Parahydrogen Polarization in Reverse Micelles and Application to Sensing of Protein-Ligand Binding

A medium containing reverse micelles supports non-hydrogenative parahydrogen induced polarization (nhPHIP) in the organic phase while solubilizing a protein in the aqueous phase. Strongly enhanced NMR signals from iridium hydride complexes report on a ligand, 4-amino-2-benzylaminopyrimidine, which crosses the phase boundary and interacts with the thiaminase protein TenA. The calculation of binding equilibria reveals a K_D of 39.7 ± 8.9 μM for protein binding. The nanoscale separation of the two phases allows the separate optimization of the parahydrogen polarization and solubilization of a biological macromolecule. The reverse micelles may be used to study other biological questions using signal enhancement by parahydrogen polarization, such as enzyme reactions, protein-protein interactions, and protein binding epitopes.