Fig. 8.
Spectra acquired with the cryogenic sample exchange equipped DNP probe. Asterisks identify spinning sidebands. a) Stack-plot showing stable enhancements of 1 M 13C-urea between sample ejections. The matrix consists of, by volume, 60% d8-glycerol, 30% H2O, 10% D2O, and 15 mM TOTAPOL [19]. The lower three spectra were collected without MW radiation, and the upper three with 250 GHz microwave irradiation, enabling ∼ 100-fold DNP enhancement. The spinning frequency was 4000 +/- 5 Hz and the temperature in the probe was 85 K for all three trials. b) 13C spectrum of natural abundance N-formyl-Met-Leu-Phe-OH (f-MLF-OH) recorded at 100 K. The linewidth at half-height of three resonances is indicated. ωr/2π = 6000 Hz. 83 KHz 1H TPPM [20] decoupling was applied for the 50.8 ms of acquisition,. No line-broadening or linear prediction was used. The recycle delay was 3.5 seconds, 2048 transients were averaged. f-MLF-OH was obtained from Bachem (King of Prussia, PA).