Spectral spin diffusion under n = 0 rotational resonance

The spectral spin diffusion process between the 31 P nuclei present in the dipotassium salt of α-D-glycopyranose-1-phosphate is investigated under magic-angle spinning conditions. The 31 P 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 tensor. First-order average Hamiltonian theory is used to provide a particularly simple physical insight into the spin diffusion mechanism, with the assumption that the 31 P- 31 P interaction may be introduced as a small perturbation of the interaction between the 31 P and 1 H nuclei. The spin diffusion rate is investigated as a function of the 1 H 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 1 H RF field amplitude during the mixing time.