Showing papers on "Carboxylic acid published in 2002"
TL;DR: The voltammetric separation of dopamine and ascorbic acid was studied with cyclic voltammetry and indicated that the resolution of DA and AA was mainly attributable to the stereo porous interfacial layer formed from aggregated pores and inner cavities of the carbon nanotubes.
Abstract: The voltammetric separation of dopamine and ascorbic acid was studied with cyclic voltammetry at two kinds of carbon nanotube-modified electrodes (coated and intercalated) The anodic peak difference reached 270 mV under the present conditions The separation mechanism and effect factors were carefully studied Using various types of surfactants as coating dispersants of carbon nanotubes, it was demonstrated that the charge nature of the surfactants had a strong effect on the electrochemical behavior of dopamine and ascorbic acid When the oxidation solution of carbon nanotubes was changed from the most commonly used mixed concentrated nitric acid and sulfuric acid (1 + 3 v/v) to dilute nitric acid and to hydrochloric acid, the anodic peak separation value of dopamine and ascorbic acid increased significantly, and it was shown that carboxylic acid groups attached to the carbon nanotubes were an adverse factor for the discrimination of DA from AA These results indicated that
the resolution of DA and AA was mainly attributable to the stereo porous interfacial layer formed from aggregated pores and inner cavities of the carbon nanotubes The modified electrodes exhibited an attractive ability to measure DA and AA simultaneously and showed good stability and reproducibility
415 citations
TL;DR: Alkaline wet oxidation was an efficient pre-treatment of wheat straw that resulted in solid fractions with high cellulose recovery and high enzymatic convertibility to glucose, and aromatic aldehyde formation was correlated to severe conditions with high temperatures and low pH.
404 citations
TL;DR: In this article, the results of probe catalytic photooxidation reactions with aliphatic and aromatic organic compounds having different acid strengths were carried out in aqueous systems by using polycrystalline TiO2 powders doped with various transition metal ions (Co, Cr, Cu, Fe, Mo, V and W).
288 citations
TL;DR: Results show that acid catalyzed hydrolysis is proportional to H+ concentration, and overall yields of glucose obtained from cellobiose and cellulose are higher for the best carboxylic acid tested, maleic acid, when compared to sulfuric acid at equivalent solution pH.
Abstract: Cellulolytic enzymes consist of a catalytic domain, a linking peptide, and a binding domain. The paper describes research on carboxylic acids that have potential as catalytic domains for constructing organic macromolecules for use in cellulose hydrolysis that mimic the action of enzymes. The tested domains consist of the series of mono-, di-, and tricarboxylic acids with a range of pK(a)'s. This paper systematically characterizes the acids with respect to hydrolysis of cellobiose, cellulose in biomass, and degradation of glucose and compares these kinetics data to dilute sulfuric acid. Results show that acid catalyzed hydrolysis is proportional to H+ concentration. The tested carboxylic acids did not catalyze the degradation of glucose while sulfuric acid catalyzed the degradation of glucose above that of water alone. Consequently, overall yields of glucose obtained from cellobiose and cellulose are higher for the best carboxylic acid tested, maleic acid, when compared to sulfuric acid at equivalent solution pH.
272 citations
TL;DR: It is suggested that fatty acids are endogenous ligands for HNF4α and establish a framework for understanding how H NF4α activity is enhanced by ligand binding and diminished by MODY1 mutations.
267 citations
TL;DR: The HPLC method was successfully used to measure a variety of organic acids and phenolic compounds in juices and beverages and could also be used to evaluate the authenticity, spoilage or micronutrient contents of juices.
264 citations
TL;DR: This structural study shows that iso-nicotinamide is a supramolecular reagent that can produce well-defined supermolecules (containing carboxylic acids) in very high yields.
Abstract: The X-ray crystal structure determinations of twelve cocrystals involving iso-nicotinamide and a variety of carboxylic acids have revealed a very consistent pattern of hydrogen-bond preferences. The combination of a monocarboxylic acid, an amide, and a pyridine moiety leads, in every case, to discrete “supermolecules” (consisting of two molecules of iso-nicotinamide and two molecules of the relevant carboxylic acid) with well-defined and robust connectivity. The two dominant (regularly occurring) supramolecular synthons in these crystal structures are (1) the heteromeric carboxylic acid···pyridine hydrogen bond and (2) a self-complementary amide···amide hydrogen-bond interaction, both of which prevail in the presence of widely differing chemical functionalities. In four of these cocrystals, a dicarboxylic acid is employed, which alters the structural outcome from discrete entities to infinite assemblies (or to a hexameric complex in a “U-shaped” dicarboxylic acid), which is fully expected since the two pr...
255 citations
TL;DR: In this paper, nonlocal density functional theory (DFT) calculations are used to examine alternative mechanisms for the hydrogenolysis of acetic acid to ethanol over Pd, and the overall surface reaction energies, at low surface coverage, are computed for a number of different possible paths by which the acid may be converted to ethanol, and binding energies of various oxygenated C 2 intermediates formed along these paths are also reported.
241 citations
TL;DR: In this paper, COOH-terminated organic surfaces were prepared by self-assembly of different organothiols, mercaptohexadecanoic acid (MHDA) and mercaptomethylterphenylcarboxylic acid (MMTA), on Au substrates.
Abstract: COOH-terminated organic surfaces were prepared by self-assembly of different organothiols, mercaptohexadecanoic acid (MHDA) and mercaptomethylterphenylcarboxylic acid (MMTA), on Au substrates. The SAMs were explored by infrared reflection−absorption spectroscopy and X-ray photoelectron spectroscopy. A rather strong dependence on preparation conditions is observed which explains inconsistencies between previous studies reported for these systems. Using optimized preparation conditions, films with a high degree of molecular orientation could be prepared. A significant amount of disorder, however, is induced by hydrogen bonds between the terminating −COOH groups. An organothiol with a more rigid backbone, MMTA, is demonstrated to yield carboxy-terminated SAMs which are more straightforward to prepare and which show a significantly higher degree of order.
232 citations
TL;DR: The utility of this nitrilase library for identifying enzymes that catalyze efficient production of valuable hydroxy carboxylic acid derivatives is demonstrated and unprecedented enantioselectivity and substrate scope are highlighted for three newly discovered and distinct nitrilases.
Abstract: The discovery, from Nature, of a large and diverse set of nitrilases is reported. The utility of this nitrilase library for identifying enzymes that catalyze efficient production of valuable hydroxy carboxylic acid derivatives is demonstrated. Unprecedented enantioselectivity and substrate scope are highlighted for three newly discovered and distinct nitrilases. For example, a wide array of (R)-mandelic acid derivatives and analogues were produced with high rates, yields, and enantiomeric excesses (95−99% ee). We also have found nitrilases that provide direct access to (S)-phenyllactic acid and other aryllactic acid derivatives, again with high yields and enantioselectivities. Finally, different nitrilases have been discovered that catalyze enantiotopic hydrolysis of 3-hydroxyglutaronitrile to afford either enantiomer of 4-cyano-3-hydroxybutyric acid with high enantiomeric excesses (>95% ee). The first enzymes are reported that effect this transformation to furnish the (R)-4-cyano-3-hydroxybutyric acid wh...
221 citations
TL;DR: X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of car boxylic acid-pyridine supramolecular synthon V in these heterocyclic acids.
Abstract: X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of carboxylic acid-pyridine supramolecular synthon V in these heterocyclic acids. Synthon V, assembled by (carboxyl)O-H...N(pyridine) and (pyridine)C-H...O(carbonyl) hydrogen bonds, controls self-assembly in the crystal structures of pyridine and pyrazine monocarboxylic acids. The recurrence of acid-pyridine heterodimer V compared to the more common acid-acid homodimer I in the crystal structures of pyridine and pyrazine monocarboxylic acids is explained by energy computations in the RHF 6-31G* basis set. Both the O-H.N and the C-H...O hydrogen bonds in synthon V result from activated acidic donor and basic acceptor atoms in 1-4. Pyrazine 2,3- and 2,5-dicarboxylic acids 10 and 11 crystallize as dihydrates with a (carboxyl)O-H...O(water) hydrogen bond in synthon VII, a recurring pattern in the diacid structures. In summary, the carboxylic acid group forms an O-H...N hydrogen bond in pyrazine monocarboxylic acids and an O-H...O hydrogen bond in pyrazine dicarboxylic acids. This structural analysis correlates molecular features with supramolecular synthons in pyridine and pyrazine carboxylic acids for future crystal engineering strategies.
TL;DR: Comparisons of reaction rates and catalytic efficiency showed that EETs are one of the best endogenous substrates so far described for rat CYP4A isoforms, suggesting a role for them as endogenous ligands for these orphan nuclear receptors.
TL;DR: The structures formed by adsorption of carboxyalkylphosphonic acids on metal oxide powders were characterized by solid-state NMR and FTIR-PAS (Fourier transform infrared photoacoustic spectroscopy) as discussed by the authors.
Abstract: The structures formed by adsorption of carboxyalkylphosphonic acids on metal oxide powders were characterized by solid-state NMR and FTIR-PAS (Fourier transform infrared photoacoustic spectroscopy). A series of diacids, HO2C(CH2)nPO3H2 (n = 2, 3, 11, and 15), were deposited on nonporous TiO2 and ZrO2 powders and nanocrystalline ZrO2 with average particle diameters of 21, 30, and 5 nm, respectively. Solid-state 31P NMR, combined with FTIR-PAS, indicates that the phosphonic acid group binds selectively to the surface, producing a monolayer of carboxylic acid terminated chains. The average chain conformation depends on the substrate in addition to the chain length. Ordered samples display thermal order/disorder transitions similar to other self-assembled monolayer systems. The more restricted chain mobility relative to analogous methyl-terminated chains is attributed to hydrogen-bonding among the pendant carboxylic acid groups. These results demonstrate that phosphonic acids are useful for selectively introd...
TL;DR: In this article, gold catalysts for selective oxidation of organic molecules are reported, all reactions investigated were performed using molecular oxygen in aqueous solution under mild conditions, and they compared with conventional Pd and Pt monometallic, bimetallic and tricomponent catalysts.
TL;DR: In this article, the effect of different molar ratios between the reactants (acid and alcohol) on the reaction rate was investigated, and the rate constants were related to the substituent effects of the reacting molecules according to the Taft equation.
Abstract: Esterification of acetic, propanoic and pentanoic acid with methanol, ethanol, 1-propanol, 2-propanol, butanol and 2-butanol was studied in the presence of a fibrous polymer-supported sulphonic acid catalyst, Smopex-101. The reaction temperature in the experiments was 60 °C. Comparative experiments were carried out on an ion-exchange resin, Amberlyst 15 and with a homogeneous catalyst, liquid HCl. The effect of different molar ratios between the reactants (acid and alcohol) on the reaction rate was investigated. The rate constants were related to the substituent effects of the reacting molecules according to the Taft equation. The substituent effects of alcohols were found to follow the Taft relationship, which was not the case for the acids. The experimental results were modelled according to a simple second-order model and a more advanced adsorption-based model. The adsorption-based model, which includes the adsorption of carboxylic acid and water and is consistent with structure–activity relationship, was superior to the second-order model.
TL;DR: The surface reactivity and functional group content of a series of oxidised active carbons has been assessed by elemental analysis, electrophoretic mobility measurements and potentiometric titrations.
TL;DR: In this article, the viability of various pathways to the formation of glycine, alanine, and serine in dilute H2O ice containing CH3OH and HCN was evaluated.
Abstract: A recent experimental study reported that glycine and other amino acids were formed when cryogenic H2O ice containing small amounts of CH3OH, NH3, and HCN was subjected to ultraviolet (UV) irradiation. Quantum chemical calculations were employed to evaluate the viability of various pathways to the formation of glycine, alanine, and serine in dilute H2O ice containing CH3OH and HCN. Under the experimental processing conditions of deposition and UV irradiation at 15 K followed by heating to room temperature, amino acids can form by recombining radicals produced by dehydrogenating H2O and CH3OH and subsequently hydrogenating HCN. The study indicates that isotopic substitution experiments would identify CH3OH as the source of the C atom in the COOH carboxylic acid group of the amino acids observed in the irradiation experiments, with the CO+OH reaction playing an important role. The remaining C and N atoms in glycine are predicted to originate from HCN via sequential hydrogenation to yield CH2NH2. Formation pathways for alanine and serine are also discussed.
TL;DR: In this article, a number of MoVTeNbO catalysts with several Mo/Te/V/Nb (1/0.15-0.9) contents have been prepared by hydrothermal synthesis and tested in the selective oxidation of propane and propene to acrylic acid.
TL;DR: The present study deals with the acid-base reaction of three solid-state forms of the nonsteroidal antiinflammatory drug indomethacin with ammonia gas, and it became apparent that the reactivity of the crystal forms depends exclusively on the molecular arrangement and not on the packing density of the indometHacin crystals.
Abstract: The present study deals with the acid-base reaction of three solid-state forms of the nonsteroidal antiinflammatory drug indomethacin with ammonia gas. X-ray powder diffraction, optical microscopy, gravimetry, and spectroscopic methods were employed to establish the extent of the reaction as well as the lattice changes of the crystal forms. The glassy amorphous form readily reacts with ammonia gas to yield a corresponding amorphous ammonium salt. In addition, the metastable crystal form of indomethacin (the alpha-form) also reacts with ammonia gas, but produces the corresponding microcrystalline ammonium salt. This reaction is anisotropic and propagates along the a-axis of the crystals. The stable crystal form (the gamma-form), however, is inert to ammonia gas. Amorphous indomethacin can react with ammonia gas because it has more molecular mobility and free volume. The reactivity differences between the alpha- and gamma-forms are dictated by the arrangement of the molecules within the respective crystal lattices. The recently determined crystal structure of the metastable alpha-form of indomethacin (monoclinic P2(1) with Z = 6, V = 2501.8 A(3), D(c) = 1.42 g.cm(-3)) has three molecules of indomethacin in the asymmetric unit. Two molecules form a mutually hydrogen-bonded carboxylic acid dimer, while the carboxylic acid of the third molecule is hydrogen bonded to one of the amide carbonyls of the dimer. The carboxylic acid groups of the alpha-form are exposed on the [100] faces and are accessible to attack by ammonia gas. After one layer of molecules reacts, the reactive groups in the subsequent layer are accessible to the ammonia gas. This process proceeds along the a-axis until the ammonia gas has penetrated the entire crystal. In contrast to the alpha-form, the gamma-form has a centrosymmetric crystal structure in which the hydrogen-bonded carboxylic acid dimers are not accessible to ammonia gas because they are caged inside a hydrophobic shield comprising the remainder of the indomethacin molecule. In view of the significantly lower density of the stable gamma-form as compared to the metastable alpha-form (1.37 and 1.42 g cm(-3), respectively), it became apparent that the reactivity of the crystal forms depends exclusively on the molecular arrangement and not on the packing density of the indomethacin crystals.
TL;DR: The FBB technology is suitable for producing value-added biochemicals directly from agricultural residues or commodities such as corn meal, suggesting that these carboxylic acids can be efficiently produced from direct fermentation of corn meal hydrolyzate.
TL;DR: The series of identified metabolites suggests that anaerobic degradation of naphthalenes proceeds via reduction of the aromatic ring system of 2-naphthoic acid to initiate ring cleavage in analogy to the benzoyl-coenzyme A pathway for monoaromatic hydrocarbons.
Abstract: Anaerobic degradation of naphthalene, 2-methylnaphthalene, and tetralin (1,2,3,4-tetrahydronaphthalene) was investigated with a sulfate-reducing enrichment culture obtained from a contaminated aquifer. Degradation studies with tetralin revealed 5,6,7,8-tetrahydro-2-naphthoic acid as a major metabolite indicating activation by addition of a C1 unit to tetralin, comparable to the formation of 2-naphthoic acid in anaerobic naphthalene degradation. The activation reaction was specific for the aromatic ring of tetralin; 1,2,3,4-tetrahydro-2-naphthoic acid was not detected. The reduced 2-naphthoic acid derivatives tetrahydro-, octahydro-, and decahydro-2-naphthoic acid were identified consistently in supernatants of cultures grown with either naphthalene, 2-methylnaphthalene, or tetralin. In addition, two common ring cleavage products were identified. Gas chromatography-mass spectrometry (GC-MS) and high-resolution GC-MS analyses revealed a compound with a cyclohexane ring and two carboxylic acid side chains as one of the first ring cleavage products. The elemental composition was C11H16O4 (C11H16O4-diacid), indicating that all carbon atoms of the precursor 2-naphthoic acid structure were preserved in this ring cleavage product. According to the mass spectrum, the side chains could be either an acetic acid and a propenic acid, or a carboxy group and a butenic acid side chain. A further ring cleavage product was identified as 2-carboxycyclohexylacetic acid and was assumed to be formed by β-oxidation of one of the side chains of the C11H16O4-diacid. Stable isotope-labeling growth experiments with either 13C-labeled naphthalene, per-deuterated naphthalene-d8, or a 13C-bicarbonate-buffered medium showed that the ring cleavage products derived from the introduced carbon source naphthalene. The series of identified metabolites suggests that anaerobic degradation of naphthalenes proceeds via reduction of the aromatic ring system of 2-naphthoic acid to initiate ring cleavage in analogy to the benzoyl-coenzyme A pathway for monoaromatic hydrocarbons. Our findings provide strong indications that further degradation goes through saturated compounds with a cyclohexane ring structure and not through monoaromatic compounds. A metabolic pathway for anaerobic degradation of bicyclic aromatic hydrocarbons with 2-naphthoic acid as the central intermediate is proposed.
TL;DR: This method is particularly valuable for the synthesis of methyl esters that contain acid-sensitive functionality and in the absence of DBU or in the presence of other bases, such as ammonium hydroxide or N-methylmorpholine, the same reaction affords no desired product.
Abstract: 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) is an effective nucleophilic catalyst for carboxylic acid esterification with dimethyl carbonate (DMC). The reaction pathway of this new class of nucleophilic catalysis has been studied. A plausible, multistep mechanism is proposed, which involves an initial N-acylation of DBU with DMC to form a carbamate intermediate. Subsequent O-alkylation of the carboxylate with this intermediate generates the corresponding methyl ester in excellent yield. In the absence of DBU or in the presence of other bases, such as ammonium hydroxide or N-methylmorpholine, the same reaction affords no desired product. This method is particularly valuable for the synthesis of methyl esters that contain acid-sensitive functionality.
TL;DR: Production of low-molecular-weight carboxylic acids from the hydrothermal treatment of representative organic wastes and compounds with or without oxidant demonstrated that the presence of oxidants favored formation of organic acids with acetic acid being the major product.
TL;DR: Adsorption capacities of rare earth elements (REEs) were significantly correlated with the cation exchange capacity (CEC) of soils and desorption of REEs varied with soils and with organic acids as well, but the adsorption increased with increasing equilibrium solution pH.
TL;DR: Nanoparticles of less than 200 nm, with potential interest for controlled release of bioactive compounds, were successfully prepared by using new amphiphilic copolymers with various hydrophilic−lipophilic balance.
Abstract: New amphiphilic polysaccharides with controlled structure were synthesized by coupling between a carboxylic function present on preformed polyester chains and a hydroxyl group naturally present on polysaccharides. First, the synthesis of poly(e-caprolactone) monocarboxylic acid (R−PCL−CO2H) was carried out by ring-opening uncatalyzed polymerization of monomer in the presence of a carboxylic acid (R−CO2H). R−PCL−CO2H was then reacted with carbonyl diimidazole, and the resulting activated intermediate (imidazolide) was further reacted with dextran (Dex) at different molar ratios to obtain amphiphilic copolymers with various hydrophilic−lipophilic balance. The coupling reaction was followed by GPC, indicating a total conversion. The copolymers were further characterized by GPC, 1H NMR, and FTIR. Nanoparticles of less than 200 nm, with potential interest for controlled release of bioactive compounds, were successfully prepared by using these new materials.
TL;DR: In this article, a reaction mechanism was modified slightly to incorporate an acyl species as the principal intermediate, rather than molecular acetic acid, and the resulting rate expression not only gives an identical fit to the kinetic data, but also possesses thermodynamically meaningful parameters, such as the heat of adsorption of H 2 on Pt, that are consistent with literature values.
TL;DR: The solubility of phenyl acetic acid, p-hydroxyphenylacetic acid and ibuprofen in water and in a range of organic solvents of relevance to industrial processing is reported in this article.
Abstract: The solubility of phenyl acetic acid, p-hydroxyphenylacetic acid, p-aminophenylacetic acid, p-hydroxybenzoic acid, and ibuprofen in water and in a range of organic solvents of relevance to industrial processing is reported. The solvents used are water, methanol, ethanol, 2-propanol, acetone, 4-methyl-2-pentanone, ethyl acetate, chloroform, and toluene. Solubility data are discussed from the standpoint of molecular aspects of solute-solvent interactions and by estimated solid-phase activity.
TL;DR: The carbon content of cloud water at a continental background site in Austria was studied during two intensive field campaigns in spring 1999 and 2000 as discussed by the authors, and the most abundant carboxylic acids were acetic (average: 0.93 μg ml−1).
TL;DR: In this article, the relative efficiency of triethylamine, tetrabutylammonium trifluoroacetate, and lithium acetate as catalysts for the conversion of 4-methoxycinnamic acid to 4mETHoxy-β-bromostyrene was evaluated.
Abstract: UV-vis spectrophotometry is utilized to measure the relative efficiency of lithium acetate, tetrabutylammonium trifluoroacetate, and triethylamine as catalysts for the conversion of 4-methoxycinnamic acid to 4-methoxy-β-bromostyrene. In acetonitrile-water as solvent, the efficiency order is lithium acetate > triethylamine > tetrabutylammonium trifluoroacetate. For triethylamine as catalyst, solvent-dependent order is acetonitrile-water > dichloromethane > acetonitrile. Using triethylamine as catalyst (5-20 mol %), cinnamic acids, and propiolic acids are converted to corresponding β-bromostyrenes and 1-halo-1-alkynes in 60-98% isolated yields within 1-5 min.
TL;DR: In this article, a kinetic model for the photocatalytic degradation of formic acid in an immobilized system is presented, including the dependency of the reaction rate on the concentration of Formic acid and oxygen, the catalyst layer thickness and the light flux.