Bruker BioSpin Solid State NMR, User Manual

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186 (327) BRUKER BIOSPIN User Manual Version 002
Symmetry Based Recoupling
12. Set the spectral window along F1. It is desirable to synchronize sampling along
F1 with the rotor spin rate in order to eliminate spinning sidebands (fold back
onto center band). This may however lead to peak fold over, since achievable
spin rates are usually smaller than the spread of DQ-frequencies along F1.
This does however not necessarily mean that the spectra are crowded and un-
interpretable, because frequently the folding does not lead to cross peak over-
lap. Of course, the synchronisation to the spin rate need not be used,
cnst31
can be set equal to the sweep width along F2 which will normally produce
spectra free of folding, but of course, spinning sidebands along F1 will occur
and signal intensity will be spread over a larger number of cross peaks. An in-
termediate sampling rate along F1 can be achieved by incrementing the evolu-
tion period synchronised to the phase shifted blocks of the sequence (one
PC7-block being 2
τ /7, τ =rotor period). This will also not generate sidebands
along F1, but provide a larger sweep width and less fold over (M. Hong 1999).
Fold over can often be tolerated,
xfshear rotate
may be used to shift the spec-
trum suitably along F1.
13. Set the acquisition time along F1 to about 10 msec for a start. Lines along the
double quantum dimension may be narrower than along the single quantum di-
mension, so a compromise between experiment time and digital resolution
along F1 must be found.
14. Start the experiment.
Data Acquisition 14.3
Sample: Fully 13C labelled tyrosine-HCl, or a suitable fully labelled small peptide
Spinning speed: 5 – 20 kHz, depends on experimental requirements, see
Table
14.1.
.
Experiment time: 1-4 hours.
Table 14.2. Acquisition parameters for DQ-SQ correlation experiments using symmetry based recou-
pling sequences
Parameter Value Comments
Pulse program spc5cp2d
spc5cp2dlsw
sc14cp2d
r14cp2d
pc7cp2d
…… See
Table 14.1.
for hints which sequence to prefer.
Rule of thumb: high field: fast spinning, sc14
low field, slow spinning, pc7. Intermediate: spc5.
N.b.: sc14 usually has low DQ yield (35%), but that may not mat-
ter
NUC1
13
C Nucleus on f1 channel
O1P 100 ppm
13
C offset
NUC2
1
H Nucleus on f2 channel
O2P 2-3 ppm
1
H offset
PL1 for > 50 kHz
ν
RF
Power level for f1 channel CP and p1
PL11 dep. on
masr
Power level for f1 channel recoupling power