Spectral spin diffusion in 13C NMR of double 13C-labelled sodium acetate trihydrate (SAC), and in 31P NMR of zinc(I1) bis(0,O'-diethyldithiophosphate) (ZNP) has been studied under magic-angle spinning conditions. Spin-diffusion time constants, qD, were determined from the intensities of the spinning sidebands in experiments using rotation-synchronized DANTE pulse sequences, at several different spinning frequencies. The theory of Suter and Ernst, developed for spectral spin diffusion in single crystals, was extended to the case of polycrystalline samples rotating under magic-angle spinning conditions. We considered two mechanisms for the spin diffusion, i.e. dipolar interaction and J-coupling. The spin-diffusion time constants, qT), were related to the zero-quantum lineshape functions in a manner similar to the theory of Suter and Ernst. The zero-quantum lineshape functions were estimated from the observed single-quantum lineshape functions. In the present studies the dependence of the experimental values for T,, on the rotational frequency v, are in good agreement with those calculated from the theory based on the dipolar interaction mechanism. The values of T,, for SAC showed a deep minimum at Am z 2m,, and a shallow minimum at Am z 3m,. This phenomenon is rotational relaxation resonance.

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The effect of dipolar interactions on the solid state 31P cross-polarization magic-angle-spinning (CP-MAS) nuclear magnetic resonance (NMR) line shapes for the coupled two-spin systems, sodium pyrophosphate decahydrate, Na4P2O7⋅10H2O, and tetraphenyl diphosphine-1-oxide, (C6H5)2PP(O)(C6H5)2, has been investigated. The one-dimensional (1D)CP-MAS spectra of Na4P2O7⋅10H2O shows spinning frequency dependent sideband splittings. A theory was developed to permit the calculation of the MAS NMR line shapes of the dipolar and J-coupled two-spin systems. An exact solution of the periodic Hamiltonian was obtained by the use of Floquet Hamiltonian theory. The experimental spectra of Na4P2O7⋅10H2O are well reproduced by the theoretical ones calculated from the present theory, in which the homonuclear dipolar interaction between the two 31P nuclei in the P2O74− group was taken into consideration. Our Hamiltonian also leads to calculated spectra which are in good agreement with the experimental observations even at low rotor spinning speeds. The two-dimensional J-resolved experiments, with rotationally synchronized acquisition in the t1 dimension, were performed for both Na4P2O7⋅10H2O and (C6H5)2PP(O)(C6H5)2. These experiments were found to be useful in distinguishing between the different mechanisms of the rotational sideband splitting of 1D spectra, as well as the dipolar interactions between spins with the same isotropic chemical shift, but different orientations of chemical shift tensors. These studies also allowed the identification of splittings caused by homonuclear J-coupled interactions, because the resolution of the 2D J-resolved spectra was greater than that of the 1D spectra.

High resolution solid state 13C NMR spectra of amino acids and nitrile compounds have been obtained by a combination of cross-polarization, dipolar decoupling, and magic angle spinning techniques (CP–MAS). The resonances of Cα and cyano carbons in the observed 13C spectra show asymmetric doublet patterns. This problem has been treated by using the adiabatic approximation since the 14N quadrupole interaction is much larger than the spinning frequency. Theoretical spectra have been simulated for these carbons and they show very good agreement with experimental observations.