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The Han lab’s research objective is the development of a novel hyperpolarization scheme that greatly enhances nuclear magnetic resonance (NMR) signal for the purpose of measuring dilute species and directly monitoring chemical processes. In particular, we focus on the study of gas phase absorbents in nanoporous materials and the direct tracing of molecules participating in chemical processes and reactions. In principle, NMR spectroscopy presents an ideal tool for these studies due to its unique capability to directly probe chemical composition, structure, and dynamics on the atomic scale if the nuclear spin polarization can be enhanced by 2-4 orders of magnitudes. The physical principle of the hyperpolarization scheme is based on the efficient transfer of spin polarization from the more highly polarized (by orders of magnitude) electron spin to the nuclear spin. The general concept of this polarization transfer is called dynamic nuclear polarization (DNP), and can occur by several different physical mechanisms which are dependent on the spin system and the experimental conditions. Utilizing emerging, high frequency, microwave technologies, the development of a novel DNP approaches is pursued that is expected to be particularly effective for the polarization of gas phase sensor species. The intellectual merit of our research is 1) the development of custom designed methodologies for the polarization of guest molecules in “host” nanoporous and macroporous materials, 2) the study of the characteristics and function of a nanoporous material by direct detection of absorbents, and 3) the production of hyperpolarized species such as 129Xe that will serve as either spectator species or starting materials, and that will be probed for the direct monitoring of chemical processes and reactions. We have developed first DNP schemes at 0.3 and 1.1 T (Fig.1) and are currently polarizing 1H nuclei of biomolecules by >15-fold under aqueous conditions (Fig. 2). Our development is broadly targeted towards 1H, 13C, 129Xe and 31P nuclei at magnetic fields from 0.3 up to 7 T. 
Figure 1: DNP-NMR set-up: 7T and 0-1.2 T magnet, NMR spectrometer, rf circuits and EPR cavity.
Figure 2: NMR signal enhancement by DNP at 0.3 T with 9.3 GHz resonant microwave irradiation and 14.5 MHz resonant rf detection (red line) versus NMR signal with thermal polarization at 0.3 T. |
