Bifunctional Gd(III) and Tb(III) chelates based on a pyridine–bis(iminodiacetate) platform, suitable optical probes and contrast agents for magnetic resonance imaging

To study the physicochemical properties of lanthanide complexes derived from a bifunctional chelating agent based on a PMN‐tetraacetic acid moiety {PMN‐tetraacetic acid (1): [2,6‐pyridinediylbis(methylene nitrilo)‐tetraacetic acid]}, 4‐carboxylic acid substituted pyridine derivative (2) was synthesized. This ligand forms heptadentate (N3O4) Ln(III) complexes (Ln = Gd, Eu, Tb), with two water molecules completing the inner coordination sphere of the metal. The parameters that govern the relaxivity of the Gd(III) complex and the luminescence of Eu(III) and Tb(III) complexes were obtained by 17O and 1H NMR studies and time‐resolved fluorescence experiments, respectively. The gadolinium and terbium complexes show interesting properties either for MRI or FOR optical imaging; that is, for the Gd complex, a high proton relaxivity (r1 = 6.4 s−1 mm−1 at 20 MHz) with short water residence time (τM = 38.5 ns); for the Tb complex, a luminescence lifetime of 1.22 ms at room temperature and a luminescence quantum yield of 10%. The kinetic stability of these complexes toward blood protein, cation or bioactive oxyanion was also examined. The Gd(2)(H2O)2 complex does not interact with human serum albumin, but undergoes a transmetalation reaction with Zn(II) in a phosphate buffer solution (pH 7.4), rather similar to that of Gd–DTPA–BMA(H2O). On the other hand, as observed for Eu and Tb complexes, these chelates do not form ternary complexes with bid...

Source: Contrast Media and Molecular Imaging - March 19, 2014 Category: Radiology Authors: Sophie Laurent, Luce Vander Elst, Chantal Galaup, Nadine Leygue, Sébastien Boutry, Claude Picard, Robert. N. Muller Tags: Full Paper Source Type: research