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Transition Metal Ions (transition + metal_ion)
Selected AbstractsKinetics of Urea Decomposition in the Presence of Transition Metal Ions: Ni2+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Bora Mavis The literature on kinetics of the urea decomposition reaction was reviewed for the 333,373 K range of temperature. Possible reactions in the pH range of 5,9 were identified. Kinetic simulations indicated significant accumulation of the cyanate intermediate in the pH-time,temperature range that was studied. The effects of Ni2+ hydrolysis and complexation with the urea decomposition products were incorporated into the simulations. The kinetic simulation of the rate of Ni2+ removal from the solutions was compared against the experimental data. The experimental results indicated an agglomerative growth mechanism for the precipitation process. Chemical analyses showed that the composition of the precipitate varies with digestion time, in agreement with the predictions of the kinetic simulation. [source] Can Electrophilicity Act as a Measure of the Redox Potential of First-Row Transition Metal Ions?CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2007Jan Moens Abstract Previous contributions concerning the computational approach to redox chemistry have made use of thermodynamic cycles and Car,Parrinello molecular dynamics simulations to obtain accurate redox potential values, whereas this article adopts a conceptual density functional theory (DFT) approach. Conceptual DFT descriptors have found widespread use in the study of thermodynamic and kinetic aspects of a variety of organic and inorganic reactions. However, redox reactions have not received much attention until now. In this contribution, we prove the usefulness of global and local electrophilicity descriptors for the prediction of the redox characteristics of first row transition metal ions (from Sc3+|Sc2+ to Cu3+|Cu2+) and introduce a scaled definition of the electrophilicity based on the number of electrons an electrophile ideally accepts. This scaled electrophilicity concept acts as a good quantitative estimate of the redox potential. We also identify the first solvation sphere together with the metal ion as the primary active region during the electron uptake process, whereas the second solvation sphere functions as a non-reactive continuum region. [source] Self-Assembly of [B -SbW9O33]9, Subunit with Transition Metal Ions (Mn2+, Cu2+, Co2+) in Aqueous Solution: Syntheses, Structures and Magnetic Properties of Sandwich Type Polyoxometalates with Subvalent SbIII HeteroatomCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2008Jing-Ping Wang Prof. Abstract Rational self-assembly of Sb2O3 and Na2WO4, or (NH4)18[NaSb9W21O86] with transition-metal ions (Mn2+, Cu2+, Co2+), in aqueous solution under controlled conditions yield a series of sandwich type complexes, namely, Na2H2[Mn2.5W1.5(H2O)8(B -,-SbW9O33)2],32,H2O (1), Na4H7[Na3(H2O)6Mn3(,-OAc)2(B -,-SbW9O33)2],20,H2O (OAc=acetate anion) (2), NaH8[Na2Cu4Cl(B -,-SbW9O33)2],21,H2O (3), Na8K[Na2K(H2O)2{Co(H2O)}3(B -,-SbW9O33)2], 10,H2O (4), and Na5H[{Co(H2O)2}3W(H2O)2(B -,-SbW9O33)2],11.5,H2O (5). These structures are determined by using the X-ray diffraction technique and further characterized by obtaining IR spectra and performing elemental analysis. Structure analysis reveals that polyoxoanions in 1 and 5 comprise of two [B -,-SbW9O33]9, building units, whereas 2, 3, and 4 consist of two isomerous [B -,-SbW9O33]9, building blocks, which are all linked by different transition-metal ions (Mn2+, Cu2+, or Co2+) with different quantitative nuclearity. It should be noted that compound 2 represents the first one-dimensional sinusoidal chain based on sandwich like tungstoantimonate building blocks through the carboxylate-bridging ligands. Additionally, 3 is constructed from sandwiched anions [Na2Cu4Cl(B -,-SbW9O33)2]9, linked to each other to form an infinitely extended 2D network, whereas 5 shows an interesting 3D framework built up from offset sandwich type polyoxoanion [{Co(H2O)2}3W(H2O)2(B -,-SbW9O33)2]6, linked by Co2+ and Na+ ions. EPR studies performed at 110,K and room temperature reveal that the metal cations (Mn2+, Cu2+, Co2+) reside in a square-pyramidal geometry in 2, 3, and 4. The magnetic behavior of 1,4 suggests the presence of weak antiferromagnetic coupling interactions between magnetic metal centers with the exchange integral J=,0.552,cm,1 in 2. [source] Investigation of the stereodynamics of tris-(, -diimine),transition metal complexes by enantioselective dynamic MEKCELECTROPHORESIS, Issue 2 2009Sabrina Bremer Abstract Enantiomerization of octahedral tris(, -diimine),transition metal complexes was investigated by enantioselective dynamic MEKC. Varying both the transition metal ion (Fe2+, Fe3+, and Ni2+) and the bidentate diimine ligand (1,10-phenanthroline and 2,2,-bipyridyl), the enantiomer separations were performed either in a 100,mM sodium tetraborate buffer (pH 9.3) or in a 100,mM sodium tetraborate/sodium dihydrogenphosphate buffer (pH 8.0) both containing sodium cholate as chiral surfactant. The unified equation of dynamic chromatography was employed to determine apparent reaction rate constants from the electropherograms showing distinct plateau formation. Apparent activation parameters ,H, and ,S, were calculated from temperature-dependent measurements between 10.0 and 35.0°C in 2.5,K steps. It was found that the nature of the central metal ion and the ligand strongly influence the enantiomerization barrier. Surprisingly, complexes containing the 2,2,-bipyridyl ligand show highly negative activation entropies between ,103 and ,116,J (K,mol),1 while the activation entropy of tris(1,10-phenanthroline) complexes is positive indicating a different mechanism of interconversion. Furthermore, it was found that the Ni2+ complexes are stereostable under the conditions investigated here making them a lucent target as enantioselective catalysts. [source] Outer-sphere electron transfer metal-catalyzed polymerization of styrene using a macrobicyclic ligandJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Craig A. Bell Abstract The CuBr-catalyzed polymerizations of styrene in the presence of a macrobicyclic mixed donor (N and S) encapsulating ligand, NH2capten, were carried out in toluene at 60 and 100 °C. The macrobicyclic nature of the ligand ensures that a transition metal ion is effectively encapsulated (caged) within the three-dimensional cavity, resulting in activation of radicals through an outer-sphere electron transfer mechanism. The kinetic data showed that the polymerizations were uncontrolled with little "living" behavior. The external orders of reaction in [CuBr], [NH2capten], and [CuBr2] were 0.5, 0.5, and close to zero, respectively, in agreement with the postulated mechanism of little or no deactivation of polymeric radicals and a significant amount of bimolecular termination. Although "living" behavior was not found using the cage ligand, it was decided that it would provide an ideal method for radical coupling experiments to make high-molecular weight multiblock copolymers from a difunctional PSTY (Br-PSTY-Br, PDI = 1.11). The coupling reaction of Br-PSTY-Br using CuBr/NH2capten and excess Cu(0) in toluene at 100 °C gave no loss of the starting Br-PSTY-Br. Changing the solvent to the aprotic DMSO resulted in a significant increase in the rate of consumption of starting Br-PSTY-Br, with over 87% being used in under 10 min at 60 °C. In addition, higher molecular weight species were also formed, suggesting that OSET gives little or no side reactions on this time scale. It was initially thought that to get such high rates of reaction that the SET-LRP disproportionation mechanism (2Cu(I) , Cu(0) + Cu(II)) was at play. However, UV,Vis experiments of the CuBr/NH2capten showed little or no disproportionation products. This important result suggests that DMSO catalyzes the OSET reaction through the stabilization of the radical-anion intermediate, which then rapidly fragments to a polymeric radical. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 146,154, 2008 [source] Electrospray mass spectrometric studies of the complexational behavior of maleonitrile thiacrown ethers with various metalsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2006Ines Starke Electrospray ionization was employed to study the mass spectrometric behavior of the maleonitrile tetrathiacrown ethers mn12S4 (1) and mn13S4 (2) and maleonitrile pentathiacrown ether mn15S5 (3) and of their complexes with various metal salts (MX2, M,=,Pd, Pt, Ni, Co, Fe; X,=,Cl, CrCl3, Ni(BF4)2, TlPF6 or Cd(NO3)2) and Cu(SO3CF3)2. Both singly charged, [MXL]+ and [MXL2]+, and doubly charged complexes, [MLn]2+ (n,=,2,5), were observed. The formation of the different complexes consisting of the transition metal ion, the counterion and the various crown ethers and their subsequent dissociation was also studied by collision-induced dissociation measurements which were also used to evaluate the relative stabilities of the complexes. It was found that the collisional voltages for the dissociation of the complexes were generally greater in the [MXL]+ complexes than in the corresponding [MXL2]+ complexes. Copyright © 2006 John Wiley & Sons, Ltd. [source] A metal-chelate affinity reverse micellar system for protein extractionBIOTECHNOLOGY PROGRESS, Issue 1 2010Xiao-Yan Dong Abstract A new nonionic reverse micellar system is developed by blending two nonionic surfactants, Triton X-45 and Span 80. At total surfactant concentrations lower than 60 mmol/L and molar fractions of Triton X-45 less than 0.6, thermodynamically stable reverse micelles of water content (W0) up to 30 are formed. Di(2-ethylhexyl) phosphoric acid (HDEHP; 1,2 mmol/L) is introduced into the system for chelating transition metal ions that have binding affinity for histidine-rich proteins. HDEHP exists in a dimeric form in organic solvents and a dimer associated with one transition metal ion, including copper, zinc, and nickel. The copper-chelate reverse micelles (Cu-RM) are characterized for their W0, hydrodynamic radius (Rh), and aggregation number (Nag). Similar with reverse micelles of bis-2-ethylhexyl sodium sulfosuccinate (AOT), Rh of the Cu-RM is also linearly related to W0. However, Nag is determined to be 30,90 at W0 of 5,30, only quarter to half of the AOT reverse micelles. Then, selective metal-chelate extraction of histidine-rich protein (myoglobin) by the Cu-RM is successfully performed with pure and mixed protein systems (myoglobin and lysozyme). The solubilized protein can be recovered by stripping with imidazole or ethylinediaminetetraacetic acid (EDTA) solution. Because various transition metal ions can be chelated to the reverse micelles, it is convinced that the system would be useful for application in protein purification as well as simultaneous isolation and refolding of recombinant histidine-tagged proteins expressed as inclusion bodies. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Lead(II) Potentiometric Sensor Based on 1,4,8,11-Tetrathiacyclotetradecane Neutral Carrier and Lipophilic AdditivesELECTROANALYSIS, Issue 11 2008Mohamed Abstract A potentiometric sensor for lead(II) ions based on the use of 1,4,8,11-tetrathiacyclotetradecane (TTCTD) as a neutral ionophore and potassium tetrakis-(p -chlorophenyl)borate as a lipophilic additive in plasticized PVC membranes is developed. The sensor exhibits linear potentiometric response towards lead(II) ions over the concentration range of 1.0×10,5,1.0×10,2,mol L,1 with a Nernstian slope of 29.9,mV decade,1 and a lower limit of detection of 2.2×10,6,mol L,1 Pb(II) ions over the pH range of 3,6.5. Sensor membrane without a lipophilic additive displays poor response. The sensor shows high selectivity for Pb(II) over a wide variety of alkali, alkaline earth and transition metal ions. The sensor shows long life span, high reproducibility, fast response and long term stability. Validation of the method by measuring the lower limit of detection, lower limit of linear range, accuracy, precision and sensitivity reveals good performance characteristics of the proposed sensor. The developed sensor is successfully applied to direct determination of lead(II) in real samples. The sensor is also used as an indicator electrode for the potentiometric titration of Pb(II) with EDTA and potassium chromate. The results obtained agree fairly well with data obtained by AAS. [source] Copper Ion Selective Membrane Electrodes Based on Some Schiff Base DerivativesELECTROANALYSIS, Issue 15-16 2003S. Sadeghi Abstract A series of Schiff base derivatives were studied to characterize their abilities as a copper ion carrier in PVC membrane electrodes. The electrode based on 2,2,-[4,4,diphenyl-methanebis(nitrilomethylidyne)]-bisphenol exhibits a Nernstian response for copper ions over the activity range 8.0×10,6,1.0×10,1 mol L,1 with detection limit of about , mol L,1 of copper ion in comparison with two other Schiff bases. The response time, pH effect and other characteristics of the electrodes were studied in a static mode. The effect of the methyl group substitute on Schiff base structure with SO2 bridging group in different positions with respect to OH group was studied. The results show that behavior of the electrodes is not considerably influenced by the position of methyl substitute. The selectivity coefficients were determined with modified fixed interference method (FIM) and matched potential method (MPM). The proposed electrodes comparatively show good selectivity with respect to alkali, alkaline earth and some transition metal ions. The electrodes were used for the determination of copper in black tea, multivitamin and mineral capsule and as an indicator electrode in potentiometric titration of copper ion. [source] Effect of transition metal ions (cobalt and nickel chlorides) on intestinal iron absorptionEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 9 2004G. O. Latunde-Dada Abstract Background, Haem biosynthesis may regulate intestinal iron absorption through changes in cellular levels of ,-aminolaevulinic acid (ALA), haem and perhaps other intermediates. CoCl2 and NiCl2 are activators of haem oxygenase, the rate-limiting enzyme in haem catabolism. Co2+ and Ni2+ may also regulate and increase iron absorption through a mechanism that simulates hypoxic conditions in the tissues. Design, We assayed intestinal iron absorption in mice dosed with CoCl2 or NiCl2. The effects of these metal ions on splenic and hepatic levels of ALA synthase and dehydratase as well as urinary levels of ALA and phosphobilinogen were also assayed. Results, While Co2+ enhanced iron absorption when administered to mice at doses of 65, 125 and 250 µmoles kg,1 body weight, Ni2+ was effective only at the highest dose. Ni2+ but not Co2+ at the highest dose reduced urinary ALA in the treated mice. Both metals ions increased splenic expression of haem oxygenase 1 and iron regulated protein 1, proteins involved, respectively, in haem degradation and iron efflux. Co2+ induced erythropoietin expression. Conclusions, The data suggest that while the effect of Ni2+ on iron absorption could be explained by effects on ALA, the effect of Co2+ may not be explained simply by changes in haem metabolism; therefore, effects mediated by alterations of specific haemoproteins by mechanisms that simulate tissue hypoxia could be important. [source] Layered [BaM(C3H2O4)2(H2O)4] (M = Fe or Co) Complexes , Spectroscopic, Magnetic and Thermal StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2003Izaskun Gil de Muro Abstract Complexes with formula [BaM(C3H2O4)2(H2O)4], where M = Fe or Co, were synthesised and characterised. These two types of complexes are isostructural and crystallise in the Pccn space group. Their structure consists of two-dimensional networks of octahedral MO6 polyhedra in which the transition metal ions are coordinated by bridging malonate ligands, through the O-C-O atoms. These M-malonate units are extended along the crystallographic [101] plane. Spectroscopic data are consistent with the cations being in a high-spin octahedral symmetry. The two types of compounds exhibit 2D antiferromagnetic interactions as well as weak ferromagnetism below the Néel temperature, as a result of an intralayer misalignment of the spins. Thermal treatment of the metallo-organic precursors gave rise to BaMO3,y oxides at lower temperatures and reaction times than those found in the literature using the ceramic method. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003). [source] Optical Power Limiters Based on Colorless Di-, Oligo-, and Polymetallaynes: Highly Transparent Materials for Eye Protection Devices,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2007G.-J. Zhou Abstract The synthesis, characterization, and photophysics of a series of solution-processable and tractable di-, oligo-, and polymetallaynes of some group 10,12 transition metals are presented. Most of these materials are colorless with very good optical transparencies in the visible spectral region and exhibit excellent optical power limiting (OPL) for nanosecond laser pulse. Their OPL responses outweigh those of the state-of-the-art reverse saturable absorption dyes such as C60, metalloporphyrins, and metallophthalocyanines that are all associated with very poor optical transparencies. On the basis of the results from photophysical studies and theoretical calculations, both the absorption of triplet and intramolecular charge-transfer states can contribute to the enhancement of the OPL properties for these materials. Electronic influence of the type, spatial arrangement, and geometry of metal groups on the optical transparency/nonlinearity optimization is evaluated and discussed in detail. The positive contribution of transition metal ions to the OPL of these compounds generally follows the order: Pt,>,Au,>,Hg,>,Pd. The optical-limiting thresholds for these polymetallaynes can be as low as 0.07,J,cm,2 at 92,% linear transmittance and these highly transparent materials manifest very impressive figure of merit ,ex/,o values (up to 22.48), which are remarkably higher than those of the benchmark C60 and metal phthalocyanine complexes. The present work demonstrates an attractive approach to developing materials offering superior OPL/optical transparency trade-offs and these metallopolyynes are thus very promising candidates for use in practical OPL devices for the protection of human eyes and other delicate optical sensors. [source] Molecular relaxation and metalloenzyme active site modelingINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2002James W. Whittaker Abstract Metalloenzymes represent a broad class of important biomolecules containing an essential metal ion cofactor in their catalytic active sites, forming biologic metal complexes that perform a wide range of important functions: activation of small molecules (O2, N2, H2, CO), atom transfer chemistry, and the control of oxidation equivalents. The structures of many metalloenzyme active sites have been defined by X-ray crystallography, revealing transition metal ions in unique low-symmetry environments. These bioinorganic complexes present significant challenges for computational studies aimed at going beyond crystal structures to develop a detailed understanding of the catalytic mechanisms. Considerable progress has been made in the theoretical characterization of these sites in recent years, supported by the availability of efficient computational tools, in particular density functional methods. However, the ultimate success of a theoretical model depends on a number of factors independent of the specific computational method used, including the quality of the initial structural data, the identification of important environmental perturbations and constraints, and experimental validation of theoretical predictions. We explore these issues in detail and illustrate the effects of molecular relaxation in calculations of two metalloenzymes, manganese superoxide dismutase and galactose oxidase. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Reduction of dissolved oxygen in boiler water using new redox polymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Christophe Waterlot Abstract New polymers were used as catalysts for the removal of dissolved oxygen in boiler water. These polymers, based upon hydroquinone-quinone redox system, were prepared by polymerization of methyl 4-(2,5-dimethoxybenzyl)cinnamate and copolymerization of this monomer with 4-(4,-vinylphenethyl)-1,10-phenanthroline. The resulting product was used to synthesize polymers containing transition metal ions. Nuclear magnetic resonance, infrared spectroscopy, and elemental analysis were achieved to characterize monomers and/or electron-transfer polymers. These polymers were used for the removal of oxygen from water. It was shown that the oxygen content was reduced to less than 0.1 mg L,1 in , 70 s. Based on the obtained results, the redox capacity of two polymers were determined. It was established that the poly-4-(2,5-dihydroxybenzyl)cinnamic acid reached a redox capacity of 69.7 mg of O2 per gram of polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Transition metal complexes of a cyclic pseudo hexapeptide: synthesis, complex formation and catalytic activities,,JOURNAL OF PEPTIDE SCIENCE, Issue 9 2008Huong Ngyen Abstract To contribute to a better understanding of metalloenzymes, we studied ion selectivity, complex formation tendencies and catalytic activities of linear and cyclic pseudopeptides. In this contribution, a linear and cyclic pseudo hexapeptide is described. The complex with transition metal ions and the sequence were designed using the programme COSMOS. Different routes of solid-phase synthesis were performed and compared using anchoring by C -terminus or a His side chain, using preformed pseudodipeptide building units or formation of N -functionalized peptide bond during stepwise assembly. The different strategies were compared regarding cyclization tendency, yield and purity. Side-chain anchoring to solid support favours the cyclization but leads to the formation of difficult to separate dioxopiperazine. Both routes require preformed building units. Complex-formation tendencies and selectivity for certain bivalent transition metal ions were experimentally estimated and compared to ones predicted theoretically. CD measurements indicate conformational changes by complex formation with different metal ions. Catalytic activities on oxidation of catechol and hydrolysis of bis-phosphate esters by some metal complexes of linear and cyclic peptide show only low catalytic activities compared to other model peptides and related metalloenzymes. The preference of the cyclic peptide for complexation of Ni2+ corresponds well to the predictions of COSMOS-NMR force field calculations. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Hydrogen peroxide overproduced in breast cancer cells can serve as an anticancer prodrug generating apoptosis-stimulating hydroxyl radicals under the effect of tamoxifen-ferrocene conjugateJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2007Wjatschesslaw A. Wlassoff A new approach to the treatment of cancer is suggested, based on the innate overproduction of hydrogen peroxide in cancer cells. Hydrogen peroxide serves as a prodrug in the presence of transition metal ions, such as iron delivered by ferrocene. Under the effect of ferrocene, hydrogen peroxide is split into hydroxyl anions and highly reactive hydroxyl radicals. The latter cause oxidative DNA damage, which induces apoptosis, leading to elimination of cancer cells. Tamoxifen, a drug that interacts with oestrogen receptors, was used as a carrier to deliver ferrocene to breast cancer cells. For this aim tamoxifen conjugated to ferrocene (Tam-Fer) was synthesized. We have shown that the frequency of apoptotic events in MCF-7 breast cancer cells treated with Tam-Fer is significantly higher than in cells treated with tamoxifen or ferrocene separately. The increase of apoptosis correlates well with the rise in generation of reactive oxygen species in cancer cells. These results show that the hydrogen peroxide overproduced in tumour cells can serve as a prodrug for the treatment of cancer. [source] Water-soluble anionic conjugated polymers for metal ion sensing: Effect of interchain aggregationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2009Yi Chen Abstract Three sulfonato-containing fluorene-based anionic water-soluble conjugated polymers, which are specially designed to link fluorene with alternating moieties such as bipyridine (P1), pyridine (P2), and benzene (P3) have been synthesized via the Pd-catalyzed Sonogashira-coupling reaction, respectively. These polymers had good solubility in water and showed different responses for transition metal ions with different valence in aqueous environments: the fluorescence of bipyridine-containing P1 can be completely quenched by addition of all transition metal ions selected and showed a good selectivity for Ni2+; the pyridine-containing P2 had a little response for monovalent and divalent metal ions while showed good quenching with the addition of trivalent metal ions (with a special selectivity for Fe3+); P3 had responses only for the trivalent metal ions within the ionic concentration we studied. After investigation of the UV-vis absorption spectra, PL emission spectra, DLS, and fluorescence lifetime of P1,P3 in aqueous solution when adding transition metal ions, we found that the different spectrum responses of these polymers are attributed to the different coordination ability of the units linked with fluorene in the main chain. The energy or electron-transfer reactions were the main reason for fluorescence quenching of P1 and P2. On the other hand, interchain aggregation caused by trivalent metal ions lead to fluorescence quenching for P3 and also caused partly fluorescence quenching of P1 and P2. These results revealed the origin of ionochromic effects of these polymers and suggested the potential application for these polymers as novel chemosensors with higher sensing sensitivity in aqueous environments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5057,5067, 2009 [source] Hyperbranched copolymer containing triphenylamine and divinyl bipyridyl units for fluorescent chemosensorsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2009Jichang Feng Abstract A fluorescent hyperbranched copolymer (HTP) and a linear copolymer (PTP) as a reference sample to HTP both containing triphenylamine and divinyl bipyridyl units were synthesized via Heck coupling reaction from 5,5,-Divinyl-2,2,-bipyridyl with tris(4-bromophenyl)amine and with 4,4,-dibromotriphenylamie, respectively. The chemical structure of HTP was confirmed by FTIR, 1H NMR, and 13C NMR. The polymer HTP had a number-average molecular weight of 1895 and a weight-average molecular weight of 2315, and good solubility in conventional organic solvents, such as THF, DMF, and chloroform, and exhibited good thermal stability. The UV,vis absorption and photoluminescence (PL) spectra exhibited absorption maximum at 428 nm and emissive maximum at 531 nm for the HTP solution. The spectroscopic results of HTP and PTP indicated that hyperbranched conjugated structure increases the effective conjugation length, as compared with corresponding linear conjugated structure. The fluorescence of the polymer in solution can be quenched by various transition metal ions. The effect of backbone structure of the conjugated polymer-based chemosensors on the sensitivity and selectivity in metal ions sensing have been investigated, and the quenching effect of HTP is more sensitive toward transition metal than linear copolymer PTP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 222,230, 2009 [source] In vitro and in vivo identification of ,pseudocatalase' activity in Dead Sea water using Fourier transform Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2002Karin U. Schallreuter Balneotherapy with Dead Sea water has been reported as a successful treatment modality for psoriasis, atopic eczema and vitiligo, but the precise mode of action has escaped definition so far. The saturating salt concentration (346 g/litre) together with the unique UV spectrum have been suggested to trigger the release of pro-inflammatory and chemotactic mediators. The results of our study show for the first time a high content of transition metal ions (manganese, iron and copper) in Dead Sea water. Using in vitro Fourier transform (FT) Raman spectroscopy, we were able to identify ,pseudocatalase' activity by observing the decomposition of hydrogen peroxide (H2O2) over time by Dead Sea water. Since patients with vitiligo accumulate millimolar levels of H2O2 in their skin, we followed the degradation of H2O2in vivo again utilizing the same technique. The results of this in vitro and in vivo study show for the first time a ,pseudocatalase' activity of Dead Sea water and provide evidence that the antioxidant properties of Dead Sea water bathing could play an important role in this unique treatment modality. Furthermore, the use of non-invasive in vivo FT-Raman spectroscopy introduces an excellent biomedical application in investigative dermatology. Copyright © 2002 John Wiley & Sons, Ltd. [source] Determination of dissociation energy for ligand exchange reaction from EXAFSJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001T. Miyanaga EXAFS (extended X-ray absorption fine structure) experiments were performed at several different temperatures for a series of 3d transition metal ions (Cr3+, Fe3+, Fe2+, Ni2+, Co2+, Zn2+) in aqueous solutions. Anharmonic EXAFS analyses, which include up to third order cumulant, were carried out to study on the metal-oxygen bonding potential. According to the model in which the dissociation process is dominant for the ligand-water exchange reaction, the dissociation energy has been first evaluated from EXAFS in solution phase. [source] Anisotropic and antisymmetric double exchange in mixed-valence clustersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004Moisey I. Belinsky Abstract In the mixed-valence dn,dn+1 clusters of transition metal ions, taking the spin,orbit coupling into account in the Anderson,Hasegawa double exchange model results in anisotropic double exchange and antisymmetric double exchange. The anisotropic double exchange results in the zero-field splittings of the double exchange levels. These zero-field splittings are described by the the effective ZFS Hamiltonian, which is active between the states of different localization of the extra electron. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Coloured inorganic-organic films on glassPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007K. Cholewa-Kowalska Abstract Two kinds of inorganic-organic hybrid materials (A and B class) were obtained in the form of thin films on glass. As starting materials were used: PhTES + TEOS (A class); PhTES + GPTMS + TBA (B class). Hybrid materials were coloured using ORASOL type dyes. The coloured coatings were put on glass by dip-coating technique. The structure of hybrid matrix was examined by spectroscopic methods: FTIR, 29Si MAS NMR, 27Al MAS NMR. On this base structural units of hybrid were identified. UV/VIS spectra of thin films were measured directly after obtainment as well as after thermal and chemical treatment of samples. It has been found that UV/VIS spectra originate from electron transitions between ligands and transition metal ions. The coloured centres in hybrid matrix show good thermal and chemical resistance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and magnetic properties of novel polymeric complexes containing bithiazole ringsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2007Weihong Lin Abstract A novel linear polymer (PFABT) containing bithiazole rings was synthesized by polycondensation of 2,2,-diamino-4,4,-bithiazole (DABT) and formaldehyde. The complexes of PFABT with two transition metal ions (Fe2+, Cu2+) were prepared for the first time. The polymer was determined through FT-IR, 1H-NMR and elemental analysis (EA), and the complexes were characterized by FT-IR. The magnetic behaviors of these complexes were measured as a function of magnetic field strength (0,50,kOe) at 4,K and as a function of temperature (4,300,K) under an applied magnetic field of 30,kOe. The results show that PFABT-Cu2+ is a ferromagnet while PFABT-Fe2+ is an anti-ferromagnet. Copyright © 2007 John Wiley & Sons, Ltd. [source] A metal-chelate affinity reverse micellar system for protein extractionBIOTECHNOLOGY PROGRESS, Issue 1 2010Xiao-Yan Dong Abstract A new nonionic reverse micellar system is developed by blending two nonionic surfactants, Triton X-45 and Span 80. At total surfactant concentrations lower than 60 mmol/L and molar fractions of Triton X-45 less than 0.6, thermodynamically stable reverse micelles of water content (W0) up to 30 are formed. Di(2-ethylhexyl) phosphoric acid (HDEHP; 1,2 mmol/L) is introduced into the system for chelating transition metal ions that have binding affinity for histidine-rich proteins. HDEHP exists in a dimeric form in organic solvents and a dimer associated with one transition metal ion, including copper, zinc, and nickel. The copper-chelate reverse micelles (Cu-RM) are characterized for their W0, hydrodynamic radius (Rh), and aggregation number (Nag). Similar with reverse micelles of bis-2-ethylhexyl sodium sulfosuccinate (AOT), Rh of the Cu-RM is also linearly related to W0. However, Nag is determined to be 30,90 at W0 of 5,30, only quarter to half of the AOT reverse micelles. Then, selective metal-chelate extraction of histidine-rich protein (myoglobin) by the Cu-RM is successfully performed with pure and mixed protein systems (myoglobin and lysozyme). The solubilized protein can be recovered by stripping with imidazole or ethylinediaminetetraacetic acid (EDTA) solution. Because various transition metal ions can be chelated to the reverse micelles, it is convinced that the system would be useful for application in protein purification as well as simultaneous isolation and refolding of recombinant histidine-tagged proteins expressed as inclusion bodies. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Can Electrophilicity Act as a Measure of the Redox Potential of First-Row Transition Metal Ions?CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2007Jan Moens Abstract Previous contributions concerning the computational approach to redox chemistry have made use of thermodynamic cycles and Car,Parrinello molecular dynamics simulations to obtain accurate redox potential values, whereas this article adopts a conceptual density functional theory (DFT) approach. Conceptual DFT descriptors have found widespread use in the study of thermodynamic and kinetic aspects of a variety of organic and inorganic reactions. However, redox reactions have not received much attention until now. In this contribution, we prove the usefulness of global and local electrophilicity descriptors for the prediction of the redox characteristics of first row transition metal ions (from Sc3+|Sc2+ to Cu3+|Cu2+) and introduce a scaled definition of the electrophilicity based on the number of electrons an electrophile ideally accepts. This scaled electrophilicity concept acts as a good quantitative estimate of the redox potential. We also identify the first solvation sphere together with the metal ion as the primary active region during the electron uptake process, whereas the second solvation sphere functions as a non-reactive continuum region. [source] The Oxidative Damage of Plasmid DNA by Ascorbic Acid Derivatives in vitro: The First Research on the Relationship between the Structure of Ascorbic Acid and the Oxidative Damage of Plasmid DNACHEMISTRY & BIODIVERSITY, Issue 9 2006Pei-Yan Liu Abstract To study the structure,function relationship of the oxidative-damage effect of ascorbic acid, we have focused on the interaction between plasmid DNA pUC19 and a series of ascorbic acid derivatives modified on different OH groups in the presence of transition metal ions. Some ascorbic acid derivatives can selectively cleave plasmid DNA from Form I to Form II in the presence of low concentration of Cu2+ just like ascorbic acid itself, while other derivatives oxidatively damage plasmid DNA slightly. We found that those derivatives with unattached 2-OH and 3-OH groups retain the ability to cleave the plasmid DNA. The derivatives that have been methylated on 2-OH or 3-OH can only cleave plasmid DNA softly, and those derivatives that have been protected on both 2-OH and 3-OH can hardly exert an oxidative damage on plasmid DNA under the same condition. Form these results, we can draw the conclusion that 2-OH and 3-OH groups of the ascorbic acid molecule contribute most to this biological activity. [source] | ||||||||||||||||||||||