Electron-nuclear double-resonance

B1.15.5.1 ELECTRON-NUCLEAR DOUBLE RESONANCE SPECTROSCOPY (ENDOR)... 

Gemperle C and Schwelger A 1991 Pulsed electron-nuclear double resonance methodology Chem. Rev. 91 1481-505... 

Electron nuclear double resonance of transition metal complexes with organic ligands. A. Schweiger, Struct. Bonding (Berlin), 1982, 51, 1-119 (294). 

Schweiger A (1982) Electron Nuclear Double Resonance of Transition Metal Complexes with Organic Ligands. 51 1-122 Scozzafava A, see Bertini I (1982) 48 45-91... 

Riedel A, S Fetzner, M Rampp, F Lingens, U Liebl, J-L Zrmmermann, W Nitschke (1995) EPR, electron spin echo envelope modulation, and electron nuclear double resonance studies of the 2Ee-2S centers of the 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS. J Biol Chem 270 30869-30873. 

Mukai, K. Tsuzuki, N. Ishizu, K. Ouchi, S. Fukuzawa K Electron nuclear double resonance studies of radicals produced by the Pb02 oxidation of a-tocopherol and its model compound in solution. Chem. Phys. Lipids 1981, 29, 129-135. 

An exception to this rule arises in the ESR spectra of radicals with small hyperfine parameters in solids. In that case the interplay between the Zeeman and anisotropic hyperfine interaction may give rise to satellite peaks for some radical orientations (S. M. Blinder, J. Chem. Phys., 1960, 33, 748 H. Sternlicht,./. Chem. Phys., 1960, 33, 1128). Such effects have been observed in organic free radicals (H. M. McConnell, C. Heller, T. Cole and R. W. Fessenden, J. Am. Chem. Soc., 1959, 82, 766) but are assumed to be negligible for the analysis of powder spectra (see Chapter 4) where A is often large or the resolution is insufficient to reveal subtle spectral features. The nuclear Zeeman interaction does, however, play a central role in electron-nuclear double resonance experiments and related methods [Appendix 2 and Section 2.6 (Chapter 2)]. 

This chapter concludes with a brief description of one advanced technique, Electron Nuclear Double Resonance (ENDOR), the capabilities for which, unlike pulsed methods, may be added as a relatively minor modification to commercial CW ESR spectrometers. 

In Chapter 2, ENDOR (electron-nuclear double resonance) was briefly described. To perform an ENDOR experiment it is necessary to apply both a radiofrequency and a microwave frequency, effectively performing simultaneous NMR and ESR, respectively, on the sample. The experiment is performed at a fixed magnetic field, with the ESR saturating frequency centered on a... 

G.R. Eaton and S.S. Eaton, Electron-nuclear double resonance spectroscopy and electron spin echo envelope modulation spectroscopy, Comprehensive Coordination Chemistry II, Elsevier, Boston, 2004, 49. 

S. Sinnecker, E. Reijerse, F. Neese and W. Lubitz, Hydrogen bond geometries from paramagnetic resonance and electron-nuclear double resonance parameters Density functional study of quinone radical anion-solvent interactions, J. Am. Chem. Soc., 2004, 126, 3280. 

M. Bennati, C.T. Farrar, J.A. Bryant, S.J. Inati, V. Weis, G.J. Gerfen, P. Riggs-Gelasco, J. Stubbe and R.G. Griffin, Pulsed electron-nuclear double resonance (ENDOR) at 140 GHz, J. Magn. Reson., 1999, 138, 232. 

The development of a wide range of special forms of EPR was initiated when the idea of double resonance (using simultaneous irradiation by two different sources) was cast in 1956 by G. Feher at Bell Telephone Labs in his seminal paper on ENDOR, electron nuclear double resonance (Feher 1956). BioEPR applications of ENDOR were later developed on flavoprotein radicals in a collaboration of A. Ehrenberg and L. E. G. Eriksson in Stockholm, Sweden, and J. S. Hyde at Varian in Palo Alto, California (Ehrenberg et al. 1968), and on metalloproteins in a joint effort of the groups of R. H. Sands in Ann Arbor, I. C. Gunsalus in Urbana, Illinois, and H. Beinert in Madison (Fritz et al. 1971). 

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... 

Ehrenberg, A., Eriksson, L.E.G., and Hyde, J.S. 1968. Electron-nuclear double resonance from flavin free radicals in NADPH dehydrogenase ( old yellow enzyme ). Biochimica et Biophysica Acta 167 482-484. 

Fritz, J., Anderson, R., Fee, J., Palmer, G, Sands, R.H., Tsibris, J.C.M., Gunsalus, I.C., Orme-Johnson, W.H., and Beinert, H. 1971. The iron electron-nuclear double resonance (ENDOR) of two-iron ferredoxins from spinach, parsley, pig adrenal cortex and Pseudomonas putida. Biochimica et Biophysica Acta 253 110-133. 

In principle LVM spectroscopy is not the only way to evidence the presence of hydrogen in bulk materials not intentionally doped with hydrogen. Shinar et al. (1986) attributed optically detected electron nuclear double resonance (ODENDOR) lines to hydrogen associated with a PGa antisite-related defect in GaP. However the identification of these ODENDOR lines is not unambiguous as it has been recently proposed that these lines could be P-related (Watkins, 1989). 

As most of the nitroxyl spin-labelled synthetic derivatives of conjugated polyenes are light yellow crystals, the bond lengths were determined by X-ray crystallography38. The spectroscopic method used to measure the conformation is electron nuclear double resonance (ENDOR). It is beyond the scope of the present review to explain the method38 but the authors of the pertinent paper conclude that ENDOR is an accurate non-crystallographic method to determine polyene structures in solution. 

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