Fig. 3

Experimental observation of amino acid-specific line shapes using BADCOP1–3. a Simulated C^β inversion profiles with the three decoupling pulses BADCOP1–3. The initial state is ρ(0) = I_z, and the final longitudinal magnetization is depicted. The mean C^β chemical shift from the BMRB is indicated for the various amino acids. b Peaks selected from four 2D HNCA planes of HCAii, acquired with the standard pulse program (left column) and with the three different optimized decoupling pulses (columns 2–4; BADCOP1–3). The same peak is represented in each row. The peaks are either singlets or doublets depending on C^β chemical shift. Therefore, the patterns code for the C^β and indirectly for the amino acid type. The selectivity is not perfect in all cases (due to secondary shifts moving the C^β). Note that there are no Bloch–Siegert shifts; all peaks appear at the correct C^α position (i.e., the same as the standard sequence in the leftmost column). Of particular interest is the loss of upfield glycine C^α (row 6) using BADCOP3 and the slightly different line shape patterns between the two aspartic acid C^α, indicating different C^β chemical shifts (rows 2 and 3). The alanine pattern is unique (row 5). All acquisition, processing, and display settings are the same for the four spectra