A Millimeter-wave Tunable Cavity for Ultra-sensitive Solids and Liquids DNP-NMR at Low Budget

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 DESCRIPTION (provided by applicant): NMR is probably the most powerful and widely used analytical technique for structure determination and function elucidation of molecules of all types, but it suffers from low sensitivity, particularly for insoluble biological macromolecules. Dynamic Nuclear Polarization (DNP) with Magic Angle Spinning (MAS) has recently demonstrated S/N gains exceeding two orders of magnitude at ~100 K compared to conventional MAS-NMR in many biological solids. Despite this enormous benefit to biomedical research, the adaptation rate of DNP will be severely limited by its very high price tag (currently $1.8-4M), mostly because of the special magnet (with sweep coils) and expensive gyrotron required, owing to the very poor microwave efficiency of current DNP probes. Our detailed simulations of a novel millimeter wave (mmw) DNP cavity have shown the potential for achieving the needed electron spin saturation with two orders of magnitude lower microwave power than the existing MAS-DNP designs for samples of similar volume (1-25 L) at the same B0 and temperature. The proposed novel DNP cavity is initially compatible only with static (non-spinning) methods, and the linewidths from static solids NMR techniques are always much greater than in MAS. However, static high-power methods, such as PISEMA, have been as fruitful as MAS methods in yielding structures of large, complex, helical membrane proteins because of the unique capability to provide correlated dipolar and anisotropic chemical shift data needed to resolve sign degeneracies. A novel stacked-plate cavity arrangement of nanostructured substrate containing macroscopically aligned and hydrated membrane proteins developed by collaborating NCSU team dramatically reduces sample heating enabling substantial DNP S/N enhancements even for lossy liquid samples at or near RT with substantially improved spectral resolution. Related cavity designs compatible with MAS-DNP, inspired by the static-DNP cavity, will also be simulated. The static DNP cavity and probe that will be initially developed for 7 T is expected to yield two orders of magnitude gain in S/N for a wide range of solids NMR experiments, and it will do so with two orders of magnitude lower mmw power than competing MAS-DNP designs. This will make it possible for virtually all current NMR groups to bring static H/X/Y/e- DNP capabilities into their labs - for both solids and liquids - for a total entry budget of under $150K, including the 0.05-0.3 W mmw source, DNP probe, waveguides, and transitions - all scalable to very high fields. Development of the Doty static-DNP cavity could allow the number of groups doing DNP-NMR worldwide to increase from a handful to hundreds over the next four to eight years. Overall, the proposed technology development is expected to provide biomedical researchers with tremendous new opportunities for the structure-function studies of membrane proteins and cellular membrane systems.