Spectroscopic studies of the hydrogen-oxygen explosion initiated by the flash photolysis of nitrogen dioxide

1952 ◽  
Vol 210 (1103) ◽  
pp. 439-460 ◽  
Keyword(s):  
Nitrogen Dioxide ◽  
Flash Photolysis ◽  
Spectroscopic Studies ◽  
Reaction Scheme ◽  
Oh Radical ◽  
Time Intervals ◽  
Induction Periods ◽  
Photochemical Decomposition ◽  
Explosive Reaction ◽  
Flash Spectroscopy

The method of flash photolysis has been used to initiate the reaction between hydrogen and oxygen, using a small amount of nitrogen dioxide as sensitizer. The dependence of the ignition limits on total pressure, capacity and the pressure of nitrogen dioxide have been studied, as well as the flash photochemical decomposition of nitrogen dioxide alone. The explosive reaction is complete in a few milliseconds, and very short induction periods are found whose duration can be explained in terms of the initial temperature rise. It is shown that the initiation of the explosion in this way is reproducible to less than 10 -4 s and flash spectroscopy is used to study the development of the reactions with time. The spectra obtained are described and the reactions of the OH radical are investigated by means of its absorption spectrum , whose intensity variations with partial pressure of hydrogen, oxygen, nitrogen and water vapour over time intervals of 0·2 ms throughout the reaction are given. Addition of hydrogen accelerates the reaction, but oxygen in excess has the same effect as an inert gas which is to decrease the rate. It is shown that the important propagation steps are exclusively bimolecular and the main reactions of the OH radical are identified. The mechanism of the overall explosion reaction is discussed and a reaction scheme is given which is in accordance with the results.

Studies of the explosive combustion of hydrocarbons by kinetic spectroscopy I. Free radical absorption spectra in acetylene combustion

1953 ◽  
Vol 216 (1125) ◽  
pp. 165-183 ◽  
Keyword(s):  
Absorption Spectra ◽  
Total Pressure ◽  
Flash Photolysis ◽  
Initial Period ◽  
Kinetic Spectroscopy ◽  
Radical Concentration ◽  
Stage 4 ◽  
Explosive Reaction ◽  
Stage 1 ◽  
Flash Spectroscopy

The explosive oxidation of acetylene, initiated homogeneously by the flash photolysis of a small quantity of nitrogen dioxide, has been investigated by flash spectroscopy. The absorption spectra of OH, CH, C 2 (singlet and triplet), C 3 , CN and NH, a number of which have not previously been observed, are described, and the relative concentrations, at all times throughout the explosion, are given. Four stages have been distinguished in the explosive reaction: 1. An initial period during which only OH appears. 2. A rapid chain branching involving all the diatomic radicals. 3. Further reaction, occurring only when oxygen is present in excess of equimolecular proportions, during which the OH concentration rises exponentially and the other radicals are totally consumed. 4. A relatively slow exponential decay of the excess radical concentration remaining after completion of stages 2 and 3. The duration of stage 1 is 0 to 3 ms. In an equimolecular mixture at 20 mm total pressure, containing 1.5 mm NO 2 , the durations of both stage 2 and stage 3 are approximately 10 -4 s and the half-life of OH in stage 4 is 0.28 ms. A preliminary interpretation of these changes and of the radical reactions is given.

On the Mechanism of Radical Polymerization of Methyl Methacrylate with Dithiobenzoic Acid as Mediator

2006 ◽  
Vol 59 (8) ◽  
pp. 549 ◽  
Author(s):  
Duc Hung Nguyen ◽  
Philipp Vana
Keyword(s):  
Methyl Methacrylate ◽  
Induction Period ◽  
Hydrogen Abstraction ◽  
Ester Group ◽  
Reaction Scheme ◽  
Ionization Mass ◽  
Controlled Polymerization ◽  
Induction Periods ◽  
Methyl Methacrylate Polymerization ◽  
Raft Agent

Dithiobenzoic acid (DTBA) induces controlled polymerization behaviour in methyl methacrylate polymerization at 60°C, accompanied by a pronounced induction period of several hours. DTBA is partially transformed during this induction period into a dithioester with a tertiary ester group moiety, which constitutes an efficient reversible addition–fragmentation chain transfer (RAFT) agent. The transformation reaction is proposed to proceed via a hydrogen abstraction from DTBA by radicals and subsequent termination of the formed phenylcarbonothioylsulfanyl radical with propagating radicals. The proposed reaction scheme was implemented into a computer model, by which the rate coefficient of the hydrogen abstraction from DTBA and of the reinitiation of the intermediate phenylcarbonothioylsulfanyl radical was estimated. The model is in agreement with all of the species observable by electrospray ionization mass spectrometry, with the extent of the experimental induction periods, and with the absolute concentrations of dithioesters that act as efficient RAFT agents during the polymerization. A protocol that uses a cocktail of initiators is introduced, by which the induction period in DTBA-mediated polymerization is effectively eliminated.

scholarly journals Significance of Conformation Changes During the Binding and Release of Chromium(III) from Human Serum Transferrin

2020 ◽  
Vol 4 (Supplement_2) ◽  
pp. 1798-1798
Author(s):  
Kyle Edwards ◽  
John Vincent
Keyword(s):  
Metal Binding ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Turnover Time ◽  
Time Intervals ◽  
Paramagnetic Resonance ◽  
Funding Sources ◽  
Research Award ◽  
Conformation Changes ◽  
Multiple Conformations

Abstract Objectives Transferrin, Tf, the protein that transports iron from the blood to the tissues via endocytosis, is believed to also transport chromium(III), Cr(III). Recently, the presence of multiple conformations was suggested by spectroscopic studies. The objective of this work is confirm whether various conformers of Cr(III)2-Tf exist and their potential significance for Cr(III) transport. Methods Cr(III) was added to apoTf in a buffered solution at pH 7.4 containing 25 mM bicarbonate at 37 °C. After time intervals, ultraviolet spectra were collected, or aliquots were removed and frozen for analysis by electron paramagnetic resonance (EPR) spectroscopy, which can distinguish free Cr(III) and Cr(III) bound to the two metal binding sites of Tf. To model the acidification of the endosome that triggers release of metal ions from Tf, the Cr(III)2-Tf conformer solutions were acidified by the addition of hydrochloric acid to pH 4.5 or 5.5. At time intervals after acidification, samples were again analyzed by ultraviolet and EPR spectroscopies. Results A combination of electronic and EPR studies reveal that the addition of Cr(III) to apoTf at near neutral pH in the presence of 25 mM bicarbonate results in the rapid binding of two Cr(III) accompanied and then followed by a series of conformation changes in Cr(III)2-Tf. These multiple conformations give rise to different spectroscopic properties and upon acidification different rates of Cr(III) release. Conclusions The conformer of Cr(III)2-Tf used in most previous studies and giving rise to EPR features at g ∼ 5.1, 5.4, and 5.6 forms too slowly to be physiologically relevant; however, two previously unknown conformers of Cr(III)2-Tf, giving rise to an EPR feature at g ∼2 and at g ∼ 5.4, respectively, were identified. The latter of these conformers has a lifespan similar to the turnover time of transferrin and releases Cr(III) rapidly, suggesting it is probably the most physiologically significant conformer of Cr(III)2-Tf. Funding Sources The University of Alabama College of Arts and Sciences Research Award.

Kinetics and spectroscopic studies of transients produced by flash photolysis of M(CO)3(PR3)2X2 (M = molybdenum, tangsten, W; X = Cl, Br)

1991 ◽  
Vol 30 (19) ◽  
pp. 3711-3718 ◽  
Author(s):  
Richard S. Herrick ◽  
Melinda S. George ◽  
Ronald R. Duff ◽  
Felicitee Henry. D'Aulnois ◽  
Ronald M. Jarret ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Spectroscopic Studies

Flash photolysis of carbon disulphide

1963 ◽  
Vol 276 (1366) ◽  
pp. 401-412 ◽  
Keyword(s):  
Vibrational Relaxation ◽  
Flash Photolysis ◽  
Carbon Disulphide ◽  
Ultra Violet ◽  
Multiple Quantum ◽  
Vibrationally Excited ◽  
Quantum Transitions ◽  
Photochemical Decomposition ◽  
Vacuum Ultra Violet

Vibrationally excited CS is produced directly by the photochemical decomposition of CS 2 . The presence of S(3 3 P ) and the absence of S(3 1 D ) during the flash photolysis was demonstrated by vacuum ultra-violet spectroscopy. It is suggested th at collision with atomic sulphur causes a fast vibrational relaxation of CS, probably involving multiple quantum transitions. The atomic sulphur decays by polymerization and not by reaction with CS 2 .

The photolysis and pyrolysis of nitromethane and methyl nitrite

1967 ◽  
Vol 299 (1458) ◽  
pp. 317-336 ◽  
Keyword(s):  
Nitric Oxide ◽  
Nitrogen Dioxide ◽  
Elevated Temperatures ◽  
Flash Photolysis ◽  
Stable Form ◽  
Methyl Radicals ◽  
Elimination Reaction ◽  
Kinetic Spectroscopy ◽  
Methyl Nitrite ◽  
A Minor

The photolysis and pyrolysis of nitromethane and methyl nitrite have been studied using the techniques of flash photolysis and kinetic spectroscopy. The results show that photolysis of nitromethane yields methyl radicals and nitrogen dioxide, and that these fragments undergo recombination and disproportionation reactions to form methyl nitrite, methoxyl, and nitric oxide. In the presence of added nitric oxide, the methyl radicals react principally with nitric oxide to form nitrosomethane, which subsequently dimerizes and also reacts further with nitric oxide to yield nitrogen dioxide. The evidence also suggests that nitrosomethane is removed by a relatively efficient reaction with nitrogen dioxide at elevated temperatures to produce nitromethane and nitric oxide. In the case of methyl nitrite, light absorption results not only in photolysis, but also in the formation of an isomer of the nitrite which then reverts slowly to the stable form. The nature of this isomer is not known, but possibilities are suggested and discussed. It is concluded that the decomposition (photolytic or pyrolytic) of methyl nitrite occurs by the rupture of the O—N bond, and that the methoxyl radicals formed disproportionate to yield methanol and form aldehyde. Nitroxyl is also formed but only as a minor product, and the marked increase in intensity of its spectrum in the presence of added nitric oxide shows that it is not formed by a molecular elimination reaction, but probably by CH 3 O + NO → CH 2 O + HNO.

scholarly journals Lokiarchaeota archaeon schizorhodopsin-2 (LaSzR2) is an inward proton pump displaying a characteristic feature of acid-induced spectral blue-shift

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Keiichi Kojima ◽  
Susumu Yoshizawa ◽  
Masumi Hasegawa ◽  
Masaki Nakama ◽  
Marie Kurihara ◽  
...  
Keyword(s):  
Schiff Base ◽  
Proton Pump ◽  
Flash Photolysis ◽  
Blue Shift ◽  
Spectroscopic Studies ◽  
Spectral Shift ◽  
Bulk Solution ◽  
Proton Pumps ◽  
Ph Titration ◽  
Retinal Chromophore

AbstractThe photoreactive protein rhodopsin is widespread in microorganisms and has a variety of photobiological functions. Recently, a novel phylogenetically distinctive group named ‘schizorhodopsin (SzR)’ has been identified as an inward proton pump. We performed functional and spectroscopic studies on an uncharacterised schizorhodopsin from the phylum Lokiarchaeota archaeon. The protein, LaSzR2, having an all-trans-retinal chromophore, showed inward proton pump activity with an absorption maximum at 549 nm. The pH titration experiments revealed that the protonated Schiff base of the retinal chromophore (Lys188, pKa = 12.3) is stabilised by the deprotonated counterion (presumably Asp184, pKa = 3.7). The flash-photolysis experiments revealed the presence of two photointermediates, K and M. A proton was released and uptaken from bulk solution upon the formation and decay of the M intermediate. During the M-decay, the Schiff base was reprotonated by the proton from a proton donating residue (presumably Asp172). These properties were compared with other inward (SzRs and xenorhodopsins, XeRs) and outward proton pumps. Notably, LaSzR2 showed acid-induced spectral ‘blue-shift’ due to the protonation of the counterion, whereas outward proton pumps showed opposite shifts (red-shifts). Thus, we can distinguish between inward and outward proton pumps by the direction of the acid-induced spectral shift.

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