Issue 27, 2019

Influence of ligand encapsulation on cobalt-59 chemical-shift thermometry


Thermometry via magnetic resonance imaging (MRI) would provide a powerful noninvasive window into physiological temperature management. Cobalt-59 nuclear spins demonstrate exceptional temperature dependence of their NMR chemical shifts, yet the insight to control this dependence via molecular design is lacking. We present the first systematic evidence that encapsulation of this spin system amplifies the temperature sensitivity. We tested the temperature dependence of the 59Co chemical shift (ΔδT) in a series of five low-spin cobalt(III) complexes as a function of increasing encapsulation within the 1st coordination sphere. This study spans from [Co(NH3)6]Cl3, with no interligand connectivity, to a fully encapsulated dinitrosarcophagine (diNOsar) complex, [Co(diNOsar)]Cl3. We discovered ΔδT values that span from 1.44(2) ppm °C−1 in [Co(NH3)6]Cl3 to 2.04(2) ppm °C−1 in [Co(diNOsar)]Cl3, the latter among the highest for a molecular complex. The data herein suggest that designing 59Co NMR thermometers toward high chemical stability can be coincident with high ΔδT. To better understand this phenomenon, variable-temperature UV-Vis, 59Co NMR relaxation, Raman spectroscopic, and variable-solvent investigations were performed. Data from these measurements highlight an unexpected impact of encapsulation – an increasingly dynamic and flexible inner coordination sphere. These results comprise the first systematic studies to reveal insight into the molecular factors that govern ΔδT and provide the first evidence of 59Co nuclear-spin control via vibrational means.

Graphical abstract: Influence of ligand encapsulation on cobalt-59 chemical-shift thermometry

Supplementary files

Article information

Article type
Edge Article
06 Apr 2019
04 Jun 2019
First published
05 Jun 2019
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2019,10, 6727-6734

Influence of ligand encapsulation on cobalt-59 chemical-shift thermometry

Tyler M. Ozvat, M. E. Peña and J. M. Zadrozny, Chem. Sci., 2019, 10, 6727 DOI: 10.1039/C9SC01689A

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