Free radical research, application

Milov, A.D., Maryasov, A.G., and Tsvetkov, Y. D. (1998) Pulsed electron double resonance (PELDOR) and its applications in free radical research, Appl. Magn. Reson., 15, 107-143. 

ESR provides a direct method of measuring the presence and concentrations of free radicals and other paramagnetic species in materials. Applications in free radical research and in biophysics were published at an early stage [1-3], Recent progress has been reviewed [4]. Compared to other methods the following advantages have been emphasized. 

Very primary events in the chemical effect of radiations on matter are excitation and ionization of molecules, which result in the formation of neutral free radicals and radical ions. These reactive species play vital roles in the radiation-induced chemical reactions. As they are paramagnetic with an unpaired electron, electron spin resonance (ESR) spectroscopy has been a useful method for elucidating the mechanism of radiation-induced reactions in solid matter where radical species can be trapped temporarily. Since the early days of the chemical application of ESR, this method has been applied very often to the identification and quantification of free radicals in polymers irradiated by radiation [1]. This is probably because, from the view-point of fundamental research, a variety of free radicals are readily trapped in solid polymers and, from the view-point of applied research, these free radicals have close correlation with radiation-induced crosslinking and degradation of polymers. 

Even though some techniques of cationic grafting 125) and of free-radical grafting4 have been developed 126,127), the number of systems that can actually be used is very small, and the search for new and more general methods, applicable to systems that cannot respond to ionic techniques, has been one of the determining factors for research in the field of macromonomers. 

Enzymatic polymerization of acrylamide has gained a lot of interest among researchers. This is because acrylamide (Fig. 7.2) is a precursor used in the synthesis of polyacrylamides used as water-soluble thickeners with applications in gel electrophoresis (SDS-PAGE), papermaking, synthesis of dyes, and the manufacture of permanent press fabrics. HRP-mediated free radical polymerization... 

In an attempt to quantify free radicals produced in ischemic and reperfused myocardium, Zweier et al. [73,74] have used low-temperature ESR and concluded that oxy radicals (peroxyl and superoxide radicals) are produced in myocardial rat hearts. In these studies, heart tissues were subjected to pulverization prior to ESR studies. At about the same time that we became interested in the application of direct ESR in myocardial research, we also became immediately aware of the grinding artifact in myocardial tissues. 

Peroxidases are ubiquitous, and many are b-type heme proteins. Several good reviews summarize years of peroxidase research and describe peroxidase applications [57 -61]. Some of the reactions catalyzed by peroxidases are listed in Tab. 10.2 and include oxidation of aromatic and heteroatom compounds, epoxidation, enantioselective reduction of racemic hydroperoxides, free radical oligomerizations and polymerizations of electron-rich aromatics, and the oxidative degradation of lignin [58, 60],... 

This article does not intend to be a survey of electron paramagnetic resonance (EPR) spectroscopy in chemical biology, but rather the focus is to provide an entry-level introduction to chemists who are interested in the research opportunities that EPR may provide for enzymology smdies. The principles of this technique will be briefly described, as well as the breadth of the technique s applicability to free radicals and metallocenters in enzymology. Potential applications in the fumre will also be outlined. 

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