Exploring the intramolecular catalysis of the proton exchange process to modulate the relaxivity of Gd(iii)-complexes of HP-DO3A-like ligands

The Gd(iii)-complexes of three novel HP-DO3A-like ligands have been investigated to assess the relationship between relaxometry and intramolecular catalysis of the proton exchange. The structures of these ligands differ from the parent HP-DO3A because the methyl group of the hydroxy-propyl arm has been replaced by-Ph-OH,-Ph-NH2 and-Ph-COOH, respectively. The phenol, amine and carboxylate functionalities display an intramolecular H-bonding with the coordinated hydroxyl moiety that affects either the pK values of the involved functionalities and the rate of the proton exchange process.