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Complex Shows (complex + shows)
Selected AbstractsNovel RuII Complexes with Bispidine-Based Bridging Ligands: Luminescence Sensing and Photocatalytic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2010Christoph Busche Abstract New ligands with a bidentate bipyridyl (bpy) and a tetradentate bispidine (bisp) subunit (bipyridyl = 2,2,-bipyridine derivative, bispidine = 3,7-diazabicyclo[3.3.1]nonane derivative) and their heterodinuclear {[Ru(bpy)3]2+ -[M(bisp)]2+} complexes (M = Cu2+, Fe2+) were prepared and characterized. The luminescence of the mononuclear RuII complexes (metal-free bisp subunit) is efficiently quenched in presence of CuII. An EPR spectroscopic study reveals thatvisible light irradiation does not alter the oxidation states of the two metal ions in {[Ru(bpy)3]2+ -[Cu(bisp)]2+}, i.e. there is energy rather than electron transfer. The heterodinuclear {[Ru(bpy)3]2+ -[Cu(bisp)]2+} complex shows a significantphotocatalytic activity in the aziridination of styrene. [source] Aerobic, Chemoselective Oxidation of Alcohols to Carbonyl Compounds Catalyzed by a DABCO-Copper Complex under Mild ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2007Sreedevi Mannam Abstract A DABCO-copper(I) chloride complex (5 mol,%) together with TEMPO (5 mol,%) in nitromethane as solvent has been used as an efficient catalytic system for the selective oxidation of benzylic and allylic alcohols into the corresponding carbonyl compounds at room temperature where molecular oxygen acts as an ultimate, stoichiometric oxidant and water is the only by-product. The solid-state structure determination of the DABCO-copper complex shows that the copper is in the +II oxidation state with trigonal bipyramidal geometry and exists in a linear polymeric structure due to strong hydrogen bonding. [source] Structural insights into the molecular organization of the S-layer from Clostridium difficileMOLECULAR MICROBIOLOGY, Issue 5 2009Robert P. Fagan Summary Clostridium difficile expresses a surface layer (S-layer) which coats the surface of the bacterium and acts as an adhesin facilitating interaction of the bacterium with host enteric cells. The S-layer contains a high-molecular-weight S-layer protein (HMW SLP) and its low-molecular-weight partner protein (LMW SLP). We show that these proteins form a tightly associated non-covalent complex, the H/L complex, and we identify the regions of both proteins responsible for complex formation. The 2.4 Ĺ X-ray crystal structure of a truncated derivative of the LMW SLP reveals two domains. Domain 1 has a two-layer sandwich architecture while domain 2, predicted to orientate towards the external environment, contains a novel fold. Small-angle X-ray scattering analysis of the H/L complex shows an elongated molecule, with the two SLPs arranged ,end-to-end' interacting with each other through a small contact area. Alignment of LMW SLPs, which exhibit high sequence diversity, reveals a core of conserved residues that could reflect functional conservation, while allowing for immune evasion through sequence variation. These structures are the first described for the S-layer of a bacterial pathogen, and provide insights into the assembly and biogenesis of the S-layer. [source] Atomic resolution structure of Escherichia coli dUTPase determined ab initioACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2001A. González Cryocooled crystals of a mercury complex of Escherichia coli dUTPase diffract to atomic resolution. Data to 1.05,Ĺ resolution were collected from a derivative crystal and the structure model was derived from a Fourier map with phases calculated from the coordinates of the Hg atom (one site per subunit of the trimeric enzyme) using the program ARP/wARP. After refinement with anisotropic temperature factors a highly accurate model of the bacterial dUTPase was obtained. Data to 1.45,Ĺ from a native crystal were also collected and the 100,K structures were compared. Inspection of the refined models reveals that a large part of the dUTPase remains rather mobile upon freezing, with 14% of the main chain being totally disordered and with numerous side chains containing disordered atoms in multiple discrete conformations. A large number of those residues surround the active-site cavity. Two glycerol molecules (the cryosolvent) occupy the deoxyribose-binding site. Comparison between the native enzyme and the mercury complex shows that the active site is not adversely affected by the binding of mercury. An unexpected effect seems to be a stabilization of the crystal lattice by means of long-range interactions, making derivatization a potentially useful tool for further studies of inhibitor,substrate-analogue complexes of this protein at very high resolution. [source] Synthesis, Crystal Structure and Characterization of [Ca(L)(H2O)2]n Constructed by Flexible Ligand 2-Nitro-benzene-1,4-di(oxyacetate)CHINESE JOURNAL OF CHEMISTRY, Issue 4 2008Li YANG Abstract A new microporous coordination polymer [Ca(nbdo)(H2O)2]n, constructed by 2-nitro-benzene-1,4-di(oxyace-tate), was obtained by a slow evaporation method and characterized by elemental analysis, FT-IR, single-crystal X-ray diffraction, DSC, TG-DTG and fluorescent spectral analysis. The crystal structure reveals that there is 1-D microporous channel, which is bridged by four kinds of hydrogen bonds to generate a 3-D supramolecular network. The thermal analysis of the complex shows that it began to lose water molecules at 375 K, and when the temperature was up to 550 K the framework of the coordination polymer began to collapse. The luminescence property was investigated and the complex shows photoluminescence in the solid state at room temperature, excited at 320 nm. [source] N -(Aryl)picolinamide Complexes of Ruthenium: Usual Coordination and Strategic CyclometalationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2007Sumon Nag Abstract Reaction of five N -(4- R -phenyl)picolinamides (R = OCH3, CH3, H, Cl, and NO2) with [Ru(PPh3)2(CO)2Cl2] in refluxing 2-methoxyethanol in the presence of a base (NEt3) affords two geometrical isomers of a group of complexes (1-R and 2-R), each of which contains an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphanes, a carbonyl, and a hydride. Similar reaction of N -(naphthyl)picolinamide with [Ru(PPh3)2(CO)2Cl2] affords an organometallic complex, 3, in which the amide ligand is coordinated to the metal center, by C,H activation of the naphthyl ring at the 8-position, as a dianionic tridentate N,N,C donor along with two triphenylphosphanes and one carbonyl. Structures of the 1-OCH3, 2-CH3, and 3 complexes have been determined by X-ray crystallography. In all the complexes the two triphenylphosphanes are trans. In the 1-R complexes the hydride is trans to the pyridine nitrogen and in the 2-R complexes it is trans to the amide-nitrogen. All the complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a RuII,RuIII oxidation within 0.71,0.93 V versus SCE. An oxidation and a reduction of the coordinated amide ligand are also observed within 1.29,1.69 V versus SCE and ,1.02 to ,1.21 V versus SCE respectively.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Structure of charge-transfer reaction complexes in anionic polymerization of isoprene: Quantum chemical calculationsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2005K. K. Kalninsh Abstract A new mechanism of isoprene anionic polymerization is proposed. Its central moment is thermal electronic excitation of a living polyisoprene,isoprene complex into the quasi-degenerate electronically excited state (S · T)1, which is of the charge (electron) transfer character. It is asserted that the probability of chemical bond formation is determined by the free valence index on carbon atoms and by the geometry of reacting complex in the excited state (S · T)1. Semi-empirical AM1 and ab initio 6-31G* quantum chemical calculations revealed low energies of triplet excited levels (<10 kcal/mole). Comparison of isoprene polymerization on free anions and on solvated ion pairs shows that both types of active centers produce vinyl 1,2 (4,3)-units. Free anions generate predominantly 1,2-units, whereas solvated ion pairs tend to form units with the 4,3-structure. Analysis of energies of excited isoprenyl lithium + isoprene complexes shows that the formation of 1,4 (4,1)- cis -polyisoprene in an inert media is most preferable. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chlorideJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2008Alexander Schöning Abstract The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH4NO3 and 0.5 M NH4Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl2) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one-to-one. However, for all heavy metals NH4Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH4Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl2) values and/or contents of OC were taken into account. In comparison to NH4Cl, NH4NO3 proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH4NO3 is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation-exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH4NO3 method. However, the applicability of the NH4NO3 method to other soils still needs to be investigated. [source] Photoinduced Energy- and Electron-Transfer Processes in Dinuclear RuII,OsII, RuII,OsIII, and RuIII,OsII Trisbipyridine Complexes Containing a Shape-Persistent Macrocyclic SpacerCHEMPHYSCHEM, Issue 1 2006Margherita Venturi Prof. Abstract The PF6,salt of the dinuclear [(bpy)2Ru(1)Os(bpy)2]4+complex, where 1 is a phenylacetylene macrocycle which incorporates two 2,2,-bipyridine (bpy) chelating units in opposite sites of its shape-persistent structure, was prepared. In acetonitrile solution, the Ru- and Os-based units display their characteristic absorption spectra and electrochemical properties as in the parent homodinuclear compounds. The luminescence spectrum, however, shows that the emission band of the RuIIunit is almost completely quenched with concomitant sensitization of the emission of the OsIIunit. Electronic energy transfer from the RuIIto the OsIIunit takes place by two distinct processes (ken=2.0×108and 2.2×107s,1at 298 K). Oxidation of the OsIIunit of [(bpy)2Ru(1)Os (bpy)2]4+by CeIVor nitric acid leads quantitatively to the [(bpy)2RuII(1)OsIII(bpy)2]5+complex which exhibits a bpy-to-OsIIIcharge-transfer band at 720 nm (,max=250,M,1cm,1). Light excitation of the RuIIunit of [(bpy)2RuII(1)OsIII(bpy)2]5+is followed by electron transfer from the RuIIto the OsIIIunit (kel,f=1.6×108and 2.7×107s,1), resulting in the transient formation of the [(bpy)2RuIII(1)OsII(bpy)2]5+complex. The latter species relaxes to the [(bpy)2RuII(1)OsIII(bpy)2]5+one by back electron transfer (kel,b=9.1×107and 1.2×107s,1). The biexponential decays of the [(bpy)2*RuII(1)OsII(bpy)2]4+, [(bpy)2*RuII(1)OsIII(bpy)2]5+, and [(bpy)2RuIII(1)OsII(bpy)2]5+species are related to the presence of two conformers, as expected because of the steric hindrance between hydrogen atoms of the pyridine and phenyl rings. Comparison of the results obtained with those previously reported for other Ru,Os polypyridine complexes shows that the macrocyclic ligand 1 is a relatively poor conducting bridge. [source] | ||||||||||