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UV/Vis Spectroscopy (vis + spectroscopy)
Selected AbstractsChemInform Abstract: Synthesis, Characterization, and Quantum-Chemical Studies of Ni(CN)2MX (M: Rb, Cs; X: Cl, Br).CHEMINFORM, Issue 42 2010Xiaohui Liu Abstract The new two-dimensional compounds (III) are characterized by single crystal XRD, FT-IR and UV/VIS spectroscopy, magnetic measurements, and DFT calculations. [source] ChemInform Abstract: Optical Properties of the Complex Perovskite Ceramic Oxide Ba2YZrO6-d.CHEMINFORM, Issue 32 2010V. R. Kumar Abstract Nanocrystalline Ba2YZrO6-d is prepared by auto-ignition combustion of an aqueous HNO3 solution of Ba(NO3)2, Y2O3, ZrOCl2, citric acid, and NH4OH, and characterized by powder XRD, TEM, and UV/VIS spectroscopy. [source] Cytotoxic Rhodium(III) Polypyridyl Complexes Containing the Tris(pyrazolyl)methane Coligand: Synthesis, DNA Binding Properties and Structure,Activity RelationshipsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2009Ruth Bieda Abstract The RhIII complexes of the type [RhCl(pp)(tpm)]2+ [pp = bpy, bpm, phen, tap, dpq, dppz] 4,9 have been prepared by stepwise treatment of RhCl3·3H2O or mer,cis -[RhCl3(DMSO-,S)2(DMSO-,O)] with the appropriate polypyridyl ligand (pp) followed by the tripodal ligand tris(pyrazolyl)methane (tpm). Intermediates of the type [RhCl3(CH3OH)(pp)] 1,3 with pp = bpy, phen, dpq were also characterized but exhibit either low (3) or no (1, 2) cytotoxicity. X-ray structural analyses of [RhCl(bpy)(tpm)][PF6]24 and [RhCl(phen)(tpm)][PF6]26 were performed, and the interaction of complexes 4,9 with DNA was investigated by CD and UV/Vis spectroscopy and by gel electrophoresis. CD and viscosity studies confirm strong intercalation of dppz complex 9 into DNA. Complexes 8 and particularly 9 (IC50 = 0.43, 0.37 ,M) are potent cytotoxic agents towards the human cancer cell lines MCF-7 and HT-29, whereas respectively little (complex 6) or no activity (complexes 4, 5, 7) is observed for the other members of the series. Our findings indicate that the cytotoxicity is dependent on the hydrophobicity of both the polypyridyl and the facial coligand in these and other half-sandwich RhIII complexes. Irradiation of bpy compound 4 in the presence of plasmid pBR322 for 30 min at 311 nm at a molar ratio of r = 0.1 leads to total conversion of the supercoiled form into the nicked version. Although dppz complex 9 also functions as a photonuclease under these conditions, the degree of cleavage is much lower. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] One-Dimensional Coordination Polymers of MnII, CuII, and ZnII Supported by Carboxylate-Appended (2-Pyridyl)alkylamine Ligands , Structure and MagnetismEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2009Himanshu Arora Abstract Four new complexes [MnII(L1OO)(H2O)][ClO4]·2H2O (1), [ZnII(L1OO)][ClO4]·2H2O (2), [CuII(L3OO)][CF3SO3]·H2O (3), and [ZnII(L3OO)][ClO4] (4) (L1OO, = 3-[(2-(pyridine-2-yl)ethyl){2-(pyridine-2-yl)methyl}amino]propionate; L3OO, = 3-[(2-(pyridine-2-yl)ethyl){(dimethylamino)ethyl}amino]propionate) have been synthesized and characterized by elemental analysis, IR, and UV/Vis spectroscopy. Structural analysis revealed that 1, 3, and 4 are one-dimensional chain-like coordination polymers. In 1 distorted octahedral MnN3O3 and in 3 square-pyramidal CuN3O2 coordination is satisfied by three nitrogen atoms and an appended carboxylate oxygen atom of the ligand, and an oxygen atom belonging to the carboxylate group of an adjacent molecule. In 4 trigonal bipyramidal ZnN3O2 coordination environment is provided by two nitrogen atoms and an appended carboxylate oxygen atom of the ligand in the equatorial plane, and the two axial positions are satisfied by a tertiary amine nitrogen and an oxygen atom belonging to the carboxylate group of an adjacent molecule. In 1 the MnII center is coordinated by an additional water molecule. In these complexes each monomeric unit is sequentially connected by syn - anti carboxylate bridges. Temperature-dependent magnetic susceptibilities for 1 and 3 are measured, revealing antiferromagnetic interactions through syn - anti carboxylate bridges between the MII centers. Analysis of the crystal packing diagram reveals that in 1 extensive ,,, stacking involving alternate pyridine rings of adjacent 1D chain exists, which eventually lead to the formation of a 2D network structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Pyrazole and Pyrazolyl Complexes of cis -Bis(2,2,-bipyridine)chlororuthenium(II): Synthesis, Structural and Electronic Characterization, and Acid-Base ChemistryEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2009Hershel Jude Abstract Complexes of the type cis -[Ru(bpy)2(Cl)(L)]+ [bpy = 2,2,-bipyridine; with L = pyrazole (1H), 4-methylpyrazole (2H), and 3,5-dimethylpyrazole (3H)] were synthesized and isolated as hexafluorophosphate salts. The molecular structures of these new complexes were fully characterized by 1H NMR spectroscopy and ESI mass spectrometry, and the crystal structure of 3H·PF6 was determined by X-ray crystallography. Compound 3H·PF6 (C25H24ClF6N6PRu) crystallizes in the monoclinic space group P21/n with a = 12.102(2) Å, b = 16.826(3) Å, c = 13.016(2) Å, , = 92.606(2)°, V = 2647.6(8) Å3, and Z = 4. The crystal structure of 3H reveals the formation of an intramolecular hydrogen bond (2.562 Å) between the pyrazole N(2),H site and the chloride ligand. The redox and electronic absorption properties of 1H, 2H, and 3H, as well as their deprotonated counterparts [L = pyrazolate (1), 4-methylpyrazolate (2), and 3,5-dimethylpyrazolate (3)], were investigated by cyclic voltammetry and UV/Vis spectroscopy. For detailed analysis of the electronic nature of this series of pyrazolyl ligands, the results are discussed along with other relevant cis -[Ru(bpy)2(X)(Y)]n+ complexes. From spectrophotometric pH titrations, the basicity associated with the coordinated pyrazole/pyrazolate couple in water was found in all three cases to be unusually high, partly owing to the N,H···Cl hydrogen bond that stabilizes the protonated, azole state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Tetranuclear Nickel Complexes Composed of Pairs of Dinuclear LNi2 Fragments Linked by 4,4,-Bipyrazolyl, 1,4-Bis(4,-pyrazolyl)benzene, and 4,4,-Bipyridazine: Synthesis, Structures, and Magnetic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2007Vasile Lozan Abstract The ability of the ligands 4,4,-bipyrazolyl (H2bpz), 1,4-bis(4,-pyrazolyl)benzene (H2bpzb), and 4,4,-bipyridazine (bpdz) to link two dioctahedral LNi2 units has been examined. Thefollowing complexes were prepared: [L1NiII2(Hbpz)][BPh4] (6[BPh4]), [L1NiII2(bpdz)][ClO4]2 (7[ClO4]2), [(L1NiII2)2(bpzb)][BPh4]2 (8[BPh4]2), and [(L2NiII2)2(bpz)][BPh4]2 (9[BPh4]2), where (L1)2, and (L2)2, represent macrocyclic hexaaza-dithiophenolate ligands. All complexes have been characterised by UV/Vis spectroscopy, IR spectroscopy, and X-ray crystallography. Whereas (Hbpz), and bpdz in 6[BPh4]2 and 7[ClO4]2 act as bidentate ligands coordinating to only one [LNi2]2+ unit, in 8[BPh4]2 and 9[BPh4]2 the (bpzb)2, and(bpz)2, units are tetradentate linkers. This is qualitatively explained in terms of the absence or presence of steric repulsions between the tBu groups of the supporting ligands and the length of the coligands. The structures of the tetranuclear complexes differ mainly in the distance between the center of the Ni···Ni axes of the isostructural [LNi2] units {14.040(1) Å in 8[BPh4]2, 9.184(1) Å in 9[BPh4]2}. The two Ni2pyrazolato planes in 9[BPh4]2 are coplanar. An analysis of the temperature-dependent magnetic susceptibility data for 9[BPh4]2 reveals the presence of weak ferromagnetic exchange interactions between the NiII ions in the binuclear [L2Ni2] subunits with values for the magnetic exchange constant J1 of 23.97 cm,1 (H = ,2JS1S2). The exchange coupling across the dipyrazolato bridge is less than 0.1 cm,1, suggesting that no significant interdimer exchange coupling occurs in 9[BPh4]2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis and Structural Characterisation of Copper(II) 15-Metallacrown-5 Complexes with PbII, HgII, AgI, NaI and YIII Central Metal IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Sabry Hamed Seda Abstract The new copper(II) 15-metallacrown-5 complexes with the central metal ions PbII, HgII, AgI, NaI and YIII, with the formula [MCu5L5]Xn {H2L is 2-picolinehydroxamic acid or (S)-phenylalaninehydroxamic acid and X, is NO3, or Cl,}, have been synthesised and characterised by NMR and UV/Vis spectroscopy, electrospray mass spectrometry and elemental analysis. The PbII - and HgII 15-metallacrown-5 complexes were obtained in the crystalline form as pyridine adducts [PbCu5(picha)5(py)6](NO3)2·3(py) and [HgCu5(picha)5(py)7](NO3)2·2(py) and their X-ray crystal structures were determined. In both complexes, each peripheral CuII ion of the metallacrown is coordinated by one pyridine molecule bonded in the axial position. In the case of the PbII derivative, one additional axial pyridine molecule is bound to the central metal ion, while in the case of the HgII derivative, two axial pyridine ligands are bound to the central HgII ion. The relative stability of the copper(II) 15-metallacrown-5 complexes with various central metal ions was determined on the basis of competition reactions. The relative preference of the 15-metallacrown-5 system for the central metal ion follows the series NaI, AgI < lanthanide(III), HgII < PbII.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Crystal Structure, Solid-State NMR Spectroscopic and Photoluminescence Studies of Organic-Inorganic Hybrid Materials (HL)6[Ge6(OH)6(hedp)6]·2(L)·nH2O, L = hqn or phen,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2006Luís Mafra Abstract Two germanium,hedp4, solids with heteroaromatic amines 8-hydroxyquinoline (hqn) and 1,10-phenanthroline (phen), (HL)6[Ge6(OH)6(hedp)6]·2(L)·nH2O (L = hqn or phen), in I and II respectively, have been prepared and characterised by single-crystal XRD, thermogravimetry, FTIR and UV/Vis spectroscopy. The complex hydrogen-bond networks, particularly in compound I, have been studied by advanced high-resolution solid-state NMR spectroscopy that combines homonuclear recoupling techniques (two-dimensional 1H- 1H DQF and 1H- 1H RFDR MAS NMR) and combined rotation and multiple-pulse spectroscopy (two-dimensional 1H- 1H FS-LG, 1H- 31P FS-LG). The fine details of the crystal structure of I have been elucidated, mainly those involving the ,,, stacking of 8-hydroxyquinoline and the relative orientation of adjacent such molecules. Compound II exhibits an emission from the lowest triplet-state energy (,,,* 0-phonon transition) of the aromatic rings at 320 nm (31250 cm,1) from 14 K to room temperature. In contrast, the triplet emission of I at 530 nm (18868 cm,1) is only detected at low temperature, because of thermally activated non-radiative mechanisms. The emission spectra of I and II display a lower-energy component with a larger life time, which results from the formation of an excimer state that originated from the ,,, phenanthroline and hydroxyquinoline interactions, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Size- and Shape-Controlled Synthesis and Assembly of a Silver Nanocomplex in UV-Irradiated TSA SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2006Liangbao Yang Abstract In this paper we describe the size-controlled synthesis ofa silver nanocomplex based on the reduction of silvernitrate (AgNO3) by UV-irradiated tungstosilicate acid [H4(SiW12O40), TSA] solution. This method allows the synthesis of ellipsoidal particles with an average size that is tunable between 2.4 and 84 nm by varying the molar ratio of silver nitrate to TSA, the pH of the reaction solution, and the reaction temperature. Silver nanorods can be formed from the ellipsoidal nanoparticles by controlling the aging time. The formation mechanism of these nanorods is also discussed. The nanoparticles are characterized by UV/Vis spectroscopy, FTIR spectroscopy, XRD analysis, XPS, electron diffraction (ED), TEM, and with a Zetasizer instrument. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Water-Soluble Sal2en- and Reduced Sal2en-Type Ligands: Study of Their CuII and NiII Complexes in the Solid State and in SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2006Isabel Correia Abstract The CuII and NiII complexes of the Schiff base pyr2en [N,N, -ethylenebis(pyridoxyliminato)] and reduced Schiff bases Rpyr2en [N,N, -ethylenebis(pyridoxylaminato)] and R(SO3,sal)2en (SO3,sal = salicylaldehyde-5-sulfonate) were prepared and characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy. The structure of Ni(pyr2en)·3H2O was determined by single-crystal X-ray diffraction. The pyr2en2, ligand is coordinated through two phenolate-O and imine-N atoms, in a distorted square-planar geometry. The complexation of CuII and NiII with Rpyr2en in aqueous solution is studied by pH-potentiometry, UV/Vis spectroscopy, as well as by EPR spectroscopy for the CuII system, and 1H NMR spectroscopy for the NiII system. Complex formation constants were determined and binding modes proposed. While for the CuII system all complexes present a 1:1 stoichiometry with different protonation states, for the NiII system the 2:1 (L/M) complexes become important in the basic pH range at a higher ligand excess. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] High-Zirconium-Content Nano-Sized Bimodal Mesoporous SilicasEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006David Ortiz de Zárate Abstract Silica-based nanoparticulated bimodal mesoporous materials with high Zr content (43 , Si/Zr , 4) have been synthesized by a one-pot surfactant-assisted procedure from a hydroalcoholic medium using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure-directing agent, and starting from molecular atrane complexes of Zr and Si as hydrolytic inorganic precursors. This preparative technique allows optimization of the dispersion of the Zr guest species in the silica walls. The bimodal mesoporous nature of the final high surface area nano-sized materials is confirmed by XRD, TEM, and N2 adsorption,desorption isotherms. The small intraparticle mesopore system (with pore sizes around 2,3 nm) is due to the supramolecular templating effect of the surfactant, while the large mesopores (around 12,24 nm) have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. The basicity of the reaction medium seems to be a key parameter in the definition of this last pore system. The effects induced by the progressive incorporation of Zr atoms on the mesostructure have been examined, and the local environment of the Zr sites in the framework has been investigated by UV/Vis spectroscopy. Observations based on the consequences of post-treatments of the as-synthesized materials with HCl/ethanol mixtures corroborate that the atrane method leads to Zr-rich materials showing enhanced site accessibility and high chemical homogeneity throughout the pore walls. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Tuning of Copper(I),Dioxygen Reactivity by Bis(guanidine) Ligands,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005Sonja Herres-Pawlis Abstract A series of bis(guanidine) ligands designed for use in biomimetic coordination chemistry, namely bis(tetramethylguanidino)-, bis(dipiperidinoguanidino)-, and bis(dimethylpropyleno)propane (btmgp, DPipG2p and DMPG2p, respectively), has been extended to include bis(dimethylethyleneguanidino)propane (DMEG2p), which has both Namine atoms of each guanidine functionality connected by a short ethylene bridge, as a member. From this series, a family of novel bis(guanidine)copper(I) compounds , [Cu2(btmgp)2][PF6]2 (1), [Cu2(DPipG2p)2][PF6]2 (2), [Cu2(DMPG2p)2][PF6]2 (3), and [Cu2(DMEG2p)2][PF6]2·2MeCN (4) , has been synthesised. Single-crystal X-ray analysis of 1,4 demonstrated that these compounds contain dinuclear complex cations that contain twelve-membered heterocyclic Cu2N4C6 rings with the Cu atoms being more than 4 Å apart. Each copper atom is surrounded by a set of two N-donor functions from different ligands, resulting in linear N,Cu,N coordination sites. Depending on their individual substitution patterns, the guanidine moieties deviate from planarity by characteristic propeller-like twists of the amino groups around their N,Cimine bonds. The influence of these groups on the reactivity of the corresponding complexes 1,4 with dioxygen was investigated at low temperatures by means of UV/Vis spectroscopy. The reaction products can be classified into ,-,2:,2 -peroxodicopper(II) or bis(,-oxo)dicopper(III) complex cations that contain the {Cu2O2}2+ core portion as different isomers. The electronic properties of the specific bis(guanidine) ligands are discussed from the viewpoint of their ,-donor and ,-acceptor capabilities, and it is shown that ,-,2:,2 -peroxodicopper(II) complexes are stabilised relative to the bis(,-oxo)dicopper(III) ones if , conjugation within the guanidine moieties is optimised. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Dinuclear Complexes of MII Thiocyanate (M = Ni and Cu) Containing a Tridentate Schiff-Base Ligand: Synthesis, Structural Diversity and Magnetic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005Suparna Banerjee Abstract A dinuclear NiII complex, [Ni2(L)2(H2O)(NCS)2]·3H2O (1) in which the metal atoms are bridged by one water molecule and two ,2 -phenolate ions, and a thiocyanato-bridged dimeric CuII complex, [Cu(L)NCS]2 (2) [L = tridentate Schiff-base ligand, N -(3-aminopropyl)salicylaldimine, derived from 1:1 condensation of salicylaldehyde and 1,3-diaminopropane], have been synthesized and characterized by IR and UV/Vis spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction studies. The structure of 1 consists of dinuclear units with crystallographic C2 symmetry in which each NiII atom is in a distorted octahedral environment. The Ni,O distance and the Ni,O,Ni angle, through the bridged water molecule, are 2.240(11) Å and 82.5(5)°, respectively. The structure of 2 consists of dinuclear units bridged asymmetrically by di-,1,3 -NCS ions; each CuII ion is in a square-pyramidal environment with , = 0.25. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complex 1 with J = 3.1 cm,1, whereas complex 2 exhibits weak antiferromagnetic coupling between the CuII centers with J = ,1.7 cm,1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Kinetic and Thermodynamic Studies of the Disproportionation of Hydrogen Peroxide by Dimanganese(ii,ii) and -(ii,iii) Complexes of a Bridging Phenolate LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Lionel Dubois Abstract The dimanganese(ii,ii) complexes [Mn2(L)(OAc)2(CH3OH)]-(ClO4) (1a) and [Mn2(L)(OBz)2(H2O)](ClO4) (1b) as well as the dimanganese(ii,iii) complex [Mn2(L)(OAc)2(CH3OH)]-(ClO4)2 (2a), where HL is the asymmetric phenol ligand2-[bis(2-pyridylmethyl)aminomethyl]-6-{[(benzyl)(2-pyridyl-methyl)amino]methyl}-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The initial reaction rates and their temperature and acid/base dependencies were investigated by monitoring the dioxygen evolution. These studies revealed a first-order dependence on both the catalyst and H2O2 and a strong influence of the carboxylate. Electrospray ionisation mass spectrometry as well as EPR and UV/Vis spectroscopy were used to monitor the reaction catalysed by 2a. The same bis(,-oxo)dimanganese(III,IV) and (,-oxo)dimanganese(ii,iii) active species as found for 1a were detected in the catalytic medium. The EPR spectra recorded during the catalase-like reaction revealed the accumulation of the magnetically uncoupled dimanganese(ii,iii) precursor of the active bis(,-oxo)dimanganese(III,IV) species which dominates the spectra in the case of 1a. This difference can be attributed to the different pH conditions generated by the reaction and reflects differences in the initiation phases for the two catalysts. Overall, the kinetic and thermodynamic studies of H2O2 disproportionation by these dimanganese complexes are fully consistent with the mechanism deduced from our previous extensive spectroscopic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis and Characterisation of Coordination Polymers of CuII and ZnII with 1,3-Bis(1,2,3,4-tetrazol-2-yl)propane , Rotational Freedom of the Donor Group Favours Structural DiversificationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2004Robert Bronisz Abstract The novel bidentate ligand 1,3-bis(1,2,3,4-tetrazol-2-yl)propane (pbtz), which possesses a flexible spacer, was synthesised in order to investigate the influence of the flexibility of ligand molecules on the architecture of coordination polymers. For that purpose the reactions between pbtz and M(ClO4)2·6H2O salts (M = CuII and ZnII) were performed. The complexes [{Cu(pbtz)3}(ClO4)2], and [{Zn(pbtz)3}(ClO4)2·2EtOH], were characterised by IR and UV/Vis spectroscopy and their crystal structures were determined by single-crystal X-ray diffraction measurements. In both compounds the pbtz ligand molecules act as N4,N4, connectors bridging the central atoms, and the 2-substituted tetrazole rings coordinate in a monodentate fashion to the central atoms forming M(tetrazole)6 cores. [{Cu(pbtz)3}(ClO4)2], was isolated as a 1D coordination polymer. The copper(II) ions are triply bridged by ligand molecules, leading to the formation of infinite 1D chains. A highly unusual manner of bridging, with the tethering of two neighbouring central atoms by the same kind of ligand molecules, although possessing different conformations, is observed. In [{Zn(pbtz)3}(ClO4)2·2EtOH], the six-coordinate zinc(II) ions, which are bridged by single ligand molecules, serve as topological nodes, leading to the formation of a 3D ,-polonium-type network. The crystal structure of the ZnII complex contains only one such net solvated by ethanol molecules. A conformational analysis of the ligand molecules in both compounds demonstrates that the flexibility of the pbtz and the ability of the tetrazole rings in particular to adopt various, relative orientations is responsible for the diversity of the architectures of the obtained complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis, Structure and Characterization of Two New Complexes [Cu2(C3H2O4)2(C4H4N2)]·2H2O and [Zn2(OH2)2(C3H2O4)2(C4H4N2)]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2003Xiutang Zhang Abstract Two new complexes with three-dimensional extended frameworks linked by pyrazine and malonate ligands, namely [Cu2(C3H2O4)2(C4H4N2)]·2H2O and [Zn2(OH2)2(C3H2O4)2(C4H4N2)], have been prepared and characterized by X-ray crystallography, IR, EPR and UV/Vis spectroscopy, their magnetic properties and electrical conductivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] A Facile Method for the Preparation of Gold Glyconanoparticles from Free Oligosaccharides and Their Applicability in Carbohydrate-Protein Interaction Studies,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2005Koen M. Halkes Abstract The weak binding affinity of monomeric oligosaccharides with carbohydrate-binding proteins are hampering their use in in-vivo and in-vitro bio-assays. Gold glyconanoparticles (GNPs), prepared from synthetic oligosaccharides, have been used to overcome this weak binding affinity. In this paper, a convenient method for the preparation of GNPs from free oligosaccharides is presented. The reductive amination of saccharides with trityl-protected cysteamine, followed by de-tritylation, afforded cysteamine-extended saccharides that could be used for the preparation of GNPs under reducing conditions in water. The robust chemistry and facile purification of intermediate and final compounds ensure high yields and reproducible results and the, subsequent, preparation of GNPs proceeded smoothly, even with minute quantities (nanomolar scale) of the cysteamine-extended saccharide. The described method was used to synthesize a series of gluco - and manno -oligosaccharide-containing GNPs. The prepared GNPs were validated in interaction studies with Con A, using either surface plasmon resonance (SPR), UV/Vis spectroscopy, or transmission electron microscopy (TEM). The described method for the preparation of water-soluble gold glyconanoparticles can be used for the identification of carbohydrate ligands for novel carbohydrate-binding proteins, and can find application as inhibitors of pathological interactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Cimetidine: antioxidant and metal-binding propertiesJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 12 2002Zaynab Lambat ABSTRACT Cimetidine is one of the most potent H2 receptor antagonists for inhibiting excessive histamine-induced acid secretion and is currently used worldwide to treat peptic ulcers. In this study, levels of free radicals were assessed and the ability of cimetidine to act as an antioxidant was determined using nitroblue-tetrazolium assay and lipid peroxidation assays. Free radical generation in the brain is promoted by the presence of iron, as occurs in the Fenton reaction. The results show that cimetidine reduces the generation of superoxide anion formed in the nitroblue-tetrazolium assay. In addition, cimetidine (1 mm) is able to reduce the iron-induced rise in lipid peroxidation in rat brain homogenates. Electrochemistry, UV/Vis spectroscopy and HPLC experiments show metal-ligand interactions between cimetidine and transition metals. The results imply that cimetidine provides a neuroprotective effect by binding to iron and copper, thus making them unavailable for free radical production. [source] Multilayer Thin Films by Layer-by-Layer Assembly of Hole- and Electron-Transport Polyelectrolytes: Optical and Electrochemical PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 20 2006Kyungsun Choi Abstract Summary: In this paper, we present the synthesis of a series of p-type and n-type semiconducting polyelectrolytes with triarylamine, oxadiazole, thiadiazole and triazine moieties. The synthesized polymeric hole and electron transport materials were examined optically and electrochemically using UV/Vis spectroscopy, PL spectroscopy and CV. Based on the optical and electrochemical data, each of the energy levels were calculated and all values suggested that they were promising hole- (p-type) or electron-transport (n-type) materials for devices. Moreover, the synthesized ionic polymers were suitable for LBL thin film deposition from dilute polymer solutions and the multilayers were fully characterized by UV/Vis, PL spectroscopy and CV. [source] Photocontrollable Peptide-Based Switches Target the Anti-Apoptotic Protein Bcl-xLCHEMBIOCHEM, Issue 18 2008Sabine Kneissl Abstract Photocontrol of Bcl-xL binding affinity has been achieved by using short BH3 domain peptides for Bak72,87 and Bid91,111 alkylated with an azobenzene crosslinker through two cysteine residues with different sequence spacings. The power to control the conformation of the crosslinker and hence peptide structure was demonstrated by CD and UV/Vis spectroscopy. The binding affinity of the alkylated peptides with Bcl-xL was determined in their dark-adapted and irradiated states by fluorescence anisotropy measurements, and use of different cysteine spacings allowed either activation or deactivation of the binding activities of these peptide-based switches by application of light pulses. Helix-stabilized peptides exhibited high Bcl-xL binding affinity with dissociation constants of 42±9, 21±1, and 55±4 nM for Bak, Bak, and Bid, respectively (superscript numbers refer to the spacing between cysteine residues), and up to 20-fold enhancements in affinity in relation to their helix-destabilized forms. Bak, Bak, and Bid each displayed more than 200-fold selectivity for binding to Bcl-xL over Hdm2, which is targeted by the N-terminal helix of the tumor suppressor p53. Structural studies by NMR spectroscopy demonstrated that the peptides bind to the same cleft in Bcl-xL as the wild-type peptide regardless of their structure. This work opens the possibility of using such photocontrollable peptide-based switches to interfere reversibly and specifically with biomacromolecular interactions to study and modulate cellular function. [source] Mechanism of Laccase,TEMPO-Catalyzed Oxidation of Benzyl AlcoholCHEMCATCHEM, Issue 7 2010Sander Abstract The oxidation of benzyl alcohol by air, catalyzed by the organocatalyst TEMPO and the enzyme laccase has been investigated. To establish the kinetically significant pathways and corresponding kinetic parameters, a series of experiments is conducted with synthesized stable oxidized and reduced forms of the organocatalyst, the oxoammonium cation, and hydroxylamine. The time course of TEMPO and its oxidized and reduced derivatives is monitored off line by a combination of GC analysis, UV/Vis spectroscopy, EPR spectroscopy, and FTIR spectroscopy. TEMPO is found to be regenerated through noncatalyzed comproportionation of the oxoammonium cation with hydroxylamine. A kinetic model is presented based on the experimentally determined kinetically significant pathways. The time dependences of the concentrations of the three redox states of TEMPO and benzyl alcohol are adequately described by the model. The results provide new leads for the development of a practical process for a combined laccase,TEMPO-catalyzed selective oxidation of alcohols. [source] Do Trinuclear Triplesalen Complexes Exhibit Cooperative Effects?CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2010Characterization, Enantioselective Catalytic Sulfoxidation by Chiral Trinuclear FeIII Triplesalen Complexes, Synthesis Abstract The chiral triplesalen ligand H6chand provides three chiral salen ligand compartments in a meta -phenylene arrangement by a phloroglucinol backbone. The two diastereomeric versions H6chandRR and H6chandrac have been used to synthesize the enantiomerically pure chiral complex [(FeCl)3(chandRR)] (3RR) and the racemic complex [(FeCl)3(chandrac)] (3rac). The molecular structure of the free ligand H6chandrac exhibits at the terminal donor sides the O-protonated phenol,imine tautomer and at the central donor sides the N-protonated keto,enamine tautomer. The trinuclear complexes are comprised of five-coordinate square-pyramidal FeIII ions with a chloride at the axial positions. The crystal structure of 3rac exhibits collinear chiral channels of ,11,Å in diameter making up 33.6,% of the volume of the crystals, whereas the crystal structure of 3RR exhibits voids of 560,Å3. Mössbauer spectroscopy demonstrates the presence of FeIII high-spin ions. UV/Vis spectroscopy is in accordance with a large delocalized system in the central backbone evidenced by strong low-energy shifts of the imine ,,,* transitions relative to that of the terminal units. Magnetic measurements reveal weak intramolecular exchange interactions but strong magnetic anisotropies of the FeIII ions. Complexes 3rac and 3RR are good catalysts for the sulfoxidation of sulfides providing very good yields and high selectivities with 3RR being enantioselective. A comparison of 3RR and [FeCl(salen,)] provides higher yields and selectivities but lower enantiomeric excess values (ee values) for 3RR relative to [FeCl(salen,)]. The low ee values of 3RR appeared to be connected to a strong ligand folding in 3RR, opening access to the catalytically active high-valent Fe,O species. The higher selectivity is assigned to a cooperative stabilization of the catalytically active high-valent Fe,O species through the phloroglucinol backbone in the trinuclear complexes. [source] Spontaneous Organization of Uniform CeO2 Nanoflowers by 3D Oriented Attachment in Hot Surfactant Solutions Monitored with an In Situ Electrical Conductance TechniqueCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2008Huan-Ping Zhou Abstract Uniform CeO2 nanoflowers were synthesized by rapid thermolysis of (NH4)2Ce(NO3)6 in oleic acid (OA)/oleylamine (OM), by a unique 3D oriented-attachment mechanism. CeO2 nanoflowers with controlled shape (cubic, four-petaled, and starlike) and tunable size (10,40,nm) were obtained by adjusting the reaction conditions including solvent composition, precursor concentration, reaction temperature, and reaction time. The nanoflower growth mechanism was investigated by in situ electrical conductance measurements, transmission electron microscopy, and UV/Vis spectroscopy. The CeO2 nanoflowers are likely formed in two major steps, that is, initial formation of ceria cluster particles capped with various ligands (e.g., OA, OM, and NO3,) via hydrolysis of (NH4)2Ce(NO3)6 at temperatures in the range 140,220,°C, and subsequent spontaneous organization of the primary particles into nanoflowers by 3D oriented attachment, due to a rapid decrease in surface ligand coverage caused by sudden decomposition of the precursor at temperatures above 220,°C in a strong redox reaction. After calcination at 400,°C for 4,h the 33.8,nm CeO2 nanoflowers have a specific surface area as large as 156,m2,g,1 with high porosity, and they are highly active for conversion of CO to CO2 in the low temperature range of 200,400,°C. The present approach has also been extended to the preparation of other transition metal oxide (CoO, NiO, and CuOx) nanoflowers. [source] Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline PhasesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Zhijian Chen Abstract A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3,a,f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1H,NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The ,,, aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted ,-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3×104 and 30,M,1. The photoluminescence spectra of the dimers of PBIs 3,a,f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective ,,, stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the , systems on their ,,, stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3,a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H -type into strongly fluorescent J -type packing of the dyes. [source] Influence of Intermolecular Interactions on the Formation of Tetra(carbomethoxy)-tetrathiafulvalene AssembliesCHEMPHYSCHEM, Issue 10 2007Núria Crivillers Abstract We study the assemblies that tetra(carbomethoxy)tetrathiafulvalene (TCM,TTF) forms in solution and when deposited on a surface depending on intermolecular interactions and on the interactions with the substrate and the solvent. Its organization on graphite and mica substrates was studied by atomic force microscopy, and different molecular assemblies were observed depending on the prevailing interactions. The promotion of molecule,molecule interactions gave rise to the formation of molecular fibers. The investigation of the influence of the solvent,molecule interactions on TCM,TTF molecular organizations was carried out by UV/Vis spectroscopy, and a new TCM,TTF polymorph was obtained by changing the nature of the solvent. Finally, an explanation for all these phenomena, supported by computational modeling, is put forward. [source] From Cloudy to Transparent: Chain Rearrangement in Hydrogen-Bonded Layer-by-Layer Assembled FilmsCHEMPHYSCHEM, Issue 3 2007Shuguang Yang Abstract The cloudiness of hydrogen-bonded LBL films assembled from polyvinylpyrrolidone (PVPON) and poly(acrylic acid) (PAA) is studied in detail by two approaches: spectroscopy (Fabry,Pérot fringes) and microscopy (AFM). Fabrication parameters such as temperature, molecular weight, pH value, and rinsing time, have notable influences on film cloudiness. The buildup of the PVPON/PAA film is a two-stage process of adsorption and chain rearrangement. Generally, adsorption is fast, while chain rearrangement is slow. The fast adsorption process traps defects, whereas the relatively slow chain-rearrangement process can not heal the defects in time; therefore, the number of defects continuously increases as LBL assembly proceeds, and a cloudy, heterogeneous film is produced. However, the as-prepared cloudy films become transparent and homogeneous on subsequent annealing in acidic water. UV/Vis spectroscopy and fluid AFM were applied to monitor this transition ex situ and in situ, respectively. It is found that increasing the annealing temperature accelerates the transition from cloudy to transparent, and the transition of the film made from higher molecular weight polymer is slower. [source] A Ru-Hbpp-Based Water-Oxidation Catalyst Anchored on Rutile TiO2,CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 4 2009Laia Francàs Abstract In support of a split: A water oxidation catalyst based on ruthenium bis-(2-pyridyl)pyrazole anchored on rutile TiO2 was prepared. The performance of this new material with regard to its capacity to catalytically oxidize water to molecular oxygen in a heterogeneous phase was evaluated. Two organic ligands based on bis-(2-pyridyl)pyrazole (Hbpp) functionalized with a para -methylenebenzoic acid (Hbpp-Ra) or its ester derivative (Hbpp-Re) were prepared and characterized. The ester-functionalized ligand was then used to prepare a series of related dinuclear ruthenium complexes of general formula [RuII2(L- L)(bpp-Rn)(trpy)2]m+ (L-L=,-Cl, ,-acetato, or (H2O)2; n=e or a; trpy=2,2,:6,,2,,-terpyridine; m=2 or 3). The complexes were characterized in solution by 1D and 2D,NMR spectroscopy, UV/Vis spectroscopy, and electrochemical techniques. The [RuII2(,-Cl)(bpp-Re)(trpy)2](PF6)2 complex was further characterized in the solid state by X-ray diffraction. The complexes containing the free carboxylic acid ligand were anchored onto rutile TiO2 and treated with 0.1,M triflic acid solution to generate the homologous water-oxidation catalysts TiO2 -[RuII2(H2O)2(bpp-Ra)(trpy)2]2+. This new hybrid material catalytically oxidizes water to molecular oxygen in a heterogeneous manner using CeIV as chemical oxidant. The generation of molecular oxygen is accompanied by the formation of carbon dioxide as well as some leaching of the Ru catalyst. [source] High Molar Extinction Coefficient Ion-Coordinating Ruthenium Sensitizer for Efficient and Stable Mesoscopic Dye-Sensitized Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2007D. Kuang Abstract Ru(4,4-dicarboxylic acid-2,2,-bipyridine) (4,4,-bis(2-(4-(1,4,7,10-tetraoxyundecyl)phenyl)ethenyl)-2,2,-bipyridine) (NCS)2, a new high molar extinction coefficient ion-coordinating ruthenium sensitizer was synthesized and characterized using 1H,NMR, Fourier transform IR (FTIR), and UV/vis spectroscopies and cyclic voltammetry. Using this sensitizer in combination with a nonvolatile organic-solvent-based electrolyte, we obtain a photovoltaic efficiency of 8.4,% under standard global AM,1.5 sunlight. These devices exhibit excellent stability when subjected to continuous thermal stress at 80,°C or light soaking at 60,°C for 1000,h. An electrochemical impedance spectroscopy study revealed that device stability is maintained by stabilizing the TiO2/dye/electrolyte and Pt/electrolyte interface during the aging process. The influence of Li+ present in the electrolyte on the device photovoltaic parameters was studied, and the FTIR spectral and photovoltage transient study showed that Li+ coordinates to the triethyleneoxide methylether side chains on the K60 sensitizer molecules. [source] Study of the Complexation, Adsorption and Electrode Reaction Mechanisms of Chromium(VI) and (III) with DTPA Under Adsorptive Stripping Voltammetric ConditionsELECTROANALYSIS, Issue 19 2003Sylvia Sander Abstract The complexation of Cr(III) and Cr(VI) with diethylenetriaminepentaacetic acid (DTPA), the redox behavior of these complexes and their adsorption on the mercury electrode surface were investigated by a combination of electrochemical techniques and UV/vis spectroscopy. A homogenous two-step reaction was observed when mixing Cr(III), present as hexaquo complex, with DTPA. The first reaction product, the electroactive 1,:,1 complex, turns into an electroinactive form in the second step. The results indicate that the second reaction product is presumably a 1,:,2 Cr(III)/DTPA complex. The electroreduction of the DTPA-Cr(III) complex to Cr(II) was found to be diffusion rather than adsorption controlled. The Cr(III) ion, generated in-situ from Cr(VI) at the mercury electrode at about ,50,mV (vs. Ag|AgCl) (3,mol,L,1 KCl), was found to form instantly an electroactive and adsorbable complex with DTPA. By means of electrocapillary measurements its surface activity was shown to be 30 times higher than that of the complex built by homogenous reaction of DTPA with the hydrated Cr(III). Both components, DTPA and the in-situ built complex Cr(III) ion were found to adsorb on the mercury electrode. The effect of nitrate, used as catalytic oxidant in the voltammetric determination method, on the complexation reaction and on the adsorption processes was found to be negligible. The proposed complex structures and an overall reaction scheme are shown. [source] Gold Nanoparticles Stabilized by Acetylene-Functionalized Multidentate Thioether Ligands: Building Blocks for Nanoparticle SuperstructuresADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Torsten Peterle Abstract Aiming at the formation of inorganic/organic hybrid gold nanoparticle superstructures, the design and synthesis of acetylene-monofunctionalized multidentate thioether ligands and their ability to stabilize gold nanoparticles are presented. Rather monodisperse gold particles with diameters of about 1,nm are obtained, which are coated by a small number of ligands, each comprising a silyl-protected acetylene. The acetylene is attached at the end of a rigid ethynylene-phenylene unit of variable length, leading to functionalized gold nanoparticles carrying acetylenes at different distances from the nanoparticle surface. These particles are interlinked by diacetylene formation and are investigated by transmission electron microscopy and UV/vis spectroscopy, revealing the formation of nanoparticle aggregates and small superstructures such as dimers or trimers while the nanoparticles themselves retain their integrity. The interparticle distance in small nanoparticle superstructures reflects the ethynylene-phenylene spacer length corroborating the wet chemical interlinking as the origin of these organic/inorganic hybrid structures. [source] | ||||||||||||||||||||||||||||