Dynamic nuclear polarization with biradicals.
Dynamic nuclear polarization (DNP) experiments in rotating solids have been performed for the first time using biradicals rather than monomeric paramagnetic centers as polarizing agents. Specifically, two TEMPO radicals were tethered with a poly(ethylene glycol) chain of variable length where the number of glycol units was 2, 3, or 4. NMR experiments show that the signal observed in DNP experiments is approximately inversely proportional to the length of the chain. Thus, the shorter chain with larger electron dipolar couplings yields larger enhancements. The size of the enhancement is a factor of 4 larger than obtained with the identical concentration of monomeric nitroxide radicals achieving a value of approximately 175 for the n = 2 chain.
Hu
Kan-Nian
KN
Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Yu
Hsiao-hua
HH
Swager
Timothy M
TM
Griffin
Robert G
RG
D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005609:Free Radicals / Q000737:chemistry; D013058:Mass Spectrometry; D009589:Nitrogen Oxides / Q000737:chemistry; D013113:Spin Labels
D003497:Cyclic N-Oxides; D005609:Free Radicals; D009589:Nitrogen Oxides; D013113:Spin Labels; C039900:nitroxyl; C003959:TEMPO