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Oxalic Acid (oxalic + acid)
Selected AbstractsMachine Vision Analysis of Antibrowning Potency for Oxalic Acid: A Comparative Investigation on Banana and AppleJOURNAL OF FOOD SCIENCE, Issue 6 2004R. Yoruk ABSTRACT: Relative antibrowning potency of oxalic acid on banana and apple slices was investigated using a machine vision system. Degree of browning on fresh-cut surfaces was evaluated visually and quantitatively by observing changes of CIE L* values and evaluating temporal changes in color spectra based on experimental variables, oxalic acid concentration, and storage time. Browning inhibition was most prominent on banana and apple slices treated with oxalic acid solutions at concentrations of 60 and 5 mM, respectively. Oxalic acid was a more potent antibrowning agent compared with other structurally related acids. Average residual oxalic acid levels in the tissues for an effective antibrowning activity were measured. [source] A Survey on the Potential Mode of Inhibition for Oxalic Acid on Polyphenol OxidaseJOURNAL OF FOOD SCIENCE, Issue 8 2003R. Yoruk ABSTRACT: The potential mode of inhibition for xalic acid on polyphenol oxidase (PPO) was investigated. The extent of inhibition was influenced not only by oxalic acid concentration but also by pH. Inhibition was most prominent at pH 4.0 where complete inhibition occurred at the 4-mM oxalic acid concentration and was less evident at higher pH values. Inhibition of PPO by oxalic acid was due to its binding with copper to form an inactive complex, and the inhibition was characterized as noncompetitive. Oxalic acid diminished the catechol-quinone product formation, and no quinone bleaching was observed. Oxalic acid was a more potent inhibitor of PPO compared with other structurally related acids. [source] Analyte-Induced Aggregation of a Water-Soluble Conjugated Polymer for Fluorescent Assay of Oxalic AcidMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18-19 2007Huan Sun Abstract An assay method has been developed to detect oxalic acid from other structurally similar dicarboxylic acids using a cationic polythiophene derivative (PFT). Upon adding oxalic acid, the PFT can be cross-linked through the bifunctional diacids of oxalic acid to form tense interpolymer , -stacking aggregation, which results in the fluorescence self-quenching of the PFT. Upon adding other dicarboxylic acids with a longer tether, loose interpolymer , -stacking aggregation forms and the PFT fluorescence is less quenched. The fluorescence analysis was carried out in solution for the aggregates prior to precipitation. As a result of the short tether of oxalic acid, the unique fluorescent response from the PFT/oxalic acid assembly can be used to detect oxalic acid. [source] Fluorescent Probe for Oxalic Acid: Design, Synthesis, and Evaluation.CHEMINFORM, Issue 11 2005Dong Ju Oh Abstract For Abstract see ChemInform Abstract in Full Text. [source] Reduction and Coupling Reaction of Carbonyl Compounds by Aluminum Powder and a Small Amount of Oxalic Acid in WaterCHINESE JOURNAL OF CHEMISTRY, Issue 1 2006Shi-Zhen Yuan Abstract A convenient pinacol coupling of aromatic aldehydes and aryl methyl ketones has been achieved with high yields by aluminum powder in the presence of oxalic acid in water. However, the diastereoselectivities of pinacols were not satisfying, and most aliphatic aldehydes and diaryl ketones have been found to be unreactive under the same conditions. [source] Sclerotinia sclerotiorum: When "to be or not to be" a pathogen?FEMS MICROBIOLOGY LETTERS, Issue 2 2005Dwayne D. Hegedus Abstract Sclerotinia sclerotiorum is unusual among necrotrophic pathogens in its requirement for senescent tissues to establish an infection and to complete the life cycle. A model for the infection process has emerged whereby the pathogenic phase is bounded by saprophytic phases; the distinction being that the dead tissues in the latter are generated by the actions of the pathogen. Initial colonization of dead tissue provides nutrients for pathogen establishment and resources to infect healthy plant tissue. The early pathogenicity stage involves production of oxalic acid and the expression of cell wall degrading enzymes, such as specific isoforms of polygalacturonase (SSPG1) and protease (ASPS), at the expanding edge of the lesion. Such activities release small molecules (oligo-galacturonides and peptides) that serve to induce the expression of a second wave of degradative enzymes that collectively bring about the total dissolution of the plant tissue. Oxalic acid and other metabolites and enzymes suppress host defences during the pathogenic phase, while other components initiate host cell death responses leading to the formation of necrotic tissue. The pathogenic phase is followed by a second saprophytic phase, the transition to which is effected by declining cAMP levels as glucose becomes available and further hydrolytic enzyme synthesis is repressed. Low cAMP levels and an acidic environment generated by the secretion of oxalic acid promote sclerotial development and completion of the life cycle. This review brings together histological, biochemical and molecular information gathered over the past several decades to develop this tri-phasic model for infection. In several instances, studies with Botrytis species are drawn upon for supplemental and supportive evidence for this model. In this process, we attempt to outline how the interplay between glucose levels, cAMP and ambient pH serves to coordinate the transition between these phases and dictate the biochemical and developmental events that define them. [source] Machine Vision Analysis of Antibrowning Potency for Oxalic Acid: A Comparative Investigation on Banana and AppleJOURNAL OF FOOD SCIENCE, Issue 6 2004R. Yoruk ABSTRACT: Relative antibrowning potency of oxalic acid on banana and apple slices was investigated using a machine vision system. Degree of browning on fresh-cut surfaces was evaluated visually and quantitatively by observing changes of CIE L* values and evaluating temporal changes in color spectra based on experimental variables, oxalic acid concentration, and storage time. Browning inhibition was most prominent on banana and apple slices treated with oxalic acid solutions at concentrations of 60 and 5 mM, respectively. Oxalic acid was a more potent antibrowning agent compared with other structurally related acids. Average residual oxalic acid levels in the tissues for an effective antibrowning activity were measured. [source] A Survey on the Potential Mode of Inhibition for Oxalic Acid on Polyphenol OxidaseJOURNAL OF FOOD SCIENCE, Issue 8 2003R. Yoruk ABSTRACT: The potential mode of inhibition for xalic acid on polyphenol oxidase (PPO) was investigated. The extent of inhibition was influenced not only by oxalic acid concentration but also by pH. Inhibition was most prominent at pH 4.0 where complete inhibition occurred at the 4-mM oxalic acid concentration and was less evident at higher pH values. Inhibition of PPO by oxalic acid was due to its binding with copper to form an inactive complex, and the inhibition was characterized as noncompetitive. Oxalic acid diminished the catechol-quinone product formation, and no quinone bleaching was observed. Oxalic acid was a more potent inhibitor of PPO compared with other structurally related acids. [source] Oxalic acid as a versatile catalyst for one pot facile synthesis of 3,4-dihydropyrimidin-2-(1H)-ones and their thione analoguesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2008Jaiprakash N. Sangshetti 3,4-Dihydropyrimidin-2-(1H)-ones and their thione analogues are synthesized from the condensation of aromatic aldehydes, ,-dicarbonyl compound and urea or thiourea in presence of 5 mol% of oxalic acid in ethanol-water (1:2; v/v) under mild reaction conditions. The yields obtained are better and also the use of very inexpensive catalyst, environmentally benign solvent and easy work-up are the advantageous aspects of the present method. [source] Studies on the growth and optical characterization of dysprosium gadolinium oxalate single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2004A. Elizebeth Abstract Preparation and optical characterization of dysprosium gadolinium oxalate (DGO) single crystal is reported. The crystals were grown using silica gel technique, by the controlled reaction of rare earth nitrates with oxalic acid. Crystals were characterized using X-ray powder diffraction, optical absorption and fluorescence studies. Radiative transition probability, fluorescence branching ratio and radiative lifetime of Dy3+ in the crystal are evaluated by the parameterization of the absorption spectrum by the Judd-Ofelt theory. The recorded fluorescence spectrum showed two well resolved peaks at 480 nm and 571 nm and are assigned to the transitions from 4F9/2 , 6H15/2 and 6H13/2 of Dy3+. Stimulated emission crossection and optical gain of these transitions are also evaluated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Barrel Plating Rhodium Electrode: Application to Flow Injection Analysis of HydrazineELECTROANALYSIS, Issue 14 2005Jun-Wei Sue Abstract We introduce here the application of barrel plating technology for mass production of disposable-type electrodes. Easy for mass production, barrel plating rhodium electrode (Rh-BPE) is for the first time demonstrated for analytical application. Hydrazine was chosen as a model analyte to elucidate the electrocatalytic and analytical ability of the Rh-BPE system in pH,7 phosphate buffer solution. Flow injection analysis (FIA) of hydrazine showed a linear calibration range of 25,1000,ppb with a slope and a regression coefficient of 5,nA/ppb and 0.9946, respectively. Twenty-two replicate injections of 25,ppb hydrazine showed a relative standard deviation of 3.17% indicating a detection limit (S/N=3) of 2.5,ppb. The system can be continuously operated for 1 day without any alteration in the FIA signals and is tolerable to the interference of oxalic acid, gelatine, Triton X-100, and albumin for even up to 100 times excess in concentration with respect to 400,ppb hydrazine. Since the fabrication cost of the electrode is cheap, it is thus disposable in nature. Furthermore, barrel plating technique can be extendable to other transition metals for application in many fields of research interest. [source] Evaluation of a sunscreen photoprotective effect by ascorbic acid assessment in human dermis using microdialysis and gas chromatography mass spectrometryEXPERIMENTAL DERMATOLOGY, Issue 3 2005Nathalie Lévêque Abstract:, Ultraviolet irradiation causes adverse effects like sunburn, photosensitivity reactions or immunologic suppression. The aim of this study was to evaluate the photo-protective outcome of a sunscreen cream (SPF8) by the determination of erythema indexes and the assessment of ascorbic acid and its metabolites in human dermis. These substances were used as markers of oxidative effect. Eight healthy female subjects were enrolled in this study. Two abdominal areas were exposed to solar simulated irradiation with three minimal erythema dose, one with SPF8 application and the other site without SPF8 application. Two other areas were used as control, one without SPF8 application and the other site after SPF8 application. Ascorbic acid and its metabolites (dehydroascorbic acid, threonic acid, oxalic acid and xylose) were collected from human dermis by microdialysis and assessed by gas chromatography mass spectrometry. Irradiated site without sunscreen application had significantly demonstrated lower dermis ascorbic acid concentrations and a higher erythema index than the three other sites (P < 0.05). Threonic acid, oxalic acid and xylose dermis concentrations were significantly higher in site III than in the control site I (P < 0.05). The protected-irradiated site did not show erythema formation and there was stability of ascorbic acid dermis concentrations with non-variation in its metabolites. The assessment of ascorbic acid and its metabolites in human dermis could be an efficient tool to demonstrate the oxidative process and consequently to control the efficiency of sunscreen creams against undesirable UV effects. [source] Sclerotinia sclerotiorum: When "to be or not to be" a pathogen?FEMS MICROBIOLOGY LETTERS, Issue 2 2005Dwayne D. Hegedus Abstract Sclerotinia sclerotiorum is unusual among necrotrophic pathogens in its requirement for senescent tissues to establish an infection and to complete the life cycle. A model for the infection process has emerged whereby the pathogenic phase is bounded by saprophytic phases; the distinction being that the dead tissues in the latter are generated by the actions of the pathogen. Initial colonization of dead tissue provides nutrients for pathogen establishment and resources to infect healthy plant tissue. The early pathogenicity stage involves production of oxalic acid and the expression of cell wall degrading enzymes, such as specific isoforms of polygalacturonase (SSPG1) and protease (ASPS), at the expanding edge of the lesion. Such activities release small molecules (oligo-galacturonides and peptides) that serve to induce the expression of a second wave of degradative enzymes that collectively bring about the total dissolution of the plant tissue. Oxalic acid and other metabolites and enzymes suppress host defences during the pathogenic phase, while other components initiate host cell death responses leading to the formation of necrotic tissue. The pathogenic phase is followed by a second saprophytic phase, the transition to which is effected by declining cAMP levels as glucose becomes available and further hydrolytic enzyme synthesis is repressed. Low cAMP levels and an acidic environment generated by the secretion of oxalic acid promote sclerotial development and completion of the life cycle. This review brings together histological, biochemical and molecular information gathered over the past several decades to develop this tri-phasic model for infection. In several instances, studies with Botrytis species are drawn upon for supplemental and supportive evidence for this model. In this process, we attempt to outline how the interplay between glucose levels, cAMP and ambient pH serves to coordinate the transition between these phases and dictate the biochemical and developmental events that define them. [source] Production of Garcinia wine: changes in biochemical parameters, organic acids and free sugars during fermentation of Garcinia mustINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 7 2010Amit Kumar Rai Summary Garcinia wine was prepared by fermentation of ameliorated must of Garcinia xanthochymus using Saccharomyces cerevisiae. The present studies focused on changes in biochemical parameters (brix, pH, aldehydes, esters and alcohols), organic acids (reduction of oxalic acid), free sugars and antioxidant activities on fermentation of Garcinia must. The wine had higher amount of residual sugars contributing to the calorific value. The aldehydes and esters content in the final wine were 0.034% and 0.26%, respectively. There was reduction of citric acid and oxalic acid (antinutritional factor) and synthesis of aspartic acid and glutamic acid. Garcinia beverage was accepted on sensory analysis with high score for desirable attributes and overall quality with alcohol content of 6.1%. There was increase in total phenolics (0.039% gallic acid equivalent) and reducing power on fermentation but decrease in 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity. [source] Effect of ethyl icosapentate on urinary calcium and oxalate excretionINTERNATIONAL JOURNAL OF UROLOGY, Issue 10 2000Eiji Konya Background: The effect of ethyl icosapentate (EPA-E) on urinary calcium and oxalic acid excretion was examined to evaluate whether EPA-E is useful in the prevention of calcium-containing urinary stones. Methods: For 6 months, urine was measured daily from 40 calcium-containing urinary stone producers at an outpatient clinic, before and after the administration of 1800 mg/day EPA-E. The urine was measured for volume, urea nitrogen, creatinine, calcium, magnesium, phosphorus, uric acid, oxalic acid and citric acid. Serum total cholesterol and triglyceride were also measured. Results: Urinary calcium excretion was not reduced in any of the patients or particular hypercalciuric groups, nor did the level of calcium change. However, nine of the 25 hypercalciuric patients experienced a significant urinary calcium reduction to the normal calciuric level (a reduction of approximately 44%). It is not known why these particular patients experienced a reduction. Urinary oxalic acid did not change, whether hypercalciuria was present or not. Conclusions: These findings suggest that EPA-E is not particularly effective in reducing urinary calcium excretion in the hypercalciuric patients, but it needs future investigation because some patients experienced significant urinary calcium reduction. [source] Enhancement of crystalline perfection by organic dopants in ZTS, ADP and KHP crystals as investigated by high-resolution XRD and SEMJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2006S. Parthiban To reveal the influence of complexing agents on crystalline perfection, tristhiourea zinc(II) sulfate (ZTS), ammonium dihydrogen phosphate (ADP) and potassium hydrogen phthalate (KHP) crystals grown by slow-evaporation solution growth technique using low concentrations (5 × 10,3M) of dopants like ethylenediamminetetraacetic acid (EDTA) and 1,10-phenanthroline (phen) were characterized by high-resolution X-ray diffractometry (XRD) and scanning electron microscopy (SEM). High-resolution diffraction curves (DCs) recorded for ZTS and ADP crystals doped with EDTA show that the specimen contains an epilayer, as observed by the additional peak in the DC, whereas undoped specimens do not have such additional peaks. On etching the surface layer, the additional peak due to the epilayer disappears and a very sharp DC is obtained, with full width at half-maximum (FWHM) of less than 10,arcsec, as expected from the plane wave dynamical theory of X-ray diffraction for an ideally perfect crystal. SEM micrographs also confirm the existence of an epilayer in doped specimens. The ZTS specimen has a layer with a rough surface morphology, having randomly oriented needles, whereas the ADP specimen contains a layer with dendric structure. In contrast to ADP and ZTS crystals, the DC of phen-doped KHP shows no additional peak, but it is quite broad (FWHM = 28,arcsec) with a high value of integrated intensity, , (area under the DC). The broadness of the DC and the high value of , indicate the formation of a mosaic layer on the surface of the crystal. However, similar to ADP and ZTS, the DC recorded after etching the surface layer of the KHP specimen shows a very sharp peak with an FWHM of 8 arcsec. An SEM photograph of phen-doped KHP shows deep cracks on the surface, confirming the mosaicity. After removing the surface layer, the SEM pictures reveal a smooth surface. A similar trend is observed with other complexing agents, like oxalic acid, bipy and picolinic acid. However, only typical examples are described in the present article where the effects were observed prominently. The investigations on ZTS, ADP and KHP crystals, employing high-resolution XRD and SEM studies, revealed that some organic dopants added to the solution during the growth lead to the formation of a surface layer, due to complexation of these dopants with the trace metal ion impurities present in the solution, which prevents the entry of impurities, including the solvent, into the crystal, thereby assisting crystal growth with high crystalline perfection. The influence of organic dopants on the second harmonic generation efficiency is also investigated. [source] Desorption of zinc by extracellularly produced metabolites of Trichoderma harzianum, Trichoderma reesei and Coriolus versicolorJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2007P. Adams Abstract Aims:, To determine the role of fungal metabolites in the desorption of metals. Methods and Results:, Desorption of Zn from charcoal by three different fungi was compared against metal desorption with reverse osmosis water, a 0·1% Tween 80 solution and a 0·1 mol l,1 CaCl2 solution. All three fungal filtrates desorbed three times more Zn than either 0·1% Tween 80 or 0·1 mol l,1 CaCl2. Metal chelator production in Trichoderma harzianum and Coriolus versicolor was constitutively expressed while chelator production in Trichoderma reesei was induced by Zn. The presence of Zn inhibited the production of metal chelators by C. versicolor. Only C. versicolor was found to produce oxalic acid (a strong metal chelator). All fungi caused a marked decrease in pH, although this was not enough to explain the increased desorption of the metals by the different fungal filtrates. Conclusions:, Metal chelation via organic acids and proteins are the main mechanisms by which the fungal filtrates increase zinc desorption. Significance and Impact of the Study:, The results of this study explain why plants inoculated with T. harzianum T22 take up more metal from soil, than noninoculated plants while metabolites produced by fungi could be used for metal leaching from contaminated soils. [source] Evaluation of the potential of polymeric carriers based on chitosan- grafted -polyacrylonitrile in the formulation of drug delivery systemsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010A. A. Sarhan Abstract Graft copolymerization of chitosan with acrylonitrile (AN) was carried out by free radical polymerization using KMnO4 and oxalic acid as a combined redox initiator system. Graft copolymerization was confirmed by Fourier transform infrared spectra (FTIR), proton nuclear magnetic resonance spectra (1H-NMR), thermal gravimetric analysis (TGA) measurements, and wide angle X-ray diffraction (WAXD). In addition, further modification of the cyano groups of the grafted copolymers was performed by partial hydrolysis into carboxylic function groups with various extents. The extent of hydrolysis was monitored using FTIR spectroscopy. The potential of the hydrolyzed and unhydrolyzed grafted copolymers as polymeric carriers for drug delivery systems was extensively studied by preparation of tablets incorporated with methyl orange (MO) as a drug model. In vitro drug release was carried out in simulated gastric and intestinal conditions. The effects of grafting percentage (GP) and the extent of hydrolysis on the release kinetics were evaluated. Release continued up to 24 h for both hydrolyzed and unhydrolysed chitosan- g -PAN copolymers. The nature of drug transport through the polymer matrices was studied by comparing with power law or Kormeyer-Peppas equation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007S. Patra Abstract There has been increasing interest on various properties and applications of electronically conducting polymers. Polyethylenedioxythiophene (PEDOT) is an interesting polymer of this type as it exhibits very high ionic conductivity. In the present study, PEDOT has been electrochemically deposited on stainless steel (SS) substrate for supercapacitor studies. PEDOT/SS electrodes prepared in 0.1M H2SO4 in presence of a surfactant, sodium dodecylsulphate (SDS), have been found to yield higher specific capacitance (SC) than the electrodes prepared from neutral aqueous electrolyte. The effects of concentration of H2SO4, concentration of SDS, potential of deposition, and nature of supporting electrolytes used for capacitor studies on SC of the PEDOT/SS electrodes have been studied. SC values as high as 250 F/g in 1M oxalic acid have been obtained during the initial stages of cycling. However, there is a rapid decrease in SC on repeated charge-discharge cycling. Spectroscopic data reflect structural changes in PEDOT on extended cycling. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] COMPOSITION OF THE SOLUBLE, NONDIALYZABLE COMPONENTS IN RAW CANE SUGARJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2001MARY AN GODSHALL The high molecular weight (HMW) material (> 12,000 Da) of ten raw cane sugars from seven countries and two U.S. states was isolated by dialysis and analyzed by gel permeation chromatography (GPC). Simultaneous detection of colorant polymers and polysaccharides was accomplished by using two detectors in series , UV at 214 nm for colorant polymers and refractive index (RI) for carbohydrate polymers. The monosaccharide composition of the nondialyzable raw sugar fraction (the tenate) was determined by hydrolysis with trifluoroacetic acid and with oxalic acid. Aconitic acid was associated with the tenate. The raw sugars were categorized into two types according to their GPC patterns and aconitic acid content. Hydrolysis of individually collected GPC peaks demonstrated that one particular peak contained most of the aconitic acid. [source] Machine Vision Analysis of Antibrowning Potency for Oxalic Acid: A Comparative Investigation on Banana and AppleJOURNAL OF FOOD SCIENCE, Issue 6 2004R. Yoruk ABSTRACT: Relative antibrowning potency of oxalic acid on banana and apple slices was investigated using a machine vision system. Degree of browning on fresh-cut surfaces was evaluated visually and quantitatively by observing changes of CIE L* values and evaluating temporal changes in color spectra based on experimental variables, oxalic acid concentration, and storage time. Browning inhibition was most prominent on banana and apple slices treated with oxalic acid solutions at concentrations of 60 and 5 mM, respectively. Oxalic acid was a more potent antibrowning agent compared with other structurally related acids. Average residual oxalic acid levels in the tissues for an effective antibrowning activity were measured. [source] A Survey on the Potential Mode of Inhibition for Oxalic Acid on Polyphenol OxidaseJOURNAL OF FOOD SCIENCE, Issue 8 2003R. Yoruk ABSTRACT: The potential mode of inhibition for xalic acid on polyphenol oxidase (PPO) was investigated. The extent of inhibition was influenced not only by oxalic acid concentration but also by pH. Inhibition was most prominent at pH 4.0 where complete inhibition occurred at the 4-mM oxalic acid concentration and was less evident at higher pH values. Inhibition of PPO by oxalic acid was due to its binding with copper to form an inactive complex, and the inhibition was characterized as noncompetitive. Oxalic acid diminished the catechol-quinone product formation, and no quinone bleaching was observed. Oxalic acid was a more potent inhibitor of PPO compared with other structurally related acids. [source] Rhubarb Juice as a Natural Antibrowning AgentJOURNAL OF FOOD SCIENCE, Issue 8 2000S.M. Son ABSTRACT: To search for natural antibrowning agents, rhubarb juice was tested on fresh-cut apple slices and found to have a potent effect. Liberty apple slices were treated in various concentrations of rhubarb juice (5%,100%), and the rate of discoloration at room temperature was measured by a Hunter Colorimeter. Apple slices treated in the 5%, 10% solution showed browning activity with dL values of 2.3 , 2.5 at two hours. However, the concentrations of rhubarb juice above 20% inhibited apple browning effectively with no change in the L value for several hours. Analysis of oxalic acid in rhubarb juice showed that the 20% solution contained about 67 mg/100g. [source] Oxalic acid as a versatile catalyst for one pot facile synthesis of 3,4-dihydropyrimidin-2-(1H)-ones and their thione analoguesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2008Jaiprakash N. Sangshetti 3,4-Dihydropyrimidin-2-(1H)-ones and their thione analogues are synthesized from the condensation of aromatic aldehydes, ,-dicarbonyl compound and urea or thiourea in presence of 5 mol% of oxalic acid in ethanol-water (1:2; v/v) under mild reaction conditions. The yields obtained are better and also the use of very inexpensive catalyst, environmentally benign solvent and easy work-up are the advantageous aspects of the present method. [source] Alkane oxidation by the system ,tert -butyl hydroperoxide,[Mn2L2O3][PF6]2 (L,=,1,4,7-trimethyl-1,4,7-triazacyclononane),carboxylic acid'JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2008Yuriy N. Kozlov Abstract The kinetics of cyclohexane (CyH) oxygenation with tert -butyl hydroperoxide (TBHP) in acetonitrile at 50,°C catalysed by a dinuclear manganese(IV) complex 1 containing 1,4,7-trimethyl-1,4,7-triazacyclononane and co-catalysed by oxalic acid have been studied. It has been shown that an active form of the catalyst (mixed-valent dimeric species ,MnIIIMnIV') is generated only in the interaction between complex 1 and TBHP and oxalic acid in the presence of water. The formation of this active form is assumed to be due to the hydrolysis of the MnOMn bonds in starting compound 1 and reduction of one MnIV to MnIII. A species which induces the CyH oxidation is radical tert -BuO. generated by the decomposition of a monoperoxo derivative of the active form. The constants of the equilibrium formation and the decomposition of the intermediate adduct between TBHP and 1 have been measured: K,=,7.4,mol,1,dm3 and k,=,8.4,×,10,2,s,1, respectively, at [H2O],=,1.5,mol,dm,3 and [oxalic acid],=,10,2,mol,dm,3. The constant ratio for reactions of the monomolecular decomposition of tert -butoxy radical (tert -BuO.,, CH3COCH3,+,CH) and its interaction with the CyH (tert -BuO.,+,CyH,,,tert -BuOH,+,Cy.) was calculated: 0.26,mol,dm,3. One of the reasons why oxalic acid accelerates the oxidation is due to the formation of an adduct between oxalic acid and 1 (K,,,103,mol,1,dm3). Copyright © 2007 John Wiley & Sons, Ltd. [source] Effects of chromium stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2010Fanrong Zeng Abstract A hydroponic experiment was carried out to study effects of chromium (Cr) stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypes differing in Cr accumulation. The results showed that Ca, Mg, Fe, and Zn ions were mainly located in cell walls and vacuoles in roots. However, large amounts of metal ions were transferred from the vacuole to the nucleus and to other functional organelles in shoots. Chromium concentrations in the nutrient solution of 50 ,M and above significantly decreased Ca concentrations in the chloroplast/trophoplast, the nucleus, and in mitochondria. It further increased Mg concentrations in the nucleus and in mitochondria, as well as Zn and Fe concentrations in the chloroplast/trophoplast. These Cr-induced changes in ion concentrations were associated with a significant reduction in plant biomass. It is suggested that Cr stress interferes with the functions of mineral nutrients in rice plants, thus causing a serious inhibition of plant growth. The chemical forms of the four nutrients were determined by successive extraction. Except for Ca, which was mainly chelated with insoluble phosphate and oxalic acid, Mg, Zn, and Fe were extractable by 80% ethanol, d-H2O, and 1,M NaCl. The results indicated that these low,molecular weight compounds, such as organic acids and amino acids, may play an important role in deposition and translocation of Mg, Zn, and Fe in the xylem system of rice plants. [source] Synthesis and characterization of polyaniline doped with organic acidsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2004Milind V. Kulkarni Abstract Spectroscopic [UV,visible and Fourier transform IR (FTIR)] and thermal properties of chemically synthesized polyanilines are found to be affected by varying the protonation media (acetic, citric, oxalic, and tartaric acid). The optical spectra show the presence of a greater fraction of fully oxidized insulating pernigraniline phase in polyaniline doped with acetic acid. In contrast, the selectivity in the formation of the conducting phase is higher in oxalic acid as a protonic acid media. The FTIR spectra of these polymers reveal a higher ratio of the relative intensities of the quinoid to benzenoid ring modes in acetic acid doped polyaniline. Scanning electron micrographs revealed a sponge-like structure derived from the aggregation of the small granules in acetic acid and oxalic acid doped polyaniline. A three-step decomposition pattern is observed in all the polymers, regardless of the protonic acid used for the doping. The second step loss related to the loss of dopant is found to be higher in the oxalic acid doped polymer. In accordance with these results the conductivity is also found to be higher in oxalic acid doped material. The temperature dependent conductivity measurements show the thermal activated behavior in all the polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2043,2049, 2004 [source] Syntheses and characterizations of bis(trialkoxysilyl)oligoimides.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2001Abstract Novel crosslinkable fluorinated oligoimides were prepared in two steps. The first involved the synthesis of oligoimides terminated with nadic or allylic double bonds, and the second step was materialized either by a radical addition of mercaptotrialkoxysilane derivatives onto nadic double bonds or a hydrosilylation reaction of hydrogenotrialkoxysilane derivative onto allylic double bonds. Three kinds of crosslinking of the trialkoxysilane end groups were studied. The first kind entailed a thermal self-crosslinking of trialkoxysilane groups. The second process of crosslinking incorporated a bicomponent system,the crosslinked agent was 1,1,1-tris(4-hydroxyphenyl)ethane (TRIOH). The trialkoxysilane groups reacted with the hydroxyl,phenol groups of TRIOH to give thermally stable phenoxysilane bonds as well as a crosslinking network. The last method was also a bicomponent system; the oxalic acid was added into an oligoimide solution where by thermal treatment water was created. The water molecules hydrolyzed the trialkoxysilane groups into silanol groups that polycondensed into a crosslinked network following a sol,gel process. The mechanism of the different crosslinking reactions was investigated by Fourier transform infrared spectroscopy and solid-state 29Si NMR. The self-crosslinked material prepared from precursor ,,,-trimethoxysilyl fluorinated oligomer (Mn = 5500 g · mol,1) exhibited a 10 wt % loss temperature under air higher than 420 °C and a low birefringence (,n = 0.008) at 1.300 ,m. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2602,2619, 2001 [source] Development and validation of an HPLC confirmatory method for the determination of seven tetracycline antibiotics residues in milk according to the European Union Decision 2002/657/ECJOURNAL OF SEPARATION SCIENCE, JSS, Issue 15 2007Victoria F. Samanidou Abstract An HPLC method with diode-array detection, at 355 nm, was developed and validated for the determination of seven tetracyclines (TCs) in milk: minocycline (MNC), TC, oxytetracycline (OTC), methacycline (MTC), demeclocycline (DMC), chlortetracycline (CTC), and doxycycline (DC). Oxalate buffer (pH 4) was used with 20% TCA as a deproteinization agent for the extraction of analytes from milk followed by SPE. The separation was achieved on an Inertsil ODS-3, 5 ,m, 250×4 mm2 analytical column at ambient temperature. The mobile phase, a mixture of A: 0.01 M oxalic acid and B: CH3CN, was delivered using a gradient program. The procedure was validated according to the European Union decision 2002/657/EC determining selectivity, stability, decision limit, detection capability, accuracy, and precision. Mean recoveries of TCs from spiked milk samples (50, 100, and 200 ng/g) were 93.8,100.9% for MNC, 96.8,103.7% for OTC, 96.3,101.8% for TC, 99.4,107.2% for DMC, 99.4,102.9% for CTC, 96.3,102.7% for MTC, and 94.6,102.1% for DC. All RSD values were lower than 8.5%. The decision limits CCa calculated by spiking 20 blank milk samples at MRL (100 ,g/kg) ranged from 101.25 to 105.84 ,g/kg, while detection capability CCbfrom 103.94 to 108.88 ,g/kg. [source] Effect of nitrogen source in the fertilizing solution on nutritional quality of three members of the Portulaca oleracea aggregateJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 12 2010Gabriella Szalai Abstract BACKGROUND:Portulaca oleracea (purslane) is nutritious but, in addition to the essential ,-linolenic acid, vitamin C and tocopherols, it contains undesirable oxalic acid. Knowing the effects of nitrate and ammonium on oxalate accumulation, we tested the agronomic potential of three members of the P. oleracea aggregate under various nitrogen fertilization conditions, by measuring biomass production and accumulation of fatty acids, organic acids and tocopherol in the commercial P. sativa (Pos) and two natural members: P. nitida (Pon) and P. papillato-stellulata (Pop). RESULTS:With nitrate as the sole N source, we measured differences between Pon and Pos in concentrations of the essential ,-3 fatty acid ,-linolenic acid. Pos also gained less dry biomass under these conditions, implying a higher agronomical and nutritional value for Pon. Increasing the fertilizer ammonium concentration and reducing that of nitrate significantly decreased oxalic acid by factors of up to 1.7, 2.6 and 3.4 in Pos, Pop and Pon, respectively, significantly increased concentrations of tocopherol and malic acid, had no effect on fatty acids or ascorbic acid, but reduced biomass. CONCLUSION:In spite of the recumbent growth habit of Pon, the present findings indicate its agronomic potential. Because early flowering and seed production may be the limiting factors in purslane agriculture, growing Pon in nitrate-poor conditions might be agriculturally favorable. Copyright © 2010 Society of Chemical Industry [source] | ||||||||||||||||||||||||||||||||||||||||