Electron paramagnetic resonance degradation

Electron paramagnetic resonance spectroscopy (EPR) (also called electron spin resonance spectroscopy, ESR) has been scarcely applied in the field of art and art conservation. Some work can be found in which EPR is used as complementary technique to SEM-EDX, NMR, and mass spectrometry (MS) for studying free radicals occurring in polymerization, pyrolytic, oxidative, and other radical degradative processes in artwork, as well as in the characterization of varnishes and oleoresinous media [42]. 

A recent electron paramagnetic resonance study (13) has shown that I also degrades by a photoreduction pathway in the presence of alcohols or water, through the intermediacy of the corresponding ketyl radical. Since corresponding ketyl radicals and triplet states often have overlapping absorption spectra, it is important to emphasize that the transient observed in our optical flash photolysis experiments is the triplet state (not the ketyl radical), the key evidence being that both the yield and the lifetime of the transient are decreased by triplet quenchers. An important question... 

Capancioni S, Schwach-Abdellaoui K, Kloeti W, et al. In vitro monitoring of poly(ortho ester) degradation by electron paramagnetic resonance imaging. Macromolecules 2003 36(16) 6135-6141. 

Electron paramagnetic resonance (EPR), or electron spin resonance (ESR), can be used to detect types and quantities of fl ee radicals. Such information is of value in studying the chemistry occurring during degradation and fracture of polymeric materials (Capancioni et al., 2003 Hauck et al., 1997 Hinojosa etal., 1972 Devries, 1971 Partridge etal., 1993 Pace and Roland, 1991). EPR can also be applied to study carbon black and other fillers in polymers (Brosseau et al., 2001 Tang et al., 1994 Hommel et al., 1993). 

Rao and co-workers [82] used an inverted emulsion process for the synthesis of the emeraldine salt of PAM using a novel oxidising agent, benzoyl peroxide. The polymerisation was carried out in a non-polar solvent in the presence of four different protonic acids as dopants and an emulsifier (sodium lauryl sulfate). The polymer salts were characterised spectroscopically by ultraviolet-visible, Fourier-transform infrared, Fourier-transform Raman and electron paramagnetic resonance spectroscopy. Thermogravimetric analysis, was used to determine the stability of the salts and the activation energy for the degradation. The conductivity of the salts was found to be in the order of 10 S/cm. 

Electron paramagnetic resonance spectroscopy showed that xanthine/xanthine oxidase in cultured rat cardiomyocytes produced superoxide and hydroxyl radicals during 10 min (Durot et al. 2000). The xanthine/xanthine oxidase system altered sharply and irreversibly the spontaneous electrical and mechanical activities of the cardiomyocytes. However, the gas chromatographic analysis showed that these drastic functional damages were associated with comparatively moderate degradation of membrane polyunsaturated fatty acids. Moreover... 

In tfiis stwfy electron paramagnetic resonance (EPR) was used to gain direct evidence of heme structures, iron forms, and flee radicals that may help elucidate degradative processes in codced beef. 

Vogel, B., Aleksandrova, E., Mitov, S. et al. 2008. Observation of fuel cell membrane degradation by ex situ and in situ electron paramagnetic resonance. Journal of the Electrochemical Society 155 B570-B574. 

Gladyshev and co-workers [1] pointed out that, during the thermo-oxidative degradation of PVC, highly conjugated systems are produced and these can be conveniently followed by electron paramagnetic resonance (EPR) and ultraviolet (UV) spectroscopy. 

Figure 8. Electron paramagnetic resonance (EPR) spectra of the degradation products from the in vitro hydrolytic degradation of TAM-polyglycolide in buffer media over a period of 55 days at 37 C. (A). 3 days (B) 23 days (C) 55 days. Note the presence of split peaks in (A) and (B) that was not there in (C).

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. 

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