New Approaches to Boost SABRE Signals

Abstract

SABRE (Signal Amplification by Reversible Exchange) methods provide a simple, fast, and cost-effective method to hyperpolarize a wide variety of molecules in solution, and have been demonstrated with protons and, more recently, with heteronuclei (X-SABRE). In this dissertation, we first present oscillating pulse SABRE that use magnetic fields far away from the resonance condition of continuous excitation and can commonly triple the polarization. An analysis with average Hamiltonian theory indicates that the oscillating pulse, in effect, adjusts the J-couplings between hydrides and target nuclei and that a much weaker coupling produces maximum polarization. This theoretical treatment, combined with simulations and experiment, shows substantial magnetization improvements relative to traditional X-SABRE methods. It also shows that, in contrast to most pulse sequence applications, waveforms with reduced time symmetry in the toggling frame make magnetization generation more robust to experimental imperfections. A high-pressure SABRE approach is presented to enhance the exchange rate of the dihydride by increasing its concentration. To achieve this, two methods are proposed to improve the concentration of hydrogen gas: the brute-force high-pressure method and the supercritical SABRE method. The brute-force approach has been found to effectively increase the polarization by over three times. Further numerical analysis has shown that combining the oscillating pulse technique with the high-pressure method, and implementing temperature control, can effectively further enhance the polarization to higher levels.