Single Crystal ENDOR

Relative signs of the hyperfine splittings of two nuclei. In single crystal ENDOR studies the relative signs between hfs constants of different nuclei may sometimes be determined from the cross-term (3.18). If this second order term between nuclei I and K is... 

Fig. 23a, b. ENDOR with circularly polarized rf fields (CP-ENDOR). Single crystal ENDOR spectra of Cu(bipyam)2 (C104)2 diluted into Zn(bipyam)2(C104)2 arbitrary orientation, temperature 20 K. a) Conventional ENDOR spectrum (linearly polarized rf field), b) CP-ENDOR spectrum applied rf field right hand rotating. The spectrum is dominated by the eight nitrogen transitions with msAN > 0. (From Ref. 104)... 

A single crystal ENDOR study comprising 1H-, 13C-, 14N- and 59Co-ENDOR investigations of the Schiffbase compound Co(acacen) (Fig. 42) doped into Ni(acacen) 1/2H20 was therefore undertaken by Rudin et al.12,59,61,219). As illustrated in Fig. 2b, ENDOR spectroscopy allows hf and quadrupole interactions of all the magnetic ligand... 

The ENDOR work on heme compounds is an impressive example of a systematic study on an important class of biological compounds. One disadvantage is that most experiments had to be performed with the B0 field parallel to the complex normals, so that the full hfs and quadrupole tensors could usually not be evaluated. A single crystal ENDOR study on aquo-Mb is in preparation to rectify this lack of information257. ... 

A single crystal ENDOR study on V(bz)2 diluted into 2,2-paracyclophane is in preparation, which will allow to get deeper insight into the dynamic behavior of the benzene rings in these types of compounds281. ... 

Nuclear spin decoupling has been widely applied in NMR to simplify complicated spectra in liquid and solid phases . Recently, similar decoupling effects have been observed in single crystal ENDOR spectra with resolved nuclear dipole-dipole couplings between neighboring protons. This interaction can be partially decoupled by a strong second rf field. 

Single crystal ENDOR measurement is an informative but not always applicable method to identify paramagnetic species in solids. It is for instance difficult to obtain single crystals of biochemical materials. In other cases the paramagnetic species are intentionally trapped in a disordered matrix or in a frozen solution. The ENDOR lines are then usually broadened by the anisotropy of the magnetic couplings. Some data that a single crystal analysis can provide are difficult to extract from a powder sample. However, a considerable amount of information can often be obtained from ENDOR spectra of disordered systems. 

Table 3.6 Li-hfs couplings (in MHz) of an irradiated Li00CH-H20 polycrystaUine sample observed by ENDOR together with theoretical values (in parentheses) calculated for the surrounding Li ions in the vicinity of the CO radical. The calculation was done with DFT, at the B3LYP/3-21G level for a model structure consisting of 113 atoms, where the central COJ component was optimized and other atoms were fixed in the same positions as in the undamaged LiOOCH H20 crystal. For comparison the hfs values obtained by single crystal ENDOR meaurements are shown in the second line of each entry...

E3.12 The hyperfine and quadrupole coupling tensors for the N2D4" cation formed by X-irradiation of Li(N2Ds)S04 were obtained by single crystal ENDOR measurements.[Y. Itagaki et al. J. Phys. Chem. A 106, 2617(2002)]. 

Fig. 9.5 X-band ESR spectra of L-a-alanine powder at room temperature. Exp. experimental powder spectrum X-irradiated to 60 kGy, Sim. reconstructed powder spectrum due to three radicals, Rl, R2, R3, with parameters determined by single crystal ENDOR measurements and with relative intensities 0.589 0.335 0.076, see text for assignment. Spectra are adapted from [M.Z. Heydari et al. J. Phys. Chem. A 106, 8971 (2002)] with permission from the American Chemical Society...

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