These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Crown ether complexes of uranyl, neptunyl, and plutonyl: hydration differentiates inclusion versus outer coordination.  

PubMed

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

Gong, Yu; Gibson, John K

2014-06-01

2

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

SciTech Connect

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

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

2012-12-03

3

On the Formation of "Hypercoordinated" Uranyl Complexes  

SciTech Connect

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

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

2011-09-05

4

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

2014-12-23

5

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

6

Dimeric uranyl complexes with bridging perrhenates.  

PubMed

The reaction between [UO2(ReO4)2.H(2)O] and two equivalents of either tri-n-butyl phosphine oxide (TBPO) or tri-iso-butyl phosphate (TiBP) results in the formation of [UO2(mu2-ReO4)(ReO4)(TBPO)2]2 (1) and [UO2(mu2-ReO4)(ReO4)(TiBP)2]2 (2) respectively. Both complexes crystallise as two structurally similar centrosymmetric dimers, the cores containing two uranyl moieties linked by bridging perrhenates. Two P=O donor ligands and one monodenatate perrhenate complete the pentagonal bipyramidal coordination sphere at each metal centre. Both complexes have also been characterised in the solid state by vibrational and absorption spectroscopy. Solution spectroscopic characterisation indicates that both perrhenate and phosphine oxide (1) or phosphate (2) remain coordinated, although it is not possible to state conclusively that the dimeric species remain intact. A low resolution structural study of a minor product from the reaction that yielded revealed a monomeric complex with only monodentate perrhenate coordination, [UO2(ReO4)2(H2O)(TiBP)2] (2'). These results represent the first structural evidence for the bridging coordination mode of perrhenate on coordination to an actinide and yields further insight into the possible solvent phase pertechnetate complexes that may exist in PUREX process phosphate rich solvent. PMID:17426862

John, Gordon H; May, Iain; Sarsfield, Mark J; Collison, David; Helliwell, Madeleine

2007-04-28

7

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

8

Uranyl-oxo coordination directed by non-covalent interactions.  

PubMed

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

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

2014-07-28

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

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

11

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

SciTech Connect

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

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

2009-12-12

12

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

13

Water versus acetonitrile coordination to uranyl. Effect of chloride ligands.  

PubMed

Optimizations at the BLYP and B3LYP levels are reported for the mixed uranyl chloro/water/acetonitrile complexes [UO(2)Cl(n)(H(2)O)(x)(MeCN)(5-n-x)](2-n) (n = 1-3) and [UO(2)Cl(n)(H(2)O)(x)(MeCN)(4-n-x)](2-n) (n = 2-4), in both the gas phase and a polarizable continuum modeling acetonitrile. Car-Parrinello molecular dynamics (CPMD) simulations have been performed for [UO(2)Cl(2)(H(2)O)(MeCN)(2)] in the gas phase and in a periodic box of liquid acetonitrile. According to population analyses and dipole moments evaluated from maximally localized Wannier function centers, uranium is less Lewis acidic in the neutral UO(2)Cl(2) than in the UO(2)(2+) moiety. In the gas phase the latter binds acetonitrile ligands more strongly than water, whereas in acetonitrile solution, the trend is reversed due to cooperative polarization effects. In the polarizable continuum the chloro complexes have a slight energetic preference for water over acetonitrile ligands, but several mixed complexes are so close in free energy ?G that they should exist in equilibrium, in accord with previous interpretations of EXAFS data in solution. The binding strengths of the fifth neutral ligands decrease with increasing chloride content, to the extent that the trichlorides should be formulated as four-coordinate [UO(2)Cl(3)L](-) (L = H(2)O, MeCN). Limitations to their accuracy notwithstanding, density functional calculations can offer insights into the speciation of a complex uranyl system in solution, a key feature in the context of nuclear waste partitioning by complexant molecules. PMID:22233256

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

2012-02-01

14

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

15

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

16

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

PubMed

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

Grohol, Daniel; Blinn, Elliott L.

1997-07-30

17

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

18

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

19

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

20

Mechanisms of uranyl and phosphate (co)sorption: complexation and precipitation at alpha-Al2O3 surfaces.  

PubMed

This study presents new in situ electrophoretic and ATR-FTIR data on the surface species controlling the cosorption of uranyl and phosphate ions in alpha-Al(2)O(3) suspensions at acidic pH (3.3). It was shown that the uranyl sorption (i) was promoted in the presence of phosphate, (ii) induced significant changes in zeta potential of P-loaded alumina, and (iii) was governed by two mechanisms, surface complexation and surface precipitation, with the predominant species being mainly dependent on phosphate surface coverage. Formation of surface precipitates of uranyl phosphate at high phosphate surface coverage was inferred from the high negative charges imparted to the surface by uranyl and phosphate (co)sorption, and from assignments of IR bands at 1107, 1024, and 971 cm(-1) to P-O-stretching vibrations for phosphate coordinated to uranyl, at the alumina surface. The ATR-FTIR study showed that the precipitates of uranyl phosphate formed at the surface of alpha-Al(2)O(3) for aqueous concentrations of uranyl at trace levels. It also evidenced that formation of surface precipitates of U(VI)-phosphate was occurring along with the transformation of alumina into secondary surface precipitates of Al-phosphate, at very high phosphate concentrations. These findings are relevant to the mechanisms of adsorption of trace uranyl on naturally occurring oxide surfaces, in soils with low pH where cosorption of phosphate and uranyl ions is known to play a crucial role in the long-term retention of U. PMID:20413126

Galindo, Catherine; Del Nero, Mirella; Barillon, Remi; Halter, Eric; Made, Benoit

2010-07-15

21

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 LIII-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 pKa = 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

2015-01-28

22

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

23

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

24

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

25

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

26

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

PubMed

Some tetradentate salen type Schiff bases and their uranyl complexes were synthesized and characterized by UV-Vis, NMR, IR, TG, C.H.N. and X-ray crystallographic studies. From these investigations it is confirmed that a solvent molecule occupied the fifth position of the equatorial plane of the distorted pentagonal bipyramidal structure. Also, the kinetics of complex decomposition by using thermo gravimetric methods (TG) was studied. The thermal decomposition reactions are first order for the studied complexes. To examine the properties of uranyl complexes according to the substitutional groups, we have carried out the electrochemical studies. The electrochemical reactions of uranyl Schiff base complexes in acetonitrile were reversible. PMID:23321220

Asadi, Zahra; Shorkaei, Mohammad Ranjkesh

2013-03-15

27

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

28

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

29

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

30

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

31

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

32

Identification of oligomeric uranyl complexes under highly alkaline conditions  

NASA Astrophysics Data System (ADS)

By utilizing X-ray absorption methods, e.g., extended x-ray absorption fine structure (EXAFS) and single crystal x-ray diffraction (XRD), as well as Raman, UV-Vis and fluorescence spectroscopy, we have shown that an equilibrium exists between the monomeric uranyl hydroxide species UO2(OH)42- and UO2(OH)53-, which is dependent upon hydroxide concentration. Upon further study of this system, we have now determined that a new hydrolysis product is present in equilibrium with the monomeric uranyl hydroxide species, which is favored at higher UO22+ concentrations.

Konze, Wayde V.; Clark, David L.; Conradson, Steven D.; Donohoe, J.; Gordon, John C.; Gordon, Pamela L.; Keogh, D. Webster; Morris, David E.; Tait, C. Drew

2000-07-01

33

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

34

Insights into uranyl chemistry from molecular dynamics simulations.  

PubMed

First-principles and purely classical molecular dynamics (MD) simulations for complexes of the uranyl ion (UO(2)(2+)) are reviewed. Validation of Car-Parrinello MD simulations for small uranyl complexes in aqueous solution is discussed. Special attention is called to the mechanism of ligand-exchange reactions at the uranyl centre and to effects of solvation and hydration on coordination and structural properties. Large-scale classical MD simulations are surveyed in the context of liquid-liquid extraction, with uranyl complexes ranging from simple hydrates to calixarenes, and nonaqueous phases from simple organic solvents and supercritical CO(2) to ionic liquids. PMID:21960471

Bhl, Michael; Wipff, Georges

2011-12-01

35

Structural characterization of environmentally relevant ternary uranyl citrate complexes present in aqueous solutions and solid state materials.  

PubMed

Organic acids are important metal chelators in environmental systems and tend to form soluble complexes in aqueous solutions, ultimately influencing the transport and bioavailability of contaminants in surface and subsurface waters. This is particularly true for the formation of uranyl citrate complexes, which have been utilized in advanced photo- and bioremediation strategies for soils contaminated with nuclear materials. Given the complexity of environmental systems, the formation of ternary or heterometallic uranyl species in aqueous solutions are also expected, particularly with Al(iii) and Fe(iii) cations. These ternary forms are reported to be more stable in aqueous solutions, potentially enhancing contaminant mobility and uptake by organisms, but the exact coordination geometries of these soluble molecular complexes have not been elucidated. To provide insight into the nature of these species, we have developed a series of geochemical model compounds ([(UO2)2Al2(C6H4O7)4](6-) (U2Al2), [(UO2)2Fe2(C6H4O7)4](6-) (U2Fe2-1) and [(UO2)2Fe2(C6H4O7)4(H2O)2](6-) (U2Fe2-2) and [(UO2)2Fe4(OH)4(C6H4O7)4](8-) (U2Fe4)) that were characterized by single-crystal X-ray diffraction and vibrational spectroscopy. Mass spectroscopy was then employed to compare the model compounds to species present in aqueous solutions to provide an enhanced understanding of the ternary uranyl citrate complexes that could be relevant in natural systems. PMID:25372632

Basile, Madeline; Unruh, Daniel K; Flores, Erin; Johns, Adam; Forbes, Tori Z

2015-01-28

36

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

37

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

38

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

39

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

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 to dissolve nitric acid in the supercritical phase. Indeed, without TBP, nitric acid alone self aggregates via

Boyer, Edmond

40

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

41

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

42

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

43

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

44

Complex coordinates in transformation optics  

SciTech Connect

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

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

2011-12-15

45

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

PubMed

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

Galindo, Catherine; Del Nero, Mirella

2013-04-15

46

Structural insights into the binding of uranyl with human serum protein apotransferrin structure and spectra of protein-uranyl interactions.  

PubMed

Ab initio quantum mechanical computational studies for the structure and IR spectra of the uranyl complex with human serum apotransferrin (TF) protein are carried out to model uranyl intake into the human cell through endocytosis and formation of a coordination complex with the protein binding sites. The computed IR spectra and structure of the uranyl-protein complex facilitate interpretation of the observed spectra and confirm the primary binding sites of the transferrin protein with the uranyl ion. Our computed equilibrium geometry and the IR spectra of the uranyl-TF complex reveal that uranyl ion is bound to two tyrosines, one aspartate group, and one carbonate ion. Our IR spectra indicate that histidine is not involved in binding to uranyl with transferrin protein. Our computations reveal a short, strong hydrogen bond, which could play an important role in the stabilization and formation of the uranyl-TF complex. Computed Laplacian charge plots indicate high chemical reactivity on this complex as both an electrophile and a nucleophile, facilitating binding to different receptors and thus entry into a number of target organs and the blood-brain barrier. The Mulliken charge density plots and the three-dimensional charge density plots suggest a donor-acceptor mechanism in the complex formation. PMID:19678663

Benavides-Garcia, Maria G; Balasubramanian, Krishnan

2009-09-01

47

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

48

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

SciTech Connect

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

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

1990-03-07

49

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

50

Citrate Enhanced Uranyl Adsorption on Geothite: An EXAFS Analysis  

SciTech Connect

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

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

2001-12-01

51

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

52

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

PubMed

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

Bhl, Michael; Sieffert, Nicolas; Wipff, Georges

2014-08-01

53

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

54

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

USGS Publications Warehouse

Macro- and molecular-scale knowledge of uranyl (U(VI)) partitioning reactions with soil/sediment mineral components is important in predicting U(VI) transport processes in the vadose zone and aquifers. In this study, U(VI) reactivity and surface speciation on a poorly crystalline aluminosilicate mineral, synthetic imogolite, were investigated using batch adsorption experiments, X-ray absorption spectroscopy (XAS), and surface complexation modeling. U(VI) uptake on imogolite surfaces was greatest at pH ???7-8 (I = 0.1 M NaNO3 solution, suspension density = 0.4 g/L [U(VI)]i = 0.01-30 ??M, equilibration with air). Uranyl uptake decreased with increasing sodium nitrate concentration in the range from 0.02 to 0.5 M. XAS analyses show that two U(VI) inner-sphere (bidentate mononuclear coordination on outer-wall aluminol groups) and one outer-sphere surface species are present on the imogolite surface, and the distribution of the surface species is pH dependent. At pH 8.8, bis-carbonato inner-sphere and tris-carbonato outer-sphere surface species are present. At pH 7, bis- and non-carbonato inner-sphere surface species co-exist, and the fraction of bis-carbonato species increases slightly with increasing I (0.1-0.5 M). At pH 5.3, U(VI) non-carbonato bidentate mononuclear surface species predominate (69%). A triple layer surface complexation model was developed with surface species that are consistent with the XAS analyses and macroscopic adsorption data. The proton stoichiometry of surface reactions was determined from both the pH dependence of U(VI) adsorption data in pH regions of surface species predominance and from bond-valence calculations. The bis-carbonato species required a distribution of surface charge between the surface and ?? charge planes in order to be consistent with both the spectroscopic and macroscopic adsorption data. This research indicates that U(VI)-carbonato ternary species on poorly crystalline aluminosilicate mineral surfaces may be important in controlling U(VI) mobility in low-temperature geochemical environments over a wide pH range (???5-9), even at the partial pressure of carbon dioxide of ambient air (pCO2 = 10-3.45 atm). ?? 2006 Elsevier Inc. All rights reserved.

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

2006-01-01

55

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

56

A surface structural model for ferrihydrite II: Adsorption of uranyl and carbonate  

NASA Astrophysics Data System (ADS)

The adsorption of uranyl (UO 22+) on ferrihydrite has been evaluated with the charge distribution (CD) model for systems covering a very large range of conditions, i.e. pH, ionic strength, CO 2 pressure, U(VI) concentration, and loading. Modeling suggests that uranyl forms bidentate inner sphere complexes at sites that do not react chemically with carbonate ions. Uranyl is bound by singly-coordinated surface groups present at particular edges of Fe-octahedra of ferrihydrite while another set of singly-coordinated surface groups may form double-corner bidentate complexes with carbonate ions. The uranyl surface speciation strongly changes in the presence of carbonate due to the specific adsorption of carbonate ions as well as the formation of ternary uranyl-carbonate surface complexes. Data analysis with the CD model suggests that a uranyl tris-carbonato surface complex, i.e. tbnd (UO 2)(CO 3) 34-, is formed. This species is most abundant in systems with a high pH and carbonate concentration. This finding differs significantly from previous interpretations made in the literature. At high pH and low carbonate concentrations, as can be prepared in CO 2-closed systems, the model suggests the additional presence of a ternary uranyl-monocarbonato complex. The binding mode (type A or type B complex) is uncertain. At high uranyl concentrations, uranyl polymerizes at the surface of ferrihydrite giving, for instance, tris-uranyl surface complexes with and without carbonate. The similarities and differences between U(VI) adsorption by goethite and ferrihydrite are discussed from a surface structural point of view.

Hiemstra, Tjisse; Riemsdijk, Willem H. Van; Rossberg, Andr; Ulrich, Kai-Uwe

2009-08-01

57

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

SciTech Connect

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

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

2001-12-01

58

Complexes of uranyl(II), vanadyl(II) and zirconyl(II) with orotic acid vitamin B13: Synthesis, spectroscopic, thermal studies and antibacterial activity  

NASA Astrophysics Data System (ADS)

A convenient method for the preparation of complexes of the uranyl [UO 2] 2+, vanadyl [VO] 2+ and [ZrO] 2+ ions with vitamin B13 (Orotic acid; H 3OA) is reported and this has enabled three complexes of orotate anion (1-) to be formulated: [M(C 5H 3N 2O 4) 2(H 2O) 2](H 2O) n [where M = [UO 2] 2+, [VO] 2+, [ZrO] 2+; n = 1, 6, 3, respectively]. The new bisorotate (H 2OA) 1- complexes were synthesis and characterized by elemental analysis, molar conductivity, spectral methods (UV-vis, mass, 1H NMR and mid infrared spectra), and simultaneous thermal analysis (TG and DTG) techniques. Physical measurements indicate that the neutral orotic acid ligand in its mono/anion form, is bonded to oxometal ions through the carboxylic groups (two monodentate orotate anions and complete the coordination sphere by coordinated water molecules). The molar conductance data confirm that the orotate complexes are non-electrolytes. The X-ray powder diffraction (XRD) as well as scanning electron microscopy (SEM) shows that the studied complexes have amorphous structures. The kinetic thermodynamic parameters, such as, E?, ? H?, ? S? and ? G? are calculated from the DTG curves. The antibacterial activity of the orotic acid and their complexes was evaluated against gram positive/negative bacteria.

Refat, Moamen S.

2007-10-01

59

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

60

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

61

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

62

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

63

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...

64

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

65

Coordination complexity of parallel Lagrangian decomposition  

SciTech Connect

We present polylogarithmically-matching upper and lower bounds on the number of parallel iterations (coordination complexity) for two wide classes of Lagrangian decomposition methods for solving general block-angular convex programs to a fixed accuracy. The lower bounds hold for multicommodity flows and even with an all-powerful coordinator. Our near-optimal upper bounds are valid for two Lagrangian decomposition methods based on the classical logarithmic barrier and the exponential potential functions. The coordination step of either method can be implemented to run in almost linear sequential or logarithmic parallel time in the number of coupling constraints. The choice of which function or method to use depends upon a theoretical characterization of an instance as a weakly- or strongly-coupled problem. Some special cases, including multicommodity flows, and a sublinear-time randomized approximation algorithm for matrix games, will be discussed. We shall also summarize computational results for large minimum-cost multicommodity network flow problems.

Grigoriadis, M.; Khachiyan, L.

1994-12-31

66

Chemical controls on uranyl citrate speciation and the self-assembly of nanoscale macrocycles and sandwich complexes in aqueous solutions.  

PubMed

Uranyl citrate forms trimeric species at pH > 5.5, but exact structural characteristics of these important oligomers have not previously been reported. Crystallization and structural characterization of the trimers suggests the self-assembly of the 3?:?3 and 3?:?2 U?:?Cit complexes into larger sandwich and macrocyclic molecules. Raman spectroscopy and ESI-MS have been utilized to investigate the relative abundance of these species in solution under varying pH and citrate concentrations. Additional dynamic light scattering experiments indicate that self-assembly of the larger molecules does occur in aqueous solution. PMID:25469487

Basile, M; Unruh, D K; Gojdas, K; Flores, E; Streicher, L; Forbes, T Z

2014-12-01

67

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

68

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

69

Influence of (calcium-)uranyl-carbonate complexation on U(VI) sorption on Ca- and Na-bentonites.  

PubMed

The influence of uranyl-carbonate and calcium-uranyl-carbonate complexations on the kinetics of U(VI) (approximately 3.4 x 10(-3) mol L(-1)) sorption from NaNO3 and Ca(NO3)2 solutions on Na- and Ca-bentonites at circumneutral ambient conditions was investigated. Complexation of U(VI) in Ca2UO2(CO3)3(aq) aqueous species, dominating the U(VI) speciation in Ca(NO3)2 solution, reduces its adsorption on bentonite by a factor of 2-3 in comparison with that in (UO2)2CO3(OH)3- species, dominating in NaNO3 solution, within the studied period of time (21 days). As a result of the dissolution of accessory calcite, Ca2UO2(CO3)3(aq) can be formed in the initially Ca-free solution in contact with either Na- or Ca-bentonite. U(VI) adsorption on Na-bentonite is a factor of approximately 2 higher than that on Ca-bentonite for solutions with the Ca2UO2(CO3)3(aq) complex dominating aqueous U(VI) speciation. This favors use of Na-bentonite over that of Ca-bentonite in final disposal of radioactive waste. Furthermore, the observed strong correlation between U(VI) adsorption and Mg release as a result of montmorillonite dissolution indicates in agreement with previous findings that under the applied conditions U(VI) is adsorbed on the edge surface of montmorillonite, which is a major mineral phase of the studied clays. PMID:19673282

Meleshyn, A; Azeroual, M; Reeck, T; Houben, G; Riebe, B; Bunnenberg, C

2009-07-01

70

Low-symmetry uranyl pyrophosphate cage clusters  

SciTech Connect

The combination of uranyl, peroxide, and pyrophosphate in aqueous solution results in the self-assembly of highly complex clusters containing 45 uranyl bipyramids and 23 pyrophosphate groups. These clusters are built from three basic structural units, and are highly unusual because they completely lack symmetry. They provide a window into the complex chemistry of evolving cluster topologies under the conditions of their formation.

Ling, Jie; Qiu, Jie; Szymanowski, Jennifer E.S.; Burns, Peter C.

2011-01-01

71

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

72

Electronic Structure and Reactivity of Three-Coordinate Iron Complexes  

PubMed Central

Conspectus The identity and oxidation state of the metal in a coordination compound are typically thought to be the most important determinants of its reactivity. However, the coordination number (the number of bonds to the metal) can be equally influential. This Account describes iron complexes with a coordination number of only three, which differ greatly from iron complexes with octahedral (six-coordinate) geometries with respect to their magnetism, electronic structure, preference for ligands, and reactivity. Three-coordinate complexes with a trigonal-planar geometry are accessible using bulky, anionic, bidentate ligands (?-diketiminates) that steer a monodentate ligand into the plane of their two nitrogen donors. This strategy has led to a variety of three-coordinate iron complexes in which iron is in the +1, +2, and +3 oxidation states. Systematic studies on the electronic structures of these complexes have been useful in interpreting their properties. The iron ions are generally high spin, with singly occupied orbitals available for ? interactions with ligands. Trends in ?-bonding show that iron(II) complexes favor electronegative ligands (O, N donors) over electropositive ligands (hydride). The combination of electrostatic ?-bonding and the availability of ?-interactions stabilizes iron(II) fluoride and oxo complexes. The same factors destabilize iron(II) hydride complexes, which are reactive enough to add the hydrogen atom to unsaturated organic molecules and to take part in radical reactions. Iron(I) complexes use strong ?-backbonding to transfer charge from iron into coordinated alkynes and N2, whereas iron(III) accepts charge from a ?-donating imido ligand. Though the imidoiron(III) complex is stabilized by ?-bonding in the trigonal-planar geometry, addition of pyridine as a fourth donor weakens the ?-bonding, which enables abstraction of H atoms from hydrocarbons. The unusual bonding and reactivity patterns of three-coordinate iron compounds may lead to new catalysts for oxidation and reduction reactions, and may be used by nature in transient intermediates of nitrogenase enzymes. PMID:18646779

Holland, Patrick L.

2008-01-01

73

Colloidal Nanocrystals Fluoresced by Surface Coordination Complexes  

PubMed Central

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

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

2014-01-01

74

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

SciTech Connect

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

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

1981-05-01

75

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

76

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

PubMed Central

An assay to detect UO22+ complexation was developed based on the chrome azurol S (CAS) assay for siderophores (B. Schwyn and J. B. Neilands, Anal. Biochem. 160:47-56, 1987) and was used to investigate the ability of fungal metabolites to complex actinides. In this assay the discoloration of two dyed agars (one containing a CAS-Fe3+ dye and the other containing a CAS-UO22+ dye) caused by ligands was quantified. The assay was tested by using the siderophore desferrioxamine B (DFO), and the results showed that there was a regular, reproducible relationship between discoloration and the amount of siderophore added. The ratio of the discoloration on the CAS-UO22+ agar to the discoloration on the CAS-Fe3+ agar was independent of the amount of siderophore added. A total of 113 fungi and yeasts were isolated from three soil samples taken from the Peak District National Park. The fungi were screened for the production of UO22+ chelators by using the CAS-based assay and were also tested specifically for hydroxamate siderophore production by using the hydroxamate siderophore auxotroph Aureobacterium flavescens JG-9. This organism is highly sensitive to the presence of hydroxamate siderophores. However, the CAS-based assay was found to be less sensitive than the A. flavescens JG-9 assay. No significant difference between the results for each site for the two tests was found. Three isolates were selected for further study and were identified as two Pencillium species and a Mucor species. Our results show that the new assay can be effectively used to screen fungi for the production of UO22+ chelating ligands. We suggest that hydroxamate siderophores can be produced by mucoraceous fungi. PMID:12788768

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

2003-01-01

77

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

78

Energy Landscape of Chelated Uranyl: Antibody Interactions by Dynamic Force Spectroscopy  

PubMed Central

We used dynamic force spectroscopy (DFS) to explore the energy landscape of interactions between a chelated uranyl compound and a monoclonal antibody raised against the uranyl-dicarboxy-phenanthroline complex. We estimated the potential energy barrier widths and the relevant thermodynamic rate constants along the dissociation coordinate. Using atomic force microscopy, four different experimental setups with or without the uranyl ion in the chelate ligand, we have distinguished specific and nonspecific binding in the binding affinity of the uranyl compound to the antibody. The force loading rates for our system were measured from 15 to 26,400 pN/s. The results showed two regimes in the plot of the most probable unbinding force versus the logarithm of the loading rate, revealing the presence of two (at least) activation barriers. Analyses of DFS suggest parallel multivalent binding present in either regime. We have also built a molecular model for the variable fragment of the antibody and used computational graphics to dock the chelated uranyl ion into the binding pocket. The structural analysis led us to hypothesize that the two regimes originate from two interaction modes: the first one corresponds to an energy barrier with a very narrow width of 0.5 0.2 , inferring dissociation of the uranyl ion from its first coordination shell (Asp residue); the second one with a broader energy barrier width (3.9 0.3 ) infers the entire chelate compound dissociated from the antibody. Our study highlights the sensitivity of DFS experiments to dissect protein-metal compound interactions. PMID:17449661

Odorico, Michael; Teulon, Jean-Marie; Bessou, Thrse; Vidaud, Claude; Bellanger, Laurent; Chen, Shu-wen W.; Qumneur, ric; Parot, Pierre; Pellequer, Jean-Luc

2007-01-01

79

Magnetic anisotropy and molecular assembling in d complex cationf complex anion type coordination compounds  

Microsoft Academic Search

The system [Fe(bpca)2][Er(NO3)4(H2O)2] (1) (Hbpca=bis(2-pyridil-carbonyl) amine) is a complex cationcomplex anion type coordination compound consisting of distinct d and f units, interlinked by hydrogen bonds. Particularly, the association of f-type complex anions in dimers is remarked and discussed. The energy decomposition analyses based on DFT calculations offered supplementary insight into the coordination effects at the lanthanide ions and the hydrogen

Marilena Ferbinteanu; Fanica Cimpoesu; Takashi Kajiwara; Masahiro Yamashita

2009-01-01

80

Coordinative saturation of cationic niobium- and rhodium-argon complexes  

NASA Astrophysics Data System (ADS)

Mass spectra of Nb + and Rh + complexes with argon ligands exhibit `magic' peaks Nb +Ar 4 and Rh +Ar 6, similar to observations for V +Ar 4 and Co +Ar 6, indicating coordinative saturation. A consistent explanation is obtained by assuming that the rare gas ligands seek out electron density minima in the valence shell of the ion, which permit a closer approach to the metal core and a stronger charge-induced dipole bond. Ab initio density functional calculations, which predict stable square planar complexes for the d 4 ions and octahedral for the d 8 species, support this interpretation and show that rare gas complexes of d 4 metal ions fit perfectly well into the coordination chemical framework based on the Jahn-Teller effect.

Beyer, Martin; Berg, Christian; Albert, Gerhard; Achatz, Uwe; Bondybey, Vladimir E.

1997-12-01

81

High-coordinate gold(I) complexes with dithiocarboxylate ligands.  

PubMed

Ferrocene dithiocarboxylate has been introduced into the chemistry of gold(I) and copper(I). First, a modified synthesis of piperidinium ferrocene dithiocarboxylate (1) is reported. Reaction of this reagent with [Au(tht)Cl] in the presence of different phosphines resulted in monomeric, dimeric, and polymeric structures. Although gold(I) is usually two coordinate, mainly three- and four-fold coordinated compounds were obtained by using ferrocene dithiocarboxylate as ligands. The isolated compounds are [(FcCSS)Au(PPh3)2] (2) (FcCSS = ferrocene dithiocarboxylate), [(FcCSS)Au2(dppm)2] (3) (dppm = bis(diphenylphosphino)methane), and [(FcCSS)Au(dppf)]n (4) (dppf = bis(diphenylphosphino)ferrocene) [{(FcCSS)Au}2(dppp)] (5) (dppp = bis(diphenylphosphino)propane). The FcCSS ligand shows a remarkable flexible coordination mode. It coordinates either in a monodentate, a chelating, or in a metal bridging mode. In the four gold(I) complexes 2-5 four different coordination modes of the FcCSS ligand are seen. Attempts to extend this rich coordination chemistry to other coinage metals were only partly successful. [(FcCSS)Cu(PPh3)2] (6) was obtained from the reaction of piperidinium ferrocene dithiocarboxylate with [(Ph3P)3CuCl]. (57)Fe-Mssbauer spectroscopy was performed for compounds 2-4. The spectra show isomer shifts and quadrupole splittings that are typical for diamagnetic ferrocenes. PMID:24735256

Kaub, Christoph; Augenstein, Timo; Bauer, Thomas O; Rothe, Elisa; Esmezjan, Lars; Schnemann, Volker; Roesky, Peter W

2014-05-01

82

Automated recognition and post-coordination of complex clinical terms.  

PubMed

One of the key tasks in integrating guideline-based decision support systems with the electronic patient record is the mapping of clinical terms contained in both guidelines and patient notes to a common, controlled terminology. However, a vocabulary of pre-coordinated terms cannot cover every possible variation - clinical terms are often highly compositional and complex. We present a rule-based approach for automated recognition and post-coordination of clinical terms using minimal, morpheme-based thesauri, neoclassical combining forms and part-of-speech analysis. The process integrates MetaMap with the open-source GATE framework. PMID:21335680

Gooch, Philip; Roudsari, Abdul

2011-01-01

83

Coordinating complex problem-solving among distributed intelligent agents  

NASA Technical Reports Server (NTRS)

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

Adler, Richard M.

1992-01-01

84

Energetic lanthanide complexes: coordination chemistry and explosives applications  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

85

Dinuclear copper complexes: coordination of Group 14 heteroborates.  

PubMed

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

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

2014-08-21

86

Role of the sodium-dependent phosphate co-transporters and of the phosphate complexes of uranyl in the cytotoxicity of uranium in LLC-PK1 cells.  

PubMed

Although uranium is a well-characterized nephrotoxic agent, very little is known at the cellular and molecular level about the mechanisms underlying the uptake and toxicity of this element in proximal tubule cells. The aim of this study was thus to characterize the species of uranium that are responsible for its cytotoxicity and define the mechanism which is involved in the uptake of the cytotoxic fraction of uranium using two cell lines derived from kidney proximal (LLC-PK(1)) and distal (MDCK) tubule as in vitro models. Treatment of LLC-PK(1) cells with colchicine, cytochalasin D, concanavalin A and PMA increased the sodium-dependent phosphate co-transport and the cytotoxicity of uranium. On the contrary, replacement of the extra-cellular sodium with N-methyl-D-glucamine highly reduced the transport of phosphate and the cytotoxic effect of uranium. Uranium cytotoxicity was also dependent upon the extra-cellular concentration of phosphate and decreased in a concentration-dependent manner by 0.1-10 mM phosphonoformic acid, a competitive inhibitor of phosphate uptake. Consistent with these observations, over-expression of the rat proximal tubule sodium-dependent phosphate co-transporter NaPi-IIa in stably transfected MDCK cells significantly increased the cytotoxicity of uranium, and computer modeling of uranium speciation showed that uranium cytotoxicity was directly dependent on the presence of the phosphate complexes of uranyl UO(2)(PO(4))(-) and UO(2)(HPO(4))(aq). Taken together, these data suggest that the cytotoxic fraction of uranium is a phosphate complex of uranyl whose uptake is mediated by a sodium-dependent phosphate co-transporter system. PMID:16476458

Muller, D; Houpert, P; Cambar, J; Heng-Napoli, M-H

2006-07-15

87

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

88

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

89

Europium (III) coordination complex with a novel phosphonated ligand  

NASA Astrophysics Data System (ADS)

An original Eu(III) complex with a phosphonated half-cage ligand (CCNPh) was synthesized and characterized. Coordination between Eu(III) and the selected ligand was investigated by FT-IR, 1H, 13C and 31P NMR spectroscopies. The stoichiometry of the Eu(III) complex in acetonitrile was determined by titrations using 1H, 31P NMR and photoluminescence. The 1M:2L stoichiometry, i.e. two CCNPh ligands for one Eu(III), has been measured. In contrast, the 1M:3L stoichiometry occurred in the solid state, from the elemental analysis. This particular behavior may be explained by the addition of a third CCNPh ligand to Eu(III) metallic core during the treatment and evaporation process for the obtention of the solid sample. An antenna effect has been observed consisting in the energy transfer from N-Ph (?exc = 276 nm) to Eu(III) (?em = 618 nm).

Villemin, E.; Elias, B.; Marchand-Brynaert, J.

2013-02-01

90

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

PubMed

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

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

2013-06-01

91

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

92

The first coordination complexes of selenones: a structural comparison with complexes of sulfones.  

PubMed

Reactivity of the two classes of very weak donors R(2)XO(2) (X = S, R = Me (1) and Ph (2); X = Se, R = Me (3) and Ph (4)) have been studied. Coordination properties of sulfones and selenones in solution and in the gas phase have been compared for the first time using a model bidentate metal complex, [Rh(2)(O(2)CCF(3))(4)]. Two coordination modes, bridging mu(2)-O,O' and terminal eta(1)-O, have been detected. These types of binding were realized in two series of sulfone and selenone metal complexes, polymeric mono-adducts [Rh(2)(O(2)CCF(3))(4).(R(2)XO(2))]( infinity ) (X = S, R = Me (1a); R = Ph (2a); X = Se, R = Ph (4a)) and discrete bis-adducts [Rh(2)(O(2)CCF(3))(4).(R(2)XO(2))(2)] (X = S, R = Ph (2b); X = Se, R = Me (3b)). The compositions and structures of new compounds have been confirmed by NMR and IR spectroscopy, chemical analyses, and X-ray diffraction studies. Compounds 3b and 4a are the first crystallographically characterized metal complexes having selenone ligands coordinated to the metal centers. Preparation and X-ray study of analogous metal complexes of sulfone and selenone ligands allow, for the first time, tracking the structural changes induced by metal coordination. In addition, the X-ray structure of dimethyl selenone, Me(2)SeO(2) (3), an analogue of Me(2)SO(2), has been determined. Geometries of coordinated sulfone and selenones ligands have been compared with those of the corresponding "free" molecules. PMID:14577777

Dikarev, Evgeny V; Becker, Renee Y; Block, Eric; Shan, Zhixing; Haltiwanger, R Curtis; Petrukhina, Marina A

2003-11-01

93

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

94

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

95

Coordinates  

NSDL National Science Digital Library

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

Stern, David

96

Synthesis and conformational study of a novel macrocyclic chiral(salen) ligand and its uranyl and Mn complexes.  

PubMed

A novel chiral macrocyclic ligand incorporating a chiral salen moiety into a framework containing two biphenyl units was synthesized. Structural properties and conformational aspects of the free ligand and an UO2 complex were studied by using NMR spectroscopy in solution and MM calculations. The Mn(III) complex was tested as catalyst in enantioselective oxidation of prochiral unfunctionalized olefins to the corresponding optically active epoxides under very mild conditions. PMID:20335992

Amato, Maria E; Ballistreri, Francesco P; Pappalardo, Andrea; Tomaselli, Gaetano A; Toscano, Rosa M

2010-03-01

97

Six-Coordinate Lanthanide Complexes: Slow Relaxation of Magnetization in the Dysprosium(III) Complex.  

PubMed

A series of six-coordinate lanthanide complexes {(H3 O)[Ln(NA)2 ]?H2 O}n (H2 NA=5-hydroxynicotinic acid; Ln=Gd(III) (1?Gd); Tb(III) (2?Tb); Dy(III) (3?Dy); Ho(III) (4?Ho)) have been synthesized from aqueous solution and fully characterized. Slow relaxation of the magnetization was observed in 3?Dy. To suppress the quantum tunneling of the magnetization, 3?Dy diluted by diamagnetic Y(III) ions was also synthesized and magnetically studied. Interesting butterfly-like hysteresis loops and an enhanced energy barrier for the slow relaxation of magnetization were observed in diluted 3?Dy. The energy barrier (?? ) and pre-exponential factor (?0 ) of the diluted 3?Dy are 75?K and 4.2110(-5) ?s, respectively. This work illustrates a successful way to obtain low-coordination-number lanthanide complexes by a framework approach to show single-ion-magnet-like behavior. PMID:25297951

Na, Bo; Zhang, Xue-Jing; Shi, Wei; Zhang, Yi-Quan; Wang, Bing-Wu; Gao, Chen; Gao, Song; Cheng, Peng

2014-11-24

98

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

PubMed

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

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

2012-04-28

99

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

100

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

101

DNA conformational analysis in solution by uranyl mediated photocleavage.  

PubMed Central

Uranyl mediated photocleavage of double stranded DNA is proposed as a general probing for DNA helix conformation in terms of minor groove width/electronegative potential. Specifically, it is found that A/T-tracts known to constitute strong distamycin binding sites are preferentially photocleaved by uranyl in a way indicating strongest uranyl binding at the center of the minor groove of the AT-region. The A-tracts of kinetoplast DNA show the highest reactivity at the 3'-end of the tract--as opposed to cleavage by EDTA/Fell--in accordance with the minor groove being more narrow at this end. Finally, uranyl photocleavage of the internal control region (ICR) of the 5S-RNA gene yields a cleavage modulation pattern fully compatible with that obtained by DNase I which also--in a more complex way--senses DNA minor groove width. Images PMID:2374711

Nielsen, P E; Mllegaard, N E; Jeppesen, C

1990-01-01

102

School nurses and care coordination for children with complex needs: an integrative review.  

PubMed

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 coordination of care within the school and between the school and service providing agencies. This integrative literature review provides a synthesis of published evidence identifying and describing the core concepts associated with the role of school nurses in providing care coordination/case management to students with complex needs. Six core essentials of nurse-provided care coordination were identified: collaboration, communication, care planning and the nursing process, continuous coordination, clinical expertise, and complementary components. Recommendations for improving care coordination were elucidated in the review. Analysis of the literature can help assure application of best practice methods for the coordination of care for students in the school setting. PMID:25266887

McClanahan, Rachel; Weismuller, Penny C

2015-02-01

103

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

SciTech Connect

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

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

2012-02-21

104

Detecting coordinated regulation of multi-protein complexes using logic analysis of gene expression  

Microsoft Academic Search

BACKGROUND: Many of the functional units in cells are multi-protein complexes such as RNA polymerase, the ribosome, and the proteasome. For such units to work together, one might expect a high level of regulation to enable co-appearance or repression of sets of complexes at the required time. However, this type of coordinated regulation between whole complexes is difficult to detect

Einat Sprinzak; Shawn J Cokus; Todd O Yeates; David Eisenberg; Matteo Pellegrini

2009-01-01

105

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 [UO2(NO3)x(H2O)yLz](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 [UO2(NO3)2L2] from the UO2(H2O)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 [UO2(NO3)2L2], [UO2(NO3)2(H2O)L2], and [UO2(NO3)(H2O)L2](+) 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-ONO3/U-OL bond distances observed in the gas phase (U-Onit < 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

2014-11-20

106

Towards Coordination Patterns for Complex Experimentations in Data Mining  

Microsoft Academic Search

In order to support the management of experimental activities\\u000ain a networked scientic community, the exploitation of serviceoriented\\u000aparadigm and technologies is a hot research topic in E-science.\\u000aIn particular, scientic workows can be modeled by resorting to the notion\\u000aof process. In this paper we present a preliminary study about the\\u000aexploitation of the formal coordination language Reo for

F. Arbab; Claudia Diamantini; Domenico Potena; Emanuele Storti

2010-01-01

107

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

108

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

109

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

MedlinePLUS

... 8428 INFO@VESTIBULAR.ORG WWW.VESTIBULAR.ORG The Human Balance System A Complex Coordination of Central and ... support. 1 A properly functioning balance system allows humans to see clearly while moving, identify orientation with ...

110

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

NASA Astrophysics Data System (ADS)

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

Alavi, Saman; Taghikhani, Mahdi

2012-06-01

111

Two-coordinate Fe? and Co? complexes supported by cyclic (alkyl)(amino)carbenes.  

PubMed

The CAAC [CAAC=cyclic (alkyl)(amino)carbene] family of carbene ligands have shown promise in stabilizing unusually low-coordination number transition-metal complexes in low formal oxidation states. Here we extend this narrative by demonstrating their utility in affording access to the first examples of two-coordinate formal Fe(0) and Co(0) [(CAAC)2M] complexes, prepared by reduction of their corresponding two-coordinate cationic Fe(I) and Co(I) precursors. The stability of these species arises from the strong ?-donating and ?-accepting properties of the supporting CAAC ligands, in addition to steric protection. PMID:24953342

Ung, Gal; Rittle, Jonathan; Soleilhavoup, Michele; Bertrand, Guy; Peters, Jonas C

2014-08-01

112

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

113

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

114

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

115

Uranyl incorporation in natural calcite.  

SciTech Connect

The occurrence of trace amounts of uranyl in natural calcite has posed a long-standing problem in crystal chemistry because of speculation that the size and shape of the uranyl ion may preclude its incorporation in a stable lattice position in calcite. This also defines an important environmental problem because of its bearing on the transport and sequestration of uranyl released from nuclear facilities and uranium mining operations. Calcite is a nearly ubiquitous mineral in soils and groundwater aquifers. X-ray absorption spectroscopy and X-ray fluorescence microprobe studies of uranium in relatively U-rich {approx}13700-year-old calcite from a speleothem in northernmost Italy indicate substitution of uranyl for a calcium and two adjacent carbonate ions in calcite. These new data imply that uranyl has a stable lattice position in natural calcite, indicating that it may be reliably sequestered in calcite over long time scales.

Kelly, S. D.; Newville, M. G.; Cheng, L.; Kemner, K. M.; Sutton, S. R.; Fenter, P.; Sturchio, N. C.; Spotl, C.; Environmental Research; Univ. of Chicago; Univ. of Illiois at Chicago; Univ. of Innsbruck

2003-01-01

116

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

E-print Network

Alkane Coordination Selectivity in Hydrocarbon Activation by [TpRh(CNneopentyl)]: The Role of Alkane Complexes Andrew J. Vetter, Christine Flaschenriem, and William D. Jones* Contribution from in many cases that activation of alkanes occurs through a two-step process: formation of a -alkane complex

Jones, William D.

117

Supramolecular coordination and antimicrobial activities of constructed mixed ligand complexes.  

PubMed

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

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

2013-03-01

118

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

119

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

120

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

121

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

122

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

123

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

SciTech Connect

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

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

2011-03-15

124

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

125

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

PubMed

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

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

2014-12-10

126

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

127

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

PubMed

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

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

2013-12-11

128

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

129

The structure of uranium (VI) sorption complexes on silica, alumina, and montmorillonite  

NASA Astrophysics Data System (ADS)

We have investigated the adsorption of the uranyl ion (UO 22+) in contact with amorphous silica (SiO 2), ?-alumina (Al 2O 3), and montmorillonite surfaces in the pH range of 3.1-6.5, using X-ray absorption fine structure (XAFS) spectroscopy to observe the local structure around the uranium atom. Analysis shows that in all samples the uranyl ion structure is preserved, with two axial oxygen atoms detected at ca. 1.8 . For the montmorillonite samples at low pH a single equatorial oxygen shell is observed at ca. 2.4 , with a coordination number of 6 1. At near-neutral pH (6.41) and high ion concentration (0.1 M NaCl), two separate equatorial shells are observed with bond lengths of ca. 2.30 and 2.48 . The samples of uranyl on silica and ?-alumina are all observed to have two separate equatorial shells with bond lengths of ca. 2.30 and 2.49 . A uranium shell at ca. 4.0 is observed in the near-neutral pH (6.5) samples of uranyl on silica and on ?-alumina. A silicon shell at ca. 3.10 is observed in the sample of uranyl on silica at pH 6.5. These results suggest that adsorption of the uranyl ion onto montmorillonite at low pH occurs via ion exchange, leaving the inner-sphere uranyl aquo-ion structure intact. At near-neutral pH and in the presence of a competing cation, inner-sphere complexation with the surface predominates. Adsorption of the uranyl onto the silica and ?-alumina surfaces appears to occur via an inner-sphere, bidentate complexation with the surface, with the formation of polynuclear surface complexes occurring at near-neutral pH.

Sylwester, E. R.; Hudson, E. A.; Allen, P. G.

2000-07-01

130

Fluorophore-linked zinc(II)dipicolylamine coordination complexes as sensors for  

E-print Network

Fluorophore-linked zinc(II)dipicolylamine coordination complexes as sensors for phosphatidylserine with an attached NBD fluorophore are synthesized and evaluated as fluorescent sensors. The sensors do not respond in the presence of anionic vesicles. A sensor with two Zn2C ­DPA units and a hydrophilic tris(ethyleneoxy) linker

Smith, Bradley D.

131

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

132

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

133

The human PAF complex coordinates transcription with events downstream of RNA synthesis.  

PubMed

The yeast PAF (yPAF) complex interacts with RNA polymerase II and coordinates the setting of histone marks associated with active transcription. We report the isolation and functional characterization of the human PAF (hPAF) complex. hPAF shares four subunits with yPAF (hCtr9, hPaf1, hLeo1, and hCdc73), but contains a novel higher eukaryotic-specific subunit, hSki8. RNAi against hSki8 or hCtr9 reduces the cellular levels of other hPAF subunits and of mono- and trimethylated H3-Lys 4 and dimethylated H3-Lys 79. The hSki8 subunit is also a component of the human SKI (hSKI) complex. Yeast SKI complex is cytoplasmic and together with Exosome mediates 3'-5' mRNA degradation. However, hSKI complex localizes to both nucleus and cytoplasm. Immunoprecipitation experiments revealed that hPAF and hSKI complexes interact, and ChIP experiments demonstrated that hSKI associates with transcriptionally active genes dependent on the presence of hPAF. Thus, in addition to coordinating events during transcription (initiation, promoter clearance, and elongation), hPAF also coordinates events in RNA quality control. PMID:16024656

Zhu, Bing; Mandal, Subhrangsu S; Pham, Anh-Dung; Zheng, Yong; Erdjument-Bromage, Hediye; Batra, Surinder K; Tempst, Paul; Reinberg, Danny

2005-07-15

134

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

135

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

136

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

137

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

PubMed

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. PMID:25375465

Iyer, Swami; Killingback, Timothy

2014-10-01

138

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

PubMed Central

Reaction of 1-adamantyl azide with iron(I) diketiminate precursors gives metastable but isolable imidoiron(III) complexes LFe=NAd (L = bulky ?-diketiminate ligand; Ad = 1-adamantyl). This paper addresses: (1) the spectroscopic and structural characterization of the Fe=N multiple bond in these interesting three-coordinate iron imido complexes, and (2) the mechanism through which the imido complexes form. The iron(III) imido complexes have been examined by 1H NMR and EPR spectroscopies and temperature-dependent magnetic susceptibility (SQUID), and structurally characterized by crystallography and/or X-ray absorption (EXAFS) measurements. These data show that the imido complexes have quartet ground states and short (1.68 0.01 ) iron-nitrogen bonds. The formation of the imido complexes proceeds through unobserved ironRN3 intermediates, which are indicated by QM/MM computations to be best described as iron(II) with an RN3 radical anion. The radical character on the organoazide bends its NNN linkage to enable easy N2 loss and imido complex formation. The product distribution between imidoiron(III) products and hexazene-bridged diiron(II) products is solvent-dependent, and the solvent dependence can be explained by coordination of certain solvents to the iron(I) precursor prior to interaction with the organoazide. PMID:20524625

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

2010-01-01

139

Multi-scale modelling of uranyl chloride solutions.  

PubMed

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 UO2 (2+)-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 UO2 (2+)-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. PMID:25591366

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

2015-01-14

140

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

141

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

142

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

NASA Astrophysics Data System (ADS)

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

Shoukry, Azza A.; Shoukry, Mohamed M.

2008-08-01

143

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

144

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

NASA Astrophysics Data System (ADS)

Two new hybrid compounds based on Keggin-type polyoxometalates: {[PMo 12O 40][Ni( Phen) 2(H 2O)] 2}K2OH - ( 1) and [Cd 2( Phen) 4Cl 2][HPW 12O 40]H 2O ( 2) ( Phen=1,10-phenanthroline), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Compound 1 exhibits a 1-D chain structure constructed from Pseudo-Keggin polyoxometalate bi-supported transition metal coordination complexes linked by K + ions. Compound 2 contains Pseudo-Keggin polyoxoanions [HPW 12O 40] 2- and novel metal-chloride-ligand coordination complexes [Cd 2( Phen) 4Cl 2] 2+.

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

2011-03-01

145

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

146

Anion-regulated assemblies of diverse CuII coordination complexes with a versatile tripyridyltriazole ligand  

NASA Astrophysics Data System (ADS)

In this work, a series of five CuII coordination complexes, {[Cu(L)(dca)(OAc)]?1.5H2O}n (1), [Cu(L)(dca)Br]2 (2), [Cu(L)(OAc)2]2 (3), [Cu(L)Cl2]2 (4), and [Cu(L)2(ClO4)2] (5), have been prepared with a novel tripyridyltriazole ligand 3,4-bis(2-pyridyl)-5-(3-pyridyl)-1,2,4-triazole (L) and different CuII sources. Single-crystal X-ray diffraction analysis reveals that these complexes show diverse 1-D (for 1), dimeric (for 2-4) and monomeric (for 5) coordination motifs, in which the L ligands exhibit different coordination fashions. These results obviously demonstrate that the structural assembly of complexes 1-5 can be exclusively dominated by the counter anions of metal salts and the auxiliary dicyanamide (dca) anion. Their thermal stabilities have also been investigated and discussed.

Wang, Fei-Fei; Guo, Wei; Jiang, Cheng-Hui; Guo, Ya-Mei

2013-08-01

147

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

PubMed Central

Flexible and asymmetric ligand L [L = 1-((pyridin-3-yl)methyl)-1H-benzotriazole], is used as a basic backbone to construct complicated metal-organic frameworks. Two new polymers, namely, [Ag2(L)2(NO3)2]n (1) and [Ag(L)(ClO4)]n (2), were synthesized and characterized by X-ray structure analysis and fluorescent spectroscopy. The complex 1 gives an S type double helical conformation, whereas complex 2 exhibits a 1D zigzag configuration. Different anions affect the silver coordination geometry and crystal packing topology. PMID:21339976

Chen, Peng; Lin, Jianhua

2011-01-01

148

The DREAM complex: master coordinator of cell cycle-dependent gene expression.  

PubMed

The dimerization partner, RB-like, E2F and multi-vulval class B (DREAM) complex provides a previously unsuspected unifying role in the cell cycle by directly linking p130, p107, E2F, BMYB and forkhead box protein M1. DREAM mediates gene repression during the G0 phase and coordinates periodic gene expression with peaks during the G1/S and G2/M phases. Perturbations in DREAM complex regulation shift the balance from quiescence towards proliferation and contribute to the increased mitotic gene expression levels that are frequently observed in cancers with a poor prognosis. PMID:23842645

Sadasivam, Subhashini; DeCaprio, James A

2013-08-01

149

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

150

Novel stable five-coordinate diorgano cobalt(III) complexes: Formation, structure, and reaction with carbon monoxide  

Microsoft Academic Search

A series of new five-coordinate acyl vinyl cobalt(III) complexes Co{?1-C(CCPh)CHPh}[C(O)CCO] L2(L=PMe3) (610) were prepared via formal insertion of diphenylbutadiyne into CoH function of mer-octahedral hydrido-acyl(phenolato)-cobalt(III) complexes. The complexes are diamagnetic. One square pyramidal structure of complex 6 was confirmed by X-ray diffraction analysis. These complexes are stable in solid state. In solution, six-coordinate acyl vinyl carbonyl cobalt(III) complex 11 is

Xiaoyan Li; Fengli Yu; Hongjian Sun; Haoqing Hou

2006-01-01

151

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

152

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.

153

The Cbp3Cbp6 complex coordinates cytochrome b synthesis with bc1 complex assembly in yeast mitochondria  

PubMed Central

Respiratory chain complexes in mitochondria are assembled from subunits derived from two genetic systems. For example, the bc1 complex consists of nine nuclear encoded subunits and the mitochondrially encoded subunit cytochrome b. We recently showed that the Cbp3Cbp6 complex has a dual function for biogenesis of cytochrome b: it is both required for efficient synthesis of cytochrome b and for protection of the newly synthesized protein from proteolysis. Here, we report that Cbp3Cbp6 also coordinates cytochrome b synthesis with bc1 complex assembly. We show that newly synthesized cytochrome b assembled through a series of four assembly intermediates. Blocking assembly at early and intermediate steps resulted in sequestration of Cbp3Cbp6 in a cytochrome bcontaining complex, thereby making Cbp3Cbp6 unavailable for cytochrome b synthesis and thus reducing overall cytochrome b levels. This feedback loop regulates protein synthesis at the inner mitochondrial membrane by directly monitoring the efficiency of bc1 complex assembly. PMID:23007649

Gruschke, Steffi; Rmpler, Katharina; Hildenbeutel, Markus; Kehrein, Kirsten; Khl, Inge; Bonnefoy, Nathalie

2012-01-01

154

Coordination geometry around copper in a Schiff-base trinuclear copper complex using EXAFS spectroscopy  

NASA Astrophysics Data System (ADS)

In the present investigation, we have studied extended X-ray absorption fine structure (EXAFS) spectra of a trinuclear Schiff-base copper complex tetraaqua-di-?3-(N-salicylidene-DL-glutamato)-tricopper(II)heptahydrate, [Cu3(C12H10NO5)2 (H2O)4]. 7H2O, in which three metal sites are present. One metal site is square-pyramidal (4+1) and other two similar metal sites are tetragonally distorted octahedral (4+2). EXAFS has been recorded at the K-edge of copper in the complex at the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. The analysis of EXAFS spectra of multinuclear metal complexes pose some problems due to the presence of many absorbing atoms, even when the absorbing atoms may be of the same element. Hence, using the available crystal structure of the complex, theoretical models have been generated for the different copper sites separately, which are then fitted to the experimental EXAFS data. The two coordination geometries around the copper sites have been determined. The contributions of the different copper sites to the experimental spectrum have been estimated. The structural parameters, which include bond-lengths, coordination numbers and thermal disorders, for the two types of copper sites have been reported. Further, copper has been found to be in +2 oxidation state at these metal sites.

Gaur, Abhijeet; Shrivastava, B. D.; Gaur, D. C.; Prasad, J.; Srivastava, K.; Jha, S. N.; Bhattacharyya, D.; Poswal, A.

2012-05-01

155

A new clover-shaped trinuclear uranium(VI) complex: Synthesis, structure and photoluminescence property  

Microsoft Academic Search

A new clover-shaped trinuclear uranium(VI) complex of the formula [(UO2)3(phen)3(?3-O)(?2-OH)2(NO2)]NO33DMFH2O (1) (phen = 1,10-phenanthroline, DMF = N,N?-dimethylformamide) was prepared by reaction of UO2(NO3)26H2O and phen under ultrasonic condition. X-ray single-crystal diffraction analysis shows that each U(VI) ion is in a seven-coordinated pentagonalbipyramidal environment, with two O atoms in axial positions forming a uranyl ion. Each uranyl ion in 1 is

Di Sun; Na Zhang; Qin-Juan Xu; Rong-Bin Huang; Lan-Sun Zheng

2010-01-01

156

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

SciTech Connect

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

Burns, C.J.

1987-10-01

157

Spectroscopic study on the reactions of bis-salophen with uranyl and then with fructose 1,6-bisphosphate and the analytical application.  

PubMed

The chelating reaction of bis-salophen with uranyl to form binuclear complex uranyl-bis-salophen (UBS) was studied by fluorescence spectroscopy. The coordination reaction of UBS with fructose 1,6-bisphosphate (F-1,6-BP) to form supramolecular polymer was then studied by resonance light scattering (RLS) spectroscopy. The reaction of bis-salophen with uranyl results in a remarkable enhancement of fluorescence intensity. The maximum emission wavelength of the fluorescence is at 471nm. The reaction of UBS with F-1,6-BP results in a remarkable enhancement of RLS intensity. The maximum scattering wavelength of the RLS is at 460nm. The two reactions were used to establish fluorescence method for the determination of uranium (VI) and RLS method for the determination of F-1,6-BP, respectively. Under optimum conditions, the linear ranges for the detection of uranium (VI) and F-1,6-BP are 0.003-0.35nmol/mL and 0.05-5.0nmol/mL, respectively. The detection limits are 0.0017nmol/mL and 0.020nmol/mL, respectively. The proposed fluorescence method has been successfully applied for the determination of uranium (VI) in environmental water samples with the recoveries of 97.0-104.0%. The proposed RLS method has also been successfully applied for the determination of F-1,6-BP in medicine injection samples with the recoveries of 98.5-102.3%. PMID:24394527

Shen, Xing; Liao, Lifu; Chen, Lin; He, Yunfei; Xu, Canhui; Xiao, Xilin; Lin, Yingwu; Nie, Changming

2014-04-01

158

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

159

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

PubMed

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

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

2013-07-01

160

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

PubMed

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

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

2011-07-01

161

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

162

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

163

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

164

TRLFS evidence for precipitation of uranyl phosphate on the surface of alumina: environmental implications.  

PubMed

We studied the ligand-enhanced sorption of uranyl ions (1-12 ?M) on ?-alumina colloids suspended in (and pre-equilibrated with) solutions at various concentrations of phosphate ions (P(T) = 0-900 ?M). A highly sensitive technique, time resolved laser-induced fluorescence spectroscopy (TRLFS), was used to examine the chemical speciation of uranyl sorbed at trace concentrations (0.4-4 ?mol Ug?). The suspensions with P(T) ? 100 ?M exhibited high uranyl adsorption, and a very high intensity of fluorescence that increased with the sorbed amounts of phosphate and uranyl. These samples exhibited similar spectral and temporal characteristics of fluorescence emission, evidencing a uniform speciation pattern and a single coordination environment for sorbed U, despite large variation in parameters such as aqueous uranyl speciation, U loading, and extent of coverage of alumina by secondary Al phosphates precipitating on the surface. The results pointed formation of surface precipitates of uranyl phosphates, which are characterized by high quantum yield, peak maxima at positions similar to those of U(VI) phosphate minerals and four lifetimes indicating distortions, in-homogeneities or varying number of water molecules in the lattice. The findings have major implications for our understanding of the mechanisms of immobilization of U at trace levels on surfaces of oxides submitted to phosphated solutions in soils with low pH. PMID:21469705

Del Nero, Mirella; Galindo, Catherine; Barillon, Rmi; Mad, Benoit

2011-05-01

165

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[double bond, length as m-dash]Ca-Cb-O-Cb-Ca[double bond, length as m-dash]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

166

Talking about the institutional complexity of the integrated rehabilitation systemthe importance of coordination  

PubMed Central

Rehabilitation in Finland is a good example of functions divided among several welfare sectors, such as health services and social services. The rehabilitation system in Finland is a complex one and there have been many efforts to create a coordinated entity. The purpose of this study is to open up a complex welfare system at the upper policy level and to understand the meaning of coordination at the level of service delivery. We shed light in particular on the national rehabilitation policy in Finland and how the policy has tried to overcome the negative effects of institutional complexity. In this study we used qualitative content analysis and frame analysis. As a result we identified four different welfare state frames with distinct features of policy problems, policy alternatives and institutional failure. The rehabilitation policy in Finland seems to be divided into different components which may cause problems at the level of service delivery and thus in the integration of services. Bringing these components together could at policy level enable a shared view of the rights of different population groups, effective management of integration at the level of service delivery and also an opportunity for change throughout the rehabilitation system. PMID:23687479

Miettinen, Sari; Ashorn, Ulla; Lehto, Juhani

2013-01-01

167

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

168

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

169

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

170

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

171

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

SciTech Connect

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

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

2008-10-03

172

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

PubMed

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

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

2013-11-01

173

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

PubMed

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

Zinovjev, Kirill; Tun, Iaki

2014-09-01

174

Modulation of amyloid-? aggregation by histidine-coordinating Cobalt(III) Schiff base complexes.  

PubMed

Oligomers of the A?42 peptide are significant neurotoxins linked to Alzheimer's disease (AD). Histidine (His) residues present at the N terminus of A?42 are believed to influence toxicity by either serving as metal-ion binding sites (which promote oligomerization and oxidative damage) or facilitating synaptic binding. Transition metal complexes that bind to these residues and modulate A? toxicity have emerged as therapeutic candidates. Cobalt(III) Schiff base complexes (Co-sb) were evaluated for their ability to interact with A? peptides. HPLC-MS, NMR, fluorescence, and DFT studies demonstrated that Co-sb complexes could interact with the His residues in a truncated A?16 peptide representing the A?42 N terminus. Coordination of Co-sb complexes altered the structure of A?42 peptides and promoted the formation of large soluble oligomers. Interestingly, this structural perturbation of A? correlated to reduced synaptic binding to hippocampal neurons. These results demonstrate the promise of Co-sb complexes in anti-AD therapeutic approaches. PMID:24961930

Heffern, Marie C; Velasco, Pauline T; Matosziuk, Lauren M; Coomes, Joseph L; Karras, Constantine; Ratner, Mark A; Klein, William L; Eckermann, Amanda L; Meade, Thomas J

2014-07-21

175

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

176

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

PubMed

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

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

2014-03-01

177

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

PubMed

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

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

2014-05-21

178

Merging of Healthy Motor Modules Predicts Reduced Locomotor Performance and Muscle Coordination Complexity Post-Stroke  

PubMed Central

Evidence suggests that the nervous system controls motor tasks using a low-dimensional modular organization of muscle activation. However, it is not clear if such an organization applies to coordination of human walking, nor how nervous system injury may alter the organization of motor modules and their biomechanical outputs. We first tested the hypothesis that muscle activation patterns during walking are produced through the variable activation of a small set of motor modules. In 20 healthy control subjects, EMG signals from eight leg muscles were measured across a range of walking speeds. Four motor modules identified through nonnegative matrix factorization were sufficient to account for variability of muscle activation from step to step and across speeds. Next, consistent with the clinical notion of abnormal limb flexion-extension synergies post-stroke, we tested the hypothesis that subjects with post-stroke hemiparesis would have altered motor modules, leading to impaired walking performance. In post-stroke subjects (n = 55), a less complex coordination pattern was shown. Fewer modules were needed to account for muscle activation during walking at preferred speed compared with controls. Fewer modules resulted from merging of the modules observed in healthy controls, suggesting reduced independence of neural control signals. The number of modules was correlated to preferred walking speed, speed modulation, step length asymmetry, and propulsive asymmetry. Our results suggest a common modular organization of muscle coordination underlying walking in both healthy and post-stroke subjects. Identification of motor modules may lead to new insight into impaired locomotor coordination and the underlying neural systems. PMID:20007501

Clark, David J.; Ting, Lena H.; Zajac, Felix E.; Neptune, Richard R.

2010-01-01

179

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

PubMed

The two-dimensional polymeric structures of the caesium complexes with the phenoxyacetic acid analogues (4-fluorophenoxy)acetic acid, (3-chloro-2-methylphenoxy)acetic acid and the herbicidally active (2,4-dichlorophenoxy)acetic acid (2,4-D), namely poly[[?5-(4-fluorophenoxy)acetato][?4-(4-fluorophenoxy)acetato]dicaesium], [Cs2(C8H6FO3)2]n, (I), poly[aqua[?5-(3-chloro-2-methylphenoxy)acetato]caesium], [Cs(C9H8ClO3)(H2O)]n, (II), and poly[[?7-(2,4-dichlorophenoxy)acetato][(2,4-dichlorphenoxy)acetic acid]caesium], [Cs(C8H5Cl2O3)(C8H6Cl2O3)]n, (III), are described. In (I), the Cs(+) cations of the two individual irregular coordination polyhedra in the asymmetric unit (one CsO7 and the other CsO8) are linked by bridging carboxylate O-atom donors from the two ligand molecules, both of which are involved in bidentate chelate Ocarboxy,Ophenoxy interactions, while only one has a bidentate carboxylate O,O'-chelate interaction. Polymeric extension is achieved through a number of carboxylate O-atom bridges, with a minimum 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

180

Spectrophotometric Determination of Uranium Through Uranyl\\/Azide System  

Microsoft Academic Search

An alternative method for the determination of uranium has been established by spectrophotometry. The procedure is based on the products of reaction between uranyl and azide ions (excess). This system furnishes yellowish complexes and the reaction was explored in water-acetonitrile medium (60% v\\/v), at 311 nm. The resulting solution has a good stability and precision of measurements about 0.4% (standard

D. R. do Carmo; J. F. de Andrade; O. M. Guimares

1995-01-01

181

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

182

Meeting the Needs of Children with Medical Complexity Using a Telehealth Advanced Practice Registered Nurse Care Coordination Model.  

PubMed

Effective care coordination is a key quality and safety strategy for populations with chronic conditions, including children with medical complexity (CMC). However, gaps remain in parent report of the need for care coordination help and receipt of care coordination help. New models must close this gap while maintaining family-centered focus. A three-armed randomized controlled trial conducted in an established medical home utilized an advanced practice registered nurse intervention based on Presler's model of clinic-based care coordination. The model supported families of CMC across settings using telephone only or telephone and video telehealth care coordination. Effectiveness was evaluated from many perspectives and this paper reports on a subset of outcomes that includes family-centered care (FCC), need for care coordination help and adequacy of care coordination help received. FCC at baseline and end of study showed no significant difference between groups. Median FCC scores of 18.0-20.0 across all groups indicated high FCC within the medical home. No significant differences were found in the need for care coordination help within or between groups and over time. No significant difference was found in the adequacy of help received between groups at baseline. However, this indicator increased significantly over time for both intervention groups. These findings suggest that in an established medical home with high levels of FCC, families of CMC have unmet needs for care coordination help that are addressed by the APRN telehealth care coordination model. PMID:25424455

Cady, Rhonda G; Erickson, Mary; Lunos, Scott; Finkelstein, Stanley M; Looman, Wendy; Celebreeze, Margaret; Garwick, Ann

2014-11-26

183

Density functional theory study of uranium(VI) aquo chloro complexes in aqueous solution.  

PubMed

Mixed uranyl aquo chloro complexes of the type [UO2(H2O)xCly]2-y (y = 1, 2, 3, 4; x + y = 4, 5) have been optimized at the BLYP, BP86, and B3LYP levels of density functional theory in vacuo and in a polarizable continuum modeling bulk water (PCM) and have been studied at the BLYP level with Car-Parrinello molecular dynamics (MD) simulations in the gas phase and in explicit aqueous solution. Free binding energies were evaluated from static PCM data and from pointwise thermodynamic integration involving constrained MD simulations in water. The computations reveal significant solvent effects on geometric and energetic parameters. Based on the comparison of PCM-optimized or MD-averaged uranyl-ligand bond distances with EXAFS-derived values, the transition between five- and four-coordination about uranyl is indicated to occur at a Cl content of y = 2 or 3. PMID:18269268

Bhl, Michael; Sieffert, Nicolas; Golubnychiy, Volodymyr; Wipff, Georges

2008-03-20

184

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

185

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

186

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

187

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

188

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

SciTech Connect

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

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

2005-12-08

189

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

PubMed

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

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

2012-05-15

190

Synthesis and structural characterization of five-coordinate aluminum complexes containing diarylamido diphosphine ligands.  

PubMed

A series of five-coordinate aluminum complexes supported by o-phenylene-derived amido diphosphine ligands, [N(o-C(6)H(4)PR(2))(2)](-) ([R-PNP](-); R = Ph, (i)Pr) and [N(o-C(6)H(4)PPh(2))(o-C(6)H(4)P(i)Pr(2))](-) ([Ph-PNP-(i)Pr](-)), have been prepared and structurally characterized. Alkane elimination reactions of trialkylaluminum with H[Ph-PNP] (1a), H[(i)Pr-PNP] (1b), and H[Ph-PNP-(i)Pr] (1c) in toluene at -35 degrees C respectively produced the corresponding dialkyl complexes [Ph-PNP]AlR(2), [(i)Pr-PNP]AlR(2), and [Ph-PNP-(i)Pr]AlR(2) (R = Me (2a-c), Et (3a-c), (i)Bu (4a-c)) in high isolated yield. The dihydride complexes [Ph-PNP]AlH(2) (6a), [(i)Pr- PNP]AlH(2) (6b), and [Ph-PNP-(i)Pr]AlH(2) (6c) were prepared in one-pot reactions of in situ prepared dichloride precursors (5a-c) with LiAlH(4) in THF at room temperature. X-ray diffraction studies of 2a-c, 3b-c, 5b, and 6b revealed a distorted trigonal-bipyramidal structure for these molecules in which the two phosphorus donors are mutually trans. The solution structures of these organoaluminum complexes were all characterized by (1)H, (13)C, and (31)P NMR spectroscopy. The NMR data are indicative of solution C(2) symmetry for [Ph-PNP](-) and [(i)Pr-PNP](-) complexes, whereas they are indicative of C(1) for [Ph-PNP-(i)Pr](-) derivatives. The (1)H NMR spectra of 3a-c and 4a-c revealed diastereotopy for the alpha-hydrogen atoms in these molecules. PMID:19400561

Lee, Pei-Ying; Liang, Lan-Chang

2009-06-15

191

Catalytic alcohol oxidation by an unsymmetrical 5-coordinate copper complex: electronic structure and mechanism.  

PubMed

Density functional theory reveals the detailed mechanism of alcohol oxidation by a model copper complex, Cu(II)L, L = cis-1-(3',5'-dimethoxy-benzylideneamino)-3,5-[2-hydroxy-(3',5'-di-tert-butyl)benzylideneimino]cyclohexane. Despite the obvious structural and functional parallels between the title compound and the enzyme galactose oxidase, the details of the catalytic pathway are fundamentally different. In the enzyme, coordination of the substrate produces an active form containing a Cu(II) centre and a tyrosyl radical, the latter being responsible for the abstraction of hydrogen from the substrate. In the model system, in marked contrast, the active form contains a Cu(II) centre, but the ligand radical character is localised on the substrate (alcoholate) oxygen, rather than the phenolate ligand. The result is a significantly higher barrier to hydrogen-atom abstraction compared to the enzyme itself. The origin of these significant differences is traced to the rigid nature of the pentadentate ligand, which resists changes in coordination number during the catalytic cycle. PMID:16357972

Zueva, Ekaterina; Walton, Paul H; McGrady, John E

2006-01-01

192

Coordinated Regulation of Polycomb Group Complexes through microRNAs in Cancer  

PubMed Central

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

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

2011-01-01

193

Synthesis, structure, and magnetic properties of two 1-D helical coordination polymeric Cu(II) complexes  

NASA Astrophysics Data System (ADS)

Two helical coordination polymeric copper(II) complexes bearing amino acid Schiff bases HL or HL', which are condensed from 2-hydroxy-1-naphthaldehyde with 2-aminobenzoic acid or L-valine, respectively, have been prepared and characterised by X-ray crystallography. In [CuL] n ( 1) the copper(II) atoms are bridged by syn- anti carboxylate groups giving infinite 1-D right-handed helical chains which are further connected by weak C-H⋯Cu interactions to build a 2-D network. While in [CuL'] n ( 2) the carboxylate group acts as a rare monatomic bridge to connect the adjacent copper(II) atoms leading to the formation of a left-handed helical chain. Magnetic susceptibility measurements indicate that 1 exhibits weak ferromagnetic interactions whereas an antiferromagnetic coupling is established for 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data.

Bian, He-Dong; Yang, Xiao-E.; Yu, Qing; Chen, Zi-Lu; Liang, Hong; Yan, Shi-Ping; Liao, Dai-Zheng

2008-01-01

194

Synthesis of neutral gold(III) pyrimidine-complexes and theoretical studies on the proton affinity of the coordinated ligands  

Microsoft Academic Search

The neutral gold(III) complexes AuCl3(pm) (pm=pyrimidine, 2-methylpyrimidine, 4-methylpyrimidine, 5-methylpyrimidine, 4,6-dimethylpyrimidine, 2-aminopyrimidine) have been synthesised and characterised. The proton affinity (PA) values of the free and coordinated N-heterocycles have been theoretically estimated on the basis of DFT calculations. The coordination to the AuCl3 metal fragment causes a strong lowering of the basicity of the residual protonation sites, with PA variations around

Marco Bortoluzzi; Bruno Pitteri

2010-01-01

195

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

196

Two-Coordinate Iron(I) Complex [Fe{N(SiMe3 )2 }2 ](-) : Synthesis, Properties, and Redox Activity.  

PubMed

First-row two-coordinate complexes are attracting much interest. Herein, we report the high-yield isolation of the linear two-coordinate iron(I) complex salt [K(L)][Fe{N(SiMe3 )2 }2 ] (L=18-crown-6 or crypt-222) through the reduction of either [Fe{N(SiMe3 )2 }2 ] or its three-coordinate phosphine adduct [Fe{N(SiMe3 )2 }2 (PCy3 )]. Detailed characterization is gained through X-ray diffraction, variable-temperature NMR spectroscopy, and magnetic susceptibility studies. One- and two-electron oxidation through reaction with I2 is further found to afford the corresponding iodo iron(II) and diiodo iron(III) complexes. PMID:25370700

Werncke, C Gunnar; Bunting, Philip C; Duhayon, Carine; Long, Jeffrey R; Bontemps, Sbastien; Sabo-Etienne, Sylviane

2015-01-01

197

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

PubMed

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

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

2009-04-01

198

Vibrational spectroscopy of mass-selected [UO2(ligand)n]2+ complexes in the gas phase: comparison with theory.  

PubMed

The gas-phase infrared spectra of discrete uranyl ([UO2]2+) complexes ligated with acetone and/or acetonitrile were used to evaluate systematic trends of ligation on the position of the O=U=O stretch and to enable rigorous comparison with the results of computational studies. Ionic uranyl complexes isolated in a Fourier transform ion cyclotron resonance mass spectrometer were fragmented via infrared multiphoton dissociation using a free electron laser scanned over the mid-IR wavelengths. The asymmetric O=U=O stretching frequency was measured at 1017 cm(-1) for [UO2(CH3COCH3)2]2+ and was systematically red shifted to 1000 and 988 cm(-1) by the addition of a third and fourth acetone ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. In contrast to the uranyl frequency shifts, the carbonyl frequencies of the acetone ligands were progressively blue shifted as the number of ligands increased from two to four and approached that of free acetone. This observation was consistent with the formation of weaker noncovalent bonds between uranium and the carbonyl oxygen as the extent of ligation increases. Similar trends were observed for [UO2(CH3CN)n]2+ complexes, although the uranyl asymmetric stretching frequencies were greater than those measured for acetone complexes having equivalent coordination, which is consistent with the fact that acetonitrile is a weaker nucleophile than is acetone. This conclusion was confirmed by the uranyl stretching frequencies measured for mixed acetone/acetonitrile complexes, which showed that substitution of one acetone for one acetonitrile produced a modest red shift of 3-6 cm(-1). PMID:16594717

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

2006-04-12

199

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

SciTech Connect

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

Gary S. Groenewold; Anita K. Gianotto

2006-03-01

200

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

201

Adsorption of uranyl on hydroxylated ?-SiO2(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

2014-12-23

202

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

203

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...

204

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

ERIC Educational Resources Information Center

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

Micera, G.; And Others

1984-01-01

205

Implementation of the external complex scaling method in spheroidal coordinates: Impact ionization of molecular hydrogen  

NASA Astrophysics Data System (ADS)

We develop an ab initio procedure based on the driven Schrdinger equation formalism and the external complex scaling method for the determination of the multifold differential cross sections of the single and double ionization of molecular hydrogen by single photon and fast electron impact. We take advantage of the separability of the two-center Schrodinger equation in prolate spheroidal coordinates in the numerical calculation of the two-electron two-center wave function of the initial and final states of the target. After having verified our procedure by reproducing existing confirmed triple differential cross sections of the (e,2e) ionization of H2 , we have extended our calculation to the double ionization of H2 . Our results on double photoionization agree with existing experimental results. We observe in the mean time a small difference with respect to the absolute results obtained by similar ab initio calculations using spherical bases. For the case of the double ionization by fast electron impact for which very few experimental results exist, our results confirm the existing disagreement between the theoretical results and the unique experimental one in the case of (e,3-1e) . This we think makes it clear that for (e,3e) the introduction of the higher terms of the Born series for mean energy electron-impact regime is necessary.

Serov, Vladislav V.; Joulakian, Boghos B.

2009-12-01

206

Coordination Sphere Tuning of the Electron Transfer Dissociation Behavior of Cu(II)-Peptide Complexes  

PubMed Central

In contrast to previous electron capture dissociation (ECD) studies, we find that electron transfer dissociation (ETD) of Cu(II)-peptide complexes can generate c- and z- type product ions when the peptide has a sufficient number of strongly coordinating residues. Double-resonance experiments, ion-molecule reactions, and collision-induced dissociation (CID) prove that the c and z product ions are formed via typical radical pathways without the associated reduction of Cu(II), despite the high second ionization energy of Cu. A positive correlation between the number of Cu(II) binding groups in the peptide sequence and the extent of c and z ion formation was also observed. This trend is rationalized by considering that the recombination energy of Cu(II) can be lowered by strong binding ligands to an extent that enables electron transfer to non-Cu sites (e.g. protonation sites) to compete with Cu(II) reduction, thereby generating c/z ions in a manner similar to that observed for protonated (i.e. non-metalated) peptides. PMID:22161629

Dong, Jia; Vachet, Richard W.

2011-01-01

207

Coordination Sphere Tuning of the Electron Transfer Dissociation Behavior of Cu(II)-Peptide Complexes  

NASA Astrophysics Data System (ADS)

In contrast to previous electron capture dissociation (ECD) studies, we find that electron transfer dissociation (ETD) of Cu(II)-peptide complexes can generate c- and z-type product ions when the peptide has a sufficient number of strongly coordinating residues. Double-resonance experiments, ion-molecule reactions, and collision-induced dissociation (CID) prove that the c and z product ions are formed via typical radical pathways without the associated reduction of Cu(II), despite the high second ionization energy of Cu. A positive correlation between the number of Cu(II) binding groups in the peptide sequence and the extent of c and z ion formation was also observed. This trend is rationalized by considering that the recombination energy of Cu(II) can be lowered by strong binding ligands to an extent that enables electron transfer to non-Cu sites (e.g., protonation sites) to compete with Cu(II) reduction, thereby generating c/z ions in a manner similar to that observed for protonated (i.e., nonmetalated) peptides.

Dong, Jia; Vachet, Richard W.

2012-02-01

208

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

PubMed Central

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

Chen, Miao; Gartenberg, Marc R.

2014-01-01

209

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

210

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

211

Macrocyclic ligands for uranium complexation. Final report, August 1, 1986March 31, 1993  

Microsoft Academic Search

Macrocycles, designed for complexation of the uranyl ion by computer modeling studies and utilizing six ligating atoms in the equatorial plane of the uranyl ions, have been prepared and their complexation of the uranyl ions evaluated. The ligating atoms, either oxygen or sulfur, were part of acylurea, biuret or thiobiuret subunits with alkane chains or pyridine units completing the macrocyclic

1993-01-01

212

Macrocyclic ligands for uranium complexation: Progress report, August 15, 1986January 28, 1989  

Microsoft Academic Search

Macrocycles, designed for complexation of the uranyl ion by computer modeling studies and utilizing six ligating atoms in the equatorial plane of the uranyl ion, have been prepared and their ability to complex the uranyl ion evaluated. The ligating atoms, either oxygen or sulfur, were part of acylurea, biuret or thiobiuret subunits with alkane chains or pyridine units completing the

1989-01-01

213

Synthesis, crystal structure and spectroscopic properties of a supramolecular zinc(II) complex with N2O2 coordination sphere.  

PubMed

A new hexa-coordinated zinc(II) complex, namely [ZnL(H2O)2]n, with N2O2 coordination sphere (H2L=4,4'-dibromo-6,6'-dichloro-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol) has been synthesized and structurally characterized by elemental analyses, IR, UV-vis spectra and TG-DTA analyses, etc. Crystallographic data are monoclinic, space group P2(1)/c, a=24.634(2), b=10.144(1), c=7.9351(6), ?=91.371(2), V=1982.4(3)(3), Dc=2.099 g/cm(3), Z=4. The zinc(II) complex exhibits a slightly distorted octahedral geometry with halogen-substituted Salen-type bisoxime forming the basal N2O2 coordination sphere and two oxygen atoms from two coordinated water molecules in the axial position. The hydrogen-bonding and ?-? stacking interactions have stabilized the zinc(II) complex molecules to form a self-assembling infinite dual metal-water chain-like structure with the nearest Zn?Zn distance of 4.954(4). PMID:24263129

Dong, Wen-Kui; Zhang, Li-Sha; Sun, Yin-Xia; Zhao, Meng-Meng; Li, Gang; Dong, Xiu-Yan

2014-01-01

214

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

215

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

216

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

PubMed Central

The terminal enzyme of the respiratory chain, cytochrome c oxidase, consists of a hydrophobic reaction center formed by three mitochondrially encoded subunits with which 910 nuclear encoded subunits are associated. The three core subunits are synthesized on mitochondrial ribosomes and inserted into the inner membrane in a co-translational reaction facilitated by the Oxa1 insertase. Oxa1 consists of an N-terminal insertase domain and a C-terminal ribosome-binding region. Mutants lacking the C-terminal region show specific defects in co-translational insertion, suggesting that the close contact of the ribosome with the insertase promotes co-translational insertion of nascent chains. In this study, we inserted flexible linkers of 100 or 200 amino acid residues between the insertase domain and ribosome-binding region of Oxa1 of Saccharomyces cerevisiae. In the absence of the ribosome receptor Mba1, these linkers caused a length-dependent decrease in mitochondrial respiratory activity caused by diminished levels of cytochrome c oxidase. Interestingly, considerable amounts of mitochondrial translation products were still integrated into the inner membrane in these linker mutants. However, they showed severe defects in later stages of the biogenesis process, presumably during assembly into functional complexes. Our observations suggest that the close proximity of Oxa1 to ribosomes is not only used to improve membrane insertion but is also critical for the productive assembly of the subunits of the cytochrome c oxidase. This points to a role for Oxa1 in the spatial coordination of the ribosome with assembly factors that are critical for enzyme biogenesis. PMID:22904327

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

2012-01-01

217

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

218

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

219

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

220

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

PubMed

In this study, we use solubility and drop-solution calorimetry measurements to determine the thermodynamic properties of the uranyl phosphate phases autunite, uranyl hydrogen phosphate, and uranyl orthophosphate. Conducting the solubility measurements from both supersaturated and undersaturated conditions and under different pH conditions rigorously demonstrates attainment of equilibrium and yields well-constrained solubility product values. We use the solubility data and the calorimetry data, respectively, to calculate standard-state Gibbs free energies of formation and standard-state enthalpies of formation for these uranyl phosphate phases. Combining these results allows us also to calculate the standard-state entropy of formation for each mineral phase. 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 to optimize and quantitatively assess the effect of phosphate amendment remediation technologies for uranium contaminated systems. PMID:19848155

Gorman-Lewis, Drew; Shvareva, Tatiana; Kubatko, Karrie-Ann; Burns, Peter C; Wellman, Dawn M; Mcnamara, Bruce; Szymanowski, Jennifer E S; Navrotsky, Alexandra; Fein, Jeremy B

2009-10-01

221

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

SciTech Connect

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

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

2006-03-01

222

Adsorption of uranyl species onto the rutile (110) surface: a periodic DFT study.  

PubMed

To model the structures of dissolved uranium contaminants adsorbed on mineral surfaces and further understand their interaction with geological surfaces in nature, we have performed periodic density funtional theory (DFT) calculations on the sorption of uranyl species onto the TiO(2) rutile (110) surface. Two kinds of surfaces, an ideal dry surface and a partially hydrated surface, were considered in this study. The uranyl dication was simulated as penta- or hexa-coordinated in the equatorial plane. Two bonds are contributed by surface bridging oxygen atoms and the remaining equatorial coordination is satisfied by H(2)O, OH(-), and CO(3)(2-) ligands; this is known to be the most stable sorption structure. Experimental structural parameters of the surface-[UO(2)(H(2)O)(3)](2+) system were well reproduced by our calculations. With respect to adsorbates, [UO(2)(L1)(x)(L2)(y)(L3)(z)](n) (L1=H(2)O, L2=OH(-), L3=CO(3)(2-), x?3, y?3, z?2, x+y+2z?4), on the ideal surface, the variation of ligands from H(2)O to OH(-) and CO(3)(2-) lengthens the U-O(surf) and U-Ti distances. As a result, the uranyl-surface interaction decreases, as is evident from the calculated sorption energies. Our calculations support the experimental observation that the sorptive capacity of TiO(2) decreases in the presence of carbonate ions. The stronger equatorial hydroxide and carbonate ligands around uranyl also result in U=O distances that are longer than those of aquouranyl species by 0.1-0.3 . Compared with the ideal surface, the hydrated surface introduces greater hydrogen bonding. This results in longer U=O bond lengths, shorter uranyl-surface separations in most cases, and stronger sorption interactions. PMID:22213421

Pan, Qing-Jiang; Odoh, Samuel O; Asaduzzaman, Abu Md; Schreckenbach, Georg

2012-01-27

223

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

224

Four-coordinate and pseudo five-coordinate Hg(II) complexes of a new bidentate phosphorus ylide: X-ray crystal structure and spectral characterization  

Microsoft Academic Search

The reaction of Ph2PCH2PPh2 (dppm) with BrCH2C(O)C6H4NO2 in chloroform produces the new phosphonium salt [Ph2PCH2PPh2CH2C(O)C6H4NO2]Br (1). Further, by reacting the phosphonium salt with appropriate base the bidentate phosphorus ylide, Ph2PCH2PPh2C(H)C(O)C6H4NO2 (2) was obtained. The reaction of ligand 2 with mercury(II) halides in dry methanol led to the formation of the P, C-coordinated mononuclear complexes [HgX2(Ph2PCH2PPh2C(H)C(O)C6H4NO2)] [X=Cl (3), Br (4), I

Seyyed Javad Sabounchei; Sepideh Samiee; Sadegh Salehzadeh; Zabihollah Bolboli Nojini; Elisabeth Irran

2010-01-01

225

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

226

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

E-print Network

forms of cooperation such as battle damage assessment or escort functions. To illustrate anticipated will depend on coordination of large teams. Automating an aircraft squadron, for example, would not only

Scerri, Paul

227

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

E-print Network

such as battle damage assessment or escort functions. To illustrate anticipated scales one scenario proposed on coordination of large teams. Automating an aircraft squadron, for example, would not only require automating

Lewis, Michael

228

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

229

Effects of task complexity on grip-to-load coordination in bimanual actions.  

PubMed

We investigated within- and between-hand grip and load force coordination in healthy young subjects during bimanual tasks involving realistic manual actions. Actions involving disparate actions of the two hands (bimanual asymmetry) were expected to result in lower overall measures of within- and between-hand measures of grip and load force coordination. As dissociation between two hands performing disparate actions may be expected, it was also hypothesized that increased task asymmetry would result in a shift toward higher within-hand force coordination. Features such as object rotation were found to reduce some, but not all indices of both within- and between-hand force coordination. The action of connecting two independent objects was associated with declines in all indices of within- and between-hand force coordination. Evidence of task-specific differences in force application timing and a trend toward within-hand grip-load coordination differences in the current data set suggest that individual hand specification emerges naturally in everyday bimanual prehension tasks, independent of the action role of the assigned to the dominant and non-dominant hands. PMID:23307159

Gorniak, Stacey L; Alberts, Jay L

2013-04-01

230

Nonrelativistic Compton scattering in Furry's picture. III. Kramers-Heisenberg transition amplitude by means of the complex-coordinate method  

NASA Astrophysics Data System (ADS)

The procedure for calculating the general Kramers-Heisenberg transition amplitude for scattering of light is presented. The procedure is based on L2 atomic structure calculations implemented within the framework of the complex-coordinate method, gives the transition amplitudes without explicit calculation of the final states, and includes the contribution from ? 2 terms, p? terms to second order, and interference terms between these scattering contributions.

Froelich, Piotr; Weyrich, Wolf

1986-08-01

231

Probing the competition among different coordination motifs in metal-ciprofloxacin complexes through IRMPD spectroscopy and DFT calculations.  

PubMed

The vibrational spectra of ciprofloxacin complexes with monovalent (Li(+), Na(+), K(+), Ag(+)) and polyvalent (Mg(2+), Al(3+)) metal ions are recorded in the range 1000-1900 cm(-1) by means of infrared multiple-photon dissociation (IRMPD) spectroscopy. The IRMPD spectra are analyzed and interpreted in the light of density functional theory (DFT)-based quantum chemical calculations in order to identify the possible structures present under our experimental conditions. For each metal-ciprofloxacin complex, four isomers are predicted, considering different chelation patterns. A good agreement is found between the measured IRMPD spectrum and the calculated absorption spectrum of the most stable isomer for each complex. Metal ion size and charge are found to drive the competition among the different coordination motifs: small size and high charge density metal ions prefer to coordinate the quinolone between the two carbonyl oxygen atoms, whereas large-size metal ions prefer the carboxylate group as a coordination site. In the latter case, an intramolecular hydrogen bond compensates the weaker interaction established by these cations. The role of the metal cation on the stabilization of ionic and nonionic structures of ciprofloxacin is also investigated. It is found that large-size metal ions preferentially stabilize charge separated motifs and that the increase of metal ion charge has a stabilizing effect on the zwitterionic form of ciprofloxacin. PMID:23252622

Piccirillo, Susanna; Ciavardini, Alessandra; Bodo, Enrico; Rondino, Flaminia; Scuderi, Debora; Steinmetz, Vincent; Paladini, Alessandra

2013-01-01

232

Redox Cycling of Copper-Amyloid ? 1-16 Peptide Complexes Is Highly Dependent on the Coordination Mode.  

PubMed

Copper (Cu)-amyloid ? (A?) interactions play a role in the etiology of Alzheimer's disease. This work presents a spectroscopic and electrochemical study of two physiologically relevant A?-Cu(II) complexes, as a function of pH and relative Cu-A?(1-16) concentrations. Our results reveal that these coordination modes display distinct redox behaviors and provide experimental evidence for the existence of an intermediate Cu(I) species. A mechanism for the redox cycling of these complexes is proposed, providing further insight into the redox relevance of A?-Cu interactions. PMID:25521160

Trujano-Ortiz, Lidia G; Gonzlez, Felipe J; Quintanar, Liliana

2015-01-01

233

Molecular orbital study of coordinated dioxygen. I. Structure and bonding of model monomeric Co(II) complexes  

NASA Astrophysics Data System (ADS)

The CNDOUHF type of MOLCAOSCP calculation is carried out for model systems of dioxygen fixation: O 2 CoCl 4L 2- complexes in which L = none and L = NH 3. A geometry variation is performed with respect to 5 internal coordinates describing the degrees of freedom of the CoO 2 group. The calculated geometry, spin densities and atomic charges agree with available data based on X-ray and ESR measurements of real dioxygen carriers. Structure and bonding of complexes are discussed in more detail.

Bo?a, R.

1980-08-01

234

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

PubMed

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

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

2013-11-13

235

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

236

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

237

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

SciTech Connect

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

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

2006-03-18

238

Reaction of the uranyl(VI) ion (UO(2)(2+)) with a triamidoamine ligand: preparation and structural characterization of a mixed-valent uranium(V/VI) oxo-imido dimer.  

PubMed

The synthesis and structural characterization of a mixed-valent uranium(V/VI) oxo-imido complex are reported. Reaction of the uranyl chloride complex [K(18-crown-6)](2)[UO(2)Cl(4)] (1) with the triamidoamine ligand Li(3)[N(CH(2)CH(2)NSiBu(t)Me(2))(3)] yields oxo-imido [K(18-crown-6)(Et(2)O)][UO(mu(2)-NuCH(2)CH(2)N(CH(2)CH(2)NSiBu(t)Me(2))(2))](2) (2) as the major isolated uranium product in moderate yield. The reaction that forms 2 involves activation of both the triamidoamine ligand and the uranyl dioxo unit of 1. An X-ray crystal structure determination of 2 reveals a dimeric complex in which the coordination geometry at each uranium center is that of a capped trigonal bipyramid. The multidentate triamidoamine ligand coordinates to uranium through the capping amine and two of the three pendant amido ligands, while the third pendant amido donor has been activated to generate a bridging imido ligand by loss of the silyl substituent. One of the uranyl oxo groups is retained as a terminal ligand to complete the coordination sphere for each uranium center. The oxo and imido nitrogen may be regarded as the axial ligands of the trigonal bipyramid, while the two amido ligands and the other imido donor occupy equatorial coordination sites. The central amine of the tripodal set serves as the capping ligand. Distortion of the axial O-U-N angle from 180 degrees emanates from the proximity of the capping amine and the bridging interaction to the other uranium center. The structure and bonding in 2 are assessed in the context of metal-ligand multiple bonding in high-valent actinide complexes. The possibility of valence averaging [5.5/5.5 vs 5.0/6.0] via delocalization or rapid intramolecular electron-transfer dynamics of the unpaired electron is also discussed in the context of crystallographic, spectroscopic (NMR, IR, Raman, and EPR), and electrochemical data. Crystal data for 2: triclinic space group P1 macro, a = 12.1144(6) A, b = 12.6084(6) A, c = 14.5072(7) A, alpha = 101.374(1) degrees, beta = 103.757(1) degrees, gamma = 109.340(1) degrees, z = 1, R1 = 0.0523, wR2 = 0.1359. PMID:11599946

Duval, P B; Burns, C J; Buschmann, W E; Clark, D L; Morris, D E; Scott, B L

2001-10-22

239

PAPER www.rsc.org/dalton | Dalton Transactions Structure and dimensionality of coordination complexes correlated to  

E-print Network

­organic frameworks (MOFs) based on coordination chemistry continues to be of great current interest to a variety studied of the hexadentate Schiff base ligand N,N¢-bis[2-{(salicylidenimine)amino}ethyl] piperazine (H2L of the reaction conditions or the presence of other co- ligands. In this regard, substituted piperazine-based

Li, Jing

240

RESOURCE MANAGEMENT IN COMPLEX SOCIO-TECHNICAL SYSTEMS: A MULTIAGENT COORDINATION FRAMEWORK  

E-print Network

Kropf£ and Brahim Chaib-draaÝ £ D´ep. d'informatique et de rech. op. Universit´e de Montr´eal Montr chaib@ift.ulaval.ca Keywords. Resource management, Multiagent systems, Coordination, Planning, Resource

Kropf, Peter

241

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

SciTech Connect

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

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

2009-01-15

242

Anion recognition by uranyl-salophen derivatives as probed by infrared multiple photon dissociation spectroscopy and ab initio modeling.  

PubMed

The vibrational features and molecular structures of complexes formed by a series of uranyl-salophen receptors with simple anions, such as Cl(-) , H(-) , and HCOO(-) , have been investigated in the gas phase. Spectra of the anionic complexes were studied in the $\\tilde \

Bodo, Enrico; Ciavardini, Alessandra; Dalla Cort, Antonella; Giannicchi, Ilaria; Yafteh Mihan, Francesco; Fornarini, Simonetta; Vasile, Silvana; Scuderi, Debora; Piccirillo, Susanna

2014-09-01

243

Making oxidation potentials predictable: coordination of additives applied to the electronic fine tuning of an iron(II) complex.  

PubMed

This work examines the impact of axially coordinating additives on the electronic structure of a bioinspired octahedral low-spin iron(II) N-heterocyclic carbene (Fe-NHC) complex. Bearing two labile trans-acetonitrile ligands, the Fe-NHC complex, which is also an excellent oxidation catalyst, is prone to axial ligand exchange. Phosphine- and pyridine-based additives are used for substitution of the acetonitrile ligands. On the basis of the resulting defined complexes, predictability of the oxidation potentials is demonstrated, based on a correlation between cyclic voltammetry experiments and density functional theory calculated molecular orbital energies. Fundamental insights into changes of the electronic properties upon axial ligand exchange and the impact on related attributes will finally lead to target-oriented manipulation of the electronic properties and consequently to the effective tuning of the reactivity of bioinspired systems. PMID:25333790

Haslinger, Stefan; Kck, Jens W; Hahn, Eva M; Cokoja, Mirza; Pthig, Alexander; Basset, Jean-Marie; Khn, Fritz E

2014-11-01

244

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

PubMed Central

A starch-urea-based biodegradable coordination polymer modified by transition metal Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) was prepared by polycondensation of starch and urea. All the synthesized polymeric compounds were characterized by Fourier transform-infrared spectroscopy (FT-IR), 1H-NMR spectroscopy, 13C-NMR spectroscopy, UV-visible spectra, magnetic moment measurements, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). The results of electronic spectra and magnetic moment measurements indicate that Mn(II), Co(II), and Ni(II) complexes show octahedral geometry, while Cu(II) and Zn(II) complexes show square planar and tetrahedral geometry, respectively. The thermogravimetric analysis revealed that all the polymeric metal complexes are more thermally stable than the parental ligand. In addition, biodegradable studies of all the polymeric compounds were also carried out through ASTM standards of biodegradable polymers by CO2 evolution method. PMID:20414461

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

2010-01-01

245

Synthesis, characterization, and DFT studies of thione and selone Cu(I) complexes with variable coordination geometries.  

PubMed

Coordination of Cu(I) halides with N,N'-dimethylimidazole selone (dmise) and thione (dmit) ligands was examined by treating CuX (X = Cl, Br, I) with one or two equivalents of dmise or dmit. The reaction of CuI and CuBr with one molar equivalent of dmise results in unusual selenium-bridged tetrameric Cu(4)(?-dmise)(4)(?-X)(2)X(2) copper complexes with average Cu-Se bond lengths of 2.42 and a Cu(2)(?-X)(2) core (X = I (1) or Br (6)) that's in a rhomboidal structure. The reaction of CuX (X = Cl, Br, and I) with two equivalents of dmit or dmise results in trigonal planar Cu(I) complexes of two different conformations with the formula Cu(dmit)(2)X (3a, 3b, 4, and 7) or Cu(dmise)(2)X (2, 5, and 8) with average Cu-S and Cu-Se bond lengths of 2.23 and 2.34 , respectively. The coordination geometry around the copper center in complexes 1 to 8 is determined by the type of halide and chalcogenone ligand used, intramolecular ?-? interactions, and short contact interactions between X-H (X = I, Br, Cl, Se or S). The theoretical DFT calculations are in good agreement with experimental X-ray structural data and indicate that dmise ligands are required for formation of the tetrameric complexes 1 and 6. Electrochemical studies show that the trigonal copper selone complexes have more negative potentials relative to analogous copper thione complexes by an average of 108 mV. PMID:21384035

Kimani, Martin M; Bayse, Craig A; Brumaghim, Julia L

2011-04-14

246

Tetradentate vs pentadentate coordination in copper(II) complexes of pyridylbis(aminophenol) ligands depends on nucleophilicity of phenol donors.  

PubMed

The ligand binding preferences of a series of potentially pentadentate pyridylbis(aminophenol) ligands were explored. In addition to the previously reported ligands 2,2'-(2-methyl-2-(pyridin-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)diphenol (H(2)L(1)) and 6,6'-(2-methyl-2-(pyridin-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)bis(2,4-di-tert-butylphenol) (H(2)L(1-tBu)), four new ligands were synthesized: 6,6'-(2-methyl-2(pyridine-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)bis(2,4-dibromophenol) (H(2)L(1-Br)), 6,6'-(2-methyl-2(pyridine-2-yl)propane-1,3diyl)bis(azanediyl)bis(methylene)bis(2-methoxyphenol) (H(2)L(1-MeO)), 2,2'-(2-methyl-2(pyridine-2-yl)propane-1,3diyl)bis(azanediyl)bis(methylene)bis(4-nitrophenol) (H(2)L(1-NO2)), and 2,2'-(2-phenylpropane-1,3-diyl)bis(azanediyl)bis(methylene)diphenol (H(2)L(2)). These ligands, when combined with copper(II) salts and base, form either tricopper(II) species or monocopper(II) species depending on the nucleophilicity of the phenol groups in the ligands. All copper complexes were characterized by X-ray crystallography, cyclic voltammetry, and spectroscopic methods in solution. The ligands in trimeric complexes [{CuL(1)(CH(3)CN)}(2)Cu](ClO(4))(2) (1), [{CuL(1)Cl}(2)Cu] (1a), and [{CuL(2)(CH(3)CN)}(2)Cu](ClO(4))(2) (1b) and monomeric complex [CuL(1-tBu)(CH(3)OH)] (2) coordinate in a tetradentate mode via the amine N atoms and the phenolato O atoms. The pyridyl groups in 1, 1a, and 2 do not coordinate, but instead are involved in hydrogen bonding. Monomeric complexes [CuL(1-Br)] (3a), [CuL(1-NO2)] (3b), and [CuL(1-MeO)Na(CH(3)OH)(2)]ClO(4) (3c) have their ligands coordinated in a pentadentate mode via the amine N atoms, the phenolato O atoms, and the pyridyl N atom. The differences in tetradentate vs pentadentate coordination preferences of the ligands correlate to the nucleophilicity of the phenolate donor groups, and coincide with the electrochemical trends for these complexes. PMID:22007639

Shakya, Rajendra; Wang, Zhaodong; Powell, Douglas R; Houser, Robert P

2011-11-21

247

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

248

Uranium-ligand multiple bonding in uranyl analogues, [L?U?L]n+, and the inverse trans influence.  

PubMed

The societal importance of uranium complexes containing the uranyl moiety [O?U?O](2+) continues to grow with the ongoing international nuclear enterprise and associated accumulating legacy waste. Further studies of the electronic structure of uranyl and its analogues are imperative for the development of crucial technologies, including lanthanide/actinide extractants and chemical and environmental remediation methodologies. Actinide oxo halides are a subset of the growing class of actinyl (uranyl) analogues. The understanding of their electronic structures links the detailed spectroscopic studies of uranyl, indicating the role of the pseudocore 6p orbitals in U-O bonding, to hypotheses about the 6p orbitals' role in the chemical bonding of uranyl analogues. These actinide oxo halides are a very small class of actinide compounds that present the inverse trans influence (ITI). This class of complexes was, until recently, limited to two crystallographically characterized compounds, namely, [UCl(5)O][PPh(4)] and [PaCl(5)O][NEt(4)](2). These complexes are important because they give a readily and clearly defined experimental observable: the difference between the M-X(trans) and M-X(cis) (here X = Cl) bond lengths in the solid state. This bond metric is a sensitive probe for the role of 6p, 6d, and 5f orbitals, as well as electrostatic interactions, in determining their electronic structure. This Viewpoint Article reviews the theoretical, experimental, and synthetic work on the ITI in actinide complexes and contextualizes it within broader studies on the electronic structure of uranyl and its analogues. Furthermore, our recent work on the ITI in high-valent uranium(V/VI) oxo and imido complexes is described as a whole. This work builds on the extant synthetic literature on the ITI and provides design parameters for the synthesis and characterization of high-valent uranium-ligand multiple bonds. PMID:23234428

La Pierre, Henry S; Meyer, Karsten

2013-01-18

249

Coordinated Beamforming for MISO Interference Channel: Complexity Analysis and Efficient Algorithms  

Microsoft Academic Search

In a cellular wireless system, users located at cell edges often suffer significant out-of-cell interference. Assuming each base station is equipped with multiple antennas, we can model this scenario as a multiple-input single-output (MISO) interference channel. In this paper we consider a coordinated beamforming approach whereby multiple base stations jointly optimize their downlink beamforming vectors in order to simul- taneously

Ya-Feng Liu; Yu-Hong Dai; Zhi-Quan Luo

2011-01-01

250

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

PubMed Central

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

Abou-Hussein, Azza A.; Linert, Wolfgang

2014-01-01

251

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

PubMed

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

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

2014-04-01

252

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

253

Dance choreography is coordinated with song repertoire in a complex avian display.  

PubMed

All human cultures have music and dance, and the two activities are so closely integrated that many languages use just one word to describe both. Recent research points to a deep cognitive connection between music and dance-like movements in humans, fueling speculation that music and dance have coevolved and prompting the need for studies of audiovisual displays in other animals. However, little is known about how nonhuman animals integrate acoustic and movement display components. One striking property of human displays is that performers coordinate dance with music by matching types of dance movements with types of music, as when dancers waltz to waltz music. Here, we show that a bird also temporally coordinates a repertoire of song types with a repertoire of dance-like movements. During displays, male superb lyrebirds (Menura novaehollandiae) sing four different song types, matching each with a unique set of movements and delivering song and dance types in a predictable sequence. Crucially, display movements are both unnecessary for the production of sound and voluntary, because males sometimes sing without dancing. Thus, the coordination of independently produced repertoires of acoustic and movement signals is not a uniquely human trait. PMID:23746637

Dalziell, Anastasia H; Peters, Richard A; Cockburn, Andrew; Dorland, Alexandra D; Maisey, Alex C; Magrath, Robert D

2013-06-17

254

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

PubMed Central

The syntheses and characterization of several complexes of Mn(II) with cyclen derivatives having variable numbers of pendant N-acetic acid or N-acetamide arms are reported. X-ray crystallographic results are presented for Mn(DOTAM)Cl22H2O (monoclinic C2/c, a=18.5798(15), b=13.6006(11), c=10.5800(8) , ?=110.490(1), Z=4), [Mn(DO3AM)][MnCl4]EtOH (monoclinic P21/n, a=8.366(8), b=19.483(2), c=16.3627(16) , ?=99.254(2), Z=4), and Mn(H2DOTA) (monoclinic C2/c, a=16.374(3), b=6.6559(13), c=16.750(3) , ?=98.381(3), Z=4), which exhibit 8-, 7-, and 6-coordinate Mn(II), respectively. 1H relaxivity data in water at 20 MHz and 37C is presented and interpreted in terms of a mechanism involving transient binding of water in an associative intermediate. Relaxivity studies in mixed water/methanol solvents are consistent with this interpretation. PMID:19072697

Wang, Sen; Westmoreland, T. David

2009-01-01

255

Ab initio study of high-lying doubly excited states of helium in static electric fields: Complex-scaling generalized pseudospectral method in hyperspherical coordinates  

E-print Network

We present a complex-scaling (CS) generalized pseudospectral (GPS) method in hyperspherical coordinates (HSC) for ab initio and accurate treatment of the resonance energies and autoionization widths of two-electron atomic systems in the presence...

Chu, Shih-I; Heslar, John

2012-09-21

256

Unexpectedly Strong Magnetic Anisotropy in a Mononuclear Eight-Coordinate Cobalt(II) Complex: a Theoretical Exploration.  

PubMed

Ab initio methods have been used to explore the unexpectedly strong magnetic anisotropy and the magnetostructural correlations in mononuclear eight-coordinate complex [Co(II)(12-crown-4)2](2+). Our calculations showed that both decreasing ? and increasing ? may enhance its magnetic anisotropy, which was rationalized by the qualitative theory proposed by Long and co-workers. Moreover, we deduced that the |D| value of [Co(II)(12-crown-4)2](2+) with ? = 52 and ? = 43 is the largest one. PMID:25614998

Wei, Jin-Mei; Zhang, Yi-Quan

2015-02-16

257

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

Microsoft Academic Search

The aim of this study was the development of 99mTc labeled bis(zinc(II)dipicolylamine) (Zn2+DPA) coordination complexes, and the in vivo evaluation of their usefulness as radiotracers for the detection of cell death. DPA ligand 1 was labeled with 99mTc via the 99mTc-tricarbonyl core ([99mTc(CO)3-1]3+) or via HYNIC (99mTc-HYNIC-1) in good radiochemical yields. Highest in vitro stabilities were demonstrated for [99mTc(CO)3-1]3+. A

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

2011-01-01

258

Anion coordination complex [Cl?Pt(bpt) 4 ]Cl (bpt= N , N ?-bis(3-pyridylmethyl)-2-thiourea)  

Microsoft Academic Search

The anion coordination complex, [Cl?Pt(bpt)4]Cl (bpt=N,N?-bis(3-pyridylmethyl)-2-thiourea), was synthesized and studied by X-ray crystal structure analysis, NMR and FAB mass spectra.\\u000a In the solid state, the Pt(bpt)4 anion receptor adopts a cone conformation to bind the chloride anion through hydrogen bonds and electrostatic interaction\\u000a in which the four branches of the thiourea ligands bind the chloride anion to form N-H?Cl? hydrogen

Xin Li; Hui Li; ShuYan Yu; YiZhi Li

2009-01-01

259

Solid-state dynamics of uranyl polyoxometalates.  

PubMed

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

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

2014-07-01

260

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

261

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

PubMed

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

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

2014-05-21

262

Variable coordination mode of chloranilic acid. Synthesis, structure, and electrochemical properties of some osmium complexes.  

PubMed

Reaction of chloranilic acid (H2ca) with [Os(bpy)2 Br2] (bpy = 2,2'-bipyridine) affords a dinuclear complex of type [{Os(bpy)2}2 (ca)]2+, isolated as the perchlorate salt. A similar reaction of H2ca with [Os(PPh3)2 (pap)Br2] (pap = 2-(phenylazo)pyridine) affords a dinuclear complex of type [{Os(PPh3)2 (pap)}2 (ca)]2+ (isolated as the perchlorate salt) and a mononuclear complex of type [Os(PPh3)2 (pap)(ca)]. Reaction of H2ca with [Os(PPh3)2(CO)2(HCOO)2] gives a dinuclear complex of type [{Os(PPh3)2(CO)2}2 (r-ca)], where r-ca is the two electron reduced form of the chloranilate ligand. The structures of the [{Os(PPh3)2 (pap)}2 (ca)](ClO4)2, [Os(PPh3)2 (pap)(ca)], and [{Os(PPh3)2(CO)2}2 (r-ca)] complexes have been determined by X-ray crystallography. In the [{Os(bpy)2}2 (ca)]2+ and [{Os(PPh3)2 (pap)}2 (ca)]2+ complexes, the chloranilate dianion is serving as a tetradentate bridging ligand. In the [Os(PPh3)2 (pap)(ca)] complex, the chloranilate dianion is serving as a bidentate chelating ligand. In the [{Os(PPh3)2(CO)2}2 (r-ca)] complex, the reduced form of the chloranilate ligand (r-ca(4-)) is serving as a tetradentate bridging ligand. All the four complexes are diamagnetic and show intense metal-to-ligand charge-transfer transitions in the visible region. The [Os(PPh3)2 (pap)(ca)] complex shows an Os(II)-Os(III) oxidation, followed by an Os(III)-Os(IV) oxidation on the positive side of a standard calomel electrode. The three dinuclear complexes show two successive oxidations on the positive side of SCE. The mixed-valent Os(II)-Os(III) species have been generated in the case of the two chloranilate-bridged complexes by coulometric oxidation of the homovalent Os(II)-Os(II) species. The mixed-valent Os(II)-Os(III) species show intense intervalence charge-transfer transitions in the near-IR region. PMID:15762736

Gupta, Parna; Das, Anindya; Basuli, Falguni; Castineiras, Alfonso; Sheldrick, William S; Mayer-Figge, Heike; Bhattacharya, Samaresh

2005-03-21

263

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

264

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

265

The S. Cerevisiae HAP Complex, a Key Regulator of Mitochondrial Function, Coordinates Nuclear and Mitochondrial Gene Expression  

PubMed Central

We have compared Saccharomyces cerevisiae global gene expression in wild-type and mutants (?hap2 and ?hap4) of the HAP transcriptional complex, which has been shown to be necessary for growth on respiratory substrates. Several hundred ORFs are under positive or negative control of this complex and we analyse here in detail the effect of HAP on mitochondria. We found that most of the genes upregulated in the wild-type strain were involved in organelle functions, but practically none of the downregulated ones. Nuclear genes encoding the different subunits of the respiratory chain complexes figure in the genes more expressed in the wild-type than in the mutants, as expected, but in this group we also found key components of the mitochondrial translation apparatus. This control of mitochondrial translation may be one of the means of coordinating mitochondrial and nuclear gene expression in elaborating the respiratory chain. In addition, HAP controls the nuclear genes involved in several other mitochondrial processes (import, mitochondrial division) that define the metabolic state of the cell, but not mitochondrial DNA replication and transcription. In most cases, a putative CCAAT-binding site is present upstream of the ORF, while in others no such sites are present, suggesting the control to be indirect. The large number of genes regulated by the HAP complex, as well as the fact that HAP also regulates some putative transcriptional activators of unknown function, place this complex at a hierarchically high position in the global transcriptional regulation of the cell. PMID:18629096

Buschlen, S.; Amillet, J-M; Guiard, B.; Fournier, A.; Marcireau, C.

2003-01-01

266

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

SciTech Connect

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

Rao, Linfeng; Tian, Guoxin

2008-12-10

267

Coordinate MicroRNA-Mediated Regulation of Protein Complexes in Prostate Cancer  

PubMed Central

MicroRNAs are a class of small non-coding regulatory RNA molecules that regulate mRNAs post-transcriptionally. Recent evidence has shown that miRNAs target entire functionally related proteins such as protein complexes and biological pathways. However, characterizing the influence of miRNAs on genes whose encoded proteins are part of protein complexes has not been studied in the context of disease. We propose an entropy-based framework to identify miRNA-mediated dysregulation of functionally related proteins during prostate cancer progression. The proposed framework uses experimentally verified miRNA-target interactions, functionally related proteins and expression data to identify miRNA-influenced protein complexes in prostate cancer, and identify genes that are dysregulated as a result. The framework constructs correlation matrixes between functionally related proteins and miRNAs that have targets in the complex, and assesses the changes in the Shannon entropy of the modules across different stages of prostate cancer. Results reveal that SMAD4 and HDAC containing protein complexes are highly affected and disrupted by miRNAs, particularly miRNA-1 and miRNA-16. Using biological pathways to define functionally related proteins reveals that NF-kB-, RAS-, and Syndecan-mediated pathways are dysregulated due to miRNA-1- and miRNA-16-mediated regulation. These results suggest that miRNA-1 and miRNA-16 are important master regulators of miRNA-mediated regulation in prostate cancer. Moreover, results reveal that miRNAs with high-influence on the disrupted protein complexes are diagnostic and prognostic biomarker candidates for prostate cancer progression. The observation of miRNA-mediated protein complex regulation and miRNA-mediated pathway regulation, with partial experimental verification from previous studies, demonstrates that our framework is a promising approach for the identification of novel miRNAs and protein complexes related to disease progression. PMID:24391925

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

2013-01-01

268

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

269

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

PubMed Central

The aim of this study was the development of 99mTc labeled bis(zinc(II)-dipicolylamine) (Zn2+-DPA) coordination complexes, and the in vivo evaluation of their usefulness as radiotracers for the detection of cell death. DPA ligand 1 was labeled with 99mTc via the 99mTc-tricarbonyl core ([99mTc(CO)3-1]3+) or via HYNIC (99mTc-HYNIC-1) in good radiochemical yields. Highest in vitro stabilities were demonstrated for [99mTc(CO)3-1]3+. A mouse model of hepatic apoptosis (anti-Fas mAb) was used to demonstrate binding to apoptotic cells. 99mTc-HYNIC-1 showed the best targeting of apoptotic hepatic tissue with a 2.2 times higher liver uptake in anti-Fas treated mice as compared to healthy animals. A rat model of ischemia-reperfusion injury was used to further explore the ability of the 99mTc-labeled Zn2+-DPA coordination complexes to target cell death. Selective accumulation could be detected for both tracers in the area at risk, correlating with histological proof of cell death. Area at risk to normal tissue uptake ratios were 3.82 for [99mTc(CO)3-1]3+ and 5.45 for 99mTc-HYNIC-1. PMID:21570306

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

2011-01-01

270

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

271

Nonrelativistic Compton scattering in Furry's picture. II. Bethe surface by means of the complex-coordinate method  

NASA Astrophysics Data System (ADS)

Bethe surface as a means of characterizing the inelastic scattering of photons and electrons on atomic targets is discussed, and framed within the two-potential Furry's picture of scattering theory. In particular, the cross section for inelastic photon scattering is considered, and its first distorted Born approximation is identified to be given in terms of Bethe surface along the path conserving energy and momentum transfer. The difficulties in obtaining accurate cross sections in situations where the energy transfer is close to the ionization threshold are indicated, and related to the so-called Compton defect. The method for calculating the inelastic photon scattering cross section, introduced in Part I of this work [J. Chem. Phys. 80, 5669 (1984)] is summarized. The scattering cross section, and the entire Bethe surface, is obtained by means of the L2 discretization of the continuum and implemented in terms of the complex-coordinate method, without explicit calculation of the final scattering waves. The method is tested for the case of photon scattering off the hydrogen atom. The results are encouraging, and may be relevant for applications of the complex-coordinate method to calculations of more general transition amplitudes. The method is predicted to be most useful in cases close to ionization threshold (e.g., appearance edges in Compton scattering, Compton defect). Although applied to the one-electron problem the procedure is readily applicable to many electron atoms.

Froelich, Piotr; Flores-Riveros, A.; Weyrich, W.

1985-03-01

272

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

NASA Astrophysics Data System (ADS)

A novel series of nickel(II) polymer complexes of 5-sulphadiazineazo-3-phenylamino-2-thio-4-thiazolidinone (HL 1), 5-sulphamethazine-3-phenylamino-2-thioxo-4-thiazolidinone (HL 2), 5-sulphamethoxazole-3-phenylamino-2-thioxo-4-thiazolidinone (HL 3), 5-sulphacetamide-3-phenyl-2-thioxo-4-thiazolidinone (HL 4) and 5-sulphaguanidine-3-phenylamino-2-thioxo-4-thiazolidinone (HL 5) 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 3(HL n) 2(?-OAc) 2(OAc) 4] 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, 1H 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.

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

2010-11-01

273

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

274

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

NASA Astrophysics Data System (ADS)

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

Alston, Jeffrey Resing

275

Some new Ni?Zn heterodinuclear complexes: square-pyramidal nickel(II) coordination  

Microsoft Academic Search

A new series of heterodinuclear nickel(II)?zinc(II) complexes, [NiLZnCl24-picoline] (1), [NiLDMZnCl24-picoline] (2), [NiLZnBr24-picoline] (3), [NiLDMZnBr24-picoline] (4), [NiLDMZnBr23-picoline] (5), [NiLDMZnBr23,5-lutidine] (6) and [NiLZnI24-picoline] (7), where L is N,N?-bis(salicylidene)-1,3-diaminopropane dianion and LDM is N,N?-bis(salicylidene)-2,2?-dimethyl-1,3-diaminopropane dianion, were prepared. The complexes were characterized by elemental analysis, thermogravimetric analysis and IR spectroscopy. X-ray crystallographic analysis of complexes 1, 2 and 4 revealed that nickel(II) ion in

Orhan Atakol; Hasan Nazir; Cengiz Arici; Sefa Durmus; Ingrid Svoboda; Hartmut Fuess

2003-01-01

276

Dihydrogen complexes as prototypes for the coordination chemistry of saturated molecules  

PubMed Central

The binding of a dihydrogen molecule (H2) to a transition metal center in an organometallic complex was a major discovery because it changed the way chemists think about the reactivity of molecules with chemically inert strong bonds such as HH and CH. Before the seminal finding of side-on bonded H2 in W(CO)3(PR3)2(H2), it was generally believed that H2 could not bind to another atom in stable fashion and would split into two separate H atoms to form a metal dihydride before undergoing chemical reaction. Metal-bound saturated molecules such as H2, silanes, and alkanes (?-complexes) have a chemistry of their own, with surprisingly varied structures, bonding, and dynamics. H2 complexes are of increased relevance for H2 production and storage in the hydrogen economy of the future. PMID:17442752

Kubas, Gregory J.

2007-01-01

277

Dinitrogen coordination and cleavage promoted by a vanadium complex of a sigma,pi,sigma-donor ligand.  

PubMed

The deprotonation of the tripyrrole MeTPH(2) [MeTPH(2) = 2,5-[(2-pyrrolyl)(C(6)H(5))2C](2)(MeNC(4)H(2))], containing one N-methylated pyrrolyl ring, was carried out with 2 equiv of KH. The corresponding dipotassium salt reacted with VCl(3)(THF)(3) to afford the complex [(MeTP)VCl(THF)].THF (1). While the two lateral pyrrolide rings are sigma-bonded, the central one is perpendicularly oriented in a sort of pi-fashion. However, the bond distances clearly indicated that only the quaternized N atom is forming a bonding contact. Subsequent reduction of 1 with Na yielded the corresponding divalent complex [(MeTP)V(THF)].(C(7)H(8))(0.5) (2) where the central N-methylated ring adopted a more regular pi-orientation. When treated with a strong Lewis acid (AlMe(3)), THF was extracted from the vanadium coordination sphere, forming the dinuclear dinitrogen complex [(MeTP)V(mu-N(2))](2).(C(7)H(8))(2.9) (3). Reduction of 3 with potassium graphite gave cleavage of dinitrogen, affording the mixed-valent nitride-bridged complex [(MeTP)V(mu-N)](2).(THF) (4). PMID:17883267

Vidyaratne, Indu; Crewdson, Patrick; Lefebvre, Emeric; Gambarotta, Sandro

2007-10-15

278

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

PubMed

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

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

2013-08-01

279

[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

280

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

PubMed Central

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

2013-01-01

281

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

PubMed

Mononuclear copper complex [CuL(NH(3))(4)]Cl(2)0.5H(2)O and three new hetero-metallic complexes: [Cu(2)Ni(L)(2)(NH(3))(2)Cl(2)6H(2)O] 2H(2)O(,) [Cu(3)Co(L)(4)8H2O]Cl4()5H(2)O, and [Cu(4)Co(2)Ni(L)(3)(OH)(4)(NH(3))Cl(4)3H(2)O]4H(2)O 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(NH(3))(4)]Cl(2)0.5H(2)O and [Cu(3)Co(L)(4)8H2O]Cl4.5H(2)O are electrolytes, while, [Cu(2)Ni(L)(2)(NH(3))(2)Cl(2)6H(2)O]2H(2)O and [Cu(4)Co(2)Ni(L)(3)(OH)(4)(NH(3))Cl(4)3H(2)O]4H(2)O 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 [Cu(4)Co(2)Ni(L)(3)(OH)(4)(NH(3))Cl(4)3H(2)O]4H(2)O 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 N(2) 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 [Cu(4)Co(2)Ni(L)(3)(OH)(4)(NH(3))Cl(4)3H(2)O]4H(2)O complex showed the most intensive activity against the tested microorganisms. Trials to prepare single crystals from complexes were failed. PMID:23026345

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

2012-12-01

282

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

283

Anticancer activity of multinuclear arene ruthenium complexes coordinated to dendritic polypyridyl scaffolds  

Microsoft Academic Search

The rational development of multinuclear arene ruthenium complexes (arene=p-cymene, hexamethylbenzene) from generation 1 (G1) and generation 2 (G2) of 4-iminopyridyl based poly(propyleneimine) dendrimer scaffolds of the type, DAB-(NH2)n (n=4 or 8, DAB=diaminobutane) has been accomplished in order to exploit the enhanced permeability and retention (EPR) effect that allows large molecules to selectively enter cancer cells. Four compounds were synthesised, i.e.

Preshendren Govender; Nathan C. Antonels; Johan Mattsson; Anna K. Renfrew; Paul J. Dyson; John R. Moss; Bruno Therrien; Gregory S. Smith

2009-01-01

284

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

285

The Electronic Structure of Mn in Oxides, Coordination Complexes, and the Oxygen-Evolving Complex of Photosystem II Studied by Resonant Inelastic X-ray Scattering  

PubMed Central

Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and to study the electronic structure in oxides, molecular coordination complexes, as well as the S1 and S2 states of the oxygen-evolving complex (OEC) of photosystem II (PS II). The RIXS data yield two-dimensional plots that can be interpreted along the incident (absorption) energy or the energy transfer axis. The second energy dimension separates the pre-edge (predominantly 1s to 3d transitions) from the main K-edge, and a detailed analysis is thus possible. The 1s2p RIXS final-state electron configuration along the energy transfer axis is identical to conventional L-edge absorption spectroscopy, and the RIXS spectra are therefore sensitive to the Mn spin state. This new technique thus yields information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, i.e., (3d,3d) and (2p,3d) two-electron interactions are crucial to describe the spectral shapes in all systems. We propose to explain the shift of the K pre-edge absorption energy upon Mn oxidation in terms of the effective number of 3d electrons (fractional 3d orbital population). The spectral changes in the Mn 1s2p3/2 RIXS spectra between the PS II S1 and S2 states are small compared to that of the oxides and two of the coordination complexes (MnIII(acac)3 and MnIV(sal)2(bipy)). We conclude that the electron in the step from S1 to S2 is transferred from a strongly delocalized orbital. PMID:15303869

Yano, Junko; Visser, Hendrik; Robblee, John H.; Gu, Weiwei; de Groot, Frank M. F.; Christou, George; Pecoraro, Vincent L.

2014-01-01

286

Regio- and stereoselective hydrosilylation of alkynes catalyzed by three-coordinate cobalt(i) alkyl and silyl complexes.  

PubMed

A three-coordinate cobalt(I) complex exhibits high catalytic efficiency and selectivity as well as good functional group compatibility in alkyne hydrosilylation. [Co(IAd)(PPh3)(CH2TMS)] (1) (IAd = 1,3-diadamantylimidazol-2-ylidene) facilitates regio- and stereoselective hydrosilylation of terminal, symmetrical internal, and trimethylsilyl-substituted unsymmetrical internal alkynes to produce single hydrosilylation products in the forms of ?-(E)-silylalkenes, (E)-silylalkenes, and (Z)-?,?-disilylalkenes, respectively, in high yields. The comparable catalytic efficiency and selectivity of the Co(I) silyl complex [Co(IAd)(PPh3)(SiHPh2)] that was prepared from the reaction of 1 with H2SiPh2, and the isolation of an alkyne Co(I) complex [Co(IAd)(?(2)-PhC?CPh)(CH2TMS)] from the reaction of 1 with the acetylene, point out a modified Chalk-Harrod catalytic cycle for these hydrosilylation reactions. The high selectivity is thought to be governed by steric factors. PMID:25426965

Mo, Zhenbo; Xiao, Jie; Gao, Yafei; Deng, Liang

2014-12-17

287

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

288

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

289

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

290

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

291

Spectroscopic characterization of alkaline earth uranyl carbonates  

NASA Astrophysics Data System (ADS)

A series of alkaline uranyl carbonates, M[UO 2(CO 3) 3] nH 2O ( M=Mg 2, Ca 2, Sr 2, Ba 2, Na 2Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). The molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba 2[UO 2(CO 3) 3]6H 2O was obtained for the first time. The EXAFS analysis showed that this compound consists of (UO 2)(CO 3) 3 clusters similar to the other alkaline earth uranyl carbonates. The average U-Ba distance is 3.900.02 .Fluorescence wavelengths and life times were measured using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The U-O bond distances determined by EXAFS, TRLFS, XPS, and Raman spectroscopy agree within the experimental uncertainties. The spectroscopic signatures observed could be useful for identifying uranyl carbonate species adsorbed on mineral surfaces.

Amayri, Samer; Reich, Tobias; Arnold, Thuro; Geipel, Gerhard; Bernhard, Gert

2005-02-01

292

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

293

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

PubMed

Four cationic ruthenium(II) complexes with the formula [Ru(eta(5)-C(5)H(5))(PPh(3))(2)](+), with L = 5-phenyl-1H-tetrazole (TzH) 1, imidazole (ImH) 2, benzo[1,2-b;4,3-b'] dithio-phen-2-carbonitrile (Bzt) 3, and [5-(2-thiophen-2-yl)-vinyl]-thiophene-2-carbonitrile] (Tvt) 4 were prepared and characterized in view to evaluate their potentialities as antitumor agents. Studies by Circular Dichroism indicated changes in the secondary structure of ct-DNA. Changes in the tertiary structure of pBR322 plasmid DNA were also observed in gel electrophoresis experiment and the images obtained by atomic force microscopy (AFM) suggest strong interaction with pBR322 plasmid DNA; the observed decreasing of the viscosity with time indicates that the complexes do not intercalate between DNA base pairs. Compounds 1, 2, and 3 showed much higher cytotoxicity than the cisplatin against human leukaemia cancer cells (HL-60 cells). PMID:20689715

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

2010-01-01

294

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

295

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

296

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

297

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

PubMed

The synthesis and in vitro cytotoxicity of a series of Ru(II)(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

298

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

299

Synthesis and structure of [C 6H 14N 2][(UO 2) 4(HPO 4) 2(PO 4) 2(H 2O)]H 2O: An expanded open-framework amine-bearing uranyl phosphate  

NASA Astrophysics Data System (ADS)

A new open-framework compound, [C 6H 14N 2][(UO 2) 4(HPO 4) 2(PO 4) 2(H 2O)]H 2O, ( DUP-1) has been synthesized under mild hydrothermal conditions. The resulting structure consists of diprotonated DABCOH 22+ (C 6H 14N 22+) cations and occluded water molecules occupying the channels of a complex uranyl phosphate three-dimensional framework. The anionic lattice contains uranophane-like sheets connected by hydrated pentagonal bipyramidal UO 7 units. [C 6H 14N 2][(UO 2) 4(HPO 4) 2(PO 4) 2(H 2O)]H 2O possesses five crystallographically unique U centers. U(VI) is present here in both six- and seven-coordinate environments. The DABCOH 22+ cations are held within the channels by hydrogen bonds to both two uranyl oxygen atoms and a ?2-O atom. Crystallographic data (193 K, Mo K?, ?=0.71073 ): DUP-1, monoclinic, P2 1/ n, a=7.017(1) , b=21.966(4) , c=17.619(3) , ?=90.198(3), Z=4, R(F)=4.76% for 382 parameters with 6615 reflections with I>2 ?( I).

Bray, Travis H.; Gorden, John D.; Albrecht-Schmitt, Thomas E.

2008-09-01

300

Coordinated regulation of retinoic acid signaling pathway by KDM5B and polycomb repressive complex 2.  

PubMed

Polycomb repressive complex 2 (PRC2) is a critical epigenetic regulator in many biological processes, including maintenance of cell identity, stem cell self-renewal, differentiation, and deregulation of PRC2 is often observed in human cancers and diseases. Here we report that KDM5B (PLU-1/JARID1B), a histone lysine demethylase of Jumonji family, associates with PRC2 and colocalizes with PRC2 in nuclear bodies, and their physical association is dependent on direct interaction between KDM5B and the SUZ12 component of PRC2. Interestingly, co-occupancy of KDM5B and PRC2 was evidenced at the conserved cis-regulatory DNA element on retinoic acid (RA) responsive genes. Transcription readout and in vitro pull-down experiments suggest that KDM5B is an essential co-activator, but not a co-repressor, for the RA signaling, and the interface between KDM5B's JMJC domain and retinoic acid receptor ? (RAR?) is crucial for RA-mediated gene expression. Detailed chromatin immunoprecipitation assays addressed the seemingly paradox by revealing a biphasic effect of KDM5B on RA-induced gene activation through decoupled H3K4me3 demethylation and PRC2-antagonizing activities. These results demonstrate that KDM5B and PRC2 regulate RA signaling cascade in a cooperative and orchestrated fashion. PMID:24619877

Zhang, Yu; Liang, Jing; Li, Qian

2014-09-01

301

Radical generating coordination complexes as tools for rapid and effective fragmentation and fluorescent labeling of nucleic acids for microchip hybridization.  

SciTech Connect

DNA microchip technology is a rapid, high-throughput method for nucleic acid hybridization reactions. This technology requires random fragmentation and fluorescent labeling of target nucleic acids prior to hybridization. Radical-generating coordination complexes, such as 1,10-phenanthroline-Cu(II) (OP-Cu) and Fe(II)-EDTA (Fe-EDTA), have been commonly used as sequence nonspecific 'chemical nucleases' to introduce single-strand breaks in nucleic acids. Here we describe a new method based on these radical-generating complexes for random fragmentation and labeling of both single- and double-stranded forms of RNA and DNA. Nucleic acids labeled with the OP-Cu and the Fe-EDTA protocols revealed high hybridization specificity in hybridization with DNA microchips containing oligonucleotide probes selected for identification of 16S rRNA sequences of the Bacillus group microorganisms.We also demonstrated cDNA- and cRNA-labeling and fragmentation with this method. Both the OP-Cu and Fe-EDTA fragmentation and labeling procedures are quick and inexpensive compared to other commonly used methods. A column-based version of the described method does not require centrifugation and therefore is promising for the automation of sample preparations in DNA microchip technology as well as in other nucleic acid hybridization studies.

Kelly, J. J.; Chernov, B. N.; Mirzabekov, A. D.; Bavykin, S. G.; Biochip Technology Center; Northwestern Univ.; Engelhardt Inst. of Molecular Biology

2002-01-01

302

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

303

Role of the Uranyl Oxo Group as a Hydrogen Bond Acceptor  

SciTech Connect

Density functional theory calculations have been used to evaluate the geometries and energetics of interactions between a number of uranyl complexes and hydrogen bond donor groups. The results reveal that although traditional hydrogen bond donors are repelled by the oxo group in the [UO{sub 2}(OH{sub 2}){sub 5}]{sup 2+} species, they are attracted to the oxo groups in [UO{sub 2}(OH{sub 2}){sub 2}(NO{sub 3}){sub 2}]{sup 0}, [UO{sub 2}(NO{sub 3}){sub 3}]{sup -}, and [UO{sub 2}Cl{sub 4}]{sup 2-} species. Hydrogen bond strength depends on the equatorial ligation and can exceed 15 kcal mol{sup -1}. The results also reveal the existence of directionality at the uranyl oxo acceptor, with a weak preference for linear U=O---H angles.

Watson, Lori A [ORNL; Hay, Benjamin [ORNL

2011-01-01

304

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

305

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

SciTech Connect

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

James C. Liao

2012-05-22

306

EXTRACTION OF PERCHLORIC ACID AND URANYL PERCHLORATE WITH TRIBUTYL PHOSPHATE  

Microsoft Academic Search

The distribution of perchloric acid between its aqueous solution and TBP ; in the solvent extraction of uranyl perchlorate was studied. It was shown that ; the transition of the uranyl perchlorate and the perchloric acid to TBP is ; determined by the ionic strength of the water phase, the TBP concentration in the ; organic phase, the nature of

V. B. Shevchenko; I. V. Shilin; A. S. Solovkin

1958-01-01

307

Can electrospray mass spectrometry quantitatively probe speciation? Hydrolysis of uranyl nitrate studied by gas-phase methods.  

PubMed

Electrospray ionization of uranyl nitrate dissolved in water generates gaseous species containing either hydroxo-uranyl [UO(2)(OH)](+) or nitrato-uranyl [UO(2)(NO(3))](+) contact ion pairs solvated by up to four water molecules. Furthermore, uranyl clusters of the general type [U(m)O(2m)(X,Y)(2m-1)(H(2)O)(n)](+) (X,Y = OH, NO(3)) with m = 1-5 and n = 2-4 are formed. Collision-induced dissociation experiments are used to probe the structures and the stoichiometries of the uranyl ions generated. A detailed investigation of the concentration-dependent behavior of the formed gaseous uranyl complexes reveals a preference for nitrate- over hydroxide-containing species with increasing concentration of the sprayed solution. This behavior reflects changes in the pH value of the bulk solutions that can be attributed to solvolysis of UO(2)(2+) in water. Further, the tendency for generation of polynuclear cluster ions is amplified with increasing concentration and can be explained by a mechanism which involves the association of cations present in solution with neutral species such as UO(2)(OH)(2), UO(2)(OH)(NO(3)), and UO(2)(NO(3))(2). The observed dependences of the cluster-ion intensities in the mass spectra from the concentration of the solutions fed to the electrospray source are used to suggest a scheme for a quantitative correlation between the gas-phase and solution-phase data. The results inter alia indicate that the effective concentrations of the spraying solution can be several orders of magnitude larger than those of the feed solutions entering the electrospray ionization source. PMID:20507105

Tsierkezos, Nikos G; Roithov, Jana; Schrder, Detlef; Onck, Milan; Slavcek, Petr

2009-07-01

308

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

309

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

310

Synthesis and structural characterization of a new heterobimetallic coordination complex of barium and cobalt for use as a precursor for chemical vapor deposition.  

PubMed

Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex. PMID:16323901

Tahir, Asif A; Molloy, Kieran C; Mazhar, Muhammad; Kociok-Khn, Gabriele; Hamid, Mazhar; Dastgir, Sarim

2005-12-12

311

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

312

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

313

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

314

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

315

A Complex Regulatory Network Coordinating Cell Cycles During C. elegans Development Is Revealed by a Genome-Wide RNAi Screen  

PubMed Central

The development and homeostasis of multicellular animals requires precise coordination of cell division and differentiation. We performed a genome-wide RNA interference screen in Caenorhabditis elegans to reveal the components of a regulatory network that promotes developmentally programmed cell-cycle quiescence. The 107 identified genes are predicted to constitute regulatory networks that are conserved among higher animals because almost half of the genes are represented by clear human orthologs. Using a series of mutant backgrounds to assess their genetic activities, the RNA interference clones displaying similar properties were clustered to establish potential regulatory relationships within the network. This approach uncovered four distinct genetic pathways controlling cell-cycle entry during intestinal organogenesis. The enhanced phenotypes observed for animals carrying compound mutations attest to the collaboration between distinct mechanisms to ensure strict developmental regulation of cell cycles. Moreover, we characterized ubc-25, a gene encoding an E2 ubiquitin-conjugating enzyme whose human ortholog, UBE2Q2, is deregulated in several cancers. Our genetic analyses suggested that ubc-25 acts in a linear pathway with cul-1/Cul1, in parallel to pathways employing cki-1/p27 and lin-35/pRb to promote cell-cycle quiescence. Further investigation of the potential regulatory mechanism demonstrated that ubc-25 activity negatively regulates CYE-1/cyclin E protein abundance in vivo. Together, our results show that the ubc-25-mediated pathway acts within a complex network that integrates the actions of multiple molecular mechanisms to control cell cycles during development. PMID:24584095

Roy, Sarah H.; Tobin, David V.; Memar, Nadin; Beltz, Eleanor; Holmen, Jenna; Clayton, Joseph E.; Chiu, Daniel J.; Young, Laura D.; Green, Travis H.; Lubin, Isabella; Liu, Yuying; Conradt, Barbara; Saito, R. Mako

2014-01-01

316

Stannylium ions, a tin(II) arene complex, and a tin dication stabilized by weakly coordinating anions.  

PubMed

The reactivity of aryl-substituted stannylenes, Ar(2)Sn (4), towards silylarenium borates, [R(3)SiArH][B(C(6)F(5))(4)] (3), was investigated. The reaction with 2,3,4-trimethyl-6-tert-butylphenyl (mebp)-substituted stannylene gave silyl-substituted stannylium ions 2a,b, which were characterized by NMR spectroscopy supported by the results of quantum-mechanical computations of molecular structures and magnetic properties. The tri-iso-propylphenyl-substituted stannylium ions 2c,d undergo a decomposition reaction in toluene to give the dicationic tin-arene complex [Sn(C(7)H(8))(3)](2+) (5) in the form of the [B(C(6)F(5))(4)] salt in high yields. The 5[B(C(6)F(5))(4)](2) salt was identified by single crystal X-ray diffraction analysis and by Mssbauer spectroscopy. The bonding situation was investigated by using natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) calculations. The substitution of the weakly coordinating borate anion by the carboranate [CB(11)H(6)Br(6)](-) results in replacement of the toluene ligands and formation of tin(II) carboranate with only weak Sn(2+)-anion interactions as suggested by the solid-state structure of the isolated salt. PMID:21919092

Schfer, Annemarie; Winter, Florian; Saak, Wolfgang; Haase, Detlev; Pttgen, Rainer; Mller, Thomas

2011-09-19

317

Coordinated control of senescence by lncRNA and a novel T-box3 co-repressor complex  

PubMed Central

Cellular senescence is a crucial tumor suppressor mechanism. We discovered a CAPER?/TBX3 repressor complex required to prevent senescence in primary cells and mouse embryos. Critical, previously unknown roles for CAPER? in controlling cell proliferation are manifest in an obligatory interaction with TBX3 to regulate chromatin structure and repress transcription of CDKN2A-p16INK and the RB pathway. The IncRNA UCA1 is a direct target of CAPER?/TBX3 repression whose overexpression is sufficient to induce senescence. In proliferating cells, we found that hnRNPA1 binds and destabilizes CDKN2A-p16INK mRNA whereas during senescence, UCA1 sequesters hnRNPA1 and thus stabilizes CDKN2A-p16INK. Thus CAPER?/TBX3 and UCA1 constitute a coordinated, reinforcing mechanism to regulate both CDKN2A-p16INK transcription and mRNA stability. Dissociation of the CAPER?/TBX3 co-repressor during oncogenic stress activates UCA1, revealing a novel mechanism for oncogene-induced senescence. Our elucidation of CAPER? and UCA1 functions in vivo provides new insights into senescence induction, and the oncogenic and developmental properties of TBX3. DOI: http://dx.doi.org/10.7554/eLife.02805.001 PMID:24876127

Kumar P, Pavan; Emechebe, Uchenna; Smith, Richard; Franklin, Sarah; Moore, Barry; Yandell, Mark; Lessnick, Stephen L; Moon, Anne M

2014-01-01

318

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

319

A complex regulatory network coordinating cell cycles during C. elegans development is revealed by a genome-wide RNAi screen.  

PubMed

The development and homeostasis of multicellular animals requires precise coordination of cell division and differentiation. We performed a genome-wide RNA interference screen in Caenorhabditis elegans to reveal the components of a regulatory network that promotes developmentally programmed cell-cycle quiescence. The 107 identified genes are predicted to constitute regulatory networks that are conserved among higher animals because almost half of the genes are represented by clear human orthologs. Using a series of mutant backgrounds to assess their genetic activities, the RNA interference clones displaying similar properties were clustered to establish potential regulatory relationships within the network. This approach uncovered four distinct genetic pathways controlling cell-cycle entry during intestinal organogenesis. The enhanced phenotypes observed for animals carrying compound mutations attest to the collaboration between distinct mechanisms to ensure strict developmental regulation of cell cycles. Moreover, we characterized ubc-25, a gene encoding an E2 ubiquitin-conjugating enzyme whose human ortholog, UBE2Q2, is deregulated in several cancers. Our genetic analyses suggested that ubc-25 acts in a linear pathway with cul-1/Cul1, in parallel to pathways employing cki-1/p27 and lin-35/pRb to promote cell-cycle quiescence. Further investigation of the potential regulatory mechanism demonstrated that ubc-25 activity negatively regulates CYE-1/cyclin E protein abundance in vivo. Together, our results show that the ubc-25-mediated pathway acts within a complex network that integrates the actions of multiple molecular mechanisms to control cell cycles during development. PMID:24584095

Roy, Sarah H; Tobin, David V; Memar, Nadin; Beltz, Eleanor; Holmen, Jenna; Clayton, Joseph E; Chiu, Daniel J; Young, Laura D; Green, Travis H; Lubin, Isabella; Liu, Yuying; Conradt, Barbara; Saito, R Mako

2014-05-01

320

Nonrelativistic Compton scattering in Furry's picture: Beyond the sudden impulse approximation by means of the complex coordinate method  

NASA Astrophysics Data System (ADS)

Basic electrodynamical and collision theory presumptions related to Compton scattering are critically reconsidered (with particular emphasis on identifying the proper transition matrix element effectively controlling the process, and on framing it within time dependent perturbation theory and scattering theory) in order to indicate the main features and the validity of the proposed method. The on-energy-shell transition matrix element governing the cross-sectional formula is obtained from Furry's two-potential formalism, which makes possible a treatment of the primary electron-photon interaction to first order while incorporating the effects of the final state Coulombic interaction to all orders. Furry's procedure, in addition to defining clearly which initial and final states should enter the transition matrix element, also brings additional insight into the nature of the so-called ``sudden impulse approximation.'' A treatment is proposed in which the decisive transition matrix element is obtained without explicit calculation of the distorted continuum solutions implied by Furry's procedure, but is instead extracted from the dispersion relations of the ``beat-frequency'' dependent generalized polarizability by means of the L2 treatment based on the complex-coordinate method. The practical advantage of the method will be its ability to incorporate correlation between the ejected electron and the electrons remaining in the ion.

Froelich, P.; Weyrich, Wolf

1984-06-01

321

The intra-annular acylamide chelate-coordinated compound: The keto-tautomer of metal (II) milrinone complex  

NASA Astrophysics Data System (ADS)

In the presence of N, N'-dimethyllformamide (DMF), two isostructural metal (II)-milrinone complexes formulated as M(C 12H 8N 3O) 2 (M = Co 1 and Ni 2) have been synthesized and characterized by elemental analysis, IR, TG and single crystal X-ray diffraction. The two compounds crystallize in the tetragonal system, chiral space group P4 32 12. They exhibit similar two dimensional (2D) square grid-like framework, in which milrinone acts as a ditopic ligand with its terminal pyridine and intra-annular acylamide groups covalently bridging different metal centers. The intra-annular acylamide ligand shows a chelate-coordinated mode. Compounds 1 and 2 are stable under 200 C. Compound 3 formulated as (C 12H 9N 3O) 4H 2O was obtained in the presence of water, the water molecule in the structure leads to the racemization of compound 3 and it crystallizes in the monoclinic system, non-chiral space group P2 1/ c. Milrinone exhibits a keto-form in the three compounds and compounds 1- 3 exhibit different photoluminescence properties.

Gong, Yun; Liu, Jinzhi; Tang, Wang; Hu, Changwen

2008-03-01

322

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

PubMed

The synthesis and characterization of (bipy)2U(N[t-Bu]Ar)2 (-(bipy)2, bipy = 2,2'-bipyridyl, Ar = 3,5-C6H3Me2), (bipy)U(N[(1)Ad]Ar)3 (-bipy), (bipy)2U(NC[t-Bu]Mes)3 (-(bipy)2, Mes = 2,4,6-C6H2Me3), and IU(bipy)(NC[t-Bu]Mes)3 (-I-bipy) are reported. X-ray crystallography studies indicate that bipy coordinates as a radical anion in -(bipy)2 and -bipy, and as a neutral ligand in -I-bipy. In -(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

2015-01-28

323

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

324

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

325

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

326

First examples of ternary lanthanide 5-aminoisophthalate complexes: Hydrothermal syntheses and structures of lanthanide coordination polymers with 5-aminoisophthalate and oxalate  

NASA Astrophysics Data System (ADS)

Two new lanthanide coordination polymers with mixed-carboxylates, [Ln(OX)(HAPA)(H 2O)] n[Ln = Eu ( 1), Ho ( 2); H 2APA = 5-aminoisophthalic acid; OX = oxalate] were obtained by hydrothermal reactions, and characterized by single crystal X-ray diffraction, elemental analysis and IR spectra. Complexes 1 and 2 are both 3-D supramolecular structure, in which lanthanide ions are bridged by oxalate and 5-aminoisophthalate ligands forming 2-D metal-organic framework, and 2-D networks are further architectured to form 3-D supramolecular structures by hydrogen bonds. The two carboxylate groups of H 2APA ligand are all deprotonated and exhibit chelating and bridging bidentate coordination modes, respectively, and the amino group in HAPA presents - NH3+ in the titled complexes. The thermogravimetric analysis was carried out to examine the thermal stability of the titled complexes. And the photoluminescence property of 1 was investigated.

Liu, Chong-Bo; Wen, Hui-Liang; Tan, Sheng-Shui; Yi, Xiu-Guang

2008-05-01

327

Spectrophotometric determination of uranium through uranyl/azide system  

SciTech Connect

An alternative method for the determination of uranium has been established by spectrophotometry. The procedure is based on the products of reaction between uranyl and azide ions (excess). This system furnishes yellowish complexes and the reaction was explored in water-acetonitrile medium (60% v/v), at 311 m. The resulting solution has a good stability and precision of measurements about 0.4% (standard deviation). The system obeys the Beer`s law over concentration range from 5.0 to 40 ppm. The molar absorptivity and Sandell`s sensitivity of the complexes are 9.23 x 10{sup 3} 1 mol{sup -1}cm{sup -1} and 0.0292 {mu}g cm{sup -2}, respectively. Effect of some diverse ions has been studied and several anions and cations do not interfere. The method was tested for a natural sample (uraninite), after different carbonate treatments. The results for uranium were compared with a conventional spectrophotometric (arsenazo) and inductively coupled plasma (ICP) methods. The possibility of the simultaneous spectrophotometric determination of uranium(VI) and iron(III) was also verified. This methodology showed good accuracy, precision, selectivity and simplicity.

Carmo, D.R. do; Andrade, J.F. de [FFCLRP-USP, Ribeirao Preto (Brazil); Guimaraes, O.M. [UFPR, Curitiba (Brazil)

1995-07-01

328

Molecular tectonics: homochiral coordination networks based on combinations of a chiral neutral tecton with Hg(II), Cu(II) or Ni(II) neutral complexes as metallatectons.  

PubMed

The use of compound 1 as an enantiomerically pure neutral and rigid organic linear tecton bearing two divergently oriented monodentate coordinating sites appended with two chiral centres of the same (S) configuration leads, in the presence of neutral metal complexes behaving either as a linear (Cu(hfac)2, Cu(OAc)2) or a V-shaped (HgCl2) 2-connecting node or a 4-connecting square node (NiCl2), to the formation of four homochiral 1- and 2-D coordination polymers. PMID:24276523

Larpent, Patrick; Jouaiti, Abdelaziz; Kyritsakas, Nathalie; Hosseini, Mir Wais

2014-02-01

329

Hybrid scorpionate/cyclopentadienyl magnesium and zinc complexes: synthesis, coordination chemistry, and ring-opening polymerization studies on cyclic esters.  

PubMed

The reaction of the hybrid scorpionate/cyclopentadienyl lithium salt [Li(bpzcp)(THF)] [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl] with 1 equiv of RMgCl proceeds cleanly to give very high yields of the corresponding monoalkyl kappa(2)-NN-eta(5)-C(5)H(4) magnesium complexes [Mg(R)(kappa(2)-eta(5)-bpzcp)] (R = Me 1, Et 2, (n)Bu 3, (t)Bu 4, CH(2)SiMe(3) 5, CH(2)Ph 6). Hydrolysis of the hybrid lithium salt [Li(bpzcp)(THF)] with NH(4)Cl/H(2)O in ether cleanly affords the two previously described regioisomers: (bpzcpH) 1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene (a) and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene (b). Subsequent reaction of the bpzcpH hybrid ligand with ZnR(2) quantitatively yields the monoalkyl kappa(2)-NN-eta(1)(pi)-C(5)H(4) zinc complexes [Zn(R){kappa(2)-eta(1)(pi)-bpzcp}] (R = Me 7, Et 8, (t)Bu 9, CH(2)SiMe(3) 10). Additionally, magnesium alkyls 1, 2, 4, and 5 can act as excellent cyclopentadienyl and alkyl transfers to the zinc metal center and yield zinc alkyls 7-10 in good yields. The single-crystal X-ray structures of the derivatives 4, 5, 7, and 10 confirm a 4-coordinative structure with the metal center in a distorted tetrahedral geometry. Interestingly, whereas alkyl magnesium derivatives 4 and 5 present a eta(5) coordination mode for the cyclopentadienyl fragment, zinc derivatives 7 and 10 feature a peripheral eta(1)(pi) arrangement in the solid state. Furthermore, the reaction of the hybrid lithium salt [Li(bpzcp)(THF)] with 1 equiv of ZnCl(2) in tetrahydrofuran (THF) affords very high yields of the chloride complex [ZnCl{kappa(2)-eta(1)(pi)-bpzcp}] (11). Compound 11 was used as a convenient starting material for the synthesis of the aromatic amide zinc compound [Zn(NH-4-MeC(6)H(4)){kappa(2)-eta(1)(pi)-bpzcp}] (12), by reaction with the corresponding aromatic primary amide lithium salt. Alternatively, aliphatic amide and alkoxide derivatives were only accessible by protonolysis of the bis(amide) complexes [M{N(SiMe(3))(2)}(2)] (M = Mg, Zn) and the mixed ligand complex [EtZnOAr)] with the hybrid ligand bpzcpH to afford [Zn(R){kappa(2)-eta(1)(pi)-bpzcp}] (R = N(SiMe(3))(2) 13, R = 2,4,6-Me(3)C(6)H(2)O 14) and [Mg{N(SiMe(3))(2)}(kappa(2)-eta(5)-bpzcp)] (15). Finally, alkyl and alkoxide-containing complexes 1-10 and 14 can act as highly effective single-component living initiators for the ring-opening polymerization of epsilon-caprolactone and lactides over a wide range of temperatures. Epsilon-caprolactone is polymerized within minutes to give high molecular weight polymers with medium-broad polydispersities (M(n) > 10(5), M(w)/M(n) = 1.45). Lactide afforded poly(lactide) materials with medium molecular weights and polydispersities as narrow as M(w)/M(n) = 1.02. Additionally, polymerization of L-lactide occurred without racemization in the propagation process and offered highly crystalline, isotactic poly(L-lactides) with very high melting temperatures (T(m) = 165 degrees C). Microstructural analysis of poly(rac-lactide) by (1)H NMR spectroscopy revealed that propagations occur without appreciable levels of stereoselectivity. Polymer end group analysis showed that the polymerization process is initiated by alkyl transfer to the monomer. PMID:20146427

Garcs, Andrs; Snchez-Barba, Luis F; Alonso-Moreno, Carlos; Fajardo, Mariano; Fernndez-Baeza, Juan; Otero, Antonio; Lara-Snchez, Agustn; Lpez-Solera, Isabel; Rodrguez, Ana Mara

2010-03-15

330

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

331

Parametric investigation of laser-induced fluorescence of solid-state uranyl compounds.  

PubMed

The combination of remote/standoff sensing and laser-induced fluorescence (LIF) spectroscopy shows potential for detection of uranyl (UO2(2+)) compounds. Uranyl compounds exhibit characteristic emission in the 450-600 nm (22,200 to 16,700 cm(-1)) spectral region when excited by wavelengths in the ultraviolet or in the short-wavelength portion of the visible spectrum. We report a parametric study of the effects of excitation wavelength [including 532 nm (18,797 cm(-1)), 355 nm (28,169 cm(-1)), and 266 nm (37,594 cm(-1))] and excitation laser power on solid-state uranium compounds. The uranium compounds investigated include uranyl nitrate, uranyl sulfate, uranyl oxalate, uranium dioxide, triuranium octaoxide, uranyl acetate, uranyl formate, zinc uranyl acetate, and uranyl phosphate. We observed the characteristic uranyl fluorescence spectrum from the uranium compounds except for uranium oxide compounds (which do not contain the uranyl moiety) and for uranyl formate, which has a low fluorescence quantum yield. Relative uranyl fluorescence intensity is greatest for 355 nm excitation, and the order of decreasing fluorescence intensity with excitation wavelength (relative intensity/laser output) is 355 nm > 266 nm > 532 nm. For 532 nm excitation, the emission spectrum is produced by two-photon excitation. Uranyl fluorescence intensity increases linearly with increasing laser power, but the rate of fluorescence intensity increase is different for different emission bands. PMID:18823105

Wang, Guangjun; Su, Yi; Monts, David L

2008-10-23

332

Species-differentiable sensing of phosphate-containing anions in neutral aqueous solution based on coordinatively unsaturated lanthanide complex probes.  

PubMed

A new chromogenic/fluorogenic molecular probe was developed for highly selective and species-differentiable detection of phosphate-containing anions in neutral aqueous solution. The coordinatively unsaturated lanthanide complex, made from Eu(III) ion and 2-[(8-hydroxy-5-sulfo-7-quinoline)azo]-1,8-dihydroxy-3,6-naphthalene disulfonic acid, changed its conformation when binding to the incoming target anions, which resulted in differential absorption or fluorescence responses. It was demonstrated that not only phosphate and pyrophosphate but also DNA and RNA could be clearly distinguished by visible absorption or fluorescence spectra. Also, differential responses in absorption spectra were observed when AMP, ADP, and ATP were added into the sensing system. Selective quantitation of these phosphate-containing anions in aqueous solutions, therefore, can be easily available. DNA and RNA were distinguished by different colors and independent fluorescence emissions due to their intrinsic differences in beta-D-ribose residues. Simultaneous or independent quantitation of DNA and RNA in a mixture sample, therefore, is possible without pretreatment with nuclease. Furthermore, the influence from the base selectivity can be eliminated by the use of the probe. The detection limits of phosphate and 5'-ATP in neutral water were 6.0 x 10(-7) and 9.0 x 10(-7)M, respectively, by the UV/Vis spectrophotometric method; the detection limits were 12.3 ng/mL for DNA by fluorimetry and 2.3mg/L for RNA by UV/Vis spectrophotometry. PMID:15265728

Li, Shun-Hua; Yuan, Wen-Tao; Zhu, Chang-Qing; Xu, Jin-Gou

2004-08-15

333

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

334

Characterizing solution and solid-phase amorphous uranyl silicates q  

E-print Network

A combination of high-energy X-ray scattering (HEXS) and X-ray diffraction (XRD) is used to structurally to propose a model for solid formation that includes a uranyl silicate building block, or synthon, which

Illinois at Chicago, University of

335

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.

336

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

337

Structures and syntheses of layered and framework amine-bearing uranyl phosphate and uranyl arsenates  

NASA Astrophysics Data System (ADS)

Two hydrated uranyl arsenates and a uranyl phosphate were synthesized by hydrothermal methods in the presence of amine structure-directing agents and their structures determined: (N 2C 6H 14)[(UO 2)(AsO 4)] 2(H 2O) 3, DabcoUAs, {NH(C 2H 5) 3}[(UO 2) 2(AsO 4)(AsO 3OH)], TriethUAs, and (N 2C 4H 12)(UO 2)[(UO 2)(PO 4)] 4(H 2O) 2, PiperUP. Intensity data were collected at room temperature using Mo K? X-radiation and a CCD-based area detector. The crystal structures were refined by full-matrix least-squares techniques on the basis of F2 to agreement indices ( DabcoUAs, TriethUAs, PiperUP) w R2=5.6%, 8.3%, 7.2% for all data, and R1=2.9%, 3.3%, 4.0%, calculated for 1777, 5822, 9119 unique observed reflections (| Fo|?4 ?F), respectively. DabcoUAs is monoclinic, space group C2/ m, Z=2, a=18.581(1), b=7.1897(4), c=7.1909(4) , ?=102.886(1), V=936.43(9) 3, Dcalc=3.50 g/cm 3. TriethUAs is monoclinic, space group P2 1/ n, Z=4, a=9.6359(4), b=18.4678(7), c=10.0708(4) , ?=92.282(1), V=1790.7(1) 3, Dcalc=3.41 g/cm 3. PiperUP is monoclinic, space group Pn, Z=2, a=9.3278(4), b=15.5529(7), c=9.6474(5) , ?=93.266(1), V=1397.3(1) 3, Dcalc=4.41 g/cm 3. The structure of DabcoUAs contains the autunite-type sheet formed by the sharing of vertices between uranyl square bipyramids and arsenate tetrahedra. The triethylenediammonium cations are located in the interlayer along with two H 2O groups and are disordered. Both TriethUAs and PiperUP contain sheets formed of uranyl pentagonal bipyramids and tetrahedra (arsenate and phosphate, respectively) with the uranophane sheet-anion topology. In TriethUAs, triethlyammonium cations are located in the interlayer. In PiperUP, the sheets are connected by a uranyl pentagonal bipyramid that shares corners with phosphate tetrahedra of adjacent sheets, resulting in a framework with piperazinium cations and H 2O groups in the cavities of the structure.

Locock, Andrew J.; Burns, Peter C.

2004-08-01

338

Syntheses, structures, photoluminescence of four dicarboxylate-controlled Zn(II) coordination complexes incorporating flexible 1-(4-pyridylmethyl)-benzimidazole ligand  

NASA Astrophysics Data System (ADS)

Four Zn(II) coordination complexes, namely {[Zn(pmbm)2(tpa)]H2O}n (1), {[Zn(pmbm)(phda)]2(H2O)}n (2), [Zn(pmbm)(aze)]n (3), {[Zn(pmbm)(1,4-ndc)]2(CH3OH)}n (4) [pmbm = 1-(4-pyridylmethyl)-benzimidazole, H2tpa = terephthalic acid, H2phda = phenylenediacetic acid, H2aze = azelaic acid, 1,4-ndcH2 = 1,4-naphthalenedicarboxylic acid] have been synthesized by solution phase ultrasonic reactions of Zn(AC)22H2O with pmbm and various dicarboxylates ligands under the ammoniacal condition. All the complexes have been characterized by elemental analyses, IR spectra and X-ray diffraction. Complexes 1 and 2 exhibit one-dimensional chains structure and complex 3 and 4 are two-dimensional sheets structure with (4,4) topology. Complexes 1-4 spanning from one-dimensional chains to two-dimensional sheets suggest that dicarboxylates play significant roles in the formation of such coordination architectures. The photoluminescences of the complexes were also investigated in the solid state at room temperature.

Hao, Hong-Jun; Du, Ming-Yue; Wang, Dan-Feng; Sun, Cheng-Jie; Wang, Zhan-Hui; Huang, Rong-Bin; Zheng, Lan-Sun

2013-09-01

339

51V Solid-state NMR and Density-Functional Theory Studies of Eight-Coordinate Non-Oxo Vanadium Complexes: Oxidized Amavadin  

PubMed Central

SUMMARY Using 51V magic angle spinning solid-state NMR spectroscopy and Density Functional Theory calculations we have characterized the chemical shift and quadrupolar coupling parameters for two eight-coordinate vanadium complexes, [PPh4][V(V)(HIDPA)2] and [PPh4][V(V)(HIDA)2]; HIDPA = 2,2?-(hydroxyimino)dipropionate and HIDA = 2,2?-(hydroxyimino)diacetate. The coordination geometry under examination is the less common non-oxo eight coordinate distorted dodecahedral geometry that has not been previously investigated by solid-state NMR spectroscopy. Both complexes were isolated by oxidizing their reduced forms: [V(IV)(HIDPA)2]2- and [V(IV)(HIDA)2]2-. V(IV)(HIDPA)22- is also known as amavadin, a vanadium-containing natural product present in the Amanita muscaria mushroom and responsible for vanadium accumulation in nature. The quadrupolar coupling constants, CQ, are found to be moderate, 5.0 to 6.4 MHz while the chemical shift anisotropies are relatively small for vanadium complexes, ?420 and 360 ppm. The isotropic chemical shifts in the solid state are ?220 and ?228 ppm for the two compounds, and near the chemical shifts observed in solution. Presumably this is a consequence of the combined effects of the increased coordination number and the absence of oxo groups. Density Functional Theory calculations of the electric field gradient parameters are in good agreement with the NMR results while the chemical shift parameters show some deviation from the experimental values. Future work on this unusual coordination geometry and a combined analysis by solid-state NMR and Density Functional Theory should provide a better understanding of the correlations between experimental NMR parameters and the local structure of the vanadium centers. PMID:19421628

Ooms, Kristopher J.; Bolte, Stephanie E.; Baruah, Bharat; Choudhary, Muhammad Aziz; Crans, Debbie C.; Polenova, Tatyana

2014-01-01

340

A structure-based analysis of the vibrational spectra of nitrosyl ligands in transition-metal coordination complexes and clusters  

NASA Astrophysics Data System (ADS)

The vibrational spectra of nitrogen monoxide or nitric oxide (NO) bonded to one or to several transition-metal (M) atom(s) in coordination and cluster compounds are analyzed in relation to the various types of such structures identified by diffraction methods. These structures are classified in: (a) terminal (linear and bent) nitrosyls, [M(?-NO)] or [M(NO)]; (b) twofold nitrosyl bridges, [M 2(? 2-NO)]; (c) threefold nitrosyl bridges, [M 3(? 3-NO)]; (d) ?/?-dihaptonitrosyls or " side-on" nitrosyls; and (e) isonitrosyls (oxygen-bonded nitrosyls). Typical ranges for the values of internuclear N-O and M-N bond-distances and M-N-O bond-angles for linear nitrosyls are: 1.14-1.20 /1.60-1.90 /180-160 and for bent nitrosyls are 1.16-1.22 /1.80-2.00 /140-110. The [M 2(? 2-NO)] bridges have been divided into those that contain one or several metal-metal bonds and those without a formal metal/metal bond (M⋯M). Typical ranges for the M-M, N-O, M-N bond distances and M-N-M bond angles for the normal twofold NO bridges are: 2.30-3.00 /1.18-1.22 /1.80-2.00 /90-70, whereas for the analogous ranges of the long twofold NO bridges these are 3.10-3.40 /1.20-1.24 /1.90-2.10 /130-110. In both situations the N-O vector is approximately at right angle to the M-M (or M⋯M) vector within the experimental error; i.e. the NO group is symmetrical bonded to the two metal atoms. In contrast the threefold NO bridges can be symmetrically or unsymmetrically bonded to an M 3-plane of a cluster compound. Characteristic values for the N-O and M-N bond-distances of these NO bridges are: 1.24-1.28 /1.80-1.90 , respectively. As few dihaptonitrosyl and isonitrosyl complexes are known, the structural features of these are discussed on an individual basis. The very extensive vibrational spectroscopy literature considered gives emphasis to the data from linearly bonded NO ligands in stable closed-shell metal complexes; i.e. those which are consistent with the " effective atomic number (EAN)" or "18-electron" rule. In the paucity of enough vibrational spectroscopic data from complexes with only nitrosyl ligands, it turned out to be very advantageous to use wavenumbers from the spectra of uncharged and saturated nitrosyl/carbonyl metal complexes as references, because the presence of a carbonyl ligand was found to be neutral in its effect on the ?(NO)-values. The wide wavenumber range found for the ?(NO) values of linear MNO complexes are then presented in terms of the estimated effects of net ionic charges, or of electron-withdrawing or electron-donating ligands bonded to the same metal atom. Using this approach we have found that: (a) the effect for a unit positive charge is [plus 100 cm -1] whereas for a unit negative charge it is [minus 145 cm -1]. (b) For electron-withdrawing co-ligands the estimated effects are: terminal CN [plus 50 cm -1]; terminal halogens [plus 30 cm -1]; bridging or quasi-bridging halogens [plus 15 cm -1]. (c) For electro donating co-ligands they are: PF 3 [plus 10 cm -1]; P(OPh) 3 [-30 cm -1]; P(OR) 3 (R = alkyl group) [-40 cm -1]; PPh 3 [-55 cm -1]; PR 3 (R = alkyl group) [-70 cm -1]; and ? 5-C 5H 5 [-60 cm -1]; ? 5-C 5H 4Me [-70 cm -1]; ? 5-C 5Me 5 [-80 cm -1]. These values were mostly derived from the spectra of nitrosyl complexes that have been corrected for the presence of only a single electronically-active co-ligand. After making allowance for ionic charges or strongly-perturbing ligands on the same metal atom, the adjusted 'neutral-co-ligand' ?(NO)*-values (in cm -1) are for linear nitrosyl complexes with transition metals of Period 4 of the Periodic Table, i.e. those with atomic orbitals (4s3d4p): [ca. 1750, Cr(NO)]; [1775,Mn(NO)]; [1796,Fe(NO)]; [1817,Co(NO)]; [ca. 1840, Ni(NO)]. Period 5 (5s4d5p): [1730 Mo(NO)]; [, Tc(NO)]; [1745,Ru(NO)]; [1790,Rh(NO)]; [ca. 1845, Pd(NO)]. Period 6 (6s4f5d6p), [1720,W(NO)]; [1730,Re(NO)]; [1738,Os(NO)]; [1760,Ir(NO)]; [, Pt] respectively. Environmental differences to these values, e.g. data taken

De La Cruz, Carlos; Sheppard, Norman

2011-01-01

341

The effect of uranyl nitrate on intestinal transfer of hexoses  

PubMed Central

1. Uranyl nitrate in a concentration of 3 10-4 M caused reduction in mucosal transfer of glucose but not of galactose nor 3-O-methyl-glucose by sacs of rat everted intestine. At this concentration uranyl nitrate had little effect on glucose metabolism (measured by glucose disappearance). 2. Uranyl nitrate in a concentration of 3 10-3 M caused reduction in transfer of glucose, galactose, 3-O-methyl-glucose and fluid, and inhibited glucose metabolism. 3. Uranyl nitrate did not inhibit entry of glucose into the intestine under anaerobic conditions. 4. Glucose was found to inhibit or stimulate galactose transfer depending on the conditions. The inhibitory action is presumably by competition for a common carrier, whereas stimulation indicates that glucose metabolism can supply energy for galactose transfer. 5. It is suggested that there are two different routes for glucose in the cell, one of which is uranyl sensitive and not used by galactose, and the other is uranyl insensitive and shared by both hexoses. The implications of this are discussed in relation to transport and metabolism. PMID:5972151

Newey, H.; Sanford, P. A.; Smyth, D. H.

1966-01-01

342

Uranyl precipitation by Pseudomonas aeruginosa via controlled polyphosphate metabolism.  

PubMed

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

2004-12-01

343

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

344

Spectroscopic, kinetic, and mechanistic study of a new mode of coordination of indole derivatives to platinum(II) and palladium(II) ions in complexes.  

PubMed

Binding of tryptophan residue to intrinsic metal ions in proteins is unknown, and very little is known about the coordinating abilities of indole. Indole-3-acetamide displaces the solvent ligands from cis-[Pt(en)(sol)2]2+, in which sol is acetone or H2O, in acetone solution and forms the complex cis-[Pt(en)(indole-3-acetamide)]2+ (3) of spiro structure, in which the new bidentate ligand coordinates to the Pt(II) atom via the C(3) atom of the indolyl group and the amide oxygen atom. This structure is supported by 1H, 13C, 15N, and 195Pt NMR spectra and by UV, IR, and mass spectra. Molecular mechanical simulations by Hyperchem and CHARMM methods give consistent structural models; the latter is optimized by density-functional quantum chemical calculations. Dipeptide-like molecules N-(3-indolylacetyl)-L-amino acid in which amino acid is alanine, leucine, isoleucine, valine, aspartic acid, or phenylalanine also displace the solvent ligands in acetone solution and form complexes cis-[Pt(en) N-(3-indolylacetyl)-L-amino acid)]2+ (6), which structurally resemble 3 but exist as two diastereomers, detected by 1H NMR spectroscopy. The bulkier the amino acid moiety, the slower the coordination of these dipeptide-like ligands to the Pt(II) atom. The indolyl group does not coordinate as a unidentate ligand; a second donor atom is necessary for bidentate coordination of this atom and the indolyl C(3) atom. The solvent-displacement reaction is of first and zeroth orders with respect to indole-3-acetamide and cis-[Pt(en)(sol)2]2+, respectively. A mechanism consisting of initial unidentate coordination of the ligand via the amide oxygen atom followed by closing of the spiro ring is supported by 1H NMR data, the kinetic effects of acid and water, and the activation parameters for the displacement reaction. In the case of N-(3-indolylacetyl)-L-phenylalanine, the bulkiest of the entering ligands, the reaction is of first order with respect to both reactants. The bidentate indole-3-acetamide ligand in 3 is readily displaced by (CH3)2SO and 2-methylimidazole, but not by CNO-, CH3COO-, and CH3CN. Complexes cis-[Pd(en)(sol)2]2+ and cis-[Pd(dtco)(sol)2]2+ react with indole-3-acetamide more rapidly than their Pt(II) analogues do and yield complexes similar to 3. This study augments our recent discovery of selective, hydrolytic cleavage of tryptophan-containing peptides by Pd(II) and Pt(II) complexes. PMID:11233196

Kaminskaia, N V; Ullmann, G M; Fulton, D B; Kostic, N M

2000-10-30

345

Seven-coordinate anion complex with a tren-based urea: Binding discrepancy of hydrogen sulfate in solid and solution states  

SciTech Connect

Structural characterization of a hydrogen sulfate complex with a tren-based urea suggests that the anion is coordinated with sixNH Obonds (dN O = 2.857 (3) to 3.092 (3)A ) and one OH O bond (dO O = 2.57 (2) A ) from three receptors; however, in solution the anion is bound within the pseudocavity of one receptor.

Pramanik, Avijit [Jackson State University; Thompson, Bethtrice [Jackson State University; Hayes, Trina [Jackson State University; Tucker, Kimberly [Jackson State University; Powell, Douglas R. [University of Oklahoma, Norman; Bonnesen, Peter V [ORNL; Ellis, Erick D [Jackson State University; Lee, Ken S. [Jackson State University; Yu, Hongtau [Jackson State University; Hossain, Md. Alamgir [Jackson State University

2011-01-01

346

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

347

Synthesis of 2D polymeric dicyanamide bridged hexa-coordinated Cu(II) complex: Structural characterization, spectral studies and TDDFT calculation  

NASA Astrophysics Data System (ADS)

A rare 2D polymeric dicyanamide bridged hexa-coordinated copper(II) complex [Cu(L1?)(?1,5-dca)2]n (1) (L1? = 2-carboxypyrazine) has been synthesized from the reaction of Cu(NO3)2?6H2O, 2-pyrazinecarbonitrile (L1) and sodium dicyanamide (Nadca) in methanolic medium. Single crystal X-ray analysis reveals that the complex has a 2D infinite zigzag chain structure in which copper(II) ions are bridged by single dicyanamide ligand in an end-to-end fashion. Such 2-carboxypyrazine can be obtained on the way of metal-assisted nitrile hydrolysis which well connected with Cu(NO3)2?6H2O and dicyanamide (dca) to give rare 2D Cu(II) polymeric complex due to the flexibility in the coordination ability of the copper(II) ions within the polymeric chain. The geometry of the asymmetric unit of the complex was optimized in singlet state by DFT method with multilayer ONIOM model at doublet spin state accordance with repeating asymmetric unit only. The electronic spectrum of the complex is explained using TDDFT calculation.

Konar, Saugata; Saha, Urmila; Dolai, Malay; Chatterjee, Sudipta

2014-10-01

348

Sensitivity of X-ray core spectroscopy to changes in metal ligation: a systematic study of low-coordinate, high-spin ferrous complexes.  

PubMed

In order to assess the sensitivity and complementarity of X-ray absorption and emission spectroscopies for determining changes in the metal ligation sphere, a systematic experimental and theoretical study of iron model complexes has been carried out. A series of high-spin ferrous complexes, in which the ligation sphere has been varied from a three-coordinate complex, [L(tBu)Fe(SPh)] (1) (where L(tBu) = bulky ?-diketiminate ligand; SPh = phenyl thiolate) to four-coordinate complexes [L(tBu)Fe(SPh)(X)] (where X = CN(t)Bu (2); 1-methylimidazole (3); or N,N-dimethylformamide (DMF) (4)), has been investigated using a combination of Fe K-edge X-ray absorption (XAS) and K? X-ray emission (XES) spectroscopies. The Fe K XAS pre-edge and edge of all four complexes are consistent with a high-spin ferrous assignment, with the largest differences in the pre-edge intensities attributed to changes in covalency of the fourth coordination site. The X-ray emission spectra show pronounced changes in the valence to core region (V2C) as the identity of the coordinated ligand is varied. The experimental results have been correlated to density functional theory (DFT) calculations, to understand key molecular orbital contributions to the observed absorption and emission features. The calculations also have been extended to a series of hypothetical high-spin iron complexes to understand the sensitivity of XAS and XES techniques to different ligand protonation states ([L(tBu)Fe(II)(SPh)(NHn)](3-n) (n = 3, 2, 1, 0)), metal oxidation states [L(tBu)Fe(SPh)(N)](n-) (n = 3, 2, 1), and changes in the ligand identity [L(tBu)Fe(IV)(SPh)(X)](n-) (X = C(4-), N(3-), O(2-); n = 2, 1, 0). This study demonstrates that XAS pre-edge data have greater sensitivity to changes in oxidation state, while valence to core (V2C) XES data provide a more sensitive probe of ligand identity and protonation state. The combination of multiple X-ray spectroscopic methods with DFT results thus has the potential to provide for detailed characterization of complex inorganic systems in both chemical and biological catalysis. PMID:23662855

Chandrasekaran, P; Chiang, Karen P; Nordlund, Dennis; Bergmann, Uwe; Holland, Patrick L; DeBeer, Serena

2013-06-01

349

A novel 3D heterometallic coordination complex with (3,4,5)-connected net topology: Synthesis, structure and luminescent property  

NASA Astrophysics Data System (ADS)

A novel three-dimensional Ag(I)-Pb(II) heteronuclear coordination polymer, namely [Ag2Pb2(BTC)2(H2O)2]n (1), where H3BTC = 1,3,5-benzenetricarboxyl acid, has been hydrothermally synthesized and structurally characterized by elemental analysis(EA), infrared spectroscopy(IR) and single crystal X-ray diffraction. The BTC3- ligand exhibits an interesting coordination mode to form a three-dimensional (3D) framework with a novel hexa-nodal (3,4,5)-connected net topology. The thermal stability and solid state fluorescence of 1 have also been investigated.

Sun, Qiao-Zhen; Yin, Yi-Biao; Chai, Li-Yuan; Liu, Hui; Hao, Peng-Fei; Yan, Xue-Ping; Guo, Yu-Qi

2014-07-01

350

Vibrational Spectra of Discrete UO?? 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 [UO?(X)(ACO)?]+ (where 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 ?? UO? 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 its binding in the complex. The ?? peak in the spectrum of the F-containing complex was 9 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 higher wavenumber was seen for the complexes with the more nucleophilic anions, consistent with the idea that they loosen solvent binding. Surprisingly, the ?1 stretch was activated when the softer anions Cl, Br and I were present in the complexes. IR studies of the anionic complexes [UO?X?]- (where X = Cl-, Br- and I-) compared the ?? UO? modes versus halide, and showed that the ?? values decreased with increasing anion nucleophilicity. This observation was consistent with DFT calculations that indicated that [UO?X?]--X. and [UO?X?].-X- dissociation energies decreased on the order F > Cl > Br > I. The trifluoro complex could not be photodissociated in these experiments.

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

2010-11-01

351

Bioreduction of hydrogen uranyl phosphate: mechanisms and U(IV) products.  

PubMed

The mobility of uranium (U) in subsurface environments is controlled by interrelated adsorption, redox, and precipitation reactions. Previous work demonstrated the formation of nanometer-sized hydrogen uranyl phosphate (abbreviated as HUP) crystals on the cell walls of Bacillus subtilis, a non-U(VI)-reducing, Gram-positive bacterium. The current study examined the reduction of this biogenic, cell-associated HUP mineral by three dissimilatory metal-reducing bacteria, Anaeromyxobacter dehalogenans strain K, Geobacter sulfurreducens strain PCA, and Shewanella putrefaciens strain CN-32, and compared it to the bioreduction of abiotically formed and freely suspended HUP of larger particle size. Uranium speciation in the solid phase was followed over a 10- to 20-day reaction period by X-ray absorption fine structure spectroscopy (XANES and EXAFS) and showed varying extents of U(VI) reduction to U(IV). The reduction extent of the same mass of HUP to U(IV) was consistently greater with the biogenic than with the abiotic material under the same experimental conditions. A greater extent of HUP reduction was observed in the presence of bicarbonate in solution, whereas a decreased extent of HUP reduction was observed with the addition of dissolved phosphate. These results indicate that the extent of U(VI) reduction is controlled by dissolution of the HUP phase, suggesting that the metal-reducing bacteria transfer electrons to the dissolved or bacterially adsorbed U(VI) species formed after HUP dissolution, rather than to solid-phase U(VI) in the HUP mineral. Interestingly, the bioreduced U(IV) atoms were not immediately coordinated to other U(IV) atoms (as in uraninite, UO2) but were similar in structure to the phosphate-complexed U(IV) species found in ningyoite [CaU(PO4)2H2O]. This indicates a strong control by phosphate on the speciation of bioreduced U(IV), expressed as inhibition of the typical formation of uraninite under phosphate-free conditions. PMID:23634690

Rui, Xue; Kwon, Man Jae; O'Loughlin, Edward J; Dunham-Cheatham, Sarrah; Fein, Jeremy B; Bunker, Bruce; Kemner, Kenneth M; Boyanov, Maxim I

2013-06-01

352

Developing predictive rules for coordination geometry from visible circular dichroism of copper(II) and nickel(II) ions in histidine and amide main-chain complexes.  

PubMed

Circular dichroism (CD) spectroscopy in the visible region (vis-CD) is a powerful technique to study metal-protein interactions. It can resolve individual d-d electronic transitions as separate bands and is particularly sensitive to the chiral environment of the transition metals. Modern quantum chemical methods enable CD spectra calculations from which, along with direct comparison with the experimental CD data, the conformations and the stereochemistry of the metal-protein complexes can be assigned. However, a clear understanding of the observed spectra and the molecular configuration is largely lacking. In this study, we compare the experimental and computed vis-CD spectra of Cu(2+)-loaded model peptides in square-planar complexes. We find that the spectra can readily discriminate the coordination pattern of Cu(2+) bound exclusively to main-chain amides from that involving both main-chain amides and a side-chain (i.e. histidine side-chain). Based on the results, we develop a set of empirical rules that relates the appearance of particular vis-CD spectral features to the conformation of the complex. These rules can be used to gain insight into coordination geometries of other Cu(2+)- or Ni(2+)-protein complexes. PMID:25039600

Stanyon, Helen F; Cong, Xiaojing; Chen, Yan; Shahidullah, Nabeela; Rossetti, Giulia; Dreyer, Jens; Papamokos, George; Carloni, Paolo; Viles, John H

2014-09-01

353

Synthesis, characterization, and in vitro evaluation of new coordination complexes of platinum(II) and rhenium(I) with a ligand targeting the translocator protein (TSPO).  

PubMed

The 18 kDa translocator protein (TSPO) is overexpressed in many types of cancers and is also abundant in activated microglial cells occurring in inflammatory neurodegenerative diseases. The TSPO-selective ligand 2-(8-(2-(bis-(pyridin-2-yl-methyl)amino)acetamido)-2-(4-chlorophenyl)H-imidazo[1,2-a]pyridin-3-yl)-N,N-dipropylacetamide (CB256), which fulfills the requirements of a bifunctional chelate approach, has been used to synthesize coordination complexes containing either Pt (1) or Re (3), or both metal ions (2). The new metal complexes showed a cellular uptake markedly greater than that of the precursor metallic compounds and were also able to induce apoptosis in C6 glioma cells. The good cytotoxicity of the free ligand CB256 towards C6, A2780, and A2780cisR tumor cell lines was attenuated after coordination of the dipicolylamine moiety to Pt while coordination of the imidazopyridine residue to Re reduces the affinity towards TSPO. The results of the present investigation are essential for the design of new imidazopyridine bifunctional chelate ligands targeted to TSPO. PMID:25069996

Margiotta, Nicola; Denora, Nunzio; Piccinonna, Sara; Laquintana, Valentino; Lasorsa, Francesco Massimo; Franco, Massimo; Natile, Giovanni

2014-11-21

354

Platinum complexes of a borane-appended analogue of 1,1'-bis(diphenylphosphino)ferrocene: flexible borane coordination modes and in situ vinylborane formation.  

PubMed

A bis(phosphine)borane ambiphilic ligand, [Fe(?(5) -C5 H4 PPh2 )(?(5) -C5 H4 PtBu{C6 H4 (BPh2 )-ortho})] (FcPPB), in which the borane occupies a terminal position, was prepared. Reaction of FcPPB with tris(norbornene)platinum(0) provided [Pt(FcPPB)] (1) in which the arylborane is ?(3) BCC-coordinated. Subsequent reaction with CO and CNXyl (Xyl=2,6-dimethylphenyl) afforded [PtL(FcPPB)] {L=CO (2) and CNXyl (3)} featuring ?(2) BC- and ?(1) B-arylborane coordination modes, respectively. Reaction of 1 or 2 with H2 yielded [PtH(?-H)(FcPPB)] in which the borane is bound to a hydride ligand on platinum. Addition of PhC2 H to [Pt(FcPPB)] afforded [Pt(C2 Ph)(?-H)(FcPPB)] (5), which rapidly converted to [Pt(FcPPB')] (6; FcPPB'=[Fe(?(5) -C5 H4 PPh2 )(?(5) -C5 H4 PtBu{C6 H4 (BPh-CPh=CHPh-Z)-ortho}]) in which the newly formed vinylborane is ?(3) BCC-coordinated. Unlike arylborane complex 1, vinylborane complex 6 does not react with CO, CNXyl, H2 or HC2 Ph at room temperature. PMID:25319095

Cowie, Bradley E; Emslie, David J H

2014-12-15

355

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

356

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

357

Synthesis, structural characterization and antimicrobial activity evaluation of metal complexes of sparfloxacin.  

PubMed

The synthesis and characterization of binary Cu(II)- (1), Co(II)- (2), Ni(II)- (3), Mn(II)- (4), Cr(III)- (5), Fe(III)- (6), La(III)- (7), UO(2)(VI)- (8) complexes with sparfloxacin (HL(1)) and ternary Cu(II)- (9), Co(II)- (10), Ni(II)- (11), Mn(II)- (12), Cr(III)- (13), Fe(III)- (14), La(III)- (15), UO(2)(VI)- (16) complexes with sparfloxacin (HL(1)) and DL-alanine (H(2)L(2)) complexes are reported using elemental analysis, molar conductance, magnetic susceptibility, IR, UV-Vis, thermal analysis and (1)H-NMR spectral studies. The molar conductance measurements of all the complexes in DMF solution correspond to non-electrolytic nature. All complexes were of the high-spin type and found to have six-coordinate octahedral geometry except the Cu(II) complexes which were four coordinate, square planar and U- and La-atoms in the uranyl and lanthanide have a pentagonal bipyramidal coordination sphere. The antimicrobial activity of these complexes has been screened against two gram-positive and two gram-negative bacteria. Antifungal activity against two different fungi has been evaluated and compared with reference drug sparfloxacin. All the binary and ternary complexes showed remarkable potential antimicrobial activity higher than the recommended standard agents. Ni(II)- and Mn(II) complexes exhibited higher potency as compared to the parent drug against gram-negative bacteria. PMID:21856215

el-Gamel, Nadia E A; Zayed, M A

2011-11-01

358

Metal ion as both a cofactor and a probe of metal-binding sites in a uranyl-specific DNAzyme: a uranyl photocleavage study  

PubMed Central

DNAzymes are known to bind metal ions specifically to carry out catalytic functions. Despite many studies since DNAzymes were discovered nearly two decades ago, the metal-binding sites in DNAzymes are not fully understood. Herein, we adopt uranyl photocleavage to probe specific uranyl-binding sites in the 39E DNAzyme with catalytically relevant concentrations of uranyl. The results indicate that uranyl binds between T23 and C25 in the bulge loop, G11 and T12 in the stem loop of the enzyme strand, as well as between T2.4 and G3 close to the cleavage site in the substrate strand. Control experiments using two 39E DNAzyme mutants revealed a different cleavage pattern of the mutated region. Another DNAzyme, the 817 DNAzyme, which has a similar secondary structure but shows no activity in the presence of uranyl, indicated a different uranyl-dependent photocleavage as well. In addition, a close correlation between the concentration-dependent photocleavage and enzymatic activities is also demonstrated. Together, these experiments suggest that uranyl photocleavage has been successfully used to probe catalytically relevant uranyl-binding sites in the 39E DNAzyme. As uranyl is the cofactor of the 39E DNAzyme as well as the probe, specific uranyl binding has now been identified without disruption of the structure. PMID:23939617

Cepeda-Plaza, Marjorie; Null, Eric L.; Lu, Yi

2013-01-01

359

Synthesis, characterization, and antitumor activity of unusual pseudo five coordinate gold(III) complexes: distinct cytotoxic mechanism or expensive ligand delivery systems?  

PubMed

Gold(III) complexes bearing bidentate ligands based on the 1,10-phenanthroline and 2,2'-bipyridine scaffolds have shown promising anticancer activity against a variety of tumor cell lines. In particular, our laboratory has previously found that a pseudo five coordinate gold(III) complex possessing the 2,9-di-sec-butyl-1,10-phenanthroline ligand {[((di-sec-butyl)phen)AuCl3]} exhibits antitumor activity against a panel of five different lung and head-neck tumor cell lines. However, the [((di-sec-butyl)phen)AuCl3] complex was determined to be less active than the free 2,9-di-sec-butyl-1,10-phenanthroline ligand. In order to determine if this class of gold(III) complexes has a distinct mechanism of initiating tumor cell death or if these gold complexes simply release the polypyridyl ligand in the intracellular environment, structural analogues of the [((di-sec-butyl)phen)AuCl3] complex have been synthesized and structurally characterized. These structural congeners were prepared by using mono-alkyl and di-phenyl substituted 1,10-phenanthroline ligands, di-alkyl and di-phenyl substituted 4-methyl-1,10-phenanthroline ligands, and mono-alkyl 2,2'-bipyridine ligands. The redox stability of this library of distorted square pyramidal gold(III) complexes has been studied and the in vitro antitumor activity of gold(III) complexes and corresponding polypyridyl ligands has been determined. The [((di-n-butyl)phen)AuCl3] and [((mono-n-butyl)phen)AuCl3] complexes have been found to be significantly more potent at inhibiting the growth of A549 lung tumor cells than the clinically used drug cisplatin. More importantly, these two gold(III) complexes are significantly more active than their respective free ligands, providing evidence that this class of pseudo five coordinate gold(III) complexes has a mechanism of initiating tumor cell death that is independent of the free ligand. PMID:25243390

Olsen, Pauline M; Ruiz, Charles; Lussier, Daniel; Le, Brian Khoa; Angel, Noah; Smith, Michelle; Hwang, Chihyun Brian; Khatib, Raneen; Jenkins, Julia; Adams, Kaitlyn; Getcher, Jonathan; Tham, Fook; Chen, Zhou Georgia; Wilson, Emma H; Eichler, Jack F

2014-12-01

360

Unusual sevenfold coordination of Ru in complex hydride Na3RuH7: Prospect for formation of [FeH7]3- anion  

NASA Astrophysics Data System (ADS)

We used density-functional calculations to clarify the origin of the unusual sevenfold coordination of Ru by H in Na3RuH7. We found that the D5h symmetry of the ligands enables the formation of strong covalent bonds of Ru and H through ligand-field effects, stabilizing the sevenfold coordination. We also examined the possible synthesis of the hypothetical 3d analog, Li3FeH7, which has a gravimetric hydrogen density of 8.4 mass%. The calculated enthalpy change of -16 kJ/mol H2 for the reaction, 3LiH+Fe+2H2?Li3FeH7, reveals a possible route to a stable complex hydride containing [FeH7]3-.

Takagi, Shigeyuki; Ikeshoji, Tamio; Matsuo, Motoaki; Sato, Toyoto; Saitoh, Hiroyuki; Aoki, Katsutoshi; Orimo, Shin-ichi

2013-09-01

361

Controlling Proton Movement: Electrocatalytic Oxidation of Hydrogen by a Nickel(II) Complex Containing Proton Relays in the Second and Outer Coordination Spheres  

SciTech Connect

A nickel bis(diphosphine) complex containing proton relays in the second and outer coordination spheres, Ni(PCy2N(CH2)2OMe)2, (PCy2N(CH2)2OMe = 1,5-di(methoxyethyl)-3,7-dicy?clohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to? the Ni(II) complex results in rapid formation of three isomers of the doubly protonated ?Ni(0) complex, [Ni(PCy2N(CH2)2OMe2H)2]2+. The three isomers show fast intramolecular interconversion at 40 ?C, unique to this complex in this class of catalysts. Under conditions of 1.0 atm H2 using H2O as a base, catalytic oxidation proceeds at a turnover frequency of 5 s?1 and an overpotential of 720 mV, as determined from the potential at half of the catalytic current. Compared to the previously reported Ni(PCy2NBn)2 complex, the new complex operates at a faster rate and at a lower overpotential. The results of this study indicate that the presence of the pendant methoxy group in the outer coordination sphere of the catalyst plays a key role, facilitating intramolecular proton movement prior to intermolecular proton removal required to complete the catalytic cycle. 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.

Das, Partha Pratim; Ho, Ming-Hsun; O'Hagan, Molly J.; Shaw, Wendy J.; Bullock, R. Morris; Raugei, Simone; Helm, Monte L.

2014-02-21

362

Extraction of nitric acid, uranyl nitrate, and bismuth nitrate from aqueous nitric acid solutions with CMPO  

SciTech Connect

DOE sponsored development of the transuranium extraction (TRUEX) process for removing actinides from radioactive wastes. The solvent is a mixture of CMPO and TBP. Since the extraction characteristics of CMPO are not as well understood as those of TBP, the extraction of nitric acid, uranyl nitrate, and bismuth nitrate with CMPO (dissolved in n-dodecane) were studied. Results indicate that CMPO extracts nitric acid with a 1:1 stoichiometry; equilibrium constant is 2. 660{plus_minus}0.092 at 25 C, and extraction enthalpy is -5. 46{plus_minus}0.46 kcal/mol. Slope analysis indicates that uranyl nitrate extracts with a mixed equilibria of 1:1 and 2:1 stoichiometries in nearly equal proportion. Equil. constant of the 2: 1 extraction was 1.213 {times} 10{sup 6}{plus_minus}3.56 {times} 10{sup 4} at 25 C; reaction enthalpy was -9.610{plus_minus}0.594 kcal/mol. Nitration complexation constant is 8.412{plus_minus}0.579, with an enthalpy of -10.72{plus_minus}1.87 kcal/mol. Bismuth nitrate also extracts with a mixed equilibria of (perhaps) 1:1 and 2:1 stoichiometries. A 2:1 extraction equilibrium and a nitrate complexation adequately model the data. Kinetics and enthalpies were also measured.

Spencer, B.B.

1995-08-01

363

Synthesis, structural characterization, and biological studies of six- and five-coordinate organotin(IV) complexes with the thioamides 2-mercaptobenzothiazole, 5-chloro-2-mercaptobenzothiazole, and 2-mercaptobenzoxazole.  

PubMed

Organotin(IV) complexes with the formulas [(C6H5)3Sn(mbzt)] (1), [(C6H5)3Sn(cmbzt)] (3), and [(C6H5)2Sn(cmbzt)2] (4) (Hmbzt = 2-mercaptobenzothiazole and Hcmbzt = 5-chloro-2-mercaptobenzothiazole) have been synthesized and characterized by elemental analysis; FT-IR, Raman, 1H, 13C, and 119Sn NMR, and Mssbauer spectroscopic techniques; and X-ray crystallography at various temperatures. The crystal structures of complexes 1, 3, and 4 were determined by X-ray diffraction at room temperature [295(1) or 293(2) K]. The complexes [(C6H5)3Sn(mbzo)] (2) and [(n-C4H9)2Sn(cmbzt)2] (5) (Hmbzo = 2-mercaptobenzoxazole) were synthesized by new improved methods, and their structures were determined at low temperature [100(1) K] and compared to those solved at room temperature. Comparison with {(CH3)2Sn(cmbzt)2]} (6), already reported, was also attempted. The influence of temperature on the geometry of the complexes is discussed. In the cases of complexes 1-3, three carbon atoms from phenyl groups and one sulfur atom and one nitrogen atom from thione ligands form a tetrahedrally distorted trigonal-bipyramidal geometry around the five-coordinate tin(IV) ion. In complexes 4-6, two carbon atoms from aryl groups and two sulfur atoms and two nitrogen atoms from thione ligands form a distorted tetrahedral geometry, tending toward octahedral, around the six-coordinate tin(IV) ions, with trans-C2, cis-N2, and cis-S2 configurations. Although the C-Sn and S-Sn bond distances are found to be constant in compounds 1-6, their N-Sn bond lengths vary significantly (from 2.635 to 3.078 A), with the longer distances found in the cases of five-coordinate complexes 1-3. PMID:17291115

Xanthopoulou, Marianna N; Hadjikakou, Sotiris K; Hadjiliadis, Nick; Kubicki, Maciej; Skoulika, Stavroula; Bakas, Thomas; Baril, Martin; Butler, Ian S

2007-02-19

364

Zirconium and hafnium complexes containing N-alkyl substituted amine biphenolate ligands: coordination chemistry and living ring-opening polymerization catalysis.  

PubMed

The coordination chemistry of zirconium and hafnium complexes containing the tridentate amine biphenolate ligands [RN(CH2-2-O-3,5-C6H2(tBu)2)2](2-) ([R-ONO](2-); R = tBu (1a), iPr (1b), nPr (1c)) featuring distinct N-alkyl substituents is described. Alcoholysis of Zr(OiPr)4(HOiPr) or Hf(OiPr)4(HOiPr) with H2[1a] in diethyl ether solutions at -35 C generates the corresponding five-coordinate [1a]M(OiPr)2 (M = Zr (2a), Hf (3a)) in high isolated yield. Similar reactions employing H2[1b] produce six-coordinate [1b]M(OiPr)2(HOiPr) (M = Zr (2bHOiPr), Hf (3bHOiPr)) as an isopropanol adduct. Repetitive trituration of 2bHOiPr and 3bHOiPr with diethyl ether gives five-coordinate 2b and 3b, respectively. Treatment of M(OiPr)4(HOiPr) with H2[1c] under similar conditions affords six-coordinate [1c]M(OiPr)2(HOiPr) (M = Zr (2cHOiPr), Hf (3cHOiPr)), subsequent recrystallization of which from acetonitrile-diethyl ether solutions leads to acetonitrile adducts 2cMeCN and 3cMeCN. Reactivity studies of these zirconium and hafnium complexes revealed that they are all active catalysts for ring-opening polymerization of ?-caprolactone. Among them, the N-isopropyl derived complexes are most reactive. Polymerizations catalyzed by 2b, 3b and 3cMeCN were proved to be living. The X-ray structures of 2aHOiPr, 2aMeCN, 2cHOiPr, 2cMeCN, and 3cMeCN are presented. PMID:23518868

Liang, Lan-Chang; Lin, Sheng-Ta; Chien, Chia-Cheng; Chen, Ming-Tsz

2013-07-01

365

(Arene)Cl?Ru(II) complexes with N-coordinated estrogen and androgen isonicotinates: interaction with sex hormone binding globulin and anticancer activity.  

PubMed

(Arene)dichloridoruthenium(II) complexes with N-coordinated isonicotinates of androgens (6) and estrogens (9) were prepared and tested for affinity to the estrogen receptor (ER?) and sex hormone binding globulin (SHBG), as well as for cytotoxicity in cancer cells. None of the new complexes bound noticeably to the ER and most of them also bound less strongly to SHBG than the corresponding unmetallated steroids 7. In MTT assays the Ru(p-cymene) complexes 9 of 2-substituted estrones were equally or even more cytotoxic than the metal-free steroids against hormone-dependent (MCF-7 breast and KB-V1 cervix carcinomas) and hormone-independent (518A2 melanoma) cells. The addition of external SHBG to MTT assays lowered the cytotoxicities of the complexes 9 and distinctly more so those of some steroids 7, probably by the way of sequestration and reduction of the cellular uptake. In the absence of SHBG the estrogen complexes 9 were internalized by 518A2 melanoma cells and ruthenated their DNA as quantified by ICP-OES. They also ruthenated salmon sperm DNA but did not change the topology of plasmid DNA in EMSA experiments. In addition, the Ru(p-cymene) complex of 2-ethoxyestrone (9c) was shown to reduce the motility of 518A2 melanoma cells in a wound-healing assay. PMID:21184767

Schobert, Rainer; Seibt, Sebastian; Effenberger-Neidnicht, Katharina; Underhill, Caroline; Biersack, Bernhard; Hammond, Geoffrey L

2011-03-01

366

RME-8 coordinates the activity of the WASH complex with the function of the retromer SNX dimer to control endosomal tubulation  

PubMed Central

ABSTRACT Retromer is a vital element of the endosomal protein sorting machinery and comprises two subcomplexes that operate together to sort membrane proteins (cargo) and tubulate membranes. Tubules are formed by a dimer of sorting nexins, a key component of which is SNX1. Cargo selection is mediated by the VPS35VPS29VPS26 trimer, which additionally recruits the WASH complex through VPS35 binding to the WASH complex subunit FAM21. Loss of function of the WASH complex leads to dysregulation of endosome tubulation, although it is unclear how this occurs. Here, we show that FAM21 also binds to the SNX1-interacting DNAJ protein RME-8. Loss of RME-8 causes altered kinetics of SNX1 membrane association and a pronounced increase in highly branched endosomal tubules. Building on previous observations from other laboratories, we show that these tubules contain membrane proteins that are dependent upon WASH complex activity for their localization to the plasma membrane. Therefore, we propose that the interaction between RME-8 and the WASH complex provides a means to coordinate the activity of the WASH complex with the membrane-tubulating function of the sorting nexins at sites where retromer-mediated endosomal protein sorting occurs. PMID:24643499

Freeman, Caroline L.; Hesketh, Geoffrey; Seaman, Matthew N. J.

2014-01-01

367

NH-S hydrogen bonding in zinc enzyme model complex with S 2N 2 binding set studied by normal coordinate analysis of vibrational spectra  

NASA Astrophysics Data System (ADS)

In order to provide theoretical evidence for the existence and effect of NH-S hydrogen bonding in the zinc enzyme model complex [Zn(S-2-C 6H 4NHCOC 6H 5) 2(1-MeIm) 2] (1-MeIm=1-methylimidazole) in addition to the spectroscopic and crystallographic investigations, normal coordinate analysis (NCA) was carried out using a modified Urey-Bradley force field. The vibrational frequencies of the complex with and without the NH-S hydrogen bonding as well as the corresponding internal coordinates were obtained. The good agreement found between the calculated and observed frequencies in the presence of the NH-S hydrogen bond, supports the reliability of the analysis. The stretching force constant of the NH-S hydrogen bond obtained from the calculation is 0.18 mdyne per . The calculation shows that the N-H bond is weakened by formation of the NH-S hydrogen bond. The results are indicative of the existence of the NH-S hydrogen bond in the complex.

Shi, Xiao-Feng; Sun, Wei-Yin; Zhang, Li; Li, Chong-De

2000-02-01

368

A theoretical study on the formation of 1 + 1 versus 2 + 2 macrocyclic Schiff base complexes in the absence of coordinated anions  

Microsoft Academic Search

This work reports a theoretical study on 1+1 against 2+2 cyclocondensation reactions between 2,6-diacetylpyridine and 3,6-dioxaoctane-l,8-diamine in the presence of Mg(II) and Pb(II) metal ions. The results of calculations at DFT(B3LYP) level of theory using LanL2DZ, SDD and CEP-121G basis sets indicate that in the absence of a coordinated anion the 1+1 macrocyclic Schiff base complexes are the preferred products

Sadegh Salehzadeh; Mehdi Bayat

2011-01-01

369

Spin-filtering, giant magnetoresistance, rectifying and negative differential resistance effects in planar four-coordinate Fe complex with graphene nanoribbon electrodes  

SciTech Connect

By using the nonequilibrium Green's function formalism combined with the density functional theory, we have investigated the spin-polarized transport properties of a planar four-coordinate Fe complex sandwiched between two zigzag-edge graphene nanoribbon (ZGNR) electrodes, where the ZGNRs are modulated by external magnetic field. The results show that the system can exhibit perfect dual spin-filtering and spin-rectifying effects at a wide bias range, giant magnetoresistance effect with large magnetoresistance ratio at small bias, and obvious negative differential resistance behavior. The mechanisms are proposed for these phenomena.

Zhao, P., E-mail: ss-zhaop@ujn.edu.cn, E-mail: ss-cheng@ujn.edu.cn; Wu, Q. H.; Chen, G., E-mail: ss-zhaop@ujn.edu.cn, E-mail: ss-cheng@ujn.edu.cn [School of Physics and Technology, University of Jinan, Jinan 250022 (China); Liu, D. S. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China) [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Department of Physics, Jining University, Qufu 273155 (China)

2014-01-28

370

Uranyl peroxide enhanced nuclear fuel corrosion in seawater  

PubMed Central

The Fukushima-Daiichi nuclear accident brought together compromised irradiated fuel and large amounts of seawater in a high radiation field. Based on newly acquired thermochemical data for a series of uranyl peroxide compounds containing charge-balancing alkali cations, here we show that nanoscale cage clusters containing as many as 60 uranyl ions, bonded through peroxide and hydroxide bridges, are likely to form in solution or as precipitates under such conditions. These species will enhance the corrosion of the damaged fuel and, being thermodynamically stable and kinetically persistent in the absence of peroxide, they can potentially transport uranium over long distances. PMID:22308442

Armstrong, Christopher R.; Nyman, May; Shvareva, Tatiana; Sigmon, Ginger E.; Burns, Peter C.; Navrotsky, Alexandra

2012-01-01

371

Rapid self-assembly of uranyl polyhedra into crown clusters.  

PubMed

Clusters built from 32 uranyl peroxide polyhedra self-assemble and crystallize within 15 min after combining uranyl nitrate, ammonium hydroxide, and hydrogen peroxide in aqueous solution under ambient conditions. These novel crown-shaped clusters are remarkable in that they form so quickly, have extraordinarily low aqueous solubility, form with at least two distinct peroxide to hydroxyl ratios, and form in very high yield. The clusters, which have outer diameters of 23 , topologically consist of eight pentagons and four hexagons. Their rapid formation and low solubility in aqueous systems may be useful properties at various stages in an advanced nuclear energy system. PMID:21608972

Sigmon, Ginger E; Burns, Peter C

2011-06-22

372

Coordination chemistry of manganesesalen complexes studied by electrospray tandem mass spectrometry: the significance of axial ligands 1 1 Dedicated to Bob Squires for his many seminal contributions to mass spectrometry and ion chemistry  

Microsoft Academic Search

Tandem mass spectrometric techniques in combination with high-level quantum chemical calculations have been employed to study the coordination chemistry of manganese and oxomanganesesalen complexes in the gas phase. Electrospray ionization was used to transfer the ionic complexes from solution to the gas phase. The formation of five- versus six-coordinate manganese(III) species was subsequently probed by ionmolecule reactions with neutral ligands,

Dietmar A Plattner; Derek Feichtinger; Jaouad El-Bahraoui; Olaf Wiest

2000-01-01

373

Seven-coordinate Co(II), Fe(II) and six-coordinate Ni(II) amide-appended macrocyclic complexes as ParaCEST agents in biological media.  

PubMed

The solution chemistry and solid-state structures of the Co(II), Fe(II), and Ni(II) complexes of 7,13-bis(carbamoylmethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L) are reported as members of a new class of paramagnetic chemical exchange saturation transfer (paraCEST) MRI contrast agents that contain transition metal ions. Crystallographic data show that nitrogen and oxygen donor atoms of the macrocyclic ligand coordinate to the metal ions to generate complexes with distorted pentagonal bipyramidal geometry for [Co(L)]Cl22H2O or [Fe(L)](CF3SO3)2. The Ni(II) complex [Ni(L)](CF3SO3)2H2O features a hexadentate ligand in a distorted octahedral geometry. The proton NMR spectra of all three complexes show highly dispersed and relatively sharp proton resonances. The complexes were further characterized by monitoring their dissociation under biologically relevant conditions including solutions containing phosphate and carbonate, ZnCl2, or acidic conditions. Solutions of the paraCEST agents in 20 mM N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (pH 7.4) and 100 mM NaCl showed highly shifted and intense CEST peaks at 59, 72, and 92 ppm away from bulk water for [Co(L)](2+), [Ni(L)](2+), and [Fe(L)](2+), respectively at 37 C on a 11.7 T NMR spectrometer. CEST spectra with corresponding rate constants for proton exchange are reported in 4% agarose gel (w/w), rabbit serum, egg white, or buffered solutions. CEST phantoms of 4 mM complex in buffer, 4% agarose gel (w/w), or rabbit serum on a 4.7 T MRI scanner at 37 C, are compared. The most substantial change was observed for the reactive [Ni(L)](2+), which showed reduced CEST contrast in rabbit serum and egg white. The complexes with the least highly shifted CEST peaks ([Co(L)](2+) and [Ni(L)](2+)) showed a reduction in CEST contrast in 4% agarose gel (w/w) compared to that in buffered solutions, while the CEST effect for [Fe(L)](2+) in 4% agarose gel (w/w) was not substantially different. PMID:24820102

Olatunde, Abiola O; Cox, Jordan M; Daddario, Michael D; Spernyak, Joseph A; Benedict, Jason B; Morrow, Janet R

2014-08-18

374

Optical properties of ammonium uranyl fluoride characterized by photoluminescence and photoacoustic spectroscopy  

NASA Astrophysics Data System (ADS)

PL and PAS studies were performed on uranyl compounds viz. uranium oxalate, uranium fluoride and ammonium uranyl fluoride. PL and PAS spectrum of ammonium uranyl fluoride is being reported for the first time. Ammonium uranyl fluoride is blue shifted with respect to uranyl fluoride, as a result of ammonium bonding. The vibronic separations were determined in the excited state and the ground state using excitation/PA spectra and emission spectra respectively. Fluorescence decay data could be fitted only with biexponential decay in all of these compounds indicating the presence of two different environments in these compounds. Low temperature luminescence leads to enhancement in emission intensity and lifetime value. The temperature dependence studies of average fluorescence lifetimes of ammonium uranyl are described in this paper. Based on this studies activation energy value for ammonium uranyl fluoride at which 3? and 1? potential surfaces will cross is calculated.

Gupta, Santosh K.; Dhobale, A. R.; Natarajan, V.; Godbole, S. V.

2014-01-01

375

Copper(II)-bis-Histidine Coordination Structure in Fibrillar Amyloid-? Peptide Fragment and Model Complexes Revealed by using Electron Spin Echo Envelope Modulation Spectroscopy  

PubMed Central

Truncated and mutated amyloid-? (A?) peptides are models for systematic study of the molecular origins of metal ion effects on A? aggregation rates, types of aggregate structures formed, and cytotoxicity, in homogeneous preparations. The 3-D geometry of bis-histidine imidazole coordination of Cu(II) in fibrils of the nonapetide, acetyl-A?(13-21)H14A, is determined by using powder 14N electron spin echo envelope modulation (ESEEM) spectroscopy. The method of simulation of the anisotropic combination modulation is described, and benchmarked for a Cu(II)-bis-cis-imidazole complex of known structure. The revealed bis-cis coordination mode, and mutual orientation of the imidazole rings, for Cu(II) in Ac-A?(13-21)H14A fibrils are consistent with the proposed ?-sheet structural model, and pair-wise peptide interaction with Cu(II), with alternating [metalvacancy]n pattern, along the N-terminal edge. Metal coordination does not significantly distort the intra-?-strand peptide interactions, which provides a rationale for the Cu(II)-acceleration of Ac-A?(13-21)H14A fibrillization, through stabilization of the associated state, and low-reorganization integration of ?-strand peptide pair precursors. PMID:24014287

Hernndez-Guzmn, Jessica; Sun, Li; Mehta, Anil K.; Dong, Jijun; Lynn, David G.; Warncke, Kurt

2013-01-01

376

Coordination of degrees of freedom and stabilization of task variables in a complex motor skill: expertise-related differences in cello bowing.  

PubMed

Stringed instrument bowing is a complex sensorimotor skill, involving fine regulation of bow orientation and motion relative to the string. In this study, we characterize this skill in terms of stabilization of specific bow parameters as well as the underlying use and coordination of the degrees of freedom (DOF) of the right bowing arm. Age-matched samples of 10 advanced cellists and 10 cello novices took part in the study. Kinematic bow movement data were analyzed with respect to task variables suggested by the cello teaching literature: position and orientation of the bow relative to the string, bow velocity, and timing. Joint motion of the bowing arm was analyzed in terms of movement amplitude and inter-joint coordination (principal component analysis). As expected, novices showed poorer control of bowing parameters. In addition, novices differed markedly from advanced players in the use and coordination of the DOF of the bowing arm, with the elbow and wrist showing less overall movement and a reduced proportion of variance explained by the first principal component (PC1). In contrast, larger amounts of shoulder variance were explained by PC1 in novices compared to experts. Our findings support Bernstein's theory of graded skill acquisition, according to which early stages of motor skill learning are characterized by a "freezing" of movement DOF, while later learning stages exploit the DOF, possibly following a proximal-to-distal sequence, for improved task performance. PMID:23109087

Verrel, Julius; Pologe, Steven; Manselle, Wayne; Lindenberger, Ulman; Woollacott, Marjorie

2013-02-01

377

Varying coordination modes of amide ligand in group 12 Hg(ii) and Cd(ii) complexes: synthesis, crystal structure and nonlinear optical properties.  

PubMed

Reactions of the amide ligand, H2L (H2L = N,N'-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide) with CdCl2 and Hg(CH3COO)2, in 1?:?1 ratio, at 298 K yield dimeric [Hg(L)]2 () and trimeric [Cd3(H2L)4Cl6] (), respectively. In , the H2L is coordinated to Hg(ii) via six N-atoms of central and terminal pyridines as well as of deprotonated amido groups, whereas the carbonyl groups remain free. However, in , the H2L is coordinated to Cd(ii) through terminal pyridine N atoms and O atoms from carbonyl groups, whereas the nitrogen atoms of the central pyridine, two terminal pyridine and of all amido groups remain free. Molecular structures of and are confirmed by single crystal X-ray studies. The varying coordination modes of H2L give rise to different electrochemical behavior of and , which has also been rationalized by theoretical calculations. Moreover, nonlinear optical (NLO) behavior of both complexes has been investigated using ultra-short femtosecond laser pulses, which ensures that the NLO response is exclusively from their electronic component. PMID:25489669

Mobin, Shaikh M; Mishra, Veenu; Rai, Dhirendra K; Dota, Krithika; Dharmadhikari, Aditya K; Dharmadhikari, Jayashree A; Mathur, Deepak; Mathur, Pradeep

2014-12-23

378

Boron-dipyrromethene-functionalized hemilabile ligands as "turn-on" fluorescent probes for coordination changes in weak-link approach complexes.  

PubMed

Herein we report a new class of hemilabile ligands with boron-dipyrromethene (Bodipy) fluorophores that, when complexed to Pt(II), can signal changes in coordination mode through changes in their fluorescence. The ligands consist of phosphino-amine or phosphino-thioether coordinating moieties linked to the Bodipy's meso carbon via a phenylene spacer. Interestingly, this new class of ligands can be used to signal both ligand displacement and chelation reactions in a fluorescence "turn-on" fashion through the choice of weakly binding heteroatom in the hemilabile moiety, generating up to 10-fold fluorescence intensity increases. The Pt(II) center influences the Bodipy emission efficiency by regulating photoinduced electron transfer between the fluorophore and its meso substituent. The rates at which the excited Bodipy-species generate singlet oxygen upon excitation suggest that the heavy Pt(II) center also influences Bodipy's emission efficiency by affecting intersystem crossing from the Bodipy excited singlet to excited triplet states. This signaling strategy provides a quantitative read-out for changes in coordination mode and potentially will enable the design of new molecular systems for sensing and signal amplification. PMID:23570551

Lifschitz, Alejo M; Shade, Chad M; Spokoyny, Alexander M; Mendez-Arroyo, Jose; Stern, Charlotte L; Sarjeant, Amy A; Mirkin, Chad A

2013-05-01

379

Preparation of a nitrate-coordinated copper(II) complex of 2-(pyrazol-3-yl)-6-(pyrazolate)pyridine as an efficient catalyst for methyl methacrylate polymerization.  

PubMed

Treatment of [CuCl(2)(bppyH(2))] (1, bppyH(2) = 2,6-di(1H-pyrazol-3-yl)pyridine) with 2 equiv. of AgNO(3) in DMF gave rise to a binuclear Cu(II) complex [Cu(2)(bppyH)(2)(NO(3))(2)] (bppyH = 2-(pyrazol-3-yl)-6-(pyrazolate)pyridine) (2). Complex 2 was characterized by elemental analysis, IR and single crystal X-ray diffraction. Complex 2 has a dimeric structure in which the two Cu(ii) centers are bridged by a couple of the in situ-generated bppyH(-) anions. Each Cu(II) center is further coordinated by one O atom of a NO(3)(-) anion and three N atoms of one bppyH(-) anion. Complex 2 exhibited a higher catalytic activity in the polymerization of methyl methacrylate (MMA) than the precursor complex 1. Even though the ratio of catalyst to MMA was raised up to 1 : 1500, the PDI for 2 (reaction time was fixed at 4 h) is 1.63 and the conversion is up to 72%. The effects of solvent, reaction temperature and the ratio of MMA to catalyst were also investigated. PMID:22301825

Miao, Li-Li; Li, Hong-Xi; Yu, Miao; Zhao, Wei; Gong, Wei-Jie; Gao, Jun; Ren, Zhi-Gang; Wang, Hui-Fang; Lang, Jian-Ping

2012-03-28

380

Examination of the coordination sphere of Al(III) in trifluoromethyl-heteroarylalkenolato complex ions by gas-phase IRMPD spectroscopy and computational modelling.  

PubMed

A series of aluminium complex ions with trifluoromethyl-heteroarylalkenolato (TMHA) ligands are studied by gas-phase infrared multiphoton-dissociation (IRMPD) spectroscopy and computational modelling. The selected series of aluminium TMHA complex ions are promising species for the initial study of intrinsic binding characteristics of Al(III) cations in the gas phase as corresponding molecular ions. They are readily available for examination by (+) and (-) electrospray ionization mass spectrometry (ESI-MS) by spraying of [Al(3+)?(L(-))(3)] solutions. The complex ions under investigation contain trivalent Al(3+) cations with two chelating anionic enolate ligands, [Al(3+)?(L(-))(2)](+), providing insights in the nature of the heteroatom-Al bonds. Additionally, the structure of a deprotonated benzimidazole ligand, L(-,) and an anionic complex ion of Al(III) with two doubly deprotonated benzimidazole ligands, [Al(3+)?(L(2-))(2)](-), are examined by (-)ESI-IRMPD spectroscopy. Experimental and computational results are highly consistent and allow a reliable identification of the ion structures. In all complex ions examined the planar TMHA ligands are oriented perpendicular to each other around the metal ion, leading to a tetrahedral coordination sphere in which aluminium interacts with the enolate oxygen and heteroaryl nitrogen atoms available in each of the bidentate ligands. PMID:22442004

Brckmann, Lisa; Tyrra, Wieland; Mathur, Sanjay; Berden, Giel; Oomens, Jos; Meijer, Anthony J H M; Schfer, Mathias

2012-06-01

381

Low-dimensional coordination polymeric structures in alkali metal complex salts of the herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D).  

PubMed

The Li, Rb and Cs complexes with the herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D), namely poly[[aqua[?3-(2,4-dichlorophenoxy)acetato-?(3)O(1):O(1):O(1')]lithium(I)] dihydrate], {[Li(C8H5Cl2O3)(H2O)]2H2O}n, (I), poly[?-aqua-bis[?3-(2,4-dichlorophenoxy)acetato-?(4)O(1):O(1'):O(1'),Cl(2)]dirubidium(I)], [Rb2(C8H5Cl2O3)2(H2O)]n, (II), and poly[?-aqua-bis[?3-(2,4-dichlorophenoxy)acetato-?(5)O(1):O(1'):O(1'),O(2),Cl(2)]dicaesium(I)], [Cs2(C8H5Cl2O3)2(H2O)]n, (III), respectively, have been determined and their two-dimensional polymeric structures are described. In (I), the slightly distorted tetrahedral LiO4 coordination involves three carboxylate O-atom donors, of which two are bridging, and a monodentate aqua ligand, together with two water molecules of solvation. Conjoined six-membered ring systems generate a one-dimensional coordination polymeric chain which extends along b and interspecies water O-H...O hydrogen-bonding interactions give the overall two-dimensional layers which lie parallel to (001). In hemihydrate complex (II), the irregular octahedral RbO5Cl coordination about Rb(+) comprises a single bridging water molecule which lies on a twofold rotation axis, a bidentate Ocarboxy,Cl-chelate interaction and three bridging carboxylate O-atom bonding interactions from the 2,4-D ligand. A two-dimensional coordination polymeric layer structure lying parallel to (100) is formed through a number of conjoined cyclic bridges, including a centrosymmetric four-membered Rb2O2 ring system with an Rb...Rb separation of 4.3312?(5)?. The coordinated water molecule forms intralayer aqua-carboxylate O-H...O hydrogen bonds. Complex (III) comprises two crystallographically independent (Z' = 2) irregular CsO6Cl coordination centres, each comprising two O-atom donors (carboxylate and phenoxy) and a ring-substituted Cl-atom donor from the 2,4-D ligand species in a tridentate chelate mode, two O-atom donors from bridging carboxylate groups and one from a bridging water molecule. However, the two 2,4-D ligands are conformationally very dissimilar, with one phenoxyacetate side chain being synclinal and the other being antiperiplanar. The minimum Cs...Cs separation is 4.4463?(5)?. Structure extension gives coordination polymeric layers which lie parallel to (001) and are stabilized by intralayer water-carboxylate O-H...O hydrogen bonds. PMID:25652282

Smith, Graham

2015-02-01

382

Improving T? and T? magnetic resonance imaging contrast agents through the conjugation of an esteramide dendrimer to high-water-coordination Gd(III) hydroxypyridinone complexes.  

PubMed

Commercial gadolinium magnetic resonance imaging (MRI) contrast agents are limited by low relaxivity (r?) and coordination to only a single water molecule (q?=?1). Consequently, gram quantities of these agents must be injected to obtain sufficient diagnostic contrast. In this study, MRI contrast agents for T(1) and T? relaxivity were synthesized using hydroxypyridinone and terephthalamide chelators with mesityl and 1,4,7-triazacyclononane capping moieties. When covalently conjugated to a highly biocompatible esteramide dendrimer, T? relaxation rates up to 52 mm(-1) ?s(-1) and T? relaxation rates up to 31 mm(-1) ?s(-1) per gadolinium were observed under clinically relevant conditions. These values are believed to be brought about by using a dendritic macromolecule to decrease the molecular tumbling time of the small molecule complexes. These agents also show high aqueous solubility and low toxicity in vitro. In this study we report six new compounds: three discrete complexes and three dendrimer conjugates. PMID:22344885

Klemm, Piper J; Floyd, William C; Smiles, Danil E; Frchet, Jean M J; Raymond, Kenneth N

2012-01-01

383

A spectroscopic study on the coordination and solution structures of the interaction systems between biperoxidovanadate complexes and the pyrazolylpyridine-like ligands.  

PubMed

In order to understand the substitution effects of pyrazolylpyridine (pzpy) on the coordination reaction equilibria, the interactions between a series of pzpy-like ligands and biperoxidovanadate ([OV(O2)2(D2O)](-)/[OV(O2)2(HOD)](-), abbrv. bpV) have been explored using a combination of multinuclear ((1)H, (13)C, and (51)V) magnetic resonance, heteronuclear single quantum coherence (HSQC), and variable temperature NMR in a 0.15 mol L(-1) NaCl D2O solution that mimics the physiological conditions. Both the direct NMR data and the equilibrium constants are reported for the first time. A series of new hepta-coordinated peroxidovanadate species [OV(O2)2L](-) (L = pzpy-like chelating ligands) are formed due to several competitive coordination interactions. According to the equilibrium constants for products between bpV and the pzpy-like ligands, the relative affinity of the ligands is found to be pzpy > 2-Ester-pzpy ? 2-Me-pzpy ? 2-Amide-pzpy > 2-Et-pzpy. In the interaction system between bpV and pzpy, a pair of isomers (Isomers A and B) are observed in aqueous solution, which are attributed to different types of coordination modes between the metal center and the ligands, while the crystal structure of NH4[OV(O2)2(pzpy)]6H2O (CCDC 898554) has the same coordination structure as Isomer A (the main product for pzpy). For the N-substituted ligands, however, Isomer A or B type complexes can also be observed in solution but the molar ratios of the isomer are reversed (i.e., Isomer B type is the main product). These results demonstrate that when the N atom in the pyrazole ring has a substitution group, hydrogen bonding (from the H atom in the pyrazole ring), the steric effect (from alkyl) and the solvation effect (from the ester or amide group) can jointly affect the coordination reaction equilibrium. PMID:24213652

Yu, Xian-Yong; Deng, Lin; Zheng, Baishu; Zeng, Bi-Rong; Yi, Pinggui; Xu, Xin

2014-01-28

384

Tuning the electronic properties in ruthenium-quinone complexes through metal coordination and substitution at the bridge.  

PubMed

A rare example of a mononuclear complex [(bpy)2 Ru(L(1) -H )](ClO4 ), 1(ClO4 ) and dinuclear complexes [(bpy)2 Ru(?-L(1) -2H )Ru(bpy)2 ](ClO4 )2 , 2(ClO4 )2 , [(bpy)2 Ru(?-L(2) -2H )Ru(bpy)2 ](ClO4 )2 , 3(ClO4 )2 , and [(bpy)2 Ru(?-L(3) -2H )Ru(bpy)2 ](ClO4 )2 , 4(ClO4 )2 (bpy=2,2'-bipyridine, L(1) =2,5-di-(isopropyl-amino)-1,4-benzoquinone, L(2) =2,5-di-(benzyl-amino)-1,4-benzoquinone, and L(3) =2,5-di-[2,4,6-(trimethyl)-anilino]-1,4-benzoquinone) with the symmetrically substituted p-quinone ligands, L, are reported. Bond-length analysis within the potentially bridging ligands in both the mono- and dinuclear complexes shows a localization of bonds, and binding to the metal centers through a phenolate-type "O(-) " and an immine/imminium-type neutral "N" donor. For the mononuclear complex 1(ClO4 ), this facilitates strong intermolecular hydrogen bonding and leads to the imminium-type character of the noncoordinated nitrogen atom. The dinuclear complexes display two oxidation and several reduction steps in acetonitrile solutions. In contrast, the mononuclear complex 1(+) exhibits just one oxidation and several reduction steps. The redox processes of 1(1+) are strongly dependent on the solvent. The one-electron oxidized forms 2(3+) , 3(3+) , and 4(3+) of the dinuclear complexes exhibit strong absorptions in the NIR region. Weak NIR absorption bands are observed for the one-electron reduced forms of all complexes. A combination of structural data, electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations is used to elucidate the electronic structures of the complexes. Our DFT results indicate that the electronic natures of the various redox states of the complexes in vacuum differ greatly from those in a solvent continuum. We show here the tuning possibilities that arise upon substituting [O] for the isoelectronic [NR] groups in such quinone ligands. PMID:24604718

Das, Hari Sankar; Schweinfurth, David; Fiedler, Jan; Khusniyarov, Marat M; Mobin, Shaikh M; Sarkar, Biprajit

2014-04-01

385

The loading of coordination complex modified polyoxometalate nanobelts on activated carbon fiber: a feasible strategy to obtain visible light active and highly efficient polyoxometalate based photocatalysts.  

PubMed

To enhance the photocatalytic properties of coordination complex modified polyoxometalates (CC/POMs) in the visible light region, its nanobelts (CC/POMNBs) were loaded on activated carbon fiber (ACF) through a simple colloidal blending process. The resulting coordination complex modified polyoxometalate nanobelts loaded activated carbon fiber composite materials (CC/POMNBs/AC