SPECTRAL SPIN-DIFFUSION UNDER N=0 ROTATIONAL RESONANCE

The spectral spin diffusion process between the P-31 nuclei present in the dipotassium salt of alpha-D-glycopyranose-1-phosphate is investigated under magic-angle spinning conditions. The P-31 nuclei in such a system are characterized by rather weak direct coupling interactions in addition to exhibiting identical isotropic chemical shifts with differing orientations of the shielding tenser. First-order average Hamiltonian theory is used to provide a particularly simple physical insight into the spin diffusion mechanism, with the assumption that the P-31-P-31 interaction may be introduced as a small perturbation of the interaction between the P-31 and H-1 nuclei. The spin diffusion rate is investigated as a function of the H-1 radiofrequency decoupling field. The time constants describing the spin diffusion process were obtained using a hybrid of TOSS and NOESY experiments with the simple modification of decoupling the proton influence to various extents in successive experiments by varying the effective H-1 RF field amplitude during the mixing time.