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At least 325 records · Page 18Linked to original sources

PubMed2003

Development of a modified medium pressure microwave vapor-phase digestion method for difficult to digest organic samples.

A previously developed microwave heated vapor-phase digestion method for biological samples was modified to enable digestion of difficult to digest organic samples. Organic samples containing ca. 100 mg of organic carbon were digested using volume calibrated quartz inserts inside second generation type medium pressure microwave vessels. As digestion reagents, 98% sulfuric acid, 70% nitric acid and 30% hydrogen peroxide were used. The accuracy of the method was tested with six certified reference materials. Elements Ca, Fe, K, Na, Mg, P and Zn were determined from NIST-SRM 8433 corn bran. Elements Al, Fe, Cd, Cu, and Zn were determined from NRCC DOLT-2 dogfish liver. The element Cd was determined from IRMM-VDA Cd in polyethylene No. 001-004 reference materials. These elements were determined from digested samples by ICP-OES. The results were close or within certified limits. The modified method could digest nearly all the materials tested, including the above mentioned reference materials, 2-nitrobenzoic acid (2-NBA), 4-NBA and copper(II) phthalosyanine-3, 4',4',4'-tetrasulfonic acid tetrasodium salt (CPS). The method could not digest 3-NBA.

Journal Article↗

PubMed2002

Histological thin-sections: a method for the microscopic study of teeth in Spanish red deer (Cervus elaphus hispanicus).

A method to obtain thin histological sections (4-5 microm thick) from teeth, using a conventional microtome, is described for incisors, molars and canines from Spanish red deer (Cervus elaphus hispanicus). Decalcifying solutions of formic acid and nitric acid at different concentrations were ineffective. This was not the case for a solution of 14% hypochloric acid and polyvinylpyrrolidone (TBD-1(R) of Shandon). However, the time needed to complete decalcification was longer than the time estimated by other authors. Incisors required between 4 and 6 days, molars between 7 and 15 days, and canines between 8 and 12 days. The preparation of histological thin-sections from teeth with a conventional microtome, required some training or prior specialization, because most of defective or lost material occurred during the preliminary stage of the study. However this technique is inexpensive enough to be implemented in any histological laboratory. The preparations obtained are suitable for growth mark observation in dentine and in cementum for dating studies. Nevertheless, they are not suitable for enamel change studies, because the enamel is completely destroyed during the decalcifying process.

Age Determination by Teeth↗

PubMed2003

Microbial and copper adsorption by smectitic clay--an experimental study.

The objective of this study was to quantify copper-, bacteria- and bacteriophage-binding capacities of natural clay with the aim of predicting the adsorption of heavy metals, human pathogenic bacteria and viruses by a clayey landfill liner. X-ray diffraction analysis of six natural clays showed that the dominant phase in all deposits consists of smectites together with illite, kaolin and, sometimes, palygorskite and sepiolite. The specific surface areas of different clay substrates were very high ranging from 293 to 351 m2 g(-1), and indicating a high proportion of phyllosilicates, consisting especially of smectites. The physico-chemical identification of separated smectites showed a high potential adsorbent character indicative of a large industrial use. The Kb12 smectite substrate chosen arbitrarily among six separated substrates, appeared as an excellent copper adsorbent. Copper was adsorbed to clay in a proportion ranging from 94.6 to 96.0% with an average of 95.1% and its adsorption occurred rapidly in less than 30 min. Organic contents of the clay substrate, evaluated as 17% of dry mass, may contribute and enhance copper adsorption. Different elution protocols using distilled water, 2 and/or 5% nitric acid revealed that while nitric acid resulted in the removal of more than 59% of the metal at the lower concentration and its complete depletion with a further elution at the higher concentration, distilled water alone was unable to remove more than 1% of adsorbed copper. This finding suggested that copper ions form high-energy bonds with layer-silicate surfaces. Interestingly, the use of a regenerated substrate as copper adsorbent subsequent to abundant washings of the used substrate consecutively, with 0.1 N HNO3 and distilled water, reduced copper adsorption by approximately 14%, suggesting a slight disturbance of clay initial structure. Batch adsorption experiments with phage T7 and raw clay Kb12 showed that the tested clay substrate appeared as a relatively moderate phage adsorbent since the quantity of adsorbed phage averaged 98.2 +/- 0.88% (2 log10 retention) as measured by infectivity for Escherichia coli ATCC 11303. As shown by two types of separating procedures, natural sedimentation and a low speed centrifugation, bacteriophage particles were bound essentially to fine and not to relatively coarse particles of the clay suspension. The retention capacity of purified clay Kb12 appeared low, with average values lower than 60 and 50%, for Pseudomonas aeruginosa ATCC 15442 and Bacillus cereus ATCC 1135, respectively. A significant increase of retention, in the order of 30%, was found for both bacteria when the mixture clay-bacteria was incubated at laboratory temperature for 6 hours.

Adsorption↗

PubMed2006

Catalytic oxidation of mixed wastes containing high organic content--emission reduction and the effect of steam.

To resolve mixed organic and radioactive waste disposal problems, Lawrence Berkeley National Laboratory (LBNL) initiated a treatability study using the catalytic chemical oxidation (CCO) system to oxidize a mixed-waste stream and to confine tritium as part of LBNL's pollution prevention program. LBNL has also adopted a legal approach by seeking an equivalent waste-treatment determination for the CCO process, and by petitioning the United States Environmental Protection Agency (EPA) to delist F-coded treatment residues. The results of this study demonstrate that (1) the CCO process can treat aqueous wastes containing a broad range of organic chemicals and achieve more than 99.999% destruction efficiency; (2) greater than 99.9% trapping efficiency for tritiated water can be achieved using an emission-reduction system that also confines the vapor of hydrochloric acid or nitric acid to the liquid residue; and (3) neutralized treatment residues can be disposed of as low-level radioactive waste at a permitted facility after EPA has approved LBNL's petitions, or the tritium in the residues can be recycled. The high oxidation efficiency of the CCO process is mainly due to the optimized operating conditions of the CCO process and the combined effect of steam reforming in the oxidation cell and the catalytic oxidation of organic mixtures and CO in the Pt/Al2O3 catalyst bed.

Catalysis↗

PubMed2001

Nephrotoxicity of immunosuppressive drugs: new insight and preventive strategies.

Cyclosporine and tacrolimus reduce allograft rejection, improve allograft half-life and patient survival. Ironically, the nephrotoxicity of these agents may adversely affect allograft survival in renal transplant recipients or cause end-stage renal diseases in other solid organ and bone marrow transplant recipients. Acute dose-dependent and chronic non-dose-dependent nephrotoxicity has been reported in both transplant recipients and patients with autoimmune disorders. Preliminary evidence suggests that drug therapeutic monitoring has little value in the diagnosis or management of nephrotoxicity associated with calcineurin inhibitors. Although the exact mechanism of nephrotoxicity is not fully understood, several factors have been implicated in the pathogenesis of immunosuppressive-induced nephrotoxicity. Renal and systemic vasoconstriction, increased release of endothelin-1, decreased production of nitric acid and increased expression of TGF-beta are the major adverse pathophysiologic abnormalities of these agents. Reducing the dose of a calcineurin inhibitor, or using protocols without calcineurin inhibition may ultimately minimize the risk of drug toxicity and improve allograft and patient survival. New experiences with non-nephrotoxic agents and protocols including mycophenolate and sirolimus allow for early calcineurin inhibitor reduction or elimination without increasing the risk of allograft rejection.

Calcineurin Inhibitors↗

PubMed2001

The effect of soil acidification on atmospheric methane uptake by a Maine forest soil(1).

Soil from the zone of maximal methanotrophic activity (approximately 5-8 cm depth) in a mixed coniferous-hardwood forest consumed atmospheric methane over a wide pH range (3.5-7.5) with a broad optimum between 4.8 and 6.0. Methane uptake at native soil pH values (4.4-4.8) was only slightly less rapid than rates at optimal pH values. Addition of mineral acids to intact soil cores in pulsed applications decreased atmospheric methane consumption. The extent of inhibition varied with the type, concentration and volume of acid added: nitric acid was more inhibitory than sulfuric acid at an equivalent soil pH, and methane uptake decreased with increasing volumes and concentrations of added acid. Although ammonium chloride at 1 µmol g fresh weight (gfw) soil(-1) inhibited methane uptake, the extent of inhibition did not vary significantly with decreasing soil pH below values of 4.4.

Journal Article↗

PubMed1998

A "Green" route to adipic acid: direct oxidation of cyclohexenes with 30 percent hydrogen peroxide

Currently, the industrial production of adipic acid uses nitric acid oxidation of cyclohexanol or a cyclohexanol/cyclohexanone mixture. The nitrous oxide emission from this process measurably contributes to global warming and ozone depletion. Therefore, the development of an adipic acid production process that is less damaging to the environment is an important subject in chemical research. Cyclohexene can now be oxidized directly to colorless crystalline adipic acid with aqueous 30 percent hydrogen peroxide under organic solvent- and halide-free conditions, which could provide an ideal solution to this serious problem.

Journal Article↗

PubMed2006

Carbon nanotube based transparent conductive thin films.

Carbon nanotube (CNT) based optically transparent and electrically conductive thin films are fabricated on plastic substrates in this study. Single-walled carbon nanotubes (SWNTs) are chemically treated with a mixture of concentrated sulfuric acid and nitric acid before being dispersed in aqueous surfactant-contained solutions. SWNT thin films are prepared from the stable SWNT solutions using wet coating techniques. The 100 nm thick SWNT thin film exhibits a surface resistivity of 6 kohms/square nanometer with an average transmittance of 88% on the visible light range, which is three times better than the films prepared from the high purity as-received SWNTs.

Crystallization↗

PubMed1990

Preparation of [3H]6-nitroquipazine, a potent and selective 5-hydroxytryptamine uptake inhibitor.

The synthesis of 6-nitroquipazine, a very potent and selective 5-hydroxytryptamine (5-HT; serotonin) uptake inhibitor, labeled with tritium is described. High specific activity [3H]6-nitroquipazine could be prepared by the nitration of [3H]quipazine using a mixture of equal volumes of sulfuric acid and nitric acid. The radiochemical yield was approximately 50% based on [3H]quipazine. The radiochemical purity was more than 95% from high performance liquid chromatography(HPLC) and thin layer chromatography(TLC) determinations. [3H]6-Nitroquipazine would be a new suitable radioligand for studying 5-HT transporter complex in brain and platelets.

Quinolines↗

PubMed2003

[Determination of chloride ion in additives of concrete by flame atomic absorption spectrometry].

Flame atomic absorption spectrometry due to its high sensitivity and selectivity has been widely used for the determination of micro levels of metal elements in various materials. But this method can not be used for the determination of Cl- directly. In this paper the determination of Cl- in additives of concrete by flame atomic absorption spectrometry was studied. Adding superfluous standard solution of Ag+ to the sample solution, the results were obtained by determining the remanent content of Ag+ having reacted with Cl- quantitatively. The acidity of the sample solution and the precision were studied. The standard rate of recovery obtained was in the range of 96%-104%. By the determination of actual samples it was proved that the method features simple sample preparation, fast determination, and little interference, especially for those samples which contain micro levels of Cl-. The procedure is as follows: weight 0.05-2 g of sample, dissolve it in water and adjust the acidity with nitric acid, add proper standard solution of Ag+, and after 2 h, measure the remanent Ag+ content by atomic absorption spectrometry. A GBC902 atomic absorption spectrometry was employed.

English Abstract↗

PubMed1979

[Atomic absorption determination of mercury vapors in the air of the work environment].

The concentration of mercury vapors in air samples obtained from work-environment may be determined by atom-adsorption technique. To this end, the most appropriate air absorption speed proved to be 0,3 dm2/min through sulphuric acid solution of potassium pemanganate. Additional oxdation of samples was performed with a mixture of sulphuric acid and nitric acid in proportion 2:1. a 24 per cent rise in the height of the adsorption peaks was thus achieved, because of reduced losses.

Air Pollutants↗

PubMed1989

A newly modified isolation method of single muscle fibers--especially useful in histological, histochemical and electron microscopic studies on branched fibers.

The nitric acid muscle fiber digestion method has generally been used to determine total numbers of muscle fibers and branched fibers. However, it is not suitable for further studies because nitric acid causes protein denaturation known as the xanthoproteic reaction which make it difficult to examine the fiber types and morphology of muscle fibers. Therefore, we attempted to modify this method to preserve the morphology of muscle fibers as much as possible. Our modifications were as follows: (1) samples were immersed in ion exchanged water before nitroc acid treatment; (2) mammalian relaxing solution was used as the post- incubation solution; (3) the temperature of nitric acid was maintained at 4 degrees C; and (4) the nitric acid concentration was reduced to 10% from 15%. The samples obtained by this method were stained with phosphotungstic acid-hematoxylin and their striations were examined by a differential interference contrast method using light microscopy. The cell organella i.e. actin filaments, myosin filaments, T-tubules and mitochondria, were also examined electron microscopy. Actin and myosin filaments in these samples were also stained immunohistochemically to clarify the preservation of antigenicity. As a result, this modified method made it possible to examine actin and myosin filaments of a single muscle fiber light-microscopically and immunohistochemically and also to examine cell organella of a single muscle by electron microscopy. These results indicate that our method is useful for studies on branched muscle fibers such as stereological analysis and innervation of a single branched muscle fiber, in addition to obtaining muscle fiber numbers.

Actins↗

PubMed2005

Retinoic acid decreases nitric oxide production in endothelial cells: a role of phosphorylation of endothelial nitric oxide synthase at Ser(1179).

The effects of retinoic acid (RA) on nitric oxide (NO) production are controversial. Furthermore, it has never been studied whether these effects are mediated by direct modulation of phosphorylation of endothelial nitric oxide synthase (eNOS). Using bovine aortic endothelial cells, we found that all-trans RA (atRA) dose- and time-dependently decreased NO production without alteration in eNOS expression. This decrease was accompanied by reduction in eNOS-Ser(1179) phosphorylation. However, atRA did not alter the phosphorylation of eNOS-Ser(116) or eNOS-Thr(497). Concurrently, atRA also decreased the expressions of vascular endothelial growth factor (VEGF) and its receptor KDR/Flk-1, and Akt phosphorylation. Co-treatment with troglitazone, an activator of VEGF expression, reversed the atRA-induced reductions in eNOS-Ser(1179) phosphorylation and NO production, with concomitant restoration in VEGF expression. Direct treatment with VEGF also reversed these inhibitory effects, suggesting an important role for VEGF. Nonetheless, the RARalpha antagonist Ro 41-5253 did not block all the inhibitory effects of atRA, indicating that these inhibitory effects are not mediated by the RA response element (RARE). Thus, atRA decreases eNOS-Ser(1179) phosphorylation through a mechanism that depends on VEGF-KDR/Flk-1-mediated Akt phosphorylation but is independent of RARE, leading to reduction in NO production.

Animals↗

PubMed1999

L-Ascorbic acid potentiates nitric oxide synthesis in endothelial cells.

Ascorbic acid has been shown to enhance impaired endothelium-dependent vasodilation in patients with atherosclerosis by a mechanism that is thought to involve protection of nitric oxide (NO) from inactivation by free oxygen radicals. The present study in human endothelial cells from umbilical veins and coronary arteries investigates whether L-ascorbic acid additionally affects cellular NO synthesis. Endothelial cells were incubated for 24 h with 0.1-100 microM ascorbic acid and were subsequently stimulated for 15 min with ionomycin (2 microM) or thrombin (1 unit/ml) in the absence of extracellular ascorbate. Ascorbate pretreatment led to a 3-fold increase of the cellular production of NO measured as the formation of its co-product citrulline and as the accumulation of its effector molecule cGMP. The effect was saturated at 100 microM and followed a similar kinetics as seen for the uptake of ascorbate into the cells. The investigation of the precursor molecule L-gulonolactone and of different ascorbic acid derivatives suggests that the enediol structure of ascorbate is essential for its effect on NO synthesis. Ascorbic acid did not induce the expression of the NO synthase (NOS) protein nor enhance the uptake of the NOS substrate L-arginine into endothelial cells. The ascorbic acid effect was minimal when the citrulline formation was measured in cell lysates from ascorbate-pretreated cells in the presence of known cofactors for NOS activity. However, when the cofactor tetrahydrobiopterin was omitted from the assay, a similar potentiating effect of ascorbate pretreatment as seen in intact cells was demonstrated, suggesting that ascorbic acid may either enhance the availability of tetrahydrobiopterin or increase its affinity for the endothelial NOS. Our data suggest that intracellular ascorbic acid enhances NO synthesis in endothelial cells and that this may explain, in part, the beneficial vascular effects of ascorbic acid.

Antioxidants↗

PubMed1982

Synthetic byproducts of tocopherol oxidation as inhibitors of platelet function.

Vitamin E and its fully oxidized form tocopherol quinone are known inhibitors of platelet aggregation. Previous results from our laboratory have shown that the quinone was approximately equal in effectiveness to vitamin E. A recent report of a far greater inhibitory activity of the quinone produced by nitric acid oxidation of vitamin E prompted this investigation. Our studies show that the unusually high inhibition of platelet aggregation, release and cyclooxygenase activity associated with nitric acid oxidized vitamin E is due to byproducts of the oxidation process and not due to tocopherol quinone. Treatment of vitamin E acetate, a substance of mild effect on aggregation and arachidonate metabolism of platelets, with nitric acid did not produce tocopherol quinone but exerted as potent an inhibition as oxidized vitamin E. We conclude that nitric acid oxidation is unsuitable for preparation of tocopherol quinone unless the latter is carefully isolated. Oxidation with permanganate proved to be an alternate method without these difficulties.

Arachidonic Acid↗

PubMed1995

Interaction of 5-aminosalicylic acid with nitric oxide on rat aortic strips and human platelets.

We have examined the interactions of 5-aminosalicylic acid with nitric oxide (NO). Phenylephrine-precontracted rat aortic strips with intact endothelium were further contracted by 5-aminosalicylic acid (50-200 microM) in a concentration-dependent manner. Removal of endothelium, inhibition of guanylate cyclase by methylene blue, inhibition of NO biosynthesis by NG-nitro-L-arginine as well as in inactivation of NO by oxyhemoglobin abolished the effect of 5-aminosalicylic acid. The antiaggregatory effects of 3-morpholinosydnonimine and rat peritoneal neutrophils, which are due to release of NO, were diminished in a concentration-dependent manner by 5-aminosalicylic acid (50-250 microM). In both experimental models the effects of 5-aminosalicylic acid were significantly reduced by superoxide dismutase in a concentration which alone exhibited no effect. Since NO might act as a cytotoxic and vasodilating mediator, our results suggest that inactivation of NO by 5-aminosalicylic acid could contribute to the therapeutic activity of the drug in inflammatory bowel disease.

Aminosalicylic Acids↗

PubMed2005

Burial of gas-phase HNO(3) by growing ice surfaces under tropospheric conditions.

The uptake of gas-phase nitric acid by ice surfaces undergoing growth by vapor deposition has been performed for the first time under conditions of the free troposphere. The investigation was performed using a coated-wall flow tube coupled to a chemical ionization mass spectrometer, at nitric acid partial pressures between 10(-7) and 10(-6) hPa, at 214, 229 and 239 K. Ice surfaces were prepared as smooth ice films from ultra-pure water. During the experiments an excess flow of water vapor was added to the carrier gas flow and the existing ice surfaces grew by depositing water vapor. The average growth rates ranged from 0.7-5 microm min(-1), values similar to those which prevail in some portions of the atmosphere. With growing ice the long term uptake of nitric acid is significantly enhanced compared to an experiment performed at equilibrium, i.e. at 100% relative humidity (RH) with respect to ice. The fraction of HNO(3) that is deposited onto the growing ice surface is independent of the growth rate and may be driven by the solubility of the nitric acid in the growing ice film rather than by condensation kinetics alone.

Atmosphere↗

PubMed1989

Effects of inhalation of acidic compounds on pulmonary function in allergic adolescent subjects.

There is concern about the human health effects of inhalation of acid compounds found in urban air pollution. It was the purpose of this study to investigate three of these acid compounds, sulfur dioxide (SO2), sulfuric acid (H2SO4), and nitric acid (HNO3) in a group of allergic adolescent subjects. Subjects were exposed during rest and moderate exercise to 0.7 mumole/m3 (68 micrograms/m3) H2SO4, 4.0 mumole/m3 (0.1 ppm) SO2, or 2.0 mumole/m3 (0.05 ppm) HNO3. Pulmonary functions (FEV1, total respiratory resistance, and maximal flow) were measured before and after exposure. Preliminary analysis based on nine subjects indicates that exposure to 0.7 mumole/m3 H2SO4 alone and in combination with SO2 caused significant changes in pulmonary function, whereas exposure to air or SO2 alone did not. FEV1 decreased an average of 6% after exposure to H2SO4 alone and 4% when the aerosol was combined with SO2. The FEV1 decrease was 2% after both air and SO2 exposures. Total respiratory resistance (RT) increased 15% after the combined H2SO4 exposures, 12% after H2SO4 alone, and 7% after exposure to air. After exposures to HNO3 alone, FEV1 decreased by 4%, and RT increased by 23%. These results are preliminary; final conclusions must wait for completion of the study.

Acid Rain↗