180 (327) BRUKER BIOSPIN User Manual Version 002
Symmetry Based Recoupling
Another important parameter to observe is the required excitation bandwidth of
these sequences. Naturally, going to higher magnetic fields, the higher chemical
shift spread requires higher RF fields for the recoupled X-nuclei, requiring even
higher RF fields for protons. So the tendency is going to high spin rates (also de
-
sired to get rid of spinning sidebands) and turning the decoupling off during recou-
pling, which represents a much lower RF load to the probes and increases
experimental stability substantially.
Table 1 shows the sample rotation rate and the required spin nutation frequencies
for the X-nucleus. The spin nutation frequency must be 7 times the sample rota
-
tion rate for C7, 5 times the sample rotation rate for SPC5 and 3.5 times the sam-
ple rotation rate for SC14. Be careful to obey the maximum allowed spin nutation
frequencies for the hardware in use.
It is essential that all these parameters are considered carefully in context with the
properties of your sample before the experiment is started, so that the appropriate
hardware is used. Especially the choice of the MAS-probe is essential to achieve
a sensible setup.
Table 14.1. shows the selection parameters for three standard
recoupling sequences.
References:
1. E.A. Bennett, R.G. Griffin, and S. Vega, Recoupling of homo- and heteronuclear dipolar interaction in
rotating solids, NMR Basic Principles and Progress 33, 3-77 (1994).
2. S Dusold and A. Sebald, Dipolar Recoupling under Magic-Angle Spinning Conditions, Annual Reports
on NMR Spectroscopy 41, 185-264 (2000).
3. M. Hohwy, H.J. Jakobsen, M. Eden, M.H. Levitt, and N.C. Nielsen, Broadband dipolar recoupling in
the nuclear magnetic resonance of rotating solids: A compensated C7 pulse sequence, J. Chem.
Phys. 108, 2686 (1998).
4. M. Hohwy, C.M. Rienstra, C.P. Jaroniec, and R.G. Griffin, Fivefold symmetric homonuclear recoupling
in rotating solids: Application to double quantum spectroscopy, J. Chem. Phys. 110, 7983 (1999).
5. M. Hong, “Solid-State Dipolar INADEQUATE NMR Spectroscopy with a Large Double-Quantum Spec-
tral Width”, J. Magn. Reson. 136, 86-91 (1999).
6. A. Brinkmann, M. Edén, and M.H. Levitt, Synchronous helical pulse sequences in magic-angle spin-
ning nuclear magnetic resonance: Double quantum recoupling of multiple-spin systems, J. Chem.
Phys. 112, 8539 (2000).
7. M. Hohwy, C.M. Rienstra, and R.G. Griffin, Band-selective homonuclear dipolar recoupling in rotating
solids, J. Chem. Phys. 117, 4974 (2002)
8. C. E. Hughes, S. Luca, and M. Baldus, RF driven polarization transfer without heteronuclear decou-
pling in rotating solids, Chem. Phys. Letters, 385, 435-440 (2004).
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