Chapter 3:Isotropic vs. Anisotropic Chemical Shift Separation

Two solid-state NMR methods with magic-angle spinning are described for separating isotropic and anisotropic chemical shift in two dimensions. Both methods are based on the idea of magic-angle turning (MAT), which averages the anisotropic shift at three equally spaced rotor angles about the magic angle. The first method is for shift anisotropy much larger than the spinning frequency. It encodes either the isotropic shift with MAT or the anisotropic shift with phase-adjusted sidebands separation (PASS) in the evolution period. A hybrid between MAT and PASS leads to a MATPASS pulse sequence that takes the advantages from MAT and PASS for isotropic vs. anisotropic separation. The second method is for recovering anisotropic shift under fast spinning. Chemical shift anisotropy is amplified using π pulses (xCSA) generating profiles of spinning sideband intensities for CSA measurement. Applications of the two methods are demonstrated with 13C and 15N CSA measurements of proteins and obtaining isotropic spectra of paramagnetic materials.