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Ammonium Ions (ammonium + ion)
Selected AbstractsPorous Capsules {(M)M5}12FeIII30 (M=MoVI, WVI): Sphere Surface Supramolecular Chemistry with 20 Ammonium Ions, Related Solution Properties, and Tuning of Magnetic Exchange Interactions,ANGEWANDTE CHEMIE, Issue 3 2010Maria Todea Dr. Eine Vielfalt von Wasserstoffbrücken-Bindungsoptionen auf einer hochfunktionalisierten Kapseloberfläche mit 20 kronenetherartigen Poren ermöglicht die Fixierung/Erkennung von 20 Ammoniumionen (siehe Bild; W grün, Fe orange, O rot, N blau, H hellgrau), die in Lösung zum Teil abgegeben werden, und zwar unter Bildung entsprechender Gleichgewichte. [source] Supramolecular Chemistry on a Cluster Surface: Fixation/Complexation of Potassium and Ammonium Ions with Crown-Ether-Like Rings,ANGEWANDTE CHEMIE, Issue 32 2009Achim Müller Prof. Gemeinsam und doch getrennt: Auf einer hochnucleophilen Clusteroberfläche lassen sich Ammonium- und Kaliumionen selektiv komplexieren und trennen. Sechs {Mo4VKO6}-Ringe mit einer Kronenether-artigen Funktionalität (siehe Bild; Mo,blau, V,grün, K,violett, O,rot) in den Löchern des untersuchten Clusterkomplexes fixieren sechs Ammoniumionen (N,orange, H,gelb). [source] ChemInform Abstract: Porous Capsules {(M)M5}12FeIII30 (M: MoVI, WVI): Sphere Surface Supramolecular Chemistry with 20 Ammonium Ions, Related Solution Properties, and Tuning of Magnetic Exchange Interactions.CHEMINFORM, Issue 15 2010Achim Mueller 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] ChemInform Abstract: Supramolecular Chemistry on a Cluster Surface: Fixation/Complexation of Potassium and Ammonium Ions with Crown-Ether-Like Rings.CHEMINFORM, Issue 41 2009Achim Mueller 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] New enzymatic assay for serum urea nitrogen using urea amidolyaseJOURNAL OF CLINICAL LABORATORY ANALYSIS, Issue 2 2003Shigeki Kimura Abstract We established an enzymatic assay for measurement of serum urea nitrogen using urea amidolyase (EC 3.5.1.45) from yeast species. The method is based on hydrolysis of urea by the enzyme. In this assay, we eliminated endogenous ammonium ion by use of glutamate dehydrogenase (EC 1.4.1.4). Then in the presence of urea amido-lyase, ATP, bicarbonate, magnesium, and potassium ions, ammonium ion was produced proportionally to urea concentration in serum. The concentra-tion of ammonium ion formed was determined by adding GLDH to produce NADP+ in the presence of 2-oxoglutarate and NADPH. We then monitored the change of absorbance at 340 nm. The inhibitory effect of calcium ion on this assay was eliminated by adding glyco-letherdiamine-N, N, N,, N,-tetraacetic acid to the reaction system. The with-in-assay coefficient of variations (CVs) of the present method were 1.80,3.76% (n = 10) at 2.8,19.0 mmol/L, respectively. The day-to-day CVs were 2.23,4.59%. Analytical recovery was 92,115%. The presence of ascorbic acid, bilirubin, hemoglobin, lipemic material, ammo-nium ion, or calcium ion did not affect this assay system. The correlation be-tween values obtained with the present method (y) and those by another enzy-matic method (x) was 0.997 (y = 1.02x , 0.10 mmol/L, Sy/x = 0.841, n = 100), with a mean difference of ,0.18 ± 0.86 mmol/L [(values by reference method , that of present method) ± SD] using the Bland-Altman technique. J. Clin. Lab. Anal. 17:52,56, 2003. © 2003 Wiley-Liss, Inc. [source] Self-assembly of daisy chain oligomers from heteroditopic molecules containing secondary ammonium ion and crown ether moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2010Harry W. Gibson Abstract MALDI-TOF MS of the heteroditopic compound 2 -(benzylammoniomethyl)dibenzo-24-crown-8 hexafluorophosphate (4) revealed oligomeric "daisy chain" species up to the hexamer. Similar results were obtained for 2-(6,-hydroxyhexylammoniomethyl)dibenzo-24-crown-8 hexafluorophosphate (8). The complexations of two substituted dibenzylammonium salts, 2,2,-dimethyldibenzylammonium hexaflurophosphate (9a) and 2,2,,5-trimethoxydibenzylammonium hexafluorophosphate (9b), with dibenzo-24-crown-8 were examined as models for slippage systems; association constants are reported for these systems. A crystal structure is reported for the new dimethylbenzylammonoium pseudorotaxane. The trimethoxy analog is shown to be capable of slippage formation of a rotaxane, albeit in low yield. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 975,985, 2010 [source] Preparation of poly(lactic acid)/poly(ethylene glycol)/organoclay nanocomposites by melt compoundingPOLYMER COMPOSITES, Issue 3 2006Shuichi Tanoue Poly(lactic acid) (PLA)/organoclay nanocomposites were prepared by melt compounding in a co-rotating twin screw extruder. Two types of commercialized organoclay (dimethyl benzyl stearyl ammonium ion and dimethyl distearyl ammonium ion intercalated between clay platelets named as Clay A and Clay B, respectively) and two grades of poly(ethylene glycol) (PEG) with different molecular weight (Mw = 2,000 and 300,000,500,000 named as PEG2k and PEG500k, respectively) were used in this study. The Young's modulus improved by the addition of organoclay to PLA matrix. The Young's modulus decreased with the addition of PEG to PLA/organoclay nanocomposites. The tensile strength and elongation of PLA/Clay B nanocomposites increased with the addition of PEG2k. The effect of the addition of PEG on d -spacing of PLA/organoclay nanocomposites is dependent upon the kind of organoclay. The sizes of clay agglomerations in PLA/PEG/organoclay nanocomposites are larger than those of PLA/organoclay ones in the same organoclay. Addition of PEG to PLA/organoclay nanocomposites during melt compounding will not be useful for the preparation of PLA/organoclay having fully exfoliated clay platelets. The shear thinning properties of the nanocomposites are independent of the addition of PEG. On the whole, PEG2k is good plasticizer for PLA/organoclay nanocomposites. POLYM. COMPOS. 27:256,263, 2006. © 2006 Society of Plastics Engineers [source] Semi-automated quantification of ivermectin in rat and human plasma using protein precipitation and filtration with liquid chromatography/tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2004Tony Pereira Ivermectin is a parasiticide commonly used in humans and livestock. It is currently under development for the treatment of pediculosis of humans (head lice) that does not respond to established treatments. A liquid chromatography/turbo ion spray tandem mass spectrometry (LC/TIS-MS/MS) method for the determination of ivermectin in rat and human plasma has been developed that uses emamectin [4,-epi-(methylamino)-4,-deoxyavermectin] as the internal standard. Sample preparation involved protein precipitation and filtration of fortified plasma in the 96-well format. Chromatographic separation was accomplished using fast gradient conditions on a C8 stationary phase. The analytes were detected with the mass spectrometer operated in the positive ion, multiple reaction monitoring mode. The method exhibited good intra- and interday accuracy and precision, and was linear over a dynamic range of 1,2000,ng/mL. In rat plasma, intraday accuracy ranged between 84,93% for the low quality control (QC) sample (1.5 ng/mL), and between 91,109% for the remaining QCs. Intraday precision ranged between 4.9,15% for the low QC, and 0.8,6.3% for the remaining QCs. Interday accuracy ranged between 88,107%, and precision between 4.1,11%. Similar data was obtained using human plasma. An investigation of matrix effects indicated that the ionization efficiency of ivermectin was favored by the presence of an ammonium ion in an aqueous environment. The implications of this observation toward assay sensitivity are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Crystallization and preliminary crystallographic characterization of glutamine synthetase from Medicago truncatulaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2009Ana Rita Seabra The condensation of ammonium and glutamate into glutamine catalyzed by glutamine synthetase (GS) is a fundamental step in nitrogen metabolism in all kingdoms of life. In plants, this is preceded by the reduction of inorganic nitrogen to an ammonium ion and therefore effectively articulates nitrogen fixation and metabolism. Although the three-dimensional structure of the dodecameric bacterial GS was determined quite some time ago, the quaternary architecture of the plant enzyme has long been assumed to be octameric, mostly on the basis of low-resolution electron-microscopy studies. Recently, the crystallographic structure of a monocotyledonous plant GS was reported that revealed a homodecameric organization. In order to unambiguously establish the quaternary architecture of GS from dicotyledonous plants, GS1a from the model legume Medicago truncatula was overexpressed, purified and crystallized. The collection of synchrotron diffraction data to 2.35,Å resolution allowed the determination of the three-dimensional structure of this enzyme by molecular replacement. [source] Metabolism of PER.C6TM cells cultivated under fed-batch conditions at low glucose and glutamine levelsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2006Luis Maranga Abstract This is the first study to examine PER.C6TM cell glucose/energy and glutamine metabolism with fed-batch cultures at controlled low glutamine, low glucose, and simultaneous low glucose and low glutamine levels. PER.C6TM cell metabolism was investigated in serum-free suspension bioreactors at two-liter scale. Control of glucose and/or glutamine concentrations had a significant effect on cellular metabolism leading to an increased efficiency of nutrient utilization, altered byproduct synthesis, while having no effect on cell growth rate. Cultivating cells at a controlled glutamine concentration of 0.25 mM reduced qGln and q by approximately 30%, qAla 85%, and qNEAA 50%. The fed-batch control of glutamine also reduced the overall accumulation of ammonium ion by approximately 50% by minimizing the spontaneous chemical degradation of glutamine. No major impact upon glucose/energy metabolism was observed. Cultivating cells at a glucose concentration of 0.5 mM reduced qGlc about 50% and eliminated lactate accumulation. Cells exhibited a fully oxidative metabolism with Y of approximately 6 mol/mol. However, despite no increase in qGln, an increased ammonium ion accumulation and Y were also observed. Effective control of lactate and ammonium ion accumulation by PER.C6TM cells was achieved using fed-batch with simultaneously controlled glucose and glutamine. A fully oxidative glucose metabolism and a complete elimination of lactate production were obtained. The qGln value was again reduced and, despite an increased q compared with batch culture, ammonium ion levels were typically lower than corresponding ones in batch cultures, and the accumulation of non-essential amino acids (NEAA) was reduced about 50%. In conclusion, this study shows that PER.C6TM cell metabolism can be confined to a state with improved efficiencies of nutrient utilization by cultivating cells in fed-batch at millimolar controlled levels of glucose and glutamine. In addition, PER.C6TM cells fall into a minority category of mammalian cell lines for which glutamine plays a minor role in energy metabolism. © 2006 Wiley Periodicals, Inc. [source] Dependence of Apparent Viscosity on Mycelial Morphology of Streptomyces fradiae Culture in Various Nitrogen SourcesBIOTECHNOLOGY PROGRESS, Issue 4 2000Du Bok Choi To examine what causes increased viscosity in culture broth in Streptomyces fradiae culture, various natural nitrogen sources were investigated. Extracellular protease activity increased with culture time and decomposed the natural nitrogen source into amino acids. In the case of gluten meal, after a culture time of 5 d, concentrations of glutamic acid and aspartic acid had increased to 600 and 200 mg/L, respectively, which were about 3- and 2-fold as high as levels in cultures under similar conditions using Pharmamedia. For various amino acids tested, the addition of glutamic acid or aspartic acid mixture to the culture medium raised the apparent viscosity to its highest demonstrated value, 260 mPa·s after 5 d of culture, which was 3-fold higher than without amino acids. Consumption of the decomposed glutamic acid and aspartic acid was dependent on the activities of glutamate dehydrogenase and aspartate aminotransferase, respectively. When ammonium ion was used as the nitrogen source, cell concentration reached 1.75 g/L measured as an intracellular nucleic acid concentration,which was about 2.3-fold higher than that with any other natural nitrogen source. However, apparent viscosity was only 75 mPa·s, a value one-third that of the amino acid mixture, and 70% of the pellets were bigger than 1.2 × 104 ,m2. In the case of gluten meal or the amino acid mixture, pellets bigger than 1.2 × 104 ,m2 comprised only 8%. This demonstrates that consumption of some amino acids affected the formation of filamentous morphology, which caused an increase in the apparent viscosity of the culture broth, and the apparent viscosity was not caused by the mycelial concentration but the mycelial morphology. [source] The Synthesis and Characterization of all Diastereomers of a Linear Symmetrically Fused Tris-Tröger's Base Analogue: New Chiral Cleft CompoundsCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2006Josep Artacho Abstract The synthesis and characterization of all diastereomers of a linear symmetrically fused tris-Tröger's base analogue are described. The diastereomers are unambiguously assigned as syn,anti1,a, anti,anti1,b, and syn,syn1,c isomers, by using X-ray diffraction analysis and NMR spectroscopy. For the first time, the anti,anti and the syn,syn diastereomers of a linear symmetrically fused tris-Tröger's base analogue have been synthesized. Molecules 1,a and 1,c are new cleft compounds and analysis of compound 1,a in the solid state shows inclusion of one molecule of CH2Cl2 in the larger aromatic cleft, whereas in isomer 1,c disordered solvent molecules are trapped in the extended aromatic cleft. Furthermore, in the solid state, isomer 1,c forms infinite open channels along one of the crystallographic axes and perpendicular to this axis there are infinitely extending "wedged-ravines". Importantly, each of the diastereomers 1,a,c is resistant to inversion at the stereogenic nitrogen atoms under strongly and weakly acidic conditions in the range from room temperature (RT) to 95,°C. This observed configurational stability at the stereogenic nitrogens of 1,a,c is unique for analogues of Tröger's base in general to date. Finally, the ratio of cleft compounds 1,a and 1,c significantly increased relative to cavity compound 1,b when ammonium chloride was used as an additive in the Tröger's base condensation to 1,a,c suggesting a templating effect of the ammonium ion. [source] DNA Topoisomerase I Inhibitory Alkaloids from Corydalis saxicolaCHEMISTRY & BIODIVERSITY, Issue 7 2008Xuanxuan Cheng Abstract Chemical studies of the Chinese herb Corydalis saxicolaBunting led to the isolation and identification of 14 alkaloids, 1,14. Seven of these compounds, 4,9 and 11, were obtained from this plant for the first time. Feruloylagmatine (7) is the first guanidine-type alkaloid to be identified in the family Papaveraceae and in dicotyledonous plants. All of the isolated compounds were assayed for inhibitory activity against human DNA topoisomerase I. A DNA cleavage assay demonstrated that these alkaloids specifically inhibit topoisomerase through stabilization of the enzyme,DNA complex. Among the isolated alkaloids, (,)-pallidine (8) and (,)-scoulerine (11) showed strong inhibitory activities toward topoisomerase I that were comparable to camptothecin, a typical topoisomerase I inhibitor. A preliminary structure,activity relationship study suggested that the quaternary ammonium ion might play an important role in topoisomerase I inhibition by the isoquinoline alkaloids. These data indicated that DNA topoisomerase I inhibition represents probably one of the anticarcinogenic mechanisms of C. saxicola. [source] Low temperature powder diffraction and DFT solid state computational study of hydrogen bonding in NH4VO3CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2009. Smr Abstract The crystal structure of NH4VO3 was refined by the geometry optimization done by total energy minimization in solid state using DFT/plane waves approach. The lattice parameters were derived by the Le Bail technique from the low temperature X-ray (40-293 K) and synchrotron (100-293 K) powder diffraction data. The structure is formed by the infinite chains of irregular VO4 tetrahedra running approximately parallel to the c -axis, which are interlinked by the ammonium ions placed between them. The ammonium ions link to the [VO4], chains through one linear, one bifurcated and two trifurcated N-H,O hydrogen bonds. Considering their stability there are six distinct N-H,O hydrogen bonds: two strong with the N-H,O bond angles close to the straight, two medium with the bond angles of 123° and 148° and two very bent (105° and 107°) and hence weak hydrogen bonds. There is a reasonable agreement between the energies of the stretching ,(NH) modes estimated using the optimised N,O contact distances and those obtained experimentally. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Estimation of net nitrogen flux between the atmosphere and a semi-natural grassland ecosystem in HungaryEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2010A. Machon The aim of this work is to estimate the net N balance (deposition , emission) between the atmosphere and a semi-arid, semi-natural grassland (Bugac station, Central Hungary, CarboEurope IP, NitroEurope IP level 3 site). Dry deposition of N compounds has been determined by the inferential method, based on continuous monitoring of NO2 gas and daily 24-hour concentration measurements of HNO3 vapour, NH3 gas, and NH4+ and NO3, particles, using dry deposition velocities from the literature, measured above surfaces with the same characteristics as Bugac station. The bi-directional flux of NH3 within the atmosphere and the canopy (excluding soil emission) has also been estimated by the inferential method. Wet deposition of nitrate and ammonium ions was calculated on the basis of daily precipitation sampling and concentration measurements of nitrate and ammonium ions. To estimate the soil-atmosphere exchange of different gaseous N forms (N2, NO, N2O, NH3), the DNDC model was used as validated by the chamber measurements of NO and N2O soil emission fluxes. Soil emissions of NO and N2O have been determined by dynamic and static soil chamber methods, respectively. The measurement and modelling activity covers a complete year. Using the measured and modelled data, the calculated N balance at Bugac station between August 2006 and July 2007 is estimated at ,8.8 kg N ha,1 year,1 (deposition) as a sum of the deposition and emission terms (,10.4 and 1.6 kg N ha,1 year,1, respectively). Due to the warm and dry weather during the examined period, wet fluxes were substantially lower than usual, which may also have altered the regular yearly course of dry deposition and emission. [source] A new molecular tool for transgenic diatomsFEBS JOURNAL, Issue 13 2005Control of mRNA, protein biosynthesis by an inducible promoter, terminator cassette Research in diatom biology has entered the postgenomic era since the recent completion of the Thalassiosira pseudonana genome project. However, the molecular tools available for genetic manipulation of diatoms are still sparse, impeding the functional analysis of diatom genes in vivo. Here we describe the first method for inducible gene expression in transgenic diatoms. This method uses a DNA cassette containing both promoter (Pnr) and terminator (Tnr) elements derived from the nitrate reductase gene of the diatom Cylindrotheca fusiformis. By using green fluorescent protein (gfp) cDNA as a reporter gene, it is demonstrated that gene expression under the control of the Pnr/Tnr cassette is switched off when cells are grown in the presence of ammonium ions and becomes switched on within 4 h when cells are transferred to medium containing nitrate. Incubating cells in nitrogen-free medium switches on transcription of the gfp gene, yet gfp mRNA does not become translated into protein. This block on translation is released by the addition of nitrate, resulting in rapid onset of GFP production with a drastically reduced delay time of only 1 h. Altogether we have demonstrated that the Pnr/Tnr cassette enables inducible gene expression and control of both the level and timing of mRNA and protein expression in transgenic diatoms. [source] Fluorescence Regeneration as a Signaling Principle for Choline and Carnitine Binding: A Refined Supramolecular Sensor System Based on a Fluorescent Azoalkane,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2006H. Bakirci Abstract The fluorescent azoalkane, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), forms inclusion complexes with p -sulfonatocalix[4]arene (CX4). The binding constants are on the order of 103,M,1 in water. The addition of CX4 to DBO solutions results in an efficient fluorescence quenching (up to 90,%). This supramolecular system can be used as a truly water-soluble sensor system to signal the binding of organic ammonium ions over a large pH range. Addition of choline and carnitine derivatives and tetraalkylammonium ions results in regeneration of this fluorescence, from which the binding constants (KC,=,103,105,M,1) are calculated by means of a competitive complexation model. Electrostatic effects are observed, namely, a more-than-one order of magnitude weaker binding of the carnitines in neutral solution. [source] Hydrothermal modification of natural zeolites to improve uptake of ammonium ionsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2005Yujiro Watanabe Abstract The modification of natural zeolites was carried out under hydrothermal conditions to improve the effectiveness of the uptake of ammonium ions. Natural zeolites originating in Japan, such as mordenite and clinoptilolite with quartz, feldspar and a trace of layered silicate, were treated with 0.1, 0.3, 1.0 and 3.0 M NaOH solutions at temperatures from 25 to 150 °C under autogenous pressure for 7 days. After the hydrothermal treatment, the transformation of the zeolites to phillipsite, hydroxyl-sodalite and analcime was observed, depending on the temperature and NaOH concentration. The amounts of ammonium ions taken up into the hydrothermally-treated zeolites were compared with those of the starting materials. The treated products, containing mainly phillipsite, took up twice the amount of ammonium ions as the starting materials. The maximum uptake of ammonium ions was 1.92 mmol g,1. The number of ammonium ions taken up into phillipsite was equal to the number of Na+ ions released from phillipsite. These results indicate that the uptake of ammonium ions proceeds by an ion-exchange mechanism with Na+ ions. Copyright © 2005 Society of Chemical Industry [source] Improved protonation, collision-induced decomposition efficiency and structural assessment for ,red tide' brevetoxins employing nanoelectrospray mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2006Weiqun Wang Abstract Brevetoxins are a group of natural neurotoxins found in blooms of red tide algae. Previous electrospray mass spectrometry (ES-MS) studies show that all brevetoxins have high affinities for sodium ions, and they form abundant sodium adduct ions, [M + Na]+, in ES-MS, even when trace contamination is the only source of sodium ions. Attempts to obtain informative product ions from the collision-induced decomposition (CID) of [M + Na]+ brevetoxin precursor ions resulted only in uninformative sodium ion signals, even under elevated collision energies. In this study, a nano-ES-MS approach was developed wherein ammonium fluoride was used to form cationic [M + NH4]+ adducts of brevetoxin-2 and brevetoxin-3; a significant increase in the abundance of protonated brevetoxin molecules [M + H]+ also resulted, whereas the abundance of sodium adducts of brevetoxins [M + Na]+ was observed to decrease. Under CID, both [M + NH4]+ and [M + H]+ gave similar, abundant product ions and thus underwent the same types of fragmentation. This indicated that ammonium ions initially attached to brevetoxins forming [M + NH4]+ easily lose neutral ammonia in a first step in the gas phase, leaving protonated brevetoxin [M + H]+ to readily undergo further fragmentation under CID. Copyright © 2006 John Wiley & Sons, Ltd. [source] Ion-pair Formation as a Strategy to Enhance Topical Delivery of Salicylic AcidJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 8 2000STELLA A. MEGWA An in-vitro study was carried out to determine the possibility of improving the efficiency of transdermal delivery of salicylate through human epidermis by ion-pair formers (alkylamines and quaternary ammonium ions). Further, the relationship between the physico-chemical properties of the counter-ions and salicylate flux was examined. It was found that flux can be related to the conductivity associated with the penetrant solution, molecular size of the counter-ion and lipophilicity expressed as either octanol/water partition coefficient of the ion pairs or the carbon chain-length of the counter-ions. Equations have been developed to predict salicylate flux from these physicochemical parameters. [source] Organoclay Nanocomposites from Ethylene,Acrylic Acid CopolymersMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006Sara Filippi Abstract Summary: A study of the structure,property relationships for nanocomposites prepared by melt compounding from ethylene,acrylic acid copolymers of varied composition and molecular architecture, and organoclays modified with different ammonium ions has been made by DSC, POM, SEM, TEM, WAXD, and rheological and mechanical tests. Within the series of clays investigated, the best levels of dispersion were displayed by those organically modified with quaternary ammonium ions containing two long alkyl tails. The relevant nanocomposites were shown to possess mixed exfoliated and intercalated morphology. The spacing of the intercalated clay stacks, most of which comprise few silicate layers, was found to be independent of clay loading, in the range of 2,50 phr, and to change with the molecular architecture of the matrix polymer. An indication that the excess surfactant present in some of the clays, and the organic material added in others to expand the interlayer spacing, were expelled from the clay galleries during melt blending and acted as plasticisers for the matrix polymer, was obtained from WAXD and rheological characterisations. TEM micrograph of the nanocomposite of EAA1 with 11 phr of 15A. [source] Electrochemical impedance spectroscopy study of surface films formed on copper in aqueous environmentsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2005A. Srivastava Abstract The electrochemical behavior of pure copper has been studied in aqueous environments using linear polarization and electrochemical impedance spectroscopy (EIS) techniques as a function of immersion time. The effect of pollutants (like chloride, sulfide and ammonium ions) on the nature of films formed on the copper surface has been studied. All the surfaces revealed the presence of a porous oxide layer. The corrosion resistance decreased with increasing amount of chloride ions. The addition of Na2S in the environments in the absence of any chloride species was beneficial for corrosion resistance. EIS data suggested that the capacitance of the films formed in chloride environments was higher. The surfaces obtained in presence of chloride ions were relatively rough and deeply attacked. The total impedance decreased after 432 h of immersion in solutions possessing chloride ions. The damaging role of chloride ions and the relatively less severe effect of sulfide ions were noted. [source] GAG Mimetic Libraries: Sulphated Peptide as Heparin-like Glycosaminoglycan Mimics in Their Interaction with FGF-1MOLECULAR INFORMATICS, Issue 8 2005Socorro Vázquez-Campos Abstract Heparin and heparan sulphate (HS) are heterogenous, linear, polysulphated polysaccharides that are important in the regulation of a wide variety of biological processes including blood coagulation, in cell differentiation, adhesion, invasion, migration and development, and in tumor-related cellular events such as growth regulation and metastasis. In general, heparin/HS interacts with proteins mainly through ionic interactions between its negatively charged groups and positively charged groups on the proteins. From a mechanistic or therapeutic standpoint, it is attractive to design less complex charged molecules, other than oligosaccharides, as mimics of heparin. In an attempt to improve the accessibility of heparin mimics, it was assumed, provided that the correct charge topography could be achieved, that sulphated peptides might also act as mimics. Therefore, sulphated peptide combinatorial libraries were generated on solid support to identify novel polyanionic structures that mimic the role of heparin/HS in its binding to fibroblast growth factors (FGFs). Libraries were synthesised by direct sulphation of the peptide on solid phase or by using O- sulphonated building blocks during peptide synthesis. Quantitative solid-phase O -sulphonation of hydroxy amino acid residues in a peptide chain was effected by sulphur trioxide pyridine (SO3 -Pyr) complex in anhydrous pyridine at 65,°C for 4,h. O- Sulphonated building blocks were successfully synthesised in solution and, after stabilisation of the sulphate group by complexion with tetrabutyl ammonium ions, were employed in the synthesis of sulphated peptide libraries, similar to those generated by direct O- sulphonation on solid supports. The libraries were incubated with fluorescent-labelled FGF-1, and analysis and sequence determination of active compounds was carried out using Edman degradation. Selected sulphated peptides from the screening were resynthesised and their affinity for FGF-1 (acidic FGF) was studied in solution competition assays using surface plasmon resonance. These studies showed that sulphated decapeptides do bind to FGF-1 and inhibit its binding to immobilised heparin in the low micromolar concentration range. [source] A pair of diastereomeric 1:1 salts of (S)- and (R)-2-methylpiperazine with (2S,3S)-tartaric acidACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009Hiroshi Katagiri The structures of diastereomeric pairs consisting of (S)- and (R)-2-methylpiperazine with (2S,3S)-tartaric acid are both 1:1 salts, namely (S)-2-methylpiperazinium (2S,3S)-tartrate dihydrate, C5H14N22+·C4H4O62,·2H2O, (I), and (R)-2-methylpiperazinium (2S,3S)-tartrate dihydrate, C5H14N22+·C4H4O62,·2H2O, (II), which reveal the formation of well defined ammonium carboxylate salts linked via strong intermolecular hydrogen bonds. Unlike the situation in the more soluble salt (II), the alternating columns of tartrate and ammonium ions of the less soluble salt (I) are packed neatly in a grid around the a axis, which incorporates water molecules at regular intervals. The increased efficiency of packing for (I) is evident in its lower `packing coefficient', and the hydrogen-bond contribution is stronger in the more soluble salt (II). [source] Glutamine metabolism: Role in acid-base balance,BIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION, Issue 5 2004Lynn Taylor Abstract The intent of this review is to provide a broad overview of the interorgan metabolism of glutamine and to discuss in more detail its role in acid-base balance. Muscle, adipose tissue, and the lungs are the primary sites of glutamine synthesis and release. During normal acid-base balance, the small intestine and the liver are the major sites of glutamine utilization. The periportal hepatocytes catabolize glutamine and convert ammonium and bicarbonate ions to urea. In contrast, the perivenous hepatocytes are capable of synthesizing glutamine. During metabolic acidosis, the kidney becomes the major site of glutamine extraction and catabolism. This process generates ammonium ions that are excreted in the urine to facilitate the excretion of acids and bicarbonate ions that are transported to the blood to partially compensate the acidosis. The increased renal extraction of glutamine is balanced by an increased release from muscle and liver and by a decreased utilization in the intestine. During chronic acidosis, this adaptation is sustained, in part, by increased renal expression of genes that encode various transport proteins and key enzymes of glutamine metabolism. The increased levels of phosphoenolpyruvate carboxykinase result from increased transcription, while the increase in glutaminase and glutamate dehydrogenase activities result from stabilization of their respective mRNAs. Where feasible, this review draws upon data obtained from studies in humans. Studies conducted in model animals are discussed where available data from humans is either lacking or not firmly established. Because there are quantitative differences in tissue utilization and synthesis of glutamine in different mammals, the review will focus more on common principles than on quantification. [source] Synthesis, Structure, Thermal and Magnetic Properties of a New Open-framework Borophosphate: NH4Mn(H2O)2BP2O8·H2O,CHINESE JOURNAL OF CHEMISTRY, Issue 9 2006Heng-Zhen Shi Abstract Using new template agent, a new borophosphate compound, NH4Mn(H2O)2BP2O8·H2O was hydrothermally prepared and structurally characterized. It crystallizes in a hexagonal space group P6122 with lattice parameters a=0.9652(2) nm, c=1.5792(5) nm, V=1.2740(5) nm3 and Z=6. The structure has a three-dimensional open-frame work with borophosphate helical ribbons 1,{[BP2O8]3, and MnO4(H2O)2 octahedra. The water molecules are positioned inside the helical channels. Very interestingly, the ammonium ions are located outside the loop of the free helical ribbons via the strong hydrogen bonds, which is different from the borophosphate analogue reported. The magnetization of the title compound is paramagnetic down to 5 K of the Curie-Weiss type within the measured range of 5,300 K with ,=,7.3 K, indicative of very weak antiferromagnetic interactions. The thermal decomposition of the compound was also described. [source] | ||||||||||||||||||||||||||||||||||