Spin trapping technique

Chalfont ei a m were the first to apply the spin trapping technique in the study of radical polymerization. They studied radicals produced during S polymerization initiated by r-butoxy radicals with 108 as the radical trap. Since... 

There are several limitations on the use of the spin trapping technique when quantitative results are required. These are ... 

On the other hand, microsomes may also directly oxidize or reduce various substrates. As already mentioned, microsomal oxidation of carbon tetrachloride results in the formation of trichloromethyl free radical and the initiation of lipid peroxidation. The effect of carbon tetrachloride on microsomes has been widely studied in connection with its cytotoxic activity in humans and animals. It has been shown that CCI4 is reduced by cytochrome P-450. For example, by the use of spin-trapping technique, Albani et al. [38] demonstrated the formation of the CCI3 radical in rat liver microsomal fractions and in vivo in rats. McCay et al. [39] found that carbon tetrachloride metabolism to CC13 by rat liver accompanied by the formation of lipid dienyl and lipid peroxydienyl radicals. The incubation of carbon tetrachloride with liver cells resulted in the formation of the C02 free radical (identified as the PBN-CO2 radical spin adduct) in addition to trichoromethyl radical [40]. It was found that glutathione rather than dioxygen is needed for the formation of this additional free radical. The formation of trichloromethyl radical caused the inactivation of hepatic microsomal calcium pump [41]. 

We have confirmed the dissociation manner of these compounds by means of the spin-trapping technique [167]. The radicals produced from 7 and 2-phenylethyl N,N-diethyldithiocarbamate (41) were trapped with 2,4,6-tri-ferf-butylnitrosobenzene (BNB) as a spin-trapping agent (Eq.44) [168] ... 

The dissociation of model compounds for co-chain ends of polymers obtained using iniferters with the DC group was examined by the spin-trapping technique, similar to the disso dation of 7 and 8 previously mentioned [174,175]. From the results of the trapping experiments, it was concluded that 46,47, and 48 as model compounds for poly(MA), poly(MMA), and poly(VAc), respectively, dissociated at the appropriate position to produce a reactive carbon-centered radical and a stable DC radical. In fact, these compounds were found to induce the living radical polymerization of St when they were used as photoiniferters. 

Special spin-trapping techniques are also available for the detection of short-lived radicals in both homogeneous and heterogeneous systems. For instance, a-phenyl A-ferf-butyl nitrone (PBN), ferf-nitrosobutanc (f-NB), -(4-pyridyl A-oxidc) A-ferf-butyl nitrone (4-POBN), or 5,5-dimethyl-l-pyrroline A-oxidc (DMPO) can be made to react with catalytic intermediates to form stable paramagnetic adducts detectable by ESR [135], Radicals evolving into the gas phase can also be trapped directly by condensation or by using matrix isolation techniques [139],... 

Britigan, B. E., Cohen, M. S., Rosen, G. M. (1987). Detection of the production of oxygen-centered free radicals by human neutrophils using spin trapping techniques A critical perspective. J. Leuk. Biol. 41, 349-62. 

Despite these interesting diversions, the vast majority of reports of investigations or applications of the spin-trapping technique depend on the use of C-nitroso-compounds or of nitrones the remainder of this review will be concerned exclusively with these two classes of scavenger. 

Spin-adduct spectra often reveal splittings to substituent atoms other than hydrogen. Indeed, since the spin-trapping technique provides a convenient route to many nitroxides containing structural features likely to be of spectroscopic interest, it has frequently been used to this end. Chlorine and bromine splittings, as well as those from fluorine, have been encountered and many nitroxide spectra have been reported in which there is splitting from a second nitrogen, from phosphorus, or even from a metal atom. 

A final note of caution regarding rate comparisons by the spin-trapping technique might be that, despite the apparent simplicity of the procedure outlined here, great care has to be taken with sample preparation in order to achieve the expected reproducibility of ca. 5-10%. Nevertheless, an early prediction that spin trapping would have little quantitative value has proved to be without foundation. 

Burlaka et al. (2004) used pristine C60 at 10 pM with visible light from a mercury lamp to produce some phototoxicity in Ehrlich carcinoma cells or rat thymocytes and used EPR spin-trapping techniques to demonstrate the formation of ROS. 

A number of reports on the thermal decomposition of peroxides have been published. The thermal decompositions of f-butyl peroxyacetate and f-butyl peroxypivalate, of HCOH and a kinetic study of the acid-induced decomposition of di-f-butyl peroxide in n-heptane at high temperatures and pressures have been reported. Thermolysis of substituted f-butyl (2-phenylprop-2-yl) peroxides gave acetophenone as the major product, formed via fragmentation of intermediate alkoxy radicals RCH2C(Ph)(Me)0. A study of the thermolysis mechanism of di-f-butyl and di-f-amyl peroxide by ESR and spin-trapping techniques has been reported. The di-f-amyloxy radical has been trapped for the first time. jS-Scission reaction is much faster in di-f-amyloxyl radicals than in r-butoxyl radicals. The radicals derived from di-f-butyl peroxide are more reactive towards hydrogen abstraction from toluene than those derived from di-f-amyl peroxide. 

Janzen EG, Towner RA, Haire DL. 1987. Detection of free radicals generated from the in vitro metabolism of carbon tetrachloride using improved esr spin trapping techniques. Free Radic Res Common 3 357-364. 

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. 

The technique of spin-trapping radicals has been applied to the measurement of atmospheric hydroxyl by Watanabe et al. (102), although there are no reports of its use for peroxy radicals. The principle involves the reaction of the radical of interest with an organic nitrone immobilized on a filter paper or other substrate. The sample is returned to the laboratory, and the nitrone-radical product is dissolved in a suitable solvent and measured with EPR. The disadvantages of the spin-trapping technique are difficulty in finding suitable organic nitrone compounds and the fact that most of these molecules are photochemically unstable. 

The interaction of aryldiazonium tetrachlorocuprates [Cu(II)] with olefins has been studied by ESR spectroscopy using the spin-trapping technique (Lyakhovich et al. 1991). The radicals ArCH2CH( )Ph and ArCH2CH( )CN have been detected in mixtures of the aryldiazonium tetrachlorocuprates [Cu(II)] with styrene and acrylonitrile using nitroso-durene as a spin adduct. However, aryl radical signals were not detected under those conditions. Obviously, aryl radicals react with the nearby ethylenic bond within the activated... 

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. 

EPR spin-trapping technique can be used to detect free radical intermediates, which are free radicals that have a short lifetime to be detected by EPR—for example, OH (Janzen, 1980). The spin-trapping technique is based on the fact that during certain reactions in solution a transient radical will interact with a diamagnetic reagent to form a more persistent radical. The radical product accumulates to a concentration where detection and, frequently, identification are possible by EPR. The key reaction is usually one of attachment.The diamagnetic reagent is said to be a spin trap and the persistent radical product is then the spin-adduct (IUPAC, 1997). 

EPR in conjuction with the spin trapping technique has provided evidence for the intermediacy of free radicals in the formation of an endoperoxide by spontaneous addition of oxygen on a dienol it has been suggested that a long-lived triplet biradical intermediate is formed by addition of 302 to dienol.232 A probable mechanism (Scheme 10) has been postulated for the formation of 1,2-dioxane and acetophenone in the reaction of an alkene with Co(II)-02-Et3SiH.233... 

Hanna PM, Mason RP. Direct evidence for inhibition of free radical formation from Cu(I) and hydrogen peroxide by glutathione and other potential ligands using the EPR spin-trapping technique. Arch Biochem Biophys 1992 295 205-213. 

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