Fig. 2.
The comparison of homonuclear (ω1 (1H)–ω2 (1H)) versions of (a) selective aliphatic-to-aromatic, (b) non-selective aliphatic-to-aromatic (see Fig. 1b), (d) selective aromatic-to-aliphatic and (e) non-selective aromatic-to-aliphatic NOESY experiments. Spectra (a) and (d) were acquired using pulse sequences shown in Fig. 1a, b, respectively. Non-selective versions (b) and (e) utilize the same pulse sequences as (a) and (d), respectively, with all the shaped pulses replaced by ‘hard’ ones. 13C spins were not evolved. Spectra (b) and (e) show that non-selective experiments suffer from many spectral artefacts due to poor broadband performance of ‘hard’ pulses and decoupling schemes at high fields. Apart from sign inversions across the spectrum, intense axial peaks as well as phase-distorted pseudo-diagonals are present (e). Selective experiments (a, d) achieve to filter-out virtually all diagonal signals with only slight decrease of intensity of cross-peaks. (c) Superimposed 1D cross-sections across ω1 (1H) from spectra (a, blue curves) and (b, green curves) for ω2 coordinates indicated by the vertical arrows (1–3). (f) ω2 (1H, direct dimension) cross-sections of spectra (d, blue) and (e, green curves) at ω1 coordinates indicated by the horizontal arrows (1–3). The cross-sections are plotted using the same intensity scale, thus they enable direct comparison of experimental sensitivity between selective and non-selective versions of experiments (a vs. b, and d vs. e). For each experiment 120 increments with 40 scans were collected (duration of 3 h). Spectral width of 8 kHz in the indirect ω1 (1H) dimension was set