RESUMEN
A series of low molecular weight lanthanide complexes were developed that have high (1)H longitudinal relaxivities (r1) and the potential to be used as dual frequency (1)H and (19)Fâ MR probes. Their behavior was investigated in more detail through relaxometry, pH-potentiometry, luminescence, and multinuclear NMR spectroscopy. Fitting of the (1)Hâ NMRD and (17)Oâ NMR profiles demonstrated a very short water residence lifetime (<10â ns) and an appreciable second sphere effect. At lower field strengths (20â MHz), two of the complexes displayed a peak in r1 (21.7 and 16.3â 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 (19)Fâ NMR spectroscopy and through the selection of optimized imaging parameters, phantom images were obtained in a MRI scanner at concentrations as low as 1â mM. The developed probes could be visualized through both (1)H and (19)Fâ MRI, showing their capability to function as dual frequency MRI contrast agents.
Asunto(s)
Elementos de la Serie de los Lantanoides/química , Organofosfonatos/química , Flúor/química , Gadolinio/química , Imagen por Resonancia Magnética/métodos , Espectroscopía de Resonancia MagnéticaRESUMEN
A study of the anion-binding properties of three structurally related lanthanide complexes, which all contain chemically identical anion-binding motifs, has revealed dramatic differences in their anion affinity. These arise as a consequence of changes in the substitution pattern on the periphery of the molecule, at a substantial distance from the binding pocket. Herein, we explore these remote substituent effects and explain the observed behaviour through discussion of the way in which remote substituents can influence and control the global structure of a molecule through their demands upon conformational space. Peripheral modifications to a binuclear lanthanide motif derived from α,α'-bis(DO3 Ayl)-m-xylene are shown to result in dramatic changes to the binding constant for isophthalate. In this system, the parent compound displays considerable conformational flexibility, yet can be assumed to bind to isophthalate through a well-defined conformer. Addition of steric bulk remote from the binding site restricts conformational mobility, giving rise to an increase in binding constant on entropic grounds as long as the ideal binding conformation is not excluded from the available range of conformers.
RESUMEN
Heteronuclear tetrametallic lanthanide complexes have been synthesized from stable complexes by diazotization and azo-compound formation. Luminescence spectroscopy has been used to show that the complexes used as building blocks are stable under the reaction conditions.
Asunto(s)
Compuestos Azo/química , Colorantes/química , Colorantes/síntesis química , Elementos de la Serie de los Lantanoides/química , Compuestos Organometálicos/química , Compuestos Organometálicos/síntesis química , Cinética , Espectroscopía de Resonancia Magnética/métodos , Estructura Molecular , Espectroscopía Infrarroja Corta/métodosRESUMEN
Four ligand systems have been prepared whose characteristics are well suited to the design of bimodal MRI and luminescence probes. The lanthanide complexes display high relaxivities and luminescence quantum yields. These properties are retained at higher magnetic fields and in a range of competitive environments including model extracellular medium and cultured cells.