Spin-trapping technique, electron

Since only free radicals give an esr spectrum, the method can be used to detect the presence of radicals and to determine their concentration. Furthermore, information concerning the electron distribution (and hence the structure) of free radicals can be obtained from the splitting pattern of the esr spectrum (esr peaks are split by nearby protons).141 Fortunately (for the existence of most free radicals is very short), it is not necessary for a radical to be persistent for an esr spectrum to be obtained. Esr spectra have been observed for radicals with lifetimes considerably less than 1 sec. Failure to observe an esr spectrum does not prove that radicals are not involved, since the concentration may be too low for direct observation. In such cases the spin trapping technique can be used.142 In this technique a compound is added that is able to combine with very reactive radicals to produce more persistent radicals the new radicals can be observed by esr. The most important spin-trapping compounds are nitroso compounds, which react with radicals to give fairly stable nitroxide radicals 143 RN=0 + R —> RR N—O. 

Kuruc, J., Zubarev, V.E., Bugaenko, L.T., Macasek, F. 1988. X- and gamma-radiolysis of phosphate esters. Electron spin resonance study by the spin trap technique. J. Radioanal. Nucl. Chem. Lett. 127(3) 177-192. 

The electron paramagnetic resonance (EPR) spin-trapping technique was used to study the photochemical-, thermal-, and electrochemical-initiated decomposition of hydrogenated 1,2-diazocines 16 <1998MRC13>. 

The existence of free hydroxyl radicals in photo-initiated AOPs can be proven by applying a well-established method, the so-called spin trapping technique. The diamagnetic spin trap 5,5 -dimethyl-1-pyrroline N-oxide (DMPO) forms a stable paramagnetic spin-adduct with OH radicals. Its formation can be detected by electron paramagnetic resonance (EPR) spectroscopy. The underlying chemistry of... 

The presence of hydroxylated compounds as reaction intermediates and the detection of hydroxyl radicals through electron spin resonance (ESR) technique lead to the conclusion that in many cases the oxidations are via HO jg-attack (Turchi and Ollis, 1989 1990). Other studies also report the detection of hydroxyl radicals with various techniques such as spin trapping with electron paramagnetic resonance (EPR) (Riegel and Bolton,... 

Use of Electron Spin Resonance Techniques. Electron spin resonance (ESR) studies have been used to examine both activity of antioxidants " and their location within the Uposome . Studies of antioxidant radicals via ESR provide data on the electron delocalization within the antioxidant, which can be correlated with antioxidant activity, although not always with very good agreement with inhibition studies . Spin traps have been themselves examined as potential antioxidants, and have been used to attempt to trap peroxyl species for study . However, trapped peroxyl species are not very stable and carbon-centered radicals have been preferentially trapped, even though in some studies other techniques (e.g. malondialdehyde/thiobarbituric acid, MDA/TEARS-technique) indicate the presence of peroxide species in the sample . Eremy s salt ((K+S03 )2N0 ) has been used in micellar systems to determine rate constants quantitatively for the antioxidants a-Toc and ascorbic acid and their derivatives, because it reacts with them in a way similar to peroxyl radicals and can be used as a spin probe in stop-flow ESR studies . ESR has also been used to monitor the loss of dPPH and galvinoxyl signal intensity... 

A54. Janzen, E.G. and J.L. Gerlock Detection of gas phase free radicals by electron spin resonance spin trapping techniques Nature 222 (1969) 867-868. 27A70. 

A55. Janzen, E.G., LG. Lopp, and T.V. Morgan Detection of fluoroalkyl and acyl radicals in the gas-phase photolysis of ketones and aldehydes by electron spin resonance gas-phase spin trapping techniques J. Phys. Chem. 77 (1973) 139. 27A71. 

The reductions of H2O2 and O2 by [Ti(EDTA)(H20)], [Ti(H20)6], [Fe(EDTA)] -, [Fe(H20)6], and [Ru(NH3)j2 produce HO radicals with H2O2 as substrate, as detected by spin trapping techniques. The reactions with O2 proceed by both inner- and outer-sphere electron transfer pathways to produce the O J anion. The reduction of O2 by either [Fe(EDTA)] or [Fe2(ttha)] proceeds by an inner-sphere pathway with the subsequent attack of the coordinated O2 either on an adjacent carboxylate moiety or on sacrificial mediators in the solvent cage. [Ru(bpy)3] is quantitatively photooxidized to [Ru(bpy)3] in strongly acidic solutions containing dissolved oxygen. The process is represented by equations(2) and (3). 

Because of interaction between the paramagnetic moment and that from nuclear spin, very small concentrations of free radicals can be detected by their influence on the hyperfine structure of electron spin resonance spectra (ESR). This technique is now much employed in free radical studies. Concentrations of the latter down to 1 in 10 M may be detected by ESR, but many free radicals are not sufficiently long-lived to attain even this concentration. Sometimes spin-trapping techniques are employed whereby highly unstable free radicals are reacted with suitable diamagnetic molecules to form relatively long-lived radical species. 

Yang 1981). Support for the theory of alkyl radical transfer was provided by Ortiz de Monellano et al. (1983) who used the electronic paramagnetic resonance spin-trapping technique to detect the 2-phenylethyl radical formed during microsomal biotransformation of phenelzine. Production of the a-(4-pyridyl 1 -oxide)-N-ferf-butylnitrone/2-phenyl-ethyl radical adduct was dependent on the presence of active microsomes, phenelzine, NADPH (or NADH), and spin trap a-(4-pyridyl l-oxide)-N-ferf-butylnitrone (Ortiz de Monellano et al. 1983). The addition of catalase and superoxide dismutase resulted in a 28.5 and 24 % decrease in radical production, respectively (Rumyantseva et al. 1991). The concentration of the a-(4-pyridyl l-oxide)-N-ferf-butylnitrone/2-phenylethyl radical adduct decreased significantly in the presence of metal chelators, i.e. EDTA, diethylenetriaminepentaacetic acid (DTPA), or deferoxamine mesylate. 

The nature of the intermediates impHcated in the photooxidation of water with Ti02 has been identified in several reports using spin traps by the electron spin resonance (esr) technique under ambient conditions (53). No evidence for OH species, even at 4.2 K, was found (43), but the esr signal... 

Despite their short half-lives, it is possible to detect free radicals in biological tissues by the addition of nonradicals such as nitrones or nitroso compounds, which act as spin traps by forming relatively stable free radicals on reaction with the endogenous radical species. Utilizing the technique of electron spin resonance (e.s.r.) spectroscopy, we have demonstrated ROM generation by human rheumatoid synovium when subjected to cycles of hypoxia/normoxia in vitro. Using 3,5-dibromo-4-nitroso-benzenesulphonate (DBNBS) as a spin trap, a... 

Carotenoid radical intermediates generated electrochemically, chemically, and photochemically in solutions, on oxide surfaces, and in mesoporous materials have been studied by a variety of advanced EPR techniques such as pulsed EPR, ESEEM, ENDOR, HYSCORE, and a multifrequency high-held EPR combined with EPR spin trapping and DFT calculations. EPR spectroscopy is a powerful tool to characterize carotenoid radicals to resolve -anisotropy (HF-EPR), anisotropic coupling constants due to a-protons (CW, pulsed ENDOR, HYSCORE), to determine distances between carotenoid radical and electron acceptor site (ESEEM, relaxation enhancement). 

This technique can be used to measure the production of free radicals because the unpaired electron in a free radical has magnetic resonance. However, because the radicals are unstable, owing to their high chemical reactivity, the technique of spin-trapping is used. In this technique, the generated radicals react with a suitable probe, and the EPR spectra arising from the reaction of the probe with different radical species can then be identified. 

Spin trapping is an often-used technique in the study of possible radical production in biological systems (for reviews see Kalyanaraman, 1982 Mason, 1984 Mottley and Mason, 1989), particularly by the detection and monitoring of spin adducts of the hydroxyl and hydroperoxyl ( OOH) radicals in view of their relation to possible damage mechanisms. This is a large area of research which it is not possible to cover in a limited review, and the treatment will therefore be restricted to a discussion of the electron transfer properties of biochemical systems (for a review on the application of the Marcus theory to reactions between xenobiotics and redox proteins, see Eberson, 1985) and... 

Registration of ROS was carried out by electron paramagnetic resonance (EPR) technique using spin trap l-hydroxy-2,2,6,6-tetramethyl-piperidine-4-OH (2 x 10 3 M). EPR spectra in the samples were registered at room temperature in quartz cuvette with the volume of 200 pi (Burlaka et al., 1994). 

The nature of the cleavage and the possible stability of sulfuranyl radicals formed after electron transfer could be advantageously revealed by ESR and the associated technique of spin trapping as well [247,248]. Spin traps such as f-butylphenylnitrone and nitrosodurene could contribute to demonstrate the structure of the leaving radical formed by cathodic decomposition of the sulfonium substrate. 

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