NOESY map must be recorded and processed in a phase-sensitive mode. As a function of the molecular size, NOE and diagonal peaks can have the same or opposite phase. Thus, for small molecules, NOE is usually positive whereas diagonal peaks appear with negative phase. On the other hand, in large biomolecules, NOE and diagonals present the same phase. Careful interpretation must be made when NOE is near to the zero point. In this case, it is highly recommended to use the ROESY experiment.

A non-diagonal cross-peak represent through-space correlation, that means the corresponding two spins are close in the space. For small molecules NOE is observed with protons up to 3.5A but in large bio-molecules NOE can be observed up to 5A.

Very important!!!! Presence of dynamic phenomena in NOESY experiments. This is quickly detected in NOESY spectra of small molecules because non-diagonal exchange cross-peaks present the same phase as diagonal peaks. Careful analysis and interpretation must be done because false NOE can be assigned. It is recommended to perform variable-temperature experiments to minimize exchange effects. In large molecules, the different phase between NOE and ROE can be used to distinguish possible exchange contributions.