Nitric spin trapping

Morkovnik et al. (1989) found experimentally that the addition of an equimolar amount of 4-morpholino- or 4-dimethylaminoaniline to a suspension of nitrosyl perchlorate in 100 % acetic acid, dioxan, or acetonitrile yields a mixture of the diazonium perchlorate and the perchlorate salt of the amine radical cation, with liberation of gaseous nitric oxide. Analogous results in benzene, including evidence for radicals by ESR spectroscopy and by spin trapping experiments, were obtained by Reszka et al. (1990). 

Cheletrophic spin trapping of nitric oxide. Ultraviolet light converts the phenolic compound to a biradical, which rapidly reacts with nitric oxide to form a stable nitroxyl radical that is readily observable by electron paramagnetic resonance. 

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.,... 

The trapped nitric oxide becomes a stable nitroxide radical that is the same chemical moiety present in most common spin-trapping reagents. Nitric oxide production from activated macrophages has been directly assayed by this method (Korth et al., 1992). 

Nitric oxide (NO-) is generated enzymatically from glutamate by the nitric acid synthase and is responsible for a large number of diverse biological processes (for a review, see Nathan 1992 for spin trapping of the ensuing radicals, see Tsai et al. 2000). It was soon realized that an excess production of NO- is toxic, and a part of its toxicity was attributed to its reaction with 02-, i.e the formation of peroxynitrite [reactions (30) and (31)] (Beckman et al. 1990 for a review, see Murphy et al. 1998). 

Tsai P, Porasuphatana S, Pou S, Rosen GM (2000) Investigations into the spin trapping of nitric oxide and superoxide models to explore free radical generation by nitric oxide synthase. J Chem Soc Perkin Trans 2 983-988... 

Finally, spin trapping may also be used to assess the interaction between oxy radicals formed in the myocardium and nitric oxide released by the vascular endothelium in isolated rat and rabbit heart models. 

Miyajima, T., Kotake, Y. (1995). Spin trap phenyl-N-tert-butyl-nitone (PBN) inhibits induction of nitric oxide synthase in endotoxin-induction in mice. Free Radio. Biol. Med. 22 463-70. 

An example of intramolecular spin trapping was studied by A. Rassat55). Heating the bicyclic compound 31 in cyclohexane leads to dinitroso compound 32. Elimination of nitric oxide occurs by irradiation of the refluxing solution, and the resulting radical suffers intramolecular spin trapping giving aminyloxide 33. 

Shinagawa, K., T. Tokomoto, and K. Shirane Spin trapping of nitric oxide in aqueous solutions of cigarette smoke Biochem. Biophys. Res. Comm. 253 (1998) 99-103. 

In recent years, much interest has been focused on the detection of reactive oxygen species (ROS) and nitric oxide (NO) radicals in viable cell cultures and tissues. The spin trapping technique has proved to be very valuable, and its general characteristics have been described elsewhere in this encyclopedia. The complex biochemistry involved requires special techniques for spin trapping ROS and NO in biological materials. Such techniques form the content of the final sections. 

Vanin A, Huisman A, and van Faassen E (2002) Iron di-thiocarbamate as spin trap for nitric oxide Pitfalls and successes. Methods in Enzymology 359 27—42. 

An interesting medical application of the nitronylnitroxide-labeled dendrimers is spin trapping of nitric oxide. Nitronyl nitroxides can spin trap NO, but are unstable... 

Nitric oxide is a low-activity free radical and can be used as a counter of radicals in gas and liquid phases. The reactions of alkyl radicals with NO lead to the formation of nitroso compounds, which are spin traps. Thus, the initiation of free-radical reactions in solid polymers in the presence of nitric oxide provides further information on their mechanism. It is well established that at room temperature NO is not able to remove allylic and tertiary hydrogen atoms and add to isolated double bonds [24-26]. There are discrepant opinions on the capability of NO to react with low molecular weight (low molar mass) dienes and polyenes. Some authors believe that NO is able to add to dienes and polyenes, for example, to substituted o-quinonedimethane, phorone and P-carotene, with the formation of free radicals [27-29]. Another way of looking at these reactions lies in the fact that they can be initiated by NO2 impurities [25, 26]. 

The chemistry and biological significance of nitric oxide continue to attract great interest. In particular, efforts have been targeted at effective methods for the detection and quantification of this molecule. Walton and Park have reported preliminary results for the use of diazo ketones as spin traps for nitric oxide. 2-Diazocycloheptanone was found to trap nitric oxide, producing the (Z)-iminoxyl radical as the major product, which could be detected by the EPR spectrum obtained from a solution of the spin trap in f-butylbenzene. However, 5-diazouracil was found to be ineffective as a spin trap. 

OjQ gen radicals have been widely investigated in biomedical systems and are of great interest because of their cytotoxic effects and involvement in processes such as inflammation. They may be observed by spin traps (Table 4). Nitric oxide is also generated in conditions such as inflammation, and can be trapped by iron complexes such as iron diethyldi-thiocarbamate. 

Electron-spin resonance (ESR) indicated free radicals in a brown polymer (mean ca 1 kDa by field-desorption MS) from a glucose-4-chloroaniline model system.185 Such free radicals (see Chapter 2) could be a source of visible colour. Exposure of the melanoidin to nitric oxide, a radical-trapping agent, diminished the ESR signal by 48% and changed the colour to red-brown. 

P. Maruthamuthu and J. C. Scaiano, Biradicals double trapping by nitric oxide. An electron spin resonance study,/. Phys. Chem. 82, 1588-1591 (1978). 

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