Bruker BioSpin Solid State NMR, User Manual

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HETCOR with Cross Polarization under LG Offset
User Manual Version 002 BRUKER BIOSPIN 135 (327)
HETCOR with Cross Polarization under LG Offset 9.3
Usually, the cross polarization step is executed at less power than what is used
for the initial excitation pulse and decoupling during observe. Therefore, a second
LG condition must be set for the power level during contact. Furthermore, the HH
condition must be re-established, since the proton spin lock pulse now must be a
square pulse, not a ramp. The ramp can be transferred to the carbon (F1) side.
The following steps are involved:
1. The RF field for protons during contact must be measured and adjusted. With
linearized transmitters, the required power level can be calculated from a
known reference pulse width.
2. The LG frequency offset must be calculated from the RF field (RF/sqrt(2)).
3. The HH condition must be reestablished, varying the F1 (
13
C)-RF field.
As the effective field, required to match for both nuclei at the HH condition, is the
vector sum of RF-field and frequency offset, a higher power pulse is required on
F1 with increasing offset. So it is recommended not to set the proton power higher
than to 50 kHz RF field. For the setup, the pulse program lgcp is used. It contains
an include file lgcalc2.incl which will calculate the LG offset from a given RF field
specified as
cnst17
. It will set the calculated offset as
cnst19
during contact. In
ased
, it will calculate also
cnst16
, which shows the effective field under
cnst17
RF field and
cnst18
,
cnst19
offset. The X contact pulse is executed as (ramp)-
shape. Any standard ramp is possible, but a flat ramp (70-100% or 90-100%) is
preferred. Usually, calculating the required RF field for the HH match can be done
in the following way:
p15
50 -500
μ
s Contact pulse width.
p10
32 or 24
μ
s 32 µs for 100 kHz field, 24 µs for better resolution at
high magnetic fields (>500 MHz).
pcpd2
≈ 2*p3 SPINAL64 /TPPM decoupling pulse.
cpdprg2
SPINAL64/TPPM15 Decoupling sequence.
F1
1
H indirect
l0
0 Start value 0, incremented during expt.
l3
2- 4 Multiples of DUMBO-periods, increment per row.
in_f1
=in0 as calculated Set according to value calculated by
ased
.
F2
13
C acquisition
d1
2s Recycle delay.
sw
310ppm Sweep width direct dimension.
aq
16-20 msec
masr
12000-13000
Table 9.5. Acquisition Parameters for DUMBO-HETCOR (on tyrosine-HCl)