Selective carbon excitation and the detection of spatial heterogeneity in cross-polarization magic-angle-spinning NMR

Abstract

The solid-state 13C NMR spectra of heterogeneous materials are often quite complex owing to superposition of signals from the various domains in the sample. Here a new class of modified cross-polarization experiments is described that can be used to selectively excite carbons in different domains of an inhomogeneous solid, provided the domains differ in their proton relaxation properties. The techniques rely on bringing the 13C spins into thermal contact with a “tailored” proton magnetization. Applications include selective observation of spectra from crystalline and amorphous domains of poly(ethylene terephthalate) and the suppression of spinner signals.