NMR is arguably the most powerful analytical technique for structure determination and function elucidation in molecules of all types, though the challenges are greater for biological macromolecules. Dynamic Nuclear Polarization (DNP) with Magic Angle Spinning (MAS) has recently demonstrated S/N gains of up to two orders of magnitude at ~100 K (the lower temperature bound using N2-MAS technology) compared to conventional NMR-MAS in many solids. Despite this enormous benefit, the adaptation rate of DNP will be severely limited by the very high price tag (~$1.5M) for the high-power millimeter-wave (mmw) gyrotron required for DNP operating in the 90-110 K range. Preliminary experiments at ~30 K (that consumed liquid helium at the rate of up to 250 L/day) have shown the potential for the use of low-power solid-state mmw sources and much higher S/N for DNP - if suitable MAS apparatus could be developed, but this will necessitate helium recycling and improved sample spinner designs. This SBIR project will enable 30K-DNP by developing: (A) the needed high-stability 30-K helium- spinner technology, (B) the needed high-efficiency closed-loop cryogenic helium recycling system, and (C) the complete quad-resonance (1H-13C-15N-electrons) DNP probe with auto sample exchange and extended variable temperature (XVT) operation for use initially in a 7T magnet. Signal acquisition with the proposed fully optimized MAS-DNP probe at 30 K could often improve sample throughput by one to two orders of magnitude compared to current state-of-the-art (100 K) MAS-DNP instrumentation, allowing the information needed for determining detailed molecular structures to be obtained on many complex biomolecules, catalysts, and other solids in an hour rather than days. The helium purification and recycling system this project will develop to enable 30K-DNP will also make it straightforward and cost-effective for the facility to then implement recycling of all the helium i is currently using for its cryo-magnets, as the additional hardware required for helium liquefaction will be relatively minor. Hence, not only will this project advance throughput of solids NMR by more than an order of magnitude, it will also begin putting NMR on a sustainable path by enabling cost-effective recycling of helium at the larger NMR facilities.
NMR is arguably the most powerful analytical technique for structure determination and function elucidation in molecules of all types, though the challenges are greater for biological macromolecules. The proposed development, a CryoMAS-DNP NMR probe with closed loop cryogenic helium recycling, will shorten acquisition times and increase sample throughput by one to two orders of magnitude compared to current technology, allowing the information needed for determining detailed molecular structures to be obtained on many complex biomolecules, catalysts, and other solids in hours rather than days.
