Figure 1. Numerical simulation of the NMR spectrum for three particular sample orientations (a–c) and for a static powder pattern (d) of a carbonyl chemical shielding tensor (left, δ _iso = 120 ppm, δ _aniso = 100 ppm, η = 0.2) and of an amide – dipolar coupling tensor (right, b _HN/2π = 10 kHz).

Figure 2. Simulated static powder spectrum of a glycine powder sample (a), along with spectra recorded using MAS with spinning frequencies of 1–10 kHz (1, 2, 5, and 10 Hz for spectra (b)–(e), respectively).

Figure 3. Intensity of the resonance in 2‐‐l‐alanine in a cross‐polarization experiment at (a) 25 and (b) 60 kHz MAS under continuous‐wave decoupling, as a function of the decoupling RF field strength. Data acquired on a Bruker Avance III spectrometer operating at a proton frequency of 500 MHz equipped with a double‐resonance 1.3‐mm cross‐polarization/MAS probe.

Figure 4. Real part of the MAS time domain signal (a and c) and MAS spectrum (b and d) of KBr spinning off the magic angle (a and b) and at the magic angle (c and d). Data acquired on a Bruker Avance III spectrometer operating at a proton frequency of 1000 MHz with a sample rotation rate of 5 kHz.

Figure 5. Pulse sequence elements for cross‐polarization and double cross‐polarization. (a) Simple acquisition. (b) Direct or acquisition (without cross‐polarization). (c) /X cross‐polarization with X detection applied with a linear ramp on‐proton. (d) Pulse sequence for calibrating / fields, as described in Section 8.4. (e) / spin‐echo pulse sequence (p2 optimized for a 180̊ pulse) as described in Section 8.5. (f) DCP experiment as described in Section 8.6.

Figure 6. Schematic Hartmann–Hahn matching profiles occurring for cross‐polarization under low spinning speed at high irradiation fields (a) or ultrafast MAS at low irradiation fields (b).

Figure 7. Pulse sequences with typical pulses and delays used for the acquisition of NCA (a) and NCOCA (b) experiments. (c) Experimental NCOCA (red) and NCA (black) spectra of microcrystalline fully /‐labeled GB1. Dashed blue lines indicate sequential walks. Experiments were performed on a Bruker Avance III spectrometer operating at a proton frequency of 1000 MHz and equipped with a triple‐resonance 1.3‐mm cross‐polarization/MAS probe. Parameters used for pulses and delays are reported for each of the pulse sequence elements (64 and 192 scans, 1 s interscan delay, total acquisition times = 4.5 and 13 h).