Mandal, Sucharita, and Snorri Th. Sigurdsson. “Water-Soluble BDPA Radicals with Improved Persistence.” Chemical Communications, 2020, 10.1039.D0CC04920D.
1,3-Bis(diphenylene)-2-phenylallyl (BDPA) radicals are promising polarizing agents for increasing the sensitivity of NMR spectroscopy through dynamic nuclear polarization (DNP), but have low persistence and solubility in aqueous media. New tetraalkyl/aryl-ammonium derivatives of BDPA are soluble in polar solvents and are highly persistent, with 5–20-fold lower initial rates of degradation than BDPA.