Reversible magnetogenic cobalt complexes

Cobalt complexes have been extensively used for their catalytic and solid-state magnetic properties, but the solution-state magnetic properties have not yet been widely exploited. Two versatile cobalt ligand scaffolds were investigated for their magnetic properties, which both demonstrated a diamagnetic to paramagnetic transition upon reduction. Notably, one of these complexes, cobalt tris(2-pyridylmethyl)amine ( Co-TPA ), was capable of cycling between a stable Co( ii ) species that could induce longitudinal and transverse relaxation of surrounding water protons, and a stable diamagnetic Co( iii ) species, exhibiting negligible relaxivity effects. Therefore, we propose Co-TPA as a dynamic redox responsive contrast agent for the magnetic resonance imaging (MRI) of hypoxia. A cobalt tris(2-pyridylmethyl)amine complex cycles between stable paramagnetic Co( ii ) and diamagnetic Co( iii ) forms with corresponding changes in the MRI contrast.