The limitations of previous dynamic nuclear polarization (DNP) experiments have been avoided by a transfer DNP approach whereby the nuclear spins are polarized by DNP at low magnetic field (0.33 T) and then quickly transferred to a high monitoring field (4.7 T). This approach provides an order of magnitude improvement in sensitivity when compared to the usual low field DNP experiment. Also high resolution spectra commonly obtainable at high magnetic fields are now possible for the DNP enhanced signals.
Using this method, we have observed large ¹H, ²D, ¹³C, ²⁹Si, and ¹⁵N scalar and dipolar enhancements (2-60 times of signal strength at 4.7 T NMR). Among the results, ¹⁵N and ²⁹Si liquid DNP enhancements are the first to be reported. The selective ¹³C and ¹H DNP enhancements at 0.33 T for different nuclei on the same molecule were observed. A mathematical model describing the low to high magnetic field transfer DNP experiments has also been developed. In ¹³C DNP, we find that the three-spin effect can significantly degrade the dipolar dominated enhancements unless high radical concentrations are used. The scalar dominated ¹³C DNP enhancements can be very large. In addition, the nitroxide radical (TEMPO) used in the present study can induce large scalar enhancements at carbon or nitrogen atoms which have weakly acidic hydrogens. These results indicate DNP can be a very sensitive probe to study weak intermolecular interactions (e.g., hydrogen bonding). / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/38778 |
| Date | 12 July 2007 |
| Creators | Tsai, Kun-Hsiang |
| Contributors | Chemistry, Dorn, Harry C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xv, 219 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 23440222, LD5655.V856_1990.T72.pdf |
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