Rate constants for the reaction of the hydrogen atom with aliphatic ketones in water

1997 ◽  
Vol 75 (8) ◽  
pp. 1114-1119 ◽  
Author(s):  
Stephen P. Mezyk ◽  
Annett Lossack ◽  
David M. Bartels
Keyword(s):  
Hydrogen Atom ◽  
Rate Constants ◽  
Radical Scavenger ◽  
Hydrogen Atoms ◽  
Paramagnetic Resonance ◽  
Kinetic Measurements ◽  
Aliphatic Ketones ◽  
Hydroxyl Radical Scavenger ◽  
Free Induction ◽  
Electron Paramagnetic

Arrhenius parameters for the reaction of hydrogen atoms with 3-methyl-2-butanone, 3-pentanone, cyclopentanone, 4-methyl-2-pentanone, and 2-butanone in aqueous solution have been directly calculated from electron paramagnetic resonance free induction decay (FID) attenuation measurements. For these compounds, absolute scavenging rate constants at 25.0 °C of (8.84 ± 0.26) × 107, (4.20 ± 0.15) × 107, (4.91 ± 0.28) × 107, (3.25 ± 0.27) × 107, and (2.20 ± 0.32) × 107 dm3 mol−1 s−1, with corresponding activation energies of 17.43 ± 0.29, 20.69 ± 0.31, 18.73 ± 0.36, 22.24 ± 0.80, and 22.30 ± 1.04 kJ mol−1 were determined, respectively. Competition kinetic measurements based on total H2 yields have established that for all of these ketones the dominant hydrogen atom reaction path is by •H atom abstraction. The new activation energy for 2-butanone is much lower than the previously reported value of 40.1 ± 0.7 kJ mol−1 with this difference attributed to interfering reactions from the added bromide previously used as a hydroxyl radical scavenger. Keywords: Arrhenius, kinetics, hydrogen atom, aqueous, ketones.

Absolute rate constant measurements for the reaction of atomic hydrogen with acetone, 2-butanone, propionaldehyde, and butyraldehyde in aqueous solution

1994 ◽  
Vol 72 (12) ◽  
pp. 2516-2520 ◽  
Author(s):  
Stephen P. Mezyk ◽  
David M. Bartels
Keyword(s):  
Aqueous Solution ◽  
Atomic Hydrogen ◽  
Free Induction Decay ◽  
Absolute Rate ◽  
Hydrogen Atoms ◽  
Paramagnetic Resonance ◽  
Kinetic Measurements ◽  
Absolute Rate Constant ◽  
Free Induction ◽  
Electron Paramagnetic

Arrhenius parameters for the reaction of hydrogen atoms with acetone, 2-butanone, propionaldehyde, and butyraldehyde in aqueous solution have been directly measured by electron paramagnetic resonance free induction decay (FID) attenuation measurements. For these compounds, absolute scavenging rate constants at 25 °C of (1.97 ± 0.10) × 106, (3.82 ± 0.32) × 107, (8.11 ± 0.47) × 107, and (1.14 ± 0.07) × 108 dm3 mol−1 s−1 with corresponding activation energies of 30.7 ± 1.3 (7.5–52.8 °C), 40.1 ± 0.7 (8.1–74.5 °C), 22.2 ± 0.9 (8.0–39.0 °C) and 23.8 ± 0.8 (5.4–67.7 °C) kJ mol−1 were measured, respectively. Competition kinetic measurements have established that greater than 95% of H atom reaction with 2-butanone is by abstraction.

Investigation of Antioxidant Activity of Pomegranate Juices by Means of Electron Paramagnetic Resonance and UV-Vis Spectroscopy

2015 ◽  
Vol 98 (4) ◽  
pp. 866-870 ◽  
Author(s):  
Violetta Kozik ◽  
Krystyna Jarzembek ◽  
Agnieszka Jędrzejowska ◽  
Andrzej Bąk ◽  
Justyna Polak ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radical ◽  
Epr Spectroscopy ◽  
Antioxidant Properties ◽  
Free Radical Scavenger ◽  
Pomegranate Juice ◽  
Radical Scavenger ◽  
Paramagnetic Resonance ◽  
Vis Spectroscopy ◽  
Electron Paramagnetic

Abstract Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r) = 0.90 and determination coefficient (r2) = 0.81 (P <0.05).

Determination of the Rates of Hydrogen Atom Reaction with NO by a Modulation Technique

1973 ◽  
Vol 51 (3) ◽  
pp. 370-372 ◽  
Author(s):  
R. Atkinson ◽  
R. J. Cvetanović
Keyword(s):  
Nitric Oxide ◽  
Hydrogen Atom ◽  
Phase Shift ◽  
Rate Constants ◽  
Hydrogen Atoms ◽  
Arrhenius Parameters ◽  
Modulation Technique ◽  
The Absolute

A modulation technique has been used to determine from phase shift measurements the absolute values of the rate constants and the Arrhenius parameters of the reaction of hydrogen atoms with nitric oxide.

scholarly journals In situ kinetic measurements of α-synuclein aggregation reveal large population of short-lived oligomers

PLoS ONE ◽  
2021 ◽  
Vol 16 (1) ◽  
pp. e0245548
Author(s):  
Enrico Zurlo ◽  
Pravin Kumar ◽  
Georg Meisl ◽  
Alexander J. Dear ◽  
Dipro Mondal ◽  
...  
Keyword(s):  
Self Assembly ◽  
Large Population ◽  
Paramagnetic Resonance ◽  
Kinetic Measurements ◽  
Toxic Species ◽  
Self Assembling ◽  
Wide Range ◽  
Electron Paramagnetic

Knowledge of the mechanisms of assembly of amyloid proteins into aggregates is of central importance in building an understanding of neurodegenerative disease. Given that oligomeric intermediates formed during the aggregation reaction are believed to be the major toxic species, methods to track such intermediates are clearly needed. Here we present a method, electron paramagnetic resonance (EPR), by which the amount of intermediates can be measured over the course of the aggregation, directly in the reacting solution, without the need for separation. We use this approach to investigate the aggregation of α-synuclein (αS), a synaptic protein implicated in Parkinson’s disease and find a large population of oligomeric species. Our results show that these are primary oligomers, formed directly from monomeric species, rather than oligomers formed by secondary nucleation processes, and that they are short-lived, the majority of them dissociates rather than converts to fibrils. As demonstrated here, EPR offers the means to detect such short-lived intermediate species directly in situ. As it relies only on the change in size of the detected species, it will be applicable to a wide range of self-assembling systems, making accessible the kinetics of intermediates and thus allowing the determination of their rates of formation and conversion, key processes in the self-assembly reaction.

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