New Spin Traps

Previous workers have outlined many of the properties of an ideal spin trap. These include  

Reaction with a wide range of initial radicals with high rate constants  

Generates adducts only via true spin-trapping  

Gives rise to readily identifiable spin adducts e.g. via a wide variation in the values of the hyperfine coupling constants and or g values with different added radicals)  

Stable to light, elevated temperature, and attack by nucleophiles or electrophiles, or cellular enzymes  

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A new spin-trap, 5-(diethoxyphosphorylmethyl)-5-methyl-4,5-dihydro-3H-pyrrole N-oxide (48), " and its hydroxyl- and superoxide-spin adducts, have been compared with the analogues obtained with 5-(diethoxyphosphoryl)-5-methyl-4,5-dihydro-3H-pyrrole N-oxide (49 DEPMPO) and with 5,5-dimethyl-1-pyrroline N-oxide (50 DMPO), and overall the spin trapping behaviour of 48 was found to be more similar to that of DMPO than DEPMPO. 

ESR spectroscopy is a new and promising technique in dairy science. In addition to numerous specific plications, it may prove to be useful in predicting the oxidative stability of dairy products. Areas for further investigation include the identification of radicals formed during production and storage of milk and dairy products, and also transfer of radicals between enzymes, lipids, proteins, etc. New spin traps, designed with specific hydrophilic/hydrophobic balance to trap specific radicals, provide good opportunities for evaluation of such radical transfer... 

New Cyclic Nitrone Spin Traps. - This area has seen the most explosive growth over the past few years and the structures of the majority of these new traps are shown in Scheme 2, together with the most widely employed abbreviations for these species. This builds on a previous compilation. Details on some of the characteristics of these new spin traps, their methods of synthesis and some key properties are given in Table 1. 

G.M. Rosen, B.E. Britigan, H.J. Halpem and S. Pou, Free Radicals Biology and Detection by Spin Trapping, Oxford University Press, New York, 1999. 

A spin trap is a diamagnetic compound that reacts with a radical by addition of the radical functionality typically to a double bond in the trap, thus forming a new radical that is more stable (better, less unstable) than the original radical. By far the most common class of spin traps are nitrone compounds that, upon addition of the primary radical, produce a stable aminoxyl radical (Figure 10.1). The compound DMPO is the paradigmatic spin trap it is readily available, widely used, and its EPR spectra are relatively easy to interpret. Some of its radical adducts have unpractically short lifetimes. 

Two possible approaches are indicated in Schemes 4 and 5. In the first, a reactive radical R> is spin-trapped in competition with its pseudo-first order reaction with a substrate SH, which occurs at a known rate to give RH and S. The growth of both spin-adducts (ST—R ) and (ST—S ) is monitored, and simple analysis leads to the trapping rate constant kT. In the second approach, R-does not react with a substrate, but undergoes unimolecular rearrangement or fragmentation at a known rate to give a new species R. This latter procedure... 

Upon slow warming of the matrix, the colour disappeared and a new species with A = 3.24 mT and gy = 2.0038 appeared, assigned to the formation of the chloro spin adduct [12] (32) after melting of the matrix at 240 K the characteristic solution epr spectrum of [12] was recorded. By y-radiolysis of the isomeric oxirane [13], which cannot sustain spin trapping, another way of direct matrix generation of PBN + was available and thus made possible further confirmation of these results (Zubarev and Brede, 1995). 

Nitric oxide has been difficult to detect with conventional spin-trapping agents. However, a new approach has been to use stable biradicals to trap nitric oxide (Fig. 19). The cheletrophic trap has two carbon centered radicals spaced the correct distance to catch nitric oxide and form a new ring (Korth et al.,... 

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. 

Janzen, E. G. (1980). A critical review of spin trapping in biological systems. In Free Radical in Biology, Pryor, W. A., ed., Academic Press, New York, pp. 115-154. 

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