Spin trap molecules

Other complexities are revealed when frozen solutions of spin trap in methanol are irradiated, and the solution is then melted. The proportions of spin adducts are markedly dependent on radiolysis temperature. One contributory factor is undoubtedly the reaction of MeO with neighbouring methanol in the solid matrix, to produce HOCH2, before diffusion to reach spin-trap molecules is possible. 

Electron spin resonance (ESR) has been used to show the formation of H02 radicals on UV-irradiated Ti02 at 77 K (11). Spin-trapping molecules... 

Short-lived free radicals can also be trapped chemically by so called spin trap molecules to produce a more stable radical detectable by ESR. The hyperfine structure of this radical is used to identify the radical initially trapped. The first experiments were reported in 1968-1969 [11-13]. The method is much used in biological applications. 

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... 

Absorption of a light quantum leads to an electron-hole pair Eq. (19). The electron reacts with an adsorbed oxygen molecule Eq. (20), and the hole semi-oxidizes a sulfide anion at the surface Eq. (21). Further oxidation of the sulfide anion occurs by O and O2 Eq. (22). The number of Cd ions formed equals that of the sulfate anions The oxidation of illuminated CdS powders was investigated by measuring the consumption and by detecting the superoxide radical,, by an ESR spin trapping method... 

Spin traps are usually not practical to stabilize radicals on biomacromolecules because the reactivity is too low, presumably due to steric hindrance. Spin traps are used to stabilize physiologically relevant radicals of relatively small size such as hydroxyl, superoxide, and carbon-based radicals on organic molecules, for example, lipids. 

From the EPR spectroscopist s viewpoint the spin-trap experiment is next to trivial the molecular mass of the radical adduct is small enough to guarantee the molecule to tumble sufficiently rapidly at ambient temperatures in aqueous solution to ensure complete averaging away of any anisotropy in the spin Hamiltonian ... 

Spectroscopic observations of alkylcarbonium ions in strong acid solutions, 4, 305 Spectroscopy, l3C NMR, in macromolecular systems of biochemical interest, 13,279 Spin alignment, in organic molecular assemblies, high-spin organic molecules and, 26,179 Spin trapping, 17, 1... 

Spin alignment, in organic molecular assemblies, high-spin organic molecules and 26, 179 Spin trapping, 17, 1... 

Photochemical spin trapping experiments are the stock in trade, and the most difficult ones to judge with respect to mechanism because of their high complexity. The method became popular at a time when the effect of light upon molecules was believed to result mainly in homolysis of bonds, principally because of its ready use in combination with epr spectroscopy and... 

A-max = 525 run) has allowed both a determination of the depolymerisation rate and the number of break points (i. e. 2 DPPH molecules per bond breakage). Evidence for the formation of macroradicals in the degradation of polymethyl methacrylate, polystyrene and polyvinylacetate has also been provided by Tabata [63] using spin trapping and esr techniques. Taranukha [64] has also used spin traps to study the degradation of aqueous polyacrylamide. 

Nitroso compounds, nitrones, and other diamagnetic molecules are used as spin traps. Capturing radicals prodnced in the reaction, spin traps form the so-called spin adducts—stable nitroxyl radicals easily detectable by ESR spectroscopy. In other words, the progress of the reaction can easily be followed by an increasing intensity of the spin-adduct signal. By and large, the method of traps reveals radicals by the disappearance (or appearance) of the ESR signal. 

The data with the spin trap DMPO were very similar to those of Tauber et al. 127, ns) measuring the formation of ethylene from methional or KMB. Unfortunately, as with the use of oxidizable organic molecules, the specificity for OH of the spin adduct identified in the experiments with ESR is not clear. A critical, cautionary review of this approach has recently appeared... 

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