MAS NMR STRUCTURE REFINEMENT OF UNIFORMLY C-13 ENRICHED CHLOROPHYLL-AWATER AGGREGATES WITH 2D DIPOLAR CORRELATION SPECTROSCOPY

2D MAS dipolar correlation spectroscopy of uniformly C-13 enriched chl orophyll a/water aggregates was performed using broadband RFDR to prom ote exchange of coherence through homonuclear dipolar couplings. It is shown experimentally that incorporation of TPPI and coherence pathway selection in the RFDR pulse scheme yields virtually pure 2D absorptio n lineshapes. From a series of 2D correlation spectra collected at two spinning speeds with different mixing times of similar to 1 and simil ar to 10 ms all C-13 resonances of the chlorophyll a molecule were ass igned. The spectra with the longer mixing times reveal through-space i ntermolecular polarization transfer. This demonstrates that structural information can be obtained from uniformly C-13 enriched samples, whi ch paves the way for a full structural characterization of amorphous s olids.