Effect of phase inversion of radiofrequency pulses on the recoupling of anisotropic NMR interactions under magic-angle spinning

The effect of phase inversion of radiofrequency pulses on the recoupling of anisotropic chemical shift and heteronuclear magnetic dipole-dipole interactions has been investigated by a simple analytical treatment. For the recoupling of chemical shift anisotropy, the evolution of the spin system will be different if the sign of all rf phases is inverted. This phenomenon is readily explained by the higher-order effect of average Hamiltonian theory. On the contrary, such dramatic phase inversion effect is not observed for heteronuclear dipolar recoupling, which can also be rationalized in our treatment. Numerical simulations are carried out to corroborate our analytical results and experimental verification is obtained for [1-C-13]-alanine. (C) 2009 Published by Elsevier B.V.