Dynamic nuclear polarization for NMR : applications and hardware development

Abstract

solid State NMR (SSNMR) can determine molecular as well as supermolecular structure and dynamics. The low signal intensities make many of these experiments prohibitively long. Dynamic Nuclear Polarization provides a method of enhancing signal intensities and reducing experimental time. DNP requires transferring polarization from unpaired electrons to nuclei. Driving this transfer requires irradiation with high power microwaves which are generated with gyrotrons oscillators. We describe a series of modifications are made to an existing 140 GHz gyrotron allows for continuous wave operation and higher power and greater stability. DNP mechanisms are primarily limited to SSNMR. A method of using DNP to enhance liquid state NMR spectra is described. Signal enhancements of over 100 are reported for a solution of glucose. To obtain maximum DNP enhancements microwave irradiation times of up to 40 s are often required. While this increases your signal intensity for a single scan it decreases the gain from signal averaging for a given time. A method of choosing the optimum irradiation time is presented. DNP enhancements in continuous wave experiments exhibit an inverse field dependence. There are several pulsed DNP experiments exhibit no field dependence. To further study these techniques a pulsed 9 GHz EPR spectrometer has been assembled.