A C-13 DOUBLE-FILTERED NOESY WITH STRONGLY REDUCED ARTIFACTS AND IMPROVED SENSITIVITY

A H-1 NOESY experiment with two C-13 half-filters is described which h as, compared to previously reported versions, an enhanced overall sens itivity and strongly reduced intramolecular cross peaks in any part of the spectrum edited for intermolecular NOEs. By adding a shaped C-13 pulse to the half-filter which selectively inverts the aromatic resona nces, the filter can be tuned separately and simultaneously for the al iphatic and aromatic regions. Contrary to recently proposed schemes, n o magnetization is destroyed, so that full sensitivity is retained for symmetric systems such as homodimers. Furthermore, by replacing the r ectangular 180 degrees C-13 pulses by high-power hyperbolic secant pul ses for inversion of the complete C-13 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 versi on of the experiment.