Figure 8.

Examples of amide protons with extreme downfield shifts. (a, b) PDB:2NCL. The D28 amide proton is near the plane of Y37 aromatic ring ( $Z$   $=$  5.21, ${\mathit{\delta }}_{\mathrm{ASP}}$   $=$  11.387 ppm, $d$   $=$  5.62 Å, $\mathit{\theta }$   $=$  72.0 ${}^{\circ }$ , ${\stackrel{\mathrm{‾}}{\mathit{\delta }}}_{\mathrm{ASP}}$   $=$  8.299 ppm, ${\mathit{\sigma }}_{\mathrm{ASP}}$   $=$  0.588 ppm). (c, d) PDB:2KKZ. The L61 amide proton forms a hydrogen bond with the sidechain nitrogen of H86 ( $Z$   $=$  6.66, ${\mathit{\delta }}_{\mathrm{LEU}}$   $=$  12.56 ppm, $d$   $=$  3.22 Å, $\mathit{\theta }$   $=$  69.7 ${}^{\circ }$ , ${\stackrel{\mathrm{‾}}{\mathit{\delta }}}_{\mathrm{LEU}}$   $=$  8.217 ppm, ${\mathit{\sigma }}_{\mathrm{LEU}}$   $=$  0.735 ppm). The amide proton is represented as a yellow sphere, and the aromatic sidechain is shown in red.