Responsive or smart magnetic resonance imaging (MRI) contrast agents are molecular sensors that alter the MRI signal upon changes in a particular parameter in their microenvironment. Consequently, they could be exploited for visualization of various biochemical events that take place at molecular and cellular levels. In this study, a set of dual-frequency calcium-responsive MRI agents are reported. These are paramagnetic, fluorine-containing complexes that produce remarkably high MRI signal changes at the (1)H and (19)F frequencies at varying Ca(2+) concentrations. The nature of the processes triggered by Ca(2+) was revealed, allowing a better understanding of these complex systems and their further improvement. The findings indicate that these double-frequency tracers hold great promise for development of novel functional MRI methods.

A synthetic approach is developed to obtain families of luminescent lanthanide complexes and markers from a generic family of precursors built from nonadentate coordination sites. The syntheses of the precursors, based on a directed regioselective nucleophilic aromatic substitution on polyfluoropyridines, are described. Functionalisation of the synthons on the aromatic moieties allowed the introduction of labelling functions and/or the extension of the electronic delocalisation, with concomitant changes in the spectroscopic properties. The synthesis of two such families of ligands and of some of their complexes of Eu(III) and Tb(III) are described, and the photo-physical properties of the complexes were measured, revealing excellent luminescence quantum yields reaching unity in some cases. For some of these complexes, the emphasis was further put on the preparation of an N-hydroxylsuccinimide (NHS) ester as activated function for labelling. The Tb and La complexes in the NHS activated form were synthesized and fully characterized. The labelling was first demonstrated on amino functionalized polymer beads and characterized by time-resolved luminescence microscopy. In a second step, the activated Tb complex was used for the labelling of GFR44 monoclonal antibody, and was applied to the detection of carcinoembryonic antigene (CEA) within the frame of a time-resolved fluoroimmunoassay. Comparison with a commercially available kit based on a europium cryptate as energy donor confirms the efficiency of Tb to act as an energy donor with an unoptimised 35% increase of the detection efficiency.

The synthesis and characterization of the new ligands L(1), L(2) and L(4) are described with the series of four europium complexes of formula [EuL(n)(TTA)(3)] in which TTA refers to 2-thenoyltrifluoroacetonate and L(n) to tridentate ligands with nitrogen containing heterocyclic structure, such as a 2,6-bis(3-methyl-pyrazolyl)-4-(p-toluyl-ethynyl)-triazine for L(1), or terpyridines functionalized at the 4' position by a phenyl-vinylene for L(2), a p-dimethylamino-phenylene for L(3), or a p-aminophenyl-ethynylene for L(4). The spectroscopic properties of the ligands and of the complexes are studied by means of UV-Vis absorption spectroscopy, as well as steady-state and time-resolved luminescence spectroscopy. All complexes display europium centred luminescence upon ligand excitation. Careful examination of the excitation spectra revealed differences in the ligand based sensitization efficiencies. For complexes of L(1) and L(2), excitation of europium is mainly achieved through the TTA moieties and the photo-physical studies on [EuL(1)(TTA)(3)] evidenced a weaker coordination of the bispyrazolyltriazine tridentate ligand, resulting from a partial decomplexation upon dilution. Complexes of L(3) and L(4) display intense excitation through the tridentate units, which extend down to 460 nm in the visible region. In the case of L(3), selective excitation reveals the presence of a ligand-centred emission band at 520 nm which is likely ascribed to a L(3) centred charge transfer state.

We report the preparation and characterization of dinuclear Pt-Ln complexes constructed from a square-planar Pt(II) core bearing an ethynyl-terpyridine residue connected to platinum by the ethynyl bond. Complexation of the neutral Eu(hfac)3 (hfac = hexafluoroacetylacetonate) fragment to free terpyridine (terpy) gives a stable bimetallic complex (log beta = 6.7). In the crystal structure, the flat Pt[triple bond]terpy core coordinates to Eu(III), which is nonacoordinated with the three nitrogen atoms of the terpy subunit and six oxygen atoms of the three hfac ligands. These atoms form a distorted monocapped square antiprism with a pseudo-C2 symmetry axis passing through the nitrogen atom of the central pyridine ring and the Eu atom. Spectroscopic measurements showed that irradiation with visible light of wavelength up to 460 nm in the 1MLCT state of the Pt subunit resulted in a quantitative energy transfer to the Eu center, which strongly luminesces in the red with an overall luminescence quantum yield of 38%. The energy-transfer process is quantitative and not sensitive to oxygen, and the complexation of Eu to the Pt metallosynthon allows the recovery of the energy lost due to triplet-oxygen quenching of the 3MLCT state observed in the uncomplexed Pt precursor.