Zero quantum artifacts in NOESY spectra

Unlike most other NMR experiments that correlate resonances via J-coupling through bonds, the NOESY experiment correlates resonances via cross-relaxation through space. Since the intensity of the correlation is strongly dependent on the distance between the interacting nuclei, the intensity of the NOE peak is related to the distance between the atoms. This makes the NOESY experiment very useful for determining three dimensional structures and assigning stereochemistry. However, interpreting NOESY spectra has to be done carefully, as artifacts due to zero-quantum transitions are often observed.

The figure below shows an expansion of a NOESY spectrum of cholesteryl acetate in deuterated chloroform. As expected for a molecule of this size the diagonal peaks (teal) are of opposite sign to the crosspeaks (blue). Most of the crosspeaks are broad and of medium intensity, but some, circled in red, are sharp with extensive splitting into positive and negative lobes like the crosspeaks seen in a DQF-COSY spectrum.

All three of the circled correlations are due to protons separated by three bonds, where large J-coupling has produced zero quantum artifacts. These peaks cannot be used to obtain reliable distance information. NOESY spectra should be recorded in a phase-sensitive manner and processed without magnitude processing so that zero quantum artifacts can be identified. All of the standard NOESY parameters provided by the SSPPS NMR Facility are set up this way.