Showing papers on "Carboxylic acid published in 1993"

Self-assembled monolayers in electroanalytical chemistry: application of .omega.-mercapto carboxylic acid monolayers for the electrochemical detection of dopamine in the presence of a high concentration of ascorbic acid

Abstract: Self-assembled monolayers of ω-mercapto carboxylic acids, HS(CH 2 ) n CO 2 H (n=2, 5, 10), C n , on gold electrodes were used as a means to induce electrochemical differentiation between a neurotransmitter, dopamine (DO), and ascorbic acid (AA) Optimum differentiation is found for n=5, and it is attributed a compromise between as well-organized system that requires long ω-mercapto carboxylic acids and a reasonable rate of electron transfer which is observed with short ω-mercapto carboxylic acids

An explanation for rapid enzyme-catalyzed proton abstraction from carbon acids: importance of late transition states in concerted mechanisms

Abstract: The rates of enzyme-catalyzed abstraction of protons from carbons adjacent to carbonyl or carboxylic acid groups (α-protons of carbon acids) are rapid (k cat s∼10 1 -10 4 s -1 ). We recently proposed that these rates can be understood if proton abstraction by an active site general basic catalyst is concerted with protonation of the carbonyl group by an active site general acidic (electrophilic) catalyst to generate an enol intermediate instead of an enolate anion (aldehyde, ketone, or thioester substrate) or dianion (carboxylic acid substrate): Gerlt, J. A.; Kozarich, J. W.; Kenyon, G. L.; Gassman, P. G. J. Am. Chem. Soc. 1991, 113, 9667. Gerlt, J. A.; Gassman, P. G. J. Am. Chem. Soc. 1992, 114, 5928

Quantitative aspects of the matrix-assisted laser desorption mass spectrometry of complex oligosaccharides.

Abstract: Comparative studies of the matrix-assisted laser desorption ionization of complex oligosaccharides were made using a range of mono, di- and tri-substituted benzoic acids, substituted coumarins and cinnamic acids. The best results were obtained with 2,5-dihydroxybenzoic acid (2,5-DHB). Detection limits using this matrix were in the range of 100 fmol for complex and high mannose sugars, some 2-fold better than those obtained with alpha-cyano-4-hydroxycinnamic acid and 10-fold better than with an earlier oligosaccharide matrix, 3-amino-4-hydroxybenzoic acid. The strongest signals were achieved with a matrix-to-sample ratio of about 5000:1. Little correlation was found between the measured peak height and sample loading when 3-amino-4-hydroxybenzoic acid was used as the matrix and the signal appeared to saturate at a sample level of around 30 pmol. However, good correlation was found between the amount of sample loaded onto the target and the response when an analogous compound was used as an internal standard and peak ratios were measured. In contrast to this, the use of 2,5-dihydroxybenzoic acid as the matrix enabled the oligosaccharide to be measured over the range 100 fmol to at least 100 pmol with an excellent linear correlation between sample quantity and response and without the need of a standard. No evidence of saturation was found with this matrix. With 2,5-DHB (other matrices were not tested), the oligosaccharide signal strength was found to fall with increasing molecular weight in a linear manner and similar to that found previously with proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Complementary deoxyribonucleic acid cloning and expression of a human liver uridine diphosphate-glucuronosyltransferase glucuronidating carboxylic acid-containing drugs.

Abstract: A cDNA clone, designated UGT2B7 variant, encoding a 529-amino acid human liver microsomal uridine diphosphate-glucuronosyltransferase (UGT) was isolated from a lambda gt11 human liver cDNA library. UGT2B7 variant synthesized in COS-7 cells was screened for activity toward a range of clinically used drugs and other xenobiotics. The expressed enzyme glucuronidated several carboxylic acid-containing nonsteroidal antiinflammatory agents including, in order of relative substrate activity, naproxen, ketoprofen, ibuprofen, fenoprofen, tiaprofenic acid, benoxprofen, zomepirac, diflunisal and indomethacin. Additionally, the stereoselectivity of ketoprofen, naproxen (S/R ratio approximately unity) and ibuprofen (S/R ratio 1.62) glucuronidation by the UGT2B7 variant was shown to differ. Two other carboxylic acid-containing drugs (clofibric acid and valproic acid) and a limited range of drugs containing an alcohol or phenolic functional group were also glucoronidated by expressed UGT2B7 variant. The deduced amino sequence of UGT2B7 variant was shown to differ only in one amino acid (tyrosine for histidine at position 268) from a previously published uridine diphosphate-glucuronosyltransferase cDNA, UGT2B7. Like the previously reported enzyme, this variant efficiently glucuronidated hyodeoxycholic acid, estriol, 4-hydroxyestrone and 2-hydroxyestriol. It is, therefore, apparent that UGT2B7 variant has the capacity to glucuronidate with a degree of specificity both endogenous compounds and xenobiotics. Preferred substrates for UGT2B7 variant include xenobiotic carboxylic acids, polyhydroxylated estrogens and hyodeoxycholic acid.

Process for the production of polysaccharide-based polycarboxylates

Abstract: A process for the production of polycarboxylic acids or salts thereof from polysaccharides by oxidation with nitrogen dioxide/dinitrogen tetroxide with at least partial conversion of the primary alcohol groups of the polysaccharides into carboxyl groups and optionally at least partial neutralization of the carboxylic acid groups formed is provided. The oxidation reaction is carried out in a closed reaction system in the presence of oxygen under pressures of 2 bar to 10 bar and at a temperature above room temperature. Nitrogen dioxide/dinitrogen tetroxide is used in such quantities that, in the event of a theoretically complete shift of the equilibrium onto the nitrogen dioxide side, the nitrogen dioxide is present in quantities of at most 2 mole equivalents, based on the content of monomer unit of the polysaccharide containing one primary alcohol group.

Gamma-, photo-, and thermally-initiated oxidation of isotactic polypropylene†

Abstract: The detailed oxidation products have been identified and compared from the γ-, photo-, and thermally-initiated oxidation of unstabilized polypropylene films. Products were identified and quantified by a combination of iodometric analysis and infrared spectroscopy. Spectral resolution was enhanced by derivatization reactions which allow the quantification of primary, secondary, and tertiary hydroperoxide and alcohol groups as well as more reliable analysis of carbonyl species. In contrast to polyethylene oxidation which yields predominantly ketone with lesser amounts of secondary hydroperoxide and carboxylic acid, polypropylene oxidizes to give predominantly tertiary hydroperoxide and lesser quantities of secondary hydroperoxide and ketone. In addition carboxylic acid groups are a minor product except at high degrees of thermal and photoinitiated oxidation. © 1993 John Wiley & Sons, Inc.

Hydrogen-bonded liquid crystals built from hydrogen-bonding donors and acceptors. Infrared study on the stability of the hydrogen bond between carboxylic acid and pyridyl moieties

Abstract: The stability of a hydrogen-bonded complex built through inter-molecular hydrogen bonding between carboxylic acid and pyridine fragments has been examined using infrared spectroscopy. Infrared spectra as a function of temperature have been recorded for the 1:1 complex of 4-hexyloxybenzoic acid and trans-4-propoxy-4′-stilbazole from the crystalline state to the isotropic state. A dependence of the stability of the hydrogen bond on molecular orientation is observed clearly in the infrared spectra. The spectra also suggest that the hydrogen bond is an unionized type with a double minimum potential energy.

Ability of Wine Lactic Acid Bacteria to Metabolize Phenol Carboxylic Acids

Abstract: Several strains of lactic acid bacteria isolated from wine were tested for their abilities to metabolize ferulic and p -coumaric acids. Using UV spectrophotometry, manometric technique, and gas chromatography, it was shown that ferulic and p -coumaric acids were strongly decarboxylated by growing cultures of Lactobacillus brevis, Lactobacillus plantarum , and Pediococcus . Resting cell decarboxylation activity was only detected for bacteria grown with these substrates suggesting inducibility of this activity. For Leuconostoc oenos , decarboxylation activity was present only with permeabilized cells grown with phenol carboxylic acid. This could indicate the absence of transport system for these acids in Leuconostoc oenos . When decarboxylation was observed, volatile phenols (4-ethylguaiacol and 4-ethylphenol) were detected indicating the possibility of reduction of the side chain before or after decarboxylation.

Oxidation of organic substrates by molecular oxygen/aldehyde/heteropolyoxometalate system

Abstract: Heteropolyoxometalate-catalyzed oxidations of organic compounds such as olefins and cyclic ketones with molecular oxygen in the presence of an aldehyde were examined. Olefins were epoxidized with dioxygen in the presence of 2 equiv of 2-methylpropanal under the influence of a catalytic amount of the mixed heteropolyoxometalate NPV 6 Mo 6 (3) to give the corresponding epoxides in moderate to good yields. This catalytic oxidation method was also applied to the epoxidation of allylic and homoallylic alcohols. In the absence of olefins, the aldehydes were efficiently converted into the corresponding carboxylic acids. In addition, the Baeyer-Villiger oxidation of cyclic ketones was accomplished by using benzaldehyde instead of 2-methylpropanal as the aldehyde

Molecular interactions between organized, surface-confined monolayers and vapor-phase probe molecules. 5. Acid-base interactions

Abstract: Interactions between self-assembled monolayers containing carboxylic or sulfonic acid terminal groups, and vapor-phase n-alkylamine probe molecules, have been studied using FTIR-external reflectance spectroscopy, mass-sensitive surface acoustic wave devices, and ellipsometry. The results indicate that proton transfer from the surface-acid group to the amine-functionalized probe is controlled by both the proton affinity and the degree of structural ordering of the surface-acid groups. In contrast to bilayers formed by hydrogen bonding between carboxylic acid-terminated monolayer, the bilayer structures that result from proton transfer are stable for periods of many hours. 19 refs., 6 figs.

Cation complexation by chemically modified calixarenes. 5. Protonation constants for calixarene carboxylates and stability constants of their alkali and alkaline-earth complexes

Abstract: The complexing properties of some calix[4]arenes in which carboxylic acid ligating groups have been progressively attached to the lower rim through the phenolic hydrogen atoms have been measured with alkali and alkaline-earth metal cations in methano by means of potentiometric titrations. The acid-base characteristics of these compounds were first determined. the weak acidities generally observed may be explained by the formation of intramolecular hydrogen bonding.

Stabilities of divalent and trivalent metal ion complexes of macrocyclic triazatriacetic acids

Abstract: Potentiomctric methods have been used to determine the stability constants of complexes of trivalent metal ions of Al 3+ , Fe 3+ , Ga 3+ , In 3+ , and Gd 3+ with the ligands 1-oxa-4,7,10-triazacyclododecane-N,N',N''-triacetic acid, 1, 1,7-dioxa-4,10,13-triazacyc1opentadecane-N,N',N''-triacetic acid, 2, and 1,7,13-trioxa-4,10,16-triazacyclooctadecaneN,N',N''-triacetic acid, 3, and of divalent metal ions of Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , and Pb 2+ with ligands 3

New triarylmethyl derivatives: "blocking groups" for rotaxanes and polyrotaxanes

Abstract: Five triarylcarbinols (8, three new compounds) were synthesized. Using carbanion chemistry the triarylmethanes (13, five new compounds) made by formic acid reduction of 8 were converted to the ω,ω,ω-triarylalkanols (15, three new compounds) and thence to the chloro (17) and iodo (18) derivatives (five new compounds). Via carbocation chemistry p-(triarylmethyl)phenols (20, two new compounds) and aniline (21, new compound) were produced. Alkylation of 20 yielded alcohol (22), benzylic bromide (23), and carboxy (25) functionalized derivatives. The alcohol, halide, phenol, aniline, and carboxylic acid functionalized triarylmethane compounds are suitable end blocking groups for rotaxanes and polyrotaxanes

Production of cellulose by the soda-anthraquinone process (sap) with recovery of the boiling chemicals

Abstract: For the production of cellulose from wood and annual plants, a boiling process is proposed in which the boiling liquor contains free soda lye and sodium salts of the alkylbenzole sulphonic acids or aromatic and aliphatic carboxylic acids. Delignification is reinforced on the addition of anthraquinone or its derivatives to the boiling liquor. There is no need to restrict the quantities of the anthraquinone additive owing to its price since anthraquinone resists wet oxidation and can be recycled in the boiling process. The solubility and hence the effect of the anthraquinone is enhanced by the use of sulphonic acid salts. In order to recover the processing chemicals contained in the black liquor it is proposed that the dissolved lignin be precipitated with mineral or carboxylic acid, the hemi-celluloses be separated by ultra-filtration and the resins by extraction, where appropriate, and the remaining organic components except for the sulphonic and carboxylic acids salts be burned in the aqueous phase with air and/or oxygen. The chemical solution freed from the wood decomposition products may be returned to the liquor after caustification of the carbonates and, after the partial crystallisation of the aliphatic carboxylic acid salts, made available in the circuit for cellulose production. The sodium acetate isolated by crystallisation can be broken down into acetic acid and sodium hydroxide by diaphragm electrolysis. The soda lye is returned to the boiling process and the acetic acid treated separately.

Alpha-keto acids are novel siderophores in the genera Proteus, Providencia, and Morganella and are produced by amino acid deaminases.

Abstract: Growth promotion and iron transport studies revealed that certain alpha-keto acids generated by amino acid deaminases, by enterobacteria of the Proteus-Providencia-Morganella group (of the tribe Proteeae), show significant siderophore activity. Their iron-binding properties were confirmed by the chrome azurol S assay and UV spectra. These compounds form ligand-to-metal charge transfer bands in the range of 400 to 500 nm. Additional absorption bands of the enolized ligands at 500 to 700 nm are responsible for color formation. Siderophore activity was most pronounced with alpha-keto acids possessing an aromatic or heteroaromatic side chain, like phenylpyruvic acid and indolylpyruvic acid, resulting from deamination of phenylalanine and tryptophan, respectively. In addition, alpha-keto acids possessing longer nonpolar side chains, like alpha-ketoisocaproic acid or alpha-ketoisovaleric acid and even alpha-ketoadipic acid, also showed siderophore activity which was absent or negligible with smaller alpha-keto acids or those possessing polar functional groups, like pyruvic acid, alpha-ketobutyric acid, or alpha-ketoglutaric acid. The fact that deaminase-negative enterobacteria, like Escherichia coli and Salmonella spp., could not utilize alpha-keto acids supports the view that specific iron-carboxylate transport systems have evolved in members of the tribe Proteeae and are designed to recognize ferric complexes of both alpha-hydroxy acids and alpha-keto acids, of which the latter can easily be generated by L-amino acid deaminases in an amino acid-rich medium. Exogenous siderophores, like ferric hydroxamates (ferrichromes) and ferric polycarboxylates (rhizoferrin and citrate), were also utilized by members of the tribe Proteeae.

Hydroxamic acid derivatives as metalloproteinase inhibitors

Abstract: Compounds of formula (I), wherein R2 represents a C2-C6 alkyl group which may contain an ether or thioether linkage; R3 represents (a) the side chain of a naturally occurring alpha-amino acid in which any carboxylic acid group may be esterified or amidated, any hydroxyl or thiol group may be acylated or alkylated (etherified) and any amino group may be acylated, or (b) a group R6(A)n- wherein n is 0 or 1, A represents a divalent C1-C6 alkyl or C2-C6 alkenyl group optionally interrupted by one or more -O-, or -S- atoms or -N(R7)- groups where R7 is hydrogen or C1-C6 alkyl, and R6 is a phenyl or heterocyclyl group either of which may be substituted, or (except where n is 0) a hydrogen atom; R4 represents hydrogen or methyl; R5 represents hydrogen, C1-C6 alkyl or phenyl(C1-C6 alkyl), and salts, solvates and hydrates thereof, are inhibitors of metalloproteinases involved in tissue degradation.

Asymmetric catalysis. 80. Mechanistic aspects of the rhodium-catalyzed enantioselective transfer hydrogenation of .alpha.,.beta.-unsaturated carboxylic acids using formic acid/triethylamine (5:2) as the hydrogen source

Abstract: The mechanism of the rhodium-catalyzed enantioselective transfer hydrogenation of methylenebutanedioic acid (itaconic acid) (1) and related [alpha],[beta]-unsaturated carboxylic acids using formic acid/triethylamine (5:2) as the hydrogen source is investigated. Kinetic studies using [sup 1]H NMR spectroscopy are presented. Formic acid decomposition is shown to be the rate-limiting step with 1 as the substrate, while hydrogen transfer turns out to be rate determining in the case of (E)-(phenylmethylene)butanedioic acid ((E)-phenylitaconic acid) (3). Furthermore, extensive use is made of deuterium labeling and the analysis of part-deuterated products by [sup 1]H and [sup 13]C[l brace][sup 1]H,[sup 2]H[r brace] NMR spectroscopy. Taken together, these results indicate that the mechanism of rhodium-catalyzed transfer hydrogenation with formic acid/triethylamine as the hydrogen source most likely involves decarboxylation of a transient formate species to form hydridic complexes of rhodium, in which the Rh-H entity has a long lifetime relative to hydrogen transfer to the substrate. 40 refs., 5 figs., 1 tab.

A highly catalytic and selective conversion of carboxylic acids to 1-alkenes of one less carbon atom

Abstract: An equimolar mixture of a carboxylic acid and acetic anhydride produces a reagent combination that undergoes a highly efficient decarbonylation/dehydration at 250[degrees]C using either Pd- or Rh-based catalyst systems, affording excellent yields of the corresponding 1-alkenes and one less carbon atom. The stoichiometric and catalytic decarbonylation of aliphatic aldehydes and acid chlorides to alkanes and alkenes, respectively, by transition-metal complexes are well-known and synthetically useful transformations. Relatively little, however, has been reported concerning the analogous decarbonylation/dehydration of aliphatic carboxylic acids to olefins, with generally poor results achieved in terms of catalyst efficiency and selectivity toward terminal olefin formation in the product. For example, the decarbonylation/dehydration of stearic acid to heptadecane using a Rh-based catalyst was reported to proceed with a maximum catalyst turnover number (TON; moles of olefin product formed per mole of catalyst used) of ca. 250, with selectivities toward 1-heptadecene formation typically below 50%. Interestingly, results were presented in this work which suggested that the decarbonylation of stearic acid proceeded via intermediate formation of stearic anhydride. Use of a preformed, symmetrical anhydride is not desirable from an economic or synthetic viewpoint, particularly since its decarbonylation should result in the formation of equal amounts of olefin and carboxylic acidmore » coproducts. The authors now report here that the use of a carboxylic acid substrate as an equimolar mixture with acetic anhydride (Ac[sub 2]O) produces a mixed anhydride system which undergoes an extremely facile decarbonylation reaction to provide a general and highly selective route to the corresponding 1-alkenes of one less carbon atom. 19 refs., 1 tab.« less

Effect of biphenyl and naphthyl groups on the structure of self-assembled monolayers: packing, orientation, and wetting properties

Abstract: The self-assembling behavior of a series of 4-alkoxybiphenyl-4'-carboxylic acid and 6-alkoxy-2-naphthoic acid compounds on the surfaces of Ag and Cu was studied. The structure of the monolayer film was probed with ellipsometry, reflection absorption IR spectroscopy, and contact angle measurements. The effect of aromatic chromophores on the packing, orientation of the molecular assembly, and wetting properties of the monolayer film was investigated. These monolayer structures were compared with those of n-alkanoic acids and n-alkanethiols to deduce the packing mechanism of carboxylic acid adsorption on metal oxides

Activation of carbon dioxide : nickel-catalyzed electrochemical carboxylation of diynes

Abstract: The simultaneous activation of carbon dioxide and diyness by electrogenerated LNi(O) complexes (L = bpy, pentamethyldiethylenetriamine: PMDTA) enables the selective incorporation of one molecule of CO[sub 2] into the unsaturated systems and the preparative-scale electrosyntheses of carboxylic acids. A series of nonconjugated diynes afforded selectively linear or cyclic adducts depending on the ligand. Diynes bearing both a terminal and an internal triple bond gave exclusive CO[sub 2] incorporation into the terminal alkynyl group, regioselectively at the 2-position. The electrocarboxylation of 1,3-diynes with the Ni-PMDTA catalytic system yielded, regio- and stereoselectively, (E)-2-vinylidene-3-yne carboxylic acids in one step. The electrosyntheses were carried out in single-compartment cells fitted with a consumable magnesium anode, and utilized a catalytic amount of an air-stable Ni(II) complex as the catalyst precursor. Cyclic voltammetry studies revealed that both carbon dioxide and the diynes are able to coordinate to LNi(O)-generated species in DMF. 39 refs., 3 figs., 5 tabs.