Dissolution Dynamic Nuclear Polarization of the ⁷⁷Se Nucleus

⁷⁷Se is a spin ½, low sensitivity nucleus with a natural abundance of 7.6%. Although ⁷⁷Se NMR is very useful in the characterization of selenium containing molecules including seleno-proteins, the detection of ⁷⁷Se is challenging in biological samples without enrichment. Therefore, the goal of this work was to establish whether the ⁷⁷Se signal could be enhanced in the liquid state by dissolution dynamic nuclear polarization (DNP) NMR without the need of enrichment. The dominant spin-lattice relaxation mechanism for ⁷⁷Se is via chemical shift anisotropy, which is highly dependent on the molecular symmetry. Here we tested three selenium compounds (sodium selenate, sodium selenite and selenocystine) with different molecular symmetries in dissolution DNP experiments and demonstrated that ⁷⁷Se DNP using commercially available hardware is feasible but the achieved NMR signal enhancements (1368-fold for selenate, 125-fold for selenite and no enhancement for selenocystine at 9.4 T) were strongly dependent on molecular symmetry.