Date of this Version
J Am Chem Soc. 2012 September 26; 134(38): 15724–15727.
We report a molecular design that provides an intravenously injectable organic radical contrast
agent (ORCA) that has molecular r1 ≈ 5 mM−1s−1. The ORCA is based on spirocyclohexyl
nitroxide radicals and polyethylene glycol chains conjugated to a generation 4 polypropylenimine
dendrimers scaffold. The metal-free ORCA has a long shelf-life and provides selectively enhanced
MRI in mice for over 1 h.