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Sample records for dinuclear metal centre

  1. Dinuclear ruthenium(ii) complexes containing one inert metal centre and one coordinatively-labile metal centre: syntheses and biological activities.

    PubMed

    Li, Xin; Heimann, Kirsten; Li, Fangfei; Warner, Jeffrey M; Richard Keene, F; Grant Collins, J

    2016-03-07

    A series of non-symmetric dinuclear polypyridylruthenium(ii) complexes (Rubbn-Cl) that contain one inert metal centre and one coordinatively-labile metal centre, linked by the bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane ligand ("bbn" for n = 7, 12 and 16), have been synthesised and their potential as antimicrobial agents examined. The minimum inhibitory concentrations (MIC) of the ruthenium(II) complexes were determined against four strains of bacteria--Gram-positive Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA), and Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa). The Rubbn-Cl complexes displayed good antimicrobial activity, with Rubb12-Cl being the most active complex against both Gram-positive and Gram-negative strains. Interestingly, Rubb7-Cl was found to be eight- and sixteen-fold more active towards E. coli than against S. aureus and MRSA, respectively. The cytotoxicities of the Rubbn-Cl complexes against three eukaryotic cell lines--two kidney cell lines (BHK and HEK-293) and one liver cell line (HepG2)--were examined. The Rubbn-Cl complexes were found to be considerably less toxic towards eukaryotic cells than S. aureus, MRSA and E. coli, with Rubb12-Cl being thirty- to eighty-times more toxic to the bacteria than to BHK, HEK-293 or HepG2 cells. Unexpectedly, Rubb7-Cl was far more toxic to HepG2 cells (24 h-IC50 = 3.7 μM) and far less toxic to BHK cells (24 h-IC50 = 238 μM) than the Rubb12-Cl and Rubb16-Cl complexes. In order to understand the unexpected large differences in the cytotoxicities of the Rubbn-Cl complexes towards eukaryotic cells, a confocal microscopic study of their intracellular localisation was undertaken. The results suggest that the observed cytotoxicity might be related to the extent of DNA binding.

  2. Photo-catalytic oxidation of a di-nuclear manganese centre in an engineered bacterioferritin 'reaction centre'.

    PubMed

    Conlan, Brendon; Cox, Nicholas; Su, Ji-Hu; Hillier, Warwick; Messinger, Johannes; Lubitz, Wolfgang; Dutton, P Leslie; Wydrzynski, Tom

    2009-09-01

    Photosynthesis involves the conversion of light into chemical energy through a series of electron transfer reactions within membrane-bound pigment/protein complexes. The Photosystem II (PSII) complex in plants, algae and cyanobacteria catalyse the oxidation of water to molecular O2. The complexity of PSII has thus far limited attempts to chemically replicate its function. Here we introduce a reverse engineering approach to build a simple, light-driven photo-catalyst based on the organization and function of the donor side of the PSII reaction centre. We have used bacterioferritin (BFR) (cytochrome b1) from Escherichia coli as the protein scaffold since it has several, inherently useful design features for engineering light-driven electron transport. Among these are: (i.) a di-iron binding site; (ii.) a potentially redox-active tyrosine residue; and (iii.) the ability to dimerise and form an inter-protein heme binding pocket within electron tunnelling distance of the di-iron binding site. Upon replacing the heme with the photoactive zinc-chlorin e6 (ZnCe6) molecule and the di-iron binding site with two manganese ions, we show that the two Mn ions bind as a weakly coupled di-nuclear Mn2II,II centre, and that ZnCe6 binds in stoichiometric amounts of 1:2 with respect to the dimeric form of BFR. Upon illumination the bound ZnCe6 initiates electron transfer, followed by oxidation of the di-nuclear Mn centre possibly via one of the inherent tyrosine residues in the vicinity of the Mn cluster. The light dependent loss of the MnII EPR signals and the formation of low field parallel mode Mn EPR signals are attributed to the formation of MnIII species. The formation of the MnIII is concomitant with consumption of oxygen. Our model is the first artificial reaction centre developed for the photo-catalytic oxidation of a di-metal site within a protein matrix which potentially mimics water oxidation centre (WOC) photo-assembly.

  3. Dinuclear transition metal complexes in carbon nanostructured materials synthesis

    NASA Astrophysics Data System (ADS)

    Ayuso, J. I.; Hernández, E.; Delgado, E.

    2013-06-01

    Carbon nanomaterials (CNMs) were prepared with two similar techniques using organometallic complexes as catalysts precursors. Chemical vapour deposition (CVD) and pyrolysis with chlorine gas approaches were employed in order to explore the effect of dinuclear transition metal compounds [Fe2(CO)6(μ-S2C6H2X2), (X=OH, Cl)] in synthesis of CNMs. Our to-date results have shown these complexes generate different carbonaceous materials when they are used in bulk, it was also observed that their performances in synthesis differ even though these compounds are analogous. With X=OH complex used in CVD process, metal nanoparticles of ca. 20-50 nm in size and embedded in carbon matrix were obtained. X=C1 complex has been used in pyrolysis experiments and showed an entire volatilisation or no reaction, depending on selected temperature. Furthermore, obtaining of a new tetranuclear iron cluster is presented in this work.

  4. Dihydrogen addition in a dinuclear rare-earth metal hydride complex supported by a metalated TREN ligand.

    PubMed

    Venugopal, Ajay; Fegler, Waldemar; Spaniol, Thomas P; Maron, Laurent; Okuda, Jun

    2011-11-09

    The dinuclear lutetium dihydride dication supported by metalated tripodal ligands undergoes facile hydrogenolysis with H(2) to form a trihydride dication. Molecular orbital analysis shows that the LUMO is a bonding Lu···Lu orbital that is poised to activate dihydrogen.

  5. Proton-induced tuning of metal-metal communication in rack-type dinuclear Ru complexes containing benzimidazolyl moieties.

    PubMed

    Kobayashi, Katsuaki; Ishikubo, Masamichi; Kanaizuka, Katsuhiko; Kosuge, Keiko; Masaoka, Shigeyuki; Sakai, Ken; Nozaki, Koichi; Haga, Masa-aki

    2011-06-14

    Ru complexes bearing a bis-tridentate benzimidazolyl ligand have been synthesized. The dinuclear ones act as a bibasic acid with pK(a1)=4.36 and pK(a2)=5.90. The protonated form of the dinuclear complex exhibited two one-electron oxidations at +0.91 and +1.02 V versus the ferrocenium/ferrocene (Fc/Fc(+)) couple (the potential difference (ΔE)=0.11 V), but the di-deprotonated form showed two waves at +0.50 and +0.58 V versus Fc/Fc(+) (ΔE=0.08 V). Since the potential difference between two waves reflects the strength of the metal-metal interaction, the deprotonation of the benzimidazole moieties in the complexes weakened the Ru-Ru communication. The degree of electronic coupling between two metal centers, estimated from the intervalence charge transfer (IVCT) band, was greater for the protonated form. DFT calculations for the protonated and deprotonated forms of the dinuclear complex suggest that the Ru(II)-L(H(2)) π* interaction plays a key role in the Ru-Ru interaction. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Metal-Organic Framework of Lanthanoid Dinuclear Clusters Undergoes Slow Magnetic Relaxation.

    PubMed

    Iwami, Hikaru; Nakanishi, Ryo; Horii, Yoji; Katoh, Keiichi; Breedlove, Brian K; Yamashita, Masahiro

    2017-01-20

    Lanthanoid metal-organic frameworks (Ln-MOFs) can adopt a variety of new structures due to the large coordination numbers of Ln metal ions, and Ln-MOFs are expected to show new luminescence and magnetic properties due to the localized f electrons. In particular, some Ln metal ions, such as Dy(III) and Tb(III) ions, work as isolated quantum magnets when they have magnetic anisotropy. In this work, using 4,4',4″-s-triazine-2,4,6-triyl-tribenzoic acid (H₃TATB) as a ligand, two new Ln-MOFs, [Dy(TATB)(DMF)₂] (1) and [Tb(TATB)(DMF)₂] (2), were obtained. The Ln-MOFs contain Ln dinuclear clusters as secondary building units, and 1 underwent slow magnetic relaxation similar to single-molecule magnets.

  7. Metal-Organic Framework of Lanthanoid Dinuclear Clusters Undergoes Slow Magnetic Relaxation

    PubMed Central

    Iwami, Hikaru; Nakanishi, Ryo; Horii, Yoji; Katoh, Keiichi; Breedlove, Brian K.; Yamashita, Masahiro

    2017-01-01

    Lanthanoid metal-organic frameworks (Ln-MOFs) can adopt a variety of new structures due to the large coordination numbers of Ln metal ions, and Ln-MOFs are expected to show new luminescence and magnetic properties due to the localized f electrons. In particular, some Ln metal ions, such as Dy(III) and Tb(III) ions, work as isolated quantum magnets when they have magnetic anisotropy. In this work, using 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoic acid (H3TATB) as a ligand, two new Ln-MOFs, [Dy(TATB)(DMF)2] (1) and [Tb(TATB)(DMF)2] (2), were obtained. The Ln-MOFs contain Ln dinuclear clusters as secondary building units, and 1 underwent slow magnetic relaxation similar to single-molecule magnets. PMID:28772440

  8. Supramolecular architecture of metal-organic frameworks involving dinuclear copper paddle-wheel complexes.

    PubMed

    Gomathi, Sundaramoorthy; Muthiah, Packianathan Thomas

    2013-12-15

    The two centrosymmetric dinuclear copper paddle-wheel complexes tetrakis(μ-4-hydroxybenzoato-κ(2)O:O')bis[aquacopper(II)] dimethylformamide disolvate dihydrate, [Cu2(C7H5O3)4(H2O)2]·2C3H7NO·2H2O, (I), and tetrakis(μ-4-methoxybenzoato-κ(2)O:O')bis[(dimethylformamide-κO)copper(II)], [Cu2(C8H7O3)4(C3H7NO)2], (II), crystallize with half of the dinuclear paddle-wheel cage unit in the asymmetric unit and, in addition, complex (I) has one dimethylformamide (DMF) and one water solvent molecule in the asymmetric unit. In both (I) and (II), two Cu(II) ions are bridged by four syn,syn-η(1):η(1):μ carboxylate groups, showing a paddle-wheel cage-type structure with a square-pyramidal coordination geometry. The equatorial positions of (I) and (II) are occupied by the carboxylate groups of 4-hydroxy- and 4-methoxybenzoate ligands, and the axial positions are occupied by aqua and DMF ligands, respectively. The three-dimensional supramolecular metal-organic framework of (I) consists of three different R2(2)(20) and an R4(4)(36) ring motif formed via O-H···O and OW-HW···O hydrogen bonds. Complex (II) simply packs as molecular species.

  9. Bent and planar structures of μ-η²:η²-N₂ dinuclear early transition metal complexes.

    PubMed

    Ma, Xuelu; Tang, Yanhui; Lei, Ming

    2014-08-14

    This work studied the bent and planar structures of M2N2 cores of a series of dinuclear early transition-metal complexes (M = Zr, Hf, Nb, Ta, Mo and W) containing a side-on bridging dinitrogen ligand using DFT method. The calculated results propose three key factors favoring a bent structure: (1) the availability of a single electron in the metal centers which leads to the bonding interaction between two metal atoms, (2) no remarkable steric effect around the metal centers, and (3) the cis conformation of the ligands in the dinitrogen dinuclear complexes. In addition, the bent and planar structures of M2N2 could be transformed into each other if the steric hindrance was slight.

  10. Unusual Metal-Metal Bonding in a Dinuclear Pt-Au Complex: Snapshot of a Transmetalation Process.

    PubMed

    Baya, Miguel; Belío, Úrsula; Fernández, Israel; Fuertes, Sara; Martín, Antonio

    2016-06-06

    The dinuclear Pt-Au complex [(CNC)(PPh3 )Pt Au(PPh3 )](ClO4 ) (2) (CNC=2,6-diphenylpyridinate) was prepared. Its crystal structure shows a rare metal-metal bonding situation, with very short Pt-Au and Au-Cipso (CNC) distances and dissimilar Pt-Cipso (CNC) bonds. Multinuclear NMR spectra of 2 show the persistence of the Pt-Au bond in solution and the occurrence of unusual fluxional behavior involving the [Pt(II) ] and [Au(I) ] metal fragments. The [Pt(II) ]⋅⋅⋅ [Au(I) ] interaction has been thoroughly studied by means of DFT calculations. The observed bonding situation in 2 can be regarded as a model for an intermediate in a transmetalation process.

  11. Electronic structure analysis of the dinuclear metal center in the bioremediator glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes.

    PubMed

    Hadler, Kieran S; Mitić, Natasa; Yip, Sylvia Hsu-Chen; Gahan, Lawrence R; Ollis, David L; Schenk, Gerhard; Larrabee, James A

    2010-03-15

    The glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes is a promiscuous, dinuclear metallohydrolase that has potential application in the remediation of organophosphate nerve agents and pesticides. GpdQ employs an unusual reaction mechanism in which the enzyme is predominantly mononuclear in the resting state, and substrate binding induces the formation of the catalytically competent dinuclear center (Hadler et al. J. Am. Chem. Soc. 2008, 130, 14129). Reactivity is further modulated by the coordination flexibility of Asn80, a ligand that binds to the second, loosely bound metal ion (Hadler et al. J. Am. Chem. Soc. 2009, 131, 11900). It is proposed that hydrolysis is initiated by a terminal, metal-bound hydroxide molecule which is activated at unusually low pH by electrostatic/hydrogen bonding interactions with a bridging hydroxide species. In this study, electronic structure analysis of the dinuclear center is employed to study the coordination environment of the dinuclear center at the resting and product-bound stage of catalysis. This is achieved through the use of variable temperature, variable field magnetic circular dichroism experiments involving the Co(II)-substituted wild type enzyme and its Asn80Asp variant. The data support the above model for the catalytic mechanism whereby the metal ion-bridging hydroxide molecule activates a terminally bound hydroxide nucleophile. Replacement of Asn80 by an aspartate residue does prevent coordination flexibility but also leads to cleavage of the mu-hydroxide bridge and reduced reactivity. This is the first study to investigate the electronic structure of an enzyme with a mu-1,1-carboxylate bridged dicobalt(II) center.

  12. Crystal structure of Escherichia coli protein ybgI, a toroidal structure with a dinuclear metal site

    PubMed Central

    Ladner, Jane E; Obmolova, Galina; Teplyakov, Alexey; Howard, Andrew J; Khil, Pavel P; Camerini-Otero, R Daniel; Gilliland, Gary L

    2003-01-01

    Background The protein encoded by the gene ybgI was chosen as a target for a structural genomics project emphasizing the relation of protein structure to function. Results The structure of the ybgI protein is a toroid composed of six polypeptide chains forming a trimer of dimers. Each polypeptide chain binds two metal ions on the inside of the toroid. Conclusion The toroidal structure is comparable to that of some proteins that are involved in DNA metabolism. The di-nuclear metal site could imply that the specific function of this protein is as a hydrolase-oxidase enzyme. PMID:14519207

  13. ProPhenol-Catalyzed Asymmetric Additions by Spontaneously Assembled Dinuclear Main Group Metal Complexes

    PubMed Central

    2016-01-01

    Conspectus The development of catalytic enantioselective transformations has been the focus of many research groups over the past half century and is of paramount importance to the pharmaceutical and agrochemical industries. Since the award of the Nobel Prize in 2001, the field of enantioselective transition metal catalysis has soared to new heights, with the development of more efficient catalysts and new catalytic transformations at increasing frequency. Furthermore, catalytic reactions that allow higher levels of redox- and step-economy are being developed. Thus, alternatives to asymmetric alkene dihydroxylation and the enantioselective reduction of α,β-unsaturated ketones can invoke more strategic C–C bond forming reactions, such as asymmetric aldol reactions of an aldehyde with α-hydroxyketone donors or enantioselective alkynylation of an aldehyde, respectively. To facilitate catalytic enantioselective addition reactions, including the aforementioned aldol and alkynylation reactions, our lab has developed the ProPhenol ligand. In this Account, we describe the development and application of the ProPhenol ligand for asymmetric additions of both carbon- and heteroatom-based nucleophiles to various electrophiles. The ProPhenol ligand spontaneously forms chiral dinuclear metal complexes when treated with an alkyl metal reagent, such as Et2Zn or Bu2Mg. The resulting complex contains both a Lewis acidic site to activate an electrophile and a Brønsted basic site to deprotonate a pronucleophile. Initially, our research focused on the use of Zn-ProPhenol complexes to facilitate the direct aldol reaction. Fine tuning of the reaction through ligand modification and the use of additives enabled the direct aldol reaction to proceed in high yields and stereoselectivities with a broad range of donor substrates, including acetophenones, methyl ynones, methyl vinyl ketone, acetone, α-hydroxy carbonyl compounds, and glycine Schiff bases. Additionally, an analogous

  14. Dinuclear vs. mononuclear complexes: accelerated, metal-dependent ring-opening polymerization of lactide.

    PubMed

    Normand, M; Roisnel, T; Carpentier, J-F; Kirillov, E

    2013-12-25

    Dinuclear complexes of aluminum and indium with a bis(phenoxy-imine) platform have been synthesized and used in the polymerization of lactide. Kinetic studies demonstrate that the dialuminum precursor provides a more favorable reaction pathway in terms of activation free energy than that of directly related monoaluminum systems. No similar trend is observed with the corresponding diindium-monoindium systems, which is attributed to a dissimilar ROP mechanism.

  15. Evidence for a conserved binding motif of the dinuclear metal site in mammalian and plant purple acid phosphatases: 1H NMR studies of the di-iron derivative of the Fe(III)Zn(II) enzyme from kidney bean.

    PubMed

    Battistuzzi, G; Dietrich, M; Löcke, R; Witzel, H

    1997-05-01

    The di-iron core of mammalian purple acid phosphatases has been reproduced in the plant enzyme from kidney bean (Mr 111000) upon insertion of an Fe(II) ion in place of the native zinc(II) in the dinuclear Fe(III)Zn(II) core. The shortening of the electronic relaxation time of the metal centre allows detection of hyperfine-shifted 1H NMR resonances, although severe broadening due to Curie relaxation prevents independent signal assignment. Nevertheless, comparison of the spectral features of the structurally characterized plant enzyme with those of the mammalian species, which were previously extensively assigned, is consistent with a close similarity of the metal-binding sites, also suggested by previous sequence-alignment studies. Some differences appear to be mainly localized at the M(II) site. Spectral comparison was also carried out on the Fe(III)Co(II) derivatives.

  16. Multifrequency EPR Spectroscopy: A Toolkit for the Characterization of Mono- and Di-nuclear Metal Ion Centers in Complex Biological Systems

    NASA Astrophysics Data System (ADS)

    Hanson, Graeme R.

    Metalloenzymes are ubiquitous in nature containing complex metal ion cofactors intimately involved in the enzymes' biological function. The application of multifrequency continuous wave and orientation selective pulsed EPR in conjunction with computer simulation and density functional theory calculations has proven to be a powerful toolkit for the geometric and electronic structural characterization of these metal ion cofactors in the resting enzyme, enzyme-substrate and -product complexes, which in turn provides a detailed understanding of the enzymes' catalytic mechanism. In this chapter, a brief description of the multifrequency EPR toolkit used to structurally (geometric and electronic) characterize metal ion binding sites in complex biological systems and its application in the structural characterization of (i) molybdenum containing enzymes and model complexes, (ii) mono- and di-nuclear copper(II) cyclic peptide complexes (marine and synthetic analogues) and (iii) dinuclear metal ion centers in purple acid phosphatases will be presented.

  17. Achieving C-N bond cleavage in dinuclear metal cyanide complexes.

    PubMed

    Cavigliasso, Germán; Christian, Gemma J; Stranger, Robert; Yates, Brian F

    2011-07-28

    Cleavage of cyanide is more difficult to achieve compared to dinitrogen and carbon monoxide, even though these species contain triple bonds of greater strength. In this work, we have used computational methods to investigate thermodynamic and mechanistic aspects of the C-N bond cleavage process in [L(3)M-CN-M'L(3)] systems consisting of a central cyanide unit bound in an end-on fashion to two terminal metal tris-amide complexes. In these systems, [M] is a d(3) transition metal from the 3d, 4d, 5d, or 6d series and groups 4 through 7, and [L] is either [NH(2)], [NMe(2)], [N(i)PrPh], or [N(t)BuAr]. A comparison of various models for the experimentally relevant [L(3)Mo-CN-MoL(3)] system has shown that while the C-N cleavage step appears to be an energetically favourable process, a large barrier exists for the dissociation of [L(3)Mo-CN-MoL(3)]((-)) into [L(3)Mo-C]((-)) and [N-MoL(3)], which possibly explains why C-N bond scission is not observed experimentally. The general structural, bonding, and thermochemical trends across the transition metal series investigated, indicate that the systems exhibiting the greatest degree of C-N activation, and most favourable energetics for C-N cleavage, also possess the most favourable electronic properties, namely, a close match between the relevant π-like orbitals on the metal-based and cyanide fragments. The negative charge on the cyanide fragment leads to significant destabilization of the π* level which needs to be populated through back-donation from the metal centres in order for C-N bond scission to be achieved. Therefore, metal-based systems with high-lying d(π) orbitals are best suited to C-N cleavage. In terms of chemical periodicity, these systems can be identified as the heavier members within a group and the earlier members within a period. As a consequence, Mo complexes are not well suited to cleaving the C-N bond, whereas the Ta analogues are the most favourable systems and should, in principle, be capable of

  18. New dinuclear copper(II) and zinc(II) complexes for the investigation of sugar-metal ion interactions.

    PubMed

    Bera, Manindranath; Patra, Ayan

    2011-10-18

    We have studied the binding interactions of biologically important carbohydrates (D-glucose, D-xylose and D-mannose) with the newly synthesized five-coordinate dinuclear copper(II) complex, [Cu(2)(hpnbpda)(μ-OAc)] (1) and zinc(II) complex, [Zn(2)(hpnbpda)(μ-OAc)] (2) [H(3)hpnbpda=N,N'-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine-N,N'-diacetic acid] in aqueous alkaline solution. The complexes 1 and 2 are fully characterized both in solid and solution using different analytical techniques. A geometrical optimization was made of the ligand H(3)hpnbpda and the complexes 1 and 2 by molecular mechanics (MM+) method in order to establish the stable conformations. All carbohydrates bind to the metal complexes in a 1:1 molar ratio. The binding events have been investigated by a combined approach of FTIR, UV-vis and (13)C NMR spectroscopic techniques. UV-vis spectra indicate a significant blue shift of the absorption maximum of complex 1 during carbohydrate coordination highlighting the sugar binding ability of complex 1. The apparent binding constants of the substrate-bound copper(II) complexes have been determined from the UV-vis titration experiments. The binding ability and mode of binding of these sugar substrates with complex 2 are indicated by their characteristic coordination induced shift (CIS) values in (13)C NMR spectra for carbon atoms C1, C2, and C3 of sugar substrates.

  19. Dinuclear complexes formed by hydrogen bonds: synthesis, structure and magnetic and electrochemical properties.

    PubMed

    Williams, Alan Francis; Granelli, Matteo; Downward, Alan M; Huber, Robin; Guenée, Laure; Besnard, Céline; Krämer, Karl W; Decurtins, Silvio; Liu, Shi-Xia; Thompson, Laurence K

    2017-03-20

    The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent M(II)M(II), mixed valent M(II)M(III) and heteronuclear M(II)M'(III) species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O…O distances for the hydrogen bonds. Magnetic measurements show the hydrogen bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen bonded structure.

  20. Mechanistic role of each metal ion in Streptomyces dinuclear aminopeptidase: PEPTIDE hydrolysis and 7x10(10)-fold rate enhancement of phosphodiester hydrolysis.

    PubMed

    Ercan, Altan; Tay, William M; Grossman, Steven H; Ming, Li-June

    2010-01-01

    The dinuclear aminopeptidase from Streptomyces griseus (SgAP) and its metal derivatives catalyze the hydrolysis of the phosphoester bis(p-nitrophenyl) phosphate (BNPP) and the phosphonate ester p-nitrophenyl phenylphosphonate with extraordinary rate enhancements at pH 7.0 and 25 degrees C [A. Ercan, H. I. Park, L.-J. Ming, Biochemistry 45, (2006) 13779-13793.], reaching 6.7 billion-fold in terms of the first-order rate constant of the di-Co(II) derivative with respect to the autohydrolytic rates. Since phosphoesters are transition state-like inhibitors in peptide hydrolysis, their hydrolysis by SgAP is quite novel. Herein, we report the investigation of this proficient alternative catalysis of SgAP and the role of each metal ion in the dinuclear site toward peptide and BNPP hydrolysis. Mn(II) selectively binds to one of the dinuclear metal sites (M1), affording MnE-SgAP with an empty (E) second site for the binding of another metal (M2), including Mn(II), Co(II), Ni(II), Zn(II), and Cd(II). Peptide hydrolysis is controlled by M2, wherein the k(cat) values for the derivatives MnM2-SgAP are different yet similar between MnCo- and CoCo-SgAP and pairs of other metal derivatives. On the other hand, BNPP hydrolysis is affected by metals in both sites. Thus, the two hydrolytic catalyses must follow different mechanisms. Based on crystal structures, docking, and the results presented herein, the M1 site is close to the hydrophobic specific site and the M2 site is next to Tyr246 that is H-bonded to a coordinated nucleophilic water molecule in peptide hydrolysis; whereas a coordinated water molecule on M1 becomes available as the nucleophile in phosphodiester hydrolysis.

  1. Femtosecond Time-Resolved Infrared Spectra of Organometallic Complexes Bound to a Dinuclear Metal Center

    NASA Astrophysics Data System (ADS)

    Brown-Xu, Samantha E.; Durr, Christopher B.

    2012-06-01

    Compounds of the form M2L2L'2, where M2 is a quadruply bonded metal center (M = Mo or W) and L and L' are conjugated organic ligands, are known to show interesting photophysical properties and exhibit intense metal-to-ligand charge transfer (MLCT) transitions throughout the visible spectrum. Recently, we have modified one of the ligands to incorporate a transition metal carbonyl complex bound to an organic moiety. Following excitation into the MLCT band, the vibrational modes of the organometallic ligand can be observed by fs time-resolved infrared (TRIR) spectroscopy. This allows for a visualization of where the electron density resides in the excited states, which provides useful information for designing new materials that could later be incorporated into solar devices.

  2. Emission and fs/ns-TRANSIENT Absorption of Organometallic Complexes Bound to a Dinuclear Metal Center

    NASA Astrophysics Data System (ADS)

    Durr, Christopher B.; Brown-Xu, Samantha E.; Chisholm, Malcolm H.

    2012-06-01

    Compounds containing a MM quadruple bond (M = Mo or W) of the form M2L2L'2, where L and L' are conjugated organic ligands, show interesting photophysical properties along with a metal-to-ligand charge transfer (MLCT) band that is tunable throughout the UV-Vis-NIR spectra. Recently, our attention has shifted towards ligands that incorporate a secondary transition metal complex bound to an organic moiety. Along with allowing for a second tunable MLCT band for better coverage of the solar spectrum, these hybrid molecules show unique spectroscopic properties that were explored using fs/ns-transient absorption and UV-Vis/NIR emission. These techniques allow for the elucidation of the electronic character of the excited states as well as their lifetimes. This knowledge will be put to use in the design of new materials that could later be incorporated into next generation photovoltaic devices.

  3. Bimetallic Reductive Elimination from Dinuclear Pd(III) Complexes

    PubMed Central

    Powers, David C.; Benitez, Diego; Tkatchouk, Ekaterina; Goddard, William A.

    2010-01-01

    In 2009, we reported C–halogen reductive elimination reactions from dinuclear Pd(III) complexes and implicated dinuclear intermediates in Pd(OAc)2-catalyzed C–H oxidation chemistry. Herein, we report results of a thorough experimental and theoretical investigation of the mechanism of reductive elimination from such dinuclear Pd(III) complexes, which establish the role of each metal during reductive elimination. Our results implicate reductive elimination from a complex in which the dinuclear core is intact and suggest that redox synergy between both metals is responsible for the facile reductive elimination reactions observed. PMID:20858006

  4. Mechanismic investigation on the cleavage of phosphate monoester catalyzed by unsymmetrical macrocyclic dinuclear complexes: the selection of metal centers and the intrinsic flexibility of the ligand.

    PubMed

    Zhang, Xuepeng; Zhu, Yajie; Zheng, Xiaowei; Phillips, David Lee; Zhao, Cunyuan

    2014-04-07

    The hydrolysis mechanisms of phosphor-monoester monoanions NPP(-) (p-nitrophenyl phosphate) catalyzed by unsymmetrical bivalent dinuclear complexes are explored using DFT calculations in this report. Four basic catalyst-substrate binding modes are proposed, and two optional compartments for the location of the nucleophile-coordinated metal center are also considered. Five plausible mechanisms are examined in this computational study. Mechanisms 1, 2, and 3 employ an unsymmetrical dizinc complex. All three mechanisms are based on concerted SN2 addition-substitution pathways. Mechanism 1, which involves more electronegative oxygen atoms attached to the imine nitrogen atoms in the nucleophile-coordinated compartment, was found to be more competitive compared to the other two mechanisms. Mechanisms 4 and 5 are based on consideration of the substitution of the bivalent metal centers and the intrinsic flexibility of the ligand. Both mechanisms 4 and 5 are based on stepwise SN2-type reactions. Magnesium ions with hard base properties and more available coordination sites were found to be good candidates as a substitute in the M(II) dinuclear phosphatases. The reaction energy barriers for the more distorted complexes are lower than those of the less distorted complexes. The proper intermediate distance and a functional second coordination sphere lead to significant catalytic power in the reactions studied. More importantly, the mechanistic differences between the concerted and the stepwise pathways suggest that a better nucleophile with more available coordination sites (from either the metal centers or a functional second coordination sphere) favors concerted mechanisms for the reactions of interest. The results reported in the paper are consistent with and provide a reasonable interpretation for experimental observations in the literature. More importantly, our present results provide some practical suggestions for the selection of the metal centers and how to approach

  5. Dinuclear metal(ii)-acetato complexes based on bicompartmental 4-chlorophenolate: syntheses, structures, magnetic properties, DNA interactions and phosphodiester hydrolysis.

    PubMed

    Massoud, Salah S; Ledet, Catherine C; Junk, Thomas; Bosch, Simone; Comba, Peter; Herchel, Radovan; Hošek, Jan; Trávníček, Zdeněk; Fischer, Roland C; Mautner, Franz A

    2016-08-09

    A series of dinuclear metal(ii)-acetato complexes: [Ni2(μ-L(Cl)O)(μ2-OAc)2](PF6)·3H2O (1), [Ni2(μ-L(Cl)O)(μ2-OAc)2](ClO4)·CH3COCH3 (2), [Cu2(μ-L(Cl)O)(μ2-OAc)(ClO4)](ClO4) (3), [Cu2(μ-L(Cl)O)(OAc)2](PF6)·H2O (4), [Zn2(μ-L(Cl)O)(μ2-OAc)2](PF6) (5) and [Mn2(L(Cl)-O)(μ2-OAc)2](ClO4)·H2O (6), where L(Cl)O(-) = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenolate, were synthesized. The complexes were structurally characterized by spectroscopic techniques and single crystal X-ray crystallography. Six-coordinate geometries with doubly bridged acetato ligands were found in Ni(ii), Zn(ii) and Mn(ii) complexes 1, 2, 5 and 6, whereas with Cu(ii) complexes a five-coordinate species was obtained with 4, and mixed five- and six-coordinate geometries with a doubly bridged dimetal core were observed in 3. The magnetic properties of complexes 1-4 and 6 were studied at variable temperatures and revealed weak to very weak antiferromagnetic interactions in 1, 2, 4 and 6 (J = -0.55 to -9.4 cm(-1)) and ferromagnetic coupling in 3 (J = 15.4 cm(-1)). These results are consistent with DFT calculations performed at the B3LYP/def2-TZVP(-f) level of theory. Under physiological conditions, the interaction of the dinculear complexes 1-5 with supercoiled plasmid ds-DNA did not show any pronounced nuclease activity, but Ni(ii) complexes 1 and 2 revealed a strong ability to unwind the supercoiled conformation of ds-DNA. The mechanistic studies performed on the interaction of the Ni(ii) complexes with DNA demonstrated the important impact of the nickel(ii) ion in the unwinding process. In combination with the DNA study, the phosphatase activity of complexes 1, 3, and 5 was examined by the phosphodiester hydrolysis of bis(2,4-dinitrophenol)phosphate (BDNPP) in the pH range of 5.5-10.5 at 25 °C. The Michaelis-Menten kinetics performed at pH 7 and 10.7 showed that catalytic efficiencies kcat/KM (kcat = catalytic rate constant, KM = substrate binding constant) decrease in the order

  6. Dinuclear rare-earth metal alkyl complexes supported by indolyl ligands in μ-η(2) :η(1) :η(1) hapticities and their high catalytic activity for isoprene 1,4-cis-polymerization.

    PubMed

    Zhang, Guangchao; Wei, Yun; Guo, Liping; Zhu, Xiancui; Wang, Shaowu; Zhou, Shuangliu; Mu, Xiaolong

    2015-02-02

    Two series of new dinuclear rare-earth metal alkyl complexes supported by indolyl ligands in novel μ-η(2) :η(1) :η(1) hapticities are synthesized and characterized. Treatment of [RE(CH2 SiMe3 )3 (thf)2 ] with 1 equivalent of 3-(tBuN=CH)C8 H5 NH (L1 ) in THF gives the dinuclear rare-earth metal alkyl complexes trans-[(μ-η(2) :η(1) :η(1) -3-{tBuNCH(CH2 SiMe3 )}Ind)RE(thf)(CH2 SiMe3 )]2 (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L1 is deprotonated by the metal alkyl species and the imino C=N group is transferred to the amido group by alkyl CH2 SiMe3 insertion, affording a new dianionic ligand that bridges two metal alkyl units in μ-η(2) :η(1) :η(1) bonding modes, forming the dinuclear rare-earth metal alkyl complexes. When L1 is reduced to 3-(tBuNHCH2 )C8 H5 NH (L2 ), the reaction of [Yb(CH2 SiMe3 )3 (thf)2 ] with 1 equivalent of L2 in THF, interestingly, generated the trans-[(μ-η(2) :η(1) :η(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (major) and cis-[(μ-η(2) :η(1) :η(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (minor) complexes. The catalytic activities of these dinuclear rare-earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio- and stereoselectivities for isoprene 1,4-cis-polymerization.

  7. Synthesis, characterization and properties of tetra((1-hydroxyimino-methylnaphthalen-2-yloxy)methyl)ethene and its homo-dinuclear metal complexes: A combined experimental and theoretical investigation

    NASA Astrophysics Data System (ADS)

    Serbest, Kerim; Karaoğlu, Kaan; Erman, Murat; Er, Mustafa; Değirmencioğlu, İsmail

    2010-10-01

    Tetra((1-hydroxyiminomethylnaphthalen-2-yloxy)methyl)ethene (THIMNYOME), H 4L, was synthesized by the agents of 2-hydroxy-1-naphtaldehyde, tetra(bromomethyl)ethene and hydroxylamine hydrochloride in two steps. Characterization of THIMNYOME and its dinuclear complexes was made by elemental analyses, IR, 1H- and 13C NMR, UV-vis, electrospray ionisation mass spectra, molar conductivities and magnetic susceptibility measurements. In the light of these results, it was suggested that the ligand coordinate to each metal atom by the two ether oxygen, two nitrogen atoms of oxime imine (C dbnd N) and an axial oxygen of perchlorate to form pseudo square-pyramidal complexes with Ni(II), Cu(II) and Zn(II). Molar conductivity measurements reveal that all the complexes are non-electrolytes. In addition, the full geometric optimization of the tetraoxime ligand ( 4) has been made by the B3LYP/6-31G(d) level in order to establish a stable conformation. Additionally, all the complex structures have been studied in the B3LYP/LANL2DZ level. NBO charge distribution and the characteristics of frontier molecular orbitals of these complexes have also been investigated in order to see the electrons movement between ligand and metal atom in the same level.

  8. Synthesis, characterization and properties of tetra((1-hydroxyimino-methylnaphthalen-2-yloxy)methyl)ethene and its homo-dinuclear metal complexes: a combined experimental and theoretical investigation.

    PubMed

    Serbest, Kerim; Karaoğlu, Kaan; Erman, Murat; Er, Mustafa; Değirmencioğlu, Ismail

    2010-10-15

    Tetra((1-hydroxyiminomethylnaphthalen-2-yloxy)methyl)ethene (THIMNYOME), H(4)L, was synthesized by the agents of 2-hydroxy-1-naphtaldehyde, tetra(bromomethyl)ethene and hydroxylamine hydrochloride in two steps. Characterization of THIMNYOME and its dinuclear complexes was made by elemental analyses, IR, (1)H- and (13)C NMR, UV-vis, electrospray ionisation mass spectra, molar conductivities and magnetic susceptibility measurements. In the light of these results, it was suggested that the ligand coordinate to each metal atom by the two ether oxygen, two nitrogen atoms of oxime imine (CN) and an axial oxygen of perchlorate to form pseudo square-pyramidal complexes with Ni(II), Cu(II) and Zn(II). Molar conductivity measurements reveal that all the complexes are non-electrolytes. In addition, the full geometric optimization of the tetraoxime ligand (4) has been made by the B3LYP/6-31G(d) level in order to establish a stable conformation. Additionally, all the complex structures have been studied in the B3LYP/LANL2DZ level. NBO charge distribution and the characteristics of frontier molecular orbitals of these complexes have also been investigated in order to see the electrons movement between ligand and metal atom in the same level.

  9. Synthesis, structure and DFT study of dinuclear iron, cobalt and nickel complexes with cyclopentadienyl-metal moieties.

    PubMed

    Liu, Nazhen; Li, Xiaoyan; Xu, Xiaofeng; Wang, Zhiping; Sun, Hongjian

    2011-07-14

    Reactions of 1,1'-bis(dipheny1phosphino)cobaltocene with Co(PMe(3))(4), Ni(PMe(3))(4), Fe(PMe(3))(4), Ni(COD)(2), FeMe(2)(PMe(3))(4) or NiMe(2)(PMe(3))(3) afford a series of novel dinuclear complexes [((Me(3)P)[lower bond 1 start]Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)M[upper bond 1 end](η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (M = Co(1), Ni(2) and Fe(3)) [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](COD)](4), [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](PMe(3))(2)] (5) and [((Me(3)P)[lower bond 1 start]Co(Me)(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)Fe[upper bond 1 end](Me)(η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (6). Reactions of 1,1'-bis(dipheny1phosphino)ferrocene with Ni(PMe(3))(4), NiMe(2)(PMe(3))(3), or Co(PMe(3))(4) gives rise to complexes [Fe(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)M[upper bond 1 end](PMe(3))(2)] (M = Ni (7), Co (8)). The complexes 1-8 were spectroscopically investigated and studied by X-ray single crystal diffraction. The possible reaction mechanisms and structural characteristics are discussed. Density functional theory (DFT) calculations strongly support the deductions.

  10. Synthesis, structure and magnetic properties of mono-, dinuclear and polymeric compounds of transition metals with 4-amino-3,5-di-2-pyridyl-4H-1,2,4-triazole

    NASA Astrophysics Data System (ADS)

    Martín-Ramos, Pablo; Silva, Manuela Ramos; de A. e Silva, Joana; Martins, Nuno D.; Yuste-Vivas, Consuelo; Pereira da Silva, Pedro S.; Sobral, Abílio J. F. N.; Pereira, Laura C. J.

    2016-03-01

    Five new complexes were obtained from solution of transition metal salts (M=Co(II), Cu(II)) with 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (abpt) in different molar ratios. X-ray structural elucidation revealed low-dimensional compounds with the metal ions assembled in monomers, dimers or chains. Two similar polymorphs were obtained for the monomer synthesized from Cu(II) chloride. Temperature-dependent magnetic susceptibility measurements were conducted for the non-monomeric compounds, and efficient super-exchange interaction was found for the mostly planar dinuclear Co(II) complex.

  11. Thermostability of proteins: role of metal binding and pH on the stability of the dinuclear CuA site of Thermus thermophilus.

    PubMed

    Sujak, Agnieszka; Sanghamitra, Nusrat J M; Maneg, Oliver; Ludwig, Bernd; Mazumdar, Shyamalava

    2007-10-15

    The dinuclear copper center (TtCuA) forming the electron entry site in the subunit II of the cytochrome c oxidase in Thermus thermophilus shows high stability toward thermal as well as denaturant-induced unfolding of the protein at ambient pH. We have studied the effect of pH on the stability of the holo-protein as well as of the apo-protein by UV-visible absorption, far-UV, and visible circular dichroism spectroscopy. The results show that the holo-protein both in the native mixed-valence state as well as in the reduced state of the metal ions and the apo-protein of TtCuA were extremely stable toward unfolding by guanidine hydrochloride at ambient pH. The thermal unfolding studies at different values of pH suggested that decreasing pH had almost no effect on the thermal stability of the protein in the absence of the denaturant. However, the stability of the proteins in presence of the denaturant was considerably decreased on lowering the pH. Moreover, the stability of the holo-protein in the reduced state of the metal ion was found to be lower than that in the mixed-valence state at the same pH. The denaturant-induced unfolding of the protein at different values of pH was analyzed using a two-state unfolding model. The values of the free energy of unfolding were found to increase with pH. The holo-protein showed that the variation of the unfolding free energy was associated with a pKa of approximately 5.5. This is consistent with the model that the protonation of a histidine residue may be responsible for the decrease in the stability of the holo-protein at low pH. The results were interpreted in the light of the reported crystal structure of the protein.

  12. Mechanical properties for irradiated face-centred cubic nanocrystalline metals.

    PubMed

    Xiao, X Z; Song, D K; Chu, H J; Xue, J M; Duan, H L

    2015-05-08

    In this paper, a self-consistent plasticity theory is proposed to model the mechanical behaviours of irradiated face-centred cubic nanocrystalline metals. At the grain level, a tensorial crystal model with both irradiation and grain size effects is applied for the grain interior (GI), whereas both grain boundary (GB) sliding with irradiation effect and GB diffusion are considered in modelling the behaviours of GBs. The elastic-viscoplastic self-consistent method with considering grain size distribution is developed to transit the microscopic behaviour of individual grains to the macroscopic properties of nanocrystals (NCs). The proposed theory is applied to model the mechanical properties of irradiated NC copper, and the feasibility and efficiency have been validated by comparing with experimental data. Numerical results show that: (i) irradiation-induced defects can lead to irradiation hardening in the GIs, but the hardening effect decreases with the grain size due to the increasing absorption of defects by GBs. Meanwhile, the absorbed defects would make the GBs softer than the unirradiated case. (ii) There exists a critical grain size for irradiated NC metals, which separates the grain size into the irradiation hardening dominant region (above the critical size) and irradiation softening dominant region (below the critical size). (iii) The distribution of grain size has a significant influence on the mechanical behaviours of both irradiated and unirradiated NCs. The proposed model can offer a valid theoretical foundation to study the irradiation effect on NC materials.

  13. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule.

    PubMed

    Zheng, Peng; Arantes, Guilherme M; Field, Martin J; Li, Hongbin

    2015-06-25

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions.

  14. The diastereoselective synthesis of octahedral cationic iridium hydride complexes with a stereogenic metal centre.

    PubMed

    Humbert, Nicolas; Mazet, Clément

    2016-08-23

    We report herein the highly diastereoselective synthesis of octahedral cationic Ir(iii) hydride complexes with a stereogenic metal centre following various strategies. The configurational stability of these compounds has also been investigated.

  15. Metal centre effects on HNO binding in porphyrins and the electronic origin: metal's electronic configuration, position in the periodic table, and oxidation state.

    PubMed

    Yang, Liu; Fang, Weihai; Zhang, Yong

    2012-04-21

    HNO binds to many different metals in organometallic and bioinorganic chemistry. To help understand experimentally observed metal centre effects, a quantum chemical investigation was performed, revealing clear general binding trends with respect to metal centre characteristics and the electronic origin for the first time. This journal is © The Royal Society of Chemistry 2012

  16. KMOS view of the Galactic Centre - II. Metallicity distribution of late-type stars

    NASA Astrophysics Data System (ADS)

    Feldmeier-Krause, A.; Kerzendorf, W.; Neumayer, N.; Schödel, R.; Nogueras-Lara, F.; Do, T.; de Zeeuw, P. T.; Kuntschner, H.

    2017-01-01

    Knowing the metallicity distribution of stars in the Galactic Centre has important implications for the formation history of the Milky Way nuclear star cluster. However, this distribution is not well known, and is currently based on a small sample of fewer than 100 stars. We obtained near-infrared K-band spectra of more than 700 late-type stars in the central 4 pc2 of the Milky Way nuclear star cluster with the integral-field spectrograph KMOS (VLT). We analyse the medium-resolution spectra using a full-spectral fitting method employing the Göttingen spectral library of synthetic PHOENIX spectra. The derived stellar metallicities range from metal-rich [M/H] > +0.3 dex to metal-poor [M/H] <-1.0 dex, with a fraction of 5.2^{+6.0}_{-3.1} per cent metal-poor ([M/H] ≤ -0.5 dex) stars. The metal-poor stars are distributed over the entire observed field. The origin of metal-poor stars remains unclear. They could originate from infalling globular clusters. For the metal-rich stellar population ([M/H] > 0 dex), a globular cluster origin can be ruled out. As there is only a very low fraction of metal-poor stars in the central 4 pc2 of the Galactic Centre, we believe that our data can discard a scenario in which the Milky Way nuclear star cluster is purely formed from infalling globular clusters.

  17. A new 3D metal-organic framework (MOF) Zn(DNBPDC)2(BPY) with a dinuclear zinc (II) clusters as SBU

    NASA Astrophysics Data System (ADS)

    Li, Song; Qin, Xiangdong; Deng, Linxin; Liu, Hui

    2017-04-01

    A new 3D framework compound 1 Zn(DNBPDC)2(BPY) (DBDBC =2,2‧-dinitro-[1,1‧-biphenyl]-4,4‧-dicarboxylic acid, BPY = 4,4‧-Bipyridine) with a dinuclear zinc (II) clusters as SBU have been synthesized and structurally characterized. This compound crystallizes in Tetragonal, space group I41/acd, with a = 21.2959(10)Å, b = 21.2959(10) Å, c = 27.969(3) Å, α = 90.00°, β = 90.00 (10)°, γ = 90.00°, V =12684.4(16) Å3, Z = 16, Dc = 1.424 mg/cm3, μ = 0.806 mm-1, F(000) = 3792. From the thermogravimetric analysis, the compound can be stabilized up to 380 °C and the skeleton collapsed occurred in about 350-550 °C. The luminescence property test shows that the compound exhibit strong emission at 485 nm. The nitrogen adsorption capacity was 10 cc/g when the compound was activated under the temperature of 77 K and reach to atmospheric pressure.

  18. Self-assembly of transition-metal-based macrocycles linked by photoisomerizable ligands: examples of photoinduced conversion of tetranuclear-dinuclear squares.

    PubMed

    Sun, Shih-Sheng; Anspach, Jason A; Lees, Alistair J

    2002-04-08

    A series of hetero- and homometallic square complexes bridged by a photoactive 4,4'-azopyridine (AZP) or 1,2-bis(4-pyridyl)ethylene (BPE) ligand, cyclobis[[cis-(dppf)M](mu-L)(2)(fac-Re(CO)(3)Br)](OTf)(4) (M = Pd, L = trans-AZP (5); M = Pt, L = trans-AZP (7); M = Pd, L = trans-BPE (8); M = Pt, L = trans-BPE (10)), cyclo[[cis-(dppf)M](mu-L)(2)(fac-Re(CO)(3)Br)](OTf)(2) (M = Pd, L = cis-AZP (6); M = Pd, L = cis-BPE (9)), [cis-(dppf)Pd(mu-trans-AZP)](4)(OTf)(8) (11), and [cis-(dppf)Pd(mu-cis-AZP)](2)(OTf)(4) (12), where dppf is 1,1'-bis(diphenylphosphino)ferrocene and OTf is trifluoromethanesulfonate anion, were prepared by thermodynamically driven self-assembly processes. The photophysical and photochemical properties of these complexes have been investigated, and all of them show a lack of luminescence in room temperature solution. Upon irradiation at 313 or 366 nm, Pd(II)-Re(I)-containing tetranuclear squares 5, 8, and 11 undergo photoisomerization and convert to their corresponding dinuclear complexes 6, 9, and 12, whereas Pt(II)-Re(I)-based squares 7 and 10 show only slow square disassembling processes. The tetranuclear squares can be fully recovered by heating the photoisomerized solution for several hours.

  19. Chiral tetranuclear and dinuclear copper(ii) complexes for TEMPO-mediated aerobic oxidation of alcohols: are four metal centres better than two?

    PubMed

    Zhang, Guoqi; Proni, Gloria; Zhao, Sherry; Constable, Edwin C; Housecroft, Catherine E; Neuburger, Markus; Zampese, Jennifer A

    2014-08-28

    The one-pot reaction of 3,5-di-tert-butyl-2-hydroxybenzaldehyde, (R)-2-aminoglycinol and Cu(OAc)2·2H2O in a 1 : 1 : 1 ratio in the presence of triethylamine led to the isolation of X-ray quality crystals of the chiral complex (R)- in high yield. The single crystal structure of (R)- reveals a tetranuclear copper(ii) complex that contains a {Cu4(μ-O)2(μ3-O)2N4O4} core. A reaction using (1S,2R)-2-amino-1,2-diphenylethanol as precursor under the same conditions generated the chiral complex (S,R)-; its structure was determined by single crystal X-ray crystallography and was found to contain a {Cu2(μ-O)2N2O2} core. Both (R)- and (S,R)- have been used for catalytic aerobic oxidation of benzylic alcohols in combination with the TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) radical. (R)- selectively catalyses the conversion of various aromatic primary alcohols to the corresponding aldehydes with high yields (99%) and TONs (770) in the air, while (S,R)- exhibits less promising catalytic performance under the same reaction conditions. The role of the cluster structures in (R)- and (S,R)- in controlling the reactivity towards aerobic oxidation reactions is discussed.

  20. Anharmonic pair potential study in face-centred-cubic structure metals

    NASA Astrophysics Data System (ADS)

    Pirog, I. V.; Nedoseikina, T. I.; Zarubin, I. A.; Shuvaev, A. T.

    2002-03-01

    Temperature dependencies of Ni, Cu and Mo metals EXAFS spectra were studied in order to determine the anharmonic pair potential. The potential parameters for metals with cubic structure - Ni, Cu, Mo as well as for Pb (Stern E A et al 1991 Phys. Rev. B 43 8850), Au, Ag (Newville M and Stern E A http://krazy.phys.washington.edu/paper/ag-au.html) - obtained earlier, were analysed to find correlations with other physical characteristics. It was found that a, b potential parameter values correlate with cohesive energy and interatomic distance for face-centred-cubic structure metals. Obtained potential parameter values were used to determine thermodynamics parameters, including the linear coefficient of thermal expansion, the Debye temperature, the bulk modulus and the Grunesien parameter.

  1. Robust silver-mediated imidazolo-dC base pairs in metal DNA: dinuclear silver bridges with exceptional stability in double helices with parallel and antiparallel strand orientation.

    PubMed

    Jana, Sunit Kumar; Guo, Xiurong; Mei, Hui; Seela, Frank

    2015-12-18

    A new unprecedented metal-mediated base pair was designed that stabilizes reverse Watson-Crick DNA (parallel strand orientation, ps) as well as canonical Watson-Crick DNA (antiparallel strand orientation, aps). This base pair contains two imidazolo-dC units decorated with furan residues. Tm measurements and spectroscopic studies reveal that each silver-mediated furano-imidazolo-dC forms exceptionally stable duplexes with ps and aps chain orientation. This stability increase by a silver-mediated base pair is the highest reported so far for ps and aps DNA helices.

  2. Synthesis, structure and reactivity of dinuclear rare earth metal bis(o-aminobenzyl) complexes bearing a 1,4-phenylenediamidinate co-ligand.

    PubMed

    Li, Meng; Hong, Jianquan; Chen, Zhenxia; Zhou, Xigeng; Zhang, Lixin

    2013-06-21

    A series of phenylenediamidinate rare earth metal complexes 1,4-C6H4[C(NR)2Ln(o-CH2C6H4NMe2)2]2 (R = 2,6-(i)Pr2-C6H3, Ln = Y (2a), Lu (2b), Sc (2c)) were synthesized by deprotonation of 1,4-C6H4[C(NR)(NHR)]2 (1) with two equivalents of n-BuLi followed by reacting with two equivalents of anhydrous LnCl3 and subsequently four equivalents of Li(o-CH2C6H4NMe2), or by protolysis of [Ln(o-CH2C6H4NMe2)3] with 0.5 equivalent of 1 in THF or toluene. Treatment of complexes 2a and 2b with four equivalents of phenyl isocyanate and phenyl isothiocyanate gave the corresponding insertion products 1,4-C6H4[C(NR)2Ln{OC(CH2C6H4NMe2-o)NPh}2(THF)]2 (Ln = Y (3a), Lu (3b)) and 1,4-C6H4[C(NR)2Ln{SC(CH2C6H4NMe2-o)NPh}2]2 (Ln = Y (4a), Lu (4b)), respectively. The structures of 1, 3b, and 4a were established by X-ray diffraction studies. Complexes 2 show high activity for rac-lactide and ε-caprolactone polymerization; for the former a synergistic effect between two metal centers is observed.

  3. Metal centre effects on HNO binding in porphyrins and the electronic origin: Metal’s electronic configuration, position in the periodic table, and oxidation state

    PubMed Central

    Yang, Liu

    2014-01-01

    HNO binds with many different metals in organometallic and bioinorganic chemistry. To help understand experimentally observed metal centre effects, a quantum chemical investigation was performed, revealing clear general binding trends with respect to metal centre characteristics and the electronic origin for the first time. PMID:22437041

  4. Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism.

    PubMed

    Ube, Hitoshi; Yasuda, Yoshihiro; Sato, Hiroyasu; Shionoya, Mitsuhiko

    2017-02-08

    Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a Pt(II)-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis-trans isomerization at the Pt(II) centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one Pt(II) ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems.

  5. Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism

    NASA Astrophysics Data System (ADS)

    Ube, Hitoshi; Yasuda, Yoshihiro; Sato, Hiroyasu; Shionoya, Mitsuhiko

    2017-02-01

    Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a PtII-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis-trans isomerization at the PtII centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one PtII ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems.

  6. Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism

    PubMed Central

    Ube, Hitoshi; Yasuda, Yoshihiro; Sato, Hiroyasu; Shionoya, Mitsuhiko

    2017-01-01

    Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a PtII-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis–trans isomerization at the PtII centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one PtII ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems. PMID:28176770

  7. Influence of complex impurity centres on radiation damage in wide-gap metal oxides

    NASA Astrophysics Data System (ADS)

    Lushchik, A.; Lushchik, Ch.; Popov, A. I.; Schwartz, K.; Shablonin, E.; Vasil'chenko, E.

    2016-05-01

    Different mechanisms of radiation damage of wide-gap metal oxides as well as a dual influence of impurity ions on the efficiency of radiation damage have been considered on the example of binary ionic MgO and complex ionic-covalent Lu3Al5O12 single crystals. Particular emphasis has been placed on irradiation with ∼2 GeV heavy ions (197Au, 209Bi, 238U, fluence of 1012 ions/cm2) providing extremely high density of electronic excitations within ion tracks. Besides knock-out mechanism for Frenkel pair formation, the additional mechanism through the collapse of mobile discrete breathers at certain lattice places (e.g., complex impurity centres) leads to the creation of complex defects that involve a large number of host atoms. The experimental manifestations of the radiation creation of intrinsic and impurity antisite defects (Lu|Al or Ce|Al - a heavy ion in a wrong cation site) have been detected in LuAG and LuAG:Ce3+ single crystals. Light doping of LuAG causes a small enhancement of radiation resistance, while pair impurity centres (for instance, Ce|Lu-Ce|Al or Cr3+-Cr3+ in MgO) are formed with a rise of impurity concentration. These complex impurity centres as well as radiation-induced intrinsic antisite defects (Lu|Al strongly interacting with Lu in a regular site) tentatively serve as the places for breathers collapse, thus decreasing the material resistance against dense irradiation.

  8. A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production.

    PubMed

    Chen, Sha; Li, Kang; Zhao, Fang; Zhang, Lei; Pan, Mei; Fan, Yan-Zhong; Guo, Jing; Shi, Jianying; Su, Cheng-Yong

    2016-11-09

    Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium-palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h(-1) and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

  9. A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

    PubMed Central

    Chen, Sha; Li, Kang; Zhao, Fang; Zhang, Lei; Pan, Mei; Fan, Yan-Zhong; Guo, Jing; Shi, Jianying; Su, Cheng-Yong

    2016-01-01

    Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium–palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h−1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications. PMID:27827376

  10. A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

    NASA Astrophysics Data System (ADS)

    Chen, Sha; Li, Kang; Zhao, Fang; Zhang, Lei; Pan, Mei; Fan, Yan-Zhong; Guo, Jing; Shi, Jianying; Su, Cheng-Yong

    2016-11-01

    Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium-palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h-1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

  11. A lattice-gas model for alkali-metal fullerides: face-centred-cubic structure

    NASA Astrophysics Data System (ADS)

    Udvardi, László; Szabó, György

    1996-12-01

    A lattice-gas model is suggested for describing the ordering phenomena in alkali-metal fullerides of face-centred-cubic structure assuming that the electric charge of alkali ions residing in either octahedral or tetrahedral sites is completely screened by the first-neighbour 0953-8984/8/50/022/img5 molecules. This approximation allows us to derive an effective ion - ion interaction. The van der Waals interaction between the ion and 0953-8984/8/50/022/img5 molecule is characterized by introducing an additional site energy at the tetrahedral sites. This model is investigated by using a three-sublattice mean-field approximation and a simple cluster-variation method. The analysis shows a large variety of phase diagrams as the site energy parameter is changed.

  12. A lattice-gas model for alkali-metal fullerides: body-centred-cubic structure

    NASA Astrophysics Data System (ADS)

    Szabó, György; Udvardi, László

    1998-05-01

    A Coulomb lattice-gas model with a host-lattice screening mechanism is adapted to describe the ordering phenomena in alkali-metal fullerides of body-centred-cubic structure. It is assumed that the electric charge of an alkali ion residing at a tetrahedral interstitial site is completely screened by its first-neighbour 0953-8984/10/19/009/img5 molecules. The electronic energy of the 0953-8984/10/19/009/img6 ion is also taken into consideration as a charged spherical shell. By means of these assumptions an effective (short-range) pair interaction between two alkali ions is obtained. The resultant lattice-gas model is analysed by using two- and six-sublattice mean-field approximations. The thermodynamic properties are summarized in phase diagrams for different shell radii.

  13. Structure of a conserved hypothetical protein SA1388 from S. aureus reveals a capped hexameric toroid with two PII domain lids and a dinuclear metal center

    SciTech Connect

    Saikatendu, Kumar Singh; Zhang, Xuejun; Kinch, Lisa; Leybourne, Matthew; Grishin, Nick V.; Zhang, Hong

    2009-01-26

    The protein encoded by the SA1388 gene from Staphylococcus aureus was chosen for structure determination to elucidate its domain organization and confirm our earlier remote homology based prediction that it housed a nitrogen regulatory PII protein-like domain. SA1388 was predicted to contain a central PII-like domain and two flanking regions, which together belong to the NIF3-like protein family. Proteins like SA1388 remain a poorly studied group and their structural characterization could guide future investigations aimed at understanding their function. The structure of SA1388 has been solved to 2.0{angstrom} resolution by single wavelength anomalous dispersion phasing method using selenium anomalous signals. It reveals a canonical NIF3-like fold containing two domains with a PII-like domain inserted in the middle of the polypeptide. The N and C terminal halves of the NIF3-like domains are involved in dimerization, while the PII domain forms trimeric contacts with symmetry related monomers. Overall, the NIF3-like domains of SA1388 are organized as a hexameric toroid similar to its homologs, E. coli ybgI and the hypothetical protein SP1609 from Streptococcus pneumoniae. The openings on either side of the toroid are partially covered by trimeric 'lids' formed by the PII domains. The junction of the two NIF3 domains has two zinc ions bound at what appears to be a histidine rich active site. A well-defined electron density corresponding to an endogenously bound ligand of unknown identity is observed in close proximity to the metal site. SA1388 is the third member of the NIF3-like family of proteins to be structurally characterized, the other two also being hypothetical proteins of unknown function. The structure of SA1388 confirms our earlier prediction that the inserted domain that separates the two NIF3 domains adopts a PII-like fold and reveals an overall capped toroidal arrangement for the protein hexamer. The six PII-like domains form two trimeric 'lids' that

  14. Cleavage of hydrogen by activation at a single non-metal centre - towards new hydrogen storage materials.

    PubMed

    Grabowski, Sławomir J

    2015-05-28

    Molecular surfaces of non-metal species are often characterized by both positive and negative regions of electrostatic potential (EP) at a non-metal centre. This centre may activate molecular hydrogen which further leads to the addition reaction. The positive EP regions at the non-metal centres correspond to σ-holes; the latter sites are enhanced by electronegative substituents. This is why the following simple moieties; PFH2, SFH, AsFH2, SeFH, BrF3, PF(CH3)2 and AsF(CH3)2, were chosen here to analyze the H2 activation and its subsequent splitting at the P, As, S, Se and Br centres. Also the reverse H-H bond reforming process is analyzed. MP2/aug-cc-pVTZ calculations were performed for systems corresponding to different stages of these processes. The sulphur centre in the SFH moiety is analyzed in detail since the potential barrier height for the addition reaction for this species is the lowest of the moieties analyzed here. The results of calculations show that the SFH + H2 → SFH3 reaction in the gas phase is endothermic but it is exothermic in polar solvents.

  15. Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

    PubMed Central

    Jouffroy, Matthieu; Gramage-Doria, Rafael; Sémeril, David; Oberhauser, Werner; Toupet, Loïc

    2014-01-01

    Summary The capacity of two cavity-shaped ligands, HUGPHOS-1 and HUGPHOS-2, to generate exclusively singly phosphorus-ligated complexes, in which the cyclodextrin cavity tightly wraps around the metal centre, was explored with a number of late transition metal cations. Both cyclodextrin-derived ligands were assessed in palladium-catalysed Mizoroki–Heck coupling reactions between aryl bromides and styrene on one hand, and the rhodium-catalysed asymmetric hydroformylation of styrene on the other hand. The inability of both chiral ligands to form standard bis(phosphine) complexes under catalytic conditions was established by high-pressure NMR studies and shown to have a deep impact on the two carbon–carbon bond forming reactions both in terms of activity and selectivity. For example, when used as ligands in the rhodium-catalysed hydroformylation of styrene, they lead to both high isoselectivity and high enantioselectivity. In the study dealing with the Mizoroki–Heck reactions, comparative tests were carried out with WIDEPHOS, a diphosphine analogue of HUGPHOS-2. PMID:25383109

  16. Design of dinuclear manganese cofactors for bacterial reaction centers.

    PubMed

    Olson, Tien L; Espiritu, Eduardo; Edwardraja, Selvakumar; Simmons, Chad R; Williams, JoAnn C; Ghirlanda, Giovanna; Allen, James P

    2016-05-01

    A compelling target for the design of electron transfer proteins with novel cofactors is to create a model for the oxygen-evolving complex, a Mn4Ca cluster, of photosystem II. A mononuclear Mn cofactor can be added to the bacterial reaction center, but the addition of multiple metal centers is constrained by the native protein architecture. Alternatively, metal centers can be incorporated into artificial proteins. Designs for the addition of dinuclear metal centers to four-helix bundles resulted in three artificial proteins with ligands for one, two, or three dinuclear metal centers able to bind Mn. The three-dimensional structure determined by X-ray crystallography of one of the Mn-proteins confirmed the design features and revealed details concerning coordination of the Mn center. Electron transfer between these artificial Mn-proteins and bacterial reaction centers was investigated using optical spectroscopy. After formation of a light-induced, charge-separated state, the experiments showed that the Mn-proteins can donate an electron to the oxidized bacteriochlorophyll dimer of modified reaction centers, with the Mn-proteins having additional metal centers being more effective at this electron transfer reaction. Modeling of the structure of the Mn-protein docked to the reaction center showed that the artificial protein likely binds on the periplasmic surface similarly to cytochrome c2, the natural secondary donor. Combining reaction centers with exogenous artificial proteins provides the opportunity to create ligands and investigate the influence of inhomogeneous protein environments on multinuclear redox-active metal centers. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

  17. Gas-phase and solution-phase polymerization of epoxides by Cr(salen) complexes: evidence for a dinuclear cationic mechanism.

    PubMed

    Schön, Eva; Zhang, Xiangyang; Zhou, Zhiping; Chisholm, Malcolm H; Chen, Peter

    2004-11-15

    The gas-phase reactions of a series of mass-selected mononuclear and dinuclear Cr(salen) complexes with propylene oxide suggest that the enhanced reactivity of the dinuclear complexes in gas-phase and in solution may derive from a dicationic mechanism in which the alkoxide chain is mu(2)-coordinated to two Lewis acidic metal centers. The double coordination is proposed to suppress backbiting, and hence chain-transfer in the gas-phase homopolymerization of epoxides.

  18. Enhancement of the third-order nonlinear optical properties in open-shell singlet transition-metal dinuclear systems: effects of the group, of the period, and of the charge of the metal atom.

    PubMed

    Fukui, Hitoshi; Inoue, Yudai; Yamada, Taishi; Ito, Soichi; Shigeta, Yasuteru; Kishi, Ryohei; Champagne, Benoît; Nakano, Masayoshi

    2012-06-07

    Metal-metal multiply bonded complexes in their singlet state have been predicted to form a novel class of "σ-dominant" third-order nonlinear optical compounds based on the results of dichromium(II) and dimolybdenum(II) systems (H. Fukui et al. J. Phys. Chem. Lett.2011, 2, 2063) whose second hyperpolarizabilities (γ) are enhanced by the contribution of the dσ electrons with an intermediate diradical character. In this study, using the spin-unrestricted coupled-cluster method with singles and doubles as well as with perturbative triples, we investigate the dependences of γ on the group and on the period of the transition metals as well as on their atomic charges in several open-shell singlet dimetallic systems. A significant enhancement of γ is observed in those dimetallic systems composed of (i) transition metals with a small group number, (ii) transition metals with a large periodic number, and (iii) transition metals with a small positive charge. From the decomposition of the γ values into the contributions of dσ, dπ, and dδ electrons, the γ enhancements are shown to originate from the dσ contribution, because it corresponds to the intermediate diradical character region. Furthermore, the amplitude of dσ contribution turns out to be related to the size of the d(z(2)) atomic orbital of the transition metal, which accounts for the dependence of γ on the group, on the period, and on the charge of the metal atoms. These dependences provide a guideline for an effective molecular design of highly efficient third-order nonlinear optical (NLO) systems based on the metal-metal bonded systems.

  19. X-Ray Absorption Spectroscopy of Dinuclear Metallohydrolases

    PubMed Central

    Tierney, David L.; Schenk, Gerhard

    2014-01-01

    In this mini-review, we briefly discuss the physical origin of x-ray absorption spectroscopy (XAS) before illustrating its application using dinuclear metallohydrolases as exemplary systems. The systems we have selected for illustrative purposes present a challenging problem for XAS, one that is ideal to demonstrate the potential of this methodology for structure/function studies of metalloenzymes in general. When the metal ion is redox active, XAS provides a sensitive measure of oxidation-state-dependent differences. When the metal ion is zinc, XAS is the only spectroscopic method that will provide easily accessible structural information in solution. In the case of heterodimetallic sites, XAS has the unique ability to interrogate each metal site independently in the same sample. One of the strongest advantages of XAS is its ability to examine metal ion site structures with crystallographic precision, without the need for a crystal. This is key for studying flexible metal ion sites, such as those described in the selected examples, because it allows one to monitor structural changes that occur during substrate turnover. PMID:25229134

  20. Chemical abundances of M giants in the Galactic centre: A single metal-rich population with low [α/Fe

    NASA Astrophysics Data System (ADS)

    Ryde, N.; Schultheis, M.

    2015-01-01

    Context. The formation and evolution of the Milky Way bulge is still largely an unanswered question. Some of the most essential observations needed for its modelling are the metallicity distribution and the trends of the α elements, as measured in stars. While bulge regions beyond R ≳ 50 pc of the centre have been targeted in several surveys, the central part has escaped a detailed study due to the extreme extinction and crowding. The abundance gradients from the centre are, however, of large diagnostic value. Aims: We aim at investigating the Galactic centre environment by probing M giants in the field by avoiding supergiants and cluster members. Methods: For nine field M-giants in the Galactic centre region, we have obtained high- and low-resolution spectra observed simultaneously with CRIRES and ISAAC on UT1 and UT3 of the VLT. The low-resolution spectra provide a means of determining the effective temperatures, and the high-resolution spectra provide detailed abundances of Fe, Mg, Si, and Ca. Results: We find a metal-rich population at [ Fe / H ] = + 0.11 ± 0.15 and a lack of the metal-poor population, which is found further out in the bulge, corroborating earlier studies. Our [α/Fe] element trends, however, show low values, by following the outer bulge trends. A possible exception of the [Ca/Fe] trend is found and needs further investigation. Conclusions: The results of the analysed field M-giants in the Galactic centre region exclude a scenario with rapid formation, in which SNIIe played a dominated role in the chemical enrichment of the gas. The high metallicities with low α-enhancement seems to indicate a bar-like population that is, perhaps, related to the nuclear bar. Based on observations collected at the European Southern Observatory, Chile, program number 089.B-0312(A)/VM/CRIRES and 089.B-0312(B)/VM/ISAAC.Figures 8 and 9 are available in electronic form at http://www.aanda.org

  1. Unprecedented dinuclear silver(I)-mediated base pair involving the DNA lesion 1,N(6)-ethenoadenine.

    PubMed

    Mandal, Soham; Hepp, Alexander; Müller, Jens

    2015-02-28

    The DNA lesion 1,N(6)-ethenoadenine (εA) has been investigated with respect to its metal-binding properties. A synthetic DNA duplex comprising an εA : εA mispair readily forms doubly silver(I)-mediated base pairs εA-Ag(I)2-εA, representing the first example for a dinuclear metal-mediated homo base pair of a purine derivative. It also constitutes the first example for a Hoogsteen-type metal-mediated homo base pair within a B-DNA duplex.

  2. Synthesis of a novel heptacoordinated Fe(III) dinuclear complex: experimental and theoretical study of the magnetic properties.

    PubMed

    Craig, Gavin A; Barrios, Leoní A; Sánchez Costa, José; Roubeau, Olivier; Ruiz, Eliseo; Teat, Simon J; Wilson, Chick C; Thomas, Lynne; Aromí, Guillem

    2010-05-28

    A new functionalized bis-pyrazol-pyridine ligand has been prepared by reaction with hydrazine of the corresponding bis-β-diketone precursor, also unprecedented. The aerobic reaction of this ligand with ferrous thiocyanate in the presence of ascorbic or oxalic acid affords the dinuclear complex of seven-coordinate Fe(III), [Fe₂(H₄L2)₂(ox)(NCS)₄] (1), as revealed by single crystal X-ray diffraction. This may represent an entry into a new family of [Fe₂] compounds with heptacoordinate metal centres. The capacity of this unusual chromophore to undergo magnetic super-exchange was investigated by means of bulk magnetization and DFT calculations. Both approaches confirmed the presence of antiferromagnetic interactions within the molecule. The theoretical investigation has served to describe the magnetic orbitals of Fe(III) in this unusual coordination geometry, as well as the exchange mechanism. A brief review of the scarce number of iron heptacoordinate complexes reported in the literature is also included and discussed.

  3. Structural alteration of the metal-organic pyrogallol[4]arene nano-capsule motif by incorporation of large metal centres.

    PubMed

    Jin, Ping; Kumari, Harshita; Kennedy, Stuart; Barnes, Charles L; Teat, Simon J; Dalgarno, Scott J; Atwood, Jerry L

    2014-05-04

    Addition of cadmium(II) nitrate to gallium-coordinated metal-organic C-alkylpyrogallol[4]arene nano-capsules affords a variation of the near spherical hexamer motif, structural changes in which are induced by the markedly different nature of the secondary incorporated metal.

  4. Crystal structure of a mixed-ligand dinuclear Ba-Zn complex with 2-meth-oxy-ethanol having tri-phenyl-acetate and chloride bridges.

    PubMed

    Utko, Józef; Sobocińska, Maria; Dobrzyńska, Danuta; Lis, Tadeusz

    2015-07-01

    The dinuclear barium-zinc complex, μ-chlorido-1:2κ(2) Cl:Cl-chlorido-2κCl-bis-(2-meth-oxy-ethanol-1κO)bis-(2-meth-oxy-ethanol-1κ(2) O,O')bis-(μ-tri-phenyl-acetato-1:2κ(2) O:O')bariumzinc, [BaZn(C20H15O2)2Cl2(C3H8O2)4], has been synthesized by the reaction of barium tri-phenyl-acetate, anhydrous zinc chloride and 2-meth-oxy-ethanol in the presence of toluene. The barium and zinc metal cations in the dinuclear complex are linked via one chloride anion and carboxyl-ate O atoms of the tri-phenyl-acetate ligands, giving a Ba⋯Zn separation of 3.9335 (11) Å. The irregular nine-coordinate BaO8Cl coordination centres comprise eight O-atom donors, six of them from 2-meth-oxy-ethanol ligands (four from two bidentate O,O'-chelate inter-actions and two from monodentate inter-actions), two from bridging tri-phenyl-acetate ligands and one from a bridging Cl donor. The distorted tetra-hedral coordination sphere of zinc comprises two O-atom donors from the tri-phenyl-acetate ligands and two Cl donors (one bridging and one terminal). In the crystal, O-H⋯Cl, O-H⋯O and C-H⋯Cl inter-molecular inter-actions form a layered structure, lying parallel to (001).

  5. Three-component entanglements consisting of three crescent-shaped bidentate ligands coordinated to an octahedral metal centre.

    PubMed

    Durola, Fabien; Russo, Luca; Sauvage, Jean-Pierre; Rissanen, Kari; Wenger, Oliver S

    2007-01-01

    3,3'-biisoquinoline ligands (biiq) L, bearing aromatic substituents on their 8 and 8' positions, have been used to generate interwoven systems consisting of three crescent-shaped ligands disposed around an octahedral metal centre. Mono-ligand complexes of the type [ReL(CO)3py]+ (py: pyridine) have also been prepared, leading to sterically non-hindering complexes in spite of the endotopic nature of the chelate used. The three-component entanglements have been prepared by using either FeII or RuII as gathering metal centre. The synthetic procedure is simple and efficient, affording fully characterised complexes as their PF6 or SbCl6 salts. X-ray crystallography clearly shows that the crescent-shaped ligands do not repel each other in the tris-chelate complexes. In an analogous way, the ReI complexes show open structures with no steric repulsion between the L ligand and the ancillary CO or py groups. The FeL3 or RuL3 compounds are very unusual in the sense that, contrary to all the other tris-bidentate chelate complexes made till now, the three organic components are tangled up, in a situation which will be very favourable to the formation of new non trivial topologies of the catenane type.

  6. Validation of primary metal-on-metal hip arthroplasties on the National Joint Registry for England, Wales and Northern Ireland using data from the London Implant Retrieval Centre

    PubMed Central

    Sabah, S. A.; Henckel, J.; Cook, E.; Whittaker, R.; Hothi, H.; Pappas, Y.; Blunn, G.; Skinner, J. A.; Hart, A. J.

    2015-01-01

    Arthroplasty registries are important for the surveillance of joint replacements and the evaluation of outcome. Independent validation of registry data ensures high quality. The ability for orthopaedic implant retrieval centres to validate registry data is not known. We analysed data from the National Joint Registry for England, Wales and Northern Ireland (NJR) for primary metal-on-metal hip arthroplasties performed between 2003 and 2013. Records were linked to the London Implant Retrieval Centre (RC) for validation. A total of 67 045 procedures on the NJR and 782 revised pairs of components from the RC were included. We were able to link 476 procedures (60.9%) recorded with the RC to the NJR successfully. However, 306 procedures (39.1%) could not be linked. The outcome recorded by the NJR (as either revised, unrevised or death) for a primary procedure was incorrect in 79 linked cases (16.6%). The rate of registry-retrieval linkage and correct assignment of outcome code improved over time. The rates of error for component reference numbers on the NJR were as follows: femoral head category number 14/229 (5.0%); femoral head batch number 13/232 (5.3%); acetabular component category number 2/293 (0.7%) and acetabular component batch number 24/347 (6.5%). Registry-retrieval linkage provided a novel means for the validation of data, particularly for component fields. This study suggests that NJR reports may underestimate rates of revision for many types of metal-on-metal hip replacement. This is topical given the increasing scope for NJR data. We recommend a system for continuous independent evaluation of the quality and validity of NJR data. Cite this article: Bone Joint J 2015;97-B:10–18. PMID:25568407

  7. International metal-on-metal multidisciplinary teams: do we manage patients with metal-on-metal hip arthroplasty in the same way? An analysis from the International Specialist Centre Collaboration on MOM Hips (ISCCoMH).

    PubMed

    Berber, R; Skinner, J; Board, T; Kendoff, D; Eskelinen, A; Kwon, Y-M; Padgett, D E; Hart, A

    2016-02-01

    There are many guidelines that help direct the management of patients with metal-on-metal (MOM) hip arthroplasties. We have undertaken a study to compare the management of patients with MOM hip arthroplasties in different countries. Six international tertiary referral orthopaedic centres were invited to participate by organising a multi-disciplinary team (MDT) meeting, consisting of two or more revision hip arthroplasty surgeons and a musculoskeletal radiologist. A full clinical dataset including history, blood tests and imaging for ten patients was sent to each unit, for discussion and treatment planning. Differences in the interpretation of findings, management decisions and rationale for decisions were compared using quantitative and qualitative methods. Overall agreement between the orthopaedic centres and the recommended treatment plans for the ten patients with MOM hip implants was moderate (kappa = 0.6). Full agreement was seen in a third of cases, however split decisions were also seen in a third of cases. Units differed in their interpretation of the significance of the investigation findings and put varying emphasis on serial changes, in the presence of symptoms. In conclusion, the management of raised or rising blood metal ions, cystic pseudotumours and peri-acetabular osteolysis led to inconsistency in the agreement between centres. Coordinated international guidance and MDT panel discussions are recommended to improve consensus in decision making. A lack of evidence and the subsequent variation in regulator guidance leads to differences in opinions, the clinical impact of which can be reduced through a multi-disciplinary team approach to managing patients with MOM hip implants. Cite this article: Bone Joint J 2016;98-B:179-86. ©2016 The British Editorial Society of Bone & Joint Surgery.

  8. Cobalt substitution of mouse R2 ribonucleotide reductase as a model for the reactive diferrous state: spectroscopic and structural evidence for a ferromagnetically coupled dinuclear cobalt cluster.

    PubMed

    Strand, Kari R; Karlsen, Solveig; Andersson, K Kristoffer

    2002-09-13

    The R2 dimer of mouse ribonucleotide reductase contains a dinuclear iron-oxygen cluster and tyrosyl radical/subunit. The dinuclear diferrous form reacts with dioxygen to generate the tyrosyl radical essential for the catalytic reaction that occurs at the R1 dimer. It is important to understand how the reactivity toward oxygen is related to the crystal structure of the dinuclear cluster. For the mouse R2 protein, no structure has been available with a fully occupied dinuclear metal ion site. A cobalt substitution of mouse R2 was performed to produce a good model for the very air-sensitive diferrous form of the enzyme. X-band EPR and light absorption studies (epsilon(550 nm) = 100 mm(-1) cm(-1)/Co(II)) revealed a strong cooperative binding of cobalt to the dinuclear site. In perpendicular mode EPR, the axial signal from mouse R2 incubated with Co(II) showed a typical S = 3/2 Co(II) signal, and its low intensity indicated that the majority of the Co(II) bound to R2 is magnetically coupled. In parallel mode EPR, a typical integer spin signal (M(s) = +/-3) with g approximately 12 is observed at 3.6 K and 10 K, showing that the two Co(II) ions (S = 3/2) in the dinuclear site are ferromagnetically coupled. We have solved the 2.4 A crystal structure of the Co(II)-substituted R2 with a fully occupied dinuclear cluster. The bridging Co(II) carboxylate ligand Glu-267 adopts an altered orientation compared with its counterpart Glu-238 in Escherichia coli R2. This might be important for proper O(2) activation of the more exposed native diferrous site in mouse R2 compared with E. coli R2.

  9. Metal levels in seston and marine fish flesh near industrial and metropolitan centres in South Australia.

    PubMed

    Edwards, J W; Edyvane, K S; Boxall, V A; Hamann, M; Soole, K L

    2001-05-01

    Port Pirie is the site of the largest lead smelter in the world, depositing 250 t of zinc, and 100 t of lead annually into Spencer Gulf. Barker Inlet is adjacent to metropolitan Adelaide, and receives unknown quantities of urban and industrial discharges. Both areas are sites of major commercial and recreational fisheries, contained within delicately balanced marine wetland ecosystems, comprising large areas of mangrove and seagrass habitats. Aldrichetta forsteri and Sillago schomburgkii are major species within these fisheries and as estuarine-dependent species were chosen for this study as indicator species for the detection and monitoring of pollutant impacts in the nearshore marine ecosystems of South Australia. Seston sediment collectors were deployed at each site and analysed seasonally for the presence of cadmium, lead and copper. Flesh samples from A. forsteri and S. schomburgkii were examined seasonally for the presence of cadmium, lead and copper and the results correlated with levels found in the seston sediment at each site. Metal concentrations were also correlated with a biomarker of genotoxicity measured in the same animals (micronuclei in erythrocytes) that were reported previously. Seston levels of cadmium, lead and copper were highest at Port Pirie, followed by Barker Inlet and were lowest at Wills Creek, with cadmium undetectable at the latter site. Metals in seston varied considerably with season, with generally higher levels in winter samples. In fish flesh, metal levels followed broadly similar trends as for seston. Spearman rank correlations between metals in seston and in flesh were strongly positive. There was also a significant correlation between flesh concentrations of each metal and the frequency of micronuclei in erythrocytes. This study has shown that seston concentration of pollutant metals are high in areas of industrial activity, and that these levels are also reflected in metal content of fish flesh. Mean flesh levels of cadmium

  10. Molecular metal-Nx centres in porous carbon for electrocatalytic hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Liang, Hai-Wei; Brüller, Sebastian; Dong, Renhao; Zhang, Jian; Feng, Xinliang; Müllen, Klaus

    2015-08-01

    Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. Here we report a novel type of robust cobalt-nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt-N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template. We identify the well-dispersed molecular CoNx sites on the carbon support as the active sites responsible for the HER. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s-1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Our results suggest the great promise of developing new families of non-precious metal HER catalysts based on the controlled conversion of homogeneous metal complexes into solid-state carbon catalysts via economically scalable protocols.

  11. Geometries of low spin states of multi-centre transition metal complexes through extended broken symmetry variational Monte Carlo

    NASA Astrophysics Data System (ADS)

    Barborini, Matteo; Guidoni, Leonardo

    2016-09-01

    The correct description of the ground state electronic and geometrical properties of multi-centre transition metal complexes necessitates of a high-level description of both dynamical and static correlation effects. In di-metallic complexes, the ground state low spin properties can be computed starting from single-determinants High-Spin (HS) and Broken Symmetry (BS) states by reconstructing an approximated low spin potential energy surface through the extended broken symmetry approach, based on the Heisenberg Hamiltonian. In the present work, we first apply this approach within the variational Monte Carlo method to tackle the geometry optimization of a Fe2S2(SH)42- model complex. To describe the HS and BS wavefunctions, we use a fully optimized unrestricted single determinant with a correlated Jastrow factor able to recover a large amount of dynamical correlation. We compared our results with those obtained by density functional theory and other multiconfigurational approaches, discussing the role of the nodal surface on the structural parameters.

  12. Geometries of low spin states of multi-centre transition metal complexes through extended broken symmetry variational Monte Carlo.

    PubMed

    Barborini, Matteo; Guidoni, Leonardo

    2016-09-28

    The correct description of the ground state electronic and geometrical properties of multi-centre transition metal complexes necessitates of a high-level description of both dynamical and static correlation effects. In di-metallic complexes, the ground state low spin properties can be computed starting from single-determinants High-Spin (HS) and Broken Symmetry (BS) states by reconstructing an approximated low spin potential energy surface through the extended broken symmetry approach, based on the Heisenberg Hamiltonian. In the present work, we first apply this approach within the variational Monte Carlo method to tackle the geometry optimization of a Fe2S2(SH)4(2-) model complex. To describe the HS and BS wavefunctions, we use a fully optimized unrestricted single determinant with a correlated Jastrow factor able to recover a large amount of dynamical correlation. We compared our results with those obtained by density functional theory and other multiconfigurational approaches, discussing the role of the nodal surface on the structural parameters.

  13. Biological processing of dinuclear ruthenium complexes in eukaryotic cells.

    PubMed

    Li, Xin; Heimann, Kirsten; Dinh, Xuyen Thi; Keene, F Richard; Collins, J Grant

    2016-10-20

    The biological processing - mechanism of cellular uptake, effects on the cytoplasmic and mitochondrial membranes, intracellular sites of localisation and induction of reactive oxygen species - of two dinuclear polypyridylruthenium(ii) complexes has been examined in three eukaryotic cells lines. Flow cytometry was used to determine the uptake of [{Ru(phen)2}2{μ-bb12}](4+) (Rubb12) and [Ru(phen)2(μ-bb7)Ru(tpy)Cl](3+) {Rubb7-Cl, where phen = 1,10-phenanthroline, tpy = 2,2':6',2''-terpyridine and bbn = bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane} in baby hamster kidney (BHK), human embryonic kidney (HEK-293) and liver carcinoma (HepG2) cell lines. The results demonstrated that the major uptake mechanism for Rubb12 and Rubb7-Cl was active transport, although with a significant contribution from carrier-assisted diffusion for Rubb12 and passive diffusion for Rubb7-Cl. Flow cytometry coupled with Annexin V/TO-PRO-3 double-staining was used to compare cell death by membrane damage or apoptosis. Rubb12 induced significant direct membrane damage, particularly with HepG2 cells, while Rubb7-Cl caused considerably less membrane damage but induced greater levels of apoptosis. Confocal microscopy, coupled with JC-1 assays, demonstrated that Rubb12 depolarises the mitochondrial membrane, whereas Rubb7-Cl had a much smaller affect. Cellular localisation experiments indicated that Rubb12 did not accumulate in the mitochondria, whereas significant mitochondrial accumulation was observed for Rubb7-Cl. The effect of Rubb12 and Rubb7-Cl on intracellular superoxide dismutase activity showed that the ruthenium complexes could induce cell death via a reactive oxygen species-mediated pathway. The results of this study demonstrate that Rubb12 predominantly kills eukaryotic cells by damaging the cytoplasmic membrane. As this dinuclear ruthenium complex has been previously shown to exhibit greater toxicity towards bacteria than eukaryotic cells, the results of the present study suggest that

  14. Novel dinuclear platinum(II) complexes containing mixed nitrogen-sulfur donor ligands.

    PubMed

    Hochreuther, Stephanie; Puchta, Ralph; van Eldik, Rudi

    2011-12-19

    A series of novel dinuclear platinum(II) complexes were synthesized containing a mixed nitrogen-sulfur donor bidentate chelate system in which the two platinum centers are connected by an aliphatic chain of variable length. The bidentate chelating ligands were selected to stabilize the complex toward decomposition. The pK(a) values and reactivity of the four synthesized complexes, namely, [Pt(2)(S(1),S(4)-bis(2-pyridylmethyl)-1,4-butanedithioether)(OH(2))(4)](4+) (4NSpy), [Pt(2)(S(1),S(6)-bis(2-pyridylmethyl)-1,6-hexanedithioether)(OH(2))(4)](4+) (6NSpy), [Pt(2)(S(1),S(8)-bis(2-pyridylmethyl)-1,8-octanedithioether)(OH(2))(4)](4+) (8NSpy), and [Pt(2)(S(1),S(10)-bis(2-pyridylmethyl)-1,10-decanedithioether)(OH(2))(4)](4+) (10NSpy), were investigated. This system is of special interest because only little is known about the substitution behavior of dinuclear platinum complexes that contain a bidentate chelate that forms part of the aliphatic bridging ligand. Moreover, the ligands as well as the dinuclear complexes were examined in terms of their cytotoxic activity, and the 10NSpy complex was found to be active. Spectrophotometric acid-base titrations were performed to determine the pK(a) values of all the coordinated water molecules. The substitution of coordinated water by thiourea was studied under pseudo-first-order conditions as a function of nucleophile concentration, temperature, and pressure, using stopped-flow techniques and UV-vis spectroscopy. The results for the dinuclear complexes were compared to those for the corresponding mononuclear reference complex [Pt(methylthiomethylpyridine)(OH(2))(2)](2+) (Pt(mtp)), by which the effect of the increasing aliphatic chain length of the bridged complexes could be investigated. The results indicate that there is a clear interaction between the two platinum centers, which becomes weaker as the chain length between the metal centers increases. Furthermore, differences and similarities of the N,S-system were compared to

  15. Thiolate-bridged dinuclear ruthenium and iron complexes as robust and efficient catalysts toward oxidation of molecular dihydrogen in protic solvents.

    PubMed

    Yuki, Masahiro; Sakata, Ken; Hirao, Yoshifumi; Nonoyama, Nobuaki; Nakajima, Kazunari; Nishibayashi, Yoshiaki

    2015-04-01

    Thiolate-bridged dinuclear ruthenium and iron complexes are found to work as efficient catalysts toward oxidation of molecular dihydrogen in protic solvents such as water and methanol under ambient reaction conditions. Heterolytic cleavage of the coordinated molecular dihydrogen at the dinuclear complexes and the sequential oxidation of the produced hydride complexes are involved as key steps to promote the present catalytic reaction. The catalytic activity of the dinuclear complexes toward the chemical oxidation of molecular dihydrogen achieves up to 10000 TON (turnover number), and electrooxidation of molecular dihydrogen proceeds quite rapidly. The result of the density functional theory (DFT) calculation on the reaction pathway indicates that a synergistic effect between the two ruthenium atoms plays an important role to realize the catalytic oxidation of molecular dihydrogen efficiently. The present dinuclear ruthenium complex is found to work as an efficient organometallic anode catalyst for the fuel cell. It is noteworthy that the present dinuclear complex worked not only as an effective catalyst toward chemical and electrochemical oxidation of molecular dihydrogen but also as a good anode catalyst for the fuel cell. We consider that the result described in this paper provides useful and valuable information to develop highly efficient and low-cost transition metal complexes as anode catalysts in the fuel cell.

  16. Self-assembly of heteroleptic dinuclear metallosupramolecular kites from multivalent ligands via social self-sorting

    PubMed Central

    Benkhäuser, Christian

    2015-01-01

    Summary A Tröger's base-derived racemic bis(1,10-phenanthroline) ligand (rac)-1 and a bis(2,2'-bipyridine) ligand with a central 1,3-diethynylbenzene unit 2 were synthesized. Each of these ligands acts as a multivalent entity for the binding of two copper(I) ions. Upon coordination to the metal ions these two ligands undergo selective self-assembly into heteroleptic dinuclear metallosupramolecular kites in a high-fidelity social self-sorting manner as evidenced by NMR spectroscopy and mass spectrometry. PMID:26124873

  17. Dinuclear copper complexes with imidazole derivative ligands: a theoretical study related to catechol oxidase activity.

    PubMed

    Martínez, Ana; Membrillo, Ingrid; Ugalde-Saldívar, Victor M; Gasque, Laura

    2012-07-19

    Catechol oxidase is a very important and interesting metalloprotein. In spite of the efforts to understand the reaction mechanism of this protein, there are important questions that remain unanswered concerning the catalytic mechanism of this enzyme. In this article, dinuclear copper compounds are used as biomimetic models of catechol oxidase to study plausible reaction paths. These dinuclear copper(II) complexes have distant metal centers (of 7.5 Å approximately) and superior catalytic activity to that of many dicopper complexes with shorter Cu-Cu distances. One mononuclear copper(II) complex is also analyzed in this investigation in order to see the influence of the two metal centers in the catalytic activity. Density functional theory calculations were performed to obtain optimized structures, vertical ionization energies, vertical electron affinities, the electrodonating power (ω(-)), the electroaccepting power (ω(+)) and the energy difference of several reaction paths. The K(M) experimental results that were previously reported compare well with the electroaccepting power (ω(+)) of the copper compounds that are included in this article, indicating that this index is useful for the interpretation of the electron transfer capacity and therefore the catalytic activity. The catechol moiety coordinates to only one Cu ion, but two metal atoms are needed in order to have a good electron acceptor capacity of the biomimetic models.

  18. Theory of magnetoresistance due to lattice dislocations in face-centred cubic metals

    NASA Astrophysics Data System (ADS)

    Bian, Q.; Niewczas, M.

    2016-06-01

    A theoretical model to describe the low temperature magneto-resistivity of high purity copper single and polycrystals containing different density and distribution of dislocations has been developed. In the model, magnetoresistivity tensor is evaluated numerically using the effective medium approximation. The anisotropy of dislocation-induced relaxation time is considered by incorporating two independent energy bands with different relaxation times and the spherical and cylindrical Fermi surfaces representing open, extended and closed electron orbits. The effect of dislocation microstructure is introduced by means of two adjustable parameters corresponding to the length and direction of electron orbits in the momentum space, which permits prediction of magnetoresistance of FCC metals containing different density and distribution of dislocations. The results reveal that dislocation microstructure influences the character of the field-dependent magnetoresistivity. In the orientation of the open orbits, the quadratic variation in magnetoresistivity changes to quasi-linear as the density of dislocations increases. In the closed orbit orientation, dislocations delay the onset of magnetoresistivity saturation. The results indicate that in the open orbit orientations of the crystals, the anisotropic relaxation time due to small-angle dislocation scattering induces the upward deviation from Kohler's rule. In the closed orbit orientations Kohler's rule holds, independent of the density of dislocations. The results obtained with the model show good agreement with the experimental measurements of transverse magnetoresistivity in deformed single and polycrystal samples of copper at 2 K.

  19. Synthesis, structural characterization, cytotoxic properties and DNA binding of a dinuclear copper(II) complex.

    PubMed

    Ferreira, B J M Leite; Brandão, P; Meireles, M; Martel, Fátima; Correia-Branco, Ana; Fernandes, Diana M; Santos, T M; Félix, V

    2016-08-01

    In this study a novel dinuclear copper(II) complex with adenine and phenanthroline has been synthesized and its structure determined by single crystal X-ray diffraction. In the dinuclear complex [Cu₂(μ-adenine)₂(phen)₂(H2O)2](NO3)4·0.5H2O (phen=1,10-phenanthroline) (1) the two Cu(II) centres exhibit a distorted square pyramidal coordination geometry linked by two nitrogen donors from adenine bridges leading to a Cu-Cu distance of 3.242(3)Å. Intramolecular and intermolecular π⋯π interactions as well as an H-bonding network were observed. The antitumor capacity of the complex has been tested in vitro against human cancer cell lines, cervical carcinoma (HeLa) and colorectal adenocarcinoma (Caco-2), by metabolic tests, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide as reagent. The complex 1 has remarkable low IC50 values of 0.87±0.06μM (HeLa) and 0.44±0.06μM (Caco-2), when compared with values for cisplatin against the same cell lines. The interaction of complex 1 with calf thymus DNA (CT DNA) was further investigated by absorption and fluorescence spectroscopic methods. A binding constant of 5.09×10(5)M(-1) was obtained from UV-vis absorption studies.

  20. Magnetism and structure in chains of copper dinuclear paddlewheel units.

    PubMed

    Perec, Mireille; Baggio, Ricardo; Sartoris, Rosana P; Santana, Ricardo C; Peña, Octavio; Calvo, Rafael

    2010-01-18

    An anhydrous copper carboxylate compound of formula [Cu(trans-2-butenoate)(2)](n) has been characterized. X-ray analysis reveals a structure built by paddlewheel units bridged by pairs of Cu...O axial bonds to give infinite chains arranged in a new topological motif. Susceptibility measurements in the 10-300 K temperature range, and isothermal magnetization curves at 2, 5, 10, and 50 K with fields up to 5 T, were obtained. Electron Paramagnetic Resonance (EPR) spectra of powder samples were measured at 33.9 GHz at 300 K, and at 9.60 GHz at temperatures in the range 90 dinuclear units yielded exchange interactions J(1) = -330.6(1) cm(-1) and J(2) = 5.9(2) cm(-1). The EPR spectra reflect the usual antiferromagnetic dinuclear behavior, with zero field splitting parameters of the excited spin triplet, D = -0.329(3) cm(-1) and E approximately 0, plus a central peak not expected for isolated dinuclear units. We interpret this peak as arising from the stochastic spin dynamics of the chain introduced by exchange couplings between spins in neighbor dinuclear units, which averages out the zero field splitting. Interactions of the units with the rest of the chain acting as a spin bath give rise to a quantum transition between localized dinuclear states and states of the spin chain. This effect competes with the condensation of the antiferromagnetic dinuclear units into the singlet ground state, producing a characteristic temperature dependence of the shape of the powder EPR spectra. We interpret these features in terms of basic theories of magnetic resonance in coupled spin systems applied to the chain array of dinuclear units.

  1. Formation, characterization and computational studies of mono- and dinuclear rhenium(I) chromone compounds

    NASA Astrophysics Data System (ADS)

    Ebinumoliseh, Ifeoma; Booysen, Irvin Noel; Akerman, Matthew Piers; Xulu, Bheki

    2016-11-01

    Herein, we report the formation and characterization of a novel dinuclear rhenium(I) compound, fac-(Re(CO)3Br)2(μ-chret) (1) [chret = N, N'-bis(2-amino-3-imino)methylenechromone-1,2-ethane] and a mononuclear metal complex, fac-[Re(CO)3(bzch)Br] (2) [bzch = 2-benzimidazole-4H-chromen-4-one]. The metal complexes were characterized by 1H NMR-, IR-, UV-Vis, melting point and conductivity measurements. The solid-state structures for 1 and 2 were confirmed via single crystal X-ray analysis. X-ray studies of 2 revealed the transformation of the chb diimine into the bzch chelator (in 2). The simulated IR spectra for the respective metal complexes provided insight in the interpretation of their corresponding experimental spectra.

  2. Pyrazole bridged dinuclear Cu(II) and Zn(II) complexes as phosphatase models: Synthesis and activity

    NASA Astrophysics Data System (ADS)

    Naik, Krishna; Nevrekar, Anupama; Kokare, Dhoolesh Gangaram; Kotian, Avinash; Kamat, Vinayak; Revankar, Vidyanand K.

    2016-12-01

    Present work describes synthesis of dibridged dinuclear [Cu2L2(μ2-NN pyr)(NO3)2(H2O)2] and [Zn2L(μ-OH)(μ-NNpyr)(H2O)2] complexes derived from a pyrazole based ligand bis(2-hydroxy-3-methoxybenzylidene)-1H-pyrazole-3,5-dicarbohydrazide. The ligand shows dimeric chelate behaviour towards copper against monomeric for zinc counterpart. Spectroscopic evidences affirm octahedral environment around the metal ions in solution state and non-electrolytic nature of the complexes. Both the complexes are active catalysts towards phosphomonoester hydrolysis with first order kcat values in the range of 2 × 10-3s-1. Zinc complex exhibited promising catalytic efficiency for the hydrolysis. The dinuclear complexes hydrolyse via Lewis acid activation, whereby the phosphate esters are preferentially bound in a bidentate bridging fashion and subsequent nucleophilic attack to release phosphate group.

  3. Collective dynamics of a dinuclear system

    NASA Astrophysics Data System (ADS)

    Mshelia, E. D.; Scheid, W.

    . There are theoretical and experimental evidences that show that the cluster model, consisting of a dinuclear system, is capable of explaining several features of deformed heavy nuclei. Examples are the fusion to super-heavy nuclei and the nuclear-structure effects arising from parity splitting in alternating rotational parity bands, especially of the actinide nuclei. The model developed by Shneidman et al. has been able to explain the parity splitting in the actinides using the cluster model in which oscillations in mass asymmetry and relative motion were considered. On the other hand, Hess and Greiner developed a model for nuclear molecules in which the degrees of freedom of butterfly, belly-dancer-type motions, γ - and β -vibrations of individual nuclei were incorporated. The purpose of this work is to extend the model of Shneidman et al. to include some of the degrees of freedom in the work of Hess et al. and, in addition, to consider nuclear molecular rotations and the coupling of these degrees of freedom among themselves, arising from mass asymmetry.

  4. New discrete and polymeric supramolecular architectures derived from dinuclear (bis-beta-diketonato)copper(II) metallocycles.

    PubMed

    Clegg, Jack K; Gloe, Karsten; Hayter, Michael J; Kataeva, Olga; Lindoy, Leonard F; Moubaraki, Boujemaa; McMurtrie, John C; Murray, Keith S; Schilter, David

    2006-09-07

    New examples of adducts between di- (and, in one instance, tetra-) functional nitrogen ligands and planar 'platform-like' dinuclear copper(II) complexes, [Cu2L2], incorporating the 1,3-aryl linked bis-beta-diketonato bridging ligand 1,1'-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H2L) have been synthesised. The X-ray structures of six adduct species are reported. The interaction of [Cu2(L)2] with the ditopic ligand aminopyrazine (apyz) yielded the sandwich-like tetranuclear species [(Cu2L2(apyz))2]. A variable-temperature magnetochemical investigation of this product indicated weak antiferromagnetic coupling between the (five-coordinate) copper centres, mediated by the 2-aminopyrazine linkers. An analogous structure, [(Cu2L2(dabco))2] (dabco=1,4-diazabicyclo[2.2.2]octane), was generated when dabco was substituted for aminopyrazine while use of 4,4'-dipyridyl sulfide (dps) and 4,4'-(1,3-xylylene)-bis(3,5-dimethylpyrazole) (xbp) as the ditopic 'spacer' ligands resulted in polymeric species of type [Cu2L2(dps)]n and [Cu2L2(xbp)]n, respectively. These latter species exist as one-dimensional chain structures in which copper(II) centres on different dinuclear platforms are linked in a 'zigzag' fashion. In contrast, with 2,2'-dipyridylamine (dpa) a discrete complex of type [Cu2L2(dpa)2] formed in which one potential pyridyl donor from each 2,2'-dipyridylamine ligand remains uncoordinated. The use of the potentially quadruply-bridging hexamethylenetetramine (hmt) ligand as the linker unit was found to give rise to an unusual two-dimensional polymeric motif of type [(Cu2(L2)2)3(hmt)2]n. The product takes the form of a (6,3) network, incorporating triply bridging hexamethylenetetramine units.

  5. On the conditions for enhanced transport through molecular junctions based on metal centres ligated by pairs of pyridazino-derived ligands

    SciTech Connect

    Ding, Bei; Washington, Victoria; Dunietz, Barry D

    2010-10-10

    Transport properties of a Ni bis-η{sup 2} complex ligated by a pair of bi-pyridazino derivative are considered. This complex provides the opportunity to avoid perpendicular alignment of the ligand π planes. We study the effects of π-bonding and of intramolecular hydrogen bonding between the ligands as mediated by the metal centre on electron transport. The complicated effect of the electronic structure equilibration with the electrodes on the transport is discussed. The analysis at the electronic structure level provides guidelines to design a molecular bridge that is based on metal complexation with effective electronic transport.

  6. Structure of the Ni(II) complex of Escherichia coli peptide deformylase and suggestions on deformylase activities depending on different metal(II) centres.

    PubMed

    Yen, Ngo Thi Hai; Bogdanović, Xenia; Palm, Gottfried J; Kühl, Olaf; Hinrichs, Winfried

    2010-02-01

    Crystal structures of polypeptide deformylase (PDF) of Escherichia coli with nickel(II) replacing the native iron(II) have been solved with chloride and formate as metal ligands. The chloro complex is a model for the correct protonation state of the hydrolytic hydroxo ligand and the protonated status of the Glu133 side chain as part of the hydrolytic mechanism. The ambiguity that recently some PDFs have been identified with Zn(2+) ion as the active-site centre whereas others are only active with Fe(2+) (or Co(2+), Ni(2+) is discussed with respect to Lewis acid criteria of the metal ion and substrate activation by the CD loop.

  7. Mono- and Dinuclear Phosphorescent Rhenium(I) Complexes: Impact of Subcellular Localization on Anticancer Mechanisms.

    PubMed

    Ye, Rui-Rong; Tan, Cai-Ping; Chen, Mu-He; Hao, Liang; Ji, Liang-Nian; Mao, Zong-Wan

    2016-06-01

    Elucidation of relationship among chemical structure, cellular uptake, localization, and biological activity of anticancer metal complexes is important for the understanding of their mechanisms of action. Organometallic rhenium(I) tricarbonyl compounds have emerged as potential multifunctional anticancer drug candidates that can integrate therapeutic and imaging capabilities in a single molecule. Herein, two mononuclear phosphorescent rhenium(I) complexes (Re1 and Re2), along with their corresponding dinuclear complexes (Re3 and Re4), were designed and synthesized as potent anticancer agents. The subcellular accumulation of Re1-Re4 was conveniently analyzed by confocal microscopy in situ in live cells by utilizing their intrinsic phosphorescence. We found that increased lipophilicity of the bidentate ligands could enhance their cellular uptake, leading to improved anticancer efficacy. The dinuclear complexes were more potent than the mononuclear counterparts. The molecular anticancer mechanisms of action evoked by Re3 and Re4 were explored in detail. Re3 with a lower lipophilicity localizes to lysosomes and induces caspase-independent apoptosis, whereas Re4 with higher lipophilicity specially accumulates in mitochondria and induces caspase-independent paraptosis in cancer cells. Our study demonstrates that subcellular localization is crucial for the anticancer mechanisms of these phosphorescent rhenium(I) complexes.

  8. Functional group migrations between boron and metal centres within transition metal-borane and -boryl complexes and cleavage of H-H, E-H and E-E' bonds.

    PubMed

    Owen, Gareth R

    2016-08-25

    This feature article examines some of the recent advances in the chemistry of Z-type transition metal-borane and X-type transition metal-boryl complexes. It focuses on the employment of these boron-based functionalities acting as stores and transfer agents for functional groups such as hydrides, alkyl groups and aryl groups which can either be abstracted or delivered to the metal centre. The review also explores the rather novel reactivity involving the cleavage of H-H, E-H and E-E' bonds (where E and E' are a range of groups) across the transition metal-boron bond in such complexes. It explores the early examples of the addition of H-H across transition metal-borane bonds and describes the new transformation in the context of other known modes of hydrogen activation including classic oxidative addition and heterolytic cleavage at transition metal centres as well as Frustrated Lewis Pair chemistry. Similar reactivity involving transition metal-boryl complexes are also described particularly those which undergo both boryl-to-borane and borane-to-borohydride transformations. The delivery of hydride to the metal centre in combination with the potential to regenerate the borohydride functional group via a recharging process is explored in the context of providing a new strategy for catalysis. Finally, a light-hearted look at the analogy of the 'stinging processes' involving Trofimenko type ligands is taken one step further to determine whether it is indeed in the nature of scorpionate ligands to repeatedly 'sting' just as the real life scorpions do.

  9. Nuclear structure in the dinuclear model with rotating clusters

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Jolos, R. V.; Palchikov, Yu. V.; Shneidman, T. M.; Scheid, W.

    2007-08-15

    The dinuclear-system model can be applied to nuclear structure. Here, we study deformed clusters which rotate with respect to the internuclear distance and exchange nucleons. The model can be used to explain the band structure of nuclear spectra, especially the parity splitting observed in actinides, e.g., in {sup 238}U.

  10. Synthesis, characterization and X-ray structural studies of four copper (II) complexes containing dinuclear paddle wheel structures

    PubMed Central

    2013-01-01

    Background Various dinuclear copper (II) complexes with octahedral geometry have been reported. The majority of these complexes contain N containing aromatic rings as axial ligands. There are also a few cases where the solvent used in the reaction occupies the axial position of the dinuclear copper (II) complex. This may occur by planned synthesis or some times by serendipity. Here we report some four copper (II) complexes containing solvent and or N containing heterocyclic ring as the axial ligand. Results Four compounds, each containing dinuclear Copper (II) units (with the most robust, frequently occurring paddle wheel structures) were synthesized and characterised by single crystal X-ray diffraction and by IR spectroscopy. The compounds 1 & 2 have the general formula Cu2(RCOO) 4(L)2 [(for (1) RCOO= 4-Chloro Benzoate, L= Isopropanol; for 2 RCOO= Benzoate, L= 2-Amino-4,6-dimethyl pyrimidine )] while 3 & 4 have the general formula, Cu2(RCOO) 4(S)2 Cu2(RCOO) 4(L)2 [RCOO=5-Chloro-thiophene-2-carboxylate L= 2-Amino-4,6-dimethyl pyrimidine, for 3 S= ethanol; for 4 S= methanol ]. A wide range of hydrogen bonds (of the O-H…O, N-H…O and N-H…N type) and π-π stacking interactions are present in the crystal structures. Conclusions All compounds contain the dinuclear units, in which two Cu (II) ions are bridged by four syn, syn-η1:η1:μ carboxylates, showing a paddle-wheel cage type with a distorted octahedral geometry. The compounds 1 &2 contain a single dimeric unit while 3 &4 contain two dimeric units. The structures 3 and 4 are very interesting co-crystals of two paddle wheel molecules. Also it is interesting to note that the compounds 3 &4 are isostructural with similar cell parameters. Both the compounds 3 &4 differ in the solvent molecule coordinated to copper in one of the dimeric units. In all the four compounds, each of the copper dimers has an inversion centre. Every copper has a distorted octahedral centre, formed by four oxygen atoms (from different

  11. Dinuclear dialkoxo-bridged cyclopentadienylsiloxo titanium complexes.

    PubMed

    Postigo, Lorena; Sánchez-Nieves, Javier; Royo, Pascual; Mosquera, Marta E G

    2009-05-21

    The dinuclear dialkoxo-bridged complexes [(TiCl)(2)(mu-O(2)L)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})] (O(2)L = 1,2-O(2)C(2)H(4), 1,2-O(2)C(6)H(4), 1,2-(OCH(2))(2)C(6)H(4), O(2)SiPh(2)) were obtained by reaction of [(TiCl(2))(2)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})] () with the corresponding dilithium salt () or diol (, , ). Alkylation of and with ClRMg afforded [(TiR)(2)(mu-O(2)L)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})] (O(2)L = 1,2-O(2)C(2)H(4), R = Me , Bz ; O(2)L = 1,2-O(2)C(6)H(4), R = Me , Bz ). Addition of four equiv. of LiOiPr to afforded [{Ti(OiPr)(2)}(2)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})] (). Reaction of with Al(C(6)F(5))(3) produced the elimination of the dialkoxo ligand to give [{TiCl(C(6)F(5))}(2)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})] (), whereas the same reaction of with Al(C(6)F(5))(3) produced the oxo-alane adduct [(TiCl)(2)(mu-O(2)L)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O.Al{C(6)F(5)}(3))})] (O(2)L = 1,2-O(2)C(6)H(4)) which was further transformed to give a mixture of and [(TiCl){Ti(C(6)F(5))}(mu-O(2)L)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})] (O(2)L = 1,2-O(2)C(6)H(4)). One benzyl group of complexes was abstracted with E(C(6)F(5))(3) (E = B, Al) to give the monoionic compounds [Ti(TiBz)(mu-O(2)L)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})][BzE(C(6)F(5))(3)] (O(2)L = 1,2-O(2)C(2)H(4), E = B , Al ; O(2)L = 1,2-O(2)C(6)H(4), E = B ), although was unstable in CD(2)Cl(2) evolving to a mixture of compounds where [(TiBz)(2)(mu-Cl)(mu-{(eta(5)-C(5)Me(4)SiMeO)(2)(mu-O)})][BzAl(C(6)F(5))(3)] () was identified, and compound was also unstable at ambient temperature. Polymerization of epsilon-caprolactone was only achieved with the tetraalkoxo compound . All of these complexes were characterized by NMR spectroscopy and , and by X-ray diffraction studies.

  12. Dinuclear indium and thallium diyls: biscarbenoids or metal cluster?

    PubMed

    Desat, Marcella E; Gärtner, Stefanie; Kretschmer, Robert

    2017-01-26

    Using bis(β-diketiminate) ligands we were able to synthesize unprecedented indium and thallium biscarbenoids. For indium, a novel four-membered metallacycle is derived from intra- and intermolecular In-In interactions in the solid state, while for thallium only an intramolecular Tl2-pseudo-dimer is obtained. Computational studies revealed that the solid-state structures benefit significantly from dispersion stabilization.

  13. Two Zn coordination polymers with meso-helical chains based on mononuclear or dinuclear cluster units

    SciTech Connect

    Qin, Ling; Qiao, Wen-Cheng; Zuo, Wei-Juan; Zeng, Si-Ying; Mei, Cao; Liu, Chang-Jiang

    2016-07-15

    Two zinc coordination polymers {[Zn_2(TPPBDA)(oba)_2]·DMF·1.5H_2O}{sub n} (1), {[Zn(TPPBDA)_1_/_2(tpdc)]·DMF}{sub n} (2) have been synthesized by zinc metal salt, nanosized tetradentate pyridine ligand with flexible or rigid V-shaped carboxylate co-ligands. These complexes were characterized by elemental analyses and X-ray single-crystal diffraction analyses. Compound 1 is a 2-fold interpenetrated 3D framework with [Zn{sub 2}(CO{sub 2}){sub 4}] clusters. Compound 2 can be defined as a five folded interpenetrating bbf topology with mononuclear Zn{sup 2+}. These mononuclear or dinuclear cluster units are linked by mix-ligands, resulting in various degrees of interpenetration. In addition, the photoluminescent properties for TPPBDA ligand under different state and coordination polymers have been investigated in detail. - Graphical abstract: Two zinc coordination polymers have been synthesized by zinc metal salt, nanosized tetradentate pyridine ligand with flexible or rigid V-shaped carboxylate co-ligands. Compound 1 is a 2-fold interpenetrated 3D framework with [Zn{sub 2}(CO{sub 2}){sub 4}] clusters. Compound 2 can be defined as a five folded interpenetrating bbf topology with mononuclear Zn{sup 2+}. In addition, the photoluminescent properties for TPPBDA ligand under different status and coordination polymers have been investigated in detail. Display Omitted - Highlights: • Two Zn coordination polymers based on mononuclear or dinuclear cluster units have been synthesized. • Compound 1 is a 2-fold interpenetrated 3D framework with [Zn{sub 2}(CO{sub 2}){sub 4}] clusters. • Compound 2 is a five folded interpenetrating bbf topology with mononuclear Zn{sup 2+}. • The photoluminescent properties for TPPBDA with different state and two coordination polymers have been investigated.

  14. Conserved histidine residues at the ferroxidase centre of the Campylobacter jejuni Dps protein are not strictly required for metal binding and oxidation.

    PubMed

    Sanchuki, Heloisa B S; Valdameri, Glaucio; Moure, Vivian R; Rodriguez, Jorge A; Pedrosa, Fábio O; Souza, Emanuel M; Korolik, Victoria; Ribeiro, Ronny Rocha; Huergo, Luciano F

    2016-01-01

    Iron is an essential micronutrient for living organisms as it is involved in a broad variety of important biological processes. However, free iron inside the cell could be potentially toxic, generating hydroxyl radicals through the Fenton reaction. Dps (DNA-binding protein from starved cells) belongs to a subfamily of ferritins and can store iron atoms inside the dodecamer. The presence of a ferroxidase centre, composed of highly conserved residues, is a signature of this protein family. In this study, we analysed the role of two conserved histidine residues (H25 and H37) located at the ferroxidase centre of the Campylobacter jejuni Dps protein by replacing them with glycine residues. The C. jejuni H25G/H37G substituted variant showed reduced iron binding and ferroxidase activities in comparison with wt Dps, while DNA-binding activity remained unaffected. We also found that both CjDps wt and CjDps H25G/H37G were able to bind manganese atoms. These results indicate that the H25 and H37 residues at the ferroxidase centre of C. jejuni Dps are not strictly required for metal binding and oxidation.

  15. An Effective Route to Dinuclear Niobium and Tantalum Imido Complexes.

    PubMed

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

    2017-10-02

    Thermal treatment of the trichloro complexes [MCl3(NR)py2] (R = tBu, Xyl; M = Nb, Ta) (Xyl = 2,6-Me2C6H3) under vacuum affords the dinuclear imido species [MCl2(μ-Cl)(NR)py]2 (R = tBu, Xyl; M = Nb 1, 3; Ta 2, 4) with loss of pyridine. Complexes 1-4 can be easily transformed to the mononuclear starting materials [MCl3(NR)py2] (R = tBu, Xyl; M = Nb, Ta) upon reaction with pyridine. While reactions of compounds 1 and 2 with a series of alkylating reagents render the mononuclear peralkylated imido complexes [MR3(NtBu)] (R = Me, CH2Ph, CH2CMe3, CH2CMePh, CH2SiMe3), the analogous treatment with allylmagnesium chloride results in the formation of the dinuclear niobium(IV) derivative [(NtBu)(η(3)-C3H5)M(μ-C3H5)(μ-Cl)2M(NtBu)py2] (5). Additionally, the treatment of the starting materials 1 and 2 with the organosilicon reductant 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene yields the pyridyl-bridged dinuclear derivatives [M2Cl2(μ-Cl)2(NtBu)2py2]2(μ-NC4H4N)2 (M = Nb 6, Ta 7). Controlled hydrolysis reaction of 1 and 2 affords the oxo chlorido-bridged products [MCl(μ-Cl)(NtBu)py]2(μ-O) (M = Nb 8, Ta 9) in a quantitative way, while the treatment of these latter with one more equivalent of pyridine led to complexes [MCl2(NtBu)py2]2(μ-O) (M = Nb 10, Ta 11). Structural study of these dinuclear imido derivatives has been also performed by X-ray crystallography.

  16. Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Gong, Jianxiao; Steinsultz, Nat; Ouyang, Min

    2016-06-01

    The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters (including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring the underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. This study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen-vacancy centres that use these freestanding hybrid nanostructures as building blocks.

  17. Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

    SciTech Connect

    Gong, Jianxiao; Steinsultz, Nat; Ouyang, Min

    2016-06-08

    The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters ( including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring the underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. Lastly, this study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen vacancy centres that use these freestanding hybrid nanostructures as building blocks.

  18. Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

    DOE PAGES

    Gong, Jianxiao; Steinsultz, Nat; Ouyang, Min

    2016-06-08

    The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters ( including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring themore » underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. Lastly, this study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen vacancy centres that use these freestanding hybrid nanostructures as building blocks.« less

  19. Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

    PubMed Central

    Gong, Jianxiao; Steinsultz, Nat; Ouyang, Min

    2016-01-01

    The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters (including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring the underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. This study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen-vacancy centres that use these freestanding hybrid nanostructures as building blocks. PMID:27273426

  20. Insights on spin delocalization and spin polarization mechanisms in crystals of azido copper(II) dinuclear complexes through the electron spin density Source Function.

    PubMed

    Gatti, Carlo; Macetti, Giovanni; Lo Presti, Leonardo

    2017-08-01

    The Source Function (SF) tool was applied to the analysis of the theoretical spin density in azido Cu(II) dinuclear complexes, where the azido group, acting as a coupler between the Cu(II) cations, is linked to the metal centres either in an end-on or in an end-end fashion. Results for only the former structural arrangement are reported in the present paper. The SF highlights to which extent the magnetic centres contribute to determine the local spin delocalization and polarization at any point in the dimetallic complex and whether an atom or group of atoms of the ligands act in favour or against a given local spin delocalization/polarization. Ball-and-stick atomic SF percentage representations allow for a visualization of the magnetic pathways and of the specific role played by each atom along these paths, at given reference points. Decomposition of SF contributions in terms of a magnetic and of a relaxation component provides further insight. Reconstruction of partial spin densities by means of the Source Function has for the first time been introduced. At variance with the standard SF percentage representations, such reconstructions offer a simultaneous view of the sources originating from specific subsets of contributing atoms, in a selected molecular plane or in the whole space, and are therefore particularly informative. The SF tool is also used to evaluate the accuracy of the analysed spin densities. It is found that those obtained at the unrestricted B3LYP DFT level, relative to those computed at the CASSCF(6,6) level, greatly overestimate spin delocalization to the ligands, but comparatively underestimate magnetic connection (spin transmission) among atoms, along the magnetic pathways. As a consequence of its excessive spin delocalization, the UB3LYP method also overestimates spin polarization mechanisms between the paramagnetic centres and the ligands. Spin delocalization measures derived from the refinement of Polarized Neutron Diffraction data seem in

  1. Luminescence properties of the dinuclear copper complex in the active site of hemocyanins.

    PubMed

    Beltramini, M; di Muro, P; Rocco, G P; Salvato, B

    1994-09-01

    The deoxygenated form of hemocyanin, containing a dinuclear Cu(I) active site, emits luminescence in the red with maximum around 1.54 microns-1 (650 nm). The luminescence of deoxyhemocyanin (deoxy-Hc) from arthropod species is detectable at room temperature, the quantum yield being 2.4-2.7 x 10(-3); in contrast, the emission from molluscan proteins can be detected only at liquid nitrogen temperature. The luminescence emission is an inherent property of the bis[Cu(I)-(histidine)3] complex of the deoxygenated form of the protein to which both Cu(I) ions contribute equally to the overall emission. Luminescence is not observed with the oxygenated and the oxidized forms of hemocyanin, in which the metal is in the Cu(II) state, and in the metal-depleted or apo-Hc form. Based on steady-state and time-resolved measurements and references to Cu(I) model compounds, the luminescence emission is attributed to a triplet excited state of a Cu(I)-to-N (histidine) charge transfer transition 3d-pi*. Acrylamide quenching experiments indicate that the metal active site is very shielded from the solvent. This property of deoxy-Hc enables us to directly follow reactions that modify either the copper oxidation number or the metal-to-protein stoichiometry.

  2. Reactions of Dinuclear Platinum(II) Complexes with Peptides.

    PubMed

    Rajković, Snežana; Živković, Marija D; Djuran, Miloš I

    2016-01-01

    The present review article highlights recent findings in the reactions between different dinuclear Pt(II) complexes with peptides containing cysteine, methionine and histidine residues. The reactions of {trans-[Pt(NH3)2Cl]2(μ-X)}(2+) and {trans-[Pt(NH3)2(H2O)]2(μ-X)}(4+) type complexes with different bridging ligands (X) (X = pyrazine, 4,4'-bipyridyl and 1,2-bis(4-pyridyl)ethane) with the tripeptide glutathione proceeded in two steps. In the first step, one water or chlorido ligand of the dinuclear Pt(II) complex was substituted by the sulfhydryl group of GSH, while in the second step, the remaining water or chlorido ligand from the dinuclear Pt(II)-peptide complex was replaced by the second molecule of glutathione, finally leading to the formation of the {trans-[Pt(NH3)2(GS)]2(μ-X)}(2+) complex. It was shown that the bridging ligand had an important influence on the reactivity of these complexes with glutathione. No hydrolytic cleavage of any amide bond was observed in the reactions between these complexes and glutathione. However, in reactions performed in acidic media (2.0 < pH < 2.5) between dinuclear Pt(II) complexes with the general formulae {[Pt(L)(H2O)]2(μ-diazine)}(4+) (L is different bidentate coordinated diamine ligands and diazine is a pyrazine- or pyridazine-bridging ligand) and Nacetylated peptides containing L-methionine and L-histidine amino acids in the side chains (Ac-L-Met-Gly, Ac-L-His-Gly and Ac-L-Met-Gly-L-His-GlyNH2), regioselective cleavage of these peptides occurred. The mechanism of these hydrolytic reactions was discussed in relation to the structure of the diazine-bridged Pt(II) complex and the investigated peptides. A systematic summary of these results could contribute to the future design of new dinuclear Pt(II) complexes as potential reagents for regioselective cleavage of peptides and proteins.

  3. A heterotrimetallic Ir(III), Au(III) and Pt(II) complex incorporating cyclometallating bi- and tridentate ligands: simultaneous emission from different luminescent metal centres leads to broad-band light emission.

    PubMed

    Muñoz-Rodríguez, Rebeca; Buñuel, Elena; Fuentes, Noelia; Williams, J A Gareth; Cárdenas, Diego J

    2015-05-14

    Di- and tri-nuclear metal complexes incorporating gold(III), iridium(III) and platinum(II) units linked via a 1,3,5-triethynylbenzene core are reported, together with the corresponding mononuclear complexes as models. The gold(III) and platinum(II) units comprise tridentate, cyclometallating, C^N^C and N^N^C-coordinating ligands, respectively, with the Ar-C≡C- directly bound to the metal at the fourth coordination site. The iridium moiety is an Ir(ppy)2(acac) unit bound to the triethynylbenzene through a phenyl substituent at the 3-position of the acac ligand. The multinuclear compounds are prepared, using a modular synthetic strategy, from the monometallic complexes. All of the compounds are luminescent in solution at room temperature, and their photophysical properties were studied. The triplet excited state energies of the mononuclear complexes lie in the order Au > Ir > Pt. Consistent with this order, energy transfer from Au to Ir and from Au to Pt is observed, leading to quenching of the Au emission in the gold-containing multinuclear complexes. Energy transfer from Ir to Pt occurs at a rate that only partially quenches the Ir-based emission. As a result, the dinuclear Ir-Pt and trinuclear Au-Ir-Pt complexes display broad emission across most of the visible region of the spectrum.

  4. Ab initio density matrix renormalization group study of magnetic coupling in dinuclear iron and chromium complexes

    SciTech Connect

    Harris, Travis V.; Morokuma, Keiji; Kurashige, Yuki; Yanai, Takeshi

    2014-02-07

    The applicability of ab initio multireference wavefunction-based methods to the study of magnetic complexes has been restricted by the quickly rising active-space requirements of oligonuclear systems and dinuclear complexes with S > 1 spin centers. Ab initio density matrix renormalization group (DMRG) methods built upon an efficient parameterization of the correlation network enable the use of much larger active spaces, and therefore may offer a way forward. Here, we apply DMRG-CASSCF to the dinuclear complexes [Fe{sub 2}OCl{sub 6}]{sup 2−} and [Cr{sub 2}O(NH{sub 3}){sub 10}]{sup 4+}. After developing the methodology through systematic basis set and DMRG M testing, we explore the effects of extended active spaces that are beyond the limit of conventional methods. We find that DMRG-CASSCF with active spaces including the metal d orbitals, occupied bridging-ligand orbitals, and their virtual double shells already capture a major portion of the dynamic correlation effects, accurately reproducing the experimental magnetic coupling constant (J) of [Fe{sub 2}OCl{sub 6}]{sup 2−} with (16e,26o), and considerably improving the smaller active space results for [Cr{sub 2}O(NH{sub 3}){sub 10}]{sup 4+} with (12e,32o). For comparison, we perform conventional MRCI+Q calculations and find the J values to be consistent with those from DMRG-CASSCF. In contrast to previous studies, the higher spin states of the two systems show similar deviations from the Heisenberg spectrum, regardless of the computational method.

  5. Photoinduced intercomponent excited-state decays in a molecular dyad made of a dinuclear rhenium(I) chromophore and a fullerene electron acceptor unit.

    PubMed

    Nastasi, Francesco; Puntoriero, Fausto; Natali, Mirco; Mba, Miriam; Maggini, Michele; Mussini, Patrizia; Panigati, Monica; Campagna, Sebastiano

    2015-05-01

    A novel molecular dyad, 1, made of a dinuclear {[Re2(μ-X)2(CO)6(μ-pyridazine)]} component covalently-linked to a fullerene unit by a carbocyclic molecular bridge has been prepared and its redox, spectroscopic, and photophysical properties - including pump-probe transient absorption spectroscopy in the visible and near-infrared region - have been investigated, along with those of its model species. Photoinduced, intercomponent electron transfer occurs in 1 from the thermally-equilibrated, triplet metal/ligand-to-ligand charge-transfer ((3)MLLCT) state of the dinuclear rhenium(I) subunit to the fullerene acceptor, with a time constant of about 100 ps. The so-formed triplet charge-separated state recombines in a few nanoseconds by a spin-selective process yielding, rather than the ground state, the locally-excited, triplet fullerene state, which finally decays to the ground state by intersystem crossing in about 290 ns.

  6. Reactivity of dinuclear copper(II) complexes towards melanoma cells: Correlation with its stability, tyrosinase mimicking and nuclease activity.

    PubMed

    Nunes, Cléia Justino; Borges, Beatriz Essenfelder; Nakao, Lia Sumie; Peyroux, Eugénie; Hardré, Renaud; Faure, Bruno; Réglier, Marius; Giorgi, Michel; Prieto, Marcela Bach; Oliveira, Carla Columbano; Da Costa Ferreira, Ana M

    2015-08-01

    In this work, the influence of two new dinuclear copper(II) complexes in the viability of melanoma cells (B16F10 and TM1MNG3) was investigated, with the aim of verifying possible correlations between their cytotoxicity and their structure. One of the complexes had a polydentate dinucleating amine-imine ligand (complex 2), and the other a tridentate imine and a diamine-bridging ligand (complex 4). The analogous mononuclear copper(II) species (complexes 1 and 3, respectively) were also prepared for comparative studies. Crystal structure determination of complex 2 indicated a square-based pyramidal geometry around each copper, coordinated to three N atoms from the ligand and the remaining sites being occupied by either solvent molecules or counter-ions. Complex 4 has a tetragonal geometry. Interactions of these complexes with human albumin protein (HSA) allowed an estimation of their relative stabilities. Complementary studies of their reactivity towards DNA indicated that all of them are able of causing significant oxidative damage, with single and double strand cleavages, in the presence of hydrogen peroxide. However, nuclease activity of the dinuclear species was very similar and much higher than that of the corresponding mononuclear compounds. Although complex 2, with a more flexible structure, exhibits a much higher tyrosinase activity than complex 4, having a more rigid environment around the metal ion, both complexes showed comparable cytotoxicity towards melanoma cells. Corresponding mononuclear complexes showed to be remarkably less reactive as tyrosinase mimics as well as cytotoxic agents. Moreover, the dinuclear complexes showed higher cytotoxicity towards more melanogenic cells. The obtained results indicated that the structure of these species is decisive for its activity towards the malignant tumor cells tested.

  7. Solid state and solution characterization of a new dinuclear nickel (II) complex: The search for synthetic models for urease

    NASA Astrophysics Data System (ADS)

    Horn, Adolfo; Fim, Luciana; Bortoluzzi, Adailton J.; Szpoganicz, Bruno; Silva, Marlon de S.; Novak, Miguel A.; Neto, Mario Benassi; Eberlin, Lívia Schiavinato; Catharino, Rodrigo Ramos; Eberlin, Marcos Nogueira; Fernandes, Christiane

    2006-09-01

    The X-ray molecular structure and, magnetic, and spectroscopic properties, as well as the analysis of the structural behavior in solution of a novel nickel (II) complex [Ni 2(HBPClNOL) 2(OAc)](ClO 4) 1 are reported. Complex 1 was prepared by the reaction between the ligand H 2BPClNOL ( N-(2-hydroxybenzyl)- N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine), [Ni(H 2O) 6](ClO 4) 2 and sodium acetate. Magnetic measurements indicate the presence of a weak antiferromagnetic coupling between the Ni(II) ions in 1, resulting in J = -4.23 cm -1. Mass spectrometric characterization of the complex 1 was also performed via ESI-MS and ESI-MS/MS experiments and reveals that there are at least three different cations in solution, one mononuclear [Ni(H 2BPClNOL)(OAc)] + and two dinuclear [Ni 2(HBPClNOL) 2(OAc)] + and [Ni 2(HBPClNOL) 2(ClO 4)] + cations, as well as likely a fourth one [Ni(HBPClNOL)] +. Potentiometric titration experiments confirm that under acid conditions, the dinuclear unit is broken. However, under neutral/basic pH values the dinuclear unit is stable and shows the presence of two water molecules coordinated to the nickel ions, resulting in the cation [Ni 2(HBPClNOL) 2(H 2O) 2] 2+. This cation shows two protonation/deprotonation equilibriums with p Ka values of 9.68 and at 10.29, which are related to the aquo/hydroxo equilibrium associated with the water molecules coordinated to the metal ions.

  8. Two dinuclear Ru(II) polypyridyl complexes with different photophysical and cation recognition properties

    NASA Astrophysics Data System (ADS)

    Cheng, Feixiang; He, Chixian; Ren, Mingli; Wang, Fan; Yang, Yuting

    2015-02-01

    Two dinuclear Ru(II) polypyridyl complexes functionalized with vacant coordination sites have been designed and synthesized. Their photophysical properties and interactions with various metal ions have been investigated at room temperature. The two complexes exhibit different UV/Vis absorption and emission intensities. When titrated with various metal ions, complex [{Ru(bpy)2}2(μ2-L1)]4+ exhibits a notable fluorescence quenching in the presence of Cu2+ in H2O-CH3CN media (1:1, v/v); its analogous complex [{Ru(bpy)2}2(μ2-L2)]4+ exhibits no cation selectivity, the fluorescence intensity of complex [{Ru(bpy)2}2(μ2-L2)]4+ has been enhanced by several transition metal ions due to prevention of the photo-induced electron transfer process. The fluorescence titration spectra and Benesi-Hildebrand expression reveal the formation of a 1:1 bonding mode between [{Ru(bpy)2}2(μ2-L1)]4+ and Cu2+ ion with the association constant of 5.50 × 104 M-1.

  9. Biochemical and spectroscopic characterization of dinuclear Mn-sites in artificial four-helix bundle proteins.

    PubMed

    Olson, Tien L; Espiritu, Eduardo; Edwardraja, Selvakumar; Canarie, Elizabeth; Flores, Marco; Williams, JoAnn C; Ghirlanda, Giovanna; Allen, James P

    2017-09-04

    To better understand metalloproteins with Mn-clusters, we have designed artificial four-helix bundles to have one, two, or three dinuclear metal centers able to bind Mn(II). Circular dichroism measurements showed that the Mn-proteins have substantial α-helix content, and analysis of electron paramagnetic resonance spectra is consistent with the designed number of bound Mn-clusters. The Mn-proteins were shown to catalyze the conversion of hydrogen peroxide into molecular oxygen. The loss of hydrogen peroxide was dependent upon the concentration of protein with bound Mn, with the proteins containing multiple Mn-clusters showing greater activity. Using an oxygen sensor, the oxygen concentration was found to increase with a rate up to 0.4μM/min, which was dependent upon the concentrations of hydrogen peroxide and the Mn-protein. In addition, the Mn-proteins were shown to serve as electron donors to bacterial reaction centers using optical spectroscopy. Similar binding of the Mn-proteins to reaction centers was observed with an average dissociation constant of 2.3μM. The Mn-proteins with three metal centers were more effective at this electron transfer reaction than the Mn-proteins with one or two metal centers. Thus, multiple Mn-clusters can be incorporated into four-helix bundles with the capability of performing catalysis and electron transfer to a natural protein. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. Retrospective cohort study of the performance of the Pinnacle metal on metal (MoM) total hip replacement: a single-centre investigation in combination with the findings of a national retrieval centre

    PubMed Central

    Langton, David John; Sidaginamale, Raghavendra Prasad; Avery, Peter; Waller, Sue; Tank, Ghanshyabhai; Lord, James; Joyce, Thomas; Cooke, Nick; Logishetty, Raj; Nargol, Antoni Viraf Francis

    2016-01-01

    Objectives To determine risk factors for revision in patients implanted with a commonly used metal on metal (MoM) hip replacement. Design Retrospective cohort study in combination with a prospective national retrieval study (Northern Retrieval Registry (NRR)). Setting Combined orthopaedic unit in combination with the NRR. Participants All patients implanted with a DePuy Pinnacle MoM hip prostheses by the 2 senior authors were invited to attend for a review which included clinical examination, blood metal ion measurements, radiographs and targeted imaging. Explanted components underwent wear analysis using validated methodology and these results were compared with those obtained from the NRR. Results 489 MoM Pinnacle hips were implanted into 434 patients (243 females and 191 males). Of these, 352 patients attended the MoM recall clinics. 64 patients had died during the study period. For the purposes of survival analysis, non-attendees were assumed to have well-functioning prostheses. The mean follow-up of the cohort as a whole was 89 months. 71 hips were revised. Prosthetic survival for the whole cohort was 83.6% (79.9–87.3) at 9 years. The majority of explanted devices exhibited signs of taper junction failure. Risk factors for revision were bilateral MoM prostheses, smaller Pinnacle liners, and implantation in 2006 and later years. A significant number of devices were found to be manufactured out of their specifications. This was confirmed with analysis of the wider data set from the NRR. Conclusions This device was found to have an unacceptably high revision rate. Bilateral prostheses, those implanted into female patients and devices implanted in later years were found to be at greater risk. A significant number of explanted components were found to be manufactured with bearing diameters outside of the manufacturer's stated tolerances. Our findings highlight the clinical importance of hitherto unrecognised variations in device production. PMID:27130159

  11. Testing bridge-mediated differences in dinuclear valence tautomeric behavior.

    PubMed

    Bin-Salamon, Sofi; Brewer, Scott H; Depperman, Ezra C; Franzen, Stefan; Kampf, Jeff W; Kirk, Martin L; Kumar, R Krishna; Lappi, Simon; Peariso, Katrina; Preuss, Kathryn E; Shultz, David A

    2006-05-29

    Two structurally characterized dinuclear valence tautomers are described. Cobalt ions are bridged by p- and m-phenylene units connected to 2,2'-bipyridines. X-ray crystal structures show that the molecules are in the [(Co(III))(Co(III))] forms at ca. 125 K, while spectroscopic studies show that both molecules can achieve the [(Co(II))(Co(II))] form above 400 K and confirm the [(Co(III))(Co(III))] form below 10 K. Magnetic susceptibility studies are also included. Our results highlight the necessity of studying both crystalline and amorphous samples to distinguish the effects of intrinsic electronic structure and intermolecular forces on valence tautomeric behavior.

  12. Geometry and magnetic interaction modulations in dinuclear Dy2 single-molecule magnets.

    PubMed

    Guo, Mei; Xu, Yonghui; Wu, Jianfeng; Zhao, Lang; Tang, Jinkui

    2017-06-27

    Geometry and magnetic interaction modulations in a series of dinuclear dysprosium compounds, [Dy2Lz2(OAc)6]·2CH3OH (1), [Dy2Lz2(C6H5CO2)6]·2CH3CN (2), and [Dy2L2(SO3CF3)4THF4] (3) (Lz = 6-pyridin-2-yl-[1,3,5]triazine-2,4-diamine; L = N-(2,3-dimethylbut-3-en-2-yl)-N-hydroxynitrous amide; THF = tetrahydrofuran), can effectively tune the relaxation dynamics of magnetization. The dysprosium centres of compounds 2 and 3 display a hula hoop-like geometry; however, those in 1 show the monocapped square antiprismatic geometries. Moreover, the Dy2 cores of compounds 1 and 3 were linked by μ2-η(1):η(1) and μ2-η(1):η(2) bridging modes, thus generating shorter intramolecular DyDy distances as compared to those in compound 2. Consequently, these three compounds demonstrate distinct magnetic properties. Compounds 1 and 2 behave as single-molecule magnets (SMMs) under an appropriate static dc field; in addition, 2 displays field-induced multiple relaxation processes under a 1000 Oe dc field. Compound 3 shows a high relaxation energy barrier of 102 K in the zero dc field. These three interesting compounds with Dy2 cores shed light on the coordination geometry and magnetic interactions for the modulation of the properties of SMMs.

  13. New dinuclear nickel(II) and iron(II) complexes with a macrocyclic ligand containing a N6S2 donor-set: synthesis, structural, MALDI-TOF-MS, magnetic and spectroscopic studies.

    PubMed

    Núñez, Cristina; Bastida, Rufina; Macías, Alejandro; Valencia, Laura; Ribas, Joan; Capelo, José Luis; Lodeiro, Carlos

    2010-09-07

    A series of dinuclear Ni(II) and Fe(II) complexes with a Py(2)N(4)S(2) coordinating octadentate macrocyclic ligand L prepared by direct reactions have been studied. The overall geometry and bonding mode have been deduced on the basis of elemental analysis data, infrared, MALDI-TOF-MS, UV-vis spectroscopy, X-ray diffraction, conductivity and magnetic susceptibility measurements. In general both M(2+) centres are sited into the macrocyclic cavity coordinated to a pyridinic nitrogen atom, one sulfur atom, two secondary amine groups from the macrocyclic backbone and completing the coordination spheres with two solvent or anionic molecules in a distorted octahedral geometry, except in the case of [Ni(2)L(mu-Cl)(H(2)O)(2)](BF(4))(3).2H(2)O, where the metal ions are sited in the macrocyclic cavity coordinated to a pyridinic nitrogen atom, one sulfur atom, two secondary amine groups from the macrocyclic backbone, one water molecule and one chloride ion acting as a bridge between the two centres in a distorted octahedral geometry. The magnetic properties of the nickel(II) complexes, [Ni(2)L(CH(3)CN)(4)](BF(4))(4).3.5CH(3)CN (11) and [Ni(2)L(mu-Cl)(H(2)O)(2)](BF(4))(3).2H(2)O (12) has been recorded in the solid state and indicates an unexpected ferromagnetic exchange in both cases, especially in compound 11 because no similar systems are previously reported in the literature presenting this magnetic behaviour. Further complexes with similar ligands are in progress to corroborate this unexpected ferromagnetic behaviour.

  14. Validation of primary metal-on-metal hip arthroplasties on the National Joint Registry for England, Wales and Northern Ireland using data from the London Implant Retrieval Centre: a study using the NJR dataset.

    PubMed

    Sabah, S A; Henckel, J; Cook, E; Whittaker, R; Hothi, H; Pappas, Y; Blunn, G; Skinner, J A; Hart, A J

    2015-01-01

    Arthroplasty registries are important for the surveillance of joint replacements and the evaluation of outcome. Independent validation of registry data ensures high quality. The ability for orthopaedic implant retrieval centres to validate registry data is not known. We analysed data from the National Joint Registry for England, Wales and Northern Ireland (NJR) for primary metal-on-metal hip arthroplasties performed between 2003 and 2013. Records were linked to the London Implant Retrieval Centre (RC) for validation. A total of 67,045 procedures on the NJR and 782 revised pairs of components from the RC were included. We were able to link 476 procedures (60.9%) recorded with the RC to the NJR successfully. However, 306 procedures (39.1%) could not be linked. The outcome recorded by the NJR (as either revised, unrevised or death) for a primary procedure was incorrect in 79 linked cases (16.6%). The rate of registry-retrieval linkage and correct assignment of outcome code improved over time. The rates of error for component reference numbers on the NJR were as follows: femoral head category number 14/229 (5.0%); femoral head batch number 13/232 (5.3%); acetabular component category number 2/293 (0.7%) and acetabular component batch number 24/347 (6.5%). Registry-retrieval linkage provided a novel means for the validation of data, particularly for component fields. This study suggests that NJR reports may underestimate rates of revision for many types of metal-on-metal hip replacement. This is topical given the increasing scope for NJR data. We recommend a system for continuous independent evaluation of the quality and validity of NJR data.

  15. Nucleation process in the cavity of a 48-tungstophosphate wheel resulting in a 16-metal-centre iron oxide nanocluster.

    PubMed

    Mal, Sib Sankar; Dickman, Michael H; Kortz, Ulrich; Todea, Ana Maria; Merca, Alice; Bögge, Hartmut; Glaser, Thorsten; Müller, Achim; Nellutla, Saritha; Kaur, Narpinder; van Tol, Johan; Dalal, Naresh S; Keita, Bineta; Nadjo, Louis

    2008-01-01

    The 16-Fe(III)-containing 48-tungsto-8-phosphate [P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)](20-) (1) has been synthesised and characterised by IR and ESR spectroscopy, TGA, elemental analyses, electrochemistry and susceptibility measurements. Single-crystal X-ray analyses were carried out on Li(4)K(16)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)]66 H(2)O2 KCl (LiK-1, orthorhombic space group Pnnm, a=36.3777(9) A, b=13.9708(3) A, c=26.9140(7) A, and Z=2) and on the corresponding mixed sodium-potassium salt Na(9)K(11)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)].100 H(2)O (NaK-1, monoclinic space group C2/c, a=46.552(4) A, b=20.8239(18) A, c=27.826(2) A, beta=97.141(2) degrees and Z=4). Polyanion 1 contains--in the form of a cyclic arrangement--the unprecedented {Fe(16)(OH)(28)(H(2)O)(4)}(20+) nanocluster, with 16 edge- and corner-sharing FeO(6) octahedra, grafted on the inner surface of the crown-shaped [H(7)P(8)W(48)O(184)](33-) (P(8)W(48)) precursor. The synthesis of 1 was accomplished by reaction of different iron species containing Fe(II) (in presence of O(2)) or Fe(III) ions with the P(8)W(48) anion in aqueous, acidic medium (pH approximately 4), which can be regarded as an assembly process under confined geometries. One fascinating aspect is the possibility to model the uptake and release of iron in ferritin. The electrochemical study of 1, which is stable from pH 1 through 7, offers an interesting example of a highly iron-rich cluster. The reduction wave associated with the Fe(III) centres could not be split in distinct steps independent of the potential scan rate from 2 to 1000 mV s(-1); this is in full agreement with the structure showing that all 16 iron centres are equivalent. Polyanion 1 proved to be efficient for the electrocatalytic reduction of NO(x), including nitrate. Magnetic and variable frequency EPR measurements on 1 suggest that the Fe(III) ions are strongly antiferromagnetically coupled and that the ground state is tentatively spin S=2.

  16. Retrospective cohort study of the performance of the Pinnacle metal on metal (MoM) total hip replacement: a single-centre investigation in combination with the findings of a national retrieval centre.

    PubMed

    Langton, David John; Sidaginamale, Raghavendra Prasad; Avery, Peter; Waller, Sue; Tank, Ghanshyabhai; Lord, James; Joyce, Thomas; Cooke, Nick; Logishetty, Raj; Nargol, Antoni Viraf Francis

    2016-04-29

    To determine risk factors for revision in patients implanted with a commonly used metal on metal (MoM) hip replacement. Retrospective cohort study in combination with a prospective national retrieval study (Northern Retrieval Registry (NRR)). Combined orthopaedic unit in combination with the NRR. All patients implanted with a DePuy Pinnacle MoM hip prostheses by the 2 senior authors were invited to attend for a review which included clinical examination, blood metal ion measurements, radiographs and targeted imaging. Explanted components underwent wear analysis using validated methodology and these results were compared with those obtained from the NRR. 489 MoM Pinnacle hips were implanted into 434 patients (243 females and 191 males). Of these, 352 patients attended the MoM recall clinics. 64 patients had died during the study period. For the purposes of survival analysis, non-attendees were assumed to have well-functioning prostheses. The mean follow-up of the cohort as a whole was 89 months. 71 hips were revised. Prosthetic survival for the whole cohort was 83.6% (79.9-87.3) at 9 years. The majority of explanted devices exhibited signs of taper junction failure. Risk factors for revision were bilateral MoM prostheses, smaller Pinnacle liners, and implantation in 2006 and later years. A significant number of devices were found to be manufactured out of their specifications. This was confirmed with analysis of the wider data set from the NRR. This device was found to have an unacceptably high revision rate. Bilateral prostheses, those implanted into female patients and devices implanted in later years were found to be at greater risk. A significant number of explanted components were found to be manufactured with bearing diameters outside of the manufacturer's stated tolerances. Our findings highlight the clinical importance of hitherto unrecognised variations in device production. Published by the BMJ Publishing Group Limited. For permission to use (where not

  17. Rational design of a cytotoxic dinuclear Cu2 complex that binds by molecular recognition at two neighboring phosphates of the DNA backbone.

    PubMed

    Jany, Thomas; Moreth, Alexander; Gruschka, Claudia; Sischka, Andy; Spiering, Andre; Dieding, Mareike; Wang, Ying; Samo, Susan Haji; Stammler, Anja; Bögge, Hartmut; Fischer von Mollard, Gabriele; Anselmetti, Dario; Glaser, Thorsten

    2015-03-16

    The mechanism of the cytotoxic function of cisplatin and related anticancer drugs is based on their binding to the nucleobases of DNA. The development of new classes of anticancer drugs requires establishing other binding modes. Therefore, we performed a rational design for complexes that target two neighboring phosphates of the DNA backbone by molecular recognition resulting in a family of dinuclear complexes based on 2,7-disubstituted 1,8-naphthalenediol. This rigid backbone preorganizes the two metal ions for molecular recognition at the distance of two neighboring phosphates in DNA of 6-7 Å. Additionally, bulky chelating pendant arms in the 2,7-position impede nucleobase complexation by steric hindrance. We successfully synthesized the Cu(II)2 complex of the designed family of dinuclear complexes and studied its binding to dsDNA by independent ensemble and single-molecule methods like gel electrophoresis, precipitation, and titration experiments followed by UV-vis spectroscopy, atomic force microscopy (AFM), as well as optical tweezers (OT) and magnetic tweezers (MT) DNA stretching. The observed irreversible binding of our dinuclear Cu(II)2 complex to dsDNA leads to a blocking of DNA synthesis as studied by polymerase chain reactions and cytotoxicity for human cancer cells.

  18. Synthesis, structural characterization, DFT studies and catalytic properties of dinuclear oxidovanadium(V) complexes derived from adipohydrazone ligands

    NASA Astrophysics Data System (ADS)

    Noei-Hootkani, Hashem; Karrari, Solmaz; Hosseini-Monfared, Hassan; Mayer, Peter; Notash, Behrouz

    2017-09-01

    Two new dinuclear oxidovanadium(V) complexes, [V2O2(L1)(OCH3)2(CH3OH)2]·2(CH3OH) (1) and [V2O2(L2)(OCH3)2(CH3OH)2]·2(CH3OH) (2), were synthesized from the reaction of VO(acac)2 and hexa-dentate N2O4-donor hydrazone ligands (H4L1 and H4L2) in methanol solvent. The ligands and complexes were characterized by elemental analysis and spectroscopic methods. Single crystal X-ray analysis of the brown crystals of complexes 1 and 2 indicated that these complexes are dinuclear oxidovanadium(V) complexes which the metal ions have distorted octahedral geometry. There are several strong and directed hydrogen bonding interactions in the crystal packing of 1 and 2 which stabilize their crystalline format. The catalytic activity of these complexes was tested in the oxidation of thioanisole using H2O2. These studies indicated both complexes have high catalytic activity in the oxidation of thioanisole. The complexes were further studied by DFT and TDDFT theoretical calculations.

  19. Synthesis and cytotoxicity of dinuclear complexes containing ruthenium(II) bipyridyl units linked by a bis(pyridylimine) ligand.

    PubMed

    McDonnell, Ursula; Kerchoffs, Jessica M C A; Castineiras, Rosa P M; Hicks, Matthew R; Hotze, Anna C G; Hannon, Michael J; Rodger, Alison

    2008-02-07

    Enantiopure dinuclear ruthenium polypyridyl complexes of the form [Ru(2)(LL)(4)L(1)](PF(6))(4) (LL = 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen); L(1)= C(25)H(20)N(4) a bis(pyridylimine) ligand containing a diphenylmethane spacer) have been synthesized using the chiral building blocks cis-[Ru(bpy)(2)(py)(2)](2+) and cis-[Ru(phen)(2)(py)(2)](2+). These dinuclear ruthenium complexes have been characterised using NMR, mass spectrometry, UV-visible absorbance, circular dichroism and linear dichroism. The compounds exhibit good photo and thermal stability. The extinction coefficient for the bpy complex at 478 nm is epsilon(478) = 15,700 mol(-1) cm(-1) dm(3) and for the phen complex is epsilon(478) = 24,900 mol(-1) cm(-1) dm(3). Both complexes have their longest wavelength (metal to ligand charge transfer) transition predominantly x/y (short axis)-polarised while the transitions at shorter wavelength are a mixture of x/y and z-polarisations, similar to both the copper helicate and iron triple helicate studied previously. Cytotoxicity studies reveal that the compounds are dramatically less active against cancer cell lines than the recently reported supramolecular cylinders prepared from the same bis(pyridylimine) ligand.

  20. Towards accurate structural characterization of metal centres in protein crystals: the structures of Ni and Cu T{sub 6} bovine insulin derivatives

    SciTech Connect

    Frankaer, Christian Grundahl; Mossin, Susanne; Ståhl, Kenny; Harris, Pernille

    2014-01-01

    The level of structural detail around the metal sites in Ni{sup 2+} and Cu{sup 2+} T{sub 6} insulin derivatives was significantly improved by using a combination of single-crystal X-ray crystallography and X-ray absorption spectroscopy. Photoreduction and subsequent radiation damage of the Cu{sup 2+} sites in Cu insulin was followed by XANES spectroscopy. Using synchrotron radiation (SR), the crystal structures of T{sub 6} bovine insulin complexed with Ni{sup 2+} and Cu{sup 2+} were solved to 1.50 and 1.45 Å resolution, respectively. The level of detail around the metal centres in these structures was highly limited, and the coordination of water in Cu site II of the copper insulin derivative was deteriorated as a consequence of radiation damage. To provide more detail, X-ray absorption spectroscopy (XAS) was used to improve the information level about metal coordination in each derivative. The nickel derivative contains hexacoordinated Ni{sup 2+} with trigonal symmetry, whereas the copper derivative contains tetragonally distorted hexacoordinated Cu{sup 2+} as a result of the Jahn–Teller effect, with a significantly longer coordination distance for one of the three water molecules in the coordination sphere. That the copper centre is of type II was further confirmed by electron paramagnetic resonance (EPR). The coordination distances were refined from EXAFS with standard deviations within 0.01 Å. The insulin derivative containing Cu{sup 2+} is sensitive towards photoreduction when exposed to SR. During the reduction of Cu{sup 2+} to Cu{sup +}, the coordination geometry of copper changes towards lower coordination numbers. Primary damage, i.e. photoreduction, was followed directly by XANES as a function of radiation dose, while secondary damage in the form of structural changes around the Cu atoms after exposure to different radiation doses was studied by crystallography using a laboratory diffractometer. Protection against photoreduction and subsequent

  1. Chalcogenide centred gold complexes.

    PubMed

    Gimeno, M Concepción; Laguna, Antonio

    2008-09-01

    Chalcogenide-centred gold complexes are an important class of compounds in which a central chalcogen is surrounded by several gold atoms or gold and other metals. They have special characteristics such as unusual geometries, electron deficiency and properties such as luminescence or non-linear optical properties. The best known species are the trinuclear [E(AuPR3)3]+, 'oxonium' type species, that have high synthetic applicability, not only in other chalcogen-centred species, but in many other organometallic derivatives. The aurophilic interactions play an important role in the stability, preference for a particular geometry and luminescence properties in this type of derivatives (critical review, 117 references).

  2. Dinuclear Zinc Salen Catalysts for the Ring Opening Copolymerization of Epoxides and Carbon Dioxide or Anhydrides.

    PubMed

    Thevenon, Arnaud; Garden, Jennifer A; White, Andrew J P; Williams, Charlotte K

    2015-12-21

    A series of four dizinc complexes coordinated by salen or salan ligands, derived from ortho-vanillin and bearing (±)-trans-1,2-diaminocyclohexane (L1) or 2,2-dimethyl-1,3-propanediamine (L2) backbones, is reported. The complexes are characterized using a combination of X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental analysis. The stability of the dinuclear complexes depends on the ligand structure, with the most stable complexes having imine substituents. The complexes are tested as catalysts for the ring-opening copolymerization (ROCOP) of CO2/cyclohexene oxide (CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity relationships reveal that the complex having both L2 and imine substituents displays the highest activity. In the ROCOP of CO2/CHO its activity is equivalent to other metal salen catalysts (TOF = 44 h(-1) at a catalyst loading of 0.1 mol %, 30 bar of CO2, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than other metal salen catalysts (TOF = 198 h(-1) at a catalyst loading of 1 mol % and 100 °C). Poly(ester-block-carbonate) polymers are also afforded using the most active catalyst by the one-pot terpolymerization of PA/CHO/CO2.

  3. Iron(III) located in the dinuclear metallo-β-lactamase IMP-1 by pseudocontact shifts.

    PubMed

    Carruthers, Thomas J; Carr, Paul D; Loh, Choy-Theng; Jackson, Colin J; Otting, Gottfried

    2014-12-15

    Heterodinuclear metalloenzymes are an important class of metalloproteins, but determining the location of the different metal ions can be difficult. Herein we present a new NMR spectroscopy method that uses pseudocontact shifts (PCS) to achieve this without assumptions about the coordinating ligands. The approach is illustrated with the dinuclear [FeZn] complex of IMP-1, which is a prototypical metallo-β-lactamase (MβL) that confers resistance to β-lactam antibiotics. Results from single-crystal X-ray diffraction were compromised by degradation during crystallization. With [GaZn]-IMP-1 as diamagnetic reference, the PCSs unambiguously identified the iron binding site in fresh samples of [FeZn]-IMP-1, even though the two metal centers are less than 3.8 Å apart and the iron is high-spin Fe(3+), which produces only small PCSs. [FeZn]-MβLs may be important drug targets, as [FeZn]-IMP-1 is enzymatically active and readily produced in the presence of small amounts of Fe(3+). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Bio-inspired electron-delivering system for reductive activation of dioxygen at metal centres towards artificial flavoenzymes

    PubMed Central

    Roux, Yoann; Ricoux, Rémy; Avenier, Frédéric; Mahy, Jean-Pierre

    2015-01-01

    Development of artificial systems, capable of delivering electrons to metal-based catalysts for the reductive activation of dioxygen, has been proven very difficult for decades, constituting a major scientific lock for the elaboration of environmentally friendly oxidation processes. Here we demonstrate that the incorporation of a flavin mononucleotide (FMN) in a water-soluble polymer, bearing a locally hydrophobic microenvironment, allows the efficient reduction of the FMN by NADH. This supramolecular entity is then capable of catalysing a very fast single-electron reduction of manganese(III) porphyrin by splitting the electron pair issued from NADH. This is fully reminiscent of the activity of natural reductases such as the cytochrome P450 reductases with kinetic parameters, which are three orders of magnitude faster compared with other artificial systems. Finally, we show as a proof of concept that the reduced manganese porphyrin activates dioxygen and catalyses the oxidation of organic substrates in water. PMID:26419885

  5. Characterization of atmospheric particulates, particle-bound transition metals and polycyclic aromatic hydrocarbons of urban air in the centre of Athens (Greece).

    PubMed

    Valavanidis, Athanasios; Fiotakis, Konstantinos; Vlahogianni, Thomais; Bakeas, Evangelos B; Triantafillaki, Styliani; Paraskevopoulou, Vasiliki; Dassenakis, Manos

    2006-10-01

    The concentrations of trace metals and polycyclic aromatic hydrocarbons (PAHs) adsorbed to total suspended particulate (TSP) and finer fractions of airborne particulate matter (PM) were determined from a site in the centre of Athens (Greece), which is characterized by heavy local traffic and is densely populated, during the winter and summer periods in 2003-2004. Also, we collected and analyzed samples of diesel and gasoline exhaust particles from local vehicles (buses, taxis and private cars) and from chimney exhaust of residential central heating appliances. A seasonal effect was observed for the size distribution of aerosol mass, with a shift to larger fine fractions in winter. The most commonly detected trace metals in the TSP and PM fractions were Fe, Pb, Zn, Cu, Cr, V, Ni and Cd and their concentrations were similar to levels observed in heavily polluted urban areas from local traffic and other anthropogenic emissions. Analysis of 16 PAHs bound to PM showed that they are mostly traffic related. In general, the fine particulate PAHs concentrations were higher than coarse particles. The most common PAHs in PM(10.2) and PM(2.1) were pyrene, phenanthrene, acenapthylene and fluoranthene, which are associated with diesel and gasoline exhaust particles. The results of this study underlined the importance of local emission sources, especially vehicular traffic, central heating and other local anthropogenic emissions. Compared with other big cities, Athens has much higher levels of airborne particles, especially of the finer fractions PM(10) and PM(2.5), correlated with traffic-related air pollution.

  6. Conformational transition of DNA by dinuclear Pt(II) complexes causes cooperative inhibition of gene expression

    NASA Astrophysics Data System (ADS)

    Shimizu, Yuta; Yoshikawa, Yuko; Kenmotsu, Takahiro; Komeda, Seiji; Yoshikawa, Kenichi

    2017-06-01

    Recently, it was reported that a cationic tetrazolato-bridged dinuclear Pt(II) complex, 5-H-Y, is a promising anticancer drug candidate. Here, we investigated the effects of a series of tetrazolato-bridged dinuclear Pt(II) complexes on the higher-order structure of DNA by using fluorescence and atomic force microscopies. The results showed that these dinuclear Pt(II) complexes cause marked shrinkage on the conformation of genomic DNA. We also found highly cooperative inhibitory effects of these drugs on in vitro gene expression. The unique mechanism of action of these dinuclear Pt(II) complexes is discussed in terms of their bridging effect on DNA segments.

  7. Zn(II) coordination to polyamine macrocycles containing dipyridine units. New insights into the activity of dinuclear Zn(II) complexes in phosphate ester hydrolysis.

    PubMed

    Bazzicalupi, Carla; Bencini, Andrea; Berni, Emanuela; Bianchi, Antonio; Fornasari, Patrizia; Giorgi, Claudia; Valtancoli, Barbara

    2004-10-04

    Zn(II) binding by the dipyridine-containing macrocycles L1-L3 has been analyzed by means of potentiometric measurements in aqueous solutions. These ligands contain one (L1, L2) or two (L3) 2,2'-dipyridine units as an integral part of a polyamine macrocyclic framework having different dimensions and numbers of nitrogen donors. Depending on the number of donors, L1-L3 can form stable mono- and/or dinuclear Zn(II) complexes in a wide pH range. Facile deprotonation of Zn(II)-coordinated water molecules gives mono- and dihydroxo-complexes from neutral to alkaline pH values. The ability of these complexes as nucleophilic agents in hydrolytic processes has been tested by using bis(p-nitrophenyl) phosphate (BNPP) as a substrate. In the dinuclear complexes the two metals play a cooperative role in BNPP cleavage. In the case of the L2 dinuclear complex [Zn(2)L2(OH)(2)](2+), the two metals act cooperatively through a hydrolytic process involving a bridging interaction of the substrate with the two Zn(II) ions and a simultaneous nucleophilic attack of a Zn-OH function at phosphorus; in the case of the dizinc complex with the largest macrocycle L3, only the monohydroxo complex [Zn(2)L3(OH)](3+) promotes BNPP hydrolysis. BNPP interacts with a single metal, while the hydroxide anion may operate a nucleophilic attack. Both complexes display high rate enhancements in BNPP cleavage with respect to previously reported dizinc complexes, due to hydrophobic and pi-stacking interactions between the nitrophenyl groups of BNPP and the dipyridine units of the complexes.

  8. Bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pair-catalyzed enantioselective sulfoxidation

    NASA Astrophysics Data System (ADS)

    Zong, Lili; Wang, Chao; Moeljadi, Adhitya Mangala Putra; Ye, Xinyi; Ganguly, Rakesh; Li, Yongxin; Hirao, Hajime; Tan, Choon-Hong

    2016-11-01

    Catalytic use of peroxomolybdate for asymmetric transformations has attracted increasing attention due to its catalytic properties and application in catalysis. Herein, we report chiral bisguanidinium dinuclear oxodiperoxomolybdosulfate [BG]2+[(μ-SO4)Mo2O2(μ-O2)2(O2)2]2- ion pair, as a catalyst for enantioselective sulfoxidation using aqueous H2O2 as the terminal oxidant. The ion pair catalyst is isolatable, stable and useful for the oxidation of a range of dialkyl sulfides. The practical utility was illustrated using a gram-scale synthesis of armodafinil, a commercial drug, with the catalyst generated in situ from 0.25 mol% of bisguanidinium and 2.5 mol% of Na2MoO4.2H2O. Structural characterization of this ion pair catalyst has been successfully achieved using single-crystal X-ray crystallography.

  9. Bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pair-catalyzed enantioselective sulfoxidation

    PubMed Central

    Zong, Lili; Wang, Chao; Moeljadi, Adhitya Mangala Putra; Ye, Xinyi; Ganguly, Rakesh; Li, Yongxin; Hirao, Hajime; Tan, Choon-Hong

    2016-01-01

    Catalytic use of peroxomolybdate for asymmetric transformations has attracted increasing attention due to its catalytic properties and application in catalysis. Herein, we report chiral bisguanidinium dinuclear oxodiperoxomolybdosulfate [BG]2+[(μ-SO4)Mo2O2(μ-O2)2(O2)2]2− ion pair, as a catalyst for enantioselective sulfoxidation using aqueous H2O2 as the terminal oxidant. The ion pair catalyst is isolatable, stable and useful for the oxidation of a range of dialkyl sulfides. The practical utility was illustrated using a gram-scale synthesis of armodafinil, a commercial drug, with the catalyst generated in situ from 0.25 mol% of bisguanidinium and 2.5 mol% of Na2MoO4·2H2O. Structural characterization of this ion pair catalyst has been successfully achieved using single-crystal X-ray crystallography. PMID:27869124

  10. Iridium(III) soft salts from dinuclear cationic and mononuclear anionic complexes for OLED devices.

    PubMed

    Nasr, Gihane; Guerlin, Audrey; Dumur, Frédéric; Beouch, Layla; Dumas, Eddy; Clavier, Gilles; Miomandre, Fabien; Goubard, Fabrice; Gigmes, Didier; Bertin, Denis; Wantz, Guillaume; Mayer, Cédric R

    2011-10-14

    Two iridium(III) soft salts based on ion-paired dinuclear cationic and mononuclear anionic complexes were designed and investigated as phosphorescent emitters for solution processed OLEDs. New dinuclear cationic complexes were prepared with two different bridging ligands, a carbazole and a phenylene spacer. Best devices were designed with the soft salt bearing a carbazole moiety. This journal is © The Royal Society of Chemistry 2011

  11. Preparation, structure, and luminescence of dinuclear lanthanide complexes of a novel imine-amine phenolate macrocycle

    SciTech Connect

    Matthews, K.D.; Kahwa, I.A. ); Williams, D.J. )

    1994-03-30

    Metal-free condensation of 2,6-diformyl-p-cresol with 3,6-dioxa-1,8-octanediamine followed by reduction with sodium tetrahydroborate and addition of lanthanide(III) nitrate salts, in that order, yield (slowly) crystalline dinuclear complexes of a novel imine-amine phenolate macrocycle 2. The decacoordination geometry of the identical Pr[sup 3+] ions in a C[sub 2v] 4A,6B-extended dodecahedron made up of two bidentate NO[sub 3]-ions, two phenolate and two either oxygens, and one imine and one amine nitrogens. Dinuclear lanthanide complexes of 2 appear to be more stable than those of the totally reduced chelate 2 in alcoholic media. The Tb[sub 2]2(NO[sub 3])[sub 4][center dot]1.2CH[sub 3]-OH and (La[sub 0.97]Tb[sub 0.03])[sub 2]2(NO[sub 3])[sub 4][center dot]1.2CH[sub 3]OH compounds exhibit strong Tb[sup 3+] ([sup 5]D[sub 4] [yields] [sup 7]F[sub J]) emission sensitized by the single state of 2 at both 77 and 295 K. No Tb[sup 3+]-Tb[sup 3+] self-quenching or N-H trapping effects are observed at 77 K (decay rate is 598 s[sup [minus]1]); the coordination cavities of 2 are therefore potentially good hosts for Tb[sup 3+] in luminescent diagnostic agents. At room temperature the complex decay kinetics of Tb[sup 3+] in Tb[sub 2]2(NO[sub 3])[sub 4][center dot]1.2CH[sub 3]OH are similar to those of Tb[sub 2]1(NO[sub 3])[sub 4][center dot]H[sub 2]O. But for the dilute complex, (La[sub 0.97]-Tb[sub 0.03])[sub 2]2(NO[sub 3])[sub 4][center dot]1.35CH[sub 3]OH, unusual thermal equilibration of the ligand triplet and Tb[sup 3+] [sup 5]D[sub 4] states occurs at room temperature; the ligand-to-Tb[sup 3+] energy-transfer rate is [approx]4.36 x 10[sup 4] s[sup [minus]1], while Tb[sup 3+]-to-ligand back-energy-transfer is [approx]7.1 x 10[sup 4] s[sup [minus]1].

  12. Glycosidase- and β-lactamase-like activity of dinuclear copper(II) patellamide complexes.

    PubMed

    Comba, Peter; Eisenschmidt, Annika; Kipper, Nora; Schießl, Jasmin

    2016-06-01

    Prochloron, a blue-green algae belonging to ancient prokaryotes, produces, like other cyanobacteria, cyclic pseudo-peptides, which are also found in its obligate symbiont ascidiae (Lissoclinum patellum). Although research has focused for some time on the putative metabolic function of these cyclic peptides, to date it is still not understood. Their role might be connected to the increased concentrations of divalent metal ions, especially Cu(II), found in ascidiae. Dinuclear copper(II) complexes of cyclic pseudo-peptides revealed a broad hydrolytic capacity, including carboanhydrase and phosphatase activity. This study reports their β-lactamase as well as α- and β-glycosidase activity with kcat=(11.34±0.91)ˑ10(-4)s(-1) for β-lactamase, kcat=(1.55±0.13)ˑ10(-4)s(-1) for α-glycosidase and kcat=(1.22±0.09)ˑ10(-4)s(-1) for β-glycosidase activity. Copyright © 2016 Elsevier Inc. All rights reserved.

  13. A Highly Effective Strategy for Encapsulating Potassium Cations in Small Crown Ether Rings on a Dinuclear Palladium Complex.

    PubMed

    Lucio-Martínez, Fátima; Bermúdez, Brais; Ortigueira, Juan M; Adams, Harry; Fernández, Alberto; Pereira, M Teresa; Vila, José M

    2017-03-16

    The potential of 15-crown-5 ethers to link large cations, such as potassium, is limited by the quasi-parallel arrangement of two oxygen donor moieties upon appropriate orientation of the corresponding ether-ring-containing molecules. Substrates bearing the two crown ethers that are capable of achieving such coordination are hitherto unknown. The synthesis and isolation of a tailor-made dinuclear palladacycle bearing 15-crown-5 ether rings on the metallated phenyls offers such a possibility, providing the adequate environment for the formation of the sandwiched [K(metallacycle-15-crown-5)2 ] moiety. This synthetic strategy also culminates in the isolation of the first palladacycle able to entrap a potassium cation through bonding to two 15-crown-5 ether rings in a single molecule.

  14. Synthesis and crystal structure of a dinuclear yttrium(III)- (lanthanide(III)-) copper(II) complex with an unusual 2-methyl-2,4,6-tris(trifluoromethyl)-1,3-dioxane-4,6-diolato ligand

    SciTech Connect

    Wang, S.; Pang, Z.; Smith, K.D.L. )

    1993-11-10

    A dinuclear Ln[sup III]-Cu[sup II] complex with an unusual 2-methyl-2,4,6-tris(trifluoromethyl)-1,3-dioxane-4,6-diolato ligand has been synthesized and characterized structurally. The 1,3-dioxane-4,6-diolato ligand is the product of cycloaddition of 1,1,1-trifluoro-2,2-propanediol to a hexafluoroacetylacetonato ligand promoted by the metal complex.

  15. Dinuclear triple-stranded complexes of ReV with bis(benzene-o-dithiolato) ligands

    NASA Astrophysics Data System (ADS)

    Gancheff, Jorge S.; Hahn, F. Ekkehardt

    2012-12-01

    The reaction of K2ReCl6 with 1,2-bis(2,3-dimercaptobenzamido)ethane (H4-1), and 1,2-bis(2,3-dimercaptobenzamido)benzene (H4-2) in the presence of Na2CO3 in methanol affords dinuclear complexes of ReV. Experimental evidence supports the presence of self-assembled complexes with two {Re(S2C6H3)3} units connected in a triple-stranded fashion. Density Functional Theory (DFT) studies on geometry and electronic properties were conducted employing the hybrid B3LYP and PBE1PBE functionals. The helical (ΔΔ and ΛΛ) and meso-helical (ΔΛ) isomers were considered. For the helicate complexes included in this study, differences in the stability of the isomers were observed originating in different steric and strain interactions between the three ligand strands. The geometries at the minimum exhibit a distorted trigonal-prismatic coordination environment at the metal centers. Natural bond orbitals (NBO) analysis indicates the presence of Re-S bonds which are strongly polarized toward the non-metal. Time-Dependent DFT (TD-DFT) calculations were performed for a further understanding of the optical spectra. The calculations show the occupied 5d orbitals of the rhenium lying beneath occupied sulfur-based MOs. The general features of the electronic spectra in the visible region are reasonably reproduced by the calculations. The analysis of molecular orbitals also allows the assignment of the origin for all experimentally detected absorption bands. In the high-energy region of the spectrum the absorptions are attributed to ligand-to-metal-ligand charge transfer (LMLCT), in which sulfur-based orbitals and unoccupied orbitals at the rhenium atom and the benzene-o-dithiolato groups are involved. Also in the blue region, shoulders originating from LMLCT are observed.

  16. Dinuclear triple-stranded complexes of Re(V) with bis(benzene-o-dithiolato) ligands.

    PubMed

    Gancheff, Jorge S; Hahn, F Ekkehardt

    2012-12-01

    The reaction of K(2)ReCl(6) with 1,2-bis(2,3-dimercaptobenzamido)ethane (H(4)-1), and 1,2-bis(2,3-dimercaptobenzamido)benzene (H(4)-2) in the presence of Na(2)CO(3) in methanol affords dinuclear complexes of Re(V). Experimental evidence supports the presence of self-assembled complexes with two {Re(S(2)C(6)H(3))(3)} units connected in a triple-stranded fashion. Density Functional Theory (DFT) studies on geometry and electronic properties were conducted employing the hybrid B3LYP and PBE1PBE functionals. The helical (ΔΔ and ΛΛ) and meso-helical (ΔΛ) isomers were considered. For the helicate complexes included in this study, differences in the stability of the isomers were observed originating in different steric and strain interactions between the three ligand strands. The geometries at the minimum exhibit a distorted trigonal-prismatic coordination environment at the metal centers. Natural bond orbitals (NBO) analysis indicates the presence of Re-S bonds which are strongly polarized toward the non-metal. Time-Dependent DFT (TD-DFT) calculations were performed for a further understanding of the optical spectra. The calculations show the occupied 5d orbitals of the rhenium lying beneath occupied sulfur-based MOs. The general features of the electronic spectra in the visible region are reasonably reproduced by the calculations. The analysis of molecular orbitals also allows the assignment of the origin for all experimentally detected absorption bands. In the high-energy region of the spectrum the absorptions are attributed to ligand-to-metal-ligand charge transfer (LMLCT), in which sulfur-based orbitals and unoccupied orbitals at the rhenium atom and the benzene-o-dithiolato groups are involved. Also in the blue region, shoulders originating from LMLCT are observed. Copyright © 2012 Elsevier B.V. All rights reserved.

  17. Dinuclear cobalt(II) and copper(II) complexes with a Py2N4S2 macrocyclic ligand.

    PubMed

    Núñez, Cristina; Bastida, Rufina; Lezama, Luis; Macías, Alejandro; Pérez-Lourido, Paulo; Valencia, Laura

    2011-06-20

    The interaction between Co(II) and Cu(II) ions with a Py(2)N(4)S(2)-coordinating octadentate macrocyclic ligand (L) to afford dinuclear compounds has been investigated. The complexes were characterized by microanalysis, conductivity measurements, IR spectroscopy and liquid secondary ion mass spectrometry. The crystal structure of the compounds [H(4)L](NO(3))(4), [Cu(2)LCl(2)](NO(3))(2) (5), [Cu(2)L(NO(3))(2)](NO(3))(2) (6), and [Cu(2)L(μ-OH)](ClO(4))(3)·H(2)O (7) was also determined by single-crystal X-ray diffraction. The [H(4)L](4+) cation crystal structure presents two different conformations, planar and step, with intermolecular face-to-face π,π-stacking interactions between the pyridinic rings. Complexes 5 and 6 show the metal ions in a slightly distorted square-pyramidal coordination geometry. In the case of complex 7, the crystal structure presents the two metal ions joined by a μ-hydroxo bridge and the Cu(II) centers in a slightly distorted square plane or a tetragonally distorted octahedral geometry, taking into account weak interactions in axial positions. Electron paramagnetic resonance spectroscopy is in accordance with the dinuclear nature of the complexes, with an octahedral environment for the cobalt(II) compounds and square-pyramidal or tetragonally elongated octahedral geometries for the copper(II) compounds. The magnetic behavior is consistent with the existence of antiferromagnetic interactions between the ions for cobalt(II) and copper(II) complexes, while for the Co(II) ones, this behavior could also be explained by spin-orbit coupling.

  18. Homo-and heterodinuclear complexes of the tris(catecholamide) derivative of a tetraazamacrocycle with Fe3+, Cu2+ and Zn2+ metal ions.

    PubMed

    Guerra, Krassimira P; Delgado, Rita

    2008-01-28

    The new ditopic catecholamide 3,7,11-tris-{N-[3,4-(dihydroxybenzoyl)-aminopropyl]} derivative of a 14-membered tetraazamacrocycle containing pyridine (H(6)L(1)) has been synthesized. The protonation constants of (L(1))(6-) and the stability constants of its mono-, homo- and hetero-dinuclear complexes with Fe(3+), Cu(2+) and Zn(2+) metal ions were determined at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO(3). The large overall basicity of the ligand was ascribed to the very high protonation constants of the catecholate groups, and its acid-base behaviour was correlated with the presence of tertiary nitrogen atoms and secondary amide functions. The UV-vis spectrum of the red solution of [FeL(1)](3-) complex exhibits the LMCT band of catecholate to iron(III), and its EPR spectrum revealed a typical isotropic signal of a rhombic distorted ferric centre in a high-spin state and E/D approximately 0.31, both characteristic of a tris-catecholate octahedral environment. The ligand forms with copper(II) and zinc(II) ions mono- and dinuclear protonated complexes and their stability constants were determined, except for the [ML(1)](4-) complexes as the last proton is released at very high pH. Electronic spectroscopic studies of the copper complexes revealed the involvement of catecholate groups in the coordination to the metal centre in the mono- and dinuclear copper(II) complexes. This information together with the determined stability constants indicated that the copper(II) ion can be involved in both types of coordination site of the ligand with comparable binding affinity. The EPR spectrum of [Cu(2)L(1)](2-) showed a well resolved seven-line hyperfine pattern of copper(II) dinuclear species typical of a paramagnetic triplet spin state with weak coupling between the two metal centres. Thermodynamically stable heterodinuclear complexes, [CuFeH(h)L(1)](h-1) (h = 0-3) and [CuZnH(h)L(1)](h-2) (h = 0-4), were formed as expected from a ditopic ligand having two dissimilar

  19. The activity of the dinuclear cobalt-β-lactamase from Bacillus cereus in catalysing the hydrolysis of β-lactams

    PubMed Central

    Badarau, Adriana; Damblon, Christian; Page, Michael I.

    2006-01-01

    Metallo-β-lactamases are native zinc enzymes that catalyse the hydrolysis of β-lactam antibiotics, but are also able to function with cobalt(II) and require one or two metal-ions for catalytic activity. The hydrolysis of cefoxitin, cephaloridine and benzylpenicillin catalysed by CoBcII (cobalt-substituted β-lactamase from Bacillus cereus) has been studied at different pHs and metal-ion concentrations. An enzyme group of pKa 6.52±0.1 is found to be required in its deprotonated form for metal-ion binding and catalysis. The species that results from the loss of one cobalt ion from the enzyme has no significant catalytic activity and is thought to be the mononuclear CoBcII. It appears that dinuclear CoBcII is the active form of the enzyme necessary for turnover, while the mononuclear CoBcII is only involved in substrate binding. The cobalt-substituted enzyme is a more efficient catalyst than the native enzyme for the hydrolysis of some β-lactam antibiotics suggesting that the role of the metal-ion is predominantly to provide the nucleophilic hydroxide, rather than to act as a Lewis acid to polarize the carbonyl group and stabilize the oxyanion tetrahedral intermediate. PMID:16961465

  20. Neutral binuclear rare-earth metal complexes with four μ₂-bridging hydrides.

    PubMed

    Rong, Weifeng; He, Dongliang; Wang, Meiyan; Mou, Zehuai; Cheng, Jianhua; Yao, Changguang; Li, Shihui; Trifonov, Alexander A; Lyubov, Dmitrii M; Cui, Dongmei

    2015-03-25

    The first neutral rare-earth metal dinuclear dihydrido complexes [(NPNPN)LnH2]2 (2-Ln; Ln = Y, Lu; NPNPN: N[Ph2PNC6H3((i)Pr)2]2) bearing μ2-bridging hydride ligands have been synthesized. In the presence of THF, 2-Y undergoes intramolecular activation of the sp(2) C-H bond to form dinuclear aryl-hydride complex 3-Y containing three μ2-bridging hydride ligands.

  1. Stereospecific formation of dinuclear vanadium(V) tartrato complexes.

    PubMed

    Gáliková, Jana; Schwendt, Peter; Tatiersky, Jozef; Tracey, Alan S; Zák, Zdirad

    2009-09-07

    The first dinuclear nonperoxido tartrato complexes of vanadium(V), (NMe(4))(2)[V(2)O(4)((2R,3R)-H(2)tart)(2)] x 6 H(2)O (1), (NMe(4))(2)[V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)] (2), (NEt(4))(2)[V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)] (3) (tart = tartrato(4-) = C(4)H(2)O(6)(4-)) have been prepared from water-ethanol medium and characterized by X-ray structure analysis and spectral methods. The formation of the complexes has been found to be stereospecific; the composition and structure of anions containing one or both enantiomers of the ligand are profoundly different. The structure of anions in 1-3 also differs significantly from the structure of other dinuclear vanadium(V) alpha-hydroxycarboxylato complexes, but, interestingly, the geometry of the [V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)](2-) ion resembles the structure of the [(VO)(2)((2R,3R)-tart)((2S,3S)-tart)](4-) ion which has a vanadium(IV) center. Using Raman and (51)V NMR spectroscopy the solvent dependent mutual transformations of [V(4)O(8)((2R,3R)-tart)(2)](4-) (V(4)L(2)-RR), [V(4)O(8)((2S,3S)-tart)(2)](4-) (V(4)L(2)-SS), [V(2)O(4)((2R,3R)-H(2)tart)(2)](2-) (V(2)L(2)-RR), [V(2)O(4)((2S,3S)-H(2)tart)(2)](2-) (V(2)L(2)-SS), and [V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)](2-) (V(2)L(2)-rac) have been established. In aqueous solution the following reactions take place; 2 V(2)L(2)-rac --> V(2)L(2)-RR + V(2)L(2)-SS followed by partial decomposition, V(2)L(2)-RR --> V(4)L(2)-RR + 2 L (V(2)L(2)-SS --> V(4)L(2)-SS + 2 L). On the other hand V(2)L(2)-rac is stable in CH(3)CN solution while V(2)L(2)-RR (V(2)L(2)-SS) decomposes into several species.

  2. Structural, MALDI-TOF-MS, magnetic and spectroscopic studies of new dinuclear copper(II), cobalt(II) and zinc(II) complexes containing a biomimicking μ-OH bridge.

    PubMed

    Núñez, Cristina; Bastida, Rufina; Macías, Alejandro; Valencia, Laura; Neuman, Nicolás I; Rizzi, Alberto C; Brondino, Carlos D; González, Pablo J; Capelo, José Luis; Lodeiro, Carlos

    2010-12-28

    The Py(2)N(4)S(2) octadentate coordinating ligand afforded dinuclear cobalt, copper and zinc complexes and the corresponding mixed metal compounds. The overall geometry and bonding modes have been deduced on the basis of elemental analysis data, MALDI-TOF-MS, IR, UV-vis and EPR spectroscopies, single-crystal X-Ray diffraction, conductivity and magnetic susceptibility measurements. In the copper and zinc complexes, a μ-hydroxo bridge links the two metal ions. In both cases, the coordination geometry is distorted octahedral. Magnetic and EPR data reveal weakly antiferromagnetic high spin Co(II) ions, compatible with a dinuclear structure. The magnetic characterization of the dinuclear Cu(II) compound indicates a ferromagnetically coupled dimer with weak antiferromagnetic intermolecular interactions. The intra-dimer ferromagnetic behaviour was unexpected for a Cu(II) dimer with such μ-hydroxo bridging topology. We discuss the influence on the magnetic properties of non-covalent interactions between the bridging moiety and the lattice free water molecules.

  3. Dinuclear manganese centers in the manganese-lead-tellurate glasses.

    PubMed

    Rada, S; Dehelean, A; Culea, M; Culea, E

    2011-07-01

    FTIR, UV-VIS and EPR spectra of manganese doped lead-tellurate glasses with composition xMnO·(100-x)[4TeO2·PbO2] where x=0, 1, 5, 10, 20, 30, 40mol% have been studied. The FTIR spectra show the formation of the Mn-O-Pb and Mn-O-Te bridging bonds by increasing of MnO concentration. The UV-VIS spectra show the Mn(+3) species exhibit pronounced absorption, which masks the Mn(+2) spin-forbidden absorption bands when Mn(+2) ions are in high concentrations in these glasses. The EPR spectra exhibit resonance signals characteristic of Mn(+2) ions. The resonance signal located at g≈2 is due to Mn(+2) ions in an environment close to octahedral symmetry, whereas the resonance at g≈4.3 and 3.3 are attributed to the rhombic surroundings of the Mn(+2) ions. The increase in the MnO content gives rise to absorption at g≈2.4 and the paramagnetic ions are involved in dinuclear manganese centers. Copyright © 2011 Elsevier B.V. All rights reserved.

  4. Luminescent supramolecular soft nanostructures from amphiphilic dinuclear Re(i) complexes

    NASA Astrophysics Data System (ADS)

    Cebrián, Cristina; Natali, Mirco; Villa, Davide; Panigati, Monica; Mauro, Matteo; D'Alfonso, Giuseppe; de Cola, Luisa

    2015-07-01

    Luminescent metallo-surfactants based on highly emissive dinuclear Re(i) complexes have been synthesized combining the peculiar photophysical behaviour of this class of neutral hydrophobic complexes with new properties imparted by hydrophilic chains anchored on the coordinated chromophoric ligand. In solution, the resulting neutral amphiphiles tend to self-assembly in soft structures. The aggregation properties have been thoroughly investigated in dioxane-water mixtures, where all the complexes assembly in globular-like supramolecular architectures with well-defined size (hydrodynamic diameter = 200-400 nm). The morphology of these nano-objects has been completely characterized with Dynamic Light Scattering (DLS) analysis, Scanning Transmission Electron Microscopy (STEM) and cryo-TEM to determine the size, polydispersity, and stability of the nanoparticles in relationship with the structure of the metallo-surfactants. The photophysical properties of both the isolated metal complexes and their aggregates have been investigated by means of UV-Vis absorption, steady-state and time-resolved emission spectroscopy. Noteworthy, the self-assembly properties of the reported luminescent rhenium metallo-amphiphiles can be modulated by solvent polarity. Even more importantly, such aggregation process yielded a small hypsochromic shift of the emission energy accompanied by a sizeable elongation of the excited-state lifetime and an enhancement of the photoluminescence quantum yield, reaching a remarkably high value of 0.20 despite the air-equilibrated aqueous condition. The presented findings endorse novel possibilities for the efficient use of soft-nanostructures based on metallo-amphiphiles in dual (electron and optical microscopy) bio-imaging applications and theranostics where the non-covalent nature of the intermolecular interactions would offer the powerful and unique possibility to reversibly assemble and disassemble imaging agents.Luminescent metallo-surfactants based on

  5. A series of dinuclear lanthanide complexes with slow magnetic relaxation for Dy2 and Ho2.

    PubMed

    Zhang, Jin; Zhang, Haifeng; Chen, Yanmei; Zhang, Xiangfei; Li, Yahong; Liu, Wei; Dong, Yaping

    2016-10-18

    The employment of a new Schiff base ligand, 2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}naphthalen-1-ol (H2L), in 4f-metal chemistry has led to the formation of seven new isostructural lanthanide(iii) complexes. More specifically the 1 : 1 reaction of Ln(NO3)3·6H2O and H2L in ethanol in the presence of 3 equivalents of pyridine yielded seven dinuclear complexes of compositions [Ln2L2(NO3)2(C2H5OH)2]·0.5py (Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); py = pyridine). The structures of the isomorphous complexes 1-7 were determined by single-crystal X-ray crystallography. X-ray crystallography data reveal that each compound is neutral, and contains two doubly-deprotonated ligands, two chelated nitrates and two coordinated ethanol molecules. The two Ln(III) atoms in 1-7 are doubly bridged by the two phenolato oxygen atoms of two L(2-) ligands. Each of the two lanthanide ions is eight-coordinated and possesses distorted dodecahedron geometry. Dc magnetic susceptibility studies in the 2-300 K range reveal probably a weak antiferromagnetic interaction for 2, 3 and 6, and a ferromagnetic interaction at low temperature for 4 and 5. Complexes 4 and 5 show slow magnetic relaxation behavior. The Ueff for 4 of 66.7 K is a relatively high value among the reported Dy2 SMMs. Complex 5 is a very rare example of a Ho2 compound which exhibits slow magnetic relaxation.

  6. Phosphate ester hydrolysis and DNA binding capacity of two new dinuclear Ni(II) complexes

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Xiao, W.; Mao, J. W.; Zhou, H.; Pan, Z. Q.

    2013-03-01

    Two new dinuclear Ni(II) complexes, [Ni2L1(OAc)2]ClO4 (1) and [Ni2L2(OAc)2] Br·0.5H2O (2) (where HL is the condensation product of 2,6-diformyl-4-X-phenol (X = CH3, Br) and N1-(2-aminoethyl)-N2-(4-nitrobenzyl)ethane-1,2-diamine), were synthesized and characterized. The coordination polyhedron of each metal ion in the complexes can be approximately described as a distorted octahedron. The Ni-Ni distances in 1 and 2 are 3.306 Å and 3.369 Å, respectively. The phosphate hydrolysis promoted by the complexes was examined using 4-nitrophenyl phosphate disodium salt hexahydrate (pNPP) as the substrate. The catalytic rate constants (kcat) are 1.29 × 10-5 s-1 for 1 and 0.47 × 10-5 s-1 for 2 at 25 °C in physiological pH condition. The binding activities of the complexes toward calf thymus (CT-DNA) were analyzed by spectroscopic and voltammetric methods, and the corresponding binding constants are 7.75 × 105 and 6.51 × 104 M-1 for 1 and 8.59 × 105 and 9.18 × 104 M-1 for 2, respectively. The linear Stern-Volmer quenching constants obtained in the fluorescent spectroscopic study of 1 and 2 are 0.7 × 103 and 1.5 × 103 M-1, respectively.

  7. Dinuclear zinc(II) complexes with hydrogen bond donors as structural and functional phosphatase models.

    PubMed

    Bosch, Simone; Comba, Peter; Gahan, Lawrence R; Schenk, Gerhard

    2014-09-02

    It is becoming increasingly apparent that the secondary coordination sphere can have a crucial role in determining the functional properties of biomimetic metal complexes. We have therefore designed and prepared a variety of ligands as metallo-hydrolase mimics, where hydrogen bonding in the second coordination sphere is able to influence the structure of the primary coordination sphere and the substrate binding. The assessment of a structure-function relationship is based on derivates of 2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol (HBPMP = HL(1)) and 2-{[bis(pyridin-2-ylmethyl)amino]methyl}-6-{[(2-hydroxybenzyl)(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol (H2BPBPMP = H2L(5)), well-known phenolate-based ligands for metallo-hydrolase mimics. The model systems provide similar primary coordination spheres but site-specific modifications in the secondary coordination sphere. Pivaloylamide and amine moieties were chosen to mimic the secondary coordination sphere of the phosphatase models, and the four new ligands H3L(2), H3L(3), HL(4), and H4L(6) vary in the type and geometric position of the H-bond donors and acceptors, responsible for the positioning of the substrate and release of the product molecules. Five dinuclear Zn(II) complexes were prepared and structurally characterized in the solid, and four also in solution. The investigation of the phosphatase activity of four model complexes illustrates the impact of the H-bonding network: the Michaelis-Menten constants (catalyst-substrate binding) for all complexes that support hydrogen bonding are smaller than for the reference complex, and this generally leads to higher catalytic efficiency and higher turnover numbers.

  8. Recognition of phosphopeptides by a dinuclear copper(ii) macrocyclic complex in a water : methanol 50 : 50 v/v solution.

    PubMed

    Mesquita, Lígia M; Mateus, Pedro; Fernandes, Rui D V; Iranzo, Olga; André, Vânia; Tiago de Oliveira, Filipe; Platas-Iglesias, Carlos; Delgado, Rita

    2017-07-25

    A new triethylbenzene-derived tetraazamacrocycle containing pyridyl spacers, L, was prepared and its dinuclear copper(ii) complex was used as a receptor for the recognition of phosphorylated peptides in aqueous solution. A detailed study of the acid-base behaviour of L and its copper(ii) complexation properties as well as of the cascade species with phosphorylated anions including two peptidic substrates was carried out in a H2O/MeOH (50 : 50 v/v) solution using different techniques, such as potentiometry, X-band EPR and DFT calculations. The association constants of the dinuclear receptor with the phosphorylated peptides and other anionic species revealed a clear preference towards phenylic phosphorylated substrates, with values ranging 3.96-5.35 log units. Single-crystal X-ray diffraction determination of the dicopper(ii) complex of L showed the copper centres at a distance of 5.812(1) Å from one another, with the phosphate group of the PhPO4(2-) substrate well accommodated between them. X-band EPR studies indicated a similar structure for this cascade complex and for the other cascade complexes with the phosphorylated anions studied. DFT studies of the [Cu2L(μ-OH)](3+) complex revealed a different conformation of the ligand that brings the two copper centres at a very short distance of 3.94 Å aided by the presence of a bridging hydroxide anion that provides a CuOCu angle of 167.3°. This complex is EPR silent, in line with the singlet ground state obtained using CASSCF(2,2) calculations and DFT calculations with the broken-symmetry approach. This species coexists in solution with a complex in a different conformation, and having a CuCu distance of 6.63 Å, in lower percentage.

  9. Crystal structures of a novel NNN pincer ligand and its dinuclear titanium(IV) alkoxide pincer complex.

    PubMed

    Pedziwiatr, Jakub; Ghiviriga, Ion; Abboud, Khalil A; Veige, Adam S

    2017-02-01

    This report describes a synthetic protocols and the crystal structures involving a novel pincer-type H3[NNN] ligand, namely di-μ-bromido-μ-{2-(2,2-di-methylpropanimido-yl)-N-[2-(2,2-di-methyl-propanimido-yl)-4-methyl-phen-yl]-4-methylaniline}-bis-[(diethyl ether)lithium], [Li2Br2(C24H33N3)(C4H10O)2] (1) and a dinuclear metal complex, namely di-μ-bromido-2:3κ(4)Br:Br-bis-{2-(2,2-di-methylpropanimido-yl)-N-[2-(2,2-di-methyl-propanimido-yl)-4-methyl-phen-yl]-4-methylaniline}-1κ(3)N,N',N'';4κ(3)N,N',N''-tetra-μ-iso-propano-lato-1:2κ(4)O:O;3:4κ(4)O:O-diiso-propano-lato-1κO,4κO-2,3-dilithium-1,4-dititanium, [Li2Ti2Br2(C24H32N3)2(C3H7O)6] or {[NHNNH]Ti(O (i) Pr)3(LiBr)2}2 (2). Complex 1, which sits on a twofold rotation axis, is a rare example of a pincer-type ligand which bears ketimine side arms. A unique feature of complex 1 is that the ketimine N atoms have an LiBr(Et2O) fragment bonded to them, with the Li atom adopting a distorted tetra-hedral geometry. This particular fragment creates an LiBr bridge between the two ketimine sidearms, which leads to a cage-type appearance of the ligand. Complex 2 consists of the previously described ligand and a Ti(IV) metal atom in an octa-hedral environment, and is located on an inversion center. Complex 2 crystallizes as a dinuclear species with the metal atoms being bridged by an LiBr entity [the Br atoms are disordered and refined in two positions with their site occupation factors refining to 0.674 (12)/0.372 (12)], and the Li cation being bonded to the isopropoxide O atoms (Li having a tetra-hedral coordination as in 1). The organic ligand of compound 2 exhibits disorder in its periphery groups; isopropyl and tert-butyl groups (occupation factors fixed at 0.6/0.4). The novel [NNN]H3 pincer-type ligand was characterized by multinuclear and multidimensional NMR, HRMS and X-ray crystallography. The dinuclear metal complex 2 was characterized by X-ray crystallography. Although each structure exhibits donor N

  10. Crystal structures of a novel NNN pincer ligand and its dinuclear titanium(IV) alkoxide pincer complex

    PubMed Central

    Pedziwiatr, Jakub; Ghiviriga, Ion; Veige, Adam S.

    2017-01-01

    This report describes a synthetic protocols and the crystal structures involving a novel pincer-type H3[NNN] ligand, namely di-μ-bromido-μ-{2-(2,2-di­methylpropanimido­yl)-N-[2-(2,2-di­methyl­propanimido­yl)-4-methyl­phen­yl]-4-methylaniline}-bis­[(diethyl ether)lithium], [Li2Br2(C24H33N3)(C4H10O)2] (1) and a dinuclear metal complex, namely di-μ-bromido-2:3κ4 Br:Br-bis­{2-(2,2-di­methylpropanimido­yl)-N-[2-(2,2-di­methyl­propanimido­yl)-4-methyl­phen­yl]-4-methylaniline}-1κ3 N,N′,N′′;4κ3 N,N′,N′′-tetra-μ-iso­propano­lato-1:2κ4 O:O;3:4κ4 O:O-diiso­propano­lato-1κO,4κO-2,3-dilithium-1,4-dititanium, [Li2Ti2Br2(C24H32N3)2(C3H7O)6] or {[NHNNH]Ti(OiPr)3(LiBr)2}2 (2). Complex 1, which sits on a twofold rotation axis, is a rare example of a pincer-type ligand which bears ketimine side arms. A unique feature of complex 1 is that the ketimine N atoms have an LiBr(Et2O) fragment bonded to them, with the Li atom adopting a distorted tetra­hedral geometry. This particular fragment creates an LiBr bridge between the two ketimine sidearms, which leads to a cage-type appearance of the ligand. Complex 2 consists of the previously described ligand and a TiIV metal atom in an octa­hedral environment, and is located on an inversion center. Complex 2 crystallizes as a dinuclear species with the metal atoms being bridged by an LiBr entity [the Br atoms are disordered and refined in two positions with their site occupation factors refining to 0.674 (12)/0.372 (12)], and the Li cation being bonded to the isopropoxide O atoms (Li having a tetra­hedral coordination as in 1). The organic ligand of compound 2 exhibits disorder in its periphery groups; isopropyl and tert-butyl groups (occupation factors fixed at 0.6/0.4). The novel [NNN]H3 pincer-type ligand was characterized by multinuclear and multidimensional NMR, HRMS and X-ray crystallography. The dinuclear metal complex 2 was characterized by X-ray crystallography. Although each structure

  11. Dinuclear cadmium(II), zinc(II), and manganese(II), trinuclear nickel(II), and pentanuclear copper(II) complexes with novel macrocyclic and acyclic Schiff-base ligands having enantiopure or racemic camphoric diamine components.

    PubMed

    Jiang, Jue-Chao; Chu, Zhao-Lian; Huang, Wei; Wang, Gang; You, Xiao-Zeng

    2010-07-05

    Four novel [3 + 3] Schiff-base macrocyclic ligands I-IV condensed from 2,6-diformyl-4-substituted phenols (R = CH(3) or Cl) and enantiopure or racemic camphoric diamines have been synthesized and characterized. Metal-ion complexations of these enantiopure and racemic [3 + 3] macrocyclic ligands with different cadmium(II), zinc(II), manganese(II), nickel(II), and copper(II) salts lead to the cleavage of Schiff-base C horizontal lineN double bonds and subsequent ring contraction of the macrocyclic ligands due to the size effects and the spatial restrictions of the coordination geometry of the central metals, the steric hindrance of ligands, and the counterions used. As a result, five [2 + 2] and one [1 + 2] dinuclear cadmium(II) complexes (1-6), two [2 + 2] dinuclear zinc(II) (7 and 8), and two [2 + 2] dinuclear manganese(II) (9 and 10) complexes together with one [1 + 1] trinuclear nickel(II) complex (11) and one [1 + 2] pentanuclear copper(II) complex (12), bearing enantiopure or racemic ligands, different substituent groups in the phenyl rings, and different anionic ligands (Cl(-), Br(-), OAc(-), and SCN(-)), have been obtained in which the chiral carbon atoms in the camphoric backbones are arranged in different ways (RRSS for the enantiopure ligands in 1, 2, 4, 5, and 7-10 and RSRS for the racemic ligands in 3, 6, 11, and 12). The steric hindrance effects of the methyl group bonded to one of the chiral carbon atoms of camphoric diamine units are believed to play important roles in the formation of the acyclic [1 + 1] trinuclear complex 11 and [1 + 2] dinuclear and pentanuclear complexes 6 and 12. In dinuclear cadmium(II), zinc(II), and manganese(II) complexes 1-10, the sequence of separations between the metal centers is consistent with that of the ionic radii shortened from cadmium(II) to manganese(II) to zinc(II) ions. Furthermore, UV-vis, circular dichroism, (1)H NMR, and fluorescence spectra have been used to characterize and compare the structural

  12. A dinuclear Ni(II) complex with two types of intramolecular magnetic couplings: Ni(II)-Ni(II) and Ni(II)-TTF*+.

    PubMed

    Liu, Shi-Xia; Ambrus, Christina; Dolder, Stefan; Neels, Antonia; Decurtins, Silvio

    2006-11-27

    A dinuclear Ni(II) complex involving tetrathiafulvalene (TTF) radicals as ligands has been prepared and characterized, [Ni2(mu-Cl)2(L*+)2(I3)4(I2)3.(H2O)2.(C4H8O)3 (1), L = 4,5-bis(2-pyridylmethylsulfanyl)-4',5'-ethylenedithiotetrathiafulvalene. There are two types of intramolecular magnetic exchange interactions, namely one ferromagnetic Ni(II)-Ni(II) and one antiferromagnetic Ni(II)-TTF*+. This study is new in the respect of revealing a magnetic exchange interaction between a TTF*+ radical and a paramagnetic transition metal ion. This is due to the fact of a direct binding of the transition metal ion to the skeleton of the TTF*+ radical.

  13. Structure and properties of Dinuclear [RuII([n]aneS4)] complexes of 3,6-Bis(2-pyridyl)-1,2,4,5-tetrazine.

    PubMed

    Newell, Mike; Ingram, James D; Easun, Timothy L; Vickers, Steven J; Adams, Harry; Ward, Michael D; Thomas, Jim A

    2006-01-23

    The synthesis of dinuclear [Ru(II)([n]aneS(4))] (where n = 12, 14) complexes of the bridging ligand 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine are reported. The X-ray structures of both of the new complexes are compared to a newly obtained structure for a dinuclear [Ru(II)([9]aneS(3))]-based analogue, whose synthesis has previously been reported. A comparison of the electrochemistry of the three complexes reveals that the first oxidation of the [Ru(II)([n]aneS(4))]-based systems is a ligand-based couple, indicating that the formation of the radical anion form of the bridging ligand is stabilized by metal center coordination. Spectroelectrochemistry studies on the mixed-valence form of the new complexes suggest that they are Robin and Day Class II systems. The electrochemical and electronic properties of these complexes is rationalized by a consideration of the pi-bonding properties of thiacrown ligands.

  14. Enzyme-like catalysis via ternary complex mechanism: alkoxy-bridged dinuclear cobalt complex mediates chemoselective O-esterification over N-amidation.

    PubMed

    Hayashi, Yukiko; Santoro, Stefano; Azuma, Yuki; Himo, Fahmi; Ohshima, Takashi; Mashima, Kazushi

    2013-04-24

    Hydroxy group-selective acylation in the presence of more nucleophilic amines was achieved using acetates of first-row late transition metals, such as Mn, Fe, Co, Cu, and Zn. Among them, cobalt(II) acetate was the best catalyst in terms of reactivity and selectivity. The combination of an octanuclear cobalt carboxylate cluster [Co4(OCOR)6O]2 (2a: R = CF3, 2b: R = CH3, 2c: R = (t)Bu) with nitrogen-containing ligands, such as 2,2'-bipyridine, provided an efficient catalytic system for transesterification, in which an alkoxide-bridged dinuclear complex, Co2(OCO(t)Bu)2(bpy)2(μ2-OCH2-C6H4-4-CH3)2 (10), was successfully isolated as a key intermediate. Kinetic studies and density functional theory calculations revealed Michaelis-Menten behavior of the complex 10 through an ordered ternary complex mechanism similar to dinuclear metallo-enzymes, suggesting the formation of alkoxides followed by coordination of the ester.

  15. Rigid rod-like dinuclear Ru(II)/Os(II) terpyridine-type complexes. Electrochemical behavior, absorption spectra, luminescence properties, and electronic energy transfer through phenylene bridges

    SciTech Connect

    Barigelletti, F.; Flamigni, L.; Balzani, V. ||

    1994-08-24

    The absorption spectra, the luminescence properties (at 293 and 77 K), and the electrochemical behavior of six dinuclear heterometallic compounds have been investigated. The compounds are made of Ru(tpy){sub 2}{sup 2+}- and Os(tpy){sub 2}{sup 2+}-type components (tpy = 2,2{prime}:6{prime},2 inches-terpyridine, which in some cases carries p-tolyl (Meph) or methylsulphone (MeO{sub 2}S) substituents in the 4{prime} position), connected by n phenylene (ph) spacers (n=0,1, and 2). In the resulting rigid rod-like structures of general formula (X{sub 1}tpy)Ru(tpy(ph){sub n}tpy)Os(tpyX{sub 2}){sup 4+} the metal-to-metal distance varies form 11 to 20 {Angstrom}. The absorption spectra of the two components are slightly perturbed in the dinuclear compounds, and metal-metal and ligand-ligand interactions are evidenced by the trends of the oxidation and reduction potentials. The luminescence of the Ru-based unit is quenched by the connected Os-based unit with practically unitary efficiency, regardless of the number of interposed phenylene spacers. Quenching is accompanied by quantitative sensitization of the Os-based luminescence. The rate of energy transfer at 293 K is larger than 10{sup 10} s{sup -1} in all cases. The Foerster (Coulombic) mechanism does not satisfactorily account for such a fast rate, particularly for the species with n=2. It is concluded that the observed energy-transfer processes take place most likely via a Dexter (electron exchange) mechanism. This is consistent with the strong electronic coupling of the Ru-based units in the compound with n=0, and with the relatively small insulating effect expected for the phenylene spacers. 37 refs., 7 figs., 3 tabs.

  16. Structural Investigation of Dinuclear Clusters Incorporated in Polyoxotungstates

    NASA Astrophysics Data System (ADS)

    Nagy, C.; Rusu, D.; Somesan, C.; Filip, S.; Rusu, M.; David, L.

    2011-10-01

    The new K10[M2Bi2W20O70]ṡH2O (M = Mn(II), Co(II), Ni(II), Cu(II)) sandwich-type complex have been investigated by spectroscopic (FT-IR, UV-VIS, ESR) methods. The main goal was to obtain information about the metal ions coordination to the trilacunary regions of Keggin polioxoanion ligands, the local symmetry around the metal ions and the presence of possible metal-metal couplings.

  17. Phthalocyanine supported dinuclear Ln(III) complexes: the solvent-induced change of magnetic properties in dysprosium(iii) analogues.

    PubMed

    Ge, Jing-Yuan; Wang, Hai-Ying; Li, Jing; Xie, Jia-Ze; Song, You; Zuo, Jing-Lin

    2017-02-24

    Three dinuclear lanthanide complexes, [Ln2(thd)4Pc]·2C6H6 (Hthd = 2,2,6,6-tetramethylheptanedione, Ln = Sm (1), Tb (2), Dy (3)), have been synthesized based on phthalocyanine (Pc). They can be reversibly transformed into [Ln2(thd)4Pc] (Ln = Sm (1'), Tb (2'), Dy (3')) via desolvation and resolvation of the lattice benzene molecules. This change generates dramatic influences on the structural and magnetic properties of the dysprosium analogue. In complex 3, one crystallographically independent metal center is observed, and it exhibits a single relaxation process of magnetization with an energy barrier of 55.7 K. Upon desolvation, the resulting complex 3' contains two types of metal centers, and shows the field-induced single-molecule magnetic behavior with two thermally activated magnetic relaxation processes. The anisotropy barriers for 3' are as high as 63.3 K and 109.6 K, respectively. This work confirms that the solvated molecules can finely tune the magnetic relaxation mechanisms.

  18. Hydrogen peroxide and dioxygen activation by dinuclear copper complexes in aqueous solution: hydroxyl radical production initiated by internal electron transfer.

    PubMed

    Zhu, Qing; Lian, Yuxiang; Thyagarajan, Sunita; Rokita, Steven E; Karlin, Kenneth D; Blough, Neil V

    2008-05-21

    Dinuclear Cu(II) complexes, CuII2Nn (n = 4 or 5), were recently found to specifically cleave DNA in the presence of a reducing thiol and O2 or in the presence of H2O2 alone. However, CuII2N3 and a closely related mononuclear Cu(II) complex exhibited no selective reaction under either condition. Spectroscopic studies indicate an intermediate is generated from CuII2Nn (n = 4 or 5) and mononuclear Cu(II) solutions in the presence of H2O2 or from CuI2Nn (n = 4 or 5) in the presence of O2. This intermediate decays to generate OH radicals and ligand degradation products at room temperature. The lack of reactivity of the intermediate with a series of added electron donors suggests the intermediate discharges through a rate-limiting intramolecular electron transfer from the ligand to the metal peroxo center to produce an OH radical and a ligand-based radical. These results imply that DNA cleavage does not result from direct reaction with a metal-peroxo intermediate but instead arises from reaction with either OH radicals or ligand-based radicals.

  19. Self-assembly and photophysical properties of lanthanide dinuclear triple-helical complexes

    SciTech Connect

    Piguet, C.; Bernardinelli, G.; Williams, A.F. ); Buenzli, J.C.G. ); Hopfgartner, G. )

    1993-09-08

    The dinucleating ligand bis[1-methyl-2-(6[prime]-[1[double prime]-(3,5-dimethoxybenzyl)benzimidazol-2[double prime]-yl]pyrid-2[prime]-yl)benzimidazol-5-yl]methane (L) reacts with lanthanide perchlorates to give dinuclear 2:3 complexes [Ln[sub 2](L)[sub 3

  20. A neutral dinuclear Ir(iii) complex for anti-counterfeiting and data encryption.

    PubMed

    Jiang, Yang; Li, Guangfu; Che, Weilong; Liu, Yingjie; Xu, Bin; Shan, Guogang; Zhu, Dongxia; Su, Zhongmin; Bryce, Martin R

    2017-03-09

    A neutral dinuclear Ir(iii) Schiff base complex PIBIP has been synthesized and shown to exhibit both piezochromic luminescence (PCL) and aggregation induced emission (AIE) behaviour. An efficient second-level anti-counterfeit trademark and a data encryption device were fabricated using PIBIP as the active material.

  1. Interpretation of the mechanism of spontaneous fission of heavy nuclei in the framework of dinuclear system conception

    NASA Astrophysics Data System (ADS)

    Volkov, V. V.; Cherepanov, E. A.; Kalandarov, Sh. A.

    2016-11-01

    The new approach to the interpretation of the process of spontaneous fission of heavy nuclei is suggested. It is based on nuclear physics data which are obtained in heavy ion collisions. The process of spontaneous fission consists of three sequential stages: clusterization of the valent nucleons of a heavy nucleus into a light nucleus-cluster, which leads to the formation of a dinuclear system; evolution of the dinuclear system which proceeds by nucleon transfer from the heavy to light nucleus and decay of the dinuclear system from the equilibrium configuration into two fragments.

  2. Non-radiative recombination centres in catalyst-free ZnO nanorods grown by atmospheric-metal organic chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Montenegro, D. N.; Hortelano, V.; Martínez, O.; Martínez-Tomas, M. C.; Sallet, V.; Muñoz-Sanjosé, V.; Jiménez, J.

    2013-06-01

    We have investigated the cathodoluminescence (CL) emission and the Raman spectra along individual ZnO nanorods grown by a catalyst-free method. The spatial correlation between the CL emission and the defect related Raman modes permits establishing a correspondence between the non-radiative recombination centres (NRRCs) and the defects responsible for the 275 cm-1 Raman band. According to this relation, the NRRCs in these nanorods are tentatively associated with complexes of zinc interstitials.

  3. Asymmetric hydrogenation of quinazolinium salts catalysed by halide-bridged dinuclear iridium complexes bearing chiral diphosphine ligands.

    PubMed

    Kita, Yusuke; Higashida, Kosuke; Yamaji, Kenta; Iimuro, Atsuhiro; Mashima, Kazushi

    2015-03-14

    Asymmetric hydrogenation of quinazolinium salts was catalysed by halogen-bridged dinuclear iridium complexes bearing chiral diphosphine ligands, yielding tetrahydroquinazoline and 3,4-dihydroquinazoline with high enantioselectivity. A derivative of chiral dihydroquinazoline was used as a chiral NHC ligand.

  4. Dinuclear osmium(II) probes for high-resolution visualisation of cellular DNA structure using electron microscopy.

    PubMed

    Wragg, Ashley; Gill, Martin R; Hill, Christopher J; Su, Xiaodi; Meijer, Anthony J H M; Smythe, Carl; Thomas, Jim A

    2014-12-04

    Two dinuclear osmium polypyridyl complexes function as convenient, easy to handle TEM contrast agents and facilitate the high-resolution visualisation of intracellular structure, particularly sub-nuclear detail.

  5. Mono- and dinuclear manganese(III) complexes showing efficient catechol oxidase activity: syntheses, characterization and spectroscopic studies.

    PubMed

    Banu, Kazi Sabnam; Chattopadhyay, Tanmay; Banerjee, Arpita; Mukherjee, Madhuparna; Bhattacharya, Santanu; Patra, Goutam Kumar; Zangrando, Ennio; Das, Debasis

    2009-10-28

    Four side-off compartmental ligands L1-L4 [L1 = N,N'-ethylenebis(3-formyl-5-methyl-salicylaldimine), L2 = N,N'-1-methylethylenebis(3-formyl-5-methylsalicylaldimine), L3 = N,N'-1,1-dimethylethylenebis(3-formyl-5-methylsalicylaldimine) and L4= N,N'-cyclohexenebis(3-formyl-5-methylsalicylaldimine)] having two binding sites, N2O2 and O4, have been chosen to synthesize mononuclear and dinuclear manganese(III) complexes with the aim to study their catecholase activity using 3,5-di-tert-butylcatechol (3,5-DTBC) as substrate in the presence of molecular oxygen. In all cases only mononuclear manganese complexes (1-4) were obtained, with manganese coordination taking place at the N2O2 binding site only, irrespective of the amount of manganese salt used. All these complexes have been characterized by routine physico-chemical techniques. Complex MnL2Cl.4H2O (2) has further been structurally characterized by X-ray single crystal structure analysis. Four dinuclear manganese complexes, 5-8, were obtained after condensing the two pending formyl groups on each ligand (L1-L4) with aniline followed by reaction with MnCl2 to put the second Mn atom onto another N2O2 site. The catalytic activity of all complexes 1-8 has been investigated following the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) with molecular oxygen in two different solvents, methanol and acetonitrile. The study reveals that the catalytic activity is influenced by the solvent and to a significant extent by the backbone of the diamine and the behavior seems to be related mainly to steric rather than electronic factors. Experimental data suggest that a correlation, the lower the E(1/2) value the higher the catalytic activity, can be drawn between E(1/2) and Vmax of the complexes in a particular solvent. The EPR measurements suggest that the catalytic property of the complexes is related to the metal center(s) participation rather than to a radical mechanism.

  6. Asymmetric mono- and dinuclear Ga(III) and Zn(II) complexes as models for purple acid phosphatases.

    PubMed

    Bosch, Simone; Comba, Peter; Gahan, Lawrence R; Schenk, Gerhard

    2016-09-01

    Derivatives of the known dinucleating ligands HL(1) (2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol) and H2L(2) (2-{[bis(pyridin-2-ylmethyl)amino]methyl}-6-{[(2-hydroxybenzyl)(pyridine-2-ylmethyl)amino]methyl}-4-methylphenol) with two pivaloylamido hydrogen bond donor substituents, H3L(3) and H3L(5), have been prepared. The mono-, homo- and heterodinuclear Zn(II) and Ga(III) complexes of these ligands have been prepared and characterized. The solution equilibria are discussed on the basis of extensive NMR spectroscopic, mass spectrometric and pH-dependent UV-vis spectroscopic titrations. The phosphoester hydrolysis activity of the complexes has been studied as a function of pH and substrate concentration and analyzed using Michaelis-Menten kinetics. It emerges that the mixed metal (mixed valent) complex of the ligand with an asymmetric disposition of the hydrogen bonding substituents (H3L(3)) is a functional model for the mixed valent, dinuclear metallohydrolase purple acid phosphatase. This complex combines the essential structural features of the active site of PAP and is the first heterodinuclear model complex mimicking the essential function of PAPs, i.e. the hydrolysis of phosphomonoesters. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. Discrete and Polymeric, Mono- and Dinuclear Silver Complexes of a Macrocyclic Tetraoxime Ligand with AgI–AgI Interactions

    PubMed Central

    Tashiro, Shohei; Tanihira, Jun-ichiro; Yamada, Mihoko; Shionoya, Mitsuhiko

    2013-01-01

    Macrocyclic compounds that can bind cationic species efficiently and selectively with their cyclic cavities have great potential as excellent chemosensors for metal ions. Recently, we have developed a tetraoxime-type tetraazamacrocyclic ligand 1 formed through a facile one-pot cyclization reaction. Aiming to explore and bring out the potential of the tetraoxime macrocycle 1 as a chelating sensor, we report herein the preparation of several kinds of silver complexes of 1 and their unique coordination structures determined by single-crystal X-ray diffraction analyses. As a result, the formation of two kinds of discrete structures, monomeric complexes [Ag(1)X] (X = counter anions) and a dimeric complex [Ag2(1)2]X2, and two kinds of polymeric structures from a mononuclear complex, [Ag(1)]nXn, and from a dinuclear complex, [Ag2(1)X2]n, was demonstrated. In the resulting complexes, the structurally flexible macrocyclic ligand 1 was found to provide several different coordination modes. Notably, in some silver complexes of 1, AgI–AgI interactions were observed with different AgI–AgI distances which depend on the kind of counter anions and the chemical composition. PMID:23645105

  8. Dinuclear Zn(II) and mixed Cu(II)-Zn(II) complexes of artificial patellamides as phosphatase models.

    PubMed

    Comba, Peter; Eisenschmidt, Annika; Gahan, Lawrence R; Hanson, Graeme R; Mehrkens, Nina; Westphal, Michael

    2016-12-21

    The patellamides (cyclic pseudo-octapeptides) are produced by Prochloron, a symbiont of the ascidians, marine invertebrate filter feeders. These pseudo-octapeptides are present in the cytoplasm and a possible natural function of putative metal complexes of these compounds is hydrolase activity, however the true biological role is still unknown. The dinuclear Cu(II) complexes of synthetic patellamide derivatives have been shown in in vitro experiments to be efficient hydrolase model catalysts. Many hydrolase enzymes, specifically phosphatases and carboanhydrases, are Zn(II)-based enzymes and therefore, we have studied the Zn(II) and mixed Zn(II)/Cu(II) solution chemistry of a series of synthetic patellamide derivatives, including solution structural and computational work, with the special focus on model phosphatase chemistry with bis-(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. The Zn(II) complexes of a series of ligands are shown to form complexes of similar structure and stability compared to the well-studied Cu(II) analogues and the phosphatase reactivities are also similar. Since the complex stabilities and phosphatase activities are generally a little lower compared to those of Cu(II) and since the concentration of Zn(II) in Prochloron cells is slightly smaller, we conclude that the Cu(II) complexes of the patellamides are more likely to be of biological importance.

  9. Self-assembly of dinuclear Pd(ii)/Pt(ii) metallacyclic receptors incorporating N-heterocyclic carbene complexes as corners.

    PubMed

    Marcos, Ismael; Domarco, Olaya; Peinador, Carlos; Fenández, Alberto; Fernández, Jesús J; Vázquez-García, Digna; García, Marcos D

    2017-03-07

    We report herein the self-assembly of a series of new square and rectangular-shaped dinuclear M2L2 metallacycles (M = Pd(ii)/Pt(ii)), receptors self-assembled in water from four different N-monoalkyl-4,4'-bipyridinium derivatives as ligands and square-planar Pd(ii) and Pt(ii) metal centers having the chelating N-heterocyclic carbene 1,1'-di(methyl)-3,3'-methylene-4-diimidazolin-2,2'-diylidene. The concentration-dependent Pd2L2 metallacycles were successfully obtained and characterized by means of NMR experiments in aqueous media. Due to the strong trans effect exerted by the carbene ligands, the synthesis of the Pt2L2 receptors was achieved as well by self-assembly of the components at room temperature in a few hours, in clear contraposition to the harsh reaction conditions usually required for the labilization of other kinetically inert Pt(ii)-N(pyridine) bonds. X-ray diffraction studies of suitable single crystals of two of the obtained receptors offered additional information on the structure of the obtained supramolecules, whose ability as receptors has been explored by the preparation and study of the corresponding inclusion complexes in water with 1,5-dihydroxynaphthalene as the model substrate.

  10. Photo-oxidation of tyrosine in a bio-engineered bacterioferritin 'reaction centre'-a protein model for artificial photosynthesis.

    PubMed

    Hingorani, Kastoori; Pace, Ron; Whitney, Spencer; Murray, James W; Smith, Paul; Cheah, Mun Hon; Wydrzynski, Tom; Hillier, Warwick

    2014-10-01

    The photosynthetic reaction centre (RC) is central to the conversion of solar energy into chemical energy and is a model for bio-mimetic engineering approaches to this end. We describe bio-engineering of a Photosystem II (PSII) RC inspired peptide model, building on our earlier studies. A non-photosynthetic haem containing bacterioferritin (BFR) from Escherichia coli that expresses as a homodimer was used as a protein scaffold, incorporating redox-active cofactors mimicking those of PSII. Desirable properties include: a di-nuclear metal binding site which provides ligands for bivalent metals, a hydrophobic pocket at the dimer interface which can bind a photosensitive porphyrin and presence of tyrosine residues proximal to the bound cofactors, which can be utilised as efficient electron-tunnelling intermediates. Light-induced electron transfer from proximal tyrosine residues to the photo-oxidised ZnCe6(•+), in the modified BFR reconstituted with both ZnCe6 and Mn(II), is presented. Three site-specific tyrosine variants (Y25F, Y58F and Y45F) were made to localise the redox-active tyrosine in the engineered system. The results indicate that: presence of bound Mn(II) is necessary to observe tyrosine oxidation in all BFR variants; Y45 the most important tyrosine as an immediate electron donor to the oxidised ZnCe6(•+) and that Y25 and Y58 are both redox-active in this system, but appear to function interchangebaly. High-resolution (2.1Å) crystal structures of the tyrosine variants show that there are no mutation-induced effects on the overall 3-D structure of the protein. Small effects are observed in the Y45F variant. Here, the BFR-RC represents a protein model for artificial photosynthesis. Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.

  11. Poster — Thur Eve — 11: Validation of the orthopedic metallic artifact reduction tool for CT simulations at the Ottawa Hospital Cancer Centre

    SciTech Connect

    Sutherland, J; Foottit, C

    2014-08-15

    Metallic implants in patients can produce image artifacts in kilovoltage CT simulation images which can introduce noise and inaccuracies in CT number, affecting anatomical segmentation and dose distributions. The commercial orthopedic metal artifact reduction algorithm (O-MAR) (Philips Healthcare System) was recently made available on CT simulation scanners at our institution. This study validated the clinical use of O-MAR by investigating its effects on CT number and dose distributions. O-MAR corrected and uncorrected images were acquired with a Philips Brilliance Big Bore CT simulator of a cylindrical solid water phantom that contained various plugs (including metal) of known density. CT number accuracy was investigated by determining the mean and standard deviation in regions of interest (ROI) within each plug for uncorrected and O-MAR corrected images and comparing with no-metal image values. Dose distributions were calculated using the Monaco treatment planning system. Seven open fields were equally spaced about the phantom around a ROI near the center of the phantom. These were compared to a “correct” dose distribution calculated by overriding electron densities a no-metal phantom image to produce an image containing metal but no artifacts. An overall improvement in CT number and dose distribution accuracy was achieved by applying the O-MAR correction. Mean CT numbers and standard deviations were found to be generally improved. Exceptions included lung equivalent media, which is consistent with vendor specified contraindications. Dose profiles were found to vary by ±4% between uncorrected or O-MAR corrected images with O-MAR producing doses closer to ground truth.

  12. Dinuclear Calcium Complexes with Intramolecularly NH.O Hydrogen-Bonded Dicarboxylate Ligands.

    PubMed

    Ueyama, Norikazu; Takeda, Jiro; Yamada, Yusuke; Onoda, Akira; Okamura Ta, Taka-aki; Nakamura, Akira

    1999-02-08

    A novel dinuclear calcium complex, [Ca(2){(2-OCO-3-CH(3)C(6)H(3)NHCO)(2)C(CH(3))(2)}(2)(CH(3)OH)(6)] (1), was synthesized as a structural model of 8-coordinated Ca(II) ions in the double calcium-binding site of thermolysin. The complex has four NH.O hydrogen bonds between the amide NH and the carboxylate oxygen anion. Two types of bridging coordination of the carboxylate ligand to Ca(II) were found in 1. The amide NH forms a strong NH.O hydrogen bond with the anionic oxygen of the two carboxylate oxygens. A ligand-exchange reaction between the dinuclear calcium complex and eight equimolar amounts of 2,4,6-trimethylbenzoic acid or 2-CH(3)-6-t-BuCONHC(6)H(3)COOH indicates that the NH.O hydrogen bond prevents the dissociation of the Ca-O bond.

  13. “Size-selectivity” in the template-directed assembly of dinuclear triple-stranded helicates

    PubMed Central

    Albrecht, Markus; Blau, Oliver; Fröhlich, Roland

    2002-01-01

    The self-assembly of supramolecular structures depends on a subtle interplay of a series of different control mechanisms. The geometric as well as electronic complementarity of the molecular building blocks is crucial for the specific formation of defined supramolecular species. In addition, secondary effects, like templating, also have an important function. The templating ability of different cations in the formation of triple-stranded helicate-type complexes from alkyl-bridged di(8-hydroxyquinoline) ligands is investigated by introduction of alkyl chains of different length as ligand spacers. Hereby a “size-selectivity” between the cations and the dinuclear helicate-type complexes {(ligand)3M2} is observed. Large cations support the formation of big dinuclear complexes, whereas small cations are able to template the formation of small complexes. PMID:11959938

  14. Determination of electronic ground state properties of a dinuclear iron(II) spin crossover complex

    NASA Astrophysics Data System (ADS)

    Bauer, T. O.; Schmitz, M.; Graf, M.; Kelm, H.; Krüger, H.-J.; Schünemann, V.

    2016-12-01

    The dinuclear complex [(Fe(L-N4Me2))2(BiBzIm)](ClO4)2ṡ2EtCN (1) has been investigated by Mössbauer spectroscopy carried out in the temperature range from 5 to 150 K with externally applied magnetic fields of up to B = 5 T. By means of a consistent simulation of all experimental data sets within the Spin Hamiltonian formalism, the zero-field splitting D and the rhombicity parameter E/ D of the ferrous high-spin (HS) site in this complex was determined to be D = -15.0 ± 1.0 cm-1 and E/ D = 0.33 respectively. The sign of the quadrupole splitting of the HS site is positive which indicates that this iron site of the dinuclear complex 1 has an electronic ground state with the dxy orbital being twofold occupied.

  15. Single-molecule magnet behaviour in a tetrathiafulvalene-based electroactive antiferromagnetically coupled dinuclear dysprosium(III) complex.

    PubMed

    Pointillart, Fabrice; Le Gal, Yann; Golhen, Stéphane; Cador, Olivier; Ouahab, Lahcène

    2011-09-05

    The reactions between the [Ln(tta)(3)]·2H(2)O precursors (tta(-)=2-thenoyltrifluoroacetonate anion) and the tetrathiafulvalene-3-pyridine-N-oxide ligands (L(1)) lead to dinuclear complexes of formula [{Ln(tta)(3)(L(1))}(2)]·xCH(2)Cl(2) (x=0.5 for Ln=Dy(III) (1) and x=0 for Ln=Gd(III) (2)). The crystal structure reveals that two {Ln(tta)(3)} moieties are bridged by two donors through the nitroxide groups. The Dy(III) centre adopts a distorted square antiprismatic oxygenated polyhedron structure. The antiferromagnetic nature of the exchange interaction between the two Dy(III) ions has been determined by two methods: 1) an empirical method using the [Dy(hfac)(3)(L(2))(2)] mononuclear complex as a model (3) (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion, L(2)=tetrathiafulvaleneamido-2-pyridine-N-oxide ligand), and 2) assuming an Ising model for the Dy(III) ion giving an exchange energy of -2.30 cm(-1), g=19.2 in the temperature range of 2-10 K. The antiferromagnetic interactions have been confirmed by a quantitative determination of J for the isotropic Gd(III) derivative (J=-0.031 cm(-1), g=2.003). Compound 1 displays a slow magnetisation relaxation without applied external magnetic fields. Alternating current susceptibility shows a thermally activated behaviour with pre-exponential factors of 5.48(4)×10(-7) s and an energy barrier of 87(1) K. The application of an external field of 1.6 kOe compensates the antiferromagnetic interactions and opens a new quantum tunnelling path. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Dinuclear Spin-Crossover Complexes Based on Tetradentate and Bridging Cyanocarbanion Ligands.

    PubMed

    Milin, Eric; Belaïd, Sabrina; Patinec, Véronique; Triki, Smail; Chastanet, Guillaume; Marchivie, Mathieu

    2016-09-06

    Spin-crossover (SCO) Fe(II) dinuclear complexes of formula [Fe2(tmpa)2(μ2-tcpd)2]·0.8(CH3OH) (1·MeOH) and [Fe2(andmpa)2(μ2-tcpd)2]·2CH3OH (2·MeOH) (tmpa = tris(2-pyridylmethyl)amine, andmpa = bis(2-pyridylmethyl)aminomethyl)aniline, (tcpd)(2-) = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, and magnetic measurements. The crystal structure determinations of the two complexes (1·MeOH and 2·MeOH) and the desolvated complex 1 (from 1·MeOH) revealed a neutral centrosymmetrical dinuclear structure in which the (tcpd)(2-) cyanocarbanion acts as a double μ2-bridging ligand between two [FeL](2+) (L = tmpa (1), andmpa (2)) units involving two free coordination sites in the cis configuration. Examination of the shortest intermolecular contacts in 1·MeOH and 1 reveals no significant hydrogen bonding between the dinuclear units, while in 2·MeOH these units are held together by significant hydrogen bonds between one of the uncoordinated nitrile groups and the anilate function, giving rise to 1D supramolecular structure. The three dinuclear complexes 1, 2·MeOH, and 2 exhibit SCO behaviors which have been evidenced by the thermal evolutions of the χmT product and by the average values of the six Fe-N distances for 1 and 2·MeOH, that reveal a gradual conversion with transition temperatures (T1/2) at ca. 352 K (1), 196 K (2), and 180 K (2·MeOH). For the solvated 1·MeOH, the sharp SCO transition observed around 365 K was induced by the desolvatation process above 330 K during the magnetic measurements.

  17. CO assisted N2 functionalization activated by a dinuclear hafnium complex: a DFT mechanistic exploration.

    PubMed

    Ma, Xuelu; Zhang, Xin; Zhang, Wenchao; Lei, Ming

    2013-01-21

    In this paper, the reaction mechanisms of CO assisted N(2) cleavage and functionalization activated by a dinuclear hafnium complex are studied using a density function theory (DFT) method. Several key intermediates (Ia, Ib, Ic and Id) with axial/equatorial N=C=O coordination structures are found to be of importance along reaction pathways of CO assisted N(2) functionalization, which could provide a profound theoretical insight into the C-N bond formation and N-N bond cleavage. There are two different attack directions to insert the first CO molecule into the Hf-N bonds of the dinuclear hafnium complex, which lead to C-N bond formation. The calculated results imply that CO insertion into the Hf(1)-N(3) bond (Path A1) reacts more easily than that into the Hf(2)-N(3) bond (Path A3). But for the insertion of the second CO insertion to give 2A, there are two possibilities (Path A1 and Path A2) according to this insertion being after/before N-N bond cleavage. Two pathways (Path A1 and Path A2) are proved to be possible to form final dinitrogen functionalized products (oxamidide 2A, 2B and 2C) in this study, which explain the formation of different oxamidide isomers in CO assisted N(2) functionalization activated by a dinuclear hafnium complex.

  18. An unusual 3D interdigitated architecture assembled from Keggin polyoxometalates and dinuclear copper(II) complexes

    SciTech Connect

    Pang, Haijun; Yang, Ming; Kang, Lu; Ma, Huiyuan; Liu, Bo; Li, Shaobin; Liu, Heng

    2013-02-15

    A novel organic-inorganic hybrid compound, [Cu{sub 2}(bipy){sub 3}({mu}{sub 1}-H{sub 2}O){sub 2}({mu}{sub 2}-H{sub 2}O)({mu}{sub 2}-OH)(H{sub 2}BW{sub 12}O{sub 40})]{center_dot}4 H{sub 2}O (1) (bipy=4,4 Prime -bipy), has been synthesized in hydrothermal condition and characterized by elemental analysis, IR spectrum, TG analysis and single-crystal X-ray diffraction. Compound 1 possesses poly-pendant layered motifs composed of 12-tungstoborates and dinuclear copper(II) complexes, in which the mono-coordinated bipy molecules are orderly appended to both sides of the layer, respectively. Adjacent layers mutually engage in a zipper-like pattern to result in a novel 3D interdigitated architecture. The variable-temperature magnetic susceptibility of 1 showed that there existed weak antiferromagnetic interaction in 1. Toward the reduction of hydrogen peroxide, 1 has good electrocatalytic activity and remarkable stability. - A new compound has been obtained, which represents the first interdigitated architecture assembled by POMs and dinuclear copper(II) complexes. Highlights: Black-Right-Pointing-Pointer The first example of interdigitated architecture assembled by POMs and dinuclear copper(II) complexes is observed. Black-Right-Pointing-Pointer A zipper-like pattern is observed in the structure. Black-Right-Pointing-Pointer The IR, TG, XRPD, magnetism and electrochemical property of the title compound were studied.

  19. Formation of hyperdeformed states by neutron emission from a dinuclear system

    SciTech Connect

    Zubov, A. S.; Antonenko, N. V.; Sargsyan, V. V.; Adamian, G. G.; Scheid, W.

    2010-02-15

    The hyperdeformed nuclei treated as dinuclear or quasimolecular configurations are suggested to be directly produced in heavy-ion reactions at bombarding energies near the Coulomb barrier. The excited dinuclear system formed in the entrance channel of the heavy-ion collision can be cooled down by neutron emission to be transformed into the hyperdeformed nuclear system. This transition from the excited dinuclear system to a hyperdeformed configuration is described within the statistical approach. The reactions {sup 48}Ca+{sup 124,128,130,132,134}Sn, {sup 48}Ca+{sup 136,138}Xe, {sup 48}Ca+{sup 137,138,140}Ba, {sup 40}Ca+{sup 83,84}Kr, {sup 48}Ca+{sup 83,84,86}Kr, {sup 40,48}Ca+{sup 40,48}Ca, {sup 58,60}Ni+{sup 58,60}Ni, and {sup 40}Ca+{sup 58}Ni are suggested for the population of hyperdeformed states. The production cross sections, quadrupole moments, and moments of inertia of hyperdeformed states formed in these reactions are calculated, and the optimal conditions for the experimental identification of such states are proposed.

  20. Counter-ligand control of the electronic structure in dinuclear copper-tetrakisguanidine complexes.

    PubMed

    Ziesak, Alexandra; Wesp, Tobias; Hübner, Olaf; Kaifer, Elisabeth; Wadepohl, Hubert; Himmel, Hans-Jörg

    2015-11-28

    The redox-active GFA (Guanidino-Functionalized Aromatic compound) 1,4,5,8-tetrakis(tetramethylguanidino)-naphthalene (6) is used to synthesize new dinuclear copper complexes of the formula [6(CuX2)2] with different electronic structures. With X = OAc, a dinuclear Cu(II) complex of the neutral GFA is obtained (electronic structure [Cu(II)-GFA-Cu(II)], two unpaired electrons), and with X = Br a diamagnetic dinuclear Cu(I) complex of the dicationic GFA (electronic structure [Cu(I)-GFA(2+)-Cu(I)], closed-shell singlet state). The different electronic structures lead to significant differences in the optical, structural and magnetic properties of the complexes. Furthermore, the complex [6(CuI)2](2+) (electronic structure [Cu(I)-GFA(2+)-Cu(I)], closed-shell singlet state) is synthesized by reaction of 6(2+) with two equivalents of CuI. Slow decomposition of this complex in solution leads to the fluorescent dye 2,7-bis(dimethylamino)-1,3,6,8-tetraazapyrene. In an improved synthesis of this tetraazapyrene, 6 is reacted with CuBr in the presence of dioxygen. Quantum chemical calculations show that the addition of counter-ligands to the trigonal planar Cu(I) atoms of [6(CuI)2](2+) favors or disfavors one of the electronic structures, depending on the nature of the counter-ligand.

  1. A novel dinuclear bismuth(III) coordination compound: bis(μ-pyridine-2,6-dicarboxylato)-κ4O2,N,O6:O6′;κ4O2:O2′,N,O6-bis[(azido-κN)(1,10-phenanthroline-κ2N,N')bismuth(III)] tetrahydrate.

    PubMed

    Zhang, Wei; Feng, Yu-Quan

    2014-06-01

    A novel dinuclear bismuth(III) coordination compound, [Bi2(C7H3NO4)2(N3)2(C12H8N2)2]·4H2O, has been synthesized by an ionothermal method and characterized by elemental analysis, energy-dispersive X-ray spectroscopy, IR, X-ray photoelectron spectroscopy and single-crystal X-ray diffraction. The molecular structure consists of one centrosymmetric dinuclear neutral fragment and four water molecules. Within the dinuclear fragment, each Bi(III) centre is seven-coordinated by three O atoms and four N atoms. The coordination geometry of each Bi(III) atom is distorted pentagonal-bipyramidal (BiO3N4), with one azide N atom and one bridging carboxylate O atom located in axial positions. The carboxylate O atoms and water molecules are assembled via O-H···O hydrogen bonds, resulting in the formation of a three-dimensional supramolecular structure. Two types of π-π stacking interactions are found, with centroid-to-centroid distances of 3.461 (4) and 3.641 (4) Å.

  2. Aqueous V(V)-peroxo-amino acid chemistry. Synthesis, structural and spectroscopic characterization of unusual ternary dinuclear tetraperoxo vanadium(V)-glycine complexes.

    PubMed

    Gabriel, C; Kaliva, M; Venetis, J; Baran, P; Rodriguez-Escudero, I; Voyiatzis, G; Zervou, M; Salifoglou, A

    2009-01-19

    Vanadium participation in cellular events entails in-depth comprehension of its soluble and bioavailable forms bearing physiological ligands in aqueous distributions of binary and ternary systems. Poised to understand the ternary V(V)-H(2)O(2)-amino acid interactions relevant to that metal ion's biological role, we have launched synthetic efforts involving the physiological ligands glycine and H(2)O(2). In a pH-specific fashion, V(2)O(5), glycine, and H(2)O(2) reacted and afforded the unusual complexes (H(3)O)(2)[V(2)(O)(2)(mu(2):eta(2):eta(1)-O(2))(2)(eta(2)-O(2))(2)(C(2)H(5)NO(2))] x 5/4 H(2)O (1) and K(2)[V(2)(O)(2)(mu(2):eta(2):eta(1)-O(2))(2)(eta(2)-O(2))(2)(C(2)H(5)NO(2))] x H(2)O (2). 1 crystallizes in the triclinic space group P1, with a = 7.805(4) A, b = 8.134(5) A, c = 12.010(7) A, alpha = 72.298(9) degrees, beta = 72.991(9) degrees, gamma = 64.111(9) degrees, V = 641.9(6) A(3), and Z = 2. 2 crystallizes in the triclinic space group P1, with a = 7.6766(9) A, b = 7.9534(9) A, c = 11.7494(13) A, alpha = 71.768(2) degrees, beta = 73.233(2) degrees, gamma = 65.660(2) degrees, V = 610.15(12) A(3), and Z = 2. Both complexes 1 and 2 were characterized by UV/visible, LC-MS, FT-IR, Raman, NMR spectroscopy, cyclic voltammetry, and X-ray crystallography. The structures of 1 and 2 reveal the presence of unusual ternary dinuclear vanadium-tetraperoxo-glycine complexes containing [(V(V)=O)(O(2))(2)](-) units interacting through long V-O bonds and an effective glycinate bridge. The latter ligand is present in the dianionic assembly as a bidentate moiety spanning both V(V) centers in a zwitterionic form. The collective physicochemical properties of the two ternary species 1 and 2 project the chemical role of the low molecular mass biosubstrate glycine in binding V(V)-diperoxo units, thereby stabilizing a dinuclear V(V)-tetraperoxo dianion. Structural comparisons of the anions in 1 and 2 with other known dinuclear V(V)-tetraperoxo binary anionic species provide insight

  3. The photochemistry of mono- and dinuclear cyclometalated bis(tridentate)ruthenium(II) complexes: dual excited state deactivation and dual emission.

    PubMed

    Kreitner, Christoph; Heinze, Katja

    2016-04-07

    The synthesis and characterization of a series of weakly emissive mononuclear cyclometalated [Ru(dpb-R)(tpy)](+) complexes with functional groups R of varying electron-donating characters at the dpb ligand are described (dpbH = 1,3-di(2-pyridyl)benzene, tpy = 2,2';6',2''-terpyridine, 1(+): R = NHCOMe, 2(+): R = NH2, 3(+): R = COOEt, 4(+): R = COOH). Steady-state emission spectroscopy in the temperature range between 298 K and 77 K revealed a previously unrecognized excited state deactivation pathway via low-lying triplet ligand-to-ligand ((3)LL'CT) charge transfer states in addition to the well-known pathway via(3)MC states. Thermal activation barriers for depopulation of the emissive metal-to-ligand charge transfer ((3)MLCT) states via the (3)MC (metal-centered) and (3)LL'CT states were determined experimentally for complexes 1(+) and 3(+). The experimental results were further corroborated by calculating the respective (3)MLCT-(3)LL'CT and (3)MLCT-(3)MC transition states and their energies with density functional theoretical methods. The R substituent modifies the energy difference between the (3)MLCT and (3)LL'CT states and the corresponding activation barrier but leaves the analogous (3)MLCT/(3)MC energetics essentially untouched. Additionally, the dinuclear complex [(tpy)Ru(dpb-NHCO-dpb)Ru(tpy)](2+), 6(2+), containing a biscyclometalating bridge was devised. Despite the asymmetric nature induced by the amide bridge, the mixed-valent cation 6(3+) is ascribed to Robin-Day class II with a broad and intense intervalence charge-transfer (IVCT) absorption (λmax = 1165 nm). Upon optical excitation, the Ru(II)/Ru(II) complex 6(2+) exhibits dual emission in liquid solution from two independently emitting (3)MLCT states localized at the two remote [Ru(tpy)] fragments. No equilibration via Dexter energy transfer is possible due to their large distance and short excited state lifetimes.

  4. Using the multi-object adaptive optics demonstrator RAVEN to observe metal-poor stars in and towards the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Lamb, M.; Venn, K.; Andersen, D.; Oya, S.; Shetrone, M.; Fattahi, A.; Howes, L.; Asplund, M.; Lardière, O.; Akiyama, M.; Ono, Y.; Terada, H.; Hayano, Y.; Suzuki, G.; Blain, C.; Jackson, K.; Correia, C.; Youakim, K.; Bradley, C.

    2017-03-01

    The chemical abundances for five metal-poor stars in and towards the Galactic bulge have been determined from the H-band infrared spectroscopy taken with the RAVEN multi-object adaptive optics science demonstrator and the Infrared Camera and Spectrograph at the Subaru 8.2-m telescope. Three of these stars are in the Galactic bulge and have metallicities between -2.1 < [Fe/H] < -1.5, and high [α/Fe] ∼ +0.3, typical of Galactic disc and bulge stars in this metallicity range; [Al/Fe] and [N/Fe] are also high, whereas [C/Fe] < +0.3. An examination of their orbits suggests that two of these stars may be confined to the Galactic bulge and one is a halo trespasser, though proper motion values used to calculate orbits are quite uncertain. An additional two stars in the globular cluster M22 show [Fe/H] values consistent to within 1σ, although one of these two stars has [Fe/H] = -2.01 ± 0.09, which is on the low end for this cluster. The [α/Fe] and [Ni/Fe] values differ by 2σ, with the most metal-poor star showing significantly higher values for these elements. M22 is known to show element abundance variations, consistent with a multipopulation scenario though our results cannot discriminate this clearly given our abundance uncertainties. This is the first science demonstration of multi-object adaptive optics with high-resolution infrared spectroscopy, and we also discuss the feasibility of this technique for use in the upcoming era of 30-m class telescope facilities.

  5. Computational, electrochemical, and spectroscopic studies of two mononuclear cobaloximes: the influence of an axial pyridine and solvent on the redox behaviour and evidence for pyridine coordination to cobalt(i) and cobalt(ii) metal centres.

    PubMed

    Lawrence, Mark A W; Celestine, Michael J; Artis, Edward T; Joseph, Lorne S; Esquivel, Deisy L; Ledbetter, Abram J; Cropek, Donald M; Jarrett, William L; Bayse, Craig A; Brewer, Matthew I; Holder, Alvin A

    2016-06-21

    [Co(dmgBF2)2(H2O)2] (where dmgBF2 = difluoroboryldimethylglyoximato) was used to synthesize [Co(dmgBF2)2(H2O)(py)]·0.5(CH3)2CO (where py = pyridine) in acetone. The formulation of complex was confirmed by elemental analysis, high resolution MS, and various spectroscopic techniques. The complex [Co(dmgBF2)2(solv)(py)] (where solv = solvent) was readily formed in situ upon the addition of pyridine to complex . A spectrophotometric titration involving complex and pyridine proved the formation of such a species, with formation constants, log K = 5.5, 5.1, 5.0, 4.4, and 3.1 in 2-butanone, dichloromethane, acetone, 1,2-difluorobenzene/acetone (4 : 1, v/v), and acetonitrile, respectively, at 20 °C. In strongly coordinating solvents, such as acetonitrile, the lower magnitude of K along with cyclic voltammetry, NMR, and UV-visible spectroscopic measurements indicated extensive dissociation of the axial pyridine. In strongly coordinating solvents, [Co(dmgBF2)2(solv)(py)] can only be distinguished from [Co(dmgBF2)2(solv)2] upon addition of an excess of pyridine, however, in weakly coordinating solvents the distinctions were apparent without the need for excess pyridine. The coordination of pyridine to the cobalt(ii) centre diminished the peak current at the Epc value of the Co(I/0) redox couple, which was indicative of the relative position of the reaction equilibrium. Herein we report the first experimental and theoretical (59)Co NMR spectroscopic data for the formation of Co(i) species of reduced cobaloximes in the presence and absence of py (and its derivatives) in CD3CN. From spectroelectrochemical studies, it was found that pyridine coordination to a cobalt(i) metal centre is more favourable than coordination to a cobalt(ii) metal centre as evident by the larger formation constant, log K = 4.6 versus 3.1, respectively, in acetonitrile at 20 °C. The electrosynthesis of hydrogen by complexes and in various solvents demonstrated the dramatic effects of the axial

  6. Excited state localization and internuclear interactions in asymmetric ruthenium(II) and osmium(II) bpy/tpy based dinuclear compounds.

    PubMed

    Halpin, Yvonne; Dini, Danilo; Ahmed, Hamid M Younis; Cassidy, Lynda; Browne, Wesley R; Vos, Johannes G

    2010-03-15

    The synthesis of two asymmetric dinuclear complexes with the formula [M(bpy)(2)(bpt)Ru(tpy)Cl](2+), where M = Ru (1a), Os(2a); bpy = 2,2'-bipyridyl; Hbpt = 3,5-bis(pyridin-2-yl)1,2,4-triazole and tpy = 2,2',6',2''-terpyridine, is reported. The compounds obtained are characterized by mass spectrometry, (1)H NMR, UV/vis/NIR absorption, luminescence, and resonance Raman spectroscopy. Deuterium isotope labeling facilitates assignment of the (1)H NMR and resonance Raman spectra. The interaction between the two metal centers, mediated by the bridging 1,2,4-triazolato moiety in the mixed valent state, is assigned as type II based on the observation of metal to metal charge transfer absorption bands at 7090 and 5990 cm(-1) for 1a and 2a, respectively. The extent of localization of the emissive excited state was determined by transient resonance Raman and emission spectroscopy. Both 1a and 2a show phosphorescence at the same wavelengths; however, whereas for compound 1a the emission is based on the Ru(tpy)Cl- center, for 2a the emissive state is localized on the Os(bpy)(2)- unit. This indicates that also in the excited state there is efficient interaction between the two metal centers.

  7. Science Learning Centres Roundup

    ERIC Educational Resources Information Center

    Education in Science, 2010

    2010-01-01

    The national network of Science Learning Centres aims to raise the quality of science teaching from Key Stage 1 through post-16 (ages 5-19). Short courses are provided locally through the regional Science Learning Centres and longer, more intensive programmes are available at the National Science Learning Centre in York. There are a growing number…

  8. Peptide-bridged dinuclear Ru(II) complex for mitochondrial targeted monitoring of dynamic changes to oxygen concentration and ROS generation in live mammalian cells.

    PubMed

    Martin, Aaron; Byrne, Aisling; Burke, Christopher S; Forster, Robert J; Keyes, Tia E

    2014-10-29

    A novel mitochondrial localizing ruthenium(II) peptide conjugate capable of monitoring dynamic changes in local O2 concentrations within living cells is presented. The complex is comprised of luminescent dinuclear ruthenium(II) polypyridyl complex bridged across a single mitochondrial penetrating peptide, FrFKFrFK-CONH2 (r = D-arginine). The membrane permeability and selective uptake of the peptide conjugate at the mitochondria of mammalian cells was demonstrated using confocal microscopy. Dye co-localization studies confirmed very precise localization and preconcentration of the probe at the mitochondria. This precision permitted collection of luminescent lifetime images of the probe, without the need for co-localizing dye and permitted semiquantitative determination of oxygen concentration at the mitochondria using calibration curves collected at 37 °C for the peptide conjugate in PBS buffer. Using Antimycin A the ability of the probe to respond dynamically to changing O2 concentrations within live HeLa cells was demonstrated. Furthermore, based on lifetime data it was evident that the probe also responds to elevated reactive oxygen species (ROS) levels within the mitochondria, where the greater quenching capacity of these species led to luminescent lifetimes of the probe at longer Antimycin A incubation times which lay outside of the O2 concentration range. Although both the dinuclear complex and a mononuclear analogue conjugated to an octaarginine peptide sequence exhibited some cytotoxicity over 24 h, cells were tolerant of the probes over periods of 4 to 6 h which facilitated imaging. These metal-peptide conjugated probes offer a valuable opportunity for following dynamic changes to mitochondrial function which should be of use across domains in which the metabolic activity of live cells are of interest from molecular biology and drug discovery.

  9. Total enantioselectivity in the DNA binding of the dinuclear ruthenium(II) complex [[Ru(Me2bpy)2]2(mu-bpm)]4+ [bpm = 2,2'-bipyrimidine; Me2bpy = 4,4'-dimethyl-2,2'-bipyridine].

    PubMed

    Smith, Jayden A; Collins, J Grant; Patterson, Bradley T; Keene, F Richard

    2004-05-07

    The binding of the three stereoisomers (DeltaDelta-, LambdaLambda- and DeltaLambda-) of the dinuclear ruthenium(II) complex [[Ru(Me2bpy)2]2(mu-bpm)]4+ [Me2bpy = 4,4'-dimethyl-2,2'-bipyridine; bpm = 2,2'-bipyrimidine] to a tridecanucleotide containing a single adenine bulge has been studied by 1H NMR spectroscopy. The addition of the DeltaDelta-isomer to d(CCGAGAATTCCGG)2 induced significant chemical shift changes for the base and sugar resonances of the residues at the bulge site (G3A4G5/C11C10), whereas small shifts were observed upon addition of the enantiomeric LambdaLambda-form. NOESY spectra of the tridecanucleotide bound with the DeltaDelta-isomer revealed intermolecular NOE's between the metal complex and the nucleotide residues at the bulge site, while only weak NOE's were observed to terminal residues to the LambdaLambda-form. Competitive binding studies were performed where both enantiomers were simultaneously added to the tridecanucleotide, and for all ratios of the two stereoisomers the DeltaDelta-isomer remained selectively bound at the bulge site with the LambdaLambda-enantiomer localised at the terminal regions of the tridecanucleotide. The meso-diastereoisomer (DeltaLambda) was found to bind to the tridecanucleotide with characteristics intermediate between the DeltaDelta- and LambdaLambda-enantiomers of the rac form. Two distinct sets of metal complex resonances were observed, with one set having essentially the same shift as the free metal complex, whilst the other set of resonances exhibited significant shifts. The NOE data indicated that the meso-diastereoisomer does not bind as selectively as the DeltaDelta-isomer, with NOE's observed to a greater number of nucleotide residues compared to the DeltaDelta-form. This study provides a rare example of total enantioselectivity in the binding of an inert transition metal complex to DNA, produced by the shape recognition of both ruthenium(II) centres.

  10. Synthesis and characterization of dinuclear rare-earth complexes supported by amine-bridged bis(phenolate) ligands and their catalytic activity for the ring-opening polymerization of l-lactide.

    PubMed

    Duan, Yu-Lai; He, Jia-Xuan; Wang, Wei; Zhou, Jing-Jing; Huang, Yong; Yang, Ying

    2016-06-28

    Reactions of amine-bridged bis(phenolate) protio-ligands N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)aminoacetic acid (L(1)-H3) and N,N-bis[3,5-bis(α,α'-dimethylbenzyl)-2-hydroxybenzyl]aminoacetic acid (L(2)-H3), with 1 equiv. M[N(SiMe3)2]3 (M = La, Nd, Sm, Gd, Y) in THF at room temperature yielded the neutral rare-earth complexes [M2(L)2(THF)4] (L = L(1), M = La (), Nd (), Sm (), Gd (), Y (); L = L(2), M = La (), Nd (), Sm (), Gd (), Y ()). All of these complexes were characterized by single-crystal X-ray diffraction, elemental analysis and in the case of yttrium and lanthanum complexes, (1)H NMR spectroscopy. The molecular structure of revealed dinuclear species in which the eight-coordinate lanthanum centers were bonded to two oxygen atoms of two THF molecules, to three oxygen atoms and one nitrogen atom of one L(1) ligand, and two oxygen atoms of the carboxyl group of another. Complexes were also dinuclear species containing seven-coordinate metal centers similar to , albeit with bonding to one rather than two carboxyl group oxygens of another ligand. Further treatment of with excess benzyl alcohol provided dinuclear complex [La2(L(1))2(BnOH)6] (), in which each lanthanum ion is eight-coordinate, bonded to three oxygen atoms and one nitrogen atom of one ligand, three oxygen atoms of three BnOH molecules, as well as one oxygen atom of bridging carboxyl group of the other ligand. In the presence of BnOH, complexes efficiently catalyzed the ring-opening polymerization of l-lactide in a controlled manner and gave polymers with relatively narrow molecular weight distributions. The kinetic and mechanistic studies associated with the ROP of l-lactide using /BnOH initiating system have been performed.

  11. Systematic Introduction of Aromatic Rings to Diphosphine Ligands for Emission Color Tuning of Dinuclear Copper(I) Iodide Complexes.

    PubMed

    Okano, Yuka; Ohara, Hiroki; Kobayashi, Atsushi; Yoshida, Masaki; Kato, Masako

    2016-06-06

    We have newly synthesized two solution-stable luminescent dinuclear copper(I) complexes, [Cu2(μ-I)2(dpppy)2] (Cu-py) and [Cu2(μ-I)2(dpppyz)2] (Cu-pyz), where dpppy = 2,3-bis(diphenylphosphino)pyridine and dpppyz = 2,3-bis(diphenylphosphino)pyrazine, using chelating diphosphine ligands composed of N-heteroaromatic rings. X-ray analysis clearly indicates that the molecular structures of Cu-py and Cu-pyz are almost identical with that of the parent complex, [Cu2(μ-I)2(dppb)2] [Cu-bz; dppb = 2,3-bis(diphenylphosphino)benzene]. Complexes Cu-py and Cu-pyz exhibit luminescence [emission quantum yield (Φem) = 0.48 and 0.02, respectively] in the solid state at 298 K. A wide emission color tuning, from 497 to 638 nm (energy = 0.55 eV, with an emission color ranging from green to reddish-orange), was achieved in the solid state by the introduction of pyridinic N atoms into the bridging phenyl group between the two diphenylphosphine groups. Density functional theory calculations suggest that the emission could originate from the effective combination of the metal-to-ligand charge-transfer excited state with the halide-to-ligand charge-transfer excited state. Thus, the emission color change is due to stabilization of the π* levels of the central aryl group in the diphosphine ligand. Furthermore, these copper(I) complexes exhibit thermally activated delayed fluorescence at 298 K because of the small singlet-triplet energy difference (ΔE = 523 and 564 cm(-1) for Cu-py and Cu-pyz, respectively). The stability of these complexes in chloroform, due to the rigid bonds between the diphosphine ligands and the Cu(I) ions, enables the preparation of emissive poly(methyl methacrylate) films by the solution-doping technique.

  12. NMR investigations of dinuclear, single-anion bridged copper(II) metallacycles: structure and antiferromagnetic behavior in solution.

    PubMed

    Reger, Daniel L; Pascui, Andrea E; Pellechia, Perry J; Ozarowski, Andrew

    2013-11-04

    The nuclear magnetic resonance (NMR) spectra of single-anion bridged, dinuclear copper(II) metallacycles [Cu2(μ-X)(μ-L)2](A)3 (L(m) = m-bis[bis(1-pyrazolyl)methyl]benzene: X = F(-), A = BF4(-); X = Cl(-), OH(-), A = ClO4(-); L(m)* = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene: X = CN(-), F(-), Cl(-), OH(-), Br(-), A = ClO4(-)) have relatively sharp (1)H and (13)C NMR resonances with small hyperfine shifts due to the strong antiferromagnetic superexchange interactions between the two S = 1/2 metal centers. The complete assignments of these spectra, except X = CN(-), have been made through a series of NMR experiments: (1)H-(1)H COSY, (1)H-(13)C HSQC, (1)H-(13)C HMBC, T1 measurements and variable-temperature (1)H NMR. The T1 measurements accurately determine the Cu···H distances in these molecules. In solution, the temperature dependence of the chemical shifts correlate with the population of the paramagnetic triplet (S = 1) and diamagnetic singlet (S = 0) states. This correlation allows the determination of antiferromagnetic exchange coupling constants, -J (Ĥ = -JŜ1Ŝ2), in solution for the L(m) compounds 338(F(-)), 460(Cl(-)), 542(OH(-)), for the L(m)* compounds 128(CN(-)), 329(F(-)), 717(Cl(-)), 823(OH(-)), and 944(Br(-)) cm(-1), respectively. These values are of similar magnitudes to those previously measured in the solid state (-Jsolid = 365, 536, 555, 160, 340, 720, 808, and 945 cm(-1), respectively). This method of using NMR to determine -J values in solution is an accurate and convenient method for complexes with strong antiferromagnetic superexchange interactions. In addition, the similarity between the solution and solid-state -J values of these complexes confirms the information gained from the T1 measurements: the structures are similar in the two states.

  13. Altered transition state for the reaction of an RNA model catalyzed by a dinuclear zinc(II) catalyst.

    PubMed

    Humphry, Tim; Iyer, Subashree; Iranzo, Olga; Morrow, Janet R; Richard, John P; Paneth, Piotr; Hengge, Alvan C

    2008-12-31

    The cyclization of 2-(hydroxypropyl)-4-nitrophenyl phosphate (HpPNP) catalyzed by the dinuclear zinc complex of 1,3-bis(1,4,7-triazacyclonon-1-yl)-2-hydroxypropane (1) proceeds by a transition state that is different from that of the uncatalyzed reaction. Kinetic isotope effects (KIEs) measured in the nucleophilic atom and in the leaving group show that the uncatalyzed cyclization has a transition state (TS) with little phosphorus-oxygen bond fission to the leaving group ((18)k(lg) = 1.0064 +/- 0.0009 and (15)k = 1.0002 +/- 0.0002) and that nucleophilic bond formation occurs in the rate-determining step ((18)k(nuc) = 1.0326 +/- 0.0008). In the catalyzed reaction, larger leaving group isotope effects ((18)k(lg) = 1.0113 +/- 0.0005 and (15)k = 1.0015 +/- 0.0005) and a smaller nucleophile isotope effect ((18)k(nuc) = 1.0116 +/- 0.0010) indicate a later TS with greater leaving group bond fission and greater nucleophilic bond formation. These observed nucleophile KIEs are the combined effect of the equilibrium effect on deprotonation of the 2'-hydroxyl nucleophile and the KIE on the nucleophilic step. An EIE of 1.0245 for deprotonation of the hydroxyl group of HPpNP was obtained computationally. The different KIEs for the two reactions indicate that the effective catalysis by 1 is accompanied by selection for an altered transition state, presumably arising from the preferential stabilization by the catalyst of charge away from the nucleophile and toward the leaving group. These results demonstrate the potential for a catalyst using biologically relevant metal ions to select for an altered transition state for phosphoryl transfer.

  14. PARACEST properties of a dinuclear neodymium(III) complex bound to DNA or carbonate.

    PubMed

    Nwe, Kido; Andolina, Christopher M; Huang, Ching-Hui; Morrow, Janet R

    2009-07-01

    A dinuclear Nd(III) macrocyclic complex of 1 (1,4-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-p-xylene) and mononuclear complexes of 1,4,7-tris-1,4,7,10-tetraazacyclododecane, 2, and 1,4,7-tris[(N-N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane, 3, are prepared. Complexes of 1 and 2 give rise to a PARACEST (paramagnetic chemical exchange saturation transfer) peak from exchangeable amide protons that resonate approximately 12 ppm downfield from the bulk water proton resonance. The dinuclear Nd(III) complex is promising as a PARACEST contrast agent for MRI applications, because it has an optimal pH of 7.5 and the rate constant for amide proton exchange (2700 s(-1)) is nearly as large as it can be within slow exchange conditions with bulk water. Dinuclear Ln(2)(1) complexes (Ln(III) = Nd(III), Eu(III)) bind tightly to anionic ligands including carbonate, diethyl phosphate, and DNA. The CEST amide peak of Nd(2)(1) is enhanced by certain DNA sequences that contain hairpin loops, but decreases in the presence of diethyl phosphate or carbonate. Direct excitation luminescence studies of Eu(2)(1) show that double-stranded and hairpin-loop DNA sequences displace one water ligand on each Eu(III) center. DNA displaces carbonate ion despite the low dissociation constant for the Eu(2)(1) carbonate complex (K(d) = 15 microM). Enhancement of the CEST effect of a lanthanide complex by binding to DNA is a promising step toward the preparation of PARACEST agents containing DNA scaffolds.

  15. Dinuclear Pt(II)-bisphosphonate complexes: a scaffold for multinuclear or different oxidation state platinum drugs.

    PubMed

    Piccinonna, Sara; Margiotta, Nicola; Pacifico, Concetta; Lopalco, Antonio; Denora, Nunzio; Fedi, Serena; Corsini, Maddalena; Natile, Giovanni

    2012-08-28

    Geminal bisphosphonates (BPs), used in the clinic for the treatment of hypercalcaemia and skeletal metastases, have been also exploited for promoting the specific accumulation of platinum antitumor drugs in bone tissue. In this work, the platinum dinuclear complex [{Pt(en)}(2)(μ-AHBP-H(2))](+) (1) (the carbon atom bridging the two phosphorous atoms carrying a 2-ammonioethyl and a hydroxyl group, AHBP-H(2)) has been used as scaffold for the synthesis of a Pt(II) trinuclear complex, [{Pt(en)}(3)(μ-AHBP)](+) (2), and a Pt(IV) adamantane-shaped dinuclear complex featuring an oxo-bridge, [{Pt(IV)(en)Cl}(2)(μ-O)(μ-AHBP-H(2))](+) (3) (X-ray structure). Compound 2 undergoes a reversible, pH dependent, rearrangement with a neat switch point around pH = 5.4. Compound 3 undergoes a one-step electrochemical reduction at E(pc) = -0.84 V affording compound 1. Such a potential is far lower than that of glutathione (-0.24 V), nevertheless compound 3 can undergo chemical reduction to 1 by GSH, most probably through a different (inner-sphere) mechanism. In vitro cytotoxicity of the new compounds, tested against murine glioma (C6) and human cervix (HeLa) and hepatoma (HepG2) cell lines, has shown that, while the Pt(IV) dimer 3 is inactive up to a concentration of 50 μM, the two Pt(II) polynuclear compounds 1 and 2 have a cytotoxicity comparable to that of cisplatin with the trinuclear complex 2 generally more active than the dinuclear complex 1.

  16. PARACEST Properties of a Dinuclear Neodymium(III) Complex Bound to DNA or Carbonate

    PubMed Central

    Nwe, Kido; Andolina, Christopher M.; Huang, Ching-Hui; Morrow, Janet R.

    2009-01-01

    A dinuclear Nd(III) macrocyclic complex of 1 (1,4-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-p-xylene) and mononuclear complexes of 1,4,7-tris-1,4,7,10-tetraazacyclododecane 2, and 1,4,7-tris[(N-N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane, 3, are prepared. Complexes of 1 and 2 give rise to a PARACEST (paramagnetic chemical exchange saturation transfer) peak from exchangeable amide protons that resonate approximately 12 ppm downfield from the bulk water proton resonance. The dinuclear Nd(III) complex is promising as a PARACEST contrast agent for MRI applications because it has an optimal pH of 7.5 and the rate constant for amide proton exchange (2700 s−1) is nearly as large as it can be within slow exchange conditions with bulk water. Dinuclear Ln2(1) complexes (Ln(III) = Nd(III), Eu(III)) bind tightly to anionic ligands including carbonate, diethylphosphate and DNA. The CEST amide peak of Nd2(1) is enhanced by certain DNA sequences that contain hairpin loops, but decreases in the presence of diethyl phosphate or carbonate. Direct excitation luminescence studies of Eu2(1) show that double-stranded and hairpin loop DNA sequences displace one water ligand on each Eu(III) center. DNA displaces carbonate ion despite the low dissociation constant for the Eu2(1) carbonate complex (Kd = 15 µM). Enhancement of the CEST effect of a lanthanide complex by binding to DNA is a promising step toward the preparation of PARACEST agents containing DNA scaffolds. PMID:19555071

  17. [Allergic contact dermatitis to metals over a 20-year period in the Centre of Portugal: evaluation of the effects of the European directives].

    PubMed

    Teixeira, Vera; Coutinho, Inês; Gonçalo, Margarida

    2014-01-01

    Introdução: Os metais são causa frequente de dermatite de contacto alérgica. Desde a introdução da Directiva Comunitária do Níquel (1994/27/CE; 2004/96/CE) e, mais recentemente, da Directiva do Cimento (2003/53/CE), nos países nórdicos tem havido uma diminuição da sensibilização aos metais. A aplicabilidade destas medidas e o seu impacto permanece por avaliar em Portugal. Material e Métodos: Foi realizado um estudo retrospectivo (1992-2011) na Consulta de Alergologia Cutânea com o principal objectivo de analisar a variação dos padrões de sensibilização aos metais (níquel [Ni], cobalto [Co] e crómio [Cr]) ao longo de 20 anos, em particular no que se refere ao género, grupo etário e relação com a actividade profissional. Resultados: Do total de 5 250 doentes estudados, em 1 626 (31%) observámos pelo menos um teste epicutâneo positivo a um metal (26,5% ao Ni; 10,0% ao Co e 7,0% ao Cr). A prevalência de sensibilização ao Ni era significativamente maior nas mulheres (34,4% versus 8,9%) e ao Cr nos homens (11,5% versus 5,0%). Não houve diminuição significativa da sensibilização ao Ni ao longo dos 20 anos, mas o contributo da faixa etária dos 16-30 anos no total de mulheres sensíveis a este metal decresceu de forma significativamente estatística ao longo dos anos (p < 0,001). A sensibilização ao Cr decresceu sobretudo nos homens (r = -0,535), muito particularmente nos casos relacionados com a construção civil (r = -0,639), enquanto a reatividade ao Cr relacionado com o uso de calçado se manteve estável. Discussão: A manutenção dos elevados níveis de sensibilização ao níquel denota ainda uma fraca implementação das Directivas comunitárias mas a redução da percentagem de mulheres jovens poderá significar já algum efeito positivo nesta faixa etária. Ao contrário, a Directiva referente à redução do Cr no cimento parece estar a ter os seus efeitos positivos. Há, contudo, necessidade de interferir com o conte

  18. Synthesis of 3-Indolylglycine Derivatives via Dinuclear Zinc Catalytic Asymmetric Friedel-Crafts Alkylation Reaction.

    PubMed

    Wang, Xin-Wei; Hua, Yuan-Zhao; Wang, Min-Can

    2016-10-07

    A direct asymmetric Friedel-Crafts (F-C) alkylation reaction between a wide range of indoles and ethyl 2-(4-methoxyphenylimino)acetate catalyzed by Trost's dinuclear complex is reported. A series of 3-indolylglycine derivatives were synthesized in enantioselectivity of up to >99% enantiomeric excess (ee) using 10 mol% catalyst loading under mild conditions. This atom economic reaction could be run on a gram scale without impacting its enantioselectivity. The absolute stereochemistry of catalytic products was determined by correlation with a known configuration compound. A possible mechanism was proposed for the asymmetric induction.

  19. A thermally stable pcu network based on ferromagnetic dinuclear Ni(II) units

    NASA Astrophysics Data System (ADS)

    Zhang, Xu-Dong; Pang, Jian-Dong; Li, Ya-Meng; Ju, Zhan-Feng

    2014-01-01

    A pcu network based on the dinuclear Ni(II) units, [Ni2(hfipbb)2(1,3-bix)2]n (1) (H2hfipbb = 4,4‧- (Hexafluoroisopropylidene)bis(benzoic Acid); 1,3-bix = 1,3-bis(imidazol-1-ylmethyl)benzene), has been hydrothermally synthesized and structurally characterized. Interestingly, the two Ni(II) cations are bridged by two carboxylate groups in the rarely-seen syn-anti mode. The magnetic data reveal the dominant ferromagnetic interactions between Ni(II) ions.

  20. Synthesis of superheavy elements and dinuclear-system concept of compound-nucleus formation

    SciTech Connect

    Antonenko, N.V.; Adamian, G.G.; Cherepanov, E.A.

    1996-12-31

    Dinuclear system concept is applied to the analysis of reactions used for the synthesis of elements with Z = 110, 112, 114, and 116. The inner fusion barriers obtained for these reactions are in good agreement with the experimental estimations resulted from the excitation energies of compound nuclei. A model is suggested for the calculation of the competition between complete fusion and quasifission in reactions with heavy nuclei. The fusion rate through the inner fusion barrier in mass asymmetry is found by using the multidimensional Kramers-type stationary solution of the Fokker-Planck equation. The influence of dissipative effects on the dynamics of nuclear fusion is considered.

  1. Synthesis and characterisation of bis-cyclen based dinuclear lanthanide complexes.

    PubMed

    Gunnlaugsson, Thorfinnur; Harte, Andrew J

    2006-04-21

    The design and synthesis of several bis-macrocyclic cyclen (1,4,7,10-tetraazacyclododecane) ligands and their corresponding lanthanum or europium complexes is described; these dinuclear lanthanide systems were made by connecting two macrocyclic cyclen moieties through a rigid, covalent, p-xylylenediamide bridge or a flexible aliphatic hexane bridge. These ligands were subsequently functionalised with six acetamide pendant arms (CONR1R2: R1 = R2 = H or CH3, or R1 = H, R2 = CH3). The corresponding lanthanide bis-complexes were then formed by reaction with La(III) and Eu(III) triflates, yielding overall cationic (+VI charged) complexes.

  2. Catalytic Asymmetric Nazarov Cyclization of Heteroaryl Vinyl Ketones through a Crystallographically Defined Chiral Dinuclear Nickel Complex.

    PubMed

    Takeda, Takuya; Harada, Shinji; Nishida, Atsushi

    2015-11-06

    A Ni(NTf2)2 and tetradentate bisimino-bisquinoline ligand complex catalyzed the enantioselective Nazarov cyclization of heteroaryl vinyl ketones. An X-ray-quality crystal was obtained from a mixture of the Ni complex and the substrate, which was the dinuclear chiral Ni complex. From information regarding the structure of the complex, the substrate was distorted to form a helical shape, and the carbon atoms involved in bond formation were close to each other. In addition, mechanistic studies revealed that the configuration of the olefin moiety was isomerized before bond formation.

  3. Four Strandberg-type polyoxometalates with organophosphine centre decorated by transition metal-2,2'-bipy/H2O complexes

    NASA Astrophysics Data System (ADS)

    Lu, Ting; Feng, Shu-Li; Zhu, Zai-Ming; Sang, Xiao-Jing; Su, Fang; Zhang, Lan-Cui

    2017-09-01

    Four inorganic-organic hybrid compounds composed of Strandberg-type organophosphomolybdate anion [(C6H5PO3)2Mo5O15]4- (abbreviated as (PhP)2Mo5) and transition metal (TM)-2,2'-bipy/H2O complex units, namely [(TM(H2O)(bipy))2(C6H5PO3)2Mo5O15]n (TM = Co, (1); Ni, (2)), [(Cu(bipy)2)2(C6H5PO3)2Mo5O15]·2H2O (3) and [(Zn(bipy)(μ-OH))2(Zn(bipy)2(C6H5PO3)2Mo5O15)2]·3H2O (4) (bipy = 2,2'-bipyridine), were successfully constructed under hydrothermal conditions, and their structures were determined by single crystal X-ray diffraction analysis and spectroscopic methods. The central heteroatoms in these polyoxometalates (POMs) are all organophosphine (RP) groups. Compound 1 and compound 2 are isostructural (PhP)2Mo5-based TM-coordination polymers with the two-dimensional layer frameworks. In compound 3, the bi-supporting structure containing one (PhP)2Mo5 unit and two [Cu(bipy)2]2+ cations. For compound 4, it can be regarded as a dimer of two bi-supporting {Zn(bipy)2(PhP)2Mo5Zn(bipy)} clusters that were connected by two μ-OH groups. The acid-catalytic activities and fluorescence properties of the four hybrids have been investigated.

  4. A dinuclear Ru(II) complex capable of photoinduced ligand exchange at both metal centers.

    PubMed

    Albani, B A; Peña, B; Saha, S; White, J K; Schaeffer, A M; Dunbar, K R; Turro, C

    2015-11-28

    {[Ru(CH3CN)3]2(tppz)}(4+) (tppz = tetra-2-pyridylpyrazine) undergoes photoinduced CH3CN exchange with λirr ≥ 610 nm in H2O. In contrast, cis-{[Ru(tpy)(L)]2(bpm)}(4+) (tpy = 2,2':6',2''-terpyridine, bpm = 2,2'-bipyrimidine, L = CH3CN) is not reactive, but the complex with L = DMSO is photoactive. These complexes are potentially useful for the release of multiply caged drugs.

  5. X-ray crystal structure and theoretical study of a new dinuclear Cu(II) complex with two different geometry centers bridged with an oxo group

    NASA Astrophysics Data System (ADS)

    Golbedaghi, Reza; Azimi, Saeid; Molaei, Atefeh; Hatami, Masoud; Notash, Behrouz

    2017-10-01

    A new Schiff base ligand HL, 1,3-bis(2-((Z)-(2-aminoethylimino)methyl)phenoxy)ethylene di amine, has been synthesized from the reaction of a new aldehyde and ethylenediamine. After preparation the Schiff base, a new dinuclear Cu(II) complex with two different geometry for each metal ion was synthesized. Single crystal X-ray structure analysis of the complex Cu(II) showed that the complex is binuclear and all nitrogen and oxygen atoms of ligand (N4O3) are coordinated to two Cu(II) center ions. The crystal structure studying shows, a perchlorate ion has been coordinated to the two Cu(II) metal centers as bridged and another perchlorate coordinated to the one of Cu(II) ion as terminal. However, two interesting structures square pyramidal and distorted octahedral Cu(II) ions are bridged asymmetrically by a perchlorate ion and oxygen of hydroxyl group of Schiff base ligand. In addition, we had a theoretical study to have a comparison of experimental and theoretical results we determined the HOMO and LUMO orbitals.

  6. μ2-Oxido bridged dinuclear vanadium(V) complex: Synthesis and characterization

    NASA Astrophysics Data System (ADS)

    Ghorbani, Maryam; Khalaji, Aliakbar Dehno; Feizi, Nourollah; Akbari, Alireza; Eigner, Vaclav; Dusek, Michal

    2017-02-01

    μ2-Oxido bridged dinuclear vanadium(V) Schiff base complex with the general formula [VO2(L)]2·2CH3OH was synthesized and characterized. The X-ray results show the complex is dinuclear with two μ-O bridging ions, and the vanadium centers have an octahedral N2O4 coordination sphere. The tridentate Schiff base ligand L coordinated to vanadium(V) center as a monoanion in the basal plane. The basal plane is completed by one of the μ-O bridges. The other μ-O bridge coordinated to vanadium(V) center as apical direction. The two oxido bridged connected the two Vv centers together with the Vv-O-Vv angle of 101.21(6)°, the Vsbnd O distances of 1.70(6) and 2.31(7) Å and the V⋯V separation of 3.113(5) Å. Finally, the complex was calcinated at 600 °C for 3 h. The FT-IR spectrum of the product shows the formation of the V2O5 particles.

  7. Structure and spectral properties of dinuclear zinc complex containing semicarbazonate ligands

    NASA Astrophysics Data System (ADS)

    Jing-Lin, Wang; Jiao, Feng; Mei-Ping, Xu; Bin-Sheng, Yang

    2011-04-01

    The dinuclear Zn 2+ complex [Zn(HSSC)OAc] 2·2DMF (H 2SSC = salicylaldehyde semicarbazone; HOAc = acetic acid; DMF = N,N-dimethylfomamide) was prepared and structurally characterized by single crystal X-ray. The basic structural unit of the complex is a dinuclear complex [Zn(HSSC)OAc] 2 in which the semicarbazone ligand adopts the phenol-imine form. The deprotonated phenol group forms a one-atom bridge between the two zinc centers, and both of the zinc centers are five-coordinated. The local coordination environment of Zn 2+ can be approximately considered as square pyramidal. UV spectral studies show that the H 2SSC provides strong binding of Zn 2+ in a 1:1 ratio in solution. The conditional binding constant of the complex is lg KZn-L = 12.89 ± 0.76 in 0.05 M Tris-HCl buffer at pH 7.4. The H 2SSC exhibits an enhanced fluorescence effect by the addition of Zn 2+, and affords an excellent selectivity for Zn 2+ under physiological conditions.

  8. Highly luminescent bis-diketone lanthanide complexes with triple-stranded dinuclear structure.

    PubMed

    Li, Hong-Feng; Yan, Peng-Fei; Chen, Peng; Wang, Yan; Xu, Hui; Li, Guang-Ming

    2012-01-21

    A new bis-β-diketone, 3,3'-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl (BTB), has been designed and prepared for the synthesis of a series of dinuclear lanthanide complexes [Ln(2)(BTB)(3)(C(2)H(5)OH)(2)(H(2)O)(2)] [Ln = Eu (1), Gd (2)], [Ln(2)(BTB)(3)(DME)(2)] [Ln = Nd (3), Yb (4); DME = ethylene glycol dimethyl ether] and [Eu(2)(BTB)(3)(L)(2)] [L = 2,2-bipydine (5); 1,10-phenanthroline (6); 4,7-diphenyl-1,10-phenanthroline (7)]. Complexes 1-7 have been characterized by various spectroscopic techniques and their photophysical properties are investigated. X-ray crystallographical analysis reveals that complexes 1, 3 and 4 adopt triple-stranded dinuclear structures which are formed by three bis-bidentate ligands with two lanthanide ions. The complexes 1 and 3-7 display strong visible red or NIR luminescence upon irradiation at ligand band around 372 nm, depending on the choice of the lanthanide. The solid-state photoluminescence quantum yields and the lifetimes of Eu(3+) complexes are determined and described.

  9. EPR interpretation, magnetism and biological study of a Cu(II) dinuclear complex assisted by a schiff base precursor.

    PubMed

    Das, Kuheli; Patra, Chiranjit; Sen, Chandana; Datta, Amitabha; Massera, Chiara; Garribba, Eugenio; El Fallah, Mohamed Salah; Beyene, Belete B; Hung, Chen-Hsiung; Sinha, Chittaranjan; Askun, Tulin; Celikboyun, Pinar; Escudero, Daniel; Frontera, Antonio

    2017-06-01

    A new Cu(II) dinuclear complex, Cu2L2 (1) was afforded employing the potentially pentatentate Schiff base precursor H2L, a refluxed product of o-vanillin and diethylenetriamine in methanol. Complex 1 was systematically characterized by FTIR, UV-Vis, emission and EPR spectrometry. The single crystal X-ray diffraction analysis of 1 reveals that the copper atom exhibits a distorted square planar geometry, comprising two pairs of phenolato-O and imine-N donors from two different H2L ligands. The temperature dependent magnetic interpretation agrees with the existence of weak antiferromagnetic interactions between the bridging dinuclear Cu(II) ions. A considerable body of experimental evidence has been accumulated to elucidate the magneto-structural relationship in this dinuclear Cu(II) complex by DFT computation. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy on M. tuberculosis H37Ra (ATCC 25177) and M. tuberculosis H37Rv (ATCC 25618) strains. The practical applicability of the ligand and complex 1 has been examined in living cells (African Monkey Vero Cells). The MTT assay proves the non-toxicity of the probe up to 100 mg mL(-1). A new homometallic dinuclear Cu(II) complex is afforded with a tetradentate Schiff base precursor. EPR interpretation and temperature dependent magnetic studies show that complex 1 has weak antiferromagnetic coupling and DFT computation is governed to explain the magneto-structural correlation.

  10. Crystal structure of the membrane-exposed domain from a respiratory quinol oxidase complex with an engineered dinuclear copper center.

    PubMed

    Wilmanns, M; Lappalainen, P; Kelly, M; Sauer-Eriksson, E; Saraste, M

    1995-12-19

    Cytochrome oxidase is a membrane protein complex that catalyzes reduction of molecular oxygen to water and utilizes the free energy of this reaction to generate a transmembrane proton gradient during respiration. The electron entry site in subunit II is a mixed-valence dinuclear copper center in enzymes that oxidize cytochrome c. This center has been lost during the evolution of the quinoloxidizing branch of cytochrome oxidases but can be restored by engineering. Herein we describe the crystal structures of the periplasmic fragment from the wild-type subunit II (CyoA) of Escherichia coli quinol oxidase at 2.5-A resolution and of the mutant with the engineered dinuclear copper center (purple CyoA) at 2.3-A resolution. CyoA is folded as an 11-stranded mostly antiparallel beta-sandwich followed by three alpha-helices. The dinuclear copper center is located at the loops between strands beta 5-beta 6 and beta 9-beta 10. The two coppers are at a 2.5-A distance and symmetrically coordinated to the main ligands that are two bridging cysteines and two terminal histidines. The residues that are distinct in cytochrome c and quinol oxidases are around the dinuclear copper center. Structural comparison suggests a common ancestry for subunit II of cytochrome oxidase and blue copper-binding proteins.

  11. Dinuclear Zinc (II) Complexes of Macrocyclic Polyamine Ligands Containing an Imidazolium Bridge: Synthesis, Characterization, and Their Interaction with Plasmid DNA

    PubMed Central

    Huang, Jun; Huang, Qing-Dong; Zhang, Ji; Zhou, Li-Hong; Li, Qiang-Lin; Li, Kun; Jiang, Ning; Lin, Hong-Hui; Wu, Jiang; Yu, Xiao-Qi

    2007-01-01

    Two novel macrocyclic polyamine ligands and their dinuclear zinc (II) complexes were synthesized and characterized. Their interaction with plasmid DNA was studied by gel electrophoresis and fluorescence quenching experiment. The result showed that these complexes could bind DNA efficiently under physiological conditions.

  12. Luminescence dynamics and {sup 13}C NMR characteristics of dinuclear complexes exhibiting coupled lanthanide(III) cation pairs

    SciTech Connect

    Matthews, K.D.; Bailey-Folkes, S.A.; Kahwa, I.A.

    1992-08-20

    Luminescence and cross-polarization magic angle spinning (CP-MAS) {sup 13}C NMR properties of lanthanide dinuclear macrocyclic complexes of a compartmental Schiff base chelate (1) derived from the condensation of 2,6-diformyl-p-cresol and 3,6-dioxa-1,8-octanediamine are reported. The Schiff base chromophore in 1 is a strong light absorber and an efficient sensitizer for intense Tb{sup 3+}({sup 5}D{sub 4}) and Eu{sup 3+}({sup 5}D{sub 0})(T < 110 K ) emission which does not exhibit self-quenching effects. Emission from Tb{sup 3+} is sensitized by the ligand singlet state; in striking contrast, Eu{sup 3+} emission is sensitized by the triplet state and reveals an unusual nonradiative quenching process at T > 110 K with a thermal barrier of {approx} 2300 cm{sup {minus}1}. Weak emission is observed from Dy{sup 3+}({sup 4}F{sub 9/2}), Sm{sup 3+}({sup 4}G{sub 5/2}), and Pr{sup 3+}({sup 1}D{sub 2}) diluted in Gd{sup 3+} (i.e., from Gd{sup 3+}-Ln{sup 3+} heteropairs, Ln = Pr, Sm, Dy). Intramolecular metal-metal (Ln-Ln = 4 {Angstrom}) interactions account for the greatly quenched emission from Sm{sup 3+}-Sm{sup 3+} and Dy{sup 3+}-Dy{sup 3+} homopairs compared to Gd{sup 3+}-Ln heteropairs (Ln = Sm, Dy). Gd{sup 3+}-Ln{sup 3+} emission lifetimes at 77 K are 1610 (Tb{sup 3+}), 890 (Eu{sup 3+}), 14 (Dy{sup 3+}) and {approx} 13 {mu}s (Sm{sup 3+}). Nonradiative relaxation processes at 77 K in dilute Ln{sup 3+}:Gd{sub 2}1(NO{sub 3}){sub 4}{center_dot}H{sub 2}O, being temperature independent for Sm{sup 3+} and Eu{sup 3+} but temperature dependent for Tb{sup 3+}, follow the energy gap law with {alpha} {approx} - 10{sup {minus}3} cm and B {approx} 2 x 10{sup 8} s{sup {minus}1}. CP-MAS data show paramagnetic broadening of {sup 13}C resonances which increases with the magnetic moment of Ln{sup 3+}. Surprisingly, no significant shifts in resonance positions corresponding to the changing nature of paramagnetic Ln{sup 3+} ions are observed. 43 refs., 8 figs., 2 tabs.

  13. Spiral Dinuclear Complexes of Tetradentate N(4) Diazine Ligands with Mn(II), Fe(II), Fe(III), Co(III), and Ni(II) Salts.

    PubMed

    Xu, Zhiqiang; Thompson, Laurence K.; Miller, David O.; Clase, Howard J.; Howard, Judith A. K.; Goeta, Andrés E.

    1998-07-13

    A series of dinuclear complexes of the tetradentate dipyridyl-diazine ligand PAHAP with Mn(II), Fe(II), Fe(III), Co(III), and Ni(II) salts is reported in which three ligands wrap themselves around the six-coordinate metal centers in a rare spiral-like fashion. A similar Fe(II) complex is found for the dipyrazinyl-diazine ligand PZHPZ. The ligands are severely twisted with dihedral angles between the metal chelate ring mean planes on each ligand in the range 50-70 degrees, values close to the expected twist angle for orthogonality between the bridging nitrogen atom p orbitals. Full structures are reported for the dinuclear complexes [Mn(2)(PAHAP)(3)](ClO(4))(4).5H(2)O (1), [Fe(2)(PAHAP)(3)](NO(3))(4).3H(2)O (2), [Fe(2)(PZHPZ)(3)](NO(3))(4).5H(2)O (5), [Co(2)(PAHAP)(3)](NO(3))(6).5H(2)O (6), and [Ni(2)(PAHAP)(3)][Ni(H(2)O)(6)](NO(3))(6).4.5H(2)O (7). Other derivatives [Fe(2)(PAHAP)(3)](ClO(4))(4).4H(2)O (3), [Fe(2)(PAHAP)(3)](ClO(4))(6).4.5H(2)O (4), [Ni(2)(PAHAP)(3)](ClO(4))(4).5H(2)O (8), and [Fe(PHAAP-H)(H(2)O)(2)(NO(3))](NO(3))(2) (9) are also reported. Complex 1 crystallized in the monoclinic system, space group C2/c, with a = 13.4086(2) Å, b = 32.0249(1) Å, c = 14.3132(2) Å, alpha = 90 degrees, beta = 115.635(1) degrees, gamma = 90 degrees, and Z = 4. Complex 2 crystallized in the cubic system, space group Pa&thremacr;, with a = b = c = 21.0024(1) Å, alpha = beta = gamma = 90 degrees, and Z = 8. Complex 5 crystallized in the monoclinic system, space group P2/n, with a = 14.039(3) Å, b = 11.335(6) Å, c = 14.6517(15) Å, beta = 96.852(11) degrees, and Z = 1. Complex 6 crystallized in the trigonal system, space group R&thremacr;c(h), with a = b = 17.386(2) Å, c = 32.15(2) Å, alpha = beta = 90 degrees, gamma = 120 degrees, and Z = 4. Complex 7 crystallized in the trigonal system, space group R&thremacr;c, with a = b = 17.3737(3) Å, c = 33.235(6) Å, alpha = beta = 90 degrees, gamma = 120 degrees, and Z = 27. Weak ferromagnetic coupling was observed for 1

  14. New dinuclear cobalt(II) and zinc(II) complexes of a carboxylate-rich dinucleating ligand: synthesis, structure, spectroscopic characterization, and their interactions with sugars.

    PubMed

    Bera, Manindranath; Curtiss, Ashley B S; Musie, Ghezai T; Powell, Douglas R

    2012-11-19

    Sugar-metal ion interactions in aqueous medium are involved in many biochemical processes such as the transport and storage of metals, the function and regulation of sugar-metabolizing metalloenzymes, the mechanism of action of metal-containing pharmaceuticals, and toxic metal metabolism. To understand such interactions we synthesized and fully characterized two new dinuclear cobalt(II) and zinc(II) complexes as carbohydrate binding models for xylose/glucose isomerases (XGI). Synthesis of the dicobalt complex, Na3[Co2(ccdp)(μ-HCO2)]BF4·9H2O·2CH3OH (1), was performed in methanol with stoichiometric amounts of Co(BF4)2·6H2O and the dinucleating ligand, H5ccdp (H5ccdp = N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol), in the presence of NaOH at ambient temperature in an argon glovebox. Similarly, the dizinc complex, [NMe4]2[Zn2(ccdp)(μ-OAc)]·CH3OH (2), was synthesized from Zn(OAc)2·2H2O and H5ccdp in the presence of NMe4OH at ambient temperature in methanol. Binding of the complexes with carbohydrates was investigated under different reaction conditions. In aqueous alkaline media, complexes 1 and 2 showed chelating ability towards the biologically important sugars, d-glucose and d-xylose, and a polyalcohol enzyme inhibitor (xylitol). In solution, each complex forms a 1:1 complex-substrate bound product with specific binding constant values. Synthesis, characterization details, and substrate binding using spectroscopic techniques and single-crystal X-ray diffraction are reported.

  15. Dissymmetrical U-shaped π-stacked supramolecular assemblies by using a dinuclear Cu(I) clip with organophosphorus ligands and monotopic fully π-conjugated ligands.

    PubMed

    El Sayed Moussa, Mehdi; Guillois, Kevin; Shen, Wenting; Réau, Régis; Crassous, Jeanne; Lescop, Christophe

    2014-11-03

    Reactions between the U-shaped binuclear Cu(I) complex A that bears short metal-metal distances and the cyano-capped monotopic π-conjugated ligands 1-5 that carry gradually bulkier polyaromatic terminal fragments lead to the formation of π-stacked supramolecular assemblies 6-10, respectively, in yields of 50-80 %. These derivatives have been characterized by multinuclear NMR spectroscopic analysis and X-ray diffraction studies. Their solid-state structures show the selective formation of U-shaped supramolecular assemblies in which two monotopic π-conjugated systems present large (6, 7, and 9) or medium (8 and 10) intramolecular π overlap, thus revealing π-π interactions. These assemblies self-organize into head-to-tail π-stacked dimers that in turn self-assemble to afford infinite columnar π stacks. The nature, extent, and complexity of the intermolecular contacts within the head-to-tail π-stacked dimer depend on the nature of the terminal polyaromatic fragment carried by the cyano-capped monotopic ligand, but it does not alter the result of the self-assembling process. These results demonstrate that the dinuclear molecular clip A that bears short metal-metal distances allows selective supramolecular assembly processes driven by the formation of intra- and intermolecular short π-π interactions in the resulting self-assembled structures; thus, demonstrating that their shape is not only dictated by the symmetry of the building blocks. This approach opens perspectives toward the formation of extended π-stacked columns based on dissymmetrical and functional π-conjugated systems.

  16. Heterobimetallic dinuclear lanthanide alkoxide complexes as acid-base difunctional catalysts for transesterification.

    PubMed

    Zeng, Ruijie; Sheng, Hongting; Zhang, Yongcang; Feng, Yan; Chen, Zhi; Wang, Junfeng; Chen, Man; Zhu, Manzhou; Guo, Qingxiang

    2014-10-03

    A practical lanthanide(III)-catalyzed transesterification of carboxylic esters, weakly reactive carbonates, and much less-reactive ethyl silicate with primary and secondary alcohols was developed. Heterobimetallic dinuclear lanthanide alkoxide complexes [Ln2Na8{(OCH2CH2NMe2)}12(OH)2] (Ln = Nd (I), Sm (II), and Yb (III)) were used as highly active catalysts for this reaction. The mild reaction conditions enabled the transesterification of various substrates to proceed in good to high yield. Efficient activation of transesterification may be endowed by the above complexes as cooperative acid-base difunctional catalysts, which is proposed to be responsible for the higher reactivity in comparison with simple acid/base catalysts.

  17. Synthesis, cytotoxicity, and apoptosis induction study of antitumor dinuclear platinum(II) complexes.

    PubMed

    Xu, Gang; Gou, Shaohua; Gao, Chuanzhu

    2013-04-01

    Five novel dinuclear platinum(II) complexes with a new chiral ligand, 3-(2-amino-cyclohexylamino)-propionic acid (HP), were designed, prepared and spectrally characterized. The in vitro cytotoxicities of these compounds were evaluated against the HepG-2, MCF-7, A549, and HCT-116 cell lines. The results indicated that all compounds showed cytotoxicity towards the HepG-2 cell line. Particularly, complex X5, which has SO 4₂₋ as a bridge, exhibited better cytotoxicity than carboplatin or oxaliplatin against all selected cell lines. Moreover, double dyeing flow cytometric resection indicated that the target compounds inhibited tumor cell growth by inducing apoptosis. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Two new oximate-bridged square-planar dinuclear nickel(II) complexes.

    PubMed

    Bera, Manindranath; Noll, Bruce C

    2007-12-01

    The synthesis and characterization of two new dinuclear nickel(II) complexes, namely bis{mu-3-[2-(dimethylamino)ethylimino]butan-2-one oximato}dinickel(II) bis(perchlorate) acetonitrile solvate, [Ni2(C8H16N3O)2](ClO4)2 x CH3CN, (I), and bis{mu-3-[2-(dimethylamino)ethylimino]-3-phenylpropan-2-one oximato}dinickel(II) bis(perchlorate), [Ni2(C13H18N3O)2](ClO4)2, (II), are reported. Single-crystal X-ray analyses of the complexes reveal that the nickel(II) ions are in square-planar N3O environments and form six-membered (NiNO)2 metallacycles. The cation in (II) possesses crystallographically imposed inversion symmetry.

  19. Magnetic exchange couplings from noncollinear perturbation theory: dinuclear CuII complexes.

    PubMed

    Phillips, Jordan J; Peralta, Juan E

    2014-08-07

    To benchmark the performance of a new method based on noncollinear coupled-perturbed density functional theory [J. Chem. Phys. 138, 174115 (2013)], we calculate the magnetic exchange couplings in a series of triply bridged ferromagnetic dinuclear Cu(II) complexes that have been recently synthesized [Phys. Chem. Chem. Phys. 15, 1966 (2013)]. We find that for any basis-set the couplings from our noncollinear coupled-perturbed methodology are practically identical to those of spin-projected energy-differences when a hybrid density functional approximation is employed. This demonstrates that our methodology properly recovers a Heisenberg description for these systems, and is robust in its predictive power of magnetic couplings. Furthermore, this indicates that the failure of density functional theory to capture the subtle variation of the exchange couplings in these complexes is not simply an artifact of broken-symmetry methods, but rather a fundamental weakness of current approximate density functionals for the description of magnetic couplings.

  20. Cellular and biomolecular responses of human ovarian cancer cells to cytostatic dinuclear platinum(II) complexes.

    PubMed

    Lin, Miaoxin; Wang, Xiaoyong; Zhu, Jianhui; Fan, Damin; Zhang, Yangmiao; Zhang, Junfeng; Guo, Zijian

    2011-03-01

    Polynuclear platinum(II) complexes represent a class of potential anticancer agents that have shown promising pharmacological properties in preclinical studies. The nature of cellular responses induced by these complexes, however, is poorly understood. In this research, the cellular responses of human ovarian cancer COC1 cells to dinuclear platinum(II) complexes {[cis-Pt(NH₃)₂Cl]₂L¹}(NO₃)₂ (1) and {[cis-Pt(NH₃)₂Cl]₂L²}(NO₃)₂ (2) (L¹ = α,α'-diamino-p-xylene, L² = 4,4'-methylenedianiline) has been studied using cisplatin as a reference. The effect of platinum complexes on the proliferation, death mode, mitochondrial membrane potential, and cell cycle progression has been examined by MTT assay and flow cytometry. The activation of cell cycle checkpoint kinases (CHK1/2), extracellular signal-regulated kinases (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) of the cells by the complexes has also been analyzed using phospho-specific flow cytometry. Complex 1 is more cytotoxic than complex 2 and cisplatin at most concentrations; complex 2 and cisplatin are comparably cytotoxic. These complexes kill the cells through an apoptotic or apoptosis-like pathway characterized by exposure of phosphatidylserine and dissipation of mitochondrial membrane potential. Complex 1 shows the strongest inductive effect on the morphological changes of the cells, followed by cisplatin and complex 2. Complexes 1 and 2 arrest the cell cycle in G2 or M phase, while cisplatin arrests the cell cycle in S phase. The influence of these complexes on CHK1/2, ERK1/2, and p38 MAPK varies with the dose of the drugs or reaction time. Activation of phospho-ERK1/2 and phospho-p38 MAPK by these complexes is closely related to the cytostatic activity. The results demonstrate that dinuclear platinum(II) complexes can induce some cellular responses different from those caused by cisplatin.

  1. Decomposition of dinuclear manganese complexes for the preparation of nanostructured oxide materials.

    PubMed

    Hill, Jonathan P; Palza, Humberto; Alam, Sher; Ariga, Katsuhiko; Schumacher, Amy Lea; D'Souza, Francis; Anson, Christopher E; Powell, Annie K

    2008-09-15

    The crystal structures of several dinuclear complexes of manganese are reported, and the decomposition and analysis of the nanostructured products derived from them are presented. 1,4,7,10-Tetraazacyclododecane (cyclen) forms dinuclear complexes 1-4 containing doubly oxo-bridged or oxo-acetato bridging ligands depending on the manganese salt used for the reaction. Doubly oxo-bridged 1 crystallizes in the orthorhombic space group Pnma, a = 22.3850(14) A, b = 9.1934(5) A, c = 13.2424(10) A, V = 2725.2(3) A(3). 2, containing [Mn(SCN)5](3-) conteranions, crystallizes in monoclinic space group I2/a with a = 18.2699(10) A, b = 11.2384(6) A, c = 18.6432(9) A, alpha = 90.00 degrees, beta = 114.510(6) degrees, gamma = 90.00 degrees, V = 3483.0(3) A(3). Oxo-acetato-bridged 3 crystallizes in orthorhombic space group Pca21, a = 13.9322(11) A, b = 16.2332(13) A, c = 14.6794(8) A, V = 3320.0(4) A(3). Compound 4 consists of a templated quasi-one-dimensional manganese oxalate crystallized in the triclinic space group P1, a = 9.5442(11) A, b = 10.3758(10) A, c = 21.851(2) A, alpha = 83.720(12) degrees, beta = 80.106(13) degrees, gamma = 85.457(13) degrees, V = 2114.9(4) A(3). Compounds 1, 3, and 4 decompose to nanostructured oxide materials, which may be isolated in bulk as lamellar-structured particles or microspheres or deposited on substrates.

  2. Catalytic photooxidation of alcohols by an unsymmetrical tetra(pyridyl)pyrazine-bridged dinuclear Ru complex.

    PubMed

    Chen, Weizhong; Rein, Francisca N; Scott, Brian L; Rocha, Reginaldo C

    2011-05-09

    The dinuclear complexes [(tpy)Ru(tppz)Ru(bpy)(L)](n+) (where L is Cl(-) or H(2)O, tpy and bpy are the terminal ligands 2,2':6',2''-terpyridine and 2,2'-bipyridine, and tppz is the bridging backbone 2,3,5,6-tetrakis(2-pyridyl)pyrazine) were prepared and structurally and electronically characterized. The mononuclear complexes [(tpy)Ru(tppz)](2+) and [(tppz)Ru(bpy)(L)](m+) were also prepared and studied for comparison. The proton-coupled, multi-electron photooxidation reactivity of the aquo dinuclear species was shown through the photocatalytic dehydrogenation of a series of primary and secondary alcohols. Under simulated solar irradiation and in the presence of a sacrificial electron acceptor, the photoactivated chromophore-catalyst complex (in aqueous solutions at room temperature and ambient pressure conditions) can perform the visible-light-driven conversion of aliphatic and benzylic alcohols into the corresponding carbonyl products (i.e., aldehydes or ketones) with 100% product selectivity and several tens of turnover cycles, as probed by NMR spectroscopy and gas chromatography. Moreover, for aliphatic substrates, the activity of the photocatalyst was found to be highly selective toward secondary alcohols, with no significant product formed from primary alcohols. Comparison of the activity of this tppz-bridged complex with that of the analogue containing a back-to-back terpyridine bridge (tpy-tpy, i.e., 6',6''-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine) demonstrated that the latter is a superior photocatalyst toward the oxidation of alcohols. The much stronger electronic coupling with significant delocalization across the strongly electron-accepting tppz bridge facilitates charge trapping between the chromophore and catalyst centers and therefore is presumably responsible for the decreased catalytic performance.

  3. Dinuclear iridium(III) complexes consisting of back-to-back tpy-(ph)n-tpy bridging ligands (n = 0, 1, or 2) and terminal cyclometallating tridentate N-C-N ligands.

    PubMed

    Auffrant, Audrey; Barbieri, Andrea; Barigelletti, Francesco; Collin, Jean-Paul; Flamigni, Lucia; Sabatini, Cristiana; Sauvage, Jean-Pierre

    2006-12-25

    Three dinuclear iridium(III) complexes consisting of a conjugated bis-tpy type bridging ligand and cyclometallating capping tridentate ligands of the 1,3-di-2-pyridylbenzene family have been prepared (tpy, 2,2',6',2' '-terpyridine). The two tpy units of the bridge are connected via their back-positions (4') either directly or with a p-phenylene or p-biphenylene spacer. The synthesis relies on the reaction between the dinuclear [Ir(dpb)Cl2]2 complex (dpb-H =1,3-dipyridyl-4,6-dimethylbenzene) and the corresponding bis-tpy ligand. Electrochemical measurements afford metal-centered oxidation and ligand-centered reduction potentials; from the oxidation steps, no evidence is obtained for a strong coupling between the two iridium(III) subunits of the dinuclear species. For all complexes, ground-state absorption data in the 380 nm to visible region show a trend which is consistent with the presence of charge-transfer (CT) transitions involving different degrees of electronic delocalization at the bridging ligands. (dpb)Ir(tpy-tpy)Ir(dpb)4+ exhibits an appreciable luminescence at room temperature (phi = 3.0 x 10(-3); tau = 3.3 ns), whereas no emission from the other binuclear complexes is detected. All binuclear complexes luminesce at 77 K, and a metal-to-ligand CT nature for (dpb)Ir(tpy-tpy)Ir(dpb)4+ is suggested, whereas a ligand-centered (LC) emission is proposed for (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+ on the basis of the comparison with the phosphorescence properties of the free bridging ligand, tpy-(ph)2-tpy. Transient absorbance experiments at room temperature afford the absorption spectra and lifetimes of the non-emissive excited states. For (dpb)Ir(tpy-ph-tpy)Ir(dpb)4+ and (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+, the spectra exhibit a broad profile peaking around 780 nm, quite intense in the case of (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+, and lifetimes of 160 and 440 ps, respectively.

  4. Theoretical Proposal for the Whole Phosphate Diester Hydrolysis Mechanism Promoted by a Catalytic Promiscuous Dinuclear Copper(II) Complex.

    PubMed

    Esteves, Lucas F; Rey, Nicolás A; Dos Santos, Hélio F; Costa, Luiz Antônio S

    2016-03-21

    The catalytic mechanism that involves the cleavage of the phosphate diester model BDNPP (bis(2,4-dinitrophenyl) phosphate) catalyzed through a dinuclear copper complex is investigated in the current study. The metal complex was originally designed to catalyze catechol oxidation, and it showed an interesting catalytic promiscuity case in biomimetic systems. The current study investigates two different reaction mechanisms through quantum mechanics calculations in the gas phase, and it also includes the solvent effect through PCM (polarizable continuum model) single-point calculations using water as solvent. Two mechanisms are presented in order to fully describe the phosphate diester hydrolysis. Mechanism 1 is of the S(N)2 type, which involves the direct attack of the μ-OH bridge between the two copper(II) ions toward the phosphorus center, whereas mechanism 2 is the process in which hydrolysis takes place through proton transfer between the oxygen atom in the bridging hydroxo ligand and the other oxygen atom in the phosphate model. Actually, the present theoretical study shows two possible reaction paths in mechanism 1. Its first reaction path (p1) involves a proton transfer that occurs immediately after the hydrolytic cleavage, so that the proton transfer is the rate-determining step, which is followed by the entry of two water molecules. Its second reaction path (p2) consists of the entry of two water molecules right after the hydrolytic cleavage, but with no proton transfer; thus, hydrolytic cleavage is the rate-limiting step. The most likely catalytic path occurs in mechanism 1, following the second reaction path (p2), since it involves the lowest free energy activation barrier (ΔG(⧧) = 23.7 kcal mol(-1), in aqueous solution). A kinetic analysis showed that the experimental k(obs) value of 1.7 × 10(-5) s(-1) agrees with the calculated value k1 = 2.6 × 10(-5) s(-1); the concerted mechanism is kinetically favorable. The KIE (kinetic isotope effect) analysis

  5. Cycloheptatrienyl trianion: an elusive bridge in the search of exchange coupled dinuclear organolanthanide single-molecule magnets.

    PubMed

    Harriman, Katie L M; Le Roy, Jennifer J; Ungur, Liviu; Holmberg, Rebecca J; Korobkov, Ilia; Murugesu, Muralee

    2017-01-01

    The preparation of η-cyclopentadienyl (η(5)-C5R5), η-arene (η(6)-C6R6), and η-cyclooctatetraenyl (η(8)-C8R8) bridging motifs are common in organometallic chemistry; however, the synthetic preparation of η-cycloheptatrienyl (η(7)-C7R7) bridging motifs has remained a synthetic challenge in 4f chemistry. To this end, we have developed a synthetic route towards a series of rare dinuclear organolanthanide inverse sandwich complexes containing the elusive η(7)-C7H7 bridge. Herein, we present the structures and magnetic properties of the lanthanide inverse sandwich complexes [KLn2(C7H7)(N(SiMe3)2)4] (Ln = Gd(III) (1), Dy(III) (2), Er(III) (3)) and [K(THF)2Er2(C7H7)(N(SiMe3)2)4] (4). These compounds are the first single-molecule magnets (SMMs) to feature this type of bridging motif. Furthermore, η(7)-C7H7 was found to efficiently promote ferromagnetic exchange interactions between metal ions. Variable temperature dc magnetic susceptibility measurements and subsequent simulations give significant exchange constants of J = +1.384, +1.798, and +3.149 cm(-1) and dipolar constants of J = -0.603, -0.601, and -0.475 cm(-1) for compounds 2-4, respectively. Frequency dependent ac susceptibility measurements under an applied static field resulted in the observation of dual relaxation processes, and brought forth a greater understanding of the intermolecularly driven process at high frequency. In particular, this type of analysis of compound 3 under 800 Oe elicited an energy barrier of Ueff = 58 K. Ab initio calculations were performed in order to understand the nature of magnetic coupling and the origin of slow relaxation of magnetisation. Through these studies, the effect of the amido ancillary ligands on the magnetic axiality of the lanthanide ions was found to be competitive with the crystal field of the η(7)-C7H7 π-electron cloud. Our findings suggest that the tunability of the dipolar and exchange components of the magnetic interactions lie within the dihedral angle

  6. Synthesis and structural characterization of dinuclear Cd2+, Hg2+ and Fe2+ complexes with neutral bi and tetradentate flexible pyrazole-based ligands

    NASA Astrophysics Data System (ADS)

    Beheshti, Azizolla; Lalegani, Arash; Behvandi, Fatemeh; Safaeiyan, Forough; Sarkarzadeh, Afsoon; Bruno, Giuseppe; Amiri Rudbari, Hadi

    2015-02-01

    Four new complexes of [Hg2Cl4(bpp)]n (1), [Hg2Cl4(tdmpp)] (2), [Cd2I4(tdmpp)] (3) and [Fe2Cl4(tdmpp)] (4) were prepared by using the neutral N-donor ligands 1,3-bis(3,5-dimethyl-1-pyrazolyl)propane (bpp) and 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazolyl)propane (tdmpp) with different flexibility and appropriate metal salts of Cd(II), Hg(II) and Fe(II) ions. These compounds were characterized by the infrared spectroscopy, elemental analysis and X-ray crystallography. Flexible ligands and non-covalent Csbnd H⋯Cl hydrogen bonds play a major role in the crystal packing of compounds 1, 2 and 4. In the two-dimensional non-covalent structure of 1, there are two distinctly different coordination modes for the mercury atoms. One mercury atom has pseudo-trigonal bipyramidal geometry and the other adopts a distorted tetrahedral environment. In the dinuclear structures of 2 and 4 the neutral molecules are linked together by the Csbnd H⋯Cl hydrogen bonds, forming an infinite one-dimensional zigzag chain structure. Compounds 2-4 are isostructural with each other.

  7. Visible Light-Induced Electron Transfer from Di-mu-oxo Bridged Dinuclear Mn Complexes to Cr Centers in Silica Nanopores

    SciTech Connect

    Frei, Heinz; Weare, Walter W.; Pushkar, Yulia; Yachandra, Vittal K.; Frei, Heinz

    2008-06-03

    The compound (bpy)2MnIII(mu-O)2MnIV(bpy)2, a structural model relevant for the photosynthetic water oxidation complex, was coupled to single CrVI charge-transfer chromophores in the channels of the nanoporous oxide AlMCM-41. Mn K-edge EXAFS spectroscopy confirmed that the di-mu-oxo dinuclear Mn core of the complex is unaffected when loaded into the nanoscale pores. Observation of the 16-line EPR signal characteristic of MnIII(mu-O)2MnIV demonstrates that the majority of the loaded complexes retained their nascent oxidation state in the presence or absence of CrVI centers. The FT-Raman spectrum upon visible light excitation of the CrVI-OII --> CrV-OI ligand-to-metal charge-transfer reveals electron transfer from MnIII(mu-O)2MnIV (Mn-O stretch at 700 cm-1) to CrVI, resulting in the formation of CrV and MnIV(mu-O)2MnIV (Mn-O stretch at 645 cm-1). All initial and final states are directly observed by FT-Raman or EPR spectroscopy, and the assignments corroborated by X-ray absorption spectroscopy measurements. The endoergic charge separation products (DELTA Eo = -0.6 V) remain after several minutes, which points to spatial separation of CrV and MnIV(mu-O)2MnIV as a consequence of hole (OI) hopping as a major contributing mechanism. This is the first observation of visible light-induced oxidation of a potential water oxidation complex by a metal charge-transfer pump in a nanoporous environment. These findings will allow for the assembly and photochemical characterization of well defined transition metal molecular units, with the ultimate goal of performing endothermic, multi-electron transformations that are coupled to visible light electron pumps in nanostructured scaffolds.

  8. Lidar Calibration Centre

    NASA Astrophysics Data System (ADS)

    Pappalardo, Gelsomina; Freudenthaler, Volker; Nicolae, Doina; Mona, Lucia; Belegante, Livio; D'Amico, Giuseppe

    2016-06-01

    This paper presents the newly established Lidar Calibration Centre, a distributed infrastructure in Europe, whose goal is to offer services for complete characterization and calibration of lidars and ceilometers. Mobile reference lidars, laboratories for testing and characterization of optics and electronics, facilities for inspection and debugging of instruments, as well as for training in good practices are open to users from the scientific community, operational services and private sector. The Lidar Calibration Centre offers support for trans-national access through the EC HORIZON2020 project ACTRIS-2.

  9. Chloride-Bridged Dinuclear Rhodium(III) Complexes Bearing Chiral Diphosphine Ligands: Catalyst Precursors for Asymmetric Hydrogenation of Simple Olefins.

    PubMed

    Kita, Yusuke; Hida, Shoji; Higashihara, Kenya; Jena, Himanshu Sekhar; Higashida, Kosuke; Mashima, Kazushi

    2016-07-11

    Efficient rhodium(III) catalysts were developed for asymmetric hydrogenation of simple olefins. A new series of chloride-bridged dinuclear rhodium(III) complexes 1 were synthesized from the rhodium(I) precursor [RhCl(cod)]2 , chiral diphosphine ligands, and hydrochloric acid. Complexes from the series acted as efficient catalysts for asymmetric hydrogenation of (E)-prop-1-ene-1,2-diyldibenzene and its derivatives without any directing groups, in sharp contrast to widely used rhodium(I) catalytic systems that require a directing group for high enantioselectivity. The catalytic system was applied to asymmetric hydrogenation of allylic alcohols, alkenylboranes, and unsaturated cyclic sulfones. Control experiments support the superiority of dinuclear rhodium(III) complexes 1 over typical rhodium(I) catalytic systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Maple Leaf Outdoor Centre.

    ERIC Educational Resources Information Center

    Maguire, Molly; Gunton, Ric

    2000-01-01

    Maple Leaf Outdoor Centre (Ontario) has added year-round outdoor education facilities and programs to help support its summer camp for disadvantaged children. Schools, youth centers, religious groups, and athletic teams conduct their own programs, collaborate with staff, or use staff-developed programs emphasizing adventure education and personal…

  11. Implementing Responsibility Centre Budgeting

    ERIC Educational Resources Information Center

    Vonasek, Joseph

    2011-01-01

    Recently, institutes of higher education (universities) have shown a renewed interest in organisational structures and operating methodologies that generate productivity and innovation; responsibility centre budgeting (RCB) is one such process. This paper describes the underlying principles constituting RCB, its origin and structural elements, and…

  12. The Iranian Documentation Centre.

    ERIC Educational Resources Information Center

    Harvey, John F.

    The purpose of the Iranian Documentation Centr (Irandoc) was to collect that portion of the world's literature which was pertinent to Iran's research interests, to organize that material, and to promote its use by Iranian researchers. Stated more succinctly, Irandoc's purpose was to obtain ready access to the world's scientific literature in order…

  13. Winnipeg Centre Project.

    ERIC Educational Resources Information Center

    Manitoba Dept. of Education, Winnipeg.

    The Winnipeg Centre Project is a field-based, work-study program that attempts to create more appropriate education for the inner-city child. Sponsored by the Planning and Research Branch of the Department of Colleges and Universities Affairs and administered by Brandon University in consultation with the Winnipeg School Division, the project is…

  14. Discovering a Discovery Centre

    ERIC Educational Resources Information Center

    McCullagh, John; Stewart, James; Greenwood, Julian

    2007-01-01

    There has recently been a growth in the popularity of "science centres" and this development provides an excellent opportunity to support the primary science curriculum. Their use is therefore well worth including within initial teacher education courses. Hence, undergraduate student teachers at Stranmillis University College Belfast may…

  15. Discovering a Discovery Centre

    ERIC Educational Resources Information Center

    McCullagh, John; Stewart, James; Greenwood, Julian

    2007-01-01

    There has recently been a growth in the popularity of "science centres" and this development provides an excellent opportunity to support the primary science curriculum. Their use is therefore well worth including within initial teacher education courses. Hence, undergraduate student teachers at Stranmillis University College Belfast may…

  16. Implementing Responsibility Centre Budgeting

    ERIC Educational Resources Information Center

    Vonasek, Joseph

    2011-01-01

    Recently, institutes of higher education (universities) have shown a renewed interest in organisational structures and operating methodologies that generate productivity and innovation; responsibility centre budgeting (RCB) is one such process. This paper describes the underlying principles constituting RCB, its origin and structural elements, and…

  17. Wycheproof Education Centre.

    ERIC Educational Resources Information Center

    Sweetnam and Godfrey, Melbourne (Australia).

    The Wycheproof township in New South Wales (Australia) is the regional center for a grain farming community. The Wycheproof Education Centre was formed by the merger of a separate primary and secondary school (on one site with existing buildings), into a single governing body that is educationally structured into junior, middle, and senior…

  18. Wycheproof Education Centre.

    ERIC Educational Resources Information Center

    Sweetnam and Godfrey, Melbourne (Australia).

    The Wycheproof township in New South Wales (Australia) is the regional center for a grain farming community. The Wycheproof Education Centre was formed by the merger of a separate primary and secondary school (on one site with existing buildings), into a single governing body that is educationally structured into junior, middle, and senior…

  19. Mono- and dinuclear osmium N,N'-di- and tetraphenylbipyridyls and extended bipyridyls. Synthesis, structure and electrochemistry.

    PubMed

    Esteruelas, Miguel A; Fernández, Israel; Gómez-Gallego, Mar; Martín-Ortíz, Mamen; Molina, Pedro; Oliván, Montserrat; Otón, Francisco; Sierra, Miguel A; Valencia, Marta

    2013-03-14

    The efficient synthesis of mono- and dinuclear Os(IV) bipyridyl complexes is reported. These compounds show a two-step oxidation process leading to notable structural changes, which are reflected in their emission properties. During the second oxidation process a tetracation with a hydride-dihydrogen structure (instead of a trihydride) is formed. This results in a significant bathochromic shift of the emission band, accompanied by a moderate increase in intensity.

  20. Luminescence Studies of the Intracellular Distribution of a Dinuclear Gold(I) N-Heterocyclic Carbene Complex

    SciTech Connect

    Barnard, Peter J.; Wedlock, Louise E.; Baker, Murray V.; Berners-Price, Susan J.; Joyce, David A.; Skelton, Brian W.; Steer, James H.

    2008-10-03

    A bidentate cyclophane N-heterocyclic carbene ligand has been used to synthesize a new dinuclear Au{sup I} complex of the formula [Au{sub 2}L{sub 2}]{sup 2+}. The short Au {hor_ellipsis} Au distance imposed by the rigid cyclophane ligand leads to a red-shifted luminescence profile that enables the complex to be used as a luminescent probe for distribution studies in single living cancer cells.

  1. Dinuclear palladium complexes with two ligand-centered radicals and a single bridging ligand: subtle tuning of magnetic properties.

    PubMed

    Broere, Daniël L J; Demeshko, Serhiy; de Bruin, Bas; Pidko, Evgeny A; Reek, Joost N H; Siegler, Maxime A; Lutz, Martin; van der Vlugt, Jarl Ivar

    2015-04-07

    The facile and tunable preparation of unique dinuclear [(L(⋅))Pd-X-Pd(L(⋅))] complexes (X = Cl or N3), bearing a ligand radical on each Pd, is disclosed, as well as their magnetochemistry in solution and solid state is reported. Chloride abstraction from [PdCl(NNO(ISQ))] (NNO(ISQ) = iminosemiquinonato) with TlPF6 results in an unusual monochlorido-bridged dinuclear open-shell diradical species, [{Pd(NNO(ISQ))}2(μ-Cl)](+), with an unusually small Pd-Cl-Pd angle (ca. 93°, determined by X-ray). This suggests an intramolecular d(8)-d(8) interaction, which is supported by DFT calculations. SQUID measurements indicate moderate antiferromagnetic spin exchange between the two ligand radicals and an overall singlet ground state in the solid state. VT EPR spectroscopy shows a transient signal corresponding to a triplet state between 20 and 60 K. Complex 2 reacts with PPh3 to generate [Pd(NNO(ISQ))(PPh3)](+) and one equivalent of [PdCl(NNO(ISQ))]. Reacting an 1:1 mixture of [PdCl(NNO(ISQ))] and [Pd(N3)(NNO(ISQ))] furnishes the 1,1-azido-bridged dinuclear diradical [{Pd(NNO(ISQ))}2(κ(1)-N;μ-N3](+), with a Pd-N-Pd angle close to 127° (X-ray). Magnetic and EPR measurements indicate two independent S = 1/2 spin carriers and no magnetic interaction in the solid state. The two diradical species both show no spin exchange in solution, likely because of unhindered rotation around the Pd-X-Pd core. This work demonstrates that a single bridging atom can induce subtle and tunable changes in structural and magnetic properties of novel dinuclear Pd complexes featuring two ligand-based radicals. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Effects of Novel Dinuclear Cisplatinum(II) Complexes on the Electrical Properties of Human Molt-4 Leukemia Cells.

    PubMed

    Dobrzyńska, Izabela; Skrzydlewska, Elżbieta; Figaszewski, Zbigniew A

    2015-04-01

    The aim of this study was to determine the influence of cisplatin and novel dinuclear platinum(II) complexes on the membrane electrical properties and lipid peroxidation levels of the Molt-4 human leukemia cell line. Changes in cell function may affect the basal electrical surface properties of cell membranes. These changes can be detected using electrokinetic measurements. Surface charge densities of Molt-4 cells were measured as a function of pH. A four-component equilibrium model was used to describe the interaction between the ions in solution and on cell membrane surfaces. Agreement was found between the experimental and theoretical charge variation curves of the leukemia cells at pH 2.5-9. Lipid peroxidation was estimated by measuring levels of 8-iso-prostaglandine F2α [isoprostanes]. Acid and base functional group concentrations and average association constants with hydroxyl ions were smaller in cisplatin- or dinuclear platinum(II) complex-treated leukemia cell membranes compared to those in untreated cancer cells, and the average association constants with hydrogen ions were higher. Levels of lipid peroxidation products in cisplatin- or dinuclear platinum(II) complex-treated leukemia cell were higher than those found in untreated cancer cells.

  3. Structural, photoluminescence, and theoretical DFT studies of gold(I) and silver(I) metallacycle dinuclear complexes of 1-methylbenzimidazolediphenyl phosphine (MBDP) ligand

    NASA Astrophysics Data System (ADS)

    Jenkins, Darkus E.; Assefa, Zerihun

    2017-04-01

    The synthesis and structural characterization of the bridging ligand, 1-methyl benzimidazole diphenylphosphine (MBDP) and its coordination with Au(I) and Ag(I) metal ions is reported. Two ligands coordinate to the metal ions in head to tail fashion forming a metallacycle coordination consisting of strong M-M bonding interaction with Ausbnd Au = 2.808 and Agsbnd Ag = 3.017 Å. Linear coordination is observed for the gold, while the silver shows distorted tetrahedral arrangement. X-ray crystal data of [(MBDP)2Au2](CH3CN)(BF4)2 (2) crystallizes in the monoclinic system with the space group of P21/n with cell constants of a = 8.9993 (8) Å, b = 19.6166 (18) Å, c = 13.4484 (12) Å, β = 100.966 (2)°, R = 0.026, and Rw = 0.064. The structure of [(MBDP)2(CH3CN)4Ag2](BF4)2, (3) crystallizes in the P (-)1 space group and the unit cell is a = 10.5423 (10) Å, b = 10.7638 (10) Å, c = 12.3530 (12) Å; α = 88.592 (3)°, β = 73.097 (3)°, γ = 84.422 (3)°, V = 1334.8 (2) Å3 with Z = 1, R = 0.034 and Rw = 0.093. The coordinating ligand as well as both dinuclear compounds reported here are luminescent in the near UV region. As supported by the DFT theoretical work, the emission is suggested to be primarily ligand based π- π* transition.

  4. SPOT4 Management Centre

    NASA Technical Reports Server (NTRS)

    Labrune, Yves; Labbe, X.; Roussel, A.; Vielcanet, P.

    1994-01-01

    In the context of the CNES SPOT4 program CISI is particularly responsible for the development of the SPOT4 Management Centre, part of the SPOT4 ground control system located at CNES Toulouse (France) designed to provide simultaneous control over two satellites. The main operational activities are timed to synchronize with satellite visibilities (ten usable passes per day). The automatic capability of this system is achieved through agenda services (sequence of operations as defined and planned by operator). Therefore, the SPOT4 Management Centre offers limited, efficient and secure human interventions for supervision and decision making. This paper emphasizes the main system characteristics as degree of automation, level of dependability and system parameterization.

  5. Elderly Care Centre

    NASA Astrophysics Data System (ADS)

    Wagiman, Aliani; Haja Bava Mohidin, Hazrina; Ismail, Alice Sabrina

    2016-02-01

    The demand for elderly centre has increased tremendously abreast with the world demographic change as the number of senior citizens rose in the 21st century. This has become one of the most crucial problems of today's era. As the world progress into modernity, more and more people are occupied with daily work causing the senior citizens to lose the care that they actually need. This paper seeks to elucidate the best possible design of an elderly care centre with new approach in order to provide the best service for them by analysing their needs and suitable activities that could elevate their quality of life. All these findings will then be incorporated into design solutions so as to enhance the living environment for the elderly especially in Malaysian context.

  6. International Seismological Centre

    USGS Publications Warehouse

    Spall, H.; Hughes, A.

    1979-01-01

    The International Seismological Centre had its origins when the British seismologist Professor John Milne returned to England from Japan in 1895 to retire at Shide on the Isle of Eight. In cooperation with the British Association for the Advancement of Science, Milne had set up a number of seismographic stations around the world and, while Tokyo, had published a Catalogue of 8,33 Earthquakes Recorded in Japan, 1885-1892. 

  7. Dinuclear [(V(V)O(putrebactin))2(μ-OCH3)2] formed in solution as established from LC-MS measurements using 50V-enriched V2O5.

    PubMed

    Soe, Cho Zin; Pakchung, Amalie A H; Codd, Rachel

    2014-06-02

    (VI)(O)2(pb)] ([M + Na(+)](+), m/zcalc 523.1, m/zobs 523.1) and dinuclear [(Mo(VI)O(pb))2(μ-O)2] ([M + Na(+)](+), m/zcalc 1019.1, m/zobs 1019.2). The steric and electronic effects of the cis-dioxido group(s) in [Mo(VI)(O)2(pb)] mitigated coordination of solvent-derived ancillary ligands. The work highlights the value of using isotopically enriched metal ion sources and deuterated solvents to deconvolute metal/siderophore solution speciation. The results have relevance for an improved understanding of the coordination chemistry of pbH2 and other marine siderophores in V(V)- and Mo(VI)-rich surface ocean waters.

  8. Can Chemistry Teachers' Centres Survive?

    ERIC Educational Resources Information Center

    Garforth, F. M.

    1972-01-01

    The difficulties faced by the Hull Chemistry Teachers' Centre in England are discussed. The lack of finances and time, as well as organizational difficulties in relationship with Science Centres and universities are among the problems. (TS)

  9. Synthetic ability of dinuclear mesocates containing 1,3-bis(diazinecarboxamide)benzene bridging ligands to form complexes of increased nuclearity. Crystal structures, magnetic properties and theoretical studies.

    PubMed

    Palacios, Maria A; Morlieras, Jessica; Herrera, Juan Manuel; Mota, Antonio J; Brechin, Euan K; Triki, Smail; Colacio, Enrique

    2017-08-08

    Triple stranded Ni-metallacyclic complexes Na2.5[Ni2(bpcb)3]·0.5OH·18.5H2O (1) and Na2[Ni2(bpzcb)3]·16H2O (2), and double stranded Cu-metallacyclic complexes [Cu2(bpcb)2(H2O)2]·8H2O (3) and [Cu2(bpzcb)2(H2O)2]·4H2O (4) have been assembled from the tailored bisbidentate bridging ligands, 1,3-bis(pyrimidine-2-carboxamide)benzene (H2bpcb) and 1,3-bis(pyrazine-2-carboxamide)benzene (H2bpzcb), and the corresponding nitrate salts of the metal ions. Following the "complex as ligand" strategy, 1 can be assembled with either Ni(2+), Co(2+) ions or the [Mn(acen)Cl] complex to afford unique, neutral, bent trinuclear molecules [M(II)Ni(bpcb)3]·xH2O (5 and 6) and the 2D honeycomb-like complex (PPh4){[Ni2(bpcb)3]2[Mn(acen)]3} (7), respectively. In these cases, the Ni2 units are linked to the corresponding metal ions through amidate oxygen atoms and the outward nitrogen atom of one of the pyrimidine rings of the bcpb ligand. The assembly of 2 with Ln(3+) ions (Ln(3+) = Tb, Gd) leads to one dimensional complexes of formula [{[Ni2(bpzcb)3]Tb(H2O)5}(CF3SO3)·THF·5H2O]n (8) and [{[Ni2(bpzcb)3]Ln(H2O)4(NO3)}·2THF·nH2O]n (9 and 10) (Ln(3+) = Gd and Tb), where the dinuclear Ni2 units are joined to two Ln(3+) ions exclusively through amidate oxygen atoms of two different ligands. The analyses of the magnetic data indicate that 1-4 exhibit intradinuclear ferromagnetic interactions between the metal ions through a spin polarisation mechanism, as supported by DFT calculations. Trinuclear complexes 5 and 6 show predominant antiferromagnetic coupling, which is a result of an antiferromagnetic interaction between one of the Ni(2+) ions of the Ni2 unit and the M(2+) ion through the pyrimidine bridging fragment that is stronger than the polarised ferromagnetic interaction between the Ni(2+) ions through the bpcb ligand in the dinuclear [Ni2(bpcb)3](2-) moiety. Complex 7 shows a dominant antiferromagnetic interaction between the Ni(2+) and Mn(2+), whereas the Ni2Ln (Ln(3+) = Gd, Tb

  10. Synthesis and cell localization of self-assembled dinuclear lanthanide bioprobes.

    PubMed

    Chauvin, Anne-Sophie; Thomas, Frédéric; Song, Bo; Vandevyver, Caroline D B; Bünzli, Jean-Claude G

    2013-07-28

    Lanthanide bioprobes and bioconjugates are ideal luminescent stains in view of their low propensity to photobleaching, sharp emission lines and long excited state lifetimes permitting time-resolved detection for enhanced sensitivity. In this paper, we expand our previous work which demonstrated that self-assembled dinuclear triple-stranded helicates [Ln2(L(C2X))3] behave as excellent cell and tissue labels in immunocytochemical and immunohistochemical assays. The synthetic strategy of the hexadentate ditopic ligands incorporating dipicolinic acid, benzimidazole units and polyoxyethylene pendants is revisited in order to provide a more straightforward route and to give access to further functionalization of the polyoxyethylene arms by incorporating a terminal function X. Formation of the helicates [Ln2(L(C2X))3] (X=COOH, CH2OH, COEt, NH2, phthalimide) is ascertained by several experimental techniques and their stability tested against diethylenetriaminepentaacetate. Their photophysical properties (quantum yield, lifetime, radiative lifetime and sensitization efficiency) are presented and compared with those of the parent helicates [Ln2(L(C2))3]. Finally, the cellular uptake of five Eu(III) helicates is monitored by time-resolved luminescence microscopy and their localization in HeLa cells established by co-staining experiments.

  11. Production cross sections of the superheavy nucleus 117 based on the dinuclear system model

    NASA Astrophysics Data System (ADS)

    Zhao, Wei-Juan; Zhang, Yong-Qi; Wang, Hua-Lei; Song, Li-Tao; Li, Lu-Lu

    2010-10-01

    Within the framework of the dinuclear system model, the capture of two colliding nuclei, and the formation and de-excitation process of a compound nucleus are described by using an empirical coupled channel model, solving the master equation numerically and the statistical evaporation model, respectively. In the process of heavy-ion capture and fusion to synthesize superheavy nuclei, the barrier distribution function is introduced and averaging collision orientations are considered. Based on this model, the production cross sections of the cold fusion system 76-82Se+209Bi and the hot fusion systems 55Mn+238U, 51V+244Pu, 59Co+232Th,48Ca+247-249 Bk and 45Sc+246-248 Cm are calculated. The isotopic dependence of the largest production cross sections is analyzed briefly, and the optimal projectile-target combination and excitation energy of the 1n-4n evaporation channels are proposed. It is shown that the hot fusion systems 48Ca+247-249 Bk in the 3n evaporation channels and 45Sc+248Cm in the 2n-4n channels are optimal for synthesizing the superheavy element 117.

  12. Electronic structure modeling of dinuclear copper(II)-methacrylic acid complex by density functional theory.

    PubMed

    Demir, Serkan; Yolcu, Zuhal; Andaç, Omer; Büyükgüngör, Orhan; Yazicilar, Turan K

    2010-09-01

    A dinuclear centrosymmetric copper(II) complex with the formula [Cu(2)(mu-maa)(4)(maaH)(2)] has been synthesized and experimentally characterized by IR, electronic spectroscopy, and X-ray single-crystal diffractometry. Starting from experimental X-ray geometry and using antiferromagnetic singlet ground state, gas phase geometry optimization was performed by density functional hybrid (B3LYP) method with 6-31G(d) and LANL2DZ basis sets. Gas-phase vibrational frequencies and single point energy (SPE) calculations have been carried out at the geometry-optimized structure. Molecular electrostatic potential calculated at the optimized geometry and natural bond orbital analysis data have been extracted from SPE output. The gas-phase electronic transitions of the title complex were investigated by the time dependent-density functional theory (TD-DFT) approach with the same theory employing LANL2DZ basis set. Also the calculated UV-Vis based upon TD-DFT results and IR spectra were simulated for comparison with the experimental ones.

  13. Synthesis, cytotoxicity, induction of apoptosis, and interaction with DNA of dinuclear platinum(II) complexes.

    PubMed

    Xu, Gang; Gao, Chuanzhu; Gou, Shaohua; Cao, Zhe

    2012-11-01

    Six dicarboxylato-bridged dinuclear platinum(II) complexes S1-S6, with a newly designed chiral ligand, 2-{[(1R,2R)-2-aminocyclohexyl]amino}propanoic acid (HL), were prepared and spectrally characterized. The in vitro cytotoxicity of all resulting platinum(II) complexes was evaluated against human HCT-116, MCF-7, and HepG-2 tumor cell lines. The results show that all compounds exhibit positive biological activity toward HCT-116 and MCF-7 cell lines, of which complexes S3, S4, and S5, with succinate and its derivatives as bridges, showing better activity than the positive controls. Moreover, double-dyeing flow cytometric resection experiments indicate that the target compounds inhibit tumor cell growth by inducing apoptosis; gel electrophoresis experiments demonstrate the compounds' ability to prompt pET22b plasmid DNA degradation in almost the same way as oxaliplatin. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Identification of dinuclear aromatics in the gas oil fraction of Kuwait petroleum

    SciTech Connect

    Ijam, M.J.; Qatami, S.Y.A.; Arif, S.F.

    1988-08-01

    For several decades removal of aromatics from crude oil fractions (e.g. kerosene and lubricating oils) has been practiced in oil refining to produce fuels and lubricants of lower aromatic content and hence of improved quality. These aromatics are suitable raw materials for the manufacture of aromatic solvents, aromatic process oils, high octane gasoline, and as basic materials for making detergents, perfumes and dyes. Detailed study of molecular structure and substituent effects on the retention characteristics of aromatic hydrocarbons have been reported on alumina, silica and various chemically bonded silicas containing -C/sub 18/, -NH/sub 2/, -R(NH)/sub 2//sub 2/, -CN, RCN, RON and phenyl-mercuric acetate for the compound class (ring-numbered) high performance liquid chromatography (2, 3, 8, 12, 24, 28). Previous work in this laboratory has demonstrated that individual normal and branched aliphatic hydrocarbons from kerosene and light gas oil were isolated and identified. This paper describes the extension of this work to cover the separation and identification of aromatic ring classes (mono-, di-, and tri-aromatics) in the gas oil fraction of Kuwait petroleum. Characterization and identification of the major components in the dinuclear aromatics is our primary objective in this study.

  15. Electrochemical behavior and dioxygen reactivity of tripodal dinuclear copper complexes linked by unsaturated rigid spacers.

    PubMed

    Gomila, Antoine; Le Poul, Nicolas; Kerbaol, Jean-Michel; Cosquer, Nathalie; Triki, Smaïl; Douziech, Bénédicte; Conan, Françoise; Le Mest, Yves

    2013-02-14

    New dinucleating ligands based on two tripodal tris(2-pyridylmethyl)amine (TMPA) units linked by a series of delocalized π-electrons spacers have been synthesized. Their di-Cu(II) complexes have been prepared and structurally characterized. As compared to the corresponding monotopic complexes, these dinuclear Cu(II) complexes reveal spectroscopic and voltammetric features ascribable to weakly perturbed electronic interactions. In the case of the anthracenyl spacer, observation both in the solid and in solution suggests that the existence of intramolecular π-π stacking interactions influences the geometry of the complex and hence its electronic properties. The bis-Cu(I) complexes were prepared electrochemically. In the specific case of the complex bearing a mono-alkyne spacer, addition of dioxygen in acetonitrile leads to the slow formation of a trans-μ-1,2 peroxo Cu(2) complex which shows good stability at 268 K (t(1/2) = 240 s). Analysis of the kinetics of the peroxo formation by UV-vis spectroscopy suggests that the increased activation barrier for intramolecular binding of dioxygen is due to the rigidity of the spacer.

  16. Synthesis and structure of dinuclear complexes of terbium(III) with 4-acetalbispyrazolone

    SciTech Connect

    Luqin Yang; Rudong Yang

    1994-12-01

    Two novel dinuclear complexes of terbium(III) with 1,5-bis(1`-phenyl-3`-methyl-5`-pyrazolone-4`)-1,5- pentanedione (H{sub 2}L), Tb{sub 2}L{sub 3}{center_dot}6H{sub 2}, Tb{sub 2}L{sub 3}{center_dot}5DMF, have been synthesized. The crystal structure of Tb{sub 2}L{sub 3}{center_dot}5DMF was determined by X-ray diffraction methods. Crystals are triclinic, space group P{rvec 1} with a = 16.957(5), b = 17.877(7), c = 18.269(2){Angstrom}, a = 110.35(2), {beta} = 101.29(2), {gamma} = 111.02(2){degrees}, V = 4511(6){Angstrom}{sup 3}, Mr = 2010.76 Z = 2, Dx = 1.48 g cm{sup -3}, {mu} = 16.45 cm{sub -1} F(000) = 2,052, R = 0.058 with 6574 reflections used in refinement. In the complex, L acts as a bridging ligand and bonds two terbium atoms with its two {beta}-diketone groups. Each terbium ion bonds to two DMF solvent molecules. The coordination number of the two terbium ions is eight. The eight oxygen atoms around the terbium make a distorted square antiprismatic coordination polyhedron.

  17. Characterization of the Activities of Dinuclear Thiolato-Bridged Arene Ruthenium Complexes against Toxoplasma gondii.

    PubMed

    Basto, Afonso P; Müller, Joachim; Rubbiani, Riccardo; Stibal, David; Giannini, Federico; Süss-Fink, Georg; Balmer, Vreni; Hemphill, Andrew; Gasser, Gilles; Furrer, Julien

    2017-09-01

    The in vitro effects of 18 dinuclear thiolato-bridged arene ruthenium complexes (1 monohiolato compound, 4 dithiolato compounds, and 13 trithiolato compounds), originally designed as anticancer agents, on the apicomplexan parasite Toxoplasma gondii grown in human foreskin fibroblast (HFF) host cells were studied. Some trithiolato compounds exhibited antiparasitic efficacy at concentrations of 250 nM and below. Among those, complex 1 and complex 2 inhibited T. gondii proliferation with 50% inhibitory concentrations (IC50s) of 34 and 62 nM, respectively, and they did not affect HFFs at dosages of 200 μM or above, resulting in selectivity indices of >23,000. The IC50s of complex 9 were 1.2 nM for T. gondii and above 5 μM for HFFs. Transmission electron microscopy detected ultrastructural alterations in the matrix of the parasite mitochondria at the early stages of treatment, followed by a more pronounced destruction of tachyzoites. However, none of the three compounds applied at 250 nM for 15 days was parasiticidal. By affinity chromatography using complex 9 coupled to epoxy-activated Sepharose followed by mass spectrometry, T. gondii translation elongation factor 1α and two ribosomal proteins, RPS18 and RPL27, were identified to be potential binding proteins. In conclusion, organometallic ruthenium complexes exhibit promising activities against Toxoplasma, and the potential mechanisms of action of these compounds as well as their prospective applications for the treatment of toxoplasmosis are discussed. Copyright © 2017 American Society for Microbiology.

  18. Slow magnetic relaxations in a ladder-type Dy(iii) complex and its dinuclear analogue.

    PubMed

    Boča, R; Stolárová, M; Falvello, L R; Tomás, M; Titiš, J; Černák, J

    2017-04-06

    The complex {[Dy2(PDOA)3(H2O)6]·2H2O}n (1) (H2PDOA = 1,2-phenylenedioxydiacetic acid) was prepared from aqueous solution. Its crystal structure, built up of {-Dy-O-C-O-}n chains interlinked by PDOA ligands yielding a ladder-like arrangement, was determined at 173 K. 1 exhibits slow magnetic relaxation under a small magnetic field BDC = 0.2 T with two (LF and HF) relaxation channels. The LF relaxation time at BDC = 0.2 T and T = 1.85 K is as slow as τ(LF) = 46 ms whereas the HF channel is τ(HF) = 1.4 ms. The mole fraction of the LF species is xLF = 0.76 at 1.85 K and it escapes progressively on heating. In the dinuclear analogue [Dy2(PDOA)3(H2O)6]·3.5H2O (2) one PDOA ligand forms a bis(chelate) bridge between the two Dy(iii) atoms yielding a local structure analogous to that in 1; however its AC susceptibility data show slightly different quantitative characteristics of the single-molecule magnetic behaviour.

  19. Transition metal complexes of the novel hexadentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine.

    PubMed

    Roggan, Stefan; Limberg, Christian; Knispel, Christina; Tilley, T Don

    2011-04-28

    The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine, bimptz, has been synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the 1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray diffraction. Upon reaction of bimptz with two equivalents of MnCl(2)·4H(2)O, CoCl(2)·6H(2)O and [Ru(dmso)(4)Cl(2)], the dinuclear complexes [Mn(2)(bimptz)(µ-Cl)(2)Cl(2)] (1), [Co(2)(bimptz)(CH(3)OH)(2)(µ-Cl)(2)](PF(6))(2) (3) and [Ru(2)(bimptz)(dmso)(2)(µ-Cl)(2)](PF(6))(2) (4), respectively, were isolated. The latter were found to have similar solid state structures with octahedrally coordinated metal centers bridged by the phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as PF(6)(-) salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)(2)](PF(6))(4) (6) was obtained from the reaction of two equivalents bimptz with [Ru(dmso)(4)Cl(2)]. In complex 6, three donor sites per ligand molecule are used for coordination of the Ru(ii) center. In each bimptz ligand, one of the remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the unprotonated N-methylimidazole ring of the other bimptz ligand.

  20. Two-electron redox chemistry at the dinuclear core of a TePt platform: chlorine photoreductive elimination and isolation of a Te(V)Pt(I) complex.

    PubMed

    Lin, Tzu-Pin; Gabbaï, François P

    2012-07-25

    As part of our interest in novel redox-active main group/transition metal platforms for energy applications, we have synthesized the chloride salt of [Te(III)Pt(I)Cl(o-dppp)(2)](+) ([1](+), o-dppp = o-(Ph(2)P)C(6)H(4)) by reaction of the new bis(phosphino) telluroether (o-(Ph(2)P)C(6)H(4))(2)Te with (Et(2)S)(2)PtCl(2). Complex [1](+) is chemically robust and undergoes a clean two-electron oxidation reaction in the presence of PhICl(2) to afford ClTe(III)Pt(III)Cl(3)(o-dppp)(2) (2), a complex combining a hypervalent four-coordinate tellurium atom and an octahedral platinum center. While the Te-Pt bond length is only slightly affected by the oxidation state of the TePt platform, DFT and NBO calculations show that this central linkage undergoes an umpolung from Te→Pt in [1](+) to Te←Pt in 2. This umpolung signals an increase in the electron releasing ability of the tellurium center upon switching from an eight-electron configuration in [1](+) to a hypervalent configuration in 2. Remarkably, the two-electron redox chemistry displayed by this new dinuclear platform is reversible as shown by the photoreductive elimination of a Cl(2) equivalent when 2 is irradiated at 350 nm in the presence of a radical trap such as 2,3-dimethyl-1,3-butadiene. This photoreductive elimination, which affords [1][Cl] with a maximum quantum yield of 4.4%, shows that main group/late transition metal complexes can mimic the behavior of their transition metal-only analogues and, in particular, undergo halogen photoelimination from the oxidized state. A last notable outcome of this study is the isolation and characterization of F(MeO)(2)Te(V)Pt(I)Cl(o-dppp)(2) (4), the first metalated hexavalent tellurium compound, which is formed by reaction of 2 with KF in the presence of MeOH.

  1. Cu(I) dinuclear complexes with tripodal ligands vs monodentate donors: triphenylphosphine, thiourea, and pyridine. A 1H NMR titration study.

    PubMed

    Gennari, Marcello; Lanfranchi, Maurizio; Marchiò, Luciano; Pellinghelli, Maria Angela; Tegoni, Matteo; Cammi, Roberto

    2006-04-17

    Complexes [PPh3Cu(Tr(Mes,Me))] (1), [PPh3Cu(Tr(Me,o-Py))] (2), and [PPh3Cu(Br(Mes)pz(o-Py))] (3) (Tr(Mes,Me) = hydrotris[1,4-dihydro-3-methyl-4-mesityl-5-thioxo-1,2,4-triazolyl]borate; Tr(Me,o-Py) = hydrotris[1,4-dihydro-4-methyl-3-(2-pyridyl)-5-thioxo-1,2,4-triazolyl]borate; Br(Mes)pz(o-Py) = hydro[bis(thioxotriazolyl)-3-(2-pyridyl)pyrazolyl]borate; PPh3 = triphenylphosphine) were synthesized by the reaction of dinuclear complexes [Cu(Tr(Mes,Me))]2, [Cu(Tr(Me,o-Py))]2, [Cu(Br(Mes)pz(o-Py))]2, and PPh3. 1-3 were characterized by 1H, 13C, and 31P NMR spectroscopy and ESI-mass spectrometry. Crystal structure analyses were performed for 1 and 2. Both complexes crystallize in the triclinic P space group with the metal in a slightly distorted tetrahedral geometry (S3P coordination) bound by a kappa3-S3 ligand and a PPh3 molecule. The solution molecular structures were investigated by means of variable-temperature (210-310 K, CDCl3, 1-2; 200-310 K, CD2Cl2, 3) and NOESY NMR spectroscopy. The solution structures of 1-2 are in accordance with the X-ray structures, and the complexes do not exhibit fluxional behavior. On the other hand, 3 is subject to an equilibrium between two species with a coalescing temperature of approximately 260 K. DFT geometry optimizations suggest that the major species of 3 consists of the Br(Mes)pz(o-Py) ligand bound to Cu(I) in the kappa3-S2H fashion with two C=S groups and a [Cu...H-B] interaction. A PPh3 completes the copper coordination (S2HP coordination). The complex [TuCu(Tr(Mes,Me))] (4) (Tu = thiourea) was crystallized using an excess of Tu with respect to [Cu(Tr(Me,2-Py))]2 (approximately a 6:1 ratio). The metal adopts a distorted tetrahedral geometry with an overall S3H coordination determined by the bound kappa3-S2H ligand (two C=S groups and a [B-H...Cu] interaction) and by a Tu. The reactivity of dinuclear complexes [Cu(Tr(Mes,Me))]2, [Cu(Tr(Me,o-Py))]2, and [Cu(Br(Mes)pz(o-Py))]2 with monodentate ligands was investigated by means of

  2. Hydride reactivity of Ni(II)-X-Ni(II) entities: mixed-valent hydrido complexes and reversible metal reduction.

    PubMed

    Gehring, Henrike; Metzinger, Ramona; Herwig, Christian; Intemann, Julia; Harder, Sjoerd; Limberg, Christian

    2013-01-28

    After the lithiation of PYR-H(2) (PYR(2-) =[{NC(Me)C(H)C(Me)NC(6)H(3)(iPr)(2)}(2)(C(5)H(3)N)](2-)), which is the precursor of an expanded β-diketiminato ligand system with two binding pockets, its reaction with [NiBr(2) (dme)] led to a dinuclear nickel(II)-bromide complex, [(PYR)Ni(μ-Br)NiBr] (1). The bridging bromide ligand could be selectively exchanged for a thiolate ligand to yield [(PYR)Ni(μ-SEt)NiBr] (3). In an attempt to introduce hydride ligands, both compounds were treated with KHBEt(3). This treatment afforded [(PYR)Ni(μ-H)Ni] (2), which is a mixed valent Ni(I)-μ-H-Ni(II) complex, and [(PYR-H)Ni(μ-SEt)Ni] (4), in which two tricoordinated Ni(I) moieties are strongly antiferromagnetically coupled. Compound 4 is the product of an initial salt metathesis, followed by an intramolecular redox process that separates the original hydride ligand into two electrons, which reduce the metal centres, and a proton, which is trapped by one of the binding pockets, thereby converting it into an olefin ligand on one of the Ni(I) centres. The addition of a mild acid to complex 4 leads to the elimination of H(2) and the formation of a Ni(II)Ni(II) compound, [(PYR)Ni(μ-SEt)NiOTf] (5), so that the original Ni(II) (μ-SEt)Ni(II) X core of compound 3 is restored. All of these compounds were fully characterized, including by X-ray diffraction, and their molecular structures, as well as their formation processes, are discussed.

  3. Factors influencing tetranuclear [2 x 2] grid vs dinuclear side-by-side structures for silver(I) complexes of pyridazine-based bis-bidentate ligands.

    PubMed

    Price, Jason R; White, Nicholas G; Perez-Velasco, Alejandro; Jameson, Geoffrey B; Hunter, Christopher A; Brooker, Sally

    2008-11-17

    Silver(I) complexes of five bis-bidentate Schiff-base ligands, derived from 3,6-diformylpyridazine and substituted anilines (2,4-dimethylaniline L ( o,p - Me ); 3,5-dichloroaniline L ( m,m - Cl ); 2-aminobiphenyl L ( o - Ph ); p-toluidine L ( p - Me ); 4-aminophenol L ( p - OH ); p-anisidine L ( p - OMe )), have been prepared. The ligands have a wide range of steric and electronic properties due to variation in the extent and nature of the substitution of the aniline rings. Four of the resulting complexes were structurally characterized by X-ray crystallography: three of the four, [Ag 2( L ( o,p - Me )) 2](BF 4) 2, [Ag 2( L ( m,m - Cl )) 2](BF 4) 2 and [Ag 2( L ( o - Ph )) 2](BF 4) 2 formed dinuclear side-by-side complexes, while [Ag 4( L ( p - Me )) 4](BF 4) 4 gave a tetranuclear [2 x 2] grid. The previously reported tetranuclear [2 x 2] grid [Ag 4( L ( p - OMe )) 4](BF 4) 4 was recrystallized in the presence of benzene to see if this would alter the architecture of this complex. It did not: the [2 x 2] grid architecture was retained despite the benzene molecules of solvation. Given the flexibility of silver(I) with regard to coordination geometry, the molecular structure of these complexes is influenced mostly by the ligand rather than the metal ion. In each case, the factors which influence the molecular architecture are presented and discussed. Substituent effects on the electrostatics of the intramolecular ligand-ligand pi-pi interactions (XED2.8) account for some of the differences observed in the structures.

  4. Spontaneous self-assembly of a giant spherical metal-oxide Keplerate: addition of one building block induces "immediate" formation of the complementary one from a constitutional dynamic library.

    PubMed

    Schäffer, Christian; Todea, Ana Maria; Gouzerh, Pierre; Müller, Achim

    2012-01-11

    The addition of dinuclear {Mo(2)} units to a dynamic library containing molybdates results in the spontaneous self-assembly of a giant spherical metal-oxide species of the type {(Mo)Mo(5)}(12){Mo(2)}(30) while the required pentagonal {(Mo)Mo(5)} building blocks are "immediately" formed.

  5. Synthesis and crystal structure of a dinuclear, monomeric Mn(II) p-semiquinonato complex.

    PubMed

    Nakamori, Harutaka; Matsumoto, Takahiro; Yatabe, Takeshi; Yoon, Ki-Seok; Nakai, Hidetaka; Ogo, Seiji

    2014-11-07

    Herein, we report the first crystal structure of a monomeric p-semiquinonato d-block complex and its reactivity toward dioxygen, closely associated with a biological system of an oxygen evolving centre of photosystem II.

  6. Formation of a dinuclear copper(II) complex through the cleavage of CN bond of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole

    SciTech Connect

    Shardin, Rosidah; Pui, Law Kung; Yamin, Bohari M.; Kassim, Mohammad B.

    2014-09-03

    A simple mononuclear octahedral copper(II) complex was attempted from the reaction of three moles of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole and one mole of copper(II) perchlorate hexahydrate in methanol. However, the product of the reaction was confirmed to be a dinuclear copper(II) complex with μ-(3-(pyridin-2-yl)-pyrazolato) and 3-(pyridin-2-yl)-1H-pyrazole ligands attached to each of the Cu(II) centre atom. The copper(II) ion assisted the cleavage of the C{sub benzoyl}N bond afforded a 3-(pyridin-2-yl)-1H-pyrazole molecule. Deprotonation of the 3-(pyridin-2-yl)-1H-pyrazole gave a 3-(pyridin-2-yl)-pyrazolato, which subsequently reacted with the Cu(II) ion to give the (3-(pyridin-2-yl)-pyrazolato)(3-(pyridin-2-yl)-1H-pyrazole)Cu(II) product moiety. The structure of the dinuclear complex was confirmed by x-ray crystallography. The complex crystallized in a monoclinic crystal system with P2(1)/n space group and cell dimensions of a = 12.2029(8) Å, b = 11.4010(7) Å, c = 14.4052(9) Å and β = 102.414(2)°. The compound was further characterized by mass spectrometry, CHN elemental analysis, infrared and UV-visible spectroscopy and the results concurred with the x-ray structure. The presence of d-d transition at 671 nm (ε = 116 dm{sup 3} mol{sup −1} cm{sup −1}) supports the presence of Cu(II) centres.

  7. Formation of a dinuclear copper(II) complex through the cleavage of CN bond of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole

    NASA Astrophysics Data System (ADS)

    Shardin, Rosidah; Pui, Law Kung; Yamin, Bohari M.; Kassim, Mohammad B.

    2014-09-01

    A simple mononuclear octahedral copper(II) complex was attempted from the reaction of three moles of 1-benzoyl-3-(pyridin-2-yl)-1H-pyrazole and one mole of copper(II) perchlorate hexahydrate in methanol. However, the product of the reaction was confirmed to be a dinuclear copper(II) complex with μ-{3-(pyridin-2-yl)-pyrazolato} and 3-(pyridin-2-yl)-1H-pyrazole ligands attached to each of the Cu(II) centre atom. The copper(II) ion assisted the cleavage of the CbenzoylN bond afforded a 3-(pyridin-2-yl)-1H-pyrazole molecule. Deprotonation of the 3-(pyridin-2-yl)-1H-pyrazole gave a 3-(pyridin-2-yl)-pyrazolato, which subsequently reacted with the Cu(II) ion to give the {3-(pyridin-2-yl)-pyrazolato}{3-(pyridin-2-yl)-1H-pyrazole}Cu(II) product moiety. The structure of the dinuclear complex was confirmed by x-ray crystallography. The complex crystallized in a monoclinic crystal system with P2(1)/n space group and cell dimensions of a = 12.2029(8) Å, b = 11.4010(7) Å, c = 14.4052(9) Å and β = 102.414(2)°. The compound was further characterized by mass spectrometry, CHN elemental analysis, infrared and UV-visible spectroscopy and the results concurred with the x-ray structure. The presence of d-d transition at 671 nm (ɛ = 116 dm3 mol-1 cm-1) supports the presence of Cu(II) centres.

  8. DNA interactions of new cytotoxic tetrafunctional dinuclear platinum complex trans,trans-[{PtCl2(NH3)}2(piperazine)].

    PubMed

    Brabec, Viktor; Christofis, Petros; Slámová, Martina; Kostrhunová, Hana; Nováková, Olga; Najajreh, Yousef; Gibson, Dan; Kaspárková, Jana

    2007-06-15

    A new tetrafunctional dinuclear platinum complex trans,trans-[{PtCl2(NH3)}2(piperazine)] with sterically rigid linking group was designed, synthesized and characterized. In this novel molecule, the DNA-binding features of two classes of the platinum compounds with proven antitumor activity are combined, namely trans oriented bifunctional mononuclear platinum complexes with a heterocyclic ligand and polynuclear platinum complexes. DNA-binding mode of this new complex was analyzed by various methods of molecular biology and biophysics. The complex coordinates DNA in a unique way and interstrand and intrastrand cross-links are the predominant lesions formed in DNA in cell-free media and in absence of proteins. An intriguing aspect of trans,trans-[{PtCl2(NH3)}2(piperazine)] is that, using a semi-rigid linker, interstrand cross-linking is diminished relative to other dinuclear platinum complexes with flexible linking groups and lesions that span several base pairs, such as tri- and tetrafunctional adducts, become unlikely. In addition, in contrast to the inability of trans,trans-[{PtCl2(NH3)}2(piperazine)] to cross-link two DNA duplexes, the results of the present work convincingly demonstrate that this dinuclear platinum complex forms specific DNA lesions which can efficiently cross-link proteins to DNA. The results substantiate the view that trans,trans-[{PtCl2(NH3)}2(piperazine)] or its analogues could be used as a tool for studies of DNA properties and their interactions or as a potential antitumor agent. The latter view is also corroborated by the observation that trans,trans-[{PtCl2(NH3)}2(piperazine)] is a more effective cytotoxic agent than cisplatin against human tumor ovarian cell lines.

  9. Reactivity of a cytostatic active N,N-donor-containing dinuclear Pt(II) complex with biological relevant nucleophiles.

    PubMed

    Hochreuther, Stephanie; van Eldik, Rudi

    2012-03-05

    A dinuclear platinum(II) complex that was recently investigated in our group was tested for its cytostatic activity and found to be active against HeLa S3 cells. The complex consists of a bidentate N,N-donor chelating ligand system in which the two platinum centers are connected by an aliphatic chain of 10 methylene groups. The complex [Pt(2)(N(1),N(10)-bis(2-pyridylmethyl)-1,10-decanediamine)(OH(2))(4)](4+) (10NNpy) is of further special interest, since only little is known about the substitution behavior of such dinuclear platinum complexes that contain a bidentate coordination sphere. The complex was investigated using different biologically relevant nucleophiles, such as thiourea (tu), L-methionine (L-Met), glutathione (GSH), and guanine-5'-monophosphate (5'-GMP), at two different pH values (2 and 7.4). The substitution of coordinated water by these nucleophiles was studied under pseudo-first-order conditions as a function of nucleophile concentration, temperature, and pressure, using stopped-flow techniques and UV-vis spectroscopy. The reactivity of 10NNpy with the selected nucleophiles was found to be tu ≫ 5'-GMP > L-Met > GSH at pH 2 and GSH > tu > L-Met at pH 7.4. The results for the dinuclear 10NNpy complex were compared to those for the corresponding mononuclear reference complex [Pt(aminomethylpyridine)(OH(2))(2)](2+), Pt(amp), studied before in our group, by which the effect of the addition of an aliphatic chain, an increase in the overall charge, and a shift in the pK(a) values of the coordinated water ligands could be investigated. The reactivity order for Pt(amp) was found to be tu > GSH > L-Met at pH 7.4.

  10. Nanochemistry of metals

    NASA Astrophysics Data System (ADS)

    Sergeev, Gleb B.

    2001-10-01

    The results of studies on the nanochemistry of metals published in recent years are generalised. Primary attention is centred on the methods for the synthesis of nanoparticles and their chemical reactions. The means of stabilisation of nanoparticles which involve individual metals and incorporate atoms of several metals are considered as well as their physicochemical properties. Self-assembling processes of nanoparticles are described. The prospects of using metal nanoparticles in semiconductor devices, catalysis, biology and medicine are discussed. The bibliography includes 165 references.

  11. Quantum transport behavior of Ni-based dinuclear complexes in presence of zigzag graphene nanoribbon as electrode

    NASA Astrophysics Data System (ADS)

    Sarkar, Sunandan; Pramanik, Anup; Sarkar, Pranab

    2016-10-01

    Quantum transport properties of some Ni-based dinuclear complexes with different polydentate organic ligands have been studied by applying abinitio density functional theory along with nonequilibrium Green's function formulations. It is demonstrated that these materials are capable of showing multifunctional spin dependent properties by the influence of edge states of zigzag edged graphene nanoribbons. The current-voltage characteristics of these materials show spin dependent negative differential resistance behavior, spin filtering effect, and also voltage rectifying property. Proper tuning of these materials can alter these effects which may be utilized in various spintronic devices.

  12. Dinuclear pyridine-4-thiolate-bridged rhodium and iridium complexes as ditopic building blocks in molecular architecture.

    PubMed

    Ferrer, Montserrat; Gómez-Bautista, Daniel; Gutiérrez, Albert; Miranda, José R; Orduña-Marco, Guillermo; Oro, Luis A; Pérez-Torrente, Jesús J; Rossell, Oriol; García-Orduña, Pilar; Lahoz, Fernando J

    2014-02-03

    A series of dinuclear pyridine-4-thiolate (4-Spy)-bridged rhodium and iridium compounds [M(μ-4-Spy)(diolef)]2 [diolef = 1,5-cyclooctadiene (cod), M = Rh (1), Ir (2); diolef = 2,5-norbornadiene (nbd), M = Rh (3)] were prepared by the reaction of Li(4-Spy) with the appropriate compound [M(μ-Cl)(diolef)]2 (M = Rh, Ir). The dinuclear compound [Rh(μ-4-Spy)(CO)(PPh3)]2 (4) was obtained by the reaction of [Rh(acac)(CO)(PPh3)] (acac = acetylacetonate) with 4-pySH. Compounds 1-4 were assessed as metalloligands in self-assembly reactions with the cis-blocked acceptors [M(cod)(NCCH3)2](BF4) [M = Rh (a), Ir (b)] and [M(H2O)2(dppp)](OTf)2 [M = Pd (c), Pt (d); dppp = 1,3-bis(diphenylphosphino)propane]. The homometallic hexanuclear metallomacrocycles [{M2(μ-4-Spy)2(cod)2}2{M(cod)}2](BF4)2 (M = Rh [(1a)2], Ir [(2b)2]) and the heterometallic hexanuclear metallomacrocycles [{Rh2(μ-4-Spy)2(cod)2}2{Ir(cod)}2](BF4)2 [(1b)2], [{Rh2(μ-4-Spy)2(cod)2}2{M'(dppp)}2](OTf)4 (M' = Pd [(1c)2], Pt [(1d)2]), and [{Ir2(μ-4-Spy)2(cod)2}2{M'(dppp)}2](OTf)4 (M' = Pd [(2c)2], Pt [(2d)2]) were obtained. NMR spectroscopy in combination with electrospray ionization mass spectrometry was used to elucidate the nature of the metalloligands and their respective supramolecular assemblies. Most of the synthesized species were found to be nonrigid in solution, and their fluxional behavior was studied by variable-temperature (1)H NMR spectroscopy. An X-ray diffraction study of the assemblies (1a)2 and (1d)2 revealed the formation of rectangular (9.6 Å × 6.6 Å) hexanuclear metallomacrocycles with alternating dinuclear (Rh2) and mononuclear (Rh or Pt) corners. The hexanuclear core is supported by four pyridine-4-thiolate linkers, which are bonded through the thiolate moieties to the dinuclear rhodium units, exhibiting a bent-anti arrangement, and through the peripheral pyridinic nitrogen atoms to the mononuclear corners.

  13. Protonation equilibrium and hydrogen production by a dinuclear cobalt-hydride complex reduced by cobaltocene with trifluoroacetic acid.

    PubMed

    Mandal, Sukanta; Shikano, Shinya; Yamada, Yusuke; Lee, Yong-Min; Nam, Wonwoo; Llobet, Antoni; Fukuzumi, Shunichi

    2013-10-16

    A dinuclear Co complex with bis(pyridyl)pyrazolato (bpp(-)) and terpyridine (trpy) ligands, [Co(III)2(trpy)2(μ-bpp)(OH)(OH2)](4+) (1(4+)), undergoes three-electron reduction by cobaltocene in acetonitrile to produce 1(+), which is in the protonation equilibrium with the Co(II)Co(III)-hydride complex, and the further protonation of the hydride by trifluoroacetic acid yields hydrogen quantitatively. The kinetic study together with the detection of the Co(II)Co(III)-hydride complex revealed the mechanism of the hydrogen production by the reaction of 1(+) with trifluoroacetic acid.

  14. The pontine micturition centres.

    PubMed

    Griffiths, Derek J

    2002-01-01

    To review recent literature on the function of the two postulated pontine regions (the M- and L-regions) concerned with lower urinary tract control. The work reviewed is based on stimulation and lesion experiments and post-operative follow-up in the cat, supported by acute chemical stimulation and blocking experiments in the rat and PET functional brain scanning in humans. The M-region in the cat, homologous to Barrington's micturition centre and to a similar area in humans, is a small region both specific and necessary to voiding, the origin of the final common pathway to bladder and urethra, and the locus of co-ordination of the bladder and the striated sphincter. The L-region in the cat is part of a larger, less specific area that probably serves sphincter control in various circumstances, not exclusively micturition. The homolog of this region in the human or in the rat has not been adequately established.

  15. [The primary healthcare centres].

    PubMed

    Brambilla, Antonio; Maciocco, Gavino

    2014-04-01

    The central attributes of primary care are: first contact (accessibility), longitudinality (person- focused preventive and curative care overtime), patient-oriented comprehensiveness and coordination (including navigation towards secondary and tertiary care). Besides taking care of the needs of the individuals, primary health care teams are also looking at the community, especially when addressing social determinants of health. The rationale for the benefits for primary care for health has been found in: 1) greater access to needed services; 2) better quality of care; 3) a greater focus on prevention; 4) early management of health problems; 5) organizing and delivering high quality care for chronic non-communicable diseases. This paper describes the role of primary healthcare centres in strengthening community primary services and in reducing health inequalities. Furthemore, the experiences of Regional Health Services from Tuscany and Emilia-Romagna are discussed, with a brief overview of the literature.

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

    PubMed

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

    2008-06-14

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

  17. Mechanistic insight into the catechol oxidase activity by a biomimetic dinuclear copper complex.

    PubMed

    Granata, Alessandro; Monzani, Enrico; Casella, Luigi

    2004-10-01

    The biomimetic catalytic oxidation of 3,5-di- tert-butylcatechol by the dicopper(II) complex of the ligand alpha,alpha'-bis(bis[1-(1'-methyl-2'-benzimidazolyl)methyl]amino)- m-xylene in the presence of dioxygen has been investigated as a function of temperature and pH in a mixed aqueous/organic solvent. The catalytic cycle occurs in two steps, the first step being faster than the second step. In the first step, one molecule of catechol is oxidized by the dicopper(II) complex, and the copper(II) centers are reduced. From the pH dependence, it is deduced that the active species of the process is the monohydroxo form of the dinuclear complex. In the second step, the second molecule of catechol is oxidized by the dicopper(I)-dioxygen complex formed upon oxygenation of the reduced complex. In both cases, catechol oxidation is an inner-sphere electron transfer process involving binding of the catechol to the active species. The binary catechol-dicopper(II) complex formed in the first step could be characterized at very low temperature (-90 degrees C), where substrate oxidation is blocked. On the contrary, the ternary complex of dicopper(I)-O(2)-catechol relevant to the second step does not accumulate in solution and could not be characterized, even at low temperature. The investigation of the biphasic kinetics of the catalytic reaction over a range of temperatures allowed the thermodynamic (Delta H degrees and Delta S degrees ) and activation parameters (Delta H( not equal) and Delta S( not equal)) connected with the key steps of the catecholase process to be obtained.

  18. Dinuclear titanium(IV) complexes from amino acid bridged dicatechol ligands: formation, structure, and conformational analysis.

    PubMed

    Albrecht, M; Napp, M; Schneider, M; Weis, P; Fröhlich, R

    2001-09-17

    Amino acid bridged dicatechol ligands 3a-e-H4 form dinuclear double-stranded coordination compounds [(3a-e)2Ti2(OCH3)2]2- with titanium(IV) ions. Due to the directionality of the ligands, the chirality of the strand, and the chiral complex units, up to seven isomers, I-VII, can be obtained for the double-stranded complexes of ligands 3a-e-H4. The composition of the mixture of isomeric compounds in solution is strongly dependent on the conditions of complex formation. Under thermodynamic control, only a few isomers are obtained, one of which is the major component of the mixture. X-ray structure analyses were performed for K2[(3b)2Ti2(OH)2] and K2[(3d)2Ti2(OH)2] (type I), and for the meso complex Na2[(3e)(3e')Ti2(OCH3)2]. A conformational analysis that uses Ramachandrans method revealed that the conformation of the amino acids in the ligand strands can be compared with those found for amino acids in helical peptide structures. The most favored isomer of [(3)2Ti2(OCH3)2]2- appears to be of type I, with the catecholamide unit located at the N terminus of the ligand strand that binds to a lambda-configurated titanium(IV) complex unit and the dihydroxybenzyl group at the C terminus that coordinates to a delta-configurated titanium(IV) complex unit. The lambda configuration at the N terminus induces the conformation of a right-handed helix in the amino acid residue, while the delta configuration induces the less favored left-handed helix.

  19. Water oxidation chemistry of a synthetic dinuclear ruthenium complex containing redox-active quinone ligands.

    PubMed

    Isobe, Hiroshi; Tanaka, Koji; Shen, Jian-Ren; Yamaguchi, Kizashi

    2014-04-21

    We investigated theoretically the catalytic mechanism of electrochemical water oxidation in aqueous solution by a dinuclear ruthenium complex containing redox-active quinone ligands, [Ru2(X)(Y)(3,6-tBu2Q)2(btpyan)](m+) [X, Y = H2O, OH, O, O2; 3,6-tBu2Q = 3,6-di-tert-butyl-1,2-benzoquinone; btpyan =1,8-bis(2,2':6',2″-terpyrid-4'-yl)anthracene] (m = 2, 3, 4) (1). The reaction involves a series of electron and proton transfers to achieve redox leveling, with intervening chemical transformations in a mesh scheme, and the entire molecular structure and motion of the catalyst 1 work together to drive the catalytic cycle for water oxidation. Two substrate water molecules can bind to 1 with simultaneous loss of one or two proton(s), which allows pH-dependent variability in the proportion of substrate-bound structures and following pathways for oxidative activation of the aqua/hydroxo ligands at low thermodynamic and kinetic costs. The resulting bis-oxo intermediates then undergo endothermic O-O radical coupling between two Ru(III)-O(•) units in an anti-coplanar conformation leading to bridged μ-peroxo or μ-superoxo intermediates. The μ-superoxo species can liberate oxygen with the necessity for the preceding binding of a water molecule, which is possible only after four-electron oxidation is completed. The magnitude of catalytic current would be limited by the inherent sluggishness of the hinge-like bending motion of the bridged μ-superoxo complex that opens up the compact, hydrophobic active site of the catalyst and thereby allows water entry under dynamic conditions. On the basis of a newly proposed mechanism, we rationalize the experimentally observed behavior of electrode kinetics with respect to potential and discuss what causes a high overpotential for water oxidation by 1.

  20. Visible Light-Induced Electron Transfer From Di-Mu-Oxo-Bridged Dinuclear Mn Complexes to Cr Centers in Silica Nanopores

    SciTech Connect

    Weare, W.W.; Pushkar, Y.; Yachandra, V.K.; Frei, H.

    2009-05-26

    The compound (bpy){sub 2}Mn{sup III}({mu}-O){sub 2}Mn{sup IV}(bpy){sub 2}, a structural model relevant for the photosynthetic water oxidation complex, was coupled to single Cr{sup VI} charge-transfer chromophores in the channels of the nanoporous oxide AlMCM-41. Mn K-edge EXAFS spectroscopy confirmed that the di-{mu}-oxo dinuclear Mn core of the complex is unaffected when loaded into the nanoscale pores. Observation of the 16-line EPR signal characteristic of Mn{sup III}({mu}-O){sub 2}Mn{sup IV} demonstrates that the majority of the loaded complexes retained their nascent oxidation state in the presence or absence of Cr{sup VI} centers. The FT-Raman spectrum upon visible light excitation of the Cr{sup VI}-O{sup II} {yields} Cr{sup V}-O{sup I} ligand-to-metal charge transfer reveals electron transfer from Mn{sup III}({mu}-O){sub 2}Mn{sup IV} (Mn-O stretch at 700 cm{sup -1}) to Cr{sup VI}, resulting in the formation of Cr{sup V} and Mn{sup IV}({mu}-O){sub 2}Mn{sup IV} (Mn-O stretch at 645 cm{sup -1}). All initial and final states are directly observed by FT-Raman or EPR spectroscopy, and the assignments are corroborated by X-ray absorption spectroscopy measurements. The endoergic charge separation products ({Delta}E{sub o} = -0.6 V) remain after several minutes, which points to spatial separation of Cr{sup V} and Mn{sup IV}({mu}-O){sub 2}Mn{sup IV} as a consequence of hole (O{sup I}) hopping as a major contributing mechanism. This is the first observation of visible light-induced oxidation of a potential water oxidation complex by a metal charge-transfer pump in a nanoporous environment. These findings will allow for the assembly and photochemical characterization of well-defined transition metal molecular units, with the ultimate goal of performing endothermic, multielectron transformations that are coupled to visible light electron pumps in nanostructured scaffolds.

  1. Should "Teacher Centred Teaching" Replace "Student Centred Learning"?

    ERIC Educational Resources Information Center

    Bailey, Patrick D.

    2008-01-01

    Mission statements of most HEIs across the UK support "student centred learning". In this paper, it is suggested that "teacher centred teaching" should also have a major role to play, improving the quality of the learning experience in higher education. Students are extremely diverse in their skills, weaknesses, and learning…

  2. Should "Teacher Centred Teaching" Replace "Student Centred Learning"?

    ERIC Educational Resources Information Center

    Bailey, Patrick D.

    2008-01-01

    Mission statements of most HEIs across the UK support "student centred learning". In this paper, it is suggested that "teacher centred teaching" should also have a major role to play, improving the quality of the learning experience in higher education. Students are extremely diverse in their skills, weaknesses, and learning…

  3. Design of a dinuclear nickel(II) bioinspired hydrolase to bind covalently to silica surfaces: synthesis, magnetism, and reactivity studies.

    PubMed

    Piovezan, Clovis; Silva, Jaqueline M R; Neves, Ademir; Bortoluzzi, Adailton J; Haase, Wolfgang; Tomkowicz, Zbigniew; Castellano, Eduardo E; Hough, Tessa C S; Rossi, Liane M

    2012-06-04

    Presented herein is the design of a dinuclear Ni(II) synthetic hydrolase [Ni(2)(HBPPAMFF)(μ-OAc)(2)(H(2)O)]BPh(4) (1) (H(2)BPPAMFF = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl)])-4-methyl-6-formylphenol) to be covalently attached to silica surfaces, while maintaining its catalytic activity. An aldehyde-containing ligand (H(2)BPPAMFF) provides a reactive functional group that can serve as a cross-linking group to bind the complex to an organoalkoxysilane and later to the silica surfaces or directly to amino-modified surfaces. The dinuclear Ni(II) complex covalently attached to the silica surfaces was fully characterized by different techniques. The catalytic turnover number (k(cat)) of the immobilized Ni(II)Ni(II) catalyst in the hydrolysis of 2,4-bis(dinitrophenyl)phosphate is comparable to the homogeneous reaction; however, the catalyst interaction with the support enhanced the substrate to complex association constant, and consequently, the catalytic efficiency (E = k(cat)/K(M)) and the supported catalyst can be reused for subsequent diester hydrolysis reactions.

  4. A new dinuclear Ru-Hbpp based water oxidation catalyst with a trans-disposition of the Ru-OH.

    PubMed

    Mola, Joaquim; Dinoi, Chiara; Sala, Xavier; Rodríguez, Montserrat; Romero, Isabel; Parella, Teodor; Fontrodona, Xavier; Llobet, Antoni

    2011-04-14

    The bis(2-pyridyl)ethylamine (bpea) ligand has been used as a starting material for the synthesis of dinuclear Ru complexes of general formula trans,fac-{[Ru(n)X(bpea)](2)(μ-bpp)}(m+) (for X = Cl, n = II, m = 1, trans-Ru(II)-Cl, 1(+); for X = OH, n = III, m = 3, trans-Ru(III)-OH, 2(3+)) where the 3,5-bis(2-pyridyl)pyrazolate anionic ligand (bpp) acts as bridging dinucleating ligand, the bpea ligand coordinates in a facial manner and the monodentate ligands X are situated in a trans fashion with regard to one another. These complexes have been characterized in solution by 1D and 2D NMR spectroscopy, UV-vis and electrochemical techniques and in the solid state by X-ray diffraction analysis. The reaction of 1(PF(6)) with Ag(+) generates the corresponding solvated complex where the Cl ligand has been removed as insoluble AgCl, followed by the oxidation of Ru(II) to Ru(III) to generate the corresponding dinuclear complex trans-Ru(III)-OH, 2(PF(6))(3). The latter has been shown to catalytically oxidize water to molecular dioxygen using Ce(IV) as oxidant. Quantitative gas evolution as a function of time has been monitored on line by both manometry and mass spectroscopy (MS) techniques. Relative initial velocities of oxygen formation together with structural considerations rule out an intramolecular O-O bond formation pathway.

  5. The English Teaching Information Centre

    ERIC Educational Resources Information Center

    Roe, Peter

    1977-01-01

    Describes the function of the British Council's English Teaching Information Centre, which serves foreign students, teachers, teacher trainers, scientists, textbook writers, etc. Emphasizes the Centre's work in English for Special Purposes, including an ample library and many services. Address: ETIC, British Council, 10 Spring Gardens, London SW…

  6. Theoretical study of effects of the entrance channel on the relative yield of complete fusion and quasifission in heavy-ion collisions within a dinuclear system approach

    NASA Astrophysics Data System (ADS)

    Soheyli, S.; Khanlari, M. Varasteh

    2016-09-01

    The relative yield of complete fusion and quasifission components for the 12C+204Pb , 19F+197Au , 30Si+186W , and 48Ca+168Er reactions which all lead to the compound nucleus 216Ra are analyzed to calculate the entrance channel effects by comparison of capture, complete fusion, and quasifission cross sections, emission barriers (Bfus*,Bq f ), as well as complete fusion probability estimated by statistical method within the framework of the dinuclear system model. The difference among complete fusion probabilities calculated by the dinuclear system model for different entrance channels can be explained by the hindrance to complete fusion due to the larger inner fusion barrier Bfus* for the transformation of the dinuclear system into a compound nucleus and the increase of the quasifission contribution due to the decreasing of the emission barrier Bq f of quasifission as a function of the angular momentum. Although these reactions with different entrance channels populate the same compound nucleus 216Ra at similar excitation energies, the model predicts the negligible quasifission probability for reactions having higher entrance channel mass asymmetry and the dominant decay channel is complete fission. For reactions induced by massive projectiles such as Si and Ca having lower entrance channel mass asymmetry, the quasifission component is dominant in the evolution of dinuclear system, and the fusion process is extremely hindered.

  7. Anion-controlled self-assembly of two NLO-active dinuclear and molecular square Cu(II) enantiomeric pairs: from antiferromagnetic to ferromagnetic coupling.

    PubMed

    Li, Xi-Li; Kang, Jia-Long; Zhang, Xue-Li; Xiao, Hong-Ping; Wang, Ai-Ling; Zhou, Liming; Fang, Shao-Ming; Liu, Cai-Ming

    2014-12-14

    Two second-order nonlinear optically (NLO)-active dinuclear and square Cu(II) enantiomeric pairs were obtained via the self-assemblies of enantiopure linear bis-bidentate ligands with different copper(II) salts under the identical reaction conditions. Their magnetic properties are switched from antiferromagnetic to ferromagnetic coupling.

  8. Colourimetric and fluorescent detection of oxalate in water by a new macrocycle-based dinuclear nickel complex: a remarkable red shift of the fluorescence band.

    PubMed

    Rhaman, Md Mhahabubur; Fronczek, Frank R; Powell, Douglas R; Hossain, Md Alamgir

    2014-03-28

    A new macrocycle-based dinuclear nickel chemosensor selectively binds oxalate anions both in solution and the solid state, displaying a remarkable red shift of the fluorescence band with a visible colour change in water at physiological pH in the presence of an external dye.

  9. CMCC Data Distribution Centre

    NASA Astrophysics Data System (ADS)

    Aloisio, Giovanni; Fiore, Sandro; Negro, A.

    2010-05-01

    The CMCC Data Distribution Centre (DDC) is the primary entry point (web gateway) to the CMCC. It is a Data Grid Portal providing a ubiquitous and pervasive way to ease data publishing, climate metadata search, datasets discovery, metadata annotation, data access, data aggregation, sub-setting, etc. The grid portal security model includes the use of HTTPS protocol for secure communication with the client (based on X509v3 certificates that must be loaded into the browser) and secure cookies to establish and maintain user sessions. The CMCC DDC is now in a pre-production phase and it is currently used only by internal users (CMCC researchers and climate scientists). The most important component already available in the CMCC DDC is the Search Engine which allows users to perform, through web interfaces, distributed search and discovery activities by introducing one or more of the following search criteria: horizontal extent (which can be specified by interacting with a geographic map), vertical extent, temporal extent, keywords, topics, creation date, etc. By means of this page the user submits the first step of the query process on the metadata DB, then, she can choose one or more datasets retrieving and displaying the complete XML metadata description (from the browser). This way, the second step of the query process is carried out by accessing to a specific XML document of the metadata DB. Finally, through the web interface, the user can access to and download (partially or totally) the data stored on the storage device accessing to OPeNDAP servers and to other available grid storage interfaces. Requests concerning datasets stored in deep storage will be served asynchronously.

  10. RTEMS CENTRE - Support and Maintenance CENTRE to RTEMS Operating System

    NASA Astrophysics Data System (ADS)

    Silva, H.; Constantino, A.; Mota, M.; Freitas, D.; Zulianello, M.

    2007-08-01

    Real Time Operating System for Multiprocessor Systems (RTEMS) CENTRE is a project under the ESA-Portugal Task Force aiming to develop a support and maintenance centre to RTEMS operating system. The project can be summarized in two main streams, first one related to design, development, maintenance and integration of tools to augment and sustain RTEMS operating system and second stream linked to the creation of technical competences with a support site to RTEMS operating system in Europe. RTEMS CENTRE intends to minimize the cost of the incorporation/integration of airborne and space applications in this Real Time Operating System. The centre started officially in the 15th of November 2006 and is currently in the study definition and system engineering phase.

  11. Minister unveils new nanotech centres

    NASA Astrophysics Data System (ADS)

    Dumé, Belle

    2009-06-01

    Three new nanotechnology research centres are to be set up in France as part of a €70m government plan to help French companies in the sector. Researchers at the new centres, which will be located in Grenoble, Saclay (near Paris) and Toulouse, will be encouraged to collaborate with industry to develop new nanotech-based products. Dubbed NANO-INNOV, the new plan includes €46m for two new buildings at Saclay, with the rest being used to buy new equipment at the three centres and to fund grant proposals from staff to the French National Research Agency (ANR).

  12. Triply Halide-Bridged Dinuclear Iridium(III) Complexes with Chiral Diphosphine Ligands as New Easy-to-Handle Iridium Catalysts for Asymmetric Hydrogenation of Imines and N-Heteroaromatics.

    PubMed

    Mashima, Kazushi; Higashida, Kosuke; Iimuro, Atsuhiro; Nagae, Haruki; Kita, Yusuke

    2016-12-01

    Iridium(III) complexes bearing chiral ligands have proved to be active species in asymmetric hydrogenation of C=N bonds, though there are only a few iridium(III) precursors. We prepared triply halide-bridged dinuclear iridium complexes bearing chiral diphosphine ligands by simple treatment of the iridium(I) precursor, chiral diphosphine, and aqueous hydrogen halide. The strong advantage of these dinuclear iridium complexes is that they are air and moisture stable, leading to easy handling in asymmetric synthesis. The dinuclear iridium complexes exhibited high catalytic activity toward asymmetric hydrogenation of imines and N-heteroaromatics. Moreover, we demonstrated the application of triply halide-bridged dinuclear ruthenium(II) and rhodium(III) catalyst precursors for the asymmetric hydrogenation of ketonic substrates and simple olefins, respectively. © 2016 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Solvent-control of photoinduced electron transfer via hydrogen bonding in a molecular triad made of a dinuclear chromophore subunit

    NASA Astrophysics Data System (ADS)

    Arrigo, Antonino; Nastasi, Francesco; La Ganga, Giuseppina; Puntoriero, Fausto; Zappalà, Gabriella; Licciardello, Antonino; Cavazzini, Marco; Quici, Silvio; Campagna, Sebastiano

    2017-09-01

    We have prepared a molecular triad containing a triphenylamine as the electron donor D subunit, an anthraquinone derivative as the acceptor A group, and a dinuclear Ru(II) species (P-P) based on terpyridine-like ligands as light-harvesting subunit, so that a linearly arranged D-(P-P)-A molecular triad is obtained. In acetonitrile solution containing 1% (in volume) of methanol, photoinduced oxidative electron transfer occurs in 380 ps, with formation of the D-(P-P)+-A- charge-separated (CS) state. However, although formation of the fully-developed D+-(P-P)-A- state is favored by about 0.23 eV, such species is not formed since charge recombination within D-(P-P)+-A- appears to be faster.

  14. Mono- and dinuclear cationic iridium(III) complexes bearing a 2,5-dipyridylpyrazine (2,5-dpp) ligand.

    PubMed

    Donato, Loïc; McCusker, Catherine E; Castellano, Felix N; Zysman-Colman, Eli

    2013-08-05

    The synthesis, X-ray structures, photophysical, and electrochemical characterization of mono- (1) and dinuclear (2) cationic iridium(III) complexes bearing a 2,5-dipyridylpyrazine (2,5-dpp) ancillary ligand are reported. Upon the complexation of a first equivalent of iridium, the photoluminescence shifts markedly into the deep red (λem = 710 nm, ΦPL = 0.9%) compared to other cationic iridium complexes such as [Ir(ppy)2(bpy)]PF6. With the coordination of a second equivalent of iridium, room temperature luminescence is completely quenched. Both 1 and 2 are luminescent at low temperatures but with distinct excited state decay kinetics; the emission of 2 is significantly red-shifted compared to 1. Emission both at 298 and 77 K results from a mixed charge-transfer state. Density functional theory (DFT) calculations and electrochemical behavior point to an electronic communication between the two iridium complexes.

  15. Unsymmetric mono- and dinuclear platinum(IV) complexes featuring an ethylene glycol moiety: synthesis, characterization, and biological activity.

    PubMed

    Pichler, Verena; Heffeter, Petra; Valiahdi, Seied M; Kowol, Christian R; Egger, Alexander; Berger, Walter; Jakupec, Michael A; Galanski, Markus; Keppler, Bernhard K

    2012-12-27

    Eight novel mononuclear and two dinuclear platinum(IV) complexes were synthesized and characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, mass spectrometry, and reversed-phase HPLC (log k(w)) and in one case by X-ray diffraction. Cytotoxicity of the compounds was studied in three human cancer cell lines (CH1, SW480, and A549) by means of the MTT assay, featuring IC(50) values to the low micromolar range. Furthermore a selected set of compounds was investigated in additional cancer cell lines (P31 and P31/cis, A2780 and A2780/cis, SW1573, 2R120, and 2R160) with regard to their resistance patterns, offering a distinctly different scheme compared to cisplatin. To gain further insights into the mode of action, drug uptake, DNA synthesis inhibition, cell cycle effects, and induction of apoptosis were determined for two characteristic substances.

  16. Unsymmetric Mono- and Dinuclear Platinum(IV) Complexes Featuring an Ethylene Glycol Moiety: Synthesis, Characterization, and Biological Activity

    PubMed Central

    Pichler, Verena; Heffeter, Petra; Valiahdi, Seied M.; Kowol, Christian R.; Egger, Alexander; Berger, Walter; Jakupec, Michael A.; Galanski, Markus; Keppler, Bernhard K.

    2014-01-01

    Eight novel mononuclear and two dinuclear platinum(IV) complexes were synthesized and characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, mass spectrometry, and reversed-phase HPLC (log kw) and in one case by X-ray diffraction. Cytotoxicity of the compounds was studied in three human cancer cell lines (CH1, SW480, and A549) by means of the MTT assay, featuring IC50 values to the low micromolar range. Furthermore a selected set of compounds was investigated in additional cancer cell lines (P31 and P31/cis, A2780 and A2780/cis, SW1573, 2R120, and 2R160) with regard to their resistance patterns, offering a distinctly different scheme compared to cisplatin. To gain further insights into the mode of action, drug uptake, DNA synthesis inhibition, cell cycle effects, and induction of apoptosis were determined for two characteristic substances. PMID:23194425

  17. Dinuclear copper(I) and copper(I)/silver(I) complexes with condensed dithiolato ligands.

    PubMed

    Vicente, José; González-Herrero, Pablo; García-Sánchez, Yolanda; Bautista, Delia

    2008-11-17

    The Cu(III) complex Pr 4N[Cu{S 2C=( t-Bu-fy)} 2] ( 1) ( t-Bu-fy = 2,7-di- tert-butylfluoren-9-ylidene) reacts with [Cu(PR 3) 4]ClO 4 in 1:1 molar ratio in MeCN to give the dinuclear complexes [Cu 2{[SC=( t-Bu-fy)] 2S}(PR 3) n ] [ n = 2, R = Ph ( 2a); n = 3, R = To ( 3b); To = p-tolyl]. The analogue of 2a with R = To ( 2b) can be obtained from the reaction of 3b with 1/8 equiv of S 8. Compound 2b establishes a thioketene-exchange equilibrium in solution leading to the formation of [Cu 4{S 2C=( t-Bu-fy)} 2(PTo 3) 4] ( 4b) and [Cu 2{[SC=( t-Bu-fy)] 3S}(PTo 3) 2] ( 5b). Solid mixtures of 4b and 5b in varying proportions can be obtained when the precipitation of 2b is attempted using MeCN. The reactions of 1 with AgClO 4 and PPh 3, PTo 3 or PCy 3 in 1:1:4 molar ratio in MeCN afford the heterodinuclear complexes [AgCu{[SC=( t-Bu-fy)] 2S}(PR 3) 3] [R = Ph ( 6a), To ( 6b), Cy ( 6c)]. Complex 6c dissociates PCy 3 in solution to give the bis(phosphine) derivative [AgCu{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 7c), which undergoes the exchange of [M(PCy 3)] (+) units in CD 2Cl 2 solution to give small amounts of [Cu 2{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 2c) and [Ag 2{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 8c). Complexes 6a and b participate in a series of successive equilibria in solution, involving the dissociation of phosphine ligands and the exchange of [M(PCy 3)] (+) units to give 2a or 3b and the corresponding disilver derivatives [Ag 2{[SC=( t-Bu-fy)] 2S}(PR 3) 2] [R = Ph ( 8a), To ( 8b)], followed by thioketene-exchange reactions to give [AgCu{[SC=( t-Bu-fy)] 3S}(PR 3) 2] [R = Ph ( 9a), To ( 9b)]. Complexes 9a and b can be directly prepared from the reactions of 1 with AgClO 4 and PPh 3 or PTo 3 in 1:1:3 molar ratio in THF. The crystal structures of 3b, 6b, 6c, 7c, and 9a have been solved by single-crystal X-ray diffraction studies and, in the cases of 7c and 9a, reveal the formation of short Ag...Cu metallophilic contacts of 2.8157(4) and 2.9606(6) A, respectively.

  18. A series of lanthanoid selenidoantimonates(V): rare examples of lanthanoid selenidoantimonates based on dinuclear lanthanide complexes.

    PubMed

    Xiao, Hong-Ping; Zhou, Jian; Zhao, Rong-Qing; Zhang, Wei-bing; Huang, Yong

    2015-04-07

    A series of new lanthanoid selenidoantimonates(V) [Ln(en)(tepa)SbSe4] (Ln = La (Ia), Ce (Ib), Pr (Ic); en = ethylenediamine, tepa = tetraethylenepentamine) and [Ln2(tepa)2(μ-OH)2Cl2]-{[Ln(tepa)]2(μ-OH)2(SbSe4)2} (Ln = Y (IIa), Sm (IIb), Gd (IIc), Tb (IId), Dy (IIe), and Tm (IIf)) were solvothermally synthesized and structurally characterized. The structures of Ia-c consist of neutral molecules [Ln(en)(tepa)SbSe4], where the tetrahedral [SbSe4](3-) anion acts as a ligand to chelate the [Ln(en)(tepa)](3+) cation. The structures of IIa-f contain isolated dinuclear [Ln2(tepa)2(μ-OH)2Cl2](2+) cations built up from two [Ln(tepa)Cl](2+) ions linked by two -OH bridging groups and organic decorated {[Ln(tepa)]2(μ-OH)2(SbSe4)2}(2-) anions based on two [Ln(tepa)SbSe4] units bridged by two -OH groups. Although a few lanthanoid selenidoantimonates(V) under solvothermal conditions have been reported, their lanthanide complexes normally appear mononuclear. Hence, IIa-f are rare examples of lanthanoid selenidoantimonates based on dinuclear lanthanide complexes. A preliminary investigation of nine lanthanoid selenidoantimonates(V) shows that the well-known lanthanide contraction has a significant influence on the formation of lanthanoid selenidoantimonates(V) under solvothermal conditions. The absorption edges of all compounds have been investigated by UV-vis spectroscopy, and density functional theory calculations for Ia and IIc have also been performed.

  19. Mono and dinuclear phosphinegold(I) sulfanylcarboxylates: influence of nuclearity and substitution of PPh3 for PEt3 on cytotoxicity.

    PubMed

    Barreiro, Elena; Casas, José S; Couce, María D; Sánchez, Agustín; Sánchez-Gonzalez, Angeles; Sordo, José; Vázquez-López, Ezequiel M

    2014-09-01

    Gold complexes of the type [Au(PEt3)(Hxspa)] were prepared by reacting triethylphosphinegold(I) chloride in ethanol/water (8:1) with the 3-(aryl)-2-sulfanylpropenoic acids H2xspa [x=p=3-phenyl-; f=3-(2-furyl)-; t=3-(2-thienyl)-; py=3-(2-pyridyl); Clp=3-(2-Chlorophenyl)-; -o-mp=3-(2-methoxyphenyl)-; -p-mp=3-(4-methoxyphenyl)-; -o-hp=3-(2-hydroxyphenyl)-; -p-hp=3-(4-hydroxyphenyl)-; -diBr-o-hp=3-(3,5-dibromo-2-hidroxyphenyl-); spa=2-sulfanylpropenoato] or 2-cyclopentylidene-2-sulfanylacetic acid (H2cpa) and KOH in a 1:1:1 mole ratio. The compounds were characterized by IR spectroscopy and FAB mass spectrometry and by (1)H, (13)C and (31)P NMR spectroscopy. The in vitro antitumor activity of these and of the previously described dinuclear [(AuPEt3)2(xspa)] complexes against the HeLa-229, A2780 and A2780cis cell lines was determined and compared with those of the analogous PPh3 complexes. The results show that the substitution of the PPh3 ligand by PEt3 is particularly effective in increasing the cytotoxicity of the dinuclear [(AuPR3)2(xspa)] complexes, giving rise to compounds that are significantly more active than cisplatin against the aforementioned cell lines. In addition, and as a preliminary test for nephrotoxicity, the cytotoxicity of the most active compounds against the normal renal LCC-PK1 cell line was evaluated and compared with that of cisplatin.

  20. Cleavage of an RNA model catalyzed by dinuclear Zn(II) complexes containing rate-accelerating pendants. Comparison of the catalytic benefits of H-bonding and hydrophobic substituents.

    PubMed

    Mohamed, Mark F; Brown, R Stan

    2010-12-17

    The transesterification of a simple RNA model, 2-hydroxypropyl p-nitrophenyl phosphate (2, HpNPP) promoted by seven dinuclear Zn(II) catalysts (3,4,5,6,7,8,9:Zn(II)2:(-OCH3)) based on the bis[bis(2-substituted-pyridinyl-6-methyl)]amine ligand system was investigated in methanol under sspH-controlled conditions at 25.0 ± 0.1 °C. The two metal complexing ligands were joined together via the amino N connected to a m-xylyl linker (3, 4, 5, 6, 7) where the 2-pyridinyl substituent = H, CH3, (CH)4, NH2, and NH(C═O)CH3, respectively, and a propyl linker (8, 9) where the ring substituent = H and CH3. All of the dinuclear complexes except 8:Zn(II)2 exhibit saturation kinetics for the kobs versus [catalyst] plots from which one can determine catalyst:substrate binding constants (KM), the catalytic rate constants for their decomposition (kcat), and the second order catalytic rate constants (k2cat = kcat/KM). In the case of 8:Zn(II)2, the plots of kobs versus [catalyst] as a function of sspH are linear, and the catalytic rate constants (k2cat) are defined as the gradients of the plots. Analysis of all of the data at the sspH optimum for each reaction indicates that the presence of the amino and acetamido H-bonding groups and the CH3 group provides similar increases of the kcat terms of 25−50 times that exhibited by the parent complex 3:Zn(II)2. However, in terms of substrate catalyst binding (KM), there is no clear trend that H-bonding groups or the CH3 group provides stronger binding than the parent complex. In terms of the overall second order catalytic rate constant, the CH3, amino, and NH(C═O)CH3 groups provide 20, 10, and 68 times the k2cat observed for the parent complex. In the case of 9:Zn(II)2, the presence of the methyl groups provides a 1000-fold increase in activity (judged by k2cat) over the parent complex 8:Zn(II)2. The results are interpreted to indicate that H-bonding effects may be important for catalysis and less so for substrate binding, but the

  1. Mono- and Dinuclear Iron Complexes of Bis(1-methylimidazol-2-yl)ketone (bik): Structure, Magnetic Properties and Catalytic Oxidation Studies

    PubMed Central

    Bruijnincx, Pieter C. A.; Buurmans, Inge L. C.; Huang, Yuxing; Juhász, Gergely; Viciano-Chumillas, Marta; Quesada, Manuel; Reedijk, Jan; Lutz, Martin; Spek, Anthony L.; Münck, Eckard; Bominaar, Emile L.; Klein Gebbink, Robertus J. M.

    2011-01-01

    The newly synthesized dinuclear complex [FeIII2(μ-OH)2(bik)4](NO3)4 (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) Å) and Fe–O distances (1.941(2)/1.949(2) Å) compared to other unsupported FeIII2(μ-OH)2 complexes. The bridging hydroxide groups of 1 are strongly hydrogen bonded to a nitrate anion. The 57Fe isomer shift (δ = 0.45 mm s−1) and quadrupole splitting (ΔEQ = 0.26 mm s−1) obtained from Mössbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm−1 and = JS1·S2) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 Å, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 Å) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [FeII(bik)3]2+ species. Variable temperature magnetic susceptibility measurements of [FeII(bik)3](OTf)2 (2) revealed spin crossover behavior. Thermal hysteresis was observed with 2, due to a loss of co-crystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [FeII(bik)3](OTf)2 (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O2, and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under

  2. Mono- and dinuclear iron complexes of bis(1-methylimidazol-2-yl)ketone (bik): structure, magnetic properties, and catalytic oxidation studies.

    PubMed

    Bruijnincx, Pieter C A; Buurmans, Inge L C; Huang, Yuxing; Juhász, Gergely; Viciano-Chumillas, Marta; Quesada, Manuel; Reedijk, Jan; Lutz, Martin; Spek, Anthony L; Münck, Eckard; Bominaar, Emile L; Klein Gebbink, Robertus J M

    2011-10-03

    The newly synthesized dinuclear complex [Fe(III)(2)(μ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) Å) and Fe-O distances (1.941(2)/1.949(2) Å) compared to other unsupported Fe(III)(2)(μ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mössbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 Å, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 Å) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen

  3. Synthesis, magnetic behaviour, and X-ray structures of dinuclear copper complexes with multiple bridges. Efficient and selective catalysts for polymerization of 2,6-dimethylphenol.

    PubMed

    Murugavel, Ramaswamy; Pothiraja, Ramasamy; Gogoi, Nayanmoni; Clérac, Rodolphe; Lecren, Lollita; Butcher, Ray J; Nethaji, Munirathinam

    2007-06-21

    The use of a potentially tridentate mono-anionic bridging ligand, 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-2-ol (bdmpp-H), in assembling new dimeric copper complexes with interesting magnetic properties has been investigated. The reaction of copper hydroxide or copper acetate with phenyl phosphinic acid or diphenyl phosphinic acid in the presence of bdmpp-H produces the dinuclear complexes [Cu(bdmpp)(ppi)]2 (1) and [Cu(bdmpp)(dppi-H)]2(dppi)2 (2) (ppi-H = phenylphosphinic acid: dppi-H = diphenylphosphinic acid), respectively. The products have been characterized with the help of analytical, thermal, and spectroscopic (IR, UV-vis, and EPR) techniques. Single crystal X-ray diffraction studies of 1 and 2 reveal that the two bdmpp ligands hold together the dimeric copper unit in each complex through mu-O alkoxide and the pyrazolyl nitrogen ligating centers. Two phenyl phosphinate ligands additionally bridge the dicopper core in 1 to result in octahedral coordination geometry around each metal ion. The diphenyl phosphinic acid acts as a terminal ligand in 2, and thus completes a square pyramidal geometry around each copper ion. Both complexes show a very short Cu...Cu separation (3.001 and 3.065 angstroms for 1 and 2, respectively). The investigation of the magnetic properties reveals the efficiency of the double alkoxide bridge between the two paramagnetic copper ions to mediate strong antiferromagnetic interactions [J/k(B) = -620(5) K (-431(4) cm(-1)) and -685(5) K (-476(4) cm(-1)) for 1 and 2, respectively]. Compounds 1 and 2, along with a few other copper phosphate complexes, were tested as catalysts for the oxidative polymerization of 2,6-dimethylphenol; 1 and 2 were found to be efficient catalysts with an increased selectivity for the formation of the polyphenylene ether. However a related mononuclear octahedral copper complex [Cu(imz)4(dtbp)2] (dtbp-H = di-tert-butylphosphate) was found to be more efficient.

  4. A Density Functional Study for the Bridged Dinuclear Center Based on a High Resolution X-ray Crystal Structure of ba3 Cytochrome c Oxidase from Thermus thermophilus

    PubMed Central

    Du, Wen-Ge Han; Noodleman, Louis

    2014-01-01

    Strong electron density for a peroxide type dioxygen species bridging the Fea3 and CuB dinuclear center (DNC) was observed in the high resolution (1.8 Å) X-ray crystal structures (PDB entries: 3S8G and 3S8F) of ba3 cytochrome c oxidase (CcO) from Thermus thermophilus (Tiefenbrunn et al. PLos ONE 2011, 7, e22348). The crystals represent the as-isolated X-ray photoreduced CcO structures. The bridging peroxide was proposed to arise from the recombination of two radiation produced HO· radicals formed either very near to or even in the space between the two metals of the DNC. It is unclear whether this peroxide species is in the O22−, O2·−, HO2−, or in the H2O2 form, and what is the detailed electronic structure and binding geometry including the DNC. In order to answer what form of this dioxygen species was observed in the DNC of the 1.8 Å X-ray CcO crystal structure (3S8G), we have applied broken-symmetry density functional theory (BS-DFT) geometric and energetic calculations (using OLYP potential) on large DNC cluster models with different Fea3-CuB oxidation and spin states and with either O22−, O2·−, HO2−, or H2O2 in the bridging position. By comparing the DFT optimized geometries with the X-ray crystal structure (3S8G), we propose that the bridging peroxide is HO2−. The X-ray crystal structure is likely to represent the superposition of the Fea32+-(HO2−)-CuB1+ DNC’s in different states (Fe2+ in low-spin (LS), intermediate-spin (IS), or high-spin (HS)) with the majority species having the proton of the HO2− residing on the oxygen atom (O1) which is closer to the Fea32+ site in the Fea32+-(HO-O)−-CuB1+ conformation. Our calculations show that the sidechain of Tyr237 is likely trapped in the deprotonated Tyr237− anion form in the 3S8G X-ray crystal structure. PMID:24262070

  5. Density functional study for the bridged dinuclear center based on a high-resolution X-ray crystal structure of ba3 cytochrome c oxidase from Thermus thermophilus.

    PubMed

    Du, Wen-Ge Han; Noodleman, Louis

    2013-12-16

    Strong electron density for a peroxide type dioxygen species bridging the Fea3 and CuB dinuclear center (DNC) was observed in the high-resolution (1.8 Å) X-ray crystal structures (PDB entries 3S8G and 3S8F) of ba3 cytochrome c oxidase (CcO) from Thermus thermophilus. The crystals represent the as-isolated X-ray photoreduced CcO structures. The bridging peroxide was proposed to arise from the recombination of two radiation-produced HO(•) radicals formed either very near to or even in the space between the two metals of the DNC. It is unclear whether this peroxide species is in the O2(2-), O2(•)(-), HO2(-), or the H2O2 form and what is the detailed electronic structure and binding geometry including the DNC. In order to answer what form of this dioxygen species was observed in the DNC of the 1.8 Å X-ray CcO crystal structure (3S8G), we have applied broken-symmetry density functional theory (BS-DFT) geometric and energetic calculations (using OLYP potential) on large DNC cluster models with different Fea3-CuB oxidation and spin states and with O2(2-), O2(•)(-), HO2(-), or H2O2 in the bridging position. By comparing the DFT optimized geometries with the X-ray crystal structure (3S8G), we propose that the bridging peroxide is HO2(-). The X-ray crystal structure is likely to represent the superposition of the Fea3(2+)-(HO2(-))-CuB(+) DNC's in different states (Fe(2+) in low spin (LS), intermediate spin (IS), or high spin (HS)) with the majority species having the proton of the HO2(-) residing on the oxygen atom (O1) which is closer to the Fea3(2+) site in the Fea3(2+)-(HO-O)(-)-CuB(+) conformation. Our calculations show that the side chain of Tyr237 is likely trapped in the deprotonated Tyr237(-) anion form in the 3S8G X-ray crystal structure.

  6. Synthesis and some first-row transition-metal complexes of the 1,2,4-triazole-based Bis(terdentate) ligands TsPMAT and PMAT.

    PubMed

    Klingele, Marco H; Moubaraki, Boujemaa; Murray, Keith S; Brooker, Sally

    2005-11-18

    The employment of a strategy based on nucleophilic substitution, rather than Schiff base condensation, for the preparation of 1,2,4-triazole-based ligands has been investigated and has led to the synthesis of two new ligands, 4-amino-3,5-bis{[N-(2-pyridylmethyl)-N-(4-toluenesulfonyl)amino]methyl}-4H-1,2,4-triazole (TsPMAT, 14) and 4-amino-3,5-bis{[(2-pyridylmethyl)amino]methyl}-4H-1,2,4-triazole (PMAT, 15). These are the first examples of bis(terdentate) ligands incorporating the 1,2,4-triazole unit. TsPMAT (14) forms a dinuclear 2:2 complex with Co(BF4)2.6 H2O even when reacted in a metal-to-ligand molar ratio of 2:1. Similarly, the reaction of PMAT (15) with Mn(ClO4)2.6H2O or M(BF4)2.6 H2O (M=Fe, Co, Ni, Zn) in a ligand-to-metal molar ratio of 1:1 has afforded a series of complexes with the general formula [M(II) (2)(PMAT)2]X4. The metal centres in these complexes of TsPMAT (14) and PMAT (15) are encapsulated by two ligand molecules and doubly bridged by the N2 units of the 1,2,4-triazole moieties, which gives rise to N6 coordination spheres that are strongly distorted from octahedral, as evidenced by the X-ray crystal structure analyses of [Co(II) (2)(TsPMAT)(2)](BF(4))(4)6 MeCN (246 MeCN) and [Fe(II) 2(PMAT)2](BF4)4DMF (27DMF). Studies of the magnetic properties of [Co(II) 2(TsPMAT)2](BF4)4.4 H2O (244 H2O), [Mn(II) 2(PMAT)2](ClO4)4 (26), and [Co(II) 2(PMAT)2](BF4)4 (28) have revealed weak antiferromagnetic coupling (J=-3.3, -0.16, and -2.4 cm(-1), respectively) between the two metal centres in these complexes.

  7. Dinuclear uranium alkoxides. Preparation and structures of KU/sub 2/(OCMe/sub 3/)/sub 9/, U/sub 2/(OCMe/sub 3/)/sub 9/, and U/sub 2/(OCHMe/sub 2/)/sub 10/, containing (U(IV),U(IV)), (U(IV),U(V)), and (U(V), U(V)), respectively

    SciTech Connect

    Cotton, F.A.; Marler, D.O.; Schwotzer, W.

    1984-12-05

    The structural results by x-ray crystallography are reported for three uranium alkoxides, two of which are new compounds. All three are dinuclear in the solid state, and they contain the following combinations of oxidation states; (U(IV), U(VI)), (U(V), U(IV)), and (U(V), U(V)). The crystal parameters and U...U bond distances are given for all three compounds. The terminal alkoxide groups in all three compounds display nearly linear U-O-C arrangements, with U-O-C bond angles between 160 and 176/sup 0/. This appears to be a general feature of uranium alkoxides and suggests a high degree of O..pi.. ..-->.. U contributions to the metal-oxygen bonds.

  8. Experimental evidence for a metallohydrolase mechanism in which the nucleophile is not delivered by a metal ion: EPR spectrokinetic and structural studies of aminopeptidase from Vibrio proteolyticus

    PubMed Central

    Kumar, Amit; Periyannan, Gopal Raj; Narayanan, Beena; Kittell, Aaron W.; Kim, Jung-Ja; Bennett, Brian

    2007-01-01

    Metallohydrolases catalyse some of the most important reactions in biology and are targets for numerous chemotherapeutic agents designed to combat bacterial infectivity, antibiotic resistance, HIV infectivity, tumour growth, angiogenesis and immune disorders. Rational design of inhibitors of these enzymes with chemotherapeutic potential relies on detailed knowledge of the catalytic mechanism. The roles of the catalytic transition ions in these enzymes have long been assumed to include the activation and delivery of a nucleophilic hydroxy moiety. In the present study, catalytic intermediates in the hydrolysis of L-leucyl-L-leucyl-L-leucine by Vibrio proteolyticus aminopeptidase were characterized in spectrokinetic and structural studies. Rapid-freeze-quench EPR studies of reaction products of L-leucyl-L-leucyl-L-leucine and Co(II)-substituted aminopeptidase, and comparison of the EPR data with those from structurally characterized complexes of aminopeptidase with inhibitors, indicated the formation of a catalytically competent post-Michaelis pre-transition state intermediate with a structure analogous to that of the inhibited complex with bestatin. The X-ray crystal structure of an aminopeptidase–L-leucyl-L-leucyl-L-leucine complex was also analogous to that of the bestatin complex. In these structures, no water/hydroxy group was observed bound to the essential metal ion. However, a water/hydroxy group was clearly identified that was bound to the metal-ligating oxygen atom of Glu152. This water/hydroxy group is proposed as a candidate for the active nucleophile in a novel metallohydrolase mechanism that shares features of the catalytic mechanisms of aspartic proteases and of B2 metallo-β-lactamases. Preliminary studies on site-directed variants are consistent with the proposal. Other features of the structure suggest roles for the dinuclear centre in geometrically and electrophilically activating the substrate. PMID:17238863

  9. Interplay of metal ions and urease

    PubMed Central

    Carter, Eric L.; Flugga, Nicholas; Boer, Jodi L.; Mulrooney, Scott B.; Hausinger, Robert P.

    2009-01-01

    Summary Urease, the first enzyme to be crystallized, contains a dinuclear nickel metallocenter that catalyzes the decomposition of urea to produce ammonia, a reaction of great agricultural and medical importance. Several mechanisms of urease catalysis have been proposed on the basis of enzyme crystal structures, model complexes, and computational efforts, but the precise steps in catalysis and the requirement of nickel versus other metals remain unclear. Purified bacterial urease is partially activated via incubation with carbon dioxide plus nickel ions; however, in vitro activation also has been achieved with manganese and cobalt. In vivo activation of most ureases requires accessory proteins that function as nickel metallochaperones and GTP-dependent molecular chaperones or play other roles in the maturation process. In addition, some microorganisms control their levels of urease by metal ion-dependent regulatory mechanisms. PMID:20046957

  10. Spherical tokamaks with plasma centre-post

    NASA Astrophysics Data System (ADS)

    Ribeiro, Celso

    2013-10-01

    The metal centre-post (MCP) in tokamaks is a structure which carries the total toroidal field current and also houses the Ohmic heating solenoid in conventional or low aspect ratio (Spherical)(ST) tokamaks. The MCP and solenoid are critical components for producing the toroidal field and for the limited Ohmic flux in STs. Constraints for a ST reactor related to these limitations lead to a minimum plasma aspect ratio of 1.4 which reduces the benefit of operation at higher betas in a more compact ST reactor. Replacing the MCP is of great interest for reactor-based ST studies since the device is simplified, compactness increased, and maintenance reduced. An experiment to show the feasibility of using a plasma centre-post (PCP) is being currently under construction and involves a high level of complexity. A preliminary study of a very simple PCP, which is ECR(Electron Cyclotron Resonance)-assisted and which includes an innovative fuelling system based on pellet injection, has recently been reported. This is highly suitable for an ultra-low aspect ratio tokamak (ULART) device. Advances on this PCP ECR-assisted concept within a ULART and the associated fuelling system are presented here, and will include the field topology for the PCP ECR-assisted scheme, pellet ablation modeling, and a possible global equilibrium simulation. VIE-ITCR, IAEA-CRP contr.17592, National Instruments-Costa Rica.

  11. The digital eczema centre utrecht.

    PubMed

    van Os-Medendorp, Harmieke; van Veelen, Carien; Hover, Maaike; Eland-de Kok, Petra; Bruijnzeel-Koomen, Carla; Sonnevelt, Gert-Jan; Mensing, Geert; Pasmans, Suzanne

    2010-01-01

    The University Medical Centre Utrecht (UMC Utrecht) has developed an eczema portal that combines e-consulting, monitoring and self-management training by a dermatology nurse online for patients and parents of young children with atopic dermatitis (AD). Patient satisfaction with the portal was high. It could be extended to become a Digital Eczema Centre for multidisciplinary collaboration between health-care providers from different locations and the patient. Before starting the construction of the Digital Eczema Centre, the feasibility was examined by carrying out a business case analysis. The purposes, strength and weaknesses showed that the Digital Eczema Centre offered opportunities to improve care for patients with AD. The financial analysis resulted in a medium/best case scenario with a positive result of euro50-240,000 over a period of five years. We expect that the Digital Eczema Centre will increase the accessibility and quality of care. The web-based patient record and the digital chain-of-care promote the involvement of patients, parents and multidisciplinary teams as well as the continuity and coordination of care.

  12. Person-centred reflective practice.

    PubMed

    Devenny, Bob; Duffy, Kathleen

    Person-centred health and person-centred care have gained prominence across the UK following the publication of reports on public inquiries exploring failings in care. Self-awareness and participation in reflective practice are recognised as vital to supporting the person-centred agenda. This article presents an education framework for reflective practice, developed and used in one NHS board in Scotland, and based on the tenets of the clinical pastoral education movement. Providing an insight into the usefulness of a spiritual component in the reflective process, the framework provides an opportunity for nurses and other healthcare professionals to examine the spiritual dimensions of patient encounters, their own values and beliefs, and the effect these may have on their practice.

  13. X-ray absorption spectroscopic studies of the dinuclear iron center in methane monooxygenase and the sulfure and chlorine centers in photographic materials

    SciTech Connect

    DeWitt, Jane G.

    1992-12-01

    The dinuclear iron center of the hydroxylase component of soluble methane monooxygenase (MMO) from Methylococcus capsulatus and Methylosinus trichosporiwn has been studied by X-ray absorption spectroscopy. Analysis of the Fe K-edge EXAFS revealed that the first shell coordination of the Fe(HI)Fe(IH) oxidized state of the hydroxylase from M. capsulatus consists of approximately 6 N and 0 atoms at an average distance of 2.04 Å. The Fe-Fe distance was determined to be 3.4 Å. No evidence for the presence of a short oxo bridge in the iron center of the oxidized hydroxylase was found, suggesting that the active site of MMO is significantly different from the active sites of the dinuclear iron proteins hemery and ribonucleotide reductase. In addition, the results of the first shell fits suggest that there are more oxygen than nitrogen donor ligands.

  14. X-ray absorption spectroscopic studies of the dinuclear iron center in methane monooxygenase and the sulfure and chlorine centers in photographic materials

    SciTech Connect

    DeWitt, J.G.

    1992-12-01

    The dinuclear iron center of the hydroxylase component of soluble methane monooxygenase (MMO) from Methylococcus capsulatus and Methylosinus trichosporiwn has been studied by X-ray absorption spectroscopy. Analysis of the Fe K-edge EXAFS revealed that the first shell coordination of the Fe(HI)Fe(IH) oxidized state of the hydroxylase from M. capsulatus consists of approximately 6 N and 0 atoms at an average distance of 2.04 [Angstrom]. The Fe-Fe distance was determined to be 3.4 [Angstrom]. No evidence for the presence of a short oxo bridge in the iron center of the oxidized hydroxylase was found, suggesting that the active site of MMO is significantly different from the active sites of the dinuclear iron proteins hemery and ribonucleotide reductase. In addition, the results of the first shell fits suggest that there are more oxygen than nitrogen donor ligands.

  15. New Cobalt-Mediated Radical Polymerization (CMRP) of Methyl Methacrylate Initiated by Two Single-Component Dinuclear β-Diketone Cobalt (II) Catalysts

    PubMed Central

    Bao, Feng; Feng, Lingling; Gao, Jie; Tan, Zhifang; Xing, Bin; Ma, Rui; Yan, Chunjie

    2010-01-01

    Two dinuclear cobalt complexes based on bis-diketonate ligands (ligand 1: 3,3′-(1,3-phenylene)bis(1-phenylpropane-1,3-dione); ligand 2: 3,3′-(1,4-phenylene)bis(1-phenylpropane-1,3-dione)) were successfully synthesized. The two neutral catalysts all showed satisfactory activities in the cobalt-mediated radical polymerization (CMRP) of methyl methacrylate (MMA) with the common initiator of azodiisobutyronitrile (AIBN). The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities. Mono- or dicomponent low polydispersity polymers could be obtained by using the two dinuclear catalysts under proper reaction conditions. All these improvements facilitate the implementation of the acrylate CMRP and open the door to the scale-up of the syntheses and applications of the multicomponent low polydispersity polymers. PMID:21049027

  16. pH Dependent synthesis of two isomeric dinuclear Cerium(II) complexes: Structures, DNA interactions, cytotoxic activity and apoptotic study.

    PubMed

    Gao, En-Jun; Su, Jun-Qi; Jin, Hai-Tao; Liu, Si-Jia; Zhao, Fu-Chen; Meng, Yang; Ma, Xiao-Yu; Ge, Jing; Sun, Ya-Guang; Zhang, Wanzhong; Zhu, Ming-Chang

    2017-05-01

    Two isomeric dinuclear Cerium(II) complexes 1 and 2, formulated as Ce2(phen)2(NO3)2(L)4 [L=phenylacetic acid, phen=1,10-phenanthroline] was synthesized under solvothermal conditions at different pH values. The two complexes were characterized by elemental analysis, IR and single crystal X-ray diffraction. Complexes 1 and 2 were studied the binding with DNA and against cytotoxic activity. Fluorescence analysis indicated that the two complexes can bind to DNA. The changes with different gradient concentration of DNA added into the complexes in absorption spectra show a strongπ-stacking interaction between the complexes and DNA base pairs. The Cerium(II) complexes showed good cytotoxic activity against cancer cell lines, being 2 the most potent complex. Apoptotic studies of the two novel dinuclear complexes showed significant inhibitory rate on cancer cell growth line KB. Copyright © 2017. Published by Elsevier B.V.

  17. Cooperative reactivity of early-late heterodinuclear transition metal complexes with polar organic substrates

    PubMed

    Gade; Memmler; Kauper; Schneider; Fabre; Bezougli; Lutz; Galka; Scowen; McPartlin

    2000-02-18

    A comprehensive investigation into the cooperative reactivity of two chemically complementary metal-complex fragments in early-late heterodinuclear complexes has been carried out. Reaction of the partially fluorinated tripodal amidozirconium complexes [HC-(SiMe2NR)3Zr(mu-Cl)2Li(OEt2)2] (R = 2-FC6H4: 2a, 2,3,4-F3C6H4: 2b) with K[CpM(CO)2] (M=Fe, Ru) afforded the stable metal-metal bonded heterodinuclear complexes [HC[SiMe2NR]3-Zr-MCp(CO)2] (3-6). Reaction of the dinuclear complexes with methyl isonitrile as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Two of these complexes, [HC[SiMe2N(2-FC6-H4)]3Zr(S2C)Fe(CO)2Cp] (9a) and [HC-[SiMe2N(2-FC2H4)]3Zr-(SCNPh)Fe(CO)2-Cp] (12), have been structurally characterized by a single crystal X-ray structure analysis, proving the structural situation of the inserted substrate as a bridging ligand between the early and late transition metal centre. The reactivity towards organic carbonyl derivatives proved to be varied. Reaction of the heterobimetallic complexes with benzyl and ethylbenzoate led to the cleavage of the ester generating the respective alkoxozirconium complexes [HC[SiMe2N(2-FC6H4)]3ZrOR] (R = Ph-CH2: 13a, Et: 13b) along with [CpFe-[C(O)Ph](CO)2], whereas the analogous reaction with ethyl formate gave 13b along with [CpFeH(CO)2]; this latter complex results from the instability of the formyliron species initially formed. Aryl aldehydes were found to react with the Zr-M complexes according to a Cannizzaro disproportionation pattern yielding the aroyliron and ruthenium complexes along with the respective benzoxyzirconium species. The transfer of the aldehyde hydrogen atom in the course of the reaction was established in a deuteriation experiment. [HC[SiMe2-N(2-FC6H4)]3Zr-M(CO)2Cp] reacted with lactones to give the ring-opened species containing an alkoxozirconium and an acyliron or acylruthenium fragment; the latter binds to the early transition metal centre through

  18. Characterisation of the DNA sequence specificity, cellular toxicity and cross-linking properties of novel bispyridine-based dinuclear platinum complexes.

    PubMed

    Johnson, Ben W; Murray, Vincent; Temple, Mark D

    2016-05-25

    The anti-tumour activity of cisplatin is thought to be a result of its capacity to form DNA adducts which prevent cellular processes such as DNA replication and transcription. These DNA adducts can effectively induce cancer cell death, however, there are a range of clinical side effects and drug resistance issues associated with its use. In this study, the biological properties of three novel dinuclear platinum-based compounds (that contain alkane bridging linkers of eight, ten and twelve carbon atoms in length) were characterised to assess their potential as anticancer agents. The properties of these compounds were determined using a DNA template containing seven tandem telomeric repeat sequences. A linear amplification reaction was used in combination with capillary electrophoresis to quantify the sequence specificity of DNA adducts formed by these compounds at base pair resolution. The DNA cross-linking ability of these compounds was assessed using denaturing agarose gel electrophoresis and cytotoxicity was determined in HeLa cells using a colorimetric cell viability assay. The dinuclear compounds were found to preferentially form DNA adducts at guanine bases and they exhibited different damage intensity profiles at the telomeric repeat sequences compared to that of cisplatin. The dinuclear compounds were found to exhibit a low level of cytotoxicity relative to cisplatin and their cytotoxicity increased as the linker length increased. Conversely, the interstrand cross-linking efficiency of the dinuclear compounds increased as the linker length decreased and the compound with the shortest alkane linker was six-fold more effective than cisplatin. Since the bifunctional compounds exhibit variation in sequence specificity of adduct formation and a greater ability to cross-link DNA relative to cisplatin they warrant further investigation towards the goal of developing new cancer chemotherapeutic agents.

  19. A novel dinuclear iridium(III) complex as a G-quadruplex-selective probe for the luminescent switch-on detection of transcription factor HIF-1α

    PubMed Central

    Lu, Lihua; Wang, Modi; Mao, Zhifeng; Kang, Tian-Shu; Chen, Xiu-Ping; Lu, Jin-Jian; Leung, Chung-Hang; Ma, Dik-Lung

    2016-01-01

    A novel dinuclear Ir(III) complex 5 was discovered to be specific to G-quadruplex DNA, and was utilized in a label-free G-quadruplex-based detection platform for transcription factor activity. The principle of this assay was demonstrated by using HIF-1α as a model protein. Moreover, this HIF-1α detection assay exhibited potential use for biological sample analysis. PMID:26932240

  20. Dinuclear Ru/Ni, Ir/Ni, and Ir/Pt complexes with bridging phenanthroline-5,6-dithiolate: synthesis, structure, and electrochemical and photophysical behavior.

    PubMed

    Schallenberg, David; Neubauer, Antje; Erdmann, Elisa; Tänzler, Marco; Villinger, Alexander; Lochbrunner, Stefan; Seidel, Wolfram W

    2014-09-02

    We report the synthesis and full characterization of dinuclear complexes with the bridging ligand phenanthroline-5,6-dithiolate (phendt(2-)) featuring the [Ru(bpy)2](2+) or Ir(ppy)2](+) fragment at the diimine donor center and the [Ni(dppe)](2+) or [Pt(phen)](2+) complex moiety at the dithiolate group. The molecular structures of the mononuclear complexes [(C5H5)2Ti(S,S'-phendt)] and [(ppy)2Ir{N,N'-phendt-(C2H4CN)2}](PF6) as well as the dinuclear complex [(C5H5)(PPh3)Ru(phendt)Ni(dppe)](PF6) determined by X-ray diffraction (XRD) studies are compared. Photophysical studies with mononuclear [(bpy)2Ru{phendt-(C2H4CN)2}](2+) and [(ppy)2Ir{phendt-(C2H4CN)2}](+) as well as dinuclear [(bpy)2Ru(phendt)Ni(dppe)](2+) and [(ppy)2Ir(phendt)Ni(dppe)](+) uncovered an effective luminescence quenching in the dinuclear complexes. Lifetime measurements at room temperature, steady-state measurements at low temperature, electrochemical investigations, and DFT calculations provide evidence for a very efficient energy transfer from the Ru/Ir to the Ni complex moiety with a rate constant k > 5 × 10(9) s(-1). In comparison, the [Ru]phendt[Ni] complex displays a higher quenching efficiency with reduced excited state lifetime, whereas the [Ir]phendt[Ni] complex is characterized by an unaltered lifetime of the thermally equilibrated excited state.

  1. A dinuclear ruthenium(II) complex as turn-on luminescent probe for hypochlorous acid and its application for in vivo imaging

    PubMed Central

    Liu, Zonglun; Gao, Kuo; Wang, Beng; Yan, Hui; Xing, Panfei; Zhong, Chongmin; Xu, Yongqian; Li, Hongjuan; Chen, Jianxin; Wang, Wei; Sun, Shiguo

    2016-01-01

    A dinuclear ruthenium(II) complex Ruazo was designed and synthesized, in which oxidative cyclization of the azo and o-amino group was employed for the detection of hypochlorous acid (HClO) in aqueous solution. The non-emissive Ruazo formed highly luminescent triazole-ruthenium(II) complex in presence of HClO and successfully imaged HClO in living cell and living mouse. PMID:27356618

  2. Synthesis, characterization, crystal structure, DNA- and HSA-binding studies of a dinuclear Schiff base Zn(II) complex derived from 2-hydroxynaphtaldehyde and 2-picolylamine

    NASA Astrophysics Data System (ADS)

    Kazemi, Zahra; Rudbari, Hadi Amiri; Mirkhani, Valiollah; Sahihi, Mehdi; Moghadam, Majid; Tangestaninejad, Sharam; Mohammadpoor-Baltork, Iraj

    2015-09-01

    A tridentate Schiff base ligand NNO donor (HL: 1-((E)-((pyridin-2-yl)methylimino)methyl)naphthalen-2-ol was synthesized from condensation of 2-hydroxynaphtaldehyde and 2-picolylamine. Zinc complex, Zn2L2(NO3)2, was prepared from reaction of Zn(NO3)2 and HL at ambient temperature. The ligand and complex were characterized by FT-IR, 1H NMR, 13C NMR and elemental analysis (CHN). Furthermore, the structure of dinuclear Zn(II) complex was determined by single crystal X-ray analysis. The complex, Zn2L2(NO3)2, is centrosymmetric dimer in which deprotonated phenolates bridge the two Zn(II) atoms and link the two halves of the dimer. In the structure, Zinc(II) ions have a highly distorted six-coordinate structure bonded to two oxygen atoms from a bidentate nitrate group, the pyridine nitrogen, an amine nitrogen and phenolate oxygens. The interaction of dinuclear Zn(II) complex with fish sperm DNA (FS-DNA) and HSA was investigated under physiological conditions using fluorescence quenching, UV-Vis spectroscopy, molecular dynamics simulation and molecular docking methods. The estimated binding constants for the DNA-complex and HSA-complex were (3.60 ± 0.18) × 104 M-1 and (1.35 ± 0.24) × 104 M-1, respectively. The distance between dinuclear Zn(II) complex and HSA was obtained based on the Förster's theory of non-radiative energy transfer. Molecular docking studies revealed the binding of dinuclear Zn(II) complex to the major groove of FS-DNA and IIA site of protein by formation of hydrogen bond, π-cation and hydrophobic interactions.

  3. A novel dinuclear iridium(III) complex as a G-quadruplex-selective probe for the luminescent switch-on detection of transcription factor HIF-1α

    NASA Astrophysics Data System (ADS)

    Lu, Lihua; Wang, Modi; Mao, Zhifeng; Kang, Tian-Shu; Chen, Xiu-Ping; Lu, Jin-Jian; Leung, Chung-Hang; Ma, Dik-Lung

    2016-03-01

    A novel dinuclear Ir(III) complex 5 was discovered to be specific to G-quadruplex DNA, and was utilized in a label-free G-quadruplex-based detection platform for transcription factor activity. The principle of this assay was demonstrated by using HIF-1α as a model protein. Moreover, this HIF-1α detection assay exhibited potential use for biological sample analysis.

  4. Elucidation of Dual Magnetic Relaxation Processes in Dinuclear Dysprosium(III) Phthalocyaninato Triple-Decker Single-Molecule Magnets Depending on the Octacoordination Geometry.

    PubMed

    Katoh, Keiichi; Aizawa, Yu; Morita, Takaumi; Breedlove, Brian K; Yamashita, Masahiro

    2017-08-07

    When applying single-molecule magnets (SMMs) to spintronic devices, control of the quantum tunneling of the magnetization (QTM) as well as a spin-lattice interactions are important. Attempts have been made to use not only coordination geometry but also magnetic interactions between SMMs as an exchange bias. In this manuscript, dinuclear dysprosium(III) (Dy(III) ) SMMs with the same octacoordination geometry undergo dual magnetic relaxation processes at low temperature. In the dinuclear Dy(III) phthalocyaninato (Pc(2-) ) triple-decker type complex [(Pc)Dy(ooPc)Dy(Pc)] (1) (ooPc(2-) =2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato) with a square-antiprismatic (SAP) geometry, the ground state is divided by the Zeeman effect, and level intersection occurs when a magnetic field is applied. Due to the ground state properties of 1, since the Zeeman diagram where the levels intersect in an Hdc of 2500 Oe, two kinds of QTM and direct processes occur. However, dinuclear Dy(III) -Pc systems with C4 geometry, which have a twist angle (ϕ) of less than 45° do not undergo dual magnetic relaxation processes. From magnetic field and temperature dependences, the dual magnetic relaxation processes were clarified. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Conformation and recognition of DNA modified by a new antitumor dinuclear PtII complex resistant to decomposition by sulfur nucleophiles

    PubMed Central

    Zerzankova, Lenka; Suchankova, Tereza; Vrana, Oldrich; Farrell, Nicholas P.; Brabec, Viktor; Kasparkova, Jana

    2011-01-01

    Reported herein is a detailed biochemical and molecular biophysics study of the molecular mechanism of action of antitumor dinuclear PtII complex [{PtCl(DACH)}2-μ-Y]4+ [DACH = 1,2-diaminocyclohexane, Y =H2N(CH2)6NH2(CH2)2NH2(CH2)6NH2] (complex 1). This new, long-chain bifunctional dinuclear PtII complex is resistant to metabolic decomposition by sulfur-containing nucleophiles. The results show that DNA adducts of 1 can largely escape repair and yet inhibit very effectively transcription so that they should persist longer than those of conventional cisplatin. Hence, they could trigger a number of downstream cellular effects different from those triggered in cancer cells by DNA adducts of cisplatin. This might lead to the therapeutic effects that could radically improve chemotherapy by platinum complexes. In addition, the findings of the present work make new insights into mechanisms associated with antitumor effects of dinuclear/trinuclear PtII complexes possible. PMID:19682435

  6. Luminescent dinuclear copper(I) complexes bearing 1,4-bis(diphenylphosphino)butane and functionalized 3-(2'-pyridyl)pyrazole mixed ligands.

    PubMed

    Chen, Jing-Lin; Guo, Zong-Hao; Yu, Hua-Guang; He, Li-Hua; Liu, Sui-Jun; Wen, He-Rui; Wang, Jin-Yun

    2016-01-14

    A family of new dinuclear Cu(i) complexes with 1,4-bis(diphenylphosphino)butane (dppb) and functionalized 3-(2'-pyridyl)pyrazole mixed ligands has been synthesized and characterized. It is revealed that all these Cu(i) complexes include a [Cu2(dppb)2](2+) framework with the two Cu(i) atoms doubly bridged by a pair of dppb to generate a fourteen-membered Cu2P4C8 ring, and functionalized 3-(2'-pyridyl)pyrazole adopts a neutral chelating coordination mode without the N-H bond cleavage of the pyrazolyl ring. All these dinuclear Cu(i) complexes display a relatively weak low-energy absorption in CH2Cl2 solution, which is closely related to the variation of the Cu-N and Cu-P bonds caused by the substituent on the pyrazolyl ring. These dinuclear Cu(i) complexes are all emissive in solution and solid states at ambient temperature, which can be well modulated through structural modification of 3-(2'-pyridyl)pyrazole. It is shown that introduction of the trifluoromethyl group into the pyrazolyl ring is helpful for enhancing the luminescence properties of Cu(i) pyrazole phosphine complexes.

  7. Structural models for the active site of acetyl-CoA synthase: synthesis of dinuclear nickel complexes having thiolate, isocyanide, and thiourea on the Ni(p) site.

    PubMed

    Ito, Mikinao; Kotera, Mai; Song, Yumei; Matsumoto, Tsuyoshi; Tatsumi, Kazuyuki

    2009-02-02

    The trinuclear nickel complex [{Ni(dadt(Et))}(2)Ni](NiBr(4)) (dadt(Et) = N,N'-diethyl-3,7-diazanonane-1,9-dithiolate) (1a), prepared by the reaction of Ni(dadt(Et)) and Ni(EtOH)(4)Br(2), was found to serve as a useful synthetic precursor of various dinuclear nickel complexes modeling the active site of acetyl-CoA synthase (ACS). The reactions of 1a with 4 equiv of the potassium salts of arenethiolates in ethanol produced a series of dinuclear nickel thiolate complexes Ni(dadt(Et))Ni(SAr)(2) (Ar = Ph (2a), p-Tol (2b), 2,4,6-triisopropylphenyl (Tip) (2c)) in good yields. The analogous reactions of 1a with Ag(OTf) in the presence of (t)BuNC and (NMe(2))(2)CS (tmtu) generated the dicationic dinuclear nickel complexes [Ni(dadt(Et))Ni((t)BuNC)(2)](OTf)(2) (3) and [Ni(dadt(Et))Ni(tmtu)(2)](OTf)(2) (4), respectively. The molecular structures of 1a, 2a-c, 3, and 4 determined by X-ray analysis compare well with that of A-cluster in ACS.

  8. Questioning Centre-Periphery Platforms

    ERIC Educational Resources Information Center

    Postiglione, Gerard A.

    2005-01-01

    How much is hegemony and how much is self-determination in the higher education systems in Southeast Asia? This paper argues that while the question of centre and periphery is still relevant to the analysis of international university systems, the analytical frameworks from which it has arisen may lose viability in the long term. Southeast Asian…

  9. The Tehran Book Processing Centre.

    ERIC Educational Resources Information Center

    Harvey, John F.

    Establishment of the Tehran Book Processing Centre (Tebroc) was proposed in the Spring of 1968. This document is a descriptive and historical account of the center, and a description of its contributions to Iranian processing development. The center was modeled, to a certain extent, after Bro-Dart's Alanar in Williamsport, Pennsylvania. Tebroc was…

  10. Reliability-centred approach evaluated.

    PubMed

    Steele, William R

    2005-02-01

    Reliability-centred maintenance is the process used to determine the most effective maintenance approach. RCM takes a system approach when evaluating the consequences of failure. Run-to-fail is sometimes an acceptable maintenance approach. Condition monitoring is often the most effective maintenance approach.

  11. Deformation-induced structural transition in body-centred cubic molybdenum

    PubMed Central

    Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.

    2014-01-01

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama–Wassermann and Kurdjumov–Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions. PMID:24603655

  12. Deformation-induced structural transition in body-centred cubic molybdenum

    NASA Astrophysics Data System (ADS)

    Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.

    2014-03-01

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.

  13. Deformation-induced structural transition in body-centred cubic molybdenum.

    PubMed

    Wang, S J; Wang, H; Du, K; Zhang, W; Sui, M L; Mao, S X

    2014-03-07

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.

  14. National Centre for Radio Astrophysics

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    India's National Centre for Radio Astrophysics (NCRA), located on the Pune University Campus, is part of the TATA INSTITUTE OF FUNDAMENTAL RESEARCH. At Khodad, 80 km from Pune, NCRA has set up the Giant Metrewave Radio Telescope (GMRT), the world's largest telescope operating at meter wavelengths. GMRT consists of 30 fully steerable dishes of 45 m diameter, spread over a 25 km area. Another meter...

  15. Metal binding studies and EPR spectroscopy of the manganese transport regulator MntR.

    PubMed

    Golynskiy, Misha V; Gunderson, William A; Hendrich, Michael P; Cohen, Seth M

    2006-12-26

    Manganese transport regulator (MntR) is a member of the diphtheria toxin repressor (DtxR) family of transcription factors that is responsible for manganese homeostasis in Bacillus subtilis. Prior biophysical studies have focused on the metal-mediated DNA binding of MntR [Lieser, S. A., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2003) Biochemistry 42, 12634-12642], as well as metal stabilization of the MntR structure [Golynskiy, M. V., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2005) Biochemistry 44, 3380-3389], but only limited data on the metal-binding affinities for MntR are available. Herein, the metal-binding affinities of MntR were determined by using electron paramagnetic resonance (EPR) spectroscopy, as well as competition experiments with the fluorimetric dyes Fura-2 and Mag-fura-2. MntR was not capable of competing with Fura-2 for the binding of transition metal ions. Therefore, the metal-binding affinities and stoichiometries of Mag-fura-2 for Mn2+, Co2+, Ni2+, Zn2+, and Cd2+ were determined and utilized in MntR/Mag-fura-2 competition experiments. The measured Kd values for MntR metal binding are comparable to those reported for DtxR metal binding [Kd from 10(-)7 to 10(-4) M; D'Aquino, J. A., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 18408-18413], AntR [a homologue from Bacillus anthracis; Sen, K. I. et al. (2006) Biochemistry 45, 4295-4303], and generally follow the Irving-Williams series. Direct detection of the dinuclear Mn2+ site in MntR with EPR spectroscopy is presented, and the exchange interaction was determined, J = -0.2 cm-1. This value is lower in magnitude than most known dinuclear Mn2+ sites in proteins and synthetic complexes and is consistent with a dinuclear Mn2+ site with a longer Mn...Mn distance (4.4 A) observed in some of the available crystal structures. MntR is found to have a surprisingly low binding affinity (approximately 160 microM) for its cognate metal ion Mn2+. Moreover, the results of DNA binding studies in

  16. Metal Binding Studies and EPR Spectroscopy of the Manganese Transport Regulator MntR†

    PubMed Central

    Golynskiy, Misha V.; Gunderson, William A.; Hendrich, Michael P.; Cohen, Seth M.

    2007-01-01

    Manganese transport regulator (MntR) is a member of the diphtheria toxin repressor (DtxR) family of transcription factors that is responsible for manganese homeostasis in Bacillus subtilis. Prior biophysical studies have focused on the metal-mediated DNA binding of MntR [Lieser, S. A., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2003) Biochemistry 42, 12634-12642], as well as metal stabilization of the MntR structure [Golynskiy, M. V., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2005) Biochemistry 44, 3380-3389], but only limited data on the metal-binding affinities for MntR are available. Herein, the metal-binding affinities of MntR were determined by using electron paramagnetic resonance (EPR) spectroscopy, as well as competition experiments with the fluorimetric dyes Fura-2 and Mag-fura-2. MntR was not capable of competing with Fura-2 for the binding of transition metal ions. Therefore, the metal-binding affinities and stoichiometries of Mag-fura-2 for Mn2+, Co2+, Ni2+, Zn2+, and Cd2+ were determined and utilized in MntR/Mag-fura-2 competition experiments. The measured Kd values for MntR metal binding are comparable to those reported for DtxR metal binding [Kd from 10-7 to 10-4 M; D’Aquino, J. A., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 18408-18413], AntR [a homologue from Bacillus anthracis; Sen, K. I. et al. (2006) Biochemistry 45, 4295-4303], and generally follow the Irving-Williams series. Direct detection of the dinuclear Mn2+ site in MntR with EPR spectroscopy is presented, and the exchange interaction was determined, J = -0.2 cm-1. This value is lower in magnitude than most known dinuclear Mn2+ sites in proteins and synthetic complexes and is consistent with a dinuclear Mn2+ site with a longer Mn···Mn distance (4.4 Å) observed in some of the available crystal structures. MntR is found to have a surprisingly low binding affinity (∼160 μM) for its cognate metal ion Mn2+. Moreover, the results of DNA binding studies in the presence

  17. Mono- and dinuclear non-heme iron–nitrosyl complexes: Models for key intermediates in bacterial nitric oxide reductases

    SciTech Connect

    Berto, Timothy C.; Speelman, Amy L.; Zheng, Sheng; Lehnert, Nicolai

    2013-01-01

    High-spin non-heme iron–nitrosyls are of direct interest to both the chemical and biological communities as these species exhibit interesting chemical properties and act as direct models for enzymatic intermediates. The electronic ground state of the ferrous NO complexes, {Fe–NO}7, is best described as high-spin FeIII antiferromagnetically coupled to NO-, generating the spectroscopically observed S = 3/2 ground state. These species have been identified as catalytically relevant to a variety of NO-reducing enzymes such as bacterial nitric oxide reductase (NorBC) and flavo(rubredoxin) nitric oxide reductase (FNOR). Recently, the corresponding one-electron reduced {Fe–NO}8 (nitroxyl) complexes have also been implicated as biologically significant species. In this review the available spectroscopic data for {Fe–NO}7 and {Fe–NO}8 mono- and dinuclear non-heme iron–nitrosyls are summarized, and the implications of these results with respect to the electronic structures and reactivities of these species, in particular towards NO reduction, are discussed.

  18. Dinuclear fluoro-peroxovanadium(v) complexes with symmetric and asymmetric peroxo bridges: syntheses, structures and DFT studies.

    PubMed

    Chrappová, Jana; Schwendt, Peter; Sivák, Michal; Repiský, Michal; Malkin, Vladimir G; Marek, Jaromír

    2009-01-21

    Two new dinuclear fluoro peroxovanadium(v) complexes, Cs3[V2O2(O2)4F] x H2O (1) and Cs3[V2O2(O2)3F3] x 2HF x H2O (2), were prepared and characterized by elemental analysis, IR spectroscopy, thermal analysis and X-ray crystallography. While the anion in possesses an asymmetric structure with a micro-eta1:eta2 bridging peroxo group, the [V2O2(O2)3F3]3- ion in exhibits a symmetrical structure with a unique mu-fluoro and micro-eta2:eta2 peroxo double bridge. The X-ray structure data were compared with equilibrium and vibrationally-averaged (effective) DFT calculated geometries. The decomposition reactions of and in aqueous solution were studied by 51V NMR spectroscopy. The calculations of vibrationally averaged NMR chemical shifts (DFT-GIAO) were used to support the empirical assignment of NMR signals and afforded excellent agreement with experimental values for the studied peroxovanadium species. The ESI mass spectra of the prepared compounds are in accordance with the assignment of NMR spectra and with DFT study.

  19. Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

    PubMed Central

    Apps, Michael G.; Johnson, Ben W.; Sutcliffe, Oliver B.; Brown, Sarah D.; Wheate, Nial J.

    2014-01-01

    Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand. PMID:24893964

  20. Chlorambucil conjugates of dinuclear p-cymene ruthenium trithiolato complexes: synthesis, characterization and cytotoxicity study in vitro and in vivo.

    PubMed

    Stíbal, David; Therrien, Bruno; Süss-Fink, Georg; Nowak-Sliwinska, Patrycja; Dyson, Paul J; Čermáková, Eva; Řezáčová, Martina; Tomšík, Pavel

    2016-07-01

    Four diruthenium trithiolato chlorambucil conjugates have been prepared via Steglich esterification from chlorambucil and the corresponding trithiolato precursors. All conjugates are highly cytotoxic towards human ovarian A2780 and A2780cisR cancer cell lines with IC50 values in the nanomolar range. The conjugates exhibit selectivity towards A2780 cells as compared to non-cancerous HEK293 cells, while being only slightly selective for RF24 and A2780cisR cells. In vivo, the conjugate [10]BF4 suppressed the growth of a solid Ehrlich tumor in immunocompetent NMRI mice but did not prolong their overall survival. The reactivity of the chlorambucil conjugates with glutathione, a potential target of the dinuclear ruthenium motive, and with the 2-deoxyguanosine 5'-monophosphate (dGMP-a model target of chlorambucil) was studied by mass spectrometry and NMR spectroscopy. The conjugates did not show catalytic activity for the oxidation of glutathione nor binding to nucleotides, indicating that glutathione oxidation and DNA alkylation are not key mechanisms of action. Four highly cytotoxic diruthenium trithiolato chlorambucil conjugates have been prepared. All conjugates exhibit selectivity towards A2780 cells as compared to HEK293 cells, while being only slightly active in RF24 and A2780cisR cells. In vivo, the best candidate suppressed the growth of a solid Ehrlich tumor in immunocompetent NMRI mice but did not prolong their overall survival.

  1. Electrochemical and photochemical-driven hydrogen evolution catalyzed by a dinuclear CoII-CoII complex

    NASA Astrophysics Data System (ADS)

    Fu, Ling-Zhi; Zhou, Ling-Ling; Tang, Ling-Zhi; Zhang, Yun-Xiao; Zhan, Shu-Zhong

    2015-04-01

    The reaction of 2,6-diamino-3-[(2-carboxymethyl) phenylazo]-pyridine (L) and CoCl2·6H2O affords a dinuclear cobalt (II) complex [Co2L2Cl3]Cl 1, a molecular catalyst. Electrochemical studies indicate that 1 can electrocatalyze hydrogen evolution both from acetic acid and purely water media (pH 7.0), with a turnover frequency of 40.64 and 750.2 mol of hydrogen per mole of catalyst per hour, respectively. Sustained proton reduction catalysis occurs at glassy carbon (GC) to give H2 over a 48 h electrolysis period with 97% Faradaic yield and no observable decomposition of the catalyst. Photocatalytic experiments indicate that complex 1 in pH 4.0 aqueous solution under air, together with [Ru(bpy)3]Cl2 and ascorbic acid as a sacrificial electron donor, in the presence of blue light (λmax = 469 nm) also can produce hydrogen with a TON = 425 mol of H2 (mol of cat)-1.

  2. Synthesis, spectral and redox switchable cubic NLO properties of chiral dinuclear iron cyanide/isocyanide-bridged complexes.

    PubMed

    Ma, Xiao; Lin, Chen-Sheng; Zhang, Hui; Lin, Yi-Ji; Hu, Sheng-Min; Sheng, Tian-Lu; Wu, Xin-Tao

    2013-09-14

    Two chiral dinuclear cyanide/isocyanide-bridged complexes (R)-[Cp(dppe)Fe-CN-Fe(dppp)Cp]PF6 (1[PF6]) and (R)-[Cp(dppe)Fe-NC-Fe(dppp)Cp]PF6 (2[PF6]), and their mono-oxidation products (R)-[Cp(dppe)Fe(II)-CN-Fe(III)(dppp)Cp] [PF6]2 (1[PF6]2) and (R)-[Cp(dppe)Fe(III)-NC-Fe(II)(dppp)Cp][PF6]2 (2[PF6]2) were synthesized and fully characterized. The electronic spectra of both the mixed-valence complexes 1[PF6]2 and 2[PF6]2 exhibit a strong and broad absorption band with two discernable peaks in the NIR region, which are attributed to Fe(II)-Fe(III) IVCT transitions. The attributions are supported by the DFT calculations. Under irradiation with a nanosecond laser at 1064 nm, the measured third-order NLO results of all four cyanide-bridged complexes showed that complexes 1(+) and 2(+) do not exhibit an NLO response, but their one-electron oxidation complexes 1(2+) and 2(2+) exhibit a strong NLO response due to a resonance enhanced effect. In addition, both complexes 1(2+) and 2(2+) display RSA and self-defocusing effects and show good optical limiting behavior in a broadband range.

  3. Aggregation-induced white-light emission from the triple-stranded dinuclear Sm(iii) complex.

    PubMed

    Leng, Jiaqi; Li, Hongfeng; Chen, Peng; Sun, Wenbin; Gao, Ting; Yan, Pengfei

    2014-08-28

    A novel bis-β-diketone ligand, 4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)(phenoxy)-1,1'-binaphthalene (BTPB), is designed for synthesis of a white light emissive lanthanide complex. The ligand bears two benzoyl β-diketonate sites linked by a 1,1'-binaphthoxy spacer. Reaction of the doubly negatively charged bis-bidentate ligand with lanthanide ions forms triple-stranded dinuclear complexes Sm2(BTPB)3(H2O)4 () and Gd2(BTPB)3(H2O)4 (), which have been fully characterized by various spectroscopic techniques. UV-Vis absorption and emission spectroscopic techniques are used to investigate photophysical properties of the ligand and its complexes in THF and CHCl3. In some cases aggregation of the ligand results in the appearance of a new luminescence band at about 510 nm in addition to the monomer fluorescence. In complex , partial energy transfer from BTPB results in Sm(iii)-based red light emission in addition to the BTPB-based blue/green emission. With the variation of the excited wavelength and concentration of the solution, complex shows a tunable white light emission with the balance of three primary colors. This is an unusual case of observation of white light emission from a single molecule Sm(iii) complex.

  4. Structural Studies on Dinuclear Ruthenium(II) Complexes That Bind Diastereoselectively to an Antiparallel Folded Human Telomere Sequence

    PubMed Central

    2013-01-01

    We report DNA binding studies of the dinuclear ruthenium ligand [{Ru(phen)2}2tpphz]4+ in enantiomerically pure forms. As expected from previous studies of related complexes, both isomers bind with similar affinity to B-DNA and have enhanced luminescence. However, when tested against the G-quadruplex from human telomeres (which we show to form an antiparallel basket structure with a diagonal loop across one end), the ΛΛ isomer binds approximately 40 times more tightly than the ΔΔ, with a stronger luminescence. NMR studies show that the complex binds at both ends of the quadruplex. Modeling studies, based on experimentally derived restraints obtained for the closely related [{Ru(bipy)2}2tpphz]4+, show that the ΛΛ isomer fits neatly under the diagonal loop, whereas the ΔΔ isomer is unable to bind here and binds at the lateral loop end. Molecular dynamics simulations show that the ΔΔ isomer is prevented from binding under the diagonal loop by the rigidity of the loop. We thus present a novel enantioselective binding substrate for antiparallel basket G-quadruplexes, with features that make it a useful tool for quadruplex studies. PMID:24088028

  5. Novel Rhenium(III, IV, and V) Tetradentate N2O2 Schiff Base Mononuclear and Dinuclear Complexes

    PubMed Central

    Rotsch, David A.; Reinig, Kimberly M.; Weis, Eric M.; Taylor, Anna B.; Barnes, Charles L.

    2013-01-01

    Reaction of (Bu4N)[ReOCl4] with the tetradentate Schiff base ligand α, α’-[(1,1-dimethylethylene)dinitrilo]di-o-cresol (sal2ibnH2) yields cis-[ReVOCl(sal2ibn)], which quickly forms trans-[μ-O(ReVO(sal2ibn))2] in solution. The dinuclear complex can also be isolated by the addition of base (Et3N) to the reaction mixture. Conversely, the mononuclear complex can be trapped as cis-[ReVO(NCS)(sal2ibn)] by addition of (Bu4N)SCN to the reaction mixture. Reduction of cis-[ReVO(NCS)sal2ibn] with triphenylphosphine gives the unique trans-[ReIII(NCS)(PPh3)(sal2ibn)] and rare μ-oxo Re(IV) dimer trans-[μ-O(ReIV(NCS)(sal2ibn))2]. All of the complexes were characterized by 1H and 13C NMR, FT-IR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), cyclic voltammetry and single crystal X-ray diffraction. PMID:23824208

  6. Metal Preferences and Metallation*

    PubMed Central

    Foster, Andrew W.; Osman, Deenah; Robinson, Nigel J.

    2014-01-01

    The metal binding preferences of most metalloproteins do not match their metal requirements. Thus, metallation of an estimated 30% of metalloenzymes is aided by metal delivery systems, with ∼25% acquiring preassembled metal cofactors. The remaining ∼70% are presumed to compete for metals from buffered metal pools. Metallation is further aided by maintaining the relative concentrations of these pools as an inverse function of the stabilities of the respective metal complexes. For example, magnesium enzymes always prefer to bind zinc, and these metals dominate the metalloenzymes without metal delivery systems. Therefore, the buffered concentration of zinc is held at least a million-fold below magnesium inside most cells. PMID:25160626

  7. European Centre for Disease Prevention and Control.

    PubMed

    Evans, Roger

    2014-11-04

    The European Centre for Disease Prevention and Control was set up in 2005 to strengthen Europe's defences against infectious diseases. The centre is an independent agency of the European Union and is based in Stockholm, Sweden.

  8. Metal-coordination-driven dynamic heteroleptic architectures.

    PubMed

    De, Soumen; Mahata, Kingsuk; Schmittel, Michael

    2010-05-01

    Dynamic heteroleptic coordination at metal centres is quite common in Nature and often related to a specific biological function, such as in zinc finger proteins and in hemoglobin for oxygen transport. To achieve the required high heteroleptic fidelity, representative biological systems avail themselves of "intramolecular" multidentate coordination using the protein backbone as a "superligand". In contrast, dynamic heteroleptic coordination at a single metal centre in solution requires to bind different freely exchanging ligands under thermodynamic control. In this tutorial review we present the emerging principles of how to assemble dissimilar ligands at dynamically exchanging metal centres, with a particular emphasis on using the precepts for the fabrication of heteroleptic supramolecular assemblies in solution.

  9. The DIY Digital Medical Centre.

    PubMed

    Timmis, James Kenneth; Timmis, Kenneth

    2017-09-01

    Healthcare systems worldwide are confronted with major economic, organizational and logistical challenges. Historic evolution of health care has led to significant healthcare sector fragmentation, resulting in systemic inefficiencies and suboptimal resource exploitation. To attain a sustainable healthcare model, fundamental, system-wide improvements that effectively network, and ensure fulfilment of potential synergies between sectors, and include and facilitate coherent strategic planning and organisation of healthcare infrastructure are needed. Critically, they must be specifically designed to sustainably achieve peak performance within the current policy environment for cost-control, and efficiency and quality improvement for service delivery. We propose creation of a new healthcare cluster, to be embedded in existing healthcare systems. It consists of (i) local 24/7 walk-in virtually autonomous do-it-yourself Digital Medical Centres performing routine diagnosis, monitoring, prevention, treatment and standardized documentation and health outcome assessment/reporting, which are online interfaced with (ii) regional 24/7 eClinician Centres providing on-demand clinical supervision/assistance to Digital Medical Centre patients. Both of these are, in turn, online interfaced with (iii) the National Clinical Informatics Centre, which houses the national patient data centre (cloud) and data analysis units that conduct patient- and population-level, personalized and predictive(-medicine) intervention optimization analyses. The National Clinical Informatics Centre also interfaces with biomedical research and prioritizes and accelerates the translation of new discoveries into clinical practice. The associated Health Policy Innovation and Evaluation Centre rapidly integrates new findings with health policy/regulatory discussions. This new cluster would synergistically link all health system components in a circular format, enable not only access by all arms of the health

  10. Communicating astronomy by the Unizul Science Centre

    NASA Astrophysics Data System (ADS)

    Beesham, A.; Beesham, N.

    2015-03-01

    The University of Zululand, situated along the east coast of KwaZulu-Natal, has a thriving Science Centre (USC) situated in the developing port city of Richards Bay. Over 30 000 learners visit the centre annually, and it consists of an exhibition area, an auditorium, lecture areas and offices. The shows consist of interactive games, science shows, competitions, quizzes and matriculation workshops. Outreach activities take place through a mobile science centre for schools and communities that cannot visit the centre.

  11. Teaching and Learning Centres: Towards Maturation

    ERIC Educational Resources Information Center

    Challis, Di; Holt, Dale; Palmer, Stuart

    2009-01-01

    Approximately 70% of Australian Teaching and Learning Centres have been restructured and/or have undergone leadership changes in the last three years. The volatility of this environment reflects the number of significant challenges faced by Teaching and Learning Centres. In determining what makes Centres successful, the issues that are likely to…

  12. Small Steps towards Student-Centred Learning

    ERIC Educational Resources Information Center

    Jacobs, George M.; Toh-Heng, Hwee Leng

    2013-01-01

    Student centred learning classroom practices are contrasted with those in teacher centred learning classrooms. The discussion focuses on the theoretical underpinnings of the former, and provides nine steps and tips on how to implement student centred learning strategies, with the aim of developing the 21st century skills of self-directed and…

  13. Dinuclear metallacycles with single M-O(H)-M bridges [M = Fe(II), Co(II), Ni(II), Cu(II)]: effects of large bridging angles on structure and antiferromagnetic superexchange interactions.

    PubMed

    Reger, Daniel L; Pascui, Andrea E; Foley, Elizabeth A; Smith, Mark D; Jezierska, Julia; Ozarowski, Andrew

    2014-02-17

    The reactions of M(ClO4)2·xH2O and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*) in the presence of triethylamine lead to the formation of monohydroxide-bridged, dinuclear metallacycles of the formula [M2(μ-OH)(μ-Lm)2](ClO4)3 (M = Fe(II), Co(II), Cu(II)) or [M2(μ-OH)(μ-Lm*)2](ClO4)3 (M = Co(II), Ni(II), Cu(II)). With the exception of the complexes where the ligand is Lm and the metal is copper(II), all of these complexes have distorted trigonal bipyramidal geometry around the metal centers and unusual linear (Lm*) or nearly linear (Lm) M-O-M angles. For the two solvates of [Cu2(μ-OH)(μ-Lm)2](ClO4)3, the Cu-O-Cu angles are significantly bent and the geometry about the metal is distorted square pyramidal. All of the copper(II) complexes have structural distortions expected for the pseudo-Jahn-Teller effect. The two cobalt(II) complexes show moderate antiferromagnetic coupling, -J = 48-56 cm(-1), whereas the copper(II) complexes show very strong antiferromagnetic coupling, -J = 555-808 cm(-1). The largest coupling is observed for [Cu2(μ-OH)(μ-Lm*)2](ClO4)3, the complex with a Cu-O-Cu angle of 180°, such that the exchange interaction is transmitted through the dz(2) and the oxygen s and px orbitals. The interaction decreases, but it is still significant, as the Cu-O-Cu angle decreases and the character of the metal orbital becomes increasingly d(x(2)-y(2)). These intermediate geometries and magnetic interactions lead to spin Hamiltonian parameters for the copper(II) complexes in the EPR spectra that have large E/D ratios and one g matrix component very close to 2. Density functional theory calculations were performed using the hybrid B3LYP functional in association with the TZVPP basis set, resulting in reasonable agreement with the experiments.

  14. Student-Centred and Teacher-Centred Learning Environments: What Students Think

    ERIC Educational Resources Information Center

    Elen, Jan; Clarebout, Geraldine; Leonard, Rebecca; Lowyck, Joost

    2007-01-01

    This contribution explores the relationship between teacher-centred and student-centred learning environments from a student's perspective. Three different views with respect to this relationship can be retrieved. The "balance" view suggests that the more teacher-centred a learning environment is, the less student-centred it is and vice versa. The…

  15. Bifunctional Zn(II)Ln(III) dinuclear complexes combining field induced SMM behavior and luminescence: enhanced NIR lanthanide emission by 9-anthracene carboxylate bridging ligands.

    PubMed

    Palacios, María A; Titos-Padilla, Silvia; Ruiz, José; Herrera, Juan Manuel; Pope, Simon J A; Brechin, Euan K; Colacio, Enrique

    2014-02-03

    There were new dinuclear Zn(II)-Ln(III) complexes of general formulas [Zn(μ-L)(μ-OAc)Ln(NO3)2] (Ln(III) = Tb (1), Dy (2), Er (3), and Yb (4)), [Zn(μ-L)(μ-NO3)Er(NO3)2] (5), [Zn(H2O)(μ-L)Nd(NO3)3]·2CH3OH (6), [Zn(μ-L)(μ-9-An)Ln(NO3)2]·2CH3CN (Ln(III) = Tb (7), Dy (8), Er (9), Yb(10)), [Zn(μ-L)(μ-9-An)Yb(9-An)(NO3)3]·3CH3CN (11), [Zn(μ-L)(μ-9-An)Nd(9-An)(NO3)3]·2CH3CN·3H2O (12), and [Zn(μ-L)(μ-9-An)Nd(CH3OH)2(NO3)]ClO4·2CH3OH (13) prepared from the reaction of the compartmental ligand N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L), with ZnX2·nH2O (X = NO3(-) or OAc(-)) salts, Ln(NO3)3·nH2O, and, in some instances, 9-anthracenecarboxylate anion (9-An). In all these complexes, the Zn(II) ions invariably occupy the internal N3O2 site whereas the Ln(III) ions show preference for the O4 external site, giving rise to a Zn(μ-diphenoxo)Ln bridging fragment. Depending on the Zn(II) salt and solvent used in the reaction, a third bridge can connect the Zn(II) and Ln(III) metal ions, giving rise to triple-bridged diphenoxoacetate in complexes 1-4, diphenoxonitrate in complex 5, and diphenoxo(9-anthracenecarboxylate) in complexes 8-13. Dy(III) and Er(III) complexes 2, 8 and 3, 5, respectively, exhibit field induced single molecule magnet (SMM) behavior, with Ueff values ranging from 11.7 (3) to 41(2) K. Additionally, the solid-state photophysical properties of these complexes are presented showing that ligand L(2-) is able to sensitize Tb(III)- and Dy(III)-based luminescence in the visible region through an energy transfer process (antenna effect). The efficiency of this process is much lower when NIR emitters such as Er(III), Nd(III), and Yb(III) are considered. When the luminophore 9-anthracene carboxylate is incorporated into these complexes, the NIR luminescence is enhanced which proves the efficiency of this bridging ligand to act as antenna group. Complexes 2, 3, 5, and 8 can be considered as dual materials

  16. The DEMETER Science Mission Centre

    NASA Astrophysics Data System (ADS)

    Lagoutte, D.; Brochot, J. Y.; de Carvalho, D.; Elie, F.; Harivelo, F.; Hobara, Y.; Madrias, L.; Parrot, M.; Pinçon, J. L.; Berthelier, J. J.; Peschard, D.; Seran, E.; Gangloff, M.; Sauvaud, J. A.; Lebreton, J. P.; Stverak, S.; Travnicek, P.; Grygorczuk, J.; Slominski, J.; Wronowski, R.; Barbier, S.; Bernard, P.; Gaboriaud, A.; Wallut, J. M.

    2006-04-01

    The DEMETER Scientific Mission Centre (SMC) has been developed and is operated by the Laboratoire de Physique et Chimie de l'Environnement (LPCE). The SMC commands the instruments of the scientific payload, collects and distributes DEMETER data and associated products to the DEMETER international community. The SMC has been designed to maximize scientific return and to reduce development and exploitation costs for the DEMETER project. This paper describes the SMC's data processing system, data server and methods of payload operation, and presents associated hardware and software architectures.

  17. Learning in interactive science centres

    NASA Astrophysics Data System (ADS)

    Beiers, Robin; McRobbie, Cam

    1992-12-01

    The potential of informal sources of science learning to supplement and interact with formal classroom science is receiving increasing recognition and attention in the research literature. In this study, a phenomenographic approach was used to determine changes in levels of understanding of 27 grade 7 primary school children as a result of a visit to an interactive science centre. The results showed that most students did change their levels of understanding of aspects of the concept “sound”. The study also provides information which will be of assistance to teachers on the levels of understanding displayed by students on this concept.

  18. Stereocontrol in dinuclear triple lithium-bridged titanium(IV) complexes: solving some stereochemical mysteries.

    PubMed

    Albrecht, Markus; Isaak, Elisabeth; Moha, Verena; Raabe, Gerhard; Fröhlich, Roland

    2014-05-26

    Compounds 1 a-f-H2 form "monomeric" triscatecholate titanium(IV) complexes [Ti(1 a-f)3](2-), which in the presence of Li cations are in equilibrium with the triple lithium-bridged "dimers" [Li3(Ti(1 a-f)3)2](-). The equilibrium strongly depends on the donor ability of the solvent. Usually, in solvents with high donor ability, the stereochemically labile monomer is preferred, whereas in nondonor solvents, the dimer is the major species. In the latter, the stereochemistry at the complex units is "locked". The configuration at the titanium(IV) triscatecholates is influenced by addition of chiral ammonium countercations. In this case, the induced stereochemical information at the monomer is transferred to the dimer. Alternatively, the configuration at the metal complexes can be controlled by enantiomerically pure ester side chains. Due to the different orientation of the ester groups in the monomer or dimer, opposite configurations of the triscatecholates were observed by circular dichroism (CD) spectroscopy for [Ti(1 c-e)3](2-) or [Li3(Ti(1 c-e)3)2](-). A surprising exception was found for the dimer [Li3(Ti(1 f)3)2](-). Herein, the dimer is the dominating species in weak donor (methanol), as well as strong donor (DMSO), solvents. This is due to the bulkiness of the ester substituent destabilizing the monomer. Due to the size of the substituent in [Li3(Ti(1 f)3)2](-) the esters have to adopt an unusual conformation in the dimer resulting in a stereocontrol of the small methyl group. Following this, opposite stereocontrol mechanisms were observed for the central metal-complex units of [Li3(Ti(1 c-e)3)2](-) or [Li3(Ti(1 f)3)2](-). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Perceptual centres in speech - an acoustic analysis

    NASA Astrophysics Data System (ADS)

    Scott, Sophie Kerttu

    Perceptual centres, or P-centres, represent the perceptual moments of occurrence of acoustic signals - the 'beat' of a sound. P-centres underlie the perception and production of rhythm in perceptually regular speech sequences. P-centres have been modelled both in speech and non speech (music) domains. The three aims of this thesis were toatest out current P-centre models to determine which best accounted for the experimental data bto identify a candidate parameter to map P-centres onto (a local approach) as opposed to the previous global models which rely upon the whole signal to determine the P-centre the final aim was to develop a model of P-centre location which could be applied to speech and non speech signals. The first aim was investigated by a series of experiments in which a) speech from different speakers was investigated to determine whether different models could account for variation between speakers b) whether rendering the amplitude time plot of a speech signal affects the P-centre of the signal c) whether increasing the amplitude at the offset of a speech signal alters P-centres in the production and perception of speech. The second aim was carried out by a) manipulating the rise time of different speech signals to determine whether the P-centre was affected, and whether the type of speech sound ramped affected the P-centre shift b) manipulating the rise time and decay time of a synthetic vowel to determine whether the onset alteration was had more affect on P-centre than the offset manipulation c) and whether the duration of a vowel affected the P-centre, if other attributes (amplitude, spectral contents) were held constant. The third aim - modelling P-centres - was based on these results. The Frequency dependent Amplitude Increase Model of P-centre location (FAIM) was developed using a modelling protocol, the APU GammaTone Filterbank and the speech from different speakers. The P-centres of the stimuli corpus were highly predicted by attributes of

  20. Quasifission and fission rates and their lifetimes in asymmetric reactions forming 216Ra within a dinuclear system approach

    NASA Astrophysics Data System (ADS)

    Khanlari, M. Varasteh; Soheyli, S.

    2017-02-01

    Background: The study of evolution of asymmetric dinuclear systems (DNSs) formed in heavy ion collisions is a topic of intense research. The DNS evolution leads to a variety of reaction channels such as deep inelastic, complete fusion, quasifission, fast fission, fusion-fission, and evaporation of particles. The time evolution of the DNS in the quasifission process and the role of relevant parameters are still not fully understood. Purpose: The influence of the entrance channel mass asymmetry on the time evolution of an excited and rotating DNS, populated via four reactions with different entrance channel mass asymmetry parameters which all lead to the compound nucleus 216Ra, is explored. Method: The driving potential, emission barriers for the binary decay (namely the quasifission and intrinsic fusion barriers), rate of the quasifission channel, and the lifetime of an excited DNS, as well as the fission rate and fission lifetime of the compound nucleus 216Ra formed in the 12C+204Pb,19F+197Au,30Si+186W , and 48Ca+168Er reactions, are calculated by the dinuclear system approach. Results: Our results show that the intrinsic fusion barrier values are equal to zero for the 12C+204Pb and 19F+197Au reactions. Therefore, the quasifission signature is extremely hindered for these reactions, while the 30Si+186W and 48Ca+168Er calculated results contain quasifission contributions. Provided the quasifission rate is nonzero, the quasifission rate increases with increasing orbital angular momentum ℓ of the composite system for a given excitation energy ECN * of the compound nucleus. On the other hand, the quasifission lifetime decreases moderately with increasing ℓ . Furthermore, both quasifission and fission rates increase with increasing excitation energy ECN *, while the quasifission and fission lifetimes decrease with increasing ECN * for a given ℓ . Conclusions: Although these reactions with different entrance channels populate the same compound nucleus 216Ra at

  1. μ-Oxo-Dinuclear-Iron(III)-Catalyzed O-Selective Acylation of Aliphatic and Aromatic Amino Alcohols and Transesterification of Tertiary Alcohols.

    PubMed

    Horikawa, Rikiya; Fujimoto, Chika; Yazaki, Ryo; Ohshima, Takashi

    2016-08-22

    A highly chemoselective and reactive μ-oxo-dinuclear iron(III) salen catalyst for transesterification was developed. The developed iron complex catalyzed acylation of aliphatic amino alcohols with nearly perfect O-selectivity, even when using activated esters, for which chemoselectivity is more difficult to control. In addition, O-selective transesterification of aromatic amino alcohols was achieved for the first time. The high activity of the iron complex enabled the use of sterically congested tertiary alcohols, including unprecedented tert-butanol. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Dinuclear iron(II)-cyanocarbonyl complexes linked by two/three bridging ethylthiolates: relevance to the active site of [Fe] hydrogenases.

    PubMed

    Liaw, Wen-Feng; Tsai, Wen-Ting; Gau, Hung-Bin; Lee, Chien-Ming; Chou, Shin-Yuan; Chen, Wen-Yuan; Lee, Gene-Hsiang

    2003-04-21

    Dinuclear iron(II)-cyanocarbonyl complex [PPN](2)[Fe(CN)(2)(CO)(2)(mu-SEt)](2) (1) was prepared by the reaction of [PPN][FeBr(CN)(2)(CO)(3)] and [Na][SEt] in THF at ambient temperature. Reaction of complex 1 with [PPN][SEt] produced the triply thiolate-bridged dinuclear Fe(II) complex [PPN][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)] (2) with the torsion angle of two CN(-) groups (C(5)N(2) and C(3)N(1)) being 126.9 degrees. The extrusion of two sigma-donor CN(-) ligands from Fe(II)Fe(II) centers of complex 1 as a result of the reaction of complex 1 and [PPN][SEt] reflects the electron-rich character of the dinuclear iron(II) when ligated by the third bridging ethylthiolate. The Fe-S distances (2.338(2) and 2.320(3) A for complexes 1 and 2, respectively) do not change significantly, but the Fe(II)-Fe(II) distance contracts from 3.505 A in complex 1 to 3.073 A in complex 2. The considerably longer Fe(II)-Fe(II) distance of 3.073 A in complex 2, compared to the reported Fe-Fe distances of 2.6/2.62 A in DdHase and CpHase, was attributed to the presence of the third bridging ethylthiolate, instead of pi-accepting CO-bridged ligand as observed in [Fe] hydrogenases. Additionally, in a compound of unusual composition ([Na.(5)/(2)H(2)O][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)])(n)((1)/(2)O(Et)(2))(n) (3), the Na(+) cations and H(2)O molecules combining with dinuclear [(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)](-) anions create a polymeric framework wherein two CN(-) ligands are coordinated via CN(-)-Na(+)/CN(-)-(Na(+))(2) linkages, respectively.

  3. Synthesis and SMM behaviour of trinuclear versus dinuclear 3d-5f uranyl(v)-cobalt(ii) cation-cation complexes.

    PubMed

    Chatelain, Lucile; Tuna, Floriana; Pécaut, Jacques; Mazzanti, Marinella

    2017-01-17

    Trinuclear versus dinuclear heterodimetallic U(V)O2(+)Co(2+) complexes were selectively assembled via a cation-cation interaction by tuning the ligand. The trimeric complex 2, with a linear [Co-O[double bond, length as m-dash]U[double bond, length as m-dash]O-Co] core, exhibits magnetic exchange and slow relaxation with a reversal barrier of 30.5 ± 0.9 K providing the first example of a U-Co exchange-coupled SMM.

  4. Fine-tuning terminal solvent ligands to rationally enhance the energy barrier in dinuclear dysprosium single-molecule magnets.

    PubMed

    Zhang, Kun; Yuan, Chen; Guo, Fu-Sheng; Zhang, Yi-Quan; Wang, Yao-Yu

    2016-12-20

    In search of simple approaches to rationally enhance the energy barriers in polynuclear dysprosium single-molecule magnets, a new system containing two structurally closely related dinuclear dysprosium complexes, namely [Dy2(L)2(DBM)2(DMF)2] (1) and [Dy2(L)2(DBM)2(DMA)2]·2DMA (2) (HDBM = dibenzoylmethane, H2L = 2-hydroxy-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide), is introduced and the structure-dependent magnetic properties are investigated. The two complexes display only slight variations in the coordination geometries of the Dy(iii) ion but display remarkably different magnetic behaviors. By replacing the DMF (dimethylformamide) ligand in complex 1 with DMA (dimethylacetamide) in 2 while retaining the same coordination atoms, we were able to create a 3-fold enhancement in the energy barrier, from 24 K for complex 1 to 77 K for complex 2. Complete-active-space self-consistent field (CASSCF) calculations revealed that the charge distribution surrounding the Dy(iii) centers in 1 and 2 is the key factor in determining the relaxation properties of the SMMs. The introduction of an electron-donating CH3 group in DMA to replace the hydrogen in DMF resulted in a larger average charge along the magnetic axes of complex 2 compared to complex 1, which resulted in a stronger easy-axis ligand field, thus increasing the energy difference between the ground and the first excited states of complex 2. This work presents a simple method to rationally enhance the energy barrier in polynuclear lanthanide SMMs through fine-tuning of the electrostatic potential of the atoms along the magnetic axis.

  5. Ligand modulation of a dinuclear platinum compound leads to mechanistic differences in cell cycle progression and arrest.

    PubMed

    Menon, Vijay R; Peterson, Erica J; Valerie, Kristoffer; Farrell, Nicholas P; Povirk, Lawrence F

    2013-12-15

    Despite similar structures and DNA binding profiles, two recently synthesized dinuclear platinum compounds are shown to elicit highly divergent effects on cell cycle progression. In colorectal HCT116 cells, BBR3610 shows a classical G2/M arrest with initial accumulation in S phase, but the derivative compound BBR3610-DACH, formed by introduction of the 1,2-diaminocyclohexane (DACH) as carrier ligand, results in severe G1/S as well as G2/M phase arrest, with nearly complete S phase depletion. The origin of this unique effect was studied. Cellular interstrand crosslinking as assayed by comet analysis was similar for both compounds, confirming previous in vitro results obtained on plasmid DNA. Immunoblotting revealed a stabilization of p53 and concomitant transient increases in p21 and p27 proteins after treatment with BBR3610-DACH. Cell viability assays and cytometric analysis of p53 and p21 null cells indicated that BBR3610-DACH-induced cell cycle arrest was p21-dependent and partially p53-dependent. However, an increase in the levels of cyclin E was observed with steady state levels of CDK2 and Cdc25A, suggesting that the G1 block occurs downstream of CDK/cyclin complex formation. The G2/M block was corroborated with decreased levels of cyclin A and cyclin B1. Surprisingly, BBR3610-DACH-induced G1 block was independent of ATM and ATR. Finally, both compounds induced apoptosis, with BBR3610-DACH showing a robust PARP-1 cleavage that was not associated with caspase-3/7 cleavage. In summary, BBR3610-DACH is a DNA binding platinum agent with unique inhibitory effects on cell cycle progression that could be further developed as a chemotherapeutic agent complementary to cisplatin and oxaliplatin.

  6. Reduction of Toxoplasma gondii Development Due to Inhibition of Parasite Antioxidant Enzymes by a Dinuclear Iron(III) Compound

    PubMed Central

    Portes, J. A.; Souza, T. G.; dos Santos, T. A. T.; da Silva, L. L. R.; Ribeiro, T. P.; Pereira, M. D.; Horn, A.; Fernandes, C.; DaMatta, R. A.; de Souza, W.

    2015-01-01

    Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan that can infect a wide range of vertebrate cells. Here, we describe the cytotoxic effects of the dinuclear iron compound [Fe(HPCINOL)(SO4)]2-μ-oxo, in which HPCINOL is the ligand 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, on T. gondii infecting LLC-MK2 host cells. This compound was not toxic to LLC-MK2 cells at concentrations of up to 200 μM but was very active against the parasite, with a 50% inhibitory concentration (IC50) of 3.6 μM after 48 h of treatment. Cyst formation was observed after treatment, as indicated by the appearance of a cyst wall, Dolichos biflorus lectin staining, and scanning and transmission electron microscopy characteristics. Ultrastructural changes were also seen in T. gondii, including membrane blebs and clefts in the cytoplasm, with inclusions similar to amylopectin granules, which are typically found in bradyzoites. An analysis of the cell death pathways in the parasite revealed that the compound caused a combination of apoptosis and autophagy. Fluorescence assays demonstrated that the redox environment in the LLC-MK2 cells becomes oxidant in the presence of the iron compound. Furthermore, a reduction in superoxide dismutase and catalase activities in the treated parasites and the presence of reactive oxygen species within the parasitophorous vacuoles were observed, indicating an impaired protozoan response against these radicals. These findings suggest that this compound disturbs the redox equilibrium of T. gondii, inducing cystogenesis and parasite death. PMID:26392498

  7. Reduction of Toxoplasma gondii Development Due to Inhibition of Parasite Antioxidant Enzymes by a Dinuclear Iron(III) Compound.

    PubMed

    Portes, J A; Souza, T G; dos Santos, T A T; da Silva, L L R; Ribeiro, T P; Pereira, M D; Horn, A; Fernandes, C; DaMatta, R A; de Souza, W; Seabra, S H

    2015-12-01

    Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan that can infect a wide range of vertebrate cells. Here, we describe the cytotoxic effects of the dinuclear iron compound [Fe(HPCINOL)(SO4)]2-μ-oxo, in which HPCINOL is the ligand 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, on T. gondii infecting LLC-MK2 host cells. This compound was not toxic to LLC-MK2 cells at concentrations of up to 200 μM but was very active against the parasite, with a 50% inhibitory concentration (IC50) of 3.6 μM after 48 h of treatment. Cyst formation was observed after treatment, as indicated by the appearance of a cyst wall, Dolichos biflorus lectin staining, and scanning and transmission electron microscopy characteristics. Ultrastructural changes were also seen in T. gondii, including membrane blebs and clefts in the cytoplasm, with inclusions similar to amylopectin granules, which are typically found in bradyzoites. An analysis of the cell death pathways in the parasite revealed that the compound caused a combination of apoptosis and autophagy. Fluorescence assays demonstrated that the redox environment in the LLC-MK2 cells becomes oxidant in the presence of the iron compound. Furthermore, a reduction in superoxide dismutase and catalase activities in the treated parasites and the presence of reactive oxygen species within the parasitophorous vacuoles were observed, indicating an impaired protozoan response against these radicals. These findings suggest that this compound disturbs the redox equilibrium of T. gondii, inducing cystogenesis and parasite death.

  8. Characteristic effect of an anticancer dinuclear platinum(II) complex on the higher-order structure of DNA.

    PubMed

    Kida, Naoko; Katsuda, Yousuke; Yoshikawa, Yuko; Komeda, Seiji; Sato, Takaji; Saito, Yoshihiro; Chikuma, Masahiko; Suzuki, Mari; Imanaka, Tadayuki; Yoshikawa, Kenichi

    2010-06-01

    It is known that a 1,2,3-triazolato-bridged dinuclear platinum(II) complex, [{cis-Pt(NH(3))(2)}(2)(micro-OH)(micro-1,2,3-ta-N (1),N (2))](NO(3))(2) (AMTA), shows high in vitro cytotoxicity against several human tumor cell lines and circumvents cross-resistance to cisplatin. In the present study, we examined a dose- and time-dependent effect of AMTA on the higher-order structure of a large DNA, T4 phage DNA (166 kbp), by adapting single-molecule observation with fluorescence microscopy. It was found that AMTA induces the shrinking of DNA into a compact state with a much higher potency than cisplatin. From a quantitative analysis of the Brownian motion of individual DNA molecules in solution, it became clear that the density of a DNA segment in the compact state is about 2,000 times greater than that in the absence of AMTA. Circular dichroism spectra suggested that AMTA causes a transition from the B to the C form in the secondary structure of DNA, which is characterized by fast and slow processes. Electrophoretic measurements indicated that the binding of AMTA to supercoiled DNA induces unwinding of the double helix. Our results indicate that AMTA acts on DNA through both electrostatic interaction and coordination binding; the former causes a fast change in the secondary structure from the B to the C form, whereas the latter promotes shrinking in the higher-order structure as a relatively slow kinetic process. The shrinking effect of AMTA on DNA is attributable to the possible increase in the number of bridges along a DNA molecule. It is concluded that AMTA interacts with DNA in a manner markedly different from that of cisplatin.

  9. Dinuclear complexes formed with the triazacyclononane derivative ENOTA4-: high-pressure 17O NMR evidence of an associative water exchange on [MnII2(ENOTA)(H2O)2].

    PubMed

    Balogh, Edina; He, Zhenjie; Hsieh, Wenyuan; Liu, Shuang; Tóth, Eva

    2007-01-08

    Mn2+ has five unpaired d-electrons, a long electronic relaxation time, and labile water exchange, all of which make it an attractive candidate for contrast agent application in medical magnetic resonance imaging. In the quest for stable and nonlabile Mn2+ complexes, we explored a novel dimeric triazacyclononane-based ligand bearing carboxylate functional groups, H4ENOTA. The protonation constants of the ligand and the stability constants of the complexes formed with some endogenously important metals (Ca2+, Cu2+, Zn2+), as well as with Mn2+ and Ce3+, have been assessed by NMR methods, potentiometry, and UV-vis spectrophotometry. Overall, the thermodynamic stability of the complexes is lower as compared to that of the corresponding NOTA analogues (H3NOTA, 1,4,7-triaazacyclononane-1,4,7-triacetic acid). The crystal structure of Mn2(ENOTA)(H2O) x 5H2O contains two six-coordinated Mn2+, in addition to the three amine nitrogens and the two oxygens from the pendent monodentate carboxylate groups, and one water (Mn2) or one bridging carboxylate oxygen (Mn1) completes the coordination sphere of the metal ion. In an aqueous solution, this bridging carboxylate is replaced by a water molecule, as evidenced by the 17O chemical shifts and proton relaxivity data that point to monohydration for both metal ions in the dinuclear complex. A variable-temperature and -pressure 17O NMR study has been performed on [Mn2(ENOTA)(H2O)2] to assess the rate and, for the first time on a Mn2+ chelate, also the mechanism of the water exchange. The inner sphere water is slightly more labile in [Mn2(ENOTA)(H2O)2] (k298ex = 5.5 x 107 s-1) than in the aqua ion (2.1 x 107 s-1, Merbach, A. E.; et al. Inorg. Chem. 1980, 19, 3696). The water exchange proceeds via an almost limiting associative mechanism, as evidenced by the large negative activation volume (deltaV = -10.7 cm3 mol-1). The proton relaxivities measured on [Mn2(ENOTA)(H2O)2] show a low-field dispersion at approximately 0.1 MHz arising from

  10. Nuclear Science Centre, New Delhi

    SciTech Connect

    Mehta, G.; Potukuchi, P.; Roy, A.

    1995-08-01

    Argonne is collaborating with the Nuclear Science Centre (NSC), New Delhi, to develop a new type of superconducting accelerating structure for low-velocity heavy ions. A copper model has been evaluated and tests on the niobium prototype are currently in progress. Some technical details of this project are described in the Superconducting Linac Development section of this report. All funding for the prototype has come from the NSC, and they have also stationed two staff members at ATLAS for the past two years to gain experience and work on this project. Additional NSC personnel visited ATLAS for extended periods during 1994 for electronics and cryogenics experience and training. Two NSC staff members are scheduled to spend several months at ANL during 1995 to continue tests and developments of the prototype resonators and to initiate fabrication of the production models for their linac project.

  11. 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 Central

    Chen, Xiaoyuan; Femia, Frank J.; Babich, John W.; Zubieta, Jon A.

    2010-01-01

    2,4,6-Tris(2-pyridyl)-1,3,5-triazine (TPT) bridged dinuclear rhenium(I) tricarbonyl halide complexes with the composition (μ-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, P21/c, a = 11.751(1) Å, b = 11.376(1) Å, c = 15.562(2) Å, β = 103.584(2)°, V = 2022.0(4) Å3, Z = 4. 2: monoclinic, P21/c, a = 11.896(1) Å, b = 11.396(1) Å, c = 15.655(1) Å, β = 104.474(2)°, V = 2054.9(3) Å3, Z = 4. 3: triclinic, P1‒, a = 11.541(2) Å, b = 12.119(2) Å, c = 13.199(2) Å, α = 80.377(2)°, β = 76.204(3)°, γ = 66.826-(2)°, V = 1642.5(4) Å3, Z ) 2. Crystals of 4 crystallized from acetone: triclinic, P1‒, a = 11.586(5) Å, b = 12.144(5) Å, c = 13.364(6) Å, α = 80.599(7)°, β = 76.271(8)°, γ = 67.158(8)°, V = 1678.0(12) Å3, Z = 2. Crystals of 4′ are obtained from CH2Cl2–pentane solution: monoclinic, C2/c, a = 17.555(4) Å, b = 15.277(3) Å, c = 13.093(3) Å, β = 111.179(3)°, V = 3274.0(12) Å3, Z = 4. By contrast, similar reactions in the presence of methanol yielded complexes with the composition [μ-C3N3(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) Å, b = 16.602(1) Å, c = 14.641(1) Å, β = 116.147(1)°, V = 5880.5(8) Å3, Z = 8. 6: monoclinic, C2/c, a = 27.513(3) Å, b = 16.740(2) Å, c = 14.837(2) Å, β = 116.925(2)°, V = 6092.8(10) Å3, 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 orientation relative to the central C3N3 ring. Reaction of TPT with [NEt4]2[ReBr3-(CO)3] in

  12. Mössbauer investigation of the photoexcited spin states and crystal structure analysis of the spin-crossover dinuclear complex [{Fe(bt)(NCS)(2)}(2)bpym] (bt=2,2'-bithiazoline, bpym=2,2'-bipyrimidine).

    PubMed

    Gaspar, Ana B; Ksenofontov, Vadim; Reiman, Sergey; Gütlich, Philipp; Thompson, Amber L; Goeta, Andrés E; Muñoz, M Carmen; Real, José A

    2006-12-13

    The crystal structure of the complex [{Fe(bt)(NCS)(2)}(2)bpym] (1) (bt=2,2'-bithiazoline, bpym=2,2'-bipyrimidine) has been solved at 293, 240, 175 and 30 K. At all four temperatures the crystal remains in the P space group with a=8.7601(17), b=9.450(2), c=12.089(3) A, alpha=72.77(2), beta=79.150(19), gamma=66.392(18) degrees , V=873.1(4) Angstrom(3) (data for 293 K structure). The structure consists of centrosymmetric dinuclear units in which each iron(II) atom is coordinated by two NCS(-) ions in the cis position and two nitrogen atoms of the bridging bpym ligand, with the remaining positions occupied by the peripheral bt ligand. The iron atom is in a severely distorted octahedral FeN(6) environment. The average Fe--N bond length of 2.15(9) Angstrom indicates that compound 1 is in the high-spin state (HS-HS) at 293 K. Crystal structure determinations at 240, 175 and 30 K gave a cell comparable to that seen at 293 K, but reduced in volume. At 30 K, the average Fe--N distance is 1.958(4) Angstrom, showing that the structure is clearly low spin (LS-LS). At 175 K the average Fe--N bond length of 2.052(11) Angstrom suggests that there is an intermediate phase. Mössbauer investigations of the light-induced excited spin state trapping (LIESST) effect (lambda=514 nm, 25 mW cm(-2)) in 1 (4.2 K, H(ext)=50 kOe) show that the excited spin states correspond to the HS-HS and HS-LS pairs. The dynamics of the relaxation of the photoexcited states studied at 4.2 K and H(ext)=50 kOe demonstrate that HS-HS pairs revert with time to both HS-LS and LS-LS configurations. The HS-LS photoexcited pairs relax with time back to the ground LS-LS configuration. Complex [{Fe(0.15)Zn(0.85)(bt)(NCS)(2)}(2)bpym] (2) exhibits a continuous spin transition centred around 158 K in contrast to the two-step transition observed for 1. The different spin-crossover behaviour observed for 2 is due to the decrease of cooperativity (intermolecular interactions) imposed by the matrix of Zn(II) ions. This

  13. Metal-ion mutagenesis: conversion of a purple acid phosphatase from sweet potato to a neutral phosphatase with the formation of an unprecedented catalytically competent Mn(II)Mn(II) active site.

    PubMed

    Mitić, Natasa; Noble, Christopher J; Gahan, Lawrence R; Hanson, Graeme R; Schenk, Gerhard

    2009-06-17

    The currently accepted paradigm is that the purple acid phosphatases (PAPs) require a heterovalent, dinuclear metal-ion center for catalysis. It is believed that this is an essential feature for these enzymes in order for them to operate under acidic conditions. A PAP from sweet potato is unusual in that it appears to have a specific requirement for manganese, forming a unique Fe(III)-mu-(O)-Mn(II) center under catalytically optimal conditions (Schenk et al. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 273). Herein, we demonstrate, with detailed electron paramagnetic resonance (EPR) spectroscopic and kinetic studies, that in this enzyme the chromophoric Fe(III) can be replaced by Mn(II), forming a catalytically active, unprecedented antiferromagnetically coupled homodivalent Mn(II)-mu-(H)OH-mu-carboxylato-Mn(II) center in a PAP. However, although the enzyme is still active, it no longer functions as an acid phosphatase, having optimal activity at neutral pH. Thus, PAPs may have evolved from distantly related divalent dinuclear metallohydrolases that operate under pH neutral conditions by stabilization of a trivalent-divalent metal-ion core. The present Mn(II)-Mn(II) system models these distant relatives, and the results herein make a significant contribution to our understanding of the role of the chromophoric metal ion as an activator of the nucleophile. In addition, the detailed analysis of strain broadened EPR spectra from exchange-coupled dinuclear Mn(II)-Mn(II) centers described herein provides the basis for the full interpretation of the EPR spectra from other dinuclear Mn metalloenzymes.

  14. Bangalore looks to new interdisciplinary science centre

    NASA Astrophysics Data System (ADS)

    Ramachandran, Ramaseshan

    2008-09-01

    A new centre to boost interdisciplinary research in India is being established in Bangalore - India's IT and software capital. The International Centre for Theoretical Sciences (ICTS) will be led by Spenta Wadia, a theoretical physicist from the Tata Institute of Fundamental Research (TIFR) in Mumbai, which is setting up the new centre. He expects construction of the ICTS, the first of its kind in India, to start by November 2009.

  15. Series of dinuclear and tetranuclear lanthanide clusters encapsulated by salen-type and β-diketionate ligands: single-molecule magnet and fluorescence properties.

    PubMed

    Sun, Wen-Bin; Han, Bing-Lu; Lin, Po-Heng; Li, Hong-Feng; Chen, Peng; Tian, Yong-Mei; Murugesu, Muralee; Yan, Peng-Fei

    2013-10-07

    Three dinuclear [Ln2H2OL(1)2(acac)2]·solvent (1, Ln = Gd, solvent = 2CH2Cl2; 2, Ln = Tb, no solvent; 3, Ln = Er, solvent = (C2H5)2O), and two tetranuclear lanthanide clusters [Ln4(μ3-OH)2L(2)2(acac)6]·2(solvent) (4, Ln = Tb, solvent = CH3OH; 5, Ln = Dy, solvent = CH3CN) were characterized in terms of structure, fluorescence and magnetism. The dinuclear lanthanide complexes were constructed by a rigid salen-type ligand H2L(1) = N,N'-bis(salicylidene)-o-phenylenediamine and β-diketonate (acac = acetylacetonate) ligands, while the tetranuclear clusters were formed from the flexible ligand H2L(2) = N,N'-bis(salicylidene)-1,2-ethanediamine. Crystal structure analysis indicates that the rigid ligand favors the double-decker sandwich structure (Ln2L(1)2), in which the two lanthanide ions have different coordination numbers and geometry, while the more flexible ligand (H2L(2)) leads to planar tetranuclear clusters. The relationship between their respective magnetic anisotropy and ligand-field geometries and their fluorescence properties was investigated. The Dy and Tb-containing clusters exhibit typical visible fluorescence properties, and single-molecule magnet behavior is seen in complex 5.

  16. Air oxygenation chemistry of 4-TBC catalyzed by chloro bridged dinuclear copper(II) complexes of pyrazole based tridentate ligands: synthesis, structure, magnetic and computational studies.

    PubMed

    Banerjee, Ishita; Samanta, Pabitra Narayan; Das, Kalyan Kumar; Ababei, Rodica; Kalisz, Marguerite; Girard, Adrien; Mathonière, Corine; Nethaji, M; Clérac, Rodolphe; Ali, Mahammad

    2013-02-07

    Four dinuclear bis(μ-Cl) bridged copper(II) complexes, [Cu(2)(μ-Cl)(2)(L(X))(2)](ClO(4))(2) (L(X) = N,N-bis[(3,5-dimethylpyrazole-1-yl)-methyl]benzylamine with X = H(1), OMe(2), Me(3) and Cl(4)), have been synthesized and characterized by the single crystal X-ray diffraction method. In these complexes, each copper(II) center is penta-coordinated with square-pyramidal geometry. In addition to the tridentate L(X) ligand, a chloride ion occupies the last position of the square plane. This chloride ion is also bonded to the neighboring Cu(II) site in its axial position forming an SP-I dinuclear Cu(II) unit that exhibits small intramolecular ferromagnetic interactions and supported by DFT calculations. The complexes 1-3 exhibit methylmonooxygenase (pMMO) behaviour and oxidise 4-tert-butylcatechol (4-TBCH(2)) with molecular oxygen in MeOH or MeCN to 4-tert-butyl-benzoquinone (4-TBQ), 5-methoxy-4-tert-butyl-benzoquinone (5-MeO-4-TBQ) as the major products along with 6,6'-Bu(t)-biphenyl-3,4,3',4'-tetraol and others as minor products. These are further confirmed by ESI- and FAB-mass analyses. A tentative catalytic cycle has been framed based on the mass spectral analysis of the products and DFT calculations on individual intermediates that are energetically feasible.

  17. Lanthanide dinuclear complexes constructed from mixed oxygen-donor ligands: the effect of substituent positions of the neutral ligand on the magnetic dynamics in Dy analogues.

    PubMed

    Zhu, Wen-Hua; Li, Shan; Gao, Chen; Xiong, Xia; Zhang, Yan; Liu, Li; Powell, Annie K; Gao, Song

    2016-03-21

    Two series of lanthanide dinuclear complexes with the general formulae, [Ln(n-PNO)(Bza)3(H2O)] {Bza = benzoic acid; n = 3, n-PNO = 3-picoline N-oxide, Dy(1) and Er(2); and n = 4, n-PNO = 4-picoline N-oxide, Nd(3), Eu(4), Gd(5), Tb(6), Dy(7), Er(8) and Y(9)} have been successfully synthesized by the hydrothermal method. Single-crystal X-ray diffraction experiments illustrate that the two series of compounds possess similar carboxylic ligand-bridged dinuclear structure and coordination geometry around the lanthanide ions despite the different methyl-substituent positions on the neutral ligand. Comparative studies of the Dy analogues in the static-field measurements reveal only a little difference with a small butterfly-shaped opening for complex 1 and a close hysteresis loop for 7 at 2.0 K. However, systematic investigations of the alternating-current (ac) measurements indicate that the different substituent positions of the picoline N-oxide ligand have a significant effect on the magnetic relaxation dynamics. A more substantial suppression of the quantum tunnelling of magnetization (QTM) effect and pronounced slow magnetic relaxation were observed in complex 7 as compared to 1 under both zero and a 1 kOe static field.

  18. Formation of dinuclear, macrocyclic, and chain structures from HgI(2) and a semirigid benzimidazole-based bridging ligand: an example of ring-opening supramolecular isomerism.

    PubMed

    Su, Cheng-Yong; Goforth, Andrea M; Smith, Mark D; zur Loye, Hans-Conrad

    2003-09-08

    The reactions of HgI(2) with the semirigid ditopic ligand 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (bbimms) afforded three new complexes, [Hg(2)(mu-I)(2)I(2)(bbimms)] (1), [Hg(2)I(4)(bbimms)(2)] (2), and catena-poly[HgI(2)(bbimms)] (3). The ligand and all complexes have been structurally characterized by single-crystal X-ray diffraction. 1 is a triply bridged dinuclear complex comprised of two Hg(II) ions, one bridging ligand, two bridging I(-) anions, and two terminal I(-) anions. 2 is a dinuclear metallamacrocycle comprised of two Hg(II) ions, two bridging ligands, and four terminal I(-) anions, while 3 is a helical chain with the repeating unit of HgI(2)(bbimms). 2 and 3 can be classified as supramolecular isomers, and both are related to the triply bridged precursor 1 via the addition of one more ligand in a ring-opening process.

  19. Enhancing effects of salt formation on catalytic activity and enantioselectivity for asymmetric hydrogenation of isoquinolinium salts by dinuclear halide-bridged iridium complexes bearing chiral diphosphine ligands.

    PubMed

    Kita, Yusuke; Yamaji, Kenta; Higashida, Kosuke; Sathaiah, Kandula; Iimuro, Atuhiro; Mashima, Kazushi

    2015-01-26

    Asymmetric hydrogenation of 1- and 3-substituted and 1,3-disubstituted isoquinolinium chlorides using triply halide-bridged dinuclear iridium complexes [{Ir(H)(diphosphine)}2 (μ-Cl)3 ]Cl has been achieved by the strategy of HCl salt formation of isoquinolines to afford the corresponding chiral 1,2,3,4-tetrahydroisoquinolines (THIQs) in high yields and with excellent enantioselectivities after simple basic work-up. The effects of salt formation have been investigated by time-course experiments, which revealed that the generation of isoquinolinium chlorides clearly prevented formation of the catalytically inactive dinuclear trihydride complex, which was readily generated in the catalytic reduction of salt-free isoquinoline substrates. Based on mechanistic investigations, including by (1) H and (31) P{(1) H} NMR studies and the isolation and characterization of several intermediates, the function of the chloride anion of the isoquinolinium chlorides has been elucidated, allowing us to propose a new outer-sphere mechanism involving coordination of the chloride anion of the substrates to an iridium dihydride species along with a hydrogen bond between the chloride ligand and the N-H proton of the substrate salt. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. The International Centre for Theoretical Physics

    NASA Astrophysics Data System (ADS)

    Hussain, Faheem

    2008-07-01

    This talk traces in brief the genesis of the Abdus Salam International Centre for Theoretical Physics, Trieste, as one of Prof. Abdus Salam's major achievements. It outlines why Salam felt the necessity for establishing such a centre to help physicists in the developing world. It situates the founding of the Centre within Salam's broader vision of the causes of underdevelopment and of science as an engine for scientific, technological, economic and social development. The talk reviews the successes and failures of the ICTP and gives a brief overall view of the current status of the Centre.

  1. Synthesis, magnetostructural correlation, and catalytic promiscuity of unsymmetric dinuclear copper(II) complexes: models for catechol oxidases and hydrolases.

    PubMed

    Osório, Renata E H M B; Peralta, Rosely A; Bortoluzzi, Adailton J; de Almeida, Vicente R; Szpoganicz, Bruno; Fischer, Franciele L; Terenzi, Hernán; Mangrich, Antonio S; Mantovani, Karen Mary; Ferreira, Dalva E C; Rocha, Willian R; Haase, Wolfgang; Tomkowicz, Zbigniew; dos Anjos, Ademir; Neves, Ademir

    2012-02-06

    Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper(II) complexes, using the unsymmetrical ligands N',N',N-tris(2-pyridylmethyl)-N-(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L1) and N',N'-bis(2-pyridylmethyl)-N,N-(2-hydroxybenzyl)(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L2). The structures of the complexes [Cu(2)(L1)(μ-OAc)](ClO(4))(2)·(CH(3))(2)CHOH (1) and [Cu(2)(L2)(μ-OAc)](ClO(4))·H(2)O·(CH(3))(2)CHOH (2) were determined by X-ray crystallography. The complex [Cu(2)(L3)(μ-OAc)](2+) [3; L3 = N-(2-hydroxybenzyl)-N',N',N-tris(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. Inorg. Chim. Acta2005, 358, 1807-1822). Magnetic data show that the Cu(II) centers in 1 and 2 are antiferromagnetically coupled and that the difference in the exchange coupling J found for these complexes (J = -4.3 cm(-1) for 1 and J = -40.0 cm(-1) for 2) is a function of the Cu-O-Cu bridging angle. In addition, 1 and 2 were tested as catalysts in the oxidation of the model substrate 3,5-di-tert-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu(II)-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis(dinitrophenyl)phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu(II) center that contains the phenol group with tert-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (K(ass.) and k(cat.)) of 1 and 2 in comparison with that found for complex 3. In fact

  2. Dual emission and excited-state mixed-valence in a quasi-symmetric dinuclear Ru-Ru complex.

    PubMed

    Kreitner, Christoph; Grabolle, Markus; Resch-Genger, Ute; Heinze, Katja

    2014-12-15

    The synthesis and characterization of the new dinuclear dipeptide [(EtOOC-tpy)Ru(tpy-NHCO-tpy)Ru(tpy-NHCOCH3)](4+) 3(4+) of the bis(terpyridine)ruthenium amino acid [(HOOC-tpy)Ru(tpy-NH2)](2+) 1(2+) are described, and the properties of the dipeptide are compared to those of the mononuclear complex [(EtOOC-tpy)Ru(tpy-NHCOCH3)](2+) 4(2+) carrying the same functional groups. 3(4+) is designed to serve a high electronic similarity of the two ruthenium sites despite the intrinsic asymmetry arising from the amide bridge. This is confirmed via UV-vis absorption and NMR spectroscopy as well as cyclic voltammetry. 4(2+) and 3(4+) are emissive at room temperature, as expected. Moreover, 3(4+) exhibits dual emission from two different triplet states with different energies and lifetimes at room temperature. This is ascribed to the presence of a unique thermal equilibrium between coexisting [Ru(II)(tpy-NHCO-tpy(·-))Ru(III)] and [Ru(III)(tpy-NHCO-tpy(·-))Ru(II)] states leading to an unprecedented excited-state Ru(II)Ru(III) mixed-valent system via the radical anion bridge tpy-NHCO-tpy(·-). The mixed-valent cation 3(5+), on the other hand, shows no measurable interaction of the Ru(II)Ru(III) centers via the neutral bridge tpy-NHCO-tpy (Robin-Day class I). Reduction of 3(4+) to the radical cation 3(3+) by decamethylcobaltocene is bridge-centered as evidenced by rapid-freeze electron paramagnetic resonance spectroscopy. Interestingly, all attempts to observe 3(3+) via NMR and UV-vis absorption spectroscopy only led to the detection of the diamagnetic complex 3-H(3+) in which the bridging amide is deprotonated. Hence 3-H(3+) (and 4-H(+)) appear to reduce protons to dihydrogen. The ease of single and double deprotonation of 4(2+) and 3(4+) to 4-H(+), 3-H(3+), and 3-2H(2+) was demonstrated using a strong base and was studied using NMR and UV-vis absorption spectroscopies. The equilibrating excited triplet states of 3(4+) are reductively quenched by N,N-dimethylaniline assisted by

  3. Targeted guanine oxidation by a dinuclear copper(II) complex at single stranded/double stranded DNA junctions.

    PubMed

    Li, Lei; Murthy, Narasimha N; Telser, Joshua; Zakharov, Lev N; Yap, Glenn P A; Rheingold, Arnold L; Karlin, Kenneth D; Rokita, Steven E

    2006-09-04

    A dinuclear copper(II) complex [Cu(II)2(PD'O-)(H2O)2](ClO4)3 (5) with terminal Cu(II)-H(2)O moieties and a Cu...Cu distance of 4.13 A (X-ray structure) has been synthesized and characterized by EPR spectroscopy (ferromagnetic coupling observed) and cyclic voltammetry. Dizinc(II) and mononuclear copper(II) analogues [Zn(II)2(PD'O-)(H2O)2]3+ (7) and [Cu(II)(mPD'OH)(H2O)]2+ (6), respectively, have also been synthesized and structurally characterized. Reacting 5/MPA/O(2) (MPA = 3-mercaptopropionic acid) with DNA leads to a highly specific oxidation of guanine (G) at a junction between single- and double-stranded DNA. Mass spectrometric analysis of the major products indicates a gain of +18 and +34 amu relative to initial DNA strands. The most efficient reaction requires G at the first and second unpaired positions of each strand extending from the junction. Less reaction is observed for analogous targets in which the G cluster is farther from the junction or contains less than four Gs. Consistent with our previous systems, the multinuclear copper center is required for selective reaction; mononuclear complex 6 is not effective. Hydrogen peroxide as a substitute for MPA/O2 also does not lead to activity. Structural analysis of a [Cu(II)2(PD'O-)(G)]3+ complex (8) and dizinc analogue [Zn(II)(2)(PD'O-)(G)](ClO4)3 (9) (G = guanosine) reveals coordination of the G O6 and N7 atoms with the two copper (or zinc) centers and suggests that copper-G coordination likely plays a role in recognition of the DNA target. The Cu2-O2 intermediate responsible for guanine oxidation appears to be different from that responsible for direct-strand scission induced by other multinuclear copper complexes; the likely course of reaction is discussed.

  4. The European NEO Coordination Centre

    NASA Astrophysics Data System (ADS)

    Perozzi, E.; Borgia, B.; Micheli, M.

    An operational approach to NEO (Near-Earth Object) hazard monitoring has been developed at European level within the framework of the Space Situational Awareness Program (SSA) of the European Space Agency (ESA). Through federating European assets and profiting of the expertise developed in European Universities and Research Centers, it has been possible to start the deployment of the so-called SSA NEO Segment. This initiative aims to provide a significant contribution to the worldwide effort to the discovery, follow-up and characterization of the near-Earth object population. A major achievement has been the inauguration in May 2013 of the ESA NEO Coordination Centre located at ESRIN (Frascati, Italy). The goal of the NEOCC Precursor Service operations is twofold: to make available updated information on the NEO population and the associated hazard and to contribute to optimize the NEO observational efforts. This is done by maintaining and improving a Web Portal publicly available at http://neo.ssa.esa.int and by performing follow-up observations through a network of collaborating telescopes and facilities. An overview of the SSA-NEO System and a summary of the first two years of NEOCC operations is presented.

  5. Capturing Reality at Centre Block

    NASA Astrophysics Data System (ADS)

    Boulanger, C.; Ouimet, C.; Yeomans, N.

    2017-08-01

    The Centre Block of Canada's Parliament buildings, National Historic Site of Canada is set to undergo a major rehabilitation project that will take approximately 10 years to complete. In preparation for this work, Heritage Conservation Services (HCS) of Public Services and Procurement Canada has been completing heritage documentation of the entire site which includes laser scanning of all interior rooms and accessible confined spaces such as attics and other similar areas. Other documentation completed includes detailed photogrammetric documentation of rooms and areas of high heritage value. Some of these high heritage value spaces present certain challenges such as accessibility due to the height and the size of the spaces. Another challenge is the poor lighting conditions, requiring the use of flash or strobe lighting to either compliment or completely eliminate the available ambient lighting. All the spaces captured at this higher level of detail were also captured with laser scanning. This allowed the team to validate the information and conduct a quality review of the photogrammetric data. As a result of this exercise, the team realized that in most, if not all cases, the photogrammetric data was more detailed and at a higher quality then the terrestrial laser scanning data. The purpose and motivation of this paper is to present these findings, as well provide the advantages and disadvantages of the two methods and data sets.

  6. The Irish Centre for Talented Youth

    ERIC Educational Resources Information Center

    Gilheany, Sheila

    2005-01-01

    Conducting potency tests on penicillin, discussing rocket technology with a NASA astronaut, analysing animal bone fragments from medieval times, these are just some of the activities which occupy the time of students at The Irish Centre for Talented Youth. The Centre identifies young students with exceptional academic ability and then provides…

  7. Student-Centred Learning (SCL): Roles Changed?

    ERIC Educational Resources Information Center

    Onurkan Aliusta, Gülen; Özer, Bekir

    2017-01-01

    This paper addresses the espoused and enacted practices of high school teachers with regard to student-centred learning (SCL). Explanatory mixed-method design, where quantitative strand is followed by qualitative one, is employed. While the quantitative strand aims to explore teachers' perceptions regarding the extent student-centred teacher and…

  8. Promotion in Call Centres: Opportunities and Determinants

    ERIC Educational Resources Information Center

    Gorjup, Maria Tatiana; Valverde, Mireia; Ryan, Gerard

    2008-01-01

    Purpose: The purpose of this paper is to examine the quality of jobs in call centres by focusing on the opportunities for promotion in this sector. More specifically, the research questions focus on discovering whether promotion is common practise in the call centre sector and on identifying the factors that affect this.…

  9. [The Adamant, an unusual care centre].

    PubMed

    Khidichian, Frédéric

    2011-01-01

    The day care centre of the central Paris area has established itself in an unusual location--a 650 m2 floating building moored on the right bank of the Seine. Patients and caregivers were involved in the design of this original and ecological care centre, which places the emphasis on comfort and safety.

  10. Student Centred Approaches: Teachers' Learning and Practice

    ERIC Educational Resources Information Center

    Vale, Colleen; Davies, Anne; Weaven, Mary; Hooley, Neil

    2010-01-01

    Student centred approaches to teaching and learning in mathematics is one of the reforms currently being advocated and implemented to improve mathematics outcomes for students from low socio-economic status (SES) backgrounds. The models, meanings and practices of student centred approaches explored in this paper reveal that a constructivist model…

  11. Promotion in Call Centres: Opportunities and Determinants

    ERIC Educational Resources Information Center

    Gorjup, Maria Tatiana; Valverde, Mireia; Ryan, Gerard

    2008-01-01

    Purpose: The purpose of this paper is to examine the quality of jobs in call centres by focusing on the opportunities for promotion in this sector. More specifically, the research questions focus on discovering whether promotion is common practise in the call centre sector and on identifying the factors that affect this.…

  12. The European standards of Haemophilia Centres

    PubMed Central

    Giangrande, Paul; Calizzani, Gabriele; Menichini, Ivana; Candura, Fabio; Mannucci, Pier Mannuccio; Makris, Michael

    2014-01-01

    Introduction The European haemophilia community of professionals and patients has agreed on the principles of haemophilia care to address comprehensive optimal delivery of care which is nowadays scattered throughout Europe. Many of the health facilities call themselves Haemophilia Centres despite their variation in size, expertise and services provided. Only a small number of countries have Haemophilia Centre accreditation systems in place. Methods In the framework of the European Haemophilia Network project, following an inclusive process of stakeholder involvement, the European Guidelines for the certification of haemophilia centres have been developed in order to set quality standards for European Haemophilia Centres and criteria for their certification. Results The Guidelines define the standards and criteria for the designation of two levels of care delivery: European Haemophilia Treatment Centres, providing local routine care, and European Haemophilia Comprehensive Care Centres, providing specialised and multi-disciplinary care and functioning as tertiary referral centres. Additionally, they define standards about general requirements, patient care, provision of an advisory service and establishment of network of clinical and specialised services. Conclusions The implementation of the European Guidelines for the certification of Haemophilia Centres will contribute to the reduction of health inequalities through the standardisation of quality of care in European Union Member States and could represent a model to be taken into consideration for other rare disease groups. PMID:24922293

  13. The Irish Centre for Talented Youth

    ERIC Educational Resources Information Center

    Gilheany, Sheila

    2005-01-01

    Conducting potency tests on penicillin, discussing rocket technology with a NASA astronaut, analysing animal bone fragments from medieval times, these are just some of the activities which occupy the time of students at The Irish Centre for Talented Youth. The Centre identifies young students with exceptional academic ability and then provides…

  14. The Press Research Centre, 1956-1976.

    ERIC Educational Resources Information Center

    Press Research Centre, Krakow (Poland).

    In 1956, the Press Research Centre was established in Cracow, Poland by a group of journalists and publishers, for the purpose of instituting press research that would have practical applications. The aims of the Centre were to conduct studies on the history of the Polish press, the contemporary press, press readership, and editorial techniques.…

  15. A new regime for mechanical annealing and strong sample-size strengthening in body centred cubic molybdenum.

    PubMed

    Huang, Ling; Li, Qing-Jie; Shan, Zhi-Wei; Li, Ju; Sun, Jun; Ma, Evan

    2011-11-22

    Because of crystal symmetry, body centred cubic (BCC) metals have large differences in lattice friction between screw and edge dislocations, and manifest generally different mechanical behaviours from face centred cubic (FCC) metals. Although mechanical annealing (significant drop in stored dislocation density in response to applied stress) has been observed in FCC metals, it has not been observed in BCC metals so far. Here we show that significant mechanical annealing does occur in BCC Mo pillars, when their diameters decrease to hundreds of nanometers. In addition, there exists a critical diameter for focused ion beam milled pillars, below which the strengthening exponent increases dramatically, from ~0.3 to ~1. Thus, a new regime of size effects in BCC metals is discovered that converges to that of FCC metals, revealing deep connection in the dislocation dynamics of the two systems.

  16. Oxidation of methane by a biological dicopper centre.

    PubMed

    Balasubramanian, Ramakrishnan; Smith, Stephen M; Rawat, Swati; Yatsunyk, Liliya A; Stemmler, Timothy L; Rosenzweig, Amy C

    2010-05-06

    Vast world reserves of methane gas are underutilized as a feedstock for the production of liquid fuels and chemicals owing to the lack of economical and sustainable strategies for the selective oxidation of methane to methanol. Current processes to activate the strong C-H bond (104 kcal mol(-1)) in methane require high temperatures, are costly and inefficient, and produce waste. In nature, methanotrophic bacteria perform this reaction under ambient conditions using metalloenzymes called methane monooxygenases (MMOs). MMOs thus provide the optimal model for an efficient, environmentally sound catalyst. There are two types of MMO. Soluble MMO (sMMO) is expressed by several strains of methanotroph under copper-limited conditions and oxidizes methane with a well-characterized catalytic di-iron centre. Particulate MMO (pMMO) is an integral membrane metalloenzyme produced by all methanotrophs and is composed of three subunits, pmoA, pmoB and pmoC, arranged in a trimeric alpha(3)beta(3)gamma(3) complex. Despite 20 years of research and the availability of two crystal structures, the metal composition and location of the pMMO metal active site are not known. Here we show that pMMO activity is dependent on copper, not iron, and that the copper active site is located in the soluble domains of the pmoB subunit rather than within the membrane. Recombinant soluble fragments of pmoB (spmoB) bind copper and have propylene and methane oxidation activities. Disruption of each copper centre in spmoB by mutagenesis indicates that the active site is a dicopper centre. These findings help resolve the pMMO controversy and provide a promising new approach to developing environmentally friendly C-H oxidation catalysts.

  17. Dinuclear oxidative addition reactions using an isostructural series of Ni2, Co2, and Fe2 complexes.

    PubMed

    Behlen, Michael J; Zhou, You-Yun; Steiman, Talia J; Pal, Sudipta; Hartline, Douglas R; Zeller, Matthias; Uyeda, Christopher

    2016-12-20

    A family of low-valent Ni2, Co2, and Fe2 naphthyridine-diimine (NDI) complexes is presented. Ligand-based π* orbitals are sufficiently low-lying to fall within the metal 3d manifold, resulting in electronic structures that are highly delocalized across the conjugated [NDI]M2 system. This feature confers stability to metal-metal interactions during two-electron redox reactions, as demonstrated in a prototypical oxidative addition of allyl chloride.

  18. Tuned by metals: the TET peptidase activity is controlled by 3 metal binding sites

    PubMed Central

    Colombo, Matteo; Girard, Eric; Franzetti, Bruno

    2016-01-01

    TET aminopeptidases are dodecameric particles shared in the three life domains involved in various biological processes, from carbon source provider in archaea to eye-pressure regulation in humans. Each subunit contains a dinuclear metal site (M1 and M2) responsible for the enzyme catalytic activity. However, the role of each metal ion is still uncharacterized. Noteworthy, while mesophilic TETs are activated by Mn2+, hyperthermophilic TETs prefers Co2+. Here, by means of anomalous x-ray crystallography and enzyme kinetics measurements of the TET3 aminopeptidase from the hyperthermophilic organism Pyrococcus furiosus (PfTET3), we show that M2 hosts the catalytic activity of the enzyme, while M1 stabilizes the TET3 quaternary structure and controls the active site flexibility in a temperature dependent manner. A new third metal site (M3) was found in the substrate binding pocket, modulating the PfTET3 substrate preferences. These data show that TET activity is tuned by the molecular interplay among three metal sites. PMID:26853450

  19. Tuned by metals: the TET peptidase activity is controlled by 3 metal binding sites.

    PubMed

    Colombo, Matteo; Girard, Eric; Franzetti, Bruno

    2016-02-08

    TET aminopeptidases are dodecameric particles shared in the three life domains involved in various biological processes, from carbon source provider in archaea to eye-pressure regulation in humans. Each subunit contains a dinuclear metal site (M1 and M2) responsible for the enzyme catalytic activity. However, the role of each metal ion is still uncharacterized. Noteworthy, while mesophilic TETs are activated by Mn(2+), hyperthermophilic TETs prefers Co(2+). Here, by means of anomalous x-ray crystallography and enzyme kinetics measurements of the TET3 aminopeptidase from the hyperthermophilic organism Pyrococcus furiosus (PfTET3), we show that M2 hosts the catalytic activity of the enzyme, while M1 stabilizes the TET3 quaternary structure and controls the active site flexibility in a temperature dependent manner. A new third metal site (M3) was found in the substrate binding pocket, modulating the PfTET3 substrate preferences. These data show that TET activity is tuned by the molecular interplay among three metal sites.

  20. Big Surveys, Big Data Centres

    NASA Astrophysics Data System (ADS)

    Schade, D.

    2016-06-01

    Well-designed astronomical surveys are powerful and have consistently been keystones of scientific progress. The Byurakan Surveys using a Schmidt telescope with an objective prism produced a list of about 3000 UV-excess Markarian galaxies but these objects have stimulated an enormous amount of further study and appear in over 16,000 publications. The CFHT Legacy Surveys used a wide-field imager to cover thousands of square degrees and those surveys are mentioned in over 1100 publications since 2002. Both ground and space-based astronomy have been increasing their investments in survey work. Survey instrumentation strives toward fair samples and large sky coverage and therefore strives to produce massive datasets. Thus we are faced with the "big data" problem in astronomy. Survey datasets require specialized approaches to data management. Big data places additional challenging requirements for data management. If the term "big data" is defined as data collections that are too large to move then there are profound implications for the infrastructure that supports big data science. The current model of data centres is obsolete. In the era of big data the central problem is how to create architectures that effectively manage the relationship between data collections, networks, processing capabilities, and software, given the science requirements of the projects that need to be executed. A stand alone data silo cannot support big data science. I'll describe the current efforts of the Canadian community to deal with this situation and our successes and failures. I'll talk about how we are planning in the next decade to try to create a workable and adaptable solution to support big data science.

  1. The Canadian Astronomy Data Centre

    NASA Astrophysics Data System (ADS)

    Ball, Nicholas M.; Schade, D.; Astronomy Data Centre, Canadian

    2011-01-01

    The Canadian Astronomy Data Centre (CADC) is the world's largest astronomical data center, holding over 0.5 Petabytes of information, and serving nearly 3000 astronomers worldwide. Its current data collections include BLAST, CFHT, CGPS, FUSE, Gemini, HST, JCMT, MACHO, MOST, and numerous other archives and services. It provides extensive data archiving, curation, and processing expertise, via projects such as MegaPipe, and enables substantial day-to-day collaboration between resident astronomers and computer specialists. It is a stable, powerful, persistent, and properly supported environment for the storage and processing of large volumes of data, a condition that is now absolutely vital for their science potential to be exploited by the community. Through initiatives such as the Common Archive Observation Model (CAOM), the Canadian Virtual Observatory (CVO), and the Canadian Advanced Network for Astronomical Research (CANFAR), the CADC is at the global forefront of advancing astronomical research through improved data services. The CAOM aims to provide homogeneous data access, and hence viable interoperability between a potentially unlimited number of different data collections, at many wavelengths. It is active in the definition of numerous emerging standards within the International Virtual Observatory, and several datasets are already available. The CANFAR project is an initiative to make cloud computing for storage and data-intensive processing available to the community. It does this via a Virtual Machine environment that is equivalent to managing a local desktop. Several groups are already processing science data. CADC is also at the forefront of advanced astronomical data analysis, driven by the science requirements of astronomers both locally and further afield. The emergence of 'Astroinformatics' promises to provide not only utility items like object classifications, but to directly enable new science by accessing previously undiscovered or intractable

  2. Synthesis, characterization, and structure-activity relationship of the antimicrobial activities of dinuclear N-heterocyclic carbene (NHC)-silver(I) complexes.

    PubMed

    Sakamoto, Ryosuke; Morozumi, Soichiro; Yanagawa, Yuki; Toyama, Mizuki; Takayama, Akihiko; Kasuga, Noriko Chikaraishi; Nomiya, Kenji

    2016-10-01

    The three dinuclear silver(I) complexes of N-heterocyclic carbene (NHC) ligands, [Ag2(L-1a)](PF6)2·2CH3CN (Ag-1a), [Ag2(L-2)2](PF6)2·H2O (Ag-2), and [Ag2(L-4)2](PF6)2·2CH3CN (Ag-4), were synthesized by reactions of Ag2O with the corresponding PF6(-) salt of the NHC precursors indicated as H4L-1(PF6)4, H2L-2(PF6)2, and H2L-4(PF6)2. H4L-1(PF6)4, which is the precursor of ligand L-1, was formed as mixed crystals of two geometric isomers, i.e., H4L-1a(PF6)4 (major) and H4L-1b(PF6)4 (minor), each of which was not isolated as single species. Ag2O reacted with the mixed isomers of H4L-1(PF6)4 to give a single, pure crystalline silver(I) complex Ag-1a with one isomer (L-1a) as the major product. The molecular structures of the precursors and their silver(I) complexes were determined by X-ray crystallography. A mononuclear NHC-silver(I) complex (Ag-3) was prepared by the reaction of Ag2O with the precursor HL-3Cl. The silver(I) complexes and NHC precursors prepared here were characterized by CHN elemental analysis, FTIR, Thermogravimetry/Differential thermal analysis, X-ray crystallography and solution ((1)H and (13)C) NMR spectroscopy. Organometallic silver(I) complexes Ag-1a, Ag-2, and Ag-4 were dinuclear C-Ag-C bonding complexes, whereas Ag-3 was a mononuclear C-Ag-Cl bonding complex. These complexes are highly soluble in organic solvents such as acetone, acetonitrile, and dimethyl sulfoxide, and light-stable in the solid-state and in solution over one year. The antimicrobial activities of four silver(I) complexes and their NHC precursors against selected bacteria, yeasts, and molds in water-suspension systems were evaluated via the minimum inhibitory concentration; the activities were strongly dependent on the molecular structures of the dinuclear silver(I) complexes, which suggests a structure-activity relationship.

  3. Review of CERN Data Centre Infrastructure

    NASA Astrophysics Data System (ADS)

    Andrade, P.; Bell, T.; van Eldik, J.; McCance, G.; Panzer-Steindel, B.; Coelho dos Santos, M.; Traylen and, S.; Schwickerath, U.

    2012-12-01

    The CERN Data Centre is reviewing strategies for optimizing the use of the existing infrastructure and expanding to a new data centre by studying how other large sites are being operated. Over the past six months, CERN has been investigating modern and widely-used tools and procedures used for virtualisation, clouds and fabric management in order to reduce operational effort, increase agility and support unattended remote data centres. This paper gives the details on the project's motivations, current status and areas for future investigation.

  4. Dinuclear dysprosium SMMs bridged by a neutral bipyrimidine ligand: two crystal systems that depend on different lattice solvents lead to a distinct slow relaxation behaviour.

    PubMed

    Sun, Wen-Bin; Yan, Bing; Jia, Li-Hui; Wang, Bing-Wu; Yang, Qian; Cheng, Xin; Li, Hong-Feng; Chen, Peng; Wang, Zhe-Ming; Gao, Song

    2016-06-07

    Two dinuclear dysprosium complexes with the Dy(iii) ions bridged by the neutral bipyrimidine (BPYM) ligand were synthesized and magnetically characterized. They crystallized in a monoclinic and triclinic crystal system, respectively, with almost the same structural core, only differing in the lattice solvent molecules. Alternating current (ac) susceptibility measurements revealed that they exhibit significant slow relaxation of magnetization until 25 K in the absence of a dc field. The single and double relaxation processes were assigned to one and two types of Dy(iii) environments in the two dimmers, respectively, with barriers of 266 and 345 K under zero field conditions. The magnetic hysteresis loops of 1 and 2 were both observed up to 2.5 K.

  5. Synthesis, crystal structures and magnetic properties of dinuclear copper(II) compounds with NNO tridentate Schiff base ligands and bridging aliphatic diamine and aromatic diimine linkers.

    PubMed

    Rigamonti, Luca; Forni, Alessandra; Pievo, Roberta; Reedijk, Jan; Pasini, Alessandro

    2011-04-07

    The synthesis and the characterization of new dinuclear copper(II) compounds of general formula [(L(a-d))(2)Cu(2)(μ-N-N)](ClO(4))(2) (1-6) with either neutral aliphatic diamine (N-N = piperazine, pip) or aromatic diimine (N-N = 4,4'-bipyridine, 4,4'-bipy) linker are reported. The copper ligands L(-) (L(a-) = (E)-2-((2-aminoethylimino)methyl)phenolate, L(b-) = (E)-2-((2-aminopropylimino)methyl)-phenolate, L(c-) = (E)-2-((2-aminoethylimino)methyl)4-nitrophenolate, L(d-) = (E)-2-((2-aminoethylimino)methyl)4-methoxyphenolate) are NNO tridentate Schiff bases derived from the monocondensation of a substituted salicylaldehyde 5-G-salH (G = NO(2), H, OMe) with ethylenediamine, en, or 1,3-propylenediamine, tn. The crystal structures of compounds [(L(a))(2)Cu(2)(MeOH)(2)(μ-4,4'-bipy)](ClO(4))(2) (1·2MeOH), [(L(b))(2)Cu(2)(MeOH)(2)(μ-4,4'-bipy)](ClO(4))(2) (2·2MeOH), [(L(d))(2)Cu(2)(μ-4,4'-bipy)](ClO(4))(2) (4), [(L(a))(2)Cu(2)(μ-pip)](ClO(4))(2) (5) and [(L(b))(2)Cu(2)(μ-pip)](ClO(4))(2) (6) have been determined, revealing the preferred (e-e)-chair conformation of the bridging piperazine in compounds 5 and 6. The presence of hydrogen-bond-mediated intermolecular interactions, that involve the methanol molecules, yields dimers of dinuclear units for 1·2MeOH, and infinite zig-zag chains for 2·2MeOH. The temperature dependences of the magnetic susceptibilities χ(M)(T) for all compounds were measured, indicating the presence of antiferromagnetic Cu-Cu exchange. For the compounds 2-4 with 4,4'-bipy, the coupling constants J are around -1 cm(-1), while in compound 1 no interaction could be detected. The compounds 5 and 6 with piperazine display higher Cu-Cu magnetic interactions through the σ-bonding backbone of the bridging molecule, with J around -8 cm(-1), and the coupling is favoured by the (e-e)-chair conformation of the diamine ring. The non-aromatic, but shorter, linker piperazine gives rise to stronger Cu-Cu antiferromagnetic couplings than the aromatic, but

  6. Chromatin folding and DNA replication inhibition mediated by a highly antitumor-active tetrazolato-bridged dinuclear platinum(II) complex

    PubMed Central

    Imai, Ryosuke; Komeda, Seiji; Shimura, Mari; Tamura, Sachiko; Matsuyama, Satoshi; Nishimura, Kohei; Rogge, Ryan; Matsunaga, Akihiro; Hiratani, Ichiro; Takata, Hideaki; Uemura, Masako; Iida, Yutaka; Yoshikawa, Yuko; Hansen, Jeffrey C.; Yamauchi, Kazuto; Kanemaki, Masato T.; Maeshima, Kazuhiro

    2016-01-01

    Chromatin DNA must be read out for various cellular functions, and copied for the next cell division. These processes are targets of many anticancer agents. Platinum-based drugs, such as cisplatin, have been used extensively in cancer chemotherapy. The drug–DNA interaction causes DNA crosslinks and subsequent cytotoxicity. Recently, it was reported that an azolato-bridged dinuclear platinum(II) complex, 5-H-Y, exhibits a different anticancer spectrum from cisplatin. Here, using an interdisciplinary approach, we reveal that the cytotoxic mechanism of 5-H-Y is distinct from that of cisplatin. 5-H-Y inhibits DNA replication and also RNA transcription, arresting cells in the S/G2 phase, and are effective against cisplatin-resistant cancer cells. Moreover, it causes much less DNA crosslinking than cisplatin, and induces chromatin folding. 5-H-Y will expand the clinical applications for the treatment of chemotherapy-insensitive cancers. PMID:27094881

  7. Towards Human-Centred Design

    NASA Astrophysics Data System (ADS)

    Bannon, Liam J.

    The field of HCI has evolved and expanded dramatically since its origin in the early 1980’s. The HCI community embraces a large community of researchers and practitioners around the world, from a variety of disciplinary backgrounds in the human and social sciences, engineering and informatics, and more recently, the arts and design disciplines. This kaleidoscope of cultures and disciplines as seen at INTERACT Conferences provides a rich pool of resources for examining our field. Applications are increasingly exploring our full range of sensory modalities, and merging the digital and physical worlds. WiFi has opened up a huge design space for mobile applications. A focus on usability of products and services has been complemented by an emphasis on engagement, enjoyment and experience. With the advent of ubiquitous computing, and the emergence of “The Internet of Things”, new kinds of more open infrastructures make possible radically new kinds of applications. The sources of innovation have also broadened, to include human and social actors outside of the computing and design organizations. The question is to what extent is our mainstream thinking in the HCI field ready for the challenges of this Brave New World? Do the technological and social innovations that we see emerging require us to re-shape, or even, re-create, our field, or is it a case of a more gradual evolution and development of that which we already know? In this closing Keynote, I will provide a perspective on the evolution and development of the HCI field, looking backwards as well as forwards, in order to determine what are some of the changes of significance in the field. This “broad-brush” approach to what I term “ human-centred design” will be complemented by the examination of specific projects and applications, to help anchor some of the discussion. Areas such as user-centred design, participatory design, computer-supported cooperative work and learning, and interaction design, in

  8. Energetics, conformation, and recognition of DNA duplexes containing a major adduct of an anticancer azolato-bridged dinuclear Pt(II) complex.

    PubMed

    Mlcouskova, Jarmila; Malina, Jaroslav; Novohradsky, Vojtech; Kasparkova, Jana; Komeda, Seiji; Brabec, Viktor

    2012-10-01

    The design of anticancer metallodrugs is currently focused on platinum complexes which form on DNA major adducts that cannot readily be removed by DNA repair systems. Hence, antitumor azolato-bridged dinuclear Pt(II) complexes, such as [{cis-Pt(NH(3))(2)}(2)(μ-OH)(μ-pyrazolate)](2+) (AMPZ), have been designed and synthesized. These complexes exhibit markedly higher toxic effects in tumor cell lines than mononuclear conventional cisplatin. Biophysical and biochemical aspects of the alterations induced in short DNA duplexes uniquely and site-specifically modified by the major DNA adduct of AMPZ, namely 1,2-GG intrastrand cross-links, were examined. Attention was also paid to conformational distortions induced in DNA by the adducts of AMPZ and cisplatin, associated alterations in the thermodynamic stability of the duplexes, and recognition of these adducts by high-mobility-group (HMG) domain proteins. Chemical probing of DNA conformation, DNA bending studies and translesion synthesis by DNA polymerase across the platinum adduct revealed that the distortion induced in DNA by the major adduct of AMPZ was significantly less pronounced than that induced by similar cross-links from cisplatin. Concomitantly, the cross-link from AMPZ reduced the thermodynamic stability of the modified duplex considerably less. In addition, HMGB1 protein recognizes major DNA adducts of AMPZ markedly less than those of cisplatin. The experimental evidence demonstrates why the major DNA adducts of the new anticancer azolato-bridged dinuclear Pt(II) complexes are poor substrates for DNA repair observed in a previously published report. The relative resistance to DNA repair explains why these platinum complexes show major pharmacological advantages over cisplatin in tumor cells. Copyright © 2012 Elsevier B.V. All rights reserved.

  9. Dinuclear and 1D iron(III) Schiff base complexes bridged by 4-salicylideneamino-1,2,4-triazolate: X-ray structures and magnetic properties.

    PubMed

    Herchel, Radovan; Pavelek, Lubomír; Trávníček, Zdeněk

    2011-11-28

    Four new iron(III) complexes were obtained by the reaction of 4-salicylideneamino-1,2,4-triazole (Hsaltrz) and selected dinuclear μ-oxo-bridged iron(III) Schiff base complexes [{FeL(4)}(2)(μ-O)], where L(4) represents a terminal tetradentate dianionic Schiff-base ligand. X-ray structural analysis revealed a novel bridging mode of κN,κO of the saltrz ligand to form dinuclear complexes [{Fe(salen)(μ-saltrz)}(2)]·CH(3)OH (1) (H(2)salen = N,N'-ethylenebis(salicylimine)) and [{Fe(salpn)(μ-saltrz)}(2)] (2) (H(2)salpn = N,N'-1,2-propylenbis(salicylimine)), whereas one-dimensional (1D) zig-zag chains were formed in the case of [{Fe(salch)(μ-saltrz)}·0.5CH(3)OH](n) (3) (H(2)salch = N,N'-cyclohexanebis(salicylimine)) and [Fe(salophen)(μ-saltrz)](n) (4) (H(2)salophen = N,N'-o-phenylenebis(salicylimine)). It was also shown that the rigidity of the terminal ligand L(4) can be considered as the key factor for the molecular dimensionality of the products. The thorough magnetic analysis based on SQUID experiments, including the isotropic exchange and the zero-field splitting of both temperature and field dependent data, was performed for dimeric (1 and 2) and also for polymeric compounds (3 and 4) and revealed weak antiferromagnetic exchange mediated by the saltrz anions with much larger D-parameter (|D|≫|J|).

  10. Antibacterial, DNA interaction and cytotoxic activities of pendant-armed polyamine macrocyclic dinuclear nickel(II) and copper(II) complexes

    NASA Astrophysics Data System (ADS)

    Arthi, P.; Haleel, A.; Srinivasan, P.; Prabhu, D.; Arulvasu, C.; Kalilur Rahiman, A.

    2014-08-01

    A series of dinuclear nickel(II) and copper(II) complexes (1-6) of hexaaza macrocycles of 2,6-diformyl-4-methylphenol with three different benzoyl pendant-arms, 2,2‧-benzoyliminodi(ethylamine) trihydrochloride (L), 2,2‧-4-nitrobenzoyliminodi(ethylamine) trihydrochloride (L‧) and 2,2‧-3,5-dinitrobenzoyliminodi(ethylamine) trihydrochloride (L″) have been synthesized and characterized by spectral methods. The electrochemical studies of these complexes depict two irreversible one electron reduction processes around E1pc = -0.62 to -0.76 V and E2pc = -1.21 to -1.31, and nickel(II) complexes (1-3) exhibit two irreversible one electron oxidation processes around E1pa = 1.08 to 1.14 V and E2pa = 1.71 to 1.74 V. The room temperature magnetic moment values (μeff, 1.52-1.54 BM) indicate the presence of an antiferromagnetic interaction in the binuclear copper(II) complexes (4-6) which is also observed from the broad ESR spectra with a g value of 2.14-2.15. The synthesized complexes (1-6) were screened for their antibacterial activity. The results of DNA interaction studies indicate that the dinuclear complexes can bind to calf thymus DNA by intercalative mode and display efficient cleavage of plasmid DNA. Further, the cytotoxic activity of complexes 2, 5 and 6 on human liver adenocarcinoma (HepG2) cell line has been examined. Nuclear-chromatin cleavage has also been observed with PI staining and comet assays.

  11. Synthesis and structure of dimeric anthracene-9-carboxylato bridged dinuclear erbium(III) complex, [Er(2)(9-AC)(6)(DMF)(2)(H(2)O)(2)].

    PubMed

    Kusrini, Eny; Adnan, Rohana; Saleh, Muhammad I; Yan, Lim-Kong; Fun, Hoong-Kun

    2009-05-01

    We study the influence of the bulky aromatic rings, e.g. anthracence-9-carboxylic acid (9-ACA) with a large conjugated pi-system on the structure and spectroscopic properties of [Er(2)(9-AC)(6)(DMF)(2)(H(2)O)(2)] complex where 9-AC=anthracence-9-carboxylato and DMF=N,N'-dimethylformamide. The complex has been prepared from the erbium chloride and 9-ACA in the mixture of H(2)O:DMF solution (4:1, v/v) followed by pH adjustment to 6. The complex is crystallized in a monoclinic system with space group P2(1)/n. The two Er(III) ions are double bridged by the deprotonated carboxyl groups of two 9-AC anions (O1 and O1A), forming an eight-coordination number. The chelating bidentate (O,O), chelating-bridging tridentate (O,O,O') and monodentate of 9-AC anions are observed in the dinuclear [Er(2)(9-AC)(6)(DMF)(2)(H(2)O)(2)] complex. The Er-Er distance is 4.015A in the dimeric unit. Intramolecular O-Hcdots, three dots, centeredO and C-Hcdots, three dots, centeredO hydrogen bonds as well as numerous of intermolecular C-Hcdots, three dots, centeredpi interactions between the anthracene rings by edge-to-face interactions linked the dinuclear dimeric units into two-dimensional supramolecular network in a propeller-arrangement. Electronic absorption spectra of the Er(III) complex and its salt were measured. The emission spectrum of the complex is composed of a broad band due to the emission of intraligand pi*-->pi transition from the 9-AC anions and a shoulder peak originating from the 4f-4f emission transition of the Er(III) ions. The complex has a high thermal stability which can be attributed to the effectively increase the rigidity of the 9-AC anions.

  12. Solvothermal synthesis of uranium(VI) phases with aromatic carboxylate ligands: A dinuclear complex with 4-hydroxybenzoic acid and a 3D framework with terephthalic acid

    SciTech Connect

    Zhang, Yingjie; Karatchevtseva, Inna; Bhadbhade, Mohan; Tran, Toan Trong; Aharonovich, Igor; Fanna, Daniel J.; Shepherd, Nicholas D.; Lu, Kim; Li, Feng; Lumpkin, Gregory R.

    2016-02-15

    With the coordination of dimethylformamide (DMF), two new uranium(VI) complexes with either 4-hydroxybenzoic acid (H{sub 2}phb) or terephthalic acid (H{sub 2}tph) have been synthesized under solvothermal conditions and structurally characterized. [(UO{sub 2}){sub 2}(Hphb){sub 2}(phb)(DMF)(H{sub 2}O){sub 3}]·4H{sub 2}O (1) has a dinuclear structure constructed with both pentagonal and hexagonal bipyramidal uranium polyhedra linked through a µ{sub 2}-bridging ligand via both chelating carboxylate arm and alcohol oxygen bonding, first observation of such a coordination mode of 4-hydroxybenzoate for 5 f ions. [(UO{sub 2})(tph)(DMF)] (2) has a three-dimensional (3D) framework built with pentagonal bipyramidal uranium polyhedra linked with µ{sub 4}-terephthalate ligands. The 3D channeled structure is facilitated by the unique carboxylate bonding with nearly linear C–O–U angles and the coordination of DMF molecules. The presence of phb ligands in different coordination modes, uranyl ions in diverse environments and DMF in complex 1, and tph ligand, DMF and uranyl ion in complex 2 has been confirmed by Raman spectroscopy. In addition, their thermal stability and photoluminescence properties have been investigated. - Graphical abstract: With the coordination of dimethylformamide, two new uranyl complexes with either 4-hydroxybenzoate or terephthalate have been synthesized under solvothermal conditions and structurally characterized. - Highlights: • Solvent facilitates the synthesis of two new uranium(VI) complexes. • A dinuclear complex with both penta- and hexagonal bipyramidal uranium polyhedral. • A unique µ{sub 2}-bridging mode of 4-hydroxybenzoate via alcohol oxygen for 5 f ions. • A 3D framework with uranium polyhedra and µ{sub 4}-terephthalate ligands. • Vibration modes and photoluminescence properties are reported.

  13. Multiple-path dissociation mechanism for mono- and dinuclear tris(hydroxamato)iron(III) complexes with dihydroxamic acid ligands in aqueous solution.

    PubMed

    Boukhalfa, H; Crumbliss, A L

    2000-09-18

    Linear synthetic dihydroxamic acids ([CH3N(OH)C=O)]2(CH2)n; H2Ln) with short (n = 2) and long (n = 8) hydrocarbon-connecting chains form mono- and dinuclear complexes with Fe(III) in aqueous solution. At conditions where the formation of Fe2(Ln)3 is favored, complexes with each of the two ligand systems undergo [H+]-induced ligand dissociation processes via multiple sequential and parallel paths, some of which are common and some of which are different for the two ligands. The pH jump induced ligand dissociation proceeds in two major stages (I and II) where each stage is shown to be comprised of multiple components (Ix, where x = 1-3 for L2 and L8, and IIy, where y = 1-3 for L2 and y = 1-4 for L8). A reaction scheme consistent with kinetic and independent ESI-MS data is proposed that includes the tris-chelated complexes (coordinated H2O omitted for clarity) (Fe2(Ln)3, Fe2(L2)2(L2H)2, Fe(LnH)3, Fe(L8)(L8H)), bis-chelated complexes (Fe2(Ln)2(2+), Fe(LnH)2+, Fe(L8)+), and monochelated complexes (Fe(LnH)2+). Analysis of kinetic data for ligand dissociation from Fe2(Ln)(LnH)3+ (n = 2, 4, 6, 8) allows us to estimate the dielectric constant at the reactive dinuclear Fe(III) site. The existence of multiple ligand dissociation paths for the dihydroxamic acid complexes of Fe(III) is a feature that distinguishes these systems from their bidentate monohydroxamic acid and hexadentate trihydroxamic acid counterparts and may be a reason for the biosynthesis of dihydroxamic acid siderophores, despite higher environmental molar concentrations necessary to completely chelate Fe(III).

  14. Dinuclear ruthenium complexes display loop isomer selectivity to c-MYC DNA G-quadriplex and exhibit anti-tumour activity.

    PubMed

    Zheng, Chuping; Liu, Yanan; Liu, Ying; Qin, Xiuying; Zhou, Yanhui; Liu, Jie

    2016-03-01

    G-quadruplex DNA, especially the cellular-myelocytomatosis viral oncogene (c-MYC) is closely associated with cell-cycle regulation, proliferation of tumour cells. In this work, the interaction between the c-MYC and two dinuclear Ru(II) complexes [(bpy)2Ru(bpibp)Ru(bpy)2](ClO4)4 (compound 1) and [(phen)2Ru(bpibp)Ru(phen)2](ClO4)4 (compound 2) have been studied. The data from UV-Visible, PCR-stop and Fluorescence resonance energy transfer (FRET) showed that two complexes can stabilize the structure of G-quadruplex in the c-MYC promoter and targeting the G-quadruplex loop isomers. Interestingly, the complex 2 has a greater effect on the 1:2:1 and 2:1:1 loop isomers while the 1 prefers to the 1:2:1 isomers. The mechanism studies revealed that complexes can induce apoptosis in HepG2 cells by generating ROS metabolites, triggering mitochondrial membrane potential loss and down-regulation of P-Akt (Akt also known as protein kinase B), P-p44/42 MAP kinase protein (P-p44/42), and c-MYC. Taken together, these results suggested that the two dinuclear complexes may both be candidates as anti-tumour agents as they may reduce the c-MYC gene expression. {bpibp: 4, 4'-bis (1, 10-phenanthroline-[5, 6-d] imidazole-2-yl)-biphenyl, bpy: 2,2-bipyridine, phen: 1,10-phenanthroline}. Copyright © 2016. Published by Elsevier Inc.

  15. Solid- and solution-state studies of the novel mu-dicyanamide-bridged dinuclear spin-crossover system {[(Fe(bztpen)]2[mu-N(CN)2]}(PF6)3 x n H2O.

    PubMed

    Ortega-Villar, Norma; Thompson, Amber L; Muñoz, M Carmen; Ugalde-Saldívar, Víctor M; Goeta, Andrés E; Moreno-Esparza, Rafael; Real, José A

    2005-09-19

    The mononuclear diamagnetic compound {Fe(bztpen)[N(CN)2]}(PF6)CH3OH (1) (bztpen = N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethylenediamine) has been synthesized and its crystal structure studied. Complex 1 can be considered to be the formal precursor of two new dinuclear, dicyanamide-bridged iron(II) complexes with the generic formula {[(Fe(bztpen)]2[mu-N(CN)2]}(PF6)3 x n H2O (n = 1 (2) or 0 (3)), which have been characterized in the solid state and in solution. In all three complexes, the iron atoms have a distorted [FeN6] octahedral coordination defined by a bztpen ligand and a terminal (1) or a bridging dicyanamide ligand (2 and 3). In the solid state, 2 and 3 can be considered to be molecular isomers that differ by the relative position of the phenyl ring of the two {Fe(bztpen)[N(CN)2]}+ halves (cis and trans, respectively). Depending on the texture of the sample, 2 exhibits paramagnetic behavior or displays a very incomplete spin transition at atmospheric pressure. Complex 3 undergoes a gradual two-step spin transition with no observed hysteresis in the solid state. Both steps are approximately 100 K wide, centered at approximately 200 K and approximately 350 K, with a plateau of approximately 80 K separating the transitions. The crystal structure of 3 has been determined in steps of approximately 50 K between 400 K and 90 K, which provides a fascinating insight into the structural behavior of the complex and the nature of the spin transition. Order-disorder transitions occur in the dicyanamide bridge and the PF6(-) ions simultaneously, with the spin-crossover behavior suggesting that these transitions may trigger the two-step character. In solution, 2 and 3 display very similar continuous spin conversions. Electrochemical studies of 2 and 3 show that the voltammograms are typical of dimeric systems with electronic coupling of the metals through the dicyanamide ligand.

  16. Identity Theft: A Study in Contact Centres

    NASA Astrophysics Data System (ADS)

    Moir, Iain; Weir, George R. S.

    This paper explores the recent phenomenon of identity theft. In particular, it examines the contact centre environment as a mechanism for this to occur. Through a survey that was conducted amongst forty-five contact centre workers in the Glasgow area we determined that contact centres can and do provide a mechanism for identity theft. Specifically, we found a particularly high incidence of agents who had previously dealt with phone calls that they considered suspicious. Furthermore, there are agents within such environments who have previously been offered money in exchange for customers' details, or who know of fellow workers who received such offers. Lastly, we identify specific practices within contact centres that may contribute to the likelihood of identity theft.

  17. Perspectives on recycling centres and future developments.

    PubMed

    Engkvist, I-L; Eklund, J; Krook, J; Björkman, M; Sundin, E

    2016-11-01

    The overall aim of this paper is to draw combined, all-embracing conclusions based on a long-term multidisciplinary research programme on recycling centres in Sweden, focussing on working conditions, environment and system performance. A second aim is to give recommendations for their development of new and existing recycling centres and to discuss implications for the future design and organisation. Several opportunities for improvement of recycling centres were identified, such as design, layout, ease with which users could sort their waste, the work environment, conflicting needs and goals within the industry, and industrialisation. Combining all results from the research, which consisted of different disciplinary aspects, made it possible to analyse and elucidate their interrelations. Waste sorting quality was recognized as the most prominent improvement field in the recycling centre system. The research identified the importance of involving stakeholders with different perspectives when planning a recycling centre in order to get functionality and high performance. Practical proposals of how to plan and build recycling centres are given in a detailed checklist. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. The Imperial College Thermophysical Properties Data Centre

    NASA Astrophysics Data System (ADS)

    Angus, S.; Cole, W. A.; Craven, R.; de Reuck, K. M.; Trengove, R. D.; Wakeham, W. A.

    1986-07-01

    The IUPAC Thermodynamic Tables Project Centre in London has at its disposal considerable expertise on the production and utilization of high-accuracy equations of state which represent the thermodynamic properties of substances. For some years they have been content to propagate this information by the traditional method of book production, but the increasing use of the computer in industry for process design has shown that an additional method was needed. The setting up of the IUPAC Transport Properties Project Centre, also at Imperial College, whose products would also be in demand by industry, afforded the occasion for a new look at the problem. The solution has been to set up the Imperial College Thermophysical Properties Data Centre, which embraces the two IUPAC Project Centres, and for it to establish a link with the existing Physical Properties Data Service of the Institution of Chemical Engineers, thus providing for the dissemination of the available information without involving the Centres in problems such as those of marketing and advertising. This paper outlines the activities of the Centres and discusses the problems in bringing their products to the attention of industry in suitable form.

  19. The Metal-Rich Universe

    NASA Astrophysics Data System (ADS)

    Israelian, Garik; Meynet, Georges

    2012-10-01

    Preface; Part I. Abundances in the Galaxy: Field Stars: 1. Metal-rich stars and stellar populations: A brief history and new results; 2. The metal-rich nature of stars with planets; 3. Solar chemical peculiarities; 4. Kinematics of metal-rich stars with and without planets; 5. Elemental abundance trends in the metal-rich thin and thick disks; 6. Metal-rich massive stars - how metal-rich are they?; 7. Hercules stream stars and the metal-rich thick disk; 8. Abundance survey of the galactic thick disk; Part II. Abundances in the Galaxy: Galactic Stars in Clusters, Bulges and Centre: 9. Galactic open clusters with super solar metallicities; 10. Old and very metal-rich open clusters in the BOCCE project; 11. Massive stars vs. nebular abundances in the Orion nebula; 12. Abundance surveys of metal-rich bulge stars; 13. Metal abundances in the galactic center; 14. Light elements in the galactic bulge; 15. Metallicity and ages of selected G-K giants; Part III. Observations - Abundances in Extragalactic Contexts: 16. Stellar abundances of early-type galaxies and galactic spheroids: Evidence for metal-rich stars; 17. Measuring chemical abundances in extragalactic metal-rich HII regions; 18. On the maximum oxygen abundance in metal-rich spiral galaxies; 19. Starbursts and their contribution to metal enrichment; 20. High metallicities at high redshifts; 21. Evolution of dust and elemental abundances in quasar DLAs and GRB afterglows as a function of cosmic time; 22. Dust, metals and diffuse interstellar bands in damped Lyman Alpha systems; 23. Tracing metallicities in the Universe with the James Webb Space Telescope; Part IV. Stellar Populations and Mass Functions: 24. The stellar initial mass function of metal-rich populations; 25. IMF effects on the metallicity and colour evolution of disk galaxies; 26. The metallicity of circumnuclear star forming regions; 27. The stellar population of bulges; 28. The metallicity distribution of the stars in elliptical galaxies; 29. Wolf

  20. An x-ray absorption near edge structure spectroscopy study of metal coordination in Co(II)-substituted Carcinus maenas hemocyanin.

    PubMed Central

    Della Longa, S; Bianconi, A; Palladino, L; Simonelli, B; Congiu Castellano, A; Borghi, E; Barteri, M; Beltramini, M; Rocco, G P; Salvato, B

    1993-01-01

    High-resolution x-ray absorption near edge structure spectroscopy was used to characterize the metal sites in three different cobalt-substituted derivatives of Carcinus maenas hemocyanin (Hc), including a mononuclear cobalt, a dinuclear cobalt and a copper-cobalt hybrid derivative. Co(II) model complexes with structures exemplifying octahedral, trigonal bipyramidal, pseudo-tetrahedral, and square planar geometries were also studied. The results provide structural information about the metal binding site(s) in the Co-Hcs that extend earlier results from EPR and optical spectroscopy (Bubacco et al. 1992. Biochemistry. 31: 9294-9303). Experimental spectra were compared to those calculated for atomic clusters of idealized geometry, generated using a multiple scattering approach. The energy of the dipole forbidden 1s-->3d transition and of the absorption edge in the spectra for all cobalt Hc derivatives confirmed the cobaltous oxidation state which rules out the presence of an oxygenated site. Comparisons between data and simulations showed that the mononuclear and dinuclear Co(II) derivatives, as well as the hybrid derivative, contain four-coordinate Co(II) in distorted tetrahedral sites. Although the spectra for Co(II) in dinuclear metal sites more closely resemble the simulated spectrum for a tetrahedral complex than do spectra for the mononuclear derivative, the Co(II) sites in all derivatives are very similar. The Cu K-edge high resolution x-ray absorption near edge structure spectrum of the hybrid Cu-Co-Hc resembles that of deoxy-Hc demonstrating the presence of three-coordinate Cu(I). PMID:8312502

  1. An x-ray absorption near edge structure spectroscopy study of metal coordination in Co(II)-substituted Carcinus maenas hemocyanin.

    PubMed

    Della Longa, S; Bianconi, A; Palladino, L; Simonelli, B; Congiu Castellano, A; Borghi, E; Barteri, M; Beltramini, M; Rocco, G P; Salvato, B

    1993-12-01

    High-resolution x-ray absorption near edge structure spectroscopy was used to characterize the metal sites in three different cobalt-substituted derivatives of Carcinus maenas hemocyanin (Hc), including a mononuclear cobalt, a dinuclear cobalt and a copper-cobalt hybrid derivative. Co(II) model complexes with structures exemplifying octahedral, trigonal bipyramidal, pseudo-tetrahedral, and square planar geometries were also studied. The results provide structural information about the metal binding site(s) in the Co-Hcs that extend earlier results from EPR and optical spectroscopy (Bubacco et al. 1992. Biochemistry. 31: 9294-9303). Experimental spectra were compared to those calculated for atomic clusters of idealized geometry, generated using a multiple scattering approach. The energy of the dipole forbidden 1s-->3d transition and of the absorption edge in the spectra for all cobalt Hc derivatives confirmed the cobaltous oxidation state which rules out the presence of an oxygenated site. Comparisons between data and simulations showed that the mononuclear and dinuclear Co(II) derivatives, as well as the hybrid derivative, contain four-coordinate Co(II) in distorted tetrahedral sites. Although the spectra for Co(II) in dinuclear metal sites more closely resemble the simulated spectrum for a tetrahedral complex than do spectra for the mononuclear derivative, the Co(II) sites in all derivatives are very similar. The Cu K-edge high resolution x-ray absorption near edge structure spectrum of the hybrid Cu-Co-Hc resembles that of deoxy-Hc demonstrating the presence of three-coordinate Cu(I).

  2. Acid-rock drainage at Skytop, Centre County, Pennsylvania, 2004

    USGS Publications Warehouse

    Hammarstrom, Jane M.; Brady, Keith; Cravotta, Charles A.

    2005-01-01

    Recent construction for Interstate Highway 99 (I?99) exposed pyrite and associated Zn-Pb sulfide minerals beneath a >10-m thick gossan to oxidative weathering along a 40-60-m deep roadcut through a 270-m long section of the Ordovician Bald Eagle Formation at Skytop, near State College, Centre County, Pennsylvania. Nearby Zn-Pb deposits hosted in associated sandstone and limestone in Blair and Centre Counties were prospected in the past; however, these deposits generally were not viable as commercial mines. The pyritic sandstone from the roadcut was crushed and used locally as road base and fill for adjoining segments of I?99. Within months, acidic (pH1,000 mg/L), seep waters at the base of the cut contain >100 mg/L dissolved Zn and >1 mg/L As, Co, Cu, and Ni. Lead is relatively immobile (<10 ?g/L in seep waters). The salts sequester metals and acidity between rainfall events. Episodic salt dissolution then contributes pulses of contamination including acid to surface runoff and ground water. The Skytop experience highlights the need to understand dynamic interactions of mineralogy and hydrology in order to avoid potentially negative environmental impacts associated with excavation in sulfidic rocks.

  3. Synthesis, Characterization, and Photochemistry of a Dinuclear Cyanide-Bridged Iron(II)-Platinum(IV) Mixed-Valence Compound and Its Implications for the Corresponding Iron(II)-Platinum(IV)-Iron(II) Complex.

    PubMed

    Pfennig, Brian W.; Lockard, Jenny V.; Cohen, Jamie L.; Watson, David F.; Ho, Douglas M.; Bocarsly, Andrew B.

    1999-06-14

    The mixed-valence compound [(NH(3))(5)Pt(IV)(&mgr;-NC)Fe(II)(CN)(5)].6H(2)O was synthesized by the substitution reaction of [Pt(IV)(NH(3))(5)OSO(2)CF(3)](OSO(2)CF(3))(3) and [Fe(II)(CN)(6)](4)(-) in aqueous solution and was characterized by UV/vis, IR, and resonance Raman spectroscopies, cyclic voltammetry, and single-crystal X-ray diffractometry. The monoclinic crystal (space group P2(1)/m (No. 11)) consists of a dinuclear, cyanide-bridged Fe(II)-Pt(IV) moiety with unit cell dimensions of a = 9.3241(5) Å, b = 14.0466(7) Å, c = 9.6938(4) Å, beta = 111.467(2) degrees, and Z = 2. There are also an average of six waters of hydration per unit cell. The R-factors for this structure are R = 3.66% and R(w) = 7.90%. The electronic spectrum reveals a broad intervalent (IT) charge-transfer absorption at approximately 420 nm (epsilon = 540 M(-)(1) cm(-)(1)). Both the ground-state spectroscopy and the electrochemistry of this compound are very similar to those of the corresponding trinuclear adduct [(NC)(5)Fe(II)(&mgr;-CN)Pt(IV)(NH(3))(4)(&mgr;-NC)Fe(II)(CN)(5)](4)(-), which has been reported previously. Classical Marcus-Hush theory has been applied in the analysis of the IT band of the dinuclear compound in an effort to elucidate a fuller understanding of the photophysics of the trinuclear complex. The data suggest that this latter, centrosymmetric species can be treated theoretically as two back-to-back dinuclear donor-acceptor (D-A) compounds of the form D-A/A-D, where the Pt(IV) inversion center acts as the acceptor for both halves of the molecule. The photochemistry of the dinuclear complex was also investigated.

  4. Dinuclear Metallacycles with Single M-X-M Bridges (X = Cl(-), Br(-); M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)): Strong Antiferromagnetic Superexchange Interactions.

    PubMed

    Reger, Daniel L; Pascui, Andrea E; Foley, Elizabeth A; Smith, Mark D; Jezierska, Julia; Wojciechowska, Agnieszka; Stoian, Sebastian A; Ozarowski, Andrew

    2017-03-06

    A series of monochloride-bridged, dinuclear metallacycles of the general formula [M2(μ-Cl)(μ-L)2](ClO4)3 have been prepared using the third-generation, ditopic bis(pyrazolyl)methane ligands L = m-bis[bis(1-pyrazolyl)methyl]benzene (Lm), M = Cu(II), Zn(II), and L = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*), M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II). These complexes were synthesized from the direct reactions of M(ClO4)2·6H2O, MCl2, and the ligand, Lm or Lm*, in the appropriate stoichiometric amounts. Three analogous complexes of the formula [M2(μ-Cl)(μ-L)2](BF4)3, L = Lm, M = Cu(II), and L = Lm*, M = Co(II), Cu(II), were prepared from the reaction of [M2(μ-F)(μ-L)2](BF4)3 and (CH3)3SiCl. The bromide-bridged complex [Cu2(μ-Br)(μ-Lm*)2](ClO4)3 was prepared by the first method. Three acyclic complexes, [Co2(μ-Lm)μ-Cl4], [Co2(μ-Lm*)Cl4], and [Co2(μ-Lm*)Br4], were also prepared. The structures of all [M2(μ-X)(μ-L)2](3+) (X = Cl(-), Br(-)) complexes have two ditopic bis(pyrazolyl)methane ligands bridging two metals in a metallacyclic arrangement. The fifth coordination site of the distorted trigonal bipyramidal metal centers is filled by a bridging halide ligand that has an unusual linear or nearly linear M-X-M angle. The NMR spectra of [Zn2(μ-Cl)(μ-Lm*)2](ClO4)3 and especially [Cd2(μ-Cl)(μ-Lm*)2](ClO4)3 demonstrate that the metallacycle structure is maintained in solution. Solid state magnetic susceptibility data for the copper(II) compounds show very strong antiferromagnetic exchange interactions, with -J values of 536 cm(-1) for [Cu2(μ-Cl)(μ-Lm)2](ClO4)3·xCH3CN, 720 cm(-1) for [Cu2(μ-Cl)(μ-Lm*)2](ClO4)3, and 945 cm(-1) for [Cu2(μ-Br)(μ-Lm*)2](ClO4)3·2CH3CN. Smaller but still substantial antiferromagnetic interactions are observed with other first row transition metals, with -J values of 98 cm(-1) for [Ni2(μ-Cl)(μ-Lm*)2](ClO4)3, 55 cm(-1) for [Co2(μ-Cl)(μ-Lm*)2](ClO4)3, and 34 cm(-1) for [Fe2(μ-Cl)(μ-Lm*)2](ClO4

  5. Recombinant purple acid phosphatase isoform 3 from sweet potato is an enzyme with a diiron metal center.

    PubMed

    Waratrujiwong, Teerawit; Krebs, Bernt; Spener, Friedrich; Visoottiviseth, Pornsawan

    2006-04-01

    Purple acid phosphatases (PAPs) from sweet potato (sp) have been classified on the basis of their primary structure and the dinuclear metal center into isoforms spPAP1 [Fe(III)-Zn(II)] and spPAP2 [Fe(III)-Mn(II)]; for spPAP3 only the cDNA is known. With the aim of unraveling the character of the dinuclear metal center we report here the characterization of this isoform at the protein level. We cloned spPAP3 cDNA in a baculovirus and overexpressed this enzyme in Sf9 insect cells. Preparation of recombinant spPAP3 in two steps afforded pure enzyme with yields of 4.5 mg.L(-1) culture medium. This enzyme is a dimeric, disulfide-linked PAP of 110 kDa, similar to known PAP isoforms from higher plants. Enzymatic studies and spectroscopic properties (max. absorption at 550-565 nm) indicated a diiron enzyme; quantitative and semiquantitative metal analysis using ICP-OES and TOF-SIMS, respectively, revealed the presence of only iron in purified spPAP3. Metal replacement in the second metal-binding site upon preparation of the semiapo-enzyme with Fe(II), Zn(II), or Mn(II) showed highest activities with Fe(II). The data show that recombinant spPAP3 has a diiron metal center. Site-directed mutagenesis was conducted to check catalytic efficiency at the atomic level. Tyr291 at the substrate-binding site in spPAP3 was mutated to His and Ala, the respective residues found in spPAP1 and spPAP2. Kinetic analysis showed that conversion of Tyr291 to His further optimized the performance of this protein as a diiron enzyme, whereas the Ala mutation weakened the catalytic efficiency regardless of the metal present in the second binding site.

  6. CMS centres worldwide: A new collaborative infrastructure

    SciTech Connect

    Taylor, Lucas; Gottschalk, Erik; /Fermilab

    2010-01-01

    The CMS Experiment at the LHC is establishing a global network of inter-connected 'CMS Centres' for controls, operations and monitoring. These support: (1) CMS data quality monitoring, detector calibrations, and analysis; and (2) computing operations for the processing, storage and distribution of CMS data. We describe the infrastructure, computing, software, and communications systems required to create an effective and affordable CMS Centre. We present our highly successful operations experiences with the major CMS Centres at CERN, Fermilab, and DESY during the LHC first beam data-taking and cosmic ray commissioning work. The status of the various centres already operating or under construction in Asia, Europe, Russia, South America, and the USA is also described. We emphasise the collaborative communications aspects. For example, virtual co-location of experts in CMS Centres Worldwide is achieved using high-quality permanently-running 'telepresence' video links. Generic Web-based tools have been developed and deployed for monitoring, control, display management and outreach.

  7. The role of the sexual assault centre.

    PubMed

    Eogan, Maeve; McHugh, Anne; Holohan, Mary

    2013-02-01

    Sexual Assault Centres provide multidisciplinary care for men and women who have experienced sexual crime. These centres enable provision of medical, forensic, psychological support and follow-up care, even if patients chose not to report the incident to the police service. Sexual Support Centres need to provide a ring-fenced, forensically clean environment. They need to be appropriately staffed and available 24 hours a day, 7 days a week to allow prompt provision of medical and supportive care and collection of forensic evidence. Sexual Assault Centres work best within the context of a core agreed model of care, which includes defined multi-agency guidelines and care pathways, close links with forensic science and police services, and designated and sustainable funding arrangements. Additionally, Sexual Assault Centres also participate in patient, staff and community education and risk reduction. Furthermore, they contribute to the development, evaluation and implementation of national strategies on domestic, sexual and gender-based violence. Copyright © 2012 Elsevier Ltd. All rights reserved.

  8. Effect of f-f interactions on quantum tunnelling of the magnetization: mono- and dinuclear Dy(III) phthalocyaninato triple-decker single-molecule magnets with the same octacoordination environment.

    PubMed

    Katoh, Keiichi; Asano, Rina; Miura, Akira; Horii, Yoji; Morita, Takaumi; Breedlove, Brian K; Yamashita, Masahiro

    2014-06-07

    The single-molecule magnet (SMM) behaviour of dinuclear Ln(III)-Pc triple-decker complexes (Dy(III)-Y(III): 1 and Dy(III)-Dy(III): 2) with the same octacoordination environment and slow magnetic relaxation behaviour were explained using X-ray crystallography and static and dynamic susceptibility measurements. In particular, interactions among the 4f electrons of dinuclear Dy(III)-Pc triple-decker type SMMs have never been discussed on the basis of the same octacoordination environment. Our results clearly show that the Dy(III) ion sites of 1 and 2 are equivalent, consistent with the crystal structure. 2 Exhibited ferromagnetic interaction between Dy(III) ions. This is clear evidence that the magnetic relaxation mechanism depends heavily on the dipole-dipole (f-f) interactions between the Dy(III) ions in the dinuclear systems. For both 1 and 2, quantum tunnelling of the magnetization (QTM) was observed. However, the magnetic relaxation time (τ) for 2 was one order of magnitude greater than that for 1, and single-component magnetic relaxation behaviour was explained. In other words, it is possible to use f-f interactions to increase τ by one order of magnitude.

  9. Identification on Membrane and Characterization of Phosphoproteins Using an Alkoxide-Bridged Dinuclear Metal Complex as a Phosphate-Binding Tag Molecule

    PubMed Central

    Nakanishi, Tsuyoshi; Ando, Eiji; Furuta, Masaru; Kinoshita, Eiji; Kinoshita-Kikuta, Emiko; Koike, Tohru; Tsunasawa, Susumu; Nishimura, Osamu

    2007-01-01

    We have developed a method for on-membrane direct identification of phosphoproteins, which are detected by a phosphate-binding tag (Phos-tag) that has an affinity to phosphate groups with a chelated Zn2+ ion. This rapid profiling approach for phosphoproteins combines chemical inkjet technology for microdispensing of reagents onto a tiny region of target proteins with mass spectrometry for on-membrane digested peptides. Using this method, we analyzed human epidermoid carcinoma cell lysates of A-431 cells stimulated with epidermal growth factor, and identified six proteins with intense signals upon affinity staining with the phosphate-binding tag. It was already known that these proteins are phosphorylated, and our new approach proved to be effective at rapid profiling of phosphoproteins. Furthermore, we tried to determine their phosphorylation sites by MS/MS analysis after in-gel digestion of the corresponding spots on the 2DE gel to the rapid on-membrane identifications. As one example of use of information gained from the rapid-profiling approach, we successfully characterized a phosphorylation site at Ser-113 on prostaglandin E synthase 3. PMID:18166671

  10. Theoretical investigation of the reaction mechanism for the phosphate diester hydrolysis using an asymmetric dinuclear metal complex as a biomimetic model of the purple acid phosphatase enzyme.

    PubMed

    Ferreira, Dalva E C; De Almeida, Wagner B; Neves, Ademir; Rocha, Willian R

    2008-12-14

    In this work we have applied quantum mechanical calculations, at the density functional theory level, to investigate the phosphate diester hydrolysis promoted by a cationic heterodinuclear Fe(III)...Zn(II) complex that mimics the structural and functional properties of the purple acid phosphatase (PAP) enzymes. The hydrolysis of the dimethyl phosphate diester was investigated in the gas phase and in solution by means of the continuum PCM model, using the B3LYP hybrid exchange-correlation functional. Our computed results showed that the hydrolysis of the dimethyl phosphate ester takes place in two steps. The first step corresponds to a slow P-O bond formation through nucleophilic attack of the coordinated (Fe(III))-OH group. The second step consists of a proton transfer process followed by the release of a methanol molecule. The first step is rate determining with activation free energy of 12.3 kcal mol(-1), which is about 3 times lower than the activation free energy for the uncatalyzed reaction. We also show that the heterodinuclear site plays an important role favoring an associative mechanism for the phosphate diester hydrolysis, favoring the formation of a high energy intermediate phosphorane, and orienting the phosphate group to the nucleophilic attack.

  11. Synthesis of a novel dinucleating aminocarboxylate macrocycle and structures of its dinuclear complexes with di- and trivalent transition and lanthanide metal ions.

    PubMed

    Brunner, Jens; Pritzkow, Hans; Krämer, Roland

    2005-01-21

    The synthesis of the new ligand L1(H4L1= 3,8,16,21-tetrakis(carboxylmethyl)-3,8,16,21,27,28-hexaazatricyclo[21.3.1.1(10,14)]octacosa-1(27),10,12,14(28),23,25-hexaen-5,18-diine) is reported. The solid-state structures of the four homodinuclear chelate complexes, [Zn2(L1)(H2O)2] x 6H2O, [Fe2(L1)(mu-O)] x 4H2O, [La2(L1)(NO3)2(H2O)2] x 6H2O and Na[Eu2(L1)(mu-AcO)3] x 3H2O, were determined by single-crystal X-ray structural analysis.

  12. Mysterious slapped face rash at holiday centre.

    PubMed Central

    Gunnell, D. J.

    1992-01-01

    OBJECTIVE--To discover the cause of an outbreak of facial rash in a holiday centre. DESIGN--Questionnaire survey of those with rash; analysis of samples of linen. SETTING--Holiday centre in south west England. PATIENTS--98 holiday-makers presenting to the first aid post with a facial rash. INTERVENTION--Replacement of bed linen with new linen in selected parts of the site. RESULTS--The attack rate was 7.0-14.2/1000 for most accommodation areas in the centre, but in one accommodation area the rate was zero. The pH of rinse water from sheets varied from 7.4 to 9.0. Those parts of the accommodation provided with new linen had zero attack rates. CONCLUSION--The facial rash resulted from irritation from washing powder retained owing to insufficient rinsing during laundering. Modifications to the rinsing process led to a gradual disappearance of the rash. PMID:1547418

  13. Emotional intelligence and patient-centred care

    PubMed Central

    Birks, Yvonne F; Watt, Ian S

    2007-01-01

    The principles of patient-centred care are increasingly stressed as part of health care policy and practice. Explanations for why some practitioners seem more successful in achieving patient-centred care vary, but a possible role for individual differences in personality has been postulated. One of these, emotional intelligence (EI), is increasingly referred to in health care literature. This paper reviews the literature on EI in health care and poses a series of questions about the links between EI and patient-centred outcomes. Papers concerning empirical examinations of EI in a variety of settings were identified to determine the evidence base for its increasing popularity. The review suggests that a substantial amount of further research is required before the value of EI as a useful concept can be substantiated. PMID:17682030

  14. Metallated metal-organic frameworks

    DOEpatents

    Bury, Wojciech; Farha, Omar K.; Hupp, Joseph T.; Mondloch, Joseph E.

    2017-08-22

    Porous metal-organic frameworks (MOFs) and metallated porous MOFs are provided. Also provided are methods of metallating porous MOFs using atomic layer deposition and methods of using the metallated MOFs as catalysts and in remediation applications.

  15. Metallated metal-organic frameworks

    DOEpatents

    Bury, Wojciech; Farha, Omar K.; Hupp, Joseph T.; Mondloch, Joseph E.

    2017-02-07

    Porous metal-organic frameworks (MOFs) and metallated porous MOFs are provided. Also provided are methods of metallating porous MOFs using atomic layer deposition and methods of using the metallated MOFs as catalysts and in remediation applications.

  16. Medication errors: pharmacovigilance centres in detection and prevention

    PubMed Central

    Bencheikh, Rachida Soulaymani; Benabdallah, Ghita

    2009-01-01

    Detecting medication errors needs collaboration between various organizations, such as patient safety institutions, pharmacovigilance centres, and poison control centres. In order to evaluate the input of pharmacovigilance centres and poison control centres in detecting and evaluating medication errors a pilot project was initiated by the World Alliance for Patient Safety in collaboration with the Uppsala Monitoring Centre; the Moroccan pharmacovigilance centre acted as project coordinator. As part of this project, a questionnaire on detecting medication errors was circulated to pharmacovigilance centres and poison control centres around the world, in order to assess their ability to detect and analyse medication errors. The results showed that through their databases pharmacovigilance centres can detect, identify, analyse, and classify medication errors and carry out root cause analysis, which is an important tool in preventing medication errors. The duties of pharmacovigilance centres in preventing medication errors include informing health-care professionals about the importance of reporting such errors and creating a culture of patient safety. Pharmacovigilance centres aim to prevent medication errors in collaboration with poison control centres. Such collaboration allows improved detection and improved preventive strategies. In addition, collaboration with regulatory authorities is important in finalizing decisions. Collaboration between pharmacovigilance centres and poison control centres should be strengthened and bridges need to be built linking pharmacovigilance centres, poison control centres, and organizations dedicated to patient safety, in order to avoid duplication of workload. PMID:19594539

  17. Medication errors: pharmacovigilance centres in detection and prevention.

    PubMed

    Bencheikh, Rachida Soulaymani; Benabdallah, Ghita

    2009-06-01

    1. Detecting medication errors needs collaboration between various organizations, such as patient safety institutions, pharmacovigilance centres, and poison control centres. In order to evaluate the input of pharmacovigilance centres and poison control centres in detecting and evaluating medication errors a pilot project was initiated by the World Alliance for Patient Safety in collaboration with the Uppsala Monitoring Centre; the Moroccan pharmacovigilance centre acted as project coordinator. As part of this project, a questionnaire on detecting medication errors was circulated to pharmacovigilance centres and poison control centres around the world, in order to assess their ability to detect and analyse medication errors. 2. The results showed that through their databases pharmacovigilance centres can detect, identify, analyse, and classify medication errors and carry out root cause analysis, which is an important tool in preventing medication errors. 3. The duties of pharmacovigilance centres in preventing medication errors include informing health-care professionals about the importance of reporting such errors and creating a culture of patient safety. Pharmacovigilance centres aim to prevent medication errors in collaboration with poison control centres. Such collaboration allows improved detection and improved preventive strategies. In addition, collaboration with regulatory authorities is important in finalizing decisions. 4. Collaboration between pharmacovigilance centres and poison control centres should be strengthened and bridges need to be built linking pharmacovigilance centres, poison control centres, and organizations dedicated to patient safety, in order to avoid duplication of workload.

  18. A Copper-Based Metal-Organic Framework as an Efficient and Reusable Heterogeneous Catalyst for Ullmann and Goldberg Type C-N Coupling Reactions.

    PubMed

    Long, Wei; Qiu, Wenge; Guo, Chongwei; Li, Chuanqiang; Song, Liyun; Bai, Guangmei; Zhang, Guizhen; He, Hong

    2015-11-27

    A highly porous metal-organic framework (Cu-TDPAT), constructed from a paddle-wheel type dinuclear copper cluster and 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine (H₆TDPAT), has been tested in Ullmann and Goldberg type C-N coupling reactions of a wide range of primary and secondary amines with halobenzenes, affording the corresponding N-arylation compounds in moderate to excellent yields. The Cu-TDPAT catalyst could be easily separated from the reaction mixtures by simple filtration, and could be reused at least five times without any significant degradation in catalytic activity.

  19. Optimizing Data Centre Energy and Environmental Costs

    NASA Astrophysics Data System (ADS)

    Aikema, David Hendrik

    Data centres use an estimated 2% of US electrical power which accounts for much of their total cost of ownership. This consumption continues to grow, further straining power grids attempting to integrate more renewable energy. This dissertation focuses on assessing and reducing data centre environmental and financial costs. Emissions of projects undertaken to lower the data centre environmental footprints can be assessed and the emission reduction projects compared using an ISO-14064-2-compliant greenhouse gas reduction protocol outlined herein. I was closely involved with the development of the protocol. Full lifecycle analysis and verifying that projects exceed business-as-usual expectations are addressed, and a test project is described. Consuming power when it is low cost or when renewable energy is available can be used to reduce the financial and environmental costs of computing. Adaptation based on the power price showed 10--50% potential savings in typical cases, and local renewable energy use could be increased by 10--80%. Allowing a fraction of high-priority tasks to proceed unimpeded still allows significant savings. Power grid operators use mechanisms called ancillary services to address variation and system failures, paying organizations to alter power consumption on request. By bidding to offer these services, data centres may be able to lower their energy costs while reducing their environmental impact. If providing contingency reserves which require only infrequent action, savings of up to 12% were seen in simulations. Greater power cost savings are possible for those ceding more control to the power grid operator. Coordinating multiple data centres adds overhead, and altering at which data centre requests are processed based on changes in the financial or environmental costs of power is likely to increase this overhead. Tests of virtual machine migrations showed that in some cases there was no visible increase in power use while in others power use

  20. Role and functions of Poisons Information Centre.

    PubMed

    Lall, S B; Peshin, S S

    1997-01-01

    The Poisons Information Centre (PIC) is a specialized unit providing information on prevention, early diagnosis and treatment of poisoning and hazard management. Most of the developed and many developing countries have well established poison control centres with poisons information service, patient management facility and analytical laboratory. In India, the National Poisons Information Centre (NPIC) was established in February, 1995 in the Department of Pharmacology at the All India Institute of Medical Sciences, New Delhi. The centre provides toxicological information and advice on the management of poisoned patients adopted to the level of the enquirer. The basis of this service are the databases on poisoning, drug reactions and also the continuous and systematic collection of data from the library. This information service is available round the clock. The PIC has the training responsibility extending to medical and other health professionals and community. The NPIC organized two successive training courses for medical professionals and para professionals at all health levels. Further, NPIC is a participant of INTOX project of IPCS/WHO, receiving regular yearly training on the use of INTOX database. Laboratory service is an essential component of a poisons control programme, providing analytical services on emergency basis to help in diagnosis and management. The NPIC is developing facilities for quick diagnosis of poisoning cases. Toxicovigilance and prevention of poisoning is another major function of PIC. The Centre has prepared manuals and leaflets on prevention and management cards on treatment of various poisonings. Thus the Centre provides a service with considerable health benefits, reducing morbidity and mortality from poisoning and gives significant financial savings to the community.

  1. Byurakan Astrophysical Observatory as Cultural Centre

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Farmanyan, S. V.

    2016-12-01

    NAS RA V. Ambartsumian Byurakan Astrophysical Observatory is presented as a cultural centre for Armenia and the Armenian nation in general. Besides being scientific and educational centre, the Observatory is famous for its unique architectural ensemble, rich botanical garden and world of birds, as well as it is one of the most frequently visited sightseeing of Armenia. In recent years, the Observatory has also taken the initiative of the coordination of the Cultural Astronomy in Armenia and in this field, unites the astronomers, historians, archaeologists, ethnographers, culturologists, literary critics, linguists, art historians and other experts.

  2. [Certification of healthcare centres: Taking stock].

    PubMed

    Ziegler, Kai; Risthaus, Franziska; Strupeit, Steve

    2014-01-01

    Healthcare facilities can use certificates to position themselves as experts to their clients and to distinguish themselves from their competitors. Different AWMF societies have addressed this topic und offer healthcare facilities the chance to get certified as a centre. In the course of this the societies develop curricula. Certification according to these curricula is then performed by the healthcare facilities or by an accredited agency. The different certificates show large differences in their certification requirements, which makes comparing them difficult. The present publication provides an overview of societies addressing certification and centres that are currently being certified. Copyright © 2014. Published by Elsevier GmbH.

  3. Byurakan Astrophysical Observatory as Cultural Centre

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Farmanyan, S. V.

    2017-07-01

    NAS RA V. Ambartsumian Byurakan Astrophysical Observatory is presented as a cultural centre for Armenia and the Armenian nation in general. Besides being scientific and educational centre, the Observatory is famous for its unique architectural ensemble, rich botanical garden and world of birds, as well as it is one of the most frequently visited sightseeing of Armenia. In recent years, the Observatory has also taken the initiative of the coordination of the Cultural Astronomy in Armenia and in this field, unites the astronomers, historians, archaeologists, ethnographers, culturologists, literary critics, linguists, art historians and other experts. Keywords: Byurakan Astrophysical Observatory, architecture, botanic garden, tourism, Cultural Astronomy.

  4. Bureaucracy, professionalization and school centred innovation strategies

    NASA Astrophysics Data System (ADS)

    Morris, Paul

    1990-03-01

    This paper examines an attempt to promote a school centred innovation strategy within a highly centralized educational system. The School Based Curriculum Project Scheme, which was introduced into Hong Kong in 1988, is analysed in terms of a professional-bureaucratic dichotomy. It is argued that the operational details of the scheme are designed to satisfy a range of bureaucratic concerns and these are not conducive to promoting the professional work ethic which is required for school centred innovation. Finally the paper identifies the implications which arise for policies designed to promote curriculum innovation.

  5. Metal content of metallo-beta-lactamase L1 is determined by the bioavailability of metal ions.

    PubMed

    Hu, Zhenxin; Gunasekera, Thusitha S; Spadafora, Lauren; Bennett, Brian; Crowder, Michael W

    2008-07-29

    In an effort to probe whether the metal content of metallo-beta-lactamase L1 is affected by metal ion bioavailability, L1 was overexpressed as mature protein (M-L1) and full-length (FL-L1) analogues, and the analogues were characterized with metal analyses, kinetics, and EPR spectroscopy. FL-L1, containing the putative leader sequence, was localized in the periplasm of Escherichia coli and shown to bind Zn(II) preferentially. The metal content of FL-L1 could be altered if the enzyme was overexpressed in minimal medium containing Fe and Mn, and surprisingly, an Fe-binding analogue was obtained. On the other hand, M-L1, lacking the putative leader sequence, was localized in the cytoplasm of E. coli and shown to bind various amounts of Fe and Zn(II), and like FL-L1, the metal content of the resulting enzyme could be affected by the amount of metal ions in the growth medium. L1 was refolded in the presence of Fe, and a dinuclear Fe-containing analogue of L1 was obtained, although this analogue is catalytically inactive. EPR spectra demonstrate the presence of an antiferromagnetically coupled Fe(III)Fe(II) center in Fe-containing L1 and suggest the presence of a Fe(III)Zn(II) center in M-L1. Metal analyses on the cytoplasmic and periplasmic fractions of E. coli showed that the concentration of metal ions in the periplasm is not tightly controlled and increases as the concentration of metal ions in the growth medium increases. In contrast, the concentration of Zn(II) in the cytoplasm is tightly controlled while that of Fe is less so.

  6. Syntheses, crystal structures, and properties of new metal--5-bromonicotinate coordination polymers

    NASA Astrophysics Data System (ADS)

    Li, Wenjie; Li, Guoting; Lv, Lulu; Zhao, Hong; Wu, Benlai

    2015-05-01

    Four metal-5-bromonicotinate (Brnic) coordination polymers [Fe(Brnic)2(H2O)2]n (1), [Ni(Brnic)2]n (2), [Ni(Brnic)(bpy)(H2O)2]n·n(Brnic)·4.5nH2O (3), and [Co2(Brnic)3(bpy)2(OH)]n·nH2O (4) have been synthesized and structurally characterized (bpy=4,4‧-bipyridine). Complex 1 has corrugated (4,4) sheets formed by μ-Brnic ligands and planar nodes Fe(II). As for 2-4, they all built up from Brnic-bridged dinuclear subunits, but have very different structure features. Complex 2 is a twin-like polymer with (4,4) layers formed by twin paddle-wheel [Ni2(Brnic)4] subunits. Through the bridge coordination of bpy ligands with dinuclear rings [Ni2(Brnic)2] and trigons [Co2(Brnic)3(OH)], 63-topological cationic layers with nanosized grids of 3 and chiral ladder-type double chains of 4 formed, respectively. Notably, halogen-related interactions play an important role in the formation of 3D metallosupermolecules 1-4. The thermostabilities of all compounds have been discussed in detail. Moreover, the magnetic investigations of 2 and 4 indicate that there exist antiferromagnetic interactions in the paddle-wheel [Ni2(Brnic)4] and trigon [Co2(Brnic)3(OH)] cores, respectively.

  7. Versatile Reactivity and Theoretical Evaluation of Mono- and Dinuclear Oxidovanadium(V) Compounds of Aroylazines: Electrogeneration of Mixed-Valence Divanadium(IV,V) Complexes.

    PubMed

    Dash, Subhashree P; Roy, Satabdi; Mohanty, Monalisa; Carvalho, M Fernanda N N; Kuznetsov, Maxim L; Pessoa, João Costa; Kumar, Amit; Patil, Yogesh P; Crochet, Aurélien; Dinda, Rupam

    2016-09-06

    The substituted hydrazones H2L(1-4) (L(1-4) = dibasic tridentate ONO(2-) donor ligands) obtained by the condensation of 2-hydroxy-1-naphthaldehyde and 2-aminobenzoylhydrazine (H2hnal-abhz) (H2L(1)) , 2-hydroxy-1-naphthaldehyde and 2-hydroxybenzoylhydrazine (H2hnal-hbhz) (H2L(2)), 2-hydroxy-1-acetonaphthone and benzoylhydrazine (H2han-bhz) (H2L(3)), or 2-hydroxy-1-acetonaphthone and 2-aminobenzoylhydrazine (H2han-abhz) (H2L(4)) are prepared and characterized. Reaction of ammonium vanadate with the appropriate H2L(1-4) results in the formation of oxidoethoxidovanadium(V) [V(V)O(OEt)(L(1-4))] (1-4) complexes. All compounds are characterized in the solid state and in solution by spectroscopic techniques (IR, UV-vis, (1)H, (13)C, and (51)V NMR, and electrospray ionization mass spectrometry). Single-crystal X-ray diffraction analysis of 1, 3, and 4 confirms the coordination of the corresponding ligands in the dianionic (ONO(2-)) enolate tautomeric form. In solution, the structurally characterized [V(V)O(OEt)(L)] compounds transform into the monooxido-bridged divanadium(V,V) [(V(V)OL)2-μ-O] complexes, with the processes being studied by IR and (1)H, (13)C, and (51)V NMR. The density functional theory (DFT) calculated Gibbs free energy of reaction 2[V(V)O(OEt)(L(4))] + H2O ⇆ [(V(V)OL(4))2-μ-O] + 2EtOH is only 2-3 kcal mol(-1), indicating that the dinuclear complexes may form in a significant amount. The electrochemical behavior of the complexes is investigated by cyclic voltammetry, with the V(V)-V(IV) E1/2(red) values being in the range 0.27-0.44 V (vs SCE). Upon controlled potential electrolysis, the corresponding (L)(O)V(IV)-O-V(V)(O)(L) mixed-valence species are obtained upon partial reduction of the [(V(V)OL)2-μ-O] complexes formed in solution, and some spectroscopic characteristics of these dinuclear mixed-valence complexes are investigated using DFT calculations and by electron paramagnetic resonance (EPR), with the formation of V(IV)-O-V(V) species being

  8. Synthesis, one- and two-photon photophysical and excited-state properties, and sensing application of a new phosphorescent dinuclear cationic iridium(III) complex.

    PubMed

    Xu, Wen-Juan; Liu, Shu-Juan; Zhao, Xin; Zhao, Ning; Liu, Zhi-Qiang; Xu, Hang; Liang, Hua; Zhao, Qiang; Yu, Xiao-Qiang; Huang, Wei

    2013-01-07

    A new phosphorescent dinuclear cationic iridium(III) complex (Ir1) with a donor-acceptor-π-bridge-acceptor-donor (D-A-π-A-D)-conjugated oligomer (L1) as a N^N ligand and a triarylboron compound as a C^N ligand has been synthesized. The photophysical and excited-state properties of Ir1 and L1 were investigated by UV/Vis absorption spectroscopy, photoluminescence spectroscopy, and molecular-orbital calculations, and they were compared with those of the mononuclear iridium(III) complex [Ir(Bpq)(2)(bpy)](+)PF(6)(-) (Ir0). Compared with Ir0, complex Ir1 shows a more-intense optical-absorption capability, especially in the visible-light region. For example, complex Ir1 shows an intense absorption band that is centered at λ=448 nm with a molar extinction coefficient (ε) of about 10(4) , which is rarely observed for iridium(III) complexes. Complex Ir1 displays highly efficient orange-red phosphorescent emission with an emission wavelength of 606 nm and a quantum efficiency of 0.13 at room temperature. We also investigated the two-photon-absorption properties of complexes Ir0, Ir1, and L1. The free ligand (L1) has a relatively small two-photon absorption cross-section (δ(max) =195 GM), but, when complexed with iridium(III) to afford dinuclear complex Ir1, it exhibits a higher two-photon-absorption cross-section than ligand L1 in the near-infrared region and an intense two-photon-excited phosphorescent emission. The maximum two-photon-absorption cross-section of Ir1 is 481 GM, which is also significantly larger than that of Ir0. In addition, because the strong B-F interaction between the dimesitylboryl groups and F(-) ions interrupts the extended π-conjugation, complex Ir1 can be used as an excellent one- and two-photon-excited "ON-OFF" phosphorescent probe for F(-) ions.

  9. Writing Centre Tutoring Sessions: Addressing Students' Concerns

    ERIC Educational Resources Information Center

    Winder, Roger; Kathpalia, Sujata S.; Koo, Swit Ling

    2016-01-01

    The guiding principle behind university writing centres is to focus on the process of writing rather than the finished product, prioritising higher order concerns related to organisation and argumentation of texts rather than lower order concerns of grammar and punctuation. Using survey-based data, this paper examines students' concerns regarding…

  10. Writing Centre Tutoring Sessions: Addressing Students' Concerns

    ERIC Educational Resources Information Center

    Winder, Roger; Kathpalia, Sujata S.; Koo, Swit Ling

    2016-01-01

    The guiding principle behind university writing centres is to focus on the process of writing rather than the finished product, prioritising higher order concerns related to organisation and argumentation of texts rather than lower order concerns of grammar and punctuation. Using survey-based data, this paper examines students' concerns regarding…

  11. In the Field: The Canadian Ecology Centre.

    ERIC Educational Resources Information Center

    Magee, Clare

    2000-01-01

    The Canadian Ecology Centre (Ontario) offers year-round residential and day programs in outdoor and environmental education for secondary students, field placement and internship opportunities for college students, and ecotourism programs, while providing employment and tax revenues to the local community. Dubbed consensus environmentalism, the…

  12. Centring the Subject in Order to Educate

    ERIC Educational Resources Information Center

    Webster, R. Scott

    2007-01-01

    It is important for educators to recognise that the various calls to decentre the subject--or self--should not be interpreted as necessarily requiring the removal of the subject altogether. Through the individualism of the Enlightenment the self was centred. This highly individualistic notion of the sovereign self has now been decentred especially…

  13. Self Assessment and Student-Centred Learning

    ERIC Educational Resources Information Center

    McDonald, Betty

    2012-01-01

    This paper seeks to show how self assessment facilitates student-centred learning (SCL) and fills a gap in the literature. Two groups of students were selected from a single class in a tertiary educational institution. The control group of 25 was selected randomly by the tossing of an unbiased coin (heads = control group). They were trained in the…

  14. Oo-Za-We-Kwun Centre Incorporated

    ERIC Educational Resources Information Center

    Findlay, P. R.; And Others

    1976-01-01

    The Centre is described as being designed to help native people participate more effectively in a modern Canadian environment. The residential family program includes a five-week Life Skills course followed by a two-year transfer of learning period during which counseling, paid employment, and community activities are available. (Author/MS)

  15. Centring the Subject in Order to Educate

    ERIC Educational Resources Information Center

    Webster, R. Scott

    2007-01-01

    It is important for educators to recognise that the various calls to decentre the subject--or self--should not be interpreted as necessarily requiring the removal of the subject altogether. Through the individualism of the Enlightenment the self was centred. This highly individualistic notion of the sovereign self has now been decentred especially…

  16. Journey to the Centre of a Triangle

    ERIC Educational Resources Information Center

    Jones, Margaret

    2008-01-01

    Using the film "Journey to the Centre of a Triangle" with a group of 15-year-old pupils, the author describes how they had done some work on constructions such as angle bisector and perpendicular bisector. The pupils were given A3 papers, rulers, compasses and pencils and they were asked to recreate their favourite scence from the film. The film…

  17. [Patients attended at a Venezuelan Toxicology Centre].

    PubMed

    Tagliaferro, Zulay A; Bracamonte, Giannina

    2010-04-01

    Characterising patients attended at a toxicological centre in the central western area of Venezuela (the state of Lara). This was a descriptive/cross-sectional study. The population consisted of 1,938 patients who registered during 2006 and 2007; data was collected from the Centre's data collection forms. 57.4 % of the patients recorded on the toxicological centre's forms during 2006 and 2007 consulted during 2006. The patients' average age was 19 during 2006 (including adults and teenagers) and 20 during 2007. Males most often attended the centre (55.4 %). The most common cause for consultation was poisoning from snake bite, more than 40 % of the cases being caused by Bothrops. Pesticide intoxication was the second cause for male consultation (20.6 %); female medication poisoning accounted for 26.6 %. Iribarren County had the highest consultation rate in the State of Lara (47.8 % of cases). 95 patients (4.9 %) came from neighbouring States (Portuguesa and Yaracuy) during the two years this study lasted. It is hoped that this study will lead to special education and attention programmes for the most commonly diagnosed pathologies being implemented with greater frequency, as well as corrective action being taken regarding individual and collective risk in the state of Lara's different geographical areas.

  18. Person-Centred (Deictic) Expressions and Autism

    ERIC Educational Resources Information Center

    Hobson, R. Peter; Garcia-Perez, Rosa M.; Lee, Anthony

    2010-01-01

    We employed semi-structured tests to determine whether children with autism produce and comprehend deictic (person-centred) expressions such as "this"/"tilde" "here"/"there" and "come"/"go", and whether they understand atypical non-verbal gestural deixis in the form of directed head-nods to indicate location. In Study 1, most participants…

  19. Examining Whiteness in a Children's Centre

    ERIC Educational Resources Information Center

    Clarke, Verity; Watson, Debbie

    2014-01-01

    This article utilises critical whiteness theory to explore the ethnic discourses observed in a children's centre in South London. Whilst critical whiteness has been used as a framework to understand race, racism and multiculturalism in a number of settings, including education, there are few studies that have sought to understand ethnicity in…

  20. In the Field: The Canadian Ecology Centre.

    ERIC Educational Resources Information Center

    Magee, Clare

    2000-01-01

    The Canadian Ecology Centre (Ontario) offers year-round residential and day programs in outdoor and environmental education for secondary students, field placement and internship opportunities for college students, and ecotourism programs, while providing employment and tax revenues to the local community. Dubbed consensus environmentalism, the…

  1. Centre National d'Etudes Spatiales

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    The Centre National d'Etudes Spatiales (CNES) draws up, proposes and conducts France's space policy. Its role is to develop the uses of space, to meet the civilian and military needs of public bodies and of the scientific community, and to foster the development and dissemination of new applications, designed to create wealth and jobs....

  2. Industry Restructuring: Extracts from Centre Publications.

    ERIC Educational Resources Information Center

    Hall, William C., Ed.

    This document contains excerpts from material previously published by Australia's TAFE (Technical and Further Education) National Centre for Research and Development on the subjects of industry restructuring, the reasons for restructuring, revising curricula, and providing a service to business and industry. Its contents are "Industry…

  3. Student-Centred Learning: A Humanist Perspective

    ERIC Educational Resources Information Center

    Tangney, Sue

    2014-01-01

    The notion of student-centred learning is often not defined; within the pedagogic literature it is generally associated with constructivism or principles associated with a constructivist environment such as building on prior knowledge, purposeful active learning and sense-making. An informal enquiry into conceptions of university staff prior to…

  4. Cactus: The Centres of a Triangle

    ERIC Educational Resources Information Center

    Hyde, Hartley

    2009-01-01

    This is the first of two articles which describe how to use "JavaSketchPad" to explore the centres of a triangle. This introductory exercise is suggested in the GSP "Workshop Guide". Students can use "JavaSketchPad Interactive Geometry" (JSP) at home at no cost. They are likely to impress their parents with their enthusiasm for geometry and all…

  5. Youth Research Centre Annual Report, 2002.

    ERIC Educational Resources Information Center

    Melbourne Univ. (Australia). Youth Research Centre.

    This report details the activities of the Youth Research Centre (YRC) at the University of Melbourne in 2002 in research project work involving a balance between the completion of projects, the development of new areas, and the continuation of longer-term projects as well as the supervision and teaching of a range of postgraduate health and…

  6. Visiting a science centre: what's on offer?

    NASA Astrophysics Data System (ADS)

    Russell, Ian

    1990-09-01

    Science centres are a valuable resource, used more frequently by family groups and primary school parties than by secondary schools. The importance of affective learning, involving attitude changes, is stressed. Provided the right approach is used, accompanying adults can help children get the most out of a visit.

  7. Crystallographic Data Centre Services and Publications.

    ERIC Educational Resources Information Center

    Cambridge Univ. (England). Chemical Lab.

    The Cambridge Crystallographic Data Centre is concerned with the retrieval, evaluation, synthesis, and dissemination of structural data based on diffraction methods. The source of input is almost entirely primary journals. Bibliographic information and numeric data on crystal and molecular structures are on magnetic tapes. The bibliographic file…

  8. Early Childhood Centre Administrator Certification. Project Report.

    ERIC Educational Resources Information Center

    Ferguson, E. Elaine

    This document presents the process for obtaining certification for the position of early childhood centre administrator (ECCA) in Nova Scotia, Canada. Following an introduction describing the development of the process and its pilot testing, Chapter 1 of the document details the four-step process: (1) application, including training in the ECCA…

  9. Myanmar: The Community Learning Centre Experience.

    ERIC Educational Resources Information Center

    Middelborg, Jorn; Duvieusart, Baudouin, Ed.

    A community learning centre (CLC) is a local educational institution outside the formal education system, usually set up and managed by local people. CLCs were first introduced in Myanmar in 1994, and by 2001 there were 71 CLCs in 11 townships. The townships are characterized by remoteness, landlessness, unemployment, dependency on one cash crop,…

  10. Improving person-centred care in dementia.

    PubMed

    Armstrong, Dorothy; Byrne, Grainne

    Failings in dementia care in acute hospitals have been reported to the Scottish Public Services Ombudsman and other scrutiny bodies in Scotland and the UK. This article sets out key knowledge and resources to help nurses provide compassionate and person-centred care.

  11. Isostructural dinuclear phenoxo-/acetato-bridged manganese(II), cobalt(II), and zinc(II) complexes with labile sites: kinetics of transesterification of 2-hydroxypropyl-p-nitrophenylphosphate.

    PubMed

    Arora, Himanshu; Barman, Suman K; Lloret, Francesc; Mukherjee, Rabindranath

    2012-05-21

    Using the dinucleating phenol-based ligand 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol] (HL(2)), in its deprotonated form, the six new dinuclear complexes [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][PF(6)] (M = Mn (2a), Co (3a), Zn (4a)) and [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][BPh(4)] (M = Mn (2b), Co (3b), Zn (4b)) have been synthesized. Crystallographic analyses on 2b·2MeCN, 3b·2MeCN, and 4b·2MeCN reveal that these complexes have closely similar μ-phenoxo bis(μ-carboxylato) structures. The physicochemical properties (absorption and ESI-MS spectral data, 2a,b, 3a,b, and 4a,b; (1)H NMR, 4a,b) of the cations of 2a-4a are identical with those of 2b-4b. Each metal ion is terminally coordinated by a pyrazole nitrogen and a pyridyl nitrogen from a 3-(pyridin-2-yl)pyrazole unit and a solvent molecule (MeCN). Thus, each metal center assumes distorted-octahedral M(II)N(3)O(3) coordination. Temperature-dependent magnetic studies on Mn(II) and Co(II) dimers reveal the presence of intramolecular antiferromagnetic (J = -8.5 cm(-1)) for 2b and ferromagnetic exchange coupling (J = +2.51 cm(-1)) for 3b, on the basis of the Hamiltonian H = -JS(1)·S(2). The exchange mechanism is discussed on the basis of magneto-structural parameters (M···M distance). Spectroscopic properties of the complexes have also been investigated. The pH titration and kinetics of phosphatase (transesterification) activity on 2-hydroxypropyl-p-nirophenylphosphate (HPNP) were studied in MeOH/H(2)O (33%, v/v) with 2a-4a, due to solubility reasons. This comparative kinetic study revealed the effect of the metal ion on the rate of hydrolysis of HPNP, which has been compared with what we recently reported for [Ni(II)(2)(L(2))(μ-O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (1a). The efficacy in the order of conversion of substrate to product (p-nitrophenolate ion) follows the order 4a > 3a > 2a > 1a, under identical experimental conditions. Notably, this trend follows the decrease of pK(a) values of

  12. Site occupancy of interstitial deuterium atoms in face-centred cubic iron

    NASA Astrophysics Data System (ADS)

    Machida, Akihiko; Saitoh, Hiroyuki; Sugimoto, Hidehiko; Hattori, Takanori; Sano-Furukawa, Asami; Endo, Naruki; Katayama, Yoshinori; Iizuka, Riko; Sato, Toyoto; Matsuo, Motoaki; Orimo, Shin-Ichi; Aoki, Katsutoshi

    2014-09-01

    Hydrogen composition and occupation state provide basic information for understanding various properties of the metal-hydrogen system, ranging from microscopic properties such as hydrogen diffusion to macroscopic properties such as phase stability. Here the deuterization process of face-centred cubic Fe to form solid-solution face-centred cubic FeDx is investigated using in situ neutron diffraction at high temperature and pressure. In a completely deuterized specimen at 988 K and 6.3 GPa, deuterium atoms occupy octahedral and tetrahedral interstitial sites with an occupancy of 0.532(9) and 0.056(5), respectively, giving a deuterium composition x of 0.64(1). During deuterization, the metal lattice expands approximately linearly with deuterium composition at a rate of 2.21 Å3 per deuterium atom. The minor occupation of the tetrahedral site is thermally driven by the intersite movement of deuterium atoms along the ‹111› direction in the face-centred cubic metal lattice.

  13. Computational studies on the photophysical properties and NMR fluxionality of dinuclear platinum(II) A-frame alkynyl diphosphine complexes.

    PubMed

    Lam, Wai Han; Yam, Vivian Wing-Wah

    2010-12-06

    The structural geometry, electronic structure, photophysical properties, and the fluxional behavior of a series of A-frame diplatinum alkynyl complexes, [Pt(2)(μ-dppm)(2)(μ-C≡CR)(C≡CR)(2)](+) [R = (t)Bu (1), C(6)H(5) (2), C(6)H(4)Ph-p (3), C(6)H(4)Et-p (4), C(6)H(4)OMe-p (5); dppm = bis(diphenylphosphino)methane], have been studied by density functional theory (DFT) and time-dependent TD-DFT associated with conductor-like polarizable continuum model (CPCM) calculations. The results show that the Pt···Pt distance strongly depends on the binding mode of the alkynyl ligands. A significantly shorter Pt···Pt distance is found in the symmetrical form, in which the bridging alkynyl ligand is σ-bound to the two metal centers, than in the unsymmetrical form where the alkynyl ligand is σ-bound to one metal and π-bound to another. For the two structural forms in 1-5, both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels show a dependence on the nature of the substituents attached to the alkynyl ligand. The energies of the HOMO and LUMO are found to increase and decrease, respectively, from R = (t)Bu to R = Ph and to R = C(6)H(4)Ph-p, because of the increase of the π- conjugation of the alkynyl ligand. On the basis of the TDDFT/CPCM calculations, the low-energy absorption band consists of two types of transitions, which are ligand-to-ligand charge-transfer (LLCT) [π(alkynyl) → σ*(dppm)]/metal-centered MC [dσ*(Pt(2)) → pσ(Pt(2))] transitions as well as interligand π → π* transition from the terminal alkynyl ligands to the bridging alkynyl ligand mixed with metal-metal-to-ligand charge transfer MMLCT [dσ*(Pt(2)) → π*(bridging alkynyl)] transition. The latter transition is lower in energy than the former. The calculation also indicates that the emission for the complexes originates from the triplet interligand π(terminal alkynyls) → π*(bridging alkynyl)/MMLCT [dσ*(Pt(2)) →

  14. Solvothermal synthesis of uranium(VI) phases with aromatic carboxylate ligands: A dinuclear complex with 4-hydroxybenzoic acid and a 3D framework with terephthalic acid

    NASA Astrophysics Data System (ADS)

    Zhang, Yingjie; Karatchevtseva, Inna; Bhadbhade, Mohan; Tran, Toan Trong; Aharonovich, Igor; Fanna, Daniel J.; Shepherd, Nicholas D.; Lu, Kim; Li, Feng; Lumpkin, Gregory R.

    2016-02-01

    With the coordination of dimethylformamide (DMF), two new uranium(VI) complexes with either 4-hydroxybenzoic acid (H2phb) or terephthalic acid (H2tph) have been synthesized under solvothermal conditions and structurally characterized. [(UO2)2(Hphb)2(phb)(DMF)(H2O)3]·4H2O (1) has a dinuclear structure constructed with both pentagonal and hexagonal bipyramidal uranium polyhedra linked through a μ2-bridging ligand via both chelating carboxylate arm and alcohol oxygen bonding, first observation of such a coordination mode of 4-hydroxybenzoate for 5 f ions. [(UO2)(tph)(DMF)] (2) has a three-dimensional (3D) framework built with pentagonal bipyramidal uranium polyhedra linked with μ4-terephthalate ligands. The 3D channeled structure is facilitated by the unique carboxylate bonding with nearly linear C-O-U angles and the coordination of DMF molecules. The presence of phb ligands in different coordination modes, uranyl ions in diverse environments and DMF in complex 1, and tph ligand, DMF and uranyl ion in complex 2 has been confirmed by Raman spectroscopy. In addition, their thermal stability and photoluminescence properties have been investigated.

  15. Bromide ion binding by a dinuclear gold(I) N-heterocyclic carbene complex: a spectrofluorescence and X-ray absorption spectroscopic study.

    PubMed

    Wedlock, Louise E; Aitken, Jade B; Berners-Price, Susan J; Barnard, Peter J

    2013-01-28

    Fluorescence and X-ray absorption spectroscopy were used to investigate the anion binding properties of a luminescent, dinuclear Au(I) N-heterocyclic carbene (NHC) complex ([1](2+)) with a short Au(I)···Au(I) contact. The addition of Br(-) ions to a DMSO solution of [1](PF(6))(2) caused a red-shift in the fluorescence emission band from 396 nm to 496 nm. Similarly, the addition of Br(-) ions to [1](PF(6))(2) caused a decrease in the energy of the Au L(3)-edge in the X-ray absorption spectrum, consistent with the formation of an association complex between the cation [1](2+) and Br(-) ions. Solution-based structural studies of the association complex were carried out using extended X-ray absorption fine structure (EXAFS) modelling of the Au(I)···Au(I) core of the cation. These studies indicate that the association complex results from Au(I)···Br(-) interactions, with the Br(-) ions occupying two partially occupied sites at ~2.9 and 3.9 Å from the Au(I) atoms.

  16. Novel dinuclear dimethylamido-3,5-dimethylpyrazolato and tetranuclear dimethylamido-3,5-dimethylpyrazolato-polyoxo zirconium(IV) complexes. Synthesis and structural characterisation.

    PubMed

    Sanz, Martial; Mosquera, Marta E G; Cuenca, Tomás

    2009-04-14

    The dinuclear dimethylamido-tris(3,5-dimethylpyrazolato)-zirconium(IV) complex [Zr(3,5-Me2Pz)3(NMe2)]2 1 is prepared by treatment of [Zr(NMe2)4] with 3 equivalents of 3,5-dimethylpyrazole (3,5-Me2PzH) with elimination of dimethylamine. When [Zr(NMe2)4] reacted with 2 equivalents of 3,5-Me2PzH, the bis(dimethylamido)-bis(3,5-dimethylpyrazolato)zirconium(IV) compound [Zr(3,5-Me2Pz)2(NMe2)2]2 2 is obtained. Hydrolysis of [Zr(3,5-Me2Pz)3(NMe2)]2 in wet toluene affords the tetranuclear oxo compound [Zr4(eta2-3,5-Me2Pz)4(NMe2)2(mu3-O)2(mu2-3,5-Me2Pz)4(mu2-NMe2)2] . All synthesised compounds are characterised by NMR spectroscopic and analytical methods. Single crystal X-ray diffraction analysis has established the molecular structures of 1 and 4.

  17. Determination of cysteine and glutathione based on the inhibition of the dinuclear Cu(II)-catalyzed luminol-H2O2 chemiluminescence reaction

    NASA Astrophysics Data System (ADS)

    Chaichi, Mohammad Javad; Ehsani, Mahjoobeh; Khajvand, Tahereh; Golchoubian, Hamid; Rezaee, Ehsan

    2014-03-01

    The catalyzed luminol chemiluminescent reaction has received a great amount of attention because of its high sensitivity and low background signal which make the reaction an attractive analytical chemistry tool. The present study, introduces the beneficial catalytic effects of dinuclear Cu(II) complex [Cu2L2(TAE)]X2, where TAE = tetraacetylethane; L = N,N'-dibenzylethylenediamine and X = ClO4 on the luminol chemiluminescent reaction as a novel probe for the determination of glutathione (GSH) and L-cysteine (CySH) in human serum and urine. The [Cu2L2(TAE)]X2 has exhibited highly efficient catalytic activity of luminol CL as an artificial peroxidase model at pH as low as 7.5 in water in the presence of H2O2ṡGSH and CySH can induce a sharp decrease in CL intensity from the [Cu2L2(TAE)]X2-catalyzed luminol system. Under the selected experimental conditions, a linear relationship was obtained between the CL intensity and the concentrations of GSH and CySH in the range of 1.0 × 10-7-1.0 × 10-4 M, with detection limits (S/N = 3) of 2.7 × 10-8 and 6.8 × 10-8 M and RSD < 4.2% (n = 7) for GSH and CySH, respectively.

  18. Determination of cysteine and glutathione based on the inhibition of the dinuclear Cu(II)-catalyzed luminol-H2O2 chemiluminescence reaction.

    PubMed

    Chaichi, Mohammad Javad; Ehsani, Mahjoobeh; Khajvand, Tahereh; Golchoubian, Hamid; Rezaee, Ehsan

    2014-03-25

    The catalyzed luminol chemiluminescent reaction has received a great amount of attention because of its high sensitivity and low background signal which make the reaction an attractive analytical chemistry tool. The present study, introduces the beneficial catalytic effects of dinuclear Cu(II) complex [Cu2L2(TAE)]X2, where TAE=tetraacetylethane; L=N,N(')-dibenzylethylenediamine and X=ClO4 on the luminol chemiluminescent reaction as a novel probe for the determination of glutathione (GSH) and L-cysteine (CySH) in human serum and urine. The [Cu2L2(TAE)]X2 has exhibited highly efficient catalytic activity of luminol CL as an artificial peroxidase model at pH as low as 7.5 in water in the presence of H2O2⋅GSH and CySH can induce a sharp decrease in CL intensity from the [Cu2L2(TAE)]X2-catalyzed luminol system. Under the selected experimental conditions, a linear relationship was obtained between the CL intensity and the concentrations of GSH and CySH in the range of 1.0×10(-7)-1.0×10(-4) M, with detection limits (S/N=3) of 2.7×10(-8) and 6.8×10(-8) M and RSD<4.2% (n=7) for GSH and CySH, respectively. Copyright © 2013 Elsevier B.V. All rights reserved.

  19. Influence of the Disposition of the Anisotropy Axes into the Magnetic Properties of Mn(III) Dinuclear Compounds with Benzoato Derivative Bridges.

    PubMed

    Garcia-Cirera, Beltzane; Gómez-Coca, Silvia; Font-Bardia, Mercè; Ruiz, Eliseo; Corbella, Montserrat

    2017-07-17

    The two new Mn(III) dinuclear compounds [{Mn(H2O)(phen)}2(μ-4-CH3C6H4COO)2(μ-O)](ClO4)2·3CH3CN·H2O (1·3CH3CN·H2O) and [{Mn(H2O)(phen)}(μ-O)(μ-2-BrC6H4COO)2{Mn(NO3)(phen)}]NO3 (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn(III) ions in both compounds. The different distortions from ideal geometry incite a very different magnetic behavior, affecting both the zero-field splitting parameters of the Mn(III) ions (DMn and EMn) and the magnetic interaction between them. Compound 1, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state S = 0) and local DMn < 0, while compound 2, with compression in the oxo bridge direction, displays a ferromagnetic interaction (ground state S = 4) and local DMn > 0. Theoretical CASSCF and DFT calculations corroborate the different magnetic anisotropy and exchange coupling found in both compounds. Moreover, with the help of theoretical calculations, some interesting magneto-structural correlations have been found between the degree of distortion of the coordination octahedra and the magnetic coupling; it becomes more antiferromagnetic when the elongation parameter, Δ, in absolute value is increased.

  20. Metals Sector

    EPA Pesticide Factsheets

    Find environmental regulatory information about the metals sector (NAICS 331 & 332), including NESHAPs for metal coatings, effluent guidelines for metal products, combustion compliance assistance, and information about foundry sand recycling.

  1. Collaborating at a distance: operations centres, tools, and trends

    SciTech Connect

    Gottschalk, Erik E.; /Fermilab

    2009-05-01

    Successful operation of the LHC and its experiments is crucial to the future of the worldwide high-energy physics program. Remote operations and monitoring centres have been established for the CMS experiment in several locations around the world. The development of remote centres began with the LHC{at}FNAL ROC and has evolved into a unified approach with distributed centres that are collectively referred to as 'CMS Centres Worldwide'. An overview of the development of remote centres for CMS will be presented, along with a synopsis of collaborative tools that are used in these centres today and trends in the development of remote operations capabilities for high-energy physics.

  2. Metal aminoboranes

    DOEpatents

    Burrell, Anthony K.; Davis, Benjamin J.; Thorn, David L.; Gordon, John C.; Baker, R. Thomas; Semelsberger, Troy Allen; Tumas, William; Diyabalanage, Himashinie Vichalya Kaviraj; Shrestha, Roshan P.

    2010-05-11

    Metal aminoboranes of the formula M(NH.sub.2BH.sub.3).sub.n have been synthesized. Metal aminoboranes are hydrogen storage materials. Metal aminoboranes are also precursors for synthesizing other metal aminoboranes. Metal aminoboranes can be dehydrogenated to form hydrogen and a reaction product. The reaction product can react with hydrogen to form a hydrogen storage material. Metal aminoboranes can be included in a kit.

  3. Dinuclear Ruthenium(II) Complexes as Two-Photon, Time-Resolved Emission Microscopy Probes for Cellular DNA**

    PubMed Central

    Baggaley, Elizabeth; Gill, Martin R; Green, Nicola H; Turton, David; Sazanovich, Igor V; Botchway, Stanley W; Smythe, Carl; Haycock, John W; Weinstein, Julia A; Thomas, Jim A

    2014-01-01

    The first transition-metal complex-based two-photon absorbing luminescence lifetime probes for cellular DNA are presented. This allows cell imaging of DNA free from endogenous fluorophores and potentially facilitates deep tissue imaging. In this initial study, ruthenium(II) luminophores are used as phosphorescent lifetime imaging microscopy (PLIM) probes for nuclear DNA in both live and fixed cells. The DNA-bound probes display characteristic emission lifetimes of more than 160 ns, while shorter-lived cytoplasmic emission is also observed. These timescales are orders of magnitude longer than conventional FLIM, leading to previously unattainable levels of sensitivity, and autofluorescence-free imaging. PMID:24458590

  4. Gamma rays from the Galactic Centre region

    NASA Astrophysics Data System (ADS)

    Su, Meng; van Eldik, Christopher

    2015-08-01

    During the last decades, increasingly precise astronomical observations of the Galactic Centre region at radio, infrared, and X-ray wavelengths laid the foundations for a detailed understanding of the high-energy astroparticle physics of this most remarkable location in the Galaxy. Recently, observations of this region in high energy (HE, 10 MeV-100 GeV) and very high energy (VHE, > 100 GeV) γ-rays added important insights into the emerging picture of the Galactic nucleus as a most violent and active region where acceleration of particles to highest energies and their transport can be studied in great detail. We review the current understanding of the γ-ray emission emanating from the Galactic Centre.

  5. User-Centred Design Using Gamestorming.

    PubMed

    Currie, Leanne

    2016-01-01

    User-centered design (UX) is becoming a standard in software engineering and has tremendous potential in healthcare. The purpose of this tutorial will be to demonstrate and provide participants with practice in user-centred design methods that involve 'Gamestorming', a form of brainstorming where 'the rules of life are temporarily suspended'. Participants will learn and apply gamestorming methods including persona development via empathy mapping and methods to translate artefacts derived from participatory design sessions into functional and design requirements.

  6. International Centre for Reproductive Health (ICRH)

    PubMed Central

    Van Braeckel, D.; Luchters, S.; Degomme, O.; Temmerman, M.

    2011-01-01

    The International Centre for Reproductive Health (ICRH) was established by Prof. dr. Marleen Temmerman in the aftermath of the UN Conference on Population and Development in Cairo in 1994. This conference called for world-wide action to improve the sexual and reproductive health situation of the global population in general and for vulnerable groups in particular, and this is exactly what ICRH is striving for and has been working on for the last 15 years. ICRH is a multidisciplinary centre of excellence, in research, capacity building and fieldwork in sexual and reproductive health and HIV prevention, and an advocate for sexual and reproductive health and rights. Right from the start, ICRH has opted for a global approach, which has resulted in a broad geographical spread of activities, with projects in Africa, Latin America, Asia and Europe. Since its inception, ICRH has participated in more than 120 projects, often as the coordinator, and through this work it has contributed considerably not only to scientific knowledge, improvement of health systems and increased accessibility of health services for vulnerable groups, but also to the quality of live of numerous individuals. Since 2004, ICRH has been recognized as a WHO Collaborating Centre for Research on Sexual and Reproductive Health.

  7. Dioxygen activation by non-adiabatic oxidative addition to a single metal center [O2 activation by non-adiabatic oxidative addition to a single metal center

    DOE PAGES

    Akturk, Eser S.; Yap, Glenn P. A.; Theopold, Klaus H.

    2015-10-16

    A chromium(I) dinitrogen complex reacts rapidly with O2 to form the mononuclear dioxo complex [TptBu,MeCrV(O)2] (TptBu,Me=hydrotris(3-tert-butyl-5-methylpyrazolyl)borate), whereas the analogous reaction with sulfur stops at the persulfido complex [TptBu,MeCrIII(S2)]. The transformation of the putative peroxo intermediate [TptBu,MeCrIII(O2)] (S=3/2) into [TptBu,MeCrV(O)2] (S=1/2) is spin-forbidden. The minimum-energy crossing point for the two potential energy surfaces has been identified. Finally, although the dinuclear complex [(TptBu,MeCr)2(μ-O)2] exists, mechanistic experiments suggest that O2 activation occurs on a single metal center, by an oxidative addition on the quartet surface followed by crossover to the doublet surface.

  8. A novel route towards water-soluble luminescent iridium(iii) complexes via a hydroxy-bridged dinuclear precursor.

    PubMed

    Scarpelli, Francesca; Ionescu, Andreea; Ricciardi, Loredana; Plastina, Pierluigi; Aiello, Iolinda; La Deda, Massimo; Crispini, Alessandra; Ghedini, Mauro; Godbert, Nicolas

    2016-11-01

    The synthesis and photophysical characterization of a new family of luminescent water-soluble ionic iridium(iii) complexes of the general formula [(ppy)2Ir(bpy)]X are reported. The Ir(iii) complexes incorporate a cyclometalated 2-phenylpyridine (ppy), the ancillary ligand 2,2'-bipyridyl (bpy) and different counterions (X(-) = EtO(-), OH(-), EtOCH2CO2(-), MeOCH2CO2(-)). These complexes were obtained starting from the cyclometalated Ir(iii) chloro-bridged dimer [(ppy)2Ir(μ-Cl)]2, for the first time synthesized through a new microwave assisted synthetic procedure, and subsequently converted into the corresponding hydroxy-bridged dimer [(ppy)2Ir(μ-OH)]2. The latter was eventually used as a sole reagent for the synthesis of all the reported complexes by simply varying the nature of the reaction solvent from water to alcohols and glycol ethers. This study demonstrates the versatility of the [(ppy)2Ir(μ-OH)]2 complex as a precursor to water soluble ionic Ir(iii) complexes. Indeed, [(ppy)2Ir(μ-OH)]2 has shown its peculiar chemical reactivity due to both a strong base character and an unexpected oxidative ability towards the alcoholic function of glycol ethers. All the synthesized complexes exhibit, in water solution, an orange emission centred at 606 nm. Moreover, all complexes display the ability to give rise to gel phases in water upon increasing their concentration, and the photophysical study evidenced the various interactions governing the gelification process. The water-solubility of these new luminescent Ir(iii) complexes makes them potentially useful in bio-related systems.

  9. Mono- and Dinuclear Manganese Carbonyls Supported by 1,8-Disubstituted (L = Py, SMe, SH) Anthracene Ligand Scaffolds.

    PubMed

    Manes, Taylor A; Rose, Michael J

    2016-06-06

    Presented herein is a synthetic scheme to generate symmetric and asymmetric ligands based on a 1,8-disubstituted anthracene scaffold. The metal-binding scaffolds were prepared by aryl chloride activation of 1,8-dichloroanthracene using Suzuki-type couplings facilitated by [Pd(dba)2] as a Pd source; the choice of cocatalyst (XPhos or SPhos) yielded symmetrically or asymmetrically substituted scaffolds (respectively): namely, Anth-SMe2 (3), Anth-N2 (4), and Anth-NSMe (6). The ligands exhibit a nonplanar geometry in the solid state (X-ray), owing to steric hindrance between the anthracene scaffold and the coupled aryl units. To determine the flexibility and binding characteristics of the anthracene-based ligands, the symmetric scaffolds were complexed with [Mn(CO)5Br] to afford the mononuclear species [(Anth-SMe2)Mn(CO)3Br] (8) and [(Anth-N2)Mn(CO)3Br] (9), in which the donor moieties chelate the Mn center in a cis fashion. The asymmetric ligand Anth-NSMe (6) binds preferentially through the py moieties, affording the bis-ligated complex [(Anth-NSMe)2Mn(CO)3Br] (10), wherein the thioether-S donors remain unbound. Alternatively, deprotection of the thioether in 6 affords the free thiol ligand Anth-NSH (7), which more readily binds the Mn center. Complexation of 7 ultimately affords the mixed-valence Mn(I)/Mn(II) dimer of formula [(Anth-NS)3Mn2(CO)3] (11), which exhibits a fac-{Mn(CO)3} unit supported by a triad of bridging thiolates, which are in turn ligated to a supporting Mn(II) center (EPR: |D| = 0.053 cm(-1), E/|D| = 0.3, Aiso = -150 MHz). All of the metal complexes have been characterized by single-crystal X-ray diffraction, IR spectroscopy and NMR/EPR measurements-all of which demonstrate that the meta-linked, anthracene-based ligand scaffold is a viable approach for the coordination of metal carbonyls.

  10. Centre-Based Child Care Quality in Urban Australia

    ERIC Educational Resources Information Center

    Ishimine, Karin; Wilson, Rachel

    2009-01-01

    This study investigates the quality of childcare centres in urban Australian communities designated according to different bands of Centre Location Demographics (CLD). Childcare centres were assessed using the Early Childhood Environment Rating Scale- Revised Edition (ECERS-R) and the Early Childhood Environment Rating Scale-Extension (ECERS-E).…

  11. Reaching the Students that Student-Centred Learning Cannot Reach

    ERIC Educational Resources Information Center

    Hockings, Christine

    2009-01-01

    Student-centred learning has the potential to engage a more academically diverse student body than the more conventional teacher-centred approaches. In spite of the evidence in favour of student-centred learning, a recent study showed that it was ineffective for around 30% of undergraduates in a large and diverse group studying business operations…

  12. Centre-Based Child Care Quality in Urban Australia

    ERIC Educational Resources Information Center

    Ishimine, Karin; Wilson, Rachel

    2009-01-01

    This study investigates the quality of childcare centres in urban Australian communities designated according to different bands of Centre Location Demographics (CLD). Childcare centres were assessed using the Early Childhood Environment Rating Scale- Revised Edition (ECERS-R) and the Early Childhood Environment Rating Scale-Extension (ECERS-E).…

  13. Centre of the Cell: Science Comes to Life

    PubMed Central

    Balkwill, Frances; Chambers, Katie

    2015-01-01

    Centre of the Cell is a unique biomedical science education centre, a widening participation and outreach project in London’s East End. This article describes Centre of the Cell’s first five years of operation, the evolution of the project in response to audience demand, and the impact of siting a major public engagement project within a research laboratory. PMID:26340279

  14. Dare to Dream: Discovery Children's Centre, Winnipeg, Manitoba, Canada

    ERIC Educational Resources Information Center

    Blatz, Ron

    2011-01-01

    This article features Discovery Children's Centre, one of the highest quality centres in the province of Manitoba, Canada. Discovery Children's Centre believes that children, who may have little or no voice in a democratic society, can be heard if some adult will speak on their behalf. Even as it has grown from 35 to 230 children, quality has…

  15. Canadian Educational Development Centre Websites: More Ebb than Flow?

    ERIC Educational Resources Information Center

    Simmons, Nicola

    2010-01-01

    This paper examines information portrayed on Canadian educational development (ED) centre websites and, in particular, whether information that corresponds to questions compiled from a literature search of ED centre practices is readily available from centre websites. This study phase is part of a larger national study of Canadian educational…

  16. Centre of the Cell: Science Comes to Life.

    PubMed

    Balkwill, Frances; Chambers, Katie

    2015-01-01

    Centre of the Cell is a unique biomedical science education centre, a widening participation and outreach project in London's East End. This article describes Centre of the Cell's first five years of operation, the evolution of the project in response to audience demand, and the impact of siting a major public engagement project within a research laboratory.

  17. Assessment of functional incontinence in disabled living centres.

    PubMed

    Chadwick, Viv

    Disabled Living is part of the network of disabled living centres throughout Britain. These centres enable anyone to try out equipment that may help them with everyday activities of living. The centres are staffed by occupational therapists, physiotherapists, nurses, information providers, administration staff and volunteers.

  18. Synthesis of [Pt(SnBu(t)3)(IBu(t))(μ-H)]2, a Coordinatively Unsaturated Dinuclear Compound which Fragments upon Addition of Small Molecules to Form Mononuclear Pt-Sn Complexes.

    PubMed

    Koppaka, Anjaneyulu; Yempally, Veeranna; Zhu, Lei; Fortman, George C; Temprado, Manuel; Hoff, Carl D; Captain, Burjor

    2016-01-04

    The reaction of Pt(COD)2 with one equivalent of tri-tert-butylstannane, Bu(t)3SnH, at room temperature yields Pt(SnBu(t)3)(COD)(H)(3) in quantitative yield. In the presence of excess Bu(t)3SnH, the reaction goes further, yielding the dinuclear bridging stannylene complex [Pt(SnBu(t)3)(μ-SnBu(t)2)(H)2]2 (4). The dinuclear complex 4 reacts rapidly and reversibly with CO to furnish [Pt(SnBu(t)3)(μ-SnBu(t)2)(CO)(H)2]2 (5). Complex 3 reacts with N,N'-di-tert-butylimidazol-2-ylidene, IBu(t), at room temperature to give the dinuclear bridging hydride complex [Pt(SnBu(t)3)(IBu(t))(μ-H)]2 (6). Complex 6 reacts with CO, C2H4, and H2 to give the corresponding mononuclear Pt complexes Pt(SnBu(t)3)(IBu(t))(CO)(H)(7), Pt(SnBu(t)3)(IBu(t))(C2H4)(H)(8), and Pt(SnBu(t)3)(IBu(t))(H)3 (9), respectively. The reaction of IBu(t) with the complex Pt(SnBu(t)3)2(CO)2 (10) yielded an abnormal Pt-carbene complex Pt(SnBu(t)3)2(aIBu(t))(CO) (11). DFT computational studies of the dimeric complexes [Pt(SnR3)(NHC)(μ-H)]2, the potentially more reactive monomeric complexes Pt(SnR3)(NHC)(H) and the trihydride species Pt(SnBu(t)3)(IBu(t))(H)3 have been performed, for NHC = IMe and R = Me and for NHC = IBu(t) and R = Bu(t). The structures of complexes 3-8 and 11 have been determined by X-ray crystallography and are reported.

  19. Metal allergy in Singapore.

    PubMed

    Goon, Anthony T J; Goh, C L

    2005-03-01

    This is a clinical epidemiologic study to determine the frequency of metal allergy among patch-tested patients in the years 2001-2003. The results are compared with those of previous studies. All patients diagnosed as having allergic contact dermatitis in the National Skin Centre, Singapore, from January 2001 to December 2003 were studied retrospectively. The frequency of positive patch tests to the following metals were nickel 19.9%, chromate 5.6%, cobalt 8.2% and gold 8.3%. The frequency of nickel allergy has been steadily rising over the last 20 years. The most common sources of nickel allergy are costume jewelry, belt buckles, wrist watches and spectacle frames. After declining from 1984 to 1990, chromate and cobalt allergies have also been steadily increasing subsequently. The most common sources of chromate allergy were cement, leather and metal objects. Most positive patch tests to cobalt are regarded as co-sensitization due to primary nickel or chromate allergies. There has been a steep increase in positive patch tests to gold from 2001 to 2003, which is difficult to explain because the relevance and sources of such positive patch tests can rarely be determined with certainty. There has been an overall rise in the frequency of metal allergy in the last 20 years.

  20. A dinuclear end-on azide-bridged copper(II) compound with weak antiferromagnetic interaction - Synthesis, characterization, magnetism and X-ray structure of bis[(μ-azido-κN1)-(azido-κN1)(1,3-bis(benzimidazol-2-yl)-2-methylpropane)copper(II)

    NASA Astrophysics Data System (ADS)

    van Albada, Gerard A.; Mutikainen, Ilpo; Roubeau, Olivier; Reedijk, Jan

    2013-03-01

    The centrosymmetric dinuclear compound of formula [Cu(μ-N3-κN1)(N3-κN1)(bbmp)]2 is reported. Synthesis, characterization, physical properties are determined in detail, together with its 3D structure. The dinuclear end-on azide-bridged copper(II) compound displays a weak antiferromagnetic interaction, despite the fact that the magnetic orbitals overlap. The Cu-Cu contact distance is 3.1867(8) Å, while the Cu-Nazide-Cu angle is 103.41(14)°. The IR spectra of the azido ligands are as expected for such coordinated azides.