Spin exchange at magic angle

Polarization inversion spin exchange at the magic angle... 

D Correlation Spectroscopy. A simple, quahtative approach has been described for the determination of membrane protein secondary structure and topology in lipid bilayer membranes." The new approach is based on the observation of wheel-like resonance patterns in the NMR H- N/ N polarization inversion with spin exchange at the magic angle (PISEMA) and H/ N HETCOR spectra of membrane proteins in oriented lipid bilayers. These patterns, named Pisa wheels, have been previously shown to reflect helical wheel projections of residues that are characteristic of a-helices associated with membranes. This study extends the analysis of these patterns to P-strands associated with membranes and demonstrates that, as for the case of a-helices, Pisa wheels are extremely sensitive to the tilt, rotation, and twist of P-strands in the membrane and provide a sensitive, visually accessible, qualitative index of membrane protein secondary structure and topology. 

The difficulties associated with the preparation of samples suitable for diffraction studies has led to much interest in the application of solid-state NMR to the investigation of the three-dimensional structure adopted by membrane proteins in their functional environment of phospholipid bilayers [14]. As an oriented sample, the NMR spectrum of a membrane protein is much simplified as compared to the case of a powder sample for perfect ordering, all structurally equivalent nuclei have the same orientation with respect to Bq, and hence the same anisotropic resonance frequency (see Section 9.2.1). This phenomenon is taken advantage of in the PISEMA (polarisation inversion with spin exchange at the magic angle) experiment [150]. This technique is closely related to the experiments described in Section 9.6.2, although it is to be noted that it is applied to static samples. 

Polarization Inversion Spin Exchange at the Magic Angle (PISEMA) Experiment... 

Polarization Inversion Spin Exchange at the Magic Angle (PISEMA) high-resolu-tion solid-state NMR techniques can be used to investigate the influence of local chain dynamics on cooperative chain motions between the OCH3 protons of PMMA and the aromatic protons of PVPh [45,47]. The 2D experimental... 

Z. Gan, Spin dynamics of polarization inversion spin exchange at the magic angle in multiple spin systems, J. Magn. Reson. 143 136-143 (2000). 

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