⁷⁷ Se Hyperpolarization Enabled by Reversible Parahydrogen Exchange and Audio-Frequency Magnetic Fields at 0.1 mT

Nuclear spin hyperpolarization boosts NMR sensitivity but typically requires complex infrastructure. Signal Amplification by Reversible Exchange (SABRE), a parahydrogen-based hyperpolarization technique, can be conducted using a remarkably low-cost polarizer (<$100) comprising only magnetic coils and a standard PC sound card, avoiding magnetic shielding. However, under these conditions, SABRE requires direct spin-coupling between parahydrogen and the target nucleus, limiting its application to distant heteronuclear spins such as 77 Se in biologically relevant selenium–nitrogen heterocycles (e.g., antioxidant, antiviral, and anticancer agents). Here, we overcome the distance restrictions by developing 15 N-mediated polarization transfer driven by oscillating magnetic fields of the audio frequency. As a proof-of-concept, we achieve a 11600-fold enhancement of the 77 Se NMR signal (>6% net polarization) at 9.4 T in a shielding-free setup using a selenadiazole derivative. These results suggest that selenadiazole-based compounds are particularly well suited for this strategy and provide a basis for extending it to other selenium-containing molecules.