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Anionic
Terms modified by Anionic Selected AbstractsAnionic Bridged Bis(amidinate) Lithium Lanthanide Complexes: Efficient Bimetallic Catalysts for Mild Amidation of Aldehydes with AminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Junfeng Wang Abstract Anionic bridged bis(amidinate) lithium lanthanide complexes have been found to be efficient catalysts for the amidation of aldehydes with amines under mild conditions. The activity follows the order: yttrium Reaction of benzohydroximinoyl chlorides and ,-(trifluoromethyl)-acetylenic esters: Synthesis of regioisomeric (trifluoromethyl)-isoxazolecarboxylate esters and oxime addition productsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2003Bruce C. Hamper The triethylamine induced reaction of benzohydroximinoyl chlorides, precursors of nitrile oxides, with ,-trifluoromethylacetylenic esters gives rise to three products: 5-trifluoromethyl-4-isoxozolecarboxylate esters, regioisomeric 4-trifluoromethyl-5-isoxazolecarboxylate esters and an unexpected oxime 1,4-addition adduct. Product distribution is rationalized in terms of two competing reaction modes, either 1,4 addition of the oxime anion to the acetylenic ester or formation of the nitrile oxide followed by 1,3-dipolar cycloaddi-tion. Anionic 1,4-addition of the oximinoyl chloride to the acetylenic ester is preferred at low temperatures, while nitrile oxide formation followed by cycloaddition is preferred at temperatures above 0 °C. Regioisomeric products from addition of nitrile oxides to various perfluoroalkylacetylenes are compared and assigned by 13C NMR. [source] Study of the solubilization of gliclazide by aqueous micellar solutionsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2003Khouloud A. Alkhamis Abstract It was of interest to increase the solubility of gliclazide in aqueous media. Therefore, solubilization of gliclazide in a variety of surfactants was investigated. Anionic and cationic surfactants exhibited dramatic solubilizing ability for gliclazide, whereas nonionic surfactants showed significantly lower solubilizing ability. It was found that gliclazide solubility increases with increasing the carbon chain length of cationic surfactants and decreases with increasing the carbon chain length of anionic surfactants. The solubilization data were analyzed on the basis of a pseudo-phase model with gliclazide exhibiting moderate partition coefficients into the micellar phase. The possible sites of solubilization of gliclazide in the micelle were examined by studying the effect of NaCl on solubilization and by comparing the absorption spectra of gliclazide in different solvents. The results obtained from these two experiments indicated that gliclazide is solubilized mainly in the inner core of the cationic surfactant micelles and in the outer regions of the anionic surfactant micelles. © 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:839,846, 2003 [source] Synthesis of Polystyrene- block -Poly(methyl methacrylate) with Fluorene at the Junction: Sequential Anionic and Controlled Radical Polymerization from a Single CarbonMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2009Nathan D. Contrella Abstract Polystyrene- block -poly(methyl methacrylate) (PS- b -PMMA) has been synthesized by sequential anionic and reverse atom transfer radical polymerization (ATRP) or a variation of nitroxide mediated polymerization (NMP) from a single initiating site, specifically the 9-carbon on 2,7-dibromofluorene or fluorene. The addition of the second arm (PS) relied on thermal decomposition of 2,2,-azoisobutyronitrile (AIBN) to generate radicals, abstracting the 9-H on the polymer-bound fluorene species to form the initiating radical. Styrene was not present in the reaction mixture when AIBN was decomposed, preventing competition between addition across the monomeric alkene and hydrogen abstraction from the fluorene. After 1,h, styrene was introduced and mediation of the subsequent radical polymerization was achieved by the presence of CuCl2/ligand or TEMPO. Characterization of the diblock copolymers by gel permeation chromatography (GPC) revealed substantial shifts in number average molecular weight () values compared to the anionically prepared PMMA macroinitiator, while polydispersity indices (PDI's) remained relatively low (typically,<,1.5). Characterization by UV detection with GPC (at 310,nm) verified that the diblock polymer is chromophore-bound, which was further verified by UV-vis spectroscopy of the isolated diblock. [source] Anionic living polymerization of tert -Aminostyrenes and application of the polymers,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3-5 2003Kazunori Se Abstract Anionic living polymerization of tertiary aminostyrenes (tAS) that serve as chemical links between two polymers are studied and the applications of the polymers to reversible recording materials are summarized in this paper. For preparing well-defined polymers that have desired molecular weights and narrow molecular weight distributions by anionic living mechanism, three conditions are satisfied and the corresponding five experimental proofs are discussed using tAS as an example. The three poly(tertiary aminostyrene)s (PtAS) were prepared. The degree of quaternization of PtAS with n -butyl bromide could be controlled from 0 to 100%. The amino groups of PtAS were quaternized by p, p,-bis(chloromethyl)azobenzene (CAB) to prepare the cross-linked film and the network concentration was characterized by an equilibrium-swelling test. Photochemical isomerization of CAB incorporated in PtAS was investigated in order to prepare the reversible recording materials. Copyright © 2003 John Wiley & Sons, Ltd. [source] Anionic and ionic coordinative polymerization of ,-caprolactonePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2001Dr Cristina Stere Abstract The polymerization of ,-caprolactone initiated by two catalyst systems was studied: (1) carbazole-potassium in the presence of 18-crown-6 ether and (2) NdCl3/TBP/TIBA (neodymiumtrichloride/tri-n-butyl-phosphate/triisobutylaluminium) at the molar ratio 1/3/1. For both initiator systems conversion/time plots were determined and the polymers were characterized by IR, GPC and by 1H - and 13C,NMR spectroscopy. Polyesters with the highest molecular weight (Mn,44 000 g/mol) were obtained for the polymerizations initiated by the carbazole-potassium/18-crown-6 ether system. The features of the polymerization initiated by the carbazole-potassium/18-crown-6 ether system are discussed on the basis of a simple scheme. The nature of this polymerization is non-living. Copyright © 2000 John Wiley & Sons, Ltd. [source] ChemInform Abstract: Thermal N,H Bond Activation on Anionic and Cationic Platinum Clusters: Non-Predetermined Reaction Pathways Indicate Transitions to a Bulk Surface Reactivity.CHEMINFORM, Issue 46 2009Milan Oncak 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 of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Anionic, in situ Generation of Formaldehyde: A Very Useful and Versatile Tool in Synthesis.CHEMINFORM, Issue 31 2007Geoffrey Deguest 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] Water Soluble Cruciforms: Effect of Surfactants on FluorescenceCHEMISTRY - AN ASIAN JOURNAL, Issue 2 2009Juan Tolosa Dr. Abstract Brighten up! Adding surfactants to aqueous solutions of three different water-soluble cruciforms (XF) improves their fluorescence quantum yields. Additionally, changes are observed in the emission wavelength of the XF around the critical micelle concentration (cmc) of the surfactant. Three 1,4-bis-(aminostyryl)-2,5-bis(phenylethynyl) benzenes carrying four, six, or eight acetic acid units were investigated for their surfactochromicity. Anionic, cationic, and nonionic surfactants as well as a surfactant-like protein (bovine serum albumin, BSA) were added to buffered solutions of the XFs in water, causing,in most cases,the fluorescence quantum yield to increase significantly and a blue- or red-shifted emission to be observed. The addition of cationic (cetyltrimethylammonium bromide, CTAB) and neutral (Brij 35, TWEEN 20 and Triton X-100) surfactants to XFs causes a red shift in their emission at low or very low surfactant concentrations that we attribute to surfactant-induced excimer formation. The fluorescence quantum yield is in most cases a monotonous function of surfactant concentration. For the investigated ionic surfactants, the fluorescence quantum yield of the XFs does not change much after the critical micelle concentration (CMC) of the surface is reached. However, in the case of non-ionic surfactants, the fluorescence quantum yields of the XFs starts to increase after the CMC has been reached, suggesting that different effects are involved. [source] Comparative Studies of Tridentate Sulfur and Nitrogen-Containing Ligands as Ionophores for Construction of Cadmium Ion-Selective Membrane SensorsELECTROANALYSIS, Issue 11 2007Ashok, 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 SamplesELECTROANALYSIS, Issue 6 2007Rodrigo 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] Cationic and anionic lipid-based nanoparticles in CEC for protein separationELECTROPHORESIS, Issue 11 2010Christian 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] Comparison of the use of anionic and cationic surfactants for the separation of steroids based on MEKC and sweeping-MEKC modesELECTROPHORESIS, Issue 5-6 2006Hui-Ju Shen Abstract In attempts to improve the selectivity and sensitivity of steroid separation and to determine their migration order, a comparison of the use of anionic and cationic surfactants based on the MEKC and sweeping-MEKC modes was made. A mixture of six steroids (progesterone, 17-hydroxy progesterone, 11-deoxycortisol, corticosterone, cortisone, and cortisol) could be separated and detected by means of the CE/UV-absorption method. The order of migration time for these steroids was compared under various conditions, including acidic/alkaline buffers, anionic/cationic surfactants, and positive/negative applied voltage, causing the direction of the EOF and the migration of micelles to change. The major rules for generally predicting the migration order of steroids are summarized. The detection limits were significantly improved when the sweeping-MEKC mode was applied. [source] Chiral ion-exchange capillary electrochromatography of arylglycine amides with dextran sulfate as a pseudostationary phaseELECTROPHORESIS, Issue 4-5 2005Yi Chen Abstract A low-cost tunable chiral ion-exchange capillary electrochromatographic method has been developed for the separation of arylglycine amide racemic mixtures with dextran sulfate (DS) as an anionic and chiral pseudostationary phase and Tris-tartrate as a buffer system. The concentrations of DS and Tris had opposite influences on retention and resolution and could serve as ideal factors to finely tune the running speed and chiral resolution. Tartrate and pH largely impact the separation but pH should be confined within 3.0,5.5, only suitable for coarse tuning, while tartrate was preserved as the key buffering reagent, normally maintained at 40 mmol/L. With a working system composed of 0.1,1.0% DS, 20,60 mmol/L Tris, and 40 mmol/L tartrate at pH 3.50,4.50, the enantioresolution of arylglycine amides was shown to be dependent on their chemical structure: The chiral resolution increased when the hydrogen at the ,-amino group or at the p -position of phenyl ring was replaced by other larger group(s) but the resolution decreased when the group at the o- or m- site on the phenyl ring was enlarged. Further, the electronegative substitute of -Cl had larger resolution increment than methyl or methoxy at the position p- of phenyl ring but much lower increment at position m- . It is possible to well explain the resolution variation phenomenon by considering the group resistance and the variation of hydrogen-bonds formed inside the amino amides and between the solutes and DS. The amido group was shown irreplaceable to have chiral resolution with DS alone as an ionic and chiral pseudostationary phase. [source] Dual injection capillary electrophoresis: Foundations and applicationsELECTROPHORESIS, Issue 23-24 2004Feliciano 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 modelsELECTROPHORESIS, Issue 1 2004Valérie 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] Investigation of an onsite wastewater treatment system in sandy soil: Site characterization and fate of anionic and nonionic surfactantsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2002Allen M. Nielsen Abstract This study reports on the fate of linear alkylbenzene sulfonate (LAS), alcohol ethoxylate (AE), and alcohol ether sulfate (AES) surfactants in a home septic system near Jacksonville (FL, USA) that has been used since 1976. The drainfield at this site resides in fine sand (<6% silt and clay) with an unsaturated zone that ranges from 0 to 1.3 m. During the wettest times of the year, it is likely that effluent from the septic system passes directly into the groundwater without exposure to an unsaturated zone of soil. Groundwater was collected during two sampling events, representing seasonal high and low groundwater table levels, and analyzed for the surfactants LAS, AES, and AE. During the wet season, the unsaturated zone was approximately 0.01 m beneath the drainfield. During the dry season, the unsaturated zone was about 0.4 m below the drainfield. Alcohol ethoxylate was not detected in any groundwater samples during either sampling. Alcohol ether sulfate was not found in the dry season sampling, but traces of AES had migrated downgradient about 4.7 m horizontally and 1.8 m vertically in the wet season. Linear alkylbenzene sulfonate was detected in some dry season samples and had moved downgradient some 11.7 m horizontally and 3.7 m vertically in the wet season. These observations demonstrate that these surfactants were removed to a great extent; otherwise, they would have traveled more than 260 m downgradient, which is the calculated distance that a conservative tracer like bromide would have moved downgradient over the life of the system. The most likely removal mechanisms for these surfactants were biodegradation and sorption. Therefore, this study indicates that LAS, AE, and AES are readily removed from groundwater in soils below septic system drainfields even in situations with minimal unsaturated soil zones. [source] Bis(salicylaldiminato)titanium Complexes Containing Bulky Imine Substituents: Synthesis, Characterization and Ethene Polymerization StudiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2005Antti Pärssinen Abstract A series of titanium complexes bearing two anionic [N, O,] bidentate salicylaldiminato ligands, namely bis[(N -salicylidene)anilinato]titanium(IV) dichloride (1), bis[(N -salicylidene)-2,6-dimethylanilinato]titanium(IV) dichloride (2), bis[(N -salicylidene)-2,6-di- i - propylanilinato]titanium(IV) dichloride (3), bis[(N -salicylidene)-(1-naphthalenylimino)]titanium(IV) dichloride (4), bis[(N -salicylidene)-2,6-difluoroanilinato]titanium(IV) dichloride (5), and bis[(N -3-fluorosalicylidene)-2,6-difluoroanilinato]titanium(IV) dichloride (6) have been synthesized with good yields by a two-step procedure. The X-ray structure analysis reveals that in complex 2, titanium has a distorted octahedral coordination sphere in which the oxygen atoms and the chloride ligands form the basal plane. Both the chloride and the phenoxy moieties have a cis orientation and the angle between the chloride ligands is 93.05°. The imine nitrogen atoms complete the octahedral coordination of the Ti center by occupying the axial positions. The newly synthesized (2 and 4,6) and already known complexes (1 and 3) were introduced in detailed ethene-polymerization studies. The activities achieved were low to moderate depending on the size and nature of the imino substituents. The polyethenes (PEs) produced had high molar masses, and the modalities of the molecular weight distributions varyied with polymerization temperature. Based on the results of ab initio calculations and on the experimental data obtained, an explanation for uni- and bimodal polymerization behavior and the differences in catalytic activities are given. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Tetracyanoquinodimethanido Derivatives of (Terpyridine)- and (Phenanthroline)metal Complexes , Structural and Magnetic Studies of Radical-Ion SaltsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2005Cristina Alonso Abstract Several derivatives of formulae [M(terpy)2](TCNQ)2 or [M(terpy)2](TCNQ)3 (M = Ni, Cu, Zn; terpy = 2,2,:6,,2"-terpyridine; TCNQ= 7,7,8,8-tetracyanoquinodimethane) and [M(phen)3](TCNQ)2 or [M(phen)3](TCNQ)4 (M = Fe, Ni; phen = 1,10-phenanthroline) have been obtained. The crystal structures of [M(terpy)2](TCNQ)2 (M = Ni, Cu) show that the metal is surrounded by the terpyridine nitrogen atoms in a closed octahedral environment and the TCNQ anions are dimerised by , overlap. The cationic [M(terpy)2]2+ and the anionic [TCNQ]22, groups alternate in the crystal. For the derivatives with three TCNQ groups, the existence of a stack of trimeric [TCNQ]32, ions having electronic delocalisation is proposed. The compound [Fe(phen)3](TCNQ)2, which shows a strong interaction between TCNQ anions, led to the formation of a , bond in the diamagnetic species [TCNQ,TCNQ], while the nickel analogue is expected to have a localised structure formed by alternation of cationic metal complexes and dimeric [TCNQ]22, anions similar to those observed in the analogous terpy derivatives. The derivatives having four TCNQ groups also show electronic delocalisation and a 1D stack based on the magnetic data is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Iminohydroxamato Early and Late Transition Metal Halide Complexes , New Precatalysts for Aluminoxane-Cocatalyzed Olefin Insertion PolymerizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Alexander Krajete Abstract We report on new families of non-metallocene metal precatalysts for olefin polymerization with titanium, zirconium, vanadium and nickel as the active metal sites. The novel ligand design concept is based on iminohydroxamic acids and their derivatives as the principal chelating units. Various anionic and neutral [N,O] and [N,N] ligand systems are easily accessible by a modular synthetic sequence of imidoyl chlorides with substituted hydroxylamines or hydrazines, respectively. Steric protection of the metal coordination site, a necessary requirement for suppression of chain termination pathways of non-metallocene catalysts, is brought about by bulky aryl substituents on the imino nitrogen atoms. Crystal structures of some of the hydroxamato ligands reveal interesting intermolecular hydrogen-bridged structures, whereas in the solid-state structure of one titanium precatalyst a five-membered chelate was observed, in line with the design principle of these systems. Preliminary ethylene polymerization studies with methylaluminoxane-activated metal complexes (M = Ti, Zr, V, Ni) show that the most active systems are [N,O]NiBr2 catalysts containing neutral O -alkyl iminohydroxamate ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Structural requirements for the apical sorting of human multidrug resistance protein 2 (ABCC2)FEBS JOURNAL, Issue 7 2002Anne T. Nies The human multidrug resistance protein 2 (MRP2, symbol ABCC2) is a polytopic membrane glycoprotein of 1545 amino acids which exports anionic conjugates across the apical membrane of polarized cells. A chimeric protein composed of C-proximal MRP2 and N-proximal MRP1 localized to the apical membrane of polarized Madin,Darby canine kidney cells (MDCKII) indicating involvement of the carboxy-proximal part of human MRP2 in apical sorting. When compared to other MRP family members, MRP2 has a seven-amino-acid extension at its C-terminus with the last three amino acids (TKF) comprising a PDZ-interacting motif. In order to analyze whether this extension is required for apical sorting of MRP2, we generated MRP2 constructs mutated and stepwise truncated at their C-termini. These constructs were fused via their N-termini to green fluorescent protein (GFP) and were transiently transfected into polarized, liver-derived human HepG2 cells. Quantitative analysis showed that full-length GFP,MRP2 was localized to the apical membrane in 73% of transfected, polarized cells, whereas it remained on intracellular membranes in 27% of cells. Removal of the C-terminal TKF peptide and stepwise deletion of up to 11 amino acids did not change this predominant apical distribution. However, apical localization was largely impaired when GFP,MRP2 was C-terminally truncated by 15 or more amino acids. Thus, neither the PDZ-interacting TKF motif nor the full seven-amino-acid extension were necessary for apical sorting of MRP2. Instead, our data indicate that a deletion of at least 15 C-terminal amino acids impairs the localization of MRP2 to the apical membrane of polarized cells. [source] pH-Responsive Flower-Type Micelles Formed by a Biotinylated Poly(2-vinylpyridine)- block -poly(ethylene oxide)- block -poly(, -caprolactone) Triblock CopolymerADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Kathy Van Butsele Abstract In the present work, a method is proposed to assemble pH-responsive, flower-like micelles that can expose a targeting unit at their periphery upon a decrease in pH. The micelles are composed of a novel biotinylated triblock copolymer of poly(,, -caprolactone)- block -poly(ethylene oxide)- block -poly(2-vinylpyridine) (PCL- b -PEO- b -P2VP) and the non-biotinylated analogue. The block copolymers are synthesized by sequential anionic and ring-opening polymerization. The pH-dependent micellization behaviour in aqueous solution of the triblock copolymers developed is studied using dynamic light scattering, zeta potential, transmission electron microscopy (TEM), and fluorimetric measurements. The shielding of the biotin at neutral pH and their availability at the micelle surface upon protonation is established by TEM and surface plasmon resonance with avidin and streptavidin-coated gold surfaces. The preliminary stealthy behavior of these pH-responsive micelles is examined using the complement activation (CH50) test. [source] Self-Organized Single-Walled Carbon Nanotube Conducting Thin Films with Honeycomb Structures on Flexible Plastic FilmsADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Nobuo Wakamatsu Abstract Complex 1, synthesized from anionic shortened single-walled carbon nanotubes and cationic ammonium lipid dissolved in organic solvents, is cast on pretreated transparent flexible poly(ethylene terephthalate) (PET) films under a higher relative humidity to form thin films with self-organized honeycomb structures. The cell sizes are controllable by changing the experimental conditions. The lipid, which is the cationic part of complex 1, is easily removed by a simple ion-exchange method, while maintaining the basic honeycomb structures. After the ion exchange, the nanotube honeycomb films on PET with thinner skeletons exhibit a dramatic decrease in the surface resistivity from insulating to conducting. Carbon nanotubes with honeycomb structures formed by the self-organization on flexible polymer films are useful in many areas of nanoscience and technology including nanomaterials, nanoelectronics, nanodevices, catalysts, sensors, and so on. [source] A Highly Sensitive Hybrid Colorimetric and Fluorometric Molecular Probe for Cyanide Sensing Based on a Subphthalocyanine Dye,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2006E. Palomares Abstract A highly sensitive, selective colorimetric and fluorometric molecular probe based on a subphthalocyanine dye has been developed for cyanide-anion determination in aqueous solution. It has also been shown that a carboxysubphthalocyanine derivative can be covalently anchored to transparent mesoporous nanocrystalline high-surface-area metal oxide films to detect low concentrations of cyanide anion in pure water with no interference from other anionic or cationic species. [source] Effect of self-assemblies of various surfactants in their single and mixed states on the BZ oscillatory reactionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2010Muzaffar Hussain Najar Micelles of different surfactants are well known to affect chemical equilibria and reactivities by selectively sequestering the reagent substrates through electrostatic and hydrophobic interactions. In this article, the effects of micelles of various surfactants on different parameters of the Ce(IV)-catalyzed Belousov,Zhabotinsky (BZ) oscillatory reaction at 35°C in nonstirred closed conditions are studied by employing spectrophotometry and tensiometry. Surfactants used in this study are the cationics hexadecyltrimethylammonium bromide (CTAB) and pentamethylene-1,5-bis(N -hexadecyl- N,N -dimethylammonium)bromide gemini (Gemini), anionic sodium dodecylbenzene sulfonate (SDBS), and nonionic Brij58, whereas the binary surfactant systems used are cationic,nonionic CTAB+Brij58 and anionic,nonionic SDBS+Brij58. The results revealed that the induction period shows a definite variation with increasing concentration of different surfactants above their critical micelle concentration (cmc). The amplitudes of oscillation and absorbance maxima and minima are enhanced in the presence of micelles of CTAB and Gemini surfactants, whereas micelles of SDBS and Brij58 have almost no effect on the nature of the oscillations. However, mixed micelles of CTAB+Brij58 and SDBS+Brij58 binary mixtures show a quite different effect on the overall behavior of the oscillations. The enhanced effect of CTAB and Gemini surfactants on the overall nature of oscillations has been attributed to the positive charge on the surface of their micelles and to some extent on the presence of nitrogen in their head group. The effect of mixed binary micelles may be attributed to their synergistic nature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 659,668, 2010 [source] The ,-effect in micelles: Nucleophilic substitution reaction of p -nitrophenyl acetate with N -phenylbenzohydroxamate ion,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2006Kallol K. Ghosh Pseudo-first-order rate constants have been determined for the nucleophilic substitution reactions of p -nitrophenyl acetate with p -chlorophenoxide (4-ClC6H4O,) and N -phenylbenzohydroxamate (C6H5CON(C6H5)O,) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij-35) surfactants has been studied. The kobs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and ,-effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26,31, 2006 [source] Targeted delivery of salicylic acid from acne treatment products into and through skin: role of solution and ingredient properties and relationships to irritationINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 4 2004L. Rhein Salicylic acid (SA) is a beta-hydroxy acid and has multifunctional uses in the treatment of various diseases in skin such as acne, psoriasis, and photoaging. One problem often cited as associated with salicylic acid is that it can be quite irritating at pH 3,4, where it exhibits the highest activity in the treatment of skin diseases. We have identified strategies to control the irritation potential of salicylic acid formulations and have focused on hydroalcoholic solutions used in acne wipes. One strategy is to control the penetration of SA into the skin. Penetration of the drug into various layers of skin, i.e. epidermis, dermis, and receptor fluid, was measured using a modified Franz in vitro diffusion method after various exposure times up to 24 h. A polyurethane polymer (polyolprepolymer-15) was found to be an effective agent in controlling delivery of SA. In a dose-dependent fashion it targeted delivery of more SA to the epidermis as compared to penetration through the skin into the receptor fluid. It also reduced the rapid rate of permeation of a large dose of SA through the skin in the first few hours of exposure. A second strategy that proved successful was incorporation of known mild nonionic surfactants like isoceteth-20. These surfactants cleanse the skin, yet due to their inherent mildness (because of their reduced critical micelle concentration and monomer concentration), keep the barrier intact. Also, they reduce the rate of salicylic acid penetration, presumably through micellar entrapment (either in solution or on the skin surface after the alcohol evaporates). Cumulative irritation studies showed that targeting delivery of SA to the epidermis and reducing the rapid early rate of penetration of large amounts of drug through the skin resulted in a reduced irritation potential. In vivo irritation studies also showed that the surfactant system is the most important factor controlling irritancy. SA delivery is secondary, as formulations with less SA content reduced the rate of delivery to the receptor and yet were some of the most irritating formulations tested, presumably due to the action of the specific anionic surfactant on the barrier. Alcohol content also did not appreciably affect irritation and SA delivery; formulations with considerably low alcohol content but containing anionic versus nonionic surfactant systems exhibited considerably higher irritancy. Thus the surfactant type was again the predominant factor in those studies, although arguably alcohol plays some role (solubilization of SA). Results showed that both polymers and mild surfactants work in concert to provide the optimal formulation benefits of targeted delivery and reduced irritation. Synergistic relationships among hydroalcoholic formulation components will be discussed along with the mechanisms likely involved in controlling delivery of SA to skin. [source] Diffusion and distribution of element-labelled surfactants in human hairINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2004F.-J. Wortmann Synopsis To directly follow the diffusion process of cosmetically relevant agents into human hair, a specific methodological approach is presented and elucidated for selected surfactants. For this, practically relevant anionic and cationic surfactants were synthesized with a chlorine atom at the end of their alkyl chain. The property changes of the surfactants through the modification are corresponding to an extension of the alkyl chain by about two methylene groups, thus representing a moderate increase of hydrophobicity. After the application of a modified surfactant to hair, it can be localized and quantified through its chlorine atom in cross-sections by scanning electron microscopy combined with micro X-ray fluorescence analysis. The determination of the diffusion coefficient D is realized through the application of the Matano-equation to element intensity profiles. Values for D vary within the chosen range of pH and temperature between 10,14 and 10,16 m2 s,1. The diffusion coefficients for the anionic surfactants increase with decreasing pH and increasing temperature, The temperature dependence follows in all cases the Arrhenius relationship with activation energies EA of 50,100 kJ mol,1, which decrease with pH. The pH-related effects, with comparable values for D and EA, are opposite for the cationic surfactant. These observations are consistently interpreted on the basis of ionic and hydrophobic interactions in hair. Résumé Afin de suivre directement le processus de diffusion d'agents cosmétiques pertinents dans le cheveu humain, une approche méthodologique spécifique est présentée et approfondie pour des tensio actifs sélectionnés. En pratique, des tensio actifs pertinents, anioniques et cationiques ont été synthétisés en introduisant un atome de Chlore à l'extrémité de leur chaîne alkyle. Les changements de propriétés de ces tensio actifs, via cette modification, correspondent à un allongement de la chaîne alkyle d'environ deux groupes méthylène, représentant ainsi une augmentation modérée de leur caractère hydrophobe. Suite à l'application sur le cheveu d'un tensio actif modifié, il peut être localisé et quantifié par l'atome de Chlore dans des coupes transverses par microscopie électronique à balayage couplée à l'analyse par micro Fluorescence X. La détermination du coefficient de diffusion D est effectuée par l'application de l'équation de Matano aux profils de l'intensité de l'élément. Les valeurs de D varient, selon l'échelle de pH et de température, entre 10,14 et 10,16 m2 s,1. Les coefficients de diffusion pour les tensio actifs anioniques augmentent avec des pH décroissants et des températures croissantes. La dépendance vis à vis de la température suit, dans tous les cas, la relation d'Arrhenius avec des énergies d'activation EA de 50 à 100 kJ mol,1, qui décroît avec le pH. Les effets liés au pH, avec des valeurs comparables de D et EA, sont opposés pour le tensio actif cationique. Ces observations sont constamment interprétées par les interactions de types ioniques et hydrophobes dans le cheveu. [source] The arsenic clusters Asn (n = 1,5) and their anions: Structures, thermochemistry, and electron affinitiesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2004Yi Zhao Abstract The molecular structures, electron affinities, and dissociation energies of the Asn/As (n = 1,5) species have been examined using six density functional theory (DFT) methods. The basis set used in this work is of double-, plus polarization quality with additional diffuse s - and p -type functions, denoted DZP++. These methods have been carefully calibrated (Chem Rev 2002, 102, 231) for the prediction of electron affinities. The geometries are fully optimized with each DFT method independently. Three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The first dissociation energies De(Asn,1 -As) for the neutral Asn species, as well as those De(As -As) and De (Asn,1 -As,) for the anionic As species, have also been reported. The most reliable adiabatic electron affinities, obtained at the DZP++ BLYP level of theory, are 0.90 (As), 0.74 (As2), 1.30 (As3), 0.49 (As4), and 3.03 eV (As5), respectively. These EAad values for As, As2, and As4 are in good agreement with experiment (average absolute error 0.09 eV), but that for As3 is a bit smaller than the experimental value (1.45 ± 0.03 eV). The first dissociation energies for the neutral arsenic clusters predicted by the B3LYP method are 3.93 eV (As2), 2.04 eV (As3), 3.88 eV (As4), and 1.49 eV (As5). Compared with the available experimental dissociation energies for the neutral clusters, the theoretical predictions are excellent. Two dissociation limits are possible for the arsenic cluster anions. The atomic arsenic results are 3.91 eV (As , As, + As), 2.46 eV (As , As + As), 3.14 eV (As , As + As), and 4.01 eV (As , As + As). For dissociation to neutral arsenic clusters, the predicted dissociation energies are 2.43 eV (As , As2 + As,), 3.53 eV (As , As3 + As,), and 3.67 eV (As , As4 + As,). For the vibrational frequencies of the Asn series, the BP86 and B3LYP methods produce good results compared with the limited experiments, so the other predictions with these methods should be reliable. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 907,920, 2004 [source] Modified Gaussian-2 level investigation of the identity ion-pair SN2 reactions of lithium halide and methyl halide with inversion and retention mechanismsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2004Yi Ren Abstract Identity ion-pair SN2 reactions LiX + CH3X , XCH3 + LiX (X = F, Cl, Br, and I) have been investigated in the gas phase and in solution at the level of the modified Gaussian-2 theory. Two possible reaction mechanisms, inversion and retention, are discussed. The reaction barriers relative to the complexes for the inversion mechanism [,H(inv)] are found to be much higher than the corresponding values for the gas phase anionic SN2 reactions, decreasing in the following order: F (263.6 kJ mol,1) > Cl (203.3 kJ mol,1) > Br (174.7 kJ mol,1) > I (150.7 kJ mol,1). The barrier gaps between the two mechanisms [,H (ret) , ,H (inv)] increase in the order F (,62.7 kJ mol,1) < Cl (4.4 kJ mol,1) < Br (24.9 kJ mol,1) < I (45.1 kJ mol,1). Thus, the retention mechanism is energetically favorable for fluorine and the inversion mechanism is favored for other halogens, in contrast to the anionic SN2 reactions at carbon where the inversion reaction channel is much more favorable for all of the halogens. The stabilization energies for the dipole,dipole complexes CH3X · · · LiX (,Hcomp) are found to be similar for the entire set of systems with X = F, Cl, Br, and I, ranging from 53.4 kJ mol,1 for I up to 58.9 kJ mol,1 for F. The polarizable continuum model (PCM) has been used to evaluate the direct solvent effects on the energetics of the anionic and ion-pair SN2 reactions. The energetic profiles are found to be still double-well shaped for most of the ion-pair SN2 reactions in the solution, but the potential profile for reaction LiI + CH3I is predicted to be unimodal in the protic solvent. Good correlations between central barriers [,H (inv)] with the geometric looseness of the inversion transition state %C,X,, the dissociation energies of the C,X bond (DC,X) and Li,X bond (DLi,X) are observed, respectively. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 461,467, 2004 [source]
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