Lanthanide complexes as paramagnetic probes for ¹⁹F magnetic resonance

The physicochemical basis of probe design for ¹⁹F MRS and MRI applications is reviewed. Complexes that give a single major resonance in solution are described, in which the Ln³⁺ ion is about 6 É from the ¹⁹F label. Sensitivity improvements of 15-fold are reported in both imaging and spectroscopy based on longitudinal relaxation enhancement. The pseudocontact shift allows an amplification of chemical shift non-equivalence in responsive ¹⁹F probes, e.g. for monitoring pH in the range between 5 and 8. Sensitivity in ¹⁹F magnetic resonance spectroscopy and imaging is enhanced by placing a paramagnetic lanthanide within 7 E of the spin label. Faster relaxation allows more rapid data acquisition for systems generating one main resonance, and the proximate lanthanide ion amplifies the chemical shift non-equivalence in responsive probes.