A magnetic resonance imaging contrast agent capable of detecting hydrogen peroxide

The redox-active ligand N-(2-hydroxy-5-methylbenzyl)-N,N′,N′- tris(2-pyridinylmethyl)-1,2-ethanediamine (Hptp1) was prepared and complexed to manganese(II). The isolated [Mn(Hptp1)(MeCN)]²⁺ serves as a magnetic resonance imaging contrast agent, with an r₁ value comparable to those of other mononuclear gadolinium(III) and manganese(II) complexes. The metal and ligand are stable in aerated aqueous solutions, but the addition of H₂O₂ causes the complex to oxidatively couple to itself through a bimolecular reaction involving the phenol groups of two Hptp1 ligands. The binuclear product is less paramagnetic per manganese(II) than its mononuclear precursor, lowering the measured r₁ per manganese(II). The manganese(II) complex with Hptp1 can thereby serve as a sensor for oxidative stress.