Aryl-phosphonate lanthanide complexes and their fluorinated derivatives: Investigation of their unusual relaxometric behavior and potential application as dual frequency 1H/19F MRI probes

摘要

A series of low molecular weight lanthanide complexes were developed that have high 1H longitudinal relaxivities (r_1) and the potential to be used as dual frequency ~1H and ~19F MR probes. Their behavior was investigated in more detail through relaxometry, pH-potentiometry, luminescence, and multinuclear NMR spectroscopy. Fitting of the ~1H NMRD and ~17O NMR profiles demonstrated a very short water residence lifetime (<10 ns) and an appreciable second sphere effect. At lower field strengths (20 MHz), two of the complexes displayed a peak in r_1 (21.7 and 16.3 mM~(-1) s~(-1)) caused by an agglomeration, that can be disrupted through the addition of phosphate anions. NMR spectroscopy revealed that at least two species are present in solution interconverting through an intramolecular binding process. Two complexes provided a suitable signal in ~19F NMR spectroscopy and through the selection of optimized imaging parameters, phantom images were obtained in a MRI scanner at concentrations as low as 1 mM. The developed probes could be visualized through both ~1H and ~19F MRI, showing their capability to function as dual frequency MRI contrast agents. Sealed in a dual: The unusually high relaxivities of a series of macrocyclic lanthanide complexes were investigated, revealing a combination of rapid water exchange rates with a significant influence of water in the second sphere. Fluorine-containing complexes could be visualized by ~1H and ~19F MR phantom imaging (see figure); these platforms are promising candidates for dual frequency Magnetic resonance imaging (MRI).