|
| ||
|
|
||
Acid Form (acid + form)
Selected AbstractsPhotoinduced Formation of Reactive Oxygen Species from the Acid Form of 6-(Hydroxymethyl)pterin in Aqueous SolutionHELVETICA CHIMICA ACTA, Issue 6 2006Andrés Abstract The photochemistry of 6-(hydroxymethyl)pterin (HPT; 1) in aqueous solution (pH 5,6) was investigated by irradiation at 350,nm at room temperature. The photochemical reactions of the acidic form 1a were followed by UV/VIS spectrophotometry, thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and enzymatic methods for the determination of the superoxide anion radical (O) and hydrogen peroxide (H2O2). When 1a is exposed to UV-A radiation, the intermediates 4 and 4, are formed reacting with O2 to yield 6-formylpterin (FPT; 5) and 6-carboxypterin (CPT; 6) under formation of O and H2O2 (Scheme,3). The quantum yields of the disappearance of HPT (1a) and of the formation of the photoproducts 5 and 6 were determined. HPT was investigated for its efficiency in singlet-oxygen (1O2) production in acidic aqueous solution. The corresponding quantum yield of 1O2 production (,,) was 0.15,±,0.02, as measured by the 1O2 luminescence in the near-IR (1270,nm) upon continuous excitation of the sensitizer. However, 1O2 does not participate in the actual photooxidation of HPT (1a) to FPT (5) and CPT (6). [source] The 28-amino acid form of an APLP1-derived A,-like peptide is a surrogate marker for A,42 production in the central nervous systemEMBO MOLECULAR MEDICINE, Issue 4 2009Kanta Yanagida Abstract Surrogate markers for the Alzheimer disease (AD)-associated 42-amino acid form of amyloid-, (A,42) have been sought because they may aid in the diagnosis of AD and for clarification of disease pathogenesis. Here, we demonstrate that human cerebrospinal fluid (CSF) contains three APLP1-derived A,-like peptides (APL1,) that are generated by ,- and ,-cleavages at a concentration of ,4.5,nM. These novel peptides, APL1,25, APL1,27 and APL1,28, were not deposited in AD brains. Interestingly, most ,-secretase modulators (GSMs) and familial AD-associated presenilin1 mutants that up-regulate the relative production of A,42 cause a parallel increase in the production of APL1,28 in cultured cells. Moreover, in CSF from patients with pathological mutations in presenilin1 gene, the relative APL1,28 levels are higher than in non-AD controls, while the relative A,42 levels are unchanged or lower. Most strikingly, the relative APL1,28 levels are higher in CSF from sporadic AD patients (regardless of whether they are at mild cognitive impairment or AD stage), than those of non-AD controls. Based on these results, we propose the relative level of APL1,28 in the CSF as a candidate surrogate marker for the relative level of A,42 production in the brain. [source] Sulfation of nitrotyrosine: Biochemistry and functional implicationsIUBMB LIFE, Issue 10 2007Ming-Cheh Liu Abstract Nitration of tyrosine, in both protein-bound form and free amino acid form, can readily occur in cells under oxidative/nitrative stress. In addition to serving as a biomarker of oxidative/nitrative stress, elevated levels of nitrotyrosine have been shown to cause DNA damage or trigger apoptosis. An important issue is whether the human body is equipped with mechanisms to counteract the potentially harmful effects of nitrotyrosine. Sulfate conjugation, as mediated by the cytosolic sulfotransferases (SULTs), is widely used for the biotransformation and disposal of a variety of drugs and other xenobiotics, as well as endogenous thyroid/steroid hormones and catecholamine neurotransmitters. Recent studies have revealed that the sulfation of nitrotyrosine occurs in cells under oxidative/nitrative stress, and have pinpointed the SULT1A3 as the responsible SULT enzyme. In this review, we summarized the available information concerning the biochemistry of nitrotyrosine sulfation and the effects of genetic polymorphisms on the nitrotyrosine sulfating activity of SULT1A3. Functional implications of the sulfation of nitrotyrosine are discussed. IUBMB Life, 622-627, 2007 [source] Purification and Kinetic Characterization of Peroxidase from Tomato Cultivated under Different Salinity ConditionsJOURNAL OF FOOD SCIENCE, Issue 1 2000J.N. Rodríguez-López ABSTRACT: By including hydrophobic chromatography in the purification scheme, 2 homogeneous tomato fruit peroxidase isoenzymes were obtained. The expression of these 2 peroxidases, one acid and the other basic, was determined in tomato fruits grown under different salinity conditions. Increased salinity modified the isoenzyme profile of tomato peroxidase. In tomatoes grown under highly saline conditions, there was an increase in the expression of the acid form with respect to the basic, the acid/basic ratio rising from 4.5 in tomatoes grown under normal saline conditions to 70 in those grown in highly saline conditions. Kinetic studies using 2,2,-azinobis(3-ethylbenzo-thiazolinesulfonic acid) as reducing substrate showed that increased salinity in the growth medium did not modify the kinetic parameter of tomato peroxidase over both hydrogen peroxide or reducing substrate. [source] Surfactant assisted polymerization of tetrafluoroethylene in supercritical carbon dioxide with a pilot scale batch reactorJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Alberto Giaconia Abstract Chain-free radical polymerization of tetrafluoroethylene (TFE) was carried out in supercritical carbon dioxide (scCO2), at 50 °C and 121,133 bar, with tertiary -amyl-per-pivalate as a free radical initiator, using a 5-L pilot scale batch reactor. Experiments were carried out both in the absence and in the presence of perfluoropolyether (PFPE) carboxylate surfactants. Stabilizers were employed under the free acid form and as sodium and calcium salts. An expanded fibrillated poly(TFE) was obtained in all experiments. In the case of surfactant-free polymerizations, the product was mainly constituted by irregular shape macroparticles having size in the range 200,500 ,m. Quite interestingly, when the free acid surfactant was used, a clear acceleration of the polymerization rate was observed and smaller polymer particles with more regular quasi-spherical morphology were obtained. Melt fusion crystallinity of as-polymerized poly(TFE) seemed not substantially affected by the presence of the stabilizers and was rather high (80,86%) suggesting that polymerization mainly occurs at polymer particle surface. All these elements suggest that FLUOROLINK® 7004H PFPE carboxylic acid decreases coagulation of primary polymer particles leading to an increase in polymer surface area. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 257,266, 2008 [source] Synthesis of an alkali-swellable emulsion and its effect on the rate of polymer diffusion in poly(vinyl acetate-butyl acrylate) latex filmsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2005Jung Kwon Oh Abstract We describe the synthesis and characterization of a weakly cross-linked poly(methacrylic acid- co -ethyl acrylate) alkali-swellable emulsion (ASE), as well as an investigation of its influence on the rate of polymer diffusion in latex films. The films examined were formed from poly(vinyl acetate- co -butyl acrylate) latex particles containing a small amount of acrylic acid as a comonomer. Polymer diffusion rates were monitored by the energy transfer technique. We found that the presence of the ASE component, either in the acid form or fully neutralized by ammonia or sodium hydroxide, had very little effect on the polymer diffusion rate. However, in the presence of 2 wt % NH4 -ASE, there was a small but significant increase in the polymer diffusion rate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5632,5642, 2005 [source] Sulfonated naphthalene dianhydride based polyimide copolymers for proton-exchange-membrane fuel cells.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2004Abstract A novel sulfonated diamine, 3,3,-disulfonic acid-bis[4-(3-aminophenoxy)phenyl]sulfone (SA-DADPS), was prepared from m -aminophenol and disodium-3,3,-disulfonate-4,4,-dichlorodiphenylsulfone. The conditions necessary to synthesize and purify SA-DADPS in high yields were investigated in some detail. This disulfonated aromatic diamine, containing ether and sulfone linkages, was used to prepare N -methyl-2-pyrrolidinone-soluble, six-membered ring polyimide copolymers containing pendent sulfonic acid groups by a catalyzed one-step high-temperature polycondensation in m -cresol. These materials showed much improved hydrolytic stability with respect to phthalimides. High-molecular-weight film-forming statistical copolymers with controlled degrees of disulfonation were prepared through variations in the stoichiometric ratio of disulfonated diamine (SA-DADPS) in its soluble triethylamine salt form to several unsulfonated diamines. Three unsulfonated diamines, bis[4-(3-aminophenoxy)phenyl] sulfone, 4,4,-oxydianiline, and 1,3-phenylenediamine, were used to prepare the copolymers. The characterization of the copolymers by 1H NMR, Fourier transform infrared, ion-exchange capacity, and thermogravimetric analysis demonstrated that SA-DADPS was quantitatively incorporated into the copolymers. Solution-cast films of the sulfonated copolymers were prepared and afforded tough, ductile membranes with high glass-transition temperatures. Methods were developed to acidify the triethylammonium salt membranes into their disulfonic acid form, this being necessary for proton conduction in a fuel cell. The synthesis and characterization of these materials are described in this article. Future articles will describe the performance of these copolymers as proton-exchange membranes in hydrogen/air and direct methanol fuel cells. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 862,874, 2004 [source] Processing behavior of polycarbonate/functionalized-ethylene copolymer blendsPOLYMER ENGINEERING & SCIENCE, Issue 12 2000Marcos L. Dias The melt blending of polycarbonate (PC) and ethylene-methacrylic acid copolymers (EFC) either in the acid form (EFC-H) or partially neutralized with sodium (EFC-Na) or zinc (EFC-Zn) was investigated. Torque monitoring of the blending showed that the polymers are capable of reacting generating new chemical species that increase the melt viscosity. As general behavior, the torque curves pass by a maximum that takes place before 30 min, the final torque being higher than that of the individual polymers. SEC analyses reveal that PC degradation also occurs and is stronger in the case of blends with EFC-Na that acts to catalyze PC degradation, promoting CO2 formation. FTIR studies on chloroform insoluble fractions of the PC/EFC-Zn blends showed that in addition to a very small number of carbonate groups, feature absorption bands of aromatic ester and hydroxyl groups appear in the new chemical species formed during the reactive processing. [source] The assessment of human regional drug absorption of free acid and sodium salt forms of Acipimox, in healthy volunteers, to direct modified release formulation strategyBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2009Rajeev Menon Abstract Acipimox is an analog of nicotinic acid and is indicated for the treatment of dyslipidemia. It is also believed to improve glucose control by enhancing insulin sensitivity. The purpose of this study was to direct modified release (MR) formulation strategy by comparing the bioavailability of two forms of acipimox (free acid and sodium salt) from the distal small bowel (DSB) and colon with an immediate release formulation. Two parallel groups of healthy volunteers completed an open label, non-randomized, three-way crossover study. The rate and extent of acipimox absorption was highest following administration of the immediate release capsules, and was not influenced by the form of the drug administered. Following administration to the DSB, the relative bioavailability was approximately 52% and 30% for the salt form and free acid form, respectively. Following administration to the colon, the extent of absorption was further reduced. The data indicate that bioavailability from the DSB was limited by the solubility of the drug coupled with an absorption window, whilst absorption from the colon was limited by permeability. The study provided detailed information to support and guide the formulation strategy for a MR form of acipimox, which may improve the treatment of adult patients with type II diabetes and dyslipidemia. Copyright © 2009 John Wiley & Sons, Ltd. [source] Hydration of polysaccharide hyaluronan observed by IR spectrometry.BIOPOLYMERS, Issue 1 2003Abstract This article is the first one in a series dedicated to the study of hyaluronan as observed by IR spectrometry. The goal is to determine its hydration mechanism and the structural changes this mechanism implies. Hyaluronan is a natural polysaccharide that is widely used in biomedical applications and cosmetics. Its macroscopic properties are significantly dependent on its degree of hydration. In this article we record the IR spectrum of a several micron thick dried film and deduce that four or five residual H2O molecules remain around each disaccharide repeat unit in the dried film. We then compare the spectra of sodium hyaluronan and its acid form to assign vibrational bands linked to the carboxylate group. We proceed with a qualitative analysis of the spectral changes induced by changes of temperature and hygroscopicity, two independent parameters that act by modifying the hydrogen bond network of the sample. This enables us to assign most of the vibrational bands of the hydrophilic groups and to distinguish the bands that are due to these hydrophilic groups when they are or are not hydrogen bonded. It constitutes a prerequisite for the quantitative analysis of hydration spectra that will be described in the following articles of this series. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 72: 10,20, 2003 [source] Chiral versus racemic building blocks in supramolecular chemistry: malate salts of organic diaminesACTA CRYSTALLOGRAPHICA SECTION B, Issue 3-2 2002Dorcas M. M. Farrell (S)-Malic acid forms a salt with N,N,-dimethylpiperazine, [MeN(CH2CH2)2NMe]H22+·2C4H5O5, (1) (triclinic, P1, Z, = 1), in which the cations link pairs of hydrogen-bonded anion chains to form a molecular ladder. With 4,4,-bipyridyl, (S)-malic acid forms a 1:1 adduct which crystallizes from methanol to yield two polymorphs, (2) (triclinic, P1, Z, = 1) and (3) (monoclinic, C2, Z, = 1), while racemic malic acid with 4,4,-bipyridyl also forms a 1:1 adduct, (4) (monoclinic, P21/c, Z, = 1). In each of (2), (3) and (4) the components are linked by O,H,N and N,H,O into chains of alternating bipyridyl and malate units, which are linked into sheets by O,H,O hydrogen bonds. In each of the 1:1 adducts (5) and (6), formed by, respectively, (S)-malic acid and racemic malic acid with 1,2-bis(4,-pyridyl)ethene, the diamine is disordered over two sets of sites, related by a 180° rotation about the N,N vector. In (5), (C12H10N2)H+·C4H5O5, (triclinic, P1, Z, = 1), the components are again linked by a combination of N,H,O and O,H,O hydrogen bonds into sheets, while in (6) (triclinic, P, Z, = 0.5) there is only partial transfer of the H atom from O to N and the malate component is disordered across a centre of inversion. With 1,4-diazabicyclo[2.2.2]octane, racemic malic acid forms a 1:2 salt, [(C6H12N2)H2]2+·2C4H5O5, (7) (monoclinic, P21/c, Z, = 2), while (S)-malic acid forms a 1:1 adduct, (8) (monoclinic, P21, Z, = 3). There are thus six independent molecular components in each. In (7) the ions are linked by an extensive series of N,H,O and O,H,O hydrogen bonds into a three-dimensional framework, but in (8) there is extensive disorder involving all six components, and no refinement proved to be feasible. [source] High-Throughput Substrate Specificity Studies of Sialidases by Using Chemoenzymatically Synthesized Sialoside LibrariesCHEMBIOCHEM, Issue 2 2007Harshal A. Chokhawala Abstract Sialidases, or neuraminidases, are enzymes that cleave terminal sialic acid (Sia) residues from complex sialic acid-containing structures. They have been found in many animals and microorganisms and are important in various physiological and pathological processes. In order to understand the biological significance of diverse sialidases, it is important to study in detail the structural determinants of their natural substrates. Here, we report the synthesis of sialoside libraries containing para -nitrophenol-tagged sialosides with different naturally occurring sialic acid forms, different sialyl linkages, and different penultimate monosaccharides using a highly efficient one-pot three-enzyme chemoenzymatic approach. By using these compounds in a 96-well plate-based colorimetric high-throughput screening platform, the diversity of substrate preference is shown for seven bacterial sialidases. The sialoside libraries and the screening method are convenient tools for unravelling the substrate specificity and the biological function of sialidases. [source] | ||||||||||||||||