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 NcaCX 2D)

Magnetisation is transferred from ¹H to ¹⁵N via cross polarisation and then selectively to the ¹³Cα 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 ¹³Cα nuclei and then detected on ¹³C, resulting in a 3D spectrum. A 2D version in which the ¹³Cα evolution time is left out is also possible.

When recorded with short mixing times for the CX step (10-50ms) this experiment is very useful for the identification of spin systems, i.e. all ¹³C and ¹⁵N resonances belonging to a single residue. 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, or links to neighbouring amino acids can help with assignment.