Conformational s-cis/trans isomerization in free radicals observed by muon level crossing resonance spectroscopy

1990 ◽  
Vol 112 (20) ◽  
pp. 7163-7167 ◽  
Author(s):  
Mary V. Barnabas ◽  
Krishnan Venkateswaran ◽  
David C. Walker
Keyword(s):  
Free Radicals ◽  
Resonance Spectroscopy ◽  
Level Crossing ◽  
Trans Isomerization

Loss of muonium in nonhomogeneous processes studied by level-crossing resonance

1990 ◽  
Vol 68 (9) ◽  
pp. 957-961
Author(s):  
Krishnan Venkateswaran ◽  
Mary V. Barnabas ◽  
Zhennan Wu ◽  
David C. Walker
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Resonance Spectroscopy ◽  
Level Crossing ◽  
Low Concentrations ◽  
High Concentrations ◽  
Radical Yield

Level-crossing resonance spectroscopy has been used to determine the yield of muonium atoms formed in water and in hexane through production of muonated free radicals. In the presence of high concentrations of solutes, which yield radicals, all muons injected into the solutions are found either in diamagnetic molecules or free radicals. However, at low concentrations, the free-radical yield was smaller and a "missing fraction" appeared. Inverse yield against inverse concentration plots were not linear, indicating that reactions leading to loss occurred with nonhomogeneously distributed species from the muon's expanding track.

scholarly journals Environmentally persistent free radicals are ubiquitous in wildfire charcoals and remain stable for years

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Gabriel Sigmund ◽  
Cristina Santín ◽  
Marc Pignitter ◽  
Nathalie Tepe ◽  
Stefan H. Doerr ◽  
...  
Keyword(s):  
Reactive Oxygen Species ◽  
Free Radicals ◽  
Reactive Oxygen ◽  
Resonance Spectroscopy ◽  
Oxygen Species ◽  
Pyrogenic Carbon ◽  
Spin Resonance ◽  
Long Time ◽  
High Concentrations

AbstractGlobally landscape fires produce about 256 Tg of pyrogenic carbon or charcoal each year. The role of charcoal as a source of environmentally persistent free radicals, which are precursors of potentially harmful reactive oxygen species, is poorly constrained. Here, we analyse 60 charcoal samples collected from 10 wildfires, that include crown as well as surface fires in forest, shrubland and grassland spanning different boreal, temperate, subtropical and tropical climate. Using electron spin resonance spectroscopy, we measure high concentrations of environmentally persistent free radicals in charcoal samples, much higher than those found in soils. Concentrations increased with degree of carbonization and woody fuels favoured higher concentrations. Moreover, environmentally persistent free radicals remained stable for an unexpectedly long time of at least 5 years. We suggest that wildfire charcoal is an important global source of environmentally persistent free radicals, and therefore potentially of harmful reactive oxygen species.

Intramolecular Motion in Organic free Radicals Studied by Muon Spin Rotation and Level-Crossing Spectroscopy

1988 ◽  
pp. 155-156
Author(s):  
P. W. Percival ◽  
J. -C. Brodovitch ◽  
S. -K. Leung ◽  
D. Yu ◽  
R. F. Kiefl ◽  
...  
Keyword(s):  
Free Radicals ◽  
Muon Spin ◽  
Spin Rotation ◽  
Muon Spin Rotation ◽  
Level Crossing ◽  
Intramolecular Motion

Über die Radikalkonzentration von Rattenleber-Mitochondrien in Abhängigkeit von verschiedenen Faktoren

1968 ◽  
Vol 23 (6) ◽  
pp. 798-803 ◽  
Author(s):  
M. Waldschmidt ◽  
H. Mönig ◽  
J. Schole
Keyword(s):  
Free Radicals ◽  
Electron Spin Resonance ◽  
Electron Spin ◽  
Mitochondrial Protein ◽  
Yeast Cells ◽  
Whole Body ◽  
Resonance Spectroscopy ◽  
Control Value ◽  
Spin Resonance ◽  
X Irradiation

The concentration of free radicals in freshly prepared ratliver-mitochondria was investigated under different conditions with the aid of electron spin resonance spectroscopy. The electron spin resonance signal at g=2.004 was measured at 77 °K and related to the weight in milligrams of mitochondrial protein. The concentration of free radicals increases with rising body weight or, in other words, with decreasing growth rate of the animals. A plateau is reached with about 1013 radicalcenters per mg protein for grown animals. The concentration of free radicals is 150% of the control value after fasting for 24 hours, whereas it is below the detectable level in cells of ascites hepatoma. We conclude that the concentration of free radicals determined at g = 2.004 is a function of mitochondrial activity. After whole body x-irradiation with a dose of 900 R, a significant decrease of 20% of the signal amplitude was measured. Increasing the dose to 1800 R did not decrease the radical concentration further. These results might be connected with the diminished activity of some flavin enzymes observed in liver mitochondria after x-irradiation in vivo. In further experiments we have incubated the mitochondria in vitro with various inhibitors of flavin enzymes. The individual inhibitors (ammonium-ions, KCN, acetonitrile, glucose) and also malonate reduce the concentration of free radicals to 80% of the control value in the mean if the particles are incubated at 37 °C for 5 minutes. The effect of malonate adds to the effects of the other inhibitors. The inhibitory effect of 2,4-dinitrophenol develops only after a longer incubation time. These results are discussed in connection with the influence of the same inhibitors on the Pasteureffect of yeast cells. Some specific inhibitors of the respiratory chain (Amytal, antimycin A, oligomycin) also diminish the concentration of free radicals.

scholarly journals Athelstan Laurence Johnson Beckwith OA FAA. 20 February 1930 — 15 May 2010

2012 ◽  
Vol 58 ◽  
pp. 3-21 ◽  
Author(s):  
Ian D. Rae
Keyword(s):  
Free Radicals ◽  
Organic Chemical ◽  
Resonance Spectroscopy ◽  
Chemical Research ◽  
Oxford University ◽  
Spin Resonance ◽  
National University ◽  
The University ◽  
Australian Academy ◽  
Australian Universities

Athelstan (‘Athel’) Laurence Johnson Beckwith was an organic chemist whose research was concerned with free radicals, the reactive intermediates that have important roles in many organic chemical reactions. After studies and junior appointments at Australian universities, he completed his doctorate at Oxford University at a time when scepticism about the very existence of free radicals was being dispelled by a small group of experimentalists. Returning to Australia, where he occupied chairs at the University of Adelaide and the Australian National University, Beckwith used studies of organic structure and mechanisms, revealed by kinetic methods and electron spin resonance spectroscopy, to become a world leader in this field of chemistry. He was honoured by election to Fellowship of the Australian Academy of Science (1973) and the Royal Society of London (1989), by several awards from the Royal Australian Chemical Institute, and by membership of the Order of Australia (2004). His extensive travels, often accompanied by his wife, Kaye, and their children, to work in overseas chemical research laboratories and to give presentations at international meetings, helped him to secure his place in networks at the highest levels of his profession. Several of those who studied with him now hold important positions in Australian chemistry.

Electron spin resonance spectroscopy of irradiated DNA

1968 ◽  
Vol 302 (1470) ◽  
pp. 361-365 ◽  
Keyword(s):  
Free Radicals ◽  
Resonance Spectroscopy ◽  
Absorbed Energy ◽  
Common Procedure ◽  
Yield Curves ◽  
Exponential Increase ◽  
Radical Concentration ◽  
Steep Part ◽  
Typical Experiment ◽  
Spin Resonance

Much work has been done in the last few years to study the effect of ionizing radiation on DNA . In a typical experiment a DNA sample is sealed off under vacuum in a quartz tube and irradiated at one end. The sample is then moved to the other (unirradiated) end and placed in the e. s. r. spectrometer. Results take the form, first, of spectra, which can obviously be obtained under a variety of irradiation and measurement conditions (variation of temperature has been a common procedure) and, secondly, of yield curves, where the area under the absorption curve is taken as a measure of the total free radicals and the radical concentration is plotted against dose. The curves usually show an exponential increase—the free radical concentration levelling off between 10 17 and 10 18 spins/g at a dose of about 1 Mrad. From the initial steep part of the curve the yield or G -value may be estimated as the number of free radicals produced by 100 eV of absorbed energy. Typical values for DNA lie between ½ and 2.

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