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Keywords:

  • Gadolinium complexes;
  • NMR Spectroscopy;
  • Contrast agents;
  • Transmetallation;
  • Molecular imaging

Abstract

To confirm the observation that [Gd(ttda)] derivatives have a significantly shorter residence time τM of the coordinated H2O molecule than [Gd(dtpa)], four new C-functionalized [Gd(ttda)] complexes, [Gd(4-Me-ttda)] (1), [Gd(4-Ph-ttda)] (2), [Gd(9-Me-ttda)] (3), and [Gd(9-Ph-ttda)] (4), were prepared and characterized (H5ttda=3,6,10-tris(carboxymethyl)-3,6,10-triazadodecanedioic acid; H5dtpa=3,6,9-tris(carboxymethyl)-3,6,9-triazaundecanedioic acid). The temperature dependence of the proton relaxivity for these complexes at 0.47 T and of the 17O transverse relaxation rate of H217O at 7.05 T confirm that the proton relaxivity is not limited by the H2O-exchange rate. The residence time of the H2O molecules in the first coordination sphere of the gadolinium complexes at 310 K, as calculated from 17O-NMR data, is 13, 43, 2.9, and 56 ns for 1, 2, 3, and 4, respectively. At 310 K, the longitudinal relaxivity of 2 is higher than for the parent compound [Gd(ttda)] and the other complexes of the series. The stability of the new compounds was studied by transmetallation with Zn2+ ions. All the new complexes are more stable than the parent compound [Gd(ttda)].