Harnessing Chemical Exchange: 19F Magnetic Resonance OFF/ON Zinc Sensing with A Tm(III) Complex

A fluorinated, thulium(III) complex (Tm-PFZ-1) serves as an off-on 19F magnetic resonance probe for Zn(II). Rapid exchange among different conformations combined with the paramagnetic relaxation and chemical shift effects of Tm(III) effectively eliminates the 19F NMR/MRI signal in Tm-PFZ-1. Chelation of Zn(II) induces increased structural rigidity and reduces exchange rate affording a robust 19F NMR/MRI signal. Tm-PFZ-1 represents a first-in-class paramagnetic 19F MR agent that exploits a novel sensing mechanism for Zn(II) and is the first 19F MR-based scaffold to provide an “off-on” response to Zn(II) in aqueous solution.