Towards the Rational Design of MRI Contrast Agents: Electron Spin Relaxation Is Largely Unaffected by the Coordination Geometry of Gadolinium(III)-DOTA-Type Complexes

• Published in: Chemistry : a European journal Vol. 14; no. 9; pp. 2658 - 2667
• Main Authors: Borel, Alain, Bean, Jonathan F., Clarkson, Robert B., Helm, Lothar, Moriggi, Loïck, Sherry, A. Dean, Woods, Mark
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.01.2008; WILEY‐VCH Verlag
• Subjects: Contrast Media - chemical synthesis; Contrast Media - chemistry; coordination geometry; Electron Spin Resonance Spectroscopy - methods; Electrons; EPR spectroscopy; gadolinium; Heterocyclic Compounds - chemical synthesis; Heterocyclic Compounds - chemistry; imaging agents; Ligands; Luminescence; macrocyclic ligands; Magnetic Resonance Imaging - methods; Magnetic Resonance Spectroscopy - methods; Magnetic Resonance Spectroscopy - standards; Models, Molecular; Molecular Conformation; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Reference Standards; Stereoisomerism; Temperature
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200701747

Electron‐spin relaxation is one of the determining factors in the efficacy of MRI contrast agents. Of all the parameters involved in determining relaxivity it remains the least well understood, particularly as it relates to the structure of the complex. One of the reasons for the poor understanding of electron‐spin relaxation is that it is closely related to the ligand‐field parameters of the Gd3+ ion that forms the basis of MRI contrast agents and these complexes generally exhibit a structural isomerism that inherently complicates the study of electron spin relaxation. We have recently shown that two DOTA‐type ligands could be synthesised that, when coordinated to Gd3+, would adopt well defined coordination geometries and are not subject to the problems of intramolecular motion of other complexes. The EPR properties of these two chelates were studied and the results examined with theory to probe their electron‐spin relaxation properties. Electron‐spin relaxation is a key parameter in the design of advanced MRI contrast agents. EPR has been used to probe the relationship between this key parameter and the coordination environment of gadolinium in complexes with DOTA‐type ligands (see figure).