Despite tremendous advances in recent years, solution NMR remains fundamentally
restricted due to its inherent insensitivity. Dynamic nuclear polarization (DNP) potentially
offers significant improvements in this respect. The basic DNP strategy is to irradiate the
EPR transitions of a stable radical and transfer this nonequilibrium polarization to the
hydrogen spins of water, which will in turn transfer polarization to the hydrogens of the
macromolecule. Unfortunately, these EPR transitions lie in the microwave range of the …