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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A novel coating technique, referred to as Electrostatic Spray Deposition (ESD), was used to deposit calcium phosphate (CaP) coatings with a variety of chemical properties. The relationship between the composition of the precursor solutions and the crystal and molecular structure of the deposited coatings was investigated by means of X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR) and Energy Dispersive Spectroscopy (EDS). It was shown that the relative Ca/P ratio in the precursor solution, the absolute precursor concentration, the acidity of the precursor solution and the type of Ca-precursor strongly influenced the chemical nature of the deposited CaP coatings. Various crystal phases and phase mixtures were obtained, such as carbonate apatite, beta-TCP, Mg-substituted whitlockite, monetite, beta/gamma-pyrophosphate, and calcite. It was shown that carbonate plays an essential role in the chemical mechanism of coating formation. Carbonate is formed due to a decomposition reaction of organic solvents. Depending on deposition conditions, carbonate anions (a) react with acidic phosphate groups, (b) are incorporated into apatitic calcium phosphate phases, and (c) react with excessive Ca(2+) cations in case of phosphate-deficient precursor solutions.
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PMID:Influence of precursor solution parameters on chemical properties of calcium phosphate coatings prepared using Electrostatic Spray Deposition (ESD). 1460 2

Ureagenesis in the liver consumes up to 1,000 mmol of HCO3-/day in humans as a result of 2NH4+ + 2HCO3- --> urea + CO2 + 3H2O. Whether the liver contributes to the regulation of acid-base equilibrium by controlling the rate of ureagenesis and, therefore, HCO3- consumption in response to changes in plasma acidity has not been adequately evaluated in humans. Rates of ureagenesis were measured in eight healthy volunteers during control, chronic metabolic acidosis (induced by oral administration of CaCl2 3.2 mmol.kg body wt-1.day-1 for 11 days), and recovery as well as during bicarbonate infusion (200 mmol over 240 min; acute metabolic alkalosis). Rates of ureagenesis were correlated negatively with plasma HCO3- concentration both during adaption to metabolic acidosis and during the chronic, steady-state phase. Thus ureagenesis, an acidifying process, increased rather than decreased in metabolic acidosis. During bicarbonate infusion, rates of ureagenesis decreased significantly. Thus ureagenesis did not appear to be involved in the regulated elimination of excess HCO3-. The finding of a negative correlation between ureagenesis and plasma HCO3- concentration over a wide range of HCO3- concentrations, altered both chronically and acutely, suggests that the ureagenic process per se is maladaptive for acid-base regulation and that ureagenesis has no discernible homeostatic effect on acid-base equilibrium.
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PMID:Ureagenesis: evidence for a lack of hepatic regulation of acid-base equilibrium in humans. 1465 59

To assess quantitatively the effect of peroxide addition to standard static tests of the neutralization potential (NP) of mine wastes, 10 specimens of carbonate minerals, including five of siderite (FeCO3) and two of rhodochrosite (MnCO3), were analyzed by electron microprobe. The compositions of the siderite span a range from 60 to 86 mol % Fe. Tests of NP for the siderite diluted with 80% (w/w) kaolinite gave values of 647 to 737 kg CaCO3 equivalent per Mg for determinations by the standard Sobek method. However, if it is assumed that the ferrous carbonate component of the mineral does not contribute to NP in field situations because oxidation of Fe(II) to Fe(III) and the subsequent hydrolysis of Fe(III) leads to the release of an equivalent amount of acid, then the calculated NP for the samples ranges from 110 to 390 kg CaCO3 equivalent per Mg. Two different methods involving the addition of peroxide to the test solutions were successful in bringing the measured NP values closer to the theoretical ones. By contrast, the tests with rhodochrosite indicated the Mn(II) to be stable. For long-term environmental planning, especially for wastes from metalliferous sulfide-poor deposits in which gradual dissolution of silicate and aluminosilicate minerals may be involved in attenuating the acidity, consideration in the overall NP budget needs to be given to the ferrous iron content of those minerals. The presence of Fe2+-bearing minerals, especially carbonates, in tested mine-waste materials may lead to overestimated Sobek NP values, thus increasing the risk of poor-quality drainage and the need for costly remediation.
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PMID:Effect of peroxide on neutralization-potential values of siderite and other carbonate minerals. 1467 62

A field experiment was conducted to determine the effect of fly ash from a coal combustion electric power facility on soil acidity in a cotton (Gossypium hirsutum L.) field. Fresh fly ash was applied to a Bosket fine sandy loam (fine-loamy, mixed, thermic Mollic Hapludalf) soil with an initial soil pH(salt) of 4.8. The fly ash was equivalent to 42 g kg(-1) calcium carbonate with 97% passing through a 60 mesh (U.S. standard) sieve. Fly ash was applied one day before cotton planting in 1999 at 0, 3.4, 6.7, and 10.1 Mg ha(-1). No fly ash was applied in 2000. Within 60 d of fly ash application in 1999, all rates of fly ash significantly increased soil pH above 6.0. Manganese levels in cotton petioles were reduced significantly by 6.7 and 10.1 Mg ha(-1) of fly ash. Soil boron (B) and sodium (Na) concentrations were significantly increased with fly ash. In 1999, B in cotton leaves ranged from 72 to 84 mg kg(-1) in plots with fly ash applications. However, no visual symptoms of B toxicity in plants were observed. In 1999, cotton lint yield decreased on average 12 kg ha(-1) for each Mg of fly ash applied. In 2000, cotton yields were significantly greater for the residual 3.4 and 6.7 Mg fly ash ha(-1) plots than the untreated check. Due to the adverse yield effects measured in the first year following application, fly ash would not be a suitable soil amendment for cotton on this soil at this time.
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PMID:Fly ash as a liming material for cotton. 1496 89

The addition of calcium carbonate to a clearwater acidic lake had a significant effect on phytoplankton abundance and on the biomass-specific rate of production. Chlorophyll concentrations and productivity: biomass ratios were strongly correlated with changes in lake acidity associated with liming and reacidification (r2=0.89 and 0.73, respectively). Summer mean chlorophyll increased by 0.9 mg m(-3) for each unit increase in lake pH, whereas productivity:biomass ratios decreased from > 2 to < 1 with an increase in pH from 5.5 to 7.0. Higher phytoplankton standing crops after liming were attributed to lower grazing rates following the decline of the dominant zooplankton taxa. A model relating biomass-specific productivity to incident light levels was found to be useful in interpreting treatment effects on productivity. Incident light and biomass (based on chlorophyll) accounted for 81% of the variability in productivity at the treated site. Comparisons of photosynthesis-irradiance curves indicated that the maximum photosynthetic capacity was higher following the watershed liming, compared to data collected after lake liming and during reacidification.
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PMID:Changes in primary productivity associated with liming and reacidification of an Adirondack lake. 1509 97

The gastric mucosa is frequently exposed to endogenously secreted hydrochloric acid of high acidity. Gastric mucosal defense mechanisms are arranged at different levels of the gastric mucosa and must work in unison to maintain its integrity. In this work, several mechanisms underlying gastric mucosal resistance to strong acid were investigated in anesthetized rats and mice. The main findings were as follows: Only when acid secretion occurred did the pH gradient in the mucus gel withstand back-diffusion of luminal acid (100 mM or 155 mM HCl), and keep the juxtamucosal pH (pH(jm)) neutral. Thus, with no on-going acid secretion and low luminal pH, the pH gradient was destroyed. Bicarbonate ions, produced concomitant with hydrogen ions in the parietal cells during acid secretion and transported by the blood to the surface epithelium, were carried transepithelially through a DIDS-sensitive transport. Prostaglandin-dependent bicarbonate secretion seemed to be less important in maintaining a neutral pH(jm). Removal of the loosely adherent mucus layer did not influence the maintenance of the pH(jm). Hence, only the firmly adherent mucus gel layer, approximately 80 microm thick, seemed to be important for the pH(jm). Staining of the mucus gel with a pH-sensitive dye revealed that secreted acid penetrated the mucus gel from the crypt openings toward the gastric lumen only in restricted paths (channels). One crypt opening was attached to one channel, and the channel was irreversibly formed during acid secretion. Gastric mucosal blood flow increased on application of strong luminal acid (155 mM HCl). This acid-induced hyperemia involved the inducible but not the neural isoform of nitric oxide synthase. These results suggest a novel role for iNOS in gastric mucosal protection and indicate that iNOS is constitutively expressed in the gastric mucosa.
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PMID:Acid transport through gastric mucus. 1512 49

A meta-analysis was conducted to examine potential empirical relationships between dietary cation-anion difference (DCAD) (Na + K - Cl) and the response of lactating dairy cows. The database was developed from 12 studies published between 1984 and 1997 that included a total of 17 trials, 69 dietary treatments, and 230 cows. Results indicated that DCAD affected performance of lactating dairy cows. Maximum milk yield and feed intake were reached when DCAD was 34 and 40 meq/100 g of feed dry matter, respectively. Blood pH and HCO3 concentrations increased with DCAD, indicating an improved acid-base balance of lactating dairy cows. Changes in urinary pH and urinary excretion of Na, K, and Cl were consistent with varying DCAD, thus dietary acidity or alkalinity. The effects of DCAD were likely mediated via modification of acid-base status in the cows.
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PMID:Dietary cation-anion difference effects on performance and acid-base status of lactating dairy cows: a meta-analysis. 1532 36

Fermentation of lactose in whey permeate directly into ethanol has had only limited commercial success, as the yields and alcohol tolerances of the organisms capable of directly fermenting lactose are low. This study proposes an alternative strategy: treat the permeate with acid to liberate monomeric sugars that are readily fermented into ethanol. We identified optimum hydrolysis conditions that yield mostly monomeric sugars and limit formation of fermentation inhibitors such as hydroxymethyl furfural by caramelization reactions. Both lactose solutions and commercial whey permeates were hydrolyzed using inorganic acids and carbonic acid. In all cases, more glucose was consumed by secondary reactions than galactose. Galactose was recovered in approximately stoichiometric proportions. Whey permeate has substantial buffering capacity-even at high partial pressures (>5500 kPa[g]), carbon dioxide had little effect on the pH in whey permeate solutions. The elevated temperatures required for hydrolysis with CO2-generated inhibitory compounds through caramelization reactions. For these reasons, carbon dioxide was not a feasible acidulant. With mineral acids reversion reactions dominated, resulting in a stable amount of glucose released. However, the Maillard browning reactions also appeared to be involved. By applying Hammet's acidity function, kinetic data from all experiments were described by a single line. With concentrated inorganic acids, low reaction temperatures allowed lactose hydrolysis with minimal by-product formation and generated a hexose-rich solution amenable to fermentation.
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PMID:Hydrolysis of lactose in whey permeate for subsequent fermentation to ethanol. 1545 74

The ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth. At present, this depth is approximately 4,500 m, with some variation between and within ocean basins. The calcite compensation depth is linked to ocean acidity, which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate. Geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the Eocene/Oligocene boundary (approximately 34 million years ago) when significant permanent ice sheets first appeared on Antarctica, but the relationship between these two events is poorly understood. Here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical Pacific Ocean that cover the Eocene/Oligocene boundary. We find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40,000 years each, synchronous with the stepwise onset of Antarctic ice-sheet growth. The glaciation was initiated, after climatic preconditioning, by an interval when the Earth's orbit of the Sun favoured cool summers. The changes in oxygen-isotope composition across the Eocene/Oligocene boundary are too large to be explained by Antarctic ice-sheet growth alone and must therefore also indicate contemporaneous global cooling and/or Northern Hemisphere glaciation.
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PMID:Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean. 1563 7

Soil extraction of lead contaminated soil collected from sites near an abandoned battery recycling and secondary lead-smelting factory was investigated for potential use in decontaminating soil at the sites. A fractionation study was conducted to elucidate soil retention mechanism for Pb at the site. Three soil pits were selected from an area surrounding the factory based on level of Pb contamination. Soil samples were collected from each pit in two layers: surface soil and subsoil (0-15 cm and 15-30 cm). Soil physical analysis showed that the soil texture was sandy loam and sandy clay loam with clay content between 11-21%. Soil pH was strongly acid to moderately acid (pH 4.8-5.9). Pb levels in the surface soil were 1620 and 153 mg kg(-1) (air-dried basis) respectively for heavily and slightly contaminated soil. A reference soil site contained 15 mg kg(-1) of Pb. Partitioning studies indicated that more than 90% of total Pb in the soil existed in three primary fractions: exchangeable, carbonate, and Fe-Mn oxide. This suggested that Pb sources entering the soil from the Pb factory remained in relatively weakly bound forms, which are mobile and have potentially biological availability. Mobility of Pb as in the soil assessed by mobility factor (MF) was as high as 75% indicating a high potential of Pb remobilization. Due to high mobility, the Pb would be amendable to remediation or removal by soil extraction procedures. To determine if such weekly bound Pb could be easily removed, both soil washing (ex situ) and soil flushing (in situ) techniques were evaluated for potential Pb remediation procedure. Particle size separation of soil into coarse (2.0-0.25 mm), medium (0.25-0.15 mm), and fine size (<0.15 mm) was conducted before initiating soil washing for comparing Pb removal efficiency in these fractions with the indigenous soil fraction. Using EDTA (2:1 mole to Pb) as a washing solution up to 85-95% of Pb was removed under the optimum conditions (retention time = 60 min), and liquid to solid ratio (L/S) at 5:1 for coarse fraction and 10:1 for smaller fraction. Pb could be removed from contaminated soil using EDTA extraction; however, the efficiency was higher in the coarse texture soil fraction. As a result particle size separation is recommended before application of the soil washing procedure. For smaller soil particle size fraction a series of extraction was needed for obtaining an adequate extraction efficiency. Three solvents tested as flushing solution showed 85, 84, and 74% of Pb was removed by EDTA (2:1 mole to Pb), 1M HNO3, and 0.2 M ammonium citrate, respectively after flushing with 20 pore volumes. The capacity of the three flushing solutions to remove Pb from the contaminated soil were ranked in the order: EDTA approximately 1 M HNO3 > 0.2 N ammonium citrate. However, in highly contaminated soil all solvent extract required several Pb leaching cycles. The flushing process using 1 M HNO3 increased soil acidity to extreme acid conditions (pH 2.0) resulting in adverse effects to physicochemical properties of the treated soil. In general, results showed three factors influenced Pb removal by the extraction techniques: (i) initial Pb concentrations, (ii) Pb partitioning within soil, and (iii) particle size of soil matrix.
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PMID:Evaluation of extraction procedures for removing lead from contaminated soil. 1571 83


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