Showing papers on "Carboxylic acid published in 1992"

Amide and Ester Surface Attachment Reactions for Alkanethiol Monolayers at Gold Surfaces As Studied by Polarization Modulation Fourier Transform Infrared Spectroscopy

Abstract: The modification of alkanethiol monolayers via amide and ester formation reactions is demonstrated as a methodology for attaching monolayer and submonolayer coveragea of specific chemical species onto metal electrodes. A monolayer of 11-mercaptoundecanolc acid (HSC 10 H 20 COOH) is used as a surface bifunctional linking agent on polycrystalllne gold surfaces. The reaction of these adsorbed molecules with gaseous thionyl chloride converts the carboxylic acid group to an acid chloride which can then be reacted further with an amine or alcohol to form an amide or ester linkage

Understanding enzyme-catalyzed proton abstraction from carbon acids: Details of stepwise mechanisms for β-elimination reactions

Abstract: The observed rates of enzyme-catalyzed abstraction of a proton from a carbon adjacent to a carbonyl/carboxylic acid group (α-proton of a carbon acid) require that the pKa of the a-proton be decreased such that it is equal to (±2-3 pK a units) or las than that of the protonated active site basic catalyst. This can be accomplished by concerted general acid-general base catalysis: Gerlt, J. A.; Kozarich, J. W.; Kenyon, G. L.; Gassman, P. G. J. Am. Chem. Soc. 1991, 113, 9667

Control of water permeation by pH and ionic strength through a porous membrane having poly(carboxylic acid) surface-grafted

Abstract: A straight-pored membrane, which controls the rate of water permeation according to pH and ionic strength, was synthesized by surface-graft polymerization of vinyl monomers carrying a carboxylic acid substituent. The rate of water permeation through the prepared membrane changed reversibly in response to pH variation of the aqueous solution. The pH response of water permeation was controlled by changing the density and length of graft chains. The most sensitive pH response was attained with a membrane having poly(carboxylic acid) of a high degree of polymerization grafted in low densities

Differences in carboxylic acid exudation among p-starved leguminous crops in relation to carboxylic acid contents in plant tissues and phospholipid level in roots

Abstract: The amount or composition of carboxylic acids in the root exudates and tissue extracts of leguminous crop plants subjected to P starvation for 3 d in water culture were compared. Also, the changes in the distribution and P content of the P fractions of the roots of the plants subjected to P starvation for 3 d were compared. In the root exudates collected over a 12 h period, malonic, succinic, fumaric, malic, citric, and t-aconitic acids were detected. A large amount of these carboxylic acids, especially citric and malic acids, was exuded from the roots of chickpea as compared with those of soybean, kidney bean, cowpea, and pigeonpea. Groundnut roots exuded an appreciable amount of carboxylic acids, especially fumaric acid. Although the contents of these carboxylic acids in the extracts of leaves and roots of chickpea were the highest as compared with soybean, kidney bean, and cowpea, the differences were much less significant than those in the root exudates. The amount and composition of carboxyl...

Synthesis of C-functionalized trans-cyclohexyldiethylenetriaminepenta-acetic acids for labelling of monoclonal antibodies with the bismuth-212 α-particle emitter

Abstract: Several C-functionalized cyclohexyldiethylenetriaminepenta-acetic acid derivatives have been prepared from (±)-4-nitrophenylalanine and (±)-trans-cyclohexane-1,2-diamine to produce two sets of diastereoisomeric enantiomers. A modification of this synthesis has been employed to prepare a single enantiomer in order to define the absolute configurations of the products.

New Heteroaromatic Complexing Agents and Luminescence of Their Europium(III) and Terbium(III) Chelates

Abstract: Twelve heteroaromatic complexing agents 9a–I were synthesized with the purpose to develop suitable labels for time-resolved luminescence-based bioaffinity assays. The relative luminescence yields, excitation maxima, and emission decay constants of their europium(III) and terbium(III) chelates were determined. According to these results, 2,2′,2″,2‴-[(2,2′-bipyridine-6,6′-diyl)bis(methylenenitrilo)]tetrakis (acetic acid) (9e) and 2,2′,2″,2‴-[(2,2′:6′,2″-terpyridine-6,6″-diyl)bis(methylenenitrilo)] tetrakis(acetic acid) (91) are the most promising agents.

Thermal decomposition of dilute aqueous formic acid solutions

Abstract: The aqueous-phase oxidation of formic acid and formate has been studied in a batch autoclave reactor at 260°C and 2 MPa of O 2 . The formate is converted to bicarbonate whereas formic acid, besides oxidation, decomposes by at least two different routes, namely a dehydration or a decarboxylation. In particular the second one is dependent on the reactor vessel used. It is shown to be catalyzed by a mixture of oxides of stainless steel components. The presence of CH 3 COOH or CH 3 CHO promotes the decomposition of HCOOH by way of both decarboxylation and oxidation. In any case formic acid is a relatively short-lived intermediate in the wet-oxidation process

Reactive derivatives of bapta used to make ion-selective chelators

Abstract: The invention relates to fluorescent and/or reactive derivatives of 1,2-bis-(2-aminophenoxyethane)-N,N,N',N'-tetraacetic acid (BAPTA) according to the formula: ##STR1## where at least one of W and X is a functional group, with or without a spacer, that terminates in an alcohol or phenol, a thiol, a haloacetamide, an alkyl halide, an amine or aniline, a carboxylic acid, an anhydride, an isocyanate, an isothiocyanate, a maleimide, or an activated ester. The BAPTA-like molecule may be further substituted, one or more times, by additional functional groups with or without spacers or by CH 3 , NO 2 , CF 3 , F, Cl, Br, I, or carboxylic acid derivatives or pharmaceutically acceptable salts thereof, or by indolyl or benzofuran fluorophores. The functional groups allow for subsequent covalent attachment of one or more oxygen heterocycle fluorophores (e.g. fluorescein, coumarin, rhodamine); or polymolecular assemblies (e.g. gel and resin polymers, polysaccharides, polypeptides, nucleic acids, and liposomes); or combinations thereof.

Carbon-hydrogen activation in aqueous medium. The diverse roles of platinum(II) and metallic platinum in the catalytic and stoichiometric oxidative functionalization of organic substrates including alkanes

Abstract: The oxidation of ethers, alcohols, esters, and light alkanes (ethane, propanes) byu K 2 Pt/l 4 and Pt/O 2 in aqueous medium has been studied. Results appear to indicate that unactivated C-H bonds were attacked and oxidized by Pt(II) whereas C-H bonds α to an oxygen were activated and catalytically oxidated by metallic Pt in the presence of O 2 . For example, Pt(II) was found to oxidize ethane selectively to the alcohols, ethanol, and ethylene glycol. In the presence of metallic Pt and O 2 , further oxidation of the alcohol functionality occurred to generate the corresponding carboxylic acids

Molecular mechanics (MM3) studies of carboxylic acids and esters

Abstract: Force field calculations using MM3 have been extended to include carboxylic acids and esters. Accurate structures for several small molecules were well reproduced, and vibrational spectra moderately so. Available thermochemical data were examined. A good portion of them were rejected as inaccurate, and the remainder were fit

Organic acids over equatorial Africa: Results from DECAFE 88

Abstract: Gaseous short chain organic acids were measured during the dry season (February) in and above the rain forest of the northern Congo. Samples were taken at ground level and during several flights up to 4 km altitude. The organic acids were concentrated from the atmosphere by using “mist scrubbers,” which expose a mist of deionized water to the air to be probed. The organic acids absorbed in the water were subsequently analyzed by ion chromatography. Formic, acetic, and pyruvic acids were identified in the samples. At ground level, average mixing ratios of gaseous formic and acetic acid of 0.5±0.6 and 0.6±0.7 parts per billion by volume (ppbv) (1 s), respectively, were found. Boundary layer mixing ratios, however, were significantly higher (3.7±1.0 and 2.7±0.9 ppbv). This indicates a downward net flux of these atmospheric trace components from the boundary layer to the surface. Free tropospheric samples taken above the cloud convection layer show lower mixing ratios again (0.9±0.3 and 0.7±0.1 ppbv). On the basis of this vertical distribution, direct emission by vegetation is not considered to be the dominant source. Biomass burning and photochemical oxidation of biogenic precursors are the major processes contributing to the enhancement of organic acids observed in the boundary layer. The organic acids parallel the profiles of ozone and CO, which suggests that their generation processes are closely related. Pyruvic acid is not correlated with formic acid, indicating that the oxidation of isoprene is not of major importance. In emissions from biomass fires, CO correlates well with formic and acetic acid, and thus some of the enhancement of organic acids in the boundary layer can be explained due to burning. However, an additional gas phase source for organic acids must exist to explain the observed ratio of formic to acetic acid. This is most likely the ozonolysis of olefins which were released as pyrolysis products from biomass burning.

Synthesis of biodegradable polyesteramides with pendant functional groups

Abstract: Morpholine-2,5-dione derivatives having substituents with benzyl-protected carboxylic acid, benzyloxycarbonyl-protected amine and p-methoxy-protected thiol groups, respectively, were prepared in 29-58% yield by cyclization of the corresponding N-[(2RS)-bromopropionyl]-L-amino acids. Polyesteramides with protected pendant functional groups were obtained by ring-opening copolymerization of either e-caprolactone or DL-lactide with morpholine-2,5-dione derivatives having protected functional substituents. The copolymerizations were carried out in the bulk at 130°C using stannous octoate as an initiator and using low mole fractions (0,05, 0,10 and 0,20) of morpholine-2,5-dione derivatives in the feed. The molecular weight of the resulting copolymers ranged from 1,4 to 8,3 · 104. The ring-opening homopolymerization of morpho-line-2,5-dione derivatives with protected functional substituents was not successful. Polyesteramides with either pendant carboxylic acid groups or pendant amine groups were prepared by catalytic hydrogenation of the corresponding protected copolymers. Treatment of copolymers having pendant p-methoxybenzyl-protected thiol groups with trifluoromethanesulfonic acid resulted not only in the removal of the p-methoxybenzyl group but also in severe degradation of the copolymers, due to acidolysis of main-chain ester bonds.

A comprehensive theoretical examination of primary dissociation pathways of formic acid

Abstract: Primary dissociation pathways have been investigated for formic acid by ab initio molecular orbital methods. Reactant, transition state, and products were fully optimized with unrestricted Hartree–Fock and unrestricted second‐order Mo/ller–Plesset wave functions. The activation energy for decarboxylation of formic acid (CO2+H2) is 65.2 kcal mol−1, while that for the dehydration process (CO+H2O) is 63.0 kcal mol−1. These theoretical results suggest that the decarboxylation and dehydration processes are competitive. The activation energy barrier for isomerization of formic acid to yield dihydroxymethylene is 73.7 kcal mol−1 and may be a competitive process. Free radical initiation processes are predicted to be minor.

The solvent extraction of rare-earth metals by carboxylic acids

Abstract: The solvent extraction of the trivalent lanthanides and yttrium from nitrate media by solutions of carboxylic acids in xylene has been studied. Commercially available carboxylic acids such as Versatic 10 and naphthenic acids were used, as well as model compounds of known structure, such as 2-ethylhexanoic and 3-cyclohexylpropanoic acids. In a few cases, extraction of the metals from sulphate and chloride solutions was also investigated. The dependence of the extraction properties of the carboxylic acids on the atomic number of the lanthanide shows a definite relationship to the steric bulk of the carboxylic acid molecule quantified by means of the steric parameter, Es′ of the substituent alkyl; group. For sterically hindered acids (− Es′ > 2) the pH0.5 of extraction decreases more or less continuously from lanthanum through to lutetium, and the behaviour of yttrium most closely resembles that of the middle lanthanides, such as gadolinium or terbium. For straight-chain and other non-hindered acids...

Structures of aspartic acid-96 in the L and N intermediates of bacteriorhodopsin: analysis by Fourier transform infrared spectroscopy

Abstract: The light-induced difference Fourier transform infrared spectrum between the L or N intermediate minus light-adapted bacteriorhodopsin (BR) was measured in order to examine the protonated states and the changes in the interactions of carboxylic acids of Asp-96 and Asp-115 in these intermediates. Vibrational bands due to the protonated and unprotonated carboxylic acid were identified by isotope shift and band depletion upon substitution of Asp-96 or -115 by asparagine. While the signal due to the deprotonation of Asp-96 was clearly observed in the N intermediate, this residue remained protonated in L. Asp-115 was partially deprotonated in L. The C = O stretching vibration of protonated Asp-96 of L showed almost no shift upon 2H2O substitution, in contrast to the corresponding band of Asp-96 or Asp-115 of BR, which shifted by 9-12 cm-1 under the same conditions. In the model system of acetic acid in organic solvents, such an absence of the shift of the C = O stretching vibration of the protonated carboxylic acid upon 2H2O substitution was seen only when the O-H of acetic acid is hydrogen-bonded. The non-hydrogen-bonded monomer showed the 2H2O-dependent shift. Thus, the O-H bond of Asp-96 enters into hydrogen bonding upon conversion of BR to L. Its increased hydrogen bonding in L is consistent with the observed downshift of the O-H stretching vibration of the carboxylic acid of Asp-96.

Products and mechanism of the reaction of ozone with phospholipids in unilamellar phospholipid vesicles

Abstract: While considerable effort has been expended on determining the health effects of exposure to typical urban concentrations of O3, little is known about the chemical events responsible for toxicity. Phospholipids containing unsaturated fatty acids in the cell membranes of lung cells are likely reaction sites for inhaled ozone (O3). In this study, we examined the reaction of O3 with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in unilamellar phospholipid vesicles. Reaction of ozone with the carbon-carbon double bond of POPC yielded an aldehyde and a hydroxy hydroperoxide. The hydroxy hydroperoxide eliminated H2O2 to yield a second aldehyde. Upon further ozonolysis, the aldehydes were oxidized to the corresponding carboxylic acids. A material balance showed that no other reaction consumed POPC and O3 or produced these products. As a mechanistic probe, we measured incorporation of oxygen-18 from 18O3 into aldehyde, carboxylic acid, and H2O2. Approximately 50% of the aldehyde oxygen atoms were derived from O3. Oxygen in H2O2 was derived solely from O3, where both oxygen atoms in a molecule of H2O2 were from the same molecule of O3. One of the carboxylic acid oxygen atoms was derived from the precursor aldehyde, while the other was derived from O3. These results support the following mechanism. Cleavage of the carbon-carbon double bond of POPC by O3 yields a carbonyl oxide and an aldehyde. Reaction of H2O with the carbonyl oxide yields a hydroxy hydroperoxide, preventing formation ozonide by reaction of the carbonyl oxide and aldehyde. Elimination of H2O2 from the hydroxy hydroperoxide yields a second aldehyde. Oxidation of the aldehydes by O3 yields carboxylic acids.