gradient	g1	g2	g3	g4	g5	g6	g7	g8	g9	g10	g11	g12	g13
duration [ms]	0.5	0.5	2	0.3	0.3	0.3	0.3	5	4.4	0.5	0.5	0.5	0.5
strength [%]	16	16	30	16	16	16	16	60	60	16	16	16	16

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]
ds: 64
ns: 16

5. Processing

Apply zero-filling to 128 real data points in F2 and to 256 real data points in F1 to obtain a matrix of 1024 × 128 × 256 real data points. This would result in a huge file of processed real data. Since only the aliphatic proton region is of interest, use strip transformation in F3 (400 points) and in F1 (100 points). Application of forward linear prediction (15 coefficients for F2 and 40 for F1) results in somewhat better resolved 3D spectra. Use Gaussian multiplication [gb = 0.1, lb = −2 Hz] in F3 and a π/3-shifted squared sinusoidal window in the other dimensions. For the data file described, extensive experimentation with different window functions may be worthwhile. Phase correction and base-line correction may be necessary for all dimensions. Further details are very dependent on the particular software you use to process such a 3D data file. Reference the carbon dimension (F2) using the Ξ-scale procedure described in the introduction to this chapter.

6. Result

The figures show the two planes of a 3D spectrum obtained on a DRX-600 spectrometer with a multinuclear inverse z-gradient triple-resonance probe-head (fixed third channel on ¹³C). We choose isoleucine I-61 as an example, since the HCCH-TOCSY method is most important for amino acids with a long aliphatic side-chain. In a, in the H,H plane with δ_C = 62.5 as parameter, one observes H_α of I-61 at δ_H = 3.40, H_β at δ_H = 1.39, H_γ at δ_H = 1.09 and the two methyl groups (γ′ and δ) at δ_H = 0.46 and 0.41. Diastereotopicity of the γ methylene protons cannot be detected in this case.