High frequency dynamic nuclear polarization in solids and liquids

PHYS 238

Robert G. Griffin, rgg@mit.edu, Francis Bitter Magnet Laboratory, Dept. of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139
Over the last few years we have developed subterahertz microwave sources (140-460 GHz) that permit DNP enhanced NMR experiments in magnetic fields of 5-16.4 T. We discuss two mechanisms that are currently used for DNP experiments in insulating solids at high fields the solid effect and the cross effect -- and the paramagnetic polarizing agents appropriate for each. These include a new class of biradicals that enable increased enhancements at reduced concentrations of the paramagnetic center. The results illustrate enhancements that are routinely available and range from 40-300 depending on experimental variables such as temperature, magnetic field, microwave B1, polarizing agent, etc. Finally, we describe extensions of these experiments that permit observation of 13C liquid state spectra where we have observed enhancements of 140-400 in small molecules and a protein.