Two-dimensional chemical exchange NMR in the solid: proton dynamics in phthalocyanine

Carbon-13 solid-state cross-polarization magic angle spinning (CP-MAS) has proved to be a powerful method for investigating dynamical processes in solids. In investigations of molecules with several resonances, the intrinsically lower resolution of CP-MAS NMR spectra compared to liquid-state spectra makes the interpretation of the spectra cumbersome due to peak overlap. In some cases, such as porphyrins or phthalocyanines, these problems arising in the /sup 13/C spectra have been overcome by observing /sup 15/N instead of /sup 13/C. This requires considerable synthetic effort because the NMR measurements must be performed on an enriched sample to overcome the low sensitivity. They present here results which show that /sup 13/C 2-D exchange exchange spectroscopy can extend the resolution, allowing the spectroscopist to extract the details of the exchange process from a natural abundance sample even when the /sup 13/C resonances strongly overlap in the one-dimensional spectrum. There is another example in which 2-D exchange spectroscopy has been exploited in a solid to determine a proton exchange rate but it was in a system where resolution was not a problem. The use of 2-D spectroscopy to extend resolution should be applicable to a large class of solid compounds.