Coupling-based editing techniques

Several strategies have been developed to measure residual dipolar couplings in 13C-,15N-labelled proteins. Residual dipolar couplings can be measured in the frequency domain of multidimensional spectra of 13C- or 15N-labelled proteins by not decoupling in either the direct or indirect dimension.107154 Alternatively, residual dipolar couplings can be measured from the J-modulation of the cross-peak intensity in multidimensional NMR experiments.155156 Frequency-based experiments are the simplest to implement but sometimes suffer because of the complexity of the spectrum created by twice the number of cross-peaks. This latter drawback may be overcome by simple editing techniques.154-157-159 Intensity-based experiments are more prone to... 

The J-coupling patterns in spectra can help to elucidate chemical structure, but they also comphcate the spectrum. Spectral-editing experiments allow such interactions to be observed in a controlled way. One such technique, DEPT (ifistortionless enhancement by polarization transfer), edits the spectrum based on scalar coupUng the pulse sequence is depicted in Fig. 15. DEPT is actually a set of three experiments, with tip angles, /, of 45°, 90°, and 135°. In NMR, appropriate addition and subtraction of the resulting subspectra separate the contributions from methyl, methylene, and methine carbons quaternaries are not observed. 

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