Dynamic nuclear polarization with biradicals.

TitleDynamic nuclear polarization with biradicals.
Publication TypeJournal Article
Year of Publication2004
AuthorsHu, K-N, Yu, H-H, Swager, TM, Griffin, RG
JournalJournal of the American Chemical Society
Date Publishedsep
KeywordsCyclic N-Oxides, Cyclic N-Oxides: chemistry, Electron Spin Resonance Spectroscopy, Electron Spin Resonance Spectroscopy: methods, Free Radicals, Free Radicals: chemistry, Mass Spectrometry, Nitrogen Oxides, Nitrogen Oxides: chemistry, Spin Labels

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.