Lumata, L., et al., DNP by Thermal Mixing under Optimized Conditions Yields >60‚000-fold Enhancement of 89Y NMR Signal. J. Am. Chem. Soc., 2011. 133(22): p. 8673-8680
Hyperpolarized 89Y complexes are attractive NMR spectroscopy and MR imaging probes due to the exceptionally long spin‚Äìlattice relaxation time (T1 ~ 10 min) of the 89Y nucleus. However, in vivo imaging of 89Y has not yet been realized because of the low NMR signal enhancement levels previously achieved for this ultra low-gamma nucleus. Here, we report liquid-state 89Y NMR signal enhancements over 60 000 times the thermal signal at 298 K in a 9.4 T magnet, achieved after the dynamic nuclear polarization (DNP) of Y(III) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) samples at 3.35 T and 1.4 K. The 89Y DNP was shown to proceed by thermal mixing and the liquid state 89Y NMR signal enhancement was maximized by (i) establishing the optimal microwave irradiation frequency, (ii) optimizing the glassing matrix, (iii) choosing a radical with negligible inhomogeneous line broadening contribution to the ESR linewidth, and (iv) addition of an electron T1e relaxation agent. The highest enhancements were achieved using a trityl OX063 radical combined with a gadolinium relaxation agent in water-glycerol matrix. Co-polarization of 89YDOTA and sodium [1-13C]pyruvate showed that both 89Y and 13C nuclear species acquired the same spin temperature, consistent with thermal mixing theory of DNP. This methodology may be applicable for the optimization of DNP of other low-gamma nuclei.