An Fe complex for 19F magnetic resonance-based reversible redox sensing and multicolor imaging

Abstract

We report a first-in-class responsive, pentafluorosulfanyl (–SF₅)-tagged ¹⁹F MRI agent capable of reversibly detecting reducing environments via an Fe^II/III redox couple. In the Fe^III form, the agent displays no ¹⁹F MR signal due to paramagnetic relaxation enhancement-induced signal broadening; however, upon rapid reduction to Fe^II with one equivalent of cysteine, the agent displays a robust ¹⁹F signal. Successive oxidation and reduction studies validate the reversibility of the agent. The –SF₅ tag in this agent enables ‘multicolor imaging’ in conjunction with sensors containing alternative fluorinated tags and this was demonstrated via simultaneous monitoring of the ¹⁹F MR signal of this –SF₅ agent and a hypoxia-responsive agent containing a –CF₃ group.