Defining the conditions for the development of the emerging class of FeIII-based MRI contrast agents

Fe(iii) complexes are attracting growing interest in chemists developing diagnostic probes for Magnetic Resonance Imaging because they leverage on an endogenous metal and show superior stability. However, in this case a detailed understanding of the relationship between the chemical structure of the complexes, their magnetic, thermodynamic, kinetic and redox properties and the molecular parameters governing the efficacy (relaxivity) is still far from being available. We have carried out an integrated H-1 and O-17 NMR relaxometric study as a function of temperature and magnetic field, on the aqua ion and three complexes chosen as reference models, together with theoretical calculations, to obtain accurate values of the parameters that control their relaxivity. Moreover, thermodynamic stability and dissociation kinetics of the Fe(iii) chelates, measured in association with the ascorbate reduction behaviour, highlight their role and mutual influence in achieving the stability required for use in vivo.

Automated summary

Fe(iii) complexes are of interest for developing diagnostic probes for Magnetic Resonance Imaging due to their use of an endogenous metal and superior stability. A detailed understanding of the relationship between their chemical structure, properties, and the molecular parameters governing efficacy is still lacking. Integrated H-1 and O-17 NMR studies, along with theoretical calculations, have provided insights into the parameters controlling their relaxivity, while thermodynamic stability and dissociation kinetics play key roles in their in vivo stability.