Radicals by spin trapping

ESI Study of free radicals by spin-trapping SimSes et al. [57]... 

A variety of studies using RF EMRI have been carried out on living mice. These include (i) oximetry in tumour tissues and the response to perfluorocarbons for their potential use in radiotherapy, (ii) the detection of hydroxyl radicals (by spin trapping) in y-irradiated tumours, (iii) the distribution of nitroxyl radicals with distinct pharmacological abdominal compartment affinities and (iv) quantitative measurement of the viscosity of a non-vascular compartment. 

Lown, J. W., S.-K. Sim, and H.-H. Chen Hydroxyl Radical Production by Free and DNA-Bound Aminoquinone Antibiotics and its Role in DNA Degradation. Electron-Spin Resonance Detection of Hydroxyl Radicals by Spin Trapping. Canad. J. Biochem. 56, 1042 (1978). 

The application of RPR in the detection and quantification of species formed by spin-trapping the products of radical-monomer reactions is described in Section 3.5.2.1, The application of time-resolved F.PR spectroscopy to study intermolecular radical-alkene reactions in solution is mentioned in Section 3.5.1. 

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). 

Samsonova and Nikiforov, 1984), and porphyrin and phthalocyanine metal complexes (Becker et al., 1985a, 1986b Becker and Grossmann, 1990) were tested. That a series of relatively simple anions such as the oxalate monoanion, tetraphenyl bor-anate (Ph4B ), bromide, chloride, and even tetrafluoroborate can act as donors is, at least for the last mentioned anion, surprising, but Becker et al. (1985 b) were able to trap aryl radicals and in some cases also donor radicals (Cl, COO ) by spin trapping with nitrosodurene and phenyl-tert-butylnitrone. The photochemical effect is postulated to be due to ion pairs ArNJ X-. 

The reaction of OH radicals with dimethyl sulfoxide in aqueous solution was studied already in 1964 by Norman and coworkers37 38. They used the system T1m-H202 to produce OH radicals and using ESR/rapid mixing techniques they were able to demonstrate elimination of a methyl radical during the OH induced oxidation. Further studies showed the formation of sulfmic radicals in this reaction either directly or by spin trapping experiments39-44. 

A number of methods are available for following the oxidative behaviour of food samples. The consumption of oxygen and the ESR detection of radicals, either directly or indirectly by spin trapping, can be used to follow the initial steps during oxidation (Andersen and Skibsted, 2002). The formation of primary oxidation products, such as hydroperoxides and conjugated dienes, and secondary oxidation products (carbohydrides, carbonyl compounds and acids) in the case of lipid oxidation, can be quantified by several standard chemical and physical analytical methods (Armstrong, 1998 Horwitz, 2000). 

Poyer, J.L., McCay, P.B., Lai, E.K., Janzen, E G. and Davis, E.R. (1980). Confirmation of assignment of the trich-loromethyl radical spin adduct detected by spin trapping during carbon tetrachloride metabolism in vim and in vivo. Biochem. Biophys. Res. Commun. 94, 1154-1160. 

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. 

Chignell etal. intensely irradiated p-aminobenzoic acid with a xenon arc lamp and showed the formation of several free radicals detected by spin traps in conjunction with ESR spectroscopy. It was suggested that such radicals could cause lipid peroxidation or react via one of the excited forms of oxygen [42, 43],... 

Many of the early reports of spin-trapping experiments were focused on mechanistic investigations, and some of these feature in the early reviews (see p. 4). Unfortunately, it is in this application that inferences drawn may be most suspect. For example, the inability of the method to differentiate between radical trapping on the one hand, and a combination of nucleophile trapping with one-electron oxidation on the other, is a serious shortcoming. An early example of this was the tentative conclusion that acetoxyl radicals were spin-trapped by PBN competitively with their decarboxylation in reactions of lead tetraacetate. In view of the rapidity of the decarboxylation reaction, trapping of acetate ion and subsequent oxidation seems a likely alternative. 

If an aqueous solution saturated with oxygen is sonicated hydrogen peroxide formation occurs. This is due to hydroxyl ( OH) and hydroperoxyl ( OOH) radical recombination outside the cavitation bubble (Scheme 4.1). These radicals result from HjO and O2 homolytic cleavage inside the bubble and have been observed by spin trapping experiments (Scheme 4.1) [19]. 

Radicals such as OH and OJ can be stabilized, and detected by epr, by spin-trapping with dmpo,... 

Cyt c is associated with the outer surface of the inner mitochondrial membrane. Phospholipids induce conformational changes in the protein and, in certain instances, the haem can convert to the high spin (S = 5/2) form, indicative of a weakening of the ligand field caused by displacement of the sixth ligand (Met-80). This has been associated with the detection of lipid radicals by direct EPR (at 11 K).65 Indeed, peroxidase-type activity is also evident in the reaction of cyt c with lipid hydroperoxides, as studied by spin trapping in conjunction with HPLC and MS.66... 

Numerous studies have indicated that pro-inflammatory mediators (cytokines) are involved in the destruction of the insulin-producing p-cells of the pancreas in the development of type I diabetes. Tabatabaie et al. introduced cytokines and PBN into the pancreas of rats. The analysis of pancreatic extracts revealed that the cytokines stimulate the formation of lipid radicals. Radical generation did not occur in rats treated with streptozotocin, which destroys the P-cells.33 Evidence for the role of radicals in diabetes has also been provided by spin trapping studies in pancreatic homogenates, showing that streptozotocin, which is often used to induce the condition in laboratory animals, stimulates OH production.332 Other workers, using EPR to observe the decay of a spin probe in the abdomen of mice (at 1.2 GHz), have demonstrated that strep-... 

Finally superoxide radicals can also be generated photochemically in chloroplasts in the presence of ascorbate or of paraquat. The formation was demonstrated by spin trapping on illumination of spinach chloroplasts in the presence of oxygen and paraquat Superoxide radicals are formed, moreover, in the near-ultraviolet photooxidation of tryptophan, as indicated by the increase of the HjO production in the presence of SOD and on irradiation in aerated solutions of protoporphyrin at 400 nm and of melanin with light of 320—600nmas shown by spintrapping. 

The production of hydroxyl radicals was demonstrated by spin-trapping in the autoxidation at pH 11.5 of 6-hydroxydopamine. The reaction was partially inhibited by SOD, by catalase, and by diethylenetriaminepenta-acetate and deferoxamine... 

Rosen, (r,M.. tree Radicals Bioloyy and Detection By Spin Trapping, Ox lord... 

Albumine-Cu2+ complexes are similarly reduced by thiols and then react with H202 (Ozawa et al. 1993). The OH radical thus formed has been detected by spin trapping. 

The 02-7H02- radicals can be trapped by spin traps, but the rate constants are low and their lifetime is often only short (Lauricella et al. 2004), i.e., they give rise to the OH-adduct radical upon hydrolysis (Chap. 3.4). To increase the... 

Many of these free radical intermediates have been detected directly with ESR. Others are too reactive to detect directly, but a method to stabilize these free radicals called spin trapping has proved successful. Spin trapping is a technique in which a short-lived reactive free radical (R ) combines with a diamagnetic molecule ( spin trap ) to form a more stable free radical ( radical adduct ) which can be detected by electron spin resonance ... 

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