Reference:
J. Pauli, M. Baldus, B.-J. van Rossum, H. de Groot and H. Oschkinat (2001) Chem. Biochem. 2 272-281. (Link to Article)

Minimum labelling: ¹⁵N, ¹³C

Dimensions: 3 (but often also recorded as an NcoCX 2D)

Magnetisation is transferred from ¹H to ¹⁵N via cross polarisation and then selectively to the ¹³CO using specific cross polarisation. A PDSD or DARR step is then used to transfer magnetisation to any other ¹³C nuclei nearby. The chemical shift is evolved on the ¹⁵N and ¹³CO nuclei and then detected on ¹³C, resulting in a 3D spectrum. A 2D version in which the ¹³CO evolution time is left out is also possible.

This spectrum is very useful during assignment. At short mixing times for the CX step (10-50ms) it links N_i to CO_i-1 and other carbon atoms from residue i. This provides unambiguously sequential links between residues. When using longer mixing times (200-500ms) it is possible to see links to other carbon atoms nearby and restraints for structure calculations can be obtained.