Direct excitation with decoupling

When an X (non-hydrogen) nucleus is to be measured with decoupling, but no NOE transfer of magnetization intensity from 1H to X is wanted, a pulse program known as inverse gated decoupling (invgate) should be used.

This applies to quantitative 13C measurements. Occasionally to measuring carbonyl or other quaternary carbons, by not enhancing the signals of the aliphatic protons relative to the carbonyl or other quaternary carbons of interest, thus using a higher receiver gain. And invgate is recommended for nuclei with a negative gyromagnetic ratio (29Si or 15N), where the NOE reduces the signal intensity.

How to run an inverse gated decoupling experiment for 13C:

  1. Reserve an overnight time slot (19:00-07:00)

  2. First acquire a single shot (ns 1, ds 0) 1H spectrum to check:
    1. Is the shimming okay?
    2. Does the sample appear as expected?
    3. Calibrate the 1D spectrum
    4. check the optimal SFO1

  3. type: new
    enter a new experiment number
    Select the type of experiment: 13C_1Hdec

  4. Check tune and match
    type: w
    shows a wobble curve for carbon in the acquisition window
    if you do not see the "dip", check the qnp position on the probe:
    1 = 29Si, 2 = 13C, 3 = 31P

    To end the wobble routine: stop

  5. check if the following parameters are good for your sample and update as needed: d1, ns, td, sw, o1p, o2p(1H)

  6. rga

  7. zg

  8. leave a note for the morning with directions on how to halt the experiment and where to leave your tube (which group), unless you plan on doing it yourself at 7:00 am.

  9. Report problems and bugs to Yael or Shifi - 3748