PISEMA performance

Fig. 6. Simulated 2D PISEMA spectra of powder samples. Correlation of dipolar coupling and chemical shift interactions associated with an amide N-H bond (A) and the histidine side chain Njt-H bond (B). For the amide N-H bond, the simulations were performed using CSA principal values of 33 = 64, 22 = 77, and Sii = 217 ppm, an N-H bond length of 1.07 A, and the Euler angles ( = () and yg=17°) to define the relative orientations of the chemical shift and dipolar coupling tensors. For the histidine side chain Nrt-H bond, the following parameters were used in the simulations CSA principal values of 533 = 77, 522 = 203, and 5 =260 ppm,...

In order to increase the sensitivity and resolution, and to reduce the experimental time, of PISEMAMAS technique, it is essential to perform the experiment with fast spinning speeds. While the PISEMA pulse sequence has been successfully used under slow spinning conditions, unfortunately, it cannot be used at high spinning speeds as the heteronuclear dipolar couplings are suppressed. However, changing the S -spin-lock rf field strength (in SEMA) to satisfy the Hartmann-Hahn condition, B s[= " ioi with... 

An alternative approach to structure determination is to fit structures to the resonance patterns in experimental PISEMA spectra when there is either no or only limited amounts of assignment information available. It is necessary to relate the geometry of a peptide to its spectrum in order to perform a structural fitting. A chain propagator (rotation operator) is defined... 

Fig. 18. Proton-detected ID PISEMA spectra of a powder sample of A-acetyl- A-D,L-valine obtained using the pulse sequence shown in Fig. 17 under static condition. The experiments were performed with a H Lee-Goldburg spin-lock RF power of...

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