EPR determination

YORDANOV N D and CHRISTOVA A G (1997) Quantitative spectrometric and EPR-determination of l,l-diphenyl-2-picryl-hyi azyl (DPPH), Fre J Anal Chem, 358, 610-13. 

WoLFRUM EJ, Ollis DE, Lim PK, Eox MA (1994) The UV-H2O2 Process Quantitative EPR Determination of Radical Concentrations, J. Photochem. Photohiol. A Chem. 78 259-265. 

Yordanov, N. D. and Christova, A. G. (1997). Quantitative spectrophotometric and EPR-determination of 1,1-diphenyl-2-picryl-hydrazyl (DPPH). Fresenius Z. Anal. Chemie, 358, 610-13. [203]... 

Volkov A, Dockter C, Bund T, Paulsen H, Jeschke G (2009) Pulsed EPR determination of water accessibility to spin-labeled amino acid residues in LHCUb. Biophys J 96(3) 1124—1141... 

Cr(VI) reduction takes place through Cr(V) spedes, readily complexed by citrate and detected by EPR spectroscopy. Quantitative EPR determinations indicate that an important fraction (nearly 15%) of the reduced Cr(VI) is transformed to Cr(V)-Cit, which also undergoes a photocatalytic transformation. 

K. Jackowska, A. Kudelski, J. Bukowska, Spectroelectrochemical and EPR determination of the number of electrons transferred in redox processes in electroactive polymers - polyindole films, Electrochimica Acta 1994, 39, 1365. 

Clarkson RB, Smirnov AI, Smirnova TI, Kang H, Belford RL, Earle K, Freed JH. 1998. Multi-frequency EPR determination of zero field splitting of high spin species in liquids Gd(III) chelates in water. Mol Phys 95 1325-1332. 

Reactivation Ratio EPR Test (Fig. 19.20c) This is a simpler and more rapid method than the single or double loop tests, and depends on the fact that the value of determined during the anodic scan of a double loop test (which produces general dissolution without intergranular attack on sensitised material) is essentially the same for all AlSl Type 304 and 304L steels. 

The reactions of cyanoisopropyl radicals with monomers have been widely studied. Methods used include time resolved EPR spectroscopy,352 radical trappingj53 355 and oligomer00 356 and polymer end group determination. 1 Absolute341 and relative reactivity data obtained using the various methods (Table 3.6) are in broad general agreement. 

Time resolved EPR spectroscopy and UV-visible spectophotometry have proved invaluable in determining the absolute rate constants for radical-monomer reactions. The results of many of these studies are summarized in the Tables included in the previous section (3.4), Absolute rate constants for the reactions of carbon-centered radicals are reported in Table 3.6. These include t-butyl374 and cyanoisopropyP2 radicals. 

EPR methods that allow a more direct determination of kv have been developed. These enable absolute radical concentrations to be determined as a function of conversion. With especially sensitive instrumentation, this can be done by direct measurement/57 160 An alternative method, applicable at high conversions, involves trapping the propagating species in a frozen matrix361 362 by rapid cooling of the sample to liquid nitrogen temperatures. 

Additional information concerning the mechanisms of solid—solid interactions has been obtained by many diverse experimental approaches, as the following examples testify adsorptive and catalytic properties of the reactant mixture [1,111], reflectance spectroscopy [420], NMR [421], EPR [347], electromotive force determinations [421], tracer experiments [422], and doping effects [423], This list cannot be comprehensive. Electron probe microanalysis has also been used as an analytical (rather than a kinetic) tool [422,424] for the determination of distributions of elements within the reactant mixture. Infrared analyses have been used [425] for the investigation of the solid state reactions between NH3 and S02 at low temperatures in the presence and in the absence of water. 

K2C03 3 H202 contains hydrogen peroxide of crystallization and the solid phase decomposition involves the production of the free radicals OH and HOi, detected by EPR measurements [661]. a—Time curves were sigmoid and E = 138 kJ mole-1 for reactions in the range 333—348 K. The reaction rate was more rapid in vacuum than in nitrogen, possibly through an effect on rate of escape of product water, and was also determined by particle size. From microscopic observations, it was concluded that centres of decomposition were related to the distribution of dislocations in the reactant particles. 

EPR spectroscopy is usually used to calibrate the clock (i.e., to determine kc). The method described here uses EPR to detect the two radicals. These are the parent (R1 ) and the product (R2 ) of its reaction, be it cyclization, decarbonylation, decarboxylation, rearrangement, or whatever. The radical R1 is produced photochemi-cally in the desired inert solvent by steady and usually quite intense light irradiation of the EPR cavity. Typically, R1 and R2 attain steady-state concentrations of 10-8 to 10 6 M. 

Magnetic resonance methods include the applications of NMR and EPR spectroscopies. The occurrence of exchange reactions leads to line broadening. The analysis of the line shapes allows the rate constant to be determined. 

Various methods have been used to determine the redox potentials (Table XI). Very commonly, EPR-monitored chemical redox titration is performed, which can be used to measure the redox potential not only in isolated complexes but also in membrane preparations. In general, there is good agreement between redox potentials determined in membranes, isolated complexes, or isolated Rieske proteins or fragments the only exception is the water-soluble Rieske fragment from spinach bef complex where differences of more than 50 mV have been observed by the same group but using different methods (31). 

A second unusual EPR spectrum was observed in the oxidized (as-isolated) protein (Fig. 3). This spectrum, which was assigned to an S = z system, was not reminiscent of any Fe-S cluster. Indeed, with g-values of 1.968, 1.953, and 1.903, it looked more like a molybdenum or tungsten spectrum. However, chemical analysis ruled out the possibility that this EPR spectrum arose from Mo or W, and the spectrum was assigned to an Fe-S center instead. The spin concentration, however, was sub stoichiometric and sample-dependent. Furthermore, when the as-isolated protein was oxidized with ferricyanide, it became EPR silent. This, together with the iron determination and the fingerprint of the reduced protein, led Hagen and colleagues to the... 

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