IMPACT-HMBC for Bruker (Julien Furrer)
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Basic facts about IMPACT
Family: 2D HMBC
Copyright: University of Neuchatel, Julien Furrer
NOTE:The pulse sequence is not yet available for download, but the author has been contacted and we expect to publish it in the future.
The IMPACT-HMBC (improved and accelerated constant-time heteronuclear multiple-bond correlation) is a pulse sequence developed by Julien Furrer. It is a variation of 2D HMBC technique where it is possible to obtain a high quality 2D spectrum with minimal artifacts, enhanced sensivity and less time consuming.
The pulse sequence combines tree-fold low pass J filter for a better supression of 1JCH with constant time (CT) to improve signal shape and ASAP method for quick recover delay. Another advantage of this HMBC is in fact the transformation of an broadband experiment in a semiselective experiment changing only the shaped pulse (spnam7).
d1 - recovery delay (1-5 x T1) (usually 0.2 s due to ASAP sequence)
d6 - Calculed autmatically based in cnst13 - evolution of long range coupling.
d9 - mixing time for ASAP method (recommended 40 ms for DIPSI-2 mixing time)
d16 - gradient recovery delay (depends on the probe) may be on the order of 100-200 μs.
d20 - delay for constant time period
Acquisition in the indirect dimension and number of scans
The incremented delay used to record evolution in the indirect dimension is 2xd0. d0 is automatically calculated within the experiment using in0.
in0 equals 1/(2*SW) one half of the inverse of the spectral window width in X dimension. (1/2) is due to nd0=2 (below).
td1 - number of experiments to record in the X dimension
nd0 = 2 - there are two delays d0 within the X dimension evolution delay.
ns - number of scans must be a multiple of 2.
ds - number od dummy scans must be 16
O1 (or O1P for the value in ppm) - in the middle of 1H spectrum.
O2 (or O2P for the value in ppm) - in the middle of 13C spectrum.
Hard RF pulses
p1 - hard 1H at power level pl1 - Length of 180o pulse (p2) is calculated automatically.
p0 - hard 1H for Enerst angle. By default, can be used an 90o pulse angle. For improve sensivity, this value can be optimized utilized the 1D version of the sequence. This values can varies from 90o to 120-130 pulse angle depending on the substance being analyzed.
p6 - 1H pulse for ASAP method (recommended - 50 μs)
p3 - hard X-nucleus 90o at power level pl2.
Shaped 180 pulses
This sequence has one shaped 180 pulses at the X-nucleus channel - p24
p24 - is a refocusing pulse at power level sp7.
spnam7 must be set to the name of the waveform file (Crp60comp.4 for a broadband excitation, G3 for band selective experiment or gaus1.1000 for selective 1D experiment).
p24 of 2 ms is recommended for spnam7 set to Crp60comp.4.
If waveform Crp60comp.4, G3 or gaus1.1000 are not available on the system they need to be prepared using the stdisp tool or an appropriate replacement used instead.
Duration of all gradients is set by:
- p16 (recommended default - 1 ms)
Shapes of all gradients are recommended to be sine bell implemented in 100 steps, i.e.:
- gpnam1 SINE.100
- gpnam2 SINE.100
- gpnam3 SINE.100
- gpnam4 SINE.100
- gpnam5 SINE.100
- gpnam6 SINE.100
Strengths of gradients are set by parameters:
- gp1:gp2:gp3:gp4:gp5:gp6 - 80:37:-19:-11:-7:-17
- cnst6 - minimal coupling constant for 1JCH (recommended - 120 Hz)
- cnst7 - maximum coupling constant for 1JCH (recommended - 170 Hz)
- cnst13 - coupling constant for long range JCH (recommended - 8 Hz)
Set PH_mod (F1) to pk or no
Process using xfb and xf2m