Enhancing the sensitivity of NMR by Dynamic Nuclear Polarisation

Abstract

Dynamic Nuclear Polarisation (DNP) is a method used to increase the signal available for nuclear magnetic resonance (NMR) experiments. DNP is one of many hyperpolarisation methods and one implementation, so called ex-situ DNP, sees the sample polarised with a stable radical doping agent at low temperature and with microwave irradiation in a magnetic field before transfer to a second higher field NMR magnet to acquire a liquid state NMR spectrum. The primary goal of this project has been to gain an understanding of the underlying reasons for unpredictable ex-situ DNP polarisation failures and to develop methods to overcome these limitations. In the course of the work an additional polarisation mechanism arising from hindered methyl rotors was discovered. This thesis describes the preparation of DNP samples and the way in which DNP-NMR experiments are performed have been optimised. The concept of a co-polarisation agent has been introduced and methods employing a Nuclear Overhauser Effect have been implemented. Additionally the identification and characterisation of a quantum tunnelling effect that is a variant of the commonly known Haupt effect. Finally these methods have been combined in a number of situations to give results that would have otherwise been unobtainable.