Preparation, spectroscopic and high field NMR relaxometry studies of gadolinium(III) complexes with the asymmetric tetraamine 1,4,7,11-tetraazaundecane

Abstract

The reaction of Gd(III) with asymmetric tetramine 1,4,7,11-tetraazaundecane (2,2,3-tet, L 1 ) ligand has been studied via NMR spectroscopy. The ligand proton longitudinal relaxation rates ( R 1) have been used to estimate the distances of these protons from the Gd(III) center, in Gd(III)– L 1 reaction solutions, in H 2O/D 2O 5/1 mixtures. Two Gd(III) complexes [Gd(III)( L 1 )(NH 3)(H 2O) 4](CH 3COO) 3·2H 2O ( 1) and [Gd(III)( L 1 )(NH 3)(H 2O) 2]Cl 3·EtOH ( 2) have been isolated and characterized by elemental analyses, TGA, IR, NMR and relaxometry measurements. The NMR relaxation measurements of 2 in aqueous solutions have been performed, under various temperature or concentration conditions, and compared with those of the commercial contrast agents Gd(III)–DTPA and Gd(III)–DTPA-BMA. It has also been studied the influence of (i) the Gd(III) inner-sphere water molecule number ( q) alteration and (ii) the steric constraint enhancement on the metal site, over the relaxation rate values of the parent aqueous solution of Gd(III)–2,2,3-tet, and of the aqueous solutions of 2.