And ENDOR

The complete spin Hamiltonian for a description of EPR and ENDOR experiments is given by... 

C. E. Poole, Jr. and H. A. Earach, eds.. Handbook of Electron Spin Resonance Datasources, Computer Technology, Relaxation and ENDOR, American Institute of Physics, New York, 1994. 

Gerson, F. Radical Ions of Phanes as Studied by ESR and ENDOR Spectroscopy. 115, 57-105 (1983). 

Geometries, hyperfme structure, and relative stabilities of the different positional isomers of monodeuterated benzene cations have been studied theoretically by density functional theory, using the B3-LYP functional, and experimentally by ESR and ENDOR spectroscopy. A comparison between theoretical and experimental results at 30 K gives acceptable agreement, but further experiments on multiply deuterated species should improve the analysis by making the effects of deuteration larger. 

The ESR spectrum of C6H6 " trapped in CFCI3 at 15 K is shown in Figure la and agrees with that reported previously [18]. The principal values of the hyperfine coupling were obtained from previous ESR and ENDOR measurements [17, 18]. The best agreement with experiment was obtained with the axes oriented as in Table 4. In the latter study, the simulated ENDOR spectra were insensitive to the orientation of the tensor axes, however, and the assignment was made on the basis of molecular orbital calculations [9]. The tensor data are reproduced here for convenience (see Table 4). 

Table 4 The g and hyperfine tensors (in Gauss) used in the ESR and ENDOR simulations of C6H5D + in CFCI3 at 30 K.

Almost simultaneously, Lindahl and co-workers proposed that Cluster C is the CO oxidation site based on EPR and ENDOR studies of the cyanide adduct of the enzyme (134). That proposal was based on the premise that CO and cyanide compete for the same binding site. Additionally, Xia and Lindahl have shown that, by mild SDS treatment, they can partially dissociate CODH/ACS, which is a tetra-meric enzyme with an subunit composition, into an isolated a subunit and an form (135). The form has the same level of CO oxidation activity as the native protein indicating that the a subunit is not involved in CO oxidation and that the /8 subunit must contain the clusters required for CO oxidation (135). In addition, CO2 alters the g values of the Credi form of the enzyme (136). 

Main advances in ESR spectroscopy have recently come about by adding new dimensions to basic ID ESR [1015]. Dimensions such as time and radiofrequency radiation have either created new spectroscopies or enriched one-dimensional forms. Examples are pulsed ESR and ENDOR. 

Bar, G., M. Bennati et al. (2001). High-frequency (140-GHz) time domain EPR and ENDOR spectroscopy The tyrosyl radical-diiron cofactor in ribonucleotide reductase from yeast. J. Am. Chem. Soc. 123 3569-3576. 

Konovalova, T. A. and L. D. Kispert (1998). EPR and ENDOR studies of carotenoid-solid Lewis acid interactions. J. Chem. Soc. Faraday Trans. 94 1465-1468. 

Wu, Y., L. Piekara-Sady et al. (1991). Photochemically generated carotenoid radicals on Nafion film and silica gel An EPR and ENDOR study. Chem. Phys. Lett. 180 573-577. 

N.D. Chasteen and P.A. Snetsinger, ESEEM and ENDOR spectroscopy, in Physical Methods in Bioinorganic Chemistry, Spectroscopy and Magnetism, ed. L. Que, Jr, University Science Books, Sausalito, CA, 2000. 

C. Finazzo, J. Harmer, B. Jaun, E.C. Duin, F. Mahlert, R.K. Thauer, S. Van Doorslaer and A. Schweiger, Characterization of the MCRred2 form of methyl-coenzyme M reductase A pulse EPR and ENDOR study, J. Biol. Inorg. Chem., 2003, 8, 586. 

S. Van Doorslaer, R. Bachmann and A. Schweiger, A pulse EPR and ENDOR investigation of the electronic and geometric structure of cobalt-ous tetraphenylporphyrin(pyridine), J. Phys. Chem. A, 1999, 103, 5446. 

Fig. 7 Esr and ENDOR spectra of 1,2-dianthrylethane [6a] for different ion-pair conditions A, DME/HMPA, K + B, MTHF, K+ at 190 K in solution.

ESR and ENDOR (electron-nucleus double resonance) spectroscopies110. 

The inactive form GOin, which displays a typical Cu(II) EPR signal, yields upon one-electron oxidation the EPR silent active form GO0X. For many years the presence of a Cu(III) ion (ct,. S = 0) in the active site (121) of the fully oxidized state GO0X was assumed. The Whittakers (122) showed in 1990 that one-electron oxidation of the copper depleted apoenzyme of GO produced an EPR active, remarkably stable Tyr radical that was studied by UV-vis, EPR, and ENDOR spectroscopy. From these studies, they concluded that the thioether modified Tyr 272 was oxidized and, consequently, they proposed that GOcx contains a Tyr 272 radical coordinated to a Cu(II) ion. 

We have reported that ESR and ENDOR (52) examination of degassed, irradiated samples of a number of polymers (PDHS, PDBS, poly(di-a-tetra-decylsilane) (PDTDS), poly(di-n-octylsilane (PDOS), poly(di-n-decylsilane) (PDDS) and poly(di-4-methylpentylsilane) (PDMPS) shows the formation of radical species which are persistent for hours and even days. The radical spectra (see Figure 4) are, however, clearly not consistent with those expected from the simple cleavage of the polymer backbone as described by Equation [2]. The structure of these radicals... 

The phenomenon of asymmetric hfs tensors was first discussed by McConnell134). Later, Kneubiihl135,136) proved the existence of asymmetric g and A tensors in paramagnetic systems with low symmetry. Evaluation of the asymmetry of A using EPR and ENDOR spectroscopy has been treated by several authors132,137 141). Recently, low-symmetry effects in EPR have been covered in a comprehensive review article by Pilbrow and Lowrey142). 

An EPR and ENDOR investigation of the planar copper complex 63Cu(sal)2 (Fig. 30) substituted into a single crystal of Ni(sal)2 has been reported by Schweiger et al.62,65). The aim of this work was to determine the structure of the internal H-bond occuring in Cu(sal)2, and to draw a detailed picture of the unpaired electron distribution on the... 

An extensive EPR and ENDOR study of Cu(TPP) and Ag(TPP) (Fig. 32) doped into (H20)Zn(TPP) single crystals has been published by Brown and Hoffman66,171. The complete set of hfs and quadrupole tensors for the 14N nuclei and the hfs tensors of the Ag(II) and Cu(II) ions and of the pyrrole protons are reported. A detailed analysis of the magnetic parameters (Table 6.1), which are measured with high accuracy, has been presented using the standard MO treatment66. ... 

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