Direct Hyperpolarization of Nitrogen-15 in Aqueous Media with Parahydrogen in Reversible Exchange

Signal amplification by reversible exchange (SABRE) is an inexpensive, fast, and even continuous hyperpolarization technique that uses para-hydrogen as hyperpolarization source. However, current SABRE faces a number of stumbling blocks for translation to biochemical and clinical settings. Difficulties include inefficient polarization in water, relatively short-lived ¹H-polarization, and relatively limited substrate scope. Here we use a water-soluble polarization transfer catalyst to hyperpolarize nitrogen-15 in a variety of molecules with SABRE-SHEATH (SABRE in shield enables alignment transfer to heteronuclei). This strategy works in pure H₂O or D₂O solutions, on substrates that could not be hyperpolarized in traditional ¹H-SABRE experiments, and we record ¹⁵N T₁ relaxation times of up to 2 min.