Efficient Generation of Hyperpolarized Molecules Utilizing the Scalar Order of Parahydrogen

Citation

Norton, Valerie Ann (2010) Efficient Generation of Hyperpolarized Molecules Utilizing the Scalar Order of Parahydrogen. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/57FW-1060. https://resolver.caltech.edu/CaltechTHESIS:05212010-154212167

Abstract

This dissertation describes methods that polarize the spin of a specific nucleus in molecules synthesized by molecular addition of parahydrogen to a precursor molecule. Nuclear magnetic resonance (NMR) pulse sequences are designed to perform efficient transfer of spin order by way of the scalar spin couplings between the two nascent protons and a heteronuclear spin label target. The result is an increase in the NMR signal from that nucleus by several orders of magnitude, approaching unity polarization. Algorithms are presented to effect the desired unitary evolution of this three-spin system over the range of couplings found in diverse molecules and in the presence of interfering spins. These methods are explored theoretically and comparisons are made to select the most advantageous method given a specific problem.

Issues concerning the choice of target molecule, portable equipment, and automation are discussed. Some design choices made for convenience in one aspect of the execution of the methods raise difficulties in other aspects. These difficulties are elucidated and methods of mitigation are discussed.

Pulse design issues are elucidated with numerical calculations which confirm analytical results for the time dependence obtained in the multiply rotating frame approximation. Failures of this approximation at low frequencies are explored numerically leading to novel pulse sequence design rules which ameliorate undesirable phenomena peculiar to low field NMR, enabling its employment for this and other applications requiring precise control of the spin degrees of freedom. Experimental results, primarily aimed at biomedical applications, are reviewed.

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