We describe three new schemes to explore homonuclear crossthat the two interactions considered have one common spin. correlation contributions to relaxation along an effective field tilted We will use the following notation: cross-correlation beby an angle u from the static magnetic field direction. Their key tween two dipolar interactions will be DD/DD, and that feature is to detect, during the evolution time t 1 , multiquantum between one dipolar and CSA interaction will be CSA/DD. transverse coherences whose frequencies are characteristic of the Although cross-correlation has been described theoretimultispin order produced by cross-correlation processes. This cally in NMR for more than 30 years (2-6), very few makes it possible to obtain in-phase magnetization in both dimenmethods have been suggested and tested experimentally for sions. The three schemes correspond to the combination of two measuring cross-correlation rates (9, 10), and there have evolutions due either to static J coupling in the transverse plane been few publications on their use for the exploration of or to cross-correlation cross-relaxation along an effective field.
structural or dynamic properties of molecules (11,12). This combination allows the conversion of one-spin order into multispin order and the reverse. If only cross-correlation cross-Starting from this surprising observation, we have tried to relaxation transfers are involved, there is no restriction on the understand why measuring cross-correlation rates presents coupling network. The quantitative exploitation of the results to difficulties.
obtain structural information from cross-correlation-induced re-
First of all, the largest effect induced by cross-correlations laxation rates requires a normalization coefficient which is prois on the evolution of transverse magnetizations (13). It vided by the simultaneous monitoring of one-spin coherence. results in a different width for each line of a multiplet These ideas have been tested experimentally in the case of dipole- (8, 13), an effect which has been called ''differential line dipole cross-correlation on a sample of cyclosporin. Buildup curves broadening'' (14), or in the observation of extra cross-peaks at various angles u are described which yield information on the in COSY experiments (15). The strong chemical shift aninternal dynamics.