Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The toxic action of nitrates and nitrites has often been summarized by methemoglobinemia and nitrosation of amines inducing carcinogenic effects; these two impacts are spectacular, but they hide varying more or less insidious actions recently studied and perceived. In the NO3/NO2 couple, it is accepted that especially nitrite ion lays down a toxicological problem, probably because of its particular chemical reactivity: nitrite ion, which is the base of nitrous acid HNO2 (pKa = 3.36) can react with many functional groups from dietary or endogenous origin; it is also a reducing agent, only oxidable by chemical oxidants or adequate enzyme systems; at the same time it is an oxidant for many reduced substrates. These different possibilities explain the chemical complexity of these compounds and almost their reactivity in biological various media with toxicological implications (modification of the redox state). In man, the presence of nitrates in the digestive tract may result in nitrite formation, because nitrate-reductase from bacterial or enterocyte origin; more particularly in stomach, nitrites are characterized by a great instability imputable to the low pH of gastric juice and to secreted factors which accelerate phenomena; at the same time, nitrates and nutrites exercise opposite effects on gastric secretion (volume, acidity, pepsin) and on gastric mucosal irrigation: while nitrates increase these different parameters, nitrites reduce secretory activity but correlations between secretion and irrigation show that nitrates induce a deep modification of hydric compartment whereas nitrites rather react through cellular anoxy. In intestine, nitrates and chiefly nitrites are very quickly absorbed by a passive mechanism and they are characterized by an extrahepatic cycle; nitrates and nitrites are also eliminated in large quantities by kidneys, and nitrates have a very high diuretic effect: these NO3- ions move Cl- ions, inducing a Na+ waste, a decrease in extracellular space and an alkalosis; this diuretic action of ionic origin is moreover increased by a rise in glomerular blood flow facilitating filtration; these compounds therefore present vasomotor effects, probably by an action on catecholamines whose metabolism is modified. Last, nitrates are suspected to be responsible for reproduction troubles, thyroid dysfunction, perturbances of vitamins availability and nutritional effects. Most of the impacts of nitrates and nitrites are now well known, but their cellular of molecular action is not clear, and as a result there is a suspicion in regard to these products very widely present in food.
 ...
PMID:[Toxicologic and nutritional aspects of nitrates and nitrites]. 702 May 46

Air pollution measurements were conducted over a 1-year period in 24 North American communities participating in a respiratory health study. Ozone, particle strong acidity, sulfate, and mass (PM10 and PM2.1) were measured in all communities. In 20 of the communities, sulfur dioxide, ammonia, nitric acid, nitrous acid, and particulate nitrate were measured. The sampler was located centrally in the community whenever possible and samples were collected every other day. Concentrations of particle strong acidity, mass, sulfate, and ozone were highly correlated both in the region of the country defined as a high-sulfur source area and in the downwind transport regions. These regions of the eastern United States and southern Canada experienced the greatest particle strong acidity, sulfate, and particle mass concentrations during the spring and summer months (May-September). The particle strong acidity concentrations were highest in regions close to the high sulfur emission areas of the United States; that is, in the area immediately to the west of the Appalachian Plateau and west of the Allegheny Mountains (western Pennsylvania, eastern Ohio, and West Virginia) up through southern Ontario. The frequency of particle strong acidity events decreased with transport distance from the region of highest sulfur emissions. Low particle strong acidity and sulfates were found at the western and midwestern sites of both the United States and Canada. Substantial concentrations of nitric acid were found in two of the California sites as well as many sites in the northeastern portion of the United States. Sites selected for the epidemiologic study provide a range of annual mean particle strong acidity exposures from below the limit of detection to more than 50 nmol/m3.
 ...
PMID:Health effects of acid aerosols on North American children: air pollution exposures. 874 36

Twenty-four-hour samples of PM10 (mass of particles with aerodynamic diameter < or = 10 microm), PM2.5, (mass of particles with aerodynamic diameter < or = 2.5 microm), particle strong acidity (H+), sulfate (SO42-), nitrate (NO3-), ammonia (NH3), nitrous acid (HONO), and sulfur dioxide were collected inside and outside of 281 homes during winter and summer periods. Measurements were also conducted during summer periods at a regional site. A total of 58 homes of nonsmokers were sampled during the summer periods and 223 homes were sampled during the winter periods. Seventy-four of the homes sampled during the winter reported the use of a kerosene heater. All homes sampled in the summer were located in southwest Virginia. All but 20 homes sampled in the winter were also located in southwest Virginia; the remainder of the homes were located in Connecticut. For homes without tobacco combustion, the regional air monitoring site (Vinton, VA) appeared to provide a reasonable estimate of concentrations of PM2.5 and SO42- during summer months outside and inside homes within the region, even when a substantial number of the homes used air conditioning. Average indoor/outdoor ratios for PM2.5 and SO42- during the summer period were 1.03 +/- 0.71 and 0.74 +/- 0.53, respectively. The indoor/outdoor mean ratio for sulfate suggests that on average approximately 75% of the fine aerosol indoors during the summer is associated with outdoor sources. Kerosene heater use during the winter months, in the absence of tobacco combustion, results in substantial increases in indoor concentrations of PM2.5, SO42-, and possibly H+, as compared to homes without kerosene heaters. During their use, we estimated that kerosene heaters added, on average, approximately 40 microg/m3 of PM2.5 and 15 microg/m3 of SO42- to background residential levels of 18 and 2 microg/m3, respectively. Results from using sulfuric acid-doped Teflon (E.I. Du Pont de Nemours & Co., Wilmington, DE) filters in homes with kerosene heaters suggest that acid particle concentrations may be substantially higher than those measured because of acid neutralization by ammonia. During the summer and winter periods indoor concentrations of ammonia are an order of magnitude higher indoors than outdoors and appear to result in lower indoor acid particle concentrations. Nitrous acid levels are higher indoors than outdoors during both winter and summer and are substantially higher in homes with unvented combustion sources.
 ...
PMID:Indoor, outdoor, and regional summer and winter concentrations of PM10, PM2.5, SO4(2)-, H+, NH4+, NO3-, NH3, and nitrous acid in homes with and without kerosene space heaters. 1006 53

The rate of reduction of nitrite by trimethylamine-borane was followed by observing the decrease in nitrite absorbance under pseudo-first-order conditions. The reaction is acid-catalyzed and exhibits a first-order dependence on both amine-borane and total nitrite concentration. The molar equivalence of NaNO(2) to (CH(3))(3)NBH(3) = 2:1. Equimolar amounts of hydrogen and nitrous oxide are formed, and the molar ratio of nitrite reacted to N(2)O produced is 2:1. In concentrated HCl or H(2)SO(4), a correlation of rate with the Hammett acidity function, h(o), is observed. The reaction is subject to a pronounced inversesolvent isotope effect (k(D)()2(O)/k(H)()2(O) approximately 2.7) and a modest normal substrate effect (k((CH)()3())()3(N.BH)()3/k((CH)()3())()3(N.BD)()3 approximately 1.4). The reaction is first-order in H(3)O(+) in the region pH 0.7-2.7, but a second-order dependence is observed above pH 4 with the transition occurring at pH approximately pK(a) for HNO(2). Results are consistent with a mechanistic model involving preequilibration protonation of molecular nitrous acid followed by rate-limiting hydride attack on H(2)ONO(+) or free NO(+) to produce nitrosyl hydride as a reactive intermediate.
 ...
PMID:Acid-Catalyzed Amine-Borane Reduction of Nitrite. 1166 11

The regioselectivity of the nitrous acid mediated dealkylation of 4-substituted-N-ethyl-N-methylanilines is a function of the acidity of the reaction mixture. At high acidity deethylation predominates, whereas demethylation is the predominant reaction in nitrosamine formation at pH 2 and above. In some cases the regioselectivity of nitrosative dealkylation changes as the run proceeds. Through the use of the corresponding 4-nitroaniline as the primary substrate, CIDNP, kinetics, kinetic deuterium isotope effects and other transformations involving nitrosations with NO2 or NOBF4 in aprotic solvents, a new mechanism of tertiary amine nitrosation has been deduced and proposed to explain regioselective deethylation. The mechanism involves the oxidation of the substrate to the amine radical cation by NO+. This is followed by the abstraction of a hydrogen atom from the carbon adjacent to the amine nitrogen by NO2 to produce an iminium ion which reacts further to produce the corresponding aldehyde and the nitrosamine. Depending upon the acidity, this process competes with three other mechanistic pathways, two of which give the nitrosamine through the iminium ion, and one leads to the formation of C-nitro compounds. The competing pathways to nitrosamine formation involve NOH elimination from a nitrosammonium ion and deprotonation of the radical cation to give an alpha-amino radical which rapidly oxidized to the iminium ion. Predominant, but not highly regioselective demethylation occurs by these pathways. Nitro compound formation principally arises from the reaction of NO2 with the radical cation followed by deprotonation, but also occurs by para C-nitrosation followed by oxidation.
 ...
PMID:The mechanistic origin of regiochemical changes in the nitrosative N-dealkylation of N,N-dialkyl aromatic amines. 1575 Jun 54

Using negative absorption rectifyingtechniquie, the authors investigated spectra of the reaction of nitrite with acridine yellow in 1.0 mol x dm(-3) (1 dm = 10 cm = 0.1 m) hydrochloric medium. The authors established the new dynamics method of mensuratiog trace nitrous acid radical by the negative absorption undertint spectrophotometry at multi-wavelengths, based on the linear relation between the negative absorbance value or the AT value of absorbance sum and the nitrous acid radical concetration in a certain range. The linear range was 7.2 x 10(-6) -3.6 x 10(-4) mol x dm(-3), RSD was 1.06%-3.12%, and CV (recovery) was 98.00%-100.20%. In application to the determination of nitrite in environmental water sample, satisfactory result was abtained with high accuracy, better selectivity and common ions ceasing to effect measuring. According to the change in the absorption peak value in the reactive system,the liquor acidity, the different order for added reagent, liquor temperature, reactive time, acid kind etc., the authors believe that the reaction of acridine yellow with mitrite is diazotization-coupling, under the condition of feasible pH value, temperature, and additive order of midium.
 ...
PMID:[Multi-wavelength negative absorption fading spectrophotometry to determine trace nitrite and it's mechanism]. 1639 10

Mucoid, mucA mutant Pseudomonas aeruginosa cause chronic lung infections in cystic fibrosis (CF) patients and are refractory to phagocytosis and antibiotics. Here we show that mucoid bacteria perish during anaerobic exposure to 15 mM nitrite (NO2) at pH 6.5, which mimics CF airway mucus. Killing required a pH lower than 7, implicating formation of nitrous acid (HNO2) and NO, that adds NO equivalents to cellular molecules. Eighty-seven percent of CF isolates possessed mucA mutations and were killed by HNO2 (3-log reduction in 4 days). Furthermore, antibiotic-resistant strains determined were also equally sensitive to HNO2. More importantly, HNO2 killed mucoid bacteria (a) in anaerobic biofilms; (b) in vitro in ultrasupernatants of airway secretions derived from explanted CF patient lungs; and (c) in mouse lungs in vivo in a pH-dependent fashion, with no organisms remaining after daily exposure to HNO2 for 16 days. HNO2 at these levels of acidity and NO2 also had no adverse effects on cultured human airway epithelia in vitro. In summary, selective killing by HNO2 may provide novel insights into the important clinical goal of eradicating mucoid P. aeruginosa from the CF airways.
 ...
PMID:Anaerobic killing of mucoid Pseudomonas aeruginosa by acidified nitrite derivatives under cystic fibrosis airway conditions. 1644 61

We present an ab initio procedure for accurately calculating aqueous-phase pKa values and apply it to study the acidity of nitrous acid (HNO2, or HONO). The aqueous-phase pK(a) of nitrous acid was obtained from calculated gas-phase acidities and solvation free energies via a thermodynamic cycle and the solvation model chemistry of Barone et al. (J. Chem. Phys. 1997, 107, 3210). Solvation free energies were calculated at the HF/6-31G(d) level using the dielectric-polarizable continuum and the integral equation formalism-polarizable continuum solvent models (D-PCM and IEF-PCM, respectively), with the D-PCM model yielding the most accurate pKa values. For HF free energies of solvation, significant improvements in accuracy could be made by moving to the larger 6-311++G(3df,3pd) and aug-cc-pVQZ basis sets. Solvation free energies were also calculated using the density functional theory (DFT) methods B3LYP, TPSS, PBE0, B1B95, VSXC, B98 and O3LYP, with the most accurate methods being TPSS and VSXC, which provided average errors of less than 0.11 pKa units. Solvation free energies calculated with the different DFT methods were relatively insensitive to the basis set used. Our theoretical calculations are compared with experimental results obtained using stopped flow spectrophotometry. The pKa of nitrous acid was measured as 3.16 at 25 degrees C, and the enthalpy and entropy of nitrous acid dissociation were calculated from measurements as 6.7 kJ mol(-1) and -38.4 J mol(-1) K(-1), respectively, between 25 and 45 degrees C. The UV/visible absorption spectra of the nitrite ion and nitrous acid were also examined, and molar extinction coefficients were obtained for each.
 ...
PMID:Ab initio procedure for aqueous-phase pKa calculation: the acidity of nitrous acid. 1700 48

Direct titration of nitrite with cerium (IV), with ferroin as indicator, is shown to give satisfactory results if the acidity is kept between 0.033 and 0.055M at the end-point. Loss of nitrous acid owing to volatilization and decomposition is discussed. From 10 to 60 mg of sodium nitrite can be estimated with a standard deviation of 5 mug and an average error of 0.2%.
 ...
PMID:Some observations concerning the direct titration of nitrite with cerium(IV). 1896 11

With a glass electrode filled with mercury as indicator electrode for hydrogen ions, the acidity constant of nitric acid and the stability constants of the complexes HA(-)(2) (A Cl(-), NO(-)(3)) in sulpholane at 303 K have been determined potentiometrically. The acidity constant of nitrous acid has also been determined in supholane medium because of the low stability of this acid in aprotic media. On the basis of the results, some aspects of the electrochemical and thermodynamic properties of oxygen-nitrogen compounds are discussed in order to explain the catalytic effect of NO(+) in aromatic nitration by N(2)O(4) and/or N(2)O(3) in aprotic solvents.
 ...
PMID:Chemical and electrochemical behaviour of nitric and nitrous acids in sulpholane. 1896 96


1 2 Next >>