A mono-aquated di-pyridine-based Gd(III) complex as T1-weighted MRI probe with high relaxivity and stability

This study reports a new octadentate tricarboxylate appended ligand (H4dphta) with enhanced relaxivity and high stability towards Gd(III) complex as an MRI probe. The designed ligand was synthesized in multiple steps. Both, the ligand and its complex were characterized by spectroscopic techniques. Structural analysis of Gd(III) complex by single crystal XRD confirms its mono-hydrated form adopting distorted capped square antiprism geometry. Protonation constants of the ligand and the thermodynamic stability constant of the [Gd(Hdphta)] and [Gd(H2dphta)]+ species have been found as log K110 = 18.6(1) and log K111 = 24.8(1) at 25.0 degrees C, and I = 0.15 mol & sdot;L-1 NaClO4 by potentiometric method. The r1 relaxivity of the complex was found to be 4.63 mM- 1s- 1 at 1.41 T, 25 degrees C, and pH 7.4 in the HEPES buffer, which remained unaltered in the pH range of 4-10. The complex sustained its stability in the presence of different physiological anions (F-, HCO3-, HPO42-, C2O42-, CH3COO- and CH2(COO-)2) as supported by insignificant changes in longitudinal relaxivity (r1) at 1.41 T, 25 degrees C. The concentration-dependent contrast ability of [Gd(Hdphta)] is investigated by T1-weighted phantom images in a 3 T MRI scanner at 20 degrees C and pH 7.4. The cell viability has been evaluated using tissue culture in HEK cells.