Lee, Youngbok (2013-05). Application of Dissolution Dynamic Nuclear Polarization to the Characterization of Reactions Involving Large Molecules. Doctoral Dissertation. | Thesis individual record

Nuclear magnetic resonance (NMR) spectroscopy is one of the most important analytical tools for organic and biological chemistry. It provides not only detailed information on the structure of small molecules and macromolecules, but also on molecular interactions. Because of the inherent low sensitivity of NMR, a long signal averaging time or a high spin concentration is often required. A variety of methods have been explored to improve the sensitivity of NMR. Especially, large signal gains can be obtained by hyperpolarization of the nuclear spins. NMR signals of hyperpolarized samples are enhanced by several orders of magnitude. Dissolution Dynamic Nuclear Polarization (D-DNP) is a versatile technique capable of polarizing many different nuclei in the solid state, and subsequently providing a hyperpolarized liquid sample following a dissolution step. The resulting signal enhancement has made it possible to obtain detailed information in research fields as varied as metabolic imaging or enzyme catalysis. This dissertation aims to extend the applicability of D-DNP into new areas of chemistry, which involve the characterization of interactions and reactions involving large molecules.

In a first project, fluorine hyperpolarization is exploited to investigate protein-ligand interactions. The enhancement of 19F signal allows for the detection of submicromolar concentrations of fluorinated ligands in the strong-, intermediate-, and weak-binding regimes. Several NMR parameters are utilized to observe ligand binding to the macromolecule, and to determine dissociation constants.

In a second project, competitive binding of ligands to the same binding pocket on a protein is investigated. Here, polarization flows from a first ligand hyperpolarized on protons to the protein, and then to the second ligand. The buildup in function of time of the signals due to this relayed nuclear Overhauser effect contains structural information on the binding epitope.

In a third project, the aim is to directly detect a larger molecule, a polymer, which has been synthesized starting from hyperpolarized monomers. Using DNP, single scan observation of 13C, a common nucleus with large chemical shift dispersion, is possible. Time resolved 13C NMR spectroscopy in combination with kinetic models permits the description of polymerization reaction of the living anionic polymerization of styrene. In summary, several approaches have been investigated for utilizing a large hyperpolarization initially produced on small molecules, for the benefit of characterizing properties of macromolecules. These developments extend the capabilities of D-DNP and demonstrate the potential for leading to new applications in fields as diverse as drug discovery and polymer science.

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