Showing papers on "Reagent published in 2006"

A modified protocol for rapid DNA isolation from plant tissues using cetyltrimethylammonium bromide.

Abstract: We describe a modification of the DNA extraction method, in which cetyltrimethylammonium bromide (CTAB) is used to extract nucleic acids from plant tissues. In contrast to the original method, the modified CTAB procedure is faster, omits the selective precipitation and CsCl gradient steps, uses less expensive and toxic reagents, requires only inexpensive laboratory equipment and is more readily adapted to high-throughput DNA extraction. This protocol yields approximately 5-30 microg of total DNA from 200 mg of tissue fresh weight, depending on plant species and tissue source. It can be completed in as little as 5-6 h.

Ionic-Liquid-Supported Synthesis: A Novel Liquid-Phase Strategy for Organic Synthesis

Abstract: Soluble ionic liquids have recently been used as supports for catalyst/reagent immobilization and synthesis in homogeneous solution phase. The wide range of ionic liquid supports available makes their use as supports compatible with most common chemistries. The solubility properties of these ionic liquid supports can be tuned by the variation of cations and anions to make them phase separate from less polar organic solvents and aqueous media. The ionic-liquid-supported species can therefore be purified from the reaction mixture by simple washings. Ionic-liquid-supported catalysts and reagents have been prepared and used, and they are easily recovered and reused. Parallel and combinatorial libraries of small molecules have been synthesized. Ionic-liquid-supported synthesis (ILSS) has been applied to the preparation of oligopeptides and oligosaccharides. The comparison of ILSS with solid-phase synthesis, soluble-polymer-supported synthesis, and fluorous phase synthesis has been highlighted where applicable.

Efficient synthesis of meso-substituted corroles in a H2O-MeOH mixture.

Abstract: New and efficient conditions for the synthesis of meso-substituted corroles were developed. The first step, involving the reaction of aldehydes with pyrrole, was carried out in a water-methanol mixture in the presence of HCl. A relatively narrow distribution of aldehyde-pyrrole oligocondensates was obtained through careful control of their solubility in the reaction medium. After thorough optimization of various reaction parameters (cosolvent, reagent, and acid concentration), high yields of bilanes were obtained. Additionally, the bilane derived from 4-cyanobenzaldehyde was isolated, and the oxidative macrocyclization reaction was performed under various reaction conditions (different solvents, different concentrations, and various oxidants). As a result, triphenylcorrole was obtained in the highest yield (32%) reported to date. The scope and limitations studied showed that this method was particularly efficient for moderately reactive aldehydes and those bearing electron-donating groups (yields 14-27%). Using these conditions, corroles bearing strongly electron-donating groups were obtained for the first time. In addition, it was found that the reaction of unhindered dipyrromethanes with aldehydes under analogous conditions afforded trans-A2B-corroles in very high yields (45-56%; 8-fold higher than previously reported) without scrambling. The fact that scrambling was not observed in this reaction despite a very high HCl concentration (0.3 M) is unprecedented. Detailed studies on the oxidation of bilane, derived from sterically hindered dipyrromethane, allowed us to unequivocally establish that the yield of macrocyclization is insensitive to the concentration. It was found the 1H NMR spectra of corroles in deuterated TFA gave very sharp signals.

Treatment of Contaminated Soils and Groundwater Using ISCO

Abstract: In situ chemical oxidation (ISCO) is a rapidly growing field for the remediation of contaminated soils and groundwater. This paper provides an overview of the four oxidation systems that are in common use for ISCO: Catalyzed H2 O2 propagations (CHP) (i.e., modified Fenton’s reagent), permanganate, ozone, and persulfate. Each of the oxidants has different characteristics; for example, CHP is a nonselective oxidizing and reducing system that is capable of degrading almost all organic contaminants and destroying dense nonaqueous phase liquids and sorbed contaminants, but it is unstable in the subsurface. In contrast, permanganate is a selective oxidant that reacts primarily with alkenes and is highly stable in groundwater. Ozone exhibits wide reactivity but is limited by mass transfer limitations and stability. Persulfate is the newest oxidant being used for ISCO; it is moderately stable in the subsurface, and appears to have widespread reactivity, but more research is needed on its chemistry in soils and gr...

Enantioselective, Palladium-Catalyzed α-Arylation of N-Boc-pyrrolidine

Abstract: This communication discloses the first instance of the enantioselective Pd-catalyzed α-arylation of N-Boc-pyrrolidine. The methodology relies on Beak's sparteine-mediated, enantioselective deprotonation of N-Boc-pyrrolidine to form the 2-pyrrolidinolithium specices in high enantiomeric ratio (er). Transmetalation of this intermediate with zinc chloride generates the stereochemically rigid, 2-pyrrolidinozinc reagent, which was readily coupled to a variety of functionalized aryl halides at room temperature using a catalyst generated from Pd(OAc)2 and PtBu3−HBF4. A diverse array of 2-aryl-N-Boc-pyrrolidines was synthesized using this methodology, providing adducts consistently in a 96:4 er. A survey of the stoichiometry revealed that as little as 0.3 equiv of zinc could be used in the coupling reaction, and the 2-pyrrolidinozinc reagent was found to exhibit stereochemical stability up to 60 °C. The method allows for the most convergent and reliable preparation of a broad range of functionalized 2-aryl-N-Boc-...

Aerobic Oxidation of Glucose with Gold Catalyst: Hydrogen Peroxide as Intermediate and Reagent

Abstract: Careful analytical determinations show that the gold-catalysed aerobic oxidation of glucose occurs through a two-electrons mechanism leading to gluconate and hydrogen peroxide. This latter decomposes before reaching the critical concentration for competing with O 2 in glucose oxidation. A mechanism of glucose oxidation on gold nanoparticles is presented.

Thin-Layer Chromatography: Reagents and Detection Methods

Abstract: Part 1 Specific detection methods: activation reactions reagents for the recognition of functional groups reagent series. Part 2 Reagents in alphabetical order.

Ultra-deep oxidative desulfurization of diesel fuel with H2O2 catalyzed under mild conditions by polymolybdates supported on Al2O3

Abstract: The evaluation of the catalytic oxidative desulfurization (OD) activity of alumina-supported polymolybdates (Mo/Al2O3) was carried out using organosulfur model compounds and diesel fuel. Hydrogen peroxide was the oxidizing reagent. Ultra-deep desulfurization, 97.8% removal of sulfur in diesel fuel, was achieved by reaction under mild conditions followed by solvent extraction. The catalyst was prepared by equilibrium adsorption and characterized by infrared, Raman, X-ray photoelectron, 31 P and 27 Al MAS NMR spectroscopies. Our results indicate that the phosphomolybdate used during synthesis of the catalysts decomposes and forms hydrated hepta- and octamolybdates as well as phosphate ions on the surface of alumina. # 2006 Published by Elsevier B.V.

Highly efficient alkylation to ketones and aldimines with Grignard reagents catalyzed by zinc(II) chloride.

Abstract: A highly efficient alkylation to ketones and aldimines with Grignard reagents in the presence of catalytic trialkylzinc(II) ate complexes derived from ZnCl2 (10 mol %) in situ was developed This simple Zn(II)-catalyzed alkylation could minimize the well-known but serious problems with the use of only Grignard reagents, which leads to reduction and aldol side products, and the yield of desired alkylation products could be improved

Electron spin resonance spin-trapping detection of radical intermediates in N-doped TiO2-assisted photodegradation of 4-chlorophenol.

Abstract: The electron spin resonance (ESR) spin-trapping technique using 5,5-dimethyl-1-pyrroline-N-oxide as the spin-trap reagent has been applied to detect free radical intermediates generated during in situ ultraviolet or visible irradiation of aqueous 4-chlorphenol (4-CP)/N-doped TiO2 suspensions. ESR measurements gave the first direct evidence that the active species (•OH and O2•-) are responsible for the photodecomposition of 4-CP over N-doped TiO2 under visible-light irradiation, strongly suggesting that the photocatalytic reaction of organic compounds in powdered N-doped TiO2 systems proceed via surface intermediates of oxygen reduction or water oxidation, not via direct reaction with holes trapped at the N-induced midgap level. These results have important implications for the evaluation of the oxidative powder of TiO2-xNx catalysts.

Polyethylenimine, a cost-effective transfection reagent

Abstract: In search for a cheap and effective transfection reagent we used the positively charged polyplex-forming compound polyethylenimine (PEI). This compound is commercially available from different companies either as a non-modified chemical reagent or with additives as a more cost intensive transfection reagent. Here we used the non-modified PEI reagent to optimize transfection protocols for different cell-lines. With these optimized conditions we were able to transiently transfect a number of cell-lines up to 40–90%.

On the mechanism of the copper-catalyzed enantioselective 1,4-addition of grignard reagents to alpha,beta-unsaturated carbonyl compounds.

Abstract: The mechanism of the enantioselective 1,4-addition of Grignard reagents to α,β-unsaturated carbonyl compounds promoted by copper complexes of chiral ferrocenyl diphosphines is explored through kinetic, spectroscopic, and electrochemical analysis. On the basis of these studies, a structure of the active catalyst is proposed. The roles of the solvent, copper halide, and the Grignard reagent have been examined. Kinetic studies support a reductive elimination as the rate-limiting step in which the chiral catalyst, the substrate, and the Grignard reagent are involved. The thermodynamic activation parameters were determined from the temperature dependence of the reaction rate. The putative active species and the catalytic cycle of the reaction are discussed.

Magnetic nanoparticles as an orthogonal support of polymer resins: applications to solid-phase suzuki cross-coupling reactions.

Abstract: Most of the reactants immobilized on conventional solid-phase resins are buried inside the interiors of lightly cross-linked polystyrene beads. An orthogonal support of solid-phase resins needs to be small enough to penetrate the interpolymeric chain spaces of a swollen resin to reach reaction sites. In this paper, we report the use of magnetic nanoparticles (∼4 nm) as an orthogonal matrix to assist solid-phase reactions. A magnetic nanoparticle-supported homogeneous Pd catalyst was employed for promoting the Suzuki cross-coupling of an aryl halide on resins and an excessive arylboronic acid in solution. The workup separating three components (the catalyst, product, and remaining arylborate) is a chromatography-free process. The Pd catalyst was magnetically isolated and recycled from the reaction mixture by applying an external magnetic field. Then, a filtration process was followed to recover the excess borate reagent from the resins/product. Our work here presents the first example of an orthogonal matr...

A simple colorimetric method for determination of hydrogen peroxide in plant tissues

Abstract: A simple colorimetric method for determination of hydrogen peroxide in plant materials is described. The method is based on hydrogen peroxide producing a stable red product in reaction with 4-aminoantipyrine and phenol in the presence of peroxidase. Plant tissues was ground with trichloroacetic acid (5% w/v) and extracts were adjusted to pH 8.4 with ammonia solution. Activated charcoal was added to the homogenate to remove pigments, antioxidants and other interfering substances. The colorimetric reagent (pH 5.6) consisted of 4-aminoantipyrine, phenol, and peroxidase. With this method, we have determined the hydrogen peroxide concentration in leaves of eight species which ranged from 0.2 to 0.8 µmol g−1 FW. Changes in hydrogen peroxide concentration of Stylosanthes guianensis in response to heat stress are also analyzed using this method.

Selective Heterogeneous Nucleation and Growth of Size‐Controlled Metal Nanoparticles on Carbon Nanotubes in Solution

Abstract: We present a novel approach to the in situ deposition of size-controlled platinum nanoparticles on the exterior walls of carbon nanotubes (CNTs). The reduction of metal ions in ethylene glycol (EG), by the addition of a salt such as sodium dodecyl sulfate (SDS), p-CH3C6H4SO3Na, LiCF3SO3, or LiClO4, results in high dispersions and high loadings of platinum nanoparticles on CNTs without aggregation. We have performed controlled experiments to elucidate the mechanism. By exploiting the salt effect, our method effectively depresses homogeneous nucleation, leading to selective heterogeneous metal nucleation and growth, even on unmodified CNTs. In the 2.3-9.6 nm size range, the size of platinum nanoparticles, at 50% loading, can be controlled by changing the concentration of metal ions, the reaction temperature, the reducing reagent or the means by which reactive solutions are added. Our method provides a flexible route towards the preparation of novel one-dimensional hybrid materials, for which a number of promising applications in a variety of fields can be envisioned.

Efficient entry to diversely functionalized spirocyclic oxindoles from isatins through carbonyl-addition/cyclization reaction sequences.

Abstract: A novel approach to diversely functionalized spirocyclic oxindoles has been developed by using different metal-mediated carbonyl-addition/cyclization reaction sequences. Spirocyclization precursors, 2-indolinone-tethered homoallylic alcohols, (buta-1,3-dien-2-yl)methanols, and α-allenols have been obtained by regioselective addition of stabilized organoindium reagents to isatins in aqueous environment. Ruthenium-, silver-, and palladium-catalyzed reactions of the above unsaturated alcohol derivatives provided oxaspiro oxindoles.