APPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2010
Shao-Hsien Huang
Abstract A reusable Pd(NH3)2Cl2/cationic 2,2,-bipyridyl system for the catalysis of the conjugate addition of arylboronic acids to ,,,-unsaturated enones in water under air was developed. Addition of arylboronic acids to both cyclic and acyclic enones progressed smoothly, providing the products in good to high yields, the best result being obtained when HBF4 was used to adjust the pH value to 1.0. After the reaction, the residual aqueous solution could be reused several times, making the reaction greener and reducing wastage of precious metals. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Cationic and anionic lipid-based nanoparticles in CEC for protein separation

ELECTROPHORESIS, Issue 11 2010
Christian Nilsson
Abstract The development of new separation techniques is an important task in protein science. Herein, we describe how anionic and cationic lipid-based liquid crystalline nanoparticles can be used for protein separation. The potential of the suggested separation methods is demonstrated on green fluorescent protein (GFP) samples for future use on more complex samples. Three different CEC-LIF approaches for protein separation are described. (i) GFP and GFP N212Y, which are equally charged, were separated with high resolution by using anionic nanoparticles suspended in the electrolyte and adsorbed to the capillary wall. (ii) High efficiency (800,000 plates/m) and peak capacity were demonstrated separating GFP samples from Escherichia coli with cationic nanoparticles suspended in the electrolyte and adsorbed to the capillary wall. (iii) Three single amino-acid-substituted GFP variants were separated with high resolution using an approach based on a physical attached double-layer coating of cationic and anionic nanoparticles combined with anionic lipid nanoparticles suspended in the electrolyte. The soft and porous lipid-based nanoparticles were synthesized by a one-step procedure based on the self-assembly of lipids, and were biocompatible with a large surface-to-volume ratio. The methodology is still under development and the optimization of the nanoparticle chemistry and separation conditions can further improve the separation system. In contrast to conventional LC, a new interaction phase is introduced for every analysis, which minimizes carry-over and time-consuming column regeneration. [source]

Water-Accelerated Cationic ,-(7- endo) Cyclisation: Application to Indole-Based Peri-Annulated Polyheterocycles,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 26 2010
Mohammad Saifuddin
Abstract An efficient and versatile method for the synthesis of indole-based polycyclic indolo-benzazepine and its derivatives through water-accelerated cationic ,-cyclisation is described. The strategy involves condensation of arylamine moieties linked to C-4 in indole/azaindole systems with arylaldehydes in water containing catalytic amount of Brønsted acids. The C,C bond formation in water is complete within 10,30 min, furnishing the title compounds in excellent yields and purities, whereas in organic solvents 10,12 h are required. Furthermore, aldehydes both with electron-donating and-withdrawing substituents facilitate the ,-cyclisation equally. [source]

Cationic, water-soluble, fluorene-containing poly(arylene ethynylene)s: Effects of water solubility on aggregation, photoluminescence efficiency, and amplified fluorescence quenching in aqueous solutions

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006
Yan-Qin Huang
Abstract Three novel fluorene-containing poly(arylene ethynylene)s with amino-functionalized side groups were synthesized through the Sonogashira reaction. They were poly{9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene}- alt - co -{2,5-bis[3,-(N,N -diethylamino)-1,-oxapropyl]-1,4-phenylene} (P1), poly{9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene} (P2), and poly({9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene}- alt - co -(1,4-phenylene)) (P3). Through the postquaternization treatment of P1,P3 with methyl iodide, we obtained their cationic water-soluble conjugated polyelectrolytes (WSCPs): P1,,P3,. The water solubility was gradually improved from P3, to P1, with increasing contents of hydrophilic side chains. After examining the ultraviolet,visible absorption and photoluminescence (PL) spectra, fluorescence lifetimes, and dynamic light scattering data, we propose that with the reduction of the water solubility from P1, to P3,, they exhibited a gradually increased degree of aggregation in H2O. The PL quantum yields of P1,,P3, in H2O displayed a decreasing tendency consistent with the increased degree of aggregation, suggesting that the pronounced degree of aggregation was an important reason for the low PL quantum yields of WSCPs in H2O. Two structurally analogous water-soluble trimers of P2, and P3,, model compounds 2,7-bis(9,,9,-bis{6,-[(N,N -diethyl)- N -methylammonium] hexyl}-2,-fluorenylethynyl)-9,9-bis{6,-[(N,N -diethyl)- N -methylammonium]hexyl}fluorene hexaiodide and 1,4-bis(9,,9,-bis{6,-[(N,N -diethyl)- N -methylammonium]hexyl}-2,-fluorenylethynyl)benzene tetraiodide, were synthesized. The amplified fluorescence quenching of these WSCPs by Fe(CN)64, in H2O was studied by comparison with a corresponding analogous trimer. The effects of aggregation on the fluorescence quenching may be two-edged in these cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5778,5794, 2006 [source]

Controlled, radical reversible addition,fragmentation chain-transfer polymerization in high-surfactant-concentration ionic miniemulsions

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2004
J. B. McLeary
Abstract Living free-radical polymerization of methacrylate and styrenic monomers with ionic surfactants was carried out with reversible addition,fragmentation chain transfer in miniemulsion with different surfactant types and concentrations. The previously reported problem of phase separation was found to be insignificant at higher surfactant concentrations, and control of the molar mass and polydispersity index was superior to that of published miniemulsion systems. Cationic and anionic surfactants were used to examine the validity of the argument that ionic surfactants interfere with transfer agents. Ionic surfactants were suitable for miniemulsion polymerization under certain conditions. The colloidal stability of the miniemulsions was consistent with the predictions of a specific model. The living character of the polymer that comprised the latex material was shown by its transformation into block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 960,974, 2004 [source]

Bio-Based Rubbers by Concurrent Cationic and Ring-Opening Metathesis Polymerization of a Modified Linseed Oil

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2009
Wonje Jeong
Abstract Bio-based rubbers prepared by tandem cationic polymerization and ROMP using a norbornenyl-modified linseed oil, DilulinÔ, and a norbornene diester, NBDC, have been prepared and characterized. Increasing the concentration of the NBDC in the mixture results in a decrease in the glass transition temperature. The new bio-based rubbers exhibit tensile test behavior ranging from relatively brittle (18% elongation) to moderately flexible (52% elongation) and with decreasing values of tensile stress with increasing NBDC content. Thermogravimetric analysis reveals that the bio-based rubbers have maximum decomposition temperatures of over 450,°C with their thermal stability decreasing with increasing loadings of NBDC. [source]

Cationic and Anionic Conjugated Polyelectrolytes: Aggregation-Mediated Fluorescence Energy Transfer to Dye-Labeled DNA

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2008
Youngeup Jin
Abstract An electrostatic complex of water-soluble conjugated polyelectrolytes (CPs) between anionic poly(9,9-bis(4,-sulfonatobutyl)fluorene- co-alt -1,4-phenylene) disodium salt (a-PFP) and cationic poly(9,9-bis((6,- N,N,N,-trimethylammonium)hexyl)fluorene- co -2,1,3-bezothiadiazole) dibromide (85:15) (c-PFB15) was tested as a fluorescence resonance energy transfer (FRET) donor to Texas Red (TR)-labeled single-stranded DNA (ssDNA-TR) via two-step FRET processes. Electrostatic complexation of a-PFP and c-PFB15 in water leads to aggregation of polymer chains, a concomitant reduction of intersegment distances, and energy transfer to the benzothiadiazole (BT) segments. The following complexation with ssDNA-TR leads to energy transfer from BT to TR via two-step FRET processes. This detection schematic shows an FRET-induced signal amplification, which can be achieved by adjusting the charge ratio in the cationic/anionic CP complex and controlling the number density of the binding CPs around the acceptor, resulting in enhanced antenna effects and sensitivity in CP-based FRET DNA detection assays. [source]

Cationic, neutral and anionic metal(II) complexes derived from 4-oxo-4H -pyran-2,6-dicarboxylic acid (chelidonic acid)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2007
Vaduganathan Yasodha
The structures of five metal complexes containing the 4-oxo-4H -pyran-2,6-dicarboxylate dianion illustrate the remarkable coordinating versatility of this ligand and the great structural diversity of its complexes. In tetraaquaberyllium 4-oxo-4H -pyran-2,6-dicarboxylate, [Be(H2O)4](C7H2O6), (I), the ions are linked by eight independent O,H...O hydrogen bonds to form a three-dimensional hydrogen-bonded framework structure. Each of the ions in hydrazinium(2+) diaqua(4-oxo-4H -pyran-2,6-dicarboxylato)calcate, (N2H6)[Ca(C7H2O6)2(H2O)2], (II), lies on a twofold rotation axis in the space group P2/c; the anions form hydrogen-bonded sheets which are linked into a three-dimensional framework by the cations. In bis(,-4-oxo-4H -pyran-2,6-dicarboxylato)bis[tetraaquamanganese(II)] tetrahydrate, [Mn2(C7H2O6)2(H2O)8]·4H2O, (III), the metal ions and the organic ligands form a cyclic centrosymmetric Mn2(C7H2O6)2 unit, and these units are linked into a complex three-dimensional framework structure containing 12 independent O,H...O hydrogen bonds. There are two independent CuII ions in tetraaqua(4-oxo-4H -pyran-2,6-dicarboxylato)copper(II), [Cu(C7H2O6)(H2O)4], (IV), and both lie on centres of inversion in the space group P; the metal ions and the organic ligands form a one-dimensional coordination polymer, and the polymer chains are linked into a three-dimensional framework containing eight independent O,H...O hydrogen bonds. Diaqua(4-oxo-4H -pyran-2,6-dicarboxylato)cadmium monohydrate, [Cd(C7H2O6)(H2O)2]·H2O, (V), forms a three-dimensional coordination polymer in which the organic ligand is coordinated to four different Cd sites, and this polymer is interwoven with a complex three-dimensional framework built from O,H...O hydrogen bonds. [source]

ChemInform Abstract: ,-Aromatic and Sulfur Nucleophilic Partners in Cationic ,-Cyclizations: Intramolecular Amidoalkylation and Thioamidoalkylation Cyclization via ,-Carbinol Lactams.

CHEMINFORM, Issue 46 2001
Nicolas Hucher
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Generation of Cationic [Zr-{tert -Butyl Enolate}] Reactive Species: Methyl Abstraction versus Hydride Abstraction

CHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004
Bing Lian Dr.
Abstract Treatment of the neutral methyl,Zr,enolate [Cp2Zr(Me){O(tBuO)CCMe2}] (1) with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] as a methyl abstractor in THF at 0,°C leads to the selective formation of the free ion pair complex [Cp2Zr(THF){O(tBuO)CCMe2}]+,[anion], (2) (anion=MeB(C6F5)3,, B(C6F5)4,), which is relevant to the controlled polymerization of methacrylates. Cation 2 rapidly decomposes at 20,°C in THF with release of one equivalent of isobutene to form the cationic Zr,carboxylate species [Cp2Zr(THF)(O2CiPr)]+ (3), through a proposed intramolecular proton transfer process from the tert -butoxy group to the enolate. The reaction of 1 with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] in CH2Cl2 leads to the direct, rapid formation of the dimeric ,-isobutyrato,Zr dicationic species [{Cp2Zr[,-(O2CiPr)]}2]2+ (4), which gives 3 upon dissolution in THF. Contrastingly, when [Ph3C][B(C6F5)4] is used to generate the cationic Zr,enolate species from 1 in CD2Cl2, a 15:85 mixture of dicationic complexes 4 and [{Cp2Zr[, -(O2CC(Me)CH2)]}2]2+[B(C6F5)4] (5 -[B(C6F5)4]2) is obtained quantitatively. The formation of 5 is proposed to arise from initial hydride abstraction from a methyl enolate group by Ph3C+, as supported by the parallel production of Ph3CH, and subsequent elimination of methane and isobutene. In addition to standard spectroscopic and analytical characterizations for the isolated complexes 2,5, complexes 4 and 5 have also been structurally characterized by X-ray diffraction studies. [source]

Comparative Studies of Tridentate Sulfur and Nitrogen-Containing Ligands as Ionophores for Construction of Cadmium Ion-Selective Membrane Sensors

ELECTROANALYSIS, Issue 11 2007
Ashok, Kumar Singh
Abstract New polymeric membrane cadmium-ion selective sensors have been prepared by incorporating nitrogen and sulfur containing tridentate ligands as the ionophores into the plasticized PVC membranes. Poly(vinyl chloride) (PVC) based membranes of potassium hydrotris[N -(2,6-xylyl)thioimdazolyl) borate] (KTt2,6-xylyl) and potassium hydrotris(3-phenyl-5-methylpyrazolyl) borate (KTpPh,Me) with sodium tetraphenyl borate (NaTPB) as an anionic excluder and dibutylphthalate (DBP), tributylphthalate (TBP), dioctylsebacate (DOS), and o -nitrophenyloctyl ether (o -NPOE) as plasticizing solvent mediators were investigated in different compositions. KTt2,6-xylyl was found to be a selective and sensitive ion carrier for Cd(II) membrane sensor. A membrane composed of KTt2,6-xylyl:NaTPB:PVC:DBP with the % mole ratio 2.3,:,1.1,:,34.8,:,61.8 (w/w) works well over a very wide concentration range (7.8×10,8,1.0×10,2,M) with a Nernstian slope of 29.4±0.2,mV/decades of activity between pH values of 3.5 to 9.0 with a detection limit of 4.37×10,8,M. The sensor displays very good discrimination toward Cd(II) ions with regard to most common cations. The proposed sensor shows a short response time for whole concentration range (ca. 8,s). The effects of the cationic (tetrabutylammonium chloride, TBC), anionic (sodium dodecyl sulfate, SDS) and nonionic (Triton X-100) surfactants were investigated on the potentiometric properties of proposed cadmium-selective sensor. The proposed sensor based on KTt2,6-xylyl ionophore has also been used for the direct determination of cadmium ions in different water samples and human urine samples. [source]

Construction and Evaluation of a Gold Tubular Electrode for Flow Analysis: Application to Speciation of Antimony in Water Samples

ELECTROANALYSIS, Issue 6 2007
Rodrigo Santos
Abstract A tubular gold electrode (TGE) is described for the first time by summarizing the important aspects of its construction and evaluation. Applicability of the TGE is evaluated in the speciation of Sb(III) and Sb(V) using anodic stripping voltammetry in a single flow manifold. Studies with surface active interferences and metallic cations were performed. The proposed conditions for antimony determination showed good tolerance towards cationic, anionic and nonionic surface active substances. A linear response for antimony was obtained for solutions containing significant amounts of several metallic cations. Linear calibration curves for Sb(III) were obtained in the range 1,10,ppb with a detection limit of 0.19,ppb (CV=2.91%, n=5, [Sb(III)]=5,ppb). For Sb(V), linear calibration curves were in the range 1,15,ppb with a detection limit of 0.32,ppb (CV=1.41%, n=5, [Sb(V)]=5,ppb). The figures of merit achieved sustain for the good applicability of the proposed method as it allows the determination of antimony at levels below maximum values permitted in consuming waters. Results of antimony concentration determined in water samples were validated against the ICP-MS reference procedure or compared with reference water samples. [source]

Iodide-Selective Electrode Based on Copper Phthalocyanine

ELECTROANALYSIS, Issue 23 2002
Saeed 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]

Cationic and anionic lipid-based nanoparticles in CEC for protein separation

Protein separations using polyelectrolyte multilayer coatings with molecular micelles in open tubular capillary electrochromatography

ELECTROPHORESIS, Issue 4 2008
Candace A. Luces
Abstract Novel polyelectrolyte multilayer (PEM) coatings for enhanced protein separations in open tubular CEC (OT-CEC) are reported. Use of four cationic polymers (poly- L -lysine, poly- L -ornithine, poly- L -lysine-serine, and poly- L -glutamic acid-lysine), and three anionic molecular micelles, sodium poly(N -undecanoyl- L -leucyl-alaninate) (poly- L -SULA), sodium poly(N -undecanoyl- L -leucyl-valinate) (poly- L -SULV), and sodium poly(undecylenic sulfate) (poly-SUS) were investigated in PEM coatings for protein separations. The simultaneous effects of cationic polymer concentration, number of bilayers, temperature, applied voltage, and pH of the BGE on the separation of four basic proteins (,-chymotrypsinogen A, lysozyme, ribonuclease A, and cytochrome c) were analyzed using a Box Behnken experimental design. The influence of NaCl on the run-to-run reproducibility was investigated for PEM coatings containing each cationic polymer. All coatings exhibited excellent reproducibilities with a %RSD of the EOF less than 1% in the presence of NaCl. Optimal conditions were dependent on both the cationic and anionic polymers used in the PEM coatings. Poly- L -glutamic acid-lysine produced the highest resolution and longest migration time. The use of molecular micelles to form PEM coatings resulted in better separations than single cationic coatings. Chiral poly- L -SULA and poly- L -SULV resulted in higher protein resolutions as compared to the achiral, poly-SUS. Furthermore, the use of poly- L -SULV reversed the elution order of lysozyme and cytochrome c when compared to poly- L -SULA and poly-SUS. [source]

Dual injection capillary electrophoresis: Foundations and applications

ELECTROPHORESIS, Issue 23-24 2004
Feliciano Priego-Capote
Abstract The state of the art of capillary electrophoresis (CE) approaches based on dual injection is here reported. Dual injection strategies have been proposed with three main objectives: (i) to provide information about reaction kinetics and/or related parameters, (ii) to perform in-capillary derivatization for improving separation and/or determination, (iii) to develop electrophoretic methods for the simultaneous analysis of anionic and cationic compounds. For the first two purposes, dual injection, which involves sample and reagent, can be realized either from the same end of the capillary (electrophoretically mediated microanalysis, EMMA) or from the two ends of the capillary (electroinjection analysis, EIA). The third objective, with dual injection of sample from the two ends of the capillary, takes advantage of moving cationic and anionic compounds with opposite directions. The foundations of each alternative, conditions necessary for working with them, restrictions, applications as well as perspectives are reviewed in order to establish the advantages, shortcomings, and convenience or no of their use in comparison to conventional CE. [source]

Microemulsion electrokinetic chromatography of drugs varying in charge and hydrophobicity: I. Impact of parameters on separation performance evaluated by multiple linear regression models

ELECTROPHORESIS, Issue 1 2004
Valérie Harang
Abstract The separation of anionic, cationic and neutral drugs in microemulsion electrokinetic chromatography (MEEKC) was studied with a statistical experimental design. The concentration of sodium dodecyl sulfate (SDS, surfactant), 1-butanol (co-surfactant) and borate buffer and the factors Brij 35 (surfactant), 2-propanol (organic solvent) and cassette temperature were varied simultaneously, while the parameters pH (9.2), the concentration of octane (oil, 0.8% w/w), the voltage (10 kV) and the dimension of the fused-silica capillary, were kept constant. Eight different model substances were chosen with different hydrophobicities. Two of the analytes were positively charged, two were negatively charged, and the remaining four were neutral or close to neutral at the pH explored. The importance of each parameter on the separation window, the plate height and the retention factor for each of the analytes was studied by means of multiple linear regression (MLR) models. A new response was evaluated for anions, the quotient between the effective mobility in the microemulsion and the effective mobility in the corresponding buffer. Factors affecting selectivity changes were also explored, and it was found that SDS and 2-propanol had the largest effect on selectivity. [source]

High-efficiency peptide analysis on monolithic multimode capillary columns: Pressure-assisted capillary electrochromatography/capillary electrophoresis coupled to UV and electrospray ionization-mass spectrometry

ELECTROPHORESIS, Issue 21 2003
Alexander R. Ivanov
Abstract High-efficiency peptide analysis using multimode pressure-assisted capillary electrochromatography/capillary electrophoresis (pCEC/pCE) monolithic polymeric columns and the separation of model peptide mixtures and protein digests by isocratic and gradient elution under an applied electric field with UV and electrospray ionization-mass spectrometry (ESI-MS) detection is demonstrated. Capillary multipurpose columns were prepared in silanized fused-silica capillaries of 50, 75, and 100 ,m inner diameters by thermally induced in situ copolymerization of methacrylic monomers in the presence of n -propanol and formamide as porogens and azobisisobutyronitrile as initiator. N -Ethylbutylamine was used to modify the chromatographic surface of the monolith from neutral to cationic. Monolithic columns were termed as multipurpose or multimode columns because they showed mixed modes of separation mechanisms under different conditions. Anion-exchange separation ability in the liquid chromatography (LC) mode can be determined by the cationic chromatographic surface of the monolith. At acidic pH and high voltage across the column, the monolithic stationary phase provided conditions for predominantly capillary electrophoretic migration of peptides. At basic pH and electric field across the column, enhanced chromatographic retention of peptides on monolithic capillary column made CEC mechanisms of migration responsible for separation. The role of pressure, ionic strength, pH, and organic content of the mobile phase on chromatographic performance was investigated. High efficiencies (exceeding 300,000 plates/m) of the monolithic columns for peptide separations are shown using volatile and nonvolatile, acidic and basic buffers. Good reproducibility and robustness of isocratic and gradient elution pressure-assisted CEC/CE separations were achieved for both UV and ESI-MS detection. Manipulation of the electric field and gradient conditions allowed high-throughput analysis of complex peptide mixtures. A simple design of sheathless electrospray emitter provided effective and robust low dead volume interfacing of monolithic multimode columns with ESI-MS. Gradient elution pressure-assisted mixed-mode separation CE/CEC-ESI-MS mass fingerprinting and data-dependent pCE/pCEC-ESI-MS/MS analysis of a bovine serum albumin (BSA) tryptic digest in less than 5 min yielding high sequence coverage (73%) demonstrated the potential of the method. [source]

Digestive peptidases in Tenebrio molitor and possibility of use to treat celiac disease

ENTOMOLOGICAL RESEARCH, Issue 3 2007
Elena N. ELPIDINA
Abstract Digestion in Tenebrio molitor larvae occurs in the midgut, where there is a sharp pH gradient from 5.6 in the anterior midgut (AM) to 7.9 in the posterior midgut (PM). Accordingly, digestive enzymes are compartmentalized to the AM or PM. Enzymes in the AM are soluble and have acidic or neutral pH optima, while PM enzymes have alkaline pH optima. The main peptidases in the AM are cysteine endopeptidases presented by two to six subfractions of anionic proteins. The major activity belongs to cathepsin L, which has been purified and characterized. Serine post-proline cleaving peptidase with pH optimum 5.3 was also found in the AM. Typical serine digestive endopeptidases, trypsin-like and chymotrypsin-like, are compartmentalized to the PM. Trypsin-like activity is due to one cationic and three anionic proteinases. Chymotrypsin-like activity consists of one cationic and four anionic proteinases, four with an extended binding site. The major cationic trypsin and chymotrypsin have been purified and thoroughly characterized. The predicted amino acid sequences are available for purified cathepsin L, trypsin and chymotrypsin. Additional sequences for putative digestive cathepsins L, trypsins and chymotrypsins are available, implying multigene families for these enzymes. Exopeptidases are found in the PM and are presented by a single membrane aminopeptidase N-like peptidase and carboxypeptidase A, although multiple cDNAs for carboxypeptidase A were found in the AM, but not in the PM. The possibility of the use of two endopeptidases from the AM , cathepsin L and post-proline cleaving peptidase , in the treatment of celiac disease is discussed. [source]

Adsorption of hydrophobic organic compounds onto a hydrophobic carbonaceous geosorbent in the presence of surfactants,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2008
Peng Wang
Abstract The adsorption of hydrophobic organic compounds (HOCs; atrazine and diuron) onto lampblack was studied in the presence of nonionic, cationic, and anionic surfactants (Triton® X-100), benzalkonium chloride [BC], and linear alkylbenzene sulfonate [LAS]) to determine the effect of the surfactant on HOC adsorption onto a hydrophobic carbonaceous geosorbent. Linear alkylbenzene sulfonate showed an adsorption capacity higher than that of BC but similar to that of Triton X-100, implying the charge property of a surfactant is not a useful indicator for predicting the surfactant's adsorption onto a hydrophobic medium. The results also indicated that the octanol-water partition coefficient (Kow) of a surfactant is not a good predictor of that surfactant's sorption onto a hydrophobic medium. Under subsaturation adsorption conditions (i.e., before sorption saturation is reached), surfactant adsorption reduced HOC adsorption to a significant extent, with the reduction in HOC adsorption increasing monotonically with the amount of surfactant adsorbed. Among the three surfactants, Triton X-100 was the most effective in reducing HOC adsorption, whereas BC and LAS showed similar effectiveness in this regard. Under the same amount of the surfactant sorbed, the reduction in atrazine adsorption was consistently greater than that for diuron because of atrazine's lower hydrophobicity. No significant difference was observed in the amount of the HOC adsorbed under different adsorption sequences. Our results showed that the presence of surfactant can significantly decrease HOC adsorption onto hydrophobic environmental media and, thus, is important in predicting HOC fate and transport in the environment. [source]

Dehydrogenation of Hydridoirida-,-diketones in Methanol: The Selective Formation of Mono- and Dinuclear Acyl Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2010
Roberto Ciganda
Abstract The hydridoirida-,-diketone [IrH{(PPh2(o -C6H4CO))2H}Cl] (1) reacts with diimines (NN) or with pyridine (py) in refluxing methanol to undergo dehydrogenation. The reactions afford selectively the cis -acyl, trans -phosphane isomers of the cationic [Ir(PPh2(o -C6H4CO))2(NN)]+ {NN = 2,2,-bipyridine (2); R,N=C(CH3),C(CH3)=N,R, [R = R, = NH2 (3); R = R, = OH (4); R = OH, R, = NH2 (5)]} or neutral [IrCl(PPh2(o -C6H4CO))2(py)] (6) derivatives. The reactions are faster for ligands containing amino substituents. Refluxing 1 in MeOH affords the formation of an equimolar mixture of dimercationic species [Ir2(,-Cl)(,-PPh2(o -C6H4CO))2(PPh2(o -C6H4CO))2]+ (7a and 7b) containing two acyls and a chloride as bridging groups. The isomers could be separated by fractional precipitation. Compound [3]Cl, containing amino substituents in the imino functionalities, catalyses the hydrogen transfer from 2-propanol to cyclohexanone to afford cyclohexanol. All the complexes were fully characterised spectroscopically. Single crystal X-ray diffraction analysis was performed on complexes 6 and [7b]ClO4. [source]

1,3,5-Triazapentadiene Nickel(II) Complexes Derived from a Ketoxime-Mediated Single-Pot Transformation of Nitriles

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2010
Maximilian N. Kopylovich
Abstract A series of cationic (2+) [Ni{HN=C(R)NHC(R)=NH}2](X)2 {R = 4-(Cl)C6H4 (1), 3-(NC)C6H4 (3), 4-(NC)C6H4 (4) and Me (7); X = Cl, (1, 3, 4) or MeCOO,·H2O (7)} and neutral [Ni{HN=C(R)NC(R)=NH}2](solvate) {R = 3-(Cl)-4-py (2), 3-py (5) and 4-py (6); solvate = MeOH and/or H2O; py = pyridyl} N,N -chelating bis(1,3,5-triazapentadiene/ato)nickel(II) [Ni(tap)2]2+/0 complexes has been easily generated by a ketoxime-mediated single-pot reaction of a nickel(II) salt [NiCl2·2H2O or Ni(MeCOO)2·4H2O] with 4-chlorobenzonitrile, isophthalonitrile, terephthalonitrile, acetonitrile, 2-chloro-4-cyanopyridine, 3-cyanopyridine or 4-cyanopyridine, respectively. The obtained compounds have been characterized by IR, 1H and 13C{1H} NMR spectroscopy, FAB-MS(+) or ESI-MS(+), elemental analyses and single-crystal X-ray diffraction [for 7 and solvated mono- {1a·(Me2CO)0.33·(MeOH)0.67} and bis-deprotonated (2b·2Me2CO, 4b·CHCl3, 5b·Me2CO and 6b·MeOH) products, formed upon recrystallization of 1, 2, 4, 5 and 6, respectively]. The crystal structures of all compounds bear similar monomeric Ni(tap)2 units with a nearly square-planar geometry. In addition, the structure of 7 features the formation of infinite 1D zig-zag water,acetate chains {[(H2O)2(MeCOO)2]2,}n, which multiply interact with the [Ni(tap)2]2+ cations to generate a 2D hydrogen-bonded supramolecular assembly. [source]

16-Electron (Arene)ruthenium Complexes with Superbasic Bis(imidazolin-2-imine) Ligands and Their Use in Catalytic Transfer Hydrogenation

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29-30 2009
Thomas Glöge
Abstract The ligands N,N, -bis(1,3,4,5-tetramethylimidazolin-2-ylidene)-1,2-ethanediamine (BLMe) and N,N, -bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,2-ethanediamine(BLiPr) react with [(,5 -C5Me5)RuCl]4 to afford cationic 16-electron half-sandwich complexes [(,5 -C5Me5)Ru(BLR)]+ (R = Me, 3; R = iPr, 4), which resist coordination of the chloride counterion because of the strong electron-donating ability of the diimine ligands. Upon reaction with [(,6 -C6H6)RuCl2]2 or [(,6 -C10H14)RuCl2]2, these ligands stabilize dicationic 16-electron benzene and cymene complexes of the type [(,6 -C6H6)Ru(BLR)]2+ (R = Me, 5; R = iPr, 6) and [(,6 -C10H14)Ru(BLR)]2+ (R = Me, 7; R = iPr, 8). The X-ray crystal structure of [5]Cl2 reveals the absence of any direct Ru,Cl interaction, whereas a long Ru,Cl bond, supported by two CH···Cl hydrogen bonds, is observed for [(6)Cl]Cl in the solid state. Treatment of the dichlorides of 6 and 8 with NaBF4 affords [6](BF4)2 and [8](BF4)2, which are composed of individual dications and tetrafluoroborate ions with no direct Ru,F interaction. All complexes catalyze the transfer hydrogenation of acetophenone in boiling 2-propanol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Reaction of 1,3,5-Triazacyclohexanes with TiCl4: Formation of Cationic Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2005
Randolf D. Köhn
Abstract N -substituted 1,3,5-triazacyclohexanes [R3TAC; R = cyclohexyl, p -fluorobenzyl or Ph(CH2)n (n = 1, 2, 3)] react with excess TiCl4 to give the corresponding cationic ,3 complexes [(R3TAC)TiCl3][Ti2Cl9]. Attempts to prepare complexes with titanium-free anions at lower Ti:R3TAC ratio or with added Me3SiOTf lead to the same cations with [Ti2Cl10]2, and [Ti2Cl8(OTf)], anions. Five complexes as well as (p -fluorobenzyl)3TAC have been characterised by X-ray crystallography. The ring C,H bonds engage in hydrogen bonding interactions in the crystals and strongly solvent and anion dependent 1H NMR signals are detected in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Polymeric, Molecular, and Cation/Anion Arrangements in Chloro-, Bromo-, and Iododiruthenium(II,III) Carboxylate Compounds

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2003
M. Carmen Barral
Abstract The synthesis and characterization of the anhydrous compounds [Ru2X(,-O2CR)4] [R = CH2CH2OPh, X = Cl (1a), Br (2a), I (3a); R = CMePh2, X = Br (5a), I (6a)] and of the solvated complexes [Ru2X(,-O2CR)4(H2O)] [R = CH2CH2OPh, X = Cl (1b), I (3b); R = CMePh2, X = Cl (4b), Br (5b), I (6b)] are described. Thermogravimetric analyses have been used to confirm the anhydrous or solvated natures of the complexes. The crystal structures of 1b·2MeOH, 3b·0.5H2O, and 4b have been investigated by X-ray diffraction and none of them shows the usual polymeric arrangement reported for tetracarboxylatodiruthenium(II,III) compounds. The structure of 3b·0.5H2O consists of cationic and anionic units, [Ru2(,-O2CCH2CH2OPh)4(H2O)2][Ru2I2(,-O2CCH2CH2OPh)4], and represents the first reported crystal structure of a tetracarboxylato(iodo)diruthenium(II,III) derivative. The structures 1b·2MeOH and 4b each show the presence of discrete dinuclear molecules. The crystal structure of [Ru2Cl(,-O2CCMePh2)4(H2O)] demonstrates that diruthenium compounds with the same halide and carboxylate ligands may adopt polymeric or discrete molecular dispositions. Magnetic susceptibility measurements of the complexes in the 2,300 K range have been carried out. Complex 2a shows a strong antiferromagnetic coupling, consistent with the existence of linear chains in the solid state. The complexes [Ru2X(,-O2CR)4(H2O)] show weak through-space antiferromagnetic coupling, in accordance with non-polymeric structures. The magnetic behaviour of 1a, 3a, 5a, and 6a suggests a mixture of arrangements. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Electrical and neurotransmitter activity of mature neurons derived from mouse embryonic stem cells by Sox-1 lineage selection and directed differentiation

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2004
R. J. Lang
Abstract Sx1TV2/16C is a mouse embryonic stem (ES) cell line in which one copy of the Sox1 gene, an early neuroectodermal marker, has been targeted with a neomycin (G418) selection cassette. A combination of directed differentiation with retinoic acid and G418 selection results in an enriched neural stem cell population that can be further differentiated into neurons. After 6,7 days post-plating (D6,7PP) most neurons readily fired tetrodotoxin (TTX)-sensitive action potentials due to the expression of TTX-sensitive Na+ and tetraethylammonium (TEA)-sensitive K+ channels. Neurons reached their maximal cell capacitance after D6,7PP; however, ion channel expression continued until at least D21PP. The percentage of cells receiving spontaneous synaptic currents (s.s.c.) increased with days in culture until 100% of cells received a synaptic input by D20PP. Spontaneous synaptic currents were reduced in amplitude and frequency by TTX, or upon exposure to a Ca2+ -free, 2.5 mm Mg2+ saline. S.s.c. of rapid decay time constants were preferentially blocked by the nonNMDA glutamatergic receptor antagonists CNQX or NBQX. Ca2+ levels within ES cell-derived neurons increased in response to glutamate receptor agonists l -glutamate, AMPA, N -methyl- d -aspartate (NMDA) and kainic acid and to acetylcholine, ATP and dopamine. ES cell-derived neurons also generated cationic and Cl, -selective currents in response to NMDA and glycine or GABA, respectively. It was concluded that ES-derived neurons fire action potentials, receive excitatory and inhibitory synaptic input and respond to various neurotransmitters in a manner akin to primary central neurons. [source]

Water-Accelerated Cationic ,-(7- endo) Cyclisation: Application to Indole-Based Peri-Annulated Polyheterocycles,

A Bifunctional Chromogenic Calix[4]arene Chemosensor for Both Cations and Anions: A Potential Ca2+ and F, Switched INHIBIT Logic Gate with a YES Logic Function

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2010
Kai-Chi Chang
Abstract A bifunctional chromogenic calix[4]arene 3, which contains both triazoles and hydroxy azophenols as both cationic and anionic recognition sites and the azophenol moiety as a coloration unit, was designed and synthesized. The recognition of Ca2+ by 3 gave rise to a marked colour change from greenish to bright yellow, whereas the recognition of F, by 3 showed a colour change from light green to bluish. The colour changes of 3 by the inputs of Ca2+ and F, have been implemented to construct a combinational logic circuit at the molecular level. [source]

Effect of the Leaving Group on the Rate and Mechanism of the Palladium-Catalyzed Isomerization of Cyclic Allylic Benzoates in Allylic Substitutions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2006
Christian Amatore
Abstract In chloroform, the reaction of cis -5-phenylcyclohex-2-enyl 4-Z-benzoate (cis - 1Z, Z = NO2, Cl, H, Me, MeO) with Pd0 complexes ligated to PPh3 is reversible and proceeds with isomerization at the allylic position. The rate of isomerization of cis - 1Z to trans - 1Z depends on the catalytic precursor: Pd0(PPh3)4 > {Pd0(dba)2 + 2PPh3} in agreement with an SN2 mechanism in the rate-determining isomerization of the cationic (,3 -allyl)palladium complexes formed in the oxidative addition. For a given precursor, the rate of isomerization of cis - 1Z to trans - 1Z also depends on the substituent Z, i.e., on the leaving group. The isomerization rate follows the same order as the leaving group properties: 4-NO2,C6H4 -CO2,> 4-Cl,C6H4 -CO2, > C6H5 -CO2, > 4-Me,C6H4 -CO2, > 4-MeO,C6H4 -CO2,. The same tendency is found for the equilibrium constant between the neutral cis - 1Z and the cationic (,3 -allyl)palladium complex in DMF. The higher the concentration of the cationic (,3 -allyl)palladium complex, the faster the isomerization of cis - 1Z to trans - 1Z is. The isomerization of cis - 1Z to trans - 1Z and that of the cationic (,3 -allyl)palladium complexes are at the origin of the lack of stereospecificity observed in catalytic nucleophilic allylic substitutions. These isomerizations are affected by both the leaving groups and the Pd0 precursors, which therefore are not "innocent" but may play an important role in palladium-catalyzed nucleophilic substitutions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Palladium-Catalyzed Preparation of Propargylic or Allenylic Sulfides from Propargyl Halides or Mesylate and Thiols

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2004
Ken Tsutsumi
Abstract In the presence of a catalytic amount of Pd0 -dppe complex [dppe: 1,2-bis(diphenylphosphanyl)ethane], generated in situ from [Pd2(dba)3·CHCl3] and dppe, propargylic bromide 1a reacted with an equimolar amount of propanethiol at 60 °C in DMF to afford propargylic sulfide 2 in an excellent yield. The reaction occurs readily when carried out in the presence of the weak base triethylamine. The choice of both the phosphane, which is employed as the palladium atom's ligand, and the solvent have a remarkable effect on this reaction. We found that the optimum conditions for the reaction are those using a bidentate phosphane ligand (dppe) in a polar solvent (DMF). Compound 1a reacted smoothly with both aromatic (PhSH) and secondary thiols (CySH) in high yields. The reactions with thiols bearing functional groups (OH or Cl) proceeded selectively in good to moderate yields. Primary chlorides 1b,e were readily converted into their corresponding propargylic sulfides 7,10 in high yields. The Pd0 -dppe catalyst was ineffective in the reaction of the bromide 1g bearing a tBu group at the propargylic position, but the reaction of the corresponding mesylate 1h using the Pd0 -DIOP catalyst [DIOP = O -isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphanyl)butane] at 100 °C afforded the product 11 in good yield. Allenylic sulfides were obtained from 1g,i. We suggest that a cationic ,3 -type complex may be a more reactive intermediate in this catalytic reaction than neutral ,1 - or ,3 -allenyl/propargylpalladium complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]