Free radicals spin trapping

Simic M, Hayon E (1973) Comparison between the electron transfer reactions from free radicals and their corresponding peroxy radicals to quinones. Biochem Biophys Res Commun 50 364-369 Sommerfeld T (2001) Electron-induced chemistry of 5-chlorouracil. Chem Phys Chem 677-679 Spalletta RA, Bernhard WA (1982) Spin-trapping free radicals by solvating X-irradiated crystalline pyrimidines. Radiat Res 89 11-24... 

Egerton TA, Murphy DM, Jenkins CA and Rowlands CC (1997) An EPR study of spin trapped free radical intermediates formed in the heterogeneously assisted photodecomposition of acetaldehyde. Journal of the Chemical Society, Perkin Transactions 2 2479-2485. 

Sphingomyehn, IR spectrophotometry, 683-4 Spin delocahzation, polar effects in decomposition, 903 Spin labels, free radicals, 665 Spin-lattice relaxation oxidized functional groups, 695 poly (methylstyrene peroxide), 709 Spin trapping artemisinin ESR, 1291 free radicals, 665... 

Photopolymerization of 7 at 25 °C resulted in approximately 80% conversion of double bonds and a Tg of 70 °C. Apparently, the Tg of the material increased as crosslinking proceeded, but the reaction stopped at only partial conversion when vitrification occurred. The result was a Tg only 20-40 °C higher than the sample temperature. In addition, trapped free radicals were detected in crosslinked films of 7 by electron spin resonance (ESR) (28). 

Reactive free radicals also react with the nitrogen of nitroso groups, forming a nitroxide one atom closer to the trapped radical than is the case with nitrone spin traps. This results in ESR spectra containing more chemical structural information. While nitroso spin traps provide radical identification, the resultant adducts are often less stable than those derived from nitrone traps. In particular, nitroso traps are unreliable for oxygen-centered radicals even in vitro. 

Electron Spin Resonance. Trapped free radicals in irradiated starch were studied utilizing an electron paramagnetic resonance instrument (Varian Associates Type 4500) fitted with a 100-kc. field modulation, Hi-lo power microwave bridge, and a multipurpose specimen cavity. The instrument is stated to have an accuracy of 10% and a minimum resolution of about lO spins per cc. Variants 0.1% pitch mixed with potassium chloride calibration standard containing 10 " spins per cm. of length was used as the reference curve. Samples and standard were contained in quartz tubes, 4 mm. in i.d., in sufficient depth to fill the cavity. 

Buettner, G.R. (1987) Spin trapping ESR parameters of spin adducts. Free Radical Biol. Med. 3 259-303. 

Since the expression ESR application to the study of molecular motion easily reminds of the so-called spin label and spin probe methods, these topics are included in the present article the related problems will be considered in Sect. 9 and 10. However, any trapped free radical must be a label for the study of molecular motion when the temperature dependences of the spectral parameters are adequately measured. The discussion described in Sect. 6 is an example of the study using peroxy radicals as labels. The discussion in Sect. 4 is another example of ESR application to molecular motion study using the spectral intensity. Examples of molecular motion based on the changes of spectral parameters of trapped free radicals are presented in Sects. 5 and 8. All this should show how the trapped radicals can be used as direct labels in order to apply ESR without substantially modifying the investigated materials. 

Trapping free radicals by the spin trapping technique. This technique is used for the detection and identification of short-lived free radicals by detecting the ESR spectra of nitroxyl addition products (spin adducts) of free radicals (R ) to nitroso (e.g. 2-nitroso-2-methyl propane, t-butyl nitroxide 10.19), nitrobenzene (10.20), pentamethylnitrobenzene (10.21)) and nitrone (phenyl-N-tert-butyl nitrone) (10.22) compounds called spin traps ... 

ESR studies on the initial free radicals were carried out by using MNP(2-methyl-2-nitrosopropane) or DMPO (5,5-dimethylpyrroline N-oxide) as the spin-trapping agent. The reactions are shown as ... 

In spin trapping, radicals are trapped by reaction with a diamagnetic molecule to give a radical product.476 This feature (i.e. that the free spin is retained in the trapped product) distinguishes it from the other trapping methods. The technique involves EPR detection of the relatively stable radicals which result front the trapping of the more transient radicals. No product isolation or separation is required. The use of the technique in studies of polymerization is covered in reviews by Kamachi477 and Yamada ft a/.478... 

In related work, the reactions of hydrogen peroxide with iron(II) complexes, including Feu(edta), were examined.3 Some experiments were carried out with added 5.5"-dimethyl-1-pyrroline-N-oxide (DMPO) as a trapping reagent fa so-called spin trap) for HO. These experiments were done to learn whether HO was truly as free as it is when generated photochemically. The hydroxyl radical adduct was indeed detected. but for some (not all) iron complexes evidence was obtained for an additional oxidizing intermediate, presumably an oxo-iron complex. 

Asahi M, Asahi K, Wang X, Lo EH. Reduction of tissue plasminogen activator-induced hemorrhage and brain injury by free radical spin trapping after embolic focal cerebral ischemia in rats. J Cereb Blood Flow Metab 2000 20 452 57. 

The technique of spin trapping was used to study the free radicals formed in the... 

It is unfortunate that typical concentrations of free-radical species present in biological systems are only at the limit of e.s.r. detection sensitivity and, of course, there are major technical difficulties in studying whole animals in this manner. Therefore, the most successful e.s.r. experiments have adopted the approach of spin trapping in which very reactive and thus transient radical species are converted to long-lived adducts via reaction with a trap such as a nitrone, e.g. Equation 1.1 ... 

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