Electron paramagnetic spectroscopy

Since the phenoxyls possess an S = ground state, they have been carefully studied by electron paramagnetic spectroscopy (EPR) and related techniques such as electron nuclear double resonance (ENDOR), and electron spin-echo envelope modulation (ESEEM). These powerful and very sensitive techniques are ideally suited to study the occurrence of tyrosyl radicals in a protein matrix (1, 27-30). Careful analysis of the experimental data (hyperfine coupling constants) provides experimental spin densities at a high level of precision and, in addition, the positions of these tyrosyls relative to other neighboring groups in the protein matrix. 

Also known as electron paramagnetic spectroscopy (EPR). The two terms are synonymous, although there is a tendency to use ESR for spectroscopy of free radicals and EPR for spectroscopy of paramagnetic metal ions. 

Similarly, enzyme activity has been correlated to solvent polarity. Oxidation of cinnamyl alcohol by horse liver alcohol dehydrogenase (LADH) (pH 7.5) was observed in anhydrous hexane, methylene chloride and acetonitrile (Guinn et al., 1991). The oxidation rates were observed to increase as the dielectric constant decreased (Table 5). Electron paramagnetic spectroscopy (EPR) and two active site directed spin labels were used to examine the effect of solvent dielectric on structural stability. As the dielectric constant of the solvent decreased, the spectra broadened, indicative of an increase in rigidity or stability. 

The identification of isomers is as important as their synthesis and purification. The technique to be used for this purpose depends on the species to be analyzed and if it is in solution or in solid state. Without doubt if there are crystals of the material to be analyzed the best way to do it is by X-ray diffraction, but there are other techniques that can be used, such as infrared and Raman spectroscopy, electronic paramagnetic spectroscopy, nuclear magnetic resonance, and electronic spectroscopy. The choice of which technique to use depends on the intrinsic property of the material to be analyzed, and whether it presents paramagnetic or magnetic properties. 

Metallic sites Temperature-programmed reduction (TPR) X-ray adsorption near-edge spectroscopy (XANES) Extended X-ray adsorption fine structure (EXAFS) Mossbauer spectroscopy X-ray photoelectron spectroscopy (XPS) Electron paramagnetic spectroscopy (EPR)... 

Superacid sites have also been identified by electron paramagnetic spectroscopy suggesting that certain sites possess enhanced acidity due to inductive effects associated with neighboring acid sites (16),... 

Keywords Biopolymers Dynamics Electron paramagnetic spectroscopy NMR spectroscopy Polymers Structure... 

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