Showing papers on "Reagent published in 2000"

Complete Destruction of p-Nitrophenol in Aqueous Medium by Electro-Fenton Method

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.

An ecologically effective water treatment technique using electrochemically generated hydroxyl radicals for in situ destruction of organic pollutants: Application to herbicide 2,4-D

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.

Reagent-Controlled Transition-Metal-Catalyzed Radical Reactions

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

A Novel B(C6F5)3-Catalyzed Reduction of Alcohols and Cleavage of Aryl and Alkyl Ethers with Hydrosilanes†

Abstract: The primary alcohols 1a−e and ethers 4a−d were effectively reduced to the corresponding hydrocarbons 2 by HSiEt3 in the presence of catalytic amounts of B(C6F5)3. To the best of our knowledge, this is the first example of catalytic use of Lewis acid in the reduction of alcohols and ethers with hydrosilanes. The secondary alkyl ethers 4j,k enabled cleavage and/or reduction under similar reaction conditions to produce either the silyl ethers 3m−n or the corresponding alcohol 5a upon subsequent deprotection with TBAF. It was found that the secondary alcohols 1g−i and tertiary alcohol 1j, as well as the tertiary alkyl ether 4l, did not react with HSiEt3/(B(C6F5)3 reducing reagent at all. The following relative reactivity order of substrates was found: primary ≫ secondary > tertiary. A plausible mechanism for this nontraditional Lewis acid catalyzed reaction is proposed.

Steady hydrogen evolution from water on Eosin Y-fixed TiO2 photocatalyst using a silane-coupling reagent under visible light irradiation

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%.

Use of firefly luciferase in ATP-related assays of biomass, enzymes, and metabolites.

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.

New Applications of Polyfunctional Organometallic Compounds in Organic Synthesis

Abstract: In the second half of the twentieth century much effort was invested in the preparation of highly reactive polar organometallic reagents. The high reactivity of these reagents precluded the presence of many functional groups and often good chemoselectivities and stereoselectivities could only by achieved by transmetalation reactions. The synthesis of increasingly complex target molecules and the desire to avoid tedious protection-deprotection steps has led inevitably to the use of functionalized organometallic reagents in retrosynthesis. In the last fifteen years, the generation of organic derivatives of numerous metals and metalloids (Li, Mg, B, Zn, Sn) was investigated. In this review the most important preparations and applications of organometallic reagents in organic synthesis will be covered, with particular emphasis on organozinc reagents.

Surface Characterization and Functionalization of MCM-41 Silicas via Silazane Silylation

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...

Target molecule attachment to surfaces

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.

An Improved Synthesis of Functionalized Biphenyl-Based Phosphine Ligands

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.

Rapid isolation method for lipopolysaccharide and lipid A from Gram-negative bacteria

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).

A new approach to preparative enzymatic synthesis.

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.

Coating of Nanosize Silver Particles with Silica

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.

A simple and efficient protocol for isolation of functional RNA from plant tissues rich in secondary metabolites

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.

A method of forming poly-(3-substituted) thiophenes

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.

Factors affecting the efficiency of a photocatalyzed process in aqueous metal-oxide dispersions: Prospect of distinguishing between two kinetic models

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.

Phenylglycine methyl ester, a useful tool for absolute configuration determination of various chiral carboxylic acids

Abstract: A new chiral anisotropic reagent, phenylglycine methyl ester (PGME), developed for the elucidation of the absolute configuration of chiral α,α-disubstituted acetic acids, has turned out to be applicable to other substituted carboxylic acids, such as chiral α-hydroxy-, α-alkoxy-, and α-acyloxy-α,α-disubstituted acetic acids, as well as to chiral β,β-disubstituted propionic acids. Because a carboxylic moiety is convertible from other functional groups, e.g., ozonolysis of an olefin and oxidative cleavage of a glycol, the present findings can expand the utility of the PGME method to the absolute configuration determination of various types of organic compounds, even those which initially lack oxygen functions. Several examples of the combination of chemical reactions and the PGME method are described.

Cellulose Solutions in Water Containing Metal Complexes

Abstract: Aqueous solutions of a number of metal complexes have been found to dissolve cellulose. Recently, a number of new metal complexes have been developed that completely dissolve cellulose by deprotonating and coordinative binding the hydroxyl groups in the C2 and C3 position of the anhydro glucose. A detailed comparative light scattering study is given for cellulose in Schweizer's reagent (cuoxam), Ni-tren, and Cd-tren. Cuoxam is the well-known solution of cupric hydroxide in aqueous ammonia, and the abbreviation tren stands for tris(2-aminoethyl)amine. Cuoxam and Ni-tren are deep blue solvents. The light scattering measurements were carried out with the blue line of an argon ion laser at wavelength I0 ) 457.9 nm, and the data from these solvents required an absorption correction according to the Lambert-Beer law. Cd-tren is almost colorless, and the data could be used without correction. Because of traces of colloid particles, possibly originating from the metal hydroxides, a special treatment for optical clarification became necessary. A large number of samples, cotton linters, various pulp celluloses, and bacterial celluloses, were studied. All three solvents exhibited good solution properties, but only Cd-tren was capable of dissolving also the highest degrees of polymerization of cotton linters and bacterial cellulose (DPw ) 9700). The limits for the two other solvents were DPw < 6300 for Ni-tren and DPw < 5300 for cuoxam. A fairly high chain stiffness was found with Kuhn segment lengths of lK ) 15.8 ( 1.4 nm for Cd-tren, lK ) 10.2 ( 0.8 nm for Ni-tren, and lK ) 13.1 ( 1.2 nm for cuoxam, corresponding to characteristic ratios of C∝ ) 24.6, 15.4, and 19.4, respectively. The problem of preferential adsorption is discussed.

Analyzing cartridge and liquid feed control device

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.

An autocatalytic mechanism of protein nitrosylation

Abstract: Comparative analysis of Cys nitrosation. (A and B) UV-visible absorption spectra of newly generated chromophore during the reaction of BSA, GSH, or free Cys with the aqueous solution of ⋅NO. After addition of 100 μM (A) or 10 μM (B) ⋅NO to the aqueous solution of either reagent, spectra were recorded immediately and repeated every 5 min for a total of six cycles. Recording was conducted against a blank sample containing BSA, GSH, or free Cys. Overlapping spectra corresponding to nitroso-Trp were subtracted. The final concentration of each of the reagents was 0.4 mM in both A and B. (C) Graphic representation of the results of A. (D) Difference between the initial nitrosation rate of BSA (RBSA) and that of free Cys (RCys) as a function of ⋅NO concentration. Experiments similar to those shown in A and B have been done by using eight other ⋅NO concentrations: 30, 60, 120, 200, 300, 500 μM, and 1 mM. In each case, the experiment was repeated four times, and the averages of RBSA and RCys were calculated. Then the ratio between RBSA and RCys was plotted as a function of ⋅NO concentration. ΔD346, absorbance (OD units) with the maximum at λ 346 nm.