Fig. 7. 1D 2QF ¹³C cross polarization MAS spectra for the four preparations described in the text. a relates to solid-phase [¹³C,¹⁵N]-NT(9-13), and b relates to frozen [¹³C,¹⁵N]-NT(8-13) in detergent-containing buffer. c and d correspond to the [¹³C,¹⁵N]-NT(8-13)/receptor preparations NT/NTS-1A and NT/NTS-1B, respectively. 2QF experiments were performed by using the POST-C7 dipolar recoupling scheme with 32-step phase cycling to suppress unwanted 1Q signals. (a and b) A total of 1,024 scans were accumulated. (c and d) Results of 10-k and 11-k scans, respectively, measured at an MAS rate of 7 kHz, are shown.