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Terms modified by Mol% Selected AbstractsLaser-induced crystal growth of nonlinear optical Ba3Ti3O6(BO3)2 on glass surfaceCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2008T. Oikawa Abstract Nonlinear optical Ba3Ti3O6(BO3)2 crystals were patterned on the surface of CuO (1 mol%)-doped 40BaO-40TiO2 -20B2O3 glass by irradiations of continuous-wave Nd:YAG (wavelength: ,=1064 nm) and Yb:YVO4 (,=1080 nm) lasers. Laser energies absorbed by Cu2+ ions were transferred to the lattice system through a nonradiative relaxation process, consequently heating the glass and inducing local crystallizations. For the lines patterned by Yb:YVO4 laser irradiations with a power of 1 W and a scanning speed of 20 ,m/s, a c -axis orientation of Ba3Ti3O6(BO3)2 crystals along the laser scanning direction is proposed from measurements of X-ray diffraction analyses, polarized optical photographs, polarized micro-Raman scattering spectra, and azimuthal dependence of second harmonic generations. The laser-induced crystallization technique is found to be applied successfully for the spatially selective patterning of nonlinear optical Ba3Ti3O6(BO3)2 crystals in glass. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Increased optical damage resistance of Zr:LiNbO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2007Liang Sun Abstract Zr: LiNbO3 crystals has been grown. The crystal composition and phase are analyzed by X-ray diffration. The optical damage resistance ability of Zr: LiNbO3 crystals is studied by the Sénarmont compensation method and the transmitted beam pattern distortion method. The saturated value of the birefringence change of 6 mol% Zr: LiNbO3 crystal is 1.01×10 -4, which is seven times smaller than that of congruent pure LiNbO3 crystal. The results of UV-Visible and IR absorption spectra of Zr: LiNbO3 crystals powerfully confirm that the optical damage resistance threshold concentration of the Zr4+ ions doped in LiNbO3 crystals is about 6 mol% in the melt. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of Mg/Er co-doping on the principal laser parameters of LiNbO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2007Liang Sun Abstract Mg: Er: LiNbO3 crystals were grown by the Czochralski technique with various concentrations of MgO = 2 mol%, 4 mol%, 6 mol% and the fixed concentration of Er2O3= 1 mol% in the melt, and the 8 mol%Mg: 1 mol%Er: LiNbO3 crystal was fabricated by the Czochralski technique with special technology process. The crystals were treated by polarization, reduction and oxidation. The segregation coefficients of Mg2+ and Er3+ in Mg: Er: LiNbO3 crystals were measured by X-ray fluorescence spectrograph, as well as the crystal's defect structure and optical properties were analyzed by the UV-Vis, IR and fluorescent spectroscopy. The pump wavelength and the surge wavelength were determined. Using m-line method tested optical damage resistance of those crystals, the results show that photodamage threshold of Mg: Er: LiNbO3 crystals are higher than that of Er: LiNbO3 crystal, and the oxidation treat could enhance the photodamage resistant ability of crystals while the reduction treat could depress the ability. The optical damage resistance of 8 mol%Mg: 1 mol%Er: LiNbO3 crystal was the strongest among the samples, which was two orders magnitude higher than that of 1 mol%Er: LiNbO3 crystal. The dependence of the optical properties on defect structure of Mg: Er: LiNbO3 crystals was discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Inhomogeneity of composition in near-stoichiometric LiNbO3 single crystal grown from Li rich meltCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2006L. Gao Abstract A near-stoichiometric LiNbO3 single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li2O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO3 crystal. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Drug,liposome distribution phenomena studied by capillary electrophoresis-frontal analysisELECTROPHORESIS, Issue 16 2008Jesper Řstergaard Professor Abstract The potential of using CE frontal analysis (CE-FA) for the study of low-molecular-weight drug,liposome interactions was assessed. The interaction of bupivacaine, brompheniramine, chlorpromazine, imipramine, and ropivacaine with net negatively charged 80/20,mol% 1-oleoyl-2-palmitoyl- sn -glycero-3-phosphocholine/egg yolk phosphatidic acid liposome suspensions in HEPES buffer at pH,7.4 was investigated. The fraction of free drug as a function of lipid concentration was measured and apparent liposome , buffer distribution coefficients were determined for the basic drug substances. The distribution coefficients increased in the order ropivacaine, bupivacaine, brompheniramine, imipramine, and chlorpromazine. The developed CE method was relatively fast allowing estimates of drug,liposome affinity to be obtained within 15,min. CE-FA may have the potential to become a valuable tool for the characterization of drug,liposome interactions in relation to estimation of drug lipophilicity and for the evaluation of drug distribution in liposomal drug delivery systems. [source] Cholesterol-rich membrane coatings for interaction studies in capillary electrophoresis: Application to red blood cell lipid extractsELECTROPHORESIS, Issue 20 2006Maria V. Lindén Abstract The purpose was to develop a stable biological membrane coating for CE useful for membrane interaction studies. The effect of cholesterol (chol) on the stability of dipalmitoylphosphatidylcholine (DPPC) and sphingomyelin (SM) coatings was studied. In addition, a fused-silica capillary for CE was coated with human red blood cell (RBC) ghost lipids. Liposomes prepared of DPPC/SM with and without chol or RBC ghost lipids were flushed through the capillary and the stability of the coating was measured electrophoretically. Similar mixtures of DPPC/SM with and without chol were further studied by differential scanning calorimetry. The presence of phosphatidylcholine as a basic component in the coating solution of DPPC/SM/chol was found to be essential to achieve a good and stable coating. The results also confirmed the stability of coatings obtained with solutions of DPPC with 0,30,mol% of chol and SM in different ratios, which more closely resemble natural membranes. Finally, the electrophoretic measurements revealed that a stable coating is formed when capillaries are coated with liposomes of RBC ghost lipids. [source] Biodegradation of poly(tetramethylene succinate-cotetramethylene abdicate) and poly(tetramethylene succinate) through water-soluble productsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2001Eiichi Kitakuni Abstract Poly(tetramethylene succinate-co-tetramethylene adipate) (PBSA) and poly(tetramethylenesuccinate) (PBS) were hydrolyzed experimentally into water-soluble oligomers and monomers by Chromobacterium extracellular lipase. The oligomers were identified by high-performance liquid chromatography,mass spectrometry and 1H-nuclear magnetic resonance, which indicated that a total of 28 oligomer species were liberated from PBSA, and that 13 of them were identical to the hydrolysates from PBS. Moreover, 20 of the species were polyester-based compounds of monomer units, and the other 8 species were small amounts of diurethane compounds. Bis(hydroxybutyl) succinate (BSB) and bis(hydroxybutyl) hexamethylene dicarbamate (BHB) were the typical oligomers and were chemically synthesized. Biodegradability of BSB and BHB was examined for 28 d in the activated sludge, and analysis of the results of this study indicated that the final conversion rate of constituent carbon to carbon dioxide was estimated at 80 mol% for BSB and 10 mol% for BHB. The remaining amount of carbon in the undegraded BHB was 20 mol%. In the presence of BSB, the biodegradability of BHB was increased by about 1.5 times. The suggestion was made that BSB induced a growth of microorganisms and helped BHB degradation. This is consistent with the observation that the biodegradation of BHB in native soil for 60 d reached > 60%. [source] Postprandial lipemic response to alpha-linolenic acid rich oil, butter, and olive oilEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 9 2010Julia Svensson Abstract Postprandial lipemia varies with composition of dietary fat due to partitioning of fatty acids between ,-oxidation, incorporation into TAG, and tissue lipids. Effects of alpha-linolenic acid (ALA) are poorly characterized. Lipase-catalyzed transesterification was used to produce a novel ALA-oil (35% ALA) from rapeseed and linseed oil. We hypothesized a lower postprandial lipemic response with ALA-oil than with olive oil and butter due to higher ,-oxidation of ALA. A randomized crossover study with 26 healthy men compared the effects on plasma lipids 7,h after a breakfast containing 35,g ALA-rich oil, butter fat, or olive oil. The incremental area under curve for plasma TAG was lower with butter than with olive oil (34%, p<0.05) and ALA-oil (25%, ns). After ALA-oil percentage ALA increased, in TAG to a constant level of 7,mol% and in NEFA to 6% after 7,h. Since total NEFA increased with time the amount of exogenous ALA in NEFA also increased. Butter resulted in lower postprandial lipemia than the oils, the difference exceeding what is expected from the presence of short and medium chain fatty acids in butter. There was a considerable recirculation of ALA into the NEFA pool available for oxidation. Practical application: Enzymatic transesterification was used to produce a dietary oil rich in ALA. By randomizing the partitioning of ALA more evenly between the TAG molecules the risk of oxidation could be reduced. Analyses showed that the ALA-oil was stable during storage for at least 3 months. Enzymatic transesterification could be used as an advantageous method to design an ALA rich dietary oil with new properties regarding fatty acid composition, susceptibility to oxidation, and effects on blood lipids. [source] Sulfatide with short fatty acid dominates in astrocytes and neuronsFEBS JOURNAL, Issue 8 2006Giorgis Isaac Glycosphingolipids are located in cell membranes and the brain is especially enriched. We speculated that the subcellular location of glycosphingolipids depends on their fatty acid chain length because their sugar residues are constant, whereas fatty acid chain length can vary within the same molecule. To test this hypothesis we analysed the glycosphingolipid sulfatide, which is highly abundant in myelin and has mostly long fatty acids. We used a negative ion electrospray tandem mass spectrometry precursor ion scan to analyse the molecular species of sulfatide in cultured astrocytes and a mouse model of the human disease metachromatic leukodystrophy. In these arylsulfatase A (ASA)-deficient mice sulfatide accumulates intracellularly in neurons and astrocytes. Immunocytochemistry was also performed on cultured astrocytes and analysed using confocal laser scanning microscopy. Analyses of the molecular species showed that cultured astrocytes contained sulfatide with a predominance of stearic acid (C18), which was located in large intracellular vesicles throughout the cell body and along the processes. The same was seen in ASA-deficient mice, which accumulated a higher proportion (15 mol% compared with 8 mol% in control mice) of sulfatide with stearic acid. We conclude that the major fatty acid composition of sulfatide differs between white and grey matter, with neurons and astrocytes containing mostly short-chain fatty acids with an emphasis on stearic acid. Based on our results, we speculate that the fatty acid chain length of sulfatide might determine its intracellular (short chain) or extracellular (long chain) location and thereby its functions. [source] Mucilaginibacter dorajii sp. nov., isolated from the rhizosphere of Platycodon grandiflorumFEMS MICROBIOLOGY LETTERS, Issue 2 2010Byung-Chun Kim Abstract A Gram-negative, nonmotile and rod-shaped bacterial strain was isolated from the rhizosphere of Platycodon grandiflorum in a study of bacterial diversity, and its taxonomic position was investigated by a genotypic and phenotypic analysis. This isolate, designated as DR-f4, grew at 4,30 °C (optimally at 20,25 °C) and in the presence of 0,1% (w/v) NaCl. It contained MK-7 as the predominant menaquinone. The isolate had activities of catalase, oxidase and ,-galactosidase and hydrolyzed aesculin, casein, carboxymethyl-cellulose, starch and l -tyrosine. The major cellular fatty acids were summed feature 3 (C16:1,7c and/or iso-C15:0 2OH) and iso-C15:0. The DNA G+C content was 42.6 mol%. This isolate belonged to the genus Mucilaginibacter based on phylogenetic analysis using 16S rRNA gene sequences. The nearest phylogenetic neighbors of strain DR-f4T were Mucilaginibacter lappiensis ANJL12T and Mucilaginibacter rigui WPCB133T, with 16S rRNA gene sequence similarity levels of 96.9% and 96.4%, respectively. The genotypic and phenotypic evidence suggests that strain DR-f4T should be classified as a novel species, for which the name Mucilaginibacter dorajii sp. nov. is proposed. The type strain for the novel species is DR-f4T (=KACC 14556T=JCM 16601T). [source] Isolation and characterization of a novel Bacillus sp., strain YAS1, capable of transforming tyrosol under hypersaline conditionsFEMS MICROBIOLOGY LETTERS, Issue 1 2005Slim Abdelkafi Abstract A moderately halotolerant, Gram-positive, aerobic, motile, spore-forming bacterium, designated as strain YAS1, was isolated from an olive-brine fermentation rich in aromatic compounds, after enrichment on tyrosol. Strain YAS1 grew between 25 and 45 °C and optimally at 37 °C. It grew in the presence of 0,15% (v/w) NaCl, with an optimum of 3,6% (v/w) NaCl. The DNA G + C content was found to be 49.9 mol%. Phylogenetic analysis of the 16S rRNA gene revealed that this isolate was a member of the genus Bacillus. The newly isolated strain YAS1 represents the first moderately halotolerant bacterium transforming tyrosol to p -hydroxyphenylacetic acid (PHPA) in the presence of yeast extract. [source] Fabrication and Electrochemical Properties of Epitaxial Samarium-Doped Ceria Films on SrTiO3 -Buffered MgO SubstratesADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Simone Sanna Abstract Thin films of samarium-oxide-doped (20,mol%) ceria (SDC) are grown by pulsed-laser deposition (PLD) on (001) MgO single-crystal substrates. SrTiO3 (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite-structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400,775,°C) in a wide range of oxygen partial pressure (pO2) values (10,25,1,atm) in order to separate ionic and electronic conductivity contributions. At 700,°C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7,×,10,2,S cm,1, down to pO2 values of about 10,15,atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation-reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure. [source] Synthesis of Luminescent ZrO2:Eu3+ Nanoparticles and Their Holographic Sub-Micrometer Patterning in Polymer CompositesADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Tsedev Ninjbadgar Abstract Here, the facile synthesis of fluorescent ZrO2:Eu3+ nanoparticles with luminescence quantum yield of up to 8.7% that can be easily dispersed in organic solvents and utilized for the preparation of organic/inorganic volume holographic gratings is presented. The nanoparticles are prepared through a one-step solvothermal process resulting in spherical particles with a mean size of 4,nm that were highly crystalline directly after the synthesis, without any need for calcination treatment. Detailed luminescence studies of the nanoparticles as a function of Eu3+ content demonstrate that the dopant concentration and its site symmetry play an important role in the emissive properties and lifetime of the luminescent centers. It is shown that the luminescence quantum yield of the colloidal ZrO2:Eu3+ nanoparticles increases with dopant concentration up to a critical concentration of 11 mol% while the luminescence lifetime is shortened from 1.8 to 1.4 ms. Holographic photopolymerization of suitable monomer mixtures containing the luminescent nanoparticles demonstrated the ability to inscribe volume Bragg gratings (refractive index contrast n1 up to 0.011) with light-emissive properties, evidencing the high suitability of this approach for the fabrication of tailored nanomaterials for elaborate and demanding applications. [source] The preparation of ZnGa2O4 doped with Mn-Mg and Tm for green and blue phosphorsIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 1 2006Binod Kumar Singh Non-member Abstract Phosphor powders of zinc gallate (ZnGa2O4) with Mg and Mn for green and Tm-Mg for blue luminescence were prepared by solid state reaction method for their improved luminescent properties. Green-luminescence emitting ZnMnGa2O4 reached maximum intensity at Mn = 0.005 mol% and further improvement was achieved by the addition of Mg2+. Tm-Mg based zinc gallate phosphor exhibited a strong blue emission, centered at ,420 nm with the maximum intensity achieved for 0.003 mol% of Mg and 0.015 mol% of Tm. This study established the possibilities of controlling the luminescent characteristics of zinc gallate by adding various elements. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Calamitic Liquid-Crystalline Elastomers Swollen in Bent-Core Liquid-Crystal SolventsADVANCED MATERIALS, Issue 16 2009Martin Chambers The swelling of calamitic liquid crystal elastomers (LCEs) with bent-core mesogens is investigated in the isotropic phase of both materials. The swelling magnitude and dynamics are determined and fitted with a dual exponential. The host LCEs imbibe bent-core molecules up to 30, 40 mol%. The swollen elastomers exhibit nematic phases, with some possessing a lower temperature smectic phase. [source] Effects of Rare-Earth Dopants on the Ferroelectric and Pyroelectric Properties of Strontium Barium Niobate CeramicsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2009Yingbang Yao Effects of various rare-earth (RE) dopants (Y3+, La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tm3+, Dy3+, Er3+, and Yb3+) on the dielectric, ferroelectric, and pyroelectric properties of Sr0.5Ba0.5Nb2O6 (SBN50) ceramics were investigated. In the present studies, the doping concentrations of all the RE dopants were fixed at 1 mol%. Their potential usefulness in pyroelectric applications was discussed based on their measured pyroelectric detectivity figure of merit (FOM). On the basis of our studies, for RE dopants with atomic numbers smaller than Nd, their dielectric constants were greatly increased, while for RE dopants with atomic numbers larger than Sm, their dielectric constants as well as dielectric losses became smaller. Among various dopants, Eu-doped SBN showed the most improved ferroelectric properties. Its remnant polarization (Pr) was increased to 4.86 ,C/cm2 as compared with 3.23 ,C/cm2 obtained in undoped SBN50. On the other hand, Gd-doped SBN exhibited the largest pyroelectric coefficient of 168 ,C/m2 K, which was over three times of that of the undoped sample (49 ,C/m2 K). The work shows that Gd-doped SBN exhibits the greatest potential for pyro-applications because it bears the largest FOM of 0.45 × 10,5 Pa,0.5 [Correction: After online publication on 11/05/2008, an error was found in this article. The original value, 1.35×10,5 Pa,0.5, was incorrect. The data has been replaced with the correct value.]. [source] Influence of Wet Mechanical Mixing on Microstructure and Vickers Hardness of Nanocrystalline Ceramic,Metal CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Tatsuo Kumagai Nanocrystalline (nc) ceramic,metal composite bulk samples have been fabricated by consolidation of mixture of attrition-milled (AM) amorphous base ceramic ((ZrO2,3 mol% Y2O3),20 mol% Al2O3) and AM amorphous base metallic (Ti,48 mol% Al) powders using a pulse-current pressure sintering system. Microstructural observations revealed that the ceramic and metallic colonies appear blocky in morphology in the composite bulk samples, and both the ceramic and the metallic colonies consist of a large number of equiaxed fine grains with the sizes of 78,82 and 81,86 nm, respectively. Mechanical mixing treatments by wet ball milling in ethanol before consolidation process are effective for refinement of the ceramic and metallic colonies. In all the obtained composite bulk samples, the ceramic colonies consist of the dominant phase of tetragonal (t) ZrO2 solid solution (ss) together with the minor phases of monoclinic (m) ZrO2ss and ,-Al2O3. On the other hand, the dominant phase in the metallic colonies changes from Ti3Al (,2) to Tiss (,) with an increase in the t -ZrO2ss volume fraction by abrasion of 3 mol% yttria-stabilized tetragonal polycrystalline zirconia balls during wet mechanical mixing treatments. Such a phase transformation from ,2 to , is considered to be due to the decrease in the aluminum content in the metallic colonies by combination of aluminum with oxygen (i.e., the formation of ,-Al2O3), which is probably taken from ethanol (C2H5OH) into the powders during wet mechanical mixing treatments. The obtained nc composite bulk samples show good Vickers hardness values, which are considerably higher than those estimated from the rule of mixture. [source] The gas-phase oxidation of n -hexadecaneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2001R. Fournet Since n -hexadecane or cetane is a reference fuel for the estimation of cetane numbers in diesel engines, a detailed chemical model of its gas-phase oxidation and combustion will help to enhance diesel performance and reduce the emission of pollutants at their outlet. However, until recently the gas-phase reactions of n -hexadecane had not been experimentally studied, prohibiting a validation of oxidation models which could be written. This paper presents a modeling study of the oxidation of n -hexadecane based on experiments performed in a jet-stirred reactor, at temperatures ranging from 1000 to 1250 K, 1-atm pressure, a constant mean residence time of 0.07 s, and high degree of nitrogen dilution (0.03 mol% of fuel) for equivalence ratios equal to 0.5, 1, and 1.5. A detailed kinetic mechanism was automatically generated by using the computer package (EXGAS) developed in Nancy. The long linear chain of this alkane necessitates the use of a detailed secondary mechanism for the consumption of the alkenes formed as a result of primary parent fuel decomposition. This high-temperature mechanism includes 1787 reactions and 265 species, featuring satisfactory agreement for both the consumption of reactants and the formation of products. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 574,586, 2001 [source] Efficient and Highly Chemoselective Direct Reductive Amination of Aldehydes using the System Silane/Oxorhenium ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Sara C. A. Sousa Abstract This work reports a novel method for direct reductive amination of aldehydes with silanes catalyzed by several high-valent oxorhenium(V) and oxorhenium(VII) complexes. The catalytic system PhSiH3/ReIO2(PPh3)2 (2.5,mol%) was very efficient for the synthesis of secondary amines and highly chemoselective, tolerating a wide range of functional groups such as NO2, CF3, SO2R, CO2R, F, Cl, Br, I, CN, OH, OCH3, SCH3, NCOR, and double bonds. This novel method was also employed in the synthesis of tertiary amines with moderate yields. [source] Cyclopalladated Ferrocenylimine as Efficient Catalyst for the Syntheses of Arylboronate EstersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Lianhui Wang Abstract The cyclopalladated ferrocenylimine I and its phosphine adducts IIa,f were prepared and evaluated in the borylation of aryl halides. The tricyclohexylphosphine adduct IIb exhibited highly catalytic activity for the coupling of aryl and heteroaryl bromides containing various functional groups with low catalyst loading (2,mol%). Aryl and heteroaryl chlorides were smoothly converted into the corresponding boronates in the presence of the monophosphinobiaryl ligand (XPhos) adduct IIf. It was proposed that palladacycle was only a reservoir of the catalytically active species from the investigation on the reaction mechanism. [source] Enantioselective Copper-Catalysed Allylic Alkylation of Cinnamyl Chlorides by Grignard Reagents using Chiral Phosphine-Phosphite LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Wibke Lölsberg Abstract The copper(I)-catalysed SN2,-type allylic substitution of E -3-aryl-allyl chlorides (cinnamyl chlorides) using Grignard reagents represents a powerful method for the synthesis of compounds carrying a benzylic stereocentre. By screening a small library of modular chiral phosphine-phosphite ligands a new copper(I)-based catalyst system was identified which allows the performance of such reactions with exceptional high degrees of regio- and enantioselectivity. Best results were obtained using TADDOL-derived ligands (3,mol%), copper(I) bromide,dimethyl sulfide (CuBr,SMe2) (2.5,mol%) and methyl tert -butyl ether (MTBE) as a solvent. Various (1-alkyl-allyl)benzene derivatives were prepared with up to 99% ee (GC) in isolated yields of up to 99%. In most cases the product contained less than 3% of the linear regioisomer (except for ortho -substituted substrates). Both electron-rich and electron-deficient cinnamyl chlorides were successfully employed. The absolute configuration of the products was assigned by comparison of experimental and calculated CD spectra. The substrates were prepared from the corresponding alcohols by reaction with thionyl chloride. Initially formed mixtures of regioisomeric allylic chlorides were homogenised by treatment with CuBr,SMe2 (2.5,mol%) in the presence of triphenyl phosphine (PPh3) (3,mol%) in MTBE at low temperature to give the pure linear isomers. In reactions with methylmagnesium bromide (MeMgBr) an ortho -diphenylphosphanyl-arylphosphite ligand with an additional phenyl substituent in ortho, -position at the aryl backbone proved to be superior. In contrast, best results were obtained in the case of higher alkyl Grignard reagents (such as ethyl-, n -butyl-, isopropyl-, and 3-butenylmagnesium bromides) with a related ligand carrying an isopropyl substituent in ortho, -position. The method was tested on a multi-mmol scale and is suited for application in natural product synthesis. [source] Iron and Copper Salts in the Synthesis of Benzo[b]furansADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Julien Bonnamour Abstract Intramolecular CO bond forming reactions of aryl 2-bromobenzyl ketones lead to benzo[b]furans. The cyclizations can be catalyzed by 10,mol% of iron trichloride (of 98% or of 99.995% purity) or sub-mol% quantities of copper(II) chloride (of 99.995% purity). [source] Highly Enantioselective Michael Addition of Cyclic 1,3-Dicarbonyl Compounds to ,,,-Unsaturated ,-Keto EstersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Xing-Kuan Chen Abstract A highly enantioselective Michael addition of cyclic 1,3-dicarbonyl compounds to ,,,-unsaturated ,-keto esters catalyzed by amino acid-derived thiourea-tertiary-amine catalysts is presented. Using 5,mol% of a novel tyrosine-derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time. [source] Ring Expansion versus Cyclization in 4-Oxoazetidine-2- carbaldehydes Catalyzed by Molecular Iodine: Experimental and Theoretical Study in ConcertADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Benito Alcaide Abstract Molecular iodine (10,mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert -butyldimethylsilyl cyanide, or allylic and propargylic trimethylsilanes to afford protected 5-functionalized-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a C3C4 bond cleavage of the ,-lactam nucleus. Interestingly, in contrast to the iodine-catalyzed reactions of 3-alkoxy-,-lactam aldehydes which lead to the corresponding ,-lactam derivatives (rearrangement adducts), the reactions of 3-aryloxy-,-lactam aldehydes under similar conditions gave ,-lactam-fused chromanes (cyclization adducts) as the sole products, through exclusive electrophilic aromatic substitution involving the C3 aromatic ring and the carbaldehyde. In order to support the mechanistic proposals, theoretical studies have been performed. [source] Extremely Efficient Cross-Coupling of Benzylic Halides with Aryltitanium Tris(isopropoxide) Catalyzed by Low Loadings of a Simple Palladium(II) Acetate/Tris(p -tolyl)phosphine SystemADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Chi-Ren Chen Abstract Highly efficient coupling reactions of benzylic bromides or chlorides with aryltitanium tris(isopropoxide) [ArTi(O- i- Pr)3] catalyzed by a simple palladium(II) acetate/tris(p -tolyl)phosphine [Pd(OAc)2/ P(p -tolyl)3] system are reported. The coupling reactions proceed in general at room temperature employing low catalyst loadings of 0.02 to 0.2,mol%, affording coupling products in excellent yields of up to 99%. For benzylic bromides bearing strong electron-withdrawing cyano (CN) or trifluoromethyl (CF3) substituents, the reactions require a higher catalyst loading of 1,mol%, or the reactions are carried out at 60,°C. The catalytic system also tolerates (1-bromoethyl)benzene bearing ,-hydrogen atoms while using a catalyst loading of 1,mol% to afford the coupling product in a 70% yield. [source] Enantioselective Organocatalytic Synthesis of Arylglycines via Friedel,Crafts Alkylation of Arenes with a Glyoxylate ImineADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Dieter Enders Abstract The enantioselective organocatalytic synthesis of arylglycines has been developed employing 1,mol% of an enantiopure N -triflyl phosphoramide Brřnsted acid as organocatalyst. Various differently substituted phenylglycine derivatives can be synthesized in good to excellent yields and enantiomeric excesses based on a Friedel,Crafts alkylation of electron-rich arenes with a glyoxylate imine. A novel protocol for the deprotection of the N - tert -butylsulfonyl (Bus) group has also been developed. [source] Ruthenium-Catalyzed Alkyne Oxidation with Part-Per-Million Catalyst LoadingsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Wei Ren Abstract Using a catalytic system of the (cymene)ruthenium dichloride dimer, [Ru(cymene)Cl2]2, (0.001,mol%) and iodine (10,mol%), a variety of alkynes bearing different functional groups were oxidized with tert -butyl hydroperoxide (TBHP; 70% solution in water) under mild conditions to give 1,2-diketones in good to excellent yields. Two noteworthy features of the method are the extremely high catalyst productivity (TON up to 420,000) and scale-up to 1,mol. Preliminary mechanism investigations showed that iodonium ion and water were involved in the transformation. [source] Metalloporphyrin/Iodine(III)-Cocatalyzed Oxygenation of Aromatic HydrocarbonsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Akira Yoshimura Abstract Hypervalent iodine species have a pronounced catalytic effect on the metalloporphyrin-mediated oxygenations of aromatic hydrocarbons. In particular, the oxidation of anthracene to anthraquinone with Oxone readily occurs at room temperature in aqueous acetonitrile in the presence of 5,20,mol% of iodobenzene and 5,mol% of a water-soluble iron(III)-porphyrin complex. 2- tert -Butylanthracene and phenanthrene also can be oxygenated under similar conditions in the presence of 50,mol% of iodobenzene. The oxidation of styrene in the presence of 20,mol% of iodobenzene leads to a mixture of products of epoxidation and cleavage of the double bond. Partially hydrogenated aromatic hydrocarbons (e.g., 9,10-dihydroanthracene, 1,2,3,4-tetrahydronaphthalene, and 2,3-dihydro-1H -indene) afford under these conditions products of oxidation at the benzylic position in moderate yields. The proposed mechanism for these catalytic oxidations includes two catalytic redox cycles: 1) initial oxidation of iodobenzene with Oxone producing the hydroxy(phenyl)iodonium ion and hydrated iodosylbenzene, and 2) the oxidation of iron(III)-porphyrin to the oxoiron(IV)-porphyrin cation-radical complex by the intermediate iodine(III) species. The oxoiron(IV)-porphyrin cation-radical complex acts as the actual oxygenating agent toward aromatic hydrocarbons. [source] Palladium-Catalyzed Aerobic Oxidation of Naturally Occurring Allylbenzenes as a Route to Valuable Fragrance and Pharmaceutical CompoundsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Luciana Abstract A palladium-catalyzed, aerobic oxidation of naturally occurring allylbenzenes, i.e., eugenol, methyleugenol, safrole, and estragole, in dimethylacetamide/water solutions under mild conditions has been developed, in which palladium(II) chloride is used in the absence of co-catalysts or special stabilizing ligands as the sole and recyclable catalyst. Methyl ketones that are important for the flavour and pharmaceutical industries have been obtained in good to excellent yields with low catalyst loadings (1,2,mol%) and high average turnover frequencies. This simple catalytic method represents an ecologically benign and economically attractive route to industrially valuable compounds starting from renewable substrates easily available from essential oils. [source] A Novel D2 -Symmetrical Chiral Tetraoxazoline Ligand for Highly Enantioselective Hydrosilylation of Aromatic KetonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010Wei Jie Li Abstract A novel D2 -symmetrical chiral tetraoxazoline ligand was synthesized from 1,2,4,5-benzenetetracarboxylic acid and L -valinol via a one-pot reaction, and the asymmetric hydrosilylation of aromatic ketones was carried out in dichloromethane in the presence of 1.0,mol% of a bivalent copper ion catalyst with the tetraoxazoline to give optically active secondary alcohols. The chiral catalyst showed excellent activities and enantioselectivities in the hydrosilylation of aryl ketones with up to 99% ee. [source] | ||||||||||||||||||||||