Nuclear magnetic resonance (NMR) spectroscopy of <sup>13</sup>C is a valuable tool for probing biological systems because it is both nondestructive and provides an abundance of structural and quantitative information. However, the low sensitivity of <sup>13</sup>C magnetic resonance due to its low natural abundance and gyromagnetic ratio make it difficult to quickly collect high quality spectra. Dynamic nuclear polarization (DNP) is an increasingly popular approach used to enhance NMR signal. In DNP, microwave irradiation of paramagnetic species at their electron frequency results in the transfer of a large electron spin polarization to surrounding nuclei. So far, many applications have been developed for solid state DNP including some structural analysis of membrane proteins and enzyme-inhibitor complexes. However, liquid state DNP applications are still in their infancy due to the challenge of applying the technique at high magnetic fields (above 10 T). At high magnetic fields, the Overhauser DNP polarization transfer efficiency between radicals and nuclei is greatly reduced. This effect is driven by electron-nuclear interactions, namely scalar interactions and dipole-dipole interactions. Due to major improvements in instrumentation large DNP enhancements are achievable via scalar interactions. In this work we focus our efforts on improving the scalar interactions by optimizing sample preparation techniques and developing new polarizing agents. In liquid Overhauser DNP, it is critical to degas the samples in order to limit relaxation via dissolved oxygen. Our group has also developed new bi-radicals, which are more effective than traditional mono-radicals in liquid DNP. In this presentation, we will discuss the physics behind the improved efficiency of the new bi-radicals.

Optimization polarizing agents for scalar overhauser DNP at 14.1 T

2019 Spring National Meeting

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