Date of Award
Doctor of Philosophy (PhD)
Dynamic nuclear polarization (DNP) is a method of generating hyperpolarization of nuclear spins for nuclear magnetic resonance (NMR) spectroscopy. Coherent, time domain techniques make the possibility of DNP directly to spins of interest at room temperature and higher feasible in magic angle spinning (MAS) NMR, allowing for optimal experimental repetition times to be limited by the T_1 of the electron, rather than a much longer T_1DNP, with excellent resolution. The strong hyperfine couplings that make such direct DNP transfers possible, however, can lead to short nuclear relaxation times that result in broadening of nuclear resonances and reduce sensitivity. This dissertation describes the implementation of electron decoupling, performed by rapidly chirping the irradiating microwave frequency through the electron resonance frequency of the narrow line Trityl Finland radical. The frequency chirps are produced by modulating the accelerating voltage of a frequency agile gyrotron. The voltage modulation is programed into the spectrometer arbitrary waveform generator using MATLAB. The experiments described here were performed both at a common DNP temperature of 90 K and with the first MAS experiments performed below 6 K. Experiments were performed using both direct polarization of the nuclei from the electrons, and with indirect polarization using cross polarization. Electron decoupling both narrows nuclear resonances and improves their integrated area. A method for performing analytical powder averaging for fast simulations of electron detected MAS DNP experiments is also described, anticipating the incorporation of electron detection into magnetic resonance experiments under ultra-fast MAS for excellent sensitivity. The simulations are performed using a home written PYTHON code.
Chair and Committee
Alexander Barnes, Joseph Ackerman, Sophia Hayes, Richard Loomis,
Saliba, Edward Paul, "Electron Decoupling with Chirped Microwave Pulses for Magic Angle Spinning Dynamic Nuclear Polarization Nuclear Magnetic Resonance Spectroscopy" (2019). Arts & Sciences Electronic Theses and Dissertations. 1945.