Supramolecular Adducts between Poly‐ L ‐arginine and [TmIIIdotp]: A Route to Sensitivity‐Enhanced Magnetic Resonance Imaging–Chemical Exchange Saturation Transfer Agents

Markedly improved sensitivity is achieved in a contrast agent through formation of a supramolecular adduct between a diamagnetic system endowed with a high number of exchangeable protons (poly-L-arginine) and a paramagnetic shift reagent ([Tm(Hdotp)]4−). The increase in the chemical shift separation between the two exchanging proton pools, induced by the shift reagent, allows irradiation of the mobile guanidine protons of the polymer, thus resulting in a very efficient saturation transfer (see graph).