DISTANCE MEASUREMENTS BY DIPOLAR RECOUPLING 2-DIMENSIONAL SOLID-STATENMR

We present a two-dimensional NMR technique for the measurement of dipo lar couplings in polycrystalline solids. This experiment is fully tran sverse and uses a windowless dipolar recoupling pulse sequence (DRAWS, described in Gregory, D. M.; et al. Chem. Phys. Lett. 1995, 246, 654- 663) to effect coherence transfer. Direct, internuclear coherence tran sfer produces negative cross-peaks in the 2D spectrum. Cross-peak deve lopment and experimental requirements for obtaining distances from the two-dimensional solid-state NMR spectra of two-and three-spin systems are discussed, and demonstrations are shown for thymidine-2,4-C-13(2) and L-alanine-C-13(3). Internuclear distances are derived by comparis on of experimental cross-peak buildup curves with numerical simulation s. In the three-spin system, indirect coherence-transfer mechanisms pr ohibit the interpretation of buildup curves as due to isolated spin pa ir interactions and limit the accuracy of some distance measurements. This 2D technique can also be used for spectral assignment, as demonst rated by an application to L-arginine HCl-U-C-13,N-15.