7. Comments

The sequence starts with an INEPT transfer from protons to ¹³C. A pair of weak gradients g] and g2 removes signals that arise from imperfect 180° pulses during the first INEPT transfer. The antiphase “C magnetization 2H, Ic, present after p11 is dephased by the gradients g3 and g4, which are applied in the form of a [gradient-180° pulse-gradient] bracket. The next step is a gradient zz-filter comprised of pl3, g5 and p14 (see Exp. 11.8) to remove further unwanted signal contributions.

During f1, 3C chemical shift develops, which is transfered back to protons via the back INEPT sandwich consisting of the pulses p5, p6, pl5 and p16 (see Exp. 6.8). This back INEPT part serves at the same time as the start of the NOE part of the sequence. Pulse p7 transfers the magnetization into the z-direction, where cross-relaxation can occur during the mixing time d3. This situation is read by the reading pulse p8. The final gradient g7, which again is applied in a [delay–180° pulse-gradient] bracket, rephases only the desired magnetization, whereas the gradient g6 removes any transverse magnetization build-up during the mixing time (see Exp. 11.12). Instead of the TPPI manner of sign determination in F), the echo/anti-echo technique as described in Experiment 12.8 could be used.

One should be aware that the method is very insensitive and comes close to the requirements of proton-detected INEPT-INADEQUATE (Exp. 12.16). Since NOE signals are usually in the 5% range and only protons bonded to '¹³C are detected, the method reaches the limit of current instrumentation. In References [3] and [4] the HSQC and the NOE parts of the sequence are interchanged.

8. Own Observations