TOTAPOL: a biradical polarizing agent for dynamic nuclear polarization experiments in aqueous media.

TitleTOTAPOL: a biradical polarizing agent for dynamic nuclear polarization experiments in aqueous media.
Publication TypeJournal Article
Year of Publication2006
AuthorsSong, C, Hu, K-N, Joo, C-G, Swager, TM, Griffin, RG
JournalJournal of the American Chemical Society
Date Publishedsep
KeywordsCyclic N-Oxides, Cyclic N-Oxides: chemical synthesis, Cyclic N-Oxides: chemistry, Electron Spin Resonance Spectroscopy, Electron Spin Resonance Spectroscopy: methods, Free Radicals, Free Radicals: chemistry, Magnetic Resonance Spectroscopy, Magnetic Resonance Spectroscopy: methods, Molecular Structure, Propanols, Propanols: chemical synthesis, Propanols: chemistry, Spin Labels, Spin Labels: chemical synthesis, Water, Water: chemistry

In a previous publication, we described the use of biradicals, in that case two TEMPO molecules tethered by an ethylene glycol chain of variable length, as polarizing agents for microwave driven dynamic nuclear polarization (DNP) experiments. The use of biradicals in place of monomeric paramagnetic centers such as TEMPO yields enhancements that are a factor of approximately 4 larger (epsilon approximately 175 at 5 T and 90 K) and concurrently the concentration of the polarizing agent is a factor of 4 smaller (10 mM electron spins), reducing the residual electron nuclear dipole broadening. In this paper we describe the synthesis and characterization by EPR and DNP/NMR of an improved polarizing agent 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL). Under the same experimental conditions and using 2.5 mm magic angle rotors, this new biradical yields larger enhancements (epsilon approximately 290) at lower concentrations (6 mM electron spins) and has the additional important property that it is compatible with experiments in aqueous media, including salt solutions commonly used in the study of proteins and nucleic acids.