d5, d6: 1/[4J(N,CO)] = 12 ms, calculated from ¹J(N,CO) with compromise for relaxation
d8: 1/[2J(N,H)] minus gradient duration = 4.5 ms
d9: effective gradient duration, 1.05 ms
g1–g5: sinusoidal-shaped field gradients, 1 ms duration and ca. 0.1 T/m strength, with gradient loop counters, ring-down delays (50 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used.

gradient	g1	g2	g3	g4	g5
strength [%]	60	−40	10	±80	8.1

¹H transmitter attenuation and 90° pulse for DIPSI-2 spin-lock [70 μs, 23 dB]
¹⁵N decoupler attenuation and 90° pulse for GARP [200 μs, 21 dB]
initial value for t₁ evolution: 3 μs
initial value for t₂ evolution: 3 μs
increment for t₁ evolution: 1/[2·sw1]
increment for t₂ evolution: 1/[2·sw2]
decrement for t₂ evolution: 1/[2·sw2] (constant time principle, make sure to set this parameter independently)
ds: 16
ns: 8

5. Processing

Apply zero-filling to 128 real data points in F, and to 128 real data points in F, to obtain a matrix of 512128128 real data points. This will result in 8 Mb of processed real data. Apply forward linear prediction for both F, and F, with ca. 20 coefficients. Use exponential multiplication in F3 (lb = 5 Hz) and a 2/2-shifted squared sinusoidal window in the other dimensions. Phase correction is necessary for all dimensions. Fur- ther details are very dependent on the particular software you use to process such a 3D data file. Note that in the processing of the F, dimension the sign has to be reversed. Reference the indirect dimensions using the =-scale described in the introduction to this chapter setting the DSS signal to 6,= 0.

6. Result

The figures show two planes of the 3D spectrum obtained on a DRX-600 spectrometer with a multinuclear inverse z-gradient triple resonance probe-head (fixed third channel on 30), For example, an H,N plane is chosen, in a which gives, besides others, the lowest-frequency NH proton signal at 6, = 6.15 and dy= 120.0. This plane can be easily found from the 3D cuboid. This H/N pair can be identified as arising from the amino acid I-36. In b the orthogonal H,C plane for the same proton is shown, which gives the CO correlation signal at & = 173.7 from the preceding amino acid G-35. In the corresponding N,C plane (not shown) with the same proton signal at 64 = 6.17 as parameter, only one correlation signal occurs, connecting the CO signal of G-35 with the ¹⁵N signal of I-36.