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Dimeric
Terms modified by Dimeric Selected AbstractsStructural Diversity in Organotin Compounds Derived from Bulky Monoaryl Phosphates: Dimeric, Tetrameric, and Polymeric Tin Phosphate ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2008Ramaswamy Murugavel Abstract Monoaryl phosphates with a bulky aryl substituent have been used to synthesize new organotin clusters and polymers. The equimolar reaction between 2,6-diisopropylphenylphosphate (dipp-H2) and Me2SnCl2 in ethanol at 25 °C leads to the formation of [Me2Sn(,3 -dipp)]n (1), while the reaction of 2,6-dimethylphenylphosphate (dmpp-H2) with Me2SnCl2 in either a 1:1 or 2:1 molar ratio proceeds to produce exclusively [Me2Sn(,-dmpp-H)2]n·nH2O (2). Compounds 1 and 2 are 1D polymers with different architectures. In compound 1, the tin atom is five-coordinate (trigonal bipyramidal). Each dipp ligand bridges three different tin atoms to form an infinite ladder-chain structure. In 2, each six-coordinate (octahedral) tin atom is surrounded by four phosphate oxygen atoms originating from four different bridging dmpp-H ligands, thus forming a spirocyclic coordination polymeric chain. The use of nBu2SnO as the diorganotin source in its reaction with dipp-H2 leads to the isolation of dimeric [nBu2Sn(,-dipp-H)(dipp-H)]2 (4), which contains a central Sn2O4P2 unit. There are two chemically different half molecules of 4 in the asymmetric part of the unit cell and hence it actually exists as a 1:1 mixture of [nBu2Sn(,-dipp-H)(dipp-H)]2 and [nBu2Sn(,-dipp)(dipp-H2)]2 in the solid state. The reaction of the monoorgano tin precursor nBuSn(O)(OH)·xH2O with dipp-H2 takes place in acetone at room temperature to yield the tetrameric cluster 5, which has different structures in the solution and in the solid state. 31P NMR spectroscopy clearly suggests that 5 has the formula [nBu4Sn4(,-O)2(,-dipp-H)8] in solution. The single-crystal X-ray diffraction studies in the solid state, however, reveal that compound 5 exists as [nBu4Sn4(,-OH)2(,-dipp-H)6(,-dipp)2]. The use of compounds 1,4 as possible precursors for the preparation of ceramic tin phosphate materials has been investigated. The thermolysis of 1 at 500 °C leads to the formation of quantitative amounts of Sn2P2O7, while the thermolysis of 2, 3, and 4 under similar conditions results in the formation of SnP2O7. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Dimeric 2,2,-Bipyridylruthenium(II) Complexes Containing 2,2,-Bis(1,2,4-triazin-3-yl)-4,4,-bipyridine-Like Bridging Ligands: Syntheses, Characterization and DNA BindingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Cai-Wu Jiang Abstract Three new bridging ligands 2,2,-bis(1,2,4-triazin-3-yl)-4,4,-bipyridine (btb), 2,2,-bis(1,2,4-triazino[5,6-f]acenaphthylen-3-yl)-4,4,-bipyridine (btapb), 2,2,-bis(5,6-diphenyl-1,2,4-triazin-3-yl)-4,4,-bipyridine (bdptb) and their dimeric 2,2,-bipyridylruthenium(II) complexes [Ru(bpy)2(btb)Ru(bpy)2]4+ (1), [Ru(bpy)2(btapb)Ru(bpy)2]4+ (2), [Ru(bpy)2(bdptb)Ru(bpy)2]4+ (3) have been synthesized and characterized by elemental analysis, fast atom bombardment (FAB) mass spectrometry or electrospray mass spectrometry (ES-MS), 1H NMR and UV/Visible spectroscopy. The binding behavior of these dimeric complexes with calf thymus DNA (CT-DNA) was investigated by electronic absorption spectroscopy, viscosity measurements, and equilibrium dialysis experiments. The hypochromism of the metal-ligand charge transfer (MLCT) band in the electronic absorption spectra of the dinuclear complexes 1, 2, and 3 is 8.7%, 19% and 33%, respectively, with bathochromic shifts of 5, 5 and 14 nm, respectively. The binding constants are 7.5×104M,1, 4.8×105M,1 and 7.6×105M,1, respectively. Increasing the size of the plane of the bridging ligand increases the hydrophobicity of their complexes, leading to stronger binding by the complexes to calf thymus DNA. The effect of increasing concentrations of these novel dimeric ruthenium(II) complexes on the relative viscosities of CT-DNA is less notable than that of well-known intercalators such as [Ru(bpy)2(dppz)]2+. The equilibrium experiments showed that ,,,3 binding is stronger than ,,,3 binding to CT-DNA. This is the first example of a dinuclear complex binding enantioselectively to CT-DNA measured by equilibrium dialysis. The experiments suggest that the three complexes may be DNA groove binders. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Kinetic and Equilibrium Studies of Reactions of N-Heterocycles with Dimeric and Monomeric Oxorhenium(V) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003James H. Espenson Abstract Equilibrium constants have been evaluated for the reaction {MeReO(edt)}2 + 2 L , 2 MeReO(edt)L, where edt is 1,2-ethanedithiolate and L is any of 13 N-donor heterocyclic ligands. The values of K range from 1.37(27)×10,2 for pyrimidine to 1.95(6)×106 for imidazole at 25 °C in chloroform. A successful correlation of logK with log (Ka) of HL+ was realized except in the case of the 2-substituted ligands 2-picoline and quinoline, where steric effects make K smaller than expected from the proton basicity of L. The kinetics of the same reactions were studied; the rate law for the reaction in the forward direction is given by ,d[{MeReO(edt)}2]/dt = {ka + kb[L]}[L] × [{MeReO(edt)}2]. Except for 2-picoline and quinoline, the major pathway is provided by the term that shows the quadratic dependence on [L]. Values of log (kb) also correlate with log K, and therefore necessarily with log (Ka). [source] Pakistolides A and B, Novel Enzyme Inhibitory and Antioxidant Dimeric 4-(Glucosyloxy)Benzoates from Berchemia pakistanicaHELVETICA CHIMICA ACTA, Issue 2 2004Naveen Mukhtar Pakistolides A and B, novel dimeric , -(glucosyloxy)benzoates were isolated from Berchemia pakistanica and assigned structures 1 and 2 on the basis of extensive NMR studies. In addition, the known compounds 7,5,-dimethoxy-3,5,2,-trihydroxyflavone (=3,5-dihydroxy-2-(2-hydroxy-5-methoxyphenyl)-7-methoxy-4H -1-benzopyran-4-one), 4,,5-dihydroxy-3,6,7-trimethoxyflavone (=5-hydroxy-2-(4-hydroxyphenyl)-3,6,7-trimethoxy-4H -1-benzopyran-4-one), 5,6-dihydroxy-4,7-dimethoxy-2-methylanthracene-9,10-dione, and 1,3,4-trihydroxy-6,7,8-trimethoxy-2-methylanthracene-9,10-dione were reported for the first time from the genus Berchemia. Both 1 and 2 showed significant , -glucosidase and lipoxygenase inhibitory activities, while 2 also showed antioxidant potential. [source] Platelet adhesion to dimeric ,2 -glycoprotein I under conditions of flow is mediated by at least two receptors: glycoprotein Ib, and apolipoprotein E receptor 2,JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2007M. T. T. PENNINGS Summary.,Background: The major antigen implicated in the antiphospholipid syndrome is beta2-glycoprotein I (,2GPI). Dimerized ,2GPI binds to apolipoprotein E receptor 2, (apoER2,) on platelets and increases platelet adhesion to collagen under conditions of flow. Aim: To investigate whether the interaction between dimerized ,2GPI and platelets is sufficiently strong to resist shear stresses. Methods: We studied the interaction of platelets with immobilized dimerized ,2GPI under conditions of flow, and further analyzed the interaction using surface plasmon resonance and solid phase immunoassays. Results: We found that dimerized ,2GPI supports platelet adhesion and aggregate formation under venous flow conditions. Adhesion of platelets to dimerized ,2GPI was completely inhibited by the addition of soluble forms of both apoER2, and GPIb,, and the addition of receptor-associated protein and the removal of GPIb, from the platelet surface. GPIb, co-precipitated with apoER2,, suggesting the presence of complexes between GPIb, and apoER2, on platelet membranes. The interaction between GPIb, and dimeric ,2GPI was of intermediate affinity (Kd = 180 nm) and Zn2+, but not Ca2+ -dependent. Deletion of domain V from dimeric ,2GPI strongly reduced its binding to both GPIb, and apoER2,. Antibodies that inhibit the binding of thrombin to GPIb, inhibited platelet adhesion to dimeric ,2GPI completely, while antibodies blocking the binding of von Willebrand factor to GPIb, had no effect. Dimeric ,2GPI showed reduced binding to low-sulfated GPIb, compared to the fully sulfated form. Conclusion: We show that platelets adhere to dimeric ,2GPI under both arterial and venous shear stresses. Platelets adhere via two receptors: GPIb, and apoER2,. These receptors are present in a complex on the platelet surface. [source] Dimeric (isoquinoline)(N -salicylidene- d,l -glutamato)copper(II) ethanol solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Vratislav Langer The title racemic complex, bis[,- N -(2-oxidobenzylidene)- d,l -glutamato(2,)]bis[(isoquinoline)copper(II)] ethanol disolvate, [Cu2(C12H11NO5)2(C9H7N)2]·2C2H6O, adopts a square-pyramidal CuII coordination mode with a tridentate N -salicylideneglutamato Schiff base dianion and an isoquinoline ligand bound in the basal plane. The apex of the pyramid is occupied by a phenolic O atom from the adjacent chelate molecule at an apical distance of 2.487,(3),Å, building a dimer located on the crystallographic inversion center. The Cu...Cu spacing within the dimers is 3.3264,(12),Å. The ethanol solvent molecules are hydrogen bonded to the dimeric complex molecules, forming infinite chains in the a direction. The biological activity of the title complex has been studied. [source] ChemInform Abstract: Structure Studies of Dimeric [Pt2(CN)10]4- Pentacyanoplatinum(III) and Monomeric Pentacyanoplatinum(IV) Complexes by EXAFS, Vibrational Spectroscopy, and X-Ray Crystallography.CHEMINFORM, Issue 27 2002Farideh Jalilehvand Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Oxidative transformation of tetrachlorophenols and trichlorophenols by manganese dioxideENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2009Ling Zhao Abstract This study examined the transformation kinetics of three tetrachlorophenols (TeCPs) and three trichlorophenols (TCPs) in the presence of MnO2 under different solution chemistry conditions. The reaction rate measured for each CP decreased as a function of solution pH, and under the same solution chemistry conditions, the measured rates may depend primarily on both the adsorbability at the MnO2 surfaces and the isomeric structures of the CPs. Isomeric effects indicated that chloro substituent on ortho or para positions exhibited faster rates of transformation than on meta positions. Gas chromatography-mass spectrometry analysis with a derivatization method showed that dimers including polychlorinated phenoxyphenols and chlorinated polyhydroxybi-phenyl were among the major products for all CPs. Monomeric products were among the major products of 2,4,6-TCP, 2,3,4-TCP, and 2,3,4,6-TeCP, whereas trimeric products also were among the major products of 2,3,4-TCP and 2,4,5-TCP. It appeared that hydroxylation of CPs and formation of dimeric or trimeric products via oxidative coupling were the major reaction mechanisms involved in the oxidation of CPs by MnO2. [source] Lithiation of a Cyclen-Derived (NNNN) Macrocycle and Its Reaction with n -ButyllithiumEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2010Sabine Standfuss Abstract Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me3TACD)H (1), was metalated with n -butyllithium in pentane to give [Li2(Me3TACD)2] (2). The structure of this compound is dimeric in the solid state as shown by single-crystal X-ray diffraction. With an excess of nBuLi, nBuLi is incorporated into the product. Depending on the stoichiometry, the compounds [Li3(nBu)(Me3TACD)2] (3) or [Li4(nBu)2(Me3TACD)2] (4) are formed. As shown by single-crystal X-ray diffraction, both molecular structures show a ladder motif. (Me3TACD)H reacted with NaI/Na2CO3 in acetonitrile to give benzene-soluble [NaI(Me3TACD)H] (5). [source] Synthesis, Structures, and Magnetic Properties of N -Trialkylsilyl-8-amidoquinoline Complexes of Chromium, Manganese, Iron, and Cobalt as well as of Wheel-Like Hexanuclear Iron(II) and Manganese(II) Bis(8-amidoquinoline)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2010Astrid Malassa Abstract The transamination of 8-(tert -butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8-(tert -butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8-(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8-(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8-aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8-amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8-amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8-amidoquinoline)manganese(II) (8) and bis(8-amidoquinoline)iron(II) (9), form hexamers with wheel-like molecular structures consisting of metal-centered nitrogen octahedra interconnected by common N···N edges. The cobalt complex, bis(8-amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6 -wheel 9 yield very close-lying ferromagnetically and antiferromagnetically coupled states. [source] Isostructural Potassium and Thallium Salts of Sterically Crowded Thio- and Selenophenols: A Structural and Computational StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2008Denis Bubrin Abstract Because of their similar cationic radii, potassium and thallium(I) compounds are usually regarded as closely related. Homologous molecular species containing either K+ or Tl+ are very rare, however. We have synthesized potassium and thallium salts MEAr* [M, E = K, S (2a); K, Se (2b); Tl, S (3a); Tl, Se (3b); Ar* = 2,6-Trip2C6H3, Trip = 2,4,6- iPr3C6H2] derived from terphenyl-substituted thio- and selenophenols. In the solid-state structures of dimeric 2a, 2b, 3a, and 3b additional metal-,n,,-arene interactions to the flanking arms of the terphenyl substituents of different hapticity n are observed. Remarkably, the homologous potassium and thallium complexes 2b and 3b crystallize in isomorphous cells. For 2a, 3a, and model complexes of the composition METph (Tph = C6H4 -2-Trip) the nature of the M,E and M···C(arene) bonding was studied by density functional theory calculations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Variable Coordination Modes of Benzaldehyde Thiosemicarbazones , Synthesis, Structure, and Electrochemical Properties of Some Ruthenium ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2008Swati Dutta Abstract Reaction of benzaldehyde thiosemicarbazones [H2LR, where H2 stands for the two protons, the hydrazinic proton, and the phenyl proton at the ortho position, with respect to the imine function and R (R = OCH3, CH3, H, Cl, and NO2) for the para substituent] with [Ru(PPh3)2(CO)2Cl2], carried out in refluxing ethanol, afforded monomeric complexes of type [Ru(PPh3)2(CO)(HLR)(H)]. The crystal structure of the [Ru(PPh3)2(CO)(HLNO2)(H)] complex was determined. The thiosemicarbazone ligand is coordinated to the ruthenium center as a bidentate N,S-donor ligand forming a four-membered chelate ring. When the reaction of the thiosemicarbazones with [Ru(PPh3)2(CO)2Cl2] was carried out in refluxing toluene, a family of dimeric complexes of type [Ru2(PPh3)2(CO)2(LR)2] were obtained. The crystal structure of [Ru2(PPh3)2(CO)2(LCl)2] was determined. Each thiosemicarbazone ligand is coordinated to one ruthenium atom, by dissociation of the two protons, as a dianionic tridentate C,N,S-donor ligand, and at the same time the sulfur atom is also bonded to the second ruthenium center. 1H NMR spectra of the complexes of both types are in excellent agreement with their compositions. All the dimeric and monomeric complexes are diamagnetic (low-spin d6, S = 0) and show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry of the [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes show the ruthenium(II),ruthenium(III) oxidation within 0.48,0.73 V vs. SCE followed by a ruthenium(III),ruthenium(IV) oxidation within 1.09,1.47 V vs. SCE. Potentials of both the oxidations are found to correlate linearly with the electron-withdrawing character of the substituent R. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Reactions of [Hg(Tab)2](PF6)2 [Tab = 4-(trimethylammonio)benzenethiolate] with NaX (X = Cl, NO2, NO3): Isolation and Structural Characterization of a Series of Mono- and Binuclear Hg/Tab/X CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2008Xiao-Yan Tang Abstract The complex [Hg(Tab)2](PF6)2 [Tab = 4-(trimethylammonio)benzenethiolate] (1) reacts with one or two equivalents of NaCl to afford the mononuclear complex [Hg(Tab)2Cl](PF6) (2) and the dinuclear complex [{Hg(,-Tab)(Tab)Cl}2]Cl2·H2O (3·H2O), respectively. Similar reactions of 1 with NaCl and NaX (molar ratio = 1:1) produce the dinuclear species [{Hg(,-Tab)(Tab)Cl}2]X2 [X = NO2 (4), NO3 (5)], while those with NaNO2 or NaNO3 give rise to [{Hg(,-Tab)(Tab)X}2]X2 [X = NO2 (6), NO3 (7)]. Complexes 2,7 have been characterised by elemental analysis, IR, UV/Vis, and 1H NMR spectroscopy, and X-ray crystallography. The Hg atom of the [Hg(Tab)2Cl]+ cation in 2 adopts a T-shaped coordination geometry. Two [Hg(Tab)2Cl]+ cations in 3·H2O, 4, and 5 are linked by a pair of weak Hg,S bonds to form a dimeric [Hg(,-Tab)(Tab)Cl]22+ dication, and the centrosymmetric [Hg(,-Tab)(Tab)X]22+ dication in 6 and 7 consists of two [Hg(Tab)2X]+ cations linked by a couple of weak Hg,S bonds. The hydrogen-bonding interactions in 2,7 lead to the formation of interesting 2D (5, 7) or 3D (2,4, 6) hydrogen-bonded networks.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Structural Diversity in Organotin Compounds Derived from Bulky Monoaryl Phosphates: Dimeric, Tetrameric, and Polymeric Tin Phosphate ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2008Ramaswamy Murugavel Abstract Monoaryl phosphates with a bulky aryl substituent have been used to synthesize new organotin clusters and polymers. The equimolar reaction between 2,6-diisopropylphenylphosphate (dipp-H2) and Me2SnCl2 in ethanol at 25 °C leads to the formation of [Me2Sn(,3 -dipp)]n (1), while the reaction of 2,6-dimethylphenylphosphate (dmpp-H2) with Me2SnCl2 in either a 1:1 or 2:1 molar ratio proceeds to produce exclusively [Me2Sn(,-dmpp-H)2]n·nH2O (2). Compounds 1 and 2 are 1D polymers with different architectures. In compound 1, the tin atom is five-coordinate (trigonal bipyramidal). Each dipp ligand bridges three different tin atoms to form an infinite ladder-chain structure. In 2, each six-coordinate (octahedral) tin atom is surrounded by four phosphate oxygen atoms originating from four different bridging dmpp-H ligands, thus forming a spirocyclic coordination polymeric chain. The use of nBu2SnO as the diorganotin source in its reaction with dipp-H2 leads to the isolation of dimeric [nBu2Sn(,-dipp-H)(dipp-H)]2 (4), which contains a central Sn2O4P2 unit. There are two chemically different half molecules of 4 in the asymmetric part of the unit cell and hence it actually exists as a 1:1 mixture of [nBu2Sn(,-dipp-H)(dipp-H)]2 and [nBu2Sn(,-dipp)(dipp-H2)]2 in the solid state. The reaction of the monoorgano tin precursor nBuSn(O)(OH)·xH2O with dipp-H2 takes place in acetone at room temperature to yield the tetrameric cluster 5, which has different structures in the solution and in the solid state. 31P NMR spectroscopy clearly suggests that 5 has the formula [nBu4Sn4(,-O)2(,-dipp-H)8] in solution. The single-crystal X-ray diffraction studies in the solid state, however, reveal that compound 5 exists as [nBu4Sn4(,-OH)2(,-dipp-H)6(,-dipp)2]. The use of compounds 1,4 as possible precursors for the preparation of ceramic tin phosphate materials has been investigated. The thermolysis of 1 at 500 °C leads to the formation of quantitative amounts of Sn2P2O7, while the thermolysis of 2, 3, and 4 under similar conditions results in the formation of SnP2O7. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Variability in the Structures of Luminescent [2-(Aminomethyl)pyridine]silver(I) Complexes: Effect of Ligand Ratio, Anion, Hydrogen Bonding, and ,-StackingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2005Rodney P. Feazell Abstract The reaction of 2-(aminomethyl)pyridine (2-amp) with silver(I) salts of triflate (OTf,), trifluoroacetate (tfa,), and tetrafluoroborate (BF4,) produce monomeric, dimeric, bridged, and polymeric structural motifs. The structural characteristics are dependent upon the ratio of ligand/metal in the structure as well as the ability of the anion to coordinate to the metal centers and form hydrogen bonds to the bound ligands. The silver coordination environment takes on several geometries including near linear (6), trigonal (4), tetrahedral (1), and both trigonal-bipyramidal and square-based pyramidal in a single structure (2). Structures 2, 3, and 5 also display short Ag,Ag contacts ranging from 2.8958(3) to 3.0305(4) Å. The species with metal,metal interactions, which are connectively very similar to their metal-isolated counterparts of 1, 4, and 6, are held together only by weak ,-stacking interactions or hydrogen bonds to their respective anions. Low-temperature luminescence spectra were collected for all compounds and are compared. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Tetracyanoquinodimethanido Derivatives of (Terpyridine)- and (Phenanthroline)metal Complexes , Structural and Magnetic Studies of Radical-Ion SaltsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2005Cristina Alonso Abstract Several derivatives of formulae [M(terpy)2](TCNQ)2 or [M(terpy)2](TCNQ)3 (M = Ni, Cu, Zn; terpy = 2,2,:6,,2"-terpyridine; TCNQ= 7,7,8,8-tetracyanoquinodimethane) and [M(phen)3](TCNQ)2 or [M(phen)3](TCNQ)4 (M = Fe, Ni; phen = 1,10-phenanthroline) have been obtained. The crystal structures of [M(terpy)2](TCNQ)2 (M = Ni, Cu) show that the metal is surrounded by the terpyridine nitrogen atoms in a closed octahedral environment and the TCNQ anions are dimerised by , overlap. The cationic [M(terpy)2]2+ and the anionic [TCNQ]22, groups alternate in the crystal. For the derivatives with three TCNQ groups, the existence of a stack of trimeric [TCNQ]32, ions having electronic delocalisation is proposed. The compound [Fe(phen)3](TCNQ)2, which shows a strong interaction between TCNQ anions, led to the formation of a , bond in the diamagnetic species [TCNQ,TCNQ], while the nickel analogue is expected to have a localised structure formed by alternation of cationic metal complexes and dimeric [TCNQ]22, anions similar to those observed in the analogous terpy derivatives. The derivatives having four TCNQ groups also show electronic delocalisation and a 1D stack based on the magnetic data is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Dimeric 2,2,-Bipyridylruthenium(II) Complexes Containing 2,2,-Bis(1,2,4-triazin-3-yl)-4,4,-bipyridine-Like Bridging Ligands: Syntheses, Characterization and DNA BindingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Cai-Wu Jiang Abstract Three new bridging ligands 2,2,-bis(1,2,4-triazin-3-yl)-4,4,-bipyridine (btb), 2,2,-bis(1,2,4-triazino[5,6-f]acenaphthylen-3-yl)-4,4,-bipyridine (btapb), 2,2,-bis(5,6-diphenyl-1,2,4-triazin-3-yl)-4,4,-bipyridine (bdptb) and their dimeric 2,2,-bipyridylruthenium(II) complexes [Ru(bpy)2(btb)Ru(bpy)2]4+ (1), [Ru(bpy)2(btapb)Ru(bpy)2]4+ (2), [Ru(bpy)2(bdptb)Ru(bpy)2]4+ (3) have been synthesized and characterized by elemental analysis, fast atom bombardment (FAB) mass spectrometry or electrospray mass spectrometry (ES-MS), 1H NMR and UV/Visible spectroscopy. The binding behavior of these dimeric complexes with calf thymus DNA (CT-DNA) was investigated by electronic absorption spectroscopy, viscosity measurements, and equilibrium dialysis experiments. The hypochromism of the metal-ligand charge transfer (MLCT) band in the electronic absorption spectra of the dinuclear complexes 1, 2, and 3 is 8.7%, 19% and 33%, respectively, with bathochromic shifts of 5, 5 and 14 nm, respectively. The binding constants are 7.5×104M,1, 4.8×105M,1 and 7.6×105M,1, respectively. Increasing the size of the plane of the bridging ligand increases the hydrophobicity of their complexes, leading to stronger binding by the complexes to calf thymus DNA. The effect of increasing concentrations of these novel dimeric ruthenium(II) complexes on the relative viscosities of CT-DNA is less notable than that of well-known intercalators such as [Ru(bpy)2(dppz)]2+. The equilibrium experiments showed that ,,,3 binding is stronger than ,,,3 binding to CT-DNA. This is the first example of a dinuclear complex binding enantioselectively to CT-DNA measured by equilibrium dialysis. The experiments suggest that the three complexes may be DNA groove binders. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis and Reaction of MnII Iodides Bearing the ,-Diketiminate Ligand: the First Divalent Manganese N-Heterocyclic Carbene Complexes [{HC(CMeNAr)2}MnI{C[N(iPr)CMe]2}] and [{HC(CMeNAr)2}MnNHAr{C[N(iPr)CMe]2}] (Ar = 2,6- iPr2C6H3)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2003Jianfang Chai Abstract The manganese mono-iodide [HC(CMeNAr)2]MnI(THF) (Ar = 2,6- iPr2C6H3) (3) was prepared in good yield from the reaction of [HC(CMeNAr)2]K with MnI2 in THF. Treatment of 3 under reflux in toluene and removing all the volatiles in vacuo afforded the dimeric compound [{HC(CMeNAr)2}Mn]2(,-I)2 (4). Displacement of the coordinated THF in 3 by a strong Lewis base C[N(iPr)CMe]2 or by adding C[N(iPr)CMe]2 to the toluene solution of 4 readily gave the N-heterocyclic carbene adduct [{HC(CMeNAr)2}]MnI{C[N(iPr)CMe]2} (5). Reduction of 5 with sodium/potassium alloy at room temperature unexpectedly resulted in the formation of the monomeric compound [{HC(CMeNAr)2}]MnNHAr{C[N(iPr)CMe]2} (6). Alternatively 6 was obtained by the salt elimination reaction of 5 with LiNHAr. Compounds 5 and 6 are the first examples of divalent manganese N-heterocyclic carbene adducts and the first manganese non-carbonyl carbene complexes. The single crystal X-ray structural analyses reveal that compounds 3 and 6 are monomeric and compound 4 is dimeric in the solid state. The manganese centers in these compounds exhibit a distorted tetrahedral geometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] The First Structurally Characterized DiorganoaluminateEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2003Colin Eaborn Abstract The first structurally characterized dialkylaluminate [{Li(THF)}(AltBu{C(SiMe3)3}H2)]2 (3) is dimeric in the solid state with [Li(THF)]+ and [AltBu{C(SiMe3)3}H2], fragments linked by Li···H,Al bridges. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Structural Characterization of N -Methylpyridoxine (MePN; PN = Vitamin B6) and Its Diorganotin Complexes [SnR2(MePN-H)]I (R = Me, Et, Bu and Ph)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2003José S. Casas Abstract For comparison with the corresponding pyridoxine complexes we have prepared dimethyl-, diethyl-, dibutyl- and diphenyltin(IV) complexes of N -methylpyridoxine (MePN). The compounds [SnMe2(MePN,H)]I (1), [SnEt2(MePN,H)]I (2), [SnBu2(MePN,H)]I (3) and [SnPh2(MePN,H)]I·H2O (4) were isolated and characterized by IR, Raman, Mössbauer, 1H, 13C and 119Sn NMR spectroscopy, and by EI and FAB mass spectrometry. The crystal structures of [HMePN]I and of compounds 1, 2·2H2O and 3 were determined by X-ray diffractometry. Their lattices contain dimeric [SnR2(MePN,H)]22+ units (R = Me, Et, Bu) in which two bridging-chelating methylpyridoxinato anions link pentacoordinate Sn atoms with coordination polyhedra closer to square pyramids than to trigonal bipyramids. NMR results show that the dimeric cations persist in (CD3)2SO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Macrocyclic Cyclo[n]malonates , Synthetic Aspects and Observation of Columnar Arrangements by X-ray CrystallographyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2006Nikos Chronakis Abstract A variety of achiral and chiral macrocyclic oligomalonates were synthesised in a one-step procedure through condensation of malonyl dichloride with ,,,-diols. We have investigated the applicability of this method by varying the length and type of the spacers in the diol. Product distribution analysis revealed that the preferential formation of monomeric, dimeric, or trimeric macrocyclic malonates can be controlled by choosing diols with specific spacers connecting the hydroxy groups. Of special interest are the macrocyclic bismalonates, as they show pronounced crystallisability and arrange into columnar motifs in the solid state. They feature distinctive dihedral angles: all ester moieties adopt anti conformations whereas the planes of the carboxy moieties of each malonate residue arrange in an approximately orthogonal fashion. The latter geometry is enforced by the macrocyclic structures, as revealed by a conformational search in the Cambridge Structural Database. The X-ray diffraction data show that C=O···H,C, and C,O···H,C hydrogen bonds stabilise the columnar arrangement of the dimeric rings with formation of tubular assemblies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Effects of the G376E and G157D mutations on the stability of yeast enolase , a model for human muscle enolase deficiencyFEBS JOURNAL, Issue 1 2008Songping Zhao The first known human enolase deficiency was reported in 2001 [Comi GP, Fortunato F, Lucchiari S, Bordoni A, Prelle A, Jann S, Keller A, Ciscato P, Galbiati S, Chiveri L et al. (2001) Ann Neurol50, 202,207]. The subject had inherited two mutated genes for ,-enolase. These mutations changed glycine 156 to aspartate and glycine 374 to glutamate. In order to study the effects of these changes on the structure and stability of enolase, we have introduced the corresponding changes (G157D and G376E) into yeast enolase. The two variants are correctly folded. They are less stable than wild-type enolase with respect to thermal denaturation, and both have increased Kd values for subunit dissociation. At 37 °C, in the presence of salt, both are partially dissociated and are extensively cleaved by trypsin. Under the same conditions, wild-type enolase is fully dimeric and is only slightly cleaved by trypsin. However, wild-type enolase is also extensively cleaved if it is partially dissociated. The identification of the cleavage sites and spectral studies of enolase have revealed some of the structural differences between the dimeric and monomeric forms of this enzyme. [source] NEMO oligomerization in the dynamic assembly of the I,B kinase core complexFEBS JOURNAL, Issue 10 2007Elisabeth Fontan NF-,B essential modulator (NEMO) plays an essential role in the nuclear factor ,B (NF-,B) pathway as a modulator of the two other subunits of the I,B kinase (IKK) complex, i.e. the protein kinases, IKK, and IKK,. Previous reports all envision the IKK complex to be a static entity. Using glycerol-gradient ultracentrifugation, we observed stimulus-dependent dynamic IKK complex assembly. In wild-type fibroblasts, the kinases and a portion of cellular NEMO associate in a 350-kDa high-molecular-mass complex. In response to constitutive NF-,B stimulation by Tax, we observed NEMO recruitment and oligomerization to a shifted high-molecular-mass complex of 440 kDa which displayed increased IKK activity. This stimulus-dependent oligomerization of NEMO was also observed using fluorescence resonance energy transfer after a transient pulse with interleukin-1,. In addition, fully activated, dimeric kinases not bound to NEMO were detected in these Tax-activated fibroblasts. By glycerol gradient ultracentrifugation, we also showed that: (a) in fibroblasts deficient in IKK, and IKK,, NEMO predominantly exists as a monomer; (b) in NEMO-deficient fibroblasts, IKK, dimers are present that are less stable than IKK, dimers. Intriguingly, in resting Rat-1 fibroblasts, 160-kDa IKK,,NEMO and IKK,,NEMO heterocomplexes were observed as well as a significant proportion of NEMO monomer. These results suggest that most NEMO molecules do not form a tripartite IKK complex with an IKK,,IKK, heterodimer as previously reported in the literature but, instead, NEMO is able to form a complex with the monomeric forms of IKK, and IKK,. [source] Selective Formation of Bi-Component Arrays Through H-Bonding of Multivalent Molecular ModulesADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Luc Piot Abstract Here, the formation of discrete supramolecular mono- and bi-component architectures from novel and multivalent molecular modules bearing complementary recognition moieties that are prone to undergo multiple H-bonds, such as 2,6-di(acetylamino)pyridine and uracil residues, is described. These nanostructured H-bonded arrays, including dimeric and pentameric species, are thoroughly characterized in solution by NMR, in the solid state by FT-IR, and at the solid,liquid interface by means of scanning tunneling microscopy. The employed strategy is extremely versatile as it relies on the tuning of the valency, size, and geometry of the molecular modules; thus, it may be of interest for the bottom-up fabrication of nanostructured functional materials with sub-nanometer precision. [source] Pakistolides A and B, Novel Enzyme Inhibitory and Antioxidant Dimeric 4-(Glucosyloxy)Benzoates from Berchemia pakistanicaHELVETICA CHIMICA ACTA, Issue 2 2004Naveen Mukhtar Pakistolides A and B, novel dimeric , -(glucosyloxy)benzoates were isolated from Berchemia pakistanica and assigned structures 1 and 2 on the basis of extensive NMR studies. In addition, the known compounds 7,5,-dimethoxy-3,5,2,-trihydroxyflavone (=3,5-dihydroxy-2-(2-hydroxy-5-methoxyphenyl)-7-methoxy-4H -1-benzopyran-4-one), 4,,5-dihydroxy-3,6,7-trimethoxyflavone (=5-hydroxy-2-(4-hydroxyphenyl)-3,6,7-trimethoxy-4H -1-benzopyran-4-one), 5,6-dihydroxy-4,7-dimethoxy-2-methylanthracene-9,10-dione, and 1,3,4-trihydroxy-6,7,8-trimethoxy-2-methylanthracene-9,10-dione were reported for the first time from the genus Berchemia. Both 1 and 2 showed significant , -glucosidase and lipoxygenase inhibitory activities, while 2 also showed antioxidant potential. [source] Uses of 2-diazo-4,5,6,7-tetrahydrobenzo[b]thiophene derivatives in the synthesis of azoles, azines, and their fused derivativesHETEROATOM CHEMISTRY, Issue 2 2002Wagnat W. Wardakhan The reactions of 2-diazo-4,5,6,7-tetrahydrobenzo[b]thiophene derivatives with dimeric adducts 2a and 2b gave the hydrazone derivatives 3a and 3b, respectively. The reactivity of the latter products towards various chemical reagents was studied in order to provide azole and azine derivatives incorporating the thiophene ring, and most of them showed high antimicrobial activity. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:108,115, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10003 [source] Palladium-Catalyzed Direct C-4 Arylation of 2,5-Disubstituted Furans with Aryl BromidesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2008Aditya Abstract A simple and atom-economic procedure for the selective C-4 arylation of 2,5-disubstituted furans via CH bond activation using electron-deficient aryl bromides is reported. Only 0.5 mol% of the commercially available dimeric (allene)palladium chloride, [Pd(C3H5)Cl]2, was employed as catalyst. This environmentally attractive procedure has been found to be tolerant to a variety of functional groups on the aryl bromide such as carbonyl, nitrile, nitro, fluoro, ester or trifluoromethyl. [source] A single pot synthesis of new dimeric 2-phenyl-10,3a-dihydro-1,3,4-oxadiazolino[3,2- a]quinazolin-6-olsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2005Anil Kumar One pot synthesis of new unsymmetrical dimeric 2-phenyl-10,3a-dihydro-1,3,4-oxadiazolino[3,2-a]-quinazolin-6-ols from 2-amino-5-phenyloxadiazole and salicylaldehydes, in solid phase, using Hg (II)-A12O3 catalyst, is described. The reaction is temperature sensitive, convenient, efficient and environmentally friendly. [source] Negative and positive ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and positive ion nano-electrospray ionization quadrupole ion trap mass spectrometry of peptidoglycan fragments isolated from various Bacillus speciesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2001Gerold Bacher Abstract A general approach for the detailed characterization of sodium borohydride-reduced peptidoglycan fragments (syn. muropeptides), produced by muramidase digestion of the purified sacculus isolated from Bacillus subtilis (vegetative cell form of the wild type and a dacA mutant) and Bacillus megaterium (endospore form), is outlined based on UV matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and nano-electrospray ionization (nESI) quadrupole ion trap (QIT) mass spectrometry (MS). After enzymatic digestion and reduction of the resulting muropeptides, the complex glycopeptide mixture was separated and fractionated by reversed-phase high-performance liquid chromatography. Prior to mass spectrometric analysis, the muropeptide samples were subjected to a desalting step and an aliquot was taken for amino acid analysis. Initial molecular mass determination of these peptidoglycan fragments (ranging from monomeric to tetrameric muropeptides) was performed by positive and negative ion MALDI-MS using the thin-layer technique with the matrix ,-cyano-4-hydroxycinnamic acid. The results demonstrated that for the fast molecular mass determination of large sample numbers in the 0.8,10 pmol range and with a mass accuracy of ±0.07%, negative ion MALDI-MS in the linear TOF mode is the method of choice. After this kind of muropeptide screening often a detailed primary structural analysis is required owing to ambiguous data. Structural data could be obtained from peptidoglycan monomers by post-source decay (PSD) fragment ion analysis, but not from dimers or higher oligomers and not with the necessary sensitivity. Multistage collision-induced dissociation (CID) experiments performed on an nESI-QIT instrument were found to be the superior method for structural characterization of not only monomeric but also of dimeric and trimeric muropeptides. Up to MS4 experiments were sometimes necessary to obtain unambiguous structural information. Three examples are presented: (a) CID MSn (n = 2,4) of a peptidoglycan monomer (disaccharide-tripeptide) isolated from B. subtilis (wild type, vegetative cell form), (b) CID MSn (n = 2,4) of a peptidoglycan dimer (bis-disaccharide-tetrapentapeptide) obtained from a B. subtilis mutant (vegetative cell form) and (c) CID MS2 of a peptidoglycan trimer (a linear hexasaccharide with two peptide side chains) isolated from the spore cortex of B. megaterium. All MSn experiments were performed on singly charged precursor ions and the MS2 spectra were dominated by fragments derived from interglycosidic bond cleavages. MS3 and MS4 spectra exhibited mainly peptide moiety fragment ions. In case of the bis-disaccharide-tetrapentapeptide, the peptide branching point could be determined based on MS3 and MS4 spectra. The results demonstrate the utility of nESI-QIT-MS towards the facile determination of the glycan sequence, the peptide linkage and the peptide sequence and branching of purified muropeptides (monomeric up to trimeric forms). The wealth of structural information generated by nESI-QIT-MSn is unsurpassed by any other individual technique. Copyright © 2001 John Wiley & Sons, Ltd. [source] Consequence of the presence of two different , subunit isoforms in a GABAA receptorJOURNAL OF NEUROCHEMISTRY, Issue 6 2005Nathalie Boulineau Abstract The major isoforms of GABAA receptors are thought to be composed of two ,, two , and one , subunit(s). GABAA receptors containing two ,1 subunits respond differently to the anticonvulsive compound loreclezole and the general anaesthetic etomidate than receptors containing two ,2 subunits. Receptors containing ,2 subunits show a much larger allosteric stimulation by these agents than those containing ,1 subunits. We were interested to know how receptors containing both ,1 and ,2 subunits, in different positions respond to loreclezole and etomidate. To answer this question, subunits were fused at the DNA level to form dimeric and trimeric subunits. Concatenated receptors (,1 -,1 -,1/,2 -,1, ,1 -,2 -,1/,2 -,1, ,1 -,1 -,1/,2 -,2 and ,1 -,2 -,1/,2 -,2) were expressed in Xenopus ooctyes and functionally compared in their response to the agonist GABA and to the positive allosteric modulators, loreclezole and etomidate. We have shown that (I) in the presence of both ,1 and ,2 subunits in the same pentamer (mixed receptors) direct gating by etomidate is similar to exclusively ,1 containing receptors; (II) In mixed receptors, stimulation by etomidate assumed characteristics intermediate to exclusively ,1 or ,2 containing receptors, but the values for the concentrations < 10 µm were always much closer to those observed in ,1 -,1 -,1/,2 -,1 receptors; and (III) mixed receptors show no positional effects. [source] | |||||||||||||||||||||||||||||||||||||