The development of transition metal MRI contrast agents is of interest to provide alternatives for patients who cannot tolerate Gd(III) MRI contrast agents. In addition, transition metal complexes may switch paramagnetic properties through oxidation or spin state changes to create molecular imaging agents that are responsive to biological environment. Our laboratory has developed both Fe(II) and Fe(III) MRI contrast agents. High spin Fe(II) and low spin Fe(III) complexes are paramagnetic shift agents that produce contrast through chemical exchange saturation transfer (CEST) whereas high spin Fe(III) is a T<sub>1</sub> MRI contrast agent. Our complexes use macrocyclic ligands for ultimate control of spin state and oxidation state with both the macrocycle backbone and pendent groups being important for controlling coordination chemistry. Efforts to produce spin state changes with pH and temperature variation will be discussed.

Coordination chemistry of Fe(II) and Fe(III) MRI contrast agents

253rd National Meeting (2017)

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