Nitroso compounds, radical identification

The effects of uv radiation on V/-nitroso compounds depend on the pH and the medium. Under neutral conditions and ia the absence of radical scavengers, these compounds often appear chemically stable, although the E—Z equiUbrium, with respect to rotation around the N—N bond, can be affected (70). This apparent stabiUty is due to rapid recombination of aminyl radicals and nitric oxide [10102-43-9] formed duting photolysis. In the presence of radical scavengers nitrosamines decay rapidly (71). At lower pH, a variety of photoproducts are formed, including compounds attributed to photoelimination, photoreduction, and photo-oxidation (69). Low concentrations of most nitrosamines, even at neutral pH, can be eliminated by prolonged kradiation at 366 nm. This technique is used ki the identification of /V-nitrosamines that are present ki low concentrations ki complex mixtures (72). 

The pre-eminent advantage of C-nitroso-compounds as spin traps is that in the spin adduct the scavenged radical is directly attached to the nitroxide nitrogen. Consequently, the esr spectrum of the spin adduct is likely to reveal splittings from magnetic nuclei in the trapped radical, and these will greatly facilitate its identification. A simple example is presented in Fig. 2, which shows the spectrum of the spin adduct of the methyl radical with 2-methyl-2-nitroso-... 

The first observations of the additions of transient radicals to nitroso compounds (equation 60) and nitrones (equation 61) to form stable nitroxyl radicals, which could be conveniently detected by ESR for the identification of the transient radicals, were reported in the mid-1960s. This technique has been extensively applied in chemical "" and biological systems. " ... 

Spin traps come in basically two types nitroso compounds and nitrone compounds. Reactive free radicals react with the carbon of the nitrone functional group to form a radical adduct that always has a nitroxide group, which is an unusually stable type of free radical. Nitrones are the most useful spin traps for the in vivo detection of free radical metabolites because of the stability of the resulting radical adduct. However, identification of the parent radicals can be difficult because adducts derived from different radicals often have very similar EPR spectra. A comprehensive review of this area through 1992 has recently been published [48]. 

Compared with nitrones, nitroso compounds like 2-methyl-2-nitrosopropane (MNP) incorporate the superoxide radical closer to the nitroxide center. Therefore, the adduct spectra provide more information on the nature of the primary radical, making its identification easier. But nitroso traps and their adducts are more susceptible to thermal, photochemical, and hydroxylative degradation as well as -ene addition. They have limited solubility and tend to... 

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 ... 

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