Pake pattern dipolar coupling

If the molecular tumbling rate is slow enough that larger electron-electron dipolar couplings are not motionally averaged, Fourier deconvolution can be used to analyze dipolar interactions in fluid solution.18 Distances in doubly spin-labelled rhodopsin were measured by Fourier deconvolution of CW line-shape changes in room temperature solution.78 The broadening function was modelled as the sum of Pake patterns from a distribution of distances. As a reference point for the distance measurements one label was attached at the cytoplasmic termination of transmembrane helix 1. The second label was attached near the cytoplasmic termination of transmembrane helix 7 or in the short helix 8. The distances and conformational flexibility in the dark state are... 

In this case, the frequencies of the Pake pattern are shifted by J and the frequency of the edge (0y) and peak (0/) of the Pake pattern do not behave like2 l (Fig. 16.8) what they do if J is zero (Fig. 16.2C). However, if the full Pake pattern is observed both contributions can be disentangled and quantified. From the frequencies at which the peaks and edges of the Pake pattern appear, the dipolar coupling constant vdd and J can be calculated using Eqs. (16.8) and (16.9) derived from Eqs. (16.7) and (16.3) (Milov etal, 1998) ... 

Figure 16.8 Pake pattern of a biradical with dipolar and exchange coupling. The edges and peaks do not behave like 1 2 (taken from Margraf ft al., 2009).

A special case occurs if the solid contains nuclear spin pairs that are sufficiently far apart from each other such that intrapair coupling dominates interpair coupling. In this situation, instead of a featureless broad lineshape, we observe a well-defined powder pattern known as a Pake doublet (Figure 15.15). Since the dipolar coupling between two nuclei... 

Figure 2.5. A. Schematic powder pattern of a spin- /2 nucleus dipolar coupled to a second spin- /2 nucleus. B. Example of a H Pake powder pattern from NaAlSi206.H20 from Yesinowski, Eckert and Rossman (1988) with permission of the American Chemical Society.

FIGURE 5.3 Measurement of dipolar couplings (Pake patterns) in solid-state H NMR spectra of H2 complexes. (Reprinted with permission from Ref. 123. Copyright 1990 Elsevier.)... 

The dipolar pattern for polystyrene shown in Figure 3 (left) is not a Pake doublet reflecting only the CH static dipolar coupling (as scaled by WAHUHA irradiation of the protons). 

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