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At least 181 records · Page 10Linked to original sources
PubMed2006

Theoretical study of stratospheric relevant anions: nitrate-nitric acid complexes.

The ion complexes NO3-(HNO3)n, n = 1-3, have been studied by means of ab initio calculations at the B3LYP/aug-cc-pVTZ level of theory. These systems are the most abundant anionic clusters below approximately 30 km altitude in the stratosphere and also in the upper troposphere. These complexes display short strong hydrogen bonds, which should be considered to explain their abundance in the atmosphere. Equilibrium geometries, harmonic frequencies, relative energies, and thermochemical data have been calculated for these anions for the first time. The calculations indicate small differences of energy in the variation of the two nitrate groups from planarity to an almost perpendicular form for n = 1. Planar geometries are found for n = 2 and 3 to give rise to a highly symmetric C(3h) NO3-(HNO3)3. In all the cases, binding energies close to those of covalent compounds are estimated. When experimental data are available, good correlations are found with our results.

Anions↗
PubMed2005

Surface modification of starch based blends using potassium permanganate-nitric acid system and its effect on the adhesion and proliferation of osteoblast-like cells.

The surface modification of three starch based polymeric biomaterials, using a KMnO4/HNO3 oxidizing system, and the effect of that modification on the osteoblastic cell adhesion has been investigated. The rationale of this work is as follows--starch based polymers have been proposed for use as tissue engineering scaffolds in several publications. It is known that in biodegradable systems it is quite difficult to have both cell adhesion and proliferation. Starch based polymers have shown to perform better than poly-lactic acid based materials but there is still room for improvement. This particular work is aimed at enhancing cell adhesion and proliferation on the surface of several starch based polymer blends that are being proposed as tissue engineering scaffolds. The surface of the polymeric biomaterials was chemically modified using a KMnO4/HNO3 system. This treatment resulted in more hydrophilic surfaces, which was confirmed by contact angle measurements. The effect of the treatment on the bioactivity of the surface modified biomaterials was also studied. The bioactivity tests, performed in simulated body fluid after biomimetic coating, showed that a dense film of calcium phosphate was formed after 30 days. Finally, human osteoblast-like cells were cultured on unmodified (control) and modified materials in order to observe the effect of the presence of higher numbers of polar groups on the adhesion and proliferation of those cells. Two of the modified polymers presented changes in the adhesion behavior and a significant increase in the proliferation rate kinetics when compared to the unmodified controls.

Body Fluids↗
PubMed2003

Effects of changes in sulfate, ammonia, and nitric acid on particulate nitrate concentrations in the southeastern United States.

A thermodynamic equilibrium model, Simulating Composition of Atmospheric Particles at Equilibrium (SCAPE2), was used to investigate the response of fine particulate NO3(-) to changes in concentrations of HNO3, NH3, and SO4(2-) in the southeastern United States. The data consisted of daily, 24-hr time resolution measurements from the Aerosol Research Inhalation Epidemiology Study (ARIES) Jefferson Street (Atlanta) site and five other sites of the Southeastern Aerosol Research and Characterization Project (SEARCH). Reductions of total NH3 (gas-phase NH3 plus particulate NH4(+)), total NO3(-) (HNO3 plus particulate NO3(-)), SO4(2-), or combined total NO3(-) (HNO3 plus particulate NO3(-)) with SO4(2-) were used to estimate the effects of changing emission levels. The conversion of SO2 to SO4(2-) and NO2 to HNO3 involves additional nonlinear reactions not incorporated into the model. For all sites, fine particulate NO3(-) concentrations decreased in response to reductions of either NH3 or total NO3(-), but the particulate NO3(-) decreases were greater for the NH3 reductions than for the total NO3(-) reductions. Particulate NO3(-) concentrations increased in response to reductions of SO4(2-). For the combined reduction (total NO3(-) plus SO4(2-)), the resulting particulate NO3(-) concentrations were on average no different than the base-case NO3(-) levels. Measurements of fine particulate NO3(-) and HNO3 support the modeling conclusions and indicate that particulate NO3(-) formation is limited by the availability of NH3 at most times at all SEARCH sites.

Air Pollutants↗
PubMedDate not supplied

Nitric acid passivation does not affect in vitro biocompatibility of titanium.

PURPOSE: In general, both chemical composition and surface features of implants affect cell response. The aim of this study was to evaluate the effect of titanium (Ti) passivation on the response of rat bone marrow cells, considering cell attachment, cell morphology, cell proliferation, total protein content, alkaline phosphatase (ALP) activity, and bonelike nodule formation. MATERIALS AND METHODS: Cells were cultured on both commercially pure titanium (cpTi) and titanium-aluminium-vanadium alloy (Ti-6Al-4V) discs, either passivated or not. For attachment evaluation, cells were cultured for 4 and 24 hours. Cell morphology was evaluated after 4 days. After 7, 14, and 21 days, cell proliferation, total protein content, and ALP activity were evaluated. Bonelike nodule formation was evaluated after 21 days. Data were compared by analysis of variance and the Duncan multiple range test. RESULTS: Cell attachment, cell morphology, cell proliferation, total protein content, ALP activity, and bonelike nodule formation all were unaffected by Ti composition or passivation. DISCUSSION AND CONCLUSION: Although the protocol for passivation used here could interfere with the pattern of ions released from Ti-6Al-4V and cpTi surfaces, the present study did not show any effect of this surface treatment on in vitro biocompatibility of Ti as evaluated by osteoblast attachment, proliferation, and differentiation.

Alkaline Phosphatase↗
PubMed2004

Atmospheric concentrations of sulfur dioxide, nitrogen oxides, ammonia, hydrogen chloride, nitric acid, formic and acetic acids in the south of Vietnam measured by the passive sampling method.

A passive sampling method was applied to measure the concentrations of air pollutants, such as sulfur dioxide, nitrogen oxides, ammonia, hydrogen chloride, and nitric, formic and acetic acids, in the ambient air at four test sites in the southern region of Vietnam. The monthly averages and the average concentrations of air pollutants during the period from July 2001 to September 2002 are reported here. The concentrations of air pollutants varied widely, depending on the test sites and the sampling periods. The average concentrations of sulfur dioxide in the air during the period from July 2001 to September 2002 at the four test sites were 3.3-16.9 ppb, and those of nitrogen dioxide were 5.4-12.8 ppb. The concentrations of nitrogen monoxide and hydrogen chloride were very low at all of the test sites. The observed concentrations of all of the above-mentioned pollutants were lower than those of the Vietnamese standards of air pollutants.

Journal Article↗
PubMed1997

[Immunocytochemical demonstration of nitric acid synthase in rat pancreatic tissue].

To investigate the age-related alterations of pancreatic distribution of nitric oxide synthase in rats, we applied light microscopic immunocytochemistry. Tissue samples were obtained from the pancreata of 5-day-old rat newborns and 120-day-old adult rats and processed for immunocytochemistry using anti neuronal nitric oxide synthase primary serum with the avidin-biotin-streptavidin complex method. Nitric oxide synthase immunopositive intrinsic nerve cells and perivascular/periacinar nerve fibers could be seen in both the newborn and the adult rat pancreas. In addition to the labelled neuronal structures we detected some immunoreactive acinar cells in the newborns, while the neonatal ductal epithelium and the islet cells were immunonegative. Strong staining for nitric oxide synthase was observed in the adult ductal epithelial cells and moderate positivity was displayed by the adult islet cells. The localization of nitric oxide shows age-related changes mainly in the non-neuronal structures of the rat pancreas: these findings could form the morphological base of pancreatic dysfunctions in the aged.

Animals↗
PubMedDate not supplied

Inhibition of N-methyl-D-aspartic acid-nitric oxide synthase in rat hippocampal slices by ethanol. Evidence for the involvement of tetrahydrobiopterin but not lipid peroxidation.

The ionotropic glutamatergic receptor system, especially the subtype mediated by N-methyl-D-aspartic acid (NMDA), is known to exhibit special sensitivity to the effect of ethanol. This is due partly to the ability of ethanol to modulate the production of nitric oxide through the NMDA-nitric oxide synthase (NOS) pathway. In this study, we examined the effects of ethanol on basal and NMDA-stimulated NOS activity in rat hippocampal slices by measuring the conversion of [(14)C]-arginine into [(14)C]-citrulline in an incubation system containing the necessary cofactors. Stimulation of hippocampal slices with NMDA (100 microM) enhanced NOS activity by 43% (n = 12). Although ethanol did not alter NOS activity when added to the incubation system during NMDA stimulation, it dose-dependently inhibited NMDA-NOS activity when added to the slices during the 90-min preincubation period. Further assay of NOS activity with brain cytosolic fraction indicated an inhibitory effect of ethanol (200 mM) when the assay was carried out in the absence of exogenous tetrahydrobiopterin (BH4), a redox-active cofactor for NOS. Incubation of brain homogenates resulted in a time-dependent increase in the levels of lipid peroxidation products, but ethanol did not further enhance these products. Taken together, these results provide evidence for the role of BH4 but not oxidative stress in the inhibitory effect of ethanol on NMDA-NOS activity in rat hippocampal slices.

Animals↗
PubMed2003

Abscisic acid, nitric oxide and stomatal closure - is nitrate reductase one of the missing links?

Once plant endogenous nitric oxide (NO) production had been proved, NO research was directed toward both the source and the targets of this extremely bioactive molecule. As in mammals, plant NO was first thought to be generated mainly by a NO synthase-like enzymatic activity. However, nitrate reductase (NR)-dependent NO production is now receiving much of the attention because of the ubiquity of this enzyme in higher plant tissues and the precise regulation of its NO-production activity. NO has been reported to be a signal in many and diverse physiological processes, such as growth and biotic and abiotic stresses. Recently, NO has been shown to affect stomatal closure and interact with abscisic acid signaling pathways. We propose NR as a putative component in the signaling cascade of ABA-induced stomatal closure.

Abscisic Acid↗
PubMed2003

Influence of chloride and sediment matrix on the extractability of HgS (cinnabar and metacinnabar) by nitric acid.

The extractability of metacinnabar and cinnabar, alone or in the presence of some sediment components, with various concentrations of HNO3 (1, 4, 6, and 14 M) was studied. Both forms of HgS (0.2-0.3 mg HgS in 10-20 mL of acid) were insoluble in all HNO3 concentrations as pure compounds. The presence of FeCl3 enhanced solubility of both cinnabar and metacinnabar, especially when concentrated HNO3 was used for the extraction. As the same effect was not obtained in the presence of FeOOH, we concluded that chloride and not Fe3+ was responsible for HgS dissolution. In fact, addition of very low chloride concentration to concentrated HNO3 provoked partial (Cl>10(-4) M) or even total dissolution (Cl>10(-2) M) of HgS. In dilute HNO3 (4-6 M) cinnabar was much less affected by chloride addition than metacinnabar. Extraction of HgS by concentrated HNO3 in the presence of sediment of various salinities demonstrated that the amount of dissolved HgS increased with the increase of the sediment salinity (from freshwater to estuarine and marine sediment), confirming that chloride enhances dissolution of HgS. Removal of chloride by washing the sediment with Milli-Q water significantly reduced dissolution of added HgS during extraction by concentrated HNO3. These results demonstrate that conclusions based on the extraction schemes using concentrated HNO3 as single extractant or as the first extractant in the sequential extraction procedures can be biased. A verification of artifactual oxidation of HgS, when using more concentrated HNO3 as extractant, would help to verify reliability of the applied extraction procedure.

Journal Article↗
PubMed1980

Corrosive jejunitis due to ingestion of nitric acid.

Corrosive damage to the small bowel is not common; stasis of acid in the stomach usually prevents extensive jejunal damage. The case presented herein is unusual because the patient had a gastroenterostomy and sustained extensive injury of the jejunum after ingesting acid. The patient survived but developed a jejunal stricture that eventually required resection.

Anti-Bacterial Agents↗
PubMed1989

Dry deposition of sulfur dioxide or nitric acid to oak, elm and pine leaves.

To improve our knowledge of atmospheric inputs to forests, experiments were performed in the field to measure the dry deposition of SO2 and HNO3 to oak, elm, and pine leaves. A tree branch was enclosed in a Teflon chamber, through which SO2 or HNO3 flowed. The dry deposition characteristics of SO2 and HNO3 were very different. The SO2 deposition occurred primarily through stomatal openings for the oak and pine leaves, and equal stomatal and cuticular deposition was observed for the elm leaves. The deposited SO2 could not be removed from the branch by extracting in water or by revolatilization. In contrast, over 90% of HNO3 dry deposition occurred to the cuticle. Most of the deposited HNO3 could be extracted from the leaves. Revolatilization of HNO3 was negligible from an active branch, but increased from a dormant or detached branch. A deposition velocity was derived from the ratio of the flux of the gas to the leaves and the gas concentration in the chamber. Deposition velocities ranged from 0.02 to 0.11 cm s(-1) for SO2 and from 0.2 to 1.2 cm s(-1) for HNO3 to individual leaf surfaces.

Journal Article↗