Electron paramagnetic resonance formation

BURNS c s, HEYERICK A, KEUKELEiRE D D and FOBES M D E (2001) Mechanism for formation of the light struck flavour in beer revealed by time-resolved electron paramagnetic resonance, Chem Eur J, 7, 4554-61. 

Scarpa, M., Rigo, A., Maiorino, M., Ursini, F. and Gregolis, C. (1984). Formation of a-tocopherol radical and recycling of alpha tocopherol by ascorbate during peroxidation of phosphatidylcholine liposomes. An electron paramagnetic resonance study. Biochim. Biophys. Acta 801, 215-219. 

However, reduced ceria is able, alone, to dissociate NO. Martinez-Arias et al. [85] have first investigated by electron paramagnetic resonance (EPR) and FTIR spectroscopies NO reaction on ceria pre-outgassed at different temperatures and showed the role of superoxides differentially coordinated in the formation of hyponitrites species further decomposed into NzO. Later Haneda et al. [86] have demonstrated that reduced ceria and reduced praseodymium oxide dissociate NO even though the presence of a noble metal (Pt) significantly increases the formation of N2 or N20. The main results of this study are summarized in Table 8.9. 

Electron paramagnetic resonance (EPR) spectroscopy proves the formation of peroxyl radicals in oxidized hydrocarbons [12—15]. 

Electron paramagnetic resonance (EPR) examination of hepatic microsomes from differently pretreated animals has lead to the conclusion that MC pretreatment leads to the formation of cytochrome P-1+50 (P-1+1+8) with high spin iron (6, 1+6). Chevion et al. (28) failed to demonstrate the presence of high spin cytochrome P-1+50 in a teleost fish even after induction with MC. The work of Chevion et al. (28 ) indicates further that the fish cytochrome P-1+50, which is inducible with PAH s and metabolizes readily PAH s, is not identical with the mammalian cytochrome P-1+1+8. 

For our purpose, it is convenient to classify the measurements according to the format of the data produced. Sensors provide scalar valued quantities of the bulk fluid i. e. density p(t), refractive index n(t), viscosity dielectric constant e(t) and speed of sound Vj(t). Spectrometers provide vector valued quantities of the bulk fluid. Good examples include absorption spectra A t) associated with (1) far-, mid- and near-infrared FIR, MIR, NIR, (2) ultraviolet and visible UV-VIS, (3) nuclear magnetic resonance NMR, (4) electron paramagnetic resonance EPR, (5) vibrational circular dichroism VCD and (6) electronic circular dichroism ECD. Vector valued quantities are also obtained from fluorescence I t) and the Raman effect /(t). Some spectrometers produce matrix valued quantities M(t) of the bulk fluid. Here 2D-NMR spectra, 2D-EPR and 2D-flourescence spectra are noteworthy. A schematic representation of a very general experimental configuration is shown in Figure 4.1 where r is the recycle time for the system. 

However, these reactions are also second order in N02 and appear to be too slow at atmospheric NOz levels to be important (Vogt and Finlayson-Pitts, 1994 Peters and Ewing, 1996). There is one aspect of the mechanism that is quite interesting, however, in that the mechanism appears to be at least in part a stepwise process involving the formation of a radical anion intermediate, C1---N02 in the solid, which has been identified by electron paramagnetic resonance (EPR) in both the NaCl and NaBr reactions at room temperature (Wan et al., 1996). This intermediate appears to be remarkably stable and may be responsible for synergistic health effects observed when rats were exposed to a combination of N02 and NaCl aerosols (Last and Warren, 1987). 

Poly (methyl methacrylate) was also subjected to mechanical reaction in a vibrating mill in common solvent for several monomers (ethylene, acrylic acid and its esters, acrylonitrile and styrene) at temperatures from —196 to 20° C (22). The formation of macroradicals and their reactions were followed by EPR (electron paramagnetic resonance). The macroradicals reacted with vinyl monomers at temperatures less than —100° C, while quinones underwent reaction as low as —196° C. The same experiments were performed also with polystyrene and polybutylenedimethacrylate. The radicals from polystyrene were more reactive than those from poly(methyl methacrylate). 

Stadler, J., Bergonia, H. A., Di Silvio, M., Sweetland, M. A., Billiar, T. R., Simmons, R. L., and Lancaster, J. R., Jr. (1993). Nonheme iron-nitrosyl complex formation in rat hepatocytes Detection by electron paramagnetic resonance spectroscopy. Arch. Biochem. Biophys. 302, 4-11. 

For the latter, the formation of photoexcited charges and their behavior were examined by electron paramagnetic resonance (EPR). Fig. 15.4 shows EPR signals obtained in a He atmosphere at 77K under UV irradiation.15) BaTi409 showed a... 

Photofragmentation of phenyl-substituted oxiranes has been shown12 to result in the formation of carbenes triphenyloxirane (3) on irradiation in methylcyclohexane at 77°K affords benzaldehyde (4) and diphenylmethylene (5), identified by fluorescence and electron paramagnetic resonance (EPR) absorption studies. The most convenient precursor of phenylcarbene (6) is stilbene oxide (7),13 and the... 

Sporer (45) gives conclusive evidence for the presence of a radical intermediate [electron paramagnetic resonance (EPR), and radical polymerization] but fails to describe the path by which the intermediate radical is converted to the cation. As possibilities he cites the crossing of the excited molecule to another, undescribed state from which it reacts, and reaction during the internal conversion step in which a molecule in the excited state converts to a molecule in a high vibrational ground state. Kinetic studies by Brown et al. (46) support the formation of ion-pair intermediates in the dark reactions. 

---