91,704 research outputs found

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

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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

    Nitrates for the Management of Acute Heart Failure Syndromes, A Systematic Review

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    © The Author(s) 2016Intravenous nitrates are widely used in the management of acute heart failure syndrome (AHFS) yet with lack of robust evidence to support their use. We therefore sought to analyze all randomized studies that evaluated the effects of nitrates on clinical outcomes in patients with AHFS. In total, 15 relevant trials comparing nitrates and alternative interventions in 1824 patients were identified. All but 3 were conducted before 1998. No trials demonstrated a beneficial effect on mortality, apart from 1 trial reporting a reduction in mortality, which was related to the time of treatment. Retrospective review suggests that there is a lack of data to draw any firm conclusions concerning the use of nitrates in patients with AHFS. More studies are needed to evaluate the safety and efficacy of these agents in the modern era of guideline-directed use of heart failure therapy.Peer reviewedFinal Accepted Versio

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

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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

    Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(−)-myrtenol nitrate

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    Here we report the chemoselective synthesis of several important, climate relevant isoprene nitrates using silver nitrate to mediate a ’halide for nitrate’ substitution. Employing readily available starting materials, reagents and Horner–Wadsworth–Emmons chemistry the synthesis of easily separable, synthetically versatile ‘key building blocks’ (E)- and (Z)-3-methyl-4-chlorobut-2-en-1-ol as well as (E)- and (Z)-1-((2-methyl-4-bromobut-2-enyloxy)methyl)-4-methoxybenzene has been achieved using cheap, ’off the shelf’ materials. Exploiting their reactivity we have studied their ability to undergo an ‘allylic halide for allylic nitrate’ substitution reaction which we demonstrate generates (E)- and (Z)-3-methyl-4-hydroxybut-2-enyl nitrate, and (E)- and (Z)-2-methyl-4-hydroxybut-2-enyl nitrates (‘isoprene nitrates’) in 66–80% overall yields. Using NOESY experiments the elucidation of the carbon–carbon double bond configuration within the purified isoprene nitrates has been established. Further exemplifying our ‘halide for nitrate’ substitution chemistry we outline the straightforward transformation of (1R,2S)-(−)-myrtenol bromide into the previously unknown monoterpene nitrate (1R,2S)-(−)-myrtenol nitrate

    Monitoring the Content of Nitrates in Vegetables and the Influence of the Pickling Technology on the Denitrification Process

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    The aim of the work was to determine the concentration of nitrites in vegetable products (tomatoes, cucumbers, white cabbage, table beet, carrot, potatoes, onion and green onion, lettuce, spinach and parsley), realized at markets of the cities Ternopil, Kamianets-Podilskyi and Chernivtsi (Ukraine), to separate the distribution of nitrates in vegetables and also to study the influence of lactic microflora on the nitrate content at pickling tomatoes. It was established, that vegetables with the maximum exceed of maximum permissible concentration (MPC) by the nitrate content up to 1,6 times for products of closed soil are realized at markets. For open soil MPC exceed was in average 2,1 times. It was revealed, that most realized samples of tomatoes and leaf salad vegetables have the over-normative exceed of nitrates up to 35 %, and onion – the least one – 20 %. It was established, that nitrates accumulate in different parts of a fruit. In cucumbers, carrot, potato and table beet, the least quantity of nitrates accumulate in the external part of vegetables (near the surface), and the most one – in the central part. At the same time in cabbage and tomatoes, on the contrary, the least quantity – in the central part, the most one – in the area near the base of vegetables (stump). It was established, that at pickling tomatoes with the nitrate content within MPC lactic fermentation takes place with the intensive growth of titrated acidity, the decrease of the nitrate content takes place at this process. Under conditions of pickling tomatoes with the nitrate content two times more than MPC, the pickling process is a bit decelerated, but the nitrate content decreases to the safe level in a finished product. It was established, that vegetables with the nitrates quantity within 1500 mg/kg and more cannot be used in the pickling technology because of the bacteriological influence of nitrates on lactic microflora. Vegetables with such nitrate content must be obligatory condemned

    Studies of Effectiveness of Commercial Home Treatment Systems

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    Eleven home water systems were tested representing six different types of filtering systems. Tests were made for Sulfates, Nitrates, Phosphate, Iron and Escherichia coli and Enterobacter aerogenes before and after passing through a home treatment system. All of the systems removed iron adequately but had little effect on the removal of nitrates, phosphates, sulfates or control of pH. Since none of the ground waters was contaminated by coli- forms, nothing was established regarding the effectiveness of bacterial removal by these systems

    Selection of medication in hospitalised elderly patients with Angina Pectoris

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    Objective: To evaluate medication changes in hospitalised elderly patients diagnosed with angina pectoris and to compare the selection of medication with evidence-based treatment guidelines. Design: Review of medical notes and patient interview. Setting: St. Luke's Hospital, Malta; January - May 2001. Subjects: 226 patients, aged 60 years or over, with a history of chronic stable angina and a discharge diagnosis of angina. Main outcome measures: Prevalence of use of antiplatelet agents, lipid lowering agents, beta-blockers, calcium channel blockers, nitrates, potassium channel openers and cellular anti-ischaemic agents; presence of co-morbidities, concurrent medication and adverse effects. Results: Prior to discharge, 77% of patients were receiving antiplatelet agents and 27% were receiving lipid lowering agents. The most frequent anti-ischaemic agents used were nitrates (97%) and second-generation dihydropyridine calcium channel blockers (59%). Beta-blockers were used in 31% of patients and non-dihydropyridine calcium channel blockers were used in 4% of patients. Potassium channel openers (nicorandil) and cellular anti-ischaemic agents (trimetazidine) were used in 5% and 19% of patients respectively. Of patients discharged on a single anti-ischaemic agent, 96% were prescribed nitrates, while 64% of those on two agents were prescribed nitrates and dihydropyridine calcium channel blockers. Beta-blockers, nicorandil and trimetazidine were generally used in conjunction with at least two other antiischaemic agents. The major medication changes involved the addition, or increase in dose, of amlodipine and isosorbide dinitrate. The major determinants affecting choice of medication were age and co-morbidities. Conclusion: Medication selection for chronic stable angina was not in accordance with treatment guidelines.peer-reviewe

    Antarctic polar stratospheric aerosols: The roles of nitrates, chlorides and sulfates

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    Nitric and hydrochloric acids have been postulated to condense in the winter polar stratosphere to become an important component of polar stratospheric clouds. One implication is that the removal of NO(y) from the gas phase by this mechanism allows high Cl(x) concentrations to react with O3, because the formation of ClNO3 is inhibited. Contributions of NO3 and Cl to the stratospheric aerosol were determined during the 1987 Airborne Antarctic Ozone Experiment by testing for the presence of nitrates and chlorides in the condensed phase. Aerosol particles were collected on four 500 micron diameter gold wires, each pretreated differently to give results that were specific to certain physical and chemical aerosol properties. One wire was carbon-coated for concentration and size analyses by scanning electron microscopy; X-ray energy dispersive analyses permitted the detection of S and Cl in individual particles. Three more wires were coated with Nitron, barium chloride and silver nitrate, respectively, to detect nitrate, sulfate and chloride in aerosol particles. All three ions, viz., sulfates, nitrates and chlorides were detected in the Antarctic stratospheric aerosol. In terms of number concentrations, the aerosol was dominated by sulfates, followed by chlorides and nitrates. An inverse linear regression can be established between nitrate concentrations and ozone mixing ratio, and between temperature and nitrates
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