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‣ Gas-Phase Nucleophilic and Elimination Reactions in Simple Alkyl Nitrates

CORRERA, Thiago C.; RIVEROS, Jose M.
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
Português
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There has been increasing interest in the gas-phase reactivity of alkyl nitrates because of their well-known applications as explosives and because of then role in atmospheric and in marine processes This manuscript describes an experimental study by FT-ICR techniques of the gas-phase reactions of OH(-) and F(-) with methyl and ethyl Innate For methyl nitrate, the main reaction channel is found to be an elimination process promoted by abstraction of an a proton from the methyl group. Nucleophilic displacement of nitrate anion through an S(N)2 process at the carbon center Is also found to he an important reaction channel with methyl nitrate In ethyl nitrate, Ruination of NO(3)(-) is greatly enhanced and this is attributed to the ease of an E2-type elimination process promoted by proton abstraction at the beta position of the ethyl group. Theoretical calculations at the MP2/6-311+G(3df,2p)//MP2/6-31+G(d) level of theory ale consistent with the relative importance of the reaction channels and suggest that these reactions proceed through a double well potential The calculations also predict that nucleophilic attack by OH(-) at the nitrogen center (Sn2@N) is energetically the rueful ad pathway but experiments with (18)OH(-) showed no evidence for this channel. Single-point calculations reveal a strong preference for approach to the emboli center and may explain the lack of reactivity at the nitrogen center. Calculations were also carried out or NH(2)(-) and SH(-) to establish the reactivity pattern to provide a better understanding of environmentally relevant nitrate esters.; Air Force Office of Scientific Research (AFOSR); U.S. Air Force Office of Scientific Research (AFOSR); Brazilian Research Council (CNPq); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Sao Paulo Research Foundation (FAPESP); National Institute of Science...

‣ Compostos de adição entre nitratos, cloretos e percloratos de ítrio e alguns lantanídeos(iii) e a 2,6-lutidina-n-oxido (2,6-LNO); Addition compounds between nitrates, chlorides and perchlorates, of yttrium and some lanthanides (III) and 2,6-lutidine N-oxide (2,6-LNO)

Oliveira, Wanda de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 16/10/1975 Português
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A reação entre nitratos, cloretos e percloratos dos lantanídeos e de ítrio com a 2,6-lutidina-N-óxido (2,6-LNO) conduziu à formação de compostos de adição de composição geral: Ln(NO3)3.4(2,6-LNO), LnCl3.3 (2,6-LNO) e Ln(ClO4)3.8(2,6-LNO) (Ln= La, Pr, Nd, Gd, Ho, Er e Y). Os produtos de reação são cristalinos, apresentam as mesmas colorações dos íons lantanídeos hidratados, porém bastante esmaecidas. Os compostos de adição contendo o íon cloreto não fundem até 300ºC. Os compostos de adição contendo os íons nitratos e percloratos são solúveis em acetona, acetonitrila, etanol, metanol, nitrobenzeno e nitrometano, ligeiramente solúveis em clorofórmio. Os compostos de adição contendo o íon cloreto são solúveis em etanol e metanol e praticamente insolúveis em acetona, acetonitrila, clorofórmio, nitrobenzeno e nitrometano. Todos os compostos de adição são praticamente insolúveis em benzeno; tetracloreto de carbono e éter etílico. Os compostos foram caracterizados por meio de análise elementar, espectros na região do infra-vermelho e do visível, medidas de condutância molar em nitrometano, acetonitrila e etanol, e diagramas de raios-x. Para alguns compostos de adição contendo o íon nitrato foram obtidos os espectros Raman. Os dados obtidos nos espectros na região do infravermelho indicam que a coordenação da 2...

‣ Avaliação das ocorrências de nitrato e fluoreto nas águas subterrâneas do Estado de São Paulo

Silva, Milena Cássia Balerine da
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Trabalho de Conclusão de Curso Formato: 50 f.
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Concerns about the quality of groundwater have been continuously rising, considering its importance for the public water supply in the State of São Paulo, and even more due to the impact that anthropic action has been causing to the original quality of that natural resource. It is extremely relevant to identify the contamination focuses along the aquifers of the State of São Paulo. This report aims to evaluate nitrates and fluorides concentrations along the aquifers present in the state, in order to identify places where change in the quality of groundwater is observed, through the comparison between measured concentrations and reference values, such as: “Intervention Value” (maximum allowed value) and “Alert Value” (attention required value). To perform this research, a full compilation and organization has been done on chemical analysis data from the “Sistema de Informações de Águas Subterrâneas - SIDAS”, made available by the “Divisão de Procedimentos de Outorga – DPO” of the “Departamento de Água e Energia Elétrica – DAEE”. This work has made possible the build-up of a database composed by 6,860 wells, with analytical data ready to be interpreted, containing information about water pH, electrical conductivity...

‣ Lanthanide nitrates as Lewis acids in the one-pot synthesis of 1,2,4-oxadiazole derivatives

Vale,Juliana A.; Faustino,Wagner M.; Zampieri,Davila de S.; Moran,Paulo J. S.; Rodrigues,José A. R.; de Sá,Gilberto F.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2012 Português
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In this work we report the use of lanthanide nitrates [Ln(NO3)3] acting as catalyst in direct one-pot synthesis of 3-benzoyl- and 3-acetyl-1,2,4-oxadiazoles derivatives from ketones, nitriles and nitric acid. This is the first example of one-pot synthesis of benzoyl- and acetyl 1,2,4-oxadiazoles derivatives preparation using acetophenones derivates with electron-donator groups.

‣ A review of nitrates in drinking water: maternal exposure and adverse reproductive and developmental outcomes

Manassaram,Deana M.; Backer,Lorraine C.; Moll,Deborah M.
Fonte: ABRASCO - Associação Brasileira de Saúde Coletiva Publicador: ABRASCO - Associação Brasileira de Saúde Coletiva
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2007 Português
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In this review, we present an update on maternal exposure to nitrates in drinking water in relation to possible adverse reproductive and developmental effects, and discuss nitrates in drinking water in the United States. The current standard for nitrates in drinking water is based on retrospective studies and approximates a level that protects infants from methemoglobinemia, but no safety factor is built into the standard. The current standard applies only to public water systems. Animal studies have found adverse reproductive effects resulting from higher doses of nitrate or nitrite. The epidemiologic evidence of a direct exposure-response relationship between drinking water nitrate level and adverse reproductive effect is still not clear. However, some reports have suggested an association between exposure to nitrates in drinking water and spontaneous abortions, intrauterine growth restriction, and various birth defects. Uncertainties in epidemiologic studies include the lack of individual exposure assessment that would rule out confounding of the exposure with some other cause. We conclude that the current literature does not provide sufficient evidence of a causal relationship between exposure to nitrates in drinking water and adverse reproductive effects.

‣ A Review of Nitrates in Drinking Water: Maternal Exposure and Adverse Reproductive and Developmental Outcomes

Manassaram, Deana M.; Backer, Lorraine C.; Moll, Deborah M.
Fonte: National Institute of Environmental Health Sciences Publicador: National Institute of Environmental Health Sciences
Tipo: Artigo de Revista Científica
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In this review we present an update on maternal exposure to nitrates in drinking water in relation to possible adverse reproductive and developmental effects, and also discuss nitrates in drinking water in the United States. The current standard for nitrates in drinking water is based on retrospective studies and approximates a level that protects infants from methemoglobinemia, but no safety factor is built into the standard. The current standard applies only to public water systems. Drinking water source was related to nitrate exposure (i.e., private systems water was more likely than community system water to have nitrate levels above the maximum contaminant limit). Animal studies have found adverse reproductive effects resulting from higher doses of nitrate or nitrite. The epidemiologic evidence of a direct exposure–response relationship between drinking water nitrate level and adverse reproductive effect is still not clear. However, some reports have suggested an association between exposure to nitrates in drinking water and spontaneous abortions, intrauterine growth restriction, and various birth defects. Uncertainties in epidemiologic studies include the lack of individual exposure assessment that would rule out confounding of the exposure with some other cause. Nitrates may be just one of the contaminants in drinking water contributing to adverse outcomes. We conclude that the current literature does not provide sufficient evidence of a causal relationship between exposure to nitrates in drinking water and adverse reproductive effects. Future studies incorporating individual exposure assessment about users of private wells—the population most at risk—should be considered.

‣ Specificity of different organic nitrates to elicit NO formation in rabbit vascular tissues and organs in vivo.

Mülsch, A.; Bara, A.; Mordvintcev, P.; Vanin, A.; Busse, R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1995 Português
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1. In the present study we assessed the formation of nitric oxide (NO) from classical and thiol-containing organic nitrates in vascular tissues and organs of anaesthetized rabbits, and established a relationship between the relaxant response elicited by nitroglycerin (NTG) and NO formation in the rabbit isolated aorta. Furthermore, the effect of isolated cytochrome P450 on NO formation from organic nitrates was investigated. 2. Rabbits received diethyldithiocarbamate (DETC; 200 mg kg-1 initial bolus i.p. and 200 mg kg-1 during 20 min, i.v.) and either saline, or one of the following organic nitrates: nitroglycerin (NTG, 0.5 mg kg-1), isosorbide dinitrate (ISDN), N-(3-nitratopivaloyl)-L-cysteine ethylester (SPM 3672), S-carboxyethyl-N-(3-nitratopivaloyl)-L-cysteine ethylester (SPM 5185), at 10 mg kg-1 each. After 20 min the animals were killed, blood vessels and organs were removed, and subsequently analyzed for spin-trapped NO by cryogenic electron spin resonance (e.s.r.) spectroscopy. 3. In the saline-treated control group, NO remained below the detection limit in all vessels and organs. In contrast, all of the nitrates tested elicited measurable NO formation, which was higher in organs (liver, kidney, heart, lung, spleen) (up to 4.8 nmol g-1 20 min-1) than in blood vessels (vena cava...

‣ Ozone and organic nitrates over the eastern United States: Sensitivity to isoprene chemistry

Mao, Jingqiu; Paulot, Fabien; Jacob, Daniel James; Cohen, Ronald C.; Crounse, John D.; Wennberg, Paul O.; Keller, Christoph Andrea; Hudman, Rynda C.; Barkley, Michael P.; Horowitz, Larry W.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
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We implement a new isoprene oxidation mechanism in a global 3-D chemical transport model (GEOS-Chem). Model results are evaluated with observations for ozone, isoprene oxidation products, and related species from the International Consortium for Atmospheric Research on Transport and Transformation aircraft campaign over the eastern United States in summer 2004. The model achieves an unbiased simulation of ozone in the boundary layer and the free troposphere, reflecting canceling effects from recent model updates for isoprene chemistry, bromine chemistry, and HO2 loss to aerosols. Simulation of the ozone-CO correlation is improved relative to previous versions of the model, and this is attributed to a lower and reversible yield of isoprene nitrates, increasing the ozone production efficiency per unit of nitrogen oxides (NOx ≡ NO + NO2). The model successfully reproduces the observed concentrations of organic nitrates (∑ANs) and their correlations with HCHO and ozone. ∑ANs in the model is principally composed of secondary isoprene nitrates, including a major contribution from nighttime isoprene oxidation. The correlations of ∑ANs with HCHO and ozone then provide sensitive tests of isoprene chemistry and argue in particular against a fast isomerization channel for isoprene peroxy radicals. ∑ANs can provide an important reservoir for exporting NOx from the U.S. boundary layer. We find that the dependence of surface ozone on isoprene emission is positive throughout the U.S....

‣ Évaluation du risque cancérigène associé à la contamination de l’eau potable de puits municipaux par les nitrates/nitrites dans certaines régions rurales du Québec

Chébékoué, Sandrine Fleur
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
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La spécialisation des techniques agricoles que nous connaissons ces dernières décennies, particulièrement dans les régions rurales, est à l’origine de l’abus de fertilisants. Ces derniers sont actuellement reconnus comme étant les causes principales de la contamination de l’eau souterraine par les nitrates. Suite à leur ingestion via l’eau potable, les nitrates sont transformés en nitrites par la flore buccale. Une fois dans l’estomac les nitrites réagissent avec certaines amines provenant de l’alimentation pour générer des nitrosamines cancérogènes. L’objectif de notre étude était d’estimer quantitativement l’excès de risque de cancer (ER) pour les populations de sept régions rurales du Québec qui consomme l’eau potable provenant de réseaux municipaux alimentés en eau souterraine. Le territoire à l’étude était caractérisé par une agriculture intensive d’élevage. Les médianes (et 95e centiles) régionales des concentrations de nitrates mesurées dans les réseaux de ces régions étaient de : 0,18 (2,74); 0,48 (10,35); 0,15 (1,28); 0,32 (11); 0,05 (0,76); 0,10 (4,69); 0,09 (2,13) mg N-NO3-/l. Nous avons envisagé un scénario de transformation complète des nitrites et de certaines amines (diméthylamine...

‣ Implementation of the European Union’s Nitrates Directive in Turkey

Yetis, Ulku; Yukseler, Hande; Valatka, Simonas; Girgin, Serkan; Semeniene, Daiva; Kerestecioglu, Merih; Jacobsen, Micheal
Fonte: Taylor and Francis Publicador: Taylor and Francis
Tipo: Artigo de Revista Científica
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The European Union (EU)’s Nitrates Directive (ND) (91/676/EEC) aims to reduce water pollution caused or induced by nitrates from agricultural sources and to prevent further such pollution. Turkey being a candidate country to EU requires heavy cost investments in achieving approximation with EU Environmental Acquis. This study provides a description of the technical measures and investment cost assessment related to the implementation of the ND in Turkey. As Turkey has not yet designated nitrate vulnerable zones (NVZs) according to requirements of the EU’s ND, three scenarios were developed to estimate the capital investments needed for implementation of the ND. Based on the developed scenarios, the low-cost scenario designating eight provinces as NVZs and requiring a total investment of EUR 270 millions for the period 2007–2023 has been selected by the Ministry of Environment and Forestry within the EU Integrated Environmental Approximation Strategy for Turkey.

‣ Misfit and mechanism in structure changes in crystals of univalent nitrates / Graham Frank Taylor.

Taylor, Graham Frank
Fonte: Adelaide, Publicador: Adelaide,
Tipo: Tese de Doutorado Formato: 156479 bytes; application/pdf
Publicado em //1966 Português
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The object of the work was to study the dependence of structure changes on interfacial misfit in crystals of univalent nitrates. Techniques used were single crystal X-ray diffraction and cinephotomicroscopy.; Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1966; Typescript; 151 leaves : ill.; Title page, contents and abstract only. The complete thesis in print form is available from the University Library.

‣ Neue Oxidnitrate als reaktive Precursoren im supraleitfähigen System (Bi,Pb)-Sr-Ca-Cu-O; New oxide nitrates as reactive precursors in the superconductive system (Bi-Pb)-Sr-Ca-Cu-O

Ziegler, Peter
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
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Die vorliegende Arbeit befasst sich mit der Darstellung neuer Oxidnitrate und ihrem gezielten Einsatz als Precursoren für die Herstellung der supraleitfähigen Bismutcuprate (Bi,Pb)2Sr2Can-1CunO2n+4+z, insbesondere des technisch wichtigen Hochtemperatursupraleiters (Bi,Pb)-2223. Es wird beschrieben, dass es möglich ist, in nitrathaltigen Gemischen die neuen Bismut-Erdalkali-Oxidnitrate bei Temperaturen um 480-500 °C zu stabilisieren. Es wird außerdem gezeigt, dass durch die Bildung und Stabilisierung solcher Oxidnitrate im weiteren Reaktionsverlauf bei höheren Temperaturen ab 700 °C die Bildung von unerwünschten Bi-Sr-Ca-Oxiden unterdrückt bzw. verlangsamt wird. Im Folgenden wird die gezielte Synthese und Charakterisierung der neuen Oxidnitrate BiMO2NO3 beschrieben, wobei neben den als Precursoren der Bismutcuprate wichtigen Verbindungen mit M = Pb, Ca und Sr auch BiBaO2NO3 dargestellt und charakterisiert wurde. Die Strukturen der Oxidnitrate, die auf Basis der Daten der Röntgenpulverdiffraktometrie gelöst und verfeinert wurden, bestehen aus abwechselnden [BiMO2]+ und [NO3]--Schichten. Sie werden mit einer ihnen strukturell eng verwandten Reihe von Oxidhalogeniden verglichen, den nach ihrem Entdecker benannten Sillén-Phasen. Um einphasige und kristalline Produkte darzustellen und die Bildung von Oxiden zu vermeiden...

‣ Strukturen, thermischer Abbau und mögliche Anwendungen von Oxidnitraten; Structures, thermal decomposition and possible applications of oxide nitrates

Dill, Simone
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
Português
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Die vorliegende Arbeit beschäftigt sich mit der Synthese und Charakterisierung von bekannten und neuen Oxidnitraten, deren Zersetzungsprodukten und der potentiellen Anwendungen der Oxidnitrate als Precursoren und NOx-Speicher. In Kapitel 3 wurde die thermische Zersetzung von Sr(NO3)2 und Ba(NO3)2, welches in NOx-Speicherkatalysatoren in der Automobilindustrie verwendet wird, untersucht. Um eventuell auftretende Zwischenstufen, bei denen es sich auch um Oxidnitrate handeln könnte, zu isolieren, wurden die Nitrate von Barium und Strontium nur kurz über ihren Schmelzpunkt erhitzt und wieder abgekühlt. Beim Abkühlen der jeweiligen Nitratschmelzen an Luft trat eine neue, unbekannte Phase auf. Dabei handelte es sich um die Verbindungen Sr2(OH)3NO3 bzw. Ba2(OH)3NO3. Die Strukturen dieser Verbindungen wurden anhand von Röntgen-Einkristall- und Pulverdaten bestimmt und verfeinert. In den hexagonalen Kristallstrukturen (P6`2m) dieser Hydroxidnitrate sind die Erdalkalimetallionen von den Hydroxidionen in Form von trigonalen Prismen umgeben. Diese Prismen sind über die trigonalen Flächen entlang der c-Richtung und über Kanten in der ab-Ebene verknüpft. Sie bilden sechseckige Röhren, in denen sich die Nitratgruppen befinden. Die Bildung und Zersetzung von Sr2(OH)3NO3 wurde mit Hilfe von DTA/TG-Messungen untersucht...

‣ Contributions of individual reactive biogenic volatile organic compounds to organic nitrates above a mixed forest

Pratt, K.A.; Mielke, L.H.; Shepson, P.B.; Bryan, A.M.; Steiner, A.L.; Ortega, J.; Daly, R.; Helmig, D.; Vogel, C.S.; Griffith, S.; Dusanter, S.; Stevens, P.S.; Alghmand, M.
Fonte: Copernicus Publications on behalf of the European Geosciences Union Publicador: Copernicus Publications on behalf of the European Geosciences Union
Tipo: Artigo de Revista Científica
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Biogenic volatile organic compounds (BVOCs) can react in the atmosphere to form organic nitrates, which serve as $ ext{NO}_{x} ( ext{NO} + ext{NO}_{2})$ reservoirs, impacting ozone and secondary organic aerosol production, the oxidative capacity of the atmosphere, and nitrogen availability to ecosystems. To examine the contributions of biogenic emissions and the formation and fate of organic nitrates in a forest environment, we simulated the oxidation of 57 individual BVOCs emitted from a rural mixed forest in northern Michigan. Key BVOC-oxidant reactions were identified for future laboratory and field investigations into reaction rate constants, yields, and speciation of oxidation products. Of the total simulated organic nitrates, monoterpenes contributed ~70% in the early morning at ~12 m above the forest canopy when isoprene emissions were low. In the afternoon, when vertical mixing and isoprene nitrate production were highest, the simulated contribution of isoprene-derived organic nitrates was greater than 90% at all altitudes, with the concentration of secondary isoprene nitrates increasing with altitude. Notably, reaction of isoprene with $ ext{NO}_{3}$ leading to isoprene nitrate formation was found to be significant (~8% of primary organic nitrate production) during the daytime...

‣ Importance of biogenic precursors to the budget of organic nitrates: observations of multifunctional organic nitrates by CIMS and TD-LIF during BEARPEX 2009

Beaver, M. R.; St. Clair, J. M.; Paulot, F.; Spencer, K. M.; Crounse, J. D.; LaFranchi, B. W.; Min, K. E.; Pusede, S. E.; Wooldridge, P. J.; Schade, G. W.; Park, C.; Cohen, R. C.; Wennberg, P. O.
Fonte: Copernicus Publications Publicador: Copernicus Publications
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 03/07/2012 Português
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Alkyl and multifunctional organic nitrates, molecules of the chemical form RONO_2, are products of chain terminating reactions in the tropospheric HO_x and NO_x catalytic cycles and thereby impact ozone formation locally. Many of the molecules in the class have lifetimes that are long enough that they can be transported over large distances. If the RONO_2 then decompose to deliver NO_x to remote regions they affect ozone production rates in locations distant from the original NO_x source. While measurements of total RONO_2 (ΣANs) and small straight chain alkyl nitrates are routine, measurements of the specific multifunctional RONO_2 molecules that are believed to dominate the total have rarely been reported and never reported in coincidence with ambient ΣANs measurements. Here we describe observations obtained during the BEARPEX 2009 experiment including ΣANs and a suite of multifunctional nitrates including isoprene derived hydroxynitrates, oxidation products of those nitrates, 2-methyl-3-buten-2-ol (MBO) derived hydroxynitrates, and monoterpene nitrates. At the BEARPEX field site, the sum of the individual biogenically derived nitrates account for two-thirds of the ΣANs, confirming predictions of the importance of biogenic nitrates to the NO_y budget. Isoprene derived nitrates...

‣ Airborne observations of total RONO2: new constraints on the yield and lifetime of isoprene nitrates

Perring, A. E.; Bertram, T. H.; Wooldridge, P. J.; Fried, A.; Heikes, B. G.; Dibb, J.; Crounse, J. D.; Wennberg, P. O.; Blake, N. J.; Blake, D. R.; Brune, W. H.; Singh, H. B.; Cohen, R. C.
Fonte: Copernicus Publications Publicador: Copernicus Publications
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 23/02/2009 Português
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Formation of isoprene nitrates (INs) is an important free radical chain termination step ending production of ozone and possibly affecting formation of secondary organic aerosol. Isoprene nitrates also represent a potentially large, unmeasured contribution to OH reactivity and are a major pathway for the removal of nitrogen oxides from the atmosphere. Current assessments indicate that formation rates of isoprene nitrates are uncertain to a factor of 2–3 and the subsequent fate of isoprene nitrates remains largely unconstrained by laboratory, field or modeling studies. Measurements of total alkyl and multifunctional nitrates (ΣANs), NO2, total peroxy nitrates (ΣPNs), HNO3, CH2O, isoprene and other VOC were obtained from the NASA DC-8 aircraft during summer 2004 over the continental US during the INTEX-NA campaign. These observations represent the first characterization of ΣANs over a wide range of land surface types and in the lower free troposphere. ΣANs were a significant, 12–20%, fraction of NOy throughout the experimental domain and ΣANs were more abundant when isoprene was high. We use the observed hydrocarbon species to calculate the relative contributions of ΣAN precursors to their production. These calculations indicate that isoprene represents at least three quarters of the ΣAN source in the summertime continental boundary layer of the US. An observed correlation between ΣANs and CH2O is used to place constraints on nitrate yields from isoprene oxidation...

‣ Isoprene photooxidation : new insights into the production of acids and organic nitrates

Paulot, F.; Crounse, J. D.; Kjaergaard, H. G.; Kroll, J. H.; Seinfeld, J. H.; Wennberg, P. O.
Fonte: Copernicus Publications Publicador: Copernicus Publications
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //2009 Português
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We describe a nearly explicit chemical mechanism for isoprene photooxidation guided by chamber studies that include time-resolved observation of an extensive suite of volatile compounds. We provide new constraints on the chemistry of the poorly-understood isoprene δ-hydroxy channels, which account for more than one third of the total isoprene carbon flux and a larger fraction of the nitrate yields. We show that the cis branch dominates the chemistry of the δ-hydroxy channel with less than 5% of the carbon following the trans branch. The modelled yield of isoprene nitrates is 12±3% with a large difference between the δ and β branches. The oxidation of these nitrates releases about 50% of the NOx. Methacrolein nitrates (modelled yield ≃15±3% from methacrolein) and methylvinylketone nitrates (modelled yield ≃11±3% yield from methylvinylketone) are also observed. Propanone nitrate, produced with a yield of 1% from isoprene, appears to be the longest-lived nitrate formed in the total oxidation of isoprene. We find a large molar yield of formic acid and suggest a novel mechanism leading to its formation from the organic nitrates. Finally, the most important features of this mechanism are summarized in a condensed scheme appropriate for use in global chemical transport models.

‣ Atmospheric photochemistry of alkyl nitrates

Turberg, M.; Giolando, D.; Tilt, C.; Soper, T.; Mason, S.; Davies, M.; Klingensmith, P.; Takacs, Gerald
Fonte: Elsevier: Journal of Photochemistry and Photobiology Publicador: Elsevier: Journal of Photochemistry and Photobiology
Tipo: Abstract Formato: 37365 bytes; application/pdf
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Photoabsorption spectra of gaseous ethyl nitrate, n-propyl nitrate, 2-propyl nitrate, n-butyl nitrate and 3-methyl-1-butyl nitrate were quantitatively measured in the laboratory at room temperature for λ >185 nm. The spectra are continuous and exhibit low- and high-intensity absorption bands. The maximum for the high-intensity band occurs at 188 ± 2 nm. Atmospheric photodissociation rate coefficients for alkyl nitrates were estimated in the range 0 – 50 km and were found to have a strong dependence on altitude. Photodissociation lifetimes were on the order of days and hours for the proposphere and stratosphere respectively. Compared with reaction with OH, photodissociation is the dominant removal process for alkyl nitrates throughout the atmosphere.

‣ The nitrite anion: the key intermediate in alkyl nitrates degradative mechanism.

Loris Grossi
Fonte: Nature Preceedings Publicador: Nature Preceedings
Tipo: Manuscript
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Alkyl nitrates, _in vivo_, are metabolized to yield nitric oxide, and thiol groups are considered necessary cofactors. This statement is based on studies that underline how these species potentiate hemodynamic responsiveness to nitrates in patients with ischemic heart disease. However, the role of thiols might be mediated by the formation of corresponding S-nitrosothiols, and a redox process is responsible for the nitrates' degradation: an enzyme, probably the cytochrome P450, is involved _in vivo_. Here, we report evidence that, in vitro, no reaction between thiols and alkyl nitrates takes place, but that stronger reducing agents, such as iron (II) derivatives, are necessary: alkoxy radicals and the nitrite anion are the reaction intermediates. The latter, in slightly acidic conditions, for instance mimicking ischemic conditions, is shown to nitrosilate thiols to the corresponding S-nitrosothiols: the real NO suppliers. Therefore, the direct release of NO from nitrates is excluded. Finally, the in vivo role of thiols on depletion and tolerance is also accounted for.

‣ A review of nitrates in drinking water: maternal exposure and adverse reproductive and developmental outcomes

Manassaram,Deana M.; Backer,Lorraine C.; Moll,Deborah M.
Fonte: ABRASCO - Associação Brasileira de Saúde Coletiva Publicador: ABRASCO - Associação Brasileira de Saúde Coletiva
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2007 Português
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In this review, we present an update on maternal exposure to nitrates in drinking water in relation to possible adverse reproductive and developmental effects, and discuss nitrates in drinking water in the United States. The current standard for nitrates in drinking water is based on retrospective studies and approximates a level that protects infants from methemoglobinemia, but no safety factor is built into the standard. The current standard applies only to public water systems. Animal studies have found adverse reproductive effects resulting from higher doses of nitrate or nitrite. The epidemiologic evidence of a direct exposure-response relationship between drinking water nitrate level and adverse reproductive effect is still not clear. However, some reports have suggested an association between exposure to nitrates in drinking water and spontaneous abortions, intrauterine growth restriction, and various birth defects. Uncertainties in epidemiologic studies include the lack of individual exposure assessment that would rule out confounding of the exposure with some other cause. We conclude that the current literature does not provide sufficient evidence of a causal relationship between exposure to nitrates in drinking water and adverse reproductive effects.