NOE DPFGSE
NOE_DPFGSE is a 1D NOE experiment combining shaped pulses and field gradients. It is very efficient, taking only a few minutes. As a comparison, the traditional 1D NOE difference experiment (NOEDIFF) usually takes one hour, while 2D NMR usually takes at least three hours. The NOE_DPFGSE result is similar to NOEDIFF, but with a much cleaner spectrum. We strongly encourage users to try this newer method. A shortcoming is that only one peak can be irradiated in each NOE_DPFGSE experiment. If you want to check several peaks, then you have to do one experiment for each peak separately, or do a 2D NOESY.
The shaped pulse is used for selectively irradiating a single peak. The typical pulse length of 50 milliseconds has a very high selectivity of only a few Hz. This high selectivity is necessary when the peak of interest is close to others. However, when the peak of interest is split or broadened by J-couplings or other mechanisms, a very selective shaped pulse will have low efficiency, dramatically reducing the signal. In this case it is necessary to reduce the selectivity. Therefore it is important to correctly select the proper shaped pulse for your sample.
There are three different sets of parameters available on our Bruker NMR machine:
NOE_DPFGSE_50Hz, with highest selectivity
NOE_DPFGSE _100Hz
NOE_DPFGSE _200Hz, with lowest selectivity
The extension at the end of the name roughly indicates the selectivity.
The rule of thumb for choosing among them is: select as low selectivity as possible. The only reason to choose a more selective shaped pulse is if you think you may also unintentionally irradiate a nearby peak.
The NOE_DPFGSE can be run with XWINNMR or ICONNMR. The key parameter needs to be entered is the ‘o1p’ value of the peak you want irradiate.
When running with XWINNMR, type:
‘rpar NOE_DPFGSE _50Hz all’
‘gpro’ (xwinnmr)
‘o1p’ and enter the value.
Then follow the general procedure for acquiring a 1D spectrum.
If you are running NOE_DPFGSE with ICONNMR and don’t know the o1p value, follow this procedure:
1. Set up a first experiment: PROTON.
2. Set up a second experiment: C13CPD. We do not really need the C13 spectrum. This step is used to keep the sample in the magnet and let you have time to look at the proton spectrum.
Do not yet set up the third experiment: NOE_DPFGSE
3. Submit the two experiments.
4. Start the run.
5. Wait until the PROTON experiment finishes.
6. Display the PROTON spectrum.
7. Get the ‘o1p’ value (the exact shift in ppm’s) of the interesting peak and decide what selectivity is needed.
8. Set up a third experiment, NOE_DPFGSE_ xxHz , and set d1 = ~ 5 times T1 of protons. (a reasonable guess is the default d1 = 5 seconds)
9. Similarly set up more NOE_DPFGSE experiments if there are more peaks of interest.
10. Submit these new NOE_DPFGSE experiments.
11. Read in the C13CPD experiment currently running (click “FID”). Click “halt” (not “stop”!). The C13CPD will be stopped and NOE_DPFGSE will automatically start.