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Excellent Selectivity (excellent + selectivity)
Selected AbstractsRoom Temperature Highly Enantioselective Nickel-Catalyzed HydrovinylationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Nicolas Lassauque Abstract At room temperature, nickel catalysts based on the new phosphoramidite (11bR)- N -[(S)-1-(naphthalen-1-yl)ethyl]- N -[(S)-1-(naphthalen-2-yl)ethyl]dinaphtho[2,1- d:1,,2,- f][1,3,2]dioxaphosphepin-4-amine provide excellent selectivities for 3-arylbut-1-enes (93,99%) with high enantioselectivities (90,95% ee) and TOFs (up to 8300,h,1) in the hydrovinylation of electron-rich and electron-poor vinylarenes. Within a few minutes, useful chiral building blocks and intermediates can be synthesized using this practical catalytic system. [source] The Influence of the Cathodic Pretreatment on the Electrochemical Detection of Dopamine by Poly(1-aminoanthracene) Modified ElectrodeELECTROANALYSIS, Issue 19 2010Estela de Pieri Troiani Abstract In this study we demonstrated the influence of the cathodic pretreatment of poly(1-aminoanthracene) (PAA) electropolymerized on a platinum electrode for determination of dopamine (DA). The DA electrochemical response was obtained after a cathodic pretreatment of the PAA electrode which consisted of applying a potential of ,0.7,V (vs. Ag/AgCl) for 3,s before each measurement. The pretreatment of the electrode changed the PAA electrocatalytic properties so that the electrode began to present electrochemical response to DA without interference of ascorbic acid (AA). The anodic peak currents determined by differential pulse voltammetry using pretreated PAA showed a linear dependence on the DA concentration from 0.56 to 100,µM with a detection limit of 0.13,µM and a correlation coefficient of 0.9986. The electrode exhibits a relative standard deviation of 1.2,% for ten successive measurements of a 0.5,mM DA solution. The analysis by scanning electron microscopy and atomic force microscopy show a homogeneous and nanostructured film with globular structures with diameter of about 20,nm. The analytical results obtained for DA determination at a pretreated PAA electrode in pharmaceutical formulation sample were in good agreement with those obtained by a comparative procedure at a 95,% confidence level. PAA electrode after the pretreatment showed electrochemical responses to DA with excellent selectivity, sensitivity, and high stability without interference of AA. [source] Amperometric Detection of Catecholamine Neurotransmitters Using Electrocatalytic Substrate Recycling at a Laccase ElectrodeELECTROANALYSIS, Issue 2 2005Yvonne Ferry Abstract An enzyme electrode based on the coimmobilization of an osmium redox polymer and laccase on glassy carbon electrodes has been applied to ultra sensitive amperometric detection of the catecholamine neurotransmitters dopamine, epinephrine and norepinephrine, resulting in nanomolar detection limits, as low as 4,nM for dopamine. The sensitivity of the electrode is due to signal amplification via oxidation of the catecholamine by the immobilized laccase, which is regenerated by concomitant reduction of oxygen to water, coupled to the electrocatalytic re-reduction of the oxidized catecholamine by the osmium redox complex: electrocatalytic substrate recycling. In addition because the sensor can be operated in reductive mode at ,0.2,V (vs. Ag/AgCl), noise and interferences are diminished. Combined with its high sensitivity this enzyme electrode also exhibited excellent selectivity allowing the detection of catecholamines in the presence of ascorbic acid. However, differentiation between the current responses achieved for the three catecholamines is not possible. The effective mode of constant recycling, resulting in amplification of the current response, of the laccase enzyme electrode sensor combined with the inherent advantages of using electrochemical techniques holds great promise for the future of catecholamine detection and monitoring. [source] Analysis of the glucosinolate pattern of Arabidopsis thaliana seeds by capillary zone electrophoresis coupled to electrospray ionization-mass spectrometryELECTROPHORESIS, Issue 7-8 2005Gerhard Bringmann Abstract An easy and rapid method for the analysis of intact, non-desulfated glucosinolates by capillary zone electrophoresis (CZE) coupled to electrospray ionization-time of flight-mass spectrometry (ESI-TOF-MS) is described. Surprisingly, an electrolyte and a sheath liquid based on formic acid provided the best results. In this strongly acidic system, the glucosinolates were separated and detected as anions, resulting in an excellent selectivity. Thus, crude plant extracts could be analyzed without any interference of matrix constituents. The sensitivity together with mass accuracy and true isotopic pattern of the TOF-MS allowed identification of a broad series of glucosinolates in Arabidopsis thaliana seeds. [source] Synthesis, Crystal Structure, and Catalytic Properties of Novel Dioxidomolybdenum(VI) Complexes with Tridentate Schiff Base Ligands in the Biomimetic and Highly Selective Oxygenation of Alkenes and SulfidesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2010Abdolreza Rezaeifard Abstract Four novel dioxidomolybdenum(VI) complexes [MoO2(Lx)(CH3OH)] have been synthesized, using 2[(E)-(2-hydroxy-2-phenylethylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H2Lx) and MoO2(acac)2. A monoclinic space group was determined by X-ray crystallography from single-crystal data of a sample of these new complexes. The epoxidation of alkenes by using tert -butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were efficiently enhanced with excellent selectivity under the catalytic influence these new MoVI complexes. The high efficiency and relative stability of the catalysts have been observed by turnover numbers and UV/Vis investigations. The electron-poor and bulky ligands promoted the effectiveness of the catalysts. [source] Lewis Basic Ionic Liquids-Catalyzed Conversion of Carbon Dioxide to Cyclic CarbonatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Zhen-Zhen Yang Abstract A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained when 1,8-diazabicyclo[5.4.0]undec-7-enium chloride ([HDBU]Cl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent-free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value-added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond-assisted ring-opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed. [source] Facile Assembly of H -Pyrazolo[5,1- a]isoquinolines via Silver Triflate-Catalyzed One-Pot Tandem Reaction of 2-Alkynyl- benzaldehyde, Sulfonohydrazide, and Ketone or AldehydeADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Xingxin Yu Abstract A novel and efficient route for the generation of H -pyrazolo[5,1- a]isoquinolines via silver triflate-catalyzed one-pot tandem reaction of 2-alkynylbenzaldehyde, sulfonohydrazide, and ketone or aldehyde is described. This reaction proceeds with good functional group tolerance under mild conditions with high efficiency and excellent selectivity. [source] TEMPO and Carboxylic Acid Functionalized Imidazolium Salts/Sodium Nitrite: An Efficient, Reusable, Transition Metal-Free Catalytic System for Aerobic Oxidation of AlcoholsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Cheng-Xia Miao Abstract An effective catalytic system comprising a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) functionalized imidazolium salt ([Imim-TEMPO]+,X,), a carboxylic acid substituted imidazolium salt ([Imim-COOH]+,X,), and sodium nitrite (NaNO2) was developed for the aerobic oxidation of aliphatic, allylic, heterocyclic and benzylic alcohols to the respective carbonyl compounds with excellent selectivity up to >99%, even at ambient conditions. Notably, the catalyst system could preferentially oxidize a primary alcohol to the aldehyde rather than a secondary alcohol to the ketone. Moreover, the reaction rate is greatly enhanced when a proper amount of water is present. And a high turnover number (TON 5000) is achieved in the present transition metal-free aerobic catalytic system. Additionally, the functionalized imidazolium salts are successfully reused at least four times. This process thus represents a greener pathway for the aerobic oxidation of alcohols into carbonyl compounds by using the present task-specific ionic liquids in place of the toxic and volatile additive, such as hydrogen bromide, bromine, or hydrogen chloride (HBr, Br2 or HCl), which is commonly required for the transition metal-free aerobic oxidation of alcohols. [source] Iridium-Catalysed Asymmetric Hydrogenation of Enamides in the Presence of 3,3,-Substituted H8-PhosphoramiditesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Giulia Erre Abstract In situ generated iridium complexes containing bulky 3,3,-substituted H8-phosphoramidites as ligands catalyse the asymmetric hydrogenation of non-functionalised enamides in high yield and good to excellent selectivity. [source] Recyclable Selective Palladium-Catalyzed Synthesis of Five-, Six- or Seven-Membered Ring Lactones and Lactams by Cyclocarbonylation in Ionic LiquidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2006Fangguo Ye Abstract The ionic liquids, BMIM PF6 or BMIM NTf2, are used successfully for the palladium-catalyzed cyclocarbonylation of 2-allylphenols and anilines, 2-vinylphenols, and 2-aminostyrenes. The reaction proceeds cleanly and efficiently to afford high yields of lactones or lactams with good or excellent selectivity for one isomer. The ionic liquid containing the palladium catalyst, and ligand, is recyclable in all cases. [source] Mass spectrometry in newborn and metabolic screening: historical perspective and future directionsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2009Donald H. Chace Abstract The growth of mass spectrometry (MS) in clinical chemistry has primarily occurred in two areas: the traditional clinical chemistry areas of toxicology and therapeutic drug monitoring and more recent, human genetics and metabolism, specifically inherited disorders of intermediary metabolism and newborn screening. Capillary gas chromatography and electrospray tandem MS are the two most common applications used to detect metabolic disease in screening, diagnostics and disease monitoring of treated patients. A few drops of blood from several million newborn infants are screened annually throughout the world making this the largest application of MS in medicine. Understanding the technique, how it grew from a few dozen samples per week in the early 1990s to increasing daily volume today will provide important information for new tests that either expand newborn screening or screening in other areas of metabolism and endocrinology. There are numerous challenges to the further expansion of MS in clinical chemistry but also many new opportunities in closely related applications. The model of newborn screening and MS in medicine may be useful in developing other applications that go beyond newborns and inherited metabolic disease. As MS continues to expand in clinical chemistry, it is clear that two features will drive its success. These features are excellent selectivity and multiple analyte or profile analysis; features recognized in the 1950s and remain true today. Copyright © 2008 John Wiley & Sons, Ltd. [source] Selective enrichment of trace copper(II) from biological and natural water samples by SPE using ion-imprinted polymerJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2008Yunhui Zhai Abstract A novel Cu(II)-imprinted polymer sorbent was prepared by an ion-imprinted polymer (IIP) technique using (2Z)- N,N,-bis(2-aminoethylic)but-2-enediamide as the functional monomer and pentaerythritol triacylate as a crosslinker. IR, XPS, and elemental analysis techniques were used to confirm the obtained product. Subsequently, when this polymer was used as sorbent in SPE, it exhibited excellent selectivity for template ion from an aqueous solution. Quantitative extraction of Cu(II) was achieved in the pH range of 4,7. The time needed to extract each sample was less than 30 min by the batch method. The distribution ratio (D) values of IIP for Cu(II) were greatly larger than that for other ions. At optimal pH value, the maximum extraction capacity of IIP and nonimprinted polymer (NIP) was found to be 29.8 and 7.0 mg/g, respectively. The adsorption behavior of Cu(II) on the sorbents could be described by Langmuir adsorption isotherm equation. The feasible flow rate of Cu(II)-containing solution for quantitative extraction onto the column packed with IIP was 1,4 mL/min, whereas for elution it was less than 1 mL/min. The developed method was successfully applied to the separation and enrichment of trace Cu(II) in biological and natural water samples with satisfactory results. [source] Palladium,dppb,borate-catalyzed regioselective synthesis of cinnamate esters by alkoxycarbonylation of phenylacetyleneAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2008Jimoh Tijani Abstract The regioselective alkoxycarbonylation of phenylacetylene into various cinnamate esters was achieved with a catalyst system formed from palladium (II), 1,4-bis(diphenylphosphino) butane (dppb) and salicylborate complex in acetonitrile as a solvent. The influence of various parameters on the overall conversion of phenylacetylene and the selectivity of the reaction were studied systematically by varying the type of palladium complex, acids promoter, CO pressure, temperature and the reaction time. This investigation allowed us to obtain the predominant formation of cinnamate esters with excellent selectivity (90,96%). Copyright © 2008 John Wiley & Sons, Ltd. [source] Efficient palladium,ferrocenylphosphine catalytic systems for allylic amination of monoterpene derivativesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 12 2006Duc Hanh Nguyen Abstract Ferrocenylphosphines added to [Pd(µ-Cl)(,3 -C3H5)]2 dimeric precursor produce efficient catalysts to effect the allylic amination of terpenic allylacetates. Particularly convenient are tetrakis(diphenylphosphino)ferrocene and 1,1,-bis(diphenylphosphino)ferrocene, which allow the amination of allylacetates with good to excellent selectivity, and have turnover numbers as high as 80 000, for instance, for the formation of allylaniline. Herein, we report on reactions that selectively transform geranylacetate, nerylacetate, linalylacetate and perillylacetate into the corresponding allylic amines. These preparative methods give facile access to various products of great potential industrial interest. Copyright © 2006 John Wiley & Sons, Ltd. [source] A Highly Selective FRET-Based Fluorescent Probe for Detection of Cysteine and HomocysteineCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2010Hoi-Yan Shiu Fluorescent probe: A "turn-on" FRET-based fluorescent probe for selective detection of cysteine (Cys) and homocysteine (Hcy) under physiological conditions was synthesised (see figure). The probe features excellent selectivity, fast response times and good linearity towards Cys and Hcy detection. [source] Heterogeneous Versus Homogeneous Palladium Catalysts for Ligandless Mizoroki,Heck Reactions: A Comparison of Batch/Microwave and Continuous-Flow ProcessingCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2009Abstract Mizoroki,Heck couplings of aryl iodides and bromides with butyl acrylate were investigated as model systems to perform transition-metal-catalyzed transformations in continuous-flow mode. As a suitable ligandless catalyst system for the Mizoroki,Heck couplings both heterogeneous and homogeneous Pd catalysts (Pd/C and Pd acetate) were considered. In batch mode, full conversion with excellent selectivity for coupling was achieved applying high-temperature microwave conditions with Pd levels as low as 10,3,mol,%. In continuous-flow mode with Pd/C as a catalyst, significant Pd leaching from the heterogeneous catalyst was observed as these Mizoroki,Heck couplings proceed by a homogeneous mechanism involving soluble Pd colloids/nanoparticles. By applying low levels of Pd acetate as homogeneous Pd precatalyst, successful continuous-flow Mizoroki,Heck transformations were performed in a high-temperature/pressure flow reactor. For both aryl iodides and bromides, high isolated product yields of the cinnamic esters were obtained. Mechanistic issues involving the Pd-catalyzed Mizoroki,Heck reactions are discussed. [source] Pd on Porous Glass: A Versatile and Easily Recyclable Catalyst for Suzuki and Heck ReactionsCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 4 2008Christine Schmöger Abstract The catalytic activity of Pd supported on porous glass was studied for both Suzuki and Heck reactions under aerobic conditions, with particular focus on the Suzuki coupling. The reactions were carried out in water under microwave irradiation. The effects of the catalyst preparation process (calcination time and temperature), as well as the base, substrate, and boron compound used on the coupling reaction were investigated in relation to the reusability of the catalyst. Various bases promote the Suzuki coupling of phenylboronic acid with bromophenol very effectively resulting in quantitative conversion and excellent selectivity for the coupling product. However, most bases lead to deactivation of the catalyst after the first reaction cycle and the catalyst must be reactivated before reuse. Therefore, excellent conversions and selectivities for individual reactions are not sufficient to conclude if the chosen conditions are suitable for a given reaction, but results from recycling studies have to be considered also. [source] Pd/C/PPh3: A Simple and Efficient Catalyst System for Double Carbonylation ReactionsCHINESE JOURNAL OF CHEMISTRY, Issue 4 2009Jianming LIU Abstract The double carbonylation of iodobenzene and diethylamine proceeds smoothly in the presence of Pd/C and carbon monoxide to afford the corresponding , -keto amide in good yields with excellent selectivity. In addition, other aryl iodides and secondary amines also react under similar conditions to form , -keto amides in good yields. [source] | ||||||||||