Advances in Zero-Field Nuclear Magnetic Resonance Spectroscopy
- Author(s): Theis, Thomas
- Advisor(s): Pines, Alexander
- et al.
In the course of the last century, Nuclear magnetic resonance (NMR) has become a powerful and ubiquitous analytical tool for the determination of molecular identity, structure, and function. Traditionally, the great analytical power of NMR comes at the cost of mobility and large expenses for cryogenic cooling. This thesis presents how zero-field NMR detected with an atomic magnetometer is emerging as a new, potentially portable and cost-effective modality of NMR with the ability of providing information-rich and high-resolution spectra. A detailed description of the zero-field NMR spectrometer and its operation is provided. The thesis details how the acquired zero-field NMR spectra result from the electron mediated scalar interaction (J-coupling) of nuclear spins in an analyte. Simple rules of addition of angular momenta are introduced for the prediction of the observed spectral lines overcoming the need for numerical simulations and enabling unambiguous assignment of peaks to different molecules. Additional information can be obtained in the near zero field regime, where the Zeeman interaction can be treated as a perturbation to the J-coupling. The presence of small magnetic fields results in splitting of the zero-field NMR lines, imparting additional information to the pure zero-field spectra. In addition to the utilization of the atomic magnetometers for enhanced sensitivity, hyperpolarization schemes can be implemented. This thesis shows that chemically specific zero-field NMR spectra can be recorded using hydrogenative and non-hydrogenative parahydrogen induced polarization (PHIP, NH-PHIP), enabling high-resolution NMR. The increased sensitivity enables detection of compounds with 13C or 15N in natural abundance. Since PHIP and NH-PHIP operate in situ, and eliminate the need for a prepolarizing magnet, they broaden the analytical capabilities of zero-field NMR. Lastly, this thesis gives insight into the PHIP and NH-PHIP mechanism by developing an appropriate theoretical framework.