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High Selectivity (high + selectivity)
Selected AbstractsDevelopment of an Artificial Lipid-Based Membrane Sensor with High Selectivity and Sensitivity to the Bitterness of Drugs and with High Correlation with Sensory ScoreIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 6 2009Yoshikazu Kobayashi Non-member Abstract This paper reports the development of membrane sensors based on an artificial lipid and plasticizers with high selectivity and sensitivity to drug bitterness by using bis(1-butylpentyl) adipate (BBPA), bis(2-ethylhexyl) sebacate (BEHS), phosphoric acid tris(2-ethylhexyl) ester (PTEH), and tributyl o-acetylcitrate (TBAC) as a plasticizer and phosphoric acid di-n-decyl ester (PADE) as an artificial lipid to optimize surface hydrophobicity of the sensors. In addition, a sensor with highly correlated bitterness sensory score was developed by blending BBPA and TBAC to detect the bitterness suppression effect of sucrose, and other bitter-masking materials. Therefore, this sensor can be used to evaluate the bitterness of various drug formulations with high accuracy. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] A Shape-Persistent Organic Molecular Cage with High Selectivity for the Adsorption of CO2 over N2,ANGEWANDTE CHEMIE, Issue 36 2010Yinghua Jin Dr. Ein organischer Käfig für Kohlenstoff: Ein formpersistenter, organischer prismatischer molekularer Käfig (siehe Struktur) wurde in einem Schritt und in hoher Ausbeute aus einfach zugänglichen Ausgangsmaterialien mithilfe dynamischer kovalenter Verknüpfungsreaktionen hergestellt. Dieses Käfigmolekül adsorbiert hoch selektiv CO2 gegenüber N2 und könnte deshalb für den Kohlenstoffeinfang geeignet sein. [source] Oxidative Cross-Coupling Through Double Transmetalation: Surprisingly High Selectivity for Palladium-Catalyzed Cross-Coupling of Alkylzinc and Alkynylstannanes.CHEMINFORM, Issue 15 2007Yingsheng Zhao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Discovery of 3-Arylpropionic Acids as Potent Agonists of Sphingosine-1-phosphate Receptor-1 (S1P1) with High Selectivity Against All Other Known S1P Receptor Subtypes.CHEMINFORM, Issue 42 2006Lin Yan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of Aromatic (E)- or (Z)-,,,-Unsaturated Amides with Total or Very High Selectivity from ,,,-Epoxyamides and Samarium Diiodide.CHEMINFORM, Issue 15 2004Jose M. Concellon Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of (E)-,-Hydroxy-,,,-Unsaturated Amides with High Selectivity from ,,,-Epoxyamides by Using Catalytic Samarium Diiodide or TriiodideCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2004José M. Concellón Dr. Abstract The highly stereoselective synthesis of (E)-,-hydroxy-,,,-unsaturated amides starting from ,,,-epoxyamides, by using catalytic SmI2 or SmI3, was achieved. This transformation can also be carried out by using SmI2 generated in situ from samarium powder and diiodomethane. The starting compounds 1 are easily prepared by the reaction of enolates derived from ,-chloroamides with ketones at ,78,°C. A mechanism to explain this transformation has been proposed. Cyclopropanation of (E)-,-hydroxy-,,,-unsaturated amides has been performed to demonstrate their synthetic applications. Se describe la síntesis con alta estereoselectividad de (E)- , -hidroxiamidas- ,,, -insaturadas a partir de ,,, -epoxiamidas, mediante el empleo de diyoduro o triyoduro de samario catalítico. Esta transformación se puede llevar a cabo con diyoduro de samario generado in situ a partir de samario en polvo y diyodometano. Los productos de partida 1 son fácilmente preparados por tratamiento de , -cloroamidas con cetonas a ,78,°C. Se propone un mecanismo para explicar el proceso. Se ha llevado a cabo la ciclopropanación de (E)- , -hidroxiamidas- ,,, -insaturadas para demostrar sus aplicaciones sintéticas. [source] Studies on the Novel Calix [4] pyrrole and Its High Selectivity for p -NitrophenolCHINESE JOURNAL OF CHEMISTRY, Issue 7 2001Xun-Cheng Su Abstract Synthesis of novel neutral molecule receptor calix [4] pyrrole (2) from pyrrole and tropinone has been described and its ability of binding neutral molecules was tested. Spectroscopic titrations indicate that receptor 2 shows the highest selectivity for p -nitrophenol among m,o,p -nitrophenols due to the coincidence between the host's binding sites and the guest's geometry. [source] Novel Structural Modulation in Ceramic Sensors Via Redox Processing in Gas BuffersINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2006Abdul-Majeed Azad High selectivity, enhanced sensitivity, short response time, and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. As the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, high aspect ratio and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of "oxygen deprivation," with exotic morphological features, has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of potential semiconducting ceramic oxide-based carbon monoxide and hydrogen sensors with enhanced characteristics. [source] Highly selective artificial gel antibodies for detection and quantification of biomarkers in clinical samples.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 22 2008Abstract High selectivity of a biomarker is a basic requirement when it is used for diagnosis, prognosis and treatment of a disease. The artificial gel antibodies, which we synthesise by a molecular imprinting method, have this property not only for proteins, but also for bioparticles, such as viruses and bacteria. However, diagnosis of a disease requires not only that the biomarker can be "fished out" from a body fluid with high selectivity, but also that its concentration in the sample can rapidly be determined and preferably by a simple technique. This paper deals primarily with the development of a spectrophotometric method, which is so simple and fast that it can be used with advantage in a Doctor's Office. The development of this method was not straight-forward. However, by modifications of the performance of these measurements we can now design standard curves in the form of a straight line, when we plot the true (not the recorded "apparent" absorption) against known protein concentrations. In an additional publication (see the following paper in this issue of JSS) we show an application of such a plot: determination of the concentration of albumin in serum and cerebrospinal fluid from patients with neurological disorders to investigate whether albumin is a biomarker for these diseases. [source] Electrospray ionisation with selected reaction monitoring for the determination of Mn-citrate, Fe-citrate, Cu-citrate and Zn-citrateRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2009Volker Nischwitz Citrate complexes of Mn and Fe, and potentially those of Cu and Zn, are considered as important low molecular mass species in human serum and cerebrospinal fluid (CSF). For example, Mn is supposed to enter the brain under excess exposure as Mn-citrate leading to neurotoxic effects. Mn-citrate has been characterised in human CSF using chromatography and electrophoresis online with inductively coupled plasma mass spectrometry, but not yet with molecular mass spectrometry. Therefore, this study explores the potential of electrospray ionisation (ESI) with selected reaction monitoring (SRM) for the detection of metal-citrate complexes, in particular Mn-citrate. The collision-induced dissociation of precursor ions with various metal:citrate stoichiometries was studied for Mn-citrate, Fe-citrate, Cu-citrate and Zn-citrate. High selectivity was achieved for Mn(II)-citrate even in respect to Fe(III)-citrate which forms isobaric precursor ions. The limit of detection for Mn-citrate was estimated to be around 250,µg,L,1 (referring to the total Mn content in the standard) using flow injection. The sensitivity was sufficient for the determination of Mn-citrate in standard solutions and in an extract of an Mn-citrate-containing supplement. An improved ESI source design is expected to reduce the limits of detection significantly. The developed ESI-SRM method has the potential to provide complementary data for the quality control of current separation methods for metal citrates using element-selective detection, with application to biomedical samples and further matrices. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preparation of Bis(m -phenylene)-32-crown-10-Based Cryptand/Bisparaquat [3]Rotaxanes with High EfficiencyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 36 2008Shijun Li Abstract Two [3]rotaxanes were synthesized from two bis(m -phenylene)-32-crown-10-based cryptands and a bisparaquat derivative by using a threading-followed-by-stoppering method. As a result of strong association and positive cooperative complexation between the cryptands and the bisparaquat derivative, high yields and high selectivities were achieved. No [2]rotaxanes were found during the preparation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Organocatalyzed Conjugate Addition of Carbonyl Compounds to Nitrodienes/Nitroenynes and Synthetic ApplicationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010Sébastien Belot Abstract The purpose of this study is to point out the synthetic utility of a new class of Michael acceptors (nitrodienes and nitroenynes). The highly enantioselective organocatalytic Michael addition of carbonyl compounds to these functionalized nitroolefins has been carried out in the presence of (S)-diphenylprolinol silyl ether to achieve some interesting building blocks in high selectivities. The adducts thus obtained can be easily converted by taking advantage of the corresponding unsaturated carbon-carbon bond. In presence of the double bond, metathesis or electrophilic activation could be carried out whereas in the presence of the triple bond electrophilic activation could be conducted. We thus focused on a gold-catalyzed cyclization of the bis-homopropargylic alcohol to afford the corresponding substituted tetrahydrofuran. Then, we also demonstrated that organic and gold catalysts were compatible in a one-pot process. Indeed, we developed a one-pot enantioselective organocatalytic Michael addition to a nitroenyne followed by a gold-catalyzed acetalization/cyclization to achieve tetrahydrofuranyl ethers in high diastereo- and enantioselectivities with excellent yields. [source] Kinetic Resolution of P-Chirogenic Compounds by Palladium-Catalyzed Alcoholysis of Vinyl EthersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Hisashi Itoh Abstract The palladium-catalyzed asymmetric alcoholysis of vinyl ethers of P-chirogenic compounds has been achieved. The kinetic resolution of aryl tert -butyl(2-vinyloxyaryl)phosphinates was catalyzed by palladium/chiral diamine complexes with high selectivities (krel: 12,196). [source] Recyclable Polymer- and Silica-Supported Ruthenium(II)-Salen Bis-pyridine Catalysts for the Asymmetric Cyclopropanation of OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Christopher Abstract Homogeneous ruthenium(II)-salen bis-pyridine complexes are known to be highly active and selective catalysts for the asymmetric cyclopropanation of terminal olefins. Here, new methods of heterogenization of these Ru-salen catalysts on polymer and porous silica supports are demonstrated for the facile recovery and recycle of these expensive catalysts. Activities, selectivities, and recyclabilities are investigated and compared to the analogous homogeneous and other supported catalysts for asymmetric cyclopropanation reactions. The catalysts are characterized with a variety of methods including solid state cross-polarization magic-angle spinning (CP MAS) 13C and 29Si,NMR, FT-IR, elemental analysis, and thermogravimetric analysis. Initial investigations produced catalysts possessing high selectivities but decreasing activities upon reuse. Addition of excess pyridine during the washing steps between cycles was observed to maintain high catalytic activities over multiple cycles with no impact on selectivity. Polymer-supported catalysts showed superior activity and selectivity compared to the porous silica-supported catalyst. Additionally, a longer, flexible linker between the Ru-salen catalyst and support was observed to increase enantioselectivity and diastereoselectivity, but had no effect on activity of the resin catalysts. Furthermore, the polymer-supported Ru-salen-Py2 catalysts were found to generate superior selectivities and yields compared to other leading heterogeneous asymmetric cyclopropanation catalysts. [source] Terephthalic acid synthesis at higher concentrations in high-temperature liquid water.AICHE JOURNAL, Issue 6 2009Abstract We synthesized terephthalic acid (TPA) from p -xylene at an initial concentration above its solubility limit in high-temperature liquid water (HTW). The nominal p -xylene loading at the reaction conditions was 0.4 mol L,1, which is the highest reported to date for generation of high TPA yields (>70 mol %) in HTW. The presence of two liquid phases during the reaction did not appear to accelerate the rate, unlike behavior reported for some other organic reactions done "on water" at lower temperatures. Adding oxygen gas in a large increment during synthesis produced a black liquid and a black solid byproduct, which is a previously undocumented problem. Adding oxygen in smaller increments prevented formation of the liquid and solid byproducts and also provided high selectivities (90 mol %) and yields (>70 mol %) of TPA. These results demonstrate the feasibility of HTW as a medium for TPA synthesis at p -xylene concentrations even higher than its solubility limit. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Terephthalic acid synthesis at higher concentrations in high-temperature liquid water.AICHE JOURNAL, Issue 3 2009Abstract We conducted terephthalic acid (TPA) synthesis from p-xylene in high-temperature liquid water (HTW) at 300°C. The p-xylene concentration at the reaction condition was 0.2 mol L,1, which is the highest to date in research that achieved at least 80 mol % yields of TPA in HTW. Pure oxygen gas was the oxidant. Increasing the MnBr2 catalyst concentration increased the rate of TPA formation only slightly. In contrast, whether oxygen was fed in small, quick, discrete bursts, or fed continuously significantly affected the p-xylene conversion and the TPA selectivity. Adding oxygen in quick bursts and small increments led to high selectivities (>90 mol %) of TPA. Continuous addition of oxygen failed to do so. In addition to identifying the sensitivity of this synthesis to the oxygen feed method, these results also demonstrate the feasibility of HTW for TPA synthesis at higher concentrations, and hence high TPA production per unit reactor volume. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Simulating cyclohexane millisecond oxidation: Coupled chemistry and fluid dynamicsAICHE JOURNAL, Issue 6 2002R. P. O'Connor Cyclohexane partial oxidation over a 40-mesh Pt,10% Rh single-gauze catalyst can produce ,85% selectivity to oxygenates and olefins at 25% cyclohexane conversion and 100% oxygen conversion, with cyclohexene and 5-hexenal as the dominant products. A detailed 2-D model of the reactor is solved using density-functional theory (with 35 reactions among 25 species) and computational fluid dynamics. Rapid quenching in the wake of the wires allows highly nonequilibrium species to be preserved. The simulations show that the competition between cyclohexyl and cyclohexylperoxy radicals is crucial in determining product selectivities. At high temperatures and low pressures, the cyclohexyl radical is favored, leading to high selectivities to cyclohexene. At lower temperatures or high pressures, cyclohexylperoxy radicals are favored, allowing the formation of parent oxygenates to dominate. Numerical simulations suggest ways to tune reactor operation for desired product distributions and allow the investigation of dangerous or costly operating conditions, such as high pressure. [source] Do Trinuclear Triplesalen Complexes Exhibit Cooperative Effects?CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2010Characterization, Enantioselective Catalytic Sulfoxidation by Chiral Trinuclear FeIII Triplesalen Complexes, Synthesis Abstract The chiral triplesalen ligand H6chand provides three chiral salen ligand compartments in a meta -phenylene arrangement by a phloroglucinol backbone. The two diastereomeric versions H6chandRR and H6chandrac have been used to synthesize the enantiomerically pure chiral complex [(FeCl)3(chandRR)] (3RR) and the racemic complex [(FeCl)3(chandrac)] (3rac). The molecular structure of the free ligand H6chandrac exhibits at the terminal donor sides the O-protonated phenol,imine tautomer and at the central donor sides the N-protonated keto,enamine tautomer. The trinuclear complexes are comprised of five-coordinate square-pyramidal FeIII ions with a chloride at the axial positions. The crystal structure of 3rac exhibits collinear chiral channels of ,11,Å in diameter making up 33.6,% of the volume of the crystals, whereas the crystal structure of 3RR exhibits voids of 560,Å3. Mössbauer spectroscopy demonstrates the presence of FeIII high-spin ions. UV/Vis spectroscopy is in accordance with a large delocalized system in the central backbone evidenced by strong low-energy shifts of the imine ,,,* transitions relative to that of the terminal units. Magnetic measurements reveal weak intramolecular exchange interactions but strong magnetic anisotropies of the FeIII ions. Complexes 3rac and 3RR are good catalysts for the sulfoxidation of sulfides providing very good yields and high selectivities with 3RR being enantioselective. A comparison of 3RR and [FeCl(salen,)] provides higher yields and selectivities but lower enantiomeric excess values (ee values) for 3RR relative to [FeCl(salen,)]. The low ee values of 3RR appeared to be connected to a strong ligand folding in 3RR, opening access to the catalytically active high-valent Fe,O species. The higher selectivity is assigned to a cooperative stabilization of the catalytically active high-valent Fe,O species through the phloroglucinol backbone in the trinuclear complexes. [source] Tertiary Carbinamine Synthesis by Rhodium-Catalyzed [3+2] Annulation of N-Unsubstituted Aromatic Ketimines and AlkynesCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2010Zhong-Ming Sun Dr. Abstract A convenient and waste-free synthesis of indene-based tertiary carbinamines by rhodium-catalyzed imine/alkyne [3+2] annulation is described. Under the optimized conditions of 0.5,2.5,mol,% [{(cod)Rh(OH)}2] (cod=1,5-cyclooctadiene) catalyst, 1,3-bis(diphenylphosphanyl)propane (DPPP) ligand, in toluene at 120,°C, N-unsubstituted aromatic ketimines and internal alkynes were coupled in a 1:1 ratio to form tertiary 1H -inden-1-amines in good yields and with high selectivities over isoquinoline products. A plausible catalytic cycle involves sequential imine-directed aromatic CH bond activation, alkyne insertion, and a rare example of intramolecular ketimine insertion into a RhI,alkenyl linkage. [source] Lable-Free Electrochemical DNA Sensor Based on Gold Nanoparticles/Poly(neutral red) Modified ElectrodeELECTROANALYSIS, Issue 6 2010Keying Zhang Abstract We present a new strategy for the label-free electrochemical detection of DNA hybridization based on gold nanoparticles (AuNPs)/poly(neutral red) (PNR) modified electrode. Probe oligonucledotides with thiol groups at the 5-end were covalently linked onto the surface of AuNPs/PNR modified electrode via S-Au binding. The hybridization event was monitored by using differential pulse voltammetry (DPV) upon hybridization generates electrochemical changes at the PNR-solution interface. A significant decrease in the peak current was observed upon hybridization of probe with complementary target ssDNA, whereas no obvious change was observed with noncomplementary target ssDNA. And the DNA sensor also showed a high selectivity for detecting one-mismatched and three-mismatched target ssDNA and a high sensitivity for detecting complementary target ssDNA, the detection limit is 4.2×10,12,M for complementary target ssDNA. In addition, the DNA biosensor showed an excellent reproducibility and stability under the DNA-hybridization conditions. [source] Glucosinolate Amperometric Bienzyme Biosensor Based on Carbon Nanotubes-Gold Nanoparticles Composite ElectrodesELECTROANALYSIS, Issue 13 2009V. Serafín Abstract A novel electrochemical biosensor design for glucosinolate determination involving bulk-incorporation of the enzymes glucose oxidase and myrosinase into a colloidal gold - multiwalled carbon nanotubes composite electrode using Teflon as binder is reported. Myrosinase catalyzes the hydrolysis of glucosinolate forming glucose, which is enzymatically oxidized. The generated hydrogen peroxide was electrochemically detected without mediator at the nanostructured composite electrode at E=+0.5,V vs. Ag/AgCl. Under the optimized conditions, the bienzyme MYR/GOx-Aucoll -MWCNT-Teflon exhibited improved analytical characteristics for the glucosinolate sinigrin with respect to a biosensor constructed without gold nanoparticles, i.e. a MYR/GOx-MWCNT-Teflon electrode, as well as with respect to other glucosinolate biosensor designs reported in the literature. The biosensor exhibits good repeatability of the amperometric measurements and good interassay reproducibility. Furthermore, the biosensor exhibited a high selectivity with respect to various potential interferents. The usefulness of the biosensor was evaluated by the determination of glucosinolate in Brussel sprout seeds. [source] A Biomimetic Potentiometric Sensor Using Molecularly Imprinted Polymer for the Cetirizine Assay in Tablets and Biological FluidsELECTROANALYSIS, Issue 18 2008Mehran Javanbakht Abstract Despite the increasing number of applications of molecularly imprinted polymers (MIPs) in analytical chemistry, the construction of a biomimetic potentiometric sensor remains still challenging. In this work, a biomimetic potentiometric sensor, based on a non-covalent imprinted polymer was fabricated for the recognition and determination of cetirizine. The MIP was synthesized by precipitation polymerization, using cetirizine dihydrochloride as a template molecule, methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross linking agent. The sensor showed high selectivity and a sensitive response to the template in aqueous system. The MIP-modified electrode exhibited Nernstian response (28.0±0.9 mV/decade) in a wide concentration range of 1.0×10,6 to 1.0×10,2 M with a lower detection limit of 7.0×10,7 M. The electrode has response time of ca. 20,s, high performance, high sensitivity, and good long term stability (more than 5,months). The method was satisfactory and used to the cetirizine assay in tablets and biological fluids. [source] A Novel Al(III)-Selective Electrochemical Sensor Based on N,N,-Bis(salicylidene)-1,2-phenylenediamine ComplexesELECTROANALYSIS, Issue 16 2006B. Gholivand Abstract A polyvinylchloride membrane sensor based on N,N,-bis(salecylidene)-1,2-phenylenediamine (salophen) as membrane carrier was prepared and investigated as a Al3+ -selective electrode. The sensor exhibits a Nernstian response toward Al(III) over a wide concentration range (8.0×10,7,3.0×10,2,M), with a detection limit of 6.0×10,7,M. The potentiometric response of the sensor is independent of the pH of the test solution in the pH range 3.2,4.5. The electrode possesses advantages of very fast response and high selectivity for Al3+ in comparison with alkali, alkaline earth and some heavy metal ions. The sensor was used as an indicator electrode, in the potentiometric titration of aluminum ion and in determination of Al3+ contents in drug, water and waste water samples. [source] Aluminum(III) Porphyrins as Ionophores for Fluoride Selective Polymeric Membrane ElectrodesELECTROANALYSIS, Issue 6 2006Jeremy Abstract Aluminum(III) porphyrins are examined as potential fluoride selective ionophores in polymeric membrane type ion-selective electrodes. Membranes formulated with Al(III) tetraphenyl (TPP) or octaethyl (OEP) porphyrins are shown to exhibit enhanced potentiometric selectivity for fluoride over more lipophilic anions, including perchlorate and thiocyanate. However, such membrane electrodes display undesirable super-Nernstian behavior, with concomitant slow response and recovery times. By employing a sterically hindered Al(III) picket fence porphyrin (PFP) complex as the membrane active species, fully reversible and Nernstian response toward fluoride is achieved. This finding suggests that the super-Nernstian behavior observed with the nonpicket fence metalloporphyrins is due to the formation of aggregate porphyrin species (likely dimers) within the membrane phase. The steric hindrance of the PFP ligand structure eliminates such chemistry, thus leading to theoretical response slopes toward fluoride. Addition of lipophilic anionic sites into the organic membranes enhances response and selectivity, indicating that the Al(III) porphyrin ionophores function as charged carrier type ionophores. Optimized membranes formulated with Al(III)-PFP in an o -nitrophenyloctyl ether plasticized PVC film exhibit fast response to fluoride down to 40,,M, with very high selectivity over SCN,, ClO4,, Cl,, Br, and NO3, (kpot<10,3 for all anions tested). With further refinements in the membrane chemistry, it is anticipated that Al(III) porphyrin-based membrane electrodes can exhibit potentiometric fluoride response and selectivity that approaches that of the classical solid-state LaF3 crystal-based fluoride sensor. [source] Simultaneous Determination of Hydroquinone and Catechol at a Glassy Carbon Electrode Modified with Multiwall Carbon NanotubesELECTROANALYSIS, Issue 10 2005Honglan Qi Abstract A simply and high selectively electrochemical method for simultaneous determination of hydroquinone and catechol has been developed at a glassy carbon electrode modified with multiwall carbon nanotubes (MWNT). It was found that the oxidation peak separation of hydroquinone and catechol and the oxidation currents of hydroquinone and catechol greatly increase at MWNT modified electrode in 0.20,M acetate buffer solution (pH,4.5). The oxidation peaks of hydroquinone and catechol merge into a large peak of 302,mV (vs. Ag/AgCl, 3,M NaCl) at bare glassy carbon electrode. The two corresponding well-defined oxidation peaks of hydroquinone in the presence of catechol at MWNT modified electrode occur at 264,mV and 162,mV, respectively. Under the optimized condition, the oxidation peak current of hydroquinone is linear over a range from 1.0×10,6,M to 1.0×10,4,M hydroquinone in the presence of 1.0×10,4,M catechol with the detection limit of 7.5×10,7,M and the oxidation peak current of catechol is linear over a range from 6.0×10,7,M to 1.0×10,4,M catechol in the presence of 1.0×10,4,M hydroquinone with the detection limit of 2.0×10,7 M. The proposed method has been applied to simultaneous determination of hydroquinone and catechol in a water sample with simplicity and high selectivity. [source] Iodide-Selective Electrode Based on Copper PhthalocyanineELECTROANALYSIS, Issue 23 2002Saeed Shahrokhian Abstract Copper phthalocyanine was used as ion carrier for preparing polymeric membrane selective sensor for detection of iodide. The electrode was prepared by incorporating the ionophore into plasticized poly(vinyl chloride) (PVC) membrane, coated on the surface of graphite electrode. This novel electrode shows high selectivity for iodide with respect to many common inorganic and organic anions. The effects of membrane composition, pH and the influence of lipophilic cationic and anionic additives and also nature of plasticizer on the response characteristics of the electrode were investigated. A calibration plot with near-Nernestian slope for iodide was observed over a wide linear range of five decades of concentration (5×10,6,1×10,1,M). The electrode has a fast response time, and micro-molar detection limit (ca. 1×10,6,M iodide) and could be used over a wide pH range of 3.0,8.0. Application of the electrode to the potentiometric titration of iodide ion with silver nitrate is reported. This sensor is used for determination of the minute amounts of iodide in lake water samples. [source] Speciation of selenium compounds by open tubular capillary electrochromatography-inductively coupled plasma mass spectrometryELECTROPHORESIS, Issue 21 2006Shu-Yu Lin Abstract We introduce a T-type interface and a crossflow nebulizer to find ways to combine CEC with inductively coupled plasma MS (ICP-MS) detection for selenium speciation. For CEC separation, we employed a macrocyclic polyamine-bonded phase capillary as the separation column and a bare fused-silica capillary filled with the make-up liquid (0.05,M,HNO3). The effect of nebulizer gas flow rate, make-up liquid flow, type, concentration and pH of the mobile phase on the separation have been studied. Tris buffer of 50,mM at pH,8.50 gave the best performance for selenium speciation. The reproducibility of the retention time indicated that sample injection by electrokinetic and nebulizer gas flow was better than that by self-aspiration alone. The detection limits for selenate, selenite, selenocystine and selenomethionine were found to be 2.40, 3.53, 12.86 and 11.25,ng/mL, respectively. Due to the high sensitivity and element-specific detection, as well as the high selectivity of the bonded phase, quantitative analysis of selenium speciation in urine was also achieved. [source] Roxarsone and transformation products in chicken manure: Determination by capillary electrophoresis-inductively coupled plasma-mass spectrometryELECTROPHORESIS, Issue 7-8 2005Charlita G. Rosal Abstract The determination of the animal feed additive roxarsone (3-nitro-4-hydroxyphenylarsonic acid) and six of its possible transformation products (arsenite, arsenate, monomethylarsonate, dimethylarsinate, 3-amino-4-hydroxyphenylarsonic acid, and 4-hydroxyphenylarsonic acid) in chicken manure was investigated using capillary electrophoresis-inductively coupled plasma-mass spectrometry (CE-ICP-MS). Initial method development was conducted using ultraviolet (UV) detection for ruggedness and time efficiency. Separation of these seven arsenic species was effected using a 20,mM phosphate buffer at pH 5.7. The CE-ICP-MS limits of detection in terms of As for each of the species was in the low µg·L,1 range, corresponding to absolute detection limits in the range 20,70,fg As (based on a 23,nL injection). Overall, the method developed in this study provides high selectivity and low limits of detection (1,3,µg·L,1 or low-ppb, based on As), uses small sample volume (low nL), and produces minimal wastes. [source] Metal Complexes of 4,11-Dimethyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) , Thermodynamic and Formation/Decomplexation Kinetic StudiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2009Ivona Svobodová Abstract The macrocyclic ligand with two methylphosphonic acid pendant arms, 4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (1,8-H4Me2te2p, H4L3), was synthesized by a new simple approach. The product of the reaction of quarternized formaldehyde cyclam aminal with the sodium salt of diethyl phosphite was hydrolyzed to give a very high yield of the title ligand. The (H6L3)2+ cation in the solid state is protonated on all ring nitrogen atoms and on each phosphonate group. In the solid-state structure of [Cu(H3L3)][Cu(H2L3)]PF6·3H2O, neutral as well as positively charged complex species are present. Molecular structures of both species are very similar having the copper(II) ion in a coordination environment between square-pyramidal and trigonal-bipyramidal arrangements (, = 0.43 and 0.48) with one pendant arm non-coordinated. The ligand forms stable complexes with transition-metal ions showing a high selectivity for divalent copper atoms. The formation of complexes of the ligand with CuII, ZnII and CdII is fast, confirming the acceleration of complexation due to the presence of the strongly coordinating pendant arms. Acid-assisted decomplexation is fast for all three metal ions. Therefore, the copper(II) complex is not suitable for medicinal applications employing copper radioisotopes, but the title ligand motive can be employed in copper(II) separation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] A New Spherical Metallacryptate Compound [Na{Cu6(Thr)8(H2O)2(ClO4)4}]·ClO4·5,H2O: Magnetic Properties and DFT CalculationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2005Sheng-Chang Xiang Abstract The hexanuclear copper(II) complex with threoninato acid has been synthesized. Its structure can be described as an octahedron cage with D2h symmetry in which six copper ions are bound by eight threoninato acids with a [3.11223130] coordination mode and one Na+ cation being captured within the center of the cage. In contrast with other hexanuclear copper compounds containing amino acids, the title compound has a prolate Cu6 octahedron with the longest axial distance and a rectangle equatorial plane, as well as special coordinated perchlorate ions. Compared with classic cryptate, hexanuclear copper(II) compounds with amino acids can be regarded as a new topologic type of spherical macrotricyclic metallacryptates [2,2,2,2] whose cages have a high selectivity for sodium ions. The analysis of magnetic susceptibility data shows that the threoninato compound has a ground state with spin S = 3. The computing coupling constant between the equatorial Cu centers and the axial ones is 4.4 cm,1,calculated by using DFT methods for a model compound. This is close to three known experimental values of 1.39, 0.56 or 0.43 cm,1 for complexes with 4-hydroxy- L -prolinato, L -prolinato or L -threoninato acid as ligands, respectively. The dominant ferromagnetic interactions for these complexes can be essentially attributed to the orthogonality between the magnetic orbitals, dxz or dyz orbitals for the equatorial CuII centers and d orbitals for the axial ones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] | ||||||||||||||||||||||||||||||||||||||||||||||