NMR spectroscopy is sometimes described as an inherently insensitive technique, especially in the solid state, which is often dominated by strong dipolar interactions, anisotropic effects and broad lines, making it difficult to resolve characteristic features associated with both high and low natural abundant nuclei, such 1H as well as 13C and 15N. In order to overcome these challenges, a number of very important advances have been made over the years, which include magic angle spinning (MAS), cross polarisation (CP), and high power 1H decoupling, which are being continually refined to this day. Together, these techniques, with specific isotopic labeling, have expanded into a flourishing research area, from proteins to biomaterials, from bones and cements to metal oxide catalysts, because they offer greater resolution and sensitivity forn analysis and ultimately insight into material structure and organisation.
Most recently, the possibility of significant signal enhancement has been realized by transferring polarisation from electrons in free radicals to nuclei such as 1H, which can in turn be transferred to the less abundant nuclei, like 13C and 15N, with so called dynamic nuclear polarization (DNP). While the discovery of DNP is more than fifty years old, the accessibility to such commercially available high-field instruments with cryogenic probes incorporating MAS means that materials and biomaterials research can be advanced in ways which were previously thought impractical if not impossible.
In this presentation, we will highlight some recent research with case studies of three polymers, both natural and synthetic, that respond particularly favourably to solid state DNP, enabling access to connectivity patterns at natural abundance with remarkable sensitivity, speed and efficiency.