A (13)C double-filtered NOESY with strongly reduced artefacts and improved sensitivity.

A (1)H NOESY experiment with two (13)C half-filters is described which has, compared to previously reported versions, an enhanced overall sensitivity and strongly reduced intramolecular cross peaks in any part of the spectrum edited for intermolecular NOEs. By adding a shaped (13)C pulse to the half-filter which selectively inverts the aromatic resonances, the filter can be tuned separately and simultaneously for the aliphatic and aromatic regions. Contrary to recently proposed schemes, no magnetization is destroyed, so that full sensitivity is retained for symmetric systems such as homodimers. Furthermore, by replacing the rectangular 180° (13)C pulses by high-power hyperbolic secant pulses for inversion of the complete (13)C spectral range, offset effects (which are another source of signal loss and artefacts) are eliminated. The spectra edited for intermolecular NOEs clearly demonstrate that residual artefacts are considerably smaller than in the original version of the experiment.