Transfer of hyperpolarization from long T ₁ storage nuclei to short T ₁ neighbors using FLOPSY-8

Nuclei with long T ₁s are optimal targets for dynamic nuclear polarization (DNP). Therefore, most of the agents used in metabolic imaging and spectroscopy studies are based on carboxylic acid moieties that lack protons, a strong source of dipolar relaxation. Metabolic flux information encoded into spectra of small molecule metabolites in the form of the ¹³C isotopomer data cannot be accessed using standard ¹³C hyperpolarization methods because protonated carbons relax too quickly through T ₁ dipolar relaxation. It is shown here that the longitudinal mixing sequence FLOPSY-8 can be used to transfer polarization from a long T ₁ storage nucleus to adjacent protonated carbons so that they may be detected with high sensitivity. We demonstrate that FLOPSY-8 allows a direct readout of isotopomer populations in butyrate and glutamate in vitro.