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Results 301 - 350 of 1684
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Kolarovic Andrej - - 2009
A very efficient protocol enabling catalytic decarboxylation of a wide range of 2-alkynoic acids is described. The reaction conditions and the scope of the process are examined. The method is further utilized in a model decarboxylative coupling.
Koller Raffael - - 2009
A variety of sulfonic acids have been trifluoromethylated using 1-trifluoromethyl-1,2-benziodoxol-3(1H)-one under mild conditions in good to excellent yields. Initial mechanistic investigations of this reaction show a clean second-order kinetics and only very weak substrate electronic effects.
Takagaki Atsushi - - 2009
5-Hydroxymethylfurfural (HMF), one of the most important intermediates derived from biomass, was directly produced from monosaccharides (fructose and glucose) and disaccharides (sucrose and cellobiose) by a simple one-pot reaction including hydrolysis, isomerization and dehydration using solid acid and base catalysts under mild conditions.
Jones Kimberly G - - 2009
Bimolecular rate constants for the hydroxyl radical, .OH, reaction with domoic acid, kainic acid, and several model compounds were determined using electron pulse radiolysis and transient absorption spectroscopy. These oxidation rate constants were determined as (9.22 +/- 0.60) x 10(9) M(-1) s(-1) and (2.46 +/- 0.19) x 10(9) M(-1) s(-1), ...
Watts Zachary I - - 2009
Photochemical reactions of free and N-acetyl alpha-amino acids with chlorine and deuterium labeled hydrogen peroxide have been used to determine both the relative rates of reaction of molecules of these classes and the relative reactivity of their different types of hydrogen toward abstraction by chlorine and oxygen centered radicals. The ...
Jin Shan - - 2009
Fluoride has been found to protect boronic acids from copper(i)-mediated decomposition; such findings should be very useful for the preparation of boronic acid-based carbohydrate sensors and boronic acid conjugates using the copper(i)-mediated click reaction.
Gross Simone - - 2009
Heterogeneous reactions between NO3 and N2O5 and diethyl sebacate (DES), glycerol, oleic acid (OA), linoleic acid (LA), and conjugated linoleic acid (CLA) were studied to understand better nighttime aerosol chemistry. The reactive uptake coefficient of NO3 on the liquid alkenoic acids (OA, LA, and CLA) was found to be >0.07, ...
Dias Joana M - - 2009
The objective of the present work was: (i) to enable biodiesel production from acid waste lard; (ii) to study the esterification reaction as possible pre-treatment at different temperatures, catalyst amount and reaction times; (iii) to evaluate biodiesel quality according to EN 14214 after basic transesterification of the pre-treated fat; and ...
N??jera Juan J - - 2009
Dicarboxylic acids, either directly emitted or formed in chemical processes, are found to be a significant component of tropospheric aerosols. To assess any potential chemical transformation of short unsaturated dicarboxylic acids in tropospheric heterogeneous chemistry, maleic and fumaric acid were selected as surrogates in this study. A novel aerosol flow ...
Zhang Zehui - - 2009
Solid acid-catalyzed hydrolysis of cellulose in ionic liquid was greatly promoted by microwave heating. H-form zeolites with a lower Si/Al molar ratio and a larger surface area showed a relatively higher catalytic activity. These solid catalysts exhibited better performance than the sulfated ion-exchanging resin NKC-9. Compared with conventional oil bath ...
Sundararaju Basker - - 2009
Selective N ,N-diallylation and N ,N, O-triallylation of free amino acids in the presence of catalytic amounts of RuCp*(MeCN)(3)PF(6) is reported. The crucial influence of the solvent makes these allylation reactions selectively possible.
Khriachtchev Leonid - - 2009
Conformation dictates many physical and chemical properties of molecules. The importance of conformation in the selectivity and function of biologically active molecules is widely accepted. However, clear examples of conformation-dependent bimolecular chemical reactions are lacking. Here we consider a case of formic acid (HCOOH) that is a valuable model system ...
Sun Wenjie - - 2009
Hydrogen abstraction from organic acids by hydroxyl radicals is the initial rate- and selectivity-determining step in the photochemical oxidation of organic acids in the troposphere. To quantify the rate and selectivity of these reactions, the abstraction of hydrogen atoms at the acid, alpha, beta, gamma, and methyl positions was studied ...
Varma Mahesh N - - 2010
The esterification of propionic acid was investigated using three different alcohols, namely, isopropyl alcohol, isobutyl alcohol, and isoamyl alcohol. The variation of conversion with time for the synthesis of isoamyl propionate was investigated in the presence of five enzymes. Novozym 435 showed the highest activity, and this was used as ...
Furuya Takeru - - 2009
A regiospecific Ag-mediated fluorination reaction of aryl- and alkenylboronic acids and esters is reported. The fluorination reaction uses commercially available reagents, does not require the addition of exogenous ligands, and can be performed on a multigram scale. This report discloses the first practical reaction sequence from arylboronic acid to aryl ...
Everett Renata - - 2009
The preparation of 5-bromo-2-naphthol (4) in three steps from 5-amino-2-naphthol (1) is described. A sulfonic acid group is introduced at the 1-position as an activating and protecting group for the Sandmeyer reaction. The sulfonate group allows for the use of only water and sulfuric acid as solvents. The sulfonic acid ...
Motokura Ken - - 2009
Acidic montmorillonite-immobilized primary amines (H-mont-NH(2)) were found to be excellent acid-base bifunctional catalysts for one-pot reaction sequences, which are the first materials with coexisting acid and base sites active for acid-base tamdem reactions. For example, tandem deacetalization-Knoevenagel condensation proceeded successfully with the H-mont-NH(2), affording the corresponding condensation product in a ...
Chhabra Meenu - - 2009
Laccase/mediator systems are important bioremediation agents as the rates of reactions can be enhanced in the presence of the mediators. The decolorization mechanism of two triarylmethane dyes, namely, Basic Green 4 and Acid Violet 17 is reported using Cyathus bulleri laccase. Basic Green 4 was decolorized through N-demethylation by laccase ...
Michielssens Servaas - - 2009
L-Aspartic acid has recently been found to be a good leaving group during HIV reverse transcriptase catalyzed incorporation of deoxyadenosine monophosphate (dAMP) in DNA. This showed that L-Asp is a good mimic for the pyrophosphate moiety of deoxyadenosine triphosphate. The present work explores the thermochemistry and mechanism for hydrolysis of ...
Gara Pedro M David - - 2009
The kinetics of the reaction of sulfate radicals with the IHSS Waskish peat fulvic acid in water was investigated in the temperature range from 289.2 to 305.2 K. The proposed mechanism considers the reversible binding of the sulfate radicals by the fulvic acid. The kinetic analysis of the data allows ...
Marcq Olivier - - 2009
The ozonation of d-glucose-1-(13)C, 2-(13)C, and 6-(13)C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC-MS, HPAEC-PAD, and (13)C NMR spectroscopy. Common oxidation products of glucose have also been submitted to identical ozonation conditions. For ...
Macht Josef - - 2009
We address here the manner in which acid catalysis senses the strength of solid acids. Acid strengths for Keggin polyoxometalate (POM) clusters and zeolites, chosen because of their accurately known structures, are described rigorously by their deprotonation energies (DPE). Mechanistic interpretations of the measured dynamics of alkane isomerization and alkanol ...
Illing H P A - - 2009
A series of chemically modified rosin resins have been tested for their potential to cause skin sensitization using the mouse LLNA. Where direct comparative evidence is available, the results of the mouse LLNA are consistent with previously obtained data using the GPMT. Reactions with sufficient fumaric acid or maleic anhydride ...
Majik Mahesh S - - 2009
The first example of a tandem Wittig-intramolecular ene reaction approach and its application toward the synthesis of kainic acid is reported. The synthetic pathway involves conversion of prenyl bromide into phosphorane 3, followed by one-pot Wittig olefination and an ene reaction with glyoxalic acid to give the cis fused pyrrolidine ...
Mädler Stefanie - - 2009
Structure elucidation of tertiary or quaternary protein structures by chemical cross-linking and mass spectrometry (MS) has recently gained importance. To locate the cross-linker modification, dedicated software is applied to analyze the mass or tandem mass spectra (MS/MS). Such software requires information on target amino acids to limit the data analysis ...
Barshteyn Nella - - 2009
Previously, our laboratory has shown that hydroxymethylvinyl ketone (HMVK), a Michael acceptor oxidation product of the 1,3-butadiene metabolite, 3-butene-1,2-diol, readily reacts with hemoglobin at physiological conditions and that mass spectrometry of trypsin-digested peptides suggested adduct formation with various nucleophilic amino acids. In the present study, we characterized reactions ofHMVK (3 ...
Schopfer F J FJ Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15213, - - 2009
Nitroalkene fatty acid derivatives manifest a strong electrophilic nature, are clinically detectable, and induce multiple transcriptionally regulated anti-inflammatory responses. At present, the characterization and quantification of endogenous electrophilic lipids are compromised by their Michael addition with protein and small-molecule nucleophilic targets. Herein, we report a trans-nitroalkylation reaction of nitro-fatty acids ...
Severin Kay - - 2009
Boronic acids are versatile building blocks for the construction of complex molecular architectures. Using reversible condensation reactions, it is possible to obtain macrocycles, cages, dendritic structures, and rotaxanes, as well as 1-, 2-, and 3-dimensional polymers in one-pot reactions from simple starting materials. This perspective highlights important recent developments in ...
Yang Jing - - 2009
Two different mechanisms: Shift 1,2-isomerization and isomerization via the disproportionation reaction are investigated for aromatic hydrocarbons over acidic mordenite zeolite by using our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) scheme. The picture shows a schematic energy profile for the isomerization of toluene catalyzed by acidic mordenite.The geometrical ...
Trakhtenberg Leonid I - - 2009
The intramolecular tunneling of hydrogen atom in formic acid HCOOH at low temperatures is considered based on literature experimental data on C-O internal rotation. The energetic and geometric parameters as well as vibrational frequencies for formic acid in cis and trans configurations surrounded by 12 Ar atoms are calculated in ...
Jiang Bo - - 2009
A new domino autocatalytic reaction of imines with Meldrum's acid was described. In this reaction, a series of polycyclic spiro[5.5]undecane-1,5,9-trione and dispiro[4.2.5.2]pentadecane-9,13-dione derivatives, with remarkable diastereoselectivity, were successfully synthesized in acidic condition, and up to six new bonds were formed accompanied by the C=N bond cleavage of the imines and ...
Ehrhardt M R - - 2010
The rheological properties of acid hydrolyzed corn stover at high solids concentration (20-35 wt.%) were investigated using torque rheometry. These materials are yield stress fluids whose rheological properties can be well represented by the Bingham model. Yield stresses increase with increasing solids concentration and decrease with increasing hydrolysis reaction temperature, ...
Ma Yan - - 2009
This paper describes experimental studies aimed at elucidating mechanisms for the formation of low-volatility organic acids in the gas-phase ozonolysis of 3-carene. Experiments were carried out in a static chamber under 'OH-free' conditions. A range of multifunctional acids-which are analogous to those observed from alpha-pinene ozonolysis-were identified in the condensed ...
Ye Yu Y Department of Chemistry, Wayne State University, Detroit, Michigan 48202, - - 2009
Experimentally, it was observed that the oxidized guanine lesion spiroiminodihydantoin (Sp) contained in highly purified oligodeoxynucleotides slowly converts to guanidinohydantoin (Gh). The reaction is accelerated in the presence of acid. The possible mechanisms of this transformation have been analyzed computationally. Specifically, the potential energy surface for formation of Gh from ...
Brodhun Florian - - 2009
The homothallic ascomycete Aspergillus nidulans serves as model organism for filamentous fungi because of its ability to propagate with both asexual and sexual life cycles, and fatty acid-derived substances regulate the balance between both cycles. These so-called psi (precocious sexual inducer) factors are produced by psi factor-producing oxygenases (Ppo enzymes). ...
Ahlquist Mårten M Materials and Process Simulation Centre (MC-139-74), California Institute of Technology, Pasadena, CA, 91125, - - 2009
Quantum mechanical (QM) results are used to establish the role of sulfuric acid solvent in facilitating the reaction between Pt(II)(bpym)Cl(2) (bpym = 2,2'-bipyrimidinyl) and methane; coordination of methane to the platinum catalyst is found to be catalyzed by the acidic medium.
Forsman Jonas J - - 2009
The mechanism of the acid-catalyzed anomerization of 1-O-acetyl-2,3,5-O-benzoyl-alpha- and -beta-L-ribofuranoses in different acetic acid-acetic anhydride mixtures was investigated. The progress of the reactions was followed by NMR spectroscopy and the rate constants for the reactions were determined by the use of a kinetic model. The site of anomeric activation was ...
Budija Franc - - 2009
Black poplar wood, diethylene glycol (DEG), and sulphuric acid as a catalyst were used as starting reactants for liquefaction. Optimal conditions for liquefaction were established: reaction temperature 150 degrees C, reaction time 95min, ratio of wood:DEG=1:5 and 3% of sulphuric acid addition. The liquid mixture obtained by the liquefaction was ...
Catak Saron - - 2009
Quantum chemical calculations are reported to provide new insights on plausible mechanisms leading to the deamidation of asparagine residues in proteins and peptides. Direct hydrolysis to aspartic acid and several succinimide-mediated mechanisms have been described. The catalytic effect of water molecules has been explicitly analyzed. Calculations have been carried out ...
Braun Birgit - - 2009
Surface modification of cellulosic nanowhiskers (CNW) is of great interest, especially to facilitate their use as polymer reinforcements. Generally, alteration of the surface chemistry is performed using multiple reaction steps. In contrast, this study demonstrates that the needed hydrolysis of amorphous cellulose chains can be performed simultaneously with the esterification ...
Yu Fei - - 2009
CuX(2)-mediated (X = Cl, Br) halolactonization of monoesters of 1,2-allenyl phosphonic acids is presented. The reaction proceeded smoothly under the mild condition for differently substituted allenic substrates giving the 4-halo-2,5-dihydro[1,2]oxaphosphole 2-oxides in good yields. The Suzuki cross-coupling reaction of these bromides and even chlorides with organic boronic acids under the ...
Zhu Jianglong - - 2009
An improved method for the synthesis of enantiomerically pure isonitriles from amino acid esters and dipeptides is described.
Wu Bian - - 2009
The phenylalanine aminomutase (PAM) from Taxus chinensis catalyses the conversion of alpha-phenylalanine to beta-phenylalanine, an important step in the biosynthesis of the N-benzoyl phenylisoserinoyl side-chain of the anticancer drug taxol. Mechanistic studies on PAM have suggested that (E)-cinnamic acid is an intermediate in the mutase reaction and that it can ...
Schopfer F J - - 2009
Nitroalkene fatty acid derivatives manifest a strong electrophilic nature, are clinically detectable and induce multiple transcriptionally-regulated anti-inflammatory responses. At present, the characterization and quantification of endogenous electrophilic lipids is compromised by their Michael addition with protein and small molecule nucleophilic targets. Herein, we report a trans-nitroalkylation reaction of nitro-fatty acids ...
Vaida Veronica - - 2009
This article focuses on the mechanism and molecular dynamics of light-initiated atmospheric reactions. The availability of photons of the correct wavelengths, the response to collisions, and the effect of heterogeneous environments will be considered in this discussion. A new class of light-initiated reactions occurring in the ground electronic state by ...
Zhu, Xiaochun
In this dissertation, we show that the apparent 4-oxo-2-nonenal (ONE)Lys Michael adducts (m+154) actually represent the isomeric 4-ketoamides. The same type of 4-ketoamide on Lys residues was formed by 9,12-dioxo-10(E)-dodecenoic acid (KODA). By incubation of β-lactoglobulin (β-LG) with 4-hydroxy-2-nonenal (HNE) and ONE, HNE was found to form Cys/His/Lys/N-terminal amine Michael ...
Lange Jean-Paul - - 2009
Furfural, a potential coproduct of levulinic acid, can be converted into levulinic acid via hydrogenation to furfuryl alcohol and subsequent ethanolysis to ethyl levulinate. The ethanolysis reaction is known to proceed in the presence of H(2)SO(4). We show here that several strongly acidic resins are comparably effective catalysts for this ...
Zhang Junhua - - 2009
In this study, we aimed to dissolve microcrystalline cellulose (MCC) with phosphoric acid to obtain high-quality fermentable saccharides. MCC was directly dissolved in phosphoric acid (the concentration was 83%) for 10 hours at temperatures of 30, 50, and 70 degrees C. The structural changes of MCC were determined in detail ...
Rinaldi Roberto - - 2009
Cellulose is a major source of glucose because it is readily available, renewable, and does not compete with the food supply. Hydrolysis of cellulose is experiencing a new research and development cycle in which this reaction is carried out over solid catalysts and coupled to other reactions for increased efficiency. ...
Cressman Erik N K EN University of Minnesota Medical School, Minneapolis, MN 55455, USA. - - 2009
To test thermochemical ablation for potential as a new method to coagulate tissue and create a prototype device for administration. Reactions of either HCl or acetic acid and either NH4OH or NaOH were run in triplicate in a gel phantom as a simple calorimeter. Data were recorded over a period ...
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