An extension of the cross-depolarization method: Subspectral editing in CP/MAS NMR

Abstract

A modification of the cross-depolarization method in CP/MAS NMR is described which allows simultaneous nulling of both methine and methylene carbon signals despite their different sensitivities to cross depolarization. Extension of the cross-depolarization time, partially inverting methine as well as methylene carbon signals, followed by a suitably chosen brief period of normal cross polarization (“cross repolarization”), nulls all signals arising from proton-bearing carbons in rigid-lattice environments. Since selective nulling of methylene or methine carbon signals is also possible by cross depolarization, spectral editing readily gives separate methine and methylene subspectra.