Fig. 1.

Double quantum–single quantum correlation data from labelled mouse fur. Bottom—One bond correlations involving amide, aromatic, and α-carbons; Top—One bond correlations among aliphatic carbons (the Ile Cα−Cβ cross peak is clear at higher contour levels as plotted in Fig. S3, and its position is asterisked in Fig. 1). Corresponding spectral regions from the 1D CP spectrum are overlaid in red. Fur was shaved from a mouse pup, and tightly packed directly into a 4 mm zirconia MAS rotor. Spectra showed insignificant interindividual variation. SsNMR was performed on a Bruker Avance I NMR spectrometer in a 9.4 T superconducting magnet, at 400 MHz ¹H, 100 MHz ¹³C, MAS rate 10 kHz, ¹H π/2 pulse 2.5 μs, contact time 2.5 ms, spin lock field 70 kHz with ramped pulse on ¹H, spinal64 ¹H decoupling (100 kHz RF field) during signal acquisition, chemical shifts relative to external glycine methylene at 43.1 ppm relative to TSP at 0 ppm. Double Quantum Filtering (DQF): Initial ¹³C CP as above, followed by a 70 kHz POST-C7 sequence (Hohwy et al. 1998) applied on ¹³C to excite double quantum coherence in 0.4 ms, and returned to zero quantum by another 0.4 ms POST-C7 sequence with 100 kHz Lee-Goldberg decoupling on ¹H, and 100 kHz spinal64 decoupling during acquisition. 256 Scans were accumulated per increment, 120 increments were used, and total experiment time was about 17 h