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Sample records for ru3oac6 py2 dicnpy

  1. Mercury Reduction and Methyl Mercury Degradation by the Soil Bacterium Xanthobacter autotrophicus Py2

    PubMed Central

    Petrus, Amanda K.; Rutner, Colin; Liu, Songnian; Wang, Yingjiao

    2015-01-01

    Two previously uncharacterized potential broad-spectrum mercury (Hg) resistance operons (mer) are present on the chromosome of the soil Alphaproteobacteria Xanthobacter autotrophicus Py2. These operons, mer1 and mer2, contain two features which are commonly found in mer operons in the genomes of soil and marine Alphaproteobacteria, but are not present in previously characterized mer operons: a gene for the mercuric reductase (MerA) that encodes an alkylmercury lyase domain typical of those found on the MerB protein, and the presence of an additional gene, which we are calling merK, with homology to glutathione reductase. Here, we demonstrate that Py2 is resistant to 0.2 μM inorganic mercury [Hg(II)] and 0.05 μM methylmercury (MeHg). Py2 is capable of converting MeHg and Hg(II) to elemental mercury [Hg(0)], and reduction of Hg(II) is induced by incubation in sub toxic concentrations of Hg(II). Transcription of the merA genes increased with Hg(II) treatment, and in both operons merK resides on the same polycistronic mRNA as merA. We propose the use of Py2 as a model system for studying the contribution of mer to Hg mobility in soil and marine ecosystems. PMID:26341208

  2. Spectroscopic, Electrochemical and Computational Characterisation of Ru Species Involved in Catalytic Water Oxidation: Evidence for a [Ru(V) (O)(Py2 (Me) tacn)] Intermediate.

    PubMed

    Casadevall, Carla; Codolà, Zoel; Costas, Miquel; Lloret-Fillol, Julio

    2016-07-11

    A new family of ruthenium complexes based on the N-pentadentate ligand Py2 (Me) tacn (N-methyl-N',N''-bis(2-picolyl)-1,4,7-triazacyclononane) has been synthesised and its catalytic activity has been studied in the water-oxidation (WO) reaction. We have used chemical oxidants (ceric ammonium nitrate and NaIO4 ) to generate the WO intermediates [Ru(II) (OH2 )(Py2 (Me) tacn)](2+) , [Ru(III) (OH2 )(Py2 (Me) tacn)](3+) , [Ru(III) (OH)(Py2 (Me) tacn)](2+) and [Ru(IV) (O)(Py2 (Me) tacn)](2+) , which have been characterised spectroscopically. Their relative redox and pH stability in water has been studied by using UV/Vis and NMR spectroscopies, HRMS and spectroelectrochemistry. [Ru(IV) (O)(Py2 (Me) tacn)](2+) has a long half-life (>48 h) in water. The catalytic cycle of WO has been elucidated by using kinetic, spectroscopic, (18) O-labelling and theoretical studies, and the conclusion is that the rate-determining step is a single-site water nucleophilic attack on a metal-oxo species. Moreover, [Ru(IV) (O)(Py2 (Me) tacn)](2+) is proposed to be the resting state under catalytic conditions. By monitoring Ce(IV) consumption, we found that the O2 evolution rate is redox-controlled and independent of the initial concentration of Ce(IV) . Based on these facts, we propose herein that [Ru(IV) (O)(Py2 (Me) tacn)](2+) is oxidised to [Ru(V) (O)(Py2 (Me) tacn)](2+) prior to attack by a water molecule to give [Ru(III) (OOH)(Py2 (Me) tacn)](2+) . Finally, it is shown that the difference in WO reactivity between the homologous iron and ruthenium [M(OH2 )(Py2 (Me) tacn)](2+) (M=Ru, Fe) complexes is due to the difference in the redox stability of the key M(V) (O) intermediate. These results contribute to a better understanding of the WO mechanism and the differences between iron and ruthenium complexes in WO reactions.

  3. Spectroscopic, Electrochemical and Computational Characterisation of Ru Species Involved in Catalytic Water Oxidation: Evidence for a [Ru(V) (O)(Py2 (Me) tacn)] Intermediate.

    PubMed

    Casadevall, Carla; Codolà, Zoel; Costas, Miquel; Lloret-Fillol, Julio

    2016-07-11

    A new family of ruthenium complexes based on the N-pentadentate ligand Py2 (Me) tacn (N-methyl-N',N''-bis(2-picolyl)-1,4,7-triazacyclononane) has been synthesised and its catalytic activity has been studied in the water-oxidation (WO) reaction. We have used chemical oxidants (ceric ammonium nitrate and NaIO4 ) to generate the WO intermediates [Ru(II) (OH2 )(Py2 (Me) tacn)](2+) , [Ru(III) (OH2 )(Py2 (Me) tacn)](3+) , [Ru(III) (OH)(Py2 (Me) tacn)](2+) and [Ru(IV) (O)(Py2 (Me) tacn)](2+) , which have been characterised spectroscopically. Their relative redox and pH stability in water has been studied by using UV/Vis and NMR spectroscopies, HRMS and spectroelectrochemistry. [Ru(IV) (O)(Py2 (Me) tacn)](2+) has a long half-life (>48 h) in water. The catalytic cycle of WO has been elucidated by using kinetic, spectroscopic, (18) O-labelling and theoretical studies, and the conclusion is that the rate-determining step is a single-site water nucleophilic attack on a metal-oxo species. Moreover, [Ru(IV) (O)(Py2 (Me) tacn)](2+) is proposed to be the resting state under catalytic conditions. By monitoring Ce(IV) consumption, we found that the O2 evolution rate is redox-controlled and independent of the initial concentration of Ce(IV) . Based on these facts, we propose herein that [Ru(IV) (O)(Py2 (Me) tacn)](2+) is oxidised to [Ru(V) (O)(Py2 (Me) tacn)](2+) prior to attack by a water molecule to give [Ru(III) (OOH)(Py2 (Me) tacn)](2+) . Finally, it is shown that the difference in WO reactivity between the homologous iron and ruthenium [M(OH2 )(Py2 (Me) tacn)](2+) (M=Ru, Fe) complexes is due to the difference in the redox stability of the key M(V) (O) intermediate. These results contribute to a better understanding of the WO mechanism and the differences between iron and ruthenium complexes in WO reactions. PMID:27324949

  4. Comprehensive Vibrational Spectroscopic Investigation of trans,trans,trans-[Pt(N3)2(OH)2(py)2], a Pt(IV) Diazido Anticancer Prodrug Candidate

    PubMed Central

    2016-01-01

    We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (C1; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for C1 and its precursors (trans-[Pt(N3)2(py)2] (C2) and trans-[PtCl2(py)2] (C3)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for C1 in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of C1 with biomolecules. PMID:27257848

  5. The influence of immobilization and reduced water activity on gaseous-alkene oxidation by Mycobacterium PY1 and Xanthobacter PY2 in a gas-solid bioreactor.

    PubMed

    Hamstra, R S; Murris, M R; Tramper, J

    1987-05-01

    Immobilization of Mycobacterium PY1 and Xanthobacter PY2 in alginate and in or on hydroculture has a minor influence on the maximum rate of oxidation of propene and ethane. The apparent K(m) values of the immobilized cells are slightly higher than those of the free cells, indicating the presence of diffusion limitation in the immobilized systems. Both bacterial strains rapidly lose their alkene-oxidizing activity when the water activity is decreased. This decrease in activity is so rapid that most of the activity is lost already when the pores of the pertinent supports are still filled with water. Therefore, it is not possible with this system to study the transition of mass transfer of substrates entirely in the water phase to mass transfer to substrates entirely through the gas phase. PMID:18576533

  6. Crystal structure analysis and chiral recognition study of Delta-[Ru(bpy)2(py)2][(+)-O,O'-dibenzoylD-tartrate].12H2O and Lambda-[Ru(bpy)2(py)2][(-)-O,O'-dibenzoyl-L-tartrate].12H2O.

    PubMed

    Kolp, B; Viebrock, H; von Zelewsky, A; Abeln, D

    2001-03-12

    The molecular structure and crystal-packing mode of the enantiopure chiral building blocks Delta-[Ru(bpy)(2)(py)(2)][(+)-O,O'-dibenzoyl-D-tartrate].12H(2)O (I) and Lambda-[Ru(bpy)(2)(py)(2)][(-)-O,O'-dibenzoyl-L-tartrate].12H(2)O (II) have been determined by single-crystal X-ray diffraction data. This study proposes a model of how the L- and D-dibenzoyltartrate anions recognize the chirality of the hydrophobic [Ru(bpy)(2)(py)(2)](2+) complex. The monoclinic unit cell contains four complex cations, four tartrate anions, and 48 water molecules. Since there are no possibilities to form hydrogen bonds between the cations and anions, chiral recognition is due to crystal packing. Two benzoyl rings of two different tartrate anions are gripping the two bpy-planes of the Ru-complex. Further a third benzoyl ring from a tartrate anion is packed between the two pyridine rings, favoring one enantiomeric form to crystallize from aqueous solution. Crystal structure data for I at 153 K: a = 15.342(3) A, b = 19.200(4) A, c = 18.872(4) A, beta = 104.841(3) degrees, monoclinic space group C(2), R(1)= 0.0239 (I > 2sigma(I)), R(2) = 0.0606, Flack parameter = 0.0115 (with esd 0.0166). For II at 293 K: a = 15.376(4) A, b = 19.388(11) A, c = 19.085(7) A, beta = 105.11(2) degrees, monoclinic space group C121, R(1)= 0.0686 (I > 2sigma(I)), R(2) = 0.1819, Flack parameter = -0.0100 (with esd 0.0521).

  7. Structure of the complex of [Ru(tpm)(dppz)py](2+) with a B-DNA oligonucleotide - a single-substituent binding switch for a metallo-intercalator.

    PubMed

    Waywell, Philip; Gonzalez, Veronica; Gill, Martin R; Adams, Harry; Meijer, Anthony J H M; Williamson, Mike P; Thomas, James A

    2010-02-22

    We report the synthesis of three new complexes related to the achiral [Ru(tpm)(dppz)py](2+) cation (tpm=tripyridazole methane, dppz=dipyrido[3,2-a:2',3'-c]phenazine, py=pyridine) that contain an additional single functional group on the monodentate ancillary pyridyl ligand. Computational calculations indicate that the coordinated pyridyl rings are in a fixed orientation parallel to the dppz axis, and that the electrostatic properties of the complexes are very similar. DNA binding studies on the new complexes reveal that the nature and positioning of the functional group has a profound effect on the binding mode and affinity of these complexes. To explore the molecular and structural basis of these effects, circular dichroism and NMR studies on [Ru(tpm)(dppz)py]Cl(2) with the octanucleotides d(AGAGCTCT)(2) and d(CGAGCTCG)(2), were carried out. These studies demonstrate that the dppz ligand intercalates into the G(2)-A(3) step, with {Ru(tpm)py} in the minor groove. They also reveal that the complex intercalates into the binding site in two possible orientations with the pyridyl ligand of the major conformer making close contact with terminal base pairs. We conclude that substitution at the 2- or 3-position of the pyridine ring has little effect on binding, but that substitution at the 4-position drastically disrupts intercalative binding, particularly with a 4-amino substituent, because of steric and electronic interactions with the DNA. These results indicate that complexes derived from these systems have the potential to function as sequence-specific light-switch systems.

  8. Structure of the complex of [Ru(tpm)(dppz)py](2+) with a B-DNA oligonucleotide - a single-substituent binding switch for a metallo-intercalator.

    PubMed

    Waywell, Philip; Gonzalez, Veronica; Gill, Martin R; Adams, Harry; Meijer, Anthony J H M; Williamson, Mike P; Thomas, James A

    2010-02-22

    We report the synthesis of three new complexes related to the achiral [Ru(tpm)(dppz)py](2+) cation (tpm=tripyridazole methane, dppz=dipyrido[3,2-a:2',3'-c]phenazine, py=pyridine) that contain an additional single functional group on the monodentate ancillary pyridyl ligand. Computational calculations indicate that the coordinated pyridyl rings are in a fixed orientation parallel to the dppz axis, and that the electrostatic properties of the complexes are very similar. DNA binding studies on the new complexes reveal that the nature and positioning of the functional group has a profound effect on the binding mode and affinity of these complexes. To explore the molecular and structural basis of these effects, circular dichroism and NMR studies on [Ru(tpm)(dppz)py]Cl(2) with the octanucleotides d(AGAGCTCT)(2) and d(CGAGCTCG)(2), were carried out. These studies demonstrate that the dppz ligand intercalates into the G(2)-A(3) step, with {Ru(tpm)py} in the minor groove. They also reveal that the complex intercalates into the binding site in two possible orientations with the pyridyl ligand of the major conformer making close contact with terminal base pairs. We conclude that substitution at the 2- or 3-position of the pyridine ring has little effect on binding, but that substitution at the 4-position drastically disrupts intercalative binding, particularly with a 4-amino substituent, because of steric and electronic interactions with the DNA. These results indicate that complexes derived from these systems have the potential to function as sequence-specific light-switch systems. PMID:20108276

  9. A comparative study of pi-arene-bridged lanthanum arylamide and aryloxide dimers. Solution behavior, exchange mechanisms, and X-ray crystal structures of La2(NH-2,6-iPr2C6H3)6, La(NH-2,6-iPr2C6H3)3(THF)3, and La(NH-2,6-iPr2C6H3)3(py)2.

    PubMed

    Giesbrecht, Garth R; Gordon, John C; Clark, David L; Hay, P Jeffrey; Scott, Brian L; Tait, C Drew

    2004-05-26

    Reaction of 3 equiv of 2,6-diisopropylaniline with La[N(SiMe(3))(2)](3) produces the dimeric species La(2)(NHAr)(6) (1). X-ray crystallography reveals a centrosymmetric structure, where the dimeric unit is bridged by intermolecular eta(6)-arene interactions of a unique arylamide ligand attached to an adjacent metal center. Exposure of 1 to THF results in formation of the monomeric tris-THF adduct La(NHAr)(3)(THF)(3) (2), which was shown by X-ray crystallography to maintain a fac-octahedral structure in the solid state. (1)H NMR spectroscopy illustrates that the binding of THF to 1 to form 2 is reversible and removal of THF under vacuum regenerates dimeric 1. Addition of pyridine to 1 yields the monomeric bis-pyridine adduct La(NHAr)(3)(py)(2) (3), which exhibits a distorted trigonal-bipyramidal La metal center. Solution (1)H NMR, IR, and Raman spectroscopy indicate that the pi-arene-bridged dimeric structure of 1 is maintained in solution. Variable-temperature (1)H NMR spectroscopic investigations of 1 are consistent with a monomer-dimer equilibrium at elevated temperature. In contrast, variable-temperature (1)H NMR spectroscopic investigations of the aryloxide analogue La(2)(OAr)(6) (4) show that the bridging and terminal aryloxide groups exchange by a mechanism in which the dimeric nature of the compound is retained. Density functional theory (DFT) calculations were carried out on model compounds La(2)(OC(6)H(5))(6), La(2)(NHC(6)H(5))(6), and (C(6)H(5)R)La(XC(6)H(5))(3), where X = O or NH and R = H, OH, or NH(2). The formation of eta(6)-arene interactions is energetically favored over monomeric LaX(3) (X = OPh or NHPh) with the aryloxide pi-arene interaction being stronger than the arylamide pi-arene interaction. Calculation of vibrational frequencies reveals the origin of the observed IR spectral behavior of both La(2)(OC(6)H(5))(6) and La(2)(NHC(6)H(5))(6), with the higher energy nu(C=C) stretch due to terminal ligands and the lower energy stretch associated

  10. Salt-free synthesis of samarium-aluminum mixed-metal alkoxides: X-ray crystal structures of [[(i-Pr-O)(i-Bu)Al(mu-O-i-Pr)(2)Sm(O-i-Pr)(HO-i-Pr)](mu-O-i-Pr)](2), [(THF)(2)Sm(O-t-Bu)(2)(mu-O-t-Bu)(2)Al(i-Bu)(2)], Sm(OAr)(3)(THF)(3) (Ar = 2,4,6-Me(3)C(6)H(2)), [Nd(mu-OAr)(OAr)(2)(py)(2)](2) (Ar = 2,4,6-Me(3)C(6)H(2)), and (ArO)(3)Sm[(mu-O-t-Bu)(2)Al(2)(O-t-Bu)(4)] (Ar = 2,6-i-Pr(2)C(6)H(3)).

    PubMed

    Giesbrecht, Garth R; Gordon, John C; Clark, David L; Scott, Brian L; Watkin, John G; Young, Kenneth J

    2002-12-01

    Reaction of equimolar quantities of Sm[N(SiMe(3))(2)](3) and Al(i-Bu)(3) with 6 equiv of iso-propyl alcohol in toluene leads to the formation of the mixed-metal alkoxide complex [[(i-Pr-O)(i-Bu)Al(mu-O-i-Pr)(2)Sm(O-i-Pr)(HO-i-Pr)](mu-O-i-Pr)](2) (1). An analogous reaction between 1:1 Sm[N(SiMe(3))(2)](3)/Al(i-Bu)(3) and 6 equiv of tert-butyl alcohol, followed by addition of THF, produces the THF adduct [(THF)(2)Sm(O-t-Bu)(2)(mu-O-t-Bu)(2)Al(i-Bu)(2)] (2). Compound 1 crystallizes in the space group P1 while 2 crystallizes in space group Cmcm. Cell parameters for 1: a = 11.028(2) A, b = 12.168(2) A, c = 12.879(2) A, alpha = 82.84(1) degrees, beta = 64.88(1) degrees, gamma = 70.80(1) degrees, Z = 1. Cell parameters for 2: a = 11.304(2) A, b = 22.429(4) A, c = 15.768(2) A, Z = 4. Attempts to prepare the bulkier derivatives result in the formation of lanthanide aryloxide species only; reaction between equimolar amounts of Ln[N(SiMe(3))(2)](3) (Ln = Sm, Nd) and Al(i-Bu)(3) with 6 equiv of HO-2,4,6-Me(3)C(6)H(2), followed by the addition of THF or pyridine, yields the Lewis base adducts Sm(OAr)(3)(THF)(3) (3) and [Nd(mu-OAr)(OAr)(2)(py)(2)](2) (4). Compound 3 crystallizes in the space group Pbca while 4 crystallizes in space group P2(1)/c. Cell parameters for 3: a = 16.5822(9) A, b = 15.5668(9) A, c = 29.902(2) A, Z = 8. Cell parameters for 4: a = 13.4496(8) A, b = 20.034(1) A, c = 16.206(1) A, beta = 113.782(1) degrees, Z = 2. Reaction of Al(2)(O-t-Bu)(6) with [Sm(OAr)(3)](2) (Ar = 2,6-i-Pr(2)C(6)H(3)) yields the adduct (ArO)(3)Sm[(mu-O-t-Bu)(2)Al(2)(O-t-Bu)(4)] (5), which crystallizes in the space group P2(1)/n. Cell parameters for 5: a = 14.0960(7) A, b = 27.3037(15) A, c = 16.7893(9) A, beta = 92.216(1) degrees, Z = 4. PMID:12444780

  11. A candidate for a single-chain magnet: [Mn3(OAc)6(py)2(H2O)2]n (OAc is acetate and py is pyridine).

    PubMed

    Caballero-Jiménez, Judith; Reyes Ortega, Yasmi; Bernès, Sylvain; Escudero, Roberto

    2014-08-01

    The title complex, catena-poly[di-μ3-acetato-κ(6)O:O:O'-tetra-μ2-acetato-κ(4)O:O;κ(4)O:O'-diaquabis(pyridine-κN)trimanganese(II)], [Mn3(CH3COO)6(C6H5N)2(H2O)2]n, is a true one-dimensional coordination polymer, in which the Mn(II) centres form a zigzag chain along [010]. The asymmetric unit contains two metal centres, one of which (Mn1) lies on an inversion centre, while the other (Mn2) is placed close to an inversion centre on a general position. Since all the acetates behave as bridging ligands, although with different μ2- and μ3-coordination modes, a one-dimensional polymeric structure is formed, based on trinuclear repeat units (Mn1...Mn2...Mn2'), in which the Mn2 and Mn2' sites are related by an inversion centre. Within this monomeric block, the metal-metal separations are Mn1...Mn2 = 3.36180 (18) Å and Mn2...Mn2' = 4.4804 (3) Å. Cation Mn1, located on an inversion centre, displays an [MnO6] coordination sphere, while Mn2, on a general position, has a slightly stronger [MnO5N] ligand field, as the sixth coordination site is occupied by a pyridine molecule. Both centres approximate an octahedral ligand field. The chains are parallel in the crystal structure and interact via hydrogen bonds involving coordinated water molecules. However, the shortest metal-metal separation between two chains [5.3752 (3) Å] is large compared with the intrachain interactions. These structural features are compatible with a single-chain magnet behaviour, as confirmed by preliminary magnetic studies.

  12. Luminescent Copper(I) Halide Butterfly Dimers Coordinated to [Au(CH3imCH2py)2]BF4 and [Au(CH3imCH2quin)2]BF4

    SciTech Connect

    Catalano, V.; Moore, A; Shearer, J; Kim, J

    2009-01-01

    The coordination chemistry of copper(I) halides to the homoleptic, N-heterocyclic carbene Au(I) complexes [Au(CH{sub 3}imCH{sub 2}quin){sub 2}]BF{sub 4} and [Au(CH{sub 3}imCH{sub 2}py){sub 2}]BF{sub 4} was explored. The reaction of CuX (X = Cl, Br, I) with either [Au(CH{sub 3}imCH{sub 2}quin){sub 2}]BF{sub 4} or [Au(CH{sub 3}imCH{sub 2}py){sub 2}]BF{sub 4} produces trimetallic complexes containing Cu{sub 2}X{sub 2}-butterfly copper clusters coordinated to the two imine moieties. The triangular arrangement of the metals places the gold(I) center in close proximity ({approx}2.5-2.6 {angstrom}) to the centroid of the Cu-Cu vector. The Cu-Cu separations vary as a function of bridging halide with the shortest Cu-Cu separations of {approx}2.5 {angstrom} found in the iodo-complexes and the longest separations of 2.9 {angstrom} found in the bridging chloride complexes. In all six complexes the Au-Cu separations range from {approx}2.8 to 3.0 {angstrom}. In the absence of halides, the dimetallic complex [AuCu(CH{sub 3}imCH{sub 2}py){sub 2}(NCCH{sub 3}){sub 2}](BF{sub 4}){sub 2}, containing a long Au-Cu distance of {approx}4.72 {angstrom} is formed. Additionally, as the byproduct of the reaction of CuBr with [Au(CH{sub 3}imCH{sub 2}quin){sub 2}]BF{sub 4} the deep-red, dimetallic compound, AuCuBr{sub 2}(CH{sub 3}imCH{sub 2}quin){sub 2}, was isolated in very low yield. All of these complexes were studied by NMR spectroscopy, mass spectrometry, and the copper containing species were additionally characterized by X-ray crystallography. In solution the copper centers dissociate from the gold complexes, but as shown by XANES and EXAFS spectroscopy, at low temperature the Cu-Cu linkage is broken, and the individual copper(I) halides reposition themselves to opposite sides of the gold complex while remaining coordinated to one imine moiety. In the solid state all of the complexes are photoluminescent, though the nature of the excited state was not determined.

  13. Antibacterial Activity and Cytotoxicity of Silver(I) Complexes of Pyridine and (Benz)Imidazole Derivatives. X-ray Crystal Structure of [Ag(2,6-di(CH2OH)py)2]NO3.

    PubMed

    Kalinowska-Lis, Urszula; Felczak, Aleksandra; Chęcińska, Lilianna; Szabłowska-Gadomska, Ilona; Patyna, Emila; Małecki, Maciej; Lisowska, Katarzyna; Ochocki, Justyn

    2016-01-28

    Selected aspects of the biological activity of a series of six nitrate silver(I) complexes with pyridine and (benz)imidazole derivatives were investigated. The present study evaluated the antibacterial activities of the complexes against three Gram-negative strains: Pseudomonas aeruginosa ATCC 15442, Escherichia coli ATCC 25922 and Proteus hauseri ATCC 13315. The results were compared with those of silver nitrate, a silver sulfadiazine drug and appropriate ligands. The most significant antibacterial properties were exerted by silver(I) complexes containing benzimidazole derivatives. The cytotoxic activity of the complexes was examined against B16 (murine melanoma) and 10T1/2 (murine fibroblasts) cells. All of the tested silver(I) compounds were not toxic to fibroblast cells in concentration inhibited cancer cell (B16) viability by 50%, which ranged between 2.44-28.65 µM. The molecular and crystal structure of silver(I) complex of 2,6-di(hydroxymethyl)pyridine was determined by single-crystal X-ray diffraction analysis. The most important features of the crystal packing and intermolecular non-covalent interactions in the Ag(I) complex were quantified via Hirshfeld surface analysis.

  14. μ1,1-R-phenylcyanamido bridges as a new safe synthetic strategy for ferromagnetic molecular clusters.

    PubMed

    Speed, Saskia; Casanovas, Berta; Vicente, Ramon

    2016-03-28

    The reaction of Ni(NO3)2·6H2O with di-2-pyridyl ketone, (py)2CO, and the R-phenylcyanamides 4Cl-3CF3-PhHNCN and 4F-3CF3-PhHNCN in CH3OH or CH3CH2OH allows the isolation of the tetranuclear compounds [(Ni4(μ-py2COOCH3)2(μ3-py2COOH)2(μ1,1-4Cl-3CF3-PhNCN)2(4Cl-3CF3-PhNCN)2]·CH3OH (1), [(Ni4(μ-py2COOCH2CH3)2(μ3-py2COOH)2(μ1,1-4Cl-3CF3-PhNCN)2(4Cl-3CF3-PhNCN)2]·2EtOH (2) and [(Ni4(μ-py2COOCH3)2(μ3-py2COOH)2(μ1,1-4F-3CF3-PhNCN)2(4F-3CF3-PhNCN)2]·4CH3OH (3). {(py)2C(OH)O}(-) and {(py)2C(OR)O}(-) are the monoanions of the gem-diol and hemiketal (R = CH3, CH2CH3) forms of (py)2CO. X-ray diffraction analysis reveals defective double-cubane tetrameric entities in which the Ni(II) atoms are linked by μ1,1-R-phenylcyanamido bridges and two kinds of O-bridges. The molar magnetic susceptibility measurements of 1-3 in the 2-300 K range indicate bulk ferromagnetic coupling.

  15. Scandium ion-enhanced oxidative dimerization and N-demethylation of N,N-dimethylanilines by a non-heme iron(IV)-oxo complex.

    PubMed

    Park, Jiyun; Morimoto, Yuma; Lee, Yong-Min; You, Youngmin; Nam, Wonwoo; Fukuzumi, Shunichi

    2011-11-21

    Oxidative dimerization of N,N-dimethylaniline (DMA) occurs with a nonheme iron(IV)-oxo complex, [Fe(IV)(O)(N4Py)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), to yield the corresponding dimer, tetramethylbenzidine (TMB), in acetonitrile. The rate of the oxidative dimerization of DMA by [Fe(IV)(O)(N4Py)](2+) is markedly enhanced by the presence of scandium triflate, Sc(OTf)(3) (OTf = CF(3)SO(3)(-)), when TMB is further oxidized to the radical cation (TMB(•+)). In contrast, we have observed the oxidative N-demethylation with para-substituted DMA substrates, since the position of the C-C bond formation to yield the dimer is blocked. The rate of the oxidative N-demethylation of para-substituted DMA by [Fe(IV)(O)(N4Py)](2+) is also markedly enhanced by the presence of Sc(OTf)(3). In the case of para-substituted DMA derivatives with electron-donating substituents, radical cations of DMA derivatives are initially formed by Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), giving demethylated products. Binding of Sc(3+) to [Fe(IV)(O)(N4Py)](2+) enhances the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), whereas binding of Sc(3+) to DMA derivatives retards the electron-transfer reaction. The complicated kinetics of the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+) are analyzed by competition between binding of Sc(3+) to DMA derivatives and to [Fe(IV)(O)(N4Py)](2+). The binding constants of Sc(3+) to DMA derivatives increase with the increase of the electron-donating ability of the para-substituent. The rate constants of Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), which are estimated from the binding constants of Sc(3+) to DMA derivatives, agree well with those predicted from the driving force dependence of the rate constants of Sc(3+) ion-coupled electron transfer from one-electron reductants to [Fe

  16. A Kagomé layer-based 3D Mn(II) framework showing coexistence of spin-canting, spin-frustration, field-induced metamagnetic and spin-flop transitions.

    PubMed

    Yang, En-Cui; Liu, Zhong-Yi; Li, Ya-Ling; Wang, Jing-Yi; Zhao, Xiao-Jun

    2011-09-14

    A novel 3D Mn(II) coordination framework with Kagomé sublattice, [Mn(3)(py)(2)(nip)(2)](n) (py(-) = 2-((1H-tetrazol-5-yl)methyl)pyridine and nip(2-) = 5-nitroisophathalate), was in situ solvothermally synthesized and shows the coexistence of spin-canting, spin-frustration as well as field-induced metamagnetic and spin-flop transitions at 2.9 K.

  17. Luminescent Mechanochromism in a Gold(I)-Copper(I) N-Heterocyclic Carbene Complex.

    PubMed

    Chen, Kelly; Nenzel, Michelle M; Brown, Thomas M; Catalano, Vincent J

    2015-07-20

    The silver(I) species [Ag(benzim(CH2py)2)2]PF6 (1) was prepared by refluxing the ligand precursor [H(benzim(CH2py)2)2]PF6 with Ag2O and aqueous sodium hydroxide in dichloromethane. Simple transmetalation of 1 with tetrahydrothiophenegold(I) chloride forms the gold(I) analogue [Au(benzim(CH2py)2)2]PF6 (2). The addition of 2 equiv of [Cu(NCCH3)4]PF6 to 2 in acetonitrile produces a blue-luminescent, trimetallic complex, [AuCu2(benzim(CH2py)2)2(NCCH3)4](PF6)3·2CH3CN (3·2CH3CN). When blue-luminescent 3·2CH3CN is exposed to air, the complex loses four acetonitrile molecules, and the emission of the desolvated complex (4) appears aquamarine. Crystallization of 4 from different solvents produces the complexes [AuCu2(benzim(CH2py)2)2](PF6)3 (5) and [AuCu2(benzim(CH2py)2)2(NCCH2CH3)2](PF6)3 (6). Upon grinding, both 3·2CH3CN and 4 exhibit mechanochromic transformations to a yellow-luminescent powder (ground-4). The reversible mechanochromic transformation of 3·2CH3CN to ground-4 is a crystalline-to-amorphous conversion accompanied by partial desolvation. The luminescent mechanochromism of 4 to ground-4 is an "amorphous-to-amorphous" process and does not require solvent loss. In addition to their mechanochromic properties, both 3·2CH3CN and 4 exhibit luminescent thermochromism through desolvation to form a weak luminescent powder (7). PMID:26155017

  18. Unexpected formal insertion of CO2 into the C-Si bonds of a zinc compound

    DOE PAGESBeta

    Kemp, Richard A.; McGrew, Genette I.; Khatri, Pathik A.; Geiger, William E.; Waterman, Rory

    2015-09-08

    Reaction of [κ2-PR2C(SiMe3)Py]2Zn (R = Ph, 2a; iPr, 2b) with CO2 affords the products of formal insertion at the C–Si bond, [κ2-PR2CC(O)O(SiMe3)Py]2Zn (R = Ph, 3a; iPr, 3b). Insertion product 3b was structurally characterized. As a result, the reaction appears to be a stepwise insertion and rearrangement of CO2 based on kinetic data.

  19. p-Tolylimido rhenium(V) complexes - synthesis, X-ray studies, spectroscopic characterization, DFT calculations and catalytic activity.

    PubMed

    Machura, Barbara; Gryca, Izabela; Małecki, Jan Grzegorz; Alonso, Francisco; Moglie, Yanina

    2014-02-14

    Novel p-tolylimido rhenium(V) complexes trans-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(py-2-COO)(PPh3)]·MeCN (1a), trans-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(py-2-COO)(PPh3)] (1b), trans-(Br,Br)-[Re(p-NC6H4CH3)Br2(py-2-COO)(PPh3)] (2), cis-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(py-2-COO)(PPh3)] (3), cis-(Br,Br)-[Re(p-NC6H4CH3)Br2(py-2-COO)(PPh3)]·H2O (4), trans-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(OMe)] (5) and trans-(Br,Br)-[Re(p-NC6H4CH3)Br2(OMe)(PPh3)2]·1/2H2O (6) were synthesized. The compounds were identified by elemental analysis, IR, NMR ((1)H, (13)C and (31)P), UV-Vis spectroscopy and X-ray crystallography. Calculations at the DFT level were undertaken in order to elucidate the structural, spectroscopic and bonding properties of the trans-(Cl,Cl) and cis-(Cl,Cl) isomers of [Re(p-NC6H4CH3)Cl2(py-2-COO)(PPh3)]. In the first step, extended tests of the ability of different DFT methods (B3LYP, BP86, and PBE1PBE) were performed to find the best overall performer in describing the geometry of the imido Re(v) complexes; then, the electronic spectra of the trans and cis isomers of [Re(p-NC6H4CH3)Cl2(py-2-COO)(PPh3)] were investigated at the TDDFT level employing the PBE1PBE functional. Additional information about bonding in the compounds [Re(p-NC6H4CH3)Cl2(py-2-COO)(PPh3)] was obtained by NBO analysis. The catalytic activity of the complexes incorporating the picolinate ligand was studied and compared in the synthesis of N-substituted ethyl glycine esters from ethyl diazoacetate and amines.

  20. Connecting mononuclear dysprosium single-molecule magnets to form dinuclear complexes via in situ ligand oxidation.

    PubMed

    Yutronkie, Nathan J; Kühne, Irina A; Korobkov, Ilia; Brusso, Jaclyn L; Murugesu, Muralee

    2016-01-14

    A Dy2 complex, exhibiting SMM behaviour, and its Y analogue were prepared via in situ oxidation of Py2TTA, a pincer type ligand, followed by dimerisation. This unique metal complexation and subsequent dimerization were followed by solution NMR studies. PMID:26567706

  1. Conversion of Nonporous Helical Cadmium Organic Famework to a Porous Form

    SciTech Connect

    Gu, Zhi-Gang; Cai, Yue-Peng; Fang, Hua-Cai; Zhou, Zheng-Yuan; Thallapally, Praveen K.; Tian, Jian; Liu, Jun; Exarhos, Gregory J.

    2010-08-07

    Two novel cadmium–organic frameworks containing achiral multiwalled helical nanotubular channels, [Cd(HImDC)(S)]n (S = Im(1) and Py(2)), have been synthesized and characterized using single crystal X-ray diffraction, in which 1 converts to 2 upon refluxing 1 in pyridine solution with noticeable porosity and hydrogen uptake at medium pressure.

  2. Halide Influence on Molecular and Supramolecular Arrangements of Iron Complexes with a 3,5-Bis(2-Pyridyl)-1,2,4,6-Thiatriazine Ligand.

    PubMed

    Harriman, Katie L M; Kühne, Irina A; Leitch, Alicea A; Korobkov, Ilia; Clérac, Rodolphe; Murugesu, Muralee; Brusso, Jaclyn L

    2016-06-01

    A series of iron centered complexes, namely, [Fe(Py2TTA)Cl2] (1), [Fe(Py2TTA)Br2] (2), and [Fe(μ-F)(Py2TTAO)F]∞ (3), were isolated via complexation of 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazine (Py2TTAH) with various ferric halides (e.g., FeF3, FeCl3, and FeBr3). Comparison of the optical and electrochemical spectroscopy, structural analysis, and magnetic studies reveal numerous similarities between the chlorido (1) and bromido (2) derivatives, which crystallize as discrete five-coordinate iron centered complexes with coordination geometries that are intermediate between trigonal bipyramidal and square base pyramid. Conversely, the fluorido derivative (3) results in a completely different structure due to oxidation of the ligand and the formation of a one-dimensional coordination polymer held together through a bridging fluoride ion. Consequently, the spectroscopic and magnetic behavior of 3 differs significantly compared with 1 and 2. Complexes 1 and 2 exhibit paramagnetic properties typical for a mononuclear S = 5/2 system with weak intermolecular antiferromagnetic interactions at low temperatures, whereas complex 3 demonstrates significant exchange couplings within the chain and weak antiferromagnetic interchain interactions, which stabilize a canted antiferromagnetic state below 4.2 K. PMID:27152549

  3. Synthetic approaches to (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) reveal redox non-innocence and C-C bond-formation.

    PubMed

    Frazier, Brenda A; Wolczanski, Peter T; Keresztes, Ivan; DeBeer, Serena; Lobkovsky, Emil B; Pierpont, Aaron W; Cundari, Thomas R

    2012-08-01

    Attempted syntheses of (smif)(2)Ti (smif =1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiCl(n)L(m) (n = 2-4) with M(smif) (M = Li, Na), in the presence of a reducing agent (Na/Hg) when necessary, failed, but several apparent Ti(II) species were identified by X-ray crystallography and multidimensional NMR spectroscopy: (smif){Li(smif-smif)}Ti (1, X-ray), [(smif)Ti](2)(μ-κ(3),κ(3)-N,N(py)(2)-smif,smif) (2), (smif)Ti(κ(3)-N,N(py)(2)-smif,(smif)H) (3), and (smif)Ti(dpma) (4, dpma = di-2-pyridylmethyl-amide). NMR spectroscopy and K-edge XAS showed that each compound possesses ligands that are redox noninnnocent, such that d(1) Ti(III) centers AF-couple to ligand radicals: (smif){Li(smif-smif)(2-)}Ti(III) (1), [(smif(2-))Ti(III)](2)(μ-κ(3),κ(3)-N,N(py)(2)-smif,smif) (2), [(smif(2-))Ti(III)](κ(3)-N,N(py)(2)-smif,(smif)H) (3), and (smif(2-))Ti(III)(dpma) (4). The instability of (smif)(2)Ti relative to its C-C coupled dimer, 2, is rationalized via the complementary nature of the amide and smif radical dianion ligands, which are also common to 3 and 4. Calculations support this contention.

  4. Actes du colloque sur le bilinguisme, Universite de Neuchatel, 14/15 Septembre, 1981 (Proceedings of the Colloquium on Bilingualism, University of Neuchatel, September 14-15, 1981).

    ERIC Educational Resources Information Center

    TRANEL, 1982

    1982-01-01

    This issue contains proceedings of a colloquium on linguistics at the University of Neuchatel: (1) "Propositions epistemologiques pour une etude du bilinguisme (Epistemological Propositions for a Study of Bilingualism)," by B. Py; (2) "Comment on di ca? Prolegomenes a une etude de la composante semantique du langage des migrants (How Do You Say…

  5. Establishment of gastro-intestinal helminth infections in free-range chickens: a longitudinal on farm study.

    PubMed

    Wongrak, Kalyakorn; Daş, Gürbüz; Moors, Eva; Sohnrey, Birgit; Gauly, Matthias

    2014-01-01

    The objective of this study was to monitor establishment and development of gastro-intestinal helminth infections in chickens over two production years (PY) on a free-range farm in Lower Saxony, Germany. The data were collected between July 2010 and June 2011 (PY1) and July 2011 and January 2013 (PY2), respectively. During PY1, Lohmann Brown classic (LB classic, N = 450) was tested, while in PY2 two different genotypes (230 LB classic, 230 LB plus) were used. The hens were kept in two mobile stalls that were moved to a new position at regular intervals. In both PY1 and PY2, 20 individual faecal samples per stall were randomly collected at monthly intervals in order to calculate the number of internal parasite eggs per gram of faeces (EPG). At the end of the laying periods, approximately 10% (N = 42) or more than 50% (N = 265) of hens were subjected to post-mortem parasitological examinations in PY1 and PY2, respectively. No parasite eggs were found in the faecal samples during PY1, whereas almost all of the hens (97.6%) were infected with Heterakis gallinarum (36 worms/hen) at the end of the period. In PY2, nematode eggs in faeces were found from the third month onwards at a low level, increasing considerably towards the final three months. There was no significant difference between the two genotypes of brown hens neither for EPG (P = 0.456) or for overall prevalence (P = 0.177). Mortality rate ranged from 18.3 to 27.4% but did not differ significantly between genotypes or production years. Average worm burden was 207 worms/hen in PY2. The most prevalent species were H. gallinarum (98.5%) followed by Ascaridia galli (96.2%) and Capillaria spp. (86.1%). Furthermore, three Capillaria species, C. obsignata, C. bursata and C. caudinflata were differentiated. In conclusion chickens kept on free-range farms are exposed to high risks of nematode infections and have high mortality rates with no obvious link to parasite infections. Once the farm environment is contaminated

  6. Design and synthesis of new 1D and 2D R-isophthalic acid-based coordination polymers (R = hydrogen or bromine).

    PubMed

    Zhang, Ren; Gong, Qihan; Emge, Thomas J; Banerjee, Debasis; Li, Jing

    2013-01-01

    Three new R-isophthalic acid-based (R = H or Br) coordination polymers have been designed and synthesized. By changing the N-containing ligand in the system, we are able to tune the dimensionality of coordination polymers from one-dimension (1D) to two-dimensions (2D) with the same basic building unit. Also, different metal ions can be incorporated into the same structures. Compound 1 [Cu(bipa)(py)2]·0.5(H2O) (H2bipa = 5-bromoisophthalic acid; py = pyridine) and compound 2 [Co(bipa)(py)2] are 1D chain structures. Compound 3 [Cu8(ipa)8(bpe)8]·2(bpe)·4(H2O) (bpe=1,2-bis(4-pyridyl)ethane) is a 2D layered structure.

  7. Mononuclear nonheme iron(IV)-oxo and manganese(IV)-oxo complexes in oxidation reactions: experimental results prove theoretical prediction.

    PubMed

    Chen, Junying; Cho, Kyung-Bin; Lee, Yong-Min; Kwon, Yoon Hye; Nam, Wonwoo

    2015-08-25

    Reactivities of mononuclear nonheme iron(IV)-oxo and manganese(IV)-oxo complexes bearing a pentadentate N4Py ligand, [M(IV)O(N4Py)](2+) (M = Fe and Mn), are compared in hydrogen atom transfer (HAT) and oxygen atom transfer (OAT) reactions; theoretical and experimental results show that Fe(IV)O is more reactive than Mn(IV)O. The latter is shown to react through excited state reactivity (ESR).

  8. Construction of nitronyl nitroxide-based 3d-4f clusters: structure and magnetism.

    PubMed

    Wang, Xiu-Feng; Hu, Peng; Li, Yun-Gai; Li, Li-Cun

    2015-02-01

    Three unprecedented nitronyl nitroxide radical-bridged 3d-4f clusters, [Ln2 Cu2 (hfac)10 (NIT-3py)2 (H2 O)2 ](Ln(III) =Y, Gd, Dy), have been obtained from the self-assembly of Ln(hfac)3 , Cu(hfac)2 , and the radical ligand. The Dy complex shows a slow relaxation of magnetization, representing the first nitronyl nitroxide radical-based 3d-4f cluster with single-molecule magnet behavior.

  9. New Ru(II) Complex for Dual Activity: Photoinduced Ligand Release and (1)O2 Production.

    PubMed

    Loftus, Lauren M; White, Jessica K; Albani, Bryan A; Kohler, Lars; Kodanko, Jeremy J; Thummel, Randolph P; Dunbar, Kim R; Turro, Claudia

    2016-03-01

    The new complex [Ru(pydppn)(biq)(py)](2+) (1) undergoes both py photodissociation in CH3CN with Φ500 =0.0070(4) and (1)O2 production with ΦΔ =0.75(7) in CH3 OH from a long-lived (3) ππ* state centered on the pydppn ligand (pydppn=3-(pyrid-2-yl)benzo[i]dipyrido[3,2-a:2',3'-c]phenazine; biq = 2,2'-biquinoline; py=pyridine). This represents an order of magnitude decrease in the Φ500 compared to the previously reported model compound [Ru(tpy)(biq)(py)](2+) (3) (tpy=2,2':6',2''-terpyridine) that undergoes only ligand exchange. The effect on the quantum yields by the addition of a second deactivation pathway through the low-lying (3) ππ* state necessary for dual reactivity was investigated using ultrafast and nanosecond transient absorption spectroscopy, revealing a significantly shorter (3) MLCT lifetime in 1 relative to that of the model complex 3. Due to the structural similarities between the two compounds, the lower values of Φ500 and ΦΔ compared to that of [Ru(pydppn)(bpy)(py)](2+) (2) (bpy=2,2'-bipyridine) are attributed to a competitive excited state population between the (3) LF states involved in ligand dissociation and the long-lived (3) ππ* state in 1. Complex 1 represents a model compound for dual activity that may be applied to photochemotherapy. PMID:26715085

  10. Metal-organic frameworks assembled from lanthanide and 2,5-pyridinedicaboxylate with cubane-like [Ln4(OH)4] building units

    NASA Astrophysics Data System (ADS)

    Abdelbaky, Mohammed S. M.; Amghouz, Zakariae; Fernández-Zapico, Eva; García-Granda, Santiago; García, José R.

    2015-09-01

    Lanthanide-organic frameworks based on 2,5-pyridinedicaboxylate (25p) ligand, formulated as [Yb4(OH)4(25p)4(H2O)3]·H2O (25pYb), [Y4(OH)4(25p)4(H2O)3]·H2O (25pY-1) and [Y6(OH)8(25p)5(H2O)2] (25pY-2), have been obtained as single phases under hydrothermal conditions. 25pYb and 25pY-1 are isostructural, and crystallize in the triclinic space group, P-1, with a=8.6075(5) Å, b=14.8478(7) Å, c=15.9164(9) Å, α=86.277(4)°, β=80.196(5)°, γ=81.785(4)°, and a=8.7166(6) Å, b=14.966(1) Å, c=15.966(1) Å, α=86.260(6)°, β=80.036(6)°, γ=81.599(6)°, respectively. 25pY-2 crystallizes in the monoclinic space group, P21/c, with a=24.9117(17) Å, b=13.7340(8) Å, c=14.3385(10) Å, β=100.551(7)°. 25pYb and 25pY-2 have been structurally characterized by single-crystal X-ray diffraction. The 25pYb structure is based on tetranuclear cubane-like [Yb4(OH)4]8+ clusters, which are interconnected to eight neighbouring clusters through teen surrounding 25p ligands leading to neutral 3D framework, while the structure of 25pY-2 is based on two independent cuban-like [Y4(OH)4]8+ clusters, which are joined together through Y1 cation leading to the formation of hexanuclear [Y6(OH)8]10+ clusters, which in turn are joined via Y2 cation resulting in infinite inorganic chain extending along c-axis, and each chain is interconnected to six adjacent chains through 25p ligands leading finally to 3D framework. The luminescence properties of Eu3+ and Tb3+ doped 25pY-1 and 25pY-2 compounds have also been investigated. All materials has been characterized by powder X-ray diffraction, thermal analyses (TG-SDTA-MS), FTIR spectroscopy, C-H-N elemental analysis, scanning electron microscopy (SEM-EDX), and powder X-ray thermodiffraction.

  11. Carbon nanotubes dispersed in aqueous solution by ruthenium(ii) polypyridyl complexes

    NASA Astrophysics Data System (ADS)

    Huang, Kewei; Saha, Avishek; Dirian, Konstantin; Jiang, Chengmin; Chu, Pin-Lei E.; Tour, James M.; Guldi, Dirk M.; Martí, Angel A.

    2016-07-01

    . These studies show that the photoluminescence of both, that is, of the ruthenium complexes and of SWCNTs, are quenched when they interact with each other. Pump-probe transient absorption experiments were performed to shed light onto the nature of the photoluminescence quenching, showing carbon nanotube-based bands with picosecond lifetimes, but no new bands which could be unambigously assigned to photoinduced charge transfer process. Thus, from the spectroscopic data, we conclude that quenching of the photoluminescence of the ruthenium complexes is due to energy transfer to proximal SWCNTs. Electronic supplementary information (ESI) available: Absorption and emission spectra of RuPy2 with HiPco SWCNTs, 3-D emission spectra of RuPy1 and RuPy2/HiPco, representative AFM and TEM figures of RuPy1 and RuPy2 with SWCNTs, emission of RuPy2/SWCNTs, photophysical parameters for RuPy1 and RuPy2, picosecond transient absorption spectra of RuPy1, RuPy2, and lifetimes. Appendix 1. See DOI: 10.1039/c6nr02577c

  12. Determination of reduction potential of an engineered Cu(A) azurin by cyclic voltammetry and spectrochemical titrations.

    PubMed

    Hwang, Hee Jung; Ang, Majorie; Lu, Yi

    2004-06-01

    The reduction potentials of an engineered CuA azurin in its native and thermally denatured states have been determined using cyclic voltammetry and spectrochemical titrations. Using a 4,4'-dipyridyl disulfide modified gold electrode, the reduction potentials of native and thermally denatured CuA azurin are the same within the experimental error (422 +/- 5 and 425 +/- 5 mV vs. NHE, respectively, in 50 mM ammonium acetate buffer, pH 5.1, 300 mM NaCl, 25 degrees C), indicating that the potential is that of a nonnative state. In contrast, using a didodecyldimethylammonium bromide (DDAB) film-pyrolytic graphite edge (PGE) electrode, the reduction potentials of native and thermally denatured CuA azurin have been determined to be 271 +/- 7 mV (50 mM ammonium acetate buffer, pH 5.1, 4 degrees C) and 420 +/- 1 mV (50 mM ammonium acetate buffer, pH 5.1, 25 degrees C), respectively. Spectroscopic redox titration using [Ru(NH3)5Py]2+ resulted in a reduction potential (254+/-4 mV) (50 mM ammonium acetate buffer, pH 5.1, 4 degrees C) similar to the value obtained using the DDAB film-PGE electrochemical method. Complete reoxidation of [Ru(NH3)5Py]2+-reduced CuA azurin is also consistent with the conclusion that this spectrochemical titration method using [Ru(NH3)5Py]2+ measures the reduction potential of native CuA azurin.

  13. Diamondoid Structure in a Metal-Organic Framework of Fe4 Single-Molecule Magnets.

    PubMed

    Rigamonti, Luca; Cotton, Carri; Nava, Andrea; Lang, Heinrich; Rüffer, Tobias; Perfetti, Mauro; Sorace, Lorenzo; Barra, Anne-Laure; Lan, Yanhua; Wernsdorfer, Wolfgang; Sessoli, Roberta; Cornia, Andrea

    2016-09-12

    A 3D metal-organic framework (MOF) having single-molecule magnet (SMM) linkers was prepared in crystalline form by using a tetrairon(III) complex functionalised with two divergent pyridyl groups, namely [Fe4 (pPy)2 (dpm)6 ] (1; H3 pPy=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm=dipivaloylmethane). Reaction of 1 with silver(I) perchlorate afforded {[Fe4 (pPy)2 (dpm)6 ]2 Ag}ClO4 (2), which crystallises in a cubic face-centred lattice and exhibits two interlocked diamondoid networks. In 2, the SMMs act as linear ditopic synthons, and silver(I) ions as tetrahedral nodes coordinated by four pyridyl nitrogen atoms. The magnetic properties of 1 (S=5 and D≈-0.4 cm(-1) in the ground spin state) are largely preserved in 2, which shows slow magnetic relaxation with an anisotropy barrier of Ueff /kB =11.46(10) K in zero field and 14.25(8) K in an applied field of 1 kOe. However, crystal symmetry triggers highly noncollinear magnetic anisotropy contributions oriented at 109.47° from each other along the threefold axes of AgN4 tetrahedra, a unique scenario fully confirmed by a single-crystal cantilever torque magnetometry investigation. Magnetisation curves down to 0.03 K demonstrated the occurrence of a wide hysteresis loop when the magnetic field was swept along one of the four Ag-N bonds. By symmetry, the crystalline compound can then be persistently magnetised parallel or antiparallel to the four main diagonals of the unit cell, although the crystals have no overall second-order anisotropy. PMID:27356278

  14. New RuII Complex for Dual Activity: Photoinduced Ligand Release and 1O2 Production

    PubMed Central

    Loftus, Lauren M.; White, Jessica K.; Albani, Bryan A.; Kohler, Lars; Kodanko, Jeremy J.; Thummel, Randolph P.

    2016-01-01

    The new complex [Ru(pydppn)(biq)(py)]2+ (1) undergoes both py photodissociation in CH3CN with Φ500=0.0070(4) and 1O2 production with ΦΔ=0.75(7) in CH3OH from a long-lived 3ππ* state centered on the pydppn ligand (pydppn=3-(pyrid-2-yl)benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine; biq = 2,2′-biquinoline; py= pyridine). This represents an order of magnitude decrease in the Φ500 compared to the previously reported model compound [Ru(tpy)(biq)(py)]2+ (3) (tpy=2,2′:6′,2″-terpyridine) that undergoes only ligand exchange. The effect on the quantum yields by the addition of a second deactivation pathway through the low-lying 3ππ* state necessary for dual reactivity was investigated using ultrafast and nanosecond transient absorption spectroscopy, revealing a significantly shorter 3MLCT lifetime in 1 relative to that of the model complex 3. Due to the structural similarities between the two compounds, the lower values of Φ500 and ΦΔ compared to that of [Ru(pydppn)(bpy)(py)]2+ (2) (bpy=2,2′-bipyridine) are attributed to a competitive excited state population between the 3LF states involved in ligand dissociation and the long-lived 3ππ* state in 1. Complex 1 represents a model compound for dual activity that may be applied to photochemotherapy. PMID:26715085

  15. Three ion-pair complexes containing bis(maleonitriledithiolate)copper(II) anion and substituted 2-aminopyridinium cations: Syntheses, crystal structures, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Liu, Yin; Ou, Shu-Hua; Li, Jin-Ni; Liao, Xiao-Lan; Zheng, Xiao-Xu; Luo, Cui-Ping; Yang, Le-Min; Zhou, Jia-Rong; Ni, Chun-Lin

    2016-04-01

    Three new ion-pair complexes, [2-ClBz-2‧-NH2Py]2[Cu(mnt)2](1), [2-Cl-4-ClBz-2-NH2Py]2[Cu(mnt)2](2) and [2-Cl-4-BrBz-2‧-NH2Py]2[Cu(mnt)2]·C2H5OH(3) ([2-Cl-4-RBz-2‧-NH2Py]+ = 1-(2‧-chloro-4‧-Rbenzyl)-2-aminopyridinium, R = H, Cl, Br; mnt2- = maleonitriledithiolate), were synthesized and characterized by elemental analyses, IR, UV-visible, single crystal X-ray diffraction and magnetic measurements. Both 1 and 2 crystallize in the monoclinic space group P2(1)/c, and the [Cu(mnt)2]2- anions and the cations form a 1D network structure through the N-HṡṡṡN hydrogen bonds. While the anions in 3 form a ladder-like chain through the C-HṡṡṡN interactions between the [Cu(mnt)2]2- anions and CH3CH2OH molecules. Some weak interactions such as πṡṡṡπ, CuṡṡṡN, ClṡṡṡC, and C-HṡṡṡCl, O-HṡṡṡCl, C-HṡṡṡS, N-HṡṡṡO, N-HṡṡṡN and C-HṡṡṡN hydrogen bonds in three molecular solids generate further a 3D network structure. The magnetic measurement reveals that 1 shows a very weak ferromagnetic interaction, and 2 exhibits a transition from ferromagnetic to antiferromagnetic coupling about 15 K, while 3 shows an antiferromagnetic coupling feature with θ = -12.51 K when the temperature is lowered.

  16. Asteroid lightcurve analysis at the Palmer Divide Observatory: July-September 2005

    NASA Astrophysics Data System (ADS)

    Warner, Brian D.

    2006-06-01

    Lightcurves for the following asteroids and one comet originally designated as an asteroid were obtained and then analyzed to determine the synodic period and amplitude: 643 Scheherezade, 663 Gerlinde, 696 Leonora, 2199 Klet, 2214 Carol, 2346 Lilio, 2382 Nonie, 2957 Tatsuo, 4116 Elachi, 4368 Pillmore, 5968 Trauger, (6065) 1987 OC, (8180) 1992 PY2, (28610) 2000 EM158, (49385) 1998 XA12, P/2002 EX12 (NEAT). Two asteroids were observed for which no definitive solution could be found: 6271 Farmer and 6911 Nancygreen.

  17. A 2-pyridyl (py) attached phosphine imine [P(Npy)(NHpy)3] and an imido phosphinate ion [P(Npy)2)(NHpy)2]- in its Ag(I) complex.

    PubMed

    Gupta, Arvind K; Chipem, Francis A S; Boomishankar, Ramamoorthy

    2012-02-14

    A new phosphine imine 3, [P(Npy)(NHpy)(3)] (py = 2-pyridyl), was synthesized from the phosphonium salt 1, [P(NHpy)(4)]Cl. Subsequent reaction of 1 or 3 with AgClO(4) lead to an unprecedented penta-nuclear Ag(I) complex 4 stabilized by two [P(Npy)(2)(NHpy)(2)](-) anions [L](-). The packing diagram of 4 shows an interesting channel structure which contains solvated molecules of methanol and toluene. The diimine ligand [L](-), which represents the N-analogue of a phosphinate ion (H(2)PO(4)(-)), was obtained in situ under the mild reaction conditions in the absence of a base. PMID:22167162

  18. Ruthenium-Aryloxide Catalysts for Olefin Metathesis

    NASA Astrophysics Data System (ADS)

    Monfette, Sebastien; Blacquiere, Johanna M.; Conrad, Jay C.; Beach, Nicholas J.; Fogg, Deryn E.

    : Advances in design of ruthenium aryloxide catalysts for olefin metathesis are described. The target complexes are accessible on reaction of RuCl2(NHC)(py)2 (CHPh) (NHC - N-heterocyclic carbene) with electron-deficient, monodentate aryl- oxides, or aryloxides that yield small, rigid chelate rings. The best of these catalysts offer activity comparable to or greater than that of the parent chloride (Grubbs) systems in ring-closing metathesis (RCM). Preliminary studies of the electronic nature of the Ru-X bond suggest that the metal center is more electropositive in the aryloxide complexes than in the Grubbs systems.

  19. Metal-to-Ligand Charge-Transfer Emissions of Ruthenium(II) Pentaammine Complexes with Monodentate Aromatic Acceptor Ligands and Distortion Patterns of their Lowest Energy Triplet Excited States.

    PubMed

    Tsai, Chia Nung; Mazumder, Shivnath; Zhang, Xiu Zhu; Schlegel, H Bernhard; Chen, Yuan Jang; Endicott, John F

    2015-09-01

    This is the first report of the 77 K triplet metal-to-ligand charge-transfer ((3)MLCT) emission spectra of pentaammine-MDA-ruthenium(II) ([Ru(NH3)5(MDA)](2+)) complexes, where MDA is a monodentate aromatic ligand. The emission spectra of these complexes and of the related trans-[Ru(NH3)4(MDA) (MDA')](2+) complexes are closely related, and their emission intensities are very weak. Density functional theory (DFT) calculations indicate that the energies of the lowest (3)MLCT excited states of Ru-MDA complexes are either similar to or lower than those of the lowest energy metal-centered excited states ((3)MC(X(Y))), that the barrier to internal conversion at 77 K is large compared to kBT, and that the (3)MC(X(Y)) excited states are weakly bound. The [Ru(NH3)5py](2+) complex is an exception to the general pattern: emission has been observed for the [Ru(ND3)5(d5-py)](2+) complex, but its lifetime is apparently very short. DFT modeling indicates that the excited state distortions of the different (3)MC excited states are very large and are in both Ru-ligand bonds along a single Cartesian axis for each different (3)MC excited state, nominally resulting in (3)MC(X(Y)), (3)MC((X)Y), and (3)MC(Z) lowest energy metal-centered states. The (3)MC(X(Y)) and (3)MC((X)Y) states appear to be the pseudo-Jahn-Teller distorted components of a (3)MC((XY)) state. The (3)MC(X(Y)) states are distorted up to 0.5 Å in each H3N-Ru-NH3 bond along a single Cartesian axis in the pentaammine and trans-tetraammine complexes, whereas the (3)MC(Z) states are found to be dissociative. DFT modeling of the (3)MLCT excited state of [Ru(NH3)5(py)](2+) indicates that the Ru center has a spin density of 1.24 at the (3)MLCT energy minimum and that the (3)MLCT → (3)MC(Z) crossing is smooth with a very small barrier (<0.5 kcal/mol) along the D3N-Ru-py distortion coordinate, implying strong (3)MLCT/(3)MC excited state configurational mixing. Furthermore, the DFT modeling indicates that the long

  20. Photorelease of Pyridyl Esters in Organometallic Ru(II) Arene Complexes.

    PubMed

    Habtemariam, Abraha; Garino, Claudio; Ruggiero, Emmanuel; Alonso-de Castro, Silvia; Mareque-Rivas, Juan C; Salassa, Luca

    2015-01-01

    New Ru(II) arene complexes of formula [(η6-p-cym)Ru(N-N)(X)]2+ (where p-cym = para-cymene, N-N = 2,2'-bipyrimidine (bpm) or 2,2'-bipyridine (bpy) and X = m/p-COOMe-Py, 1-4) were synthesised and characterized, including the molecular structure of complexes [(η6-p-cym)Ru(bpy)(m-COOMe-Py)]2+ (3) and [(η6-p-cym)Ru(bpy) (p-COOMe-Py)]2+ (4) by single-crystal X-ray diffraction. Complexes 1-4 are stable in the dark in aqueous solution over 48 h and photolysis studies indicate that they can photodissociate the monodentate m/p-COOMe-Py ligands selectively with yields lower than 1%. DFT and TD-DFT calculations (B3LYP/LanL2DZ/6-31G**) performed on singlet and triplet states pinpoint a low-energy triplet state as the reactive state responsible for the selective dissociation of the monodentate pyridyl ligands. PMID:25905605

  1. Homogeneous reduction of CO2 by photogenerated pyridinyl radicals.

    PubMed

    Riboni, Francesca; Selli, Elena; Hoffmann, M R; Colussi, A J

    2015-05-14

    We report that 1-hydropyridinyl radicals (1-PyH(•)) photogenerated in solution react with dissolved CO2 en route to its 2e(-) reduction into carboxylic acids. The 254 nm excitation of pyridine (Py) in deaerated 2-PrOH/H2O mixtures saturated with 1 atm of CO2 yields a suite of products, among which we identified Na(HCOO)2(-) (m/z(-) = 113), C5H6NCOO(-) (m/z(-) = 124), and C5H10O2NCOO(-) (m/z(-) = 160) species by electrospray ionization mass spectrometry. These products demonstrably contain carboxylate functionalities that split CO2 neutrals via collisionally induced dissociation. We infer that 1-PyH(•) [from (1) (3)Py* + 2-PrOH → 1-PyH(•) + (•)PrOH] adds to CO2, in competition with radical-radical reactions, leading to intermediates that are in turn reduced by (•)PrOH into the observed species. The formation of carboxylates in this system, which is shown to require CO2, Py, 2-PrOH, and actinic radiation, amounts to the homogeneous 2e(-) reduction of CO2 by 2-PrOH initiated by Py*. We evaluate a rate constant (2) k2(1-PyH(•) + CO2 → (•)Py-1-COOH) ≈ O (10) M(-1) s(-1) and an activation energy E2 ≥ 9 kcal mol(-1) that are compatible with thermochemical estimates for this reaction.

  2. Platinum-group element concentrations in pyrite from the Main Sulfide Zone of the Great Dyke of Zimbabwe

    NASA Astrophysics Data System (ADS)

    Piña, R.; Gervilla, F.; Barnes, S.-J.; Oberthür, T.; Lunar, R.

    2016-02-01

    The Main Sulfide Zone (MSZ) of the Great Dyke of Zimbabwe hosts the world's second largest resource of platinum-group elements (PGE) after the Bushveld Complex in South Africa. The sulfide assemblage of the MSZ comprises pyrrhotite, pentlandite, chalcopyrite, and minor pyrite. Recently, several studies have observed in a number of Ni-Cu-PGE ore deposits that pyrite may host significant amounts of PGE, particularly Pt and Rh. In this study, we have determined PGE and other trace element contents in pyrite from the Hartley, Ngezi, Unki, and Mimosa mines of the Great Dyke by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Based on the textures and PGE contents, two types of pyrite can be differentiated. Py1 occurs as individual euhedral or subhedral grains or clusters of crystals mostly within chalcopyrite and pentlandite, in some cases in the form of symplectitic intergrowths, and is PGE rich (up to 99 ppm Pt and 61 ppm Rh; 1.7 to 47.1 ppm Ru, 0.1 to 7.8 ppm Os, and 1.2 to 20.2 ppm Ir). Py2 occurs as small individual euhedral or subhedral crystals within pyrrhotite, pentlandite, and less frequently within chalcopyrite and silicates and has low PGE contents (<0.11 ppm Pt, <0.34 ppm Rh, <2.5 ppm Ru, <0.37 ppm Ir, and <0.40 ppm Os). Py1 contains higher Os, Ir, Ru, Rh, and Pt contents than the associated pyrrhotite, pentlandite, and chalcopyrite, whereas Py2 has similar PGE contents as coexisting pyrrhotite and pentlandite. Based on the textural relationships, two different origins are attributed for each pyrite type. Py1 intergrowth with pentlandite and chalcopyrite is inferred to have formed by late, low temperature (<300 °C) decomposition of residual Ni-rich monosulfide solid solution, whereas Py2 is suggested to have formed by replacement of pyrrhotite and pentlandite caused by late magmatic/hydrothermal fluids.

  3. Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N-(2-Pyridylethyl)-N'-(2,6-diisopropylphenyl)pivalamidine.

    PubMed

    Kalden, Diana; Oberheide, Ansgar; Loh, Claas; Görls, Helmar; Krieck, Sven; Westerhausen, Matthias

    2016-07-25

    N-(2,6-Diisopropylphenyl)-N'-(2-pyridylethyl)pivalamidine (Dipp-N=C(tBu)-N(H)-C2 H4 -Py) (1), reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates [(tmeda)Li{Dipp-N=C(tBu)-N-C2 H4 -Py}] (6), [Mg{Dipp-N=C(tBu)-N-C2 H4 -Py}2 ] (3), and heteroleptic [{(Me3 Si)2 N}Ae{Dipp-N=C(tBu)-N-C2 H4 -Py}], with Ae being Ca (2 a) and Sr (2 b). In contrast to this straightforward deprotonation of the amidine units, the reaction of 1 with the bis(trimethylsilyl)amides of sodium or potassium unexpectedly leads to a β-metalation and an immediate deamidation reaction yielding [(thf)2 Na{Dipp-N=C(tBu)-N(H)}] (4 a) or [(thf)2 K{Dipp-N=C(tBu)-N(H)}] (4 b), respectively, as well as 2-vinylpyridine in both cases. The lithium derivative shows a similar reaction behavior to the alkaline earth metal congeners, underlining the diagonal relationship in the periodic table. Protonation of 4 a or the metathesis reaction of 4 b with CaI2 in tetrahydrofuran yields N-(2,6-diisopropylphenyl)pivalamidine (Dipp-N=C(tBu)-NH2 ) (5), or [(thf)4 Ca{Dipp-N=C(tBu)-N(H)}2 ] (7), respectively. The reaction of AN(SiMe3 )2 (A=Na, K) with less bulky formamidine Dipp-N=C(H)-N(H)-C2 H4 -Py (8) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp-N=C(H)-N-C2 H4 -Py}]2 (9 a) or [(thf)K{Dipp-N=C(H)-N-C2 H4 -Py}]2 (9 b), respectively, are isolated as dinuclear complexes. From these experiments it is obvious, that β-metalation/deamidation of N-(2-pyridylethyl)amidines requires bases with soft metal ions and also steric pressure. The isomeric forms of all compounds are verified by single-crystal X-ray structure analysis and are maintained in solution. PMID:27355970

  4. Platinum-group element concentrations in pyrite from the Main Sulfide Zone of the Great Dyke of Zimbabwe

    NASA Astrophysics Data System (ADS)

    Piña, R.; Gervilla, F.; Barnes, S.-J.; Oberthür, T.; Lunar, R.

    2016-10-01

    The Main Sulfide Zone (MSZ) of the Great Dyke of Zimbabwe hosts the world's second largest resource of platinum-group elements (PGE) after the Bushveld Complex in South Africa. The sulfide assemblage of the MSZ comprises pyrrhotite, pentlandite, chalcopyrite, and minor pyrite. Recently, several studies have observed in a number of Ni-Cu-PGE ore deposits that pyrite may host significant amounts of PGE, particularly Pt and Rh. In this study, we have determined PGE and other trace element contents in pyrite from the Hartley, Ngezi, Unki, and Mimosa mines of the Great Dyke by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Based on the textures and PGE contents, two types of pyrite can be differentiated. Py1 occurs as individual euhedral or subhedral grains or clusters of crystals mostly within chalcopyrite and pentlandite, in some cases in the form of symplectitic intergrowths, and is PGE rich (up to 99 ppm Pt and 61 ppm Rh; 1.7 to 47.1 ppm Ru, 0.1 to 7.8 ppm Os, and 1.2 to 20.2 ppm Ir). Py2 occurs as small individual euhedral or subhedral crystals within pyrrhotite, pentlandite, and less frequently within chalcopyrite and silicates and has low PGE contents (<0.11 ppm Pt, <0.34 ppm Rh, <2.5 ppm Ru, <0.37 ppm Ir, and <0.40 ppm Os). Py1 contains higher Os, Ir, Ru, Rh, and Pt contents than the associated pyrrhotite, pentlandite, and chalcopyrite, whereas Py2 has similar PGE contents as coexisting pyrrhotite and pentlandite. Based on the textural relationships, two different origins are attributed for each pyrite type. Py1 intergrowth with pentlandite and chalcopyrite is inferred to have formed by late, low temperature (<300 °C) decomposition of residual Ni-rich monosulfide solid solution, whereas Py2 is suggested to have formed by replacement of pyrrhotite and pentlandite caused by late magmatic/hydrothermal fluids.

  5. Oxygen Atom Exchange between H2O and Non-Heme Oxoiron(IV) Complexes: Ligand Dependence and Mechanism.

    PubMed

    Puri, Mayank; Company, Anna; Sabenya, Gerard; Costas, Miquel; Que, Lawrence

    2016-06-20

    Detailed studies of oxygen atom exchange (OAE) between H2(18)O and synthetic non-heme oxoiron(IV) complexes supported by tetradentate and pentadentate ligands provide evidence that they proceed by a common mechanism but within two different kinetic regimes, with OAE rates that span 2 orders of magnitude. The first kinetic regime involves initial reversible water association to the Fe(IV) complex, which is evidenced by OAE rates that are linearly dependent on [H2(18)O] and H2O/D2O KIEs of 1.6, while the second kinetic regime involves a subsequent rate determining proton-transfer step between the bound aqua and oxo ligands that is associated with saturation behavior with [H2(18)O] and much larger H2O/D2O KIEs of 5-6. [Fe(IV)(O)(TMC)(MeCN)](2+) (1) and [Fe(IV)(O)(MePy2TACN)](2+) (9) are examples of complexes that exhibit kinetic behavior in the first regime, while [Fe(IV)(O)(N4Py)](2+) (3), [Fe(IV)(O)(BnTPEN)](2+) (4), [Fe(IV)(O)(1Py-BnTPEN)](2+) (5), [Fe(IV)(O)(3Py-BnTPEN)](2+) (6), and [Fe(IV)(O)(Me2Py2TACN)](2+) (8) represent complexes that fall in the second kinetic regime. Interestingly, [Fe(IV)(O)(PyTACN)(MeCN)](2+) (7) exhibits a linear [H2(18)O] dependence below 0.6 M and saturation above 0.6 M. Analysis of the temperature dependence of the OAE rates shows that most of these complexes exhibit large and negative activation entropies, consistent with the proposed mechanism. One exception is complex 9, which has a near-zero activation entropy and is proposed to undergo ligand-arm dissociation during the RDS to accommodate H2(18)O binding. These results show that the observed OAE kinetic behavior is highly dependent on the nature of the supporting ligand and are of relevance to studies of non-heme oxoiron(IV) complexes in water or acetonitrile/water mixtures for applications in photocatalysis and water oxidation chemistry. PMID:27275633

  6. Phosphorescence versus thermally activated delayed fluorescence. Controlling singlet-triplet splitting in brightly emitting and sublimable Cu(I) compounds.

    PubMed

    Leitl, Markus J; Krylova, Valentina A; Djurovich, Peter I; Thompson, Mark E; Yersin, Hartmut

    2014-11-12

    Photophysical properties of two highly emissive three-coordinate Cu(I) complexes, (IPr)Cu(py2-BMe2) (1) and (Bzl-3,5Me)Cu(py2-BMe2) (2), with two different N-heterocyclic (NHC) ligands were investigated in detail (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; Bzl-3,5Me = 1,3-bis(3,5-dimethylphenyl)-1H-benzo[d]imidazol-2-ylidene; py2-BMe2 = di(2-pyridyl)dimethylborate). The compounds exhibit remarkably high emission quantum yields of more than 70% in the powder phase. Despite similar chemical structures of both complexes, only compound 1 exhibits thermally activated delayed blue fluorescence (TADF), whereas compound 2 shows a pure, yellow phosphorescence. This behavior is related to the torsion angles between the two ligands. Changing this angle has a huge impact on the energy splitting between the first excited singlet state S1 and triplet state T1 and therefore on the TADF properties. In addition, it was found that, in both compounds, spin-orbit coupling (SOC) is particularly effective compared to other Cu(I) complexes. This is reflected in short emission decay times of the triplet states of only 34 μs (1) and 21 μs (2), respectively, as well as in the zero-field splittings of the triplet states amounting to 4 cm(-1) (0.5 meV) for 1 and 5 cm(-1) (0.6 meV) for 2. Accordingly, at ambient temperature, compound 1 exhibits two radiative decay paths which are thermally equilibrated: one via the S1 state as TADF path (62%) and one via the T1 state as phosphorescence path (38%). Thus, if this material is applied in an organic light-emitting diode, the generated excitons are harvested mainly in the singlet state, but to a significant portion also in the triplet state. This novel mechanism based on two separate radiative decay paths reduces the overall emission decay time distinctly. PMID:25260042

  7. Unusually efficient pyridine photodissociation from Ru(II) complexes with sterically bulky bidentate ancillary ligands.

    PubMed

    Knoll, Jessica D; Albani, Bryan A; Durr, Christopher B; Turro, Claudia

    2014-11-13

    The introduction of steric bulk to the bidentate ligand in [Ru(tpy)(bpy)(py)](2+) (1; tpy = 2,2':2',6″-terpyridine; bpy = 2,2'-bipyridine; py = pyridine) to provide [Ru(tpy)(Me2bpy)(py)](2+) (2; Me2bpy = 6,6'-dimethyl-2,2'-bipyridine) and [Ru(tpy)(biq)(py)](2+) (3; biq = 2,2'-biquinoline) facilitates photoinduced dissociation of pyridine with visible light. Upon irradiation of 2 and 3 in CH3CN (λirr = 500 nm), ligand exchange occurs to produce the corresponding [Ru(tpy)(NN)(NCCH3)](2+) (NN = Me2bpy, biq) complex with quantum yields, Φ500, of 0.16(1) and 0.033(1) for 2 and 3, respectively. These values represent an increase in efficiency of the reaction by 2-3 orders of magnitude as compared to that of 1, Φ500 < 0.0001, under similar experimental conditions. The photolysis of 2 and 3 in H2O with low energy light to produce [Ru(tpy)(NN)(OH2)](2+) (NN = Me2bpy, biq) also proceeds rapidly (λirr > 590 nm). Complexes 1-3 are stable in the dark in both CH3CN and H2O under similar experimental conditions. X-ray crystal structures and theoretical calculations highlight significant distortion of the planes of the bidentate ligands in 2 and 3 relative to that of 1. The crystallographic dihedral angles defined by the bidentate ligand, Me2bpy in 2 and biq in 3, and the tpy ligand were determined to be 67.87° and 61.89°, respectively, whereas only a small distortion from the octahedral geometry is observed between bpy and tpy in 1, 83.34°. The steric bulk afforded by Me2bpy and biq also result in major distortions of the pyridine ligand in 2 and 3, respectively, relative to 1, which are believed to weaken its σ-bonding and π-back-bonding to the metal and play a crucial role in the efficiency of the photoinduced ligand exchange. The ability of 2 and 3 to undergo ligand exchange with λirr > 590 nm makes them potential candidates to build photochemotherapeutic agents for the delivery of drugs with pyridine binding groups.

  8. Unusually Efficient Pyridine Photodissociation from Ru(II) Complexes with Sterically Bulky Bidentate Ancillary Ligands

    PubMed Central

    2015-01-01

    The introduction of steric bulk to the bidentate ligand in [Ru(tpy)(bpy)(py)]2+ (1; tpy = 2,2′:2′,6″-terpyridine; bpy = 2,2′-bipyridine; py = pyridine) to provide [Ru(tpy)(Me2bpy)(py)]2+ (2; Me2bpy = 6,6′-dimethyl-2,2′-bipyridine) and [Ru(tpy)(biq)(py)]2+ (3; biq = 2,2′-biquinoline) facilitates photoinduced dissociation of pyridine with visible light. Upon irradiation of 2 and 3 in CH3CN (λirr = 500 nm), ligand exchange occurs to produce the corresponding [Ru(tpy)(NN)(NCCH3)]2+ (NN = Me2bpy, biq) complex with quantum yields, Φ500, of 0.16(1) and 0.033(1) for 2 and 3, respectively. These values represent an increase in efficiency of the reaction by 2–3 orders of magnitude as compared to that of 1, Φ500 < 0.0001, under similar experimental conditions. The photolysis of 2 and 3 in H2O with low energy light to produce [Ru(tpy)(NN)(OH2)]2+ (NN = Me2bpy, biq) also proceeds rapidly (λirr > 590 nm). Complexes 1–3 are stable in the dark in both CH3CN and H2O under similar experimental conditions. X-ray crystal structures and theoretical calculations highlight significant distortion of the planes of the bidentate ligands in 2 and 3 relative to that of 1. The crystallographic dihedral angles defined by the bidentate ligand, Me2bpy in 2 and biq in 3, and the tpy ligand were determined to be 67.87° and 61.89°, respectively, whereas only a small distortion from the octahedral geometry is observed between bpy and tpy in 1, 83.34°. The steric bulk afforded by Me2bpy and biq also result in major distortions of the pyridine ligand in 2 and 3, respectively, relative to 1, which are believed to weaken its σ-bonding and π-back-bonding to the metal and play a crucial role in the efficiency of the photoinduced ligand exchange. The ability of 2 and 3 to undergo ligand exchange with λirr > 590 nm makes them potential candidates to build photochemotherapeutic agents for the delivery of drugs with pyridine binding groups. PMID:25027458

  9. Measurement of solid liquid interfacial energy in the pyrene succinonitrile monotectic system

    NASA Astrophysics Data System (ADS)

    Akbulut, S.; Ocak, Y.; Böyük, U.; Erol, M.; Keslioglu, K.; Marasli, N.

    2006-09-01

    The equilibrated grain boundary groove shapes for solid pyrene (PY) in equilibrium with the PY succinonitrile (SCN) monotectic liquid were directly observed. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient and solid-liquid interfacial energy for solid PY in equilibrium with the PY SCN monotectic liquid have been determined to be (8.72 ± 0.87) × 10-8 K m and (21.9 ± 3.28) × 10-3 J m-2 with the present numerical method and Gibbs-Thomson equation, respectively. The grain boundary energy of the solid PY phase has been determined to be (42.84 ± 7.28) × 10-3 J m-2 from the observed grain boundary groove shapes. Thermal conductivities of solid and liquid phases for PY-2.5 mol% SCN alloy and pure PY have also been measured.

  10. Generation of photocurrent by visible-light irradiation of conjugated dawson polyoxophosphovanadotungstate-porphyrin copolymers.

    PubMed

    Azcarate, Iban; Huo, Zhaohui; Farha, Rana; Goldmann, Michel; Xu, Hualong; Hasenknopf, Bernold; Lacôte, Emmanuel; Ruhlmann, Laurent

    2015-05-26

    Four hybrid polyoxometalate-porphyrin copolymer films were obtained by the electrooxidation of zinc octaethylporphyrin in the presence of four different Dawson-type polyoxometalates bearing two pyridyl groups (POM(py)2) with various spacers. The POM monomers were designed around 1,3,5-trisubstituted benzene rings. Two of the substituents of the benzene ring are linked to the pyridyl groups, and the third is connected to the POM subunit. The four monomers vary in the relative positions of the nitrogen atoms of the pyridine rings or in the distance from the carbonyl group. The monomers were fully characterized by (1)H, (31)P, and (13)C NMR spectroscopy, electrospray mass spectrometry, IR and UV/Vis spectroscopy, and electrochemistry. The copolymers were characterized by UV/Vis spectroscopy, X-ray photoelectron spectroscopy, electrochemistry, and AFM. Their photovoltaic performance under visible light irradiation was investigated by photocurrent transient measurements under visible illumination. PMID:25900250

  11. Synthesis and characterization of polymeric azido Zn(II) and Ni(II) complexes based on 3-hydroxypyridine

    NASA Astrophysics Data System (ADS)

    Mautner, Franz A.; Berger, Christian; Domian, Elisabeth; Fischer, Roland C.; Massoud, Salah S.

    2016-10-01

    The synthesis and structural characterization of two new complexes catena-[Ni(3-O-py)(3-HO-py)2(μ1,3-N3)(H2O)] (1) and catena-[Zn(μ-3-O-py)(μ1,1-N3)] (2), where 3-HO-py = 3-hydroxypyridine, are reported. The complexes were characterized by the elemental microanalyses, IR, and X-ray crystallography and by UV-Vis spectroscopy for complex 1. Single crystal X-ray crystallography revealed the polymeric nature of the complexes: 1 as 1D with a single EE azide bridging, and 2 as 2D with μ(O,O‧,N) bridging of the deprotonated 3-O-py anions and di-EO azide groups, respectively. In 1 the neutral and deprotonated 3-hydroxypyridine molecules act only as N-terminal ligands. The emission spectral properties of the Zn(II) complex were investigated.

  12. Variation of electronic transitions and reduction potentials of cerium(IV) complexes.

    PubMed

    Williams, Ursula J; Schneider, David; Dorfner, Walter L; Maichle-Mössmer, Cäcilia; Carroll, Patrick J; Anwander, Reiner; Schelter, Eric J

    2014-11-21

    The trivalent compound K[Ce[N(SiHMe2)2]4] was synthesized and oxidized, providing a convenient route to the reported cerium(IV) compound Ce[N(SiHMe2)2]4. Protonolysis reactions of Ce[N(SiHMe2)2]4 with tert-butanol, substituted benzyl alcohols, and 2,6-diphenylphenol yielded the neutral tetravalent compounds Ce(O(t)Bu)4(py)2, Ce2(OCH2C6R5)8(thf)2 (R = Me, F), and Ce(Odpp)4 (dpp = 2,6-(C6H5)2-C6H3). Spectroscopic and electrochemical characterization of the monometallic cerium(IV) silylamide, alkoxide, and aryloxide compounds revealed variable ligand-to-metal charge transfer transitions and metal-based reduction potentials. Computational bonding analyses were performed to complement the physical characterization of the complexes.

  13. New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and 1O2 Generation

    PubMed Central

    Knoll, Jessica D.; Albani, Bryan A.; Turro, Claudia

    2016-01-01

    CONSPECTUS Uncovering the factors that govern the electronic structure of Ru(II)–polypyridyl complexes is critical in designing new compounds for desired photochemical reactions, and strategies to tune excited states for ligand dissociation and 1O2 production are discussed herein. The generally accepted mechanism for photoinduced ligand dissociation proposes that population of the dissociative triplet ligand field (3LF) state proceeds through thermal population from the vibrationally cooled triplet metal-to-ligand charge transfer (3MLCT) state; however, temperature-dependent emission spectroscopy provides varied activation energies using the emission and ligand exchange quantum yields for [Ru(bpy)2(L)2]2+ (bpy = 2,2′-bipyridine; L = CH3CN or py). This suggests that population of the 3LF state proceeds from the vibrationally excited 3MLCT state. Because the quantum yield of ligand dissociation for nitriles is much more efficient than that for py, steric bulk was introduced into the ligand set to distort the pseudo-octahedral geometry and lower the energy of the 3LF state. The py dissociation quantum yield with 500 nm irradiation in a series of [Ru(tpy)(NN)(py)]2+ complexes (tpy = 2,2′:6′,2″-terpyridine; NN = bpy, 6,6′-dimethyl-2,2′-bipyridine (Me2bpy), 2,2′-biquinoline (biq)) increases by 2–3 orders of magnitude with the sterically bulky Me2bpy and biq ligands relative to bpy. Ultrafast transient absorption spectroscopy reveals population of the 3LF state within 3–7 ps when NN is bulky, and density functional theory calculations support stabilized 3LF states. Dual activity via ligand dissociation and 1O2 production can be achieved by careful selection of the ligand set to tune the excited-state dynamics. Incorporation of an extended π system in Ru(II) complexes such as [Ru(bpy)(dppn)(CH3CN)2]2+ (dppn = benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine) and [Ru(tpy)(Me2dppn)(py)]2+ (Me2dppn = 3,6-dimethylbenzo[i]dipyrido[3,2-a:2′,3

  14. Asymmetric and symmetric triazenido cyclopalladated complexes: Synthesis, structural analysis and DFT calculations

    NASA Astrophysics Data System (ADS)

    Härter Vaniel, Ana Paula; Mauro, Antonio Eduardo; de Godoy Netto, Adelino Vieira; de Almeida, Eduardo Tonon; Piquini, Paulo Cesar; Zambiazi, Priscilla; Back, Davi Fernando; Hörner, Manfredo

    2015-03-01

    The reaction of [Pd{dmba}(μ-N3)]2 (dmba = N,N-dimethylbenzylamine) with 1-(2-fluorophenyl)-3-(4-nitrophenyl)triazenido (L1) or 1,3-bis(4-nitrophenyl)triazenido (L2) anions, in methanol, and subsequent treatment with pyridine (py) allows the preparation of the corresponding cyclopalladated compounds [Pd(dmba)(L1)(py)] (1) and [Pd(dmba)(L2)(py)]ṡpy (2). The acentric mononuclear entities of (1) and (2) are connected by weak intermolecular non-classical Csbnd H⋯C hydrogen bonds, which results in 2-D arrangements by translation, along the [1 0 0] and [0 0 1] crystallographic directions, respectively.

  15. LETTER: Scaling law for effective heat diffusivity in ELMy H-mode plasmas

    NASA Astrophysics Data System (ADS)

    Becker, G.

    2004-11-01

    Transport simulations of high density scenarios of ITER and other reactor-grade devices require a scaling law for the effective heat diffusivity, χ, in the ELMy H-mode regime. A comprehensive empirical scaling, χH98, compatible with the ITER reference scaling, ITERH-98P(y, 2), for the thermal energy confinement time has been set up. It follows from a power law ansatz for χ and integration of the single-fluid energy equation and recovers all the exponents of the global confinement law. The dependences on temperature and temperature gradient are consistent with the power degradation of confinement and the experimental χ profiles. The χH98 scaling is validated by JET, DIII-D, ASDEX Upgrade and ASDEX discharges covering a wide parameter range. Simulations of the inductive scenario of ITER with χH98 yield an energy confinement time which agrees with the global scaling prediction.

  16. Pyrene based conjugated materials: synthesis, characterization and electroluminescent properties.

    PubMed

    Salunke, Jagadish K; Sonar, Prashant; Wong, F L; Roy, V A L; Lee, C S; Wadgaonkar, Prakash P

    2014-11-14

    In this work, three novel pyrene cored small conjugated molecules, namely 1,3,6,8-tetrakis(6-(octyloxy)naphthalene-2-yl)pyrene (PY-1), 1,3,6,8-tetrakis((E)-2-(6-(n-octyloxy)naphthalene-2-yl)vinyl)pyrene (PY-2) and 1,3,6,8-tetrakis((6-(n-octyloxy)naphthalene-2-yl)ethynyl)pyrene (PY-3) have been synthesized by Suzuki, heck and Sonogashira organometallic coupling reactions, respectively. The effects of single, double and triple bonds on their optical, electrochemical, and thermal properties are studied in detail. These are all materials fluorescent and they have been used in organic light-emitting diodes (OLEDs) and their electroluminescent properties have been studied.

  17. Efficient Pathway for the Preparation of Aryl(isoquinoline)iodonium(III) Salts and Synthesis of Radiofluorinated Isoquinolines.

    PubMed

    Yuan, Zheliang; Cheng, Ran; Chen, Pinhong; Liu, Guosheng; Liang, Steven H

    2016-09-19

    Iodonium compounds play a pivotal role in (18) F-fluorination of radiopharmaceuticals containing non-activated arenes. However, preparation of these species is limited to oxidation conditions or exchange with organometallics that are prepared from aryl halides. Herein we describe a novel "one-pot" process to assemble aryl(isoquinoline)iodonium salts in 40-94 % yields from mesoionic carbene silver complex and Aryl-I-Py2 (OTf)2 . The method is general, practical, and compatible with well-functionalized molecules as well as useful for the preparation of a wide range of (18) F-labeled isoquinolines resulting in up to 92 % radiochemical conversion. As proof of concept, a fluorinated isoquinoline alkaloid, (18) F-aspergillitine is prepared in 10 % isolated radiochemical yield from the corresponding phenyl(aspergillitine)iodonium salt. PMID:27554850

  18. On the structural and electronic considerations concerning the reactivity of metal-metal multiple bonds

    NASA Astrophysics Data System (ADS)

    Glasgow, Katherine Campbell

    2000-10-01

    The previously known compound W2(OCH2tBu) 6(py)2 is crystallographically characterized. Its solid state structure is described and compared with other M2(OR)6L 2 complexes. Upon treatment with isoprene, the complex W2(OCH 2tBu)6(py)(mu-isoprene) forms. The solid state structure is disordered with respect to the orientation of the diene; two different configurations are seen in the crystal structure. These two isomers are in equilibrium in solution and are visible by 1H NMR spectroscopy. Multidimensional NMR experiments are used to assign the structures of the two isomers in solution. Through the use of spin magnetization transfer, it has been determined that the two isomers interconvert through the loss of isoprene. The DeltaH° and DeltaS° values for the equilibrium are determined. The starting material W2(OCH2tBu) 6(py)2 had been previously determined to be an olefin hydrogenation catalyst. It has been determined that cyclic olefins are hydrogenated in a cis manner, and a kinetic isotope effect of 1.7 has been measured. It has been determined that olefins which form isolable adducts with W 2(OCH2tBu)6(py)2, such as isoprene, undergo hydrogenation at approximately the same rate as olefins which do not show evidence of adduct formation. The complex W2(OCH2tBu)6(py) 2had been found to couple aldehydes and ketones stoichiometrically to give olefins. The reaction was found to proceed in a stepwise manner through the alkylidene intermediate W2(OCH2tBu) 6(py)(O)(mu-CHR), allowing the selective cross coupling of aldehydes and ketones. More studies have been undertaken to help determine the scope of the reaction. Competition experiments have been performed to determine reaction preferences. Unsaturated and functionalized aldehydes have been studied to determine the tolerance of the reaction to certain chemical groups. The role of pyridine in this reaction has been studied, especially concerning its reactivity with the alkylidene intermediate. The dimetal tetracarboxylate

  19. Synthesis and structural features of U VI and V IV chelate complexes with (hhmmbH)Cl·H 2O [hhmmb = {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide], a new Schiff base ligand derived from vitamin B6

    NASA Astrophysics Data System (ADS)

    Back, Davi Fernando; Ballin, Marco Aurélio; de Oliveira, Gelson Manzoni

    2009-10-01

    The Schiff base ligand {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide hydrochloride monohydrated {(hhmmbH)Cl·H 2O} ( 1) was prepared by reaction of pyridoxine hydrochloride with benzoic acid hydrazide. The reaction of 1 with [VO(acac) 2] and triethylamine yields the neutral vanadium IV complex [VO 2(hhmmb)]·Py ( 2), with a distorted quadratic pyramidal configuration. The Schiff base 1 reacts also with UO 2(NO 3) 2·6H 2O and triethylamine under deprotonation giving the uranium VI cationic complexes [UO 2(hhmmb)(H 2O)Cl] + ( 3) and [UO 2(hhmmb)(CH 3OH)Cl] + ( 4), both showing the classical pentagonal bipyrimidal geometry of UO22+ complexes. The structural features of all compounds are discussed.

  20. Intramolecular Proton Transfer Boosts Water Oxidation Catalyzed by a Ru Complex.

    PubMed

    Matheu, Roc; Ertem, Mehmed Z; Benet-Buchholz, Jordi; Coronado, Eugenio; Batista, Victor S; Sala, Xavier; Llobet, Antoni

    2015-08-26

    We introduce a new family of complexes with the general formula [Ru(n)(tda)(py)2](m+) (n = 2, m = 0, 1; n = 3, m = 1, 2(+); n = 4, m = 2, 3(2+)), with tda(2-) being [2,2':6',2″-terpyridine]-6,6″-dicarboxylate, including complex [Ru(IV)(OH)(tda-κ-N(3)O)(py)2](+), 4H(+), which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 3(2+) under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV-vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), including solid-state monocrystal X-ray diffraction analysis. In oxidation state IV, the Ru center is seven-coordinated and diamagnetic, whereas in oxidation state II, the complex has an unbonded dangling carboxylate and is six-coordinated while still diamagnetic. With oxidation state III, the coordination number is halfway between the coordination of oxidation states II and IV. Species generated in situ have also been characterized by spectroscopic, computational, and electrochemical techniques, together with the related species derived from a different degree of protonation and oxidation states. 4H(+) can be generated potentiometrically, or voltammetrically, from 3(2+), and both coexist in solution. While complex 3(2+) is not catalytically active, the catalytic performance of complex 4H(+) is characterized by the foot of the wave analysis, giving an impressive turnover frequency record of 8000 s(-1) at pH 7.0 and 50 000 s(-1) at pH 10.0. Density functional theory calculations provide a complete description of the water oxidation catalytic cycle of 4H(+), manifesting the key functional role of the dangling carboxylate in lowering the activation free energies that lead to O-O bond formation. PMID:26226390

  1. Intramolecular proton transfer boosts water oxidation catalyzed by a Ru complex

    DOE PAGESBeta

    Matheu, Roc; Ertem, Mehmed Z.; Benet-Buchholz, J.; Coronado, Eugenio; Batista, Victor S.; Sala, Xavier; Llobet, Antoni

    2015-07-30

    We introduce a new family of complexes with the general formula [Run(tda)(py)2]m+ (n = 2, m = 0, 1; n = 3, m = 1, 2+; n = 4, m = 2, 32+), with tda2– being [2,2':6',2"-terpyridine]-6,6"-dicarboxylate, including complex [RuIV(OH)(tda-κ-N3O)(py)2]+, 4H+, which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 32+ under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV–vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), including solid-state monocrystal X-ray diffraction analysis. In oxidation state IV, the Rumore » center is seven-coordinated and diamagnetic, whereas in oxidation state II, the complex has an unbonded dangling carboxylate and is six-coordinated while still diamagnetic. With oxidation state III, the coordination number is halfway between the coordination of oxidation states II and IV. Species generated in situ have also been characterized by spectroscopic, computational, and electrochemical techniques, together with the related species derived from a different degree of protonation and oxidation states. 4H+ can be generated potentiometrically, or voltammetrically, from 32+, and both coexist in solution. While complex 32+ is not catalytically active, the catalytic performance of complex 4H+ is characterized by the foot of the wave analysis, giving an impressive turnover frequency record of 8000 s–1 at pH 7.0 and 50,000 s–1 at pH 10.0. Density functional theory calculations provide a complete description of the water oxidation catalytic cycle of 4H+, manifesting the key functional role of the dangling carboxylate in lowering the activation free energies that lead to O–O bond formation.« less

  2. Intramolecular Proton Transfer Boosts Water Oxidation Catalyzed by a Ru Complex.

    PubMed

    Matheu, Roc; Ertem, Mehmed Z; Benet-Buchholz, Jordi; Coronado, Eugenio; Batista, Victor S; Sala, Xavier; Llobet, Antoni

    2015-08-26

    We introduce a new family of complexes with the general formula [Ru(n)(tda)(py)2](m+) (n = 2, m = 0, 1; n = 3, m = 1, 2(+); n = 4, m = 2, 3(2+)), with tda(2-) being [2,2':6',2″-terpyridine]-6,6″-dicarboxylate, including complex [Ru(IV)(OH)(tda-κ-N(3)O)(py)2](+), 4H(+), which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 3(2+) under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV-vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), including solid-state monocrystal X-ray diffraction analysis. In oxidation state IV, the Ru center is seven-coordinated and diamagnetic, whereas in oxidation state II, the complex has an unbonded dangling carboxylate and is six-coordinated while still diamagnetic. With oxidation state III, the coordination number is halfway between the coordination of oxidation states II and IV. Species generated in situ have also been characterized by spectroscopic, computational, and electrochemical techniques, together with the related species derived from a different degree of protonation and oxidation states. 4H(+) can be generated potentiometrically, or voltammetrically, from 3(2+), and both coexist in solution. While complex 3(2+) is not catalytically active, the catalytic performance of complex 4H(+) is characterized by the foot of the wave analysis, giving an impressive turnover frequency record of 8000 s(-1) at pH 7.0 and 50 000 s(-1) at pH 10.0. Density functional theory calculations provide a complete description of the water oxidation catalytic cycle of 4H(+), manifesting the key functional role of the dangling carboxylate in lowering the activation free energies that lead to O-O bond formation.

  3. Silver-pyrazole complexes as hybrid multifunctional materials with metallomesogenic and photoluminescent behaviour.

    PubMed

    Ovejero, Paloma; Asensio, Eduardo; Heras, José Vicente; Campo, José Antonio; Cano, Mercedes; Torres, M Rosario; Núñez, Cristina; Lodeiro, Carlos

    2013-02-14

    New pyridine-functionalised pyrazole compounds [Hpz(R(n)py)] (R(n) = C(6)H(4)OC(n)H(2n+1); n = 12, 14, 16, 18; 1-4) and their corresponding silver complexes [Ag(Hpz(R(n)py))(2)][A] ([A] = NO(3)(-), BF(4)(-); ) have been synthesised and characterised. All of them, with the exception of 1, are liquid crystal materials exhibiting monotropic or enantiotropic SmA mesophases, in contrast to the non-mesomorphic related R(n)-monosubstituted compounds. Because the molecular shape is a factor determinant in the organisation of molecules in the liquid crystal phase, we were interested in solving the crystal structure of representative examples of the mentioned compounds, such as 1 and 6. So, the X-ray crystal structure of [Hpz(R(12)py)] 1 shows the presence of dimeric units through N-H···N hydrogen bonds, which conform to an elongated molecular shape containing a double chain length. On the other hand, the structure of [Ag(Hpz(R(14)py))(2)][NO(3)] 6 also evidenced Ag-Ag bonded dimers from 'U'-shaped cationic entities. These dimers exhibit four chains, two by two alternated, so giving rise to a longer molecular length. Of particular interest was to observe that in both structures, the dimers are layer-like packed, their lamellar structures being related to that of the mesophases found in both kinds of compounds. Furthermore, the analysis of the optical data of the compounds 2 and 4 and the silver compounds 5, 6, 9 and 10 as representative examples pointed out their luminescent behaviour as well as their good ability to act as fluorescent probes for Zn(2+), Cu(2+) and Ag(+). An increase in the fluorescence quantum yields is observed in the final complexes produced in the titrations, this fact being specially notable when 9 was used as the starting compound.

  4. Magnetic properties of 1:2 mixed cobalt(II) salicylaldehyde Schiff-base complexes with pyridine ligands carrying high-spin carbenes (Scar = 2/2, 4/2, 6/2, and 8/2) in dilute frozen solutions: role of organic spin in heterospin single-molecule magnets.

    PubMed

    Karasawa, Satoru; Nakano, Kimihiro; Yoshihara, Daisuke; Yamamoto, Noriko; Tanokashira, Jun-ichi; Yoshizaki, Takahito; Inagaki, Yuji; Koga, Noboru

    2014-06-01

    The 1:2 mixtures of Co(p-tolsal)2, p-tolsal = N-p-tolylsalicylideniminato, and diazo-pyridine ligands, DXpy; X = 1, 2, 3l, 3b, and 4, in MTHF solutions were irradiated at cryogenic temperature to form the corresponding 1:2 cobalt-carbene complexes Co(p-tolsal)2(CXpy)2, with Stotal = 5/2, 9/2, 13/2, 13/2, and 17/2, respectively. The resulting Co(p-tolsal)2(CXpy)2, X = 1, 2, 3l, 3b, and 4, showed magnetic behaviors characteristic of heterospin single-molecule magnets with effective activation barriers, Ueff/kB, of 40, 65, 73, 72, and 74 K, for reorientation of the magnetic moment and temperature-dependent hysteresis loops with a coercive force, Hc, of ∼0, 6.2, 10, 6.5, and 9.0 kOe at 1.9 K, respectively. The relaxation times, τQ, due to a quantum tunneling of magnetization (QTM) were estimated to be 1.6 s for Co(p-tolsal)2(C1py)2, ∼2.0 × 10(3) s for Co(p-tolsal)2(C2py)2, and >10(5) s for Co(p-tolsal)2(CXpy)2; X = 3b, 3l, and 4. In heterospin complexes, organic spins, carbenes interacted with the cobalt ion to suppress the QTM pathway, and the τQ value increased with increasing the Stotal values.

  5. Systematic Approach for the Construction of Niobium and Tantalum Sulfide Clusters.

    PubMed

    Gómez, Manuel; Hernández-Prieto, Cristina; Martín, Avelino; Mena, Miguel; Santamaría, Cristina

    2016-04-18

    Treatment of the imido complexes [MCl3(NR)py2] (R = (t)Bu, 2,6-Me2C6H3; M = Nb 1, 3; Ta 2, 4) (Xyl = 2,6-Me2C6H3) with (Me3Si)2S in a 1:1 ratio afforded the new cube-type sulfide clusters [MCl(NR)py(μ3-S)]4 (R = (t)Bu, 2,6-Me2C6H3; M = Nb 5, 7; Ta 6, 8) with loss of Me3SiCl. Reactions of 5 and 6 with cyclopentadienyllithium in 1:4 ratio resulted in the rupture of the coordinative M-S bonds and the replacement of a pyridine molecule and a chlorine atom by an η(5)-cyclopentadienyl group in each metal center, affording the compounds [M(η(5)-C5H5)(N(t)Bu)(μ-S)]4 (M = Nb 9, Ta 10). These processes may develop through formation of the complexes [M4(η(5)-C5H5)2(μ-Cl)(N(t)Bu)4py2(μ3-S)2(μ-S)2](C5H5) (M = Nb 11, Ta 12), also obtained by reaction of 5 and 6 with cyclopentadienyllithium in 1:3 ratio. As further evidence, 11 and 12 led to complexes 9 and 10 by treatment with one more equivalent of the lithium reagent. The structural study of these metal sulfide clusters has been also performed by X-ray crystallography. PMID:27050923

  6. Metal–organic frameworks assembled from lanthanide and 2,5-pyridinedicaboxylate with cubane-like [Ln{sub 4}(OH){sub 4}] building units

    SciTech Connect

    Abdelbaky, Mohammed S.M.; Amghouz, Zakariae; Fernández-Zapico, Eva; García-Granda, Santiago; García, José R.

    2015-09-15

    Lanthanide–organic frameworks based on 2,5-pyridinedicaboxylate (25p) ligand, formulated as [Yb{sub 4}(OH){sub 4}(25p){sub 4}(H{sub 2}O){sub 3}]·H{sub 2}O (25pYb), [Y{sub 4}(OH){sub 4}(25p){sub 4}(H{sub 2}O){sub 3}]·H{sub 2}O (25pY-1) and [Y{sub 6}(OH){sub 8}(25p){sub 5}(H{sub 2}O){sub 2}] (25pY-2), have been obtained as single phases under hydrothermal conditions. 25pYb and 25pY-1 are isostructural, and crystallize in the triclinic space group, P-1, with a=8.6075(5) Å, b=14.8478(7) Å, c=15.9164(9) Å, α=86.277(4)°, β=80.196(5)°, γ=81.785(4)°, and a=8.7166(6) Å, b=14.966(1) Å, c=15.966(1) Å, α=86.260(6)°, β=80.036(6)°, γ=81.599(6)°, respectively. 25pY-2 crystallizes in the monoclinic space group, P2{sub 1}/c, with a=24.9117(17) Å, b=13.7340(8) Å, c=14.3385(10) Å, β=100.551(7)°. 25pYb and 25pY-2 have been structurally characterized by single-crystal X-ray diffraction. The 25pYb structure is based on tetranuclear cubane-like [Yb{sub 4}(OH){sub 4}]{sup 8+} clusters, which are interconnected to eight neighbouring clusters through teen surrounding 25p ligands leading to neutral 3D framework, while the structure of 25pY-2 is based on two independent cuban-like [Y{sub 4}(OH){sub 4}]{sup 8+} clusters, which are joined together through Y1 cation leading to the formation of hexanuclear [Y{sub 6}(OH){sub 8}]{sup 10+} clusters, which in turn are joined via Y2 cation resulting in infinite inorganic chain extending along c-axis, and each chain is interconnected to six adjacent chains through 25p ligands leading finally to 3D framework. The luminescence properties of Eu{sup 3+} and Tb{sup 3+} doped 25pY-1 and 25pY-2 compounds have also been investigated. All materials has been characterized by powder X-ray diffraction, thermal analyses (TG–SDTA–MS), FTIR spectroscopy, C–H–N elemental analysis, scanning electron microscopy (SEM-EDX), and powder X-ray thermodiffraction. - Graphical abstract: Nowadays, lanthanide–organic frameworks (LOFs) attract tremendous attention due to the unique characteristic of lanthanide cations, such as variable coordination numbers and geometries which often lead to novel complex structures, and also to their magnetic and photoluminescence properties. Herein, three LOFs formulated as [Ln{sub 4}(OH){sub 4}(25p){sub 4}(H{sub 2}O){sub 3}]·H{sub 2}O (Ln=Y, Yb) and [Y{sub 6}(OH){sub 8}(25p){sub 5}(H{sub 2}O){sub 2}] have been obtained by hydrothermal method and characterized, and the photoluminescence properties of the Eu and Tb doped compounds are discussed. - Highlights: • Three novel LnOFs has been synthesized and characterized. • Crystal structures are based on tetranuclear cuban-like [Ln{sub 4}(OH){sub 4}]{sup 8+} clusters. • 25pYb and 25pY-1 are based on isolated [Ln{sub 4}(OH){sub 4}]{sup 8+} clusters. • 25pY-2 is based on infinite inorganic chains built up from [Y{sub 4}(OH){sub 4}]{sup 8+} clusters. • Photoluminescence studies show strong red and green light emissions.

  7. Synthesis, structures, and DFT bonding analysis of new titanium hydrazido(2-) complexes.

    PubMed

    Parsons, Thomas B; Hazari, Nilay; Cowley, Andrew R; Green, Jennifer C; Mountford, Philip

    2005-11-14

    The reaction of 1,1-diphenylhydrazine with Ti(NMe2)2Cl2 produced the monomeric terminal titanium hydrazido(2-) species Ti(NNPh2)Cl2(HNMe2)2 (1) in near-quantitative yield. The reaction of Ti(NMe2)2Cl2 with the less sterically demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric mu-eta2,eta1-bridged compounds Ti2(mu-eta2,eta1-NNMe2)2Cl4(HNMe2)2 (2) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(HNMe2)3 (3). The X-ray structures of 2 and 3 showed the formation of N-H...Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an excess of pyridine formed [Ti(NNPh2)Cl2(py)2]n (4, n = 1 or 2). The reaction of the tert-butyl imido complex Ti(N(t)Bu)Cl2(py)3 with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-bridged dimeric complexes, namely Ti2(mu-eta2,eta1-NNMe2)2Cl4(py)2 (5, structurally characterized) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(py)2 (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2-) chemistry of titanium. Compound 1 reacted with neutral fac-N3 donor ligands to form Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti(NNPh2)Cl2(Me3[6]aneN3) (8), Ti(NNPh2)Cl2[HC(Me2pz)3] (9, structurally characterized), and Ti(NNPh2)Cl2[HC(n)Bupz)3] (10) in good yields (Me3[9]aneN3 = trimethyl-1,4,7-triazacyclononane, Me3[6]aneN3 = trimethyl-1,3,5-triazacyclohexane, HC(Me2pz)3 = tris(3,5-dimethylpyrazolyl)methane, and HC((n)Bupz)3 = tris(4-(n)butylpyrazolyl)methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh2)Cl2[HC(pz)3] (I) and the corresponding imido compounds Ti(NMe)Cl2[HC(pz)3] (II) and Ti(NPh)Cl2[HC(pz)3] (III). The NNPh2 ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metalligand triple bond), but with one of the Ti=N(alpha) pi components significantly destabilized by a pi interaction with the lone pair of the N(beta) atom. The NR ligand sigma donor ability was found to be NMe > NPh

  8. Diverse levels of sequence selectivity and catalytic efficiency of protein-tyrosine phosphatases.

    PubMed

    Selner, Nicholas G; Luechapanichkul, Rinrada; Chen, Xianwen; Neel, Benjamin G; Zhang, Zhong-Yin; Knapp, Stefan; Bell, Charles E; Pei, Dehua

    2014-01-21

    The sequence selectivity of 14 classical protein-tyrosine phosphatases (PTPs) (PTPRA, PTPRB, PTPRC, PTPRD, PTPRO, PTP1B, SHP-1, SHP-2, HePTP, PTP-PEST, TCPTP, PTPH1, PTPD1, and PTPD2) was systematically profiled by screening their catalytic domains against combinatorial peptide libraries. All of the PTPs exhibit similar preference for pY peptides rich in acidic amino acids and disfavor positively charged sequences but differ vastly in their degrees of preference/disfavor. Some PTPs (PTP-PEST, SHP-1, and SHP-2) are highly selective for acidic over basic (or neutral) peptides (by >10(5)-fold), whereas others (PTPRA and PTPRD) show no to little sequence selectivity. PTPs also have diverse intrinsic catalytic efficiencies (kcat/KM values against optimal substrates), which differ by >10(5)-fold due to different kcat and/or KM values. Moreover, PTPs show little positional preference for the acidic residues relative to the pY residue. Mutation of Arg47 of PTP1B, which is located near the pY-1 and pY-2 residues of a bound substrate, decreased the enzymatic activity by 3-18-fold toward all pY substrates containing acidic residues anywhere within the pY-6 to pY+5 region. Similarly, mutation of Arg24, which is situated near the C-terminus of a bound substrate, adversely affected the kinetic activity of all acidic substrates. A cocrystal structure of PTP1B bound with a nephrin pY(1193) peptide suggests that Arg24 engages in electrostatic interactions with acidic residues at the pY+1, pY+2, and likely other positions. These results suggest that long-range electrostatic interactions between positively charged residues near the PTP active site and acidic residues on pY substrates allow a PTP to bind acidic substrates with similar affinities, and the varying levels of preference for acidic sequences by different PTPs are likely caused by the different electrostatic potentials near their active sites. The implications of the varying sequence selectivity and intrinsic catalytic activities with respect to PTP in vivo substrate specificity and biological functions are discussed.

  9. Synthesis and structural and magnetic characterisation of cobalt(ii) complexes of mixed phosphonate-antimonate ligands.

    PubMed

    Ali, Shoaib; Muryn, Christopher A; Tuna, Floriana; Winpenny, Richard E P

    2010-10-28

    The polynucleating oxygen donor ligands, [(SbAr)(4)O(2)(PhPO(3)H)(4)(PhPO(3))(4)] 1 and [(SbAr)(2)O(HO(3)P(t)Bu)(6)] 2, based on condensation of p-chlorophenylstibonic acid (ArSbO(3)H(2)) and phosphonic acids, were used to prepare polymetallic cobalt(ii) complexes. Reaction of 1 with cobalt acetate under solvothermal conditions produces three different types of polymetallic cobalt complexes. With LiOMe/pyridine as base in MeOH a dinuclear cobalt cage, [Co(2)(SbAr)(4)O(4)(O(3)PPh)(4)(OMe)(4)py(2)] 3, is formed, with four Sb(ii) and two Co(ii) centres bridged by μ(3)-oxides and phosphonates. The pyridine in the structure can be replaced by 3-picoline 4, 4-picoline 5, quinoline 6, 1,2-diazole 7, 4-phenylpyridine 8, 4-ethyl pyridine 9 and methanol 10. Using pyrazine (pyz) instead of pyridine under the same conditions a polymer, [Co(2)(SbAr)(4)O(4)(O(3)PPh)(4)(OMe)(4)(C(4)H(4)N(2))](n)11, is formed. A similar 1D-polymer forms with 4,4'-bipyridyl-ethylene 12 in place of pyrazine. With Et(3)N/pyridine as base in MeCN a tetranuclear cobalt cage, [Co(4)(SbAr)(5)O(9)(O(3)PPh)(6)(py)(4)] 13, with five Sb(ii) centres forming a "bowtie" and bridging to four Co(ii) centres by phosphonates and μ(3)-oxides, is formed. The reaction of 2 with cobalt acetate using LiOMe/pyridine as base in methanol, under solvothermal conditions, produces a dinuclear Co(ii) complex, [Co(2)(SbAr)(2)(O(3)P(t)Bu)(3)O(2)(OMe)(2)(py)(2)] 14, with two Co(II) and two Sb centres at the vertices of a distorted tetrahedron. Magnetic measurements on selected number of these cobalt cages are reported.

  10. Vibrational quenching of excitonic splittings in H-bonded molecular dimers: The electronic Davydov splittings cannot match experiment

    NASA Astrophysics Data System (ADS)

    Ottiger, Philipp; Leutwyler, Samuel; Köppel, Horst

    2012-05-01

    The S1/S2 state exciton splittings of symmetric doubly hydrogen-bonded gas-phase dimers provide spectroscopic benchmarks for the excited-state electronic couplings between UV chromophores. These have important implications for electronic energy transfer in multichromophoric systems ranging from photosynthetic light-harvesting antennae to photosynthetic reaction centers, conjugated polymers, molecular crystals, and nucleic acids. We provide laser spectroscopic data on the S1/S2 excitonic splitting Δexp of the doubly H-bonded o-cyanophenol (oCP) dimer and compare to the splittings of the dimers of (2-aminopyridine)2, [(2AP)2], (2-pyridone)2, [(2PY)2], (benzoic acid)2, [(BZA)2], and (benzonitrile)2, [(BN)2]. The experimental S1/S2 excitonic splittings are Δexp = 16.4 cm-1 for (oCP)2, 11.5 cm-1 for (2AP)2, 43.5 cm-1 for (2PY)2, and <1 cm-1 for (BZA)2. In contrast, the vertical S1/S2 energy gaps Δcalc calculated by the approximate second-order coupled cluster (CC2) method for the same dimers are 10-40 times larger than the Δexp values. The qualitative failure of this and other ab initio methods to reproduce the exciton splitting Δexp arises from the Born-Oppenheimer (BO) approximation, which implicitly assumes the strong-coupling case and cannot be employed to evaluate excitonic splittings of systems that are in the weak-coupling limit. Given typical H-bond distances and oscillator strengths, the majority of H-bonded dimers lie in the weak-coupling limit. In this case, the monomer electronic-vibrational coupling upon electronic excitation must be accounted for; the excitonic splittings arise between the vibronic (and not the electronic) transitions. The discrepancy between the BO-based splittings Δcalc and the much smaller experimental Δexp values is resolved by taking into account the quenching of the BO splitting by the intramolecular vibronic coupling in the monomer S1 ← S0 excitation. The vibrational quenching factors Γ for the five dimers (oCP)2, (2AP)2

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

    PubMed

    Call, Arnau; Codolà, Zoel; Acuña-Parés, Ferran; Lloret-Fillol, Julio

    2014-05-12

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

  12. Synthesis, structure determination, and spectroscopic/computational characterization of a series of Fe(II)-thiolate model complexes: implications for Fe-S bonding in superoxide reductases.

    PubMed

    Fiedler, Adam T; Halfen, Heather L; Halfen, Jason A; Brunold, Thomas C

    2005-02-16

    A combined synthetic/spectroscopic/computational approach has been employed to prepare and characterize a series of Fe(II)-thiolate complexes that model the square-pyramidal [Fe(II)(N(His))(4)(S(Cys))] structure of the reduced active site of superoxide reductases (SORs), a class of enzymes that detoxify superoxide in air-sensitive organisms. The high-spin (S = 2) Fe(II) complexes [(Me(4)cyclam)Fe(SC(6)H(4)-p-OMe)]OTf (2) and [FeL]PF(6) (3) (where Me(4)cyclam = 1,4,8,11-tetramethylcyclam and L is the pentadentate monoanion of 1-thioethyl-4,8,11-trimethylcyclam) were synthesized and subjected to structural, magnetic, and electrochemical characterization. X-ray crystallographic studies confirm that 2 and 3 possess an N(4)S donor set similar to that found for the SOR active site and reveal molecular geometries intermediate between square pyramidal and trigonal bipyramidal for both complexes. Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature variable-field MCD (VTVH-MCD) spectroscopies were utilized, in conjunction with density functional theory (DFT) and semiemperical INDO/S-CI calculations, to probe the ground and excited states of complexes 2 and 3, as well as the previously reported Fe(II) SOR model [(L(8)py(2))Fe(SC(6)H(4)-p-Me)]BF(4) (1) (where L(8)py(2) is a tetradentate pyridyl-appended diazacyclooctane macrocycle). These studies allow for a detailed interpretation of the S-->Fe(II) charge transfer transitions observed in the absorption and MCD spectra of complexes 1-3 and provide significant insights into the nature of Fe(II)-S bonding in complexes with axial thiolate ligation. Of the three models investigated, complex 3 exhibits an absorption spectrum that is particularly similar to the one reported for the reduced SOR enzyme (SOR(red)), suggesting that this model accurately mimics key elements of the electronic structure of the enzyme active site; namely, highly covalent Fe-S pi- and sigma-interactions. These spectral

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

    PubMed

    Call, Arnau; Codolà, Zoel; Acuña-Parés, Ferran; Lloret-Fillol, Julio

    2014-05-12

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

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

    PubMed

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

    2014-03-01

    The reaction of UO2Cl2·3THF with the tridentate nitrogen donor ligand 2,6-bis(2-benzimidazolyl)pyridine (H2BBP) in pyridine leads to the formation of three different complexes: [(UO2)(H2BBP)Cl2] (1), [(UO)2(HBBP)(Py)Cl] (2), and [(UO2)(BBP)(Py)2] (3) after successive deprotonation of H2BBP with a strong base. Crystallographic determination of 1-3 reveals that increased charge through ligand deprotonation and displacement of chloride leads to equatorial planarity about uranyl as well as a more compact overall coordination geometry. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectra of 1-3 at the U-4d edges have been recorded using a soft X-ray Scanning Transmission X-ray Microscope (STXM) and reveal the uranium 4d5/2 and 4d3/2 transitions at energies associated with uranium in the hexavalent oxidation state. First-principles Density Functional Theory (DFT) electronic structure calculations for the complexes have been performed to determine and validate the coordination characteristics, which correspond well to the experimental results.

  15. Measurement of solid-liquid interfacial energy in the pyrene succinonitrile monotectic system.

    PubMed

    Akbulut, S; Ocak, Y; Böyük, U; Erol, M; Keşlioğlu, K; Maraşli, N

    2006-09-20

    The equilibrated grain boundary groove shapes for solid pyrene (PY) in equilibrium with the PY succinonitrile (SCN) monotectic liquid were directly observed. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient and solid-liquid interfacial energy for solid PY in equilibrium with the PY SCN monotectic liquid have been determined to be (8.72 ± 0.87) × 10(-8) K m and (21.9 ± 3.28) × 10(-3) J m(-2) with the present numerical method and Gibbs-Thomson equation, respectively. The grain boundary energy of the solid PY phase has been determined to be (42.84 ± 7.28) × 10(-3) J m(-2) from the observed grain boundary groove shapes. Thermal conductivities of solid and liquid phases for PY-2.5 mol% SCN alloy and pure PY have also been measured. PMID:21690896

  16. Synthesis and characterization of mixed-ligand complexes using a precursor mononuclear oxidovanadium(V) complex derived from a tridentate salicylhydrazone oxime ligand

    NASA Astrophysics Data System (ADS)

    Sutradhar, Manas; Roy Barman, Tannistha; Ghosh, Saktiprosad; Drew, Michael G. B.

    2013-04-01

    The mononuclear oxidovanadium(V) complex [VO(L)(OEt)(EtOH)] (1), where H2L = Salicyloyl hydrazone of diacetyl monooxime, reacts separately with five different reactants viz. pyridine (py), 4-methylpyridine (4mepy), 4,4'bipyridine (4,4'bipy), 8-hydroxyquinoline (Hox) and KOH to yield the mononuclear oxidovanadium complexes [VO(L)(OEt)(py)] (2), and [VO(L)(OEt)(4mepy)] (3), the binuclear complex [VO(L)(OEt)]2(μ-4,4'bipy) (4), the mononuclear bis chelate complex [VO(L)(ox)] (5) and the water soluble dioxidovanadium salt K[VO2L]·H2O (6) respectively. Complex 5 has been characterized by X-ray crystallography, and crystallizes in the orthorhombic space group Pna21 having a distorted octahedral O4N2 coordination environment. All five complexes are characterized by elemental analysis, various spectroscopic techniques (UV-Vis, IR, NMR and ESI Mass) and cyclic voltammetry. The spectral and electrochemical data of these five complexes are compared with those of the precursor complex.

  17. Effect of particle pinch on the fusion performance and profile features of an international thermonuclear experimental reactor-like fusion reactor

    NASA Astrophysics Data System (ADS)

    Wang, Shijia; Wang, Shaojie

    2015-04-01

    The evolution of the plasma temperature and density in an international thermonuclear experimental reactor (ITER)-like fusion device has been studied by numerically solving the energy transport equation coupled with the particle transport equation. The effect of particle pinch, which depends on the magnetic curvature and the safety factor, has been taken into account. The plasma is primarily heated by the alpha particles which are produced by the deuterium-tritium fusion reactions. A semi-empirical method, which adopts the ITERH-98P(y,2) scaling law, has been used to evaluate the transport coefficients. The fusion performances (the fusion energy gain factor, Q) similar to the ITER inductive scenario and non-inductive scenario (with reversed magnetic shear) are obtained. It is shown that the particle pinch has significant effects on the fusion performance and profiles of a fusion reactor. When the volume-averaged density is fixed, particle pinch can lower the pedestal density by ˜30 % , with the Q value and the central pressure almost unchanged. When the particle source or the pedestal density is fixed, the particle pinch can significantly enhance the Q value by 60 % , with the central pressure also significantly raised.

  18. Synthesis and Single-Molecule Conductance Study of Redox-Active Ruthenium Complexes with Pyridyl and Dihydrobenzo[b]thiophene Anchoring Groups.

    PubMed

    Ozawa, Hiroaki; Baghernejad, Masoud; Al-Owaedi, Oday A; Kaliginedi, Veerabhadrarao; Nagashima, Takumi; Ferrer, Jaime; Wandlowski, Thomas; García-Suárez, Víctor M; Broekmann, Peter; Lambert, Colin J; Haga, Masa-Aki

    2016-08-26

    The ancillary ligands 4'-(4-pyridyl)-2,2':6',2''-terpyridine and 4'-(2,3-dihydrobenzo[b]thiophene)-2,2'-6',2"-terpyridine were used to synthesize two series of mono- and dinuclear ruthenium complexes differing in their lengths and anchoring groups. The electrochemical and single-molecular conductance properties of these two series of ruthenium complexes were studied experimentally by means of cyclic voltammetry and the scanning tunneling microscopy-break junction technique (STM-BJ) and theoretically by means of density functional theory (DFT). Cyclic voltammetry data showed clear redox peaks corresponding to both the metal- and ligand-related redox reactions. Single-molecular conductance demonstrated an exponential decay of the molecular conductance with the increase in molecular length for both the series of ruthenium complexes, with decay constants of βPY =2.07±0.1 nm(-1) and βBT =2.16±0.1 nm(-1) , respectively. The contact resistance of complexes with 2,3-dihydrobenzo[b]thiophene (BT) anchoring groups is found to be smaller than the contact resistance of ruthenium complexes with pyridine (PY) anchors. DFT calculations support the experimental results and provided additional information on the electronic structure and charge transport properties in those metal|ruthenium complex|metal junctions. PMID:27472889

  19. Measurement of the exclusive Υ production cross-section in pp collisions at √{s}=7 TeV and 8 TeV

    NASA Astrophysics Data System (ADS)

    Aaij, R.; Adeva, B.; Adinolfi, M.; Affolder, A.; Ajaltouni, Z.; Akar, S.; Albrecht, J.; Alessio, F.; Alexander, M.; Ali, S.; Alkhazov, G.; Alvarez Cartelle, P.; Alves, A. A.; Amato, S.; Amerio, S.; Amhis, Y.; An, L.; Anderlini, L.; Anderson, J.; Andreotti, M.; Andrews, J. E.; Appleby, R. B.; Aquines Gutierrez, O.; Archilli, F.; d'Argent, P.; Artamonov, A.; Artuso, M.; Aslanides, E.; Auriemma, G.; Baalouch, M.; Bachmann, S.; Back, J. J.; Badalov, A.; Baesso, C.; Baldini, W.; Barlow, R. J.; Barschel, C.; Barsuk, S.; Barter, W.; Batozskaya, V.; Battista, V.; Bay, A.; Beaucourt, L.; Beddow, J.; Bedeschi, F.; Bediaga, I.; Bel, L. J.; Belyaev, I.; Ben-Haim, E.; Bencivenni, G.; Benson, S.; Benton, J.; Berezhnoy, A.; Bernet, R.; Bertolin, A.; Bettler, M.-O.; van Beuzekom, M.; Bien, A.; Bifani, S.; Bird, T.; Birnkraut, A.; Bizzeti, A.; Blake, T.; Blanc, F.; Blouw, J.; Blusk, S.; Bocci, V.; Bondar, A.; Bondar, N.; Bonivento, W.; Borghi, S.; Borsato, M.; Bowcock, T. J. V.; Bowen, E.; Bozzi, C.; Braun, S.; Brett, D.; Britsch, M.; Britton, T.; Brodzicka, J.; Brook, N. H.; Bursche, A.; Buytaert, J.; Cadeddu, S.; Calabrese, R.; Calvi, M.; Calvo Gomez, M.; Campana, P.; Campora Perez, D.; Capriotti, L.; Carbone, A.; Carboni, G.; Cardinale, R.; Cardini, A.; Carniti, P.; Carson, L.; Carvalho Akiba, K.; Casanova Mohr, R.; Casse, G.; Cassina, L.; Castillo Garcia, L.; Cattaneo, M.; Cauet, Ch.; Cavallero, G.; Cenci, R.; Charles, M.; Charpentier, Ph.; Chefdeville, M.; Chen, S.; Cheung, S.-F.; Chiapolini, N.; Chrzaszcz, M.; Cid Vidal, X.; Ciezarek, G.; Clarke, P. E. L.; Clemencic, M.; Cliff, H. V.; Closier, J.; Coco, V.; Cogan, J.; Cogneras, E.; Cogoni, V.; Cojocariu, L.; Collazuol, G.; Collins, P.; Comerma-Montells, A.; Contu, A.; Cook, A.; Coombes, M.; Coquereau, S.; Corti, G.; Corvo, M.; Couturier, B.; Cowan, G. A.; Craik, D. C.; Crocombe, A.; Cruz Torres, M.; Cunliffe, S.; Currie, R.; D'Ambrosio, C.; Dalseno, J.; David, P. N. Y.; Davis, A.; De Bruyn, K.; De Capua, S.; De Cian, M.; De Miranda, J. M.; De Paula, L.; De Silva, W.; De Simone, P.; Dean, C.-T.; Decamp, D.; Deckenhoff, M.; Del Buono, L.; Déléage, N.; Derkach, D.; Deschamps, O.; Dettori, F.; Dey, B.; Di Canto, A.; Di Ruscio, F.; Dijkstra, H.; Donleavy, S.; Dordei, F.; Dorigo, M.; Dosil Suárez, A.; Dossett, D.; Dovbnya, A.; Dreimanis, K.; Dujany, G.; Dupertuis, F.; Durante, P.; Dzhelyadin, R.; Dziurda, A.; Dzyuba, A.; Easo, S.; Egede, U.; Egorychev, V.; Eidelman, S.; Eisenhardt, S.; Eitschberger, U.; Ekelhof, R.; Eklund, L.; El Rifai, I.; Elsasser, Ch.; Ely, S.; Esen, S.; Evans, H. M.; Evans, T.; Falabella, A.; Färber, C.; Farinelli, C.; Farley, N.; Farry, S.; Fay, R.; Ferguson, D.; Fernandez Albor, V.; Ferrari, F.; Ferreira Rodrigues, F.; Ferro-Luzzi, M.; Filippov, S.; Fiore, M.; Fiorini, M.; Firlej, M.; Fitzpatrick, C.; Fiutowski, T.; Fol, P.; Fontana, M.; Fontanelli, F.; Forty, R.; Francisco, O.; Frank, M.; Frei, C.; Frosini, M.; Fu, J.; Furfaro, E.; Gallas Torreira, A.; Galli, D.; Gallorini, S.; Gambetta, S.; Gandelman, M.; Gandini, P.; Gao, Y.; García Pardiñas, J.; Garofoli, J.; Garra Tico, J.; Garrido, L.; Gascon, D.; Gaspar, C.; Gastaldi, U.; Gauld, R.; Gavardi, L.; Gazzoni, G.; Geraci, A.; Gerick, D.; Gersabeck, E.; Gersabeck, M.; Gershon, T.; Ghez, Ph.; Gianelle, A.; Gianì, S.; Gibson, V.; Giubega, L.; Gligorov, V. V.; Göbel, C.; Golubkov, D.; Golutvin, A.; Gomes, A.; Gotti, C.; Grabalosa Gándara, M.; Graciani Diaz, R.; Granado Cardoso, L. A.; Graugés, E.; Graverini, E.; Graziani, G.; Grecu, A.; Greening, E.; Gregson, S.; Griffith, P.; Grillo, L.; Grünberg, O.; Gui, B.; Gushchin, E.; Guz, Yu.; Gys, T.; Hadjivasiliou, C.; Haefeli, G.; Haen, C.; Haines, S. C.; Hall, S.; Hamilton, B.; Hampson, T.; Han, X.; Hansmann-Menzemer, S.; Harnew, N.; Harnew, S. T.; Harrison, J.; He, J.; Head, T.; Heijne, V.; Hennessy, K.; Henrard, P.; Henry, L.; Hernando Morata, J. A.; van Herwijnen, E.; Heß, M.; Hicheur, A.; Hill, D.; Hoballah, M.; Hombach, C.; Hulsbergen, W.; Humair, T.; Hussain, N.; Hutchcroft, D.; Hynds, D.; Idzik, M.; Ilten, P.; Jacobsson, R.; Jaeger, A.; Jalocha, J.; Jans, E.; Jawahery, A.; Jing, F.; John, M.; Johnson, D.; Jones, C. R.; Joram, C.; Jost, B.; Jurik, N.; Kandybei, S.; Kanso, W.; Karacson, M.; Karbach, T. M.; Karodia, S.; Kelsey, M.; Kenyon, I. R.; Kenzie, M.; Ketel, T.; Khanji, B.; Khurewathanakul, C.; Klaver, S.; Klimaszewski, K.; Kochebina, O.; Kolpin, M.; Komarov, I.; Koopman, R. F.; Koppenburg, P.; Korolev, M.; Kravchuk, L.; Kreplin, K.; Kreps, M.; Krocker, G.; Krokovny, P.; Kruse, F.; Kucewicz, W.; Kucharczyk, M.; Kudryavtsev, V.; Kurek, K.; Kvaratskheliya, T.; La Thi, V. N.; Lacarrere, D.; Lafferty, G.; Lai, A.; Lambert, D.; Lambert, R. W.; Lanfranchi, G.; Langenbruch, C.; Langhans, B.; Latham, T.; Lazzeroni, C.; Le Gac, R.; van Leerdam, J.; Lees, J.-P.; Lefèvre, R.; Leflat, A.; Lefrançois, J.; Leroy, O.; Lesiak, T.; Leverington, B.; Li, Y.; Likhomanenko, T.; Liles, M.; Lindner, R.; Linn, C.; Lionetto, F.; Liu, B.; Lohn, S.; Longstaff, I.; Lopes, J. H.; Lucchesi, D.; Lucio Martinez, M.; Luo, H.; Lupato, A.; Luppi, E.; Lupton, O.; Machefert, F.; Maciuc, F.; Maev, O.; Malde, S.; Malinin, A.; Manca, G.; Mancinelli, G.; Manning, P.; Mapelli, A.; Maratas, J.; Marchand, J. F.; Marconi, U.; Marin Benito, C.; Marino, P.; Märki, R.; Marks, J.; Martellotti, G.; Martinelli, M.; Martinez Santos, D.; Martinez Vidal, F.; Martins Tostes, D.; Massafferri, A.; Matev, R.; Mathad, A.; Mathe, Z.; Matteuzzi, C.; Matthieu, K.; Mauri, A.; Maurin, B.; Mazurov, A.; McCann, M.; McCarthy, J.; McNab, A.; McNulty, R.; Meadows, B.; Meier, F.; Meissner, M.; Merk, M.; Milanes, D. A.; Minard, M.-N.; Mitzel, D. S.; Molina Rodriguez, J.; Monteil, S.; Morandin, M.; Morawski, P.; Mordà, A.; Morello, M. J.; Moron, J.; Morris, A. B.; Mountain, R.; Muheim, F.; Müller, J.; Müller, K.; Müller, V.; Mussini, M.; Muster, B.; Naik, P.; Nakada, T.; Nandakumar, R.; Nasteva, I.; Needham, M.; Neri, N.; Neubert, S.; Neufeld, N.; Neuner, M.; Nguyen, A. D.; Nguyen, T. D.; Nguyen-Mau, C.; Niess, V.; Niet, R.; Nikitin, N.; Nikodem, T.; Ninci, D.; Novoselov, A.; O'Hanlon, D. P.; Oblakowska-Mucha, A.; Obraztsov, V.; Ogilvy, S.; Okhrimenko, O.; Oldeman, R.; Onderwater, C. J. G.; Osorio Rodrigues, B.; Otalora Goicochea, J. M.; Otto, A.; Owen, P.; Oyanguren, A.; Palano, A.; Palombo, F.; Palutan, M.; Panman, J.; Papanestis, A.; Pappagallo, M.; Pappalardo, L. L.; Parkes, C.; Passaleva, G.; Patel, G. D.; Patel, M.; Patrignani, C.; Pearce, A.; Pellegrino, A.; Penso, G.; Pepe Altarelli, M.; Perazzini, S.; Perret, P.; Pescatore, L.; Petridis, K.; Petrolini, A.; Petruzzo, M.; Picatoste Olloqui, E.; Pietrzyk, B.; Pilař, T.; Pinci, D.; Pistone, A.; Playfer, S.; Plo Casasus, M.; Poikela, T.; Polci, F.; Poluektov, A.; Polyakov, I.; Polycarpo, E.; Popov, A.; Popov, D.; Popovici, B.; Potterat, C.; Price, E.; Price, J. D.; Prisciandaro, J.; Pritchard, A.; Prouve, C.; Pugatch, V.; Puig Navarro, A.; Punzi, G.; Qian, W.; Quagliani, R.; Rachwal, B.; Rademacker, J. H.; Rakotomiaramanana, B.; Rama, M.; Rangel, M. S.; Raniuk, I.; Rauschmayr, N.; Raven, G.; Redi, F.; Reichert, S.; Reid, M. M.; dos Reis, A. C.; Ricciardi, S.; Richards, S.; Rihl, M.; Rinnert, K.; Rives Molina, V.; Robbe, P.; Rodrigues, A. B.; Rodrigues, E.; Rodriguez Lopez, J. A.; Rodriguez Perez, P.; Roiser, S.; Romanovsky, V.; Romero Vidal, A.; Rotondo, M.; Rouvinet, J.; Ruf, T.; Ruiz, H.; Ruiz Valls, P.; Saborido Silva, J. J.; Sagidova, N.; Sail, P.; Saitta, B.; Salustino Guimaraes, V.; Sanchez Mayordomo, C.; Sanmartin Sedes, B.; Santacesaria, R.; Santamarina Rios, C.; Santovetti, E.; Sarti, A.; Satriano, C.; Satta, A.; Saunders, D. M.; Savrina, D.; Schiller, M.; Schindler, H.; Schlupp, M.; Schmelling, M.; Schmelzer, T.; Schmidt, B.; Schneider, O.; Schopper, A.; Schune, M.-H.; Schwemmer, R.; Sciascia, B.; Sciubba, A.; Semennikov, A.; Sepp, I.; Serra, N.; Serrano, J.; Sestini, L.; Seyfert, P.; Shapkin, M.; Shapoval, I.; Shcheglov, Y.; Shears, T.; Shekhtman, L.; Shevchenko, V.; Shires, A.; Silva Coutinho, R.; Simi, G.; Sirendi, M.; Skidmore, N.; Skillicorn, I.; Skwarnicki, T.; Smith, E.; Smith, E.; Smith, J.; Smith, M.; Snoek, H.; Sokoloff, M. D.; Soler, F. J. P.; Soomro, F.; Souza, D.; Souza De Paula, B.; Spaan, B.; Spradlin, P.; Sridharan, S.; Stagni, F.; Stahl, M.; Stahl, S.; Steinkamp, O.; Stenyakin, O.; Sterpka, F.; Stevenson, S.; Stoica, S.; Stone, S.; Storaci, B.; Stracka, S.; Straticiuc, M.; Straumann, U.; Stroili, R.; Sun, L.; Sutcliffe, W.; Swientek, K.; Swientek, S.; Syropoulos, V.; Szczekowski, M.; Szczypka, P.; Szumlak, T.; T'Jampens, S.; Tekampe, T.; Teklishyn, M.; Tellarini, G.; Teubert, F.; Thomas, C.; Thomas, E.; van Tilburg, J.; Tisserand, V.; Tobin, M.; Todd, J.; Tolk, S.; Tomassetti, L.; Tonelli, D.; Topp-Joergensen, S.; Torr, N.; Tournefier, E.; Tourneur, S.; Trabelsi, K.; Tran, M. T.; Tresch, M.; Trisovic, A.; Tsaregorodtsev, A.; Tsopelas, P.; Tuning, N.; Ukleja, A.; Ustyuzhanin, A.; Uwer, U.; Vacca, C.; Vagnoni, V.; Valenti, G.; Vallier, A.; Vazquez Gomez, R.; Vazquez Regueiro, P.; Vázquez Sierra, C.; Vecchi, S.; Velthuis, J. J.; Veltri, M.; Veneziano, G.; Vesterinen, M.; Viaud, B.; Vieira, D.; Vieites Diaz, M.; Vilasis-Cardona, X.; Vollhardt, A.; Volyanskyy, D.; Voong, D.; Vorobyev, A.; Vorobyev, V.; Voß, C.; de Vries, J. A.; Waldi, R.; Wallace, C.; Wallace, R.; Walsh, J.; Wandernoth, S.; Wang, J.; Ward, D. R.; Watson, N. K.; Websdale, D.; Weiden, A.; Whitehead, M.; Wiedner, D.; Wilkinson, G.; Wilkinson, M.; Williams, M.; Williams, M. P.; Williams, M.; Wilson, F. F.; Wimberley, J.; Wishahi, J.; Wislicki, W.; Witek, M.; Wormser, G.; Wotton, S. A.; Wright, S.; Wyllie, K.; Xie, Y.; Xu, Z.; Yang, Z.; Yuan, X.; Yushchenko, O.; Zangoli, M.; Zavertyaev, M.; Zhang, L.; Zhang, Y.; Zhelezov, A.; Zhokhov, A.; Zhong, L.

    2015-09-01

    A study is presented of central exclusive production of Υ( nS) states, where the Υ( nS) resonances decay to the μ + μ - final state, using pp collision data recorded by the LHCb experiment. The cross-section is measured in the rapidity range 2 < y(Υ) < 4 .5 where the muons are reconstructed in the pseudorapidity range 2 < η( μ ±) < 4 .5. The data sample corresponds to an integrated luminosity of 2.9 fb-1 and was collected at centre-of-mass energies of 7 TeV and 8 TeV. The measured Υ(1 S) and Υ(2 S) production cross-sections are σ ( ppto pY(1S)p)=9.0± 2.1± 1.7 pb and σ ( ppto pY(2S)p)=1.3± 0.8± 0.3 pb, where the first uncertainties are statistical and the second are systematic. The Υ(1 S) crosssection is also measured as a function of rapidity and is found to be in good agreement with Standard Model predictions. An upper limit is set at 3.4 pb at the 95% confidence level for the exclusive Υ(3 S) production cross-section, including possible contamination from χ b (3 P ) → Υ(3 S)γ decays. [Figure not available: see fulltext.

  20. Mechanistic Studies of Wacker-Type Intramolecular Aerobic Oxidative Amination of Alkenes Catalyzed by Pd(OAc)2/Pyridine

    PubMed Central

    Ye, Xuan; Liu, Guosheng; Popp, Brian V.; Stahl, Shannon S.

    2011-01-01

    Wacker-type oxidative cyclization reactions have been the subject of extensive research for several decades, but few systematic mechanistic studies of these reactions have been reported. The present study features experimental and DFT computational studies of Pd(OAc)2/pyridine-catalyzed intramolecular aerobic oxidative amination of alkenes. The data support a stepwise catalytic mechanism that consists of (1) steady-state formation of a PdII-amidate-alkene chelate with release of one equivalent of pyridine and AcOH from the catalyst center, (2) alkene insertion into a Pd–N bond, (3) reversible β-hydride elimination, (4) irreversible reductive elimination of AcOH, and (5) aerobic oxidation of palladium(0) to regenerate the active trans-Pd(OAc)2(py)2 catalyst. Evidence is obtained for two energetically viable pathways for the key C–N bond-forming step, featuring a pyridine-ligated and a pyridine-dissociated PdII species. Analysis of natural charges and bond lengths of the alkene-insertion transition state suggest that this reaction is best described as an intramolecular nucleophilic attack of the amidate ligand on the coordinated alkene. PMID:21250706

  1. Molecular [(Fe3)–(Fe3)] and [(Fe4)–(Fe4)] coordination cluster pairs as single or composite arrays.

    PubMed

    Sañudo, E Carolina; Uber, Jorge Salinas; Pons Balagué, Alba; Roubeau, Olivier; Aromí, Guillem

    2012-08-01

    The synthesis of molecular cluster pairs is a challenge for coordination chemists due to the potential applications of these species in molecular spintronics or quantum computing. The ligand H(4)L, 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene, has been successfully used to obtain a series of such complexes using the basic Fe(III) trinuclear carboxylates as starting materials. Synthetic control has allowed the isolation of the two molecular cluster pairs that form the composite [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2)[Fe(3)O(PhCO(2))(5)(py)(H(2)L)](2) (1). The dimers of trinuclear units, [Fe(3)O(PhCO(2))(5)(H(2)O)(H(2)L)](2) (2) and [Fe(3)O(o-MePhCO(2))(5)(H(2)L)(py)](2) (3), and the dimers of tetranuclear units, [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2) (4) and [Fe(4)O(2)(o-MePhCO(2))(6)(H(2)L)(pz)](2) (5), are presented here. The magnetic properties of the reported aggregates show that they are pairs of semi-independent clusters weakly interacting magnetically as required for two-qubit quantum gates.

  2. Molecular [(Fe3)–(Fe3)] and [(Fe4)–(Fe4)] coordination cluster pairs as single or composite arrays.

    PubMed

    Sañudo, E Carolina; Uber, Jorge Salinas; Pons Balagué, Alba; Roubeau, Olivier; Aromí, Guillem

    2012-08-01

    The synthesis of molecular cluster pairs is a challenge for coordination chemists due to the potential applications of these species in molecular spintronics or quantum computing. The ligand H(4)L, 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene, has been successfully used to obtain a series of such complexes using the basic Fe(III) trinuclear carboxylates as starting materials. Synthetic control has allowed the isolation of the two molecular cluster pairs that form the composite [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2)[Fe(3)O(PhCO(2))(5)(py)(H(2)L)](2) (1). The dimers of trinuclear units, [Fe(3)O(PhCO(2))(5)(H(2)O)(H(2)L)](2) (2) and [Fe(3)O(o-MePhCO(2))(5)(H(2)L)(py)](2) (3), and the dimers of tetranuclear units, [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2) (4) and [Fe(4)O(2)(o-MePhCO(2))(6)(H(2)L)(pz)](2) (5), are presented here. The magnetic properties of the reported aggregates show that they are pairs of semi-independent clusters weakly interacting magnetically as required for two-qubit quantum gates. PMID:22803762

  3. Oxo-group-14-element bond formation in binuclear uranium(V) Pacman complexes.

    PubMed

    Jones, Guy M; Arnold, Polly L; Love, Jason B

    2013-07-29

    Simple and versatile routes to the functionalization of uranyl-derived U(V)-oxo groups are presented. The oxo-lithiated, binuclear uranium(V)-oxo complexes [{(py)3LiOUO}2(L)] and [{(py)3LiOUO}(OUOSiMe3)(L)] were prepared by the direct combination of the uranyl(VI) silylamide "ate" complex [Li(py)2][(OUO)(N")3] (N" = N(SiMe3)2) with the polypyrrolic macrocycle H4L or the mononuclear uranyl (VI) Pacman complex [UO2(py)(H2L)], respectively. These oxo-metalated complexes display distinct U-O single and multiple bonding patterns and an axial/equatorial arrangement of oxo ligands. Their ready availability allows the direct functionalization of the uranyl oxo group leading to the binuclear uranium(V) oxo-stannylated complexes [{(R3Sn)OUO}2(L)] (R = nBu, Ph), which represent rare examples of mixed uranium/tin complexes. Also, uranium-oxo-group exchange occurred in reactions with [TiCl(OiPr)3] to form U-O-C bonds [{(py)3LiOUO}(OUOiPr)(L)] and [(iPrOUO)2(L)]. Overall, these represent the first family of uranium(V) complexes that are oxo-functionalised by Group 14 elements.

  4. Tryptophan switch for a photoactivated platinum anticancer complex.

    PubMed

    Butler, Jennifer S; Woods, Julie A; Farrer, Nicola J; Newton, Mark E; Sadler, Peter J

    2012-10-10

    The octahedral Pt(IV) complex trans,trans,trans-[Pt(N(3))(2)(OH)(2)(py)(2)] (1) is potently cytotoxic to cancer cells when irradiated with visible (blue) light. We show that the acute photocytotoxicity can be switched off by low doses (500 μM) of the amino acid l-tryptophan. EPR and NMR spectroscopic experiments using spin traps show that l-Trp quenches the formation of azidyl radicals, probably by acting as an electron donor. l-Trp is well-known as a mediator of electron transfer between distant electron acceptor/donor centers in proteins, and such properties may make the free amino acid clinically useful for controlling the activity of photochemotherapeutic azido Pt(IV) drugs. Since previous work has demonstrated the ability of photoactivated 1 to platinate DNA, this suggests that the high potency of such photoactive platinum complexes is related to their dual attack on cancer cells by radicals and Pt(II) photoproducts. PMID:22991971

  5. Synthesis and electrochemical characterisation of Molybdenum(VI) complexes of disalicylaldehyde malonoyl-dihydrazone

    NASA Astrophysics Data System (ADS)

    Ahmed, Aziz; Lal, Ram A.

    2013-09-01

    Molybdenum(VI) complexes composition [(μ2-O)2(MoO2)2(H4L)2]ṡ2A (where H4L = H4slmh; A = H2O (1), pyridine (py, 2), 2-picoline (2-pic, 3), 3-picoline (3-pic, 4), 4-picoline (4-pic, 5)) have been isolated in solid state from the reaction of MoO2(acac)2 and disalicylaldehyde malonoyldihydrazone in 1:1 M ratio in ethanol at higher temperature. The complexes have been synthesised and characterised by various physiochemical and spectroscopic studies. The structure of the molybdenum(VI) of all complexes has been established by elemental analyses, electronic, IR, 1H NMR and CV spectral studies. The dihydrazone is coordinated to the metal centres in keto enol form in all the complexes (1)-(5). The electronic spectra of the complexes are dominated by strong charge transfer bands. All of the complexes involve six coordinated molybdenum centre with octahedral arrangement of donor atoms.

  6. Synthesis, spectroscopic and electrochemical characterisation of binuclear dioxomolybdenum complexes derived from disalicylaldehyde succinoyldihydrazone

    NASA Astrophysics Data System (ADS)

    Ahmed, Aziz; Chanu, Oinam B.; Koch, Angira; Lal, R. A.

    2012-12-01

    The diamagnetic dioxomolybdenum (VI) complexes [(MoO2)2(L).(H2O)2] where H4L = H4slsh have been isolated in solid state from the reaction of MoO2(acac)2 and disalicylaldehyde succinoyldihydrazone (H4L) in 3:1 molar ratio in ethanol at higher temperature. The reaction of the complex with electron donor bases gives diamagnetic molybdenum(VI) complexes having composition [(MoO2)2(L)(A)2]·H2O (where A = pyridine (py, 2), 2-picoline (2-pic, 3), 3-picoline (3-pic, 4), 4-picoline (4-pic, 5). The composition of the complexes have been established by analytical, thermo-analytical data. The structure of the molybdenum (VI) complexes has been established by mass, electronic, IR, 1H NMR and CV spectral studies. The dihydrazone is coordinated to the metal centres in staggered configuration in all the complexes. The electronic spectra of the complexes are dominated by strong charge transfer bands. All of the complexes involve six coordinated molybdenum centre with octahedral arrangement of donor atoms.

  7. Synthesis, Structure, and Conformational Dynamics of Rhodium and Iridium Complexes of Dimethylbis(2-pyridyl)borate†

    PubMed Central

    Pennington-Boggio, Megan K.; Conley, Brian L.; Richmond, Michael G.; Williams, Travis J.

    2014-01-01

    Rhodium(I) and Iridium(I) borate complexes of the structure [Me2B(2-py)2]ML2 (L2 = (tBuNC)2, (CO)2, (C2H4)2, cod, dppe) were prepared and structurally characterized (cod = 1,5-cyclooctadiene; dppe = 1,2-diphenylphosphinoethane). Each contains a boat-configured chelate ring that participates in a boat-to-boat ring flip. Computational evidence shows that the ring flip proceeds through a transition state that is near planarity about the chelate ring. We observe an empirical, quantitative correlation between the barrier of this ring flip and the π acceptor ability of the ancillary ligand groups on the metal. The ring flip barrier correlates weakly to the Tolman and Lever ligand parameterization schemes, apparently because these combine both σ and π effects while we propose that the ring flip barrier is dominated by π bonding. This observation is consistent with metal-ligand π interactions becoming temporarily available only in the near-planar transition state of the chelate ring flip and not the boat-configured ground state. Thus, this is a first-of-class observation of metal-ligand π bonding governing conformational dynamics. PMID:25435645

  8. Combined analysis of chemical bonding in a Cu(II) dimer using QTAIM, Voronoi tessellation and Hirshfeld surface approaches.

    PubMed

    Vologzhanina, Anna V; Kats, Svitlana V; Penkova, Larisa V; Pavlenko, Vadim A; Efimov, Nikolay N; Minin, Vadim V; Eremenko, Igor L

    2015-10-01

    Interaction of 1-(1H-pyrazol-5-yl)ethanone oxime (H2PzOx) with copper(II) chloride in the presence of pyridine afforded a binuclear discrete [Cu2(HPzOx)2Cl2py2] complex, which was characterized by Fourier transform-IR and electron paramagnetic resonance (EPR) spectra, magnetochemistry and high-resolution X-ray diffraction experiments. Multipole refinement of X-ray diffraction data and density-functional theory (DFT) calculations of an isolated molecule allowed charge and spin distributions to be obtained for this compound. Magnetochemistry data, EPR spectra and DFT calculations of an isolated molecule show antiferromagnetic coupling between copper(II) ions. The spin distribution suggests an exchange pathway via the bridging pyrazole ring in the equatorial plane of the CuN4Cl coordination polyhedron, thus providing support for the classical superexchange mechanism; the calculated value of the magnetic coupling constant -2J is equal to 220 cm(-1), which compares well with the experimental value of 203 ± 2 cm(-1). Chemical connectivity was derived by Bader's 'quantum theory of atoms in molecules' and compared with Voronoi tessellation and Hirshfeld surface representations of crystal space. All methodologies gave a similar qualitative and semi-quantitative description of intra- and intermolecular connectivity. PMID:26428404

  9. Mixed Ligand Complexes of N-Methyl-N-phenyl Dithiocarbamate: Synthesis, Characterisation, Antifungal Activity, and Solvent Extraction Studies of the Ligand

    PubMed Central

    Ekennia, Anthony C.; Onwudiwe, Damian C.; Ume, Cyril; Ebenso, Eno E.

    2015-01-01

    A series of mixed ligand dithiocarbamate complexes with a general formula [ML2(py)2], where M = Mn(II), Co(II), Ni(II), and Cu(II), py = pyridine, and L = N-methyl-N-phenyl dithiocarbamate have been prepared and characterised by elemental analysis, FTIR and Uv spectroscopy, magnetic moment, and thermogravimetric and conductance analysis. The infrared spectra showed that symmetrical bidentate coordination occurred with the dithiocarbamate moiety through the sulfur atoms, while neutral monodentate coordination occurred through the nitrogen atom for the pyridine molecule in the complexes. The electronic spectra, elemental analysis, and magnetic moment results proved that the complexes adopted octahedral geometry. The conductance measurement showed that the complexes are nonelectrolytes proving their nonionic nature. The compounds were screened for three human pathogenic fungi: Aspergillus flavus, Aspergillus niger, and Candida albicans. The cobalt complex showed the best antifungal activity among the test compounds. Liquid-liquid extractive abilities of the ligand towards copper and nickel ions in different solvent media were investigated. The ligand showed a strong binding affinity towards the metals ions with an extractive efficiency of about 99%. PMID:26543441

  10. Getting a Handle on the Role of Coenzyme M in Alkene Metabolism

    SciTech Connect

    Krishnakumar, A.M.; Sliwa, D.; Endrizzi, J.A.; Boyd, E.S.; Ensign, S.A.; Peters, J.W.

    2009-05-20

    Coenzyme M (2-mercaptoethanesulfonate; CoM) is one of several atypical cofactors discovered in methanogenic archaea which participate in the biological reduction of CO{sub 2} to methane. Elegantly simple, CoM, so named for its role as a methyl carrier in all methanogenic archaea, is the smallest known organic cofactor. It was thought that this cofactor was used exclusively in methanogenesis until it was recently discovered that CoM is a key cofactor in the pathway of propylene metabolism in the gram-negative soil microorganism Xanthobacter autotrophicus Py2. A four-step pathway requiring CoM converts propylene and CO{sub 2} to acetoacetate, which feeds into central metabolism. In this process, CoM is used to activate and convert highly electrophilic epoxypropane, formed from propylene epoxidation, into a nucleophilic species that undergoes carboxylation. The unique properties of CoM provide a chemical handle for orienting compounds for site-specific redox chemistry and stereospecific catalysis. The three-dimensional structures of several of the enzymes in the pathway of propylene metabolism in defined states have been determined, providing significant insights into both the enzyme mechanisms and the role of CoM in this pathway. These studies provide the structural basis for understanding the efficacy of CoM as a handle to direct organic substrate transformations at the active sites of enzymes.

  11. Polymer complexes. LIV. Structural and spectral studies of supramolecular coordination polymers built from Ni(II), Fe(II) and Pd(II) with sulphadrug

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    Polymer complexes of p-acrylamidyl sulphaguanidine (HL) with Ni(II), Fe(II) and Pd(II) salts have been prepared. The structures of the polymer complexes were elucidated using elemental analysis, 1H NMR, UV-Vis, IR spectroscopies, magnetic moment, molar conductance and thermal analysis. The polymer complexes were isolated in 1:1 and 1:2 (M:L) ratios. The solid monocomplexes (1:1) (M:L) were isolated in the general formula [Fe(HL)O 2SO 2(OH 2) 2]. The biscomplexes (1:2) (M:L) solid chelates found to have the general formula [Ni(HL) 2X 2] n (X = Cl -, Br -, I -, NO3-, NCS -), [Fe(HL)(en)(OSO 3)(OH 2)] n and [Ni(HL) 2(Py) 2] nX 2, while {[Pd(L)X] 2} n (1:1) (X = Cl - or Br -). In all the polymer complexes the ligand and anions were found to be coordinated to the Ni(II) and Fe(II) ions. The bidentate nature of the ligand is evident from IR spectra. The magnetic and spectroscopic data indicate a octahedral geometry for complexes. The thermal behaviour of these chelates shows that the hydrated complexes loss water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps.

  12. FMR spin pumping in YIG/ferromagnet bilayers (ferromagnet = Fe, Co, Ni, Py)

    NASA Astrophysics Data System (ADS)

    Yang, Fengyuan; Wang, Hailong; Du, Chunhui; Hammel, P. Chris

    2014-03-01

    Generation of pure spin currents from ferromagnets (FM) to normal metals (NM) has been extensively studied by thermal and ferromagnetic resonance (FMR) spin pumping. Recently, Miao et al. demonstrated thermal injection of spin currents from Y3Fe5O12 (YIG) into Py detected by inverse spin Hall effect (ISHE) in the FM. The ISHE in FM is in fact the inverse anomalous Hall effect (SHE), but with all the signatures of ISHE in NMs. Here we report robust FMR spin pumping in YIG/FM bilayers with FM = Fe, Co, Ni and Py using cavity FMR. The resonance fields of the FMs and YIG are clearly separated, which allows distinction of spin pumping induced ISHE voltages at the YIG resonance field and the voltage signals at the FM resonance fields. The ISHE voltages reaches 220 uV for YIG/Py(2nm) bilayer and tens of uV for all YIG/FM bilayers with 10-nm FM at an rf power of 200 mW. The sign of the ISHE voltages for Py and Ni are opposite to those for Fe and Co, which agrees with the opposite signs of AHE in Ni as compared to Fe and Co.

  13. Iron-oxidation-state-dependent O-O bond cleavage of meta-chloroperbenzoic acid to form an iron(IV)-oxo complex

    PubMed Central

    Ray, Kallol; Lee, Sang Mok; Que, Lawrence

    2008-01-01

    The mechanism of formation of [FeIV(O)(N4Py)]2+ (2, N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) from the reaction of [FeII(N4Py)(CH3CN)]2+ (1) with m-chloroperbenzoic acid (mCPBA) in CH2Cl2 at −30 °C has been studied on the basis of the visible spectral changes observed and the reaction stoichiometry. It is shown that the conversion of 1 to 2 in 90% yield requires 1.5 equiv peracid and takes place in two successive one-electron steps via an [FeIII(N4Py)OH]2+(3) intermediate. The first oxidation step uses 0.5 equiv peracid and produces 0.5 equiv 3-chlorobenzoic acid, while the second step uses 1 equiv peracid and affords byproducts derived from chlorophenyl radical. We conclude that the FeII(N4Py) center promotes O-O bond heterolysis, while the FeIII(N4Py) center favors O-O bond homolysis, so the nature of O-O bond cleavage is dependent on the iron oxidation state. PMID:18443654

  14. 9-Triptycenecarboxylate-Bridged Diiron(II) Complexes

    PubMed Central

    Friedle, Simone; Kodanko, Jeremy J.; Fornace, Kyrstin L.; Lippard, Stephen J.

    2008-01-01

    The synthesis and characterization of diiron(II) complexes supported by 9-triptycenecarboxylate ligands (-O2CTrp) is described. The interlocking nature of the triptycenecarboxylates facilitates formation of quadruply bridged diiron(II) complexes of the type [Fe2(μ-O2CTrp)4(L)2] (L = THF, pyridine or imidazole derivative) with a paddlewheel geometry. A systematic lengthening of the Fe-Fe distance occurs with the increase in steric bulk of the neutral donor L, resulting in values of up to 3 Å without disassembly of the paddlewheel structure. Reactions with an excess of water do not lead to decomposition of the diiron(II) core, indicating that these quadruply bridged complexes are of exceptional stability. The red-colored complexes [Fe2(μ-O2CTrp)4(4-AcPy)2] (10) and [Fe2(μ-O2CTrp)4(4-CNPy)2] (11) exhibit solvent-dependent thermochromism in coordinating solvents that was studied by variable temperature UV-vis spectroscopy. Reaction of [Fe2(μ-O2CTrp)4(THF)2] with N,N,N’,N’-tetramethylethylenediamine (TMEDA), tetra-n-butyl ammonium thiocyanate, or excess 2-methylimidazole resulted in the formation of mononuclear complexes [Fe(O2CTrp)2(TMEDA)] (13), (n-Bu4N)2[Fe(O2CTrp)2(SCN)2] (14), and [Fe(O2CTrp)2(2-MeIm)2] (15) having an O4/N2 coordination sphere composition. PMID:19915653

  15. Ab initio MO study on equilibrium bond distance between Fe and pyridine in bis(pyridine)(porphinato) iron for various electronic states

    NASA Astrophysics Data System (ADS)

    Saito, Minoru; Kashiwagi, Hiroshi

    1985-04-01

    For bis(pyridine)(porphinato) iron [FeP(py)2], a correlation between the iron electronic state and the equilibrium Fe-Npy distance was investigated. Potential energy curves as a function of the Fe-Npy distance were calculated for low-spin, intermediate-spin, and high-spin states of the ferric and ferrous ions by the ab initio SCF MO method. The equilibrium Fe-Npy distances were obtained from the potential curves. The values obtained for the ferric low-spin and high-spin states were in good agreement with the experimental values for Fe(III)(OEP)(3-Clpy)2 within the differences, ±0.05 Å. The following significant features were found. The equilibrium distance is elongated by the occupation of the 3dz2 orbital and is shortened by the oxidation of the iron atom. The distance and the force constant for the symmetrical py-Fe-py stretching are strongly correlated with the overlap population between the 3dz2 orbital and pyridine-nitrogen orbitals.

  16. Ultrafast electronic and vibrational dynamics in brominated aluminum corroles: Energy relaxation and triplet formation.

    PubMed

    Stensitzki, T; Yang, Y; Berg, A; Mahammed, A; Gross, Z; Heyne, K

    2016-07-01

    We combined femtosecond (fs) VIS pump-IR probe spectroscopy with fs VIS pump-supercontinuum probe spectroscopy to characterize the photoreaction of the hexacoordinated Al(tpfc-Br8)(py)2 in a comprehensive way. Upon fs excitation at ∼400 nm in the Soret band, the excitation energy relaxes with a time constant of (250 ± 80) fs to the S2 and S1 electronic excited states. This is evident from the rise time of the stimulated emission signal in the visible spectral range. On the same time scale, narrowing of broad infrared signals in the C=C stretching region around 1500 cm(-1) is observed. Energy redistribution processes are visible in the vibrational and electronic dynamics with time constants between ∼2 ps and ∼20 ps. Triplet formation is detected with a time constant of (95 ± 3) ps. This is tracked by the complete loss of stimulated emission. Electronic transition of the emerging triplet absorption band overlaps considerably with the singlet excited state absorption. In contrast, two well separated vibrational marker bands for triplet formation were identified at 1477 cm(-1) and at 1508 cm(-1). These marker bands allow a precise identification of triplet dynamics in corrole systems. PMID:27226980

  17. [Ru(η5-C5H5)(η6-C10H8)]PF6 as a catalyst precursor for the one-pot direct C-H alkenylation of nitrogen heterocycles.

    PubMed

    Lynam, Jason M; Milner, Lucy M; Mistry, Neetisha S; Slattery, John M; Warrington, Sally R; Whitwood, Adrian C

    2014-03-21

    The ruthenium naphthalene complex [Ru(η(5)-C5H5)(η(6)-C10H8)](+) is a catalyst precursor for the direct C-H alkenylation of pyridine and related nitrogen heterocycles by terminal alkynes. Stoichiometric studies have demonstrated that the naphthalene ligand may be displaced by either pyridine, 4-methylpyridine or dimethylaminopyridine (DMAP) to give species [Ru(η(5)-C5H5)L3](+) (L = nitrogen-based ligand). Reaction of in situ-generated [Ru(η(5)-C5H5)(py)3](+) (py = pyridine) with PPh3 results in the formation of [Ru(η(5)-C5H5)(PPh3)(py)2](+), the active catalyst for direct alkenylation, some [Ru(η(5)-C5H5)(PPh3)2(py)](+) is also formed in this reaction. A one-pot procedure is reported which has allowed for the nature of the nitrogen heterocycle and phosphine ligand to be evaluated. The sterically demanding phosphine PCy3 inhibits catalysis, and only trace amounts of product are formed when precursors containing a pentamethylcyclopentadienyl group were used. The greatest conversion was observed with PMe3 when used as co-ligand with [Ru(η(5)-C5H5)(η(6)-C10H8)](+). PMID:24481140

  18. “Systematic Synthesis of a Metal Organic Framework Based on Triangular Cu3(μ3-OH) Secondary Building Units: From a 0-D Complex, to an 1-D Chain and a 3-D Lattice”

    PubMed Central

    Rivera-Carrillo, Marlyn; Chakraborty, Indranil; Raptis, Raphael G.

    2010-01-01

    Reactions of Cu(CF3SO3)2 and pyrazole in methanolic solutions in the presence of stoichiometric amounts of py, py/4,4′-bpy, or 4,4′-bpy have yielded two new complexes [Cu3(μ3-OH)(μ-pz)3(py)3](CF3SO3)2·0.5H2O (1) and [{Cu3(μ3-OH)(μ-pz)3(py)2}2(μ-4,4′-bpy)](CF3SO3)4 (2), a one-dimensional coordination polymer, {[Cu3(μ3-OH)(μ-pz)3(py)(μ-4,4′-bpy)](CF3SO3)2·0.5H2O}n (3), and a three-dimensional, eight-fold interpenetrated extended lattice, {[Cu3(μ3-OH)(μ-pz)3(μ-4,4′-bpy)1.5](CF3SO3)2·1.5H2O}n (4). PMID:20625464

  19. Effect of particle pinch on the fusion performance and profile features of an international thermonuclear experimental reactor-like fusion reactor

    SciTech Connect

    Wang, Shijia Wang, Shaojie

    2015-04-15

    The evolution of the plasma temperature and density in an international thermonuclear experimental reactor (ITER)-like fusion device has been studied by numerically solving the energy transport equation coupled with the particle transport equation. The effect of particle pinch, which depends on the magnetic curvature and the safety factor, has been taken into account. The plasma is primarily heated by the alpha particles which are produced by the deuterium-tritium fusion reactions. A semi-empirical method, which adopts the ITERH-98P(y,2) scaling law, has been used to evaluate the transport coefficients. The fusion performances (the fusion energy gain factor, Q) similar to the ITER inductive scenario and non-inductive scenario (with reversed magnetic shear) are obtained. It is shown that the particle pinch has significant effects on the fusion performance and profiles of a fusion reactor. When the volume-averaged density is fixed, particle pinch can lower the pedestal density by ∼30%, with the Q value and the central pressure almost unchanged. When the particle source or the pedestal density is fixed, the particle pinch can significantly enhance the Q value by  60%, with the central pressure also significantly raised.

  20. Periodic motion in perturbed elliptic oscillators revisited

    NASA Astrophysics Data System (ADS)

    Corbera, M.; Llibre, J.; Valls, C.

    2016-10-01

    We analytically study the Hamiltonian system in R4 with Hamiltonian H= 1/2 bigl(px2+py2 bigr)+1/2 bigl(ω12 x 2+ω22 y2 bigr)- ɛ V(x,y) being V(x,y)=-(x2y+ax3) with ain{R}, where ɛ is a small parameter and ω1 and ω2 are the unperturbed frequencies of the oscillations along the x and y axis, respectively. Using averaging theory of first and second order we analytically find seven families of periodic solutions in every positive energy level of H when the frequencies are not equal. Four of these seven families are defined for all ain{R} whereas the other three are defined for all a≠0. Moreover, we provide the shape of all these families of periodic solutions. These Hamiltonians may represent the central parts of deformed galaxies and thus have been extensively used and studied mainly numerically in order to describe local motion in galaxies near an equilibrium point.

  1. Ultrafast electronic and vibrational dynamics in brominated aluminum corroles: Energy relaxation and triplet formation

    PubMed Central

    Stensitzki, T.; Yang, Y.; Berg, A.; Mahammed, A.; Gross, Z.; Heyne, K.

    2016-01-01

    We combined femtosecond (fs) VIS pump–IR probe spectroscopy with fs VIS pump–supercontinuum probe spectroscopy to characterize the photoreaction of the hexacoordinated Al(tpfc-Br8)(py)2 in a comprehensive way. Upon fs excitation at ∼400 nm in the Soret band, the excitation energy relaxes with a time constant of (250 ± 80) fs to the S2 and S1 electronic excited states. This is evident from the rise time of the stimulated emission signal in the visible spectral range. On the same time scale, narrowing of broad infrared signals in the C=C stretching region around 1500 cm−1 is observed. Energy redistribution processes are visible in the vibrational and electronic dynamics with time constants between ∼2 ps and ∼20 ps. Triplet formation is detected with a time constant of (95 ± 3) ps. This is tracked by the complete loss of stimulated emission. Electronic transition of the emerging triplet absorption band overlaps considerably with the singlet excited state absorption. In contrast, two well separated vibrational marker bands for triplet formation were identified at 1477 cm−1 and at 1508 cm−1. These marker bands allow a precise identification of triplet dynamics in corrole systems. PMID:27226980

  2. Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens.

    PubMed

    Cuerva, Cristián; Campo, José A; Cano, Mercedes; Sanz, Jesús; Sobrados, Isabel; Diez-Gómez, Virginia; Rivera-Calzada, Alberto; Schmidt, Rainer

    2016-07-18

    In this work we report on water-free proton conductivity in liquid-crystal pyridylpyrazolate-based Pt(II) and Pd(II) complexes [M(pz(R(n,n)py))2] (pz(R(n,n)py) = 3-(3,5-dialkyloxyphenyl)-5-(pyridin-2-yl)pyrazolate, R(n,n) = C6H3(OCnH2n+1)2; n = 4, 12, 16, M = Pd; n = 12, M = Pt) with potential application as electrolyte materials in proton exchange membrane fuel cells. The columnar ordering of the complexes in the liquid-crystalline phase opens nanochannels, which are used for fast proton exchange as detected by impedance spectroscopy and NMR. The NMR spectra indicate that the proton conduction mechanism is associated with a novel C-H···N proton transfer, which persists above the clearing point of the material. The highest conductivity of ∼0.5 μS cm(-1) at 180 °C with an activation energy of 1.2 eV is found for the Pt(II) compound in the mesophase. The Pd(II) complexes with different chain length (n = 4, 12, and 16) show lower conductivity but smaller activation energies, in the range of 0.74-0.93 eV. PMID:27362555

  3. Synthesis and Single-Molecule Conductance Study of Redox-Active Ruthenium Complexes with Pyridyl and Dihydrobenzo[b]thiophene Anchoring Groups.

    PubMed

    Ozawa, Hiroaki; Baghernejad, Masoud; Al-Owaedi, Oday A; Kaliginedi, Veerabhadrarao; Nagashima, Takumi; Ferrer, Jaime; Wandlowski, Thomas; García-Suárez, Víctor M; Broekmann, Peter; Lambert, Colin J; Haga, Masa-Aki

    2016-08-26

    The ancillary ligands 4'-(4-pyridyl)-2,2':6',2''-terpyridine and 4'-(2,3-dihydrobenzo[b]thiophene)-2,2'-6',2"-terpyridine were used to synthesize two series of mono- and dinuclear ruthenium complexes differing in their lengths and anchoring groups. The electrochemical and single-molecular conductance properties of these two series of ruthenium complexes were studied experimentally by means of cyclic voltammetry and the scanning tunneling microscopy-break junction technique (STM-BJ) and theoretically by means of density functional theory (DFT). Cyclic voltammetry data showed clear redox peaks corresponding to both the metal- and ligand-related redox reactions. Single-molecular conductance demonstrated an exponential decay of the molecular conductance with the increase in molecular length for both the series of ruthenium complexes, with decay constants of βPY =2.07±0.1 nm(-1) and βBT =2.16±0.1 nm(-1) , respectively. The contact resistance of complexes with 2,3-dihydrobenzo[b]thiophene (BT) anchoring groups is found to be smaller than the contact resistance of ruthenium complexes with pyridine (PY) anchors. DFT calculations support the experimental results and provided additional information on the electronic structure and charge transport properties in those metal|ruthenium complex|metal junctions.

  4. Velocity of the high-spin low-spin interface inside the thermal hysteresis loop of a spin-crossover crystal, via photothermal control of the interface motion.

    PubMed

    Slimani, Ahmed; Varret, François; Boukheddaden, Kamel; Garrot, Damien; Oubouchou, Hassane; Kaizaki, Sumio

    2013-02-22

    We investigated by optical microscopy the thermal transition of the spin-crossover dinuclear iron(II) compound [(Fe(NCSe)(py)(2))(2)(m-bpypz)]. In a high-quality crystal the high-spin (HS) low-spin (LS) thermal transition took place with a sizable hysteresis, at ~108 K and ~116 K on cooling and heating, respectively, through the growth of a single macroscopic domain with a straight LS and HS interface. The interface orientation was almost constant and its propagation velocity was close to ~6 and 26 μ m s(-1) for the on-cooling and on-heating processes, respectively. We found that the motion of the interface was sensitive to the intensity of the irradiation beam of the microscope, through a photothermal effect. By fine-tuning the intensity we could stop and even reverse the interface motion. This way we stabilized a biphasic state of the crystal, and we followed the spontaneous motion of the interface at different temperatures inside the thermal hysteresis loop. This experiment gives access for the first time to an accurate determination of the equilibrium temperature in the case of thermal hysteresis--which was not accessible by the usual quasistatic investigations. The temperature dependence of the propagation velocity inside the hysteretic interval was revealed to be highly nonlinear, and it was quantitatively reproduced by a dynamical mean-field theory, which made possible an estimate of the macroscopic energy barrier.

  5. Synthesis, spectral and thermal studies of pyridyl adducts of Zn(II) and Cd(II) dithiocarbamates, and their use as single source precursors for ZnS and CdS nanoparticles.

    PubMed

    Onwudiwe, Damian C; Strydom, Christien A; Oluwafemi, Oluwatobi S; Hosten, Eric; Jordaan, Anine

    2014-06-21

    The synthesis, spectroscopic characterisation, and thermal studies of pyridyl adducts of Zn(II) and Cd(II) complexes of N-ethyl-N-phenyl dithiocarbamate, represented as [ZnL2py] and [CdL2py2], are reported. Single-crystal X-ray structural analysis of the Zn compound showed that it is five-coordinate with four sulphurs from dithiocarbamate and one nitrogen from pyridine in a distorted square pyramidal geometry. The thermogravimetric studies indicate that the zinc and cadmium compounds undergo fast weight loss, and the temperature at maximum rate of decomposition is at 277 °C and 265 °C respectively, to give the metal (Zn or Cd) sulphide residues. These compounds were used as single molecule precursors to produce nanocrystalline MS (M = Zn, Cd) after thermolysis in hexadecylamine. The morphological and optical properties of the resulting MS nanocrystallites were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-Vis absorption and photoluminescence (PL) spectroscopy, and powdered X-ray diffraction (XRD). By varying the growth time, the temporal evolution of the optical properties and morphology of the nanocrystals were investigated. PMID:24769861

  6. The reaction of [Fe(pic)3] with hydrogen peroxide: a UV-visible and EPR spectroscopic study (Hpic = picolinic acid).

    PubMed

    Jain, Sneh L; Bhattacharyya, Pravat

    2005-08-21

    The Gif family of catalysts, based on an iron salt and O2 or H2O2 in pyridine, allows the oxygenation of cyclic saturated hydrocarbons to ketones and alcohols under mild conditions. The reaction between [Fe(pic)3] and hydrogen peroxide in pyridine under GoAgg(III)(Fe(III)/Hpic catalyst) conditions was investigated by UV-visible spectrophotometry. Reactions were monitored at 430 and 520 nm over periods ranging from a few minutes to several hours at 20 degrees C. A number of kinetically stable intermediates were detected, and their relevance to the processes involved in the assembly of the active GoAgg(III) catalyst was determined by measuring the kinetics in the presence and absence of cyclohexane. EPR measurements at 110 K using hydrogen peroxide and t-BuOOH as oxidants were used to further probe these intermediates. Our results indicate that in wet pyridine [Fe(pic)3] undergoes reversible dissociation of one picolinate ligand, establishing an equilibrium with [Fe(pic)2(py)(OH)]. Addition of aqueous hydrogen peroxide rapidly generates the high-spin complex [Fe(pic)2(py)(eta1-OOH)] from the labilised hydroxy species. Subsequently the hydroperoxy species undergoes homolysis of the Fe-O bond, generating HOO. and [Fe(pic)2(py)2], the active oxygenation catalyst.

  7. Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens.

    PubMed

    Cuerva, Cristián; Campo, José A; Cano, Mercedes; Sanz, Jesús; Sobrados, Isabel; Diez-Gómez, Virginia; Rivera-Calzada, Alberto; Schmidt, Rainer

    2016-07-18

    In this work we report on water-free proton conductivity in liquid-crystal pyridylpyrazolate-based Pt(II) and Pd(II) complexes [M(pz(R(n,n)py))2] (pz(R(n,n)py) = 3-(3,5-dialkyloxyphenyl)-5-(pyridin-2-yl)pyrazolate, R(n,n) = C6H3(OCnH2n+1)2; n = 4, 12, 16, M = Pd; n = 12, M = Pt) with potential application as electrolyte materials in proton exchange membrane fuel cells. The columnar ordering of the complexes in the liquid-crystalline phase opens nanochannels, which are used for fast proton exchange as detected by impedance spectroscopy and NMR. The NMR spectra indicate that the proton conduction mechanism is associated with a novel C-H···N proton transfer, which persists above the clearing point of the material. The highest conductivity of ∼0.5 μS cm(-1) at 180 °C with an activation energy of 1.2 eV is found for the Pt(II) compound in the mesophase. The Pd(II) complexes with different chain length (n = 4, 12, and 16) show lower conductivity but smaller activation energies, in the range of 0.74-0.93 eV.

  8. catena-Poly[[[iodidocopper(I)]-{μ-N-[(pyridin-2-yl-κN)methyl-idene]pyridin-3-amine-κ(2)N(3):N(1)}] acetonitrile hemisolvate].

    PubMed

    Mahmoudi, Ali; Dehghanpour, Saeed; Babakhodaverdi, Mojtaba

    2012-10-01

    In the asymmetric unit of the title polymeric complex, {[CuI(C(11)H(9)N(3))]·0.5CH(3)CN}(n), there are two Cu(I) atoms, two N-[(pyridin-2-yl-κN)methyl-idene]pyridin-3-amine (PyPy) ligands and two I atoms. Both Cu(I) atoms have a distorted tetra-hedral geometry, each being coordinated by one I atom, two N atoms of one PyPy ligand and one N atom from an adjacent PyPy ligand. In the crystal, infinite helical chains of [Cu(2)(PyPy)(2)](n) are formed propagating along the b axis. These chains are linked via weak C-H⋯I hydrogen bonds and π-π stacking inter-actions [shortest centroid-centroid distance = 3.2727 (14) Å]. During the refinement, electron-density peaks were located that were believed to be highly disordered solvent mol-ecules (possibly acetonitrile). The SQUEEZE option in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148-155] indicated there were solvent cavities with a total volume of 196 Å(3) containing approximately 60 electrons per unit cell, which equated to one mol-ecule of acetonitrile per asymmetric unit. PMID:23125600

  9. Inhibition of the purified 20S proteasome by non-heme iron complexes

    PubMed Central

    Prakash, Jai; Schmitt, Sara M.; Dou, Q. Ping; Kodanko, Jeremy J.

    2013-01-01

    Polypyridyl pentadentate ligands N4Py (1) and Bn-TPEN (2), along with their respective iron complexes, have been investigated for their ability to inhibit the purified 20S proteasome. Results demonstrated that the iron complexes of both ligands are potent inhibitors of the 20S proteasome (IC50 = 9.2 μM for [FeII(OH2)(N4Py)]2+ (3) and 4.0 μM for [FeII(OH2)(Bn-TPEN)]2+ (4)). Control experiments showed that ligand 1 or FeII alone showed no inhibition, whereas 2 was moderately active (IC50 = 96 μM), suggesting that iron, when bound to these ligands, plays a key role in proteasome inhibition. Results from time-dependent inactivation studies suggest different modes of action for the iron complexes. Time-dependent decay of proteasome activity was observed upon incubation in the presence of 4, which accelerated in the presence of DTT, suggesting reductive activation of O2 and oxidation of the 20S proteasome as a mode of action. In contrast, loss of 20S proteasome activity was not observed with 3 over time, suggesting inhibition through direct binding of the iron complex to the enzyme. Inhibition of the 20S proteasome by 4 was not blocked by reactive oxygen species scavengers, consistent with a unique oxidant being responsible for the time-dependent inhibition observed. PMID:22170477

  10. Tyrosine Phosphorylation of the Lyn Src Homology 2 (SH2) Domain Modulates Its Binding Affinity and Specificity*

    PubMed Central

    Jin, Lily L.; Wybenga-Groot, Leanne E.; Tong, Jiefei; Taylor, Paul; Minden, Mark D.; Trudel, Suzanne; McGlade, C. Jane; Moran, Michael F.

    2015-01-01

    Src homology 2 (SH2) domains are modular protein structures that bind phosphotyrosine (pY)-containing polypeptides and regulate cellular functions through protein-protein interactions. Proteomics analysis showed that the SH2 domains of Src family kinases are themselves tyrosine phosphorylated in blood system cancers, including acute myeloid leukemia, chronic lymphocytic leukemia, and multiple myeloma. Using the Src family kinase Lyn SH2 domain as a model, we found that phosphorylation at the conserved SH2 domain residue Y194 impacts the affinity and specificity of SH2 domain binding to pY-containing peptides and proteins. Analysis of the Lyn SH2 domain crystal structure supports a model wherein phosphorylation of Y194 on the EF loop modulates the binding pocket that engages amino acid side chains at the pY+2/+3 position. These data indicate another level of regulation wherein SH2-mediated protein-protein interactions are modulated by SH2 kinases and phosphatases. PMID:25587033

  11. Characterization of the Gene Cluster Involved in Isoprene Metabolism in Rhodococcus sp. Strain AD45

    PubMed Central

    van Hylckama Vlieg, Johan E. T.; Leemhuis, Hans; Spelberg, Jeffrey H. Lutje; Janssen, Dick B.

    2000-01-01

    The genes involved in isoprene (2-methyl-1,3-butadiene) utilization in Rhodococcus sp. strain AD45 were cloned and characterized. Sequence analysis of an 8.5-kb DNA fragment showed the presence of 10 genes of which 2 encoded enzymes which were previously found to be involved in isoprene degradation: a glutathione S-transferase with activity towards 1,2-epoxy-2-methyl-3-butene (isoI) and a 1-hydroxy-2-glutathionyl-2-methyl-3-butene dehydrogenase (isoH). Furthermore, a gene encoding a second glutathione S-transferase was identified (isoJ). The isoJ gene was overexpressed in Escherichia coli and was found to have activity with 1-chloro-2,4-dinitrobenzene and 3,4-dichloro-1-nitrobenzene but not with 1,2-epoxy-2-methyl-3-butene. Downstream of isoJ, six genes (isoABCDEF) were found; these genes encoded a putative alkene monooxygenase that showed high similarity to components of the alkene monooxygenase from Xanthobacter sp. strain Py2 and other multicomponent monooxygenases. The deduced amino acid sequence encoded by an additional gene (isoG) showed significant similarity with that of α-methylacyl-coenzyme A racemase. The results are in agreement with a catabolic route for isoprene involving epoxidation by a monooxygenase, conjugation to glutathione, and oxidation of the hydroxyl group to a carboxylate. Metabolism may proceed by fatty acid oxidation after removal of glutathione by a still-unknown mechanism. PMID:10715003

  12. Operation of a tokamak reactor in the radiative improved mode

    NASA Astrophysics Data System (ADS)

    Morozov, D. Kh.; Mavrin, A. A.

    2016-03-01

    The operation of a nuclear fusion reactor has been simulated within a model based on experimental results obtained at the TEXTOR-94 tokamak and other facilities in which quasistationary regimes were achieved with long confinement times, high densities, and absence of the edge-localized mode. The radiative improved mode of confinement studied in detail at the TEXTOR-94 tokamak is the most interesting such regime. One of the most important problems of modern tokamaks is the problem of a very high thermal load on a divertor (or a limiter). This problem is quite easily solved in the radiative improved mode. Since a significant fraction of the thermal energy is reemitted by an impurity, the thermal loading is significantly reduced. As the energy confinement time τ E at high densities in the indicated mode is significantly larger than the time predicted by the scaling of ITERH-98P(y, 2), ignition can be achieved in a facility much smaller than the ITER facility at plasma temperatures below 20 keV. The revealed decrease in the degradation of the confinement time τ E with an increase in the introduced power has been analyzed.

  13. Poly(cyclooctene)-based monolithic columns for capillary high performance liquid chromatography prepared via ring-opening metathesis polymerization.

    PubMed

    Schlemmer, Bettina; Gatschelhofer, Christina; Pieber, Thomas R; Sinner, Frank M; Buchmeiser, Michael R

    2006-11-01

    Monolithic columns for capillary HPLC were prepared via ring-opening metathesis polymerization (ROMP) from cis-cyclooctene (COE), tris(cyclooct-4-enyl-1-oxy)methylsilane (CL) as monomers, 2-propanol and toluene as porogens and RuCl(2)(Py)(2)(IMesH(2))(CHC(6)H(5)) (Py=pyridine, IMesH(2)=1,3-dimesityl-4,5-dihydroimidazolin-2-ylidene) as initiator within the confines of 200 microm i.d. fused silica columns. For evaluation of the novel monolithic capillary HPLC columns, a protein standard consisting of six proteins in the molecular weight range of 5800-66000 g/mol, i.e. ribonuclease A, insulin, albumin, lysozyme, myoglobin and beta-lactoglobulin, was used. Reproducibility of synthesis was checked by determining the relative standard deviation (RSD) in retention times (t(R)), which was found to be in the range of 2.9-3.9% for all analytes. Variations in polymer kinetics were realized by adding different amounts of free pyridine and had a significant influence on the monolith's morphology, the backpressure and retention times. On the contrary, variations in monomer content and COE to CL ratio showed only minor changes on these parameters. Long-term stability of 1000 runs at 50 degrees C showed excellent stability of the columns and no significant alteration in separation performance was observed in combination with slightly decreased retention times (approx. 1.6-7.2% for all analytes).

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

    PubMed

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

    2014-03-01

    The reaction of UO2Cl2·3THF with the tridentate nitrogen donor ligand 2,6-bis(2-benzimidazolyl)pyridine (H2BBP) in pyridine leads to the formation of three different complexes: [(UO2)(H2BBP)Cl2] (1), [(UO)2(HBBP)(Py)Cl] (2), and [(UO2)(BBP)(Py)2] (3) after successive deprotonation of H2BBP with a strong base. Crystallographic determination of 1-3 reveals that increased charge through ligand deprotonation and displacement of chloride leads to equatorial planarity about uranyl as well as a more compact overall coordination geometry. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectra of 1-3 at the U-4d edges have been recorded using a soft X-ray Scanning Transmission X-ray Microscope (STXM) and reveal the uranium 4d5/2 and 4d3/2 transitions at energies associated with uranium in the hexavalent oxidation state. First-principles Density Functional Theory (DFT) electronic structure calculations for the complexes have been performed to determine and validate the coordination characteristics, which correspond well to the experimental results. PMID:24528285

  15. Taming Tin(IV) Polyazides.

    PubMed

    Campbell, Rory; Davis, Martin F; Fazakerley, Mathew; Portius, Peter

    2015-12-14

    The first charge-neutral Lewis base adducts of tin(IV) tetraazide, [Sn(N3)4(bpy)], [Sn(N3)4(phen)] and [Sn(N3)4(py)2], and the salt bis{bis(triphenylphosphine)iminium} hexa(azido)stannate [(PPN)2Sn(N3)6] (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; py = pyridine; PPN = N(PPh3)2) have been prepared using covalent or ionic azide-transfer reagents and ligand-exchange reactions. The azides were isolated on the 0.3 to 1 g scale and characterized by IR and NMR spectroscopies, microanalytical and thermal methods and their molecular structures determined by single-crystal XRD. All complexes have a distorted octahedral Sn[N]6 coordination geometry and possess greater thermal stability than their Si and Ge homologues. The nitrogen content of the adducts of up to 44% exceed any Sn(IV) compound known hitherto. PMID:26767331

  16. Synthesis, spectroscopic, DFT calculations and biological activity studies of ruthenium carbonyl complexes with 2-picolinic acid and a secondary ligand

    NASA Astrophysics Data System (ADS)

    Shohayeb, Shahera M.; Mohamed, Rania G.; Moustafa, H.; El-Medani, Samir M.

    2016-09-01

    Thermal reaction of [Ru3(CO)12] with 2-picolinic acid (Hpic) in the absence and presence of a secondary ligand (pyridine, Py, bipyridine, Bipy, or thiourea, Tu) was investigated. Four complexes with molecular formulae: [Ru(CO)3(Hpic)], 1, [Ru2(CO)5(Hpic)(Py)], 2, [Ru2(CO)5(Hpic)(Tu)], 3 and [Ru2(CO)4(Hpic)(Bipy)], 4, were isolated. All complexes were characterized based on elemental analyses, IR, 1H NMR, magnetic studies, mass spectrometry and thermal analysis. The ligand and its complexes have been screened for antibacterial activities. Density Functional Theory (DFT) calculations at the B3LYP/6-311G (d,p)_ level of theory have been carried out to investigate the equilibrium geometry of the ligands. The optimized geometry parameters of the complexes were evaluated using B3LYP method and LANL2DZ basis set. The extent of natural charge population (core, valence and rydberg), exact electronic configuration, total Lewis and total non-Lewis are estimated and discussed in terms of natural bond orbitals (NBO) analysis.

  17. Cooperative ligation, back-bonding, and possible pyridine-pyridine interactions in tetrapyridine-vanadium(II): a visible and X-ray spectroscopic study.

    PubMed

    Frank, Patrick; Ghosh, Phalguni; Hodgson, Keith O; Taube, Henry

    2002-06-17

    The binding of pyridine by V(II) in aqueous solution shows evidence for the late onset of cooperativity. The K(1) governing formation of [V(py)](2+) (lambda(max) = 404 nm, epsilon(max) = 1.43 +/- 0.3 M(-1) cm(-1)) was determined spectrophotometrically to be 11.0 +/- 0.3 M(-)(1), while K(1) for isonicotinamide was found to be 5.0 +/- 0.1 M(-1). These values are in the low range for 3d M(2+) ions and indicate that V(II).py back-bonding is not significant in the formation of the 1:1 complex. Titration of 10.5 mM V(II) with pyridine in aqueous solution showed an absorption plateau at about 1 M added pyridine, indicating a reaction terminus. Vanadium K-edge EXAFS analysis of 63 mM V(II) in 2 M pyridine solution revealed six first-shell N/O ligands at 2.14 A and 4 +/- 1 pyridine ligands per V(II). UV/vis absorption spectroscopy indicated that the same terminal V(II) species was present in both experiments. Model calculations showed that in the absence of back-bonding only 2.0 +/- 0.2 and 2.4 +/- 0.2 pyridine ligands would be present, respectively. Cooperativity in multistage binding of pyridine by [V(aq)](2+) is thus indicated. XAS K-edge spectroscopy of crystalline [V(O(3)SCF(3))(2)(py)(4)] and of V(II) in 2 M pyridine solution each exhibited the analogous 1s --> (5)E(g) and 1s --> (5)T(2g) transitions, at 5465.5 and 5467.5 eV, and 5465.2 and 5467.4 eV, respectively, consistent with the EXAFS analysis. In contrast, [V(py)(6)](PF(6))(2) and [V(H(2)O)(6)]SO(4) show four 1s --> 3d XAS transitions suggestive of a Jahn-Teller distorted excited state. Comparison of the M(II)[bond]N(py) bond lengths in V(II) and Fe(II) tetrapyridines shows that the V(II)[bond]N(py) distances are about 0.06 A shorter than predicted from ionic radii. For [VX(2)(R-py)(4)] (X = Cl(-), CF(3)SO(3)(-); R = 4-Et, H, 3-EtOOC), the E(1/2) values of the V(II)/V(III) couples correlate linearly with the Hammett sigma values of the R group. These findings indicate that pi back-bonding is important in [V

  18. A Mononuclear Carboxylate-Rich Oxoiron(IV) Complex: a Structural and Functional Mimic of TauD Intermediate 'J'

    PubMed

    McDonald, Aidan R; Guo, Yisong; Vu, Van V; Bominaar, Emile L; Münck, Eckard; Que, Lawrence

    2012-01-01

    The pentadentate ligand (n)Bu-P2DA (2(b), (n)Bu-P2DA = N-(1',1'-bis(2-pyridyl)pentyl)iminodiacetate) was designed to bind an iron center in a carboxylate-rich environment similar to that found in the active sites of TauD and other α-ketoglutarate-dependent mononuclear non-heme iron enzymes. The iron(II) complex (n)Bu(4)N[Fe(II)(Cl)((n)Bu-P2DA)] (3(b)-Cl) was synthesized and crystallographically characterized to have a 2-pyridine-2-carboxylate donor set in the plane perpendicular to the Fe-Cl bond. Reaction of 3(b)-Cl with N-heterocyclic amines such as pyridine or imidazole yielded the N-heterocyclic amine adducts [Fe(II)(N)((n)Bu-P2DA)]. These adducts in turn reacted with oxo-transfer reagents at -95 °C to afford a short-lived oxoiron(IV) complex [Fe(IV)(O)((n)Bu-P2DA)] (5(b)) in yields as high as 90% depending on the heterocycle used. Complex 5(b) exhibits near-IR absorption features (λ(max) = 770 nm) and Mossbauer parameters (δ = 0.04 mm/s; ΔE(Q) = 1.13 mm/s; D = 27±2 cm(-1)) characteristic of an S = 1 oxoiron(IV) species. Direct evidence for an Fe=O bond of 1.66 Å was found from EXAFS analysis. DFT calculations on 5(b) in its S =1 spin state afforded a geometry-optimized structure consistent with the EXAFS data. They further demonstrated that the replacement of two pyridine donors in [Fe(IV)(O)(N4Py)](2+) (N4Py = N,N-(bis(2-pyridyl)methyl)N-bis(2-pyridylmethyl)amine) with carboxylate donors in 5(b) decreased the energy gap between the ground S = 1 and the excited S = 2 states, reflecting the weaker equatorial ligand field of 5(b) and accounting for its larger D value. Complex 5(b) reacted readily with dihydrotoluene, methyldiphenylphosphine and ferrocene at -60 °C, and in all cases was approximately a 5-fold more reactive oxidant than [Fe(IV)(O)(N4Py)](2+). The reactivity differences between these two complexes may arise from a combination of electronic and steric factors. Carboxylate-rich 5(b) represents the closest structural mimic reported thus far of

  19. Strategies for the Hyperpolarization of Acetonitrile and Related Ligands by SABRE

    PubMed Central

    2014-01-01

    We report on a strategy for using SABRE (signal amplification by reversible exchange) for polarizing 1H and 13C nuclei of weakly interacting ligands which possess biologically relevant and nonaromatic motifs. We first demonstrate this via the polarization of acetonitrile, using Ir(IMes)(COD)Cl as the catalyst precursor, and confirm that the route to hyperpolarization transfer is via the J-coupling network. We extend this work to the polarization of propionitrile, benzylnitrile, benzonitrile, and trans-3-hexenedinitrile in order to assess its generality. In the 1H NMR spectrum, the signal for acetonitrile is enhanced 8-fold over its thermal counterpart when [Ir(H)2(IMes)(MeCN)3]+ is the catalyst. Upon addition of pyridine or pyridine-d5, the active catalyst changes to [Ir(H)2(IMes)(py)2(MeCN)]+ and the resulting acetonitrile 1H signal enhancement increases to 20- and 60-fold, respectively. In 13C NMR studies, polarization transfers optimally to the quaternary 13C nucleus of MeCN while the methyl 13C is hardly polarized. Transfer to 13C is shown to occur first via the 1H–1H coupling between the hydrides and the methyl protons and then via either the 2J or 1J couplings to the respective 13Cs, of which the 2J route is more efficient. These experimental results are rationalized through a theoretical treatment which shows excellent agreement with experiment. In the case of MeCN, longitudinal two-spin orders between pairs of 1H nuclei in the three-spin methyl group are created. Two-spin order states, between the 1H and 13C nuclei, are also created, and their existence is confirmed for Me13CN in both the 1H and 13C NMR spectra using the Only Parahydrogen Spectroscopy protocol. PMID:25539423

  20. The complete genomic sequence of pepper yellow leaf curl virus (PYLCV) and its implications for our understanding of evolution dynamics in the genus polerovirus.

    PubMed

    Dombrovsky, Aviv; Glanz, Eyal; Lachman, Oded; Sela, Noa; Doron-Faigenboim, Adi; Antignus, Yehezkel

    2013-01-01

    We determined the complete sequence and organization of the genome of a putative member of the genus Polerovirus tentatively named Pepper yellow leaf curl virus (PYLCV). PYLCV has a wider host range than Tobacco vein-distorting virus (TVDV) and has a close serological relationship with Cucurbit aphid-borne yellows virus (CABYV) (both poleroviruses). The extracted viral RNA was subjected to SOLiD next-generation sequence analysis and used as a template for reverse transcription synthesis, which was followed by PCR amplification. The ssRNA genome of PYLCV includes 6,028 nucleotides encoding six open reading frames (ORFs), which is typical of the genus Polerovirus. Comparisons of the deduced amino acid sequences of the PYLCV ORFs 2-4 and ORF5, indicate that there are high levels of similarity between these sequences to ORFs 2-4 of TVDV (84-93%) and to ORF5 of CABYV (87%). Both PYLCV and Pepper vein yellowing virus (PeVYV) contain sequences that point to a common ancestral polerovirus. The recombination breakpoint which is located at CABYV ORF3, which encodes the viral coat protein (CP), may explain the CABYV-like sequences found in the genomes of the pepper infecting viruses PYLCV and PeVYV. Two additional regions unique to PYLCV (PY1 and PY2) were identified between nucleotides 4,962 and 5,061 (ORF 5) and between positions 5,866 and 6,028 in the 3' NCR. Sequence analysis of the pepper-infecting PeVYV revealed three unique regions (Pe1-Pe3) with no similarity to other members of the genus Polerovirus. Genomic analyses of PYLCV and PeVYV suggest that the speciation of these viruses occurred through putative recombination event(s) between poleroviruses co-infecting a common host(s), resulting in the emergence of PYLCV, a novel pathogen with a wider host range.

  1. Fish-Bite structure by three-dimensional hydrogen-bond acceptor: IR spectroscopy of pyrrole and N-methylpyrrole binary clusters

    NASA Astrophysics Data System (ADS)

    Matsumoto, Yoshiteru; Murakami, Sunao; Honma, Kenji

    2012-08-01

    The N-H…π hydrogen-bonded (H-bonded) structures of pyrrole (Py) and N-methylpyrrole (NMPy) binary clusters have been studied by IR cavity ringdown spectroscopy and density functional theory calculations. The Py1-NMPy1 cluster has an "L-shape" structure, which is formed by an ordinary H-bond between a N-H donor of Py and a π-electron cloud acceptor of NMPy. The Py2-NMPy1 cluster has a "Cyclic" structure, which is also formed by ordinary N-H…π H-bonds as well as the weak C-H…π H-bond between the methyl CH group and the π cloud acceptor of Py. On the other hand, the Py1-NMPy2 cluster shows an extraordinary structure, in which the single donor NH group is surrounded by a three-dimensional H-bond acceptor formed by two aromatic π electron clouds. We call the Py1-NMPy2 cluster as the "Fish-Bite" structure. The Py1-NMPy2 cluster exhibits a redshifted NH stretch by 157 cm-1 from the Py monomer, which is larger than 94 cm-1 of the Py1-NMPy1 cluster. However, both Py1-NMPy1 and Py1-NMPy2 clusters have calculated IR intensities of 169 and 163 km/mol, respectively. This result indicates that not only the N-H…π H-bonds but also the dipole-dipole interaction between Py and NMPy contributes to the Fish-Bite Py1-NMPy2 cluster formation.

  2. Strategies for the hyperpolarization of acetonitrile and related ligands by SABRE.

    PubMed

    Mewis, Ryan E; Green, Richard A; Cockett, Martin C R; Cowley, Michael J; Duckett, Simon B; Green, Gary G R; John, Richard O; Rayner, Peter J; Williamson, David C

    2015-01-29

    We report on a strategy for using SABRE (signal amplification by reversible exchange) for polarizing (1)H and (13)C nuclei of weakly interacting ligands which possess biologically relevant and nonaromatic motifs. We first demonstrate this via the polarization of acetonitrile, using Ir(IMes)(COD)Cl as the catalyst precursor, and confirm that the route to hyperpolarization transfer is via the J-coupling network. We extend this work to the polarization of propionitrile, benzylnitrile, benzonitrile, and trans-3-hexenedinitrile in order to assess its generality. In the (1)H NMR spectrum, the signal for acetonitrile is enhanced 8-fold over its thermal counterpart when [Ir(H)2(IMes)(MeCN)3](+) is the catalyst. Upon addition of pyridine or pyridine-d5, the active catalyst changes to [Ir(H)2(IMes)(py)2(MeCN)](+) and the resulting acetonitrile (1)H signal enhancement increases to 20- and 60-fold, respectively. In (13)C NMR studies, polarization transfers optimally to the quaternary (13)C nucleus of MeCN while the methyl (13)C is hardly polarized. Transfer to (13)C is shown to occur first via the (1)H-(1)H coupling between the hydrides and the methyl protons and then via either the (2)J or (1)J couplings to the respective (13)Cs, of which the (2)J route is more efficient. These experimental results are rationalized through a theoretical treatment which shows excellent agreement with experiment. In the case of MeCN, longitudinal two-spin orders between pairs of (1)H nuclei in the three-spin methyl group are created. Two-spin order states, between the (1)H and (13)C nuclei, are also created, and their existence is confirmed for Me(13)CN in both the (1)H and (13)C NMR spectra using the Only Parahydrogen Spectroscopy protocol.

  3. Photoinduced Stepwise Oxidative Activation of a Chromophore–Catalyst Assembly on TiO2

    SciTech Connect

    Song, Wenjing; Glasson, Christopher R. K.; Luo, Hanlin; Hanson, Kenneth G.; Brennaman, Kyle M.; Concepcion, Javier J.; Meyer, Thomas J.

    2011-07-08

    To probe light-induced redox equivalent separation and accumulation, we prepared ruthenium polypyridyl molecular assembly [(dcb)2Ru(bpy-Mebim2py)Ru(bpy)(OH2)]4+ (RuaII–RubII–OH2) with Rua as light-harvesting chromophore and Rub as water oxidation catalyst (dcb = 4,4'-dicarboxylic acid-2,2'-bipyridine; bpy-Mebim2py = 2,2'-(4-methyl-[2,2':4',4''-terpyridine]-2'',6''-diyl)bis(1-methyl-1H-benzo[d]imidazole); bpy = 2,2'-bipyridine). When bound to TiO2 in nanoparticle films, it undergoes MLCT excitation, electron injection, and oxidation of the remote -RubII–OH2 site to give TiO2(e–)–RuaII–RubIII–OH23+ as a redox-separated transient. The oxidized assembly, TiO2–RuaII–RubIII–OH23+, similarly undergoes excitation and electron injection to give TiO2(e–)–RuaII–RubIV=O2+, with RubIV=O2+ a known water oxidation catalyst precursor. Injection efficiencies for both forms of the assembly are lower than those for [Ru(bpy)2(4,4'-(PO3H2)2bpy)]2+ bound to TiO2 (TiO2–Ru2+), whereas the rates of back electron transfer, TiO2(e–) → RubIII–OH23+ and TiO2(e–) → RubIV=O2+, are significantly decreased compared with TiO2(e–) → Ru3+ back electron transfer.

  4. Changes of biomarkers with oral exposure to benzo(a)pyrene, phenanthrene and pyrene in rats

    PubMed Central

    Kang, Hwan Goo; Cho, Myung Haing; Cho, Joon Hyoung

    2007-01-01

    Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants present in air and food. Among PAHs, benzo(a)pyrene(BaP), phenanthrene (PH) and pyrene (PY) are considered to be important for their toxicity or abundance. To investigate the changes of biomarkers after PAH exposure, rats were treated with BaP (150 µg/kg) alone or with PH (4,300 µg/kg) and PY (2,700 µg/kg) (BPP group) by oral gavage once per day for 30 days. 7-ethoxyresorufin-O-deethylase activity in liver microsomal fraction was increased in only BaP groups. The highest concentration (34.5 ng/g) of BaP, was found in muscle of rats treated with BaP alone at 20 days of treatment; it was 23.6 ng/g in BPP treated rats at 30 days of treatment. The highest PH concentration was 47.1 ng/g in muscle and 118.8 ng/g in fat, and for PY it was 29.7 ng/g in muscle and 219.9 ng/g in fat, in BPP groups. In urine, 114-161 ng/ml 3-OH-PH was found, while PH was 41-69 ng/ml during treatment. 201-263 ng/ml 1-OH-PY was found, while PH was 9-17 ng/ml in urine. The level of PY, PH and their metabolites in urine was rapidly decreased after withdrawal of treatment. This study suggest that 1-OH-PY in urine is a sensitive biomarker for PAHs; it was the most highly detected marker among the three PAHs and their metabolites evaluated during the exposure period and for 14 days after withdrawal. PMID:17993750

  5. Tuning the Reactivity of Chromium(III)-Superoxo Species by Coordinating Axial Ligands.

    PubMed

    Goo, Yi Re; Maity, Annada C; Cho, Kyung-Bin; Lee, Yong-Min; Seo, Mi Sook; Park, Young Jun; Cho, Jaeheung; Nam, Wonwoo

    2015-11-01

    Metal-superoxo species have attracted much attention recently as key intermediates in enzymatic and biomimetic oxidation reactions. The effect(s) of axial ligands on the chemical properties of metal-superoxo complexes has never been explored previously. In this study, we synthesized and characterized chromium(III)-superoxo complexes bearing TMC derivatives with pendant pyridine and imidazole donors, such as [Cr(III)(O2)(TMC-Py)](2+) (1, TMC-Py = 4,8,11-trimethyl-1-(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane) and [Cr(III)(O2)(TMC-Im)](2+) (2, TMC-Im = 4,8,11-trimethyl-1-(2-methylimidazolmethyl)-1,4,8,11-tetraazacyclotetradecane). The reactivity of chromium(III)-superoxo complexes binding different axial ligands, such as 1, 2, and [Cr(III)(O2)(TMC)(Cl)](+) (3, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was then investigated in C-H bond activation and oxygen atom transfer reactions. Kinetic studies revealed that the reactivity of the Cr(III)-superoxo complexes depends on the axial ligands, showing the reactivity order of 1 > 2 > 3 in those electrophilic oxidation reactions. It was also shown that there is a good correlation between the reactivity of the chromium(III)-superoxo complexes and their redox potentials, in which the redox potentials of the chromium(III)-superoxo complexes are in the order 1 > 2 > 3. DFT calculations reproduced the reactivity order between 1 and 3 in both C-H bond activation and oxygen atom transfer reactions, and the latter reaction is described using orbital interactions. The calculations are also in agreement with the experimentally obtained redox potentials. The present results provide the first example showing that the reactivity of metal-superoxo species can be tuned by the electron-donating ability of axial ligands bound trans to the metal-superoxo moiety.

  6. Fish-Bite structure by three-dimensional hydrogen-bond acceptor: IR spectroscopy of pyrrole and N-methylpyrrole binary clusters.

    PubMed

    Matsumoto, Yoshiteru; Murakami, Sunao; Honma, Kenji

    2012-08-21

    The N-H...π hydrogen-bonded (H-bonded) structures of pyrrole (Py) and N-methylpyrrole (NMPy) binary clusters have been studied by IR cavity ringdown spectroscopy and density functional theory calculations. The Py(1)-NMPy(1) cluster has an "L-shape" structure, which is formed by an ordinary H-bond between a N-H donor of Py and a π-electron cloud acceptor of NMPy. The Py(2)-NMPy(1) cluster has a "Cyclic" structure, which is also formed by ordinary N-H...π H-bonds as well as the weak C-H...π H-bond between the methyl CH group and the π cloud acceptor of Py. On the other hand, the Py(1)-NMPy(2) cluster shows an extraordinary structure, in which the single donor NH group is surrounded by a three-dimensional H-bond acceptor formed by two aromatic π electron clouds. We call the Py(1)-NMPy(2) cluster as the "Fish-Bite" structure. The Py(1)-NMPy(2) cluster exhibits a redshifted NH stretch by 157 cm(-1) from the Py monomer, which is larger than 94 cm(-1) of the Py(1)-NMPy(1) cluster. However, both Py(1)-NMPy(1) and Py(1)-NMPy(2) clusters have calculated IR intensities of 169 and 163 km/mol, respectively. This result indicates that not only the N-H...π H-bonds but also the dipole-dipole interaction between Py and NMPy contributes to the Fish-Bite Py(1)-NMPy(2) cluster formation.

  7. Isolation of a Rhizobium phaseoli cytochrome mutant with enhanced respiration and symbiotic nitrogen fixation.

    PubMed Central

    Soberón, M; Williams, H D; Poole, R K; Escamilla, E

    1989-01-01

    Cultured cells of a Rhizobium phaseoli wild-type strain (CE2) possess b-type and c-type cytochromes and two terminal oxidases: cytochromes o and aa3. Cytochrome aa3 was partially expressed when CE2 cells were grown on minimal medium, during symbiosis, and in well-aerated liquid cultures in a complex medium (PY2). Two cytochrome mutants of R. phaseoli were obtained and characterized. A Tn5-mob-induced mutant, CFN4201, expressed diminished amounts of b-type and c-type cytochromes, showed an enhanced expression of cytochrome oxidases, and had reduced levels of N,N,N',N'-tetramethyl-p-phenylenediamine, succinate, and NADH oxidase activities. Nodules formed by this strain had no N2 fixation activity. The other mutant, CFN4205, which was isolated by nitrosoguanidine mutagenesis, had reduced levels of cytochrome o and higher succinate oxidase activity but similar NADH and N,N,N',N'-tetramethyl-p-phenylenediamine oxidase activities when compared with the wild-type strain. Strain CFN4205 expressed a fourfold-higher cytochrome aa3 content when cultured on minimal and complex media and had twofold-higher cytochrome aa3 levels during symbiosis when compared with the wild-type strain. Nodules formed by strain CFN4205 fixed 33% more N2 than did nodules formed by the wild-type strain, as judged by the total nitrogen content found in plants nodulated by these strains. Finally, low-temperature photodissociation spectra of whole cells from strains CE2 and CFN4205 reveal cytochromes o and aa3. Both cytochromes react with O2 at -180 degrees C to give a light-insensitive compound. These experiments identify cytochromes o and aa3 as functional terminal oxidases in R. phaseoli. PMID:2644201

  8. An Unusual Cobalt Azide Adduct That Produces a Nitrene Species for Carbon-Hydrogen Insertion Chemistry.

    PubMed

    Grant, Lauren N; Carroll, Maria E; Carroll, Patrick J; Mindiola, Daniel J

    2016-08-15

    A family of Co(II) complexes supported by the bulky, dianionic bis(pyrrolyl)pyridine pincer ligand pyrr2py [pyrr2py(2-) = 3,5-(t)Bu2-bis(pyrrolyl)pyridine] are reported in this work. These compounds include 1-OEt2, 1·toluene, and 1-N3Ad (Ad = 1-adamantyl), the latter which is prepared via addition of N3Ad to 1-OEt2 [1 = (pyrr2py)Co]. While complexes 1-OEt2 and 1-N3Ad are four-coordinate systems having a Co(II) ion confined in a cis-divacant octahedral geometry, complex 1·toluene possesses a Co(II) ion in a T-shaped environment where the toluene is interstitial and intercalated between two (pyrr2py)Co molecules. Complex 1-N3Ad is notable in that the organic azide binds to the metal through γ-N in a κ(1) fashion. Photolysis of 1-N3Ad results in N2 extrusion and formation of C-H insertion product [(pyrrpypyrrNHAd)Co] (2). We propose complex 2 form via insertion of the nitrene (NAd) into one (t)Bu C-H bond, thus resulting in a pincer ligand having a pendant secondary amine. Complexes 1-OEt2, 1·toluene, and 1-N3Ad and C-H insertion product 2 have been structurally characterized, and in the case of 1-OEt2, we also present electrochemical data. PMID:27454286

  9. Facile modulation of optical properties of octagold clusters through the control of ligand-mediated interactions.

    PubMed

    Iwasaki, Mitsuhiro; Kobayashi, Naoki; Shichibu, Yukatsu; Konishi, Katsuaki

    2016-07-28

    In the recent development of structurally defined ligand-stabilized gold clusters, it has been revealed that not only the inorganic units but also the surrounding organic ligands substantially affect their electronic/optical properties. In this work, a series of core + exo type Au8 clusters decorated by dppp (Ph2P(CH2)3PPh2) and arylthiolate ligands ([Au8(dppp)4(SR)2](2+), 1-5) were synthesized, and their optical properties were studied in order to gain insights into the perturbation effects of the organic ligands. 1-5 showed visible absorption and photoluminescence emission bands at longer wavelengths compared to their chloro- and acetylide-modified analogues, suggesting the contribution of weak non-bonding interactions of the Au framework with the ligand heteroatoms. Upon acid treatment, 2- and 4-pyridinethiolate clusters (R = Py, 2 and 4) showed larger red shifts of the absorption and emission bands than the 3-pyridyl isomer (3), implying the involvement of the resonance structures of the SPy units. On the other hand, all regioisomers (2-4) showed large photoluminescence enhancements upon pyridine protonation. X-ray crystallographic and NMR analyses of 4 and its protonated form (4') showed that the electron-deficient pyridinium rings of 4' form π-stacks with neighbouring phenyl groups of dppp, suggesting that the orientation of the surface aromatics is a plausible factor governing the emission efficiency. These observations provide examples of successful modulation of optical properties of small gold clusters through the electronic and/or steric perturbation by the proximal organic ligands, highlighting the importance of the ligand design in the fine tuning of cluster properties directed for optical chemosensors and luminescent materials. PMID:27378218

  10. The Complete Genomic Sequence of Pepper Yellow Leaf Curl Virus (PYLCV) and Its Implications for Our Understanding of Evolution Dynamics in the Genus Polerovirus

    PubMed Central

    Dombrovsky, Aviv; Glanz, Eyal; Lachman, Oded; Sela, Noa; Doron-Faigenboim, Adi; Antignus, Yehezkel

    2013-01-01

    We determined the complete sequence and organization of the genome of a putative member of the genus Polerovirus tentatively named Pepper yellow leaf curl virus (PYLCV). PYLCV has a wider host range than Tobacco vein-distorting virus (TVDV) and has a close serological relationship with Cucurbit aphid-borne yellows virus (CABYV) (both poleroviruses). The extracted viral RNA was subjected to SOLiD next-generation sequence analysis and used as a template for reverse transcription synthesis, which was followed by PCR amplification. The ssRNA genome of PYLCV includes 6,028 nucleotides encoding six open reading frames (ORFs), which is typical of the genus Polerovirus. Comparisons of the deduced amino acid sequences of the PYLCV ORFs 2-4 and ORF5, indicate that there are high levels of similarity between these sequences to ORFs 2-4 of TVDV (84-93%) and to ORF5 of CABYV (87%). Both PYLCV and Pepper vein yellowing virus (PeVYV) contain sequences that point to a common ancestral polerovirus. The recombination breakpoint which is located at CABYV ORF3, which encodes the viral coat protein (CP), may explain the CABYV-like sequences found in the genomes of the pepper infecting viruses PYLCV and PeVYV. Two additional regions unique to PYLCV (PY1 and PY2) were identified between nucleotides 4,962 and 5,061 (ORF 5) and between positions 5,866 and 6,028 in the 3' NCR. Sequence analysis of the pepper-infecting PeVYV revealed three unique regions (Pe1-Pe3) with no similarity to other members of the genus Polerovirus. Genomic analyses of PYLCV and PeVYV suggest that the speciation of these viruses occurred through putative recombination event(s) between poleroviruses co-infecting a common host(s), resulting in the emergence of PYLCV, a novel pathogen with a wider host range. PMID:23936244

  11. The Yeast Mitochondrial RNA Polymerase and Transcription Factor Complex Catalyzes Efficient Priming of DNA Synthesis on Single-stranded DNA.

    PubMed

    Ramachandran, Aparna; Nandakumar, Divya; Deshpande, Aishwarya P; Lucas, Thomas P; R-Bhojappa, Ramanagouda; Tang, Guo-Qing; Raney, Kevin; Yin, Y Whitney; Patel, Smita S

    2016-08-01

    Primases use single-stranded (ss) DNAs as templates to synthesize short oligoribonucleotide primers that initiate lagging strand DNA synthesis or reprime DNA synthesis after replication fork collapse, but the origin of this activity in the mitochondria remains unclear. Herein, we show that the Saccharomyces cerevisiae mitochondrial RNA polymerase (Rpo41) and its transcription factor (Mtf1) is an efficient primase that initiates DNA synthesis on ssDNA coated with the yeast mitochondrial ssDNA-binding protein, Rim1. Both Rpo41 and Rpo41-Mtf1 can synthesize short and long RNAs on ssDNA template and prime DNA synthesis by the yeast mitochondrial DNA polymerase Mip1. However, the ssDNA-binding protein Rim1 severely inhibits the RNA synthesis activity of Rpo41, but not the Rpo41-Mtf1 complex, which continues to prime DNA synthesis efficiently in the presence of Rim1. We show that RNAs as short as 10-12 nt serve as primers for DNA synthesis. Characterization of the RNA-DNA products shows that Rpo41 and Rpo41-Mtf1 have slightly different priming specificity. However, both prefer to initiate with ATP from short priming sequences such as 3'-TCC, TTC, and TTT, and the consensus sequence is 3'-Pu(Py)2-3 Based on our studies, we propose that Rpo41-Mtf1 is an attractive candidate for serving as the primase to initiate lagging strand DNA synthesis during normal replication and/or to restart stalled replication from downstream ssDNA.

  12. Oxidatively Triggered Carbon-Carbon Bond Formation in Ene-amide Complexes.

    PubMed

    Jacobs, Brian P; Wolczanski, Peter T; Lobkovsky, Emil B

    2016-05-01

    Ene-amides have been explored as ligands and substrates for oxidative coupling. Treatment of CrCl2, Cl2Fe(PMe3)2, and Cl2Copy4 with 2 equiv of {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}Li afforded pseudosquare planar {η(3)-C,C,N-(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Cr (1-Cr, 78%), trigonal {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Fe(PMe3) (2-Fe, 80%), and tetrahedral {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Co(py)2 (3-Co, 91%) in very good yields. The addition of CrCl3 to 1-Cr, and FeCl3 to 2-Fe, afforded oxidatively triggered C-C bond formation as rac-2,2'-di(2,6-(i)Pr2C6H3N═)2dicyclohexane (EA2) was produced in modest yields. Various lithium ene-amides were similarly coupled, and the mechanism was assessed via stoichiometric reactions. Some ferrous compounds (e.g., 2-Fe, FeCl2) were shown to catalyze C-arylation of {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}Li with PhBr, but the reaction was variable. Structural characterizations of 1-Cr, 2-Fe, and 3-Co are reported. PMID:27064509

  13. Effect of phenyl and benzyl group in heterocyclic dithiocarbamates on the ZnS 4N chromophore: Synthesis, spectral, valence-bond parameters and single crystal X-ray structural studies on (pyridine)bis(1,2,3,4-tetrahydroquinolinedithiocarbamato)zinc(II) and (pyridine)bis(1,2,3,4-tetrahydroisoquinolinedithiocarbamato)zinc(II)

    NASA Astrophysics Data System (ADS)

    Srinivasan, N.; Thirumaran, S.; Ciattini, Samuele

    2009-03-01

    Two Zn(II)dithiocarbamates with ZnS 4N chromophores have been synthesized ([Zn(thqdtc) 2(py)] ( 1) and [Zn(thiqdtc) 2(py)] ( 2) (where thqdtc = 1,2,3,4-tetrahydroquinolinedithiocarbamate, thiqtc = 1,2,3,4-tetrahydroisoquinolinedithiocarbamate and py = pyridine)) from [Zn(thqdtc) 2] ( 3) and [Zn(thiqdtc) 2] ( 4), respectively. Their structures and properties have been characterized by IR and NMR spectra. The structures of both the complexes were determined by single crystal X-ray crystallography. The observed deshielding of the H-2 protons for 1 and 3 and H-1 and H-3 protons for 2 and 4 in the 1H NMR spectra is attributed to the drift of electrons from the nitrogen of the NR 2 group, forcing a high electron density towards sulfur via the thioureide π-system. In the 13C NMR spectra, the most important thioureide (N 13CS 2) carbon signals are observed in the region 204-207 ppm. The upfield shift of NCS 2 carbon signal for 1 (204.2 ppm) from the chemical shift value of 2 (206.9 ppm) is due to electron withdrawing resonance effect of phenyl ring thereby decreasing the double bond character in tetrahydroquinolinedithiocarbamate, whereas benzyl group in tetrahydroisoquinolinedithiocarbamate cannot participate in resonance delocalization in the same way. Single crystal X-ray structural analysis of 1 and 2 showed that the zinc atom is pentacoordinated with four sulfur atoms from the dithiocarbamate ligands and one nitrogen atom from the pyridine. VBS values support the correctness of the determined structure. The lower VBS value of 2 is due to the steric effect exerted by the thiqdtc. The phenyl and benzyl group in the heterocyclic dithiocarbamates influences the electronic properties of 1 and 2. The shift of ν C- N(thioureide) and thioureide N 13CS 2 carbon signals are correlated with the electronic effects of the dithiocarbamate ligands.

  14. Iron coordination chemistry with new ligands containing triazole and pyridine moieties. Comparison of the coordination ability of the N-donors.

    PubMed

    Ségaud, Nathalie; Rebilly, Jean-Noël; Sénéchal-David, Katell; Guillot, Régis; Billon, Laurianne; Baltaze, Jean-Pierre; Farjon, Jonathan; Reinaud, Olivia; Banse, Frédéric

    2013-01-18

    We report the synthesis, characterization, and solution chemistry of a series of new Fe(II) complexes based on the tetradentate ligand N-methyl-N,N'-bis(2-pyridyl-methyl)-1,2-diaminoethane or the pentadentate ones N,N',N'-tris(2-pyridyl-methyl)-1,2-diaminoethane and N,N',N'-tris(2-pyridyl-methyl)-1,3-diaminopropane, modified by propynyl or methoxyphenyltriazolyl groups on the amino functions. Six of these complexes are characterized by X-ray crystallography. In particular, two of them exhibit an hexadentate coordination environment around Fe(II) with two amino, three pyridyl, and one triazolyl groups. UV-visible and cyclic voltammetry experiments of acetonitrile solutions of the complexes allow to deduce accurately the structure of all Fe(II) species in equilibrium. The stability of the complexes could be ranked as follows: [L(5)Fe(II)-py](2+) > [L(5)Fe(II)-Cl](+) > [L(5)Fe(II)-triazolyl](2+) > [L(5)Fe(II)-(NCMe)](2+), where L(5) designates a pentadentate coordination sphere composed of the two amines of ethanediamine and three pyridines. For complexes based on propanediamine, the hierarchy determined is [L(5)Fe(II)-Cl](+) > [L(5)Fe(II)(OTf)](+) > [L(5)Fe(II)-(NCMe)](2+), and no ligand exchange could be evidenced for [L(5)Fe(II)-triazolyl](2+). Reactivity of the [L(5)Fe(II)-triazolyl](2+) complexes with hydrogen peroxide and PhIO is similar to the one of the parent complexes that lack this peculiar group, that is, generation of Fe(III)(OOH) and Fe(IV)(O), respectively. Accordingly, the ability of these complexes at catalyzing the oxidation of small organic molecules by these oxidants follows the tendencies of their previously reported counterparts. Noteworthy is the remarkable cyclooctene epoxidation activity by these complexes in the presence of PhIO.

  15. The complete genomic sequence of pepper yellow leaf curl virus (PYLCV) and its implications for our understanding of evolution dynamics in the genus polerovirus.

    PubMed

    Dombrovsky, Aviv; Glanz, Eyal; Lachman, Oded; Sela, Noa; Doron-Faigenboim, Adi; Antignus, Yehezkel

    2013-01-01

    We determined the complete sequence and organization of the genome of a putative member of the genus Polerovirus tentatively named Pepper yellow leaf curl virus (PYLCV). PYLCV has a wider host range than Tobacco vein-distorting virus (TVDV) and has a close serological relationship with Cucurbit aphid-borne yellows virus (CABYV) (both poleroviruses). The extracted viral RNA was subjected to SOLiD next-generation sequence analysis and used as a template for reverse transcription synthesis, which was followed by PCR amplification. The ssRNA genome of PYLCV includes 6,028 nucleotides encoding six open reading frames (ORFs), which is typical of the genus Polerovirus. Comparisons of the deduced amino acid sequences of the PYLCV ORFs 2-4 and ORF5, indicate that there are high levels of similarity between these sequences to ORFs 2-4 of TVDV (84-93%) and to ORF5 of CABYV (87%). Both PYLCV and Pepper vein yellowing virus (PeVYV) contain sequences that point to a common ancestral polerovirus. The recombination breakpoint which is located at CABYV ORF3, which encodes the viral coat protein (CP), may explain the CABYV-like sequences found in the genomes of the pepper infecting viruses PYLCV and PeVYV. Two additional regions unique to PYLCV (PY1 and PY2) were identified between nucleotides 4,962 and 5,061 (ORF 5) and between positions 5,866 and 6,028 in the 3' NCR. Sequence analysis of the pepper-infecting PeVYV revealed three unique regions (Pe1-Pe3) with no similarity to other members of the genus Polerovirus. Genomic analyses of PYLCV and PeVYV suggest that the speciation of these viruses occurred through putative recombination event(s) between poleroviruses co-infecting a common host(s), resulting in the emergence of PYLCV, a novel pathogen with a wider host range. PMID:23936244

  16. A mixture of mantle and crustal derived He-Ar-C-S ore-forming fluids at the Baogutu reduced porphyry Cu deposit, western Junggar

    NASA Astrophysics Data System (ADS)

    Cao, MingJian; Qin, KeZhang; Li, GuangMing; Evans, Noreen J.; He, HuaiYu; Jin, LuYing

    2015-02-01

    Most large to huge porphyry Cu deposits (PCDs) are oxidized, making the Baogutu reduced porphyry Cu deposit (RPCD) a relative rarity. CH4-bearing ore-forming fluids formed at several hydrothermal stages, however, their source is still unclear. To address this issue, isotopic investigations of sulfide He-Ar-S and calcite C were conducted. Fluid inclusions hosted in sulfides (arsenopyrite, chalcopyrite and pyrite) showed 3He/4He ratios of 0.06-0.30 Ra (Ra is the 3He/4He ratio of air = 1.39 × 10-6), 40Ar/36Ar of 311-405, 40Ar∗/4He of 0.06-1.01, and F4He ratios of 902-11,074 (sample BGT-Py 2 yielded a ratio of 100), indicating a predominantly crustal source for the fluids with minor mantle input (less than 5%). The δ13C values of carbonate yielded a value of -7.8‰ (n = 3), implying that CO2 was probably sourced from mantle or juvenile lower crust. According to the restricted sulfide δ34S values, the total S isotopic composition of the hydrothermal system was estimated to be 0.0-0.5‰, suggesting that the sulfur was derived from mantle or lower crust magmatic source. According to the published granitoids Nd isotopic compositions at the Baogutu RPCD, fairly young TDM model ages (450-650 Ma) suggest that the granitoids were derived from partial melting of a juvenile basaltic lower crust. Thus, we propose that small proportion of mantle-derived fluids (less than 5%), probably rise up and then mix with the fluids of juvenile lower crust under an extensional tectonic setting, forming the mantle-derived Sr-Nd-Pb-S-C but crustal He-Ar isotopic compositions.

  17. The Yeast Mitochondrial RNA Polymerase and Transcription Factor Complex Catalyzes Efficient Priming of DNA Synthesis on Single-stranded DNA.

    PubMed

    Ramachandran, Aparna; Nandakumar, Divya; Deshpande, Aishwarya P; Lucas, Thomas P; R-Bhojappa, Ramanagouda; Tang, Guo-Qing; Raney, Kevin; Yin, Y Whitney; Patel, Smita S

    2016-08-01

    Primases use single-stranded (ss) DNAs as templates to synthesize short oligoribonucleotide primers that initiate lagging strand DNA synthesis or reprime DNA synthesis after replication fork collapse, but the origin of this activity in the mitochondria remains unclear. Herein, we show that the Saccharomyces cerevisiae mitochondrial RNA polymerase (Rpo41) and its transcription factor (Mtf1) is an efficient primase that initiates DNA synthesis on ssDNA coated with the yeast mitochondrial ssDNA-binding protein, Rim1. Both Rpo41 and Rpo41-Mtf1 can synthesize short and long RNAs on ssDNA template and prime DNA synthesis by the yeast mitochondrial DNA polymerase Mip1. However, the ssDNA-binding protein Rim1 severely inhibits the RNA synthesis activity of Rpo41, but not the Rpo41-Mtf1 complex, which continues to prime DNA synthesis efficiently in the presence of Rim1. We show that RNAs as short as 10-12 nt serve as primers for DNA synthesis. Characterization of the RNA-DNA products shows that Rpo41 and Rpo41-Mtf1 have slightly different priming specificity. However, both prefer to initiate with ATP from short priming sequences such as 3'-TCC, TTC, and TTT, and the consensus sequence is 3'-Pu(Py)2-3 Based on our studies, we propose that Rpo41-Mtf1 is an attractive candidate for serving as the primase to initiate lagging strand DNA synthesis during normal replication and/or to restart stalled replication from downstream ssDNA. PMID:27311715

  18. Trinuclear ruthenium clusters as bivalent electrochemical probes for ligand-receptor binding interactions.

    PubMed

    Feld, Daniel J; Hsu, Hsiao-Tieh; Eckermann, Amanda L; Meade, Thomas J

    2012-01-10

    Despite their popularity, electrochemical biosensors often suffer from low sensitivity. One possible approach to overcome low sensitivity in protein biosensors is to utilize multivalent ligand-receptor interactions. Controlling the spatial arrangement of ligands on surfaces is another crucial aspect of electrochemical biosensor design. We have synthesized and characterized five biotinylated trinuclear ruthenium clusters as potential new biosensor platforms: [Ru(3)O(OAc)(6)CO(4-BMP)(py)](0) (3), [Ru(3)O(OAc)(6)CO(4-BMP)(2)](0) (4), [Ru(3)O(OAc)(6)L(4-BMP)(py)](+) (8), [Ru(3)O(OAc)(6)L(4-BMP)(2)](+) (9), and [Ru(3)O(OAc)(6)L(py)(2)](+) (10) (OAc = acetate, 4-BMP = biotin aminomethylpyridine, py = pyridine, L = pyC16SH). HABA/avidin assays and isothermal titration calorimetry were used to evaluate the avidin binding properties of 3 and 4. The binding constants were found to range from (6.5-8.0) × 10(6) M(-1). Intermolecular protein binding of 4 in solution was determined by native gel electrophoresis. QM, MM, and MD calculations show the capability for the bivalent cluster, 4, to intramolecularly bind to avidin. Electrochemical measurements in solution of 3a and 4a show shifts in E(1/2) of -58 and -53 mV in the presence of avidin, respectively. Self-assembled monolayers formed with 8-10 were investigated as a model biosensor system. Diluent/cluster ratio and composition were found to have a significant effect on the ability of avidin to adequately bind to the cluster. Complexes 8 and 10 showed negligible changes in E(1/2), while complex 9 showed a shift in E(1/2) of -43 mV upon avidin addition. These results suggest that multivalent interactions can have a positive impact on the sensitivity of electrochemical protein biosensors.

  19. Synthesis and characterization of a series of Group 4 phenoxy-thiol derivatives

    DOE PAGESBeta

    Boyle, Timothy J.; Neville, Michael L.; Parkes, Marie V.

    2016-02-11

    In this study, a series of Group 4 phenoxy-thiols were developed from the reaction products of a series of metal tert-butoxides ([M(OBut)4]) with four equivalents of 4-mercaptophenol (H-4MP). The products were found by single crystal X-ray diffraction to adopt the general structure [(HOBut)(4MP)3M(μ-4MP)]2 [where M = Ti (1), Zr (2), Hf (3)] from toluene and [(py)2M(4MP)] where M = Ti (4), Zr (5) and [(py)(4MP)3Hf(μ-4MP)]2 (6) from pyridine (py). Varying the [Ti(OR)4] precursors (OR = iso-propoxide (OPri) or neo-pentoxide (ONep)) in toluene led to [(HOR)(4MP)3Ti(μ-4MP)]2 (OR = OPri (7), ONep (8)), which were structurally similar to 1. Lower stoichiometric reactionsmore » in toluene led to partial substitution by the 4MP ligands yielding [H][Ti(μ-4MP)(4MP)(ONep)3]2 (9). Independent of the stoichiometry, all of the Ti derivatives were found to be red in color, whereas the heavier congeners were colorless. Attempts to understand this phenomenon led to investigation with a series of varied –SH substituted phenols. From the reaction of H-2MP and H-3MP (2-mercaptophenol and 3-mercaptophenol, respectively), the isolated products had identical arrangements: [(ONep)2(2MP)Ti(μ,η2-2MP)]2 (10) and [(HOR)(3MP)M(μ-3MP)]2 (M/OR = Ti/ONep (11); Zr/OBut (12)) with a similar red color. Based on the simulated and observed UV–Vis spectra, it was reasoned that the color was generated due to a ligand-to-metal charge transfer for Ti that was not available for the larger congeners.« less

  20. High Performance Discharges in the Lithium Tokamak eXperiment (LTX) with Liquid Lithium Walls

    NASA Astrophysics Data System (ADS)

    Schmitt, John

    2014-10-01

    The possibility of a liquid metal first wall for a fusion reactor has been extensively discussed. Small-area liquid lithium limiters and divertor targets have been installed in tokamaks, but no confinement device has ever operated with a large-area liquid lithium wall. Here we report the first-ever successful operation of a tokamak with a large area (2 m2, or 40% of the total plasma surface area) liquid lithium wall in the Lithium Tokamak eXperiment (LTX). These results were obtained with a new, electron beam-based lithium evaporation system, which can deposit a lithium coating on the hot (300 C) wall of LTX in a five-minute period. Preliminary analyses of diamagnetic and other data for discharges operated with a liquid lithium wall indicate that confinement times increased by 10 × compared to discharges with helium-dispersed solid lithium coatings. Ohmic confinement times exceeded ITER98P(y,2) scaling by up to a factor of four. LTX lacks auxiliary heating, so these confinement improvements represent changes in electron confinement. Spectroscopic analysis of the discharges using the John Hopkins University transmission grating extreme ultraviolet spectrometer indicates that oxygen levels in the discharges run against liquid walls were significantly reduced compared to discharges operated against solid lithium walls. This differs strongly from earlier trials of molten lithium walls in LTX, which showed evidence for strong oxygen influx from walls operated at similar temperatures. At present, the Thomson scattering system is undergoing upgrades and realignment, after which confinement times obtained with magnetic diagnostics will be compared with kinetic measurements. A second electron beam will be installed to extend liquid lithium wall operation to 4 m2 coverage, or >80% of the total plasma surface area. Results with expanded liquid lithium wall area will be presented. Supported by US DOE Contracts DE-AC02-09CH11466 and DE-AC52-07NA27344.

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

    PubMed

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

    2014-11-01

    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

  2. Nitrate-Dependent Degradation of Acetone by Alicycliphilus and Paracoccus Strains and Comparison of Acetone Carboxylase Enzymes ▿

    PubMed Central

    Dullius, Carlos Henrique; Chen, Ching-Yuan; Schink, Bernhard

    2011-01-01

    A novel acetone-degrading, nitrate-reducing bacterium, strain KN Bun08, was isolated from an enrichment culture with butanone and nitrate as the sole sources of carbon and energy. The cells were motile short rods, 0.5 to 1 by 1 to 2 μm in size, which gave Gram-positive staining results in the exponential growth phase and Gram-negative staining results in the stationary-growth phase. Based on 16S rRNA gene sequence analysis, the isolate was assigned to the genus Alicycliphilus. Besides butanone and acetone, the strain used numerous fatty acids as substrates. An ATP-dependent acetone-carboxylating enzyme was enriched from cell extracts of this bacterium and of Alicycliphilus denitrificans K601T by two subsequent DEAE Sepharose column procedures. For comparison, acetone carboxylases were enriched from two additional nitrate-reducing bacterial species, Paracoccus denitrificans and P. pantotrophus. The products of the carboxylase reaction were acetoacetate and AMP rather than ADP. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of cell extracts and of the various enzyme preparations revealed bands corresponding to molecular masses of 85, 78, and 20 kDa, suggesting similarities to the acetone carboxylase enzymes described in detail for the aerobic bacterium Xanthobacter autotrophicus strain Py2 (85.3, 78.3, and 19.6 kDa) and the phototrophic bacterium Rhodobacter capsulatus. Protein bands were excised and compared by mass spectrometry with those of acetone carboxylases of aerobic bacteria. The results document the finding that the nitrate-reducing bacteria studied here use acetone-carboxylating enzymes similar to those of aerobic and phototrophic bacteria. PMID:21841031

  3. Postsynthetic modifications of [2,2,2-(H)(PPh3)2-closo-2,1-RhSB8H8] with Lewis bases: cluster modular tuning.

    PubMed

    Luaces, Susana; Passarelli, Vincenzo; Artigas, María José; Lahoz, Fernando J; Oro, Luis A; Macías, Ramón

    2016-05-17

    It has been demonstrated that the reaction of [2,2,2-(H)(PPh3)2-closo-2,1-RhSB8H8] () with PPh3 affords the boron substituted rhodathiaborane-PPh3 adduct, [6,6-(PPh3)2-9-(PPh3)-arachno-6,5-RhSB8H9] (). Building upon this reaction, we report herein that the 10-vertex hydridorhodathiaborane reacts with the Lewis bases, PCy3, py, 2-Mepy, 2-Etpy, 3-Mepy and 4-Mepy to form the rhodathiaborane-ligand adducts, [6,6-(PPh3)2-9-(L)-arachno-6,5-RhSB8H9], where L = PCy3 (), 2-Mepy (), 2-Etpy (), py (), 3-Mepy () or 4-Mepy (), and [8,9-μ-(H)-9-(PPh3)2-8-(L)-arachno-9,6-RhSB8H8], where L = py (), 3-Mepy () or 4-Mepy (). The selectivity of the reactions depended on the nature of the entering Lewis bases, affording the 6,5-isomers, , , and as single products for PPh3, PCy3, 2-Mepy and 2-Etpy; and mixtures of the 6,5-/9,6-regioisomers, /, / and / for py, 3-Mepy and 4-Mepy, respectively. The molecular structures of both regioisomers were characterized by X-ray diffraction analysis for the 6,5-isomers, and , and for the 9,6-isomers, and . Variable temperature NMR studies of the reaction between and PPh3 or 2-Mepy demonstrated that at low temperatures there is formation of the 9,6-species that subsequently isomerizes to the 6,5-regioisomer, indicating that for the more sterically hindered Lewis bases, PPh3, 2-Mepy and PCy3, the latter isomer is more stable and accessible through an intramolecular {Rh(PPh3)2} vertex flip. The formation of both isomers with py, 3-Mepy and 4-Mepy indicates that the kinetic and thermodynamic energies of the 6,5 and 9,6 rhodathiaborane-ligand adducts are similar for these Lewis bases. Lewis base bonding to exo-polyhedral boron vertices results in a change of the metal coordination from pseudo-octahedral Rh(iii) in to pseudo-square planar Rh(i) in the adducts. The chemistry described here highlights the remarkable structural flexibility of these polyhedral boron-containing compounds, their modular architecture and their easy postsynthetic modification.

  4. Supramolecular tetrad featuring covalently linked bis(porphyrin)-phthalocyanine coordinated to fullerene: construction and photochemical studies.

    PubMed

    K C, Chandra B; Lim, Gary N; Karr, Paul A; D'Souza, Francis

    2014-06-16

    (CR), for the (ZnP-ZnP)-ZnPc(⋅+):Py2C60(⋅-) radical ion pair (from the time profile of 849 nm peak) were found to be 2.20×10(11) and 6.10×10(8) s(-1) in toluene, and 6.82×10(11) and 1.20×10(9) s(-1) in o-dichlorobenzene, respectively. These results revealed efficient energy transfer followed by charge separation in the newly assembled supramolecular tetrad.

  5. Two Polymorphic Forms of a Six-Coordinate Mononuclear Cobalt(II) Complex with Easy-Plane Anisotropy: Structural Features, Theoretical Calculations, and Field-Induced Slow Relaxation of the Magnetization.

    PubMed

    Roy, Subhadip; Oyarzabal, Itziar; Vallejo, Julia; Cano, Joan; Colacio, Enrique; Bauza, Antonio; Frontera, Antonio; Kirillov, Alexander M; Drew, Michael G B; Das, Subrata

    2016-09-01

    A mononuclear cobalt(II) complex [Co(3,5-dnb)2(py)2(H2O)2] {3,5-Hdnb = 3,5-dinitrobenzoic acid; py = pyridine} was isolated in two polymorphs, in space groups C2/c (1) and P21/c (2). Single-crystal X-ray diffraction analyses reveal that 1 and 2 are not isostructural in spite of having equal formulas and ligand connectivity. In both structures, the Co(II) centers adopt octahedral {CoN2O4} geometries filled by pairs of mutually trans terminal 3,5-dnb, py, and water ligands. However, the structures of 1 and 2 disclose distinct packing patterns driven by strong intermolecular O-H···O hydrogen bonds, leading to their 0D→2D (1) or 0D→1D (2) extension. The resulting two-dimensional layers and one-dimensional chains were topologically classified as the sql and 2C1 underlying nets, respectively. By means of DFT theoretical calculations, the energy variations between the polymorphs were estimated, and the binding energies associated with the noncovalent interactions observed in the crystal structures were also evaluated. The study of the direct-current magnetic properties, as well as ab initio calculations, reveal that both 1 and 2 present a strong easy-plane magnetic anisotropy (D > 0), which is larger for the latter polymorph (D is found to exhibit values between +58 and 117 cm(-1) depending on the method). Alternating current dynamic susceptibility measurements show that these polymorphs exhibit field-induced slow relaxation of the magnetization with Ueff values of 19.5 and 21.1 cm(-1) for 1 and 2, respectively. The analysis of the whole magnetic data allows the conclusion that the magnetization relaxation in these polymorphs mainly takes place through a virtual excited state (Raman process). It is worth noting that despite the notable difference between the supramolecular networks of 1 and 2, they exhibit almost identical magnetization dynamics. This fact suggests that the relaxation process is intramolecular in nature and that the virtual state involved in the

  6. Intramolecular Gas Phase Reactions of Synthetic Non-heme Oxoiron(IV) Ions: Proximity and Spin-State Reactivity Rules

    PubMed Central

    Mas-Ballesté, Rubén; McDonald, Aidan R.; Reed, Dana; Usharani, Dandamudi; Schyman, Patric; Milko, Petr

    2012-01-01

    The intramolecular gas phase reactivity of four oxoiron(IV) complexes supported by tetradentate N4 ligands (L) has been studied by means of tandem mass spectrometry measurements where the gas-phase ions [FeIV(O)(L)(OTf)]+ and [FeIV(O)(L)]2+ were isolated and then allowed to fragment by collision-induced decay (CID). CID fragmentation of cations derived from oxoiron(IV) complexes of TMC (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and L8Py2 (N,N’-bis(2-pyridylmethyl)-1,5-diazacyclooctane) afforded the same predominant products irrespective of whether they were hexacoordinate or pentacoordinate. These products resulted from the loss of water by dehydrogenation of ethylene or propylene linkers on the tetradentate ligand. In contrast, CID fragmentation of ions derived from oxoiron(IV) complexes of linear tetradentate ligands BPMEN (N,N’-bis(2-pyridylmethyl)-1,2-diaminoethane) and BPMPN (N,N’-bis(2-pyridylmethyl)-1,3-diaminopropane) showed predominant oxidative N-dealkylation for the hexacoordinate [FeIV(O)(L)(OTf)]+ cations and predominant dehydrogenation of the diaminoethane/propane backbone for the pentacoordinate [FeIV(O)(L)]2+ cations. DFT calculations on [FeIV(O)(BPMEN)] ions showed that the experimentally observed preference for oxidative N-dealkylation versus dehydrogenation of the diaminoethane linker for the hexa- and pentacoordinate ions, respectively, is dictated by the proximity of the target C–H bond to the oxoiron(IV) moiety and the reactive spin state. Therefore, there must be a difference in ligand topology between the two ions. More importantly, despite the constraints on the geometries of the TSs that prohibit the usual upright σ-trajectory and prevent optimal σCH-σ*z2 overlap, all the reactions still proceed preferentially on the quintet (S = 2) state surface, which increases the number of exchange interactions in the d-block of iron and leads thereby to exchange enhanced reactivity (EER). As such, EER is responsible for the

  7. Theoretical studies on two-dimensional nonlinear optical chromophores with pyrazinyl cores and organic or ruthenium(II) ammine electron donors.

    PubMed

    Coe, Benjamin J; Pilkington, Rachel A

    2014-03-27

    Density functional theory calculations have been carried out on twelve cationic, 2D nonlinear optical chromophores with pyrazinylbis(pyridinium) electron acceptors. These species contain either 4-(methoxy/dimethylamino)phenyl or pyridyl-coordinated {Ru(II)(NH3)5}(2+)/trans-{Ru(II)(NH3)4(py)}(2+) (py = pyridine) electron donor groups. The results are compared with data obtained by using experimental techniques including hyper-Rayleigh scattering and Stark (electroabsorption) spectroscopy previously (Coe, B. J.; et al. Inorg. Chem. 2010, 49, 10718; J. Org. Chem. 2010, 75, 8550). The B3LYP/6-311G(d) level of theory models the visible absorption spectra in MeCN for the -NMe2 derivatives relatively well, whereas CAM-B3LYP/6-311G(d) gives better results for the -OMe-substituted species. These spectra are dominated by intramolecular charge-transfer (ICT) bands. Static first hyperpolarizabilities β0 are computed also at the B3LYP/6-311G(d) level. The overall extent of prediction of trends in the ICT bands and β0 responses is partial, with the main discrepancies relating to the progression from one to two electron donor groups. The experimental data show that this structural change red-shifts the ICT bands and increases β0 significantly, but only the second trend is reproduced to some extent by the calculations. The UV-vis absorption spectra of the Ru complexes in MeCN are modeled relatively well with B3LYP and the LANL2DZ/6-311G(d) mixed basis set, including 100 excited states. However, again, some degree of disagreement between theory and experiment is evident, even when a larger basis set like def2-TZVP is used for Ru. In particular, substantial red shifts are predicted on adding a third metal center, whereas the measured spectra show corresponding small blue shifts. The experimental trend of the total β0 value increasing on moving from one to two Ru centers is predicted in the gas phase, but not in MeCN. For both classes of chromophore, the β(xxx) tensor component

  8. Intramolecular gas-phase reactions of synthetic nonheme oxoiron(IV) ions: proximity and spin-state reactivity rules.

    PubMed

    Mas-Ballesté, Rubén; McDonald, Aidan R; Reed, Dana; Usharani, Dandamudi; Schyman, Patric; Milko, Petr; Shaik, Sason; Que, Lawrence

    2012-09-10

    The intramolecular gas-phase reactivity of four oxoiron(IV) complexes supported by tetradentate N(4) ligands (L) has been studied by means of tandem mass spectrometry measurements in which the gas-phase ions [Fe(IV)(O)(L)(OTf)](+) (OTf = trifluoromethanesulfonate) and [Fe(IV) (O)(L)](2+) were isolated and then allowed to fragment by collision-induced decay (CID). CID fragmentation of cations derived from oxoiron(IV) complexes of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmc) and N,N'-bis(2-pyridylmethyl)-1,5-diazacyclooctane (L(8)Py(2)) afforded the same predominant products irrespective of whether they were hexacoordinate or pentacoordinate. These products resulted from the loss of water by dehydrogenation of ethylene or propylene linkers on the tetradentate ligand. In contrast, CID fragmentation of ions derived from oxoiron(IV) complexes of linear tetradentate ligands N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane (bpmen) and N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane (bpmpn) showed predominant oxidative N-dealkylation for the hexacoordinate [Fe(IV)(O)(L)(OTf)](+) cations and predominant dehydrogenation of the diaminoethane/propane backbone for the pentacoordinate [Fe(IV)(O)(L)](2+) cations. DFT calculations on [Fe(IV)(O)(bpmen)] ions showed that the experimentally observed preference for oxidative N-dealkylation versus dehydrogenation of the diaminoethane linker for the hexa- and pentacoordinate ions, respectively, is dictated by the proximity of the target C-H bond to the oxoiron(IV) moiety and the reactive spin state. Therefore, there must be a difference in ligand topology between the two ions. More importantly, despite the constraints on the geometries of the TS that prohibit the usual upright σ trajectory and prevent optimal σ(CH)-σ*(z2) overlap, all the reactions still proceed preferentially on the quintet (S = 2) state surface, which increases the number of exchange interactions in the d block of iron and leads thereby to exchange enhanced

  9. Smoking and mortality after breast cancer diagnosis: the health and functioning in women study.

    PubMed

    Izano, Monika; Satariano, William A; Hiatt, Robert A; Braithwaite, Dejana

    2015-02-01

    We examined the effect of smoking on long-term mortality from breast cancer and other causes among a cohort of women with breast cancer. A total of 975 women diagnosed with breast cancer and aged 40-84 years were followed for a median follow-up of 11 years in the U.S. Health and Functioning in Women (HFW) study. The impact of the individual smoking status and smoking intensity reported in the first few months following breast cancer diagnosis on the risk of mortality from breast cancer and other causes was examined using Cox proportional hazards models. In this study, former smoking was associated with increased risk of other-cause mortality (hazard ratio [HR] = 1.47, 95% confidence interval [CI]: 1.13-1.90), and the risk doubled with increased intensity (HR for <50 pack-years [py]: 1.36, 95% CI: 1.03-1.79; HR for ≥50 py: 2.45, 95% CI: 1.41-4.23). Current smoking (HR = 2.45, 95% CI: 1.81-3.32) and each additional 10 py smoked (HR = 1.16, 95% CI: 1.11-1.22) were associated with statistically significant increases in the risk of other-cause mortality. The effect of current smoking on other-cause mortality decreased with advancing stage and increasing body mass index (BMI). Breast cancer-specific mortality was associated with current smoking of ≥50 py (HR = 2.36, 95% CI: 1.26-4.44), and each additional 10 py smoked (HR = 1.07, 95% CI: 1.01-1. 14). Current smoking, but not former smoking, was associated with increased risk of breast cancer-specific mortality in women with local disease (HR = 2.32, 95% CI: 1.32-4.09), but not in those with regional and distant disease (HR = 1.10, 95% CI: 0.73-1.68). Our findings suggest that current smoking at the time of breast cancer diagnosis may be associated with increased risk of breast-cancer specific and other-cause mortality, whereas former smoking is associated with increased risk of other-cause mortality. Smoking cessation at the time of diagnosis may lead to better prognosis among women with breast cancer.

  10. Dioxygen-Initiated Oxidation of Heteroatomic Substrates Incorporated into Ancillary Pyridine Ligands of Carboxylate-Rich Diiron(II) Complexes

    PubMed Central

    Carson, Emily C.; Lippard, Stephen J.

    2008-01-01

    Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Thiol, sulfide, sulfoxide, and phosphine moieties incorporated into a pyridine ligand were allowed to react with the preassembled diiron(II) complex [Fe2(μ-O2CArR)2(O2CArR)2(THF)2], where -O2CArR is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). The resulting diiron(II) complexes were characterized crystallographically. Triply- and doubly-bridged compounds [Fe2(μ-O2CArTol)3(O2CArTol)(2-MeSpy)] (4) and [Fe2(μ-O2CArTol)2(O2CArTol)2(2-MeS(O)py)2] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS(O)py), respectively, were employed. Another triply-bridged diiron(II) complex, [Fe2(μ-O2CAr4-FPh)3(O2CAr4-FPh)(2-Ph2Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph2Ppy). Use of 2-mercaptopyridine (2-HSpy) afforded the mononuclear complex [Fe(O2CArTol)2(2-HSpy)2] (6a). Together with that of previously reported [Fe2(μ-O2CArTol)3(O2CArTol)(2-PhSpy)] (2) and [Fe2(μ-O2CArTol)3(O2CArTol)(2-Ph2Ppy)] (1), the dioxygen reactivity of these iron(II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O2, the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH2Cl2 affords [Fe2(μ-OH)2(μ-O2CAr4-FPh)(O2CAr4-FPh)3(OH2)(2-Ph2P(O)py)] (8), which contains the biologically relevant {Fe2(μ-OH)2(μ-O2CR)}3+ core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analog 1 yielded a hexanuclear species, 7, upon oxidation. PMID:16411722

  11. Vanadium bisimide bonding investigated by X-ray crystallography, 51V and 13C nuclear magnetic resonance spectroscopy, and V L(3,2)-edge X-ray absorption near-edge structure spectroscopy.

    PubMed

    La Pierre, Henry S; Minasian, Stefan G; Abubekerov, Mark; Kozimor, Stosh A; Shuh, David K; Tyliszczak, Tolek; Arnold, John; Bergman, Robert G; Toste, F Dean

    2013-10-01

    Syntheses of neutral halide and aryl vanadium bisimides are described. Treatment of VCl2(NtBu)[NTMS(N(t)Bu)], 2, with PMe3, PEt3, PMe2Ph, or pyridine gave vanadium bisimides via TMSCl elimination in good yield: VCl(PMe3)2(N(t)Bu)2 3, VCl(PEt3)2(N(t)Bu)2 4, VCl(PMe2Ph)2(N(t)Bu)2 5, and VCl(Py)2(N(t)Bu)2 6. The halide series (Cl-I) was synthesized by use of TMSBr and TMSI to give VBr(PMe3)2(N(t)Bu)2 7 and VI(PMe3)2(N(t)Bu)2 8. The phenyl derivative was obtained by reaction of 3 with MgPh2 to give VPh(PMe3)2(N(t)Bu)2 9. These neutral complexes are compared to the previously reported cationic bisimides [V(PMe3)3(N(t)Bu)2][Al(PFTB)4] 10, [V(PEt3)2(N(t)Bu)2][Al(PFTB)4] 11, and [V(DMAP)(PEt3)2(N(t)Bu)2][Al(PFTB)4] 12 (DMAP = dimethylaminopyridine, PFTB = perfluoro-tert-butoxide). Characterization of the complexes by X-ray diffraction, (13)C NMR, (51)V NMR, and V L(3,2)-edge X-ray absorption near-edge structure (XANES) spectroscopy provides a description of the electronic structure in comparison to group 6 bisimides and the bent metallocene analogues. The electronic structure is dominated by π bonding to the imides, and localization of electron density at the nitrogen atoms of the imides is dictated by the cone angle and donating ability of the axial neutral supporting ligands. This phenomenon is clearly seen in the sensitivity of (51)V NMR shift, (13)C NMR Δδ(αβ), and L3-edge energy to the nature of the supporting phosphine ligand, which defines the parameters for designing cationic group 5 bisimides that would be capable of breaking stronger σ bonds. Conversely, all three methods show little dependence on the variable equatorial halide ligand. Furthermore, this analysis allows for quantification of the electronic differences between vanadium bisimides and the structurally analogous mixed Cp/imide system CpV(N(t)Bu)X2 (Cp = C5H5(1-)). PMID:24024833

  12. Roles of the redox-active disulfide and histidine residues forming a catalytic dyad in reactions catalyzed by 2-ketopropyl coenzyme M oxidoreductase/carboxylase.

    PubMed

    Kofoed, Melissa A; Wampler, David A; Pandey, Arti S; Peters, John W; Ensign, Scott A

    2011-09-01

    NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase (2-KPCC), an atypical member of the disulfide oxidoreductase (DSOR) family of enzymes, catalyzes the reductive cleavage and carboxylation of 2-ketopropyl-coenzyme M [2-(2-ketopropylthio)ethanesulfonate; 2-KPC] to form acetoacetate and coenzyme M (CoM) in the bacterial pathway of propylene metabolism. Structural studies of 2-KPCC from Xanthobacter autotrophicus strain Py2 have revealed a distinctive active-site architecture that includes a putative catalytic triad consisting of two histidine residues that are hydrogen bonded to an ordered water molecule proposed to stabilize enolacetone formed from dithiol-mediated 2-KPC thioether bond cleavage. Site-directed mutants of 2-KPCC were constructed to test the tenets of the mechanism proposed from studies of the native enzyme. Mutagenesis of the interchange thiol of 2-KPCC (C82A) abolished all redox-dependent reactions of 2-KPCC (2-KPC carboxylation or protonation). The air-oxidized C82A mutant, as well as wild-type 2-KPCC, exhibited the characteristic charge transfer absorbance seen in site-directed variants of other DSOR enzymes but with a pK(a) value for C87 (8.8) four units higher (i.e., four orders of magnitude less acidic) than that for the flavin thiol of canonical DSOR enzymes. The same higher pK(a) value was observed in native 2-KPCC when the interchange thiol was alkylated by the CoM analog 2-bromoethanesulfonate. Mutagenesis of the flavin thiol (C87A) also resulted in an inactive enzyme for steady-state redox-dependent reactions, but this variant catalyzed a single-turnover reaction producing a 0.8:1 ratio of product to enzyme. Mutagenesis of the histidine proximal to the ordered water (H137A) led to nearly complete loss of redox-dependent 2-KPCC reactions, while mutagenesis of the distal histidine (H84A) reduced these activities by 58 to 76%. A redox-independent reaction of 2-KPCC (acetoacetate decarboxylation) was not decreased for any of the

  13. Compatibility of grain-stabilized platinum with candidate propellants for resistojets

    NASA Technical Reports Server (NTRS)

    Whalen, M. V.; Grisnik, S. P.

    1985-01-01

    Resistojets are candidates for space station auxiliary propulsion, and should be characterized by both long life and multipropellant operations, requirements limited by available materials. Grain stabilized platinum is examined for use as a resistojet thruster material. Use of platinum in other applications indicates it can be used at moderately high temperatures for extended periods of time. Past results indicate that grain-stabilized platinum should be sufficiently inert in candidate propellant environments. Therefore, compatibility of platinum-yttria (P/Y2O3) and platinum-zirconia (Pt/ZrO2) with carbon dioxide, methane, hydrogen and ammonia is examined. A series of 1000 hr tests in CO2, H2, and NH3 is conducted at 1400 C and a series of 1000 hr tests in CH4 is conducted at about 500 C. Scanning electron microscopy, Auger electron spectroscopy and depth profiling analysis are then used to determine the effects of propellants on the material surface, to evaluate possible material contamination and to evaluate grain growth. The results indicate that there is carbon deposition on the surface of the Pt/Y2O3 and Pt/ZrO2 in both the CO2 and CH4 environments. In the H2 environment, the Pt/Y2O3 and Pt/ZrO2 specimen surfaces are roughened. After exposure to the NH3 environment, the Pt/Y2O3 and Pt/ZrO2 are roughened and pitted over the entire heated area with some pitted areas along the grain boundaries. SEM photos show grain growth in cross-sectional views of all the Pt/Y2O3 samples and the Pt/ZrO2 samples, except that tested in methane. Mass loss measurements indicate that Pt/Y2O3 and Pt/ZrO2 would last in excess of 200,000 hr in each propellant environment. However, in NH3 both Pt/Y2O3 and Pt/ZrO2 are severely pitted, with voids up to 50 percent into the material. Pt/Y2O3 and Pt/ZrO2 are not recommended for high temperature service in NH3.

  14. Solvent effect-driven assembly of W/Cu/S cluster-based coordination polymers from the cluster precursor [Et4N][Tp*WS3(CuBr)3] and CuCN: isolation, structures and enhanced NLO responses.

    PubMed

    Liu, Quan; Ren, Zhi-Gang; Deng, Li; Zhang, Wen-Hua; Zhao, Xin; Sun, Zhen-Rong; Lang, Jian-Ping

    2015-01-01

    We herein describe a coordination polymer system built upon the reactions of a W/Cu/S cluster precursor [Et4N][Tp*WS3(CuBr)3] (1, Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate) with three equivalents of CuCN through solvent modulation. Four coordination polymers, namely, [Tp*WS3Cu3(μ3-DMF)(CN)3Cu(Py)] (2), [Tp*WS3Cu3(μ3-DMF)(CN)3Cu] (3), [Tp*WS3Cu3(μ3-DMF)(CN)3Cu]·4aniline (4·4aniline) and [Tp*WS3Cu3(μ3-DMF)(CN)3Cu]·2(DMF)0.5 (5·2(DMF)0.5), are isolated in different solvent systems and characterized by means of elemental analysis, FT-IR, UV-Vis, ESI-MS and single-crystal X-ray diffraction. Compounds 2-5 feature μ3-DMF association with the nest-shaped [WS3Cu3] cluster cores, yielding cubane-type [WS3Cu3O] clusters which are further linked to single Cu(I) ions through CN bridges to provide 1D or 2D structures. Compounds 3-5 have identical chemical compositions in their main fragments but with distinctively different structural features, and are therefore topological isomers. Compound 2 has a ladder-type structure in which the side rails contain alternately linked cluster cores and Cu(I) ions. Compound 3 has a 2D (6,3) network with alternately arranged cluster cores and Cu(I) ions. Both 4 and 5 have 2D structures with 4·8(2) topology. In 4, a pair of cluster cores and Cu(I) ions form a 4-membered ring which is further linked to four equivalent rings through four CN ligands via a cluster core-to-Cu arrangement; while in the structure of 5, the same 4-membered rings as those in 4 are extended to equivalent rings via a cluster core-to-cluster and Cu-to-Cu arrangement. The hyperpolarizabilities (γ) of the polymeric networks exhibit an enhancement of more than 10 times compared to their parent cluster, 1. PMID:25353691

  15. Porphyrins as Second Order Nonlinear Optical Materials

    NASA Astrophysics Data System (ADS)

    Chou, Homer

    Because of the unusually high thermal and chemical stability of porphyrins as well as their very large pi-conjugated systems, three classes of high beta-value push-pull porphyrins were synthesized and subsequently successfully engineered into Langmuir-Blodgett (LB) films for a systematic evaluation of porphyrins as chi^{(2)} materials. Class I explored the effects of the number of donor-acceptor groups on the porphyrin periphery (i.e., H_2(an_3P), H_2 (cis-a_2n_2P), H_2(a_3nP), H _2(a_4P) where a = 4-(N-octadecylamido)phenyl or 4-(N-octadecyl-amino)phenyl; n = 4-nitrophenyl; P = 5,10,15,20 substituted tetraarylporphyrinate (2-).). Class II examined the effect of varying the strength of cis-substituted donor-acceptor pairs on the porphyrin periphery (i.e., H_2(cis-a_2n _2P), H_2(cis-c _2p_2P), and H_2 (cis-h_2py_2P) where c = 4-(2-cholesteryloxy)-ethoxyphenyl; h = 4-hydroxyphenyl or 4-methoxyphenyl; and py = 4-pyridyl or 4-(N-octadecyl) pyridiniumyl). Class III looked at the respone of a heterosubstituted bis- push-pull cerium sandwich porphyrin complex, (Ce ^{IV}(TPyP)(TMeP)) ^{4+}I_4 (where Py = 4-(N-octadecyl)pyridiniumyl and Me = 4-methoxyphenyl). Characterization of the porphyrin LB films reveals rather surprising behavior. The isotherm data show that the mean molecular area of the porphyrins increase smoothly from 80-200A as the number of aliphatic chains increase around the porphyrin periphery from one to four. In addition, based on UV-visible linear dichroism, all of the porphyrin films possess C _{infty v} symmetry and adopt a tilt angle, theta, of about 33^circ with respect to the fused quartz substrate. The proposed fixed orientation model suggests that the interporphyrin pi -pi interactions dominate the porphyrin orientation while the number of aliphatic chains around the porphyrin periphery determines the porphyrin's packing density in the LB film. After these monolayers were transferred to fused quartz substrates, the chi^{(2)} response of these

  16. Synthesis and structure of mono-, bi- and trimetallic amine-bis(phenolate) cobalt(II) complexes.

    PubMed

    Das, Uttam K; Bobak, Julia; Fowler, Candace; Hann, Sarah E; Petten, Chad F; Dawe, Louise N; Decken, Andreas; Kerton, Francesca M; Kozak, Christopher M

    2010-06-21

    A series of cobalt(ii) amine-bis(phenolate) complexes has been prepared and characterized. The protonated tripodal tetradentate ligand precursors; dimethylaminoethylamino-N,N-bis(2-methylene-4-tert-butyl-6-methylphenol), H(2)[O(2)NN'](BuMeNMe2), dimethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)[O(2)NN'](BuBuNMe2), diethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H(2)[O(2)NN'](AmAmNEt2) and 2-pyridylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H(2)[O(2)NN'](AmAmPy); were reacted with cobaltous acetate tetrahydrate under varying conditions to afford a range of monometallic, bimetallic and trimetallic species. An unusual four coordinate complex Co[O(2)NN'](AmAmNEt2) containing Co(II) in a trigonal monopyramidal environment was structurally characterized, whereas using a less sterically demanding ligand a series of five coordinate complexes Co[O(2)NN'](BuBuNMe2)(L) (L = H(2)O, CH(3)OH, (CH(3))(2)C[double bond, length as m-dash]O, propylene oxide) containing Co(II) in a trigonal bipyramidal environment was prepared. A new angular structural parameter related to tau is defined, where tau' may be used to compare complexes with trigonal monopyramidal structures. In contrast, ligands containing a pendant pyridyl donor afford dimeric species including {Co(mu-CH(3)OH)[O(2)NN'](AmAmPy)}(2). In the absence of base and in the presence of excess cobaltous acetate, trimetallic complexes were isolated containing a central Co(II) in an octahedral environment coordinated to four CH(3)OH and two bridging acetate ligands between two Co[O(2)NN'] fragments with Co(II) in a trigonal bipyramidal setting. The paramagnetic Co(II) complexes reported were also characterized by UV-vis spectroscopy, mass spectrometry, cyclic voltammetry and magnetic measurements.

  17. Two Polymorphic Forms of a Six-Coordinate Mononuclear Cobalt(II) Complex with Easy-Plane Anisotropy: Structural Features, Theoretical Calculations, and Field-Induced Slow Relaxation of the Magnetization.

    PubMed

    Roy, Subhadip; Oyarzabal, Itziar; Vallejo, Julia; Cano, Joan; Colacio, Enrique; Bauza, Antonio; Frontera, Antonio; Kirillov, Alexander M; Drew, Michael G B; Das, Subrata

    2016-09-01

    A mononuclear cobalt(II) complex [Co(3,5-dnb)2(py)2(H2O)2] {3,5-Hdnb = 3,5-dinitrobenzoic acid; py = pyridine} was isolated in two polymorphs, in space groups C2/c (1) and P21/c (2). Single-crystal X-ray diffraction analyses reveal that 1 and 2 are not isostructural in spite of having equal formulas and ligand connectivity. In both structures, the Co(II) centers adopt octahedral {CoN2O4} geometries filled by pairs of mutually trans terminal 3,5-dnb, py, and water ligands. However, the structures of 1 and 2 disclose distinct packing patterns driven by strong intermolecular O-H···O hydrogen bonds, leading to their 0D→2D (1) or 0D→1D (2) extension. The resulting two-dimensional layers and one-dimensional chains were topologically classified as the sql and 2C1 underlying nets, respectively. By means of DFT theoretical calculations, the energy variations between the polymorphs were estimated, and the binding energies associated with the noncovalent interactions observed in the crystal structures were also evaluated. The study of the direct-current magnetic properties, as well as ab initio calculations, reveal that both 1 and 2 present a strong easy-plane magnetic anisotropy (D > 0), which is larger for the latter polymorph (D is found to exhibit values between +58 and 117 cm(-1) depending on the method). Alternating current dynamic susceptibility measurements show that these polymorphs exhibit field-induced slow relaxation of the magnetization with Ueff values of 19.5 and 21.1 cm(-1) for 1 and 2, respectively. The analysis of the whole magnetic data allows the conclusion that the magnetization relaxation in these polymorphs mainly takes place through a virtual excited state (Raman process). It is worth noting that despite the notable difference between the supramolecular networks of 1 and 2, they exhibit almost identical magnetization dynamics. This fact suggests that the relaxation process is intramolecular in nature and that the virtual state involved in the

  18. Intramolecular proton transfer boosts water oxidation catalyzed by a Ru complex

    SciTech Connect

    Matheu, Roc; Ertem, Mehmed Z.; Benet-Buchholz, J.; Coronado, Eugenio; Batista, Victor S.; Sala, Xavier; Llobet, Antoni

    2015-07-30

    We introduce a new family of complexes with the general formula [Run(tda)(py)2]m+ (n = 2, m = 0, 1; n = 3, m = 1, 2+; n = 4, m = 2, 32+), with tda2– being [2,2':6',2"-terpyridine]-6,6"-dicarboxylate, including complex [RuIV(OH)(tda-κ-N3O)(py)2]+, 4H+, which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 32+ under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV–vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), including solid-state monocrystal X-ray diffraction analysis. In oxidation state IV, the Ru center is seven-coordinated and diamagnetic, whereas in oxidation state II, the complex has an unbonded dangling carboxylate and is six-coordinated while still diamagnetic. With oxidation state III, the coordination number is halfway between the coordination of oxidation states II and IV. Species generated in situ have also been characterized by spectroscopic, computational, and electrochemical techniques, together with the related species derived from a different degree of protonation and oxidation states. 4H+ can be generated potentiometrically, or voltammetrically, from 32+, and both coexist in solution. While complex 32+ is not catalytically active, the catalytic performance of complex 4H+ is characterized by the foot of the wave analysis, giving an impressive turnover frequency record of 8000 s–1 at pH 7.0 and 50,000 s–1 at pH 10.0. Density functional theory calculations provide a complete description of the water oxidation catalytic cycle of 4H+, manifesting the key functional role of the dangling carboxylate in lowering

  19. Morphological and Phase Controlled Tungsten Based Nanoparticles: Synthesis and Characterization of Scheelites, Wolframites, and Oxides Nanomaterials

    PubMed Central

    Hernandez-Sanchez, Bernadette A.; Boyle, Timothy J.; Pratt, Harry D.; Rodriguez, Mark A.; Brewer, Luke N.; Dunphy, Darren R.

    2009-01-01

    For the first time tungsten based nanoparticles (WNPs) of scheelite (MWO4; M = Ca, Sr, Ba, Pb), wolframite (MWO4; M = Mn, Fe, Zn & (Mg0.60Mn0.17Fe0.26)WO4), and the oxide (WO3 and W18O49) were synthesized from solution precipitation (i.e.,trioctylamine or oleic acid) and solvothermal (i.e., benzyl alcohol) routes. The resultant WNPs were prepared directly from tungsten (VI) ethoxide (W(OCH2CH3)6, 1) and stoichiometeric mixtures of the following precursors: [Ca(N(SiMe3)2)2]2 (2), Pb(N(SiMe3)2)2 (3), Mn[(μ-Mes)2Mn(Mes)]2 (4), [Fe(μ-Mes)(Mes)]2 (5), Fe(CO)5 (6), H+[Ba2(μ3-ONep)(μ-ONep)2(ONep)(ONep)3(py)]−2 (7), H+[Sr5(μ4-O)(μ3-ONep)4(μ-ONep)4(ONep)(py)4]− (8), and [Zn(Et)(ONep)(py)]2 (9) where Mes = C6H2(CH3)3-2,4,6, ONep = OCH2CMe3, Et = CH2CH3, and py = pyridine. Through these routes, the WNP morphologies were found to be manipulated by the processing conditions, while precursor selection influenced the final phase observed. For the solution precipitation route, 1 yielded (5 × 100 nm) W18O49 rods while stochiometeric reactions between 1 and (2 – 9) generated homogenous sub 30 nm nano-dots, -diamonds, -rods, and -wires for the MWO4 systems. For the solvothermal route, 1 was found to produce wires of WO3 with aspect ratios of 20 while (1 & 2) formed 10 – 60 nm CaWO4 nanodots. Room temperature photoluminescent (PL) emission properties of select WNPs were also examined with fluorescence spectroscopy (λex = 320 nm). Broad PL emissions = 430, 420, 395, 420 nm were noted for 5 × 100 nm W18O49 rods, 5 × 15 nm, CaWO4 rods, 10 – 30 nm CaWO4 dots, and 10 nm BaWO4 diamonds, respectively. PMID:19911034

  20. Oligo-nuclear silver thiocyanate complexes with monodentate tertiary phosphine ligands, including novel 'cubane' and 'step' tetramer forms of AgSCN : PR3 (1:1)4.

    PubMed

    Bowmaker, Graham A; Di Nicola, Corrado; Effendy; Hanna, John V; Healy, Peter C; King, Scott P; Marchetti, Fabio; Pettinari, Claudio; Robinson, Ward T; Skelton, Brian W; Sobolev, Alexandre N; Tăbăcaru, Aurel; White, Allan H

    2013-01-01

    Adducts of a number of tertiary pnicogen ligands ER(3) (triphenyl-phosphine and -arsine (PPh(3),AsPh(3)), diphenyl,2-pyridylphosphine (PPh(2)py), tris(4-fluorophenyl)phosphine (P(C(6)H(4)-4F)(3)), tris(2-tolyl)phosphine (P(o-tol)(3)), tris(cyclohexyl)phosphine (PCy(3))), with silver(I) thiocyanate, AgSCN are structurally and spectroscopically characterized. The 1:3 AgSCN : ER(3) complexes structurally defined (for PPh(3),AsPh(3) (diversely solvated)) take the form [(R(3)E)(3)AgX], the thiocyanate X = NCS being N-bound, thus [(Ph(3)E)Ag(NCS)]. A 1:2 complex with PPh(2)py, takes the binuclear form [(pyPh(2)P)(2)Ag()Ag(PPh(2)py)(2)] with an eight-membered cyclic core. 1:1 complexes are defined with PPh(2)py, P(o-tol)(3) and PCy(3); binuclear forms [(R(3)P)Ag()Ag(PR(3))] are obtained with P(o-tol)(3) (two polymorphs), while novel isomeric tetranuclear forms, which may be envisaged as dimers of dimers, are obtained with PPh(2)py, and, as further polymorphs, with PCy(3); these latter may be considered as extensions of the 'cubane' and 'step' forms previously described for [(R(3)E)AgX](4) (X = halide) complexes. Solvent-assisted mechanochemical or solvent-assisted solid-state synthesis methods were employed in some cases, where complexes could not be obtained by conventional solution methods, or where such methods yielded a mixture of polymorphs unsuitable for solid-state spectroscopy. The wavenumbers of the ν(CN) bands in the IR spectra are in broad agreement with the empirical rule that distinguishes bridging from terminal bonding, but exceptions occur for compounds that have a double SCN bridged dimeric structure, and replacement of PPh(3) with PPh(2)py apparently causes a significant decrease in ν(CN) to well below the range expected for bridging SCN in these structures. (31)P CP MAS NMR spectra yield additional parameters that allow a correlation between the structures and spectra.

  1. Hydrogen-extraction experiments on grossular

    NASA Astrophysics Data System (ADS)

    Kurka, A.; Blanchard, M.; Ingrin, J.

    2003-04-01

    Grossular generally contains the highest amount of hydrogen within the garnet-group and is a minor component in many pyrope-rich mantle garnets, despite some mantle garnets are known showing significant grossular-component. Gemmy, orange-brown colored, grossular-samples from Madagascar of composition Gr 83.2 Py 2.2 An 14.3 were used to study the hydrogen-extraction behaviour. Five doubly polished, single crystal-slices with a thickness ranging from about 350 to 500 microns were cut. The slices were heated in air at temperatures of 800^o, 900^o, 950^o, 1000^o and 1050^o C for 2 hours up to 900 hours. The hydrogen content was determined using FTIR-spectroscopy. Our material shows a spectra characteristic for grossular with about 12 absorption-bands in the OH-region. The initial OH content was determined as 0.022 wt% H_2O. The diffusion coefficients calculated using the equation proposed by Hercule &Ingrin (1999) range from 7 10-15 to 2 10-12 (m2/s) leading to an activation energy for H-extraction in grossular at about 260 kJ/mol, which is similar to that of pyrope from Dora Maira (personal communication M. Blanchard) but slightly higher than pyrope investigated by Wang et al. (1996). It should be further noticed that the extraction rate of some bands at lower energies shows slightly different behaviour than that of other bands. This may affect the model of H-incorporation in grossular, that is usually described by the classic hydrogen-incorporation via O_4H_4 - SiO_4, and may support more sophisticated models of OH-substitution in garnet as proposed recently by Andrut et al. (2002). This study was financially supported by the EU through the Human Potential Program HPRN-CT-2000-0056. References: [1] Wang, L., Zhang, Y., Essene, E. (1996) Diffusion of the hydrous component in pyrope. Am. Mineral., 81, 701-718. [2] Hercule, S. and Ingrin, J. (1999) Hydrogen in diopside: Diffusion, kinetics of extraction-incorporation, and solubility. Am. Mineral., 84, 1577-1587. [3

  2. Modular reweighting software for statistical mechanical analysis of biased equilibrium data

    NASA Astrophysics Data System (ADS)

    Sindhikara, Daniel J.

    2012-07-01

    version supersede the previous version?: Yes Nature of problem: While equilibrium reweighting is ubiquitous, there are no public programs available to perform the reweighting in the general case. Further, specific programs often suffer from many library dependencies and numerical instability. Solution method: This package is written in a modular format that allows for easy applicability of reweighting in the general case. Modules are small, numerically stable, and require minimal libraries. Reasons for new version: Some minor bugs, some upgrades needed, error analysis added. analyzeweight.py/analyzeweight.py2 has been replaced by “multihist.py”. This new program performs all the functions of its predecessor while being versatile enough to handle other types of histograms and probability analysis. “bootstrap.py” was added. This script performs basic bootstrap resampling allowing for error analysis of data. “avg_dev_distribution.py” was added. This program computes the averages and standard deviations of multiple distributions, making error analysis (e.g. from bootstrap resampling) easier to visualize. WRE.cpp was slightly modified purely for cosmetic reasons. The manual was updated for clarity and to reflect version updates. Examples were removed from the manual in favor of online tutorials (packaged examples remain). Examples were updated to reflect the new format. An additional example is included to demonstrate error analysis. Running time: Preprocessing scripts 1-5 minutes, WHAM engine <1 minute, postprocess script ∼1-5 minutes.

  3. Halo, Alkyl, Aryl, and Bis(imido) Complexes of Niobium Supported by the β-Diketiminato Ligand

    PubMed Central

    Tomson, Neil C.; Arnold, John; Bergman, Robert G.

    2010-01-01

    Synthesis of the complex (BDI)Nb(NtBu)Cl2py (BDI = HC[C(Me)N(2,6-iPr2-C6H3)]2) was achieved in high yield following the treatment of Nb(NtBu)Cl3py2 with Li(BDI)(OEt2). Substitution of the chlorides for fluorides was effected by introducing 2.0 equiv of Me3SnF in toluene, providing the pyridine-coordinated difluoride complex (BDI)Nb(NtBu)F2py in modest yield. The pyridine ligands from both halide compounds were removed by treatment of the pyridine adducts with B(C6F5)3, affording the Lewis base-free complexes (BDI)Nb(NtBu)X2 (X = Cl, F). Additionally, the Lewis base-free dichlorides of the tBu-imido and Ar-imido (Ar = 2,6-iPr2-C6H3) complexes were obtained following treatment of Nb(NR)Cl3(dme) (R = tBu, Ar) with Li(BDI)(OEt2). The pyridine-coordinated dichloride was alkylated and arylated to form the dimethyl complex (BDI)Nb(NtBu)Me2 (described previously, see text) and the mono(p-tolyl) complex (BDI)Nb(NtBu)Cl(p-tol), the latter of which was methylated with MeMgBr to yield the mixed alkyl/aryl complex (BDI)Nb(NtBu)Me(p-tol) in good yield. A rare example of a Group 5 bis(tBu-imido) species was synthesized in good yield via treatment of (BDI)Nb(NtBu)Cl2py with 2.0 equiv of LiNHtBu to form (BDI)Nb(NtBu)2py. Exchange of the coordinated pyridine ligand for either pyridine-d5 or dmap (p-(dimethylamino)pyridine) was shown to occur through a dissociative mechanism, allowing for removal of the coordinated Lewis base by treatment with B(C6F5)3. The resulting average C2v-symmetric tetracoordinate bis(imido) complex (BDI)Nb(NtBu)2 was characterized in solution by NMR spectroscopy and observed to undergo clean thermal decomposition to yield (BDI#)Nb(NtBu)(NHtBu) (BDI# = H2C=C(NAr)CH=C(NAr)Me) over several hours at room temperature. Treatment of the four-coordinate bis(imido) with tBuNCO resulted in clean [2 + 2] cycloaddition to yield an oxaazametallacyclobutane complex, which was further observed to extrude tBuN=C=NtBu over 12 h at room temperature. The molecular structures of

  4. Towards a Unified Architecture for Data-Intensive Seismology in VERCE

    NASA Astrophysics Data System (ADS)

    Klampanos, I.; Spinuso, A.; Trani, L.; Krause, A.; Garcia, C. R.; Atkinson, M.

    2013-12-01

    Modern seismology involves managing, storing and processing large datasets, typically geographically distributed across organisations. Performing computational experiments using these data generates more data, which in turn have to be managed, further analysed and frequently be made available within or outside the scientific community. As part of the EU-funded project VERCE (http://verce.eu), we research and develop a number of use-cases, interfacing technologies to satisfy the data-intensive requirements of modern seismology. Our solution seeks to support: (1) familiar programming environments to develop and execute experiments, in particular via Python/ObsPy, (2) a unified view of heterogeneous computing resources, public or private, through the adoption of workflows, (3) monitoring the experiments and validating the data products at varying granularities, via a comprehensive provenance system, (4) reproducibility of experiments and consistency in collaboration, via a shared registry of processing units and contextual metadata (computing resources, data, etc.) Here, we provide a brief account of these components and their roles in the proposed architecture. Our design integrates heterogeneous distributed systems, while allowing researchers to retain current practices and control data handling and execution via higher-level abstractions. At the core of our solution lies the workflow language Dispel. While Dispel can be used to express workflows at fine detail, it may also be used as part of meta- or job-submission workflows. User interaction can be provided through a visual editor or through custom applications on top of parameterisable workflows, which is the approach VERCE follows. According to our design, the scientist may use versions of Dispel/workflow processing elements offered by the VERCE library or override them introducing custom scientific code, using ObsPy. This approach has the advantage that, while the scientist uses a familiar tool, the resulting

  5. The bis metallacyclic anion [U(N{SiMe3}2)(CH2SiMe2N{SiMe3})2]-.

    PubMed

    Bénaud, Olivier; Berthet, Jean-Claude; Thuéry, Pierre; Ephritikhine, Michel

    2010-09-01

    A series of bis metallacyclic compounds [M(THF)(x)UN*(CH(2)SiMe(2)N{SiMe(3)})(2)](n) [M = Na (2), Li (3), or K (4), N* = N(SiMe(3))(2)] were isolated from reactions of UCl(4) or [UN*(3)Cl] with MN* or by treatment of [UN*(2)(CH(2)SiMe(2)N{SiMe(3)})] (1) or [UN*(3)] with MN*, MH, or LiCH(2)SiMe(3) in tetrahydrofuran (THF). Crystals of 2a x 1/6n-pentane (x = 0), 2b (x = 1), 2c (x = 2), and 4b (x = 1) were obtained by crystallization of 2 and 4 from pentane, and [Na(18-crown-6)(THF)][UN*(CH(2)SiMe(2)N{SiMe(3)})(2)] (2d) and [Na(15-crown-5)][UN*(CH(2)SiMe(2)N{SiMe(3)})(2)] (2e) were formed upon addition of the crown ether. The crystal structures of 2a-2e and 4b exhibit the same [UN*(CH(2)SiMe(2)N{SiMe(3)})(2)] units which are linked to Na or K atoms via methylene or methyl groups, giving either tight cation-anion pairs (2d and 2e) or one-dimensional (1D) or two-dimensional (2D) polymeric compounds with Na or K atoms in bridging position between methylene groups of adjacent units. Reaction of 2 with CO gave the double insertion derivative [Na(2)(THF)U(2)N*(2)(OC{=CH(2)}SiMe(2)N{SiMe(3)})(4)] (5b) and [Na(15-crown-5)UN*(OC{=CH(2)}SiMe(2)N{SiMe(3)})(2)] (5c) in the presence of the crown ether. Thermal decomposition of 5b gave [Na(2)(THF)U(OC{=CH(2)}SiMe(2)N{SiMe(3)})(3)](2) (6), the product of CO insertion into the putative tris metallacycle [Na(2)(THF)(x)U(CH(2)SiMe(2)N{SiMe(3)})(3)]. The crystal structures of 5b, 5c, and 6 show the interaction of the Na atoms with the exocyclic C=CH(2) bonds. Diffusion of CO(2) into a THF solution of 2 led to the formation of [Na(THF)(x)UN*(OC{O}CH(2)SiMe(2)N{SiMe(3)})(2)] (7) which crystallized from pyridine/pentane to give [Na(THF)(2)(py)(2)UN*(OC{O}CH(2)SiMe(2)N{SiMe(3)})(2)] x 0.5 py (8 x 0.5 py), the first crystallographically characterized complex resulting from CO(2) insertion into a M(CH(2)SiMe(2)N{SiMe(3)}) metallacycle. Compound 2 reacted with I(2) to give [UN*(CH(2)SiMe(2)N{SiMe(3)})(N{SiMe(3)}SiMe(2)CH(2)I)] (9) which would

  6. Rhenium(I) carbonyl complexes of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPT). Rhenium(I)-promoted methoxylation of the triazine ring carbon atom in dinuclear rhenium complexes.

    PubMed

    Chen, X; Femia, F J; Babich, J W; Zubieta, J A

    2001-06-01

    2,4,6-Tris(2-pyridyl)-1,3,5-triazine (TPT) bridged dinuclear rhenium(I) tricarbonyl halide complexes with the composition (mu-TPT)[ReX(CO)(3)](2) (3, X = Cl; 4, X = Br) can be made either by one-pot reaction of TPT with 2 equiv of [ReX(CO)(5)] (X = Cl and Br) in chloroform or by reacting mononuclear [ReX(CO)(3)(TPT)] (2) (1, X = Cl; 2, X = Br) with an excess amount of [ReX(CO)(5)]. Crystal data are as follows. 1: monoclinic, P2(1)/c, a = 11.751(1) A, b = 11.376(1) A, c = 15.562(2) A, beta = 103.584(2) degrees, V = 2022.0(4) A(3), Z = 4. 2: monoclinic, P2(1)/c, a = 11.896(1) A, b = 11.396(1) A, c = 15.655(1) A, beta = 104.474(2) degrees, V = 2054.9(3) A(3), Z = 4. 3: triclinic, P1, a = 11.541(2) A, b = 12.119(2) A, c = 13.199(2) A, alpha = 80.377(2) degrees, beta = 76.204(3) degrees, gamma = 66.826(2) degrees, V = 1642.5(4) A(3), Z = 2. Crystals of 4 crystallized from acetone: triclinic, P1, a = 11.586(5) A, b = 12.144(5) A, c = 13.364(6) A, alpha = 80.599(7) degrees, beta = 76.271(8) degrees, gamma = 67.158(8) degrees, V = 1678.0(12) A(3), Z = 2. Crystals of 4' are obtained from CH(2)Cl(2)-pentane solution: monoclinic, C2/c, a = 17.555(4) A, b = 15.277(3) A, c = 13.093(3) A, beta = 111.179(3) degrees, V = 3274.0(12) A(3), Z = 4. By contrast, similar reactions in the presence of methanol yielded complexes with the composition [mu-C(3)N(3)(OMe)(py)(2)(pyH)][ReX(CO)(3)](2) (5, X = Cl; 6, X = Br). Crystal data for 5: monoclinic, C2/c, a = 26.952(2) A, b = 16.602(1) A, c = 14.641(1) A, beta = 116.147(1) degrees, V = 5880.5(8) A(3), Z = 8. 6: monoclinic, C2/c, a = 27.513(3) A, b = 16.740(2) A, c = 14.837(2) A, beta = 116.925(2) degrees, V = 6092.8(10) A(3), Z = 8. An unusual metal-induced methoxylation at the carbon atom of the triazine ring of the bridging TPT ligand was observed. The nucleophilic attack of MeO(-) on C(3) results in a tetrahedral geometry around the carbon atom. Concomitantly, the uncoordinated pyridyl ring is protonated and rotated into a perpendicular

  7. Mantle Samples Included in Volcanic Rocks: Xenoliths and Diamonds

    NASA Astrophysics Data System (ADS)

    Pearson, D. G.; Canil, D.; Shirey, S. B.

    2003-12-01

    and phlogopite. Can be polycrystalline.Colorado-Wyoming craton (Eggler et al., 1979)Kimberley and Jagersfontein ( Boyd et al., 1984b) Miscellaneous: mostly garnets and pyroxenes with no clear paragenetic association or links to other megacryst suites. May represent disrupted peridotites/eclogites/pyroxenites. AXI: polymict aggregatesPolymict aggregates of peridotite, eclogite and megacrysts, of variable grain size, some containing quenched melt. Mineral assemblages not in elemental or isotopic equilibrium.Bultfontein, De Beers and Premier mines, Kaapvaal (Lawless et al., 1979). MalaitaHighly variable AXII: diamond and inclusions in diamondsWidespread and closely related to cratons. Abundance varies from <1 ppm to 100 ppm by weight. Size <<0.1 g to c. 750 g. Type I diamonds contain abundant N, type II low N (Harris, 1987).All cratons (Harris, 1987; Meyer, 1987)93-96 Inclusion suites divided into peridotitic (P-type) and eclogitic (E-type) parageneses. P-type inclusions: high-Cr, low Ca garnet, Cr-diopside, Fo-rich olivine, orthopyroxene, chromite, wustite, Ni-rich sulfide, have restricted, high Mg, high Ni chemistry. Equilibration temperatures 900-1,100 °C. E-Type inclusions: pyrope-almandine, high Na garnet (>0.1 wt.%), omphacite, coesite, low-Ni sulfide. AXIII: ultra-deep peridotitesRare and restricted to Jagersfontein (Kaapvaal Craton) and Koidu (W. African craton). Four-phase garnet lherzolite. Close association of pyrope-garnet (˜70% py; 2 wt.% Cr2O3) and jadeite-rich clinopyroxene (20% Jd, & 4% Di). Clinopyroxene forms either orientated rods in garnet host or as discrete grains attached to garnet in cuspate contact. Both pyroxenes exsolved from garnet at 100-150 km depth. Recombination of garnet gives original depths of derivation of 300-400 km. Discrete garnets and "lherzolites" with eclogitic affinities also found (Sautter et al., 1991).All samples so far from the Jagersfontein kimberlite, S. Africa (Haggerty and Sautter, 1990; Sautter et al., 1991) and Koidu