A Responsive Co(II) 19F PARAShift Probe: Activation of Fermi Contact Interactions Triggered by pH-dependent Coordination Changes

Abstract

We report a novel ¹⁹F MR imaging probe CoNO2ASF₅ exhibiting a large ¹⁹F chemical shift change of over 30 ppm in response to physiologically relevant pH changes. This shift occurs with the deprotonation of the anilide proton and subsequent coordination change to Co(II). Calculations identify Fermi contact interactions in the deprotonated species as the mechanism of enhanced ¹⁹ F MR shift.