Showing papers on "Oxalic acid published in 1999"

Fungal production of citric and oxalic acid: importance in metal speciation, physiology and biogeochemical processes.

Abstract: The production of organic acids by fungi has profound implications for metal speciation, physiology and biogeochemical cycles. Biosynthesis of oxalic acid from glucose occurs by hydrolysis of oxaloacetate to oxalate and acetate catalysed by cytosolic oxaloacetase, whereas on citric acid, oxalate production occurs by means of glyoxylate oxidation. Citric acid is an intermediate in the tricarboxylic acid cycle, with metals greatly influencing biosynthesis: growth limiting concentrations of Mn, Fe and Zn are important for high yields. The metal-complexing properties of these organic acids assist both essential metal and anionic (e.g. phosphate) nutrition of fungi, other microbes and plants, and determine metal speciation and mobility in the environment, including transfer between terrestrial and aquatic habitats, biocorrosion and weathering. Metal solubilization processes are also of potential for metal recovery and reclamation from contaminated solid wastes, soils and low-grade ores. Such ‘heterotrophic leaching’ can occur by several mechanisms but organic acids occupy a central position in the overall process, supplying both protons and a metal-complexing organic acid anion. Most simple metal oxalates [except those of alkali metals, Fe(III) and Al] are sparingly soluble and precipitate as crystalline or amorphous solids. Calcium oxalate is the most important manifestation of this in the environment and, in a variety of crystalline structures, is ubiquitously associated with free-living, plant symbiotic and pathogenic fungi. The main forms are the monohydrate (whewellite) and the dihydrate (weddelite) and their formation is of significance in biomineralization, since they affect nutritional heterogeneity in soil, especially Ca, P, K and Al cycling. The formation of insoluble toxic metal oxalates, e.g. of Cu, may confer tolerance and ensure survival in contaminated environments. In semiarid environments, calcium oxalate formation is important in the formation and alteration of terrestrial subsurface limestones. Oxalate also plays an important role in lignocellulose degradation and plant pathogenesis, affecting activities of key enzymes and metal oxidoreduction reactions, therefore underpinning one of the most fundamental roles of fungi in carbon cycling in the natural environment. This review discusses the physiology and chemistry of citric and oxalic acid production in fungi, the intimate association of these acids and processes with metal speciation, physiology and mobility, and their importance and involvement in key fungal-mediated processes, including lignocellulose degradation, plant pathogenesis and metal biogeochemistry.

Oxalate content of foods and its effect on humans

Abstract: Oxalic acid and its salts occur as end products of metabolism in a number of plant tissues. When these plants are eaten they may have an adverse effect because oxalates bind calcium and other minerals. While oxalic acid is a normal end product of mammalian metabolism, the consumption of additional oxalic acid may cause stone formation in the urinary tract when the acid is excreted in the urine. Soaking and cooking of foodstuffs high in oxalate will reduce the oxalate content by leaching. The mean daily intake of oxalate in English diets has been calculated to be 70‐150 mg, with tea appearing to contribute the greatest proportion of oxalate in these diets; rhubarb, spinach and beet are other common high oxalate-content foods. Vegetarians who consume greater amounts of vegetables will have a higher intake of oxalates, which may reduce calcium availability. This may be an increased risk factor for women, who require greater amounts of calcium in the diet. In humans, diets low in calcium and high in oxalates are not recommended but the occasional consumption of high oxalate foods as part of a nuritious diet does not pose any particular problem.

Lipid synthesis under hydrothermal conditions by Fischer-Tropsch-type reactions.

Abstract: Ever since their discovery in the late 1970's, mid-ocean-ridge hydrothermal systems have received a great deal of attention as a possible site for the origin of life on Earth (and environments analogous to mid-ocean-ridge hydrothermal systems are postulated to have been sites where life could have originated or Mars and elsewhere as well) Because no modern-day terrestrial hydrothermal systems are free from the influence of organic compounds derived from biologic processes, laboratory experiments provide the best opportunity for confirmation of the potential for organic synthesis in hydrothermal systems Here we report on the formation of lipid compounds during Fischer-Tropsch-type synthesis from aqueous solutions of formic acid or oxalic acid Optimum synthesis occurs in stainless steel vessels by heating at 175 degrees C for 2-3 days and produces lipid compounds ranging from C2 to > C35 which consist of n-alkanols, n-alkanoic acids, n-alkenes, n-alkanes and alkanones The precursor carbon sources used are either formic acid or oxalic acid, which disproportionate to H2, CO2 and probably CO Both carbon sources yield the same lipid classes with essentially the same ranges of compounds The synthesis reactions were confirmed by using 13C labeled precursor acids

Preparation and characterization of Fischer-Tropsch active Co/SiO2 catalysts

Abstract: Silica supported cobalt catalysts have been prepared by a new method combining the precipitation of the metal precursor (cobalt nitrate) by oxalic acid with the hydrolysis and condensation of the silicium precursor (tetraethoxysilane). Depending on the pH during preparation, the textural properties (BET specific surface area, porosity) of the Co/SiO 2 catalysts can be modified. In an acid medium (pathway A), the resulting silica is constituted by a polymeric net with few branchings, the catalysts are microporous. In basic medium (pathway B) silica is composed of more branched polymers leading to mesoporous catalytic systems. After calcination, the only crystallized phase detected by XRD is the Co 3 O 4 spinel. At 773 K, the surface degrees of reduction of the catalysts at cobalt isocontent (25 wt.% Co) as determined by XPS is of 81% and 69% for systems prepared by pathways A and B, respectively. The presence of small unreduced Co II suggests the existence of non-crystallized cobalt silicate formed during the reduction by reaction of CoO with silica. The activity for the CO + H 2 reaction for the 25 wt.% catalysts prepared by pathway A increased with the specific surface area which can be controlled by the preparation parameters. The reduction degree has a direct influence on the selectivity for the Co/SiO 2 catalysts. The presence of a part of unreduced cobalt (in interaction with the support) results in a better selectivity to the C 5 –C 13 fraction (gasoline), whereas a higher reduction degree of cobalt favors the production of higher molecular weight hydrocarbons (waxes) (C 22 + selectivity > 40%).

Oxalic acid production by Aspergillus niger: an oxalate-non-producing mutant produces citric acid at pH 5 and in the presence of manganese.

Abstract: The external pH appeared to be the main factor governing oxalic acid production by Aspergillus niger. A glucose-oxidase-negative mutant produced substantial amounts of oxalic acid as long as the pH of the culture was 3 or higher. When pH was decreased below 2, no oxalic acid was formed. The activity of oxaloacetate acetylhydrolase (OAH), the enzyme believed to be responsible for oxalate formation in A. niger, correlated with oxalate production. OAH was purified from A. niger and characterized. OAH cleaves oxaloacetate to oxalate and acetate, but A. niger never accumulated any acetate in the culture broth. Since an A. niger acuA mutant, which lacks acetyl-CoA synthase, did produce some acetate, wild-type A. niger is apparently able to catabolize acetate sufficiently fast to prevent its production. An A. niger mutant, prtF28, previously isolated in a screen for strains deficient in extracellular protease expression, was shown here to be oxalate non-producing. The prtF28 mutant lacked OAH, implying that OAH is the only enzyme involved in oxalate production in A. niger. In a traditional citric acid fermentation low pH and absence of Mn2+ are prerequisites. Remarkably, a strain lacking both glucose oxidase (goxC) and OAH (prtF) produced citric acid from sugar substrates in a regular synthetic medium at pH 5 and under these conditions production was completely insensitive to Mn2+.

Layer-By-Layer Assembly of Core-Shell Magnetite Nanoparticles: Effect of Silica Coating on Interparticle Interactions and Magnetic Properties

Abstract: Monodisperse PS spheres were synthesized and packed into colloidal crystals by centrifugation as described previously [6]. Sphere diameters in various batches ranged from 420 ‐ 50 nm to 660 ‐ 30 nm. To prepare macroporous nickel oxide, nickel(II) acetate (2 g) was dissolved in either acetic acid (5 mL) or a mixture of H2O (5 mL)and ethanol (5 mL) at 60 C. After cooling to room temperature, any undissolved solid was removed by filtration. Centimeter-scale, close-packed, colloidal polystyrene crystals (1 g) were soaked in this solution for 3‐5 min. Excess solution was removed from the impregnated colloidal crystals by vacuum filtration. The samples were dried at 60 C for 2 h. The dried composites were soaked in 10 mL of a saturated solution of oxalic acid in ethanol (ca. 25‐30 g in 100 mL) for 3‐5 min. After additional vacuum filtration and drying, the PS spheres were removed by calcination in flowing air at 360‐575 C for 7‐10 h (heating rate: 1 C/ min). Macroporous Ni was prepared by heating macroporous NiO in flowing H2 at 300 C for 2‐5 h (heating rate: 1 C/min) or by heating the nickel oxalate/PS composite in flowing nitrogen at 450‐500 C for 10 h. Preparation of partially reduced samples containing both NiO and Ni was possible by decreasing the reduction time or temperature, or by carrying out a fast calcination, for example at 360 C for 1 h in fast flowing air. Electrochemical tests were performed in two electrode cells using 1 M aqueous KOH as the electrolyte and nickel pellets as both electrodes. Pellets were made by pressing a mixture of 10 wt.-% poly(vinylidene fluoride) binder with 90 wt.-% nickel to 1500 psi for 30 s. An SEM of the material indicated that a porous structure was still maintained. No carbon powder was needed to enhance the pellet conductivity. Impedance analysis was performed using a Solartron 1260 Impedance/Gain-Phase Analyzer along with a Solartron 1287 Electrochemical Interface. Other product characterization was carried out as described previously [6].

Synthesis and sintering of rare-earth-doped ceria powder by the oxalate coprecipitation method

Abstract: Doped ceria, which has a higher oxygen ion conductivity than yttria-stabilized zirconia, is one of the possible electrolytes for solid oxide fuel cell at low temperatures. This study concerns powder preparation and densification of rare-earth-doped ceria. Rare-earth-doped ceria powders with a composition of Ce0.8R0.2O1.9 (R = Yb, Y, Gd, Sm, Nd, and La) were prepared by heating the oxalate coprecipitate when a mixed rare earth/cerium nitrate solution was added to an oxalic solution. The oxalate and derived-oxide powders were characterized by x-ray diffraction (XRD), thermogravimetry differential thermal analysis (TG-DTA), particle size analyzer with laser diffraction, inductively coupled plasma (ICP), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). This method provided the oxalate solid solutions containing Ce and R, which were calcined to form the oxide solid solutions at 600 °C in air. The lattice parameter of oxide powders increased linearly with increasing ionic radius of doped rare earth. The size of platelike particles of oxalates and oxides depended on the concentration of oxalic acid and showed a minimum at 0.4 M oxalic acid. Dry milling of oxide powder with α–Al2O3 ball was effective in reducing the size and aspect ratios of particles with little contamination of Al2O3. These rare-earth-doped ceria powders with various sizes were formed by uniaxial pressing (49 MPa) followed by cold isostatic pressing (294 MPa), and sintered at 900–1600 °C in air for 4 h. The micrometer-sized-doped CeO2 powders were densified above 95% of the theoretical density at 1200 °C. The grain size of rare-earth-doped ceria after sintering at 1600 °C was larger in the samples with the larger rare-earth element.

A solution chemistry approach to the study of rare earth element precipitation by oxalic acid

Abstract: A solution chemistry approach is developed to study oxalic acid efficiency (OAE) in recovering rare earth (RE) elements from the leachates of weathered clays. The optimal pH for precipitation (approximately 2) to obtain the highest RE recovery with the highest purity is identified experimentally and confirmed by solution chemistry calculations. Applying the solution chemistry approach to three case studies, the cause for a larger oxalic acid consumption than that calculated from stoichiometry of RE oxalate precipitation is identified. A typical OAE of approximately 60 pct was determined with 40 pct of excess oxalic acid consumed by precipitating and complexing non-RE elements while maintaining a low residual RE element concentration. Both solution chemistry calculations and experimental results showed that OAE can be improved by processing leachates of high initial RE concentrations.

Intestinal hyperabsorption of oxalate in calcium oxalate stone formers: application of a new test with [13C2]oxalate.

Abstract: In up to one-third of patients with calcium oxalate stones, a hyperoxaluria can be detected. Hyperoxaluria can result from increased endogenous production, from excessive oxalate content of the food, or from intestinal hyperabsorption. For a causal therapy, it is important to discriminate between metabolic and hyperabsorptive hyperoxaluria. Our new 13C-oxalate test allows this differentiation. Under standardized conditions, 50 mg of disodium salt of [13C2]oxalic acid was applied. From the amount of labeled oxalate excreted in urine as measured by a gas chromatographic-mass spectrometric assay, the intestinal absorption was calculated. Seventy patients with recurrent calcium oxalate urolithiasis who had no signs of inflammatory bowel disease were tested. Their mean intestinal oxalate absorption was 9.2+/-5.1%. This was significantly higher than the mean absorption of 50 healthy volunteers (6.7+/-3.9%). There was no difference in oxalate absorption between male (n = 25) and female volunteers. Oxalate absorption correlated with the oxalate excretion in the 24-h urine (volunteers: r = 0.46, P < 0.01; patients: r = 0.62, P < 0.001). Oxalate hyperabsorption was defined as an absorption exceeding 10%. According to this definition, 34% of the patients had oxalate hyperabsorption; 20% of the volunteers showed a hyperabsorption, too. The 13C-oxalate absorption test allows reliable determination of intestinal oxalate absorption. Because of the use of a stable isotope, this test may be repeated as often as required. It will allow the control of therapeutic regimens and also help to unravel genetic influences in stone formation.

Lithium bisoxalatoborate, the production thereof and its use as a conducting salt

Abstract: The invention relates to the novel lithium bisoxalatoborate compound, and to a method for producing this compound, on the basis of a lithium compound, an oxalic acid or an oxalate, and a boron compound. The invention also relates to another production method on the basis of lithium boron hydride and oxalic acid, and to the use of lithium bisoxalatoborate as a conducting salt in lithium-ion batteries.

Wet Oxidation Kinetics of Refractory Low Molecular Mass Carboxylic Acids

Abstract: Wet oxidation kinetics of aqueous solutions of formic, acetic, oxalic, and glyoxalic acids was studied in a titanium autoclave at a temperature range of 150−320 °C and oxygen partial pressures between 8 and 60 bar. Oxidation reactions obeyed a first-order kinetics with respect to concentration of all substrates. On the basis of acid concentration decay, the activation energy for acetic, oxalic, and glyoxalic acid oxidation was 178, 137, and 97 kJ/mol, respectively; whereas on the total organic carbon (TOC) conversion basis, these values were slightly higher, namely 182, 141, and 104 kJ/mol. The activation energy for formic acid took a unique value of 149 kJ/mol regardless of the type of concentration used. The rate of oxidation was proportional to a square root of oxygen concentration (partial pressure) for acetic, formic, and oxalic acids, whereas it was linearly proportional for glyoxalic acid. When sufficiently high oxygen partial pressure was applied (≥22 bar), the individual acid conversion in a mixt...

Microbial Formation of Oxalate Films on Monument Surfaces: Bioprotection or Biodeterioration?

Abstract: Oxalate films observed on stone monument surfaces deserve greater interest because of their possible role in protecting against deterioration. Their origin remains controversial. We present here the results of research conducted on production of oxalic acid and other organic acids by bacterial communities isolated from two monuments. Both communities were developed in vitro, and oxalate production was evaluated in a context of global metabolic activities that could eventually lead to protection or to degradation of the surface itself. HPLC analyses of organic acids production revealed that all mixed cultures produced oxalic acid but in different amounts. Besides oxalic acid, other organic acids are released that can solubilize stone calcium carbonate and have a deteriorating activity. Calcium carbonate solubilization, evaluated both by mixed cultures and isolated strains, was stronger with mixed cultures than with single strains. Our data show that oxalate production is promoted by the bacterial communiti...

Iron Removal Process for High-Purity Silica Sands Production by Oxalic Acid Leaching

Abstract: In this article, a leaching study, carried out on a quartz sample to obtain high-purity silica sands, has been presented. A leaching process by using oxalic acid to remove low iron content from the ore under study and to obtain a material suitable for fiber optic production has been evaluated. A characterization study has been carried out to establish the location of the iron impurities on the ore: 77 g/t was the maximum iron contamination, whereas, a final iron content <10 g/t (as Fe) has to be achieved for the application considered. The effect of the grinding process on the iron extraction yield has been established; the maximum iron extraction yield obtained with the ore as-is was about 45−50%, whereas extraction yields greater than 80−90% can be obtained after grinding the ore in different experimental conditions. An empirical model was evaluated to correlate the iron extraction yield obtained after 3 h of leaching at 80 °C, with 3 g/L of oxalic acid and 10% (w/v) of ore concentration, as a function...

Absorption of Calcium Oxalate Does Not Require Dissociation in Rats

Abstract: Calcium absorption is thought to occur only if calcium is in a soluble or dissociated form, although experimental evidence is lacking. The intestinal absorption of calcium oxalate, a small, neutral and virtually insoluble calcium salt, was elucidated in the whole body of awake rats. Suspensions of 45Ca ascorbate, 14C-oxalic acid and doubly labeled 45Ca-[14C]-oxalate were given by gavage to separate groups of rats. Following dosing, blood samples were drawn for up to 240 min through a previously inserted intravenous catheter. Serum was assayed for radioactive tracers, and data were then plotted as fraction of dose over time. Calcium absorption was 15% [with a loading of 0.3 mmol (15 mg) calcium], oxalic acid absorption was 22% and Ca-oxalate absorption was <2%. Appearance of 45Ca from calcium ascorbate and 14C from oxalic acid differed, whereas 45Ca and 14C from doubly labeled Ca-oxalate had identical serum appearance profiles. Therefore, we conclude that calcium oxalate was absorbed intact. Addition of excess, unlabeled calcium to the doubly-labeled calcium oxalate did not alter the relationship of the serum level of the two tracers, confirming absorption of calcium oxalate as the intact salt. Thus, calcium bound as a small, neutral, calcium salt such as calcium oxalate does not have to be dissociated prior to absorption. Possibly other small compounds would be similarly absorbed. These results alter our current understanding of calcium bioavailability from foods and therapeutic agents.

Water-repellent surface treatment

Abstract: The present invention relates to a method of improving the durability of water-repellent films deposited on the surface of a substrate and to a coated article having water-repellent film of improved durability deposited on the substrate surface. The method includes the steps of simultaneously abrasively and chemically preparing the surface to expose an increased number of bonding sites on the substrate surface by applying a dispersion including an acid solution and an abrasive material to the surface. The dispersion is then removed and the water-repellent film is formed over the prepared surface. The bonding sites react with the water-repellent film to more effectively bond the film to the substrate and thereby improve the durability of the water-repellent film. The abrading material is preferably selected from the group consisting of alumina, ceria, iron oxide, garnet, zirconia, silica, silicon carbide, chromic oxide, pumice and diamond, and the acid solution is preferably selected from the group consisting of solutions of hydrochloric acid, sulfuric acid, tartaric acid, phosphoric acid, hydrobromic acid, nitric acid, acetic acid, trifluoroacetic acid, oxalic acid and citric acid.

Induction of systemic resistance to Sclerotiniasclerotiorum by oxalic acid in oilseed rape

Abstract: Treatment of the lowermost leaf of flowering plants of oilseed rape cv. Linetta with 20 m m oxalic acid induced systemic disease resistance in the three next youngest leaves. Resistance was not caused by the translocation of fungitoxic concentrations of oxalic acid. Resistance was also expressed in the stem; in oxalic acid-treated plants the vertical spread of stem lesions was halted and the signal travelled both acropetally and basipetally. Expression of resistance in the leaves was detected 6 h after treatment and continued for at least 5 weeks. Twenty-four h after treatment, resistance was detectable in the leaves following the use of as little as 0.5 m m oxalic acid. Local resistance in the oxalic acid-sprayed leaf was detectable only at certain times (12 and 48 but not 24 h after treatment) and at very low (0.25 m m) or high (≥40 m m) oxalic acid concentrations. When oxalic acid was applied to a discrete area of the leaf, significant local resistance was expressed in the surrounding leaf tissue, maximum resistance being exhibited by the tissue closest to the site of petiole attachment.