Redox-Activated Manganese-Based MR Contrast Agent

Here we report a simple Mn coordination complex with utility as a redox-sensitive MR probe. The HBET ligand stabilizes both the Mn²⁺ and Mn³⁺ oxidation states. In the presence of glutathione (GSH), low relaxivity Mn^III-HBET is converted to high relaxivity Mn^II-HBET with a 3-fold increase in relaxivity, and concomitant increase in MR signal. Alternately, hydrogen peroxide can convert Mn^II-HBET to Mn^III-HBET with a reduction in MR signal