Free Radicals Generated in Photocatalytic Oxidation of Some Amines and Diamines

1996 ◽  
Vol 1 (2) ◽  
Author(s):  
Ciping Chen ◽  
Daohui Lu ◽  
Guangzhi Xu
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Photocatalytic Oxidation ◽  
Spin Trapping ◽  
Experimental Results ◽  
Epr Spectra ◽  
Radical Species ◽  
Radical Intermediates ◽  
Radical Adduct ◽  
Spin Trapping Technique

AbstractFree radical intermediates produced during photocatalytic oxidation of some typical amines and diamines were investigated by a spin trapping technique. The EPR spectra of N-centered radical adduct and Ccentered radical adduct were observed. Experimental results disclose that these radicals are participants in the initial steps of photodegradation of these compounds. A mechanism which is consistent with the observation of these radical species is discussed.

Glutathione Peroxidase-Like Activity of Simple Selenium Compounds. Peroxides and the Heterocyclic N-Oxide Resazurin Acting as O-Atom Donors

1995 ◽  
Vol 50 (3-4) ◽  
pp. 209-219 ◽  
Author(s):  
Walter A. Prtitz
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Glutathione Peroxidase ◽  
Crystal Violet ◽  
The Other ◽  
Atom Transfer ◽  
Selenium Compounds ◽  
Radical Intermediates ◽  
Leuco Crystal Violet ◽  
Acid Pathway

Selenite and selenocystamine [(CyaSe)2] efficiently activate the decomposition of H2O2 y GSH and by other thiols, as demonstrated using a leuco crystal violet POD-based H2O2 assay which is applicable (unlike other assays) also in presence of thiols. The GPx-like activities were estimated to be 3.6 and 2.7 μmol H2O2/min per μmol SeO32- and (CyaSe)2, respectively. Both selenium compounds also activate reduction of the heterocyclic N-oxide resazurin (RN→O) to resorufin (RN) by GSH; H2O2 competes with reduction of this dye. GSSeH and CyaSeH, formed by interaction of GSH with SeO32- and (CyaSe)2, respectively, are likely to be the active reductants. CyaSeH, generated γ-radiolytically from (CyaSe)2, exhibits an absorption peak at 243 nm and is removed by H2O2 with a rate constant of 9.7x102 ᴍ-1 s-1, and slightly slower by hydroperoxides. We have no evidence for one-electron interactions between GSSeH or CyaSeH and H2O2, with formation of free radical intermediates, as previously proposed in the case of selenium-activated reduction of cytochrome c by GSH (Levander et al., Biochemistry 23, 4591-4595 (1973)). Our results can be explained by O-atom transfer from the substrate to the active selenol group. RSeH + H2O2 (RN→O)→RSeOH + H2O (RN), and recycling of RSeOH to RSeH (+ H2O) by GSH, analogous to the selenenic acid pathway of GPx. The substrate specificity appears to be different, however, in that GPx is unable to catalyse RN→O reduction, and GSSeH hardly catalyses the decomposition of cumene- or t-butyl-hydroperoxide; CyaSeH, on the other hand, is active also with the hydroperoxides. RN→O is reduced to RN also by certain oxidizing free radicals, e.g. by the thiyl CyaS·; O -atom transfer may in this case lead to the generation of reactive oxyl radicals.

Quantitative Electron Paramagnetic Resonance: The Importance of Matching the Q-Factor of Standards and Samples

2001 ◽  
Vol 55 (10) ◽  
pp. 1375-1381 ◽  
Author(s):  
Richard L. Blakley ◽  
Dwight D. Henry ◽  
Walter T. Morgan ◽  
William L. Clapp ◽  
Carr J. Smith ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radicals ◽  
Free Radical ◽  
Spin Trapping ◽  
Microwave Energy ◽  
Q Factor ◽  
Paramagnetic Resonance ◽  
Tert Butyl ◽  
Electron Paramagnetic ◽  
Stable Free Radicals

Electron paramagnetic resonance (EPR) quantification of free radicals from different samples facilitates comparison of free radical concentrations. Stable free radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), in a suitable solvent (e.g., benzene) can be used as a quantification standard. Free radicals found in samples can be shorter lived than radicals in prepared standards and require stabilizing spin-trapping agents such as N-tert-butyl-α-phenylnitrone (PBN) in an appropriate solvent (e.g., benzene). Analysis in our laboratory showed that free radicals from spin-trapped samples quantified against a standard of TEMPO in benzene displayed large differences among identical samples measured on either a Micro-Now 8300, Micro-Now 8400, or Bruker EMX EPR instrument. The Bruker instrument reported that the typical TEMPO in benzene standard had a Q-factor of ∼4400 while the Q-factor of our PBN-containing samples was ∼2500. (The Q-factor is inversely proportional to the amount of dissipated microwave energy in an EPR cavity.) By placing the TEMPO standard in a PBN/benzene solvent matrix we were able to match the Q-factor of our standards and samples, resulting in each of the three EPR instruments giving the same quantified free radical yields for the samples. This result points out the importance of matching the Q-factor between samples and standards for any quantitative EPR measurement.

scholarly journals Observations on nitroxyl free radicals in arylamine carcinogenesis and on spin-trapping hydroxyl free radicals

1982 ◽  
Vol 60 (12) ◽  
pp. 1577-1586 ◽  
Author(s):  
Robert A Floyd
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Spin Trapping ◽  
Biological Processes ◽  
Radical Chemistry ◽  
Free Radical Chemistry ◽  
Hydroxyl Free Radicals

The work presented illustrates the valuable ways that spin-trapping and nitoxyl free radical chemistry has helped us in gaining a better view of the nature of certain biological processes and thus, hopefully, will help to disentangle the principles governing the causes of certain diseases.

Thermolysis of α-hydroperoxyalkyl diazenes. Spin trapping of radical intermediates and spin trapping kinetics

1991 ◽  
Vol 69 (9) ◽  
pp. 1398-1402 ◽  
Author(s):  
Lukose Mathew ◽  
Emmanuel Y. Osei-Twum ◽  
John Warkentin
Keyword(s):  
Free Radical ◽  
Rate Constant ◽  
Ring Opening ◽  
Spin Trapping ◽  
Ethyl Vinyl Ether ◽  
Trapping Rate ◽  
Ethyl Vinyl ◽  
Enol Ethers ◽  
Radical Intermediates ◽  
Radical Trapping

α-Hydroperoxyalkyl diazenes (Me2C(OOH)N=NR, 1, R = CH2CF3, CH2CH2OMe, CH(Me)2, CMe3, CH2Ph, Ph, CH2CH2OPh, and c-C3H5CD2) decompose in benzene, at 50 °C or less, by a mechanism involving free radical (R•) intermediates. The radicals were trapped with 1-methyl-4-nitroso-3,5-diphenylpyrazole, 2, to afford spin adducts (nitroxyls) that were observed by ESR spectroscopy. When the solvent was ethyl vinyl ether, radicals from 1 (R = CH2CH2OPh) were trapped by the solvent and the adduct radicals so formed were spin trapped by 2. These observations support free radical mechanisms for thermolysis of 1 and for the hydroxyalkylations that occur when 1 are decomposed in solutions containing enol ethers or other unsaturated substrates. The ring-opening of cyclopropylmethyl radicals (cpm) to 3-butenyl radicals was used to estimate the rate constant for radical trapping by 2. For cpm the rate constant is given by log kcpm = (10.7 ± 0.4) − (3.9 ± 0.5)/θ where θ = 2.3 RT kcal mol−1. At 25 °C, the spin trapping rate constant has the value 6.9 × 107 M−1 s−1. Key words: hydroperoxyalkyl diazenes; radicals, spin trapping; spin trapping, rate constant.

Substituent effects in the kinetic analysis of free radical reactions with nitrone spin traps

1982 ◽  
Vol 60 (12) ◽  
pp. 1560-1564 ◽  
Author(s):  
C L Greenstock ◽  
R H Wiebe
Keyword(s):  
Free Radical ◽  
Substituent Effects ◽  
Spin Trapping ◽  
High Reactivity ◽  
Water Radiolysis ◽  
Radical Species ◽  
Effective Spin ◽  
Spin Traps ◽  
Kinetic Spectrophotometry ◽  
Radiation Induced

The kinetics of reactions of the water radiolysis species with substituted phenyl-N-tert-butyl nitrones (PBN), have been studied directly, in situ, using a pulsed Van de Graaff accelerator and kinetic spectrophotometry. The spin trapping of other secondary radiation-induced electrophilic and nucleophilic free radical species was also studied. The mechanistic aspects of these reactions are discussed in terms of the kinetic data. The effect of structure and substituents on the rate of spin trapping was tested for five para-substituted PBN’s. It was found that electron-withdrawing groups increase the rate of nucleophilic reactions involving hydrated electrons, formyl anions, and α-hydroxyalkyl radicals with substitued PBN. Electron-donating substituents produce the opposite effect. These studies confirm that nitrones are effective spin traps because of their high reactivity towards radiation-induced free radicals. Caution must be observed, however, in view of their lack of specificity, in interpreting spin-trapping data in complex steady-state systems involving more than one primary or secondary radical species, or where unstable spin-adducts are formed.

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