Using increasingly strong magnetic fields improves NMR signal strength and spectral resolution. Until now, it has been assumed that the magnitude of the field does not affect the chemical shift of the nuclei, although Nobel laureate N. F. Ramsey predicted the opposite as early as 1970. According to him, the magnetic field modifies the electron cloud of matter and thus the chemical shift.
The NMR Spectroscopy Research Unit of the University of Oulu has now been able to experimentally confirm Ramsey's prediction. In precision measurements, the chemical shift of the 59Co isotope was found to follow the predicted quadratic dependence on the magnetic field of the spectrometer. The sign and order of magnitude of the experimental field dependence were confirmed by advanced electronic structure theory and computation.
Central to the success of the new experiments was the use of the simultaneously measured 129Xe signal both to set the temperature to be equal in NMR instruments with different field strengths and to serve as accurate frequency standard. The now-verified field dependence represents a fundamental paradigm change in increasingly higher-field NMR studies. The field dependence also introduces a new experimental observable to materials research by NMR.
Joint publication of the University of Oulu and the National Institute of Chemical Physics and Biophysics in Estonia: A.M. Kantola, P. Lantto, I. Heinmaa, J. Vaara and J. Jokisaari, Direct magnetic-field dependence of NMR chemical shift, Phys. Chem. Chem. Phys. 22, 8485-8490 (2020), https://doi.org/10.1039/D0CP01372B
Phys. Chem. Chem. Phys. also picked the group's article in its “HOT article” collection.
Last updated: 8.5.2020