SENSITIVITY COMPARISON OF 2-DIMENSIONAL CORRELATION SPECTROSCOPY IN THE LABORATORY FRAME AND IN THE ROTATING-FRAME

The cross-peak intensity in two-dimensional correlation spectroscopy is quantitatively compared for coherence transfer in the laboratory frame (COSY) and in the rotating frame (TOCSY). The evaluation of a two-spin model in the presence of dipolar and external-random-field relaxation shows that for small molecules with short rotational correlation times, the two experiments are equivalent with regard to cross-peak intensity, while for large molecules with long correlation times, the rotating-frame experiment can have a sensitivity advantage that may exceed a factor of 7. The gain is due to the in-phase character of the multiplet structure. It is, however, limited by transverse relaxation effects. The theoretical predictions are verified by experiments on basic pancreatic trypsin inhibitor under various experimental conditions with rotational correlation times ranging from 2 to 18 ns. The maximum sensitivity advantage of TOCSY, found in the present experiments, is a factor of 3.2. © 1993 by Academic Press, Inc.