PISEMA
User Manual Version 002 BRUKER BIOSPIN 195 (327)
Figure 15.1.: Pisema pulse sequence a.) straight PISEMA, b.) “clean PISEMA”
variation for further suppression of phase glitches (Ramamoorthy et al. Solid State
NMR 4).
Setup 15.2
Sample: 15N labelled α-glycine powder for power level determination, 15N la-
belled acetylated glycine or acetylated valine or leucine for running the PISEMA
experiment, preferably as single crystal.
Setup time: 0.5 h on labelled glycine.
Experiment time: 15h on a labelled powder sample, 1-2 h on a good size single
crystal.
1. Set up for static 15N CP observation on the α-glycine powder sample, pulse
program cp. Use a ramp pulse if the HH condition is unknown, with power level
settings for an approximate 5 µsec pulse on both channels.
2. Determine the proton 90 degree pulse p3 at the respective power level, reset
the conditions for a square shape and about 50 kHz on both channels for con
-
tact. Load the pulse program cplg. With cnst17=0, pl2=pl13 and pl1 all set for
50 kHz, reestablish the HH condition.
3. To adjust the CP condition under a LG-offset, load the pulse program cplg.
Cnst 17 sets the LG-offset during the contact, the offset frequencies are calcu
-
lated as cnst 18 and cnst19. Start with cnst17=0.
4. Two possibilities exist to set the FSLG power levels and offset frequencies.
a. Either, use the appropriate offset frequency for the chosen contact power level
of
1
H and set cnst20 accordingly to e.g. 50 kHz, i.e cnst17 = 50000.0. This
would give an offset frequency of approximately 35 kHz (cnst19 should show
this number in the ased display) Then adjust the
15
N power level during the
FSLG period to best HH match - which is at a power level of appropriately
20*log(sin(54.7))=1.8 dB higher than for the on resonance contact.
If that option is not adequate because of power limitations on
15
N, one can also
leave the on resonance contact levels of
15
N and calculate the offset frequency
and power level for
1
H. That reduces the required proton RF power by about 70%
as compared to the power level for a resonant HH match. For the new nutation
frequency (B1 field for LG condition):
the offset frequency for the Lee-Goldburg condition is:
with the inverse of a 360º pulse.
)(*82.0)(*)sin()(
1
_
1
1
_
1
1
1
HBHBHB
resonreson
m
LG
==
θ
)(*578.0)(*)cos(
1
_
1
1
_
1
HBHBf
resonreson
mLG
==
θ
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