Lilly Thankamony, A., et al., Solvent-Free High-Field Dynamic Nuclear Polarization of Mesoporous Silica Functionalized with TEMPO. Appl. Magn. Reson., 2012: p. 1-14.
http://dx.doi.org/10.1007/s00723-012-0364-3
We report high-field magic-angle spinning dynamic nuclear polarization (MAS DNP) of mesoporous silica functionalized with nitroxide radicals. These results demonstrate that co-condensation can be employed to incorporate DNP polarizing agents into inorganic materials and that solvent-free DNP is feasible for porous materials. For the investigated material, the direct MAS DNP enhances the 29 Si nuclear magnetic resonance (NMR) spectra, whereas the indirect MAS DNP via protons is inapplicable owing to the inefficiency of ${}^{1}hbox{H}rightarrow{}^{29}hbox{Si}$ cross polarization transfer. Furthermore, the 29 Si signals in direct experiments build up in a few seconds at 100 K. This fast polarization buildup improves the NMR sensitivity and will be useful for the investigation of direct DNP below 100 K.