Fig. 3

Comparison between experimental and DFT-calculated ¹H-¹⁴N 2D correlation spectra. a Expansion of the amide region of the 2D spectrum of Fig. 2(b). The arrows indicate the positions in the proton spectrum where the ¹⁴N cross sections shown below were extracted. b Simulated spectrum analogous to that of (a) resulting from isotropic chemical shifts and quadrupolar parameters calculated by DFT methods. The 2D correlations and extracted ¹⁴N second-order lineshapes of the four distinct NH sites are highlighted with different colors. The simulated numbers of points were 32 and 128, for direct and indirect dimensions, respectively. The corresponding line broadenings were 350 and 300 Hz