A high-frequency dynamic nuclear polarization (DNP)/electron copy to systems with nuclei that are few in number, have low paramagnetic resonance spectrometer operating at 211 MHz for gyromagnetic ratios, and/or have low natural abundance. 1 H and 140 GHz for g ร
2 paramagnetic centers (5 T static field) Dynamic nuclear polarization (DNP) is a technique which is described. The salient feature of the instrument is a cyclotroncan significantly enhance the signal-to-noise ratio in NMR resonance maser (gyrotron) which generates high-frequency, highexperiments. The method, which involves irradiating either power microwave radiation. This gyrotron, which under convenendogenous or doped electron spins at or near their Larmor tional operation produces millisecond pulses at kilowatt powers, frequency and transferring this large polarization to nuclei, has been adapted to operate at ร100 W for 1 to 20 s pulses and was first proposed by Overhauser (2) and subsequently demin the continuous wave mode at the 10 W power level. Experiments combining DNP with magic-angle spinning (MAS) nuclear mag-onstrated by Carver and Slichter (3). Its primary application netic resonance were performed on samples consisting of 2% by has been the production of polarized targets for nuclear scatweight of the free radical BDPA doped into polystyrene. Roomtering experiments which are normally conducted at millitemperature DNP enhancement factors of 10 for 1 H and 40 for Kelvin temperatures and often achieve overall nuclear spin 13 C were obtained in the NMR-MAS spectra. Static DNP NMR has polarizations approaching 70 to 90% (4). These large DNP also been performed on samples containing nitroxides dissolved in enhancements would clearly benefit NMR spectroscopy, water:glycerol solvent mixtures. Enhancements of approximately which under typical experimental conditions exhibits nuclear 200 have been obtained for low-temperature (14 K) 1 H NMR. A polarization well below 1%. Recent interest has focused on pulsed/CW EPR spectrometer operating at 140 GHz has been the integration of DNP into the repertoire of high-resolution developed in conjunction with the DNP spectrometer. Microwave solid-state NMR experiments, such as magic-angle spinning sources include Gunn-diode oscillators which provide low-power (20 mW) radiation, and the gyrotron, which has been used to (MAS). In this class of experiments, signal enhancements deliver higher power levels in pulsed experiments. Results using can have dramatic consequences, particularly for the study of this spectrometer are presented for continuous-wave and echobiological systems where sample amounts are often severely detected EPR, electron spin-echo-envelope modulation (ESEEM), limited.