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Results 401 - 450 of 1682
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Wang Xiaoqiong - - 2008
A simple, rapid ligand exchange route to prepare highly fluorescent, stable and water-soluble CdSe quantum dots (QDs) is reported by using p-sulfonatocalix(n)arene (SFCA(n), n = 4 or 6) instead of original trioctylphosphine oxide (TOPO) ligands. The ligands were found to have a profound effect on the luminescence response of QDs ...
Massah Ahmad Reza - - 2008
Silica sulfuric acid catalyzes efficiently the reaction of sulfonamides with both carboxylic acid anhydrides and chlorides under solvent-free and heterogeneous conditions. All the reactions were done at room temperature and the N-acylsulfonamides were obtained with high yields and purity via an easy work-up procedure. This method is attractive and is ...
Nematollahi D - - 2008
Electrochemical oxidation of catechols has been studied in the presence of Meldrum's acid derivatives as nucleophiles in aqueous solution, by means of cyclic voltammetry and controlled-potential coulometry. Catechols in the Michael addition reaction react with Meldrum's acids to form adducts that can undergo electrooxidation. Such products were obtained in good ...
Martínez-Ruiz Antonio - - 2008
This paper reports a study of the enzymatic esterification of oleic acid and ethanol. The reaction was catalyzed by lipases produced by solid-state fermentation with Rhizopus sp. Olive oil and perlite were used as an inducer and inert support, respectively. Synthesis of ethyl oleate was carried out in a 10-mL ...
Garbe Leif Alexander - - 2008
The reaction pathways of amino acids and reducing sugars are now fully understood. The focus in the last few years, however, has turned to the reaction of peptides and proteins with reducing sugars. We have investigated the reaction of gamma-aminobutanoic acid, the heptapeptide Nalpha-Acetyl-Lys-Lys-beta-Ala-Lys-beta-Ala-Lys-Gly, and the model protein beta-casein in ...
Hidalgo Francisco J - - 2008
Amino acid degradation plays an important role in the formation of both flavors and toxic compounds during food processing. These reactions are produced, to a significant extent, as a consequence of the Maillard reaction among amino acids and carbohydrates. However, recent studies have shown that lipids also take part in ...
Morawicki R O - - 2008
1-Octen-3-ol and 10-oxo-trans-8-decenoic acid are metabolites of the breakdown of linoleic acid (LA) by mushroom enzymes. These compounds can be produced in a bioreactor using a crude mushroom homogenate and the exogenous addition of LA and oxygen. The factors' duration of blending, mushroom-buffer ratio, effect of a surfactant, whole against ...
Tseng Yao-Hung - - 2008
We demonstrate that glutaric acid can be used to prepare nanorods of hydroxyapatite under hydrothermal condition at 100 degrees C with a Ca(2+):glutaric acid molar ratio of 1:4. Frequency-switched Lee-Goldburg irradiation is employed to obtain high-resolution (31)P{(1)H} correlation spectra of the reaction mixture at two different reaction periods, from which ...
Lemma Kelemu - - 2008
The kinetics and mechanism of the hydrolysis of cysteine sulfenyl thiocyanate (CySSCN) to give cysteine thiosulfinate ester (CyS(=O)SCy) have been investigated between pH 0 and 4. The reaction is reversible. The hydrolysis of CySSCN is second-order in [CySSCN] and inverse first-order in [H+] and [SCN-]. The following mechanism is proposed ...
Narai-Kanayama Asako - - 2008
Papain polymerizes L-glutamic acid diethyl ester (Glu-di-OEt) regioselectively, resulting in the formation of poly (gamma-ethyl alpha-L-glutamic acid) with various degrees of polymerization of less than 13. Reaction temperatures below 20 degrees C were appropriate for the reaction in terms of suppression of non-enzymatic degradation of Glu-di-OEt and an increase in ...
Wiitala Keith W - - 2008
Penam acids 6-8 [i.e., (2S,5R,6R)-, (2S,5S,6R)-, and (2S,5R,6S)-isomers of 6-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid] were prepared by deesterification of the corresponding methyl esters 2-4. The same methodology applied to ester 1 did not lead to the (2S,5S,6S)-isomer 5 but rather a 72% yield of the thiazoline derivative 9. High-resolution mass spectrometry analysis of ...
Xu Hui - - 2008
Mandelic acid was synthesized from benzaldehyde with chloroform in a 81% yield at 60 degrees C for 2 h by using triethylbenzylammonium chloride (TEBA) and poly(ethylene glycol)-800 (PEG-800) as a complex phase transfer catalyst under ultrasonic irradiation. The main advantages of this present method are that the reaction time is ...
Adams An - - 2008
Alkylpyrazines are a very important class of Maillard flavor compounds, but their mechanism of formation is complex and consists of different pathways. The model reaction of 20 different amino acids with 1,3-dihydroxyacetone, as a precursor of 2-oxopropanal, was studied by means of SPME-GC-MS to investigate the involvement of the amino ...
Lamoolphak Wiwat - - 2008
Non-catalytic hydrothermal decomposition of sericin and fibroin from silk waste into useful protein and amino acids was examined in a closed batch reactor at various temperatures, reaction times, and silk to water ratios to examine their effects on protein and amino acid yields. For the decomposition of sericin, the highest ...
Nozière Barbara - - 2008
The amino acid catalyzed aldol condensation is of great interest in organic synthesis and natural environments such as atmospheric particles. However, kinetic and mechanistic information on these reactions is limited. In this work the kinetics of the aldol condensation of acetaldehyde in water and aqueous salt solutions (NaCl, CaCl2, Na2SO4, ...
Islam Nazneen Naher - - 2008
The detailed properties of the enzyme from Pseudomonas aeruginosa, which catalyzes the N-acyl linkage between myristic acid and the N-terminal glycine residue of the octapeptide GNAAAARR-NH(2) (PKA) in aqueous solution without ATP and CoA, were studied. The substrate specificity for the acyl peptide in the synthetic reaction was examined, and ...
Yoshida Ken-ichi - - 2008
The iolABCDEFGHIJ operon of Bacillus subtilis is responsible for myo-inositol catabolism involving multiple and stepwise reactions. Previous studies demonstrated that IolG and IolE are the enzymes for the first and second reactions, namely dehydrogenation of myo-inositol to give 2-keto-myo-inositol and the subsequent dehydration to 3D-(3,5/4)-trihydroxycyclohexane-1,2-dione. In the present studies the ...
Lorello Gianni R - - 2008
Herein we report the synthesis of a novel amino acid with orthogonal functionality to the natural amino acid side chains. Tyrosine was O-alkylated with a cyclic 5-membered alpha,beta-unsaturated ketone ring (5). We have established that this amino acid analogue can undergo cycloaddition reactions in aqueous media with in situ generated ...
Tsivgoulis Gerasimos M - - 2008
A reinvestigation of the reactions leading to arsonolipids (2,3-diacyloxypropylarsonic acids) has been carried out in order to understand why the yields of their preparation were only moderate, although they are better than those reported for 2,3-diacyloxypropylphosphonic acid (phosphotidic acid). Thus, the reaction of glycidol and of 3-chloro-1,2-propanediol with alkaline sodium ...
Montgomery W - - 2008
We have studied cyanuric acid (H(3)C(3)N(3)O(3)) at static pressures up to 8.1 GPa and simultaneous temperatures up to 750 K, using primarily infrared absorption spectroscopy and visual observation. The corresponding phase diagram compares favorably with theoretical predictions of metastable organic materials. Two reactions were observed and characterized; both are irreversible. ...
Rabetafika Holy N - - 2008
Hydroperoxide lyase activity was found in sugar beet leaves. Its optimum pH and temperature were, respectively, 6.7 and 22 degrees C. Under these conditions, conversion of linolenic acid 13-hydroperoxide to cis-3-hexenal with a maximum yield of 80% was reached after only 2 min. The stability of cis-3-hexenal was improved by ...
Schreiner Eduard - - 2008
Free energy landscapes and reaction mechanisms underlying the synthesis of diglycine in water were studied computationally. It was found that amino acid activation by carbonyl sulfide, leading to the formation of a cyclic alpha-amino acid N-carboxyanhydride (NCA, or Leuchs anhydride), preferentially follows an indirect pathway that involves an isocyanate intermediate. ...
Clarke K - - 2008
We report the direct observation of the quenching of the weakly absorbing transient due to the amino radical by oxygen and, hence determine, by a totally direct method, the corresponding rate constant (k = (1.1 +/- 0.1) x 10(9) dm3 mol(-1) s(-1)). We also report the rate constants for the ...
Caregnato Paula - - 2008
By monitoring the decay of SO4*- after flash photolysis of aqueous solutions of S2O82- at different pH values, the kinetics of the reaction of SO4*- radicals with gallic acid and the gallate ion was investigated. The bimolecular rate constants for the reactions of the sulfate radicals with gallic acid and ...
Basak Sankar - - 2008
Isomerization-free reactions of dienyl carbonates (1-3) with chelated amino acid ester enolates at -78 degrees C provide important information concerning the mechanism of these dienylations. The formation of regioisomeric products can be explained by competing SN2/SN2' reactions, and the product distribution can be influenced by proper choice of the reaction ...
Hyyryläinen Anna R M - - 2008
Stereochemical differentiation of diasteromeric pairs of cis- and trans-2-aminocyclohexane-, -2-amino-4-cyclohexene-, and -2-aminocyclopentanecarboxylic acids was investigated with host-guest complexes where tetraethyl resorcarene was the host molecule. Diastereoselectivity was evaluated by ion/molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS). The effect of varying the ...
Kojima Naoshi - - 2008
We previously reported a series of new amino-linkers, consisting of an aminoethyl carbamate structure (Komatsu, 2008). We have now examined the chemical properties of oligonucleotides modified with an ssH-linker, which is the simplest and most cost-effective derivative of the series. Although it was previously shown that monomethoxytrityl protection on a ...
Elders Niels - - 2008
Selective formation of 2H-2-imidazolines and 2-substituted oxazoles by using a multicomponent reaction of amines, either aldehydes or ketones, and alpha-acidic isocyano amides or esters is described. By selecting the appropriate solvent, Ag(I) or Cu(I) catalyst, or by employing a weak Brønsted acid, the product formation can be fully controlled and ...
Motokura Ken - - 2008
Acid-base bifunctional heterogeneous catalysts were prepared by the reaction of an acidic silica-alumina (SA) surface with silane-coupling reagents possessing amino functional groups. The obtained SA-supported amines (SA-NR2) were characterized by solid-state 13C and 29Si NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The solid-state NMR spectra revealed that the amines were ...
Sarma Bani Kanta - - 2008
A revised mechanism that accounts for the glutathione peroxidase (GPx)-like catalytic activity of the organoselenium compound ebselen is described. It is shown that the reaction of ebselen with H(2)O(2) yields seleninic acid as the only oxidized product. The X-ray crystal structure of the seleninic acid shows that the selenium atom ...
Rauf Abdul - - 2008
N-acyl-1H-1,2,3-benzotriazoles were prepared in good yields by the reaction of benzotriazole and thionyl chloride with olefinic fatty acids under mild reaction conditions. The new compounds 1-(undec-10-enoyl)-1H-1,2,3-benzotriazole (5a),1-[(Z)-octadec-9-enoyl]-1H-1,2,3-benzotriazole (5b), 1-[(9Z,12R)-12-hydroxyoctadec-9-enoyl]-1H-1,2,3-benzotriazole (5c), 1-[(9R,12Z)-9-hydroxyoctadec-12-enoyl]-1H-1,2,3-benzotriazole (5d) formed were characterized on the basis of elemental analysis and spectral data. All the newly synthesized compounds (5a-5d) ...
Sawant Dhanashri P - - 2008
The preparation of SBA-15/TiO(2) nanocomposites with different loadings of Keggin-type 12-tungstophosphoric acid (TPA) nanocrystals in their mesochannels through a simple and effective vacuum impregnation method is reported for the first time. The catalysts have been characterised by various sophisticated techniques, including XRD, HRSEM, and TEM. It has been found that ...
Hofmann Eckhard - - 2008
Jasmonates, a collective term combining both jasmonic acid (JA) and related derivatives, are ubiquitously distributed in the plant kingdom. They are characterized as lipid-derived signal molecules which mediate a plethora of physiological functions, in particular stress responses, male fertility, and a multitude of developmental processes. In the course of JA ...
García-García Miguel - - 2008
d-Amino acid oxidase (DAAO) was used to study the oxidative deamination of racemic mixtures of d,l-methionine in its soluble and immobilized forms and thus obtain the corresponding alpha-keto acid. The soluble enzyme form was obtained from a Trigonopsis variabilis CBS 4095 extract, free of l-amino acid oxidase, and was co-immobilized ...
Yusubov Mekhman S - - 2008
Preparation, structural characterization, and reactivity of 3-[bis(trifluoroacetoxy)iodo]benzoic acid and 3-[hydroxy(tosyloxy)iodo]benzoic acid, new recyclable iodine(III) reagents derived from 3-iodosylbenzoic acid, are described. The reduced form of these reagents, 3-iodobenzoic acid, can be easily recovered from the reaction mixtures using ion-exchange resin or basic aqueous workup followed by acidification with HCl.
Lira Alfredo Lopez - - 2007
The stability and the reactivity of mono- and diprotonated 4-heterocyclohexanones as well as cyclohexanone in triflic acid have been studied at the PBE0/aug-cc-pvtz//PBE0/6-31+G** level of theory. In all cases the first protonation is an exergonic process occurring at a carbonyl oxygen except for 4-piperidone where a nitrogen atom is protonated ...
Findrik Z - - 2007
D-Methionine was converted to L-methionine in a reaction system where four enzymes were used. D-amino acid oxidase (D-AAO) from Arthrobacter protophormiae was used for the complete conversion of D-methionine to 2-oxo-4-methylthiobutyric acid. Catalase was added to prevent 2-oxo-4-methylthiobutyric acid decarboxylation. In the second reaction step, L-phenylalanine dehydrogenase (L-PheDH) from Rhodococcus ...
Skaff Ojia - - 2007
Hypohalous acids are generated from the oxidation of halide ions by myeloperoxidase and eosinophil peroxidase in the presence of H2O2. These oxidants are potent antibacterial agents, but excessive production can result in host tissue damage, with this implicated in a number of human pathologies. Rate constants for HOCl with lipid ...
Zhou Chun-Hui Clayton - - 2008
New opportunities for the conversion of glycerol into value-added chemicals have emerged in recent years as a result of glycerol's unique structure, properties, bioavailability, and renewability. Glycerol is currently produced in large amounts during the transesterification of fatty acids into biodiesel and as such represents a useful by-product. This paper ...
Novak Michael - - 2007
Quinol esters 2b, 2c, and 3b and sulfonamide 4c were investigated as possible precursors to 4-alkylaryloxenium ions, reactive intermediates that have not been previously detected. These compounds exhibit a variety of interesting reactions, but with one possible exception, they do not generate oxenium ions. The 4-isopropyl ester 2b predominantly undergoes ...
Vafiadi Christina - - 2008
The potential of the Aspergillus niger type A feruloyl esterase (AnFaeA) for the synthesis of various phenolic acid esters was examined using a ternary-organic reaction system consisting of a mixture of n-hexane, 1- or 2-butanol and water. Reaction parameters including the type of methyl hydroxycinnamate, the composition of the reaction ...
Castagnolo Daniele - - 2007
The direct kinetic formation of spiroketals from mixed ketal-alcohol precursors under acid catalysis was studied using four differently substituted systems. In all cases, the exclusive formation of the anomeric isomer was observed under equilibrating conditions. However, the formation of the nonanomeric spiroketal isomer was observed if the reaction was performed ...
Crich David - - 2007
Reaction of cyclic thioanhydrides with amines affords amides functionalized with thioacids, which can be trapped in situ with electron-deficient azides or, preferably, 2,4-dinitrobenzenesulfonamides. In this manner the cyclic thioanhydride serves as a linchpin in a three-component coupling sequence. The use of thiomaleic anhydride and a bifunctional nucleophile extends the process ...
Selmar Dirk - - 2008
When green coffee is stored for a prolonged time the coffee quality decreases distinctively. Apart from well-known 'off-notes' that arise from undesired oxidations of lipids, a typical 'flattening' of the cup quality is detectable. In order to elucidate the biological causes for this phenomenon, differentially processed coffees (wet, dry, semi-dry ...
Seeliger Florian - - 2007
The kinetics of reactions of acceptor-stabilized carbanions 2a-m with benzylidenebarbituric and -thiobarbituric acids 1a-e has been determined in a dimethyl sulfoxide solution at 20 degrees C. Second-order rate constants were employed to determine the electrophilicity parameters E of the benzylidenebarbituric and -thiobarbituric acids 1a-e according to the correlation equation log ...
Parthasarathy Anand - - 2007
Utility of a water-soluble deep cavity cavitand, octa acid, as a reaction medium is illustrated by carrying out photochemical reactions of a stilbene and a styrene included within the octa acid in water. Geometric isomerization of trans-4,4'-dimethyl stilbene is restricted while dimerization of 4-methyl styrene is facilitated within the octa ...
Nagy Péter - - 2007
Cysteine sulfenic acid has been generated in alkaline aqueous solution by oxidation of cysteine with hypohalous acid (HOX, X = Cl or Br). The kinetics and mechanisms of the oxidation reaction and the subsequent reactions of cysteine sulfenic acid have been studied by stopped-flow spectrophotometry between pH 10 and 14. ...
Chan Lai C - - 2007
The kinetics of formation of amide, 4, from the corresponding carboxylic acid by reaction with the isopropyl ester of methionine (MIPE), mediated by carbodiimide EDCI, 1, and HOBt, 2, have been studied in 1-methyl-2-pyrrolidinone (NMP) using reaction calorimetry. The reaction rates have been found to be independent of the concentration ...
Sadlej-Sosnowska Nina - - 2007
We propose a new similarity measure operating in the space spanned by the potential values, evaluated at atoms constituting the benzene ring and the COOH group in para-substituted benzoic acids and at benzene ring atoms in monosubstituted benzenes. The similarity measures are equivalent to the Euclidean distance between points in ...
Torpo Leena - - 2007
We apply accurate quantum chemistry methods to study the thermochemistry of molecular clusters containing ammonia, water, and sulfuric acid and investigate initial reaction steps in atmospheric nucleation by calculating free energies for the related reactions. The results indicate that ammonia is a key reactant enhancing the growth of small water-sulfuric ...
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