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 Ni to COi-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.