Solid-state NMR spectra were acquired with a Bruker Avance II 400 Ultra Shield instrument, operating at 400.23, 100.63 and 40.56 MHz, for 1 H, C and 15 N nuclei, respectively. Diflunisal-caffeine and diflunisal-adenine powdered sample was packed into cylindrical zirconia rotors with a 4 mm o.d. and a 90 mL volume. C and 15 N CPMAS spectra were acquired using a ramp cross-polarisation pulse sequence with a 90°1H pulse of 3.60 ms, a contact time of 3 ( 13 C) or 4 ( 15 N) ms, an optimized recycle delays, and a spinning speed of 12 kHz and 9 kHz, respectively. The 13 C CPMAS spectra were registered for 140 scans for diflunisalcaffeine and 880 scans for diflunisal-adenine, while the 15 N spectra for 13064 and 26400 scans, respectively. For every spectrum, a two-pulse phase modulation (TPPM) decoupling scheme was used, with a radiofrequency field of 69.4 kHz. The 13 C and 15 N chemical shift scales were calibrated through the signals of γ-glycine ( 13 C methylenic peak at 43.7 ppm and 15 N peak at 33.4 ppm with reference to NH 3 ) as an external standard.