Fig. 6.

Two-dimensional ¹H–¹⁵N PISEMA spectra of the ¹³C_α, ¹⁵N labeled single crystal of N-acetyl leucine (¹³C_α, ¹⁵N NAL). (a) ¹⁵N detected. (b) ¹³C detected. Sixteen scans were acquired for each of 128 points in the indirect dimension for spectrum a and 32 scans for spectrum b. The contact time was 1.0 ms during the double cross-polarization from ¹⁵N to ¹³C, and the recycle delay was 5 s.