)](-), comprising a superoxo ligand. The comparative rates for the oxidation reactions were measured, ranging from relatively fast [UO2(OH)2](-) to slow [UO2I2](-). The reaction rates of [UO2X2](-) ions containing polyatomic ligands were significantly faster than those containing the monatomic halogens, which can be attributed to the greater number of vibrational degrees of freedom in the polyatomic ligands to dissipate the energy of the initial O2-association complexes. The effect of the basicity of the X(-) ligands was also apparent in the relative rates for O2 addition, with a general correlation between increasing ligand basicity and O2-addition efficiency for polyatomic ligands. Collision-induced dissociation of the superoxo complexes showed in all cases loss of O2 to form the [UO2X2](-) anions, indicating weaker binding of the O2(-) ligand compared to the X(-) ligands. Density functional theory computations of the structures and energetics of selected species are in accord with the experimental observations. PMID:25807358

Lucena, Ana F; Carretas, Jos M; Maralo, Joaquim; Michelini, Maria C; Gong, Yu; Gibson, John K

2015-04-16

91

Experimental and Theoretical Studies on the Fragmentation of Gas-Phase Uranyl-, Neptunyl- and Plutonyl-Diglycolamide Complexes  

SciTech Connect

Fragmentation of actinyl(VI) complexes UVIO2(L)22+, NpVIO2(L)22+ and PuVIO2(L)22+ (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 UVIO2(L)(L-86)+ with charge reduction, and NpVIO2(L)(L-101)2+ and PuVIO2(L)(L-101)2+ with charge conservation. The neptunyl and plutonyl complexes also exhibited substantial L+ loss to give pentavalent complexes NpVO2(L)+ and PuVO2(L)+, whereas the uranyl complex did not, consistent with the comparative An 5f-orbital energies and the AnVIO22+/AnVO2+ (An = U, Np, Pu) reduction potentials. CID of NpVO2(L)2+ and PuVO2(L)2+ was dominated by neutral ligand loss to form NpVO2(L)+ and PuVO2(L)+, which hydrated by addition of residual water in the ion trap; UVO2(L)2+ was not observed. Theoretical calculations of the structures and bonding of the AnVIO2(L)22+ complexes using density functional theory reveal that the metal centers are coordinated by six oxygen atoms from the two TMOGA ligands. The results are compared with radiolytic decomposition of TMOGA in solution.

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

2013-10-10

92

The study of the speciation of uranylsulphate complexes by UVVis absorption spectra decomposition  

Microsoft Academic Search

Uranylsulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium\\u000a ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical\\u000a significance. The spectra of UO2(NO3)2+Na2SO4 solutions of different ?\\u000a S=[SO42?]\\/[U(VI)] ratio at pH=2 were recorded for this purpose. As the presence of uranyl-nitrate

Duan Voplka; Karel tamberg; Alois Motl; Barbora Drtinov

2010-01-01

93

Scale-dependent rates of uranyl surface complexation reaction in sediments  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

94

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 NaNO 3 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

95

Aqueous uranyl complexes. 3. Potentiometric measurements of the hydrolysis of uranyl(VI) ion at 25{degrees}C  

SciTech Connect

Potentiometric titrations of uranyl(VI) solutions were conducted using a standard glass/calomel electrode combination over the pH range 3 to 12 at 0.1 mol-kg{sup {minus}1} ionic strength with tetramethylammonium trifluoromethanesulfonate as the supporting electrolyte. The electrodes were calibrated directly on the hydrogen ion concentration scale during the initial stage of each titration. The species, UO{sub 2}{sup 2+}, (UO{sub 2}){sub 2}(OH){sub 2}{sup 2+}, (UO{sub 2}){sub 3}(OH){sub 5}{sup +}, (UO{sub 2}){sub 3}(OH){sub 7}{sup {minus}}, (UO{sub 2}){sub 3}(OH){sub 8}{sup 2-}, and (UO{sub 2}){sub 3}(OH){sub 10}{sup 4-} identified in an earlier Raman study were compatible with the analysis of the titration data. Based on this analysis and application of the extended Debye-Hueckel treatment, the polynuclear species indicated above were assigned overall formation constants at 25{degrees}C and at infinite dilution of -5.51{plus_minus}0.04, -15.3{plus_minus}0.1, -27.77{plus_minus}0.09, -37.65{plus_minus}0.14, and -62.4{plus_minus}0.3, respectively. The results are discussed in reference to hydrolysis quotients reported in the literature for the first three species. Formation quotients for the last two species have not been reported previously.

Palmer, D.A.; Nguyen-Trung, C. [Oak Ridge National Lab., TN (United States)

1995-12-01

96

Structural and thermal characterization of cerium, thorium and uranyl complexes of sulfasalazine  

NASA Astrophysics Data System (ADS)

Cerium(IV), Thorium(IV) and Uranyl(II) complexes with the ammonium salt of sulfasalazine drug (H 2SSZ, HL -) have been studied. The structures of the complexes were elucidated using elemental analysis, IR and mass spectroscopy and thermal analysis. The complexes were isolated in 1:1 and 1:2 (M:L) ratios. The solid monocomplexes (1:1) (M:H 2SSZ) were isolated in the general formulae [UO 2(L)(H 2O) 2]2H 2O and [M(L)(X) z(H 2O) n] yH 2O (M = Ce(IV) and Th(IV) (X = NO 3, z = 2, n = 2, y = 0-3)). The biscomplexes (1:2) (M:H 2SSZ) solid chelates found to have the general formulae [UO 2(HL) 2]2H 2O and [M(L) 2(H 2O) 2] (M = Ce(IV) and Th(IV)). The thermal decomposition of the complexes should be discussed in relation to structure, and the thermodynamic parameters of the decomposition stages were evaluated applying Coats-Redfern and Horwitz-Mitzger methods.

Mohamed, Gehad G.; Soliman, Ahmed A.; El-Mawgood, Mohamed A.

2005-12-01

97

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

Microsoft Academic Search

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

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

2011-01-01

98

Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments  

SciTech Connect

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

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

2013-03-15

99

A calorimetric study of the hydrolysis and peroxide complex formation of the uranyl(VI) ion.  

PubMed

The enthalpies of reaction for the formation of uranyl(vi) hydroxide {[(UO2)2(OH)2](2+), [(UO2)3(OH)4](2+), [(UO2)3(OH)5](+), [(UO2)3(OH)6](aq), [(UO2)3(OH)7](-), [(UO2)3(OH)8](2-), [(UO2)(OH)3](-), [(UO2)(OH)4](2-)} and peroxide complexes {[UO2(O2)(OH)](-) and [(UO2)2(O2)2(OH)](-)} have been determined from calorimetric titrations at 25 C in a 0.100 M tetramethyl ammonium nitrate ionic medium. The hydroxide data have been used to test the consistency of the extensive thermodynamic database published by the Nuclear Energy Agency (I. Grenthe, J. Fuger, R. J. M. Konings, R. J. Lemire, A. B. Mueller, C. Nguyen-Trung and H. Wanner, Chemical Thermodynamics of Uranium, North-Holland, Amsterdam, 1992 and R. Guillaumont, T. Fanghnel, J. Fuger, I. Grenthe, V. Neck, D. J. Palmer and M. R. Rand, Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, Amsterdam, 2003). A brief discussion is given about a possible structural relationship between the trinuclear complexes [(UO2)3(OH)n](6-n), n = 4-8. PMID:24301256

Zanonato, Pier Luigi; Di Bernardo, Plinio; Grenthe, Ingmar

2014-02-14

100

Polymer complexes. LX. Supramolecular coordination and structures of N(4-(acrylamido)-2-hydroxybenzoic acid) polymer complexes.  

PubMed

A number of novel polymer complexes of various anions of copper(II), cobalt(II), nickel(II) and uranyl(II) with N(4-(acrylamido)-2-hydroxy benzoic acid) (ABH) have been synthesized and characterized by elemental analysis, IR, 1H NMR, magnetic susceptibility measurements, electronic spin resonance, vibrational spectra and thermal analysis. The molecular structures of the ligand are optimized theoretically and the quantum chemical parameters are calculated. Tentative structures for the polymeric metal complexes due to their potential application are also suggested. The IR data exhibit the coordination of ONO2/OAc/SO4 with the metal ions in the polymeric metal complex. Vibrational spectra indicate coordination of carboxylate oxygen and phenolic OH of the ligand giving a MO4 square planar chromophore. Ligand field ESR spectra support square planar geometry around Cu(II). The thermal decomposition of the polymer complexes were discussed in relation to structure, and the thermodynamic parameters of the decomposition stages were evaluated applying Coast-Redfern and Horowitz-Metzger methods. PMID:25589393

Ghoneim, M M; El-Sonbati, A Z; El-Bindary, A A; Diab, M A; Serag, L S

2015-04-01

101

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

102

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

103

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

104

Uncertainty Analysis and Extrapolation of Additive Uranyl Surface Complexation Kinetic Models  

NASA Astrophysics Data System (ADS)

Tremendous progress has been made in the last few years in using Multi-rate Skinetic surface Complex complexation Reactionreaction (SCR) models for the analysis and predicting prediction of uranyl (U(VI) )adsorption/desorption in sediments. However, such analysis and prediction s with the model are often deterministic, and as such they focusing only on the most probable forecastscenario, without considering various model uncertaintiesan explicit estimate of the associated uncertainty. In this presentationstudy, thewe will describe a generalized likelihood uncertainty estimation method framework was adopted in the Differential Evolution Markov Chain Monte Caro framework to explore the explicit consider model structure and parameter uncertaintiesy in the U(VI) SCR models and their effects on the model extrapolation. Both sStirred-flow cell and column experiments were conducted carried out to investigate derive experimental data of U(VI) sorption/desorption for model application and uncertainty analysis.uranium release from different size fractions of sediments from US DOE Hanford site. The U(VI)-contaminated sediment used in the experiments was collected from US DOE Hanford site, and was air-dried and dry-sieved to four size fractions (<75 ?m, 75-500?m, 500-2000 ?m and 2000-8000?m) to investigate desorption kinetics. The experimental results were used to parameterize SCR kinetic models and to determine model structure and parameter uncertainties for individual size fractions. The individual size fraction models were then used to evaluate the predictivity of the size-additivity model and to analyze the extrapolation of both parameter and model structure uncertainties. The results demonstrated that model uncertainty, especially model structure uncertainty, is an important factor to be considered in model prediction and evalution of the applicability of the extrapolated models.

Zhang, X.; Liu, C.; Hu, Q.; Hu, X. B.

2012-12-01

105

Role of citrate as a complexing ligand which permits enzymically-mediated uranyl ion bioaccumulation  

SciTech Connect

Microorganisms can be used to remove toxic heavy metals from liquid industrial wastes. One potentially useful system utilizes the enzymically-mediated biomineralization of heavy metals at the surface of bacterial cells. This well-documented system harnesses a metal-resistant phosphatase enzyme overproduced by a Citrobacter sp.; metal uptake is mediated by the activity of this enzyme, which persists in non-growing cells, to liberate HPO{sub 4}{sup 2-} from glycerol 2-phosphate with stoichiometric deposition of heavy metals(M) as cell-bound MHPO{sub 4}. Recent attention has focused on the treatment of wastes from nuclear power and nuclear fuel reprocessing activities, together with discharges of native uranium in mining wastes. Previous investigations using the Citrobacter sp. demonstrated removal of uranium and the transuranic elements, plutonium and americium. Although uranium is inhibitory to the growth of the Citrobacter strain, and the activity of the cellular phosphatase, uranyl phosphate accumulates as polycrystalline HUO{sub 2}PO{sub 4} at the cell surface. The rate of uranyl removal into the growing crystal is primarily dependent on the rate of phosphate release by the enzyme catalysed reaction. This is inconsistent with the reported toxicity of uranyl ion to the mediating phosphatase; however, in the presence of an excess of substrate, the rapid rate of phosphate release facilitated metal precipitation without toxic effect. Under substrate-limiting conditions uranyl toxicity was seen. The present investigation shows the inhibition of Citrobacter sp. phosphatase is related to the concentration of uranyl ion, and that citrate buffer can protect against this toxicity, and permit metal bioaccumulation. The toxicity pattern is dependent upon the substrate used; possible reasons for these effects, and environmental implications are discussed. 18 refs., 5 figs.

Yong, P.; Macaskie, L.E. [Univ. of Birmingham (United Kingdom)

1995-06-01

106

Self-assembly of a 3d-5f trinuclear single-molecule magnet from a pentavalent uranyl complex.  

PubMed

Mixed-metal uranium compounds are very attractive candidates in the design of single-molecule magnets (SMMs), but only one 3d-5f hetero-polymetallic SMM containing a uranium center is known. Herein, we report two trimeric heterodimetallic 3d-5f complexes self-assembled by cation-cation interactions between a uranyl(V) complex and a TPA-capped M(II) ?complex (M=Mn (1), Cd (2); TPA=tris(2-pyridylmethyl)amine). The metal centers were strategically chosen to promote the formation of discrete molecules rather than extended chains. Compound 1, which contains an almost linear {Mn?O?U?O?Mn} core, exhibits SMM behavior with a relaxation barrier of 810.5?K-the highest reported for a mono-uranium system-arising from intramolecular Mn-U exchange interactions combined with the high Ising anisotropy of the uranyl(V) moiety. Compound 1 also exhibits an open magnetic hysteresis loop at temperatures less than 3?K, with a significant coercive field of 1.9?T at 1.8?K. PMID:25284018

Chatelain, Lucile; Walsh, James P S; Pcaut, Jacques; Tuna, Floriana; Mazzanti, Marinella

2014-12-01

107

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...

108

Structural and spectroscopy studies of complexes of the uranyl ion with 2,2?-bipyridine-N,N?-dioxide  

Microsoft Academic Search

2,2?-Bipyridine-N,N?-dioxide (bypO2=L) complexes of the composition [UO2(bypO2)2(NO3)2]2H2O (UO2L2NO3), [UO2(bypO2)2H2O](ClO4)2 (UO2L2ClO4) and [UO2bypO2(H2O)2SO4] (UO2LSO4) have been prepared by the reactions of the respective hydrated uranyl salts with the bypO2 ligand in water. The structures of the complexes were elucidated using elemental and thermal analyses, IR and luminescence spectroscopy as well as luminescence lifetime measurements. The IR spectra show that the bonding

Zbigniew Hnatejko; Stefan Lis; Zdzis?aw Stry?a; Przemys?aw Starynowicz

2010-01-01

109

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

SciTech Connect

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

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

2007-03-20

110

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

PubMed

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

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

2013-10-21

111

Unexpected oxidation of cis-1,3-dithiane-1,3-dioxide ( cis-DTSO 2) during the preparation of the uranyl nitrate complex  

Microsoft Academic Search

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

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

2003-01-01

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

2011-09-01

113

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

114

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

NASA Astrophysics Data System (ADS)

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

Mohamed, Gehad G.

2005-12-01

115

Photoconversion and photocatalytic activity of uranyl in acetone solutions  

NASA Astrophysics Data System (ADS)

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

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

2007-09-01

116

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

117

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

118

Giant regular polyhedra from calixarene carboxylates and uranyl  

PubMed Central

Self-assembly of large multi-component systems is a common strategy for the bottom-up construction of discrete, well-defined, nanoscopic-sized cages. Icosahedral or pseudospherical viral capsids, built up from hundreds of identical proteins, constitute typical examples of the complexity attained by biological self-assembly. Chemical versions of the so-called 5 Platonic regular or 13 Archimedean semi-regular polyhedra are usually assembled combining molecular platforms with metals with commensurate coordination spheres. Here we report novel, self-assembled cages, using the conical-shaped carboxylic acid derivatives of calix[4]arene and calix[5]arene as ligands, and the uranyl cation UO22+ as a metallic counterpart, which coordinates with three carboxylates at the equatorial plane, giving rise to hexagonal bipyramidal architectures. As a result, octahedral and icosahedral anionic metallocages of nanoscopic dimensions are formed with an unusually small number of components. PMID:22510690

Pasquale, Sara; Sattin, Sara; Escudero-Adn, Eduardo C.; Martnez-Belmonte, Marta; de Mendoza, Javier

2012-01-01

119

The Reactivity Patterns of Low-Coordinate Iron Hydride Complexes  

PubMed Central

We report a survey of the reactivity of the first isolable iron-hydride complexes with a coordination number less than five. The high-spin iron(II) complexes [(?-diketiminate)Fe(?-H)]2 react rapidly with representative cyanide, isocyanide, alkyne, N2, alkene, diazene, azide, CO2, carbodiimide and Brnsted acid containing substrates. The reaction outcomes fall into three categories: (1) addition of Fe-H across a multiple bond of the substrate, (2) reductive elimination of H2 to form iron(I) products, and (3) protonation of the hydride to form iron(II) products. The products include imide, isocyanide, vinyl, alkyl, azide, triazenido, benzo[c]cinnoline, amidinate, formate, and hydroxo complexes. These results expand the range of known bond transformations at iron complexes. Additionally, they give insight into the elementary transformations that may be possible at the iron-molybdenum cofactor of nitrogenases, which may have hydride ligands on high-spin, low coordinate metal atoms. PMID:18444648

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

2008-01-01

120

Tuning Coordination in s-Block Carbazol-9-yl Complexes.  

PubMed

1,3,6,8-Tetra-tert-butylcarbazol-9-yl and 1,8-diaryl-3,6-di(tert-butyl)carbazol-9-yl ligands have been utilized in the synthesis of potassium and magnesium complexes. The potassium complexes (1,3,6,8-tBu4 carb)K(THF)4 (1; carb=C12 H4 N), [(1,8-Xyl2 -3,6-tBu2 carb)K(THF)]2 (2; Xyl=3,5-Me2 C6 H3 ) and (1,8-Mes2 -3,6-tBu2 carb)K(THF)2 (3; Mes=2,4,6-Me3 C6 H2 ) were reacted with MgI2 to give the Hauser bases 1,3,6,8-tBu4 carbMgI(THF)2 (4) and 1,8-Ar2 -3,6-tBu2 carbMgI(THF) (Ar=Xyl 5, Ar=Mes 6). Structural investigations of the potassium and magnesium derivatives highlight significant differences in the coordination motifs, which depend on the nature of the 1- and 8-substituents: 1,8-di(tert-butyl)-substituted ligands gave ?-type compounds (1 and 4), in which the carbazolyl ligand acts as a multi-hapto donor, with the metal cations positioned below the coordination plane in a half-sandwich conformation, whereas the use of 1,8-diaryl substituted ligands gave ?-type complexes (2 and 6). Space-filling diagrams and percent buried volume calculations indicated that aryl-substituted carbazolyl ligands offer a steric cleft better suited to stabilization of low-coordinate magnesium complexes. PMID:25783772

Ortu, Fabrizio; Moxey, Graeme J; Blake, Alexander J; Lewis, William; Kays, Deborah L

2015-04-27

121

Uranyl clay photocatalysts  

SciTech Connect

Uranyl-exchanged clay photocatalysts have been used to photooxidize alcohols to ketones. Luminescence excitation, emission, and lifetime studies have been used to characterize these materials before, during, and after reaction. The absorption maxima for most of the uranyl-exchanged clays shift to higher wavelengths with respect to those for other aluminosilicate catalysts. Lifetime results indicate that several sites exist on these catalysts. Saturation of alcohol/clay slurries with oxygen leads to increasing rates of ketone formation. These uranyl-sensitized photoautoxidation reactions also produce coupled products as well as aldehydes, such as acetaldehyde, as identified by gas chromatography/mass spectrometry techniques. Different clays yield different amounts of product and rates of product formation. Hectorite exchange with uranyl ions is the most active catalyst of all aluminosilicate materials we have studied over short photolysis mass. 22 references, 6 figures, 6 tables.

Suib, S.L.; Carrado, K.A.

1985-03-13

122

Isocyanide and Phosphine Oxide Coordination in Binuclear Chromium Pacman Complexes  

PubMed Central

The new binuclear chromium Pacman complex [Cr2(L)] of the Schiff base pyrrole macrocycle H4L has been synthesized and structurally characterized. Addition of isocyanide, C?NR (R = xylyl, tBu), or triphenylphosphine oxide donors to [Cr2(L)] gives contrasting chemistry with the formation of the new coordination compounds [Cr2(?-CNR)(L)], in which the isocyanides bridge the two Cr(II) centers, and [Cr2(OPPh3)2(L)], a Cr(II) phosphine oxide adduct with the ligands exogenous to the cleft. PMID:24489428

2013-01-01

123

Uranyl peroxide closed clusters containing topological squares  

SciTech Connect

Four self-assembling clusters of uranyl peroxide polyhedra have been formed in alkaline aqueous solutions and structurally characterized. These clusters consist of 28, 30, 36 and 44 uranyl polyhedra and exhibit complex new topologies. Each has a structure that contains topological squares, pentagons and hexagons. Analysis of possible topologies within boundary constraints indicates a tendency for adoption of higher symmetry topologies in these cases. Small angle X-ray scattering data demonstrated that crystals of one of these clusters can be dissolved in ultrapure water and that the clusters remain intact for at least several days.

Unruh, Daniel K.; Burtner, Alicia; Pressprich, Laura; Sigmon, Ginger E.; Burns, Peter C

2010-01-01

124

Expanding the crystal chemistry of uranyl peroxides: four hybrid uranyl-peroxide structures containing EDTA.  

PubMed

The first four uranyl peroxide compounds containing ethylenediaminetetra-acetate (EDTA) were synthesized and characterized from aqueous uranyl peroxide nitrate solutions with a pH range of 5-7. Raman spectra demonstrated that reaction solutions that crystallized [NaK15[(UO2)8(O2)8(C10H12O10N2)2(C2O4)4](H2O)14] (1) and [Li4K6[(UO2)8(O2)6(C10H12O10N2)2(NO3)6](H2O)26] (2) contained excess peroxide, and their structures contained oxidized ethylenediaminetetraacetate, EDTAO2(4-). The solutions from which [K4[(UO2)4(O2)2(C10H13O8N2)2(IO3)2](H2O)16] (3) and LiK3[(UO2)4(O2)2(C10H12O8N2)2(H2O)2](H2O)18 (4) crystallized contained no free peroxide, and the structures incorporated intact EDTA(4-). In contrast to the large family of uranyl peroxide cage clusters, coordination of uranyl peroxide units in 1-4 by EDTA(4-) or EDTAO2(4-) results in isolated tetramers or dimers of uranyl ions that are bridged by bidentate peroxide groups. Two tetramers are bridged by EDTAO2(4-) to form octamers in 1 and 2, and dimers of uranyl polyhedra are linked through iodate groups in 3 and EDTA(4-) in 4, forming chains in both cases. In each structure the U-O2-U dihedral angle is strongly bent, at ?140, consistent with the configuration of this linkage in cage clusters and other recently reported uranyl peroxides. PMID:25350361

Qiu, Jie; Ling, Jie; Sieradzki, Claire; Nguyen, Kevin; Wylie, Ernest M; Szymanowski, Jennifer E S; Burns, Peter C

2014-11-17

125

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

SciTech Connect

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

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

1995-01-01

126

Similarities between GCS and human motor cortex: complex movement coordination  

NASA Astrophysics Data System (ADS)

The "Gran Telescopio de Canarias" (GTC1) is an optical-infrared 10-meter segmented mirror telescope at the ORM observatory in Canary Islands (Spain). The GTC control system (GCS), the brain of the telescope, is is a distributed object & component oriented system based on RT-CORBA and it is responsible for the management and operation of the telescope, including its instrumentation. On the other hand, the Human motor cortex (HMC) is a region of the cerebrum responsible for the coordination of planning, control, and executing voluntary movements. If we analyze both systems, as far as the movement control of their mechanisms and body parts is concerned, we can find extraordinary similarities in their architectures. Both are structured in layers, and their functionalities are comparable from the movement conception until the movement action itself: In the GCS we can enumerate the Sequencer high level components, the Coordination libraries, the Control Kit library and the Device Driver library as the subsystems involved in the telescope movement control. If we look at the motor cortex, we can also enumerate the primary motor cortex, the secondary motor cortices, which include the posterior parietal cortex, the premotor cortex, and the supplementary motor area (SMA), the motor units, the sensory organs and the basal ganglia. From all these components/areas we will analyze in depth the several subcortical regions, of the the motor cortex, that are involved in organizing motor programs for complex movements and the GCS coordination framework, which is composed by a set of classes that allow to the high level components to transparently control a group of mechanisms simultaneously.

Rodrguez, Jose A.; Macias, Rosa; Molgo, Jordi; Guerra, Dailos

2014-07-01

127

The Anaphase-promoting Complex Coordinates Initiation of Lens Differentiation  

PubMed Central

Lens development requires the precise coordination of cell division and differentiation. The mechanisms by which the differentiation program is initiated after cell cycle arrest remains not well understood. Cyclin-dependent kinase inhibitors (CKIs), such as p15 and p21, have been suggested to be critical components that inhibit G1 progression and therefore, their activation is necessary for quiescence and important for the onset of differentiation. Regulation of p15 and p21 is principally governed by transforming growth factor (TGF)-?signaling pathway. We have identified that Cdh1/APC, a critical ubiquitin protein ligase, plays an important role in regulating lens differentiation by facilitating TGF-?induced degradation of SnoN, a transcriptional corepressor that needs to be removed for transcriptional activation of p15 and p21. The depletion of Cdh1 by RNA interference attenuates the TGF-?mediated induction of p15 and p21 and significantly blocks lens differentiation. Expression of nondegradable SnoN also noticeably attenuates lens induction. Furthermore, we have shown that Cdh1 and SnoN form a complex at the onset of lens differentiation. In vivo histological analysis confirms our biochemical and genetic results. Thus, Cdh1/APC is crucial to the coordination of cell cycle progression and the initiation of lens differentiation through mediating TGF-?signaling-induced destruction of SnoN. PMID:17215516

Wu, George; Glickstein, Sara; Liu, Weijun; Fujita, Takeo; Li, Wenqi; Yang, Qi; Duvoisin, Robert

2007-01-01

128

N -(1,5-dimethyl-3-oxo-2-phenyl-1,2-dihydropyrazol-4-yl)- P , P -diphenylamidophosphinate and its complexes with neodymium(III), erbium(III), thorium(IV), and uranyl nitrates: Synthesis and crystal and molecular structure  

Microsoft Academic Search

A new phosphoryl-containing ligand based on 4-aminoantipyrine-N-(1,5-dimethyl-3-oxo-2-phenyl-1,2-dihydropyrazol-4-yl)-P,P-diphenylamidophosphinate (L) was synthesized. In crystals, the L molecules were found to be combined in centrosymmetric dimers\\u000a through N-HO=C hydrogen bonds. The complexes of L with neodymium(III), erbium(III), thorium(IV), and uranyl nitrates were\\u000a obtained, and their structures were determined. The bands of the C=O and P=O groups in the IR spectra of these complexes

E. I. Matrosov; I. B. Goryunova; K. A. Lysenko; M. S. Grigorev; A. M. Safiulina; E. I. Goryunov; E. E. Nifantev

2011-01-01

129

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

130

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. PMID:3416028

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

1988-01-01

131

Coordinates  

NSDL National Science Digital Library

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

David Stern

132

Ionothermal synthesis of uranyl compounds that incorporate imidazole derivatives  

NASA Astrophysics Data System (ADS)

Ionothermal reactions of uranyl nitrate with various salts in methylimidazolium-based ionic liquids have produced single crystals of three uranyl compounds that incorporate imidazole derivatives as charge-balancing cations. (C4H7N2)[(UO2)(PO3F)(F)] (1) crystallizes in space group C2, a=17.952(1) , b=6.9646(6) , c=8.5062(7) , ?=112.301(1), (C6H11N2)2[(UO2)(SO4)2] (2) crystallizes in space group C2/c, a=31.90(1) , b=9.383(5) , c=13.770(7) , ?=93.999(7) and (C6H11N2)[(UO2)2(PO4)(HPO4) (3) crystallizes in space group P21/n, a=9.307(2), b=18.067(4), c=9.765(2), ?=93.171(2). The U6+ cations are present as (UO2)2+ uranyl ions coordinated by three O atoms and two F atoms in 1 and five O atoms in 2 and 3 to give pentagonal bipyramids. The structural unit in 1 is composed of F-sharing dimers of uranyl pentagonal bipyramids linked into sheets through corner-sharing fluorophosphate tetrahedra. The structural unit in 2 is composed of uranyl pentagonal bipyramids with one chelating sulfate tetrahedron linked into chains by three other corner-sharing sulfate tetrahedra. In 3, the structural unit is composed of chains of uranyl pentagonal bipyramids linked into sheets through edge- and corner-sharing phosphate and hydrogen phosphate tetrahedra. N-methylimidazolium cations occupy the interstitial space between the uranyl fluorophosphate sheets in 1, whereas 1-ethyl-3-methylimidazolium cations link the uranyl sulfate and phosphate units in 2 and 3 into extended structures.

Wylie, Ernest M.; Dustin, Megan K.; Smith, Jeremy S.; Burns, Peter C.

2013-01-01

133

Uranyl-water-containing complexes: solid-state UV-MALDI mass spectrometric and IR spectroscopic approach for selective quantitation.  

PubMed

Since primary environmental concept for long storage of nuclear waste involved assessment of water in uranium complexes depending on migration processes, the paper emphasized solid-state matrix-assisted laser desorption/ionization (MALDI) mass spectrometric (MS) and IR spectroscopic determination of UO2(NO3)26H2O; UO2(NO3)23H2O, ?-, ?-, and ?-UO3 modifications; UO3xH2O (x?=?1 or 2); UO3H2O, described chemically as UO2(OH)2, ?- and ?-UO2(OH)2 modifications; and UO42H2O, respectively. Advantages and limitation of vibrational spectroscopic approach are discussed, comparing optical spectroscopic data and crystallographic ones. Structural similarities occurred in ?-? modifications of UO3, and UO2(OH)2 compositions are analyzed. Selective speciation achieved by solid-state mass spectrometry is discussed both in terms of its analytical contribution for environmental quality assurance and assessment of radionuclides, and fundamental methodological interest related the mechanistic complex water exchange of UO3H2O forms in the gas phase. In addition to high selectivity and precision, UV-MALDI-MS, employing an Orbitrap analyzer, was a method that provided fast steps that limited sample pretreatment techniques for direct analysis including imaging. Therefore, random and systematic errors altering metrology and originating from the sample pretreatment stages in the widely implemented analytical protocols for environmental sampling determination of actinides are significantly reduced involving the UV-MALDI-Orbitrap-MS method. The method of quantum chemistry is utilized as well to predict reliably the thermodynamics and nature of U-O bonds in uranium species in gas and condensed phases. PMID:23942998

Ivanova, Bojidarka; Spiteller, Michael

2014-01-01

134

Luminescence of uranyl nitrate trihydrate crystals at high exciting-light intensities  

Microsoft Academic Search

The characteristic features of the luminescence of uranyl nitrate crystals at high excitation power densities have been considered.\\u000a It is shown that there occurs accumulation of excitations in a system of uranyl centers, whereas the presence of forced absorption\\u000a enhances the migration processes over the uranyl complexes. An increase in the power density of excitation leads to the amplification\\u000a of

I. V. Barsukov; V. V. Sytko; D. S. Umreiko

2005-01-01

135

Ligand sensitized luminescence of uranyl by benzoic acid in acetonitrile medium: A new luminescent uranyl benzoate specie  

NASA Astrophysics Data System (ADS)

Benzoic acid (BA) is shown to sensitize and enhance the luminescence of uranyl ion in acetonitrile medium. Luminescence spectra and especially UV-Vis spectroscopy studies reveal the formation of tri benzoate complex of uranyl i.e. [UO2(C6H5COO)3]- which is highly luminescent. In particular, three sharp bands at 431, 443, 461 nm of absorption spectra provides evidence for tri benzoate specie of uranyl in acetonitrile medium. The luminescence lifetime of uranyl in this complex is 68 ?s which is much more compared to the lifetime of uncomplexed uranyl (20 ?s) in acetonitrile medium. In contrary to aqueous medium where uranyl benzoate forms 1:1 and 1:2 species, spectroscopic data reveal formation of 1:3 complex in acetonitrile medium. Addition of water to acetonitrile results in decrease of luminescence intensity of this specie and the luminescence features implode at 20% (v/v) of water content. For the first time, to the best of our knowledge, the existence of [UO2(C6H5COO)3]- specie in acetonitrile is reported. Mechanism of luminescence enhancement is discussed.

Kumar, Satendra; Maji, S.; Joseph, M.; Sankaran, K.

2015-03-01

136

Ligand sensitized luminescence of uranyl by benzoic acid in acetonitrile medium: a new luminescent uranyl benzoate specie.  

PubMed

Benzoic acid (BA) is shown to sensitize and enhance the luminescence of uranyl ion in acetonitrile medium. Luminescence spectra and especially UV-Vis spectroscopy studies reveal the formation of tri benzoate complex of uranyl i.e. [UO2(C6H5COO)3](-) which is highly luminescent. In particular, three sharp bands at 431, 443, 461nm of absorption spectra provides evidence for tri benzoate specie of uranyl in acetonitrile medium. The luminescence lifetime of uranyl in this complex is 68?s which is much more compared to the lifetime of uncomplexed uranyl (20?s) in acetonitrile medium. In contrary to aqueous medium where uranyl benzoate forms 1:1 and 1:2 species, spectroscopic data reveal formation of 1:3 complex in acetonitrile medium. Addition of water to acetonitrile results in decrease of luminescence intensity of this specie and the luminescence features implode at 20% (v/v) of water content. For the first time, to the best of our knowledge, the existence of [UO2(C6H5COO)3](-) specie in acetonitrile is reported. Mechanism of luminescence enhancement is discussed. PMID:25528510

Kumar, Satendra; Maji, S; Joseph, M; Sankaran, K

2015-03-01

137

Reactivity of the "yl"-bond in uranyl(VI) complexes. 1. Rates and mechanisms for the exchange between the trans-dioxo oxygen atoms in (UO2)2(OH)2 2+ and mononuclear UO2(OH)n 2-n complexes with solvent water.  

PubMed

The stoichiometric mechanism, rate constant, and activation parameters for the exchange of the "yl"-oxygen atoms in the dioxo uranium(VI) ion with solvent water have been studied using 17O NMR spectroscopy. The experimental rate equation, (-->)v= k(2obs)[UO2(2+)]tot2/[H+]2, is consistent with a mechanism where the first step is a rapid equilibrium 2U(17)O2(2+) + 2H2O<==>(U(17)O2)2(OH)2(2+) + 2H+, followed by the rate-determining step (U(17)O2)2(OH)2(2+) + H2O<==>(UO2)2*(OH)2(2+) + H2(17)O, where the back reaction can be neglected because the (17)O enrichment in the water is much lower than in the uranyl ion. This mechanism results in the following rate equation (-->)v= d[(UO2)2(OH)2(2+)]/dt = k(2,2)[(UO2)2(OH)2(2+)] = k(2,2*)beta(2,2)[UO2(2+)]2/[H + ]2; with k(2,2) = (1.88 +/- 0.22) x 10(4) h(-1), corresponding to a half-life of 0.13 s, and the activation parameters DeltaH++ = 119 +/- 13 kJ mol-1 and DeltaS++ = 81 +/- 44 J mol(-1) K(-1). *Beta(2,)2 is the equilibrium constant for the reaction 2UO2(2+) + 2H2O<==>(UO2)2(OH)2(2+) + 2H+. The experimental data show that there is no measurable exchange of the "yl"-oxygen in UO2(2+), UO2(OH)+, and UO2(OH)4(2-)/ UO2(OH)5(3-), indicating that "yl"-exchange only takes place in polynuclear hydroxide complexes. There is no "yl"-exchange in the ternary complex (UO2)2(mu-OH)2(F)2(oxalate)2(4-), indicating that it is also necessary to have coordinated water in the first coordination sphere of the binuclear complex, for exchange to take place. The very large increase in lability of the "yl"-bonds in (UO2)2(OH)2(2+) as compared to those of the other species is presumably a result of proton transfer from coordinated water to the "yl"-oxygen, followed by a rapid exchange of the resulting OH group with the water solvent. "Yl"-exchange through photochemical mediation is well-known for the uranyl(VI) aquo ion. We noted that there was no photochemical exchange in UO2(CO3)3(4-), whereas there was a slow exchange or photo reduction in the UO2(OH)4(2-) / UO2(OH)5(3-) system that eventually led to the appearance of a black precipitate, presumably UO2. PMID:17887747

Szab, Zoltan; Grenthe, Ingmar

2007-10-29

138

A new uranyl phosphate chain in the structure of parsonsite  

SciTech Connect

The structure of parsonsite, Pb{sub 2}[(UO{sub 2})(PO{sub 4}){sub 2}] has been solved by direct methods and refined to R = 6.0 and a goodness-of-fit (S) of 0.92 using 1187 unique observed reflections collected with MoK{alpha} X-rays and a CCD-based detector. The single unique U{sup 6+} cation is present as a (UO{sub 2}){sup 2+} uranyl ion (Ur) and is coordinated by five additional atoms of O arranged at the equatorial corners of a pentagonal bipyramid capped by the O{sub Ur} atoms. Uranyl polyhedra share an edge-forming dimers, which are cross-linked by edge- and vertex-sharing with two distinct phosphate tetrahedra, resulting in a new uranyl phosphate chain. Two symmetrically distinct Pb{sup 2+} cations are coordinated by nine and six oxygen atoms, and link adjacent uranyl phosphate chains. Parsonsite is the first uranyl phosphate mineral structure that is based upon chains of polymerized polyhedra of higher bond-valence; others contain sheets that are either based upon the autunite or phosphuranylite anion-topologies.

Burns, P.C.

2000-06-01

139

Gas-phase ion-molecule reactions of transition metal complexes: the effect of different coordination spheres on complex reactivity.  

PubMed

Using a modified quadrupole ion trap mass spectrometer, a series of metal complex ions have been reacted with acetonitrile in the gas phase. Careful control of the coordination number and the type of coordinating functionality in diethylenetriamine-substituted ligands enable the effects of the coordination sphere on metal complex reactivity to be examined. The association reaction kinetics of acetonitrile with these pentacoordinate complexes are followed in order to obtain information about the starting complexes and the reaction dynamics. The kinetics and thermodynamics of acetonitrile addition to the metal complex ions are strongly affected by the chemical environment around the metal center such that significant differences in reactivity are observed for Co(II) and Cu(II) complexes with various coordination spheres. When thiophene, furan, or benzene moieties are present in the coordination sphere of the complex, addition of two acetonitrile molecules is readily observed. In contrast, ligands with better sigma donors react mainly to add one acetonitrile molecule. Among the ligands with good sigma donors, a clear trend in reactivity is observed in which complexes with nitrogen-containing ligands are the least reactive, sulfur-containing complexes are more reactive, and oxygen-containing complexes are the most reactive. In general, equilibrium and reaction rate constants seem to be consistent with the hard and soft acid and base (HSAB) principle. Interestingly, the presence of certain groups (e.g., pyridine and imidazole) in the coordination sphere clearly can change the acid character of the metal as seen by their effect on the binding properties of other functional groups in the same ligand. Finally, we conclude that because complexes with different coordination spheres react to noticeably different extents, ion-molecule (I-M) reactions may be potentially useful for obtaining coordination structure information for transition metal complexes. PMID:12148806

Combariza, Marianny Y; Vachet, Richard W

2002-07-01

140

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

141

Uranyl extraction by N,N-dialkylamide ligands studied using static and dynamic DFT simulations.  

PubMed

We report DFT static and dynamic studies on uranyl complexes [UO(2)(NO(3))x(H(2)O)(y)L(z)](2-x) involved in the uranyl extraction from water to an "oil" phase (hexane) by an amide ligand L (N,N-dimethylacetamide). Static DFT results "in solution" (continuum SMD models for water and hexane) predict that the stepwise formation of [UO(2)(NO(3))(2)L(2)] from the UO(2)(H(2)O)(5)(2+) species is energetically favourable, and allow us to compare cis/trans isomers of penta- and hexa-coordinated complexes and key intermediates in the two solvents. DFT-MD simulations of [UO(2)(NO(3))(2)L(2)], [UO(2)(NO(3))(2)(H(2)O)L(2)], and [UO(2)(NO(3))(H(2)O)L(2)](+) species in explicit solvent environments (water, hexane, or the water/hexane interface) represented at the MM or full-DFT level reveal a versatile solvent dependent binding mode of nitrates, also evidenced by metadynamics simulations. In water and at the interface, the latter exchange from bi- to monodentate, via in plane rotational motions in some cases. Remarkably, structures of complexes at the interface are more "water-like" than gas phase- or hexane-like. Thus, the order of U-O(NO(3))/U-O(L) bond distances observed in the gas phase (U-O(nit) < U-OL) is inverted at the interface and in water. Overall, the results are consistent with the experimental observation of uranyl extraction from nitric acid solutions by amide analogues (bearing "fatty" substituents), and allow us to propose possible extraction mechanisms, involving complexation of L "right at the interface". They also point to the importance of the solvent environment and the dynamics on the structure and stability of the complexes. PMID:25412447

Sieffert, Nicolas; Wipff, Georges

2015-02-14

142

Recent advances in nanoparticle carriers for coordination complexes.  

PubMed

Coordination compounds are substances in which a central metal atom is bonded to nonmetal atoms, or groups of atoms, called ligands. Examples include vitamin B12, hemoglobin, chlorophyll, dyes and pigments, as well as catalysts used in organic synthesis. Coordination compounds have received much attention in recent years. This interest was prompted by the discovery that several coordination compounds exhibit activity against bacteria, fungi and cancer. Some coordination compounds are not in clinical use, because of poor water solubility. Because they are unable to cross the lipid membranes of cells, bioavailability and efficacy are low. Some researchers have applied nanotechnology to coordination compounds, hoping to reduce the number of doses required and the severity of side effects, and also to improve biological activity. Nanotechnology can deliver active components in sufficient concentrations throughout treatment, guiding it to the desired location of action; conventional treatments do not meet these requirements. In this study we review some drug delivery systems based on nanotechnology, such as microemulsions (MEs), cyclodextrin (CD), polymeric nanoparticles (PN), solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), magnetic and gold nanoparticles (MNPs / AuNPs) and liquid crystalline systems (LC), and coordination compounds. PMID:25579344

Sato, Mariana Rillo; da Silva, Patricia Bento; de Souza, Rodrigo Alves; dos Santos, Karen Cristina; Chorilli, Marlus

2015-01-01

143

Ionothermal synthesis of uranyl compounds that incorporate imidazole derivatives  

SciTech Connect

Ionothermal reactions of uranyl nitrate with various salts in methylimidazolium-based ionic liquids have produced single crystals of three uranyl compounds that incorporate imidazole derivatives as charge-balancing cations. (C{sub 4}H{sub 7}N{sub 2})[(UO{sub 2})(PO{sub 3}F)(F)] (1) crystallizes in space group C2, a=17.952(1) A, b=6.9646(6) A, c=8.5062(7) A, {beta}=112.301(1) Degree-Sign , (C{sub 6}H{sub 11}N{sub 2}){sub 2}[(UO{sub 2})(SO{sub 4}){sub 2}] (2) crystallizes in space group C2/c, a=31.90(1) A, b=9.383(5) A, c=13.770(7) A, {beta}=93.999(7) Degree-Sign and (C{sub 6}H{sub 11}N{sub 2})[(UO{sub 2}){sub 2}(PO{sub 4})(HPO{sub 4}) (3) crystallizes in space group P2{sub 1}/n, a=9.307(2), b=18.067(4), c=9.765(2), {beta}=93.171(2). The U{sup 6+} cations are present as (UO{sub 2}){sup 2+} uranyl ions coordinated by three O atoms and two F atoms in 1 and five O atoms in 2 and 3 to give pentagonal bipyramids. The structural unit in 1 is composed of F-sharing dimers of uranyl pentagonal bipyramids linked into sheets through corner-sharing fluorophosphate tetrahedra. The structural unit in 2 is composed of uranyl pentagonal bipyramids with one chelating sulfate tetrahedron linked into chains by three other corner-sharing sulfate tetrahedra. In 3, the structural unit is composed of chains of uranyl pentagonal bipyramids linked into sheets through edge- and corner-sharing phosphate and hydrogen phosphate tetrahedra. N-methylimidazolium cations occupy the interstitial space between the uranyl fluorophosphate sheets in 1, whereas 1-ethyl-3-methylimidazolium cations link the uranyl sulfate and phosphate units in 2 and 3 into extended structures. - Graphical abstract: The synthesis of uranyl compounds by ionothermal treatment is explored, and provides three novel compounds and insights concerning the role of water in controlling the structural units. Highlights: Black-Right-Pointing-Pointer Ionothermal syntheses have produced three new uranyl compounds. Black-Right-Pointing-Pointer Imidazole derivatives are incorporated as charge-balancing agents. Black-Right-Pointing-Pointer X-ray and spectroscopic analyses reveal variability between imidazole derivatives. Black-Right-Pointing-Pointer This method offers synthetic insight in the absence of water at low temperatures.

Wylie, Ernest M.; Dustin, Megan K.; Smith, Jeremy S. [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556 (United States); Burns, Peter C., E-mail: pburns@nd.edu [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556 (United States)

2013-01-15

144

Novel uranyl(VI) complexes incorporating propylene-bridged salen-type N2O2-ligands: a structural and computational approach.  

PubMed

The synthesis of the tetradentate dianionic ligand, H2L (2,2'-(1E,1'E)-(2,2-dimethylpropane-1,3-dyl)bis(azanylylidene)bis(methanylylidene)diphenol), from 2,2-dimethyl-1,3-diaminopropane and its reaction with UO2(CH3COO)22H2O in a 1:1 molar ratio in methanol to produce the complex [UO2(L)(CH3OH)] are reported. The isolated compounds have been characterized by elemental analysis, ionization mass spectrometry (ESI-MS), UV/Vis, FT-IR, (1)H- and (13)C-NMR, DEPT-135 spectroscopy, TGA and single-crystal X-ray diffraction. As shown by X-ray crystallography, the coordination geometry around the uranium centre is distorted pentagonal bipyramidal with two imine nitrogen atoms, two phenolic oxygen atoms and one methanol O atom occupying equatorial sites, together with two axial oxo groups. To obtain insights into the structure and spectral properties of the studied complex, density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations have been carried out. The computed results show that LUMO of the complex is featured with uranium f orbital character. TD-DFT results indicate that the complex displays two intense bands and one weak charge transfer band. The charge transfer band is primarily due to HOMO ? LUMO (53%). Two intense bands have main contributions from HOMO-2 ? LUMO (81%) and HOMO-3 ? LUMO (77%) transitions, respectively. TD-DFT results indicate that the complex displays the charge transfer band primarily due to HOMO ? LUMO (53%) and other two charge transfer bands have main contributions from HOMO-2 ? LUMO (81%), HOMO-3 ? LUMO (77%) transitions, respectively. NBO analysis reveals that the ground state of the complex is mainly stabilized by n?n* interaction. EDA analysis reveals that the interaction existing between the ligand and other parts of the complex is mainly electrostatic in nature. PMID:25380389

Azam, Mohammad; Al-Resayes, Saud I; Velmurugan, Gunasekaran; Venuvanalingam, Ponnambalam; Wagler, Jrg; Kroke, Edwin

2015-01-14

145

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

SciTech Connect

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

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

2001-03-01

146

A comparative quantum mechanical charge field study of uranyl mono- and dicarbonate species in aqueous solution.  

PubMed

A theoretical study of the structure and dynamics of the uranyl mono- and dicarbonate species in aqueous solution employing the quantum mechanical charge field-molecular dynamics (QMCF-MD) method is presented. The obtained structural and dynamical data were found to be in good agreement with several experimental data and theoretical investigations available in the literature. The five-fold coordination pattern observed for the equatorially bounded ligands of the uranyl ion was found to deviate from the results of a number of previous studies based on quantum chemical cluster calculations and classical molecular dynamics studies, however. The reason for the different description of the system can be seen on the one hand in the capability of QM/MM-type simulations to take charge transfer, polarization, and many-body effects into account, while the presence of a large number of MM solvent molecules ensures that the simulation system mimics the environment in the bulk of a liquid. In addition to pair, three-body and angular distributions, the use of spatial density data enabled a detailed characterization of the three-dimensional arrangement of ligands in the vicinity of the complex. Further analysis of dynamical data such as hydrogen-bond correlation functions and mean lifetime analysis enabled a detailed characterization of the properties of the complexes in aqueous solution. It could be shown that the bulk-oriented oxygen atoms of the carbonate ions form strong hydrogen bonds with bulk molecules, while the tendency of the oxygen atoms of the uranyl(VI) show decreasing tendency to form hydrogen bonds upon complexation. PMID:24256443

Tirler, Andreas O; Weiss, Alexander K H; Hofer, Thomas S

2013-12-19

147

Three-coordinate, luminescent, water-soluble gold(I) phosphine complexes: structural characterization and photoluminescence  

E-print Network

characterization and photoluminescence properties in aqueous solution Zerihun Assefa a , Jennifer M. Forward The photoluminescent properties of several types of three-coordinate gold(I) complexes in organic solvents

Abdou, Hanan E.

148

Speciation of uranyl sorbed at multiple binding sites on montmorillonite  

NASA Astrophysics Data System (ADS)

We have investigated the structures of U (VI) complexes as uranyl moieties sorbed onto a reference montmorillonite, SAz-1, using X-ray absorption fine structure spectroscopy (XAFS). The uranyl-loaded clays were prepared from aqueous solutions of uranyl nitrate in the pH range from 3.0 to 3.5. The U concentrations on the clay ranged from 1.7 to 34.6% of the reported cation exchange capacity (CEC = 1.2 meq/g) of the clay. For all samples, XAFS results indicate that there are two axial oxygen atoms at 1.78-1.80 , as expected for the uranyl moiety. The average numbers and distances of equatorial oxygen atoms about uranyl sorbed on the clay vary significantly as a function of surface coverage. At high coverage (34.6% CEC), the average number and distance of equatorial oxygen atoms are near those found for the fully hydrated uranyl species in aqueous solution. However, there are fewer equatorial oxygen atoms at a shorter average distance about uranyl sorbed at low coverage (1.7% CEC). At moderate coverage (7.3% CEC), the average number and distance of equatorial oxygen atoms are intermediate between those at higher and lower coverage. These changes suggest that sorbing U is reacting with at least three different sites on the clay as U concentration increases. The existence of multiple surface sites and sorption complexes which are structurally distinct from solution species need to be considered for rigorous modeling of sorption processes.

Chisholm-Brause, Catherine; Conradson, Steven D.; Buscher, C. T.; Eller, P. Gary; Morris, David E.

1994-09-01

149

Cucurbit[n]uril-based coordination chemistry: from simple coordination complexes to novel poly-dimensional coordination polymers.  

PubMed

Cucurbit[n]urils are a family of molecular container hosts bearing a rigid hydrophobic cavity and two identical carbonyl fringed portals. They have attracted much attention in supramolecular chemistry because of their superior molecular recognition properties in aqueous media. This review highlights the recent advances and challenges in the field of cucurbit[n]uril-based coordination chemistry. It not only presents progress in the knowledge of such macrocyclic compounds, which range from simple to complicated architectures, but also presents new routes of synthesis and their advantages in hybrid porous solids. The concept of structure "inducer" for their structural design to achieve predictable structures and controlled pores is described. The large pore sizes and hydrophobic cavities of these compounds that lead to unprecedented properties and potential applications are also discussed. PMID:24048328

Ni, Xin-Long; Xiao, Xin; Cong, Hang; Liang, Li-Li; Cheng, Kai; Cheng, Xiao-Jie; Ji, Ning-Ning; Zhu, Qian-Jiang; Xue, Sai-Feng; Tao, Zhu

2013-12-21

150

Distributed detection of communities in complex networks using synthetic coordinates  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

151

Coordinating complex decision support activities across distributed applications  

NASA Technical Reports Server (NTRS)

Knowledge-based technologies have been applied successfully to automate planning and scheduling in many problem domains. Automation of decision support can be increased further by integrating task-specific applications with supporting database systems, and by coordinating interactions between such tools to facilitate collaborative activities. Unfortunately, the technical obstacles that must be overcome to achieve this vision of transparent, cooperative problem-solving are daunting. Intelligent decision support tools are typically developed for standalone use, rely on incompatible, task-specific representational models and application programming interfaces (API's), and run on heterogeneous computing platforms. Getting such applications to interact freely calls for platform independent capabilities for distributed communication, as well as tools for mapping information across disparate representations. Symbiotics is developing a layered set of software tools (called NetWorks! for integrating and coordinating heterogeneous distributed applications. he top layer of tools consists of an extensible set of generic, programmable coordination services. Developers access these services via high-level API's to implement the desired interactions between distributed applications.

Adler, Richard M.

1994-01-01

152

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

153

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. PMID:17295475

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

154

A structural study on uranyl (VI) nitrate complexes with cyclic amides: N- n-butyl-2-pyrrolidone, N-cyclohexylmethyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidone  

Microsoft Academic Search

Structural analyses of UO2(NO3)2L2 [L=N-n-butyl-2-pyrrolidone (NBP), N-cyclohexylmethyl-2-pyrrolidone (NCMeP), and 1,3-dimethyl-2-imidazolidone (DMI)] have been carried out using X-ray diffraction method. These uranyl complexes were found to have a hexagonal bipyramidal structure. The bond distances () of UO and UO(ligand), and bond angles () of UOC(carbonyl) are determined as follows: 1.774(2), 2.374(2), and 137.6(2) for UO2(NO3)2(NBP)2; 1.770(1), 2.383(2), and 135.3(1) for UO2(NO3)2(NCMeP)2;

Nobuyoshi Koshino; Masayuki Harada; Masanobu Nogami; Yasuji Morita; Toshiaki Kikuchi; Yasuhisa Ikeda

2005-01-01

155

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

156

Understanding the bonding nature of uranyl ion and functionalized graphene: a theoretical study.  

PubMed

Studying the bonding nature of uranyl ion and graphene oxide (GO) is very important for understanding the mechanism of the removal of uranium from radioactive wastewater with GO-based materials. We have optimized 22 complexes between uranyl ion and GO applying density functional theory (DFT) combined with quasi-relativistic small-core pseudopotentials. The studied oxygen-containing functional groups include hydroxyl, carboxyl, amido, and dimethylformamide. It is observed that the distances between uranium atoms and oxygen atoms of GO (U-OG) are shorter in the anionic GO complexes (uranyl/GO(-/2-)) compared to the neutral GO ones (uranyl/GO). The formation of hydrogen bonds in the uranyl/GO(-/2-) complexes can enhance the binding ability of anionic GO toward uranyl ions. Furthermore, the thermodynamic calculations show that the changes of the Gibbs free energies in solution are relatively more negative for complexation reactions concerning the hydroxyl and carboxyl functionalized anionic GO complexes. Therefore, both the geometries and thermodynamic energies indicate that the binding abilities of uranyl ions toward GO modified by hydroxyl and carboxyl groups are much stronger compared to those by amido and dimethylformamide groups. This study can provide insights for designing new nanomaterials that can efficiently remove radionuclides from radioactive wastewater. PMID:24592814

Wu, Qun-Yan; Lan, Jian-Hui; Wang, Cong-Zhi; Xiao, Cheng-Liang; Zhao, Yu-Liang; Wei, Yue-Zhou; Chai, Zhi-Fang; Shi, Wei-Qun

2014-03-20

157

Composition for detecting uranyl  

DOEpatents

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

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

1994-01-01

158

Metal ion coordination, conditional stability constants, and solution behavior of chelating surfactant metal complexes.  

PubMed

Coordination complexes of some divalent metal ions with the DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) have been examined in terms of chelation and solution behavior. The headgroup of 4-C12-DTPA contains eight donor atoms that can participate in the coordination of a metal ion. Conditional stability constants for five transition metal complexes with 4-C12-DTPA were determined by competition measurements between 4-C12-DTPA and DTPA, using electrospray ionization mass spectrometry (ESI-MS). Small differences in the relative strength between the coordination complexes of DTPA and 4-C12-DTPA indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. The coordination of Cu(2+) ions was investigated in particular, using UV-visible spectroscopy. By constructing Job's plots, it was found that 4-C12-DTPA could coordinate up to two Cu(2+) ions. Surface tension measurements and NMR diffusometry showed that the coordination of metal ions affected the solution behavior of 4-C12-DTPA, but there were no specific trends between the studied divalent metal complexes. Generally, the effects of the metal ion coordination could be linked to the neutralization of the headgroup charge of 4-C12-DTPA, and the resulting reduced electrostatic repulsions between adjacent surfactants in micelles and monolayers. The pH vs concentration plots, on the other hand, showed a distinct difference between 4-C12-DTPA complexes of the alkaline earth metals and the transition metals. This was explained by the difference in coordination between the two groups of metal ions, as predicted by the hard and soft acid and base (HSAB) theory. PMID:24702119

Svanedal, Ida; Boija, Susanne; Almesker, Ann; Persson, Gerd; Andersson, Fredrik; Hedenstrm, Erik; Bylund, Dan; Norgren, Magnus; Edlund, Hkan

2014-04-29

159

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

160

Uranyl peroxide pyrophosphate cage clusters with oxalate and nitrate bridges.  

PubMed

Two complex cage clusters built from uranyl hexagonal bipyramids and multiple types of bridges between uranyl ions, U(30)Py(10)Ox(5) and U(38)Py(10)Nt(4), were crystallized from aqueous solution under ambient conditions. These are built from 30 uranyl hexagonal bipyramids, 10 pyrophosphate groups, and five oxalate bridges in one case, and 38 uranyl hexagonal bipyramids, 10 pyrophosphate groups, and four nitrate groups in the other. The crystal compositions are (H(3)O)(10)Li(18)K(22)[(UO(2))(30)(O(2))(30)(P(2)O(7))(10)(C(2)O(4))(5)](H(2)O)(22) and Li(24)K(36)[(UO(2))(38)(O(2))(40)(OH)(8)(P(2)O(7))(10)(NO(3))(4)](NO(3))(4)(H(2)O)(n) for U(30)Py(10)Ox(5) and U(38)Py(10)Nt(4), respectively. Cluster U(30)Py(10)Ox(5) crystallizes over a narrow range of solution pH that encourages incorporation of both oxalate and pyrophosphate, with incorporation of oxalate only being favored under more acidic conditions, and pyrophosphate only under more alkaline conditions. Cluster U(38)Py(10)Nt(4) contains two identical lobes consisting of uranyl polyhedra and pyrophosphate groups, with these lobes linked into the larger cluster through four nitrate groups. The synthesis conditions appear to have prevented closure of these lobes, and a relatively high nitrate concentration in solution favored formation of the larger cluster. PMID:22569991

Ling, Jie; Ozga, Michael; Stoffer, Megan; Burns, Peter C

2012-06-28

161

A spectroscopic study of uranyl-cytochrome b5/cytochrome c interactions  

NASA Astrophysics Data System (ADS)

Uranium is harmful to human health due to its radiation damage and the ability of uranyl ion (UO22+) to interact with various proteins and disturb their biological functions. Cytochrome b5 (cyt b5) is a highly negatively charged heme protein and plays a key role in mediating cytochrome c (cyt c) signaling in apoptosis by forming a dynamic cyt b5-cyt c complex. In previous molecular modeling study in combination with UV-Vis studies, we found that UO22+ is capable of binding to cyt b5 at surface residues, Glu37 and Glu43. In this study, we further investigated the structural consequences of cyt b5 and cyt c, as well as cyt b5-cyt c complex, upon uranyl binding, by fluorescence spectroscopic and circular dichroism techniques. Moreover, we proposed a uranyl binding site for cyt c at surface residues, Glu66 and Glu69, by performing a molecular modeling study. It was shown that uranyl binds to cyt b5 (KD = 10 ?M), cyt c (KD = 87 ?M), and cyt b5-cyt c complex (KD = 30 ?M) with a different affinity, which slightly alters the protein conformation and disturbs the interaction of cyt b5-cyt c complex. Additionally, we investigated the functional consequences of uranyl binding to the protein surface, which decreases the inherent peroxidase activity of cyt c. The information of uranyl-cyt b5/cyt c interactions gained in this study likely provides a clue for the mechanism of uranyl toxicity.

Sun, Mei-Hui; Liu, Shuang-Quan; Du, Ke-Jie; Nie, Chang-Ming; Lin, Ying-Wu

2014-01-01

162

Modeling and simulation of complex network attributes on coordinating large multiagent system.  

PubMed

With the expansion of distributed multiagent systems, traditional coordination strategy becomes a severe bottleneck when the system scales up to hundreds of agents. The key challenge is that in typical large multiagent systems, sparsely distributed agents can only communicate directly with very few others and the network is typically modeled as an adaptive complex network. In this paper, we present simulation testbed CoordSim built to model the coordination of network centric multiagent systems. Based on the token-based strategy, the coordination can be built as a communication decision problem that agents make decisions to target communications and pass them over to the capable agents who will potentially benefit the team most. We have theoretically analyzed that the characters of complex network make a significant difference with both random and intelligent coordination strategies, which may contribute to future multiagent algorithm design. PMID:24955399

Xu, Yang; Li, Xiang; Liu, Ming

2014-01-01

163

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

PubMed Central

With the expansion of distributed multiagent systems, traditional coordination strategy becomes a severe bottleneck when the system scales up to hundreds of agents. The key challenge is that in typical large multiagent systems, sparsely distributed agents can only communicate directly with very few others and the network is typically modeled as an adaptive complex network. In this paper, we present simulation testbed CoordSim built to model the coordination of network centric multiagent systems. Based on the token-based strategy, the coordination can be built as a communication decision problem that agents make decisions to target communications and pass them over to the capable agents who will potentially benefit the team most. We have theoretically analyzed that the characters of complex network make a significant difference with both random and intelligent coordination strategies, which may contribute to future multiagent algorithm design. PMID:24955399

Li, Xiang; Liu, Ming

2014-01-01

164

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

165

Siderophilin metal coordination. 1. Complexation of thorium by transferrin: structure-function implications  

Microsoft Academic Search

As part of a program to develop actinide-specific sequestering agents, the coordination of actinide ions by human transferrin is being investigated. Therapeutically useful synthetic ligands must be able to compete with this iron-transport protein for the bound actinide ion. As in the Fe(III) complex of the native protein, two Th(IV) ions bind at pH 7. This coordination has been monitored

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

1981-01-01

166

A normal coordinate analysis of monomethylhydrazine and its bidentate nickel (II) chloride complex  

NASA Astrophysics Data System (ADS)

A full normal coordinate analysis (NCA) has been carried out on monomethylhydrazine and N-deuterated monomethylhydrazine. The C3? symmetry of the methyl group is lost; nevertheless the concept of specific methyl group modes is still valuable. The N?N stretching mode is relatively pure enabling it to be used as a criteria of coordination. An NCA has also been carried out for the bidentate nickel complex NiCl 2(NH 2NHCH 3) 2. Interesting effects are observed for the wagging and twisting modes of the NH 2 group on coordination.

Dowling, D. P.; Glass, W. K.

167

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

SciTech Connect

The mixed-valence chromium uranyl compounds Li{sub 5}[(UO{sub 2}){sub 4}(Cr(V)O{sub 5})(Cr(VI)O{sub 4}){sub 4}](H{sub 2}O){sub 17} (1), (Mg(H{sub 2}O){sub 6}){sub 5}[(UO{sub 2}){sub 8}(Cr(V)O{sub 5}){sub 2}(Cr(VI)O{sub 4}){sub 8}] (2) and (NH{sub 4}){sub 5}[(UO{sub 2}){sub 4}(Cr(V)O{sub 5})(Cr(VI)O{sub 4}){sub 2}]H{sub 2}O{sub 11} (3) have been synthesized and characterized. Each contains an identical sheet of cation-centered polyhedra. Central to the connectivity of the sheet are four uranyl pentagonal bipyramids that share some of their equatorial vertices, giving a four-membered ring. The Cr(V) cation located near the center of this ring is coordinated by O atoms in a square pyramidal arrangement. The Cr(VI) is tetrahedrally coordinated by O atoms, and these tetrahedra link the four-membered rings of bipyramids. The mixed-valence nature of the sheet was verified by XANES, an EPR spectrum, and bond-valence analysis. Low-valence cations and H{sub 2}O groups reside between the sheets of uranyl and chromate polyhedra, where they provide linkages between adjacent sheets. - Graphical abstract: Three uranyl chromate compounds contain both pentavalent and hexavalent chromium. The unusual topology of the uranyl chromate sheet contains unusual pentavalent chromium in a square pyramidal coordination environment. Highlights: Black-Right-Pointing-Pointer The first uranyl compounds with mixed Cr valences are reported. Black-Right-Pointing-Pointer A sheet of uranyl polyhedra stabilizes pentavalent chromium. Black-Right-Pointing-Pointer Uranyl and chromate polyhedra form a topologically novel sheet.

Unruh, Daniel K.; Quicksall, Andrew; Pressprich, Laura; Stoffer, Megan; Qiu, Jie [Department of Civil Engineering and Geological Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556 (United States); Nuzhdin, Kirill; Wu, Weiqiang; Vyushkova, Mariya [Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556 (United States); Burns, Peter C., E-mail: pburns@nd.edu [Department of Civil Engineering and Geological Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556 (United States)

2012-07-15

168

Secondary coordination sphere effects in ruthenium(III) tetraammine complexes: role of the coordinated water molecule.  

PubMed

The complexes trans-[Ru(III)(NH3)4(4-pic)(H2O)](CF3SO3)3 (1) and [Ru(III)(NH3)5(4-pic)](CF3SO3)3 (2) were isolated and studied experimentally by electron paramagnetic resonance (EPR) and UV-vis spectroscopies, cyclic voltammetry, and X-ray crystallography and theoretically by ligand-field theory (LFT) and density functional theory (DFT) calculations. Complex 1 is reported in two different crystal forms, 1a (100 K) and 1b (room temperature). EPR and UV-vis spectroscopies suggest that aqua ligand interaction in this low-spin ruthenium(III) complex changes as a function of hydrogen bonding with solvent molecules. This explicit water solvent effect was explained theoretically by DFT calculations, which demonstrated the effect of rotation of the aqua ligand about the Npic-Ru-Oaq axis. The UV-vis spectrum of 1 shows in an aqueous acid solution a broad- and low-intensity absorption band around 28,500 cm(-1) (? ? 500 M(-1) cm(-1)) that is assigned mainly to a charge-transfer (CT) transition from the equatorial ligands to the Ru ?-4dxy orbital (?-LUMO) using DFT calculations. The electronic reflectance spectrum of 1 shows a broad and intense absorption band around 25,500 cm(-1) that is assigned to a CT transition from 4-picoline to the Ru ?-4dxz orbital (?-LUMO) using DFT calculations. The t2g(5) set of orbitals had its energy splitting investigated by LFT. LFT analysis shows that a rhombic component arises from C2v symmetry by a simple ?-bonding ligand (H2O in our case) twisting about the trans (C2) axis. This twist was manifested in the EPR spectra, which were recorded for 1 as a function of the solvent in comparison with [Ru(NH3)5(4-pic)](3+) and [Ru(NH3)5(H2O)](3+). Only 1 shows an evident change in the g-tensor values, wherein an increased rhombic component is correlated with a higher nucleophilicity (donor) solvent feature, as parametrized by the Abraham system. PMID:25654246

Souza, Maykon L; Castellano, Eduardo E; Telser, Joshua; Franco, Douglas W

2015-02-16

169

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

PubMed

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

Monier, M; Elsayed, Nadia H

2014-06-01

170

Multi-scale modelling of uranyl chloride solutions  

NASA Astrophysics Data System (ADS)

Classical molecular dynamics simulations with explicit polarization have been successfully used to determine the structural and thermodynamic properties of binary aqueous solutions of uranyl chloride (UO2Cl2). Concentrated aqueous solutions of uranyl chloride have been studied to determine the hydration properties and the ion-ion interactions. The bond distances and the coordination number of the hydrated uranyl are in good agreement with available experimental data. Two stable positions of chloride in the second hydration shell of uranyl have been identified. The UO 22 + -Cl- association constants have also been calculated using a multi-scale approach. First, the ion-ion potential averaged over the solvent configurations at infinite dilution (McMillan-Mayer potential) was calculated to establish the dissociation/association processes of UO 22 + -Cl- ion pairs in aqueous solution. Then, the association constant was calculated from this potential. The value we obtained for the association constant is in good agreement with the experimental result (KUO2Cl+ = 1.48 l mol-1), but the resulting activity coefficient appears to be too low at molar concentration.

Nguyen, Thanh-Nghi; Duvail, Magali; Villard, Arnaud; Molina, John Jairo; Guilbaud, Philippe; Dufrche, Jean-Franois

2015-01-01

171

Pyridine versus acetonitrile coordination in rhodium-N-heterocyclic carbene square-planar complexes.  

PubMed

Experimental and theoretical studies on the factors that control the coordination chemistry of N-donor ligands in square-planar complexes of the type RhCl(NHC)L(1)L(2) (NHC = N-heterocyclic carbene) are presented. The dinuclear complexes [Rh(?-Cl)(IPr)(?(2)-olefin)]2 {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-carbene} have been reacted with different combinations of ligands including pyridine, acetonitrile, 2-pyridylacetonitrile, triphenylphosphine, tricyclohexylphosphine, carbon monoxide or molecular oxygen. In addition, the reactivity of RhCl(IPr)(PPh3)2 has also been studied. Pyridine preferentially coordinates trans to the carbene ligand whereas ?-acceptor ligands (olefin, CO or PPh3) are prone to bind cis to IPr and trans to chlorido, unless steric bulk hinders the coordination of the ligand (PCy3). In contrast, acetonitrile is more labile than pyridine but is able to form complexes coordinated cis-to-IPr. Molecular dioxygen also displaces the labile cyclooctene ligand in RhCl(IPr)(?(2)-coe)(py) to give a square-planar dioxygen adduct which can be transformed into a peroxo derivative by additional coordination of pyridine. Charge decomposition analysis (CDA) shows that ?-donation values are similar for coordination at cis- or trans-IPr positions, whereas efficient ?-backbonding is significantly observed at cis position being the favoured coordination site for ?-acceptor ligands. The Rh-IPr rotational barrier in a series of square-planar complexes has been analysed. It has been found that the main contribution is the steric hindrance of the ancillary ligand. The presence of a ?-donor ligand such as chlorido slows down the dynamic process. PMID:25714797

Palacios, Laura; Di Giuseppe, Andrea; Castarlenas, Ricardo; Lahoz, Fernando J; Prez-Torrente, Jess J; Oro, Luis A

2015-03-10

172

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

173

Polar Coordinates and Multiplication In the last chapter we wrote complex numbers in the form x + iy where x  

E-print Network

Polar Coordinates and Multiplication In the last chapter we wrote complex numbers in the form x + iy where x and y are real numbers. We can think of this as writing complex numbers using Cartesian coordinates. Every complex number is the sum of a number on the real axis and a number on the imaginary axis

Wortman, Kevin

174

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

2013-11-19

175

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. PMID:24107799

Xu, Zhiping

2013-01-01

176

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

177

Coordination of the ankle joint complex during walking.  

PubMed

A simple model of the joint between the leg and the rearfoot is that of two hinges each with one degree of freedom. The superior hinge at the talocrural joint caters for most of the sagittal plane motion due to its mediolateral orientation. Motion in the transverse and coronal planes is largely taken up by the subtalar joint which has an inclination of 42 degrees to the transverse plane and deviates 23 degrees to the medial side. It could be expected from the orientation of this joint that rearfoot motion in the coronal plane (inversion/eversion) would be tightly coupled to motion in the transverse plane (adduction/abduction). A simple, non-viscous mechanical hinge joint would produce an in-phase, fixed gain relationship between inversion/eversion and adduction/abduction. This relation could be adequately quantified by Pearson's product moment correlation (r(P)). In contrast, muscular control of the joint, which introduces visco-elastic elements and time-delayed control lines and feedback loops, could be characterised by more complex phase and gain relations among the frequency components of the signals. These relations can be characterised by a transfer function relation (gain and phase angle) computed using a dynamic analysis. In the present study, both Pearson's correlation and linear systems analysis were employed. For 43 normal adults, five trials of one walking stride (stance and swing phases) were videographed at 30 Hz with three markers placed on each of the leg and rearfoot. Using inversion/eversion as the input and adduction/abduction as the output, the proportion of the total variance accounted for by a dynamic relation was measured by the coherence square function, which is analogous to the correlation squared (r(P)(2)). The mean r(P)(2) was 0.26, whereas the mean overall coherence was 0.62, thus accounting for more than twice the variance. This result suggests that while there may be a degree of simple mechanical coupling between inversion/eversion and adduction/abduction during walking, the major control is via muscular and/or visco-elastic passive elements. PMID:11750672

Smith, R; Rattanaprasert, U; O'Dwyer, N

2001-11-01

178

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

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

Teamwork Coordination for Realistically Complex Multi Robot Systems Michael Lewis and Jijun Wang Paul Scerri  

E-print Network

after operator verification of each MP-HFM-135-17 17-1 #12;TEAMWORK COORDINATION UAV-detected target@cs.cmu.edu ABSTRACT 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

Lewis, Michael

181

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

2013-10-11

182

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

183

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

NASA Astrophysics Data System (ADS)

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

Kasthurirathna, Dharshana; Piraveenan, Mahendra; Harr, Michael

2014-01-01

184

Speciation of uranyl species in nitric acid medium by time-resolved laser-induced fluorescence  

NASA Astrophysics Data System (ADS)

The aim of this work is the development of an on-line analytical procedure for uranyl trace determination in the nuclear fuel reprocessing process using time-resolved laser-induced fluorescence. Because the uranyl fluorescence spectrum is strongly affected by the nitrate concentration, knowledge of composition of the medium is necessary to normalize measurements. This paper reports the assumptions made on the spectral distortion, leading to a spectral deconvolution model. Uranyl complex formation constants are obtained from the spectral deconvolution and validate the method. In this way, spectral distortion allows the determination of the nitrate concentration with good accuracy.

Couston, Laurent; Pouyat, Dominique; Moulin, Christophe; Decambox, Pierre

1995-03-01

185

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. PMID:23627362

2013-01-01

186

Siderophilin metal coordination. 1. Complexation of thorium by transferrin: structure-function implications  

SciTech Connect

As part of a program to develop actinide-specific sequestering agents, the coordination of actinide ions by human transferrin is being investigated. Therapeutically useful synthetic ligands must be able to compete with this iron-transport protein for the bound actinide ion. As in the Fe(III) complex of the native protein, two Th(IV) ions bind at pH 7. This coordination has been monitored at several pH values by using difference ultraviolet spectroscopy. The corresponding coordination of a phenolic ligand, ethylenebis(o-hydroxyphenylglycine) (EHPG), has been used to determine ..delta..epsilon upon protein coordination, the number of transferrin tyrosine residues that coordinate. Maxima in the Th(IV) + EHPG difference UV spectra occur at 292 and 238 nm, with corresponding ..delta..epsilon values per phenolic group of 2330 and 8680 cm/sup -1/ M/sup -1/, respectively. At pH 7.2, the Th(IV) transferring spectrum is closely similar to the Th/sup IV/EHPG spectrum, with maxima at 292 and 240 nm. The ..delta..epsilon at 240 nm reaches a maximum of 24700 cm/sup -1/ m/sup -1/, which corresponds to coordination of three tyrosine residues in the dithorium-transferrin complex; the stronger binding site (A or C-terminal) coordinates via two tyrosines and the weaker (B or N-terminal) via one. There is evidence suggesting that the N-terminal site is slightly smaller than the C-terminal site; while Th(IV) easily fit into both sites.s into the C-terminal site, the large ionic radius of Th(IV) makes this ion of borderline size to fit into the N-terminal site. This may be an important biological difference between Th(IV) and the slightly smaller Pu(IV), which should easily fit into both sites.

Harris, W.R.; Carrano, C.J.; Pecoraro, V.L.; Raymond, K.N.

1981-05-06

187

Chitosan-Copper (II) complex as antibacterial agent: synthesis, characterization and coordinating bond- activity correlation study  

NASA Astrophysics Data System (ADS)

The antimicrobial activity of chitosan is unstable and sensitive to many factors such as molecular weight. Recent investigations showed that low molecular weight chitosan exhibited strong bactericidal activities compared to chitosan with high molecular weight. Since chitosan degradation can be caused by the coordinating bond, we attempt to synthesize and characterize the chitosan-Cu (II) complex, and thereafter study the coordinating bond effect on its antibacterial activity against Salmonella enteritidis. Seven chitosan-copper complexes with different copper contents were prepared and characterized by FT-IR, UV-vis, XRD and atomic absorption spectrophotometry (AAS). Results indicated that for chitosan-Cu (II) complexes with molar ratio close to 1:1, the inhibition rate reached 100%.

Mekahlia, S.; Bouzid, B.

2009-11-01

188

Evolutionary dynamics of the traveler's dilemma and minimum-effort coordination games on complex networks  

NASA Astrophysics Data System (ADS)

The traveler's dilemma game and the minimum-effort coordination game are social dilemmas that have received significant attention resulting from the fact that the predictions of classical game theory are inconsistent with the results found when the games are studied experimentally. Moreover, both the traveler's dilemma and the minimum-effort coordination games have potentially important applications in evolutionary biology. Interestingly, standard deterministic evolutionary game theory, as represented by the replicator dynamics in a well-mixed population, is also inadequate to account for the behavior observed in these games. Here we study the evolutionary dynamics of both these games in populations with interaction patterns described by a variety of complex network topologies. We investigate the evolutionary dynamics of these games through agent-based simulations on both model and empirical networks. In particular, we study the effects of network clustering and assortativity on the evolutionary dynamics of both games. In general, we show that the evolutionary behavior of the traveler's dilemma and minimum-effort coordination games on complex networks is in good agreement with that observed experimentally. Thus, formulating the traveler's dilemma and the minimum-effort coordination games on complex networks neatly resolves the paradoxical aspects of these games.

Iyer, Swami; Killingback, Timothy

2014-10-01

189

Characterization of five- and six-coordinate iron(III) complexes of N-methylporphyrins  

Microsoft Academic Search

The coordination chemistry of iron(III) in the environment of N-methylporphyrins has been expanded to include a crystallographic characterization of a high-spin, five-coordinate complex, (N-methyltetra-p-tolylporphyrin Fe{sup III}Cl)-(SbCl){center dot}1.5(toluene), which crystallizes in the triclinic space group P{anti 1} with a = 13.170 (6) , b = 14.591 (1) , c = 15.702 (14) , α = 83.78 (7)°, β = 79.82 (6)°,

Alan L. Balch; Charles R. Cornman; M. M. Olmstead; L. Latos-Grazynski

1990-01-01

190

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

Microsoft Academic Search

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

Hirohide Nakamatsu; Turgut Bastug; Shoichi Tachimori; Rika Sekine; Jun Onoe

2000-01-01

191

Theoretical study of the microhydration of mononuclear and dinuclear uranium(VI) species derived from solvolysis of uranyl nitrate in water.  

PubMed

The structures and energetics of mononuclear and dinuclear uranium species formed upon speciation of uranyl(VI) nitrate, UO(2)(NO(3))(2), in water are investigated by quantum chemistry using density functional theory and the wavefunction-based methods (MP2, CCSD, CCSD(T)). We provide a discussion of the basic coordination patterns of the various mono- and dinuclear uranyl compounds [(UO(2))(m)(X,Y)(2m-1)(H2O)(n)](+) (m = 1, 2; n = 0-4) found in a recent mass spectrometric study (Tsierkezos et al., Inorg Chem 2009, 48, 6287). The energetics of the complexation of the uranyl dication to the counterions OH(-) and NO(3) (-) as well as the degradation of the dinuclear species were studied by reference to a test set of 16 representative molecules with the MP2 method and the B3LYP, M06, M06-HF, and M06-2X DFT functionals. All DFT functionals provide structures and energetics close to MP2 results, with M06 family being slightly superior to the standard B3LYP functional. PMID:20340110

Onck, Milan; Schrder, Detlef; Slavcek, Petr

2010-09-01

192

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. PMID:18076009

DiVittorio, Kristy M.; Leevy, W. Matthew; ONeil, 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

193

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

PubMed

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

Rodrguez-Jeangros, Nicols; Seminario, Jorge M

2014-03-01

194

Prebiotic coordination chemistry: The potential role of transition-metal complexes in the chemical evolution  

NASA Technical Reports Server (NTRS)

In approaching the extremely involved and complex problem of the origin of life, consideration of the coordination chemistry appeared not only as a possibility but as a necessity. The first model experiments appear to be promising because of prebiotic-type synthesis by means of transition-metal complexes. It is especially significant that in some instances various types of vitally important substances (nucleic bases, amino acids) are formed simultaneously. There is ground to hope that systematic studies in this field will clarify the role of transition-metal complexes in the organizatorial phase of chemical evolution. It is obvious that researchers working in the fields of the chemistry of cyano and carbonyl complexes, and of the catalytic effect of transition-metal complexes are best suited to study these aspects of the attractive and interesting problem of the origin of life.

Beck, M.

1979-01-01

195

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

E-print Network

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

Girolami, Gregory S.

196

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

197

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

SciTech Connect

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

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

1980-08-01

198

Reactivity of coordinatively unsaturated iron complexes towards carbon monoxide: to bind or not to bind?  

PubMed

An overview of the reactivity of coordinatively unsaturated iron complexes (in most cases Fe(II)) towards carbon monoxide is presented. Unsaturated iron complexes are known with coordination numbers (CN) of two to five adopting linear or slightly bent (CN = 2), trigonal (CN = 3), tetrahedral, square planar or trigonal pyramidal (CN = 4), and square-pyramidal or trigonal-bipyramidal geometries (CN = 5), respectively. The binding of CO depends strongly on the number and the nature of co-ligands (overall ligand field strength), the charge of the complex, the complex geometry, and the spin state of the unsaturated metal center. In many cases, CO addition to high-spin iron complexes takes place with concomitant spin state changes forming compounds in the lowest possible spin state, i.e., with S = 0. In several other cases, however, the addition of CO is reversible or is even totally rejected altogether for either thermodynamic or kinetic reasons. In the case of the latter such reactions are termed "spin-blocked" or "spin forbidden". PMID:21380474

Benito-Garagorri, David; Lagoja, Irene; Veiros, Luis F; Kirchner, Karl A

2011-05-14

199

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. PMID:24052834

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

2011-01-01

200

Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations  

Microsoft Academic Search

The intrinsic hydration of three monopositive uranyl-anion complexes (UO2A)+ (where A = acetate, nitrate, or hydroxide) was investigated using ion-trap mass spectrometry (IT-MS). The relative rates\\u000a for the formation of the monohydrates [(UO2A)(H2O)]+, with respect to the anion, followed the trend: Acetate ? nitrate ? hydroxide. This finding was rationalized in terms of\\u000a the donation of electron density by the

Winnie Chien; Victor Anbalagan; Melvin Zandler; Michael Van Stipdonk; Dorothy Hanna; Garold Gresham; Gary Groenewold

2004-01-01

201

Volatile adducts of uranyl nitrate. Sublimation and mass spectra  

Microsoft Academic Search

Adducts of uranyl nitrate with strong neutral ligands: trimethyl phosphate (TMP), triethyl phosphate (TEP), trimethylphosphine oxide (TMPO), hexamethylphosphoric triamide (HMPTA), with a 1:2 composition, and phenanthroline (phen) (with a 1:1 composition), and also a complex with a composition of UO(NO) (NCS) x 2HMPTA were synthesized. The above enumerated compounds sublime in vacuo (adducts with TMP and TEP in a vapor

V. M. Adamov; B. N. Belyaev; G. V. Sidorenko; D. N. Suglobov

1988-01-01

202

Isostructural series of nine-coordinate chiral lanthanide complexes based on triazacyclononane.  

PubMed

Nonadentate ligands based on triazacyclononane incorporating pyridyl-2-phosphinate groups form an isostructural series of complexes with Ln ions in the solid state and in solution. The Ln ion is effectively shielded from the solvent environment. Crystal structures reveal a rigid C(3)-symmetric tricapped trigonal-prismatic coordination geometry that is maintained in solution for the methyl and phenylphosphinate series, as shown by multinuclear NMR analysis. Variable-temperature measurements of the field dependence of the water proton relaxivity in gadolinium complexes indicate that these systems exclude solvent from the primary coordination environment and minimize the second sphere of solvation. The electronic relaxation time for the gadolinium methylphosphinate complex has been estimated to be 550 (150) ps by EPR and NMR methods, compared to values of around 0.30-0.05 ps for the terbium-ytterbium series, deduced by analyzing the field dependence (4.7-16.5 T) of the (31)P NMR longitudinal relaxation times. Values are compared with analogous azacarboxylate ligand complexes, supporting a key role for donor atom polarizability in determining the electronic relaxation. Spectral emission behavior in solution of samarium, europium, terbium, and dysprosium complexes is compared, and the resolved RRR-? and SSS-? complexes show strong circularly polarized luminescence. The molecular quadratic hyperpolarizability ??(HLS)? has been measured in solution using hyper-Raleigh light-scattering methods, for the whole series of lanthanide complexes of one ligand. The values of ??(HLS)? reach a maximum around the center of the series and are not simply dependent on the number of f electrons, suggesting a dominant contribution from the octupolar rather than the dipolar term. PMID:22809198

Walton, James W; Carr, Rachel; Evans, Nicholas H; Funk, Alexander M; Kenwright, Alan M; Parker, David; Yufit, Dmitry S; Botta, Mauro; De Pinto, Sara; Wong, Ka-Leung

2012-08-01

203

Magnetism and crystal structure of an N3O3-coordinated iron(II) complex.  

PubMed

The reaction of [FeL(MeOH)2] {where L is the tetradentate N2O2-coordinating Schiff base-like ligand (E,E)-diethyl 2,2'-[1,2-phenylenebis(nitrilomethylidyne)]bis(3-oxobutanoate)(2-) and MeOH is methanol} with 3-aminopyridine (3-apy) in methanol results in the formation of the octahedral complex (3-aminopyridine-kappaN1){(E,E)-diethyl 2,2'-[1,2-phenylenebis(nitrilomethylidyne)]bis(3-oxobutanoato)(2-)-kappa4O3,N,N',O3'}(methanol-kappaO)iron(II), [Fe(C20H22N2O6)(C5H6N2)(CH4O)] or [FeL(3-apy)(MeOH)], in which the Fe(II) ion is centered in an N3O3 coordination environment with two different axial ligands. This is the first example of an octahedral complex of this multidentate ligand type with two different axial ligands, and the title compound can be considered as a precursor for a new class of complexes with potential spin-crossover behavior. An infinite two-dimensional hydrogen-bond network is formed, involving the amine NH group, the methanol OH group and the carbonyl O atoms of the equatorial ligand. T-dependent susceptibility measurements revealed that the complex remains in the high-spin state over the entire temperature range investigated. PMID:18535332

Bauer, Wolfgang; Weber, Birgit

2008-06-01

204

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.

205

Axial coordination and conformational heterogeneity of nickel(II) tetraphenylprophyrin complexes with nitrogenous bases  

SciTech Connect

Axial ligation of nickel(II) 5,10,15,20-tetraphenylporphyrin (NiTPP) with pyrrolidine or piperidine has been investigated using X-ray crystallography, UV-visible spectroscopy, resonance Raman spectroscopy, and molecular mechanics (MM) calculations. Distinct v{sub 4} Raman lines are found for the 4-, 5-, and 6-coordinate species of NiTPP. The equilibrium constants for addition of the first and second pyrrolidine axial ligands are 1.1 and 3.8 M{sup {minus}1}, respectively. The differences in the calculated energies of the conformers having different ligand rotational angles are small so they may coexist in solution. Because of the similarity in macrocyclic structural parameters of these conformers and the free rotation of the axial ligands, narrow and symmetric v{sub 2} and v{sub 8} Raman lines are observed. Nonetheless, the normal-coordinate structural-decomposition analysis of the nonplanar distortions of the calculated structures and the crystal structure of the bis(piperidine) complex reveals a relationship between the orientations of axial ligand(s) and the macrocyclic distortions. For the 5-coordinate complex with the plane of the axial ligand bisecting the Ni-N{sub pyrrole} bonds, a primarily ruffled deformation results. With the ligand plane eclipsing the Ni-N{sub pyrrole} bonds, a mainly saddled deformation occurs. With the addition of the second axial ligand, the small doming of the 5-coordinate complexes disappears, and ruffling or saddling deformations change depending on the relative orientation of the two axial ligands. The crystal structure of the NiTPP bis(piperidine) complex shows a macrocycle distortion composed of wav(x) and wav(y) symmetric deformations, but no ruffling, saddling, or doming. The difference in the calculated and observed distortions results partly from the phenyl group orientation imposed by crystal packing forces. MM calculations predict three stable conformers (ruf, sad, and planar) for 4-coordinate NiTPP, and resonance Raman evidence for these conformers was given previously.

Jia, S.L.; Song, X.Z.; Ma, J.G.; Shelnutt, J.A. [Sandia National Labs., Albuquerque, NM (United States). Materials Theory and Computation Dept.] [Sandia National Labs., Albuquerque, NM (United States). Materials Theory and Computation Dept.; [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Chemistry; Jentzen, W. [Sandia National Labs., Albuquerque, NM (United States). Materials Theory and Computation Dept.] [Sandia National Labs., Albuquerque, NM (United States). Materials Theory and Computation Dept.; [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Chemistry; [Univ. GH Essen (Germany). Klinik und Poliklinik fuer Nuklearmedizin; Shang, M.; Scheidt, W.R. [Univ. of Notre Dame, IN (United States). Dept. of Chemistry and Biochemistry] [Univ. of Notre Dame, IN (United States). Dept. of Chemistry and Biochemistry

1998-08-24

206

Uranyl carboxyphosphonates that incorporate Cd(II)  

SciTech Connect

The hydrothermal treatment of UO{sub 3}, Cd(CH{sub 3}CO{sub 2}){sub 2}.2H{sub 2}O, and triethyl phosphonoacetate results in the formation of Cd{sub 2}[(UO{sub 2}){sub 6}(PO{sub 3}CH{sub 2}CO{sub 2}){sub 3}O{sub 3}(OH)(H{sub 2}O){sub 2}].16H{sub 2}O (CdUPAA-1), [Cd{sub 3}(UO{sub 2}){sub 6}(PO{sub 3}CH{sub 2}CO{sub 2}){sub 6}(H{sub 2}O){sub 13}].6H{sub 2}O (CdUPAA-2), and Cd(H{sub 2}O){sub 2}[(UO{sub 2})(PO{sub 3}CH{sub 2}CO{sub 2})(H{sub 2}O)]{sub 2} (CdUPAA-3). CdUPAA-1 adopts a cubic three-dimensional structure constructed from planar uranyl oxide clusters containing both UO{sub 7} pentagonal bipyramids and UO{sub 8} hexagonal bipyramids that are linked by Cd(II) cations and phosphonoacetate to yield large cavities approximately 16 A across that are filled with disordered water molecules. CdUPAA-2 forms a rhombohedral three-dimensional channel structure that is assembled from UO{sub 7} pentagonal bipyramids that are bridged by phosphonoacetate. CdUPAA-3 is layered with the hydrated Cd(II) cations incorporated directly into the layers linking one-dimensional uranyl phosphonate substructures together. In this structure, there are complex networks of hydrogen bonds that exist within the sheets, and also stitch the sheets together. -- Graphical abstract: A view of part of the cubic structure of Cd{sub 2}[(UO{sub 2}){sub 6}(PO{sub 3}CH{sub 2}CO{sub 2}){sub 3}O{sub 3}(OH)(H{sub 2}O){sub 2}].16H{sub 2}O. Display Omitted highlights: > High symmetry uranyl compounds. > Three-dimensional structures. > Porous materials. > Heterobimetallic compounds.

Alsobrook, Andrea N. [Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States); Alekseev, Evgeny V.; Depmeier, Wulf [Institut fuer Geowissenschaften, Universitaet zu Kiel, 24118 Kiel (Germany); Albrecht-Schmitt, Thomas E., E-mail: talbrec1@nd.ed [Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States)

2011-05-15

207

One-step assembly of coordination complexes for versatile film and particle engineering.  

PubMed

The development of facile and versatile strategies for thin-film and particle engineering is of immense scientific interest. However, few methods can conformally coat substrates of different composition, size, shape, and structure. We report the one-step coating of various interfaces using coordination complexes of natural polyphenols and Fe(III) ions. Film formation is initiated by the adsorption of the polyphenol and directed by pH-dependent, multivalent coordination bonding. Aqueous deposition is performed on a range of planar as well as inorganic, organic, and biological particle templates, demonstrating an extremely rapid technique for producing structurally diverse, thin films and capsules that can disassemble. The ease, low cost, and scalability of the assembly process, combined with pH responsiveness and negligible cytotoxicity, makes these films potential candidates for biomedical and environmental applications. PMID:23846899

Ejima, Hirotaka; Richardson, Joseph J; Liang, Kang; Best, James P; van Koeverden, Martin P; Such, Georgina K; Cui, Jiwei; Caruso, Frank

2013-07-12

208

Enhancing Phosphate Diester Cleavage by a Zinc Complex through Controlling Nucleophile Coordination.  

PubMed

Metal-ion complexes are the most effective artificial catalysts capable of cleaving phosphate diesters under mild aqueous conditions. A central strategy for making these complexes highly reactive has been to use ligand-based alcohols that are coordinated to the ion, providing an ionised nucleophile under neutral conditions but at the expense of deactivating it. We have created a highly reactive Zn complex that is 350-fold more reactive than an alcohol analogue by preventing the nucleophile binding to the metal ion. This strategy successfully delivers the benefits of efficient nucleophile delivery without strongly deactivating the metal ion Lewis acidity nor the oxyanion nucleophilicity. Varying the leaving group reveals that the transition state of the reaction is much further advanced than the reaction with hydroxide. PMID:25787696

Tirel, Emmanuel Y; Williams, Nicholas H

2015-05-01

209

A Codeposition Route to CuI-Pyridine Coordination Complexes for OLEDs  

PubMed Central

We demonstrate a new approach to utilize copper(I) iodide coordination complexes as emissive layers in organic light-emitting diodes (OLEDs), by in situ codeposition of copper(I) iodide and 3,5-bis(carbazol-9-yl)pyridine (mCPy). With a simple three-layer device structure, pure green electroluminescence at 530 nm from a copper(I) complex was observed. Maximum luminance and external quantum efficiency (EQE) of 9700 cd/m2 and 4.4% have been achieved, respectively. The luminescent species has been identified as [CuI(mCPy)2]2 based on photophysical studies of model complexes and X-ray absorption spectroscopy (XAS). PMID:21366248

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

2011-01-01

210

Metal-organic frameworks based on uranyl and phosphonate ligands.  

PubMed

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

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

2014-02-01

211

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

PubMed

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

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

2005-10-01

212

An europium(III) diglycolamide complex: insights into the coordination chemistry of lanthanides in solvent extraction.  

PubMed

The synthesis, stoichiometry, and structural characterization of a homoleptic, cationic europium(III) complex with three neutral tetraalkyldiglycolamide ligands are reported. The tri(bismuth tetrachloride)tris(N,N,N',N'-tetra-n-octyldiglycolamide)Eu salt, [Eu(TODGA)3][(BiCl4)3] obtained from methanol was examined by Eu L3-edge X-ray absorption spectroscopy (XAS) to reveal an inner-sphere coordination of Eu(3+) that arises from 9 O atoms and two next-nearest coordination spheres that arise from 6 carbon atoms each. A structural model is proposed in which each TODGA ligand with its O=Ca-Cb-O-Cb-Ca=O backbone acts as a tridentate O donor, where the two carbonyl O atoms and the one ether O atom bond to Eu(3+). Given the structural rigidity of the tridentate coordination motif in [Eu(TODGA)3](3+) with six 5-membered chelate rings, the six Eu-Ca and six Eu-Cb interactions are readily resolved in the EXAFS (extended X-ray absorption fine structure) spectrum. The three charge balancing [BiCl4](-) anions are beyond the cationic [Eu(TODGA)3](3+) cluster in an outer sphere environment that is too distant to be detected by XAS. Despite their sizeable length and propensity for entanglement, the four n-octyl groups of each TODGA (for a total of twelve) do not perturb the Eu(3+) coordination environment over that seen from previously reported single-crystal structures of tripositive lanthanide (Ln(3+)) complexes with tetraalkyldiglycolamide ligands (of the same 1:3 metal-to-ligand ratio stoichiometry) but having shorter i-propyl and i-butyl groups. The present results set the foundation for understanding advanced solvent extraction processes for the separation of the minor, tripositive actinides (Am, Cm) from the Ln(3+) ions in terms of the local structure of Eu(3+) in a solid state coordination complex with TODGA. PMID:25310364

Antonio, Mark R; McAlister, Daniel R; Horwitz, E Philip

2015-01-14

213

PREPARATION AND PROPERTIES OF LANTHANUM URANYL CARBONATE  

Microsoft Academic Search

Lanthanum uranyl carbonate was prepared by mixing sodium uranyl ; carbonate solutions with lanthanum nitrate solutions. The reaction was studied ; by measuring the electric conductivity and the pH. The thermal decomposition of ; the product obtained was also studied. (tr-auth);

M. Bachelet; H. Gueniffey

1959-01-01

214

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

215

Extremely Facile Template Synthesis of Gold(III) Complexes of a Saturated Azamacrocycle and Crystal Structure of a Six-Coordinate Gold(III) Complex  

E-print Network

Extremely Facile Template Synthesis of Gold(III) Complexes of a Saturated Azamacrocycle and Crystal Structure of a Six-Coordinate Gold(III) Complex Myunghyun Paik Suh,* Il Soon Kim, Boo Yong Shim, Daewon Hong University, Seoul 151-742, Republic of Korea ReceiVed February 2, 1996X Two gold(III) complexes

Paik Suh, Myunghyun

216

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

PubMed

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

Hashimoto, Takayoshi; Ohki, Yasuhiro; Tatsumi, Kazuyuki

2010-07-01

217

VO2+-hydroxyapatite complexes as models for vanadyl coordination to phosphate in bone  

PubMed Central

We describe a 1D and 2D ESEEM investigation of VO2+ adsorbed on hydroxyapatite (HA) at different concentrations and compare with VO2+-triphosphate (TPH) complexes studied previously in detail, in an effort to provide more insight into the structure of VO2+coordination in bone. Structures of this interaction are important because of the role of bone in the long-term storage of administered vanadium, and the likely role of bone in the steady-state release of vanadium leading to the chronic insulin-enhancing anti-diabetic effects of vanadyl complexes. Three similar sets of cross-peaks from phosphorus nuclei observed in the 31P HYSCORE spectra of VO2+-HA, VO2+-TPH, and VO2+-bone suggest a common tridentate binding motif for triphosphate moieties to the vanadyl ion. The similarities between the systems present the possibility that in vivo vanadyl coordination in bone is relatively uniform. Experiments with HA samples containing different amounts of adsorbed VO2+ demonstrate additional peculiarities of the ion-adsorbent interaction which can be expected in vivo. HYSCORE spectra of HA samples show varying relative intensities of 31P lines from phosphate ligands and 1H lines, especially lines from protons of coordinated water molecules. This result suggests that the number of equatorial phosphate ligands in HA could be different depending on the water content of the sample and the VO2+ concentration; complexes of different structure probably contribute to the spectra of VO2+-HA. Similar behavior can be also expected in vivo during VO2+ accumulation in bones. PMID:24829511

Dikanov, Sergei A.; Liboiron, Barry D.; Orvig, Chris

2013-01-01

218

Optical apparatus and method for sensing uranyl  

DOEpatents

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

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

1994-01-01

219

The DREAM complex: Master coordinator of cell cycle dependent gene expression  

PubMed Central

Preface The dimerization partner (DP), retinoblastoma (RB)-like, E2F and MuvB (DREAM) complex provides a previously unsuspected unifying role in the cell cycle by directly linking p130, p107, E2F, BMYB and FOXM1. DREAM mediates gene repression during G0 and coordinates periodic gene expression with peaks during G1/S and G2/M. Perturbations in DREAM regulation shift the balance from quiescence towards proliferation and contribute to increased mitotic gene expression levels frequently observed in cancers with poor prognosis. PMID:23842645

Sadasivam, Subhashini; DeCaprio, James A.

2014-01-01

220

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

221

Small molecule regulation of self-association and catalytic activity in a supramolecular coordination complex.  

PubMed

Herein, we report the synthesis and characterization of the first weak-link approach (WLA) supramolecular construct that employs the small molecule regulation of intermolecular hydrogen bonding interactions for the in situ control of catalytic activity. A biaryl urea group, prone to self-aggregation, was functionalized with a phosphinoalkyl thioether (P,S) hemilabile moiety and incorporated into a homoligated Pt(II) tweezer WLA complex. This urea-containing construct, which has been characterized by a single crystal X-ray diffraction study, can be switched in situ from a rigid fully closed state to a flexible semiopen state via Cl(-) induced changes in the coordination mode at the Pt(II) structural node. FT-IR and (1)H NMR spectroscopy studies were used to demonstrate that while extensive urea self-association persists in the flexible semiopen complex, these interactions are deterred in the rigid, fully closed complex because of geometric and steric restraints. Consequently, the urea moieties in the fully closed complex are able to catalyze a Diels-Alder reaction between cyclopentadiene and methyl vinyl ketone to generate 2-acetyl-5-norbornene. The free urea ligand and the semiopen complex show no such activity. The successful incorporation and regulation of a hydrogen bond donating catalyst in a WLA construct open the doors to a vast and rapidly growing catalogue of allosteric catalysts for applications in the detection and amplification of organic analytes. PMID:24628075

McGuirk, C Michael; Stern, Charlotte L; Mirkin, Chad A

2014-03-26

222

Characterization of Two Different 5-Coordinate Soluble Guanylate Cyclase Ferrous Nitrosyl Complexes  

PubMed Central

Soluble guanylate cyclase (sGC), a hemoprotein, is the primary nitric oxide (NO) receptor in higher eukaryotes. The binding of NO to sGC leads to the formation of a 5-coordinate ferrous-nitrosyl complex, and a several hundred-fold increase in cGMP synthesis. NO activation of sGC is influenced by GTP and the allosteric activators YC-1 and BAY 41-2272. Electron paramagnetic resonance (EPR) spectroscopy shows that the spectrum of the sGC ferrous-nitrosyl complex shifts in the presence of YC-1, BAY 41-2272, or GTP in the presence of excess NO relative to the heme. These molecules shift the EPR signal from one characterized by g1 = 2.083, g2 = 2.036, g3 = 2.012 to a signal characterized by g1 = 2.106, g2 = 2.029, g3 = 2.010. The truncated heme domain constructs ?1(1-194) and ?2(1-217) were compared to the full-length enzyme. The EPR spectrum of the ?2(1-217)-NO complex is characterized by g1 = 2.106, g2 = 2.025, g3 = 2.010 indicating the protein is a good model for the sGC-NO complex in the presence of the activators, while the ?1(1-194)-NO complex resembles the EPR spectrum of sGC in the absence of the activators. Low-temperature resonance Raman spectra of the ?1(1-194)-NO and ?2(1-217)-NO complexes show that the Fe-NO stretching vibration of the ?2(1-217)-NO complex (535 cm?1) is significantly different than that of the ?1(1-194)-NO complex (527 cm?1). This shows that sGC can adopt different 5-coordinate ferrous nitrosyl conformations, and suggests that the Fe-NO conformation characterized by this unique EPR signal and Fe-NO stretching vibration represents a highly active sGC state. PMID:18302323

Derbyshire, Emily R.; Gunn, Alexander; Ibrahim, Mohammed; Spiro, Thomas G.; Britt, R. David; Marletta, Michael A.

2009-01-01

223

U(III)-CN versus U(IV)-NC Coordination in Tris(silylamide) Complexes.  

PubMed

Treatment of the metallacycle [UN*2(N,C)] [N* = N(SiMe3)2; N,C = CH2SiMe2N(SiMe3)] with [HNEt3][BPh4], [HNEt3]Cl, and [pyH][OTf] (OTf = OSO2CF3) gave the cationic compound [UN*3][BPh4] (1) and the neutral complexes [UN*3X] [X = Cl (3), OTf (4)], respectively. The dinuclear complex [{UN*(?-N,C)(?-OTf)}2] (5) and its tetrahydrofuran (THF) adduct [{UN*(N,C)(THF)(?-OTf)}2] (6) were obtained by thermal decomposition of 4. The successive addition of NEt4CN or KCN to 1 led to the formation of the cyanido-bridged dinuclear compound [(UN*3)2(?-CN)][BPh4] (7) and the mononuclear mono- and bis(cyanide) complexes [UN*3(CN)] (2) and [M][UN*3(CN)2] [M = NEt4 (8), K(THF)4 (9)], while crystals of [K(18-crown-6)][UN*3(CN)2] (10) were obtained by the oxidation of [K(18-crown-6)][UN*3(CN)] with pyridine N-oxide. The THF adduct of 1, [UN*3(THF)][BPh4], and complexes 2-7, 9 and 10 were characterized by their X-ray crystal structure. In contrast to their U(III) analogues [NMe4][UN*3(CN)] and [K(18-crown-6)]2[UN*3(CN)2] in which the CN anions are coordinated to the metal center via the C atom, complexes 2 and 9 exhibit the isocyanide U-NC coordination mode of the cyanide ligand. This U(III)/U(IV) differentiation has been analyzed using density functional theory calculations. The observed preferential coordinations are well explained considering the electronic structures of the different species and metal-ligand bonding energies. A comparison of the different quantum descriptors, i.e., bond orders, NPA/QTAIM data, and energy decomposition analysis, has allowed highlighting of the subtle balance between covalent, ionic, and steric factors that govern the U-CN/NC bonding. PMID:25686295

Herv, Alexandre; Bouzidi, Yamina; Berthet, Jean-Claude; Belkhiri, Lotfi; Thury, Pierre; Boucekkine, Abdou; Ephritikhine, Michel

2015-03-01

224

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

PubMed

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

Smith, Graham; Lynch, Daniel E

2014-06-01

225

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

226

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

NASA Astrophysics Data System (ADS)

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

Balboni, Enrica; Burns, Peter C.

2014-05-01

227

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

228

Syntheses and Characterization of Ruthenium(II) Tetrakis(pyridine)complexes: An Advanced Coordination Chemistry Experiment or Mini-Project  

ERIC Educational Resources Information Center

An experiment for third-year undergraduate a student is designed which provides synthetic experience and qualitative interpretation of the spectroscopic properties of the ruthenium complexes. It involves the syntheses and characterization of several coordination complexes of ruthenium, the element found directly beneath iron in the middle of the

Coe, Benjamin J.

2004-01-01

229

Self-assembly as a route to dinuclear lanthanide complexes with rare coordination pattern of salen-type ligand  

Microsoft Academic Search

The self-assembled formation of dinuclear lanthanide salicylaldimines is proved by the X-ray diffraction analysis of europium\\u000a and gadolinium nitrate complexes containing N,N?-bis(salicylidene)-4-methyl-1,3-phenylenediamine (H2L). The [Eu2(H2L)2(?-H2L)2(NO3)6] complex, isostructural with the gadolinium complex, displays nine-coordinate distorted tricapped trigonal prism geometry\\u000a with a different coordination mode of four undeprotonated salicylaldimines, which act as terminal monodentate and ?-bridging\\u000a ditopic ligands using exclusively the oxygens

Ma?gorzata T. Kaczmarek; Maciej Kubicki; Wanda Radecka-Paryzek

2010-01-01

230

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. PMID:23088792

2012-01-01

231

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

2011-07-01

232

Adsorption of uranyl on hydroxylated ?-SiO?(001): a first-principle study.  

PubMed

The adsorption of [UO2(H2O)5](2+) on a hydroxylated ?-SiO2(001) surface was studied by periodic density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulation. The effects of pH, CO2, aqua solution and anionic ligands (OH(-), NO3(-) and Cl(-)) on the adsorption geometry and stability were investigated. The results show that the adsorption of uranyl on a hydroxylated ?-SiO2(001) surface leads to the formation of inner-sphere complexes, in which the bidentate complex at the double deprotonated site is most favored. The binding strengths of bidentate and monodentate complexes at the same site are similar, and they become weaker as the number of protons increases at the adsorption site, indicating an enhancement of the adsorption strength at higher pH values within a certain range. Strong chemical interaction plays an important role in all inner-sphere complexes. The hydrogen bonds are formed between uranyl and the hydroxylated surface in all inner- and outer-sphere complexes. The presence of CO2 weakens the adsorption of uranyl on the surface by forming uranyl carbonate (CO3(2-), HCO3(-)) complexes. The effect of the anion ligands depends on their charged state and their concentration in solutions. The explicit treatment of water environment in the models has a slight effect on the adsorption configuration. These results are consistent with the experimental observations. PMID:25437449

Wang, Hui; Chai, Zhifang; Wang, Dongqi

2015-01-28

233

[Functioning of macromolecular complexes at successive stages of gene expression as self-coordinated molecular machines].  

PubMed

The results of systemic investigations devoted to the role of the proteins SAYP and ENY2 from Drosophila melanogaster in the regulation of different stages of gene expression are presented. The gene expression is a system of multistage processes involving the preparation of the chromatin matrix, initiation of transcription, mRNA synthesis, as well as the formation of mPNR particles, their export, and translation in the cytoplasm. At each of these stages, a great number of factors present6ed usually by protein complexes consisting of different subunits work. An analysis of the available evidence indicated that the transcription coactivators SAYP and ENY2 act in gene expression as cooperative nanoregulators, thereby determining the molecular mechanisms of coordination of spatial and temporal characteristics of the processes involved in the realization of genetic information. PMID:22117439

Brechalov, A V; Gurski?, D Ia; Georgieva, S G; Shidlovski?, Iu V

2011-01-01

234

The HITECH Act and electronic health records' limitation in coordinating care for children with complex chronic conditions.  

PubMed

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

Cook, Jason E

2014-01-01

235

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

236

Uranyl fluoride luminescence in acidic aqueous solutions  

SciTech Connect

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

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

1996-08-01

237

Coordination-induced spin-state change in manganese(v) complexes: the electronic structure of manganese(v) nitrides.  

PubMed

This work illustrates that manganese(V) nitrido complexes are able to undergo a coordination-induced spin-state change by altering the ligand field from trigonal to tetragonal symmetry. For the reversible coordination of acetonitrile to trigonal [(TIMEN(xyl))Mn(N)](2+) (1; high-spin S = 1; with TIMEN(xyl) = tris[2-(3-xylylimidazol-2-ylidene)ethyl]-amine), a temperature-dependent coordination-induced spin-state switch is established. Starting from the manganese(V) nitrido complex 1, the synthesis and characterization of a series of octahedral, low-spin (S = 0) manganese(V) nitrido complexes of the type [(TIMEN(xyl))Mn(N)(L)](n+) (L = MeCN (2), (t)BuNC (3), CN(-) (4), NCS(-) (5), F(-) (6), ?-{Ag(CN)2}(-) (7), with n = 1, 2) is described. These represent the first examples of d(2) transition metal complexes showing a coordination-induced spin-state change. Spectroscopic, as well as ligand-field theory and density functional theory studies suggest a transition from a 2 + 2 + 1 orbital splitting in the trigonal case to a 1 + 2 + 1 + 1 splitting in tetragonal symmetry as the origin of the coordination-induced spin-state change. PMID:25811888

Kropp, Henning; Scheurer, Andreas; Heinemann, Frank W; Bendix, Jesper; Meyer, Karsten

2015-04-01

238

Synthesis, structure, and spectroscopic characterization of three uranyl phosphates with unique structural units  

NASA Astrophysics Data System (ADS)

Single crystals of Zn4(OH)2[(UO2)(PO4)2(OH)2(H2O)] (UZnP), Cs[(UO2)(HPO4)NO3] (UCsP), and In3[(UO2)2(PO4)4OH(H2O)6].2H2O (UInP) were obtained from hydrothermal reactions and have been structurally and chemically characterized. UZnP crystallizes in space group Pbcn, a=8.8817(7), b=6.6109(5), c=19.569(1) ; UCsP crystallizes in P-1, a=7.015(2), b=7.441(1), c=9.393(2) , ?=72.974(2), ?=74.261(2), ?=79.498(2); and UInP crystallizes in P-1, a=7.9856(5), b=9.159(1), c=9.2398(6) ?=101.289(1), ?=114.642(1), ?=99.203(2). The U6+ cations are present as (UO2)2+ uranyl ions coordinated by five O atoms to give pentagonal bipyramids. The structural unit in UZnP is a finite cluster containing a uranyl pentagonal bipyramid that shares corners with two phosphate tetrahedra. The structural unit in UCsP is composed of uranyl pentagonal bipyramids with one chelating nitrate group that are linked into chains by three bridging hydrogen phosphate tetrahedra. In UInP, the structural unit contains pairs of edge-sharing uranyl pentagonal bipyramids with two chelating phosphate tetrahedra that are linked into chains through two bridging phosphate tetrahedra. Indium octahedra link these uranyl phosphate chains into a 3-dimensional framework. All three compounds exhibit unique structural units that deviate from the typical layered structures observed in uranyl phosphate solid-state chemistry.

Wylie, Ernest M.; Dawes, Colleen M.; Burns, Peter C.

2012-12-01

239

Enhanced environmental detection of uranyl compounds based on luminescence characterization  

NASA Astrophysics Data System (ADS)

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

Nelson, Jean Dennis

240

Temperature programmed decomposition of uranyl nitrate hexahydrate  

NASA Astrophysics Data System (ADS)

Temperature programmed decomposition (TPD) of uranyl nitrate hexahydrate has been studied using evolved gas analysis mass spectrometry (EGA-MS) in the temperature range 300-1400 K. Thermogravimetric (TGA) investigations were performed in the temperature range 300-1100 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 decomposition stages could be deduced from EGA-MS data. The corresponding activation energies and frequency factors were also evaluated. Kinetics based on random nucleation and diffusion was found to be rate controlling. The residue left over after each decomposition stage was analysed by XRD and XPS to determine structure and composition. The ultimate product was found to be a mixture of UO 3H 1.17 and U 3O 8: the former being a topotactic hydrogen spill over compound of UO 3. Complete conversion of this residue to U 3O 8 was noticed during ion beam exposure of the residue which was performed in the course of XPS investigations.

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

1999-01-01

241

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

242

Efficient water oxidation catalysts based on readily available iron coordination complexes.  

PubMed

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 O(2), with high efficiency during a period of hours. Turnover numbers >350 and >1,000 were obtained using cerium ammonium nitrate at pH 1 and sodium periodate at pH 2, respectively. Spectroscopic monitoring of the catalytic reactions, in combination with kinetic studies, show that high valent oxo-iron species are responsible for the O-O forming event. A systematic study of iron complexes that contain a broad family of neutral tetradentate organic ligands identifies first-principle structural features to sustain water oxidation catalysis. Iron-based catalysts described herein open a novel strategy that could eventually enable sustainable artificial photosynthetic schemes. PMID:21941254

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

2011-10-01

243

Efficient water oxidation catalysts based on readily available iron coordination complexes  

NASA Astrophysics Data System (ADS)

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 efficiency during a period of hours. Turnover numbers >350 and >1,000 were obtained using cerium ammonium nitrate at pH 1 and sodium periodate at pH 2, respectively. Spectroscopic monitoring of the catalytic reactions, in combination with kinetic studies, show that high valent oxo-iron species are responsible for the O-O forming event. A systematic study of iron complexes that contain a broad family of neutral tetradentate organic ligands identifies first-principle structural features to sustain water oxidation catalysis. Iron-based catalysts described herein open a novel strategy that could eventually enable sustainable artificial photosynthetic schemes.

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

2011-10-01

244

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

245

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

246

Long Patch Base Excision Repair Proceeds via Coordinated Stimulation of the Multienzyme DNA Repair Complex*  

PubMed Central

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 ? (pol ?), 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 ? 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 ? 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 ? 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.

2009-01-01

247

Synthesis, complexation studies and structural characterization of d and f metal ion complexes with 4-chloroquinaldinic acid N-oxide  

NASA Astrophysics Data System (ADS)

The behavior of 4-chloroquinaldinic acid N-oxide (4Cl-QNO) towards divalent 3d transition elements and 4f or 5f elements has been investigated. Four coordinate copper(II), six coordinate cobalt(II), manganese(II), zinc(II) and uranyl as well as seven coordinate europium(III) complexes were synthesized and structurally characterized on the basis of spectral (infrared absorption spectra), thermogravimetric and X-ray diffraction studies. Crystals of Zn(II), Co(II) and Mn(II) complexes suitable for single crystal X-ray diffraction were obtained and their structures were reported together with the crystal structure of the 4Cl-QNO ligand. The 4-chloroquinaldinic acid N-oxide ion is bidentate, it coordinates with metal ions through the N-O oxygen and one of the COO- oxygens. Lattice water and methanol are also present in these complexes.

Hnatejko, Zbigniew; Manszewski, Tomasz; Barczy?ski, Piotr; Kubicki, Maciej; Szyczewski, Andrzej; Lis, Stefan

2012-02-01

248

THE COEXTRACTION OF NITRIC ACID AND URANYL NITRATE BY TRIBUTYL PHOSPHATE  

Microsoft Academic Search

The most satisfactory method for the determination of nitric acid in the ; presence of uranyl nitrate was the sodium oxalate complexing of uranium. The ; determinaiion of nitric acid in the organic phase was carried out by back ; extraction into a constant volume of water, addition of 2% sodium oxalate ; solution to the aqueous backwash, and titration

T Sato

1959-01-01

249

Effect of uranyl ion concentration on structure and dynamics of aqueous uranyl solution: a molecular dynamics simulation study.  

PubMed

The effect of uranyl ion concentration on structure and dynamics of aqueous solutions of uranyl ions is investigated by molecular dynamics simulations. In order to get an idea about the effect of concentration of uranyl ions on local structural arrangements of water molecules around the uranyl ion, radial distribution functions of water molecules around the uranyl ion are analyzed for aqueous uranyl solutions of various concentrations. The concentration effect on translational dynamics has also been analyzed by calculating diffusion coefficients of uranyl ion, water, and nitrate ions in solution from their respective mean squared displacements. Mobility of water as well as uranyl ions has been found to decrease with increasing concentration of the uranyl ions. Orientational dynamics of water about different molecular axes of water have also been analyzed and decreasing orientational mobility of water with increasing uranyl concentration has been found. In order to get further insight into origin of slowing down of the translational mobility of water molecules with increasing uranyl ion concentration, two separate effects namely long-range effect of uranyl ions on the dynamics of water molecules beyond the solvation shell and short-range effect involving dynamics of solvation shell water have been analyzed. It is found that long-range effect is responsible for the slowing down of translational dynamics of water molecules in the presence of uranyl ions. PMID:25426866

Chopra, Manish; Choudhury, Niharendu

2014-12-11

250

Synthesis, structure, and spectroscopic characterization of three uranyl phosphates with unique structural units  

SciTech Connect

Single crystals of Zn{sub 4}(OH){sub 2}[(UO{sub 2})(PO{sub 4}){sub 2}(OH){sub 2}(H{sub 2}O)] (UZnP), Cs[(UO{sub 2})(HPO{sub 4})NO{sub 3}] (UCsP), and In{sub 3}[(UO{sub 2}){sub 2}(PO{sub 4}){sub 4}OH(H{sub 2}O){sub 6}].2H{sub 2}O (UInP) were obtained from hydrothermal reactions and have been structurally and chemically characterized. UZnP crystallizes in space group Pbcn, a=8.8817(7), b=6.6109(5), c=19.569(1) A; UCsP crystallizes in P-1, a=7.015(2), b=7.441(1), c=9.393(2) A, {alpha}=72.974(2), {beta}=74.261(2), {gamma}=79.498(2); and UInP crystallizes in P-1, a=7.9856(5), b=9.159(1), c=9.2398(6) A {alpha}=101.289(1), {beta}=114.642(1), {gamma}=99.203(2). The U{sup 6+} cations are present as (UO{sub 2}){sup 2+} uranyl ions coordinated by five O atoms to give pentagonal bipyramids. The structural unit in UZnP is a finite cluster containing a uranyl pentagonal bipyramid that shares corners with two phosphate tetrahedra. The structural unit in UCsP is composed of uranyl pentagonal bipyramids with one chelating nitrate group that are linked into chains by three bridging hydrogen phosphate tetrahedra. In UInP, the structural unit contains pairs of edge-sharing uranyl pentagonal bipyramids with two chelating phosphate tetrahedra that are linked into chains through two bridging phosphate tetrahedra. Indium octahedra link these uranyl phosphate chains into a 3-dimensional framework. All three compounds exhibit unique structural units that deviate from the typical layered structures observed in uranyl phosphate solid-state chemistry. - Graphical abstract: Three new uranyl phosphates with unique structural units are reported. Black-Small-Square Highlights: Black-Right-Pointing-Pointer Three new uranyl phosphates have been synthesized hydrothermally. Black-Right-Pointing-Pointer Single crystal analyses reveal unique structural units. Black-Right-Pointing-Pointer The dimensionality of these compounds deviate from typical U{sup 6+} layered structures.

Wylie, Ernest M.; Dawes, Colleen M. [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556 (United States)] [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556 (United States); Burns, Peter C., E-mail: pburns@nd.edu [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556 (United States)

2012-12-15

251

NMR crystallography for structural characterization of oxovanadium(v) complexes: deriving coordination geometry and detecting weakly coordinated ligands at atomic resolution in the solid state.  

PubMed

NMR crystallography is an emerging method for atomic-resolution structural analysis of ubiquitous vanadium(V) sites in inorganic and bioinorganic complexes as well as vanadium-containing proteins. NMR crystallography allows for characterization of vanadium(V) containing solids, based on the simultaneous measurement of (51)V-(15)N internuclear distances and anisotropic spin interactions, described by (13)C, (15)N, and (51)V chemical shift anisotropy and (51)V electric field gradient tensors. We show that the experimental (51)V, (13)C, and (15)N NMR parameters are essential for inferring correct coordination numbers and deriving correct geometries in density functional theory (DFT) calculations, particularly in the absence of single-crystal X-ray structures. We first validate this approach on a structurally known vanadium(V) complex, ((15)N-salicylideneglycinate)-(benzhydroxamate)oxovanadium(V), VO(15)NGlySalbz. We then apply this approach to derive the three-dimensional structure of (methoxo)((15)N-salicylidene-glycinato)oxovanadium(V) with solvated methanol, [VO((15)NGlySal)(OCH3)](CH3OH). This is a representative complex with potentially variable coordination geometry depending on the solvation level of the solid. The solid material containing molecules of CH3OH, formally expressed as [VO((15)NGlySal)(OCH3)](CH3OH), is found to have one molecule of CH3OH weakly coordinated to the vanadium. The material is therefore best described as [VO((15)NGlySal)(OCH3)(CH3OH)] as deduced by the combination of multinuclear solid-state NMR experiments and DFT calculations. The approach reported here can be used for structural analysis of systems that are not amenable to single-crystal X-ray diffraction characterization and which can contain weakly associated solvents. PMID:25590382

Li, Mingyue; Yehl, Jenna; Hou, Guangjin; Chatterjee, Pabitra B; Goldbourt, Amir; Crans, Debbie C; Polenova, Tatyana

2015-02-16

252

Three new silver uranyl diphosphonates: structures and properties.  

PubMed

The hydrothermal reaction of uranium trioxide and methylenediphosphonic acid in the presence of silver nitrate resulted in the formation of three new uranyl coordination polymers: AgUO2[CH2(PO3)(PO3H)] (Ag-1), [Ag2(H2O)1.5]{(UO2)2[CH2(PO3)2]F2}(H2O)0.5 (Ag-2), and Ag2UO2[CH2(PO3)2] (Ag-3). All consist of uranyl pentagonal bipyramids that form two-dimensional layered structures. Ag-1 and Ag-3 possess the same structural building unit, but the structures are different; Ag-3 is formed through edge-sharing of F atoms to form UO5F2 dimers. The pH and silver cation have significant effects on the structure that is synthesized. Raman spectra of single crystals of Ag-1, Ag-2, and Ag-3 reveal v1 UO2(2+) symmetric stretches of 816 and 829, 822, and 802 cm(-1), respectively. Electronic structure calculations were performed using the projector augmented wave (PAW) method with density functional theory (DFT) to gain insight into the nature of bonding and electronic characteristics of the synthesized compounds. Herein, we report the syntheses, crystal structures, Raman spectroscopy, and luminescent behavior of these three compounds. PMID:24524249

Nelson, Anna-Gay D; Rak, Zsolt; Albrecht-Schmitt, Thomas E; Becker, Udo; Ewing, Rodney C

2014-03-17

253

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

SciTech Connect

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

Gary S. Groenewold; Jean-Jacques Gaumet

2011-12-01

254

ORNL/TM-2008/048 Uranyl Nitrate Flow Loop  

E-print Network

ORNL/TM-2008/048 Uranyl Nitrate Flow Loop October 2008 Jennifer L. Ladd-Lively #12;DOCUMENT Government or any agency thereof. #12;ORNL/TM-2008/048 Nuclear Science and Technology Division URANYL NITRATE

Pennycook, Steve

255

Vibrational spectra, normal coordinate treatment and simulation of the vibrational spectra of piperazine glyoxime and its Co(III) complex  

NASA Astrophysics Data System (ADS)

Newly synthesized Co(III) complexes of piperazine glyoxime (PGO) are examined from the vibrational spectroscopy point of view. A complete interpretation of the vibrational spectra of both the ligand and the complex has been carried out on the basis of normal coordinate analysis. A valence force field has been developed for both of the compounds. The vibrational spectra of the compounds are simulated by a visual basic program prepared to run on an MS Excel data sheet.

zpozan, T.; Kkusta, D.; Bykmumcu, Z.

2003-12-01

256

cis, trans - or both: Steric bulk determines coordination mode of dimeric palladium complexes with bridging pyridine-phosphane ligands  

Microsoft Academic Search

The coordination mode in a metal complex is critically dependent on the ligands surrounding the metal, on the precursors used, and on the conditions during synthesis. Our goal was to obtain palladium compounds with pyridine-phosphane ligands for catalysis. Therefore, we synthesized ligands 1a-d, which differ in the bulky aryl substituent at the pyridyl moiety. The palladium complexes 6a-d of these

Jitte Flapper; Philip Wormald; Martin Lutz; Anthony L. Spek; Leeuwen van P. W. N. M; Cornelis J. Elsevier; Paul C. J. Kamer

2008-01-01

257

COORDINATING, COMMUNICATING AND PERFORMING COMPLEX RESEARCH THAT IDENTIFIES VULNERABLE STREAM ECOSYSTEM IN THE MID-ATLANTIC REGION  

EPA Science Inventory

The USEPA's Regional Vulnerability Assessment (ReVA) program was created to advance the scientific basis for protecting vulnerable ecosystems at a regional scale. As a first step, the ReVa program will coordinate, communicate and perform complex research that will identify vulner...

258

Coordination properties of ionic liquid-mediated chromium(II) and copper(II) chlorides and their complexes with glucose.  

PubMed

The structural and coordination properties of complexes formed upon the interaction of copper(II) and chromium(II) chlorides with dialkylimidazolium chloride (RMIm(+)Cl(-)) ionic liquids and glucose are studied by a combination of density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS). In the absence of the carbohydrate substrate, isolated mononuclear four-coordinated MeCl(4)(2-) species (Me = Cu, Cr) dominate in the ionic liquid solution. The organic part of the ionic liquid does not directly interact with the metal centers. The interactions between the RMIm(+) cations and the anionic metal chloride complexes are limited to hydrogen bonding with the basic Cl(-) ligands and the overall electrostatic stabilization of the anionic metal complexes. Exchange of Cl(-) ligands by a hydroxyl group of glucose is only favorable for CrCl(4)(2-). For Cu(2+) complexes, the formation of hydrogen bonded complexes between CuCl(4)(2-) and glucose is preferred. No preference for the coordination of metal chloride species to specific hydroxyl group of the carbohydrate is found. The formation of binuclear metal chloride complexes is also considered. The reactivity and selectivity patterns of the Lewis acid catalyzed reactions of glucose are discussed in the framework of the obtained results. PMID:20929259

Pidko, Evgeny A; Degirmenci, Volkan; van Santen, Rutger A; Hensen, Emiel J M

2010-11-01

259

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

2013-02-01

260

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

PubMed Central

A three-coordinate Cu-NR2 system (R = p-tolyl) supported by the anionic bis(phosphino)borate ligand [Ph2B(CH2PtBu2)2]? has been isolated and structurally characterized in both its anionic CuI and neutral (formally) CuII oxidation states. A rapid rate constant kS ? 107 M?1 s?1 for the self-exchange electron transfer reaction makes this system a functional model for the type-1 active sites in blue copper proteins. Multi-edge XAS, multi-frequency EPR, and DFT analyses collectively indicate that the oxidized form is best regarded as a CuI-aminyl radical complex rather than a CuII-amido species, with about 70% localization of the unpaired electron on the NR2 unit. Hydrogen atom transfer and C-C coupling reactions are presented as examples of chemical reactivity manifested by this unusual electronic structure. PMID:19253942

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

2011-01-01

261

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

262

EXAFS study of uranyl nitrate dimer at high and low temperature  

SciTech Connect

X-ray absorption spectroscopy (XAS) has become an increasingly important technique for the study and characterization of metal species in materials, heterogeneous catalysts, and bioinorganic substrates. More recently, a number of environmental applications have also been reported in which information concerning the local coordination sphere around transuranium elements has been obtained from both near edge (XANES) and fine structure (EXAFS) studies. This paper describes EXAFS studies on the hydroxy-bridged uranyl nitrate dimer HIm{sub 2}[{l{underscore}brace}UO{sub 2}({mu}-OH)(NO{sub 3}){sub 2}{r{underscore}brace}{sub 2}] (1) (HIm = imidazolium (C{sub 3}H{sub 5}N{sub 2})), which are used to model possible species found in vitreous glasses used in the safe, long-term storage of transuranic wastes. A pronounced temperature effect on the U{hor{underscore}ellipsis}U feature in the XAS spectrum of 1 was observed. Complete interpretation and analysis of the EXAFS observed for this complex are described.

Barnes, C.E.; Shin, Y.; Saengkerdsub, S.; Dai, S.

2000-02-21

263

Two coordination modes around the Cu(II) cations in complexes with benzo[b]furancarboxylic acids  

NASA Astrophysics Data System (ADS)

Three Cu(II) complexes with derivatives of the benzo[b]furancarboxylic acid have been synthesized and characterized by the elemental and thermal analyses, and IR spectroscopy. The geometry of metal-ligand interaction for all compounds has been described using X-ray absorption spectroscopy and for one of them by X-ray crystallography. Two mononuclear Cu(II) complexes, with 7-acetyl-5-bromo-6-hydroxy-3-methylbenzo[b]furan-2-carboxylic and 6-acetyl-5-hydroxy-2-methylbenzo[b]furan-3-carboxylic acids, exhibit a tetra-fold coordination, CuO4. The Cu(II) cation in crystals with 7-acetyl-6-methoxy-3-methyl-benzo[b]furan-2-carboxylic acid is penta-coordinated; the bridging COO- groups and ethanol molecule stabilize the dinuclear center Cu2O10. The powdered form of this complex is based on the Cu2O8 units, indicating the absence of the ethanol molecules.

Drzewiecka, Aleksandra; Koziol, Anna E.; Klepka, Marcin T.; Wolska, Anna; Jimenez-Pulido, Sonia B.; Lis, Tadeusz; Ostrowska, Kinga; Struga, Marta

2013-02-01

264

Biological activity and coordination modes of copper(II) complexes of Schiff base-derived coumarin ligands.  

PubMed

The coordination modes of copper(II) complexes of Schiff base-derived coumarin ligands, which had previously shown good anti-Candida activity, were investigated by pH-potentiometric and UV-Vis spectroscopic methods. These studies confirmed the coordination mode of the ligands to be through the N of the imine and deprotonated phenol of the coumarin-derived ligand in solution. In addition, the more active complexes and their corresponding ligands were investigated in the presence of copper(II) in liquid and frozen solution by ESR spectroscopic methods. A series of secondary amine derivatives of the Schiff base ligands, were isolated with good solubility characteristics but showed little anti-Candida activity. However, cytotoxicity studies of the secondary amines, together with the copper complexes and their corresponding ligands, against human colon cancer and human breast cancer cells identified the chemotherapeutic potential of these new ligands. PMID:20949224

Creaven, Bernadette Sarah; Czegldi, Eszter; Devereux, Michael; Enyedy, va Anna; Foltyn-Arfa Kia, Agnieszka; Karcz, Dariusz; Kellett, Andrew; McClean, Siobhn; Nagy, Nra Veronika; Noble, Andy; Rockenbauer, Antal; Szab-Plnka, Terzia; Walsh, Maureen

2010-12-01

265

Cooperative Iron(II) spin crossover complexes with N4O2 coordination sphere.  

PubMed

Two new spin crossover complexes [FeL(py)(2)] (1) and [FeL(DMAP)(2)] (2) with L being a tetradentate N(2)O(2)(2-) coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentanedionato)(2-)-N,N',O(2),O(2)'], py = pyridine and DMAP = p-dimethylaminopyridine have been investigated using temperature-dependent susceptibility and thermogravimetric and photomagnetic measurements as well as Mssbauer spectroscopy and X-ray structure analysis. Both complexes show a cooperative spin transition with an approximately 9 K wide thermal hysteresis loop in the case of 2 (T(1/2) upward arrow = 183 K and T(1/2) downward arrow = 174 K) and an approximately 2 K wide thermal hysteresis loop in the case of the pyridine diadduct 1 (T(1/2) upward arrow = 191 K and T(1/2) downward arrow = 189 K). The spin transition was additionally followed by different temperature-scanning calorimetry and Mssbauer spectroscopy for 2, and a good agreement for the transition temperatures obtained with the different methods was found. Results from X-ray structure analysis indicate that the cooperative interactions are due to elastic interactions in both compounds. They are more pronounced in the case of 2 with very short intermolecular iron-iron distances of 7.2 A and several intense C-C contacts. The change of the spin state at the iron center is accompanied by a change of the O-Fe-O angle, the so-called bit of the equatorial ligand, from 108 degrees in the high-spin state to 90 degrees in the low-spin state. The reflectivity measurements of both compounds give at low temperature indication that at the sample surface the light-induced excited spin state trapping (LIESST) effect occurs. In bulk condition using a SQUID magnetometer the complex 2 displays some photomagnetic properties with an photoexcitation level of 60% and a T(LIESST) value of 53 K. PMID:18095669

Weber, Birgit; Kaps, Eike; Weigand, Jan; Carbonera, Chiara; Ltard, Jean-Franois; Achterhold, Klaus; Parak, Fritz G

2008-01-21

266

How does a coordinated radical ligand affect the spin crossover properties in an octahedral iron(II) complex?  

PubMed

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

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

2014-06-01

267

Efficient organic light-emitting diodes with phosphorescent platinum complexes containing N?C?N-coordinating tridentate ligand  

Microsoft Academic Search

We describe the phosphorescent characteristics of two platinum complexes containing an N?C?N-coordinating tridentate ligand: platinum(II) 3,5-di(2-pyridyl)toluene chloride [Pt(dpt)Cl] and a newly synthesized platinum(II) 3,5-di(2-pyridyl)toluene phenoxide [Pt(dpt)(oph)], together with the performance of organic light-emitting diodes (OLEDs) prepared with these complexes as phosphors. Films containing each one of the complexes in a 4,4'-N,N'-dicalbazolylbiphenyl (CBP) host showed highly efficient photoluminescence. The fabricated OLEDs

Wataru Sotoyama; Tasuku Satoh; Norio Sawatari; Hiroshi Inoue

2005-01-01

268

Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations.  

PubMed

The intrinsic hydration of three monopositive uranyl-anion complexes (UO(2)A)(+) (where A = acetate, nitrate, or hydroxide) was investigated using ion-trap mass spectrometry (IT-MS). The relative rates for the formation of the monohydrates [(UO(2)A)(H(2)O)](+), with respect to the anion, followed the trend: Acetate > or = nitrate > hydroxide. This finding was rationalized in terms of the donation of electron density by the strongly basic OH(-) to the uranyl metal center, thereby reducing the Lewis acidity of U and its propensity to react with incoming nucleophiles, viz., H(2)O. An alternative explanation is that the more complex acetate and nitrate anions provide increased degrees of freedom that could accommodate excess energy from the hydration reaction. The monohydrates also reacted with water, forming dihydrates and then trihydrates. The rates for formation of the nitrate and acetate dihydrates [(UO(2)A)(H(2)O)(2)](+) were very similar to the rates for formation of the monohydrates; the presence of the first H(2)O ligand had no influence on the addition of the second. In contrast, formation of the [(UO(2)OH)(H(2)O)(2)](+) was nearly three times faster than the formation of the monohydrate. PMID:15144967

Chien, Winnie; Anbalagan, Victor; Zandler, Melvin; Van Stipdonk, Michael; Hanna, Dorothy; Gresham, Garold; Groenewold, Gary

2004-06-01

269

Trinuclear complexes and coordination polymers of redox-active guanidino-functionalized aromatic (GFA) compounds with a triphenylene core.  

PubMed

Herein, we report on the synthesis, redox activity, and coordination chemistry of 2,3,6,7,10,11-hexakis(tetramethylguanidino)triphenylene. CV measurements indicated that the new compound could be oxidized in three separate reversible two-electron oxidation events. The HOMO and LUMO energies were estimated from the oxidation wave and the onset of absorption in the UV/vis spectrum. Our discussion also includes the related new compound 2,3,6,7,10,11-hexakis(N,N'-dimethylethyleneguanidino)triphenylene. Then trinuclear Cu(I) and Cu(II) complexes of the new triphenylene ligands were characterized, and their electronic properties are discussed. In contrast to previously studied redox-active GFA ligands, oxidation of trinuclear copper(I) iodide complexes with I2 leads to copper instead of ligand oxidation. In the tetra-coordinated Cu(II) complexes, the coordination mode is intermediate between tetrahedral and square planar. The optical properties of the complexes were studied, and low-energy electronic transitions were assigned to ligand-to-metal charge-transfer (LMCT) excitations. We then extended our analysis to trinuclear Ni(II) and Co(II) complexes. The magnetic coupling mediated through the triphenylene ligand in the trinuclear Cu(II) and Co(II) complexes was studied by SQUID magnetometry, revealing ferromagnetic coupling of the spin centers and different degrees of spin delocalization into the guanidino groups. Finally, we show that the GFA ligands could be linked to one- or two-dimensional coordination polymers and porous materials with a layer structure by reaction with silver halides. PMID:25188743

Lebkcher, Anna; Wagner, Christoph; Hbner, Olaf; Kaifer, Elisabeth; Himmel, Hans-Jrg

2014-09-15

270

Terminal and Four-Coordinate Vanadium(IV) Phosphinidene Complexes. A Pseudo Jahn-Teller Effect of Second Order Stabilizing the V-P Multiple  

E-print Network

Terminal and Four-Coordinate Vanadium(IV) Phosphinidene Complexes. A Pseudo Jahn-Teller Effect via a pseudo Jahn-Teller effect of second order.7 To prepare a vanadium phosphinidene by R-hydrogen migration, we first synthesized a four-coordinate vanadium-neopentylidene complex [(Nacnac

Baik, Mu-Hyun

271

A Planar Three-Coordinate Vanadium(II) Complex and the Study of Terminal Vanadium Nitrides from N2: A Kinetic or Thermodynamic  

E-print Network

A Planar Three-Coordinate Vanadium(II) Complex and the Study of Terminal Vanadium Nitrides from N2 Supporting Information ABSTRACT: We report the first mononuclear three-coordinate vanadium(II) complex with a topologically linear V(III)N2V(III) core and where each vanadium center antiferromagnetically couples to give

Baik, Mu-Hyun

272

AI Support of Teamwork for Coordinated Care of Children with Complex Ofra Amir and Barbara J. Grosz and Krzysztof Z. Gajos  

E-print Network

AI Support of Teamwork for Coordinated Care of Children with Complex Conditions Ofra Amir University leesanders@stanford.edu Abstract Children with complex health conditions require care from a large types of medical professionals. Coordination of their care is essential for good outcomes, and extensive

Gajos, Krzysztof

273

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

PubMed

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

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

2013-02-28

274

Preparation and characterization of uranyl oxalate powders  

NASA Astrophysics Data System (ADS)

Uranyl oxalate powders are prepared by adding 0.5 M oxalic acid solution to the uranyl nitrate (UNH) solutions purified with TBP extraction from dissolution of the Canada originated U 3O 8 commercial concentrate. Uranyl oxalate powders are identified by chemical analysis, TGA/DTG analysis, IR analysis and by single-crystal X-ray diffraction. The effects of the precipitation conditions on the powder properties are determined. A broad particle size distribution is obtained for all precipitation variants. These powders including very fine particles are difficult to filter and are not free flowing. The reactor and mixing type have a considerable effect on the powder properties of the uranyl oxalate powders. It was possible to ameliorate the filtration and the flowability to a certain degree using a conical air agitated reactor. The flowability of these powders is 0.4 g/s with a specific surface area 6.64 m 2/g and an average particle size of 11 ?m.

Tel, H.; Blbl, M.; Eral, M.; Alta?, Y.

1999-10-01

275

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. PMID:21998195

DiPetrillo, Christen G.; Smith, Elizabeth F.

2011-01-01

276

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

PubMed

The compound [Ni(QM)2], QM = 4,6-di-tert-butyl-N-(2-methylthiomethylphenyl)-o-iminobenzoquinone, is a singlet diradical species with approximately planar configuration at the tetracoordinate metal atom and without any Ni-S bonding interaction. One-electron oxidation results in additional twofold Ni-S coordination (dNi-S ?2.38?) to produce a complex cation of [Ni(QM)2](PF6) with hexacoordinate Ni(II) and two distinctly different mer-configurated tridentate ligands. The O,O'-trans arrangement in the neutral precursor is changed to an O,O'-cis configuration in the cation. The EPR signal of [Ni(QM)2](PF6) has a very large g anisotropy and the magnetic measurements indicate an S = 3/2 state. The dication was structurally characterized as [Ni(QM)2](ClO4)2 to exhibit a similar NiN2O2S2 framework as the monocation. However, the two tridentate (O,N,S) ligands are now equivalent according to the formulation [Ni(II)(QM(0))2](2+). Cyclic voltammetry reflects the qualitative structure change on the first, but not on the second oxidation of [Ni(QM)2], and spectroelectrochemistry reveals a pronounced dependence of the 800-900?nm absorption on the solvent and counterion. Reduction of the neutral form occurs in an electrochemically reversible step to yield an anion with an intense near-infrared absorption at 1345?nm (? = 10,400?M(-1) ?cm(-1)) and a conventional g factor splitting for a largely metal-based spin (S = 1/2), suggesting a [(QM(-))Ni(II)(QM(2-))](-) configuration with a tetracoordinate metal atom with antiferromagnetic Ni(II)-(QM(-)) interactions and symmetry-allowed ligand-to-ligand intervalence charge transfer (LLIVCT). Calculations are used to understand the Ni-S binding activity as induced by remote electron transfer at the iminobenzoquinone redox system. PMID:24665084

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

2014-04-25

277

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

278

Carbene rearrangements in three-coordinate N-heterocyclic carbene complexes of cobalt(II) bis(trimethylsilyl)amide.  

PubMed

The synthesis and molecular structures of the cobalt(II) N-heterocyclic carbene (NHC) complexes [(NHC)Co{N(SiMe3)2}2], where NHC = 1,3-bis(diisopropylphenyl)imidazolylidene (IPr) (6), 1,3-bis(mesityl)imidazolylidene (IMes) (7), and 1,3-bis(tert-butyl)imidazol-2-ylidene (I(t)Bu) (8), are reported. Complexes 6-8 are rare examples of three-coordinate cobalt NHC complexes. The steric congestion within the coordination environments of the cobalt(II) centers in 6 and 7 results in the longest Co-C(NHC) distances currently known. Investigating the thermal stability of 6-8, we have found that the steric congestion in 6 is such that heating the complex to reflux in toluene prompts a rearrangement from the normal, C2-bonding mode of the IPr ligand to the corresponding "abnormal" or mesoionic bonding mode. The rearrangement results in formation of [(aIPr)Co{N(SiMe3)2}2] (9), which is the first cobalt complex of an abnormal NHC ligand. The Co-C bond in 9 is 0.06 shorter than the analogous bond in 6, suggesting that, although the rearrangement occurs due to the spatial demands of the IPr ligand, there is also a thermodynamic driving force in terms of the Co-C bond. In contrast to the case for 6, complex 7 is stable with respect to the normal-to-abnormal rearrangement. Refluxing complex 8 in toluene results in activation of a tert-butyl substituent, which is eliminated as isobutene, followed by formation of the 1-tert-butylimidazole complex [((t)BuIm)Co{N(SiMe3)2}2] (10). PMID:25203858

Day, Benjamin M; Pal, Kuntal; Pugh, Thomas; Tuck, Jessica; Layfield, Richard A

2014-10-01

279

Behavior of the potential antitumor V(IV)O complexes formed by flavonoid ligands. 1. Coordination modes and geometry in solution and at the physiological pH.  

PubMed

The coordination modes and geometry assumed in solution by the potent antitumor oxidovanadium(IV) complexes formed by different flavonoids were studied by spectroscopic (Electron Paramagnetic Resonance, EPR) and computational (Density Functional Theory, DFT) methods. A series of bidentate flavonoid ligands (L) with increasing structural complexity was examined, which can involve (CO, O(-)) donors and formation of five- and six-membered chelate rings, or (O(-), O(-)) donors and five-membered chelate rings. The geometry corresponding to these coordination modes can be penta-coordinated, [VOL2], or cis-octahedral, cis-[VOL2(H2O)]. The results show that, at physiological pH, ligands provided with (CO, O(-)) donor set yield cis-octahedral species with "maltol-like" coordination when five-membered chelate rings are formed (as with 3-hydroxyflavone), while penta-coordinated structures with "acetylacetone-like" coordination are preferred when the chelate rings are six-membered (as with chrysin). When both the binding modes are possible, as with morin, the "acetylacetone-like" coordination is observed. For the ligands containing a catecholic donor set, such as 7,8-dihydroxyflavone, baicalein, fisetin, quercetin and rutin, the formation of square pyramidal complexes with (O(-), O(-)) "catechol-like" coordination and five-membered chelate rings is preferred at physiological pH. The determination of the different coordination modes and geometry is important to define the biotransformation in the blood and the interaction of these complexes with the biological membranes. PMID:25127230

Sanna, Daniele; Ugone, Valeria; Lubinu, Giuseppe; Micera, Giovanni; Garribba, Eugenio

2014-11-01

280

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

281

A density functional theory study of uranium(VI) nitrate monoamide complexes.  

PubMed

Density functional theory calculations were performed on uranyl complexed with nitrate and monoamide ligands (L) [UO(2)(NO(3))(2)2L]. The obtained results show that the complex stability is mainly governed by two factors: (i) the maximization of the polarizability of the coordinating ligand and (ii) the minimization of the steric hindrance effects. Furthermore, the electrostatic interaction between ligands and uranium(vi) was found to be a crucial parameter for the complex stability. These results pave the way to the definition of (quantitative) property/structure relationships for the in silico screening of monoamide ligands with improved extraction efficiency of uranium(vi) in nitrate acidic solution. PMID:21952360

Prestianni, Antonio; Joubert, Laurent; Chagnes, Alexandre; Cote, Grard; Adamo, Carlo

2011-11-21

282

Three-coordinate nickel(II) and nickel(I) thiolate complexes based on the ?-diketiminate ligand system.  

PubMed

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

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

2014-07-01

283

[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

2012-01-01

284

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

MedlinePLUS

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

285

Synthesis and Structural Studies of Nickel(0) Tetracarbene Complexes with the Introduction of a New Four-Coordinate Geometric Index, ??.  

PubMed

The synthesis and characterization of two homoleptic chelating nickel(0) tetracarbene complexes are reported. These are the first group 10 M(0) (M = Ni, Pd, Pt) tetracarbene complexes. These species have geometries intermediate between C2v sawhorse and tetrahedral and show high UV-vis absorption in the 350-600 nm range, with extinction coefficients (?) between 5600 and 9400 M(-1) cm(-1). Density functional theory analysis indicates that this high absorptivity is due to metal-to-ligand charge transfer. In order to better describe the unusual geometries encountered in these complexes, an adjustment to the popular ?4 index for four-coordinate geometries is introduced in order to better delineate between sawhorse and distorted tetrahedral geometries. PMID:25757047

Reineke, Mark H; Sampson, Matthew D; Rheingold, Arnold L; Kubiak, Clifford P

2015-04-01

286

The Pex1/Pex6 Complex Is a Heterohexameric AAA+ Motor with Alternating and Highly Coordinated Subunits.  

PubMed

Pex1 and Pex6 are Type-2 AAA+ ATPases required for the de novo biogenesis of peroxisomes. Mutations in Pex1 and Pex6 account for the majority of the most severe forms of peroxisome biogenesis disorders in humans. Here, we show that the ATP-dependent complex of Pex1 and Pex6 from Saccharomyces cerevisiae is a heterohexamer with alternating subunits. Within the Pex1/Pex6 complex, only the D2 ATPase ring hydrolyzes ATP, while nucleotide binding in the D1 ring promotes complex assembly. ATP hydrolysis by Pex1 is highly coordinated with that of Pex6. Furthermore, Pex15, the membrane anchor required for Pex1/Pex6 recruitment to peroxisomes, inhibits the ATP-hydrolysis activity of Pex1/Pex6. PMID:25659908

Gardner, Brooke M; Chowdhury, Saikat; Lander, Gabriel C; Martin, Andreas

2015-03-27

287

Spectroscopic, Kinetic, and Mechanistic Study of a New Mode of Coordination of Indole Derivatives to Platinum(II) and Palladium(II) Ions in Complexes  

E-print Network

Derivatives to Platinum(II) and Palladium(II) Ions in Complexes Natalia V. Kaminskaia, G. Matthias Ullmann, D structure, in which the new bidentate ligand coordinates to the Pt(II) atom via the C(3) atom of the indolyl, the slower the coordination of these dipeptide-like ligands to the Pt(II) atom. The indolyl group does

Ullmann, G. Matthias

288

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

PubMed Central

Docking and fusion of transport vesicles/carriers with the target membrane involve a tethering factormediated initial contact followed by soluble N-ethylmaleimidesensitive factor attachment protein receptor (SNARE)catalyzed membrane fusion. The multisubunit tethering CATCHR family complexes (Dsl1, COG, exocyst, and GARP complexes) share very low sequence homology among subunits despite likely evolving from a common ancestor and participate in fundamentally different membrane trafficking pathways. Yeast Tip20, as a subunit of the Dsl1 complex, has been implicated in retrograde transport from the Golgi apparatus to the endoplasmic reticulum. Our previous study showed that RINT-1, the mammalian counterpart of yeast Tip20, mediates the association of ZW10 (mammalian Dsl1) with endoplasmic reticulumlocalized SNARE proteins. In the present study, we show that RINT-1 is also required for endosome-totrans-Golgi network trafficking. RINT-1 uncomplexed with ZW10 interacts with the COG complex, another member of the CATCHR family complex, and regulates SNARE complex assembly at the trans-Golgi network. This additional role for RINT-1 may in part reflect adaptation to the demand for more diverse transport routes from endosomes to the trans-Golgi network in mammals compared with those in a unicellular organism, yeast. The present findings highlight a new role of RINT-1 in coordination with the COG complex. PMID:23885118

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

2013-01-01

289

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. PMID:20380465

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

2010-01-01

290

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

291

Cyanex based uranyl sensitive polymeric membrane electrodes.  

PubMed

Novel uranyl selective polymeric membrane electrodes were prepared using three different low-cost and commercially available Cyanex extractants namely, bis(2,4,4-trimethylpentyl) phosphinic acid [L1], bis(2,4,4-trimethylpentyl) monothiophosphinic acid [L2] and bis(2,4,4-trimethylpentyl) dithiophosphinic acid [L3]. Optimization and performance characteristics of the developed Cyanex based polymer membrane electrodes were determined. The influence of membrane composition (e.g., amount and type of ionic sites, as well as type of plasticizer) on potentiometric responses of the prepared membrane electrodes was studied. Optimized Cyanex-based membrane electrodes exhibited Nernstian responses for UO?(2+) ion over wide concentration ranges with fast response times. The optimized membrane electrodes based on L1, L2 and L3 exhibited Nernstian responses towards uranyl ion with slopes of 29.4, 28.0 and 29.3 mV decade(-1), respectively. The optimized membrane electrodes based on L1-L3 showed detection limits of 8.3 10(-5), 3.0 10(-5) and 3.3 10(-6) mol L(-1), respectively. The selectivity studies showed that the optimized membrane electrodes exhibited high selectivity towards UO?(2+) ion over large number of other cations. Membrane electrodes based on L3 exhibited superior potentiometric response characteristics compared to those based on L1 and L2 (e.g., widest linear range and lowest detection limit). The analytical utility of uranyl membrane electrodes formulated with Cyanex extractant L3 was demonstrated by the analysis of uranyl ion in different real samples for nuclear safeguards verification purposes. The results obtained using direct potentiometry and flow-injection methods were compared with those measured using the standard UV-visible and inductively coupled plasma spectroscopic methods. PMID:24274282

Badr, Ibrahim H A; Zidan, W I; Akl, Z F

2014-01-01

292

Complex coordinate L2 calculation of partial photoionization cross sections: theory and a model computation  

Microsoft Academic Search

It has been known for quite some time that L2 methods can be used to obtain the total photoabsorption cross sections for atomic and molecular photo-detachment or ionization without explicit enforcement of coordinate space boundary conditions. Such methods use matrix manipulations followed by use of moment-imaging techniques or various implementations of analytic continuation to construct the total cross section from

Seungsuk Han; W. P. Reinhardt

1995-01-01

293

Complexity in Object Manipulation by Japanese Macaques (Macaca fuscata): A Cross-Sectional Analysis of Manual Coordination in Stone Handling Patterns  

Microsoft Academic Search

Defined as a spontaneous stone-directed noninstrumental manipulative behavior, and comprised of multiple one-handed and (a)symmetrical\\/(un)coordinated two-handed patterns, stone handling (SH) is a good candidate for the study of complexity in object manipulation. We present a cross-sectional developmental analysis of SH complexity in Japanese macaques (Macaca fuscata), through the combined investigation of bimanuality, coordination, and symmetry in hand use. Bimanual SH

Jean-Baptiste Leca; Nolle Gunst; Michael Huffman

2011-01-01

294

Influence of the ligand frameworks on the coordination environment and properties of new phenylmercury(ii) ?-oxodithioester complexes.  

PubMed

New phenylmercury(ii) complexes of the form [PhHg(L1), PhHg(L2) and PhHg(L3)] (L1 = methyl-3-hydroxy-3-(p-methoxyphenyl)-2-propenedithioate (), L2 = methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate () and L3 = methyl-3-hydroxy-(3-pyridyl)-2-propenedithioate ()) have been synthesized and characterized by elemental analysis, IR, UV-Vis, (1)H and (13)C NMR. The crystal structures of reveal a linear geometry about the mercury atom via ipso-C and S11 atoms. and exhibited O,S-coordination whereas preferred S,S-coordination. Intramolecular HgO bonding interactions are also observed in and at distances of 2.638(14), 2.644(10) respectively. However in , incorporation of the 3-pyridyl substituent on the ligand enhanced the proximity of S13 and N14, giving rise to significant intramolecular HgS and intermolecular HgN interactions at 3.141(5) and 2.77(2) respectively generating a 1-D polymeric chain motif. The O,S- or S,S-coordination preference and HgN interactions have been assessed by DFT calculations. All the complexes show metal perturbed ligand-centred luminescence characteristics in solution and in the solid phase. The band gap values 2.54, 2.66 and 2.61 eV for , and , respectively, evaluated from the diffuse reflectance spectroscopy show the semiconducting nature of the complexes. PMID:25720560

Rajput, Gunjan; Yadav, Manoj Kumar; Drew, Michael G B; Singh, Nanhai

2015-03-10

295

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

296

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 3O] 2{(UO 2) 6[C 6H 4(PO 3)(PO 2OH)] 2[C 6H 4(PO 2OH) 2] 2[C 6H 4(PO 3) 2]}(H 2O) 2 ( Ubbp-1), [H 3O] 4{(UO 2) 4[C 6H 4(PO 3) 2] 2F 4}H 2O ( Ubbp-2), and {(UO 2)[C 6H 2F 2(PO 2OH) 2(H 2O)} 2H 2O ( 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 5F 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

297

Aerobic oxidative dehydrogenation of coordinated imidazoline units of pincer ruthenium complex  

Microsoft Academic Search

A new pincer ruthenium complex (1; [RuL1(tpy)](PF6); L1=1,3-di(2-imidazoline-2-yl)benzene, tpy=2,2?:6?,2?-terpyridine) having a ?3NCN pincer ligand with two imidazoline units and related ruthenium complexes were synthesized and characterized. The imidazoline units of 1 were oxidized in air to give an imidazole-ligated pincer complex (2; [RuL2(tpy)](PF6); L2=1,3-di(2-imidazolyl)benzene). Results of the 1H NMR spectroscopic and cyclic voltammetric studies of the complexes indicate that the

Shusaku Maeda; Take-aki Koizumi; Takakazu Yamamoto; Koji Tanaka; Takaki Kanbara

2007-01-01

298

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

299

Slow magnetization dynamics in a series of two-coordinate iron(II) complexes  

E-print Network

rigorous DNh geometry on the d-orbital splittings and the electronic state energies. Asymmetry Mononuclear transition metal complexes provide a fertile new platform for research in the eld. Experimental- sition metal complexes.8 Synthetic efforts have occurred in tandem with theoretical studies

300

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

301

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

2013-06-17

302

Complex regulatory pathways coordinate cell cycle progression and development in Caulobacter crescentus  

PubMed Central

Caulobacter crescentus has become the predominant bacterial model system to study the regulation of cell cycle progression. Stage specific processes such as chromosome replication and segregation, and cell division are coordinated with the development of four polar structures: the flagellum, pili, stalk, and holdfast. The production, activation, localization, and proteolysis of specific regulatory proteins at precise times during the cell cycle culminate in the ability of the cell to produce two physiologically distinct daughter cells. We examine the recent advances that have enhanced our understanding of the mechanisms of temporal and spatial regulation that occur during cell cycle progression. PMID:18929067

Brown, Pamela J.B.; Hardy, Gail G.; Trimble, Michael J.; Brun, Yves V.

2008-01-01

303

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

304

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

NASA Technical Reports Server (NTRS)

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

Brinton, Christopher R.

1996-01-01

305

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

PubMed

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

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

2013-10-01

306

The HILDA Complex Coordinates a Conditional Switch in the 3?-Untranslated Region of the VEGFA mRNA  

PubMed Central

Cell regulatory circuits integrate diverse, and sometimes conflicting, environmental cues to generate appropriate, condition-dependent responses. Here, we elucidate the components and mechanisms driving a protein-directed RNA switch in the 3?UTR of vascular endothelial growth factor (VEGF)-A. We describe a novel HILDA (hypoxia-inducible hnRNP LDRBP76hnRNP A2/B1) complex that coordinates a three-element RNA switch, enabling VEGFA mRNA translation during combined hypoxia and inflammation. In addition to binding the CA-rich element (CARE), heterogeneous nuclear ribonucleoprotein (hnRNP) L regulates switch assembly and function. hnRNP L undergoes two previously unrecognized, condition-dependent posttranslational modifications: IFN-? induces prolyl hydroxylation and von Hippel-Lindau (VHL)-mediated proteasomal degradation, whereas hypoxia stimulates hnRNP L phosphorylation at Tyr359, inducing binding to hnRNP A2/B1, which stabilizes the protein. Also, phospho-hnRNP L recruits DRBP76 (double-stranded RNA binding protein 76) to the 3?UTR, where it binds an adjacent AU-rich stem-loop (AUSL) element, flipping the RNA switch by disrupting the GAIT (interferon-gamma-activated inhibitor of translation) element, preventing GAIT complex binding, and driving robust VEGFA mRNA translation. The signal-dependent, HILDA complex coordinates the function of a trio of neighboring RNA elements, thereby regulating translation of VEGFA and potentially other mRNA targets. The VEGFA RNA switch might function to ensure appropriate angiogenesis and tissue oxygenation during conflicting signals from combined inflammation and hypoxia. We propose the VEGFA RNA switch as an archetype for signal-activated, protein-directed, multi-element RNA switches that regulate posttranscriptional gene expression in complex environments. PMID:23976881

Yao, Peng; Potdar, Alka A.; Ray, Partho Sarothi; Eswarappa, Sandeepa M.; Flagg, Andrew C.; Willard, Belinda; Fox, Paul L.

2013-01-01

307

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

PubMed Central

Growing evidence demonstrates that aging not only leads to structural and functional alterations of individual components of the neuro-musculo-skeletal system (NMSS) but also results in a systemic re-organization of interactions within and between the different levels and functional domains. Understanding the principles that drive the dynamics of these re-organizations is an important challenge for aging research. The present Hypothesis and Theory paper is a contribution in this direction. We propose that age-related declines in brain and behavior that have been characterized in the literature as dedifferentiation and the loss of complexity (LOC) are: (i) synonymous; and (ii) integrated. We argue that a causal link between the aforementioned phenomena exists, evident in the dynamic changes occurring in the aging NMSS. Through models and methods provided by a dynamical systems approach to coordination processes in complex living systems, we: (i) formalize operational hypotheses about the general principles of changes in cross-level and cross-domain interactions during aging; and (ii) develop a theory of the aging NMSS based on the combination of the frameworks of coordination dynamics (CD), dedifferentiation, and LOC. Finally, we provide operational predictions in the study of aging at neural, muscular, and behavioral levels, which lead to testable hypotheses and an experimental agenda to explore the link between CD, LOC and dedifferentiation within and between these different levels. PMID:25018731

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

2014-01-01

308

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

2011-09-20

309

Complexation of lanthanides with nitrate at variable temperatures: thermodynamics and coordination modes.  

PubMed

Complexation of neodymium(III) with nitrate was studied at variable temperatures (25, 40, 55, and 70 degrees C) by spectrophotometry and microcalorimetry. The NdNO(3)(2+) complex is weak and becomes slightly stronger as the temperature is increased. The enthalpy of complexation at 25 degrees C was determined by microcalorimetry to be small and positive, 1.5 +/- 0.2 kJ x mol(-1), in good agreement with the trend of the stability constant at variable temperatures. Luminescence emission spectra and the lifetime of Eu(III) in nitrate solutions suggest that inner-sphere and bidentate complexes form between trivalent lanthanides (Nd(3+) and Eu(3+)) and nitrate in aqueous solutions. A specific ion interaction approach was used to obtain the stability constants of NdNO(3)(2+) at infinite dilution and variable temperatures. PMID:19115981

Rao, Linfeng; Tian, Guoxin

2009-02-01

310

Polymer complexes: XLXII-interplay of coordination ?-? stacking and hydrogen bonding in supramolecular assembly of [sulpha drug derivatives-N,S:N,O] complexes.  

PubMed

A novel series of nickel(II) polymer complexes of 5-sulphadiazineazo-3-phenylamino-2-thio-4-thiazolidinone (HL?), 5-sulphamethazine-3-phenylamino-2-thioxo-4-thiazolidinone (HL?), 5-sulphamethoxazole-3-phenylamino-2-thioxo-4-thiazolidinone (HL?), 5-sulphacetamide-3-phenyl-2-thioxo-4-thiazolidinone (HL?) and 5-sulphaguanidine-3-phenylamino-2-thioxo-4-thiazolidinone (HL?) were prepared and characterized. IR spectra show that HL(n) (n=1-5) is coordinated to the metal ion in a neutral tetradentate manner with NSNO donor sites of NH (hydrazone's), NH (3-phenylamine), carbonyl group and Ph-NH. The title [Ni?(HL(n))?(?-OAc)?(OAc)?](n) consists of three Ni(II) atoms linked by interchain ?-? interaction are observed between aromatic rings of two ligands (HL(n)) which are further doubly bridged two adjacent nickel atoms by acetate group. The geometrical structures of these complexes are found to be octahedral. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, thermal, infrared, H NMR, electronic spectra, magnetic susceptibility and conductivity measurements. The richness of electronic spectral in these complexes is also supporting evidence for the trinuclearity of the Ni(II) polymer complexes. PMID:20692866

El-Sonbati, A Z; Diab, M A; El-Halawany, M M; Salam, N E

2010-11-01

311

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+) (1), Eu(3+) (2), Tb(3+) (3) and Dy(3+) (4)] 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 1, and 3 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 4 does not display any emission. The different luminescent intensities and lifetimes among them were further discussed in detail. Moreover, the magnetic properties of complexes 1-4 were assessed with a special emphasis on the Dy(3+) complex 4. Alternating-current (ac) magnetic susceptibility measurements indicated that field-induced two-step slow magnetic relaxation processes were observed in 4, indicating the single-molecule magnet (SMM) behavior of 4. In addition, the noncentrosymmetric complexes 1-4 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

2013-11-21

312

Molecular modeling study of uranyl nitrate extraction with monoamides. 2: Molecular mechanics and lipophilicity calculations -- Structure-activity relationships  

SciTech Connect

This report describes the second part of a theoretical approach aimed at establishing structure-activity relationships in a data base made of twenty-two monoamides (A) used as uranium (VI) nitrate extractants. It was found that predominant factors determining the extracting ability of a monoamide are of three kinds: (1) electron density of the coordinating atoms or groups, which should be as high as possible; (2) steric effects, which should be as low as possible; and (3) lipophilicity of the ligands, which should be above a minimum threshold value. In the first paper of this series, quantum chemistry calculations were reported to account for electronic properties of the ligands. This second paper reports molecular mechanics calculations made on UO{sub 2}(NO{sub 3}){sub 2}A{sub 2} complexes in order to determine the influence of steric effects on the formation of these compounds. Calculations of monoamide lipophilicity using Rekker`s method showed that all the molecules of the data base were lipophilic enough and, consequently, that this parameter was not significantly important for the extraction of uranyl nitrate by these monoamides. A quantitative relationship was established between the U(VI) distribution ratio and the two parameters, calculated by quantum chemistry and molecular mechanics methods.

Rabbe, C.; Madic, C. [CEA-DCC-DRRV, Bagnols-sur-Ceze (France); Sella, C. [E.S.P.C.I., Paris (France). Lab. de Chimie Analytique; Godard, A. [INSA Rouen, Mont-Saint-Aignan (France)

1999-01-01

313

Influence of a thioether function in short-bite diphosphine ligands on the nature of their silver complexes: structure of a trinuclear complex and of a coordination polymer.  

PubMed

New cationic Ag(I) complexes were prepared by reaction of AgBF4 with two thioether-functionalized bis(diphenylphosphino)amine ligands, Ph2PN(p-ArSMe)PPh2 (L1) and Ph2PN(n-PrSMe)PPh2 (L2), and compared with those obtained from the unfunctionalized ligands Ph2PN(Ph)PPh2 (L3) and Ph2PN(n-Bu)PPh2 (L4), respectively. The complex [Ag3(?3-Cl)2(?2-L1-P,P)3](BF4) (1BF4) contains a triangular array of Ag centres supported by three bridging L1 ligands and two triply-bridging chlorides. In contrast, ligand L2 led to the coordination polymer [{Ag2(?3-L2,-P,P,S)2(MeCN)2}{Ag2(?2-L2-P,P)2(MeCN)2}(BF4)4]n (2) in which the tethered thioether group connects intermolecularly a Ag2 unit to the diphosphine bridging the other Ag2 unit. With L3 and L4, two similar complexes were obtained, [Ag2(?2-L3)(BF4)2] (3) and [Ag2(?2-L4)(BF4)2] (4), respectively, with bridging diphosphine ligands and a BF4 anion completing the coordination sphere of the metal. Complexes 1BF4CH2Cl2, 2THF, 33CH2Cl2 and 4 have been fully characterized, including by single crystal X-ray diffraction. PMID:23615622

Rosa, Vitor; Fliedel, Christophe; Ghisolfi, Alessio; Pattacini, Roberto; Avils, Teresa; Braunstein, Pierre

2013-09-14

314

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

SciTech Connect

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

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

2013-01-15

315

Raman spectra of zeolites exchanged with uranyl(VI) cationsII. Zeolite X  

NASA Astrophysics Data System (ADS)

The formation of hydrolysed uranyl(VI) species in UO 2X zeolites prepared by various methods has been investigated by Raman spectroscopy. Ion-exchange in aqueous (pH>3) and non-aqueous (anhydrous methanol and uranyl nitrate melts) media resulted in the formation of hydroxy-bridged complexes such as [(UO 2) 3(OH) 4] 2+, [(UO 2) 3(OH) 5] +, and [(UO 2) 4(OH) 7] +. Ion-exchange in more acidic media (initial pH < 3) was accompanied by the formation of a disordered phase incorporating UO 3, following extensive collapse of the zeolite framework structure. Cation speciation in the UO 2X system is compared to that in UO 2Y zeolites.

Bartlett, John R.; Cooney, Ralph P.

1989-01-01

316

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

PubMed

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

Balderhaar, Henning J kleine; Ungermann, Christian

2013-03-15

317

Dimeric versus polymeric coordination in copper(II) cationic complexes with bis(chelating) oxime and amide ligands.  

PubMed

A series of copper(ii) complexes with earlier reported ligands N,N'-bis(2-hydroxyiminopropionyl)-1,2-diaminoethane (H(2)pen) and 1,3-diaminopropane (H(2)pap) and novel open chain oxime and amide ligands, N,N'-bis(2-hydroxyiminopropionyl)-1,5-diaminopentane (H(2)papt), 1,6-diaminohexane (H(2)pah) and 1,7-diaminoheptane (H(2)pahp), were prepared and characterized by a variety of spectroscopic methods and X-ray structure analysis. Although a pH-potentiometric study revealed only monomeric species in solution, formation of both binuclear dimeric and 1D-polymeric topologies was found in solid state. In all complexes ligands provide bis-bidentate coordination to Cu(2+) ions via the nitrogen atoms of the oxime groups and the oxygen atoms of the amide groups to form CuN(2)O(2) planar fragments. Compound [Cu(Hpap)(ClO(4))(H(2)O)](x) was isolated in both dimeric (x = 2) and polymeric (x = n) state, representing an example of supramolecular isomerism. All the complexes are additionally stabilized by short intramolecular hydrogen bonds =N-O-H...O-N= between cis-arranged oximato-groups. Stabilization is more effective in the case of dimeric complexes compared to 1D-polymeric chain, which appears to be the reason of preferable dimerization versus polymerization in the studied set of compounds. The effect of polymethylene linker length on the conformation of the dimers is described. PMID:20520918

Buvailo, Andrii I; Gumienna-Kontecka, Elzbieta; Pavlova, Svetlana V; Fritsky, Igor O; Haukka, Matti

2010-07-21

318

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

NASA Astrophysics Data System (ADS)

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

Baranwal, B. P.; Fatma, Talat

2005-08-01

319

Syntheses and characterization of novel lanthanide adamantine-dicarboxylate coordination complexes  

NASA Astrophysics Data System (ADS)

Hydrothermal reactions of 1,10-phenanthroline (phen), 1,3-adamantanedicarboxylic acid (H 2L) and lanthanide chlorides yielded six compounds: [ Ln(L)(HL)(phen)] ( Ln=Pr, 1; Nd, 2), [ Ln(L)(HL)(phen)(H 2O)] (Sm, 3; Eu, 4), [Tb(L)(HL)(phen)(H 2O)] 22H 2O ( 5), [Er 3(L) 4(OH)(phen)] 2 ( 6). Compounds 1- 4 are structurally featured by one-dimensional polymeric chains; 5 hold binuclear structure constructed from eight-coordinated lanthanide center LnN 2O 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 ? 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.

Li, Xing; Wei, Dan-Yi; Huang, Shi-Jie; Zheng, Yue-Qing

2009-01-01

320

Specific capture of uranyl protein targets by metal affinity chromatography.  

PubMed

To improve general understanding of biochemical mechanisms in the field of uranium toxicology, the identification of protein targets needs to be intensified. Immobilized metal affinity chromatography (IMAC) has been widely developed as a powerful tool for capturing metal binding proteins from biological extracts. However uranyl cations (UO2(2+)) have particular physico-chemical characteristics which prevent them from being immobilized on classical metal chelating supports. We report here on the first development of an immobilized uranyl affinity chromatography method, based on the cation-exchange properties of aminophosphonate groups for uranyl binding. The cation distribution coefficient and loading capacity on the support were determined. Then the stability of the uranyl-bonded phase under our chromatographic conditions was optimized to promote affinity mechanisms. The successful enrichment of uranyl binding proteins from human serum was then proven using proteomic and mass spectral analysis. PMID:18308325

Basset, Christian; Dedieu, Alain; Gurin, Philippe; Qumneur, Eric; Meyer, Daniel; Vidaud, Claude

2008-03-28

321

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

PubMed

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

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

2014-01-01

322

Removal and recovery of uranyl ion using various microorganisms.  

PubMed

The adsorption of uranyl ion by microorganisms was examined. Among the 76 strains of 69 species tested (23 bacteria, 20 actinomycetes, 18 fungi, and 15 yeasts), high uranyl ion adsorption ability was exhibited by strains of the bacteria, Arthrobacter nicotianae, Bacillus subtilis, and Micrococcus luteus. A. nicotianae cells, which showed the best performance, could adsorb about 698 mg uranyl ion (2.58 mmol) per gram dry wt. of microbial cells. The adsorption of uranyl ion was rapid, selective, and mostly dependent on physico-chemical binding to the cell components. As well as uranyl ion, A. nicotianae could adsorb thorium ion with high efficiency. Cells immobilized with polyacrylamide gel could be used during repeated adsorption-desorption cycles. PMID:16233264

Tsuruta, Takehiko

2002-01-01

323

Complexity in object manipulation by Japanese macaques (Macaca fuscata): a cross-sectional analysis of manual coordination in stone handling patterns.  

PubMed

Defined as a spontaneous stone-directed noninstrumental manipulative behavior, and comprised of multiple one-handed and (a)symmetrical/(un)coordinated two-handed patterns, stone handling (SH) is a good candidate for the study of complexity in object manipulation. We present a cross-sectional developmental analysis of SH complexity in Japanese macaques (Macaca fuscata), through the combined investigation of bimanuality, coordination, and symmetry in hand use. Bimanual SH patterns were more frequent than unimanual patterns. Among bimanual patterns, coordinated actions were more frequent than uncoordinated ones. We recorded five asymmetrical coordinated SH patterns with manual role differentiation, a form of hand use reminiscent of complex actions involving the use of tools in monkeys and apes. Bimanuality in SH was affected by body posture. Aging individuals performed less bimanual and less coordinated SH patterns than younger individuals. Our result on senescent males performing less bimanual patterns than senescent females was consistent with sex differences found in the late deterioration of complex manual movements in other species. Although some SH patterns represent a high degree of behavioral complexity, our results suggest that SH behavior is not as complex as tool-use or tool-manufacture in other nonhuman primates and hominids. PMID:21244141

Leca, Jean-Baptiste; Gunst, Nolle; Huffman, Michael

2011-02-01

324

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

SciTech Connect

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 /sup 0/C (log K/sub ML/ = 14.5-16.5) is comparable to the stability of the EDTA complexes. A competition method with the oxalate anion as a probe had to be used for determining the formation constants of the DOTA lanthanide chelates because of the high stability of these compounds. The relative stability of the DOTA and TETA complexes in accounted for by steric factors with reference to known solution- and solid-state structures. 20 references, 2 tables.

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

1986-07-16

325

Removal of toxic uranium from synthetic nuclear power reactor effluents using uranyl ion imprinted polymer particles.  

PubMed

Major quantities of uranium find use as nuclear fuel in nuclear power reactors. In view of the extreme toxicity of uranium and consequent stringent limits fixed by WHO and various national governments, it is essential to remove uranium from nuclear power reactor effluents before discharge into environment. Ion imprinted polymer (IIP) materials have traditionally been used for the recovery of uranium from dilute aqueous solutions prior to detection or from seawater. We now describe the use of IIP materials for selective removal of uranium from a typical synthetic nuclear power reactor effluent. The IIP materials were prepared for uranyl ion (imprint ion) by forming binary salicylaldoxime (SALO) or 4-vinylpyridine (VP) or ternary SALO-VP complexes in 2-methoxyethanol (porogen) and copolymerizing in the presence of styrene (monomer), divinylbenzene (cross-linking monomer), and 2,2'-azobisisobutyronitrile (initiator). The resulting materials were then ground and sieved to obtain unleached polymer particles. Leached IIP particles were obtained by leaching the imprint ions with 6.0 M HCl. Control polymer particles were also prepared analogously without the imprint ion. The IIP particles obtained with ternary complex alone gave quantitative removal of uranyl ion in the pH range 3.5-5.0 with as low as 0.08 g. The retention capacity of uranyl IIP particles was found to be 98.50 mg/g of polymer. The present study successfully demonstrates the feasibility of removing uranyl ions selectively in the range 5 microg - 300 mg present in 500 mL of synthetic nuclear power reactor effluent containing a host of other inorganic species. PMID:16719113

Preetha, Chandrika Ravindran; Gladis, Joseph Mary; Rao, Talasila Prasada; Venkateswaran, Gopala

2006-05-01

326

Pillared and open-framework uranyl diphosphonates  

SciTech Connect

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 deg. C results in the formation of three different uranyl diphosphonate compounds, [H{sub 3}O]{sub 2}{l_brace}(UO{sub 2}){sub 6}[C{sub 6}H{sub 4}(PO{sub 3})(PO{sub 2}OH)]{sub 2}[C{sub 6}H{sub 4}(PO{sub 2}OH){sub 2}]{sub 2}[C{sub 6}H{sub 4}(PO{sub 3}){sub 2}]{r_brace}(H{sub 2}O){sub 2} (Ubbp-1), [H{sub 3}O]{sub 4}{l_brace}(UO{sub 2}){sub 4}[C{sub 6}H{sub 4}(PO{sub 3}){sub 2}]{sub 2}F{sub 4}{r_brace}.H{sub 2}O (Ubbp-2), and {l_brace}(UO{sub 2})[C{sub 6}H{sub 2}F{sub 2}(PO{sub 2}OH){sub 2}(H{sub 2}O){r_brace}{sub 2}.H{sub 2}O (Ubbp-3). The crystal structures of these compounds were determined by single crystal X-ray diffraction experiments. Ubbp-1 consists of UO{sub 7} pentagonal bipyramids that are bridged by the phosphonate moieties to form a three-dimensional pillared structure. Ubbp-2 is composed of UO{sub 5}F{sub 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 10.9x10.9 A. Ubbp-1 and Ubbp-2 fluoresce at room temperature. - Graphical Abstract: Illustration of the three-dimensional open-framework structure of {l_brace}(UO{sub 2})[C{sub 6}H{sub 2}F{sub 2}(PO{sub 2}OH){sub 2}(H{sub 2}O){r_brace}{sub 2}.H{sub 2}O viewed along the c-axis. The structure is constructed from UO{sub 7} units, pentagonal bipyramids=green, oxygen=red, phosphorus=magenta, carbon=black, hydrogen=white. Highlights: > The influence of the uranyl salt anions and pH were critically examined in relation to structural variation. > The acetate and nitrate counter ions of uranyl may be acting as structure directing agents. > The use of rigid phenyl spacer yield a three-dimensional network of pillared structures of uranyl diphosphonates that fluoresce. > The fluorination of the phenyl ring under hydrothermal condition. > The large voids in this structure are suggestive of potential applications in sorption, separation of gases and in catalytic processes.

Adelani, Pius O. [Department of Civil Engineering and Geological Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556 (United States); Albrecht-Schmitt, Thomas E., E-mail: talbrec1@nd.edu [Department of Civil Engineering and Geological Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556 (United States)

2011-09-15

327

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

PubMed

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/Chd4-nucleosome 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. PMID:23471993

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

2013-03-19

328

Ipsilateral coordination at preferred rate: Effects of age, body side and task complexity  

Microsoft Academic Search

Functional imaging studies have shown that elderly individuals activate widespread additional brain networks, compared to young subjects, when performing motor tasks. However, the parameters that effect this unique neural activation, including the spatial distribution of this activation across hemispheres, are still largely unknown. Here, we examined the effect of task complexity and body side on activation differences between older and

Annouchka Van Impe; James P. Coxon; Daniel J. Goble; Nici Wenderoth; Stephan Patrick Swinnen

2009-01-01

329

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

PubMed

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

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

2014-05-15

330

Alkane Coordination Selectivity in Hydrocarbon Activation by [TpRh(CNneopentyl)]: The Role of Alkane Complexes  

E-print Network

of Alkane Complexes Andrew J. Vetter, Christine Flaschenriem, and William D. Jones* Contribution from; Revised Manuscript Received June 20, 2005; E-mail: jones@chem.rochester.edu Abstract: The competitive. K.; McMaster, A. D.; Graham, W. A. G. J. Am. Chem. Soc. 1983, 105, 7190. (e) Jones, W. D.; Feher, F

Jones, William D.

331

NATO/PfP UNCLASSIFIED Teamwork Coordination for Realistically Complex Multi Robot Systems  

E-print Network

UAV-detected target, for example, is O(n) because demand increases linearly with the number of UAVs.edu pscerri@cs.cmu.edu ABSTRACT 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

Scerri, Paul

332

School Nurses and Care Coordination for Children with Complex Needs: An Integrative Review  

ERIC Educational Resources Information Center

Health care for students with chronic needs can be complex and specialized, resulting in fragmentation, duplication, and inefficiencies. Students who miss school due to chronic conditions lose valuable educational exposure that contributes to academic success. As health-related disabilities increase in prevalence so does the need for the

McClanahan, Rachel; Weismuller, Penny C.

2015-01-01

333

Effect of High Pressure on Uranyl Nanocages  

NASA Astrophysics Data System (ADS)

Uranyl nanocages U24Py12, U60, and U24 were studied in situ at high pressure in order to understand the response of these structures to pressure. Single crystals of the nanocage structures were analyzed by in situ Raman spectroscopy, synchrotron X-ray diffraction and small angle X-Ray scattering in diamond anvil cells, as well as electrospray ionization mass spectrometry. At ambient pressure conditions, U24Py12 is tetragonal (P42/mnm: a = 22.746(2) , c = 30.426(4) ), U60 is isometric (Fm-3: a=37.884(2) ), and U24 is triclinic (P1-: a=19.2111(11), b=31.003(2), c=32.252(2), ?=102.404(4), ?=99.506(4) , ?=95.362(4) ). Pressures ranged from ambient to 50 GPa; single crystals less than 200 microns in diameter were used. Two symmetric stretch modes of the uranyl ion are evident in the Raman spectra of all three nanocages with Raman shifts of 810 and 830 cm-1. The modes are clearly evident at pressures ranging from ambient to 4-8 GPa. At pressures higher than this range, the uranyl ion vibrational mode broadens further and shifts to higher stretching frequencies. The signal for U60 is irreversibly lost at 17 GPa, but for U24 and U24Py12, the signal persists and continues to broaden at pressures up to 50 GPa. After pressure quenching, there was still no signal from the U60, but U24 and U24Py12 both show one broad Raman mode at 840 cm-1. High pressure synchrotron X-ray diffraction measurements were completed at Argonne National Laboratory to quantify structural unit cell changes over the pressure ranges investigated. U24Py12 undergoes a phase transition to higher symmetry at approximately 5 GPa, and eventually partially amorphizes at 17 GPa, irreversibly. U60 undergoes a phase transition from isometric to tetragonal at 4.4 GPa, and amorphizes irreversibly at 10 GPa. Small angle X-ray scattering measurements show that the cluster topology is maintained even after amorphization of U24Py12 and U60. Mass spectrometry data indicate that these clusters remain intact at high pressures, despite the loss of long-range periodicity. These experiments provide insight into the stability of different types of uranyl nanocages, as well the relation between cluster topology and stability with increasing pressure.

Turner, K. M.; Zhang, F.; Pellegrini, K.; McGrail, B. T.; Burns, P. C.; Ewing, R. C.

2013-12-01

334

Uranyl heteropolyoxometalate: synthesis, structure, and spectroscopic properties.  

PubMed

A novel uranium heteropolyoxometalate, [H(3)O](4)[Ni(H(2)O)(3)](4){Ni[(UO(2))(PO(3)C(6)H(4)CO(2))](3)(PO(4)H)}(4)2.72H(2)O, has been prepared under mild hydrothermal conditions using the diethyl(2-ethoxycarbonylphenyl)phosphonate ligand and in situ ligand synthesis of the HPO(4)(2-) anion. The cluster is derived from a common UO(7), pentagonal bipyramid and is constructed by employing nickel(II) metal ions as linkers. The 3d-5f heteropolyoxometalate core incorporates 12 classical pentagonal uranyl groups and four Ni(2+) octahedral units. PMID:22519716

Adelani, Pius O; Oliver, Allen G; Albrecht-Schmitt, Thomas E

2012-05-01

335

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

336

Isolation of two different Ni2Zn complexes with an unprecedented cocrystal formed by one of them and a "coordination positional isomer" of the other.  

PubMed

A new homometallic trinuclear Ni(II) complex [(NiL)2Ni(NCS)2] (1) and three heterometallic trinuclear Ni(II)-Zn(II)-Ni(II) complexes [(NiL)2Zn(NCS)2] (2), [(NiL)2Zn(NCS)2(CH3OH)2]2CH3OH (3) and {[(NiL)2Zn(NCS)2(CH3OH)2]} {[(NiL)2Zn(NCS)2]} (4) have been synthesized by using the "complex as ligand" approach with the "metalloligand" [NiL] (H2L = N,N'-bis(salicylidene)-1,3-propanediamine) and thiocyanate in different ratios. All the complexes have been structurally and magnetically characterized. In the isomorphous complexes 1 and 2, the two terminal square planar Ni atoms and the central octahedral nickel atom (in 1) or zinc atom (in 2) are arranged in a bent structure where two cis ?N-SCN(-) thiocyanate ions are coordinated to the central atom. The chemical composition of 3 is very similar to that of 2 but, in 3, the central Zn atom is tetrahedral and the ?N-SCN(-) thiocyanate ions occupy an axial position of each terminal nickel atom (which now are octahedral with the sixth position occupied by a methanol molecule). Complex 4 consists of two closely related trinuclear units 4A and 4B. In 4A, the coordination environments of the metals are identical to those of 3 whereas 4B is a "coordination position isomer" of complex 2 with the central square pyramidal Zn and one of the terminal square pyramidal Ni atoms coordinated by two ?N-SCN(-) thiocyanate ions. Complex 4 is a unique example of a cocrystal formed by two similar trinuclear units (4A and 4B) where 4A is identical to an existing complex (3) and 4B is a "coordination position isomer" of another existing complex (2). PMID:24350719

Das, Lakshmi Kanta; Biswas, Apurba; Gmez-Garca, Carlos J; Drew, Michael G B; Ghosh, Ashutosh

2014-01-01

337

Reactivity of coordinatively unsaturated bis(N-heterocyclic carbene) Pt(II) complexes toward H(2). Crystal structure of a 14-electron Pt(II) hydride complex.  

PubMed

The reactivity toward H2 of coordinatively unsaturated Pt(II) complexes, stabilized by N-heterocyclic carbene (NHC) ligands, is herein analyzed. The cationic platinum complexes [Pt(NHC')(NHC)](+) (where NHC' stands for a cyclometalated NHC ligand) react very fast with H2 at room temperature, leading to hydrogenolysis of the Pt-CH2 bond and concomitant formation of hydride derivatives [PtH(NHC)2](+) or hydrido-dihydrogen complexes [PtH(H2)(NHC)2](+). The latter species release H2 when these compounds are subjected to vacuum. The X-ray structure of complex [PtH(IPr)2][SbF6] revealed its unsaturated nature, exhibiting a true T-shaped structure without stabilization by agostic interactions. Density functional theory calculations indicate that the binding and reaction of H2 in complexes [PtH(H2)(NHC)2](+) is more favored for derivatives bearing aryl-substituted NHCs (IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and IMes = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) than for those containing tert-butyl groups (I(t)Bu). This outcome is related to the higher close-range steric effects of the I(t)Bu ligands. Accordingly, H/D exchange reactions between hydrides [PtH(NHC)2](+) and D2 take place considerably faster for IPr and IMes* derivatives than for I(t)Bu ones. The reaction mechanisms for both H2 addition and H/D exchange processes depend on the nature of the NHC ligand, operating through oxidative addition transition states in the case of IPr and IMes* or by a ?-complex assisted-metathesis mechanism in the case of I(t)Bu. PMID:24716606

Rivada-Wheelaghan, Orestes; Rosell-Merino, Marta; Ortuo, Manuel A; Vidossich, Pietro; Gutirrez-Puebla, Enrique; Lleds, Agust; Conejero, Salvador

2014-04-21

338

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

339

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

2009-09-21

340

Magnetic observation of anion binding in iron coordination complexes: toward spin-switching chemosensors.  

PubMed

Many spin-crossover complexes exhibit high sensitivity to small environmental changes. Here, we demonstrate proof-of-concept exploitation of this property to report anion binding events in solution. Dichloromethane solutions of the cationic receptor complex [Fe(H(2)bip)(3)](BPh(4))(2) (bip = 2,2'-bi-1,4,5,6-tetrahydropyrimidine) (1) undergo subtle color changes at room temperature when interrogated by anions capable of hydrogen bonding interactions. Significantly, at -40 degrees C, these secondary binding interactions cause a change from a high- to low-spin state that is qualitatively linked to the strength of the host-guest interaction. The anion recognition property is combined with spin-state switching in a synergistic fashion and offers the possibility of using magnetometry to report host-guest interactions. PMID:19072046

Ni, Zhaoping; Shores, Matthew P

2009-01-14

341

A five-coordinate copper complex with superoxide dismutase mimetic activity from Streptomyces antibioticus.  

PubMed

A Cu(II) complex of desferrithiocin from Streptomyces antibioticus was prepared and characterized. The first shell atoms, including one nitrogen and four oxygens, were arranged around the copper in a square-planar pyramide. Due to the axially Jahn-Teller-distorted Cu-O distance at 224.7 pm, a distinct Cu2Zn2superoxide dismutase mimetic activity was measured. The Cu-complex survived 600 microM bovine serum albumin and the thermodynamic stability (pK = 17.4) was not very different from that of Cu-EDTA. The electronic absorption properties, circular dichroism and electron paramagnetism were in accordance with those of the type-II copper species. PMID:2856345

Schechinger, T; Hiller, W; Maichle, C; Strhle, J; Weser, U

1988-01-01

342

Oxidatively Stable, Aqueous Europium(II) Complexes through Steric and Electronic Manipulation of Cryptand Coordination Chemistry**  

PubMed Central

A series of cryptands have been prepared and they demonstrate the relationship between oxidative stability of aqueous EuII and ligand properties (see figure). One of these EuII complexes is more stable than FeII in hemoglobin and appears to be the most oxidatively-stable aqueous EuII species known. The high stability of EuII is expected to enable the use of the unique magnetic and optical properties of this ion in vivo. PMID:20927788

Gamage, Nipuni-Dhanesha H.; Mei, Yujiang; Garcia, Joel

2010-01-01

343

Allosteric interactions coordinate catalytic activity between successive metabolic enzymes in the tryptophan synthase bienzyme complex.  

PubMed

Tryptophan synthase from enteric bacteria is an alpha 2 beta 2 bienzyme complex that catalyzes the final two reactions in the biosynthesis of L-tryptophan (L-Trp) from 3-indole-D-glycerol 3'-phosphate (IGP) and L-serine (L-Ser). The bienzyme complex exhibits reciprocal ligand-mediated allosteric interactions between the heterologous subunits [Houben, K., & Dunn, M. F. (1990) Biochemistry 29, 2421-2429], but the relationship between allostery and catalysis had not been completely defined. We have utilized rapid-scanning stopped-flow (RSSF) UV-visible spectroscopy to study the relationship between allostery and catalysis in the alpha beta-reaction catalyzed by the bienzyme complex from Salmonella typhimurium. The pre-steady-state spectral changes that occur when L-Ser and IGP are mixed simultaneously with the alpha 2 beta 2 complex show that IGP binding to the alpha-site accelerates the formation of alpha-aminoacrylate [E(A-A)] from L-Ser at the beta-site. Through the use of L-Ser analogues, we show herein that the formation of the E(A-A) intermediate is the chemical signal which triggers the conformational transition that activates the alpha-subunit. beta-subunit ligands, such as L-Trp, that react to form covalent intermediates at the beta-site, but are incapable of E(A-A) formation, do not stimulate the activity of the alpha-subunit. Titration experiments show that the affinity of G3P and GP at the alpha-site is dependent upon the nature of the chemical intermediate present at the beta-active site.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1567839

Brzovi?, P S; Ngo, K; Dunn, M F

1992-04-21

344

Coordinated aqua vs methanol substitution kinetics in fac-Re(I) tricarbonyl tropolonato complexes.  

PubMed

Water-soluble fac-[Re(CO)(3)(L,L'-Bid)(X)] (L,L'-Bid = tropolonato, X = H(2)O, methanol) complexes have been synthesized, and the aqua and methanol substitution reactions were investigated in water (pH range 6.3-10.0) and methanol, respectively, and compared. Thiocyanate ions were used as monodentate entering ligand. The complexes were characterized by UV-vis, IR, and NMR spectroscopy. The crystal structures of the complexes [NEt(4)] fac-[Re(Trop)(CO)(3)(H(2)O)].NO(3).H(2)O (reactant) and fac-[Re(CO)(3)(Trop)(Py)], a substitution product, are reported. Overall it was found that the aqua substitution of fac-[Re(CO)(3)(Trop)(H(2)O)] is about 10 times faster than the methanol substitution reaction for fac-[Re(CO)(3)(Trop)(MeOH)], with forward and reverse rate and stability constants [k(1) (M(-1) s(-1)), k(-1) (s(-1)), K(1), (M(-1))] for thiocyanate as monodentate entering ligand as follows: fac-[Re(CO)(3)(Trop)(H(2)O)] = 2.54 0.03, 0.0077 0.0005, 330 22/207 14 and fac-[Re(CO)(3)(Trop)(MeOH)] = 0.268 0.002, 0.0044 0.0002, (61 3)/(52 4). The activation parameters [?H()(k1) (kJ mol(-1)), ?S()(k1) (J K(-1) mol(-1))] for the aqua and methanol complex respectively are 56.1 0.7, -49 2 and 64 1, -43 5. PMID:23088314

Schutte, Marietjie; Roodt, Andreas; Visser, Hendrik G

2012-11-01

345

Liquid-liquid extraction of uranyl by an amide ligand: interfacial features studied by MD and PMF simulations.  

PubMed

We report a molecular dynamics study of biphasic systems involved in the liquid-liquid extraction of uranyl nitrate by a monoamide ligand (L = N,N-di(2-ethylhexyl)isobutyramide, DEHiBA) to hexane, from pH neutral or acidic (3 M nitric acid) aqueous solutions. We first describe the neat interfaces simulated with three electrostatic models, one of which including atomic polarizabilities. The free energy profiles for crossing the water/hexane interface by L or its UO2(NO3)2L2 complex are then investigated by PMF (potential of mean force) calculations. They indicate that the free ligand and its complex are surface active. With the polarizable force field, however, the complexes have a lower affinity for the interface than without polarization. When DEHiBA gets more concentrated and in acidic conditions, their surface activity diminishes. Surface activity of UO2(NO3)2L2 complexes is further demonstrated by demixing simulations of randomly mixed DEHiBA, hexane, and neutral or acidic water. Furthermore, demixing of randomly mixed solvents, L molecules, UO2(NO3)2 salts, and nitric acid shows in some cases complexation of L to form UO2(NO3)2L2 and UO2(NO3)2L complexes that adsorb at the aqueous interfaces. These features suggest that uranyl complexation by amide ligands occurs "right at the interface", displaying marked analogies with the liquid-liquid extraction of uranyl by TBP (tri-n-butyl phosphate). Regarding the positive effect of nitric acid on extraction, the simulations point to several facets involving enhanced ion pairing of uranyl nitrate, decreased affinity of the complex for the interface, and finally, stabilization of the complex in the organic phase. PMID:23746355

Benay, G; Wipff, G

2013-06-20

346

Iron Complexes for the Electrocatalytic Oxidation of Hydrogen: Tuning Primary and Secondary Coordination Spheres  

SciTech Connect

A series of iron hydride complexes featuring PRNR'PR (PRNR'PR = R2PCH2N(R')CH2PR2 where R = Ph, R' = Me; R = Et, R' = Ph, Bn, Me, tBu) and cyclopentadienyl (CpX = C5H4X where X = H, C5F4N) ligands has been synthesized, characterized by NMR spectroscopy, X-ray diffraction and cyclic voltammetry, and examined by quantum chemistry calculations. Each compound was tested for the electrocatalytic oxidation of H2 and the most active complex, (CpC5F4N)Fe(PEtNMePEt)(H), exhibited a turnover frequency of 8.6 s-1 at 1 atm of H2 with an overpotential of 0.41 V, as measured from the half peak potential of the catalytic wave. Control complexes that do not contain pendant amine groups were also prepared and characterized, but no catalysis was observed. This work demonstrates the importance of the pendant amine in facilitating heterolytic H2 cleavage and subsequent proton movement necessary for electrocatalytic H2 oxidation. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Darmon, Jonathan M.; Raugei, Simone; Liu, Tianbiao L.; Hulley, Elliott B.; Weiss, Charles J.; Bullock, R. Morris; Helm, Monte L.

2014-04-04

347

Donor-acceptor ligand-to-ligand charge-transfer coordination complexes of nickel(II).  

PubMed

A family of charge-transfer chromophores comprising square-planar nickel(II) complexes with one catecholate donor ligand and one ?-diimine acceptor ligand is reported. The nine new chromophores were prepared using three different catecholate ligands and three different ?-diimine ligands. Single-crystal X-ray diffraction studies on all members of the series confirm a catecholate donor-nickel(II)-?-diimine acceptor electronic structure. The coplanar arrangement of donor and acceptor ligands manifests an intense ligand-to-ligand charge-transfer (LL'CT) absorption band that can be tuned incrementally from 650 nm (1.9 eV) to 1370 nm (0.9 eV). Electrochemical studies of all nine complexes reveal rich redox chemistry with two one-electron reduction processes and two one-electron oxidation processes. For one dye, both the singly reduced anion and the singly oxidized cation were prepared, isolated, and characterized by EPR spectroscopy to confirm ligand-localization of the redox processes. The optical and electrochemical properties of these new complexes identify them as attractive candidates for charge-transfer photochemistry and solar-energy conversion applications. PMID:25100175

Kramer, Wesley W; Cameron, Lindsay A; Zarkesh, Ryan A; Ziller, Joseph W; Heyduk, Alan F

2014-08-18

348

A new arene-Ru based supramolecular coordination complex for efficient binding and selective sensing of green fluorescent protein.  

PubMed

A new dipyridyl ligand is encoded with 120 angularity between its coordination vectors by using a central pyridine carboxamide scaffold to orient two 4-(pyridin-4-ylethynyl)phenyl moieties. The N,N'-bis(4-(pyridin-4-ylethynyl)phenyl)pyridine-2,6-dicarboxamide ligand undergoes self-assembly with a diruthenium arene complex to furnish a [2 + 2] metallacycle with a wedge-like structure. The metallacycle binds to the enhanced green fluorescent protein (EGFP) variant of GFP, resulting in steady-state spectral changes in UV-Vis absorption and emission experiments. These studies indicate that the metallacycle induces conformation changes to the EGFP, disrupting the tripeptide chromophore. Furthermore, gel electrophoresis, circular dichroism and atomic force microscopy studies indicate that binding ultimately leads to aggregation of the protein. Computational investigations indicate a favorable interaction, predominantly between the metallacycle and the Arg168 residue of the EGFP. An interaction with Arg168 and related residues was previously observed for an emission-attenuating antibody, supporting that these interactions induce changes to the photophysical properties of EGFP by disrupting the tripeptidechromophore in a similar manner. Additionally, we have also described the quenching study of the reporter GFP protein in vivo by a new metal complex using reflected fluorescence microscopy. We anticipate that such metal complexes which can passively diffuse into the cells in vivo can serve as potential tools in molecular and drug targeting based biological studies. PMID:24390643

Mishra, Anurag; Ravikumar, Sambandam; Song, Young Ho; Prabhu, Nadarajan Saravanan; Kim, Hyunuk; Hong, Soon Ho; Cheon, Seyeon; Noh, Jaegeun; Chi, Ki-Whan

2014-04-28

349

Spectrophotometric Studies of the Synergistic System Uranyl Ion-Di2- Ethylhexyl Phosphoric Acid-Tri-n-Octylphosphine Oxide; SPEKTROPHOTOMETRISCHE UNTERSUCHUNGEN ZUM SYNERGISTISCHEN SYSTEM URANYL-ION\\/Di2-ATHYLHEXYLPHOSPHORSAURE\\/Tri-N-OKTYLPHOSPHINOXYD  

Microsoft Academic Search

For the system uranyl-ion--tri(n-octyl)phosphine oxide (TOPO) -excess di ; (2-ethylhexyi)phosphoric acid (D2EHPA) in kerosene the ratio U: TOPO of the ; complex formed was investigated spectrophotometrically using the method of ; continuous variations. In solutions 0.1M in D2EHPA and 10⁻2 to 10⁻³M ; in hexavalent uranium and TOPO, a complex with the molar ratio U: TOPO = 1: 1 was

H. Ihle; H. Michael; A. Murrenhoff

1962-01-01

350

Investigations of iron coordination and redox reactions in seawater using 59Fe radiometry and ion-pair solvent extraction of amphiphilic iron complexes  

Microsoft Academic Search

Hudson, R.J.M., Covault, D.T. and Morel, F.M.M., 1992. Investigations of iron coordination and redox reactions in seawater using 59Fe radiometry and ion-pair solvent extraction of amphiphilic iron complexes. Mar. Chem., 38: 209-235. Iron coordination and redox reactions in synthetic and coastal seawater were investigated at na- nomolar concentrations using 59Fe radiometry and ion-pair solvent extraction of iron chelated by sulfoxine

Robert J. M. Hudson; Dianne T. Covault; Francois M. M. Morel

1992-01-01

351

Electronic structure and slow magnetic relaxation of low-coordinate cyclic alkyl(amino) carbene stabilized iron(I) complexes.  

PubMed

Cyclic alkyl(amino) carbene stabilized two- and three-coordinate Fe(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe][B(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet of analytical techniques as well as theoretical calculations. Magnetic susceptibility and Mssbauer spectroscopy reveal the +1 oxidation state and S = 3/2 spin ground state of iron in both compounds. 2 and 3 show slow magnetic relaxation typical for single molecule magnets under an applied direct current magnetic field. The high-frequency EPR measurements confirm the S = 3/2 ground state with a large, positive zero-field splitting (?20.4 cm(-1)) and reveal easy plane anisotropy for compound 2. CASSCF/CASPT2/RASSI-SO ab initio calculations using the MOLCAS program package support the experimental results. PMID:25072104

Samuel, Prinson P; Mondal, Kartik Chandra; Amin Sk, Nurul; Roesky, Herbert W; Carl, Elena; Neufeld, Roman; Stalke, Dietmar; Demeshko, Serhiy; Meyer, Franc; Ungur, Liviu; Chibotaru, Liviu F; Christian, Jonathan; Ramachandran, Vasanth; van Tol, Johan; Dalal, Naresh S

2014-08-27

352

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

PubMed Central

SUMMARY Background Epithelial remodeling, in which apical-basal polarized cells switch to a migratory phenotype, plays a central role in development and disease of multicellular organisms. Although dynamic microtubules (MTs) are required for directed migration on flat surfaces, how MT dynamics are controlled or contribute to epithelial remodeling in a more physiological three-dimensional (3D) environment is not understood. We use confocal live cell imaging to analyze MT function and dynamics during 3D epithelial morphogenesis and remodeling of polarized Madin-Darby canine kidney (MDCK) epithelial cells that undergo partial epithelial-to-mesenchymal transition (EMT) in response to hepatocyte growth factor (HGF). Results We find that HGF treatment increases MT growth rate before morphological changes are evident, and that large numbers of MTs grow into HGF-induced cell extensions independent of centrosome reorientation. Using lentivirus-mediated shRNA, we demonstrate that EB1, an adaptor protein that mediates recruitment of numerous other +TIP proteins to growing MT plus ends, is required for this HGF-induced MT reorganization. We further show that protrusion and adhesion dynamics are disorganized, and that vesicular trafficking to the tip of HGF-induced cell extensions is disrupted in EB1-depleted cells. Conclusions We conclude that EB1-mediated interactions with growing MTs are important to coordinate cell shape changes and directed migration into the surrounding extracellular matrix during epithelial remodeling in a physiological 3D environment. In contrast, EB1 is not required for the establishment or maintenance of apical-basal cell polarity, suggesting different functions of +TIPs and MTs in different types of cell polarity. PMID:22483942

Gierke, Sarah; Wittmann, Torsten

2012-01-01

353

Electron and Hydrogen-Atom Self-Exchange Reactions of Iron and Cobalt Coordination Complexes  

E-print Network

and between cobalt 2,2-biimidazoline (H2bim) complexes. The 1 H NMR resonances of [FeII (H2- bip)3 of [Co(H2bim)3]2+ -d24 with [Co(H2bim)3]3+ or [Co(Hbim)(H2bim)2]2+ occur with scrambling of ligands [Co(H2bim)3]2+ and [Co(H2bim)3]3+ is estimated to be 10-6 M-1 s-1 by application of the Marcus cross

Roth, Justine P.

354

Cobalt Complexes Containing Pendant Amines in the Second Coordination Sphere as Electrocatalysts for H2 Production  

SciTech Connect

A series of heteroleptic 17e- cobalt complexes, [CpCoII(PtBu2NPh2)](BF4), [CpC6F5CoII(PtBu2NPh2)](BF4), [CpC5F4NCoII(PtBu2NPh2)](BF4), [where P2tBuN2Ph = 1,5-diphenyl-3,7-di(tert-butyl)-1,5-diaza-3,7-diphosphacyclooctane, CpC6F5 = C5H4(C6F5), and CpC5F4N = C5H4(C5F4N)] were synthesized, and structures of all three were determined by X-ray crystallography. Electrochemical studies showed that the CoIII/II couple of [CpC5F4NCoII(PtBu2NPh2)]+ appears 250 mV positive of the CoIII/II couple of [CpCoII(PtBu2NPh2)] as a result of the strongly electron-withdrawing perfluorpyridyl substituent on the Cp ring. Reduction of these paramagnetic CoII complexes by KC8 led to the diamagnetic 18e- complexes CpICo(PtBu2NPh2), CpC6F5CoI(PtBu2NPh2), CpC5F4NCoI(PtBu2NPh2), which were also characterized by crystallography. Protonation of these neutral CoI complexes led to the cobalt hydrides [CpCoIII(PtBu2NPh2)H](BF4), [CpC6F5CoIII(PtBu2NPh2)H](BF4), and [CpC5F4NCoIII(PtBu2NPh2)H](BF4). The cobalt hydride with the most electron-withdrawing Cp ligand, [CpC5F4NCoIII(PtBu2NPh2)H]+ is an electrocatalyst for production of H2 using 4-MeOC6H4NH3BF4 (pKaMeCN = 11.86) with a turnover frequency of 350 s-1 and an overpotential of 0.75 V. Experimental measurement of thermochemical data provided further insights into the thermodynamics of H2 elimination. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Fang, Ming; Wiedner, Eric S.; Dougherty, William G.; Kassel, W. S.; Liu, Tianbiao L.; DuBois, Daniel L.; Bullock, R. Morris

2014-10-27

355

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

SciTech Connect

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

Ling, Jie; Ward, Matthew [Department of Civil Engineering and Geological Science, University of Notre Dame, Notre Dame, IN 46556 (United States); Burns, Peter C., E-mail: pburns@nd.ed [Department of Civil Engineering and Geological Science, University of Notre Dame, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556 (United States)

2011-02-15

356

Determination of uranyl incorporation into biogenic manganese oxides using X-ray absorption spectroscopy and scattering  

USGS Publications Warehouse

Biogenic manganese oxides are common and an important source of reactive mineral surfaces in the environment that may be potentially enhanced in bioremediation cases to improve natural attenuation. Experiments were performed in which the uranyl ion, UO22+ (U(VI)), at various concentrations was present during manganese oxide biogenesis. At all concentrations, there was strong uptake of U onto the oxides. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) studies were carried out to determine the molecular-scale mechanism by which uranyl is incorporated into the oxide and how this incorporation affects the resulting manganese oxide structure and mineralogy. The EXAFS experiments show that at low concentrations (2 mol % U, >4 ??M U(VI) in solution), the presence of U(VI) affects the stability and structure of the Mn oxide to form poorly ordered Mn oxide tunnel structures, similar to todorokite. EXAFS modeling shows that uranyl is present in these oxides predominantly in the tunnels of the Mn oxide structure in a tridentate complex. Observations by XRD corroborate these results. Structural incorporation may lead to more stable U(VI) sequestration that may be suitable for remediation uses. These observations, combined with the very high uptake capacity of the Mn oxides, imply that Mn-oxidizing bacteria may significantly influence dissolved U(VI) concentrations in impacted waters via sorption and incorporation into Mn oxide biominerals. ?? 2006 American Chemical Society.

Webb, S.M.; Fuller, C.C.; Tebo, B.M.; Bargar, J.R.

2006-01-01

357

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

358

Ab initio study of intriguing coordination complexes: a metal field theory picture.  

PubMed

Two noninnocent ligands are theoretically studied using wave function based methods to demonstrate their ability to undergo singlet-triplet transition under the effect of an external charge mimicking the electrostatic role of a metal ion. It is shown that the singlet-triplet energy difference is very sensitive to the metal ion charge which tunes the HOMO-LUMO energy difference of these ligands. While the latter is reduced as the charge is enhanced in the glyoxal-bis-(2-mercaptoanil) (gma) ligand, it is increased in the bis(imino)pyridine diradical ligand. This result shows a strong analogy with the crystal field theory, interchanging the roles played by the metal ion and the ligand. As the metal ion is explicitly treated in the Fe(gma)CN complex, this analogy can be pushed further resulting in a "metal field theory" conceptualization. PMID:18811129

Guihry, Nathalie; Robert, Vincent; Neese, Frank

2008-12-18

359

Influence of the ?-coordinated arene on the anticancer activity of ruthenium(II) carbohydrate organometallic complexes  

PubMed Central

The synthesis and in vitro cytotoxicity of a series of RuII(arene) complexes with carbohydrate-derived phosphite ligands and various arene co-ligands is described. The arene ligand has a strong influence on the in vitro anticancer activity of this series of compounds, which correlates fairly well with cellular accumulation. The most lipophilic compound bearing a biphenyl moiety and a cyclohexylidene-protected carbohydrate is the most cytotoxic with unprecedented IC50 values for the compound class in three human cancer cell lines. This compound shows reactivity to the DNA model nucleobase 9-ethylguanine, but does not alter the secondary structure of plasmid DNA, indicating that other biological targets are responsible for its cytotoxic effect. PMID:24790955

Hanif, Muhammad; Meier, Samuel M.; Nazarov, Alexey A.; Risse, Julie; Legin, Anton; Casini, Angela; Jakupec, Michael A.; Keppler, Bernhard K.; Hartinger, Christian G.

2013-01-01

360

MicroRNA-128 coordinately targets Polycomb Repressor Complexes in glioma stem cells  

PubMed Central

Background The Polycomb Repressor Complex (PRC) is an epigenetic regulator of transcription whose action is mediated by 2 protein complexes, PRC1 and PRC2. PRC is oncogenic in glioblastoma, where it is involved in cancer stem cell maintenance and radioresistance. Methods We used a set of glioblastoma patient samples, glioma stem cells, and neural stem cells from a mouse model of glioblastoma. We characterized gene/protein expression and cellular phenotypes by quantitative PCR/Western blotting and clonogenic, cell-cycle, and DNA damage assays. We performed overexpression/knockdown studies by lentiviral infection and microRNA/small interfering RNA oligonucleotide transfection. Results We show that microRNA-128 (miR-128) directly targets mRNA of SUZ12, a key component of PRC2, in addition to BMI1, a component of PRC1 that we previously showed as a target as well. This blocks the partially redundant functions of PRC1/PRC2, thereby significantly reducing PRC activity and its associated histone modifications. MiR-128 and SUZ12/BMI1 show opposite expression in human glioblastomas versus normal brain and in glioma stemlike versus neural stem cells. Furthermore, miR-128 renders glioma stemlike cells less radioresistant by preventing the radiation-induced expression of both PRC components. Finally, miR-128 expression is significantly reduced in neural stem cells from the brain of young, presymptomatic mice in our mouse model of glioblastoma. This suggests that loss of miR-128 expression in brain is an early event in gliomagenesis. Moreover, knockdown of miR-128 expression in nonmalignant mouse and human neural stem cells led to elevated expression of PRC components and increased clonogenicity. Conclusions MiR-128 is an important suppressor of PRC activity, and its absence is an early event in gliomagenesis. PMID:23733246

Peruzzi, Pierpaolo; Bronisz, Agnieszka; Nowicki, Michal O.; Wang, Yan; Ogawa, Daisuke; Price, Richard; Nakano, Ichiro; Kwon, Chang-Hyuk; Hayes, Josie; Lawler, Sean E.; Ostrowski, Michael C.; Chiocca, E. Antonio; Godlewski, Jakub

2013-01-01

361

Incorporation of neptunium(VI) into a uranyl selenite.  

PubMed

The incorporation of neptunium(VI) into the layered uranyl selenite Cs[(UO(2))(HSeO(3))(SeO(3))] has yielded the highest level of neptunium uptake in a uranyl compound to date with an average of 12(3)% substitution of Np(VI) for U(VI). Furthermore, this is the first case in nearly 2 decades of dedicated incorporation studies in which the oxidation state of neptunium has been determined spectroscopically in a doped uranyl compound and also the first time in which neptunium incorporation has resulted in a structural transformation. PMID:23030830

Meredith, Nathan A; Polinski, Matthew J; Lin, Jian; Simonetti, Antonio; Albrecht-Schmitt, Thomas E

2012-10-15

362

Coordination effects on electron distributions for rhodium complexes of the redox-active bis(3,5-di-tert-butyl-2-phenolate)amide ligand.  

PubMed

New rhodium complexes of bis(3,5-di-tert-butyl-2-phenol)amine ([ONO(cat)]H(3)) were synthesized, and their electronic properties were investigated. These compounds were prepared by combining [ONO(q)]K and [(cod)Rh(?-Cl)](2) in the presence of an auxiliary donor ligand to yield complexes of the type [ONO]RhL(n) (n = 3, L = py (1); n = 2, L = PMe(3) (2a), L = PMe(2)Ph (2b), PMePh(2) (2c), PPh(3) (2d)). Single-crystal X-ray diffraction studies on [ONO]Rh(py)(3) (1) revealed a six-coordinate, octahedral rhodium complex. In the case of [ONO]Rh(PMe(3))(2) (2a), X-ray diffraction showed a five-coordinate, distorted square-pyramidal coordination environment around the rhodium center. While 1 is static on the NMR time scale, complexes 2a-d are fluxional, displaying both rapid isomerization of the square-pyramidal structure and exchange of coordinated and free phosphine ligands. UV-vis spectroscopy shows stark electronic differences between 1 and 2a-d. Whereas 1 displays a strong absorbance at 380 nm with a much weaker band at 585 nm in the absorption spectrum, complexes 2a-d display an intense (? > 10(4) M(-1) cm(-1)), low-energy absorption band in the region 580-640 nm; however, in the cases of 2a and 2b, the addition of excess phosphine resulted in changes to the UV-vis spectrum indicating the formation of six-coordinate adducts [ONO]Rh(PMe(3))(3) (3a) and [ONO]Rh(PMe(2)Ph)(3) (3b), respectively. The experimental and DFT computational data for the six-coordinate complexes 1, 3a, and 3b are consistent with their formulation as classical, d(6), pseudo-octahedral, coordination complexes. In the five-coordinate complexes 2a-2d, ?-bonding between the rhodium center and the [ONO] ligand leads to a high degree of covalency and metal-ligand electron distributions that are not accurately described by formal oxidation state assignments. PMID:22482509

Szigethy, Gza; Shaffer, David W; Heyduk, Alan F

2012-12-01

363

Solvation of uranyl(II), europium(III) and europium(II) cations in "basic" room-temperature ionic liquids: a theoretical study.  

PubMed

We report a molecular dynamics study of the solvation of UO2(2+), Eu3+ and Eu2+ ions in two "basic" (Lewis acidity) room-temperature ionic liquids (IL) composed of the 1-ethyl-3-methylimidazolium cation (EMI+) and a mixture of AlCl4- and Cl- anions, in which the Cl-/AlCl4- ratio is about 1 and 3, respectively. The study reveals the importance of the [UO2Cl4]2- species, which spontaneously form during most simulations, and that the first solvation shell of europium is filled with Cl- and AlCl4- ions embedded in a cationic EMI+ shell. The stability of the [UO2Cl4]2- and [Eu(III)Cl6]3- complexes is supported by quantum mechanical calculations, according to which the uranyl and europium cations intrinsically prefer Cl- to the AlCl4- ion. In the gas phase, however, [Eu(III)Cl6]3- and [Eu(II)Cl6]4- complexes are predicted to be metastable and to lose two to three Cl- ions. This contrasts with the results of simulations of complexes in ILs, in which the "solvation" of the europium complexes increases with the number of coordinated chlorides, leading to an equilibrium between different chloro species. The behavior of the hydrated [Eu(OH2)8]3+ complex is considered in the basic liquids; the complex exchanges H2O molecules with Cl- ions to form mixed [EuCl3(OH2)4] and [EuCl4(OH2)3]- complexes. The results of the simulations allow us to better understand the microscopic nature and solvation of lanthanide and actinide complexes in "basic" ionic liquids. PMID:15317055

Chaumont, Alain; Wipff, Georges

2004-08-20

364

Assessment of accidental intakes of uranyl acetylacetonate (UAA)  

SciTech Connect

Uranyl acetylacetonate (UAA) is an organic complex of uranium used for military applications as a chemical catalyst in high explosives. It is prepared from depleted uranium metal (in lots of 5 kg to 7 kg) by dissolution in nitric acid, neutralization, and complexation with 2,4-pentanedione; the precipitate is dissolved in benzene and recrystallized, dried, ground, and packaged. About six workers at a small chemical company were exposed over a period of time to UAA powders during routine preparation and packaging of the uranium catalyst. The dissolution characteristics of the inhaled material were unknown and could not be determined from the published scientific literature. A 1.05-g sample of UAA powder was obtained from the responsible regulatory authority for further study to determine its chemical composition, and for dissolution in simulated lung fluid. We found the solubility of UAA to be equivalent to a mixture of 52% ICRP class D and 48% ICRP class W material. The annual limit on intake and the derived air concentration for radiological protection were estimated from this result for airborne exposure to UAA. A recycling biokinetic model was used to estimate both material-specific variations in urinary excretion rates and lung retention with time after accidental intakes. This study provides new information for evaluating future exposures to UAA.

Fisher, D.R.; Briant, J.K.

1993-12-01

365

Volatile adducts of uranyl nitrate. Sublimation and mass spectra  

SciTech Connect

Adducts of uranyl nitrate with strong neutral ligands: trimethyl phosphate (TMP), triethyl phosphate (TEP), trimethylphosphine oxide (TMPO), hexamethylphosphoric triamide (HMPTA), with a 1:2 composition, and phenanthroline (phen) (with a 1:1 composition), and also a complex with a composition of UO/sub 2/(NO/sub 3/) (NCS) x 2HMPTA were synthesized. The above enumerated compounds sublime in vacuo (adducts with TMP and TEP in a vapor current of the corresponding trialkyl phosphate) with a partial decomposition at temperatures of 160-280/sup 0/C. A mass-spectrometric examination of the complexes synthesized has been carried out. It was shown that after splitting off of the ligand, the fragmentation of the adducts with TMPO and phen proceeds by the path consisting in splitting off of the NO/sub 2/ group, while in the case of an adduct with TEP, a rearrangement takes places with the elimination of C/sub 2/H/sub 5/NO/sub 3/. The last path is similar to the processes proceeding during the thermal decomposition of UO/sub 2/(NO/sub 3/)/sub 2/ x 2TBP.

Adamov, V.M.; Belyaev, B.N.; Sidorenko, G.V.; Suglobov, D.N.

1988-03-01

366

Yttrium and lanthanide complexes of ?-dialdehydes: synthesis, characterization, luminescence and electrochemistry of coordination compounds with the conjugate base of bromomalonaldehyde.  

PubMed

Novel yttrium, europium and terbium coordination compounds having formulae [AsPh4][Ln(BrMA)4] (6LN), Ln(BrMA)3(bipyO2) (7Ln), Ln(NMA)3(phen) (8Ln) and Ln(NMA)3(terpy) (9Ln) (Ln = Y, Eu, Tb; BrMA = conjugate base of bromomalonaldehyde; bipyO2 = 2,2'-bipyridine-N,N'-dioxide; phen = 1,10-phenantroline; terpy = 2,2':6',2''-terpyridine) were synthesized and characterized by using spectroscopic and electrochemical techniques. Uncharged europium and, to a lesser extent, terbium complexes showed appreciable luminescence in the solid state upon excitation with UV light. Polymeric materials and ionic liquids containing BrMA and lanthanides were prepared and photoluminescence measurements were carried out. From an electrochemical point of view, europium(III) BrMA-complexes showed a quasi-reversible one-electron reduction process. The one electron transfer reaction Eu(III) to Eu(II) allowed the photoluminescence tuning of 8Eu deposited on the surface of a glassy carbon electrode. PMID:24819039

Bortoluzzi, Marco; Battistel, Dario; Roppa, Stefania; Daniele, Salvatore; Perosa, Alvise; Enrichi, Francesco

2014-06-28

367

Basolateral membrane expression of the Kir 2.3 channel is coordinated by PDZ interaction with Lin-7/CASK complex.  

PubMed

The basolateral membrane sorting determinant of an inwardly rectifying potassium channel, Kir 2.3, is comprised of a unique arrangement of trafficking motifs containing tandem, conceivably overlapping, biosynthetic targeting and PDZ-based signals. In the present study, we elucidate a mechanism by which a PDZ interaction coordinates one step in a basolateral membrane sorting program. In contrast to apical missorting of channels lacking the entire sorting domain, deletion of the PDZ binding motif caused channels to accumulate into an endosomal compartment. Here, we identify a new human ortholog of a Caenorhabditis elegans PDZ protein, hLin-7b, that interacts with the COOH-terminal tail of Kir 2.3 in renal epithelia. hLin-7b associates with the channel as a part of a multimeric complex on the basolateral membrane similar to a basolateral membrane complex in C. elegans vulva progenitor cells. Coexpression of hLin-7b with Kir 2.3 dramatically increases channel activity by stabilizing plasma membrane expression. The discovery identifies one component of the sorting machinery and provides evidence for a retention mechanism in a hierarchical basolateral trafficking program. PMID:11742811

Olsen, Olav; Liu, Hui; Wade, James B; Merot, Jean; Welling, Paul A

2002-01-01

368

Thermodynamic properties of autunite, uranyl hydrogen phosphate, and uranyl orthophosphate from solubility and calorimetric measurements  

SciTech Connect

In this study, we use solubility and oxide melt solution calorimetry measurements to determine the thermodynamic properties of the uranyl phosphate phases autunite (abbreviated: CaUP), uranyl hydrogen phosphate (HUP), and uranyl orthophosphate (UP). Solubility measurements from both supersaturated and undersaturated conditions, as well as under different pH conditions, rigorously demonstrate attainment of equilibrium and yield well-constrained solubility product values of -48.36 (-0.03 /+ 0.03), -13.17 (-0.11 / +0.07), and -49.36 (-0.04 / +0.02) for CaUP, HUP, and UP, respectively. We use the solubility data to calculate standard state Gibbs free energies of formation for all phases (-7630.61 9.69, -3072.27 4.76, and -6138.95 12.24 kJ mol-1 for CaUP, HUP, and UP, respectively), and calorimetry data to calculate standard state enthalpies of formation of -3223.22 4.00 and -7001.01 15.10 kJ mol-1 for HUP and UP, respectively. Combining these results allows us also to calculate the standard state entropies of formation of -506.54 10.48 and -2893.12 19.44 kJ mol-1 K-1 for HUP and UP phases, respectively. The results from this study are part of a combined effort to develop reliable and internally consistent thermodynamic data for environmentally relevant uranyl minerals. Data such as these are required in order to optimize and quantitatively assess the effect of phosphate amendment remediation technologies for uranium contaminated systems.

Gorman-Lewis, Drew; Shareva, Tatiana; kubatko, Karrie-Ann; burns, Peter; Wellman, Dawn M.; McNamara, Bruce K.; szymanowski, jennifer; Navrotsky, Alexandra; Fein, Jeremy B.

2009-10-01

369

Time-resolved self-assembly of a fullerene-topology core-shell cluster containing 68 uranyl polyhedra.  

PubMed

A complex core-shell cluster consisting of 68 uranyl peroxo polyhedra, 16 nitrate groups, and ~44 K(+) and Na(+) cations was obtained by self-assembly in alkaline aqueous solution under ambient conditions. Crystals formed after a month and were characterized. The cluster, designated as {U(1)?U(28)?U(40R)}, contains a fullerene-topology cage built from 28 uranyl polyhedra. A ring consisting of 40 uranyl polyhedra linked into five-membered rings and 16 nitrate groups surrounds this cage cluster. Topological pentagons in the cage and ring are aligned, and their corresponding rings of uranyl bipyramids are linked through K(+) cations located between the two shells. A partially occupied U site is located at the center of the cluster. Time-resolved small-angle X-ray scattering and electrospray ionization mass spectrometry demonstrated that the U(28) cage cluster formed in solution within an hour, whereas the U(40R) shell formed around the cage cluster after more than several days. PMID:22191457

Qiu, Jie; Ling, Jie; Sui, Audrey; Szymanowski, Jennifer E S; Simonetti, Antonio; Burns, Peter C

2012-01-25

370

Association of uranyl with the cell wall of Pseudomonas fluorescens inhibits metabolism  

NASA Astrophysics Data System (ADS)

Citric acid is found along with uranyl in the subsurface of former nuclear facilities because of its use as a decontamination agent in the nuclear industry. Citrate's metal chelating properties affect the mobility of uranyl in the subsurface and consequently, citrate biodegradation may significantly impact uranyl fate and transport. Under the non-growth conditions considered, low (micromolar) uranyl concentrations inhibit the biodegradation of citrate by Pseudomonas fluorescens, a common subsurface denitrifying bacterium. Additionally, uranyl is found readily associated with the cell envelope of P. fluorescens. The observed inhibition appears to be linked to the binding of uranyl to the cell surface and is reversible by desorbing cell-bound uranyl. This study establishes a link between uranyl association with the cell surface and the observed inhibitory effect of uranyl on cell metabolism.

Bencheikh-Latmani, Rizlan; Leckie, James O.

2003-11-01

371

Uranyl phthalocyanines show promise in the treatment of brain tumors  

NASA Technical Reports Server (NTRS)

Processes synthesize sulfonated and nonsulfonated uranyl phthalocyanines for application in neutron therapy of brain tumors. Tests indicate that the compounds are advantageous over the previously used boron and lithium compounds.

Frigerio, N. A.

1967-01-01

372

Molecular dynamics simulations of the structure and thermodynamics of carrier-assisted uranyl ion extraction.  

PubMed

We present molecular dynamics simulations of interfaces relevant to the selective chemical extraction of uranyl ions from aqueous solution. These molecular-level simulations model ion transfer in the PUREX process and in synthetic, selective membranes. We first present simulations of water/oil interfaces modified by incorporation of tributyl phosphate (TBP) into the oil phase (hexane). A range of concentrations is examined, from a single TBP molecule to values close to those utilized in the PUREX process. The TBP molecules exhibit strong interfacial activity, and the interface broadens relative to the water/oil case with increasing TBP concentrations. Additional structural features, including radial distribution functions and orientational distributions, are examined to elucidate the molecular ordering at the interface; the interface structure changes substantially with increasing TBP concentration. Finally, free-energy profiles are computed for (1) a single TBP molecule and a single uranyl nitrate complex [UO2(NO3)2] across the water/oil interface and (2) a UO2(NO3)2.TBP2 complex across both water/oil and water/(oil+TBP) interfaces. The UO2(NO3)2 complex is strongly repelled from the water/oil interface, while the UO2(NO3)2.TBP2 complex exhibits interfacial activity that decreases with increasing TBP concentration. The UO2(NO3)2.TBP2 complex displays a net free-energy driving force for partitioning into the oil phase that increases with increasing TBP concentration. PMID:19845396

Jayasinghe, Manori; Beck, Thomas L

2009-08-27

373

Raman studies of uranyl nitrate and its hydroxy bridged dimer  

NASA Astrophysics Data System (ADS)

In this paper, the authors report Raman spectra obtained on imidazolium di-?-hydroxybis[dioxobis-(nitrato)uranium(VI)], (UO 2(NO 3) 2(OH)) 2.2C 3H 5N 2 (IUNH). An assignment of the Raman bands is made by comparing the spectrum of IUNH with those of uranyl nitrate hexahydrate (UNH) and imidazole (IMID). The electron charge transfer from the imidazole ring to the uranyl ion has been empirically determined.

Faulques, Eric; Russo, Richard E.; Perry, Dale L.

374

Roentgenoluminescence of hexahydrate of uranyl nitrate in phosphoric acid solution  

NASA Astrophysics Data System (ADS)

The fluorescence (FL) and roentgenoluminescence (XRL) spectra of yellow aqueous solution of hexahydrate of uranyl nitrate phosphoric acid solution have been measured. The XRL spectrum was compared with the XRL of the green alkali alumino-phosphate glasses doped with uranium. It was shown that both the FL and XRL were due to uranyl groups. The radiative transitions are ascribed to3?1u ?1?{g/+}.

Ovoldov, M.

1992-08-01

375

Chronic Uremia Syndrome in Dogs Induced with Uranyl Nitrate  

Microsoft Academic Search

11 adult female dogs were given periodic intravenous injections of uranyl nitrate [UO2(NO3)2 6H2O] to create a syndrome of chronic uremia. Initially, dogs usually received 2.0 mg\\/kg of uranyl nitrate; subsequent doses were generally less. After the initial injection, there was an abrupt fall in creatinine clearance and rise in plasma urea nitrogen. Low and relatively constant creatinine clearances (10.2

Sukemoto Fukuda; Joel D. Kopple

1980-01-01

376

Bimetallic ?6,?1 NCN-pincer ruthenium palladium complexes with ?6-RuCp coordination: synthesis, X-ray structures, and catalytic properties  

Microsoft Academic Search

The synthesis, structure, and catalytic activity of a series of bimetallic ?6,?1-NCN-pincer ruthenium palladium complexes, [3]+?[5]+, have been studied, in which ?6-coordination of [Ru(C5R5)]+ (R = H or Me) is realized either directly to the central arene ring of the NCN-pincer palladium complex ([3]+ and [4]+) or to the para-phenyl substituent ([5]+). The X-ray structures of [4]+ and [5]+, as

Sylvestre Bonnet; Joop H. van Lenthe; Maxime A. Siegler; Anthony L. Spek; Gerard van Koten; Robertus J. M. Klein Gebbink

2009-01-01

377

?6Coordination of a ruthenium(II) organometallic fragment to the arene ring of N,C,N-pincer metal complexes  

Microsoft Academic Search

Stable heterobimetallic complexes of the type [MX(NCN)Ru(C5R5)]+ (R = H or Me), where the phenylene ring of an NCN-pincer ligand coordinates first to a platinum or palladium center via a ?-bond, and second to a ruthenium organometallic fragment via a ?-bond, are synthesized in a single step involving electrophilic attack of a cationic Ru species on the aryl metal complex.

Sylvestre A. Bonnet; Martin Lutz; Anthony L. Spek; Gerard van Koten; Robertus J. M. Klein Gebbink

2008-01-01

378

Uranyl Precipitation by Pseudomonas aeruginosa via Controlled Polyphosphate Metabolism  

PubMed Central

The polyphosphate kinase gene from Pseudomonas aeruginosa was overexpressed in its native host, resulting in the accumulation of 100 times the polyphosphate seen with control strains. Degradation of this polyphosphate was induced by carbon starvation conditions, resulting in phosphate release into the medium. The mechanism of polyphosphate degradation is not clearly understood, but it appears to be associated with glycogen degradation. Upon suspension of the cells in 1 mM uranyl nitrate, nearly all polyphosphate that had accumulated was degraded within 48 h, resulting in the removal of nearly 80% of the uranyl ion and >95% of lesser-concentrated solutions. Electron microscopy, energy-dispersive X-ray spectroscopy, and time-resolved laser-induced fluorescence spectroscopy (TRLFS) suggest that this removal was due to the precipitation of uranyl phosphate at the cell membrane. TRLFS also indicated that uranyl was initially sorbed to the cell as uranyl hydroxide and was then precipitated as uranyl phosphate as phosphate was released from the cell. Lethal doses of radiation did not halt phosphate secretion from polyphosphate-filled cells under carbon starvation conditions. PMID:15574942

Renninger, Neil; Knopp, Roger; Nitsche, Heino; Clark, Douglas S.; Keasling, Jay D.

2004-01-01

379

Intramolecular N-HCl hydrogen bonds in the outer coordination sphere of a bipyridyl bisurea-based ligand stabilize a tetrahedral FeLCl2 complex.  

PubMed

A bipyridyl-based anion receptor is utilized as a ligand in a tetrahedral FeCl2 complex and demonstrates secondary coordination sphere influence through intramolecular hydrogen bonding to the chloride ligands as evidenced by X-ray crystallography. PMID:24854889

Gavette, Jesse V; Klug, Christina M; Zakharov, Lev N; Shores, Matthew P; Haley, Michael M; Johnson, Darren W

2014-07-11

380

Synthesis, crystal structures, and urease inhibition of an acetohydroxamate-coordinated oxovanadium(V) complex derived from N'-(3-bromo-2-hydroxybenzylidene)-4-methoxybenzohydrazide.  

PubMed

A new benzohydrazone compound N'-(3-bromo-2-hydroxybenzylidene)-4-methoxybenzohydrazide (H2L) was prepared. Reaction of H2L and acetohydroxamic acid (HAHA) with VO(acac)2 in methanol gave the complex [VOL(AHA)]. Both H2L and the oxovanadium complex were characterized by elemental analysis, IR, UV-vis and (1)H NMR spectra, and single crystal X-ray diffraction. H2L was also characterized by high-resolution mass spectrum. Thermal analysis of the oxovanadium complex was carried out. The benzohydrazone ligand, in its dianionic form, coordinates to V atom through the phenolate oxygen, imino nitrogen and enolate oxygen. The acetohydroxamic acid coordinates to V atom through the carbonyl oxygen and deprotonated hydroxyl oxygen. The V atom is in octahedral coordination. H2L, HAHA and the oxovanadium complex were tested for their urease inhibitory activities. The percent inhibition at concentration of 100?molL(-1) on Helicobacter pylori urease is 78% for the oxovanadium complex. The IC50 value for the complex is 36.5?molL(-1). Molecular docking study was performed to study the inhibition. PMID:25840795

Qu, Dan; Niu, Fang; Zhao, Xinlu; Yan, Ke-Xiang; Ye, Yu-Ting; Wang, Jia; Zhang, Mei; You, Zhonglu

2015-05-01

381

Characterization and Dioxygen Reactivity of a New Series of Coordinatively Unsaturated Thiolate-Ligated Manganese(II) Complexes  

PubMed Central

The synthesis, structural, and spectroscopic characterization of four new coordinatively unsaturated mononuclear thiolate-ligated manganese(II) complexes ([MnII(SMe2N4(6-Me-DPEN))](BF4) (1), [MnII(SMe2N4(6-Me-DPPN))](BPh4)MeCN (3), [MnII(SMe2N4(2-QuinoPN))](PF6)MeCNEt2O (4), and [MnII(SMe2N4(6-H-DPEN)(MeOH)](BPh4) (5)) is described, along with their magnetic, redox, and reactivity properties. These complexes are structurally-related to recently reported [MnII(SMe2N4(2-QuinoEN))](PF6) (2) Dioxygen addition to complexes 1-5 is shown to result in the formation of five new rare examples of Mn(III) dimers containing a single, unsupported oxo bridge: [MnIII(SMe2N4(6-Me-DPEN)]2-(?-O)(BF4)22MeOH (6), [MnIII(SMe2N4(QuinoEN)]2-(?-O)(PF6)2Et2O (7), [MnIII(SMe2N4(6-Me-DPPN)]2-(?-O)(BPh4)2 (8), [MnIII(SMe2N4(QuinoPN)]2-(?-O)(BPh4)2 (9), and [MnIII(SMe2N4(6-H-DPEN)]2-(?-O)(PF6)22MeCN (10). Labeling studies show that the oxo atom is derived from 18O2. Ligand modifications, involving either the insertion of a methylene into the backbone, or the placement of an ortho substituent on the N-heterocyclic amine, are shown to noticeably modulate the magnetic and reactivity properties. Fits to solid-state magnetic susceptibility data show that the Mn(III) ions of ? -oxo dimers 6-10 are moderately antiferromagnetically coupled, with coupling constants (2J) that fall within the expected range. Metastable intermediates, which ultimately convert to ?-oxo bridged 6 and 7, are observed in low-temperature reactions between 1 and 2 and dioxygen. Complexes 3-5, on the other hand, do not form observable intermediates, thus illustrating the effect that relatively minor ligand modifications have upon the stability of metastable dioxygen-derived species. PMID:22642272

Coggins, Michael K.; Toledo, Santiago; Shaffer, Erika; Kaminsky, Werner; Shearer, Jason; Kovacs, Julie A.

2012-01-01

382

Uranyl(VI) nitrate salts: modeling thermodynamic properties using the binding mean spherical approximation theory and determination of "fictive" binary data.  

PubMed

This work is aimed at a description of the thermodynamic properties of highly concentrated aqueous solutions of uranyl nitrate at 25 degrees C. A new resolution of the binding mean spherical approximation (BIMSA) theory, taking into account 1-1 and also 1-2 complex formation, is developed and used to reproduce, from a simple procedure, experimental uranyl nitrate osmotic coefficient variation with concentration. For better consistency of the theory, binary uranyl perchlorate and chloride osmotic coefficients are also calculated. Comparison of calculated and experimental values is made. The possibility of regarding the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O as a "simple" solution (in the sense of Zdanovskii, Stokes, and Robinson) is examined from water activity and density measurements. Also, an analysis of existing uranyl nitrate binary data is proposed and compared with our obtained data. On the basis of the concept of "simple" solution, values for density and water activity for the binary system UO(2)(NO(3))(2)/H(2)O are proposed in a concentration range on which uranyl nitrate precipitates from measurements on concentrated solutions of the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O. This new set of binary data is "fictive" in the sense that the real binary system is not stable chemically. Finally, a new, interesting predictive capability of the BIMSA theory is shown. PMID:16494358

Ruas, Alexandre; Bernard, Olivier; Caniffi, Barbara; Simonin, Jean-Pierre; Turq, Pierre; Blum, Lesser; Moisy, Philippe

2006-02-23

383

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

384

Separation performance of cucurbit[8]uril and its coordination complex with cadmium (II) in capillary gas chromatography.  

PubMed

Here we report the investigation of using cucurbit[8]uril (CB8) and its coordination complex with cadmium (II) (CB8-Cd) as stationary phases for capillary gas chromatography (GC). The prepared capillary columns of CB8 and CB8-Cd stationary phases achieved column efficiency of 2200plates/m and 1508plates/m, respectively, and showed weak polarity based on the measured McReynolds constants. Their separation performance was investigated by GC separation of mixtures of different types while a commercial column was used for comparison. The CB8 stationary phase achieved high resolution for a wide range of analytes from nonpolar to polar while the CB8-Cd stationary phase exhibited good separation mainly for nonpolar to weak polar analytes. The CB stationary phases differ from the commercial one in terms of retention behaviors and resolving ability due to their different molecular interactions with analytes. Moreover, energy effect on the retention of analytes on CB8 and CB8-Cd stationary phases was examined, showing that retention on CB8 column was determined mainly by enthalpy change for polar analytes and by both enthalpy change and entropy change for weak polar analytes whereas retention on CB8-Cd column was mainly controlled by entropy change. This work demonstrates the great potential of CB8 and CB8-Cd stationary phases as a new type of GC stationary phases in GC analysis. PMID:24745846

Sun, Tao; Ji, Ningning; Qi, Meiling; Tao, Zhu; Fu, Ruonong

2014-05-23

385

Radical anionic versus neutral 2,2'-bipyridyl coordination in uranium complexes supported by amide and ketimide ligands.  

PubMed

The synthesis and characterization of (bipy)(2)U(N[t-Bu]Ar)(2) (1-(bipy)(2), bipy = 2,2'-bipyridyl, Ar = 3,5-C(6)H(3)Me(2)), (bipy)U(N[(1)Ad]Ar)(3) (2-bipy), (bipy)(2)U(NC[t-Bu]Mes)(3) (3-(bipy)(2), Mes = 2,4,6-C(6)H(2)Me(3)), and IU(bipy)(NC[t-Bu]Mes)(3) (3-I-bipy) are reported. X-ray crystallography studies indicate that bipy coordinates as a radical anion in 1-(bipy)(2) and 2-bipy, and as a neutral ligand in 3-I-bipy. In 3-(bipy)(2), one of the bipy ligands is best viewed as a radical anion, the other as a neutral ligand. The electronic structure assignments are supported by NMR spectroscopy studies of exchange experiments with 4,4'-dimethyl-2,2'-bipyridyl and also by optical spectroscopy. In all complexes, uranium was assigned a +4 formal oxidation state. PMID:25510329

Diaconescu, Paula L; Cummins, Christopher C

2015-02-14

386

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

PubMed Central

ADP ribosylation factor (Arf) 6 anchors to the plasma membrane, where it coordinates membrane trafficking and cytoskeleton remodelling, but how it assembles actin filaments is unknown. By reconstituting membrane-associated actin assembly mediated by the WASP family veroprolin homolog (WAVE) regulatory complex (WRC), we recapitulated an Arf6-driven actin polymerization pathway. We show that Arf6 is divergent from other Arf members, as it was incapable of directly recruiting WRC. We demonstrate that Arf6 triggers actin assembly at the membrane indirectly by recruiting the Arf guanine nucleotide exchange factor (GEF) ARNO that activates Arf1 to enable WRC-dependent actin assembly. The pathogen Salmonella usurped Arf6 for host cell invasion by recruiting its canonical GEFs EFA6 and BRAG2. Arf6 and its GEFs facilitated membrane ruffling and pathogen invasion via ARNO, and triggered actin assembly by generating an Arf1WRC signaling hub at the membrane in vitro and in cells. This study reconstitutes Arf6-dependent actin assembly to reveal a mechanism by which related Arf GTPases orchestrate distinct steps in the WRC cytoskeleton remodelling pathway. PMID:24085844

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

2013-01-01

387

Metal coordination study at Ag and Cd sites in crown thioether complexes through DFT calculations and hyperfine parameters.  

PubMed

Structural and electronic properties of [C12H24S6X], [C13H26S6OX], and [C14H28S6OX] (X: Ag(+), Cd(2+)) crown thioether complexes were investigated within the framework of the density functional theory (DFT) using the projector augmented wave (PAW) method. The theoretical results were compared with time-differential perturbed ?-? angular correlations (TDPAC) experiments reported in the literature using the (111)Ag?(111)Cd probe. In the case of X=Ag(+), a refinement of the structure was performed and the predicted equilibrium structures compared with available X-ray diffraction experimental data. Structural distortions induced by replacing Ag(+) with Cd(2+) were investigated as well as the electric-field gradient (EFG) tensor at the Cd(2+) sites. Our results suggest that the EFG at Cd(2+) sites corresponds to the Ag(+) coordination sphere structure, i.e., before the structural relaxations of the molecule with X=Cd(2+) are completed. The results are discussed in terms of the characteristics of the TDPAC (111)Ag?(111)Cd probe and the time window of the measurement, and provide an interesting tool with which to probe molecular relaxations. PMID:25814377

do Nascimento, Rafael R; Lima, Filipe C D A; Gonalves, Marcos B; Errico, Leonardo A; Rentera, Mario; Petrilli, Helena M

2015-04-01

388

Tetrapositive plutonium, neptunium, uranium, and thorium coordination complexes: chemistry revealed by electron transfer and collision induced dissociation.  

PubMed

The Pu(4+), Np(4+), and U(4+) ions, which have large electron affinities of ?34.6, ?33.6, and ?32.6 eV, respectively, were stabilized from solution to the gas phase upon coordination by three neutral tetramethyl-3-oxa-glutaramide ligands (TMOGA). Both collision induced dissociation (CID) and electron transfer dissociation (ETD) of Pu(TMOGA)3(4+) reveal the propensity for reduction of Pu(IV) to Pu(III), by loss of TMOGA(+) in CID and by simple electron transfer in ETD. The reduction of Pu(IV) is in distinct contrast to retention of Th(IV) in both CID and ETD of Th(TMOGA)3(4+), where only the C-Oether bond cleavage product was observed. U(TMOGA)3(4+) behaves similarly to Th(TMOGA)3(4+) upon CID and ETD, while the fragmentation patterns of Np(TMOGA)3(4+) lie between those of Pu(TMOGA)3(4+) and U(TMOGA)3(4+). It is notable that the gas-phase fragmentation behaviors of these exceptional tetrapositive complexes parallel fundamental differences in condensed phase chemistry within the actinide series, specifically the tendency for reduction from the IV to III oxidation states. PMID:24660979

Gong, Yu; Tian, Guoxin; Rao, Linfeng; Gibson, John K

2014-04-17

389

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

390

Solid-state and solution-state coordination chemistry of lanthanide(III) complexes with (pyrazol-1-yl)acetic acid.  

PubMed

As a precursor of carboxyl-functionalized task-specific ionic liquids (TSILs) for f-element separations, (pyrazol-1-yl)acetic acid (L) can be deprotonated as a functionalized pyrazolate anion to coordinate with hard metal cations. However, the coordination chemistry of L with f-elements remains unexplored. We reacted L with lanthanides in aqueous solution at pH = 5 and synthesized four lanthanide complexes of general formula [Ln(L)3(H2O)2]nH2O (1, Ln = La, n = 2; 2, Ln = Ce, n = 2; 3, Ln = Pr, n = 2; 4, Ln = Nd, n = 1). All complexes were characterized by single crystal X-ray diffraction analysis revealing one-dimensional chain formations. Two distinct crystallographic structures are governed by the different coordination modes of carboxylate groups in L: terminal bidentate and bridging tridentate (1-3); terminal bidentate, bridging bidentate, and tridentate coordination in 4. Comparison of the solid state UV-vis-NIR diffuse reflectance spectra with solution state UV-vis-NIR spectra suggests a different species in solution and solid state. The different coordination in solid state and solution was verified by distinctive (13)C NMR signals of the carboxylate groups in the solid state NMR. PMID:23458903

Chen, Xiao-Yan; Goff, George S; Scott, Brian L; Janicke, Michael T; Runde, Wolfgang

2013-03-18

391

Potentiometric determination of free acidity and uranium in uranyl nitrate solutions  

Microsoft Academic Search

Free acid and uranium in uranyl nitrate solutions have been determined potentiometrically using Na2SO4NaOH, Na2SO4Na2CO3 and (NH4)2SO4NaOH complexant-titrant combinations. The overall recovery of nitric acid varies in the range of 95.25 to 118.5%, depending upon the acid as well as the total uranium present, while that of uranium always a positive bias ranging from 100.2 to 106.4%. The results have

M. Anwar; D. Mohammad

1989-01-01

392

The investigation of the solvent effect on coordination of nicotinato ligand with cobalt(II) complex containing tris(2-benzimidazolylmethyl)amine: A computational study  

NASA Astrophysics Data System (ADS)

The electronic structure of [Co(ntb)(nic)]+ complex ion are optimized by using density functional theory (DFT) method with mix basis set. Where (ntb) represents tris(2-benzimidazolylmethyl)amine ligand and (nic) is the anion of nicotinic acids. Six different fields, vacuum, chloroform, butanonitrile, methanol, water and formamide solvents are used in these calculations. The calculated structural parameters indicate that (nic) ligand coordinates to cobalt(II) containing (ntb) ligand with one oxygen atom in butanonitrile, methanol, water and formamide solvents but coordinates with two oxygen atoms in vacuum. These results are supported with IR, UV and 1H NMR spectra. According to the calculated results, the geometry of [Co(ntb)(nic)]+ complex ion is distorted octahedral in vacuum while the geometry is distorted square pyramidal in the all other solvents. Distorted octahedral [Co(ntb)(nic)]+ complex ion have not been synthesized as experimentally and it is predicted with computational chemistry methods.

Sayin, Koray; Karaka?, Duran

2014-11-01

393

Extraction of uranyl nitrate from concentrated aqueous salt solutions in diisoamyl methylphosponate  

SciTech Connect

The isotherm of extraction of uranyl nitrate from concentrated aqueous salt solutions of 100% diisoamyl methylphosphonate has been described. Allowance was made for formation of uranyl nitrate di- and trisolvates in the organic phase.

Pyartman, A.K.; Kopyrin, A.A.; Puzikov, E.A. [St. Petersburg Technological Institute (Russian Federation)

1995-09-10

394

Preparation and Reactions of the 1,1-Dithiolato Complexes of Ni(II). An Undergraduate Coordination Chemistry Experiment.  

ERIC Educational Resources Information Center

Described is an undergraduate coordination chemistry experiment that enables students to relate concepts developed in class about the stereochemistry and coordination numbers to the interpretation of the electronic and infrared spectra and their magnetic behavior. Indicates that thermal decomposition and x-ray diffraction studies can also be

Ballester, L.; Perpinan, M. F.

1988-01-01

395

The Principle of Hard and Soft Acids and Bases and the Problem of Competitive Coordination in Complex Compounds  

Microsoft Academic Search

A systematic and general account is given of data on the location of the coordinate bond in systems with several potential electron-donating centres (competitive coordination). The problem is examined from the standpoint of the principle of hard and soft acids and bases. The bibliography includes 441 references.

Alexander D. Garnovskii; O. A. Osipov; Sergey B. Bulgarevich

1972-01-01

396

Mixed-ligand rhenium-188 complexes with tetradentate/monodentate NS3/P ('4 + 1') coordination: relation of structure with antioxidation stability.  

PubMed

Development of new radiopharmaceuticals based on rhenium-188 depends on finding appropriate ligands able to give complexes with high in vivo stability. Rhenium(III) mixed-ligand complexes with tetradentate/monodentate ('4 + 1') coordination of the general formula [Re(NS(3))(PRR'R' ')] (NS(3) = tris(2-mercaptoethyl)amine and derivatives thereof, PRR'R' ' = phosphorus(III) ligands) appear to be among the promising tools to achieve this goal. According to this approach, we synthesized and characterized a series of rhenium model complexes. In vitro stabilities of the corresponding rhenium-188 complexes were determined by incubating 2-3 MBq or alternatively 37 MBq of the complexes in phosphate buffer, human plasma, and rat plasma, respectively, at 22 degrees C or 37 degrees C, followed by checking the amount of (188)ReO(4)(-) formed after 1 h, 24, and 48 h by thin-layer chromatography. The rate of perrhenate formation varied over a wide range, depending primarily on the nature of the phosphorus(III) ligand. Physicochemical parameters of the corresponding nonradioactive rhenium complexes were analyzed in detail to find out the factors influencing their different stability and furthermore to design new substitution-inert '4 + 1' complexes. Tolman's cone angle of phosphorus(III) ligands and the lipophilic character of the inner coordination sphere were found to be crucial factors to build up stable rhenium '4 + 1' complexes. Additional information useful to describe electronic and steric properties of these compounds were selected from electronic spectra (wavelength of the Re-->S charge-transfer band), cyclovoltammetric measurements (E degrees of the Re(III)/Re(IV) couple), and NMR investigations ((31)P chemical shift of coordinated P(III) ligands). PMID:15898732

Schiller, Eik; Seifert, Sepp; Tisato, Francesco; Refosco, Fiorenzo; Kraus, Werner; Spies, Hartmut; Pietzsch, Hans-Juergen

2005-01-01

397

Self-assembly of Alkali-uranyl-peroxide Clusters  

SciTech Connect

The hexavalent uranium specie, uranyl triperoxide, UO{sub 2}(O{sub 2}){sub 3}{sup 4?}, has been shown recently to behave like high oxidation-state d0 transition-metals, self-assembling into polyoxometalate-like clusters that contain up to 60 uranyl cations bridged by peroxide ligands. There has been much less focus on synthesis and structural characterization of salts of the monomeric UO{sub 2}(O{sub 2}){sub 3}{sup 4?} building block of these clusters. However, these could serve as water-soluble uranyl precursors for both clusters and materials, and also be used as simple models to study aqueous behavior by experiment and modeling. The countercation is of utmost importance to the assembly of these clusters, and Li{sup +} has proven useful for the crystallization of many of the known cluster geometries to date. We present in this paper synthesis and structural characterization of two monomeric lithium uranyl-peroxide salts, Li{sub 4}[UO{sub 2}(O{sub 2}){sub 3}]10H{sub 2}O (1) and [UO{sub 2}(O{sub 2}){sub 3}]{sub 12}[(UO{sub 2}(OH){sub 4})Li{sub 16}(H{sub 2}O){sub 28}]{sub 3}Li{sub 6}[H{sub 2}O]{sub 26} (2). They were obtained from aqueous-alcohol solutions rather than the analogous aqueous solutions from which lithium uranyl-peroxide clusters are crystallized. Rapid introduction of the alcohol gives the structure of (1) whereas slow diffusion of alcohol results in crystallization of (2). (2) is an unusual structure featuring uranyl-centered alkali clusters that are linked into ring and spherical arrangements via [UO{sub 2}(O{sub 2}){sub 3}] anions. Furthermore, partial substitution of Rb or Cs into the synthesis results in formation of (2) with substitution of these larger alkalis into the uranyl-centered clusters. We surmise that the slow crystallization allows for direct bonding of alkali metals to the uranyl-peroxide oxygen ligands that is observed in (2), and its Rb and Cs-substituted derivatives. In contrast, the only interaction between UO{sub 2}(O{sub 2}){sub 3}{sup 4?} and Li+ observed in (1) is through hydrogen bonding of the lithium-bound water. These structures potentially provide some insight to understanding how alkali counterions interact with the UO{sub 2}(O{sub 2}){sub 3}{sup 4?} anions during the self-assembly, crystallization and even redissolution of uranyl-peroxide polyanionic clusters.

Nyman, May; Rodriquez, M. A.; Campana, Charles F.

2010-01-01

398

Multispecies diffusion models: A study of uranyl species diffusion  

SciTech Connect

Rigorous numerical description of multi-species diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication for imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multi-species diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multi-species diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multi-species U(VI) diffusion under steady-state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that a fully coupled diffusion model can be well approximated by a component-based diffusion model, which considers difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be rigorously enforced, if necessary, by adding an artificial kinetic reaction term induced by the charge separation. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from US Department of Energy's Hanford 300A where intragrain diffusion is a rate-limiting process controlling U(VI) adsorption and desorption. The grain-scale reactive diffusion model was able to describe U(VI) adsorption/desorption kinetics that has been described using a semi-empirical, multi-rate model. Compared with the multi-rate model, the diffusion models have the advantage to provide spatiotemporal speciation evolution within the diffusion domains.

Liu, Chongxuan; Shang, Jianying; Zachara, John M.

2011-12-14

399

Vibrational spectra of discrete UO22+ halide complexes in the gas phase  

SciTech Connect

The intrinsic binding of halide ions to the metal center in the uranyl molecule is a topic of ongoing research interest in both the actinide separations and theoretical communities. Investigations of structure in the condensed phases is frequently obfuscated by solvent interactions, that can alter ligand binding and spectroscopic properties. The approach taken in this study is to move the uranyl halide complexes into the gas phase where they are free from solvent interactions, and then interrogate their vibrational spectroscopy using infrared multiple photon dissociation (IRMPD). The spectra of cationic coordination complexes having the composition [UO2(X)(ACO)3]+ (X = F, Cl, Br and I; ACO = acetone) were acquired using electrospray for ion formation, and monitoring the ion signal from the photoelimination of ACO ligands. The studies showed that the asymmetric v3 UO2 frequency was insensitive to halide identity as X was varied from Cl to I, suggesting that in these pseudo octahedral complexes, changing the nucleophilicity of the halide did not appreciably alter the binding in the complex. The v3 peak in the spectrum of the F-containing complex was ~ 10 cm-1 lower indicating stronger coordination in this complex. Similarly the ACO carbonyl stretches showed that the C=O frequency was relatively insensitive to the identity of the halide, although a modest shift to the blue was seen for the complexes with the more nucleophilic anions, consistent with the idea that they loosen solvent binding. Surprisingly, the v1 stretch was activated when the softer anions Cl, Br and I were present in the complexes. IR studies of the anionic complexes were conducted by measuring the v3 UO2 frequencies of [UO2X3]-, where X = Cl-, Br- and I-. The trifluoro complex could not be photodissociated. In these negatively charged complexes, the UO2 v3 values decreased with increasing anion nucleophilicity. This observation was consistent with DFT calculations that indicated that dissociation energy decreased on the order F > Cl > Br > I.

Gary S. Groenewold; Michael J. van Stipdonk; Wibe A. de Jong; Jos Oomens; Garold L. Gresham

2010-11-01

400

Hydrothermal Phase Relations Among Uranyl Minerals at the Nopal I Analog Site  

SciTech Connect

Uranyl mineral paragenesis at Nopal I is an analog of spent fuel alteration at Yucca Mountain. Petrographic studies suggest a variety of possible hydrothermal conditions for uranium mineralization at Nopal I. Calculated equilibrium phase relations among uranyl minerals show uranophane stability over a broad range of realistic conditions and indicate that uranyl mineral variety reflects persistent chemical potential heterogeneity. (author)

Murphy, William M. [Geological and Environmental Sciences, California State University, Chico, CA, 95929 (United States)

2007-07-01