A Ca2+-Responsive H-1/F-19 MRI Molecular Probe Based on Competitive Coordination

Herein, we report a complex manganese(II) 3,2-bis(2-oxo-2-((2,2,2-trifluoroethyl)amino)ethyl), 9-dioxa-3,12-diazatetradecanediate (Mn(II)-L, 1) as a Ca2+-responsive H-1/F-19 magnetic resonance imaging (MRI) molecular probe. Transversal relaxation time T-2 of F-19 nuclei is shortened dramatically by the paramagnetic relaxation enhancement (PRE) effect imposed by paramagnetic Mn2+ ions, resulting in significantly decreased F-19 MRI signals. Mn2+ ions can be specifically replaced by Ca2+ ions via competitive coordination, leading to the increased distance between Mn2+ ions and F-19 nuclei and the recovery of F-19 MRI signals. At the same time, the higher longitudinal relaxivity r(1) of free Mn2+ ions also brings about brighter H-1 MRI signals. As demonstrated by our experiments, this complex is a Ca2+-responsive molecular probe for H-1/F-19 MRI.