Paramagnetic relaxation enhancement
In nuclear magnetic resonance (NMR), magnetic field dependent phenomena attract considerable interest: Paramagnetic relaxation enhancement (PRE) of NMR relaxivities induced by paramagnetic relaxation agents is theoretically, experimentally and from the application point of view a growing research area.
PRE is generated by the fluctuating hyperfine interaction between the magnetic moment of the paramagnetic compound in solution and the nuclear spin of the environment, often protons of water. This process enhances the longitudinal and transverse nuclear spin relaxation rates.
The burning question here concerns the development of effective and efficient relaxation agents which can be discovered through an improved understanding of PRE mechanisms. PRE plays an increasingly important role in technical magnetic resonance imaging (MRI) for process engineering and material science. There, the image contrast quality can be significantly enhanced through application of an appropriate contrast agent for exploration of the question and sample under investigation.
Moreover, technical MRI tends to use very high magnetic fields with 28.2 T (1200 MHz) commercially available. Since conventional relaxation agents have been tailored for much smaller magnetic fields and actually decrease in efficiency above 4.7 T (200 MHz), there is a need to develop new relaxation agents for the high magnetic field applications which are now available.
The PRE activity at LNCMI Grenoble responds to this need and allows PRE studies up to 1.4 GHz/33 T using resistive magnets. It also includes the development of tailored NMR hardware and methods.
The activity benefits from a strong collaboration with research teams at the Karlsruhe Institute of Technology (KIT) in Germany.
Research staff
Research topics
PRE studies on lanthanide compounds
Aequeous solutions of molecular compounds containing lanthanide ions with a total spin J>0 are known to exhibit intersting PRE properties up to highest magnetic fields. The short electronic correlation times of the lanthanide ions can cause a strong increase of the PRE with magnetic field due to a Curie spin contribution, i.e., the time averaged magnetic moment of the lanthanide.
PRE studies of such compounds up to highest magnetic fields are important not only for the theoretical description and understanding of the interaction of the compounds with the solvent, but also with respect to their applications in MRI.
Since 2014, LNCMI has been conducting systematic high-field PRE studies on inorganic paramagnetic complexes containing lanthanide ions.
NMR hardware and methods development
Most proton PRE studies end up at frequencies below 800 MHz/18.8 T. However, recent progress in superconducting magnets has opened the way for a new generation of very homogeneous and stable high-field magnets. Nowadays, commercial high-resolution NMR magnets operate up to 1200 MHz/28.2 T.
Despite this progress, the high-power, water-cooled resistive magnets of facilities dedicated to intense magnetic fields, such as the LNCMI in Grenoble, still exceed these field strengths and enable PRE studies at even more intense magnetic fields.
However, NMR experiments in resistive high field magnets are hampered by their intrinsically low field homogeneity and field stability, as well as by a limited access time and high running costs.
In order to overcome these limitions, we constantly develop tailored NMR instruments (broadband tunable NMR probes, microliter sample volumes) and methods (single scan NMR, deconvolution techniques, saturation recovery and CPMG sequences) for PRE studies up to highest possible fields.
Experimental technique
Nuclear Magnetic Resonance
Selected publications
PRE studies of lanthanide compounds
- N. Schork et al., NMR Relaxivities of Paramagnetic, Ultra-High Spin Heterometallic Clusters within Polyoxometalate Matrix as a Function of Solvent and Metal Ion, ChemPhysChem 2022, 23, e202200215
- A. C. Venu et al., NMR Relaxivities of Paramagnetic Lanthanide-Containing Polyoxometalates, Molecules 2021, 26(24), 7481
- M. Ibrahim et al.,Polyoxometalate-based high-spin cluster systems: a NMR relaxivity study up to 1.4 GHz/33 T, Dalton Transactions 2019, 48.41, 15597-15604
- G. Guthausen et al.,Characterisation and application of ultra-high spin clusters as magnetic resonance relaxation agents, Dalton Transactions 2015 44.11, 5032-5040
Development of NMR hardware and methods for PRE in high magnetic fields
- R. Nasser Din et al., Longitudinal and Transverse 1H Nuclear Magnetic Resonance Relaxivities of Lanthanide Ions in Aqueous Solution up to 1.4 GHz/33 T, Molecules 2024, 29(20), 4956
- R. Nasser Din, Nuclear magnetic resonance studies of paramagnetic relaxation enhancement at high magnetic fields : methods and applications, PhD thesis, Université Grenoble Alpes, 2024
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