OPTIMIZED SPECTRAL EDITING OF C-13 MAS NMR-SPECTRA OF RIGID SOLIDS USING CROSS-POLARIZATION METHODS

Combinations of C-13 magic-angle spinning (MAS) NMR experiments employing cross polarization (CP), cross polarization-depolarization (CPD), and cross polarization-depolarization-repolarization are analyzed quantitatively to derive simple and general procedures for optimized spectral editing of C-13 CP/MAS NMR spectra of rigid solids by separation of the C-13 resonances into CHn subspectra (n = 0, 1, 2, and 3). Special attention is devoted to a differentiation by CPD/MAS of CH and CH2 resonances since these groups behave quite similarly during spin lock under Hartmann-Hahn match and are therefore generally difficult to distinguish unambiguously. A general procedure for the design of subexperiments and linear combinations of their spectra to provide optimized signal-to-noise ratios for the edited subspectra is described. The technique is illustrated by a series of edited C-13 CP/MAS spectra for a number of rigid solids ranging from simple organic compounds (sucrose and l-menthol) to complex pharmaceutical products (calcipotriol monohydrate and vitamin D-3) and polymers (polypropylene, polyvinyl alcohol, polyvinyl chloride, and polystyrene). (C) 1994 Academic Press, Inc.