Lanthanide(III) complexes of diethylenetriaminepentaacetic acid (DTPA)-bisamide derivatives as potential agents for bimodal (Optical/Magnetic Resonance) imaging

Article abstract of DOI:10.1002/ejic.201300196

Diethylenetriaminepentaacetic acid (DTPA)-bisamide derivatives functionalized with p-toluidine, 6-aminocoumarin, 1-naphthalene methylamine and 4-ethynylaniline were synthesized and fully characterized by mass spectrometry, NMR spectroscopy, FTIR spectroscopy and elemental analysis. Ln^III complexes (Ln = Gd, Eu, Tb, Y) of the ligands DTPA-bis-p-toluidineamide (DTPA-BTolA), DTPA-bis-6-coumarinamide (DTPA-BCoumA), DTPA-bis-1- naphthylmethylamide (DTPA-BNaphA) and DTPA-bis-4-ethynylphenylamide (DTPA-BEthA) were prepared and studied for their bimodal magnetic resonance imaging/optical properties. Eu^III and Tb^III derivatives in aqueous solutions exhibit characteristic red and green emission, respectively, with quantum yields of 0.73 % for Eu^III-DTPA-BNaphA and 2.5 % for Tb ^III-DTPA-BEthA. Ligand-centred photophysical properties of the Gd^III complexes were investigated to gain insight into energy-transfer processes that take place in these systems. The Gd^III complexes were also analyzed by nuclear magnetic relaxation dispersion (NMRD) techniques. The relaxivity (r₁) at 20 MHz and 310 K equals 4.1 s ^-1 mM^-1 for Gd-DTPA-BTolA, 5.1 s^-1 mM ^-1 for Gd-DTPA-BCoumA, 6.4 s^-1 mM^-1 for Gd-DTPA-BNaphA and 5.7 s^-1 mM^-1 for Gd-DTPA-BEthA. These values are higher than the value of 3.8 s^-1 mM^-1 for Gd-DTPA (Magnevist). The improved relaxivity is due to the increase in the rotational tumbling time τ_R with a factor of 1.6 for Gd-DTPA-BTolA, 2.1 for Gd-DTPA-BCoumA, 3.1 for Gd-DTPA-BNaphA and 6.5 for Gd-DTPA-BEthA. In a 4 % human serum albumin solution, the apparent relaxivity at 20 MHz increases to values of 13.9 and 19.1 s^-1 mM^-1 for Gd-DTPA-BNaphA and Gd-DTPA-BEthA, respectively. All these features assist the search for optimal bimodal optical and magnetic resonance imaging probes. Copyright