IDENTIFICATION OF NITROGEN COMPOUNDS AND THEIR EVOLUTIONDURINGAGEING NABSENCE ANDPRESENCE OF ADDITIVES EFFICIENCYOFHYDROTREATMENT

As established by several previous works, nitrogen compounds play a prominent role in the evolution of middle distillates containing cracked components, particularly regarding sediment formation and color evolution.

In a first part, this paper describes and compares stability properties of fuel blends using both an accelerated ageing method at 120°C (248°F ) and long term storage methods at 43°C(110°F) -ASTM 0 4625 - and at ambient temperature. Effectiveness of stabilizing additives is also evaluated. In mixtures containing LCOs, insoluble products are formed progressively during ageings, more or less rapidly according to the chemical constitution of the mixtures.

Then, it reports the complete identification of nitrogen compounds using gas chromatography equipped with a selective nitrogen detector and mass spectrometry showing that in light cycle oils, alkyl indoles and carbazoles are the main families.

Evolution of these compounds was followed kinetically during ageings in absence and presence of additives and alkyl indoles appeared as the moat evolutionary.

It appeared that some additives avoided evolutions of alkyl indoles without preventing sediment formation and color evolution. Oxidation mechanism involving nitrogen compounds should not be the only one to explain the storage evolutions of middle distillates.

Hydrotreatment converts all the alkyl indoles of LCO and prevents coloration end deposits in the storage of the mixtures of steaight-run distillates and LCOs.     

Prebiotic synthesis of sequential peptides on the Hadean beach by a molecular engine working with nitrogen oxides as energy sources

Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry.     

How to optimize high-Tc superconductive cuprates

Different ways to optimizeT _c 's and the magnetic properties of high-T _c superconductive cuprates are described and discussed. Oxygen intercalation-desintercalation phenomena and cationic substitutions (M³⁺ for M²⁺ or vice versa) lead to a variation of the hole carrier density and can have a drastic influence onT _c 's, as shown for bismuth, thallium, and lead-based cuprates, as well as for La₂CuO₄ and “123”-type superconductors. In the former, the role of hole reservoirs for the rock salt type layers is outlined. The modification of the hybridization of orbitals can also explain the variations ofT _c 's observed in some systems like Y_1?x Ca _x Ba₂Cu_3?x :Fe _x O₇ in which the oxidation state of copper remains constant. A critical current density enhancement can be realized by irradiating high-T _c materials by high-energy heavy ions because of the peculiar columnar structure of the heavy ion-induced tracks. The effects of such columnar defects, 70 Å in diameter, on flux pinning, magnetic relaxation, and location of the irreversibility line of bismuth-based 2212 crystals irradiated by 6-GeV Pb ions are reported. We observe a strong shift of the irreversibility line toward high fields and temperatures, indicating that pinning effects must be taken into account in the vortex lattice motion. Such induced changes are accompanied by a strong enhancement of the critical current density and a significant enlargement of the irreversibility region in theH,T plane.     

Nicotine-stimulated release of [3H]norepinephrine from fetal rat locus coeruleus cells in culture

Acute nicotine administration stimulated [3H]norepinephrine ([3H]NE) release from cultured fetal locus coeruleus (LC) cells. The effect was concentration dependent, with an EC50 of 0.9 microM, and was abolished by removal of calcium from, or addition of tetrodotoxin (500 nM) to, the assay buffer. Other nicotinic receptor agonists stimulated [3H]NE release, with the rank order of potency being (+)-epibatidine > (-)-nicotine > 1,1-dimethyl-4-phenylpiperazinium (DMPP). Whereas (-)-nicotine and (+/-)-epibatidine exhibited equal maximal responses, DMPP was a partial agonist and (-)-cytisine had no agonist activity. Nicotine-stimulated release of [3H]NE was blocked by nicotinic receptor antagonists, with an order of potency of mecamylamine > lobeline > cytisine > methyllycaconitine > dihydro-beta-erythroidine. The pharmacological profile of this nicotinic receptor is largely consistent with that described previously for an alpha4beta2 subunit combination, although discrepancies in the efficacies of agonists were observed. No additivity in NMDA- and nicotine-stimulated [3H]NE release was observed, suggesting a common signal transduction mechanism. However, the pharmacological characteristics of MK-801 blockade of nicotine-induced responses were not consistent with those of an NMDA receptor. We therefore conclude that nicotine directly releases [3H]NE from LC cells and does not act indirectly via activation of glutamate release.     

Determination of Magnetic and Nuclear Quadrupole Interactions in La@C82 from EPR Linewidth Data

From the analysis of the temperature dependence of the EPR line width, an estimate of the anisotropic parts of the dipolar and quadrupolar hyperfine couplings of lanthanum was derived. Furthermore, the rotational correlation time of the nearly spherical molecule was found to deviate considerably from that of the solvent molecules.     

Pharmacological specificities and modalities of prescriptions for corticoids for asthmatic adults

The efficacy of corticosteroids in asthma has been recognized over 40 years ago. Since that time, the advent of inhaled forms has further improved the therapeutic of these drugs which are now recognized as the fundamental treatment for asthma, and described in detail by national and international consensus. Based on a large body of literature, it can now be recommended to prescribe inhaled corticosteroids for symptomatic asthma patients. Long-term treatment is required and dosage not exceeding 1000 micrograms/d (beclometasone dipropionate equivalent) in adults are safe. Differences in the pharmacological characteristics of the various systematic and inhaled corticosteroids can be used to adapt treatment and administration route to each patient and achieve good patient compliance with optimal therapeutic efficacy.     

Nitrogen dioxide effect in the reduction of nitric oxide by propane in oxidizing atmosphere

The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO₂ and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C₃H₈ does not differ significantly from that of NO₂. In the absence of oxygen, the reduction of NO₂ by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO₂ formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process.