Zero- to ultralow-field nuclear magnetic resonance is a modality of magnetic resonance experiment which does not require strong superconducting magnets. Contrary to conventional high-field nuclear magnetic resonance, it has the advantage of allowing high resolution detection of nuclear magnetism through metal as well as within heterogeneous media. To achieve high sensitivity, it is common to couple zero-field nuclear magnetic resonance with hyperpolarization techniques. To date, the most common technique is parahydrogen-induced polarization, which is only compatible with a small number of compounds. In this article, we establish dissolution dynamic nuclear polarization as a versatile method to enhance signals in zero-field nuclear magnetic resonance experiments on virtually all small molecules with > 1 s relaxation times. We show as first examples J-spectra of hyperpolarized [13C]sodium formate, [1-13C]glycine and [2-13C]sodium acetate. We find signal enhancements of up to 11000 compared with thermal prepolarization in a 2 T permanent magnet. To increase the signal in future experiments, we investigate the relaxation effects of the TEMPOL radicals used for the hyperpolarization process at zero- and ultralow-field.
The theory section is now described in an Appendix at the end of the manuscript.