Photolyse du butyne-2 dans la région de l'uv sous vide

1980 ◽  
Vol 58 (19) ◽  
pp. 2108-2114 ◽  
Author(s):  
Jovette Deschênes ◽  
Hélène Deslauriers ◽  
Guy J. Collin
Keyword(s):  
Nitric Oxide ◽  
Radical Polymerization ◽  
Pressure Effect ◽  
Hydrogen Iodide ◽  
Radical Scavenger ◽  
Methyl Radical ◽  
Vibrationally Excited ◽  
Fast Decrease ◽  
Sous Vide ◽  
Vacuum Uv

The vacuum uv photolysis of gaseous 2-butyne has been studied at 147, 163, and 174 nm. The use of hydrogen iodide as radical scavenger shows the importance of methyl radical formation in the fragmentation of the photoexcited molecule. It is concluded that the principal fragmentation of the photoexcited molecule involves the cleavage of a C—CH3 bond: [Formula: see text] and [Formula: see text]. Unfortunately, it was not possible to scavenge the corresponding C3H3 radicals. From the fast decrease of the transparency of the window it is concluded that an important radical polymerization takes place, even in the presence of oxygen or nitric oxide. Finally, from the pressure effect, it is shown that propyne results from the fragmentation of the vibrationally excited butenyl radical and vinylacetylene arises from the fragmentation of an excited C4H5 radical.

La photochimie du cis-penta-1,3-diène, en phase gazeuse à 184,9 et 147,0 nm

1991 ◽  
Vol 69 (8) ◽  
pp. 1245-1251
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers ◽  
George R. De Maré
Keyword(s):  
Key Words ◽  
Energy Content ◽  
Phase Gazeuse ◽  
Radical Scavenger ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Lower Yield ◽  
Uv Photolysis ◽  
Vacuum Uv

We have studied the 184.9 and 147.0 nm photochemistry of gaseous cw-1,3-pentadiene: the main products observed at 184.9 nm are trans-1,3-pentadiene and 1,3-cyclopentadiene. The formation of radicals also occurs as shown through the use of DI as a radical scavenger. Cyclopentadiene is the likely product of successive eliminations of two hydrogen atoms from the photoexcited molecule after rearrangement of the pentadienyl radical to the cyclopentenyl structure: Ф0(cyclo-C5H6) ≈ 0.25. Elimination of a methyl radical (Ф0 ≈ 0.50) also occurs, with formation of CH2=CHCH=ĊH* and, in a lower yield, CH2=C=CHĊH2*. However, it is not possible to identify properly the mechanism of the formation of the latter radical. It may be the result of the isomerization of either the first photoexcited molecule or the excited 1,3-butadienyl radicals. A small amount of 1,4-pentadiene formation is also observed (Ф0 ≈ 0.035 ± 0.015). At 147.0 nm, the same characteristics are observed, together with higher fragmentation due to the higher energy content of the photoexcited molecules. It appears that the photofragmentation at both wavelengths is more in line with that of acyclic alkenes than with that of 1,3-butadiene, which tends to undergo isomerization of the photoexcited molecules to the 1,2-butadiene structure. Key words: 1,3-pentadiene, far UV, vacuum UV, photolysis, monomolecular, fragmentation, stabilization.

Gas-phase photolysis of spiropentane at 147.0 nm

1985 ◽  
Vol 63 (12) ◽  
pp. 3593-3596 ◽  
Author(s):  
M. Paller ◽  
R. D. Doepker
Keyword(s):  
Nitric Oxide ◽  
Hydrogen Sulfide ◽  
Gas Phase ◽  
Hydrogen Iodide ◽  
Radical Scavenger ◽  
Relative Importance ◽  
Molecular Processes ◽  
Primary Reaction ◽  
Reaction Channels

The gas-phase photolysis of spiropentane has been investigated using xenon (147.0 nm) resonance radiation. Major products observed in order of decreasing importance are ethylene, aliène, methylacetylene, 1,2-butadiene, acetylene, propylene, and vinylacetylene. Nitric oxide was used as a radical scavenger while hydrogen sulfide and hydrogen iodide were employed as radical interceptors in the determination of the relative importance of radical and molecular processes. CH3/CH2 and CH3C=C• radicals were identified and quantified. Seven primary reaction channels were postulated of which those involving the "elimination" of ethylene were the most predominant accounting for 71% of the photodecomposition.

scholarly journals Direct measurement of nitric oxide release in gastric mucosa during ischemia-reperfusion in rats

1998 ◽  
Vol 274 (3) ◽  
pp. G465-G471 ◽  
Author(s):  
Kouichirou Wada ◽  
Yoshinori Kamisaki ◽  
Tsuyoshi Ohkura ◽  
Gaku Kanda ◽  
Kentaro Nakamoto ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Gastric Mucosa ◽  
Superoxide Radical ◽  
Ischemia Reperfusion ◽  
Mucosal Injury ◽  
Celiac Artery ◽  
Radical Scavenger ◽  
Gastric Mucosal Lesions ◽  
Nitric Oxide Release ◽  
Pentobarbital Sodium Anesthesia

Nitric oxide (NO) generation in the rat gastric mucosa during ischemia-reperfusion was measured using an NO-sensitive electrode. Under pentobarbital sodium anesthesia, an electrode was inserted into the submucosa from the serous membrane side in the fundus. After steady-state baseline recording, the celiac artery was clamped for 30 min, and then ischemia-reperfusion was achieved by removing the clamp. The clamping of the celiac artery caused a decrease in blood flow and an increase in NO level in the gastric tissue. Just after the removal of the clamp, the NO level rapidly fell and returned to the baseline level. Administration of N G-nitro-l-arginine methyl ester (an NO synthase inhibitor, 30 mg/kg ip) before ischemia significantly attenuated both the increase in NO level during ischemia and the formation of acute gastric mucosal lesions observed after 60 min reperfusion. Administration of superoxide dismutase (a superoxide radical scavenger, 10,000 U/kg iv) at the end of ischemia inhibited both the rapid decrease in NO level during the reperfusion and the gastric mucosal erosions. Because NO and superoxide radical produce a highly reactive peroxynitrite, it can be argued that NO has an important pathological role in acute gastric mucosal injury induced by ischemia-reperfusion. Our conclusion was strongly supported by immunohistochemical staining of nitrotyrosine residues, an indication of peroxynitrite formation.

Towards Vibrationally Excited Nitric Oxide Monitoring (VENOM) in a Laminar, Hypersonic Boundary Layer

2020 ◽  
Author(s):  
Zachary D. Buen ◽  
Casey Broslawski ◽  
Madeline Smotzer ◽  
Jason E. Kuszynski ◽  
Simon North ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Boundary Layer ◽  
Hypersonic Boundary Layer ◽  
Vibrationally Excited

The gas-phase photolysis of 2-methyl-1,3-butadiene at 123.6 nm

1984 ◽  
Vol 62 (9) ◽  
pp. 1731-1735
Author(s):  
Valerie I. Lang ◽  
Richard D. Doepker
Keyword(s):  
Nitric Oxide ◽  
Hydrogen Sulfide ◽  
Gas Phase ◽  
Quantum Efficiency ◽  
Hydrogen Iodide ◽  
Quantum Yields ◽  
Primary Decomposition ◽  
Radical Scavengers ◽  
Molecule Reaction ◽  
Reaction Channels

The gas-phase photolysis of 2-methyl-1,3-butadiene has been investigated using krypton (123.6 nm) resonance radiation. The observed neutral products of the primary decomposition were vinylacetylene, ethylene, acetylene, methylacetylene, propylene, allene, 2-methy-1-buten-3-yne, pentatriene/1-penten-3-yne, 1,3-butadiene, 2-butyne and butatriene, listed in decreasing order of concentration. There was also evidence of the presence of several radical fragments: CH2/CH3, C2H3, C3H3, and C4H5. Quantum yields for each of the products were determined in the photolysis of 2-methyl-1,3-butadiene, performed both in the presence and the absence of additives. Nitric oxide and oxygen were employed as radical scavengers, while hydrogen sulfide and hydrogen iodide were used as radical interceptors. Twelve primary, neutral molecule, reaction channels were proposed and the quantum efficiency assigned for each. The ionization efficiency of 2-methyl-1,3-butadiene was established as n = 0.55 at 10.03 eV. No products formed exclusively via an ion–molecule pathway were identified and therefore the fate of the C5H8+ ion was not determined.

Effects of activated polymorphonuclear leukocytes on vascular smooth muscle tone

1991 ◽  
Vol 261 (2) ◽  
pp. H327-H334 ◽  
Author(s):  
J. L. Mehta ◽  
D. L. Lawson ◽  
F. A. Nicolini ◽  
M. H. Ross ◽  
D. W. Player
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Polymorphonuclear Leukocytes ◽  
Muscle Tone ◽  
Endothelial Damage ◽  
Superoxide Radicals ◽  
Radical Scavenger ◽  
Ionophore A23187 ◽  
Vasorelaxant Effect

Unstimulated polymorphonuclear leukocytes (PMNLs) release nitric oxide or a like material that relaxes vascular tissues. To determine the effects of activated PMNLs on vascular tone, precontracted rat aortic rings were exposed to ionophore A23187-treated PMNLs. Whereas "unstimulated" PMNLs caused 29 +/- 4% relaxation, "stimulated" PMNLs caused initial contraction followed by 90 +/- 7% relaxation of aortic rings. Indomethacin or the 5-lipoxygenase blocker piriprost had no effect on PMNL-induced initial contraction or subsequent relaxation. However, initial contraction was abolished and the subsequent vasorelaxation attenuated (22 +/- 5%) by the superoxide radical scavenger superoxide dismutase (SOD), suggesting that release of superoxide radicals may have induced vascular contraction and caused endothelial damage that would permit unopposed vasorelaxant effect of PMNLs. To examine this hypothesis, aortic rings were exposed to superoxide radicals (generated by xanthine plus xanthine oxidase, X + XO) or manually deendothelialized. These rings revealed marked relaxation (78 +/- 6 and 85 +/- 6%, respectively) in response to unstimulated PMNLs. These observations suggest that stimulated PMNLs exert an initial vasoconstrictor effect and a subsequent vasorelaxant effect in response to release of superoxide radicals and nitric oxide, respectively. Arachidonate metabolites or 5-lipoxygenase products do not appear to be important in the actions of PMNLs on vascular smooth muscle.

Photolyse du butyne-1 dans la région de 147 à 174 nm

1980 ◽  
Vol 58 (19) ◽  
pp. 2100-2107 ◽  
Author(s):  
Hélène Deslauriers ◽  
Jovette Deschênes ◽  
Guy J. Collin
Keyword(s):  
Quantum Yield ◽  
Radical Scavenging ◽  
Hydrogen Iodide ◽  
Radical Scavengers ◽  
Methyl Radical ◽  
Radical Intermediate ◽  
Scavenging Effect ◽  
Radical Scavenging Effect ◽  
Propargyl Radicals

We have studied the 147, 163, and 174 nm photolysis of 1-butyne. Several products from C1 to C5 were observed under various conditions such as in the presence of additives, or at different pressures between 0.5 and 100 Torr (65 to 13 300 N m−2). The methyl radical is the most important radical intermediate. Acetylene, ethylene, and vinylacetylene are produced in the presence of radical scavengers and are probably the result of the fragmentation of the photoexcited molecule. Propargyl radicals are thought to be produced but appear not to be scavenged by hydrogen iodide. Polymerization was observed even in the presence of radical scavengers. Secondary processes are numerous and make the interpretation of our results difficult; for example, the ethylene quantum yield increased upon addition of 10% oxygen, the simple radical scavenging effect of this additive does not explain such an effect.

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