scholarly journals Novel free radicals in synthetic and natural pheomelanins: distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy.

1982 ◽  
Vol 79 (9) ◽  
pp. 2885-2889 ◽  
Author(s):  
R. C. Sealy ◽  
J. S. Hyde ◽  
C. C. Felix ◽  
I. A. Menon ◽  
G. Prota ◽  
...  
Keyword(s):  
Free Radicals ◽  
Esr Spectroscopy

The effect of cation concentration on the nitrogen splitting constant of nitroxide free radicals

1990 ◽  
Vol 55 (10) ◽  
pp. 2377-2380
Author(s):  
Hamza A. Hussain
Keyword(s):  
Hydrogen Peroxide ◽  
Hydrogen Bonding ◽  
Free Radicals ◽  
Esr Spectroscopy ◽  
The Other ◽  
Tetraethylammonium Bromide ◽  
Splitting Constant ◽  
The One ◽  
Positively Charged ◽  
Two Equilibria

Nitroxide free radicals prepared from diethylamine, piperidine and pyrrolidine by oxidation with hydrogen peroxide were studied by ESR spectroscopy. The changes in the 14N splitting constant (aN) caused by the addition of KBr or tetraethylammonium bromide were measured in dependence on the concentration of the ions. For diethylamine nitroxide and piperidine nitroxide, the results are discussed in terms of two equilibria: the one, involving the anion, is associated with a gain or loss of hydrogen bonds to the nitroxide oxygen atom, the other is associated with the formation of solvent shared units involving the cation, which results in changes in the hydrogen bonding strenght. The large increase in the aN value in the case of pyrrolidine nitroxide is explained in terms of an interaction from one side of the positively charged N atom; the increase in aN in the case of diethylamine and piperidine nitroxides is explained in terms of interactions with both sides of the positively charged N atom.

Investigation of free radicals induced by light ions in CR-39 using ESR spectroscopy

2005 ◽  
Vol 40 (2-6) ◽  
pp. 218-223 ◽  
Author(s):  
S. Böhlke ◽  
D. Hermsdorf ◽  
J. Sichelschmidt ◽  
S. Starke
Keyword(s):  
Free Radicals ◽  
Esr Spectroscopy ◽  
Light Ions

Electron Spin Resonance Study of Phenolic Antioxidants. Correlations of Organic Free Radical Stability with Antioxidant Activity

1972 ◽  
Vol 45 (2) ◽  
pp. 402-422 ◽  
Author(s):  
J. C. Westfahl ◽  
C. J. Carman ◽  
R. W. Layer
Keyword(s):  
Molecular Structure ◽  
Free Radicals ◽  
Electron Spin Resonance ◽  
Electron Spin ◽  
Esr Spectroscopy ◽  
Spectroscopic Technique ◽  
Electron Spin Resonance Study ◽  
Phenolic Antioxidants ◽  
Radical Concentration ◽  
Spin Resonance

Abstract Electron spin resonance (ESR) is a well established, sensitive spectroscopic technique for determining the molecular structure, as well as the lifetime or stability of organic free radicals. Consequently, ESR spectroscopy provides a logical method for gaining insight into the role that free radicals play in the stabilization of rubber by organic antioxidants. We used ESR spectroscopy to determine the molecular structure of the phenoxyl free radicals derived from a series of twelve phenolic antioxidants. We also used ESR to measure relative radical concentrations of the free radicals and evaluated the twelve phenolic antioxidants relative to each other. We have found that the ESR measurement of relative radical concentration is a measure of relative radical stability, and that the relative radical stability is temperature dependent. By plotting relative radical concentration (or stability) as a function of temperature, we can rank these twelve antioxidants relative to each other. This ranking is in good agreement with the activity of these antioxidants in EPDM. These data were discussed in relation to antioxidant mechanism.

Application of ESR Spectroscopy in Bleaching Studies

Holzforschung ◽  
2003 ◽  
Vol 57 (2) ◽  
pp. 171-180 ◽  
Author(s):  
D. Cardona-Barrau ◽  
C. Matéo ◽  
D. Lachenal ◽  
C. Chirat
Keyword(s):  
Free Radicals ◽  
Metal Ions ◽  
Esr Spectroscopy ◽  
Lignin Content ◽  
Transition Metal Ions ◽  
Organic Radicals ◽  
Residual Lignin ◽  
Metal Retention ◽  
Formation And Evolution ◽  
The Impact

Summary In this study several pulp components were characterized by ESR spectroscopy. Free radicals present in the pulp lignin gave a well-defined signal, and the residual lignin content during a bleaching sequence could be followed using this technique. Organic radicals on the pulp carbohydrates were also detected and could be related to the formation of chromophore structures in pulp. Further, ESR spectroscopy made it possible to characterize several transition metal ions in pulp. Special attention was paid to metal retention and the impact of a sodium borohydride treatment, and the formation and evolution of complexes between metal ions and pulp components was scrutinized.

Measurement of Free Radicals from Smoke Inhalation and Oxygen Exposure by Spin Trapping and Esr Spectroscopy

1992 ◽  
Vol 16 (3) ◽  
pp. 167-174 ◽  
Author(s):  
K. T. Yamaguchi ◽  
R. J. Stewart ◽  
H. M. Wang ◽  
S. E. Hudson ◽  
M. Vierra ◽  
...  
Keyword(s):  
Free Radicals ◽  
Esr Spectroscopy ◽  
Spin Trapping ◽  
Smoke Inhalation ◽  
Oxygen Exposure

Electron Spin Resonance Study of Phenolic Antioxidants. II. Free Radical Structures Arising from Antioxidants Containing the 3,5-DI-Tert.-Butyl-4-Hydroxy-Benzyl Group

1973 ◽  
Vol 46 (5) ◽  
pp. 1134-1155 ◽  
Author(s):  
J. C. Westfahl
Keyword(s):  
Free Radicals ◽  
Electron Spin Resonance ◽  
Esr Spectroscopy ◽  
Quinone Methide ◽  
Electron Spin Resonance Study ◽  
Phenolic Antioxidants ◽  
Primary Radical ◽  
Tert Butyl ◽  
Spin Resonance ◽  
Spin Resonance Study

Abstract Oxidation of a series of phenolic antioxidants, or compounds related to antioxidants, was carried out using ferricyanide ion in dimethylsulfoxide solution. The free radicals produced were studied by ESR spectroscopy. Most of the antioxidants examined contained one or more 3,5-di-tert-butyl-4-hy-droxybenzyl groups. Based on their behavior on oxidation, the compounds can be divided into two classes. One class forms a relatively unstable primary radical which decomposes to give 2,6-di-tert-butyl quinone methide.

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