Fig. 1.

2D ¹³C–¹³C correlation spectra of sparsely ¹³C-labeled samples of GB1, 750 MHz ¹H frequency, 300 ms longitudinal DARR mixing, 12.5 kHz MAS rate. (a) Aliphatic region, sample E. (b) Expansion of the near-diagonal CA region (sample E), illustrating medium and long-range CA[i]-CA[j] correlations. (c) Aliphatic region, sample D. (d) Expansion of the methyl region (sample D). Detailed acquisition and processing parameters are described in SI Figs. 7–9. Peak intensities are interpreted semiempirically in terms of internuclear distances.