Versatile Nickel(II) Scaffolds as Coordination‐Induced Spin‐State Switches for ¹⁹F Magnetic Resonance‐Based Detection

Abstract

19F magnetic resonance (MR) based detection coupled with well‐designed inorganic systems shows promise in biological investigations. Two proof‐of‐concept inorganic probes that exploit a novel mechanism for 19F MR sensing based on converting from low‐spin (S=0) to high‐spin (S=1) Ni2+ are reported. Activation of diamagnetic NiL1 and NiL2 by light or β‐galactosidase, respectively, converts them into paramagnetic NiL0, which displays a single 19F NMR peak shifted by >35 ppm with accelerated relaxation rates. This spin‐state switch is effective for sensing light or enzyme expression in live cells using 19F MR spectroscopy and imaging that differentiate signals based on chemical shift and relaxation times. This general inorganic scaffold has potential for developing agents that can sense analytes ranging from ions to enzymes, opening up diverse possibilities for 19F MR based biosensing.

Rational Ligand Design Enables pH Control over Aqueous Iron Magnetostructural Dynamics and Relaxometric Properties

“…Fe 2+ and Ni 2+ complexes which switch from low to high spin in response to enzyme activity, and pH change have been reported. 29,30 pH-and temperature-triggered Fe 2+ spin crossover have been shown to influence the CEST effect and the 19 F chemical shift. 31,32 Although underexplored in the context of MR imaging, discrete Fe 3+ complexes have a rich aqueous solution chemistry that we hypothesize can be exploited to profoundly influence r 1 .…”