In situ SABRE Polarisation of 1H and 19F Nuclei with Earth’s Field NMR Detection

Demonstrated in this thesis is a route to directly explore ultra-low-field (ULF) polarisation transfer within Signal Amplification by Reversible Exchange (SABRE) without the need for a sample transfer step. Integration of an Earth’s Field NMR (EFNMR) instrument that operates in the same field regime as SABRE polarisation transfer, with external solenoids and an automated p-H2 gas flow system allows SABRE polarisation transfer to occur in situ of the detector. The rapid acquisition of SABRE-polarised NMR signals under the strong coupling conditions required for polarisation transfer offers a way to directly probe the transfer mechanism, thus providing a route toward maximising the efficiency of SABRE for different nuclei. A reproducible flow of p-H2 into the EFNMR probe, combined with precise control over the timing and strength of the external field during SABRE polarisation transfer and NMR detection led to the acquisition of reproducible hyperpolarisation on the 1H and 19F nuclei of different fluorinated pyridine derivatives. Of the four different substrates, 3,5-difluoropyridine and 3-difluoromethylpyridine proved suitable candidates for interrogating the magnetic field dependence of SABRE polarisation transfer via ULF-cycling experiments, owing to their large heteronuclear J-coupling interactions of 9 and 55.4 Hz, respectively, that form hyperpolarised EFNMR signals with fine structure and minimal peak overlap. This was necessary to observe subtle changes to the signal shape under varying polarisation transfer conditions, where strong coupling and the collapse of chemical shift in the ULF regime led to the formation of complex NMR signals. The very strong coupling network of 3-difluoromethylpyridine exhibited polarisation transfer mechanics that differed from what was observed with the other more weakly coupled substrates. Numerical simulations were also employed to aid in interpreting the complex EFNMR spectra.