The proposed research is focused on fundamental advances in the field of Dynamic Nuclear Polarization (DNP) NMR that will make this powerful technique far more readily available and useful to the national and international biomedical research communities. In DNP NMR, a high frequency microwave source is used to irradiate electron- nuclear transitions, thereby transferring the high spin polarization in the electron spin reservoir to the nuclear spin system through hyperfine and dipolar interactions. The resulting enhancements in NMR signals have been demonstrated to exceed a factor of 400, and thus DNP NMR is now considered a major advance in NMR spectroscopy. The required microwave frequency for the excitation of the electron spin system is in the terahertz regime: 263 GHz, 395 GHz and 527 GHz for 400 MHz, 600 MHz, and 800 MHz 1H frequencies respectively. To date, DNP for magic angle spinning (MAS) NMR experiments has relied on gyrotron oscillators with continuous power output of tens of Watts. Gyrotrons are now commercially available and more than 40 such systems have been installed worldwide in the past decade. However, gyrotrons for DNP are very costly, exceeding the $600k cost limit for NIH Shared Instrument Grants. Gyrotrons are also relatively large, creating additional issues with the demand for lab space and siting. The main thrust of the proposed research is to radically reduce the required power levels for DNP/NMR down to the point where smaller and cheaper sources are available, including terahertz klystrons and solid-state sources. This will be done by dramatically improving the coupling of power to the sample and by significantly improving the transmission efficiency of the transmission lines. We propose these specific research activities: 1.) We will use state-of-the-art electromagnetics simulations to optimize the coupling of the microwave power from the launching antenna in the DNP NMR probe to the biochemical sample of interest. Preliminary results show that an optimized system can reduce the needed terahertz power by a factor of five, sufficient to allow replacement of the gyrotron by a lower power source. We will use our electromagnetics simulations to design, build and test EPR resonators with higher quality factors in order to more efficiently couple the terahertz power. 2.) In order to design optimized coupling of the terahertz power to the sample, we must know the complex permittivity (real and imaginary ?) of the biochemical samples at cryogenic temperatures. We will measure the sample permittivity using a vector network analyzer. 3.) The efficient transmission of the output power from the terahertz source to the DNP/NMR sample is an advanced microwave engineering challenge. We will conduct experimental and theoretical research to reduce all transmission losses. 4.) We propose to build and test a powerful gyroamplifier for pulsed DNP at 527 GHz / 800 MHz (16T magnetic field), where high resolution DNP experiments are currently being performed. The gyroamplifier will use an existing magnet and electron gun to greatly reduce the cost. Collectively, these studies will help make DNP/NMR a far more accessible and useful tool in modern biochemistry research.
The proposed research is focused on fundamental advances in the field of Dynamic Nuclear Polarization (DNP) NMR that will make this powerful technique far more readily available and useful to the national and international biomedical research communities. DNP has been demonstrated to increase the signal to noise ratio by a factor of more than 400 in NMR spectroscopy and has application in the study of membrane, soluble and amyloid proteins. The proposed research will include the demonstration of: greatly improved coupling of terahertz power to DNP samples using state-of-the-art electromagnetic simulations; higher quality resonators for EPR spectroscopy at high magnetic field; highly efficient transmission lines for terahertz radiation; and a 527 GHz high power amplifier for pulsed DNP/NMR.
| Nanni, Emilio A; Jawla, Sudheer; Lewis, Samantha M et al. (2017) Photonic-band-gap gyrotron amplifier with picosecond pulses. Appl Phys Lett 111:233504 |
| Soane, Alexander V; Shapiro, Michael A; Jawla, Sudheer et al. (2017) Operation of a 140 GHz Gyro-amplifier using a Dielectric-loaded, Sever-less Confocal Waveguide. IEEE Trans Plasma Sci IEEE Nucl Plasma Sci Soc 45:2835-2840 |
| Ni, Qing Zhe; Yang, Fengyuan; Can, Thach V et al. (2017) In Situ Characterization of Pharmaceutical Formulations by Dynamic Nuclear Polarization Enhanced MAS NMR. J Phys Chem B 121:8132-8141 |
| Soane, Alexander V; Shapiro, Michael A; Stephens, Jacob C et al. (2017) Theory of Linear and Nonlinear Gain in a Gyroamplifier using a Confocal Waveguide. IEEE Trans Plasma Sci IEEE Nucl Plasma Sci Soc 45:2438-2449 |
| Schaub, S C; Shapiro, M A; Temkin, R J (2016) Simple Expressions for the Design of Linear Tapers in Overmoded Corrugated Waveguides. J Infrared Millim Terahertz Waves 37:100-110 |
| Kowalski, Elizabeth J; Shapiro, Michael A; Temkin, Richard J (2014) Simple Correctors for Elimination of High-Order Modes in Corrugated Waveguide Transmission Lines. IEEE Trans Plasma Sci IEEE Nucl Plasma Sci Soc 42:29-37 |
| Michaelis, Vladimir K; Ong, Ta-Chung; Kiesewetter, Matthew K et al. (2014) Topical Developments in High-Field Dynamic Nuclear Polarization. Isr J Chem 54:207-221 |
| Jawla, Sudheer K; Shapiro, Michael A; Idei, Hiroshi et al. (2014) Corrugated Waveguide Mode Content Analysis Using Irradiance Moments. IEEE Trans Plasma Sci IEEE Nucl Plasma Sci Soc 42:3358-3364 |
| Lewis, Samantha M; Nanni, Emilio A; Temkin, Richard J (2014) Direct Machining of Low-Loss THz Waveguide Components With an RF Choke. IEEE Microw Wirel Compon Lett 24:842-844 |
| Jawla, Sudheer; Ni, Qing Zhe; Barnes, Alexander et al. (2013) Continuously Tunable 250 GHz Gyrotron with a Double Disk Window for DNP-NMR Spectroscopy. J Infrared Millim Terahertz Waves 34:42-52 |
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