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 employ ing cross polarization (CP), cross polarization-depolarization (CPD), and cross polarization-depolarization-repolarization are analyzed quan titatively to derive simple and general procedures for optimized spect ral editing of C-13 CP/MAS NMR spectra of rigid solids by separation o f the C-13 resonances into CHn subspectra (n = 0, 1, 2, and 3). Specia l attention is devoted to a differentiation by CPD/MAS of CH and CH2 r esonances since these groups behave quite similarly during spin lock u nder Hartmann-Hahn match and are therefore generally difficult to dist inguish unambiguously. A general procedure for the design of subexperi ments and linear combinations of their spectra to provide optimized si gnal-to-noise ratios for the edited subspectra is described. The techn ique is illustrated by a series of edited C-13 CP/MAS spectra for a nu mber of rigid solids ranging from simple organic compounds (sucrose an d l-menthol) to complex pharmaceutical products (calcipotriol monohydr ate and vitamin D-3) and polymers (polypropylene, polyvinyl alcohol, p olyvinyl chloride, and polystyrene). (C) 1994 Academic Press, Inc.