Static and Dynamic Studies in the Solid State by NMR

H transfer between two very unequally populated tautomers 

H transfer plus 90° rotation between two equally populated tautomers 

H transfer between two equally or near equally populated tautomers 

In the same paper, Limbach et al. (87AGE934) reported the study of the compound related to porphyrins, porphycene 79. Porphycene behaves very differently from FI2P in CPMAS DNMR experiments. Its behavior was explained assuming that the four porphycene tautomers (two cis and two trails) are present in the crystal and interconverting very rapidly due to short N-H...N distances in the seven-membered pseudorings. 

In (87BBPC941), Limbach made a major contribution to understanding crystalline and amorphous environments using compounds that in the gas phase show symmetric double minimum potentials. Several compounds were used to illustrate the periodic (crystal) and random (glass) distortions of the potential surface, among them H2P and porphycene. Tlie seminal paper on the tautomerism of porphyrins in the solid state is that of Limbach 

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Nuclear magnetic resonance spectroscopy (NMR) is the determination of molecular structures by analysis of static and dynamic features of the materials [42]. In NMR experiments both a magnetic field and a radiofrequency field are applied to a solid sample or a solution resulting in an absorption of energy which is detected as a nuclear magnetic resonance. Spectrometers are also available for high resolution solid state NMR. Nuclei in different chemical environments resonate at different frequencies and thus differ in their chemical shift. Chemical shifts are used to assign these resonances to the specific structure of the sample. The nuclear environment of a nucleus results in multiple resonances that are also used to determine structural information. NMR studies are conducted to deter-... 

We have also begun to structurally characterize fibrillar states of a-synuclein (140 residues) and of the K19 domain of protein tau. Both systems are involved in possibly related neuro-degenerative diseases.Preliminary results of two- and three-dimensional correlation spectroscopy, as outlined above, reveal that many of the NMR detectable resonances exhibit narrow or line widths, consistent with the occurrence of well-ordered domains in both proteins. On the other hand, other segments of the considered proteins cannot readily be detected suggesting that they may display static or dynamic disorder under the experimental conditions considered. While the effect of molecular dynamics of NMR relaxation parameters has been studied in the context of solution- or solid-state NMR for a long time, recent progress in the study of uniformly labelled proteins by MAS NMR has created novel means by which to study dynamics of entire polypeptide sequences using 2D methods. For example, Bockmann and Emsley have... 

Structure and membrane interactions of antimicrobial peptides as viewed by solid-state NMR spectroscopy have been reviewed by Ouellet and Auger. They discuss several solid-state NMR experiments to extract information on the peptide structure and dynamics as well as on the effect of antimicrobial peptides on model membranes. More specifically, studies of peptide dynamics by C and N CP MAS and static experiments are reported. In addition, examples of peptide structure determination by isotropic chemical shifts, internuclear distance and torsion angle measurements are described. 

K.A. Muller on phase transitions or the Encyclopedia of Magnetic Resonance edited by Grant and Harris with, for instance, the contributions of F. Borsa, A. Rigamonti, R. Blinc and others to the high relevancy of NMR and NQR techniques to the studies of phase transitions in solid-state physics are very important sources of knowledge.18-22 The end of the section is particularly devoted to the static contribution of the average structure to the NMR lineposition and lineshape, and methods to gain resolution and sensitivity. The dynamics will be treated in the next section. 

Membranes and model membranes exhibit liquid crystalline behavior and this has been exploited in a number of studies to obtain valuable information on the structure and dynamics of membrane associated peptides and proteins as well as on the interaction of the peptides with the membranes themselves. NMR spectroscopy of nuclei such as proton, carbon, deuterium, nitrogen and phosphorus has been utilized for such purposes. Structure elucidation of membrane-associated peptides and proteins in oriented bilayers by solid-state NMR spectroscopy has been reviewed. A survey on the use of static uniaxially oriented samples for structural and topological analysis of membrane-associated polypeptides is available. The theoretical background has been dealt with and a number of examples of applications provided. In addition, ongoing developments combining this method with information from solution NMR spectroscopy and molecular modelling as well as exploratory studies using dynamic nuclear polarization solid-state NMR have been presented. The use of N chemical shift anisotropy, dipolar interactions and the deuterium quadrupolar split-... 

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