HYSCORE cross-peaks

The hyperfine coupling tensors of carotenoids were determined from the HYSCORE analysis of the contour line-shapes of the cross-peaks (Dikanov and Bowman 1995,1998, Dikanov et al. 2000), which provided the principal components of the tensors that appear to be rhombic. Such tensors are characteristic of planar conjugated radicals with the unpaired spin in a pz orbital of the carbon of the C-H group. 

Fig. 17. First HYSCORE data from GdDTPA at 4 K, 3502 G. The correlated cross peaks, with splittings from 0.6-1.0 MHz, may reveal 14N-Gd couplings that can be probed [92]...

Figure 7. Peaks in HYSCORE spectra. Full circles represent the wanted cross-peaks, open circles represent axial peaks due to transfer of nuelear coherence to polarization, and vice versa, by the mixing it pulse. Open squares represent diagonal peaks caused by pulse nonideality (a) Weak-coupling ease, (ts < 2 tO and (b) Strong coupling case (4s > 2 rO. Modified with permission from [7]. Copyright 2001, Oxford University Press.

In the HYSCORE experiment only nuclear frequencies in different manifolds belonging to the same paramagnetic center are eorrelated with each other. For multinuclear spin systems the assignment of nuelear frequencies is often not straightforward, since some of the correlation peaks may not be observed in the HYSCORE speetrum due to the small intensity of the nuelear transitions in one of the two Ws manifolds. Additional information can be gained if correlations of nuclear frequencies within the same manifold can be obtained. Cross-peaks that represent such correlations can be created by replacing the nonselective transfer n pulse in the HYSCORE sequence by the double nuclear-coherence transfer (DONUT) mixer % - t - n [58]. This DONUT-HYSCORE experiment with the pulse sequence ji/2 -ti nil - echo results in crosspeaks and (twp i, copj). The presence of these cross-peaks in the DONUT-... 

Figure 24. Sequences for chirp ENDOR experiments (a) Davies-type chirp ENDOR (b) Mims-type chirp ENDOR (c) Chirp-ENDOR-HYSCORE sequence and (d) Two-dimensional chirp ENDOR-HYSCORE spectram of a Cu(II)-doped glycine single-crystal. Cross-peaks in the first quadrant correspond to proton ENDOR lines, cross-peaks in the second quadrant to nitrogen ENDOR hnes. Modified with permission from [7]. Copyright 2001, Oxford University Press.

Dikanov SA, Tyryshkin AM, Bowman MK. 2000. Intensity of cross-peaks in Hyscore spectra of 5 = /4, / = /4 spin systems. J Magn Reson 144 228-242. 

Figure 4. X-band SMART HYSCORE spectrum of aquometmyoglobin taken at observer position g = 6. The double-quantum cross-peaks are separated over four times the effective nuclear Zeeman frequency, which clearly differs from the tabulated value (dashed lines, separation 4vv). From this shift, the positive sign of the hyperfine value can be determined [93,94],...

HYSCORE and SMART HYSCORE (see Fig. 4 manuseript in preparation). The pseudonuclear effect to the g value can nicely be observed in the double-quantum cross-peaks and used beneficially to determine flic sign of the hyperfine values (Fig. 4). Furthermore, die use of ELDOR (electron double resonance) detected NMR techniques [57] at W-band largely facilitates the analysis of high-spin iron(III) heme proteins [94]. 

Complete interpretation of the low-frequency peaks was obtained through the applieation of the two-dimensional four-pulse HYSCORE experiment. The HYSCORE spectrum of VO(ema)2-treated rat bone is shown in Figure 11. Three sets of eross-peaks were evident, one of which appeared as an extended are about the P matrix peak (Fig. 11, cross-peak 3). Careful selection of the interpulse times led to suppression of the matrix peak to allow for better observation of the third cross-peak. Interpretation of the HYSCORE spectrum was carried out using eon-... 

Figure 11. HYSCORE spectrum of VO(ema)2-treated rat bone, acquired on the orientation nonseleotive Af/ = -1/2 peak of the FS-ESE speetrum. Numbers indicate the cross-peak sets corresponding to three different P superhyperfine coupiing constants. The nuciear matrix peaks of P and H are labeled. Reprinted with permission from [95]. Copyright 1999, American Chemical Society.

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