Figure 1.

Pulse sequences for (a) RN-¹H(X_und) and RN-¹H(X_dec), and (b) RN-X 2D experiments. In the present applications, X and Y represent ¹⁵N and ¹³C, or ¹³C and ¹⁵N, respectively. Rotor synchronized RN_n^v symmetry rf pulses are applied during t₁ evolution time to reintroduce ¹H CSA and ¹H−X dipolar interactions under MAS conditions. Empty and solid rectangles denote π/2 and π pulses, respectively. In (a), the time dependence of ¹H z-magnetization is monitored, either with application of the X decoupling π pulses for RN-¹H(X_dec), or without for RN-¹H(X_und). This optional decoupling pulse is marked by a dotted-line enclosure. Y is decoupled by π pulses during t₁. Site-selective ¹H detection is accomplished by short-contact-time CP to X. In (b), the time evolution of X x-magnetization is monitored with refocusing of the chemical shift over a constant evolution period T.