How the catalysis of the prototropic exchange affects the properties of lanthanide(III) complexes in their applications as MRI contrast agents

Controlling prototropic exchange in aqueous solutions of paramagnetic Gd(III) complexes is a task of relevant importance for the design of MRI contrast agents that are endowed with higher sensitivities than those currently used in clinical practice, and this is because the number of mobile protons directly scales with the observed relaxivities. On the basis of general acid-base theory, the exchange of mobile protons on ligands can be accounted for in terms of the interactions with the Bronsted acid/base pairs that are either present as components of the buffered solutions or available upon the introduction of suitable functionalities onto the ligand itself in the proximity of the group that contains the mobile proton. In addition to providing new insights into improvements in Gd-containing contrast agents, these studies have also proven to be instrumental for the development of new concepts in the field of CEST agents (Chemical Exchange Saturation Transfer).