Showing papers on "Reagent published in 2000"
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TL;DR: In this paper, the influence of carbonization and activating reagent on the pore structure of the activated carbon was investigated, and it was found that the maximum surface area were obtained at the carbonization temperature of 600°C in both ZnCl2 and H3PO4 activation, and that the surface areas were as large as those of the commercial activated carbons.
633 citations
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TL;DR: An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described in this paper, which is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds.
Abstract: An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described. The method, named electro-Fenton, is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds. An industrial pollutant, p-nitrophenol (PNP), was chosen for this study and was eventually mineralized. The major intermediary degradation products such as hydroquinone, benzoquinone, 4-nitrocatechol, 1,2,4-trihydroxybenzene and 3,4,5-trihydroxy- nitrobenzene were unequivocally identified by HPLC and GC-MS methods. The rate constants of the hydroxylation reactions were determined. The mineralization of the initial pollutant and the intermediates formed during electro-Fenton treatment was followed by total organic carbon (TOC) analyses. Dependence of mineralization on the amount of electrical energy consumed is shown by the relative decrease of TOC values. A mineralization reaction mechanism is proposed.
511 citations
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TL;DR: In this paper, the possibility of using electrochemically produced hydroxyl radicals for solving environmental problems is investigated, which is achieved by electrochemical reduction of O2 in the presence of a catalytic amount of ferric or ferrous ion.
Abstract: The electrochemical production of Fenton’s reagent by simultaneous reduction of dioxygen and ferric ions on a carbon felt electrode, permits a controlled, in situ generation of hydroxyl (OH AE ) radicals. The possibility of using electrochemically produced OH AE radicals for solving environmental problems is investigated. Continuous and controlled production of hydroxyl radicals was achieved by electrochemical reduction of O2 in the presence of a catalytic amount of ferric or ferrous ion. These radicals are used for remediation of water containing toxic-persistent-bioaccumulative organic pollutants through their transformation into biodegradable compounds or through their mineralization into H2O and CO2. A widely used herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), was selected as a model for a toxic organic pollutant. High pressure liquid chromatography (HPLC) was used to quantify the distribution of the hydroxylated products obtained. Rate constants for the hydroxylation reactions of 2,4-D, 2,4-dichlorophenol (2,4-DCP), 2,4-dichlororesorcinol (2,4-DCR) and 4,6-dichlororesorcinol (4,6-DCR) were determined. The mineralization of 2,4-D and its derivatives was followed by total organic carbon (TOC) measurements. More than 95% of 2,4-D and the intermediates generated during the electrolysis can be mineralized.
363 citations
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TL;DR: Chain reactions constituted an important breakthrough in the application of radical chemistry in organic synthesis, and the use of chain reactions has resulted in a number of very impressive total syntheses of natural products.
Abstract: reactions constituted an important breakthrough in the application of radical chemistry in organic synthesis.2 An important and very attractive feature of these reactions is their high degree of functional group tolerance. Since radicals are usually stable under protic conditions, alcohols or even water can, in principle, be used as solvents in radical chemistry. Consequently, protic functional groups do not need protection. As soon as the underlying principles of the kinetic and thermodynamic behavior of free radicals were firmly established, efficient synthetic applications became feasible.3 The use of chain reactions has resulted in a number of very impressive total syntheses of natural products. An example is shown in eq 1.4 The characteristic features of free radicals can by now be deduced from ESR data.5 The course of some radical reactions can be understood by theoretical means.6
339 citations
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TL;DR: In this article, a chemical fixation of xanthene dyes on platinized TiO 2 particles via silane-coupling reagent was attempted in order to construct a stable dye-sensitized photocatalyst system in water.
Abstract: A chemical fixation of xanthene dyes on platinized TiO 2 particles via silane-coupling reagent was attempted in order to construct a stable dye-sensitized photocatalyst system in water. The Eosin Y fixed Pt-TiO 2 (E.Y-TiO 2 ) exhibited steady H 2 production from aqueous triethanolamine solution (TEOA aq.) under visible light irradiation for long time, and the H 2 evolution reproduced even after the exchange of TEOA aq., while the H 2 evolution from the mixture of Eosin Y (E.Y) and Pt-TiO 2 ceased in 10 h. The turnover number of the dye molecule fixed on TiO 2 surface reached more than 10,000, and the quantum yield of the E.Y-TiO 2 at 520 nm was determined to be about 10%.
267 citations
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TL;DR: The kinetics of ATP reagents not affected by product inhibition or other forms of inactivation of luciferase during the measurement time has been clarified and it is concluded that one should select the ideal ATP reagent carefully for each application.
Abstract: The kinetics of ATP reagents not affected by product inhibition or other forms of inactivation of luciferase during the measurement time has been clarified. Under these conditions the decay rate of the light emission expressed as percentage per minute is a measure of luciferase activity and can be given as the rate constant k (min-1), directly reflecting the degradation of ATP in the luciferase reaction. Three types of reagents with different analytical characteristics and different application possibilities have been identified. Stable light-emitting reagents are suitable for measurements of ATP down to 1000 amol. This is the only type of reagent suitable for monitoring ATP-converting reactions, i.e., assays of enzymes or metabolites, assays of oxidative phosphorylation, photophosphorylation, and so on. A higher luciferase activity resulting in a slow decay of the light emission by approximately 10% per minute (k = 0.1 min-1) gives a reagent suitable for measurements down to 10-100 amol. The slow decay of light emission allows use of manual luminometers without reagent dispensers. A further increase of the luciferase activity resulting in a decay rate of approximately 235% per min (k = 2.35 min-1) and only 10% of the light emission remaining after 1 min is suitable for measurements down to 1 amol corresponding to half a bacterial cell. With this type of flash reagent the total light emission can be calculated from two measurements of the light intensity on the decay part of the light emission curve. This new measure is not affected by moderate variations in luciferase activity, but only by changes in quantum yield and self-absorption of the light in the sample. Flash-type reagents require the use of reagent dispensers. The stringent requirements for ATP-free cuvettes, pipette tips, and contamination-free laboratory techniques make it unlikely that flash reagents would be useful in nonlaboratory surroundings. A potential application for this type of reagent is sterility testing. In general, it is concluded that one should select the ideal ATP reagent carefully for each application. Obviously the reagents used in a particular application do not have to match the decay rates given earlier exactly. However, various applications of the ATP technology and the properties of manual and automatic luminometers fall quite nicely into categories corresponding to the properties of the three reagents described. The rapidly growing interest in ATP technology has already resulted in the development of a greater variety of luminometers, from hand-held instruments to high-throughput systems. The continuation of efforts in both reagent and instrument development will undoubtedly result in many new applications.
246 citations
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TL;DR: In this paper, the surface coverage varies from 0.74 to 1.85 silyl groups/nm 2.8 nm according to the BJH pore size analysis of the desorption branch.
Abstract: Disilazane reagents of type HN(SiR1R22)2 carrying organic substituents R1,2 = H, Me, Ph, n-Bu, n-Oct, Vin (Vin = vinyl) of varying longitudinal and lateral extension are reacted with high quality MCM-41 samples of different pore sizes, i.e., effective pore diameters of 2.8 and 3.8 nm according to the BJH pore size analysis of the desorption branch. The reaction of the standard silylating reagent hexamethyldisilazane, HN(SiMe3)2, is shown to be controlled by the amount of added silylamine and the contact time, resulting in effective pore size engineering. Calculations from elemental analysis revealed that the degree of silylation (silylation efficiency) and hence the surface hydroxyl consumption depend on the steric bulk/shape of the groups R. The surface coverage varies from 0.74 to 1.85 silyl groups/nm2. The sterically least demanding tetramethyldisilazane, HN(SiHMe2)2, is the most efficient silylating reagent, while silyl groups with bulky phenyl substituents produce the lowest surface coverage featurin...
237 citations
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10 Jan 2000
TL;DR: In this paper, a method and reagent composition for covalent attachment of target molecules, such as nucleic acids, onto the surface of a substrate is presented, which can be used to provide activated slides for use in preparing microarrays of nucleic acid.
Abstract: Method and reagent composition for covalent attachment of target molecules, such as nucleic acids, onto the surface of a substrate. The reagent composition includes groups capable of covalently binding to the target molecule. Optionally, the composition can contain photoreactive groups for use in attaching the reagent composition to the surface. The reagent composition can be used to provide activated slides for use in preparing microarrays of nucleic acids.
218 citations
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TL;DR: A variety of ligands can be produced in useful amounts by a procedure that is simple, with starting materials that are relatively inexpensive, and, in most cases, without chromatographic purification.
Abstract: Functionalized dicyclohexyl- and di-tert-butylphosphinobiphenyl ligands are prepared by the reaction of arylmagnesium halides with benzyne, followed by the addition of a chlorodialkylphosphine. This one-pot procedure is considerably less expensive and time-consuming than the method used previously to prepare such ligands. The cost of introducing the dicyclohexylphosphine group can be decreased by preparing chlorodicyclohexylphosphine from PCl3 and cyclohexylmagnesium chloride, and using the reagent without further purification. The new method is significant, as a variety of ligands can be produced in useful amounts by a procedure that is simple, with starting materials that are relatively inexpensive, and, in most cases, without chromatographic purification.
210 citations
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TL;DR: In this paper, various methods used for the enhancement of reactivity and selectivity of NaBH4 in organic synthesis are described, and the selectivities realised in such reductions can be enhanced by adding another additive.
207 citations
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TL;DR: SDS-PAGE showed that LPS and lipid A isolated using the Tri-Reagent approach were cleaner and suffered less degradation through loss of phosphate and (or) fatty acyl side chains from lipid A.
Abstract: A fast, convenient extraction method for lipopolysaccharide (LPS), using a commercial RNA isolating reagent, allows the isolation of LPS or lipid A from low milligram (dry weight) quantities of bacterial cells. The method avoids the use of specialized equipment and has been used for processing relatively large numbers of samples. The major components of the commercial RNA isolating reagent, Tri-Reagent, are phenol and guanidinium thiocyanate in aqueous solution. The bacterial cell membranes are disrupted with guanidinium thiocyanate, which eliminates the need for mechanical cell disruption (e.g. French press) or heating. LPS and its degradation products, with particular attention paid to its bioactive lipid A portion, were measured and compared with those from the most common conventional extraction method, hot phenol-water. Negative ion quadrupole ion trap and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, fatty acid composition analysis by capillary gas chromatography, total and free phosphate by UV spectrophotometry and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that LPS and lipid A isolated using the Tri-Reagent approach were cleaner and suffered less degradation through loss of phosphate and (or) fatty acyl side chains from lipid A. The Tri-Reagent extraction method generated low free phosphate contamination, 11% of the total phosphate concentration, whereas the hot phenol-water extraction method gave approximately 58% as free, inorganic phosphate. Similar results were observed for the degradation of fatty acyl side chains. The time required by the new method is considerably shorter (two or three days) than that required by conventional hot phenol-water extraction (about two weeks).
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TL;DR: A new approach to preparative organic synthesis in aqueous–organic systems is suggested, based on the idea that the enzymatic process is carried out in a biphasic system “water–water‐immiscible organic solvent,” which eliminates the traditional problem of stabilizing the enzyme against inactivation by a nonaqueous solvent.
Abstract: A new approach to preparative organic synthesis in aqueous–organic systems is suggested. It is based on the idea that the enzymatic process is carried out in a biphasic system “water–water-immiscible organic solvent.” Thereby the enzyme is localized in the aqueous phase—this eliminates the traditional problem of stabilizing the enzymes against inactivation by a nonaqueous solvent. Hence, in contrast to the commonly used combinations “water–water-miscible organic solvent,” in the suggested system the content of water may be infinitely low. This allows one to dramatically shift the equilibrium of the reactions forming water as a reaction product (synthesis of esters and amides, polymerization of amino acids, sugars and nucleotides, dehydration reactions, etc.) toward the products. The fact that the system consists of two phases provides another very important sources for an equilibrium shift, i.e., free energies of the transfer of a reagent from one phase to the other. Equations are derived describing the dependence of the equilibrium constant in a biphasic system on the ratio of the volumes of the aqueous and nonaqueous phases and the partition coefficients of the reagents between the phases. The approach has been experimentally verified with the systhesis of N-acetyl-L-tryptophan ethyl ester from the respective alcohol and acid. Porous glass was impregnated with aqueous buffer solution of chymotrypsin and suspended in chloroform containing N-acetyl-L-tryptophan and ethanol. In water (no organic phase) the yield of the ester is about 0.01%, whereas in this biphasic system it is practically 100%. The idea is applicable to a great number of preparative enzymatic reactions.
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01 Jan 2000TL;DR: The formation of silica shells on core silver particles by a modified Stöber process was investigated and the coated particles were characterized using UV-visible spectroscopy, transmission electron microscopy, and electrophoresis.
Abstract: The formation of silica shells on core silver particles by a modified Stober process was investigated and the coated particles were characterized using UV–visible spectroscopy, transmission electron microscopy, and electrophoresis. The deposition conditions, such as reagent concentrations and reaction time, were optimized in order to obtain uniform surface layers of silica and to avoid excess precipitation of the latter.
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TL;DR: The improvement in the decomposition levels reached by the combined processes, due to the generation of the very reactive hydroxyl radicals, in relation to the single oxidants is clearly demonstrated and evaluated by kinetic modeling.
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TL;DR: A protocol is described for rapid RNA isolation from various plant species and tissues rich in polyphenolics and polysaccharides based on the Nucleon PhytoPure™ system without the use of phenol.
Abstract: A protocol is described for rapid RNA isolation from various plant species and tissues rich in polyphenolics and polysaccharides. The method is based on the Nucleon PhytoPure™ system without the use of phenol. The procedure can be completed within 1 h and many samples can be processed at the same time. The yield ranged from 240 μg up to 3 mg per gram of tissue with an average purity measured as A260/280 of 1.85. The RNA was of sufficient quality for use in RT-PCR reactions. Quantitation of single-stranded cDNA was carried out with the RiboGreen™ reagent and of PCR products with the PicoGreen™ reagent.
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09 Feb 2000TL;DR: In this article, a method of forming a regioregular polythiophene from a polymerization reaction is described, which proceeds by combining a soluble thiophene having at least two leaving groups with an organomagnesium reagent, and adding thereto an effective amount of Ni(II) catalyst to initiate the reaction.
Abstract: A method of forming a regioregular polythiophene from a polymerization reaction is described. The method proceeds by combining a soluble thiophene having at least two leaving groups with an organomagnesium reagent to form a regiochemical isomer intermediate, and adding thereto an effective amount of Ni(II) catalyst to initiate the polymerization reaction.
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TL;DR: In this article, the photooxidative degradation of phenol in aqueous TiO2 dispersions has been revisited to determine the dependencies of the rate on the concentration of the phenol and on the photon flow (ρ) of the actinic light at 365nm.
Abstract: The photooxidative degradation of phenol in aqueous TiO2 dispersions has been revisited to determine the dependencies of the rate on the concentration of phenol and on the photon flow (ρ) of the actinic light at 365 nm. The principal objective was to assess the factors that influence the efficiency of the photocatalytic process, the rate of which is described by the function d C d t (ρ,C)=( const )C n ρ m where n and m are orders of the reaction with respect to concentration and photon flow (light intensity), respectively. The reaction order m varies with reagent concentration C, whereas the order n depends on photon flow ρ. The description indicates that m→1 if n→0, whereas n→1 if m→0. Therefore, the reaction orders m and n of phenol photodegradation are interdependent. A detailed kinetic description of the process is given based on two well-known mechanistic/kinetic models, namely (i) the Langmuir–Hinshelwood (LH) model whereby the organic reagent is pre-adsorbed on the photocatalyst surface prior to UV illumination, and (ii) the Eley–Rideal (ER) model for which the organic reagent diffuses from the solution bulk onto the photocatalyst surface to interact with the activated state of the photocatalyst. The kinetic treatment infers that it is possible (under certain conditions) to delineate between the LH and ER mechanistic models on the basis of the magnitude of the Langmuir constant KL at very high photon flow, i.e. when ρ→∞ {for the LH pathway, KL→K; for the ER model KL→0}, and on the dependence of kobs of the process on ρ. For the ER model, kobs scales linearly with ρ at high photon flow, whereas for the LH pathway kobs displays a sub-linear dependence on ρ and tends toward saturation at high photon flow.
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TL;DR: In this article, a thermogravimetric study showed that ZnCl2, H3PO4 and KOH were capable of suppressing the evolution of tarry substances during carbonization.
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TL;DR: In this article, two silica gel phases loaded with dithizone were synthesized based on chemical binding and physical adsorption approaches, and the application of these two gel phases for sorption of a series of metal ions was performed by using different controlling factors such as the pH of metal ion solution and the equilibration shaking time by static technique.
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TL;DR: The Pd2(dba)3/P(tBu)3 was found to promote the Sonogashira reaction of aryl bromides at room temperature and without CuI as the co-catalyst in high yield as mentioned in this paper.
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TL;DR: The potential of the Fenton's reagent for oxidation of p-aminophenols, which are the main developers used in white and black processes, was assessed in this article.
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11 Aug 2000
TL;DR: In this article, an analyzing cartridge has a plurality of reservoirs and capillaries connected for communication between these reservoirs, and provided therein with a reagent required for analyzing, wherein the reservoirs are provided with openings leading to the outside of the cartridge, and the openings are covered with vents each consisting of a gas-permeable/non-liquid permeable, hydrophobic, porous film.
Abstract: An analyzing cartridge having a plurality of reservoirs and capillaries connected for communication between these reservoirs, and provided therein with a reagent required for analyzing, wherein the reservoirs are provided with openings leading to the outside of the cartridge, and the openings are covered with vents each consisting of a gas-permeable/non-liquid-permeable, hydrophobic, porous film. The analyzing cartridge requires only trace amounts of a sample and a reagent and no maintenance, is suitable for POC analysis or the like, and is provided with a non-fluid reagent in vent-carrying reservoirs, thereby making it possible to formulate a very trace amount of reagent solution in the cartridge by injecting a reagent dissolving liquid into the reservoirs immediately before analyzing. A liquid feed control device which controls the feeding of the liquid between the reservoirs via the capillaries when it is attached to the analyzing cartridge to allow or control an air entry/exit via the vents.
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TL;DR: In this paper, a spectrophotometric sequential injection (SI) determination of phosphate and silicate in environmental samples and cell cultivation medium using the molybdenum blue reaction was presented.
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TL;DR: Montmorillonite impregnated with bismuth nitrate was found to be an excellent reagent for aromatic nitration in high yield as discussed by the authors, and it was used in the synthesis of aromatic nitrate.
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05 Oct 2000TL;DR: A reagent test strip for measuring an analyte concentration in a biological fluid has a spreading mesh sandwiched between a support and a reagent matrix as discussed by the authors, which is covered by the mesh.
Abstract: A reagent test strip for measuring an analyte concentration in a biological fluid has a spreading mesh sandwiched between a support and a reagent matrix. The support has a through hole that is covered by the mesh. In use, a sample of the fluid is applied through the hole in the support to the spreading mesh. The sample then passes through the mesh to the matrix, which contains a reagent that indicates the analyte concentration by causing a corresponding change in reflectance at its free surface. Optionally, an adhesive layer attaches the mesh, and optionally the matrix as well, to the support.
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TL;DR: The analysis of twenty underivatized protein amino acids has been achieved on porous graphitic carbon packing material (Hypercarb) and the chromatographic methodology developed can also be easily coupled with pneumatically assisted electrospray mass spectrometry.
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TL;DR: In this article, the authors examined the use of three advanced oxidation processes in degrading the textile dye, Reactive Red 235, using ozonation, standard Fenton's reagent (Fe2+/H2O2) and a modified photo-Fenton's process (UV/Fe oxalate/H 2O2).
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27 Oct 2000
TL;DR: In this paper, an enzyme electrosensor, e.g., electroimmunosensor, device for electrochemical detection and preferably, real-time measurement, which is suitable for use at point-of-care settings by unskilled personnel.
Abstract: The present invention relates to devices comprising electrosensors containing capture reagents, their preparation thereof, and their use for detecting, preferably, quantitative measurement, of analyte in a liquid sample. In particular, the invention relates to an enzyme electrosensor, e.g., electroimmunosensor, device for electrochemical detection and preferably, real-time measurement, which is suitable for use at point-of-care settings by unskilled personnel.
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TL;DR: Assessment of phosphate species for bicarbonate-bearing lowland rivers of the Thames valley, England and acidic Welsh upland streams reveal problems of silica interference when employing standard automated 'phosphomolybdic acid' colorimetric methodologies.
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TL;DR: A process design based on treating only the aromatic fraction of petroleum may provide significantly lower costs when using modified Fenton's reagent for the treatment of contaminated soils and groundwater.