Recoupling schemes

Recently, numerous studies reported the application of homonuclear and heteronuclear selective recoupling schemes on uniformly labelled ligand interacting with membrane receptors. The polarization exchange curves were fitted with the two-spin model and showed that it is possible to determine intemuclear distances up to 4.5 A.118... 

Tab. 11.2 Characteristics of heteronuclear and homonuclear dipolar recoupling schemes...

The most direct result of higher resolution and higher sensitivity brought about by the advances mentioned, as well as those reviewed in previous article,1 is perhaps the blossoming of correlation spectroscopy in solid-state NMR. Indeed, many recoupling schemes were motivated by implementing certain types of correlation spectroscopy. Various types of correlation spectroscopy are reviewed in Section 5. 

Section 6 reviews developments in cross-polarization and spin diffusion/ exchange. This section is closely related to Section 4 because of the interplay between these spin dynamics processes and the recoupling schemes at highspeed spinning, which now is almost invariably used for high resolution. Actually, many recoupling techniques were motivated by effecting crosspolarization and spin diffusion under fast MAS. 

Through SIMPSON numerical simulations. Fig. 4 compares the coherence transfer curves for a variety of the most popular and efficient heteronuclear dipolar recoupling schemes. Specifically, we evaluate the 07, POST-C7, off-resonance C7, R14, DCP, SPfCP, " SPECIFIC, and /DCP pulse sequences, realizing that many new powerful schemes enter the scene every year. For the present purpose, we address a three-spin system in a peptide backbone using parameters established for a... 

A new heteronuclear dipolar interaction recoupling scheme suitable for the characterization of heteronuclear dipolar couplings for multiple-spin systems under very fast MAS condition has been proposed The new technique has been shown to be superior to the rotational echo double resonance method and other recoupling schemes as far as the interference of homonuclear dipolar interaction is concerned. The potential of the technique is illustrated for fluorapatite sample at a spinning frequency of 25 kHz. 

Scheme 5 The spin recoupling scheme in the intermediates of the reaction...

Lu et al. have presented a detailed analysis of the Symmetry-based Resonance-Echo Saturation-Pulse DOuble-Resonance (S-RESPDOR) method in order to measure the inter-nuclear distances between spin-1/2 and quadrupolar nuclei. This recently introduced sequence employs a symmetry-based recoupling scheme on the observed spin-1/2 channel and a... 

Table 4.1 Main characteristics of the recoupling schemes presented earlier...

One and two-dimensional solid-state NMR experiments have been discussed that permit probing local structure and overall molecular conformation of membrane-embedded polypeptides under fast MAS. The functional dependence of a series of anisotropic recoupling schemes was analysed using theoretical and numerical methods. Experimental results were shown for a randomly oriented peptide and for two model membrane-peptides reconstituted into lipid bilayers and oriented on polymer films. 

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