Gradient-Enhanced Proton-Detected Heteronuclear NMR at Improved Resolution

The two-dimensional gradient-enhanced heteronuclear multiple-quantum experiment, ge-HMQC, can be modified to produce spectra that are unaffected by magnetic field inhomogeneity broadening along the evolution dimension. Two sequences are proposed. In the first one, ge-SHARP1-HMQC, refocusing is accomplished by asymmetric partitioning of the evolution time. In the second, ge-SHARP-HMQC, an additional heteronuclear 180° pulse is applied during the evolution time. The two sequences differ in their response to the evolution of heteronuclear scalar couplings and chemical shifts. Results on model solutions demonstrate the expected immunity of the ¹³C spectral resolution to poor shimming and the concomitant higher detection sensitivity of the narrowed signals.