Dynamic nuclear polarization at 9T using a novel 250 GHz gyrotron microwave source

In this communication, we report enhancements of nuclear spin polarization by dynamic nuclear polarization (DNP) in static and spinning solids at a magnetic field strength of 9 T (250 GHz for g = 2 electrons, 380 MHz for (1)H). In these experiments, (1)H enhancements of up to 170 +/- 50 have been observed in I-(13)C-glycine dispersed in a 60:40 glycerol/water matrix at temperatures of 20 K; in addition, we have observed significant enhancements in (15)N spectra of unoriented pf1-bacteriophage. Finally, enhancements of similar to17 have been obtained in two-dimensional (13)C-(13)C chemical shift correlation spectra of the amino acid U-(13)C, (15)N-proline during magic angle spinning (MAS), demonstrating the stability of the DNP experiment for sustained acquisition and for quantitative experiments incorporating dipolar recoupling. In all cases, we have exploited the thermal mixing DNP mechanism with the nitroxide radical 4-amino-TEMPO as the paramagnetic dopant. These are the highest frequency DNP experiments performed to date and indicate that significant signal enhancements can be realized using the thermal mixing mechanism even at elevated magnetic fields. In large measure, this is due to the high microwave power output of the 250 GHz gyrotron oscillator used in these experiments. (C) 2003 Elsevier Science (USA). All rights reserved.