[90(ph1), 180(ph2), 90(ph1)}> phl: x, ph2: y . [90(ph3), 180(ph4), 90(ph3)]; ph3: -x, ph4: -y (90(ph1), 180(ph2), 90(ph1)}2 [90(ph3), 180(ph4), 90(ph3)]3 aq: x [90(ph1), 180(ph2), 90(ph1)]s [90(ph3), 180(ph4), 90(ph3)}, [90(ph1), 180(ph2), 90(ph1)];

4. Acquisition

Time requirement: 10 min Sample: 3% strychnine in CDCl₃ Run a normal ¹H NMR spectrum of the sample and optimize the spectral width. Change to the 2D mode of the spectrometer and load the gs-TOCSY pulse program. The 90° pulse-width and attenuation of the spin-lock pulses must be calibrated prior to the experiment (see Exp. 2.9). For optimum results one should take into account the phase difference between the hard pulse p! and the spin-lock pulses, either in the pulse program or in the adjustable parameter set if the software allows (see Exp. 7.1). The duration of the spin-lock is an adjustable parameter. You have to set:

td2: 1 k data points in F, tdl: 256 data points in F, sw2: 9 ppm swl: 9 ppm o1: middle of ¹H NMR spectrum p1: 90° ¹H transmitter pulse p2: series of composite 180° pulses (90°, 180°, 90°) at transmitter attenuation of spin-lock; 90° pulse-width and transmitter attenuation typically in the order of 40 μs and 16 dB, corresponding to an effective spin-lock field of ca. 7000 Hz (magnetic-field-dependent). Duration of spin-lock set to 100 ms by loop parameter of spin-lock sequence. The loop parameter must be an even number (38 was used here). dl:2s initial value for ¢; evolution: 3 ys increment for f; evolution: 1/sw1 g1, g2: sinusoidal-shaped field gradients with 5% truncation, 2 ms duration and ca. 0.1 T/m strength, with gradient loop counters, ring-down delays (100 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient strength ratio: | : –1 ds: 4