Dipolar truncation

Multiple-Oscillating Field Techniques Dipolar Truncation,... 

Multiple-Oscillating Field Techniques Dipolar Truncation, Recoupling of Native Dipolar Coupling, and Recoupling Without Decoupling... 

One solution to the dipolar truncation of small coupling interactions by larger coupling interactions is to use sparsely labeled samples, e.g., using differently 13C-labeled glycerol in the expression as now used frequently for solid-state NMR structure determination, despite the need for more costly samples and extraction of structural parameters from several samples (which accordingly need to be identical). This approach has, along with recommendations on experimental protocols, recently been analyzed by Bayro et al. [144],... 

In an alternative approach, which as we shall see in this section also serves to improve on some of the other problems in addition to dipolar truncation, the groups of Khaneja and Nielsen introduced a novel approach for dipolar recoupling involving multiple-oscillating fields [46—49]. The first of these experiments involved the... 

New NMR methods which should be suitable for fully hydrated membrane samples with better measurement accuracy and less dipolar truncation effects. 

Structure and dynamics studies of deuterated peptides and proteins by MAS solid-state NMR have been reviewed by Reif. It has been shown that perdeuteration and back substitution of exchangeable protons in microcrystalline proteins, in combination with recrystallization from D2O-containing buffers, significantly reduce H- H dipolar interactions leading to amide proton line widths on the order of 20 Hz. Aliphatic protons are accessible either via specifically protonated precursors or by using low amounts of H2O in the bacterial growth medium. As emphasised in this article, the labelling scheme enables characterization of structure and dynamics in the solid-state without dipolar truncation artifacts. 

Second-order recoupling may be less sensitive to dipolar truncation, and several methods have been developed, based on the assistance of strongly coupled nuclei. However, many proton-driven spin diffusion experiments fail at ultrafast MAS. Among those that have been tested at ultrafast MAS, we can mention proton-assisted recoupling (PAR), efficient for providing long-range distances in the GBl protein at v = 65 kHz [153] (PAR... 

M.J. Bayro, M. Huber, R. Ramachandran, T.C. Davenport, B.H. Meier, M. Ernst, R.G. Griffin, Dipolar truncation in magic-angle spinning NMR recouphng experiments, J. Chem. Phys. 130 (2009) 114506. 

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