Suppressing zero quantum artifacts

In the previous post zero quantum artifacts in NOESY spectra were described. Misintrepretation of these artifacts can lead to errors in structure elucidation. A method for suppressing zero quantum artifacts has been developed¹ and it is quite effective.

The figure below shows expansions of two NOESY spectra recorded using the same sample of cholesteryl acetate in CDCl3. The expansion on the left is the same as in the previous post. This spectrum was recorded with the classical NOESY pulse sequence. The zero quantum artifacts are highlighted with red ovals. The spectrum on the right was recorded with essentially the same parameters and a zero quantum suppression NOESY pulse sequence.

The zero quantum suppressed NOESY experiment does not show the artifacts of the classical NOESY experiment, and it also shows less noise in general. The zero quantum suppressed NOESY does not take any longer than the classical experiment. The main drawback seems to be a slight reduction in sensitivity, however, this is offset by the reduction in artifacts. The standard NOESY parameters implemented at the SSPPS NMR Facility now use the zero quantum suppressed NOESY sequence.

The zero quantum suppression module consists of a broadband adiabatic pulse applied simultaneously with a weak gradient pulse. This technique can also be applied to COSY and TOCSY pulse sequences¹. Like the NOESY, these experiments give cleaner spectra with a slight reduction in sensitivity that may be worth accepting.

References
1. M.J. Thrippleton and J. Keeler
Elimination of Zero-Quantum interference in Two-Dimensional NMR spectra.
Angewandte Chemie International Edition, 2003 42(33):3938-3941.