Dramatic enhancement in pH sensitivity and signal intensity through ligand modification of a dicobalt PARACEST probe

The employment of an ancillary amine-substituted bisphosphonate ligand affords a dicobalt complex able to quantitate pH with a remarkably high sensitivity of 8.8(5) pH unit−1 at 37 °C through a ratiometric paramagnetic chemical exchange saturation transfer (PARACEST) approach, where the different pH dependences of amine and amide CEST peak intensities are utilized.