Improving the relaxivity by dimerizing Gd-AAZTA: Insights for enhancing the sensitivity of MRI contrast agents

The synthesis of a dimeric derivative of Gd-AAZTA is reported. It retains the basic properties of the parent complex (q = 2, high stability) and displays a relaxivity of 14.0 mM−1 s−1 at 20 MHz and 298 K. The outstanding relaxivity is the result of the increased molecular reorientational time and of the contribution arising from 4 to 5 water molecules in the second coordination sphere of the Gd(III) ions.