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Nuclear spin hyperpolarization by parahydrogen enables the measurement of biomolecular interactions without the need for a superconducting or permanent magnet. Observed is a fluorine signal of a purpose-designed reporter ligand for a target protein. 

Nuclear spin hyperpolarization through signal amplification by reversible exchange (SABRE), the non-hydrogenative version of para -hydrogen induced polarization, is demonstrated to enhance sensitivity for the detection of biomacromolecular interactions. A target ligand for the enzyme trypsin includes the binding motif for the protein, and at a distant location a heterocyclic nitrogen atom for interacting with a SABRE polarization transfer catalyst. This molecule, 4-amidinopyridine, is hyperpolarized with 50% para -hydrogen to yield enhancement values ranging from −87 and −34 in the ortho and meta positions of the heterocyclic nitrogen, to −230 and −110, for different solution conditions. Ligand binding is identified by flow-NMR, in a two-step process that separately optimizes the polarization transfer in methanol while detecting the interaction in a predominantly aqueous medium. A single scan Carr–Purcell–Meiboom–Gill (CPMG) experiment identifies binding by the change in R 2 relaxation rate. The SABRE hyperpolarization technique provides a cost effective means to enhance NMR of biological systems, for the identification of protein–ligand interactions and other applications. 

A series of bidentate N-heterocyclic carbene (NHC) iridium catalysts, [Ir(κC,N-NHC)H 2 L 2 ]BPh 4 , are proposed for SABRE hyperpolarization. The steric and electronic properties of the NHCs are used to tune substrate affinity and thereby SABRE efficiency. The sterically hindered substrates 2,4-diaminopyrimidine and trimethoprim yielded maximum proton NMR signal enhancements of ∼300-fold and ∼150-fold, respectively.