Extending the lifetime of hyperpolarisation

In nuclear magnetic resonance (NMR), one of the most serious inherent challenges is the low sensibility of nuclei. In order to enhance the signal of NMR experiments, the technique of dynamic nuclear hyperpolarisation (DNP) was introduced in the 1950s, leading to a high field prototype apparatus in the 1990s for solid-state applications under MAS conditions. In 2003, the coupling between low-temperature polarisation and room temperature detection also came into reality, which is known as dissolution-DNP (d-DNP). In this thesis, we present a new sample formulation for d-DNP experiments. Also, a new scheme for separating the preparation of hyperpolarised materials and detection apparatus is proposed, which would allow us to overcome the usual requirement that the apparatus for hyperpolarisation and the device for signal detection have to be in close proximity. A numerical model based on the finite element method (FEM) is proposed to study the dynamics of nuclear magnetic energy in both conventional spin glasses and biphasic d-DNP samples. This method first permits a visualisation of the process of the build-up of polarisation and of the relaxation of magnetisation during a DNP experiment. Based on such calculations, we could estimate the optimal experimental parameters for the preparation of hyperpolarised samples, including but not limited to the chemical composition of the samples, the length of spin locking pulses, and the duration of intervals between spin locking pulses in pulse sequences. An interesting conclusion from our simulations is that, under suitable conditions of storage, the lifetime of the hyperpolarisation can be extended to hours or even days in carefully designed biphasic samples. This allows us to propose two experimental approaches aiming at drawing benefit from such an attenuated relaxation. One method deals with the molecules of interest (MOIs) that are in crystalline form at room temperature and normal pressure. Such powders can be impregnated with radical-doped organic glass-forming solvents that have an orthogonal solubility. Under the DNP conditions, the magnetisation is transferred from the single electron of the polarising agent (PA) to the nuclei in the glassy organic solvents. The nuclear polarisation is then relayed to the particles of MOI. We can further confine the nuclear hyperpolarisation overnight in a moderate static magnetic field in a liquid helium bath. On the other hand, for the MOIs that are liquid or even gaseous at room temperature and normal pressure, we propose a spin-labelled solid matrix with interconnecting pores. The fluids can be filled into the pores of the matrix. Under the DNP conditions, the DNP process begins from inside the polarising matrix, and then passes to the fluids that are frozen in the pores.

    Keywords: NMR ; DNP ; Sample formulation ; Spin diffusion ; Numerical simulation

    Thèse École polytechnique fédérale de Lausanne EPFL, n° 7873 (2017)
    Programme doctoral Chimie et Génie chimique
    Faculté des sciences de base
    Institut des sciences et ingénierie chimiques
    Laboratoire de résonance magnétique biomoléculaire
    Jury: Prof. Sandrine Gerber (présidente) ; Prof. Geoffrey Bodenhausen, Prof. Jean-Philippe Ansermet (directeurs) ; Prof. Lothar HELM, Prof. Sami JANNIN, Prof. Matthias Ernst (rapporteurs)

    Public defense: 2017-7-13


    Record created on 2017-07-10, modified on 2017-07-18

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