Nuclear magnetic resonance (NMR) spectroscopy is the most common experimental tool to investigate the microstructure of molecules and materials as it provides unique information on molecular electronic structure, geometry, and reactivity. The application of NMR on paramagnetic species (open-shell systems with unpaired electrons) has though been quite restricted until recently although it potentially provides a rich field of applications on radicals in general, and particularly on bioradicals that play vital roles in the catalytic activity of enzymes. The usefulness of this spectroscopy derives from the facts that the interaction between unpaired electrons and a resonating nucleus causes hyperfine shifts in the NMR spectra that can be used for daignostics. The sign and magnitude of the electron spin density can then be evaluated from the contact shifts without further approximations and only moderate magnetic fields are required in order to obtain spectra with resolved hyperfine structure. These intrinsic properties make paramagnetic NMR an attractive alternative to EPR for studying radicals.
There has not been a concomitant development in the theoretical modeling of paramagntic NMR using rigorous first principles electronic structure methods. In order to contribute to this unexplored field of NMR theory, we have implemented a formalism for nuclear shielding calculations, within ab initio as well as density functional theory.
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An important part of this project is given by simulations of paramagnetic NMR of membrane proteins
