5. Processing

Use standard ¹H processing as described in Experiment 3.1.

6. Result

The figure shows the result obtained on an AMX-500 spectrometer with a BGU (10 A) gradient unit and an inverse gradient probe-head with self-shielded gradients. In a an expanded portion of the normal ¹H NMR spectrum is shown, and in b H-12 was selected, giving the responses of both H-11 protons, H-13 and H-8, when a spin-lock of 250 ms was used. In c (spin-lock 76 ms), H-16 was selected, giving the responses of both H-15 protons and H-14; in d (spin-lock 215 ms), H-22 was selected, giving responses of both H-23 protons, but also of protons 20 and 14 reached via an allylic coupling, and further transfers to H-15, H-16 and H-13. Note that no signals have pure phase, but do have components of in- and anti-phase magnetization.

7. Comments

The first 90° ¹H transmitter pulse excites all proton resonances. In the following [gra- dient pulse, selective 180° pulse, gradient pulse] sandwich, all these resonances are dephased and only the one chosen by the selective 180° pulse is retained. Since a selective 180° pulse is applied, its relative phase with respect to the "hard" pulses does not need to be determined. The MLEV-16 spin-lock does not introduce a further change of the coherence level; the solid line in the coherence diagram depicts the coherence chosen by the selective pulse.

Since the experiment requires only one scan, it is ideal for studying the influence of the spin-lock length on the number of signal responses as well as their relative intensities and signal shapes.

8. Own Observations