Sideband intensities in two-dimensional NMR spectra of rotating solids

Abstract

In the presence of magic angle sample spinning (MASS), two-dimensional solid-state NMR spectra of magnetically dilute I=1/2 nuclei split into rotational sidebands spaced at the spinning frequency in both dimensions. The intensities of these sidebands contain information on the sizes and relative orientations of the interactions present in the two experimental time domains. Here we extend an earlier analysis of sideband intensities in one-dimensional MASS spectra to two-dimensional MASS spectra. The resulting equations are applicable to heteronuclear and homonuclear correlation spectra, dipolar/chemical shift spectra, and slow chemical exchange spectra. We use the equations to deduce the orientation of the 15N chemical shift tensor in the amide group of L-asparagine⋅H2O from the sideband intensities in the 15N–1H dipolar/chemical shift spectrum. This application to an AX2 system enlarges on previous work with AX systems and may be generalized to AXn systems.