Novel Two-Dimensional Methods that Combine Single-Quantum Cross-Polarization and Multiple-Quantum MAS of Quadrupolar Nuclei

A new approach to combining cross-polarization with multiple-quantum MAS in a two-dimensional NMR experiment is demonstrated, involving cross-polarization from H-1 to the single-quantum coherences of a quadrupolar nucleus. These coherences are then converted directly to multiple-quantum coherences rather than via a population state. In two separate methods, pure-absorption lineshapes are obtained using a z-filter and a shined echo, respectively, with the latter, a 'reversed split-t(1)' method, demonstrated to be particularly effective. The efficiency of both sequences may be improved by incorporating 'fast-amplitude-modulation' (FAM) pulses for both the conversion and excitation of triple-quantum coherences. (C) 2001 Elsevier Science B.V. All rights reserved.