Broadband Polarization Transfer under Magic-Angle Spinning: Application to Total Through-Space-Correlation NMR Spectroscopy
✍ Scribed by M. Baldus; B.H. Meier
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 631 KB
- Volume
- 128
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
A pulse sequence is described that leads to a broadband retion experiment. The classification ''through-space'' and coupling of the dipolar interaction in magic-angle-spinning solid-''through-bond'' interactions is determined on grounds of state NMR experiments of 13 C spins. The sequence is based on a the type of interactions; dipolar transfer between covalently combination of rotating frame and laboratory frame transfer peribond nuclei is denoted as ''through space.'' In the liquid ods. The recovered dipolar interaction is only weakly dependent on state, the dipolar interaction is averaged out by the molecular spectral parameters but is a faithful measure for the internuclear tumbling of the individual molecules but remains observable distances. Furthermore, a pure zero-quantum term is recovered through cross-relaxation effects.
(of the type found in static ''spin-diffusion'' experiments). This
Sufficient spectral resolution is sometimes difficult to makes the pulse sequence particularly suited for incorporation into achieve in the solid phase, and usually, the application of two-dimensional total through-space correlation experiments that magic-angle spinning (MAS) ( 7) is mandatory to remove deliver simultaneous information about all dipolar couplings in a single 2D experiment. It is found that the necessary decoupling the chemical-shielding anisotropy. MAS does, however, refrom abundant protons is best performed in two steps: first, the move the dipolar interaction and therefore destroys the strong homonuclear couplings between the high-g spins are averthrough-space-distance information. A number of ''reaged by Lee-Goldburg irradiation and, second, the heteronuclear coupling'' schemes have been proposed to interfere with the dipolar interaction is averaged by the combined application of an MAS averaging process and to at least partially recover the RF field to the low-g spins and magic-angle sample spinning. dipolar interaction:
Phase-inversion and amplitude attenuation in the rotating frame
Frequency-selective through-space MAS polarization and refocusing pulses in the laboratory frame part of the pulse transfer between spins whose resonance offsets differ by a sequence are introduced to achieve an optimum chemical-shift multiple of the MAS spinning frequency can be achieved offset-independence and for the suppression of unwanted doublewithout the application of pulses to the observed spins (8quantum transitions. The design principles are explained in detail.
11). Attempts have been made to broaden this rather narrow
Finally, the pulse scheme is applied to total-correlation spectros-''rotational resonance'' condition and to reduce the sensitivcopy of a uniformly labeled amino acid. The experimental crosspeak intensities are in qualitative agreement with the known crys-ity of the polarization transfer to experimental settings (12).
tal structure of the model compound. ᭧ 1997 Academic Press
The main application of rotational resonance is to determine distances in selectively doubly labeled compounds (13-16).
For the observation of total-correlation spectra where the