Synergy and destructive interferences between local magnetic anisotropies in binuclear complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guihéry, Nathalie; Ruamps, Renaud; Maurice, Rémi

2015-12-31

Magnetic anisotropy is responsible for the single molecule magnet behavior of transition metal complexes. This behavior is characterized by a slow relaxation of the magnetization for low enough temperatures, and thus for a possible blocking of the magnetization. This bistable behavior can lead to possible technological applications in the domain of data storage or quantum computing. Therefore, the understanding of the microscopic origin of magnetic anisotropy has received a considerable interest during the last two decades. The presentation focuses on the determination of the anisotropy parameters of both mono-nuclear and bi-nuclear types of complexes and on the control and optimizationmore » of the anisotropic properties. The validity of the model Hamiltonians commonly used to characterize such complexes has been questioned and it is shown that neither the standard multispin Hamiltonian nor the giant spin Hamiltonian are appropriate for weakly coupled ions. Alternative models have been proposed and used to properly extract the relevant parameters. Rationalizations of the magnitude and nature of both local anisotropies of single ions and the molecular anisotropy of polynuclear complexes are provided. The synergy and interference effects between local magnetic anisotropies are studied in a series of binuclear complexes.« less

Synthesis, spectroscopic characterization, electrochemistry and biological evaluation of some binuclear transition metal complexes of bicompartmental ONO donor ligands containing benzo[b]thiophene moiety

NASA Astrophysics Data System (ADS)

Mahendra Raj, K.; Vivekanand, B.; Nagesh, G. Y.; Mruthyunjayaswamy, B. H. M.

2014-02-01

A series of new binucleating Cu(II), Co(II), Ni(II) and Zn(II) complexes of bicompartmental ligands with ONO donor were synthesized. The ligands were obtained by the condensation of 3-chloro-6-substituted benzo[b]thiophene-2-carbohydrazides and 4,6-diacetylresorcinol. The synthesized ligands and their complexes were characterized by elemental analysis and various spectroscopic techniques. Elemental analysis, IR, 1H NMR, ESI-mass, UV-Visible, TG-DTA, magnetic measurements, molar conductance and powder-XRD data has been used to elucidate their structures. The bonding sites are the oxygen atom of amide carbonyl, azomethine nitrogen and phenolic oxygen for ligands 1 and 2. The binuclear nature of the complexes was confirmed by ESR spectral data. TG-DTA studies for some complexes showed the presence of coordinated water molecules and the final product is the metal oxide. All the complexes were investigated for their electrochemical activity, only the Cu(II) complexes showed the redox property. Cu(II) complexes were square planar, whereas Co(II), Ni(II) and Zn(II) complexes were octahedral. Powder-XRD pattern have been studied in order to test the degree of crystallinity of the complexes and unit cell calculations were made. In order to evaluate the effect of antimicrobial activity of metal ions upon chelation, both the ligands and their metal complexes were screened for their antibacterial and antifungal activities by minimum inhibitory concentration (MIC) method. The results showed that the metal complexes were found to be more active than free ligands. The DNA cleaving capacities of all the complexes were analyzed by agarose gel electrophoresis method against supercoiled plasmid DNA. Among the compounds tested for antioxidant capacity, ligand 1 displayed excellent activity than its metal complexes.

Reduction of Carbon Monoxide. Past Research Summary

DOE R&D Accomplishments Database

Schrock, R. R.

1982-01-01

Research programs for the year on the preparation, characterization, and reactions of binuclear tantalum complexes are described. All evidence to date suggest the following of these dimeric molecules: (1) the dimer does not break into monomers under mild conditions; (2) intermolecular hydride exchange is not negligible, but it is slow; (3) intermolecular non-ionic halide exchange is fast; (4) the ends of the dimers can rotate partially with respect to one another. The binuclear tantalum hydride complexes were found to react with carbon monoxide to give a molecule which is the only example of reduction of CO by a transition metal hydride to give a complex containing a CHO ligand. Isonitrides also reacted in a similar manner with dimeric tantalum hydride. (ATT)

Crystal Structure of Phosphatidylglycerophosphatase (PGPase), a Putative Membrane-Bound Lipid Phosphatase, Reveals a Novel Binuclear Metal Binding Site and Two Proton Wires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumaran,D.; Bonnano, J.; Burley, S.

2006-01-01

Phosphatidylglycerophosphatase (PGPase), an enzyme involved in lipid metabolism, catalyzes formation of phosphatidylglycerol from phosphatidylglycerophosphate. Phosphatidylglycerol is a multifunctional phospholipid, found in the biological membranes of many organisms. Here, we report the crystal structure of Listeria monocytogenes PGPase at 1.8 Angstroms resolution. PGPase, an all-helical molecule, forms a homotetramer. Each protomer contains an independent active site with two metal ions, Ca{sup 2+} and Mg{sup 2+}, forming a hetero-binuclear center located in a hydrophilic cavity near the surface of the molecule. The binuclear center, conserved ligands, metal-bound water molecules, and an Asp-His dyad form the active site. The catalytic mechanism of thismore » enzyme is likely to proceed via binuclear metal activated nucleophilic water. The binuclear metal-binding active-site environment of this structure should provide insights into substrate binding and metal-dependent catalysis. A long channel with inter-linked linear water chains, termed 'proton wires', is observed at the tetramer interface. Comparison of similar water chain structures in photosynthetic reaction centers (RCs), Cytochrome f, gramicidin, and bacteriorhodopsin, suggests that PGPase may conduct protons via proton wires.« less

Straightforward Preparation Method for Complexes Bearing a Bidentate N-Heterocyclic Carbene to Introduce Undergraduate Students to Research Methodology

ERIC Educational Resources Information Center

Fernández, Alberto; López-Torres, Margarita; Fernández, Jesús J.; Vázquez-García, Digna; Marcos, Ismael

2017-01-01

A laboratory experiment for students in advanced inorganic chemistry is described. In this experiment, students prepare two metal complexes with a potentially bidentate-carbene ligand. The complexes are synthesized by reaction of a bisimidazolium salt with silver(I) oxide or palladium(II) acetate. Silver and palladium complexes are binuclear and…

Structural analysis of the coordination of dinitrogen to transition metal complexes.

PubMed

Peigné, Benjamin; Aullón, Gabriel

2015-06-01

Transition-metal complexes show a wide variety of coordination modes for the nitrogen molecule. A structural database study has been undertaken for dinitrogen complexes, and geometrical parameters around the L(n)M-N2 unit are retrieved from the Cambridge Structural Database. These data were classified in families of compounds, according to metal properties, to determine the degree of lengthening for the dinitrogen bonding. The importance of the nature of the metal center, such as coordination number and electronic configuration, is reported. Our study reveals poor activation by coordination of dinitrogen in mononuclear complexes, always having end-on coordination. However, partial weakening of nitrogen-nitrogen bonding is found for end-on binuclear complexes, whereas side-on complexes can be completely activated.

Structural diversity of benzil bis(benzoylhydrazone): Mononuclear, binuclear and trinuclear complexes.

PubMed

López-Torres, Elena; Mendiola, M Antonia

2009-10-07

The coordination behaviour of the Schiff-base, benzil bis(benzoylhydrazone), LH(2) towards divalent nickel, lead, cadmium, zinc and copper ions has been investigated. The complexes have been fully characterized by techniques including (113)Cd and (207)Pb NMR, as well as (13)C and (113)Cd CP/MAS NMR and by single crystal X-ray diffraction. All the complexes have the general formula [ML](n) (n = 1-3 depending on the metal ion), with the ligand doubly deprotonated. The nickel complex [NiL] is a monomeric compound, the lead complex [PbL](2) shows a binuclear structure, whereas zinc [ZnL](3) and copper [CuL](3) complexes are trinuclear helicates. The cadmium complex seems to be a dimer with a structure similar to that of . In the nickel and lead derivatives, the ligand behaves as a tetradentate N(2)O(2) chelate and in complex also as a bridge through one of the O atoms. In the crystal structures of Zn and Cu complexes [ML](3) each metal is in a pentadentate N(3)O(2) environment formed by two different ligands, one tridentate chelate and the other bidentate chelate, giving rise to trinuclear helicates. These results point out the versatility of benzil bis(benzoylhydrazone) on its coordination.

Studies on the synthesis, spectra, catalytic and antibacterial activities of binuclear ruthenium(II) complexes.

PubMed

Krishnamoorthy, P; Sathyadevi, P; Deepa, K; Dharmaraj, N

2010-09-15

A new series of stable binuclear ruthenium(II) carbonyl complexes of the general formula [{RuX(CO)(EPh(3))(2)}(2)L] (where X=H or Cl; E=P or As and L=dibasic tetradentate diacetyl resorcinol (H(2)-DAR)) have been synthesised by reacting ruthenium(II) starting complexes [RuHX(CO)(EPh(3))(3)] (where X=H or Cl; E=P or As) and 4,6-diacetylresorcinol (H(2)-DAR) ligand in benzene medium. The structure of the new binuclear ruthenium(II) carbonyl complexes was established using elemental analysis, spectra (FT-IR, UV-vis and (1)H NMR), electrochemical and thermal studies. In these reactions, the 4,6-diacetylresorcinol (H(2)-DAR) ligand behaves as a binegative tetradentate chelating ligand coordinating through O,O atoms of both the carbonyl and phenolic C-O groups by replacing a molecule of PPh(3)/AsPh(3) and a hydride ion from the starting complexes. Further, all these complexes were also employed as new catalysts for the oxidation of primary and secondary alcohols in the presence of N-methylmorpholine-N-oxide (NMO) as a more viable co-oxidant. The free ligand and their metal complexes have also been screened for their antibacterial activity against the growth of gram +ve and gram -ve bacterial cultures. Copyright 2010 Elsevier B.V. All rights reserved.

Structural variety of mono- and binuclear transition metal complexes of 3-[(2-hydroxy-benzylidene)-hydrazono]-1-(2-hydroxyphenyl)-butan-1-one: Synthesis, spectral, thermal, molecular modeling, antimicrobial and antitumor studies

NASA Astrophysics Data System (ADS)

Shebl, Magdy; Adly, Omima M. I.; El-Shafiy, Hoda F.; Khalil, Saied M. E.; Taha, A.; Mahdi, Mohammed A. N.

2017-04-01

A new polydentate Schiff base ligand and its metal complexes were synthesized and characterized by elemental analyses, IR, 1H NMR, electronic, ESR and mass spectra, conductivity and magnetic susceptibility measurements as well as thermal analyses. The free ligand was synthesized by condensation of o-acetoacetylphenol with salicylaldehyde hydrazone. The analytical and spectroscopic tools showed that the obtained complexes are mono- and binuclear complexes, which can be generally formulated as: [(L)M2X2(H2O)m]·nZ; M = Cr, Fe, Ni or Cu, X = OAc or NO3, m = 5 or nil and n = 3, 1.5 or 0.5 and Z = EtOH or H2O, [(H2L)2M(X)m].nH2O; M = Mn, Zn, or Cd, X = EtOH, H2O or nil, m = 2 or nil and n = 3.5 or 0, [(HL)2Co2]·0.5H2O and [(H2L)2UO2(H2O)]. The metal complexes displayed octahedral, tetrahedral and square-planar geometrical arrangements, while uranium complex displayed seven-coordinate. Kinetic parameters (Ea, A, ΔH, ΔS and ΔG) of the thermal decomposition stages have been evaluated using Coats-Redfern equations. The molecular structural parameters of the ligand and its metal complexes have been calculated and correlated with the experimental data such as IR. The antimicrobial activity of the ligand and its complexes was screened against some kinds of bacteria and fungi. The antitumor activity of the ligand and its Ni(II) and Cu(II) complexes was investigated against HepG2 cell line.

Structural basis for the metal-selective activation of the manganese transport regulator of Bacillus subtilis.

PubMed

Kliegman, Joseph I; Griner, Sarah L; Helmann, John D; Brennan, Richard G; Glasfeld, Arthur

2006-03-21

The manganese transport regulator (MntR) of Bacillus subtilis is activated by Mn(2+) to repress transcription of genes encoding transporters involved in the uptake of manganese. MntR is also strongly activated by cadmium, both in vivo and in vitro, but it is poorly activated by other metal cations, including calcium and zinc. The previously published MntR.Mn(2+) structure revealed a binuclear complex of manganese ions with a metal-metal separation of 3.3 A (herein designated the AB conformer). Analysis of four additional crystal forms of MntR.Mn(2+) reveals that the AB conformer is only observed in monoclinic crystals at 100 K, suggesting that this conformation may be stabilized by crystal packing forces. In contrast, monoclinic crystals analyzed at room temperature (at either pH 6.5 or pH 8.5), and a second hexagonal crystal form (analyzed at 100 K), all reveal the shift of one manganese ion by 2.5 A, thereby leading to a newly identified conformation (the AC conformer) with an internuclear distance of 4.4 A. Significantly, the cadmium and calcium complexes of MntR also contain binuclear complexes with a 4.4 A internuclear separation. In contrast, the zinc complex of MntR contains only one metal ion per subunit, in the A site. Isothermal titration calorimetry confirms the stoichiometry of Mn(2+), Cd(2+), and Zn(2+) binding to MntR. We propose that the specificity of MntR activation is tied to productive binding of metal ions at two sites; the A site appears to act as a selectivity filter, determining whether the B or C site will be occupied and thereby fully activate MntR.

Synthesis, magnetic, spectral, and antimicrobial studies of Cu(II), Ni(II) Co(II), Fe(III), and UO 2(II) complexes of a new Schiff base hydrazone derived from 7-chloro-4-hydrazinoquinoline

NASA Astrophysics Data System (ADS)

El-Behery, Mostafa; El-Twigry, Haifaa

2007-01-01

A new hydrazone ligand, HL, was prepared by the reaction of 7-chloro-4-hydrazinoquinoline with o-hydroxybenzaldehyde. The ligand behaves as monoprotic bidentate. This was accounted for as the ligand contains a phenolic group and its hydrogen atom is reluctant to be replaced by a metal ion. The ligand reacted with Cu(II), Ni(II), Co(II), Fe(III), and UO 2(II) ions to yield mononuclear complexes. In the case of Fe(III) ion two complexes, mono- and binuclear complexes, were obtained in the absence and presence of LiOH, respectively. Also, mixed ligand complexes were obtained from the reaction of the metal cations Cu(II), Ni(II) and Fe(III) with the ligand (HL) and 8-hydroxyquinoline (8-OHqu) in the presence of LiOH, in the molar ratio 1:1:1:1. It is clear that 8-OHqu behaves as monoprotic bidentate ligand in such mixed ligand complexes. The ligand, HL, and its metal complexes were characterized by elemental analyses, IR, UV-vis, mass, and 1H NMR spectra, as well as magnetic moment, conductance measurements, and thermal analyses. All complexes have octahedral configurations except Cu(II) complex which has an extra square-planar geometry, while Ni(II) mixed complex has also formed a tetrahedral configuration and UO 2(II) complex which formed a favorable pentagonal biprymidial geometry. Magnetic moment of the binuclear Fe(III) complex is quite low compared to calculated value for two iron ions complex and thus shows antiferromagnetic interactions between the two adjacent ferric ions. The HL and metal complexes were tested against one stain Gram positive bacteria ( Staphylococcus aureus), Gram negative bacteria ( Escherichia coli), and fungi ( Candida albicans). The tested compounds exhibited higher antibacterial acivities.

Synthesis, spectral and electrochemical studies of binuclear Ru(III) complexes containing dithiosemicarbazone ligand

NASA Astrophysics Data System (ADS)

Kanchana Devi, A.; Ramesh, R.

2014-01-01

Synthesis of several new octahedral binuclear ruthenium(III) complexes of the general composition [(EPh3)2(X)Ru-L-Ru(X)(EPh3)2] containing benzene dithiosemicarbazone ligands (where E = P or As; X = Cl or Br; L = binucleating ligands) is presented. All the complexes have been fully characterized by elemental analysis, FT-IR, UV-vis and EPR spectroscopy together with magnetic susceptibility measurements. IR study shows that the dithiosemicarbazone ligands behave as dianionic tridentate ligands coordinating through the oxygen atom of the deprotonated phenolic group, nitrogen atom of the azomethine group and thiolate sulphur. In DMF solution, all the complexes exhibit intense d-d transition and ligand-to-metal charge transfer (LMCT) transition in the visible region. The magnetic moment values of the complexes are in the range 1.78-1.82 BM, which reveals the presence of one unpaired electron on each metal ion. The EPR spectra of the liquid samples at LNT show the presence of three different 'g' values (gx ≠ gy ≠ gz) indicate a rhombic distortion around the ruthenium ion. All the complexes exhibit two quasi-reversible one electron oxidation responses (RuIII-RuIII/RuIII-RuIV; RuIII-RuIV/RuIV-RuIV) within the E1/2 range of 0.61-0.74 V and 0.93-0.98 V respectively, versus Ag/AgCl.

Surface complexation of carboxylate adheres Cryptosporidium parvum öocysts to the hematite-water interface

USGS Publications Warehouse

Gao, X.; Metge, D.W.; Ray, C.; Harvey, R.W.; Chorover, J.

2009-01-01

The interaction of viable Cryptosporidium parvum öocysts at the hematite (α-Fe2O3)−water interface was examined over a wide range in solution chemistry using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Spectra for hematite-sorbed öocysts showed distinct changes in carboxylate group vibrations relative to spectra obtained in the absence of hematite, indicative of direct chemical bonding between carboxylate groups and Fe metal centers of the hematite surface. The data also indicate that complexation modes vary with solution chemistry. In NaCl solution, öocysts are bound to hematite via monodentate and binuclear bidentate complexes. The former predominates at low pH, whereas the latter becomes increasingly prevalent with increasing pH. In a CaCl2 solution, only binuclear bidentate complexes are observed. When solution pH is above the point of zero net proton charge (PZNPC) of hematite, öocyst surface carboxylate groups are bound to the mineral surface via outer-sphere complexes in both electrolyte solutions.

A new trinuclear complex of platinum and iron efficiently promotes cleavage of plasmid DNA.

PubMed Central

Lempers, E L; Bashkin, J S; Kostić, N M

1993-01-01

The compound [[Pt(trpy)]2Arg-EDTA]+ is synthesized in five steps, purified, and characterized by 1H, 13C, and 195Pt NMR spectroscopy, mass spectrometry, UV-vis spectrophotometry, and elemental analysis. The binuclear [[(Pt(trpy)]2Arg]3+ moiety binds to double-stranded DNA, and the chelating EDTA moiety holds metal cations. In the presence of ferrous ions and the reductant dithiothreitol, the new compound cleaves DNA. It cleaves a single strand in the pBR322 plasmid nearly as efficiently as methidiumrpropyl-EDTA (MPE), and it cleaves a restriction fragment of the XP10 plasmid nonselectively and more efficiently than [Fe(EDTA)]2-. The mechanism of cleavage was studied in control experiments involving different transition-metal ions, superoxide dismutase, catalase, glucose oxidase with glucose, metal-sequestering agents, and deaeration. These experiments indicate that adventitious iron and copper ions, superoxide anion, and hydrogen peroxide are not involved and that dioxygen is required. The cleavage apparently is done by hydroxyl radicals generated in the vicinity of the DNA molecule. The reagent [[Pt(trypy)]2Arg-EDTA]+ differs from methidiumpropyl-EDTA in not containing an intercalator. This difference in binding modes between the binuclear platinum(II) complex and the planar heterocycle may cause useful differences between the two reagents in cleavage of nucleic acids. Images PMID:8493109

Selective Anion Binding by a Cofacial Binuclear Zinc Complex of a Schiff-Base Pyrrole Macrocycle

PubMed Central

Devoille, Aline M. J.; Richardson, Patricia; Bill, Nathan; Sessler, Jonathan L.; Love, Jason B.

2011-01-01

The synthesis of the new cofacial binuclear zinc complex [Zn2(L)] of a Schiff-base pyrrole macrocycle is reported. It was discovered that the binuclear microenvironment between the two metals of [Zn2(L)] is suited for the encapsulation of anions, leading to the formation of [K(THF)6][Zn2(μ-Cl)(L)].2THF and [Bun4N][Zn2(μ-OH)(L)] which were characterized by X-ray crystallography. Unusually obtuse Zn-X-Zn angles (X=Cl: 150.54(9)° and OH: 157.4(3)°) illustrate the weak character of these interactions and the importance of the cleft pre-organization to stabilize the host. In the absence of added anion, aggregation of [Zn2(L)] was inferred and investigated by successive dilutions and by the addition of coordinating solvents to [Zn2(L)] solutions using NMR spectroscopy as well as isothermal microcalorimetry (ITC). On anion addition, evidence for de-aggregation of [Zn2(L)], combined with the formation of the 1:1 host-guest complex, was observed by NMR spectroscopy and ITC titrations. Furthermore, [Zn2(L)] binds to Cl− selectively in THF as deduced from the ITC analyses, while other halides induce only de-aggregation. These conclusions were reinforced by DFT calculations, which indicated that the binding energies of OH− and Cl− were significantly greater than for the other halides. PMID:21391550

Mechanistic Insight from Calorimetric Measurements of the Assembly of the Binuclear Metal Active Site of Glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes.

PubMed

Pedroso, Marcelo M; Ely, Fernanda; Carpenter, Margaret C; Mitić, Nataša; Gahan, Lawrence R; Ollis, David L; Wilcox, Dean E; Schenk, Gerhard

2017-07-05

Glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes is a binuclear metallohydrolase with a high affinity for metal ions at its α site but a lower affinity at its β site in the absence of a substrate. Isothermal titration calorimetry (ITC) has been used to quantify the Co(II) and Mn(II) binding affinities and thermodynamics of the two sites in wild-type GpdQ and two mutants, both in the absence and in the presence of phosphate. Metal ions bind to the six-coordinate α site in an entropically driven process with loss of a proton, while binding at the β site is not detected by ITC. Phosphate enhances the metal affinity of the α site by increasing the binding entropy and the metal affinity of the β site by enthalpic (Co) or entropic (Mn) contributions, but no additional loss of protons. Mutations of first- and second-coordination sphere residues at the β site increase the metal affinity of both sites by enhancing the binding enthalpy. In particular, loss of the hydrogen bond from second-sphere Ser127 to the metal-coordinating Asn80 has a significant effect on the metal binding thermodynamics that result in a resting binuclear active site with high catalytic activity. While structural and spectroscopic data with excess metal ions have indicated a bridging hydroxide in the binuclear GpdQ site, analysis of ITC data here reveals the loss of a single proton in the assembly of this site, indicating that the metal-bound hydroxide nucleophile is formed in the resting inactive mononuclear form, which becomes catalytically competent upon binding the second metal ion.

Co-complexes derived from alkene insertion to alkyne-dicobaltpentacarbonyl complexes: insight into the regioselectivity of pauson-khand reactions of cyclopropenes.

PubMed

Pallerla, Mahesh K; Yap, Glenn P A; Fox, Joseph M

2008-08-15

Described are the X-ray crystallographic and spectral properties of Co-complexes that were isolated from two Pauson-Khand reactions of chiral cyclopropenes. These are the first examples of isolated Co-complexes derived from the putative alkene-insertion intermediates of Pauson-Khand reactions. The binuclear Co-complexes are coordinated to mu-bonded, five-carbon "flyover" carbene ligands. It is proposed that the complexes result from cyclopropane fragmentation subsequent to alkene insertion. The observation of these metal complexes provides a rationale for the origin of regioselectivity in Pauson-Khand reactions of cyclopropenes.

Metal-promoted binuclear C-H activation of ethylene and formation of a novel heterobimetallic Ir-Pt complex. X-ray crystal structure of ((Ph sub 3 P) sub 2 (CO)Ir(. mu. -H)(. mu. -. eta. sup 2 :. eta. sup 1 -CH double bond CH sub 2 )Pt(PPh sub 3 ) sub 2 ) sup + CF sub 3 SO sub 3 sup minus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yohsin; Stang, P.J.; Arif, A.M.

1990-07-04

Heterobimetallic complexes containing asymmetric metal-metal bonds as well as homogeneous C-H bond activation by organometallic compounds are of considerable current interest largely because of their relevance to catalysis. Although coordination of an alkene to transition metal systems is generally considered a necessary activation step in many catalytic and stoichiometric organometallic reactions, little is known about alkene C-H bond activation of precomplexed olefin substrates. In this paper the authors report the first intermolecular example of olefin C-H activation by a second, different metal system of a precomplexed {pi}-ethylene transition-metal complex and the concomitant formation of a novel alkene-bridged heterobimetallic Ir-Pt complex.

Acidity of a Cu-bound histidine in the binuclear center of cytochrome C oxidase.

PubMed

Fadda, Elisa; Chakrabarti, Nilmadhab; Pomès, Régis

2005-12-01

Cytochrome c oxidase (CcO) is a crucial enzyme in the respiratory chain. Its function is to couple the reduction of molecular oxygen, which takes place in the Fea3-CuB binuclear center, to proton translocation across the mitochondrial membrane. Although several high-resolution structures of the enzyme are known, the molecular basis of proton pumping activation and its mechanism remain to be elucidated. We examine a recently proposed scheme (J. Am. Chem. Soc. 2004, 126, 1858; FEBS Lett. 2004, 566, 126) that involves the deprotonation of the CuB-bound imidazole ring of a histidine (H291 in mammalian CcO) as a key element in the proton pumping mechanism. The central feature of that proposed mechanism is that the pKa values of the imidazole vary significantly depending on the redox state of the metals in the binuclear center. We use density functional theory in combination with continuum electrostatics to calculate the pKa values, successively in bulk water and within the protein, of the Cu-bound imidazole in various Cu- and Cu-Fe complexes. From pKas in bulk water, we derived a value of -266.34 kcal.mol(-1) for the proton solvation free energy (Delta). This estimate is in close agreement with the experimental value of -264.61 kcal.mol(-1) (J. Am. Chem. Soc. 2001, 123, 7314), which reinforces the conclusion that Delta is more negative than previous values used for pKa calculations. Our approach, on the basis of the study of increasingly more detailed models of the CcO binuclear center at different stages of the catalysis, allows us to examine successively the effect of each of the two metals' redox states and of solvation on the acidity of imidazole, whose pKa is approximately 14 in bulk water. This analysis leads to the following conclusions: first, the effect of Cu ligation on the imidazole acidity is negligible regardless of the redox state of the metal. Second, results obtained for Cu-Fe complexes in bulk water indicate that Cu-bound imidazole pKa values lie within the range of 14.8-16.6 throughout binuclear redox states corresponding to the catalytic cycle, demonstrating that the effect of the Fe oxidation states is also negligible. Finally, the low-dielectric CcO proteic environment shifts the acid-base equilibrium toward a neutral imidazole, further increasing the corresponding pKa values. These results are inconsistent with the proposed role of the Cu-bound histidine as a key element in the pumping mechanism. Limitations of continuum solvation models in pKa calculations are discussed.

Co-complexes Derived from Alkene Insertion to Alkyne-dicobaltpentacarbonyl complexes: Insight into the Regioselectivity of Pauson-Khand Reactions of Cyclopropenes

PubMed Central

Pallerla, Mahesh K.; Yap, Glenn P. A.; Fox, Joseph M.

2009-01-01

Described are the X-ray crystallographic and spectral properties of Co-complexes that were isolated from two Pauson-Khand reactions of chiral cyclopropenes. These are the first examples of isolated Co-complexes derived from the putative alkene-insertion intermediates of Pauson-Khand reactions. The binuclear Co-complexes are coordinated to μ-bonded, five-carbon “flyover” carbene ligands. It is proposed that the complexes result from cyclopropane fragmentation subsequent to alkene insertion. The observation of these metal complexes provides a rationale for the origin of regioselectivity in Pauson-Khand reactions of cyclopropenes. PMID:18637694

Synthesis, spectral characterization and structural studies of a novel O, N, O donor semicarbazone and its binuclear copper complex with hydrogen bond stabilized lattice

NASA Astrophysics Data System (ADS)

Layana, S. R.; Saritha, S. R.; Anitha, L.; Sithambaresan, M.; Sudarsanakumar, M. R.; Suma, S.

2018-04-01

A novel O,N,O donor salicylaldehyde-N4-phenylsemicarbazone, (H2L) has been synthesized and physicochemically characterized. Detailed structural studies of H2L using single crystal X-ray diffraction technique reveals the existence of intra and inter molecular hydrogen bonding interactions, which provide extra stability to the molecule. We have successfully synthesized a binuclear copper(II) complex, [Cu2(HL)2(NO3)(H2O)2]NO3 with phenoxy bridging between the two copper centers. The complex was characterized by elemental analysis, magnetic susceptibility and conductivity measurements, FT-IR, UV-Visible, mass and EPR spectral methods. The grown crystals of the copper complex were employed for the single crystal X-ray diffraction studies. The complex possesses geometrically different metal centers, in which the ligand coordinates through ketoamide oxygen, azomethine nitrogen and deprotonated phenoxy oxygen. The extensive intermolecular hydrogen bonding interactions of the coordinated and the lattice nitrate groups interconnect the complex units to form a 2D supramolecular assembly. The ESI mass spectrum substantiates the existence of 1:1 complex. The g values obtained from the EPR spectrum in frozen DMF suggest dx2 -y2 ground state for the unpaired electron.

Theoretical studies on all-metal binuclear sandwich-like complexes M2(η 4-E 4) 2 (M=Al, Ga, In; E=Sb, Bi).

PubMed

Wang, Congzhi; Zhang, Xiuhui; Lu, Jian; Li, Qianshu

2012-08-01

A series of all-metal binuclear sandwich-like complexes with the formula M(2)(η(4)-E(4))(2) (M=Al, Ga, In; E=Sb, Bi) was studied by density functional theory (DFT). The most stable conformer for each of the M(2)(η(4)-E(4))(2) species is the staggered one with D (4d) symmetry. The centred metal-metal bond in each M(2)(η(4)-E(4))(2) species is a covalent single bond, with the main contributors to these covalent bonds being the a(1) and e orbitals. For all these species, the interactions between the centred metal atoms and the all-metal ligands are covalent; η(4)-Sb (4) (2-) has a stronger ability to stabilize metal-metal bonds than η(4)-Bi (4) (2-). Nucleus-independent chemical shifts (NICS) values and molecular orbital (MO) analysis reveal that the all-metal η(4)-Sb (4) (2-) and η(4)-Bi (4) (2-) ligands in M(2)(η(4)-E(4))(2) possess conflicting aromaticity (σ antiaromaticity and π aromaticity), which differs from the all-metal multiple aromatic unit Al (4) (2-). In addition, all of these M(2)(η(4)-E(4))(2) species are stable according to the dissociation energies of M(2)(η(4)-E(4))(2) → 2 M(η(4)-E(4)) and M(2)(η(4)-E(4))(2) → 2 M + 2E(4), and these stable species can be synthesized by two-step substitution reactions: CpZnZnCp + 2E (4) (2-)  → [E(4)ZnZnE(4)](2-) + 2Cp(-) and [E(4)ZnZnE(4)](2-) + 2 M (2) (+)  → E(4)MME(4) + 2Zn(+).

Binuclear transition-metal complexes as new reagents for selective cross-linking of proteins. Coordination of cytochrome c to dirhodium(II). mu. -tetraacetate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, J.; Kostic, N.M.

1988-07-27

This study introduces binuclear transition-metal complexes as reagents for selective covalent cross-linking of proteins. Incubation of horse cytochrome c (designated cyt) with Rh{sub 2}(OAc){sub 4} under mild conditions yields the diprotein complex, Rh{sub 2}(OAc){sub 4}(cyt){sub 2}, whose composition is established by size-exclusion chromatography, uv-vis spectroscopy, and {sup 1}H NMR spectroscopy. The protein molecules are coordinated to the Rh atoms via the imidazole (Im) rings of their His 33 residues, as shown by uv difference and {sup 1}H NMR spectroscopy, by the pH effect on the complex formation, and by the control experiments with tuna cytochrome c. The diprotein complex ismore » stable under ordinary conditions, and yet it can be cleaved, and the native protein recovered, by treatment with a suitable strong nucleophile. Spectroscopic and electrochemical measurements show that the structural and redox properties of cytochrome c are not perturbed significantly by cross-linking. Comparison between Rh{sub 2}(OAc){sub 4}(Im){sub 2} and Rh{sub 2}(OAc){sub 4}(cyt){sub 2} shows that the complex containing small ligands is not an entirely realistic model of the complex containing proteins. In particular, the enhanced stability of the latter toward hydrolysis may be due to steric bulk of the protein ligands and to hydrogen bonds that amino acid side chains may form with the inorganic link. Some of the findings of this study may pertain to the mechanism of antitumor action of the Rh{sub 2}(RCOO){sub 4} complexes. 86 refs., 2 tabs.« less

Mono- and binuclear molybdenum and tungsten complexes containing asymmetric bridging ligands: Effects of ligand conjugation and conformation on metal-metal interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, A.; Jeffery, J.C.; Maher, J.P.

The authors have prepared the new monodentate ligands 4-(4-methoxyphenyl)pyridine, 1-(4-pyridyl)-2-(4-methoxyphenyl)ethene, 1-(4-pyridyl)-2-(3-methoxyphenyl)ethene, and 1-(3-pyridyl)-2-(4-methoxyphenyl)ethene (L[sup 5]-L[sup 8]); demethylation of the methoxy group in each case afforded the new bridging bidentate ligands HL[sup 1]-HL[sup 4], which contain one pyridyl and one phenolate donor. Attachment of a MoL*(NO)Cl [L* = hydrotris(3,5-dimethylpyrazolyl)borate] moiety to the pyridyl groups of L[sup 5]-L[sup 8] gave the 17-electron complexes [Mo(NO)L*ClL[prime

Investigating the pharmacodynamic and magnetic properties of pyrophosphate-bridged coordination complexes

NASA Astrophysics Data System (ADS)

Ikotun, Oluwatayo (Tayo) F.

The multidentate nature of pyrophosphate makes it an attractive ligand for complexation of metal cations. The participation of pyrophosphate in a variety of biological pathways and its metal catalyzed hydrolysis has driven our investigation into its coordination chemistry. We have successfully synthesized a library of binuclear pyrophosphate bridge coordination complexes. The problem of pyrophosphate hydrolysis to phosphate in the presence of divalent metal ions was overcome by incorporating capping ligands such as 1,10-phenanthroline and 2,2'-bipyridine prior to the addition of the pyrophosphate. The magnetic properties of these complexes was investigated and magneto-structural analysis was conducted. The biological abundance of pyrophosphate and the success of metal based drugs such as cisplatin, prompted our investigation of the cytotoxic properties of M(II) pyrophosphate dimeric complexes (where M(II) is CoII, CuII, and NiII) in adriamycin resistant human ovarian cancer cells. Thess compounds were found to exhibit toxicity in the nanomolar to picomolar range. We conducted in vitro stability studies and the mechanism of cytoxicity was elucidated by performing DNA mobility and binding assays, enzyme inhibition assays, and in vitro oxidative stress studies.

Chemical rescue of the post-translationally carboxylated lysine mutant of allantoinase and dihydroorotase by metal ions and short-chain carboxylic acids.

PubMed

Ho, Ya-Yeh; Huang, Yen-Hua; Huang, Cheng-Yang

2013-04-01

Bacterial allantoinase (ALLase) and dihydroorotase (DHOase) are members of the cyclic amidohydrolase family. ALLase and DHOase possess similar binuclear metal centers in the active site in which two metals are bridged by a post-translationally carboxylated lysine. In this study, we determined the effects of carboxylated lysine and metal binding on the activities of ALLase and DHOase. Although DHOase is a metalloenzyme, purified DHOase showed high activity without additional metal supplementation in a reaction mixture or bacterial culture. However, unlike DHOase, ALLase had no activity unless some specific metal ions were added to the reaction mixture or culture. Substituting the metal binding sites H59, H61, K146, H186, H242, or D315 with alanine completely abolished the activity of ALLase. However, the K146C, K146D and K146E mutants of ALLase were still active with about 1-6% activity of the wild-type enzyme. These ALLase K146 mutants were found to have 1.4-1.7 mol metal per mole enzyme subunit, which may indicate that they still contained the binuclear metal center in the active site. The activity of the K146A mutant of the ALLase and the K103A mutant of DHOase can be chemically rescued by short-chain carboxylic acids, such as acetic, propionic, and butyric acids, but not by ethanol, propan-1-ol, and imidazole, in the presence of Co2+ or Mn2+ ions. However, the activity was still ~10-fold less than that of wild-type ALLase. Overall, these results indicated that the 20 natural basic amino acid residues were not sufficiently able to play the role of lysine. Accordingly, we proposed that during evolution, the post-translational modification of carboxylated lysine in the cyclic amidohydrolase family was selected for promoting binuclear metal center self-assembly and increasing the nucleophilicity of the hydroxide at the active site for enzyme catalysis. This kind of chemical rescue combined with site-directed mutagenesis may also be used to identify a binuclear metal center in the active site for other metalloenzymes.

Hybrid binuclear-cobalt-phthalocyanine as oxygen reduction reaction catalyst in single chamber microbial fuel cells

NASA Astrophysics Data System (ADS)

Li, Baitao; Zhou, Xiuxiu; Wang, Xiujun; Liu, Bingchuan; Li, Baikun

2014-12-01

A novel hybrid binuclear-cobalt-phthalocyanine (Bi-CoPc) is developed as the cathode catalyst to replace the costly platinum (Pt) in single chamber microbial fuel cells (SCMFCs). Bi-CoPc/C is integrated with metal oxides (NiO and CoO) to form macrocyclic complex for enhanced oxygen reduction rate (ORR). The characteristics of hybrid catalysts (Bi-CoPc/C-CoO and Bi-CoPc/C-NiO) are compared with Co-contained catalysts (CoPc/C and Bi-CoPc/C) and metal oxide catalysts (NiO and CoO). The increase in O and N functional groups indicates the benefits of NiO and CoO to the cathode catalysts. The cyclic voltammetry (CV) shows the reduction peak for Bi-CoPc/C-NiO and Bi-CoPc/C-CoO at -0.12 V and -0.22 V, respectively. The power densities (368 mW m-2 and 400 mW m-2) of SCMFCs with Bi-CoPc/C-CoO and Bi-CoPc-NiO/C are the highest among the cathodes tested, and close to that of Pt (450 mW m-2). This study demonstrates that hybrid Bi-CoPc/C with metal oxides has a great potential as a cost-effective catalyst in MFCs.

Nature-Inspired, Highly Durable CO2 Reduction System Consisting of a Binuclear Ruthenium(II) Complex and an Organic Semiconductor Using Visible Light.

PubMed

Kuriki, Ryo; Matsunaga, Hironori; Nakashima, Takuya; Wada, Keisuke; Yamakata, Akira; Ishitani, Osamu; Maeda, Kazuhiko

2016-04-20

A metal-free organic semiconductor of mesoporous graphitic carbon nitride (C3N4) coupled with a Ru(II) binuclear complex (RuRu') containing photosensitizer and catalytic units selectively reduced CO2 into HCOOH under visible light (λ > 400 nm) in the presence of a suitable electron donor with high durability, even in aqueous solution. Modification of C3N4 with Ag nanoparticles resulted in a RuRu'/Ag/C3N4 photocatalyst that exhibited a very high turnover number (>33000 with respect to the amount of RuRu'), while maintaining high selectivity for HCOOH production (87-99%). This turnover number was 30 times greater than that reported previously using C3N4 modified with a mononuclear Ru(II) complex, and by far the highest among the metal-complex/semiconductor hybrid systems reported to date. The results of photocatalytic reactions, emission decay measurements, and time-resolved infrared spectroscopy indicated that Ag nanoparticles on C3N4 collected electrons having lifetimes of several milliseconds from the conduction band of C3N4, which were transferred to the excited state of RuRu', thereby promoting photocatalytic CO2 reduction driven by two-step photoexcitation of C3N4 and RuRu'. This study also revealed that the RuRu'/Ag/C3N4 hybrid photocatalyst worked efficiently in water containing a proper electron donor, despite the intrinsic hydrophobic nature of C3N4 and low solubility of CO2 in an aqueous environment.

Highly efficient binuclear ruthenium catalyst for water oxidation.

PubMed

Sander, Anett C; Maji, Somnath; Francàs, Laia; Böhnisch, Torben; Dechert, Sebastian; Llobet, Antoni; Meyer, Franc

2015-05-22

Water splitting is one of the key steps in the conversion of sunlight into a usable renewable energy carrier such as dihydrogen or more complex chemical fuels. Developing rugged and highly efficient catalysts for the oxidative part of water splitting, the water oxidation reaction generating dioxygen, is a major challenge in the field. Herein, we introduce a new, and rationally designed, pyrazolate-based diruthenium complex with the highest activity in water oxidation catalysis for binuclear systems reported to date. Single-crystal X-ray diffraction showed favorable preorganization of the metal ions, well suited for binding two water molecules at a distance adequate for OO bond formation; redox titrations as well as spectroelectrochemistry allowed characterization of the system in several oxidation states. Low oxidation potentials reflect the trianionic character of the elaborate compartmental pyrazolate ligand furnished with peripheral carboxylate groups. Water oxidation has been mediated both by a chemical oxidant (Ce(IV) )-by means of manometry and a Clark electrode for monitoring the dioxygen production-and electrochemically with impressive activities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Syntheses, structures and magnetic properties of four coordination polymers based on nitrobenzene dicarboxylate and various N-donor coligands

NASA Astrophysics Data System (ADS)

Li, Gui-Lian; Yin, Wei-Dong; Liu, Guang-Zhen; Ma, Lu-Fang; Wang, Li-Ya

2014-12-01

Four new coordination polymers {[Ni(4-Nbdc)(bpa)(H2O)]}n (1), {[Co(4-Nbdc)(bpp) (H2O)]}n (2), {[Ni(4-Nbdc)(bpp)(H2O)]·H2O}n (3), and {[Mn2(3-Nbdc)2(bib)3]·2H2O}n (4) (4-Nbdc=4-nitrobenzene-1,2-dicarboxylate, 3-Nbdc=3-nitrobenzene-1,2-dicarboxylate, bpa=1,2-bi(4-pyridyl)ethane, bpp=1,3-bis(4-pyridyl)propane, and bib=1,4-bis(1-imidazoly)benzene), were synthesized by hydrothermal reactions, and characterized by single-crystal X-ray diffractions, elemental analysis, FT-IR, PXRD, TGA and magnetic analysis. Complexes 1 and 2 display quasi-trapezoidal chain and brick-wall layer, and both of them contain metal-carboxylate binuclear units. Complexes 3 and 4 exhibit three-dimensional frameworks with the (66) dia topology and (44.610.8)(44.62) fsc topology, and both of them contain metal-carboxylate chains. The carboxyl groups with syn-anti coordination mode mediate effectively the weak ferromagnetic coupling interaction within Ni(II)-carboxylate binuclear in 1 (J=1.27 cm-1) and Ni(II)-carboxylate chain in 3 (J=1.44 cm-1), respectively, and the carboxyl groups with anti-anti coordination mode leads to the classic antiferromagnetic coupling interaction within Mn(II)-carboxylate chain in 4 (J=-0.77 cm-1).

Characterization of metastable intermediates formed in the reaction between a Mn(II) complex and dioxygen, including a crystallographic structure of a binuclear Mn(III)-peroxo species.

PubMed

Coggins, Michael K; Sun, Xianru; Kwak, Yeonju; Solomon, Edward I; Rybak-Akimova, Elena; Kovacs, Julie A

2013-04-17

Transition-metal peroxos have been implicated as key intermediates in a variety of critical biological processes involving O2. Because of their highly reactive nature, very few metal-peroxos have been characterized. The dioxygen chemistry of manganese remains largely unexplored despite the proposed involvement of a Mn-peroxo, either as a precursor to, or derived from, O2, in both photosynthetic H2O oxidation and DNA biosynthesis. These are arguably two of the most fundamental processes of life. Neither of these biological intermediates has been observed. Herein we describe the dioxygen chemistry of coordinatively unsaturated [Mn(II)(S(Me2)N4(6-Me-DPEN))] (+) (1), and the characterization of intermediates formed en route to a binuclear mono-oxo-bridged Mn(III) product {[Mn(III)(S(Me2)N4(6-Me-DPEN)]2(μ-O)}(2+) (2), the oxo atom of which is derived from (18)O2. At low-temperatures, a dioxygen intermediate, [Mn(S(Me2)N4(6-Me-DPEN))(O2)](+) (4), is observed (by stopped-flow) to rapidly and irreversibly form in this reaction (k1(-10 °C) = 3780 ± 180 M(-1) s(-1), ΔH1(++) = 26.4 ± 1.7 kJ mol(-1), ΔS1(++) = -75.6 ± 6.8 J mol(-1) K(-1)) and then convert more slowly (k2(-10 °C) = 417 ± 3.2 M(-1) s(-1), ΔH2(++) = 47.1 ± 1.4 kJ mol(-1), ΔS2(++) = -15.0 ± 5.7 J mol(-1) K(-1)) to a species 3 with isotopically sensitive stretches at νO-O(Δ(18)O) = 819(47) cm(-1), kO-O = 3.02 mdyn/Å, and νMn-O(Δ(18)O) = 611(25) cm(-1) consistent with a peroxo. Intermediate 3 releases approximately 0.5 equiv of H2O2 per Mn ion upon protonation, and the rate of conversion of 4 to 3 is dependent on [Mn(II)] concentration, consistent with a binuclear Mn(O2(2-)) Mn peroxo. This was verified by X-ray crystallography, where the peroxo of {[Mn(III)(S(Me2)N4(6-Me-DPEN)]2(trans-μ-1,2-O2)}(2+) (3) is shown to be bridging between two Mn(III) ions in an end-on trans-μ-1,2-fashion. This represents the first characterized example of a binuclear Mn(III)-peroxo, and a rare case in which more than one intermediate is observed en route to a binuclear μ-oxo-bridged product derived from O2. Vibrational and metrical parameters for binuclear Mn-peroxo 3 are compared with those of related binuclear Fe- and Cu-peroxo compounds.

Quantum chemical calculations and experimental investigations on 2-aminobenzoic acid-cyclodiphosph(V)azane derivative and its homo-binuclear Cu(II) complex

NASA Astrophysics Data System (ADS)

El-Gogary, Tarek M.; Alaghaz, Abdel-Nasser M. A.; Ammar, Reda A. A.

2012-03-01

A novel 2-aminobenzoic acid-cyclodiphosph(V)azane ligand H4L and its homo-binuclear Cu(II) complex of the type [Cu2L(H2O)2].2.5 H2O in which L is 1,3-di(-o-pyridyl)-2,4-(dioxo)-2',4'-bis-(2-iminobenzoic acid) cyclodiphosph(V)azane, were synthesized and characterized by different physical techniques. Infrared spectra of the complex indicate deprotonation and coordination of the imine NH and carboxyl COOH groups. It also confirms that nitrogen atom of the pyridine ring contribute to the complexation. Electronic spectra and magnetic susceptibility measurements reveal square-planar geometry for the Cu(II) complex. The elemental analyses and thermogravimetric results have justified the [Cu2L(H2O)2]·2.5H2O composition of the complex. Quantum chemical calculations were utilized to explore the electronic structure and stability of the H4L as well as the binuclear Cu(II) complex. Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of H4L and its binuclear Cu(II) complex. Different tautomers and geometrical isomers of the ligand were optimized at the ab initio DFT level. Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV-VIS spectra which show good agreement with measured electronic spectra.

Dinuclear lanthanide complexes based on amino alcoholate ligands: Structure, magnetic and fluorescent properties

NASA Astrophysics Data System (ADS)

Sun, Gui-Fang; Zhang, Cong-Ming; Guo, Jian-Ni; Yang, Meng; Li, Li-Cun

2017-05-01

Two binuclear lanthanide complexes [Ln2(hfac)6(HL)2] (LnIII = Dy(1), Tb(2); hfac = hexafluoroacetylacetonate, HL = (R)-2-amino-2-phenylethanol) have been successfully obtained by using amino alcoholate ligand. In two complexes, the Ln(III) ions are bridged by two alkoxido groups from HL ligands, resulting in binuclear complexes. The variable-temperature magnetic susceptibility studies indicate that there exists ferromagnetic interaction between two Ln(III) ions. Frequency dependent out-of-phase signals are observed for complex 1, suggesting SMM type behavior. Complexes 1 and 2 display intensely characteristic luminescent properties.

Indirect cooperative effects leading to synergism in bimetallic homogeneous catalysts containing azolates as bridging ligands

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esteruelas, M.A.; Garcia, M.P.; Lopez, A.M.

1991-01-01

The binuclear compounds (H(CO)(PPh{sub 3}){sub 2}Ru({mu}-bim)Ir(COD)) (1) (bim = 2,2{prime}-biimidazolate, COD = 1,5-cyclooctadiene) and (H(CO)(PPh{sub 3}){sub 2}Ru({mu}-pz){sub 2}Ir(TFB)) (2) (pz = pyrazolate, TFB = tetrafluorobenzobarrelene) are more active catalysts for the hydrogenation of cyclohexene than the mononuclear parent compounds (RuH(Hbim)(CO)(PPh{sub 3}){sub 2}), (Ir(Hbim)(COD)), (RuH(pa)(CO)(Hpz)(PPh{sub 3}){sub 2}), and (Ir(TFB)(Hpz){sub 2})BF{sub 4}. In the presence of 1, the reaction rate is first order with respect to the concentration of 1 and cyclohexene, second order with respect to hydrogen pressure, and inversely proportional to the concentration of added phosphine. For the reaction catalyzed by 2, the experimental data are in accordance with amore » rate expression of the form {minus}d(cyclohexene)/dt = k(2)(cyclohexene)P(H{sub 2}) (P(H{sub 2}) = hydrogen pressure). On the basis of the kinetic results and experimental evidence, the origin of the catalytic synergism is assigned to indirect cooperative effects between the metallic centers of the binuclear complexes. The kinetic investigation of the hydrogenation of cyclohexene catalyzed by (Ir({mu}-pz)(TFB)){sub 2} (3) is also reported, suggesting that the full catalytic cycle involves binuclear species.« less

The structures of the crystalline phase and columnar mesophase of rhodium (II) heptanoate and of its binary mixture with copper (II) heptanoate probed by EXAFS

NASA Astrophysics Data System (ADS)

Inb-Elhaj, M.; Guillon, D.; Skoulios, A.; Maldivi, P.; Giroud-Godquin, A. M.; Marchon, J.-C.

1992-12-01

EXAFS was used to investigate the local structure of the polar spines of rhodium (II) soaps in the columnar liquid crystalline state. It was also used to ascertain the degree of blending of the cores in binary mixtures of rhodium (II) and copper (II) soaps. For the pure rhodium soaps, the columns are shown to result from the stacking of binuclear metal-metal bonded dirhodium tetracarboxylate units bonded to one another by apical ligation of the metal atom of each complex with one of the oxygen atoms of the adjacent molecule. Mixtures of rhodium (II) and copper (II) soaps give a hexagonal columnar mesophase in which pure rhodium and pure copper columns are randomly distributed.

Comparison of reactivity of Pt(II) center in the mononuclear and binuclear organometallic diimineplatinum complexes toward oxidative addition of methyl iodide

NASA Astrophysics Data System (ADS)

Hashemi, Majid

2016-01-01

The reactivities of Pt(II) center in a series of organometallic mononuclear Pt(II), binuclear Pt(II) and binuclear mixed-valence Pt(II)-Pt(IV) complexes toward oxidative addition of MeI have been compared from a theoretical point of view. The nucleophilicity index and electron-donation power were calculated for each of these complexes. The energies of HOMO and dZ2 orbital were determined for these complexes. Very good correlations were found between logk2 (k2 is the experimentally determined second order rate constant for the oxidative addition of MeI on these complexes) and nucleophilicity index or electron-donation power for these complexes. The correlation between logk2 and the energy of HOMO or the energy of dZ2 orbital were also very good. The condensed-to-atom Fukui functions for electrophilic attack on these complexes showed that the Pt(II) center is the preferred site for the oxidative addition of MeI. All of these observations are in agreement with the proposed SN2 type mechanism in the oxidative addition of MeI on the Pt(II) center in these complexes.

Synthesis, characterization and properties of some divalent metal(II) complexes: Their electrochemical, catalytic, thermal and antimicrobial activity studies

NASA Astrophysics Data System (ADS)

Tümer, Mehmet; Ekinci, Duygu; Tümer, Ferhan; Bulut, Akif

2007-07-01

In this study, we synthesized the amine compound 2-(2-aminoethyliminomethyl)phenol (H 3A) as the starting material, and then we prepared the polydentate Schiff base ligands from the reactions of the amine compound (H 3A) with phtaldialdehyde (H 2L), 4-methyl-2,6-di-formlyphenol (H 3L 1) and 4- t-butyl-2,6-di-formylphenol (H 3L 2) in the ethanol solution. Moreover, the complexes Cd(II), Cu(II), Co(II), Ni(II), Zn(II) and Sn(II) of the ligands H 2L, H 3L 1 and H 3L 2 have been prepared. All compounds have been characterized by the analytical and spectroscopic methods. In addition, the magnetic susceptibility and molar conductance measurements have been made. The catalytic properties of the mono- and binuclear Co(II) and Cu(II) complexes have been studied on the 3,5-di- tert-butylcatechol (3,5-DTBC) and ascorbic acid (aa) as a substrate. The oxidative C-C coupling properties of the Co(II) and Cu(II) complexes have been investigated on the sterically hindered 2,6-di- tert-butylphenol (dtbp). The antimicrobial activity properties of the ligands and their mono- and binuclear complexes have been studied against the bacteria and fungi. The results have been compared to the antibacterial and fungi drugs. The TGA curves show that the decomposition takes place in three steps for all complexes. Electrochemical properties of the complexes Cu(II) and Ni(II) have been investigated for the first time in acetonitrile by cyclic voltammetry.

Binuclear ruthenium(III) bis(thiosemicarbazone) complexes: Synthesis, spectral, electrochemical studies and catalytic oxidation of alcohol

NASA Astrophysics Data System (ADS)

Mohamed Subarkhan, M.; Ramesh, R.

2015-03-01

A new series of binuclear ruthenium(III) thiosemicarbazone complexes of general formula [(EPh3)2(X)2Ru-L-Ru(X)2(EPh3)2] (where E = P or As; X = Cl or Br; L = NS chelating bis(thiosemicarbazone ligands) has been synthesized and characterized by analytical and spectral (FT-IR, UV-Vis and EPR). IR spectra show that the thiosemicarbazones behave as monoanionic bidentate ligands coordinating through the azomethine nitrogen and thiolate sulphur. The electronic spectra of the complexes indicate that the presence of d-d and intense LMCT transitions in the visible region. The complexes are paramagnetic (low spin d5) in nature and all the complexes show rhombic distortion around the ruthenium ion with three different 'g' values (gx ≠ gy ≠ gz) at 77 K. All the complexes are redox active and exhibit an irreversible metal centered redox processes (RuIII-RuIII/RuIV-RuIV; RuIII-RuIII/RuII-RuII) within the potential range of 0.38-0.86 V and -0.39 to -0.66 V respectively, versus Ag/AgCl. Further, the catalytic efficiency of one of the complexes [Ru2Cl2(AsPh3)4(L1)] (4) has been investigated in the case of oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of N-methylmorpholine-N-oxide(NMO) as co-oxidant. The formation of high valent RuVdbnd O species is proposed as catalytic intermediate for the catalytic cycle.

Synthesis, Characterization and Antibacterial Activity of 1,4-di[ aminomethylene carboxyl] phenylene (H2L) and its Complexes Co(II), Cu (II), Zn(II) and Cd (II)

NASA Astrophysics Data System (ADS)

Sultan, J. S.; Fezea, S. M.; Mousa, F. H.

2018-05-01

A binucleating tetradentate Schiff base ligand, 1,4- di[amino methylene carboxylic] phenylene (H2L) and its forth new binuclear complexes [Co(II), Cu(II), Zn(II) and Cd(II)] were prepared via reaction metal (II) chloride with ligand (H2L) using 2:1 (M:L) in ethanol solvent. The new ligand (H2L) and its complexes were characterized by elemental microanalysis (C.H.N), atomic absorption, chloride content, molar conductance’s magnetic susceptibility, FTIR UV- Vis spectral and, 1H, 13 C- NMR (for H2L). The antibacterial activity with bacteria activity with bacteria, Staphylococcus aureus, Bacillus and Esccherichia Coli were studied.

High-spin ribbons and antiferromagnetic ordering of a Mn(II)-biradical-Mn(II) complex.

PubMed

Fatila, Elisabeth M; Clérac, Rodolphe; Rouzières, Mathieu; Soldatov, Dmitriy V; Jennings, Michael; Preuss, Kathryn E

2013-09-11

A binuclear metal coordination complex of the first thiazyl-based biradical ligand 1 is reported (1 = 4,6-bis(1,2,3,5-dithiadiazolyl)pyrimidine; hfac =1,1,1,5,5,5,-hexafluoroacetylacetonato-). The Mn(hfac)2-biradical-Mn(hfac)2 complex 2 is a rare example of a discrete, molecular species employing a neutral bridging biradical ligand. It is soluble in common organic solvents and can be easily sublimed as a crystalline solid. Complex 2 has a spin ground state of S(T) = 4 resulting from antiferromagnetic coupling between the S(birad) = 1 biradical bridging ligand and two S(Mn) = 5/2 Mn(II) ions. Electrostatic contacts between atoms with large spin density promote a ferromagnetic arrangement of the moments of neighboring complexes in ribbon-like arrays. Weak antiferromagnetic coupling between these high-spin ribbons stabilizes an ordered antiferromagnetic ground state below 4.5 K. This is an unusual example of magnetic ordering in a molecular metal-radical complex, wherein the electrostatic contacts that direct the crystal packing are also responsible for providing an efficient exchange coupling pathway between molecules.

A novel ruthenium(II)-cobaloxime supramolecular complex for photocatalytic H2 evolution: Synthesis, characterisation, and mechanistic studies

PubMed Central

Cropek, Donald M.; Metz, Anja; Müller, Astrid M.; Gray, Harry B.; Horne, Toyketa; Horton, Dorothy C.; Poluektov, Oleg; Tiede, David M.; Weber, Ralph T.; Jarrett, William L.; Phillips, Joshua D.

2012-01-01

We report the synthesis and characterization of novel mixed-metal binuclear ruthenium(II)-cobalt(II) photocatalysts for hydrogen evolution in acidic acetonitrile. First, 2-(2′-pyridyl)benzothiazole (pbt), 1, was reacted with RuCl3·xH2O to produce [Ru(pbt)2Cl2] ·0.25CH3COCH3, 2, which was then reacted with 1,10-phenanthroline-5,6-dione (phendione), 3 in order to produce [Ru(pbt)2(phendione)](PF6)2·4H2O, 4. Compound 4 was then reacted with 4-pyridinecarboxaldehyde in order to produce [Ru(pbt)2(L-pyr)](PF6)2·9.5H2O, 5 (where L-pyr = (4-pyridine)oxazolo[4,5-f]phenanthroline). Compound 5 was then reacted with [Co(dmgBF2)2(H2O)2] (where dmgBF2 = difluorboryldimethylglyoximate) in order to produce the mixed-metal binuclear complex, [Ru(pbt)2(L-pyr)Co(dmgBF2)2(H2O)](PF6)2·11H2O·1.5CH3COCH3, 6. [Ru(Me2bpy)2(L-pyr)Co(dmgBF2)2(OH2)](PF6)2, 7 (where Me2bpy = 1,10-phenanthroline, 4,4′-dimethyl-2,2′-bipyridine) and [Ru(phen)2(L-pyr)Co(dmgBF2)2(OH2)](PF6)2, 8 were also synthesised. All complexes were characterized by elemental analysis, UV-visible absorption, 11B, 19F, and 59Co NMR, ESR spectroscopy, and cyclic voltammetry, where appropriate. Photocatalytic studies carried out in acidified acetonitrile demonstrated constant hydrogen generation longer than a 42 hour period as detected by gas chromatography. Time resolved spectroscopic measurements were performed on compound 6, which proved an intramolecular electron transfer from an excited Ru(II) metal centre to the Co(II) metal centre via the bridging L-pyr ligand. This resulted in the formation of a cobalt(I)-containing species that is essential for the production of H2 gas in the presence of H+ ions. A proposed mechanism for the generation of hydrogen is presented. PMID:23001132

Formation of reactive oxygen by N2O decomposition over binuclear cationic sites of Fe-ferrierite zeolite: Periodic DFT + U study

NASA Astrophysics Data System (ADS)

Avdeev, Vasilii I.; Bedilo, Alexander F.

2018-03-01

The electronic nature of sites over Fe-ferrierite zeolite stabilizing active α-oxygen is analyzed by the periodic DFT + U approach. It is shown that two antiferromagnetically coupled Fe2+ cations with bridging OH-bonds form a stable bi-nuclear site of the [Fe2+<2OH>Fe2+] doped FER complex. Frontier orbitals of this complex populated by two electrons with minority spins are localized in the bandgap. As a result, [Fe2+<2OH>Fe2+] unit acquires the properties of a binuclear Lewis acid dipolarophile for 1,3-dipole N2O. First reaction step of N2O decomposition follows the Huisgen‧s concept of the 1,3-dipolar cycloaddition concept followed by the formation of reactive oxygen species Fesbnd O.

Mononuclear thiocyanate containing nickel(II) and binuclear azido bridged nickel(II) complexes of N4-coordinate pyrazole based ligand: Syntheses, structures and magnetic properties

NASA Astrophysics Data System (ADS)

Solanki, Ankita; Monfort, Montserrat; Kumar, Sujit Baran

2013-10-01

Two mononuclear nickel(II) complexes [NiL1(NCS)2] (1) and [NiL2(NCS)2] (2) and two azido bridged binuclear nickel(II) complexes [Ni(()2()2] (3) and [Ni(()2()2] (4), where L1, L2, L1‧ and L2‧ are N,N-diethyl-N‧,N‧-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)ethane-1,2-diamine (L1), N,N-bis((1H-pyrazol-1-yl)methyl)-N‧,N‧-diethylethane-1,2-diamine (L2), N,N-diethyl-N‧-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)ethane-1,2-diamine (L1‧) and N-((1H-pyrazol-1-yl)methyl)-N‧,N‧-diethylethane-1,2-diamine (L2‧) have been synthesized and characterized by microanalyses and physico-chemical methods. Single crystal X-ray diffraction analyses revealed that complexes 1 and 2 are mononuclear NCS- containing Ni(II) complex with octahedral geometry and complexes 3 and 4 are end-on (μ-1,1) azido bridged binuclear Ni(II) complexes with distorted octahedral geometry. Variable temperature magnetic studies of the complexes 3 and 4 display ferromagnetic interaction with J values 19 and 32 cm-1, respectively.

Spectral characterization, thermal and biological activity studies of Schiff base complexes derived from 4,4‧-Methylenedianiline, ethanol amine and benzil

NASA Astrophysics Data System (ADS)

Emam, Sanaa Moustafa

2017-04-01

Some new metal(II) complexes of asymmetric Schiff base ligand were prepared by template technique. The shaped complexes are in binuclear structures and were explained through elemental analysis, molar conductivity, various spectroscopic methods (IR, U.V-Vis, XRD, ESR), thermal (TG) and magnetic moment measurements. The IR spectra were done demonstrating that the Schiff base ligand acts as neutral tetradentate moiety in all metal complexes. The electronic absorption spectra represented octahedral geometry for all complexes, while, the ESR spectra for Cu(II) complex showed axially symmetric g-tensor parameter with g׀׀ > g⊥ > 2.0023 indicating to 2B1g ground state with (dx2-y2)1 configuration. The nature of the solid residue created from TG estimations was affirmed utilizing IR and XRD spectra. The biological activity of the prepared complexes was studied against Land Snails. Additionally, the in vitro antitumor activity of the synthesized complexes with Hepatocellular Carcinoma cell (Hep-G2) was examined. It was observed that Zn(II) complex (5), exhibits a high inhibition of growth of the cell line with IC50 of 7.09 μg/mL.

A Binuclear 1,1'-Bis(boratabenzene) Complex: Unprecedented Intramolecular Metal-Metal Communication through a B-B Bond.

PubMed

Braunschweig, Holger; Demeshko, Serhiy; Ewing, William C; Krummenacher, Ivo; Macha, Bret B; Mattock, James D; Meyer, Franc; Mies, Jan; Schäfer, Marius; Vargas, Alfredo

2016-06-27

We report the synthesis of the first 1,1'-bis(boratabenzene) species by tetrabromodiborane(4)-induced ring-expansion reactions of cobaltocene. Six equivalents of cobaltocene are required as the species plays the dual role of reagent and reductant to yield [{(η(5) -C5 H5 )Co}2 {μ:η(6) ,η(6) -(BC5 H5 )2 }]. The formally dianionic bis(boratabenzene) moiety with a boron-boron single bond can be viewed as a symmetric dimer of the parent boratabenzene anion as well as the first example of a diboron analogue of biphenyl. The solution electrochemistry of the bimetallic complex shows four stepwise redox events, indicating significant intramolecular interaction between the cobalt ions across the 1,1'-bis(boratabenzene) unit. The magnetic properties, as investigated by variable-temperature SQUID magnetometry, reveal weak intramolecular antiferromagnetic interactions. Density functional theory calculations support the experimental results and add insight into the various electronic states of the complex. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural and magnetic characterization of a tetranuclear copper(II) cubane stabilized by intramolecular metal cation-π interactions.

PubMed

Papadakis, Raffaello; Rivière, Eric; Giorgi, Michel; Jamet, Hélène; Rousselot-Pailley, Pierre; Réglier, Marius; Simaan, A Jalila; Tron, Thierry

2013-05-20

A novel tetranuclear copper(II) complex (1) was synthesized from the self-assembly of copper(II) perchlorate and the ligand N-benzyl-1-(2-pyridyl)methaneimine (L(1)). Single-crystal X-ray diffraction studies revealed that complex 1 consists of a Cu4(OH)4 cubane core, where the four copper(II) centers are linked by μ3-hydroxo bridges. Each copper(II) ion is in a distorted square-pyramidal geometry. X-ray analysis also evidenced an unusual metal cation-π interaction between the copper ions and phenyl substituents of the ligand. Calculations based on the density functional theory method were used to quantify the strength of this metal-π interaction, which appears as an important stabilizing parameter of the cubane core, possibly acting as a driving parameter in the self-aggregation process. In contrast, using the ligand N-phenethyl-1-(2-pyridyl)methaneimine (L(2)), which only differs from L(1) by one methylene group, the same synthetic procedure led to a binuclear bis(μ-hydroxo)copper(II) complex (2) displaying intermolecular π-π interactions or, by a slight variation of the experimental conditions, to a mononuclear complex (3). These complexes were studied by X-ray diffraction techniques. The magnetic properties of complexes 1 and 2 are reported and discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lingerfelt, David B.; Lestrange, Patrick J.; Radler, Joseph J.

Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a binuclear platinum complex, where a persistent periodic beating in the transient absorption signal’s anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of binuclear platinum complexes exhibiting a range of interplatinum distances. Results suggest that the long-lived coherence can only result when competitive electronic couplings are inmore » balance. At longer Pt-Pt distances, the electronic couplings between the two halves of the binuclear system weaken, and exciton localization and recombination is favored on short time scales. For short Pt-Pt distances, electronic couplings between the states in the coherent superposition are stronger than the coupling with other excitonic states, leading to long-lived coherence.« less

Corrigendum to "Synthesis, structural features, and methyl methacrylate polymerisation of binuclear zinc(II) complexes with tetradentate pyrazolyl ligands" [J. Mol. Struct. 1063 (2014) 70-76

NASA Astrophysics Data System (ADS)

Kim, Sunghoon; Kim, Dongil; Lee, Ha-Jin; Lee, Hyosun

2015-05-01

The authors regret to inform that 4,4‧-bis-(N,N-di(1H-pyrazolyl-1-methyl)phenyl)methane (L2) and its binuclear 4,4‧-bis-(N,N-di-(1H-pyrazolyl-1-methyl)phenyl)methane(dichloro)Zn(II) complex, namely, [L2Zn2Cl4] in the paper were published as the thesis for the degree of master in the Department of Chemistry at Kyungpook National University in 2003.

Metal complexes of fluorophosphines. 13. Reaction of fac-(CH/sub 3/CN)/sub 3/Mo(CO)/sub 3/ with (methylamino)bis(difluorophosphine). X-ray crystal structure analysis of a novel binuclear molybdenum fluorophosphine carbonyl complex with a bridging chlorine atom: (CO)/sub 2/Mo(/sup +/-CH/sub 3/N(PF/sub 2/)/sub 2/)/sub 2/(. mu. -PF/sub 2/)(. mu. -Cl)Mo(CO)(PF/sub 2/NHCH/sub 3/)

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, R.B.; Shimura, M.; Brown, G.M.

1984-01-01

Reaction of fac-(CH/sub 3/CN)/sub 3/Mo(CO)/sub 3/ with CH/sub 3/N(PF/sub 2/)/sub 2/ in acetonitrile solution at room temperature gives white, volatile, crystalline fac-(CH/sub 3/N(PF/sub 2/)/sub 2/)/sub 2/Mo(CO)/sub 3/, containing one monodentate and one bidentate CH/sub 3/N(PF/sub 2/)/sub 2/ ligand. The same reactants in boiling acetonitrile give yellow (CH/sub 3/N(PF/sub 2/)/sub 2/)/sub 4/Mo/sub 2/(CO)/sub 3/ in considerably better yield than the previously reported preparation of this binuclear complex from the cycloheptatriene complex C/sub 7/H/sub 8/Mo(CO)/sub 3/ and CH/sub 3/N(PF/sub 2/)/sub 2/ in boiling methylcyclohexane. Reaction in acetonitrile solution of fac-(CH/sub 3/CN)/sub 3/Mo(CO)/sub 3/ with CH/sub 3/N(PF/sub 2/)/sub 2/ containing about 0.2% HClmore » gives brown-red, volatile (CO)/sub 2/Mo(/sup +/-CH/sub 3/N(PF/sub 2/)/sub 2/)/sub 2/(..mu..-PF/sub 2/)(..mu..-Cl)-Mo(CO)(PF/sub 2/NHCH/sub 3/), whose composition and structure were established by single-crystal X-ray structure analysis. This novel quadruply bridged binuclear complex is obtained in considerably better yield from the reaction of (CH/sub 3/N(PF/sub 2/)/sub 2/)/sub 3/Mo/sub 2/(CO)/sub 5/ with ((C/sub 2/H/sub 5/)/sub 3/NH)Cl in acetonitirle solution. The complex has a Mo-Mo bond 2.975 A in length. Crystal data: monoclinic, space group P2/sub 1//c, a = 17.546 (4) A, b = 9.725 (2) A, c = 14.558 (3), ..beta.. = 107.20 (2)/sup 0/, Z = 4. 30 references, 2 figures, 3 tables.« less

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.

New coordination polymers from 1D chain, 2D layer to 3D framework constructed from 1,2-phenylenediacetic acid and 1,3-bis(4-pyridyl)propane flexible ligands

NASA Astrophysics Data System (ADS)

Xin, Ling-Yun; Liu, Guang-Zhen; Wang, Li-Ya

2011-06-01

The hydrothermal reactions of Cd, Zn, or Cu(II) acetate salts with H 2PHDA and BPP flexible ligands afford three new coordination polymers, including [Cd(PHDA)(BPP)(H 2O)] n(1), [Zn(PHDA)(BPP)] n(2), and [Cu 2(PHDA) 2(BPP)] n(3) (H 2PHDA=1,2-phenylenediacetic acid, BPP=1,3-bis(4-pyridyl)propane). The single-crystal X-ray diffractions reveal that all three complexes feature various metal carboxylate subunits extended further by the BPP ligands to form a diverse range of structures, displaying a remarked structural sensitivity to metal(II) cation. Complex 1 containing PHDA-bridged binuclear cadmium generates 1D double-stranded chain, complex 2 results in 2D→2D interpenetrated (4,4) grids, and complex 3 displays a 3D self-penetrated framework with 4 86 68 rob topology. In addition, fluorescent analyses show that both 1 and 2 exhibit intense blue-violet photoluminescence in the solid state.

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

NASA Astrophysics Data System (ADS)

Abou-Hussein, Azza A.; Linert, Wolfgang

2014-01-01

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

Mono and binuclear ruthenium(II) complexes containing 5-chlorothiophene-2-carboxylic acid ligands: Spectroscopic analysis and computational studies

NASA Astrophysics Data System (ADS)

Swarnalatha, Kalaiyar; Kamalesu, Subramaniam; Subramanian, Ramasamy

2016-11-01

New Ruthenium complexes I, II and III were synthesized using 5-chlorothiophene-2-carboxylic acid (5TPC), as ligand and the complexes were characterized by elemental analysis, FT-IR, 1H, 13C NMR, and mass spectroscopic techniques. Photophysical and electrochemical studies were carried out and the structures of the synthesized complex were optimized using density functional theory (DFT). The molecular geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energies and Mulliken atomic charges of the molecules are determined at the B3LYP method and standard 6-311++G (d,p) basis set starting from optimized geometry. They possess excellent stabilities and their thermal decomposition temperatures are 185 °C, 180 °C and 200 °C respectively, indicating that the metal complexes are suitable for the fabrication processes of optoelectronic devices.

[Transport of dinitrosyl iron complexes into animal lungs].

PubMed

Mojokina, G N; Elistratova, N A; Mikoyan, V D; Vanin, A F

2015-01-01

Effective accumulation of binuclear dinitrosyl iron complexes with glutathione was shown after a subcutaneous para lymphatic injection of an aqueous solution of a dinitrosyl-iron complex into animal lung tissue at a single-dose of 2 micromoles per kilogram two times a day with a 2-h interval. Two hours later after the administration was repeated the concentration of these complexes was 16 micromoles per kilogram of tissue dropping down for the last two hours to 7 micromoles per kilogram of tissue. At one dose injection of binuclear dinitrosyl iron complexes with glutathione their concentration in 2 and 4 hours was two times lower than in the previous experiments. Presumably at the obtained concentration of dinitrosyl iron complexes a bactericidal effect in lungs can be observed against mycobacterium tuberculosis and rapidly proliferating lung tumors.

Structure and properties of bis(1-phenyl-1h-tetrazole-5-thiolate)diiron tetranitrosyl

NASA Astrophysics Data System (ADS)

Sanina, N. A.; Kozub, G. I.; Kondrat'eva, T. A.; Shilov, G. V.; Korchagin, D. V.; Emel'yanova, N. S.; Poleshchuk, O. Kh.; Chernyak, A. V.; Kulikov, A. V.; Mushenok, F. B.; Ovanesyan, N. S.; Aldoshin, S. M.

2013-06-01

New tetranitrosyl binuclear iron complex [Fe2(SС7H5N4)2(NO)4] (I) has been synthesized by interaction of aqueous solutions of anionic salts [Fе(S2O3)2(NO)2]3- and [SС7H5N4]-. The latter one was synthesized by reduction of bis-(1-phenyl-1H-tetrazole-5-yl) disulfide with hydrazine hydrate in ethanol at T = 25 °C. Molecular and crystalline structure of I was determined by X-ray analysis; the complex has binuclear structure of "μ-SCN" type with ˜4.02 Å between the iron atoms. Shortened О⋯О contacts (2.81 Å) between the NO groups of similar type are observed. Parameters of Mössbauer spectrum for I are: isomer shift δFe = 0.311(1) mm/s, quadrupole splitting ΔEQ = 1.044(1) mm/s, line width Γ = 0.267(1) mm/s at 85 K. From SQUID magnetometry data, the temperature and field dependences of the magnetic moment of I are well described in the frame of a simple model of binuclear iron complex with magnetic centers S1 = S2 = ½. In solution, binuclear structure of the complex remains, though the NO groups are non-equivalent. For solutions of I five-line hyperfine structure of spectrum (HFS) is observed, g-factor = 2.03. For polycrystals of I, no HFS was observed due to averaged exchange interaction between the electron spins of adjacent complexes. In polycrystals of I, the number of spins per one binuclear complex is <2, this being the evidence of antiferromagnetic exchange interaction of unpaired electrons of two iron atoms. The average number of spins in crystals (0.65) and solutions (0.55) are close. The maximum amount of NO generated by I in 1% dimethylsulfoxide (DMSO) aqueous solution is ˜13.8 nM, it halves in 8 min after decomposition starts, and reaches ˜3.8 nM in anaerobic conditions at Т = 25 °С, pH 7.0. This is due, according to quantum-chemical calculations, to the presence of a more stable Fesbnd NO bond in I than in its isostructural analog - nitrosyl iron complex with 1-methyltetrazole-5-yl (II).

Oxidized derivatives of Octopus vulgaris and Carcinus aestuarii hemocyanins at pH 7.5 and related models by x-ray absorption spectroscopy.

PubMed Central

Borghi, Elena; Solari, Pier Lorenzo; Beltramini, Mariano; Bubacco, Luigi; Di Muro, Paolo; Salvato, Benedetto

2002-01-01

The binuclear copper sites of the met and met-azido derivatives of Octopus vulgaris and Carcinus aestuarii hemocyanins at pH 7.5 were characterized by high-resolution x-ray absorption spectroscopy in the low energy region (XANES) and in the higher region (EXAFS). The accuracy of the analysis of the data was tested with two mononuclear and six binuclear copper(II) complexes of the poly(benzimidazole) ligand systems 2-BB, L-5,5 and L-6,6 (Casella et al., 1993, Inorg. Chem. 32:2056-2067; 1996, Inorg. Chem. 35:1101-1113). Their structural and reactivity properties are related to those of the protein's derivatives. The results obtained for those models with resolved x-ray structure (the 2-BB-aquo and azido mononuclear complexes, and the binuclear L-5,5 Cu(II)-bis(hydroxo) (Casella et al., unpublished)), extends the validity of our approach to the other poly(benzimidazole)-containing complexes and to the hemocyanin derivatives. Comparison between the protein's and the complexes' data, support a description of the met-derivatives as a five-coordinated O-bridged binuclear copper(II) center and favors, for both species, a bis(hydroxo) structure with a 3-A Cu-Cu distance. For O. vulgaris met-azido derivative a mu-1,3 bridging mode for the ligand appears the most likely. The structural situation of C. aestuarii met-azido-derivative is less clear: a mu-1,1 mode is favored, but a terminal mode cannot be excluded. PMID:12023249

Crystal structure of aqua-1κO-{μ-2-[(2-hydroxy-ethyl)methylamino]ethanolato-2:1κ(4) O (1),N,O (2):O (1)}[μ-2,2'-(methylimino)diethanolato-1:2κ(4) O,N,O':O]dithiocyanato-1κN,2κN-chromium(III)copper(II).

PubMed

Rusanova, Julia A; Semenaka, Valentina V; Dyakonenko, Viktoriya V; Shishkin, Oleg V

2015-09-01

The title compound, [CrCu(C5H11NO2)(C5H12NO2)(NCS)2(H2O)] or [Cr(μ-mdea)Cu(μ-Hmdea)(NCS)2H2O], (where mdeaH2 is N-methylethanolamine, C5H13NO2) is formed as a neutral heterometal Cu(II)/Cr(III) complex. The mol-ecular structure of the complex is based on a binuclear {CuCr(μ-O)2} core. The coordination environment of each metal atom involves the N,O,O atoms of the tridentate ligand, one bridging O atom of the ligand and the N atom of the thio-cyanato ligands. The Cu(II) ion adopts a distorted square-pyramidal coordination while the Cr(III) ion has a distorted octa-hedral coordination geometry completed by the aqua ligand. In the crystal, the binuclear complexes are linked via two pairs of O-H⋯O hydrogen bonds to form inversion dimers, which are arranged in columns parallel to the a axis. In the μ-mdea ligand two -CH2 groups and the methyl group were refined as disordered over two sets of sites with equal occupancies. The structure was refined as a two-component twin with a twin scale factor of 0.242 (1).

Nitric oxide production by visible light irradiation of aqueous solution of nitrosyl ruthenium complexes.

PubMed

Sauaia, Marília Gama; de Lima, Renata Galvão; Tedesco, Antonio Claudio; da Silva, Roberto Santana

2005-12-26

[Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](PF(6))(5) (L is NH(3), py, or 4-acpy) was prepared with good yields in a straightforward way by mixing an equimolar ratio of cis-[Ru(NO(2))(bpy)(2)(NO)](PF(6))(2), sodium azide (NaN(3)), and trans-[RuL(NH(3))(4)(pz)] (PF(6))(2) in acetone. These binuclear compounds display nu(NO) at ca. 1945 cm(-)(1), indicating that the nitrosyl group exhibits a sufficiently high degree of nitrosonium ion (NO(+)). The electronic spectrum of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex in aqueous solution displays the bands in the ultraviolet and visible regions typical of intraligand and metal-to-ligand charge transfers, respectively. Cyclic voltammograms of the binuclear complexes in acetonitrile give evidence of three one-electron redox processes consisting of one oxidation due to the Ru(2+/3+) redox couple and two reductions concerning the nitrosyl ligand. Flash photolysis of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex is capable of releasing nitric oxide (NO) upon irradiation at 355 and 532 nm. NO production was detected and quantified by an amperometric technique with a selective electrode (NOmeter). The irradiation at 532 nm leads to NO release as a consequence of a photoinduced electron transfer. All species exhibit similar photochemical behavior, a feature that makes their study extremely important for their future application in the upgrade of photodynamic therapy in living organisms.

Synthesis, characterization, biological evaluation and docking studies of macrocyclic binuclear manganese(II) complexes containing 3,5-dinitrobenzoyl pendant arms

NASA Astrophysics Data System (ADS)

Arthi, P.; Shobana, S.; Srinivasan, P.; Mitu, L.; Kalilur Rahiman, A.

2015-05-01

A series of bis(phenoxo) bridged binuclear manganese(II) complexes of the type [Mn2L1-3](ClO4)2 (1-3) containing 3,5-dinitrobenzoyl pendant-arms have been synthesized by cyclocondensation of 2,6-diformyl-4-R-phenols (where R = sbnd CH3, sbnd C(CH3)3 or sbnd Br) with 2,2‧-3,5-dinitrobenzoyliminodi(ethylamine) trihydrochloride in the presence of manganese(II) perchlorate. The IR spectra of complexes indicate the presence of uncoordinated perchlorate anions. The UV-Vis spectra of complexes suggest the distorted octahedral geometry around manganese(II) nuclei. The EPR spectra of Mn(II) complexes show a broad signal with g value 2.03-2.04, which is characteristic for octahedral high spin Mn2+ complex. The observed room temperature magnetic moment values of the Mn(II) complexes (5.60-5.62 B.M.) are less than the normal value (5.92 B.M.), indicating weak antiferromagnetic coupling interaction between the two metal ions. Electrochemical studies of the complexes show two distinct quasi-reversible one electron transfer processes in the cathodic (E1pc = -0.73 to -0.76 V, E2pc = -1.30 to -1.36 V), and anodic (E1pa = 1.02-1.11 V, E2pa = 1.32-1.79 V) potential regions. Antibacterial efficacy of complexes have been screened against four Gram (-ve) and two Gram (+ve) bacterial strains. The DNA interaction studies suggest that these complexes bind with CT-DNA by intercalation, giving the binding affinity in the order 1 > 2 > 3. All the complexes display significant cleavage activity against circular plasmid pBR322 DNA. Docking simulation was performed to insert complexes into the crystal structure of EGFR tyrosine kinase and B-DNA at active site to determine the probable binding mode.

Effect of silicic acid on arsenate and arsenite retention mechanisms on 6-L ferrihydrite: A spectroscopic and batch adsorption approach

PubMed Central

Gao, Xiaodong; Root, Robert A.; Farrell, James; Ela, Wendell; Chorover, Jon

2014-01-01

The competitive adsorption of arsenate and arsenite with silicic acid at the ferrihydrite-water interface was investigated over a wide pH range using batch sorption experiments, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) modeling. Batch sorption results indicate that the adsorption of arsenate and arsenite on the 6-L ferrihydrite surface exhibits a strong pH-dependence, and the effect of pH on arsenic sorption differs between arsenate and arsenite. Arsenate adsorption decreases consistently with increasing pH; whereas arsenite adsorption initially increases with pH to a sorption maximum at pH 7–9, where after sorption decreases with further increases in pH. Results indicate that competitive adsorption between silicic acid and arsenate is negligible under the experimental conditions; whereas strong competitive adsorption was observed between silicic acid and arsenite, particularly at low and high pH. In-situ, flow-through ATR-FTIR data reveal that in the absence of silicic acid, arsenate forms inner-sphere, binuclear bidentate, complexes at the ferrihydrite surface across the entire pH range. Silicic acid also forms inner-sphere complexes at ferrihydrite surfaces throughout the entire pH range probed by this study (pH 2.8 – 9.0). The ATR-FTIR data also reveal that silicic acid undergoes polymerization at the ferrihydrite surface under the environmentally-relevant concentrations studied (e.g., 1.0 mM). According to ATR-FTIR data, arsenate complexation mode was not affected by the presence of silicic acid. EXAFS analyses and DFT modeling confirmed that arsenate tetrahedra were bonded to Fe metal centers via binuclear bidentate complexation with average As(V)-Fe bond distance of 3.27 Å. The EXAFS data indicate that arsenite forms both mononuclear bidentate and binuclear bidentate complexes with 6-L ferrihydrite as indicated by two As(III)-Fe bond distances of ~2.92–2.94 and 3.41–3.44 Å, respectively. The As-Fe bond distances in both arsenate and arsenite EXAFS spectra remained unchanged in the presence of Si, suggesting that whereas Si diminishes arsenite adsorption preferentially, it has a negligible effect on As-Fe bonding mechanisms. PMID:25382933

Synthesis and Crystal and Electronic Structures of the Dinuclear Platinum Compounds [PEtPh(3)](2)[Pt(2)(&mgr;-PPh(2))(2)(C(6)F(5))(4)] and [Pt(2)(&mgr;-PPh(2))(2)(C(6)F(5))(4)]: A Computational Study by Density Functional Theory.

PubMed

Alonso, Ester; Casas, José M.; Cotton, F. Albert; Feng, Xuejung; Forniés, Juan; Fortuño, Consuelo; Tomas, Milagros

1999-11-01

The electrolytic behavior of the dinuclear complexes [NBu(4)](2)[MM'(&mgr;-PPh(2))(2)(C(6)F(5))(4)] (M = M' = Pt (1), Pd (1a); M = Pt, M' = Pd (1b)) has been studied, showing electrochemically irreversible oxidation and related reduction processes. The chemical oxidation of the binuclear compound for M = M' = Pt, results in the formation of the binuclear Pt(III) compound [Pt(2)(&mgr;-PPh(2))(2)(C(6)F(5))(4)]. The crystal structure analysis of both complexes has been carried out, showing very similar structures with similar Pt-C and Pt-P distances and analogous skeletons. However the Pt-Pt distances are very different, 3.621(1) Å for the Pt(II) compound and 2.7245(7) Å for the Pt(III) derivative (as are the parameters geometrically related to this Pt-Pt distance), suggesting that, in the Pt(III) compound, there is a strong Pt-Pt bond. Results of DFT calculations on [Pt(2)(&mgr;-PH(2))(2)(C(6)F(5))(4)](n)()(-) (n = 2, 0) agree very well with the crystallographic data and indicate that, in the Pt(III) compound, there is approximately a single sigma bond between the metal atoms.

Cd(II) complexes with different nuclearity and dimensionality based on 3-hydrazino-4-amino-1,2,4-triazole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Cai-Xia; Zhang, Jian-Guo, E-mail: zjgbit@bit.edu.cn; Yin, Xin

2015-03-15

A series of zero- to two-dimensional Cd(II) coordination compounds have been synthesized by the reaction of Cd(II) salts and 3-hydrazino-4-amino-1,2,4-triazole di-hydrochloride (HATr·2HCl). [CdCl{sub 2}(HATr){sub 2}] (1) and [Cd{sub 2}Cl{sub 4}(HATr){sub 2}(H{sub 2}O){sub 2}] (2) have discrete mononuclear and binuclear structures, respectively. [Cd(HATr){sub 2}(ClO{sub 4}){sub 2}]{sub n} (3) presents polymeric 1-D chain and [Cd{sub 2}(NO{sub 3}){sub 2}Cl{sub 2}(HATr){sub 2}]{sub n} (4) shows 2-D frameworks. All Cd(II) ions exhibit distorted octahedral configurations in 1–3, whilst both hexa and heptacoordinated Cd(II) are formed in 4. The HATr ligands adopt chelating coordinated mode in 1, while tri-dentate bridging–chelating mode in 2–4. The chloride ionmore » is a mono-coordinated ligand in 1 and 2, but it bridges two adjacent metal ions in 4. Furthermore, thermal behaviors have been investigated and the results reveal that all complexes have good thermal stability. The impact sensitivity test indicates that complex 3 is sensitive to impact stimuli. - Graphical abstract: Four Cd(II) complexes based on 3-hydrazino-4-amino-1,2,4-triazole ligands exhibit diverse structures from mononuclear to 2D networks. - Highlights: • Cd(II) complexes containing 3-hydrazino-4-amino-1,2,4-triazole ligands. • Mononuclear, binuclear, 1-D and 2-D structures. • Good thermal stability. • Thermal decomposition kinetics.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xiao-Ling; Liu, Guang-Zhen, E-mail: gzliuly@126.com; Xin, Ling-Yun

Two topologically new Mn(II) coordination polymers, namely ([Mn{sub 2}(H{sub 4}ipca)(4,4′-bpy){sub 1.5}(CH{sub 3}CH{sub 2}OH){sub 0.5}(H{sub 2}O){sub 1.5}]·0.5CH{sub 3}CH{sub 2}OH·2.5H{sub 2}O){sub n} (1) and (Mn{sub 4}(H{sub 4}ipca){sub 2}(bze)(H{sub 2}O){sub 4}){sub n} (2) were prepared by the solvothermal reactions of Mn(II) acetate with 5-(2’,3’-dicarboxylphenoxy)isophthalic acid (H{sub 4}ipca) in the presence of different N-donor coligands (4,4′-bpy=4,4′-bipyridyl and bze=1, 4-bis(1-imidazoly)benzene). The single crystal X-ray diffractions reveal that two complexes display 3D metal-organic frameworks with binuclear and tetranuclear Mn(II) units, respectively. Complex 1 features a (3,4,6)-connected porous framework based on dinuclear Mn(II) unit with the (4.5{sup 2}){sub 2}(4{sup 2}.6{sup 8}.8{sup 3}.9{sup 2})(5{sup 2}.8.9{sup 2}.10) new topology,more » and complex 2 possesses a (3,8)-connected network based on tetranuclear Mn(II) unit with the (4{sup 2}.6){sub 2}(4{sup 4}.6{sup 14}.7{sup 7}.8{sup 2}.9) new topology. Magnetic analyses indicate that both two compounds show weak antiferromagnetic interactions within binuclear and tetranuclear Mn(II) units. - Graphical abstract: Two topologically new Mn(II) metal-organic frameworks with dinuclear and tetranuclear Mn(II) units respectively were assembled by using 5-(2′,3′-Dicarboxylphenoxy)isophthalic acid and N-donor ancillary coligands. Magnetic analysis revealed the existence of dominant antiferromagnetic interactions within the polynuclear Mn(II) units. - Highlights: • Mixed ligand strategy produces two topologically new MOFs with dinuclear and tetranuclear Mn(II) respectively. • Magnetic fitting gives weak antiferromagnetic interactions within the polynuclear Mn(II) units.« less

Two binuclear cyanide-bridged Cr(III)-Mn(III) complexes based-on [Cr(2,2'-bipy)(CN)4]- building block: synthesis, crystal structures and magnetic properties.

PubMed

Zhanga, Daopeng; Kong, Lingqian; Zhang, Hongyan

2015-01-01

Tetracyanide building block [Cr(2,2'-bipy)(CN)(4)]- and two bicompartimental Schiff-base based manganese(III) compounds have been employed to assemble cyanide-bridged heterometallic complexes, resulting in two cyanide-bridged CrIII-MnIII complexes: [Mn(L(1))(H(2)O)][Cr(2,2'-bipy)(CN)(4)]·CH(3)OH·2.5H(2)O (1) and [Mn(L(2))(H(2)O)][Cr(2,2'-bipy)(CN)(4)]·CH(3)OH·(3)H(2)O (2) (L1 = N,N'-(1,3-propylene)-bis(3-methoxysalicylideneiminate), L2 = N,N'-ethylene-bis(3-ethoxysalicylideneiminate)). Single X-ray diffraction analysis shows their similar cyanide-bridged binuclear structures, in which the cyanide precursor acting as monodentate ligand connects the manganese(III) ion. The binuclear complexes are self-complementary through coordinated aqua ligand and the free O4 compartment from the neighboring complex, giving H-bond linking dimer structure. Investigation over magnetic properties reveals the antiferromagnetic magnetic coupling between the cyanide-bridged Cr(III) and Mn(III) ions. A best-fit to the magnetic susceptibilities of these two complexes leads to the magnetic coupling constants J = -5.95 cm(-1), j = -0.61 cm(-1) (1) and J = -4.15 cm(-1), j = -0.57 cm(-1) (2), respectively.

Alkoxy bridged binuclear rhenium (I) complexes as a potential sensor for β-amyloid aggregation.

PubMed

Sathish, Veerasamy; Babu, Eththilu; Ramdass, Arumugam; Lu, Zong-Zhan; Velayudham, Murugesan; Thanasekaran, Pounraj; Lu, Kuang-Lieh; Rajagopal, Seenivasan

2014-12-01

Alkoxy bridged binuclear rhenium(I) complexes are used as a probe for the selective and sensitive detection of aggregation of β-amyloid fibrils that are consorted with Alzheimer's disease (AD). The strong binding of the complexes is affirmed by the fluorescence enhancement and calculated binding constant value in the order of 10(5)M(-1) is obtained from the Scatchard plots. The binding of β-amyloid can be attributed to π-π stacking interaction of naphthalene moiety present in rhenium(I) complexes, and it is supported by docking studies. The selectivity is quite high towards other proteins and the formation of fibrils can be observed in the range of 30-40 nm through the AFM and TEM techniques. Copyright © 2014 Elsevier B.V. All rights reserved.

Two novel macroacyclic schiff bases containing bis-N 2O 2 donor set and their binuclear complexes: synthesis, spectroscopic and magnetic properties

NASA Astrophysics Data System (ADS)

Karaoglu, Kaan; Baran, Talat; Serbest, Kerim; Er, Mustafa; Degirmencioglu, Ismail

2009-03-01

Herein, we report two novel macroacyclic Schiff bases derived from tetranaphthaldehyde derivative compound and their binuclear Mn(II), Ni(II), Cu(II) and Zn(II) complexes. The structures of the compounds have been proposed by elemental analyses, spectroscopic data i.e. IR, 1H and 13C NMR, UV-Vis, electrospray ionisation mass spectra, molar conductivities and magnetic susceptibility measurements. The stoichiometries of the complexes derived from mass and elemental analysis correspond to the general formula [M 2L(ClO 4) n](ClO 4) 4-n, (where M is Mn(II), Ni(II), Cu(II), Zn(II) and L represents the Schiff base ligands).

Crystal structure of aqua-1κO-{μ-2-[(2-hydroxy­ethyl)methylamino]ethanolato-2:1κ4 O 1,N,O 2:O 1}[μ-2,2′-(methylimino)diethanolato-1:2κ4 O,N,O′:O]dithiocyanato-1κN,2κN-chromium(III)copper(II)

PubMed Central

Rusanova, Julia A.; Semenaka, Valentina V.; Dyakonenko, Viktoriya V.; Shishkin, Oleg V.

2015-01-01

The title compound, [CrCu(C5H11NO2)(C5H12NO2)(NCS)2(H2O)] or [Cr(μ-mdea)Cu(μ-Hmdea)(NCS)2H2O], (where mdeaH2 is N-methylethanolamine, C5H13NO2) is formed as a neutral heterometal CuII/CrIII complex. The mol­ecular structure of the complex is based on a binuclear {CuCr(μ-O)2} core. The coordination environment of each metal atom involves the N,O,O atoms of the tridentate ligand, one bridging O atom of the ligand and the N atom of the thio­cyanato ligands. The CuII ion adopts a distorted square-pyramidal coordination while the CrIII ion has a distorted octa­hedral coordination geometry completed by the aqua ligand. In the crystal, the binuclear complexes are linked via two pairs of O—H⋯O hydrogen bonds to form inversion dimers, which are arranged in columns parallel to the a axis. In the μ-mdea ligand two –CH2 groups and the methyl group were refined as disordered over two sets of sites with equal occupancies. The structure was refined as a two-component twin with a twin scale factor of 0.242 (1). PMID:26396853

Synthesis, spectroscopic properties, molecular docking, anti-colon cancer and anti-microbial studies of some novel metal complexes for 2-amino-4-phenylthiazole derivative

NASA Astrophysics Data System (ADS)

Al-Harbi, Sami A.; Bashandy, Mahmoud S.; Al-Saidi, Hammed M.; Emara, Adel A. A.; Mousa, Tarek A. A.

2015-06-01

This article describes the synthesis of novel bidentate Schiff base (H2L) from condensation of 2-amino-4-phenylthiazole (APT) with 4,6-diacetylresorcinol (DAR) in the molar ratio 2:1. We studied interaction of ligand (H2L) with transition metal ions such as Cr(III), Fe(III), Cu(II), Zn(II) and Cd(II). The ligand (H2L) has two bidentate sets of (N-O) units which can coordinate with two metal ions to afford novel binuclear metal complexes. The directions of coordinate bonds are from nitrogen atoms of azomethine groups and oxygen atoms of the phenolic groups. Structures of the newly synthesized complexes were confirmed by elemental analysis, IR, UV, 1H NMR, ESR, TGA and mass spectral data. All of the newly synthesized complexes were evaluated for their antibacterial and anti-fungal activities. They were also evaluated for their in vitro anticancer activity against human colon carcinoma cells (HCT-116) and mammalian cells of African green monkey kidney (VERO). The Cu(II) complex with selectivity index (S.I.) = 21.26 exhibited better activity than methotrexate (MTX) as a reference drug with S.I. value = 13.30, while Zn(II) complex with S.I. value = 10.24 was found to be nearly as active as MTX. Molecular docking studies further helped in understanding the mode of action of the compounds through their various interactions with active sites of dihydrofolate reductase (DHFR) enzyme. The observed activity of Fe(III) and Cu(II) complexes gave rise to the conclusion that they might exert their action through inhibition of the DHFR enzyme.

Synthesis, spectroscopic properties, molecular docking, anti-colon cancer and anti-microbial studies of some novel metal complexes for 2-amino-4-phenylthiazole derivative.

PubMed

Al-Harbi, Sami A; Bashandy, Mahmoud S; Al-Saidi, Hammed M; Emara, Adel A A; Mousa, Tarek A A

2015-06-15

This article describes the synthesis of novel bidentate Schiff base (H2L) from condensation of 2-amino-4-phenylthiazole (APT) with 4,6-diacetylresorcinol (DAR) in the molar ratio 2:1. We studied interaction of ligand (H2L) with transition metal ions such as Cr(III), Fe(III), Cu(II), Zn(II) and Cd(II). The ligand (H2L) has two bidentate sets of (N-O) units which can coordinate with two metal ions to afford novel binuclear metal complexes. The directions of coordinate bonds are from nitrogen atoms of azomethine groups and oxygen atoms of the phenolic groups. Structures of the newly synthesized complexes were confirmed by elemental analysis, IR, UV, (1)H NMR, ESR, TGA and mass spectral data. All of the newly synthesized complexes were evaluated for their antibacterial and anti-fungal activities. They were also evaluated for their in vitro anticancer activity against human colon carcinoma cells (HCT-116) and mammalian cells of African green monkey kidney (VERO). The Cu(II) complex with selectivity index (S.I.)=21.26 exhibited better activity than methotrexate (MTX) as a reference drug with S.I. value=13.30, while Zn(II) complex with S.I. value=10.24 was found to be nearly as active as MTX. Molecular docking studies further helped in understanding the mode of action of the compounds through their various interactions with active sites of dihydrofolate reductase (DHFR) enzyme. The observed activity of Fe(III) and Cu(II) complexes gave rise to the conclusion that they might exert their action through inhibition of the DHFR enzyme. Copyright © 2015 Elsevier B.V. All rights reserved.

Cyclopalladation of dimesityl selenide: synthesis, reactivity, structural characterization, isolation of an intermediate complex with C-H···Pd intra-molecular interaction and computational studies.

PubMed

Kolay, Siddhartha; Wadawale, Amey; Das, Dasarathi; Kisan, Hemanta K; Sunoj, Raghavan B; Jain, Vimal K

2013-08-14

The reaction of dimesityl selenide (Mes2Se) with either PdCl2(PhCN)2 in toluene or PdCl2 in toluene-acetonitrile yields a chloro-bridged binuclear palladium complex, [Pd2Cl2(μ-Cl)2(Mes2Se)2] (1), whereas with Na2PdCl4 in refluxing ethanol, a cyclometallated palladium complex, [Pd2(μ-Cl)2{MesSeC6H2(Me2)CH2}2] (2) is afforded. 2 can also be obtained when 1 is refluxed in ethanol. On treatment with Pb(Epy)2 in dichloromethane, 2 afforded the Epy-bridged binuclear complexes, [Pd2(μ-Epy)2{MesSeC6H2(Me2)CH2}2] (3; E = S (3a) or Se (3b)). Treatment of 2 with PPh3 yields a bridge-cleaved monomeric complex, [PdCl{MesSeC6H2(Me2)CH2}(PPh3)]. The molecular structures of 1-3 were established by X-ray diffraction analyses. All the complexes are dimeric, with the palladium atoms acquiring a distorted square planar configuration. There are intra-molecular C-H···Pd interactions (d(M-H): 2.75 Å and

Electrochemistry of Simple Organometallic Models of Iron-Iron Hydrogenases in Organic Solvent and Water.

PubMed

Gloaguen, Frederic

2016-01-19

Synthetic models of the active site of iron-iron hydrogenases are currently the subjects of numerous studies aimed at developing H2-production catalysts based on cheap and abundant materials. In this context, the present report offers an electrochemist's view of the catalysis of proton reduction by simple binuclear iron(I) thiolate complexes. Although these complexes probably do not follow a biocatalytic pathway, we analyze and discuss the interplay between the reduction potential and basicity and how these antagonist properties impact the mechanisms of proton-coupled electron transfer to the metal centers. This question is central to any consideration of the activity at the molecular level of hydrogenases and related enzymes. In a second part, special attention is paid to iron thiolate complexes holding rigid and unsaturated bridging ligands. The complexes that enjoy mild reduction potentials and stabilized reduced forms are promising iron-based catalysts for the photodriven evolution of H2 in organic solvents and, more importantly, in water.

Cytotoxicity of copper(II)-complexes with some S-alkyl derivatives of thiosalicylic acid. Crystal structure of the binuclear copper(II)-complex with S-ethyl derivative of thiosalicylic acid

NASA Astrophysics Data System (ADS)

Nikolić, Miloš V.; Mijajlović, Marina Ž.; Jevtić, Verica V.; Ratković, Zoran R.; Novaković, Slađana B.; Bogdanović, Goran A.; Milovanović, Jelena; Arsenijević, Aleksandar; Stojanović, Bojana; Trifunović, Srećko R.; Radić, Gordana P.

2016-07-01

The spectroscopically predicted structure of the obtained copper(II)-complex with S-ethyl derivative of thiosalicylic acid was confirmed by X-ray structural study and compared to previously reported crystal structure of the Cu complex with S-methyl derivative. Single crystals suitable for X-ray measurements were obtained by slow crystallization from a water solution. Cytotoxic effects of S-alkyl (R = benzyl (L1), methyl (L2), ethyl (L3), propyl (L4) and butyl (L5)) derivatives of thiosalicylic acid and the corresponding binuclear copper(II)-complexes on murine colon carcinoma cell lines, CT26 and CT26.CL25 and human colon carcinoma cell line HCT-116 were reported here. The analysis of cancer cell viability showed that all the tested complexes had low cytotoxic effect on murine colon carcinoma cell lines, but several times higher cytotoxicity on normal human colon carcinoma cells.

Synthesis and characterization of the tetranuclear iron(III) complex of a new asymmetric multidentate ligand. A structural model for purple acid phosphatases.

PubMed

Boudalis, Athanassios K; Aston, Robyn E; Smith, Sarah J; Mirams, Ruth E; Riley, Mark J; Schenk, Gerhard; Blackman, Allan G; Hanton, Lyall R; Gahan, Lawrence R

2007-11-28

The ligand, 2-((2-hydroxy-5-methyl-3-((pyridin-2-ylmethylamino)methyl)benzyl)(2-hydroxybenzyl)amino)acetic acid (H(3)HPBA), which contains a donor atom set that mimics that of the active site of purple acid phosphatase is described. Reaction of H(3)HPBA with iron(III) or iron(II) salts results in formation of the tetranuclear complex, [Fe(4)(HPBA)(2)(OAc)(2)(mu-O)(mu-OH)(OH(2))(2)]ClO(4) x 5H(2)O. X-Ray structural analysis reveals the cation consists of four iron(III) ions, two HPBA(3-) ligands, two bridging acetate ligands, a bridging oxide ion and a bridging hydroxide ion. Each binucleating HPBA(3-) ligand coordinates two structurally distinct hexacoordinate iron(III) ions. The two metal ions coordinated to a HPBA(3-) ligand are linked to the two iron(III) metal ions of a second, similar binuclear unit by intramolecular oxide and hydroxide bridging moieties to form a tetramer. The complex has been further characterised by elemental analysis, mass spectrometry, UV-vis and MCD spectroscopy, X-ray crystallography, magnetic susceptibility measurements and variable-temperature Mössbauer spectroscopy.

Yb3+ can be much better than Dy3+: SMM properties and controllable self-assembly of novel lanthanide 3,5-dinitrobenzoate-acetylacetonate complexes.

PubMed

Gavrikov, Andrey V; Efimov, Nikolay N; Ilyukhin, Andrey B; Dobrokhotova, Zhanna V; Novotortsev, Vladimir M

2018-05-01

The first representatives of the binuclear lanthanide 3,5-dinitrobenzoate-acetylacetonate complexes, namely isostructural compounds [Ln(dnbz)(acac)2(H2O)(EtOH)]2 (Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6), Tm (7), and Yb (8); dnbz - 3,5-dinitrobenzoate anion; acac - acetylacetonate (pentane-2,4-dionate) anion) were prepared and characterized. The SMM behavior of the Yb compound 8 was shown to be surprisingly less sensitive to the composition of the Yb3+ coordination environment in comparison with that of the Dy derivative. For Yb compound 8, the anisotropy barrier is Δeff/kB = 26 K under the dc field of 2000 Oe. This value is the highest one currently known for binuclear Yb complexes.

Studies with an immobilized metal affinity chromatography cassette system involving binuclear triazacyclononane-derived ligands: automation of batch adsorption measurements with tagged recombinant proteins.

PubMed

Petzold, Martin; Coghlan, Campbell J; Hearn, Milton T W

2014-07-18

This study describes the determination of the adsorption isotherms and binding kinetics of tagged recombinant proteins using a recently developed IMAC cassette system and employing automated robotic liquid handling procedures for IMAC resin screening. These results confirm that these new IMAC resins, generated from a variety of different metal-charged binuclear 1,4,7-triaza-cyclononane (tacn) ligands, interact with recombinant proteins containing a novel N-terminal metal binding tag, NT1A, with static binding capacities similar to those obtained with conventional hexa-His tagged proteins, but with significantly increased association constants. In addition, higher kinetic binding rates were observed with these new IMAC systems, an attribute that can be positively exploited to increase process productivity. The results from this investigation demonstrate that enhancements in binding capacities and affinities were achieved with these new IMAC resins and chosen NT1A tagged protein. Further, differences in the binding performances of the bis(tacn) xylenyl-bridged ligands were consistent with the distance between the metal binding centres of the two tacn moieties, the flexibility of the ligand and the potential contribution from the aromatic ring of the xylenyl group to undergo π/π stacking interactions with the tagged proteins. Copyright © 2014 Elsevier B.V. All rights reserved.

Comparative study of mono- and dinuclear complexes of late 3d-metal chlorides with N,N-dimethylformamide in the gas phase.

PubMed

Duchácková, Lucie; Roithová, Jana; Milko, Petr; Zabka, Jan; Tsierkezos, Nikos; Schröder, Detlef

2011-02-07

Mono- and binuclear complexes of N,N-dimethylformamide (DMF) with chlorides of the divalent, late 3d metals M = Co, Ni, Cu, and Zn are investigated by means of electrospray ionization (ESI). Specifically, ESI leads to monocations of the type [(DMF)(n)MCl](+) and [(DMF)(n)M(2)Cl(3)](+), of which the species with n = 2 and 3 were selected for in-depth studies. The latter include collision-induced dissociation experiments, gas-phase infrared spectroscopy, and calculations using density functional theory. The mononuclear complexes [(DMF)(n)MCl](+) almost exclusively lose neutral DMF upon collisional activation with the notable exception of the copper complex, for which also a reduction from Cu(II) to Cu(I) concomitant with the release of atomic chlorine is observed. For the dinuclear clusters, there exists a competition between loss of a DMF ligand and cluster degradation via loss of neutral MCl(2) with decreasing cluster stability from cobalt to zinc. For the specific case of [(DMF)(n)ZnCl](+) and [(DMF)(n)Zn(2)Cl(3)](+), ion-mobility mass spectrometry indicates the existence of two isomeric cluster ions in the case of [(DMF)(2)Zn(2)Cl(3)](+) which corroborates parallel theoretical predictions.

Hydrothermal synthesis, photoluminescence and photocatalytic properties of two silver(I) complexes

NASA Astrophysics Data System (ADS)

Yang, Yuan-Yuan; Zhou, Lin-Xia; Zheng, Yue-Qing; Zhu, Hong-Lin; Li, Wen-Ying

2017-09-01

Two new dinuclear silver(I) coordination complexes [Ag(Hntph)(tpyz)2/2]n1 and [Ag2(dtrz)2(Hntph)2] 2 (H2ntph=2-nitroterephthalic acid, tpyz=2,3,5-trimethylpyrazine, dtrz=3,5-dimethyl-4H-1,2,4-triazol-4-amine) have been obtained by hydrothermal reactions of Ag(I) salts with H2ntph and various N-donor ligands. Complex 1 exhibits a 2D layer structure constructed by the binuclear Ag2(Hntph)2 units and tpyz ligands. Complex 2 also shows a different binuclear unit Ag2(dtrz)2, which was assembled via hydrogen bonds interactions to a 3D supramolecular architecture. The photocatalytic experiments showed that complex 2 is an excellent visible light candidate for degradation of RhB, and the degradation ratio of RhB reached 91.4% after 7 h under the light of 90 W white LED lamp. Moreover, the photoluminescent properties and the optical band gaps of 1-2 have also been investigated.

Design and synthesis of binucleating macrocyclic clefts derived from Schiff-base calixpyrroles.

PubMed

Givaja, Gonzalo; Volpe, Manuel; Leeland, James W; Edwards, Michael A; Young, Thomas K; Darby, S Barnie; Reid, Stuart D; Blake, Alexander J; Wilson, Claire; Wolowska, Joanna; McInnes, Eric J L; Schröder, Martin; Love, Jason B

2007-01-01

The syntheses, characterisation and complexation reactions of a series of binucleating Schiff-base calixpyrrole macrocycles are described. The acid-templated [2+2] condensations between meso-disubstituted diformyldipyrromethanes and o-phenylenediamines generate the Schiff-base pyrrolic macrocycles H(4)L(1) to H(4)L(6) upon basic workup. The single-crystal X-ray structures of both H(4)L(3).2 EtOH and H(4)L(6).H2O confirm that [2+2] cyclisation has occurred, with either EtOH or H2O hydrogen-bonded within the macrocyclic cleft. A series of complexation reactions generate the dipalladium [Pd2(L)] (L=L(1) to L(5)), dinickel [Ni2(L(1))] and dicopper [Cu2(L)] (L=L(1) to L(3)) complexes. All of these complexes have been structurally characterised in the solid state and are found to adopt wedged structures that are enforced by the rigidity of the aryl backbone to give a cleft reminiscent of the structures of Pacman porphyrins. The binuclear nickel complexes [Ni2(mu-OMe)2Cl2(HOMe)2(H(4)L(1))] and [Ni2(mu-OH)2Cl2(HOMe)(H(4)L(5))] have also been prepared, although in these cases the solid-state structures show that the macrocyclic ligand remains protonated at the pyrrolic nitrogen atoms, and the Ni(II) cations are therefore co-ordinated by the imine nitrogen atoms only to give an open conformation for the complex. The dicopper complex [Cu2(L(3))] was crystallised in the presence of pyridine to form the adduct [Cu2(py)(L(3))], in which, in the solid state, the pyridine ligand is bound within the binuclear molecular cleft. Reaction between H(4)L(1) and [Mn(thf){N(SiMe(3))2}2] results in clean formation of the dimanganese complex [Mn2(L(1))], which, upon crystallisation, formed the mixed-valent complex [Mn2(mu-OH)(L(1))] in which the hydroxo ligand bridges the metal centres within the molecular cleft.

Design and its limitations in the construction of bi- and poly-nuclear coordination complexes and coordination polymers (aka MOFs): a personal view.

PubMed

Robson, R

2008-10-14

This article, presented from a personal point of view, is concerned with the design of ligands intended to give specifically either binuclear or tetranuclear metal complexes or coordination polymers. No attempt is made to provide a comprehensive coverage of these topics, the focus being mainly upon results from our laboratory. Some emphasis is placed upon aspects of the historical development of the deliberate construction of coordination polymers (aka MOFs)--materials promising useful applications, the study of which continues to expand exponentially. Some of our recent research is described in which the carbonate ion and the tetracyanoquinodimethane dianion are used as bridging ligands to generate targeted coordination polymers. It is intended that Dalton Perspectives be easily comprehensible to non-specialists in the field; an average second year university chemistry student should be easily able to understand the present contribution.

Synthesis, characterization and extraction studies of some metal (II) complexes containing (hydrazoneoxime and bis-acylhydrazone) moieties

NASA Astrophysics Data System (ADS)

Al-Ne'aimi, Mohammed Mahmmod; Al-Khuder, Mohammed Moudar

2013-03-01

In this study, diacetylmonoximebenzoylhydrazone (L1H2) and 1,4-diacetylbenzene bis(benzoyl hydrazone) (L2H2) were synthesized by the condensation of benzohydrazide with diacetyl monoxime and 1,4-diacetylbenzene, respectively. Complexes of these ligands with Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) inos were prepared with a metal:ligand ratio of 1:2 for L1H2 ligand, and 1:1 for L2H2 ligand. The ligands and their complexes were elucidated on the basis of elemental analyses CHN, AAS, FT-IR, 1H- and 13C NMR spectra, UV-vis spectra and magnetic susceptibility measurements. Results show the L1H2 ligand act as monoanionic O,N,N-tridentate and coordination takes place in the enol form through the oxime nitrogen, the imine nitrogen and the enolate oxygen atoms with a N4O2 donor environment, while the L2H2 ligand act as a dianionic O,N,N,O-tetradentate and coordination takes place in the enol form through the enolate oxygen and the azomethine nitrogen atoms with a N2O2 donor environment. These results are consistent with the formation of mononuclear metal (II) complexes [M(L1H)2], and binuclear polymeric metal (II) complexes [{M2(L2)}n]. The extraction ability of both ligands were examined in chloroform by the liquid-liquid extraction of selected transition metal [Co2+, Ni2+, Cu2+, Zn2+ and Pb2+] cations. The effects of pH and contact time on the percentage extraction of metal (II) ions were studied under the optimum extraction conditions. The (L1H2) ligand shows strong binding ability toward copper(II) and lead(II) ions, while the (L2H2) ligand shows strong binding ability toward nickel(II) and zinc(II) ions.

Synthesis, characterization and extraction studies of some metal (II) complexes containing (hydrazoneoxime and bis-acylhydrazone) moieties.

PubMed

Al-Ne'aimi, Mohammed Mahmmod; Al-Khuder, Mohammed Moudar

2013-03-15

In this study, diacetylmonoximebenzoylhydrazone (L(1)H(2)) and 1,4-diacetylbenzene bis(benzoyl hydrazone) (L(2)H(2)) were synthesized by the condensation of benzohydrazide with diacetyl monoxime and 1,4-diacetylbenzene, respectively. Complexes of these ligands with Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) inos were prepared with a metal:ligand ratio of 1:2 for L(1)H(2) ligand, and 1:1 for L(2)H(2) ligand. The ligands and their complexes were elucidated on the basis of elemental analyses CHN, AAS, FT-IR, (1)H- and (13)C NMR spectra, UV-vis spectra and magnetic susceptibility measurements. Results show the L(1)H(2) ligand act as monoanionic O,N,N-tridentate and coordination takes place in the enol form through the oxime nitrogen, the imine nitrogen and the enolate oxygen atoms with a N(4)O(2) donor environment, while the L(2)H(2) ligand act as a dianionic O,N,N,O-tetradentate and coordination takes place in the enol form through the enolate oxygen and the azomethine nitrogen atoms with a N(2)O(2) donor environment. These results are consistent with the formation of mononuclear metal (II) complexes [M(L(1)H)(2)], and binuclear polymeric metal (II) complexes [{M(2)(L(2))}(n)]. The extraction ability of both ligands were examined in chloroform by the liquid-liquid extraction of selected transition metal [Co(2+), Ni(2+), Cu(2+), Zn(2+) and Pb(2+)] cations. The effects of pH and contact time on the percentage extraction of metal (II) ions were studied under the optimum extraction conditions. The (L(1)H(2)) ligand shows strong binding ability toward copper(II) and lead(II) ions, while the (L(2)H(2)) ligand shows strong binding ability toward nickel(II) and zinc(II) ions. Copyright © 2012 Elsevier B.V. All rights reserved.

Selective photoswitching of the binuclear spin crossover compound {[Fe(bt)(NCS)2]2(bpm)} into two distinct macroscopic phases.

PubMed

Moussa, N Ould; Molnár, G; Bonhommeau, S; Zwick, A; Mouri, S; Tanaka, K; Real, J A; Bousseksou, A

2005-03-18

The low-spin (LS-LS, S = 0) diamagnetic form of the binuclear spin crossover complex {[Fe(bt)(NCS)(2)](2)(bpm)} was selectively photoconverted into two distinct macroscopic phases at different excitation wavelengths (1342 or 647.1 nm). These long-lived metastable phases have been identified, respectively, as the symmetry-broken paramagnetic form (HS-LS, S = 2) and the antiferromagnetically coupled (HS-HS, S = 0) high-spin form of the compound. The selectivity may be explained by the strong coupling of the primary excited states to the paramagnetic state.

E.S.R., magnetic, electronic and superoxide dismutase studies of imidazolate-bridged Cu(II)-Cu(II) complexes with ethylenediamine as capping ligand.

PubMed

Patel, R N; Singh, Nripendra; Shukla, K K; Gundla, V L N

2005-06-01

X-band E.S.R., magnetic and electronic spectra of some imidazolate-bridged homometallic complexes [(en)2Cu-R-Im-Cu(en)2](ClO4)3 where en, ethylenediamine; R-ImH, R = H imidazole (ImH); if R = CH3, 2-methylimidazole (M-ImH) and if R = C2H5, 2-ethylimidazole (E-ImH), and mononuclear complexes [(en)Cu-dien](ClO4)2 and [(en)Cu-PMDT](ClO4)2 where dien, diethylenetriamine; PMDT, pentamethyldiethylenetriamine have been described. Superoxide dismutase (SOD) activity has also been measured and compared with earlier reported complexes. In frozen solution at 77 K, the spectra show axial symmetry with a d(x2-y2) ground state. Difference in lambda(max) between mononuclear and binuclear complexes was found to be approximately 65-75 nm. Magnetic susceptibility and E.S.R. spectral measurements for all these binuclear complexes revealed that the copper(II) ions are involved in antiferromagnetic exchange interactions propagated by the imidazolate bridge.

Stereochemical investigations of a novel class of chiral phosphapalladacycle complexes derived from 1-[(2,5-dimethyl)phenyl]ethyldiphenylphosphine.

PubMed

Ng, Joseph Kok-Peng; Li, Yongxin; Tan, Geok-Kheng; Koh, Lip-Lin; Vittal, Jagadese J; Leung, Pak-Hing

2005-12-26

The phosphapalladacycle derived from 1-(2',5'-dimethylphenyl)ethyldiphenylphosphine has been prepared in the optically active and racemic forms. The phosphine was synthesized as a racemate by the treatment of 1-chloro-1-(2',5'-dimethylphenyl)ethane with sodium diphenylphosphide in THF. The racemic phosphapalladacycle was subsequently obtained as the chloro-bridged dimer by the treatment of the phosphine with palladium(II) acetate followed by anion metathesis with lithium chloride. Alternatively, the phosphine could be optically resolved via metal complexation using (R,R)-bis(mu-chloro)bis{1-[1-(N,N-dimethylamino)ethyl]naphthyl-C(2),N}dipalladium(II) as the resolving agent. An efficient separation of the resulting diastereomeric complexes was achieved by silica gel chromatography. The obtained optically resolved diastereomers were next subject to chemoselective removal of the (R)-N,N-(dimethylamino)-1-(1-naphthyl)ethylaminate auxiliary by treatment with concentrated hydrochloric acid. This process yielded the binuclear dimer complexes containing the resolved eta(1)-P ligand. Cyclopalladation of the coordinated phosphine could next be performed by treatment of its eta(1)-P binuclear dimer with silver(I) hexafluorophosphate(V) in a dichloromethane/water mixture followed by treatment with lithium chloride, giving rise to a pair of optically pure enantiomeric dimers with [alpha](D) -322 and +319 degrees in CH(2)Cl(2). Despite the possibilities of the phosphine to attain a five- membered structure by ortho-palladation or a six-membered ring formation by aliphatic C-H bond activation, only the former was observed. X-ray crystallographic data of the meso dimer and an acetylacetonate derivative indicated that the phosphapalladacycle alpha-C methyl substituent was axially located. The 2-D (1)H-(1)H ROESY spectrum of the acetylacetonate derivative further revealed that the phosphapalladacycle was conformationally rigid in CDCl(3).

Electronic properties of thiolate compounds of oxomolybdenum(V) and their tungsten and selenium analogues. Effects of /sup 17/O, /sup 98/Mo, and /sup 95/Mo isotope substitution upon ESR spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanson, G.R.; Brunette, A.A.; McDonell, A.C.

1981-04-22

The series of crystalline, mononuclear B/sup +/(MO(XR)/sub 4/)/sup -/ and triply bridged binuclear B/sup +/(M/sub 2/O/sub 2/(XR)/sub 6/(OMe))/sup -/(M = Mo, W; X = S, Se; R = aryl; B = quaternary cation) salts have been isolated and the anions (MoO(SR)/sub 4/)/sup -/ (R = Et, CH/sub 2/Ph) stabilized in solution at -60/sup 0/C. The mononuclear anions are intensely colored due to a ligand-to-metal charge-transfer transition which is absent in the binuclear species. The magnetic susceptibilities of (Et/sub 4/N)(MO(SPh)/sub 4/) show a Curie dependence in the range 300 to 4.2 K with minor deviations in the tungsten compound. The behaviormore » is essentially that of magnetically dilute 4d/sup 1/ and 5d/sup 1/ systems exhibiting a tetragonal ligand field and greatly reduced spin-orbit coupling on the metal. The presence of strong spin-spin coupling in the binuclear compounds leads to magnetic moments close to 0. ESR spectra (at X- and Q-band frequencies) of the mononuclear anions exhibit axial symmetry, and /sup 98/Mo and /sup 95/Mo isotope substitution and computer simulation permit accurate extraction of the g and hyperfine tensor anisotropies. Exceptionally arrow line widths permit observation of /sup 17/O-superhyperfine coupling in /sup 17/O-enriched (/sup 98/MoO(SPh)/sub 4/)/sup -/(a = 2.2 x 10/sup -4/cm/sup -1/).« less

Preparation, characterization, and stereochemistry of binuclear vanadyl(IV) monomethyl- and dimethyltartrate(4-) complexes and the crystal structure of tetrasodium (. mu. -(+)-dimethyltartrato(4-))-(. mu. -(-)-dimethyltartrato(4-))-bis(oxovanadate(IV)) dodecahydrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hahs, S.K.; Ortega, R.B.; Tapscott, R.E.

1982-02-01

The syntheses and characterizations (by ESR, IR, and electronic spectroscopies) of the sodium salts of the DL and DD (or LL) binuclear complexes of vanadyl(IV) with dimethyltartrate(4-), dmt, and with monomethyltartrate(4-), mmt, are described. Na/sub 4/((VO)/sub 22/((+)-dmt)((-)-dmt)) exists in two crystal forms - a blue dodecahydrate and a pink hexahydrate. An x-ray diffraction study of the former shows that the V-V distance (3.429 (3) A) of the binuclear anion is decreased relative to that of the unsubstituted tartrate(4-), tart, complex, as predicted from earlier ESR studies, and that this decrease is due in part to a dropping of the vanadiummore » atom into the plane of the four coordinating equatorial oxygen atoms. A sixth oxygen atom is weakly coordinated (2.377 (3) A) trans to the vanadyl oxygen atom. A purple tetradecahydrate also obtained with racenic dmt contains a mixture of ((VO)/sub 2/ ((+)-dmt)/sub 2/)/sup 4 -/ and ((VO)/sub 2/((-)-dmt)/sub 2/)/sup 4 -/). The aqueous solution ligand-exchange reaction between the DD and LL complexes of this salt to give the more stable DL isomer is remarkably slow (several hours at room temperature). Stereoselective effects allow the production of mixed-ligand species containing two of the three ligands tart, dmt, and mmt, and potentiometric titrations indicate a decreasing stability of the DL isomer (relative to the DD and LL isomers) as methyl substitution increases.« less

Bimetallic cooperative effect on O-O bond formation: copper polypyridyl complexes as water oxidation catalyst.

PubMed

Su, Xiao-Jun; Zheng, Chu; Hu, Qin-Qin; Du, Hao-Yi; Liao, Rong-Zhen; Zhang, Ming-Tian

2018-06-13

The performance of water oxidation catalysis by a Cu-based polypyridyl complex, [CuII(TPA)(OH2)]2+ (1H; TPA = tris-(pyridylmethyl)amine), has been investigated in neutral aqueous solution by electrochemical methods. Compared with our previously reported binuclear catalyst, [(BPMAN)(CuII)2(μ-OH)]3+ (2; BPMAN = 2,7-[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine), mononuclear catalyst 1 has a higher overpotential and lower catalytic activity toward water oxidation under the same conditions. Experimental results revealed that the O-O bond formation occurred via a water nucleophilic attack mechanism in which formal CuIV(O) is proposed as a key intermediate for the mononuclear catalyst 1H. In contrast, for the binuclear catalyst, O-O bond formation was facilitated by bimetallic cooperation between the two CuIII centers.

Nano optical sensor binuclear Pt-2-pyrazinecarboxylic acid -bipyridine for enhancement of the efficiency of 3-nitrotyrosine biomarker for early diagnosis of liver cirrhosis with minimal hepatic encephalopathy.

PubMed

Attia, M S; Al-Radadi, Najlaa S

2016-12-15

A new, precise, and very selective method for increasing the impact and assessment of 3-nitrotyrosine (3-Nty) as a biomarker for early diagnosis of liver cirrhosis with minimal hepatic encephalopathy (MHE) disease was developed. The method depends on the formation of the ion pair associate between 3-nitrotyrosine and the optical sensor binuclear Pt-2-pyrazinecarboxylic acid (pca)-Bipyridine (bpy) complex doped in sol-gel matrix in buffer solution of pH 7.3. The binuclear Pt (pca)(bpy) has +II net charge which is very selective and sensitive for [3-Nty](-2) at pH 7.3 in serum sample of liver cirrhosis with MHE diseases. 3-nitrotyrosine (3-Nty) quenches the luminescence intensity of the nano optical sensor binuclear Pt(pca) (bpy) at 528nm after excitation at 370nm, pH 7.3. The remarkable quenching of the luminescence intensity at 528nm of nano binuclear Pt(pca) (bpy) doped in sol-gel matrix by various concentrations of the 3-Nty was successfully used as an optical sensor for the assessment of 3-Nty in different serum samples of (MHE) in patients with liver cirrhosis. The calibration plot was achieved over the concentration range 1.85×10(-5) - 7.95×10(-10)molL(-1) 3-Nty with a correlation coefficient of (0.999) and a detection limit of (4.7×10(-10)molL(-1)). The method increases the sensitivity (93.75%) and specificity (96.45%) of 3-Nty as a biomarker for early diagnosis of liver cirrhosis with MHE in patients. Copyright © 2016 Elsevier B.V. All rights reserved.

Different mechanisms at different temperatures for the ring-opening polymerization of lactide catalyzed by binuclear magnesium and zinc alkoxides.

PubMed

Sun, Yangyang; Cui, Yaqin; Xiong, Jiao; Dai, Zhongran; Tang, Ning; Wu, Jincai

2015-10-07

Two binuclear magnesium and zinc alkoxides supported by a bis-salalen type dinucleating heptadentate Schiff base ligand were synthesized and fully characterized. The two complexes are efficient initiators for the ring-opening polymerization (ROP) of L-lactide, affording polymers with narrow polydispersities and desirable molecular weights. Interestingly, the mechanisms for the ROP of lactide are different at different temperatures. At a high temperature of 130 °C, a coordination-insertion mechanism is reasonable for the bulk melt polymerization of lactide. At a low temperature, the alkoxide cannot initiate the ROP reaction; however, upon the addition of external benzyl alcohol into the system, the ROP of lactide can smoothly proceed via an "activated monomer" mechanism. In addition, these complexes display slight stereo-selectivity for the ring-opening polymerization of rac-lactide, affording partially isotactic polylactide in toluene with a Pm value of 0.59.

Adsorption mechanisms of selenium oxyanions at the aluminum oxide/water interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peak, Derek

2008-06-09

Sorption processes at the mineral/water interface typically control the mobility and bioaccessibility of many inorganic contaminants such as oxyanions. Selenium is an important micronutrient for human and animal health, but at elevated concentrations selenium toxicity is a concern. The objective of this study was to determine the bonding mechanisms of selenate (SeO{sub 4}{sup 2-}) and selenite (SeO{sub 3}{sup 2-}) on hydrous aluminum oxide (HAO) over a wide range of reaction pH using extended X-ray absorption fine structure (EXAFS) spectroscopy. Additionally, selenate adsorption on corundum ({alpha}-Al{sub 2}O{sub 3}) was studied to determine if adsorption mechanisms change as the aluminum oxide surfacemore » structure changes. The overall findings were that selenite forms a mixture of outer-sphere and inner-sphere bidentate-binuclear (corner-sharing) surface complexes on HAO, selenate forms primarily outer-sphere surface complexes on HAO, and on corundum selenate forms outer-sphere surface complexes at pH 3.5 but inner-sphere monodentate surface complexes at pH 4.5 and above. It is possible that the lack of inner-sphere complex formation at pH 3.5 is caused by changes in the corundum surface at low pH or secondary precipitate formation. The results are consistent with a structure-based reactivity for metal oxides, wherein hydrous metal oxides form outer-sphere complexes with sulfate and selenate, but inner-sphere monodentate surface complexes are formed between sulfate and selenate and {alpha}-Me{sub 2}O{sub 3}.« less

Interaction with biomacromolecules and antiproliferative activities of Mn(II), Ni(II), Zn(II) complexes of demethylcantharate and 2,2'-bipyridine

NASA Astrophysics Data System (ADS)

Zhang, Fan; Lin, Qiu-Yue; Hu, Wan-Li; Song, Wen-Ji; Shen, Shu-Ting; Gui, Pan

2013-06-01

Three new transition metal complexes [Mn2(DCA)2(bipy)2]·5H2O (1), [M2(DCA)2(bipy)2(H2O)]·10H2O(M = Ni(II)(2);Zn(II)(3)), (DCA = demethylcantharate, 7-oxabicyclo[2,2,1]heptane-2,3-dicarboxylate, C8H8O5) were synthesized and characterized by elemental analysis, molar conductance, infrared spectra and X-ray diffraction techniques. Each metal ion was six-coordinated in complexes. Complex 1 has a Mn2O2 center. Complexes 2 and 3 have asymmetric binuclear structure. Great amount of intermolecular hydrogen-bonding and π-π* stacking interactions were formed in these complex structures. The DNA-binding properties of complexes were investigated by electronic absorption spectra and viscosity measurements. The DNA binding constants Kb/(L mol-1) were 1.71 × 104 (1), 2.62 × 104 (2) and 1.59 × 104 (3) at 298 K. The complexes could quench the intrinsic fluorescence of bovine serum albumin (BSA) strongly through static quenching. The protein binding constants Ka/(L mol-1) were 7.27 × 104 (1), 4.55 × 104 (2) and 7.87 × 104 L mol-1 (3) and binding site was one. The complexes bind more tightly with DNA and BSA than with ligands. Complexes 1 and 3 had stronger inhibition ratios than Na2(DCA) against human hepatoma cells (SMMC-7721) lines and human gastric cancer cells (MGC80-3) lines in vitro. Complex 3 showed the strongest antiproliferative activity against SMMC-7721 (IC50 = 29.46 ± 2.12 μmol L-1) and MGC80-3 (IC50 = 27.02 ± 2.38 μmol L-1), which shows potential in anti-cancer drug development.

Multi-electron oxygen reduction by a hybrid visible-light-photocatalyst consisting of metal-oxide semiconductor and self-assembled biomimetic complex.

PubMed

Naya, Shin-ichi; Niwa, Tadahiro; Negishi, Ryo; Kobayashi, Hisayoshi; Tada, Hiroaki

2014-12-08

Adsorption experiments and density functional theory (DFT) simulations indicated that Cu(acac)2 is chemisorbed on the monoclinic sheelite (ms)-BiVO4 surface to form an O2-bridged binuclear complex (OBBC/BiVO4) like hemocyanin. Multi-electron reduction of O2 is induced by the visible-light irradiation of the OBBC/BiVO4 in the same manner as a blue Cu enzyme. The drastic enhancement of the O2 reduction renders ms-BiVO4 to work as a good visible-light photocatalyst without any sacrificial reagents. As a model reaction, we show that this biomimetic hybrid photocatalyst exhibits a high level of activity for the aerobic oxidation of amines to aldehydes in aqueous solution and imines in THF solution at 25 °C giving selectivities above 99% under visible-light irradiation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Supramolecular architectures constructed by lanthanum, amino acids and 1,10-phenanthroline via non-covalent bond interactions

NASA Astrophysics Data System (ADS)

Zheng, Xiang-Jun; Jin, Lin-Pei

2003-07-01

Three supramolecular lanthanum coordination compounds of amino acids, with 1,10-phenanthroline (phen), [La 2(APA) 6(phen) 2(H 2O) 2](ClO 4) 6(phen) 4·2H 2O ( 1), [La 2(ABA) 6(phen) 2(H 2O) 2](ClO 4) 6 (phen) 6·4H 2O ( 2), and [La 2(AHA) 4(phen) 4](ClO 4) 6(phen) 4·2H 2O ( 3) (APA=3-aminopropionic acid; ABA=4-aminobutanoic acid; AHA=6-aminohexanoic acid) were synthesized and characterized by single crystal X-ray diffraction. The results show that the three coordination compounds are all composed of binuclear coordination cations built by metal-ligand coordination. Through hydrogen bonding and π-π stacking interactions, complex 1 forms a two-dimensional supramolecular sheet structure extending in the (001) plane, complex 2 forms a three-dimensional supramolecular network with many cavities occupied by ClO 4- and lattice H 2O molecules, and complex 3 forms a two-dimensional supramolecular lamellar structure in the (100) plane.

Direct detection of formate ligation in cytochrome c oxidase by ATR-FTIR spectroscopy.

PubMed

Iwaki, Masayo; Rich, Peter R

2004-03-03

The IR signature of binding of formate to the heme a(3-)Cu(B) binuclear site of bovine cytochrome c oxidase has been obtained by perfusion ATR-FTIR spectroscopy. The data show unequivocally that formate binds in its anionic form despite its binding being electroneutral overall. The bound formate can be distinguished from free ligand by the binding-induced sharpening and downshifting of vibrational bands. Formate ligation also causes shifts of vibrational modes of heme a(3) and its substituents and perturbation of histidine residues. The association of the accompanying protonation change with a carboxylate or tyrosine can be ruled out and may involve a histidine metal ligand or, more likely, a simple displacement into the bulk phase of a hydroxide ligand to heme a(3) or CU(B), a reaction which would account for stoichiometric proton uptake and maintenance of net charge within the binuclear center domain.

Calculation of the exchange coupling constants of copper binuclear systems based on spin-flip constricted variational density functional theory.

PubMed

Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

2011-11-14

We have recently developed a methodology for the calculation of exchange coupling constants J in weakly interacting polynuclear metal clusters. The method is based on unrestricted and restricted second order spin-flip constricted variational density functional theory (SF-CV(2)-DFT) and is here applied to eight binuclear copper systems. Comparison of the SF-CV(2)-DFT results with experiment and with results obtained from other DFT and wave function based methods has been made. Restricted SF-CV(2)-DFT with the BH&HLYP functional yields consistently J values in excellent agreement with experiment. The results acquired from this scheme are comparable in quality to those obtained by accurate multi-reference wave function methodologies such as difference dedicated configuration interaction and the complete active space with second-order perturbation theory. © 2011 American Institute of Physics

Modification of 1,2,4,5-tetrazine with cationic rhenium(I) polypyridine units to afford phosphorogenic bioorthogonal probes with enhanced reaction kinetics.

PubMed

Choi, Alex Wing-Tat; Tso, Karson Ka-Shun; Yim, Vicki Man-Wai; Liu, Hua-Wei; Lo, Kenneth Kam-Wing

2015-02-25

New phosphorogenic bioorthogonal probes derived from mononuclear and binuclear rhenium(I) polypyridine complexes containing a 1,2,4,5-tetrazine moiety were designed; these complexes displayed substantial dienophile-induced emission enhancement, and accelerated reaction kinetics and could target a protein conjugate in living cells.

Reconstitution of active mycobacterial binuclear iron monooxygenase complex in Escherichia coli.

PubMed

Furuya, Toshiki; Hayashi, Mika; Kino, Kuniki

2013-10-01

Bacterial binuclear iron monooxygenases play numerous physiological roles in oxidative metabolism. Monooxygenases of this type found in actinomycetes also catalyze various useful reactions and have attracted much attention as oxidation biocatalysts. However, difficulties in expressing these multicomponent monooxygenases in heterologous hosts, particularly in Escherichia coli, have hampered the development of engineered oxidation biocatalysts. Here, we describe a strategy to functionally express the mycobacterial binuclear iron monooxygenase MimABCD in Escherichia coli. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the mimABCD gene expression in E. coli revealed that the oxygenase components MimA and MimC were insoluble. Furthermore, although the reductase MimB was expressed at a low level in the soluble fraction of E. coli cells, a band corresponding to the coupling protein MimD was not evident. This situation rendered the transformed E. coli cells inactive. We found that the following factors are important for functional expression of MimABCD in E. coli: coexpression of the specific chaperonin MimG, which caused MimA and MimC to be soluble in E. coli cells, and the optimization of the mimD nucleotide sequence, which led to efficient expression of this gene product. These two remedies enabled this multicomponent monooxygenase to be actively expressed in E. coli. The strategy described here should be generally applicable to the E. coli expression of other actinomycetous binuclear iron monooxygenases and related enzymes and will accelerate the development of engineered oxidation biocatalysts for industrial processes.

Crystal structure of bis-[tetra-kis-(tetra-hydro-furan-κO)lithium] bis[μ-2,2',2''-methanetriyltris(4,6-di-tert-butylphenolato)-κ4O,O':O',O'']-dimagnesiate.

PubMed

Zhou, Hongyan; Wang, Lei

2017-07-01

The title ion-association metal complex, [Li(C 4 H 8 O) 4 ] 2 [Mg 2 (C 43 H 61 O 3 ) 2 ], has been synthesized from the tridentate phenolic ligand tris-(3,5-di- tert -butyl-2-hy-droxy-phen-yl)methane in tetra-hydro-furan (THF). The aryl-oxo magnesiate complex anion is binuclear with each Mg 2 O 4 complex unit inversion-related and bridged through the two tridentate chelating phenolate O-donors of the ligand. The complex centres have a distorted tetra-hedral stereochemistry [Mg-O range 1.8796 (17)-2.0005 (16) Å] and an Mg⋯Mg separation of 2.9430 (14) Å]. The LiO 4 coodination sphere of the cation comprises four THF O-donor atoms and has a slightly distorted tetra-hedral conformation [Li-O range 1.899 (5)- 1.953 (5) Å]. In the crystal, a number of stabilizing intra-anion C-H⋯O hydrogen-bonding inter-actions are present but no inter-species associations are found.

Phosphorescent binuclear iridium complexes based on terpyridine-carboxylate: an experimental and theoretical study.

PubMed

Andreiadis, Eugen S; Imbert, Daniel; Pécaut, Jacques; Calborean, Adrian; Ciofini, Ilaria; Adamo, Carlo; Demadrille, Renaud; Mazzanti, Marinella

2011-09-05

The phosphorescent binuclear iridium(III) complexes tetrakis(2-phenylpyridine)μ-(2,2':6',2''-terpyridine-6,6''-dicarboxylic acid)diiridium (Ir1) and tetrakis(2-(2,4-difluorophenyl) pyridine))μ-(2,2':6',2''-terpyridine-6,6''-dicarboxylic acid)diiridium (Ir2) were synthesized in a straightforward manner and characterized using X-ray diffraction, NMR, UV-vis absorption, and emission spectroscopy. The complexes have similar solution structures in which the two iridium centers are equivalent. This is further confirmed by the solid state structure of Ir2. The newly reported complexes display intense luminescence in dichloromethane solutions with maxima at 538 (Ir1) and 477 nm (Ir2) at 298 K (496 and 468 nm at 77 K, respectively) and emission quantum yields reaching ~18% for Ir1. The emission quantum yield for Ir1 is among the highest values reported for dinuclear iridium complexes. It shows only a 11% decrease with respect to the emission quantum yield reported for its mononuclear analogue, while the molar extinction coefficient is roughly doubled. This suggests that such architectures are of potential interest for the development of polymetallic assemblies showing improved optical properties. DFT and time-dependent-DFT calculations were performed on the ground and excited states of the complexes to provide insights into their structural, electronic, and photophysical properties.

Selective detection of Cu2 + and Co2 + in aqueous media: Asymmetric chemosensors, crystal structure and spectroscopic studies

NASA Astrophysics Data System (ADS)

Dogaheh, Samira Gholizadeh; Khanmohammadi, Hamid; Carolina Sañudo, E.

2017-05-01

Two new azo-azomethine receptors, H2L1 and H2L2, containing hydrazine, naphthalene and different electron withdrawing groups, Cl and NO2, have been designed and synthesized for qualitative and quantitative detection of Cu2 + and Co2 + in aqueous media. The crystal structure of H2L1is reported. The H2L1was used as a chemosensor for selective detection of trace amount of Cu2 + in aqueous media. H2L2 was also applied to naked-eye distinction of Cu2 + and Co2 + from other transition metal ions in aqueous media. Detection limit of Cu2 + is 1.13 μM and 1.26 μM, in water, for H2L1 and H2L2, respectively, which are lower than the World Health Organization (WHO) recommended level. The binuclear Cu2 + and Co2 + complexes of the receptors have been also prepared and characterized using spectroscopic methods and MALDI-TOF mass analysis. Furthermore, the binding stoichiometry between the receptors upon the addition Cu2 + and Co2 + has been investigated using Job's plot. Moreover, the fluorescence emission spectra of the receptors and their metal complexes are also reported.

Self-assembly of metal-organic supramolecules: from a metallamacrocycle and a metal-organic coordination cage to 1D or 2D coordination polymers based on flexible dicarboxylate ligands.

PubMed

Dai, Fangna; Dou, Jianmin; He, Haiyan; Zhao, Xiaoliang; Sun, Daofeng

2010-05-03

To assemble metal-organic supramolecules such as a metallamacrocycle and metal-organic coordination cage (MOCC), a series of flexible dicarboxylate ligands with the appropriate angle, 2,2'-(2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene)bis(sulfanediyl)dibenzoic acid (H(2)L(1)), 2,2'-(2,5-dimethyl-1,4-phenylene)bis(methylene)bis(sulfanediyl)dibenzoic acid (H(2)L(2)), 2,2'-(2,4,6-trimethyl-1,3-phenylene)bis(methylene)bis(sulfanediyl)dinicotinic acid (H(2)L(3)), and 2,2'-(2,4,6-trimethyl-1,3-phenylene)bis(methylene)bis(sulfanediyl)dibenzoic acid (H(2)L(4)), have been designed and synthesized. Using these flexible ligands to assemble with metal ions, six metal-organic supramolecules, Cd(2)(L(1))(2)(dmf)(4)(H(2)O)(2).H(2)O (1), Mn(3)((1)L(2))(2)((2)L(2))(dmf)(2)(H(2)O)(2).5dmf (2), Cu(4)(L(3))(4)(H(2)O)(4).3dmf (3), Cu(4)(L(4))(4)(dmf)(2)(EtOH)(2).8dmf.6H(2)O (4), Mn(4)(L(4))(4)(dmf)(4)(H(2)O)(4).6dmf.H(2)O (5), and Mn(3)(L(4))(3)(dmf)(4).2dmf.3H(2)O (6), possessing a rectangular macrocycle, MOCCs or their extensions, and 1D or 2D coordination polymers, have been isolated. All complexes have been characterized by single-crystal X-ray diffraction, elemental analysis, and thermogravimetric analysis. Complex 1 is a discrete rectangular macrocycle, while complex 2 is a 2D macrocycle-based coordination polymer in which the L(2) ligand adopts both syn and anti conformations. Complexes 3-5 are discrete MOCCs in which two binuclear metal clusters are engaged by four organic ligands. The different geometries of the secondary building units (SBUs) and the axial coordinated solvates on the SBUs result in their different symmetries. Complex 6 is a 1D coordination polymer, extended from a MOCC made up of two metal ions and three L(4) ligands. All of the flexible dicarboxylate ligands adopt a syn conformation except that in complex 2, indicating that the syn conformational ligand is helpful for the formation of a metallamacrocycle and a MOCC. The magnetic properties of complexes 5 and 6 have also been studied.

Ternary complexes of Zn(II) and Cu(II) with 1-((2-hydroxynaphthalen-1-yl)methylene)-4-phenylthiosemicarbazide in the presence of heterocyclic bases as auxiliary ligands: Synthesis, spectroscopic and structural characterization and antibacterial activity

NASA Astrophysics Data System (ADS)

Azarkish, Mohammad; Akbari, Alireza; Sedaghat, Tahereh; Simpson, Jim

2018-03-01

The new ternary complexes, ZnLL‧ [L = 1-((2-hydroxynaphthalen-1-yl)methylene)-4-phenylthiosemicarbazide and L‧ = imidazole (1), 2, 2‧-bipyridine (2) and 2-methyimidazole (3)], Zn2L2L‧ [L‧ = 4, 4‧-bipy (4)] and CuLL‧ [L‧ = 2, 2‧-bipy (5)] have been synthesized by the reaction of a metal(II) acetate salt with the thiosemicarbazone and in presence of heterocyclic bases as auxiliary ligands. The synthesized compounds were investigated by elemental analysis and IR, 1H NMR, and 13C NMR spectroscopy and complex 5 was structurally characterized by X-ray crystallography. The results indicate the thiosemicarbazone doubly deprotonated and coordinates to metal through the thiolate sulfur, imine nitrogen and phenolic oxygen atoms. The nitrogen atom(s) of the auxiliary ligand complete the coordination sphere. Complex 4 is binuclear with 4, 4‧-bipy acting as a bridging ligand. The structure of 5 is a distorted square pyramid with one of the bipyridine nitrogen atoms in the apical position. This compound creates an inversion dimer in solid state by intermolecular hydrogen bonds of Nsbnd H⋯S type. The in vitro antibacterial activity of the synthesized compounds were evaluated against Gram-positive (B. subtilis and S. aureus) and Gram-negative (P. aeruginosa) bacteria and is compared to that of standard antibacterial drugs. All complexes exhibit good inhibitory effects and are significantly more effective than the parent ligand.

The binuclear form of dinitrosyl iron complexes with thiol-containing ligands in animal tissues.

PubMed

Mikoyan, Vasak D; Burgova, Evgeniya N; Borodulin, Rostislav R; Vanin, Anatoly F

2017-01-30

It has been established that treatment of mice with sodium nitrite, S-nitrosoglutathione and the water-soluble nitroglycerine derivative isosorbide dinitrate (ISDN) as NO donors initiates in vivo synthesis of significant amounts of EPR-silent binuclear dinitrosyl iron complexes (B-DNIC) with thiol-containing ligands in the liver and other tissues of experimental mice. This effect is especially apparent if NO donors are administered to mice simultaneously with the Fe 2+ -citrate complex. Similar results were obtained in experiments on isolated liver and other mouse tissues treated with gaseous NО in vitro and during stimulation of endogenous NO synthesis in the presence of inducible NO synthase. B-DNIC appeared in mouse tissues after in vitro treatment of tissue samples with an aqueous solution of diethyldithiocarbamate (DETC), which resulted in the transfer of iron-mononitrosyl fragments from B-DNIC to the thiocarbonyl group of DETC and the formation of EPR-detectable mononitrosyl iron complexes (MNIC) with DETC. EPR-Active MNIC with N-methyl-d-glucamine dithiocarbamate (MGD) were synthesized in a similar way. MNIC-MGD were also formed in the reaction of water-soluble MGD-Fe 2+ complexes with sodium nitrite, S-nitrosoglutathione and ISDN. Copyright © 2016. Published by Elsevier Inc.

Binuclear cyclometalated organoplatinum complexes containing 1,1'-bis(diphenylphosphino)ferrocene as spacer ligand: kinetics and mechanism of MeI oxidative addition.

PubMed

Jamali, Sirous; Nabavizadeh, S Masoud; Rashidi, Mehdi

2008-06-16

The binuclear complex [Pt2Me2(ppy)2(mu-dppf)], 1, in which ppy = deprotonated 2-phenylpyridyl and dppf = 1,1'-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe2)(ppy)] with 0.5 equiv of dppf at room temperature. In this reaction when 1 equiv of dppf was used, the dppf chelating complex 2, [PtMe(dppf)(ppy-kappa1C)], was obtained. The reaction of Pt(II)-Pt(II) complex 1 with excess MeI gave the Pt(IV)-Pt(IV) complex [Pt2I2Me4(ppy)2(mu-dppf)], 3. When the reaction was performed with 1 equiv of MeI, a mixture containing unreacted complex 1, a mixed-valence Pt(II)-Pt(IV) complex [PtMe(ppy)(mu-dppf)PtIMe2(ppy)], 4, and complex 3 was obtained. In a comparative study, the reaction of [PtMe(SMe2)(ppy)] with 1 equiv of monodentate phosphine PPh3 gave [PtMe(ppy)(PPh3)], A. MeI was reacted with A to give the platinum(IV) complex [PtMe2I(ppy)(PPh3)], C. All the complexes were fully characterized using multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy, and complex 2 was further identified by single crystal X-ray structure determination. The reaction of binuclear Pt(II)-Pt(II) complex 1 with excess MeI was monitored by low temperature 31P NMR spectroscopy and further by 1H NMR spectroscopy, and the kinetics of the reaction was studied by UV-vis spectroscopy. On the basis of the data, a mechanism has been suggested for the reaction which overall involved stepwise oxidative addition of MeI to the two Pt(II) centers. In this suggested mechanism, the reaction proceeded through a number of Pt(II)-Pt(IV) and Pt(IV)-Pt(IV) intermediates. Although MeI in each step was trans oxidatively added to one of the Pt(II) centers, further trans to cis isomerizations of Me and I groups were also identified. A comparative kinetic study of the reaction of monomeric platinum(II) complex A with MeI was also performed. The rate of reaction of MeI with complex 1 was some 3.5 times faster than that with complex A, indicating that dppf in the complex 1, as compared with PPh 3 in the complex A, has significantly enhanced the electron richness of the platinum centers.

Comparison of two binuclear vanadium-catecholate complexes: Synthesis, X-ray structure and effects in cancer cells

NASA Astrophysics Data System (ADS)

Chi, Zixiang; Zhu, Linli; Lu, Xiaoming

2011-08-01

Two binuclear vanadium-catecholate complexes [Et 3NH] 2[V VO 2(μ-cat)] 2( 1) and [Et 3NH] 2[V VO 2(μ-N-2,3-D)] 2( 2) (cat = catechol, N-2,3-D = naphthalene-2,3-diol) have been synthesized and characterized by X-ray diffraction, IR, UV-vis spectroscopy and cyclic voltammetry (CV). X-ray analysis reveals that the structures of complexes 1 and 2 are both in the anion form of V. Et 3N works as counter-ions and connects the main frame by hydrogen bonding. The electrochemical behavior of the two complexes is studied in comparison to that of the free ligands and the two complexes display different redox potentials. Pharmaceutical screenings of complexes 1 and 2 have been made against two representative cancer cell-lines A-549 (lung cancer) and Bel-7402 (liver cancer) by MTT assay. The inhibition of cell proliferation was determined 72 h after cells were exposed to the tested compounds at a concentration of 5 μg/mL. Complex 1 exhibits well inhibition ratio against both two cell-lines (76.28% and 75.94%), while 2 displays positive and negative effect (65.36% and -68.82%) respectively. In association with X-ray and electrochemistry, a preliminary analysis about the possible inhibitory mechanism is provided.

The Analysis of Cyanide and Its Breakdown Products in Biological Samples

DTIC Science & Technology

2010-01-01

simultaneous GC-mass spectrometric (MS) analysis of cyanide and thiocyanate, and Funazo et al. (53) quantita- tively methylated cyanide and thiocyanate for...selective membrane electrode for thiocyanate ion based on a bis-taurine- salicylic binuclear copper(II) complex as ionophore. Chinese Journal of Chemistry

Syntheses, spectroscopic characterization, SOD-like properties and antibacterial activities of dimer copper (II) and nickel (II) complexes based on imine ligands containing 2-aminothiophenol moiety: X-ray crystal structure determination of disulfide Schiff bases

NASA Astrophysics Data System (ADS)

Bharti, Sulakshna; Choudhary, Mukesh; Mohan, Bharti; Rawat, S. P.; Sharma, S. R.; Ahmad, K.

2018-07-01

A series of new dimer complexes of copper (II) and nickel (II) were designed and synthesized using the Schiff base ligands which was formed by the condensation of 2-aminothiophenol with 2- methoxybenzaldehyde, 3-formylbenzonitrile and 3-bromo-2-hydroxy-5-nitrobenzaldehyde, respectively. The synthesized metallic complexes were characterized by using different physicochemical and spectroscopic methods. The most plausible geometry for the 1:2 complexes appeared to be distorted square-planar or tetrahedral environments. All the synthesized metal complexes are found to be binuclear and confirmed by elemental analyses, magnetic susceptibility measurements and ESR spectroscopy. The Schiff base ligands (HL1/HL2/H2L) were coordinated to the metal ions through the ONS/SNN and/or N, S donor atoms. In order to prevent the oxidation of the thiol group during the formation of Schiff bases and its complexes, all of the reactions were carried out under an inert atmosphere of argon. The X-ray structures of the Schiff base ligands showed that in the crystalline form the SH groups were oxidized to produce a disulfide Schiff bases as a new double Schiff base ligands (L1a/L2a/H2La). The L1b ligand is a bicyclic ring system of N, S-containing heterocyclic. The crystal structures of the double Schiff bases were determined by single crystal X-ray diffraction. The molar conductivity values of the complexes in DMSO implied the presence of non-electrolyte species. The SOD-like activity of Schiff bases and its complexes were investigated by NBT-DMSO assay and IC50 values were evaluated. Their biological properties have also been studied. These complexes were also tested for their in vitro antibacterial screening activities against three bacteria (Streptococcus aureus, Salmonella typhi, and Escherichia coli) comparing with the Schiff base ligands. Most of the complexes have higher antibacterial activities than those of the free Schiff bases, double Schiff bases and the control.

A new crystal form of Aspergillus oryzae catechol oxidase and evaluation of copper site structures in coupled binuclear copper enzymes.

PubMed

Penttinen, Leena; Rutanen, Chiara; Saloheimo, Markku; Kruus, Kristiina; Rouvinen, Juha; Hakulinen, Nina

2018-01-01

Coupled binuclear copper (CBC) enzymes have a conserved type 3 copper site that binds molecular oxygen to oxidize various mono- and diphenolic compounds. In this study, we found a new crystal form of catechol oxidase from Aspergillus oryzae (AoCO4) and solved two new structures from two different crystals at 1.8-Å and at 2.5-Å resolutions. These structures showed different copper site forms (met/deoxy and deoxy) and also differed from the copper site observed in the previously solved structure of AoCO4. We also analysed the electron density maps of all of the 56 CBC enzyme structures available in the protein data bank (PDB) and found that many of the published structures have vague copper sites. Some of the copper sites were then re-refined to find a better fit to the observed electron density. General problems in the refinement of metalloproteins and metal centres are discussed.

Syntheses, crystal structures, and properties of four complexes based on polycarboxylate and imidazole ligands

NASA Astrophysics Data System (ADS)

Qiao, Rui; Chen, Shui-Sheng; Sheng, Liang-Quan; Yang, Song; Li, Wei-Dong

2015-08-01

Four metal-organic coordination polymers [Zn(HL)(H2O)]·4H2O (1), [Zn(HL)(L1)]·4H2O (2), [Cu(HL)(H2O)]·3H2O (3) and [Cu(HL)(L1)]·5H2O (4) were synthesized by reactions of the corresponding metal(II) salts with semirigid polycarboxylate ligand (5-((4-carboxypiperidin-1-yl)methyl)isophthalic acid hydrochloride, H3L·HCl) or auxiliary ligand (1,4-di(1H-imidazol-4-yl)benzene, L1). The structures of the compounds were characterized by elemental analysis, FT-IR spectroscopy and single-crystal X-ray diffraction. The use of auxiliary ligand L1 has great influence on the structures of two pairs of complexes 1, 2 and 3, 4. Complex 1 is a uninodal 3-connected rare 2-fold interpenetrating ZnSc net with a Point (Schlafli) symbol of (103) while 2 is a one-dimensional (1D) ladder structure. Compound 3 features a two-dimensional (2D) honeycomb network with typical 63-hcb topology, while 4 is 2D network with (4, 4) sql topology based on binuclear CuII subunits. The non-covalent bonding interactions such as hydrogen bonds, π···π stacking and C-H···π exist in complexes 1-4, which contributes to stabilize crystal structure and extend the low-dimensional entities into high-dimensional frameworks. And the photoluminescent property of 1 and 2 and gas sorption property of 4 have been investigated.

The binuclear nickel center in the A-cluster of acetyl-CoA synthase (ACS) and two biomimetic dinickel complexes studied by X-ray absorption and emission spectroscopy

NASA Astrophysics Data System (ADS)

Schrapers, P.; Mebs, S.; Ilina, Y.; Warner, D. S.; Wörmann, C.; Schuth, N.; Kositzki, R.; Dau, H.; Limberg, C.; Dobbek, H.; Haumann, M.

2016-05-01

Acetyl-CoA synthase (ACS) is involved in the bacterial carbon oxide conversion pathway. The binuclear nickel sites in ACS enzyme and two biomimetic synthetic compounds containing a Ni(II)Ni(II) unit (1 and 2) were compared using XAS/XES. EXAFS analysis of ACS proteins revealed similar Ni-N/O/S bond lengths and Ni-Ni/Fe distances as in the crystal structure in oxidized ACS, but elongated Ni-ligand bonds in reduced ACS, suggesting more reduced nickel species. The XANES spectra of ACS and the dinickel complexes showed overall similar shapes, but less resolved pre-edge and edge features in ACS, attributed to more distorted square-planar nickel sites in particular in reduced ACS. DFT calculation of pre-edge absorption and Kβ2,5 emission features reproduced the experimental spectra of the synthetic complexes, was sensitive even to the small geometry differences in 1 and 2, and indicated low-spin Ni(II) sites. Comparison of nickel sites in proteins and biomimetic compounds is valuable for deducing structural and electronic differences in response to ligation and redox changes.

Coupling molecular catalysts with nanostructured surfaces for efficient solar fuel production

NASA Astrophysics Data System (ADS)

Jin, Tong

Solar fuel generation via carbon dioxide (CO2) reduction is a promising approach to meet the increasing global demand for energy and to minimize the impact of energy consumption on climate change. However, CO2 is thermodynamically stable; its activation often requires the use of appropriate catalysts. In particular, molecular catalysts with well-defined structures and tunability have shown excellent activity in photochemical CO2 reduction. These homogenous catalysts, however, suffer from poor stability under photochemical conditions and difficulty in recycling from the reaction media. Heterogenized molecular catalysts, particularly those prepared by coupling molecular catalysts with solid-state surfaces, have attracted more attention in recent years as potential solutions to address the issues associated with molecular catalysts. In this work, solar CO2 reduction is investigated using systems coupling molecular catalysts with robust nanostructured surfaces. In Chapter 2, heterogenization of macrocyclic cobalt(III) and nickel (II) complexes on mesoporous silica surface was achieved by different methods. Direct ligand derivatization significantly lowered the catalytic activity of Co(III) complex, while grafting the Co(III) complex onto silica surface through Si-O-Co linkage resulted in hybrid catalysts with excellent activity in CO2 reduction in the presence of p-terphenyl as a molecular photosensitizer. An interesting loading effect was observed, in which the optimal activity was achieved at a medium Co(III) surface density. Heterogenization of the Ni(II) complex on silica surface has also been implemented, the poor photocatalytic activity of the hybrid catalyst can be attributed to the intrinsic nature of the homogeneous analogue. This study highlighted the importance of appropriate linking strategies in preparing functional heterogenized molecular catalysts. Coupling molecular complexes with light-harvesting surfaces could avoid the use of expensive molecular photosensitizers. In Chapter 3, effective coupling of the macrocyclic Co(III) complex with titanium dioxide (TiO¬2) nanoparticles was achieved by two deposition methods. The synthesized hybrid photocatalysts were thoroughly characterized with a variety of techniques. Upon UV light irradiation, photoexcited electrons in TiO2 nanoparticles were transferred to the surface Co(III) catalyst for CO2 reduction. Production of carbon monoxide (CO) from CO2 was confirmed by isotope labeling combined with infrared spectroscopy. Deposition of the Co(III) catalyst through Ti-O-Co linkages was essential for the photo-induced electron transfer and CO2-reduction activity using the hybrid photocatalysts. In Chapter 4, molecular Re(I) and Co(II) catalysts were coupled with silicon-based photoelectrodes, including a silicon nanowire (SiNW) photoelectrode, to achieve photoelectrochemical CO2 reduction. Photovoltages between 300-600 mV were obtained using the molecular catalysts on the silicon photoelectrodes. SiNWs exhibited enhanced properties, including significantly higher photovoltages than a planar silicon photoelectrode, the ability to protect one of the molecular catalysts from photo-induced decomposition, and excellent selectivity towards CO production in CO2 reduction. Recent theoretical and experimental work have demonstrated low-energy, binuclear pathways for CO2-to-CO conversion using several molecular catalysts. In such binuclear pathways, two metal centers work cooperatively to achieve two-electron CO2 reduction. Chapter 5 describes our effort to promote the binuclear pathway by grafting the molecular Co(III) catalyst onto silica surfaces. Different linking strategies were attempted to achieve this goal by planting the surface Co(III) sites in close proximity.

Insights into Substrate Specificity and Metal Activation of Mammalian Tetrahedral Aspartyl Aminopeptidase*

PubMed Central

Chen, Yuanyuan; Farquhar, Erik R.; Chance, Mark R.; Palczewski, Krzysztof; Kiser, Philip D.

2012-01-01

Aminopeptidases are key enzymes involved in the regulation of signaling peptide activity. Here, we present a detailed biochemical and structural analysis of an evolutionary highly conserved aspartyl aminopeptidase called DNPEP. We show that this peptidase can cleave multiple physiologically relevant substrates, including angiotensins, and thus may play a key role in regulating neuron function. Using a combination of x-ray crystallography, x-ray absorption spectroscopy, and single particle electron microscopy analysis, we provide the first detailed structural analysis of DNPEP. We show that this enzyme possesses a binuclear zinc-active site in which one of the zinc ions is readily exchangeable with other divalent cations such as manganese, which strongly stimulates the enzymatic activity of the protein. The plasticity of this metal-binding site suggests a mechanism for regulation of DNPEP activity. We also demonstrate that DNPEP assembles into a functionally relevant tetrahedral complex that restricts access of peptide substrates to the active site. These structural data allow rationalization of the enzyme's preference for short peptide substrates with N-terminal acidic residues. This study provides a structural basis for understanding the physiology and bioinorganic chemistry of DNPEP and other M18 family aminopeptidases. PMID:22356908

Structural, molecular orbital and optical characterizations of binuclear mixed ligand copper (II) complex of phthalate with N,N,N',N'-tetramethylethylenediamine and its applications.

PubMed

Taha, A; Farag, A A M; Ammar, A H; Ahmed, H M

2014-09-15

A new binuclear mixed ligand complex, [Cu2(Phth)(Me4en)2(H2O)2(NO3)2]·H2O (where, Phth=phthalate, and (Me4en)=N,N,N',N'tetramethylethylenediamine) was synthesized and characterized using analytical, spectral, magnetic, molar conductance, thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The XRD data of Cu(II)-complex was analyzed on the basis of Williamson-Hall (W-H) and compared with TEM results. The results indicate that the complex is well crystalline and correspond to hexagonal crystal structure. Analysis of the absorption coefficient near the absorption edge reveals that the optical band gaps are indirect allowed transition with values of 1.17 and 1.78 eV. The d-d absorption bands of the complex (dissolved in various solvents) exhibit a color changes (solvatochromic). Specific and non-specific interactions of solvent molecules with the complex were investigated using Multiple Linear Regression Analysis (MLRA). Transient photocurrent characteristics of Cu(II)-complex/n-Si heterojunctions indicate that photocurrent under illumination increase with increasing of light intensity and explained by continuous distribution of traps. Structural parameters of the free ligands and their Cu(II)-complex were calculated on the basis of semi-empirical PM3 level and compared with the experimental data. The present copper (II) complex was screened for its antimicrobial activity against some Gram-positive and Gram-negative bacteria and fungus strain. Copyright © 2014 Elsevier B.V. All rights reserved.

Synthesis, characterization and antimicrobial activity of some nickel, cadmium and mercury complexes of 5-methyl pyrazole-3yl-N-(2‧-methylthiophenyl) methyleneimine, (MPzOATA) ligand

NASA Astrophysics Data System (ADS)

Mandal, Susmita; Mondal, Monojit; Biswas, Jayanta Kumar; Cordes, David B.; Slawin, Alexandra M. Z.; Butcher, Ray J.; Saha, Manan; Chandra Saha, Nitis

2018-01-01

Herein, we report the syntheses and structures of Ni(II) complexes, [Ni(MPzOATA)2] (Cl) (PF6) (I), [Ni(MPzOATA)2](ClO4)2.CH3CN (II) & [Ni(MPzOATA)2](BF4)2.H2O (III); Cd(II) complex, [Cd(MPzOATA)Cl2]2 (IV) and a Hg(II) complex, [Hg(MPzOATA)Cl2] (V), of a pyrazole based 'NNS' donor ligand, 5-methylpyrazole-3yl-N-(2‧-methylthiophenyl)methyleneimine, (MPzOATA). The complexes are characterized by elemental analyses, electronic, IR, 1H- NMR (only for IV &V) spectral parameters, conductivity and fluorescence measurements. X-ray crystallographic data of the complexes reveal that the Ni(II) complexes have NiN4S2 octahedral coordination, one of them is a mixed-anion complex having Cl- and PF6- as counter anions; the Cd(II) complex is a chloro bridged binuclear complex with octahedral coordination environment around each metal centre, while the Hg(II) complex is a square pyramidal one. Among the reported complex species, the Ni(II) complexes are non-fluorescent, while the Cd(II) and Hg(II) complexes can be used as potential photoactive materials as indicated from their characteristic emission properties. The reported complexes are screened for their antimicrobial activities against some Gram positive and Gram negative microbial strains, and they are found to be potential antimicrobial agents in broad spectrum against both Gram positive and Gram negative bacteria.

Electrocatalytic behaviour of surface confined pentanethio cobalt (II) binuclear phthalocyanines towards the oxidation of 4-chlorophenol

NASA Astrophysics Data System (ADS)

Makinde, Zainab O.; Louzada, Marcel; Mashazi, Philani; Nyokong, Tebello; Khene, Samson

2017-12-01

Cobalt binuclear phthalocyanine (CoBiPc) bearing pentanethio substituents at the peripheral positions were synthesized. The immobilization of the synthesized cobalt phthalocyanines on gold electrode was achieved using self-assembled monolayer method (SAM). X-ray photoelectron spectroscopy (XPS) and Kelvin Probe (KP) techniques were used to characterise the formation of monomeric and binuclear phthalocyanine SAMs on the gold surface. The phthalocyanine SAMs on gold electrodes were investigated for electrocatalytic oxidation of 4-chlorophenol. The electrocatalytic properties of tetra- and octa- pentanethio substituted cobalt binuclear phthalocyanine (CoBiPc) are compared with their tetra- and octa-pentanethio substituted phthalocyanine (CoPc). The SAMs modified gold electrode surfaces showed a peak current enhancement and stability and reduction in electrocatalytic potentials compared to the bare or unmodified electrodes towards the detection of the 4-chlorophenol. The SAMs of cobalt binuclear phthalocyanines exhibited more enhanced electrocatalytic properties in terms of stability, detection peak current and reduction of the electrocatalytic over potential.

Lanthanide coordination polymers based on multi-donor ligand containing pyridine and phthalate moieties: Structures, luminescence and magnetic properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Xun; Liu, Lang; College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang 471022

2013-10-15

A new family of five lanthanide-organic coordination polymers incorporating multi-functional N-hetrocyclic dicarboxylate ligand, namely, [Ln{sub 2}(Hdpp){sub 2}(dpp){sub 2}]{sub n}Ln=Pr(1), Eu(2), Gd(3), Dy(4), Er(5) (H{sub 2}dpp=1-(3, 4-dicarboxyphenyl) pyridin-4-ol) have been fabricated successfully through solvothermal reaction of 1-(3,4-dicarboxyphenyl)-4-hydroxypyridin-1-ium chloride with trivalent lanthanide salts, and have been characterized systematically. The complexes 1–5 are isomorphous and isostructural. They all feature three dimensional (3D) frameworks based on the interconnection of 1D double chains composed of the binuclear moiety [Ln{sub 2}(Hdpp){sub 2}]{sup 4+} basic carboxylate as secondary building unit (SBU). The results of magnetic analysis shows the same bridging fashion of carboxylic group in this casemore » results in the different magnetic properties occurring within lanthanide polymers. Moreover, the Eu(III) and Dy(III) complexes display characteristic luminescence emission in the visible regions. - Graphical abstract: A new family of lanthanide-organic frameworks incorporating multi-donor twisted ligand has been fabricated successfully, and has been characterized systematically. The complexes 1–5 are isostructural, and all feather three dimensional (3D) frameworks based on the interconnection of 1D double stride chains composed of the binuclear moiety [Ln{sub 2}(Hdpp){sub 2}]{sup 2+} basic carboxylate as secondary building unit (SBU). Display Omitted - Highlights: • New family of lanthanide–organic coordination polymers incorporating multifunctional N-hetrocyclic dicarboxylate ligand has been fabricated. • They have been characterized systematically. • They all feather three dimensional frameworks based on the binuclear moiety of [Ln{sub 2}(Hdpp){sub 2}]{sup 2+}. • The Eu(III) and Dy(III) analogues exhibit intense photoluminescence.« less

Antibacterial, antibiofilm and antioxidant screening of copper(II)-complexes with some S-alkyl derivatives of thiosalicylic acid. Crystal structure of the binuclear copper(II)-complex with S-propyl derivative of thiosalicylic acid

NASA Astrophysics Data System (ADS)

Bukonjić, Andriana M.; Tomović, Dušan Lj.; Nikolić, Miloš V.; Mijajlović, Marina Ž.; Jevtić, Verica V.; Ratković, Zoran R.; Novaković, Slađana B.; Bogdanović, Goran A.; Radojević, Ivana D.; Maksimović, Jovana Z.; Vasić, Sava M.; Čomić, Ljiljana R.; Trifunović, Srećko R.; Radić, Gordana P.

2017-01-01

The spectroscopically predicted structure of the obtained copper(II)-complex with S-propyl derivative of thiosalicylic acid was confirmed by X-ray structural study. The binuclear copper(II)-complex with S-propyl derivative of thiosalicylic acid crystallized in two polymorphic forms with main structural difference in the orientation of phenyl rings relative to corresponding carboxylate groups. The antibacterial activity was tested determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) by using microdilution method. The influence on bacterial biofilm formation was determined by tissue culture plate method. In general, the copper(II)-complexes manifested a selective and moderate activity. The most sensitive bacteria to the effects of Cu(II)-complexes was a clinical isolate of Pseudomonas aeruginosa. For this bacteria MIC and biofilm inhibitory concentration (BIC) values for all tested complexes were in the range or better than the positive control, doxycycline. Also, for the established biofilm of clinical isolate Staphylococcus aureus, BIC values for the copper(II)-complex with S-ethyl derivative of thiosalicylic acid,[Cu2(S-et-thiosal)4(H2O)2] (C3) and copper(II)-complex with S-butyl derivative of thiosalicylic acid, [Cu2(S-bu-thiosal)4(H2O)2] (C5) were in range or better than the positive control. All the complexes acted better against Gram-positive bacteria (Staphylococcus aureus and Staphylococcus aureus ATCC 25923) than Gram-negative bacteria (Proteus mirabilis ATCC 12453, Pseudomonas aeruginosa, and P. aeruginosa ATCC 27855). The complexes showed weak antioxidative properties tested by two methods (1,1-diphenyl-2-picrylhydrazyl (DPPH) and reducing power assay).

Synthesis, structure, NO-donor and redox activity of bis-(2-methylfuranethiolate)tetranitrosyl diiron

NASA Astrophysics Data System (ADS)

Sanina, N. A.; Kozub, G. I.; Kondratéva, T. A.; Korchagin, D. V.; Shilov, G. V.; Emelýanova, N. S.; Manzhos, R. A.; Krivenko, A. G.; Aldoshin, S. M.

2014-10-01

The new tetranitrosyl binuclear iron complex [Fe2(SС5H5O)2(NO)4] (I) has been synthesized by the reaction of aqueous solutions of anionic salts [Fе(S2O3)2(NO)2]3- and [SС5H5O]-. The latter one has been obtained by the reduction of methyl furfuryl disulfide by hydrazine hydrate in ethanol at T = 25 °C. The molecular and crystalline structure of I has been determined by X-ray method. The complex has binuclear structure of “μ-S” type with the distance between the iron atoms ∼2.70 Å. In the crystalline structure shortened intermolecular contacts of the nitrosyl groups of the adjacent molecules are observed. The maximum amount of NO generated by I in 1% aqueous solution of dimethylsulfoxide (DMSO) is ∼5 nM, and it reduces to zero in 8 min after decomposition starts in anaerobic conditions at Т = 25 °С, pH 6.5. As follows from the method of natural bond orbital analysis (NBO analysis), complex I has rather strong Fesbnd NO bond, as compared to other NO donors. Using CVA method, the values of reduction potentials for I in an aprotic solvent have been determined, and the scheme for its reduction has been suggested.

Binary and ternary copper(II) complexes of a new Schiff base ligand derived from 4-acetyl-5,6-diphenyl-3(2H)-pyridazinone: Synthesis, spectral, thermal, antimicrobial and antitumor studies

NASA Astrophysics Data System (ADS)

Shebl, Magdy; Adly, Omima M. I.; Abdelrhman, Ebtesam M.; El-Shetary, B. A.

2017-10-01

A new Schiff base ligand was synthesized by the reaction of 4-acetyl-5,6-diphenyl-3(2H)-pyridazinone with ethylenediamine. A series of binary copper(II) Schiff base complexes have been synthesized by using various copper(II) salts; AcO-, NO3-, ClO4-, Cl- and Br-. Ternary complexes were synthesized by using auxiliary ligands (L‧) [N,O-donor; 8-hydroxyquinoline and glycine or N,N-donor; 1,10-phenanthroline, bipyridyl and 2-aminopyridine]. The structures of the Schiff base and its complexes were characterized by elemental and thermal analyses, IR, electronic, mass, 1H NMR and ESR spectra in addition to conductivity and magnetic susceptibility measurements. The obtained complexes include neutral binuclear complexes as well as neutral and cationic mononuclear complexes according to the anion used and the experimental conditions. The ESR spin Hamiltonian parameters of some complexes were calculated and discussed. The metal complexes exhibited octahedral and square planar geometrical arrangements depending on the nature of the anion. Kinetic parameters (Ea, A, ΔH, ΔS and ΔG) of the thermal decomposition stages were evaluated using Coats-Redfern equations. The antimicrobial activity of the Schiff base and its complexes was screened against Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), Gram-negative bacteria (Salmonella typhimurium and Escherichia coli), yeast (Candida albicans) and fungus (Aspergillus fumigatus). The antitumor activity of the Schiff base and some of its Cu(II) complexes was investigated against HepG-2 cell line.

Convergent Use of Heptacoordination for Cation Selectivity by RNA and Protein Metalloregulators.

PubMed

Bachas, Sharrol T; Ferré-D'Amaré, Adrian R

2018-05-04

The large yybP-ykoY family of bacterial riboswitches is broadly distributed phylogenetically. Previously, these gene-regulatory RNAs were proposed to respond to Mn 2+ . X-ray crystallography revealed a binuclear cation-binding pocket. This comprises one hexacoordinate site, with six oxygen ligands, which preorganizes the second, with five oxygen and one nitrogen ligands. The relatively soft nitrogen ligand was proposed to confer affinity for Mn 2+ , but how this excludes other soft cations remained enigmatic. By subjecting representative yybP-ykoY riboswitches to diverse cations in vitro, we now find that these RNAs exhibit limited transition metal ion selectivity. Among the cations tested, Cd 2+ and Mn 2+ bind most tightly, and comparison of three new Cd 2+ -bound crystal structures suggests that these riboswitches achieve selectivity by enforcing heptacoordination (favored by high-spin Cd 2+ and Mn 2+ , but otherwise uncommon) in the softer site. Remarkably, the Cd 2+ - and Mn 2+ -selective bacterial transcription factor MntR also uses heptacoordination within a binuclear site to achieve selectivity. Published by Elsevier Ltd.

Magnetic exchange couplings from constrained density functional theory: an efficient approach utilizing analytic derivatives.

PubMed

Phillips, Jordan J; Peralta, Juan E

2011-11-14

We introduce a method for evaluating magnetic exchange couplings based on the constrained density functional theory (C-DFT) approach of Rudra, Wu, and Van Voorhis [J. Chem. Phys. 124, 024103 (2006)]. Our method shares the same physical principles as C-DFT but makes use of the fact that the electronic energy changes quadratically and bilinearly with respect to the constraints in the range of interest. This allows us to use coupled perturbed Kohn-Sham spin density functional theory to determine approximately the corrections to the energy of the different spin configurations and construct a priori the relevant energy-landscapes obtained by constrained spin density functional theory. We assess this methodology in a set of binuclear transition-metal complexes and show that it reproduces very closely the results of C-DFT. This demonstrates a proof-of-concept for this method as a potential tool for studying a number of other molecular phenomena. Additionally, routes to improving upon the limitations of this method are discussed. © 2011 American Institute of Physics

A micrometer-sized europium(iii)-organic framework for selective sensing of the Cr2O72- anion and picric acid in water systems.

PubMed

He, Hongming; Chen, Si-Hang; Zhang, De-Yu; Hao, Rui; Zhang, Chao; Yang, En-Cui; Zhao, Xiao-Jun

2017-10-10

A micrometer-sized europium(iii)-organic framework with asymmetric binuclear metal subunits extended by 4,5-dichlorophthalaten (DCPA), [Eu 2 (H 2 O)(DCPA) 3 ] n , was easily obtained using a reverse microemulsion method. The framework exhibits good dispersibility, excellent thermal and environmental stability and easy regeneration ability. More importantly, the complex displays strong red emission and can selectively and sensitively detect both inorganic Cr 2 O 7 2- anions (K sv = 8.7 × 10 3 M -1 ) and organic picric acid contaminants (K sv = 1.07 × 10 4 M -1 ) in water systems through fluorescence quenching. A luminescent film of 1 was further prepared and successfully used to detect the Cr 2 O 7 2- anion in an aqueous system. These interesting results indicate that the well-dispersed europium(iii)-organic framework can serve as a promising dual-responsive luminescent sensor for environmental pollutant monitoring.

Synthesis, interface (Au/M2Pc2/p-Si), electrochemical and electrocatalytic properties of novel ball-type phthalocyanines.

PubMed

Şengül, Abdurrahman; Doğan, H Zekeriya; Altındal, Ahmet; Özkaya, Ali Rıza; Salih, Bekir; Bekaroğlu, Özer

2012-07-07

The phthalodinitrile derivative (3) was prepared by the reaction of 4,4'-(octahydro-4,7-methano-5H-inden-5-ylidene)bisphenol (1) and 4-nitrophthalonitrile (2) with dry DMF as the solvent in the presence of the base K(2)CO(3) by the method of nucleophilic substitution of an activated nitro group in an aromatic ring. The template reaction of 3 with the corresponding metal salts gave the novel bi-nuclear ball-type metallophthalocyanines, MPcs {M = Co (4), Cu (5), Zn (6)}. Newly synthesized compounds were characterized by elemental analysis, UV-vis, FT-IR (ATR), MALDI-TOF mass and (1)H-NMR spectroscopy techniques. The electronic spectra exhibit an intense π→π* transition of characteristic Q and B bands of the Pc core. The dielectric properties and interface between the spin coated films of 4-6 and a p-type silicon substrate have been studied by fabricating metal-insulator-semiconductor capacitors. The results indicated that the frequency dependence of the dielectric permittivity, ε'(ω), exhibits non-Debye type relaxation for all the temperatures investigated. The ac conductivity results indicated that the conduction mechanism can be explained by a hopping model at low temperatures (<430 K) and a free band conduction mechanism at high temperatures (≥430 K). The density of interface state calculations on these novel compounds showed that the combination of Au/4/p-Si is a promising structure with a high dielectric constant and a low interface trap density suitable for metal-oxide-semiconductor devices. The electrochemical properties of the Pc complexes were examined by cyclic voltammetry, differential voltammetry and controlled potential coulometry on platinum in non-aqueous media. The complexes showed ring-based and/or metal-based mixed-valence behaviours as a result of the remarkable interaction between the two Pc rings and/or metal centres. The mixed-valence splitting values for the complexes suggested that the mixed valence species are considerably stable. The Vulcan XC-72(VC)/Nafion(Nf)/4 modified glassy carbon electrode showed much a higher catalytic performance towards oxygen reduction than those of VC/Nf/5 and VC/Nf/6 modified ones.

A series of Ln-p-chlorobenzoic acid–terpyridine complexes: lanthanide contraction effects, supramolecular interactions and luminescent behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carter, Korey P.; Pope, Simon J. A.; Cahill, Christopher L.

Fifteen new lanthanide p-chlorobenzoic acid complexes, [PrL3(terpy)(H2O)]2 (1), [LnL3(terpy)(H2O)]2 (Ln = Nd (2), Sm (3), and Eu (4)), and [LnL3(terpy)(H2O)] (Ln = Sm (3'), Eu (4'), Gd (5), Tb (6), Dy (7), Ho (8), Er (9), Tm (10), Yb (11), Lu (12), and Y (13); HL: p-chlorobenzoic acid; terpy: 2,2':6',2''-terpyridine), have been synthesized hydrothermally at varying temperatures and structurally characterized by single crystal and powder X-ray diffraction. The series is comprised of binuclear molecular units (Pr–Eu) that give way to mononuclear molecular complexes (Sm–Y) as the lanthanide contraction takes effect. All fifteen complexes feature a tridentate terpyridine ligand, p-chlorobenzoic acidmore » ligands exhibiting multiple binding modes, bidentate, bridging bidentate, and monodentate, and a bound water molecule. Binuclear complexes 1–4 are stitched together via intermolecular interactions: aromatic–aromatic interactions for 1, halogen•••halogen interactions for 2–4, to form 1D chains. Mononuclear complexes 3', 4', and 5–13 utilize supramolecular hydrogen and halogen bonding to form 2D sheets. Visible and near-IR solid state luminescence studies were performed on complexes 2, 3, 3', 4, 4', 6, 7 and 11 and the characteristic visible luminescence of Sm(III), Eu(III), Tb(III), and Dy(III) was exhibited. The near-IR spectra of the Nd(III) and Yb(III) complexes exhibit weak characteristic luminescence, showing that terpy can act as a sensitizing chromophore in these systems.« less

Assessing the exchange coupling in binuclear lanthanide(iii) complexes and the slow relaxation of the magnetization in the antiferromagnetically coupled Dy2 derivative.

PubMed

Chow, Chun Y; Bolvin, Hélène; Campbell, Victoria E; Guillot, Régis; Kampf, Jeff W; Wernsdorfer, Wolfgang; Gendron, Frédéric; Autschbach, Jochen; Pecoraro, Vincent L; Mallah, Talal

2015-07-01

We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga 4 Ln 2 (shi 3- ) 4 (Hshi 2- ) 2 (H 2 shi - ) 2 (C 5 H 5 N) 4 (CH 3 OH) x (H 2 O) x ]· x C 5 H 5 N· x CH 3 OH· x H 2 O (where H 3 shi = salicylhydroxamic acid and Ln = Gd III 1 ; Tb III 2 ; Dy III 3 ; Er III 4 ; Y III 5 ; Y III 0.9 Dy III 0.1 6 ). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field. The dynamic susceptibility studies of 3 and of the diluted DyY 6 complexes reveal the presence of two relaxation processes for 3 that are due to the excited ferromagnetic state and to the uncoupled Dy III ions. The antiferromagnetic coupling in 3 was shown to be mainly due to an exchange mechanism, which accounts for about 2/3 of the energy gap between the antiferro- and the ferromagnetic states. The overlap integrals between the Natural Spin Orbitals (NSOs) of the mononuclear fragments, which are related to the magnitude of the antiferromagnetic exchange, are one order of magnitude larger for the Dy 2 than for the Er 2 complex.

Unusual saccharin-N,O (carbonyl) coordination in mixed-ligand copper(II) complexes: Synthesis, X-ray crystallography and biological activity

NASA Astrophysics Data System (ADS)

Mokhtaruddin, Nur Shuhada Mohd; Yusof, Enis Nadia Md; Ravoof, Thahira B. S. A.; Tiekink, Edward R. T.; Veerakumarasivam, Abhi; Tahir, Mohamed Ibrahim Mohamed

2017-07-01

Three tridentate Schiff bases containing N and S donor atoms were synthesized via the condensation reaction between S-2-methylbenzyldithiocarbazate with 2-acetyl-4-methylpyridine (S2APH); 4-methyl-3-thiosemicarbazide with 2-acetylpyridine (MT2APH) and 4-ethyl-3-thiosemicarbazide with 2-acetylpyridine (ET2APH). Three new, binuclear and mixed-ligand copper(II) complexes with the general formula, [Cu(sac)(L)]2 (sac = saccharinate anion; L = anion of the Schiff base) were then synthesized, and subsequently characterized by IR and UV/Vis spectroscopy as well as by molar conductivity and magnetic susceptibility measurements. The Schiff bases were also spectroscopically characterized using NMR and MS to further confirm their structures. The spectroscopic data indicated that the Schiff bases behaved as a tridentate NNS donor ligands coordinating via the pyridyl-nitrogen, azomethine-nitrogen and thiolate-sulphur atoms. Magnetic data indicated a square pyramidal environment for the complexes and the conductivity values showed that the complexes were essentially non-electrolytes in DMSO. The X-ray crystallographic analysis of one complex, [Cu(sac)(S2AP)]2 showed that the Cu(II) atom was coordinated to the thiolate-S, azomethine-N and pyridyl-N donors of the S2AP Schiff base and to the saccharinate-N from one anion, as well as to the carbonyl-O atom from a symmetry related saccharinate anion yielding a centrosymmetric binuclear complex with a penta-coordinate, square pyramidal geometry. All the copper(II) saccharinate complexes were found to display strong cytotoxic activity against the MCF-7 and MDA-MB-231 human breast cancer cell lines.

Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO 2 reduction using time-resolved IR measurements

DOE PAGES

Koike, Kazuhide; Grills, David C.; Tamaki, Yusuke; ...

2018-02-14

Supramolecular photocatalysts in which Ru(II) photosensitizer and Re(I) catalyst units are connected to each other by an ethylene linker are among the best known, most effective and durable photocatalytic systems for CO 2 reduction. In this paper we report, for the first time, time-resolved infrared (TRIR) spectra of three of these binuclear complexes to uncover why the catalysts function so efficiently. Selective excitation of the Ru unit with a 532 nm laser pulse induces slow intramolecular electron transfer from the 3MLCT excited state of the Ru unit to the Re unit, with rate constants of (1.0–1.1) × 10 4 smore » -1 as a major component and (3.5–4.3) × 10 6 s -1 as a minor component, in acetonitrile. The produced charge-separated state has a long lifetime, with charge recombination rate constants of only (6.5–8.4) × 10 4 s -1. Thus, although it has a large driving force (-ΔG 0 CR ~ 2.6 eV), this process is in the Marcus inverted region. On the other hand, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH), reductive quenching of the excited Ru unit proceeds much faster (k q[BNAH (0.2 M)] = (3.5–3.8) × 10 6 s -1) than the abovementioned intramolecular oxidative quenching, producing the one-electron-reduced species (OERS) of the Ru unit. Nanosecond TRIR data clearly show that intramolecular electron transfer from the OERS of the Ru unit to the Re unit (k ET > 2 × 10 7 s -1) is much faster than from the excited state of the Ru unit, and that it is also faster than the reductive quenching process of the excited Ru unit by BNAH. To measure the exact value of k ET, picosecond TRIR spectroscopy and a stronger reductant were used. Thus, in the case of the binuclear complex with tri(p-fluorophenyl)phosphine ligands (RuRe(FPh)), for which intramolecular electron transfer is expected to be the fastest among the three binuclear complexes, in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), k ET was measured as k ET = (1.4 ± 0.1) × 10 9 s -1. This clearly shows that intramolecular electron transfer in these RuRe binuclear supramolecular photocatalysts is not the rate-determining process in the photocatalytic reduction of CO 2, which is one of the main reasons why they work so efficiently.« less

Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO 2 reduction using time-resolved IR measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koike, Kazuhide; Grills, David C.; Tamaki, Yusuke

Supramolecular photocatalysts in which Ru(II) photosensitizer and Re(I) catalyst units are connected to each other by an ethylene linker are among the best known, most effective and durable photocatalytic systems for CO 2 reduction. In this paper we report, for the first time, time-resolved infrared (TRIR) spectra of three of these binuclear complexes to uncover why the catalysts function so efficiently. Selective excitation of the Ru unit with a 532 nm laser pulse induces slow intramolecular electron transfer from the 3MLCT excited state of the Ru unit to the Re unit, with rate constants of (1.0–1.1) × 10 4 smore » -1 as a major component and (3.5–4.3) × 10 6 s -1 as a minor component, in acetonitrile. The produced charge-separated state has a long lifetime, with charge recombination rate constants of only (6.5–8.4) × 10 4 s -1. Thus, although it has a large driving force (-ΔG 0 CR ~ 2.6 eV), this process is in the Marcus inverted region. On the other hand, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH), reductive quenching of the excited Ru unit proceeds much faster (k q[BNAH (0.2 M)] = (3.5–3.8) × 10 6 s -1) than the abovementioned intramolecular oxidative quenching, producing the one-electron-reduced species (OERS) of the Ru unit. Nanosecond TRIR data clearly show that intramolecular electron transfer from the OERS of the Ru unit to the Re unit (k ET > 2 × 10 7 s -1) is much faster than from the excited state of the Ru unit, and that it is also faster than the reductive quenching process of the excited Ru unit by BNAH. To measure the exact value of k ET, picosecond TRIR spectroscopy and a stronger reductant were used. Thus, in the case of the binuclear complex with tri(p-fluorophenyl)phosphine ligands (RuRe(FPh)), for which intramolecular electron transfer is expected to be the fastest among the three binuclear complexes, in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), k ET was measured as k ET = (1.4 ± 0.1) × 10 9 s -1. This clearly shows that intramolecular electron transfer in these RuRe binuclear supramolecular photocatalysts is not the rate-determining process in the photocatalytic reduction of CO 2, which is one of the main reasons why they work so efficiently.« less

Magnetic anisotropy in binuclear complexes in the weak-exchange limit: From the multispin to the giant-spin Hamiltonian

NASA Astrophysics Data System (ADS)

Maurice, Rémi; de Graaf, Coen; Guihéry, Nathalie

2010-06-01

This paper studies the physical basis of the giant-spin Hamiltonian, which is usually used to describe the anisotropy of single-molecule magnets. A rigorous extraction of the model has been performed in the weak-exchange limit of a binuclear centrosymmetric Ni(II) complex, using correlated ab initio calculations and effective Hamiltonian theory. It is shown that the giant-spin Hamiltonian is not appropriate to describe polynuclear complexes as soon as spin mixing becomes non-negligible. A relevant model is proposed involving fourth-order operators, different from the traditionally used Stevens operators. The new giant-spin Hamiltonian correctly reproduces the effects of the spin mixing in the weak-exchange limit. A procedure to switch on and off the spin mixing in the extraction has been implemented in order to separate this effect from other anisotropic effects and to numerically evaluate both contributions to the tunnel splitting. Furthermore, the new giant-spin Hamiltonian has been derived analytically from the multispin Hamiltonian at the second order of perturbation and the theoretical link between the two models is studied to gain understanding concerning the microscopic origin of the fourth-order interaction in terms of axial, rhombic, or mixed (axial-rhombic) character. Finally, an adequate method is proposed to extract the proper magnetic axes frame for polynuclear anisotropic systems.

Influence of the redox active ligand on the reactivity and electronic structure of a series of Fe(TIM) complexes.

PubMed

Hess, Corinna R; Weyhermüller, Thomas; Bill, Eckhard; Wieghardt, Karl

2010-06-21

The redox properties of Fe and Zn complexes coordinated by an alpha-diimine based N(4)-macrocyclic ligand (TIM) have been examined using spectroscopic methods and density functional theory (DFT) computational analysis. DFT results on the redox series of [Zn(TIM*)](n) and [Fe(TIM*)](n) molecules indicate the preferential reduction of the alpha-diimine ligand moiety. In addition to the previously reported [Fe(TIM*)](2) dimer, we have now synthesized and characterized a further series of monomeric and dimeric complexes coordinated by the TIM ligand. This includes the five-coordinate monomeric [Fe(TIM*)I], the neutral and cationic forms of a monomeric phosphite adduct, [Fe(TIM*)(P(OPh)(3))] and [Fe(TIM*)(P(OPh)(3))](PF(6)), as well as a binuclear hydroxy-bridged complex, [{Fe(TIM*)}(2)(mu-OH)](PF(6)). Experimental and computational data for these synthetic compounds denote the presence of ferrous and ferric species, suggesting that the alpha-diimine based macrocycles do not readily support the formation of formally low-valent (M(0) or M(I)) metal complexes as previously speculated. Magnetochemical, Mossbauer, electron paramagnetic resonance (EPR), and electronic spectral data have been employed to experimentally determine the oxidation state of the central metal ion and of the macrocyclic ligand (TIM*) in each compound. The series of compounds is described as follows: [Fe(II)(TIM(0))(CH(3)CN(2))](2+), S(Fe) = S(T) = 0; [Fe(2.5)(TIM(2.5-))](2), S(T) = 1; [{Fe(III)(TIM(2-))}(2)(mu-OH)](+), S(Fe) = 3/2, S(T) = 0; [Fe(III)(TIM(2-))I], S(Fe) = 3/2, S(T) = 1/2; [Fe(II)(TIM(2-))(P(OPh(3)))], S(Fe) = S(T) = 0; and [Fe(II)(TIM(1-))(P(OPh(3)))](1+)/[Fe(I)(TIM(0))(P(OPh(3)))](1+), S(T) = 1/2. The results have been corroborated by DFT calculations.

Synthesis, structural, photophysical and thermal studies of benzoate bridged Sm(III) complexes

NASA Astrophysics Data System (ADS)

Singh, Udai P.; Kumar, Rajeev; Upreti, Shailesh

2007-04-01

One samarium coordination polymer (chain like) 1 with composition [{Sm(OBz) 3(MeO) 2} 2] n has been prepared from the reaction of SmCl 3 and sodium benzoate in 1:3 ratio whereas four binuclear samarium complexes with chemical composition [{(tp)Sm(μ- p-X-OBz) 2} 2] have been prepared by the reaction of SmCl 3, potassium hydrotris(pyrazol-1-yl)borate [K(tp)] and sodium p-X-benzoate (where X = H, Cl, F, NO 2) in 1:1:2 ratio. These complexes have been characterized by elemental analysis, IR spectroscopy, thermogravimetry, optical properties, X-ray and magnetic measurement studies. The X-ray structure shows that the complexes 2- 5 are isostructural whereas the structure of 1 is different. The coordination number around metal center in 1 is eight whereas in complexes 2- 5, each samarium is seven coordinate. The X-ray studies indicate that the complex 1 crystallizes in monoclinic space group P2(1)/ c with the cell dimensions a = 9.75(7), b = 21.83(15), c = 22.28(15) Å, whereas the complexes 2 and 3 crystallizes isostructurally in the triclinic space group P1¯ with the cell dimension a = 11.77(10), b = 12.60(10), c = 17.57(13) Å and a = 9.55(3), b = 12.80(4), c = 14.47(5) Å, respectively. The samarium ions in 2 and 3 are coordinated by three N atoms of pyrazolylborate ligand and four O atoms from benzoate groups. The photophysical properties of above complexes have been studied with ultraviolet absorption, excitation and emission spectral studies. The complexes 1- 5 excited at 240 nm wavelength produced characteristic luminescence features, arising mostly due to the f-f transitions.

Synthesis, characterization, and ligand exchange reactivity of a series of first row divalent metal 3-hydroxyflavonolate complexes.

PubMed

Grubel, Katarzyna; Rudzka, Katarzyna; Arif, Atta M; Klotz, Katie L; Halfen, Jason A; Berreau, Lisa M

2010-01-04

A series of divalent metal flavonolate complexes of the general formula [(6-Ph(2)TPA)M(3-Hfl)]X (1-5-X; X = OTf(-) or ClO(4)(-); 6-Ph(2)TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II); 3-Hfl = 3-hydroxyflavonolate) were prepared and characterized by X-ray crystallography, elemental analysis, FTIR, UV-vis, (1)H NMR or EPR, and cyclic voltammetry. All of the complexes have a bidentate coordinated flavonolate ligand. The difference in M-O distances (Delta(M-O)) involving this ligand varies through the series, with the asymmetry of flavonolate coordination increasing in the order Mn(II) approximately Ni(II) < Cu(II) < Zn(II) < Co(II). The hypsochromic shift of the absorption band I (pi-->pi*) of the coordinated flavonolate ligand in 1-5-OTf (relative to that in free anion) increases in the order Ni(II) < Mn(II) < Cu(II) < Zn(II), Co(II). Previously reported 3-Hfl complexes of divalent metals fit well with this ordering. (1)H NMR studies indicate that the 3-Hfl complexes of Co(II), Ni(II), and Zn(II) exhibit a pseudo-octahedral geometry in solution. EPR studies suggest that the Mn(II) complex 1-OTf may form binuclear structures in solution. The mononuclear Cu(II) complex 4-OTf has a distorted square pyramidal geometry. The oxidation potential of the flavonolate ligand depends on the metal ion present and/or the solution structure of the complex, with the Mn(II) complex 1-OTf exhibiting the lowest potential, followed by the pseudo-octahedral Ni(II) and Zn(II) 3-Hfl complexes, and the distorted square pyramidal Cu(II) complex 4-OTf. The Mn(II) complex [(6-Ph(2)TPA)Mn(3-Hfl)]OTf (1-OTf) is unique in the series in undergoing ligand exchange reactions in the presence of M(ClO(4))(2).6H(2)O (M = Co, Ni, Zn) in CD(3)CN to produce [(6-Ph(2)TPA)M(CD(3)CN)(n)](X)(2), [Mn(3-Hfl)(2).0.5H(2)O], and MnX(2) (X = OTf(-) or ClO(4)(-)). Under similar conditions, the 3-Hfl complexes of Co(II), Ni(II), and Cu(II) undergo flavonolate ligand exchange to produce [(6-Ph(2)TPA)M(CD(3)CN)(n)](X)(2) (M = Co, Ni, Cu; n = 1 or 2) and [Zn(3-Hfl)(2).2H(2)O]. An Fe(II) complex of 3-Hfl, [(6-Ph(2)TPA)Fe(3-Hfl)]ClO(4) (8), was isolated and characterized by elemental analysis, FTIR, UV-vis, (1)H NMR, cyclic voltammetry, and a magnetic moment measurement. This complex reacts with O(2) to produce the diiron(III) mu-oxo compound [(6-Ph(2)TPAFe(3Hfl))(2)(mu-O)](ClO(4))(2) (6).

Novel homo- and heterobinuclear ball-type phthalocyanines: synthesis and electrochemical, electrical, EPR and MCD spectral properties.

PubMed

Odabaş, Zafer; Dumludağ, Fatih; Ozkaya, Ali Riza; Yamauchi, Seigo; Kobayashi, Nagao; Bekaroğlu, Ozer

2010-09-21

The mononuclear Fe(II) phthalocyanine 2 and ball-type homobinuclear Fe(II)-Fe(II) and Cu(II)-Cu(II) phthalocyanines, 3 and 4 respectively, were synthesized from the corresponding 4,4'-[1,1'-methylenebis-(naphthalene-2,1-diyl)]bis(oxy)diphthalonitrile 1, and then ball-type heterobinuclear Fe(II)-Cu(II) phthalocyanine 5 was synthesized from 2. The novel compounds 4 and 5 have been characterized by elemental analysis, UV/vis, IR and MALDI-TOF mass spectroscopies. Electron paramagnetic resonance and magnetic circular dichroism measurements of 3, 4 and 5 were also examined. The voltammetric measurements of the complexes showed the formation of various electrochemically stable ligand- and metal-based mixed-valence species, due to the intramolecular interactions between the two MPc units, especially in ball-type binuclear iron(II) phthalocyanine. Impedance spectroscopy and d.c. conductivity measurements of 4 and 5 were performed as a function of temperature (295-523 K) and frequency (40-10(5) Hz). While room temperature impedance spectra consist of a curved line, a transformation into a full semicircle with increasing temperature was observed for both compounds.

N,N-Diethylamine appended binuclear Zn(ii) complexes: highly selective and sensitive fluorescent chemosensors for picric acid.

PubMed

Kumar, Amit; Kumar, Ashish; Pandey, Daya Shankar

2016-05-28

Novel binuclear Zn(ii) complexes (1-2) derived from bis-chelating salen type ligands (H2L(1) and H2L(2)) possessing N,N-diethylamine moieties on the periphery of the molecules have been synthesized and thoroughly characterized by satisfactory elemental analyses and spectral (FT-IR, (1)H, (13)C NMR, UV-vis, fluorescence and ESI-MS) studies. The structures of H2L(1) and 1 have been authenticated by single crystal X-ray diffraction analyses. Complexes 1 and 2 strongly fluoresce and act as highly selective and sensitive chemosensors for picric acid in different organic as well as aqueous media. Both 1 and 2 showed strong potential to detect traces of PA in vapour/solid phase through contact mode analysis. Spectral and theoretical (DFT) studies suggested that the observed fluorescence quenching may be associated with ground state (GS) charge transfer as well as electrostatic interactions between 1/2 and PA. The fluorescence lifetime for the representative complex 1 displayed a double exponential curve and unaltered lifetime (τav, 0.63 nm) in the absence and presence of PA and strongly suggested that quenching follows a static mechanism. Further, DFT calculations on 1 and 2 strongly supported the static mechanism through GS charge transfer between complexes and PA. In addition, (1)H NMR spectral studies on 1-2 in the presence of PA firmly advocated strong hydrogen bonding and π-π stacking between the phenolic rings of 1-2 and the aromatic ring of PA. These complexes are capable of detecting PA either individually or in a competitive environment of other nitro- explosives. Florescence spectral studies on the model complex M lacking N,N-diethylamine groups revealed moderate selectivity and sensitivity towards PA and supported the key role of N,N-diethylamine moieties in the selectivity and sensitivity of complexes.

Properties of Reactive Atomic Species Generated at High Temperatures and Their Low Temperature Reactions to Form Novel Substances

DTIC Science & Technology

1979-01-01

product is magnesium pinacolate, minor but important are the magnesium enolate of acetone and isopropoxide in 1:1 ratio. The double ketyl is a...tungsten, molybdenum and titanium were either unknown or had been made in very poor yield. Our vaporization techniques make these compounds readily...excess cyclooctatetraene. Mono and binuclear complexes of titanium have been isolated; the latter, triscyclooctatetraenedititanium was shown to be a

Variation of the ground spin state in homo- and hetero-octanuclear copper(II) and nickel(II) double-star complexes with a meso-helicate-type metallacryptand core.

PubMed

Pardo, Emilio; Dul, Marie-Claire; Lescouëzec, Rodrigue; Chamoreau, Lise-Marie; Journaux, Yves; Pasán, Jorge; Ruiz-Pérez, Catalina; Julve, Miguel; Lloret, Francesc; Ruiz-García, Rafael; Cano, Joan

2010-05-28

Homo- and heterometallic octanuclear complexes of formula Na₂{[Cu₂(mpba)₃][Cu(Me₅dien)]₆}-(ClO₄)₆·12H₂O (1), Na₂{[Cu₂(Mempba)₃][Cu(Me₅dien)]₆}(ClO₄)₆·12H₂O (2), Na₂{[Ni₂(mpba)₃]-[Cu(Me₅dien)]₆}(ClO₄)₆·12H₂O (3), Na₂{[Ni₂(Mempba)₃][Cu(Me₅dien)]₆}(ClO₄)₆·9H₂O (4), {[Ni₂(mpba)₃][Ni(dipn)(H₂O)]₆}(ClO₄)₄·12.5H₂O (5), and {[Ni₂(Mempba)₃][Ni(dipn)-(H₂O)]₆}(ClO₄)₄·12H₂O (6) [mpba = 1,3-phenylenebis(oxamate), Mempba = 4-methyl-1,3-phenylenebis(oxamate), Me₅dien = N,N,N',N'',N''-pentamethyldiethylenetriamine, and dipn = dipropylenetriamine] have been synthesized through the "complex-as-ligand/complex-as-metal" strategy. Single-crystal X-ray diffraction analyses of 1, 3, and 5 show cationic M(II)₂M'(II)₆ entities (M, M' = Cu and Ni) with an overall double-star architecture, which is made up of two oxamato-bridged M(II)M'(II)₃ star units connected through three meta-phenylenediamidate bridges between the two central metal atoms leading to a binuclear metallacryptand core of the meso-helicate-type. Dc magnetic susceptibility data for 1-6 in the temperature range 2-300 K have been analyzed through a "dimer-of-tetramers" model [H = - J(S(1A)·S(3A) + S(1A)·S(4A) + S(1A)·S(5A) + S(2B)·S(6B) + S(2B)·S(7B) + S(2B)·S(8B)) - J'S(1A)·S(2B), with S(1A) = S(2B) = S(M) and S(3A) = S(4A) = S(5A) = S(6B) = S(7B) = S(8B) = S(M')]. The moderate to strong antiferromagnetic coupling between the M(II) and M'(II) ions through the oxamate bridge in 1-6 (-J(Cu-Cu) = 52.0-57.0 cm⁻¹, -J(Ni-Cu) = 39.1-44.7 cm⁻¹, and -J(Ni-Ni) = 26.3-26.6 cm⁻¹) leads to a non-compensation of the ground spin state for the tetranuclear M(II)M'(II)₃ star units [S(A) = S(B) = 3S(M') - S(M) = 1 (1 and 2), 1/2 (3 and 4), and 2 (5 and 6)]. Within the binuclear M(II)₂ meso-helicate cores of 1-4, a moderate to weak antiferromagnetic coupling between the M(II) ions (-J'(Cu-Cu) = 28.0-48.0 cm⁻¹ and -J'(Ni-Ni) = 0.16-0.97 cm⁻¹) is mediated by the triple m-phenylenediamidate bridge to give a ground spin singlet (S = S(A) - S(B) = 0) state for the octanuclear M(II)₂Cu(II)₆ molecule. Instead, a weak ferromagnetic coupling between the Ni(II) ions (J'(Ni-Ni) = 2.07-3.06 cm⁻¹) operates in the binuclear Ni(II)₂ meso-helicate core of 5 and 6 leading thus to a ground spin nonet (S = S(A) + S(B) = 4) state for the octanuclear Ni(II)₈ molecule. Dc magnetization data for 5 reveal a small but non-negligible axial magnetic anisotropy (D = -0.23 cm⁻¹) of the S = 4 Ni(II)₈ ground state with an estimated value of the energy barrier for magnetization reversal of 3.7 cm⁻¹ (U = -DS²). Ac magnetic susceptibility data for 5 show an unusual slow magnetic relaxation behaviour at low temperatures which is typical of "cluster glasses". The temperature dependence of the relaxation time for 5 has been interpreted on the basis of the Vogel-Fulcher law for weakly interacting clusters, with values of 2.5 K, 1.4 × 10⁻⁶ s, and 4.0 cm⁻¹ for the intermolecular interaction parameter (T₀), the pre-exponential factor (τ₀), and the effective energy barrier (U(eff)), respectively.

Tryptophan 334 Oxidation in Bovine Cytochrome c Oxidase Subunit I Involves Free Radical Migration

PubMed Central

Lemma-Gray, Patrizia; Weintraub, Susan T.; Carroll, Christopher A.; Musatov, Andrej; Robinson, Neal C.

2007-01-01

A single tryptophan (W334(I)) within the mitochondrial-encoded core subunits of cytochrome c oxidase (CcO) is selectively oxidized when hydrogen peroxide reacts with the binuclear center. W334(I) is converted to hydroxytryptophan as identified by HPLC-ESI/MS/MS analysis of peptides derived from the three SDS-PAGE purified subunits (total sequence coverage of subunits I, II and III was limited to 84%, 66% and 54%, respectively). W334(I) is located on the surface of CcO at the membrane interface. Two other surface tryptophans within nuclear-encoded subunits, W48(IV) and W19(VIIc), are also oxidized when hydrogen peroxide reacts with the binuclear center (Musatov et. al., 2004, Biochemistry 43, 1003–1009). Two aromatic-rich networks of amino acids were identified that link the binuclear center to the three oxidized tryptophans. We propose the following mechanism to explain these results. Electron transfer through the aromatic networks moves the free radicals generated at the binuclear center to the surface-exposed tryptophans, where they produce hydroxytryptophan. PMID:17239857

Synchronicity of mononuclear and dinuclear events in homogeneous catalysis. Hydroformylation of cyclopentene using Rh4(CO)12 and HRe(CO)5 as precursors.

PubMed

Li, Chuanzhao; Chen, Li; Garland, Marc

2007-10-31

The combined application of two or more metals in homogeneous catalysis can lead to synergistic effects; however, the phenomenological basis for these observations often goes undetermined. The hetero-bimetallic catalytic binuclear elimination reaction, a system involving both mononuclear and dinuclear intermediates, has been repeatedly suggested as a possible mechanism. In the present contribution, the simultaneous application of Rh4(CO)12 and HRe(CO)5 as precursors in the hydroformylation reaction leads to a very strong synergistic rate effect. In situ spectroscopic measurements confirm the presence of both mononuclear and dinuclear intermediates such as RCORh(CO)4 and RhRe(CO)9 in the active system. Moreover, kinetic analysis confirms interconversion of these intermediates as well as their statistical correlation with organic product formation. Specifically, the rate of hydrogen activation by RhRe(CO)9 is exactly equal to the rate of aldehyde formation from binuclear elimination between HRe(CO)5 and RCORh(CO)4 at all reaction conditions studied. Thus the catalytic events involving mononuclear species and those involving dinuclear species are synchronized. In the present experiments, the new topology is orders of magnitude more efficient than the corresponding unicyclic rhodium system.

Assessing the exchange coupling in binuclear lanthanide(iii) complexes and the slow relaxation of the magnetization in the antiferromagnetically coupled Dy2 derivative† †Electronic supplementary information (ESI) available: Additional magnetic data, additional figures and computational details. CCDC 1020818–1020822. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc01029b

PubMed Central

Chow, Chun Y.; Bolvin, Hélène; Campbell, Victoria E.; Guillot, Régis; Kampf, Jeff W.; Wernsdorfer, Wolfgang; Gendron, Frédéric; Autschbach, Jochen

2015-01-01

We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga4Ln2(shi3–)4(Hshi2–)2(H2shi–)2(C5H5N)4(CH3OH)x(H2O)x]·xC5H5N·xCH3OH·xH2O (where H3shi = salicylhydroxamic acid and Ln = GdIII1; TbIII2; DyIII3; ErIII4; YIII5; YIII0.9DyIII0.16). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field. The dynamic susceptibility studies of 3 and of the diluted DyY 6 complexes reveal the presence of two relaxation processes for 3 that are due to the excited ferromagnetic state and to the uncoupled DyIII ions. The antiferromagnetic coupling in 3 was shown to be mainly due to an exchange mechanism, which accounts for about 2/3 of the energy gap between the antiferro- and the ferromagnetic states. The overlap integrals between the Natural Spin Orbitals (NSOs) of the mononuclear fragments, which are related to the magnitude of the antiferromagnetic exchange, are one order of magnitude larger for the Dy2 than for the Er2 complex. PMID:29218180

Malonate-bound structure of the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ) and characterization of the native Fe[superscript 2+] metal-ion preference

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Colin J.; Hadler, Kieran S.; Carr, Paul D.

2011-09-28

The structure of a malonate-bound form of the glycerophosphodiesterase from Enterobacter aerogenes, GpdQ, has been refined at a resolution of 2.2 {angstrom} to a final R factor of 17.1%. The structure was originally solved to 2.9 {angstrom} resolution using SAD phases from Zn{sup 2+} metal ions introduced into the active site of the apoenzyme [Jackson et al. (2007), J. Mol. Biol. 367, 1047-1062]. However, the 2.9 {angstrom} resolution was insufficient to discern significant details of the architecture of the binuclear metal centre that constitutes the active site. Furthermore, kinetic analysis revealed that the enzyme lost a significant amount of activitymore » in the presence of Zn2+, suggesting that it is unlikely to be a catalytically relevant metal ion. In this communication, a higher resolution structure of GpdQ is presented in which malonate is visibly coordinated in the active site and analysis of the native metal-ion preference is presented using atomic absorption spectroscopy and anomalous scattering. Catalytic implications of the structure and its Fe{sup 2+} metal-ion preference are discussed.« less

Malonate-bound structure of the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ) and characterization of the native Fe[supscript 2+] metal-ion preference

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Colin J.; Hadler, Kieran S.; Carr, Paul D.

2010-09-20

The structure of a malonate-bound form of the glycerophosphodiesterase from Enterobacter aerogenes, GpdQ, has been refined at a resolution of 2.2 {angstrom} to a final R factor of 17.1%. The structure was originally solved to 2.9 {angstrom} resolution using SAD phases from Zn{sup 2+} metal ions introduced into the active site of the apoenzyme [Jackson et al. (2007), J. Mol. Biol. 367, 1047-1062]. However, the 2.9 {angstrom} resolution was insufficient to discern significant details of the architecture of the binuclear metal centre that constitutes the active site. Furthermore, kinetic analysis revealed that the enzyme lost a significant amount of activitymore » in the presence of Zn{sup 2+}, suggesting that it is unlikely to be a catalytically relevant metal ion. In this communication, a higher resolution structure of GpdQ is presented in which malonate is visibly coordinated in the active site and analysis of the native metal-ion preference is presented using atomic absorption spectroscopy and anomalous scattering. Catalytic implications of the structure and its Fe{sup 2+} metal-ion preference are discussed.« less

EPR Characterization of Dinitrosyl Iron Complexes with Thiol-Containing Ligands as an Approach to Their Identification in Biological Objects: An Overview.

PubMed

Vanin, Anatoly F

2018-06-01

The overview demonstrates how the use of only one physico-chemical approach, viz., the electron paramagnetic resonance method, allowed detection and identification of dinitrosyl iron complexes with thiol-containing ligands in various animal and bacterial cells. These complexes are formed in biological objects in the paramagnetic (electron paramagnetic resonance-active) mononuclear and diamagnetic (electron paramagnetic resonance-silent) binuclear forms and control the activity of nitrogen monoxide, one of the most universal regulators of metabolic processes in the organism. The analysis of electronic and spatial structures of dinitrosyl iron complex sheds additional light on the mechanism whereby dinitrosyl iron complex with thiol-containing ligands function in human and animal cells as donors of nitrogen monoxide and its ionized form, viz., nitrosonium ions (NO + ).

Coordination polymers with the chiral ligand N-p-tolylsulfonyl-L-glutamic acid: Influence of metal ions and different bipyridine ligands on structural chirality

DOE Office of Scientific and Technical Information (OSTI.GOV)

He Rong; Song Huihua, E-mail: songhuihua@mail.hebtu.edu.c; Wei Zhen

2010-09-15

Four new polymers, namely [Ni(-tsgluO)(2,4'-bipy){sub 2}(H{sub 2}O){sub 2}]{sub n}.5nH{sub 2}O (1), [Co(-tsgluO)(2,4'-bipy){sub 2}(H{sub 2}O){sub 2}]{sub n}.5nH{sub 2}O (2), [Ni(-tsgluO)(4,4'-bipy)]{sub n}.0.5nH{sub 2}O (3), and [Co(-tsgluO)(4,4'-bipy)]{sub n}.0.5nH{sub 2}O (4), where tsgluO{sup 2-}=(+)-N-p-tolylsulfonyl-L-glutamate dianion, 2,4'-bipy=2,4'-bipyridine, and 4,4'-bipy=4,4'-bipyridine, have been prepared and structurally characterized. Compounds 1 and 2 are isostructural and mononuclear, and crystallize in the acentric monoclinic space group Cc, forming 1D chain structures. Compound 3 is also mononuclear, but crystallizes in the chiral space group P2{sub 1}, forming a homochiral 2D architecture. In contrast to the other complexes, compound 4 crystallizes in the space group P-1 and is composed of binuclear [Co{submore » 2}O{sub 6}N{sub 2}]{sub n}{sup 4-} units, which give rise to a 2D bilayer framework. Moreover, compounds 1, 2, and 4 self-assemble to form 3D supramolecular structures through {pi}-{pi} stacking and hydrogen-bonding interactions, while compound 3 is further hydrogen-bonded to form 3D frameworks. We have demonstrated the influence of the central metal and bipyridine ligands on the framework chirality of the coordination complexes. - Graphical abstract: Four novel polymers based on a chiral ligand were prepared and structurally characterized; it represents the first series of investigations about the effect of central metals and bipyridine ligands on framework chirality.« less

Generation of a Mn(IV)-Peroxo or Mn(III)-Oxo-Mn(III) Species upon Oxygenation of Mono- and Binuclear Thiolate-Ligated Mn(II) Complexes.

PubMed

Lee, Chien-Ming; Wu, Wun-Yan; Chiang, Ming-Hsi; Bohle, D Scott; Lee, Gene-Hsiang

2017-09-05

A thiolate-bridged binuclear complex [PPN] 2 [(Mn II ( TMS PS3)) 2 ] (1, PPN = bis(triphenylphosphine)iminium and TMS PS3H 3 = (2,2',2″-trimercapto-3,3',3″-tris(trimethylsilyl)triphenylphosphine)), prepared from the reaction of MnCl 2 /[PPN]Cl and Li 3 [ TMS PS3], converts into a mononuclear complex [PPN][Mn II ( TMS PS3)(DABCO)] (2) in the presence of excess amounts of DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane). Variable temperature studies of solution containing 1 and DABCO by UV-vis spectroscopy indicate that 1 and 2 exist in significant amounts in equilibrium and mononuclear 2 is favored at low temperature. Treatment of 1 or 2 with the monomeric O 2 -side-on-bound [PPN][Mn IV (O 2 )( TMS PS3)] (3) produces the mono-oxo-bridged dimer [PPN] 2 [(Mn III ( TMS PS3)) 2 (μ-O)] (4). The electrochemistry of 1 and 2 reveals anodic peak(s) for a Mn III/ Mn II redox couple at shifted potentials against Fc/Fc + , indicating that both complexes can be oxidized by dioxygen. The O 2 activation mediated by 1 and 2 is investigated in both solution and the solid state. Microcrystals of 2 rapidly react with air or dry O 2 to generate the Mn(IV)-peroxo 3 in high yield, revealing a solid-to-solid transformation and two-electron reduction of O 2 . Oxygenation of 1 or 2 in solution, however, is affected by diffusion and transient concentration of dioxygen in the two different substrates, leading to generation of 3 and 4 in variable ratios.

Excited-state decay processes of binuclear rhodium(I) isocyanide complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miskowski, V.M.; Rice, S.F.; Gray, H.B.

1993-04-29

Emission lifetimes, quantum yields, and polarized excitation spectra of Rh[sub 2]b[sub 4][sup 2+] and Rh[sub 2](TMB)[sub 4][sup 2+] (b = 1,3-diisocyanopropane; TMB = 2,5-diisocyano-2,5-dimethylhexane) have been determined. The singlet and triplet d[sigma]* [yields] p[sigma]([sup 1,3]A[sub 2u]) excited states are luminescent with radiative rates of ca. 10[sup 8] and 10[sup 4] s[sup [minus

Strong DNA deformation required for extremely slow DNA threading intercalation by a binuclear ruthenium complex

PubMed Central

Almaqwashi, Ali A.; Paramanathan, Thayaparan; Lincoln, Per; Rouzina, Ioulia; Westerlund, Fredrik; Williams, Mark C.

2014-01-01

DNA intercalation by threading is expected to yield high affinity and slow dissociation, properties desirable for DNA-targeted therapeutics. To measure these properties, we utilize single molecule DNA stretching to quantify both the binding affinity and the force-dependent threading intercalation kinetics of the binuclear ruthenium complex Δ,Δ-[μ‐bidppz‐(phen)4Ru2]4+ (Δ,Δ-P). We measure the DNA elongation at a range of constant stretching forces using optical tweezers, allowing direct characterization of the intercalation kinetics as well as the amount intercalated at equilibrium. Higher forces exponentially facilitate the intercalative binding, leading to a profound decrease in the binding site size that results in one ligand intercalated at almost every DNA base stack. The zero force Δ,Δ-P intercalation Kd is 44 nM, 25-fold stronger than the analogous mono-nuclear ligand (Δ-P). The force-dependent kinetics analysis reveals a mechanism that requires DNA elongation of 0.33 nm for association, relaxation to an equilibrium elongation of 0.19 nm, and an additional elongation of 0.14 nm from the equilibrium state for dissociation. In cells, a molecule with binding properties similar to Δ,Δ-P may rapidly bind DNA destabilized by enzymes during replication or transcription, but upon enzyme dissociation it is predicted to remain intercalated for several hours, thereby interfering with essential biological processes. PMID:25245944

High Intensity Organic Light-emitting Diodes

NASA Astrophysics Data System (ADS)

Qi, Xiangfei

This thesis is dedicated to the fabrication, modeling, and characterization to achieve high efficiency organic light-emitting diodes (OLEDs) for illumination applications. Compared to conventional lighting sources, OLEDs enabled the direct conversion of electrical energy into light emission and have intrigued the world's lighting designers with the long-lasting, highly efficient illumination. We begin with a brief overview of organic technology, from basic organic semiconductor physics, to its application in optoelectronics, i.e. light-emitting diodes, photovoltaics, photodetectors and thin-film transistors. Due to the importance of phosphorescent materials, we will focus on the photophysics of metal complexes that is central to high efficiency OLED technology, followed by a transient study to examine the radiative decay dynamics in a series of phosphorescent platinum binuclear complexes. The major theme of this thesis is the design and optimization of a novel architecture where individual red, green and blue phosphorescent OLEDs are vertically stacked and electrically interconnected by the compound charge generation layers. We modeled carrier generation from the metal-oxide/doped organic interface based on a thermally assisted tunneling mechanism. The model provides insights to the optimization of a stacked OLED from both electrical and optical point of view. To realize the high intensity white lighting source, the efficient removal of heat is of a particular concern, especially in large-area devices. A fundamental transfer matrix analysis is introduced to predict the thermal properties in the devices. The analysis employs Laplace transforms to determine the response of the system to the combined effects of conduction, convection, and radiation. This perspective of constructing transmission matrices greatly facilitates the calculation of transient coupled heat transfer in a general multi-layer composite. It converts differential equations to algebraic forms, and can be expanded to study other thermal issues in more sophisticated structures.

A microporous lanthanum metal-organic framework as a bi-functional chemosensor for the detection of picric acid and Fe(3+) ions.

PubMed

Zhang, Chuanqi; Yan, Yan; Pan, Qinhe; Sun, Libo; He, Hongming; Liu, Yunling; Liang, Zhiqiang; Li, Jiyang

2015-08-07

A microporous lanthanum metal-organic framework [La(TPT)(DMSO)2]·H2O (La-MOF ()), has been synthesized using a rigid unsymmetrical tricarboxylate ligand of p-terphenyl-3,4'',5-tricarboxylic acid (H3TPT). The structure of is constructed by bi-nuclear lanthanum clusters and fully deprotonated TPT(3-) ligands, which can be simplified into a 3,6-connected flu-3,6-C2/c topology with a point symbol of (4(4)·6)2(4·6(2)·8(7)·10(2)). The π-electron rich ligand H3TPT enables to have blue luminescence when excited at 342 nm at ambient temperature. Meanwhile, exhibits the selective detection of picric acid (PA) and Fe(3+) ions in ethanol solution over other nitroaromatic compounds and metal ions. The high quenching efficiency and selectivity of makes it a potential bi-functional chemosensor for both PA and Fe(3+) ions.

Coligand-regulated assembly, fluorescence, and magnetic properties of Co(II) and Cd(II) complexes with a non-coplanar dicarboxylate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xin, Ling-Yun; Liu, Guang-Zhen, E-mail: gzliuly@126.com; Ma, Lu-Fang

A non-coplanar dicarboxylate ndca (H{sub 2}ndca=5-norbornene-2,3-dicarboxylic acid), combining with various dipyridyl-typed tectons, constructs six Cd(II)/Co(II) coordination polymers under hydrothermal conditions, namely [Co(ndca)(H{sub 2}O)]{sub n} (1), ([Co(ndca)(bpe)(H{sub 2}O)]·H{sub 2}O){sub n} (2), [Co(ndca)(bpa){sub 0.5}(H{sub 2}O)]{sub n} (3), [Cd(ndca)(bpe)(H{sub 2}O)]{sub n} (4), ([Cd(ndca)(bpa)(H{sub 2}O)]·0.5H{sub 2}O){sub n} (5), and ([Cd(ndca)(bpp) (H{sub 2}O)]·H{sub 2}O){sub n} (6) (bpe=1,2-di(4-pyridyl)ethylene, bpa=1,2-bi(4-pyridyl)ethane, and bpp=1,3-bis(4-pyridyl)propane). All these compounds contain various metal(II)–carboxylate motifs, including carboxylate binuclear (2, 4, 5), carboxylate chain (1, 6) and carboxylate layer (3), which are further extended by dipyridyl-typed coligands to afford a vast diversity of the structures with 2D pyknotic layers (1, 6), 2D open layermore » (5), 2D→3D interpenetrated networks (2,4), and 3D pillared-layer framework (3), respectively. In addition, fluorescent spectra of Cd(II) complexes and magnetic properties of Co(II) complexes are also given. - Graphical abstract: Six various cadmium(II)/cobalt(II)–organic frameworks were constructed by 5-norbornene-2,3-dicarboxylic acid and different bis(pyridine) rod-like tectons, and Cd (II) complexes exhibit blue–violet emissions, whereas Co (II) complexes show antiferromagnetic behaviours. Display Omitted.« less

Single and double C-Cl-activation of methylene chloride by P,N-ligand coordinated rhodium complexes.

PubMed

Blank, Benoît; Glatz, Germund; Kempe, Rhett

2009-02-02

Two in one: The simultaneous formation of bimetallic mu-methylene bridged Rh(III) complexes as well as dimeric Rh(III) complexes with terminal chloromethyl groups is observed for P,N-ligand stabilized Rh(I) complexes by C-Cl bond activation of methylene chloride. A mechanistic proposal for the formation of both activation products is also discussed. The synthesis of Rh(I) complexes with P-functionalized aminopyridine ligands is reported as well as the first simultaneous observation of a single and double activation of C-Cl bonds of methylene chloride affording both a dimeric Rh(III) complex bearing terminal CH(2)Cl groups in addition to a binuclear Rh(III) complex with a bridging mu-CH(2) group. The structures of the oxidative addition products were obtained by X-ray diffraction studies and NMR experiments were performed to elucidate some aspects of the reaction pathway.

Facile construction of terpridine-based metallo-polymers in hydrogels, crystals and solutions directed by metal ions.

PubMed

Li, Yajuan; Guo, Jiangbo; Dai, Bo; Geng, Lijun; Shen, Fengjuan; Zhang, Yajun; Yu, Xudong

2018-07-01

Driven by tunable metal-ligand interactions, a polydentate ligand TC containing terpyridine and carboxylic acid units was developed to construct metallo-polymers that showed multiple aggregation modes with controlled macroscopic properties. In the presence of different kind of Zn 2+ ions or NaOH, TC could form metallo-polymers via π-π stacking and metal-ligand interaction that further trapped water molecules, resulting in hydrogels and crystals. Moreover, these TC/Zn 2+ hydrogels could transform to soluble and fluorescent aggregates in the presence of NaOH due to the formation of binuclear metallo-polymers with enhanced ICT emission. The metal-ligand interactions tuned by different metal salts in gels, crystals, and sols were also studied and illustrated in detail, it was also proved that water was an essential linker for constructing Na + -based metallo-polymers from the TC/NaOH crystal data. This work demonstrated the engineered coordination pathways in generating controllable hydrogels and metallo-polymers for the first time, which led to novel approach for facilely constructing a number of hydrogels with tailorable macroscopic properties. Copyright © 2018 Elsevier Inc. All rights reserved.

Metal-organic frameworks with dynamic interlocked components

NASA Astrophysics Data System (ADS)

Vukotic, V. Nicholas; Harris, Kristopher J.; Zhu, Kelong; Schurko, Robert W.; Loeb, Stephen J.

2012-06-01

The dynamics of mechanically interlocked molecules such as rotaxanes and catenanes have been studied in solution as examples of rudimentary molecular switches and machines, but in this medium, the molecules are randomly dispersed and their motion incoherent. As a strategy for achieving a higher level of molecular organization, we have constructed a metal-organic framework material using a [2]rotaxane as the organic linker and binuclear Cu(II) units as the nodes. Activation of the as-synthesized material creates a void space inside the rigid framework that allows the soft macrocyclic ring of the [2]rotaxane to rotate rapidly, unimpeded by neighbouring molecular components. Variable-temperature 13C and 2H solid-state NMR experiments are used to characterize the nature and rate of the dynamic processes occurring inside this unique material. These results provide a blueprint for the future creation of solid-state molecular switches and molecular machines based on mechanically interlocked molecules.

Include dispersion in quantum chemical modeling of enzymatic reactions: the case of isoaspartyl dipeptidase.

PubMed

Zhang, Hai-Mei; Chen, Shi-Lu

2015-06-09

The lack of dispersion in the B3LYP functional has been proposed to be the main origin of big errors in quantum chemical modeling of a few enzymes and transition metal complexes. In this work, the essential dispersion effects that affect quantum chemical modeling are investigated. With binuclear zinc isoaspartyl dipeptidase (IAD) as an example, dispersion is included in the modeling of enzymatic reactions by two different procedures, i.e., (i) geometry optimizations followed by single-point calculations of dispersion (approach I) and (ii) the inclusion of dispersion throughout geometry optimization and energy evaluation (approach II). Based on a 169-atom chemical model, the calculations show a qualitative consistency between approaches I and II in energetics and most key geometries, demonstrating that both approaches are available with the latter preferential since both geometry and energy are dispersion-corrected in approach II. When a smaller model without Arg233 (147 atoms) was used, an inconsistency was observed, indicating that the missing dispersion interactions are essentially responsible for determining equilibrium geometries. Other technical issues and mechanistic characteristics of IAD are also discussed, in particular with respect to the effects of Arg233.

Hydrothermal preparation and physicochemical studies of new copper nano-complexes for antitumor application

NASA Astrophysics Data System (ADS)

Saif, M.; El-Shafiy, Hoda F.; Mashaly, Mahmoud M.; Eid, Mohamed F.; Nabeel, A. I.; Fouad, R.

2018-03-01

Two novel nano-complexes [(Cu)2(L) (NO3)2(OH2)] (CuH) and [Cu(HL) (OH2)2(NO3)] (CuCTH)were synthesized by hydrothermal method at 200 °C for 48 h in absence and presence of surfactant (CTAB), respectively. Introducing surfactant (CTAB) leads to changing stoichiometric metal/ligand ratio from binuclear (CuH) to mononuclear (CuCTH) nano-complexes. CuH shows irregular nano-flake shape while CuCTH have separately uniform nano-spherical morphology. Thermal analysis revealed that CuCTH is thermally stable in comparison with CuH Nano-complex. CuCTH absorption peak shifted to shorter wavelength (blue shift) and sharpness of the peak also decreased in presence of CTAB. The role of CTAB in the crystal growth is discussed. CuH and CuCTH nano-complexes were tested for their in vitro cytotoxicity against Ehrlich Ascites Carcinoma cell line (E.A.C.). Both nano-complexes effectively inhibited E.A.C. growth with IC50value of 37 and 25 μM for CuH and CuCTH, respectively. The high antitumor activity of CuCTH was attributed to several factors such as spherical morphology, smaller size, chemical structure, and geometry. The LD50 for high cytotoxic CuCTH nano-complex on mice was found to be 100 mg/kg with strong abscess in abdomen side effect. To overcome this side effect, different molar ratio of CuCTH and previously prepared ZnNano-complexes were tested for their in vitrocytotoxicity and in vivo toxicity. Obtained results show that the 2:8 M ratio between CuCTH and Zn nano-complexes gives very low toxicity without any side effects. Also, geometric optimization and conformational analysis were performed using semi-empirical PM3 method. Energy gap (ΔE), dipole moment, and structure activity relationship were performed and discussed.

Crystal structure of Agaricus bisporus mushroom tyrosinase: identity of the tetramer subunits and interaction with tropolone.

PubMed

Ismaya, Wangsa T; Rozeboom, Henriëtte J; Weijn, Amrah; Mes, Jurriaan J; Fusetti, Fabrizia; Wichers, Harry J; Dijkstra, Bauke W

2011-06-21

Tyrosinase catalyzes the conversion of phenolic compounds into their quinone derivatives, which are precursors for the formation of melanin, a ubiquitous pigment in living organisms. Because of its importance for browning reactions in the food industry, the tyrosinase from the mushroom Agaricus bisporus has been investigated in depth. In previous studies the tyrosinase enzyme complex was shown to be a H(2)L(2) tetramer, but no clues were obtained of the identities of the subunits, their mode of association, and the 3D structure of the complex. Here we unravel this tetramer at the molecular level. Its 2.3 Å resolution crystal structure is the first structure of the full fungal tyrosinase complex. The complex comprises two H subunits of ∼392 residues and two L subunits of ∼150 residues. The H subunit originates from the ppo3 gene and has a fold similar to other tyrosinases, but it is ∼100 residues larger. The L subunit appeared to be the product of orf239342 and has a lectin-like fold. The H subunit contains a binuclear copper-binding site in the deoxy-state, in which three histidine residues coordinate each copper ion. The side chains of these histidines have their orientation fixed by hydrogen bonds or, in the case of His85, by a thioether bridge with the side chain of Cys83. The specific tyrosinase inhibitor tropolone forms a pre-Michaelis complex with the enzyme. It binds near the binuclear copper site without directly coordinating the copper ions. The function of the ORF239342 subunits is not known. Carbohydrate binding sites identified in other lectins are not conserved in ORF239342, and the subunits are over 25 Å away from the active site, making a role in activity unlikely. The structures explain how calcium ions stabilize the tetrameric state of the enzyme.

Electronic structure of binuclear acetylacetonates of boron difluoride

NASA Astrophysics Data System (ADS)

Tikhonov, Sergey A.; Svistunova, Irina V.; Samoilov, Ilya S.; Osmushko, Ivan S.; Borisenko, Aleksandr V.; Vovna, Vitaliy I.

2018-05-01

The electronic structure of boron difluoride acetylacetonate and its three derivatives was studied using photoelectron and absorption spectroscopy, as well as the density functional theory. In a series of binuclear acetylacetonate complexes containing bridge-moieties of sulfur and selenium atoms, it was found an appreciable mixing of the π3-orbital of the chelate cycle with atomic orbitals S 3p and Se 4p resulting in destabilization of the HOMO levels by 0.4-0.6 eV, in comparison with the monomer. The positively charged fragment C(CH3)-CX-C(CH3) causes the field effect, which leads to stabilization of the LUMO levels by 0.3-0.4 eV and C 1s-levels by 0.5-1.2 eV. An analysis of the research results on the electronic structure made it possible to determine the effect of substituents in the γ position on the absorption spectra, which is mainly determined by the electron density transfer from the chalcogen atoms to the chelate cycles. It is shown that the calculated energy intervals between electron levels correlate well with the structure of the photoelectron spectra of valence and core electrons.

Progress of pancreatitis disease biomarker alpha amylase enzyme by new nano optical sensor.

PubMed

Attia, M S; Al-Radadi, Najlaa S

2016-12-15

A new nano optical sensor binuclear Pd-(2-aminothiazole) (urea), Pd(atz,ur) complex was prepared and characterized for the assessment of the activity of alpha amylase enzyme in urine and serum samples for early diagnosis of Pancreatitis disease. The assessment of alpha amylase activity is carried out by the quenching of the luminescence intensity of the nano optical sensor binuclear Pd(atz,ur) complex at 457nm by the 2-chloro-4-nitrophenol (2-CNP) which produced from the reaction of the enzyme with 2-chloro-4-nitrophenyl-α-d-maltotrioside (CNPG3) substrate. The remarkable quenching of the luminescence intensity at 457nm of nano Pd(atz,ur) doped in sol-gel matrix by various concentrations of the 2-CNP was successfully used as an optical sensor for the assessment of α-amylase activity. The calibration plot was achieved over the concentration range 8.5×10(-6) to 1.9×10(-9)molL(-1) 2-CNP with a correlation coefficient of (0.999) and a detection limit of (7.4×10(-10)molL(-1)). The method was used satisfactorily for the assessment of the α-amylase activity over activity range (3-321U/L) in different urine and serum samples of pancreatitis patients. The assessment of the alpha amylase biomarker by the proposed method increases its sensitivity (96.88%) and specificity (94.41%) for early diagnosis of pancreatitis diseases. Copyright © 2016 Elsevier B.V. All rights reserved.

Synthesis, structures and properties of three copper complexes with dibutyldithiocarbamate ligand

NASA Astrophysics Data System (ADS)

Wang, Chen; Niu, Jiao; Li, Jun; Ma, Xiaoxun

2017-05-01

Three copper complexes constructed with sulfur-containing dibutyldithiocarbamate ligand (DDTC), [(Et2NCS2)4Cu2] (1), [(Et2NCS2)(EtO)Cu]2 (2) and [(Et2NCS2)6Cu13I10]n (3) have been synthesized through the reaction of CuI with different mole ratios of DDTC under solution-diffusion conditions. The single crystal X-ray diffraction revealed that divalent Cu cations in complexes 1 and 2 imply that the reactant, Cu(I), was involved in the redox process. They formed binuclear complexes according to bridging S from DDTC ligands and O atoms from ethanol molecules respectively. The mixed valence Cu cations had two types of coordination environments in complex 3 and formed a two-dimensional layered coordination polymer by bridging the five-core Cu(I) clusters and Cu(II). The powder X-ray diffraction, luminescent, thermogravimetric analysis, etc. were also studied in this paper.

Iron chelates: a challenge to chemists and Mössbauer spectroscopists

NASA Astrophysics Data System (ADS)

Homonnay, Z.; Szilágyi, P. Á.; Vértes, A.; Kuzmann, E.; Sharma, V. K.; Molnár, G.; Bousseksou, A.; Grenèche, J.-M.; Brausam, A.; Meier, R.; van Eldik, R.

2008-02-01

The speciation of iron in aqueous solutions containing Fe3 + and selected chelates such as EDTA, EDDA, CDTA and HEDTA has been studied using transmission 57Fe Mössbauer spectrometry in frozen solutions. The protonation of various complexes as well as binuclear complex formation could be detected as a function of pH. Autoreduction of Fe3 + to Fe2 + was observed in several cases. Reaction with hydrogen peroxide proved to be rather different for the four ligands, while the dihapto complex [XFe( η 2-O2)]3 - had surprisingly identical Mössbauer parameters for X = EDTA, CDTA or HEDTA. Paramagnetic spin relaxation observed in the Mössbauer spectra was found to be strongly influenced by the identity of the chelating ligand, despite the basically spin-spin origin of the phenomenon.

A series of binuclear lanthanide(III) complexes: Crystallography, antimicrobial activity and thermochemistry properties studies

NASA Astrophysics Data System (ADS)

Zhang, Ying-Ying; Ren, Ning; Xu, Su-Ling; Zhang, Jian-Jun; Zhang, Da-Hai

2015-02-01

A series of novel lanthanide complexes with the general formula [Ln(3,4-DClBA)3phen]2 (Ln = Ho(1), Nd(2), Sm(3), Dy(4), Eu(5), Tb(6), Yb(7) and Er(8), 3,4-DClBA = 3,4-dichlorobenzoate, phen = 1,10-phenanthroline) were prepared at room temperature and characterized. The crystal structures of complexes 1-8 have been determined by single crystal X-ray diffraction. These complexes are isomorphous and lanthanide ions are all eight-coordinated to oxygen atoms and nitrogen atoms with distorted square-antiprism geometry. The thermal decomposition mechanism and TG-FTIR spectra of gaseous products of thermal decomposition processes for complexes 1-8 were acquired through TG/DSC-FTIR system. The heat capacities of complexes 1-8 were measured using DSC technology and fitted to a polynomial equation by the least-squares method. Complexes 3-6 display characteristic lanthanide emission bands in the visible region. Meanwhile, these complexes exhibit in good antimicrobial activity against Candida albicans, Escherichia coli, and Staphylococcus aureu.

Silicic acid competes for dimethylarsinic acid (DMA) immobilization by the iron hydroxide plaque mineral goethite.

PubMed

Kersten, Michael; Daus, Birgit

2015-03-01

A surface complexation modeling approach was used to extend the knowledge about processes that affect the availability of dimethylarsinic acid (DMA) in the soil rhizosphere in presence of a strong sorbent, e.g., Fe plaques on rice roots. Published spectroscopic and molecular modeling information suggest for the organoarsenical agent to form bidentate-binuclear inner-sphere surface complexes with Fe hydroxides similar to the inorganic As oxyanions. However, since also the ubiquitous silicic acid oxyanion form the same bidentate binuclear surface complexes, our hypothesis was that it may have an effect on the adsorption of DMA by Fe hydroxides in soil. Our experimental batch equilibrium data show that DMA is strongly adsorbed in the acidic pH range, with a steep adsorption edge in the circumneutral pH region between the DMA acidity constant (pKa=6.3) and the point of zero charge value of the goethite adsorbent (pHpzc=8.6). A 1-pK CD-MUSIC surface complexation model was chosen to fit the experimental adsorption vs. pH data. The same was done for silicic acid batch equilibrium data with our goethite adsorbent. Both model parameters for individual DMA and silicic acid adsorption were then merged into one CD-MUSIC model to predict the binary DMA+Si adsorption behavior. Silicic acid (500 μM) was thus predicted by the model to strongly compete for DMA with up to 60% mobilization of the latter at a pH6. This model result could be verified subsequently by experimental batch equilibrium data with zero adjustable parameters. The thus quantified antagonistic relation between DMA and silicic acid is discussed as one of factors to explain the increase of the DMA proportion in rice grains as observed upon silica fertilization of rice fields. Copyright © 2014 Elsevier B.V. All rights reserved.

Five novel lanthanide complexes with 2-chloroquinoline-4-carboxylic acid and 1,10-phenanthroline: Crystal structures, molecular spectra, thermal properties and bacteriostatic activities

NASA Astrophysics Data System (ADS)

Wang, Ye; Jin, Cheng-Wei; He, Shu-Mei; Ren, Ning; Zhang, Jian-Jun

2016-12-01

Five novel lanthanide complexes [Ln2(2-ClQL)6(phen)2(H2O)2]·2H2O (Ln = Pr(1), Sm(2), Eu(3), Ho(4), Er(5)); 2-ClQL: 2-chloroquinoline-4-carboxylate; phen: 1,10-phenanthroline; were synthesized by conventional solution method at room temperature and characterized via elemental analysis, powder x-ray diffraction, Infrared spectroscopy and Raman spectrometry. The results indicate that complexes 1-5 are isostructural, and each Ln3+ ion is eight-coordinated adopting a distorted square antiprismatic molecular geometry. Binuclear complex 1 are stitched together via hydrogen bonding interactions to form 1D chains, and further to form 2D sheets by the π-π interactions. Luminescence investigation reveals that complex 3 displays strong red emission. TG/DTG-FTIR, reveal the thermal decomposition processes and products of title complexes. The bacteriostatic activities of the complexes were evaluated against Candida albicans, Escherichia coli, and Staphylococcus aureus.

The structure of an unconventional HD-GYP protein from Bdellovibrio reveals the roles of conserved residues in this class of cyclic-di-GMP phosphodiesterases.

PubMed

Lovering, Andrew L; Capeness, Michael J; Lambert, Carey; Hobley, Laura; Sockett, R Elizabeth

2011-01-01

Cyclic-di-GMP is a near-ubiquitous bacterial second messenger that is important in localized signal transmission during the control of various processes, including virulence and switching between planktonic and biofilm-based lifestyles. Cyclic-di-GMP is synthesized by GGDEF diguanylate cyclases and hydrolyzed by EAL or HD-GYP phosphodiesterases, with each functional domain often appended to distinct sensory modules. HD-GYP domain proteins have resisted structural analysis, but here we present the first structural representative of this family (1.28 Å), obtained using the unusual Bd1817 HD-GYP protein from the predatory bacterium Bdellovibrio bacteriovorus. Bd1817 lacks the active-site tyrosine present in most HD-GYP family members yet remains an excellent model of their features, sharing 48% sequence similarity with the archetype RpfG. The protein structure is highly modular and thus provides a basis for delineating domain boundaries in other stimulus-dependent homologues. Conserved residues in the HD-GYP family cluster around a binuclear metal center, which is observed complexed to a molecule of phosphate, providing information on the mode of hydroxide ion attack on substrate. The fold and active site of the HD-GYP domain are different from those of EAL proteins, and restricted access to the active-site cleft is indicative of a different mode of activity regulation. The region encompassing the GYP motif has a novel conformation and is surface exposed and available for complexation with binding partners, including GGDEF proteins. It is becoming apparent that many bacteria use the signaling molecule cyclic-di-GMP to regulate a variety of processes, most notably, transitions between motility and sessility. Importantly, this regulation is central to several traits implicated in chronic disease (adhesion, biofilm formation, and virulence gene expression). The mechanisms of cyclic-di-GMP synthesis via GGDEF enzymes and hydrolysis via EAL enzymes have been suggested by the analysis of several crystal structures, but no information has been available to date for the unrelated HD-GYP class of hydrolases. Here we present the multidomain structure of an unusual member of the HD-GYP family from the predatory bacterium Bdellovibrio bacteriovorus and detail the features that distinguish it from the wider structural family of general HD fold hydrolases. The structure reveals how a binuclear iron center is formed from several conserved residues and provides a basis for understanding HD-GYP family sequence requirements for c-di-GMP hydrolysis.

Synthesis, structure, biochemical, and docking studies of a new dinitrosyl iron complex [Fe2(μ-SC4H3SCH2)2(NO)4

NASA Astrophysics Data System (ADS)

Davidovich, P. B.; Fischer, A. I.; Korchagin, D. V.; Panchuk, V. V.; Shchukarev, A. V.; Garabadzhiu, A. V.; Belyaev, A. N.

2015-07-01

A new dinitrosyl iron complex of binuclear structure [Fe2(μ-S-2-methylthiophene)2(NO)4] was first synthesized and structurally characterized by XRD and theoretical methods. Using caspase-3 as an example it was shown that [Fe2(μ-S-2-methylthiophene)2(NO)4] and its analog [Fe2(μ-S-2-methylfurane)2(NO)4] can inhibit the action of active site cysteine proteins; the difference in inhibitory activity was explained by molecular docking studies. Biochemical and in silico studies give grounds that the biological activity of dinitrosyl iron complexes is a μ-SR bridging ligand structure function. Thus the rational design strategy of [Fe2(μ-SR)2(NO)4] complexes can be applied to make NO prodrugs with high affinity to therapeutically significant targets involved in cancer and inflammation.

Highly preorganized pyrazolate-bridged palladium(II) and nickel(II) complexes in bimetallic norbornene polymerization.

PubMed

Sachse, Anna; Demeshko, Serhiy; Dechert, Sebastian; Daebel, Venita; Lange, Adam; Meyer, Franc

2010-04-28

New derivatives of pyrazolate-based binucleating ligands HL with appended imine functions have been synthesized to provide a versatile set of ligand systems with different backbone substituents both at the pyrazole-C(4) and the imine-C (H, Me, Ph). These scaffolds have two adjacent coordination compartments akin to the alpha-diimine type. A series of binuclear palladium(II) complexes [LPd(2)Cl(3)] (1-4) and tetranuclear nickel(II) complexes [L(2)Ni(4)Br(6)(solvent)(4)] (5, 6) of the various ligands have been prepared and characterized, including X-ray structural analyses for two representative Pd and the two Ni complexes. Complexes 5 and 6 were found to contain an unusual central mu(4)-bromide. Mononuclear nickel(II) complexes [L(2)Ni] were detected as intermediates in the formation of the tetranuclear complexes and have been characterized by X-ray analyses in two cases (7, 8). The interconversion between 5' and 7 has been investigated by UV/Vis spectroscopy and ESI mass spectrometry, and magnetic coupling in the [L(2)Ni(4)Br(6)(solvent)(4)] complexes has been studied (SQUID). Trans-coupling via the central mu(4)-bromide is suggested to mediate significant antiferromagnetic interaction. The reactivity of such types of Pd and Ni complexes has been tested for the vinyl/addition polymerization of norbornene. In the presence of an excess of cocatalyst methylaluminoxane (MAO) the palladium complexes show high activity up to 5.9 x 10(6) g(PNB) mol(Pd)(-1) h(-1) at 20 degrees C, while activities of the nickel systems are much lower, but strongly solvent dependent. Detailed studies on the dependence of activity on polymerization conditions such as molar ratios of catalyst and cocatalyst, temperature, reaction time and solvent were carried out. All obtained polynorbornenes (PNB) were noncrystalline and insoluble, but have high glass transition temperatures (T(g)). Microstructures were analyzed by IR spectroscopy and solid state (CP/MAS) (13)C NMR, revealing distinct patterns for the PNB produced by Ni- or Pd-catalysts. Structure/activity correlations deduced for the complexes with different ligand systems suggest that activities and polymer microstructures depend rather on the metal type than on ligand intricacies.

Glycine and metformin as new counter ions for mono and dinuclear vanadium(V)-dipicolinic acid complexes based on the insulin-enhancing anions: Synthesis, spectroscopic characterization and crystal structure

NASA Astrophysics Data System (ADS)

Ghasemi, Fatemeh; Rezvani, Ali Reza; Ghasemi, Khaled; Graiff, Claudia

2018-02-01

Complexes [VO(dipic) (H2O)2]·2H2O (1), [H2Met][V2O4(dipic)2] (2) and [HGly][VO2(dipic)] (3), where H2dipic = 2,6-pyridinedicarboxylic acid, Met = Metformin (N,N-dimethylbiguanide) and Gly = glycine, were synthesized. The three complexes were characterized by elemental analysis, FTIR, 1H and 13C NMR, and UV-Vis spectroscopy. Solid-state structures of (2) and (3) were determined by single-crystal X-ray diffraction analysis. The coordination geometry around the vanadium atoms in 2 is octahedral, while the coordination geometry in 3 is between trigonal bipyramidal and squared pyramidal. In the binuclear complex 2 and mononuclear complex 3, metformin and glycine are diprotonated and monoprotonated respectively, and act as a counter ion. The redox behavior of the complexes was also investigated by cyclic voltammetry.

Effect of additives on chemoselectivity and diastereoselectivity in the catalytic epoxidation of chiral allylic alcohols with hydrogen peroxide and binuclear manganese complexes.

PubMed

Kilic, Hamdullah; Adam, Waldemar; Alsters, Paul L

2009-02-06

The catalytic oxidations of chiral allylic alcohols 2 by manganese complexes of the cyclic triamine 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) 1 and hydrogen peroxide as oxygen donor in the presence of co-catalyst are investigated to understand the factors that affect the catalyst selectivity. Chemoselectivity and diastereoselectivity of catalyst 1 are significantly affected by the structure of the allylic alcohol and the nature and amount of co-catalyst. More pronounced is the influence of the amount of added molar equivalents of H(2)O(2) (20-110 mol % with respect to the substrate). Our present results reflect the complex redox chemistry of the Mn catalyst 1/H(2)O(2)/co-catalyst system in the early phase of the alkene oxidation.

Catalytic function of the mycobacterial binuclear iron monooxygenase in acetone metabolism.

PubMed

Furuya, Toshiki; Nakao, Tomomi; Kino, Kuniki

2015-10-01

Mycobacteria such as Mycobacterium smegmatis strain mc(2)155 and Mycobacterium goodii strain 12523 are able to grow on acetone and use it as a source of carbon and energy. We previously demonstrated by gene deletion analysis that the mimABCD gene cluster, which encodes a binuclear iron monooxygenase, plays an essential role in acetone metabolism in these mycobacteria. In the present study, we determined the catalytic function of MimABCD in acetone metabolism. Whole-cell assays were performed using Escherichia coli cells expressing the MimABCD complex. When the recombinant E. coli cells were incubated with acetone, a product was detected by gas chromatography (GC) analysis. Based on the retention time and the gas chromatography-mass spectrometry (GC-MS) spectrum, the reaction product was identified as acetol (hydroxyacetone). The recombinant E. coli cells produced 1.02 mM of acetol from acetone within 24 h. Furthermore, we demonstrated that MimABCD also was able to convert methylethylketone (2-butanone) to 1-hydroxy-2-butanone. Although it has long been known that microorganisms such as mycobacteria metabolize acetone via acetol, this study provides the first biochemical evidence for the existence of a microbial enzyme that catalyses the conversion of acetone to acetol. © FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF

DOE PAGES

Park, Kiyoung; Li, Ning; Kwak, Yeonju; ...

2017-05-01

Binuclear non-heme iron enzymes activate O 2 for diverse chemistries that include oxygenation of organic substrates and hydrogen atom abstraction. This process often involves the formation of peroxo-bridged biferric intermediates, only some of which can perform electrophilic reactions. To elucidate the geometric and electronic structural requirements to activate peroxo reactivity, the active peroxo intermediate in 4-aminobenzoate N-oxygenase (AurF) has been characterized spectroscopically and computationally. A magnetic circular dichroism study of reduced AurF shows that its electronic and geometric structures are poised to react rapidly with O 2. Nuclear resonance vibrational spectroscopic definition of the peroxo intermediate formed in this reactionmore » shows that the active intermediate has a protonated peroxo bridge. Density functional theory computations on the structure established here show that the protonation activates peroxide for electrophilic/single-electron-transfer reactivity. As a result, this activation of peroxide by protonation is likely also relevant to the reactive peroxo intermediates in other binuclear non-heme iron enzymes.« less

Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Kiyoung; Li, Ning; Kwak, Yeonju

Binuclear non-heme iron enzymes activate O 2 for diverse chemistries that include oxygenation of organic substrates and hydrogen atom abstraction. This process often involves the formation of peroxo-bridged biferric intermediates, only some of which can perform electrophilic reactions. To elucidate the geometric and electronic structural requirements to activate peroxo reactivity, the active peroxo intermediate in 4-aminobenzoate N-oxygenase (AurF) has been characterized spectroscopically and computationally. A magnetic circular dichroism study of reduced AurF shows that its electronic and geometric structures are poised to react rapidly with O 2. Nuclear resonance vibrational spectroscopic definition of the peroxo intermediate formed in this reactionmore » shows that the active intermediate has a protonated peroxo bridge. Density functional theory computations on the structure established here show that the protonation activates peroxide for electrophilic/single-electron-transfer reactivity. As a result, this activation of peroxide by protonation is likely also relevant to the reactive peroxo intermediates in other binuclear non-heme iron enzymes.« less

Bimetallic catalysis for C–C and C–X coupling reactions

PubMed Central

Pye, Dominic R.

2017-01-01

Bimetallic catalysis represents an alternative paradigm for coupling chemistry that complements the more traditional single-site catalysis approach. In this perspective, recent advances in bimetallic systems for catalytic C–C and C–X coupling reactions are reviewed. Behavior which complements that of established single-site catalysts is highlighted. Two major reaction classes are covered. First, generation of catalytic amounts of organometallic species of e.g. Cu, Au, or Ni capable of transmetallation to a Pd co-catalyst (or other traditional cross-coupling catalyst) has allowed important new C–C coupling technologies to emerge. Second, catalytic transformations involving binuclear bond-breaking and/or bond-forming steps, in some cases involving metal–metal bonds, represent a frontier area for C–C and C–X coupling processes.

Poly[(μ-3,5-dinitro­benzoato)(μ-3,5-dinitro­benzoic acid)rubidium

PubMed Central

Miao, Yanqing; Fan, Tao

2011-01-01

The asymmetric unit of the title compound, [Rb(C7H3N2O6)(C7H4N2O6)]n, comprises an Rb+ cation, a 3,5-dinitro­benzoate anion and a 3,5-dinitro­benzoic acid ligand. The Rb+ cation is nine-coordinated by O atoms from four 3,5-dinitro­benzoate anions and three neutral 3,5-dinitro­benzoic acid ligands. The metal atom is firstly linked by four bridging carboxyl groups, forming a binuclear motif, which is further linked by the nitro groups into a two-dimensional framework along the [110] direction. A short O—H⋯O hydrogen bond between two adjacent carboxy/carboxylate groups occurs. PMID:22090832

A novel polyhedron-based metal-organic framework with high performance for gas uptake and light hydrocarbon separation.

PubMed

Sun, Qiushi; Yao, Shuo; Liu, Bing; Liu, Xinyao; Li, Guanghua; Liu, Xiaoyang; Liu, Yunling

2018-04-03

A novel polyhedron-based metal-organic framework [(CH3)2NH2]2[Zn3(TADIPA)2(DMF)2]·4DMF (JLU-Liu40), which possesses three types of cages with different shapes and sizes, has been successfully synthesized. The framework of JLU-Liu40 is constructed by two inorganic secondary building units (SBUs) of 4-connected square binuclear Zn-paddlewheel and 4-connected tetrahedron mononuclear Zn unit and one organic SBU, which has abundant Lewis basic sites (LBSs), and the framework can be simplified as a pair of 3-connected triangle geometries. Moreover, JLU-Liu40 shows a new (3, 4, 4)-connected topology with the Schläfli symbol {72, 9}2{74, 82}. With the benefit of its high density of open metal sites (OMSs) and LBSs, JLU-Liu40 shows good adsorption ability for some small gases such as N2, CO2, CH4, C2H6 and C3H8. In addition, the theoretical ideal adsorbed solution theory (IAST) calculation indicates that JLU-Liu40 should be a promising material for light gas separation.

Spectrophotometric Determination of Metoprolol Tartrate in Pharmaceutical Dosage Forms on Complex Formation with Cu(II)

PubMed Central

Cesme, Mustafa; Tarinc, Derya; Golcu, Aysegul

2011-01-01

A new, simple, sensitive and accurate spectrophotometric method has been developed for the assay of metoprolol tartrate (MPT), which is based on the complexation of drug with copper(II) [Cu(II)] at pH 6.0, using Britton-Robinson buffer solution, to produce a blue adduct. The latter has a maximum absorbance at 675 nm and obeys Beer's law within the concentration range 8.5-70 μg/mL. Regression analysis of the calibration data showed a good correlation coefficient (r = 0.998) with a limit of detection of 5.56 μg/mL. The proposed procedure has been successfully applied to the determination of this drug in its tablets. In addition, the spectral data and stability constant for the binuclear copper(II) complex of MPT (Cu2MPT2Cl2) have been reported.

The Structure of an Unconventional HD-GYP Protein from Bdellovibrio Reveals the Roles of Conserved Residues in this Class of Cyclic-di-GMP Phosphodiesterases

PubMed Central

Lovering, Andrew L.; Capeness, Michael J.; Lambert, Carey; Hobley, Laura; Sockett, R. Elizabeth

2011-01-01

ABSTRACT Cyclic-di-GMP is a near-ubiquitous bacterial second messenger that is important in localized signal transmission during the control of various processes, including virulence and switching between planktonic and biofilm-based lifestyles. Cyclic-di-GMP is synthesized by GGDEF diguanylate cyclases and hydrolyzed by EAL or HD-GYP phosphodiesterases, with each functional domain often appended to distinct sensory modules. HD-GYP domain proteins have resisted structural analysis, but here we present the first structural representative of this family (1.28 Å), obtained using the unusual Bd1817 HD-GYP protein from the predatory bacterium Bdellovibrio bacteriovorus. Bd1817 lacks the active-site tyrosine present in most HD-GYP family members yet remains an excellent model of their features, sharing 48% sequence similarity with the archetype RpfG. The protein structure is highly modular and thus provides a basis for delineating domain boundaries in other stimulus-dependent homologues. Conserved residues in the HD-GYP family cluster around a binuclear metal center, which is observed complexed to a molecule of phosphate, providing information on the mode of hydroxide ion attack on substrate. The fold and active site of the HD-GYP domain are different from those of EAL proteins, and restricted access to the active-site cleft is indicative of a different mode of activity regulation. The region encompassing the GYP motif has a novel conformation and is surface exposed and available for complexation with binding partners, including GGDEF proteins. PMID:21990613

Mono- and binuclear non-heme iron chemistry from a theoretical perspective.

PubMed

Rokob, Tibor András; Chalupský, Jakub; Bím, Daniel; Andrikopoulos, Prokopis C; Srnec, Martin; Rulíšek, Lubomír

2016-09-01

In this minireview, we provide an account of the current state-of-the-art developments in the area of mono- and binuclear non-heme enzymes (NHFe and NHFe2) and the smaller NHFe(2) synthetic models, mostly from a theoretical and computational perspective. The sheer complexity, and at the same time the beauty, of the NHFe(2) world represents a challenge for experimental as well as theoretical methods. We emphasize that the concerted progress on both theoretical and experimental side is a conditio sine qua non for future understanding, exploration and utilization of the NHFe(2) systems. After briefly discussing the current challenges and advances in the computational methodology, we review the recent spectroscopic and computational studies of NHFe(2) enzymatic and inorganic systems and highlight the correlations between various experimental data (spectroscopic, kinetic, thermodynamic, electrochemical) and computations. Throughout, we attempt to keep in mind the most fascinating and attractive phenomenon in the NHFe(2) chemistry, which is the fact that despite the strong oxidative power of many reactive intermediates, the NHFe(2) enzymes perform catalysis with high selectivity. We conclude with our personal viewpoint and hope that further developments in quantum chemistry and especially in the field of multireference wave function methods are needed to have a solid theoretical basis for the NHFe(2) studies, mostly by providing benchmarking and calibration of the computationally efficient and easy-to-use DFT methods.

Family ties after divorce: long-term implications for children.

PubMed

Ahrons, Constance R

2007-03-01

Drawing on the data from the longitudinal Binuclear Family Study, 173 grown children were interviewed 20 years after their parents' divorce. This article addresses two basic questions: (1) What impact does the relationship between parents have on their children 20 years after the divorce? and (2) When a parent remarries or cohabits, how does it impact a child's sense of family? The findings show that the parental subsystem continues to impact the binuclear family 20 years after marital disruption by exerting a strong influence on the quality of relationships within the family system. Children who reported that their parents were cooperative also reported better relationships with their parents, grandparents, stepparents, and siblings. Over the course of 20 years, most of the children experienced the remarriage of one or both parents, and one third of this sample remembered the remarriage as more stressful than the divorce. Of those who experienced the remarriage of both of their parents, two thirds reported that their father's remarriage was more stressful than their mother's. When children's relationships with their fathers deteriorated after divorce, their relationships with their paternal grandparents, stepmother, and stepsiblings were distant, negative, or nonexistent. Whether family relationships remain stable, improve, or get worse is dependent on a complex interweaving of many factors. Considering the long-term implications of divorce, the need to emphasize life course and family system perspectives is underscored.

Five chiral Cd(II) complexes with dual chiral components: Effect of positional isomerism, luminescence and SHG response

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Lin, E-mail: lcheng@seu.edu.cn; Jiangsu Province Hi-Tech Key Laboratory for Bio-medical Research, Southeast University, Nanjing 211189; Wang, Jun

2015-01-15

Five chiral Cd(II) complexes with dual chiral components have been synthesized by using a series of (1R,2R)–N{sup 1},N{sup 2}-bis(pyridinylmethyl)cyclohexane-1,2-diamine ligands with different N-positions of pyridyl rings and Cd(NO{sub 3}){sub 2}. The circular dichroism (CD) spectra and second-harmonic generation (SHG) efficiency measurements confirmed that they are of structural chirality in the bulk samples. The luminescent properties indicated that they may have potential applications as optical materials. The formation of discrete mononuclear and binuclear complexes, and one-dimensional chains may be attributed to positional isomerism of the ligands. - Graphical abstract: Five chiral Cd(II) complexes with dual chiral components have been synthesized bymore » using a series of chiral ligands with different N-positions of pyridyl rings. - Highlights: • Five chiral Cd(II) complexes with dual chiral components have been synthesized. • CD spectra and SHG efficiency of the bulk samples have been measured. • The complexes display luminescent properties.« less

A binuclear complex constituted by diethyldithiocarbamate and copper(I) functions as a proteasome activity inhibitor in pancreatic cancer cultures and xenografts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Jinbin, E-mail: hanjinbin@gmail.com; Department of Oncology, Shanghai Medical College, Fudan University, Shanghai 200032; Shanghai Clinical Center, Chinese Academy of Sciences/Xuhui Central Hospital, Shanghai 200031

2013-12-15

It is a therapeutic strategy for cancers including pancreatic to inhibit proteasome activity. Disulfiram (DSF) may bind copper (Cu) to form a DSF–Cu complex. DSF–Cu is capable of inducing apoptosis in cancer cells by inhibiting proteasome activity. DSF is rapidly converted to diethyldithiocarbamate (DDTC) within bodies. Copper(II) absorbed by bodies is reduced to copper(I) when it enters cells. We found that DDTC and copper(I) could form a binuclear complex which might be entitled DDTC–Cu(I), and it had been synthesized by us in the laboratory. This study is to investigate the anticancer potential of this complex on pancreatic cancer and themore » possible mechanism. Pancreatic cancer cell lines, SW1990, PANC-1 and BXPC-3 were used for in vitro assays. Female athymic nude mice grown SW1990 xenografts were used as animal models. Cell counting kit-8 (cck-8) assay and flow cytometry were used for analyzing apoptosis in cells. A 20S proteasome assay kit was used in proteasome activity analysis. Western blot (WB) and immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays were used in tumor sample analysis. The results suggest that DDTC–Cu(I) inhibit pancreatic cancer cell proliferation and proteasome activity in vitro and in vivo. Accumulation of ubiquitinated proteins, and increased p27 as well as decreased NF-κB expression were detected in tumor tissues of DDTC–Cu(I)-treated group. Our data indicates that DDTC–Cu(I) is an effective proteasome activity inhibitor with the potential to be explored as a drug for pancreatic cancer. - Highlights: • A new structure of DDTC–Cu(I) was reported for the first time. • DDTC–Cu(I) dissolved directly in water was for in vitro and in vivo uses. • DDTC–Cu(I) demonstrated significant anticancer effect in vitro and in vivo. • DDTC–Cu(I) is capable of inhibiting proteasome activity in vitro and in vivo.« less

Phosphate forms an unusual tripodal complex with the Fe–Mn center of sweet potato purple acid phosphatase

PubMed Central

Schenk, Gerhard; Gahan, Lawrence R.; Carrington, Lyle E.; Mitić, Nataša; Valizadeh, Mohsen; Hamilton, Susan E.; de Jersey, John; Guddat, Luke W.

2005-01-01

Purple acid phosphatases (PAPs) are a family of binuclear metalloenzymes that catalyze the hydrolysis of phosphoric acid esters and anhydrides. A PAP in sweet potato has a unique, strongly antiferromagnetically coupled Fe(III)–Mn(II) center and is distinguished from other PAPs by its increased catalytic efficiency for a range of activated and unactivated phosphate esters, its strict requirement for Mn(II), and the presence of a μ-oxo bridge at pH 4.90. This enzyme displays maximum catalytic efficiency (kcat/Km) at pH 4.5, whereas its catalytic rate constant (kcat) is maximal at near-neutral pH, and, in contrast to other PAPs, its catalytic parameters are not dependent on the pKa of the leaving group. The crystal structure of the phosphate-bound Fe(III)–Mn(II) PAP has been determined to 2.5-Å resolution (final Rfree value of 0.256). Structural comparisons of the active site of sweet potato, red kidney bean, and mammalian PAPs show several amino acid substitutions in the sweet potato enzyme that can account for its increased catalytic efficiency. The phosphate molecule binds in an unusual tripodal mode to the two metal ions, with two of the phosphate oxygen atoms binding to Fe(III) and Mn(II), a third oxygen atom bridging the two metal ions, and the fourth oxygen pointing toward the substrate binding pocket. This binding mode is unique among the known structures in this family but is reminiscent of phosphate binding to urease and of sulfate binding to λ protein phosphatase. The structure and kinetics support the hypothesis that the bridging oxygen atom initiates hydrolysis. PMID:15625111

CD/MCD/VTVH-MCD Studies of Escherichia coli Bacterioferritin Support a Binuclear Iron Cofactor Site.

PubMed

Kwak, Yeonju; Schwartz, Jennifer K; Huang, Victor W; Boice, Emily; Kurtz, Donald M; Solomon, Edward I

2015-12-01

Ferritins and bacterioferritins (Bfrs) utilize a binuclear non-heme iron binding site to catalyze oxidation of Fe(II), leading to formation of an iron mineral core within a protein shell. Unlike ferritins, in which the diiron site binds Fe(II) as a substrate, which then autoxidizes and migrates to the mineral core, the diiron site in Bfr has a 2-His/4-carboxylate ligand set that is commonly found in diiron cofactor enzymes. Bfrs could, therefore, utilize the diiron site as a cofactor rather than for substrate iron binding. In this study, we applied circular dichroism (CD), magnetic CD (MCD), and variable-temperature, variable-field MCD (VTVH-MCD) spectroscopies to define the geometric and electronic structures of the biferrous active site in Escherichia coli Bfr. For these studies, we used an engineered M52L variant, which is known to eliminate binding of a heme cofactor but to have very minor effects on either iron oxidation or mineral core formation. We also examined an H46A/D50A/M52L Bfr variant, which additionally disrupts a previously observed mononuclear non-heme iron binding site inside the protein shell. The spectral analyses define a binuclear and an additional mononuclear ferrous site. The biferrous site shows two different five-coordinate centers. After O2 oxidation and re-reduction, only the mononuclear ferrous signal is eliminated. The retention of the biferrous but not the mononuclear ferrous site upon O2 cycling supports a mechanism in which the binuclear site acts as a cofactor for the O2 reaction, while the mononuclear site binds the substrate Fe(II) that, after its oxidation to Fe(III), migrates to the mineral core.

Catalytic Mechanism and Three-Dimensional Structure of Adenine Deaminase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamat, S.S.; Swaminathan, S.; Bagaria, A.

2011-03-22

Adenine deaminase (ADE) catalyzes the conversion of adenine to hypoxanthine and ammonia. The enzyme isolated from Escherichia coli using standard expression conditions was low for the deamination of adenine (k{sub cat} = 2.0 s{sup -1}; k{sub cat}/K{sub m} = 2.5 x 10{sup 3} M{sup -1} s{sup -1}). However, when iron was sequestered with a metal chelator and the growth medium was supplemented with Mn{sup 2+} prior to induction, the purified enzyme was substantially more active for the deamination of adenine with kcat and kcat/Km values of 200 s{sup -1} and 5 x 10{sup 5} M{sup -1} s{sup -1}, respectively. Themore » apoenzyme was prepared and reconstituted with Fe{sup 2+}, Zn{sup 2+}, or Mn{sup 2+}. In each case, two enzyme equivalents of metal were necessary for reconstitution of the deaminase activity. This work provides the first example of any member of the deaminase subfamily of the amidohydrolase superfamily to utilize a binuclear metal center for the catalysis of a deamination reaction. [Fe{sup II}/Fe{sup II}]-ADE was oxidized to [Fe{sup III}/Fe{sup III}]-ADE with ferricyanide with inactivation of the deaminase activity. Reducing [Fe{sup III}/Fe{sup III}]-ADE with dithionite restored the deaminase activity, and thus, the diferrous form of the enzyme is essential for catalytic activity. No evidence of spin coupling between metal ions was evident by electron paramagnetic resonance or Moessbauer spectroscopy. The three-dimensional structure of adenine deaminase from Agrobacterium tumefaciens (Atu4426) was determined by X-ray crystallography at 2.2 {angstrom} resolution, and adenine was modeled into the active site on the basis of homology to other members of the amidohydrolase superfamily. On the basis of the model of the adenine-ADE complex and subsequent mutagenesis experiments, the roles for each of the highly conserved residues were proposed. Solvent isotope effects, pH-rate profiles, and solvent viscosity were utilized to propose a chemical reaction mechanism and the identity of the rate-limiting steps.« less

Catalytic Mechanism and Three-Dimensional Structure of Adenine Deaminase

DOE Office of Scientific and Technical Information (OSTI.GOV)

S Kamat; A Bagaria; D Kumaran

2011-12-31

Adenine deaminase (ADE) catalyzes the conversion of adenine to hypoxanthine and ammonia. The enzyme isolated from Escherichia coli using standard expression conditions was low for the deamination of adenine (k{sub cat} = 2.0 s{sup -1}; k{sub cat}/K{sub m} = 2.5 x 10{sup 3} M{sup -1} s{sup -1}). However, when iron was sequestered with a metal chelator and the growth medium was supplemented with Mn{sup 2+} prior to induction, the purified enzyme was substantially more active for the deamination of adenine with k{sub cat} and k{sub cat}/K{sub m} values of 200 s{sup -1} and 5 x 10{sup 5} M{sup -1} s{supmore » -1}, respectively. The apoenzyme was prepared and reconstituted with Fe{sup 2+}, Zn{sup 2+}, or Mn{sup 2+}. In each case, two enzyme equivalents of metal were necessary for reconstitution of the deaminase activity. This work provides the first example of any member of the deaminase subfamily of the amidohydrolase superfamily to utilize a binuclear metal center for the catalysis of a deamination reaction. [Fe{sup II}/Fe{sup II}]-ADE was oxidized to [Fe{sup III}/Fe{sup III}]-ADE with ferricyanide with inactivation of the deaminase activity. Reducing [Fe{sup III}/Fe{sup III}]-ADE with dithionite restored the deaminase activity, and thus, the diferrous form of the enzyme is essential for catalytic activity. No evidence of spin coupling between metal ions was evident by electron paramagnetic resonance or Moessbauer spectroscopy. The three-dimensional structure of adenine deaminase from Agrobacterium tumefaciens (Atu4426) was determined by X-ray crystallography at 2.2 {angstrom} resolution, and adenine was modeled into the active site on the basis of homology to other members of the amidohydrolase superfamily. On the basis of the model of the adenine-ADE complex and subsequent mutagenesis experiments, the roles for each of the highly conserved residues were proposed. Solvent isotope effects, pH-rate profiles, and solvent viscosity were utilized to propose a chemical reaction mechanism and the identity of the rate-limiting steps.« less

Positional isomeric tunable two Co(II) 6-connected 3-D frameworks with pentanuclear to binuclear units: structures, ion-exchange and magnetic properties.

PubMed

Han, Min-Le; Duan, Ya-Ping; Li, Dong-Sheng; Wang, Hai-Bin; Zhao, Jun; Wang, Yao-Yu

2014-11-07

Two new Co(II) based metal-organic frameworks, namely {[Co5(μ3-OH)2(m-pda)3(bix)4]·2ClO4}n (1) and {[Co2(p-pda)2(bix)2(H2O)]·H2O}n (2), were prepared by hydrothermal reactions of Co(II) salt with two isomeric dicarboxyl tectons 1,3-phenylenediacetic acid (m-pda) and 1,4-phenylenediacetic acid (p-pda), along with 1,3-bis(imidazol-L-ylmethyl)benzene (bix). Both complexes 1 and 2 have been characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). 1 shows a 6-connected 3-D pcu cationic framework with pentanuclear [Co5(μ3-OH)2(COO)6(bix)2](2+) units, while 2 exhibits a 6-connected 3-D msw net based on [Co2(μ2-H2O)(COO)2](2+) clusters. The results indicate that the different dispositions of the carboxylic groups of dicarboxylates have an important effect on the overall coordination frameworks. Perchlorate anions in 1 can be partly exchanged by thiocyanate and azide anions, however they are unavailable to nitrate anions. Magnetic susceptibility measurements indicate that both 1 and 2 show weak antiferromagnetic interactions between the adjacent Co(II) ions.

A series of novel lanthanide complexes with 2-bromine-5-methoxybenzoic acid and 2,2‧-bipyridine: Syntheses, crystal structures, and luminescent properties

NASA Astrophysics Data System (ADS)

Zhao, Qing-Qing; Zhu, Min-Min; Ren, Ning; Zhang, Jian-Jun

2017-12-01

Six new lanthanide complexes [Ln(2-Br-5-MOBA)3(2,2‧-DIPY)]2 (Ln = Nd(1), Eu(2), Gd(3), Tb(4), Ho(5), Er(6); 2-Br-5-MOBA = 2-bromine-5-methoxybenzoate; 2,2‧-DIPY = 2,2‧-bipyridine) have been successfully synthesized and characterized. The complexes 1-5 are isostructural and nine-coordinated by the single-crystal X-ray diffraction analyses, while the complex 6 is eight-coordinated. The difference of crystal structure may be the result of the lanthanide contraction effect. The binuclear units were further assembled into 1D, 2D, 3D supramolecular structures by the π-π stacking and Csbnd H⋯O hydrogen bonding interactions. The thermal decomposition mechanism of complexes 1-6 was studied by TG analysis and further authenticated by TG/DSC-FTIR techniques. The solid-state luminescence properties of complexes 2 and 4 were investigated at room temperature. The results indicate that complexes 2 and 4 show characteristic emission of Eu3+ ion and Tb3+ ion, respectively. What's more, the title complexes have good antibacterial activities against Candida albicans.

Structural and catalytic characterization of a heterovalent Mn(II)Mn(III) complex that mimics purple acid phosphatases.

PubMed

Smith, Sarah J; Riley, Mark J; Noble, Christopher J; Hanson, Graeme R; Stranger, Robert; Jayaratne, Vidura; Cavigliasso, Germán; Schenk, Gerhard; Gahan, Lawrence R

2009-11-02

The binuclear heterovalent manganese model complex [Mn(II)Mn(III)(L1)(OAc)(2)] ClO(4) x H(2)O (H(2)L1 = 2-(((3-((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino)-methyl)phenol) has been prepared and studied structurally, spectroscopically, and computationally. The magnetic and electronic properties of the complex have been related to its structure. The complex is weakly antiferromagnetically coupled (J approximately -5 cm(-1), H = -2J S(1) x S(2)) and the electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectra identify the Jahn-Teller distortion of the Mn(III) center as predominantly a tetragonal compression, with a significant rhombic component. Electronic structure calculations using density functional theory have confirmed the conclusions derived from the experimental investigations. In contrast to isostructural M(II)Fe(III) complexes (M = Fe, Mn, Zn, Ni), the Mn(II)Mn(III) system is bifunctional possessing both catalase and hydrolase activities, and only one catalytically relevant pK(a) (= 8.2) is detected. Mechanistic implications are discussed.

Surface complexation model for multisite adsorption of copper(II) onto kaolinite

NASA Astrophysics Data System (ADS)

Peacock, Caroline L.; Sherman, David M.

2005-08-01

We measured the adsorption of Cu(II) onto kaolinite from pH 3-7 at constant ionic strength. EXAFS spectra show that Cu(II) adsorbs as (CuO 4H n) n-6 and binuclear (Cu 2O 6H n) n-8 inner-sphere complexes on variable-charge ≡AlOH sites and as Cu 2+ on ion exchangeable ≡X-H + sites. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed at least up to pH 6.5. Inner-sphere complexes are bound to the kaolinite surface by corner-sharing with two or three edge-sharing Al(O,OH) 6 polyhedra. Our interpretation of the EXAFS data are supported by ab initio (density functional theory) geometries of analog clusters simulating Cu complexes on the {110} and {010} crystal edges and at the ditrigonal cavity sites on the {001}. Having identified the bidentate (≡AlOH) 2Cu(OH) 20, tridentate (≡Al 3O(OH) 2)Cu 2(OH) 30 and ≡X-Cu 2+ surface complexes, the experimental copper(II) adsorption data can be fit to the reactions

Syntheses, crystal structures, and properties of four complexes based on polycarboxylate and imidazole ligands

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiao, Rui; Chen, Shui-Sheng, E-mail: chenss@fync.edu.cn; Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093

2015-08-15

Four metal–organic coordination polymers [Zn(HL)(H{sub 2}O)]·4H{sub 2}O (1), [Zn(HL)(L{sub 1})]·4H{sub 2}O (2), [Cu(HL)(H{sub 2}O)]·3H{sub 2}O (3) and [Cu(HL)(L{sub 1})]·5H{sub 2}O (4) were synthesized by reactions of the corresponding metal(II) salts with semirigid polycarboxylate ligand (5-((4-carboxypiperidin-1-yl)methyl)isophthalic acid hydrochloride, H{sub 3}L·HCl) or auxiliary ligand (1,4-di(1H-imidazol-4-yl)benzene, L{sub 1}). The structures of the compounds were characterized by elemental analysis, FT-IR spectroscopy and single-crystal X-ray diffraction. The use of auxiliary ligand L{sub 1} has great influence on the structures of two pairs of complexes 1, 2 and 3, 4. Complex 1 is a uninodal 3-connected rare 2-fold interpenetrating ZnSc net with a Point (Schlafli) symbolmore » of (10{sup 3}) while 2 is a one-dimensional (1D) ladder structure. Compound 3 features a two-dimensional (2D) honeycomb network with typical 6{sup 3}-hcb topology, while 4 is 2D network with (4, 4) sql topology based on binuclear Cu{sup II} subunits. The non-covalent bonding interactions such as hydrogen bonds, π···π stacking and C–H···π exist in complexes 1–4, which contributes to stabilize crystal structure and extend the low-dimensional entities into high-dimensional frameworks. And the photoluminescent property of 1 and 2 and gas sorption property of 4 have been investigated. - Graphical abstract: Four new coordination polymers have been obtained and their photoluminescent and gas sorption properties have also been investigated. - Highlights: • Two pairs of Zn{sup II}/ Cu{sup II} compounds have been synthesized. • Auxiliary ligand-controlled assembly of the complexes is reported. • The luminescent properties of complexes 1–2 were investigated. • The gas sorption property of 4 has been investigated.« less

Concurrent synergism and inhibition in bimetallic catalysis: catalytic binuclear elimination, solute-solute interactions and a hetero-bimetallic hydrogen-bonded complex in rh-mo hydroformylations.

PubMed

Li, Chuanzhao; Cheng, Shuying; Tjahjono, Martin; Schreyer, Martin; Garland, Marc

2010-04-07

Hydroformylations of cyclopentene and 3,3-dimethylbut-1-ene were performed using both Rh(4)(CO)(12) and (eta(5)-C(5)H(5))Mo(CO)(3)H as precursors in n-hexane at 298 K. Both stoichiometric and catalytic hydroformylations were conducted as well as isotopic labeling experiments. Six organometallic pure component spectra were recovered from the high-pressure FTIR experiments, namely the known species Rh(4)(CO)(12), (eta(5)-C(5)H(5))Mo(CO)(3)H, RCORh(CO)(4), and the new heterobimetallic complexes RhMo(CO)(7)(eta(5)-C(5)H(5)), a weak hydrogen bonded species (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4), and a substituted RhMo(CO)(7-y)(eta(5)-C(5)H(5))L(y), where y = 1 or 2 and L = (pi-C(5)H(8)). The main findings were (1) catalytic binuclear elimination (CBER) occurs between (eta(5)-C(5)H(5))Mo(CO)(3)H and RCORh(CO)(4) resulting in aldehyde and RhMo(CO)(7)(eta(5)-C(5)H(5)), and this mechanism is responsible for ca. 10% of the product formation; (2) molecular hydrogen is readily activated by the new heterobimetallic complex(es); (3) FTIR and DFT spectroscopic evidence suggests that the weak hydrogen bonded species (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4) has an interaction of the type eta(5)-C(5)H(4)-H...O=C; and (4) independent physicochemical experiments for volumes of interaction confirm that significant solute-solute interactions are present. With respect to the efficiency of the catalytic cycle, the formation of a weak (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4) complex results in a significant decrease in the measured turnover frequency (TOF) and is the primary reason for the inhibition observed in the bimetallic catalytic hydroformylation. Such hydrogen bonding through the eta(5)-C(5)H(5) ring might have relevance to inhibition observed in other catalytic metallocene systems. The present catalytic system is an example of concurrent synergism and inhibition in bimetallic homogeneous catalysis.

The Structure of RdDddP from Roseobacter denitrificans Reveals That DMSP Lyases in the DddP-Family Are Metalloenzymes

PubMed Central

Hehemann, Jan-Hendrik; Law, Adrienne; Redecke, Lars; Boraston, Alisdair B.

2014-01-01

Marine microbes degrade dimethylsulfoniopropionate (DMSP), which is produced in large quantities by marine algae and plants, with DMSP lyases into acrylate and the gas dimethyl sulfide (DMS). Approximately 10% of the DMS vents from the sea into the atmosphere and this emission returns sulfur, which arrives in the sea through rivers and runoff, back to terrestrial systems via clouds and rain. Despite their key role in this sulfur cycle DMSP lyases are poorly understood at the molecular level. Here we report the first X-ray crystal structure of the putative DMSP lyase RdDddP from Roseobacter denitrificans, which belongs to the abundant DddP family. This structure, determined to 2.15 Å resolution, shows that RdDddP is a homodimeric metalloprotein with a binuclear center of two metal ions located 2.7 Å apart in the active site of the enzyme. Consistent with the crystallographic data, inductively coupled plasma mass spectrometry (ICP-MS) and total reflection X-ray fluorescence (TRXF) revealed the bound metal species to be primarily iron. A 3D structure guided analysis of environmental DddP lyase sequences elucidated the critical residues for metal binding are invariant, suggesting all proteins in the DddP family are metalloenzymes. PMID:25054772

Theory for electron transfer from a mixed-valence dimer with paramagnetic sites to a mononuclear acceptor

NASA Astrophysics Data System (ADS)

Bominaar, E. L.; Achim, C.; Borshch, S. A.

1999-06-01

Polynuclear transition-metal complexes, such as Fe-S clusters, are the prosthetic groups in a large number of metalloproteins and serve as temporary electron storage units in a number of important redox-based biological processes. Polynuclearity distinguishes clusters from mononuclear centers and confers upon them unique properties, such as spin ordering and the presence of thermally accessible excited spin states in clusters with paramagnetic sites, and fractional valencies in clusters of the mixed-valence type. In an earlier study we presented an effective-mode (EM) analysis of electron transfer from a binuclear mixed-valence donor with paramagnetic sites to a mononuclear acceptor which revealed that the cluster-specific attributes have an important impact on the kinetics of long-range electron transfer. In the present study, the validity of these results is tested in the framework of more detailed theories which we have termed the multimode semiclassical (SC) model and the quantum-mechanical (QM) model. It is found that the qualitative trends in the rate constant are the same in all treatments and that the semiclassical models provide a good approximation of the more rigorous quantum-mechanical description of electron transfer under physiologically relevant conditions. In particular, the present results corroborate the importance of electron transfer via excited spin states in reactions with a low driving force and justify the use of semiclassical theory in cases in which the QM model is computationally too demanding. We consider cases in which either one or two donor sites of a dimer are electronically coupled to the acceptor. In the case of multiconnectivity, the rate constant for electron transfer from a valence-delocalized (class-III) donor is nonadditive with respect to transfer from individual metal sites of the donor and undergoes an order-of-magnitude change by reversing the sign of the intradimer metal-metal resonance parameter (β). In the case of single connectivity, the rate constant for electron transfer from a valence-localized (class-II) donor can readily be tuned over several orders of magnitude by introducing differences in the electronic potentials at the two metal sites of the donor. These results indicate that theories of cluster-based electron transfer, in order to be realistic, need to consider both intrinsic electronic structure and extrinsic interactions of the cluster with the protein environment.

Enhanced third-order nonlinear optical properties determined in thin films using the Z-scan technique: bis(μ-4,4'-oxydibenzoato)bis[(4'-phenyl-2,2':6',2''-terpyridine)cobalt(II)].

PubMed

Liu, Runqiang; Zhao, Ning; Liu, Ping; An, Caixia; Lian, Zhaoxun

2016-05-01

π-Conjugated organic materials exhibit high and tunable nonlinear optical (NLO) properties, and fast response times. 4'-Phenyl-2,2':6',2''-terpyridine (PTP) is an important N-heterocyclic ligand involving π-conjugated systems, however, studies concerning the third-order NLO properties of terpyridine transition metal complexes are limited. The title binuclear terpyridine Co(II) complex, bis(μ-4,4'-oxydibenzoato)-κ(3)O,O':O'';κ(3)O'':O,O'-bis[(4'-phenyl-2,2':6',2''-terpyridine-κ(3)N,N',N'')cobalt(II)], [Co2(C14H8O5)2(C21H15N3)2], (1), has been synthesized under hydrothermal conditions. In the crystal structure, each Co(II) cation is surrounded by three N atoms of a PTP ligand and three O atoms, two from a bidentate and one from a symmetry-related monodentate 4,4'-oxydibenzoate (ODA(2-)) ligand, completing a distorted octahedral coordination geometry. Neighbouring [Co(PTP)](2+) units are bridged by ODA(2-) ligands to form a ring-like structure. The third-order nonlinear optical (NLO) properties of (1) and PTP were determined in thin films using the Z-scan technique. The title compound shows a strong third-order NLO saturable absorption (SA), while PTP exhibits a third-order NLO reverse saturable absorption (RSA). The absorptive coefficient β of (1) is -37.3 × 10(-7) m W(-1), which is larger than that (8.96 × 10(-7) m W(-1)) of PTP. The third-order NLO susceptibility χ((3)) values are calculated as 6.01 × 10(-8) e.s.u. for (1) and 1.44 × 10(-8) e.s.u. for PTP.

Binuclear Cu A formation in biosynthetic models of Cu A in azurin proceeds via a novel Cu(Cys) 2His mononuclear copper intermediate

DOE PAGES

Chakraborty, Saumen; Polen, Michael J.; Chacon, Kelly N.; ...

2015-09-09

Cu A is a binuclear electron transfer (ET) center found in cytochrome c oxidases (C cOs), nitrous oxide reductases (N 2ORs), and nitric oxide reductase (NOR). In these proteins, the Cu A centers facilitate efficient ET ( k ET > 10 4 s –1) under low thermodynamic driving forces (10–90 mV). While the structure and functional properties of Cu A are well understood, a detailed mechanism of the incorporation of copper into the protein and the identity of the intermediates formed during the Cu A maturation process are still lacking. Previous studies of the Cu A assembly mechanism in vitromore » using a biosynthetic model Cu A center in azurin (Cu AAz) identified a novel intermediate X (I x) during reconstitution of the binuclear site. However, because of the instability of I x and the coexistence of other Cu centers, such as Cu A' and type 1 copper centers, the identity of this intermediate could not be established. In this paper, we report the mechanism of Cu A assembly using variants of Glu114XCu AAz (X = Gly, Ala, Leu, or Gln), the backbone carbonyl of which acts as a ligand to the Cu A site, with a major focus on characterization of the novel intermediate I x. We show that Cu A assembly in these variants proceeds through several types of Cu centers, such as mononuclear red type 2 Cu, the novel intermediate I x, and blue type 1 Cu. Our results show that the backbone flexibility of the Glu114 residue is an important factor in determining the rates of T2Cu → I x formation, suggesting that Cu A formation is facilitated by swinging of the ligand loop, which internalizes the T2Cu capture complex to the protein interior. The kinetic data further suggest that the nature of the Glu114 side chain influences the time scales on which these intermediates are formed, the wavelengths of the absorption peaks, and how cleanly one intermediate is converted to another. Through careful understanding of these mechanisms and optimization of the conditions, we have obtained I x in ~80–85% population in these variants, which allowed us to employ ultraviolet–visible, electron paramagnetic resonance, and extended X-ray absorption fine structure spectroscopic techniques to identify the I x as a mononuclear Cu(Cys) 2(His) complex. Finally, because some of the intermediates have been proposed to be involved in the assembly of native Cu A, these results shed light on the structural features of the important intermediates and mechanism of Cu A formation.« less

Synthesis, spectral and quantum chemical studies on NO-chelating sulfamonomethoxine-cyclophosph(V)azane and its Er(III) complex.

PubMed

Alaghaz, Abdel-Nasser M A; Ammar, Reda A A; Koehler, Gottfried; Wolschann, Karl Peter; El-Gogary, Tarek M

2014-07-15

Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of novel ethane-1,2-diol-dichlorocyclophosph(V)azane of sulfamonomethoxine (L), and its binuclear Er(III) complex. Different tautomers of the ligand were optimized at the ab initio DFT level. Keto-form structure is about 15.8 kcal/mol more stable than the enol form (taking zpe correction into account). Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV-VIS spectra which show good agreement with measured electronic spectra. The structures of the novel isolated products are proposed based on elemental analyses, IR, UV-VIS, (1)H NMR, (31)P NMR, SEM, XRD spectra, effective magnetic susceptibility measurements and thermogravimetric analysis (TGA). Copyright © 2014 Elsevier B.V. All rights reserved.

Dynamic structural change of the self-assembled lanthanum complex induced by lithium triflate for direct catalytic asymmetric aldol-Tishchenko reaction.

PubMed

Horiuchi, Yoshihiro; Gnanadesikan, Vijay; Ohshima, Takashi; Masu, Hyuma; Katagiri, Kosuke; Sei, Yoshihisa; Yamaguchi, Kentaro; Shibasaki, Masakatsu

2005-09-05

The development of a direct catalytic asymmetric aldol-Tishchenko reaction and the nature of its catalyst are described. An aldol-Tishchenko reaction of various propiophenone derivatives with aromatic aldehydes was promoted by [LaLi3(binol)3] (LLB), and reactivity and enantioselectivity were dramatically enhanced by the addition of lithium trifluoromethanesulfonate (LiOTf). First, we observed a dynamic structural change of LLB by the addition of LiOTf using 13C NMR spectroscopy, electronspray ionization mass spectrometry (ESI-MS), and cold-spray ionization mass spectrometry (CSI-MS). X-ray crystallography revealed that the structure of the newly generated self-assembled complex was a binuclear [La2Li4(binaphthoxide)5] complex 6. A reverse structural change of complex 6 to LLB by the addition of one equivalent of Li2(binol) was also confirmed by ESI-MS and experimental results. The drastic concentration effects on the direct catalytic asymmetric aldol-Tishchenko reaction suggested that the addition of LiOTf to LLB generated an active oligomeric catalyst species.

Self-assembly of five 8-hydroxyquinolinate-based complexes: tunable core, supramolecular structure, and photoluminescence properties.

PubMed

Yuan, Guozan; Shan, Weilong; Qiao, Xuelong; Ma, Li; Huo, Yanping

2014-07-01

Five new Zn(II) complexes, namely [Zn(3)(L)(6)] (1), [Zn(2)(Cl)(2)(L)(2) (py)(2)] (2), [Zn(2)(Br)(2) (L)(2)(py)(2)] (3), [Zn(L)(2)(py)] (4), and [Zn(2)(OAc)(2)(L)(2)(py)(2)] (5), were prepared by the solvothermal reaction of ZnX(2) (X(-) =Cl(-), Br(-), F(-), and OAc(-)) salts with a 8-hydroxyquinolinate ligand (HL) that contained a trifluorophenyl group. All of the complexes were characterized by elemental analysis, IR spectroscopy, and powder and single-crystal X-ray crystallography. The building blocks exhibited unprecedented structural diversification and their self-assembly afforded one mononuclear, three binuclear, and one trinuclear Zn(II) structures in response to different anions and solvent systems. Complexes 1-5 featured four types of supramolecular network controlled by non-covalent interactions, such as π⋅⋅⋅π-stacking, C-H⋅⋅⋅π, hydrogen-bonding, and halogen-related interactions. Investigation of their photoluminescence properties exhibited disparate emission wavelengths, lifetimes, and quantum yields in the solid state. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kanzler, Charlotte R.; Lian, Peng; Trainer, Emma Leverich

Alkylated mercury species (monomethylmercury, MeHg, and dimethylmercury, DMeHg) exhibit significant bioaccumulation, and pose significant risks to ecosystems and human health. Although decades of research have been devoted to understanding MeHg formation and degradation, little is known about the DMeHg formation in aquatic systems. Here, we combine complementary experimental and computational approaches to examine MeHg speciation and DMeHg formation in sulfidic aqueous solutions, with an emphasis on the formation and decomposition of the binuclear bis(methylmercuric(II)) sulfide complex (CH3Hg)2S. Experimental data indicate that the reaction 2CH3Hg+ + HS- = (CH3Hg)2S has a log K = 26.0. Thus, the binuclear (CH3Hg)2S complex ismore » likely to be the dominant MeHg species under high MeHg concentrations typically used in experimental investigations of MeHg degradation by sulfate-reducing bacteria (SRB). Our finding of a significant abiotic removal mechanism for MeHg in sulfidic solutions through the formation of relatively insoluble (CH3Hg)2S suggests careful reexamination of reported “oxidative demethylation” of MeHg by SRB and perhaps other obligate anaerobes. We provide evidence for slow decomposition of (CH3Hg)2S to DMeHg and HgS, with a first-order rate constant k = 1.5 0.4 x 10-6 h-1. Quantum chemical calculations suggest that the reaction proceeds by a novel mechanism involving rearrangement of the (CH3Hg)2S complex facilitated by strong Hg-Hg interactions that activate a methyl group for intramolecular transfer. Predictions of DMeHg formation rates under a variety of field and laboratory conditions indicate that this pathway for DMeHg formation will be significant in laboratory experiments utilizing high MeHg concentrations, favoring (CH3Hg)2S formation. In natural systems with relatively high MeHg/[H2S]T ratios (the oxic/anoxic interface, for example), DMeHg production may be observed, and warrants further investigation.Experimental and computational evidence show that dimethylmercury is produced from decomposition of bis(methylmercury(ii)) sulfide.« less

Volumetric and x-ray investigations of the crystalline and columnar phases of copper (II) soaps under pressure

NASA Astrophysics Data System (ADS)

Ibn-Elhaj, M.; Guillon, D.; Skoulios, A.

1992-12-01

Binuclear copper (II) carboxylates, Cu2(CnH2n+1O2)4, crystallize at room temperature in layered systems in which planes of polar cores are separated by a double layer of alkyl chains. These compounds are mesomorphic in nature above ca. 100 °C. Pseudopolymeric chains of regularly stacked binuclear cores are located at the nodes of a two-dimensional hexagonal lattice and are surrounded by disordered aliphatic chains. The transition from the crystal to the columnar mesophase is characterized by a change in the repeat distance of the binuclear cores along the pseudopolymeric axis. In the crystalline phase, these cores are all oriented in the same direction with a repeat distance of 5.2 Å in the columnar mesophase, the polar cores are perpendicular to the columnar axis and superposed in a fourfold helicoidal fashion, at least on a local scale, with a repeat distance of 4.7 Å. We present here the effect of pressure on these anisotropic systems in a direction parallel to the columnar axis, and in the plane of the two-dimensional lattice. In a first part, we report the pressure-volume-temperature (P-V-T) relationship of these compounds (n=12, 18, and 24) in the temperature range from 30 to 200 °C, and in the pressure range from 1 to 2000 bars. Isothermal compressibility and isobaric expansion are determined in the crystalline and mesomorphic phases. In the mesophase, pressure-volume isotherms can be described by the Tait equation, as in most liquids or molten polymers. In a second part, we discuss the x-ray-diffraction experiments performed under pressure. In the mesophase, the area of the two-dimensional lattice decreases with increasing pressure and, at sufficiently high pressure, the columnar mesophase transforms into a crystalline lamellar phase. By combining P-V-T and x-ray results, we deduce an increase of the stacking period of the binuclear cores as a function of increasing pressure.

Binuclear Pt-Tl bonded complex with square pyramidal coordination around Pt: a combined multinuclear NMR, EXAFS, UV-Vis, and DFT/TDDFT study in dimethylsulfoxide solution.

PubMed

Purgel, Mihály; Maliarik, Mikhail; Glaser, Julius; Platas-Iglesias, Carlos; Persson, Ingmar; Tóth, Imre

2011-07-04

The structure and bonding of a new Pt-Tl bonded complex formed in dimethylsulfoxide (dmso), (CN)(4)Pt-Tl(dmso)(5)(+), have been studied by multinuclear NMR and UV-vis spectroscopies, and EXAFS measurements in combination with density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. This complex is formed following the equilibrium reaction Pt(CN)(4)(2-) + Tl(dmso)(6)(3+) ⇆ (CN)(4)Pt-Tl(dmso)(5)(+) + dmso. The stability constant of the Pt-Tl bonded species, as determined using (13)C NMR spectroscopy, amounts to log K = 2.9 ± 0.2. The (NC)(4)Pt-Tl(dmso)(5)(+) species constitutes the first example of a Pt-Tl bonded cyanide complex in which the sixth coordination position around Pt (in trans with respect to the Tl atom) is not occupied. The spectral parameters confirm the formation of the metal-metal bond, but differ substantially from those measured earlier in aqueous solution for complexes (CN)(5)Pt-Tl(CN)(n)(H(2)O)(x)(n-) (n = 0-3). The (205) Tl NMR chemical shift, δ = 75 ppm, is at extraordinary high field, while spin-spin coupling constant, (1)J(Pt-Tl) = 93 kHz, is the largest measured to date for a Pt-Tl bond in the absence of supporting bridging ligands. The absorption spectrum is dominated by two strong absorption bands in the UV region that are assigned to MMCT (Pt → Tl) and LMCT (dmso → Tl) bands, respectively, on the basis of MO and TDDFT calculations. The solution of the complex has a bright yellow color as a result of a shoulder present on the low energy side of the band at 355 nm. The geometry of the (CN)(4)Pt-Tl core can be elucidated from NMR data, but the particular stoichiometry and structure involving the dmso ligands are established by using Tl and Pt L(III)-edge EXAFS measurements. The Pt-Tl bond distance is 2.67(1) Å, the Tl-O bond distance is 2.282(6) Å, and the Pt-C-N entity is linear with Pt-C and Pt···N distances amounting to 1.969(6) and 3.096(6) Å, respectively. Geometry optimizations on the (CN)(4)Pt-Tl(dmso)(5)(+) system by using DFT calculations (B3LYP model) provide bond distances in excellent agreement with the EXAFS data. The four cyanide ligands are located in a square around the Pt atom, while the Tl atom is coordinated in a distorted octahedral fashion with the metal being located 0.40 Å above the equatorial plane described by four oxygen atoms of dmso ligands. The four equatorial Tl-O bonds and the four cyano ligands around the Pt atom are arranged in an alternate geometry. The coordination environment around Pt may be considered as being square pyramidal, where the apical position is occupied by the Tl atom. The optimized geometry of (CN)(4)Pt-Tl(dmso)(5)(+) is asymmetrical (C(1) point group). This low symmetry might be responsible for the unusually large NMR linewidths observed due to intramolecular chemical exchange processes. The nature of the Pt-Tl bond has been studied by MO analysis. The metal-metal bond formation in (CN)(4)Pt-Tl(dmso)(5)(+) can be simply interpreted as the result of a Pt(5d(z(2)))(2) → Tl(6s)(0) donation. This bonding scheme may rationalize the smaller thermodynamic stability of this adduct compared to the related complexes with (CN)(5)Pt-Tl entity, where the linear C-Pt-Tl unit constitutes a very stable bonding system. © 2011 American Chemical Society

Syntheses, structures and magnetic properties of four coordination polymers based on nitrobenzene dicarboxylate and various N-donor coligands

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Gui-Lian; Yin, Wei-Dong; Liu, Guang-Zhen

Four new coordination polymers ([Ni(4-Nbdc)(bpa)(H{sub 2}O)]){sub n} (1), ([Co(4-Nbdc)(bpp) (H{sub 2}O)]){sub n} (2), ([Ni(4-Nbdc)(bpp)(H{sub 2}O)]·H{sub 2}O){sub n} (3), and ([Mn{sub 2}(3-Nbdc){sub 2}(bib){sub 3}]·2H{sub 2}O){sub n} (4) (4-Nbdc=4-nitrobenzene-1,2-dicarboxylate, 3-Nbdc=3-nitrobenzene-1,2-dicarboxylate, bpa=1,2-bi(4-pyridyl)ethane, bpp=1,3-bis(4-pyridyl)propane, and bib=1,4-bis(1-imidazoly)benzene), were synthesized by hydrothermal reactions, and characterized by single-crystal X-ray diffractions, elemental analysis, FT-IR, PXRD, TGA and magnetic analysis. Complexes 1 and 2 display quasi-trapezoidal chain and brick-wall layer, and both of them contain metal–carboxylate binuclear units. Complexes 3 and 4 exhibit three-dimensional frameworks with the (6{sup 6}) dia topology and (4{sup 4}.6{sup 10}.8)(4{sup 4}.6{sup 2}) fsc topology, and both of them contain metal–carboxylate chains. The carboxyl groupsmore » with syn-anti coordination mode mediate effectively the weak ferromagnetic coupling interaction within Ni(II)–carboxylate binuclear in 1 (J=1.27 cm{sup −1}) and Ni(II)–carboxylate chain in 3 (J=1.44 cm{sup −1}), respectively, and the carboxyl groups with anti-anti coordination mode leads to the classic antiferromagnetic coupling interaction within Mn(II)–carboxylate chain in 4 (J=−0.77 cm{sup −1}). - Highlights: • Four novel coordination polymers were hydrothermally synthesized. • 1 is 1D quasi-trapezoidal chain and 2 is brick-wall layer both with dinuclear units. • 3 and 4 show 3D frameworks both with 1D metal–carboxylate chains. • 1 and 3 exhibit ferromagnetic coupling, while 4 shows antiferromagnetic coupling.« less

Sonochemical synthesis and characterization of a novel hetro-binuclear metal organic nano polymer based on picolinic acid ligand

NASA Astrophysics Data System (ADS)

Hayati, Payam; Souri, Bagher; Rezvani, Ali Reza; Morsali, Ali; Gutierrez, Angel

2017-12-01

Nanoparticles of one new lead and K coordination polymer (CP), {[Pb6(pyc)6(N3)7K].½H2O}n (1) Hpyc = picolinic acid ligand, has been synthesized by use of a sonochemical process and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR) spectroscopy and elemental analyses. The single crystal X-ray data of compound 1 imply that the Pb ion is seven coordinated. The thermal stability of compound 1 has been studied by thermogravimetric (TG) and differential scanning calorimetry (DSC). The role of temperature, reaction time and ultrasound irradiation power on the size and morphfology of the nano-structured compound obtained from 1, have been investigated. Results indicate that an increase of temperature and sonication power and a decrease in time reaction led to a decrease of particle size.

Investigation of Gasochromic Rhodium Complexes Towards Their Reactivity to CO and Integration into an Optical Gas Sensor for Fire Gas Detection.

PubMed

Pannek, Carolin; Tarantik, Karina R; Schmitt, Katrin; Wöllenstein, Jürgen

2018-06-21

The detection of the toxic gas carbon monoxide (CO) in the low ppm range is required in different applications. We present a study of the reactivity of different gasochromic rhodium complexes towards the toxic gas carbon monoxide (CO). Therefore, variations of binuclear rhodium complexes with different ligands were prepared. They were characterized by FTIR spectroscopy, ¹H NMR spectroscopy, and differential scanning calorimetry. All complexes are spectroscopically distinguishable and temperature stable up to at least 187 °C. The gasochromic behavior of all different compounds was tested. Therefore, the compounds were dissolved in toluene and exposed to 100 ppm CO for 10 min to investigate their gas sensitivity and reaction velocity. The changes in the transmission spectra were recorded by UV/vis spectroscopy. Furthermore, a significant influence of the solvent to the color dyes’ gasochromic reaction and behavior was observed. After characterization, one complex was transferred as sensing element into an optical gas sensor. Two different measurement principles (reflection- and waveguide-based) were built up and tested towards their capability as gasochromic CO sensors. Finally, different gas-dependent measurements were carried out.

Cd(II)-coordination polymers based on tetracarboxylic acid and diverse bis(imidazole) ligands: Synthesis, structural diversity and photoluminescence properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arıcı, Mürsel, E-mail: marici@ogu.edu.tr; Yeşilel, Okan Zafer; Taş, Murat

Three new Cd(II)-coordination polymers, namely, ([Cd{sub 2}(μ{sub 6}-ao{sub 2}btc)(μ-1,5-bipe){sub 2}]·2H{sub 2}O){sub n} (1), ([Cd{sub 2}(μ{sub 6}-ao{sub 2}btc)(μ-1,4-bix){sub 2}]{sub n}·2DMF) (2) and ([Cd{sub 2}(μ{sub 8}-abtc)(μ-1,4-betix)]·DMF·H{sub 2}O){sub n} (3) (ao{sub 2}btc=di-oxygenated form of 3,3′,5,5′-azobenzenetetracarboxylate, 1,5-bipe: 1,5-bis(imidazol-1yl)pentane, 1,4-bix=1,4-bis(imidazol-1ylmethyl)benzene, 1,4-betix=1,4-bis(2-ethylimidazol-1ylmethyl)benzene) were synthesized with 3,3′,5,5′-azobenzenetetracarboxylic acid and flexible, semi-flexible and semi-flexible substituted bis(imidazole) linkers. They were characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction, powder X-ray diffractions (PXRD) and thermal analyses (TG/DTA). Complexes 1–3 exhibited structural diversities depending on flexible, semi-flexible and semi-flexible substituted bis(imidazole) ligands. Complex 1 was 2D structure with 3,6L18 topology. Complex 2 had a 3D pillar-layered framework with the raremore » sqc27 topology. When semi-flexible substituted bis(imidazole) linker was used, 3D framework of complex 3 was obtained with the paddlewheel Cd{sub 2}(CO{sub 2}){sub 4}-type binuclear SBU. Moreover, thermal and photoluminescence properties of the complexes were determined in detailed. - Graphical abstract: In this study, three novel Cd(II)-coordination polymers were synthesized with 3,3′,5,5′-azobenzenetetracarboxylic acid and flexible, semi-flexible and semi-flexible substituted bis(imidazole) linkers. They were characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction, powder X-ray diffractions (PXRD) and thermal analyses (TG/DTA). Complexes 1–3 exhibited structural diversities depending on flexible, semi-flexible and semi-flexible substituted bis(imidazole) ligands. Complex 1 was 2D structure with 3,6L18 topology. Complex 2 had a 3D pillar-layered framework with the rare sqc27 topology. When semi-flexible substituted bis(imidazole) linker was used, 3D framework of complex 3 was obtained with the paddlewheel Cd{sub 2}(CO{sub 2}){sub 4}-type binuclear SBU. - Highlights: • Three new Cd(II)-coordination polymers with azobenzenetetracarboxylic acid and diverse bis(imidazole) linkers. • Complex 1 is 2D structure with 3,6L18 topology. • 3D pillar-layered framework of 2 with the rare sqc27 topology. • 3D framework of 3 with the paddlewheel Cd{sub 2}(CO{sub 2}){sub 4}-type SBU.« less

Superhalogen properties of hetero-binuclear anions MM‧F4- and MM″F5- (M = Li, Na, M‧ = Be, Mg, Ca; M″ = B, Al, Ga)

NASA Astrophysics Data System (ADS)

Yang, Hui; Li, Ying; He, Hui-Min; Tong, Jing; Wu, Di; Li, Zhi-Ru

2017-09-01

Hetero-binuclear superhalogen anions, namely MM‧F4- and MM″F5- (M = Li, Na; M‧ = Be, Mg, Ca; M″ = B, Al, Ga), have been theoretically characterized at the MP2(FULL)/6-311+G(3df) level. It is found that two central atoms can be linked by at most three fluorine ligands. The large vertical electron detachment energies (VDEs, 7.449-8.978 eV) verify the superhalogen identity of these anions. The VDEs of both MM‧F4- and MM″F5- decrease when the atomic size of M increases whereas increase with the size of M‧ and M″. Besides, the extra electron distribution also has effect on the VDEs of such superhalogen anions.

Complex formation of divalent metal ions with uridine 5'-O-thiomonophosphate or methyl thiophosphate: comparison of complex stabilities with those of the parent phosphate ligands.

PubMed

Da Costa, Carla P; Okruszek, Andrzej; Sigel, Helmut

2003-07-07

The stability constants of the 1:1 complexes formed in aqueous solution between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Zn2+, or Cd2+ (M2+) and methyl thiophosphate (MeOPS(2-)) or uridine 5'-O-thiomonophosphate (UMPS(2-)) (PS(2-)=MeOPS(2-) or UMPS(2-)) have been determined (potentiometric pH titrations; 25 degrees C; I = 0.1 M, NaNO(3)). Comparison of these results for M(PS) complexes with those known for the parent M(PO) phosphate species, where PO(2-)=CH(3)OPO(2-)(3) or UMP(2-) (uridine 5'-monophosphate), shows that the alkaline earth metal ions, as well as Mn2+, Co2+, and Ni2+ have a higher affinity for phosphate groups than for their thio analogues. However, based on the linear log K(M)(M(R-PO3)) versus pK(H)(H(R-PO3)) relationships (R-PO(2-)(3) simple phosphate monoester or phosphonate ligands with a non-interacting residue R) it becomes clear that the indicated observation is only the result of the lower basicity of the thiophosphate residue. In contrast, the thio complexes of Zn2+ and Cd2+ are more stable than their parent phosphate ones, and this despite the lower basicity of the PS(2-) ligands. This stability increase is identical for M(MeOPS) and M(UMPS) species and amounts to about 0.6 and 2.4 log units for Zn(PS) and Cd(PS), respectively. Since no other binding site is available in MeOPS(2-), this enhanced stability has to be attributed to the S atom. Indeed, from the mentioned stability differences it follows that Cd2+ in Cd(PS) is coordinated by more than 99% to the thiophosphate S atom; the same value holds for Pb(PS), which was studied earlier. The formation degree of the Sbonded isomer amounts to 76+/-6 % for Zn(PS) and is close to zero for the corresponding Mg2+, Ca2+, and Mn2+ species. It is further shown that Zn(MeOPS)(aq)(2+) releases a proton from a coordinated water molecule with pK(a) approximately 6.9; i.e., this deprotonation occurs at a lower pH value than that for the same reaction in Zn(aq)(2+). Since Mg2+, Ca2+, Mn2+, and Cd2+ have a relatively low tendency for hydroxo complex formation, it was possible, for these M2+, to also quantify the stability of the binuclear complexes, M(2)(UMPS-H)+, where one M2+ is thiophosphate-coordinated and the other is coordinated at (N3)(-) of the uracil residue. The impact of the results presented herein regarding M2+/nucleic acid interactions, including those of ribozymes (rescue experiments), is briefly discussed.

Phosphoester hydrolysis: the incoming substrate turns the bridging hydroxido nucleophile into a terminal one.

PubMed

Gouré, Eric; Carboni, Michaël; Troussier, Angélique; Lebrun, Colette; Pécaut, Jacques; Jacquot, Jean-François; Dubourdeaux, Patrick; Clémancey, Martin; Blondin, Geneviève; Latour, Jean-Marc

2015-05-26

Identifying the active nucleophile in hydrolysis reactions catalyzed by binuclear hydrolases is a recurrent problem and a matter of intense debate. We report on the phosphate ester hydrolysis by a Fe(III)Fe(II) complex of a binucleating ligand. This complex presents activities in the range of those observed for similar biomimetic compounds in the literature. The specific electronic properties of the Fe(III)Fe(II) complex allowed us to use (1)H NMR and Mössbauer spectroscopies to investigate the nature of the various species present in the solution in the pH range of 5-10. Both techniques showed that the hydrolysis activity is associated to a μ-hydroxido Fe(III)Fe(II) species. Further (1)H NMR experiments show that binding of anions or the substrate changes this bonding mode suggesting that a terminal hydroxide is the likely nucleophile in these hydrolysis reactions. This view is further supported by the structure determination of the hydrolysis product. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Arsenic Re-Mobilization in Water Treatment Adsorbents Under Reducing Conditions: Part II, XAS and Modeling Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu,S.; Jing, C.; Meng, X.

2008-01-01

The mechanism of arsenic re-mobilization in spent adsorbents under reducing conditions was studied using X-ray absorption spectroscopy and surface complexation model calculations. X-ray absorption near edge structure (XANES) spectroscopy demonstrated that As(V) was partially reduced to As(III) in spent granular ferric hydroxide (GFH), titanium dioxide (TiO2), activated alumina (AA) and modified activated alumina (MAA) adsorbents after 2 years of anaerobic incubation. As(V) was completely reduced to As(III) in spent granular ferric oxide (GFO) under 2-year incubation. The extended X-ray absorption fine structure (EXAFS) spectroscopy analysis showed that As(III) formed bidentate binuclear surface complexes on GFO as evidenced by an averagemore » As(III)-O bond distance of 1.78 Angstroms and As(III)-Fe distance of 3.34 Angstroms . The release of As from the spent GFO and TiO2 was simulated using the charge distribution multi-site complexation (CD-MUSIC) model. The observed redox ranges for As release and sulfate mobility were described by model calculations.« less

Three novel coordination polymers based on tris(p-carboxyphenyl)phosphane oxide: Syntheses, structural characterization and magnetic properties

NASA Astrophysics Data System (ADS)

Huo, Liangqin; Fan, Liming; Zhang, Jie; Gao, Lingling; Zhai, Lijun; Wang, Xiaoqing; Hu, Tuoping

2018-05-01

Three coordination polymers (CPs), namely, {[Co3(HL)2(bib)3 (H2O)7]·12H2O}n (1), {[Co(HL)(bib)]·H2O}n (2), and {[Co1.5(L)(bibp)1.5 (H2O)]·1.5DMF·2EtOH·3H2O}n (3), have been synthesized from the tripodal ligand of tris(p-carboxyphenyl)phosphane oxide (H3L) with the help of 1,4-bis(imidazol-1-yl)benzene (bib) or 4,4‧-bis(imidazol-1-yl)biphenyl (bibp). Structural analyses reveal that complex 1 features a 3D 4-connected {650.8}-cds net. 2 displays a 2D 6-connected {360.460.53}-hxl sheet based on the binuclear {Co2(COO)2} SBUs. Complex 3 shows a 3D (3,4,4)-connected net with {6·82}2{6·840.10}2{620.820.102} point symbol. Furthermore, the results of the variable-temperature magnetic susceptibilities indicate that complexes 1-3 have antiferromagnetic behavior between Co(II) ions.

Uncovering the transmembrane metal binding site of the novel bacterial major facilitator superfamily-type copper importer CcoA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khalfaoui-Hassani, Bahia; Verissimo, Andreia F.; Koch, Hans -Georg

In this study, uptake and trafficking of metals and their delivery to their respective metalloproteins are important processes. Cells need precise control of each step to avoid exposure to excessive metal concentrations and their harmful consequences. Copper (Cu) is a required micronutrient used as a cofactor in proteins. However, in large amounts, it can induce oxidative damage; hence, Cu homeostasis is indispensable for cell survival. Biogenesis of respiratory heme-Cu oxygen (HCO) reductases includes insertion of Cu into their catalytic subunits to form heme-Cu binuclear centers. Previously, we had shown that CcoA is a major facilitator superfamily (MFS)-type bacterial Cu importermore » required for biogenesis of cbb 3-type cytochrome coxidase ( cbb 3-Cox). Here, using Rhodobacter capsulatus, we focused on the import and delivery of Cu to cbb 3-Cox. By comparing the CcoA amino acid sequence with its homologues from other bacterial species, we located several well-conserved Met, His, and Tyr residues that might be important for Cu transport. We determined the topology of the transmembrane helices that carry these residues to establish that they are membrane embedded, and substituted for them amino acids that do not ligand metal atoms. Characterization of these mutants for their uptake of radioactive 64Cu and cbb 3-Cox activities demonstrated that Met233 and His261 of CcoA are essential and Met237 and Met265 are important, whereas Tyr230 has no role for Cu uptake or cbb3-Cox biogenesis. These findings show for the first time that CcoA-mediated Cu import relies on conserved Met and His residues that could act as metal ligands at the membrane-embedded Cu binding domain of this transporter.« less

Uncovering the transmembrane metal binding site of the novel bacterial major facilitator superfamily-type copper importer CcoA

DOE PAGES

Khalfaoui-Hassani, Bahia; Verissimo, Andreia F.; Koch, Hans -Georg; ...

2016-01-19

In this study, uptake and trafficking of metals and their delivery to their respective metalloproteins are important processes. Cells need precise control of each step to avoid exposure to excessive metal concentrations and their harmful consequences. Copper (Cu) is a required micronutrient used as a cofactor in proteins. However, in large amounts, it can induce oxidative damage; hence, Cu homeostasis is indispensable for cell survival. Biogenesis of respiratory heme-Cu oxygen (HCO) reductases includes insertion of Cu into their catalytic subunits to form heme-Cu binuclear centers. Previously, we had shown that CcoA is a major facilitator superfamily (MFS)-type bacterial Cu importermore » required for biogenesis of cbb 3-type cytochrome coxidase ( cbb 3-Cox). Here, using Rhodobacter capsulatus, we focused on the import and delivery of Cu to cbb 3-Cox. By comparing the CcoA amino acid sequence with its homologues from other bacterial species, we located several well-conserved Met, His, and Tyr residues that might be important for Cu transport. We determined the topology of the transmembrane helices that carry these residues to establish that they are membrane embedded, and substituted for them amino acids that do not ligand metal atoms. Characterization of these mutants for their uptake of radioactive 64Cu and cbb 3-Cox activities demonstrated that Met233 and His261 of CcoA are essential and Met237 and Met265 are important, whereas Tyr230 has no role for Cu uptake or cbb3-Cox biogenesis. These findings show for the first time that CcoA-mediated Cu import relies on conserved Met and His residues that could act as metal ligands at the membrane-embedded Cu binding domain of this transporter.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medyantseva, E.P.; Budnikov, G.K.; Balakaeva, T.A.

The interest in the analytical chemistry of ruthenium and its compounds has recently been increasing. Ruthenium compounds can be used an antitumor agents and in the treatment of tuberculosis and fungal infections. It has been suggested that there is a specific relationship between the reduction potentials of the compounds and their biological activity. Of greatest interest among the biologically active compounds are the compounds with nitrogen-containing heterocycles. In order to obtain information on the degree of oxidation of the central atom in the complexes and to select the optimum conditions for the determination of the mono- and bi-nuclear complexes ofmore » ruthenium compounds with biologically active ligands such as imidazole (Im), histidine (His), benzimidazole (BIm) and its methyl derivative [1,2(CH{sub 3}){sub 2} - BIm], benzohyroxamic acid (Bha), and 1-phenyl-2-methylamino-1-propanol or ephedrine (Eph) in the present work, the authors studied their electrochemical behavior at dropping mercury (dme) and a platinum electrodes. 6 refs., 1 fig., 2 tabs.« less

Covalent Co–O–V and Sb–N Bonds Enable Polyoxovanadate Charge Control

PubMed Central

2017-01-01

The formation of [{CoII(teta)2}{CoII2(tren)(teta)2}VIV15SbIII6O42(H2O)]·ca.9H2O [teta = triethylenetetraamine; tren = tris(2-aminoethyl)amine] illustrates a strategy toward reducing the molecular charge of polyoxovanadates, a key challenge in their use as components in single-molecule electronics. Here, a V–O–Co bond to a binuclear Co2+-centered complex and a Sb–N bond to the terminal N atom of a teta ligand of a mononuclear Co2+ complex allow for full charge compensation of the archetypal molecular magnet [V15Sb6O42(H2O)]6–. Density functional theory based electron localization function analysis demonstrates that the Sb–N bond has an electron density similar to that of a Sb–O bond. Magnetic exchange coupling between the VIV and CoII spin centers mediated via the Sb–N bridge is comparably weakly antiferromagnetic. PMID:28541697

Dioxygen Binding, Activation, and Reduction to H2O by Cu Enzymes.

PubMed

Solomon, Edward I

2016-07-05

Oxygen intermediates in copper enzymes exhibit unique spectroscopic features that reflect novel geometric and electronic structures that are key to reactivity. This perspective will describe: (1) the bonding origin of the unique spectroscopic features of the coupled binuclear copper enzymes and how this overcomes the spin forbiddenness of O2 binding and activates monooxygenase activity, (2) how the difference in exchange coupling in the non-coupled binuclear Cu enzymes controls the reaction mechanism, and (3) how the trinuclear Cu cluster present in the multicopper oxidases leads to a major structure/function difference in enabling the irreversible reductive cleavage of the O-O bond with little overpotential and generating a fully oxidized intermediate, different from the resting enzyme studied by crystallography, that is key in enabling fast PCET in the reductive half of the catalytic cycle.

Facet-Dependent Cr(VI) Adsorption of Hematite Nanocrystals.

PubMed

Huang, Xiaopeng; Hou, Xiaojing; Song, Fahui; Zhao, Jincai; Zhang, Lizhi

2016-02-16

In this study, the adsorption process of Cr(VI) on the hematite facets was systematically investigated with synchrotron-based Cr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, density-functional theory calculation, and surface complexation models. Structural model fitting of EXAFS spectroscopy suggested that the interatomic distances of Cr-Fe were, respectively, 3.61 Å for the chromate coordinated hematite nanoplates with exposed {001} facets, 3.60 and 3.30 Å for the chromate coordinated hematite nanorods with exposed {001} and {110} facets, which were characteristic of inner-sphere complexation. In situ ATR-FTIR spectroscopy analysis confirmed the presence of two inner-sphere surface complexes with C3ν and C2ν symmetry, while the C3ν and C2ν species were assigned to monodentate and bidentate inner-sphere surface complexes with average Cr-Fe interatomic distances of 3.60 and 3.30 Å, respectively. On the basis of these experimental and theoretical results, we concluded that HCrO4(-) as dominated Cr(VI) species was adsorbed on {001} and {110} facets in inner-sphere monodentate mononuclear and bidentate binuclear configurations, respectively. Moreover, the Cr(VI) adsorption performance of hematite facets was strongly dependent on the chromate complexes formed on the hematite facets.

Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism.

PubMed

Soldatova, Alexandra V; Tao, Lizhi; Romano, Christine A; Stich, Troy A; Casey, William H; Britt, R David; Tebo, Bradley M; Spiro, Thomas G

2017-08-23

The bacterial protein complex Mnx contains a multicopper oxidase (MCO) MnxG that, unusually, catalyzes the two-electron oxidation of Mn(II) to MnO 2 biomineral, via a Mn(III) intermediate. Although Mn(III)/Mn(II) and Mn(IV)/Mn(III) reduction potentials are expected to be high, we find a low reduction potential, 0.38 V (vs Normal Hydrogen Electrode, pH 7.8), for the MnxG type 1 Cu 2+ , the electron acceptor. Indeed the type 1 Cu 2+ is not reduced by Mn(II) in the absence of molecular oxygen, indicating that substrate oxidation requires an activation step. We have investigated the enzyme mechanism via electronic absorption spectroscopy, using chemometric analysis to separate enzyme-catalyzed MnO 2 formation from MnO 2 nanoparticle aging. The nanoparticle aging time course is characteristic of nucleation and particle growth; rates for these processes followed expected dependencies on Mn(II) concentration and temperature, but exhibited different pH optima. The enzymatic time course is sigmoidal, signaling an activation step, prior to turnover. The Mn(II) concentration and pH dependence of a preceding lag phase indicates weak Mn(II) binding. The activation step is enabled by a pK a > 8.6 deprotonation, which is assigned to Mn(II)-bound H 2 O; it induces a conformation change (consistent with a high activation energy, 106 kJ/mol) that increases Mn(II) affinity. Mnx activation is proposed to decrease the Mn(III/II) reduction potential below that of type 1 Cu(II/I) by formation of a hydroxide-bridged binuclear complex, Mn(II)(μ-OH)Mn(II), at the substrate site. Turnover is found to depend cooperatively on two Mn(II) and is enabled by a pK a 7.6 double deprotonation. It is proposed that turnover produces a Mn(III)(μ-OH) 2 Mn(III) intermediate that proceeds to the enzyme product, likely Mn(IV)(μ-O) 2 Mn(IV) or an oligomer, which subsequently nucleates MnO 2 nanoparticles. We conclude that Mnx exploits manganese polynuclear chemistry in order to facilitate an otherwise difficult oxidation reaction, as well as biomineralization. The mechanism of the Mn(III/IV) conversion step is elucidated in an accompanying paper .

Influence of ligand-bridged substitution on the exchange coupling constant of chromium-wheels host complexes: a density functional theory study

NASA Astrophysics Data System (ADS)

Sadeghi Googheri, Motahare; Abolhassani, Mohammad Reza; Mirzaei, Mahmoud

2018-05-01

Designing and introducing novel wheel-shaped supramolecular as host complexes with new magnetic properties is the theme of the day. So in this study, new eight binuclear chromium (III) complexes, as models of real chromium-wheel host complexes, were designed based on changing of bridged-ligands and exchange coupling constants (J) of them were calculated using the broken symmetry density functional theory approach. Substitution of fluorine ligand in fluoro-bridged model [Cr2F(tBuCO2)2(H2O)2(OH)4]-1 by halogen anions (Cl-, Br- and I- ) decreased the antiferromagnetic exchange coupling between Cr(III) centres such that by going from F- to I- the J values became more positive. In the case of hydroxo-bridged model [Cr2OH(tBuCO2)2(H2O)2(OH)4]-1, replacement of hydroxyl by methoxy anion (OMe-) strengthened the antiferromagnetic property of the complex but substitution by sulfanide (SH-) and amide (NH2-) anions weakened it and changed the nature of complexes to ferromagnetic. Because of their different magnetic properties, these new investigated complexes can be suggested as interesting synthetic targets. Also, the J value changes due to ligand substitution were evaluated and it was found that the Cr-X bond strength and partial charges of involved atoms were the most effective factors on it.

The Hydrogenase Activity of the Molybdenum/Copper-containing Carbon Monoxide Dehydrogenase of Oligotropha carboxidovorans*

PubMed Central

Wilcoxen, Jarett; Hille, Russ

2013-01-01

The reaction of the air-tolerant CO dehydrogenase from Oligotropha carboxidovorans with H2 has been examined. Like the Ni-Fe CO dehydrogenase, the enzyme can be reduced by H2 with a limiting rate constant of 5.3 s−1 and a dissociation constant Kd of 525 μm; both kred and kred/Kd, reflecting the breakdown of the Michaelis complex and the reaction of free enzyme with free substrate in the low [S] regime, respectively, are largely pH-independent. During the reaction with H2, a new EPR signal arising from the Mo/Cu-containing active site of the enzyme is observed which is distinct from the signal seen when the enzyme is reduced by CO, with greater g anisotropy and larger hyperfine coupling to the active site 63,65Cu. The signal also exhibits hyperfine coupling to at least two solvent-exchangeable protons of bound substrate that are rapidly exchanged with solvent. Proton coupling is also evident in the EPR signal seen with the dithionite-reduced native enzyme, and this coupling is lost in the presence of bicarbonate. We attribute the coupled protons in the dithionite-reduced enzyme to coordinated water at the copper site in the native enzyme and conclude that bicarbonate is able to displace this water from the copper coordination sphere. On the basis of our results, a mechanism for H2 oxidation is proposed which involves initial binding of H2 to the copper of the binuclear center, displacing the bound water, followed by sequential deprotonation through a copper-hydride intermediate to reduce the binuclear center. PMID:24165123

Cytochrome bo(3) from Escherichia coli: the binding and turnover of nitric oxide.

PubMed

Butler, Clive; Forte, Elena; Maria Scandurra, Francesca; Arese, Marzia; Giuffré, Alessandro; Greenwood, Colin; Sarti, Paolo

2002-09-06

The reaction of nitric oxide (NO) with fast and reduced cytochrome bo(3)(cyt bo(3)) from Escherichia coli has been investigated. The stoichiometry of NO binding to cyt bo(3) was determined using an NO electrode in the [NO] range 1-14 microM. Under reducing conditions, the initial decrease in [NO] following the addition of cyt bo(3) corresponded to binding of 1 NO molecule per cyt bo(3) functional unit. After this "rapid" NO binding phase, there was a slow, but significant rate of NO consumption ( approximately 0.3molNOmol bo(3)(-1)min(-1)), indicating that cyt bo(3) possesses a low level of NO reductase activity. The binding of NO to fast pulsed enzyme was also investigated. The results show that in the [NO] range used (1-14 microM) both fast and pulsed oxidised cyt bo(3) bind NO with a stoichiometry of 1:1 with an observed dissociation constant of K(d)=5.6+/-0.6 microM and that NO binding was inhibited by the presence of Cl(-). The binding of nitrite to the binuclear centre causes spectral changes similar to those observed upon NO binding to fast cyt bo(3). These results are discussed in relation to the model proposed by Wilson and co-workers [FEBS Lett. 414 (1997) 281] where the binding of NO to Cu(B)(II) results in the formation of the nitrosonium (Cu(B)(I)-NO(+)) complex. NO(+) then reacts with OH(-), a Cu(B) ligand, to form nitrite, which can bind at the binuclear centre. This work suggests for the first time that the binding of NO to oxidised cyt bo(3) does result in the reduction of Cu(B).

Formation of a cytochrome c-nitrous oxide reductase complex is obligatory for N2O reduction by Paracoccus pantotrophus.

PubMed

Rasmussen, Tim; Brittain, Thomas; Berks, Ben C; Watmough, Nicholas J; Thomson, Andrew J

2005-11-07

Nitrous oxide reductase (N2OR) catalyses the final step of bacterial denitrification, the two-electron reduction of nitrous oxide (N2O) to dinitrogen (N2). N2OR contains two metal centers; a binuclear copper center, CuA, that serves to receive electrons from soluble donors, and a tetranuclear copper-sulfide center, CuZ, at the active site. Stopped flow experiments at low ionic strengths reveal rapid electron transfer (kobs=150 s-1) between reduced horse heart (HH) cytochrome c and the CuA center in fully oxidized N2OR. When fully reduced N2OR was mixed with oxidized cytochrome c, a similar rate of electron transfer was recorded for the reverse reaction, followed by a much slower internal electron transfer from CuZ to CuA(kobs=0.1-0.4 s-1). The internal electron transfer process is likely to represent the rate-determining step in the catalytic cycle. Remarkably, in the absence of cytochrome c, fully reduced N2OR is inert towards its substrate, even though sufficient electrons are stored to initiate a single turnover. However, in the presence of reduced cytochrome c and N2O, a single turnover occurs after a lag-phase. We propose that a conformational change in N2OR is induced by its specific interaction with cytochrome c that in turn either permits electron transfer between CuA and CuZ or controls the rate of N2O decomposition at the active site.

Rates of proton transfer to Fe-S-based clusters: comparison of clusters containing {MFe(mu(2)-S)(2)}n+ and {MFe(3)(mu(3)-S)(4)}n+ (M = Fe, Mo, or W) cores.

PubMed

Bates, Katie; Garrett, Brendan; Henderson, Richard A

2007-12-24

The rates of proton transfer from [pyrH]+ (pyr = pyrrolidine) to the binuclear complexes [Fe2S2Cl4]2- and [S2MS2FeCl2]2- (M = Mo or W) are reported. The reactions were studied using stopped-flow spectrophotometry, and the rate constants for proton transfer were determined from analysis of the kinetics of the substitution reactions of these clusters with the nucleophiles Br- or PhS- in the presence of [pyrH]+. In general, Br- is a poor nucleophile for these clusters, and proton transfer occurs before Br- binds, allowing direct measure of the rate of proton transfer from [pyrH]+ to the cluster. In contrast, PhS- is a better nucleophile, and a pathway in which PhS- binds preferentially to the cluster prior to proton transfer from [pyrH]+ usually operates. For the reaction of [Fe2S2Cl4]2- with PhS- in the presence of [pyrH]+ both pathways are observed. Comparison of the results presented in this paper with analogous studies reported earlier on cuboidal Fe-S-based clusters allows discussion of the factors which affect the rates of proton transfer in synthetic clusters including the nuclearity of the cluster core, the metal composition, and the nature of the terminal ligands. The possible relevance of these findings to the protonation sites of natural Fe-S-based clusters, including FeMo-cofactor from nitrogenase, are presented.

Structural and functional determination of homologs of the Mycobacterium tuberculosisN-acetylglucosamine-6-phosphate deacetylase (NagA).

PubMed

Ahangar, Mohd Syed; Furze, Christopher M; Guy, Collette S; Cooper, Charlotte; Maskew, Kathryn S; Graham, Ben; Cameron, Alexander D; Fullam, Elizabeth

2018-05-04

The Mycobacterium tuberculosis (Mtb) pathogen encodes an N -acetylglucosamine-6-phosphate deacetylase enzyme, NagA (Rv3332), that belongs to the amidohydrolase superfamily. NagA enzymes catalyze the deacetylation of N -acetylglucosamine-6-phosphate (GlcNAc6P) to glucosamine-6-phosphate (GlcN6P). NagA is a potential anti-tubercular drug target because it represents the key enzymatic step in the generation of essential amino-sugar precursors required for Mtb cell wall biosynthesis and also influences recycling of cell wall peptidoglycan fragments. Here, we report the structural and functional characterization of NagA from Mycobacterium smegmatis (MSNagA) and Mycobacterium marinum (MMNagA), close relatives of Mtb Using a combination of X-ray crystallography, site-directed mutagenesis, and biochemical and biophysical assays, we show that these mycobacterial NagA enzymes are selective for GlcNAc6P. Site-directed mutagenesis studies revealed crucial roles of conserved residues in the active site that underpin stereo-selective recognition, binding, and catalysis of substrates. Moreover, we report the crystal structure of MSNagA in both ligand-free form and in complex with the GlcNAc6P substrate at 2.6 Å and 2.0 Å resolutions, respectively. The GlcNAc6P-complex structure disclosed the precise mode of GlcNAc6P binding and the structural framework of the active site, including two divalent metals located in the α/β binuclear site. Furthermore, we observed a cysteine residue located on a flexible loop region that occludes the active site. This cysteine is unique to mycobacteria and may represent a unique subsite for targeting mycobacterial NagA enzymes. Our results provide critical insights into the structural and mechanistic properties of mycobacterial NagA enzymes having an essential role in amino-sugar and nucleotide metabolism in mycobacteria. Published under license by The American Society for Biochemistry and Molecular Biology, Inc.

Hetero-metallic {3d-4f-5d} complexes: preparation and magnetic behavior of trinuclear [(L(Me2)Ni-Ln){W(CN)(8)}] compounds (Ln = Gd, Tb, Dy, Ho, Er, Y; L(Me2) = Schiff base) and variable SMM characteristics for the Tb derivative.

PubMed

Sutter, Jean-Pascal; Dhers, Sébastien; Rajamani, Raghunathan; Ramasesha, S; Costes, Jean-Pierre; Duhayon, Carine; Vendier, Laure

2009-07-06

Assembling bimetallic {Ni-Ln}(3+) units and {W(CN)(8)}(3-) is shown to be an efficient route toward heteronuclear {3d-4f-5d} compounds. The reaction of either the binuclear [{L(Me2)Ni(H(2)O)(2)}{Ln(NO(3))(3)}] complexes or their mononuclear components [L(Me2)Ni] and Ln(NO(3))(3) with (HNBu(3))(3){W(CN)(8)} in dmf followed by diffusion of tetrahydrofuran yielded the trinuclear [{L(Me2)NiLn}{W(CN)(8)}] compounds 1 (Ln = Y), 2a,b (Gd), 3a,b (Tb), 4 (Dy), 5 (Ho), and 6 (Er) as crystalline materials. All of the derivatives possess the trinuclear core resulting from the linkage of the {W(CN)(8)} to the Ni center of the {Ni-Ln} unit. Differences are found in the solvent molecules acting as ligands and/or in the lattice depending on the crystallization conditions. For all the compounds ferromagnetic {Ni-W} and {Ni-Ln} (Ln = Gd, Tb, Dy, and Er} interactions are operative resulting in high spin ground states. Parameterization of the magnetic behaviors for the Y and Gd derivatives confirmed the strong cyano-mediated {Ni-W} interaction (J(NiW) = 27.1 and 28.5 cm(-1)) compared to the {Ni-Gd} interaction (J(NiGd) = 2.17 cm(-1)). The characteristic features for slow relaxation of the magnetization are observed for two Tb derivatives, but these are modulated by the crystal phase. Analysis of the frequency dependence of the alternating current susceptibility data yielded U(eff)/k(B) = 15.3 K and tau(0) = 4.5 x 10(-7) s for one derivative whereas no maxima of chi(M)'' appear above 2 K for the second one.

Phosphate bonding to goethite and pyrolusite surfaces

USGS Publications Warehouse

Weiner, Eugene R.; Goldberg, M.C.; Boymel, P.M.

1984-01-01

Fourier transform infrared (FTIR) spectra were obtained from pure and phosphated goethite (??-FeOOH), and pyrolusite (MnO2). The nature of the phosphate-surface bond was determined to be binuclear for goethite and bidentate for pyrolusite.

Fluorescence and electron paramagnetic resonance studies of norfloxacin and N-donor mixed-ligand ternary copper(II) complexes: Stability and interaction with SDS micelles

NASA Astrophysics Data System (ADS)

Vignoli Muniz, Gabriel S.; Incio, Jimmy Llontop; Alves, Odivaldo C.; Krambrock, Klaus; Teixeira, Letícia R.; Louro, Sonia R. W.

2018-01-01

The stability of ternary copper(II) complexes of a heterocyclic ligand, L (L being 2,2‧-bipyridine (bipy) or 1,10-phenanthroline (phen)) and the fluorescent antibacterial agent norfloxacin (NFX) as the second ligand was studied at pH 7.4 and different ionic strengths. Fluorescence quenching upon titration of NFX with the binary complexes allowed to obtain stability constants for NFX binding, Kb, as a function of ionic strength. The Kb values vary by more than two orders of magnitude when buffer concentration varies from 0.5 to 100 mM. It was observed that previously synthesized ternary complexes dissociate in buffer according with the obtained stability constants. This shows that equimolar solutions of NFX and binary complexes are equivalent to solutions of synthesized ternary complexes. The interaction of the ternary copper complexes with anionic SDS (sodium dodecyl sulfate) micelles was studied by fluorescence and electron paramagnetic resonance (EPR). Titration of NFX-loaded SDS micelles with the complexes Cu:L allowed to determine the stability constants inside the micelles. Fluorescence quenching demonstrated that SDS micelles increase the stability constants by factors around 50. EPR spectra gave details of the copper(II) local environment, and demonstrated that the structure of the ternary complexes inside SDS micelles is different from that in buffer. Mononuclear ternary complexes formed inside the micelles, while in buffer most ternary complexes are binuclear. The results show that anionic membrane interfaces increase formation of copper fluoroquinolone complexes, which can influence bioavailability, membrane diffusion, and mechanism of action of the antibiotics.

Time-resolved single-turnover of caa(3) oxidase from Thermus thermophilus. Fifth electron of the fully reduced enzyme converts O(H) into E(H) state.

PubMed

Siletsky, Sergey A; Belevich, Ilya; Belevich, Nikolai P; Soulimane, Tewfik; Verkhovsky, Michael I

2011-09-01

The oxidative part of the catalytic cycle of the caa(3)-type cytochrome c oxidase from Thermus thermophilus was followed by time-resolved optical spectroscopy. Rate constants, chemical nature and the spectral properties of the catalytic cycle intermediates (Compounds A, P, F) reproduce generally the features typical for the aa(3)-type oxidases with some distinctive peculiarities caused by the presence of an additional 5-th redox-center-a heme center of the covalently bound cytochrome c. Compound A was formed with significantly smaller yield compared to aa(3) oxidases in general and to ba(3) oxidase from the same organism. Two electrons, equilibrated between three input redox-centers: heme a, Cu(A) and heme c are transferred in a single transition to the binuclear center during reduction of the compound F, converting the binuclear center through the highly reactive O(H) state into the final product of the reaction-E(H) (one-electron reduced) state of the catalytic site. In contrast to previous works on the caa(3)-type enzymes, we concluded that the finally produced E(H) state of caa(3) oxidase is characterized by the localization of the fifth electron in the binuclear center, similar to the O(H)→E(H) transition of the aa(3)-type oxidases. So, the fully-reduced caa(3) oxidase is competent in rapid electron transfer from the input redox-centers into the catalytic heme-copper site. 2011 Elsevier B.V. All rights reserved.

Spectroscopic definition of the biferrous and biferric sites in de novo designed four-helix bundle DFsc peptides: implications for O2 reactivity of binuclear non-heme iron enzymes.

PubMed

Bell, Caleb B; Calhoun, Jennifer R; Bobyr, Elena; Wei, Pin-Pin; Hedman, Britt; Hodgson, Keith O; Degrado, William F; Solomon, Edward I

2009-01-13

DFsc is a single chain de novo designed four-helix bundle peptide that mimics the core protein fold and primary ligand set of various binuclear non-heme iron enzymes. DFsc and the E11D, Y51L, and Y18F single amino acid variants have been studied using a combination of near-IR circular dichroism (CD), magnetic circular dichroism (MCD), variable temperature variable field MCD (VTVH MCD), and X-ray absorption (XAS) spectroscopies. The biferrous sites are all weakly antiferromagnetically coupled with mu-1,3 carboxylate bridges and one 4-coordinate and one 5-coordinate Fe, very similar to the active site of class I ribonucleotide reductase (R2) providing open coordination positions on both irons for dioxygen to bridge. From perturbations of the MCD and VTVH MCD the iron proximal to Y51 can be assigned as the 4-coordinate center, and XAS results show that Y51 is not bound to this iron in the reduced state. The two open coordination positions on one iron in the biferrous state would become occupied by dioxygen and Y51 along the O(2) reaction coordinate. Subsequent binding of Y51 functions as an internal spectral probe of the O(2) reaction and as a proton source that would promote loss of H(2)O(2). Coordination by a ligand that functions as a proton source could be a structural mechanism used by natural binuclear iron enzymes to drive their reactions past peroxo biferric level intermediates.

Spectroscopic definition of the biferrous and biferric sites of de novo designed 4-helix bundle DFsc peptides: Implications for O2 reactivity of binuclear non-heme iron enzymes

PubMed Central

Bell, Caleb B.; Calhoun, Jennifer R.; Bobyr, Elena; Wei, Pin-pin; Hedman, Britt; Hodgson, Keith O.; DeGrado, William F.; Solomon, Edward I.

2009-01-01

DFsc is a single chain de novo designed 4-helix bundle peptide that mimics the core protein fold and primary ligand set of various binuclear non-heme iron enzymes. DFsc and the E11D, Y51L and Y18F single amino acid variants have been studied using a combination of near-IR circular dichroism (CD), magnetic circular dichroism (MCD), variable temperature variable field MCD (VTVH MCD) and x-ray absorption (XAS) spectroscopies. The biferrous sites are all weakly antiferromagnetically coupled with μ-1,3 carboxylate bridges and one 4-coordinate and one 5-coordinate Fe, very similar to the active site of Class I ribonucleotide reductase (R2) providing open coordination positions on both irons for dioxygen to bridge. From perturbations of the MCD and VTVH MCD the iron proximal to Y51 can be assigned as the 4-coordinate center and XAS results show that Y51 is not bound to this iron in the reduced state. The two open coordination positions on one iron in the biferrous state would become occupied by dioxygen and Y51 along the O2 reaction coordinate. Subsequent binding of Y51 functions as an internal spectral probe of the O2 reaction and as a proton source that would promote loss of H2O2. Coordination by a ligand that functions as a proton source could be a structural mechanism used by natural binuclear iron enzymes to drive their reactions past peroxo biferric level intermediates. PMID:19090676

Cytogenetic toxicity effects of inorganic nickel and organic Ni(II) complexes on Brassica oleracea L. root meristem.

PubMed

Molas, J

2001-01-01

Experiments were carried out on the effect of nickel as an inorganic compound (NiSO4.7H2O) and organic Ni(II) complexes (i.e. Ni(II)-Glu and Ni(II)-EDTA) in concentrations of 20, 40 and 85 ?M dm-3 on meristematic cells of root tips of Brassica oleracea L. cv. Sława from Enkhouizen. All three tested chemical forms of nickel had a mitodepressive effect and inhibited root elongation. With respect to the degree of root elongation inhibition and mitodepressive effect, the tested forms of nickel can be put in the following order: Ni(II)-Glu NiSO4.7H2O Ni(II)-EDTA. In all three tested forms, nickel caused disturbances in mitotic divisions, resulting in anaphase bridges and binuclear cells, whose nuclei were joined by a bridge of condensed chromatin or separated. Inorganic nickel and Ni(II)-Glu in higher concentrations damaged nuclei (the amount of condensed chromatin increased), nucleoli (their structure became more condensed and vacuolisation was observed), endoplasmic reticulum (fragmentation, swelling of cisternae) and mitochondria (structure condensation).

Two-electron Reduction versus One-electron Oxidation of the Type 3 Pair in the Multicopper Oxidases

PubMed Central

Kjaergaard, Christian H.; Jones, Stephen M.; Gounel, Sébastien; Mano, Nicolas; Solomon, Edward I.

2015-01-01

Multicopper Oxidases (MCOs) utilize an electron shuttling Type 1 Cu (T1) site in conjunction with a mononuclear Type 2 (T2) and a binuclear Type 3 (T3) site, arranged in a trinuclear copper cluster (TNC), to reduce O2 to H2O. Reduction of O2 occurs with limited overpotential indicating that all the coppers in the active site can be reduced via high-potential electron donors. Two forms of the resting enzyme have been observed in MCOs: the Alternative Resting form (AR), where only one of the three TNC Cu’s is oxidized, and the Resting Oxidized form (RO), where all three TNC Cu’s are oxidized. In contrast to the AR form, we show that in the RO form of a high-potential MCO, the binuclear T3 Cu(II) site can be reduced via the 700 mV T1 Cu. Systematic spectroscopic evaluation reveals that this proceeds by a two-electron process, where delivery of the first electron, forming a high energy, meta-stable half reduced T3 state, is followed by the rapid delivery of a second energetically favorable electron to fully reduce the T3 site. Alternatively, when this fully reduced binuclear T3 site is oxidized via the T1 Cu, a different thermodynamically favored half oxidized T3 form, i.e. the AR site, is generated. This behavior is evaluated by DFT calculations, which reveal that the protein backbone plays a significant role in controlling the environment of the active site coppers. This allows for the formation of the meta-stable, half reduced state and thus the complete reductive activation of the enzyme for catalysis. PMID:26075678

Theoretical investigation on the mechanism and dynamics of oxo exchange of neptunyl(VI) hydroxide in aqueous solution.

PubMed

Yang, Xia; Chai, Zhifang; Wang, Dongqi

2015-03-21

Four types of reaction mechanisms for the oxo ligand exchange of monomeric and dimeric neptunyl(VI) hydroxide in aqueous solution were explored computationally using density functional theory (DFT) and ab initio classical molecular dynamics. The obtained results were compared with previous studies on the oxo exchange of uranyl hydroxide, as well as with experiments. It is found that the stable T-shaped [NpO3(OH)3](3-) intermediate is a key species for oxo exchange in the proton transfer in mononuclear Path I and binuclear Path IV, similar to the case of uranyl(VI) hydroxide. Path I is thought to be the preferred oxo exchange mechanism for neptunyl(VI) hydroxide in our calculations, due to the lower activation energy (22.7 and 13.1 kcal mol(-1) for ΔG(‡) and ΔH(‡), respectively) of the overall reaction. Path II via a cis-neptunyl structure assisted by a water molecule might be a competitive channel against Path I with a mononuclear mechanism, owing to a rapid dynamical process occurring in Path II. In Path IV with the binuclear mechanism, oxo exchange is accomplished via the interaction between [NpO2(OH)4](2-) and T-shaped [NpO3(OH)3](3-) with a low activation energy for the rate-determining step, however, the overall energy required to fulfill the reaction is slightly higher than that in mononuclear Path I, suggesting a possible binuclear process in the higher energy region. The chemical bonding evolution along the reaction pathways was discussed by using topological methodologies of the electron localization function (ELF).

A multi-responsive luminescent sensor based on a super-stable sandwich-type terbium(iii)-organic framework.

PubMed

Wen, Guo-Xuan; Han, Min-Le; Wu, Xue-Qian; Wu, Ya-Pan; Dong, Wen-Wen; Zhao, Jun; Li, Dong-Sheng; Ma, Lu-Fang

2016-10-04

A super-stable multifunctional terbium(iii)-organic framework, namely {[Tb(TATAB) (H 2 O) 2 ]·NMP·H 2 O} n (Tb-MOF, H 3 TATAB = 4,4',4''-s-triazine-1,3,5-triyltri-m-aminobenzoic acid, NMP = N-methyl-2-pyrrolidone) was synthesized. Tb-MOF exhibits a 2D sql structure with binuclear [Tb 2 (COO) 4 (H 2 O) 4 ] 2+ units as 4-connected nodes, and free water and NMP molecules are inserted between 2D layers through hydrogen-bonding interactions, forming a sandwich-type architecture. Observably, such a framework remains intact in a remarkable variety of environments such as common solvents and aqueous solutions with metal cations and inorganic anions, as well as with a pH ranging from 1 to 13. In particular, Tb-MOF can not only detect small organic molecules, metal cations and inorganic anions with high sensitivity and high selectivity, but also can accurately detect explosive 2-nitrophenol, 3-nitrophenol, 4-nitrophenol and 2,4,6-trinitrophenol in water. Its luminescence quenching response to Fe 3+ and Cr 2 O 7 2- ions can be explained in terms of the competitive absorption mechanism. In addition, the luminescence intensity of Tb-MOF is strongly correlated with the pH value in a pH range from 1 to 13. Thus, this material can be potentially used as a multi-responsive luminescent sensor.

Ultrafast excited-state relaxation of a binuclear Ag(i) phosphine complex in gas phase and solution.

PubMed

Kruppa, S V; Bäppler, F; Klopper, W; Walg, S P; Thiel, W R; Diller, R; Riehn, C

2017-08-30

The binuclear complex [Ag 2 (dcpm) 2 ](PF 6 ) 2 (dcpm = bis(dicyclohexylphosphino)methane) exhibits a structure with a close silver-silver contact mediated by the bridging ligand and thus a weak argentophilic interaction. Upon electronic excitation this cooperative effect is strongly increased and determines the optical and luminescence properties of the compound. We have studied here the ultrafast electronic dynamics in parallel in gas phase by transient photodissociation and in solution by transient absorption. In particular, we report the diverse photofragmentation pathways of isolated [Ag 2 (dcpm) 2 ] 2+ in an ion trap and its gas phase UV photodissociation spectrum. By pump-probe fragmentation action spectroscopy (λ ex = 260 nm) in the gas phase, we have obtained fragment-specific transients which exhibit a common ultrafast multiexponential decay. This is fitted to four time constants (0.6/5.8/100/>1000 ps), highlighting complex intrinsic photophysical processes. Remarkably, multiexponential dynamics (0.9/8.5/73/604 ps) are as well found for the relaxation dynamics in acetonitrile solution. Ab initio calculations at the level of approximate coupled-cluster singles-doubles (CC2) theory of ground and electronically excited states of the reduced model system [Ag 2 (dmpm) 2 ] 2+ (dmpm = bis(dimethylphosphino)methane) indicate a shortening of the Ag-Ag distance upon excitation by 0.3-0.4 Å. In C 2 geometry two close-lying singlet states S 1 ( 1 MC(dσ*-pπ), 1 B, 4.13 eV) and S 2 ( 1 MC(dσ*-pσ), 1 A, 4.45 eV) are found. The nearly dark S 1 state has not been reported so far. The excitation of the S 2 state carries a large oscillator strength for the calculated vertical transition (266 nm). Two related triplets are calculated at T 1 (3.87 eV) and T 2 (3.90 eV). From these findings we suggest possible relaxation pathways with the two short time constants ascribed to ISC/IVR and propose from the obtained similar values in gas phase that the fast solution dynamics is dominated by intramolecular processes. A further relaxation by IC/IVR in the triplet manifold is likely to account for the observed intermediate time constants. For the acetonitrile relaxation dynamics additional modifications are invoked based on solvent-induced shifts of the energy levels and the possible formation of solvent and counterion exciplexes on a longer timescale.

A study of binuclear zirconium hydride catalysts of the hydrogenolysis of alkanes by the density functional theory method

NASA Astrophysics Data System (ADS)

Ustynyuk, L. Yu.; Fast, A. S.; Ustynyuk, Yu. A.; Lunin, V. V.

2012-06-01

Binuclear hydride centers containing two Zr(IV) atoms are suggested as promising catalysts for the hydrogenolysis of alkanes under mild conditions ( T < 450 K, p ˜ 1 atm). Reactions of model compounds L2(H)Zr(X)2Zr(H)L2 (X = H, L = OSi≡ ( 4a), X = L = OMe ( 4d)), L(H)Zr(O)2Zr(H)L (L = OSi≡ ( 4b), Cp( 4c)) and (≡SiO)2(H)Zr-O-Zr(H)(OSi≡)2 ( 4e and 4f) with the propane molecule were studied using the density functional theory method. The results show that centers of the 4a, 4e, and 4f types and especially 4b are promising catalysts of the hydrogenolysis of alkanes due to a high degree of unsaturation of two Zr atoms and their sequential participation in the splitting of the C-C bond and hydrogenation of ethylene formed as a result of splitting.

Cyclometalated platinum(ii) complexes of 2,2'-bipyridine N-oxide containing a 1,1'-bis(diphenylphosphino)ferrocene ligand: structural, computational and electrochemical studies.

PubMed

Shahsavari, Hamid R; Fereidoonnezhad, Masood; Niazi, Maryam; Mosavi, S Talaat; Habib Kazemi, Sayed; Kia, Reza; Shirkhan, Shima; Abdollahi Aghdam, Siamak; Raithby, Paul R

2017-02-14

The preparation and characterization of new heteronuclear-platinum(ii) complexes containing a 1,1'-bis(diphenylphosphino)ferrocene (dppf) ligand are described. The reaction of the known starting complex [PtMe(κ 2 N,C-bipyO-H)(SMe 2 )], A, in which bipyO-H is a cyclometalated rollover 2,2'-bipyridine N-oxide, with the dppf ligand in a 2 : 1 ratio or an equimolar ratio led to the formation of the corresponding binuclear complex [Pt 2 Me 2 (κ 2 N,C-bipyO-H) 2 (μ-dppf)], 1, or the mononuclear complex [PtMe(κ 1 C-bipyO-H)(dppf)], 2, respectively. According to the reaction conditions, the dppf ligand in 1 and 2 behaves as either a bridging or chelating ligand. All complexes were characterized by NMR spectroscopy. The solid-state structure of 2 was determined by the single-crystal X-ray diffraction method and it was shown that the chelating dppf ligand in this complex was arranged in a "synclinal-staggered" conformation. Also, the occurrence of intermolecular C-H Cp O bipyO-H interactions in the solid-state gave rise to an extended 1-D network. The electronic absorption spectra and the electrochemical behavior of these complexes are discussed. Density functional theory (DFT) was used for geometry optimization of the singlet states in solution and for electronic structure calculations. The analysis of the molecular orbital (MO) compositions in terms of occupied and unoccupied fragment orbitals in 2 was performed.

Insertion reactions into Pd[bond]O and Pd[bond]N bonds: preparation of alkoxycarbonyl, carbonato, carbamato, thiocarbamate, and thioureide complexes of palladium(II).

PubMed

Ruiz, José; Martínez, M Teresa; Florenciano, Félix; Rodríguez, Venancio; López, Gregorio; Pérez, José; Chaloner, Penny A; Hitchcock, Peter B

2003-06-02

Mononuclear palladium hydroxo complexes of the type [Pd(N[bond]N)(C(6)F(5))(OH)] [(N[bond]N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bipy), 1,10-phenanthroline (phen), or N,N,N',N'-tetramethylethylenediamine (tmeda)] have been prepared by reaction of [Pd(N[bond]N)(C(6)F(5))(acetone)]ClO(4) with KOH in methanol. These hydroxo complexes react, in methanol, with CO (1 atm, room temperature) to yield the corresponding methoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)Me)]. Similar alkoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)R)] (N[bond]N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me, Et, or (i)Pr) are obtained when [Pd(N[bond]N)(C(6)F(5))Cl] is treated with KOH in the corresponding alcohol ROH and CO is bubbled through the solution. The reactions of [Pd(N[bond]N)(C(6)F(5))(OH)] (N[bond]N = bipy or Me(2)bipy) with CO(2), in tetrahydrofuran, lead to the formation of the binuclear carbonate complexes [(N[bond]N)(C(6)F(5))Pd(mu-eta(2)-CO(3))Pd(C(6)F(5))(N[bond]N)]. Complexes [Pd(N[bond]N)(C(6)F(5))(OH)] react in alcohol with PhNCS to yield the corresponding N-phenyl-O-alkylthiocarbamate complexes [Pd(N[bond]N)(C(6)F(5))[SC(OR)NPh

Precise Design of Phosphorescent Molecular Butterflies with Tunable Photoinduced Structural Change and Dual Emission.

PubMed

Zhou, Chenkun; Tian, Yu; Yuan, Zhao; Han, Mingu; Wang, Jamie; Zhu, Lei; Tameh, Maliheh Shaban; Huang, Chen; Ma, Biwu

2015-08-10

Photoinduced structural change (PSC) is a fundamental excited-state dynamic process in chemical and biological systems. However, precise control of PSC processes is very challenging, owing to the lack of guidelines for designing excited-state potential energy surfaces (PESs). A series of rationally designed butterfly-like phosphorescent binuclear platinum complexes that undergo controlled PSC by Pt-Pt distance shortening and exhibit tunable dual (greenish-blue and red) emission are herein reported. Based on the Bell-Evans-Polanyi principle, it is demonstrated how the energy barrier of the PSC, which can be described as a chemical-reaction-like process between the two energy minima on the first triplet excited-state PES, can be controlled by synthetic means. These results reveal a simple method to engineer the dual emission of molecular systems by manipulating PES to control PSC. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanisms of antimony adsorption onto soybean stover-derived biochar in aqueous solutions.

PubMed

Vithanage, Meththika; Rajapaksha, Anushka Upamali; Ahmad, Mahtab; Uchimiya, Minori; Dou, Xiaomin; Alessi, Daniel S; Ok, Yong Sik

2015-03-15

Limited mechanistic knowledge is available on the interaction of biochar with trace elements (Sb and As) that exist predominantly as oxoanions. Soybean stover biochars were produced at 300 °C (SBC300) and 700 °C (SBC700), and characterized by BET, Boehm titration, FT-IR, NMR and Raman spectroscopy. Bound protons were quantified by potentiometric titration, and two acidic sites were used to model biochar by the surface complexation modeling based on Boehm titration and NMR observations. The zero point of charge was observed at pH 7.20 and 7.75 for SBC300 and SBC700, respectively. Neither antimonate (Sb(V)) nor antimonite (Sb(III)) showed ionic strength dependency (0.1, 0.01 and 0.001 M NaNO3), indicating inner sphere complexation. Greater adsorption of Sb(III) and Sb(V) was observed for SBC300 having higher -OH content than SBC700. Sb(III) removal (85%) was greater than Sb(V) removal (68%). Maximum adsorption density for Sb(III) was calculated as 1.88 × 10(-6) mol m(-2). The Triple Layer Model (TLM) successfully described surface complexation of Sb onto soybean stover-derived biochar at pH 4-9, and suggested the formation of monodentate mononuclear and binuclear complexes. Spectroscopic investigations by Raman, FT-IR and XPS further confirmed strong chemisorptive binding of Sb to biochar surfaces. Copyright © 2014 Elsevier Ltd. All rights reserved.

Enhanced removal of As (V) from aqueous solution using modified hydrous ferric oxide nanoparticles

PubMed Central

Huo, Lijuan; Zeng, Xibai; Su, Shiming; Bai, Lingyu; Wang, Yanan

2017-01-01

Hydrous ferric oxide (HFO) is most effective with high treatment capacity on arsenate [As(V)] sorption although its transformation and aggregation nature need further improvement. Here, HFO nanoparticles with carboxymethyl cellulose (CMC) or starch as modifier was synthesized for the purpose of stability improvement and As(V) removal from water. Comparatively, CMC might be the optimum stabilizer for HFO nanoparticles because of more effective physical and chemical stability. The large-pore structure, high surface specific area, and the non-aggregated nature of CMC-HFO lead to increased adsorption sites, and thus high adsorption capacities of As(V) without pre-treatment (355 mg·g−1), which is much greater than those reported in previous studies. Second-order equation and dual-mode isotherm model could be successfully used to interpret the sorption kinetics and isotherms of As(V), respectively. FTIR, XPS and XRD analyses suggested that precipitation and surface complexation were primary mechanisms for As(V) removal by CMC modified HFO nanoparticles. A surface complexation model (SCM) was used to simulate As adsorption over pH 2.5–10.4. The predominant adsorbed arsenate species were modeled as bidentate binuclear surface complexes at low pH and as monodentate complexes at high pH. The immobilized arsenic remained stable when aging for 270 d at room temperature. PMID:28098196

Enhanced removal of As (V) from aqueous solution using modified hydrous ferric oxide nanoparticles

NASA Astrophysics Data System (ADS)

Huo, Lijuan; Zeng, Xibai; Su, Shiming; Bai, Lingyu; Wang, Yanan

2017-01-01

Hydrous ferric oxide (HFO) is most effective with high treatment capacity on arsenate [As(V)] sorption although its transformation and aggregation nature need further improvement. Here, HFO nanoparticles with carboxymethyl cellulose (CMC) or starch as modifier was synthesized for the purpose of stability improvement and As(V) removal from water. Comparatively, CMC might be the optimum stabilizer for HFO nanoparticles because of more effective physical and chemical stability. The large-pore structure, high surface specific area, and the non-aggregated nature of CMC-HFO lead to increased adsorption sites, and thus high adsorption capacities of As(V) without pre-treatment (355 mg·g-1), which is much greater than those reported in previous studies. Second-order equation and dual-mode isotherm model could be successfully used to interpret the sorption kinetics and isotherms of As(V), respectively. FTIR, XPS and XRD analyses suggested that precipitation and surface complexation were primary mechanisms for As(V) removal by CMC modified HFO nanoparticles. A surface complexation model (SCM) was used to simulate As adsorption over pH 2.5-10.4. The predominant adsorbed arsenate species were modeled as bidentate binuclear surface complexes at low pH and as monodentate complexes at high pH. The immobilized arsenic remained stable when aging for 270 d at room temperature.

Experimental and modeling study of the uranium (VI) sorption on goethite.

PubMed

Missana, Tiziana; García-Gutiérrez, Miguel; Maffiotte, Cesar

2003-04-15

Acicular goethite was synthesized in the laboratory and its main physicochemical properties (composition, microstructure, surface area, and surface charge) were analyzed as a previous step to sorption experiments. The stability of the oxide, under the conditions used in sorption studies, was also investigated. The sorption of U(VI) onto goethite was studied under O(2)- and CO(2)-free atmosphere and in a wide range of experimental conditions (pH, ionic strength, radionuclide, and solid concentration), in order to assess the validity of different surface complexation models available for the interpretation of sorption data. Three different models were used to fit the experimental data. The first two models were based on the diffuse double layer concept. The first one (Model 1) considered two different monodentate complexes with the goethite surface and the second (Model 2) a single binuclear bidentate complex. A nonelectrostatic (NE) approach was used as a third model and, in that case, the same species considered in Model 1 were used. The results showed that all the models are able to describe the sorption behavior fairly well as a function of pH, electrolyte concentration, and U(VI) concentration. However, Model 2 fails in the description of the uranium sorption behavior as a function of the sorbent concentration. This demonstrates the importance of checking the validity of any surface complexation model under the widest possible range of experimental conditions.

Redox Biochemistry | Bioenergy | NREL

Science.gov Websites

binuclear cofactors of the hydrogenase catalytic sites. (A) shows the NiFe cluster of [NiFe(Se font) are labeled. Ni, nickel; Se, selenium; Fe, iron. [FeFe]- and [NiFe]-hydrogenase diversity [NiFe]-hydrogenase diversity, mechanism, and maturation. Read more Previous Story Next Story Featured

Divorce: A Crisis of Family Transition and Change.

ERIC Educational Resources Information Center

Ahrons, Constance R.

1980-01-01

Presents a conceptualization of the process of divorce as a crisis of family transition. Rather than dissolving the family, divorce culminates in its redefinition from a nuclear to a binuclear system. Continuation of meaningful bonds between parents and children reduces major stresses associated with the process of family change. (Author)

1,8-Naphthalene Linked Cofacial Binuclear Phthalocyanines.

DTIC Science & Technology

1987-06-01

Chemistry University of Utah Indiana University Salt Lake City, Utah 84112 Bloomington, Indiana 47405 Dr. J. 0. Thomas Dr. Mark A. McHugh University...2.0g, 5.3mmol) in a mixed coupling reaction, in the presence of elementary nickel powder under conditions described for homocoupling reactions[8 ,9

Cd(II)-coordination polymers based on tetracarboxylic acid and diverse bis(imidazole) ligands: Synthesis, structural diversity and photoluminescence properties

NASA Astrophysics Data System (ADS)

Arıcı, Mürsel; Yeşilel, Okan Zafer; Taş, Murat

2017-01-01

Three new Cd(II)-coordination polymers, namely, {[Cd2(μ6-ao2btc)(μ-1,5-bipe)2]·2H2O}n (1), {[Cd2(μ6-ao2btc)(μ-1,4-bix)2]n·2DMF} (2) and {[Cd2(μ8-abtc)(μ-1,4-betix)]·DMF·H2O}n (3) (ao2btc=di-oxygenated form of 3,3‧,5,5‧-azobenzenetetracarboxylate, 1,5-bipe: 1,5-bis(imidazol-1yl)pentane, 1,4-bix=1,4-bis(imidazol-1ylmethyl)benzene, 1,4-betix=1,4-bis(2-ethylimidazol-1ylmethyl)benzene) were synthesized with 3,3‧,5,5‧-azobenzenetetracarboxylic acid and flexible, semi-flexible and semi-flexible substituted bis(imidazole) linkers. They were characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction, powder X-ray diffractions (PXRD) and thermal analyses (TG/DTA). Complexes 1-3 exhibited structural diversities depending on flexible, semi-flexible and semi-flexible substituted bis(imidazole) ligands. Complex 1 was 2D structure with 3,6L18 topology. Complex 2 had a 3D pillar-layered framework with the rare sqc27 topology. When semi-flexible substituted bis(imidazole) linker was used, 3D framework of complex 3 was obtained with the paddlewheel Cd2(CO2)4-type binuclear SBU. Moreover, thermal and photoluminescence properties of the complexes were determined in detailed.

Azilsartan and its Zn(II) complex. Synthesis, anticancer mechanisms of action and binding to bovine serum albumin.

PubMed

Martínez, Valeria R; Aguirre, María V; Todaro, Juan S; Piro, Oscar E; Echeverría, Gustavo A; Ferrer, Evelina G; Williams, Patricia A M

2018-04-01

Azilsartan is the eighth approved member of angiotensin II receptor blockers for hypertension treatment. Considering that some drugs have additional effects when administered, we studied its effects and mechanisms of action on a human lung cancer cell line A549. We have also modified the structure of the drug by complexation with Zn(II) cation and assayed the anticancer effect. The crystal structure of the new binuclear Zn(II) complex, for short [Zn 2 (azil) 2 (H 2 O) 4 ]·2H 2 O (ZnAzil), was determined by X-ray diffraction methods. The zinc ions are bridged by azilsartan ligands through their carboxylate oxygen and oxadiazol nitrogen atoms. The compounds were examined for their cytotoxic effects against human lung fibroblast (MRC5) and human lung cancer (A549) cell lines. Azilsartan displayed low cytotoxic effects at 150 μM concentrations in A549 human lung cancer cells but the higher effect measured for the Zn complex suggested that this compound may act as an anticancer agent. An apoptotic oxidative stress mechanism of action via the mitochondrial-dependent intrinsic pathway has been determined. Besides, the compounds exerted weak cytotoxic effects in the normal lung related cell line MRC5. Binding constants of the complex formed between each compound and bovine serum albumin (BSA) are in the intermediate range, hence suggesting that azilsartan and ZnAzil could be bonded and transported by BSA. Copyright © 2018 Elsevier Ltd. All rights reserved.

UTSA-74: A MOF-74 Isomer with Two Accessible Binding Sites per Metal Center for Highly Selective Gas Separation.

PubMed

Luo, Feng; Yan, Changsheng; Dang, Lilong; Krishna, Rajamani; Zhou, Wei; Wu, Hui; Dong, Xinglong; Han, Yu; Hu, Tong-Liang; O'Keeffe, Michael; Wang, Lingling; Luo, Mingbiao; Lin, Rui-Biao; Chen, Banglin

2016-05-04

A new metal-organic framework Zn2(H2O)(dobdc)·0.5(H2O) (UTSA-74, H4dobdc = 2,5-dioxido-1,4-benzenedicarboxylic acid), Zn-MOF-74/CPO-27-Zn isomer, has been synthesized and structurally characterized. It has a novel four coordinated fgl topology with one-dimensional channels of about 8.0 Å. Unlike metal sites in the well-established MOF-74 with a rod-packing structure in which each of them is in a five coordinate square pyramidal coordination geometry, there are two different Zn(2+) sites within the binuclear secondary building units in UTSA-74 in which one of them (Zn1) is in a tetrahedral while another (Zn2) in an octahedral coordination geometry. After activation, the two axial water molecules on Zn2 sites can be removed, generating UTSA-74a with two accessible gas binding sites per Zn2 ion. Accordingly, UTSA-74a takes up a moderately high and comparable amount of acetylene (145 cm(3)/cm(3)) to Zn-MOF-74. Interestingly, the accessible Zn(2+) sites in UTSA-74a are bridged by carbon dioxide molecules instead of being terminally bound in Zn-MOF-74, so UTSA-74a adsorbs a much smaller amount of carbon dioxide (90 cm(3)/cm(3)) than Zn-MOF-74 (146 cm(3)/cm(3)) at room temperature and 1 bar, leading to a superior MOF material for highly selective C2H2/CO2 separation. X-ray crystal structures, gas sorption isotherms, molecular modeling, and simulated and experimental breakthroughs comprehensively support this result.

Luminescent hybrid lanthanide sulfates and lanthanide sulfonate-carboxylates with 1,10-phenanthroline involving in-situ oxidation of 2-mercaptonbenzoic acid

NASA Astrophysics Data System (ADS)

Zhong, Jie-Cen; Wan, Fang; Sun, Yan-Qiong; Chen, Yi-Ping

2015-01-01

A series of lanthanide sulfates and lanthanide sulfonate-carboxylates, [Ln2(phen)2(SO4)3(H2O)2]n (I:Ln=Nd(1a), Sm(1b), Eu(1c), phen=1,10-phenanthroline) and [Ln(phen)(2-SBA)(BZA)]n (II: Ln=Sm(2a), Eu(2b), Dy(2c), 2-SBA=2-sulfobenzoate, BZA=benzoate) have been hydrothermally synthesized from lanthanide oxide, 2-mercaptonbenzoic acid with phen as auxiliary ligand and characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, TG analyses and luminescence spectroscopy. Interestingly, SO4 2 - anions in I came from the in situ deep oxidation of thiol groups of 2-mercaptonbenzoic acid while 2-sulfobenzoate and benzoate ligands in II from the middle oxidation and desulfuration reactions of 2-mercaptonbenzoic acid. Compounds I are organic-inorganic hybrid lanthanide sulfates, which have rare one-dimensional column-like structures. Complexes II are binuclear lanthanide sulfonate-carboxylates with 2-sulfobenzoate and benzoate as bridges and 1,10-phenanthroline as terminal. Photoluminescence studies reveal that complexes I and II exhibit strong lanthanide characteristic emission bands in the solid state at room temperature.

Electronic structure and nature of the ground state of the mixed-valence binuclear tetra(mu-1,8-naphthyridine-N,N')-bis(halogenonickel) tetraphenylborate complexes: experimental and DFT characterization.

PubMed

Bencini, Alessandro; Berti, Elisabetta; Caneschi, Andrea; Gatteschi, Dante; Giannasi, Elisa; Invernizzi, Ivana

2002-08-16

The ground state electronic structure of the mixed-valence systems [Ni(2)(napy)(4)X(2)](BPh(4)) (napy=1,8-naphthyridine; X=Cl, Br, I) was studied with combined experimental (X-ray diffraction, temperature dependence of the magnetic susceptibility, and high-field EPR spectroscopy) and theoretical (DFT) methods. The zero-field splitting (zfs) ground S=3/2 spin state is axial with /D/ approximately 3 cm(-1). The iodide derivative was found to be isostructural with the previously reported bromide complex, but not isomorphous. The compound crystallizes in the monoclinic system, space group P2(1)/n, with a=17.240(5), b=26.200(5), c=11.340(5) A, beta=101.320(5) degrees. DFT calculations were performed on the S=3/2 state to characterize the ground state potential energy surface as a function of the nuclear displacements. The molecules can thus be classified as Class III mixed-valence compounds with a computed delocalization parameter, B=3716, 3583, and 3261 cm(-1) for the Cl, Br, and I derivatives, respectively.

Spectral and quantum chemical studies on 1,3-bis(N(1)-4-amino-6-methoxypyrimidinebenzenesulfonamide-2,2,4,4-ethane-1,2-dithiol)-2,4-dichlorocyclodiphosph(V)azane and its erbium complex.

PubMed

Al-Mogren, Muneerah M; Alaghaz, Abdel-Nasser M A; El-Gogary, Tarek M

2014-01-24

Novel 1,3-bis(N(1)-4-amino-6-methoxypyrimidine-benzenesulfonamide-2,2,4,4-ethane-1,2-dithiol)-2,4-dichlorocyclodiphosph(V)azane (L), was prepared and their coordinating behavior towards the lanthanide ion Er(III) was studied. The structures of the isolated products are proposed based on elemental analyses, IR, UV-VIS., (1)H NMR, (13)C NMR, (31)P NMR, SEM, XRD, mass spectra, effective magnetic susceptibility measurements and thermogravimetric analysis (TGA). Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of L and its binuclear Er(III) complex. Different tautomers of the ligand were optimized at the ab initio DFT level. Keto-form structure is about 17.7 kcal/mol more stable than the enol form (taking zpe correction into account). Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV-VIS spectra which compared by the measured electronic spectra. Copyright © 2013 Elsevier B.V. All rights reserved.

Remediation of Organic and Inorganic Arsenic Contaminated Groundwater using a Nonocrystalline TiO2 Based Adsorbent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jing, C.; Meng, X; Calvache, E

2009-01-01

A nanocrystalline TiO2-based adsorbent was evaluated for the simultaneous removal of As(V), As(III), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in contaminated groundwater. Batch experimental results show that As adsorption followed pseudo-second order rate kinetics. The competitive adsorption was described with the charge distribution multi-site surface complexation model (CD-MUSIC). The groundwater containing an average of 329 ?g L-1 As(III), 246 ?g L-1 As(V), 151 ?g L-1 MMA, and 202 ?g L-1 DMA was continuously passed through a TiO2 filter at an empty bed contact time of 6 min for 4 months. Approximately 11 000, 14 000, and 9900 bed volumesmore » of water had been treated before the As(III), As(V), and MMA concentration in the effluent increased to 10 ?g L-1. However, very little DMA was removed. The EXAFS results demonstrate the existence of a bidentate binuclear As(V) surface complex on spent adsorbent, indicating the oxidation of adsorbed As(III). A nanocrystalline TiO2-based adsorbent could be used for the simultaneous removal of As(V), As(III), MMA, and DMA in contaminated groundwater.« less

Pyrolyzed binuclear-cobalt-phthalocyanine as electrocatalyst for oxygen reduction reaction in microbial fuel cells.

PubMed

Li, Baitao; Wang, Mian; Zhou, Xiuxiu; Wang, Xiujun; Liu, Bingchuan; Li, Baikun

2015-10-01

A novel platinum (Pt)-free cathodic materials binuclear-cobalt-phthalocyanine (Bi-CoPc) pyrolyzed at different temperatures (300-1000 °C) were examined as the oxygen reduction reaction (ORR) catalysts, and compared with unpyrolyzed Bi-CoPc/C and Pt cathode in single chamber microbial fuel cells (SCMFCs). The results showed that the pyrolysis process increased the nitrogen abundance on Bi-CoPc and changed the nitrogen types. The Bi-CoPc pyrolyzed at 800 °C contained a significant amount of pyrrolic-N, and exhibited a high electrochemical catalytic activity. The power density and current density increased with temperature: Bi-CoPc/C-800 > Bi-CoPc/C-1000 > Bi-CoPc/C-600 > Bi-CoPc/C-300 > Bi-CoPc/C. The SCMFC with Bi-CoPc/C-800 cathode had a maximum power density of 604 mW m(-2). The low cost Bi-CoPc compounds developed in this study showed a potential in air-breathing MFC systems, with the proper pyrolysis temperature being chosen. Copyright © 2015 Elsevier Ltd. All rights reserved.

Functional Identification and Structure Determination of Two Novel Prolidases from cog1228 in the Amidohydrolase Superfamily

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiang, Dao Feng; Patskovsky, Yury; Xu, Chengfu

2010-12-07

Two uncharacterized enzymes from the amidohydrolase superfamily belonging to cog1228 were cloned, expressed, and purified to homogeneity. The two proteins, Sgx9260c (gi|44242006) and Sgx9260b (gi|44479596), were derived from environmental DNA samples originating from the Sargasso Sea. The catalytic function and substrate profiles for Sgx9260c and Sgx9260b were determined using a comprehensive library of dipeptides and N-acyl derivative of L-amino acids. Sgx9260c catalyzes the hydrolysis of Gly-L-Pro, L-Ala-L-Pro, and N-acyl derivatives of L-Pro. The best substrate identified to date is N-acetyl-L-Pro with a value of k{sub cat}/K{sub m} of 3 x 10{sup 5} M{sup -1} s{sup -1}. Sgx9260b catalyzes the hydrolysismore » of L-hydrophobic L-Pro dipeptides and N-acyl derivatives of L-Pro. The best substrate identified to date is N-propionyl-L-Pro with a value of k{sub cat}/K{sub m} of 1 x 10{sup 5} M{sup -1} s{sup -1}. Three-dimensional structures of both proteins were determined by X-ray diffraction methods (PDB codes 3MKV and 3FEQ). These proteins fold as distorted ({beta}/{alpha})8-barrels with two divalent cations in the active site. The structure of Sgx9260c was also determined as a complex with the N-methylphosphonate derivative of L-Pro (PDB code 3N2C). In this structure the phosphonate moiety bridges the binuclear metal center, and one oxygen atom interacts with His-140. The {alpha}-carboxylate of the inhibitor interacts with Tyr-231. The proline side chain occupies a small substrate binding cavity formed by residues contributed from the loop that follows {beta}-strand 7 within the ({beta}/{alpha})8-barrel. A total of 38 other proteins from cog1228 are predicted to have the same substrate profile based on conservation of the substrate binding residues. The structure of an evolutionarily related protein, Cc2672 from Caulobacter crecentus, was determined as a complex with the N-methylphosphonate derivative of L-arginine (PDB code 3MTW).« less

Cobalt(II) chloride adducts with acetonitrile, propan-2-ol and tetrahydrofuran: considerations on nuclearity, reactivity and synthetic applications.

PubMed

Stinghen, Danilo; Rüdiger, André Luis; Giese, Siddhartha O K; Nunes, Giovana G; Soares, Jaísa F; Hughes, David L

2017-02-01

High-spin cobalt(II) complexes are considered useful building blocks for the synthesis of single-molecule magnets (SMM) because of their intrinsic magnetic anisotropy. In this work, three new cobalt(II) chloride adducts with labile ligands have been synthesized from anhydrous CoCl 2 , to be subsequently employed as starting materials for heterobimetallic compounds. The products were characterized by elemental, spectroscopic (EPR and FT-IR) and single-crystal X-ray diffraction analyses. trans-Tetrakis(acetonitrile-κN)bis(tetrahydrofuran-κO)cobalt(II) bis[(acetonitrile-κN)trichloridocobaltate(II)], [Co(C 2 H 3 N) 4 (C 4 H 8 O) 2 ][CoCl 3 (C 2 H 3 N)] 2 , (1), comprises mononuclear ions and contains both acetonitrile and tetrahydrofuran (thf) ligands, The coordination polymer catena-poly[[tetrakis(propan-2-ol-κO)cobalt(II)]-μ-chlorido-[dichloridocobalt(II)]-μ-chlorido], [Co 2 Cl 4 (C 3 H 8 O) 4 ], (2'), was prepared by direct reaction between anhydrous CoCl 2 and propan-2-ol in an attempt to rationalize the formation of the CoCl 2 -alcohol adduct (2), probably CoCl 2 (HO i Pr) m . The binuclear complex di-μ-chlorido-1:2κ 4 Cl:Cl-dichlorido-2κ 2 Cl-tetrakis(tetrahydrofuran-1κO)dicobalt(II), [Co 2 Cl 4 (C 4 H 8 O) 4 ], (3), was obtained from (2) after recrystallization from tetrahydrofuran. All three products present cobalt(II) centres in both octahedral and tetrahedral environments, the former usually less distorted than the latter, regardless of the nature of the neutral ligand. Product (2') is stabilized by an intramolecular hydrogen-bond network that appears to favour a trans arrangement of the chloride ligands in the octahedral moiety; this differs from the cis disposition found in (3). The expected easy displacement of the bound solvent molecules from the metal coordination sphere makes the three compounds good candidates for suitable starting materials in a number of synthetic applications.

Spectroscopic and pH-metric studies of the complexation of 3-[2-(4-methylquinolin-2-yl)hydrazono]butan-2-one oxime compound.

PubMed

Seleem, H S; El-Inany, G A; Mousa, M; Hanafy, F I

2010-05-01

The electronic absorption spectra of the oximic quinolinyl hydrazone (MHQ; H(2)L) and its Co(II) and Cu(II)-complexes have been studied in Britton-Rhobinson buffer solutions of varying pH's in 75% dioxane-water. The dissociation constant of the hydrazone (pK(H)) as well as the stability constants (logK) of its chelates were determined spectrophotometrically and pH-metrically. The obtained data are in good agreement. Beer's law is valid in the ranges (0.64-6.99) and (2.36-6.48)mug/mL for Cu(II) and Co(II)-ions, respectively. On the other hand, the pK(H) and logK were determined pH-metrically in 75% solvent-water; (solvent=dioxane, ethanol, methanol and isopropanol). The variation of pK(H) or logK as a function of solvent parameters viz. 1/D, E(T), AN and pi* was used to evaluate the dissociation and stability constants in the aqueous medium. Furthermore, the reaction of the oximic hydrazone (H(2)L) with copper(II)-nitrate and chloride in addition to copper(I)-iodide afforded square planar mononuclear and binuclear complexes in which the oximic hydrazone showed three different modes of bonding. The obtained complexes reflect the strong bridging ability of the oximato group as well as its ambidentate and flexidentate characters. Copyright 2010 Elsevier B.V. All rights reserved.

Interaction between Eu(III) and graphene oxide nanosheets investigated by batch and extended X-ray absorption fine structure spectroscopy and by modeling techniques.

PubMed

Sun, Yubing; Wang, Qi; Chen, Changlun; Tan, Xiaoli; Wang, Xiangke

2012-06-05

The interaction mechanism between Eu(III) and graphene oxide nanosheets (GONS) was investigated by batch and extended X-ray absorption fine structure (EXAFS) spectroscopy and by modeling techniques. The effects of pH, ionic strength, and temperature on Eu(III) adsorption on GONS were evaluated. The results indicated that ionic strength had no effect on Eu(III) adsorption on GONS. The maximum adsorption capacity of Eu(III) on GONS at pH 6.0 and T = 298 K was calculated to be 175.44 mg·g(-1), much higher than any currently reported. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Eu(III) adsorption on GONS was an endothermic and spontaneous process. Results of EXAFS spectral analysis indicated that Eu(III) was bound to ∼6-7 O atoms at a bond distance of ∼2.44 Å in the first coordination shell. The value of Eu-C bond distance confirmed the formation of inner-sphere surface complexes on GONS. Surface complexation modeling gave an excellent fit with the predominant mononuclear monodentate >SOEu(2+) and binuclear bidentate (>SO)(2)Eu(2)(OH)(2)(2+) complexes. This paper highlights the application of GONS as a suitable material for the preconcentration and removal of trivalent lanthanides and actinides from aqueous solutions in environmental pollution management.

Phosphate and phytate adsorption and precipitation on ferrihydrite surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaoming; Hu, Yongfeng; Tang, Yadong

Phosphorous (P) sorption on mineral surfaces largely controls P mobility and bioavailability, hence its pollution potential, but the sorption speciation and mechanism remain poorly understood. In this study, we have identified and quantified the speciation of both phosphate and phytate sorbed on ferrihydrite with various P loadings at pH 3–8 using differential atomic pair distribution function (d-PDF) analysis, synchrotron-based X-ray diffraction (XRD), and P and Fe K-edge X-ray absorption near edge structure (XANES) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. With increasing P sorption loading for both phosphate and phytate, the sorption mechanism transits from bidentate-binuclear surface complexation tomore » unidentified ternary complexation and to precipitation of amorphous FePO 4 and amorphous Fe-phytate. At a given P sorption loading, phosphate precipitates more readily than phytate. Both phosphate and phytate promote ferrihydrite dissolution with phytate more intensively, but the dissolved FeIII concentration in the bulk solution is low because the majority of the released Fe III precipitate with the anions. Results also show that amorphous FePO 4 and amorphous Fe-phytate have similar PO 4 local coordination environment. In conclusion, these new insights into the P surface complexation and precipitation, and the ligand-promoted dissolution behavior improve our understanding of P fate in soils, aquatic environment and water treatment systems as mediated by mineral-water interfacial reactions.« less

Phosphate and phytate adsorption and precipitation on ferrihydrite surfaces

DOE PAGES

Wang, Xiaoming; Hu, Yongfeng; Tang, Yadong; ...

2017-09-26

Phosphorous (P) sorption on mineral surfaces largely controls P mobility and bioavailability, hence its pollution potential, but the sorption speciation and mechanism remain poorly understood. In this study, we have identified and quantified the speciation of both phosphate and phytate sorbed on ferrihydrite with various P loadings at pH 3–8 using differential atomic pair distribution function (d-PDF) analysis, synchrotron-based X-ray diffraction (XRD), and P and Fe K-edge X-ray absorption near edge structure (XANES) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. With increasing P sorption loading for both phosphate and phytate, the sorption mechanism transits from bidentate-binuclear surface complexation tomore » unidentified ternary complexation and to precipitation of amorphous FePO 4 and amorphous Fe-phytate. At a given P sorption loading, phosphate precipitates more readily than phytate. Both phosphate and phytate promote ferrihydrite dissolution with phytate more intensively, but the dissolved FeIII concentration in the bulk solution is low because the majority of the released Fe III precipitate with the anions. Results also show that amorphous FePO 4 and amorphous Fe-phytate have similar PO 4 local coordination environment. In conclusion, these new insights into the P surface complexation and precipitation, and the ligand-promoted dissolution behavior improve our understanding of P fate in soils, aquatic environment and water treatment systems as mediated by mineral-water interfacial reactions.« less

Competitive sorption of carbonate and arsenic to hematite: combined ATR-FTIR and batch experiments.

PubMed

Brechbühl, Yves; Christl, Iso; Elzinga, Evert J; Kretzschmar, Ruben

2012-07-01

The competitive sorption of carbonate and arsenic to hematite was investigated in closed-system batch experiments. The experimental conditions covered a pH range of 3-7, arsenate concentrations of 3-300 μM, and arsenite concentrations of 3-200 μM. Dissolved carbonate concentrations were varied by fixing the CO(2) partial pressure at 0.39 (atmospheric), 10, or 100 hPa. Sorption data were modeled with a one-site three plane model considering carbonate and arsenate surface complexes derived from ATR-FTIR spectroscopy analyses. Macroscopic sorption data revealed that in the pH range 3-7, carbonate was a weak competitor for both arsenite and arsenate. The competitive effect of carbonate increased with increasing CO(2) partial pressure and decreasing arsenic concentrations. For arsenate, sorption was reduced by carbonate only at slightly acidic to neutral pH values, whereas arsenite sorption was decreased across the entire pH range. ATR-FTIR spectra indicated the predominant formation of bidentate binuclear inner-sphere surface complexes for both sorbed arsenate and sorbed carbonate. Surface complexation modeling based on the dominant arsenate and carbonate surface complexes indicated by ATR-FTIR and assuming inner-sphere complexation of arsenite successfully described the macroscopic sorption data. Our results imply that in natural arsenic-contaminated systems where iron oxide minerals are important sorbents, dissolved carbonate may increase aqueous arsenite concentrations, but will affect dissolved arsenate concentrations only at neutral to alkaline pH and at very high CO(2) partial pressures. Copyright © 2012 Elsevier Inc. All rights reserved.

Synthesis, characterization, nano-sized binuclear nickel complexes, DFT calculations and antibacterial evaluation of new macrocyclic Schiff base compounds

NASA Astrophysics Data System (ADS)

Parsaee, Zohreh; Mohammadi, Khosro

2017-06-01

Some new macrocyclic bridged dianilines tetradentate with N4coordination sphere Schiff base ligands and their nickel(II)complexes with general formula [{Ni2LCl4} where L = (C20H14N2X)2, X = SO2, O, CH2] have been synthesized. The compounds have been characterized by FT-IR, 1H and 13C NMR, mass spectroscopy, TGA, elemental analysis, molar conductivity and magnetic moment techniques. Scanning electron microscopy (SEM) shows nano-sized structures under 100 nm for nickel (II) complexes. NiO nanoparticle was achieved via the thermal decomposition method and analyzed by FT-IR, SEM and X-ray powder diffraction which indicates closeaccordance to standard pattern of NiO nanoparticle. All the Schiff bases and their complexes have been detected in vitro both for antibacterial activity against two gram-negative and two gram-positive bacteria. The nickel(II) complexes were found to be more active than the free macrocycle Schiff bases. In addition, computational studies of three ligands have been carried out at the DFT-B3LYP/6-31G+(d,p) level of theory on the spectroscopic properties, including IR, 1HNMR and 13CNMR spectroscopy. The correlation between the theoretical and the experimental vibrational frequencies, 1H NMR and 13C NMR of the ligands were 0.999, 0.930-0.973 and 0.917-0.995, respectively. Also, the energy gap was determined and by using HOMO and LUMO energy values, chemical hardness-softness, electronegativity and electrophilic index were calculated.

Normal coordinate analysis of the vibrational spectrum of benzil molecule

NASA Astrophysics Data System (ADS)

Volovšek, V.; Colombo, L.

1993-03-01

Normal coordinate analysis is performed for the benzil molecule. Force constants of phenyl rings are transferred from earlier studies on binuclear aromatic molecules. The existance of some low-frequency internal modes have been proved, thus eliminating the earlier explanations of the excess of the bands observed in the low-frequency Raman and FIR spectra of benzil crystal.

ElaC encodes a novel binuclear zinc phosphodiesterase.

PubMed

Vogel, Andreas; Schilling, Oliver; Niecke, Manfred; Bettmer, Jorg; Meyer-Klaucke, Wolfram

2002-08-09

ElaC is a widespread gene found in eubacteria, archaebacteria, and mammals with a highly conserved sequence. Two human ElaC variants were recently associated with cancer (Tavtigian, S. V., Simard, J., Teng, D. H., Abtin, V., Baumgard, M., Beck, A., Camp, N. J., Carillo, A. R., Chen, Y., Dayananth, P., Desrochers, M., Dumont, M., Farnham, J. M., Frank, D., Frye, C., Ghaffari, S., Gupte, J. S., Hu, R., Iliev, D., Janecki, T., Kort, E. N., Laity, K. E., Leavitt, A., Leblanc, G., McArthur-Morrison, J., Pederson, A., Penn, B., Peterson, K. T., Reid, J. E., Richards, S., Schroeder, M., Smith, R., Snyder, S. C., Swedlund, B., Swensen, J., Thomas, A., Tranchant, M., Woodland, A. M., Labrie, F., Skolnick, M. H., Neuhausen, S., Rommens, J., and Cannon-Albright, L. A. (2001) Nat. Genet. 27, 172-180; Yanaihara, N., Kohno, T., Takakura, S., Takei, K., Otsuka, A., Sunaga, N., Takahashi, M., Yamazaki, M., Tashiro, H., Fukuzumi, Y., Fujimori, Y., Hagiwara, K., Tanaka, T., and Yokota, J. (2001) Genomics 72, 169-179). Analysis of the primary sequence indicates homology to an arylsulfatase and predicts a metallo-beta-lactamase fold. At present, no ElaC gene product has been investigated. We cloned the Escherichia coli ElaC gene and purified the recombinant gene product. An enzymatic analysis showed that ElaC does not encode an arylsulfatase but rather encodes a phosphodiesterase that hydrolyzes bis(p-nitrophenyl)phosphate with a k(cat) of 59 s(-1) and K' of 4 mm. Kinetic analysis of the dimeric enzyme revealed positive cooperativity for the substrate bis(p-nitrophenyl)phosphate with a Hill coefficient of 1.6, whereas hydrolysis of the substrate thymidine-5'-p-nitrophenyl phosphate followed Michaelis-Menten kinetics. Furthermore, the enzyme is capable of binding two zinc or two iron ions. However, it displays phosphodiesterase activity only in the zinc form. The metal environment characterized by zinc K-edge x-ray absorption spectroscopy was modeled with two histidine residues, one carboxylate group, and 1.5 oxygen atoms. This corresponds to the coordination found in other metallo-beta-lactamase domain proteins. Phosphodiesterase activity is strongly dependent on the presence of zinc. These results identify the currently unassigned gene product ElaC to be a novel binuclear zinc phosphodiesterase.

Tripolar acytokinetic mitosis and formation of feto-maternal syncytia in the bovine placentome: different modes of the generation of multinuclear cells.

PubMed

Klisch, K; Pfarrer, C; Schuler, G; Hoffmann, B; Leiser, R

1999-08-01

The vast majority of trophoblast giant cells in the ruminant placenta are binuclear and are believed to derive from mononuclear trophoblastic cells by a single acytokinetic mitosis. There is no satisfactory explanation for the generation of the small proportion of trophoblast giant cells with one, three, or more nuclei. In this light-and electronmicroscopic study of bovine placentomal tissue from the second half of gestation, developmental stages of the trophoblast giant cells are investigated. Large mitotic figures indicate mitotic polyploidization, which is proposed to be due to two subsequent acytokinetic mitoses. Tripolar mitoses offer an explanation for the development of trinucleate trophoblast giant cells. Measurements of nuclear volumes in a series of semithin sections revealed that three size classes of trophoblast giant cells occur. The approximately doubling of nuclear volume between each class is thought to reflect different levels of DNA content that result from polyploidization in this cell type. Although trinuclear feto-maternal hybrid cells are the standard outcome of the fusion of binuclear trophoblast giant cells with uterine epithelial cells, some syncytia with at least five nuclei were observed in the uterine epithelium.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hai, Yang; Christianson, David W.

Leishmaniaarginase is a potential drug target for the treatment of leishmaniasis because this binuclear manganese metalloenzyme initiatesde novopolyamine biosynthesis by catalyzing the hydrolysis of L-arginine to generate L-ornithine and urea. The product L-ornithine subsequently undergoes decarboxylation to yield putrescine, which in turn is utilized for spermidine biosynthesis. Polyamines such as spermidine are essential for the growth and survival of the parasite, so inhibition of enzymes in the polyamine-biosynthetic pathway comprises an effective strategy for treating parasitic infections. To this end, two X-ray crystal structures ofL. mexicanaarginase complexed with α,α-disubstituted boronic amino-acid inhibitors based on the molecular scaffold of 2-(S)-amino-6-boronohexanoic acidmore » are now reported. Structural comparisons with human and parasitic arginase complexes reveal interesting differences in the binding modes of the additional α-substituents,i.e.the D side chains, of these inhibitors. Subtle differences in the three-dimensional contours of the outer active-site rims among arginases from different species lead to different conformations of the D side chains and thus different inhibitor-affinity trends. The structures suggest that it is possible to maintain affinity while fine-tuning intermolecular interactions of the D side chain of α,α-disubstituted boronic amino-acid inhibitors in the search for isozyme-specific and species-specific arginase inhibitors.« less

Quantum Electron Tunneling in Respiratory Complex I1

PubMed Central

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

2014-01-01

We have simulated the atomistic details of electronic wiring of all Fe/S clusters in complex I, a key enzyme in the respiratory electron transport chain. The tunneling current theory of many-electron systems is applied to the broken-symmetry (BS) states of the protein at the ZINDO level. One-electron tunneling approximation is found to hold in electron tunneling between the anti-ferromagnetic binuclear and tetranuclear Fe/S clusters with moderate induced polarization of the core electrons. Calculated tunneling energy is about 3 eV higher than Fermi level in the band gap of the protein, which supports that the mechanism of electron transfer is quantum mechanical tunneling, as in the rest of electron transport chain. Resulting electron tunneling pathways consist of up to three key contributing protein residues between neighboring Fe/S clusters. A distinct signature of the wave properties of electrons is observed as quantum interferences when multiple tunneling pathways exist. In N6a-N6b, electron tunnels along different pathways depending on the involved BS states, suggesting possible fluctuations of the tunneling pathways driven by the local protein environment. The calculated distance dependence of the electron transfer rates with internal water molecules included are in good agreement with a reported phenomenological relation. PMID:21495666

Method and apparatus for dissociating metals from metal compounds extracted into supercritical fluids

DOEpatents

Wai, Chien M.; Hunt, Fred H.; Smart, Neil G.; Lin, Yuehe

2000-01-01

A method for dissociating metal-ligand complexes in a supercritical fluid by treating the metal-ligand complex with heat and/or reducing or oxidizing agents is described. Once the metal-ligand complex is dissociated, the resulting metal and/or metal oxide form fine particles of substantially uniform size. In preferred embodiments, the solvent is supercritical carbon dioxide and the ligand is a .beta.-diketone such as hexafluoroacetylacetone or dibutyldiacetate. In other preferred embodiments, the metals in the metal-ligand complex are copper, silver, gold, tungsten, titanium, tantalum, tin, or mixtures thereof. In preferred embodiments, the reducing agent is hydrogen. The method provides an efficient process for dissociating metal-ligand complexes and produces easily-collected metal particles free from hydrocarbon solvent impurities. The ligand and the supercritical fluid can be regenerated to provide an economic, efficient process.

40 CFR 721.4596 - Diazo substituted carbomonocyclic metal complex.

Code of Federal Regulations, 2010 CFR

2010-07-01

... metal complex. 721.4596 Section 721.4596 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.4596 Diazo substituted carbomonocyclic metal complex. (a) Chemical... as a diazo substituted carbomonocyclic metal complex (PMN P-94-1039) is subject to reporting under...

40 CFR 721.4596 - Diazo substituted carbomonocyclic metal complex.

Code of Federal Regulations, 2011 CFR

2011-07-01

... metal complex. 721.4596 Section 721.4596 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.4596 Diazo substituted carbomonocyclic metal complex. (a) Chemical... as a diazo substituted carbomonocyclic metal complex (PMN P-94-1039) is subject to reporting under...

Frustration across the periodic table: heterolytic cleavage of dihydrogen by metal complexes.

PubMed

Bullock, R Morris; Chambers, Geoffrey M

2017-08-28

This perspective examines frustrated Lewis pairs (FLPs) in the context of heterolytic cleavage of H 2 by transition metal complexes, with an emphasis on molecular complexes bearing an intramolecular Lewis base. FLPs have traditionally been associated with main group compounds, yet many reactions of transition metal complexes support a broader classification of FLPs that includes certain types of transition metal complexes with reactivity resembling main group-based FLPs. This article surveys transition metal complexes that heterolytically cleave H 2 , which vary in the degree that the Lewis pairs within these systems interact. Many of the examples include complexes bearing a pendant amine functioning as the base with the metal functioning as the hydride acceptor. Consideration of transition metal compounds in the context of FLPs can inspire new innovations and improvements in transition metal catalysis.This article is part of the themed issue 'Frustrated Lewis pair chemistry'. © 2017 The Author(s).

Metal Complexation in Xylem Fluid 1

PubMed Central

White, Michael C.; Chaney, Rufus L.; Decker, A. Morris

1981-01-01

The capacity of ligands in xylem fluid to form metal complexes was tested with a series of in vitro experiments using paper electrophoresis and radiographs. The xylem fluid was collected hourly for 8 hours from soybean (Glycine max L. Merr.) and tomato (Lycopersicon esculentum Mill.) plants grown in normal and Zn-phytotoxic nutrient solutions. Metal complexation was assayed by anodic or reduced cathodic movement of radionuclides (63Ni, 65Zn, 109Cd, 54Mn) that were presumed to have formed negatively charged complexes. Electrophoretic migration of Ni, Zn, Cd, and Mn added to xylem exudate and spotted on KCl- or KNO3-wetted paper showed that stable Ni, Zn, and Cd metal complexes were formed by exudate ligands. No anodic Mn complexes were observed in this test system. Solution pH, plant species, exudate collection time, and Zn phytotoxicity all affected the amount of metal complex formed in exudate. As the pH increased, there was increased anodic metal movement. Soybean exudate generally bound more of each metal than did tomato exudate. Metal binding usually decreased with increasing exudate collection time, and less metal was bound by the high-Zn exudate. Ni, Zn, Cd, and Mn in exudate added to exudate-wetted paper demonstrated the effect of ligand concentration on stable metal complex formation. Complexes for each metal were demonstratable with this method. Cathodic metal movement increased with time of exudate collection, and it was greater in the high-Zn exudate than in the normal-Zn exudate. A model study illustrated the effect of ligand concentration on metal complex stability in the electrophoretic field. Higher ligand (citric acid) concentrations increased the stability for all metals tested. Images PMID:16661666

Copper(II) sorption onto goethite, hematite and lepidocrocite: a surface complexation model based on ab initio molecular geometries and EXAFS spectroscopy

NASA Astrophysics Data System (ADS)

Peacock, Caroline L.; Sherman, David M.

2004-06-01

We measured the adsorption of Cu(II) onto goethite (α-FeOOH), hematite (α-Fe 2O 3) and lepidocrocite (γ-FeOOH) from pH 2-7. EXAFS spectra show that Cu(II) adsorbs as (CuO 4H n) n-6 and binuclear (Cu 2O 6H n) n-8 complexes. These form inner-sphere complexes with the iron (hydr)oxide surfaces by corner-sharing with two or three edge-sharing Fe(O,OH) 6 polyhedra. Our interpretation of the EXAFS data is supported by ab initio (density functional theory) geometries of analogue Fe 2(OH) 2(H 2O) 8Cu(OH) 4and Fe 3(OH) 4(H 2O) 10Cu 2(OH) 6 clusters. We find no evidence for surface complexes resulting from either monodentate corner-sharing or bidentate edge-sharing between (CuO 4H n) n-6 and Fe(O,OH) 6 polyhedra. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed even though we are supersaturated with respect to CuO and Cu(OH) 2. Having identified the bidentate (FeOH) 2Cu(OH) 20 and tridentate (Fe 3O(OH) 2)Cu 2(OH) 30 surface complexes, we are able to fit the experimental copper(II) adsorption data to the reactions 3( FeOH)+2 Cu2++3 H2O=( Fe3O( OH) 2) Cu2( OH) 30+4 H+ and 2( FeOH)+ Cu2++2 H2O=( FeOH) 2Cu( OH) 20+2 H+. The two stability constants are similar for the three iron (hydr)oxide phases investigated.

Preparation and properties of chitosan-metal complex: Some factors influencing the adsorption capacity for dyes in aqueous solution.

PubMed

Rashid, Sadia; Shen, Chensi; Yang, Jing; Liu, Jianshe; Li, Jing

2018-04-01

Chitosan-metal complexes have been widely studied in wastewater treatment, but there are still various factors in complex preparation which are collectively responsible for improving the adsorption capacity need to be further studied. Thus, this study investigates the factors affecting the adsorption ability of chitosan-metal complex adsorbents, including various kinds of metal centers, different metal salts and crosslinking degree. The results show that the chitosan-Fe(III) complex prepared by sulfate salts exhibited the best adsorption efficiency (100%) for various dyes in very short time duration (10min), and its maximum adsorption capacity achieved 349.22mg/g. The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan-metal complex. SO 4 2- ions not only had the effect of crosslinking through electrostatic interaction with amine group of chitosan polymer, but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process. Additionally, the pH sensitivity and the sensitivity of ionic environment for chitosan-metal complex were analyzed. We hope that these factors affecting the adsorption of the chitosan-metal complex can help not only in optimizing its use but also in designing new chitosan-metal based complexes. Copyright © 2017. Published by Elsevier B.V.

40 CFR 721.10104 - Halophosphate mixed metal complex (generic).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Halophosphate mixed metal complex... Specific Chemical Substances § 721.10104 Halophosphate mixed metal complex (generic). (a) Chemical... as halophosphate mixed metal complex (PMN P-04-254) is subject to reporting under this section for...

40 CFR 721.10104 - Halophosphate mixed metal complex (generic).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Halophosphate mixed metal complex... Specific Chemical Substances § 721.10104 Halophosphate mixed metal complex (generic). (a) Chemical... as halophosphate mixed metal complex (PMN P-04-254) is subject to reporting under this section for...

40 CFR 721.10104 - Halophosphate mixed metal complex (generic).

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Halophosphate mixed metal complex... Specific Chemical Substances § 721.10104 Halophosphate mixed metal complex (generic). (a) Chemical... as halophosphate mixed metal complex (PMN P-04-254) is subject to reporting under this section for...

40 CFR 721.10104 - Halophosphate mixed metal complex (generic).

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Halophosphate mixed metal complex... Specific Chemical Substances § 721.10104 Halophosphate mixed metal complex (generic). (a) Chemical... as halophosphate mixed metal complex (PMN P-04-254) is subject to reporting under this section for...

40 CFR 721.10104 - Halophosphate mixed metal complex (generic).

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Halophosphate mixed metal complex... Specific Chemical Substances § 721.10104 Halophosphate mixed metal complex (generic). (a) Chemical... as halophosphate mixed metal complex (PMN P-04-254) is subject to reporting under this section for...

Effect of Arsenic on the Formation and Adsorption Property of Ferric Hydroxide Precipitates in ZVI Treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Xing; Xi, Beidou; Zhao, Ying

Treatment of arsenic by zerovalent iron (ZVI) has been studied extensively. However, the effect of arsenic on the formation of ferric hydroxide precipitates in the ZVI treatment has not been investigated. We discovered that the specific surface area (ca. 187 m2/g) and arsenic content (ca. 67 mg/g) of the suspended solids (As-containing solids) generated in the ZVI treatment of arsenic solutions were much higher than the specific surface area (ca. 37 m2/g) and adsorption capacity (ca.12 mg/g) of the suspended solids (As-free solids) generated in the arsenic-free solutions. Arsenic in the As-containing solids was much more stable than the adsorbedmore » arsenic in As-free solids. XRD, SEM, TEM, and selected area electron diffraction (SAED) analyses showed that the As-containing solids consisted of amorphous nanoparticles, while the As-free solids were composed of micron particles with weak crystallinity. Extended X-ray absorption fine structure (EXAFS) analysis determined that As(V) was adsorbed on the As-containing suspended solids and magnetic solid surfaces through bidentate binuclear complexation; and As(V) formed a mononuclear complex on the As-free suspended solids. The formation of the surface As(V) complexes retarded the bonding of free FeO6 octahedra to the oxygen sites on FeO6 octahedral clusters and prevented the growth of the clusters and their development into 3-dimensional crystalline phases.« less

Hybrid genetic algorithm with an adaptive penalty function for fitting multimodal experimental data: application to exchange-coupled non-Kramers binuclear iron active sites.

PubMed

Beaser, Eric; Schwartz, Jennifer K; Bell, Caleb B; Solomon, Edward I

2011-09-26

A Genetic Algorithm (GA) is a stochastic optimization technique based on the mechanisms of biological evolution. These algorithms have been successfully applied in many fields to solve a variety of complex nonlinear problems. While they have been used with some success in chemical problems such as fitting spectroscopic and kinetic data, many have avoided their use due to the unconstrained nature of the fitting process. In engineering, this problem is now being addressed through incorporation of adaptive penalty functions, but their transfer to other fields has been slow. This study updates the Nanakorrn Adaptive Penalty function theory, expanding its validity beyond maximization problems to minimization as well. The expanded theory, using a hybrid genetic algorithm with an adaptive penalty function, was applied to analyze variable temperature variable field magnetic circular dichroism (VTVH MCD) spectroscopic data collected on exchange coupled Fe(II)Fe(II) enzyme active sites. The data obtained are described by a complex nonlinear multimodal solution space with at least 6 to 13 interdependent variables and are costly to search efficiently. The use of the hybrid GA is shown to improve the probability of detecting the global optimum. It also provides large gains in computational and user efficiency. This method allows a full search of a multimodal solution space, greatly improving the quality and confidence in the final solution obtained, and can be applied to other complex systems such as fitting of other spectroscopic or kinetics data.

40 CFR 721.4594 - Substituted azo metal complex dye.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Substituted azo metal complex dye. 721... Substances § 721.4594 Substituted azo metal complex dye. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as a substituted azo metal complex...

40 CFR 721.4594 - Substituted azo metal complex dye.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Substituted azo metal complex dye. 721... Substances § 721.4594 Substituted azo metal complex dye. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as a substituted azo metal complex...

The catalase activity of diiron adenine deaminase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamat S. S.; Swaminathan S.; Holmes-Hampton, G. P.

2011-12-01

Adenine deaminase (ADE) from the amidohydrolase superfamily (AHS) of enzymes catalyzes the conversion of adenine to hypoxanthine and ammonia. Enzyme isolated from Escherichia coli was largely inactive toward the deamination of adenine. Molecular weight determinations by mass spectrometry provided evidence that multiple histidine and methionine residues were oxygenated. When iron was sequestered with a metal chelator and the growth medium supplemented with Mn{sup 2+} before induction, the post-translational modifications disappeared. Enzyme expressed and purified under these conditions was substantially more active for adenine deamination. Apo-enzyme was prepared and reconstituted with two equivalents of FeSO{sub 4}. Inductively coupled plasma mass spectrometrymore » and Moessbauer spectroscopy demonstrated that this protein contained two high-spin ferrous ions per monomer of ADE. In addition to the adenine deaminase activity, [Fe{sup II}/Fe{sup II}]-ADE catalyzed the conversion of H{sub 2}O{sub 2} to O{sub 2} and H{sub 2}O. The values of k{sub cat} and k{sub cat}/K{sub m} for the catalase activity are 200 s{sup -1} and 2.4 x 10{sup 4} M{sup -1} s{sup -1}, respectively. [Fe{sup II}/Fe{sup II}]-ADE underwent more than 100 turnovers with H{sub 2}O{sub 2} before the enzyme was inactivated due to oxygenation of histidine residues critical for metal binding. The iron in the inactive enzyme was high-spin ferric with g{sub ave} = 4.3 EPR signal and no evidence of anti-ferromagnetic spin-coupling. A model is proposed for the disproportionation of H{sub 2}O{sub 2} by [Fe{sup II}/Fe{sup II}]-ADE that involves the cycling of the binuclear metal center between the di-ferric and di-ferrous oxidation states. Oxygenation of active site residues occurs via release of hydroxyl radicals. These findings represent the first report of redox reaction catalysis by any member of the AHS.« less

Process for the enhanced capture of heavy metal emissions

DOEpatents

Biswas, Pratim; Wu, Chang-Yu

2001-01-01

This invention is directed to a process for forming a sorbent-metal complex. The process includes oxidizing a sorbent precursor and contacting the sorbent precursor with a metallic species. The process further includes chemically reacting the sorbent precursor and the metallic species, thereby forming a sorbent-metal complex. In one particular aspect of the invention, at least a portion of the sorbent precursor is transformed into sorbent particles during the oxidation step. These sorbent particles then are contacted with the metallic species and chemically reacted with the metallic species, thereby forming a sorbent-metal complex. Another aspect of the invention is directed to a process for forming a sorbent metal complex in a combustion system. The process includes introducing a sorbent precursor into a combustion system and subjecting the sorbent precursor to an elevated temperature sufficient to oxidize the sorbent precursor and transform the sorbent precursor into sorbent particles. The process further includes contacting the sorbent particles with a metallic species and exposing the sorbent particles and the metallic species to a complex-forming temperature whereby the metallic species reacts with the sorbent particles thereby forming a sorbent-metal complex under UV irradiation.

40 CFR 721.4680 - Metal salts of complex inorganic oxyacids (generic name).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Metal salts of complex inorganic... New Uses for Specific Chemical Substances § 721.4680 Metal salts of complex inorganic oxyacids... substances identified generically as metal salts of complex inorganic oxyacids (PMNs P-89-576 and P-89-577...

Environmental and Body Concentrations of Heavy Metals at Sites Near and Distant from Industrial Complexes in Ulsan, Korea.

PubMed

Sung, Joo Hyun; Oh, Inbo; Kim, Ahra; Lee, Jiho; Sim, Chang Sun; Yoo, Cheolin; Park, Sang Jin; Kim, Geun Bae; Kim, Yangho

2018-01-29

Industrial pollution may affect the heavy metal body burden of people living near industrial complexes. We determined the average concentrations of atmospheric heavy metals in areas close to and distant from industrial complexes in Korea, and the body concentrations of these heavy metals in residents living near and distant from these facilities. The atmospheric data of heavy metals (lead and cadmium) were from the Regional Air Monitoring Network in Ulsan. We recruited 1,148 participants, 872 who lived near an industrial complex ("exposed" group) and 276 who lived distant from industrial complexes ("non-exposed" group), and measured their concentrations of blood lead, urinary cadmium, and urinary total mercury. The results showed that atmospheric and human concentrations of heavy metals were higher in areas near industrial complexes. In addition, residents living near industrial complexes had higher individual and combined concentrations (cadmium + lead + mercury) of heavy metals. We conclude that residents living near industrial complexes are exposed to high concentrations of heavy metals, and should be carefully monitored. © 2018 The Korean Academy of Medical Sciences.

Environmental and Body Concentrations of Heavy Metals at Sites Near and Distant from Industrial Complexes in Ulsan, Korea

PubMed Central

2017-01-01

Background Industrial pollution may affect the heavy metal body burden of people living near industrial complexes. We determined the average concentrations of atmospheric heavy metals in areas close to and distant from industrial complexes in Korea, and the body concentrations of these heavy metals in residents living near and distant from these facilities. Methods The atmospheric data of heavy metals (lead and cadmium) were from the Regional Air Monitoring Network in Ulsan. We recruited 1,148 participants, 872 who lived near an industrial complex (“exposed” group) and 276 who lived distant from industrial complexes (“non-exposed” group), and measured their concentrations of blood lead, urinary cadmium, and urinary total mercury. Results The results showed that atmospheric and human concentrations of heavy metals were higher in areas near industrial complexes. In addition, residents living near industrial complexes had higher individual and combined concentrations (cadmium + lead + mercury) of heavy metals. Conclusion We conclude that residents living near industrial complexes are exposed to high concentrations of heavy metals, and should be carefully monitored. PMID:29349943

Insights into aquatic toxicities of the antibiotics oxytetracycline and ciprofloxacin in the presence of metal: complexation versus mixture.

PubMed

Zhang, Yu; Cai, Xiyun; Lang, Xianming; Qiao, Xianliang; Li, Xuehua; Chen, Jingwen

2012-07-01

Co-contamination of ligand-like antibiotics (e.g., tetracyclines and quinolones) and heavy metals prevails in the environment, and thus the complexation between them is involved in environmental risks of antibiotics. To understand toxicological significance of the complex, effects of metal coordination on antibiotics' toxicity were investigated. The complexation of two antibiotics, oxytetracycline and ciprofloxacin, with three heavy metals, copper, zinc, and cadmium, was verified by spectroscopic techniques. The antibiotics bound metals via multiple coordination sites and rendered a mixture of various complexation speciations. Toxicity analysis indicated that metal coordination did modify the toxicity of the antibiotics and that antibiotic, metal, and their complex acted primarily as concentration addition. Comparison of EC(50) values revealed that the complex commonly was highest toxic and predominately correlated in toxicity to the mixture. Finally, environmental scenario analysis demonstrated that ignoring complexation would improperly classify environmental risks of the antibiotics. Copyright © 2012 Elsevier Ltd. All rights reserved.

Metal complexes of quinolone antibiotics and their applications: an update.

PubMed

Uivarosi, Valentina

2013-09-11

Quinolones are synthetic broad-spectrum antibiotics with good oral absorption and excellent bioavailability. Due to the chemical functions found on their nucleus (a carboxylic acid function at the 3-position, and in most cases a basic piperazinyl ring (or another N-heterocycle) at the 7-position, and a carbonyl oxygen atom at the 4-position) quinolones bind metal ions forming complexes in which they can act as bidentate, as unidentate and as bridging ligand, respectively. In the polymeric complexes in solid state, multiple modes of coordination are simultaneously possible. In strongly acidic conditions, quinolone molecules possessing a basic side nucleus are protonated and appear as cations in the ionic complexes. Interaction with metal ions has some important consequences for the solubility, pharmacokinetics and bioavailability of quinolones, and is also involved in the mechanism of action of these bactericidal agents. Many metal complexes with equal or enhanced antimicrobial activity compared to the parent quinolones were obtained. New strategies in the design of metal complexes of quinolones have led to compounds with anticancer activity. Analytical applications of complexation with metal ions were oriented toward two main directions: determination of quinolones based on complexation with metal ions or, reversely, determination of metal ions based on complexation with quinolones.

Proton-coupled electron transfer and the role of water molecules in proton pumping by cytochrome c oxidase

PubMed Central

Sharma, Vivek; Enkavi, Giray; Vattulainen, Ilpo; Róg, Tomasz; Wikström, Mårten

2015-01-01

Molecular oxygen acts as the terminal electron sink in the respiratory chains of aerobic organisms. Cytochrome c oxidase in the inner membrane of mitochondria and the plasma membrane of bacteria catalyzes the reduction of oxygen to water, and couples the free energy of the reaction to proton pumping across the membrane. The proton-pumping activity contributes to the proton electrochemical gradient, which drives the synthesis of ATP. Based on kinetic experiments on the O–O bond splitting transition of the catalytic cycle (A → PR), it has been proposed that the electron transfer to the binuclear iron–copper center of O2 reduction initiates the proton pump mechanism. This key electron transfer event is coupled to an internal proton transfer from a conserved glutamic acid to the proton-loading site of the pump. However, the proton may instead be transferred to the binuclear center to complete the oxygen reduction chemistry, which would constitute a short-circuit. Based on atomistic molecular dynamics simulations of cytochrome c oxidase in an explicit membrane–solvent environment, complemented by related free-energy calculations, we propose that this short-circuit is effectively prevented by a redox-state–dependent organization of water molecules within the protein structure that gates the proton transfer pathway. PMID:25646428

Structure-activity relationships in cytotoxic Au(I)/Au(III) complexes derived from 2-(2'-pyridyl)benzimidazole.

PubMed

Maiore, Laura; Aragoni, Maria Carla; Deiana, Carlo; Cinellu, Maria Agostina; Isaia, Francesco; Lippolis, Vito; Pintus, Anna; Serratrice, Maria; Arca, Massimiliano

2014-04-21

Gold(I) and gold(III) complexes derived from 2-(2'-pyridyl)benzimidazole (pbiH) were proven to be a promising class of in vitro antitumor agents against A2780 human ovarian cancer cells. In this paper, a comparative electrochemical, UV-vis absorption, and emission spectroscopic investigation is reported on pbiH, the two mononuclear Au(III) complexes [(pbi)AuX2] (X = Cl (1), AcO (2)), the four mononuclear Au(I) derivatives [(pbiH)AuCl] (3), [(pbiH)Au(PPh3)]PF6 ((4(+))(PF6(-))), [(pbi)Au(PPh3)] (5), and [(pbi)Au(TPA)] (6), the three mixed-valence Au(III)/Au(I) complexes [(μ-pbi)Au2Cl3] (7), [(Ph3P)Au(μ-pbi)AuX2]PF6 (X = Cl ((8(+))(PF6(-))), AcO ((9(+))(PF6(-)))), and the binuclear Au(I)-Au(I) compound [(μ-pbi)Au2(PPh3)2]PF6 ((10(+))(PF6(-))). All complexes feature irreversible reduction processes related to the Au(III)/Au(I) or Au(I)/Au(0) processes and peculiar luminescent emission at about 360-370 nm in CH2Cl2, with quantum yields that are remarkably lower ((0.7-14.5) × 10(-2)) in comparison to that determined for the free pbiH ligand (31.5 × 10(-2)) in the same solvent. The spectroscopic and electrochemical properties of all complexes were interpreted on the grounds of time-dependent PBE0/DFT calculations carried out both in the gas phase and in CH2Cl2 implicitly considered within the IEF-PCM SCRF approach. The electronic structure of the complexes, and in particular the energy and composition of the Kohn-Sham LUMOs, can be related to the antiproliferative properties against the A2780 ovarian carcinoma cell line, providing sound quantitative structure-activity relationships and shedding a light on the role played by the global charge and nature of ancillary ligands in the effectiveness of Au-based antitumor drugs.

Iridium Cyclooctene Complex That Forms a Hyperpolarization Transfer Catalyst before Converting to a Binuclear C-H Bond Activation Product Responsible for Hydrogen Isotope Exchange.

PubMed

Iali, Wissam; Green, Gary G R; Hart, Sam J; Whitwood, Adrian C; Duckett, Simon B

2016-11-21

[IrCl(COE) 2 ] 2 (1) reacts with pyridine (py) and H 2 to form crystallographically characterized IrCl(H) 2 (COE)(py) 2 (2). 2 undergoes py loss to form 16-electron IrCl(H) 2 (COE)(py) (3), with equivalent hydride ligands. When this reaction is studied with parahydrogen, 1 efficiently achieves hyperpolarization of free py (and nicotinamide, nicotine, 5-aminopyrimidine, and 3,5-lutudine) via signal amplification by reversible exchange (SABRE) and hence reflects a simple and readily available precatayst for this process. 2 reacts further over 48 h at 298 K to form crystallographically characterized (Cl)(H)(py)(μ-Cl)(μ-H)(κ-μ-NC 5 H 4 )Ir(H)(py) 2 (4). This dimer is active in the hydrogen isotope exchange process that is used in radiopharmaceutical preparations. Furthermore, while [Ir(H) 2 (COE)(py) 3 ]PF 6 (6) forms upon the addition of AgPF 6 to 2, its stability precludes its efficient involvement in SABRE.

Structural Basis for Rab1 De-AMPylation by the Legionella pneumophila Effector SidD

PubMed Central

Neunuebel, M. Ramona; Pallara, Chiara; Brady, Jacqueline; Kinch, Lisa N.; Fernández-Recio, Juan; Rojas, Adriana L.; Machner, Matthias P.; Hierro, Aitor

2013-01-01

The covalent attachment of adenosine monophosphate (AMP) to proteins, a process called AMPylation (adenylylation), has recently emerged as a novel theme in microbial pathogenesis. Although several AMPylating enzymes have been characterized, the only known virulence protein with de-AMPylation activity is SidD from the human pathogen Legionella pneumophila. SidD de-AMPylates mammalian Rab1, a small GTPase involved in secretory vesicle transport, thereby targeting the host protein for inactivation. The molecular mechanisms underlying Rab1 recognition and de-AMPylation by SidD are unclear. Here, we report the crystal structure of the catalytic region of SidD at 1.6 Å resolution. The structure reveals a phosphatase-like fold with additional structural elements not present in generic PP2C-type phosphatases. The catalytic pocket contains a binuclear metal-binding site characteristic of hydrolytic metalloenzymes, with strong dependency on magnesium ions. Subsequent docking and molecular dynamics simulations between SidD and Rab1 revealed the interface contacts and the energetic contribution of key residues to the interaction. In conjunction with an extensive structure-based mutational analysis, we provide in vivo and in vitro evidence for a remarkable adaptation of SidD to its host cell target Rab1 which explains how this effector confers specificity to the reaction it catalyses. PMID:23696742

Mechanism and energetics by which glutamic acid 242 prevents leaks in cytochrome c oxidase.

PubMed

Kaila, Ville R I; Verkhovsky, Michael I; Hummer, Gerhard; Wikström, Mårten

2009-10-01

Cytochrome c oxidase (CcO) is the terminal enzyme of aerobic respiration. The energy released from the reduction of molecular oxygen to water is used to pump protons across the mitochondrial or bacterial membrane. The pump function introduces a mechanistic requirement of a valve that prevents protons from flowing backwards during the process. It was recently found that Glu-242, a key amino acid in transferring protons to be pumped across the membrane and to the site of oxygen reduction, fulfils the function of such a valve by preventing simultaneous contact to the pump site and to the proton-conducting D-channel (Kaila V.R.I. et al. Proc. Natl. Acad. Sci. USA 105, 2008). Here we have incorporated the valve model into the framework of the reaction mechanism. The function of the Glu valve is studied by exploring how the redox state of the surrounding metal centers, dielectric effects, and membrane potential, affects the energetics and leaks of this valve. Parallels are drawn between the dynamics of Glu-242 and the long-standing obscure difference between the metastable O(H) and stable O states of the binuclear center. Our model provides a suggestion for why reduction of the former state is coupled to proton translocation while reduction of the latter is not.

Dissolution of Fe(III) (hydr) oxides by metal-EDTA complexes

NASA Astrophysics Data System (ADS)

Ngwack, Bernd; Sigg, Laura

1997-03-01

The dissolution of Fe(III)(hydr)oxides (goethite and hydrous ferric oxide) by metal-EDTA complexes occurs by ligand-promoted dissolution. The process is initiated by the adsorption of metal-EDTA complexes to the surface and is followed by the dissociation of the complex at the surface and the release of Fe(III)EDTA into solution. The dissolution rate is decreased to a great extent if EDTA is complexed by metals in comparison to the uncomplexed EDTA. The rate decreases in the order EDTA CaEDTA ≫ PbEDTA > ZnEDTA > CuEDTA > Co(II)EDTA > NiEDTA. Two different rate-limiting steps determine the dissolution process: (1) detachment of Fe(III) from the oxide-structure and (2) dissociation of the metal-EDTA complexes. In the case of goethite, step 1 is slower than step 2 and the dissolution rates by various metals are similar. In the case of hydrous ferric oxide, step 2 is rate-limiting and the effect of the complexed metal is very pronounced.

Studies on DNA binding behaviour of biologically active transition metal complexes of new tetradentate N2O2 donor Schiff bases: inhibitory activity against bacteria.

PubMed

Sobha, S; Mahalakshmi, R; Raman, N

2012-06-15

A series of Cu(II), Ni(II) and Zn(II) complexes of the type ML have been synthesized with Schiff bases derived from o-acetoacetotoluidide, 2-hydroxybenzaldehyde and o-phenylenediamine/1,4-diaminobutane. The complexes are insoluble in common organic solvents but soluble in DMF and DMSO. The measured molar conductance values in DMSO indicate that the complexes are non-electrolytic in nature. All the six metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic data. The analytical data helped to elucidate the structure of the metal complexes. The Schiff bases are found to act as tetradentate ligands using N(2)O(2) donor set of atoms leading to a square-planar geometry for the complexes around all the metal ions. The binding properties of metal complexes with DNA were investigated by absorption spectra, viscosity measurements and cyclic voltammetry. Detailed analysis reveals that the metal complexes intercalate into the DNA base stack as intercalators. All the metal complexes cleave the pUC19 DNA in presence of H(2)O(2.) The Schiff bases and their complexes have been screened for their antibacterial activity against five bacterial strains (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, Klebsiella pneumoniae) by disk diffusion method. All the metal complexes have potent biocidal activity than the free ligands. Copyright © 2012 Elsevier B.V. All rights reserved.

Frustration across the periodic table: heterolytic cleavage of dihydrogen by metal complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bullock, R. Morris; Chambers, Geoffrey M.

2017-07-24

This Perspective examines the field of Frustrated Lewis Pairs (FLPs) in the context of transition metal mediated heterolytic cleavage of H2, with a particular emphasis on molecular complexes bearing an intramolecular Lewis base. FLPs have traditionally been associated with group compounds, yet many transition metal reactions support a broader classification of FLPs to include certain types of transition metal complexes with reactivity resembling main group based FLPs. This article surveys transition metal complexes that heterolytically cleave H2, which vary in the degree that the Lewis pairs within these systems interact. Particular attention is focused on complexes bearing a pendant aminemore » function as the base. Consideration of transition metal compounds in the context of FLPs can inspire new innovations and improvements in transition metal catalysis.« less

Process for the displacement of cyanide ions from metal-cyanide complexes

DOEpatents

Smith, Barbara F.; Robinson, Thomas W.

1997-01-01

The present invention relates to water-soluble polymers and the use of such water-soluble polymers in a process for the displacement of the cyanide ions from the metal ions within metal-cyanide complexes. The process waste streams can include metal-cyanide containing electroplating waste streams, mining leach waste streams, mineral processing waste streams, and related metal-cyanide containing waste streams. The metal ions of interest are metals that give very strong complexes with cyanide, mostly iron, nickel, and copper. The physical separation of the water-soluble polymer-metal complex from the cyanide ions can be accomplished through the use of ultrafiltration. Once the metal-cyanide complex is disrupted, the freed cyanide ions can be recovered for reuse or destroyed using available oxidative processes rendering the cyanide nonhazardous. The metal ions are released from the polymer, using dilute acid, metal ion oxidation state adjustment, or competing chelating agents, and collected and recovered or disposed of by appropriate waste management techniques. The water-soluble polymer can then be recycled. Preferred water-soluble polymers include polyethyleneimine and polyethyleneimine having a catechol or hydroxamate group.

Gas phase reactions of doubly charged alkaline earth and transition metal(II)-ligand complexes generated by electrospray ionization

NASA Astrophysics Data System (ADS)

Kohler, Martin; Leary, Julie A.

1997-03-01

Doubly charged metal(II)-complexes of [alpha] 1-3, [alpha] 1-6 mannotriose and the conserved trimannosyl core pentasaccharide as well as doubly charged complexes of Co(II), Mn(II), Ca(II) and Sr(II) with acetonitrile generated by electrospray ionization were studied by low energy collision induced dissociation (CID). Two main fragmentation pathways were observed for the metal(II)-oligosaccharide complexes. Regardless of the coordinating metal, loss of a neutral dehydrohexose residue (162 Da) from the doubly charged precursor ion is observed, forming a doubly charged product ion. However, if the oligosaccharide is coordinated to Co(II) or Mn(II), loss of a dehydroxyhexose cation is also observed. Investigation of the low mass region of the mass spectra of the metal coordinated oligosaccharides revealed intense signals corresponding to [metal(II) + (CH3CN)n2+ (where n = 1-6) species which were being formed by the metal(II) ions and the acetonitrile present in the sample. Analysis of these metal(II)-acetonitrile complexes provided further insight into the processes occurring upon low energy CID of doubly charged metal complexes. The metal(II)-acetonitrile system showed neutral loss and ligand cleavage as observed with the oligosaccharide complexes, as well as a series of six different dissociation mechanisms, most notable among them reduction from [metal(II) + (CH3CN)n2+ to the bare [metal(I)]+ species by electron transfer. Depending on the metal and collision gas chosen, one observes electron transfer from the ligand to the metal, electron transfer from the collision gas to the metal, proton transfer between ligands, heterolytic cleavage of the ligands, reactive collisions and loss of neutral ligands.

The molecular structure and vibrational spectra of corrolazine metal complexes (CzM) by density functional theory

NASA Astrophysics Data System (ADS)

Wang, Hongming; Yang, Chuanlu; Zhang, Zhihong; Wang, Meishan; Han, Keli

2006-06-01

The ground-state geometries, electronic structures and vibrational frequencies of metal corrolazine complexes, CzM (M = Mn, Co, Ni and Fe) have been studied using B3LYP/6-311g(d) method. The molecular geometries are sensitive to the species of the metal, and the bond length of the M sbnd N is increase with the metal atom radii. The ground-state electronic structures indicate that there are strong interactions between d of the metal fragments and the corrolazine fragments. The calculations also indicate that the CzNi is the stabilest among the four metal corrolazine complexes. Vibrational frequencies of these metal corrolazine complexes were also calculated and were assigned to the local coordinates of the corrolazine ring, which reveals the some common feature of the molecular vibrations of the metal corrolazine complexes as four-coordination metallocorrolazines.

Extracting metal ions with diphosphonic acid, or derivative thereof

DOEpatents

Horwitz, Earl P.; Gatrone, Ralph C.; Nash, Kenneth L.

1994-01-01

Thermodynamically-unstable complexing agents which are diphosphonic acids and diphosphonic acid derivatives (or sulphur containing analogs), like carboxyhydroxymethanediphosphonic acid and vinylidene-1,1-diphosphonic acid, are capable of complexing with metal ions, and especially metal ions in the II, III, IV, V and VI oxidation states, to form stable, water-soluble metal ion complexes in moderately alkaline to highly-acidic media. However, the complexing agents can be decomposed, under mild conditions, into non-organic compounds which, for many purposes are environmentally-nondamaging compounds thereby degrading the complex and releasing the metal ion for disposal or recovery. Uses for such complexing agents as well as methods for their manufacture are also described.

Extracting metal ions with diphosphonic acid, or derivative thereof

DOEpatents

Horwitz, E.P.; Gatrone, R.C.; Nash, K.L.

1994-07-26

Thermodynamically-unstable complexing agents which are diphosphonic acids and diphosphonic acid derivatives (or sulfur containing analogs), like carboxyhydroxymethanediphosphonic acid and vinylidene-1,1-diphosphonic acid, are capable of complexing with metal ions, and especially metal ions in the II, III, IV, V and VI oxidation states, to form stable, water-soluble metal ion complexes in moderately alkaline to highly-acidic media. However, the complexing agents can be decomposed, under mild conditions, into non-organic compounds which, for many purposes are environmentally-nondamaging compounds thereby degrading the complex and releasing the metal ion for disposal or recovery. Uses for such complexing agents as well as methods for their manufacture are also described. 1 fig.

Reactions of monodithiolene tungsten(VI) sulfido complexes with copper(I) in relation to the structure of the active site of carbon monoxide dehydrogenase.

PubMed

Groysman, Stanislav; Majumdar, Amit; Zheng, Shao-Liang; Holm, R H

2010-02-01

Reactions directed at the synthesis of structural analogues of the active site of molybdenum-containing carbon monoxide dehydrogenase have been investigated utilizing [WO(2)S(bdt)](2-) (1) and [WOS(2)(bdt)](2-) (2) and sterically hindered [Cu(R)L] or [Cu(SSiR'(3))(2)](-) as reactants. All successful reactions of 2 afford the binuclear W(VI)/Cu(I) products [WO(bdt)(mu(2)-S)(2)Cu(L)](2-/-) with L = carbene (3), Ar*S (4), Ar* (7), SSiR(3) (R = Ph (5), Pr(i) (6)). Similarly, [W(bdt)(OSiPh(3))S(2)](-) leads to [W(bdt)(OSiPh(3))(mu(2)-S)(2)Cu(SAr*)](-) (8). These complexes, with apical oxo and basal dithiolato and sulfido coordination (excluding 8), terminal thiolate ligation at Cu(I) (4-6, 8), and W-(mu(2)-S)-Cu bridging, bear a structural resemblance to the enzyme site. Differences include two bridges instead of one and the absence of basal oxo/hydroxo ligation. Complex 8 differs from the others by utilizing apical and basal sulfido ligands in bridge formation. Related reaction systems based on 1 gave 4 in small yield or product mixtures in which the desired monobridged complex [WO(2)(bdt)(mu(2)-S)Cu(R)](2-) was not detected. Mass spectrometric analysis of the reaction system with L = carbene suggests that any monobridged species forms may converted to the dibridged form by disproportionation. In these experiments, the use of W(VI) preserves the structural integrity of Mo(VI), whose analogues of 1 and 2 have not been isolated. (Ar* = 2,6-bis(2,4,6-triisopropylphenyl)phenyl, bdt = benzene-1,2-dithiolate(2-)).

Reactions of Metal-Metal Multiple Bonds. 14. Synthesis and Characterization of Triangulo-W3 and Mo2W-oxo Capped Alkoxide Clusters. Comproportionation of M-M Triple Bonds, sigma(2)pi(4) and d(o) Metal-oxo Groups: M Triple Bond M + M Triple Bond O Yields M3(micron 3-O).

DTIC Science & Technology

1984-05-02

the syntheses of dinuclear and trinuclear complexes employing metal -alkylidyne or -alkylidene fragments.8 Reaction 1 also has a parallel with the...1 0 which was previously examined. The mixed metal complex is undoubtedly disordered with respect to the disposition of molybdenum and tungsten atoms...than for the analogous Mo3 complex suggests greater metal - metal overlap and possibly stronger bonding interactions in the W3 complex which would not

Synthesis, structure, vapour pressure and deposition of ZnO thin film by plasma assisted MOCVD technique using a novel precursor bis[(pentylnitrilomethylidine) (pentylnitrilomethylidine-μ-phenalato)]dizinc(II)

NASA Astrophysics Data System (ADS)

Chandrakala, C.; Sravanthi, P.; Raj Bharath, S.; Arockiasamy, S.; George Johnson, M.; Nagaraja, K. S.; Jeyaraj, B.

2017-02-01

A novel binuclear zinc schiff's base complex bis[(pentylnitrilomethylidine)(pentylnitrilomethylidine-μ-phenalato)]dizinc(II) (hereafter referred as ZSP) was prepared and used as a precursor for the deposition of ZnO thin film by MOCVD. The dynamic TG run of ZSP showed sufficient volatility and good thermal stability. The temperature dependence of vapour pressure measured by transpiration technique yielded a value of 55.8 ± 2.3 kJ mol-1 for the enthalpy of sublimation (ΔH°sub) in the temperature range of 423-503 K. The crystal structure of ZSP was solved by single crystal XRD which exhibits triclinic crystal system with the space group of Pī. The molecular mass of ZSP was determined by mass spectrometry which yielded the m/z value of 891 and 445 Da corresponding to its dimeric as well as monomeric form. The complex ZSP was further characterized by FT-IR and NMR. The demonstration of ZnO thin film deposition was carried out by using plasma assisted MOCVD. The thin film XRD confirmed the highly oriented (002) ZnO thin films on Si(100) substrate. The uniformity and composition of the thin film were analyzed by SEM/EDX. The band gap of ZnO thin film measurement indicated the blue shift with the value of 3.79 eV.

Quantum electron tunneling in respiratory complex I.

PubMed

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A

2011-05-12

We have simulated the atomistic details of electronic wiring of all Fe/S clusters in complex I, a key enzyme in the respiratory electron transport chain. The tunneling current theory of many-electron systems is applied to the broken-symmetry (BS) states of the protein at the ZINDO level. While the one-electron tunneling approximation is found to hold in electron tunneling between the antiferromagnetic binuclear and tetranuclear Fe/S clusters without major orbital or spin rearrangement of the core electrons, induced polarization of the core electrons contributes significantly to decrease the electron transfer rates to 19-56 %. Calculated tunneling energy is about 3 eV higher than Fermi level in the band gap of the protein, which supports that the mechanism of electron transfer is quantum mechanical tunneling, as in the rest of the electron transport chain. Resulting electron tunneling pathways consist of up to three key contributing protein residues between neighboring Fe/S clusters. A signature of the wave properties of electrons is observed as distinct quantum interferences when multiple tunneling pathways exist. In N6a-N6b, electron tunnels along different pathways depending on the involved BS states, suggesting possible fluctuations of the tunneling pathways driven by the local protein environment. The calculated distance dependence of the electron transfer rates with internal water molecules included is in good agreement with a reported phenomenological relation.

Redox Transformations of As and Se at the Surfaces of Natural and Synthetic Ferric Nontronites: Role of Structural and Adsorbed Fe(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilgen, Anastasia G.; Kruichak, Jessica N.; Artyushkova, Kateryna

Adsorption and redox transformations on clay mineral surfaces are prevalent in surface environments. We examined the redox reactivity of iron Fe(II)/Fe(III) associated with natural and synthetic ferric nontronites. Specifically, we assessed how Fe(II) residing in the octahedral sheets, or Fe(II) adsorbed at the edge sites alters redox activity of nontronites. To probe the redox activity we used arsenic (As) and selenium (Se). Activation of both synthetic and natural ferric nontronites was. observed following the introduction of Fe(II) into predominantly-Fe(III) octahedral sheets or through the adsorption of Fe(II) onto the mineral surface. The oxidation of As(III) to As(V) was observed viamore » catalytic (oxic conditions) and, to a lesser degree, via direct (anoxic conditions) pathways. We provide experimental evidence for electron transfer from As(III) to Fe(111) at the natural and synthetic nontronite surfaces, and illustrate that only a fraction of structural Fe(III) is accessible for redox transformations. We show that As adsorbed onto natural and synthetic nontronites forms identical adsorption complexes, namely inner-sphere binuclear bidentate. In conclusion, we show that the formation of an inner-sphere adsorption complex may be a necessary step for the redox transformation via catalytic or direct oxidation pathways.« less

Redox Transformations of As and Se at the Surfaces of Natural and Synthetic Ferric Nontronites: Role of Structural and Adsorbed Fe(II)

DOE PAGES

Ilgen, Anastasia G.; Kruichak, Jessica N.; Artyushkova, Kateryna; ...

2017-08-29

Adsorption and redox transformations on clay mineral surfaces are prevalent in surface environments. We examined the redox reactivity of iron Fe(II)/Fe(III) associated with natural and synthetic ferric nontronites. Specifically, we assessed how Fe(II) residing in the octahedral sheets, or Fe(II) adsorbed at the edge sites alters redox activity of nontronites. To probe the redox activity we used arsenic (As) and selenium (Se). Activation of both synthetic and natural ferric nontronites was. observed following the introduction of Fe(II) into predominantly-Fe(III) octahedral sheets or through the adsorption of Fe(II) onto the mineral surface. The oxidation of As(III) to As(V) was observed viamore » catalytic (oxic conditions) and, to a lesser degree, via direct (anoxic conditions) pathways. We provide experimental evidence for electron transfer from As(III) to Fe(111) at the natural and synthetic nontronite surfaces, and illustrate that only a fraction of structural Fe(III) is accessible for redox transformations. We show that As adsorbed onto natural and synthetic nontronites forms identical adsorption complexes, namely inner-sphere binuclear bidentate. In conclusion, we show that the formation of an inner-sphere adsorption complex may be a necessary step for the redox transformation via catalytic or direct oxidation pathways.« less

Synthesis, characterization and molecular modeling of some transition metal complexes of Schiff base derived from 5-aminouracil and 2-benzoyl pyridine

NASA Astrophysics Data System (ADS)

Abdel-Monem, Yasser K.; Abouel-Enein, Saeyda A.; El-Seady, Safa M.

2018-01-01

Multidentate Schiff base (H2L) ligand results from condensation of 5-aminouracil and 2-benzoyl pyridine and its metal chloride (Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Fe(III), Cr(III), Ru(III), Zr(IV) and Hf(IV)) complexes were prepared. The structural features of the ligand and its metal complexes were confirmed by elemental analyses, spectroscopic methods (IR, UV-Vis, 1H NMR, mass), magnetic moment measurements and thermal studies. The data refer to the ligand coordinates with metal ions in a neutral form and shows different modes of chelation toward the metal atom. All complexes have octahedral skeleton structure, tetrahedrally Mn(II), Ni(II), trigonalbipyramidal Co(II) and square planner Pd(II). Thermal decomposition of complexes as well as the interaction of different types of solvent of crystallization are assigned by thermogravimetric analysis. Molecular modeling of prepared complexes were investigated to study the expected anticancer activities of the prepared complexes. All metal complexes have no interaction except the complexes of Pd(II), Fe(III) and Mn(II).

Study of distorted octahedral structure in 3d transition metal complexes using XAFS

NASA Astrophysics Data System (ADS)

Gaur, A.; Nitin Nair, N.; Shrivastava, B. D.; Das, B. K.; Chakrabortty, Monideepa; Jha, S. N.; Bhattacharyya, D.

2018-01-01

Distortion in octahedral structure of 3d transition metal complexes (Mn, Fe, Co, Ni, Cu, Zn) has been studied using XAFS showing divergent nature of Cu complex. EXAFS analysis showed elongated metal-oxygen bonds for Cu complex leading to more distorted structure. Derivative XANES spectrum at Cu K-edge exhibits splitting of main edge which is correlated to elongated Cu-O bond length. Using these coordination geometry around metal centers, theoretical XANES spectra have been generated and features observed have been correlated to the corresponding metals p-DOS. It has been shown that distorted octahedral field in Cu complex is responsible for splitting of p-DOS.

Self-assembly of discrete metal complexes in aqueous solution via block copolypeptide amphiphiles.

PubMed

Kuroiwa, Keita; Masaki, Yoshitaka; Koga, Yuko; Deming, Timothy J

2013-01-21

The integration of discrete metal complexes has been attracting significant interest due to the potential of these materials for soft metal-metal interactions and supramolecular assembly. Additionally, block copolypeptide amphiphiles have been investigated concerning their capacity for self-assembly into structures such as nanoparticles, nanosheets and nanofibers. In this study, we combined these two concepts by investigating the self-assembly of discrete metal complexes in aqueous solution using block copolypeptides. Normally, discrete metal complexes such as [Au(CN)(2)]-, when molecularly dispersed in water, cannot interact with one another. Our results demonstrated, however, that the addition of block copolypeptide amphiphiles such as K(183)L(19) to [Au(CN)(2)]- solutions induced one-dimensional integration of the discrete metal complex, resulting in photoluminescence originating from multinuclear complexes with metal-metal interactions. Transmission electron microscopy (TEM) showed a fibrous nanostructure with lengths and widths of approximately 100 and 20 nm, respectively, which grew to form advanced nanoarchitectures, including those resembling the weave patterns of Waraji (traditional Japanese straw sandals). This concept of combining block copolypeptide amphiphiles with discrete coordination compounds allows the design of flexible and functional supramolecular coordination systems in water.

Evaluation of the tratment of metal-EDTA complexes using Ti0{sub 2} photocatalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Madden, T.; Datyte, A.K.; Prairie, M.R.

1996-03-01

This study has demonstrated the feasibility of TiO{sub 2} photocatalysis to treat EDTA and several metal-EDTA complexes that can be found in industrial wastewaters. For the EDTA complexes of metals capable of photodeposition, such as Cu and Pb, certain reaction conditions were shown to facilitate the simultaneous complex degradation and photodeposition of these metals onto the catalyst. With metals that do not easily photodeposit, such as Ni and Cd, it is shown that the complex degradation is still facilitated, and can enhance other metals removal processes after photocatalytic treatment. Because the treatment of these metal-EDTA complexes typically requires special measures,more » there may exist situations where TiO{sub 2} photocatalysis could actually be the preferred method of treatment. However, its use should be compared economically to other more established advanced oxidation technologies. This necessity is demonstrated in the economic comparison to ozone treatment for EDTA degradation alone, where ozone treatment appears to be the clear choice in this application.« less

Determination of stability constants of aminoglycoside antibiotics with their metal complexes

NASA Astrophysics Data System (ADS)

Tiwow, Vanny M. A.

2014-03-01

One group of aminoglycoside antibiotics contains aminosugars. The aminosugar neomycin B with its derivate product neamine (2-Deoxy-4-0-(2,6-diamino-2,6-dideoxy-α-D-glucopyranosyl)-D-Streptamine) was identified as a free ligands and metal complexes. In particular, the stability constants of metal complexes by potentiometric titration techniques were investigated. Our previous study had determined the acid dissociation constants of these aminosugars with few metal complexes in fair depth. In this work, the complexation of two pyridine-containing amino alcohols and an amino sugar (neamine) have been measured potentiometrically. For instance, the stability constant of copper(II) complexation were determine and the model system generated an excellent fit. Stability constants with several metals have been determined and will be reported.

Heterobimetallic Complexes Comprised of Nb and Fe: Isolation of a Coordinatively Unsaturated NbIII/Fe0 Bimetallic Complex Featuring a Nb≡Fe Triple Bond.

PubMed

Culcu, Gursu; Iovan, Diana A; Krogman, Jeremy P; Wilding, Matthew J T; Bezpalko, Mark W; Foxman, Bruce M; Thomas, Christine M

2017-07-19

Heterometallic multiple bonds between niobium and other transition metals have not been reported to date, likely owing to the highly reactive nature of low-valent niobium centers. Herein, a C 3 -symmetric tris(phosphinoamide) ligand framework is used to construct a Nb/Fe heterobimetallic complex Cl-Nb( i PrNPPh 2 ) 3 Fe-Br (2), which features a Fe→Nb dative bond with a metal-metal distance of 2.4269(4) Å. Reduction of 2 in the presence of PMe 3 affords Nb( i PrNPPh 2 ) 3 Fe-PMe 3 (6), a compound with an unusual trigonal pyramidal geometry at a Nb III center, a Nb≡Fe triple bond, and the shortest bond distance (2.1446(8) Å) ever reported between Nb and any other transition metal. Complex 6 is thermally unstable and degrades via P-N bond cleavage to form a Nb V ═NR imide complex, i PrN═Nb( i PrNPPh 2 ) 3 Fe-PMe 3 (9). The heterobimetallic complexes i PrN═Nb( i PrNPPh 2 ) 3 Fe-Br (8) and 9 are independently synthesized, revealing that the strongly π-bonding imido functionality prevents significant metal-metal interactions. The 57 Fe Mössbauer spectra of 2, 6, 8, and 9 show a clear trend in isomer shift (δ), with a decrease in δ as metal-metal interactions become stronger and the Fe center is reduced. The electronic structure and metal-metal bonding of 2, 6, 8, and 9 are explored through computational studies, and cyclic voltammetry is used to better understand the effect of metal-metal interaction in early/late heterobimetallic complexes on the redox properties of the two metals involved.

The DFT Calculations of Structures and EPR Parameters for the Dinuclear Paddle-Wheel Copper(II) Complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) as Powder or Single Crystal

NASA Astrophysics Data System (ADS)

Ding, Chang-Chun; Wu, Shao-Yi; Xu, Yong-Qiang; Zhang, Li-Juan; Zhang, Zhi-Hong; Zhu, Qin-Sheng; Wu, Ming-He; Teng, Bao-Hua

2017-10-01

Density functional theory (DFT) calculations of the structures and the Cu2+ g factors (gx, gy and gz ) and hyperfine coupling tensor A (Ax , Ay and Az ) were performed for the paddle-wheel (PW)-type binuclear copper(II) complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) powder and single crystal. Calculations were carried out with the ORCA software using the functionals BHandHlyp, B3P86 and B3LYP with five different basis sets: 6-311g, 6-311g(d,p), VTZ, def-2 and def2-TZVP. Results were tested by the MPAD analysis to find the most suitable functional and basis sets. The electronic structure and covalency between copper and oxygen were investigated by the electron localisation function and the localised orbital locator as well as the Mayer bond order for the [CuO5] group. The optical spectra were theoretically calculated by the time-dependent DFT module and plotted by the Multiwfn program for the [CuO5] group and reasonably associated with the local structure in the vicinity of the central ion copper. In addition, the interactions between the OCNH2CH3, NH3 and H2O molecules and the uncoordinated PW copper(II) complex were studied, and the corresponding adsorption energies, the frequency shifts with respect to the free molecules and the changes of the Cu-Cu distances were calculated and compared with the relevant systems.

Identification of metal species by ESI-MS/MS through release of free metals from the corresponding metal-ligand complexes

PubMed Central

Tsednee, Munkhtsetseg; Huang, Yu-Chen; Chen, Yet-Ran; Yeh, Kuo-Chen

2016-01-01

Electrospray ionization-mass spectrometry (ESI-MS) is used to analyze metal species in a variety of samples. Here, we describe an application for identifying metal species by tandem mass spectrometry (ESI-MS/MS) with the release of free metals from the corresponding metal–ligand complexes. The MS/MS data were used to elucidate the possible fragmentation pathways of different metal–deoxymugineic acid (–DMA) and metal–nicotianamine (–NA) complexes and select the product ions with highest abundance that may be useful for quantitative multiple reaction monitoring. This method can be used for identifying different metal–ligand complexes, especially for metal species whose mass spectra peaks are clustered close together. Different metal–DMA/NA complexes were simultaneously identified under different physiological pH conditions with this method. We further demonstrated the application of the technique for different plant samples and with different MS instruments. PMID:27240899

Quantitative Interpretation of Multifrequency Multimode EPR Spectra of Metal Containing Proteins, Enzymes, and Biomimetic Complexes.

PubMed

Petasis, Doros T; Hendrich, Michael P

2015-01-01

Electron paramagnetic resonance (EPR) spectroscopy has long been a primary method for characterization of paramagnetic centers in materials and biological complexes. Transition metals in biological complexes have valence d-orbitals that largely define the chemistry of the metal centers. EPR spectra are distinctive for metal type, oxidation state, protein environment, substrates, and inhibitors. The study of many metal centers in proteins, enzymes, and biomimetic complexes has led to the development of a systematic methodology for quantitative interpretation of EPR spectra from a wide array of metal containing complexes. The methodology is now contained in the computer program SpinCount. SpinCount allows simulation of EPR spectra from any sample containing multiple species composed of one or two metals in any spin state. The simulations are quantitative, thus allowing determination of all species concentrations in a sample directly from spectra. This chapter will focus on applications to transition metals in biological systems using EPR spectra from multiple microwave frequencies and modes. © 2015 Elsevier Inc. All rights reserved.

A Study on Spectro-Analytical Aspects, DNA - Interaction, Photo-Cleavage, Radical Scavenging, Cytotoxic Activities, Antibacterial and Docking Properties of 3 - (1 - (6 - methoxybenzo [d] thiazol - 2 - ylimino) ethyl) - 6 - methyl - 3H - pyran - 2, 4 - dione and its Metal Complexes.

PubMed

Ravi, Mudavath; Chennam, Kishan Prasad; Ushaiah, B; Eslavath, Ravi Kumar; Perugu, Shyam; Ajumeera, Rajanna; Devi, Ch Sarala

2015-09-01

The focus of the present work is on the design, synthesis, characterization, DNA-interaction, photo-cleavage, radical scavenging, in-vitro cytotoxicity, antimicrobial, docking and kinetic studies of Cu (II), Cd (II), Ce (IV) and Zr (IV) metal complexes of an imine derivative, 3 - (1 - (6 - methoxybenzo [d] thiazol - 2 - ylimino) ethyl) - 6 - methyl - 3H - pyran - 2, 4 - dione. The investigation of metal ligand interactions for the determination of composition of metal complexes, corresponding kinetic studies and antioxidant activity in solution was carried out by spectrophotometric methods. The synthesized metal complexes were characterized by EDX analysis, Mass, IR, (1)H-NMR, (13)C-NMR and UV-Visible spectra. DNA binding studies of metal complexes with Calf thymus (CT) DNA were carried out at room temperature by employing UV-Vis electron absorption, fluorescence emission and viscosity measurement techniques. The results revealed that these complexes interact with DNA through intercalation. The results of in vitro antibacterial studies showed the enhanced activity of chelating agent in metal chelated form and thus inferring scope for further development of new therapeutic drugs. Cell viability experiments indicated that all complexes showed significant dose dependent cytotoxicity in selected cell lines. The molecular modeling and docking studies were carried out with energy minimized structures of metal complexes to identify the receptor to metal interactions.

Report: complexation of β-sitosterol with tris (dibenzylideneacetone) dipalladium and its anti-microbial activity.

PubMed

Mahmood, Talat; Bibi, Yasmeen; Zafar, Raana; Wahab, Aneela; Mahmood, Iffat; Arshad, Nuzhat; Sherwani, Sikandar Khan

2015-03-01

β-sitosterol is a naturally occurring plant sterol (phytosterol) present in many fruits and vegetables. Scientific research has proven that β-sitosterol is helpful in maintaining the proper functioning of our body. Previously we described the complexation of β-sitosterol with trace metals (Mahmood et al., 2013). Trace metals after the formation of complex unable to absorb in the body and hence eliminated out from the body thus reducing metal toxicity (Marsha, 1996). The present article describes the complexation of μ-sitosterol with Palladium (Pd) metal. Palladium is a toxic metal and due to polluted and hazardous environment traces of this metal can be transferred into the body, which is harmful for human health. Our aim is to make Pd-sterol complex so that this toxic metal (Pd) does not absorb in the body and hence excreted out from the body in the complex form. In order to form this complex μ-sitosterol (Ib) is reacted with Tris (dibenzylideneacetone) dipalladium or [Pd(2) (DBA)(3)] (Ia) in 2:1 ratio in an inert atmosphere and dimethylformamid (DMF) added as a solvent. The resulting complex [Pd(2) (DBA)(3).(β-sitosterol) (Ic) was identified by various spectroscopic techniques such as IR, Mass and (1)H-NMR. This new organo metallic complex (Ic) also showed significant antibacterial and antifungal activity. The present work revealed that Pd-sterol complex does not only reduce metal toxicity but also helpful in minimizing bacterial and fungal infections present in the body. Our research also concluded that we must take plenty of fruits and vegetables in our diet so that natural plant sterol such as β-sitosterol can enhance our defense mechanism and maintain other functions of our body.

Synthesis and characterization of nitrile functionalized silver(I)-N-heterocyclic carbene complexes: DNA binding, cleavage studies, antibacterial properties and mosquitocidal activity against the dengue vector, Aedes albopictus.

PubMed

Asekunowo, Patrick O; Haque, Rosenani A; Razali, Mohd R; Avicor, Silas W; Wajidi, Mustafa F F

2018-04-25

A series of four benzimidazolium based nitrile-functionalized mononuclear-Ag(I)-N-heterocyclic carbene and binuclear-Ag(I)-N-heterocyclic carbene (Ag(I)-NHC) hexafluorophosphate complexes (5b-8b) were synthesized by reacting the corresponding hexafluorophosphate salts (1b-4b) with Ag 2 O in acetonitrile, respectively. These compounds were characterized by 1 H NMR, 13 C NMR, IR, UV-visible spectroscopic techniques, elemental analyses and molar conductivity. Additionally, 8b was structurally characterized by single crystal X-ray diffraction technique. Preliminary in vitro antibacterial evaluation was conducted for all the compounds against two standard bacteria; gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacterial strains. Most of the Ag(I)-NHC complexes (5b-8b) showed moderate to good antibacterial activity with MIC values in the range of 12.5-100 μg/mL. Especially, compound 8b exhibited promising anti-Staphylococcus aureus activity with a low MIC value (12.5 μg/mL). However, all the hexafluorophosphate salts (1b-4b) were inactive against the bacteria strains. The preliminary interactive investigation revealed that the most active compound, 8b, could effectively intercalate into DNA to form 8b-DNA complex which shows a better binding ability for DNA (K b  = 3.627 × 10 6 ) than the complexes 5b-7b (2.177 × 10 6 , 8.672 × 10 5 and 6.665 × 10 5 , respectively). Nuclease activity of the complexes on plasmid DNA and Aedes albopictus genomic DNA was time-dependent, although minimal. The complexes were larvicidal to the mosquito, with 5b, 6b and 8b being highly active. Developmental progression from the larval to the adult stage was affected by the complexes, progressively being toxic to the insect's development with increasing concentration. These indicate the potential use of these complexes as control agents against bacteria and the dengue mosquito Ae. albopictus. Copyright © 2018 Elsevier Masson SAS. All rights reserved.

Copper(II) hexaaza macrocyclic binuclear complexes obtained from the reaction of their copper(I) derivates and molecular dioxygen.

PubMed

Costas, Miquel; Ribas, Xavi; Poater, Albert; López Valbuena, Josep Maria; Xifra, Raül; Company, Anna; Duran, Miquel; Solà, Miquel; Llobet, Antoni; Corbella, Montserrat; Usón, Miguel Angel; Mahía, José; Solans, Xavier; Shan, Xiaopeng; Benet-Buchholz, Jordi

2006-05-01

Density functional theory (DFT) calculations have been carried out for a series of Cu(I) complexes bearing N-hexadentate macrocyclic dinucleating ligands and for their corresponding peroxo species (1c-8c) generated by their interaction with molecular O2. For complexes 1c-7c, it has been found that the side-on peroxodicopper(II) is the favored structure with regard to the bis(mu-oxo)dicopper(III). For those complexes, the singlet state has also been shown to be more stable than the triplet state. In the case of 8c, the most favored structure is the trans-1,2-peroxodicopper(II) because of the para substitution and the steric encumbrance produced by the methylation of the N atoms. Cu(II) complexes 4e, 5e, and 8e have been obtained by O2 oxidation of their corresponding Cu(I) complexes and structurally and magnetically characterized. X-ray single-crystal structures for those complexes have been solved, and they show three completely different types of Cu(II)2 structures: (a) For 4e, the Cu(II) centers are bridged by a phenolate group and an external hydroxide ligand. The phenolate group is generated from the evolution of 4c via intramolecular arene hydroxylation. (b) For 5e, the two Cu(II) centers are bridged by two hydroxide ligands. (c) For the 8e case, the Cu(II) centers are ligated to terminally bound hydroxide ligands, rare because of its tendency to bridge. The evolution of complexes 1c-8c toward their oxidized species has also been rationalized by DFT calculations based mainly on their structure and electrophilicity. The structural diversity of the oxidized species is also responsible for a variety of magnetic behavior: (a) strong antiferromagnetic (AF) coupling with J = -482.0 cm(-1) (g = 2.30; rho = 0.032; R = 5.6 x 10(-3)) for 4e; (b) AF coupling with J = -286.3 cm(-1) (g = 2.07; rho = 0.064; R = 2.6 x 10(-3)) for 5e; (c) an uncoupled Cu(II)2 complex for 8e.

Design, synthesis, spectral characterization, DNA interaction and biological activity studies of copper(II), cobalt(II) and nickel(II) complexes of 6-amino benzothiazole derivatives

NASA Astrophysics Data System (ADS)

Daravath, Sreenu; Kumar, Marri Pradeep; Rambabu, Aveli; Vamsikrishna, Narendrula; Ganji, Nirmala; Shivaraj

2017-09-01

Two novel Schiff bases, L1 = (2-benzo[d]thiazol-6-ylimino)methyl)-4,6-dichlorophenol), L2 = (1-benzo[d]thiazol-6-ylimino)methyl)-6-bromo-4-chlorophenol) and their bivalent transition metal complexes [M(L1)2] and [M(L2)2], where M = Cu(II), Co(II) and Ni(II) were synthesized and characterized by elemental analysis, NMR, IR, UV-visible, mass, magnetic moments, ESR, TGA, SEM, EDX and powder XRD. Based on the experimental data a square planar geometry around the metal ion is assigned to all the complexes (1a-2c). The interaction of synthesized metal complexes with calf thymus DNA was explored using UV-visible absorption spectra, fluorescence and viscosity measurements. The experimental evidence indicated that all the metal complexes strongly bound to CT-DNA through an intercalation mode. DNA cleavage experiments of metal(II) complexes with supercoiled pBR322 DNA have also been explored by gel electrophoresis in the presence of H2O2 as well as UV light, and it is found that the Cu(II) complexes cleaved DNA more effectively compared to Co(II), Ni(II) complexes. In addition, the ligands and their metal complexes were screened for antimicrobial activity and it is found that all the metal complexes were more potent than free ligands.

Reactions catalyzed by haloporphyrins

DOEpatents

Ellis, P.E. Jr.; Lyons, J.E.

1996-02-06

The invention provides novel methods for the oxidation of hydrocarbons with oxygen-containing gas to form hydroxy-group containing compounds and for the decomposition of hydroperoxides to form hydroxy-group containing compounds. The catalysts used in the methods of the invention comprise transition metal complexes of a porphyrin ring having 1 to 12 halogen substituents on the porphyrin ring, at least one of said halogens being in a meso position and/or the catalyst containing no aryl group in a meso position. The catalyst compositions are prepared by halogenating a transition metal complex of a porphyrin. In one embodiment, a complex of a porphyrin with a metal whose porphyrin complexes are not active for oxidation of alkanes is halogenated, thereby to obtain a haloporphyrin complex of that metal, the metal is removed from the haloporphyrin complex to obtain the free base form of the haloporphyrin, and a metal such as iron whose porphyrin complexes are active for oxidation of alkanes and for the decomposition of alkyl hydroperoxides is complexed with the free base to obtain an active catalyst for oxidation of alkanes and decomposition of alkyl hydroperoxides.

Haloporphyrins and their preparation and use as catalysts

DOEpatents

Ellis, Jr., Paul E.; Lyons, James E.

1997-01-01

The invention provides novel catalyst compositions, useful in the oxidation of hydrocarbons with air or oxygen to form hydroxy-group containing compounds and in the decomposition of hydroperoxides to form hydroxy-group containing compounds. The catalysts comprise transition metal complexes of a porphyrin ring having 1 to 12 halogen substituents on the porphyrin ring, at least one of said halogens being in a meso position and/or the catalyst containing no aryl group in a meso position. The compositions are prepared by halogenating a transition metal complex of a porphyrin. In one embodiment, a complex of a porphyrin with a metal whose porphyrin complexes are not active for oxidation of hydrocarbons is halogenated, thereby to obtain a haloporphyrin complex of that metal, the metal is removed from the haloporphyrin complex to obtain the free base form of the haloporphyrin, and a metal such as iron whose porphyrin complexes are active for oxidation of hydrocarbons and for the decomposition of alkyl hydroperoxides is complexed with the free base to obtain an active catalyst for oxidation of hydrocarbons and decomposition of alkyl hydroperoxides.

Reactions catalyzed by haloporphyrins

DOEpatents

Ellis, Jr., Paul E.; Lyons, James E.

1996-01-01

The invention provides novel methods for the oxidation of hydrocarbons with oxygen-containing gas to form hydroxy-group containing compounds and for the decomposition of hydroperoxides to form hydroxygroup containing compounds. The catalysts used in the methods of the invention comprise transition metal complexes of a porphyrin ring having 1 to 12 halogen substituents on the porphyrin ring, at least one of said halogens being in a meso position and/or the catalyst containing no aryl group in a meso position. The catalyst compositions are prepared by halogenating a transition metal complex of a porphyrin. In one embodiment, a complex of a porphyrin with a metal whose porphyrin complexes are not active for oxidation of alkanes is halogenated, thereby to obtain a haloporphyrin complex of that metal, the metal is removed from the haloporphyrin complex to obtain the free base form of the haloporphyrin, and a metal such as iron whose porphyrin complexes are active for oxidation of alkanes and for the decomposition of alkyl hydroperoxides is complexed with the free base to obtain an active catalyst for oxidation of alkanes and decomposition of alkyl hydroperoxides.

Haloporphyrins and their preparation and use as catalysts

DOEpatents

Ellis, P.E. Jr.; Lyons, J.E.

1997-09-02

The invention provides novel catalyst compositions, useful in the oxidation of hydrocarbons with air or oxygen to form hydroxy-group containing compounds and in the decomposition of hydroperoxides to form hydroxy-group containing compounds. The catalysts comprise transition metal complexes of a porphyrin ring having 1 to 12 halogen substituents on the porphyrin ring, at least one of said halogens being in a meso position and/or the catalyst containing no aryl group in a meso position. The compositions are prepared by halogenating a transition metal complex of a porphyrin. In one embodiment, a complex of a porphyrin with a metal whose porphyrin complexes are not active for oxidation of hydrocarbons is halogenated, thereby to obtain a haloporphyrin complex of that metal, the metal is removed from the haloporphyrin complex to obtain the free base form of the haloporphyrin, and a metal such as iron whose porphyrin complexes are active for oxidation of hydrocarbons and for the decomposition of alkyl hydroperoxides is complexed with the free base to obtain an active catalyst for oxidation of hydrocarbons and decomposition of alkyl hydroperoxides.

Transition metal-chelating surfactant micelle templates for facile synthesis of mesoporous silica nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hye Sun; Department of Materials Science and Engineering, Yonsei University, Seoul 120-749; Kim, Won Hee

2012-01-15

Highly ordered mesoporous silica nanoparticles with tunable morphology and pore-size are prepared by the use of a transition metal-chelating surfactant micelle complex using Co{sup 2+}, Ni{sup 2+}, Cu{sup 2+}, and Zn{sup 2+} ions. These metal ions formed a metal-P123 micelle complex in an aqueous solution, while the metal ions are chelated to the hydrophilic domain such as the poly(ethylene oxide) group of a P123 surfactant. The different complexation abilities of the utilized transition metal ions play an important role in determining the formation of nano-sized ordered MSNs due to the different stabilization constant of the metal-P123 complex. Consequently, from amore » particle length of 1700 nm in the original mesoporous silica materials, the particle length of ordered MSNs through the metal-chelating P123 micelle templates can be reduced to a range of 180-800 nm. Furthermore, the variation of pore size shows a slight change from 8.8 to 6.6 nm. In particular, the Cu{sup 2+}-chelated MSNs show only decreased particle size to 180 nm. The stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism of MSNs by the metal-chelating P123 complex templates. In addition, solid-state {sup 29}Si, {sup 13}C-NMR and ICP-OES measurements are used for quantitative characterization reveal that the utilized metal ions affect only the formation of a metal-P123 complex in a micelle as a template. - Graphical abstract: Metal-chelating surfactant micelle templates support a simple and facile preparations of size-tunable ordered MSNs. Black-Small-Square Highlights: Black-Right-Pointing-Pointer Facile preparation of mesoporous silica nanoparticles (MSNs) was achieved by metal-chelating surfactant micelle complex using Co{sup 2+}, Ni{sup 2+}, Cu{sup 2+}, and Zn{sup 2+} ions. Black-Right-Pointing-Pointer Different complexation of metal ions plays an important role in determining the formation of nano-sized ordered MSNs. Black-Right-Pointing-Pointer Systematic characterization of the synthesized materials was achieved by solid-state {sup 29}Si and {sup 13}C-NMR techniques, BET, FT-IR, and XPS. Black-Right-Pointing-Pointer Stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism.« less

[The role of essential metal ions in the human organism and their oral supplementation to the human body in deficiency states].

PubMed

Lakatos, Béla; Szentmihályi, Klára; Vinkler, Péter; Balla, József; Balla, György

2004-06-20

The role of essential nutrient metal ions (Mg, Fe, Cu, Zn, Mn and Co) often deficient in our foodstuffs, although vitally essential in the function of the human organism as well as the different reasons for these deficiencies both in foods and in the human body have been studied. The most frequent nutritional disease is iron deficient anaemia. Inorganic salts, artificial synthetic monomer organic metal complexes of high stability or organic polymer complexes of high molecular mass are unsatisfactory for supplementation to the human body, owing to poor absorption, low availability and/or harmful side effects. In contrast, we have recently found that mixed metal complexes of oligo/polygalacturonic acids with medium molecular weight prepared from natural pectin of plant origin are efficient for oral supplementation. Sufficient absorption of essential metal ions from metal oligo/polygalacturonate mixed complexes with polynuclear innersphere structure is due to the high ionselectivity and medium stability values. Metal oligo/polygalacturonate mixed complexes contain all deficient essential metal ions in adequate amounts and ratios for higher bioavailability of metal ions and optimal vital function. Therefore, by oral administration of these complexes, metal ion homeostasis and optimal interactions with vitamins and hormones can be ensured. Prelatent or latent macroelement Mg deficiency can often be observed among clinical or ambulance patients. Latent or manifest mesoelement iron deficiency is the most common, however, the occurrence of microelement copper, zinc, manganese and cobalt latent deficiencies is not seldom either. Supplementation studies utilizing essential metal oligo/polygalacturonate complexes led to satisfactory outcome without harmful side effects.

Synthesis, crystal structure, fluorescence and electrochemical studies of a new tridentate Schiff base ligand and its nickel(II) and palladium(II) complexes

NASA Astrophysics Data System (ADS)

Shafaatian, Bita; Soleymanpour, Ahmad; Kholghi Oskouei, Nasim; Notash, Behrouz; Rezvani, Seyyed Ahmad

2014-07-01

A new unsymmetrical tridentate Schiff base ligand was derived from the 1:1 M condensation of ortho-vanillin with 2-mercaptoethylamine. Nickel and palladium complexes were obtained by the reaction of the tridentate Schiff base ligand with nickel(II) acetate tetrahydrate and palladium(II) acetate in 2:1 M ratio. In nickel and palladium complexes the ligand was coordinated to metals via the imine N and enolic O atoms. The S groups of Schiff bases were not coordinated to the metals and S-S coupling was occured. The complexes have been found to possess 1:2 Metal:Ligand stoichiometry and the molar conductance data revealed that the metal complexes were non-electrolytes. The complexes exhibited octahedral coordination geometry. The emission spectra of the ligand and its complexes were studied in methanol. Electrochemical properties of the ligand and its metal complexes were investigated in the CH3CN solvent at the 100 mV s-1 scan rate. The ligand and metal complexes showed both reversible and quasi-reversible processes at this scan rate. The Schiff base and its complexes have been characterized by IR, 1H NMR, UV/Vis, elemental analyses and conductometry. The crystal structure of nickel complex has been determined by single crystal X-ray diffraction.

Novel Dialkylamino Derivatives of Phosphorus and Silicon.

DTIC Science & Technology

1987-10-19

Metal Carbonyl Complexes ," Inorg. Chem. 1985, 24, 3136-3139. (7) King, R. B., Fu, W.-K.; Holt, E. M. "The Synthesis of Heterobimetallic Complexes from...Carbonyl Complexes of Diisopropylaminohalophosphines and their Application for the Synthesis of Novel Bimetallic Complexes ," presented by W.-K. Fu at the...necessary and identify by block number) FIELD -GROUP SUB-GROUP Phosphorus /Metal Complexes Silicon Dialkylamino Metal Carbonyls Boron Cyclopolyphosphinesl

Metal-organic complexes in geochemical processes: temperature dependence of the standard thermodynamic properties of aqueous complexes between metal cations and dicarboxylate ligands

NASA Astrophysics Data System (ADS)

Prapaipong, Panjai; Shock, Everett L.; Koretsky, Carla M.

1999-10-01

By combining results from regression and correlation methods, standard state thermodynamic properties for aqueous complexes between metal cations and divalent organic acid ligands (oxalate, malonate, succinate, glutarate, and adipate) are evaluated and applied to geochemical processes. Regression of experimental standard-state equilibrium constants with the revised Helgeson-Kirkham-Flowers (HKF) equation of state yields standard partial molal entropies (S¯°) of aqueous metal-organic complexes, which allow determination of thermodynamic properties of the complexes at elevated temperatures. In cases where S¯° is not available from either regression or calorimetric measurement, the values of S¯° can be estimated from a linear correlation between standard partial molal entropies of association (ΔS¯°r) and standard partial molal entropies of aqueous cations (S¯°M). The correlation is independent of cation charge, which makes it possible to predict S¯° for complexes between divalent organic acids and numerous metal cations. Similarly, correlations between standard Gibbs free energies of association of metal-organic complexes (ΔḠ°r) and Gibbs free energies of formation (ΔḠ°f) for divalent metal cations allow estimates of standard-state equilibrium constants where experimental data are not available. These correlations are found to be a function of ligand structure and cation charge. Predicted equilibrium constants for dicarboxylate complexes of numerous cations were included with those for inorganic and other organic complexes to study the effects of dicarboxylate complexes on the speciation of metals and organic acids in oil-field brines. Relatively low concentrations of oxalic and malonic acids affect the speciation of cations more than similar concentrations of succinic, glutaric, and adipic acids. However, the extent to which metal-dicarboxylate complexes contribute to the speciation of dissolved metals depends on the type of dicarboxylic acid ligand; relative concentration of inorganic, mono-, and dicarboxylate ligands; and the type of metal cation. As an example, in the same solution, dicarboxylic acids have a greater influence on the speciation of Fe+2 and Mg+2 than on the speciation of Zn+2 and Mn+2.

Membrane extraction with thermodynamically unstable diphosphonic acid derivatives

DOEpatents

Horwitz, Earl Philip; Gatrone, Ralph Carl; Nash, Kenneth LaVerne

1997-01-01

Thermodynamically-unstable complexing agents which are diphosphonic acids and diphosphonic acid derivatives (or sulphur containing analogs), like carboxyhydroxymethanediphosphonic acid and vinylidene-1,1-diphosphonic acid, are capable of complexing with metal ions, and especially metal ions in the II, III, IV, V and VI oxidation states, to form stable, water-soluble metal ion complexes in moderately alkaline to highly-acidic media. However, the complexing agents can be decomposed, under mild conditions, into non-organic compounds which, for many purposes are environmentally-nondamaging compounds thereby degrading the complex and releasing the metal ion for disposal or recovery. Uses for such complexing agents as well as methods for their manufacture are also described.

Intercalation of Transition Metals into Stacked Benzene Rings: A Model Study of the Intercalation of Transition Metals into Bilayered Graphene.

PubMed

Youn, Il Seung; Kim, Dong Young; Singh, N Jiten; Park, Sung Woo; Youn, Jihee; Kim, Kwang S

2012-01-10

Structures of neutral metal-dibenzene complexes, M(C6H6)2 (M = Sc-Zn), are investigated by using Møller-Plesset second order perturbation theory (MP2). The benzene molecules change their conformation and shape upon complexation with the transition metals. We find two types of structures: (i) stacked forms for early transition metal complexes and (ii) distorted forms for late transition metal ones. The benzene molecules and the metal atom are bound together by δ bonds which originate from the interaction of π-MOs and d orbitals. The binding energy shows a maximum for Cr(C6H6)2, which obeys the 18-electron rule. It is noticeable that Mn(C6H6)2, a 19-electron complex, manages to have a stacked structure with an excess electron delocalized. For other late transition metal complexes having more than 19 electrons, the benzene molecules are bent or stray away from each other to reduce the electron density around a metal atom. For the early transition metals, the M(C6H6) complexes are found to be more weakly bound than M(C6H6)2. This is because the M(C6H6) complexes do not have enough electrons to satisfy the 18-electron rule, and so the M(C6H6)2 complexes generally tend to have tighter binding with a shorter benzene-metal length than the M(C6H6) complexes, which is quite unusual. The present results could provide a possible explanation of why on the Ni surface graphene tends to grow in a few layers, while on the Cu surface the weak interaction between the copper surface and graphene allows for the formation of a single layer of graphene, in agreement with chemical vapor deposition experiments.

Theoretical evidence of the observed kinetic order dependence on temperature during the N(2)O decomposition over Fe-ZSM-5.

PubMed

Guesmi, Hazar; Berthomieu, Dorothee; Bromley, Bryan; Coq, Bernard; Kiwi-Minsker, Lioubov

2010-03-28

The characterization of Fe/ZSM5 zeolite materials, the nature of Fe-sites active in N(2)O direct decomposition, as well as the rate limiting step are still a matter of debate. The mechanism of N(2)O decomposition on the binuclear oxo-hydroxo bridged extraframework iron core site [Fe(II)(mu-O)(mu-OH)Fe(II)](+) inside the ZSM-5 zeolite has been studied by combining theoretical and experimental approaches. The overall calculated path of N(2)O decomposition involves the oxidation of binuclear Fe(II) core sites by N(2)O (atomic alpha-oxygen formation) and the recombination of two surface alpha-oxygen atoms leading to the formation of molecular oxygen. Rate parameters computed using standard statistical mechanics and transition state theory reveal that elementary catalytic steps involved into N(2)O decomposition are strongly dependent on the temperature. This theoretical result was compared to the experimentally observed steady state kinetics of the N(2)O decomposition and temperature-programmed desorption (TPD) experiments. A switch of the reaction order with respect to N(2)O pressure from zero to one occurs at around 800 K suggesting a change of the rate determining step from the alpha-oxygen recombination to alpha-oxygen formation. The TPD results on the molecular oxygen desorption confirmed the mechanism proposed.

Bio-inspired cofacial Fe porphyrin dimers for efficient electrocatalytic CO2 to CO conversion: Overpotential tuning by substituents at the porphyrin rings

PubMed Central

Zahran, Zaki N.; Mohamed, Eman A.; Naruta, Yoshinori

2016-01-01

Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe−containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push−pull mechanism. Bio−inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe−Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe−Fe separation distance. PMID:27087483

Bio-inspired cofacial Fe porphyrin dimers for efficient electrocatalytic CO2 to CO conversion: Overpotential tuning by substituents at the porphyrin rings.

PubMed

Zahran, Zaki N; Mohamed, Eman A; Naruta, Yoshinori

2016-04-18

Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push-pull mechanism. Bio-inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe-Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe-Fe separation distance.

Bio-inspired cofacial Fe porphyrin dimers for efficient electrocatalytic CO2 to CO conversion: Overpotential tuning by substituents at the porphyrin rings

NASA Astrophysics Data System (ADS)

Zahran, Zaki N.; Mohamed, Eman A.; Naruta, Yoshinori

2016-04-01

Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push-pull mechanism. Bio-inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe-Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe-Fe separation distance.

Synthesis, structure, luminescent, and magnetic properties of carbonato-bridged Zn(II)2Ln(III)2 complexes [(μ4-CO3)2{Zn(II)L(n)Ln(III)(NO3)}2] (Ln(III) = Gd(III), Tb(III), Dy(III); L(1) = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, L(2) = N,N'-bis(3-ethoxy-2-oxybenzylidene)-1,3-propanediaminato).

PubMed

Ehama, Kiyomi; Ohmichi, Yusuke; Sakamoto, Soichiro; Fujinami, Takeshi; Matsumoto, Naohide; Mochida, Naotaka; Ishida, Takayuki; Sunatsuki, Yukinari; Tsuchimoto, Masanobu; Re, Nazzareno

2013-11-04

Carbonato-bridged Zn(II)2Ln(III)2 complexes [(μ4-CO3)2{Zn(II)L(n)Ln(III)(NO3)}2]·solvent were synthesized through atmospheric CO2 fixation reaction of [Zn(II)L(n)(H2O)2]·xH2O, Ln(III)(NO3)3·6H2O, and triethylamine, where Ln(III) = Gd(III), Tb(III), Dy(III); L(1) = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, L(2) = N,N'-bis(3-ethoxy-2-oxybenzylidene)-1,3-propanediaminato. Each Zn(II)2Ln(III)2 structure possessing an inversion center can be described as two di-μ-phenoxo-bridged {Zn(II)L(n)Ln(III)(NO3)} binuclear units bridged by two carbonato CO3(2-) ions. The Zn(II) ion has square pyramidal coordination geometry with N2O2 donor atoms of L(n) and one oxygen atom of a bridging carbonato ion at the axial site. Ln(III) ion is coordinated by nine oxygen atoms consisting of four from the deprotonated Schiff-base L(n), two from a chelating nitrate, and three from two carbonate groups. The temperature-dependent magnetic susceptibilities in the range 1.9-300 K, field-dependent magnetization from 0 to 5 T at 1.9 K, and alternating current magnetic susceptibilities under the direct current bias fields of 0 and 1000 Oe were measured. The magnetic properties of the Zn(II)2Ln(III)2 complexes are analyzed on the basis of the dicarbonato-bridged binuclear Ln(III)-Ln(III) structure, as the Zn(II) ion with d(10) electronic configuration is diamagnetic. ZnGd1 (L(1)) and ZnGd2 (L(2)) show a ferromagnetic Gd(III)-Gd(III) interaction with J(Gd-Gd) = +0.042 and +0.028 cm(-1), respectively, on the basis of the Hamiltonian H = -2J(Gd-Gd)ŜGd1·ŜGd2. The magnetic data of the Zn(II)2Ln(III)2 complexes (Ln(III) = Tb(III), Dy(III)) were analyzed by a spin Hamiltonian including the crystal field effect on the Ln(III) ions and the Ln(III)-Ln(III) magnetic interaction. The Stark splitting of the ground state was so evaluated, and the energy pattern indicates a strong easy axis (Ising type) anisotropy. Luminescence spectra of Zn(II)2Tb(III)2 complexes were observed, while those of Zn(II)2Dy(III)2 were not detected. The fine structure assignable to the (5)D4 → (7)F6 transition of ZnTb1 and ZnTb2 is in good accord with the energy pattern from the magnetic analysis. The Zn(II)2Ln(III)2 complexes (Ln(III) = Tb(III), Dy(III)) showed an out-of-phase signal with frequency-dependence in alternating current susceptibility, indicative of single molecule magnet. Under a dc bias field of 1000 Oe, the signals become significantly more intense and the energy barrier, Δ/kB, for the magnetic relaxation was estimated from the Arrhenius plot to be 39(1) and 42(8) K for ZnTb1 and ZnTb2, and 52(2) and 67(2) K for ZnDy1 and ZnDy2, respectively.

Multiheteromacrocycles that Complex Metal Ions. Ninth Progress Report (includes results of last three years), 1 May 1980 -- 30 April 1983

DOE R&D Accomplishments Database

Cram, D. J.

1982-09-15

The overall objective of this research is to design, synthesize, and evaluate cyclic and polycyclic host organic compounds for the abilities to complex and lipophilize guest metal ions, their complexes, and their clusters. Host organic compounds consist of strategically placed solvating, coordinating, and ion-pairing sites tied together by covalent bonds through hydrocarbon units around cavities shaped to be occupied by guest metal ions, or by metal ions plus their ligands. Specificity in complexation is sought by matching the following properties of host and guest: cavity and metal ion sizes; geometric arrangements of binding sites; numbers of binding sites; characters of binding sites; and valences. The hope is to synthesize new classes of compounds useful in the separation of metal ions, their complexes, and their clusters.

Energetic lanthanide complexes: coordination chemistry and explosives applications

NASA Astrophysics Data System (ADS)

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

2014-05-01

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

Energetic Lanthanide Complexes: Coordination Chemistry and Explosives Applications

NASA Astrophysics Data System (ADS)

Manner, Virginia; Barker, Beau; Sanders, Eric; Laintz, Kenneth; Scott, Brian; Preston, Daniel; Sandstrom, Mary; Reardon, Bettina

2013-06-01

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

Interaction between transition metals and phenylalanine: a combined experimental and computational study.

PubMed

Elius Hossain, Md; Mahmudul Hasan, Md; Halim, M E; Ehsan, M Q; Halim, Mohammad A

2015-03-05

Some transition metal complexes of phenylalanine of general formula [M(C9H10NO2)2]; where M=Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) are prepared in aqueous medium and characterized by spectroscopic, thermo-gravimetric (TG) and magnetic susceptibility analysis. Density functional theory (DFT) has been employed calculating the equilibrium geometries and vibrational frequencies of those complexes at B3LYP level of theory using 6-31G(d) and SDD basis sets. In addition, frontier molecular orbital and time-dependent density functional theory (TD-DFT) calculations are performed with CAM-B3LYP/6-31+G(d,p) and B3LYP/SDD level of theories. Thermo-gravimetric analysis confirms the composition of the complexes by comparing the experimental and calculated data for C, H, N and metals. Experimental and computed IR results predict a significant change in vibrational frequencies of metal-phenylalanine complexes compared to free ligand. DFT calculation confirms that Mn, Co, Ni and Cu complexes form square planar structure whereas Zn adopts distorted tetrahedral geometry. The metal-oxygen bonds in the optimized geometry of all complexes are shorter compared to the metal-nitrogen bonds which is consistent with a previous study. Cation-binding energy, enthalpy and Gibbs free energy indicates that these complexes are thermodynamically stable. UV-vis and TD-DFT studies reveal that these complexes demonstrate representative metal-to-ligand charge transfer (MLCT) and d-d transitions bands. TG analysis and IR spectra of the metal complexes strongly support the absence of water in crystallization. Magnetic susceptibility data of the complexes exhibits that all except Zn(II) complex are high spin paramagnetic. Copyright © 2014 Elsevier B.V. All rights reserved.

The Effect of Complex Formation upon the Redox Potentials of Metallic Ions. Cyclic Voltammetry Experiments.

ERIC Educational Resources Information Center

Ibanez, Jorge G.; And Others

1988-01-01

Describes experiments in which students prepare in situ soluble complexes of metal ions with different ligands and observe and estimate the change in formal potential that the ion undergoes upon complexation. Discusses student formation and analysis of soluble complexes of two different metal ions with the same ligand. (CW)

Electronic Structure and Bonding in Transition Metal Inorganic and Organometallic Complexes: New Basis Sets, Linear Semibridging Carbonyls and Thiocarbonyls, and Oxidative Addition of Molecular Hydrogen to Square - Iridium Complexes.

NASA Astrophysics Data System (ADS)

Sargent, Andrew Landman

Approximate molecular orbital and ab initio quantum chemical techniques are used to investigate the electronic structure, bonding and reactivity of several transition metal inorganic and organometallic complexes. Modest-sized basis sets are developed for the second-row transition metal atoms and are designed for use in geometry optimizations of inorganic and organometallic complexes incorporating these atoms. The basis sets produce optimized equilibrium geometries which are slightly better than those produced with standard 3-21G basis sets, and which are significantly better than those produced with effective core potential basis sets. Linear semibridging carbonyl ligands in heterobimetallic complexes which contain a coordinatively unsaturated late transition metal center are found to accept electron density from, rather than donate electron density to, these centers. Only when the secondary metal center is a coordinatively unsaturated early transition metal center does the semibridging ligand donate electron density to this center. Large holes in the d shell around the metal center are more prominent and prevalent in early than in late transition metal centers, and the importance of filling in these holes outweighs the importance of mitigating the charge imbalance due to the dative metal-metal interaction. Semibridging thiocarbonyl ligands are more effective donors of electron density than the carbonyl ligands since the occupied donor orbitals of pi symmetry are higher in energy. The stereoselectivity of H_2 addition to d^8 square-planar transition metal complexes is controlled by the interactions between the ligands in the plane of addition and the concentrations of electronic charge around the metal center as the complex evolves from a four-coordinate to a six-coordinate species. Electron -withdrawing ligands help stabilize the five-coordinate species while strong electron donor ligands contribute only to the destabilizing repulsive interactions. The relative thermodynamic stabilities of the final complexes can be predicted based on the relative orientations of the strongest sigma-donor ligands.

Metal adsorption onto bacterial surfaces: development of a predictive approach

NASA Astrophysics Data System (ADS)

Fein, Jeremy B.; Martin, Aaron M.; Wightman, Peter G.

2001-12-01

Aqueous metal cation adsorption onto bacterial surfaces can be successfully modeled by means of a surface complexation approach. However, relatively few stability constants for metal-bacterial surface complexes have been measured. In order to determine the bacterial adsorption behavior of cations that have not been studied in the laboratory, predictive techniques are required that enable estimation of the stability constants of bacterial surface complexes. In this study, we use a linear free-energy approach to compare previously measured stability constants for Bacillus subtilis metal-carboxyl surface complexes with aqueous metal-organic acid anion stability constants. The organic acids that we consider are acetic, oxalic, citric, and tiron. We add to this limited data set by conducting metal adsorption experiments onto Bacillus subtilis, determining bacterial surface stability constants for Co, Nd, Ni, Sr, and Zn. The adsorption behavior of each of the metals studied here was described well by considering metal-carboxyl bacterial surface complexation only, except for the Zn adsorption behavior, which required carboxyl and phosphoryl complexation to obtain a suitable fit to the data. The best correlation between bacterial carboxyl surface complexes and aqueous organic acid anion stability constants was obtained by means of metal-acetate aqueous complexes, with a linear correlation coefficient of 0.97. This correlation applies only to unhydrolyzed aqueous cations and only to carboxyl binding of those cations, and it does not predict the binding behavior under conditions where metal binding to other bacterial surface site types occurs. However, the relationship derived in this study permits estimation of the carboxyl site adsorption behavior of a wide range of aqueous metal cations for which there is an absence of experimental data. This technique, coupled with the observation of similar adsorption behaviors across bacterial species (Yee and Fein, 2001), enables estimation of the effects of bacterial adsorption on metal mobilities for a large number of environmental and geologic applications.

Assigning Oxidation States to Some Metal Dioxygen Complexes of Biological Interest.

ERIC Educational Resources Information Center

Summerville, David A.; And Others

1979-01-01

The bonding of dioxygen in metal-dioxygen complexes is discussed, paying particular attention to the problems encountered in assigning conventional oxidation numbers to both the metal center and coordinated dioxygen. Complexes of iron, cobalt, chromium, and manganese are considered. (BB)

Metal complex-based electron-transfer mediators in dye-sensitized solar cells

DOEpatents

Elliott, C. Michael; Sapp, Shawn A.; Bignozzi, Carlo Alberto; Contado, Cristiano; Caramori, Stefano

2006-03-28

This present invention provides a metal-ligand complex and methods for using and preparing the same. In particular, the metal-ligand complex of the present invention is of the formula: L.sub.a-M-X.sub.b where L, M, X, a, and b are those define herein. The metal-ligand complexes of the present invention are useful in a variety of applications including as electron-transfer mediators in dye-sensitized solar cells and related photoelectrochromic devices.

Ursolic Acid Hydrazide Based Organometallic Complexes: Synthesis, Characterization, Antibacterial, Antioxidant and Docking Studies

NASA Astrophysics Data System (ADS)

Jabeen, Muafia; Ahmad, Sajjad; Shahid, Khadija; Sadiq, Abdul; Rashid, Umer

2018-03-01

In the current research work,eleven metal complexes were synthesized from the hydrazide derivative of ursolic acid. Metal complexes of tin, antimony and iron were synthesized and characterized by FT-IR and NMR spectroscopy. The antibacterial and antioxidant activities were performed for these complexes, which revealed that the metal complexes synthesized are more potent than their parent compounds. We observed that antioxidant activity showed by triphenyltin complex was significant and least activity have been shown by antimony trichloride complex.The synthesized metal complexes were then evaluated against two Gram-negative and two Gram-positive bacterial strains. Triphenyl tin complex emerged as potent antibacterial agent with MIC value of 8 μg/ml each against Shigellaspp, S. typhi and S. aureus. While, the MIC value againstS. pneumoniae is 4 μg/ml.Computational docking studies were carried out on molecular targets to interpret the results of antioxidant and antibacterial activities. Based on the results, it may be inferred that the metal complexes of ursolic acid are more active as compared to the parent drug and may be proved for some other pharmacological potential by further analysis.

Methods of selectively incorporating metals onto substrates

DOEpatents

Ernst; Richard D. , Eyring; Edward M. , Turpin; Gregory C. , Dunn; Brian C.

2008-09-30

A method for forming multi-metallic sites on a substrate is disclosed and described. A substrate including active groups such as hydroxyl can be reacted with a pretarget metal complex. The target metal attached to the active group can then be reacted with a secondary metal complex such that an oxidation-reduction (redox) reaction occurs to form a multi-metallic species. The substrate can be a highly porous material such as aerogels, xerogels, zeolites, and similar materials. Additional metal complexes can be reacted to increase catalyst loading or control co-catalyst content. The resulting compounds can be oxidized to form oxides or reduced to form metals in the ground state which are suitable for practical use.

Surface-enhanced Raman scattering and DFT investigation of 1,5-diphenylcarbazide and its metal complexes with Ca(II), Mn(II), Fe(III) and Cu(II)

NASA Astrophysics Data System (ADS)

Szabó, László; Herman, Krisztian; Mircescu, Nicoleta Elena; Tódor, István Szabolcs; Simon, Botond Lorand; Boitor, Radu Alex; Leopold, Nicolae; Chiş, Vasile

2014-09-01

In recent years, surface-enhanced Raman scattering (SERS) has become an increasingly viable method for the detection of metal ions, evidenced by the existing studies on metal complexes. In this study, 1,5-diphenylcarbazide (DPC) and its Ca(II), Mn(II), Fe(III) and Cu(II) complexes were investigated by FTIR/ATR, FT-Raman and surface-enhanced Raman spectroscopies. The hybrid B3LYP exchange-correlation functional was used for the molecular geometry optimizations, molecular electrostatic potential (MEP) distribution and vibrational frequencies calculations of the DPC molecule and its complexes. Based on experimental and theoretical data, we were able to accurately identify unique and representative features for each DPC-metal complex, features that enable the detection of said metal complexes in millimolar concentrations.

Application of Δ- and λ-isomerism of octahedral metal complexes for inducing chiral nematic phases.

PubMed

Sato, Hisako; Yamagishi, Akihiko

2009-11-20

The Delta- and Lambda-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(beta-diketonato)metal(III) complexes exhibit an extremely high value of helical twisting power. The mechanism of induction of the chiral nematic phase is postulated on the basis of a surface chirality model. The strategy for designing an efficient dopant is described, together with the results using a number of examples of Co(III), Cr(III) and Ru(III) complexes with C(2) symmetry. The development of photo-responsive dopants to achieve the photo-induced structural change of liquid crystal by use of photo-isomerization of chiral metal complexes is also described.

Application of Δ- and Λ-Isomerism of Octahedral Metal Complexes for Inducing Chiral Nematic Phases

PubMed Central

Sato, Hisako; Yamagishi, Akihiko

2009-01-01

The Δ- and Λ-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(β-diketonato)metal(III) complexes exhibit an extremely high value of helical twisting power. The mechanism of induction of the chiral nematic phase is postulated on the basis of a surface chirality model. The strategy for designing an efficient dopant is described, together with the results using a number of examples of Co(III), Cr(III) and Ru(III) complexes with C2 symmetry. The development of photo-responsive dopants to achieve the photo-induced structural change of liquid crystal by use of photo-isomerization of chiral metal complexes is also described. PMID:20057959

Synthesis, spectral studies and biological evaluation of 2-aminonicotinic acid metal complexes

NASA Astrophysics Data System (ADS)

Nawaz, Muhammad; Abbasi, Muhammad Waseem; Hisaindee, Soleiman; Zaki, Muhammad Javed; Abbas, Hira Fatima; Mengting, Hu; Ahmed, M. Arif

2016-05-01

We synthesized 2-aminonicotinic acid (2-ANA) complexes with metals such as Co(II), Fe(III), Ni(II), Mn(II), Zn(II), Ag(I),Cr(III), Cd(II) and Cu(II) in aqueous media. The complexes were characterized and elucidated using FT-IR, UV-Vis, a fluorescence spectrophotometer and thermo gravimetric analysis (TGA). TGA data showed that the stoichiometry of complexes was 1:2 metal/ligand except for Ag(I) and Mn(II) where the ratio was 1:1. The metal complexes showed varied antibacterial, fungicidal and nematicidal activities. The silver and zinc complexes showed highest activity against Bacillus subtilis and Bacillus licheniformis respectively. Fusarium oxysporum was highly susceptible to nickel and copper complexes whereas Macrophomina phaseolina was completely inert to the complexes. The silver and cadmium complexes were effective against the root-knot nematode Meloidogyne javanica.

Synthesis and Spectral Characterization of Antifungal Sensitive Schiff Base Transition Metal Complexes

PubMed Central

Sakthivel, A.; Rajasekaran, K.

2007-01-01

New N2O2 donor type Schiff base has been designed and synthesized by condensing acetoacetanilido-4-aminoantipyrine with 2-aminobenzoic acid in ethanol. Solid metal complexes of the Schiff base with Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV), Hg(II) and Cd(II) metal ions were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conduction, fast atom bombardment (FAB) mass, IR, UV-Vis, and 1H NMR spectral studies. The data show that the complexes have the composition of ML type. The UV-Vis. and magnetic susceptibility data of the complexes suggest a square-planar geometry around the central metal ion except VO(IV) complex which has square-pyramidal geometry. The in vitro antifungal activities of the compounds were tested against fungi such as Aspergillus niger, Aspergillus flavus, Rhizopus stolonifer, Candida albicans, Rhizoctonia bataicola and Trichoderma harizanum. All the metal complexes showed stronger antifungal activities than the free ligand. The minimum inhibitory concentrations (MIC) of the metal complexes were found in the range of 10~31 µg/ml. PMID:24015086

On the existence of free and metal complexed sulfide in the Arabian Sea and its oxygen minimum zone

NASA Astrophysics Data System (ADS)

Theberge, Stephen M.; Luther, George W.; Farrenkopf, Anna M.

Free hydrogen sulfide was not detected in the oxygen minimum zone (OMZ) of the Arabian Sea during legs D1 (September 1992) and D3 (October-November 1992) of the Netherlands Indian Ocean Programme (NIOP). However, sulfide complexed to metals was detected by cathodic stripping square wave voltammetry at 2 nM or less throughout the water column. A slight increase in sulfide was measured in the OMZ relative to the surface waters and may be related to sulfur release from organic matter during decomposition. Sulfide complexes are of two general types at low concentrations of metal and sulfide. First, metals such as Mn, Fe, Co and Ni form complexes with bisulfide ion (HS -) that are kinetically labile to dissociation and are reactive. Second, metals such as Cu and Zn form multinuclear complexes with sulfide (S 2-) that are kinetically inert to dissociation; thus, they are less reactive than free (bi)sulfide and the labile metal bisulfide complexes. Zinc and copper sulfide complexes are important in allowing hydrogen sulfide to persist in seawater which contains measurable oxygen.

Solubility enhancement of seven metal contaminants using carboxymethyl-β-cyclodextrin (CMCD)

NASA Astrophysics Data System (ADS)

Skold, Magnus E.; Thyne, Geoffrey D.; Drexler, John W.; McCray, John E.

2009-07-01

Carboxymethyl-β-cyclodextrin (CMCD) has been suggested as a complexing agent for remediation of sites co-contaminated with metals and organic pollutants. As part of an attempt to construct a geochemical complexation model for metal-CMCD interactions, conditional formation constants for the complexes between CMCD and 7 metal ions (Ba, Ca, Cd, Ni, Pb, Sr, and Zn) are estimated from experimental data. Stable metal concentrations were reached after approximately 1 day and estimated logarithmic conditional formation constants range from - 3.2 to - 5.1 with confidence intervals within ± 0.08 log units. Experiments performed at 10 °C and 25 °C show that temperature affects the solubility of the metal salts but the strength of CMCD-metal complexes are not affected by this temperature variation. The conditional stability constants and complexation model presented in this work can be used to screen CMCD as a potential remediation agent for clean-up of contaminated soil and groundwater.

Nuclear reactor cooling system decontamination reagent regeneration. [PWR; BWR

DOEpatents

Anstine, L.D.; James, D.B.; Melaika, E.A.; Peterson, J.P. Jr.

1980-06-06

An improved method for decontaminating the coolant system of water-cooled nuclear power reactors and for regenerating the decontamination solution is described. A small amount of one or more weak-acid organic complexing agents is added to the reactor coolant, and the pH is adjusted to form a decontamination solution which is circulated throughout the coolant system to dissolve metal oxides from the interior surfaces and complex the resulting metal ions and radionuclide ions. The coolant containing the complexed metal ions and radionuclide ions is passed through a strong-base anion exchange resin bed which has been presaturated with a solution containing the complexing agents in the same ratio and having the same pH as the decontamination solution. As the decontamination solution passes through the resin bed, metal-complexed anions are exchanged for the metal-ion-free anions on the bed, while metal-ion-free anions in the solution pass through the bed, thus removing the metal ions and regenerating the decontamination solution.

Mass balance of metal species in supercritical fluid extraction using sodium diethyldithiocarbamate and dibutylammonium dibutyldithiocarbamate.

PubMed

Wang, Joanna Shaofen; Chiu, Kong-Hwa

2006-03-01

The objective of this work is to track the amount of metal complexes distributed in the extraction cell, collection vial, and tubing used in supercritical fluid extraction (SFE) systems after progressive removal of metal ions in supercritical carbon dioxide (SC-CO2). Sodium diethyldithiocarbamate (NaDDC) and dibutylammonium dibutyldithiocarbamate (DBDC) ligands were used to form complexes with Cd, Cu, Pb, and Zn and CO(2)/5% methanol as a supercritical fluid. The mass balance of metal complexes were obtained before and after extraction, and metals in different locations in the system were flushed out using an organic solvent and nitric acid (HNO3). These results infer that the stability constant (beta) of the metal-ligand complex has a strong correlation with SFE. Because of the composition of the stainless-steel cell, Fe, Cr, and Ni or other trace elements in the cell might interfere with the mass balance of metal complexes in SFE due to an exchange mechanism taking place between the cell and the sample.

Nuclear reactor cooling system decontamination reagent regeneration

DOEpatents

Anstine, Larry D.; James, Dean B.; Melaika, Edward A.; Peterson, Jr., John P.

1985-01-01

An improved method for decontaminating the coolant system of water-cooled nuclear power reactors and for regenerating the decontamination solution. A small amount of one or more weak-acid organic complexing agents is added to the reactor coolant, and the pH is adjusted to form a decontamination solution which is circulated throughout the coolant system to dissolve metal oxides from the interior surfaces and complex the resulting metal ions and radionuclide ions. The coolant containing the complexed metal ions and radionuclide ions is passed through a strong-base anion exchange resin bed which has been presaturated with a solution containing the complexing agents in the same ratio and having the same pH as the decontamination solution. As the decontamination solution passes through the resin bed, metal-complexed anions are exchanged for the metal-ion-free anions on the bed, while metal-ion-free anions in the solution pass through the bed, thus removing the metal ions and regenerating the decontamination solution.

Electrokinetic treatment of an agricultural soil contaminated with heavy metals.

PubMed

Figueroa, Arylein; Cameselle, Claudio; Gouveia, Susana; Hansen, Henrik K

2016-07-28

The high organic matter content in agricultural soils tends to complex and retain contaminants such as heavy metals. Electrokinetic remediation was tested in an agricultural soil contaminated with Co(+2), Zn(+2), Cd(+2), Cu(+2), Cr(VI), Pb(+2) and Hg(+2). The unenhanced electrokinetic treatment was not able to remove heavy metals from the soil due to the formation of precipitates in the alkaline environment in the soil section close to the cathode. Moreover, the interaction between metals and organic matter probably limited metal transportation under the effect of the electric field. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used in the catholyte as complexing agents in order to enhance the extractability and removal of heavy metals from soil. These complexing agents formed negatively charged complexes that migrated towards the anode. The acid front electrogenerated at the anode favored the dissolution of heavy metals that were transported towards the cathode. The combined effect of the soil pH and the complexing agents resulted in the accumulation of heavy metals in the center of the soil specimen.

Membrane extraction with thermodynamically unstable diphosphonic acid derivatives

DOEpatents

Horwitz, E.P.; Gatrone, R.C.; Nash, K.L.

1997-10-14

Thermodynamically-unstable complexing agents which are diphosphonic acids and diphosphonic acid derivatives (or sulphur containing analogs), like carboxyhydroxymethanediphosphonic acid and vinylidene-1,1-diphosphonic acid, are capable of complexing with metal ions, and especially metal ions in the II, III, IV, V and VI oxidation states, to form stable, water-soluble metal ion complexes in moderately alkaline to highly-acidic media. However, the complexing agents can be decomposed, under mild conditions, into non-organic compounds which, for many purposes are environmentally-nondamaging compounds thereby degrading the complex and releasing the metal ion for disposal or recovery. Uses for such complexing agents as well as methods for their manufacture are also described. 1 fig.

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation

DOEpatents

Lilga, Michael A.; Hallen, Richard T.

1990-01-01

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately .pi.-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancilliary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H.sub.2 from mixed gas streams such as the produce gas from coal gasification processes.

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation

DOEpatents

Lilga, M.A.; Hallen, R.T.

1991-10-15

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately [pi]-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancillary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H[sub 2] from mixed gas streams such as the product gas from coal gasification processes. 3 figures.

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation

DOEpatents

Lilga, M.A.; Hallen, R.T.

1990-08-28

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately [pi]-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancillary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H[sub 2] from mixed gas streams such as the producer gas from coal gasification processes. 3 figs.

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation

DOEpatents

Lilga, Michael A.; Hallen, Richard T.

1991-01-01

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately .pi.-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancilliary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H.sub.2 from mixed gas streams such as the product gas from coal gasification processes.

Multiheteromacrocycles that Complex Metal Ions. Sixth Progress Report, 1 May 1979-30 April 1980

DOE R&D Accomplishments Database

Cram, D. J.

1980-01-15

Objective is to design synthesize, and evaluate cyclic and polycyclic host organic compounds for their abilities to complex and lipophilize guest metal ions, their complexes, and their clusters. Host organic compounds consist of strategically placed solvating, coordinating, and ion-pairing sites tied together by covalent bonds through hydrocarbon units around cavities shaped to be occupied by guest metal ions or by metal ions plus their ligands. Specificity in complexation is sought by matching the following properties of host and guest: cavity and metal ion sizes; geometric arrangements of binding sites; number of binding sites; character of binding sites; and valences. During this period, hemispherands based on an aryloxy or cyclic urea unit, spherands based on aryloxyl units only, and their complexes with alkali metals and alkaline earths were investigated. An attempt to separate {sup 6}Li and {sup 7}Li by gel permeation chromatography of lithiospherium chloride failed. (DLC)

Drug Delivery Systems For Anti-Cancer Active Complexes of Some Coinage Metals.

PubMed

Zhang, Ming; Saint-Germain, Camille; He, Guiling; Sun, Raymond Wai-Yin

2018-02-12

Although cisplatin and a number of platinum complexes have widely been used for the treatment of neoplasia, patients receiving these treatments have frequently suffered from their severe toxic side effects, the development of resistance with consequent relapse. In the recent decades, numerous complexes of coinage metals including that of gold, copper and silver have been reported to display promising in vitro and/or in vivo anti-cancer activities as well as potent activities towards cisplatin-resistant tumors. Nevertheless, the medical development of these metal complexes has been hampered by their instability in aqueous solutions and the nonspecific binding in biological systems. One of the approaches to overcome these problems is to design and develop adequate drug delivery systems (DDSs) for the transport of these complexes. By functionalization, encapsulation or formulation of the metal complexes, several types of DDSs have been reported to improve the desired pharmacological profile of the metal complexes, improving their overall stability, bioavailability, anti-cancer activity and reducing their toxicity towards normal cells. In this review, we summarized the recent findings for different DDSs for various anti- cancer active complexes of some coinage metals. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Spectral characterization, cyclic voltammetry, morphology, biological activities and DNA cleaving studies of amino acid Schiff base metal(II) complexes

NASA Astrophysics Data System (ADS)

Neelakantan, M. A.; Rusalraj, F.; Dharmaraja, J.; Johnsonraja, S.; Jeyakumar, T.; Sankaranarayana Pillai, M.

2008-12-01

Metal complexes are synthesized with Schiff bases derived from o-phthalaldehyde (opa) and amino acids viz., glycine (gly) L-alanine (ala), L-phenylalanine (pal). Metal ions coordinate in a tetradentate or hexadentate manner with these N 2O 2 donor ligands, which are characterized by elemental analysis, molar conductance, magnetic moments, IR, electronic, 1H NMR and EPR spectral studies. The elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). Based on EPR studies, spin-Hamiltonian and bonding parameters have been calculated. The g-values calculated for copper complexes at 300 K and in frozen DMSO (77 K) indicate the presence of the unpaired electron in the d orbital. The evaluated metal-ligand bonding parameters showed strong in-plane σ- and π-bonding. X-ray diffraction (XRD) and scanning electron micrography (SEM) analysis provide the crystalline nature and the morphology of the metal complexes. The cyclic voltammograms of the Cu(II)/Mn(II)/VO(II) complexes investigated in DMSO solution exhibit metal centered electroactivity in the potential range -1.5 to +1.5 V. The electrochemical data obtained for Cu(II) complexes explains the change of structural arrangement of the ligand around Cu(II) ions. The biological activity of the complexes has been tested on eight bacteria and three fungi. Cu(II) and Ni(II) complexes show an increased activity in comparison to the controls. The metal complexes of opapal Schiff base were evaluated for their DNA cleaving activities with calf-thymus DNA (CT DNA) under aerobic conditions. Cu(II) and VO(II) complexes show more pronounced activity in presence of the oxidant.

Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

NASA Astrophysics Data System (ADS)

Lichtenberg, Dennis L.

During this period some important breakthroughs were accomplished in understanding the relationships between molecular ionization energies and bond energies in transition metal complexes, in understanding the electronic factors of carbon-hydrogen bond activation by transition metals, in characterizing small molecule bonding interactions with transition metals, and in investigating intermolecular interactions in thin films of transition metal complexes. The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies was developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. The relationship was used to clarify the fundamental thermodynamic information relating to metal-hydrogen, metal-alkyl, and metal-metal bond energies. The ionization energies were also used to correlate the rates of carbonyl substitution reactions of (eta(sup 5)-C5H4X)Rh(CO)2 complexes, and to reveal the factors that control the stability of the transition state. The investigations of the fundamental interactions of C-H sigma and sigma* orbitals metals were continued with study of eta(sup 3)-1-methylallyl metal complexes. Direct observation and measurement of the stabilization energy provided by the agostic interaction of the C-H bond with the metal was obtained. The ability to observe the electronic effects of intermolecular interactions by comparing the ionizations of metal complexes in the gas phase with the ionizations of thin solid organometallic films prepared in ultra-high vacuum was established. Most significantly, the scanning tunneling microscope imaging of these thin films was accomplished.

Synthesis, characterization, single crystal X-ray determination, fluorescence and electrochemical studies of new dinuclear nickel(II) and oxovanadium(IV) complexes containing double Schiff base ligands

NASA Astrophysics Data System (ADS)

Shafaatian, Bita; Ozbakzaei, Zahra; Notash, Behrouz; Rezvani, S. Ahmad

2015-04-01

A series of new bimetallic complexes of nickel(II) and vanadium(IV) have been synthesized by the reaction of the new double bidentate Schiff base ligands with nickel acetate and vanadyl acetylacetonate in 1:1 M ratio. In nickel and also vanadyl complexes the ligands were coordinated to the metals via the imine N and enolic O atoms. The complexes have been found to possess 1:1 metals to ligands stoichiometry and the molar conductance data revealed that the metal complexes were non-electrolytes. The nickel and vanadyl complexes exhibited distorted square planar and square pyramidal coordination geometries, respectively. The emission spectra of the ligands and their complexes were studied in methanol. Electrochemical properties of the ligands and their metal complexes were also investigated in DMSO solvent at 150 mV s-1 scan rate. The ligands and metal complexes showed both quasi-reversible and irreversible processes at this scan rate. The Schiff bases and their complexes have been characterized by FT-IR, 1H NMR, UV/Vis spectroscopies, elemental analysis and conductometry. The crystal structure of the nickel complex has been determined by single crystal X-ray diffraction.

Factors that control catalytic two- versus four-electron reduction of dioxygen by copper complexes.

PubMed

Fukuzumi, Shunichi; Tahsini, Laleh; Lee, Yong-Min; Ohkubo, Kei; Nam, Wonwoo; Karlin, Kenneth D

2012-04-25

The selective two-electron reduction of O(2) by one-electron reductants such as decamethylferrocene (Fc*) and octamethylferrocene (Me(8)Fc) is efficiently catalyzed by a binuclear Cu(II) complex [Cu(II)(2)(LO)(OH)](2+) (D1) {LO is a binucleating ligand with copper-bridging phenolate moiety} in the presence of trifluoroacetic acid (HOTF) in acetone. The protonation of the hydroxide group of [Cu(II)(2)(LO)(OH)](2+) with HOTF to produce [Cu(II)(2)(LO)(OTF)](2+) (D1-OTF) makes it possible for this to be reduced by 2 equiv of Fc* via a two-step electron-transfer sequence. Reactions of the fully reduced complex [Cu(I)(2)(LO)](+) (D3) with O(2) in the presence of HOTF led to the low-temperature detection of the absorption spectra due to the peroxo complex [Cu(II)(2)(LO)(OO)] (D) and the protonated hydroperoxo complex [Cu(II)(2)(LO)(OOH)](2+) (D4). No further Fc* reduction of D4 occurs, and it is instead further protonated by HOTF to yield H(2)O(2) accompanied by regeneration of [Cu(II)(2)(LO)(OTF)](2+) (D1-OTF), thus completing the catalytic cycle for the two-electron reduction of O(2) by Fc*. Kinetic studies on the formation of Fc*(+) under catalytic conditions as well as for separate examination of the electron transfer from Fc* to D1-OTF reveal there are two important reaction pathways operating. One is a rate-determining second reduction of D1-OTF, thus electron transfer from Fc* to a mixed-valent intermediate [Cu(II)Cu(I)(LO)](2+) (D2), which leads to [Cu(I)(2)(LO)](+) that is coupled with O(2) binding to produce [Cu(II)(2)(LO)(OO)](+) (D). The other involves direct reaction of O(2) with the mixed-valent compound D2 followed by rapid Fc* reduction of a putative superoxo-dicopper(II) species thus formed, producing D.

Influence of metal ions on flavonoid protection against asbestos-induced cell injury.

PubMed

Kostyuk, V A; Potapovich, A I; Vladykovskaya, E N; Korkina, L G; Afanas'ev, I B

2001-01-01

Influence of metal ions (Fe2+, Fe3+, Cu2+, Zn2+) on the protective effect of rutin, dihydroquercetin, and green tea epicatechins against in vitro asbestos-induced cell injury was studied. Metals have been found to increase the capacity of rutin and dihydroquercetin to protect peritoneal macrophages against chrysotile asbestos-induced injury. The data presented here show that this effect is due to the formation of flavonoid metal complexes, which turned out to be more effective radical scavengers than uncomplexed flavonoids. At the same time epicatechins and their metal complexes have similar antiradical properties and protective capacities against the asbestos induced injury of macrophages. Metal complexes of all flavonoids were found to be considerably more potent than parent flavonoids in protecting red blood cells against asbestos-induced injury. It was also found that the metal complexes of all flavonoids were absorbed by chrysotile asbestos fibers considerably better than uncomplexed compounds and probably for this reason flavonoid metal complexes have better protective properties against asbestos induced hemolysis. Thus, the results of the present study show that flavonoid metal complexes may be effective therapy for the inflammatory response associated with the inhalation of asbestos fiber. The advantage of their application could be the strong increase in ROS scavenging by flavonoids and finally a better cell protection under the conditions of cellular oxidative stress.

Chemical behavior of Cu, Zn, Cd, and Pb in a eutrophic reservoir: speciation and complexation capacity.

PubMed

Tonietto, Alessandra Emanuele; Lombardi, Ana Teresa; Choueri, Rodrigo Brasil; Vieira, Armando Augusto Henriques

2015-10-01

This research aimed at evaluating cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) speciation in water samples as well as determining water quality parameters (alkalinity, chlorophyll a, chloride, conductivity, dissolved organic carbon, dissolved oxygen, inorganic carbon, nitrate, pH, total suspended solids, and water temperature) in a eutrophic reservoir. This was performed through calculation of free metal ions using the chemical equilibrium software MINEQL+ 4.61, determination of labile, dissolved, and total metal concentrations via differential pulse anodic stripping voltammetry, and determination of complexed metal by the difference between the total concentration of dissolved and labile metal. Additionally, ligand complexation capacities (CC), such as the strength of the association of metals-ligands (logK'ML) and ligand concentrations (C L) were calculated via Ruzic's linearization method. Water samples were taken in winter and summer, and the results showed that for total and dissolved metals, Zn > Cu > Pb > Cd concentration. In general, higher concentrations of Cu and Zn remained complexed with the dissolved fraction, while Pb was mostly complexed with particulate materials. Chemical equilibrium modeling (MINEQL+) showed that Zn(2+) and Cd(2+) dominated the labile species, while Cu and Pb were complexed with carbonates. Zinc was a unique metal for which a direct relation between dissolved species with labile and complexed forms was obtained. The CC for ligands indicated a higher C L for Cu, followed by Pb, Zn, and Cd in decreasing amounts. Nevertheless, the strength of the association of all metals and their respective ligands was similar. Factor analysis with principal component analysis as the extraction procedure confirmed seasonal effects on water quality parameters and metal speciation. Total, dissolved, and complexed Cu and total, dissolved, complexed, and labile Pb species were all higher in winter, whereas in summer, Zn was mostly present in the complexed form. A high degree of deterioration of the reservoir was confirmed by the results of this study.

Metal–organic complexation in the marine environment

PubMed Central

Luther, George W; Rozan, Timothy F; Witter, Amy; Lewis, Brent

2001-01-01

We discuss the voltammetric methods that are used to assess metal–organic complexation in seawater. These consist of titration methods using anodic stripping voltammetry (ASV) and cathodic stripping voltammetry competitive ligand experiments (CSV-CLE). These approaches and a kinetic approach using CSV-CLE give similar information on the amount of excess ligand to metal in a sample and the conditional metal ligand stability constant for the excess ligand bound to the metal. CSV-CLE data using different ligands to measure Fe(III) organic complexes are similar. All these methods give conditional stability constants for which the side reaction coefficient for the metal can be corrected but not that for the ligand. Another approach, pseudovoltammetry, provides information on the actual metal–ligand complex(es) in a sample by doing ASV experiments where the deposition potential is varied more negatively in order to destroy the metal–ligand complex. This latter approach gives concentration information on each actual ligand bound to the metal as well as the thermodynamic stability constant of each complex in solution when compared to known metal–ligand complexes. In this case the side reaction coefficients for the metal and ligand are corrected. Thus, this method may not give identical information to the titration methods because the excess ligand in the sample may not be identical to some of the actual ligands binding the metal in the sample. PMID:16759421

Infrared Spectroscopic Analysis of Linkage Isomerism in Metal-Thiocyanate Complexes

ERIC Educational Resources Information Center

Baer, Carl; Pike, Jay

2010-01-01

We developed an experiment suitable for an advanced inorganic chemistry laboratory that utilizes a cooperative learning environment, which allows students to develop an empirical method of determining the bonding mode of a series of unknown metal-thiocyanate complexes. Students synthesize the metal-thiocyanate complexes and obtain the FT-IR…

Water-in-Supercritical CO2 Microemulsion Stabilized by a Metal Complex.

PubMed

Luo, Tian; Zhang, Jianling; Tan, Xiuniang; Liu, Chengcheng; Wu, Tianbin; Li, Wei; Sang, Xinxin; Han, Buxing; Li, Zhihong; Mo, Guang; Xing, Xueqing; Wu, Zhonghua

2016-10-17

Herein we propose for the first time the utilization of a metal complex for forming water-in-supercritical CO 2 (scCO 2 ) microemulsions. The water solubility in the metal-complex-stabilized microemulsion is significantly improved compared with the conventional water-in-scCO 2 microemulsions stabilized by hydrocarbons. Such a microemulsion provides a promising route for the in situ CO 2 reduction catalyzed by a metal complex at the water/scCO 2 interface. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparison of the toxicity of some metals and their tetracyanide complexes on the respiration of non acclimated activated sludges.

PubMed

Morozzi, G; Cenci, G

1978-12-01

The toxic effect of the metal ions of cadmium, zinc, nickel and mercury and their tetracyanide salt complexes, on the activated sludge not previously acclimated, has been studied. The evaluation of the effect was carried out using both the Warburg and TTC-method. The results obtained have shown that the toxicity of the cadmium and zinc complexes is higher than that of the corresponding metals, while the toxicity of Ni(CN)4(2-) is lower than that of the corresponding metals. No differences have been found between the effect of mercury and the corresponding tetracyanide complex. From the data obtained it appears that it is not possible to generalize about the biological effect of complexation with the CN- group, but it should be stated that, generally, there are substantial differences between metals and their cyanide complexes as far as toxicity for activated sludge is concerned.

Synthesis, spectral studies and biological evaluation of 2-aminonicotinic acid metal complexes.

PubMed

Nawaz, Muhammad; Abbasi, Muhammad Waseem; Hisaindee, Soleiman; Zaki, Muhammad Javed; Abbas, Hira Fatima; Mengting, Hu; Ahmed, M Arif

2016-05-15

We synthesized 2-aminonicotinic acid (2-ANA) complexes with metals such as Co(II), Fe(III), Ni(II), Mn(II), Zn(II), Ag(I),Cr(III), Cd(II) and Cu(II) in aqueous media. The complexes were characterized and elucidated using FT-IR, UV-Vis, a fluorescence spectrophotometer and thermo gravimetric analysis (TGA). TGA data showed that the stoichiometry of complexes was 1:2 metal/ligand except for Ag(I) and Mn(II) where the ratio was 1:1. The metal complexes showed varied antibacterial, fungicidal and nematicidal activities. The silver and zinc complexes showed highest activity against Bacillus subtilis and Bacillus licheniformis respectively. Fusarium oxysporum was highly susceptible to nickel and copper complexes whereas Macrophomina phaseolina was completely inert to the complexes. The silver and cadmium complexes were effective against the root-knot nematode Meloidogyne javanica. Copyright © 2016 Elsevier B.V. All rights reserved.

Antimalarial and antimicrobial activities of 8-Aminoquinoline-Uracils metal complexes

PubMed Central

Phopin, Kamonrat; Sinthupoom, Nujarin; Treeratanapiboon, Lertyot; Kunwittaya, Sarun; Prachayasittikul, Supaluk; Ruchirawat, Somsak; Prachayasittikul, Virapong

2016-01-01

8-Aminoquinoline (8AQ) derivatives have been reported to have antimalarial, anticancer, and antioxidant activities. This study investigated the potency of 8AQ-5-substituted (iodo and nitro) uracils metal (Mn, Cu, Ni) complexes (1-6) as antimalarial and antimicrobial agents. Interestingly, all of these metal complexes (1-6) showed fair antimalarial activities. Moreover, Cu complexes 2 (8AQ-Cu-5Iu) and 5 (8AQ-Cu-5Nu) exerted antimicrobial activities against Gram-negative bacteria including P. shigelloides and S. dysenteriae. The results reveal application of 8AQ and its metal complexes as potential compounds to be further developed as novel antimalarial and antibacterial agents. PMID:27103894

Antimalarial and antimicrobial activities of 8-Aminoquinoline-Uracils metal complexes.

PubMed

Phopin, Kamonrat; Sinthupoom, Nujarin; Treeratanapiboon, Lertyot; Kunwittaya, Sarun; Prachayasittikul, Supaluk; Ruchirawat, Somsak; Prachayasittikul, Virapong

2016-01-01

8-Aminoquinoline (8AQ) derivatives have been reported to have antimalarial, anticancer, and antioxidant activities. This study investigated the potency of 8AQ-5-substituted (iodo and nitro) uracils metal (Mn, Cu, Ni) complexes (1-6) as antimalarial and antimicrobial agents. Interestingly, all of these metal complexes (1-6) showed fair antimalarial activities. Moreover, Cu complexes 2 (8AQ-Cu-5Iu) and 5 (8AQ-Cu-5Nu) exerted antimicrobial activities against Gram-negative bacteria including P. shigelloides and S. dysenteriae. The results reveal application of 8AQ and its metal complexes as potential compounds to be further developed as novel antimalarial and antibacterial agents.

Binuclear Phthalocyanines as Model Electrocatalysts for the Reduction of Oxygen.

DTIC Science & Technology

1985-05-01

solution, in which case the final product is Co(II)Pc. Aqueous acid addition (under nitrogen) to Co(I)Pc (in DCB/OH-) yields Co(II)Pc and presumably hydrogen ...little doubt, given the tendency for Co(I) to reduce aqueous acid to hydrogen [101, that hydrogen is produced in this reaction, though it was not proven...reduction occurs in water by a 2-electron process to hydrogen peroxide or a 4-electron process to water. This latter process must be catalysed on a

The pressure tunning Raman and IR spectral studies on the multinuclear metal carbyne complexes

NASA Astrophysics Data System (ADS)

Xu, Zhenhua; Butler, Ian S.; Mayr, Andreas

2005-03-01

The Raman and infrared (IR) spectra of four tungsten metal carbyne complexes I, II, IV and V [Cl(CO) 2(L)W tbnd CC 6H 4sbnd (C tbnd CC 6H 4) nsbnd N tbnd C sbnd ] 2M (L = TMEDA, n = 0, M = PdI 2 or ReCl(CO) 3; L = DPPE, n = 1, M = PdI 2 or ReCl(CO) 3) were studied at high external pressure. Their pressure-induced phase transitions were observed near 20 kbar (complexes I), 15 kbar (complexes II), 25 kbar (complex IV) and 30 kbar (complex V). The pressure-induced phase transition likely is first order in complex I and the pressure-induced phase transitions of complexes II, IV and V are mostly second order. The pressure sensitivities d ν/d p of ν(W tbnd C) are high in the low-pressure phase area and very low in the high-pressure phase area due to the pressure strengthening π back-bonding from metal W to π * orbital of C tbnd O in fragment Cl(CO) 2(L)W tbnd C. The pressure strengthening metal π back-bonding from metal Re or Pd to π * orbital of C tbnd O or C tbnd N also happened to both of central metal centers of NCPd(I 2)CN in complex I and NCReCl(CO) 3CN in complex II.

Low frequency vibrational spectra and the nature of metal-oxygen bond of alkaline earth metal acetylacetonates

NASA Astrophysics Data System (ADS)

Fakheri, Hamideh; Tayyari, Sayyed Faramarz; Heravi, Mohammad Momen; Morsali, Ali

2017-12-01

Theoretical quantum chemistry calculations were used to assign the observed vibrational band frequencies of Be, Mg, Ca, Sr, and Ba acetylacetonates complexes. Density functional theory (DFT) calculations have been carried out at the B3LYP level, using LanL2DZ, def2SVP, and mixed, GenECP, (def2SVP for metal ions and 6-311++G** for all other atoms) basis sets. The B3LYP level, with mixed basis sets, was utilized for calculations of vibrational frequencies, IR intensity, and Raman activity. Analysis of the vibrational spectra indicates that there are several bands which could almost be assigned mainly to the metal-oxygen vibrations. The strongest Raman band in this region could be used as a measure of the stability of the complex. The effects of central metal on the bond orders and charge distributions in alkaline earth metal acetylacetonates were studied by the Natural Bond Orbital (NBO) method for fully optimized compounds. Optimization were performed at the B3LYP/6-311++G** level for the lighter alkaline earth metal complexes (Be, Mg, and Ca acetylacetonates) while the B3LYP level, using LanL2DZ (extrabasis, d and f on oxygen and metal atoms), def2SVP and mixed (def2SVP on metal ions and 6-311++G** for all other atoms) basis sets for all understudy complexes. Calculations indicate that the covalence nature of metal-oxygen bonds considerably decreases from Be to Ba complexes. The nature of metal-oxygen bond was further studied by using Atoms In Molecules (AIM) analysis. The topological parameters, Wiberg bond orders, natural charges of O and metal ions, and also some vibrational band frequencies were correlated with the stability constants of understudy complexes.

Luminescent Organometallic Nanomaterials with Aggregation-Induced Emission.

PubMed

Shu, Tong; Wang, Jianxing; Su, Lei; Zhang, Xueji

2018-07-04

Recent researches in metal nanoclusters (NCs) have prompted their promising practical applications in biomedical fields as novel inorganic luminophores. More recently, to further improve the photoluminescence (PL) performance of NCs, the aggregation-induced emission (AIE) effect has been introduced to develop highly luminescent metal NCs and metal complex materials. In this review, we start our discussion from recent progresses on AIE materials developments. Then, we address our understandings on the PL properties of thiolated metal NCs. Subsequently, we link thiolated metal NCs with AIE effect. We also highlight some recent advances in synthesizing the AIE-type metal complex nanomaterials. We finally discuss visions and directions for future development of AIE-type metal complex nanomaterials.

Allylic amination reactivity of Ni, Pd, and Pt heterobimetallic and monometallic complexes.

PubMed

Carlsen, Ryan W; Ess, Daniel H

2016-06-14

Transition metal heterobimetallic complexes with dative metal-metal interactions have the potential for novel fast reactivity. There are few studies that both compare the reactivity of different metal centers in heterobimetallic complexes and compare bimetallic reactivity to monometallic reactivity. Here we report density-functional calculations that show the reactivity of [Cl2Ti(N(t)BuPPh2)2M(II)(η(3)-methallyl)] heterobimetallic complexes for allylic amination follows M = Ni > Pd > Pt. This reactivity trend was not anticipated since the amine addition transition state involves M(II) to M(0) reduction and this could disadvantage Ni. Comparison of heterobimetallic complexes to the corresponding monometallic (CH2)2(N(t)BuPPh2)2M(II)(η(3)-methallyl) complexes reveals that this reactivity trend is due to the bimetallic interaction and that the bimetallic interaction significantly lowers the barrier height for amine addition by >10 kcal mol(-1). The impact of the early transition metal center on the amination addition barrier height depends on the late transition metal center. The lowest barrier heights for this reaction occur when late and early transition metal centers are from the same periodic table row.

Correlation between oxygen adsorption energy and electronic structure of transition metal macrocyclic complexes.

PubMed

Liu, Kexi; Lei, Yinkai; Wang, Guofeng

2013-11-28

Oxygen adsorption energy is directly relevant to the catalytic activity of electrocatalysts for oxygen reduction reaction (ORR). In this study, we established the correlation between the O2 adsorption energy and the electronic structure of transition metal macrocyclic complexes which exhibit activity for ORR. To this end, we have predicted the molecular and electronic structures of a series of transition metal macrocyclic complexes with planar N4 chelation, as well as the molecular and electronic structures for the O2 adsorption on these macrocyclic molecules, using the density functional theory calculation method. We found that the calculated adsorption energy of O2 on the transition metal macrocyclic complexes was linearly related to the average position (relative to the lowest unoccupied molecular orbital of the macrocyclic complexes) of the non-bonding d orbitals (d(z(2)), d(xy), d(xz), and d(yz)) which belong to the central transition metal atom. Importantly, our results suggest that varying the energy level of the non-bonding d orbitals through changing the central transition metal atom and/or peripheral ligand groups could be an effective way to tuning their O2 adsorption energy for enhancing the ORR activity of transition metal macrocyclic complex catalysts.

Biomedical Applications of Organometal-Peptide Conjugates

NASA Astrophysics Data System (ADS)

Metzler-Nolte, Nils

Peptides are well suited as targeting vectors for the directed delivery of metal-based drugs or probes for biomedical investigations. This chapter describes synthetic strategies for the preparation of conjugates of medically interesting peptides with covalently bound metal complexes. Peptides that were used include neuropeptides (enkephalin, neuropeptide Y, neurotensin), uptake peptides (TAT and poly-Arg), and intracellular localization sequences. To these peptides, a whole variety of transition metal complexes has been attached in recent years by solid-phase peptide synthesis (SPPS) techniques. The metal complex can be attached to the peptide on the resin as part of the SPPS scheme. Alternatively, the metal complex may be attached to the peptide as a postsynthetic modification. Advantages as well as disadvantages for either strategy are discussed. Biomedical applications include radiopharmaceutical applications, anticancer and antibacterial activity, metal-peptide conjugates as targeted CO-releasing molecules, and metal-peptide conjugates in biosensor applications.

Chemodynamics of aquatic metal complexes: from small ligands to colloids.

PubMed

Van Leeuwen, Herman P; Buffle, Jacques

2009-10-01

Recent progress in understanding the formation/dissociation kinetics of aquatic metal complexes with complexants in different size ranges is evaluated and put in perspective, with suggestions for further studies. The elementary steps in the Eigen mechanism, i.e., diffusion and dehydration of the metal ion, are reviewed and further developed. The (de)protonation of both the ligand and the coordinating metal ion is reconsidered in terms of the consequences for dehydration rates and stabilities of the various outer-sphere complexes. In the nanoparticulate size range, special attention is given to the case of fulvic ligands, for which the impact of electrostatic interactions is especially large. In complexation with colloidal ligands (hard, soft, and combination thereof) the diffusive transport of metal ions is generally a slower step than in the case of complexation with small ligands in a homogeneous solution. The ensuing consequences for the chemodynamics of colloidal complexes are discussed in detail and placed in a generic framework, encompassing the complete range of ligand sizes.

DFT study of the interaction between DOTA chelator and competitive alkali metal ions.

PubMed

Frimpong, E; Skelton, A A; Honarparvar, B

2017-09-01

1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetracetic acid (DOTA) is an important chelator for radiolabeling of pharmaceuticals. The ability of alkali metals found in the body to complex with DOTA and compete with radio metal ions can alter the radiolabeling process. Non-covalent interactions between DOTA complexed with alkali metals Li + , Na + , K + and Rb + , are investigated with density functional theory using B3LYP and ωB97XD functionals. Conformational possibilities of DOTA were explored with a varying number of carboxylic pendant arms of DOTA in close proximity to the ions. It is found that the case in which four arms of DOTA are interacting with ions is more stable than other conformations. The objective of this study is to explore the electronic structure properties upon complexation of alkali metals Li + Na + , K + and Rb + with a DOTA chelator. Interaction energies, relaxation energies, entropies, Gibbs free energies and enthalpies show that the stability of DOTA, complexed with alkali metals decreases down the group of the periodic table. Implicit water solvation affects the complexation of DOTA-ions leading to decreases in the stability of the complexes. NBO analysis through the natural population charges and the second order perturbation theory, revealed a charge transfer between DOTA and alkali metals. Conceptual DFT-based properties such as HOMO/LUMO energies, ΔE HOMO-LUMO and chemical hardness and softness indicated a decrease in the chemical stability of DOTA-alkali metal complexes down the alkali metal series. This study serves as a guide to researchers in the field of organometallic chelators, particularly, radiopharmaceuticals in finding the efficient optimal match between chelators and various metal ions. Copyright © 2017 Elsevier Inc. All rights reserved.

Spectroscopic, cyclic voltammetric and biological studies of transition metal complexes with mixed nitrogen-sulphur (NS) donor macrocyclic ligand derived from thiosemicarbazide

NASA Astrophysics Data System (ADS)

Chandra, Sulekh; Gupta, Lokesh Kumar; Sangeetika

2005-11-01

The complexation of new mixed thia-aza-oxa macrocycle viz., 2,12-dithio-5,9,14,18-tetraoxo-7,16-dithia-1,3,4,10,11,13-hexaazacyclooctadecane containing thiosemicarba-zone unit with a series of transition metals Co(II), Ni(II) and Cu(II) has been investigated, by different spectroscopic techniques. The structural features of the ligand have been studied by EI-mass, 1H NMR and IR spectral techniques. Elemental analyses, magnetic moment susceptibility, molar conductance, IR, electronic, and EPR spectral studies characterized the complexes. Electronic absorption and IR spectra of the complexes indicate octahedral geometry for chloro, nitrato, thiocyanato or acetato complexes. The dimeric and neutral nature of the sulphato complexes are confirmed from magnetic susceptibility and low conductance values. Electronic spectra suggests square-planar geometry for all sulphato complexes. The redox behaviour was studied by cyclic voltammetry, show metal-centered reduction processes for all complexes. The complexes of copper show both oxidation and reduction process. The redox potentials depend on the conformation of central atom in the macrocyclic complexes. Newly synthesized macrocyclic ligand and its transition metal complexes show markedly growth inhibitory activity against pathogenic bacterias and plant pathogenic fungi under study. Most of the complexes have higher activity than that of the metal free ligand.

Synthesis, spectroscopic, biological activity and thermal characterization of ceftazidime with transition metals

NASA Astrophysics Data System (ADS)

Masoud, Mamdouh S.; Ali, Alaa E.; Elasala, Gehan S.; Kolkaila, Sherif A.

2018-03-01

Synthesis, physicochemical characterization and thermal analysis of ceftazidime complexes with transition metals (Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)) were discussed. It's obtained that ceftazidime act as bidentate ligand. From magnetic measurement and spectral data, octahedral structures were proposed for all complexes except for cobalt, nickel and mercury had tetrahedral structural. Hyper chemistry program confirmed binding sites of ceftazidime. Ceftazidime complexes show higher activity than ceftazidime for some strains. From TG and DTA curves the thermal decomposition mechanisms of ceftazidime and their metal complexes were suggested. The thermal decomposition of the complexes ended with the formation of metal oxides as a final product except in case of Hg complex.

Functional microporous materials of metal carboxylate: Gas-occlusion properties and catalytic activities

NASA Astrophysics Data System (ADS)

Mori, Wasuke; Sato, Tomohiko; Ohmura, Tesushi; Nozaki Kato, Chika; Takei, Tohru

2005-08-01

Copper(II) terephthalate is the first transition metal complex found capable of adsorbing gases. This complex has opened the new field of adsorbent complex chemistry. It is recognized as the lead complex in the construction of microporous complexes. This specific system has been expanded to a systematic series of derivatives of other isomorphous transition metals, molybdenum(II), ruthenium(II, III), and rhodium(II). These complexes with open frameworks are widely recognized as very useful materials for applications to catalysis, separation at molecular level, and gas storage.

A Stable, Narrow-Gap Oxyfluoride Photocatalyst for Visible-Light Hydrogen Evolution and Carbon Dioxide Reduction.

PubMed

Kuriki, Ryo; Ichibha, Tom; Hongo, Kenta; Lu, Daling; Maezono, Ryo; Kageyama, Hiroshi; Ishitani, Osamu; Oka, Kengo; Maeda, Kazuhiko

2018-05-30

Mixed anion compounds such as oxynitrides and oxychalcogenides are recognized as potential candidates of visible-light-driven photocatalysts since, as compared with oxygen 2p orbitals, p orbitals of less electronegative anion (e.g., N 3- , S 2- ) can form a valence band that has more negative potential. In this regard, oxyfluorides appear unsuitable because of the higher electronegativity of fluorine. Here we show an exceptional case, an anion-ordered pyrochlore oxyfluoride Pb 2 Ti 2 O 5.4 F 1.2 that has a small band gap (ca. 2.4 eV). With suitable modification of Pb 2 Ti 2 O 5.4 F 1.2 by promoters such as platinum nanoparticles and a binuclear ruthenium(II) complex, Pb 2 Ti 2 O 5.4 F 1.2 worked as a stable photocatalyst for visible-light-driven H 2 evolution and CO 2 reduction. Density functional theory calculations have revealed that the unprecedented visible-light-response of Pb 2 Ti 2 O 5.4 F 1.2 arises from strong interaction between Pb-6s and O-2p orbitals, which is enabled by a short Pb-O bond in the pyrochlore lattice due to the fluorine substitution.

Binding of [alpha, alpha]-Disubstituted Amino Acids to Arginase Suggests New Avenues for Inhibitor Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilies, Monica; Di Costanzo, Luigi; Dowling, Daniel P.

Arginase is a binuclear manganese metalloenzyme that hydrolyzes L-arginine to form L-ornithine and urea, and aberrant arginase activity is implicated in various diseases such as erectile dysfunction, asthma, atherosclerosis, and cerebral malaria. Accordingly, arginase inhibitors may be therapeutically useful. Continuing our efforts to expand the chemical space of arginase inhibitor design and inspired by the binding of 2-(difluoromethyl)-L-ornithine to human arginase I, we now report the first study of the binding of {alpha},{alpha}-disubstituted amino acids to arginase. Specifically, we report the design, synthesis, and assay of racemic 2-amino-6-borono-2-methylhexanoic acid and racemic 2-amino-6-borono-2-(difluoromethyl)hexanoic acid. X-ray crystal structures of human arginase Imore » and Plasmodium falciparum arginase complexed with these inhibitors reveal the exclusive binding of the L-stereoisomer; the additional {alpha}-substituent of each inhibitor is readily accommodated and makes new intermolecular interactions in the outer active site of each enzyme. Therefore, this work highlights a new region of the protein surface that can be targeted for additional affinity interactions, as well as the first comparative structural insights on inhibitor discrimination between a human and a parasitic arginase.« less

Trace Metal-Humic Complexes in Natural Waters: Insights From Speciation Experiments

NASA Astrophysics Data System (ADS)

Stern, J. C.; Salters, V.; Sonke, J.

2006-12-01

The DOM cycle is intimately linked to the cycling and bioavailability of trace metals in aqueous environments. The presence or absence of DOM in the water column can determined whether trace elements will be present in limited quantities as a nutrient, or in surplus quantities as a toxicant. Humic substances (HS), which represent the refractory products of DOM degradation, strongly affect the speciation of trace metals in natural waters. To simulate metal-HS interactions in nature, experiments must be carried out using trace metal concentrations. Sensitive detection systems such as ICP-MS make working with small (nanomolar) concentrations possible. Capillary electrophoresis coupled with ICP-MS (CE-ICP-MS) has recently been identified as a rapid and accurate method to separate metal species and calculate conditional binding constants (log K_c) of metal-humic complexes. CE-ICP-MS was used to measure partitioning of metals between humic substances and a competing ligand (EDTA) and calculate binding constants of rare earth element (REE) and Th, Hf, and Zr-humic complexes at pH 3.5-8 and ionic strength of 0.1. Equilibrium dialysis ligand exchange (EDLE) experiments to validate the CE-ICP-MS method were performed to separate the metal-HS and metal-EDTA species by partitioning due to size exclusion via diffusion through a 1000 Da membrane. CE-ICP-MS experiments were also conducted to compare binding constants of REE with humic substances of various origin, including soil, peat, and aquatic DOM. Results of our experiments show an increase in log K_c with decrease in ionic radius for REE-humic complexes (the lanthanide contraction effect). Conditional binding constants of tetravalent metal-humic complexes were found to be several orders of magnitude higher than REE-humic complexes, indicating that tetravalent metals have a very strong affinity for humic substances. Because thorium is often used as a proxy for the tetravalent actinides, Th-HS binding constants can allow us to assess the importance of tetravalent actinide-humic complexes in groundwater transport from nuclear repositories. Our results suggest that tetravalent actinide-humic complexes couild be more important to account for in predictive speciation models than previously thought.

Preservation of NOM-metal complexes in a modern hyperalkaline stalagmite: Implications for speleothem trace element geochemistry

NASA Astrophysics Data System (ADS)

Hartland, Adam; Fairchild, Ian J.; Müller, Wolfgang; Dominguez-Villar, David

2014-03-01

We report the first quantitative study of the capture of colloidal natural organic matter (NOM) and NOM-complexed trace metals (V, Co, Cu, Ni) in speleothems. This study combines published NOM-metal dripwater speciation measurements with high-resolution laser ablation ICPMS (LA-ICPMS) and sub-annual stable isotope ratio (δ18O and δ13C), fluorescence and total organic carbon (TOC) analyses of a fast-growing hyperalkaline stalagmite (pH ˜11) from Poole’s Cavern, Derbyshire UK, which formed between 1997 and 2008 AD. We suggest that the findings reported here elucidate trace element variations arising from colloidal transport and calcite precipitation rate changes observed in multiple, natural speleothems deposited at ca. pH 7-8. We find that NOM-metal(aq) complexes on the boundary between colloidal and dissolved (˜1 nm diameter) show an annual cyclicity which is inversely correlated with the alkaline earth metals and is explained by calcite precipitation rate changes (as recorded by kinetically-fractionated stable isotopes). This relates to the strength of the NOM-metal complexation reaction, resulting in very strongly bound metals (Co in this system) essentially recording NOM co-precipitation (ternary complexation). More specifically, empirical partition coefficient (Kd) values between surface-reactive metals (V, Co, Cu, Ni) [expressed as ratio of trace element to Ca ratios in calcite and in solution] arise from variations in the ‘free’ fraction of total metal in aqueous solution (fm). Hence, differences in the preservation of each metal in calcite can be explained quantitatively by their complexation behaviour with aqueous NOM. Differences between inorganic Kd values and field measurements for metal partitioning into calcite occur where [free metal] ≪ [total metal] due to complexation reactions between metals and organic ligands (and potentially inorganic colloids). It follows that where fm ≈ 0, apparent inorganic Kd app values are also ≈0, but the true partition coefficient (Kd actual) is significantly higher. Importantly, the Kd of NOM-metal complexes [organic carbon-metal ratio) approaches 1 for the most stable aqueous complexes, as is shown here for Co, but has values of 24-150 for V, Ni and Cu. This implies that ternary surface complexation (metal-ligand co-adsorption) can occur (as for NOM-Co), but is the exception rather than the rule. We also demonstrate the potential for trace metals to record information on NOM composition as expressed through changing NOM-metal complexation patterns in dripwaters. Therefore, a suite of trace metals in stalagmites show variations clearly attributable to changes in organic ligand concentration and composition, and which potentially reflect the state of overlying surface ecosystems. The heterogeneous speciation and size distribution of aqueous NOM and metals (Lead and Wilkinson, 2006; Aiken et al., 2011). The variability in NOM-metal transport in caves that arises from the interaction between infiltration, flow routing, and the hydrodynamic properties of the fine colloids and particulates (Hartland et al., 2012). Variable dissociation kinetics through time as a function of (a) (Hartland et al., 2011). The surface charge of calcite and the availability of CaCO3 lattice sites as well as increased incidence of crystallographic defects with implications for incorporation of a range of trace species (Fairchild and Treble, 2009; Fairchild and Hartland, 2010). Thus, incorporation in speleothem calcite with consistent surface site properties will be determined by: The size and composition (i.e. hydrophilicity/hydrophobicity) of the NOM ligand, affecting adsorption and stability at the calcite surface. The lability (i.e. exchangeability) of the complexed metal and its binding affinity for the calcite surface. The concentration of aqueous complexes. Given the complexities, a partitioning approach to the problem is appropriate as a first approximation rather than a precise description. This study seeks to make the first quantitative connection between the organic and inorganic compositions of speleothems and thus determine the potential for speleothems to encode fluctuations in colloid-facilitated trace metal transport in karst aquifers. Recent findings of direct relevance to the present studyThe conjugate dripwater (PE1) to the stalagmite studied here (PC-08-1) was characterised in June 2009 using an array of complementary techniques, in which the size, speciation and lability of NOM-metal complexes was characterised (Hartland et al., 2011), where lability is defined as the capacity for complexes to dissociate in the context of the on-going interfacial process at the stalagmite surface. In PE1 dripwater, the most stable aqueous complexes were formed between Co and the finest, low molecular weight component of the NOM spectrum (Hartland et al., 2011). Speciation experiments demonstrated that Co was essentially non-exchangeable (free metal (fm) = <0.05), being retained in aqueous complexes, whilst Cu, Ni and V were all predominantly bound by NOM (fm = 0.2-0.3).In contrast, Sr and Ba were freely exchangeable between the solution and solid phase (Hartland et al., 2011) and Mg was absent, presumably due to the poor solubility of Mg(OH)2 at hyperalkaline pH (Ksp = 1.5 × 10-11): Mg2+(aq)+2OH-(aq)↔Mg( On the other hand, the transition metals were not lost as insoluble hydroxides (Hartland et al., 2012), despite having lower solubility than Mg (e.g. Cu(OH)2Ksp = 2.2 × 10-20); and this is consistent with the dominant role of NOM in solubilising and transporting the transition metals in this system (Hartland et al., 2011).The transport of metals by complexes with NOM in PE1 dripwater through the hydrological year was studied by Hartland et al. (2012). This study had two findings of direct relevance to the study of trace metal variations in the conjugate PC-08-1 stalagmite: Complexes between metals and the smallest, low-molecular weight fraction of NOM showed an attenuated delivery in dripwaters consistent with the non-conservative behaviour of analogous tracers in fractured-rock studies due to diffusion into micro-fractures. This mode of transport was termed ‘low-flux’ and was the dominant mode of transport for Co and V. Complexes between metals and coarse colloids (>100 nm) and particulates (>1000 nm) showed a rapid responsiveness to infiltration events. This was termed the ‘high-flux’ mode of NOM-metal transport and was interpreted as being dominantly fracture-fed. This mode of transport was dominated by Cu, Zn and Ni. The ‘high-flux’ vs ‘low-flux’ interplay of trace metal transport is summarised in Fig. 1.The PC-08-1 stalagmite studied here was deposited following the removal of stalagmite PC-97-1 studied by Baker et al. (1999b) and which grew under the PE1 drip point between 1927 and 1997. Both the PC-97-1 stalagmite and its regrowth (PC-08-1) are characterised by annual lamina couplets consisting of a porous pale layer and a dense fluorescent layer. Fluorescence in the PC-97-1 stalagmite displayed a marked sinusoidal pattern with 10% of laminae exhibiting a double band structure (Baker et al., 1999b).

Formation of metal-nicotianamine complexes as affected by pH, ligand exchange with citrate and metal exchange. A study by electrospray ionization time-of-flight mass spectrometry.

PubMed

Rellán-Alvarez, Rubén; Abadía, Javier; Alvarez-Fernández, Ana

2008-05-01

Nicotianamine (NA) is considered as a key element in plant metal homeostasis. This non-proteinogenic amino acid has an optimal structure for chelation of metal ions, with six functional groups that allow octahedral coordination. The ability to chelate metals by NA is largely dependent on the pK of the resulting complex and the pH of the solution, with most metals being chelated at neutral or basic pH values. In silico calculations using pKa and pK values have predicted the occurrence of metal-NA complexes in plant fluids, but the use of soft ionization techniques (e.g. electrospray), together with high-resolution mass spectrometers (e.g. time-of-flight mass detector), can offer direct and metal-specific information on the speciation of NA in solution. We have used direct infusion electrospray ionization mass spectrometry (time-of-flight) ESI-MS(TOF) to study the complexation of Mn, Fe(II), Fe(III), Ni, Cu by NA. The pH dependence of the metal-NA complexes in ESI-MS was compared to that predicted in silico. Possible exchange reactions that may occur between Fe-NA and other metal micronutrients as Zn and Cu, as well as between Fe-NA and citrate, another possible Fe ligand candidate in plants, were studied at pH 5.5 and 7.5, values typical of the plant xylem and phloem saps. Metal-NA complexes were generally observed in the ESI-MS experiments at a pH value approximately 1-2 units lower than that predicted in silico, and this difference could be only partially explained by the estimated error, approximately 0.3 pH units, associated with measuring pH in organic solvent-containing solutions. Iron-NA complexes are less likely to participate in ligand- and metal-exchange reactions at pH 7.5 than at pH 5.5. Results support that NA may be the ligand chelating Fe at pH values usually found in phloem sap, whereas in the xylem sap NA is not likely to be involved in Fe transport, conversely to what occurs with other metals such as Cu and Ni. Some considerations that need to be addressed when studying metal complexes in plant compartments by ESI-MS are also discussed.

Co(II) and Cd(II) Complexes Derived from Heterocyclic Schiff-Bases: Synthesis, Structural Characterisation, and Biological Activity

PubMed Central

Ahmed, Riyadh M.; Yousif, Enaam I.; Al-Jeboori, Mohamad J.

2013-01-01

New monomeric cobalt and cadmium complexes with Schiff-bases, namely, N′-[(E)-(3-hydroxy-4-methoxyphenyl)methylidene]furan-2-carbohydrazide (L1) and N′-[(E)-(3-hydroxy-4-methoxyphenyl)methylidene]thiophene-2-carbohydrazide (L2) are reported. Schiff-base ligands L1 and L2 were derived from condensation of 3-hydroxy-4-methoxybenzaldehyde (iso-vanillin) with furan-2-carboxylic acid hydrazide and thiophene-2-carboxylic acid hydrazide, respectively. Complexes of the general formula [M(L)2]Cl2 (where M = Co(II) or Cd(II), L = L1 or L2) have been obtained from the reaction of the corresponding metal chloride with the ligands. The ligands and their metal complexes were characterised by spectroscopic methods (FTIR, UV-Vis, 1H, and 13C NMR spectra), elemental analysis, metal content, magnetic measurement, and conductance. These studies revealed the formation of four-coordinate complexes in which the geometry about metal ion is tetrahedral. Biological activity of the ligands and their metal complexes against gram positive bacterial strain Bacillus (G+) and gram negative bacteria Pseudomonas (G−) revealed that the metal complexes become less resistive to the microbial activities as compared to the free ligands. PMID:24027449

Influence of Humic Acid Complexation with Metal Ions on Extracellular Electron Transfer Activity.

PubMed

Zhou, Shungui; Chen, Shanshan; Yuan, Yong; Lu, Qin

2015-11-23

Humic acids (HAs) can act as electron shuttles and mediate biogeochemical cycles, thereby influencing the transformation of nutrients and environmental pollutants. HAs commonly complex with metals in the environment, but few studies have focused on how these metals affect the roles of HAs in extracellular electron transfer (EET). In this study, HA-metal (HA-M) complexes (HA-Fe, HA-Cu, and HA-Al) were prepared and characterized. The electron shuttle capacities of HA-M complexes were experimentally evaluated through microbial Fe(III) reduction, biocurrent generation, and microbial azoreduction. The results show that the electron shuttle capacities of HAs were enhanced after complexation with Fe but were weakened when using Cu or Al. Density functional theory calculations were performed to explore the structural geometry of the HA-M complexes and revealed the best binding sites of the HAs to metals and the varied charge transfer rate constants (k). The EET activity of the HA-M complexes were in the order HA-Fe > HA-Cu > HA-Al. These findings have important implications for biogeochemical redox processes given the ubiquitous nature of both HAs and various metals in the environment.

Parametrization of a force field for metals complexed to biomacromolecules: applications to Fe(II), Cu(II) and Pb(II)

NASA Astrophysics Data System (ADS)

David, Laurent; Amara, Patricia; Field, Martin J.; Major, François

2002-08-01

Although techniques for the simulation of biomolecules, such as proteins and RNAs, have greatly advanced in the last decade, modeling complexes of biomolecules with metal ions remains problematic. Precise calculations can be done with quantum mechanical methods but these are prohibitive for systems the size of macromolecules. More qualitative modeling can be done with molecular mechanical potentials but the parametrization of force fields for metals is often difficult, particularly if the bonding between the metal and the groups in its coordination shell has significant covalent character. In this paper we present a method for deriving bond and bond-angle parameters for metal complexes from experimental bond and bond-angle distributions obtained from the Cambridge Structural Database. In conjunction with this method, we also introduce a non-standard energy term of gaussian form that allows us to obtain a stable description of the coordination about a metal center during a simulation. The method was evaluated on Fe(II)-porphyrin complexes, on simple Cu(II) ion complexes and a number of complexes of the Pb(II) ion.

Effect of the metal environment on the ferromagnetic interaction in the Co-NC-W pairs of octacyanotungstate(V)-Cobalt(II) three-dimensional networks.

PubMed

Clima, Sergiu; Hendrickx, Marc F A; Chibotaru, Liviu F; Soncini, Alessandro; Mironov, Vladimir; Ceulemans, Arnout

2007-04-02

State of the art CASSCF and CASPT2 calculations have been performed to elucidate the nature of ferromagnetism of CoII-NC-WV pairs in the three-dimensional compound [[WV(CN)2]2[(micro-CN)4CoII(H2O)2]3.4H2O]n, which has been recently synthesized and investigated by a number of experimental techniques (Herrera, J. M.; Bleuzen, A.; Dromzée, Y.; Julve, M.; Lloret, F.; Verdaguer, M. Inorg. Chem. 2003, 42, 7052-7059). In this network, the Co ions are in the high-spin (S = 3/2) state, while the single unpaired electron on the W centers occupies the lowest orbital of the dz2 type of the 5d shell. In agreement with the suggestion made by Herrera et al., we find that the ferromagnetism is due to a certain occupation scheme of the orbitals from the parent octahedral t2g shell on CoII sites, in which the orbital accommodating the unpaired electron is orthogonal to the dz2 orbitals of the surrounding W ions. We investigate the stabilization of such an orbital configuration on the Co sites and find that it cannot be achieved in the ground state of isolated mononuclear fragments [CoII(NC)4(OH2)2]2- for any conformations of the coordinated water molecules and Co-N-C bond angles. On the other hand, it is stabilized by the interaction of the complex with neighboring W ions, which are simulated here by effective potentials. The calculated exchange coupling constants for the CoII-NC-WV binuclear fragments are in reasonable agreement with the measured Curie-Weiss constant for this compound. As additional evidence for the inferred electronic configuration on the Co sites, the ligand-field transitions, the temperature-dependent magnetic susceptibility, and the field-dependent low-temperature magnetization, simulated ab initio for the mononuclear Co fragments, are in agreement with the available data for another compound [WIV[(micro-CN)4-CoII(H2O)2]2.4H2O]n containing diamagnetic W and high-spin Co ions in an isostructural environment.

Schiff bases in medicinal chemistry: a patent review (2010-2015).

PubMed

Hameed, Abdul; Al-Rashida, Mariya; Uroos, Maliha; Abid Ali, Syed; Khan, Khalid Mohammed

2017-01-01

Schiff bases are synthetically accessible and structurally diverse compounds, typically obtained by facile condensation between an aldehyde, or a ketone with primary amines. Schiff bases contain an azomethine (-C = N-) linkage that stitches together two or more biologically active aromatic/heterocyclic scaffolds to form various molecular hybrids with interesting biological properties. Schiff bases are versatile metal complexing agents and have been known to coordinate all metals to form stable metal complexes with vast therapeutic applications. Areas covered: This review aims to provide a comprehensive overview of the various patented therapeutic applications of Schiff bases and their metal complexes from 2010 to 2015. Expert opinion: Schiff bases are a popular class of compounds with interesting biological properties. Schiff bases are also versatile metal complexing ligands and have been used to coordinate almost all d-block metals as well as lanthanides. Therapeutically, Schiff bases and their metal complexes have been reported to exhibit a wide range of biological activities such as antibacterial including antimycobacterial, antifungal, antiviral, antimalarial, antiinflammatory, antioxidant, pesticidal, cytotoxic, enzyme inhibitory, and anticancer including DNA damage.

Water-soluble polymers for recovery of metal ions from aqueous streams

DOEpatents

Smith, Barbara F.; Robison, Thomas W.

1998-01-01

A process of selectively separating a target metal contained in an aqueous solution by contacting the aqueous solution containing a target metal with an aqueous solution including a water-soluble polymer capable of binding with the target metal for sufficient time whereby a water-soluble polymer-target metal complex is formed, and, separating the solution including the water-soluble polymer-target metal complex from the solution is disclosed.

Labile Pd-sulphur and Pt-sulphur bonds in organometallic palladium and platinum complexes [(COD)M(alkyl)(S-ligand)]n+-A speciation study.

PubMed

Lingen, Verena; Lüning, Anna; Krest, Alexander; Deacon, Glen B; Schur, Julia; Ott, Ingo; Pantenburg, Ingo; Meyer, Gerd; Klein, Axel

2016-12-01

Reaction of various sulphur ligands L (SEt - , SPh - , SC 6 F 4 H-4 - , SEt 2 , StBu 2 , SnBu 2 , DMSO, DPSO) with the precursors [(COD)M(R)Cl] (COD=1,5-cyclooctadiene, M=Pd or Pt; R=methyl (Me) or benzyl (Bn); DMSO=dimethyl sulfoxide; DPSO=diphenyl sulfoxide) allowed isolation and characterisation of mononuclear neutral (n=0) or cationic (n=1) complexes [(COD)Pt(R)(L)] n+ . Reaction of l-cysteine (HCys) with [(COD)Pt(Me)Cl] under similar conditions gave the binuclear cationic complex in [{(COD)Pt(Me)} 2 (μ-Cys)]Cl. Detailed NMR spectroscopy and single crystal X-ray diffraction in the case of [(COD)Pt(Me)(SEt 2 )][SbF 6 ] and [(COD)Pt(Me)(DMSO)][SbF 6 ] reveal markedly labilised Pt-S bonds as a consequence of the highly covalent Pt-C bonds of the R coligands in these organometallic species. Cationic charge (n=1) seems to lower the Pt-S bond strength further. Consequently, most of these complexes are not stable long-term in aqueous DMF (N,N-dimethylformamide) solutions. This made the evaluation of their antiproliferative properties towards HT-29 colon carcinoma and MCF-7 breast adenocarcinoma cell lines impossible. Only the two complexes [(COD)Pt(R)(SC 6 F 4 H-4)] with R=Me or SC 6 F 4 H-4 coligands could be tested with the R=Me complex showing promising activity (in the range of cisplatin), while the R=SC 6 F 4 H-4 derivative is largely inactive, as were the phosphane complexes [(dppe)Pt(SC 6 F 4 H-4) 2 ] (dppe=1,2-bis(diphenylphosphino)ethane), cis-[(PPh 3 ) 2 Pt(SC 6 F 4 H-4) 2 ] and cis-[(PPh 3 ) 2 PtCl 2 ] which were tested for comparison. In turn, our findings might pave the way to new Pt anti-cancer drugs with largely reduced unwanted depletion of incorporated drugs and reduced side-effects from binding to S-containing biomolecules. Copyright © 2016 Elsevier Inc. All rights reserved.

Diverse roles of hydrogen in rhenium carbonyl chemistry: hydrides, dihydrogen complexes, and a formyl derivative.

PubMed

Li, Nan; Xie, Yaoming; King, R Bruce; Schaefer, Henry F

2010-11-04

Rhenium carbonyl hydride chemistry dates back to the 1959 synthesis of HRe(CO)₅ by Hieber and Braun. The binuclear H₂Re₂(CO)₈ was subsequently synthesized as a stable compound with a central Re₂(μ-H)₂ unit analogous to the B₂(μ-H)₂ unit in diborane. The complete series of HRe(CO)(n) (n = 5, 4, 3) and H₂Re₂(CO)(n) (n = 9, 8, 7, 6) derivatives have now been investigated by density functional theory. In contrast to the corresponding manganese derivatives, all of the triplet rhenium structures are found to lie at relatively high energies compared with the corresponding singlet structures consistent with the higher ligand field splitting of rhenium relative to manganese. The lowest energy HRe(CO)₅ structure is the expected octahedral structure. Low-energy structures for HRe(CO)(n) (n = 4, 3) are singlet structures derived from the octahedral HRe(CO)₅ structure by removal of one or two carbonyl groups. For H₂Re₂(CO)₉ a structure HRe₂(CO)₉(μ-H), with one terminal and one bridging hydrogen atom, lies within 3 kcal/mol of the structure Re₂(CO)₉(η²-H₂), similar to that of Re₂(CO)₁₀. For H₂Re₂(CO)(n) (n = 8, 7, 6) the only low-energy structures are doubly bridged singlet Re₂(μ-H)₂(CO)(n) structures. Higher energy dihydrogen complex structures are also found.

[Dinitrosyl iron complexes with glutathione recover rats with experimental endometriosis].

PubMed

Adamian, L V; Burgova, E N; Tkachev, N A; Mikoian, V D; Stepanian, A A; Sonova, M M; Vanin, A F

2013-01-01

The effect of binuclear dinitrosyl iron complexes (DNIC) with glutathione on endometrioid tumors in rats with experimental endometriosis has been studied. The latter was induced by an autotransplantation model, where two fragments of endometrium with myometrium (2 x 2 mm) from the left uterine horn was grafted to the inner surface of the anterior abdominal wall. The test animals received intraperitoneal injections of 0.5 ml DNIC-glutathione at the dose of 12.5 micromole per kg daily for 12 days 28 days after operation. The injections resulted in more than a 2-fold decrease in the total volume of both large tumors formed from grafts and small additive tumors formed nearby grafts. The disappearance of the additive tumors was also observed in test animals. The EPR signal with g(av) = 2.03 characteristic of protein bound DNIC with thiol-containing ligands was recorded in livers, graft and additive tumors of test and control animals pointing out intensive generation of nitric oxide in rats with experimental endometriosis. Ribonucleotide reductase activation discovered by doublet the EPR signal at g = 2.0 with 2.3 mT hyperfine structure splitting was found in small tumors. The cytotoxic effect of DNIC-glutathione on endometrioid tumors was suggested to be due to DNIC degradation nearby the tumors induced by iron chelating compounds released from the tumors. The degradation resulted in release of a high amount of nitric oxide molecules and nitrosonium ions from DNICs affecting the tumors by way of the cytotoxic effect.

Highly versatile heteroditopic ligand scaffolds for accommodating group 8, 9 & 11 heterobimetallic complexes.

PubMed

Gatus, Mark R D; Bhadbhade, Mohan; Messerle, Barbara A

2017-10-24

Two highly versatile xanthene scaffolds containing pairs of heteroditopic ligands were found to be capable of accommodating a range of transition metal ions, including Au(i), Ir(i), Ir(iii), Rh(i), and Ru(ii) to generate an array of heterobimetallic complexes. The metal complexes were fully characterised and proved to be stable in the solid and solution state, with no observed metal-metal scrambling. Heterobimetallic complexes containing the Rh(i)/Ir(i) combinations were tested as catalysts for the two-step dihydroalkoxylation reaction of alkynediols and sequential hydroamination/hydrosilylation reaction of alkynamines.

Charge-separated and molecular heterobimetallic rare earth-rare earth and alkaline earth-rare earth aryloxo complexes featuring intramolecular metal-pi-arene interactions.

PubMed

Deacon, Glen B; Junk, Peter C; Moxey, Graeme J; Ruhlandt-Senge, Karin; St Prix, Courtney; Zuniga, Maria F

2009-01-01

Treatment of a rare earth metal (Ln) and a potential divalent rare earth metal (Ln') or an alkaline earth metal (Ae) with 2,6-diphenylphenol (HOdpp) at elevated temperatures (200-250 degrees C) afforded heterobimetallic aryloxo complexes, which were structurally characterised. A charge-separated species [(Ln'/Ae)(2)(Odpp)(3)][Ln(Odpp)(4)] was obtained for a range of metals, demonstrating the similarities between the chemistry of the divalent rare earth metals and the alkaline earth metals. The [(Ln'/Ae)(2)(Odpp)(3)](+) cation in the heterobimetallic structures is unusual in that it consists solely of bridging aryloxide ligands. A molecular heterobimetallic species [AeEu(Odpp)(4)] (Ae = Ca, Sr, Ba) was obtained by treating an alkaline earth metal and Eu metal with HOdpp at elevated temperatures. Similarly, [BaSr(Odpp)(4)] was prepared by treating Ba metal and Sr metal with HOdpp. Treatment of [Ba(2)(Odpp)(4)] with [Mg(Odpp)(2)(thf)(2)] in toluene afforded [Ba(2)(Odpp)(3)][Mg(Odpp)(3)(thf)]. Analogous solution-based syntheses were not possible for [(Ln'/Ae)(2)(Odpp)(3)][Ln(Odpp)(4)] complexes, for which the free-metal route was essential. As a result of the absence of additional donor ligands, the crystal structures of the heterobimetallic complexes feature extensive pi-Ph-metal interactions involving the pendant phenyl groups of the Odpp ligands, thus enabling the large electropositive metal atoms to attain coordination saturation. The charge-separated heterobimetallic species were purified by extraction with toluene/thf mixtures at ambient temperature (Ba-containing compounds) or by extraction with toluene under pressure above the boiling point of the solvent (other products). In donor solvents, heterobimetallic complexes other than those containing barium were found to fragment into homometallic species.

Spectro Analytical, Computational and In Vitro Biological Studies of Novel Substituted Quinolone Hydrazone and it's Metal Complexes.

PubMed

Nagula, Narsimha; Kunche, Sudeepa; Jaheer, Mohmed; Mudavath, Ravi; Sivan, Sreekanth; Ch, Sarala Devi

2018-01-01

Some novel transition metal [Cu (II), Ni (II) and Co (II)] complexes of nalidixic acid hydrazone have been prepared and characterized by employing spectro-analytical techniques viz: elemental analysis, 1 H-NMR, Mass, UV-Vis, IR, TGA-DTA, SEM-EDX, ESR and Spectrophotometry studies. The HyperChem 7.5 software was used for geometry optimization of title compound in its molecular and ionic forms. Quantum mechanical parameters, contour maps of highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) and corresponding binding energy values were computed using semi empirical single point PM3 method. The stoichiometric equilibrium studies of metal complexes carried out spectrophotometrically using Job's continuous variation and mole ratio methods inferred formation of 1:2 (ML 2 ) metal complexes in respective systems. The title compound and its metal complexes screened for antibacterial and antifungal properties, exemplified improved activity in metal complexes. The studies of nuclease activity for the cleavage of CT- DNA and MTT assay for in vitro cytotoxic properties involving metal complexes exhibited high activity. In addition, the DNA binding properties of Cu (II), Ni (II) and Co (II) complexes investigated by electronic absorption and fluorescence measurements revealed their good binding ability and commended agreement of K b values obtained from both the techniques. Molecular docking studies were also performed to find the binding affinity of synthesized compounds with DNA (PDB ID: 1N37) and "Thymidine phosphorylase from E.coli" (PDB ID: 4EAF) protein targets.

Ammonia release method for depositing metal oxides

DOEpatents

Silver, Gary L.; Martin, Frank S.

1994-12-13

A method of depositing metal oxides on substrates which is indifferent to the electrochemical properties of the substrates and which comprises forming ammine complexes containing metal ions and thereafter effecting removal of ammonia from the ammine complexes so as to permit slow precipitation and deposition of metal oxide on the substrates.

Radical bonding: structure and stability of bis(phenalenyl) complexes of divalent metals from across the periodic table.

PubMed

Craciun, Smaranda; Donald, Kelling J

2009-07-06

We examine the bonding possibilities of the bis(phenalenyl) MP(2) sandwich complexes of the divalent metals M = Be, Mg, Ca, Sr, Ba, Zn, Cd, and Hg, at the B3LYP level of theory. The outcome is an extraordinarily diverse class of low symmetry bis(phenalenyl)metal complexes in which bonding preferences and binding enthalpies differ dramatically. The lowest energy group 2 metal MP(2) complexes include an intriguing eta(1),eta(3) BeP(2) structure, and bent eta(6),eta(6) systems for M = Ca, Sr, and Ba. The group 12 bis(phenalenyl) complexes are thermodynamically unstable eta(1),eta(1) slip-sandwich structures. To better understand changes in the structural preferences going from the (eta(6),eta(6)) group 2 to the (eta(1),eta(1)) group 12 complexes, we explored the bonding in the bis(phenalenyl) complexes of transition metals with stable +2 oxidations states between Ca and Zn in period 4. The computed binding enthalpies are large and negative for nearly all of the minimum energy bis(phenalenyl) complexes of the group 2 and the transition metals; they are tiny for MgP(2), and are quite positive for the group 12 systems. The structural preferences and stability of the complexes is a subtle negotiation of several influences: the (un)availability of (n - 1)d and np, orbitals for bonding, the cost of the rehybridization at carbon sites in the phenalenyl rings in preparation for bonding to the metals, and the (P---P) interaction between the phenalenyl radicals.

Mechanism of selenite removal by a mixed adsorbent based on Fe-Mn hydrous oxides studied using X-ray absorption spectroscopy.

PubMed

Chubar, Natalia; Gerda, Vasyl; Szlachta, Małgorzata

2014-11-18

Selenium cycling in the environment is greatly controlled by various minerals, including Mn and Fe hydrous oxides. At the same time, such hydrous oxides are the main inorganic ion exchangers suitable (on the basis of their chemical nature) to sorb (toxic) anions, separating them from water solutions. The mechanism of selenite adsorption by the new mixed adsorbent composed of a few (amorphous and crystalline) phases [maghemite, MnCO3, and X-ray amorphous Fe(III) and Mn(III) hydrous oxides] was studied by extended X-ray absorption fine structure (EXAFS) spectroscopy [supported by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) data]. The complexity of the porous adsorbent, especially the presence of the amorphous phases of Fe(III) and Mn(III) hydrous oxides, is the main reason for its high selenite removal performance demonstrated by batch and column adsorption studies shown in the previous work. Selenite was bound to the material via inner-sphere complexation (via oxygen) to the adsorption sites of the amorphous Fe(III) and Mn(III) oxides. This anion was attracted via bidentate binuclear corner-sharing coordination between SeO3(2-) trigonal pyramids and both FeO6 and MnO6 octahedra; however, the adsorption sites of Fe(III) hydrous oxides played a leading role in selenite removal. The contribution of the adsorption sites of Mn(III) oxide increased as the pH decreased from 8 to 6. Because most minerals have a complex structure (they are seldom based on individual substances) of various crystallinity, this work is equally relevant to environmental science and environmental technology because it shows how various solid phases control cycling of chemical elements in the environment.

Groundwater arsenic removal by coagulation using ferric(III) sulfate and polyferric sulfate: A comparative and mechanistic study.

PubMed

Cui, Jinli; Jing, Chuanyong; Che, Dongsheng; Zhang, Jianfeng; Duan, Shuxuan

2015-06-01

Elevated arsenic (As) in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric(III) sulfate (FS) and polyferric sulfate (PFS) performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5mg/L Ca(ClO)2. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water (<10 μg/L) was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure (XANES) and As k-edge extended X-ray absorption fine structure (EXAFS) analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As (0.9 μg/L-0.487 mg/L) than the US EPA regulatory limit (5 mg/L). Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water. Copyright © 2015. Published by Elsevier B.V.

Utility of Lithium in Rare-Earth Metal Reduction Reactions to Form Nontraditional Ln2+ Complexes and Unusual [Li(2.2.2-cryptand)]1+ Cations.

PubMed

Huh, Daniel N; Darago, Lucy E; Ziller, Joseph W; Evans, William J

2018-02-19

The utility of lithium compared to other alkali metals in generating Ln 2+ rare-earth metal complexes via reduction of Ln 3+ precursors in reactions abbreviated as LnA 3 /M (Ln = rare-earth metal; A = anionic ligand; M = alkali metal) is described. Lithium reduction of Cp' 3 Ln (Cp' = C 5 H 4 SiMe 3 ; Ln = Y, Tb, Dy, Ho) under Ar in the presence of 2.2.2-cryptand (crypt) forms new examples of crystallographically characterizable Ln 2+ complexes of these metals, [Li(crypt)][Cp' 3 Ln]. In each complex, lithium is found in an N 2 O 4 donor atom coordination geometry that is unusual for the cryptand ligand. Magnetic susceptibility data on these new examples of nontraditional divalent lanthanide complexes are consistent with 4f n 5d 1 electronic configurations. The Dy and Ho complexes have exceptionally high single-ion magnetic moments, 11.35 and 11.67 μ B , respectively. Lithium reduction of Cp' 3 Y under N 2 at -35 °C forms the Y 2+ complex (Cp' 3 Y) 1- , which reduces dinitrogen upon warming to room temperature to generate the (N 2 ) 2- complex [Cp' 2 Y(THF)] 2 (μ-η 2 :η 2 -N 2 ). These results provide insight on the factors that lead to reduced dinitrogen complexes and/or stable divalent lanthanide complexes as a function of the specific reducing agent and conditions.

Supramolecular control of transition metal complexes in water by a hydrophobic cavity: a bio-inspired strategy.

PubMed

Bistri, Olivia; Reinaud, Olivia

2015-03-14

Supramolecular chemistry in water is a very challenging research area. In biology, water is the universal solvent where transition metal ions play major roles in molecular recognition and catalysis. In enzymes, it participates in substrate binding and/or activation in the heart of a pocket defined by the folded protein. The association of a hydrophobic cavity with a transition metal ion is thus a very appealing strategy for controlling the metal ion properties in the very competitive water solvent. Various systems based on intrinsically water-soluble macrocyclic structures such as cyclodextrins, cucurbituryls, and metallo-cages have been reported. Others use calixarenes and resorcinarenes functionalized with hydrophilic substituents. One approach for connecting a metal complex to these cavities is to graft a ligand for metal ion binding at their edge. Early work with cyclodextrins has shown Michaelis-Menten like catalysis displaying enhanced kinetics and substrate-selectivity. Remarkable examples of regio- and stereo-selective transformation of substrates have been reported as well. Dynamic two-phase systems for transition metal catalysis have also been developed. They rely on either water-transfer of the metal complex through ligand embedment or synergistic coordination of a metal ion and substrate hosting. Another strategy consists in using metallo-cages, which provide a well-defined hydrophobic space, to stabilize metal complexes in water. When the cages can host simultaneously a substrate and a reactive metal complex, size- and regio-selective catalysis was obtained. Finally, construction of a polydentate coordination site closely interlocked with a calixarene or resorcinarene macrocycle has been shown to be a very fruitful strategy for obtaining metal complexes with remarkable hosting properties. For each of these systems, the synergism resulting from the biomimetic association of a hydrophobic cavity and a metal ion is discussed within the objective of developing new tools for either selective molecular recognition (with analytical perspectives) or performant catalysis, in water.

Complex transition metal hydrides: linear correlation of countercation electronegativity versus T-D bond lengths.

PubMed

Humphries, T D; Sheppard, D A; Buckley, C E

2015-06-30

For homoleptic 18-electron complex hydrides, an inverse linear correlation has been established between the T-deuterium bond length (T = Fe, Co, Ni) and the average electronegativity of the metal countercations. This relationship can be further employed towards aiding structural solutions and predicting physical properties of novel complex transition metal hydrides.

Analysis of Supercritical-Extracted Chelated Metal Ions From Mixed Organic-Inorganic Samples

NASA Technical Reports Server (NTRS)

Sinha, Mahadeva P. (Inventor)

1996-01-01

Organic and inorganic contaminants of an environmental sample are analyzed by the same GC-MS instrument by adding an oxidizing agent to the sample to oxidize metal or metal compounds to form metal ions. The metal ions are converted to chelate complexes and the chelate complexes are extracted into a supercritical fluid such as CO2. The metal chelate extract after flowing through a restrictor tube is directly injected into the ionization chamber of a mass spectrometer, preferably containing a refractory metal filament such as rhenium to fragment the complex to release metal ions which are detected. This provides a fast, economical method for the analysis of metal contaminants in a sample and can be automated. An organic extract of the sample in conventional or supercritical fluid solvents can be detected in the same mass spectrometer, preferably after separation in a supercritical fluid chromatograph.

Humic Acid Complexation of Th, Hf and Zr in Ligand Competition Experiments: Metal Loading and Ph Effects

NASA Technical Reports Server (NTRS)

Stern, Jennifer C.; Foustoukos, Dionysis I.; Sonke, Jeroen E.; Salters, Vincent J. M.

2014-01-01

The mobility of metals in soils and subsurface aquifers is strongly affected by sorption and complexation with dissolved organic matter, oxyhydroxides, clay minerals, and inorganic ligands. Humic substances (HS) are organic macromolecules with functional groups that have a strong affinity for binding metals, such as actinides. Thorium, often studied as an analog for tetravalent actinides, has also been shown to strongly associate with dissolved and colloidal HS in natural waters. The effects of HS on the mobilization dynamics of actinides are of particular interest in risk assessment of nuclear waste repositories. Here, we present conditional equilibrium binding constants (Kc, MHA) of thorium, hafnium, and zirconium-humic acid complexes from ligand competition experiments using capillary electrophoresis coupled with ICP-MS (CE- ICP-MS). Equilibrium dialysis ligand exchange (EDLE) experiments using size exclusion via a 1000 Damembrane were also performed to validate the CE-ICP-MS analysis. Experiments were performed at pH 3.5-7 with solutions containing one tetravalent metal (Th, Hf, or Zr), Elliot soil humic acid (EHA) or Pahokee peat humic acid (PHA), and EDTA. CE-ICP-MS and EDLE experiments yielded nearly identical binding constants for the metal- humic acid complexes, indicating that both methods are appropriate for examining metal speciation at conditions lower than neutral pH. We find that tetravalent metals form strong complexes with humic acids, with Kc, MHA several orders of magnitude above REE-humic complexes. Experiments were conducted at a range of dissolved HA concentrations to examine the effect of [HA]/[Th] molar ratio on Kc, MHA. At low metal loading conditions (i.e. elevated [HA]/[Th] ratios) the ThHA binding constant reached values that were not affected by the relative abundance of humic acid and thorium. The importance of [HA]/[Th] molar ratios on constraining the equilibrium of MHA complexation is apparent when our estimated Kc, MHA values attained at very low metal loading conditions are compared to existing literature data. Overall, experimental data suggest that the tetravalent transition metal/-actinide-humic acid complexation is important over a wide range of pH values, including mildly acidic conditions, and thus, these complexes should be included in speciation models.

Different binding modes of Cu and Pb vs. Cd, Ni, and Zn with the trihydroxamate siderophore desferrioxamine B at seawater ionic strength

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schijf, Johan; Christenson, Emily A.; Potter, Kailee J.

2015-07-01

The solution speciation in seawater of divalent trace metals (Cd, Cu, Ni, Pb, Zn) is dominated by strong, ostensibly metal-specific organic ligands that may play important roles in microbial metal acquisition and/or detoxification processes. We compare the effective stabilities of these metal-organic complexes to the stabilities of their complexes with a model siderophore, desferrioxamine B (DFOB). While metal-DFOB complexation has been studied in various dilute but often moderately coordinating media, for the purpose of this investigation we measured the stability constants in a non-coordinating background electrolyte at seawater ionic strength (0.7 M NaClO4). Potentiometric titrations of single metals (M) weremore » performed in the presence of ligand (L) at different M:L molar ratios, whereupon the stability constants of multiple complexes were simultaneously determined by non-linear regression of the titration curves with FITEQL, using the optimal binding mode for each metal. Cadmium, Ni, and Zn, like trivalent Fe, sequentially form a bi-, tetra-, and hexadentate complex with DFOB as pH increases, consistent with their coordination number of 6 and regular octahedral geometry. Copper has a Jahn-Teller-distorted square-bipyramidal geometry whereas the geometry of Pb is cryptic, involving a range of bond lengths. Supported by a thermodynamic argument, our data suggest that this impedes binding of the third hydroxamate group and that the hexadentate Cu-DFOB and Pb-DFOB complex identified in earlier reports may instead be a deprotonated tetradentate complex. Absence of the hexadentate complex promotes the formation of a dinuclear (bidentate-tetradentate) complex, M2HL2+, albeit not for Pb in 0.7 M NaCl, evidently due to extensive complexation with chloride. Stabilities of the hexadentate Ni-DFOB, Zn-DFOB, and the tetradentate Pb-DFOB complex are nearly equal, yet about 2 orders of magnitude higher and 4 orders of magnitude lower than those of the hexadentate Cd-DFOB and tetradentate Cu-DFOB complex, respectively. Linear free-energy relations defined by the rare earth elements are able to predict stabilities of the Cd, Zn, and one of the Pb complexes, but underestimate those of the Ni and Cu complexes. The comparison with metal-specific organic ligands detected in seawater yields fair agreement for three of the five metals, implying that they could be siderophore-like. The Cd- and Ni-specific ligands are much stronger and may contain quite different functional groups. Calculations with MINEQL incorporating our new stability constants indicate that very high DFOB concentrations would be required to match the extent of metal-organic complexation observed in seawater, however DFOB may well represent a much broader class of structurally related ligands.« less

Metal Ion Binding at the Catalytic Site Induces Widely Distributed Changes in a Sequence Specific Protein–DNA Complex

PubMed Central

2016-01-01

Metal ion cofactors can alter the energetics and specificity of sequence specific protein–DNA interactions, but it is unknown if the underlying effects on structure and dynamics are local or dispersed throughout the protein–DNA complex. This work uses EcoRV endonuclease as a model, and catalytically inactive lanthanide ions, which replace the Mg2+ cofactor. Nuclear magnetic resonance (NMR) titrations indicate that four Lu3+ or two La3+ cations bind, and two new crystal structures confirm that Lu3+ binding is confined to the active sites. NMR spectra show that the metal-free EcoRV complex with cognate (GATATC) DNA is structurally distinct from the nonspecific complex, and that metal ion binding sites are not assembled in the nonspecific complex. NMR chemical shift perturbations were determined for 1H–15N amide resonances, for 1H–13C Ile-δ-CH3 resonances, and for stereospecifically assigned Leu-δ-CH3 and Val-γ-CH3 resonances. Many chemical shifts throughout the cognate complex are unperturbed, so metal binding does not induce major conformational changes. However, some large perturbations of amide and side chain methyl resonances occur as far as 34 Å from the metal ions. Concerted changes in specific residues imply that local effects of metal binding are propagated via a β-sheet and an α-helix. Both amide and methyl resonance perturbations indicate changes in the interface between subunits of the EcoRV homodimer. Bound metal ions also affect amide hydrogen exchange rates for distant residues, including a distant subdomain that contacts DNA phosphates and promotes DNA bending, showing that metal ions in the active sites, which relieve electrostatic repulsion between protein and DNA, cause changes in slow dynamics throughout the complex. PMID:27786446

Magnetic behavior control in niccolite structural metal formate frameworks [NH2(CH3)2][Fe(III)M(II)(HCOO)6] (M = Fe, Mn, and Co) by varying the divalent metal ions.

PubMed

Zhao, Jiong-Peng; Hu, Bo-Wen; Lloret, Francesc; Tao, Jun; Yang, Qian; Zhang, Xiao-Feng; Bu, Xian-He

2010-11-15

By changing template cation but introducing trivalent iron ions in the known niccolite structural metal formate frameworks, three complexes formulated [NH(2)(CH(3))(2)][Fe(III)M(II)(HCOO)(6)] (M = Fe for 1, Mn for 2, and Co for 3) were synthesized and magnetically characterized. The variation in the compositions of the complexes leads to three different complexes: mixed-valent complex 1, heterometallic but with the same spin state complex 2, and heterometallic heterospin complex 3. The magnetic behaviors are closely related to the divalent metal ions used. Complex 1 exhibits negative magnetization assigned as Néel N-Type ferrimagnet, with an asymmetric magnetization reversal in the hysteresis loop, and complex 2 is an antiferromagnet with small spin canting (α(canting) ≈ 0.06° and T(canting) = 35 K), while complex 3 is a ferrimagnet with T(N) = 32 K.

Changing hydration level in an internal cavity modulates the proton affinity of a key glutamate in cytochrome c oxidase.

PubMed

Goyal, Puja; Lu, Jianxun; Yang, Shuo; Gunner, M R; Cui, Qiang

2013-11-19

Cytochrome c oxidase contributes to the transmembrane proton gradient by removing two protons from the high-pH side of the membrane each time the binuclear center active site is reduced. One proton goes to the binuclear center, whereas the other is pumped to the low-pH periplasmic space. Glutamate 286 (Glu286) has been proposed to serve as a transiently deprotonated proton donor. Using unrestrained atomistic molecular dynamics simulations, we show that the size of and water distribution in the hydrophobic cavity that holds Glu286 is controlled by the protonation state of the propionic acid of heme a3, a group on the proton outlet pathway. Protonation of the propionate disrupts hydrogen bonding to two side chains, allowing a loop to swing open. Continuum electrostatics and atomistic free-energy perturbation calculations show that the resultant changes in hydration and electrostatic interactions lower the Glu proton affinity by at least 5 kcal/mol. These changes in the internal hydration level occur in the absence of major conformational transitions and serve to stabilize needed transient intermediates in proton transport. The trigger is not the protonation of the Glu of interest, but rather the protonation of a residue ∼10 Å away. Thus, unlike local water penetration to stabilize a new charge, this finding represents a specific role for water molecules in the protein interior, mediating proton transfers and facilitating ion transport.

Enhanced activity and stability of binuclear iron (III) phthalocyanine on graphene nanosheets for electrocatalytic oxygen reduction in acid

NASA Astrophysics Data System (ADS)

Li, Tengfei; Peng, Yingxiang; Li, Kai; Zhang, Rui; Zheng, Lirong; Xia, Dingguo; Zuo, Xia

2015-10-01

Binuclear iron (III) phthalocyanine (bi-FePc) and iron (III) phthalocyanine (FePc) are synthesized in situ on graphene nanosheets (GNS) by a microwave-assisted method. TEM, ultraviolet-visible spectroscopy and Raman spectroscopy confirm that bi-FePc is supported on GNS through π-π interactions. The catalytic activity of the bi-FePc/GNS and FePc/GNS composites in the oxygen reduction reaction (ORR) is investigated by CV and RDE measurements. The bi-FePc/GNS composite shows a more positive onset potential (0.12 V vs. Hg/Hg2SO4) for the ORR than FePc/GNS (-0.02 V vs. Hg/Hg2SO4), and a four-electron mechanism similar to commercial Pt/C (0.22 V vs. Hg/Hg2SO4). Moreover, bi-FePc/GNS exhibits good stability with 100% retention after 36,000 s, while Pt/C has a retention of only 50% after the same period. Additionally, bi-FePc/GNS shows higher tolerance toward methanol than the Pt/C catalyst. XPS and X-ray absorption fine structure spectroscopy demonstrate that compared with FePc/GNS, bi-FePc/GNS possesses a higher concentration of Fe3+ and smaller skeleton radius of the phthalocyanine ring, which has a square-planar structure that evidently favors the ORR. Thus, bi-FePc/GNS is a promising candidate as a cathode catalyst in direct methanol fuel cells.

High incidence of micronuclei in lymphocytes from residents of the area near the Semipalatinsk nuclear explosion test site.

PubMed

Tanaka, K; Tchaijunusova, N J; Takatsuji, T; Gusev, B I; Sakerbaev, A K; Hoshi, M; Kamada, N

2000-03-01

The Semipalatinsk area is highly contaminated with radioactive fallout from 40 years of continuous nuclear testing. The biological effects on human health in this area have not been studied. Significant remaining radioactivities include long-lived radioisotopes of 238,239,400Pu, 137Cs and 90Sr. To evaluate the long-term biological effects of the radioactive fallout, the incidence of micronuclei in lymphocytes from residents of the area was observed. Blood was obtained from 10 residents (5 females and 5 males, aged 47 to 55 years old) from each of the 3 areas of Znamenka, Dolon and Semipalatinsk, which are about 50-150 km from the nuclear explosion test site. For micronucleus assay, PHA-stimulated lymphocytes were cultured for 72 h and cytochalasin B was added at 44 h for detecting binuclear lymphocytes. Five thousand binuclear lymphocytes in each resident were scored. The means of micronucleus counts in 1,000 lymphocytes in residents of Semipalatinsk, Dolon and Znamenka were 16.3, 12.6, and 7.80, respectively, which were higher than those of the normal Japanese persons (4.66). These values were equivalent to the results obtained from 0.187-0.47 Gy of chronic exposure to gamma-rays at a dose rate of 0.02 cGy/min. The high incidence of micronuclei in residents of the Semipalatinsk nuclear test site area was mainly caused by internal exposure rather than external exposure received for the past 40 years.

Characterization of oxidation products of TNT metabolism in aquatic phytoremediation systems of Myriophyllum aquaticum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhadra, R.; Spanggord, R.J.; Wayment, D.G.

TNT transformation processes in sediment-free, natural, aquatic phytoremediation systems of Myriophyllum aquaticum were investigated with specific interest in oxidation products. Extraction procedures combining liquid-liquid extractions and solid-phase extractions were developed for the isolation of the mostly acidic, oxidized TNT metabolites. Six compounds unique from the reduction products of TNT were isolated and characterized by UV-vis, {sup 1}H, and {sup 13}C NMR spectroscopy, by mass spectroscopy, and by chemical synthesis where feasible. These compounds include 2-amino-4,6-dinitrobenzoic acid, 2,4-dinitro-6-hydroxyl-benzyl alcohol, 2-N-acetoxyamino-4,6-dinitrobenzaldehyde, 2,4-dinitro-6,hydroxytoluene, and two binuclear metabolites unique from the customary azoxytetranitrotoluenes. The monoaryl compounds show clear evidence of oxidative transformations, methyl oxidationmore » and/or aromatic hydroxylation. It is possible that oxidative transformation(s) preceded nitro reduction since studies on exposure of M. aquaticum to either 2-amino-4,6-dinitrotoluene or 4-amino-2,6-dinitrotoluene did not yield any of the oxidation products identified here. The accumulation of oxidation products was significant: 2-amino-4,6-dinitrobenzoic acid, 4.4%; 2,4-dinitro-6-hydroxy-benzyl alcohol, 8.1%; 2-N-acetoxyamino-4,6-dinitrobenzaldehyde, 7.8%; and, 2,4-dinitro-6-hydroxytoluene, 15.6%. The binuclear metabolites accounted for an estimated 5.6%. This study is the first direct evidence for oxidative transformations in aquatic phytoremediation systems.« less

Probing the Properties of Polynuclear Superhalogens without Halogen Ligand via ab Initio Calculations: A Case Study on Double-Bridged [Mg2 (CN)5 ](-1) Anions.

PubMed

Li, Jin-Feng; Li, Miao-Miao; Bai, Hongcun; Sun, Yin-Yin; Li, Jian-Li; Yin, Bing

2015-12-01

An ab initio study of the superhalogen properties of eighteen binuclear double-bridged [Mg2 (CN)5 ](-1) clusters is reported herein by using various theoretical methods. High-level CCSD(T) results indicate that all the clusters possess strong superhalogen properties owing to their high vertical electron detachment energies (VDEs), which exceed 6.8 eV (highest: 8.15 eV). The outer valence Green's function method provides inaccurate relative VDE values; hence, this method is not suitable for this kind of polynuclear superhalogens. Both the HF and MP2 results are generally consistent with the CCSD(T) level regarding the relative VDE values and-especially interesting-the average values of the HF and MP2 VDEs are extremely close to the CCSD(T) results. The distributions of the extra electrons of the anions are mainly aggregated into the terminal CN units. These distributions are apparently different from those of previously reported triple-bridged isomers and may be the reason for the decreased VDE values of the clusters. In addition, comparisons of the VDEs of binuclear and mononuclear superhalogens as well as studies of the thermodynamic stabilities with respect to the detachment of various CN(-1) ligands are also performed. These results confirm that polynuclear structures with pseudohalogen ligands can be considered as probable new superhalogens with enhanced properties. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Syntheses, spectroscopic characterization, thermal study, molecular modeling, and biological evaluation of novel Schiff's base benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) with Ni(II), and Cu(II) metal complexes

NASA Astrophysics Data System (ADS)

Chandra, Sulekh; Gautam, Seema; Rajor, Hament Kumar; Bhatia, Rohit

2015-02-01

Novel Schiff's base ligand, benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) was synthesized by the condensation of benzil and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio. The structure of ligand was determined on the basis of elemental analyses, IR, 1H NMR, mass, and molecular modeling studies. Synthesized ligand behaved as tetradentate and coordinated to metal ion through sulfur atoms of thiol ring and nitrogen atoms of imine group. Ni(II), and Cu(II) complexes were synthesized with this nitrogen-sulfur donor (N2S2) ligand. Metal complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, IR, electronic spectra, EPR, thermal, and molecular modeling studies. All the complexes showed molar conductance corresponding to non-electrolytic nature, expect [Ni(L)](NO3)2 complex, which was 1:2 electrolyte in nature. [Cu(L)(SO4)] complex may possessed square pyramidal geometry, [Ni(L)](NO3)2 complex tetrahedral and rest of the complexes six coordinated octahedral/tetragonal geometry. Newly synthesized ligand and its metal complexes were examined against the opportunistic pathogens. Results suggested that metal complexes were more biological sensitive than free ligand.

N-heterocyclic carbene metal complexes as bio-organometallic antimicrobial and anticancer drugs.

PubMed

Patil, Siddappa A; Patil, Shivaputra A; Patil, Renukadevi; Keri, Rangappa S; Budagumpi, Srinivasa; Balakrishna, Geetha R; Tacke, Matthias

2015-01-01

Late transition metal complexes that bear N-heterocyclic carbene (NHC) ligands have seen a speedy growth in their use as both, metal-based drug candidates and potentially active homogeneous catalysts in a plethora of C-C and C-N bond forming reactions. This review article focuses on the recent developments and advances in preparation and characterization of NHC-metal complexes (metal: silver, gold, copper, palladium, nickel and ruthenium) and their biomedical applications. Their design, syntheses and characterization have been reviewed and correlated to their antimicrobial and anticancer efficacies. All these initial discoveries help validate the great potential of NHC-metal derivatives as a class of effective antimicrobial and anticancer agents.

Structural characterization of 1,8-naphthalimides and in vitro microbiological activity of their Cu(II) and Zn(II) complexes

NASA Astrophysics Data System (ADS)

Grabchev, Ivo; Yordanova, Stanislava; Bosch, Paula; Vasileva-Tonkova, Evgenia; Kukeva, Rositsa; Stoyanov, Stanimir; Stoyanova, Radostina

2017-02-01

Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characterized. The photophysical properties of the new compounds have been investigated in organic solvents of different polarity. It has been shown that both compounds are solvent depended. Cu(II) and Zn(II) complexes of NI2 were obtained and characterized by IR-NMR, fluorescence and EPR spectroscopy. The influence of different metal cations on the fluorescence intensity has been investigated in acetonitrile solution. Antimicrobial composite PLA-metal complexes materials have been obtained for the first time. Microbiological activity of both metal complexes has been investigated in vitro against different Gram-positive and Gram-negative bacteria and two yeasts. The various antimicrobial activities and the minimum inhibitory concentrations (MICs) of both complexes have been determined. The microbiological activity of composite materials PLA-metal complexes in thin polymeric film has also been investigated. The results suggest that the new metal complexes could find application in designing new antimicrobial preparations to control the spread of infections.

Synthesis, characterization and solid state electrical properties of 1-D coordination polymer of the type [Cu{sub x}Ni{sub 1-x}(dadb){center_dot}yH{sub 2}O]{sub n}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasad, R.L., E-mail: rlpjc@yahoo.co.in; Kushwaha, A.; Shrivastava, O.N.

2012-12-15

New heterobimetallic complexes [Cu{sub x}Ni{sub 1-x}(dadb){center_dot}yH{sub 2}O]{sub n} {l_brace}where dadb=2,5-Diamino-3,6-dichloro-1,4-benzoquinone (1); x=1 (2), 0.5 (4), 0.25 (5), 0.125 (6), 0.0625 (7) and 0 (3); y=2; n=degree of polymerization{r_brace} were synthesized and characterized. Heterobimetallic complexes show normal magnetic moments, whereas, monometallic complexes exhibit magnetic moments less than the value due to spin only. Thermo-gravimetric analysis shows that degradation of the ligand dadb moiety is being controlled by the electronic environment of the Cu(II) ions in preference over Ni(II) in heterobimetallic complexes. Existence of the mixed valency/non-integral oxidation states of copper and nickel metal ions in the complex 4 has been attributedmore » from magnetic moment and ESR spectral results. Solid state dc electrical conductivity of all the complexes was investigated. Monometallic complexes were found to be semiconductors, whereas heterobimetallic coordination polymer 4 was found to exhibit metallic behaviour. Existence of mixed valency/ non-integral oxidation state of metal ions seems to be responsible for the metallic behaviour. - Graphical abstract: Contrast to the semiconductor monometallic complexes 2 and 3, the heterobimetallic complex 4 exhibits metallic behaviour attributed to the mixed valency/non-integral oxidation state of the metal ions concluded from magnetic and ESR spectral studies. Highlights: Black-Right-Pointing-Pointer 1-D coordination compounds of the type Cu{sub x}Ni{sub 1-x}(dadb){center_dot}yH{sub 2}O were synthesized and characterized. Black-Right-Pointing-Pointer Thermal degradation of the complexes provides an indication of long range electronic communication between metal to ligand. Black-Right-Pointing-Pointer On inclusion of Ni(II) into 1-D coordination polymer of Cu(II). (a) Cu(II) and Ni(II) ions exhibit non-integral oxidation state. (b) resulting heterobimetallic complex 4 exhibits metallic behaviour at all temperature range of the present study whereas monometallic complexes are semiconductor.« less

Charge Transfer Between Quantum Dots and Peptide-Coupled Redox Complexes

DTIC Science & Technology

2009-01-01

labeled with reactive metal complexes includ- ing a ruthenium chelate (Ru), a bis-bipyridine ruthe- nium chelate (ruthenium-bpy), and a ferrocene metal...of unconjugated QDs and the metal complex–labeled peptides immobilized on indium tin oxide (ITO) electrodes. The ruthenium and ferrocene peptide...Ag/AgCI E v s. N H E E v s. v ac uu m (e V ) Ruthenium Ferrocene Ruthenium-bpy DHLA QDs DHLA-PEG QDs Quantum dot Metal complex CB VB E0X of QDs Fe

Bifunctional chelating agent for the design and development of site specific radiopharmaceuticals and biomolecule conjugation strategy

DOEpatents

Katti, Kattesh V.; Prabhu, Kandikere R.; Gali, Hariprasad; Pillarsetty, Nagavara Kishore; Volkert, Wynn A.

2003-10-21

There is provided a method of labeling a biomolecule with a transition metal or radiometal in a site specific manner to produce a diagnostic or therapeutic pharmaceutical compound by synthesizing a P.sub.2 N.sub.2 -bifunctional chelating agent intermediate, complexing the intermediate with a radio metal or a transition metal, and covalently linking the resulting metal-complexed bifunctional chelating agent with a biomolecule in a site specific manner. Also provided is a method of synthesizing the --PR.sub.2 containing biomolecules by synthesizing a P.sub.2 N.sub.2 -bifunctional chelating agent intermediate, complexing the intermediate with a radiometal or a transition metal, and covalently linking the resulting radio metal-complexed bifunctional chelating agent with a biomolecule in a site specific manner. There is provided a therapeutic or diagnostic agent comprising a --PR.sub.2 containing biomolecule.

Modelling of trace metal uptake by roots taking into account complexation by exogenous organic ligands

NASA Astrophysics Data System (ADS)

Jean-Marc, Custos; Christian, Moyne; Sterckeman, Thibault

2010-05-01

The context of this study is phytoextraction of soil trace metals such as Cd, Pb or Zn. Trace metal transfer from soil to plant depends on physical and chemical processes such as minerals alteration, transport, adsorption/desorption, reactions in solution and biological processes including the action of plant roots and of associated micro-flora. Complexation of metal ions by organic ligands is considered to play a role on the availability of trace metals for roots in particular in the event that synthetic ligands (EDTA, NTA, etc.) are added to the soil to increase the solubility of the contaminants. As this role is not clearly understood, we wanted to simulate it in order to quantify the effect of organic ligands on root uptake of trace metals and produce a tool which could help in optimizing the conditions of phytoextraction.We studied the effect of an aminocarboxilate ligand on the absorption of the metal ion by roots, both in hydroponic solution and in soil solution, for which we had to formalize the buffer power for the metal. We assumed that the hydrated metal ion is the only form which can be absorbed by the plants. Transport and reaction processes were modelled for a system made up of the metal M, a ligand L and the metal complex ML. The Tinker-Nye-Barber model was adapted to describe the transport of solutes M, L and ML in the soil and absorption of M by the roots. This allowed to represent the interactions between transport, chelating reactions, absorption of the solutes at the root surface, root growth with time, in order to simulate metal uptake by a whole root system.Several assumptions were tested such as i) absorption of the metal by an infinite sink and according to a Michaelis-Menten kinetics, solutes transport by diffusion with and without ii) mass flow and iii) soil buffer power for the ligand L. In hydroponic solution (without soil buffer power), ligands decreased the trace metal flux towards roots, as they reduced the concentration of hydrated metal ion. In soil, depending on the L/M ratio, the presence of metal complexes could increase the metal flux taken up by roots since the ligand desorbed the metal on soil solid phase while the complex dissociated and provided metal ions to the solution in the vicinity of the root.The model enabled to surround the conditions in which phytoextraction is thus optimized. In addition of complexation by organic ligands added to the soil, we expect to integrate complexation by roots organic exudates and by soil organic matter, as well as the competition of the metal ions with Ca2+ et H+.

Ammonia release method for depositing metal oxides

DOEpatents

Silver, G.L.; Martin, F.S.

1994-12-13

A method is described for depositing metal oxides on substrates which is indifferent to the electrochemical properties of the substrates and which comprises forming ammine complexes containing metal ions and thereafter effecting removal of ammonia from the ammine complexes so as to permit slow precipitation and deposition of metal oxide on the substrates. 1 figure.

Synthesis and Properties of Ortho-Nitro-Fe Complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mishra, A.; Mishra, Niyati; Sharma, R.

2011-07-15

Ortho-Nitro-Fe complex (Transition metal complex) has synthesized by chemical route method and properties of made complex has characterized by X-Ray diffraction (XRD), Moessbauer spectroscopy, Fourier transformation infra-red spectroscopy (FTIR) and X-Ray photoelectron spectroscopy (XPS). XRD analysis shows that sample is crystalline in nature and having particle size in the range of few nano meters. Moessbauer spectroscopy at room temperature shows the oxidation state of Iron (central metal ion) after complaxasion. FTIR spectra of the complex confirms the coordination of metal ion with ligand.

Fabrication of carbon nanotube films from alkyne-transition metal complexes

DOEpatents

Iyer, Vivekanantan S [Delft, NL; Vollhardt, K Peter C. [Oakland, CA

2007-08-28

A simple method for the production or synthesis of carbon nanotubes as free-standing films or nanotube mats by the thermal decomposition of transition metal complexed alkynes with aryl, alkyl, alkenyl, or alkynyl substituents. In particular, transition metal (e.g. Co, Ni, Fe, Mo) complexes of diarylacetylenes, e.g. diphenylacetylene, and solid mixtures of these complexes with suitable, additional carbon sources are heated in a vessel. More specifically, the heating of the transition metal complex is completed at a temperature between 400-800.degree. C. and more particularly 550-700.degree. C. for between 0.1 to 24 hours and more particularly 0.5-3 hours in a sealed vessel under a partial pressure of argon or helium.

Homo- and Heterometallic Bis(Pentafluorobenzoyl)Methanide Complexes of Copper(II) and Cobalt(II)

NASA Astrophysics Data System (ADS)

Crowder, Janell M.

beta-Diketones are well known to form metal complexes with practically every known metal and metalloid. Metal complexes of fluorinated beta-diketones generally exhibit increased volatility and thermal stability compared to the non-fluorinated analogues, and thus are used extensively in various chemical vapor deposition (CVD) processes for the deposition of metal, simple or mixed metal oxides, and fluorine-doped metal oxide thin films. Furthermore, the electron-withdrawing nature of the fluorinated ligand enhances the Lewis acidity of a coordinatively unsaturated metal center which facilitates additional coordination reactions. The physical and structural properties of fluorinated beta-diketonate complexes are discussed in Chapter 1 and a few key application examples are given. The focus of this work is the synthesis and single crystal X-ray structural characterization of unsolvated and coordinatively unsaturated metal complexes of bis(pentafluorobenzoyl)- methanide (L, C6F5COCHCOC 6F5-). In Chapter 2, we present the preparation and isolation of the unsolvated complex [Cu(L)2] in pure crystalline form for the first time. We subsequently investigated the reaction of unsolvated [Cu(L)2] with sodium hexafluoroacetylacetonate [Na(hfac)] in a solvent-free environment. This reaction allowed the isolation of the first heterometallic Na-Cu diketonate [Na2Cu2(L) 4(hfac)2] structurally characterized by single crystal X-ray crystallography. Thermal decomposition of [Na2Cu2(L) 4(hfac)2] was investigated for its potential application in MOCVD processes. In the final chapter, we present the first exploration of the anhydrous synthesis of Co(II) complexed with bis(pentafluorobenzoyl)methanide in order to produce a complex without ligated water. Single crystal X-ray crystallographic investigations revealed the isolation of the ethanol adduct, [Co2(L)4(C2H5OH)2], and following the removal of ethanol, a 1,4-dioxane adduct, [{Co 2(L)4}2(C4H8O2)]. In this work, we have provided the first investigation of the synthesis, isolation and single crystal X-ray structural characterization of unsolvated and coordinatively unsaturated Cu(II) and Co(II) complexes of bis(pentafluorobenzoyl)methanide ligand. These studies demonstrate how the electrophilicity of a coordinatively unsaturated metal complexed to highly-fluorinated â-diketone ligands can be utilized for the formation of new adducts or new and interesting heterometallic complexes. This body of work provides a basis upon which future research into unsolvated and unligated bis(pentafluorobenzoyl)methanide metal complexes can expand.

Surface Modification and Nanojunction Fabrication with Molecular Metal Wires

DTIC Science & Technology

2014-02-17

Title: Transition Metal Complexes of a Super Rigid Anthyridine Ligand: Structural, Magnetic and DFT Studies. Transition metal complexes of iron ( II ...Compounds with Masked Diazonium Capping Groups (J. Organomet. Chem. 2013, 745, 93). (3) New Diruthenium( II ,III) Compounds Bearing Terminal Olefin Groups...2012, 36, 2340). (2) Synthesis , Structure, Magnetism, and Single Molecular Conductance of Linear Trinickel String Complexes with Sulfur-Containing

Transition Metal d-Orbital Splitting Diagrams: An Updated Educational Resource for Square Planar Transition Metal Complexes

ERIC Educational Resources Information Center

Bo¨rgel, Jonas; Campbell, Michael G.; Ritter, Tobias

2016-01-01

The presentation of d-orbital splitting diagrams for square planar transition metal complexes in textbooks and educational materials is often inconsistent and therefore confusing for students. Here we provide a concise summary of the key features of orbital splitting diagrams for square planar complexes, which we propose may be used as an updated…

Electrolyte salts for nonaqueous electrolytes

DOEpatents

Amine, Khalil; Zhang, Zhengcheng; Chen, Zonghai

2012-10-09

Metal complex salts may be used in lithium ion batteries. Such metal complex salts not only perform as an electrolyte salt in a lithium ion batteries with high solubility and conductivity, but also can act as redox shuttles that provide overcharge protection of individual cells in a battery pack and/or as electrolyte additives to provide other mechanisms to provide overcharge protection to lithium ion batteries. The metal complex salts have at least one aromatic ring. The aromatic moiety may be reversibly oxidized/reduced at a potential slightly higher than the working potential of the positive electrode in the lithium ion battery. The metal complex salts may also be known as overcharge protection salts.

Labile Low-Molecular-Mass Metal Complexes in Mitochondria: Trials and Tribulations of a Burgeoning Field.

PubMed

Lindahl, Paul A; Moore, Michael J

2016-08-02

Iron, copper, zinc, manganese, cobalt, and molybdenum play important roles in mitochondrial biochemistry, serving to help catalyze reactions in numerous metalloenzymes. These metals are also found in labile "pools" within mitochondria. Although the composition and cellular function of these pools are largely unknown, they are thought to be comprised of nonproteinaceous low-molecular-mass (LMM) metal complexes. Many problems must be solved before these pools can be fully defined, especially problems stemming from the lability of such complexes. This lability arises from inherently weak coordinate bonds between ligands and metals. This is an advantage for catalysis and trafficking, but it makes characterization difficult. The most popular strategy for investigating such pools is to detect them using chelator probes with fluorescent properties that change upon metal coordination. Characterization is limited because of the inevitable destruction of the complexes during their detection. Moreover, probes likely react with more than one type of metal complex, confusing analyses. An alternative approach is to use liquid chromatography (LC) coupled with inductively coupled plasma mass spectrometry (ICP-MS). With help from a previous lab member, the authors recently developed an LC-ICP-MS approach to analyze LMM extracts from yeast and mammalian mitochondria. They detected several metal complexes, including Fe580, Fe1100, Fe1500, Cu5000, Zn1200, Zn1500, Mn1100, Mn2000, Co1200, Co1500, and Mo780 (numbers refer to approximate masses in daltons). Many of these may be used to metalate apo-metalloproteins as they fold inside the organelle. The LC-based approach also has challenges, e.g., in distinguishing artifactual metal complexes from endogenous ones, due to the fact that cells must be disrupted to form extracts before they are passed through chromatography columns prior to analysis. Ultimately, both approaches will be needed to characterize these intriguing complexes and to elucidate their roles in mitochondrial biochemistry.

Headgroup interactions and ion flotation efficiency in mixtures of a chelating surfactant, different foaming agents, and divalent metal ions.

PubMed

Svanedal, Ida; Boija, Susanne; Norgren, Magnus; Edlund, Håkan

2014-06-10

The correlation between interaction parameters and ion flotation efficiency in mixtures of chelating surfactant metal complexes and different foaming agents was investigated. We have recently shown that chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) forms strong coordination complexes with divalent metal ions, and this can be utilized in ion flotation. Interaction parameters for mixed micelles and mixed monolayer formation for Mg(2+) and Ni(2+) complexes with the chelating surfactant 4-C12-DTPA and different foaming agents were calculated by Rubingh's regular solution theory. Parameters for the calculations were extracted from surface tension measurements and NMR diffusometry. The effects of metal ion coordination on the interactions between 4-C12-DTPA and the foaming agents could be linked to a previously established difference in coordination chemistry between the examined metal ions. As can be expected from mixtures of amphoteric surfactants, the interactions were strongly pH-dependent. Strong correlation was found between interaction parameter β(σ) for mixed monolayer formation and the phase-transfer efficiency of Ni(2+) complexes with 4-C12-DTPA during flotation in a customized flotation cell. In a mixture of Cu(2+) and Zn(2+), the significant difference in conditional stability constants (log K) between the metal complexes was utilized to selectively recover the metal complex with the highest log K (Cu(2+)) by ion flotation. Flotation experiments in an excess concentration of metal ions confirmed the coordination of more than one metal ion to the headgroup of 4-C12-DTPA.

Spectral and in vitro antimicrobial properties of 2-oxo-4-phenyl-6-styryl-1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid transition metal complexes

NASA Astrophysics Data System (ADS)

Dhankar, Raksha P.; Rahatgaonkar, Anjali M.; Chorghade, Mukund S.; Tiwari, Ashutosh

2-oxo-4-phenyl-6-styryl-1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid (ADP) was complexed with acetates of Mn(II), Ni(II), Cu(II) and Zn(II). The structures of the ligand and its metal complexes were characterized by microanalysis, IR, NMR, UV-vis spectroscopy, magnetic susceptibility and TGA-DTA analyses. Octahedral and square planar geometries were suggested for the complexes in which the central metal ion coordinated with sbnd O donors of ligand and acetate ions. Each ligand binds the metal using carboxylate oxygens. The ligand and complexes were evaluated for their antimicrobial activities against different species of pathogenic bacteria and fungi. The present novel pyrimidine containing complexes could constitute a new group of antibacterial and antifungal agents.

Features of proteolytic properties of tetraphenylporphyrin complex with lanthanide group metals

NASA Astrophysics Data System (ADS)

Tobolkina, Elena A.; Skripnikova, Tatiana A.; Starikova, Anna A.; Shumilova, Galina I.; Pendin, Andrey A.

2018-01-01

Demetallation of metalloporphyrin molecules is one of the essential degradation reactions in photosynthesis. The effect of metalloporphyrin nature on removal of central metals from tetraphenylporphyrin complexes based on lanthanide group metals (Dy, Er, Lu, Ho) has been studied. pH values, at which the metal ions leave the metalloporphyrin complex were established using two-phase spectrophotometric titration with potentiometric pH-control. The pH values decrease with the increase of atomic numbers of lanthanide groups, as well as with increase of 4f-electrons. The reaction of an extra ligand exchange for the hydroxide ion was studied. For Dy-, Er- and Ho-tetraphenylporphyrin complexes one particle of extra ligand coordinates with one porphyrin complex. A complex with dimeric particles can be formed for the system of Lu-tetraphenylporphyrin. Constants of the ion exchange reactions were calculated.

Metal-organic complexes in geochemical processes: Estimation of standard partial molal thermodynamic properties of aqueous complexes between metal cations and monovalent organic acid ligands at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Shock, Everetr L.; Koretsky, Carla M.

1995-04-01

Regression of standard state equilibrium constants with the revised Helgeson-Kirkham-Flowers (HKF) equation of state allows evaluation of standard partial molal entropies ( overlineSo) of aqueous metal-organic complexes involving monovalent organic acid ligands. These values of overlineSo provide the basis for correlations that can be used, together with correlation algorithms among standard partial molal properties of aqueous complexes and equation-of-state parameters, to estimate thermodynamic properties including equilibrium constants for complexes between aqueous metals and several monovalent organic acid ligands at the elevated pressures and temperatures of many geochemical processes which involve aqueous solutions. Data, parameters, and estimates are given for 270 formate, propanoate, n-butanoate, n-pentanoate, glycolate, lactate, glycinate, and alanate complexes, and a consistent algorithm is provided for making other estimates. Standard partial molal entropies of association ( Δ -Sro) for metal-monovalent organic acid ligand complexes fall into at least two groups dependent upon the type of functional groups present in the ligand. It is shown that isothermal correlations among equilibrium constants for complex formation are consistent with one another and with similar correlations for inorganic metal-ligand complexes. Additional correlations allow estimates of standard partial molal Gibbs free energies of association at 25°C and 1 bar which can be used in cases where no experimentally derived values are available.

Quantitative description and local structures of trivalent metal ions Eu(III) and Cm(III) complexed with polyacrylic acid.

PubMed

Montavon, G; Bouby, M; Huclier-Markai, S; Grambow, B; Geckeis, H; Rabung, T; Pashalidis, I; Amekraz, B; Moulin, C

2008-11-15

The trivalent metal ion (M(III)=Cm, Eu)/polyacrylic acid (PAA) system was studied in the pH range between 3 and 5.5 for a molar PAA-to-metal ratio above 1. The interaction was studied for a wide range of PAA (0.05 mg L(-1)-50 g L(-1)) and metal ion concentrations (2x10(-9)-10(-3) M). This work aimed at 3 goals (i) to determine the stoichiometry of M(III)-PAA complexes, (ii) to determine the number of complexed species and the local environment of the metal ion, and (iii) to quantify the reaction processes. Asymmetric flow-field-flow fractionation (AsFlFFF) coupled to ICP-MS evidenced that size distributions of Eu-PAA complexes and PAA were identical, suggesting that Eu bound to only one PAA chain. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements performed with Eu and Cm showed a continuous shift of the spectra with increasing pH. The environment of complexed metal ions obviously changes with pH. Most probably, spectral variations arose from conformational changes within the M(III)-PAA complex due to pH variation. Complexation data describing the distribution of complexed and free metal ion were measured with Cm by TRLFS. They could be quantitatively described in the whole pH-range studied by considering the existence of only a single complexed species. This indicates that the slight changes in M(III) speciation with pH observed at the molecular level do not significantly affect the intrinsic binding constant. The interaction constant obtained from the modelling must be considered as a mean interaction constant.

Electrochemistry of mixed-metal bimetallic complexes containing the pentacyanoferrate(II) or pentaammineruthenium(II) metal center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, K.J.; Lee, L.; Mabbott, G.A.

1983-03-30

The electrochemistry of a series of mixed-metal bimetallic complexes of the type B/sub 5/MLM'B'/sub 5/, where B/sub 5/M = (CNN)/sub 5/Fe/sup II/ or (NH/sub 3/)/sub 5/Ru/sup II/, L = pyrazine, 4,4'-bipyridine, or 4-cyanopyridine, M'B'/sub 5/ = Rh/sup III/(NH/sub 3/)/sub 5/ or Co/sup III/(CN)/sub 5/, is reported. The bimetallic complexes all have metal-to-ligand charge-transfer (MLCT) bands associated with the M-B unit (d/sub ..pi../M ..-->.. p/sub ..pi../*L). The effect of the remote metal center, M'B'/sub 5/, is to function as a Lewis acid, shifting the MLCT maximum to lower energy and shifting the M/sup III///sup II/ reduction potential more positive with respectmore » to free B/sub 5/ML. The remote metal influence is attenuated by longer bridging ligands and by reduced ..pi..-overlap. A comparison of the electrochemical data of the mixed-valence Fe(II)/Fe(III) and Ru(II)/Ru(III) complexes to the mixed-metal Fe(II)/Co(III) and Ru(II)/Rh(III) complexes has enabled a quantitative measure of the stabilization due to electron delocalization in the mixed-valence complexes. The results show that electron delocalization is greater for the ruthenium complexes than for the iron complexes, is a small contributor to the total stabilization of the mixed-valence state, and even in ruthenium drops off rapidly as the length of the bridge increases.« less

Synthesis, spectral, thermal and antimicrobial studies of transition metal complexes of 14-membered tetraaza[N4] macrocyclic ligand

NASA Astrophysics Data System (ADS)

Shankarwar, Sunil G.; Nagolkar, Bhagwat B.; Shelke, Vinod A.; Chondhekar, Trimbak K.

2015-06-01

A series of metal complexes of Mn(II), Co(II), Ni(II), Cu(II), have been synthesized with newly synthesized biologically active macrocyclic ligand. The ligand was synthesized by condensation of β-diketone 1-(4-chlorophenyl)-3-(2-hydroxyphenyl)propane-1,3-dione and o-phenylene diamine. All the complexes were characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, 1H-NMR, UV-Vis spectroscopy and mass spectroscopy. From the analytical data, stoichiometry of the complexes was found to be 1:2 (metal:ligand). Thermal behavior (TG/DTA) and kinetic parameters suggest more ordered activated state in complex formation. All the complexes are of high spin type and six coordinated. On the basis of IR, electronic spectral studies and magnetic behavior, an octahedral geometry has been assigned to these complexes. The antibacterial and antifungal activities of the ligand and its metal complexes, has been screened in vitro against Staphylococcus aureus, Escherichia coli and Aspergillus niger, Trichoderma respectively.

Affinity to bovine serum albumin and anticancer activity of some new water-soluble metal Schiff base complexes

NASA Astrophysics Data System (ADS)

Asadi, Mozaffar; Asadi, Zahra; Zarei, Leila; Sadi, Somaye Barzegar; Amirghofran, Zahra

2014-12-01

Metal Schiff-base complexes show biological activity but they are usually insoluble in water so four new water-soluble metal Schiff base complexes of Na2[M(5-SO3-1,2-salben]; (5-SO3-1,2-salben denoted N,N";-bis(5-sulphosalicyliden)-1,2-diaminobenzylamine and M = Mg, Mn, Cu, Zn) were synthesized and characterized. The formation constants of the metal complexes were determined by UV-Vis absorption spectroscopy. The interaction of these complexes with bovine serum albumin (BSA) was studied by fluorescence spectroscopy. Type of quenching, binding constants, number of binding sites and binding stoichiometries were determined by fluorescence quenching method. The results showed that the mentioned complexes strongly bound to BSA. Thermodynamic parameters indicated that hydrophobic association was the major binding force and that the interaction was entropy driven and enthalpically disfavoured. The displacement experiment showed that these complexes could bind to the subdomain IIA (site I) of albumin. Furthermore the synchronous fluorescence spectra showed that the microenvironment of the tryptophan residues was not apparently changed. Based on the Förster theory of non-radiation energy transfer, the distance between the donor (Trp residues) and the acceptor metal complexes was obtained. The growth inhibitory effect of complexes toward the K562 cancer cell line was measured.

Preparation of nanoporous metal foam from high nitrogen transition metal complexes

DOEpatents

Tappan, Bryce C.; Huynh, My Hang V.; Hiskey, Michael A.; Son, Steven F.; Oschwald, David M.; Chavez, David E.; Naud, Darren L.

2006-11-28

Nanoporous metal foams are prepared by ignition of high nitrogen transition metal complexes. The ammonium salts of iron(III) tris[bi(tetrazolato)-amine], cobalt(III) tris(bi(tetrazolato)amine), and high nitrogen compounds of copper and silver were prepared as loose powders, pressed into pellets and wafers, and ignited under an inert atmosphere to form nanoporous metal foam monoliths having very high surface area and very low density.

A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence

NASA Astrophysics Data System (ADS)

Chábera, Pavel; Liu, Yizhu; Prakash, Om; Thyrhaug, Erling; Nahhas, Amal El; Honarfar, Alireza; Essén, Sofia; Fredin, Lisa A.; Harlang, Tobias C. B.; Kjær, Kasper S.; Handrup, Karsten; Ericson, Fredric; Tatsuno, Hideyuki; Morgan, Kelsey; Schnadt, Joachim; Häggström, Lennart; Ericsson, Tore; Sobkowiak, Adam; Lidin, Sven; Huang, Ping; Styring, Stenbjörn; Uhlig, Jens; Bendix, Jesper; Lomoth, Reiner; Sundström, Villy; Persson, Petter; Wärnmark, Kenneth

2017-03-01

Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)3]3+ (where btz is 3,3‧-dimethyl-1,1‧-bis(p-tolyl)-4,4‧-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(III) d5 complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

Metal-isonitrile adducts for preparing radionuclide complexes for labelling and imaging agents

DOEpatents

Jones, Alun G.; Davison, Alan; Abrams, Michael J.

1987-01-01

A method for preparing a coordination complex of an isonitrile ligand and radionuclide such as Tc, Ru, Co, Pt, Fe, Os, Ir, W, Re, Cr, Mo, Mn, Ni, Rh, Pd, Nb and Ta is disclosed. The method comprises preparing a soluble metal adduct of said isonitrile ligand by admixing said ligand with a salt of a displaceable metal having a complete d-electron shell selected from the group consisting of Zn, Ga, Cd, In, Sn, Hg, Tl, Pb and Bi to form a soluble metal-isonitrile salt, and admixing said metal isonitrile salt with a salt comprising said radioactive metal in a suitable solvent to displace said displaceable metal with the radioactive metal thereby forming said coordination. The complex is useful as a diagnostic agent for labelling liposomes or vesicles, and selected living cells containing lipid membranes, such as blood clots, myocardial tissue, gall bladder tissue, etc.

Group transfer and electron transfer reactions of organometallic complexes

NASA Astrophysics Data System (ADS)

Atwood, Jim D.

During 1994, despite the disruptions, the authors have made progress in several aspects of their research on electron transfer reactions between organometallic complexes. This summary covers three areas that are relatively complete: (1) reactions between metal carbonyl anions and metal carbonyl halides, (2) reactions of hydrido- and alkyl-containing anions (RFe(CO)4(-) and RW(CO)5(-) with metal carbonyl cations; and (3) reactions of a seventeen-electron complex (Cp* Cr(CO)3*) with metal carbonyl derivatives. Two areas of examination that have just begun (possible carbene transfer and the possible role of metal carbonyl anions in carbon-hydrogen bond activation) will also be described.

Syntheses, spectroscopic characterization, thermal study, molecular modeling, and biological evaluation of novel Schiff's base benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) with Ni(II), and Cu(II) metal complexes.

PubMed

Chandra, Sulekh; Gautam, Seema; Rajor, Hament Kumar; Bhatia, Rohit

2015-02-25

Novel Schiff's base ligand, benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) was synthesized by the condensation of benzil and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio. The structure of ligand was determined on the basis of elemental analyses, IR, (1)H NMR, mass, and molecular modeling studies. Synthesized ligand behaved as tetradentate and coordinated to metal ion through sulfur atoms of thiol ring and nitrogen atoms of imine group. Ni(II), and Cu(II) complexes were synthesized with this nitrogen-sulfur donor (N2S2) ligand. Metal complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, IR, electronic spectra, EPR, thermal, and molecular modeling studies. All the complexes showed molar conductance corresponding to non-electrolytic nature, expect [Ni(L)](NO3)2 complex, which was 1:2 electrolyte in nature. [Cu(L)(SO4)] complex may possessed square pyramidal geometry, [Ni(L)](NO3)2 complex tetrahedral and rest of the complexes six coordinated octahedral/tetragonal geometry. Newly synthesized ligand and its metal complexes were examined against the opportunistic pathogens. Results suggested that metal complexes were more biological sensitive than free ligand. Copyright © 2014 Elsevier B.V. All rights reserved.

New technique for heterogeneous vapor-phase synthesis of nanostructured metal layers from low-dimensional volatile metal complexes

NASA Astrophysics Data System (ADS)

Badalyan, A. M.; Bakhturova, L. F.; Kaichev, V. V.; Polyakov, O. V.; Pchelyakov, O. P.; Smirnov, G. I.

2011-09-01

A new technique for depositing thin nanostructured layers on semiconductor and insulating substrates that is based on heterogeneous gas-phase synthesis from low-dimensional volatile metal complexes is suggested and tried out. Thin nanostructured copper layers are deposited on silicon and quartz substrates from low-dimensional formate complexes using a combined synthesis-mass transport process. It is found that copper in layers thus deposited is largely in a metal state (Cu0) and has the form of closely packed nanograins with a characteristic structure.

Fabrication of transparent ceramics using nanoparticles

DOEpatents

Cherepy, Nerine J; Tillotson, Thomas M; Kuntz, Joshua D; Payne, Stephen A

2012-09-18

A method of fabrication of a transparent ceramic using nanoparticles synthesized via organic acid complexation-combustion includes providing metal salts, dissolving said metal salts to produce an aqueous salt solution, adding an organic chelating agent to produce a complexed-metal sol, heating said complexed-metal sol to produce a gel, drying said gel to produce a powder, combusting said powder to produce nano-particles, calcining said nano-particles to produce oxide nano-particles, forming said oxide nano-particles into a green body, and sintering said green body to produce the transparent ceramic.

Vanadium and nickel complexes in petroleum resid acid, base, and neutral fractions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pearson, C.D.; Green, J.D.

1993-01-01

Acid and base fractions from petroleum vacuum resids with no detectable (by visible spectrophotometry) quantities of porphyrinic Ni or V complexes were hydrotreated under various conditions to determine if significant amounts of porphyrinic metals were released, via disassociation or other means, upon hydrotreating. No significant quantities were observed, thereby indicating that nonporphyrinic metals were not simply associated, complexed or otherwise masked (in terms of visible spectrophotometric response) porphyrinic metal complexes. However, it is possible that hydrotreating was simply not effective in breaking up these associates and/or that some porphyrinic forms of metal were in fact released but were rapidly destroyedmore » by hydrotreating. In addition, three liquid chromatographic (LC) separation methods were sequentially applied to Cerro Negro (Orinoco belt Venezuelan heavy crude) >700[degree]C resid in an effort to separate and concentrate the metal complexes present. Nonaqueous ion exchange chromatography was used initially to separate the resid into acid, base and neutral types. Two concentrates containing 19,500 and 13,500 ppm total V, or an estimated 19 and 13 wt % V-containing compounds respectively, were obtained. The degree of enrichment of Ni compounds obtained was significantly lower. By visible spectrophotometry, using vanadyl etioporphyrin as a standard, each of the concentrates contained near a 1:1 ratio of porphyrinic:nonporphyrinic V complexes. Analogous separation behavior for porphyrinic versus nonporphyrinic metal forms was observed throughout much of the work, thereby suggesting that a comparable diversity of structures existed within each general class of metal compounds. The generally wide dispersion of both Ni and V over the LC separation scheme suggests a structural variety of metal complexes that is comparable to that observed for other heteroatoms (N, S, O) in petroleum.« less

Vanadium and nickel complexes in petroleum resid acid, base, and neutral fractions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pearson, C.D.; Green, J.D.

1993-01-01

Acid and base fractions from petroleum vacuum resids with no detectable (by visible spectrophotometry) quantities of porphyrinic Ni or V complexes were hydrotreated under various conditions to determine if significant amounts of porphyrinic metals were released, via disassociation or other means, upon hydrotreating. No significant quantities were observed, thereby indicating that nonporphyrinic metals were not simply associated, complexed or otherwise masked (in terms of visible spectrophotometric response) porphyrinic metal complexes. However, it is possible that hydrotreating was simply not effective in breaking up these associates and/or that some porphyrinic forms of metal were in fact released but were rapidly destroyedmore » by hydrotreating. In addition, three liquid chromatographic (LC) separation methods were sequentially applied to Cerro Negro (Orinoco belt Venezuelan heavy crude) >700{degree}C resid in an effort to separate and concentrate the metal complexes present. Nonaqueous ion exchange chromatography was used initially to separate the resid into acid, base and neutral types. Two concentrates containing 19,500 and 13,500 ppm total V, or an estimated 19 and 13 wt % V-containing compounds respectively, were obtained. The degree of enrichment of Ni compounds obtained was significantly lower. By visible spectrophotometry, using vanadyl etioporphyrin as a standard, each of the concentrates contained near a 1:1 ratio of porphyrinic:nonporphyrinic V complexes. Analogous separation behavior for porphyrinic versus nonporphyrinic metal forms was observed throughout much of the work, thereby suggesting that a comparable diversity of structures existed within each general class of metal compounds. The generally wide dispersion of both Ni and V over the LC separation scheme suggests a structural variety of metal complexes that is comparable to that observed for other heteroatoms (N, S, O) in petroleum.« less

Metal species involved in long distance metal transport in plants

PubMed Central

Álvarez-Fernández, Ana; Díaz-Benito, Pablo; Abadía, Anunciación; López-Millán, Ana-Flor; Abadía, Javier

2014-01-01

The mechanisms plants use to transport metals from roots to shoots are not completely understood. It has long been proposed that organic molecules participate in metal translocation within the plant. However, until recently the identity of the complexes involved in the long-distance transport of metals could only be inferred by using indirect methods, such as analyzing separately the concentrations of metals and putative ligands and then using in silico chemical speciation software to predict metal species. Molecular biology approaches also have provided a breadth of information about putative metal ligands and metal complexes occurring in plant fluids. The new advances in analytical techniques based on mass spectrometry and the increased use of synchrotron X-ray spectroscopy have allowed for the identification of some metal-ligand species in plant fluids such as the xylem and phloem saps. Also, some proteins present in plant fluids can bind metals and a few studies have explored this possibility. This study reviews the analytical challenges researchers have to face to understand long-distance metal transport in plants as well as the recent advances in the identification of the ligand and metal-ligand complexes in plant fluids. PMID:24723928

Speciation of heavy metals in landfill leachate: a review.

PubMed

Baun, Dorthe L; Christensen, Thomas H

2004-02-01

The literature was reviewed with respect to metal speciation methods in aquatic samples specifically emphasizing speciation of heavy metals in landfill leachate. Speciation here refers to physical fractionation (particulate, colloidal, dissolved), chemical fractionation (organic complexes, inorganic complexes, free metal ions), as well as computer-based thermodynamic models. Relatively few landfill leachate samples have been speciated in detail (less than 30) representing only a few landfills (less than 15). This suggests that our knowledge about metal species in landfill leachate still is indicative. In spite of the limited database and the different definitions of the dissolved fraction (< 0.45 microm or < 0.001 microm) the studies consistently show that colloids as well as organic and inorganic complexes are important for all heavy metals in landfill leachate. The free metal ion constitutes less than 30%, typically less than 10%, of the total metal concentration. This has significant implications for sampling, since no standardized procedures exist, and for assessing the content of metals in leachate in the context of its treatment, toxicity and migration in aquifers.

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

NASA Technical Reports Server (NTRS)

Beck, M.

1979-01-01

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

Synthesis, structure and DFT study of cymantrenyl Fischer carbene complexes of group VI and VII transition metals

NASA Astrophysics Data System (ADS)

Fraser, Roan; van Rooyen, Petrus H.; Landman, Marilé

2016-02-01

Bi- and trimetallic carbene complexes of group VI and VII transition metals (Cr, Mo, W, Mn and Re), with CpMn(CO)3 as the initial synthon, have been synthesised according to the classical Fischer methodology. Crystal structures of the novel carbene complexes with general formula [Mx(CO)y-1{C(OEt)(MnCp(CO)3)}], where x = 1 then y = 3 or 6; x = 2 then y = 10, of the complexes are reported. A density functional theory (DFT) study was undertaken to determine natural bonding orbitals (NBOs) and conformational as well as isomeric aspects of the polymetallic complexes. Application of the second-order perturbation theory (SOPT) of the natural bond orbital (NBO) method revealed stabilizing interactions between the methylene C-H bonds and the carbonyl ligands of the carbene metal moiety. These stabilization interactions show a linear decrease for the group VI metal carbene complexes down the group.

Self-templated formation of uniform NiCo2O4 hollow spheres with complex interior structures for lithium-ion batteries and supercapacitors.

PubMed

Shen, Laifa; Yu, Le; Yu, Xin-Yao; Zhang, Xiaogang; Lou, Xiong Wen David

2015-02-02

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, characterization, spectroscopic and antioxidation studies of Cu(II)-morin complex

NASA Astrophysics Data System (ADS)

Panhwar, Qadeer Khan; Memon, Shahabuddin; Bhanger, M. I.

2010-04-01

Complex formation between copper (II) sulfate and morin (3,5,7,2',4'-pentahydroxyflavone) have been studied in methanol. Structure of the complex was determined through various analytical techniques including UV-vis, IR, 1H NMR, thermal, gravimetric and elemental analyses. The stoichiometric ratio for the reaction between the flavonoid and the metal ion in methanol has been determined by Job's method and elemental analysis for metal content of complex by titration with EDTA, which confirm that morin forms a 1:1 metal:ligand complex. 1H NMR study reveals that, 3OH and 4CO groups of morin take part in complexation with a copper ion. Individual stress was given to the site of central ion and composition of the complex. Antioxidant activity of the complex was evaluated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method, which showed that the antioxidant activity of complexed morin has higher value as compared to the free morin. Moreover, it was observed that the metal complex is sufficiently stable as well as the data indicates the spontaneous formation of complex (-Δ G) that is exothermic in nature (-Δ H) and entropically unfavourable (-Δ S).

General Synthesis of Transition-Metal Oxide Hollow Nanospheres/Nitrogen-Doped Graphene Hybrids by Metal-Ammine Complex Chemistry for High-Performance Lithium-Ion Batteries.

PubMed

Chen, Jiayuan; Wu, Xiaofeng; Gong, Yan; Wang, Pengfei; Li, Wenhui; Mo, Shengpeng; Peng, Shengpan; Tan, Qiangqiang; Chen, Yunfa

2018-02-09

We present a general and facile synthesis strategy, on the basis of metal-ammine complex chemistry, for synthesizing hollow transition-metal oxides (Co 3 O 4 , NiO, CuO-Cu 2 O, and ZnO)/nitrogen-doped graphene hybrids, potentially applied in high-performance lithium-ion batteries. The oxygen-containing functional groups of graphene oxide play a prerequisite role in the formation of hollow transition-metal oxides on graphene nanosheets, and a significant hollowing process occurs only when forming metal (Co 2+ , Ni 2+ , Cu 2+ , or Zn 2+ )-ammine complex ions. Moreover, the hollowing process is well correlated with the complexing capacity between metal ions and NH 3 molecules. The significant hollowing process occurs for strong metal-ammine complex ions including Co 2+ , Ni 2+ , Cu 2+ , and Zn 2+ ions, and no hollow structures formed for weak and/or noncomplex Mn 2+ and Fe 3+ ions. Simultaneously, this novel strategy can also achieve the direct doping of nitrogen atoms into the graphene framework. The electrochemical performance of two typical hollow Co 3 O 4 or NiO/nitrogen-doped graphene hybrids was evaluated by their use as anodic materials. It was demonstrated that these unique nanostructured hybrids, in contrast with the bare counterparts, solid transition-metal oxides/nitrogen-doped graphene hybrids, perform with significantly improved specific capacity, superior rate capability, and excellent capacity retention. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Solar chemistry of metal complexes

NASA Astrophysics Data System (ADS)

Gray, H. B.; Maverick, A. W.

1981-12-01

Electronic excited states of certain transition metal complexes undergo oxidation-reduction reactions that store chemical energy. Such reactions have been extensively explored for mononuclear complexes. Two classes of polynuclear species exhibit similar properties, and these complexes are now being studied as possible homogeneous sensitizer-catalysts for hydrogen production from aqueous solutions.

Synthesis, characterization of 1,2,4-triazole Schiff base derived 3d-metal complexes: Induces cytotoxicity in HepG2, MCF-7 cell line, BSA binding fluorescence and DFT study

NASA Astrophysics Data System (ADS)

Tyagi, Prateek; Tyagi, Monika; Agrawal, Swati; Chandra, Sulekh; Ojha, Himanshu; Pathak, Mallika

2017-01-01

Two novel Schiff base ligands H2L1 and H2L2 have been synthesized by condensation reaction of amine derivative of 1,2,4-triazole moiety with 2-hydroxy-4-methoxybenzaldehyde. Co(II), Ni(II), Cu(II) and Zn(II) of the synthesized Schiff bases were prepared by using a molar ratio of ligand:metal as 1:1. The structure of the Schiff bases and synthesized metal complexes were established by 1H NMR, UV-Vis, IR, Mass spectrometry and molar conductivity. The thermal stability of the complexes was study by TGA. Fluorescence quenching mechanism of metal complexes 1-4 show that Zn(II) and Cu(II) complex binds more strongly to BSA. In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6-31 + g(d,p) basis set. The spectral data shows that the ligands behaves as binegative tridentate. On the basis of the spectral studies, TGA and DFT data an octahedral geometry has been assigned for Co(II), Ni(II), square planar for Cu(II) and tetrahedral for Zn(II) complexes. The anticancer activity were screened against human breast cancer cell line (MCF-7) and human hepatocellular liver carcinoma cell line (Hep-G2). Result indicates that metal complexes shows increase cytotoxicity in proliferation to cell lines as compared to free ligand.

Synthesis and antimalarial activity of metal complexes of cross-bridged tetraazamacrocyclic ligands.

PubMed

Hubin, Timothy J; Amoyaw, Prince N-A; Roewe, Kimberly D; Simpson, Natalie C; Maples, Randall D; Carder Freeman, TaRynn N; Cain, Amy N; Le, Justin G; Archibald, Stephen J; Khan, Shabana I; Tekwani, Babu L; Khan, M O Faruk

2014-07-01

Using transition metals such as manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II), several new metal complexes of cross-bridged tetraazamacrocyclic chelators namely, cyclen- and cyclam-analogs with benzyl groups, were synthesized and screened for in vitro antimalarial activity against chloroquine-resistant (W2) and chloroquine-sensitive (D6) strains of Plasmodium falciparum. The metal-free chelators tested showed little or no antimalarial activity. All the metal complexes of the dibenzyl cross-bridged cyclam ligand exhibited potent antimalarial activity. The Mn(2+) complex of this ligand was the most potent with IC50s of 0.127 and 0.157μM against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) P. falciparum strains, respectively. In general, the dibenzyl hydrophobic ligands showed better anti-malarial activity compared to the activity of monobenzyl ligands, potentially because of their higher lipophilicity and thus better cell penetration ability. The higher antimalarial activity displayed by the manganese complex for the cyclam ligand in comparison to that of the cyclen, correlates with the larger pocket of cyclam compared to that of cyclen which produces a more stable complex with the Mn(2+). Few of the Cu(2+) and Fe(2+) complexes also showed improvement in activity but Ni(2+), Co(2+) and Zn(2+) complexes did not show any improvement in activity upon the metal-free ligands for anti-malarial development. Published by Elsevier Ltd.

Structure-activity relationships of mononuclear metal-thiosemicarbazone complexes endowed with potent antiplasmodial and antiamoebic activities.

PubMed

Bahl, Deepa; Athar, Fareeda; Soares, Milena Botelho Pereira; de Sá, Matheus Santos; Moreira, Diogo Rodrigo Magalhães; Srivastava, Rajendra Mohan; Leite, Ana Cristina Lima; Azam, Amir

2010-09-15

A useful concept for the rational design of antiparasitic drug candidates is the complexation of bioactive ligands with transition metals. In view of this, an investigation was conducted into a new set of metal complexes as potential antiplasmodium and antiamoebic agents, in order to examine the importance of metallic atoms, as well as the kind of sphere of co-ordination, in these biological properties. Four functionalized furyl-thiosemicarbazones (NT1-4) treated with divalent metals (Cu, Co, Pt, and Pd) to form the mononuclear metallic complexes of formula [M(L)2Cl2] or [M(L)Cl2] were examined. The pharmacological characterization, including assays against Plasmodium falciparum and Entamoeba histolytica, cytotoxicity to mammalian cells, and interaction with pBR 322 plasmid DNA was performed. Structure-activity relationship data revealed that the metallic complexation plays an essential role in antiprotozoal activity, rather than the simple presence of the ligand or metal alone. Important steps towards identification of novel antiplasmodium (NT1Cu, IC50 of 4.6 microM) and antiamoebic (NT2Pd, IC50 of 0.6 microM) drug prototypes were achieved. Of particular relevance to this work, these prototypes were able to reduce the proliferation of these parasites at concentrations that are not cytotoxic to mammalian cells. Copyright (c) 2010. Published by Elsevier Ltd.

Neutralization by Metal Ions of the Toxicity of Sodium Selenide

PubMed Central

Dauplais, Marc; Lazard, Myriam; Blanquet, Sylvain; Plateau, Pierre

2013-01-01

Inert metal-selenide colloids are found in animals. They are believed to afford cross-protection against the toxicities of both metals and selenocompounds. Here, the toxicities of metal salt and sodium selenide mixtures were systematically studied using the death rate of Saccharomyces cerevisiae cells as an indicator. In parallel, the abilities of these mixtures to produce colloids were assessed. Studied metal cations could be classified in three groups: (i) metal ions that protect cells against selenium toxicity and form insoluble colloids with selenide (Ag+, Cd2+, Cu2+, Hg2+, Pb2+ and Zn2+), (ii) metal ions which protect cells by producing insoluble metal-selenide complexes and by catalyzing hydrogen selenide oxidation in the presence of dioxygen (Co2+ and Ni2+) and, finally, (iii) metal ions which do not afford protection and do not interact (Ca2+, Mg2+, Mn2+) or weakly interact (Fe2+) with selenide under the assayed conditions. When occurring, the insoluble complexes formed from divalent metal ions and selenide contained equimolar amounts of metal and selenium atoms. With the monovalent silver ion, the complex contained two silver atoms per selenium atom. Next, because selenides are compounds prone to oxidation, the stabilities of the above colloids were evaluated under oxidizing conditions. 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), the reduction of which can be optically followed, was used to promote selenide oxidation. Complexes with cadmium, copper, lead, mercury or silver resisted dissolution by DTNB treatment over several hours. With nickel and cobalt, partial oxidation by DTNB occurred. On the other hand, when starting from ZnSe or FeSe complexes, full decompositions were obtained within a few tens of minutes. The above properties possibly explain why ZnSe and FeSe nanoparticles were not detected in animals exposed to selenocompounds. PMID:23342137

Transition Metal Intercalators as Anticancer Agents—Recent Advances

PubMed Central

Deo, Krishant M.; Pages, Benjamin J.; Ang, Dale L.; Gordon, Christopher P.; Aldrich-Wright, Janice R.

2016-01-01

The diverse anticancer utility of cisplatin has stimulated significant interest in the development of additional platinum-based therapies, resulting in several analogues receiving clinical approval worldwide. However, due to structural and mechanistic similarities, the effectiveness of platinum-based therapies is countered by severe side-effects, narrow spectrum of activity and the development of resistance. Nonetheless, metal complexes offer unique characteristics and exceptional versatility, with the ability to alter their pharmacology through facile modifications of geometry and coordination number. This has prompted the search for metal-based complexes with distinctly different structural motifs and non-covalent modes of binding with a primary aim of circumventing current clinical limitations. This review discusses recent advances in platinum and other transition metal-based complexes with mechanisms of action involving intercalation. This mode of DNA binding is distinct from cisplatin and its derivatives. The metals focused on in this review include Pt, Ru and Cu along with examples of Au, Ni, Zn and Fe complexes; these complexes are capable of DNA intercalation and are highly biologically active. PMID:27809241

Simultaneous separation of inorganic anions and metal-citrate complexes on a zwitterionic stationary phase with on-column complexation.

PubMed

Nesterenko, Ekaterina P; Nesterenko, Pavel N; Paull, Brett

2008-12-05

The retention and separation selectivity of inorganic anions and on-column derivatised negatively charged citrate or oxalate metal complexes on reversed-phase stationary phases dynamically coated with N-(dodecyl-N,N-dimethylammonio)undecanoate (DDMAU) has been investigated. The retention mechanism for the metal-citrate complexes was predominantly anion exchange, although the amphoteric/zwitterionic nature of the stationary phase coating undoubtedly also contributed to the unusual separation selectivity shown. A mixture of 10 inorganic anions and metal cations was achieved using a 20 cm monolithic DDMAU modified column and a 1 mM citrate eluent, pH 4.0, flow rate equal to 0.8 mL/min. Selectivity was found to be strongly pH dependent, allowing additional scope for manipulation of solute retention, and thus application to complex samples. This is illustrated with the analysis of an acidic mine drainage sample with a range of inorganic anions and transition metal cations, varying significantly in their concentrations levels.

Synthesis and characterization of a metal complex containing naringin and Cu, and its antioxidant, antimicrobial, antiinflammatory and tumor cell cytotoxicity.

PubMed

Pereira, Regina M S; Andrades, Norma E D; Paulino, Niraldo; Sawaya, Alexandra C H F; Eberlin, Marcos N; Marcucci, Maria C; Favero, Giovani Marino; Novak, Estela Maria; Bydlowski, Sérgio Paulo

2007-07-09

The antioxidant activity of flavonoids is believed to increase when they are coordinated with transition metal ions. However, the literature on this subject is contradictory and the outcome seems to largely depend on the experimental conditions. In order to understand the contribution of the metal coordination and the type of interaction between a flavonoid and the metal ion, in this study a new metal complex of Cu (II) with naringin was synthesized and characterized by FT-IR, UV-VIS, mass spectrometry (ESI-MS/MS), elemental analysis and 1H-NMR. The results of these analyses indicate that the complex has a Cu (II) ion coordinated via positions 4 and 5 of the flavonoid. The antioxidant, anti-inflammatory and antimicrobial activities of this complex were studied and compared with the activity of free naringin. The Naringin-Cu (II) complex 1 showed higher antioxidant, anti-inflammatory and tumor cell cytotoxicity activities than free naringin without reducing cell viability.

The QSAR study of flavonoid-metal complexes scavenging rad OH free radical

NASA Astrophysics Data System (ADS)

Wang, Bo-chu; Qian, Jun-zhen; Fan, Ying; Tan, Jun

2014-10-01

Flavonoid-metal complexes have antioxidant activities. However, quantitative structure-activity relationships (QSAR) of flavonoid-metal complexes and their antioxidant activities has still not been tackled. On the basis of 21 structures of flavonoid-metal complexes and their antioxidant activities for scavenging rad OH free radical, we optimised their structures using Gaussian 03 software package and we subsequently calculated and chose 18 quantum chemistry descriptors such as dipole, charge and energy. Then we chose several quantum chemistry descriptors that are very important to the IC50 of flavonoid-metal complexes for scavenging rad OH free radical through method of stepwise linear regression, Meanwhile we obtained 4 new variables through the principal component analysis. Finally, we built the QSAR models based on those important quantum chemistry descriptors and the 4 new variables as the independent variables and the IC50 as the dependent variable using an Artificial Neural Network (ANN), and we validated the two models using experimental data. These results show that the two models in this paper are reliable and predictable.

Curcumin derivatives as metal-chelating agents with potential multifunctional activity for pharmaceutical applications.

PubMed

Ferrari, Erika; Benassi, Rois; Sacchi, Stefania; Pignedoli, Francesca; Asti, Mattia; Saladini, Monica

2014-10-01

Curcuminoids represent new perspectives for the development of novel therapeutics for Alzheimer's disease (AD), one probable mechanism of action is related to their metal complexing ability. In this work we examined the metal complexing ability of substituted curcuminoids to propose new chelating molecules with biological properties comparable with curcumin but with improved stability as new potential AD therapeutic agents. The K2T derivatives originate from the insertion of a -CH2COOC(CH3)3 group on the central atom of the diketonic moiety of curcumin. They retain the diketo-ketoenol tautomerism which is solvent dependent. In aqueous solution the prevalent form is the diketo one but the addition of metal ion (Ga(3+), Cu(2+)) causes the dissociation of the enolic proton creating chelate complexes and shifting the tautomeric equilibrium towards the keto-enol form. The formation of metal complexes is followed by both NMR and UV-vis spectroscopy. The density functional theory (DFT) calculations on K2T21 complexes with Ga(3+) and Cu(2+) are performed and compared with those on curcumin complexes. [Ga(K2T21)2(H2O)2](+) was found more stable than curcumin one. Good agreement is detected between calculated and experimental (1)H and (13)C NMR data. The calculated OH bond dissociation energy (BDE) and the OH proton dissociation enthalpy (PDE), allowed to predict the radical scavenging ability of the metal ion complexed with K2T21, while the calculated electronic affinity (EA) and ionization potential (IP) represent yardsticks of antioxidant properties. Eventually theoretical calculations suggest that the proton-transfer-associated superoxide-scavenging activity is enhanced after binding metal ions, and that Ga(3+) complexes display possible superoxide dismutase (SOD)-like activity. Copyright © 2014 Elsevier Inc. All rights reserved.

The preparation and use of metal salen complexes derived from cyclobutane diamine

NASA Astrophysics Data System (ADS)

Patil, Smita

The helix is an important chiral motif in nature, there is increasing development in field of helical transition metal complexes and related supramolecular structures. Hence, the goals of this work are to apply the principles of helicity in order to produce metal complexes with predictable molecular shapes and to study their properties as asymmetric catalysts. Computational studies suggest that the (1R,2 R)-cyclobutyldiamine unit can produce highly twisted salen complexes with a large energy barrier between the M and P helical forms. To test this prediction, the tartrate salt of (1R,2R)-cyclobutyldiamine was synthesized and condensed with a series of saliclaldehydes to produce novel salen ligands. The salicylaldehydes chosen have extended phenanthryl or benz[a]anthryl sidearms to encourage formation of helical coordination complexes. These ligands were metallated with zinc, iron and manganese salts to produce salen metal complexes which were characterized by NMR analysis, high-resolution mass spectrometry, and IR spectroscopy. A second ligand type, neutral bis(pyridine-imine) has also been synthesized from (1R,2R)-cyclobutyldiamine and quinolylaldehydes. The synthesis of bis(pyridine-imine) ligands was conducted using greener method, solvent assisted grinding. These ligands, in-situ with nickel metal salts, showed good catalytic activity for asymmetric Diels-Alder reactions. The third ligand type studied was chiral acid-functionalized Schiff-base ligands. These were synthesized by the condensation of 3-formyl-5-methyl salicylic acid and (1R,2R)-cyclobutyldiamine. With this type of ligand, there is possibility of producing both mono and dinuclear metal complexes. In our studies, we were only able to synthesize mononuclear complexs. These were tested as catalysts for asymmetric direct Mannich-type reaction, but were found to be ineffective.

Structural Characterization and Function Determination of a Nonspecific Carboxylate Esterase from the Amidohydrolase Superfamily with a Promiscuous Ability To Hydrolyze Methylphosphonate Esters

PubMed Central

2015-01-01

The uncharacterized protein Rsp3690 from Rhodobacter sphaeroides is a member of the amidohydrolase superfamily of enzymes. In this investigation the gene for Rsp3690 was expressed in Escherichia coli and purified to homogeneity, and the three-dimensional structure was determined to a resolution of 1.8 Å. The protein folds as a distorted (β/α)8-barrel, and the subunits associate as a homotetramer. The active site is localized to the C-terminal end of the β-barrel and is highlighted by the formation of a binuclear metal center with two manganese ions that are bridged by Glu-175 and hydroxide. The remaining ligands to the metal center include His-32, His-34, His-207, His-236, and Asp-302. Rsp3690 was shown to catalyze the hydrolysis of a wide variety of carboxylate esters, in addition to organophosphate and organophosphonate esters. The best carboxylate ester substrates identified for Rsp3690 included 2-naphthyl acetate (kcat/Km = 1.0 × 105 M–1 s–1), 2-naphthyl propionate (kcat/Km = 1.5 × 105 M–1 s–1), 1-naphthyl acetate (kcat/Km = 7.5 × 103 M–1 s–1), 4-methylumbelliferyl acetate (kcat/Km = 2.7 × 103 M–1 s–1), 4-nitrophenyl acetate (kcat/Km = 2.3 × 105 M–1 s–1), and 4-nitrophenyl butyrate (kcat/Km = 8.8 × 105 M–1 s–1). The best organophosphonate ester substrates included ethyl 4-nitrophenyl methylphosphonate (kcat/Km = 3.8 × 105 M–1 s–1) and isobutyl 4-nitrophenyl methylphosphonate (kcat/Km = 1.1 × 104 M–1 s–1). The (SP)-enantiomer of isobutyl 4-nitrophenyl methylphosphonate was hydrolyzed 10 times faster than the less toxic (RP)-enantiomer. The high inherent catalytic activity of Rsp3690 for the hydrolysis of the toxic enantiomer of methylphosphonate esters make this enzyme an attractive target for directed evolution investigations. PMID:24832101

Identification of different coordination geometries by XAFS in copper(II) complexes with trimesic acid

NASA Astrophysics Data System (ADS)

Gaur, A.; Klysubun, W.; Soni, Balram; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

2016-10-01

X-ray absorption spectroscopy (XAS) is very useful in revealing the information about geometric and electronic structure of a transition-metal absorber and thus commonly used for determination of metal-ligand coordination. But XAFS analysis becomes difficult if differently coordinated metal centers are present in a system. In the present investigation, existence of distinct coordination geometries around metal centres have been studied by XAFS in a series of trimesic acid Cu(II) complexes. The complexes studied are: Cu3(tma)2(im)6 8H2O (1), Cu3(tma)2(mim)6 17H2O (2), Cu3(tma)2(tmen)3 8.5H2O (3), Cu3(tma) (pmd)3 6H2O (ClO4)3 (4) and Cu3(tma)2 3H2O (5). These complexes have not only Cu metal centres with different coordination but in complexes 1-3, there are multiple coordination geometries present around Cu centres. Using XANES spectra, different coordination geometries present in these complexes have been identified. The variation observed in the pre-edge features and edge features have been correlated with the distortion of the specific coordination environment around Cu centres in the complexes. XANES spectra have been calculated for the distinct metal centres present in the complexes by employing ab-initio calculations. These individual spectra have been used to resolve the spectral contribution of the Cu centres to the particular XANES features exhibited by the experimental spectra of the multinuclear complexes. Also, the variation in the 4p density of states have been calculated for the different Cu centres and then correlated with the features originated from corresponding coordination of Cu. Thus, these spectral features have been successfully utilized to detect the presence of the discrete metal centres in a system. The inferences about the coordination geometry have been supported by EXAFS analysis which has been used to determine the structural parameters for these complexes.

Metal (II) Complexes Derived from Naphthofuran-2-carbohydrazide and Diacetylmonoxime Schiff Base: Synthesis, Spectroscopic, Electrochemical, and Biological Investigation

PubMed Central

Sumathi, R. B.; Halli, M. B.

2014-01-01

A new Schiff base and a new series of Co(II), Ni(II), Cu(II), Cd(II), and Hg(II) complexes were synthesized by the condensation of naphthofuran-2-carbohydrazide and diacetylmonoxime. Metal complexes of the Schiff base were prepared from their chloride salts of Co(II), Ni(II), Cu(II), Cd(II), and Hg(II) in ethanol. The ligand along with its metal complexes have been characterized on the basis of analytical data, IR, electronic, mass, 1HNMR, ESR spectral data, thermal studies, magnetic susceptibility, and molar conductance measurements. The nonelectrolytic behaviour of the complexes was assessed from the measured low conductance data. The elemental analysis of the complexes confirm the stoichiometry of the type CuL2Cl2 and MLCl2 where M = Ni(II), Co(II), Cd(II), and Hg(II) and L = Schiff base. The redox property of the Cu(II) complex was investigated by electrochemical method using cyclic voltammetry. In the light of these results, Co(II), Ni(II), and Cu(II) complexes are assigned octahedral geometry, Cd(II), and Hg(II) complexes tetrahedral geometry. In order to evaluate the effect of metal ions upon chelation, both the ligand and its metal complexes were screened for their antibacterial and antifungal activities by minimum inhibitory concentration (MIC) method. The DNA cleaving capacity of all the complexes was analysed by agarose gel electrophoresis method. PMID:24592203

Solvation Effect on Complexation of Alkali Metal Cations by a Calix[4]arene Ketone Derivative.

PubMed

Požar, Josip; Nikšić-Franjić, Ivana; Cvetnić, Marija; Leko, Katarina; Cindro, Nikola; Pičuljan, Katarina; Borilović, Ivana; Frkanec, Leo; Tomišić, Vladislav

2017-09-14

The medium effect on the complexation of alkali metal cations with a calix[4]arene ketone derivative (L) was systematically examined in methanol, ethanol, N-methylformamide, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile. In all solvents the binding of Na + cation by L was rather efficient, whereas the complexation of other alkali metal cations was observed only in methanol and acetonitrile. Complexation reactions were enthalpically controlled, while ligand dissolution was endothermic in all cases. A notable influence of the solvent on NaL + complex stability could be mainly attributed to the differences in complexation entropies. The higher NaL + stability in comparison to complexes with other alkali metal cations in acetonitrile was predominantly due to a more favorable complexation enthalpy. The 1 H NMR investigations revealed a relatively low affinity of the calixarene sodium complex for inclusion of the solvent molecule in the calixarene hydrophobic cavity, with the exception of acetonitrile. Differences in complex stabilities in the explored solvents, apart from N,N-dimethylformamide and acetonitrile, could be mostly explained by taking into account solely the cation and complex solvation. A considerable solvent effect on the complexation equilibria was proven to be due to an interesting interplay between the transfer enthalpies and entropies of the reactants and the complexes formed.

Molecular Speciation of Trace Metal Organic Complexes in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Repeta, D.; Boiteau, R. M.; Bundy, R. M.; Babcock-Adams, L.

2017-12-01

Microbial production across approximately one third of the surface ocean is limited by extraordinarily low (picomolar) concentrations of dissolved iron, essentially all of which is complexed to strong organic ligands of unknown composition. Other biologically important trace metals (cobalt, copper, zinc, nickel) are also complexed to strong organic ligands, which again have not been extensively characterized. Nevertheless, organic ligands exert a strong influence on metal bioavailability and toxicity. For example, amendment experiments using commercially available siderophores, organic compounds synthesized by microbes to facilitate iron uptake, show these ligands can both facilitate or impede iron uptake depending on the siderophore composition and available uptake pathways. Over the past few years we have developed analytical techniques using high pressure liquid chromatography interfaced with inductively coupled plasma and electrospray ionization mass spectrometry to identify and quantify trace metal organic complexes in laboratory cultures of marine microbes and in seawater. We found siderophores to be widely distributed in the ocean, particularly in regions characterized by low iron concentrations. We also find chemically distinct complexes of copper, zinc, colbalt and nickel that we have yet to fully characterize. We will discuss some of our recent work on trace metal organic speciation in seawater and laboratory cultures, and outline future efforts to better understand the microbial cycling of trace metal organic complexes in the sea.

Understanding M-ligand bonding and mer-/fac-isomerism in tris(8-hydroxyquinolinate) metallic complexes.

PubMed

Lima, Carlos F R A C; Taveira, Ricardo J S; Costa, José C S; Fernandes, Ana M; Melo, André; Silva, Artur M S; Santos, Luís M N B F

2016-06-28

Tris(8-hydroxyquinolinate) metallic complexes, Mq3, are one of the most important classes of organic semiconductor materials. Herein, the nature of the chemical bond in Mq3 complexes and its implications on their molecular properties were investigated by a combined experimental and computational approach. Various Mq3 complexes, resulting from the alteration of the metal and substitution of the 8-hydroxyquinoline ligand in different positions, were prepared. The mer-/fac-isomerism in Mq3 was explored by FTIR and NMR spectroscopy, evidencing that, irrespective of the substituent, mer- and fac-are the most stable molecular configurations of Al(iii) and In(iii) complexes, respectively. The relative M-ligand bond dissociation energies were evaluated experimentally by electrospray ionization tandem mass spectrometry (ESI-MS-MS), showing a non-monotonous variation along the group (Al > In > Ga). The results reveal a strong covalent character in M-ligand bonding, which allows for through-ligand electron delocalization, and explain the preferred molecular structures of Mq3 complexes as resulting from the interplay between bonding and steric factors. The mer-isomer reduces intraligand repulsions, being preferred for smaller metals, while the fac-isomer is favoured for larger metals where stronger covalent M-ligand bonds can be formed due to more extensive through-ligand conjugation mediated by metal "d" orbitals.