Showing papers on "Carboxylic acid published in 1999"
TL;DR: The results suggest that P deficiency-induced exudation of carboxylic acids depends on the ability to accumulate carboxYlic acids in the root tissue, which in turn is determined by biosynthesis, degradation and partitioning of car boxylic acid or related precursors between roots and shoot.
Abstract: Phosphorus deficiency-induced metabolic changes related to exudation of carboxylic acids and protons were compared in roots of wheat (Triticum aestivum L. cv Haro), tomato (Lycopersicon esculentum L., cv. Moneymaker), chickpea (Cicer arietinum) and white lupin (Lupinus albus L. cv. Amiga), grown in a hydroponic culture system. P deficiency strongly increased the net release of protons from roots of tomato, chickpea and white lupin, but only small effects were observed in wheat. Release of protons coincided with increased exudation of carboxylic acids in roots of chickpea and white lupin, but not in those of tomato and wheat. P deficiency-induced exudation of carboxylic acids in chickpea and white lupin was associated with a larger increase of carboxylic acid concentrations in the roots and lower accumulation of carboxylates in the shoot tissue compared to that in wheat and tomato. - Citric acid was one of the major organic acids accumulated in the roots of all investigated species in response to P deficiency, and this was associated with increased activity and enzyme protein levels of PEP carboxylase, which is required for biosynthesis of citrate. Accumulation of citric acid was most pronounced in the roots of P-deficient white lupin, chickpea and tomato. Increased PEP carboxylase activity in the roots of these plants coincided with decreased activity of aconitase, which is involved in the breakdown of citric acid in the TCA cycle. In the roots of P-deficient wheat plants, however, the activities of both PEP carboxylase and aconitase were enhanced, which was associated with little accumulation of citric acid. The results suggest that P deficiency-induced exudation of carboxylic acids depends on the ability to accumulate carboxylic acids in the root tissue, which in turn is determined by biosynthesis, degradation and partitioning of carboxylic acids or related precursors between roots and shoot. In some plant species such as white lupin, there are indications for a specific transport mechanism (anion channel), involved in root exudation of extraordinary high amounts of citric acid.
570 citations
TL;DR: Evidence from experiments on UGT interactions with inhibitors directed at specific amino acids, photoaffinity labeling, and analysis of amino acid alignments suggest that UDP-GIcUA interacts with residues in both the N- and C-terminal domains, whereas aglycon binding sites are localized in the N -terminal domain.
Abstract: UDP-Glucuronosyltransferases (UGTs) are glycoproteins localized in the endoplasmic reticulum (ER) which catalyze the conjugation of a broad variety of lipophilic aglycon substrates with glucuronic acid using UDP-glucuronic acid (UDP-GIcUA) as the sugar donor. Glucuronidation is a major factor in the elimination of lipophilic compounds from the body. In this review, current information on the substrate specificities of UGT1A and 2B family isoforms is discussed. Recent findings with regard to UGT structure and topology are presented, including a dynamic topological model of UGTs in the ER. Evidence from experiments on UGT interactions with inhibitors directed at specific amino acids, photoaffinity labeling, and analysis of amino acid alignments suggest that UDP-GIcUA interacts with residues in both the N- and C-terminal domains, whereas aglycon binding sites are localized in the N-terminal domain. The amino acids identified so far as crucial for substrate binding and catalysis are arginine, lysine, histidine, proline, and residues containing carboxylic acid. Site-directed mutagenesis experiments are critical for unambiguous identification of the active-site architecture.
491 citations
TL;DR: In this paper, the authors proposed a method to reduce undesirable effects caused by CO2 induced swelling in CO2/CH4 separation processes by stabilizing the polyimide structure with crosslinks.
382 citations
TL;DR: In this paper, the reactivity of organic compounds composed of C, H, and O, dyes, amides, and water-soluble polymers was correlated well with their carbon content in the molecule (C/MW).
Abstract: The wet oxidation of organic compounds composed only of C, H, and O, dyes, amides, and water-soluble polymers is discussed to clarify the basic nature of this process. The reactivity of the organic compounds composed of C, H, and O, dyes, and some amides was correlated well with their carbon content in the molecule (C/MW) or carbon content in their skeletal structure (C/MW‘). This C/MW index can be applied to roughly estimate the behavior of wastewaters containing various organic compounds. Polymers are easily decomposed by the wet oxidation because they can undergo intramolecular hydrogen abstraction in the chain-propagation step. The biodegradability of polymers and amides was improved by wet oxidation treatment, indicating an asset of this process. The function of homogeneous copper salts and the effect of hydrogen peroxide are discussed. The action of Co/Bi composite oxide designed for the treatment of refractory carboxylic acids, Mn/Ce composite oxide for ammonia and other organic compounds, and Ru/C...
277 citations
TL;DR: In this paper, secondary aerosols from the reaction of α-pinene with ozone were generated in a 190 m3 outdoor Teflon chamber, and products of these aerosols were characterized.
224 citations
TL;DR: In this paper, the reaction of 3,4-dihydro-3,6-dimethyl-2H-1,3-benzoxazine using strong and weak carboxylic acids and phenols as catalysts has been studied using Fourier transform infrared (FTIR) spectroscopy.
Abstract: The reaction of 3,4-dihydro-3,6-dimethyl-2H-1,3-benzoxazine using strong and weak carboxylic acids and phenols as catalysts has been studied using Fourier transform infrared (FTIR) spectroscopy. The auto-accelerated curing using sebacic acid as catalyst is further documented using 1H-nuclear magnetic resonance (NMR) and dielectric analysis. Termination of curing, using strong acids or no catalyst, are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1913–1921, 1999
215 citations
TL;DR: In this article, a hydrogen-terminated Si(111) surface has been covalently modified by UV irradiation in the presence of ethyl undecylenate leading to a Si (111)-C10H20CO2Et surface.
Abstract: A hydrogen-terminated Si(111) surface has been covalently modified by UV irradiation in the presence of ethyl undecylenate leading to a Si(111)-C10H20CO2Et surface. It is possible to carry out a diverse range of chemical manipulations of the ester group on the surface. For example, reduction with sodium borohydride provides a surface terminated with a primary alcohol. Reaction with an alkyl Grignard reagent gives a tertiary alcohol that can be acylated with acetyl chloride. Finally, hydrolysis of the ester leads to a carboxylic acid terminated surface that can be coupled to an amino acid using a standard solid phase amide coupling protocol. The surface density of the ester function can be controlled by dilution of the reacting ester with a long-chain alkene. This has the beneficial effects of minimizing the disruption of the alkyl chain packing in the monolayers and avoiding steric blocking of the ester group. It is expected that the ability to precisely control the average distance between large biomolec...
214 citations
TL;DR: Sagerinic acid and salvianolic acid derived from rosmarinic acid were isolated together with the parent compound from polar solvent extracts of Salvia officinalis by NMR and the stereochemistry of the substituents on the cyclobutane moiety was established as 3 β, 4a-diaryl-1a, 2 β -dicarboxylicacid diester (m-truxinate form) as mentioned in this paper.
187 citations
TL;DR: To attain water solubility under basic conditions the authors enzymatically grafted the hydrophilic compound chlorogenic acid onto chitosan and tyrosinase, which converts a wide range of phenolic substrates into electrophilic o-quinones, which can undergo reaction with the nucleophilic amino groups of chitan.
Abstract: Chitosan is a natural biopolymer whose rich amine functionality confers water solubility at low pH. At higher pH's (greater than 6. 5), the amines are deprotonated and chitosan is insoluble. To attain water solubility under basic conditions we enzymatically grafted the hydrophilic compound chlorogenic acid onto chitosan. Despite its name, chlorogenic acid is a nonchlorinated phenolic natural product that has carboxylic acid and hydroxyl functionality. The enzyme in this study was tyrosinase, which converts a wide range of phenolic substrates into electrophilic o-quinones. The o-quinones are freely diffusible and can undergo reaction with the nucleophilic amino groups of chitosan. Using slightly acidic conditions (pH = 6), it was possible to modify chitosan under homogeneous conditions. When the amount of chlorogenic acid used in the modification reaction exceeded 30% relative to chitosan's amino groups, the modified chitosan was observed to be soluble under both acidic and basic conditions, and to have a pH window of insolubility at near neutral pH. 1H NMR spectra confirmed that chitosan was chemically modified, although the degree of modification was low. Copyright 1999 John Wiley & Sons, Inc.
177 citations
TL;DR: The hypothesis is that cyclization of RGD peptides via disulphide bond linkage can induce structural rigidity, thereby preventing degradation mediated by the aspartic acid residue, as a function of pH and buffer concentration.
Abstract: Arg-Gly-Asp (RGD) peptides contain an aspartic acid residue that is highly susceptible to chemical degradation and leads to the loss of biological activity. Our hypothesis is that cyclization of RGD peptides via disulphide bond linkage can induce structural rigidity, thereby preventing degradation mediated by the aspartic acid residue. In this paper, we compared the solution stability of a linear peptide (Arg-Gly-Asp-Phe-OH; 1) and a cyclic peptide (cyclo-(1, 6)-Ac-Cys-Arg-Gly-Asp-Phe-Pen-NH2; 2) as a function of pH and buffer concentration. The decomposition of both peptides was studied in buffers ranging from pH 2-12 at 50 degrees C. Reversed-phase HPLC was used as the main tool in determining the degradation rates and pathways of both peptides. Fast atom bombardment mass spectrometry (FAB-MS), electrospray ionization mass spectrometry (ESI-MS), matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry, liquid chromatography-mass spectrometry (LC-MS), and one- and two-dimensional nuclear magnetic resonance spectroscopy (NMR) were used to characterize peptides 1 and 2 and their degradation products. In addition, co-elution with authentic samples was used to identify degradation products. Both peptides displayed pseudo-first-order kinetics at all pH values studied. The cyclic peptide 2 appeared to be 30-fold more stable than the linear peptide 1 at pH 7. The degradation mechanisms of linear (1) and cyclic (2) peptides primarily involved the aspartic acid residue. However, above pH 8 the stability of the cyclic peptide decreased dramatically due to disulphide bond degradation. Both peptides also exhibited a change in degradation mechanism upon an increase in pH. The increase in stability of cyclic peptide 2 compared to linear peptide 1, especially at neutral pH, may be due to decreased structural flexibility imposed by the ring. This rigidity would prevent the Asp side chain carboxylic acid from orientating itself in the appropriate position for attack on the peptide backbone.
168 citations
TL;DR: In this paper, amorphous iron particles were coated by various carboxylic acids and their physical properties (differential scanning calorimetry, thermogravimetric analysis, temperature-programmed desorption, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopic, and magnetism) were measured.
Abstract: Nanophased amorphous iron particles were coated by various carboxylic acids and their physical properties (differential scanning calorimetry, thermogravimetric analysis, temperature-programmed desorption, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and magnetism) were measured. The various properties were measured as a function of the alkyl chain length. The desorption pattern at 400 °C revealed a keto derivative.
TL;DR: In this article, a chiral stationary phase was prepared by immobilization of the naturally occurring alkaloid quinine onto a 3-mercaptopropyl-modified silica gel via a radical addition reaction and it was evaluated for direct HPLC enantioseparation of acidic chiral compounds under buffered hydro-organic mobile phase conditions.
TL;DR: A novel and efficient method for the production of enantiomerically pure (R)-(-)-hydroxycarboxylic acids by in vivo depolymerization of microbial polyester polyhydroxyalkanoates (PHAs) was developed.
Abstract: A novel and efficient method for the production of enantiomerically pure (R)-(-)-hydroxycarboxylic acids by in vivo depolymerization of microbial polyester polyhydroxyalkanoates (PHAs) was developed. Using this method, several model compounds, (R)-(-)-3-hydroxyalkanoic acids, consisting of 4 to 12 carbon atoms, and (R)-(-)-3-hydroxy-5-phenylvaleric acid, could be prepared. In particular, (R)-(-)-3-hydroxybutyric acid could be efficiently prepared by this method. By providing the environmental condition in which cells possess high activity of intracellular PHA depolymerase and low activity of (R)-(-)-3-hydroxybutyric acid dehydrogenase, (R)-(-)-3-hydroxybutyric acid could be produced with a yield of 96% in only 30 min by in vivo depolymerization of polyhydroxybutyrate (PHB) accumulated in Alcaligenes latus.
Patent•
29 Oct 1999TL;DR: The present invention relates to a compound of the formula "STR1" wherein R 1, R 2, R 3 are as defined above, to pharmaceutical compositions and methods of treatment as discussed by the authors.
Abstract: The present invention relates to a compound of the formula ##STR1## wherein R 1 , R 2 , R 3 are as defined above, to pharmaceutical compositions and methods of treatment.
TL;DR: In this article, the effect that similarly ligated species with substantially varied structures have on the final densification of the resultant ceramic (in this case TiO2) was studied.
Abstract: Carboxylic acid (HORc)-modified Ti(OR)4 products were used to study the effect that similarly ligated species with substantially varied structures have on the final densification of the resultant ceramic (in this case TiO2). The 1:1 stoichiometric products isolated from the reactions of [Ti(μ-ONep)(ONep)3]2 (1, ONep = OCH2CMe3) and a variety of sterically hindered carboxylic acids [HORc: HOFc (HO2CH), HOAc (HO2CCH3), HOPc (HO2CCHMe2), HOBc (HO2CCMe3), or HONc (HO2CCH2CMe3)] were identified by single-crystal X-ray diffraction and solid-state 13C MAS NMR spectroscopy as Ti3(μ3-O)(OFc)2(ONep)8 (2), Ti3(μ3-O)(OAc)2(ONep)8 (3), Ti6(μ3-O)6(OPc)6(ONep)6 (4), Ti2(μ-OBc)2(ONep)6 (5), and Ti3(μ3-O)(ONc)2(ONep)8 (6). Compounds 2, 3, and 6 adopt a triangular arrangement of Ti atoms linked by a μ3-oxide moiety with ORc and ONep ligands supporting the basic framework. Compound 4 adopts a distorted, hexagon-prism geometry of two offset [Ti−O−]3 rings with each six-coordinated metal possessing a terminal ONep and two mo...
TL;DR: In this article, a GC-MS method for simultaneous quantification of mono- di- and trisaccharides, sugar alcohols and acids, measured as their trimethylsilyl-oxime ether/ester derivatives, prepared in presence of the fruit matrix, from one solution by one injection has been extended.
TL;DR: In this article, high performance size-exclusion chromatography was used to study the changes in molecular size of different humic substances brought about by addition of mineral (HCl) and monocarboxylic (formic, acetic, propionic, and butyric) acids.
Abstract: Summary
The conformational structure of dissolved humic substances is an important property that controls the reactivity of humus in the soil solution. High performance size-exclusion chromatography was used here to study the changes in molecular size of different humic substances brought about by addition of mineral (HCl) and monocarboxylic (formic, acetic, propionic, and butyric) acids. The CPMAS-NMR spectra showed that humic substances had varying chemical composition and that the ratio of hydrophilic to hydrophobic carbon (HI/HB) was greater for a humic acid from soil than for ones from oxidized coal and lignite. All humic substances showed a decrease in UV absorbance of chromatographic peaks when treated with either HCl or monocarboxylic acids. This was due to the hypochromic effect by which the absorptivity of associated molecules is decreased when they are separated. We attributed the molecular separation upon acid treatment to the formation of intermolecular hydrogen bonding that alters the original conformation stabilized mainly by weaker hydrophobic interactions. Addition of organic acids not only further decreased peak absorbances of humic acids but also caused their shift to larger elution volumes, indicating a larger conformational disruption than with HCl. The extent of the molecular size changes showed a relation to the number of carbons of monocarboxylic acids and to the HI/HB ratios of humic materials. The larger the carbon content of organic acids and the smaller the HI/HB ratio of humic materials, the larger was the decrease of the average molecular size of humic acids. These results suggest that dissolved humic substances associate predominantly by hydrophobic forces and that the apolar components of humic substances largely control their aggregation and reactivity in the environment.
Patent•
06 Jul 1999
TL;DR: An amide of hyaluronic acid or a derivative thereof which comprises at least one repetitive unit of general formula (I): wherein R = NR6R7, or alcoholic group of the aliphatic, aromatic, aryl-al-phatic, cyclo-aliphatic or heterocyclic series, OH, O-, alcoholic group as discussed by the authors.
Abstract: An amide of hyaluronic acid or a derivative thereof which comprises at least one repetitive unit of general formula (I): wherein R = NR6R7, or alcoholic group of the aliphatic, aromatic, arylaliphatic, cycloaliphatic, heterocyclic series, OH, O-, alcoholic group of hyaluronic acid, amino group of deacylated hyaluronic acid; R1, R2, R3, R4 = H, SO3-, acyl group derived from a carboxylic acid of the aliphatic, aromatic, arylaliphatic, cycloaliphatic, heterocyclic series, -CO- (CH2)2-COOY; Y = negative charge, or H; R5 = -CO-CH3, H, SO3-, acyl group derived from a carboxylic acid of the aliphatic, aromatic, arylaliphatic, cycloaliphatic, heterocyclic series, acylic group of hyaluronic acid; R6 = is H or a aliphatic, aromatic, arylaliphatic, cycloaliphatic, or heterocyclic group, substituted or unsubstituted; R7 = is H or an aliphatic, aromatic, arylaliphatic, cycloaliphatic, or heterocyclic group, substituted or unsubstituted; wherein at least one of R or R5 forms an amide group.
TL;DR: Curtius rearrangement of the resulting carboxylic acid provided the enantiopure benzyloxycarbonyl (Cbz)-protected β-amino esters 6 in good yields (74−79%).
Abstract: A general procedure for the synthesis of enantiopure β-substituted, β-amino acids is presented. Alkylation of the sodium enolates derived from chiral N-acyloxazolidinone imides 2 (R = Me, i-Pr, t-Bu, Ph, Bn) with tert-butyl bromoacetate afforded the 2-substituted succinate derivatives 3 in good yields (82−89%) and with high selectivity (≥93:7). Following hydrolysis, Curtius rearrangement of the resulting carboxylic acid provided the enantiopure benzyloxycarbonyl (Cbz)-protected β-amino esters 6 in good yields (74−79%).
TL;DR: In this article, NaOH is added to a mixture of 4-bromo-3-methylaniline, 4-chlorobutyryl chloride, and catalytic TBAC in THF/H2O.
TL;DR: The mechanism of enantiodifferentiation in the hydrogenation of alkenoic acids over cinchona-modified Pd has been investigated using the tiglic acid → 2-methyl-butanoic acid transformation as test reaction as discussed by the authors.
TL;DR: The swelling ratio increased with an increase of the DS of the MA segment (ionizable moiety that affects swelling ratio) in the Dex-MA hydrogel, which exhibited the highest swelling ratio in neutral pH, followed by acidic (pH 3) and alkaline pH (10).
Abstract: A new class of hydrogel precursor, dextran-maleic acid (Dex-MA), was synthesized by the reaction of dextran with maleic anhydride in the presence of the catalyst triethylamine. The effects of temperature, time, catalyst amount, and reactant concentration on the degree of substitution (DS) by MA was studied to establish an optimum reaction condition. The new hydrogel precursor had excellent solubility in various common organic solvents. The hydrogels based on Dex-MA precursor were made by the irradiation of Dex-MA with a long wave UV lamp. The Dex-MA hydrogels showed a very high swelling ratio in water, and the magnitude of swelling depended on the pH of the medium and the DS by MA. The Dex-MA hydrogels exhibited the highest swelling ratio in neutral pH, followed by acidic (pH 3) and alkaline pH (10). The most distinctive characteristic of Dex-MA hydrogels was that a carboxylic acid group was generated by the reaction of dextran with maleic anhydride. As a result, the swelling ratio increased with an increase of the DS of the MA segment (ionizable moiety that affects swelling ratio) in the Dex-MA hydrogel.
TL;DR: The structure and monomeric composition of the highly aliphatic and non-saponifiable fraction of cutans isolated from the leaf cuticles of Agave americana L. and Clivia miniata Reg.
Abstract: The structure and monomeric composition of the highly aliphatic and non-saponifiable fraction of cutans isolated from the leaf cuticles of Agave americana L. and Clivia miniata Reg. have been elucidated. Spectroscopic Fourier transform infrared and 13C-nuclear magnetic resonance, calorimetric and X-ray diffraction studies, together with biopolymer analysis after exhaustive ozonolysis, showed that the cutan fraction consists of an amorphous three-dimensional network linked by ether bonds containing double bonds and free carboxylic acid functions. Data obtained from fatty acid sorption indicated that the new biopolymer investigated here has a highly hydrophobic character constituting an additional barrier biopolymer in those cuticles where it is present. Labelled [14C]linoleic acid was preferentially incorporated into the non-ester part of C. miniata leaf disks in comparison with the cutin fraction of the cuticular membrane. This indicates that the cis-pentadiene system of polyunsaturated fatty acids is involved in the formation of intramolecular linkages, mainly ether bonds, of the aliphatic biopolymer.
TL;DR: In this paper, the formation of helical inclusion complexes when aqueous mixtures of high-amylose starch and lauric, myristic, palmitic and stearic acids are processed by steam jet cooking at 140°C was investigated.
TL;DR: It is demonstrated that amino acid conjugates of betulinic acid can produce potentially important derivatives, which may be developed as antitumor agents, and improved water solubility as well as selective cytotoxicity.
TL;DR: In this article, the surface Sn contents of catalysts characterized by X-ray photoelectron spectroscopy (XPS) depended on the preparation method, reaction temperature and the structure of substrate.
Abstract: Ru–Sn–Al2O3 catalysts were prepared by sol–gel, impregnation and their combination methods and the relationship between catalyst properties and reaction profiles in the hydrogenation of dicarboxylic acids and saturated fatty acids were examined. The surface Sn contents of catalysts characterized by X-ray photoelectron spectroscopy (XPS) depended on the preparation method in spite of almost the same bulk Ru and Sn compositions measured by X-ray fluorescence analyses. Temperature programmed reduction (TPR) and CO adsorption of the catalysts also depended on preparation methods. The preparation method, Sn/Ru ratio, reaction temperature and the structure of substrate have influence on the yield of diol. Ru–Sn–Al2O3 catalysts gave fatty alcohols with good yield in the hydrogenation of the corresponding saturated fatty acids. The conversion of the acids increased with increase in their carbon number.
TL;DR: The results obtained by the quantum chemical method are compared to results obtained from linear free energy relationships (LFER) and the merits of each approach are discussed.
Patent•
29 Jun 1999TL;DR: In this paper, a method for removing organometallic and organosilicate residues remaining after a dry etch process from semiconductor substrates is presented, where the substrate is exposed to a conditioning solution of phosphoric acid, hydrofluoric acid and a carboxylic acid, such as acetic acid.
Abstract: A method for removing organometallic and organosilicate residues remaining after a dry etch process from semiconductor substrates. The substrate is exposed to a conditioning solution of phosphoric acid, hydrofluoric acid, and a carboxylic acid, such as acetic acid, which removes the remaining dry etch residues while minimizing removal of material from desired substrate features. The approximate proportions of the conditioning solution are typically 80 to 95 percent acetic acid, 1 to 15 percent phosphoric acid, and 0.01 to 5.0 percent hydrofluoric acid.
TL;DR: In this article, the effect of various organic acids (carboxylic and amino acids) on the uptake and translocation of root-absorbed trivalent chromium by tomato ( Lycopersicum esculentum) plants grown in sand and soil culture was investigated.
Abstract: Pot experiments were conducted to investigate the effect of various organic acids (carboxylic and amino acids) on the uptake and translocation of root-absorbed trivalent chromium by tomato ( Lycopersicum esculentum) plants grown in sand and soil culture Statistically significant increases in chromium accumulation from Cr(III) treated plants in the presence of increasing concentrations of organic acid suggest the existence of Cr(III) — organic acid interactions in the soil-plant system However, the amino acids have been less effective in the mobilization of chromium compared to carboxylic acids The results are discussed on the basis of the potential of organic acids to form complexes with Cr(III)