This project is joint between our group and the Biomedical Engineering at ETHZ. It aims at the study of solutions, consisting of i) highly fluorinated ionic liquids and paramagnetic metal complexes or ii) paramagnetic complexes carrying highly fluorinated ligands and non-fluorinated ionic liquids, respectively.
The ultimate objective is an NMR field probe, which contains one of these combinations, suitable for the real-time monitoring of the spatiotemporal magnetic field evolution in MRI scanners. An important research challenge to be tackled in this project is the request for homo-(per)fluorinated ligands or ionic liquids (ILs), i.e. systems which contain exclusively magnetically equivalent fluorines. From a physical point of view, the compounds and solutions being developed must possess quantifiable parameters in order to be applicable in NMR field probes for MRI field monitoring. The most important parameters are; single fluorine resonance, high density in fluorine (>30 M), relaxation times T1 » T2 < 200 msec, chemical stability and low viscosity. Aiming at highly homo-fluorinated IL, perfluorinated “Cp*” ([C5(CF3)5]-) is a main focus and also anions such as [Al(OC(CF3))4]- are included.
|Figure 9. ORTEP presentation of perfluorinated Cp* together with its counter-ion [18crown-6-H3O]+|
We have improved the synthesis of [C5(CF3)5]- (Cp-F*) to an acceptable yield of about 30%. Combination with appropriate cations leads to ionic liquids of variable viscosity. Dissolution of Gd3+ in these IL gives paramagnetic solutions, which are close to fulfil the above-mentioned conditions. To complement the ILs with Cp-F*, different ILs with other homo-perfluorinated ions are currently under study. The design of such paramagnetic fluids in which T1 » T2 is the most difficult criteria to meet since trends are often of opposite direction.
|Scheme 1: One step reaction scheme to perfluorinated Cp*|
Design and preparation of anions or cations with a very high F:hetero-atom ratio – coordination to paramagnetic ions – viscosity of as prepared ILs – device preparation
Anna Loser (PhD student)
Christoph Barmet, Jennifer Nussbaum, Simon Gross, Prof. Klaas Prüssmann, Institute for Biomedical Imaging, ETHZ