DNP Enhanced Solid-State NMR for Characterisation of Surface Species and Pharmaceuticals Seminar

Surface enhanced NMR spectroscopy (SENS) can be achieved by using dynamic nuclear polarization (DNP). In a DNP SENS experiment electron polarization is transferred from an organic radical to proton nuclei at the surface of a material. Enhanced proton polarization may then be transferred to the surface hetero-nuclei (e.g., 13C, 29Si, 119Sn, etc.) by cross-polarization (CP), improving the sensitivity of surface selective NMR experiments by a factor 100-200. An overview of the successful application of DNP SENS for the characterization of high surface area materials such as mesoporous and nano-particulate silicas, metal oxide nano-particles, and metal organic frameworks will be given. DNP enhanced solid-state NMR can also be applied to ordinary micro-crystalline solids. The sensitivity enhancements of up to two orders of magnitude from DNP enable the rapid acquisition of natural isotopic abundance 13C homonuclear correlation spectra and 1H-15N CPMAS spectra. It is also shown that is straightforward to acquire 1H-14N overtone CPMAS spectra and two-dimensional 13C-14N overtone HMQC correlation spectra for organic compounds. Finally, we demonstrate how these techniques can be applied to characterize pharmaceutical formulations with low active pharmaceutical ingredient (API) contents.