Nitrite

Résumé

L'ion nitrite est la base conjuguée de l'acide nitreux. L'acide nitreux est un acide faible instable de formule HNO. La formule de l'ion nitrite est NO2−. Confusions possibles Il ne faut pas confondre l'ion nitrite avec le dioxyde d'azote auquel il ressemble beaucoup par la structure chimique, mais qui est une molécule, et donc de charge électrique neutre. Toxicité Dans les cours d'eau, notamment canalisés, et dans les régions densément habitées ou d'agriculture intensive, les nitrites (ou bien les nitrates) sont souvent une source de pollution. Chez l'humain et autres mammifères, la présence de nitrites dans le sang empêche l'hémoglobine de fixer convenablement l'oxygène. C'est l'une des causes de la « maladie bleue du nourrisson », plus savamment appelée « méthémoglobinémie » . En , trois enfants en sont morts en Chine. C'est pourquoi la teneur en nitrites dans l'eau potable est réglementée (notamment pour la préparation des biberons) et, indirectement

Source officielle

https://fr.wikipedia.org/wiki/Nitrite

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Reduction of nitrite-ions in water over Pd-supported on structured fibrous materials

Volker Höller, Lioubov Kiwi, Albert Renken

Catalytic hydrogenation of NO2- in water to N2 over Pd-supported on different woven fibrous materials was studied. Low porosity C fiber, low porosity D-type glass fiber, and composite (glass covered by g-Al2O3) fiber were used. Pd dispersion was compared for different supports at various Pd loadings and correlated with catalytic activity. NH3 as an undesired byproduct was also obsd. and main parameters to suppress its formation are discussed. A reactor concept based on woven fibrous catalysts is suggested and main design parameters for tech. application were estd. [on SciFinder (R)]

2001

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Structured multiphase reactors based on fibrous catalysts: nitrite hydrogenation as a case study

Volker Höller, Lioubov Kiwi, Albert Renken

A reactor concept designed as a bubble column staged with fibrous catalytic layers is tested on pilot-scale for the redn. of nitrite to N by H. CO2 is used to neutralize the hydroxide ions produced during hydrogenation of nitrite. The effective reaction rate was found to depend on the superficial gas velocity ug0. The fibrous catalysts demonstrated a high selectivity towards nitrogen. The influence of the mass transport on the effective kinetics is discussed and the volumetric liq.-solid mass transfer coeff. kSaS is estd. as a function of the superficial gas velocity ug0. The selectivity was found to be independent of the hydrodynamics.

Elsevier2001

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, ,

Tyrosine nitration, often observed during neurodegenerative disorders under nitrative stress, is usually considered to be induced chemically either by nitric oxide and oxygen forming nitrogen dioxide or by the decomposition of peroxynitrite. It can also be induced enzymatically by peroxidases or superoxide dismutases in the presence of both hydrogen peroxide and nitrite forming nitrogen dioxide and/or peroxynitrite. In this study, the role of cupric ions for catalyzing tyrosine nitration in the presence of hydrogen peroxide and nitrite, by a chemical mechanism rather similar to enzymatic pathways where nitrite is oxidized to form nitrogen dioxide, was investigated by development of a microreactor also capable of acting as an emitter for electrospray ionization mass spectrometry analysis. Indeed, cupric ions and peptide–cupric ion complexes are found to be excellent Fenton catalysts, even better than Fe(III) or heme, for the formation of •OH radicals and/or copper(II)-bound •OH radicals from hydrogen peroxide. These radicals are efficiently scavenged by nitrite anions to form •NO2 and by tyrosine to form tyrosine radicals, leading to tyrosine nitration in polypeptides. We also show that cupric ions can catalyze tyrosine nitration from nitric oxide, oxygen, and hydrogen peroxide as the formation of tyrosine radicals is increased in the presence of diffusible and/or copper(II) bound hydroxyl radicals. This study shows that copper has a polyvalent role in the processes of tyrosine nitration.

2011

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