FIGURE 7.

HCNH measurement of the ϕ backbone angle. (A) Pulse sequence for the HCNH experiment, where MREV-8 is used to achieve ¹H-¹³C/¹⁵N dipolar recoupling of ¹³C-¹⁵N correlations. (B) Example dipolar lineshapes for four different ϕ angles, based on simulations. Note that one lineshape often represents two distinct ϕ angles, as indicated. The figure also lists the matching secondary structures, showing that each type of secondary structure has a characteristic spectral lineshape. (C) Pulse sequence of a HCNH experiment based on a transfer-like implementation similar to those shown in Figure 6. (D,E) Representative results showing how also this variant points to multiple minima. Adapted with permission from (A,B) ref. (Hong et al., 1997a) and (C–E) (Rienstra et al., 2002a), Copyright 1997 and 2002 American Chemical Society.