SIMPLE SOLUTIONS TO RESOLVE EXTREME NMR SPECTRAL OVERCROWDING USING SHAPED PULSES

Improved two-dimensional H-1 NMR sequences including shaped pulses are proposed for increasing the separation of cross peaks in the case of severe spectral overcrowding. Ways around limitations in soft 2D experiments are proposed for increasing the resolution and the apparent peak separation in both dimensions. Modulated shaped pulses leading to multi-selective excitation are proposed for reducing the size of data matrices at a given F2 resolution and for simplifying coherence transfer pathways. Separation of the signals in F1 is achieved by either introduction of refocusing soft pulses or constant-time experiments. These methods were applied to inclusion complexes of cyclodextrin derivatives where, although of considerable value in deriving the 3D structure of the complex, a total assignment of NMR spectra is not, at first glance, a simple task. It is demonstrated that the proposed solutions overcome the apparently discouraging complexity of the 1D NMR spectra and yield a wealth of important data for further structural determination.