Acquiring 1D NOE on a Varian Gemini or MercuryAcquiring 1D NOE on a Varian
Gemini or Mercury

Noedif is the standard steady-state NOE difference technique for Gemini and Mercury spectrometers..

noedif:

Set up appropriate 1H parameters. Normally should acquire 1D 1H spectrum first.
Then, type noedif

pw = 1H pulse, must be 90º pulse

tpwr = high power for 1H; should be set according to pw, or is correlated to pw.

f0, f1, f2 ...f5 = frequencies to saturate for NOE; can be determined by putting cursor halfway up peak to saturate and typing sd (set decoupler). Then, read value. Set f0 = that value. Then halfway up peak on other side, and set f2 = that number. This could be set to multiple peaks of multiplet, by finding another line and setting f2 and then f3 to frequencies to irradiate.

dofoff = frequency for off-resonance saturation (where there are no peaks). This will be used for data subtraction. This can be set in the same way as f0; find a point where there are no peaks, type sd, then read value and set control = that value. It is preferable for dofoff to be close to the f0 to be sure all conditions are the same (particularly no off resonance effects)

tau = time spent on a single irradiation point during cycling (cycling cycles what part of multiplet is irradiated), usually ~100 ms

ctrl = 'n' for subtraction after alternate scans

dpwr = power of saturation higher power will saturate over a larger frequency range. Low power may not fully saturate the resonance. Standard value ~5.

d1 = length of time for saturation = saturate too long and there are many indirect NOEs, not long enough and the signal-to-noise is low. d1 can be set to hundreds of milliseconds to seconds. NOE buildup is T1 dependent.

dmm = 'ynn' for saturation during d1 delay, required for NOE bulidup

nt = mutliple of 16 scans

at = acquisition time; longer acquisition time gives higher resolution, but takes longer to acquire, so normally ~4 seconds as in standard 1D

sw = spectral width, should be large enough to cover all proton resonances

tof = transmitter offset, center of 1H spectrum

solvent should be set appropriately

np = number of points, is set by setting at and sw

bs = block size; data will be written after block size is reached, so you cannot accidentally acquire an odd number of scans, or an incomplete phase cycle. If bs =1 then you will see where you are saturating, to be sure you have picked the right peak; if you set bs = 16 then you can be sure to process data only after the full phase cycle


Steps to acquire

1) acquire 1D, set sw, tof, np, at, pw, tpwr

2) type noedif

3) measure f0, f1 ... and dofoff

5) set bs

6) acquire spectrum, type go or ga

7) spectrum should be acquired non-spinning and with temperature regulation (if it were possible), especially if acquisition is going to take more than a few minutes.


Data should be processed with a weighting function. Line broadening of 1-2 Hz (lb = 1) might be good to increase signal-to-noise and eliminate any truncation artifacts.