COHERENCE TRANSFER IN DIPOLAR-COUPLED HOMONUCLEAR SPIN SYSTEMS IN SOLIDS ROTATING AT THE MAGIC-ANGLE

Two routes for the exploitation of the t-SEDRA pulse scheme, which ind uces coherence transfer in dipolar-coupled homonuclear spin systems in rotating samples, are demonstrated and discussed. This sequence is ut ilized to deduce intramolecular connectivities by creating an initial coherence of one spin only, applying the t-SEDRA sequence, and monitor ing the signal enhancement of the coupled spin. Probing the signal amp litude variations of the two spins and comparing them to simulations c an also yield molecular distances. Using 2D spectroscopy, t-SEDRA can also be utilized to establish spin correlations. In this case, the t-S EDRA sequence is applied during the mixing time of a 2D dipolar-correl ation experiment. These two approaches are demonstrated by performing N-15 CPMAS NMR experiments on a N-15-doubly labeled sample of 3(5)-met hyl-5(3)-phenylpyrazole. (C) 1994 Academic Press, Inc.