Novel suppression of the diagonal signals in the NOESY experiment

A pulse sequence is presented to record diagonal-peak-free NOESY spectra. The technique is based on the principle that those peaks which do not undergo chemical shift changes (via NOE) during the mixing time are suppressed. This is achieved by two jump-return units before and after the mixing time. A pulsed field gradient echo is used to obtain the suppression in one scan. The diagonal-peak-free NOESY spectrum exhibits a sine modulation of the cross-peak intensities caused by the jump-return selection. Unwanted zero quantum coherence (ZQC) is partially suppressed by the pulse sequence in each scan and residual ZQC is destroyed by z-filtering. The resulting spectra display a strong suppression of all diagonal peaks. Almost all residual ZQC artifact magnetization detected is absorptive in-phase. Hence almost all cross peaks of J-coupled protons are absorptive in-phase, reducing overlap. A practical application is presented, where additional experimental NOE data were obtained between amide protons of a cyclic peptide.