Showing papers on "Oxalic acid published in 1993"

Biogeochemistry of oxalate in the antarctic cryptoendolithic lichen-dominated community

Abstract: Cryptoendolithic (hidden in rock) lichen-dominated microbial communities from the Ross Desert of Antarctica were shown to produce oxalate (oxalic acid). Oxalate increased mineral dissolution, which provides nutrients, creates characteristic weathering patterns, and may ultimately influence the biological residence time of the community. Oxalate was the only organic acid detectable by HPLC, and its presence was verified by GC/MS. Community photosynthetic metabolism was involved in oxalate production since rates of 14C-oxalate production from 14C02 were higher in light than in dark incubations. Flaking of the sandstone at the level of the lichen-dominated zone a few millimeters beneath the rock surface can be explained by dissolution of the sandstone cement, which was enhanced by Si, Fe, and Al oxalate complex formation. Added oxalate was observed to increase the solubility of Si, Fe, Al, P, and K. Oxalate's ability to form soluble trivalent metal-oxalate complexes correlated with the observed order of metal oxide depletion from the lichen-dominated zone (Mn > Fe > Al). Thermodynamic calculations predict that Fe oxalate complex formation mobilizes amorphous Fe oxides (ferrihydrite) in the lichen-dominated zone, and where oxalate is depleted, ferrihydrite should precipitate. Hematite, a more crystalline Fe oxide, should remain solid at in situ oxalate concentrations. Oxalate was not a carbon source for the indigenous heterotrophs, but the microbiota were involved in oxalate mineralization to CO2, since oxalate mineralization was reduced in poisoned incubations. Photooxidation of oxalate to C02 coupled with photoreduction of Fe(Ill) may be responsible for oxalate removal in situ, since rates of 14C-oxalate mineralization in dark incubations were at least 50% lower than those in the light. Removal of oxalate from Si, Fe, and Al complexes should allow free dissolved Si, Fe, and Al to precipitate as amorphous silicates and metal oxides. This may explain increased siliceous crust (rock varnish or desert varnish) formation near the surface of colonized rocks were light intensity is greatest.

Organic intermediates in the degradation of 2,4-dichlorophenoxyacetic acid by Fe3+/H2O2 and Fe3+/H2O2/UV

Abstract: The transient products formed during mineralization of 2,4-D by Fe 3+ -catalyzed hydrogen peroxide in the dark or under 350-nm UV were identified in connection with studies of these advanced oxidation processes for wastewater treatment. Ethyl acetate extracts revealed 2,4-dichlorophenol as the major product (≤15% yield) and ≤3% each of 2,4-dichlorophenyl formate, 2,4-dichloro-1-(chloromethoxy)-benzene, and 6,8-dichloro-2H-1,4-benzodioxan-3-one. The aqueous phase contained oxalic acid in dark reactions and oxalic and formic acids in photoassisted reactions, identified as their 1-propanol esters

The influence of dietary factors on the risk of urinary stone formation.

Abstract: The action of various beverages and foods on the composition of the urine in the circadian rhythm and in the 24-hour urine has been investigated under standardized conditions. Orange juice leads to a significant increase of urinary pH and citric acid excretion. Black tea leads to a raised excretion of oxalic acid by only 7.9%. In the short term, beer increases diuresis, but afterwards leads to a compensatory antidiuresis with increased risk of stone formation. Depending on their composition, mineral waters have very different effects on the urinary constituents. Milk as well as cocoa beverage significantly increase calcium excretion; moreover, cocoa causes an increase in the oxalic acid excretion. The leafy vegetable foods containing oxalate, e.g., spinach and rhubarb, lead to peaks of oxalate excretion of 300-400% in the circadian excretion curve. Cheese leads to a significant rise of calcium excretion with acidification of the urine and lowering of citrate excretion. Calcium excretion is increased by 30% by sodium chloride. Foods containing purine result in an increased uric acid excretion over several days. Depending on their phytic acid content, brans bind calcium, but lead to an increased oxalic acid excretion. Analysis of the urine indicates that average diet in Germany entails a high risk of urinary stone formation. As a result of the change to a balanced mixed or vegetarian diet, according to the requirements, significant alterations in urinary pH, calcium, magnesium, uric acid, citric acid, cystine, and glycosaminoglycan excretion are measured, resulting in a drastic reduction in the risk of urinary stone formation.

Effects of etching time on enamel bond strengths.

Abstract: This study evaluated the effects of etching time on bond strengths of composite to enamel. Proximal surfaces of extracted molars were etched with either a conventional etchant (35% phosphoric acid) or one of two dentin/enamel conditioners, 10% maleic acid (Scotchbond Multi-Purpose Etchant), or a solution of oxalic acid, aluminum nitrate, and glycine (Gluma 1 & 2 Conditioner). Each agent was applied for 15, 30, or 60 seconds. Specimens etched with 35% phosphoric acid had the highest mean bond strengths at each etching time. At the manufacturer's recommended application times, the other two agents gave significantly lower shear bond strengths than phosphoric acid.

Use of formic or oxalic acid for the regioselective hydrocarboxylation of alkenes and alkynes catalyzed by Pd/C and 1,4-bis(diphenylphosphino) butane

Abstract: The authors report the synthesis of carboxylic acids from alkenes and alkynes in a regioselective fashion. The process is catalyzed by carbon supported palladium with activity rivaling homogeneous analogs. The process is promoted by the presence of formic and oxalic acid.

Photoreduction of carbon dioxide on zinc sulfide to give four-carbon and two-carbon acids

Abstract: Aqueous solutions of CO2 containing tetramethylammonium chloride were photolysed with visible light in the presence of colloidal ZnS to yield tartaric acid, glyoxylic acid, oxalic acid, formic acid and formaldehyde.

Shear bond strengths of new enamel etchants.

Abstract: Many dental adhesive systems now rely on simultaneous etching of enamel and dentin. Instead of the traditional 35-40% phosphoric acid, new etchants (including 10% maleic acid, 10% phosphoric acid, and oxalic acid/aluminum nitrate) are used. This in vitro study determined the shear bond strengths of resin composite to enamel which was etched with these agents according to manufacturers' instructions. The control etchant, 35% phosphoric acid, gave a mean bond strength of 24.5 MPa. 10% maleic acid and 10% phosphoric acid had significantly lower shear bond strengths (13.2 MPa). Gluma 1 & 2 Conditioner (oxalic acid/aluminum nitrate) had a mean bond strength of 6.3 MPa, which was significantly less than the other etchants. Bond strengths for each etchant were not affected by the type of unfilled resin used.

Characteristics of the transport of oxalate and other ions across rabbit proximal colon

Abstract: In order to characterize oxalate handling by the P2 segment of the rabbit proximal colon, the fluxes of [14C]oxalate, 22Na+, and 36Cl- were measured in vitro using conventional short-circuiting techniques. In standard buffer the proximal colon exhibited net secretion of Na+ (-2.31 +/- 0.64 mu equiv cm-2 h-1), negligible net Cl- transport, and net secretion of oxalate (-12.7 +/- 1.6 pmol cm-2 h-1). Replacement of buffer Na+ or Cl- abolished net oxalate secretion, while HCO(3-)-free media revealed a net absorption of oxalate (19.3 +/- 4.2 pmol cm-2 h-1) and stimulated NaCl absorption. Mucosal amiloride and dimethylamiloride (1 mM) significantly reduced the unidirectional fluxes of oxalate and enhanced sodium secretion by decreasing JNams. The anion exchange inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS; 0.1 mM, both sides) reduced the unidirectional fluxes of oxalate and chloride. Serosal epinephrine (50 microM) stimulated oxalate absorption (21.3 +/- 6.3 pmol cm-2 h-1) and sodium absorption (5.71 +/- 1.20 mu equiv cm-2 h-1), whereas dibutyryl-cAMP enhanced oxalate secretion (-43.4 +/- 6.9 pmol cm-2 h-1) and stimulated chloride secretion (-7.27 +/- 0.64 mu equiv cm-2 h-1). These results indicate that the P2 segment of the proximal colon possesses (a) secretory as well as absorptive capacities, (b) oxalate fluxes that are mediated by pathways involving Na+, Cl-, HCO3- transport and (c) a net oxalate flux that is sensitive to absorptive and secretory stimuli.

Correlation Between Catalytic and Structural Properties of Modified Molybdenum and Vanadium Oxides in the Oxidation of Ethane in Acetic Acid or Ethylene

Abstract: The structural and catalytic properties in the oxidation and dehydrogenation of ethane of two catalytic systems, VPO (P/V = 1.15/1) and MoVNb (Mo/V/Nb = 0.73/0.18/0.09) are examined. Methods of preparation are improved and seen to influence strongly the catalytic behavior. A general scheme is the formation of acetic acid at low temperature (200–300°C) and low conversion, and of ethylene at high temperature (350–500°C). The presence of ethylene with acetic acid at low temperature is observed when VPO is doped or when MoVNb is prepared in oxalic acid. Considerations on the nature of active oxygens on the surface of the solids are proposed.

Selective transport of metal ions through cation exchange membrane in the presence of a complexing agent

Abstract: Selective transport of metal ions through a cation exchange membrane was studied in stirred batch dialyzer for the systems Ni[sup 2+]-Cu[sup 2+] and Cu[sup 2+]-Fe[sup 3+]. Oxalic acid, malonic acid, citric acid, glycine, and ethylenediaminetetraacetic acid were employed as the complexing agents added in the feed solution in order to increase the permselectivity of metal ions. The experimental results show that the selective transport behavior of metal ions depends on the valence and the concentration of metal ions, the stoichiometric ratio of complexing agent to metal ions, and the pH value of the feed solution, but is independent of the concentration of counterion in the stripping phase. A theoretical approach was formulated on the basis of the Nernst-Planck equation and interface quasi-equilibrium. Theoretical solutions obtained from numerical calculation were in agreement with the experimental data.

Studies on the rejuvenation of spent catalysts : effectiveness and selectivity in the removal of foulant metals from spent hydroprocessing catalysts in coked and decoked forms

Abstract: Two routes were used to rejuvenate spent residue hydroprocessing catalysts by leaching foulant metals. In the first, deoiled spent catalyst containing coke and deposited metals in sulfide form was chemically treated to remove the metal foulants. In the second, deoiled spent catalyst was decoked by controlled combustion of coke and the resultant coke-free catalyst containing metals in oxide form was subjected to leaching. Oxalic acid, a chelating agent which is able to form soluble metal complexes, was used for metal leaching in both routes. The influence of adding an oxidizing agent such as H 2 O 2 to oxalic acid in particular its effect on the leaching efficiency was examined in both routes. The spent and treated catalysts were characterized and the improvements in surface area, pore volume and hydrodesulphurization-activity of the catalysts were compared. The selectivity for leaching of the major metal foulant (vanadium) was better, and activity recovery was higher for the catalyst rejuvenated by metal leaching prior to decoking.

Fungal physiology and the formation of calcium oxalate films on stone monuments

Abstract: Extensive, uniform, yellow-brown films are observed on many monuments. The origin of these films, composed predominantly of calcium oxalate, has been investigated by several authors. Oxalate film formation may be related, in some cases, to the activity of such microorganisms as fungi, which presumably form oxalic acid via the metabolic transformation of organic substances already present on the stone. The present work provides an overview of the physiological factors affecting oxalate synthesis by fungi and of oxalic acid in fungi metabolism.

Chemical modification by ascorbic acid and oxalic acid in graphite furnace atomic absorption spectrometry

Abstract: The effects of addition of ascorbic and oxalic acids on the atomic absorption signal for lead are explained by a gas-phase thermodynamic equilibrium model. The gas-phase composition of the graphite furnace was determined as samples containing ascorbic or oxalic acid were pyrolyzed. Hydrogen and carbon monoxide were identified as two of the major pyrolysis products. The amounts of these reducing gases, formed in the atomization cycle, varied with the modifier used, the charring temperature employed, and the condition of the surface of the pyrolytically coated graphite tube. The extent of the shift in the appearance temperature showed correlation with variations in concentrations of hydrogen and carbon monoxide produced by pyrolysis

Ternary complexes of nickel(II) with AMP , ADP and ATP as primary ligands and some biologically important polybasic oxygen acids as secondary ligands

Abstract: Potentiometric equilibrium measurements have been made at 25±0.1 °C (μ=0.1 mol dm−3 KNO3) for the interaction of adenosine-5′-mono-, -di-, and-triphosphate (AMP,ADP, andATP) and Ni(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP and secondary ligand acid, have been refined with SUPERQUAD computer program. In some systems Δ logK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. H-bond formation seems to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increases in the orderAMP maleic>tartaric>malic>citric>oxalic acid.

Method for production of colored article of aluminum or aluminum alloy

Abstract: A fast and brightly colored oxide film of aluminum which excels in durability and allows no separation of pigment is produced by using an aqueous dispersion of an organic pigment or carbon black finely divided to a size in the range between 3 and 150 nm, forming on a surface of an aluminum member an anodic oxide film containing pores larger in diameter than the ordinary pores, and causing the organic pigment or carbon black to migrate and deposit in the pores of the oxide film by means of electrophoresis. The formation of the anodic oxide film containing the pores larger in diameter than the ordinary pores is accomplished in the first method by subjecting the aluminum member to anodic oxidation at a high voltage in an aqueous solution of acid. In the second method, the anodic oxide film is subjected either to a treatment of immersion in an aqueous solution of at least one acid selected from among phosphoric acid, sulfuric acid, oxalic acid, and sulfamic acid or to a combination treatment of immersion and AC electrolysis repeated in a prescribed number of cycles in the solution, to enlarge the pores in the anodic oxide film.

Characterization of aluminium complexes in tea extract. Part I—27Al NMR studies

Abstract: The high-field 27Al NMR spectrum of aqueous tea extract contained two narrow resonances at 9.85 and 16.15 ppm. The spectra of aluminium chelates with a number of model ligands (catechol, pyrogallol, catechin, kojic acid, protocatechuic acid, ascorbic acid and salicylic acid) containing chelating moieties present in the constituents of tea showed broad resonances in the range 8–36 ppm. Potentiometric and NMR studies indicate the formation of a monohydroxo 1:1 Al-catechin chelate (δ 8.3 ppm) with highly distorted symmetry. From a comparison of the NMR spectra of tea infusions at different pH values with those of aluminium chelates with malic acid and oxalic acid (minor constituents in tea), the resonance at 16.15 ppm was assigned to the highly symmetric octahedral anionic chelate trisoxalatoaluminium, [Al(C2O4)3]3−. This was confirmed by anion-exchange separation of the chelate and its identification by 27Al NMR spectroscopy. The signal at 9.8 ppm could be due to a mixed ligand chelate containing oxalate. In the case of the aluminium-malate system, the resonance at 20 ppm was assigned to a 1:2 chelate in which malate functions as a tridentate resulting in five- and six-membered chelate rings.

Preparation of [11C]diethyl oxalate and [11C]oxalic acid and demonstration of their use in the synthesis of [11C]-2,3-dihydroxyquinoxaline

Abstract: A method for the production of two new carbon-11 labelled difunctional radiolabelling precursors, [11C]diethyl oxalate, 2, and [11C]oxalic acid, 3, is described. Methyl chloroformate was reacted with no-carrier-added [11C]cyanide to generate the intermediate nitrile, methyl [11C]cyanoformate. Alcoholysis with HCl in ethanol generated 2, with could subsequently be converted to 3, with aqueous acid. The total time of preparation from end-of-trapping of [11C]cyanide was 6-7 min using combined microwave and thermal treatment or, by exclusively thermal treatment, 15 and 20 min for 2 and 3, respectively. The radiochemical conversion of [11C]cyanide to 2 and 3 was ∼80% and ∼70%, respectively. Both 2 and 3 were used in a model reaction with 1,2-phenylenediamine to synthesize the heterocyclic compound, 2,3-dihydroxyquinoxaline, a basic structural unit in antagonists for the excitatory amino acid receptor system.

Electrosynthesis of glyoxylic acid using a continuously electrogenerated lead cathode

Abstract: Glyoxylic acid is an important intermediate in organic synthesis. Its production by electroreduction of oxalic acid is very well known. However, attempts to scale up the process have failed due to rapid deactivation of the cathode. In this paper a process for overcoming this problem is described. The cathode activity can be continuously restored by adding small amounts of a Pb(II) salt in both anolyte and catholyte. In this way, the process has been continuously run for more than 300 h with a current efficiency of 92% and a selectivity higher than 95%.

Electrochemical process for preparing glyoxylic acid

Abstract: A process is disclosed for preparing glyoxylic acid by electrochemical reduction of oxalic acid in an aqueous solution within divided or non-divided electrolytic cells. The cathode is composed of carbon or of at least 50 % by weight of at least one of the metals Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn and Cr. The aqueous electrolytic solution in the non-divided cells or in the cathode chamber of divided cells further contains at least one salt of metals having at least 0.25 V hydrogen overvoltage, with respect to 2500 A/m2 current density. This process has the advantage that technically available and cost-effective materials, in particular stainless chromium-nickel steel or graphite, may be used as cathode materials.

Electrooxidation of ethylene glycol on bismuth-modified Pt(111)

Abstract: The influence of predosed bismuth upon the electrooxidation kinetics and pathways of ethylene glycol on Pt(111) in 0.1 mol dm–3 HClO4 has been examined by means of voltammetry combined with real-time infrared spectroscopy. On both unmodified and bismuth-modified Pt(111), two major oxidation products, oxalic acid and CO2, are formed via distinct reaction pathways. The presence of predosed bismuth adatoms significantly alters the selectivity of the electrocatalyst in that the production of CO2 increases monotonically with the bismuth coverage at the expense of the oxalic acid yield. The formation of CO2 was also observed starting from oxalic acid and other partial oxidation products, yet bismuth exerts little effect on the reaction kinetics in these cases. Adsorbed CO was also seen to be produced at positive potentials prior to, and during, the electrooxidation of ethylene glycol and especially from aldehyde-containing partially oxidized species. While the presence of predosed bismuth efficiently eliminates adsorbed CO formation from ethylene glycol, it has little effect for the aldehyde reactants. Significantly and surprisingly, the results suggest that ensembles of contiguous active sites are required for the partial oxidation of ethylene glycol to form oxalic acid but not for the exhaustive electrooxidation pathway yielding CO2.

Characterization of the bisphosphonate recognition site on hydroxyapatite using radioligand binding techniques with [14C]citric acid.

Abstract: The present studies characterize the binding of [14C]citric acid to synthetic hydroxyapatite (HA) crystals. [14C]Citric acid specifically bound to HA and was dependent upon the concentration of HA in the assay. The binding of [14C]citric acid to HA reached equilibrium within 20 min and remained stable for at least 90 min. Dissociation of bound [14C]citric acid was biphasic in nature since both rapid and more slowly reversible binding components were detected. Saturation experiments also indicated that [14C]citric acid labeled two recognition sites with different affinity (KdH=42 nM and KdL=24,000 nM) and density (BmaxH=161 fmol/μg HA and BmaxL=8.8 pmol/μg HA). Ligand competition experiments revealed that compounds that are known to readily bind bone (e.g., sodium pyrophosphate, methylene diphosphonic acid, etidronate) potently inhibited the binding of [14C]citric acid to HA, whereas compounds known to have poorer affinity for bone (e.g., oxalic acid and GABA) did not. Computer analysis of these inhibition curves revealed specific ligand interactions at two different affinity recognition sites. The present results indicate that [14C]citric acid binds discrete sites on synthetic HA in a fashion consistent with a specific labeling of the bisphosphonate recognition site. Analysis of the binding of [14C]citric acid to HA provides a useful method to further explore the structure activity relationships of novel compounds that have binding affinity for bone.

Ion-chromatographic determination of plasma oxalate reexamined.

Abstract: This new procedure for determining oxalic acid in plasma is based on sample deproteinization with hydrochloric acid and acetonitrile and subsequent ion-chromatographic assay of the neutralized supernate. Sample pretreatment produces very clean samples, which ensures long column life. Mean analytical recovery of oxalate (5.0-10.0 mumol/L) added to plasma samples averaged 98.6 +/- 6.2%; imprecision (CV) was 5.2% (at 2.2 mumol/L) and the detection limit was 0.5 mumol/L at a signal-to-noise ratio of 5:1. Ascorbate to oxalate conversion was < 0.2%, indicating that the procedure is free from ascorbate interference. Plasma oxalate concentrations, measured in samples from 31 healthy persons, ranged from 0.8 to 3.4 mumol/L (mean 1.89, SD 0.75 mumol/L), which agrees with results from indirect radioisotopic dilution methods.