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Acidic Conditions (acidic + condition)
Kinds of Acidic Conditions Selected AbstractsA Study on the Effect of Template Chain Length on the Synthesis of Mesoporous Silica in An Acidic ConditionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Yang Yu-Xiang Hexagonal mesoporous silica materials were synthesized in an acidic medium using different chain length of the quaternary ammonium surfactants as a template. The effects of chain length on the physical property, morphology of mesoporous materials, and the temperature on synthesis of materials in CnTMBr,TEOS,HNO3,H2O (n=12,14,16,18) system were systematically studied. The synthesized products were characterized by X-ray diffraction patterns, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption analysis. It was found that degree of ordering, the d spacing values, and pore size all increase with an increase in the chain length of the template. The optimum synthesis temperature for mesoporous silica using C18TMBr,TEOS,HNO3,H2O system is slightly higher than the Krafft point. The temperature and pH can all affect the expandability of micelles, and so an increase in temperature and decrease in pH all lead to an increase in the pore size. It is also found that the shear flow and chain length are two key factors inducing the formation of millimeter-scaled silica ropes and micrometer-scaled rope fibers. [source] Solvolysis of Some Arenediazonium Salts in Binary EtOH/H2O Mixtures under Acidic ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2003Román Pazo-Llorente Abstract We have determined the product distribution, the rate constants for dediazoniation product formation, and the solvolytic rate constants for 2-, 3-, and 4-methylbenzenediazonium ions (2-, 3-, and 4-MBD, respectively) loss in acidic ethanol/water mixtures over the whole composition range by a combination of spectrophotometric (UV/Vis) and high performance liquid chromatography (HPLC) measurements. The observed rate constants (kobs) for substrate loss are equal to those for product formation, and they remain essentially constant (2-MBD) with changing solvent composition but increase by a factor of ,2 (4MBD) on going from water to 100% EtOH. Up to four dediazoniation products , cresols (ArOH), chlorotoluene (ArCl), methylphenetole (ArOEt), and toluene (ArH) , were detected, depending on the solvent composition; the major dediazoniation products were the ArOH and ArOEt derivatives. The product selectivity (S) of the reaction towards nucleophiles is low and essentially constant with changing solvent composition, and good linear correlations between log kobs and YCl (solvent ionizing power) were observed for the three ArN2+ ions. All data are consistent with the rate-determining formation of an aryl cation, which reacts immediately with available nucleophiles. The data suggest that the distribution of neutral and anionic nucleophiles in the neighborhood of the ground state arenediazonium ion remains essentially unchanged upon dediazoniation, the observed product distribution reflecting the concentrations of nucleophiles in their immediate environment (i.e., in the first solvation shells of the arenediazonium ions). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Selective Oxidation of Glycerol under Acidic Conditions Using Gold Catalysts,ANGEWANDTE CHEMIE, Issue 26 2010Alberto Villa Dr. Base? Wozu? PtAu-Nanopartikel auf H-Mordenit-Trägern vermitteln hoch aktiv und selektiv die Oxidation von Glycerin unter sauren Bedingungen, was die direkte Bildung der freien Säuren ermöglicht (siehe Bild). Anders als bei PtAu-Nanopartikeln auf Aktivkohle bedingt hier die hohe Selektivität für C3 -Verbindungen eine minimale H2O2 -Bildung. [source] A Free Radical Mannich Type Reaction: Selective ,-CH Aminomethylation of Ethers by Ti(III)/t-BuOOH System under Aqueous Acidic Conditions.CHEMINFORM, Issue 41 2006Angelo Clerici 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] Efficient Osmium/Rhenium-Catalyzed Dihydroxylation of Olefins with Hydrogen Peroxide under Acidic Conditions.CHEMINFORM, Issue 47 2003Alida H. Ell No abstract is available for this article. [source] CO2 Fixation and Transformation by a Dinuclear Copper Cryptate under Acidic ConditionsCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2007Jia-Mei Chen Abstract CO2 fixation and transformation by metal complexes continuously receive attention from the viewpoint of carbon resources and environmental concerns. We found that the dinuclear copper(II) cryptate [Cu2L1](ClO4)4 (1; L1=N[(CH2)2NHCH2(m -C6H4)CH2NH-(CH2)2]3N) can easily take up atmospheric CO2 even under weakly acidic conditions at room temperature and convert it from bicarbonate into carbonate monoesters in alcohol solution. The compounds [Cu2L1(, - O2COH)](ClO4)3 (2), [Cu2L1(,-O2COR)](ClO4)3 (3: R=CH3; 4: R=C2H5; 5: R=C3H7; 6: R=C4H9; 7: R=C5H11; 8: R=CH2CH2OH), [Cu2L1(, - O2CCH3)](ClO4)3 (9), and [Cu2L1(OH2)(NO3)](NO3)3 (10) were characterized by IR spectroscopy and ESI-MS. The crystal structures of 2,6 and 10 were studied by single-crystal X-ray diffraction analysis. On the basis of the crystal structures, solution studies, and DFT calculations, a possible mechanism for CO2 fixation and transformation is given. [source] Adsorption of fulvic acids from aqueous solutions by carbon nanotubesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2007Shu-Guang Wang Abstract Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g,1 at 5 °C and equilibrium concentration of 18 mg dm,3. The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (,G0), standard enthalpy change (,H0) and standard entropy change (,S0), have been obtained. Acidic conditions (pH = 2,5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm,3). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions. Copyright © 2007 Society of Chemical Industry [source] Assessment of matrix effects and determination of niacin in human plasma using liquid,liquid extraction and liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 11 2008Michael C. Peoples Abstract A simple, sensitive and rapid liquid,liquid extraction method for the analysis of nicotinic acid (niacin) and its labeled internal standard nicotinic acid-d4 (niacin-d4) in human plasma was developed and validated. The analyte and its internal standard were isolated from acidified plasma using a single liquid,liquid extraction procedure with methyl- t -butyl ether. The extracted samples were analyzed by liquid chromatography,tandem mass spectrometry in positive electrospray ionization mode with multiple reaction monitoring. The calibration curves were linear in the measured range between 5 and 1000 ng/mL and the limit of detection was calculated as 122 pg/mL. The method required 250 µL of human plasma and the total run time between injections was 3.5 min. Matrix effects were assessed by post-column infusion experiments, phospholipids monitoring and post-extraction addition experiments. The extraction of phospholipids and niacin from plasma was studied under acidic, neutral and basic conditions. Acidic conditions were optimal for both the recovery of niacin and the removal of phospholipids; the degree of matrix effects for niacin was determined to be 2.5%. It was concluded that effective removal of matrix components can overcome low recovery issues associated with liquid,liquid extractions of polar analytes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Reinvestigation of the Mechanism of gem -Diacylation: Chemoselective Conversion of Aldehydes to Various gem -Diacylates and Their Cleavage under Acidic and Basic ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2005Veerababurao Kavala Abstract The mechanism of gem -diacylate formation has been studied extensively using tetrabutylammonium tribromide (TBATB) as the catalyst. The reaction proceeds by a nucleophilic attack of an anhydride on an aldehydic carbonyl group, nucleophilic attack of the hemiacylate intermediate on a second molecule of the anhydride, followed by an intermolecular attack of a second acetate group to regenerate the anhydride. gem -Diacylates of various aliphatic and aromatic aldehydes were obtained directly from the reaction of a variety of aliphatic and aromatic acid anhydrides in the presence of a catalytic quantity of tetrabutylammonium tribromide (TBATB) under solvent-free conditions. A significant electronic effect was observed during its formation as well as deprotection to the corresponding aldehyde. Chemoselective gem -diacylation of the aromatic aldehyde containing an electron-donating group has been achieved in the presence of an aldehyde containing an electron-withdrawing group. Deprotection of the gem -diacylate to the parent carbonyl compound can be accomplished in methanol in presence of the same catalyst. Here again, chemoselective deprotection of the gem -diacylate of a substrate containing an electrondonating group has been achieved in the presence of a substrate containing an electron-withdrawing group. Both the acid and base stability order of the various gem -diacylates examined follow a similar order. The stability order determined from the present study is: gem -dibenzoate > gemdipivalate > gem -diisobutyrate > gem -diacetate > gem -dipropionate. All the gem -diacylals are more stable under basic conditions than acidic condition. No correlation was found between the stability order and the pKa's of the corresponding acids; rather, the stability order is directly related to the steric crowding around the carbonyl carbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Structural Evolution of Self-Assembling Nanohybrid Thin Films from Functionalized Urea Precursors,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2007I. Karatchevtseva Abstract Hybrid organic-inorganic thin films exhibiting patterned structuring on the nanometer scale have been prepared through the controlled hydrolysis-condensation of enantiomerically pure chiral urea-based silyl compounds. The thin films are obtained by spin-coating of sols obtained via acid- or base-catalyzed hydrolytic condensation of these molecular precursors. A self-templating process is demonstrated via atomic force and transmission electron microscopy, showing the formation of nanometer size aggregates consisting of interconnected spherulates under acidic condition and of assembled fibers under basic conditions. [source] Release behavior of freeze-dried alginate beads containing poly(N -isopropylacrylamide) copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Jae-Hyung Choi Abstract Beads composed of alginate, poly(N -isopropylacrylamide) (PNIPAM), the copolymers of N -isopropylacrylamide and methacrylic acid (P(NIPAM- co -MAA)), and the copolymers of N -isopropylacrylamide, methacrylic acid, and octadecyl acrylate (P(NIPAM- co -MAA- co -ODA)), were prepared by dropping the polymer solutions into CaCl2 solution. The beads were freeze-dried and the release of blue dextran entrapped in the beads was observed in distilled water with time and pH. The degree of release was in the order of alginate bead < alginate/PNIPAM bead , alginate/P(NIPAM- co -MAA) bead < alginate/P(NIPAM- co -MAA- co -ODA) bead. On the other hand, swelling ratios reached steady state within 20 min, and the values were 200,800 depending on the bead composition. The degree of swelling showed the same order as that of release. Among the beads, only alginate/P(NIPAM- co -MAA- co -ODA) bead exhibited pH-dependent release. At acidic condition, inter- and intraelectrostatic repulsion is weak and P(NIPAM- co -MAA- co -ODA) could readily be assembled into an aggregate due to the prevailing hydrophobic interaction of ODA. Thus, it could block the pore of bead matrix, leading to a suppressed release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Electrical behavior of polyurethane composites with acid treatment-induced damage to multiwalled carbon nanotubesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Pill Gyu Jang Abstract We have studied the electrical conductivity and percolation threshold of polyurethane (PU) composites filled with multiwalled carbon nanotubes (MWCNT) purified by increasing immersion time in aqueous solutions of either nitric acid or a mixture of nitric and sulfuric acids at 80°C. The MWCNT crystallinity peaks after 2 h of treatment, which enables the PU composites to enhance the percolation threshold and electrical conductivity in the conductive network formation region. MWCNT treated under either a milder or severer acidic condition deteriorate the electrical behavior of the composites, since MWCNT are poorly dispersed in the PU matrix in the former condition, but lost their intrinsic electrical conductivity due to the partial destruction of their crystalline structure in the latter. Therefore, the acid treatment needs to be carefully controlled to effectively purify the MWCNT, maintain the crystalline structure without further damage, and thereby improve the electrical behavior of PU/MWCNT composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] ACTIVITY DISTRIBUTION OF DIGESTIVE PROTEASES FROM NEMIPTERUS VIRGATUS AND THEIR RESPONSES TO pH VALUE AND TEMPERATUREJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2008HONG TAO ABSTRACT In the present study, three groups (I,III) of Nemipterus virgatus, with average body weights of 154.36, 250.72 and 329.09 g, respectively, were used to investigate the changes in the activity and distribution of digestive proteases in different organs and sections of the digestive tract. Another group of N. virgatus (average body weight of 188.41 g) was used to analyze the changes in the activity of digestive proteases in response to various pH values and temperatures. The activity of digestive proteases in all analyzed organs increased with the increase of body weight at the range of 154.36,329.09 g. The activities of digestive proteases in the different sections of the digestive tract were compared, and a similar change was found among groups I,III. The activities of digestive proteases from various organs were in a descending order: pylorus ceca > stomach > foregut > midgut > hindgut > hepatopancreas. Through observing the zymograms of substrate,sodium dodecil sulphate-polyacrylamide gel electrophoresis, many kinds of digestive proteases could be found in different organs and the varieties were changed with the change of body weight. Two peaks in the diagram between protease activity and pH value were found at pH 3.0 and 10.0, respectively. The activity under alkaline condition was 60% higher than that under acidic condition. The optimal temperature for protease activity was 50C, while the protease activity at 10C was only 30% of that at 50C. PRACTICAL APPLICATIONS Nemipterus virgatus is one of the most important commercial fishes in the East China Sea and South China Sea. The digestive tract of N. virgatus is rich in digestive proteases and they can be employed as important biotechnological tools. The activities of digestive proteases from various organs and the effects of pH value and temperature on them were investigated in this study. The effect of body weight of N. virgatus was also evaluated. All these information would be helpful to extensively utilize this resource for the fish process industry. [source] Synthesis of 9-[2-(2-hydroxymethyl-2-methyl-, -(2-acetoxymethyl-2-methyl-, -(2,2-di(hydroxymethyl)-, and -(2,2-Di(acetoxymethyl)-1,3-dioxan-5-yl)ethyl] derivatives of guanine and 2-aminopurineJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2000Dae-Kee Kim Synthesis of 9-[2-(2-hydroxymethyl-2-methyl-, -(2-acetoxymethyl-2-methyl-, -(2,2-di(hydroxymethyl)-, and -(2,2-di(acetoxymethyl)-1,3-dioxan-5-yl)ethyl] derivatives of guanine and 2-aminopurine, 2,9, has been accomplished in seven to eight step sequences from readily available 1-(tert -butyldiphenylsilyloxy)-acetone, 1,3-di(tert -butyldiphenylsilyloxy)acetone, and the diol 10. Formation of cyclic ketals 11 and 12 was carried out successfully under an acidic condition using a catalytic amount of methanesulfonic acid along with excess anhydrous copper(II) sulfate in toluene. Subsequent reactions of desilylation, acetylation, hydrogenolysis, and bromination afforded the key intermediates 19 and 20, which were coupled with 2-amino-6-chloropurine to produce the purine compounds 21 and 22 in good yields. Guanine derivatives 2,5 were obtained from 21 and 22 by hydrolysis and acetylation, while the dechlorination and hydrolysis of 21 and 22 yielded the 2-aminopurine compounds 6,9. [source] Physicochemical responses of Pythium porphyrae (Oomycota), the causative organism of red rot disease in Porphyra to acidificationAQUACULTURE RESEARCH, Issue 15 2009Eun Kyoung Hwang Abstract Physicochemical responses to acidification in Pythium porphyrae, the causative organism of red rot disease in Porphyra, were investigated. The acid tolerance of P. porphyrae mycelia under pH 4 (acidic condition) condition increased significantly compared with that of the mycelia under pH 8 (condition equivalent to seawater) condition. Free amino acid levels in the mycelia decreased 1.3,8.8-fold under pH 4 condition. However, some free amino acids such as the d -cysteinolic acid-like component, phosphoethanolamine, glutamic acid, aminoadipic acid and methionine increased 2.6,21.7-fold under the same condition. Proton flux on the mycelia exposed to pH 8 increased significantly compared with the mycelia exposed to pH 4. The patterns of proteins present (examined by two-dimensional polyacrylamide gel electrophoresis) differed among the pH conditions. These results suggest that P. porphyrae acquires acid tolerance and is able to adapt to the changing pH conditions. This has significant implications for the use of acidic fungicide treatment for prevention of red rot disease on Porphyra farms. [source] Preparation of bioadsorbents for effective adsorption of a reactive dye in aqueous solutionASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Shariff Ibrahim Abstract The surface of barley straw, an agricultural waste, was modified chemically using a cationic surfactant hexadecylpyridinium chloride monohydrate (CPC) and used as an adsorbent for removal of Reactive Blue 4 (RB4) from aqueous solution. The raw and surfactant-modified barley straws (SMBS) were characterized by Fourier transform infrared and elemental analysis. The stability of CPC adsorbed on straw surface was evaluated by exposing to water and organic solvents. The adsorption was performed on removing RB4 from wastewater in a batch adsorption system. The effects of contact time, initial concentration of dye and pH of solution on RB4 uptake were investigated and discussed. It was found that the removal percentage of RB4 increased with the increase in contact time. Adsorption was favorable at acidic condition and the maximum removal of 100% was obtained at pH 3. Dye-loaded SMBS was stable and percentage of desorption was less than 7% in water. The kinetic studies revealed that the kinetic data fitted well to the pseudo-second-order model. The isotherm study also indicated that RB4 adsorption on SMBS matched well with the Langmuir model other than the Freundlich model. The maximum adsorption capacity determined from the Langmuir isotherm was 29.2 mg g,1 at 25 °C. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Glucose Oxidation Catalyzed by Liposomal Glucose Oxidase in the Presence of Catalase-Containing LiposomesBIOTECHNOLOGY PROGRESS, Issue 3 2006Makoto Yoshimoto A catalase-containing liposome (CAL) was prepared and characterized in terms of stability during storage and catalysis of the decomposition of hydrogen peroxide (H2O2) that was initially added or produced in the oxidation of glucose catalyzed by the glucose oxidase-containing liposomes (GOL). The reactors used were a test tube and an external loop airlift bubble column as the static liquid and circulating liquid flow systems, respectively. The free catalase (CA) at low concentrations was unstable during storage at 4 °C as a result of dissociation of the tetrameric CA subunits. On the other hand, the deactivation of the CA activity in the CAL was depressed because of the high CA concentration in the CAL liposome. The CAL effectively catalyzed the repeated decompositions at 25 °C with 10 mM H2O2 added initially, whereas the free CA was significantly deactivated during the repeated reactions. The high stability of the CAL was attributed to the moderately depressed reactivity, which was essentially derived from the diffusion limitation of the CAL membrane to H2O2 in the liquid bulk. In the GOL-catalyzed prolonged oxidation of 10 mM glucose at 40 °C in the static liquid in a test tube, both the free CA and CAL could continuously catalyze the decomposition of H2O2 produced. This was because the glucose oxidation rate was small due to the limited reactivity of the GOL to glucose with its low permeability through the GOL membrane. In the glucose oxidation catalyzed by the GOL with the free CA or the CAL in the airlift, much larger oxidation rates were observed compared to those in the test tube because the permeability of the GOL membrane to glucose was increased in the gas-liquid two phase flow in the airlift. The GOL/CAL system in the airlift operated in an acidic condition, which was preferable to the GO activity, gave the largest oxidation rate with negligible accumulation of the H2O2 produced. On the other hand, the GOL/free CA system gave an oxidation rate smaller than that of the GOL/CAL system even under the acidic condition due to an unfavorable interaction of the free CA molecules with the GOL membranes leading to the decreased reactivity of the GOL. [source] Retraction: Blockage of intracellular proton extrusion with proton pump inhibitor induces apoptosis in gastric cancerCANCER SCIENCE, Issue 1 2008Marie Yeo The following article from Cancer Science, ,Blockage of intracellular proton extrusion with proton pump inhibitor induces apoptosis in gastric cancer' by Marie Yeo, Dong-Kyu Kim, Hee Jin Park, Sung Won Cho, Jae Youn Cheong and Kwang Jae Lee (doi: 10.1111/j.1349-7006.2007.00642.x), published online on 23 October 2007 on Blackwell Synergy (http://www.blackwell-synergy.com), has been retracted by agreement between the authors, the journal Editor in Chief, Takashi Tsuruo, and Blackwell Publishing. All authors wish to retract this paper because of the use of RGM-1 without the prior permission of the original establisher. Proton pump inhibitors have been used for treatment of acid-related gastroesophageal diseases and they act as potent inhibitors of gastric acid pump, H+/K+ -ATPase. Since cancer cells in vivo often exist in an ischemic microenvironment with a lower pH, maintenance of cellular pH is important for cell survival. In this study, we evaluated whether blocking of proton extrusion with proton pump inhibitors could inhibit the viability of gastric cancer cells. Treatment of human gastric cancer cells with proton pump inhibitors significantly attenuated cell viability in a time- and dose-dependent manner. The pro-apoptotic activity of proton pump inhibitors was mediated by release of cytochrome c and caspases activation. Gastric cancer cells showed the resistance to acidity of culture medium, which was related with a remarkable increase of extracellular signal-regulated protein kinase 1/2 (ERK1/2) phosphorylation in the acidic condition. This ERK1/2 phosphorylation was completely inhibited by pretreatment with proton pump inhibitors, suggesting that its inhibitory action on phosphorylation of ERK1/2 might contribute to the induction of apoptosis in gastric cancer cells. In conclusion, our results suggest novel therapeutic approaches for gastric cancer with proton pump inhibitors. (Cancer Sci 2008; 99: 185,185) [source] Electrochemical Reduction of S(IV) Compounds in Water-Ethanol Solutions at Nafion/Tetraruthenated Porphyrins Glassy Carbon Modified ElectrodesELECTROANALYSIS, Issue 3 2010Karla Calfumán Abstract This work describes electrocatalytic detection of S(IV) compounds in water-ethanol solutions under acidic conditions, on a glassy carbon electrode modified with Co(II) tetraruthenated porphyrin electrostatically assembled onto a Nafion film. The Ipc current shows a linear relationship with the concentration of S(IV) oxo-anions. Controlled potential electrolysis shows that thiosulfate was detected as reaction product. Rotating disk electrode and UV-visible spectroelectrochemistry experiments showed a kinetic limitation to the electron transfer controlled by charge propagation in the film and the formation of an intermediary between Co center and S(IV) species. The reproducibility of the modification methodology presents a RSD of 4.1%. [source] Improved 2-DE of microorganisms after acidic extractionELECTROPHORESIS, Issue 8 2006Ben R. Herbert Professor Abstract 2-DE separations of protein extracts sometimes have problems with poor resolution and streaking. This problem is particularly apparent with microorganisms, most notably those with a large cell wall. Here we describe a novel, rapid protocol for the extraction of microorganisms in acidic conditions, leading to increased resolution and 2-D gel quality. The efficiency of the protocol is demonstrated with extracts of bacteria, Escherichia coli and Bacillus subtilis; fungus, Trichoderma harzianum and yeast, Saccharomyces cerevisiae. We also demonstrate using a membrane centrifugal filtration, that large acidic molecules in excess of 100,kDa, probably including cell wall material, are responsible for the separation difficulties. A range of acidic extraction conditions were investigated, and it was found that optimal extraction is achieved using an extraction solution acidified to pH,3 by 80,mM citric acid. These findings have significant implications for the proteomic study of many medically, agriculturally and environmentally significant microorganisms, as the cell walls of these organisms are often considerably more complex than many commonly studied laboratory strains. [source] Capillary electrophoresis analysis of glucooligosaccharide regioisomersELECTROPHORESIS, Issue 6 2004Gilles Joucla Abstract Complex gluco-oligosaccharide mixtures of two regioisomer series were successfully separated by CE. The gluco-oligosaccharide series were synthesized, employing a dextransucrase from Leuconostoc mesenteroides NRRL B-512F, by successive glucopyranosyl transfers from sucrose to the acceptor glucose or maltose. The glucosyl transfer to both acceptors, occurring through the formation of ,1,6 linkages, differed for the two series only in the glucosidic bond to the reducing end namely ,1,6 or ,1,4 bond for glucose or maltose acceptor, respectively. Thus, the combination of the two series results in mixed pairs of gluco-oligosaccharide regioisomers with different degrees of polymerization (DP). These regioisomer series were first derivatized by reductive amination with 9-aminopyrene-1,4,6-trisulfonate (APTS). Under acidic conditions using triethyl ammonium acetate as electrolyte, the APTS-gluco-oligosaccharides of each series were separated enabling unambiguous size determination by coupling CE to electrospray-mass spectrometry. However, neither these acidic conditions nor alkaline buffer systems could be adapted for the separation of the gluco-oligosaccharide regioisomers arising from the two combined series. By contrast, increased resolution was observed in an alkaline borate buffer, using differential complexation of the regioisomers with the borate anions. Such conditions were also successfully applied to the separation of glucodisaccharide regioisomers composed of ,1,2, ,1,3, ,1,4, and ,1,6 linkages commonly synthesized by glucansucrase enzymes. [source] A simple polyacrylamide gel electrophoresis procedure for separation of polyamidoamine dendrimersELECTROPHORESIS, Issue 16 2003Ajit Sharma Abstract A simple, inexpensive, and rapid electrophoresis technique was developed for use as a routine tool for evaluating purity of polyamidoamine (PAMAM) dendrimers. A variety of factors influencing migration of generations 0,7 dendrimers on nongradient polyacrylamide gels were evaluated. The low generation dendrimers were found to be very sensitive to diffusion during or after electrophoresis. The proposed method incorporates steps that minimize diffusion, in order to obtain improved resolution and sensitivity, especially for the lower-molecular-weight dendrimers. This was accomplished by inclusion of a dendrimer fixation step with glutaraldehyde and performing the electrophoresis separation, fixation, staining, and destaining at 4°C. PAMAM dendrimer separation was studied under basic and acidic conditions. Electrophoresis under acidic conditions gave increased resolution and sensitivity over separation at alkaline pH. Oligomers and trailing generations could be clearly separated and visualized under these conditions. The smallest PAMAM dendrimer, generation 0, was visible at 1.5 ,g under the optimized acidic conditions. With slight modifications, this technique should be applicable to separation of other water-soluble dendrimers. [source] The effect of pH and ionic strength on the sorption of sulfachloropyridazine, tylosin, and oxytetracycline to soilENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2006Thomas L. ter Laak Abstract Antimicrobial agents are the most heavily used pharmaceuticals in intensive husbandry. Their usual discharge pathway is application to agricultural land as constituents of animal manure, which is used as fertilizer. Many of these compounds undergo pH-dependent speciation and, therefore, might occur as charged species in the soil environment. Hence, pH and ionic strength of the soil suspension can affect the sorption behavior of these compounds to soil. Consequently, the soil sorption of three antimicrobial agents,sulfachloropyridazine (SCP), tylosin (TYL), and oxytetracycline (OTC),was investigated. Their respective sorption coefficients in two agricultural soils ranged from 1.5 to 1,800 L/kg. Sorption coefficients were greater under acidic conditions. Addition of an electrolyte to the solution led to decreased sorption of TYL and OTC by a factor of 3 to 20, but it did not influence the sorption of SCP. This behavior was analyzed by accounting for the pH-dependent speciation of TYL and OTC and considering the presence of OTC-calcium complexes. It appears that the decreased sorption of TYL and OTC with increasing ionic strength results from competition of the electrolyte cations with the positively charged TYL species and the positively charged OTC complexes. A model linking sorbate speciation with species-specific sorption coefficients can describe the pH dependence of the apparent sorption coefficients. This modeling approach is proposed for implementation in the assessment of sorption of ionizable compounds. [source] Kinetics of the reduction of chromium(VI) by vitamin CENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2005Xiang-Rong Xu Abstract The kinetics of the reduction of Cr(VI) to Cr(III) by vitamin C was studied using potassium dichromate solution as the model pollutant. Effects of the concentration of vitamin C, pH, temperature, and irradiation on the reduction of Cr(VI) were examined. The kinetics of Cr(VI) reduction by vitamin C can be described as - d[Cr(VI)]/dt = 0.0156 (,M s,1).[Cr(VI)][vitamin C] (pH 5), where dt is the differential function (d) of time (t). The activation entropy (,S,) and enthalpy (,H,) are 42.4 kJ mol,1 and -71.0 J mol,1 K,1, respectively, and the activation energy at 298 K is 63.5 kJ mol,1. The advantages of vitamin C as a reductant are as follows: It is an important biological reductant in humans and animals, and it is not toxic. Toxic Cr(VI) can be reduced by vitamin C not only in acidic conditions but also in alkaline solutions (pH 9); furthermore, the reduction was shown to occur both under the irradiation and in the dark. The present results suggest that vitamin C could be used effectively in the remediation of Cr(VI)-contaminated soil and groundwater in a wide range of pH, with or without sunlight. [source] Synthesis, Structure, Characterization, and Redox Properties of the Porous MIL-68(Fe) SolidEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2010Alexandra Fateeva Abstract A new porous FeIII -based MOF, formulated Fe(OH)(BDC)·(dmf)x with x , 1.1 and presenting the MIL-68 topology, was prepared by reaction of an iron(III) salt and terephthalic acid (H2BDC) in N,N, -dimethylformamide (dmf) under acidic conditions. The structure and properties of this solid were studied by means of X-ray diffraction, thermogravimetric analysis, nitrogen sorption, 57Fe Mössbauer spectrometry, and electrochemical lithium insertion. [source] Direct Synthesis of Zr-Containing Hybrid Periodic Mesoporous Organosilicas with Tunable Zirconium ContentEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2007Shang-Ru Zhai Abstract Highly ordered Zr-containing periodic mesoporous organosilicas (ZrPMO) with different Zr/Si ratios were successfully synthesized, for the first time, by employing a ZrOCl2/NaCl combination as the promoting agent and by simply adjusting the molar ratio of the zirconium species to the organosilica precursor; no addition of mineral acids was necessary. The effect of preparation parameters on the structural and textural properties were carefully investigated by using different ratios of NaCl/Si and Zr/Si. It was found that both salts are essential for this system and highly ordered ZrPMOs can be prepared within fairly wide Si/Zr ratios (5,100) while keeping the NaCl/Si ratio constant. To prove the effectiveness of this synthetic pathway with a higher Zr incorporation, ZrPMO materials were also synthesized under strongly acidic conditions for the purpose of comparison. The synthesized ZrPMO materials were thoroughly characterized by ICP-AES, SAXS, N2 sorption, TEM, SEM, 13C CP/29Si MAS NMR spectroscopy, XPS, and TGA. Elemental analyses show that the amount of Zr incorporated into ZrPMO, which was synthesized under mild conditions, is greater than that obtained in a strongly acidic environment, and the Zr content, with a Si/Zr ratio up to 12, is close to that in the initial gel composition. A plausible assembly mechanism based on the synergistic effect of both "nonhydrolyzable" (NaCl) and "hydrolyzable" (ZrOCl2) inorganic salts was discussed in detail, where the "salting out" effect and self-generated acidity from both inorganic salts, respectively, are believed to be key factors for the formation of ordered SBA-15-type ZrPMO materials under the synthetic conditions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] In Situ Synthesis, Characterization of SiPMo-X, and Different Catalytic Properties of SiPMo-X and SiPW-XEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2006Chunfeng Shi Abstract SBA-15 frameworks with encapsulated Keggin type heteropolyacids (HPAs) were synthesized in situ under strongly acidic conditions (pH,<,0). During the hydrolysis of tetraethyl orthosilicate (TEOS), a P- and a Mo source were added into the initial sol,gel system to form Keggin type HPAs. The texture of the final products was studied by the N2 adsorption,desorption isotherms and transmission electron microscopy (TEM), and their structure was systematically characterized by X-ray diffraction (XRD), UV/Vis diffuse reflectance- (DRS), infrared- (IR), and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Characterization results suggest that the samples show very ordered hexagonal mesostructure, and the HPAs that are incorporated into the framework of meso-silica are insoluble during catalysis. Results of catalytic tests indicate that the materials demonstrated catalytic activity comparable with or even surpassing those of the bulk HPAs in catalytic tests implementing chemical reactions of bulky molecules (1,3,5-triisopropylbenzene cracking, esterification of benzoic acid with tert -butyl alcohol, and 2,3,6-trimethylphenol hydroxylation with H2O2). Additionally, some other properties, such as easy separation and stability when recycled, ensure their potential applications in the chemical industries. Here, we report not only the in situ synthesis and characterization of SiPMo-X, but also the difference in the catalytic properties of SiPMo-X and SiPW-X. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Asymmetric Aza-Morita,Baylis,Hillman Reactions of Alkyl Vinyl Ketones with N -Protected Imines or In Situ Generated N -Protected IminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2010Xiao-Yang Guan Abstract DABCO-catalyzed aza-MBH reactions of N -Boc imines with MVK and EVK have been thoroughly investigated in the paper. The asymmetric version of this aza-MBH reaction was also systematically investigated by using a chiral amine or a chiral phosphane catalyst. It was found that most of the N -protected imines are suitable substrates under the mild reaction conditions and are able to give the corresponding adducts in moderate yields with high ee values. The TQO- or LB1-catalyzed aza-MBH reactions of N -protected ,-amidoalkyl phenyl sulfones or ,-amidoalkyl p -tolyl sulfones with MVK could be well conducted, which provides a facile and direct route to obtain highly enantioselective aza-MBH adducts. The Boc protecting group of the aza-MBH product could be easily removed under acidic conditions to give the corresponding ,-methylene-,-amino ketone or ,-methylene-,-amino alcohol derivatives in good yields. [source] Transannular Hydride Migration in Pseudo-Geminally Substituted [2.2]Paracyclophanes: A Vinylogous Pinacol RearrangementEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2005M. Lucian Birsa Abstract A vinylogous pinacol,pinacolone rearrangement is reported that takes place although the two hydroxyl groups are formally separated by seven bonds. It involves a transannular hydride shift that occurs between the benzylic positions of the pseudo-geminally substituted [2.2]paracyclophanes 1a,c, 7, 8 and 9. Under mild acidic conditions the corresponding pseudo-geminally substituted cyclic ethers were established as stable intermediates. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Regioselective Spiroannulations of ,-Acetyl LactonesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2003Jens Christoffers Abstract Monocyclic spiroannulation precursors 3a,c were obtained by Michael reactions of ,-acetyl lactones 6a,c with methyl vinyl ketone (7). The selective formation of either regioisomer of both ,-oxo (5a,c) and ,-oxo (4a,c) lactones from 3a,c was achieved by varying the reaction conditions. The ,-oxo lactones 4a,c were obtained under basic (buffered) conditions in a pyrrolidine/AcOH system. Under acidic conditions, the annulation reaction afforded ,-oxo lactones 5a,c. Byproducts 8b,c were identified to be the decomposition products of ,-oxo lactones 5b and 5c by comparison with the spectra of the alcohols 10b,c derived directly from ,-oxo lactones 4b and 4c by saponification/decarboxylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] | |||||||||||||||||||||||||||||||||||||||||||||||||